JP2002122065A - Capacity control device of variable displacement hydraulic motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and automatically switch motor capacity into three stages of small, intermediate and large capacities corresponding to the load, and to inhibit generation of hunting or the like. SOLUTION: A land 28A of a maximum diameter is mounted on one end of a spool 28, and an annular pilot pressure receiving part 28J is formed to continuously receive the pilot pressure. Pistons 30, 35 are slidably inserted and fitted into shaft holes 29, 34 and extended in the axial direction of the spool 28 to define oil chambers 31, 36, and their bottom sides are used as shaft hole pressure receiving parts 29A, 34A to the pilot pressure. The oil chambers 31, 36 selectively communicate with and are cut from a tank port 25A and a pilot port 25B, corresponding to a sliding position of the spool 28 to change the total pressure receiving area by the pilot pressure receiving part 28J and the shaft hole pressure receiving parts 29A, 34A in three stages.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement control apparatus for a variable displacement hydraulic motor, which is preferably used for variably controlling the motor displacement of a variable displacement hydraulic motor provided in a construction machine such as a hydraulic shovel. .

[0002]

2. Description of the Related Art Generally, a variable displacement hydraulic motor is used as a traveling or turning hydraulic motor in a construction machine such as a hydraulic shovel. And, for example, when used as a traveling hydraulic motor, by switching the motor capacity between large capacity and small capacity with a variable capacity actuator, the hydraulic motor is rotated at high torque at low speed at large capacity, and at small capacity at large capacity. It rotates at high speed with low torque.

In order to control the motor displacement variably in accordance with the load pressure acting on the hydraulic motor from the outside, the displacement control device for the hydraulic motor supplies the load pressure of the hydraulic motor as a pilot pressure to the displacement control valve. A self-pressure control type capacity control device configured to selectively control the pressure oil supplied to and discharged from the variable capacity actuator by selectively switching the capacity control valve between a large capacity position and a small capacity position in accordance with the pilot pressure. Are known.

[0004] Further, in order to switch the motor capacity in three stages of large capacity, intermediate capacity and small capacity, a capacity variable actuator that drives a capacity variable section of the hydraulic motor to change the motor capacity, and receives a pilot pressure to receive the pilot pressure. There is also known a displacement control device for a variable displacement hydraulic motor comprising a hydraulic pilot type displacement control valve that switches pressure oil supplied to and discharged from a displacement variable actuator in accordance with a pilot pressure (for example, Japanese Utility Model Laid-Open No. 1-173383). etc).

In this type of conventional capacity control apparatus for a hydraulic motor, the motor capacity is switched in three stages of large capacity, intermediate capacity and small capacity, so that the capacity ratio between the large capacity and the small capacity (maximum capacity / The minimum capacity can be increased, for example, the traveling speed can be increased, the traction force can be increased, and the shock at the time of capacity switching can be reduced by interposing an intermediate capacity between the large capacity and the small capacity. There are advantages such as.

[0006]

By the way, in the above-mentioned prior art, although there is an advantage that the motor capacity can be switched in three stages of large capacity, intermediate capacity and small capacity,
In this case, the capacity control valve has a constant pressure receiving area with respect to the pilot pressure, so the capacity control valve can handle large, medium, and small capacities unless the pilot pressure value is changed in at least three stages. Cannot switch to the three positions.

When the load pressure of the hydraulic motor (motor driving pressure) is used as the pilot pressure, the output torque of the hydraulic motor switches with respect to the motor driving pressure as shown by a characteristic line in FIG. When the motor capacity is switched to a small capacity, an intermediate capacity, or a large capacity, the output torque of the hydraulic motor is between the torque values T1 and T2 and the torque value T.
There is a problem that a step is generated as shown between 3 and T4, and the torque performance and the like cannot be fully utilized.

Further, the motor capacity is changed to the pressure P1 (for example, 10
MPa) or less and the pressure is reduced to P1 to P2 (for example, 1
When the motor displacement is controlled in three stages such that the intermediate displacement is between 0 and 20 MPa and the displacement is large at a pressure P2 (for example, 20 MPa) or more, for example, the pressure changes due to the change in load pressure accompanying the displacement. Before and after P1 and P2, the hunting phenomenon is likely to occur in the motor driving pressure, causing a problem that the control at the time of switching the capacity becomes unstable.

On the other hand, for example, by guiding an external command pressure from a pilot pump or the like to the hydraulic pilot portion of the displacement control valve, the displacement control valve can be arbitrarily moved to any of the large displacement position, the intermediate displacement position and the small displacement position in accordance with the operation of the operator. It is also possible to adopt a configuration in which crab switching control is performed.

However, in this case, since the switching control of the capacity needs to be performed manually by the operator, the operator has to repeat the manual operation every time the switching control is performed.
There is a problem that operation becomes complicated.

In order to automate such an operation, it is necessary to provide a plurality of pressure sensors in the middle of the hydraulic circuit or to additionally provide a control unit for processing signals from these sensors. As a result, new problems such as a complicated overall device and an expensive device occur.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to reduce the burden on the operator without complicating the apparatus, and to reduce the motor capacity to a small capacity corresponding to the load. An object of the present invention is to provide a displacement control device for a variable displacement hydraulic motor that can be automatically switched while being stabilized in three stages of an intermediate displacement and a large displacement.

Another object of the present invention is to make it possible to appropriately fix the motor displacement by using an external command pressure, to automate the displacement switching control, and to surely suppress the occurrence of hunting and the like. It is another object of the present invention to provide a displacement control device for a variable displacement hydraulic motor.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a variable displacement hydraulic motor having a variable displacement section and driven to rotate by pressure oil from a hydraulic source, and A capacity variable actuator that drives a capacity variable section of the hydraulic motor by supplying and discharging to change the motor capacity to a large capacity, an intermediate capacity and a small capacity, and receives at least a load pressure of the hydraulic motor as a pilot pressure. The present invention is applied to a displacement control device for a variable displacement hydraulic motor comprising a hydraulic pilot type displacement control valve for switching pressure oil supplied to and discharged from the displacement variable actuator.

According to a first aspect of the present invention, the displacement control valve switches the motor displacement between a large displacement, an intermediate displacement, and a small displacement by the variable displacement actuator. The present invention has a configuration in which a plurality of switching positions including capacity positions are provided, and a pressure receiving area for the pilot pressure is changed for each switching position.

With this configuration, the displacement control valve can be switched to one of the large displacement position, the intermediate displacement position and the small displacement position in accordance with the load pressure (pilot pressure) of the hydraulic motor. At times, the pressure receiving area for the pilot pressure can be reduced to the minimum area, the pressure receiving area can be set to an intermediate area when at the intermediate capacity position, and the pressure receiving area can be expanded to the maximum area when at the large capacity position. Therefore, the displacement of the displacement control valve can be automatically switched according to the pilot pressure. At this time, the change in the pressure receiving area gives a hysteresis characteristic to the switching pressure (pilot pressure) of the displacement control valve, thereby suppressing the occurrence of hunting.

According to a second aspect of the present invention, the capacity control valve has a spool sliding hole, and the external control pressure port, the pilot port, the tank port, the high pressure A valve housing provided with a port and a pressure oil supply / discharge port to a variable capacity actuator; and a spool inserted by fitting into a spool sliding hole of the valve housing and receiving the pilot pressure guided from the pilot port. A spool that slides and displaces in the sliding hole in the axial direction and selectively communicates and shuts off the pressure oil supply / discharge port with the high pressure port and the tank port. At one time, the pressure receiving area for the pilot pressure is set to the minimum pressure receiving area, and when switched to the intermediate capacity position, the pressure receiving area for the pilot pressure is set to the intermediate pressure receiving area. And pressure area, and a configuration in which the largest pressure receiving area of the pressure receiving area to receive the pilot pressure when switched to a large volume position.

Thus, when the displacement control valve is at the large displacement position, the pressure receiving area of the spool with respect to the pilot pressure can be reduced to a minimum area, and when the displacement control valve is switched to the intermediate displacement position, the pressure receiving area with respect to the pilot pressure of the spool is reduced. The area can be an intermediate pressure receiving area, and when switching to the large capacity position, the pressure receiving area for the pilot pressure can be the maximum pressure receiving area.

According to the third aspect of the present invention, the displacement control valve has a spool sliding hole, and at least a pilot port, a tank port, a high pressure port, and a variable capacity are spaced apart in the axial direction of the spool sliding hole. A valve housing provided with a pressure oil supply / discharge port to an actuator; and a pressure oil supply / discharge port inserted in a spool sliding hole of the valve housing and slidingly displaced in the spool sliding hole in an axial direction. A spool that selectively communicates and shuts off with a high-pressure port and a tank port, a pilot pressure receiving unit that is provided on the spool and that displaces the spool in the axial direction by receiving a pilot pressure guided from the pilot port;
First and second shaft holes, each of which has a bottomed hole formed apart from each other in the spool, and extends in the axial direction of the spool and is open at one end face on one side and the other end face; The first and second oil chambers are slidably inserted into the respective shaft holes so as to close the open ends of the shaft holes, and define first and second oil chambers with the bottom of each of the shaft holes. , Formed by first and second pistons for receiving a hydraulic reaction force in the second oil chamber and bottoms of the first and second shaft holes, and configured to reduce the pressure in the first and second oil chambers. First and second shaft hole pressure receiving portions for changing the total pressure receiving area of the spool with respect to the pilot pressure together with the pilot pressure receiving portion by receiving pressure; and the spool at a position corresponding to the first and second oil chambers. And the first and second oil chambers when the spool is displaced in the spool sliding hole. It said first selectively communicating to different ports of the pressure out of the port has a configuration and a second oil passage.

With this configuration, the first and second oil passages connect the first and second oil chambers to ports having different pressures, for example, a pilot port and a tank port according to the sliding displacement of the spool. Selectively communicate. When the first and second oil chambers communicate with the pilot port, the spool receives the pilot pressure guided into the first and second oil chambers by the first and second shaft hole pressure receiving portions, When communicating with the tank port, the pressure receiving of the pilot pressure by the first and second shaft hole pressure receiving portions is substantially released, so that the sum of the spools by the pilot pressure receiving portion and the first and second shaft hole pressure receiving portions is reduced. The pressure receiving area changes depending on which port the first and second oil chambers communicate with through the first and second oil passages, and the capacity control is performed by utilizing the change in the pressure receiving area. Hysteresis characteristics can be given to the switching pressure (pilot pressure) of the valve.

According to the fourth aspect of the present invention, the pilot pressure receiving portion has a larger pressure receiving area than the first shaft hole pressure receiving portion, and the first shaft hole pressure receiving portion is provided with a first oil chamber. When communicating with the pilot port via the first oil passage, the pilot pressure is received in a direction opposite to the pilot pressure receiving portion, and the second shaft hole pressure receiving portion is connected to the second oil chamber via the second oil passage. When communicating with the pilot port, the pilot pressure is received in the same direction as the pilot pressure receiving portion.

Thus, while the first oil chamber is in communication with the pilot port via the first oil passage, the pilot pressure is guided into the first oil chamber. The pilot pressure is received in a direction opposite to the pilot pressure receiving portion, and the pressure receiving area of the pilot pressure receiving portion is offset by the pressure receiving area of the first shaft hole pressure receiving portion, so that the pressure receiving area of the entire spool with respect to the pilot pressure can be reduced. . Further, when the first oil chamber communicates with a low-pressure tank port or the like via the first oil passage, the pressure in the first oil chamber decreases to a low pressure level, and the spool is moved in the opposite direction to the pilot pressure receiving portion. Since the acting pressure is reduced, the spool can receive the pilot pressure with a large pressure receiving area by the pilot pressure receiving portion, and the pressure receiving area of the entire spool with respect to the pilot pressure can be relatively increased.

On the other hand, while the second oil chamber is in communication with the pilot port via the second oil passage, the pilot pressure is guided into the second oil chamber, so that the second shaft hole pressure receiving portion is formed. The pilot pressure can be received in the same direction as the pilot pressure receiving portion, and the pressure receiving area of the entire spool with respect to the pilot pressure can be increased by the pressure receiving area of the second shaft hole pressure receiving portion. Further, when the second oil chamber communicates with a low-pressure tank port or the like via the second oil passage, the pressure in the second oil chamber decreases to a low pressure level, and the spool is provided in the same direction as the pilot pressure receiving portion. Since the acting pressure becomes small, the pressure receiving area of the entire spool can be reduced by the pressure receiving area of the second shaft hole pressure receiving portion, and as a result, the pressure receiving area of the entire spool with respect to the pilot pressure can be changed in three stages.

According to the fifth aspect of the invention, the first and second oil passages selectively communicate the first and second oil chambers with the pilot port and the tank port in accordance with the sliding position of the spool.
The first oil chamber communicates with a pilot port via a first oil passage, and
When the oil chamber communicates with the tank port via the second oil passage, the pilot pressure receiving portion and the first shaft hole pressure receiving portion receive pilot pressure with a minimum pressure receiving area,
When the second oil chamber communicates with the pilot port via the first and second oil passages, the pilot pressure is received by the pilot pressure receiving portion and the first and second shaft hole pressure receiving portions with an intermediate pressure receiving area. Further, when the first oil chamber communicates with the tank via the first oil passage and the second oil chamber communicates with the pilot port via the second oil passage, the pilot pressure receiving portion and the second oil chamber communicate with each other. The pilot pressure is received with the largest pressure receiving area by the two shaft hole pressure receiving portions.

Thus, the pressure receiving area of the pilot pressure receiving section is Sa, the pressure receiving area of the first shaft hole pressure receiving section is S1,
When the pressure receiving area of the second shaft hole pressure receiving section is S2, the pilot pressure receiving section continues to receive the pilot pressure with the pressure receiving area Sa, so that the first and second oil chambers communicate with the pilot port. During this time, the first and second shaft hole pressure receiving portions receive the pilot pressure in opposite directions with the pressure receiving areas S1 and S2, and reduce the pressure receiving area of the entire spool to an intermediate pressure receiving area (S
a-S1 + S2).

When the first oil chamber communicates with the pilot port and the second oil chamber communicates with the tank port,
Since the pilot pressure receiving portion and the first shaft hole pressure receiving portion receive pilot pressure in opposite directions, the pressure receiving area in this case is the minimum pressure receiving area (Sa-S1). Further, when the first oil chamber communicates with the tank side and the second oil chamber communicates with the pilot port, the pilot pressure receiving portion and the second shaft hole pressure receiving portion receive pilot pressure in the same direction. ,
The pressure receiving area in this case is the maximum pressure receiving area (Sa + S2).

On the other hand, according to the invention of claim 6, the spool comprises a stepped spool in which one side in the axial direction has a larger diameter than the other part, and the pilot pressure receiving portion is provided on the large diameter side of the spool. It is configured to be formed by a step portion on the outer peripheral side located. Thus, an annular pilot pressure receiving portion can be formed on the outer periphery of one side of the spool at the position of the step portion having a large diameter, and the spool can be slid by the pilot pressure acting on the pilot pressure receiving portion.

According to the seventh aspect of the present invention, the spool has a plurality of lands for shutting off ports having different pressures from each other, and the first and second oil passages have a pressure higher than that of the pilot port among the ports. A throttle hole is provided at a position where the first and second oil chambers communicate with and block the low port.

Thus, after the pilot pressure from the pilot port is introduced into the first and second oil chambers to increase the pressure in the first and second oil chambers, for example, the first or second oil chamber is moved in accordance with the sliding displacement of the spool. Even when the second oil chamber communicates with the tank port, the high pressure in this oil chamber can be prevented from flowing out as a jet to the tank port side by the throttle hole. The occurrence of abnormal pressure can be prevented.

On the other hand, according to the invention of claim 8, between the valve housing and the spool, a first urging means for urging the spool in the axial direction is larger than the first urging means. Second biasing means for biasing the spool in the axial direction with a biasing force is provided.

In this case, by using the first and second biasing means, the spool of the displacement control valve can be moved to the small displacement position.
The spool can be stably held at either the intermediate capacity position or the large capacity position, and it is possible to compensate for the sliding displacement of the spool toward another switching position according to the increase or decrease of the pilot pressure.

According to the ninth aspect of the present invention, the first biasing means biases the spool from one side in the axial direction to the other side in a direction opposite to the direction in which the pilot pressure receiving portion receives the pilot pressure. The second biasing means is provided between the valve housing and the first biasing means so as to be in series with the first biasing means, and the spool is disposed between the valve housing and the axially central switching position. The spool is biased from one side in the axial direction to the other side when located between the switching position on one side in the axial direction.

Thus, when the pilot pressure due to the motor load pressure is in a low pressure state, the spool is slid from one side to the other side by the first biasing means, and the displacement control valve is moved to, for example, the small displacement position. Can be placed. When the pilot pressure becomes higher than the reference switching pressure due to the increase of the motor load pressure, the spool receives the pressure, thereby causing the spool to move in one axial direction against the first urging means. And the displacement control valve can be switched to, for example, an intermediate displacement position. In this intermediate capacity position, the spool can be biased to the other side in the axial direction by the second biasing means, and when the pilot pressure rises beyond the biasing force at this time, the spool is opposed to the second biasing means. As a result, the displacement control valve can be switched to, for example, a large capacity position by the sliding displacement of the spool to one side in the axial direction.

On the other hand, according to the tenth aspect of the present invention, the first biasing means biases the spool from the other side in the axial direction to one side in the same direction as the direction in which the pilot pressure receiving portion receives the pilot pressure. The second urging means moves the spool from one side in the axial direction to the other side when the spool is located between the switching position at the center in the axial direction and the switching position on one axial side. It is configured to be energized.

Thus, when the pilot pressure due to the motor load pressure is low, the spool is slid from the other side in the axial direction toward the one side by the first urging means, and the displacement control valve is moved to the center in the axial direction. (For example, an intermediate capacity position). When the pilot pressure rises beyond the urging force of the second urging means as the motor load pressure rises, the spool is largely displaced to one side in the axial direction against the second urging means. And by this,
For example, the displacement control valve can be switched to a large displacement position.

According to the eleventh aspect, the displacement control valve is configured to control the switching of the motor displacement in accordance with the external command pressure generated by the external command pressure generating means. In this case, switching control of the capacity control valve can also be performed by an external command pressure, and for example, control for fixing a large capacity can be easily performed.

According to the twelfth aspect of the present invention, the displacement control valve has a spool sliding hole, and the external control pressure port, the pilot port,
A valve housing provided with a tank port, a high-pressure port, and a pressure oil supply / discharge port to a variable capacity actuator; and a pilot pressure inserted into a spool sliding hole of the valve housing to receive the pilot pressure guided from the pilot port. Thereby, the inside of the spool sliding hole is slid and displaced in the axial direction,
An external command pressure port to which an external command pressure generated by an external command pressure generating means is introduced is provided in the valve housing. The spool is provided with a command pressure receiving portion for receiving the external command pressure guided from the external command pressure port in the same direction as the direction in which the pilot pressure is received.

Thus, the spool can receive the pilot pressure due to the motor load pressure and the external command pressure in the same direction, and can move the spool in the small capacity position, the intermediate capacity position, and the large capacity position according to the pilot pressure and the external command pressure. Switching control can be performed to either.

According to a thirteenth aspect of the present invention, between the valve housing and the spool, the spool is biased from one side in the axial direction opposite to the direction of receiving the pilot pressure from the other side. When the spool is located between a switching position at the center in the axial direction and a switching position on one side in the axial direction, the spool has a larger biasing force than the first biasing unit. Second biasing from one side in the axial direction to the other side
And an urging means.

Thus, when the pilot pressure due to the motor load pressure and the external command pressure are both in a low pressure state, the spool is slid and displaced from one side in the axial direction to the other side by the first urging means, thereby controlling the capacity. The valve can be located, for example, in a small volume position. When the pilot pressure becomes higher than the reference switching pressure due to the increase of the motor load pressure, the spool receives the pressure as the pilot pressure, thereby causing the spool to move in the axial direction against the first urging means. , The displacement control valve can be switched to the intermediate displacement position. When the pilot pressure rises beyond the urging force of the second urging means, the spool is further displaced to one side in the axial direction against the second urging means, and the capacity control valve is enlarged. It can be switched to the capacity position.

Also, for example, even when the external command pressure is set to a high pressure level, the command pressure receiving portion receives the external command pressure, thereby causing the spool to move in the axial direction against the first urging means. Because of the slidable displacement to one side, this allows the displacement control valve to be switched, for example, from a small displacement position to an intermediate displacement position. When the external command pressure is further increased and the spool is largely slid toward one side in the axial direction against the second urging means, this causes the displacement of the displacement control valve from the intermediate displacement position to the large displacement position. , And control for fixing a large capacity can be performed. When the external command pressure is reduced, the displacement control valve can be automatically switched according to the pilot pressure (load pressure) as described above.

According to the fourteenth aspect of the present invention, when the external pressure is set to the lowest pressure state by the command pressure generating means, the capacity control valve balances the pilot pressure with the first and second urging means. When the external command pressure is set to an intermediate pressure state, the spool is switched to any one of a switching position on the other side in the axial direction, a switching position on the center in the axial direction, and a switching position on the one side in the axial direction. When the spool is switched to one of two positions, a switching position at the center in the axial direction and a switching position on one side in the axial direction, according to the balance between the external command pressure and the second urging means, and the external command pressure is in the highest pressure state The spool is held at the switching position on one side in the axial direction regardless of the pilot pressure against the second urging means.

Thus, when the external command pressure is set to the lowest pressure state, the displacement control valve is moved to any one of the small displacement position, the intermediate displacement position and the large displacement position with the pilot pressure and the first and second urging means. When the external command pressure is set to an intermediate pressure state, the switching control between the intermediate displacement position and the large displacement position can be performed according to the balance between the pilot pressure and the second urging means. When the external command pressure is set to the highest pressure state, the displacement control valve can be fixed at the large displacement position regardless of the pilot pressure.

According to a fifteenth aspect of the present invention, the displacement control valve has a spool sliding hole, and the external control pressure port, the pilot port,
A valve housing provided with a tank port, a high pressure port, and a pressure oil supply / discharge port to a variable capacity actuator; and a pilot pressure inserted into a spool sliding hole of the valve housing and guided by the pilot port. A spool that slides in the spool sliding hole in the axial direction to selectively communicate and shut off the pressure oil supply / discharge port with the high pressure port and the tank port. An external command pressure port through which an external command pressure generated by the means is guided is provided, and the spool receives an external command pressure guided from the external command pressure port in a direction opposite to a direction in which the pilot pressure is received. A command pressure receiving unit is provided.

Thus, the spool can receive the pilot pressure due to the motor load pressure and the external command pressure in opposite directions, and the spool is moved in the small capacity position, the intermediate capacity position, and the large capacity position in accordance with the pilot pressure and the external command pressure. Switching control.

According to the sixteenth aspect of the present invention, between the valve housing and the spool, the spool is biased from the other side in the axial direction which is the same as the pilot pressure receiving direction toward one side. When the spool is located between a switching position at the center in the axial direction and a switching position on one side in the axial direction, the spool has a larger biasing force than the first biasing unit. Second biasing means for biasing from one side in the axial direction toward the other side is provided.

Thus, when the pilot pressure due to the motor load pressure and the external command pressure are both in a low pressure state, the spool is slid from the other side in the axial direction to one side by the first urging means, thereby controlling the capacity. The valve can be located in an axially central switching position (e.g., an intermediate displacement position). When the pilot pressure rises beyond the urging force of the second urging means as the motor load pressure rises, the spool is largely displaced to one side in the axial direction against the second urging means. And
Thereby, the displacement control valve can be switched to, for example, the large displacement position.

On the other hand, when the external command pressure is set to a high pressure, the external command pressure is received by the command pressure receiving portion, whereby the spool is moved to the other side in the axial direction against the first urging means. Due to the sliding displacement, this allows the displacement control valve to be switched to, for example, a small displacement position. When the pilot pressure rises above the reference switching pressure in this state, the spool receives the pressure as the pilot pressure, and the spool is pressed together with the first urging means against the pressing force by the external command pressure. By sliding displacement to one side in the axial direction, the displacement control valve can be switched to the intermediate displacement position. When the pilot pressure rises beyond the urging force of the second urging means, the spool is further displaced to one side in the axial direction against the second urging means, and the capacity control valve is enlarged. It can be switched to the capacity position.

Further, according to the seventeenth aspect of the present invention, when the external command pressure is set to a low pressure state by the command pressure generating means, the capacity control valve pivots the spool in accordance with the balance between the pilot pressure and the second urging means. When the external command pressure is set to a high pressure state, the balance between the pilot pressure and the first and second urging means. Accordingly, the spool is switched to one of three positions: a switching position on the other side in the axial direction, a switching position on the center in the axial direction, and a switching position on the one side in the axial direction.

Thus, when the external command pressure is set to a low pressure state, the capacity control valve can be switched to one of the intermediate capacity position and the large capacity position in accordance with the balance between the pilot pressure and the second urging means. When the external command pressure is set to a high pressure state, it is possible to perform switching control to any of the small capacity position, the intermediate capacity position and the large capacity position in accordance with the balance between the pilot pressure and the first and second urging means.

[0051]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a displacement control apparatus for a variable displacement hydraulic motor according to an embodiment of the present invention; This will be described in detail.

FIGS. 1 to 9 show a first embodiment of the present invention. In the drawings, reference numeral 1 denotes a hydraulic pump constituting a hydraulic source together with a tank 2, and the hydraulic pump 1 is a prime mover of a hydraulic shovel. (Not shown), the tank 2
The hydraulic oil sucked from the inside is supplied to a hydraulic motor 3 and the like described later as high-pressure hydraulic oil.

Reference numeral 3 denotes a traveling hydraulic motor for driving a vehicle as an inertial body on the output shaft 3A side. The hydraulic motor 3 is constituted by, for example, a swash plate type or a swash plate type variable displacement hydraulic motor. Or, it has a variable capacity portion 3B composed of a valve plate or the like. Then, when the hydraulic motor 3 is driven to tilt in the direction of arrow A where the tilt angle becomes large by using the servo actuator 10 described later, the motor capacity is increased to the large capacity side, When tilting drive is performed in the direction of arrow B where the turning angle becomes smaller, the motor capacity is reduced to the smaller capacity side.

Reference numerals 4A and 4B denote the hydraulic motor 3 and the hydraulic pump 1
And a pair of main pipelines connected to the tank 2, the main pipelines 4A,
4B supplies and discharges hydraulic oil from the hydraulic pump 1 to the hydraulic motor 3 through a directional control valve 5 and the like described later, whereby the hydraulic motor 3 rotates forward or backward, and moves the hydraulic shovel (vehicle) forward or backward. It is to let.

In the main pipelines 4A and 4B, between the counter balance valve 6 and the directional control valve 5, which will be described later, become pipeline sections 4A1 and 4B1 on the hydraulic power source side, and between the counter balance valve 6 and the hydraulic motor 3. Are the pipe sections 4A2, 4 on the actuator side.
B2.

Reference numeral 5 denotes a traveling directional control valve provided in the middle of the main pipelines 4A and 4B. The directional control valve 5 is configured as a directional control valve having, for example, four ports and three positions as shown in FIG. When the operator of the shovel switches the operation lever 5A, the switch is switched from the neutral position (a) to the switch positions (b) and (c).

The direction control valve 5 is switched to the switching position (b).
The hydraulic oil from the hydraulic pump 1 is supplied to the main pipeline 4A (the pipeline 4A).
1, 4A2) to the hydraulic motor 3 to rotate the hydraulic motor 3 in the forward direction, for example.
The return oil from the tank is discharged to the tank 2 via the main pipeline 4B (the pipelines 4B1, 4B2). When the direction control valve 5 is switched to the switching position (C), the supply direction of the pressure oil is reversed, and the hydraulic motor 3 is driven to rotate in the reverse direction.

Numeral 6 denotes a counterbalance valve which constitutes a brake valve attached to the hydraulic motor 3. The counterbalance valve 6 includes pipe sections 4A1 and 4B1 on the hydraulic source side and pipe sections 4A2 and 4B2 on the actuator side. And a pair of check valves 7A, 7B provided between the hydraulic pressure source side pipe sections 4A1, 4B1 and the actuator side pipe sections 4A2, 4B2 in a parallel relationship with the check valves 7A, 7B. And a pressure control valve 8 disposed at

The pressure control valve 8 of the counter balance valve 6 is switched from the neutral position (a) to the switching positions (b) and (c) almost in conjunction with the direction control valve 5, and the pressure from the hydraulic pump 1 is changed. It compensates for the supply and discharge of oil to and from the hydraulic motor 3. When the pressure control valve 8 returns to the neutral position (a) when the hydraulic motor 3 is rotated by inertia or the like, the counter balance valve 6 is connected between the hydraulic motor 3 and the counter balance valve 6 on the actuator side. The brake pressure is generated within 4A2 or 4B2.

Here, the pressure control valve 8 of the counterbalance valve 6 is composed of, for example, a hydraulic pilot type directional control valve having 6 ports and 3 positions, and has a center bypass port 8A serving as a high pressure outlet port. When the pressure control valve 8 is switched from the neutral position (a) to the switching position (b), the high-pressure-side pipeline portion 4A of the hydraulic-source-side pipeline portions 4A1 and 4B1.
A1 is connected to the center bypass port 8A, and when it is switched to the switching position (C), it is connected to the pipeline section 4B1.

Thus, the center bypass port 8A of the pressure control valve 8 guides the motor driving pressure, which is the load pressure of the hydraulic motor 3, into the pilot pipeline 16 described later, and connects the capacity control valve 21 described later to the pilot pipeline 16. Pilot pressure from
Switching control is performed according to px. When the pressure control valve 8 returns to the neutral position (A), the center bypass port 8A is connected to a tank line 17 described later,
The pilot pressure in pilot line 16 automatically drops to the tank pressure level.

9 is a hydraulic motor 3 and a counterbalance valve 6
And the pipeline portions 4A2, 4 of the main pipelines 4A, 4B
A shuttle valve provided between B2 and as a high pressure selection valve.
The shuttle valve 9 is connected to the pipe sections 4A2, 4A of the main pipes 4A, 4B.
The pressure oil on the high pressure side is selected from B2, and the selected pressure oil is supplied to the servo actuator 10 via a high pressure pipe 20 and a capacity control valve 21 described later.

Reference numeral 10 denotes a servo actuator serving as a variable displacement actuator attached to the hydraulic motor 3. The servo actuators 10 are disposed to face each other as shown in FIG. 1, for example, and hydraulic oil is provided in the hydraulic chambers 11A and 12A. The first and second tilting pistons 1 that drive the variable displacement portion 3B of the hydraulic motor 3 in the directions indicated by arrows A and B by supplying and discharging
1 and 12, and a spring 13 that constantly urges the variable capacity portion 3B in the direction of arrow A toward a large tilt (large capacity).

In the servo actuator 10, pressure oil is supplied into the hydraulic chamber 11A via a supply / discharge pipe 51 described later, and the pressure oil in the hydraulic chamber 12A is supplied via a supply / discharge pipe 52 described later. When discharged to the tank 2 side, the tilting piston 1
In step 1, the variable displacement unit 3B is driven against the spring 13 in the direction of arrow B where the tilt angle is minimized, and the motor displacement is switched to the minimum small displacement.

When the hydraulic oil is supplied into the hydraulic chambers 11A, 12A via the supply / discharge conduits 51, 52 together, the tilting piston 12 for intermediate tilting together with the spring 13 is pressed by the pressure in the hydraulic chamber 12A. The displacement variable portion 3B is driven in the direction of arrow A against the pressing force of the displacement piston 11 from the minimum position of the displacement angle to the intermediate displacement position to switch the motor displacement to the intermediate displacement.

On the other hand, when the pressure oil in the hydraulic chamber 11A is discharged to the outside of the supply / discharge pipe line 51 while the pressure oil is supplied to the hydraulic chamber 12A and the pressure is reduced to about the tank pressure, the tilting occurs. When the pressing force by the piston 11 is released, the variable displacement portion 3B is driven by the spring 13 in the direction of arrow A where the tilt angle is maximized, and the displacement of the motor is increased to the maximum by the biasing force of the spring 13. Switch. At this time, the tilt piston 12 remains at the intermediate tilt position while reaching the stroke end.

Reference numeral 14 denotes a negative type brake device attached to the hydraulic motor 3. The brake device 14 has a hydraulic chamber 14A, a brake spring 14B, and the like. The output shaft 3A of the hydraulic motor 3 is normally operated by the brake spring 14B. It functions as a parking brake by applying a braking force to the side.

The brake device 14 is provided with a hydraulic chamber 14A.
Is connected to a control line 15 described later, and when a brake release pressure is supplied through the control line 15, the braking state of the output shaft 3A of the hydraulic motor 3 is released, whereby the hydraulic motor 3 The vehicle is driven to rotate in accordance with a motor driving pressure in order to drive the vehicle on a road.

Reference numeral 15 denotes a brake control pipe connected to the center bypass port 8A of the pressure control valve 8, and the control pipe 15 is used to switch the pressure control valve 8 from the neutral position (a) to the switching position (b). When the pressure is switched to the above, the motor drive pressure from the center bypass port 8A is guided to the hydraulic chamber 14A of the brake device 14 as the brake release pressure, and the braking of the hydraulic motor 3 by the brake device 14 is released.

When the pressure control valve 8 returns to the neutral position (A), the center bypass port 8A is connected to a tank line 17 described later, so that the inside of the control line 15 automatically reaches the tank pressure level. To the brake device 1
Numeral 4 is for applying a braking force to the output shaft 3A of the hydraulic motor 3 by the urging force of the brake spring 14B.

Reference numeral 16 denotes a pilot line connected to the center bypass port 8A of the pressure control valve 8 together with the control line 15 for the brake. The pilot line 16 is connected to the center bypass port 8A of the pressure control valve 8 and will be described later. Capacity control valve 2
The pilot port 25B is connected to the pilot port 25B of the displacement control valve 21 as the pilot pressure Ppx.

Reference numeral 17 denotes a tank line connected to the center bypass port 8A of the pressure control valve 8. The tank line 17 connects the center bypass port 8A when the pressure control valve 8 returns to the neutral position (A). It is connected to the tank 2 to reduce the pilot pressure Ppx in the pilot line 16 together with the brake control line 15 to the tank pressure level.

Reference numeral 18 denotes another tank line. The tank line 18 is connected to a tank port 25 of a capacity control valve 21 described later.
A, 25C and 25G are connected to the tank 2.
A drain pipe 19 for discharging drain (leakage oil) from the hydraulic motor 3 to the tank 2 is connected to an intermediate position of the tank pipe 18.

Reference numeral 20 denotes a high-pressure pipe connecting the outflow side of the shuttle valve 9 to the capacity control valve 21. The high-pressure pipe 20 is selected from the pipe sections 4A2 and 4B2 of the main pipes 4A and 4B by the shuttle valve 9. The pressure oil on the high pressure side is guided to a high pressure port 25E of the capacity control valve 21 described later.

Reference numeral 21 denotes a displacement control valve attached to the hydraulic motor 3 together with the servo actuator 10.
2 includes a valve housing 22, which will be described later, a spool 28, pistons 30, 35, return springs 39, 40, and the like, as shown in FIGS.

The capacity control valve 21 is composed of, for example, a 9-port, 3-position hydraulic pilot type switching valve as shown in FIG. 1, and is controlled by a pilot pressure Ppx or an external command pressure Pgx, which will be described later. It is selectively switched to any one of the capacitance position (b) and the small capacitance position (c).

When the displacement control valve 21 is at the small displacement position (c), the hydraulic chamber 12A is connected to the supply / discharge conduit 52 in order to reduce the tilt piston 12 of the servo actuator 10.
And the tilting piston 11 is extended by supplying hydraulic oil from the high-pressure line 20 to the hydraulic chamber 11A through the supply / discharge line 51 through the tilting piston 11.
As a result, the variable capacity portion 3B is driven in the direction of arrow B against the spring 13 to a position where the tilt angle becomes minimum.

When the displacement control valve 21 is switched to the intermediate displacement position (b), the pressure oil from the high pressure line 20 is supplied to the hydraulic chambers 11A and 12A of the servo actuator 10 to supply and discharge lines 51 and 52. The tilt pistons 11 and 12 are operated in the extending direction by driving the displacement variable portion 3B to a position where the tilt angle is intermediate, and the motor displacement is set to an intermediate displacement.

On the other hand, when the displacement control valve 21 is in the large displacement position (a)
Is switched to the supply / discharge line 51, the tank line 18
To release the hydraulic oil in the hydraulic chamber 11A toward the tank 2 to release the operation of the tilting piston 11,
The variable displacement section 3B is driven by the spring 13 of the servo actuator 10 in the direction indicated by the arrow A to the position where the tilt angle becomes the maximum.

Reference numeral 22 denotes a valve housing which is an outer shell of the displacement control valve 21.
A spool slide hole 23 having a stepped shape and having a bottom as shown in FIG.
And oil grooves 24A to 24H and ports 25A to
25H and the like are formed.

The spool sliding hole 23 of the valve housing 22 has a large-diameter hole 23 having a maximum diameter at one end which is an open end.
A, and the diameter is reduced in, for example, two stages toward the closed end 23B on the other end side. On the bottom side of the large-diameter hole 23A, an annular step 23C is formed between the bottom of the large-diameter hole 23A and an oil groove 24A described later, and a spring receiver 41 described below abuts the step 23C.

Here, annular oil grooves 24 A, 24 B, 24 are provided in the valve housing 22 on the outer peripheral side of the spool sliding hole 23.
C, 24D, 24E, 24F, 24G, 24H are sequentially formed in the axial direction from one end side to the other end side, and the oil groove 2 is formed.
4A is disposed adjacent to the step 23C of the spool sliding hole 23.

Further, the tank port 25A, the pilot port 25
B, tank port 25C, pressure oil supply / discharge port 25D, high pressure port 25E, pressure oil supply / discharge port 25F, tank port 2
5G and an external command pressure port 25H are formed, and these ports 25A to 25H are provided with annular oil grooves 24A to 24H.
Through the spool sliding hole 23.

Reference numeral 26 denotes a large-diameter hole portion 23 of the spool sliding hole 23.
A cover closed on the A side, and the cover 26
And a spring chamber 27 formed of a large-diameter hole portion 23A and an oil groove 24A and formed of a stepped space is formed between one end of a spool 28 described later.

Reference numeral 28 denotes a spool inserted into a spool sliding hole 23 of the valve housing 22. The spool 28 has lands 28A, 28 on its outer peripheral side as shown in FIGS.
B, 28C, 28D, and 28E are formed apart from each other in the axial direction, and between the land 28B and the land 28C, an annular groove 28F for communicating between the oil grooves 24C and 24D is formed.

Also, between the land 28C and the land 28D of the spool 28, between the oil grooves 24D and 24E,
Another annular groove 28G for communicating between E and 24F or between oil grooves 24D, 24E and 24F is formed. Another annular groove 28H is formed between the land 28D and the land 28E of the spool 28 to communicate between the oil grooves 24F and 24G.

Then, these annular grooves 28F, 28G,
28H and lands 28B, 28C, 28D, 28E, the hydraulic oil supply / discharge ports 25D, 25F are connected to the high pressure port 25E.
And the tank ports 25C and 25G selectively.

Here, the spool 28 is formed as a stepped spool having a maximum diameter on the land 28A side located on one end side, and the annular stepped portion (end face side) of the land 28A facing the land 28B is And a pilot pressure receiving section 28J that receives the pilot pressure Ppx.

Further, a portion of the spool 28 located on one side in the axial direction is a stopper portion 28K having a minimum diameter, and the other side in the axial direction is a command pressure receiving portion 28L. In the spool 28, as shown in FIG. 5, the land 28A has an outer diameter Da and the land 28B has an outer diameter Db, so that the pilot pressure receiving portion 28J has a pressure receiving area Sa according to the equation (1). Have.

[0090]

## EQU1 ## Sa = (Da ² × π / 4) − (Db ² × π / 4) =
(Da ² −Db ² ) × π / 4

As a result, the pilot pressure receiving portion 28J receives the pilot pressure Ppx from the pilot line 16 with the pressure receiving area Sa, and causes the spool 28 to oppose the later-described return springs 39 and 40 as the pilot pressure Ppx increases. Arrow C
The sliding displacement is performed in the direction.

The command pressure receiving portion 28L of the spool 28
Faces the external command pressure chamber 43, which will be described later, in a direction away from the pilot pressure receiving portion 28J in the axial direction, and receives the external command pressure Pgx in the arrow C direction which is the same direction as the pilot pressure receiving portion 28J.

In this case, the command pressure receiving portion 28L has a land 28E having the same outer diameter D as the land 28B as shown in FIG.
b, the pressure receiving area Sb is calculated by the equation (2).
To receive the external command pressure Pgx, and this external command pressure Pgx
The spool 28 is slidably displaced in the direction of arrow C against the return springs 39 and 40 when the pressure rises.

[0094]

## EQU2 ## Sb = Db ² × π / 4

On the other hand, as shown in FIG. 3, when the spool 28 is displaced to the axially middle switching position, which is the intermediate capacity position (b), the stopper 28K formed at one end of the spool 28 has its front end side end face. Abuts against a spring receiver 41 described later, and restricts a return spring 39 described later from being further bent and deformed.

The land 28A of the spool 28 has
Annular narrow grooves 28A1, 28A2 are formed on the outer peripheral side thereof so as to be spaced apart in the axial direction. And these narrow grooves 2
8A1 and 28A2 are located at the opening ends of the small holes 32 and the oil holes 33, which will be described later, and communicate and shut off the oil chamber 31 described below with the tank port 25A and the pilot port 25B with almost zero lap.

Therefore, when the narrow groove 28A1 communicates with the oil groove 24A as shown in FIG. 4, the narrow groove 28A2 is cut off from the oil groove 24B almost simultaneously with the oil groove 24A.
When 8A1 is cut off from the oil groove 24A as shown in FIG. 3, the narrow groove 28A2 is almost simultaneously formed with the oil groove 24B.
Communicated with

On the other hand, the land 28B of the spool 28
Annular narrow grooves 28B1, 28B2 are formed on the outer peripheral side thereof so as to be spaced apart in the axial direction. And these narrow grooves 2
8B1 and 28B2 are located at the opening ends of oil holes 37 and small holes 38 to be described later.
B and the tank port 25C are communicated with each other with almost zero lap and cut off.

Therefore, when the narrow groove 28B1 communicates with the oil groove 24B as shown in FIG. 3, the narrow groove 28B2 is cut off from the oil groove 24C almost simultaneously with the oil groove 24B.
When the groove 8B1 is cut off from the oil groove 24B as shown in FIG. 2, the narrow groove 28B2 is almost simultaneously formed with the oil groove 24C.
Communicated with

Reference numeral 29 denotes a first shaft hole formed in the spool 28 and having a bottomed hole extending in the axial direction. The shaft hole 29 has one end opening to the end face of the spool 28 and the other end forming a bottom. It is closed. The shaft hole 29 has a relatively small hole diameter D1 (D1 <Db <Da) as shown in FIG.

Here, the bottom side of the shaft hole 29 is expressed by the following equation (3).
The first pressure receiving portion 29A receives the pressure in the oil chamber 31, which will be described later, with the pressure receiving area S1 according to the following formula.
The shaft pressure receiving portion 29A has a pressure receiving area S1 (S1 <Sa) smaller than the pressure receiving area Sa of the pilot pressure receiving portion 28J.
Is formed.

[0102]

S 3 = D 1 ² × π / 4

When the pilot pressure Ppx is introduced into the oil chamber 31 as shown in FIGS. 2 and 3, the first shaft pressure receiving portion 29A reverses the pilot pressure Ppx to the pilot pressure receiving portion 28J. When the pressure is received in the direction (the direction indicated by the arrow D) and the inside of the oil chamber 31 communicates with the tank port 25A as shown in FIG. 4, the receiving of the pilot pressure Ppx is released. Accordingly, the pressure receiving area of the bottom side of the shaft hole 29 is the area S1.
And acts as a shaft hole pressure receiving portion 29A which changes between the pressure and zero.

Reference numeral 30 denotes a first piston slidably inserted into the first shaft hole 29. The piston 30 always closes the opening end of the shaft hole 29, and the other end thereof is the shaft hole 29. An oil chamber 31 is defined between the oil chamber 31 and the bottom of the oil chamber. Further, one end of the piston 30 projects axially from the end surface of the spool 28 as shown in FIG. 2, and abuts a stopper 42 described later to receive a hydraulic reaction force due to the pilot pressure Ppx in the oil chamber 31. .

Reference numeral 32 denotes a small hole as a throttle hole formed in the radial direction of the spool 28 at the position of the oil chamber 31. The small hole 32 opens on the outer peripheral surface of the spool 28 at the position of the narrow groove 28A1. The oil chamber 31 is selectively connected to and disconnected from the tank port 25A (spring chamber 27) according to the sliding position of the spool 28.

Reference numeral 33 denotes an oil hole formed in the radial direction of the spool 28 at the position of the oil chamber 31. The oil hole 33 forms an oil passage together with the small hole 32 formed by the throttle hole. The oil hole 33 opens at the outer peripheral surface of the spool 28 at the position of the narrow groove 28A2, and selectively communicates the oil chamber 31 with the pilot port 25B (oil groove 24B) according to the sliding position of the spool 28. It shuts off.

In this case, the oil hole 33 communicates with the pilot port 25B through the narrow groove 28A2 and the oil groove 24B and is shut off, and the small hole 32 communicates with the tank port 25A through the narrow groove 28A1 and the oil groove 24A. , Be cut off. When the spool 28 slides and displaces, the small hole 32 and the oil hole 33 are connected to the oil chamber 31, the pilot port 25 </ b> B, and the tank port 2.
In order to perform communication with 5A and shut off with zero lap, small holes 32,
The narrow grooves 28A1 and 28A2, which are always in communication with the oil hole 33,
The oil grooves 24A and 24B are formed with an axial interval corresponding to the distance between the oil grooves 24A and 24B.

The small hole 32 forms a throttle passage formed to have a smaller diameter than the oil hole 33. And small hole 3
2, when the oil chamber 31 is communicated with the spring chamber 27 and the tank port 25A as shown in FIG. 4, the pressure oil in the oil chamber 31 is suppressed from spouting toward the tank port 25A, and the tank port 25A Side has a function of suppressing generation of surge pressure or the like.

Reference numeral 34 denotes a second shaft hole formed in the spool 28 so as to face the first shaft hole 29 and formed of another bottomed hole extending in the axial direction. And the other end side is open to the end face of the spool 28. The shaft hole 34 has a relatively small hole diameter D2 as shown in FIG.
(D2 <Db <Da). In addition,
The hole diameter D2 of the shaft hole 34 is formed to be substantially the same as the hole diameter D1 of the first shaft hole 29, but there is no particular problem even if there is a magnitude relationship between the two.

Here, the bottom side of the shaft hole 34 is expressed by the following equation (4).
The pressure receiving area S2 according to the following formula is used as a second shaft hole pressure receiving portion 34A for receiving the pressure in the oil chamber 36 described later.
The pressure receiving area S2 (S2 <Sa) is smaller than the pressure receiving area Sa of the pilot pressure receiving section 28J.
Is formed.

[0111]

## EQU4 ## S2 = D2 ² × π / 4

When the pilot pressure Ppx is introduced into the oil chamber 36 as shown in FIGS. 3 and 4, the second shaft hole pressure receiving portion 34A uses the same pilot pressure Ppx as the pilot pressure receiving portion 28J. In the direction (arrow C direction).
When the inside of the oil chamber 36 communicates with the tank port 25C as shown in FIG. 7, the receiving of the pilot pressure Ppx is released.
Thereby, the pressure receiving area of the bottom side of the shaft hole 34 is the area S
It functions as the shaft hole pressure receiving portion 34A which changes between 2 and zero.

A second piston 35 is slidably inserted into the second shaft hole 34. The piston 35 always closes the open end of the shaft hole 34, and one end of the second piston 35 is An oil chamber 36 is defined between the oil chamber 36 and the bottom of the oil chamber. The other end of the piston 35 projects axially from the end surface of the spool 28 as shown in FIG. 3, and is a closed end of the spool sliding hole 23 for receiving a hydraulic reaction force due to the pilot pressure Ppx in the oil chamber 36. 23B
Is in contact with

Reference numeral 37 denotes an oil hole formed in the radial direction of the spool 28 at the position of the oil chamber 36. The oil hole 37 is a small hole 38 described later.
Together, they constitute an oil passage. The oil hole 37 opens in the outer peripheral surface of the spool 28 at the position of the narrow groove 28B1, and selectively communicates the oil chamber 36 with the pilot port 25B (oil groove 24B) according to the sliding position of the spool 28. It shuts off.

Reference numeral 38 denotes a small hole as a throttle hole formed in the radial direction of the spool 28 at the position of the oil chamber 36. The small hole 38 opens at the outer peripheral surface of the spool 28 at the position of the narrow groove 28B2. The oil chamber 36 is selectively communicated with the tank port 25C (oil groove 24C) in accordance with the sliding position of the spool 28 and shut off.

In this case, the oil hole 37 communicates with the pilot port 25B via the narrow groove 28B1 and the oil groove 24B and is shut off, and the small hole 38 communicates with the tank port 25C via the narrow groove 28B2 and the oil groove 24C. , Be cut off. The oil hole 37 and the small hole 38 are used for the oil chamber 36, the pilot port 25B, and the tank port 2 when the spool 28 slides.
The oil hole 37,
The narrow width grooves 28B1 and 28B2, which are always in communication with the small holes 38,
The oil grooves 24B and 24C are formed with an axial distance corresponding to the distance between the oil grooves 24B and 24C.

The small hole 38 constitutes a throttle passage having a smaller diameter than the oil hole 37. And small hole 3
8, when the oil chamber 36 is communicated with the oil groove 24C and the tank port 25C as shown in FIG. 2, the pressure oil in the oil chamber 36 is prevented from spouting toward the tank port 25C, and the tank port 25C Side has a function of suppressing generation of surge pressure or the like.

Reference numeral 39 denotes a return spring which is located between the spool 28 and a spring receiver 41 which will be described later and constitutes a first urging means disposed in the spring chamber 27. The return spring 39 has a spring at one end. The other end is inserted into the outer peripheral side of the stopper 28K of the spool 28 and is in contact with the end of the land 28A. The return spring 39 is connected to a return spring 40 described later.
At the same time, the spool 28 is directed toward the closed end 23B side (in the direction of arrow D) and is constantly urged with an urging force fa as shown in the following equation (8), whereby the displacement control valve 21 is moved to the small displacement position (c ).

A return spring 40 is located between the lid 26 and the spring receiver 41 and constitutes a second urging means disposed in the spring chamber 27. The return spring 40 is a stopper 42 which will be described later.
And one end thereof is in contact with the lid 26. Further, the other end of the return spring 40 is in contact with the first return spring 39 so as to form a series relationship with the first return spring 39, and the return spring 40 has a biasing force fb (fb> fa) greater than that of the return spring 39. To the valve housing 22 (spool sliding hole 2).
3) is pressed against the step 23C.

The return spring 40 has an intermediate capacity position (b) in which the spool 28 is at the axial center switching position shown in FIG. 3 and a large capacity position (one axial switching position) shown in FIG. The spool 28 is urged by the urging force fb toward the closed end 23B side (in the direction of arrow D) via the spring receiver 41 during the sliding displacement between the spool 28 and (a).

Reference numeral 41 denotes a spring receiver which constitutes second biasing means together with the return spring 40. The spring receiver 41 is formed of an annular plate.
The outer peripheral side is pressed by the return spring 40 so as to be able to separate and contact the step 23C of the spool sliding hole 23. Further, the piston 30 is inserted into the inner peripheral side of the spring receiver 41, whereby the distal end side of the piston 30 penetrates the center side of the spring receiver 41 and abuts on the end face of the stopper 42.

Reference numeral 42 denotes a stopper located in the spring chamber 27 and provided on the lid 26. The stopper 42 is
And is arranged on the center side of the spring chamber 27. The stopper 42 contacts the spool 28 via the spring receiver 41 when the spool 28 is displaced to a stroke end on one side in the axial direction (a switching position on one side in the axial direction) as shown in FIG. 40 restricts further bending and deformation.

43 is a closed end 23B of the spool sliding hole 23.
And an external command pressure chamber 43 defined between the command pressure receiving portion 28L of the spool 28 and the external command pressure chamber 43.
The external command pressure Pgx, which is cut off from the tank port 25G and the like by the land 28E of No. 8 and guided from the external command pressure port 25H, acts on the command pressure receiving portion 28L.

Reference numeral 44 denotes a command pressure line connected to the external command pressure port 25H of the capacity control valve 21, and reference numeral 45 denotes a command pressure supply device serving as command pressure generation means. The command pressure supply device 45 is, as shown in FIG. A pilot pump 46, a pressure selection valve 48, pressure reducing valves 49 and 50, a tank 2 and the like, which will be described later. It is.

Reference numeral 46 denotes a pilot pump serving as a hydraulic pressure source for external command pressure. Reference numeral 47 denotes a relief valve for determining the maximum discharge pressure of the pilot pump 46. The relief valve 47 opens when excessive pressure is generated on the discharge side of the pilot pump 46. A valve is provided to relieve the excess pressure to the tank 2 side.

Reference numeral 48 denotes a pressure selection valve as an external selection means for selectively connecting the command pressure line 44 to the tank 2 and the pilot pump 46. The pressure selection valve 48 is operated by a hydraulic shovel operator or the like by operating the operation lever 48A. By manual operation, it can be switched to any of the large capacity fixed position (d), the second speed automatic switching position (e) and the third speed automatic switching position (f).

While the pressure selection valve 48 is being switched to the small-volume to large-volume three-speed automatic switching position (f) as shown in FIG. 1, the command pressure line 44 is connected to the tank 2. The external command pressure Pgx is kept at a low pressure level such as the tank pressure. Then, the pressure of the external command pressure port 25H (external command pressure chamber 43) becomes the tank pressure level, and the displacement control valve 21 switches the small-capacity position (c) shown in FIG. The spool 28 is returned to the initial position)
Allow to be energized at 9,40.

For this reason, the spool 28 of the capacity control valve 21
Is slidable within the valve housing 22 in accordance with the pressure value of the pilot pressure Ppx received by the pilot pressure receiving portion 28J and the first and second shaft hole pressure receiving portions 29A and 34A. When the pilot pressure Ppx exceeds a switching pressure Pp3, which will be described later, the spool 28 is pushed from the position shown in FIG. 2 to the position shown in FIG. The capacity control valve 21 is switched from the small capacity position (c) shown in FIG. 1 to the intermediate capacity position (b).

In this intermediate capacity position (b), as long as the pilot pressure Ppx changes within the range of switching pressures Pp1 to Pp3 described later, the spool 28 is held at the axially central switching position shown in FIG. In this state, the pilot pressure P
When px exceeds the switching pressure Pp4 described later, the return spring 4
The spool 28 is pushed in the direction of arrow C from the position shown in FIG. 3 to the position shown in FIG. 4 against the position 0, and the displacement control valve 21 is moved from the intermediate displacement position (b) shown in FIG. Is switched to

On the other hand, the pressure selection valve 48 is moved from the third speed automatic switching position (f) to the intermediate speed to large capacity second speed automatic switching position (e).
, The command pressure pipeline 44 is connected to the pilot pump 46 side, and the external command pressure Pgx of the pressure Pga set by the pressure reducing valve 49 described later is supplied to the external command pressure port 25H of the capacity control valve 21.

For this reason, the spool 28 is connected to the command pressure receiving portion 2
By receiving the external command pressure Pgx of the pressure Pga at 8L, the spool 28 is pushed from the position of FIG. 2 to the position of FIG.
1 is forcibly switched from the small capacity position (c) shown in FIG. 1 to the intermediate capacity position (b).

Thereafter, the pilot pressure receiving section 28
J, the spool 28 slides and displaces inside the valve housing 22 according to the pressure value of the pilot pressure Ppx received by the first and second shaft hole pressure receiving portions 29A and 34A, and the intermediate capacity position (b) and the large capacity position (A) is switched to the second speed.

When the pressure selection valve 48 is switched from the second speed automatic switching position (e) to the large capacity fixed position (d),
The command pressure line 44 is connected to the pilot pump 46 side,
An external command pressure Pgx of a pressure Pgb set by a pressure reducing valve 50 described later is supplied to an external command pressure port 25H of the capacity control valve 21.

Then, the spool 28 of the capacity control valve 21
Is pressed in the direction of arrow C against the return spring 40 when the command pressure receiving portion 28L receives the external command pressure Pgx of the pressure Pgb. Thereby, the capacity control valve 21 is switched from the small capacity position (c) or the intermediate capacity position (b) shown in FIG. 1 to the large capacity position (a), and is held at the large capacity position (a). .

Reference numeral 49 denotes a low pressure side pressure reducing valve provided between the pilot pump 46 and the pressure selection valve 48.
Reference numeral 9 denotes a valve for suppressing the external command pressure Pgx supplied into the command pressure line 44 from rising to the pressure Pga or higher. The valve is normally opened, and is closed when the discharge pressure from the pilot pump 46 rises to the pressure Pga or higher. A valve is provided to stop the supply of the discharge pressure.

Reference numeral 50 denotes a high pressure side pressure reducing valve provided between the pilot pump 46 and the pressure selection valve 48.
9 is a pressure Pgb (Pgb> P) in which the external command pressure Pgx supplied into the command pressure line 44 is higher than the pressure Pga by the pressure reducing valve 49.
ga) Regulate any further rise.

The pressure reducing valve 50 is normally open to keep the external command pressure Pgx supplied to the command pressure line 44 at the pressure Pgb while the pressure selection valve 48 is switched to the large capacity fixed position (d). When the discharge pressure from the pilot pump 46 rises above the pressure Pgb, the valve is closed to stop supplying the discharge pressure.

Reference numeral 51 denotes a first supply / discharge conduit connecting the hydraulic chamber 11A of the servo actuator 10 to a pressure oil supply / discharge port 25F of the capacity control valve 21, and reference numeral 52 denotes a servo actuator 10
The hydraulic chamber 12A is connected to the pressure oil supply / discharge port 25 of the capacity control valve 21.
This is a second supply / discharge conduit connected to D. Then, the servo actuator 10 tilts the variable capacity portion 3B of the hydraulic motor 3 in the directions of arrows B and A by supplying and discharging the pressure oil into the hydraulic chambers 11A and 12A through the supply and discharge conduits 51 and 52. When the motor is driven, the motor capacity is switched to a small capacity, an intermediate capacity, or a large capacity.

The traveling hydraulic circuit of the hydraulic shovel provided with the displacement control valve 21 and the like according to the present embodiment has the above-described configuration. Next, the operation thereof will be described.

First, when the operator of the hydraulic excavator switches the directional control valve 5 shown in FIG. 1 from the neutral position (a) to the switching position (b) in order to drive the vehicle, the hydraulic oil from the hydraulic pump 1 It is supplied to the hydraulic motor 3 from the main pipeline 4A side as a motor drive pressure. At this time, the pressure control valve 8 of the counter balance valve 6 is connected to the pipe sections 4A1, 4B1.
The pressure is switched from the neutral position (a) to the switching position (b) by the pressure difference, and the return oil from the hydraulic motor 3 is transferred to the tank 2 from the main pipeline 4B (the pipeline 4B1) via the pressure control valve 8. And the vehicle is driven to travel in the forward direction.

On the other hand, when the traveling direction control valve 5 is switched from the neutral position (A) to the switching position (C), the motor driving pressure is supplied to the main pipeline 4B side, and the hydraulic motor 3 is different from the above case. It is driven to rotate in the opposite direction. In this case, the pressure control valve 8 is switched from the neutral position (a) to the switching position (c).
And the return oil from the hydraulic motor 3 is supplied to the pressure control valve 8.
Through the main pipeline 4A (the pipeline section 4A1) to the tank 2, whereby the vehicle is driven to travel in the reverse direction.

Here, when the direction control valve 5 (pressure control valve 8) is switched from the neutral position (a) to the switching position (b) or (c) during running of the vehicle, the pipeline sections 4A2, 4B2 on the actuator side are provided. Valve 9 selects the high-pressure side hydraulic oil (motor driving pressure) on the side, and the high-pressure hydraulic oil composed of the motor driving pressure is supplied from the high-pressure line 20 to the high-pressure port 25 of the capacity control valve 21.
It is led to E.

When the pressure control valve 8 is switched from the neutral position (a) to the switching position (b) or (c), the motor drive pressure, which is the load pressure of the hydraulic motor 3, is applied from the center bypass port 8A to the pilot The displacement control valve 21 is guided into the line 16 and the pilot pressure Ppx from the pilot line 16 is set.
The switching is controlled in accordance with.

Further, the pilot pressure Ppx in the pilot line 16 is also supplied to the hydraulic chamber 14A of the brake device 14 via the control line 15, and the brake spring 14B is bent and deformed as the brake release pressure. The braking state of the hydraulic motor 3 by the device 14 is released. Thus, the hydraulic motor 3 is driven to rotate in accordance with the motor driving pressure in order to drive the vehicle on the road.

In the state where the pressure selection valve 48 for external command pressure is returned to the small- to large-capacity three-speed automatic switching position (f), the pilot port 25B of the displacement control valve 21 is maintained.
Is applied to the pilot pressure receiving portion 28J of the spool 28 shown in FIG. 2, and the pilot pressure receiving portion 28J pushes the spool 28 by the expression 5 using the pressure receiving area Sa according to the expression 1. It is pressed in the direction of arrow C against the urging force fa of the return spring 39 by the pressure Fa.

[0146]

## EQU5 ## Fa = Sa × Ppx

At this time, the pilot pressure Ppx supplied to the pilot port 25B of the displacement control valve 21 is supplied into the oil chamber 31 through the oil hole 33 of the spool 28 shown in FIG. It also acts on the first shaft hole pressure receiving portion 29A made of And this shaft hole pressure receiving portion 29A
Presses the spool 28 in the direction of arrow D with the pressing force F1 according to the equation (6) with the pressure receiving area S1 according to the equation (3).

[0148]

[Formula 6] F1 = S1 × Ppx

Therefore, the spool 28 shown in FIG. 2 has a total pressure receiving area (Sa-S1) with respect to the pilot pressure Ppx by the pilot pressure receiving portion 28J and the first shaft hole pressure receiving portion 29A.
The pressing force (Fa-F1) obtained by combining the two is pressed against the urging force fa of the return spring 39 in the direction of arrow C in FIG.

[0150]

## EQU7 ## Fa−F1 = (Sa−S1) × Ppx

In this case, the urging force f of the return spring 39
a is preset so as to satisfy the following equation (8), and the hysteresis is applied to the motor capacity of the hydraulic motor 3 while the pilot pressure Ppx changes at the switching pressures Pp1 to Pp3 as indicated by a characteristic line 53 shown in FIG. A characteristic is given, and the motor displacement is stably controlled to be switched between the small displacement and the intermediate displacement.

[0152]

## EQU8 ## fa = (Sa-S1) .times.Pp3 = (Sa-S1 +
S2) × Pp1

That is, for example, when the vehicle is traveling uphill on a slope having a medium gradient, the load pressure of the hydraulic motor 3 increases, and the pilot pressure Ppx increases to the switching pressure Pp3 or more. At this time, the spool 28 receives the pilot pressure Ppx in the direction indicated by the arrow C with the total pressure receiving area (Sa-S1) by the pilot pressure receiving portion 28J and the first shaft hole pressure receiving portion 29A. Force (Fa −
With F1), the return spring 39 is bent and deformed as shown in FIG. 3, and the stopper portion 28K is slid and displaced to the axial center switching position where it comes into contact with the spring receiver 41, that is, the intermediate capacity position (b).

Thus, the displacement control valve 21 is connected to the return spring 3
9 is switched from the small capacity position (c) shown in FIG. 1 to the intermediate capacity position (b) against the urging force fa, and the high pressure port 25E of the capacity control valve 21 is connected to the lands 28C and 28 of the spool 28.
Between the pressure oil supply / discharge ports 25D, 25
Communicated to F together.

For this reason, in the servo actuator 10, the hydraulic chambers 11A and 12A have the supply / discharge pipelines 51 and 52, the pressure oil supply / discharge ports 25F and 25D of the capacity control valve 21, and the high pressure port 25.
The first and second tilting pistons 11 and 12 are connected to the high-pressure line 20 via E, and are driven in the extending direction together with the pressure oil in the hydraulic chambers 11A and 12A, so that the capacity of the hydraulic motor 3 is increased. The variable displacement unit 3B is driven to an intermediate tilt position, and the motor displacement is controlled to an intermediate displacement so that the hydraulic motor 3 can be rotated at an intermediate torque at an intermediate speed in preparation for a middle-grade uphill traveling.

At this time, the capacity control valve 21 is connected to the oil chambers 31 and 36 in the spool 28 as shown in FIG.
The first and second shaft hole pressure receiving portions 29A and 34A in the shaft holes 29 and 34 both receive the pilot pressure Ppx by being connected to the pilot port 25B via the ports 3 and 37. They are opposite to each other.

In this case, the spool 28 is pressed by the pilot pressure receiving portion 28J in the direction indicated by the arrow C with the pressing force Fa (pressure receiving area Sa) as described above, and the first shaft hole pressure receiving portion 2J is pressed.
At 9A, it is pressed in the direction of arrow D by the pressing force F1 (pressure receiving area S1). Then, the second shaft hole pressure receiving portion 34A presses the spool 28 in the direction indicated by the arrow C with the pressing force F2 according to the equation (9) with the pressure receiving area S2 according to the equation (4).

[0158]

## EQU9 ## F2 = S2.times.Ppx

For this reason, the spool 28 shown in FIG. 3 includes the pilot pressure receiving portion 28J and the first and second shaft hole pressure receiving portions 29.
A and 34A respectively receive the pilot pressure Ppx, so that the total pressure receiving area with respect to the pilot pressure Ppx is changed from the pressure receiving area (Sa-S1) to the pressure receiving area (Sa-S1).
+ S2).

The spool 28 is pressed against the urging force fa of the return spring 39 (the urging force fb of the return spring 40) by a pressing force (Fa-F1 + F2) according to the following equation (10). Direction.

[0161]

## EQU10 ## Fa−F1 + F2 = (Sa−S1 + S2) ×
Ppx

As a result, even when the capacity of the hydraulic motor 3 changes from a small capacity to an intermediate capacity and the motor drive pressure (load pressure) slightly decreases, the spool pressure remains as long as the pilot pressure Ppx is equal to or higher than the pressure Pp1. As shown in FIG. 3, the return spring 39 bends and deforms the return spring 39 in the direction of arrow C as shown in FIG. 3 by the pressing force (Fa−F1 + F2) according to the equation (10).
At the intermediate capacity position (b).

[0163]

(Fa−F1 + F2) ≧ fa (where, Ppx ≧ Pp1)

On the other hand, when the vehicle has finished climbing up a sloping road having a medium slope, for example, going straight on flat ground, the pilot pressure Ppx becomes equal to the pressure Pp1 shown in FIG.
It falls to below. Thus, the pressing force (Fa-F1 + F2) of the spool 28 is reduced by the urging force fa of the return spring 39.
The spool 28 is pushed back in the direction indicated by the arrow D by the return spring 39, slides to the initial position shown in FIG. 2, and the capacity control valve 21 returns to the small capacity position (c) again.

At this time, since the high pressure port 25E of the capacity control valve 21 is connected to the pressure oil supply / discharge port 25F and the pressure oil supply / discharge port 25D is connected to the tank port 25C, the hydraulic chamber 12A of the servo actuator 10 Although connected to the tank 2 via the supply / discharge line 52 and the like, the high-pressure line 20 selected by the shuttle valve 9 is provided in the hydraulic chamber 11A.
Is supplied via the supply / discharge conduit 51 and the like.

For this reason, although the pressing force of the tilt piston 12 is released from the servo actuator 10, the displacement variable portion 3 B of the hydraulic motor 3 is reduced by the tilt piston 11 in the direction of arrow B against the spring 13. Drive to the tilting side.
As a result, the capacity of the hydraulic motor 3 can be controlled to a small capacity suitable for traveling on level ground, and the vehicle can run at high speed with low torque.

At this time, although the capacity control valve 21 allows the oil chamber 31 in the spool 28 to communicate with the pilot port 25B through the oil hole 33 as shown in FIG.
6 communicates with the tank port 25C through the small hole 38, so that the pilot pressure Ppx at this time is supplied only into the oil chamber 31, and only the first shaft hole pressure receiving portion 29A located on the bottom side of the shaft hole 29 is piloted. Pressure Ppx to pilot pressure receiving section 28
It receives pressure in the opposite direction to J.

Accordingly, the pressing force F2 of the spool 28 received from the shaft hole pressure receiving portion 34A in the oil chamber 36 becomes substantially zero. The pressure receiving area of the spool 28 is reduced to the pressure receiving area (Sa-S1) of the pilot pressure receiving portion 28J and the first shaft hole pressure receiving portion 29A. 28 presses the return spring 39 in the direction of arrow C.

As a result, even if the capacity of the hydraulic motor 3 changes from the intermediate capacity to a small capacity and the motor driving pressure (load pressure) slightly increases, the pilot pressure Ppx is maintained at the switching pressure Pp3.
, The spool 28 only presses the return spring 39 in the direction indicated by the arrow C in FIG. 2 with the pressing force (Fa-F1) according to the equation (7) and the following equation (12). It is urged to the initial position by the return spring 39 to hold the displacement control valve 21 at the small displacement position (c).

[0170]

(Fa−F1) <fa (where Ppx <Pp3)

On the other hand, when the vehicle climbs a medium slope,
In the state where the motor capacity is switched to the intermediate capacity, the slope of the slope becomes even greater, and the vehicle may travel uphill on a steep slope. Then, at this time, the load pressure of the hydraulic motor 3 further increases, and for example, the pilot pressure Ppx is increased to the switching pressure Pp4 or more.

At this time, in the spool 28, the pilot pressure receiving portion 28J and the second shaft hole pressure receiving portion 34A receive the pilot pressure Ppx in the direction of arrow C, and the first shaft hole pressure receiving portion 29A By receiving Ppx in the direction of arrow D, the pressing force (F1 -F1 +
F2), the return spring 40 is bent and deformed as shown in FIG.
Slides to the stroke end where it comes into contact with.

[0173]

(Fa−F1 + F2) ≧ fb (where Ppx ≧ Pp4)

In this case, the urging force f of the return spring 40
b is preset so as to satisfy the following equation (14),
While the pilot pressure Ppx changes in the range of the switching pressures Pp2 to Pp4 as indicated by the characteristic line 53 shown in FIG. 6, the motor capacity of the hydraulic motor 3 is given a hysteresis characteristic, and the motor capacity is determined by the intermediate capacity and the large capacity. The switching control is stably performed to one of them.

[0175]

Fb = (Sa−S1 + S2) × Pp4 = (Sa
+ S2) × Pp2

Thus, when the pilot pressure Ppx rises to the switching pressure Pp4 or more, for example, when the vehicle is traveling uphill on a steep slope, the displacement control valve 21 resists the urging force fb of the return spring 40 and the intermediate pressure shown in FIG. Switching from the capacity position (b) to the large capacity position (a), the high pressure port 25 of the capacity control valve 21
E is communicated only with the pressure oil supply / discharge port 25D.

The high pressure port 25 of the capacity control valve 21
E is shut off from the pressure oil supply / discharge port 25F by the land 28D of the spool 28, and the pressure oil supply / discharge port 25F is connected to the tank line 18 via the tank port 25G.

For this reason, the servo actuator 10
The pressure oil in the hydraulic chamber 11 </ b> A is discharged to the tank line 18 via the suction / discharge line 51, and the pressing force by the tilting piston 11 is released.
B is driven in the direction of the arrow A at which the tilt angle becomes the maximum, and is switched to the large capacity at which the motor capacity becomes the maximum by the biasing force of the spring 13. At this time, the tilt piston 12 remains at the intermediate tilt position while reaching the stroke end.

Then, the hydraulic motor 3 is rotated at a high torque at a low speed with a high torque in preparation for a steep hill-climbing operation by driving the variable capacity portion 3B in the direction of arrow A to the large tilt side. At this time, the capacity control valve 21
8, the oil chamber 31 is connected to the tank port 25A through the small hole 32, the narrow groove 28A1, the oil groove 24A, etc., as shown in FIG. The pressure will be reduced to about the pressure.

For this reason, in the spool 28, the pressing force F1 received from the shaft hole pressure receiving portion 29A in the oil chamber 31 becomes substantially zero, and the pilot pressure receiving portion 28J and the second shaft hole pressure receiving portion 34
A and pilot pressure P with pressure receiving area (Sa + S2)
px, and the total pressure receiving area of the spool 28 at this time increases from the pressure receiving area (Sa-S1 + S2) to the pressure receiving area (Sa + S2).

As a result, even when the capacity of the hydraulic motor 3 changes from the intermediate capacity to the large capacity and the motor driving pressure (load pressure) slightly decreases, the spool pressure is maintained as long as the pilot pressure Ppx is equal to or higher than the pressure Pp2. With the pressing force (Fa + F2) given by the following equations (15) and (16), the return spring 40 bends and deforms in the direction of arrow C as shown in FIG. 4, and the capacity control valve 21 is moved to the large capacity position (a). Can be kept.

[0182]

## EQU15 ## Fa + F2 = (Sa + S2) .times.Ppx

[0183]

(Fa + F2) ≧ fb (where Ppx ≧ Pp2)

Further, when the gradient during the uphill running is changed to a gentle middle gradient, and the vehicle is driven straight ahead on such a slope, the pilot pressure Ppx decreases to the pressure Pp2 or less shown in FIG. I do. As a result, the pressing force (Fa + F2) of the spool 28 becomes smaller than the urging force fb of the return spring 40, so that the spool 28 is pushed back in the direction indicated by the arrow D by the return spring 40, and the axial center shown in FIG. And the displacement control valve 21 returns to the intermediate displacement position (b) again.

At this time, the high pressure port 25E of the capacity control valve 21 is connected to both the pressure oil supply / discharge ports 25D and 25F.
1A, 12A are connected to the high-pressure line 20 via supply / discharge lines 51, 52 and the like, and the first and second tilt pistons 11, 12 are connected.
Are driven in the extension direction by the pressure oil in the hydraulic chambers 11A and 12A.

As a result, the hydraulic motor 3
B is driven to the intermediate tilt position by the servo actuator 10, and the motor capacity is again switched to the intermediate capacity so that the hydraulic motor 3 can be rotated at an intermediate torque at a medium speed in preparation for a middle-grade uphill traveling. Will be.

[0187] At this time, the capacity control valve 21 moves the oil chambers 31 and 36 in the spool 28 into the oil holes 3 as shown in FIG.
By being connected to the pilot port 25B via the ports 3 and 37, the pressure receiving area of the spool 28 can be adjusted to the pilot pressure receiving section 28J and the first and second shaft hole pressure receiving sections 29A and 34.
A, the pressure receiving area is reduced to the pressure receiving area (Sa-S1 + S2), and the pressing force (F
a -F1 + F2) and the return springs 39 and 40 are indicated by arrows C
Press in the direction.

As a result, even when the capacity of the hydraulic motor 3 changes from a large capacity to an intermediate capacity and the motor driving pressure (load pressure) slightly increases, the pilot pressure Ppx is maintained at the switching pressure Pp4.
, The spool 28 only presses the return spring 40 in the direction indicated by the arrow C in FIG. 3 with the pressing force (Fa−F1 + F2) in accordance with the equation (10) and the following equation (17). Is located at the axial center switching position by the pressing force (Fa-F1 + F2) by the pilot pressure Ppx and the urging force fb of the return spring 40, and holds the displacement control valve 21 at the intermediate displacement position (b). is there.

[0189]

(Fa−F1 + F2) <fb (where Ppx <Pp4)

As described above, the pressure selection valve 4 for the external command pressure is
8 is returned to the small- to large-capacity three-speed automatic switching position (f).
With the pilot pressure Ppx supplied to 5B, the motor displacement can be selectively switched among small displacement, intermediate displacement, and large displacement as shown by the characteristic line 53 shown in FIG. You can do it.

In the capacity control valve 21, the total pressure receiving area of the spool 28 with respect to the pilot pressure Ppx becomes the minimum pressure receiving area (Sa-S1) when the capacity is small, and the intermediate pressure receiving area (Sa-S1 + S2) when the capacity is intermediate. ), And when the displacement is large, the pressure receiving area (Sa + S2) gradually changes to the maximum pressure receiving area (Sa + S2).
Hysteresis characteristics can be provided in the range of Pp4, and the hunting phenomenon accompanying the switching of the capacitance can be favorably suppressed.

During this time, the output torque of the hydraulic motor 3 is controlled so as to increase and decrease in proportion to the pilot pressure Ppx as indicated by characteristic lines 54A, 54B and 54C in FIG.
Problems such as fluctuations in output torque when the motor capacity is switched can be eliminated, and the output torque characteristics can be fully utilized.

Next, when the operator of the excavator switches the pressure selection valve 48 from the third-speed automatic switching position (f) to the second-speed automatic switching position (e) of intermediate capacity to large capacity, the outside of the capacity control valve 21 is changed. An external command pressure Pgx of the pressure Pga is supplied to the command pressure chamber 43 through a command pressure pipeline 44 and an external command pressure port 25H.

In this case, the command pressure receiving portion 2 of the spool 28
8L receives the external command pressure Pgx of the pressure Pga in the external command pressure chamber 43 with the pressure receiving area Sb according to the above equation (2), thereby returning the spool 28 to the spring 39 with the pressing force Fga according to the following equation (18). Press in the direction of arrow C in opposition. Thereby, the displacement control valve 21 is switched from the small displacement position (c) shown in FIG. 1 to the intermediate displacement position (b).

[0195]

[Equation 18] Fga = Sb × Pga

The pressure Pga of the external command pressure Pgx is set in advance so as to satisfy Expression 19 with respect to the urging force fa of the return spring 39.

[0197]

[Equation 19] Pga> fa / Sb

The pressing force Fga at this time acts in the same direction as the pressure receiving direction of the pilot pressure receiving portion 28J with respect to the pilot pressure Ppx (the direction indicated by the arrow C in FIG. 3).
When the pilot pressure Ppx changes between the switching pressures Ppa and Ppb (Ppa <Ppb) shown in FIG. 8, the spool 28 gives a hysteresis characteristic to the switching control pressure of the motor displacement between the intermediate displacement and the large displacement.

The switching pressures Ppa and Ppb in this case are the pressing force Fga by the external command pressure Pgx and the urging force fb of the return spring 40.
Are determined as shown in the following equations (20) and (21).

[0200]

Ppa = (fb-Fga) / (Sa + S2)

[0201]

Ppb = (fb-Fga) / (Sa-S1 + S2)
)

That is, when the load pressure of the hydraulic motor 3 increases during the uphill traveling of the vehicle and the pilot pressure Ppx is increased to the switching pressure Ppb or more, the pilot pressure Ppx expressed by the equation (10) is used. Pressing force of spool 28 (Fa
−F1 + F2) and the pressing force Fga by the external command pressure Pgx of the pressure Pga are equal to the return spring 4 as expressed by the following equation (22).
It becomes smaller than the urging force fb of zero.

[0203]

Fb> (Fa-F1 + F2) + Fga (where Ppx <Ppb)

Therefore, the displacement control valve 21 is held at the middle displacement position (b), and the hydraulic motor 3 is kept at the middle displacement. The output torque of the hydraulic motor 3 during this time is equal to the pilot pressure Ppx as indicated by the characteristic line 55A in FIG.
Is proportionally increased or decreased in accordance with

However, the pilot pressure Ppx is changed to the switching pressure Ppb.
When the pressure is increased as described above, the pressing force (Fa-F1 + F2) of the spool 28 due to the pilot pressure Ppx and the pressure P
Since the sum of ga and the pressing force Fga by the external command pressure Pgx is equal to or greater than the urging force fb of the return spring 40 as shown in the following equation (23), the displacement control valve 21 is moved from the intermediate displacement position (b) to the large displacement position. Switching to (a), the hydraulic motor 3 has a large motor capacity.

[0206]

Fb ≦ (Fa−F1 + F2) + Fga (where Ppx ≧ Ppb)

When the displacement control valve 21 is switched from the intermediate displacement position (b) to the large displacement position (a), the total pressure receiving area for the pilot pressure Ppx of the spool 28 becomes the intermediate pressure receiving area (as described above). (Sa-S1 + S2) to the maximum pressure receiving area (Sa + S2).

For this reason, the pilot pressure Ppx changes to the switching pressure P
Until the pressure drops below pa, the pressing force (Fa + F2) of the spool 28 by the pilot pressure Ppx shown in the equation (15).
The sum of the pressure Pga and the pressing force Fga by the external command pressure Pgx is equal to the urging force fb of the return spring 40 as expressed by the following equation (24).
Larger than.

[0209]

Fb <(Fa + F2) + Fga (where Ppx> Ppa)

As a result, the displacement control valve 21 is held at the large displacement position (a), and the hydraulic motor 3 is kept at a large displacement.
The output torque of the hydraulic motor 3 during this time is proportionally increased or decreased according to the pilot pressure Ppx as indicated by a characteristic line 55B shown in FIG.

When the pilot pressure Ppx falls below the switching pressure Ppa, the sum of the pressing force (Fa + F2) of the spool 28 by the pilot pressure Ppx and the pressing force Fga by the external command pressure Pgx of the pressure Pga is as follows. As shown in the equation 25, the urging force fb of the return spring 40 becomes equal to or less than the value, the displacement control valve 21 switches from the large displacement position (a) to the intermediate displacement position (b), and the hydraulic motor 3 returns the motor displacement to the intermediate displacement. It is.

[0212]

Fb ≧ (Fa + F2) + Fga (where Ppx ≦ Ppa)

When the displacement control valve 21 is switched to the intermediate displacement position (b), the total pressure received by the spool 28 with respect to the pilot pressure Ppx is maintained until the pilot pressure Ppx rises to the switching pressure Ppb again in this state. When the area is reduced to the area (Sa-S1 + S2), the displacement control valve 21 is held at the intermediate displacement position (b),
The hydraulic motor 3 is maintained at an intermediate capacity. During this time, the output torque of the hydraulic motor 3 is increased or decreased as indicated by a characteristic line 55A in FIG.

On the other hand, when the operator of the excavator switches the pressure selection valve 48 to the large-capacity fixed position (d), the external pressure chamber 43 of the capacity control valve 21 has the command pressure line 44 and the external command pressure port 25H. Through the pressure Pgb (Pgb
> Pga) is supplied.

In this case, the command pressure receiving portion 2 of the spool 28
8L receives the external command pressure Pgx of the pressure Pgb in the external command pressure chamber 43 with the pressure receiving area Sb according to the above equation (2), thereby returning the spool 28 with the pressing force Fgb according to the following equation (26). It is pressed in the direction of arrow C against 40. As a result, the displacement control valve 21 is switched to the large displacement position (a) and is held at the large displacement position (a).

[0216]

Fgb = Sb × Pgb

The pressure Pgb of the external command pressure Pgx is given by
7 is set in advance so as to satisfy the equation (7).

[0218]

[Equation 27] Pgb> fb / Sb

The pressing force Fgb at this time acts in the same direction as the pressure receiving direction of the pilot pressure receiving portion 28J with respect to the pilot pressure Ppx (the direction indicated by the arrow C in FIG. 4). Irrespective of the increase or decrease, the displacement is slid to the stroke end shown in FIG. 4 by the external command pressure Pgx of the pressure Pgb, the displacement control valve 21 is held at the large displacement position (a) shown in FIG. Fixed to large capacity.

Therefore, for example, when the hydraulic excavator is driven at a narrow work site to perform a fine operation of the hydraulic motor 3, even if the load pressure (pilot pressure Ppx) of the hydraulic motor 3 becomes low. The motor capacity can be fixed to a large capacity, and the hydraulic motor 3 is rotated at a high torque and at a low speed, thereby improving the fine operability of the operating lever 5A and the like by the operator and reliably reducing the load during operation. Can be.

In this case, the output torque of the hydraulic motor 3 is increased or decreased in proportion to the pilot pressure Ppx as indicated by a characteristic line 56 in FIG. 9, and the motor capacity can be fixed at a large capacity. .

Thus, according to the present embodiment, an annular pilot pressure receiving portion 28J is formed by providing the largest diameter land 28A at one end of the spool 28, and the pilot pressure from the pilot port 25B is formed by the pilot pressure receiving portion 28J. Ppx is received with a pressure receiving area Sa.

A first oil chamber 31 is defined by slidably inserting a first piston 30 into a first shaft hole 29 extending from one end of the spool 28 in the axial direction. The oil chamber 31
Is selectively communicated with the tank port 25A and the pilot port 25B by the small hole 32 and the oil hole 33 in accordance with the sliding position of the spool 28, and is shut off.

Further, a second piston 35 is slidably inserted into a second shaft hole 34 extending in the axial direction from the other end of the spool 28 to define a second oil chamber 36. , The oil chamber 3
6 is connected to the pilot port 25B and the tank port 25C by the oil hole 37 and the small hole 38 according to the sliding position of the spool 28.
To selectively communicate and cut off.

When the spool 28 is at the switching position (initial position) on the other side in the axial direction shown in FIG. 2, that is, while the capacity control valve 21 is at the small capacity position (c), the first oil chamber 31 is connected to the pilot port. 25B, and the second oil chamber 36 communicates with the tank port 25C, thereby reducing the total pressure receiving area of the spool 28 with respect to the pilot pressure Ppx by the pressure receiving area of the pilot pressure receiving portion 28J and the first shaft hole pressure receiving portion 29A. (Sa-S1).

Thus, the spool 28 can be held at the initial position on the other side in the axial direction by the return spring 39 until the motor driving pressure (pilot pressure Ppx) rises above the switching pressure Pp3 shown in FIGS. The control valve 21 can be kept at the small capacity position (c).

When the motor drive pressure rises above the switching pressure Pp3, the spool 28 slides to the axially central switching position against the return spring 39, and the displacement control valve 2
1 is switched to the intermediate capacity position (b), as shown in FIG.
B, the pressure receiving area of the spool 28 can be increased from the pressure receiving area (Sa-S1) to the pressure receiving area (Sa-S1 + S2), and the pilot pressure Ppx is continuously received with this pressure receiving area (Sa-S1 + S2). Can be.

Therefore, even when the motor driving pressure slightly decreases as the capacity of the hydraulic motor 3 increases from a small capacity to an intermediate capacity, a larger pressure receiving area (Sa-S
1 + S2), the spool 28 can be held at the position shown in FIG. 3, and the displacement control valve 21 is switched to the intermediate displacement position (b) until the motor drive pressure falls to or below the pressure Pp1 during flat-land running. The motor capacity of the hydraulic motor 3 can be maintained at an intermediate capacity.

When the motor driving pressure rises above the switching pressure Pp4 illustrated in FIGS.
4 slides to the stroke end on one side in the axial direction against the return spring 40, and switches the capacity control valve 21 to the large capacity position (a), thereby connecting the first oil chamber 31 to the tank port as shown in FIG. The second oil chamber 36 is communicated with the pilot port 25B.

Thus, the pressure receiving area of the spool 28 can be
The pressure receiving area (Sa + S2) can be increased from the intermediate pressure receiving area (Sa-S1 + S2) to the maximum pressure receiving area (Sa + S2).
With 2), the pilot pressure Ppx can be continuously received and the motor capacity can be switched to a large capacity.

Therefore, even if the motor driving pressure slightly decreases as the capacity of the hydraulic motor 3 increases to a large capacity, the spool 28 is moved with the maximum pressure receiving area (Sa + S2) as shown in FIG. The motor capacity of the hydraulic motor 3 can be maintained at a large capacity by switching the capacity control valve 21 to the large capacity position (a) until the motor drive pressure can be maintained at the end position and the motor drive pressure falls to the pressure Pp2 or less. it can.

Therefore, according to the present embodiment, for example, three levels of hysteresis characteristics of small, medium and large can be given to the switching control pressure of the capacity control valve 21 within the range of the switching pressures Pp1 to Pp4. In addition to preventing the hunting phenomenon that accompanies the switching, the capacity control can be stably performed automatically.

Further, the displacement control valve 21 is connected to the valve housing 2.
2. Since it can be constituted by the spool 28, the pistons 30, 35, the return springs 39, 40, etc., the number of parts can be reduced, the workability at the time of assembling can be improved, and the whole can be made compact to reduce the size. Can be.

While the pressure selection valve 48 for external command pressure is switched to the third-speed automatic switching position (f) as described above, the pilot pressure Ppx and the first and second return springs 39 and 4 are maintained.
The motor drive pressure (pilot pressure P
The motor capacity of the hydraulic motor 3 can be automatically switched to three stages of small capacity, intermediate capacity or large capacity according to the increase / decrease of (px), so that the operator does not need to perform the capacity switching operation specially. The associated burden can be reduced.

On the other hand, the pressure selection valve 48 for external command pressure is set to 3
While switching from the automatic speed switching position (f) to the intermediate speed to large capacity two-speed automatic switching position (e), in addition to the external command pressure Pgx of the pressure Pga, the pilot pressure Ppx and the second return spring 4
The motor drive pressure (pilot pressure P
The motor capacity of the hydraulic motor 3 can be automatically switched between the intermediate capacity and the large capacity in two stages according to the increase or decrease of (px), and the burden on the operator can be reduced.

Further, while the pressure selection valve 48 for the external command pressure is switched to the large capacity fixing position (d), the motor capacity can be fixed to a large capacity regardless of the increase or decrease of the pilot pressure Ppx.
The operability when the operator finely operates the operation lever 5A or the like in a narrow work site or the like can be enhanced, and for example, the steering operation of the vehicle can be easily performed, and the burden on the operator can be reduced.

Thus, the operator can easily select an appropriate displacement switching mode according to the operating conditions and operating environment of the hydraulic shovel, and the capacity control device of the hydraulic motor 3 can be a high-performance device. .

When the pressure selection valve 48 is switched to the automatic switching position (d), the external command pressure Pgx is set to a pressure corresponding to the tank pressure.
Even for a vehicle not equipped with the gx command pressure supply device 45 or the like, the three-speed automatic switching control can be performed only by connecting the external command pressure port 25H to the tank 2, and the motor capacity by the external command pressure The capacity control valve 21 and the like can be incorporated with compatibility into a vehicle that does not perform the above control.

Further, for example, two modes of three-speed automatic switching control and large-capacity fixed control are selected or two modes of three-speed automatic switching control and two-speed automatic switching control are selected according to the pressure value of the external command pressure Pgx. Can be selected, so that the displacement control valve 21 and the like can be incorporated into various vehicles that perform switching control of the motor displacement, and the displacement control device is mounted. A highly versatile device can be obtained without limiting the type of vehicle.

Next, FIGS. 10 to 14 show the second embodiment of the present invention.
The feature of the present embodiment is that a spool is slidably provided in a valve housing of a capacity control valve, and the spool is disposed between both ends of the spool in the axial direction with a valve housing.
Second urging means are provided apart from each other, and the spools are urged in opposite directions by the first and second urging means.
In this configuration, the urging means is operated in a direction opposite to the urging direction.

In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the figure, reference numeral 61 denotes a displacement control valve attached to the hydraulic motor 3 together with the servo actuator 10. The displacement control valve 61 includes a valve housing 62, a spool 68, and a piston 68, which will be described later, as shown in FIGS. 70, 75 and return springs 80, 82 and the like.

The capacity control valve 61 is, for example, a 9-port 3 valve similarly to the capacity control valve 21 described in the first embodiment.
And a switching position of any one of a large capacity position (a), an intermediate capacity position (b) or a small capacity position (c) according to a pilot pressure Ppx or an external command pressure Pgx described later. Can be selectively switched over.

Numeral 62 designates a valve housing serving as an outer shell of the displacement control valve 61. The valve housing 62 is also configured substantially in the same manner as the valve housing 22 described in the first embodiment, and has a stepped bottomed shape. Spool sliding hole 63 and an oil groove 64 described later.
A to 64F and ports 65A to 65G are formed respectively.

The spool sliding hole 63 of the valve housing 62 has a large-diameter hole 63 having a maximum diameter at one end serving as an open end.
A, and the diameter is reduced in, for example, two stages toward the closed end 63B on the other end side. On the bottom side of the large-diameter hole 63A, an annular step 63C is formed between the bottom of the large-diameter hole 63A and an oil groove 64A described later, and a spring receiver 83 described later abuts the step 63C.

Here, in the valve housing 62, annular oil grooves 64A, 64B, 64 are formed on the outer peripheral side of the spool sliding hole 63.
C, 64D, 64E, and 64F are sequentially formed in the axial direction from one end to the other end, and the oil groove 64A is disposed adjacent to the step 63C of the spool sliding hole 63.

In the valve housing 62, the external command pressure port 65A, the pilot port 65B, the tank port 65C, the pressure oil supply / discharge port 65 are separated from each other in the axial direction.
D, a high pressure port 65E, a pressure oil supply / discharge port 65F, and a tank port 65G are formed.
65F communicates with the inside of the spool sliding hole 63 via annular oil grooves 64A to 64F, and the tank port 65G communicates with the spool sliding hole 63 via a spring chamber 79 described later.

Reference numeral 66 denotes a large-diameter hole portion 63 of the spool sliding hole 63.
The lid 66 is closed on the A side, and the lid 66 is
And a spring chamber 67, which is located in the large-diameter hole 63A and the oil groove 64A and is formed as a stepped space, is formed between one end of a spool 68 to be described later. In the present embodiment, the spring chamber 67 also serves as an external command pressure chamber.

Reference numeral 68 denotes a spool inserted into the spool sliding hole 63 of the valve housing 62. The spool 68 has lands 68A, 6 on its outer peripheral side as shown in FIGS.
8B, 68C, and 68D are formed to be spaced apart from each other in the axial direction, and an oil groove 64 is provided between the land 68B and the land 68C.
An annular groove 68E for communicating between C and 64D is formed.

Further, between the land 68C and the land 68D of the spool 68, between the oil grooves 64D and 64E,
Another annular groove 68F for communicating between E and 64F or between oil grooves 64D, 64E and 64F is formed. And these annular grooves 68E, 68F and lands 68B, 6
8C, 68D, the pressure oil supply / discharge ports 65D, 65F
Is selectively connected to and disconnected from the high-pressure port 65E and the tank ports 65C and 65G.

Here, the spool 68 is formed as a stepped spool having the largest diameter on the land 68A side located at one end side, and the annular stepped portion (end face side) of the land 68A facing the land 68B is connected to the pilot conduit 16. And a pilot pressure receiving portion 68G for receiving the pilot pressure Ppx.

A portion of the spool 68 located on one side in the axial direction is a one-side stopper portion 68H, and its end surface is provided with a command pressure receiving portion 68J for receiving an external command pressure Pgx in the spring chamber 67 together with the end surface of the land 68A. Has become. On the other hand, the other side of the spool 68 in the axial direction is a short other side stopper 68K, and the other side stopper 68K has a return spring 80 described later.
Are fitted and mounted.

In the spool 68 employed in this embodiment, the land 68A having the maximum diameter is formed with the outer diameter Da as shown in FIG. 14, and the land 68B is formed with the outer diameter Db.
Therefore, the pilot pressure receiving portion 68G has a pressure receiving area Sa according to the equation (1), similarly to the pilot pressure receiving portion 28J described in the first embodiment.

A command pressure receiving portion 68J of the spool 68
The spring chamber 6 is axially opposed to the pilot pressure receiving portion 68G with the land 68A interposed therebetween, and also serves as an external command pressure chamber.
7, the external command pressure Pgx is received in the direction of arrow D opposite to the pilot pressure receiving portion 68G.

In this case, the command pressure receiving portion 68J is
Since the land 68A is formed with the outer diameter Da as shown in FIG. 7, the pressure receiving area Sg (Sg> Sa) is calculated by the following equation (28).
) Receives the external command pressure Pgx, and when the external command pressure Pgx rises, the spool 68 is slid in the direction of arrow D against the return spring 80.

[0256]

Sg = Da ² × π / 4

On the other hand, the land 68A of the spool 68 has
On its outer peripheral side, annular narrow grooves 68A1, 68A2 are formed spaced apart in the axial direction. The land 68B of the spool 68 has annular narrow grooves 68B1, 6B on its outer peripheral side.
8B2 are formed spaced apart in the axial direction.

The narrow grooves 68A1 and 68A
2 and the narrow grooves 68B1 and 68B2 correspond to the narrow grooves 28A1 and 28A2 and the narrow grooves 28B1 and 28 described in the first embodiment.
Like the 8B2, it has a function to perform communication and interruption at zero lap.

A first shaft hole 69 is formed in the spool 68 and has a bottomed hole extending in the axial direction. The shaft hole 69 has one end opening to the end surface of the spool 68 and the other end forming a bottom. It is closed. The shaft hole 69 is formed with a relatively small hole diameter D1 (D1 <Db <Da) as shown in FIG.

The bottom side of the shaft hole 69 serves as a first shaft hole pressure receiving portion 69A for receiving the pressure in the oil chamber 71 described later. The first shaft hole pressure receiving portion 69A is used in the first embodiment. Like the first shaft hole pressure receiving portion 29A described in the embodiment, the pressure receiving surface S1 has a pressure receiving area S1 according to the equation (3).

Here, the first shaft hole pressure receiving portion 69A is the same as that shown in FIG.
When the pilot pressure Ppx is introduced into the oil chamber 71 as shown in FIGS. 1 and 12, the pilot pressure Ppx is received in a direction opposite to the pilot pressure receiving portion 68G (in the direction indicated by the arrow D). Also, as shown in FIG.
When communicating with 5A, the receiving of the pilot pressure Ppx is released.

The external command pressure Pgx led to the external command pressure port 65A is significantly lower than the pilot pressure Ppx (for example, a pressure of 1/10 to 1/30 or less).
Therefore, the pressing force when the shaft hole pressure receiving portion 69A receives the external command pressure Pgx is a force that is substantially negligible.

Reference numeral 70 denotes a first piston slidably inserted into the first shaft hole 69. The piston 70 always closes the opening end side of the shaft hole 69, and the other end side has the shaft hole 69. An oil chamber 71 is defined between the oil chamber 71 and the bottom of the oil chamber 71. Further, one end of the piston 70 projects axially from the end face of the spool 68 as shown in FIG. 11, and abuts a stopper 84 described later to receive a hydraulic reaction force due to the pilot pressure Ppx in the oil chamber 71. .

Numeral 72 denotes a small hole as a throttle hole formed in the radial direction of the spool 68 at the position of the oil chamber 71. The small hole 72 opens on the outer peripheral surface of the spool 68 at the position of the narrow groove 68A1. The oil chamber 71 is selectively communicated with the external command pressure port 65A (spring chamber 67) in accordance with the sliding position of the spool 68, and is shut off.

Numeral 73 denotes an oil hole formed in the radial direction of the spool 68 at the position of the oil chamber 71. The oil hole 73 forms an oil passage together with the small hole 72 comprising the throttle hole. The oil hole 73 opens in the outer peripheral surface of the spool 68 at the position of the narrow groove 68A2, and selectively communicates the oil chamber 71 with the pilot port 65B (oil groove 64B) according to the sliding position of the spool 68. It shuts off.

In this case, the oil hole 73 communicates with the pilot port 65B via the narrow groove 68A2 and the oil groove 64B and is shut off, and the small hole 72 communicates with the external command pressure port 65A via the narrow groove 68A1 and the oil groove 64A. And is cut off. And
The small hole 72 and the oil hole 73 are used to perform zero-lap communication between the oil chamber 71 and the pilot port 65B and the external command pressure port 65A when the spool 68 is slid and displaced. Narrow grooves 68A1, 68 always communicating with
A2 is formed with an axial interval corresponding to the distance between the oil grooves 64A and 64B.

The small hole 72 forms a throttle passage having a smaller diameter than the oil hole 73. And small hole 7
2, when the oil chamber 71 is communicated with the spring chamber 67 and the external command pressure port 65A as shown in FIG. 13, the pressure oil in the oil chamber 71 is prevented from spouting toward the external command pressure port 65A. And a function of suppressing generation of a surge pressure or the like on the external command pressure port 65A side.

A second shaft hole 74 is formed in the spool 68 so as to face the first shaft hole 69 and includes another bottomed hole extending in the axial direction. The one end of the second shaft hole 74 is a bottom. And the other end side is open to the end face of the spool 68. The shaft hole 74 has a relatively small hole diameter D2 as shown in FIG.
(D2 <Db <Da). In addition,
The hole diameter D2 of the shaft hole 74 is formed to be substantially the same as the hole diameter D1 of the first shaft hole 69, but there is no particular problem even if there is a magnitude relationship between the two.

Here, the bottom side of the shaft hole 74 serves as a second shaft hole pressure receiving portion 74A for receiving the pressure in the oil chamber 76 described later, and the second shaft hole pressure receiving portion 74A is provided in the first embodiment. Similarly to the shaft hole pressure receiving portion 34A described in the above embodiment, the pressure receiving area S2 is obtained by the equation (4).

The second shaft hole pressure receiving portion 74A is
2. When the pilot pressure Ppx is introduced into the oil chamber 76 as shown in FIG. 13, the pilot pressure Ppx is received in the same direction (the direction of arrow C) as the pilot pressure receiving portion 68G, as shown in FIG. When the inside of the oil chamber 76 communicates with the tank port 65C, the receiving of the pilot pressure Ppx is released. As a result, the bottom side of the shaft hole 74 functions as a shaft hole pressure receiving portion 74A whose pressure receiving area changes between the area S2 and zero.

Reference numeral 75 denotes a second piston slidably inserted into the second shaft hole 74. The piston 75 always closes the opening end of the shaft hole 74, and one end of the second piston 75 has the shaft hole 74. An oil chamber 76 is defined between the oil chamber 76 and the bottom of the oil chamber 76. The other end of the piston 75 projects axially from the end face of the spool 68 as shown in FIG. 12, and receives a hydraulic reaction force caused by the pilot pressure Ppx in the oil chamber 76 via a stopper 81 described later. The sliding hole 63 is in contact with the closed end 63B.

Reference numeral 77 denotes an oil hole formed in the radial direction of the spool 68 at the position of the oil chamber 76. The oil hole 77 is a small hole 78 described later.
Together, they constitute an oil passage. The oil hole 77 opens in the outer peripheral surface of the spool 68 at the position of the narrow groove 68B1, and selectively communicates the oil chamber 76 with the pilot port 65B (oil groove 64B) according to the sliding position of the spool 68. It shuts off.

Reference numeral 78 denotes a small hole as a throttle hole formed in the radial direction of the spool 68 at the position of the oil chamber 76. The small hole 78 opens on the outer peripheral surface of the spool 68 at the position of the narrow groove 68B2. The oil chamber 76 is selectively communicated with the tank port 65C (oil groove 64C) in accordance with the sliding position of the spool 68, and is shut off.

In this case, the oil hole 77 communicates with the pilot port 65B through the narrow groove 68B1 and the oil groove 64B, and is shut off. The small hole 78 communicates with the tank port 65C through the narrow groove 68B2 and the oil groove 64C. , Be cut off. The oil hole 77 and the small hole 78 are used for the oil chamber 76, the pilot port 65B, and the tank port 6 when the spool 68 slides.
The oil hole 77,
The narrow width grooves 68B1 and 68B2, which are always in communication with the small holes 78,
The oil grooves 64B and 64C are formed with an axial interval corresponding to the distance between them.

The small hole 78 forms a throttle passage having a smaller diameter than the oil hole 77. And small hole 7
8, when the oil chamber 76 is communicated with the oil groove 64C and the tank port 65C as shown in FIG. 11, the pressure oil in the oil chamber 76 is prevented from spouting toward the tank port 65C, and the tank port 65C Side has a function of suppressing generation of surge pressure or the like.

Reference numeral 79 denotes a closed end 63B of the spool sliding hole 63.
A spring chamber 80 formed between the spring chamber 79 and the stopper 68K of the spool 68 is located in the spring chamber 79 and has a closed end 63B of the spool sliding hole 63 and the stopper 68 of the spool 68.
9 shows a return spring that constitutes a first urging means disposed between the first spring and the first spring.

Here, one end of the return spring 80 is fitted and attached to the stopper 68K of the spool 68, and the other end is in contact with the closed end 63B of the spool sliding hole 63. Then, the return spring 80 directs the spool 68 in the direction of arrow C and constantly urges it with an urging force fc as shown in the following equation (29), whereby the displacement control valve 61 moves the small displacement position (c) shown in FIG. To the intermediate capacity position (b).

Reference numeral 81 denotes a stopper provided in the spring chamber 79 on the closed end 63B side of the spool sliding hole 63. As shown in FIG. When the return spring 80 is displaced to (the switching position on the other side in the axial direction), it comes into contact with the stopper portion 68K of the spool 68 to restrict the return spring 80 from being further bent and deformed.

A return spring 82 is located between the lid 66 and the spring receiver 83 and constitutes a second biasing means disposed in the spring chamber 67. The return spring 82 is a stopper 84 described later.
And one end thereof is in contact with the lid 66. The other end of the return spring 82 is in contact with the spring receiver 83, and the biasing force fd (f) is greater than that of the first return spring 80.
The spring receiver 83 is pressed against the step 63C of the valve housing 62 (spool sliding hole 63) with d> fc).

The return spring 82 has an intermediate capacity position (b) in which the spool 68 is at the axial center switching position shown in FIG. 12, and a large capacity position (one axial switching position shown in FIG. 13). The spool 68 is urged by the urging force fd toward the closed end 63B (in the direction of the arrow D) via the spring receiver 83 during the sliding displacement between the spool 68 and (a).

Reference numeral 83 denotes a spring receiver which constitutes a second biasing means together with a return spring 82. The spring receiver 83 is formed of an annular plate or the like, and its outer peripheral side is fitted to the step 63C of the spool sliding hole 63. Is pressed so that it can be separated and contacted. Further, a piston 70 is inserted into the inner peripheral side of the spring receiver 83,
Thus, the distal end side of the piston 70 penetrates through the center side of the spring receiver 83 and abuts on the end face of the stopper 84.

Reference numeral 84 denotes a stopper provided in the lid 66 located in the spring chamber 67. The stopper 84 is
And is disposed on the center side of the spring chamber 67. When the spool 68 is displaced to the stroke end on one side in the axial direction (the switching position on one side in the axial direction), the stopper 84 comes into contact with the spool 68 via the spring receiver 83 as shown in FIG. 82 regulates further bending and deformation.

Reference numeral 85 denotes a command pressure line connected to the external command pressure port 65A of the capacity control valve 61; 86, a command pressure supply device serving as command pressure generating means; In substantially the same manner as the command pressure supply device 45 described in the embodiment, the command pressure supply device 45 includes a tank 2, a pilot pump 46, a pressure selection valve 87 and a pressure reducing valve 88 described below, and the like. To supply an external command pressure Pgx via a command pressure line 85 to the control unit.

Reference numeral 87 denotes a pressure selection valve as an external selection means for selectively connecting the command pressure line 85 to the tank 2 and the pilot pump 46. The pressure selection valve 87 is operated by a hydraulic shovel operator or the like by operating the operation lever 87A. By manual operation, the gear can be switched to either the third-speed automatic switching position (g) or the second-speed automatic switching position (h).

While the pressure selection valve 87 is switched to the small- to large-capacity three-speed automatic switching position (g) as shown in FIG. 10, the command pressure line 85 is connected to the pilot pump 46 side. Pressure P set by pressure reducing valve 88 described later
The external command pressure Pgx of gc is supplied to the external command pressure port 65A of the capacity control valve 61.

For this reason, as shown in FIG. 11, the spool 68 receives the external command pressure Pgx of the pressure Pgc by the command pressure receiving portion 68J as shown in FIG. As shown in FIG. 10, the displacement control valve 61 is pushed to the intermediate displacement position (b).
Is forcibly switched to the small capacity position (c).

The spool 68 of the displacement control valve 61
Can slide in the valve housing 62 in accordance with the pressure value of the pilot pressure Ppx received by the pilot pressure receiving portion 68G and the first and second shaft hole pressure receiving portions 69A and 74A.
Similarly to the spool 28 described in the first embodiment, when the pilot pressure Ppx exceeds the switching pressure Pp3 illustrated in FIGS. 6 and 7, the spool 68 moves from the position in FIG. 11 to the position in FIG. Pushed in the direction of arrow C, the displacement control valve 61
The position is switched from the small capacity position (c) shown at 0 to the intermediate capacity position (b).

At the intermediate capacity position (b), the pilot pressure Ppx is changed to the switching pressures Pp1 to Pp1 shown in FIGS.
As long as it changes within the range of Pp3, the spool 68 is held at the axially central switching position shown in FIG. Further, in this state, the pilot pressure Ppx is changed to the switching pressure P illustrated in FIGS.
When it exceeds p4, the spool 6 is pressed against the return spring 82.
8 is pushed in the direction of arrow C from the position of FIG. 12 to the position of FIG. 13, and the displacement control valve 61 shown in FIG. 10 is switched from the intermediate displacement position (b) to the large displacement position (a). .

On the other hand, the pressure selection valve 87 is moved from the third speed automatic switching position (g) to the intermediate speed to large capacity second speed automatic switching position (h).
When the command pressure is switched to the command pressure line 85, the command pressure line 85 is connected to the tank 2 so that the external command pressure Pgx is in a low pressure state of about the tank pressure.

Then, since the pressure of the external command pressure port 65A (spring chamber 67) becomes the tank pressure level, the displacement control valve 61 moves to the axial center switching position shown in FIG. 12, ie, the intermediate displacement position (b). The spool 68 is urged by the return spring 80, and the displacement control valve 61 is forcibly switched from the small displacement position (c) shown in FIG.

After that, the pilot pressure receiving section 68
G, the spool 68 slides and displaces inside the valve housing 62 in accordance with the pressure value of the pilot pressure Ppx received by the first and second shaft hole pressure receiving portions 69A and 74A, and the intermediate capacity position (b) and the large capacity position (A) is switched to the second speed.

Reference numeral 88 denotes a pressure reducing valve provided between the pilot pump 46 and the pressure selection valve 87. The pressure reducing valve 88 increases the external command pressure Pgx supplied to the command pressure line 85 to a pressure Pgc or more. When the discharge pressure from the pilot pump 46 rises above the pressure Pgc, the valve is closed and the supply of the discharge pressure is stopped.

Thus, in the present embodiment configured as described above, substantially the same operation and effect as those of the first embodiment can be obtained.
The second return springs 80 and 82 urge the spool 68 in opposite directions, and the external command pressure Pgx acts on the spool 68 in a direction opposite to the urging direction of the first return spring 80. Therefore, the following operation and effect can be obtained.

First, the pressure selection valve 87 for external command pressure is set
As shown in FIG. 10, when the switching operation is performed to the small- to large-capacity three-speed automatic switching position (g), a command pressure line 85 and an external command pressure are provided in a spring chamber 67 serving as an external command pressure chamber of the capacity control valve 61. External command pressure Pgx of pressure Pgc through port 65A
Is supplied.

In this case, the command pressure receiving portion 6 of the spool 68
8J receives the external command pressure Pgx of the pressure Pgc in the external command pressure chamber (spring chamber 67) with the pressure receiving area Sg according to the above equation 28, thereby obtaining a pressing force F according to the following equation 29.
With the gc, the spool 68 is pressed against the return spring 80 as indicated by arrow D.
Press in the direction. As a result, the displacement control valve 61 shown in FIG. 10 is forcibly switched from the intermediate displacement position (b) to the small displacement position (c).

[0296]

Fgc = Sg × Pgc

The pressure Pgc of the external command pressure Pgx is set in advance so as to satisfy Expression 30 with respect to the urging force fc of the return spring 80.

[0298]

[Equation 30] Pgc> fc / Sg

The pressing force Fgc at this time is opposite to the pressure receiving direction of the pilot pressure receiving portion 68G with respect to the pilot pressure Ppx, and is also opposite to the biasing direction of the return spring 80 (the direction indicated by the arrow D in FIG. 11). ), The spool 68
The pilot pressures Ppx are the switching pressures Pp1, Pp illustrated in FIG.
When changing between p3 (Pp1 <Pp3), a hysteresis characteristic is given to the switching control pressure of the motor displacement between the small displacement and the intermediate displacement.

In this case, the pressing force Fgc of the spool 68 by the external command pressure Pgx of the pressure Pgc and the urging force fc of the return spring 80 are expressed by the following equation 31 with respect to the switching pressures Pp1 and Pp3 of the pilot pressure Ppx. What is necessary is just to set so that it may be satisfied.

[0301]

Fgc−fc = (Sa−S1) × Pp3 = (Sa
−S1 + S2) × Pp1

When the displacement control valve 61 is switched to the small displacement position (c), the valve housing 6
The pilot pressure Ppx supplied to the second pilot port 65B acts on the pilot pressure receiving portion 68G of the spool 68 shown in FIG. 11, and the pilot pressure receiving portion 68G returns the spool 68 with the pressure receiving area Sa according to the equation (1). It is pressed in the same direction as the biasing direction of the spring 80 (the direction indicated by the arrow C in FIG. 11).

At this time, the pilot pressure Ppx supplied to the pilot port 65B of the displacement control valve 61 is supplied into the oil chamber 71 through the oil hole 73 of the spool 68 shown in FIG. This also acts on the first shaft hole pressure receiving portion 69A made of: And, this shaft hole pressure receiving portion 69A
Is the spool 6 having the pressure receiving area S1 according to the equation (3).
8 is pressed in the direction of arrow D.

Therefore, the spool 68 shown in FIG. 11 has a total pressure receiving area (Sa-S1) with respect to the pilot pressure Ppx by the pilot pressure receiving portion 68G and the first shaft hole pressure receiving portion 69A.
The spool 68 is pressed in the direction of arrow C by the pressing force (Fa-F1) according to the above equation (7) and the urging force fc of the return spring 80, and the external command pressure Pgc in the direction of arrow D. It is pressed by the pressing force Fgc by Pgx.

Next, in this state, for example, when the vehicle is traveling uphill on a sloping road having a medium gradient, the load pressure of the hydraulic motor 3 increases, and the pilot pressure Ppx increases to the switching pressure Pp3 or more. Then, at this time, the spool 68 receives the pilot pressure Ppx in the arrow C direction with the total pressure receiving area (Sa-S1) in the pilot pressure receiving portion 68G and the first shaft hole pressure receiving portion 69A.

Therefore, in the spool 68, the pressing force (Fa-F1) and the urging force fc of the return spring 80 are larger than the pressing force Fgc by the external command pressure Pgx of the pressure Pgc as shown in the following Expression 32. And the stopper 68H is
3 is slid and displaced to a switching position at the center in the axial direction, that is, an intermediate capacity position (b).

[0307]

Fgc <(Fa−F1) + fc (where Ppx> Pp3)

As a result, the spool 6 of the capacity control valve 61
8 switches from the small capacity position (c) shown in FIG. 10 to the intermediate capacity position (b) against the pressing force Fgc acting on the command pressure receiving portion 68J, and the high pressure port 65E of the capacity control valve 61 is As shown in FIG. 12, an annular groove 68F connects between the lands 68C and 68D of the spool 68 to the pressure oil supply / discharge ports 65D and 65F.

As a result, in the servo actuator 10, the hydraulic chambers 11A and 12A have the supply / discharge pipe lines 51 and 52, the pressure oil supply / discharge ports 65F and 65D of the capacity control valve 61, and the high pressure port 65.
The first and second tilt pistons 11, 12 are connected to the high-pressure line 20 via E, and are driven in the extending direction by the pressure oil in the hydraulic chambers 11A, 12A.

Thus, the servo actuator 10 drives the variable capacity portion 3B of the hydraulic motor 3 to the intermediate tilt position, and the hydraulic motor 3 can rotate at intermediate speed with intermediate torque in preparation for the middle graded uphill traveling. Thus, the motor capacity is controlled to an intermediate capacity between the small capacity and the large capacity.

At this time, the capacity control valve 61 is connected to the pilot port 65B through the oil holes 73 and 77, as shown in FIG. The first and second shaft hole pressure receiving portions 69A and 74A in the holes 69 and 74 both receive the pilot pressure Ppx, and the pressure receiving directions are opposite to each other.

In this case, the spool 68 is pressed by the pilot pressure receiving portion 68G in the direction of the arrow C with the pressing force Fa (pressure receiving area Sa) as described above, and the first shaft hole pressure receiving portion 6G is pressed.
At 9A, it is pressed in the direction of arrow D by the pressing force F1 (pressure receiving area S1). Then, the second shaft hole pressure receiving portion 74A presses the spool 68 in the direction indicated by the arrow C with the pressing force F2 according to the expression (9) with the pressure receiving area S2 according to the expression (4).

Therefore, the spool 68 shown in FIG.
Pilot pressure receiving portion 68G and first and second shaft hole pressure receiving portions 69
A and 74A respectively receive the pilot pressure Ppx, so that the total pressure receiving area with respect to the pilot pressure Ppx is changed from the pressure receiving area (Sa-S1) to the pressure receiving area (Sa-S1).
+ S2).

The spool 68 is a pressing force obtained by adding the pressing force (Fa-F1 + F2) according to the above equation (10) and the urging force fc of the return spring 80, and the external command pressure Pgx of the pressure Pgc is obtained.
12 is pressed against the pressing force Fgc (the urging force fd of the return spring 82).

As a result, even when the capacity of the hydraulic motor 3 changes from a small capacity to an intermediate capacity and the motor drive pressure (load pressure) slightly decreases, the following applies while the pilot pressure Ppx is equal to or higher than the pressure Pp1. As shown in Equation 33, the spool 68 is moved by the return spring 80 with the pressing force (Fa-F1 + F2).
At the same time, the displacement control valve 61 is maintained at the intermediate displacement position (b).

[0316]

(Fa−F1 + F2) ≧ Fgc−fc (where Ppx ≧ Pp1)

[0317] On the other hand, when the vehicle finishes climbing up a hill having a moderate slope, for example, when the vehicle moves straight ahead on flat ground, etc., the pilot pressure Ppx falls to or below the pressure Pp1 illustrated in FIG. I do. As a result, the pressing force (Fa-F1 + F2) of the spool 68 is reduced, and the spool 68 is pushed back against the return spring 80 in the direction of arrow D by the pressing force Fgc by the external command pressure Pgx of the pressure Pgc. After the sliding displacement to the initial position shown in FIG. 11, the displacement control valve 61 returns to the small displacement position (c) again.

At this time, the high pressure port 65E of the capacity control valve 61 is connected to the pressure oil supply / discharge port 65F, and the pressure oil supply / discharge port 65D is connected to the tank port 65C. As a result, the variable displacement portion 3B of the hydraulic motor 3 is driven in the direction of the arrow B toward the small tilt side against the spring 13. As a result, the capacity of the hydraulic motor 3 can be controlled to a small capacity suitable for traveling on level ground, and the vehicle can run at high speed with low torque.

At this time, the capacity control valve 61 is arranged such that the oil chamber 71 in the spool 68 communicates with the pilot port 65B through the oil hole 73 as shown in FIG. 65C, the pilot pressure Ppx at this time is supplied only into the oil chamber 71, and only the first shaft hole pressure receiving portion 69A located on the bottom side of the shaft hole 69 applies the pilot pressure Ppx to the pilot pressure receiving portion 6A.
It receives pressure in the opposite direction to 8G.

For this reason, the pressing force F2 of the spool 68 received from the shaft hole pressure receiving portion 74A in the oil chamber 76 becomes substantially zero. Then, the pressure receiving area of the spool 68 is reduced to the pressure receiving area (Sa-S1) of the pilot pressure receiving section 68G and the first shaft hole pressure receiving section 69A, and the spool receives the pressing force (Fa-F1) again by the equation (7). 68 is pressed together with the return spring 80 in the direction of arrow C.

As a result, the capacity of the hydraulic motor 3 changes from the intermediate capacity to a small capacity, and even when the motor driving pressure (load pressure) slightly increases, the pilot pressure Ppx is maintained at the switching pressure Pp3.
Until the spool 68 is pressed, the spool 68 is pressed together with the return spring 80 in the direction indicated by the arrow C in FIG. 11 with the pressing force (Fa-F1) according to the equation (7). It is held at the small capacity position (c) by the pressure Pgx.

On the other hand, when the vehicle climbs a medium slope,
In the state where the motor capacity is switched to the intermediate capacity, the slope of the slope becomes even greater, and the vehicle may travel uphill on a steep slope. Then, at this time, the load pressure of the hydraulic motor 3 further increases, and for example, the pilot pressure Ppx is increased to the switching pressure Pp4 or more.

At this time, in the spool 68, the pilot pressure receiving portion 68G and the second shaft hole pressure receiving portion 74A receive the pilot pressure Ppx in the direction of arrow C, and the first shaft hole pressure receiving portion 69A receives the pilot pressure Pxx. Ppx is received in the direction of arrow D, and the command pressure receiving portion 68J receives the external command pressure Pgx of the pressure Pgc.

Thus, the spool 68 receives the pressing force Fgc based on the external command pressure Pgx of the pressure Pgc, and receives the pressing force (F1-F1 + F2) based on the pilot pressure Ppx as shown in the following equation (34). As shown in FIG. 13, the return spring 82 of the force fd is flexed and deformed, and the spool 68 is slid and displaced through the spring receiver 83 to the stroke end in contact with the stopper 84.

[0325]

(Fa−F1 + F2) −fc ≧ Fgc + fd (where Ppx ≧ Pp4)

Also, in this case, the urging force f of the return spring 82
d is set in advance so as to satisfy the following Expression 35,
While the pilot pressure Ppx changes in the range of the switching pressures Pp2 to Pp4 as indicated by the characteristic line 53 illustrated in FIG. 6, the motor capacity of the hydraulic motor 3 is given a hysteresis characteristic, and the motor capacity is set to an intermediate capacity and a large capacity. The switching control is stably performed to either of the above.

[0327]

Fd = (Sa−S1 + S2) × Pp4 + (fc
−Fgc) = (Sa + S2) × Pp2 + (fc−Fgc)

Thus, when the pilot pressure Ppx rises to the switching pressure Pp4 or more, for example, when the vehicle is traveling uphill on a steep hill, the displacement control valve 61 resists the urging force fd of the return spring 82 and the intermediate pressure shown in FIG. Switching from the capacity position (b) to the large capacity position (a), the high pressure port 65 of the capacity control valve 61
E is communicated only with the pressure oil supply / discharge port 65D.

Then, the high pressure port 65 of the capacity control valve 61
E is shut off from the pressure oil supply / discharge port 65F by the land 68D of the spool 68, and the pressure oil supply / discharge port 65F is connected to the tank line 18 via the tank port 65G. 13 drives the variable capacity portion 3B of the hydraulic motor 3 in the direction of arrow A to the large tilt side, and the hydraulic motor 3 is rotated at a low speed with a high torque at a high torque in preparation for a steep ascent of the vehicle.

At this time, the capacity control valve 61 is connected to the oil chamber 71 in the spool 68 as shown in FIG.
By being connected to the external command pressure port 65A via the narrow groove 68A1, the oil groove 64A, etc., the pressure in the oil chamber 71 decreases to the pressure Pgc by the external command pressure Pgx.

The pressure Pgc of the external command pressure Pgx is normally set to a pressure sufficiently lower than the pressure Pp4 of the pilot pressure Ppx (for example, Pgc <Pp4 / 20).

For this reason, the spool 68 receives the pressure receiving area 69A in the oil chamber 71 from the shaft pressure receiving portion 69A so as to be negligible, so that the pilot pressure receiving portion 68G and the second shaft pressure receiving portion 74A receive a pressure receiving area. The pilot pressure Ppx is received with (Sa + S2), and the total pressure receiving area of the spool 68 at this time is the pressure receiving area (Sa-S1 + S
2) to the pressure receiving area (Sa + S2).

As a result, even when the capacity of the hydraulic motor 3 changes from the intermediate capacity to the large capacity and the motor drive pressure (load pressure) slightly decreases, the spool pressure remains at or above the pilot pressure Ppx at or above the pressure Pp2. 68 is the pressing force (F
a + F2), the return spring 82 is bent and deformed in the direction of arrow C as shown in FIG. 13 according to the following equation 36, and the displacement control valve 61 can be maintained at the large displacement position (a).

[0334]

(Fa + F2) ≧ Fgc + fd−fc (where Ppx ≧ Pp2)

In addition, when the gradient at the time of traveling uphill changes to a gentle moderate gradient, and the vehicle shifts to traveling straight on such a slope, the pilot pressure Ppx becomes lower than the pressure Pp2 illustrated in FIG. descend. Thereby, the spool 68
The pressing force (Fa + F2) of the return spring 82 is the urging force fd of the return spring 82.
12, the spool 68 is pushed back in the direction of arrow D by the return spring 82, and slidably displaced to the axial center switching position shown in FIG. 12, and the displacement control valve 61 is again moved to the intermediate displacement position (b). Return to.

At this time, since the high-pressure port 65E of the capacity control valve 61 is connected to both the pressure oil supply / discharge ports 65D and 65F, the hydraulic motor 3 moves the capacity variable section 3B to the middle tilt position by the servo actuator 10. The motor capacity is again switched to the intermediate capacity so that the hydraulic motor 3 can be driven to rotate at an intermediate torque at an intermediate speed in preparation for the middle grade uphill traveling.

At this time, the capacity control valve 61 is connected to the pilot port 65B through the oil holes 73 and 77, as shown in FIG. The pressure receiving area of the pilot pressure receiving part 68G and the first and second shaft hole pressure receiving parts 69A, 7
4A, the pressure receiving area (Sa-S1 + S2) is reduced, and the spool 68 presses the pressing force (F
a-F1 + F2) and presses the return spring 82 in the direction of arrow C.

As a result, even when the capacity of the hydraulic motor 3 changes from a large capacity to an intermediate capacity and the motor driving pressure (load pressure) slightly increases, the pilot pressure Ppx is maintained at the switching pressure Pp4.
, The spool 68 only presses the return spring 82 in the direction indicated by the arrow C in FIG. 12 with the pressing force (Fa-F1 + F2) as shown in the following equation (37).
8 is a pressing force (Fa-F1 + F) by the pilot pressure Ppx.
2) and the biasing force fd of the return spring 82 is used to hold the displacement control valve 61 at the intermediate displacement position (b) at the axial center switching position.

[0339]

(Fa−F1 + F2) <Fgc + fd−fc (where Ppx <Pp4)

As described above, the pressure selection valve 8 for external command pressure
In the state in which the position 7 is switched to the small- to large-capacity three-speed automatic switching position (g), the pilot pressure Ppx supplied to the pilot port 65B of the displacement control valve 61 causes the characteristic line 53 shown in FIG. As described above, the motor capacity can be selectively switched to any of small capacity, intermediate capacity, and large capacity,
The third-speed automatic switching control can be stably performed.

In the capacity control valve 61, the total pressure receiving area of the spool 68 with respect to the pilot pressure Ppx becomes the minimum pressure receiving area (Sa-S1) when the capacity is small, and the intermediate pressure receiving area (Sa-S1 + S2) when the capacity is medium. ), And when the displacement is large, the pressure receiving area (Sa + S2) changes stepwise, so that the switching control pressure of the displacement control valve 61 is changed to the switching pressure Pp1 ~.
Hysteresis characteristics can be provided in the range of Pp4, and the hunting phenomenon accompanying the switching of the capacitance can be favorably suppressed.

Next, when the operator of the hydraulic shovel switches the pressure selection valve 87 from the third speed automatic switching position (g) to the intermediate speed to large capacity second speed automatic switching position (h), the command pressure line 85 Because the selection valve 87 is connected to the tank 2, an external command pressure Pgx corresponding to the tank pressure is supplied to the external command pressure chamber (spring chamber 67) of the capacity control valve 61 through the command pressure pipeline 85 and the external command pressure port 65 </ b> A. You.

As a result, the pressure of the spring chamber 67 serving as the command pressure receiving chamber of the capacity control valve 61 decreases to the tank pressure, and the spool 68 loses the pressing force of the command pressure receiving portion 68J in the direction indicated by the arrow D. The return spring 80 is pushed in the direction of arrow C to the switching position at the center in the axial direction. Thereby, the capacity control valve 6
1 is switched from the small capacity position (c) shown in FIG. 10 to the intermediate capacity position (b).

Then, in this case, the urging force fc of the return spring 80 is applied to the pilot pressure receiving portion 6 with respect to the pilot pressure Ppx.
The same direction as the pressure receiving direction of 8G (the direction indicated by arrow C in FIG. 12)
The urging force fd of the return spring 82 acts in the direction opposite to the pressure receiving direction of the pilot pressure receiving portion 68G (the direction indicated by the arrow D in FIG. 12).

As a result, the spool 68 changes the pilot pressure Ppx to the switching pressures Ppa, Ppb (P
When changing between pa <Ppb), the hysteresis characteristic is given to the switching control pressure of the motor displacement between the intermediate displacement and the large displacement.

In this case, the switching pressures Ppa and Ppb are determined by the urging force fc of the return spring 80 and the urging force fd of the return spring 82 as in the following equations (38) and (39).

[0347]

Ppa = (fd−fc) / (Sa + S2)

[0348]

## EQU39 ## Ppb = (fd-fc) / (Sa-S1 + S2)
)

That is, when the load pressure of the hydraulic motor 3 increases when the vehicle is traveling uphill, the pilot pressure Ppx is increased by the pilot pressure Ppx shown in the equation (10) until the pilot pressure Ppx rises to the switching pressure Ppb or more. Pressing force of spool 68 (Fa
-F1 + F2) and the urging force fc of the return spring 80 are:
It becomes smaller than the urging force fd of the return spring 82 as in the following equation (40).

[0350]

Fd> (Fa-F1 + F2) + fc (where Ppx <Ppb)

Therefore, the displacement control valve 61 is held at the middle displacement position (b), and the hydraulic motor 3 is kept at the middle displacement. The output torque of the hydraulic motor 3 during this time is proportionally increased or decreased according to the pilot pressure Ppx as indicated by a characteristic line 55A illustrated in FIG.

However, the pilot pressure Ppx is changed to the switching pressure Ppb.
When the pressure is increased as described above, the sum of the pressing force (Fa-F1 + F2) of the spool 68 due to the pilot pressure Ppx and the urging force fc of the return spring 80 becomes the urging force fd of the return spring 82 as in the following equation (41). As described above, the capacity control valve 6
1 switches from the intermediate capacity position (b) to the large capacity position (a), and the hydraulic motor 3 has a large motor capacity.

[0353]

Fd ≦ (Fa−F1 + F2) + fc (where Ppx ≧ Ppb)

When the displacement control valve 61 is switched from the intermediate displacement position (b) to the large displacement position (a), the total pressure receiving area for the pilot pressure Ppx of the spool 68 becomes the intermediate pressure receiving area (as described above). (Sa-S1 + S2) to the maximum pressure receiving area (Sa + S2).

For this reason, the pilot pressure Ppx is changed to the switching pressure P
Until the pressure drops below pa, the pressing force (Fa + F2) of the spool 68 by the pilot pressure Ppx shown in the equation (15).
And the urging force fc of the return spring 80 becomes larger than the urging force fd of the return spring 82 as in the following equation (42).

[0356]

Fd <(Fa + F2) + fc (where Ppx> Ppa)

As a result, the displacement control valve 61 is held at the large displacement position (a), and the hydraulic motor 3 is kept at a large displacement.
The output torque of the hydraulic motor 3 during this time is proportionally increased or decreased according to the pilot pressure Ppx as indicated by the characteristic line 55B illustrated in FIG.

When the pilot pressure Ppx falls below the switching pressure Ppa, the sum of the pressing force (Fa + F2) of the spool 68 due to the pilot pressure Ppx and the urging force fc of the return spring 80 is calculated by the following equation (43). The displacement control valve 61 is switched from the large displacement position (a) to the intermediate displacement position (b), and the motor displacement of the hydraulic motor 3 is returned to the intermediate displacement.

[0359]

Fd ≧ (Fa + F2) + fc (where Ppx ≦ Ppa)

When the displacement control valve 61 is switched to the intermediate displacement position (b), the total pressure received by the spool 68 relative to the pilot pressure Ppx until the pilot pressure Ppx rises again to the switching pressure Ppb again in this state. By reducing the area to the area (Sa-S1 + S2), the capacity control valve 61 is held at the intermediate capacity position (b),
The hydraulic motor 3 is maintained at an intermediate capacity. The output torque of the hydraulic motor 3 during this time is represented by the characteristic line 55 illustrated in FIG.
It is increased or decreased as in A.

Therefore, according to the present embodiment, while the pressure selection valve 87 for external command pressure is switched to the third-speed automatic switching position (g) as described above, the pilot pressure Ppx and the pressure P
gc external command pressure Pgx and first and second return springs 80 and 82
And the motor drive pressure (pilot pressure Pp
The motor capacity of the hydraulic motor 3 can be automatically switched to three stages of small capacity, intermediate capacity or large capacity according to the increase or decrease of x),
It is not necessary for the operator to perform the capacity switching operation specially, and the burden associated therewith can be reduced.

The pressure selection valve 87 for external command pressure is set to 3
While switching from the automatic speed changeover position (g) to the automatic 2nd speed changeover position (h) of intermediate capacity to large capacity, the pilot pressure Ppx
And the first and second return springs 80 and 82 automatically adjust the motor capacity of the hydraulic motor 3 between the intermediate capacity and the large capacity in two stages according to the increase or decrease of the motor drive pressure (pilot pressure Ppx). Switching can be performed, and the burden on the operator can be reduced.

In the first embodiment, the command pressure supply device 45 for supplying the external command pressure Pgx to the external command pressure port 25H of the capacity control valve 21 via the command pressure line 44.
To the tank 2, the pilot pump 46, the pressure selection valve 48
And the pressure reducing valves 49 and 50, but instead of this, as shown in a modified example shown in FIG. It is good also as a structure provided for every 50.

In this case, a pilot pump 91 located on one pressure reducing valve 49 side and serving as a hydraulic pressure source for external command pressure has a relief valve 93 for determining the maximum discharge pressure of the pilot pump 91 between the pilot pump 91 and the tank 2. The connection is provided. The relief valve 93 is connected to the pilot pump 91
When excessive pressure is generated on the discharge side of the valve, the valve is opened, and the excessive pressure is released to the tank 2 side.

A relief valve 94 for determining the maximum discharge pressure of the pilot pump 92 is provided between the tank 2 and the pilot pump 92 located on the pressure reducing valve 50 side. The relief valve 94 is opened when excessive pressure is generated on the discharge side of the pilot pump 92, and the excessive pressure is released toward the tank 2 side.

In the first embodiment, the pressure value of the external command pressure Pgx is changed to the pressures Pga and Pgb and the tank pressure by combining the pressure selection valve 48 and the pressure reducing valves 49 and 50. However, the present invention is not limited to this. For example, a configuration may be adopted in which a pressure selection valve including an electromagnetic proportional pressure reducing valve or the like is used in place of the pressure selection valve 48 and the pressure reducing valves 49 and 50.

In this case, the pressure value of the external command pressure Pgx can be variably controlled to an arbitrary pressure by using an electromagnetic proportional pressure reducing valve as the pressure selecting valve. There is no need to provide it separately. This point is the same in the second embodiment.

In each of the above embodiments, the pressure control valve 8 of the counter balance valve 6, the pilot line 16 and the like are used to control the load pressure (motor drive pressure) of the hydraulic motor 3 in the capacity control valve 21 (61). Pilot port 25B (65B)
However, instead of this, for example, the hydraulic oil selected by the shuttle valve 9 is taken out as a pilot pressure from an intermediate portion of the high-pressure pipe 20, and this pilot pressure is used as the pilot port of the capacity control valve 21 (61). 25B (65
The configuration leading to B) may be adopted.

On the other hand, in the first embodiment,
Although it has been described that the pilot pressure from the pilot port 25B is supplied / discharged into the oil chambers 31 and 36 of the capacity control valve 21, the pressure from the pilot port 25B does not necessarily need to be introduced. It is also possible to adopt a configuration for guiding as pilot pressure. This is the same for the second embodiment.

In the first embodiment, the description has been made assuming that the hydraulic oil from the shuttle valve 9 is guided to the high-pressure port 25E of the capacity control valve 21. However, the present invention is not limited to this. Pressure oil from the high pressure port 25
It is good also as composition leading to E. This is the same for the second embodiment.

In each of the above embodiments, the servo actuator 10 is connected to the first and second tilt pistons 11 and 12.
And the like, and the pressure oil is supplied to and discharged from each of the hydraulic chambers 11A and 12A via the capacity control valve 21 (61). However, the present invention is not limited to this, and the prior art described above (for example, (Japanese Unexamined Utility Model Publication No. 1-173383) may be applied to a variable displacement actuator.

Further, in each of the above embodiments, the case where the traveling hydraulic motor 3 is used as the variable displacement hydraulic motor has been described as an example. However, the present invention is not limited to this, and for example, the turning hydraulic motor may be used. Alternatively, the present invention can be applied to a hydraulic motor for a rope winch or the like. Further, the present invention can be widely applied to a displacement control device of a variable displacement hydraulic motor such as a hydraulic pump serving as a hydraulic pressure source of a hydraulic shovel, a hydraulic crane, or the like.

[0373]

As described in detail above, according to the first aspect of the present invention, the displacement control valve is moved to one of the large displacement position, the intermediate displacement position and the small displacement position in accordance with the pilot pressure consisting of the load pressure of the hydraulic motor. So that the switching control
For example, the capacity control valve can reduce the pressure receiving area for the pilot pressure to the minimum area when in the small capacity position, can set the pressure receiving area to an intermediate area when in the intermediate capacity position, and can set the pressure receiving area when in the large capacity position. Can be expanded to the largest area. Therefore, the displacement of the displacement control valve can be automatically switched according to the pilot pressure. At this time, the change in the pressure receiving area gives a hysteresis characteristic to the switching pressure (pilot pressure) of the displacement control valve, thereby suppressing the occurrence of hunting. The performance can be improved without complicating and increasing the size of the capacity control device, and the burden on the operator can be reduced. In addition, the motor capacity can be automatically switched to three stages of small capacity, intermediate capacity, and large capacity corresponding to the load. Stability and reliability at the time of automatic switching can be improved.

According to the second aspect of the present invention, when the displacement control valve is at the large displacement position, the pressure receiving area of the spool with respect to the pilot pressure can be reduced to the minimum.
When the displacement control valve is switched to the intermediate displacement position, the pressure receiving area of the spool with respect to the pilot pressure can be an intermediate pressure receiving area. When the displacement control valve is switched to the large displacement position, the pressure receiving area with respect to the pilot pressure can be the maximum pressure receiving area. Therefore, such a change in the pressure receiving area causes the switching pressure (pilot pressure) of the displacement control valve to change. , The occurrence of hunting can be suppressed, and three-stage automatic switching control of small, medium, and large capacity corresponding to the load of the motor can be performed.

According to the third aspect of the present invention, the displacement control valve includes a valve housing, a spool, a pilot pressure receiving portion, first and second shaft holes, first and second pistons,
Since it is configured to include the second shaft hole pressure receiving portion and the first and second oil passages, the first and second oil passages press the first and second oil chambers in accordance with the sliding displacement of the spool. , For example, the pilot port and the tank port, and the total pressure receiving area of the spool by the pilot pressure receiving portion and the first and second shaft hole pressure receiving portions is reduced by the first and second oil chambers. Can be changed depending on which port is connected via the first and second oil passages. And
By utilizing the change in the pressure receiving area, the switching pressure (pilot pressure) of the capacity control valve can be given a hysteresis characteristic, and the stability and reliability at the time of automatic capacity switching can be improved.

According to the fourth aspect of the present invention, the first and second oil chambers communicate with the pilot port via the first and second oil passages or communicate with the low pressure tank port side. The pressure receiving area of the entire spool with respect to the pilot pressure can be changed in three steps, thereby giving a hysteresis characteristic to the switching pressure (pilot pressure) of the capacity control valve, and providing stability and reliability during capacity switching. Can be increased.

[0377] Further, according to the present invention, the first and second oil passages allow the first and second oil passages to move in accordance with the sliding position of the spool.
The first oil chamber communicates with the pilot port via the first oil passage, and the second oil chamber communicates with the second oil passage through the first oil passage. When communicating with the tank port through the first port, the pressure receiving area of the entire spool is minimized by the pilot pressure receiving portion and the first shaft hole pressure receiving portion, and the first and second oil chambers are connected to the first and second oil passages. When both are communicated with the pilot port via the same, the pressure receiving area is set to an intermediate pressure, and the first oil chamber communicates with the tank side via the first oil passage, and the second oil chamber communicates with the second oil passage. When it communicates with the pilot port via the air, it is configured to have a maximum pressure receiving area.

Therefore, for example, when the pressure receiving area of the pilot pressure receiving portion is Sa, the pressure receiving area of the first shaft hole pressure receiving portion is S1, and the pressure receiving area of the second shaft hole pressure receiving portion is S2,
While the first and second oil chambers are in communication with the pilot port, the pressure receiving area of the entire spool is changed to an intermediate pressure receiving area (Sa−
S1 + S2). Further, when the first oil chamber communicates with the pilot port and the second oil chamber communicates with the tank port, the pressure receiving area of the entire spool can be made the minimum pressure receiving area (Sa-S1). When the first oil chamber communicates with the tank side and the second oil chamber communicates with the pilot port, the pressure receiving area of the entire spool can be the maximum pressure receiving area (Sa + S2).

According to the present invention, the spool is a stepped spool in which one side in the axial direction has a larger diameter than the other part, and the pilot pressure receiving portion is a large diameter portion of the spool. Is formed by a step portion on the outer peripheral side located on the side, so that a pilot pressure receiving portion that forms an annular shape at the position of the step portion having a large diameter can be formed on the outer periphery of one side of the spool, and the pilot pressure receiving portion can be formed. The spool can be slid and displaced by the pilot pressure acting on the spool.

According to the seventh aspect of the present invention, the spool has a plurality of lands for shutting off ports having different pressures from each other, and the oil passage is connected to one of the ports having a pressure lower than that of the pilot port. Since the throttle hole is provided at the position where the oil chamber communicates with and shuts off, the pilot pressure from the pilot port is introduced into the oil chamber to increase the pressure in the oil chamber. Even when the oil chamber communicates with the tank port, high pressure in the oil chamber can be prevented from flowing out as a jet to the tank port by the throttle hole, and abnormal pressure is generated on the low-pressure tank port side. Can be prevented.

On the other hand, according to the present invention, the first urging means and the second urging force having a larger urging force than the first urging means are provided between the valve housing and the spool. With the configuration provided with the urging means, the first and second urging means can stably hold the spool of the capacity control valve at any of the small capacity position, the intermediate capacity position and the large capacity position, and It is possible to compensate for the sliding displacement of the spool toward another switching position according to the increase or decrease of the pilot pressure.

According to the ninth aspect of the present invention, the first urging means urges the spool in a direction opposite to the direction in which the pilot pressure receiving portion receives the pilot pressure, and the second urging means operates the second urging means. When the spool is in a series relationship with the first urging means and is located between a switching position at the center in the axial direction and a switching position on one axial side, the spool is biased from one axial side to the other axial side. When the pilot pressure due to the motor load pressure is in a low pressure state, the spool is slid from one side toward the other side by the first urging means,
The displacement control valve can be arranged, for example, at a small displacement position. And
When the pilot pressure becomes higher than the reference switching pressure due to the increase in the motor load pressure, the spool receives the pressure, and the spool is moved to one side in the axial direction against the first urging means. The displacement can be slid and the displacement control valve can be switched, for example, to an intermediate displacement position. In this intermediate capacity position, the spool can be biased to the other side in the axial direction by the second biasing means, and when the pilot pressure rises beyond the biasing force at this time, the spool is opposed to the second biasing means. As a result, the displacement control valve can be switched to, for example, a large capacity position by the sliding displacement of the spool to one side in the axial direction.

According to the tenth aspect of the present invention,
The first biasing means biases the spool in the same direction as the direction in which the pilot pressure receiving portion receives the pilot pressure, and the second biasing means switches the spool between a switching position at the center in the axial direction and one side in the axial direction. When the pilot pressure due to the motor load pressure is in a low pressure state, the spool is biased from the first side to the other side in the axial direction. The displacement control valve can be slid and displaced from the other side in the axial direction toward one side by the biasing means, and the displacement control valve can be disposed at, for example, an intermediate displacement position. In this intermediate capacity position, the spool can be urged to the other side in the axial direction by the second urging means. When the pilot pressure rises beyond the urging force of the second urging means, the second urging means is pressed. The displacement of the displacement control valve can be switched to, for example, a large displacement position by sliding the spool in one axial direction against the urging means.

According to the eleventh aspect of the present invention,
Since the displacement control valve is configured to control the switching of the motor displacement according to the external command pressure generated by the external command pressure generating means, the motor displacement can be appropriately switched or fixed by the external command pressure, It is possible to execute the capacity switching control according to the working conditions, to improve the operation performance of the entire apparatus, and to achieve high functionality.

According to the twelfth aspect of the present invention,
The valve housing has an external command pressure port through which the external command pressure is guided from the command pressure generating means, and the spool receives the command pressure from the external command pressure port in the same direction as the direction in which the pilot pressure is received. Since the pressure receiving pressure portion has a configuration, the spool receives the pilot pressure by the motor load pressure and the external command pressure in the same direction, the capacity control valve to the small capacity position according to the pilot pressure and external command pressure, Switching control to either the intermediate capacity position or the large capacity position can be performed.

[0386] Further, according to the thirteenth aspect, the first urging means and the first urging means are provided between the valve housing and the spool.
And the second urging means for urging the spool from one side in the axial direction to the other side with an urging force larger than that of the urging means. When the pressures are both low, the spool is slid and displaced from one side in the axial direction to the other side by the first biasing means, and the displacement control valve can be disposed at, for example, a small displacement position. When the pilot pressure rises with an increase in the motor load pressure, the displacement control valve can be switched to the intermediate displacement position against the first biasing means, and the pilot pressure can be switched to the second biasing position. When it rises beyond the urging force of the means, the displacement control valve can be switched to the large displacement position, and the automatic switching control of the third speed can be performed.

Also, for example, when the external command pressure is set to a high pressure level, the external command pressure is received by the command pressure receiving portion, whereby the spool is moved in the axial direction against the first urging means. Since the displacement can be slid to one side, the displacement control valve can be automatically switched at a second speed, for example, between a small displacement position and an intermediate displacement position. When the external command pressure is further increased and the spool is largely slid toward one side in the axial direction against the second urging means, this causes the displacement of the displacement control valve from the intermediate displacement position to the large displacement position. , And control for fixing a large capacity can be performed.

According to the fourteenth aspect of the present invention,
When the external command pressure is at the lowest pressure state, the displacement control valve can be switched to any one of the small displacement position, the intermediate displacement position and the large displacement position in accordance with the balance between the pilot pressure and the first and second urging means. 3rd speed automatic switching control can be performed. Further, when the external command pressure is set to an intermediate pressure state, switching between the intermediate displacement position and the large displacement position can be controlled in accordance with the balance between the pilot pressure and the second urging means. Can be performed. When the external command pressure is set to the highest pressure state, the capacity control valve can be fixed at the large capacity position regardless of the pilot pressure, and control for fixing the large capacity can be performed.

According to the fifteenth aspect of the present invention,
The valve housing has an external command pressure port through which the external command pressure is guided from the command pressure generating means, and the spool receives the external command pressure guided from the external command pressure port in a direction opposite to the direction in which the pilot pressure is received. Since the pressure receiving portion is configured to have the pressure receiving portion, the spool can receive the pilot pressure by the motor load pressure and the external command pressure in opposite directions, and the capacity control valve is set to the small capacity position, intermediate position according to the pilot pressure and the external command pressure. Switching control to either the capacity position or the large capacity position can be performed.

According to the sixteenth aspect,
First urging means for urging the spool in the same direction as the pilot pressure receiving direction between the valve housing and the spool; and urging the spool with an urging force larger than the first urging means. When the external command pressure is set to a low pressure equivalent to the tank pressure, the capacity control valve is set to the pilot pressure because the second urging means for urging from one side in the axial direction toward the other side is provided. By the first and second urging means, for example, automatic switching control between the intermediate capacity position and the large capacity position at the second speed can be performed. On the other hand, when the external command pressure is set to a high pressure, the external command pressure is received by the command pressure receiving portion, so that the spool slides toward the other side in the axial direction against the first urging means. As a result, the capacity control valve can be automatically switched to, for example, a small capacity position, an intermediate capacity, or a large capacity position at three speeds.

Further, according to the present invention, when the external command pressure is set to a low pressure state, the capacity control valve moves the pilot pressure and the second pressure to one of the intermediate capacity position and the large capacity position.
Switching control according to the balance with the urging means, and automatic 2-speed switching control can be performed. Further, when the external command pressure is set to a high pressure state, it is possible to control switching to any of the small capacity position, the intermediate capacity position and the large capacity position according to the balance between the pilot pressure and the first and second urging means, At this time, automatic three-speed switching control can be performed.

[Brief description of the drawings]

FIG. 1 is a traveling hydraulic circuit diagram of a hydraulic shovel to which a displacement control device according to a first embodiment of the present invention is applied.

FIG. 2 is an enlarged longitudinal sectional view showing a capacity control valve in FIG. 1 at a small capacity position.

FIG. 3 is a longitudinal sectional view of the displacement control valve showing a state in which a spool is slid to a middle displacement position.

FIG. 4 is a longitudinal sectional view of the displacement control valve showing a state in which the spool has been slid to the large displacement position.

FIG. 5 is a longitudinal sectional view showing the spool in FIG. 2 alone;

FIG. 6 is a characteristic diagram showing a relationship between pilot pressure and motor displacement when the pressure selection valve in FIG. 1 is switched to a three-speed automatic switching position.

7 is a characteristic diagram showing a relationship between pilot pressure and output torque of a hydraulic motor when the pressure selection valve in FIG. 1 is switched to a three-speed automatic switching position.

FIG. 8 is a characteristic diagram showing a relationship between pilot pressure and output torque of a hydraulic motor when the pressure selection valve in FIG. 1 is switched to a second-speed automatic switching position.

9 is a characteristic diagram showing a relationship between pilot pressure and output torque of a hydraulic motor when the pressure selection valve in FIG. 1 is switched to a large-capacity fixed position.

FIG. 10 is a traveling hydraulic circuit diagram of a hydraulic shovel to which the displacement control device according to the second embodiment is applied.

FIG. 11 is an enlarged longitudinal sectional view showing the capacity control valve in FIG. 10 at a small capacity position.

FIG. 12 is a longitudinal sectional view of the displacement control valve showing a state where the spool has been slid to the intermediate displacement position.

FIG. 13 is a longitudinal sectional view of the displacement control valve showing a state where the spool is slid to the large displacement position.

14 is a longitudinal sectional view showing the spool in FIG. 11 alone.

FIG. 15 is a traveling hydraulic circuit diagram of a hydraulic shovel showing a command pressure supply device according to a modification in an enlarged manner.

FIG. 16 is a characteristic diagram showing a relationship between pilot pressure and output torque of a hydraulic motor according to a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Hydraulic pump 2 Tank 3 Hydraulic motor 3B Variable capacity part 4A, 4B Main line 5 Directional control valve 10 Servo actuator (variable capacity actuator) 21, 61 Capacity control valve 22, 62 Valve housing 23, 63 Spool sliding hole 25A, 25C , 25G, 65C, 65G Tank port 25B, 65B Pilot port 25E, 65E High pressure port 25D, 25F, 65D, 65F Hydraulic oil supply / discharge port 25H, 65A External command pressure port 28, 68 Spool 28J, 68G Pilot pressure receiving part 28L, 68J Command pressure receiving portion 29, 69 First shaft hole 29A, 69A First shaft hole pressure receiving portion 30, 70 First piston 31, 71 First oil chamber 32, 72 Small hole (throttle hole) 33, 73 Oil Holes (first oil passage) 34, 74 Second shaft hole 34A, 74A Second shaft hole Pressure part 35,75 Second piston 36,76 Second oil chamber 37,77 Oil hole (second oil passage) 38,78 Small hole (throttle hole) 39,80 Return spring (first biasing means) ) 40, 82 Return spring (second biasing means) 41, 83 Spring support 43 External command pressure chamber 44, 85 Command pressure line 45, 86 Command pressure supply device (command pressure generating means) 48, 87 Pressure selection valve 49 , 50,88 Pressure reducing valve 67 Spring chamber (external command pressure chamber)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Go Tsuyoshi Kobayashi 650, Kandate-cho, Tsuchiura-shi, Ibaraki Pref.Hitachi Construction Machinery Co., Ltd. F-term in the Tsuchiura Plant (reference) 3H053 AA03 BA02 BA04 CA03 DA11 3H084 AA01 AA43 AA45 BB12 BB13 BB14 BB30 CC41 CC47 CC48 CC70 3H089 AA35 AA60 CC09 DA02 DB75 EE22 GG02 JJ02

Claims (17)

[Claims] 1. A variable displacement type hydraulic motor having a variable capacity section and driven to rotate by pressure oil from a hydraulic source, and a motor configured to drive the variable capacity section of the hydraulic motor by supplying and discharging pressure oil. A capacity variable actuator that changes the capacity to a large capacity, an intermediate capacity, and a small capacity, and a hydraulic pilot type capacity that switches pressure oil supplied to and discharged from the capacity variable actuator by receiving at least the load pressure of the hydraulic motor as a pilot pressure. A displacement control device for a variable displacement hydraulic motor comprising a control valve, wherein the displacement control valve switches the motor displacement between a large displacement, an intermediate displacement and a small displacement by the displacement variable actuator. It has a plurality of switching positions consisting of capacity positions, and the pressure receiving area for the pilot pressure is changed for each switching position. Variable displacement hydraulic motor of the displacement control device, characterized in that the the. 2. The capacity control valve has a spool sliding hole, and is spaced apart in the axial direction of the spool sliding hole to an external command pressure port, a pilot port, a tank port, a high pressure port, and the variable capacity actuator. A valve housing provided with a pressure oil supply / discharge port, and an axial direction in the spool sliding hole by receiving the pilot pressure guided from the pilot port by being fitted into a spool sliding hole of the valve housing. A spool that slides and displaces the pressure oil supply / discharge port selectively to and from a high pressure port and a tank port. The spool is configured to control the pilot pressure when the displacement control valve is at a small displacement position. The pressure receiving area with respect to the pilot pressure is set to an intermediate pressure receiving area when switching to the intermediate capacity position. 2. The displacement control device for a variable displacement hydraulic motor according to claim 1, wherein a pressure receiving area for the pilot pressure is set to a maximum pressure receiving area when the position is switched to a position. 3. The displacement control valve has a spool sliding hole, and supplies at least a pilot port, a tank port, a high pressure port, and a pressure oil supply to the variable displacement actuator at an axial distance from the spool sliding hole. A valve housing provided with a discharge port; and a pressure oil supply / discharge port inserted into a spool sliding hole of the valve housing and slidably displaced in the spool sliding hole in the axial direction, thereby connecting the pressure oil supply / discharge port to a high pressure port and a tank port. A spool that selectively communicates with and shuts off the spool; a pilot pressure receiving portion provided on the spool and configured to receive the pilot pressure guided from the pilot port to displace the spool in the axial direction; A first and a second shaft hole extending in the axial direction of the spool and opened at one end and the other end surface; , Are slidably inserted into the respective shaft holes so as to close the open ends of the second shaft holes, and define first and second oil chambers between the shaft holes and the bottom thereof. The first and second pistons are formed by first and second pistons for receiving a hydraulic reaction force in the first and second oil chambers, and the bottoms of the first and second shaft holes. And first and second shaft hole pressure receiving portions for changing the total pressure receiving area with respect to the pilot pressure of the spool together with the pilot pressure receiving portion by receiving the pressure of the pilot pressure portion, and a position corresponding to the first and second oil chambers. And the first and second oil chambers are selectively communicated with ports having different pressures among the ports when the spool is displaced in the spool sliding hole. 2. A structure comprising a first oil passage and a second oil passage.
3. The displacement control device for a variable displacement hydraulic motor according to claim 1. 4. The pressure receiving section of the pilot has a larger pressure receiving area than the pressure receiving section of the first shaft hole, and the first pressure receiving section of the first shaft hole receives a first oil chamber via a first oil passage. When receiving the pilot pressure in the opposite direction to the pilot pressure receiving portion when communicating with the pilot port, the second shaft hole pressure receiving portion has a second oil chamber communicating with the pilot port via a second oil passage. 4. The displacement control device for a variable displacement hydraulic motor according to claim 3, wherein the displacement control device is configured to receive the pilot pressure in the same direction as the pilot pressure receiving portion. 5. The first and second oil passages are configured to selectively communicate and shut off the first and second oil chambers with a pilot port and a tank port according to a sliding position of a spool.
The spool receives the pilot pressure when the first oil chamber communicates with a pilot port via a first oil passage and the second oil chamber communicates with a tank port via a second oil passage. And the first shaft hole pressure receiving portion receives the pilot pressure with a minimum pressure receiving area, and the first and second oil chambers communicate with the pilot port together via the first and second oil passages. The pilot pressure receiving portion and the first and second shaft hole pressure receiving portions receive the pilot pressure with an intermediate pressure receiving area, and further the first oil chamber communicates with the tank side via a first oil passage, and The second oil chamber communicates with the pilot port via the second oil passage, wherein the pilot pressure is received by the pilot pressure receiving portion and the second shaft hole pressure receiving portion with a maximum pressure receiving area. 4
3. The displacement control device for a variable displacement hydraulic motor according to claim 1. 6. The spool comprises a stepped spool in which one portion in the axial direction has a larger diameter than the other portion, and the pilot pressure receiving portion has a step on the outer peripheral side located on the large diameter portion side of the spool. 6. The displacement control device for a variable displacement hydraulic motor according to claim 3, wherein the displacement control device is formed by a portion. 7. The spool has a plurality of lands for shutting off the ports having different pressures from each other, and the first and second oil passages are provided for each of the ports having a lower pressure than a pilot port. And a throttle hole at a position where the first and second oil chambers communicate with and block each other.
7. The displacement control device for a variable displacement hydraulic motor according to 5 or 6. 8. A first urging means for axially urging the spool between the valve housing and the spool;
8. The variable capacity according to claim 3, further comprising a second urging means for urging the spool in an axial direction with a larger urging force than the first urging means. Type hydraulic motor capacity control device. 9. The first urging means urges the spool from one side in the axial direction to the other side in a direction opposite to a direction in which the pilot pressure receiving portion receives the pilot pressure. The urging means is provided between the valve housing and the first urging means so as to form a serial relationship with the first urging means, and the spool is located at a central switching position in the axial direction and at one side in the axial direction. The displacement control device for a variable displacement hydraulic motor according to claim 8, wherein the spool is biased from one side in the axial direction to the other side when the spool is positioned between the first and second switching positions. 10. The first urging means urges the spool from the other side in the axial direction to one side in the same direction as the direction in which the pilot pressure receiving portion receives the pilot pressure. The biasing means, when the spool is located between the switching position at the center in the axial direction and the switching position on one side in the axial direction,
9. The displacement control device for a variable displacement hydraulic motor according to claim 8, wherein the spool is biased from one side in the axial direction to the other side. 11. The displacement control device for a variable displacement hydraulic motor according to claim 1, wherein the displacement control valve is configured to control the switching of the motor displacement in accordance with an external command pressure generated by an external command pressure generating means. . 12. The capacity control valve has a spool sliding hole, and is spaced apart from the spool sliding hole in the axial direction to an external command pressure port, a pilot port, a tank port, a high pressure port, and the capacity variable actuator. A valve housing provided with a pressure oil supply / discharge port, and an axial direction in the spool sliding hole by receiving the pilot pressure guided from the pilot port by being fitted into a spool sliding hole of the valve housing. An external command pressure generated by an external command pressure generating means is provided to the valve housing. An external command pressure port is provided, and an external finger guided from the external command pressure port is provided on the spool in the same direction as the direction in which the pilot pressure is received. Variable displacement hydraulic motor of the displacement control device according to claim 1 comprising a configuration in which the command pressure receiving pressure section for receiving the pressure. 13. A first urging means between the valve housing and the spool for urging the spool from one side in the axial direction opposite to the direction of receiving the pilot pressure toward the other side. And when the spool is located between a switching position at the center in the axial direction and a switching position on one side in the axial direction, the spool is moved to one side in the axial direction with a biasing force greater than the first biasing means. 13. The displacement control device for a variable displacement hydraulic motor according to claim 12, wherein the displacement control device further comprises a second biasing unit for biasing the variable displacement hydraulic motor toward the other side. 14. The capacity control valve, when the command pressure generating means sets the external command pressure to the lowest pressure state, rotates the spool in accordance with the balance between the pilot pressure and the first and second urging means. When the external command pressure is switched to one of three positions, a switching position on the other side in the direction, a switching position on the center in the axial direction, and a switching position on one side in the axial direction, and when the external command pressure is in the intermediate pressure state, the pilot pressure and the second pressure are switched. The spool is switched to one of two positions, a switching position at the center in the axial direction and a switching position on one side in the axial direction, according to the balance with the urging means. 14. The displacement control device for a variable displacement hydraulic motor according to claim 13, wherein the displacement control device is configured to be held at the switching position on one side in the axial direction regardless of the pressure against the second urging means. 15. The displacement control valve has a spool sliding hole, and is spaced apart from the spool sliding hole in the axial direction to an external command pressure port, a pilot port, a tank port, a high pressure port, and the capacity variable actuator. A valve housing provided with a pressure oil supply / discharge port, and an axial direction in the spool sliding hole by receiving the pilot pressure guided from the pilot port by being fitted into a spool sliding hole of the valve housing. An external command pressure generated by an external command pressure generating means is provided to the valve housing. The spool is provided with an external command pressure port, and the spool is provided with an external command pressure port that is guided from the external command pressure port in a direction opposite to a direction in which the pilot pressure is received. Variable displacement hydraulic motor of the displacement control device according to claim 1 comprising a configuration in which the command pressure receiving pressure section for receiving the command pressure. 16. A first urging means between the valve housing and the spool for urging the spool from one side in the axial direction, which is the same as the direction in which the pilot pressure is received, toward one side. When the spool is located between the switching position at the center in the axial direction and the switching position on one side in the axial direction, the spool is moved from one side in the axial direction with a biasing force larger than the first biasing means. 16. The displacement control device for a variable displacement hydraulic motor according to claim 15, wherein the displacement control device includes a second biasing unit that biases toward the other side. 17. The capacity control valve switches the spool in the axial center according to the balance between the pilot pressure and the second urging means when the external command pressure is set to a low pressure state by the command pressure generating means. When the external command pressure is switched to a high pressure state, the spool is switched according to the balance between the pilot pressure and the first and second urging means. 17. The displacement control device for a variable displacement hydraulic motor according to claim 16, wherein the displacement control device is configured to switch to one of three positions of a switching position on the other side in the axial direction, a switching position on the center in the axial direction, and a switching position on one side in the axial direction.