JPH0988905A - Constant pressure controlled liquid hydraulic driven device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain sufficient holding force (braking force) at the time when a command means indicates neutral in a constant pressure controlled liquid hydraulic driven device. SOLUTION: A first cam 27 shifts a directional control valve 20 to neutral at the time when an operation lever 9 is neutral and in a braking range 9a, 9b and when shifted to a drive range 9c, 9d the directional control valve 20 is shifted to a position (a) or a position (b) according to the operation direction. A second cam 28 controls the inclination of an oil hydraulic motor 4 to the maximum when the operation lever 9 is neutral, and when it is in the braking range 9a, 9b the inclination of the oil hydraulic motor 4 is controlled according to the operation, when it is in the drive range 9c, 9d the inclination of the oil hydraulic motor is controlled according to the operation signal. Check valves 23, 24 allowing flow only to a high pressure conduit 7 from a first conduit 21 and a second conduit 22 and check valves 25, 26 preventing the generation of negative pressure of the first conduit 21 and the second conduit 22 are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic drive device for driving a rotary load, and more particularly, a variable displacement hydraulic motor is connected to a constant pressure hydraulic source to control the displacement of the hydraulic motor. The present invention relates to a constant pressure control hydraulic drive device that drives a rotary load having a large moment of inertia while adjusting drive torque and braking torque generated by doing so.

[0002]

2. Description of the Related Art A hydraulic drive system for adjusting a drive torque or a braking torque generated by connecting a variable displacement hydraulic actuator to a constant pressure hydraulic source and controlling the displacement of the hydraulic actuator is known. , "Secondary control system" or "constant pressure control system". For example, the International Conference on Fluids was held at Tampere University, Finland, March 24-26, 1987.
Power) Proceedings, p2-3, “Secondary control hydraulic system energy considerations and control strategies (Se
condary Controlled Hydraulic System-Energy Aspec
t and Control Strategies).

FIG. 4 shows the configuration of a conventional constant pressure control system (secondary control system). In FIG. 4, the high pressure port 2 of the constant pressure source 1 is connected to the high pressure line 7, and the low pressure port 3 is connected to the variable displacement hydraulic actuator 4 by the low pressure line 8. The displacement variable mechanism 5 of the variable displacement hydraulic actuator 4 can be adjusted in the positive direction 5a or the negative direction 5b by the operation lever 9. The output shaft of the variable displacement hydraulic actuator 4 is connected to the rotary load 6. The variable displacement hydraulic actuator 4 is generally a bi-tilt type hydraulic motor, and when a swash plate motor is used as this hydraulic motor, the swash plate serves as the variable capacity mechanism 5. The operation will be described below.

Consider the operation from the state where the rotary load 6 is stopped. In the neutral state in which the operation lever 9 is not operated, the swash plate 5 of the hydraulic motor 4 is also in the neutral position, torque is not generated even if a pressure difference is applied from the high pressure line 7 and the low pressure line 8, and the rotating load 6 is stopped. It is still done. When the operating lever 9 is moved in the forward rotation direction (arrow 9a) side, the swash plate 5 of the hydraulic motor 4 moves in the forward rotation direction (arrow 5a) side, and the displacement capacity by tilting the swash plate is q, and the high pressure pipe is When the differential pressure between the path 7 and the low-pressure line 8 is p, the rotational load 6 is driven to the forward rotation side with a torque of p × q. At this time, the larger the operating lever 9 is operated, the larger the displacement q due to tilting of the swash plate becomes, so that a large driving force can be obtained. When the operating lever 9 is returned to the neutral position while the rotary load 6 is rotating, the swash plate tilting of the hydraulic motor 4 also returns to neutral. In this case, since the displacement capacity is 0, the torque input / output to / from the rotational load 6 is 0, and the rotational load 6 continues idling at the same rotation speed (actually, it is gradually decelerated due to various resistances). .

In order to decelerate the idling state, the operating lever 9 is operated in the reverse direction (arrow 9b). The hydraulic motor 6 tilts to the 5b side in the drawing in accordance with the operation amount of the operation lever 9 and tries to send the working fluid from the low pressure pipe line 8 side to the high pressure pipe line 7 side. That is, it operates like a pump driven from the rotary load 6 side. At this time, the hydraulic motor 4 applies a braking torque to the rotary load 6 to decelerate it.
The magnitude of the braking torque is p × q (however, q
Is a negative value), and the larger the operating lever 9 is operated, the larger the braking torque is obtained. Further, the hydraulic energy generated by the pump action of the hydraulic motor 4 is supplied to the constant pressure source 1
It is collected in the accumulator included in the and is reused for the next drive.

In order to stop the rotating load 6 which is rotating in the normal direction, the operating lever 9 is operated in the reverse direction to decelerate,
When the operation is stopped, the operation lever 9 may be returned to the neutral position.

Driving, braking and stopping in the reverse direction may be performed by operating the operation lever 9 in the opposite direction.

Such a constant pressure control system has a characteristic as an energy saving type system because the hydraulic energy generated by the pump action of the hydraulic motor 4 can be recovered and reused, and the torque including the rotation direction can be used to control the torque. The operation method instructed by is often used for a turning device for a crane.

[0009]

The conventional constant pressure control system is convenient for a swing hydraulic circuit of a machine which is installed and used on a flat ground such as a crane. However, in a swing hydraulic circuit of a machine that must operate even on a sloping ground such as a hydraulic excavator, when the operating lever 9 is in a neutral state, the hydraulic motor is driven by the weight of the work device such as the front, There is an inconvenience that the working device flows to the lower side. A similar problem also exists in a traveling hydraulic circuit of a vehicle such as a wheel loader. That is,
When the present invention is applied to the traveling hydraulic circuit, the hydraulic motor may rotate due to the weight of the vehicle body and the vehicle body may move while the vehicle is stopped on a slope.

An object of the present invention is to provide a constant pressure control hydraulic drive device capable of exerting a sufficient holding force (braking force) when the command means indicates neutral.

[0011]

In order to achieve the above object, the present invention adopts the following configurations. That is, a constant pressure source for supplying a constant pressure, a variable displacement hydraulic actuator connected to the constant pressure source via a high pressure line and a low pressure line, and command means for giving a command to the hydraulic actuator. In the constant pressure control hydraulic drive device for controlling the displacement of the hydraulic actuator according to the command of the command means, for driving a rotational load, the constant pressure source via the high pressure line and the low pressure line. A directional control valve connected to the hydraulic actuator via first and second conduits, the high pressure conduit, the low pressure conduit, and the first conduit.
A neutral position for shutting off all ports of the pipeline and the second pipeline; a first switching position for connecting the high pressure pipeline to the first pipeline and a low pressure pipeline to the second pipeline; and a high pressure pipeline A directional control valve having a second switching position for connecting the low pressure line to the first line and a second switching position for connecting the low pressure line to the second line; and the directional control valve when the command means is within a predetermined command range including neutral. To a neutral position, and when the commanding means is operated beyond the predetermined command range, the directional control valve is switched to the first switching position or the second switching position according to the operating direction. When the command means is within the predetermined command range, the displacement of the hydraulic actuator becomes maximum at neutral, and the displacement of the hydraulic actuator gradually decreases as it is operated from neutral. Second control means for controlling, when the command means is operated beyond the predetermined command range, so as to gradually increase the displacement of the hydraulic actuator according to the operation amount; Is provided.

In the present invention configured as described above, when the command means is operated beyond a predetermined command range including neutral, the first control means operates the directional control valve and the high pressure pipe in accordance with the operating direction. A first switching position in which the line is connected to the first line and the low pressure line is connected to the second line or a second switching position in which the high pressure line is connected to the second line and the low pressure line is connected to the first line Switching to the position, the second control means gradually increases the displacement of the hydraulic actuator according to the operation amount. Therefore, the hydraulic actuator is driven according to the operation direction and the operation amount of the command means as in the conventional case.

On the other hand, when the command means is in the predetermined command range including neutral, the first control means switches the directional control valve to the neutral position where it blocks all the ports of the first pipeline and the second pipeline. The second control means maximizes the displacement of the hydraulic actuator when the command means is neutral, and gradually reduces the displacement of the hydraulic actuator as the command means is operated from neutral. For this reason, when the command of the command means is returned to the above-mentioned predetermined command range from the state in which the hydraulic actuator is driven as described above, the hydraulic actuator has both ports blocked and the displacement is in the return amount. As the rotational torque of the hydraulic actuator applied by the load is T, the first pipe line and the second pipe line are increased.
A differential pressure of p = T / q (q is displacement of the variable displacement hydraulic actuator) is generated between the pipelines, and this differential pressure exerts a braking force according to the command return amount, and the load is gradually reduced. To be done. When the command means is returned to neutral, the first conduit and the second conduit are
A differential pressure of p = T / qmax (qmax is the maximum displacement of the variable displacement hydraulic actuator) is generated between the pipelines, and the maximum braking force is exerted.

When the command means is in the neutral position, the hydraulic actuator has both ports blocked and the displacement capacity is maximum. Therefore, when the rotational torque T is received from the outside, the first pipeline and the second pipeline are connected. Between the conduits, p = T /
A differential pressure of qmax is generated, and this differential pressure prevents external rotation. As a result, in the swing hydraulic circuit of a machine that must operate even on a sloping ground such as a hydraulic excavator, when the operator does not input an operation input and a neutral command is issued, the weight of the work equipment such as the front is heavy. Therefore, it is possible to prevent the working device from flowing downward.

The constant pressure control hydraulic drive system preferably includes a backflow preventing means for permitting only a flow from the first and second pipelines toward the high pressure pipeline, and the first and second pipelines. It is configured to further include replenishing means for preventing the generation of negative pressure in the two pipelines.

As described above, according to the present invention constructed so that the two ports of the variable displacement hydraulic actuator are shut off by the directional control valve during braking, the load is braked and decelerated from the rotating state. A flow path through which the variable displacement hydraulic actuator sucks and discharges hydraulic oil is required in the process. Further, in order to obtain the acceleration / deceleration characteristics equivalent to those of the conventional system, the flow path for suction maintains a low pressure line or a pressure level equivalent to it, and the flow path for discharge maintains a high pressure line or a pressure level equivalent thereto. There is a need to. In the present invention, since the first pipe line or the second pipe line, which is blocked by the direction switching valve and corresponds to the discharge side, is connected to the high pressure pipe line via the backflow prevention means, the discharge side pipe line is a high pressure pipe. After raising the pressure to the same pressure as the line, the discharged hydraulic oil flows into the high pressure line. Further, the first pipe line or the second pipe line corresponding to the suction side has a replenishing means for preventing the generation of negative pressure, and can replenish the suction flow rate from this. Due to the action of the backflow prevention means and the reinforcing means, the braking force according to the command of the command means can be exerted. Further, the hydraulic energy generated in the discharge side pipe line of the hydraulic actuator can be collected in the constant pressure source.

Further, preferably, the command means is an operation lever which is rotated, and the first control means controls a first cam which is moved by a rotation operation of the operation lever and a movement of the first cam. Valve operation means for switching the direction switching valve in response to the second cam means, and the second control means operates a second cam in synchronism with the first cam by rotating the operation lever. Actuator displacement operating means for controlling the displacement of the hydraulic actuator according to the movement. In this case, preferably the first
The cam and the second cam are rotary type integrated cams having a rotation center at the rotation center of the operation lever.

Further, the command means is an operation lever that is operated to rotate, and the first control means includes an angle detection means for detecting a rotation angle of the operation lever and a rotation detected by the angle detection means. It has a first calculation means for outputting a corresponding valve switching command according to the angle, and a valve operating means for switching the directional switching valve according to the valve switching command, and the second control means is detected by the angle detecting means. Second, which outputs the corresponding displacement command according to the rotation angle
It may be configured to have a computing means and an actuator capacity operating means for controlling the displacement of the hydraulic actuator according to the displacement capacity command.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

First, a first embodiment of the present invention will be described with reference to FIGS.

In FIG. 1, 1 is a constant pressure source for supplying a set constant pressure, and a high pressure port 2 of the constant pressure source 1,
The low pressure port 3 is connected to the P port and the T port of the directional control valve 20 by a high pressure line 7 and a low pressure line 8, respectively. The A port and the B port of the directional control valve 20 are connected to the variable displacement hydraulic actuator 4 by a first conduit 21 and a second conduit 22. The variable displacement hydraulic actuator 4 is, for example, a bi-tilt type hydraulic motor, and when a swash plate motor is used as this hydraulic motor, the swash plate serves as the variable capacity mechanism 5. The directional control valve 20 connects the high pressure pipe 7 to the first pipe 21 and the low pressure pipe 8 to the second pipe 22 in a neutral position where all the ports P, T, A and B are shut off. The first switching position (position a) and the high pressure line 7 are set to the second position.
It is a pilot operated valve that has a second switching position (position b) that connects to the conduit 22 and connects the low pressure conduit 8 to the first conduit 21.

The first conduit 21 and the second conduit 22 are connected to the high-pressure conduit 7 via check valves 23 and 24 so that only the flow toward the high-pressure conduit 7 is allowed. Further, the first conduit 21 and the second conduit 22 are connected to the low pressure conduit 8 by the check valves 25, 2
It is connected via 6 and allows only the flow from the low pressure line 7.

The operation lever 9 is command means for giving a command, and is rotated about the shaft 9a. Two first and second cams 27, 28 are provided on the shaft 9a.
The first cam 27 on the right side in the figure operates the pilot valve 30 to generate pilot pressure, and controls the switching of the direction switching valve 20 by this pilot pressure. The second cam 28 on the left side in the figure operates the pressure reducing valve 31. The control pressure is generated, and the hydraulic pressure regulator 32 is driven by this control pressure to control the displacement of the hydraulic motor 4.
The operation lever 9 has a neutral position, and braking ranges 9a and 9b and a drive range 9 are provided from the neutral position to the forward rotation side and the reverse rotation side, respectively.
c and 9d.

The cam shapes of the first and second cams 27 and 28 are set as follows. While the operating lever 9 is in the neutral position and in the braking ranges 9a and 9b, the first cam 27 controls the directional control valve 20 to be in the neutral position, and the second cam 28 controls the hydraulic motor 6 to operate the lever 9. The control is performed so that the tilt (displacement capacity) of the hydraulic motor 6 is increased as is closer to the neutral position. When the operating lever 9 is in the neutral position, the hydraulic motor 6 is tilted to the maximum. Further, when the operating lever 9 is in the forward drive range 9c, the first cam 27 controls the direction switching valve 20 to switch to the a position, and the high-pressure pipe 7 to the first pipe 21. The low pressure line 8 is connected to the second line 22. Further, in the forward rotation drive range 9c, the second cam 28 controls the hydraulic motor 6 to increase the tilt of the hydraulic motor 6 as the operation amount (operation command) of the operation lever 9 increases. When the operating lever 9 is operated to the maximum, the hydraulic motor 6 becomes the maximum tilt. Reverse drive range 9d
Then, the first cam 27 switches the direction switching valve 20 to the b position, the high pressure pipe 7 is set to the second pipe 22, and the low pressure pipe 8 is set to the first pipe.
It is the same as in the normal rotation drive except that it is connected to the pipe line 21.

The constitution of the constant pressure source 1 is known, and for example, as shown in FIG. 2, a swash plate type variable displacement hydraulic pump 40 is provided.
A pump line 41 connecting the discharge port of the hydraulic pump 40 to the high pressure port 2, an accumulator 42 for absorbing pressure fluctuations connected to the pump line 41, a tank line 44 connecting the low pressure port 3 to the tank 43, and a pump line The pressure sensor 45 for detecting the pressure of 41, the command signal of the target pressure Pref given by a setter (not shown) and the detection signal of the pressure sensor 45 are input, and the discharge pressure of the hydraulic pump 40 becomes the target pressure Pref. And a pump regulator 46 for controlling tilting (displacement capacity) of the hydraulic pump 40.

In the above, the first cam 27 and the pilot valve 30 have the directional control valve 20 in the neutral position when the operating lever (command means) 9 is in a predetermined command range (braking range 9a, 9b) including the neutral position. When the operating lever 9 is operated beyond the predetermined command range, the direction switching valve 20 is moved to the first switching position (position a) according to the operating direction.
Alternatively, the second cam 28, the pressure reducing valve 31, and the hydraulic regulator 32 constitute the first control means for switching to the second switching position (position b), and the operation lever (command means) 9 of the second cam 28, the pressure reducing valve 31, and the hydraulic regulator 32 are arranged in the predetermined command range (braking range 9a). , 9b), the displacement (tilt) of the hydraulic motor 4 is maximized in the neutral position, and the displacement is controlled so that the displacement of the hydraulic motor 4 gradually decreases as it is operated from the neutral position. When the operating lever 9 is operated beyond a predetermined command range, the displacement is controlled so that the displacement of the hydraulic motor 4 is gradually increased according to the operation amount.
It constitutes a control means.

Further, the check valves 23, 24 constitute a backflow preventing means for allowing only the flow from the first conduit 21 and the second conduit 22 toward the high pressure conduit 7, and the check valves 25, 2
Reference numeral 6 constitutes a replenishing means for preventing the generation of negative pressure in the first conduit 21 and the second conduit 22.

The operation of this embodiment configured as described above is as follows.

When the operating lever 9 is operated to the forward rotation side (right side in the drawing) from the state where the rotary load 6 is stopped, the direction switching valve 20 is in the neutral position while the operating lever 9 is in the braking range 9a. Since both the first pipe line 21 and the second pipe line 22 are shut off, the hydraulic motor 4 continues to stop unless rotational torque is input from the rotating load 6 side. When the operation lever 9 enters the forward rotation drive range 9c, the directional switching valve 20 is switched to the a position by the first cam 27 on the right side, the first pipe line 21 becomes the high pressure pipe line 7, and the second pipe line 22 becomes the low pressure line. When the hydraulic pressure is connected to the pipe line 8 and the differential pressure thereof is p, the hydraulic motor 4 rotates the rotational load 6 to the forward rotation side with a torque of p × q (q is displacement capacity of the hydraulic motor 4). However, from the braking range 9a to the driving range 9
At the point of switching to c, the displacement of the hydraulic motor 4 is at a minimum, so the generated torque is also small. For smooth acceleration / deceleration, it is desirable that the displacement of the hydraulic motor 4 be 0 at the point where the braking range 9a is switched to the drive range 9c. In this embodiment as well, the minimum value of q is 0. Suppose there is. Therefore, the torque for driving the rotary load 6 is 0 at the time of entering the normal rotation drive range 9c,
If the operation is continued to be further increased, the displacement of the hydraulic motor 4 is gradually increased by the second cam 28 on the left side, and the drive torque is also increased. When the operating lever 9 is operated to the maximum, it accelerates with the maximum torque.

When the operating lever 9 is operated to the maximum on the forward rotation side,
When the rotational load 6 decelerates from the state of accelerating rotation and stops, the operating lever 9 is gradually returned. While the operating lever 9 is in the normal rotation drive range 9c, the driving torque is gradually reduced, but the acceleration is in progress and the rotational load 6 continues to accelerate. When the operating lever 9 is returned to the position where it is switched from the normal rotation drive range 9c to the braking range 9a, the displacement of the hydraulic motor 4 becomes 0, the torque for the rotary load 6 becomes 0, and the rotary load 6 becomes idling. When the operating lever 9 enters the braking range 9a, the direction switching valve 20 returns to the neutral position and the first
Both the pipe line 21 and the second pipe line 22 are turned off. At this time, since the displacement of the hydraulic motor 4 is initially 0, no deceleration torque is generated yet.

When the operating lever 9 is returned further, the hydraulic motor 4
Since the displacement capacity of the hydraulic pressure increases again, the rotary load 6 drives the hydraulic motor 4, the hydraulic motor 4 performs a pumping action, sucks the hydraulic oil from the first pipe line 21, and the second pipe line 22.
To discharge. Since the second conduit is blocked by the direction switching valve 20, the pressure immediately rises even with a slight discharge amount.
When this pressure reaches the pressure in the high pressure line 7, the check valve 2
4 is opened, and the hydraulic oil discharged by the hydraulic motor 4 is absorbed by the accumulator 42 of the constant pressure source 1 through the high pressure line 7 and the high pressure port 2. At this time, the constant pressure source 1 described above
With this configuration, the pressure in the high-pressure pipe 7 is kept at the constant pressure p of the target pressure Pref, and the pressure in the second pipe 22 is kept at the pressure (constant pressure) in the high-pressure pipe 7. The pressure energy absorbed by the actuator 42 is used to drive the next hydraulic motor 4. On the other hand, since the hydraulic oil in the first pipeline 21 is absorbed by the hydraulic motor 4 by the pump action of the hydraulic motor 4, the pressure in the first pipeline 21 tends to decrease.
When the pressure drops to the pressure in the low pressure line 8, the check valve 2
5 can be opened and the suction flow rate can be replenished from the low pressure line 8 to prevent the first line 21 from becoming negative pressure. In this way, the differential pressure between the second pipeline 22 and the first pipeline 21 is kept substantially the same as the differential pressure between the high pressure pipeline 7 and the low pressure pipeline 8, which is supplied by the constant pressure source 1. It becomes a constant pressure p.

As the operating lever 9 approaches the neutral position, the displacement capacity q of the hydraulic motor 4 is driven by the second cam 28 on the left side.
Will increase. At this time, the torque required for the pump action of the hydraulic motor 4 is p × q, and this torque becomes the torque for decelerating the rotary load 6. Therefore, in the braking range 9a, a larger braking torque can be applied as the operating lever 9 approaches neutral.

The operation in the case of accelerating and decelerating in the forward rotation direction has been described above, but the same explanation holds when the operation is performed in the reverse rotation direction.

Further, the above-described operation in which the larger the operation lever 9 is operated, the greater the acceleration can be obtained, and the more the operation lever 9 is returned to the neutral position, the greater the deceleration can be accepted by the operator, the operation is easy to use. Can be said.

Next, consider a state in which the operating lever 9 is in the neutral state and the hydraulic motor 4 is stopped and the rotational torque is applied from the rotational load 6 side. This is applied to a swing hydraulic circuit of a machine that must operate even on a sloping ground such as a hydraulic excavator, and assumes a state in which a working device such as the front is laterally stopped on the sloping ground. . In the conventional method, there is a disadvantage that the work device flows downward due to the weight of the work device.

In the case of this embodiment, when the operating lever 9 is in the neutral position, the directional control valve 20 is in the neutral position, that is, the first conduit 2
The first and second pipe lines 22 are shut off, and the displacement of the hydraulic motor 4 is at the maximum (qmax). In this state, when a rotational torque in the forward rotation direction is applied to the hydraulic motor 4 from the rotational load 6 side, the second pipe line 2 is generated according to the torque T.
2 until the differential pressure pb (= T / qmax) is generated between the first pipeline 21 and the differential pressure pb reaches the differential pressure p between the high pressure pipeline 7 and the low pressure pipeline 8. Since there is no flow path for the oil to flow, the hydraulic motor 4 can be kept stopped without rotating.
When this differential pressure pb reaches the differential pressure p between the high-pressure line 7 and the low-pressure line 8, the check valve 24 opens and it cannot withstand any more torque, but this torque is the maximum drive of this drive circuit. Equivalent to torque. Therefore, it is possible to withstand the rotational torque from the rotational load 6 side in a state in which it is stopped up to the maximum drive torque of the system, which is sufficient performance to hold the revolving structure on the slope of the hydraulic excavator, for example. .

As described above, according to this embodiment, the constant pressure source 1 is provided, and the hydraulic drive capable of adjusting the torque for driving the rotary load 6 by adjusting the displacement of the variable displacement hydraulic motor 4. In the apparatus, when the load 6 is decelerated from the rotating state and then stopped, the check valves 23, 2 are provided in the first conduit 21 and the second conduit 22 on the hydraulic motor discharge side.
4 (reverse flow prevention means) to the high pressure pipeline 7, and the hydraulic motor suction side pipeline is connected to the low pressure pipeline 8 via check valves 25 and 26 (replenishment means), which is the same as the conventional control system. Power can be generated to decelerate and stop the load 6. Further, when the operating lever 9 is in the neutral position (non-operating state), even if the hydraulic motor 4 receives a rotational force from the rotational load side, the braking force is generated and the load 6 can be held so as not to rotate.

When the rotational load 6 is decelerated or stopped, the hydraulic lines on the hydraulic motor discharge side of the first pipe line 21 and the second pipe line 22 are at high pressure via check valves 23 and 24 (backflow prevention means). Since it is connected to the pipe line 7, the hydraulic energy generated by the pumping action of the hydraulic motor 4 is recovered by the accumulator 42 of the constant pressure source 1, and the characteristic of the constant pressure control system as an energy saving type is not lost.

Further, the conventional constant pressure control system requires a variable displacement type hydraulic motor capable of tilting in both forward and reverse directions in order to apply a braking force to the hydraulic motor 4 by operating the operating lever in the reverse direction. I was there. According to the present invention, since it is not necessary to operate the operation lever 9 in the reverse rotation direction to generate the braking force, the variable displacement hydraulic motor capable of tilting in one direction can be implemented. Further, the direction switching valve 20 and the check valves 23 to 26 are easily available and marketable devices. For this reason, the device can be realized at low cost even in consideration of the addition of the direction switching valve and the check valve.

A second embodiment of the present invention will be described with reference to FIG.

In FIG. 3, the directional control valve 20A is a solenoid operated valve, and the operation amount of the operation lever 9 is detected by the potentiometer 50. The detected value of the potentiometer 50 is converted into an electric signal and input to the first arithmetic unit 51 and the second arithmetic unit 52 which are configured by an electric circuit or a microcomputer. The first arithmetic unit 51 controls switching of the directional control valve 20A,
When the operating lever 9 is in the braking range 9a, 9b including the neutral position, the directional control valve 20A is set to the neutral position and the normal rotation drive range 9 is set.
An electric signal for switching the directional control valve 20A to the a position when it is in the c position and to the directional switch valve 20A when it is in the reverse drive range 9d is output to the directional control valve 20A. Also, the second
The control device 32 outputs a tilting command to the electric regulator 32A to control the tilting of the hydraulic motor 4, and detects the maximum operating position on the forward rotation side and the reverse rotation side when the operation lever 9 is in the neutral position. When the values are j and k, the tilt command of the maximum value qmax is output, and when the detection values 1 and m are switched from the forward rotation side and reverse rotation side braking ranges 9a and 9b to the drive ranges 9c and 9d. , 0 tilt command is output, and when the braking range 9a, 9b and the driving range 9c, 9d on the forward rotation side and the reverse rotation side are present, interpolation between the maximum value qmax and 0 rotation is performed with a straight line or a smooth curve. The tilt command is output based on the relationship between the tilt command and the operation amount of the operation lever 9 obtained as described above.

In the above, the potentiometer 50 and the first arithmetic unit 51 set the directional control valve 20 to the neutral position when the operating lever (command means) 9 is in a predetermined command range (braking range 9a, 9b) including the neutral position. When the operating lever 9 is operated beyond the predetermined command range, the directional switching valve 20 is switched to the first switching position (position a) or the second switching position (position b) according to the operating direction. When the operating lever (command means) 9 is in the predetermined command range (braking range 9a, 9b), the second arithmetic unit 52 and the electric regulator 32A constitute one control means.
At the neutral position, the displacement (tilt) of the hydraulic motor 4 becomes maximum, and the displacement is controlled so that the displacement of the hydraulic motor 4 gradually decreases as it is operated from the neutral position, and the operating lever 9 gives a predetermined command. The second control means is configured to control the displacement so that the displacement of the hydraulic motor 4 gradually increases according to the amount of operation when the displacement exceeds the range.

The present embodiment also operates in exactly the same manner as the first embodiment and obtains the same effect.

In the above embodiments, the case where the hydraulic drive system of the present invention is adopted in the turning hydraulic circuit of a hydraulic excavator has been described, but it may be applied to a traveling hydraulic circuit of a vehicle such as a wheel loader. Also in this case, sufficient holding force is exerted when the operation lever is instructing neutral, and it is possible to prevent the hydraulic motor from rotating due to the weight of the vehicle body while the vehicle is stopped on a sloping ground to move.

[0045]

According to the present invention, when the load is decelerated from the rotating state and then stopped, the braking force can be generated to decelerate and stop the load as in the conventional case, and the command means can be used. Is neutral (non-operating state), even if the hydraulic actuator receives a rotational force from the rotating load side, it can generate a holding force (braking force) and hold it so that the load does not rotate. In a turning hydraulic circuit of a machine that must operate even on sloping ground like this, the hydraulic motor is driven by the weight of the work device, the work device flows to the lower side, and the traveling of the vehicle such as a wheel loader. The hydraulic circuit can prevent the hydraulic motor from rotating due to the weight of the vehicle body and the vehicle body from moving.

Further, since it is not necessary to operate the command means in the reverse direction to generate the braking force, it is possible to implement even a variable displacement hydraulic motor capable of tilting in one direction, and the device can be manufactured at low cost. realizable.

Further, according to the present invention, when the load is decelerated or stopped, the pipelines on the hydraulic actuator discharge side of the first pipeline and the second pipeline are connected to the high pressure pipeline via the backflow prevention means. Therefore, the hydraulic energy generated by the pumping action of the hydraulic actuator is recovered by the constant pressure source, and the characteristic of the constant pressure control system as the energy saving type is not lost.

[Brief description of drawings]

FIG. 1 is a diagram showing a constant pressure control hydraulic drive device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing details of the constant pressure source shown in FIG.

FIG. 3 is a diagram showing a constant pressure control hydraulic drive device according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a conventional constant pressure control hydraulic drive device.

[Explanation of symbols]

 1 constant pressure source 2 high pressure port 3 low pressure port 4 hydraulic motor 5 variable capacity mechanism 6 rotating load 7 high pressure line 8 low pressure line 9 operating levers 9a, 9b braking range (predetermined command range) 9c, 9d drive range 20 direction switching Valve 21 First line 22 Second line 23,24 Check valve (backflow prevention means) 25,26 Check valve (replenishment means) 27 First cam 28 Second cam 30 Pilot valve 31 Pressure reducing valve 32 Regulator 50 Potentiometer 51 Number 1 arithmetic unit 52 2nd arithmetic unit

Claims (5)

[Claims] 1. A constant pressure source for supplying a constant pressure, a variable displacement type hydraulic actuator connected to the constant pressure source through a high pressure line and a low pressure line, and a command for the hydraulic pressure actuator. A constant pressure control hydraulic drive device for controlling a displacement of the hydraulic actuator according to a command of the command means to drive a rotational load, wherein the constant pressure source includes the high pressure line and the low pressure line. A high-pressure line, which is a directional control valve connected via
Neutral position where all ports of the low pressure line, the first line and the second line are shut off, and the first switching where the high pressure line is connected to the first line and the low pressure line is connected to the second line. A directional control valve having a position and a second switching position connecting the high pressure line to the second line and the low pressure line to the first line; and the command means is within a predetermined command range including neutral. In this case, the directional control valve is switched to the neutral position, and when the command means is operated beyond the predetermined command range, the directional control valve is moved to the first switching position or the second switching position according to the operating direction. A first control means for switching; when the command means is in the predetermined command range, the displacement of the hydraulic actuator becomes maximum at neutral, and the displacement of the hydraulic actuator gradually decreases as it is operated from neutral. To do A second control for controlling the displacement and controlling the displacement so that when the command means is operated beyond the predetermined command range, the displacement of the hydraulic actuator is gradually increased according to the operation amount. A constant pressure control hydraulic drive device. 2. The constant pressure control hydraulic drive system according to claim 1, wherein the backflow prevention means allows only a flow from the first pipeline and the second pipeline toward the high pressure pipeline;
A constant pressure control hydraulic drive device, further comprising: replenishing means for preventing negative pressure from being generated in the pipeline and the second pipeline. 3. The constant pressure control hydraulic drive system according to claim 1, wherein the command means is an operation lever which is operated to rotate, and the first control means is moved by a rotation operation of the operation lever. 1 cam and a valve operating means for switching the direction switching valve according to the movement of the first cam, and the second control means is operated in synchronization with the first cam by the turning operation of the operating lever. A constant pressure control hydraulic drive device, comprising: a second cam that is operated; and an actuator displacement operating means that controls the displacement of the hydraulic actuator according to the movement of the second cam. 4. The constant pressure control hydraulic drive device according to claim 3, wherein the first cam and the second cam are rotary integral type cams having a rotation center at a rotation center of the operation lever. A constant pressure control hydraulic drive device. 5. The constant-pressure control hydraulic drive device according to claim 1, wherein the command means is an operation lever that is operated to rotate, and the first control means is an angle that detects a rotation angle of the operation lever. It has a detecting means, a first computing means for outputting a corresponding valve switching command according to the rotation angle detected by the angle detecting means, and a valve operating means for switching the directional switching valve according to the valve switching command. The second control means controls the displacement of the hydraulic actuator by the second computing means which outputs a displacement capacity command corresponding to the rotation angle detected by the angle detection means, and the displacement capacity command. A constant pressure control hydraulic drive device comprising an actuator capacity operating means.