JP2017026085A - Hydraulic control device of work machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decide the target discharge pressure of a hydraulic pump according to operation amount, without using a controller.SOLUTION: A hydraulic control device of a work vehicle, includes: a variable displacement hydraulic pump 2; a direction control valve 13 which controls a flow of pressure oil supplied from the hydraulic pump 2 to an actuator 107; a servo piston device 3 which has a servo piston 3a coupled to a swash plate 2a of the hydraulic pump 2, a large-diameter cylinder chamber 3b, and a small-diameter cylinder chamber 3c connected to an output line 6a of a pilot hydraulic source 6; and a boom 104 actuated by the actuator 107. The hydraulic control device is equipped with a discharge pressure control valve 4 which has a pressure control spool 4a moving so as to balance instruction pressure Pb from an operation device 19 and pump discharge Pp inputted in directions opposite to each other, and switches a connecting destination of a large-diameter cylinder chamber 3b of the servo piston device 3 to either one of an output line 6a of the pilot hydraulic source 6 or a tank 9 according to a position of the pressure control spool 4a.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a hydraulic control device for a work machine such as a hydraulic excavator.

  In a bleed-off type hydraulic control device conventionally used in a work machine such as a hydraulic excavator, a part of the pressure oil discharged from the hydraulic pump is returned to the tank without work depending on the position of the directional control valve. , That much energy is wasted. The flow rate of the pressure oil discharged from the hydraulic pump and returned to the tank without being supplied to the actuator is called a bleed-off flow rate. On the other hand, from the viewpoint of energy efficiency, the bleed-off flow rate can be reduced by controlling the discharge flow rate with a controller so that the discharge pressure of the variable displacement hydraulic pump (hereinafter referred to as pump discharge pressure) becomes a predetermined pressure. The illustrated hydraulic control device has already been proposed (see Patent Document 1).

  On the other hand, when the load on the actuator increases and the discharge pressure rises, it is necessary to reduce the discharge flow rate of the hydraulic pump (hereinafter referred to as the pump discharge amount) in order to prevent the motor that drives the hydraulic pump from stalling. There is. In the hydraulic control device of Patent Document 1, the controller also supports the pump discharge amount limitation. However, if a failure occurs in the electric system, the control can be disabled. On the other hand, there is also a mechanical hydraulic control device that reduces the discharge flow rate when the pump discharge pressure is increased by a hydraulic drive type regulator (see Patent Document 2, etc.).

Japanese Patent No. 3745038 JP 2002-364549 A

  However, in any of the hydraulic control devices of Patent Documents 1 and 2, the pump discharge pressure fluctuates depending on the load of the actuator. For example, even when the operation lever is largely operated when excavating with a hydraulic excavator, the bucket The actuator is not loaded until is physically touching the ground. In other words, during this time, the pump discharge pressure is low for the amount of operation, so the bucket may not bite smoothly into the ground. In such a case, the gap between the operation amount and the machine operation may be uncomfortable depending on the operator, and there is room for improvement in terms of operation feeling.

  The objective of this invention is providing the hydraulic control apparatus of the working machine which can determine the target discharge pressure of a hydraulic pump according to the operation amount, without using a controller.

  In order to achieve the above object, a hydraulic control device for a working machine according to the present invention includes a tank that stores hydraulic oil, a variable displacement hydraulic pump that is driven by a prime mover and sucks and discharges the hydraulic oil in the tank. A directional control valve for controlling the flow of pressure oil supplied from the hydraulic pump to the actuator, a pilot hydraulic source, a servo piston connected to a swash plate of the hydraulic pump, a large-diameter cylinder chamber, and the pilot hydraulic source A hydraulic control device for a work machine comprising a servo piston device having a small-diameter cylinder chamber connected to the output line and a work member operated by the actuator, from an operation device that is input in directions facing each other. A pressure control spool that moves so that the command pressure and the discharge pressure of the hydraulic pump are balanced, and the position of the pressure control spool; In response, characterized in that the connection destination diameter cylinder chamber of the servo piston device comprising a discharge pressure control valve which switches to one of the output line or the tank of the pilot hydraulic source.

  According to the present invention, the target discharge pressure of the hydraulic pump can be determined according to the operation amount without using a controller, which can contribute to the improvement of operation feeling.

1 is a perspective view illustrating an external configuration of a hydraulic excavator that is an example of a work machine to which a hydraulic control device according to the present invention is applied. 1 is a hydraulic circuit diagram showing a main part of a hydraulic control device according to a first embodiment of the present invention. It is a schematic diagram showing the structure of the regulator with which the hydraulic control apparatus which concerns on 1st Embodiment of this invention was equipped. It is a schematic diagram for demonstrating the horsepower control valve with which the hydraulic control apparatus which concerns on 1st Embodiment of this invention was equipped. It is a figure showing the PQ diagram set with the hydraulic control apparatus which concerns on 1st Embodiment of this invention. It is a hydraulic circuit diagram which shows the principal part of the hydraulic control apparatus which concerns on 2nd Embodiment of this invention. It is a figure showing the PQ diagram set with the hydraulic control apparatus which concerns on 2nd Embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

<First Embodiment>
1. FIG. 1 is a perspective view showing an external configuration of a hydraulic excavator as an example of a working machine to which a hydraulic control device according to the present invention is applied. When there is no notice in the following description, the front of the driver's seat (the left direction in the figure) is the front of the aircraft. However, the illustration of the hydraulic excavator does not limit the application target of the hydraulic control device according to the present invention, and the hydraulic control device according to the present invention can be applied to other types of work machines such as cranes, bulldozers, wheel loaders and the like.

  The illustrated hydraulic excavator includes a traveling body 101, a revolving body 102 provided on the traveling body 101, and a working device (front work machine) 103 attached to the revolving body 102. The traveling body 101 is a crawler type that travels with the left and right crawler belts 111a and 111b. The swivel body 102 includes a driver's cab 110, and a seat (not shown) on which an operator sits and an operating device (such as the operating lever device 19 in FIG. 2) operated by the operator are disposed. The work device 103 includes a boom 104 attached to the front portion of the swing body 102 so as to be pivotable in the vertical direction, an arm 105 attached to the tip of the boom 104 so as to be pivotable in the vertical direction, and a vertical motion at the tip of the arm 105. A bucket 106 is mounted so as to be rotatable in the direction.

  The hydraulic excavator is also used as a hydraulic actuator to drive left and right traveling motors 112a and 112b that respectively drive the crawler belts 111a and 111b of the traveling body 101, and swiveling wheels (not shown), thereby turning the revolving body 102 relative to the traveling body 101. A swing motor 113 that drives the boom 104, an arm cylinder 108 that drives the arm 105, and a bucket cylinder 109 that drives the bucket 106. Accordingly, in addition to the boom 104, the arm 105, and the bucket 106, the crawler belts 111a and 111b and the swivel wheel constitute a working member that is operated by the actuator.

2. FIG. 2 is a hydraulic circuit diagram showing the main part of the hydraulic control apparatus according to the first embodiment of the present invention. The hydraulic control device shown in FIG. 2 includes a tank 9, a hydraulic pump 2, a directional control valve 13, a high pressure selection valve 15, a horsepower control device 17, a pilot hydraulic power source 6, and a regulator 1.

[Hydraulic pump]
The hydraulic pump 2 is connected to a prime mover 12 (for example, a diesel engine), and is driven by the prime mover 12 to suck in hydraulic oil stored in the tank 9 and discharge it as pressure oil. The hydraulic pump 2 is a variable displacement type, and the discharge flow rate varies depending on the angle (tilt angle) of the swash plate 2a.

[Directional control valve]
The direction control valve 13 is a three-position switching valve that controls the flow (direction) of pressure oil supplied from the hydraulic pump 2 to the boom cylinder 107, and is provided on the discharge line 2 b of the hydraulic pump 2. The position of the directional control valve 13 changes depending on the operation direction of the operation lever device 19, and the supply destination of the pressure oil discharged from the hydraulic pump 2 is switched to the rod side oil chamber or the bottom side oil chamber of the boom cylinder 107. The connection between 107 and the discharge line 2b is interrupted. The direction control valve 13 may be of a type that controls not only the direction but also the flow rate. In the present embodiment, other actuators such as the arm cylinder 108 and the corresponding directional control valve are not shown, and the directional control valve 13 corresponding to the boom cylinder 107 is exemplarily illustrated.

[High pressure selection valve]
The high pressure selection valve 15 is, for example, a shuttle valve provided on the output lines 18a and 18b of the operation lever device 19, and selectively opens the high pressure side of the output lines 18a and 18b. That is, it plays a role of selecting and outputting the command pressure Pb generated in either of the output lines 18a and 18b according to the operation direction of the operation lever device 19. Although only the operation system corresponding to the boom cylinder 107 is illustrated as an example, the high pressure selection valve 15 is similarly provided in the operation system of other actuators such as the arm cylinder 108.

[regulator]
FIG. 3 is a schematic diagram showing the structure of the regulator 1. As shown in FIGS. 2 and 3, the regulator 1 includes a servo piston device 3, a discharge pressure control valve 4, and a discharge flow rate control valve 5. In the present embodiment, the servo piston device 3, the discharge pressure control valve 4 and the discharge flow rate control valve 5 constitute an integrated regulator 1, and the regulator 1 is independent (separated) from the horsepower control device 17. It has a configuration. The configuration of the servo piston device 3, the discharge pressure control valve 4, and the discharge flow rate control valve 5 will be described sequentially.

Servo piston device The servo piston device 3 includes a servo piston 3a, a large diameter cylinder chamber 3b, and a small diameter cylinder chamber 3c. The servo piston 3a is connected to the swash plate 2a of the hydraulic pump 2 via a link, and the servo piston device 3 changes the tilt angle of the hydraulic pump 2 by the displacement of the servo piston 3a. The small diameter cylinder chamber 3c is directly connected to the output line 6a of the pilot hydraulic power source 6 (fixed capacity pump), and the pilot pressure Pc generated by the pilot hydraulic power source 6 is always input to the small diameter cylinder chamber 3c. The large-diameter cylinder chamber 3b has a larger pressure receiving area than the small-diameter cylinder chamber 3c, and an output line 6a of the pilot hydraulic power source 6 is connected to the large-diameter cylinder chamber 3b via the discharge pressure control valve 4 and the discharge flow rate control valve 5. Is done.

Discharge pressure control valve The discharge pressure control valve 4 includes a pressure control spool 4a (hereinafter referred to as spool 4a), a sleeve 4b, pressure receiving chambers 4c and 4d, and a spring 4s. The spool 4a is provided with lands 4x and 4y projecting from the outer periphery. The sleeve 4b covers the outer periphery of the spool 4a and includes ports 4p, 4q, and 4r (see FIG. 3) in the peripheral body portion. The sleeve 4b slides in the axial direction independently of the spool 4a, and is connected to the servo piston 3a by a link so that the displacement of the servo piston 3a is mechanically fed back. It has become. The control port 4q of the sleeve 4b is connected to the large-diameter cylinder chamber 3b of the servo piston device 3, and always opens at a position between the lands 4x and 4y. The high pressure port 4p is connected to the output line 6a of the pilot hydraulic power source 6 while being opened and closed by the land 4x. The low pressure port 4r is connected to a tank line 9a connected to the tank 9, while being opened and closed by a land 4y. The command pressure Pb of the operating lever device 19 output from the high pressure selection valve 15 is supplied to the pressure receiving chamber 4c on one side, and the discharge pressure Pp (hereinafter referred to as pump discharge pressure Pp) of the hydraulic pump 2 is written to the pressure receiving chamber 4d on the other side. ) Is entered. That is, the spool 4a is driven by the command pressure Pb and the pump discharge pressure Pp that are input to the pressure receiving chambers 4c and 4d so as to face each other. Displacement to balance the biasing force.

  With the above configuration, the discharge pressure control valve 4 switches the connection destination of the large-diameter cylinder chamber 3b of the servo piston device 3 to either the output line 6a or the tank line 9a of the pilot hydraulic power source 6 according to the position of the spool 4a. The servo piston 3a is displaced by adjusting the pressure oil from the pilot hydraulic power source 6 to the large diameter cylinder chamber 3b. At this time, the servo piston 3a is displaced according to the position of the spool 4a to change the discharge flow rate Qp of the hydraulic pump 2 (hereinafter referred to as pump discharge amount Qp), while the spool 4a has the pump discharge pressure Pp and the command pressure. Since Pb moves so as to balance, the discharge flow rate command value to the hydraulic pump 2 by the discharge pressure control valve 4 is such that the pump discharge pressure Pp is the command pressure in the range where the pump discharge pressure Pp does not exceed the upper limit (described later). The command value becomes equal to Pb.

-Discharge flow rate control valve The discharge flow rate control valve 5 includes a flow rate control spool 5a (hereinafter referred to as spool 5a), a sleeve 5b, a pressure receiving chamber 5c, and a spring 5s. The spool 5a is provided with lands 5x and 5y protruding on the outer peripheral portion. The sleeve 5b covers the outer periphery of the spool 5a and includes ports 5p, 5q, and 5t (see FIG. 3) in the peripheral body portion. The sleeve 5b slides in the axial direction independently of the spool 5a, and is linked to the servo piston 3a via the sleeve 4b of the discharge pressure control valve 4 so that the displacement of the servo piston 3a is reduced. Mechanical feedback is provided. The control port 5q is connected to the low pressure port 4r of the discharge pressure control valve 4 and is always opened at a position between the lands 5x and 5y. The high pressure port 5p is connected to the output line 6a of the pilot hydraulic power source 6 and is opened and closed by the land 5x. The low pressure port 5t is connected to the tank line 9a, and is opened and closed by the land 5y. An output pressure Ps of a low pressure selection valve 8 (described later) is input to the pressure receiving chamber 5c. That is, the spool 5a is driven by the output pressure Ps input to the pressure receiving chamber 5c, and is displaced so that the urging force by the output pressure Ps and the urging force by the spring 5s are balanced. Unlike the spring 4 s of the discharge pressure control valve 4, the spring 5 s alone balances the output pressure Ps, so that the spring force is set larger than that of the spring 4 s.

  With the above configuration, similarly to the discharge pressure control valve 4, the discharge flow rate control valve 5 connects the connection destination of the large-diameter cylinder chamber 3 b of the servo piston device 3 to the output line 6 a of the pilot hydraulic power source 6 or the tank according to the position of the spool 5 a. By switching to one of the lines 9a, the servo piston 3a is displaced. At this time, the pump discharge pressure Pp changes according to the position of the spool 5a, and the position of the spool 5a changes according to the command pressure Pb within a range where the pump discharge pressure Pp does not exceed an upper limit (described later). Therefore, the discharge flow rate command value to the hydraulic pump 2 by the discharge flow rate control valve 5 is a command value that is equal to the required flow rate according to the operation amount of the operation lever device 19 in a range where the pump discharge pressure Pp does not exceed the upper limit value. .

[Horsepower control device]
Returning to FIG. 2, the horsepower control device 17 is operated by the pump discharge pressure Pp, and when the pump discharge pressure Pp increases, the connection destination of the pressure receiving chamber 5c of the discharge flow rate control valve 5 is connected to the output line 18a or 18b ( The tank 9 is switched from the output line of the high pressure selection valve 15). Although the horsepower control device 17 can be configured as an integral valve device, in the present embodiment, the horsepower control device 17 includes the horsepower control valve 11 and the low pressure selection valve 8 which are independent (separated) from each other (including other piping and the like). The configurations of the low pressure selection valve 8 and the horsepower control valve 11 will be described sequentially.

Low pressure selection valve The low pressure selection valve 8 is provided in the input line 5 u of the pressure receiving chamber 5 c of the discharge flow rate control valve 5, and the command pressure Pb of the operation lever device 19 (output pressure of the high pressure selection valve 15) and the horsepower control valve 11 It is driven by the output pressure Pa. This low pressure selection valve 8 selectively connects the output line of the operating lever device 19 and the low pressure side of the output line of the horsepower control valve 11 to the input line 5u, and reduces the lower one of the command pressure Pb and the output pressure Pa. The pressure is output to the pressure receiving chamber 5c of the discharge flow rate control valve 5.

Horsepower control valve The horsepower control valve 11 includes a horsepower control spool 11a (hereinafter referred to as spool 11a), a pressure receiving chamber 11b, and a horsepower setting spring 11s, and the pressing force by the pump discharge pressure Pp is a set value (horsepower setting). Actuates when (or approaches) the pushing force of the spring force of the spring 11s = the pushing force by the upper limit value of the pump discharge pressure Pp, and operates the discharge flow rate control valve 5 to reduce the discharge flow rate of the hydraulic pump 2. do.

  Specifically, the spool 11 a includes an A port (output port) connected to the low pressure selection valve 8, a T port connected to the tank line 9 a of the tank 9, and a P port connected to the output line 6 a of the pilot hydraulic power source 6. The connection ratio of the T port and the P port to the A port is changed depending on the position. A pressure receiving chamber 11b is provided on one side of the spool 11a, and a horsepower setting spring 11s is provided on the other side, and is attached by a pump discharge pressure Pp input to the pressure receiving chamber 11b through an oil passage 7 branched from the discharge line 2b. The position of the spool 11a is determined by the balance between the force and the urging force by the horsepower setting spring 11s. That is, the horsepower control valve 11 is driven by the pump discharge pressure Pp, and the connection ratio of the output line 6a of the pilot hydraulic power source 6 and the tank line 9a to the pressure receiving chamber 5c of the discharge flow rate control valve 5 is changed. The output pressure Pa is changed according to the above. Next, the relationship between the pump discharge pressure Pp and the output pressure Pa will be described.

FIG. 4 is a schematic diagram for explaining the horsepower control valve 11. As shown in FIG. 4, the spool 11a of the horsepower control valve 11 includes a fixed throttle 20 connected to the P port and a variable throttle 21 connected to the T port. The opening area of the variable throttle 21 varies depending on the balance between the pressing force by the pump discharge pressure Pp guided from the oil passage 7 and the pressing force by the horsepower setting spring 11s. As a result, the ratio of the opening areas of the fixed throttle 20 and the variable throttle 21 changes, and the output pressure Pa changes according to the area ratio. As for the output pressure Pa, when the opening area of the variable throttle 21 is At, the opening area of the fixed throttle 20 is Ap, the pilot pressure from the pilot hydraulic power source 6 is Pc, and the tank pressure is 0 (zero), the output pressure Pa = Pc × Ap ² / (At ² + Ap ² ) As described above, the opening area of the variable throttle 21 is increased as the pump discharge pressure Pp increases, and the pump discharge is determined by the shape and size of the spool 11a and the pressure receiving chamber 11b and the spring force of the horsepower setting spring 11s. An upper limit value of the pump discharge amount Qp (pump capacity) with respect to the pressure Pp can be set.

  Here, in FIG. 5, a curve (a curve in which the prime mover 12 stalls when the pump absorption horsepower exceeds a certain limit value) is indicated by a dotted line. In the present embodiment, as shown in FIG. 5, an upper limit value (PQ line) of the pump discharge amount Qp with respect to the pump discharge pressure Pp that does not exceed the dotted line is set. The PQ line is set so that the upper limit value of the pump discharge amount Qp decreases as the pump discharge pressure Pp increases, and the absorption horsepower of the hydraulic pump 2 does not exceed the output horsepower of the prime mover 12. The setting of the PQ line is set by the spring force or the like of the horsepower setting spring 11s.

  In FIG. 4, the opening area of the variable throttle 21 increases as the pump discharge pressure Pp increases. However, the variable throttle 21 and the fixed throttle 20 are interchanged, and the pump discharge pressure Pp increases. A configuration in which the opening area of the variable diaphragm 21 decreases may be adopted.

3. Operation When the operation lever device 19 is operated, the hydraulic control device of the present embodiment operates as follows according to the relationship between the pump discharge pressure Pp and the upper limit value and the relationship between the command pressure Pb of the operation lever device 19 and the pump discharge pressure Pp. To do. In the following description, the positional relationship between the spools 4a and 5a is based on the position of the right end surface of the left lands 4x and 5x in FIG. For example, when the right end surface of the land 5x is on the left side of the right end surface of the land 4x, the spool 5a is on the left side of the drawing with respect to the spool 4a.

(1) Qp control by the discharge flow rate control valve 5 For example, when the operation lever device 19 is not operated, the spool 11a of the horsepower control valve 11 is pushed upward in FIG. 2 by the pressing force of the horsepower setting spring 11s ( The pilot pressure Pc from the pilot hydraulic pressure source 6 is output as the output pressure Pa of the horsepower control valve 11. In this case, the spool of the low pressure selection valve 8 is pushed upward in the figure, and the pressure receiving chamber 5c of the discharge flow rate control valve 5 is connected to the output line 18a or 19b of the operation lever device 19 via the high pressure selection valve 15. .

  When the operation lever device 19 is operated under the condition that the pump discharge pressure Pp is less than the PQ line described in FIG. 5 and the operation amount is relatively small, the pump discharge pressure Pp is less than the command pressure Pb. The command pressure Pb corresponding to the operation amount is input to both the pressure receiving chambers 4c and 5c, and the spools 4a and 5a of the discharge pressure control valve 4 and the discharge flow rate control valve 5 are urged to the right side in the figure. At this time, since the pump discharge pressure Pp input to the pressure receiving chamber 4d is low, the spool 4a of the discharge pressure control valve 4 is positioned on the right side of the spool 5a of the discharge flow rate control valve 5, and the low pressure port of the discharge pressure control valve 4 4r and the control port 4q are opened, and the high-pressure port 4p is closed. Under this state, the connection partner of the large-diameter cylinder chamber 3 b is switched depending on the discharge flow rate control valve 5. Depending on the position of the sleeve 5b, the discharge flow rate control valve 5 is open when the high pressure port 5p is open and the low pressure port 5t is closed, when the high pressure port 5p is closed and the low pressure port 5t is open, and when the high pressure port 5p is open. The low-pressure port 5t may be closed together (or may be opened slightly depending on the structure).

(1-1) High pressure port 5p: closed, low pressure port 5t: closed When the command pressure Pb does not change, the high pressure port 5p and the low pressure port 5t are closed by the lands 5x and 5y of the spool 5a (or minutely) If it is open), the pressure oil that fills the large-diameter cylinder chamber 3b is held, the servo piston 3a does not move, and the pump discharge amount Qp is also maintained.

(1-2) High-pressure port 5p: open, low-pressure port 5t: closed For example, when the operation amount decreases, the command pressure Pb decreases, the spool 5a of the discharge flow rate control valve 5 moves to the left side, and the high-pressure port 5p opens to low pressure. Port 5t is closed. As a result, the pressure oil from the pilot hydraulic power source 6 flows into the high pressure port 5p and passes through the control port 5q of the discharge flow rate control valve 5, the low pressure port 4r of the discharge pressure control valve 4 and the control port 4q, and the large diameter cylinder chamber. It flows into 3b. When pressure oil flows into the large-diameter cylinder chamber 3b, the servo piston 3a moves to the left in the figure due to the pressure receiving area difference, and the pump discharge amount Qp decreases. Further, the sleeves 4b and 5b of the discharge pressure control valve 4 and the discharge flow rate control valve 5 move to the left side in conjunction with the servo piston 3a. As the sleeve 5b moves to the left in the figure following the spool 5a, the opening of the high pressure port 5p of the discharge flow rate control valve 5 is gradually narrowed, and when the sleeve 5b catches up with the spool 5a, the high pressure port 5p is closed. When the high-pressure port 5p is closed, the pressure oil flowing into the large-diameter cylinder chamber 3b is damped, the servo piston 3a is stopped, and the pump discharge amount Qp is maintained.

(1-3) High pressure port 5p: closed, low pressure port 5t: open For example, when the operation amount increases, the command pressure Pb rises, the spool 5a of the discharge flow rate control valve 5 moves to the right side, and the high pressure port 5p is closed. The low pressure port 5t opens. As a result, the pressure oil flows out from the large-diameter cylinder chamber 3b to the tank 9 via the control port 4q and low-pressure port 4r of the discharge pressure control valve 4 and the control port 5q and low-pressure port 5t of the discharge flow rate control valve 5. When pressure oil flows out from the large-diameter cylinder chamber 3b, the servo piston 3a moves to the right side in the figure, and the pump discharge amount Qp increases. Further, the sleeves 4b and 5b of the discharge pressure control valve 4 and the discharge flow rate control valve 5 move to the right side in conjunction with the servo piston 3a. As the sleeve 5b moves to the right following the spool 5a, the opening of the low pressure port 5t of the discharge flow rate control valve 5 is gradually narrowed, and when the sleeve 5b catches up with the spool 5a, the low pressure port 5t is closed. When the low pressure port 5t is closed, the pressure oil flowing out from the large diameter cylinder chamber 3b is blocked, and the servo piston 3a is stopped to maintain the pump discharge amount Qp.

(2) Qp control by the discharge pressure control valve 4 For example, even when the operation amount is relatively large, if the pump discharge pressure Pp does not satisfy the PQ line described with reference to FIG. The command pressure Pb is input to both the pressure receiving chambers 4c and 5c, and the spools 4a and 5a of the discharge pressure control valve 4 and the discharge flow rate control valve 5 are urged to the right side in the figure. At this time, since the command pressure Pb (the output pressure Ps of the low pressure selection valve 8) increases, the spool 5a of the discharge flow control valve 5 is pushed to the right side of the spool 4a of the discharge pressure control valve 4, and the discharge flow control valve When the low pressure port 5t and the control port 5q are opened and the high pressure port 5p is closed, the connection partner of the large-diameter cylinder chamber 3b is switched depending on the discharge pressure control valve 4. Depending on the position of the sleeve 4b, the discharge pressure control valve 4 is open when the high pressure port 4p is open and the low pressure port 4r is closed, when the high pressure port 4p is closed and the low pressure port 4r is open, and when the high pressure port 4p is open. The low-pressure port 4r may be closed together (or slightly opened depending on the structure).

(2-1) High pressure port 4p: Closed, Low pressure port 4r: Closed For example, when the command pressure Pb does not change, the high pressure port 4p and the low pressure port 4r are closed by the lands 4x, 4y of the spool 4a (or minutely). In this case, the pressure oil that fills the large-diameter cylinder chamber 3b is retained, the servo piston 3a does not move, and the pump discharge amount Qp is also maintained.

(2-2) High pressure port 4p: open, low pressure port 4r: closed For example, when the operation amount decreases, the command pressure Pb decreases, the spool 4a of the discharge pressure control valve 4 moves to the left side, the high pressure port 4p opens, and the low pressure Port 4r is closed. As a result, the pressure oil flows from the pilot hydraulic power source 6 into the high pressure port 4p of the discharge pressure control valve 4 and flows into the large diameter cylinder chamber 3b via the control port 4q. As a result, the servo piston 3a moves to the left in the figure, and the pump discharge amount Qp decreases. When the sleeve 4b follows the spool 4a in conjunction with the servo piston 3a and the sleeve 4b catches up with the spool 4a, the high pressure port 4p is closed, the servo piston 3a is stopped, and the pump discharge amount Qp is maintained. Since the pump discharge amount Qp is determined by the discharge flow rate command by the discharge pressure control valve 4, it becomes a value corresponding to the command pressure Pb as described above.

(2-3) High pressure port 4p: closed, low pressure port 4r: open For example, when the operation amount increases, the command pressure Pb rises, the spool 4a of the discharge pressure control valve 4 moves to the right side, and the high pressure port 4p closes. The low pressure port 4r opens. As a result, the pressure oil flows out from the large-diameter cylinder chamber 3 b to the tank 9 via the control port 4 q and the low-pressure port 4 r of the discharge pressure control valve 4 and the low-pressure port 5 t of the discharge flow rate control valve 5. As a result, the servo piston 3a moves to the right side in the figure, and the pump discharge amount Qp increases. When the sleeve 4b follows the spool 4a in conjunction with the servo piston 3a and the sleeve 4b catches up with the spool 4a, the low pressure port 4r is closed, the servo piston 3a is stopped, and the pump discharge amount Qp is maintained. Also in this case, since the pump discharge amount Qp is determined by the discharge flow rate command by the discharge pressure control valve 4, it becomes a value corresponding to the command pressure Pb as described above.

(3) Qp control by the horsepower control device 17 When the pump discharge pressure Pp rises to the PQ line described with reference to FIG. The pressing force by the pump discharge pressure Pp input to the chamber 11b exceeds the pressing force by the horsepower setting spring 11s, and the horsepower control valve 11 is pushed downward in FIG. 2 (switches to the upper switching position). Then, as the output pressure Pa of the horsepower control valve 11 decreases, the spool of the low pressure selection valve 8 is pushed downward in the figure, and the pressure receiving chamber 5c of the discharge flow rate control valve 5 is connected to the tank 9 to control the discharge flow rate. The valve 5 moves to the left side in the figure. As a result, the pressure oil from the pilot hydraulic power source 6 is input to the large-diameter cylinder chamber 3b, the servo piston 3a moves to the left side, and the pump discharge amount Qp decreases. Since the horsepower control valve 11 moves again upward in the figure when the pump discharge pressure Pp decreases and leaves the PQ line, the pump discharge pressure while the horsepower control valve 11 is operating (moving downward). Even if the required flow rate corresponding to the operation amount exceeds the upper limit value (PQ line), the pump discharge amount Qp is limited to the upper limit value.

4). Effects (1) Basic Effects According to the present embodiment, the servo piston device 3 is driven by the discharge pressure control valve 4 in which the spool 4a is displaced so that the pump discharge pressure Pp is balanced with the command pressure Pb of the operation lever device 19. Thus, the target discharge pressure of the hydraulic pump 2 can be determined according to the operation amount without using a controller. Since the target discharge pressure can be determined according to the operation amount, the operability can be improved. And, by controlling the pump discharge pressure Pp according to the operation amount, which has conventionally relied on the electric control, by mechanical, the electrical failure factor is eliminated from the mechanism that controls the discharge flow rate Pp according to the operation amount. Can contribute to improving the reliability of the machine.

(2) Compactness In this embodiment, by using the regulator 1 provided with the servo piston device 3, the discharge pressure control valve 4 and the discharge flow rate control valve 5, and using the low pressure selection valve 8 and the horsepower control valve 11 separately from this. In addition to the control of the pump discharge pressure Pp according to the operation amount described above, the control of the pump discharge amount Qp according to the operation amount and the horsepower control for suppressing the stall of the prime mover 12 are also realized mechanically. Thereby, not only the operability of the work machine but also the effect of improving the energy efficiency by reducing the bleed-off flow rate and the effect of improving the work efficiency by suppressing the stall of the prime mover 12 can be obtained.

  Here, the spool valve device that outputs a pump discharge amount command according to the operation amount, and the discharge to an existing regulator (see Japanese Patent Application Laid-Open No. 2002-364549, etc.) that incorporates a spool valve device that controls horsepower control It is assumed that a regulator having a function equivalent to that of the hydraulic control device of the present embodiment is manufactured by adding a spool valve device corresponding to the pressure control valve 4. In this case, the manufactured regulator is increased in size because a spool valve device corresponding to the discharge pressure control valve 4 is additionally provided. However, due to the recent demand for environmental protection, work machines are required to be equipped with additional equipment such as an exhaust gas aftertreatment device, and restrictions on the equipment layout are increasing. For this reason, when the regulator is made larger in size, the degree of freedom of layout is reduced, and not only the layout of the equipment becomes difficult, but also the manufacture and maintenance of the work machine become difficult as the layout becomes difficult.

  On the other hand, the regulator 1 of the present embodiment can be made as large as an existing regulator. By manufacturing the discharge pressure control valve 4 using a spool valve device that controls horsepower, the regulator 1 can be manufactured based on an existing regulator. Further, the horsepower control device 17 for realizing the horsepower control is separated from the regulator 1 and has an external structure that is separated from and connected to the regulator 1 through a pipe, whereby the regulator 1 and the horsepower control device. As compared with the case where the positional relationship of 17 is eliminated and the regulator is increased in size alone, a much higher degree of freedom in device layout can be ensured when the above three controls are realized mechanically. In particular, in the present embodiment, the horsepower control device 17 is configured by the horsepower control valve 11 and the low pressure selection valve 8 and the like (including piping). Therefore, the horsepower control device 17 itself can also be divided and the layout can be freely set. The degree can be further improved.

  Accordingly, it is possible to secure the degree of freedom of layout while mounting the above three control mechanisms, and it is possible to suppress the difficulty in manufacturing and maintaining the work machine. Of course, it is also a great merit that high reliability is ensured because there are no electrical failure factors in the three control mechanisms.

Second Embodiment
FIG. 6 is a hydraulic circuit diagram showing the main part of the hydraulic control apparatus according to the second embodiment of the present invention. FIG. 6 is a diagram corresponding to FIG. 2, and the elements described above are denoted by the same reference numerals as those in the above-described drawings, and description thereof is omitted.

  The hydraulic control device according to this embodiment is different from the hydraulic control device of the first embodiment in that a proportional pressure reducing valve 16 is used instead of the horsepower control valve 11. That is, the horsepower control device 27 of this embodiment includes the proportional pressure reducing valve 16 in addition to the low pressure selection valve 8. The proportional pressure reducing valve 16 is provided on the output line 6a of the pilot hydraulic power source 6, and inputs the pump discharge pressure Pp from the direction opposite to the biasing direction of the spring 16s. The output pressure Pa is decreased in proportion to the increase in the pump discharge pressure Pp, and the output pressure Pa becomes constant (minimum value) when the pump discharge pressure Pp exceeds a certain value. The low pressure selection valve 8 outputs the smaller one of the command pressure Pb of the operating lever device 19 and the output pressure Pa of the proportional pressure reducing valve 16 to the discharge flow rate control valve 5. Other configurations are the same as those of the first embodiment.

  In this embodiment, since the upper limit of the pump discharge amount Qp is determined by the output pressure Pa of the proportional pressure reducing valve 16, the pump discharge amount Qp is a broken line type PQ line as shown by a solid line in FIG. 7 with respect to the pump discharge pressure Pp. Is set. Even if the PQ line has such a shape, as long as the PQ line is set so as not to exceed the limit value indicated by the dotted line in the figure, the prime mover as long as the pump discharge amount Qp changes within the range not exceeding the PQ line. 12 stalls can be suppressed.

  Also in this embodiment, when the pump discharge pressure Pp is low, the output pressure Pa of the proportional solenoid valve 16 is high, the command pressure Pb of the operating lever device 19 is selected by the low pressure selection valve 8, and the pump discharge pressure Pp is PQ in FIG. The pump discharge amount Qp is controlled so that the required flow rate or the pump discharge pressure Pp corresponding to the operation amount is within a range not exceeding the line. Further, when the pump discharge pressure Pp increases, the output pressure Pa decreases, and when the output pressure Pa is output from the low pressure selection valve 8, the spool 5a of the discharge flow rate control valve 5 goes left, and the pump discharge amount Qp becomes PQ. Decrease along the line. Therefore, the same effect as the first embodiment can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Regulator, 2 ... Hydraulic pump, 2a ... Swash plate, 3 ... Servo piston apparatus, 3a ... Servo piston, 3b ... Large diameter cylinder chamber, 3c ... Small diameter cylinder chamber,
DESCRIPTION OF SYMBOLS 4 ... Discharge pressure control valve, 4a ... Pressure control spool, 5 ... Discharge flow control valve, 5a ... Flow control spool, 5c ... Pressure receiving chamber, 6 ... Pilot hydraulic power source, 6a ... Output line of pilot hydraulic power source, 8 ... Low pressure selection Valve 9, Tank 11, Horsepower control valve 11 a Horsepower control spool 12 Motor, 13 Directional control valve 16 Proportional pressure reducing valve 17 Horsepower controller 18 a 18 b Output line of operation device, DESCRIPTION OF SYMBOLS 19 ... Operation lever apparatus (operation apparatus), 104 ... Boom (working member), 105 ... Arm (working member), 106 ... Bucket (working member), 107 ... Boom cylinder (actuator), 108 ... Arm cylinder (actuator), 109 ... Bucket cylinder (actuator), 111a, 111b ... crawler belt (working member), 112a, 112b ... travel motor (actuator) Chromatography data), 113 ... swing motor (actuator), A ... A port (output port), the output pressure of Pa ... horsepower control valve, Pb ... command pressure, Pp ... pump discharge pressure (discharge pressure of the hydraulic pump)

Claims (5)

A tank storing hydraulic fluid;
A variable displacement hydraulic pump that is driven by a prime mover and sucks and discharges the hydraulic fluid of the tank;
A directional control valve for controlling the flow of pressure oil supplied to the actuator from the hydraulic pump;
A pilot hydraulic source,
A servo piston device having a servo piston coupled to a swash plate of the hydraulic pump, a large diameter cylinder chamber, and a small diameter cylinder chamber connected to an output line of the pilot hydraulic power source;
A hydraulic control device for a work machine including a work member operated by the actuator,
A pressure control spool that moves so as to balance the command pressure from the operating device and the discharge pressure of the hydraulic pump that are input in directions facing each other, and according to the position of the pressure control spool, A hydraulic control device for a work machine, comprising a discharge pressure control valve that switches a connection destination of a large-diameter cylinder chamber to either an output line of the pilot hydraulic power source or the tank. The hydraulic control device for a work machine according to claim 1,
A flow control spool that moves in response to a command pressure from the operating device, and the connection destination of the large-diameter cylinder chamber of the servo piston device is connected to the output line of the pilot hydraulic power source or the position according to the position of the flow control spool; A discharge flow rate control valve for switching to one of the tank lines connected to the tank;
And a horsepower control device that operates by the discharge pressure of the hydraulic pump and switches the connection destination of the pressure receiving chamber of the discharge flow rate control valve from the output line of the operation device to the tank when the discharge pressure rises. Hydraulic control device for working machines. The hydraulic control device for a work machine according to claim 2,
The servo piston device, the discharge pressure control valve and the discharge flow rate control valve constitute an integrated regulator,
The hydraulic control device for a work machine, wherein the horsepower control device is provided apart from the regulator. The hydraulic control device for a work machine according to claim 3,
The horsepower control device is:
A horsepower control valve that has a horsepower control spool that moves according to the discharge pressure of the hydraulic pump, and that changes a connection ratio of the output line of the pilot hydraulic power source and the tank to an output port according to the position of the horsepower control spool; ,
A hydraulic pressure for a work machine, comprising: a low pressure selection valve that selects a low pressure side of a command pressure from the operating device and an output pressure of the horsepower control valve and outputs the low pressure side valve to a pressure receiving chamber of the discharge flow rate control valve. Control device. The hydraulic control device for a work machine according to claim 3,
The horsepower control device is:
A proportional pressure reducing valve that decreases the output pressure as the discharge pressure of the hydraulic pump increases;
A hydraulic pressure for a work machine, comprising: a low pressure selection valve that selects a low pressure side of a command pressure from the operating device and an output pressure of the proportional pressure reducing valve and outputs the pressure to a pressure receiving chamber of the discharge flow rate control valve. Control device.

Images