JP4408406B2 - Pump variable displacement controller with unload function - Google Patents

Description

  The present invention relates to a pump variable displacement control device with an unload function.

  Patent Document 1 discloses a displacement control device that has an unload valve suitable for a work vehicle and variably controls the discharge volume of a hydraulic pump. Patent Document 1 is an engine load control device for suppressing the generation of white smoke at a low temperature start in a diesel engine that directly drives a hydraulic pump, and an example of a hydraulic device for a work vehicle shown in FIG. 3 as its prior art. A hydraulic circuit diagram is shown. The displacement control device of the variable displacement hydraulic pump of the hydraulic device 61 shown in FIG. 3 unloads the hydraulic oil of the hydraulic pump 64 from the unload valve 71 and discharges the hydraulic pump 64 when the work machine operation valve 66 is not operated. This is a capacity control device that minimizes the volume and increases the discharge volume when the work machine operation valve 66 is operated.

  In the hydraulic circuit shown in FIG. 3, a closed center load sensing hydraulic circuit (referred to as a CLSS circuit) is used. The CLSS circuit can obtain the speed of a hydraulic actuator or the like according to the operation amount of the operation valve, and can reduce the load. It is frequently used in work vehicles because it has fine control characteristics that are not affected, combined operability in which distribution performance is determined by the opening area of the spool during combined operation, and energy saving by variable pump control.

  In FIG. 3, a variable displacement hydraulic pump 64 driven by a diesel engine 62 is connected to an oil tank 63. A discharge circuit 65 of the hydraulic pump 64 is connected to a hydraulic actuator 67 for the working machine via a working machine operation valve 66. The work machine operation valve 66 has a pressure compensation valve (not shown) that uses the discharge pressure of the hydraulic pump 64 and the load detection circuit pressure as a control differential pressure.

  The discharge circuit 65 includes a safety valve 70 that returns oil to the oil tank 63 when the discharge pressure of the hydraulic pump 64 exceeds a predetermined value (for example, 32.0 MPa), the discharge pressure of the hydraulic pump 64, and the load pressure of the hydraulic actuator 67. And an unloading valve 71 that operates in response to the differential pressure.

  The set differential pressure of the unload valve 71 is, for example, 2.0 MPa. The hydraulic pump 64 has a capacity control cylinder 72 that increases or decreases the discharge amount. The head side of the capacity control cylinder 72 communicates with the discharge circuit 65, and the bottom side via the capacity control valve 73 serves as a discharge circuit 65 or an oil tank. 63 communicates. That is, the capacity control valve 73 has two positions A and B. The bottom side communicates with the discharge circuit 65 at the A position, and is connected to the oil tank 63 at the B position.

  The A position side of the capacity control valve 73 is connected to the discharge circuit 65 and is urged to the A position side by the discharge pressure oil, and the B position side is urged to the B position side by the spring. The load detection circuit 74 is a circuit that detects the hydraulic pressure of the hydraulic actuator 67 of the work machine of the work vehicle. One end of the load detection circuit 74 is connected to the work machine operation valve 66, and the other end is connected to the spring chamber side of the capacity control valve 73. is doing. The capacity control valve 73 can be switched between the A and B positions in accordance with the differential pressure between the hydraulic pressure of the load detection circuit 74 and the hydraulic pressure of the pump discharge circuit 65.

  The unload valve 71 is connected to a load detection circuit 74 via an unload pilot circuit 75, and the unload valve 71 operates in accordance with the differential pressure between the hydraulic pressure of the load detection circuit 74 and the hydraulic pressure of the pump discharge circuit 65. It is like that. The load detection circuit 74 is provided with a drain circuit 76 and communicates with the oil tank 63 through a throttle 77.

  Next, the operation will be described. When the work implement operation valve 66 is closed and the hydraulic actuator 67 is not operated, the load detection circuit 74 communicates with the oil tank 63 via the throttle 77, and the hydraulic pressure of the load detection circuit 74 is the drain pressure. When the diesel engine 62 is operating in this state, the oil in the discharge circuit 65 is returned from the unload valve 71 to the oil tank 63. The hydraulic pressure of the discharge circuit 65 at this time is, for example, 2.0 MPa as described above. This value is larger than the set pressure of the displacement control valve 73, and the displacement control valve 73 is switched to the A position, the displacement control cylinder 72 is activated and extended, the displacement of the hydraulic pump 64 is minimized, and the discharge amount is minimized. It has become.

  Therefore, the load of the diesel engine 62 for driving the hydraulic pump 64 is small. When the work implement operation valve 66 is opened and the hydraulic actuator 67 for the work implement is operated, pressure oil on the load side of the hydraulic actuator 67 flows through the load detection circuit 74. Then, the differential pressure between the hydraulic pressure of the load detection circuit 74 and the hydraulic pressure of the discharge circuit 65 of the hydraulic pump 64 is reduced, and the unload valve 71 is closed. Then, the discharge pressure of the hydraulic pump 64 increases. Further, the capacity control valve 73 is switched to the B position, and the capacity control cylinder 72 is operated and contracted to increase the capacity of the hydraulic pump 64. When the discharge pressure of the hydraulic pump 64 exceeds the set pressure of the safety valve 70, the pressurized oil is returned from the safety valve 70 to the oil tank 63.

Japanese Patent Laid-Open No. 2002-61602 (pages 2, 3 and 4)

  However, in the hydraulic device 61 of Patent Document 1, an unload valve 71 is provided in the discharge circuit 65 and an unload pilot circuit 75 is provided in the load detection circuit 74 in order to unload the pressure oil of the hydraulic pump 64 to the oil tank 63. Is provided. As shown by a broken line in FIG. 2, the hydraulic device 61 is configured to have a small swash plate angle Θa and a predetermined minimum discharge volume (minimum displacement volume cc / rev) + Va. The unloading valve 71 and the unloading pilot circuit 75 are necessary as inevitable parts because the hydraulic oil of the hydraulic pump 64 is unloaded during rotation and when the work implement operation valve 66 is not operated.

  A safety valve 70 is used to prevent the hydraulic pressure of the pressure oil acting on the hydraulic pump 64 from rising abnormally. Although not shown in FIG. 3, the load detection circuit 74 is provided with the load pressure relief valve 17 shown in FIG. 1 to protect the load detection circuit 74.

  In this CLSS circuit, since the unload valve 71, the unload pilot circuit 75, the safety valve 70, and the capacity control valve 73 are used, there are many components. The passage flow rate of the unload valve 71 is {fixed volume × engine speed} when the hydraulic pump 64 has a fixed volume, and {minimum volume × engine speed + transient when the hydraulic pump 64 has a variable volume. In order to flow a flow rate of a typical discharge flow rate}, the area is large.

  Such a CLSS circuit has a problem that a work vehicle such as a forklift having a simple structure has a large space and is difficult to mount, and has a large number of parts and high cost.

  The present invention has been made paying attention to the above-mentioned problems, and an object thereof is to provide a pump variable displacement control device with an unload function that is useful for cost reduction with a simple structure.

In order to achieve the above object, in the pump variable displacement control device with an unload function according to the present invention, in the pump variable displacement control device that variably controls the discharge amount of the pump, the pressure oil is driven by the power source. A variable displacement pump that discharges, a load pressure sensitive directional control valve that feeds pressure oil discharged from the variable displacement pump to the actuator, and discharges the oil from the actuator to the tank, and a load pressure that guides the load pressure of the actuator It has a detection circuit, a cylinder that performs control to increase or decrease the discharge volume of the variable displacement pump, and a control valve that supplies pressure oil discharged from the variable displacement pump to the cylinder or discharges it from the cylinder to the tank. The control valve is provided at one end portion for receiving pressure oil discharged from the variable displacement pump, and the other end portion is provided with a load pressure detecting circuit. When the first oil pressure in the first pressure chamber is larger than the resultant force of the second oil pressure in the second pressure chamber and the spring force, The variable displacement pump pressure oil is fed to the cylinder while maintaining the discharge pressure to reduce the discharge volume of the variable displacement pump, and the variable displacement pump pressure oil is discharged to the tank and unloaded. When the first oil pressure in the first pressure chamber is balanced with the resultant force of the second oil pressure in the second pressure chamber and the spring force while having an unload function for loading , the pressure oil of the variable displacement pump is used. A capacity control valve that feeds the cylinder while maintaining the discharge pressure without discharging to the tank , and the cylinder receives pressure oil discharged from the variable capacity pump in each of the bottom chamber and the head chamber, And a cylinder spring in the head chamber Is obtained by Bei, characterized in that it is intended to operate due to a balance between the pressure and the spring force of the cylinder spring pressure oil discharged from the variable displacement pump.

  According to the above configuration, since the capacity control valve that variably controls the discharge volume (push-off volume cc / rev) of the variable displacement hydraulic pump has an unload function, a dedicated unload valve becomes unnecessary. Along with this, the conventional unload valve and unload pilot circuit can be eliminated, the structure is simplified, and the cost can be reduced. In addition, since the variable displacement hydraulic pump has a swash plate angle that makes the discharge volume almost zero, the unload function and discharge capacity control function can be integrated with the capacity control valve with unload function. The control device can be reduced in size.

  In addition, the capacity control valve with an unload function operates according to the differential pressure between the discharge pressure of the hydraulic pump and the load pressure of the hydraulic actuator, so the peak pressure can be released even at a pressure lower than the set pressure of the conventional safety valve. Thus, the frequency of occurrence of peak pressure can be reduced.

  Therefore, the pressure control valve or safety valve can be abolished by the capacity control valve with the unloading function, the structure can be simplified, the cost can be reduced, and the peak pressure can be reduced. Durability can be improved.

Embodiments of a pump variable displacement control device with an unload function according to the present invention will be described below with reference to the drawings.
First, the configuration of a hydraulic apparatus including an unload function-equipped pump variable displacement control apparatus according to an embodiment will be described with reference to FIGS. FIG. 1 is a circuit diagram of a hydraulic system using a pump variable displacement control device with an unload function, and FIG. 2 explains a relationship between a swash plate angle Θ and a discharge volume (a displacement volume cc / rev) of the variable displacement pump. FIG.

  In FIG. 1, in a hydraulic device 1, a drive source 3 such as an engine or an electric motor drives a variable displacement hydraulic pump 5 (hereinafter referred to as a pump 5), and the pump 5 sucks oil from a tank 7 to obtain pressure oil. The pressure oil is fed to a load pressure sensitive directional control valve 11 (hereinafter referred to as a directional control valve 11) through the discharge pipe 9, and the pressure oil to the actuator 13 is supplied and discharged by the operation of the directional control valve 11.

  The directional control valve 11 is a 5-port 3-position closed center type control valve. In the neutral position (a), the pump port 11a is connected to the pump 5, the reduction port 11b, and the expansion port 11c are connected to the actuator 13. The tank port 11d and the load port 11e are connected internally, the tank port 11d is connected to the tank 7, and the load port 11e is connected to the load pressure pipe 15 which is a load circuit.

  At the contracted position (b) of the directional control valve 11, the pump port 11a, the contracting port 11b and the load port 11e are connected. At the extended position (c), the pump port 11a, the expanding port 11c and the load port 11e are connected. The port 11e is connected to supply pressure oil from the pump 5 to the actuator 13 and the load pressure pipe 15.

  The direction control valve 11 generates a differential pressure ΔLS between the discharge pressure Pp of the pump 5 and the pressure PLS at the outlet of the direction control valve 11 (load pressure PLS of the actuator 13) when the actuator 13 is extended or contracted. The pressure oil of the load pressure PLS is supplied to the load pressure pipe 15.

  The load pressure PLS is sent to the capacity control valve 23 to control the swash plate angle of the pump 5 so that the differential pressure ΔLS becomes the predetermined differential pressure ΔLS0. For example, the swash plate angle Θ of the pump 5 increases when the differential pressure ΔLS becomes lower than the predetermined differential pressure ΔLS 0 set by the capacity control valve 23, and the swash plate angle Θ decreases when it increases. The predetermined differential pressure ΔLS0 is set to 2.5 MPa, for example. The load pressure pipe 15 is provided with a load pressure relief valve 17.

  The pump 5 is provided with a pump variable displacement control device 21 with an unload function (hereinafter referred to as a variable displacement control device 21). The variable displacement control device 21 mainly includes a displacement control valve 23 with an unload function ( Hereinafter, it is formed of a capacity control valve 23) and a cylinder 25.

  The cylinder 25 receives the pressure oil of the pump 5 through the discharge pipe 9, the capacity pipe 27, the capacity control valve 23, and the extension pipe 29 in the bottom chamber 25a, and the cylinder spring 37 and the head chamber 25b housed therein. When the oil is extended against the pressure oil, the discharge volume of the pump 5 is reduced. On the other hand, the cylinder 25 receives the pressure oil of the pump 5 by the head chamber 25b through the discharge pipe 9 and the reduction pipe 39, presses the piston 25P by the pressure oil of the head chamber 25b and the cylinder spring 37, and the bottom 25 When the oil in the chamber 25a is discharged from the capacity control valve 23 to the tank 7 and reduced, the discharge volume of the pump 5 is increased.

  For example, in the cylinder 25, the discharge volume (push-off volume) of the pump 5 is variable between 0 cc / rev and 45 cc / rev, and when the cylinder 25 is reduced, the pump 5 has a maximum discharge volume (+ Vb) as shown in FIG. In contrast, when the cylinder 25 is extended, the discharge volume of the pump 5 is made substantially zero. The cylinder 25 may set the discharge volume of the pump 5 to a negative discharge volume (−Vc), that is, a side where the oil from the tank 7 is not sucked and discharged as shown in FIG.

  The capacity control valve 23 is formed at the 3 port 3 position. The pump port 23 a is connected to the pump 5 via the capacity pipe 27 branched from the discharge pipe 9, and the cylinder port 23 b is connected to the cylinder 25 via the extension pipe 29. In addition, a tank port 23 c is connected to the tank 7. The capacity control valve 23 is provided with a first pressure chamber 31 at one end and a second pressure chamber 33 at the other end. The first pressure chamber 31 is connected to the pump 5 via a control pipe 27S branched from the capacity pipe 27. The first oil pressure Fa is generated by the pressure oil and acts on one end.

  The second pressure chamber 33 is connected to the load port 11e of the direction control valve 11 via the load pressure pipe 15, and a second oil pressure Fb is generated by the pressure oil. Further, a spring force B is generated by the valve spring 35, and a resultant force Fk (Fk = Fb + B) obtained by adding the second hydraulic pressure Fb and the spring force B acts on the other end.

  The capacity control valve 23 switches to the position (d) when the first oil pressure Fa in the first pressure chamber 31 is greater than the resultant force Fk of the second oil pressure Fb in the second pressure chamber 32 and the spring force B, and the pump Port 23a, cylinder port 23b, and tank port 23c are connected to supply pressure oil from pump 5 to cylinder 25 from extension pipe 29 and to discharge to tank 7 to maintain the position of cylinder 25. Acts to make the discharge amount of the pump 5 substantially zero.

  Further, the capacity control valve 23 switches to the position (e) when the first oil pressure Fa in the first pressure chamber 31 is balanced with the resultant force Fk of the second oil pressure Fb and the spring force B. The port 23a and the cylinder port 23b are connected and the tank port 23c is shut off. Then, the pressure oil of the pump 5 is supplied from the extension pipe 29 to the bottom chamber 25a of the cylinder 25, and the cylinder 25 is extended against the pressure oil of the head chamber 25b and the cylinder spring 37.

  Further, the capacity control valve 23 switches to the position (f) when the first oil pressure Fa in the first pressure chamber 31 is smaller than the resultant force Fk of the second oil pressure Fb in the second pressure chamber 32 and the spring force B. The cylinder port 23b and the tank port 23c are connected and the pump port 23a is shut off, and the piston 25P is pressed by the pressure oil from the reduction pipe 39 to the head chamber 25b and the cylinder spring 37 to The oil in the bottom chamber 25a is discharged from the expansion pipe 29 to the tank 7, and the cylinder 25 is reduced.

  Next, the operation of the hydraulic device 1 will be described. When the drive source 3 is stopped, the pump 5 is also stopped, so that the displacement control valve 23 is sent to the position (f) by the valve spring 35 and pressure oil is also supplied to the cylinder 25. In other words, the cylinder 25 is kept at the minimum reduction length by the cylinder spring 37. For this reason, the pump 5 is maintained at the maximum discharge volume and stopped.

  Next, when the drive source 3 is started to operate the hydraulic apparatus 1, the pressure oil of the pump 5 is supplied from the discharge pipe 9 to the direction control valve 11. When the directional control valve 11 is not operated, the directional control valve 11 is in the neutral position (a). Since the neutral position (a) is formed by cutting off the circuit by the closed center, the hydraulic pressure of the pressure oil in the pump 5 increases.

  The increased pressure oil is sent to the first pressure chamber 31 of the capacity control valve 23 through the discharge pipe 9, the capacity pipe 27, and the control pipe 27S. The pressure oil in the first pressure chamber 31 switches the displacement control valve 23 from the position (f) to the position (d) against the valve spring 35.

  The position (d) of the capacity control valve 23 is connected to the pump port 23a, the cylinder port 23b, and the tank port 23c, and supplies the pressure oil of the pump 5 to the cylinder 25 from the extension pipe 29. 25 and the excess pressure oil is discharged to the tank 7.

  As a result, the pressure oil discharged from the pump 5 is discharged from the position (d) to the tank 7 and unloaded, and is supplied to the cylinder 25 until the discharge volume of the pump 5 becomes substantially zero. Elongate. The position of the capacity control valve 23 is balanced at position (e). This discharge amount is substantially zero, and the discharge volume is maintained at a substantially zero position. As described above, the capacity control valve 23 has an unloading function for returning the pressure oil discharged from the pump 5 to the tank 7 and a control function for a swash plate angle for making the discharge volume of the pump 5 variable. .

  Next, the actuator 13 is operated. When the directional control valve 11 is operated, for example, to the extended position (c) to operate the actuator 13, the pressure oil of the pump 5 extends from the discharge pipe 9 to the pump port 11a at the extended position (c) of the directional control valve 11. It is fed to the bottom side of the actuator 13 through the port 11c and extends the actuator 13. At the same time, at the extension position (c), the pump port 11a, the load port 11e, and the extension port 11c are connected, and the pressure oil of the pump 5 is supplied from the load pipe 15 to the second pressure chamber 33 of the capacity control valve 23. Is done.

  The second oil pressure Fb due to the pressure oil fed to the second pressure chamber 33 and the resultant force Fk due to the spring force B of the valve spring 35 act on the capacity control valve 23, and the first pressure oil in the first pressure chamber 31 is the first. The capacity control valve 23 is switched from the position (d) to the position (f) against the oil pressure Fa.

  At the position (f) of the capacity control valve 23, the cylinder port 23b and the tank port 23c are connected and the pump port 23a is shut off. As a result, the piston 25P is pressed by the pressure oil in the head chamber 25b supplied from the pipe 39 and the cylinder spring 37, and the cylinder 25 is supplied to the tank 25 through the capacity control valve 23 from the extension pipe 29. 7 is discharged, the length is reduced, the discharge volume of the pump 5 is increased, and the discharge oil amount is increased.

  As the amount of oil discharged from the pump 5 increases, the directional control valve 11 supplies pressure oil to the actuator 13 and pressure oil at the load pressure PLS to the second pressure chamber 33 from the load pressure pipe 15.

  The pressure oil of the load pressure PLS in the second pressure chamber 33 increases the second oil pressure Fb, adds the spring force B of the valve spring 35 to increase the resultant force Fk, and positions the spool of the capacity control valve 23. Push and balance from (f) to position (e). Thereby, the increase in the discharge volume of the pump 5 is stopped, and the discharge amount of the pump 5 corresponding to the predetermined differential pressure ΔLS0 is obtained.

  In this state, when the load acting on the actuator 13, that is, the load pressure PLS of the actuator 13 increases and exceeds the set pressure of the load pressure relief valve 17, for example, 21.0 MPa, the load pressure relief valve 17 is activated and the load The pressure oil at the pressure PLS is discharged to the tank 7.

  Further, when the load pressure PLS acting on the actuator 13 exceeds 21.0 MPa, the discharge pressure Pp of the pump 5 is based on a hydraulic pressure value Pq obtained by adding 2.5 MPa of the predetermined differential pressure ΔLS0 to 21.0 MPa of the load pressure PLS. The hydraulic pressure value Pq acts on the first pressure chamber 31 via the control pipe 27S. This hydraulic pressure value Pq switches the displacement control valve 23 to the position (d), supplies the pressure oil of the pump 5 from the expansion pipe 29 to the cylinder 25, extends the cylinder 25, and reduces the discharge volume of the pump 5. The pressure oil of the pump 5 is discharged to the tank 7 and the discharge pressure Pp of the pump 5 is maintained within a predetermined value (for example, 23.5 MPa).

  In addition, the load pressure PLS acting on the actuator 13 suddenly increases, or the directional control valve 11 is switched from operation to non-operation to return to the neutral position (a), and the discharge pressure of the pump 5 suddenly increases to give a predetermined differential pressure. When a hydraulic pressure equal to or greater than ΔLS0 is generated between the pump 5 and the actuator 13, the capacity control valve 23 is switched to the position (d) in the same manner as described above, and the pressure oil of the pump 5 is capacity-controlled from the capacity pipe 27. It can be discharged to the tank 7 through the valve 23 to prevent the peak pressure from occurring.

  Even if the load pressure PLS acting on the actuator 13 does not exceed 21.0 MPa, this peak pressure may prevent the peak pressure from being generated by operating the capacity control valve 23 if a hydraulic pressure equal to or higher than the predetermined differential pressure ΔLS0 is generated. The frequency with which the peak pressure occurs can be reduced.

  In the above-described embodiment, the pump 5 maximizes the discharge volume when stopped, decreases the discharge volume when starting rotation, and unloads the discharge amount. However, the pump 5 minimizes the discharge volume when stopped and increases the discharge volume during work. You may make it do. Although the pump 5 has been described with a swash plate angle, it may be a swash shaft. Although the load circuit is connected only to the second pressure chamber 33, it may be connected to the tank 7 using a throttle as in the conventional example. Moreover, you may use the safety valve 10 together like a prior art example.

1 is a circuit diagram of a hydraulic device using a pump variable displacement control device with an unload function according to the present invention. It is a figure explaining the relationship between the swash plate angle | corner and displacement volume of a variable displacement pump. It is a hydraulic circuit diagram of the conventional hydraulic device for work vehicles.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hydraulic device, 3 ... Drive source, 5 ... Variable displacement pump, 7 ... Tank, 11 ... Load pressure sensitive directional control valve, 13 ... Actuator, 15 ... Load pressure piping (load circuit), 17 ... Load pressure relief Valve: 21 ... Pump variable displacement control device with unload function, 23 ... Capacity control valve with unload function, 25 ... Cylinder, 31 ... First pressure chamber, 33 ... Second pressure chamber, 35 ... Valve spring, 37 ... Cylinder spring.

Claims (1)

In the pump variable capacity control device that variably controls the pump discharge amount,
A variable displacement pump driven by a power source and discharging pressure oil;
A load pressure sensitive directional control valve that feeds pressure oil discharged from the variable displacement pump to the actuator and discharges the oil from the actuator to the tank;
A load pressure detection circuit for guiding the load pressure of the actuator;
A cylinder that performs control to increase or decrease the discharge volume of the variable displacement pump;
A control valve that supplies pressure oil discharged from the variable displacement pump to the cylinder or discharges it from the cylinder to the tank;
The control valve is provided at one end to receive pressure oil discharged from the variable displacement pump, receives pressure oil from a load pressure detection circuit provided at the other end, and includes a spring. A second pressure chamber is provided, and when the first oil pressure in the first pressure chamber is greater than the resultant force of the second oil pressure in the second pressure chamber and the spring force, the pressure oil of the variable displacement pump is discharged. While supplying pressure to the cylinder while maintaining the pressure, the discharge volume of the variable displacement pump is reduced, and the pressure oil of the variable displacement pump is discharged to the tank and has an unload function for unloading . When the first oil pressure in the pressure chamber is balanced with the resultant force of the second oil pressure in the second pressure chamber and the spring force, the discharge pressure is maintained without discharging the variable displacement pump pressure oil to the tank. A capacity control valve that feeds the cylinder in the
The cylinder receives pressure oil discharged from the variable displacement pump in each of the bottom chamber and the head chamber, and includes a cylinder spring in the head chamber. A pump variable displacement control device with an unload function, which operates by a balance between pressure and spring force of a cylinder spring.

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