Hydraulic drive circuit and hydraulic valve device

Abstract

To prevent situations in which oil supply to a hydraulic cylinder is insufficient and fuel consumption worsens, this invention comprises a hydraulic cylinder 2 operated by oil from a hydraulic pump 1, a direction selector valve 10 provided in oil passages 50A, 50B between the hydraulic pump 1 and the hydraulic cylinder 2, a load check valve 20 that is provided in the oil passage 50B between the direction selector valve 10 and the hydraulic cylinder 2 and that permits only the passage of oil from the direction selector valve 10 to the hydraulic cylinder 2, and a lock valve 30 blocking the flow of oil from the hydraulic cylinder 2, the lock valve 30 being connected to the hydraulic cylinder 2 through a branching oil passage 50C that branches from the oil passage 50B between the hydraulic cylinder 2 and the load check valve 20.

Description

Hydraulic drive circuit and hydraulic valve device

[0001] The present invention relates to a hydraulic drive circuit and a hydraulic valve device that drive a hydraulic cylinder.

[0002] Some hydraulic drive circuits that drive hydraulic cylinders are provided with a directional control valve and a lock valve in the oil passage between the hydraulic pump and the hydraulic cylinder. The lock valve prevents oil from leaking from the hydraulic cylinder when the directional control valve is in the neutral position, thereby preventing the hydraulic cylinder from operating unintentionally (see, for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 7-279905

[0004] The lock valve described above is opened when oil is supplied from the hydraulic pump to the hydraulic cylinder, but this causes a pressure loss, which may lead to a shortage of oil to the hydraulic cylinder or a deterioration in fuel efficiency.

[0005] In view of the above circumstances, an object of the present invention is to provide a hydraulic drive circuit and a hydraulic valve device that can prevent situations in which oil is not sufficiently supplied to a hydraulic cylinder and fuel economy deteriorates.

[0006] In order to achieve the above object, a hydraulic drive circuit according to the present invention comprises a hydraulic cylinder operated by oil from a hydraulic pump, a directional control valve provided in an oil passage between the hydraulic pump and the hydraulic cylinder, a load check valve provided in the oil passage between the directional control valve and the hydraulic cylinder and allowing oil to pass only from the directional control valve to the hydraulic cylinder, and a lock valve that blocks the flow of oil from the hydraulic cylinder, and is characterized in that the lock valve is connected to the hydraulic cylinder through a branch oil passage branching off from the oil passage between the hydraulic cylinder and the load check valve.

[0007] According to the present invention, when the directional control valve is disposed in the neutral position, the load check valve prevents oil leakage through the oil passage, and the lock valve prevents oil leakage through the branch oil passage. Moreover, when oil is supplied to the hydraulic cylinder, no pressure loss occurs at the lock valve, making it possible to prevent situations where oil is insufficiently supplied or fuel consumption deteriorates.

[0008] Fig. 1 shows a hydraulic drive circuit to which a hydraulic valve device according to an embodiment of the present invention is applied, with the spool positioned in a neutral position. Fig. 2 is a cross-sectional view showing the structure of the hydraulic valve device shown in Fig. 1. Fig. 3 is a hydraulic drive circuit diagram showing a state in which the spool has moved to the left from the neutral state in Fig. 1. Fig. 4 is a hydraulic drive circuit diagram showing a state in which the spool has moved to the right from the neutral state in Fig. 1. Fig. 5A is a schematic diagram of the appearance of the hydraulic valve device shown in Fig. 1, as seen from the direction of arrow A in Fig. 2. Fig. 5B is a view as seen from the direction of arrow B in Fig. 5A.

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a hydraulic drive circuit and a hydraulic valve device according to the present invention will be described in detail below with reference to the accompanying drawings.

[0010] FIG. 1 shows a hydraulic drive circuit to which a hydraulic valve device according to an embodiment of the present invention is applied. The hydraulic drive circuit shown here is for driving a hydraulic cylinder 2 with oil discharged from a hydraulic pump 1. The hydraulic pump 1 is a variable displacement pump whose displacement volume changes by changing the tilt angle of the swash plate or inclined axis. The hydraulic cylinder 2 moves an actuating rod 2b relative to a cylinder body 2a when oil is supplied to a pressure chamber. For convenience, the illustrated example shows a hydraulic drive circuit that controls the supply of oil to a bottom chamber 2c provided in the cylinder body 2a.

[0011] A hydraulic valve device 3 is provided between the hydraulic pump 1 and the hydraulic cylinder 2. The hydraulic valve device 3 is interposed between the bottom chamber 2c of the hydraulic cylinder 2 and the hydraulic pump 1, and is provided with a directional control valve 10, a load check valve 20, a lock valve 30, and a suction safety valve (suction valve and safety valve) 40 in a valve body 3A.

[0012] The valve body 3A is shaped like a single block and has a pump port 3a, a cylinder port 3b, and three tank ports 3c, 3d, and 3e. The pump port 3a is connected to the hydraulic pump 1 via a supply oil passage 4. The cylinder port 3b is connected to the bottom chamber 2c of the hydraulic cylinder 2 via a bottom oil passage 5. The three tank ports 3c, 3d, and 3e are connected to the tank T via drain oil passages 6c, 6d, and 6e, respectively. In the following description, when distinguishing between them, they will be referred to as the first tank port 3c, the second tank port 3d, and the third tank port 3e.

[0013] The directional control valve 10 is configured by providing a spool 11, which serves as a first valve element, in a valve body 3A. As shown in FIG. 2, the spool 11 is cylindrical with a plurality of lands and is disposed in a spool hole 12 in the valve body 3A so as to be movable along an axis (first axis) C1. The spool hole 12 is provided with a pump oil supply port 12a, a meter port 12b, a meter-out port 12c, and a drain port 12d, in this order from the end located at the bottom in FIG. 2. When the spool 11 moves along the axis C1, the connection states of the pump oil supply port 12a and the drain port 12d with respect to the meter port 12b and the meter-out port 12c are switched.

[0014] More specifically, when the spool 11 is disposed in the neutral position, both the meter port 12b and the meter-out port 12c are blocked. When the spool 11 moves from the neutral position to the left in Fig. 1, the meter port 12b and the pump oil supply port 12a are connected, while the meter-out port 12c remains blocked, as shown in Fig. 3. When the spool 11 moves from the neutral position to the right in Fig. 1, the meter port 12b remains blocked, while the meter-out port 12c and the drain port 12d are connected (meter-out position), as shown in Fig. 4.

[0015] The pump oil supply port 12a is connected to the pump port 3a via a first oil passage (oil passage) 50A. The meter port 12b is connected to the cylinder port 3b via a second oil passage (oil passage) 50B. The meter-out port 12c is connected to a third oil passage (branch oil passage) 50C branching from the second oil passage 50B. The drain port 12d is connected to the first tank port 3c via a fourth oil passage 50D.

[0016] As is clear from FIG. 2 , the spool 11 has a neutral spring 13 at one end and pressure chambers 14 at both ends. The neutral spring 13 maintains the spool 11 in a neutral position and is housed inside a spring box 15 located on one side of the valve body 3A. The pressure chambers 14 house the ends of the spool 11 and are filled with oil. Although not shown in the figure, each pressure chamber 14 is individually connected to a pilot oil passage for applying pilot pressure output from the control valve. When the pilot pressure output in response to operation of the control valve is applied to one pressure chamber 14 through the pilot oil passage, the spool 11 can be moved along the axis C1 against the spring force of the neutral spring 13. When the pilot pressure applied to the pressure chamber 14 is removed, the spring force of the neutral spring 13 returns the spool 11 to the neutral position.

[0017] As shown in FIG. 1 , the load check valve 20 is configured by providing a second valve body 21 in the valve body 3A at an intermediate portion of the second oil passage 50B, more specifically, between the branch point 50E with the third oil passage 50C and the meter port 12b of the spool 11. In this embodiment, the load check valve 20 includes a check valve function portion 20a and a piston portion 20b. The check valve function portion 20a allows oil to pass from the meter port 12b to the cylinder port 3b while preventing oil from passing from the cylinder port 3b to the meter port 12b. The piston portion 20b operates to provide a pressure compensation function for the check valve function portion 20a based on the pressure on the cylinder port 3b side and the load pressure input from the external LS passage 22. More specifically, the pressure on the cylinder port 3b side is compared with the load pressure input from the external LS passage 22, and when the pressure on the cylinder port 3b side is higher, the check valve function portion 20a is opened more widely. As shown in FIG. 2, the second valve element 21 is cylindrical with a tapered surface at its tip and is housed in the second valve hole 23 of the valve body 3A. The second valve hole 23 is disposed so that the second valve element 21 can move along an axis (second axis) C2. As shown in FIGS. 5A and 5B, the axis C2 of the second valve hole 23 extends in a direction perpendicular to the axis C1 of the spool 11.

[0018] As shown in FIG. 1 , the lock valve 30 is configured by providing a third valve body 31 in the valve body 3A at a position that is the middle of the third oil passage portion 50C. Under normal conditions, the lock valve 30 is configured to block the flow of oil from the branch point 50E with the second oil passage portion 50B to the meter-out port 12c. However, when pilot pressure is applied to the built-in switching valve 32 from an operating valve (not shown), the lock valve 30 is configured to allow oil to flow from the branch point 50E with the second oil passage portion 50B to the meter-out port 12c. That is, when pilot pressure is applied to the switching valve 32, the back pressure applied to the third valve body 31 is discharged to the tank T through the second tank port 3d and the drain oil passage 6d, so that the third valve body 31 is in a communicating state, allowing oil to flow from the cylinder port 3b to the meter-out port 12c. When the pilot pressure to the switching valve 32 is removed, the third valve element 31 returns to its shutoff state, shutting off the flow of oil from the branch point 50E with the second oil passage portion 50B to the meter-out port 12c. As shown in FIG. 2 , the third valve element 31 is cylindrical with a tapered surface at its tip and is housed in the third valve hole 33 of the valve body 3A. The third valve hole 33 is disposed so that the third valve element 31 can move along its axis (third axis) C3. As shown in FIGS. 5A and 5B , the axis C3 of the third valve hole 33 is perpendicular to the axis C1 of the spool 11 and is located on an imaginary plane P that includes the axis C1 of the spool 11 and the axis C2 of the second valve element 21.

[0019] 1, the suction safety valve 40 is configured by providing a fourth valve body 41 in the middle of a fifth oil passage portion (second branch oil passage) 50F provided in the valve body 3A. The fifth oil passage portion 50F is provided in the second oil passage portion 50B between a branch point 50E with the third oil passage portion 50C and the third tank port 3e. The suction safety valve 40 has a safety valve portion 40a that allows oil to pass from the branch point 50E to the third tank port 3e only when the pressure in the cylinder port 3b exceeds a set value, and a suction valve portion 40b that allows oil to pass from the third tank port 3e to the branch point 50E when the cylinder port 3b becomes negative pressure. 2, the fourth valve body 41 is cylindrical with a tapered tip, is housed inside a case 42 so as to be movable along an axis (fourth axis) C4, and is attached to a fourth valve hole 43 in the valve body 3A via the case 42. The fourth valve hole 43 is disposed so that the fourth valve body 41 is movable along the axis relative to the case 42. As shown in FIGS. 5A and 5B, the axis C4 of the fourth valve hole 43 is perpendicular to the axis C1 of the spool 11 and is located on an imaginary plane P that includes the axis C1 of the spool 11 and the axis C2 of the second valve body 21.

[0020] In the hydraulic drive circuit configured as described above, when the spool 11 is positioned in the neutral position, both the meter-in port 12b and the meter-out port 12c are shut off. Therefore, no oil flows to the bottom chamber 2c of the hydraulic cylinder 2, and the hydraulic cylinder 2 is stopped. In this state, the hydraulic drive circuit described above prevents oil from leaking from the bottom chamber 2c of the hydraulic cylinder 2 through the hydraulic valve device 3. Specifically, in the hydraulic valve device 3 described above, three oil passages 50B, 50C, and 50F are connected to the bottom chamber 2c of the hydraulic cylinder 2. The second oil passage 50B is provided with a load check valve 20 having a check valve function portion 20a, the third oil passage 50C is provided with a lock valve 30, and the fifth oil passage 50F is provided with a suction safety valve 40. Therefore, there is no risk of oil leaking from the bottom chamber 2c of the hydraulic cylinder 2, and there is no concern that the operating rod 2b will naturally descend. Incidentally, if the pressure in the bottom chamber 2c exceeds the set value from the above-mentioned state, the safety valve portion 40a of the suction safety valve 40 opens, and the oil in the bottom chamber 2c is discharged to the tank T via the bottom oil passage 5, the cylinder port 3b, the second oil passage portion 50B up to the branch point 50E, the fifth oil passage portion 50F, the safety valve portion 40a of the suction safety valve 40, the third tank port 3e, and the oil drain passage 6e. Therefore, there is no risk of a pressure above the set value being applied to the bottom chamber 2c, and damage to the hydraulic cylinder 2 can be prevented.

[0021] 1, by operating the operating valve, the pump oil supply port 12a of the spool 11 is connected to the meter port 12b, as shown in FIG. 3. Therefore, oil from the hydraulic pump 1 is supplied to the bottom chamber 2c of the hydraulic cylinder 2 through the oil supply passage 4, pump port 3a, first oil passage 50A, pump oil supply port 12a of the spool 11, meter port 12b, second oil passage 50B, load check valve 20, cylinder port 3b, and bottom oil passage 5, and the operating rod 2b of the hydraulic cylinder 2 advances relative to the cylinder body 2a. If negative pressure occurs in the bottom chamber 2c at this time, oil from the tank T is supplied to the bottom chamber 2c through the suction valve portion 40b of the suction safety valve 40, so there is no risk of the operating rod 2b being hindered from advancing.

[0022] 1 by operating the operating valve, the meter-out port 12c and the drain port 12d of the spool 11 are connected, and the lock valve 30 is opened, as shown in Fig. 4. Therefore, oil is discharged from the bottom chamber 2c of the hydraulic cylinder 2 through the bottom oil passage 5, the cylinder port 3b, the second oil passage portion 50B to the branch point 50E, the third oil passage portion 50C, the lock valve 30, the meter-out port 12c of the spool 11, the drain port 12d, the fourth oil passage portion 50D, the first tank port 3c, and the drain oil passage 6c to the tank T, and the operating rod 2b of the hydraulic cylinder 2 is retracted relative to the cylinder body 2a.

[0023] In this way, with the above-described hydraulic drive circuit, oil from the hydraulic pump 1 can be supplied to the bottom chamber 2c of the hydraulic cylinder 2 without passing through the lock valve 30. This allows the hydraulic cylinder 2 to operate with reduced pressure loss, making it possible to prevent oil supply shortages and improve fuel efficiency when driving the hydraulic pump 1.

[0024] Furthermore, the second valve body 21 of the load check valve 20, the third valve body 31 of the lock valve 30, and the fourth valve body 41 of the suction safety valve 40 are arranged in the valve body 3A so that their respective axes C2, C3, and C4 are perpendicular to the axis C1 of the spool 11 and are located on the same plane P that includes the axis C1 of the spool 11. Therefore, the second valve body 21, the third valve body 31, and the fourth valve body 41 can be arranged efficiently in the valve body 3A, and the external dimensions of the valve body 3A can be reduced.

[0025] While the above-described embodiment illustrates the hydraulic valve device 3 controlling the supply of oil to the bottom chamber 2c of the hydraulic cylinder 2, the present invention is not limited thereto and can be similarly applied to a case where oil supply to a rod chamber is controlled. Furthermore, while the hydraulic valve device 3 is illustrated as including the suction safety valve 40, the present invention is not necessarily limited thereto. For example, the fifth oil passage portion 50F may be provided with only a safety valve (equivalent to the safety valve portion 40a) that limits the load pressure of the hydraulic cylinder, or may be provided with only a suction valve (equivalent to the suction valve portion 45b) that supplies oil from a tank to the hydraulic cylinder when the hydraulic cylinder becomes negative pressure.

[0026] REFERENCE SIGNS LIST 1 Hydraulic pump 2 Hydraulic cylinder 2c Bottom chamber 3 Hydraulic valve device 3A Valve body 3a Pump port 3b Cylinder port 3c, 3d, 3e Tank port 10 Directional switching valve 11 Spool 20 Load check valve 20a Check valve function portion 20b Piston portion 21 Second valve body 22 LS passage 30 Lock valve 31 Third valve body 40 Suction safety valve 40a Safety valve portion 40b Suction valve portion 41 Fourth valve body 50A First oil passage portion 50B Second oil passage portion 50C Third oil passage portion 50F Fifth oil passage portion C1 First axis center C2 Second axis center C3 Third axis center C4 Fourth axis center P Imaginary plane T Tank

Claims

1. A hydraulic drive circuit comprising: a hydraulic cylinder operated by oil from a hydraulic pump; a directional control valve provided in an oil passage between said hydraulic pump and said hydraulic cylinder; a load check valve provided in said oil passage between said directional control valve and said hydraulic cylinder, for allowing oil to pass only from said directional control valve to said hydraulic cylinder; and a lock valve for blocking the flow of oil from said hydraulic cylinder, wherein said lock valve is connected to said hydraulic cylinder through a branch oil passage branching off from said oil passage between said hydraulic cylinder and said load check valve.

2. A hydraulic drive circuit as claimed in claim 1, characterized in that the load check valve has a pressure compensation function for controlling the flow rate of oil supplied to the hydraulic cylinder in accordance with the load pressure of the hydraulic cylinder.

3. The hydraulic drive circuit according to claim 1, characterized in that the branch oil passage is provided between the oil passage and the directional control valve, and the lock valve is in a communicating state when the directional control valve is switched to the meter-out position.

4. The hydraulic drive circuit as described in claim 1, characterized in that at least one of a safety valve that limits the load pressure of the hydraulic cylinder and a suction valve that supplies oil from a tank to the hydraulic cylinder when the hydraulic cylinder becomes negative pressure is connected to the hydraulic cylinder through a second branch oil passage that branches off from the oil passage between the hydraulic cylinder and the load check valve.

5. A valve body provided with a pump port connected to a hydraulic pump, a cylinder port connected to a hydraulic cylinder, and a tank port connected to a tank, the valve body being provided with: a directional control valve for switching the connection state between the pump port and the cylinder port by a first valve body moving along a first axis between the pump port and the cylinder port; a load check valve for allowing only the passage of oil from the first valve body to the cylinder port by a second valve body moving along a second axis between the first valve body and the cylinder port; and a lock valve for communicating or blocking the flow of oil from the cylinder port to the tank port by a third valve body moving along a third axis between the cylinder port and the tank port, the second axis and the third axis being disposed so as to be perpendicular to the first axis, and the third axis being disposed on an imaginary plane including the first axis and the second axis; the load check valve having a pressure compensation function for controlling the supply flow rate of oil from the first valve body to the cylinder port in accordance with the pressure of the cylinder port, a lock valve connected to the cylinder port through a branch oil passage which branches off from an oil passage between the cylinder port and the first valve body; 6. The hydraulic valve device according to claim 5, characterized in that the valve body is provided with a suction safety valve which sets an upper limit for the pressure of the cylinder port by moving a fourth valve body along a fourth axis between the cylinder port and the tank port, and allows oil to pass from the tank port to the cylinder port when the cylinder port becomes negative pressure, the fourth axis being perpendicular to the first axis and disposed on the imaginary plane, and the suction safety valve being connected to the cylinder port through a second branch oil passage which branches off from the oil passage between the cylinder port and the first valve body.

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