Flow rate control device and pressure compensation valve

Abstract

A flow rate control device according to the present invention comprises: a flow rate control valve that is interposed between a hydraulic pump and a first hydraulic actuator and controls the rate of flow from the hydraulic pump to the first hydraulic actuator by adjusting the degree of opening; a pressure compensation valve that is interposed between the hydraulic pump and the first hydraulic actuator together with the flow rate control valve and adjusts the differential pressure across the flow rate control valve by controlling the degree of opening between the hydraulic pump and the first hydraulic actuator according to the differential pressure between the upstream pressure and the back pressure; and a load sensing device that applies, as back pressure to the pressure compensation valve, a selected load pressure, which is the higher load pressure from among a first load pressure, which is the load pressure of the first hydraulic actuator, and a second load pressure, which is the load pressure of a second hydraulic actuator. When the first load pressure is higher than the selected load pressure, the pressure compensation valve uses the first load pressure as the back pressure instead of the selected load pressure and closes the path between the hydraulic pump and the first hydraulic actuator.

Description

Flow control device and pressure compensation valve

[0001] The present disclosure relates to a flow control device for controlling the flow rate of hydraulic fluid supplied from a hydraulic pump to each of a plurality of hydraulic actuators, and a pressure compensation valve.

[0002] There is a flow control device for controlling the flow rate of hydraulic fluid supplied from a hydraulic pump to each of a plurality of hydraulic actuators. As the flow control device, a hydraulic drive device such as that disclosed in Patent Document 1 is known. In the hydraulic drive device of Patent Document 1, a flow control valve and a pressure compensation valve are provided in association with each hydraulic actuator. Each pressure compensation valve makes the differential pressure before and after the corresponding flow control valve constant by adjusting its opening degree. Thereby, the flow control valve can supply a flow rate corresponding to its opening degree to the corresponding hydraulic actuator.

[0003] More specifically, in the hydraulic drive device of Patent Document 1, the maximum pressure load pressure of a plurality of hydraulic actuators and the upstream pressure of the corresponding flow control valve act against each other on the spool of the pressure compensation valve. Therefore, the opening of the pressure compensation valve is adjusted to an opening degree corresponding to the differential pressure between the maximum pressure and the upstream pressure, whereby the differential pressure before and after the flow control valve becomes constant.

[0004] Japanese Unexamined Patent Application Publication No. 2021 - 156355

[0005] In the hydraulic drive device of Patent Document 1, when the load pressure of the hydraulic actuator suddenly increases, it is conceivable that the hydraulic fluid flows backward from the hydraulic actuator toward the flow control valve. Therefore, a load check valve is provided between the hydraulic actuator and the flow control valve in the hydraulic drive device. On the other hand, providing a load check valve between the hydraulic actuator and the flow control valve increases the number of parts of the hydraulic drive device. Therefore, it is desired to reduce the number of parts of the hydraulic drive device.

[0006] Therefore, an object of the present disclosure is to provide a flow control device and a pressure compensation valve capable of reducing the number of parts.

[0007] The flow control device of this disclosure controls the flow rate of a working fluid supplied from a hydraulic pump to a first hydraulic actuator and a second hydraulic actuator, and comprises: a flow control valve interposed between the hydraulic pump and the first hydraulic actuator, which controls the flow rate from the hydraulic pump to the first hydraulic actuator by adjusting its opening degree; a pressure compensation valve interposed together with the flow control valve between the hydraulic pump and the first hydraulic actuator, which adjusts the differential pressure across the flow control valve by controlling the opening degree between the hydraulic pump and the first hydraulic actuator according to the differential pressure between the upstream pressure and the back pressure; and a load sensing device which provides the pressure compensation valve with a selectable load pressure, which is the higher of a first load pressure (the load pressure of the first hydraulic actuator) and a second load pressure (the load pressure of the second hydraulic actuator), as back pressure, wherein when the first load pressure becomes higher than the selectable load pressure, the pressure compensation valve replaces the selectable load pressure with the first load pressure as back pressure and closes the gap between the hydraulic pump and the first hydraulic actuator.

[0008] According to this disclosure, when the first load pressure becomes higher than the selected load pressure, the pressure compensation valve replaces the selected load pressure with the first load pressure as the back pressure and closes the gap between the hydraulic pump and the first hydraulic actuator. Therefore, when the first load pressure becomes high and the working fluid attempts to flow back from the first actuator, the pressure compensation valve can close the gap between the hydraulic pump and the first hydraulic actuator to prevent backflow of the working fluid. Thus, the pressure compensation valve has a backflow prevention function and can act as a load check valve. This reduces the number of parts in the flow control device.

[0009] The pressure compensation valve of the present disclosure comprises a housing including a valve passage connecting an inlet and an outlet, a back pressure chamber, and a guide passage connected to the back pressure chamber and introducing a signal pressure into the back pressure chamber, and a main valve body movably provided in the housing to adjust the opening of the valve passage in accordance with the differential pressure between the upstream pressure, which is the pressure at the inlet, and the back pressure, which is the liquid pressure in the back pressure chamber, wherein the main valve body further includes a back pressure passage connecting the outlet and the back pressure chamber, and closes the valve passage when the pressure in the back pressure chamber becomes high.

[0010] According to this disclosure, the main valve body includes a back pressure passage connecting the outlet and the back pressure chamber. Therefore, the higher of the downstream pressure (the fluid pressure at the outlet) and the signal pressure can be directed to the back pressure chamber. As a result, when the downstream pressure becomes higher than the upstream pressure, the valve body closes the valve passage, preventing the working fluid from flowing back from the outlet to the inlet. Thus, a pressure compensating valve with a backflow prevention function can be realized.

[0011] The flow control device of this disclosure can reduce the number of parts.

[0012] Furthermore, the pressure compensation valve of this disclosure makes it possible to realize a pressure compensation valve with a backflow prevention function.

[0013] The above-mentioned objectives, other objectives, features, and advantages of the present invention will become apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

[0014] This is a circuit diagram showing the hydraulic circuit of the flow control device of the present disclosure. This is an enlarged circuit diagram showing the area around the flow control valve and pressure compensation valve (region X in Figure 1) in the hydraulic circuit of the flow control device of Figure 1. This is a cross-sectional view showing the flow control device of Figure 2 in a cutaway view. This is an enlarged cross-sectional view showing region Y in the flow control device of Figure 3. This is an enlarged cross-sectional view showing the pressure compensation valve provided in the flow control device of Figure 4.

[0015] Hereinafter, the flow control device 1 and pressure compensation valves 14, 15 of the embodiments relating to this disclosure will be described with reference to the aforementioned drawings. Note that the concept of direction used in the following description is for convenience of explanation and does not limit the orientation of the components of this disclosure to that direction. Furthermore, the flow control device 1 and pressure compensation valves 14, 15 described below are merely embodiments of this disclosure. Therefore, this disclosure is not limited to these embodiments, and additions, deletions, and modifications are permitted without departing from the spirit of this disclosure.

[0016] <Flow Control Device> The flow control device 1 shown in Figure 1 is installed in construction machinery such as wheel loaders, excavators, and cranes. Construction machinery is equipped with multiple hydraulic actuators. For example, a wheel loader is equipped with hydraulic actuators such as a bucket cylinder 2 and a boom cylinder 3. More specifically, a wheel loader is further equipped with hydraulic actuators such as a bar arm cylinder, a steering cylinder, and a travel motor. The wheel loader can perform various tasks by operating the aforementioned multiple hydraulic actuators. The hydraulic actuators and their related configurations installed in the wheel loader are similar to each other. Therefore, the following will mainly describe the bucket cylinder 2 and the boom cylinder 3 and their related configurations. Descriptions of other hydraulic actuators and their configurations will be omitted below, with reference to the descriptions of cylinders 2 and 3 and their related configurations.

[0017] The wheel loader further includes a hydraulic pump 4 and a flow control device 1. The hydraulic pump 4 is, for example, a variable displacement pump that discharges a working fluid (for example, oil or water). The working fluid discharged from the hydraulic pump 4 is supplied to cylinders 2 and 3, respectively. This allows the wheel loader to operate cylinders 2 and 3, respectively. The flow control device 1 controls the movement of cylinders 2 and 3 by controlling the flow rate of the working fluid supplied from the hydraulic pump 4 to each of cylinders 2 and 3 (more specifically, the flow rate and direction of the working fluid, i.e., the flow of the working fluid). The flow control device 1 will be described in more detail below.

[0018] <Flow Control Device> The flow control device 1 is connected to the hydraulic pump 4 and controls the flow of the working fluid supplied from the hydraulic pump 4 to the cylinders 2 and 3 as described above. The flow control device 1 is, for example, a multi-control valve and comprises a plurality of flow control valves 11 and 12, a load sensing device 13, and a plurality of pressure compensation valves 14 and 15. The flow control device 1 also comprises a pair of relief valves 16 and 17, a lock valve 19, and a selector valve 18. Furthermore, the flow control device 1 comprises a valve block 10 shared by each of the components 11 to 19.

[0019] As described above, the valve block 10 is shared by each of the components 11 to 19 and constitutes a part of each of the components 11 to 19. In addition, the valve block 10 has multiple passages 21 to 31 that connect each of the components 11 to 19. One of the multiple passages 21 to 31, the pump passage 21, is connected to the hydraulic pump 4, and working fluid is supplied to the pump passage 21 from the hydraulic pump 4.

[0020] The flow control valves 11 and 12 are associated with cylinders 2 and 3, respectively, and are interposed between the hydraulic pump 4 and the corresponding cylinders 2 and 3. The flow control valves 11 and 12 control the flow rate of the hydraulic fluid supplied from the hydraulic pump 4 to the corresponding cylinders 2 and 3. For example, the bucket flow control valve 11 is associated with bucket cylinder 2 and controls the flow rate of the hydraulic fluid supplied from the hydraulic pump 4 to bucket cylinder 2. Similarly, the boom flow control valve 12 is associated with boom cylinder 3 and controls the flow rate of the hydraulic fluid supplied from the hydraulic pump 4 to boom cylinder 3. The flow control valves 11 and 12 control the flow rate of the hydraulic fluid supplied to the corresponding cylinders 2 and 3 according to the input command signal.

[0021] More specifically, the flow control valves 11 and 12 control the flow of hydraulic fluid to the corresponding cylinders 2 and 3. For example, cylinders 2 and 3 each include head-side ports 2a and 3a and rod-side ports 2b and 3b, respectively. The flow control valves 11 and 12 supply hydraulic fluid to one of the two ports 2a, 2b, 3a, and 3b of the corresponding cylinders 2 and 3, and discharge hydraulic fluid from the other. The flow control valves 11 and 12 switch the ports 2a, 2b, 3a, and 3b to which the hydraulic fluid is supplied and discharged, that is, they switch the direction in which the hydraulic fluid flows. More specifically, the flow control valves 11 and 12 switch the direction in which the hydraulic fluid flows according to the input command signal. The flow control valves 11 and 12 then control the flow rate of hydraulic fluid supplied to the corresponding cylinders 2 and 3 according to the input command signal, as described above. In this way, the flow control valves 11 and 12 control the flow of hydraulic fluid to the corresponding cylinders 2 and 3. In this embodiment, the flow control valves 11 and 12 are arranged with respect to the pump passage 21 as follows.

[0022] In other words, the flow control valves 11 and 12 are connected in parallel to the pump passage 21. In this embodiment, the flow control valves 11 and 12 are connected to the pump passage 21 via supply passages 22 and 23, respectively. One of the flow control valves 11 and 12, the bucket flow control valve 11, is connected to the head-side port 2a of the bucket cylinder 2 via the head-side passage 24, and also to the rod-side port 2b of the bucket cylinder 2 via the rod-side passage 25. The other of the flow control valves 11 and 12, the boom flow control valve 12, is connected to the head-side port 3a of the boom cylinder 3 via the head-side passage 26, and also to the rod-side port 3b of the boom cylinder 3 via the rod-side passage 27.

[0023] Furthermore, the flow control valves 11 and 12 are connected to connecting passages 28 and 29 as follows: The bucket-side connecting passage 28 is connected to the hydraulic pump 4 and the bucket cylinder 2 via the bucket flow control valve 11. The boom-side connecting passage 29 is connected to the hydraulic pump 4 and the boom cylinder 3 via the boom flow control valve 12. Therefore, the working fluid supplied from the hydraulic pump 4 is guided to the connecting passages 28 and 29 via the flow control valves 11 and 12, and then from the connecting passages 28 and 29 to the cylinders 2 and 3 via the flow control valves 11 and 12. In addition, the flow control valves 11 and 12 are connected to the tank 20 via tank passages 30 and 31, and the working fluid discharged from the cylinders 2 and 3 is discharged to the tank 20 via the tank passages 30 and 31.

[0024] The flow control valves 11 and 12 configured in this way are, for example, solenoid spool valves, each containing spools 11a and 12a and two solenoid valves 11b, 11c, 12b, and 12c, respectively. In the flow control valves 11 and 12, a pilot pressure is output from one of the two solenoid valves 11b, 11c, 12b, and 12c to the spools 11a and 12a in response to an input command signal, causing the spools 11a and 12a to stroke to a position corresponding to the pilot pressure.

[0025] For example, when a head-side command signal, one of the command signals, is input to the flow control valves 11 and 12, solenoid valves 11b and 12b output pilot pressure corresponding to the head-side command signal. This causes spools 11a and 12a to stroke toward the first offset positions A1 and B1. As a result, supply passages 22 and 23 connect to head-side passages 24 and 26 via connection passages 28 and 29, and rod-side passages 25 and 27 connect to tank passages 30 and 31. This supplies working fluid to head-side ports 2a and 3a and discharges working fluid from rod-side ports 2b and 3b. On the other hand, when a rod-side command signal, one of the command signals, is input to the flow control valves 11 and 12, solenoid valves 11c and 12c output pilot pressure corresponding to the rod-side command signal. This causes spools 11a and 12a to stroke toward the second offset positions A2 and B2. As a result, supply passages 22 and 23 are connected to rod-side passages 25 and 27 via connecting passages 28 and 29, and head-side passages 24 and 26 are connected to tank passages 30 and 31. This supplies working fluid to rod-side ports 2b and 3b, and discharges working fluid from head-side ports 2a and 3a. Additionally, spools 11a and 12a are positioned at neutral positions A0 and B0 when no command signals are input to flow control valves 11 and 12, blocking all passages 22 to 31 connected to flow control valves 11 and 12, respectively. This stops the supply and discharge of working fluid to cylinders 2 and 3. Furthermore, spools 11a and 12a stroke to a position corresponding to the magnitude of the pilot pressure, and the opening degree of flow control valves 11 and 12 is changed according to the amount of stroke. This allows flow control valves 11 and 12 to control the flow rate of working fluid supplied to the corresponding cylinders 2 and 3.

[0026] The load sensing device 13 selects the higher of the bucket load pressure and the boom load pressure as the selected load pressure. Here, the bucket load pressure is the load pressure of the bucket cylinder 2, and the boom load pressure is the load pressure of the boom cylinder 3. In practice, the load sensing device 13 selects the highest load pressure, i.e., the maximum pressure, among the load pressures of each hydraulic actuator provided in the wheel loader, including the bucket cylinder 2 and boom cylinder 3, as well as the arm cylinder, steering cylinder, and travel motor, as the selected load pressure. In this embodiment, for the sake of explanation, only the configurations relating to the bucket cylinder 2 and boom cylinder 3 of the load sensing device 13 will be described, and the description of other configurations will be omitted.

[0027] In this embodiment, the load sensing device 13 has a load sensing passage 13a and a plurality of check valves 13b. The load sensing passage 13a is connected in parallel to the bucket cylinder 2 and the boom cylinder 3. More specifically, the load sensing passage 13a is connected to the bucket cylinder 2 and the boom cylinder 3, respectively, via check valves 13b. In this embodiment, the load sensing passage 13a is connected to connecting passages 28 and 29, respectively, via check valves 13b. Each of the check valves 13b allows working fluid to flow from each cylinder 2 and 3 to the load sensing passage 13a, and prevents working fluid from flowing in the reverse direction. Therefore, the load sensing passage 13a is guided to the higher of the bucket load pressure and the boom load pressure. In this way, the load sensing device 13 selects the higher of the bucket load pressure and the boom load pressure as the selected load pressure. Furthermore, pressure compensation valves 14 and 15 are connected in parallel to the load sensing passage 13a, and a selective load pressure is supplied to the pressure compensation valves 14 and 15. More specifically, the load sensing passage 13a is connected to the back pressure chamber 36 of the pressure compensation valves 14 and 15, which will be described in detail later, and the selective load pressure can be supplied to the back pressure chamber 36 as back pressure.

[0028] The pressure compensation valves 14 and 15 are associated with the flow control valves 11 and 12, respectively, and are interposed together with the corresponding flow control valves 11 and 12 between the hydraulic pump 4 and the cylinders 2 and 3, respectively. More specifically, the bucket pressure compensation valve 14 is associated with the bucket flow control valve 11 and is interposed together with the bucket flow control valve 11 between the hydraulic pump 4 and the bucket cylinder 2. On the other hand, the boom pressure compensation valve 15 is associated with the boom flow control valve 12 and is interposed together with the boom flow control valve 12 between the hydraulic pump 4 and the boom cylinder 3. In this embodiment, the bucket pressure compensation valve 14 is interposed in the connecting passage 28, and the boom pressure compensation valve 15 is interposed in the connecting passage 29.

[0029] Furthermore, the pressure compensation valves 14 and 15 control the opening degree between the hydraulic pump 4 and cylinders 2 and 3 (in this embodiment, the opening degree of the connecting passages 28 and 29) according to the differential pressure between the upstream pressure and back pressure acting in opposition to each other. As a result, the pressure compensation valves 14 and 15 adjust the differential pressure across the corresponding flow control valves 11 and 12 (in other words, the differential pressure between the upstream and downstream pressures of the flow control valves 11 and 12). The back pressure is derived from the load sensing device 13 as the selected load pressure. Also, in the pressure compensation valves 14 and 15, when the load pressure of the corresponding cylinders 2 and 3 (hereinafter referred to as "corresponding load pressure") becomes higher than the selected load pressure, the corresponding load pressure becomes the back pressure instead of the selected load pressure, and the pressure compensation valves 14 and 15 close the connecting passages 28 and 29.

[0030] More specifically, the pressure compensation valves 14 and 15 include a main valve body 35, a back pressure chamber 36, a back pressure passage 37, and a guide passage 38 (see also Figure 2). Furthermore, the pressure compensation valves 14 and 15 include a check valve body 42. The main valve body 35 acts so that the upstream pressure and back pressure resist each other. The main valve body 35 adjusts the opening of the connecting passages 28 and 29 according to the pressure difference between the upstream pressure and the back pressure. The upstream pressure is the hydraulic pressure of the working fluid flowing upstream of the pressure compensation valves 14 and 15, and in this embodiment, it is the hydraulic pressure of the working fluid flowing in the portion of the connecting passages 28 and 29 upstream of the pressure compensation valves 14 and 15 (the upstream portion 28d, which will be described in detail later). The back pressure is the hydraulic pressure of the back pressure chamber 36, which will be described in detail later.

[0031] The back pressure chamber 36 is a chamber that applies back pressure to the main valve body 35. The back pressure passage 37 is a passage that connects the back pressure chamber 36 to the cylinders 2 and 3, and guides the corresponding load pressure to the back pressure chamber 36. More specifically, the back pressure passage 37 is connected to the downstream side (downstream portions 28a and 28b, which will be described in detail later) of the pressure compensation valves 14 and 15 in the corresponding connecting passages 28 and 29, and guides the downstream pressure of the pressure compensation valves 14 and 15 corresponding to the corresponding load pressure to the back pressure chamber 36.

[0032] The guide passage 38 is connected to the back pressure chamber 36 and the load sensing device 13. More specifically, the guide passages 38 of each pressure compensation valve 14, 15 are connected to the load sensing passage 13a in parallel with each other, and guide the selected load pressure selected by the load sensing device 13 to the back pressure chamber 36. In addition, each of the guide passages 38 is connected to the back pressure chamber 36 via a throttle 35a, and the selected load pressure is guided to the back pressure chamber 36 via the throttle 35a. More specifically, the guide passage 38 is connected to the back pressure passage 37 via the throttle 35a, and further connected to the back pressure chamber 36 via the back pressure passage 37. Note that the guide passage 38 may be directly connected to the back pressure chamber 36 without going through the back pressure passage 37. Alternatively, the guide passage 38 may be directly connected to the back pressure chamber 36, and the back pressure passage 37 may be connected to the back pressure chamber 36 via the guide passage 38.

[0033] Furthermore, the pressure compensation valves 14 and 15 include a check valve body 42. The check valve body 42 selects the higher of the corresponding load pressure and the selected load pressure and makes it the back pressure. As a result, when the corresponding load pressure is higher than the selected load pressure, the corresponding load pressure becomes the back pressure instead of the selected load pressure. More specifically, the check valve body 42 is interposed in the back pressure passage 37. More specifically, the check valve body 42 is interposed in the back pressure passage 37 on the cylinder 2 and 3 side, i.e., on the connection passage 28 and 29 side, from the connection point with the guide passage 38. The check valve body 42 closes the back pressure passage 37 when the selected load pressure is higher than the corresponding load pressure. On the other hand, when the corresponding load pressure is higher than the selected load pressure, the check valve body 42 opens the back pressure passage 37, allowing the corresponding load pressure to be guided into the back pressure chamber 36.

[0034] A pair of relief valves 16 and 17 are provided in correspondence with the bucket cylinder 2, and when the hydraulic pressure of the working fluid supplied to and discharged from the bucket cylinder 2 exceeds a set pressure, they discharge the working fluid into the tank 20. More specifically, the pair of relief valves 16 and 17 are connected, for example, to the head-side passage 24 and the rod-side passage 25, respectively. When the hydraulic pressure of the working fluid flowing through the connected passages 24 and 25 exceeds a set pressure, the pair of relief valves 16 and 17 connect the connected passages 24 and 25 to the tank 20 and discharge the working fluid into the tank 20.

[0035] The selector valve 18 outputs a command pressure to the lock valve 19 in accordance with the command signal. More specifically, when a rod-side command signal is output to the bucket flow control valve 11, the selector valve 18 outputs the tank pressure as the command pressure to the lock valve 19. On the other hand, when no rod-side command signal is output, the selector valve 18 outputs a command pressure corresponding to the head pressure of the bucket cylinder 2 (i.e., the hydraulic pressure at the head-side port 2a).

[0036] The lock valve 19 can stop the supply and discharge of working fluid to and from the head-side port 2a of the bucket cylinder 2. More specifically, the lock valve 19 is interposed in the head-side passage 24 and opens and closes the head-side passage 24 in response to a command pressure from the selector valve 18. In this embodiment, when a rod-side command signal is output to the flow control valve 11, the tank pressure is input to the lock valve 19 as a command pressure from the selector valve 18. This allows working fluid to flow from the head-side port 2a to the flow control valve 11. On the other hand, when no rod-side command signal is output to the flow control valve 11, the lock valve 19 receives a pressure corresponding to the head pressure as a command pressure from the selector valve 18. This prevents working fluid from flowing from the head-side port 2a to the flow control valve 11, thereby preventing the bucket cylinder 2 from retracting. Furthermore, in the lock valve 19, regardless of whether or not a command signal is output from the rod side, it is permitted for the working fluid to flow from the flow control valve 11 to the head side port 2a, allowing the bucket cylinder 2 to be extended.

[0037] <Specific Configuration of the Flow Control Device> The components of the flow control device 1 are arranged in the valve block 10 as follows, as shown in Figure 3, for example. That is, in the valve block 10, for example, the flow control valves 11 and 12 are arranged in different vertical cross-sections, and the components related to the flow control valves 11 and 12 are arranged in the same vertical cross-section, for example. Here, the vertical cross-section is a cross-section cut by a virtual plane perpendicular to the first direction (the direction perpendicular to the plane of the paper in Figure 3), as shown in Figure 3. However, the components related to the flow control valves 11 and 12 do not necessarily have to be formed in the same vertical cross-section. Also, the arrangement of the components related to the flow control valves 11 and 12 in the vertical cross-section is similar. Therefore, in the following, the arrangement of the components related to the bucket flow control valve 11 will be mainly described, and the arrangement of the components related to the boom flow control valve 12 will be omitted, referring to the arrangement of the components related to the bucket flow control valve 11.

[0038] A flow control valve 11 is positioned in the valve block 10 in the intermediate portion in the second direction, so as to penetrate in the third direction. Here, the second direction is perpendicular to the first direction, and in Figure 3, it is the up and down direction. The third direction is perpendicular to both the first and second directions, and in Figure 3, it is the left and right direction. More specifically, the valve block 10 has a spool hole 10a formed in the intermediate portion in the second direction, which penetrates in the third direction. A spool 11a is slidably inserted through the spool hole 10a. Furthermore, a spring mechanism 11d for the flow control valve 11 is provided on one side of the valve block 10 in the third direction so as to close the opening of the spool hole 10a, and a cover member 11e is provided on the other side of the valve block 10 in the third direction so as to close the opening of the spool hole 10a. The spring mechanism 11d is a spring mechanism for returning to the neutral position, and when the spool 11a strokes from the neutral position A0 to the respective offset positions A1 and A2, it biases the spool 11a to return to the neutral position A0. In addition, pilot chambers 11f and 11g are formed in the spring mechanism 11d and the cover member 11e, respectively. Solenoid valves 11b and 11c are provided on one side and the other side of the valve block 10 in the third direction, respectively. Each solenoid valve 11b and 11c is connected to the respective pilot chambers 11f and 11g, respectively, and pilot pressure output from each solenoid valve 11b and 11c is directed to each pilot chamber 11f and 11g. When pilot pressure is directed, the spool 11a strokes from the neutral position A0 to either the first offset position A1 or the second offset position A2.

[0039] Furthermore, a pump passage 21 is formed in the valve block 10 in the third intermediate direction, on one side of the flow control valve 11 in the second direction (i.e., one side of the spool hole 10a in the second direction). The pump passage 21 extends in the first direction and is connected to the flow control valve 11 via a supply passage 22 that extends in the second direction. In this embodiment, the pump passage 21 is connected to the spool hole 10a via the supply passage 22, i.e., to the spool 11a. In addition, a connecting passage 28 is formed in the valve block 10 on the other side of the flow control valve 11 in the second direction (i.e., one side of the spool hole 10a in the second direction). One end of the connecting passage 28 is connected to the flow control valve 11 (more specifically, the spool hole 10a) adjacent to the supply passage 22, and the opening between the supply passage 22 and the connecting passage 28 is controlled according to the stroke amount of the spool 11a.

[0040] Furthermore, the connecting passage 28 is formed in an inverted W shape, and both ends of its extension are connected to the flow control valve 11. More specifically, the connecting passage 28 extends from the flow control valve 11 in the other of the second direction, and branches into two downstream sections 28a and 28b at the end of the extension in the second direction. The downstream sections 28a and 28b branch from the branching section 28c to one and the other of the third direction. Furthermore, the downstream sections 28a and 28b are each folded back in one of the second directions toward the flow control valve 11, and the connecting passage 28 is once again connected to the flow control valve 11. The ends of the folded downstream sections 28a and 28b are connected to the flow control valve 11 on one and the other of the third direction of the supply passage 22, respectively, so as to straddle the supply passage 22.

[0041] Furthermore, the flow control valve 11 is connected to the head-side passage 24 and the tank passage 30 on one side of the connection passage 28 in the third direction, and to the rod-side passage 25 and the tank passage 31 on the other side of the connection passage 28 in the third direction. Both the head-side passage 24 and the rod-side passage 25 extend from the flow control valve 11 in the other side of the second direction, while the tank passages 30 and 31 extend in the first direction. The head-side passage 24 and the rod-side passage 25 are both arranged adjacent to the connection passage 28, and the opening between the head-side passage 24 and the connection passage 28, and the opening between the rod-side passage 25 and the connection passage 28 are controlled according to the stroke amount of the spool 11a. The head-side passage 24 and the tank passage 30 are also arranged adjacent to each other, and the opening between the head-side passage 24 and the tank passage 30 is controlled according to the stroke amount of the spool 11a. Furthermore, the rod-side passage 25 and the tank passage 31 are also arranged adjacent to each other, and the opening between the rod-side passage 25 and the tank passage 31 is controlled according to the stroke amount of the spool 11a. In this way, the flow control valve 11 is connected to each of the passages 22 to 31, and controls the flow of the working fluid by changing the opening between adjacent passages 22 to 31 by stroking the spool 11a.

[0042] The lock valve 19 is provided on the valve block 10 so as to be interposed in the head-side passage 24. More specifically, the lock valve 19 is inserted from the side of the valve block 10 on the other side in the second direction toward the head-side passage 24, with the tip portion of the lock valve 19 protruding into the head-side passage 24. In this way, the lock valve 19 is interposed in the head-side passage 24 and opens and closes the head-side passage 24. The relief valves 16 and 17 are provided on one side and the other side of the valve block 10 in the third direction. The tip portions of the relief valves 16 and 17 are inserted through the valve block 10. One of the relief valves 16 is connected to the head-side passage 24 and the tank passage 30, and the other relief valve 17 is connected to the rod-side passage 25 and the tank passage 31. As described above, one of the relief valves 16 opens when the hydraulic pressure in the head-side passage 24 exceeds the set pressure, and discharges the working fluid from the head-side passage 24 to the tank 20. Furthermore, as described above, the other relief valve 17 opens when the hydraulic pressure in the rod-side passage 25 exceeds the set pressure, and discharges the working fluid in the rod-side passage 25 into the tank 20.

[0043] Furthermore, a load sensing passage 13a is formed in the valve block 10. More specifically, the load sensing passage 13a extends in a first direction in cross-section and is connected to a connecting passage 28 (more specifically, one downstream portion 28a) via a check valve 13b. In this embodiment, the check valve 13b is inserted from the other side of the valve block 10 in the second direction to the one downstream portion 28a, and the check valve 13b is connected to one downstream portion 28a. The load sensing passage 13a is connected to one downstream portion 28a via the check valve 13b, and the check valve 13b allows working fluid to flow from the connecting passage 28 to the load sensing passage 13a and prevents working fluid from flowing in the reverse direction. In other words, the check valve 13b allows working fluid to flow from the bucket cylinder 2 to the load sensing passage 13a and prevents working fluid from flowing in the reverse direction.

[0044] The pressure compensation valve 14 is arranged in the valve block 10 as follows as shown in FIGS. 4 and 5. That is, the pressure compensation valve 14 is arranged in the valve block 10 so as to be interposed in the connection passage 28. More specifically, the pressure compensation valve 14 is inserted with the main valve body 35 from the side surface on the other side in the second direction of the valve block 10 toward the branch portion 28c of the connection passage 28 (that is, in one direction of the second direction), and the tip side portion of the main valve body 35 protrudes into the branch portion 28c. In this way, the pressure compensation valve 14 is interposed in the branch portion 28c and adjusts the opening degree of the branch portion 28c. In the present embodiment, the branch portion 28c, which is an example of the valve passage, is connected to the upstream portion 28d via the inlet 28e, for example, and is connected to the downstream portions 28a and 28b via the outlet 28f. Further, the branch portion 28c connects the inlet 28e and the outlet 28f. And the pressure compensation valve 14 adjusts the opening degree of the branch portion 28c. The pressure compensation valve 14 arranged in this way is configured as follows, for example.

[0045] That is, the pressure compensation valve 14 includes, for example, the main valve body 35 described above, a back pressure chamber 36, a back pressure passage 37, and a guide passage 38. Further, the pressure compensation valve 14 further includes a biasing member 43 and the valve block 10. In the valve block 10, which is an example of the housing, an insertion hole 10b extending from the side surface on the other side in the second direction toward the connection passage 28 is formed. More specifically, the insertion hole 10b extends in one direction of the second direction from the side surface on the other side in the second direction toward the branch portion 28c. The opening of the insertion hole 10b is blocked by a plug 41, and the main valve body 35 is slidably inserted into the insertion hole 10b.

[0046] The main valve body 35 is, for example, cylindrical and is slidably inserted into the insertion hole 10b in the second direction. The tip portion of the main valve body 35 protrudes from the insertion hole 10b into the connecting passage 28. More specifically, the branch portion 28c extends in the second direction. The tip portion of the main valve body 35 protrudes into the branch portion 28c and is slidably fitted into the branch portion 28c. This closes the branch portion 28c, i.e., closes the connecting passage 28. The main valve body 35 also has a recess 35b in its tip portion, and a plurality of communication openings 35d are formed on the side surface of the tip portion corresponding to the recess 35b. The communication openings 35d reach the outlet 28f when the main valve body 35 moves in the other direction of the second direction. This opens the branch portion 28c, i.e., opens the connecting passage 28. The recess 35b is connected to the upstream portion 28d via the inlet 28e, and when the branch portion 28c is opened, the upstream portion 28d of the connecting passage 28 is connected to the downstream portions 28a and 28b. As a result, the working fluid flows through the connecting passage 28. The main valve body 35 also receives the fluid pressure of the working fluid flowing through the upstream portion 28d, which is the fluid pressure at the inlet 28e, in the second direction to the other (i.e., the direction in which the branch portion 28c is opened, i.e., the opening direction) at its tip end.

[0047] The back pressure chamber 36 is formed on the proximal end side (i.e., the other side in the second direction) of the main valve body 35 in the insertion hole 10b. More specifically, the proximal end side portion of the main valve body 35 is separated from the plug 41, and the back pressure chamber 36 is formed between the proximal end side portion and the plug 41. The back pressure passage 37 is formed in the main valve body 35 and connects the outlet 28f and the back pressure chamber 36. More specifically, the back pressure passage 37 includes an internal passage 35c and a spring receiving recess 35f. The internal passage 35c is formed in the main valve body 35 and has a plurality of inlets 35e and an outlet 35g. The plurality of inlets 35e are formed on the side surface of the main valve body 35 so as to connect to the outlet 28f (i.e., the downstream portions 28a, 28b). In the present embodiment, the internal passage 35c has four inlets 35e. The four inlets 35e are formed at equal intervals in the circumferential direction at positions corresponding to the outlet 28f on the side surface of the main valve body 35. The outlet 35g is connected to the spring receiving recess 35f described in detail below. The spring receiving recess 35f is formed in the main valve body 35 so as to recess the proximal end side portion of the main valve body 35 in the axial direction (in the present embodiment, the second direction). Further, the spring receiving recess 35f is connected to the back pressure chamber 36, and the outlet 35g is connected to the back pressure chamber 36 via the spring receiving recess 35f. That is, the internal passage 35c is connected to the back pressure chamber 36 via the spring receiving recess 35f. Thus, the back pressure passage 37 connects the downstream portions 28a, 28b and the back pressure chamber 36, and can guide the working fluid flowing through the downstream portions 28a, 28b, i.e., the bucket load pressure, to the back pressure chamber 36.

[0048] Also, a valve seat 37a is formed in the back pressure passage 37. More specifically, the valve seat 37a is formed in the internal passage 35c. In the present embodiment, the internal passage 35c has a first passage portion 35h and a plurality of second passage portions 35i. The first passage portion 35h extends along the axis of the main valve body 35 (i.e., in the second direction) and is connected to the spring receiving recess 35f via the outlet 35g. The second passage portions 35i extend radially from the first passage portion 35h and are connected to the outlet 28f (i.e., the downstream portions 28a, 28b) via the inlets 35e on the side surface of the main valve body 35. The valve seat 37a is formed in the middle portion in the second direction in the first passage portion 35h.

[0049] More specifically, the main valve body 35 has a through hole 35j extending along its axis from a spring receiving recess 35f, and a plug 40 is screwed into the through hole 35j. The plug 40 has an inner passage portion 40a. The inner passage portion 40a connects to the through hole 35j and opens to the spring receiving recess 35f via an outlet 35g. Together with the through hole 35j, the inner passage portion 40a constitutes a first passage portion 35h.

[0050] Furthermore, a throttle 35a is formed in the main valve body 35. More specifically, the throttle 35a penetrates radially through the base end portion of the main valve body 35 and is connected to a back pressure passage 37 (more specifically, a spring receiving recess 35f). In addition, a guide passage 38 is formed in the valve block 10 at a position corresponding to the throttle 35a. A selective load pressure, which is an example of a signal pressure, is guided to the guide passage 38, and the selective load pressure is guided from the guide passage 38 to the back pressure chamber 36 via the throttle 35a and the back pressure passage 37.

[0051] The check valve body 42 is located within the main valve body 35. The check valve body 42 is, for example, a ball and, as described above, is interposed in the back pressure passage 37. More specifically, the check valve body 42 is interposed in the first passage portion 35h of the internal passage 35c and can seat away from the valve seat 37a. The check valve body 42 receives the corresponding load pressure (here, the bucket load pressure) and the back pressure guided from the downstream portions 28a and 28b in opposition to each other. The check valve body 42 opens the back pressure passage 37 by seating away from the valve seat 37a when the bucket load pressure is higher than the back pressure, and closes the back pressure passage 37 by seating on the valve seat 37a when the bucket load pressure is lower than the back pressure. For example, if the selective load pressure is higher than the bucket load pressure, the selective load pressure is guided into the back pressure chamber 36, causing the back pressure to become higher than the bucket load pressure. Consequently, the back pressure passage 37 is closed by the check valve body 42. On the other hand, when the bucket load pressure becomes higher than the selective load pressure, the check valve body 42 moves away from the valve seat 37a and the back pressure passage 37 opens. As a result, the bucket load pressure is guided to the back pressure chamber 36 via the back pressure passage 37, and the bucket load pressure becomes the back pressure instead of the selective load pressure. The main valve body 35 receives this back pressure at its base end portion in a direction that opposes the upstream pressure (i.e., in the second direction). In other words, the main valve body 35 receives back pressure in a direction that closes the branch portion 28c (i.e., in the closing direction).

[0052] The biasing member 43 biases the main valve body 35 in the closing direction against the upstream pressure. More specifically, the biasing member 43 is, for example, a compression coil spring and is interposed between the main valve body 35 and the plug 41. In this embodiment, the biasing member 43 is interposed between the main valve body 35 and the plug 41 with a portion of it inserted into the spring receiving recess 35f. As described above, the biasing member 43 biases the main valve body 35 in the closing direction against the upstream pressure.

[0053] <Operation of the Flow Control Device> The flow control device 1 configured as described above operates as follows. In the flow control device 1 shown in Figure 1, when the operating device (not shown) is operated, a command signal corresponding to the operation (direction of operation and amount of operation) is output from the control device (not shown) to the flow control device 1. Then, pilot pressure corresponding to the command signal is output from the solenoid valves 11b, 11c, 12b, and 12c of the flow control valves 11 and 12, causing the spools 11a and 12a to stroke. This allows each cylinder 2 and 3 to be extended and retracted. In the following, in order to explain in more detail, we will take the case in which the operating device is operated to retract the bucket cylinder 2 and extend the boom cylinder 3 shown in Figure 1 as an example. For other cases (for example, when both cylinders 2 and 3 are extended), a detailed explanation will be omitted, referring to the case in which the bucket cylinder 2 is retracted and the boom cylinder 3 is extended.

[0054] When the operating device is operated, the control device outputs command signals to the flow control valves 11 and 12, respectively. As a result, pilot pressure is output from the solenoid valves 11c and 12b in the flow control valves 11 and 12, causing the spools 11a and 12a to stroke to offset positions A2 and B1. This connects the supply passage 22 to the rod-side passage 25 via the connecting passage 28, and the supply passage 23 to the head-side passage 26 via the connecting passage 29. In addition, the output of pilot pressure from the solenoid valve 11c opens the lock valve 19. As a result, the working fluid discharged from the hydraulic pump 4 into the pump passage 21 is supplied to the rod-side port 2b and the head-side port 3a as follows: The working fluid from the hydraulic pump 4 is supplied to the rod-side port 2b of the bucket cylinder 2 through the bucket flow control valve 11 and the pressure compensation valve 14, respectively. Furthermore, the bucket flow control valve 11 connects the head-side passage 24 to the tank passage 30, and the working fluid is discharged from the head-side port 2a to the tank 20 via the lock valve 19 and the bucket flow control valve 11. On the other hand, the working fluid from the hydraulic pump 4 is supplied to the head-side port 3a of the boom cylinder 3 through the boom flow control valve 12 and the pressure compensation valve 15, respectively. The boom flow control valve 12 also connects the rod-side passage 27 to the tank passage 31, and the working fluid is discharged from the rod-side port 3b to the tank 20 via the boom flow control valve 12. In this way, the bucket cylinder 2 retracts and the boom cylinder 3 extends as the working fluid is supplied to and discharged from cylinders 2 and 3.

[0055] Furthermore, the hydraulic pressure in the downstream portions 28a and 28b of the connection passages 28 and 29, i.e., the corresponding load pressure, is directed to the load sensing device 13. The higher of the two corresponding load pressures is then selected by the two check valves 13b and directed to the load sensing passage 13a. The selected load pressure directed to the load sensing passage 13a is then applied to the back pressure chambers 36 of the pressure compensation valves 14 and 15 via the throttle 35a, becoming the back pressure. The main valve bodies 35 of the pressure compensation valves 14 and 15 are stroked by the biasing member 43 to a position corresponding to the differential pressure between the upstream pressure and the back pressure. This opens the branch portion 28c, which is then adjusted to an opening degree corresponding to the stroke amount of the main valve body 35. As a result, the differential pressure across the flow control valves 11 and 12 is adjusted to a constant pressure. Consequently, the flow rate of the working fluid supplied to each cylinder 2 and 3 is controlled to a flow rate corresponding to the opening degree of the flow control valves 11 and 12. In other words, each cylinder 2 and 3 is supplied with a flow rate of working fluid corresponding to the command signal (i.e., the amount of operation to the operating device) input to the flow control valves 11 and 12, regardless of their load pressure. Therefore, each cylinder 2 and 3 can be operated with an amount of operation corresponding to the amount of operation to the operating device, regardless of the load pressure of each cylinder 2 and 3.

[0056] Furthermore, during excavation, the bucket cylinder 2 may be subjected to a large load, causing the bucket load pressure to rise suddenly. In such cases, the working fluid will attempt to flow back from ports 2a and 2b of the bucket cylinder 2 towards the pressure compensation valve 14. At this time, the pressure compensation valve 14 operates as follows. Note that the pressure compensation valve 15 also operates in the same way as the pressure compensation valve 14 when the load pressure of the boom cylinder 3 (i.e., the boom load pressure) rises suddenly. Therefore, for an explanation of the operation of the pressure compensation valve 15, please refer to the explanation of the operation of the pressure compensation valve 14, and a detailed explanation will be omitted.

[0057] As mentioned above, when the working fluid attempts to flow backward, the bucket load pressure becomes higher than the back pressure in the pressure compensation valve 14. More specifically, the selected load pressure is basically guided to the back pressure chamber 36, and the pressure compensation valve 14 controls the opening of the branch section 28c according to the selected load pressure. On the other hand, the selected load pressure is guided to the back pressure chamber 36 through the load sensing device 13 as the corresponding load pressure. More specifically, the selected load pressure is guided to the back pressure chamber 36 through the load sensing device 13 as the corresponding load pressure is guided to the back pressure chamber 36 via the load sensing device 13 and the throttle 35a. Therefore, there is a time lag between when the corresponding load pressure is guided to the load sensing device 13 and when it is guided to the back pressure chamber 36 through the load sensing device 13. In other words, even if the bucket load pressure rises suddenly, it takes time for the back pressure to rise to an equivalent pressure. Therefore, immediately after the bucket load pressure rises, the bucket load pressure is higher than the back pressure. Consequently, the check valve body 42 separates from the valve seat 37a, the back pressure passage 37 opens, and the bucket load pressure is guided to the back pressure chamber 36 via the back pressure passage 37 (see also Figure 5). Therefore, the back pressure can be quickly increased to the bucket load pressure. In the case of backflow of the working fluid, the bucket load pressure is considerably greater than the upstream pressure, and the main valve body 35, receiving the bucket load pressure as back pressure, strokes in the closing direction and closes the branch portion 28c. As a result, the pressure compensation valve 14 can prevent backflow of the working fluid. Furthermore, by preventing backflow, if the bucket load pressure becomes high, working fluid is discharged from the relief valves 16 and 17, preventing the working fluid pressure from becoming excessively high.

[0058] In the flow control device 1 of this embodiment, when the corresponding load pressure becomes higher than the selected load pressure, the pressure compensation valves 14 and 15 replace the selected load pressure with the corresponding load pressure as the back pressure and close the branch portion 28c. That is, when the corresponding load pressure becomes high and the working fluid attempts to flow back from the cylinders 2 and 3, the pressure compensation valves 14 and 15 can close the branch portion 28c to prevent backflow of the working fluid. Therefore, the pressure compensation valves 14 and 15 have a backflow prevention function and can act as load check valves. This reduces the number of parts in the flow control device 1.

[0059] Furthermore, in the flow control device 1 of this embodiment, the guide passage 38 is connected to the back pressure chamber 36 via a throttle 35a by the load sensing device 13. Therefore, when the opening degree of the branch section 28c is adjusted according to the selected load pressure, hunting due to fluctuations in the selected load pressure can be suppressed in the pressure compensation valves 14 and 15. On the other hand, since the back pressure passage 37 is connected to the back pressure chamber 36 without going through the throttle 35a, the corresponding load pressure can be applied to the main valve body 35 without going through the throttle 35a. Therefore, the branch section 28c can be quickly closed when the first load pressure rises suddenly. In other words, the responsiveness when the first load pressure rises suddenly and the branch section 28c is closed can be improved.

[0060] Furthermore, in the flow control device 1 of this embodiment, the back pressure passage 37 is formed in the main valve body 35, and the check valve body 42 is interposed in the back pressure passage 37. Therefore, the check valve body 42 is provided inside the main valve body 35. Since the check valve body 42 simply guides the corresponding load pressure to the back pressure chamber 36 in place of the selected load pressure, it can be made compact. By incorporating the check valve body 42 configured in this way into the pressure compensation valves 14 and 15, the flow control device 1 can be made more compact compared to when the check valve body 42 is configured separately from the pressure compensation valves 14 and 15. In addition, by configuring the check valve body 42 inside the main valve body 35, the back pressure passage 37 can be made shorter, thereby improving responsiveness.

[0061] Furthermore, in the flow control device 1 of this embodiment, the main valve body 35 has a back pressure passage 37 connected to the cylinders 2 and 3, respectively, and a throttle 35a connecting the guide passage 38 and the back pressure passage 37. The main valve body 35 is also movably provided in the valve block 10 to adjust the opening degree of the branch portion 28c. Therefore, the pressure compensation valves 14 and 15 can be configured to have a backflow prevention function, and a flow control device 1 equipped with pressure compensation valves 14 and 15 with a backflow prevention function can be realized.

[0062] Furthermore, in the flow control device 1 of this embodiment, the pressure compensation valves 14 and 15 are interposed in the connecting passages 28 and 29. This allows the pressure compensation valves 14 and 15 with load check function to be placed between the hydraulic pump 4 and the corresponding cylinders 2 and 3 without having to be placed upstream of the flow control valves 11 and 12. As a result, even if the load pressure increases, it is possible to suppress the increase in the downstream pressure of the flow control valves 11 and 12, thereby preventing the working fluid from ceasing to flow to each cylinder 2 and 3.

[0063] In the pressure compensation valves 14 and 15 of this embodiment, the main valve body 35 includes a back pressure passage 37 connecting the outlet 28f and the back pressure chamber 36. Therefore, the higher of the selected load pressure and the downstream pressure (corresponding load pressure in this embodiment) can be guided to the back pressure chamber 36. As a result, when the corresponding load pressure becomes higher than the upstream pressure, the main valve body 35 closes the branch portion 28c, thereby preventing the working fluid from flowing back from the outlet 28f to the inlet 28e. Thus, pressure compensation valves 14 and 15 with a backflow prevention function can be realized.

[0064] Furthermore, in the pressure compensation valves 14 and 15 of this embodiment, the check valve body 42 is interposed in the back pressure passage 37 on the outlet 28f side from the throttle 35a, and closes the back pressure passage 37 when the selected load pressure becomes higher than the corresponding load pressure. Since such a check valve body 42 has a simple structure, it can be incorporated into the main valve body 35, and the pressure compensation valves 14 and 15 can be made compact when incorporated. In addition, by incorporating the check valve body 42 into the main valve body 35, the back pressure passage 37 can be made shorter, thereby improving responsiveness.

[0065] <Other Embodiments> In this embodiment, the flow rate control device 1 is mounted on a wheel loader, but as mentioned above, it may also be mounted on other construction machinery such as shovels and cranes. In this embodiment, the case in which the flow rate control device 1 controls the flow of working fluid supplied to and discharged from the bucket cylinder 2 and boom cylinder 3 has been described, but the hydraulic actuator may be an arm cylinder, a travel motor, a steering motor, etc. Furthermore, the hydraulic actuators that control the flow of working fluid in the flow rate control device 1 are not limited to two, but may be three or more.

[0066] The pressure compensation valves 14 and 15 are equipped with a spool-type main valve body 35, but may also be equipped with a piston-type main valve body. In addition, the back pressure passage 37 is formed in the main valve body 35 in the pressure compensation valves 14 and 15, but may also be formed in the valve block 10. Furthermore, the check valve body 42 does not necessarily have to be located within the main valve body 35, but may also be formed in the valve block 10. In this case, the back pressure passage 37 and the check valve body 42 can be made more compact than a load check valve in order to guide the load pressure into the back pressure chamber 36 as back pressure. Moreover, the pressure compensation valves 14 and 15 do not necessarily have to be interposed in the connecting passages 28 and 29, respectively, and may be provided on the upstream and downstream sides of the flow control valves 11 and 12. Also, the pressure compensation valves 14 and 15 do not necessarily have to be provided in the flow control device 1, but may be provided in another device or used independently.

[0067] <Exemplary Embodiment> The flow control device in the first phase is a flow control device that controls the flow rate of working fluid supplied from a hydraulic pump to a first hydraulic actuator and a second hydraulic actuator, and comprises: a flow control valve interposed between the hydraulic pump and the first hydraulic actuator and controlling the flow rate flowing from the hydraulic pump to the first hydraulic actuator by adjusting the degree of opening; a pressure compensation valve interposed together with the flow control valve between the hydraulic pump and the first hydraulic actuator and adjusting the differential pressure across the flow control valve by controlling the degree of opening between the hydraulic pump and the first hydraulic actuator according to the differential pressure between the upstream pressure and the back pressure; and a load sensing device that provides the pressure compensation valve with a selectable load pressure, which is the higher of the first load pressure, which is the load pressure of the first hydraulic actuator, and the second load pressure, which is the load pressure of the second hydraulic actuator, as back pressure, wherein when the first load pressure becomes higher than the selectable load pressure, the pressure compensation valve replaces the selectable load pressure with the first load pressure as back pressure and closes the gap between the hydraulic pump and the first hydraulic actuator.

[0068] According to the above scenario, when the first load pressure becomes higher than the selected load pressure, the pressure compensation valve uses the first load pressure as the back pressure instead of the selected load pressure, and closes the gap between the hydraulic pump and the first hydraulic actuator. Therefore, when the first load pressure becomes high and the working fluid attempts to flow back from the first actuator, the pressure compensation valve can close the gap between the hydraulic pump and the first hydraulic actuator to prevent backflow of the working fluid. Thus, the pressure compensation valve has a backflow prevention function and can act as a load check valve. This reduces the number of parts in the flow control device.

[0069] The flow control device in the second phase is a flow control device in the first phase in which the pressure compensation valve includes a main valve body that adjusts the opening between the hydraulic pump and the first hydraulic actuator according to the differential pressure between the upstream pressure and the back pressure, a back pressure chamber that applies back pressure to the main valve body, a back pressure passage connecting the back pressure chamber and the first hydraulic actuator, and a guide passage connecting the load sensing device and the back pressure chamber, wherein the guide passage is connected to the back pressure chamber via a throttle.

[0070] In the above scenario, the guide passage is connected to the back pressure chamber via a throttle through the load sensing device. Therefore, when the opening between the hydraulic pump and the first hydraulic actuator is adjusted according to the selected load pressure, hunting due to fluctuations in the selected load pressure can be suppressed in the pressure compensation valve. On the other hand, since the back pressure passage is connected to the back pressure chamber without a throttle, the first load pressure can be applied to the main valve body without a throttle. Therefore, when the first load pressure rises suddenly, the gap between the hydraulic pump and the first hydraulic actuator can be quickly closed. In other words, the responsiveness when the gap between the hydraulic pump and the first hydraulic actuator is closed due to a sudden rise in the first load pressure can be improved.

[0071] The flow control device in the third phase is the flow control device in the second phase, wherein the pressure compensation valve includes a check valve body that guides a first load pressure to the back pressure chamber in place of the selected load pressure, the back pressure passage is formed in the main valve body, and the check valve body is interposed in the back pressure passage.

[0072] In the above configuration, the back pressure passage is formed in the main valve body, and the check valve body is interposed in the back pressure passage. Therefore, the check valve body is provided inside the main valve body. Since the check valve body only guides the first load pressure to the back pressure chamber in place of the selected load pressure, it can be made compactly. By incorporating the check valve body configured in this way into the pressure compensation valve, the flow control device can be made more compact compared to the case where the check valve body is configured separately from the pressure compensation valve.

[0073] The flow control device in the fourth phase is a flow control device in the second or third phase, wherein the pressure compensation valve further includes a housing, the housing having the back pressure chamber and the guide passage, the main valve body having the back pressure passage connected to the first hydraulic actuator and a throttle connecting the guide passage and the back pressure passage, and is movably provided in the housing to adjust the opening degree of the hydraulic pump and the first hydraulic actuator.

[0074] According to the above description, the main valve body has a back pressure passage connected to the first hydraulic actuator and a throttle connecting the guide passage and the back pressure passage. Furthermore, the main valve body is movably mounted in the housing to adjust the opening degree of the hydraulic pump and the first hydraulic actuator. Therefore, the pressure compensation valve can be configured to have a backflow prevention function, and a flow control device equipped with a pressure compensation valve with a backflow prevention function can be realized.

[0075] In the fifth phase, the flow control device is configured such that, in the flow control device of any of the first to fourth phases, the pressure compensation valve is interposed in a connection passage that connects to the hydraulic pump and the first hydraulic actuator via the flow control valve.

[0076] According to the above description, the pressure compensation valve is interposed in the connecting passage. This allows the pressure compensation valve with load-checking function to be placed between the hydraulic pump and the first hydraulic actuator without having to place it upstream of the flow control valve. This prevents the downstream pressure of the flow control valve from increasing even when the load pressure is high, thus preventing the hydraulic fluid from ceasing to flow to the first hydraulic actuator.

[0077] The pressure compensation valve in the sixth phase comprises a housing including a valve passage connecting an inlet and an outlet, a back pressure chamber, and a guide passage connected to the back pressure chamber and introducing a signal pressure into the back pressure chamber, and a main valve body movably provided in the housing to adjust the opening of the valve passage in accordance with the pressure difference between the upstream pressure, which is the pressure at the inlet, and the back pressure, which is the liquid pressure in the back pressure chamber, wherein the main valve body further includes a back pressure passage connecting the outlet and the back pressure chamber, and closes the valve passage when the pressure in the back pressure chamber becomes high.

[0078] According to the above description, the main valve body includes a back pressure passage connecting the outlet and the back pressure chamber. Therefore, the higher of the downstream pressure (the fluid pressure at the outlet) and the signal pressure can be guided into the back pressure chamber. As a result, when the downstream pressure becomes higher than the upstream pressure, the valve body closes the valve passage, preventing the working fluid from flowing back from the outlet to the inlet. Thus, a pressure compensating valve with a backflow prevention function can be realized.

[0079] The pressure compensation valve in the seventh phase further comprises a check valve body interposed in the back pressure passage and closing the back pressure passage when the selected load pressure is higher than the first load pressure, in addition to the pressure compensation valve in the sixth phase.

[0080] According to the above procedure, the check valve body is interposed in the back pressure passage on the outlet side of the throttling, and closes the back pressure passage when the signal pressure becomes higher than the downstream pressure. Since such a check valve body has a simple structure, it can be incorporated into the main valve body, and the pressure compensation valve can be formed compactly in the incorporated state.

[0081] From the above description, many improvements and other embodiments of the present invention will be apparent to those skilled in the art. Therefore, the above description should be interpreted as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of its structure and / or function can be substantially modified without departing from the spirit of the invention.

Claims

1. A flow control device for controlling the flow rate of working fluid supplied from a hydraulic pump to a first hydraulic actuator and a second hydraulic actuator, comprising: a flow control valve interposed between the hydraulic pump and the first hydraulic actuator and controlling the flow rate from the hydraulic pump to the first hydraulic actuator by adjusting its opening degree; a pressure compensation valve interposed together with the flow control valve between the hydraulic pump and the first hydraulic actuator and adjusting the differential pressure across the flow control valve by controlling the opening degree between the hydraulic pump and the first hydraulic actuator according to the differential pressure between the upstream pressure and the back pressure; and a load sensing device that provides the pressure compensation valve with a selectable load pressure, which is the higher of a first load pressure (the load pressure of the first hydraulic actuator) and a second load pressure (the load pressure of the second hydraulic actuator), as back pressure, wherein when the first load pressure becomes higher than the selectable load pressure, the pressure compensation valve replaces the selectable load pressure with the first load pressure as back pressure and closes the gap between the hydraulic pump and the first hydraulic actuator.

2. The flow control device according to claim 1, wherein the pressure compensation valve includes a main valve body that adjusts the opening between the hydraulic pump and the first hydraulic actuator according to the differential pressure between the upstream pressure and the back pressure, a back pressure chamber that applies back pressure to the main valve body, a back pressure passage connecting the back pressure chamber and the first hydraulic actuator, and a guide passage connecting the load sensing device and the back pressure chamber, the guide passage being connected to the back pressure chamber via a throttle.

3. The flow control device according to claim 2, wherein the pressure compensation valve includes a check valve body that guides a first load pressure to the back pressure chamber in place of the selected load pressure, the back pressure passage is formed in the main valve body, and the check valve body is interposed in the back pressure passage.

4. The flow control device according to claim 2, wherein the pressure compensation valve further includes a housing, the housing having the back pressure chamber and the guide passage, the main valve body having the back pressure passage connected to the first hydraulic actuator and a throttle connecting the guide passage and the back pressure passage, and is movably provided in the housing to adjust the opening degree of the hydraulic pump and the first hydraulic actuator.

5. The flow control device according to claim 1, wherein the pressure compensation valve is interposed in a connection passage connected to the hydraulic pump and the first hydraulic actuator via the flow control valve.

6. A pressure compensating valve comprising: a housing including a valve passage connecting an inlet and an outlet; a back pressure chamber; a guide passage connected to the back pressure chamber and introducing a signal pressure into the back pressure chamber; and a main valve body movably provided in the housing to adjust the opening of the valve passage in accordance with the pressure difference between the upstream pressure, which is the pressure at the inlet, and the back pressure, which is the liquid pressure in the back pressure chamber, wherein the main valve body further includes a back pressure passage connecting the outlet and the back pressure chamber, and closes the valve passage when the pressure in the back pressure chamber becomes high.

7. The pressure compensation valve according to claim 6, further comprising a check valve body interposed in the back pressure passage and closing the back pressure passage when the selected load pressure is higher than the first load pressure.

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