Hydraulic system for work equipment

Abstract

To secure a requested working speed of a hydraulic actuator which is of higher priority when simultaneously operating a plurality of hydraulic actuators.SOLUTION: A hydraulic system for a working machine comprises: a first hydraulic actuator and a second hydraulic actuator which operate with a working fluid discharged from a hydraulic pump; a first flow rate controller for controlling a first supply flow rate of working fluid supplied to the first hydraulic actuator so as to coincide with a first required flow rate which is set via a first operation member; a second flow rate controller for controlling a second supply flow rate of working fluid supplied to the second hydraulic actuator so as to coincide with a second required flow rate which is set via a second operation member; and a special flow rate control system which brings the second supply flow rate closer to the second required flow rate by reducing the first supply flow rate when a total required flow rate as a total sum of the first required flow rate and the second required flow rate exceeds a maximum discharge flow rate, which is a maximum flow rate of working fluid that can be discharged from the hydraulic pump.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a hydraulic system for work machines such as skid steer loaders and compact track loaders. [Background technology]

[0002] Conventionally, as a work machine equipped with a hydraulic actuator, a work machine referred to as a compact track loader, as disclosed in Patent Document 1, is known. This work machine has a pair of left and right lift arms, and the lift arms are swung up and down relative to the machine body by the drive of a lift arm cylinder, which acts as a hydraulic actuator.

[0003] Furthermore, to accommodate the attachment of hydraulic actuators, such as sweepers, to the lift arms, one of the pair of left and right lift arms is provided with a port for extracting hydraulic fluid (auxiliary (AUX) port). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-57494 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In the above-mentioned work machine, the lift arm cylinder and the attachment's hydraulic actuator may be operated simultaneously. However, if the sum of the required flow rate of the lift arm cylinder and the required flow rate of the attachment's hydraulic actuator exceeds the maximum discharge flow rate of the common hydraulic pump, the supply flow rate to both the lift arm cylinder and the attachment's hydraulic actuator will fall below their respective required flow rates, making it impossible to achieve the desired work speed, work efficiency, etc. [Means for solving the problem]

[0006] To solve the above problems, the hydraulic system for a work machine according to the present invention comprises a hydraulic pump, a first hydraulic actuator operated by hydraulic fluid discharged from the hydraulic pump, a second hydraulic actuator operated by hydraulic fluid discharged from the hydraulic pump, a first operating member operable to set a first required flow rate, a second operating member operable to set a second required flow rate, a first flow rate control device that controls a first supply flow rate, which is the flow rate of hydraulic fluid supplied to the first hydraulic actuator, to match the first required flow rate set by the operation of the first operating member, a second flow rate control device that controls a second supply flow rate, which is the flow rate of hydraulic fluid supplied to the second hydraulic actuator, to match the second required flow rate set by the operation of the second operating member, and the first required flow rate The special flow control system comprises: a first requested flow rate detection device for detecting a first requested flow rate; a second requested flow rate detection device for detecting a second requested flow rate; a first supply flow rate detection device for detecting a first supply flow rate of hydraulic fluid supplied to the first hydraulic actuator; a second supply flow rate detection device for detecting a second supply flow rate of hydraulic fluid supplied to the second hydraulic actuator; and a discharge flow rate detection device for detecting a discharge flow rate of hydraulic fluid discharged from the hydraulic pump. The special flow control system comprises: The total requested flow rate, which is the sum of the first requested flow rate and the second requested flow rate, The discharge flow rate detection device is detected It is determined that the maximum discharge flow rate, which is the maximum flow rate of hydraulic fluid that can be discharged by the aforementioned hydraulic pump, is exceeded. From that point until a predetermined period has elapsed, the first supply flow rate is maintained at a flow rate that is one deficiency less than the first requested flow rate, and the second supply flow rate is maintained at a flow rate that is two deficiencies less than the second requested flow rate, and after the predetermined period has elapsed, By reducing the first supply flow rate, the second supply flow rate is brought closer to the second requested flow rate. ru.

[0007] When the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, it sets a limited requested flow rate that is lower than the first requested flow rate. After the aforementioned predetermined period has elapsed, The second supply flow rate may be brought closer to the second required flow rate by reducing the first supply flow rate to the limited required flow rate.

[0008] When the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, it sets a limited requested flow rate that is less than or equal to the difference between the maximum discharge flow rate and the second requested flow rate. After the aforementioned predetermined period has elapsed, The second supply flow rate may be brought closer to the second required flow rate by reducing the first supply flow rate to the limited required flow rate.

[0009] The special flow rate control system, after the first requested flow rate has been set and the second requested flow rate has been set, determines that the total requested flow rate exceeds the maximum discharge flow rate. After the aforementioned predetermined period has elapsed,By further reducing the first supply flow rate below the first required flow rate to an even lower value, the second supply flow rate may be brought closer to the second required flow rate.

[0010] When the special flow control system determines that the total required flow rate exceeds the maximum discharge flow rate, After the aforementioned predetermined period has elapsed, the second supply flow rate may be brought closer to the second required flow rate by gradually reducing the first supply flow rate.

[0011] When the special flow control system determines that the total required flow rate exceeds the maximum discharge flow rate, After the aforementioned predetermined period has elapsed, the second supply flow rate may be brought closer to the second required flow rate by gradually reducing the first supply flow rate at a constant reduction rate.

[0012] When the special flow control system determines that the total required flow rate exceeds the maximum discharge flow rate, After the aforementioned predetermined period has elapsed, the second supply flow rate may be brought closer to the second required flow rate by gradually reducing the first supply flow rate step by step.

[0013] After the special flow control system determines that the total required flow rate has exceeded the maximum discharge flow rate, if the first operating member or the second operating member is operated and it is determined that the total required flow rate has become below the maximum discharge flow rate, the first supply flow rate that has been decreased may be increased to approach the first required flow rate.

[0014] The hydraulic system may further include a pump control device for controlling the flow rate of the hydraulic oil discharged from the hydraulic pump. The pump control device may control the hydraulic pump so that the discharge pressure of the hydraulic oil discharged from the hydraulic pump is higher than the maximum load pressures of the first hydraulic actuator and the second hydraulic actuator by a set load sensing differential pressure.

[0015] The hydraulic system may further include a pressure compensation valve for compensating the hydraulic pressure set for the hydraulic oil supplied to the first hydraulic actuator.

[0016] The hydraulic system may further include: a discharge oil passage for carrying hydraulic fluid discharged from the hydraulic pump; a first branch oil passage branching off from the discharge oil passage; a first control valve operable to supply hydraulic fluid supplied from the discharge oil passage via the first branch oil passage to the first hydraulic actuator; a second branch oil passage branching off from the discharge oil passage in parallel with the first branch oil passage; and a second control valve operable to supply hydraulic fluid supplied from the discharge oil passage via the second branch oil passage to the second hydraulic actuator. The first flow rate control device may control the position of the first control valve so that the first supply flow rate matches the first requested flow rate. The second flow rate control device may control the position of the second control valve so that the second supply flow rate matches the second requested flow rate. If the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, the second flow rate control device may, while holding the second control valve in a position that matches the second supply flow rate to the second requested flow rate, have the first flow rate control device change the position of the first control valve to reduce the first supply flow rate, thereby bringing the second supply flow rate closer to the second requested flow rate.

[0017] The first control valve may be positioned by receiving pilot pressure oil. The first flow rate control device may control the supply of the pilot pressure oil to the first control valve.

[0018] The hydraulic system may further include a solenoid valve that supplies the pilot pressure oil to the first control valve. The first flow control device may output a control signal for controlling the opening degree of the solenoid valve.

[0019] The first control valve may be a solenoid valve. The first flow rate control device may output a control signal to the first control valve to control the excitation of the solenoid.

[0020] The special flow rate control system may include a variable throttle provided in the oil passage through which the hydraulic fluid supplied to the first hydraulic actuator flows. If the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, it may increase the degree of throttling of the variable throttle to reduce the first supply flow rate, thereby bringing the second supply flow rate closer to the second requested flow rate.

[0021] The hydraulic system may further include: a discharge oil passage for carrying hydraulic fluid discharged from the hydraulic pump; a first branch oil passage branching off from the discharge oil passage; a first control valve operable to supply hydraulic fluid supplied from the discharge oil passage via the first branch oil passage to the first hydraulic actuator; a second branch oil passage branching off from the discharge oil passage in parallel with the first branch oil passage; and a second control valve operable to supply hydraulic fluid supplied from the discharge oil passage via the second branch oil passage to the second hydraulic actuator. The first flow rate control device may control the position of the first control valve so that the first supply flow rate matches the first requested flow rate. The second flow rate control device may control the position of the second control valve so that the second supply flow rate matches the second requested flow rate. If the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, the second flow rate control device may hold the second control valve in a position that matches the second supply flow rate to the second requested flow rate, and while the first flow rate control device holds the first control valve in a position that matches the first supply flow rate to the first requested flow rate, the second supply flow rate may be brought closer to the second requested flow rate by increasing the degree of throttling of the variable throttle to decrease the first supply flow rate. [Effects of the Invention]

[0022] According to the present invention, when two hydraulic actuators are driven simultaneously, the flow rate of hydraulic fluid supplied to the lower-priority hydraulic actuator is reduced, and the desired flow rate of hydraulic fluid is supplied to the higher-priority hydraulic actuator. This allows the higher-priority hydraulic actuator to be driven at the desired speed and efficiency, thereby achieving work with desirable work efficiency. [Brief explanation of the drawing]

[0023] [Figure 1] This is a side view of the work machine. [Figure 2] This is a circuit diagram of the hydraulic system of the work machine according to the first embodiment. [Figure 3] This graph shows the first pattern of the reduction in required flow rate due to the flow control system. [Figure 4] This graph shows the second pattern of reduction in required flow rate due to the flow control system. [Figure 5] This flowchart shows the flow control process by the flow control system. [Figure 6] This is a circuit diagram of the hydraulic system of the work machine according to the second embodiment. [Figure 7] This is a circuit diagram of the hydraulic system of the work machine according to the third embodiment. [Modes for carrying out the invention]

[0024] Hereinafter, embodiments of the hydraulic system for a work machine according to the present invention will be described with reference to the drawings as appropriate.

[0025] Referring to Figure 1, the overall configuration of the implement according to an embodiment of the present invention will be outlined. In this embodiment, a compact track loader (CTL) 1 is used as the implement. In addition to the compact track loader, other implements to which the hydraulic system according to the present invention can be applied include, for example, tractors, skid steer loaders, backhoes, etc.

[0026] CTL1 comprises a body 2, a cabin 3, a work device 4, and a travel device 5. The cabin 3, work device 4, and travel device 5 are mounted on the body 2. In Figure 1, the direction indicated by arrow F is considered the front, and the opposite side is considered the rear. When viewing CTL1 from the rear along arrow F, the left side is considered the left, and when viewing it from the front, the right side is considered the right.

[0027] The CTL1 according to this embodiment is a track loader and is equipped with a pair of left and right crawler-type running gears 5 provided on the left and right sides of the machine body 2. However, the running gear is not limited to crawler-type running gear. For example, the work machine may be a wheel loader equipped with a wheel-type running gear having front and rear wheels.

[0028] The engine 6 is mounted in the rear portion of the aircraft body 2, for example, behind the cabin 3. The engine 6 could be an internal combustion engine or an electric motor. The pair of left and right running gears 5 are driven by the output of the engine 6.

[0029] Specifically, each of the left and right running gears 5 is equipped with a separate hydraulic actuator for driving, such as a hydraulic motor (not shown in the diagram). The hydraulic fluid discharged from a hydraulic pump driven by the output of the prime mover 6 is supplied to the running hydraulic actuator, thereby operating the running hydraulic actuator and driving, for example, the drive wheels of each running gear 5.

[0030] For example, a pair of hydraulic pumps may be provided as hydraulic pumps to supply hydraulic fluid to the hydraulic actuators for travel, and each hydraulic pump may be fluidly connected to the corresponding hydraulic motor to constitute a pair of hydraulic continuously variable transmissions (HSTs) for driving each of the pair of travel devices 5.

[0031] It should be noted that the drive configuration of the CTL1's travel device 5 according to this embodiment is not limited to the configuration described above. For example, instead of the prime mover 6, a battery may be mounted on the body 2, and the left and right travel devices 5 may each have their own electric motors, which are driven by current supplied from the battery.

[0032] Aircraft 2 is equipped with a cockpit 7. Cabin 3 is mounted on aircraft 2 so as to surround the cockpit 7. Cabin 3 is a type of protective mechanism that protects the operator sitting in cockpit 7 and various operating components such as levers and switches, as well as instruments, that are located around cockpit 7. Similar protective mechanisms such as a canopy or ROPS (Road-Operated Propulsion System) could also be installed on aircraft 2.

[0033] Inside the cabin 3, a work operation lever 8, which is a type of operating member that is manually operated by an operator sitting in the driver's seat 7, is provided. The work operation lever 8 is operated to control the up-and-down swinging of the pair of left and right lift arms 10 of the work device 4 (described later) or the up-and-down rotation of the attachments (described later) (specifically, to control the extension and retraction of the pair of left and right lift arm cylinders 14 or the pair of left and right attachment cylinders 15).

[0034] Furthermore, referring to Figure 2, within the cabin 3, an auxiliary drive switch (AUX operation switch) 9, not shown in Figure 1, is located near the driver's seat 7. The AUX operation switch 9 is operated to control the supply of hydraulic fluid to the hydraulic actuator (e.g., hydraulic motor 24, described later) of the attachment (e.g., sweeper 23, described later) mounted on the work device 4.

[0035] The work device 4 has a pair of left and right lift arms 10 mounted on the machine body 2 so as to be able to swing up and down. Of the pair of left and right lift arms 10, the left lift arm 10 is positioned to the left of the cabin 3, and the right lift arm 10 is positioned to the right of the cabin 3. Each lift arm 10 is positioned so that its longitudinal direction is aligned with the front-rear direction of the CTL 1.

[0036] In front of cabin 3, the front ends of the left and right lift arms 10 are connected via a connecting member (not shown). Also, behind cabin 3, the rear ends of the left and right lift arms 10 are connected via a connecting member (not shown).

[0037] Thus, the main body 4a of the work device 4, which is formed by integrally combining the left and right lift arms 10 and the front and rear connecting members (not shown), is attached to the machine body 2 so as to be able to rotate up and down.

[0038] Furthermore, the connection method between the left and right lift arms 10 is not limited to the front and rear connecting members described above; any configuration is acceptable as long as the left and right lift arms 10 can be integrated and swing up and down relative to the aircraft body 2.

[0039] The work device 4 includes a pair of left and right lift links 12 and a pair of left and right control links 13 to support the main body 4a, which includes the left and right lift arms 10, at the rear of the machine body 2.

[0040] Furthermore, the work device 4 is equipped with a pair of left and right lift arm cylinders 14 as hydraulic actuators for rotating the main body 4a, which includes the left and right lift arms 10, up and down relative to the machine body 2.

[0041] Figure 1, a left side view of the CTL1, shows the left lift arm 10, lift link 12, control link 13, and lift arm cylinder 14, which are located to the left of the cabin 3. Similarly, the right lift arm 10, lift link 12, control link 13, and lift arm cylinder 14 are located to the right of the cabin 3, but are omitted from Figure 1.

[0042] Figure 1 shows the left and right lift arms 10 (including the main body 4a of the work device 4), which are capable of vertically swinging relative to the machine body 2, in their lowest position in the vertical swing direction. Hereafter, the positions and directions of each part of the work device 4 will be explained assuming that the left and right lift arms 10 are in this lowest position.

[0043] Each lift link 12 extends in a substantially vertical direction, its upper end being pivotally connected to the rear end of each lift arm 10 via a pivot 16 having a left-right axis, and its lower end being pivotally connected to the rear upper part of the aircraft body 2 via a pivot 17 having a left-right axis.

[0044] Furthermore, a recess 12a is formed at the front end edge of each lift link 12. As shown in Figure 1, when the stopper 10a provided on the side of each lift arm 10 is fitted into the recess 12a, the lift arm 10 cannot swing from there toward the lift link 12 around the pivot 16. In other words, when the stopper 10a is fitted into the recess 12a, the angle formed between the lift arm 10 and the lift link 12 around the pivot 16 is minimized.

[0045] A bracket 10b is formed at the rear of each lift arm 10 forward of each pivot 16, and the tip of the piston rod of each lift arm cylinder 14 is pivotally connected to the bracket 10b via a pivot 18 having an axis in the left-right direction. Furthermore, below each pivot 17, the bottom end of each lift arm cylinder 14 is pivotally connected to the rear lower part of the machine body 2 via a pivot 19 having an axis in the left-right direction.

[0046] Each lift arm cylinder 14 houses a piston (not shown in Figure 1) and is configured to extend and retract the piston rod by moving the piston hydraulically. The lift arm cylinder 14 shown in Figure 1 is in the most retracted state. That is, when the stopper 10a is fitted into the recess 12a and the angle between each lift arm 10 and each lift link 12 is minimized, and each lift arm cylinder 14 is most retracted, the left and right lift arms 10 are positioned in their lowest position.

[0047] In the front-rear direction, a downwardly projecting bracket 10c is formed at the rear of each lift arm 10 between each pivot 16 and each pivot 18. Each control link 13 extends substantially in the front-rear direction, its front end pivotally connected to the front portion of each pivot 16 at the rear upper part of the machine body 2 via a pivot 20 having an axis in the left-right direction, and its rear end pivotally connected to each bracket 10c via a pivot 21 having an axis in the left-right direction.

[0048] As shown in Figure 1, when the left and right lift arms 10 are in their lowest position, the piston rods of the left and right lift arm cylinders 14 are extended upward, causing the piston rods to lift the brackets 10b of the lift arms 10.

[0049] As described above, behind the bracket 10b, the rear end of the lift arm 10 and the upper end of the lift link 12 are pivotally connected via the pivot 16. As the bracket 10b is raised, these rotate downward and rearward around the axis of the pivot 17 while maintaining the minimum angle between the lift arm 10 and the lift link 12 (i.e., with the stopper 10a engaged in the recess 12a). Consequently, the front end of the lift arm 10 rises from its lowest position.

[0050] As the piston rods of the left and right lift arm cylinders 14 are further extended upward, the left and right lift links 12 remain in a rearward-upward inclined position, and as the bracket 10b is further lifted, the stopper 10a eventually disengages from the recess 12a, causing the lift arm 10 to rotate around the axis of the pivot 16 so that the angle between the lift arm 10 and the lift link 12 increases. Consequently, the control link 13 rotates forward and upward around the pivot 20, and the front end of the lift arm 10 moves further upward.

[0051] When the control link 13 rotates forward and upward, and the pivot 21 reaches the highest position within its vertical range of movement, the left and right lift arms 10 (the main body 4a of the work device 4) can no longer be lifted any further. In other words, when the pivot 21 reaches this position, the left and right lift arms 10 (the main body 4a of the work device 4) reach their highest position, and the lift arm cylinders 14 are fully extended.

[0052] Each lift arm 10 extends forward from the bracket 10b (downward and forward when in the lowest position), has a bent section 10d in front of the cabin 3, and extends downward from the bent section 10d to the front end of the lift arm 10. The front ends of the left and right lift arms 10 are configured to allow attachment of work devices.

[0053] The work device 4 is equipped with a pair of left and right attachment cylinders 15. These are hydraulic actuators that support attachments mounted on the left and right lift arms 10 and also rotate the attachments up and down relative to the lift arms 10.

[0054] A bracket 10e is formed at the bent portion 10d of each lift arm 10, and the cylinder bottom (upper end) of each attachment cylinder 15 is pivotally connected to the bracket 10e via a pivot 22 having an axis in the left-right direction. The left and right pair of attachment cylinders 15 The tip (lower end) of the tonnage rod is pivotally connected to an attachment mounted on the front end of the left and right lift arms 10.

[0055] Furthermore, one or more AUX ports (hydraulic fluid outlet ports) 11 are provided on the bent portion 10d of one of the pair of left and right lift arms 10 (the left lift arm in this embodiment). The AUX ports 11 are couplers, and the connecting end of an oil pipe, such as a hose, can be connected to a hydraulic actuator (AUX actuator) located on an attachment mounted on the front end of the left and right lift arms 10.

[0056] The work device 4 can be fitted with various types of attachments. These attachments are configured to be connectable to at least the front ends of the left and right lift arms 10. In other words, by connecting the attachments to the front ends of both the left and right lift arms 10, the attachments can be mounted on the work device 4.

[0057] Various types of attachments that can be mounted on the work device 4 (connectable to the left and right lift arms 10) include, for example, buckets, hydraulic crushers, hydraulic breakers, angle brooms, earth augers, pallet forks, sweepers, mowers, snow blowers, etc. Figure 1 shows an embodiment in which a sweeper 23 is mounted on the work device 4 of the CTL1.

[0058] The sweeper 23 comprises a rotating brush 23a having a rotation axis in the left-right direction, a sweeper cover 23b that covers the rotating brush 23a and pivots its rotation axis, and a hydraulic motor 24 which is a hydraulic actuator (AUX actuator) for driving the rotation axis of the rotating brush 23a.

[0059] The sweeper 23 is supported so as to be able to swing up and down on the main body 4a of the work device 4, which includes the left and right lift arms 10, by pivoting the lower rear end of the sweeper cover 23b to the front ends of both the left and right lift arms 10, and further pivoting the upper rear end of the sweeper cover 23b to the tips (lower ends) of the piston rods of both the left and right attachment cylinders 15.

[0060] Furthermore, the sweeper 23 is equipped with a hydraulic oil pipe 25 for supplying hydraulic fluid to the hydraulic motor 24, and a coupler formed at the upper end of the hydraulic oil pipe 25 is connected to the AUX port 11 provided on the bent portion 10d of one of the lift arms 10.

[0061] This makes it possible to extract and supply hydraulic fluid from the hydraulic circuit installed inside the machine body 2, which is used to supply hydraulic fluid to the lift arm cylinder 14 and attachment cylinder 15, etc., to the hydraulic motor 24 of the sweeper 23 attached to the work device 4.

[0062] Next, with reference to the hydraulic circuit diagram in Figure 2, the hydraulic system 30 of the CTL1 for controlling the hydraulic actuators of the work device 4 and the attachment (sweeper 23 in this embodiment) mounted on the work device 4 will be described.

[0063] As shown in Figure 2, the hydraulic system 30 includes hydraulic pumps 31 and 32. Both hydraulic pumps 31 and 32 are driven by the power of the prime mover 6, draw in oil stored in a common reservoir tank 33, and discharge oil from their respective outlets.

[0064] The hydraulic pump 31 is a variable displacement pump. In this embodiment, a movable swashplate type axial piston pump is used as the hydraulic pump 31, but any variable displacement pump with a different structure may be used.

[0065] The hydraulic pump 31 of this embodiment has a movable swash plate 31a, and the inclination angle of the movable swash plate 31a is By making this change, the flow rate of the discharged oil (discharge flow rate D) can be altered. Furthermore, the discharge flow rate D of the hydraulic pump 31 can also be changed by changing the rotational speed of the prime mover 6.

[0066] The hydraulic pump 32 is a fixed-displacement pump, typically a gear pump. The flow rate of oil discharged by the hydraulic pump 32 can be changed by changing the output rotational speed of the prime mover 6.

[0067] Although not shown in Figure 2, the hydraulic actuators of the work device 4, that is, the pair of hydraulic actuators (HST, etc.) for travel provided by the left and right crawler travel devices 5, may also be configured to supply the hydraulic fluid discharged by the hydraulic pump 32.

[0068] The hydraulic pump 31 is a hydraulic pump that discharges hydraulic fluid supplied to the hydraulic actuators (i.e., a pair of left and right lift arm cylinders 14 and a pair of left and right attachment cylinders 15) of the work device 4 of the CTL1, and to the hydraulic actuators (in this embodiment, the hydraulic motor 24 of the sweeper 23) of the attachments mounted on the work device 4.

[0069] The machine body 2 is equipped with multiple control valves that control the supply of hydraulic fluid to multiple hydraulic actuators. Of these multiple control valves, Figure 2 discloses a lift arm control valve 41 that controls the flow of hydraulic fluid supplied to the left and right lift arm cylinders 14, an attachment control valve 42 that controls the flow of hydraulic fluid supplied to the left and right attachment cylinders 15, and an AUX control valve 43 that controls the flow of hydraulic fluid supplied to the AUX port 11.

[0070] A discharge oil passage 34 extends from the discharge port of the hydraulic pump 31. A branch oil passage 36, which branches off from the discharge oil passage 34, is connected to the pump port of the lift arm control valve 41. A branch oil passage 37, which branches off from the downstream portion of the discharge oil passage 34 where it branches off to branch oil passage 36, is connected to the pump port of the attachment control valve 42. A branch oil passage 38, which branches off from the downstream portion of the discharge oil passage 34 where it branches off to branch oil passage 37, is connected to the pump port of the AUX control valve 43. In other words, the control valves 41, 42, and 43 are connected in parallel to the discharge oil passage 34 via their respective branch oil passages 36, 37, and 38.

[0071] The lift arm cylinder 14 is a double-acting hydraulic cylinder, and its interior is divided into a bottom (lower end) oil chamber and a rod (upper end) oil chamber by a piston. Oil supply and discharge passages 44 and 45 extend from the lift arm control valve 41, with the oil supply and discharge passage 44 communicating with the rod-side oil chambers of both the left and right lift arm cylinders 14, and the oil supply and discharge passage 45 communicating with the bottom-side oil chambers of both the left and right lift arm cylinders 14.

[0072] The attachment cylinder 15 is a double-acting hydraulic cylinder, and its interior is divided by a piston into a rod (lower end) side oil chamber and a bottom (upper end) side oil chamber. Oil supply and discharge passages 46 and 47 extend from the attachment control valve 42, with the oil supply and discharge passage 46 communicating with the bottom side oil chambers of both the left and right attachment cylinders 15, and the oil supply and discharge passage 47 communicating with the rod side oil chambers of both the left and right attachment cylinders 15.

[0073] Oil supply and discharge passages 48 and 49 extend from the AUX control valve 43 and are connected to the corresponding ports among the multiple AUX ports 11, respectively. In addition, the hydraulic motor 24 (hydraulic actuator) of the sweeper 23 (attachment) is fluidly connected to the AUX port 11 via the hydraulic oil pipe 25 (see Figure 1).

[0074] In the following description of the hydraulic system 30, "lift arm 10" refers to a pair of left and right lift arms 10, "lift arm cylinder 14" refers to a pair of left and right lift arm cylinders 14, and "attachment cylinder 15" refers to a pair of left and right attachment cylinders This refers to the 15th cylinder.

[0075] The control valves 41, 42, and 43 are pilot-pressure controlled directional control valves having pressure-receiving sections on both sides of the spool to receive pilot pressure. The hydraulic pump 32 is a pilot-pressure oil pump for supplying pilot-pressure oil to the control valves 41 and 42.

[0076] The operation lever 8 shown in Figures 1 and 2 is manually operated by an operator seated in the driver's seat 7. By tilting it in the front-to-back direction, it causes the lift arm 10 to swing up and down relative to the machine body 2. By tilting it in the left-to-right direction, it causes the attachment (sweeper 23 in this embodiment) to rotate up and down relative to the lift arm 10.

[0077] In CTL1, operating valves 51, 52, 53, and 54 are arranged around the base of the work lever 8. A discharge oil passage 50 extends from the discharge port of the hydraulic pump 32 and is connected to the operating valves 51, 52, 53, and 54.

[0078] The operating valves 51, 52, 53, and 54 are each activated by the tilting of the work lever 8, and discharge the oil supplied from the hydraulic pump 32 via the discharge oil passage 50 as pilot pressure oil.

[0079] When the operation lever 8 is tilted forward from the neutral position, a pilot pressure oil in an amount corresponding to the tilt angle (amount of operation) from the neutral position is discharged from the operation valve 51. This pilot pressure oil is supplied to the upper pressure receiving part of the lift arm control valve 41 via the pilot oil passage 55 in Figure 2, causing the spool of the lift arm control valve 41 to shift downward in Figure 2.

[0080] As a result, hydraulic fluid is supplied from the lift arm control valve 41 to the rod-side oil chamber of the lift arm cylinder 14 via the oil supply and discharge passage 44, and hydraulic fluid is discharged from the bottom-side oil chamber of the lift arm cylinder 14 to the lift arm control valve 41 via the oil supply and discharge passage 45, causing the lift arm cylinder 14 to contract and the lift arm 10 to descend.

[0081] When the operation lever 8 is tilted backward from the neutral position, a pilot pressure oil in an amount corresponding to the tilt angle (amount of operation) from the neutral position is discharged from the operation valve 52. This pilot pressure oil is supplied to the lower pressure receiving part of the lift arm control valve 41 via the pilot oil passage 56 in Figure 2, causing the spool of the lift arm control valve 41 to shift upward in Figure 2.

[0082] As a result, hydraulic fluid is supplied from the lift arm control valve 41 to the bottom oil chamber of the lift arm cylinder 14 via the supply and discharge oil passage 45, and hydraulic fluid is discharged from the rod-side oil chamber of the lift arm cylinder 14 to the lift arm control valve 41 via the supply and discharge oil passage 44, causing the lift arm cylinder 14 to extend and the lift arm 10 to rise.

[0083] Here, the lifting speed of the lift arm 10 is determined by the flow rate of hydraulic fluid (in the supply and discharge passages 44 and 45) supplied from the lift arm control valve 41 to the lift arm cylinder 14. The tilt angle of the work operation lever 8 in the forward and backward direction, i.e., the amount of operation, represents the set value of the hydraulic fluid flow rate to the lift arm cylinder 14, i.e., the required flow rate of hydraulic fluid to the lift arm cylinder 14.

[0084] The operating valves 51 and 52 operate in accordance with the forward and backward tilting of the work lever 8, and discharge pilot pressure oil to the lift arm control valve 41 so that the supply flow rate (actual value) of hydraulic fluid from the lift arm control valve 41 to the lift arm cylinder 14 becomes the required flow rate.

[0085] In other words, the operating valves 51 and 52 control the flow rate supplied to the lift arm cylinder 14 during the operation. The flow rate control device 27 controls the position of the lift arm control valve 41 to match the required flow rate to the lift arm cylinder 14, which is set by the forward and backward rotation operation of the bar 8.

[0086] When the operation lever 8 is tilted to the left from the neutral position, a pilot pressure oil in an amount corresponding to the tilt angle (amount of operation) from the neutral position is discharged from the operation valve 53. This pilot pressure oil is supplied to the upper pressure receiving part of the attachment control valve 42 via the pilot oil passage 57 in Figure 2, causing the spool of the attachment control valve 42 to shift downward in Figure 2.

[0087] As a result, hydraulic fluid is supplied from the attachment control valve 42 to the bottom oil chamber of the attachment cylinder 15 via the supply and discharge passage 46, and hydraulic fluid is discharged from the rod-side oil chamber of the attachment cylinder 15 to the attachment control valve 42 via the supply and discharge passage 47, causing the attachment cylinder 15 to extend and the attachment (sweeper 23 in this embodiment) to rotate downward relative to the lift arm 10.

[0088] When the operation lever 8 is tilted to the right from the neutral position, a pilot pressure oil in an amount corresponding to the tilt angle (amount of operation) from the neutral position is discharged from the operation valve 54. This pilot pressure oil is supplied to the lower pressure receiving part of the attachment control valve 42 via the pilot oil passage 58 in Figure 2, causing the spool of the attachment control valve 42 to shift upward in Figure 2.

[0089] As a result, hydraulic fluid is supplied from the attachment control valve 42 to the rod-side oil chamber of the attachment cylinder 15 via the oil supply and discharge passage 47, and hydraulic fluid is discharged from the bottom-side oil chamber of the attachment cylinder 15 to the attachment control valve 42 via the oil supply and discharge passage 46, causing the attachment cylinder 15 to retract and the attachment (sweeper 23 in this embodiment) to rotate upward relative to the left and right lift arms 10.

[0090] Here, the vertical rotation speed of the attachment relative to the lift arm 10 is determined by the flow rate of hydraulic fluid (in the supply and discharge passages 46 and 47) supplied from the attachment control valve 42 to the attachment cylinder 15. The left-right tilt angle of the work operation lever 8, i.e., the amount of operation, represents the set value of the hydraulic fluid flow rate to the attachment cylinder 15, i.e., the required flow rate of hydraulic fluid to the attachment cylinder 15.

[0091] The operating valves 53 and 54 operate in accordance with the left and right tilting of the work lever 8, and discharge pilot pressure oil to the attachment control valve 42 so that the supply flow rate (actual value) of hydraulic fluid from the attachment control valve 42 to the attachment cylinder 15 becomes the required flow rate.

[0092] In other words, the operating valves 53 and 54 constitute a flow rate control device 28 that controls the position of the attachment control valve 42 so that the flow rate supplied to the attachment cylinder 15 matches the required flow rate to the attachment cylinder 15, which is set by the left and right rotation operation of the work operation lever 8.

[0093] Furthermore, the operation lever 8 may be tiltable in all four directions from the neutral position, and this tilting in the diagonal directions may allow for simultaneous raising and lowering of the left and right lift arms 10 and vertical rotation of the attachment (sweeper 23).

[0094] In this case, for example, tilting the work operation lever 8 forward and to the left from the neutral position may lower the lift arm 10 while rotating the attachment downwards; tilting the work operation lever 8 forward and to the right from the neutral position may lower the lift arm 10 while rotating the attachment upwards; tilting the work operation lever 8 rear and to the left from the neutral position may raise the lift arm 10 while rotating the attachment downwards; and tilting the work operation lever 8 rear and to the right from the neutral position may raise the lift arm 10 while rotating the attachment upwards.

[0095] As shown in Figure 2, in this embodiment, the hydraulic motor 24 of the sweeper 23, which is an attachment mounted on the work device 4, is fluidly connected to the AUX port 11 via the hydraulic oil pipe 25 (see Figure 1), etc.

[0096] The ON / OFF switching of the hydraulic fluid supply to the hydraulic motor 24 (hydraulic actuator) of the sweeper 23 (attachment), as well as the flow rate and direction of the hydraulic fluid supplied to the hydraulic motor 24 (hydraulic actuator), can be controlled by operating the AUX operation switch 9 located around the driver's seat 7, as described above.

[0097] The hydraulic system 30 includes solenoid valves 59 and 60 for position control of the AUX control valve 43. The solenoid valves 59 and 60 are controlled by a control device (flow rate control device) 26 based on the operation of the AUX operation switch 9.

[0098] The AUX control switch 9 is composed of, for example, a swingable seesaw-type switch, a sliding-type switch, or a push-type switch. The control device 26 is composed of electrical and electronic circuits including a CPU, MPU, memory, etc.

[0099] The AUX operation switch 9 is electrically connected to the input interface of the control device 26. When the AUX operation switch 9 is operated, an input signal, which is an electrical signal corresponding to the direction and amount of operation, is output from the AUX operation switch 9 and input to the control device 26.

[0100] For example, if the AUX operation switch 9 is a slide switch, input signals corresponding to its sliding direction (operating direction) and sliding amount (operating amount) are input to the control device 26.

[0101] Solenoid valves 59 and 60 are electrically connected to the output interface of the control device 26. The control device 26 outputs a current as the control signal CS1 to solenoid valves 59 and 60 in response to the electrical signal from the AUX operation switch 9. Unless otherwise specified, "solenoid valves 59 and 60" refers to "solenoid valve 59 and / or solenoid valve 60".

[0102] The solenoid valves 59 and 60 are supplied with hydraulic fluid, for example, discharged from the hydraulic pump 31 via the discharge oil passage 34, which serves as the pilot pressure oil for the AUX control valve 43. The source of the oil supplying the pilot pressure oil for the AUX control valve 43 to the solenoid valves 59 and 60 is not shown in Figure 2.

[0103] Solenoid valves 59 and 60 each open from their initial closed state as the solenoid is energized by the control signal CS1 output from the control device 26, and discharge the supplied oil as pilot pressure oil to the AUX control valve 43.

[0104] The ON / OFF state and operating direction of the AUX operation switch 9 determine which of the solenoid valves 59 and 60 the control signal CS1 is output to from the control device 26 (or whether it is output to neither).

[0105] Furthermore, the control signal CS1 is set so that the opening amount of the pilot pressure oil discharge port to the AUX control valve 43 of each of the solenoid valves 59 and 60 corresponds to the amount of operation of the AUX operation switch 9.

[0106] When the solenoid valve 59 receives the control signal CS1, pilot pressure oil is supplied from the solenoid valve 59 to the upper pressure-receiving part of the AUX control valve 43 in Figure 2 via the pilot oil passage 61, causing the AUX control valve 43 to shift downward in Figure 2.

[0107] As a result, hydraulic fluid is supplied from the AUX control valve 43 to the hydraulic motor 24 (hydraulic actuator) of the sweeper 23 (attachment) via the oil supply and discharge passage 48 and the AUX port 11 (the relevant port among the multiple AUX ports 11; the same applies to "AUX port 11" hereinafter), and the hydraulic fluid is returned from the hydraulic motor 24 to the AUX control valve 43 via the AUX port 11 and the oil supply and discharge passage 49. This causes the hydraulic motor 24 to rotate in the first rotational direction, and the rotating brush 23a rotates in the corresponding direction.

[0108] When the solenoid valve 60 receives the control signal CS1, pilot pressure oil is supplied from the solenoid valve 60 to the pressure-receiving part of the AUX control valve 43 on the lower side in Figure 2 via the pilot oil passage 62, causing the AUX control valve 43 to shift upward in Figure 2.

[0109] As a result, hydraulic fluid is supplied from the AUX control valve 43 to the hydraulic motor 24 (hydraulic actuator) of the sweeper 23 (attachment) via the oil supply and discharge passage 49 and the AUX port 11, and the hydraulic fluid is returned from the hydraulic motor 24 to the AUX control valve 43 via the AUX port 11 and the oil supply and discharge passage 48. This causes the hydraulic motor 24 to rotate in a second rotational direction opposite to the first rotational direction, and the rotating brush 23a rotates in the corresponding direction.

[0110] Here, the rotational speed of the hydraulic motor 24 is determined by the flow rate of hydraulic fluid supplied to the hydraulic motor 24 from the AUX control valve 43 (in the supply and discharge passages 48 and 49). The amount operated by the AUX operation switch 9 represents the set value of the hydraulic fluid flow rate to the hydraulic motor 24, that is, the required flow rate of hydraulic fluid to the hydraulic motor 24.

[0111] Therefore, the control device 26 reads the requested flow rate from the input signal from the AUX operation switch 9 and outputs a control signal CS1 to the solenoid valves 59 and 60 so that the supply flow rate (actual value) of hydraulic fluid from the AUX control valve 43 to the hydraulic motor 24 matches the requested flow rate (set value).

[0112] A bleed-off oil passage 35 branches off from the upstream portion of the discharge oil passage 34 at the point where it branches off to a branch oil passage 36. A flow control valve 39 on the bleed-off oil passage 35 adjusts the flow rate of the hydraulic fluid discharged from the hydraulic pump 31 and flowing through the discharge oil passage 34 until it reaches the branch point of the branch oil passage 36 leading to the lift arm control valve 41. The bleed-off oil passage 35 leads to a reservoir tank 33, and the oil released from the flow control valve 39 is recovered into the reservoir tank 33 via the bleed-off oil passage 35.

[0113] Downstream of the flow control valve 39, the drain oil passage 63 from the tank port of the lift arm control valve 41 is connected to the bleed-off oil passage 35. Furthermore, downstream of the connection point with the drain oil passage 63, the drain oil passage 64 from the tank port of the attachment control valve 42 is connected to the bleed-off oil passage 35. Further downstream of the connection point with the drain oil passage 64, the drain oil passage 65 from the tank port of the AUX control valve 43 is connected to the bleed-off oil passage 35.

[0114] Furthermore, separate flow control valves 40 are also installed between the respective oil supply and discharge passages 44-49 and the bleed-off oil passage 35, which are interposed between the control valves 41, 42, and 43 and the hydraulic actuators (lift arm cylinder 14, attachment cylinder 15, hydraulic motor 24). This allows for adjustment of the flow rate of the hydraulic fluid used to drive the hydraulic actuators flowing through each of the oil supply and discharge passages 44-49.

[0115] Furthermore, a communication oil passage 66 is interposed between the downstream portion of the connection point between the bleed-off oil passage 35 and the drain oil passage 65, and the operating valves 51-54. This allows each control valve 41 It is possible to introduce the oil flow in the bleed-off oil passage 35, which is formed by the confluence of oil discharged from tank ports 42 and 43 and oil released from each flow control valve 39 and 40, to the control valves 51 to 54 via the connecting oil passage 66. Conversely, it is also possible to combine the oil discharged from the control valves 51 to 54 with the oil flow in the bleed-off oil passage 35 via the connecting oil passage 66.

[0116] Furthermore, a connecting oil passage 67 is interposed between the solenoid valves 59 and 60 and the connecting oil passage 66. Through the connecting oil passage 67, oil can be discharged from the solenoid valves 59 and 60 to the connecting oil passage 66, and oil can be introduced from the connecting oil passage 66 to the solenoid valves 59 and 60.

[0117] The hydraulic system 30 includes a load sensing (LS) system 70, which acts as a pump control device that controls the discharge flow rate of the hydraulic pump 31 according to the work performed by the CTL1. More specifically, the LS system 70 sets a predetermined load sensing (LS) differential pressure and controls the discharge flow rate of the hydraulic pump 31 so that the discharge pressure of the hydraulic pump 31 is higher than the maximum load pressure of the working hydraulic actuator by the LS differential pressure.

[0118] The LS system 70 includes pressure compensating valves 71, 72, 73, oil passages 74, 75, 76, flow compensating valve 77, and swashplate control actuator 78.

[0119] Each pressure compensation valve 71, 72, and 73 is fluidly connected to each control valve 41, 42, and 43, respectively. When the hydraulic actuator to which each control valve 41, 42, and 43 is operating, the hydraulic fluid introduced from the discharge oil passage 34 is supplied to the corresponding hydraulic actuator via the pressure compensation valve 71, 72, and 73.

[0120] Depending on the flow rate of the hydraulic fluid through the pressure compensation valves 71, 72, and 73, the maximum load pressure of the hydraulic actuator in question is detected, and pilot pressure oil corresponding to the detected pressure is led to the flow compensation valve 77 via the oil passage 74.

[0121] On the other hand, an oil passage 75 branches off from a discharge oil passage 34 extending from the discharge port of the hydraulic pump 31 (more specifically, the portion upstream of the branching point to the bleed-off oil passage 35 in the discharge oil passage 34), allowing a portion of the hydraulic fluid discharged by the hydraulic pump 31 to be introduced into the flow compensation valve 77 via the oil passage 75.

[0122] The flow compensation valve 77 is fluidly connected to the swash plate control actuator 78 via an oil passage 76. The hydraulic pump 31 is equipped with a movable swash plate 31a. The swash plate control actuator 78 is a hydraulic cylinder, and its piston rod is connected to the movable swash plate 31a. The extension and retraction of this piston rod changes the tilt angle of the movable swash plate 31a, thereby changing the discharge flow rate D of the hydraulic pump 31.

[0123] The flow compensation valve 77 has an LS differential pressure setting spring 77a (hereinafter simply referred to as "spring 77a") that biases the flow compensation valve 77 to its initial position (the position in which the amount of oil supplied to the swashplate control actuator 78 is set to 0). The spring force of spring 77a corresponds to the target load sensing (LS) differential pressure P0 set in the LS system 70.

[0124] The target LS differential pressure P0 is the target value of the differential pressure P3 between the maximum load pressure P1 applied to the hydraulic fluid by each hydraulic actuator 14, 15, and 24 and the discharge pressure P2 of the hydraulic pump 31. In other words, in the hydraulic system 30, it is required that the discharge pressure P2 of the hydraulic pump 31 is always higher than the maximum load pressure P1 by the amount of the target LS differential pressure P0 (P2 = P1 + P0), and the LS system 70 is a system that constantly ensures this required hydraulic state.

[0125] The flow compensation valve 77 is positioned at a location where the differential pressure P3 between the pilot hydraulic pressure from the oil passage 74 corresponding to the maximum load pressure P1 and the hydraulic pressure in the oil passage 75 corresponding to the discharge pressure P2 balances with the spring force of the spring 77a (target LS differential pressure P0), and supplies an amount of oil corresponding to that position to the swash plate control actuator 78.

[0126] The swash plate control actuator 78 extends its piston rod with a stroke corresponding to the amount of oil supplied by the flow compensation valve 77, setting the tilt angle of the movable swash plate 31a to an angle corresponding to that stroke. The hydraulic pump 31 discharges hydraulic fluid at a discharge flow rate D corresponding to the tilt angle of the movable swash plate 31a.

[0127] When the maximum load pressure P1 increases and the differential pressure P3 decreases, the flow compensation valve 77 moves in a direction that increases the amount of oil supplied to the swash plate control actuator 78 due to the biasing force of the spring 77a which exceeds the differential pressure P3. This increases the tilt angle of the movable swash plate 31a and increases the discharge flow rate D, thereby increasing the discharge pressure P2. The tilt angle of the movable swash plate 31a is increased until the biasing force of the spring 77a balances out, that is, until the differential pressure P3 becomes the target LS differential pressure P0.

[0128] When the maximum load pressure P1 decreases and the differential pressure P3 increases, the flow compensation valve 77 moves in a direction that reduces the amount of oil supplied to the swash plate control actuator 78 due to the biasing force of the differential pressure P3 which exceeds the spring force of the spring 77a. This reduces the tilt angle of the movable swash plate 31a and decreases the discharge flow rate D, thereby reducing the discharge pressure P2. The tilt angle of the movable swash plate 31a is reduced until the differential pressure P3 and the biasing force of the spring 77a are balanced, that is, until the differential pressure P3 becomes the target LS differential pressure P0.

[0129] The LS system 70 also allows for adjustment of the target LS differential pressure P0. More specifically, the LS system 70 is structured to adjust the target LS differential pressure P0 according to the rotational speed, load, temperature, etc., of the prime mover 6. This structure will be explained below.

[0130] The flow compensation valve 77 is linked to the pressure regulating actuator 79. The pressure regulating actuator 79 is a hydraulic cylinder, and the oil chamber inside the cylinder is fluidly connected to the reservoir tank 33 via an oil passage 82.

[0131] Furthermore, the piston rod of the pressure adjustment actuator 79, which is a hydraulic cylinder, is connected to the flow compensation valve 77. The extension and retraction of this piston rod changes the position of the flow compensation valve 77 where the spring force of the spring 77a of the flow compensation valve 77 balances the differential pressure P3, thereby changing the target LS differential pressure.

[0132] Meanwhile, a branch oil passage 80 branches off from the discharge oil passage 50 and is connected to an oil passage 82. A solenoid valve 81 is provided on the branch oil passage 80. The solenoid valve 81 is electrically connected to the output interface of the control device 26, and the solenoid of the solenoid valve 81 is energized by receiving a control signal CS2 output from the control device 26.

[0133] The opening degree of the solenoid valve 81 is adjusted according to the control signal CS2, and an amount of oil corresponding to that opening degree is supplied from the solenoid valve 81 to the oil chamber of the pressure regulating actuator 79 via the oil passage 82. The extension stroke of the piston rod of the pressure regulating actuator 79 is determined according to the amount of oil supplied to this oil chamber.

[0134] Furthermore, a line filter 84 is provided above the discharge oil passage 50, and a branch oil passage 80 branches off from the discharge oil passage 50 downstream of the line filter 84. In addition, a flow control valve 83 is fluid-connected to the discharge oil passage 50, which extends from the discharge port of the hydraulic pump 32, and the hydraulic pump The oil discharged from the pump 32 into the discharge oil passage 50 has its flow rate adjusted by the flow control valve 83, and after passing through the line filter 84, a portion of it is diverted to the branch oil passage 80.

[0135] The input interface of the control device 26 is electrically connected to a prime mover speed detection device 85, a temperature detection device 86, and a pair of travel speed setting operation devices 87.

[0136] The prime mover speed detection device 85 detects the output rotational speed of the prime mover 6. The temperature detection device 86 detects temperatures such as the oil temperature of the hydraulic fluid circulating in the hydraulic system 30, the oil temperature of the engine oil if the prime mover 6 is an internal combustion engine, or the water temperature of the cooling water used to cool the prime mover 6, etc.

[0137] The control device 26 receives detection signals (electrical signals) corresponding to the rotational speed detected by the prime mover rotational speed detection device 85, and detection signals (electrical signals) corresponding to the temperature detected by the temperature detection device 86.

[0138] Furthermore, the pair of travel speed setting devices 87 are for setting the travel drive speed of each of the left and right travel devices 5 (more specifically, the output rotation speed of each hydraulic actuator (hydraulic motor, HST, etc.) provided in each travel device 5), and are located inside the cabin 3 and are to be operated by an operator sitting in the driver's seat 7.

[0139] When each travel speed setting device 87 is operated by an operator, an input signal (electrical signal) corresponding to the amount of operation is transmitted to the control device 26. Each travel speed setting device 87 is, for example, a foot pedal, in which case the amount of the pedal is pressed corresponds to the amount of operation.

[0140] The control device 26 determines whether or not it is necessary to change the target LS differential pressure P0 based on the electrical signals input from the prime mover speed detection device 85, the temperature detection device 86, and the pair of travel speed setting operation devices 87, and if it determines that it is necessary to change it, it calculates the amount of change.

[0141] Furthermore, based on the input signals from these input devices 85, 86, and 87, an index (load ratio) representing the engine load state may be calculated, and based on this calculated value, a determination may be made as to whether or not the target LS differential pressure P0 needs to be changed, and the amount of change may be calculated.

[0142] The control device 26 transmits a control signal CS2 corresponding to the calculated change amount to the solenoid of the solenoid valve 81, thereby exciting the solenoid. The solenoid valve 81 opens to an opening amount corresponding to the change amount calculated by the control device 26, and supplies oil from the discharge oil passage 50 to the pressure regulating actuator 79 via the branch oil passage 80 and the oil passage 82.

[0143] In accordance with the amount of oil supplied, the piston rod of the pressure regulating actuator 79 extends, and the position of the flow compensation valve 77 where the spring force of the spring 77a balances the differential pressure P3 is changed according to the amount of extension. In other words, the target LS differential pressure P0 is changed.

[0144] In the hydraulic system 30, the LS system 70 configured as described above functions to increase the discharge flow rate D of the hydraulic pump 31 up to the maximum discharge flow rate Dm in response to an increase in the maximum load pressure, etc., when the required flow rate of hydraulic fluid increases to operate multiple hydraulic actuators, thereby bringing the supply flow rate to each hydraulic actuator closer to their respective required flow rates.

[0145] Furthermore, the hydraulic system 30 includes a special flow rate control system 90 for controlling the flow rate of hydraulic fluid in cases where the sum of the required flow rates of hydraulic fluid to multiple hydraulic actuators exceeds the maximum discharge flow rate, such as when the hydraulic actuators and lift arm cylinders 14 of the attachment are operated simultaneously.

[0146] The following describes a special flow control system 90 that corresponds to the case where the lift arm 10 is raised and lowered while driving the rotating brush 23a of the sweeper 23 as an attachment, with reference to Figures 1 to 5.

[0147] The special flow rate control system 90 uses a control device 26 that outputs control signals CS1 and CS2 to solenoid valves 59 and 60 that control the AUX control valve 43 and to a solenoid valve 81 for changing the target LS differential pressure.

[0148] As shown in Figure 2, the special flow rate control system 90 includes, as input devices for inputting electrical signals to the control device 26, a first requested flow rate detection device 91 for detecting the requested flow rate R1 of hydraulic fluid to the AUX port 11 (hydraulic motor 24), a second requested flow rate detection device 92 for detecting the requested flow rate R2 of hydraulic fluid to the lift arm cylinder 14, a first supply flow rate detection device 93 for detecting the actual supply flow rate Q1 of hydraulic fluid flowing through the supply and discharge oil passages 48 and 49, a second supply flow rate detection device 94 for detecting the actual supply flow rate Q2 of hydraulic fluid flowing through the supply and discharge oil passages 44 and 45, and a discharge flow rate detection device 95 for detecting the actual discharge flow rate of hydraulic fluid from the hydraulic pump 31 flowing through the discharge oil passage 34.

[0149] The first required flow rate detection device 91 measures the amount of operation of the AUX operation switch 9 (or the amount of sliding if it is a slide-type switch), and may overlap with the AUX operation switch 9 shown in Figure 2. The second required flow rate detection device 92 measures the amount of operation of the work operation lever 8 (tilt angle in the front-rear direction), and may be composed of an angle sensor or the like. It may also detect the operating position of the control valves 51 and 52.

[0150] The control device 26 includes a calculation unit 26a and a signal generation unit 26b. The calculation unit 26a calculates the total required flow rate SR and the limited required flow rate R1a, etc., based on the input signals from the detection devices 91 to 95. The signal generation unit 26b generates control signals CS1 and CS2, which are output to one of the solenoid valves 59, 60, or 81, based on the calculated values ​​from the calculation unit 26a.

[0151] More precisely, the term "requested flow rate" includes both the meaning of the requested flow rate set by the operator arbitrarily operating the input device, which is the operating member (operation lever 8, AUX operation switch 9) (referred to as "input requested flow rate"), and the meaning of the requested flow rate corresponding to the control signal (pilot pressure, electrical signal) output for position control of the control valves (lift arm control valve 41, AUX control valve 43) that control the flow rate of hydraulic fluid supplied to the hydraulic actuator (referred to as "output requested flow rate").

[0152] Normally, the output request flow rate, which corresponds to the control signal (pilot pressure, electrical signal) output to the control valve, is matched to the input request flow rate, so it is simply referred to as the "requested flow rate" without any particular distinction. However, in the special flow rate control system 90 according to this embodiment, a control signal CS1 is output that corresponds to a requested flow rate (output request flow rate) that is different from (more specifically, lower than) the requested flow rate (input request flow rate) set by the AUX operation switch 9.

[0153] Therefore, with regard to the control of the supply flow rate Q1 to the hydraulic motor 24, which is fluid-connected to the AUX port 11, the input requested flow rate set by operating the AUX operation switch 9 is simply referred to as "requested flow rate R1," and the output requested flow rate corresponding to the control signal CS1 output from the control device 26 is referred to as "output requested flow rate R1out."

[0154] First, let's explain the situations that the special flow rate control system 90 can handle. When the CTL1 is performing cleaning work on roads, etc., it attaches the sweeper 23 to the work device 4, positions the left and right pair of lift arms 10 in the lowest position as shown in Figure 1, and drives the left and right pair of traveling devices 5 while rotating the rotating brushes 23a of the sweeper 23 attached to the front ends of the left and right lift arms 10 with the ground in contact with the ground.

[0155] As the CTL1 performs cleaning operations, it is sometimes necessary to raise the lift arm 10 for changing direction, etc. However, there are also cases where it is not desirable to stop the rotation of the rotating brush 23a so that cleaning operations can be resumed immediately after the change of direction, etc., is completed and the lift arm 10 is lowered.

[0156] This applies when the AUX operation switch 9 is set to ON so that the rotating brush 23a rotates at a certain speed, and the operator tilts the work operation lever 8 backward. In other words, this is the case when a requested flow rate (input requested flow rate) R1 greater than zero is set according to the amount of operation of the AUX operation switch 9, and a requested flow rate (input requested flow rate) R2 greater than zero is set according to the amount of operation of the work operation lever 8 (rearward tilt angle from the neutral position).

[0157] In this case, the hydraulic fluid discharged from the discharge oil passage 34 by the hydraulic pump 31 is distributed and supplied at equal pressure to the control valves 41 and 43 via the branch oil passages 36 and 38. The lift arm control valve 41 supplies hydraulic fluid at a flow rate equal to the required flow rate R2 to the lift arm cylinder 14, and the AUX control valve 43 supplies hydraulic fluid at a flow rate equal to the required flow rate R1 to the hydraulic motor 24 of the sweeper 23 via the AUX port 11.

[0158] Specifically, the lift arm control valve 41 controls the supply flow rate Q2 of hydraulic fluid to both lift arm cylinders 14 to be equal to the requested flow rate R2 by pilot pressure from the operating valves 51 and 52, and the AUX control valve 43 sets the output requested flow rate R1out, which corresponds to the control signal CS1 to the solenoid valves 59 and 60, to be equal to the requested flow rate (input requested flow rate) R1 set by the AUX operating switch 9, and controls the supply flow rate Q1 of hydraulic fluid to the hydraulic motor 24 to be equal to the requested flow rate R1 by pilot pressure from the solenoid valves 59 and 60 controlled by this control signal CS1.

[0159] However, if the total required flow rate SR, which is the sum of the required flow rates R1 and R2, exceeds the maximum discharge flow rate Dm of the hydraulic pump 31, the flow rate of hydraulic fluid supplied from the discharge oil passage 34 to each control valve 41 and 43 will be insufficient. As a result, the supply flow rate Q2 from the lift arm control valve 41 to the lift arm cylinder 14 will fall below the required flow rate R2, and the supply flow rate Q1 from the AUX control valve 43 to the hydraulic motor 24 will fall below the required flow rate R1.

[0160] To avoid this situation, the special flow rate control system 90 readjusts the required flow rate for the hydraulic actuator with lower priority among the simultaneously operating hydraulic actuators to a value lower than the required flow rate set by the corresponding operating member, thereby reducing the flow rate supplied to that hydraulic actuator, and ensuring that the flow rate supplied to the hydraulic actuator with higher priority meets the required flow rate.

[0161] If the sweeper 23 is in operation, as described above, this corresponds to the situation when the lift arm 10 is raised for a change of direction or the like while the rotating brush 23a is being driven. In this case, the lift arm 10 is required to rise at the speed requested by the operator, while the rotating brush 23a is not used while the lift arm 10 is rising, so it does not need to rotate at the drive speed required during operation.

[0162] Therefore, the supply flow rate Q1 to the hydraulic motor 24 is reduced, and the supply flow rate Q2 to the lift arm cylinder 14 is increased accordingly to approach or reach the required flow rate R2.

[0163] Furthermore, when the supply flow rate Q1 to the hydraulic motor 24 decreases, the flow rate of hydraulic fluid from the discharge oil passage 34 to the branch oil passage 38 decreases. As a result, the flow rate of hydraulic fluid supplied from the discharge oil passage 34 to the lift arm control valve 41 via the branch oil passage 36, which is connected to the discharge oil passage 34 in parallel with the branch oil passage 38, naturally increases, and the supply flow rate Q2 of hydraulic fluid from the lift arm control valve 41 to the lift arm cylinder 14 also naturally increases to approach the required flow rate R2 (or until it reaches the required flow rate R2).

[0164] One method for reducing the supply flow rate Q1 is to shift the AUX control valve 43 in a direction that reduces the supply flow rate Q1 by reducing the value (duty ratio, etc.) of the control signal CS1 to the solenoid valves 59 and 60 that control the AUX control valve 43. In other words, the output request flow rate R1out, which corresponds to the control signal CS1, is temporarily reduced to a value lower than the request flow rate (input request flow rate) R1 set by the AUX operation switch 9.

[0165] Here, using Figure 3, we will explain the decrease pattern of the output request flow rate R1out from the requested flow rate R1 to the limited requested flow rate R1a, corresponding to the case where the total requested flow rate SR, which is the sum of the requested flow rates R1 and R2, exceeds the maximum discharge flow rate Dm, as well as the change in the supply flow rate Q1 accompanying the decrease in the output request flow rate R1out, and the resulting increase in the supply flow rate Q2 to the lift arm cylinder 14.

[0166] Figure 3 shows the changes over time in the output request flow rate R1out, the individual supply flow rates Q1 and Q2, and the total supply flow rate SQ (sum of supply flow rates Q1 and Q2) as line graphs with time T (unit: seconds, for example) on the horizontal axis and flow rate Q (unit: ml, for example) on the vertical axis. The change in the output request flow rate R1out is shown with a dashed line, and the changes in the individual supply flow rates Q1 and Q2, and the total supply flow rate SQ are shown with solid lines. For the sake of illustration and explanation, it is assumed that the requested flow rate R1 set by the operation lever 8 and the requested flow rate R2 set by the AUX operation switch 9 are equal in value.

[0167] When the total required flow rate SR, which is the sum of the required flow rates R1 and R2, exceeds the maximum discharge flow rate Dm, initially, the supply flow rate Q1 is insufficient to reach the required flow rate R1. R1 Only a small amount is lacking, and the supply flow rate Q2 is insufficient to reach the required flow rate R2. R2 Assume there is a shortage of only L. In this case, the shortage of flow rate until the total supply flow rate SQ, which is equal to the maximum discharge flow rate Dm, reaches the total required flow rate SR is L R1 and L R2 The sum of (L R1 +L R2 )

[0168] In this state, the control device 26 compares the total requested flow rate SR, which is the sum of the requested flow rates R1 and R2, with the maximum discharge flow rate Dm in the calculation unit 26a, for example, at time T 10 If it is determined that the total required flow rate SR exceeds the maximum discharge flow rate Dm, a limited required flow rate R1a is calculated, which is less than or equal to the difference (Dm-R2) between the maximum discharge flow rate Dm of the hydraulic pump 31 and the required flow rate R2 set for the lift arm cylinder 14.

[0169] The control device 26 initially generates, in the signal generation unit 26b, a control signal CS1 corresponding to an output required flow rate R1out equal to the required flow rate R1, and outputs the control signal CS1 to the solenoid valve 59 or the solenoid valve 60. After calculating the limited required flow rate R1a, the output required flow rate R1out is gradually decreased to the limited required flow rate R1a (that is, over a certain period of time (the time from time point T0 to time point T3 in FIG. 3)), and in response to the decrease in this output required flow rate R1out, the control signal CS1 output to the solenoid valve 59 or the solenoid valve 60 is changed accordingly.

[0170] In response to the change in the control signal CS1 corresponding to the decrease in this output required flow rate R1out, the spool of the AUX control valve 43 gradually moves in the direction of decreasing the supply flow rate Q1. Note that when the output required flow rate R1out is less than the required flow rate R1 by the shortage flow rate L R1 and equal to the initial actual supply flow rate Q1 (R1 - L R1 ), until it decreases (from time point T 10 to time point T 11 ), the supply flow rates Q1 and Q2 remain at their initial values (R1 - L ), (R2 - L R1 ), (R2 - L R2 ).

[0171] And when the output required flow rate R1out further decreases and becomes lower than the initial value (R1 - L R1 ) of the supply flow rate Q1 (after time point T1), as the spool of the AUX control valve 43 moves in response to the decrease in this output required flow rate R1out, the supply flow rate Q1 decreases.

[0172] As described above, due to the structure in which the branch oil paths 36 and 38 are connected in parallel to the discharge oil path 34, the hydraulic oil with the maximum discharge flow rate Dm in the discharge oil path 34 is shared by the lift arm control valve 41 and the AUX control valve 43. Therefore, the supply flow rate Q2 of the hydraulic oil from the lift arm control valve 41 to the lift arm cylinder 14 increases by the amount by which the supply flow rate Q1 from the AUX control valve 43 to the hydraulic motor 24 decreases. Note that the supply flow rate Q2 has room for an increase by the shortage flow rate L R2 until it reaches the required flow rate R2.

[0173] As the output request flow rate R1out decreases further, and the supply flow rate Q1 decreases due to the movement of the spool of the AUX control valve 43, the supply flow rate Q2 increases further, until eventually the supply flow rate Q1 decreases to a value equal to the difference between the maximum discharge flow rate Dm and the request flow rate R2 (Dm-R2) (time T in Figure 3). 12 At this point, the supply flow rate Q2 reaches the required flow rate R2. Thereafter, hydraulic fluid at a supply flow rate Q2 equal to the required flow rate R2 is supplied to the lift arm cylinder 14, and the lift arm 10 rises at the speed set by the work operation lever 8.

[0174] In this embodiment, since the limited required flow rate R1a is set to a value smaller than the difference between the maximum discharge flow rate Dm and the required flow rate R2 (Dm-R2), the supply flow rate Q2 equal to the required flow rate R2 is supplied to the lift arm cylinder 14 from time T 12 (After) the decrease in the requested output flow rate R1out until the limited requested flow rate R1a (at time T 13 The supply flow rate Q1 will continue to decrease until [date / time].

[0175] After the requested output flow rate R1out reaches the limited requested flow rate R1a (at time T) 13 After this, the hydraulic motor 24 continues to be supplied with hydraulic fluid at a supply flow rate Q1 equal to the limited required flow rate R1a. That is, as long as the operating position (operating state) of the work operation lever 8 and the AUX operation switch 9 is maintained and the required flow rates R1 and R2 are maintained at the set values, the lift arm cylinder 14 is supplied with hydraulic fluid at a supply flow rate Q2 equal to the required flow rate R2, and the lift arm 10 continues to operate at the speed desired by the operator, while the hydraulic motor 24 is supplied with hydraulic fluid at a supply flow rate Q1 equal to the limited required flow rate R1a, which is lower than the required flow rate R1, and the rotating brush 23a continues to rotate at a reduced rotational speed.

[0176] As described above, by shifting the AUX control valve 43 in a direction that reduces the supply flow rate Q1, the lift arm cylinder 14 is supplied with hydraulic fluid at or near the required flow rate R2 from the lift arm control valve 41, and the lift arm 10 rises at or near the speed set by the work operation lever 8. While the lift arm 10 is rising, the rotating brush 23a of the sweeper 23 continues to rotate, but its rotational speed decreases as the supply flow rate Q1 decreases.

[0177] Furthermore, when reducing the supply flow rate Q1, it is not necessarily required to reduce it to a level that brings the supply flow rate Q2 to the required flow rate R2. For example, if the supply flow rate Q1 is gradually reduced, the supply flow rate Q2 will also gradually increase, and the lift arm 10 may reach the target position before the required flow rate R2 is reached. At that point, the further reduction of the supply flow rate Q1 may be stopped.

[0178] Furthermore, even if the supply flow rate Q2 does not reach the required flow rate R2, if it is close to it, the worker will be able to... Therefore, it is possible that this may be satisfactory. For example, the limited required flow rate R1a does not have to be set to a low value such as the difference between the maximum discharge flow rate Dm and the required flow rate R2 (Dm-R2). It may be a value lower than the required flow rate R1, and that allows the supply flow rate Q2 to be increased to a value close to the required flow rate R2.

[0179] In other words, if the special flow rate control system 90 determines that the total requested flow rate SR exceeds the maximum discharge flow rate Dm, it may reduce the supply flow rate Q1 so that the supply flow rate Q2 approaches the requested flow rate Q2.

[0180] Furthermore, the reduction in the actual supply flow rate Q1 from the sweeper 23 to the hydraulic motor 24 has the effect of increasing the actual supply flow rate Q2 to the lift arm cylinder 14 to reach the required flow rate R2, as well as improving the durability of the pressure compensation valve 73 connected to the AUX control valve 43.

[0181] In other words, if the supply flow rate Q1 remains high, that much hydraulic fluid will pass through the pressure compensation valve 73, causing the pressure compensation valve 73 to overheat and thus reducing its durability. However, by reducing the actual supply flow rate Q1, the amount of hydraulic fluid passing through the pressure compensation valve 73 is also reduced, and the overheating of the pressure compensation valve 73 is suppressed.

[0182] As mentioned above, the special flow rate control system 90 reduces the output request flow rate R1out from the requested flow rate R1 to the limited request flow rate R1a over a certain period of time (i.e., gradually), thereby reducing the supply flow rate Q1 of hydraulic fluid to the AUX port 11 (reducing the rotational speed of the rotating brush 23a of the sweeper 23) over a certain period of time (i.e., gradually).

[0183] This is because a sudden decrease in the supply flow rate Q1 could cause the rotating brush 23a to suddenly slow down, which the operator might interpret as an abnormality (malfunction) of the sweeper 23, potentially leading to errors such as unnecessarily stopping the operation of the CLT1.

[0184] The decrease pattern of the output request flow rate R1out from the requested flow rate R1 to the limited request flow rate R1a can be, for example, a decrease at a constant rate (decrease amount per unit time). In Figure 3, this decrease pattern of the output request flow rate R1out is represented by a sloping straight line graph with a constant slope. Furthermore, it can be seen that the decrease in supply flow rate Q1, the increase in supply flow rate Q2, and the change (decrease) in total supply flow rate SQ resulting from the decrease in the output request flow rate R1out are also represented by sloping straight lines with a constant slope.

[0185] Alternatively, the requested output flow rate R1out can be gradually reduced from the requested flow rate R1 to the limited requested flow rate R1a. If the change in the requested output flow rate R1out in this case is graphed with time T on the horizontal axis and flow rate Q on the vertical axis, as in Figure 3, it will result in a stepped line graph (a dashed line graph in Figure 4), as shown in Figure 4.

[0186] Furthermore, as with Figure 3, Figure 4 also shows the changes in each supply flow rate Q1, Q2, and the total supply flow rate SQ (sum of supply flow rates Q1 and Q2) in response to the change in the output demand flow rate R1out. It can be seen that these changes resulting from the gradual decrease in the output demand flow rate R1out (decrease in supply flow rate Q1, increase in supply flow rate Q2, and decrease in total supply flow rate SQ) are also represented by a stepped line (solid line graph in Figure 4).

[0187] In other words, in the embodiment shown in Figure 4, the point in time T is determined to be when the total required flow rate SR exceeds the maximum discharge flow rate Dm. 20 The output request flow rate R1out gradually decreases in stages. The gradually decreasing output request flow rate R1out becomes equal to the initial actual supply flow rate Q1 (R1-L R1 Until it reaches ), both the supply flow rates Q1 and Q2 will remain at their initial values ​​(R1-L R1 ), (R2-L R2 )of It remains the same.

[0188] The supply flow rate Q1 is the initial value of the supply flow rate Q1 (R1-L) when the output request flow rate R1out is equal to the supply flow rate Q1. R1 The stage where the value decreases to a lower value than (time point T) 21 As a result, the spool of the AUX control valve 43 moves, causing the supply flow rate Q1 to decrease to a lower value. This decrease in supply flow rate Q1 causes the supply flow rate Q2 to increase to a higher value. Thereafter, as the output request flow rate R1out decreases in stages, the supply flow rate Q1 decreases in stages, and as a result, the supply flow rate Q2 increases in stages.

[0189] Eventually, the output request flow rate R1out decreases to the limited request flow rate R1a (time T). 22 At this point, the supply flow rate Q1 decreases to the limited required flow rate R1a, and consequently, the supply flow rate Q2 increases to reach the required flow rate Q2. Thereafter, as long as the required flow rates R1 and R2 remain set, the lift arm cylinder 14 continues to be supplied with hydraulic fluid at a supply flow rate Q2 equal to the required flow rate R2, and the hydraulic motor 24 continues to be supplied with hydraulic fluid at a supply flow rate Q1 equal to the limited required flow rate R1a, which is lower than the required flow rate R1.

[0190] In this embodiment, by reducing the supply flow rate Q1 in stages as described above, for example, without calculating and setting a limited required flow rate R1a, it is possible to gradually reduce the supply flow rate Q1 by checking whether the supply flow rate Q2 has reached the required flow rate R2 after a certain period of time has elapsed while supplying hydraulic fluid at a certain amount of supply flow rate Q1, and if it has not reached the required flow rate R2, reducing the supply flow rate Q1 to a lower value and continuing to supply hydraulic fluid at that value for a certain period of time, and if it has reached the required flow rate R2, stopping any further reduction of the supply flow rate Q1.

[0191] The graph of the output request flow rate R1out shown in Figure 3 or Figure 4 may be used as the map for the control device 26 to generate the control signal CS1 in the signal generation unit 26b. Alternatively, such a map may be stored in a memory unit configured within the control device 26 or in a memory device attached to (or remotely connected to) the control device 26.

[0192] The lift arm 10 is swung upward to raise the sweeper 23. After completing the desired operation, such as changing direction, the operator operates the work operation lever 8 to retract the piston rod of the lift arm cylinder 14, lowering the lift arm 10 to the lowest position shown in Figure 1, and bringing the rotating brush 23a of the sweeper 23 to the ground. When the rotating brush 23a touches the ground, or immediately before or after, the control device 26 returns the rotation speed of the rotating brush 23a to the speed originally set by the AUX operation switch 9, and resumes the cleaning operation by the CTL1.

[0193] Furthermore, the return of the rotational speed of the rotating brush 23a does not need to be done gradually (over time), as is the case when the rotational speed of the rotating brush 23a decreases while the lift arm 10 is swinging upward. Instead, it may be quickly returned to its original speed just before the rotating brush 23a touches the ground, when it is installed, or immediately after it touches the ground. In other words, the output request flow rate R1out corresponding to the control signal CS1 transmitted from the control device 26 to the solenoid valves 59 and 60 may be quickly changed from the limited request flow rate R1a to the request flow rate R1.

[0194] Furthermore, the increase in the supply flow rate Q1 in this case does not necessarily have to reach the required flow rate R1; it is sufficient if it at least approaches the required flow rate R1.

[0195] Furthermore, the reduction in the supply flow rate Q1 to bring the supply flow rate Q2 closer to the required flow rate R2 does not necessarily have to be done gradually (over a certain period of time).

[0196] The flowchart in Figure 5 shows the flow control process in the special flow control system 90 described above. This flowchart will now be explained. Note that the flowchart in Figure 5 is based on the assumption of application to the flow control process shown in Figure 3, but the contents of the steps will be explained later. By appropriately modifying the parameters or skipping steps, this method can also be applied to flow rate control processes such as the one shown in Figure 4.

[0197] First, the control device 26 determines whether a value greater than 0 is set as the required flow rate R1 to the hydraulic motor 24 based on the input signal from the AUX operation switch 9 (S01). If a value greater than 0 is set as the required flow rate R1 (S01, YES), the control device 26 further determines whether a value greater than 0 is set as the required flow rate R2 to the lift arm cylinder 14 for the upward swing of the lift arm 10 by detecting the rearward tilt angle of the work operation lever 8, the opening degree of the operation valve 51, or the flow rate of the pilot pressure oil flowing through the pilot oil passage 55 (S02).

[0198] If a requested flow rate R2 greater than 0 is set (S02, YES), the control device 26 compares the total requested flow rate SR, which is the sum of the requested flow rates R1 and R2, with the maximum discharge flow rate Dm of the hydraulic pump 31 (S03).

[0199] If the total required flow rate SR is less than or equal to the maximum discharge flow rate Dm (S03, YES), hydraulic fluid at a supply flow rate Q1 equal to the required flow rate R1 is supplied to the hydraulic motor 24, and hydraulic fluid at a supply flow rate Q2 equal to the required flow rate R2 is supplied to the lift arm cylinder 14 (S04).

[0200] If the total requested flow rate SR exceeds the maximum discharge flow rate Dm (S03, NO), the calculation unit 26a calculates a limited requested flow rate R1a that is less than or equal to the difference between the maximum discharge flow rate Dm and the requested flow rate R2, and sets this as the target value for the output requested flow rate R1out (S05).

[0201] Once the limited required flow rate R1a is determined, the output required flow rate R1out, which corresponds to the control signal CS1 to the solenoid valves 59 and 60, is (preferably gradually) reduced from a value equal to the initial required flow rate R1 to the limited required flow rate R1a (S06).

[0202] This decrease in the requested output flow rate R1out means that the AUX control valve 43 moves (shifts) in the direction of decreasing the supply flow rate Q1. Eventually, the requested output flow rate R1out decreases to a certain extent (specifically, to a value corresponding to the difference between the maximum discharge flow rate Dm and the requested flow rate R2 (Dm-R2)), and as the requested output flow rate R1out is further decreased from there, the supply flow rate Q1 from the AUX control valve 43 to the hydraulic motor 24 decreases (preferably gradually), and the supply flow rate Q2 from the lift arm control valve 41 to the lift arm cylinder 14 increases by that amount (S07).

[0203] In other words, the supply flow rate Q2 increases as the output request flow rate R1out decreases, so the decrease in the output request flow rate R1out continues at least until the supply flow rate Q2 reaches the request flow rate R2 (S08, NO) (S09).

[0204] After the supply flow rate Q2 to the lift arm cylinder 14 reaches the required flow rate R2 (S08, YES), that is, while the lift arm 10 is swinging upward at the speed set by the work operation lever 8, the supply flow rate Q1 to the hydraulic motor 24, which has been decreasing, reaches the limited required flow rate R1a, the decrease stops, and hydraulic fluid at a supply flow rate Q1 equal to the limited required flow rate R1a continues to be supplied to the hydraulic motor 24 (S09). In other words, the rotating brush 23a of the sweeper 23 continues to rotate at a low speed.

[0205] Subsequently, if it is confirmed that the total requested flow rate SR (sum of requested flow rates R1 and R2) is less than or equal to the maximum discharge flow rate Dm, for example by rotating the operation lever 8 towards the neutral position (S08, YES), the supply flow rate Q1 to the hydraulic motor 24 is returned to a value equal to the requested flow rate R1 (S04). This is achieved by returning the output requested flow rate R1out to a value equal to the requested flow rate R1.

[0206] As shown in Figure 5, the flowchart can be modified in various ways, including changing the steps or skipping steps.

[0207] For example, in step S05 of the flowchart in Figure 5, the value of the limited required flow rate R1a does not necessarily have to be a low value such as the difference between the maximum discharge flow rate Dm and the required flow rate R2 (Dm-R2). It can be a value lower than the required flow rate R1 that can actually cause a decrease in the supply flow rate Q1 (in this embodiment, (R1-L R1 It is sufficient if the value is less than ).

[0208] Alternatively, steps S05 and S09 may be skipped. That is, instead of setting a limited required flow rate R1a, the supply flow rate Q1 may be gradually reduced while observing the increasing state of the supply flow rate Q2, for example, as described in relation to the flow rate control process in Figure 4.

[0209] Furthermore, step S08 may be skipped. That is, as mentioned above, if the total required flow rate SR exceeds the maximum discharge flow rate Dm, it is not necessarily required to increase the supply flow rate Q2 until it reaches the required flow rate R2; it may be increased at least to approach the required flow rate R2.

[0210] Similarly, when the total required flow rate SR exceeds the maximum discharge flow rate Dm and the special flow rate control system 90 reduces the supply flow rate Q1, and then the total required flow rate SR falls below the maximum discharge flow rate Dm, it is not necessarily required to increase the supply flow rate Q1 until it reaches the required flow rate R1; it may be increased to at least approach the required flow rate R1.

[0211] In the special flow rate control system 90 configured as described above, the output request flow rate R1out, which is reduced in order to increase the supply flow rate Q2 to the requested flow rate R2, corresponds to the control signal CS1 output from the control device 26 to the solenoid valves 59 and 60 that control the flow of pilot pressure oil to the AUX control valve 43, which is a pilot hydraulic directional control valve, as described above.

[0212] In other words, the hydraulic system 30 in Figure 2 is equipped with a special flow rate control system 90 that reduces the supply flow rate Q1 in order to bring the supply flow rate Q2 to the required flow rate R2. The special flow rate control system 90 consists of a control device 26 (calculation unit 26a, signal generation unit 26b), which is a flow rate control device for matching the supply flow rate Q1 to the AUX port 11 (hydraulic motor 24) to the required flow rate R1; input devices 91 to 95 electrically connected to the control device 26; and solenoid valves 59, 60 and an AUX control valve 43, which are output devices electrically connected to the control device 26.

[0213] However, other flow control systems can be conceivable that reduce the supply flow rate Q1 in order to bring the supply flow rate Q2 to (or approach) the required flow rate R2. Figures 6 and 7 show alternative examples.

[0214] In the hydraulic system 30A shown in Figure 6, instead of the pilot-operated hydraulic AUX control valve 43 that supplies hydraulic fluid to the AUX port 11, an AUX control valve 96, which is a solenoid valve, is provided. The AUX control valve 96 has solenoids on both sides of the spool, instead of the pressure-receiving parts on both sides of the spool of the AUX control valve 43.

[0215] In the hydraulic system 30A shown in Figure 6, the solenoid valves 59 and 60 for supplying pilot pressure oil are unnecessary and are not directed to them. Instead, the output interface of the control device 26 and both solenoids of the AUX control valve 96 are electrically connected.

[0216] Apart from the points mentioned above, the structure of hydraulic system 30A is the same as that of hydraulic system 30 in Figure 2. Furthermore, the hydraulic actuator 30A is equipped with a special flow rate control system 90A that reduces the supply flow rate Q1 in order to bring the supply flow rate Q2 to reach (or approach) the required flow rate R2. The special flow rate control system 90A consists of a control device 26 (calculation unit 26a, signal generation unit 26b), input devices 91 to 95 electrically connected to the control device 26, and an AUX control valve 96 which serves as an output device electrically connected to the control device 26.

[0217] Normally, the control device 26 outputs a control signal CS1a to the solenoid of the AUX control valve 96, which corresponds to the output request flow rate R1out, equal to the request flow rate R1 set by the AUX operation switch 9.

[0218] Furthermore, when the upward swing (rise) of the lift arm 10 and the rotational drive of the rotating brush 23a of the sweeper 23 are performed simultaneously, if the total required flow rate SR (sum of required flow rates R1 and R2) exceeds the maximum discharge flow rate Dm, the control signal CS1a output from the control device 26 to the solenoid of the AUX control valve 96 is changed.

[0219] This change in the control signal CS1a corresponds to, for example, gradually decreasing the output request flow rate R1out from the requested flow rate R1 to the limited request flow rate R1a, as shown in Figure 3, or decreasing the output request flow rate R1out from the requested flow rate R1, as shown in Figure 4.

[0220] This change in the control signal CS1a causes the AUX control valve 96 (or its spool) to shift in a direction that reduces the supply flow rate Q1 to the AUX port 11, thereby actually decreasing the supply flow rate Q1. Consequently, the supply flow rate Q2 from the lift arm control valve 41 to the lift arm cylinder 14 increases to reach the required flow rate R2.

[0221] As described above, in the special flow rate control systems 90 and 90A shown in Figures 2 and 6, the AUX control valves 43 and 96, which are basically controlled to supply hydraulic fluid at a supply flow rate Q1 equal to the required flow rate R1 set by the AUX operation switch 9 to the AUX port 11 (and the connected hydraulic actuator), are also used as valves that are controlled when reducing the supply flow rate Q1 in order to bring the supply flow rate Q2 to the required flow rate R2. In other words, the control device 26, which controls the position of the AUX flow control valves 43 and 96 in order to match the supply flow rate Q1 to the required flow rate R1, is configured to bring the supply flow rate Q2 closer to the required flow rate R2 by changing the position of the AUX flow control valves 43 and 96 in order to decrease the supply flow rate Q1.

[0222] In contrast, the embodiment shown in Figure 7 includes a valve that is controlled separately from the AUX control valve 43 (or AUX control valve 96) to reduce the supply flow rate Q1 for that purpose.

[0223] In other words, the hydraulic system 30B shown in Figure 7 includes a variable throttle 97 on the supply / discharge oil passage 48 or supply / discharge oil passage 49 (in this embodiment, the supply / discharge oil passage 48) interposed between the AUX control valve 43 (or AUX control valve 96) and the AUX port 11 as a component of the special flow rate control system 90B that responds when the total required flow rate SR exceeds the maximum discharge flow rate Dm. The variable throttle 97 may also be provided on both supply / discharge oil passages 48 and 49.

[0224] In the hydraulic system 30B shown in Figure 7, the special flow rate control system 90B has a control device 26, similar to the special flow rate control systems 90 and 90A, and also has input devices 91 to 95 connected to the control device 26.

[0225] In the hydraulic system 30B, the AUX control valve 43(96) is controlled by the control device 26 to a position where it discharges hydraulic fluid at a supply flow rate Q1 equal to the requested flow rate R1 set by the AUX operation switch 9, regardless of whether the total requested flow rate SR is less than or equal to the maximum discharge flow rate Dm.

[0226] On the other hand, in the special flow rate control system 90B, the variable aperture 97 is electrically connected to the output interface of the control device 26, and the aperture degree of the variable aperture 97 is controlled by the control device 26.

[0227] As long as the calculation unit 26a of the control device 26 determines that the total requested flow rate SR is less than or equal to the maximum discharge flow rate Dm, the variable throttle 97 is set to a throttle degree of 0 (i.e., fully open), allowing the hydraulic fluid equivalent to the total flow rate (i.e., a supply flow rate Q1 equal to the requested flow rate R1) discharged from the AUX control valve 43 to the hydraulic motor 24 to pass through.

[0228] Then, when the calculation unit 26a of the control device 26 determines that the total requested flow rate SR exceeds the maximum discharge flow rate Dm, it calculates a limited requested flow rate R1a, which is less than or equal to the difference between the maximum discharge flow rate Dm and the requested flow rate R2, similar to the control device 26 of the special flow rate control systems 90 and 90A. It then gradually increases the aperture (gradually decreases the opening) so as to gradually reduce the supply flow rate Q1 to the limited requested flow rate R1a (or gradually reduce the supply flow rate Q1 so that the supply flow rate Q2 approaches the requested flow rate R2 without setting a limited requested flow rate R1a). For this reason, the signal generation unit 26b generates a control signal CS3 to control the aperture of the variable aperture 97 and outputs it to the variable aperture 97.

[0229] In the special flow rate control system 90B shown in Figure 7, a control device 26 is used to control the position of the AUX control valves 43 and 96 in order to generate a control signal CS3 that controls the aperture degree of the variable aperture 97 and output it to the variable aperture 97. However, in this embodiment, even while the control signal CS3 is output to the variable aperture 97 to reduce the supply flow rate Q1, the control device 26 controls the AUX control valves 43 and 96 to a position where the supply flow rate Q1 matches the required flow rate R1.

[0230] Therefore, in the special flow rate control system 90B, a flow rate control device for controlling the variable aperture 97 may be provided separately from the control device 26. In this case, the flow rate control device for controlling the variable aperture 97 may be connected to input devices similar to the input devices 91 to 95 described above, and the flow rate control device may also be equipped with a calculation unit that calculates the total required flow rate SR, the limited required flow rate R1a, etc., based on the input signals from these input devices, and a signal generation unit for generating the control signal CS3, etc.

[0231] Furthermore, as shown in Figure 7, when the special flow rate control system 90B uses the control device 26, the control device 26 can implement the process of reducing the supply flow rate Q1 simply by obtaining a program for a simple control process, such as controlling the aperture degree of the variable aperture 97.

[0232] Furthermore, in the flow control systems 90 and 90A, it is not always necessary to use the control device 26 that controls the position of the AUX control valves 43 and 96 so that the supply flow rate Q1 matches the required flow rate R1, in order to change the position of the AUX control valves 43 and 96 in order to reduce the supply flow rate Q1 to a lower value than the required flow rate R1. In addition, a separate control device may be provided that controls the position of the AUX control valves 43 and 96 to further reduce the supply flow rate Q1 to a lower value than the required flow rate R1 if it is determined that the total required flow rate SR exceeds the total discharge flow rate Dm.

[0233] The following describes the effects obtained from the various features of the hydraulic systems 30, 30A, and 30B of the aforementioned work machines.

[0234] The hydraulic systems 30, 30A, and 30B of the CTL (Compact Track Loader) 1 (work equipment) include a hydraulic pump 31, a hydraulic motor 24 (first hydraulic actuator) operated by the hydraulic fluid discharged from the hydraulic pump 31, a lift arm cylinder 14 (second hydraulic actuator) operated by the hydraulic fluid discharged from the hydraulic pump 31, an AUX operation switch 9 (first operating member) that can be operated to set the required flow rate R1 (first required flow rate), a work operation lever 8 (second operating member) that can be operated to set the required flow rate R2 (second required flow rate), and a flow rate that matches the required flow rate R1 set by operating the AUX operation switch 9. The system includes a control device 26 (first flow rate control device) that controls the supply flow rate Q1 (first supply flow rate) of hydraulic fluid to the hydraulic motor 24, a flow rate control device 27 (second flow rate control device) that controls the supply flow rate Q2 (second supply flow rate) of hydraulic fluid to the lift arm cylinder 14 to match the required flow rate R2 set by the operation of the work lever 8, and special flow rate control systems 90, 90A, and 90B that, when it is determined that the total required flow rate SR, which is the sum of the required flow rate R1 and the required flow rate R2, exceeds the maximum discharge flow rate Dm, which is the maximum flow rate of hydraulic fluid that the hydraulic pump 31 can discharge, reduce the supply flow rate Q1 to bring the supply flow rate Q2 closer to the required flow rate R2.

[0235] With the above configuration, for example, a CTL1 (work implement) equipped with a sweeper 23 will achieve the following effects. In other words, when the AUX operation switch 9 (first operating member) for driving the rotating brush 23a of the sweeper 23 and the work operation lever 8 (second operating member) for rotating the lift arm 10 up and down are operated simultaneously, and the total required flow rate SR exceeds the maximum discharge flow rate Dm, the supply flow rate Q1 (first supply flow rate) of hydraulic fluid to the hydraulic motor 24 (first hydraulic actuator) for driving the rotating brush 23a and the supply flow rate Q2 (second supply flow rate) of hydraulic fluid to the lift arm cylinder 14 (second hydraulic actuator) for driving the lift arm 10 will both fall short of their respective required flow rates R1 and R2 (first required flow rate, second required flow rate). This avoids a situation where both the rotating brush 23a and the lift arm 10 will have insufficient driving speed. For the higher-priority lift arm cylinder 14, the supply flow rate Q2 is brought closer to the required flow rate R2, thereby ensuring operation at the desired speed or a speed close to the desired speed. On the other hand, for the hydraulic motor 24, which has a lower priority, the supply flow rate Q1 is kept low, thereby reducing the load on the components related to driving the hydraulic motor 24 in the hydraulic systems 30, 30A, and 30B, and improving their durability.

[0236] When the special flow rate control systems 90, 90A, and 90B determine that the total requested flow rate SR exceeds the maximum discharge flow rate Dm, they set a limited requested flow rate R1a that is lower than the requested flow rate R1, and reduce the supply flow rate Q1 to the limited requested flow rate R1a, thereby bringing the supply flow rate Q2 closer to the requested flow rate R2.

[0237] With the above configuration, the supply flow rate Q1 is reduced to a limited required flow rate R1a, which is set to a value lower than the required flow rate R1. As a result, the supply flow rate Q2 can reliably approach the required flow rate R2.

[0238] When the special flow rate control systems 90, 90A, and 90B determine that the total requested flow rate SR exceeds the maximum discharge flow rate Dm, they set a limited requested flow rate R1a, which is less than or equal to the difference between the maximum discharge flow rate Dm and the requested flow rate R2 (Dm-R2), and reduce the supply flow rate Q1 to the limited requested flow rate R1a, thereby bringing the supply flow rate Q2 closer to the requested flow rate R2.

[0239] With the above configuration, the supply flow rate Q1 is reduced to a limited required flow rate R1a, which is set to a value less than or equal to the difference between the maximum discharge flow rate Dm and the required flow rate R2 (Dm-R2). As a result, the supply flow rate Q2 can be reliably brought closer to the required flow rate R2.

[0240] The special flow rate control systems 90, 90A, and 90B, after a requested flow rate R1 has been set and a requested flow rate R2 has been set, if they determine that the total requested flow rate SR exceeds the maximum discharge flow rate Dm, reduce the supply flow rate Q1 to bring the supply flow rate Q2 closer to the requested flow rate R2.

[0241] The above configuration can be applied, for example, to a CTL1 (work machine) equipped with a sweeper 23, when the AUX operation switch 9 is turned ON to rotate the rotating brush 23a and the CTL1 is being driven while the sweeper 23 is cleaning the ground, and the operator operates the work operation lever 8 to raise the lift arm 10 in order to change direction. In other words, by applying the above configuration, after the AUX operation switch 9 is turned ON to set the requested flow rate R1 (first requested flow rate) to the hydraulic motor 24, and then the operator operates the work operation lever 8 to set the requested flow rate R2 (second requested flow rate) to the lift arm cylinder 14, the control device 26 compares the total requested flow rate SR, which is the sum of the requested flow rates R1 and R2, with the maximum discharge flow rate Dm of the hydraulic pump 31. If it determines that the total requested flow rate SR exceeds the maximum discharge flow rate Dm, it reduces the supply flow rate Q1 to the hydraulic motor 24, which has a lower priority because the sweeper 23 does not perform cleaning work while the lift arm 10 is rotating upward, and brings the supply flow rate Q2 to the lift arm cylinder 14 closer to the requested flow rate R2. As a result, the lift arm 10 rises at the speed desired by the operator or a speed close to the desired speed, enabling a smooth change of direction of the CLT 1.

[0242] The special flow rate control systems 90, 90A, and 90B, when they determine that the total required flow rate SR exceeds the maximum discharge flow rate Dm, gradually reduce the supply flow rate Q1 to bring the supply flow rate Q2 closer to the required flow rate R2.

[0243] With the above configuration, by gradually reducing the supply flow rate Q1, it is possible to avoid situations where a sudden decrease in the supply flow rate Q1 causes a sudden drop in the rotation speed of the rotating brush 23a, leading the operator to mistakenly believe that the sweeper 23 is malfunctioning and stop the operation of the CTL1. In other words, it is possible to prevent operator errors caused by confusion.

[0244] The special flow rate control systems 90, 90A, and 90B, when they determine that the total required flow rate SR exceeds the maximum discharge flow rate Dm, gradually reduce the supply flow rate Q1 at a constant rate, thereby bringing the supply flow rate Q2 closer to the required flow rate R2.

[0245] With the above configuration, the supply flow rate Q1 decreases continuously at a constant rate, so even when the rotational speed of the rotating brush 23a decreases, the phenomenon of sudden drops in speed from time to time does not occur, further enhancing the effect that the operator does not notice the decrease in the rotational speed of the rotating brush 23a.

[0246] When the special flow rate control systems 90, 90A, and 90B determine that the total required flow rate SR exceeds the maximum discharge flow rate Dm, they gradually reduce the supply flow rate Q1, which is less than the required flow rate R1, to an even lower value, thereby bringing the supply flow rate Q2 closer to the required flow rate R2.

[0247] With the above configuration, for example, after a certain amount of hydraulic fluid has been supplied at a constant supply flow rate Q1 for a certain period of time, it is checked whether the supply flow rate Q2 has reached the required flow rate R2, and if it has not, the supply flow rate Q1 is lowered by one level and the supply of hydraulic fluid at that value is continued for a certain period of time, thereby gradually reducing the supply flow rate Q1.

[0248] The special flow rate control systems 90, 90A, and 90B, after the total requested flow rate SR exceeds the maximum discharge flow rate Dm, increase the supply flow rate Q1, which had been reduced, to bring it closer to the requested flow rate R1 when the AUX operation switch 9 or the work operation lever 8 is operated and it is determined that the total requested flow rate SR has fallen below the maximum discharge flow rate Dm.

[0249] The above configuration is applicable, for example, to a CTL1 (work machine) equipped with a sweeper 23, when, as described above, the rotating brush 23a is rotated at a low speed while the lift arm 10 is raised to change direction, and then the operation lever 8 is operated to lower the lift arm 10 and lower the sweeper 23 to the ground to resume cleaning work. That is, the supply flow rate Q1, which was reduced while the lift arm 10 was being raised when the total required flow rate SR exceeded the maximum discharge flow rate Dm, is increased to the required flow rate R1 as soon as the operation lever 8 is operated to lower the lift arm 10 and the total required flow rate SR becomes less than or equal to the maximum discharge flow rate Dm, so that the rotating brush 23a can be set immediately after the sweeper 23 is lowered to the ground again by operating the AUX operation switch 9. It rotates at a fixed speed or a speed close to it, allowing the sweeper 23 to resume cleaning.

[0250] The hydraulic systems 30, 30A, and 30B are further equipped with an LS system 70 (pump control device) for controlling the flow rate D of the hydraulic fluid discharged from the hydraulic pump 31. The LS system 70 controls the hydraulic pump 31 so that the discharge pressure P2 of the hydraulic fluid discharged from the hydraulic pump 31 is higher than the maximum load pressure P1 of the hydraulic motor 24 and the lift arm cylinder 14 by a set load sensing differential pressure P0.

[0251] With the above configuration, when the hydraulic motor 24 and lift arm cylinder 14 (multiple hydraulic actuators) are driven simultaneously as described above, if the total required flow rate SR is less than or equal to the maximum discharge flow rate Dm, the LS system 70 (pump control device) can increase the discharge flow rate D of the hydraulic pump 31 up to the maximum discharge flow rate Dm. By ensuring a discharge flow rate D equal to or greater than the total required flow rate SR, it is possible to supply both hydraulic actuators 24 and 14 with hydraulic fluid at supply flow rates Q1 and Q2 equal to their respective required flow rates D1 and D2. In other words, in hydraulic systems 30, 30A, and 30B, the LS system 70 is responsible for controlling the discharge flow rate D when the total required flow rate SR is less than or equal to the maximum discharge flow rate Dm, and the special flow rate control system 90 is responsible for controlling the supply flow rates Q1 and Q2 when the total required flow rate SR exceeds the maximum discharge flow rate Dm.

[0252] The hydraulic systems 30, 30A, and 30B further include a pressure compensation valve 73 for compensating the set hydraulic pressure for the hydraulic fluid supplied to the hydraulic motor 24 (first hydraulic actuator).

[0253] With the above configuration, by reducing the supply flow rate Q1 to the hydraulic motor 24, the flow rate of hydraulic fluid passing through the pressure compensation valve 73 can be reduced accordingly, thereby suppressing the overheating of the pressure compensation valve 73 and improving the durability of the pressure compensation valve 73.

[0254] The hydraulic systems 30 and 30A further include a discharge oil passage 34 through which hydraulic fluid discharged from a hydraulic pump 31 flows, a branch oil passage 38 (first branch oil passage) branching off from the discharge oil passage 34, AUX control valves 43 and 96 (first control valves) that can be operated to supply the hydraulic fluid supplied from the discharge oil passage 34 via the branch oil passage 38 to the hydraulic motor 24, a branch oil passage 36 (second branch oil passage) branching off from the discharge oil passage 34 in parallel with the branch oil passage 38, and a lift arm control valve 41 (second control valve) that can be operated to supply the hydraulic fluid supplied from the discharge oil passage 34 via the branch oil passage 36 to the lift arm cylinder 14. The control device 26 controls the position of the AUX control valves 43 and 96 so that the supply flow rate Q1 matches the required flow rate R1. The flow rate control device 27 controls the position of the lift arm control valve 41 so that the supply flow rate Q2 matches the required flow rate R2. When the special flow rate control systems 90 and 90A determine that the total requested flow rate SR exceeds the maximum discharge flow rate Dm, the flow rate control device 27 holds the lift arm control valve 41 in a position that matches the supplied flow rate Q2 to the requested flow rate R2. At the same time, the control device 26 changes the position of the AUX control valves 43 and 96 to gradually decrease the supplied flow rate Q1, which is less than the requested flow rate R1, to an even lower value, thereby bringing the supplied flow rate Q2 closer to the requested flow rate R2.

[0255] With the above configuration, the AUX control valves 43 and 96 (first control valve) and the lift arm control valve 41 (second control valve), which are connected in parallel to the discharge oil passage 34 via branch oil passages 38 and 36, share the hydraulic fluid in the discharge oil passage 34 (the hydraulic fluid in the discharge oil passage 34 is distributed). Therefore, when the total required flow rate SR exceeds the maximum discharge flow rate Dm, both the supply flow rate Q1 to the hydraulic motor 24 and the supply flow rate Q2 to the lift arm cylinder 14 become insufficient compared to their respective required flow rates R1 and R2. In such a situation, reducing the supply flow rate Q1 causes the supply flow rate Q2 to naturally increase so as to approach the required flow rate R2. Consequently, when the total required flow rate SR exceeds the maximum discharge flow rate Dm, the flow control device 27 (second flow control device) remains in its normal state of controlling the position of the lift arm control valve 41 to match the supply flow rate Q2 to the required flow rate R1, and only the control device 26 needs to be specially configured to reduce the supply flow rate Q1. In other words, when multiple hydraulic actuators are driven simultaneously, a hydraulic system can be constructed at a low cost that does not experience a shortage (or a serious shortage) of the required flow rate to the high-priority hydraulic actuator.

[0256] In the hydraulic system 30, the AUX control valve 43 is positioned by receiving pilot pressure oil. The control device 26 controls the supply of pilot pressure oil to the AUX control valve 43.

[0257] With the above configuration, if, for example, all control valves for each hydraulic actuator in the hydraulic system 30, including the AUX control valve 43, are pilot-pressure controlled control valves, the control device 26 only needs to be configured to gradually reduce the supply flow rate Q1, which is less than the required flow rate R1, when the total required flow rate SR exceeds the maximum discharge flow rate Dm, thereby providing the present invention at low cost without adding any special new components.

[0258] The hydraulic system 30 further includes solenoid valves 59 and 60 that supply pilot pressure oil to the AUX control valve 43. The control device 26 outputs a control signal CS1 for controlling the opening degree of the solenoid valves 59 and 60.

[0259] With the above configuration, the supply control of pilot pressure oil to the AUX control valve 43 can be changed by changing the electrical signal CS1, which is the control signal to the solenoid valves 59 and 60. In other words, in order to gradually reduce the supply flow rate Q1, which is less than the required flow rate R1, when the total required flow rate SR exceeds the maximum discharge flow rate Dm, it is only necessary to perform a simple action such as changing the program of the control device 26 to change the control signal CS1, and the present invention can be provided at low cost without adding any special new components.

[0260] In the hydraulic system 30A, the AUX control valve 96 is a solenoid valve, and the control device 26 outputs a control signal CS1a to the AUX control valve 96 to control the excitation of the solenoid.

[0261] With the above configuration, since the AUX control valve 96, whose position is controlled to control the supply flow rate Q1 to the hydraulic motor 24, is a solenoid valve, the control device 26 only needs to output the control signal CS1a, which is an electrical signal for position control of the AUX control valve 96, directly to the AUX control valve 96. As mentioned above, there is no need to provide a separate solenoid valve, such as the solenoid valves 59 and 60 for controlling the supply of pilot pressure oil, thus reducing the number of components and leading to simplification and compactness of the hydraulic system.

[0262] The special flow rate control system 90B is equipped with a variable throttle 97 in the supply and discharge passage 48 through which the hydraulic fluid supplied to the hydraulic motor 24 flows. When the special flow rate control system 90B determines that the total required flow rate SR exceeds the maximum discharge flow rate Dm, it increases the throttle degree of the variable throttle 97 to reduce the supply flow rate Q1, thereby bringing the supply flow rate Q2 closer to the required flow rate R2.

[0263] With the above configuration, by simply providing a variable throttle 97 in the supply and discharge passage 48 through which the hydraulic fluid supplied to the hydraulic motor 24 flows, it is possible to easily provide a configuration in which the supply flow rate Q1 is reduced when the total required flow rate SR exceeds the maximum discharge flow rate Dm, thereby bringing the supply flow rate Q2 to the required flow rate R2.

[0264] The hydraulic system 30B includes a discharge oil passage 34 through which the hydraulic fluid discharged from the hydraulic pump 31 flows, a branch oil passage 38 (first branch oil passage) branching off from the discharge oil passage 34, and a discharge oil passage 38 through the branch oil passage 38. The system further includes AUX control valves 43 and 96 (first control valves) supplied with hydraulic fluid from the oil passage 34 and whose position is controlled by the control device 26 to control the supply flow rate Q1, a branch oil passage 36 (second branch oil passage) branching from the discharge oil passage 34 in parallel with the branch oil passage 38, and a lift arm control valve 41 (second control valve) supplied with hydraulic fluid from the discharge oil passage 34 via the branch oil passage 36 and whose position is controlled by the flow rate control device 27 to control the supply flow rate Q2. The control device 26 controls the position of the AUX control valves 43 and 96 so that the supply flow rate Q1 matches the required flow rate R1. The flow rate control device 27 controls the position of the lift arm control valve 41 so that the supply flow rate Q2 matches the required flow rate R2. When the special flow rate control system 90B determines that the total requested flow rate SR exceeds the maximum discharge flow rate Dm, the flow rate control device 27 holds the lift arm control valve 41 in a position that matches the supplied flow rate Q2 to the requested flow rate R2, and the control device 26 holds the AUX control valve 43 (96) in a position that matches the supplied flow rate Q1 to the requested flow rate R1. While doing so, the system increases the throttling degree of the variable throttle 97 to decrease the supplied flow rate Q1, thereby bringing the supplied flow rate Q2 closer to the requested flow rate R2.

[0265] With the above configuration, the AUX control valves 43 and 96 (first control valve) and the lift arm control valve 41 (second control valve), which are connected in parallel to the discharge oil passage 34 via branch oil passages 38 and 36, share the hydraulic fluid in the discharge oil passage 34 (the hydraulic fluid in the discharge oil passage 34 is distributed). Therefore, when the total required flow rate SR exceeds the maximum discharge flow rate Dm, both the supply flow rate Q1 to the hydraulic motor 24 and the supply flow rate Q2 to the lift arm cylinder 14 become insufficient compared to their respective required flow rates R1 and R2. In such a situation, reducing the supply flow rate Q1 causes the supply flow rate Q2 to naturally increase so as to approach the required flow rate R2. Furthermore, by reducing the supply flow rate Q1 through the control of the variable throttle 97, the position control of the AUX control valves 43 and 96 only needs to be controlled to a position where the supply flow rate Q1 matches the required flow rate R1, thus simplifying the control of the AUX control valves 43 and 96.

[0266] The above is the description of the present invention. However, it should be considered that all the disclosed embodiments are illustrative and not restrictive in all respects. The scope of the present invention is defined not by the above description but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

Description of Reference Numerals

[0267] 1: CLT (Compact Track Loader) (working machine) 4: Working device 8: Working operation lever (second operating member) 9: AUX operation switch (first operating member) 10: Lift arm 11: AUX port (hydraulic oil extraction port) 14: Lift arm cylinder (second hydraulic actuator) 23: Sweeper 24: Hydraulic motor (first hydraulic actuator) 26: Control device (first flow control device) 27: Flow control device (second flow control device) 30: Hydraulic system 30A: Hydraulic system 30B: Hydraulic system 31: Hydraulic pump 34: Discharge oil passage 36: Branch oil passage (second branch oil passage) 38: Branch oil passage (first branch oil passage) 41: Lift arm control valve (second control valve) 43: AUX control valve (first control valve) 48: Supply and discharge oil passage 51: Operation valve 52: Operation valve 59: Solenoid valve 60: Solenoid valve 70: Load sensing (LS) system (pump control device) 73: Pressure compensation valve 96: AUX control valve (first control valve) 97: Variable aperture D:Discharge flow rate Dm: Maximum discharge flow rate Q1: Supply flow rate (1st supply flow rate) Q2: Supply flow rate (second supply flow rate) R1:Required flow rate (1st required flow rate) R2:Required flow rate (second required flow rate) SR: Total requested flow rate (sum of the first and second requested flow rates)

Claims

1. Hydraulic pump and A first hydraulic actuator that operates using hydraulic fluid discharged from the hydraulic pump, A second hydraulic actuator operated by hydraulic fluid discharged from the aforementioned hydraulic pump, A first operating member that can be operated to set a first requested flow rate, A second operating member that can be operated to set a second required flow rate, A first flow rate control device controls a first supply flow rate, which is the flow rate of hydraulic fluid supplied to the first hydraulic actuator, to match the first requested flow rate set by the operation of the first operating member. A second flow control device controls the second supply flow rate, which is the flow rate of hydraulic fluid supplied to the second hydraulic actuator, to match the second requested flow rate set by the operation of the second operating member, A special flow control system comprising: a first requested flow rate detection device for detecting the first requested flow rate; a second requested flow rate detection device for detecting the second requested flow rate; a first supply flow rate detection device for detecting the first supply flow rate of hydraulic fluid supplied to the first hydraulic actuator; a second supply flow rate detection device for detecting the second supply flow rate of hydraulic fluid supplied to the second hydraulic actuator; and a discharge flow rate detection device for detecting the discharge flow rate of hydraulic fluid discharged from the hydraulic pump, The special flow rate control system is From the point in time when it is determined that the total requested flow rate, which is the sum of the first requested flow rate and the second requested flow rate, exceeds the maximum discharge flow rate, which is the maximum flow rate of hydraulic fluid that can be discharged by the hydraulic pump as detected by the discharge flow rate detection device, until a predetermined period has elapsed, the first supply flow rate is maintained at a flow rate that is one deficiency flow rate smaller than the first requested flow rate, and the second supply flow rate is maintained at a flow rate that is two deficiencies smaller than the second requested flow rate. A hydraulic system for a work machine that, after the predetermined period has elapsed, reduces the first supply flow rate to bring the second supply flow rate closer to the second requested flow rate.

2. The hydraulic system for a work machine according to claim 1, wherein the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, sets a limited requested flow rate lower than the first requested flow rate, and after a predetermined period has elapsed, reduces the first supply flow rate to the limited requested flow rate, thereby bringing the second supply flow rate closer to the second requested flow rate.

3. The hydraulic system for a work machine according to claim 1, wherein the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, sets a limited requested flow rate that is less than or equal to the difference between the maximum discharge flow rate and the second requested flow rate, and after the predetermined period has elapsed, reduces the first supply flow rate to the limited requested flow rate, thereby bringing the second supply flow rate closer to the second requested flow rate.

4. The hydraulic system for a work machine according to claim 1, wherein the special flow rate control system, after the first requested flow rate is set and the second requested flow rate is set, determines that the total requested flow rate exceeds the maximum discharge flow rate, and after the predetermined period has elapsed, further reduces the first supply flow rate, which is less than the first requested flow rate, to an even lower value, thereby bringing the second supply flow rate closer to the second requested flow rate.

5. The hydraulic system for a work machine according to claim 1, wherein the special flow rate control system, after the first requested flow rate is set and the second requested flow rate is set, determines that the total requested flow rate exceeds the maximum discharge flow rate, and after the predetermined period has elapsed, reduces the first supply flow rate to bring the second supply flow rate closer to the second requested flow rate.

6. The hydraulic system for a work machine according to claim 1, wherein the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, and after a predetermined period of time has elapsed, gradually reduces the first supply flow rate to bring the second supply flow rate closer to the second requested flow rate.

7. The hydraulic system for a work machine according to claim 1, wherein the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, and after a predetermined period has elapsed, gradually reduces the first supply flow rate at a constant rate of decrease, thereby bringing the second supply flow rate closer to the second requested flow rate.

8. The hydraulic system for a work machine according to claim 1, wherein the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, and after a predetermined period of time has elapsed, gradually reduces the first supply flow rate in stages to bring the second supply flow rate closer to the second requested flow rate.

9. The hydraulic system for a work machine according to claim 1, wherein the special flow rate control system, after the total requested flow rate exceeds the maximum discharge flow rate, determines that the total requested flow rate has become less than or equal to the maximum discharge flow rate when the first operating member or the second operating member is operated, increases the first supply flow rate, which had been reduced, to bring it closer to the first requested flow rate.

10. The system further includes a pump control device for controlling the flow rate of hydraulic fluid discharged from the hydraulic pump, The hydraulic system for a work machine according to claim 1, wherein the pump control device controls the hydraulic pump such that the discharge pressure of the hydraulic fluid discharged from the hydraulic pump is higher than the maximum load pressure of the first hydraulic actuator and the second hydraulic actuator by a set load sensing differential pressure.

11. The hydraulic system for a work machine according to claim 10, further comprising a pressure compensation valve for compensating the hydraulic pressure set for the hydraulic fluid supplied to the first hydraulic actuator.

12. A discharge oil passage through which the hydraulic fluid discharged from the aforementioned hydraulic pump flows, A first branch oil passage that branches off from the aforementioned discharge oil passage, A first control valve that can be operated to supply the hydraulic fluid supplied from the discharge oil passage via the first branch oil passage to the first hydraulic actuator, A second branch oil passage branches off from the discharge oil passage in parallel with the first branch oil passage, The system further includes a second control valve that can be operated to supply the hydraulic fluid supplied from the discharge oil passage via the second branch oil passage to the second hydraulic actuator, The first flow rate control device controls the position of the first control valve so that the first supply flow rate matches the first requested flow rate. The second flow rate control device controls the position of the second control valve so that the second supply flow rate matches the second requested flow rate. The hydraulic system for a work machine according to claim 1, wherein when the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, the second flow rate control device holds the second control valve in a position that makes the second supply flow rate match the second requested flow rate, and while the second flow rate control device holds the second control valve in a position that makes the second supply flow rate match the second requested flow rate, the first flow rate control device changes the position of the first control valve to decrease the first supply flow rate, thereby bringing the second supply flow rate closer to the second requested flow rate.

13. The first control valve is positioned by receiving pilot pressure oil, The hydraulic system for a work machine according to claim 12, wherein the first flow rate control device controls the supply of the pilot pressure oil to the first control valve.

14. The first control valve is further provided with a solenoid valve that supplies the pilot pressure oil, The hydraulic system for a work machine according to claim 13, wherein the first flow rate control device outputs a control signal for controlling the opening degree of the solenoid valve.

15. The first control valve is a solenoid valve, The hydraulic system for a work machine according to claim 12, wherein the first flow rate control device outputs a control signal to the first control valve for controlling the excitation of the solenoid.

16. The special flow rate control system includes a variable throttle provided in the oil passage through which the hydraulic fluid supplied to the first hydraulic actuator flows, The hydraulic system for a work machine according to claim 1, wherein the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, and the first flow rate control device increases the degree of throttling of the variable throttle to reduce the first supply flow rate after a predetermined period has elapsed, thereby bringing the second supply flow rate closer to the second requested flow rate.

17. A discharge oil passage through which the hydraulic fluid discharged from the aforementioned hydraulic pump flows, A first branch oil passage that branches off from the aforementioned discharge oil passage, A first control valve that can be operated to supply the hydraulic fluid supplied from the discharge oil passage via the first branch oil passage to the first hydraulic actuator, A second branch oil passage branches off from the discharge oil passage in parallel with the first branch oil passage, The system further includes a second control valve that can be operated to supply the hydraulic fluid supplied from the discharge oil passage via the second branch oil passage to the second hydraulic actuator, The first flow rate control device controls the position of the first control valve so that the first supply flow rate matches the first requested flow rate. The second flow rate control device controls the position of the second control valve so that the second supply flow rate matches the second requested flow rate. When the special flow rate control system determines that the total requested flow rate exceeds the maximum discharge flow rate, the second flow rate control device holds the second control valve in a position that matches the second supply flow rate to the second requested flow rate, and while the first flow rate control device holds the first control valve in a position that matches the first supply flow rate to the first requested flow rate, the degree of throttling of the variable throttle is increased to decrease the first supply flow rate, thereby reducing the second supply flow rate to the second requested flow rate. A hydraulic system for a work machine according to claim 16 that brings it closer to [the desired state].

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