Work machine, control method, and controller

Abstract

In the present invention, a controller executes processing for increasing the amount of hydraulic oil flowing into a oil discharge passage or the amount of hydraulic oil supplied from a hydraulic pump to a first actuator when there is a possibility that the hydraulic oil flowing into at least one of one or more actuators from the oil discharge passage via an oil suction passage becomes insufficient along with the deceleration of the actuator.

Description

Work machine, control method, and controller

[0001] The present disclosure relates to a work machine, a control method, and a controller. This application claims priority from Japanese Patent Application No. 2024-169250 filed in Japan on September 27, 2024, the content of which is incorporated herein by reference.

[0002] Work machines driven by hydraulic pressure using hydraulic oil are known (see, for example, Patent Document 1).

[0003] International Publication No. 2006 / 123704

[0004] In a work machine driven by hydraulic pressure, by closing the valves on the inflow side and outflow side of the hydraulic oil, the actuator being driven can be stopped. On the other hand, when trying to decelerate a moving actuator, the larger its inertial mass and moment of inertia, the more difficult it is to decelerate. The actuator during deceleration moves by inertia. At this time, the pressure on the outflow side of the actuator becomes higher than the pressure on the inflow side, and the actuator draws in hydraulic oil from the inflow side and pushes out hydraulic oil from the outflow side. This phenomenon can occur regardless of whether the actuator is a hydraulic motor or a hydraulic cylinder. For example, when the actuator is a hydraulic motor, the hydraulic motor behaves like a hydraulic pump. Since the volumetric efficiency of a hydraulic pump is less than 100%, the hydraulic oil flowing out of the actuator is less than the hydraulic oil flowing into the actuator. Therefore, as a means to supply the insufficient hydraulic oil, the work machine includes a discharge oil passage maintained at a constant pressure by a back pressure valve and through which the hydraulic oil discharged from a plurality of actuators and bleed valves passes, and a suction oil passage that sucks the hydraulic oil from the discharge oil passage into the inflow side of each actuator. The actuator can secure the hydraulic oil during inertial movement by sucking the hydraulic oil from the discharge oil passage into the inflow side through the suction oil passage.

[0005] However, the amount of hydraulic fluid flowing through the discharge passage varies depending on the operating state of other actuators, which may result in insufficient hydraulic fluid for actuators moving by inertia. When hydraulic fluid is insufficient, the hydraulic fluid in the tank flows back through the back pressure valve and into the actuator via the discharge and suction passages. At this time, the pressure of the hydraulic fluid flowing into the actuator decreases, which may cause abnormal noise from the actuator, and cavitation may also occur due to the pressure drop. Thus, insufficient hydraulic fluid flowing into a decelerating actuator is undesirable. The object of this disclosure is to provide a work machine, a control method, and a controller that can prevent insufficient hydraulic fluid flowing into a decelerating actuator.

[0006] According to one aspect of the present invention, the work machine comprises at least one hydraulic pump, one or more actuators driven by hydraulic fluid discharged by the hydraulic pump, a discharge oil passage for discharging hydraulic fluid from the one or more actuators, a back pressure valve for adjusting the pressure of the discharge oil passage, a suction oil passage provided in a first actuator which is at least one of the one or more actuators, connecting the discharge oil passage to the inlet side of the first actuator and suppressing the flow of hydraulic fluid from the inlet side of the first actuator to the discharge oil passage, and a controller, wherein the controller performs a process to increase the amount of hydraulic fluid flowing into the discharge oil passage or the amount of hydraulic fluid supplied from the hydraulic pump to the first actuator when there is a possibility that the amount of hydraulic fluid flowing into the first actuator will be insufficient due to the deceleration of at least one of the one or more actuators.

[0007] According to the above embodiment, the working machine can prevent a shortage of hydraulic fluid flowing into the decelerating actuator.

[0008] This is a perspective view showing the configuration of a work machine according to the first embodiment. This is a schematic block diagram showing the configuration of a drive system according to the first embodiment. This is a schematic block diagram showing the configuration of a control device according to the first embodiment. This is a flowchart showing a method for predicting a target flow rate after a certain period of time according to the first embodiment. This is a flowchart showing a method for determining a target flow rate of a hydraulic pump according to the first embodiment. This is a diagram showing an example of a hydraulic circuit for a slewing motor and other actuators according to the first embodiment. This is a flowchart showing cavitation prevention according to the first embodiment. This is a diagram showing an example of a hydraulic circuit for a slewing motor and other actuators according to the second embodiment. This is a schematic block diagram showing the configuration of a computer according to at least one embodiment.

[0009] <First Embodiment> <Configuration of the Working Machine> The embodiment will be described in detail below with reference to the drawings. Figure 1 is a perspective view showing the configuration of the working machine 1 according to the first embodiment. The working machine 1 according to the first embodiment is a hydraulic excavator.

[0010] The work machine 1 comprises a traveling body 110, a rotating body 120, a work implement 130, a driver's cab 140, and a machine room 150. The work machine 1, which is a hydraulic excavator, excavates and levels soil and other materials at work sites. The traveling body 110 and the rotating body 120 constitute the vehicle body.

[0011] The vehicle body 110 supports the work machine 1 so that it can move. The vehicle body 110 has a pair of left and right tracks 111. The work machine 1 moves forward, turns, or moves backward by the rotation of the pair of tracks 111. Hereinafter, the drive motor 112 for driving the right track 111 will be called the first drive motor 112R, and the drive motor 112 for driving the left track 111 will be called the second drive motor 112L.

[0012] The slewing body 120 is supported by the traveling body 110 so that it can rotate. The slewing body 120 rotates relative to the traveling body 110 by a slewing motor 127. The slewing body 120 supports the work equipment 130, the operator's cab 140, and the machine room 150.

[0013] The work machine 130 is movably supported on the body (slewing body 120) of the work machine 1. The work machine 130 comprises a boom 131, an arm 132, and a bucket 133 which is a work tool. The base end of the boom 131 is rotatably attached to the slewing body 120. The base end of the arm 132 is rotatably attached to the tip of the boom 131. The bucket 133 is rotatably attached to the tip of the arm 132.

[0014] The work machine 130 is driven by a plurality of actuators. The plurality of actuators include, for example, a boom cylinder 131C, an arm cylinder 132C, and a bucket cylinder 133C.

[0015] The boom cylinder 131C is a hydraulic cylinder for driving the boom 131. The base end of the boom cylinder 131C is attached to the slewing body 120. The tip end of the boom cylinder 131C is attached to the boom 131. The arm cylinder 132C is a hydraulic cylinder for driving the arm 132. The base end of the arm cylinder 132C is attached to the boom 131. The tip end of the arm cylinder 132C is attached to the arm 132. The bucket cylinder 133C is a hydraulic cylinder for driving the bucket 133. The base end of the bucket cylinder 133C is attached to the arm 132. The tip end of the bucket cylinder 133C is attached to the bucket 133.

[0016] The operator's cab 140 is where the operator of the work machine 1 sits and operates and controls it. The operator's cab 140 is located, for example, on the left side of the front end of the slewing body 120. The operator's cab 140 of the work machine 1 is equipped with a driver's seat 141 for the operator to sit in, an operating device 142 for operating the work machine 1, and a control device 145 for controlling the work machine 1. The operating device 142 is operated by the operator to operate the work machine 1. The operating device 142 outputs an operation signal in response to the operator's operation.

[0017] The control device 145 controls the work machine 1. The control device 145 receives operation signals from the operating device 142. Based on the operation signals from the operating device 142, the control device 145 controls the movement of the traveling body 110, the driving of the work machine 130, and the rotational movement of the rotating body 120.

[0018] The machine room 150 houses the drive system 20, which will be described later. The machine room 150 is located, for example, behind the driver's cab 140. The machine room 150 forms a space for housing the drive system 20.

[0019] 《Configuration of the drive system 20》 Figure 2 is a schematic block diagram showing the configuration of the drive system 20 according to the first embodiment. The drive system 20 includes an engine 121, a front hydraulic pump 122A, a rear hydraulic pump 122B, a front main oil passage 123A, a rear main oil passage 123B, a main connecting oil passage 124, a front control valve 126A, a rear control valve 126B, a swing motor 127, a boom cylinder 131C, an arm cylinder 132C, a bucket cylinder 133C, a first travel motor 112R, and a second travel motor 112L. Hereinafter, the front hydraulic pump 122A and the rear hydraulic pump 122B will be collectively referred to as the hydraulic pump 122. Also, hereafter, the front main oil passage 123A and the rear main oil passage 123B will be collectively referred to as the main oil passage 123. Also, hereafter, the front control valve 126A and the rear control valve 126B will be collectively referred to as the control valve 126.

[0020] The engine 121 is a prime mover that drives the hydraulic pump 122. In the first embodiment, the engine 121 is a diesel engine. Examples of engines 121 in other embodiments may include a gasoline engine or an electric motor. The front hydraulic pump 122A and the rear hydraulic pump 122B are variable displacement pumps driven by the engine 121. The front hydraulic pump 122A supplies hydraulic fluid to the front main oil passage 123A. The rear hydraulic pump 122B supplies hydraulic fluid to the rear main oil passage 123B. The front hydraulic pump 122A is provided with a front swash plate angle sensor 1221A that measures the inclination angle of the swash plate of the front hydraulic pump 122A. The rear hydraulic pump 122B is provided with a rear swash plate angle sensor 1221B that measures the inclination angle of the swash plate of the rear hydraulic pump 122B. Since the capacity of the hydraulic pump 122 is determined by the inclination angle of the swash plate, the control device 145 can determine the discharge amount of the hydraulic pump 122 based on the measurement value of the swash plate angle sensor 1221. Note that the discharge amount of the hydraulic pump 122 also changes depending on the rotational speed in addition to the capacity, so if the work machine 1 according to other embodiments controls the discharge amount of the hydraulic pump 122 by rotational speed, the work machine 1 may be equipped with a sensor that measures the rotational speed of the hydraulic pump 122 instead of the swash plate angle sensor 1221.

[0021] The main oil passage 123 is equipped with a pump discharge pressure sensor 1231 and a bleed valve 1232. The pump discharge pressure sensor 1231 measures the pressure of the hydraulic fluid discharged by the hydraulic pump 122. The bleed valve 1232 discharges the hydraulic fluid supplied when the actuator is not being driven. Even when the actuator is not being driven, the hydraulic pump 122 discharges the minimum flow rate of hydraulic fluid. Hereinafter, the pump discharge pressure sensor 1231 provided in the front main oil passage 123A will also be called the front pump discharge pressure sensor 1231A, and the pump discharge pressure sensor 1231 provided in the rear main oil passage 123B will also be called the rear pump discharge pressure sensor 1231B. Furthermore, the bleed valve 1232 provided in the front main oil passage 123A will also be called the front bleed valve 1232A, and the bleed valve 1232 provided in the rear main oil passage 123B will also be called the rear bleed valve 1232B.

[0022] The main connecting oil passage 124 connects the front main oil passage 123A and the rear main oil passage 123B. The main connecting oil passage 124 is equipped with a main confluence / separation valve 1241. The main confluence / separation valve 1241 is a shut-off valve that controls the opening and closing of the main connecting oil passage 124. This allows the main confluence / separation valve 1241 to switch between confluence or separation of the hydraulic fluid flowing through the front main oil passage 123A and the hydraulic fluid flowing through the rear main oil passage 123B.

[0023] The front control valve 126A is connected to the front main oil passage 123A. The front control valve 126A distributes the hydraulic fluid supplied from the front main oil passage 123A to the swing motor 127, the arm cylinder 132C, and the first travel motor 112R. Hereinafter, the set of the swing motor 127, arm cylinder 132C, and first travel motor 112R connected to the front control valve 126A will also be referred to as the front actuator unit UA. In other embodiments, the front actuator unit UA may consist of a single actuator. The swing motor 127 is provided with a swing load pressure sensor 127P that measures the pressure (load pressure) on the inlet side of the swing motor 127. The arm cylinder 132C is provided with an arm load pressure sensor 132CP that measures the pressure (load pressure) on the inlet side of the arm cylinder 132C. The first travel motor 112R is equipped with a front travel load pressure sensor 112RP that measures the pressure (load pressure) on the inlet side of the first travel motor 112R.

[0024] The rear control valve 126B is connected to the rear main oil passage 123B. The rear control valve 126B distributes the hydraulic fluid supplied from the rear main oil passage 123B to the boom cylinder 131C, the bucket cylinder 133C, and the second travel motor 112L. Hereinafter, the set of boom cylinder 131C, bucket cylinder 133C, and second travel motor 112L connected to the rear control valve 126B will also be referred to as the rear actuator unit UB. In other embodiments, the rear actuator unit UB may consist of a single actuator. The boom cylinder 131C is provided with a boom load pressure sensor 131CP that measures the pressure (load pressure) on the inlet side of the boom cylinder 131C. The bucket cylinder 133C is provided with a bucket load pressure sensor 133CP that measures the pressure (load pressure) on the inlet side of the bucket cylinder 133C. The second travel motor 112L is equipped with a rear travel load pressure sensor 112LP that measures the pressure (load pressure) on the inlet side of the second travel motor 112L. The front control valve 126A or the rear control valve 126B may be equipped with a port that supplies hydraulic fluid to actuators (such as breakers, grapples, and tilt rotators) provided on the work tool (attachment).

[0025] The control valve 126 has a flow control valve 1261 and a pressure compensation valve 1262 for each actuator. The flow control valve 1261 adjusts the flow rate of hydraulic fluid supplied to the corresponding actuator in response to a command from the control device 145. The pressure compensation valve 1262 prevents the hydraulic fluid from being unevenly distributed to the actuators on the low-load side, even if the load pressures of each actuator provided in the same control valve 126 (main oil passage 123) are different. In the first embodiment, the pressure compensation valve 1262 applies a pressure loss to the low-load shaft so that the outlet pressure of the flow control valve 1261 of the low-load actuator becomes equal to the outlet pressure of the flow control valve 1261 of the actuator with the maximum load pressure. As a result, the differential pressure between the inlet and outlet sides of each flow control valve 1261 becomes equal, so that flow rate distribution using the meter-in opening area ratio can be realized. For this reason, the same control valve 126 is provided with an LS (load sensing) oil passage 128 that shares the hydraulic fluid at the outlet of each flow control valve 1261. Each pressure compensation valve 1262 is connected to the LS oil passage 128. This allows the pressure compensation valve 1262 to detect the maximum load pressure. Hereinafter, the LS oil passage 128 of the front control valve 126A will be referred to as the front LS oil passage 128A, and the LS oil passage 128 of the rear control valve 126B will be referred to as the rear LS oil passage 128B. In other embodiments, the pressure compensation valve 1262 may be provided upstream of the flow control valve 1261.

[0026] The LS connecting oil passage 129 connects the front LS oil passage 128A and the rear LS oil passage 128B. The LS connecting oil passage 129 is provided with an LS confluence / separation valve 1291. The LS confluence / separation valve 1291 is a shut-off valve that controls the opening and closing of the LS connecting oil passage 129. This allows the LS confluence / separation valve 1291 to switch between confluence or separation of the hydraulic fluid flowing through the front LS oil passage 128A and the hydraulic fluid flowing through the rear LS oil passage 128B. When the front LS oil passage 128A and the rear LS oil passage 128B confluence, the maximum load pressure of the actuators connected to the front control valve 126A and the actuator connected to the rear control valve 126B is applied to each pressure compensation valve 1262.

[0027] 《Configuration of Control Device 145》 Figure 3 is a schematic block diagram showing the configuration of the control device 145 according to the first embodiment. The control device 145 according to the first embodiment includes a measurement value acquisition unit 51, an operation amount acquisition unit 52, a target flow rate determination unit 53, a pump control unit 54, a valve control unit 55, and a cavitation prevention unit 56.

[0028] The measurement value acquisition unit 51 acquires sensor data indicating the measured values ​​from various sensors (front pump discharge pressure sensor 1231A, rear pump discharge pressure sensor 1231B, slewing load pressure sensor 127P, arm load pressure sensor 132CP, front travel load pressure sensor 112RP, boom load pressure sensor 131CP, bucket load pressure sensor 133CP, rear travel load pressure sensor 112LP). If the front control valve 126A or the rear control valve 126B has a port for supplying hydraulic fluid to the attachment, the work machine 1 may also be equipped with a load pressure sensor for the attachment. The operation amount acquisition unit 52 receives operation commands from the operation device 142 and identifies the operation amount for each actuator. If the work machine 1 has an automatic control function, the operation amount acquisition unit 52 may acquire the operation amount calculated by the automatic control function.

[0029] The target flow rate determination unit 53 determines a target value for the flow rate of hydraulic fluid required to drive each actuator, according to the manipulated amount acquisition unit 52.

[0030] The pump control unit 54 controls the swash plate angle of each hydraulic pump 122 based on the target flow rate determined by the target flow rate determination unit 53 and the merging and separation state of the main oil passage 123. The valve control unit 55 controls the opening degree of the flow rate adjustment valve 1261 and the bleed valve 1232 of each control valve 126 based on the target flow rate determined by the target flow rate determination unit 53 and the merging and separation state of the main oil passage 123. The cavitation prevention unit 56 performs control to ensure that hydraulic fluid flows into the slewing motor 127 in order to prevent cavitation from occurring due to the deceleration of the slewing motor 127, based on the target flow rate determined by the target flow rate determination unit 53.

[0031] 《Determination of Target Flow Rate》 The target flow rate determination unit 53 determines the required flow rate corresponding to the operating amount of each actuator based on a conversion table that shows the relationship between the operating amount of each actuator and the required flow rate, which is predetermined. On the other hand, since the discharge amount of the hydraulic pump 122 does not change instantaneously, it takes time for the flow rate of the hydraulic fluid to reach the required flow rate. Therefore, the target flow rate determination unit 53 predicts the target value of the flow rate in the actuator unit U after a certain period of time, based on the current transient target flow rate and the steady-state target flow rate. The certain period of time is the time equivalent to the response delay of the controlled equipment.

[0032] Figure 4 is a flowchart showing the method for predicting the target flow rate after a certain period of time according to the first embodiment. The target flow rate determination unit 53 predicts the target flow rate after a certain period of time for each actuator unit U and each actuator in the following procedure.

[0033] The target flow rate determination unit 53 obtains the manipulated amount of each actuator from the manipulated amount acquisition unit 52 and determines the required flow rate for each actuator from the acquired manipulated amounts according to a predetermined conversion table (step S1). The target flow rate determination unit 53 determines whether the sum of the required flow rates of the actuators is greater than the sum of the maximum flow rates of the hydraulic pump 122, or the total upper limit flow rate of the actuator unit U obtained by dividing the upper limit horsepower of the multiple actuators by the pump discharge pressure (step S2). The pump discharge pressure used in calculating the total upper limit flow rate of the actuator unit U is determined based on the measured value of the pump discharge pressure sensor 1231. If the sum of the required flow rates of the actuators is greater than the sum of the maximum flow rates of the hydraulic pump 122 or the total upper limit flow rate (step S2: YES), the target flow rate determination unit 53 determines a target value for the required flow rate of each actuator so that its sum matches the sum of the maximum flow rates of the hydraulic pump 122 or the total upper limit flow rate, while maintaining the ratio of the required flow rates of each actuator (step S3). If the sum of the requested flow rates of the actuators is less than or equal to the sum of the maximum flow rates of the hydraulic pumps 122 and the total upper limit flow rate (step S2: NO), the target flow rate determination unit 53 determines the requested flow rate obtained in step S1 as the target value for the requested flow rate of each actuator (step S4).

[0034] The target flow rate determination unit 53 performs the following steps S5 to S8 for each of the front main oil passage 123A and the rear main oil passage 123B. First, the target flow rate determination unit 53 determines the target flow rate for the next calculation cycle based on the current target flow rate and the target required flow rate identified in step S3 or step S4 (step S5). Specifically, the target flow rate determination unit 53 determines the target flow rate after one calculation cycle by adding the current target flow rate to a value obtained by applying a predetermined filter to the difference between the current target flow rate and the target required flow rate. The filter may be, for example, a low-pass filter or a limiter that limits the rate of change. By applying a filter to the difference between the current target flow rate and the target required flow rate, the target flow rate determination unit 53 can prevent abrupt changes in the target flow rate. Next, the target flow rate determination unit 53 estimates the target flow rate for the next calculation cycle (the nth calculation cycle from the current point in time) based on the target flow rate for the next calculation cycle (the nth calculation cycle from the current point in time) and the target required flow rate identified in step S3 or step S4 (step S6). The target flow rate determination unit 53 repeats the calculation in step S6 until the time taken for the n+1th calculation cycle coincides with a time a certain period of time after the current point in time (step S7). If the time taken for the n+1th calculation cycle coincides with a time a certain period of time after the current point in time (step S7: YES), the target flow rate determination unit 53 determines the target flow rate obtained in the n+1th calculation as the target flow rate after the certain period of time (step S8). For example, if one calculation cycle is 10 milliseconds and the certain period of time is 1 second, the target flow rate determination unit 53 can estimate the target flow rate after 1 second by repeating the calculation in step S6 99 times. Hereinafter, the target flow rate value of the front actuator unit UA after a certain period of time will be referred to as target value Tua, and the target flow rate value of the rear actuator unit UB after a certain period of time will be referred to as target value Tub.

[0035] Figure 5 is a flowchart illustrating the method for determining the target flow rate of the hydraulic pump 122 according to the first embodiment. Hereinafter, of the front actuator unit UA and the rear actuator unit UB, the one with the larger target flow rate will be called the first actuator unit U1, and the one with the smaller target flow rate will be called the second actuator unit U2. Also, of the front hydraulic pump 122A and the rear hydraulic pump 122B, the one corresponding to the first actuator unit will be called the first hydraulic pump, and the one corresponding to the second actuator unit will be called the second hydraulic pump. For example, if the target flow rate Qua of the front actuator unit is greater than the target flow rate Qub of the rear actuator unit, then the first actuator unit U1 is the front actuator unit UA, the second actuator unit U2 is the rear actuator unit UB, the first hydraulic pump is the front hydraulic pump 122A, and the second hydraulic pump is the rear hydraulic pump 122B. In this case, the target flow rate of the first actuator unit Qu1 = Qua, and the target flow rate of the second actuator unit Qu2 = Qub.

[0036] The target flow rate determination unit 53 determines whether the target value Qu1 of the flow rate of the first actuator unit, obtained by the process shown in Figure 4, is less than or equal to the flow rate threshold Qt1 (first flow rate threshold) of the first hydraulic pump, and whether the target value Qu2 of the flow rate of the second actuator unit is less than or equal to the flow rate threshold Qt2 (second flow rate threshold) of the second hydraulic pump (step S13). The flow rate threshold Qt may be a value obtained by subtracting a margin based on a predetermined safety factor from the maximum flow rate Qmax of the hydraulic pump 122. For example, the flow rate threshold Qt may be 90% of the maximum flow rate Qmax of the hydraulic pump 122.

[0037] If the target flow rate Qu1 of the first actuator unit is less than or equal to the flow rate threshold Qt1 of the first hydraulic pump and the target flow rate Qu2 of the second actuator unit is less than or equal to the flow rate threshold Qt2 of the second hydraulic pump (step S13: YES), the target flow rate determination unit 53 determines the target flow rate Qp1 of the first hydraulic pump to be the target flow rate Qu1 of the first actuator unit, and determines the target flow rate Qp2 of the second hydraulic pump to be the target flow rate Qu2 of the second actuator unit (step S14).

[0038] If the target flow rate of the first actuator unit exceeds the flow rate threshold of the first hydraulic pump, or if the target flow rate of the second actuator unit exceeds the flow rate threshold of the second hydraulic pump (step S13: NO), the target flow rate determination unit 53 determines whether the main connecting oil passage 124 is in a merged state or not (step S15). If the main connecting oil passage 124 is in a separated state (step S15: NO), the target flow rate determination unit 53 determines the target flow rate Qp1 of the first hydraulic pump to be the smaller of the target flow rate Qu1 of the first actuator unit and the maximum flow rate Qmax1 of the first hydraulic pump (step S16). The target flow rate determination unit 53 determines the target flow rate Qu2 of the second actuator unit to be the target flow rate Qp2 of the second hydraulic pump (step S17).

[0039] If the main connecting oil passage 124 is in a merging state (step S15: YES), the target flow rate determination unit 53 calculates a determined flow rate Qs by adding the larger of zero and the value obtained by subtracting the maximum flow rate Qmax1 of the first hydraulic pump from the required flow rate Qu1 of the first actuator unit to the target value Qu2 of the flow rate of the second actuator unit (step S18). The target flow rate determination unit 53 determines whether the determined flow rate Qs is smaller than the minimum flow rate Qmin2 of the second hydraulic pump (step S19).

[0040] If the determined flow rate Qs is smaller than the minimum flow rate Qmin2 of the second hydraulic pump (step S19: YES), the target flow rate determination unit 53 determines the target value Qp2 of the flow rate of the second hydraulic pump to be the minimum flow rate Qmin2 of the second hydraulic pump (step S20). Next, the target flow rate determination unit 53 determines the target value Qp1 of the first hydraulic pump to be the flow rate obtained by subtracting the minimum flow rate Qmin2 of the second pump from the sum of the target value Qu1 of the flow rate of the first actuator unit and the target value Qu2 of the flow rate of the second actuator unit (step S21). In this case, a support flow rate (Qp2 - Qu2), which is the total flow rate of the hydraulic fluid discharged by the second hydraulic pump minus the flow rate consumed by the second actuator unit, is supplied to the first actuator unit. The support flow rate at this time is the difference between the target value Qp1 of the flow rate of the first hydraulic pump and the target value Qu1 of the flow rate of the first actuator unit.

[0041] If the determined flow rate Qs is greater than or equal to the minimum flow rate Qmin2 of the second hydraulic pump (step S19: NO), the target flow rate determination unit 53 determines the target value Qp2 of the flow rate of the second hydraulic pump to be the determined flow rate Qs obtained in step S18 (step S22). Next, the target flow rate determination unit 53 determines the target value Qp1 of the first hydraulic pump to be the smaller of the maximum flow rate Qmax1 of the first hydraulic pump and the required flow rate Qu1 of the first actuator unit (step S23). In this case, the support flow rate (Qp2 - Qu2), which is the total flow rate of hydraulic fluid discharged by the second hydraulic pump minus the flow rate consumed by the second actuator unit, is supplied to the first actuator unit. The support flow rate at this time is the difference between the minimum flow rate Qmin2 of the second hydraulic pump and the target value Qp2 of the flow rate of the second actuator unit. As a result, the control device 145 can use the difference between the minimum flow rate Qmin2 output by the second hydraulic pump and the flow rate Qp2 consumed by the second actuator unit as a support flow rate for the first actuator unit without releasing it through the bleed valve 1232.

[0042] As a result, the target flow rate determination unit 53 can determine the target value Qa for the flow rate of each actuator, the target value Qu for the flow rate of each actuator unit U, and the target value Qp for the flow rate of each hydraulic pump 122. By determining the target value Qp for the flow rate of the hydraulic pump 122 using the procedure described above, the supply flow rates of each hydraulic pump 122 can be made different even if the main oil passage 123 is merged. As a result, the control device 145 can supply a support flow rate from the second hydraulic pump to the first actuator unit if the target flow rate Qu1 of the first actuator unit cannot be met by the maximum flow rate of the first hydraulic pump. The support flow rate according to the first embodiment is smaller than the flow rate passing through the main merge / separation valve 1241 when the supply flow rates of each hydraulic pump 122 are the same. As a result, the control device 145 can suppress the pressure loss that occurs in the main merge / separation valve 1241.

[0043] 《Determination of the Risk of Hydraulic Fluid Shortage in the Swivel Motor》 Figure 6 shows an example of the hydraulic circuit of the slewing motor 127 and other actuators according to the first embodiment. After the flow control valve 1261 (meter-in valve 1261i and meter-out valve 1261o) and pressure compensation valve 1262 connected to the slewing motor 127 according to the first embodiment, a first check valve 1263i, a second check valve 1264i, a third check valve 1263o, a fourth check valve 1264o, and a relief valve 1267 are provided.

[0044] The meter-in valve 1261i is a flow control valve that adjusts the flow rate of the hydraulic oil flowing into the swing motor 127. The meter-out valve 1261o is a flow control valve that adjusts the flow rate of the hydraulic oil discharged from the swing motor 127. Among the oil passages connecting the swing motor 127 and the flow control valve 1261, the oil passage connecting the meter-in valve 1261i and the swing motor 127 is called the meter-in oil passage Pi, and the oil passage connecting the meter-out valve 1261o and the swing motor 127 is called the meter-out oil passage Po. Between the meter-in oil passage Pi and the meter-out oil passage Po of the swing motor 127, a first connection oil passage Pc1 and a second connection oil passage Pc2 that connect the meter-in oil passage Pi and the meter-out oil passage Po are provided. The first connection oil passage Pc1 is provided on the flow control valve 1261 side from the second connection oil passage Pc2, and the second connection oil passage Pc2 is provided on the pressure compensation valve 1262 side from the first connection oil passage Pc1. Also, the second connection oil passage Pc2 and the first connection oil passage Pc1 are connected by a third connection oil passage Pc3. Although not shown in FIG. 6, the swing motor 127 has not only a circuit related to left rotation (a circuit in which the meter-in valve 1261i is provided on the lower side of the paper surface and the meter-out valve 1261o is provided on the upper side of the paper surface) but also a circuit related to right rotation (a circuit in which the meter-in valve 1261i is provided on the upper side of the paper surface and the meter-out valve 1261o is provided on the lower side of the paper surface).

[0045] The first check valve 1263i is installed in the first connecting oil passage Pc1 between the connection point with the third connecting oil passage Pc3 and the connection point with the meter-in oil passage Pi. The first check valve 1263i allows hydraulic fluid to flow from the third connecting oil passage Pc3 to the meter-in oil passage Pi, and stops the hydraulic fluid to flow from the meter-in oil passage Pi to the third connecting oil passage Pc3. The second check valve 1264i is installed in the second connecting oil passage Pc2 between the connection point with the third connecting oil passage Pc3 and the connection point with the meter-in oil passage Pi. The second check valve 1264i allows hydraulic fluid to flow from the meter-in oil passage Pi to the third connecting oil passage Pc3, and stops the hydraulic fluid to flow from the third connecting oil passage Pc3 to the meter-in oil passage Pi. The third check valve 1263o is installed in the first connecting oil passage Pc1 between the connection point with the third connecting oil passage Pc3 and the connection point with the meter-out oil passage Po. The third check valve 1263o allows hydraulic fluid to flow from the third connecting oil passage Pc3 to the meter-out oil passage Po, and stops the flow of hydraulic fluid from the meter-out oil passage Po to the third connecting oil passage Pc3. The fourth check valve 1264o is installed in the second connecting oil passage Pc2 between the connection point with the third connecting oil passage Pc3 and the connection point with the meter-out oil passage Po. The fourth check valve 1264o allows hydraulic fluid to flow from the meter-out oil passage Po to the third connecting oil passage Pc3, and stops the flow of hydraulic fluid from the third connecting oil passage Pc3 to the meter-out oil passage Po. The relief valve 1267 is installed in the third connecting oil passage Pc3 and allows hydraulic fluid to flow when the pressure of the hydraulic fluid flowing in from the second connecting oil passage Pc2 exceeds a predetermined cracking pressure.

[0046] Downstream of the relief valve 1267 in the third connecting oil passage Pc3, a discharge oil passage 123C is connected for discharging hydraulic fluid to a tank. As a result, when the pressure in the meter-in oil passage Pi or the meter-out oil passage Po exceeds the cracking pressure, hydraulic fluid is discharged from the second connecting oil passage Pc2 through the relief valve 1267 to the discharge oil passage 123C. The discharge oil passage 123C is equipped with a back pressure valve 1233 to maintain the pressure in the discharge oil passage 123C at a constant back pressure. Upstream of the back pressure valve 1233 in the discharge oil passage 123C, the hydraulic fluid flowing from the relief valve 1267, the hydraulic fluid flowing from the front bleed valve 1232A, the hydraulic fluid flowing from the rear bleed valve 1232B, and the hydraulic fluid flowing from the meter-out valves 1261o of each actuator converge.

[0047] Among the actuators of the work machine 1, the slewing motor 127 has a large moment of inertia because it rotates the slewing body with the work machine. Therefore, when the meter-in valve 1261i and meter-out valve 1261o of the slewing motor 127 are closed, the slewing motor 127 does not stop immediately but gradually decelerates. When the slewing motor 127 begins to decelerate, it acts as a pump that discharges the hydraulic fluid that has flowed in from the meter-in side to the meter-out side. At this time, since the meter-in valve 1261i is closed, the slewing motor 127 is not supplied with hydraulic fluid discharged by the front hydraulic pump 122A. Also, since the meter-out valve 1261o is closed, the hydraulic fluid discharged by the slewing motor 127 does not flow into the discharge oil passage 123C via the meter-out valve 1261o. Therefore, the hydraulic fluid discharged from the swing motor 127 is returned to the meter-in oil passage Pi through the fourth check valve 1264o, the relief valve 1267, and the first check valve 1263i. In other words, the first connecting oil passage Pc1, the second connecting oil passage Pc2, and the third connecting oil passage Pc3 function as a circulation circuit that flows the hydraulic fluid from the discharge side to the inlet side of the swing motor 127. Note that even if the meter-in valve 1261i and the meter-out valve 1261o are not fully closed, the hydraulic fluid can flow through the circulation circuit when the swing motor 127 operates by inertia while decelerating.

[0048] However, since the volumetric efficiency of the hydraulic pump is less than 100%, the hydraulic oil discharged by the swing motor 127 acting as a hydraulic pump is less than the hydraulic oil flowing into the swing motor 127. Therefore, the hydraulic oil returning to the inflow side via the circulation circuit alone cannot supply the hydraulic oil sucked by the swing motor 127. Among the hydraulic oil sucked by the swing motor 127, the shortage of the consumed hydraulic oil is sucked from the discharge oil passage 123C through the first check valve 1263i into the meter-in oil passage Pi. In addition, as described above, the hydraulic oil discharged from the meter-out valve 1261o of other actuators and each bleed valve 1232 flows into the discharge oil passage 123C. That is, the first connection oil passage Pc1 functions as a suction oil passage for circulating the hydraulic oil from the discharge oil passage 123C to the inflow side of the swing motor 127. The pressure of the discharge oil passage 123C is maintained at a predetermined back pressure or higher by the back pressure valve 1233.

[0049] On the other hand, when other actuators are operating at a sufficient speed, the hydraulic oil flowing out from the bleed valve 1232 becomes zero. Therefore, when other actuators are operating, if the hydraulic oil discharged from other actuators into the discharge oil passage 123C is small, the hydraulic oil in the tank may flow backward into the discharge oil passage 123C and be sucked into the swing motor 127. At this time, the pressure on the meter-in side of the swing motor 127 may become lower than the pressure compensated by the back pressure valve 1233. When the pressure decreases in the hydraulic machine, cavitation is likely to occur, which may cause performance degradation and damage of the hydraulic equipment.

[0050] The control device 145 according to the first embodiment controls so that a shortage of the supplied hydraulic oil does not occur with respect to the hydraulic oil consumed by the swing motor 127 when the swing motor 127 is decelerated, in order to prevent cavitation of the swing motor 127 and decelerate the swing motor 127.

[0051] Figure 7 is a flowchart illustrating cavitation prevention control according to the first embodiment. Once the target flow rate determination unit 53 determines the target flow rates for each hydraulic pump 122 and each actuator, the measurement value acquisition unit 51 checks for any abnormalities in the pump discharge pressure sensor 1231 (step S41). For example, the measurement value acquisition unit 51 determines that there is an abnormality in the pump discharge pressure sensor 1231 if the measured value of the pump discharge pressure sensor 1231 is greater than a threshold for determining a sensor fault. Alternatively, the measurement value acquisition unit 51 determines that there is an abnormality in the pump discharge pressure sensor 1231 if the measured value of the pump discharge pressure sensor 1231 is less than a threshold for determining a sensor fault.

[0052] If there is no abnormality in the pump discharge pressure sensor 1231 (step S41: NO), the cavitation prevention unit 56 calculates the flow rate of hydraulic fluid flowing from the bleed valve 1232 to the discharge oil passage 123C based on the measured value of the pump discharge pressure sensor and the opening area of ​​the bleed valve 1232 (step S42). On the other hand, if there is an abnormality in the pump discharge pressure sensor 1231 (step S41: YES), the cavitation prevention unit 56 considers the flow rate of hydraulic fluid flowing from the bleed valve 1232 to the discharge oil passage 123C to be a predetermined minimum value (step S43).

[0053] The cavitation prevention unit 56 may determine the discharge flow rate from the bleed valve 1232 from the difference between the amount of hydraulic fluid discharged by the hydraulic pump 122 and the estimated sum of the flow rates passing through the meter-in openings of each actuator. The amount of hydraulic fluid discharged by the hydraulic pump 122 may be determined from the capacity and rotational speed of the hydraulic pump 122. If there is a malfunction in the swash plate angle sensor or rotational speed sensor, the cavitation prevention unit 56 will calculate the discharge flow rate by considering the amount of hydraulic fluid discharged by the hydraulic pump 122 as zero. The cavitation prevention unit 56 may also determine the discharge flow rate from the bleed valve 1232 from the difference between the target value of the flow rate of the hydraulic pump 122 determined by the target flow rate determination unit 53 and the estimated sum of the flow rates passing through the meter-in openings of each actuator.

[0054] The cavitation prevention unit 56 estimates the total flow rate of hydraulic fluid (flow rate passing through the meter-out opening) discharged from the meter-out valve 1261o of each actuator to the discharge oil passage 123C (step S43). The cavitation prevention unit 56 estimates the flow rate passing through the meter-out opening of each actuator, for example, by the method shown below. The first method by which the cavitation prevention unit 56 estimates the flow rate passing through the meter-out opening is to calculate the flow rate from the meter-out pressure of the actuator and the estimated opening value of the meter-out valve 1261o. The estimated opening value of the meter-out valve 1261o can be obtained, for example, from the measured value of a stroke sensor (not shown) provided on the flow control valve 1261. If there is an abnormality in the sensor that measures the meter-out pressure or the stroke sensor, the cavitation prevention unit 56 estimates the discharge flow rate by the second method described below. A second method by which the cavitation prevention unit 56 estimates the flow rate passing through the meter-out opening is to consider the target flow rate on the meter-out side of the actuator, determined by the target flow rate determination unit 53 from the operating amount of the operating device 142, as the flow rate of the hydraulic fluid discharged from the meter-out valve 1261o to the discharge oil passage 123C. The target flow rate on the meter-out side may be obtained by multiplying the target flow rate on the meter-in side by the pressure-receiving area ratio (the ratio of the pressure-receiving area on the meter-out side to the pressure-receiving area on the meter-in side).

[0055] The cavitation prevention unit 56 determines the sum of the discharge flow rate from the bleed valve 1232 estimated in step S42 or step S43 and the discharge flow rate from the meter-out valve 1261o estimated in step S44 as the flow rate of the hydraulic fluid flowing into the discharge oil passage 123C (step S45).

[0056] The cavitation prevention unit 56 determines whether there is an abnormality in the sensor (such as a cylinder stroke sensor) used to calculate the speed of each actuator for each actuator (step S46). For actuators where there is no abnormality in the sensor (step S46: NO), the cavitation prevention unit 56 calculates the hydraulic fluid consumption flow rate by the actuator from the actuator speed estimated from the sensor measurement value and the pressure receiving area or displacement capacity of the actuator (step S47). For actuators where there is an abnormality in the sensor (step S46: YES), the cavitation prevention unit 56 estimates the maximum value of the hydraulic fluid consumption flow rate by that actuator in advance as the hydraulic fluid consumption flow rate by the actuator (step S48). The cavitation prevention unit 56 calculates the sum of the consumption flow rates of each actuator (step S49).

[0057] The cavitation prevention unit 56 calculates the sum of the flow rates of hydraulic fluid passing through the openings of the meter-in valves 1261i of each actuator (flow rates passing through the meter-in openings) (step S50). The cavitation prevention unit 56 estimates the flow rates passing through the meter-in openings of each actuator, for example, by the method shown below. The first method by which the cavitation prevention unit 56 estimates the flow rates passing through the meter-in openings is to calculate the flow rate from the target differential pressure of the meter-in valves 1261i of the actuator and the estimated value of the opening of the meter-in valves 1261i. The target differential pressure may be a predetermined value. The estimated value of the opening of the meter-in valves 1261i can be obtained, for example, from the measured value of the stroke sensor. If there is an abnormality in the stroke sensor, the cavitation prevention unit 56 estimates the flow rates passing through the meter-in openings by the second method described below. A second method by which the cavitation prevention unit 56 estimates the flow rate passing through the meter-in opening is to consider the target value of the actuator flow rate determined by the target flow rate determination unit 53 from the operating amount of the operating device 142 as the flow rate passing through the meter-in opening.

[0058] The cavitation prevention unit 56 estimates the flow rate (circulation flow rate) of the hydraulic fluid circulating from the outlet side to the inlet side of the slewing motor 127 by the circulation circuit of the slewing motor 127 (step S51). The cavitation prevention unit 56 estimates the circulation flow rate, for example, by the following method. The first method by which the cavitation prevention unit 56 estimates the circulation flow rate is to estimate it based on the pressure in the meter-out oil passage Po of the slewing motor 127 and the pressure-to-flow rate characteristics of the relief valve 1267. If there is an abnormality in the sensor that measures the pressure in the meter-out oil passage Po, the cavitation prevention unit 56 estimates the circulation flow rate by the second method described below. The second method by which the cavitation prevention unit 56 estimates the circulation flow rate is to subtract the flow rate through the meter-out opening of the slewing motor 127 estimated in step S43 from the flow rate of the hydraulic fluid discharged by the slewing motor 127. The flow rate of the hydraulic fluid discharged by the swing motor 127 can be estimated by taking into account the volumetric efficiency of the flow rate passing through the meter-out opening of the swing motor 127, which was estimated in step S43.

[0059] The cavitation prevention unit 56 calculates the flow rate of hydraulic fluid drawn into the actuator from the discharge oil passage 123C (suction flow rate) by subtracting the sum of the flow rates passing through the meter-in opening (obtained in step S50) and the sum of the circulating flow rate (obtained in step S51) from the sum of the flow rates consumed by each actuator (obtained in step S49) (step S52).

[0060] The cavitation prevention unit 56 determines whether the flow rate flowing into the discharge oil passage 123C, estimated in step S45, is greater than the suction flow rate from the discharge oil passage 123C, estimated in step S52 (step S53). If the flow rate flowing into the discharge oil passage 123C is greater than the suction flow rate (step S53: YES), no backflow from the tank to the discharge oil passage 123C occurs, and the pressure of the hydraulic fluid drawn from the discharge oil passage 123C to the swivel motor 127 is compensated by the back pressure valve 1233. In other words, the cavitation prevention unit 56 determines that there is no possibility of cavitation occurring in the actuator (step S54).

[0061] On the other hand, if the flow rate into the discharge oil passage 123C is not greater than the suction flow rate (step S53: NO), the cavitation prevention unit 56 determines that cavitation may occur in the actuator.

[0062] If the cavitation prevention unit 56 determines that there is a possibility that the amount of hydraulic fluid flowing into the swing motor 127 may become insufficient due to the deceleration of the swing motor 127, it determines whether the main connecting oil passage 124 is in a merging state (step S55). If the main connecting oil passage 124 is in a merging state (step S55: YES), the cavitation prevention unit 56 decides to separate the front main oil passage 123A and the rear main oil passage 123B and closes the main merging separation valve 1241 (step S56).

[0063] As a result, the target flow rate determination unit 53 recalculates the target flow rates of the hydraulic fluid for each hydraulic pump 122 and each actuator under the condition that the front main oil passage 123A and the rear main oil passage 123B are separated. By separating the main connecting oil passage 124 and eliminating the support flow rate, the flow rates of the hydraulic fluid for each hydraulic pump 122 and each actuator change, and it is possible that the shortage of hydraulic fluid will be resolved. For example, if the meter-in valve 1261i and meter-out valve 1261o of the swing motor 127 are fully closed and all the hydraulic fluid discharged by the front hydraulic pump 122A is supplied to the rear actuator unit UB, separating the main connecting oil passage 124 allows the hydraulic fluid discharged by the front hydraulic pump 122A to be discharged from the front bleed valve 1232A to the discharge oil passage 123C. After that, the cavitation prevention unit 56 determines again whether or not cavitation may occur.

[0064] If the main connecting oil passage 124 is in a separated state (step S54: NO), the cavitation prevention unit 56 increases the target flow rate of the hydraulic pump 122 so that the flow rate discharged to the discharge oil passage 123C increases by the difference between the suction flow rate and the discharge flow rate, which is the insufficient flow rate (step S56).

[0065] The pump control unit 54 controls the hydraulic pump 122 according to the target flow rate updated by the cavitation prevention unit 56. The valve control unit 55 also controls the opening of the flow control valve 1261 and the bleed valve 1232 according to the target flow rate updated by the cavitation prevention unit 56. As a result, the control device 145 can prevent cavitation from occurring in the actuator.

[0066] <Operation and Effects> In the first embodiment, the control device 145 performs a process to increase the amount of hydraulic fluid flowing into the discharge oil passage 123C when there is a possibility that the amount of hydraulic fluid flowing into the swing motor 127 will become insufficient due to the deceleration of the swing motor 127. This prevents a shortage of hydraulic fluid flowing into the swing motor 127. In addition, since the pressure of the hydraulic fluid flowing through the discharge oil passage 123C is compensated by the back pressure valve 1233, a large pressure drop in the swing motor 127 can be prevented.

[0067] In the first embodiment, the control device 145 closes the main confluence separation valve 1241 when there is a possibility that the amount of hydraulic fluid flowing into the swing motor 127 will be insufficient due to the deceleration of the swing motor 127. By closing the main confluence separation valve 1241, the boost flow rate supplied across the main confluence separation valve 1241 is eliminated, and the amount of hydraulic fluid flowing into the swing motor 127 can be increased.

[0068] In the first embodiment, the control device 145 increases the discharge flow rate of the hydraulic pump 122 by more than the potentially insufficient flow rate when there is a possibility that the hydraulic fluid flowing into the swing motor 127 may become insufficient due to the deceleration of the swing motor 127. This ensures that hydraulic fluid flows to the swing motor 127 without any shortage from the discharge oil passage 123C.

[0069] <Second Embodiment> Figure 8 shows an example of a hydraulic circuit for a swing motor 127 and other actuators according to the second embodiment. The arm cylinder 132C of the work machine 1 according to the second embodiment is equipped with a regeneration circuit that allows some or all of the hydraulic fluid discharged from the meter-out side (head side) to flow into the meter-in side (bottom side). The regeneration circuit is equipped with a fifth check valve 1268 and a throttle 1269. The fifth check valve 1268 is provided in a bypass oil passage that connects the meter-in oil passage, through which the hydraulic fluid flowing into the arm cylinder 132C passes, and the meter-out oil passage, through which the hydraulic fluid discharged from the arm cylinder 132C passes. The fifth check valve 1268 stops the flow of hydraulic fluid from the meter-in oil passage to the meter-out oil passage. The throttle 1269 is provided downstream of the connection point with the bypass oil passage in the meter-out oil passage. The flow rate of hydraulic fluid flowing through the bypass oil passage to the meter-in oil passage is controlled by the opening of the throttle 1269. When the throttle 1269 is fully closed, all the hydraulic fluid discharged by the arm cylinder 132C is supplied to the meter-in side of the arm cylinder 132C (the entire amount is regenerated). In other embodiments of the regeneration circuit, an independent throttle different from the throttle 1269 may be connected in series with the fifth check valve 1268. By providing a regeneration circuit in the arm cylinder 132C, the flow rate of hydraulic fluid that the front hydraulic pump 122A should supply to the arm cylinder 132C during excavation by the arm 132 can be reduced. Although not shown in Figure 8, the arm cylinder 132C has not only a circuit for pushing out the rod (a circuit with a meter-in valve 1261i on the bottom side and a meter-out valve 1261o on the head side) but also a circuit for retracting the rod (a circuit with a meter-in valve 1261i on the head side and a meter-out valve 1261o on the bottom side). However, the circuit for retracting the rod does not have a regeneration circuit. In other words, the hydraulic fluid is regenerated during the excavation operation of the arm 132, but not during the soil removal operation of the arm 132. In other embodiments, the circuit related to the retraction of the rod may also have a regeneration circuit.

[0070] On the other hand, the regeneration circuit reduces the amount of hydraulic fluid discharged from the meter-out valve 1261o to the discharge oil passage 123C. In particular, if the entire amount of hydraulic fluid is regenerated, no hydraulic fluid is discharged to the discharge oil passage 123C. In this case, there is a high possibility that the amount of hydraulic fluid flowing into the swing motor 127 will be insufficient as the swing motor 127 decelerates. Therefore, the cavitation prevention unit 56 of the control device 145 according to the second embodiment determines the possibility that the amount of hydraulic fluid flowing into the swing motor 127 will be insufficient as the swing motor 127 decelerates, taking into account the flow of hydraulic fluid in the regeneration circuit of the arm cylinder 132C.

[0071] In step S43 of cavitation prevention shown in Figure 7, the cavitation prevention unit 56 estimates the discharge flow rate from the meter-out valve 1261o of the arm cylinder 132C in the following manner. First, the cavitation prevention unit 56 estimates the flow rate of hydraulic fluid discharged from the meter-out side of the arm cylinder 132C by multiplying the pressure-receiving area on the meter-out side of the arm cylinder 132C by the speed of the actuator. Next, the cavitation prevention unit 56 determines whether the movement of the arm cylinder 132C is an excavation operation. If the movement of the arm cylinder 132C is an excavation operation, the cavitation prevention unit 56 estimates the flow rate of hydraulic fluid flowing from the meter-out side to the meter-in side (regeneration flow rate) by multiplying the flow rate of hydraulic fluid discharged from the meter-out side by the regeneration ratio in the regeneration circuit. The cavitation prevention unit 56 can estimate the flow rate through the throttle 1269 by using, for example, the opening area of ​​the throttle 1269 and the differential pressure at both ends of the throttle 1269, and then estimate the regeneration flow rate by subtracting the estimated flow rate from the flow rate discharged from the meter-out side. In the case of a regeneration circuit according to another embodiment, if there is an independent throttle different from the throttle 1269 connected in series with the fifth check valve 1268, the regeneration flow rate may be estimated from the differential pressure at both ends and the opening area of ​​the throttle connected in series with the fifth check valve 1268. If there is a malfunction in the stroke sensor for calculating the opening area of ​​the throttle 1269 or the pressure sensor for calculating the differential pressure at both ends of the throttle 1269, the cavitation prevention unit 56 considers the target value of the regeneration flow rate to be the regeneration flow rate of the regeneration circuit. If the movement of the arm cylinder 132C is not an excavation operation, the cavitation prevention unit 56 estimates the regeneration flow rate to be zero. This is because the circuit for retracting the rod of the arm cylinder 132C (i.e., the circuit for the soil removal operation of the arm 132) does not have a regeneration circuit. The cavitation prevention unit 56 estimates the discharge flow rate from the meter-out valve 1261o of the arm cylinder 132C by subtracting the regeneration flow rate from the flow rate of the hydraulic fluid discharged from the meter-out side of the arm cylinder 132C.In other embodiments, actuators other than the arm cylinder 132C may have regeneration circuits. In this case, the cavitation prevention unit 56 determines the regeneration flow rate of each actuator and estimates the suction flow rate by subtracting the sum of the regeneration flow rates, the sum of the consumption flow rates, and the circulating flow rate from the sum of the flow rates passing through the meter-out opening.

[0072] Furthermore, in step S55 of the cavitation prevention shown in Figure 7, the cavitation prevention unit 56 can eliminate the support flow from the rear hydraulic pump 122B to the arm cylinder 132C by separating the main connecting oil passage 124. This increases the flow rate of hydraulic fluid discharged from the rear bleed valve 1232B or the meter-out valve 1261o of the rear actuator unit UB to the discharge oil passage 123C, thereby increasing the amount of hydraulic fluid that can flow from the discharge oil passage 123C to the swing motor 127.

[0073] Furthermore, in step S56 of cavitation prevention shown in Figure 7, the cavitation prevention unit 56 updates the target flow rate of the actuators belonging to the rear actuator unit UB and the target flow rate of the rear hydraulic pump 122B. Even if the target flow rate of actuators with regeneration circuits is increased, if the proportion of regeneration circuits is high, the increase in the flow rate discharged from the meter-out valve 1261o is small. Therefore, the cavitation prevention unit 56 can selectively increase the target flow rate of actuators without regeneration circuits, thereby suppressing the amount of increase in the target flow rate necessary to achieve an increase in the flow rate discharged from the meter-out valve 1261o.

[0074] Furthermore, if it is possible to switch whether or not to supply hydraulic fluid to the regeneration circuit, the cavitation prevention unit 56 may increase the amount of hydraulic fluid flowing into the discharge oil passage 123C by shutting off the regeneration circuit in step S56 of cavitation prevention shown in Figure 7. In this case, the cavitation prevention unit 56 may increase the target flow rate of the front hydraulic pump 122A to compensate for the decrease in hydraulic fluid flowing into the arm cylinder 132C due to the shutdown of the regeneration circuit. Also, if the regeneration ratio of the regeneration circuit can be changed, for example, if the opening degree of the throttle 1269 can be adjusted, the cavitation prevention unit 56 may decrease the regeneration ratio of the regeneration circuit in step S56 of cavitation prevention shown in Figure 7 so that the discharge flow rate from the meter-out valve 1261o of the arm cylinder 132C increases by the amount of the insufficient flow rate identified in step S53. The cavitation prevention unit 56 may also increase the target flow rate of the front hydraulic pump 122A accordingly. In this case, the cavitation prevention unit 56 may increase the target flow rate of the front hydraulic pump 122A to compensate for the decrease in the amount of hydraulic fluid flowing into the arm cylinder 132C due to the change in the opening degree of the regeneration circuit.

[0075] <Third Embodiment> The control device 145 according to the first and second embodiments compares the suction flow rate of the slewing motor 127 with the sum of the discharge flow rates from the bleed valve 1232 and the actuator to determine whether there is a possibility that the amount of hydraulic fluid flowing into the slewing motor 127 will be insufficient as the slewing motor 127 decelerates. In contrast, the control device 145 according to the third embodiment determines the possibility of a shortage of hydraulic fluid in the work machine 1 based on the operating state of the slewing motor 127 and the other actuators.

[0076] The cavitation prevention unit 56 of the work machine 1 according to the third embodiment determines the possibility of a shortage of hydraulic fluid in the work machine 1 based on any one or a combination of the following conditions. The conditions include: - The slewing speed of the slewing motor 127 is faster than a threshold. - The slewing motor 127 is decelerating. - The opening of the meter-in valve 1261i of the slewing motor 127 is below a threshold (for example, fully closed). - The pressure in the meter-in oil passage Pi of the slewing motor 127 is below a threshold. - A combined operation is being performed between the slewing body 120 and the work machine 130 (especially an actuator with a regeneration circuit). - The amount of operation of the work machine 130 is less than a threshold. - The work machine 130 is holding a load.

[0077] For example, the cavitation prevention unit 56 according to the third embodiment determines that if the rotation speed of the slewing motor 127 is faster than a threshold, the meter-in valve 1261i of the slewing motor 127 is fully closed, and a combined operation of the slewing body 120 and the work machine 130 is being performed, there is a possibility that the amount of hydraulic fluid flowing into the slewing motor 127 will be insufficient due to the deceleration of the slewing motor 127.

[0078] Of the conditions mentioned above, the fact that the slewing speed of the slewing motor 127 is faster than the threshold, that the slewing motor 127 is decelerating, that the opening of the meter-in valve 1261i of the slewing motor 127 is below the threshold, and that the pressure in the meter-in oil passage Pi of the slewing motor 127 is below the threshold are all related to the operating state of the slewing motor 127 (especially the slewing speed). The faster the speed of the slewing motor 127, the more hydraulic fluid is consumed. Therefore, the cavitation prevention unit 56 can estimate the possibility of insufficient hydraulic fluid flowing into the slewing motor 127 due to deceleration, based on the operating state of the slewing motor 127. In addition, of the conditions mentioned above, the fact that a combined operation of the slewing body 120 and the work machine 130 is being performed, that the amount of operation of the work machine 130 is below the threshold, and that the work machine 130 is holding a load are all related to the moment of inertia related to the slewing operation. If other actuators are being driven and the pressure-receiving area on the meter-in side is larger than the pressure-receiving area on the meter-out side, less hydraulic fluid will be discharged into the discharge oil passage 123C. Also, if the driven actuator has a regeneration circuit, less hydraulic fluid will be discharged into the discharge oil passage 123C. Therefore, the cavitation prevention unit 56 can estimate the possibility of insufficient hydraulic fluid flowing into the swing motor 127 due to deceleration, based on the operating status of other actuators.

[0079] Furthermore, in the case where the arm cylinder 132C has a regeneration circuit, as in the second embodiment, the possibility of insufficient hydraulic fluid flowing into the swing motor 127 due to deceleration may be estimated based on whether or not an excavation operation is being performed by the arm 132 in addition to the swing operation. When an actuator with a regeneration circuit is driven, less hydraulic fluid is discharged from the meter-out valve 1261o, so the possibility of insufficient hydraulic fluid flowing into the swing motor 127 due to deceleration increases.

[0080] <Other Embodiments> Although several embodiments have been described in detail above with reference to the drawings, the specific configuration is not limited to those described above, and various design changes are possible. That is, in other embodiments, the order of the above-described processes may be changed as appropriate. Also, some processes may be executed in parallel.

[0081] The work machine 1 in the above-described embodiment is a hydraulic excavator, but is not limited to this, and the work machine 1 in other embodiments may be other work machines such as a wheel loader or a bulldozer.

[0082] The work machine 1 according to the above embodiment is equipped with a swashplate type variable displacement pump as the hydraulic pump 122, but is not limited thereto. For example, the hydraulic pump according to another embodiment may be a pump that changes the discharge amount by individually varying the rotation speed. In this case, the pump control unit 54 can control the rotation speed of the hydraulic pump 122.

[0083] The drive system 20 of the work machine 1 according to the above-described embodiment comprises two hydraulic pumps 122 and two main oil passages 123, but is not limited thereto. The drive system 20 of the work machine 1 according to another embodiment may comprise three or more hydraulic pumps 122 and three or more main oil passages 123. Furthermore, the work machine 1 according to another embodiment may comprise one main oil passage 123 and one hydraulic pump 122.

[0084] In the above-described embodiment of the work machine 1, the control device 145 focuses on the slewing motor 127 because its moment of inertia is relatively large, and a lack of hydraulic fluid during deceleration can damage the slewing motor 127, such as causing cavitation. However, it is not limited to this. For example, in another embodiment, when the arm is used for digging with a load in the bucket, the arm involved in the digging operation has a large moment of inertia. In this case, cavitation may occur in the hydraulic circuit involved in the arm digging operation.

[0085] Furthermore, the main oil passage 123 of the work machine 1 according to the above-described embodiment is connected to the discharge oil passage 123C via a bleed valve 1232, but is not limited to this. For example, the main oil passage 123 according to other embodiments may be connected to the discharge oil passage 123C via an unload valve or a relief valve. The unload valve and relief valve are examples of return valves that, like the bleed valve 1232, discharge a portion of the hydraulic fluid discharged by the hydraulic pump 122 to the discharge oil passage. In this case, the cavitation prevention unit 56 estimates the flow rate discharged from the unload valve or relief valve to the discharge oil passage 123C based on the measured value of the pump discharge pressure sensor 1231 and the known pressure-to-flow rate characteristics of the unload valve or relief valve. For example, the cavitation prevention unit 56 can estimate the flow rate discharged from the unload valve to the discharge oil passage 123C from the differential pressure between the measured value of the pump discharge pressure sensor 1231 and the maximum load pressure, and the flow rate characteristics. For example, the cavitation prevention unit 56 can estimate the flow rate discharged from the relief valve to the discharge oil passage 123C based on the differential pressure between the measured value of the pump discharge pressure sensor 1231 and the back pressure, as well as the flow rate characteristics. Furthermore, if there is an abnormality in the pump discharge pressure sensor 1231, the cavitation prevention unit 56 considers the discharge flow rate from the unload valve or relief valve to be a predetermined minimum value.

[0086] Furthermore, while the back pressure valve 1233 of the work machine 1 according to the above embodiment does not prevent the backflow of hydraulic fluid from the tank to the discharge oil passage 123C, the back pressure valve 1233 according to other embodiments may be equipped with a check valve or the like to prevent the backflow of hydraulic fluid from the tank to the discharge oil passage 123C.

[0087] Furthermore, the cavitation prevention unit 56 of the work machine 1 according to the above embodiment separates the main connecting oil passage 124 when there is a possibility that the amount of hydraulic fluid flowing into the slewing motor 127 will be insufficient due to the deceleration of the slewing motor 127, but is not limited to this. For example, in the cavitation prevention unit 56 according to another embodiment, when there is a possibility that the amount of hydraulic fluid flowing into the slewing motor 127 will be insufficient, the cavitation prevention unit 56 may increase the amount of hydraulic fluid flowing into the discharge oil passage 123C by increasing the target flow rate of the actuator and hydraulic pump 122 while keeping the main connecting oil passage 124 merged.

[0088] Furthermore, the cavitation prevention unit 56 of the work machine 1 according to the above embodiment increases the amount of hydraulic fluid flowing into the discharge oil passage 123C when there is a possibility that the amount of hydraulic fluid flowing into the slewing motor 127 may become insufficient due to the deceleration of the slewing motor 127, but is not limited to this. In other embodiments, the cavitation prevention unit 56 may resolve the hydraulic fluid shortage by increasing the opening area of ​​the meter-in valve 1261i of actuators such as the slewing motor 127, which may experience a shortage of hydraulic fluid, and increasing the flow rate of the hydraulic pump 122.

[0089] <Computer Configuration> Figure 9 is a schematic block diagram showing the configuration of a computer according to at least one embodiment. The computer 90 includes a processor 91, main memory 92, storage 93, and interface 94. The control device 145 described above is implemented in the computer 90. The operation of each of the above-described processing units is stored in the storage 93 in the form of a program. The processor 91 reads the program from the storage 93, loads it into the main memory 92, and executes the above-described processing according to the program. The processor 91 also allocates storage areas in the main memory 92 corresponding to each of the above-described storage units according to the program. Examples of the processor 91 include a CPU (Central Processing Unit), a GPU (Graphic Processing Unit), and a microprocessor.

[0090] The program may be for implementing a part of the functions to be performed by the computer 90. For example, the program may perform functions in combination with other programs already stored in storage, or in combination with other programs implemented on other devices. In other embodiments, the computer 90 may include a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to, or instead of, the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), and FPGA (Field Programmable Gate Array). In this case, some or all of the functions implemented by the processor 91 may be implemented by the integrated circuit. Such an integrated circuit is also included as an example of a processor. In other embodiments, the computer 90 may be virtualized on one or more computers.

[0091] Examples of storage 93 include magnetic disks, magneto-optical disks, optical disks, and semiconductor memory. Storage 93 may be an internal medium directly connected to the bus of the computer 90, or it may be an external medium connected to the computer 90 via an interface 94 or a communication line. Furthermore, if this program is distributed to the computer 90 via a communication line, the computer 90 that receives the distribution may expand the program into the main memory 92 and execute the above processing. In at least one embodiment, storage 93 is a tangible storage medium that is not temporary.

[0092] Furthermore, the program may be intended to implement some of the functions described above. In addition, the program may be a so-called differential file (differential program) that implements the functions described above in combination with other programs already stored in the storage 93.

[0093] The control device 145 according to the above-described embodiment may be composed of a single computer 90, or the configuration of the control device 145 may be divided and arranged among multiple computers 90, with the multiple computers cooperating with each other to function as the control device 145. In this case, some of the computers 90 constituting the control device 145 may be mounted inside the work machine 1, and the other computers 90 may be provided outside the work machine 1. For example, if the work machine 1 is a remotely operated vehicle that receives operation commands from a remotely provided operating device and is driven accordingly, the control device 145 may be provided separately for the work machine 1 and the remote operating device. Also, for example, if the work machine 1 is a remotely operated vehicle that autonomously drives according to operation commands transmitted from a control device, the control device 145 may be provided separately for the work machine 1 and the control device.

[0094] According to the above embodiment, the working machine can prevent a shortage of hydraulic fluid flowing into the decelerating actuator.

[0095]

Claims

At least one hydraulic pump, One or more actuators driven by the hydraulic fluid discharged by the hydraulic pump, A discharge oil passage for discharging hydraulic fluid from one or more actuators, A back pressure valve for adjusting the pressure in the aforementioned oil discharge passage, A suction oil passage is provided in each of the one or more actuators, connecting the discharge oil passage and the inlet side of the actuator, and suppressing the flow of hydraulic fluid from the inlet side of the actuator to the discharge oil passage. Controller and Equipped with, The aforementioned controller, If the deceleration of at least one of the one or more actuators may result in insufficient hydraulic fluid flowing from the discharge oil passage to at least one of the one or more actuators via the suction oil passage, the system performs a process to increase the amount of hydraulic fluid flowing into the discharge oil passage or the amount of hydraulic fluid supplied from the hydraulic pump to at least one of the one or more actuators. A type of machinery used for industrial work. 　 The aforementioned controller, If the flow rate of hydraulic fluid flowing into the discharge oil passage is less than the flow rate of hydraulic fluid supplied from the discharge oil passage to at least one of the one or more actuators via the suction oil passage, it is determined that there may be a shortage of hydraulic fluid flowing into at least one of the one or more actuators. The work machine according to claim 1. 　 The hydraulic pump is equipped with a return valve that discharges a portion of the hydraulic fluid discharged by the hydraulic pump into the discharge oil passage. The aforementioned controller, The flow rate of hydraulic fluid flowing into the discharge oil passage is estimated based on the flow rate of hydraulic fluid discharged from one or more actuators to the discharge oil passage and the flow rate of hydraulic fluid discharged from the return valve to the discharge oil passage. The working machine according to claim 2. 　 The aforementioned controller, Based on the difference between the flow rate of hydraulic fluid supplied from the hydraulic pump to the first actuator, which is at least one of the one or more actuators, and the flow rate of hydraulic fluid consumed by the first actuator according to the speed of the first actuator, the flow rate of hydraulic fluid supplied from the discharge oil passage to the first actuator via the suction oil passage is estimated. The work machine according to claim 1. 　 The first actuator, which is at least one of the one or more actuators, includes a circulation circuit that connects the outlet side and the inlet side and suppresses the flow of hydraulic fluid from the inlet side to the outlet side. The aforementioned controller, Based on the difference between the flow rate of hydraulic fluid consumed by the first actuator according to the speed of the first actuator and the flow rate of hydraulic fluid flowing through the circulation circuit, the flow rate of hydraulic fluid supplied to the first actuator from the discharge oil passage via the suction oil passage is estimated. The work machine according to claim 1. 　 The first actuator includes a circuit that connects the outlet side and the inlet side, and a circulation circuit that suppresses the flow of hydraulic fluid from the inlet side to the outlet side. The aforementioned controller, The flow rate of hydraulic fluid supplied to the first actuator via the suction passage from the discharge passage is estimated by subtracting the flow rate of hydraulic fluid consumed by the first actuator from the sum of the flow rate of hydraulic fluid supplied from the hydraulic pump to the first actuator and the flow rate of hydraulic fluid flowing through the circulation circuit. The work machine according to claim 4. 　 The aforementioned controller, Based on information regarding the operating state of at least one of the one or more actuators, it is determined whether there is a possibility that the amount of hydraulic fluid flowing into at least one of the one or more actuators may become insufficient due to the deceleration of at least one of the one or more actuators. The work machine according to claim 1. 　 The at least one hydraulic pump includes a first hydraulic pump and a second hydraulic pump, The first main oil passage connected to the first hydraulic pump, The second main oil passage connected to the second hydraulic pump, A merger / separation valve for merging or separating the first main oil passage and the second main oil passage, Equipped with, Each of the one or more actuators is connected to the first main oil passage or the second main oil passage. The aforementioned controller, If the hydraulic fluid flowing into at least one of the one or more actuators becomes insufficient due to the deceleration of at least one of the actuators, the confluence separation valve is closed. The work machine according to claim 1. 　 The aforementioned controller, If the hydraulic fluid flowing into at least one of the one or more actuators may become insufficient due to the deceleration of at least one of the actuators, the discharge flow rate of the hydraulic pump is increased to a level greater than the potentially insufficient flow rate. The work machine according to claim 1. 　 The at least one hydraulic pump includes a first hydraulic pump and a second hydraulic pump, At least one of the one or more actuators is provided with a regeneration oil passage that connects the outlet side and the inlet side and supplies at least a portion of the hydraulic fluid discharged from the outlet side to the inlet side. A first actuator unit, which includes an actuator that is part of one or more actuators and is equipped with the regenerative oil passage, and a first main oil passage connecting the first hydraulic pump, A second main oil passage connects a second actuator unit, which is part of one or more actuators, to the second hydraulic pump, A merger / separation valve for merging or separating the first main oil passage and the second main oil passage, Equipped with, The aforementioned controller, If the hydraulic fluid flowing into at least one of the one or more actuators may become insufficient due to the deceleration of at least one of the actuators, the confluence separation valve is closed to increase the discharge flow rate of the second hydraulic pump to a level greater than or equal to the potentially insufficient flow rate. The working machine according to claim 9. 　 The one or more actuators include a second actuator driven by the hydraulic fluid discharged by the hydraulic pump, which has a regeneration oil passage connecting the outlet side and the inlet side, and which supplies at least a portion of the hydraulic fluid discharged from the outlet side to the inlet side. The aforementioned controller, If the amount of hydraulic fluid flowing into at least one of the one or more actuators becomes insufficient due to the deceleration of at least one of the actuators, the flow rate through the regeneration oil passage of the second actuator is reduced. The work machine according to claim 1. 　 The machine is equipped with a sensor for measuring the state of the work machine, The aforementioned controller, Based on the values ​​measured by the sensor, the flow rate of hydraulic fluid flowing into the discharge oil passage or the flow rate of hydraulic fluid supplied from the discharge oil passage to at least one of the one or more actuators via the suction oil passage is estimated. If an abnormality occurs in the sensor, the flow rate of hydraulic fluid flowing into the discharge oil passage is replaced with a assumed minimum value, or the flow rate of hydraulic fluid supplied from the discharge oil passage to at least one of the one or more actuators via the suction oil passage is replaced with a assumed minimum value. The working machine according to claim 2. 　 The car body and, A work machine supported by the aforementioned vehicle body, Equipped with, The one or more actuators drive the vehicle body or the work implement. The work machine according to claim 1. 　 At least one hydraulic pump, One or more actuators driven by the hydraulic fluid discharged by the hydraulic pump, A discharge oil passage for discharging hydraulic fluid from one or more actuators, A back pressure valve for adjusting the pressure in the aforementioned oil discharge passage, A suction oil passage is provided in each of the one or more actuators, connecting the discharge oil passage and the inlet side of the actuator, and suppressing the flow of hydraulic fluid from the inlet side of the actuator to the discharge oil passage. A control method for a work machine equipped with, If the deceleration of at least one of the one or more actuators may result in insufficient hydraulic fluid flowing from the discharge oil passage to at least one of the one or more actuators via the suction oil passage, the step of performing a process to increase the amount of hydraulic fluid flowing into the discharge oil passage or the amount of hydraulic fluid supplied from the hydraulic pump to at least one of the one or more actuators, A control method comprising the following features. 　 At least one hydraulic pump, One or more actuators driven by the hydraulic fluid discharged by the hydraulic pump, A discharge oil passage for discharging hydraulic fluid from one or more actuators, A back pressure valve for adjusting the pressure in the aforementioned oil discharge passage, A suction oil passage is provided in each of the one or more actuators, connecting the discharge oil passage and the inlet side of the actuator, and suppressing the flow of hydraulic fluid from the inlet side of the actuator to the discharge oil passage. A controller for controlling a work machine equipped with the following features: If the deceleration of at least one of the one or more actuators may result in insufficient hydraulic fluid flowing from the discharge oil passage to at least one of the one or more actuators via the suction oil passage, the system performs a process to increase the amount of hydraulic fluid flowing into the discharge oil passage or the amount of hydraulic fluid supplied from the hydraulic pump to at least one of the one or more actuators. controller.

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