Work machine

Abstract

A hydraulic shovel comprises: a hydraulic pump; a pump regulator; a hydraulic cylinder supplied with hydraulic oil discharged from the hydraulic pump; an accumulator for storing the hydraulic oil discharged from the hydraulic pump; a control valve for controlling the flow rate of the hydraulic oil supplied from the accumulator to the hydraulic cylinder; a pressure sensor for detecting a pump load which is a load of the hydraulic pump; and a control device to which a signal from the pressure sensor is input, and which controls the pump regulator and the control valve. The control device controls the control valve so that the hydraulic oil supplied from the accumulator to the hydraulic cylinder increases as the pump load increases, and controls the pump regulator so that the flow rate of the hydraulic oil discharged from the hydraulic pump decreases as the hydraulic oil supplied from the accumulator to the hydraulic cylinder increases.

Description

Work machinery

[0001] The present invention relates to a work machine such as a hydraulic excavator.

[0002] An example of a document disclosing prior art related to a hydraulic drive system mounted on a work machine such as a hydraulic excavator is Patent Document 1. Patent Document 1 describes a hydraulic drive system including a first hydraulic pump and a second hydraulic pump that are mechanically connected to an engine and driven by engine power, a boom cylinder, an arm cylinder, a bucket cylinder, and a swing motor that are actuators driven by pressure oil discharged from the respective hydraulic pumps, and a first accumulator that stores pressure oil from the first hydraulic pump and the second hydraulic pump.

[0003] International Publication No. 2018 / 061165

[0004] According to the hydraulic drive system described in Patent Document 1, by supplying pressurized oil from an accumulator to a hydraulic actuator, the flow rate of pressurized oil supplied from the hydraulic pump to the hydraulic actuator can be reduced, and the rotation speed of the engine that drives the hydraulic pump can be reduced, making it possible to use the engine at a rotation speed that is highly fuel-efficient.

[0005] However, in the hydraulic drive system of Patent Document 1, in order to stably reduce the engine rotation speed while ensuring the speed of the hydraulic actuator, a large flow rate of pressurized oil needs to be supplied from the accumulator, which raises concerns about reduced mountability on the vehicle body and increased costs due to the increased size of the accumulator.On the other hand, if an attempt is made to increase the capacity of the hydraulic pump to compensate for the insufficient flow rate caused by the reduced engine rotation speed in order to reduce the size of the accumulator, the torque acting on the hydraulic pump increases, which could reduce the reliability of the hydraulic pump.

[0006] The present invention has been made in view of the above-mentioned problems, and its object is to provide a work machine that can ensure the reliability of the hydraulic pump even when the capacity of the hydraulic pump is increased in accordance with a reduction in engine speed.

[0007] In order to achieve the above object, the present invention provides a work machine including a hydraulic pump, a pump flow rate control device that controls the flow rate of pressurized oil discharged from the hydraulic pump, a hydraulic actuator to which the pressurized oil discharged from the hydraulic pump is supplied, a pressure accumulator that accumulates the pressurized oil discharged from the hydraulic pump, a pressure accumulator flow rate control device that controls the flow rate of pressurized oil supplied from the pressure accumulator to the hydraulic actuator, a pump load detection device that detects a pump load that is a load on the hydraulic pump, and a control device that receives a signal from the pump load detection device and controls the pump flow rate control device and the pressure accumulator flow rate control device, wherein the control device controls the pressure accumulator flow rate control device so that the amount of pressurized oil supplied from the pressure accumulator to the hydraulic actuator increases as the pump load increases, and controls the pump flow rate control device so that the flow rate of pressurized oil discharged from the hydraulic pump decreases in accordance with the increase in the pressure oil supplied from the pressure accumulator to the hydraulic actuator.

[0008] According to the present invention, even when the capacity of the hydraulic pump is increased in accordance with a reduction in engine speed in a work machine, the reliability of the hydraulic pump can be ensured.

[0009] Fig. 1 is a perspective view of a hydraulic excavator according to a first embodiment of the present invention. Fig. 2 is a hydraulic circuit diagram of a hydraulic drive system according to a first embodiment of the present invention. Fig. 3 is a block diagram showing the processing of a controller according to the first embodiment of the present invention. Fig. 4 is a hydraulic circuit diagram of a hydraulic drive system according to a second embodiment of the present invention. Fig. 5 is a block diagram showing the processing of a controller according to a second embodiment of the present invention. Fig. 6 is a block diagram showing the processing of a controller according to a third embodiment of the present invention. Fig. 7 is a block diagram showing the processing of a controller according to a fourth embodiment of the present invention.

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a hydraulic excavator will be described as an example of a work machine, but the present invention can also be applied to other work machines such as a wheel loader, a dump truck, and a hydraulic crane.

[0011] 1 is a perspective view of a hydraulic excavator according to a first embodiment of the present invention. The hydraulic excavator 200 includes a lower traveling structure 201, an upper rotating structure 202, and a working device 203. The upper rotating structure 202 is driven by a traveling motor 204 (hydraulic actuator). The upper rotating structure 202 is rotatably provided on the lower traveling structure 201, and is driven by a swing motor (hydraulic actuator) (not shown).

[0012] The work device 203 has a boom 205, an arm 206, and a bucket 207. The boom 205 is rotatably supported by the upper rotating body 202 and is driven by a boom cylinder 208 (hydraulic actuator). The arm 206 is rotatably supported by the boom 205 and is driven by an arm cylinder 209 (hydraulic actuator). The bucket 207 is rotatably supported by the arm 206 and is driven by a bucket cylinder 210 (hydraulic actuator).

[0013] Fig. 2 is a hydraulic circuit diagram of a hydraulic drive system mounted on the hydraulic excavator 200. Note that Fig. 2 only shows the parts related to the drive of the hydraulic cylinder 5, which is any one of the boom cylinder 208, arm cylinder 209, and bucket cylinder 210, and omits the parts related to the drive of the other actuators.

[0014] The hydraulic drive system 100 includes an engine 1 as a power source, a hydraulic pump 3 driven by the engine 1 and sucking in and discharging hydraulic oil from a hydraulic oil tank 2, a pump regulator 4 (pump flow rate control device) that controls the flow rate of the hydraulic pump 3, a hydraulic cylinder 5 driven by pressure oil supplied from the hydraulic pump 3, a center bypass type control valve 6 (first control valve) that controls the flow rate of pressure oil supplied from the hydraulic pump 3 to the bottom side or rod side of the hydraulic cylinder 5 and the flow rate of pressure oil discharged from the rod side or bottom side of the hydraulic cylinder 5 to the hydraulic oil tank 2, and an accumulator 7 (pressure accumulation device) that stores the pressure oil discharged from the hydraulic pump 3. The hydraulic system includes a control valve 8 (second control valve) that controls the flow rate of pressurized oil flowing from the hydraulic pump 3 into the accumulator 7 and also controls the flow rate of pressurized oil supplied from the accumulator 7 to the hydraulic cylinder 5 via the control valve 6; a control valve 9 that controls the flow rate of pressurized oil discharged from the hydraulic pump 3 to the hydraulic oil tank 2; an operating lever 10 (operating device) that instructs the operation of the hydraulic cylinder 5; a pressure sensor 11 (first pressure sensor) that detects the pressure of the hydraulic pump 3; and a control device 12 that receives signals from the operating lever 10 and the pressure sensor 11 and controls the rotation speed of the engine 1, the flow rate of the hydraulic pump 3, and the flow rates or openings of the control valves 6, 8, and 9.

[0015] The discharge port of the hydraulic pump 3 is connected to the hydraulic oil tank 2 via a center bypass oil passage 13 (first oil passage). Control valves 6 and 9 are arranged in this order from upstream to downstream in the center bypass oil passage 13. The control valve 6 is an open-center type flow control valve, and the control valve 9 is a center bypass cut valve. The control valve 6 is connected to the bottom side of the hydraulic cylinder 5 via an oil passage 14, and to the rod side of the hydraulic cylinder 5 via an oil passage 15. The meter port of the control valve 6 is connected to the center bypass oil passage 13 via a check valve 16. The check valve 16 prevents backflow of pressurized oil from the hydraulic cylinder 5 to the center bypass oil passage 13.

[0016] The accumulator 7 is connected via an oil passage 17 (second oil passage) to a portion of the center bypass oil passage 13 that connects the hydraulic pump 3 and the control valve 6. The control valve 8 is disposed in the oil passage 17.

[0017] The control device 12 is equipped with an arithmetic unit such as a CPU, memory devices such as ROM and RAM, and an input / output interface for signal input / output between external devices, and realizes the following functions by executing programs stored in the ROM etc.

[0018] When a signal is input from the operating lever 10, the control device 12 increases the flow rate of the hydraulic pump 3 in accordance with the amount of lever operation and switches the control valve 6 in a direction corresponding to the lever operation direction. As a result, pressure oil is supplied from the hydraulic pump 3 to one side (bottom side or rod side) of the hydraulic cylinder 5, and pressure oil is discharged from the other side (rod side or bottom side) of the hydraulic cylinder 5 to the hydraulic oil tank 2, thereby extending or retracting the hydraulic cylinder 5. Furthermore, when the load on the hydraulic pump 3 is high, the control device 12 opens the control valve 8 to send pressure oil from the accumulator 7 to the hydraulic cylinder 5 and reduce the flow rate of the hydraulic pump 3. With this configuration, even if the pressure oil from the hydraulic pump 3 is reduced, the corresponding pressure oil can be supplied from the accumulator 7. This allows the desired operation desired by the operator to be performed and the torque acting on the hydraulic pump 3 to be reduced. As a result, even if the engine speed is reduced and the capacity of the hydraulic pump 3 is increased to improve fuel efficiency, the increase in torque of the hydraulic pump 3 is suppressed, thereby ensuring the reliability of the hydraulic pump 3.

[0019] 3 is a block diagram showing the processing of the control device 12. The lever operation signal 110 is a signal generated by operating the control lever 10 and corresponds to the amount of lever operation. A function generator 130 receives the lever operation signal 110 as an input and outputs a required flow rate of the hydraulic pump 3 according to the amount of lever operation. A function generator 131 receives the lever operation signal 110 as an input and outputs an assist flow rate according to the amount of lever operation. The assist flow rate is the flow rate supplied from the accumulator 7 to the hydraulic cylinder 5. The characteristics of the function generator 131 are set to be equivalent to those of the function generator 130. This makes it possible to match the flow rate of pressure oil supplied to the hydraulic cylinder 5 to a flow rate corresponding to the amount of lever operation, regardless of the amount of assist flow rate.

[0020] The pressure sensor signal 111 is a signal corresponding to the pressure of the hydraulic pump 3, and is input to a multiplier 132 together with the required pump flow rate output from a function generator 130. The multiplier 132 calculates the load of the hydraulic pump 3 by multiplying the required pump flow rate by the pressure of the hydraulic pump 3. The output of the multiplier 132 is input to a function generator 133. The function generator 133 outputs a coefficient ranging from 0 to 1 according to the output of the multiplier 132 (the load of the hydraulic pump 3). This coefficient is input to a multiplier 134 together with the output of the function generator 131 (the assist flow rate of the accumulator 7). With this configuration, the assist flow rate of the accumulator 7 can be increased when the load of the hydraulic pump 3 is high, and decreased when the load is low.

[0021] The output of the multiplier 134 (assist flow rate of the accumulator 7) and the output of the function generator 130 (required flow rate of the hydraulic pump 3) are input to a subtractor 135. The subtractor 135 outputs the differential flow rate obtained by subtracting the assist flow rate from the required flow rate of the hydraulic pump 3 as the target flow rate of the hydraulic pump 3. With this configuration, pressure oil at a flow rate that is the difference from the required flow rate of the hydraulic pump 3 is supplied from the accumulator 7 to the hydraulic cylinder 5, making it possible to achieve the operation desired by the operator. Furthermore, since the torque acting on the hydraulic pump 3 is reduced, the reliability of the hydraulic pump 3 can be ensured.

[0022] The output of the subtractor 135 (the target flow rate of the hydraulic pump 3) is input to the output conversion unit 136. The output conversion unit 136 generates a displacement control signal 104 according to the target flow rate of the hydraulic pump 3 and outputs it to the pump regulator 4. This makes it possible to match the flow rate of the hydraulic pump 3 with the target flow rate.

[0023] The output of the multiplier 134 (assist flow rate of the accumulator 7) is input to an output conversion unit 137. The output conversion unit 137 generates a solenoid valve control signal 108 according to the assist flow rate of the accumulator 7 and outputs it to the control valve 8. This allows the flow rate of the control valve 8 to match the assist flow rate.

[0024] (Summary) In the first embodiment, in a hydraulic excavator 200 (work machine) including a hydraulic pump 3, a pump regulator 4 (pump flow rate control device) that controls the flow rate of pressurized oil discharged from the hydraulic pump 3, a hydraulic cylinder 5 (hydraulic actuator) to which the pressurized oil discharged from the hydraulic pump 3 is supplied, an accumulator 7 (pressure accumulator) that accumulates the pressurized oil discharged from the hydraulic pump 3, a control valve 8 (pressure accumulator flow rate control device) that controls the flow rate of pressurized oil supplied from the accumulator 7 to the hydraulic cylinder 5, a pressure sensor 11 (pump load detection device) that detects a pump load that is a load on the hydraulic pump 3, and a control device 12 that receives a signal from the pressure sensor 11 and controls the pump regulator 4 and the control valve 8, the control device 12 controls the control valve 8 so that the amount of pressurized oil supplied from the accumulator 7 to the hydraulic cylinder 5 increases as the pump load increases, and controls the pump regulator 4 so that the flow rate of pressurized oil discharged from the hydraulic pump 3 decreases in accordance with the increase in the pressurized oil supplied from the accumulator 7 to the hydraulic cylinder 5.

[0025] According to the first embodiment configured as described above, when the load on the hydraulic pump 3 is large, the flow rate of the hydraulic pump 3 decreases and pressure oil is supplied from the accumulator 7 to the hydraulic cylinder 5, thereby suppressing an increase in the torque of the hydraulic pump 3. As a result, in the hydraulic excavator 200, even when the capacity of the hydraulic pump 3 is increased in accordance with a reduction in engine speed of the engine 1, the reliability of the hydraulic pump 3 can be ensured.

[0026] Moreover, in the first embodiment, there is further provided an operation lever 10 (operation device) that instructs the operation of the hydraulic cylinder 5 (hydraulic actuator), and the pump load detection device has a pressure sensor 11 (pump pressure detection device) that detects the pump pressure, which is the pressure of the hydraulic pump 3, and the control device 12 calculates a required pump flow rate, which is a required value for the flow rate of pressurized oil discharged from the hydraulic pump 3, based on a signal input from the operation lever 10, and calculates the pump load based on the required pump flow rate and the pump pressure. This makes it possible to calculate the load of the hydraulic pump 3 based on the pressure of the hydraulic pump 3.

[0027] Moreover, in the first embodiment, the hydraulic system further includes a control valve 6 (first control valve) that controls the flow rate of pressurized oil supplied from the hydraulic pump 3 to the hydraulic cylinder 5, and the pressure-accumulation flow control device has a control valve 8 (second control valve) that is arranged in an oil passage 17 (second oil passage) that connects the accumulator 7 (pressure accumulator) with a center bypass oil passage 13 (first oil passage) that connects the hydraulic pump 3 and the control valve 6. This makes it possible to control the flow rate of pressurized oil stored in the accumulator 7 from the hydraulic pump 3 and the flow rate of pressurized oil supplied from the accumulator 7 to the hydraulic cylinder 5 with a single control valve 8.

[0028] Furthermore, in the first embodiment, the control device 12 controls the control valve 8 (accumulator flow rate control device) so that the flow rate of pressure oil supplied from the accumulator 7 (pressure accumulator) to the hydraulic cylinder 5 (hydraulic actuator) continuously increases as the pump load increases, and also controls the pump regulator 4 (pump flow rate control device) so that the flow rate of pressure oil discharged from the hydraulic pump 3 continuously decreases. This makes it possible to prevent the occurrence of shocks caused by switching between the presence and absence of assist.

[0029] The second embodiment of the present invention will be described, focusing on the differences from the first embodiment.

[0030] 4 is a hydraulic circuit diagram of a hydraulic drive system 100 according to a second embodiment. The hydraulic drive system 100 according to this embodiment further includes a pressure sensor 20 that detects the pressure of the accumulator 7, a pressure sensor 21 that detects the pressure on the bottom side of the hydraulic cylinder 5, and a control valve 22 (third control valve) that controls the flow rate of pressurized oil supplied from the accumulator 7 to the bottom side or rod side of the hydraulic cylinder 5 and the flow rate of pressurized oil discharged from the rod side or bottom side of the hydraulic cylinder 5 to the hydraulic oil tank 2. Signals from the pressure sensors 20 and 21 are input to the control device 12, and the control valve 22 is controlled by the control device 12. The control valve 22 is disposed in an oil line 23 (third oil line) that connects the hydraulic cylinder 5 to a portion of the oil line 17 that connects the accumulator 7 and the control valve 8. Therefore, the pressurized oil from the accumulator 7 can be supplied to the hydraulic cylinder 5 without passing through the control valves 6 and 8.

[0031] 5 is a block diagram showing the processing of the control device 12 in the second embodiment. The control device 12 in this embodiment further includes a subtractor 140, a function generator 141, a multiplier 142, and a function generator 143.

[0032] The subtractor 140 receives as input a signal (pressure sensor signal 120) from the pressure sensor 20 that detects the pressure of the accumulator 7 and a signal (pressure sensor signal 121) from the pressure sensor 21 that detects the pressure of the hydraulic cylinder 5. The subtractor 140 outputs a difference obtained by subtracting the pressure of the hydraulic cylinder 5 from the pressure of the accumulator 7. This difference is input to a function generator 141. The function generator 141 outputs 1 if the difference is greater than a preset threshold value P1, and outputs 0 if the difference is equal to or less than the threshold value P1. The output of the function generator 141, together with the value of the assist flow rate output from the function generator 131, is input to a multiplier 142. The multiplier 142 outputs the product of the assist flow rate and the output of the function generator 141. The output of the multiplier 142, together with the output of the function generator 133, is input to a multiplier 134. With this configuration, even when the accumulator 7 is unable to assist due to insufficient pressure in the accumulator 7, the flow rate of the hydraulic pump 3 does not decrease, making it possible to prevent a decrease in the speed of the hydraulic cylinder 5.

[0033] The differential pressure output from the subtractor 140 is input to a function generator 143 together with the assist flow rate output from the multiplier 134. The function generator 143 has a function that opens the control valve 22 in response to an increase in the assist flow rate, thereby increasing the flow rate from the accumulator 7 to the hydraulic cylinder 5. The differential pressure obtained by subtracting the pressure of the hydraulic cylinder 5 from the pressure of the accumulator 7 is also input to the function generator 143. The function generator 143 calculates the aperture of the control valve 22 so that the aperture of the control valve 22 is reduced when the differential pressure is large, and the aperture of the control valve 22 is increased when the differential pressure is small. By adjusting the aperture of the control valve 22 in this way, it is possible to supply pressure oil at a target flow rate from the accumulator 7 to the hydraulic cylinder 5 even if the differential pressure between the pressure of the accumulator 7 and the pressure of the hydraulic cylinder 5 fluctuates.

[0034] Furthermore, instead of the signal (pressure sensor signal 111) of the pressure sensor 11, the signal (pressure sensor signal 121) of the pressure sensor 21 is input to the multiplier 132. In the first embodiment, the load of the hydraulic pump 3 is calculated using the pressure of the hydraulic pump 3 (pressure sensor signal 111), but since the pressure of the hydraulic pump 3 can be approximated by the pressure of the hydraulic cylinder 5, in this embodiment, the load of the hydraulic pump 3 is calculated using the pressure of the hydraulic cylinder 5.

[0035] (Summary) In the second embodiment, the pressure accumulation flow control device that controls the flow rate of pressurized oil supplied from the accumulator 7 to the hydraulic cylinder 5 further has a control valve 22 (third control valve) that is arranged in an oil passage 23 (third oil passage) that connects an oil passage portion that connects the accumulator 7 (pressure accumulation device) and the control valve 8 (second control valve) in the oil passage 17 (second oil passage) with the hydraulic cylinder 5 (hydraulic actuator).

[0036] The second embodiment configured as described above also provides the same effects as those of the first embodiment. Furthermore, since the pressure oil in the accumulator 7 can be supplied to the hydraulic cylinder 5 only via the control valve 22 without passing through the control valves 6 and 8, it is possible to reduce the pressure loss when the pressure oil in the accumulator 7 is supplied to the hydraulic cylinder 5.

[0037] In the second embodiment, the hydraulic excavator 200 further includes an operation lever 10 (operation device) that instructs the operation of the hydraulic cylinder 5 (hydraulic actuator), the pump load detection device has a pressure sensor 21 (actuator pressure detection device) that detects the actuator pressure, which is the pressure of the hydraulic cylinder 5, and the control device 12 calculates a required pump flow rate, which is a required value for the flow rate of pressure oil discharged from the hydraulic pump 3, based on a signal input from the operation lever 10, and calculates the load of the hydraulic pump 3 (pump load) based on the required pump flow rate and the actuator pressure. This makes it possible to calculate the load of the hydraulic pump 3 based on the pressure of the hydraulic cylinder 5.

[0038] Moreover, in the second embodiment, the hydraulic excavator 200 further includes a pressure sensor 20 (accumulator pressure detection device) that detects the pressure of the accumulator 7 (accumulator), and a pressure sensor 21 (pressure detection device) that detects the pressure of the hydraulic cylinder 5 (hydraulic actuator). The control device 12 controls the control valve 22 (accumulator flow rate control device) so that the amount of pressurized oil supplied from the accumulator 7 to the hydraulic cylinder 5 increases as the pump load increases, only when a differential pressure obtained by subtracting the pressure detected by the pressure sensor 21 (pressure of the hydraulic cylinder 5) from the pressure detected by the pressure sensor 20 (accumulator 7 pressure) is greater than a predetermined threshold value P1, and also controls the pump regulator 4 (pump flow rate control device) so that the flow rate of pressurized oil discharged from the hydraulic pump 3 decreases in accordance with the increase in the amount of pressurized oil supplied from the accumulator 7 to the hydraulic cylinder 5. As a result, when the accumulator 7 cannot assist due to insufficient pressure, the flow rate of the hydraulic pump 3 does not decrease, making it possible to prevent a decrease in the speed of the hydraulic cylinder 5.

[0039] The third embodiment of the present invention will be described, focusing on the differences from the second embodiment.

[0040] 6 is a block diagram showing the processing of the control device 12 in the third embodiment. The difference from the second embodiment (shown in FIG. 5) is that the pressure sensor signal 111 indicating the pressure of the hydraulic pump 3 is input to the multiplier 132 and the subtractor 140 instead of the pressure sensor signal 121 indicating the pressure of the hydraulic cylinder 5.

[0041] In the second embodiment, whether or not pressure oil can be supplied from the accumulator 7 to the hydraulic cylinder 5 is determined by comparing the pressure of the accumulator 7 with the pressure of the hydraulic cylinder 5. However, since the pressure of the hydraulic cylinder 5 can be approximated by the pressure of the hydraulic pump 3, in the present embodiment, a similar determination is made by comparing the pressure of the accumulator 7 with the pressure of the hydraulic pump 3.

[0042] (Summary) In the third embodiment, the hydraulic excavator 200 further includes a pressure sensor 20 (pressure accumulator pressure detection device) that detects the pressure of the accumulator 7 (pressure accumulator), and a pressure sensor 11 (pressure detection device) that detects the pressure of the hydraulic pump 3, and the control device 12 controls the control valve 22 (pressure accumulator flow rate control device) so that pressurized oil is supplied from the accumulator 7 to the hydraulic cylinder 5 in accordance with the load on the hydraulic pump 3 (pump load) only when the differential pressure obtained by subtracting the pressure detected by the pressure sensor 11 (pressure of the hydraulic pump 3) from the pressure detected by the pressure sensor 20 (pressure of the accumulator 7) is greater than a predetermined threshold value P1, and also controls the pump regulator 4 (pump flow rate control device) so that the flow rate of pressurized oil discharged from the hydraulic pump 3 is reduced.

[0043] In the second embodiment configured as above, the same effects as those of the second embodiment can be obtained.

[0044] The fourth embodiment of the present invention will be described, focusing on the differences from the second embodiment.

[0045] 7 is a block diagram showing the processing of the control device 12 in the fourth embodiment. The control device 12 in this embodiment has a function generator 144 instead of the function generator 133 (shown in FIG. 5). The function generator 144 outputs 1 when the output of the multiplier 132 (the load on the hydraulic pump 3) is greater than a preset threshold value L1, and outputs 0 when the output is equal to or less than the threshold value L1. With this configuration, no assistance by the accumulator 7 is performed when the load on the hydraulic pump 3 is low, and assistance by the accumulator 7 is performed only when the load on the hydraulic pump 3 is high.

[0046] (Summary) In the fourth embodiment, the control device 12 controls the control valve 22 (pressure accumulation flow control device) so that pressurized oil is supplied from the accumulator 7 (pressure accumulation device) to the hydraulic cylinder 5 (hydraulic actuator) only when the load (pump load) of the hydraulic pump 3 is greater than a predetermined threshold value L1, and controls the pump regulator 4 (pump flow control device) so that the flow rate of pressurized oil discharged from the hydraulic pump 3 is reduced.

[0047] The fourth embodiment configured as described above also provides the same effects as the second embodiment. Furthermore, since assistance by the accumulator 7 is provided only when the load on the hydraulic pump 3 is high, it is possible to reduce the consumption of pressure oil in the accumulator 7.

[0048] The present invention is not limited to the above-described embodiments, but includes various modifications. For example, the above-described embodiments are presented to clearly explain the present invention, and are not necessarily limited to those including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations.

[0049] 1...engine, 2...hydraulic oil tank, 3...hydraulic pump, 4...pump regulator, 5...hydraulic cylinder (hydraulic actuator), 6...control valve, 7...accumulator (pressure accumulator), 8...control valve (pressure accumulator flow control device), 9...control valve, 10...operation lever (operation device), 11...pressure sensor (pump load detection device, pump pressure detection device), 12...control device, 13...center bypass oil passage, 14, 15...oil passage, 16...check valve, 20...pressure sensor (pressure accumulator pressure detection device), 21...pressure sensor (pump load detection device, accumulator pressure detection device), 22...control valve (pressure accumulator flow control device), 23...oil passage, 100...hydraulic drive device, 104...tilt control signal, 108...solenoid valve control signal, 1 10... lever operation signal, 111, 120, 121... pressure sensor signal, 130, 131... function generator, 132... multiplier, 133... function generator, 134... multiplier, 135... subtractor, 136, 137... output conversion unit, 140... subtractor, 141... function generator, 142... multiplier, 143, 144... function generator, 200... hydraulic excavator (work machine), 201... lower traveling body, 202... upper rotating body, 203... work device, 204... traveling motor (hydraulic actuator), 205... boom, 206... arm, 207... bucket, 208... boom cylinder (hydraulic actuator), 209... arm cylinder (hydraulic actuator), 210... bucket cylinder (hydraulic actuator).

Claims

1. A work machine comprising: a hydraulic pump; a pump flow rate control device that controls the flow rate of pressurized oil discharged from the hydraulic pump; a hydraulic actuator to which the pressurized oil discharged from the hydraulic pump is supplied; a pressure accumulator that accumulates the pressurized oil discharged from the hydraulic pump; a pressure accumulator flow rate control device that controls the flow rate of pressurized oil supplied from the pressure accumulator to the hydraulic actuator; a pump load detection device that detects a pump load that is a load on the hydraulic pump; and a control device that receives a signal from the pump load detection device and controls the pump flow rate control device and the pressure accumulator flow rate control device, wherein the control device controls the pressure accumulator flow rate control device so that the amount of pressurized oil supplied from the pressure accumulator to the hydraulic actuator increases as the pump load increases, and controls the pump flow rate control device so that the flow rate of pressurized oil discharged from the hydraulic pump decreases in accordance with the increase in the pressure oil supplied from the pressure accumulator to the hydraulic actuator.

2. A work machine as claimed in claim 1, further comprising an operating device for instructing the operation of the hydraulic actuator, wherein the pump load detection device has a pump pressure detection device for detecting the pump pressure, which is the pressure of the hydraulic pump, and wherein the control device calculates a required pump flow rate, which is a required value for the flow rate of pressurized oil discharged from the hydraulic pump, based on a signal input from the operating device, and calculates the pump load based on the required pump flow rate and the pump pressure.

3. A work machine as claimed in claim 1, further comprising an operating device for instructing the operation of the hydraulic actuator, wherein the pump load detection device has an actuator pressure detection device for detecting the actuator pressure, which is the pressure of the hydraulic actuator, and wherein the control device calculates a required pump flow rate, which is a required value for the flow rate of pressurized oil discharged from the hydraulic pump, based on a signal input from the operating device, and calculates the load on the hydraulic pump based on the required pump flow rate and the actuator pressure.

4. A work machine as claimed in claim 1, further comprising a first control valve for controlling the flow rate of pressurized oil supplied from the hydraulic pump to the hydraulic actuator, and wherein the pressure accumulation flow control device is arranged in a second oil passage connecting a first oil passage connecting the hydraulic pump and the first control valve to the pressure accumulation device, and has a second control valve for controlling the flow rate passing through the second oil passage.

5. A work machine according to claim 4, wherein the pressure accumulation flow control device further has a third control valve arranged in a third oil passage that connects the hydraulic actuator to a portion of the second oil passage that connects the pressure accumulation device and the second control valve.

6. A work machine as defined in claim 1, further comprising a pressure accumulator pressure detection device that detects the pressure of the pressure accumulator, and a pressure detection device that detects the pressure of the hydraulic pump or the hydraulic actuator, wherein the control device controls the pressure accumulator flow rate control device so that the amount of pressurized oil supplied from the pressure accumulator to the hydraulic actuator increases as the pump load increases, only when a differential pressure obtained by subtracting the pressure detected by the pressure detection device from the pressure detected by the pressure accumulator pressure detection device is greater than a predetermined threshold value, and controls the pump flow rate control device so that the flow rate of pressurized oil discharged from the hydraulic pump decreases in accordance with an increase in pressurized oil supplied from the pressure accumulator to the hydraulic actuator.

7. A work machine as claimed in claim 1, characterized in that the control device controls the pressure accumulator flow rate control device so that the flow rate of pressurized oil supplied from the pressure accumulator to the hydraulic actuator increases continuously as the pump load increases, and controls the pump flow rate control device so that the flow rate of pressurized oil discharged from the hydraulic pump decreases continuously.

8. A work machine as claimed in claim 1, characterized in that the control device controls the pressure accumulator flow rate control device so that pressurized oil is supplied from the pressure accumulator to the hydraulic actuator only when the pump load is greater than a predetermined threshold value, and controls the pump flow rate control device so that the flow rate of pressurized oil discharged from the hydraulic pump is reduced.

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