Hydraulic systems, work vehicles, control methods, and computer programs

Abstract

This technology provides the ability to obtain higher output than normal when necessary. [Solution] The hydraulic system S disclosed herein comprises a hydraulic pump 32, a supply oil passage 58 for supplying hydraulic fluid from the hydraulic pump 32 to a hydraulically operated front loader 4, a pump motor 30 for driving the hydraulic pump 32, and a processing device 18 for performing a selection process to select a control mode for the pump motor 30 from a first mode and a second mode. The first mode is a mode in which the upper limit of the torque command value indicating the torque that the pump motor 30 should output is a first command value. The second mode is a mode in which the upper limit is a second command value that is greater than the first command value.

Description

【Technical Field】 , , 【0006】 【0001】 The present disclosure relates to a hydraulic system, a work vehicle, a control method, and a computer program. 【Background Art】 【0002】 Patent Document 1 discloses a work vehicle. This work vehicle includes a work device that is lifted and lowered hydraulically. The hydraulic system that operates this work device includes a hydraulic cylinder and a hydraulic pump that generates the hydraulic pressure supplied to the hydraulic cylinder. This hydraulic pump is driven by an electric motor (see, for example, Patent Document 1). 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Unexamined Patent Application Publication No. 2024-96596 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 In the above hydraulic system, as the work device operates, an external load may act on the hydraulic cylinder, causing sudden hydraulic pressure fluctuations. For this reason, a relief valve may be provided to prevent the hydraulic pressure from rising beyond a predetermined upper limit value. The upper limit of the output of the work device is determined by the upper limit value of the hydraulic pressure. Therefore, the upper limit of the output of the work device is determined by the opening pressure of the relief valve, which is the upper limit value of the hydraulic pressure. 【0005】 By the way, when performing work with the work device, an output greater than the current output may be required depending on the work content. However, in a hydraulic system having the above-described relief valve, the hydraulic pressure does not rise above the pressure at which the relief valve opens, and an output greater than the current output cannot be obtained. 【0006】 Therefore, this disclosure aims to provide a technology that can obtain a higher output than the normal output as needed. [Means for solving the problem] 【0007】 The hydraulic system disclosed herein comprises a hydraulic pump, a supply oil passage for supplying hydraulic fluid from the hydraulic pump to a hydraulically operated work device, an electric motor for driving the hydraulic pump, and a processing unit for performing a selection process to select a control mode for the electric motor from a first mode and a second mode. The first mode is a mode in which the upper limit of the torque command value indicating the torque to be output by the electric motor is a first command value. The second mode is a mode in which the upper limit is a second command value that is greater than the first command value. [Effects of the Invention] 【0008】 According to this disclosure, a higher output than the normal output can be obtained as needed. [Brief explanation of the drawing] 【0009】 [Figure 1] Figure 1 is a side view of a work vehicle according to an embodiment. [Figure 2] Figure 2 is a block diagram showing an example of a power system for a work vehicle. [Figure 3] Figure 3 is a block diagram showing an example of a hydraulic system for a work vehicle according to the first embodiment. [Figure 4] Figure 4 is a flowchart showing an example of a selection process performed by the processing unit. [Figure 5] Figure 5 is a block diagram showing a part of the hydraulic system according to the second embodiment. [Modes for carrying out the invention] 【0010】 First, the details of the embodiment will be listed and explained. [Summary of the Embodiment] (1) The hydraulic system disclosed herein comprises a hydraulic pump, a supply oil passage for supplying hydraulic fluid from the hydraulic pump to a work device operated by hydraulics, an electric motor for driving the hydraulic pump, and a processing unit for performing a selection process to select a control mode for the electric motor from a first mode and a second mode. The first mode is a mode in which the upper limit of the torque command value indicating the torque to be output by the electric motor is a first command value. The second mode is a mode in which the upper limit is a second command value which is greater than the first command value. With the above configuration, the control mode of the electric motor can be selected from a first mode and a second mode, each having different upper limits for the torque command value to the electric motor. Therefore, under normal circumstances, the first mode with a lower upper limit for the torque command value can be selected, and when higher output is required in the work device, the second mode with a higher upper limit for the torque command value can be selected. This allows, for example, the second command value to be increased to a level acceptable for short-term use, thereby enabling the work device to produce output higher than normal as needed. 【0011】 (2) In the hydraulic system described in (1) above, if it is further equipped with an operating switch capable of receiving operator input, the selection process may be configured to select the control mode based on the output of the operating switch. In this case, the operator can select the control mode as needed. 【0012】 (3) In the hydraulic system described in (1) or (2) above, if a relief valve is further provided that opens when the hydraulic pressure in the supply oil passage reaches a predetermined opening pressure, the first hydraulic pressure value generated in the supply oil passage by the hydraulic pump driven by the electric motor operating at the first command value may be smaller than the opening pressure. In this case, in the first mode, the electric motor can be operated within the range in which the relief valve does not open. 【0013】 (4) In the hydraulic system of (3) above, the second hydraulic value generated in the supply oil passage by the hydraulic pump driven by the electric motor operating at the second command value may be not less than the valve opening pressure. In this case, in the first mode, the electric motor can be operated within the range where the relief valve opens. 【0014】 (5) In the hydraulic system of (1) or (2) above, when further provided with a first relief valve that opens when the hydraulic pressure of the supply oil passage reaches the first valve opening pressure, a solenoid valve that opens and closes a connection oil passage connecting between the first relief valve, the first relief valve, and the supply oil passage, and a second relief valve that opens when the hydraulic pressure of the supply oil passage reaches a second valve opening pressure higher than the first valve opening pressure, the first valve opening pressure is the hydraulic value generated in the supply oil passage by the hydraulic pump driven by the electric motor operating at the first command value, and the second valve opening pressure is the hydraulic value generated in the supply oil passage by the hydraulic pump driven by the electric motor operating at the second command value. Also, the selection process may include a process of opening and closing the solenoid valve. In this case, two modes can be set by the two relief valves. 【0015】 (6) In any one of the hydraulic systems of (1) to (5) above, when the second mode is executed for a predetermined period or longer, the processing device may perform a process of selecting the control mode again. In this case, the second mode with a high upper limit value of hydraulic pressure can be used as a temporary mode. Thereby, in the second mode, the hydraulic pressure can be increased to an acceptable level for short-term use, and a higher output can be obtained from the working device. 【0016】 (7) From another perspective, the present disclosure is a work vehicle. This work vehicle includes a working device and the hydraulic system according to any one of (1) to (6) above. 【0017】 (8) Further, from another perspective, the present disclosure is a control method for an electric motor that drives a hydraulic pump for supplying hydraulic oil to a work device. This control method includes a step of selecting a control mode of the electric motor from a first mode and a second mode. The first mode is a mode in which an upper limit value of a torque command value indicating torque that the electric motor should output is a first command value. The second mode is a mode in which the upper limit value is a second command value greater than the first command value. 【0018】 (9) Further, from another perspective, the present disclosure is a computer program. This computer program is a computer program for causing a computer to execute control of an electric motor that drives a hydraulic pump for supplying hydraulic oil to a work device. This computer program is a computer program for causing a computer to execute a selection process of selecting a control mode of the electric motor from a first mode and a second mode. The first mode is a mode in which an upper limit value of a torque command value indicating torque that the electric motor should output is a first command value. The second mode is a mode in which the upper limit value is a second command value greater than the first command value. 【0019】 [Details of Embodiment] Hereinafter, preferred embodiments will be described with reference to the drawings. Note that at least a part of each of the embodiments described below may be arbitrarily combined. 【0020】 [Regarding the Overall Configuration of the Work Vehicle] FIG. 1 is a side view of a work vehicle according to an embodiment. The work vehicle 1 is a vehicle used for agricultural work, specifically a tractor. However, the work vehicle 1 is not limited to a tractor and may be a moving body such as an agricultural machine, a construction machine, and a utility vehicle. 【0021】 As shown in FIG. 1, the work vehicle 1 includes a vehicle body 2, a traveling mechanism 3, a front loader 4, a driver's cab 5, and the like. The running mechanism 3 includes a pair of left and right front wheels 6 and a pair of left and right rear wheels 7. The front and rear wheels 6 and 7 are rotatably mounted on axles provided on the vehicle body 2. The running mechanism 3 has the function of transmitting driving force from the driving motor 24 (described later) to the front and rear wheels 6 and 7, and rotating the front and rear wheels 6 and 7. Therefore, in addition to the front and rear wheels 6 and 7, the running mechanism 3 has a transmission mechanism (not shown) that transmits driving force to the front and rear wheels 6 and 7. The transmission mechanism includes rotating shafts such as drive shafts and propeller shafts, a differential, and a transmission. 【0022】 The vehicle body 2 includes the chassis 8, hood 9, and fenders 10, etc. The chassis 8 includes the frame 8a and the transmission case 8b. The frame 8a and the transmission case 8b are connected to each other. The front wheels 6 are mounted on the frame 8a and the rear wheels 7 are mounted on the transmission case 8b. The chassis 8 is equipped with various parts of the work vehicle 1, such as the running mechanism 3, driver's unit 5, and front loader 4. The hood 9 is located at the front of the vehicle body 2. The fender 10 is located above the rear wheels 7. 【0023】 The driver's unit 5 is located at the rear of the vehicle body 2. The driver's unit 5 includes a steering wheel 5a, a driver's seat 5b, operating levers 5c, and operating switches 5d. The driver's seat 5b is the seat where the operator driving the work vehicle 1 sits. The steering wheel 5a is for steering the front wheels 6. The operating levers 5c include a lever for adjusting the speed of the work vehicle 1, and an operating lever for the front loader 4. The operation switch 5d is a switch for selecting the control mode for the upper limit of the hydraulic system (described later). The operation lever 5c and the operation switch 5d have the function of receiving operation input from the operator. The operation lever 5c and the operation switch 5d provide an output to the operation control unit 16 (described later) according to the received operation input. 【0024】 The operation switch 5d is, for example, a push-button switch. When the operation switch 5d is pressed by an operator, it provides an output to the operation control unit 16 indicating that it is in the ON state. When the operation switch 5d is not pressed by an operator, it provides an output to the operation control unit 16 indicating that it is in the OFF state. 【0025】 The front loader 4 is a work device located at the front of the vehicle body 2. The front loader 4 includes a pair of left and right frames 4a, a pair of left and right arms 4b, a bucket 4c, a pair of left and right arm cylinders 12, and a pair of left and right bucket cylinders 13. Frame 4a is located on the left and right sides of the hood 9. Frame 4a is fixed to frame 8a. Arm 4b connects frame 4a and bucket 4c. The rear end of arm 4b and frame 4a are connected by shaft 4d. The axial direction of shaft 4d is along the left-right direction. Arm 4b is pivotable around shaft 4d. 【0026】 The front end of the arm 4b and the bucket 4c are connected to each other by a shaft 4e. The axial direction of the shaft 4e is aligned in the left-right direction. The bucket 4c is pivotable around the shaft 4e. 【0027】 A pair of arm cylinders 12 are connected to a pair of frames 4a and a pair of arms 4b. When the arm cylinders 12 extend or retract, the arms 4b swing up and down around the shaft 4d. A pair of bucket cylinders 13 are connected to a pair of arms 4b and a bucket 4c. When the bucket cylinders 13 extend and retract, the bucket 4c swings around the shaft 4e. A pair of arm cylinders 12 and a pair of bucket cylinders 13 extend and retract in response to the operation of the operating lever 5c. 【0028】 [Regarding the power system of work vehicles] Figure 2 is a block diagram showing an example of the power system of work vehicle 1. As shown in Figure 2, the work vehicle 1 further includes an operation control unit 16, a processing unit 18, a battery 20, an inverter 22, a drive motor 24, a continuously variable transmission 26, a PTO device 28, a pump motor 30, and a hydraulic pump 32. In this embodiment, the work vehicle 1 is configured to generate hydraulic pressure through the driving force of the travel motor 24 and the pump motor 30, and to operate the travel mechanism 3 and the front loader 4 with this hydraulic pressure. The drive motor 24 and the pump motor 30 are electric motors that output rotational force using electricity stored in the battery 20. 【0029】 The driving force from the traction motor 24 is transmitted to the continuously variable transmission 26. The continuously variable transmission 26 is a hydrostatic continuously variable transmission. The continuously variable transmission 26 can continuously change the driving force from the traction motor 24. The continuously variable transmission 26 can be operated by an operator. The continuously variable transmission 26 changes the speed of the driving force from the traction motor 24 and transmits the changed speed of the driving force to the traction mechanism 3 and the PTO device 28. The driving mechanism 3 drives the front and rear wheels 6 and 7 with the driving force transmitted from the continuously variable transmission 26. The PTO device 28 outputs the driving force transmitted from the continuously variable transmission 26 to, for example, a work device mounted on the work vehicle 1. A clutch is provided between the continuously variable transmission 26 and the PTO device 28 to intermittently transmit the driving force. The driving force from the continuously variable transmission 26 is transmitted to the PTO device 28 by the clutch as needed. The drive motor 24 is located at the front of the vehicle body 2, inside the hood 9. The continuously variable transmission 26 and the PTO device 28 are housed in the transmission case 8b. The driving force from the drive motor 24 is transmitted to the continuously variable transmission 26 via a transmission shaft or the like. 【0030】 The driving force from the pump motor 30 is transmitted to the hydraulic pump 32. The hydraulic pump 32 supplies hydraulic fluid to the arm cylinder 12 and bucket cylinder 13 of the front loader 4. The hydraulic fluid is a lubricating oil stored in the transmission case 8b. Therefore, the hydraulic pump 32 is installed in the transmission case 8b. The hydraulic pump 32 is driven by the driving force from the pump motor 30, sucks the hydraulic fluid from the transmission case 8b, and pumps the sucked hydraulic fluid to the arm cylinder 12 and bucket cylinder 13 of the front loader 4. 【0031】 The inverter 22 supplies power from the battery 20 to the traction motor 24 and the pump motor 30. The inverter 22 includes a drive circuit connected to the traction motor 24 and a drive circuit connected to the pump motor 30. These drive circuits supply power from the battery 20 to the traction motor 24 and the pump motor 30 and control the traction motor 24 and the pump motor 30 based on torque command values ​​from the processing unit 18. 【0032】 The processing unit 18 has the function of controlling the travel motor 24 and the pump motor 30 by providing torque command values ​​(current command values) to the drive circuit. The processing unit 18 performs feedback control so that the travel motor 24 and the pump motor 30 reach the target rotational speed. The processing unit 18 is supplied with the output of a rotation sensor that detects the rotational speed of the travel motor 24 and the pump motor 30, respectively. The processing unit 18 determines the torque command value based on the rotational speed of the travel motor 24 and the pump motor 30, respectively, and the target rotational speed. The target rotational speed is determined by the operation control unit 16. 【0033】 The operation control unit 16 determines the target rotational speed based on the output from the operation lever 5c and provides this information to the processing unit 18. Thus, the operation control unit 16 determines the target rotational speed corresponding to the operation of the work vehicle 1 requested by the operator. Furthermore, the operation control unit 16 generates information indicating the state of the operation switch 5d based on the output from the operation switch 5d and provides it to the processing unit 18. The information indicating the state of the operation switch 5d includes information indicating that the operation switch 5d is in the ON state and information indicating that the operation switch 5d is in the OFF state. 【0034】 [Regarding the hydraulic system according to the first embodiment] Figure 3 is a block diagram showing an example of the hydraulic system of the work vehicle 1 according to the first embodiment. Note that in Figure 3, for ease of understanding, the bucket cylinder 13 of the front loader 4 is omitted from the arm cylinder 12 and bucket cylinder 13. In Figure 3, the hydraulic system S includes an oil circulation circuit 50 and a pump control device 52. The oil circulation circuit 50 is a circuit for circulating the differential oil in the transmission case 8b and supplying and discharging hydraulic fluid to the arm cylinders 12. In addition to the hydraulic pump 32, the pair of arm cylinders 12, and the transmission case 8b mentioned above, the oil circulation circuit 50 includes a control valve 54, a relief valve 56, a supply oil passage 58, four supply and discharge oil passages 60, a return oil passage 62, and a suction oil passage 64. 【0035】 The hydraulic pump 32 draws hydraulic fluid from the transmission case 8b through the suction oil passage 64 and discharges it into the supply oil passage 58. The supply oil passage 58 connects the hydraulic pump 32 to the control valve 54. The hydraulic pump 32 pressurizes the hydraulic fluid to the control valve 54 via the supply oil passage 58. The control valve 54 is connected to a pair of arm cylinders 12 via four oil supply and discharge passages 60. The control valve 54 has the function of supplying and discharging hydraulic fluid to the pair of arm cylinders 12 based on commands from the operation control unit 16, etc. The pair of arm cylinders 12 extend and retract according to the hydraulic fluid supply and discharge control by the control valve 54. Therefore, the pair of arm cylinders 12 extend and retract in response to the operator's input to the operation lever 5c. 【0036】 Furthermore, a return oil passage 62 is connected to the control valve 54. The hydraulic fluid discharged from the pair of arm cylinders 12 is returned to the transmission case 8b through the control valve 54 and the return oil passage 62. In this way, the oil circulation circuit 50 circulates the hydraulic fluid within the transmission case 8b. 【0037】 The relief valve 56 is located in the bypass oil passage 66. The bypass oil passage 66 connects the supply oil passage 58 and the return oil passage 62. The relief valve 56 closes the bypass oil passage 66 when the hydraulic pressure of the hydraulic fluid in the supply oil passage 58 is lower than a preset opening pressure. The relief valve 56 opens the bypass oil passage 66 when the hydraulic pressure of the hydraulic fluid in the supply oil passage 58 is equal to or greater than the opening pressure. In this way, the relief valve 56 sets an upper limit for the hydraulic pressure in the supply oil passage 58. In other words, the opening pressure of the relief valve 56 is the upper limit for the hydraulic pressure in the supply oil passage 58. 【0038】 The pump control device 52 has the function of controlling the pump motor 30 and controlling the operation of the hydraulic pump 32. The pump control device 52 includes the processing device 18, the drive circuit 22a of the inverter 22, and the pump motor 30, etc. The drive circuit 22a is a drive circuit included in the inverter 22 that controls the pump motor 30. 【0039】 The processing unit 18 is composed of a computer or the like, which includes a processing unit and a storage unit. The processing unit consists of various processors suitable for computer control, such as a CPU (Central Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), and FPGA (Field Programmable Gate Array). The memory unit includes, for example, flash memory, hard disk, SSD (Solid State Drive), ROM (Read Only Memory), etc. The memory unit stores computer programs to be executed by the processing unit, as well as necessary information. The processing unit realizes the various processing functions of the processing unit 18 by executing the computer programs stored on a computer-readable, non-transient recording medium such as the memory unit. 【0040】 The processing unit 18 is supplied with the target rotation speed and the output of the rotation sensor from the operation control unit 16. The processing unit 18 is also supplied with information indicating the state of the operation switch 5d from the operation control unit 16. The rotation sensor includes, for example, a Hall element in the pump motor 30, and a rotation sensor attached to the pump motor 30 that detects the rotational speed of the pump motor 30. 【0041】 The processing unit 18 has the function of determining the torque command value to be given to the drive circuit 22a based on the output of the rotation sensor and the state of the operation switch 5d. The torque command value is a value that indicates the torque that the pump motor 30 should output. The processing unit 18 determines the rotational speed of the pump motor 30 based on the output of the rotation sensor and performs PID control based on the difference between the target rotational speed and the current rotational speed. The processing unit 18 then calculates the torque command value based on the PID control. The processing unit 18 controls the pump motor 30 according to the torque command value. 【0042】 [Regarding the selection process] The processing unit 18 has a function to perform a selection process to select either the first mode or the second mode for the control mode of the pump motor 30. The first mode is the mode in which the upper limit of the torque command value is the first command value. The second mode is a mode in which the upper limit of the torque command value is greater than the first command value. 【0043】 The processing unit 18 of this embodiment sets two control modes by changing the upper limit of the torque command value. In the first mode, the processing unit 18 sets the upper limit of the torque command value to the first command value. As a result, the processing unit 18 limits the current supplied to the pump motor 30 and limits the upper limit of the output torque of the pump motor 30 to the torque corresponding to the first command value. The first hydraulic pressure value generated in the supply oil passage 58 by the hydraulic pump 32, which is driven by the pump motor 30 operating at the first command value, is smaller than the opening pressure of the relief valve 56. Therefore, in the first mode, the processing unit 18 operates the pump motor 30 within the range in which the relief valve 56 does not open. The first hydraulic pressure value is the upper limit of the hydraulic pressure that the hydraulic pump 32 can generate in the supply oil passage 58 when there is no load associated with the work operation acting via the arm cylinder 12 or bucket cylinder 13. 【0044】 In the second mode, the processing unit 18 sets the upper limit of the torque command value to the second command value. As a result, the processing unit 18 limits the current supplied to the pump motor 30 and limits the upper limit of the output torque of the pump motor 30 to the torque corresponding to the second command value. The second hydraulic pressure value generated in the supply oil passage 58 by the hydraulic pump 32, driven by the pump motor 30 operating at the second command value, is equal to or greater than the valve opening pressure. In the second mode, the upper limit of the hydraulic pressure in the supply oil passage 58 is the valve opening pressure of the relief valve 56. Therefore, in the second mode, the processing unit 18 operates the pump motor 30 within the range in which the relief valve 56 is open. 【0045】 The second hydraulic pressure value, which is the upper limit of hydraulic pressure in the second mode, is greater than the first hydraulic pressure value, which is the upper limit of hydraulic pressure in the first mode. Therefore, the output obtained from the front loader 4 operating in the second mode is higher than the output obtained from the front loader 4 operating in the first mode. In other words, the first mode is a low-power mode, and the second mode is a high-power mode. 【0046】 The processing unit 18 performs mode selection through a selection process based on information indicating the state of the operation switch 5d. Therefore, the operator can select the control mode of the pump motor 30 as needed. 【0047】 Figure 4 is a flowchart showing an example of a selection process performed by the processing unit 18. The processing unit 18 first determines whether the state of the operation switch 5d is ON or OFF (step S1). The processing unit 18 refers to information indicating the state of the operation switch 5d, and if the information indicates an OFF state, it selects the first mode (step S2) and returns to step S1. If the information indicates an ON state, the processing unit 18 selects the second mode (step S3) and determines whether a predetermined time has elapsed (step S4). The processing unit 18 repeats step S4 until the predetermined time has elapsed. After a predetermined time has elapsed, the processing unit 18 returns to step S1. 【0048】 If the operator does not press the operation switch 5d, the processing unit 18 selects the first mode. In other words, the first mode is the normal mode selected when the operator is not operating the device. On the other hand, when the operator presses the operation switch 5d, the processing unit 18 selects the second mode. The second mode is a temporary mode selected by the operator. After selecting the second mode, the processing unit 18 maintains the second mode for a predetermined time. After the predetermined time, if the operator releases their hand from the operation switch 5d, the processing unit 18 selects the first mode again. 【0049】 Thus, in this embodiment, the second mode, which has a higher upper limit for hydraulic pressure, can be used by the operator as a temporary mode. This allows the hydraulic pressure to be increased to a level that is acceptable for short-term use in the second mode, and a higher output can be obtained from the front loader 4. 【0050】 With the above configuration, the control mode of the pump motor 30 can be selected from a first mode and a second mode, each having different upper limits for the torque command value to the pump motor 30. Therefore, under normal circumstances, the first mode with a lower upper limit for the torque command value can be selected, and when higher output is required from the front loader 4, the second mode with a higher upper limit for the torque command value can be selected. This makes it possible to obtain a higher output from the front loader 4 than the normal output as needed. 【0051】 Furthermore, in this embodiment, the work vehicle 1 is equipped with a drive motor 24 that generates hydraulic pressure for moving the work vehicle 1, in addition to the pump motor 30 that drives the hydraulic pump 32. Therefore, even if the control of the pump motor 30 is changed, it will not affect the movement of the work vehicle 1. For this reason, the control mode of the pump motor 30 can be configured to be selected from a first mode and a second mode. 【0052】 [Regarding the second embodiment] Figure 5 is a block diagram showing a part of the hydraulic system according to the second embodiment. The oil circulation circuit 50 of the hydraulic system S in this embodiment differs from the oil circulation circuit 50 of the first embodiment in that it has two relief valves, and that one of the two relief valves has an electromagnetic valve connected in parallel. 【0053】 The oil circulation circuit 50 of this embodiment includes a first relief valve 74, a second relief valve 70, and a solenoid valve 76. The first relief valve 74 is located in the bypass oil passage 72. The bypass oil passage 72 connects the supply oil passage 58 and the return oil passage 62. The first relief valve 74 closes the bypass oil passage 72 if the hydraulic pressure value of the hydraulic fluid in the supply oil passage 58 is lower than a preset first opening pressure. The first relief valve 74 opens the bypass oil passage 72 if the hydraulic pressure value of the hydraulic fluid in the supply oil passage 58 is equal to or greater than the first opening pressure. 【0054】 The second relief valve 70 has the same configuration as the relief valve 56 in the first embodiment. That is, the second relief valve 70 is provided in the bypass oil passage 66. The bypass oil passage 66 connects the supply oil passage 58 and the return oil passage 62. The second relief valve 70 closes the bypass oil passage 66 when the hydraulic pressure value of the hydraulic fluid in the supply oil passage 58 is lower than the preset second opening pressure. The second relief valve 70 opens the bypass oil passage 66 when the hydraulic pressure value of the hydraulic fluid in the supply oil passage 58 is equal to or greater than the second opening pressure. The second valve opening pressure is higher than the first valve opening pressure. 【0055】 The electromagnetic valve 76 is installed in the connecting oil passage that connects the supply oil passage 58 and the first relief valve 74 of the bypass oil passage 72. The electromagnetic valve 76 opens and closes the connecting oil passage. The electromagnetic valve 76 is connected to the processing unit 18. The electromagnetic valve 76 opens and closes the connecting oil passage based on commands given by the processing unit 18. 【0056】 The processing device 18 in this embodiment performs the selection process by opening and closing the electromagnetic valve 76. In the selection process of this embodiment, when the first mode is selected (step S2), the processing unit 18 opens the electromagnetic valve 76. As a result, the first relief valve 74 is connected to the supply oil passage 58. Therefore, the upper limit of the hydraulic pressure in the supply oil passage 58 becomes the first opening pressure of the first relief valve 74. 【0057】 On the other hand, if the second mode is selected during the selection process (step S3), the processing unit 18 closes the electromagnetic valve 76. This disconnects the oil passages between the first relief valve 74 and the supply oil passage 58. Therefore, the upper limit of the hydraulic pressure in the supply oil passage 58 becomes the second opening pressure of the second relief valve 70. 【0058】 The second valve opening pressure, which is the upper limit of hydraulic pressure in the second mode, is greater than the first valve opening pressure, which is the upper limit of hydraulic pressure in the first mode. Therefore, the output obtained from the front loader 4 operating in the second mode is higher than the output obtained from the front loader 4 operating in the first mode. 【0059】 Here, the first mode is the mode in which the upper limit of the torque command value is the first command value, and the second mode is the mode in which the upper limit of the torque command value is the second command value, which is greater than the first command value. Therefore, the first valve opening pressure is the hydraulic pressure generated in the supply oil passage 58 by the hydraulic pump 32 driven by the pump motor 30 operating at the first command value, and the second valve opening pressure is the hydraulic pressure generated in the supply oil passage 58 by the hydraulic pump 32 driven by the pump motor 30 operating at the second command value. In the first mode, the upper limit of the hydraulic pressure is the first valve opening pressure, so the upper limit of the torque command value is the first command value. Furthermore, in the second mode, since the upper limit of the hydraulic pressure is the second valve opening pressure, the upper limit of the torque command value becomes the second command value. 【0060】 In this embodiment as well, the control mode of the pump motor 30 can be selected from a first mode, which is a low-output mode, and a second mode, which is a high-output mode, so that a higher output than the normal output can be obtained from the front loader 4 as needed. 【0061】 〔others〕 It should be noted that the embodiments disclosed herein are illustrative in all respects and not restrictive. For example, in this embodiment, the example given is that the work device of the work vehicle 1 is a front loader 4, but the work device operated by hydraulics may be a backhoe, or both a front loader and a backhoe may be provided. 【0062】 The scope of the present invention is indicated by the claims, not in the sense described above, and is intended to include all modifications within the meaning and scope of the claims, equivalent to the claims. [Explanation of Symbols] 【0063】 1. Work vehicles 2 car bodies 3. Running mechanism 4 Front Loader 4a frame 4b Arm 4c bucket 4d shaft 4e Shaft 5. Driver's Unit 5a Handle 5b Driver's seat 5c Operating lever 5d Operation switch 6 Front wheels 7 Rear wheel 8 Chassis 8a frame 8b Transmission Case 9. Hood 10 Fender 12 Arm Cylinder 13 Bucket Cylinder 16 Operation Control Unit 18 Processing device 20 batteries 22 Inverters 22a Drive Circuit 24. Motor for driving 26 Continuously Variable Transmission 28 PTO device 30 Pump motor 32 Hydraulic pumps 50 Oil circulation circuit 52 Pump control device 54 Control valve 56 Relief Valve 58 Supply oil channels 60 Oil supply and drainage passage 62 Return oil route 64 Suction oil path 65 Branch oil passage 66 Bypass Oil Channel 70. Second relief valve 72 Bypass Oil Channel 74. First relief valve 76 Solenoid valve S Hydraulic System

Claims

[Claim 1] Hydraulic pump and A supply oil passage that supplies hydraulic fluid from the hydraulic pump to a work device that operates by hydraulics, An electric motor that drives the hydraulic pump, The system includes a processing unit that performs a selection process to select the control mode of the electric motor from a first mode and a second mode, The first mode is a mode in which the upper limit of the torque command value indicating the torque that the electric motor should output is the first command value, The second mode is a mode in which the upper limit is a second command value that is greater than the first command value. Hydraulic system. [Claim 2] It is further equipped with an operating switch that can accept user input, In the selection process, the control mode is selected based on the output of the operation switch. The hydraulic system according to claim 1. [Claim 3] The system further includes a relief valve that opens when the hydraulic pressure in the supply oil passage reaches a predetermined opening pressure. The first hydraulic pressure value generated in the supply oil passage by the hydraulic pump driven by the electric motor operating at the first command value is smaller than the valve opening pressure. The hydraulic system according to claim 2. [Claim 4] The second hydraulic pressure value generated in the supply oil passage by the hydraulic pump driven by the electric motor operating at the second command value is equal to or greater than the valve opening pressure. The hydraulic system according to claim 3. [Claim 5] A first relief valve that opens when the hydraulic pressure in the supply oil passage reaches the first opening pressure, A solenoid valve that opens and closes a connecting oil passage connecting the first relief valve and the supply oil passage, The system further includes a second relief valve that opens when the hydraulic pressure in the supply oil passage reaches a second opening pressure higher than the first opening pressure, The first valve opening pressure is the hydraulic pressure generated in the supply oil passage by the hydraulic pump driven by the electric motor operating at the first command value. The second valve opening pressure is the hydraulic pressure generated in the supply oil passage by the hydraulic pump driven by the electric motor operating at the second command value. The selection process includes the process of opening and closing the solenoid valve. The hydraulic system according to claim 2. [Claim 6] If the second mode is executed for a predetermined period of time or longer, the processing unit performs the process of selecting the control mode again. A hydraulic system according to any one of claims 1 to 5. [Claim 7] Work equipment and A work vehicle comprising the hydraulic system described in claim 1. [Claim 8] A control method for an electric motor that drives a hydraulic pump for supplying hydraulic fluid to a work device, The process includes the step of selecting the control mode of the electric motor from a first mode and a second mode, The first mode is a mode in which the upper limit of the torque command value indicating the torque that the electric motor should output is the first command value, The second mode is a mode in which the upper limit is a second command value that is greater than the first command value. Control method. [Claim 9] A computer program for causing a computer to control an electric motor that drives a hydraulic pump for supplying hydraulic fluid to a work device, to the computer This is a computer program that performs a selection process to select the control mode of the electric motor from a first mode and a second mode. The first mode is a mode in which the upper limit of the torque command value indicating the torque that the electric motor should output is the first command value, The second mode is a mode in which the upper limit is a second command value that is greater than the first command value. Computer program.

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