Hydraulic system

Abstract

To provide a hydraulic system in which an electric motor having a rated output smaller than required maximum output with respect to the motor can be used.SOLUTION: A hydraulic system 1 in one embodiment includes: a variable displacement hydraulic pump 2 supplying hydraulic oil to a hydraulic actuator 12 during the operation of the hydraulic actuator 12; an electric motor 3 driving the hydraulic pump 2; a regulator 21 changing the capacity of the hydraulic pump 2; and a control device 4 controlling the electric motor 3 and the regulator 21. When the state that the torque of the electric motor 3 exceeds a rated torque is continued for a predetermined time, the control device 4 reduces the capacity of the hydraulic pump 2 and increases the number of revolution of the electric motor 3 in such a manner that the torque of the electric motor 3 is equal to or lower than the rated torque under the condition that the delivery flow volume of the hydraulic pump 2 is maintained.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a hydraulic system for electrically changing the discharge flow rate of a hydraulic pump.

Background Art

[0002] Conventionally, a hydraulic system for electrically changing the discharge flow rate of a hydraulic pump has been known. For example, Patent Document 1 discloses a hydraulic system including a variable displacement hydraulic pump, an electric motor for driving the hydraulic pump, a regulator for changing the capacity of the hydraulic pump, and a control device for controlling the electric motor. In Patent Document 1, the hydraulic system is called an "inverter-driven hydraulic device", and the regulator is called a "pressure regulating mechanism". Also, in Patent Document 1, the control device includes an inverter and a main control unit, and the main control unit is called a "controller".

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the hydraulic system of Patent Document 1, the regulator mechanically changes the capacity of the hydraulic pump based on the discharge pressure of the hydraulic pump. More specifically, when the discharge pressure of the hydraulic pump is lower than the cut-off start pressure, the regulator maximizes the capacity of the hydraulic pump, and when the discharge pressure of the hydraulic pump exceeds the cut-off start pressure, the capacity of the hydraulic pump decreases as the discharge pressure of the hydraulic pump increases.

[0005] On the other hand, when the discharge pressure of the hydraulic pump is lower than the cutoff start pressure, the control device decreases the rotational speed of the electric motor as the discharge pressure of the hydraulic pump increases, and when the discharge pressure of the hydraulic pump exceeds the cutoff start pressure, it increases the rotational speed of the electric motor as the torque of the electric motor increases.

[0006] Incidentally, in a hydraulic system that includes an electric motor driving a hydraulic pump, it is possible to use an electric motor with a rated output greater than the maximum required output for the motor. However, in this case, the size of the motor will be large and the cost will be high. On the other hand, an electric motor can temporarily produce an output higher than its rated output. However, it is desirable thereafter to change the rotational speed of the motor and the capacity of the hydraulic pump to reduce the motor's output to below its rated output.

[0007] Therefore, the object of this disclosure is to provide a hydraulic system that can use an electric motor having a rated output smaller than the maximum required output for the electric motor. [Means for solving the problem]

[0008] This disclosure provides a hydraulic system comprising: a variable displacement hydraulic pump that supplies hydraulic fluid to a hydraulic actuator when the hydraulic actuator is operating; an electric motor that drives the hydraulic pump; a regulator that changes the capacity of the hydraulic pump; and a control device that controls the electric motor and the regulator, wherein the control device, when the torque of the electric motor exceeds the rated torque for a predetermined period of time, reduces the capacity of the hydraulic pump and increases the rotational speed of the electric motor so that the torque of the electric motor becomes less than or equal to the rated torque, while maintaining the discharge flow rate of the hydraulic pump. [Effects of the Invention]

[0009] According to this disclosure, a hydraulic system is provided that can use an electric motor having a rated output smaller than the maximum required output for the electric motor. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of a hydraulic system according to one embodiment. [Figure 2] This is a flowchart of the control system's operation. [Figure 3] This graph shows the relationship between motor speed and torque, illustrating how the motor's operating state shifts along a line that passes within the rated range. [Figure 4] This graph shows the relationship between motor speed and torque, illustrating the case where the motor's operating state shifts along a line that passes outside the rated range. [Figure 5] This is a map of electric motor efficiency. [Figure 6] This is a map of pump efficiency. [Modes for carrying out the invention]

[0011] Figure 1 shows a hydraulic system 1 according to one embodiment. The hydraulic system 1 electrically changes the discharge flow rate Q of a variable displacement hydraulic pump 2.

[0012] Specifically, the hydraulic system 1 includes a hydraulic pump 2, an electric motor 3 that drives the hydraulic pump 2, a regulator 21 that changes the capacity q of the hydraulic pump 2, and a control device 4 that controls the electric motor 3 and the regulator 21. The capacity q is the discharge amount per revolution of the hydraulic pump 2, and the discharge flow rate Q is the product of the capacity q of the hydraulic pump 2 and the rotational speed N of the electric motor 3. For example, the unit of Q is L / min, the unit of q is L / revolution, and the unit of N is revolutions / min.

[0013] The hydraulic pump 2 supplies hydraulic fluid to the hydraulic actuator 12 when the hydraulic actuator 12 is operating. For example, the hydraulic pump 2 is connected to the hydraulic actuator 12 via a switching valve 11. The hydraulic actuator 12 may be an actuator that operates bidirectionally by the supply of pressurized oil, such as a hydraulic motor or a double-acting cylinder, or it may be an actuator that operates unidirectionally by the supply of pressurized oil, such as a single-acting cylinder. In the former case, the switching valve 11 is a three-position valve, and in the latter case, the switching valve 11 is a two-position valve.

[0014] In this embodiment, the hydraulic pump 2 is an axial piston pump such as a swashplate pump or a swash-shaft pump. However, the hydraulic pump 2 may be other types of pumps such as a vane pump.

[0015] The regulator 21 receives a capacity command from the control device 4, and the regulator 21 changes the capacity of the hydraulic actuator 12 according to the capacity command. For example, the capacity command is a command current. For example, if the hydraulic pump 2 is a swashplate pump, the regulator 21 may electrically change the hydraulic pressure acting on the servo piston connected to the swashplate of the hydraulic pump 2, or it may be an electric actuator connected to the swashplate of the hydraulic pump 2.

[0016] The electric motor 3 is, for example, a servo motor. However, the electric motor 3 may be other motors such as induction motors.

[0017] With respect to the control device 4, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, dedicated processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuits. In this disclosure, a circuit, unit, or means is hardware that performs the enumerated functions, or hardware programmed to perform the enumerated functions. The hardware may be hardware disclosed herein, or other known hardware that is programmed or configured to perform the enumerated functions. If the hardware is a processor, which is considered a type of circuit, then the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or the processor.

[0018] In this embodiment, the control device 4 includes an inverter 5 interposed between the electric motor 3 and the power source 8, and a main control unit 6 that outputs a command to the inverter 5. The power source 8 may be a battery or an AC commercial power source. In the former case, the inverter 5 includes an inverter circuit, and in the latter case, the inverter 5 includes a converter circuit and an inverter circuit.

[0019] Also, in this embodiment, an operation device 7 that receives an operation for operating the hydraulic actuator 12 is adopted, and a speed command for the hydraulic actuator 12 is input from the operation device 7 to the main control unit 6. For example, when the operation device 7 includes an operation lever, the speed command for the hydraulic actuator 12 increases as the tilt angle of the operation lever increases.

[0020] In this embodiment, the main control unit 6 outputs a rotation speed command to the inverter 5. The inverter 5 can grasp the rotation speed N and torque T of the electric motor 3, and performs speed feedback control and torque feedback control. The rotation speed N and torque T of the electric motor 3 are input from the inverter 5 to the main control unit 6. However, the main control unit 6 may perform speed feedback control and output the resulting torque command to the inverter 5, and the inverter 5 may perform torque feedback control.

[0021] Next, referring to FIG. 2, the control performed by the control device 4 will be described. The control device 4 first controls the regulator 21 so that the capacity q of the hydraulic pump 2 becomes the reference capacity qr (step S1). The reference capacity qr is, for example, the maximum capacity qmax.

[0022] In this state, when the operation device 7 is operated, the control device 4 controls the electric motor 3 so that the rotation speed N of the electric motor 3 becomes the rotation speed corresponding to the speed command for the hydraulic actuator 21 (step S2). Specifically, the main control unit 6 of the control device 4 outputs a larger rotation speed command to the inverter 5 as the speed command increases.

[0023] Next, the control device 4 determines whether the torque T of the electric motor 3 has exceeded the rated torque Tt for a predetermined period of time (step S3). The rated torque Tt of the electric motor 3 is stored in advance in the main control unit 6. The predetermined time may be a fixed value (for example, about 10 seconds), but since it depends on the torque T, the predetermined time may be made variable according to the torque T. Since the torque T changes moment by moment, the value of the torque T may be determined by the time average value or a filtered value.

[0024] If the torque T of the electric motor 3 does not exceed the rated torque Tt for a predetermined time (NO in step S3), the control device 4 repeats step S2. On the other hand, if the torque T of the electric motor 3 exceeds the rated torque Tt for a predetermined time, the control device 4 decreases the capacity q of the hydraulic pump 2 and increases the rotational speed N of the electric motor 3, while maintaining the discharge flow rate Q of the hydraulic pump 2 (step S4). As a result, the operating state of the electric motor 3 shifts along line 61 as shown in Figures 3 and 4. For example, line 61 is the equihorsepower line when the product of the discharge flow rate and discharge pressure of the hydraulic pump 6 is constant.

[0025] Subsequently, the control device 4 determines whether the torque T of the electric motor 3 has become less than or equal to the rated torque Tt (step S5). If the torque T of the electric motor 3 is not less than or equal to the rated torque Tt (NO in step S5), the control device 4 repeats step S4. On the other hand, if the torque T of the electric motor 3 has become less than or equal to the rated torque Tt (YES in step S5), the control device 4 determines whether the rotational speed N of the electric motor 3 is less than the rated rotational speed Nt (step S6).

[0026] If the rotational speed N of the electric motor 3 is not below the rated rotational speed Nt (NO in step S6), in other words, if the operating state of the electric motor 3 shifts along the line 61 that passes outside the rated range determined by the rated rotational speed Nt and rated torque Tt, as shown in Figure 4, the control device 4 sets the rotational speed N of the electric motor 3 to the rated rotational speed Nt (step S10). That is, if the rotational speed N of the electric motor 3 exceeds the rated rotational speed Nt, the control device 4 reduces the rotational speed N of the electric motor 3 to the rated rotational speed Nt. If the rotational speed N of the electric motor 3 exceeds the rated rotational speed Nt when the torque T of the electric motor 3 is less than or equal to the rated torque Tt, the output of the electric motor 3 will exceed the rated output, but in this case, the output of the electric motor 3 is kept below the rated output by sacrificing the speed of the hydraulic actuator 12.

[0027] On the other hand, if the rotational speed N of the electric motor 3 falls below the rated rotational speed Nt (YES in step S6), in other words, if the operating state of the electric motor 3 shifts along the line 61 that passes inside the rated range as shown in Figure 3, the control device 4 decreases the capacity q of the hydraulic pump 2 and increases the rotational speed N of the electric motor 3, while maintaining the discharge flow rate Q of the hydraulic pump 2 (step S7).

[0028] Subsequently, the control device 4 determines whether the overall efficiency η in converting electrical energy to hydraulic energy has improved (step S8). Electrical energy is the product of voltage, current, and time, and hydraulic energy is the product of pressure, flow rate, and time. The overall efficiency η is the product of the motor efficiency ηm and the pump efficiency ηp.

[0029] The main control unit 6 has pre-stored maps of motor efficiency ηm, as shown in Figure 5, and pump efficiency ηp, as shown in Figure 6. However, motor efficiency ηm and pump efficiency ηp may be expressed as functions instead of maps. Motor efficiency ηm uses rotational speed and torque as parameters, and pump efficiency ηp uses discharge pressure and the capacity ratio to maximum capacity, i.e., q / qmax, as parameters. In this embodiment, as shown in Figure 1, the discharge pressure of the hydraulic pump 2 is detected by the pressure sensor 9.

[0030] If the overall efficiency η improves (YES in step S8), in other words, if the overall efficiency η increases, the control device 4 repeats steps S6 and S7. On the other hand, if the overall efficiency η does not improve (NO in step S8), in other words, if the overall efficiency η decreases, the control device 4 returns the capacity q of the hydraulic pump 2 and the rotational speed N of the electric motor 3 to the values ​​of the previous step S7 (step S9). That is, if step S7 has been performed n times before reaching step S9, the capacity q of the hydraulic pump 2 and the rotational speed N of the electric motor 3 are set to the values ​​of the (n-1)th step S7.

[0031] In the hydraulic system 1 with the configuration described above, the output of the electric motor 3 exceeds the rated output only temporarily. Thereafter, the torque T of the electric motor 3 decreases to below the rated torque Tt due to the decrease in the capacity q of the hydraulic pump 2 and the increase in the rotational speed N of the electric motor 3. Therefore, an electric motor 3 with a rated output smaller than the maximum required output for the electric motor 3 can be used. Moreover, since the discharge flow rate Q of the hydraulic pump 2 is maintained while the torque of the electric motor 3 is decreasing, there is no effect on the speed of the hydraulic actuator 12.

[0032] Furthermore, in this embodiment, after the torque T of the electric motor 3 falls below the rated torque Tt, the process of decreasing the capacity q of the hydraulic pump 2 and increasing the rotational speed N of the electric motor 3 is repeated so as to increase the overall efficiency η. This allows the electric motor 3 to be operated with low energy consumption within the rated range. Moreover, when the overall efficiency η decreases, the capacity q of the hydraulic pump 2 and the rotational speed N of the electric motor 3 are returned to the values ​​of the previous process, making it easy to determine the state in which the energy consumption of the electric motor 3 is minimized.

[0033] <Variation> This disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the gist of this disclosure.

[0034] For example, the control device 7 may be omitted, and automatic operation may be performed. In this case, the control device 4 may generate speed commands for the hydraulic actuator 12 based on camera images or the like.

[0035] Furthermore, steps S6 to S10 in the flowchart shown in Figure 2 can be omitted.

[0036] <Summary> In a first aspect, the present disclosure provides a hydraulic system comprising: a variable displacement hydraulic pump that supplies hydraulic fluid to a hydraulic actuator when the hydraulic actuator is operating; an electric motor that drives the hydraulic pump; a regulator that changes the capacity of the hydraulic pump; and a control device that controls the electric motor and the regulator, wherein the control device, when the torque of the electric motor exceeds the rated torque for a predetermined period of time, reduces the capacity of the hydraulic pump and increases the rotational speed of the electric motor so that the torque of the electric motor becomes less than or equal to the rated torque, while maintaining the discharge flow rate of the hydraulic pump.

[0037] With the above configuration, the motor's output only temporarily exceeds its rated output. Subsequently, the motor's torque decreases to below its rated torque due to a decrease in the hydraulic pump's capacity and an increase in the motor's rotational speed. Therefore, a motor with a rated output smaller than the maximum required output can be used. Moreover, since the hydraulic pump's discharge flow rate is maintained while the motor's torque is decreasing, there is no impact on the hydraulic actuator's speed.

[0038] In a second embodiment, in the first embodiment, when the torque of the electric motor falls below the rated torque and the rotational speed of the electric motor falls below the rated rotational speed, the control device may repeatedly reduce the capacity of the hydraulic pump and increase the rotational speed of the electric motor, while maintaining the discharge flow rate of the hydraulic pump, in order to increase the overall efficiency when converting electrical energy to hydraulic energy. With this configuration, the electric motor can be operated with low energy consumption within the rated range.

[0039] In a third embodiment, in the second embodiment, if the overall efficiency decreases after the process, the control device may return the capacity of the hydraulic pump and the rotational speed of the electric motor to the values ​​of the previous process. With this configuration, the state in which the energy consumption of the electric motor is minimized can be easily determined.

[0040] In a fourth embodiment, in any of the first to third embodiments, if the rotational speed of the motor exceeds the rated rotational speed when the torque of the motor falls below the rated torque, the control device may reduce the rotational speed of the motor to the rated rotational speed. With this configuration, if the rotational speed of the motor exceeds the rated rotational speed when the torque of the motor falls below the rated torque, the output of the motor will exceed the rated output. However, in this case, the output of the motor is kept below the rated output by sacrificing the speed of the hydraulic actuator.

[0041] In a fifth embodiment, in any of the first to fourth embodiments, for example, the control device may include an inverter interposed between the electric motor and the power supply, and a main control unit that outputs commands to the inverter. [Explanation of Symbols]

[0042] 1. Hydraulic System 12 Hydraulic Actuators 2. Hydraulic pump 21 Regulator 3 Electric motor 4. Control device 5 Inverter 6. Main control unit 7 Operating device 8 Power supply

Claims

1. A variable displacement hydraulic pump that supplies hydraulic fluid to the hydraulic actuator when the hydraulic actuator is operating, An electric motor that drives the aforementioned hydraulic pump, A regulator for changing the capacity of the aforementioned hydraulic pump, The system comprises a control device for controlling the electric motor and the regulator, The control device is a hydraulic system that, when the torque of the electric motor exceeds the rated torque for a predetermined period of time, reduces the capacity of the hydraulic pump and increases the rotational speed of the electric motor so that the torque of the electric motor becomes less than or equal to the rated torque, while maintaining the discharge flow rate of the hydraulic pump.

2. The hydraulic system according to claim 1, wherein when the torque of the electric motor falls below the rated torque, and the rotational speed of the electric motor falls below the rated rotational speed, the control device repeatedly reduces the capacity of the hydraulic pump and increases the rotational speed of the electric motor, under the condition of maintaining the discharge flow rate of the hydraulic pump, so as to increase the overall efficiency when converting electrical energy to hydraulic energy.

3. The hydraulic system according to claim 2, wherein if the overall efficiency decreases after the processing, the control device returns the capacity of the hydraulic pump and the rotational speed of the electric motor to the values ​​of the previous processing.

4. The hydraulic system according to any one of claims 1 to 3, wherein the control device reduces the rotational speed of the electric motor to the rated rotational speed when the torque of the electric motor falls below the rated torque and the rotational speed of the electric motor exceeds the rated rotational speed.

5. The hydraulic system according to any one of claims 1 to 3, wherein the control device includes an inverter interposed between the electric motor and the power supply, and a main control unit that outputs commands to the inverter.

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