KR20250131259A - hydraulic system - Google Patents

Abstract

A hydraulic system (1) according to one embodiment includes a variable displacement hydraulic pump (2) for supplying operating fluid to a hydraulic actuator (12) when the hydraulic actuator (12) is operated, an electric motor (3) for driving the hydraulic pump (2) by receiving power from a battery (8), a regulator (21) for changing the capacity of the hydraulic pump (2), and a control device (4) for controlling the electric motor (3). The control device (4) updates a torque-rotational speed characteristic of the electric motor (3) based on a voltage of the battery (8), and if an operating point determined from the rotational speed of the electric motor (3) and the torque of the electric motor (3) according to a speed command for the hydraulic actuator (12) is outside the torque-rotational speed characteristic, the control device (4) changes the rotational speed of the electric motor (3) to a rotational speed corresponding to the torque of the electric motor (3) within the torque-rotational speed characteristic.

Description

hydraulic system

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

Conventionally, hydraulic systems that electrically change the discharge flow rate of a hydraulic pump have been known. For example, Patent Document 1 discloses a hydraulic system comprising a variable displacement hydraulic pump, an electric motor for driving the hydraulic pump, a regulator for mechanically changing the displacement of the hydraulic pump, and a control device for controlling the electric motor. In this regard, Patent Document 1 refers to the hydraulic system as an "inverter-driven hydraulic device" and the regulator as a "pressure regulating mechanism." Furthermore, Patent Document 1 refers to the control device as including an inverter and a main control unit, and refers to the main control unit as a "controller."

Japanese Patent Publication No. 2019-183944

However, electric motors have torque-speed characteristics based on maximum torque (Tmax) and maximum rotational speed (Nmax). It is known that when the motor is powered by a battery, the torque-speed characteristics deteriorate as the battery voltage drops. More specifically, as illustrated in Fig. 4, the maximum horsepower that the motor can output decreases as the battery voltage drops. Here, horsepower is the product of torque and rotational speed.

In this case, the operating point determined from the motor's rotational speed and torque according to the speed command for the hydraulic actuator may fall outside the torque-rotational speed characteristics, resulting in the required output from the motor exceeding its maximum output. It is desirable to maintain stable control of the motor even in such situations.

Accordingly, the present disclosure aims to provide a hydraulic system capable of stably controlling an electric motor even when the voltage of a battery is reduced.

The present disclosure provides a hydraulic system comprising a variable displacement hydraulic pump for supplying operating fluid to a hydraulic actuator when the hydraulic actuator is operated, an electric motor for driving the hydraulic pump by receiving power from a battery, a regulator for changing the capacity of the hydraulic pump, and a control device for controlling the electric motor, wherein the control device updates the torque-rotational speed characteristic of the electric motor based on the voltage of the battery, and when an operating point determined from the rotational speed of the electric motor and the torque of the electric motor according to a speed command for the hydraulic actuator is outside the torque-rotational speed characteristic, changes the rotational speed of the electric motor to a rotational speed corresponding to the torque of the electric motor within the torque-rotational speed characteristic.

According to the present disclosure, a hydraulic system capable of stably controlling an electric motor even when the voltage of a battery is reduced is provided.

[Figure 1] A schematic diagram of a hydraulic system according to one embodiment.
[Figure 2] This is a flow chart of control performed by the control device.
[Figure 3] This is a diagram showing the reduced torque-rpm characteristics and the shift of the operating point due to the above control.
[Figure 4] This is a diagram showing how the torque-rotation speed characteristics are deteriorated.
[Figure 5] This is a map of motor efficiency.
[Figure 6] This is a map of pump efficiency.

In Fig. 1, a hydraulic system (1) according to one embodiment is illustrated. The hydraulic system (1) electrically changes the discharge flow rate (Q) of a variable displacement hydraulic pump (2).

Specifically, the hydraulic system (1) includes a hydraulic pump (2), an electric motor (3) driving the hydraulic pump (2), a regulator (21) changing the capacity (q) of the hydraulic pump (2), and a control device (4) controlling the electric motor (3) and the regulator (21). The capacity (q) is the discharge amount per rotation 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).

The hydraulic pump (2) supplies operating fluid to the hydraulic actuator (12) when the hydraulic actuator (12) operates. 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 supplying hydraulic fluid, such as a hydraulic motor or a double-acting cylinder, or may be an actuator that operates unidirectionally by supplying hydraulic fluid, 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.

In this embodiment, the hydraulic pump (2) is an axial piston pump such as a swash plate pump or a swash plate pump. However, the hydraulic pump (2) may be another type of pump such as a vane pump.

A capacity command is output from the control device (4) to the regulator (21), and the regulator (21) changes the capacity (q) of the hydraulic pump (2) according to the capacity command. For example, the capacity command is a command current. For example, when the hydraulic pump (2) is a swash plate pump, the regulator (21) may be one that electrically changes the hydraulic pressure applied to a servo piston connected to the swash plate of the hydraulic pump (2), or may be an electric actuator connected to the swash plate of the hydraulic pump (2).

The electric motor (3) is supplied with power from a battery (8). The electric motor (3) is, for example, a servo motor. However, the electric motor (3) may be another motor, such as an induction motor.

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

In this embodiment, the control device (4) includes an inverter (5) interposed between the electric motor (3) and the battery (8), and a main control unit (6) that outputs a command to the inverter (5). In addition, in this embodiment, an operating device (7) that receives an operation for operating a hydraulic actuator (12) is employed, and a speed command for the hydraulic actuator (12) is input from the operating device (7) to the main control unit (6). For example, when the operating device (7) includes an operating lever, the speed command for the hydraulic actuator (12) increases as the inclination angle of the operating lever increases.

In this embodiment, the main control unit (6) outputs a rotation speed command to the inverter (5). The inverter (5) can detect the rotation speed (N) and torque (T) of the motor (3) and performs speed feedback control and torque feedback control. The rotation speed (N) and torque (T) of the 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, at the same time, output a torque command obtained from the result to the inverter (5), and the inverter (5) may perform torque feedback control.

The inverter (5) can also detect the voltage of the battery (8), and the voltage of the battery (8) is input from the inverter (5) to the main control unit (6). However, the voltage of the battery (8) may also be detected by a voltmeter.

Next, with reference 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).

In this state, when the operating device (7) is operated, the control device (4) controls the motor (3) so that the rotation speed (N) of the motor (3) becomes the rotation speed according to the speed command for the hydraulic actuator (12) (step (S2)). Specifically, the main control unit (6) of the control device (4) outputs to the inverter (5) a rotation speed command that increases as the speed command increases.

Next, the control device (4) updates the torque-rpm characteristics of the electric motor (3) based on the voltage of the battery (8) (step (S3)). As illustrated in Fig. 4, the main control unit (6) of the control device (4) stores in advance the torque-rpm characteristics of a plurality of electric motors (3) corresponding to the voltage of the battery (8).

Thereafter, the control device (4) determines whether the operating point determined from the rotation speed (N) and torque (T) of the motor (3) is within the torque-rotation speed characteristic (step (S4)). Here, “within the torque-rotation speed characteristic” also includes cases where the operating point is located on the line of the torque-rotation speed characteristic.

If the operating point of the motor (3) is within the torque-rpm characteristic (YES in step (S4)), the control device (4) repeats steps (S2) and (S3). On the other hand, as illustrated in Fig. 3, if the operating point of the motor (3) is outside the torque-rpm characteristic, the control device (4) changes the rotation speed (N) of the motor (3) to a rotation speed corresponding to the torque (T) of the motor (3) within the torque-rpm characteristic (step (S5)). Accordingly, the operating point of the motor (3) shifts to the left on a graph in which the horizontal axis represents the rotation speed and the vertical axis represents the torque. The rotation speed at which the change is made may be a rotation speed on the line of the torque-rpm characteristic or a rotation speed lower than the rotation speed on the line of the torque-rpm characteristic.

Next, the control device (4) reduces the capacity (q) of the hydraulic pump (2) while simultaneously increasing the rotational speed (N) of the electric motor (3) under the condition of maintaining the discharge flow rate (Q) of the hydraulic pump (2) (step (S6)). Accordingly, the operating point of the electric motor (3) shifts downward to the right on a graph in which the horizontal axis represents the rotational speed and the vertical axis represents the torque.

Thereafter, the control device (4) determines whether the overall efficiency (η) when converting electrical energy into hydraulic energy has improved (step (S7)). Electrical energy is the product of voltage, current, and time, and hydraulic energy is the product of pressure, flow rate, and time. In addition, the overall efficiency (η) is the product of the motor efficiency (ηm) and the pump efficiency (ηp).

The main control unit (6) has a map of the motor efficiency (ηm) as shown in Fig. 5 and a map of the pump efficiency (ηp) as shown in Fig. 6 stored in advance. However, the motor efficiency (ηm) and the pump efficiency (ηp) may be functions instead of maps. The motor efficiency (ηm) has the rotational speed and torque as parameters, and the pump efficiency (ηp) has the discharge pressure and the capacity ratio to the maximum capacity, i.e., q/qmax, as parameters. In the present embodiment, the discharge pressure of the hydraulic pump (2) is detected by the pressure sensor (9) as shown in Fig. 1.

If the overall efficiency (η) is improved (YES in step (S7)), in other words, if the overall efficiency (η) increases, the control device (4) repeats step (S6). On the other hand, if the overall efficiency (η) is not improved (NO in step (S7)), 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 (S6) (step (S8)). That is, if step (S6) is performed n times before reaching step (S8), 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 (S6).

In the hydraulic system (1) of the configuration described above, when the required output for the electric motor (3) exceeds the maximum output of the electric motor (3), the rotational speed (N) of the electric motor (3) is reduced to a rotational speed within the torque-rotational speed characteristic. Therefore, the electric motor (3) can be stably controlled even when the voltage of the battery (8) is reduced.

In addition, in this embodiment, since 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 that the overall efficiency (η) increases after the rotational speed (N) of the electric motor (3) is changed, the electric motor (3) can be operated in a state of low energy consumption within the torque-rotation speed characteristics. Furthermore, since the capacity (q) of the hydraulic pump (2) and the rotational speed (N) of the electric motor (3) return to the values of the previous process when the overall efficiency (η) decreases, the state in which the energy consumption of the electric motor (3) is minimum can be easily determined.

<Variations>

The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

For example, the reference capacity (qr) may not be the maximum capacity (qmax). In this case, the control device (4) may repeat the process of increasing the capacity (q) of the hydraulic pump (2) and decreasing the rotational speed (N) of the electric motor (3) so that the overall efficiency (η) increases under the condition of maintaining the discharge flow rate (Q) of the hydraulic pump (2) after step (S5). In this case, after step (S5), the control device (4) may calculate the overall efficiency (η1) when the rotational speed (N) of the electric motor (3) is increased so that the discharge flow rate (Q) of the hydraulic pump (2) is maintained while reducing the capacity (q) of the hydraulic pump (2) by a predetermined amount (Δq), and may also calculate the overall efficiency (η2) when the rotational speed (N) of the electric motor (3) is decreased so that the discharge flow rate (Q) of the hydraulic pump (2) is maintained while increasing the capacity (q) of the hydraulic pump (2) by a predetermined amount (Δq). And, the control device (4) may proceed to step (S5) when η1 is greater than η2 and repeat the process of decreasing the capacity (q) of the hydraulic pump (2) and increasing the rotation speed (N) of the electric motor (3), and may repeat the process of increasing the capacity (q) of the hydraulic pump (2) and decreasing the rotation speed (N) of the electric motor (3) when η2 is greater than η1.

Additionally, the control device (4) may not perform the processing of steps (S5) to (S8). In this case, the regulator (21) may mechanically change the capacity of the hydraulic pump (2) without being controlled by the control device (4).

Summary

In a first aspect, the present disclosure provides a hydraulic system comprising: a variable displacement hydraulic pump for supplying operating fluid to a hydraulic actuator when the hydraulic actuator is operated; an electric motor for driving the hydraulic pump by receiving power from a battery; a regulator for changing the capacity of the hydraulic pump; and a control device for controlling the electric motor, wherein the control device updates a torque-rotational speed characteristic of the electric motor, and when an operating point determined from the rotational speed of the electric motor and the torque of the electric motor according to a speed command for the hydraulic actuator is outside the torque-rotational speed characteristic, changes the rotational speed of the electric motor to a rotational speed corresponding to the torque of the electric motor within the torque-rotational speed characteristic.

According to the above configuration, when the required output for the motor exceeds the maximum output of the motor, the motor's rotational speed is reduced to a speed within the torque-rotational speed characteristic. Therefore, the motor can be stably controlled even when the battery voltage drops.

In a second aspect, in the first aspect, the control device controls the regulator, and the control device may, after changing the rotational speed of the electric motor to a rotational speed corresponding to the torque of the electric motor within the torque-rotational speed characteristic, repeat the process of decreasing the capacity of the hydraulic pump and increasing the rotational speed of the electric motor, or repeat the process of increasing the capacity of the hydraulic pump and decreasing the rotational speed of the electric motor, so as to increase the overall efficiency when converting electric energy into hydraulic energy under the condition of maintaining the discharge flow rate of the hydraulic pump. According to this configuration, the electric motor can be operated with low energy consumption within the torque-rotational speed characteristic.

As a third aspect, in the first or second aspect, if the overall efficiency decreases after the processing, 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 processing. With this configuration, it is possible to simply determine a state in which the energy consumption of the electric motor is minimized.

As a fourth aspect, in any one of the first to third aspects, for example, the control device may include an inverter interposed between the electric motor and the battery, and a main control unit that outputs a command to the inverter.

Claims (4)

A variable displacement hydraulic pump that supplies operating fluid to the hydraulic actuator when the hydraulic actuator is in operation,
An electric motor that is powered by a battery and drives the hydraulic pump,
A regulator that changes the capacity of the above hydraulic pump,
Equipped with a control device for controlling the above motor,
A hydraulic system characterized in that the control device updates the torque-rotational speed characteristic of the electric motor based on the voltage of the battery, and if the operating point determined from the rotational speed of the electric motor and the torque of the electric motor according to the speed command for the hydraulic actuator is outside the torque-rotational speed characteristic, the control device changes the rotational speed of the electric motor to a rotational speed corresponding to the torque of the electric motor within the torque-rotational speed characteristic. In the first paragraph,
The above control device controls the above regulator,
A hydraulic system characterized in that the control device repeats the process of decreasing the capacity of the hydraulic pump and increasing the rotational speed of the electric motor, or repeats the process of increasing the capacity of the hydraulic pump and decreasing the rotational speed of the electric motor, so as to increase the overall efficiency when converting electric energy into hydraulic energy under the condition of maintaining the discharge flow rate of the hydraulic pump after changing the rotational speed of the electric motor to a rotational speed corresponding to the torque of the electric motor within the torque-rotational speed characteristic. In the second paragraph,
A hydraulic system characterized in that the control device, when the overall efficiency decreases after the processing, returns the capacity of the hydraulic pump and the rotational speed of the electric motor to the values of the processing before. In any one of the first to third paragraphs,
A hydraulic system characterized in that the control device includes an inverter interposed between the electric motor and the battery, and a main control unit that outputs a command to the inverter.