EP4660463A1

EP4660463A1 - Hydraulic system

Info

Publication number: EP4660463A1
Application number: EP23919826.0A
Authority: EP
Inventors: Hideki Tanaka; Yukito Imamura
Original assignee: Kawasaki Heavy Industries Ltd; Kawasaki Jukogyo KK
Current assignee: Kawasaki Heavy Industries Ltd; Kawasaki Motors Ltd
Priority date: 2023-02-03
Filing date: 2023-09-05
Publication date: 2025-12-10
Also published as: WO2024161690A1; JP2024110754A; CN117597514A

Abstract

A hydraulic system (1) according to one embodiment includes: a hydraulic pump (2) that supplies hydraulic oil to a hydraulic actuator (12) at a time of moving the hydraulic actuator (12), the hydraulic pump (2) being a variable displacement pump; an electric motor (3) that is supplied with electric power from a battery (8) and that drives the hydraulic pump (2); a regulator (21) that changes a displacement of the hydraulic pump (2); and control circuitry (4) that controls the electric motor (3). The control circuitry (4) updates a torque-rotation speed characteristic of the electric motor (3) based on a voltage of the battery (8), and in a case where an operating point that is defined by a rotation speed of the electric motor (3) and a torque of the electric motor (3), the rotation speed of the electric motor (3) corresponding to a speed command to the hydraulic actuator (12), is out of the torque-rotation speed characteristic, the control circuitry (4) changes the rotation speed of the electric motor (3) into a rotation speed that corresponds to the torque of the electric motor (3) and that is within the torque-rotation speed characteristic.

Description

Technical Field

The present disclosure relates to a hydraulic system that electrically changes the delivery flow rate of a hydraulic pump.

Background Art

Conventionally, there has been a known hydraulic system that electrically changes the delivery flow rate of a hydraulic pump. For example, Patent Literature 1 discloses a hydraulic system that includes: a hydraulic pump of a variable displacement type; an electric motor that drives the hydraulic pump; a regulator that mechanically changes the displacement of the hydraulic pump; and control circuitry that controls the electric motor. In Patent Literature 1, the hydraulic system is referred to as an "inverter-driven hydraulic apparatus" and the regulator is referred to as a "pressure regulating mechanism". In Patent Literature 1, the control circuitry includes an inverter and main controlling circuitry, and the main controlling circuitry is referred to as a "controller".

Citation List

Patent Literature

PTL 1: Japanese Laid-Open Patent Application Publication No. 2019-183944

Summary of Invention

Technical Problem

Incidentally, an electric motor has a torque-rotation speed characteristic that is based on a maximum torque Tmax and a maximum rotation speed Nmax. In a case where the electric motor is supplied with electric power from a battery, it is known that the torque-rotation speed characteristic deteriorates in accordance with a decrease in the voltage of the battery. Specifically, as shown in FIG. 4, the maximum horsepower that can be outputted by the electric motor decreases in accordance with a decrease in the voltage of the battery. Horsepower is the product of the torque and the rotation speed.
In this case, an operating point that is defined by the rotation speed of the electric motor and the torque of the electric motor, the rotation speed of the electric motor corresponding to a speed command to a hydraulic actuator, may fall out of the torque-rotation speed characteristic, and an output required for the electric motor may exceed the maximum output of the electric motor. Even in such a situation, it is desired that the electric motor be stably controlled.
In view of the above, an object of the present disclosure is to provide a hydraulic system that is capable of stably controlling the electric motor even when the voltage of the battery has decreased.

Solution to Problem

The present disclosure provides a hydraulic system including: a hydraulic pump that supplies hydraulic oil to a hydraulic actuator at a time of moving the hydraulic actuator, the hydraulic pump being a variable displacement pump; an electric motor that is supplied with electric power from a battery and that drives the hydraulic pump; a regulator that changes a displacement of the hydraulic pump; and control circuitry that controls the electric motor. The control circuitry updates a torque-rotation speed characteristic of the electric motor based on a voltage of the battery, and in a case where an operating point that is defined by a rotation speed of the electric motor and a torque of the electric motor, the rotation speed of the electric motor corresponding to a speed command to the hydraulic actuator, is out of the torque-rotation speed characteristic, the control circuitry changes the rotation speed of the electric motor into a rotation speed that corresponds to the torque of the electric motor and that is within the torque-rotation speed characteristic.

Advantageous Effects of Invention

The present disclosure provides a hydraulic system that is capable of stably controlling the electric motor even when the voltage of the battery has decreased.

Brief Description of Drawings

FIG. 1 shows a schematic configuration of a hydraulic system according to one embodiment.
FIG. 2 is a flowchart of control performed by control circuitry.
FIG. 3 shows a torque-rotation speed characteristic that has deteriorated, and shows an operating point being shifted by the control.
FIG. 4 shows how the torque-rotation speed characteristic deteriorates.
FIG. 5 is a map of electric motor efficiency.
FIG. 6 is a map of pump efficiency.

Description of Embodiments

FIG. 1 shows a hydraulic system 1 according to one embodiment. The hydraulic system 1 electrically changes a delivery flow rate Q of a hydraulic pump 2, which is a variable displacement pump.
Specifically, the hydraulic system 1 includes: the hydraulic pump 2; an electric motor 3, which drives the hydraulic pump 2; a regulator 21, which changes a displacement q of the hydraulic pump 2; and control circuitry 4, which controls the electric motor 3 and the regulator 21. The displacement q is a delivery amount per rotation of the hydraulic pump 2, and the delivery flow rate Q is the product of the displacement q of the hydraulic pump 2 and a rotation speed N of the electric motor 3.
The hydraulic pump 2 supplies hydraulic oil to a hydraulic actuator 12 at the time of moving the hydraulic actuator 12. 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 moves bi-directionally in accordance with the supply of pressurized oil thereto, such as a hydraulic motor or a double-acting cylinder, or may be an actuator that moves in a single direction in accordance with the supply of the pressurized oil thereto, such as a single-acting cylinder. In the former case, the switching valve 11 is a three-position valve, whereas in the latter case, the switching valve 11 is a two-position valve.
In the present embodiment, the hydraulic pump 2 is an axial piston pump, such as a swash plate pump or a bent axis pump. Alternatively, the hydraulic pump 2 may be a different type of pump, such as a vane pump.
A displacement command is outputted from the control circuitry 4 to the regulator 21, and the regulator 21 changes the displacement q of the hydraulic pump 2 in accordance with the displacement command. For example, the displacement command is a command current. For example, in a case where the hydraulic pump 2 is a swash plate pump, the regulator 21 may electrically change a hydraulic pressure applied to a servo piston coupled to the swash plate of the hydraulic pump 2, or may be an electric actuator coupled to the swash plate of the hydraulic pump 2.
The electric motor 3 is supplied with electric power from a battery 8. The electric motor 3 is, for example, a servomotor. Alternatively, the electric motor 3 may be a different type of motor, such as an induction motor.
Regarding the control circuitry 4, the functionality of the elements disclosed herein may be implemented using circuitry or processing circuitry which includes general purpose processors, special purpose processors, integrated circuits, ASICs ("Application Specific Integrated Circuits"), conventional circuitry and/or combinations thereof which are configured or programmed to perform the disclosed functionality. Processors are considered processing circuitry or circuitry as they include transistors and other circuitry therein. In the disclosure, the circuitry, units, or means are hardware that carry out or are programmed to perform the recited functionality. The hardware may be any hardware disclosed herein or otherwise known which is programmed or configured to carry out the recited functionality. When the hardware is a processor which may be considered a type of circuitry, the circuitry, means, or units are a combination of hardware and software, the software being used to configure the hardware and/or processor.
In the present embodiment, the control circuitry 4 includes: an inverter 5 located between the electric motor 3 and the battery 8; and main controlling circuitry 6, which outputs a command to the inverter 5. The present embodiment adopts an operator 7, which receives an operation to move the hydraulic actuator 12. A speed command to the hydraulic actuator 12 is inputted from the operator 7 to the main controlling circuitry 6. For example, in a case where the operator 7 includes an operating lever, the speed command to the hydraulic actuator 12 increases in accordance with an increase in the inclination angle of the operating lever.
In the present embodiment, the main controlling circuitry 6 outputs a rotation speed command to the inverter 5. The inverter 5 can acquire 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 inputted to the main controlling circuitry 6 from the inverter 5. Alternatively, the main controlling circuitry 6 may perform the speed feedback control and output a torque command obtained therefrom to the inverter 5. Then, the inverter 5 may perform the torque feedback control.
The inverter 5 can also acquire the voltage of the battery 8. The voltage of the battery 8 is inputted to the main controlling circuitry 6 from the inverter 5. Alternatively, the voltage of the battery 8 may be detected by a voltmeter.
Next, control performed by the control circuitry 4 is described with reference to FIG. 2. First, the control circuitry 4 controls the regulator 21 such that the displacement q of the hydraulic pump 2 is a reference displacement qr (step S1). The reference displacement qr is, for example, a maximum displacement qmax.
In this state, when the operator 7 is operated, the control circuitry 4 controls the electric motor 3 such that the rotation speed N of the electric motor 3 is a rotation speed corresponding to a speed command to the hydraulic actuator 12 (step S2). Specifically, the main controlling circuitry 6 of the control circuitry 4 outputs, to the inverter 5, a rotation speed command that increases in accordance with an increase in the speed command.
Then, the control circuitry 4 updates the torque-rotation speed characteristic of the electric motor 3 based on the voltage of the battery 8 (step S3). Multiple torque-rotation speed characteristics of the electric motor 3 corresponding to different voltages of the battery 8, respectively, as shown in FIG. 4 are prestored in the main controlling circuitry 6 of the control circuitry 4.
Thereafter, the control circuitry 4 determines whether or not an operating point that is defined by the rotation speed N and the torque T of the electric motor 3 is within the torque-rotation speed characteristic (step S4). The operating point being "within the torque-rotation speed characteristic" encompasses a case where the operating point is positioned on the line of the torque-rotation speed characteristic.
In a case where the operating point of the electric motor 3 is within the torque-rotation speed characteristic (YES in step S4), the control circuitry 4 performs step S2 and step S3 again. On the other hand, in a case where the operating point of the electric motor 3 is out of the torque-rotation speed characteristic as shown in FIG. 3, the control circuitry 4 changes the rotation speed N of the electric motor 3 into a rotation speed that corresponds to the torque T of the electric motor 3 and that is within the torque-rotation speed characteristic (step S5). Consequently, the operating point of the electric motor 3 shifts to the left on a graph whose horizontal axis represents the rotation speed and whose vertical axis represents the torque. The rotation speed that has been thus changed may be a rotation speed on the line of the torque-rotation speed characteristic, or may be less than the rotation speed on the line of the torque-rotation speed characteristic.
Next, the control circuitry 4 decreases the displacement q of the hydraulic pump 2 and increases the rotation speed N of the electric motor 3 under the condition that the delivery flow rate Q of the hydraulic pump 2 is maintained (step S6). Consequently, the operating point of the electric motor 3 shifts to the lower right on the graph whose horizontal axis represents the rotation speed and whose vertical axis represents the torque.
Thereafter, the control circuitry 4 determines whether or not an overall efficiency η in converting electrical energy into hydraulic energy has improved (step S7). The electrical energy is the product of a voltage, an electric current, and a time, whereas the hydraulic energy is the product of a pressure, a flow rate, and a time. The overall efficiency η is the product of an electric motor efficiency ηm and a pump efficiency ηp.
The main controlling circuitry 6 prestores therein a map of the electric motor efficiency ηm as shown in FIG. 5 and a map of the pump efficiency ηp as shown in FIG. 6. Alternatively, instead of using these maps, each of the electric motor efficiency ηm and the pump efficiency ηp may be converted into a function. The electric motor efficiency ηm takes the rotation speed and the torque as parameters, whereas the pump efficiency ηp takes the delivery pressure and the ratio of the displacement to the maximum displacement, i.e., q / qmax, as parameters. In the present embodiment, as shown in FIG. 1, the delivery pressure of the hydraulic pump 2 is detected by a pressure sensor 9.
In a case where the overall efficiency η has improved (YES in step S7), in other words, in a case where the overall efficiency η has increased, the control circuitry 4 performs step S6 again. On the other hand, in a case where the overall efficiency η has not improved (NO in step S7), in other words, in a case where the overall efficiency η has decreased, the control circuitry 4 brings the displacement q of the hydraulic pump 2 and the rotation speed N of the electric motor 3 back to their values in step S6 immediately previously performed (step S8). Specifically, in a case where step S6 has been performed n times before reaching step S8, the displacement q of the hydraulic pump 2 and the rotation speed N of the electric motor 3 are set to their values in step S6 performed for the n-1th time.
In the hydraulic system 1 configured as described above, when the output required for the electric motor 3 exceeds the maximum output of the electric motor 3, the rotation speed N of the electric motor 3 decreases to a rotation speed that is within the torque-rotation speed characteristic. Therefore, even when the voltage of the battery 8 has decreased, the electric motor 3 can be stably controlled.
Further, in the present embodiment, after the rotation speed N of the electric motor 3 has been changed, a process of decreasing the displacement q of the hydraulic pump 2 and increasing the rotation speed N of the electric motor 3 is repeatedly performed such that the overall efficiency η increases. This makes it possible to operate the electric motor 3 within the torque-rotation speed characteristic with less energy consumption. Still further, in a case where the overall efficiency η has decreased, the displacement q of the hydraulic pump 2 and the rotation speed N of the electric motor 3 are brought back to their values in the process immediately previously performed. This makes it possible to readily determine a state where the energy consumption of the electric motor 3 is minimized.

The present disclosure is not limited to the above-described embodiment. Various modifications can be made without departing from the scope of the present disclosure.
For example, the reference displacement qr need not be the maximum displacement qmax. In this case, after step S5, the control circuitry 4 may repeatedly perform a process of increasing the displacement q of the hydraulic pump 2 and decreasing the rotation speed N of the electric motor 3 under the condition that the delivery flow rate Q of the hydraulic pump 2 is maintained, such that the overall efficiency η increases. In this case, after step S5, the control circuitry 4 may calculate an overall efficiency η1, which is the overall efficiency when decreasing the displacement q of the hydraulic pump 2 by a predetermined displacement Δq and increasing the rotation speed N of the electric motor 3 such that the delivery flow rate Q of the hydraulic pump 2 is maintained, and also, the control circuitry 4 may calculate an overall efficiency η2, which is the overall efficiency when increasing the displacement q of the hydraulic pump 2 by the predetermined displacement Δq and decreasing the rotation speed N of the electric motor 3 such that the delivery flow rate Q of the hydraulic pump 2 is maintained. Then, if η1 if greater than η2, the control circuitry 4 may proceed to step S5 and repeatedly perform the process of decreasing the displacement q of the hydraulic pump 2 and increasing the rotation speed N of the electric motor 3, whereas if n2 is greater than η1, the control circuitry 4 may repeatedly perform the process of increasing the displacement q of the hydraulic pump 2 and decreasing the rotation speed N of the electric motor 3.
The control circuitry 4 need not perform the processes in step S5 to step S8. In this case, the regulator 21 may mechanically change the displacement of the hydraulic pump 2 without being controlled by the control circuitry 4.

The present disclosure provides, as a first mode, a hydraulic system including: a hydraulic pump that supplies hydraulic oil to a hydraulic actuator at a time of moving the hydraulic actuator, the hydraulic pump being a variable displacement pump; an electric motor that is supplied with electric power from a battery and that drives the hydraulic pump; a regulator that changes a displacement of the hydraulic pump; and control circuitry that controls the electric motor. The control circuitry updates a torque-rotation speed characteristic of the electric motor based on a voltage of the battery, and in a case where an operating point that is defined by a rotation speed of the electric motor and a torque of the electric motor, the rotation speed of the electric motor corresponding to a speed command to the hydraulic actuator, is out of the torque-rotation speed characteristic, the control circuitry changes the rotation speed of the electric motor into a rotation speed that corresponds to the torque of the electric motor and that is within the torque-rotation speed characteristic.
According to the above configuration, when the output required for the electric motor exceeds the maximum output of the electric motor, the rotation speed of the electric motor decreases to a rotation speed that is within the torque-rotation speed characteristic. Therefore, even when the voltage of the battery has decreased, the electric motor can be stably controlled.
As a second mode, in the first mode, the control circuitry may control the regulator, and after changing the rotation speed of the electric motor into the rotation speed that corresponds to the torque of the electric motor and that is within the torque-rotation speed characteristic, the control circuitry may repeatedly perform, under a condition that a delivery flow rate of the hydraulic pump is maintained, a process of decreasing the displacement of the hydraulic pump and increasing the rotation speed of the electric motor or a process of increasing the displacement of the hydraulic pump and decreasing the rotation speed of the electric motor, such that an overall efficiency in converting electrical energy into hydraulic energy increases. This configuration makes it possible to operate the electric motor within the torque-rotation speed characteristic with less energy consumption.
As a third mode, in the first or second mode, in a case where the overall efficiency has decreased after the process, the control circuitry may bring the displacement of the hydraulic pump and the rotation speed of the electric motor back to their values in the process immediately previously performed. This configuration makes it possible to readily determine a state where the energy consumption of the electric motor is minimized.
As a fourth mode, in any one of the first to third modes, for example, the control circuitry may include: an inverter located between the electric motor and the battery; and main controlling circuitry that outputs a command to the inverter.

Claims

A hydraulic system comprising:
a hydraulic pump that supplies hydraulic oil to a hydraulic actuator at a time of moving the hydraulic actuator, the hydraulic pump being a variable displacement pump;

an electric motor that is supplied with electric power from a battery and that drives the hydraulic pump;

a regulator that changes a displacement of the hydraulic pump; and

control circuitry that controls the electric motor, wherein

the control circuitry updates a torque-rotation speed characteristic of the electric motor based on a voltage of the battery, and in a case where an operating point that is defined by a rotation speed of the electric motor and a torque of the electric motor, the rotation speed of the electric motor corresponding to a speed command to the hydraulic actuator, is out of the torque-rotation speed characteristic, the control circuitry changes the rotation speed of the electric motor into a rotation speed that corresponds to the torque of the electric motor and that is within the torque-rotation speed characteristic.
The hydraulic system according to claim 1, wherein
the control circuitry controls the regulator, and

after changing the rotation speed of the electric motor into the rotation speed that corresponds to the torque of the electric motor and that is within the torque-rotation speed characteristic, the control circuitry repeatedly performs, under a condition that a delivery flow rate of the hydraulic pump is maintained, a process of decreasing the displacement of the hydraulic pump and increasing the rotation speed of the electric motor or a process of increasing the displacement of the hydraulic pump and decreasing the rotation speed of the electric motor, such that an overall efficiency in converting electrical energy into hydraulic energy increases.
The hydraulic system according to claim 2, wherein
in a case where the overall efficiency has decreased after the process, the control circuitry brings the displacement of the hydraulic pump and the rotation speed of the electric motor back to their values in the process immediately previously performed.
The hydraulic system according to any one of claims 1 to 3, wherein
the control circuitry includes:
an inverter located between the electric motor and the battery; and

main controlling circuitry that outputs a command to the inverter.