CN114207224B

CN114207224B - Construction machine

Info

Publication number: CN114207224B
Application number: CN202080055522.5A
Authority: CN
Inventors: 石井刚史; 高桥究
Original assignee: Hitachi Construction Machinery Tierra Co Ltd
Current assignee: Hitachi Construction Machinery Tierra Co Ltd
Priority date: 2019-09-25
Filing date: 2020-06-12
Publication date: 2022-12-16
Anticipated expiration: 2040-06-12
Also published as: CN114207224A; WO2021059617A1; EP3995632A1; JP2021050546A; JP7110164B2; US20220282457A1; EP3995632A4

Abstract

Provided is a construction machine which can detect the operation state of an operation device even if the idle rotation speed of a prime mover is set low, and can set the idle rotation speed of the prime mover low. The hydraulic excavator is provided with: an operation device for generating a pilot pressure corresponding to an operation amount of the operation lever and switching the control valve by the generated pilot pressure; and a control device for controlling the rotation speed of the electric motor to a preset idle rotation speed when the non-operation state of the operation device is continuously generated. Further, the hydraulic excavator includes: a hydraulic signal line connected between the discharge side of the pilot pump and the oil tank and having a control valve interposed therebetween; a fixed throttle valve provided between a discharge side of the pilot pump and the control valve in the hydraulic signal line; and pressure sensors that detect the hydraulic pressures on the upstream side and the downstream side of the fixed throttle, respectively. The control device detects the operation state of the operation device based on the detection result of the pressure sensor.

Description

Construction machine

Technical Field

The present invention relates to a construction machine having an automatic idling control function.

Background

A hydraulic excavator as one of construction machines includes: a prime mover (specifically, for example, an engine or an electric motor); a hydraulic pump driven by the prime mover; a plurality of hydraulic actuators; a plurality of control valves for controlling the flow of hydraulic oil from the hydraulic pump to the plurality of hydraulic actuators, respectively; and a plurality of operation devices that switch the plurality of control valves. In recent years, from the viewpoint of energy saving, noise reduction, and the like, an automatic idle speed control function is provided that reduces the rotational speed of a motor from a standard rotational speed to an idle rotational speed when a non-operation state of a plurality of operation devices continues to occur (for example, see patent document 1).

The hydraulic excavator of patent document 1 includes: a pilot pump driven by the prime mover; a hydraulic signal line which is connected between the discharge side of the pilot pump and the tank, has the plurality of control valves interposed therebetween, and is shut off when any one of the plurality of control valves is switched from the neutral position; a pilot overflow valve provided on the discharge side of the pilot pump; a fixed throttle valve provided between a discharge side of the pilot pump in the hydraulic signal line and the plurality of control valves; a pressure sensor that detects the hydraulic pressure on the downstream side of the fixed throttle (in other words, between the fixed throttle and the control valve); and a control device that detects the operation states of the plurality of operation devices based on the detection result of the pressure sensor.

When any one of the plurality of operation devices is operated (that is, when any one of the plurality of control valves is switched from the neutral position), the hydraulic pressure signal line is blocked, and the hydraulic pressure detected by the pressure sensor rises to the vicinity of the relief pressure of the pilot relief valve. When all the operation devices are not operated (that is, when all the control valves are in the neutral positions), the hydraulic pressure signal lines are brought into a communication state, and the hydraulic pressure detected by the pressure sensors is reduced. The control device determines whether any one of the operation devices is operated, based on whether or not the hydraulic pressure detected by the pressure sensor exceeds a preset threshold value.

The control device determines that all the operation devices are not operated when the hydraulic pressure detected by the pressure sensor is equal to or less than a threshold value. When all the operation devices have not been operated for a predetermined time, the rotation speed of the motor is reduced to the idle rotation speed. Further, the control device determines that any one of the operation devices is operated when the hydraulic pressure detected by the pressure sensor exceeds a threshold value. The rotational speed of the prime mover is maintained or returned to the standard rotational speed.

Documents of the prior art

Patent literature

Patent document 1: japanese laid-open patent publication No. 2012-225050

Disclosure of Invention

In the above-described conventional technique, a pressure sensor that detects the hydraulic pressure on the downstream side of the fixed throttle is provided, and the operating state of the operating device is detected by comparing the hydraulic pressure detected by the pressure sensor with a threshold value. However, the above-described conventional techniques still have room for improvement as described below.

The threshold value needs to be set higher than the hydraulic pressure detected by the pressure sensor when the rotational speed of the motor is the standard rotational speed and the hydraulic pressure signal line is in the communication state (specifically, the hydraulic pressure obtained by adding the tank pressure to the pressure loss in the portion from the pressure sensor to the tank in the hydraulic pressure signal line increases as the oil temperature decreases). Further, the hydraulic pressure detected by the pressure sensor needs to be set lower than the hydraulic pressure detected when the rotational speed of the motor is the idling rotational speed and the hydraulic pressure signal line is blocked.

However, when the rotation speed of the motor is reduced to the idling rotation speed, the discharge flow rate of the pilot pump is reduced. The pilot relief valve has an overshoot characteristic in which the relief pressure decreases in proportion to a decrease in the flow rate of the oil. Therefore, if the idling rotation speed of the motor is too low, the hydraulic pressure detected by the pressure sensor may not exceed the threshold value when the rotation speed of the motor is the idling rotation speed and the hydraulic pressure signal line is blocked. That is, there is a possibility that the operation state of the operation device cannot be detected. Therefore, it is difficult to set the idle rotation speed of the motor low.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a construction machine capable of detecting an operation state of an operation device even when an idle rotation speed of a prime mover is set low, and setting the idle rotation speed of the prime mover low.

In order to achieve the above object, a construction machine according to the present invention includes: a prime mover; a hydraulic pump driven by the prime mover; a hydraulic actuator; a control valve that controls a flow of hydraulic oil from the hydraulic pump to the hydraulic actuator; an operation device that generates a pilot pressure corresponding to an operation amount of an operation lever and switches the control valve by the generated pilot pressure; and a control device that controls a rotation speed of the prime mover to a preset idle rotation speed when a non-operation state of the operation device continues to occur, wherein the construction machine includes: a pilot pump that is driven by the prime mover and in which a discharge pressure is used as a base pressure of the pilot pressure; a pilot relief valve provided on a discharge side of the pilot pump; a hydraulic signal line connected between a discharge side of the pilot pump and a tank, sandwiching the control valve, and blocked when the control valve is switched from a neutral position; a fixed throttle provided between the discharge side of the pilot pump in the hydraulic signal line and the control valve; a 1 st pressure sensor that detects a hydraulic pressure on an upstream side of the fixed throttle; and a 2 nd pressure sensor that detects a hydraulic pressure on a downstream side of the fixed throttle, the control device detecting an operation state of the operation device based on detection results of the 1 st pressure sensor and the 2 nd pressure sensor.

Effects of the invention

According to the present invention, the operation state of the operation device can be detected even if the idle rotation speed of the motor is set low, and the idle rotation speed of the motor can be set low.

Drawings

Fig. 1 is a side view showing a structure of a hydraulic excavator according to an embodiment of the present invention.

Fig. 2 is a plan view showing the structure of a hydraulic excavator according to an embodiment of the present invention.

Fig. 3 is a diagram showing a configuration of a hydraulic drive apparatus according to an embodiment of the present invention.

Fig. 4 is a flowchart showing a processing procedure of the control device according to the embodiment of the present invention.

Detailed Description

Hereinafter, one embodiment of the present invention will be described with reference to the drawings by taking a hydraulic excavator as an example of an application object of the present invention.

Fig. 1 is a side view showing a structure of a hydraulic excavator according to the present embodiment, and fig. 2 is a plan view. Hereinafter, the front side (right side in fig. 1 and 2), the rear side (left side in fig. 1 and 2), the left side (back side in the paper of fig. 1, upper side in fig. 2), and the right side (front side in the paper of fig. 1, lower side in fig. 2) of the driver in the case where the driver is seated in the driver seat in the state shown in fig. 1 and 2 of the hydraulic excavator will be simply referred to as front side, rear side, left side, and right side.

The hydraulic excavator of the present embodiment includes: a lower traveling structure 1 capable of traveling; an upper swing structure 2 rotatably provided on an upper side of the lower traveling structure 1; and a working device 3 connected to the front side of the upper rotating body 2.

Lower carrier 1 has a track frame 4 having an H-shape as viewed from above. A drive wheel 5 and a driven wheel 6 are provided on the right side of the track frame 4, and a right crawler (crawler) 7A is wound therebetween. The right drive wheel 5 is rotated by driving the right traveling motor 8, and the right crawler belt 7A is rotated. A drive wheel (not shown) and a driven wheel (not shown) are also provided on the left side of the track frame 4, and a left crawler belt 7B is wound around between these wheels. The left drive wheel is rotated by a left travel motor (not shown), and the left crawler belt 7B is further rotated.

A shovel 9 for removing soil is provided on the front side of the track frame 4 so as to be movable up and down. The blade 9 is driven by a blade hydraulic cylinder (not shown) to move up and down.

The working device 3 includes: a swing post 10 connected to a front side of the upper rotating body 2 (in detail, a rotating frame described later) so as to be rotatable in a left-right direction; a boom 11 connected to the swing post 10 so as to be rotatable in the vertical direction; an arm 12 connected to the boom 11 so as to be rotatable in the vertical direction; and a bucket 13 coupled to arm 12 so as to be rotatable in the vertical direction. The swing post 10, the boom 11, the arm 12, and the bucket 13 are rotated by driving a swing cylinder (not shown), a boom cylinder 14, an arm cylinder 15, and a bucket cylinder 16, respectively. The bucket 13 can be replaced with an attachment (not shown) in which a hydraulic actuator for selection is incorporated.

The upper rotating body 2 includes: a rotating frame 17 constituting a base structure; a cabin-type cab 18 provided on the front left side of the rotating frame 17; and a weight 19 provided at the rear end of the rotating frame 17. The swivel frame 17 of the upper swivel 2 is coupled to the upper side of the track frame 4 of the lower traveling structure 1 via the swivel wheel 20. The upper rotating body 2 is rotated by driving a rotating motor (not shown).

A door lock lever (not shown) that can be operated by the driver to a raised position (a boarding/alighting allowance position) and a lowered position (a boarding/alighting restriction position) is provided at the boarding/alighting port of the cab 18. An operator's seat 21 on which an operator sits is provided inside the cab 18; and a plurality of operation lever devices (described in detail later) and a rotation speed indicator 22 (see fig. 3 described later) that can be operated by the driver.

The hydraulic excavator includes a hydraulic drive device that drives a plurality of hydraulic actuators (specifically, the right travel motor 8, the left travel motor, the blade cylinder, the swing cylinder, the boom cylinder 14, the arm cylinder 15, the bucket cylinder 16, the hydraulic actuator for selection, and the rotating electric machine) in response to an operation of a plurality of control lever devices. The configuration of the hydraulic drive apparatus will be described with reference to fig. 3.

Fig. 3 is a diagram showing a configuration of the hydraulic drive apparatus according to the present embodiment. Fig. 3 typically shows the configurations of the right-side travel motor 8 and the boom cylinder 14.

The hydraulic drive device of the present embodiment includes: an electric motor 23 (prime mover); a battery 24 as an electric power source of the motor 23; an inverter 25 that controls the rotation speed of the motor 23; a hydraulic pump 26 and a pilot pump 27 driven by the electric motor 23; a right travel control valve 28 that controls the flow of hydraulic oil from the hydraulic pump 26 to the right travel motor 8; a boom control valve 29 that controls the flow of hydraulic oil from the hydraulic pump 26 to the boom cylinder 14; an operation lever device 30 for switching the right travel control valve 28; an operation lever device 31 for switching the boom control valve 29; and a control device 32.

The operation lever device 30 includes: a not-shown travel operation lever that can be operated by the driver; a 1 st pressure reducing valve operated according to a front side operation of the travel operation lever; and a 2 nd pressure reducing valve operated according to a rear side operation of the travel operation lever. The 1 st pressure reducing valve generates a pilot pressure corresponding to the amount of front side operation of the travel control lever using the discharge pressure of the pilot pump 27 as a base pressure, and outputs the generated pilot pressure to the pressure receiving portion on the side of the right travel control valve 28. As a result, the right-side travel control valve 28 is switched from the neutral position to the one-side switching position, and the right-side travel motor 8 is rotated in one direction. The 2 nd pressure reducing valve generates a pilot pressure corresponding to the rear side operation amount of the travel operation lever with the discharge pressure of the pilot pump 27 as a base pressure, and outputs the generated pilot pressure to the other pressure receiving portion of the right travel control valve 28. As a result, the right-side travel control valve 28 is switched from the neutral position to the other switching position, and the right-side travel motor 8 is rotated in the opposite direction.

The operation lever device 31 includes: a working lever, not shown, which can be operated by the driver; a 3 rd pressure reducing valve operated according to a front side operation of the operation lever; and a 4 th pressure reducing valve operated according to a rear side operation of the working lever. The 3 rd pressure reducing valve generates a pilot pressure corresponding to the front side operation amount of the working lever with the discharge pressure of the pilot pump 27 as a base pressure, and outputs the generated pilot pressure to the pressure receiving portion on the boom control valve 29 side. Thereby, the boom control valve 29 is switched from the neutral position to the one switching position, and the boom cylinder 14 is shortened. The 4 th pressure reducing valve generates a pilot pressure corresponding to the rear side operation amount of the working lever with the discharge pressure of the pilot pump 27 as a base pressure, and outputs the generated pilot pressure to the pressure receiving portion on the boom control valve 29 side. Thereby, the boom control valve 29 is switched from the neutral position to the other switching position, and the boom cylinder 14 is extended.

The

lever devices

30 and 31 constitute an operation device that generates a pilot pressure corresponding to an operation amount of the lever and switches the control valve by the generated pilot pressure. Although not shown, the left-side travel motor, the blade cylinder, the swing cylinder, the arm cylinder 15, the bucket cylinder 16, the hydraulic actuator for selection, and the rotating electric machine are configured in substantially the same manner.

A pilot relief valve 33 and a lock valve 34 are provided on the discharge side of the pilot pump 27. When the discharge pressure of the pilot pump 27 is equal to or higher than the relief pressure, the pilot relief valve 33 is opened, and a part of the hydraulic oil discharged from the pilot pump 27 is returned to the tank. Thereby, the discharge pressure of the pilot pump 27 is maintained at the relief pressure.

The lock valve 34 is switched according to the operation of the door lock lever described above. Specifically, a lock switch (not shown) is provided which is closed when the door lock lever is at the lowered position and opened when the door lock lever is at the raised position. When the lock switch is in the closed state, the solenoid portion of the lock valve 34 is energized via the lock switch, and the lock valve 34 is switched from the neutral position to the switching position. Thereby, the discharge line of the pilot pump 27 is communicated, and the discharge pressure of the pilot pump 27 is introduced into the

operation lever devices

30, 31 and the like. On the other hand, when the lock switch is in the on state, the solenoid portion of the lock valve 34 is not energized, and the lock valve 34 is set to the neutral position by the biasing force of the spring. Thereby, the discharge line of the pilot pump 27 is blocked. As a result, even if the

operation lever devices

30 and 31 are operated, the pilot pressure is not generated, and the plurality of hydraulic actuators do not operate.

A hydraulic signal line 35 is connected to the discharge side of the pilot pump 27. The hydraulic signal line 35 is connected between the discharge side of the pilot pump 27 and the tank 36, and includes a plurality of control valves (specifically, not only the right-side travel control valve 28 and the boom control valve 29 described above, but also a left-side travel control valve, a blade control valve, a swing column control valve, an arm control valve, a bucket control valve, a selection control valve, and a rotation control valve, which are not shown), and the hydraulic signal line 35 is in a communication state when all the control valves are in the neutral position, and the hydraulic signal line 35 is in a blocking state when any one of the control valves is switched from the neutral position.

A fixed throttle 37 is provided between the discharge side of the pilot pump 27 and the plurality of control valves in the hydraulic signal line 35. Further, a pressure sensor 38 (1 st pressure sensor) that detects the hydraulic pressure on the upstream side of the fixed throttle 37 and a pressure sensor 39 (2 nd pressure sensor) that detects the hydraulic pressure on the downstream side of the fixed throttle 37 (in other words, between the fixed throttle 37 and the control valve) are provided.

The rotation indicator 22 can indicate that the standard rotation speed of the motor 23 is within a predetermined range (specifically, 2000 to 1500rpm, for example) by, for example, the rotational operation position of the dial, and output a signal corresponding to the standard rotation speed. The controller 32 sets a standard rotation speed of the motor 23 based on a signal from the rotation speed indicator 22, and controls the inverter 25 so that the rotation speed of the motor 23 becomes the standard rotation speed.

When all the operation devices have not been operated for a predetermined time, the controller 32 controls the inverter 25 so that the rotation speed of the motor 23 becomes an idle rotation speed (specifically, a low rotation speed preset so as to be lower than the standard rotation speed) (automatic idle control). Here, as the most characteristic feature of the present embodiment, the control device 32 detects the operation states of the plurality of operation devices based on the detection results of the

pressure sensors

38, 39. Specifically, the control device 32 detects the operation states of the plurality of operation devices based on a differential pressure between the hydraulic pressure detected by the pressure sensor 38 and the hydraulic pressure detected by the pressure sensor 39 (hereinafter referred to as a differential pressure of the fixed throttle 37).

When all the operation devices are not operated (that is, when all the control valves are in the neutral positions), the hydraulic signal line 35 is in a communication state, and the differential pressure of the fixed throttle 37 increases. On the other hand, when any one of the operating devices is operated (that is, when any one of the control valves is switched from the neutral position), the hydraulic pressure signal line 35 is blocked, and the differential pressure of the fixed throttle 37 becomes smaller to near zero. When the differential pressure of the fixed throttle 37 is equal to or greater than a predetermined threshold value, the controller 32 determines that all the operation devices are not operated. When all the operation devices have not been operated for a predetermined time, the rotation speed of the electric motor 23 is reduced to the idle rotation speed. When the differential pressure of the fixed throttle 37 is less than the threshold value, the controller 32 determines that any one of the operation devices has been operated. Then, the rotation speed of the motor 23 is maintained or returned to the standard rotation speed.

Next, a processing procedure of the control device of the present embodiment will be described. Fig. 4 is a flowchart showing a processing procedure of the control device in the present embodiment. Further, the processing shown in fig. 4 is performed periodically.

In step S1, the control device 32 calculates the differential pressure of the fixed throttle 37 based on the detection results of the

pressure sensors

38 and 39. Then, the process proceeds to step S2, and it is determined whether or not the differential pressure of the fixed throttle 37 is equal to or greater than a threshold value. When the differential pressure of the fixed throttle 37 is equal to or higher than the threshold value (that is, all the operation devices are not operated), the process proceeds to step S3.

In step S3, the control device 32 determines whether the rotation speed of the motor 23 is controlled to the idle rotation speed (in other words, whether the motor 23 is in the idle state). If the rotation speed of the motor 23 is not controlled to the idling rotation speed (in other words, the motor 23 is not in the idling state), the process proceeds to step S4.

In step S4, the control device 32 accumulates the non-operation duration. Then, the process proceeds to step S5, and it is determined whether or not the non-operation duration time reaches a predetermined time.

If the non-operation duration time does not reach the predetermined time in step S5, the process proceeds to step S6. In step S6, the control device 32 drives the motor 23 at the standard rotation speed. On the other hand, when the non-operation duration has reached the predetermined time in step S5, the process proceeds to step S7. In step S7, the control device 32 drives the motor 23 at the idling rotation speed. When the rotation speed of the motor 23 is controlled to the idling rotation speed in step S3 (in other words, when the motor 23 is in the idling state), the process proceeds to step S7 without going through steps S4 and S5 described above.

If the differential pressure of the fixed throttle 37 is less than the threshold value (that is, any one of the control valves is operated) in step S2, the process proceeds to step S6 described above via step S8. In step S8, the control device 32 clears the non-operation duration.

As described above, in the present embodiment, the control device 32 calculates the differential pressure of the fixed throttle 37 based on the detection results of the

pressure sensors

38 and 39, and detects the operation states of the plurality of operation devices based on the differential pressure. The differential pressure of the fixed throttle 37 used in the present embodiment can suppress the influence of the rotation speed of the motor 23 and the like compared to the hydraulic pressure on the downstream side of the fixed throttle 37 used in the conventional technique. Specifically, even when the rotation speed of the motor 23 is low and the hydraulic pressure on the upstream side of the fixed throttle 37 is low, and when the pressure loss in the portion from the fixed throttle 37 to the tank 36 in the hydraulic pressure signal line 35 is high and the hydraulic pressure on the downstream side of the fixed throttle 37 is high, the differential pressure of the fixed throttle 37 when any one of the operation devices is operated becomes small to near zero, and the differential pressure when all the operation devices are not operated becomes large. Therefore, it is easy to set the threshold value for determining the operation states of the plurality of operation devices. In addition, even if the idling rotation speed of the electric motor 23 is set low, the operation state of the operation device can be detected. Therefore, the idle rotation speed of the motor 23 can be set low.

In the above-described embodiment, the case where the control device 32 calculates the differential pressure of the fixed throttle 37 (specifically, the differential pressure between the hydraulic pressure detected by the pressure sensor 38 and the hydraulic pressure detected by the pressure sensor 39) and compares the differential pressure with the threshold value to determine the operation states of the plurality of operation devices has been described as an example, but the present invention is not limited thereto. The control device may set a threshold value by adding a predetermined differential pressure to the hydraulic pressure detected by the pressure sensor 39, and determine the operation states of the plurality of operation devices by comparing the hydraulic pressure detected by the pressure sensor 38 with the threshold value. In such a modification, the same effects as described above can be obtained.

In the above-described embodiment, the case where the control lever device includes the pressure reducing valve that generates the pilot pressure corresponding to the operation amount of the control lever using the discharge pressure of the pilot pump 27 as the base pressure and outputs the generated pilot pressure to the pressure receiving portion of the control valve has been described as an example (in other words, the case where the operation device for switching the control valve is configured only by the control lever device), but the present invention is not limited to this. The operation lever device may have, for example, a potentiometer that detects an operation amount of the operation lever and outputs a corresponding electric operation signal. The control device generates a command current based on an electric operation signal from the operation lever device and outputs the command current to the electromagnetic proportional valve. The electromagnetic proportional valve generates a pilot pressure corresponding to a command current from the control device using the discharge pressure of the pilot pump 27 as a base pressure, and outputs the generated pilot pressure to the pressure receiving portion of the control valve. That is, the operation device for switching the control valve may be constituted by the lever device, the control device, and the electromagnetic proportional valve. In such a modification, the same effects as described above can be obtained.

In the above-described embodiment, the case where the hydraulic excavator is provided with the electric motor 23 as the prime mover has been described as an example, but the present invention is not limited to this, and an engine may be provided.

In addition, although the hydraulic excavator has been described as an example of the application object of the present invention, the present invention is not limited to this, and other construction machines such as a wheel loader may be used.

Description of the reference numerals

8 right side running motor

14 boom cylinder

15 bucket rod hydraulic cylinder

16 bucket hydraulic cylinder

23 electric motor (prime mover)

26 hydraulic pump

27 pilot pump

28 control valve for right-side running

29 boom control valve

30 operating lever device

31 operating lever device

32 control device

33 pilot overflow valve

35 hydraulic signal line

36 oil tank

37 fixed throttle valve

38 pressure sensor (1 st pressure sensor)

39 pressure sensor (No. 2 pressure sensor).

Claims

1. A construction machine is provided with: a prime mover; a hydraulic pump driven by the prime mover; a hydraulic actuator; a control valve that controls a flow of hydraulic oil from the hydraulic pump to the hydraulic actuator; an operation device for generating a pilot pressure corresponding to an operation amount of the operation lever and switching the control valve by the generated pilot pressure; and a control device for controlling the rotation speed of the prime mover to a preset idle rotation speed when the non-operation state of the operation device continues to occur,

the construction machine is characterized by comprising:

a pilot pump that is driven by the prime mover and in which a discharge pressure is used as a base pressure of the pilot pressure;

a pilot relief valve provided on a discharge side of the pilot pump;

a hydraulic signal line connected between a discharge side of the pilot pump and a tank, sandwiching the control valve, and blocked when the control valve is switched from a neutral position;

a fixed throttle provided between the discharge side of the pilot pump in the hydraulic signal line and the control valve;

a 1 st pressure sensor that detects a hydraulic pressure on an upstream side of the fixed throttle; and

a 2 nd pressure sensor that detects a hydraulic pressure on a downstream side of the fixed throttle,

the control device detects an operation state of the operation device based on detection results of the 1 st pressure sensor and the 2 nd pressure sensor.

2. The work machine of claim 1,

the control device detects an operation state of the operating device based on a pressure difference between the hydraulic pressure detected by the 1 st pressure sensor and the hydraulic pressure detected by the 2 nd pressure sensor.

3. A working machine according to claim 1,

the prime mover is an electric motor.