Hydraulic system

Patent metadata

Field	Value
Publication number	US-2022010792-A1
Application number	US-201917295245-A
Country	US
Kind code	A1
Filing date	Nov 15, 2019
Priority date	Nov 19, 2018
Publication date	Jan 13, 2022
Grant date	—

Abstract

A hydraulic system includes: a cylinder that moves a moving object in a vertical direction by extension and retraction of a rod; a first bidirectional pump connected to a head-side chamber of the cylinder by a first supply/discharge line; a second bidirectional pump connected to a rod-side chamber of the cylinder by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and a servomotor that drives the first or second bidirectional pump. At least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

First claim

1 . A hydraulic system comprising:
a cylinder that moves a moving object in a vertical direction by extension and retraction of a rod and in which an interior of a tube is divided by a piston into a head-side chamber and a rod-side chamber; a first bidirectional pump connected to the head-side chamber by a first supply/discharge line; a second bidirectional pump connected to the rod-side chamber by a second supply/discharge line and coupled to the first bidirectional pump in a manner enabling torque to be transmitted between the first and second bidirectional pumps; a relay line connecting the first and second bidirectional pumps such that a hydraulic liquid discharged from one of the first and second bidirectional pumps is introduced into the other of the first and second bidirectional pumps; and a servomotor that drives the first or second bidirectional pump, wherein at least one of the first and second bidirectional pumps is a variable displacement pump whose delivery capacity per rotation is freely variable.

2 . The hydraulic system according to claim 1 , wherein
the first bidirectional pump is a variable displacement pump whose delivery capacity per rotation is freely variable, the hydraulic system further comprises
a first regulator that regulates a tilt angle of the first bidirectional pump in response to an electrical signal,
a servo amplifier that controls a rotational speed of the servomotor,
a controller that outputs a rotational speed command to the servo amplifier and outputs a tilt angle command to the first regulator, and
a head-side pressure sensor that detects a pressure in the head-side chamber or the first supply/discharge line, and
when the moving object is moved to a predetermined position by extension of the rod, the controller outputs the rotational speed command to the servo amplifier such that the moving object is moved at a predetermined speed and outputs the tilt angle command to the regulator such that the pressure detected by the head-side pressure sensor is maintained within a predetermined range.

3 . The hydraulic system according to claim 2 , wherein the second bidirectional pump is a fixed displacement pump whose delivery capacity per rotation is invariable or a variable displacement pump whose delivery capacity per rotation is selectively switchable between a first fixed value and a second fixed value.

4 . The hydraulic system according to claim 2 , wherein
the hydraulic system is incorporated in a press machine, and during pressing in which the moving object is further moved from the predetermined position by extension of the rod, the controller outputs the rotational speed command to the servo amplifier such that the moving object is moved at a predetermined speed and outputs the tilt angle command to the regulator such that the pressure detected by the head-side pressure sensor increases to a target pressure.

5 . The hydraulic system according to claim 4 , wherein
after the pressure detected by the head-side pressure sensor reaches the target pressure, the controller outputs the rotational speed command to the servo amplifier such that the rotational speed of the servomotor becomes a predetermined value and outputs the tilt angle command to the regulator such that the pressure detected by the head-side pressure sensor is maintained at the target pressure.

6 . The hydraulic system according to claim 2 , wherein
the cylinder is disposed to lower the moving object by extension of the rod, the hydraulic system further comprises a rod-side pressure sensor that detects a pressure in the rod-side chamber or the second supply/discharge line, the servo amplifier further controls a regenerative torque of the servomotor, and when the moving object is lowered by its own weight, the controller outputs a regenerative torque command to the servo amplifier such that the pressure detected by the rod-side pressure sensor becomes a predetermined value.

7 . The hydraulic system according to claim 1 , wherein
the second bidirectional pump is a variable displacement pump whose delivery capacity per rotation is freely variable, the hydraulic system further comprises
a second regulator that regulates a tilt angle of the second bidirectional pump in response to an electrical signal,
a servo amplifier that controls a rotational speed of the servomotor,
a controller that outputs a rotational speed command to the servo amplifier and outputs a tilt angle command to the second regulator, and
a head-side pressure sensor that detects a pressure in the head-side chamber or the first supply/discharge line,
when the moving object is moved to a predetermined position by extension of the rod, the controller outputs the tilt angle command to the second regulator such that the delivery capacity of the second bidirectional pump becomes a predetermined value, outputs the rotational speed command to the servo amplifier such that the moving object is moved at a predetermined speed, and corrects the rotational speed command output to the servo amplifier if the pressure detected by the head-side pressure sensor falls outside a predetermined range.

8 . The hydraulic system according to claim 7 , wherein the first bidirectional pump is a fixed displacement pump whose delivery capacity per rotation is invariable or a variable displacement pump whose delivery capacity per rotation is selectively switchable between a first fixed value and a second fixed value.

9 . The hydraulic system according to claim 7 , wherein
the hydraulic system is incorporated in a press machine, during pressing in which the moving object is further moved from the predetermined position by extension of the rod, the controller outputs the rotational speed command to the servo amplifier such that the moving object is moved at a predetermined speed, adjusts the rotational speed command output to the servo amplifier such that the pressure detected by the head-side pressure sensor increases to a target pressure, and adjusts the tilt angle command output to the second regulator such that when the rotational speed has been increased, the tilt angle decreases as a function of the increase in the rotational speed and that when the rotational speed has been decreased, the tilt angle increases as a function of the decrease in the rotational speed.

10 . The hydraulic system according to claim 9 , wherein after the pressure detected by the head-side pressure sensor reaches the target pressure, the controller continues the adjustment of the rotational speed command and the adjustment of the tilt angle command such that the pressure detected by the head-side pressure sensor is maintained at the target pressure.

11 . The hydraulic system according to claim 7 , wherein
the cylinder is disposed to lower the moving object by extension of the rod, the servo amplifier further controls a regenerative torque of the servomotor, the hydraulic system further comprises a rod-side pressure sensor that detects a pressure in the rod-side chamber or the second supply/discharge line, and when the moving object is lowered by its own weight, the controller outputs a regenerative torque command to the servo amplifier such that the pressure detected by the rod-side pressure sensor becomes a predetermined value.

Assignees

• Kawasaki Heavy Ind Ltd

Inventors

• Kondo Akihiro
• Mitsui Hiroaki
• Toyota Toshihisa
• Mibu Koki
• Nakatsuji Takashi

Classifications

• B30B15/166

  Electrical control arrangements · CPC title

• B30B15/20

  controlling the speed of the ram, e.g. the speed of the approach, pressing or return strokes · CPC title

• F15B2211/6651

  Control of the prime mover, e.g. control of the output torque or rotational speed · CPC title

• F15B2211/88

  Control measures for saving energy · CPC title

• F15B11/022

  in which a rapid approach stroke is followed by a slower, high-force working stroke (F15B11/0325 takes precedence) · CPC title