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US 12,618,467 B2Granted
Hydraulic system
AssigneeKawasaki Jukogyo Kabushiki Kaisha
InventorsRyo Yamamoto, Hideki Tanaka, Hiroaki Mitsui
Life of this patent
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Abstract
A hydraulic system includes: a first bi-directional pump connected to a head-side chamber of a single-rod cylinder by a head-side line and connected to a rod-side chamber of the single-rod cylinder by a rod-side line; and a second bi-directional pump connected to the head-side line by a supply/discharge line, the second bi-directional pump being a variable displacement pump. The hydraulic system further includes a low-pressure selection valve connected to the head-side line by a first discharge line and connected to the rod-side line by a second discharge line, wherein the low-pressure selection valve allows the second discharge line or the first discharge line to communicate with a relief line on which a relief valve is located.
Claims16
A hydraulic system for a single-rod cylinder including a head-side chamber and a rod-side chamber, the hydraulic system comprising:
- a first bi-directional pump connected to the head-side chamber by a head-side line and connected to the rod-side chamber by a rod-side line;
- a second bi-directional pump connected to the head-side line by a supply/discharge line, the second bi-directional pump being a variable displacement pump;
- an electric motor that drives the first bi-directional pump and the second bi-directional pump in a same direction;
- a low-pressure selection valve connected to the head-side line by a first discharge line and connected to the rod-side line by a second discharge line, wherein when a pressure of the rod-side chamber is lower than a pressure of the head-side chamber, the low-pressure selection valve allows the second discharge line to communicate with a relief line on which a relief valve is located, and when the pressure of the head-side chamber is lower than the pressure of the rod-side chamber, the low-pressure selection valve allows the first discharge line to communicate with the relief line;
- a regulator that changes a displacement of the second bi-directional pump;
- and
- control circuitry that controls the electric motor and the regulator, wherein
- when a pressure difference between the pressure of the head-side chamber and the pressure of the rod-side chamber has become greater than or equal to a threshold, the low-pressure selection valve is switched from a neutral position in which the low-pressure selection valve blocks the first discharge line and the second discharge line to a head-side discharge position in which the low-pressure selection valve allows the first discharge line to communicate with the relief line or to a rod-side discharge position in which the low-pressure selection valve allows the second discharge line to communicate with the relief line, and
- at a time of extending the single-rod cylinder, the control circuitry controls the regulator such that when the low-pressure selection valve is in the neutral position, the displacement of the second bi-directional pump is a reference displacement, and when the low-pressure selection valve is in the head-side discharge position or the rod-side discharge position, the displacement of the second bi-directional pump is greater than the reference displacement by a first predetermined amount.
6 more elements
A hydraulic system for a single-rod cylinder including a head-side chamber and a rod-side chamber, the hydraulic system comprising:
- a first bi-directional pump connected to the head-side chamber by a head-side line and connected to the rod-side chamber by a rod-side line;
- a second bi-directional pump connected to the head-side line by a supply/discharge line, the second bi-directional pump being a variable displacement pump;
- an electric motor that drives the first bi-directional pump and the second bi-directional pump in a same direction;
- a low-pressure selection valve connected to the head-side line by a first discharge line and connected to the rod-side line by a second discharge line, wherein when a pressure of the rod-side chamber is lower than a pressure of the head-side chamber, the low-pressure selection valve allows the second discharge line to communicate with a relief line on which a relief valve is located, and when the pressure of the head-side chamber is lower than the pressure of the rod-side chamber, the low-pressure selection valve allows the first discharge line to communicate with the relief line;
- a regulator that changes a displacement of the second bi-directional pump;
- and
- control circuitry that controls the electric motor and the regulator, wherein
- when a pressure difference between the pressure of the head-side chamber and the pressure of the rod-side chamber has become greater than or equal to a threshold, the low-pressure selection valve is switched from a neutral position in which the low-pressure selection valve blocks the first discharge line and the second discharge line to a head-side discharge position in which the low-pressure selection valve allows the first discharge line to communicate with the relief line or to a rod-side discharge position in which the low-pressure selection valve allows the second discharge line to communicate with the relief line, and
- at a time of retracting the single-rod cylinder, the control circuitry controls the regulator such that when the low-pressure selection valve is in the neutral position, the displacement of the second bi-directional pump is a reference displacement, and when the low-pressure selection valve is in the head-side discharge position or the rod-side discharge position, the displacement of the second bi-directional pump is less than the reference displacement by a second predetermined amount.
6 more elements
Dependencies are inferred from the claim text.