US-12618467-B2 - Hydraulic system

US12618467B2US 12618467 B2US12618467 B2US 12618467B2US-12618467-B2

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.

Inventors

Ryo Yamamoto
Hideki Tanaka
Hiroaki Mitsui

Assignees

KAWASAKI JUKOGYO KABUSHIKI KAISHA

Dates

Publication Date: 20260505
Application Date: 20230419
Priority Date: 20220711

Claims (16)

1 . 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.
2 . The hydraulic system according to claim 1 , wherein the reference displacement is a result of multiplying a displacement of the first bi-directional pump by a ratio of a cross-sectional area of a rod of the single-rod cylinder to a pressure receiving area of the rod-side chamber.
3 . The hydraulic system according to claim 1 further comprising: a first lock valve located on the head-side line, the first lock valve being an on-off valve; and a second lock valve located on the rod-side line, the second lock valve being an on-off valve.
4 . The hydraulic system according to claim 1 , wherein the pressure of the head-side chamber is led to the low-pressure selection valve through a first pilot line, and the pressure of the rod-side chamber is led to the low-pressure selection valve through a second pilot line, and the hydraulic system further comprises: a first on-off valve located on the first pilot line; and a second on-off valve located on the second pilot line.
5 . The hydraulic system according to claim 1 , further comprising: a head-side relief valve located on a head-side relief line that is branched off from the head-side line; a first check valve located on a first bypass line that bypasses the head-side relief valve; a rod-side relief valve located on a rod-side relief line that is branched off from the rod-side line; and a second check valve located on a second bypass line that bypasses the rod-side relief valve.
6 . The hydraulic system according to claim 1 , further comprising: a pressure difference meter that detects a pressure difference between the pressure of the head-side chamber and the pressure of the rod-side chamber.
7 . The hydraulic system according to claim 1 , wherein the hydraulic system further comprises a position detector that detects whether a position of the low-pressure selection valve is the neutral position, the rod-side discharge position, or the head-side discharge position.
8 . The hydraulic system according to claim 1 , wherein the first predetermined amount is determined by taking into account a factor that causes a loss of balance among a delivery flow rate of the first bi-directional pump, a delivery flow rate of the second bi-directional pump, an inflow flow rate to the single-rod cylinder, and an outflow flow rate from the single-rod cylinder, and the factor that causes a loss of the balance include performance of the regulator, efficiency of the first bi-directional pump, efficiency of the second bi-directional pump, leakage of a hydraulic liquid to outside, and changes that occur over years.
9 . 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.
10 . The hydraulic system according to claim 9 , wherein the reference displacement is a result of multiplying a displacement of the first bi-directional pump by a ratio of a cross-sectional area of a rod of the single-rod cylinder to a pressure receiving area of the rod-side chamber.
11 . The hydraulic system according to claim 9 , further comprising: a first lock valve located on the head-side line, the first lock valve being an on-off valve; and a second lock valve located on the rod-side line, the second lock valve being an on-off valve.
12 . The hydraulic system according to claim 9 , wherein the pressure of the head-side chamber is led to the low-pressure selection valve through a first pilot line, and the pressure of the rod-side chamber is led to the low-pressure selection valve through a second pilot line, and the hydraulic system further comprises: a first on-off valve located on the first pilot line; and a second on-off valve located on the second pilot line.
13 . The hydraulic system according to claim 9 , further comprising: a head-side relief valve located on a head-side relief line that is branched off from the head-side line; a first check valve located on a first bypass line that bypasses the head-side relief valve; a rod-side relief valve located on a rod-side relief line that is branched off from the rod-side line; and a second check valve located on a second bypass line that bypasses the rod-side relief valve.
14 . The hydraulic system according to claim 9 , further comprising: a pressure difference meter that detects a pressure difference between the pressure of the head-side chamber and the pressure of the rod-side chamber.
15 . The hydraulic system according to claim 9 , wherein the hydraulic system further comprises a position detector that detects whether a position of the low-pressure selection valve is the neutral position, the rod-side discharge position, or the head-side discharge position.
16 . The hydraulic system according to claim 9 , wherein the second predetermined amount is determined by taking into account a factor that causes a loss of balance among a delivery flow rate of the first bi-directional pump, a delivery flow rate of the second bi-directional pump, an inflow flow rate to the single-rod cylinder, and an outflow flow rate from the single-rod cylinder, and the factor that causes a loss of the balance include performance of the regulator, efficiency of the first bi-directional pump, efficiency of the second bi-directional pump, leakage of a hydraulic liquid to outside, and changes that occur over years.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This is a U.S. National Phase Application of PCT/JP2023/015569 filed on Apr. 19, 2023, which designates the United States and claims priority to Japanese Patent Application No. 2022-111245, filed on Jul. 11, 2022, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to a hydraulic system for a single-rod cylinder. BACKGROUND ART Conventionally, there is a known hydraulic system for a single-rod cylinder, the hydraulic system including a bi-directional pump that is connected to the single-rod cylinder in a manner to form a closed circuit. For example, Patent Literature 1 discloses a hydraulic system 100 as shown in FIG. 10. The hydraulic system 100 includes a first bi-directional pump 110 and a second bi-directional pump 120. The first bi-directional pump 110 is connected to a head-side chamber 210 of a single-rod cylinder 200 by a head-side line 111, and is connected to a rod-side chamber 220 of the single-rod cylinder 200 by a rod-side line 112. The second bi-directional pump 120 is a pump with which to eliminate a flow rate difference between the head-side chamber 210 and the rod-side chamber 220 of the single-rod cylinder 200 (i.e., a difference between an inflow flow rate and an outflow flow rate), and is connected to the head-side line 111 by a supply/discharge line 121. The first bi-directional pump 110 and the second bi-directional pump 120 are driven in the same direction by an electric motor 130. To be more specific, at the time of extending the single-rod cylinder 200 (i.e., at the time of moving the rod forward), the electric motor 130 drives the first bi-directional pump 110 and the second bi-directional pump 120 in a first direction, and at the time of retracting the single-rod cylinder 200 (i.e., at the time of moving the rod backward), the electric motor 130 drives the first bi-directional pump 110 and the second bi-directional pump 120 in a second direction opposite to the first direction. When the first bi-directional pump 110 and the second bi-directional pump 120 are driven in the first direction, these pumps deliver a hydraulic liquid to the head-side chamber 210, and when the first bi-directional pump 110 and the second bi-directional pump 120 are driven in the second direction, these pumps suck the hydraulic liquid from the head-side chamber 210. Further, in the hydraulic system 100, the second bi-directional pump 120 is a variable displacement pump, and the displacement of the second bi-directional pump 120 is changed by a regulator 140. In the hydraulic system 100, assuming that the displacement of the second bi-directional pump 120 when there is neither excess nor deficiency in the inflow flow rate to the single-rod cylinder 200 or in the outflow flow rate from the single-rod cylinder 200 is a reference displacement, then in a case where, at the time of extending the single-rod cylinder 200, the displacement of the second bi-directional pump 120 is greater than the reference displacement, pressure confinement occurs on either the rod side (the rod-side chamber 220 and the rod-side line 112) or the head side (the head-side chamber 210 and the head-side line 111), whichever side has a lower pressure. On the other hand, in a case where, at the time of extending the single-rod cylinder 200, the displacement of the second bi-directional pump 120 is less than the reference displacement, cavitation occurs on either the rod side or the head side, whichever side has a lower pressure. Further, at the time of retracting the single-rod cylinder 200, in a case where the displacement of the second bi-directional pump 120 is greater than the reference displacement, cavitation occurs on either the rod side or the head side, whichever side has a lower pressure, and in a case where the displacement of the second bi-directional pump 120 is less than the reference displacement, pressure confinement occurs on either the rod side or the head side, whichever side has a lower pressure. The regulator 140 is controlled based on the pressure of the head-side chamber 210 or the rod-side chamber 220 of the single-rod cylinder 200 to suppress the pressure confinement or the cavitation. CITATION LIST Patent Literature PTL 1: Japanese Laid-Open Patent Application Publication No. 2013-245740PTL 2: Japanese Laid-Open Patent Application Publication No. 2002-54602 SUMMARY OF INVENTION Technical Problem As described above, in the hydraulic system 100 of Patent Literature 1, the occurrence of pressure confinement on either the rod side or the head side, whichever side has a lower pressure, is suppressed by performing control. In this respect, there is a desire to physically prevent the occurrence of pressure confinement on either the rod side or the head side, whichever side has a lower pressure. FIG. 2 of Patent Literature 2 discloses, as a conventional technique, a hydraulic circuit in which only one bi-directional pum