Hydraulic circuit for controlling booms of construction equipment

Patent metadata

Field	Value
Publication number	US-9482214-B2
Application number	US-201114006116-A
Country	US
Kind code	B2
Filing date	Apr 19, 2011
Priority date	Apr 19, 2011
Publication date	Nov 1, 2016
Grant date	Nov 1, 2016

Abstract

Disclosed is a hydraulic circuit for controlling booms of construction equipment, wherein working oil which is relieved from a large chamber of a boom cylinder passes through an orifice so as to prevent the boom from lowering if an overload is applied when the boom is not being operated. The hydraulic circuit for controlling booms of construction equipment includes: a boom cylinder which is connected to a hydraulic pump via a first path and a second path; a boom control valve which is mounted on the path between the hydraulic pump and the boom cylinder; a holding valve which is mounted between the boom control valve and the first path of the boom cylinder and prevents the natural lowering of a boom when the boom control valve is in a neutral position; a port relief valve which is mounted to the first path at the lower side of a holding poppet and relieves working oil when an overload is generated at the first path; and an orifice valve which is mounted at the lower side of the port relief valve, relieves the working oil which passes through the port relief valve when the boom control valve is neutral so as to relieve the working oil through an orifice, and discharges the working oil which passes through the port relief valve to a hydraulic tank at the time of conversion due to boom-up pilot signal pressure which is applied to the boom control valve.

First claim

The invention claimed is:

1. A hydraulic circuit for controlling a boom of a construction machine, comprising:
a hydraulic pump connected to an engine;
a boom cylinder connected to the hydraulic pump through a first path and a second path;
a boom control valve shiftably installed in a flow path provided between the hydraulic pump 1 and the boom cylinder and configured to be shifted to control a start, a stop, and a direction change of the boom cylinder;
a holding valve including a holding poppet installed between the boom control valve and the first flow path of the boom cylinder and a drain valve configured to supply or discharge a hydraulic fluid to or from a back pressure chamber of the holding poppet so that the natural descending movement of the boom is prevented when the boom control valve is in a neutral state;
a port relief valve installed in the first path at the downstream side of the holding poppet and configured to relieve the hydraulic fluid when an overload occurs in the first path; and
an orifice valve installed at the downstream side of the port relief valve and configured such that when the boom control valve is in a neutral state, the hydraulic fluid passing through the port relief valve passes through an orifice to relieve the hydraulic fluid, and when the boom control valve is shifted by a boom-up pilot signal pressure that is applied thereto and a part of the boom-up pilot signal pressure is applied to a signal pressure-receiving portion of the orifice valve, the hydraulic fluid passing through the port relief valve is discharged to a hydraulic tank.

2. The hydraulic circuit for controlling a boom of a construction machine according to claim 1 , wherein the orifice valve is shifted by the boom-up pilot signal pressure that is generated by the lever manipulation of a remote control valve for manipulating a work apparatus.

3. A hydraulic circuit for controlling a boom of a construction machine, the hydraulic circuit comprising:
a hydraulic pump connected to an engine;
a boom cylinder connected to the hydraulic pump through a first path and a second path;
a boom control valve arranged in a flow path provided between the hydraulic pump and the boom cylinder, the boom control valve configured to be shifted to control a start, a stop, and a direction change of the boom cylinder;
a holding valve including:
a holding poppet arranged between the boom control valve and the first flow path of the boom cylinder; and
a drain valve configured to supply or discharge a hydraulic fluid to or from a back pressure chamber of the holding poppet so that the natural descending movement of the boom is prevented when the boom control valve is in a neutral state;

a port relief valve arranged in the first path at the downstream side of the holding poppet and configured to relieve the hydraulic fluid when an overload occurs in the first path;
an orifice valve including an orifice and arranged on a downstream side of the port relief valve, the orifice valve movable between a first position and a second position, in the first position hydraulic fluid relieved after passing through the relief port valve passes through the orifice prior to being discharged to a hydraulic tank, in the second position hydraulic fluid relieved after passing through the relief port valve does not pass through the orifice prior to being discharged to the hydraulic tank;
a remote control valve, actuation of the remote control valve to raise the boom supplies a boom-up pilot signal pressure to the boom control valve to shift the boom control valve, and supplies the boom-up pilot signal pressure to the orifice valve to move the orifice valve to the second position;
wherein:
when an overload is applied to the boom cylinder in a descending direction when the boom is not being manipulated and is thus in a neutral state, the orifice valve is arranged in the first position such that hydraulic fluid relieved after passing through the port relief valve passes through the orifice of the orifice valve and is subsequently discharged to the hydraulic tank so as to reduce a discharge rate of the hydraulic fluid and reduce a descending rate at which the boom descends in response to the overload; and
when an overload is applied to the boom cylinder in the descending direction when the boom is being raised, the orifice valve is arranged in the second position such that hydraulic fluid relieved after passing through the port relief valve passes through the orifice valve to the discharge tank without passing through the orifice and without the discharge rate being reduced.

Assignees

• Kim Sung-Gon
• Volvo Constr Equip Ab

Inventors

• Kim Sung-Gon

Classifications

• E02F9/2271

  Actuators and supports therefor and protection therefor · CPC title

• E02F9/2296

  Systems with a variable displacement pump · CPC title

• E02F9/2203 Primary

  Arrangements for controlling the attitude of actuators, e.g. speed, floating function · CPC title

• F15B11/003

  Systems with load-holding valves · CPC title

• F15B2211/41581

  being connected to an output member and a return line · CPC title