Hydraulic drive system for construction machine

Patent metadata

Field	Value
Publication number	US-11280059-B2
Application number	US-201716082447-A
Country	US
Kind code	B2
Filing date	Mar 24, 2017
Priority date	Mar 24, 2017
Publication date	Mar 22, 2022
Grant date	Mar 22, 2022

Abstract

A hydraulic drive system for a hydraulic excavator that enables leveling work and a jack-up operation by a blade in a float state, that can prevent a body from falling even when an operator has falsely operated the hydraulic excavator during the jack-up operation by the blade, and that yet can perform favorable leveling work with the blade turned into the float state is provided. A float switch 37, a float valve 38, and a controller 34 are provided, the float valve 38 is changed over to a float position VI upon operating the float switch 37 when the blade is not in a jack-up state, the float valve 38 is changed over from the float position VI to a normal position V when the float valve 38 is in a state of being at the float position VI and an operation lever device 22 has been operated, and the float valve 38 is kept at the normal position V when the float valve 38 is at the normal position V and the float switch 37 has been operated in the jack-up state.

First claim

The invention claimed is:

1. A hydraulic drive system for a hydraulic excavator, comprising:
a machine body that has a lower travel structure and an upper swing structure swingably mounted on the lower travel structure;
a front work implement attached to the upper swing structure in such a manner as to be vertically rotatable; and
a blade attached to a front portion of the lower travel structure, wherein
the hydraulic drive system for the hydraulic excavator comprises:
a plurality of actuators driven by a hydraulic fluid delivered from at least one hydraulic pump;
a plurality of directional control valves that control flows of the hydraulic fluid supplied to the plurality of actuators from the hydraulic pump; and
a plurality of operation lever devices that are connected to a pilot hydraulic fluid source and that generate control pilot pressures for operating the plurality of directional control valves with a hydraulic pressure of the pilot hydraulic fluid source assumed as a main pressure, wherein
the plurality of actuators include a blade cylinder for driving the blade, and
the plurality of directional control valves include a blade directional control valve that controls the flow of the hydraulic fluid supplied to the blade cylinder, and the plurality of operation lever devices include a blade operation lever device that generates the control pilot pressures for operating the blade directional control valve,
characterized in that:
the hydraulic drive system for the hydraulic excavator further comprises:
a float instruction device;
a float valve having a normal position that enables the blade cylinder to be driven, and a float position in which a bottom-side hydraulic chamber and a rod-side hydraulic chamber of the blade cylinder are communicated with a tank and in which the blade is turned into a float state; and
a float control device configured to change over the float valve to the float position when the blade is not in a state of jacking up the machine body and the float instruction device has been operated, to change over the float valve from the float position to the normal position when the float valve is in a state of being at the float position and the blade operation lever device has been operated, and to keep the float valve at the normal position irrespectively of an instruction by the float instruction device when the float valve is at the normal position, the blade is in the state of jacking up the machine body, and the float instruction device has been operated.

2. The hydraulic drive system for the hydraulic excavator according to claim 1 , wherein
the float valve is a valve device that is disposed in an actuator hydraulic line between the blade directional control valve and the blade cylinder and that has the position changeable over between the normal position and the float position,
the float instruction device is a float switch operated by an operator, and
the float control device includes:
a jack-up sensor that detects whether the blade is jacking up the machine body;
a blade operation sensor that detects whether the blade operation lever device has been operated; and
a controller configured to change over the float valve to one of the normal position and the float position on the basis of detection results of the jack-up sensor and the blade operation sensor and an instruction signal of the float switch.

3. The hydraulic drive system for the hydraulic excavator according to claim 1 , wherein
the float instruction device is the blade operation lever device,
the float valve is incorporated into the blade directional control valve,
the blade directional control valve is configured such that the blade directional control valve is changed over to the normal position when the blade operation lever device has been operated in a lowering direction of the blade and the control pilot pressure rises up to a first set pressure, and such that the directional control valve is changed over to the float position and the blade directional control valve functions as the float valve when the blade operation lever device has been operated in the lowering direction of the blade and the control pilot pressure rises up to a second set pressure higher than the first set pressure,
the float control device includes:
a jack-up sensor that detects whether the blade is jacking up the machine body;
a solenoid pressure reducing valve that is disposed between the blade operation lever device and the blade directional control valve; and
a controller configured to output a control signal to the solenoid pressure reducing valve when the jack-up sensor has detected that the blade is jacking up the machine body, and to reduce a pressure of the blade operation lever device in such a manner that the blade directional control valve is kept at the normal position.

4. The hydraulic drive system for the hydraulic excavator according to claim 2 or 3 , wherein
the jack-up sensor includes a first pressure sensor that detects a pressure of a bottom-side hydraulic chamber of the blade cylinder and a second pressure sensor that detects a pressure of a rod-side hydraulic chamber of the blade cylinder, and
the controller determines that the blade is jacking up the machine body when the pressure of the bottom-side hydraulic chamber of the blade cylinder is equal to or higher than a first determination pressure and the pressure of the rod-side hydraulic chamber of the blade cylinder is equal to or lower than a second determination pressure lower than the first determination pressure.

Assignees

• Hitachi Construction Machinery Tierra Co Ltd

Inventors

• Mori Kazushige
• Yoshida Hajime
• Takebayashi Yoshifumi
• Nakamura Natsuki
• Oka Daisuke

Classifications

• E02F3/844 Primary

  for positioning the blade, e.g. hydraulically · CPC title

• E02F9/2203

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

• E02F9/2221

  Control of flow rate; Load sensing arrangements (E02F9/2203 take precedence over E02F9/2221) · CPC title

• E02F9/2267

  Valves or distributors (position of valves arrangements on upper-structures E02F9/0875) · CPC title

• E02F3/961

  with several digging elements or tools mounted on one machine (for backhoes E02F3/964 takes precedence) · CPC title