Hydraulic drive unit

Details Hydraulic drive unit Hydraulic drive unit

2006-10-31

2006-10-31

Look, Edward K. (Department: 3745)

Power plants

Pressure fluid source and motor

Having condition responsive control in a system of distinct...

C060S413000, C091S452000

Reexamination Certificate

active

07127888

ABSTRACT:
A hydraulic drive unit is provided with a boom cylinder, an arm cylinder, a communication line communicating a rod chamber of the boom cylinder and a bottom chamber of the arm cylinder with each other, and a switching valve arranged on the communication line for communicating or shutting off the communication line in accordance with a rod pressure of the boom cylinder. When an arm-crowding single operation is performed and by its digging counterforce, a rod pressure of the boom cylinder rises to a high pressure of at least a predetermined pressure, the switching valve is changed over from a shut-off position to a communicating position to feed pressure oil from the rod chamber to the bottom chamber. The boom cylinder is hence caused to automatically extend, thereby avoiding lifting of a hydraulic excavator body.

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