Patent ID: 6619037
Filing Date: 2003-09-16
Classification: E02F

Abstract:
A hydraulic drive system for a civil engineering or construction machine, said system comprising:a first hydraulic pump and a second hydraulic pump; a first control valve group connected to said first hydraulic pump; a bypass on/off valve having an open position and a closed position for selectively maintaining a bypass passage in or out of communication, the bypass on/off valve being disposed on a most downstream side of said first control valve group; a second control valve group connected to said second hydraulic pump and including a plurality of directional control valves including a reserve directional control valve; a communication line connecting the most upstream side of said first control valve group with a supply line to said reserve directional control valve; a merge control valve having an open position and a closed position to selectively open and close said communication line; an interlocked control means for permitting an operation to change said merge control valve to said open position and said bypass on/off valve to said closed position in association with a change-over operation of a reserve control device for changing said reserve directional control valve; a selective change means capable of selectively taking one of a state, in which said operation to change said merge control valve to said open position by said interlocked control means is feasible, and another state, in which said operation to change said merge control valve to said open position by said interlocked control means is infeasible; wherein said first control valve group, said second control valve group, said communication line and said merge control valve are arranged in a single housing; wherein said reserve directional control valve comprises a hydraulically-operated pilot valve, said reserve control device including a pilot-operated control device for outputting a pilot pressure to change said reserve directional control valve, and each of said merge control valve and said bypass on/off valve including a hydraulically-operated pilot valve; wherein said interlocked control means includes a first shuttle valve, which is designed to detect a pilot pressure outputted from said reserve control device and is designed to output said pilot pressure as a pressure signal for changing said merge control valve to said open position and said bypass on/off valve to said closed position, and a first pilot line connecting said first shuttle valve with respective drive portions of said merge control valve and said bypass on/off valve; wherein said selective change means includes a selective control valve arranged in a part of said first pilot line, which connects said first shuttle valve with said drive portion of said merge control valve, and is capable of selectively taking one of a first state in which a pilot pressure outputted from said first shuttle valve is able to be supplied to said drive portion of said merge control valve and a second state in which the pilot pressure outputted from said first shuttle valve is not supplied to said drive portion of said merge control valve; a merge control valve control means for controlling said merge control valve such that said merge control valve is changed to said closed position in response to an operation of a predetermined directional control valve that is included in said first control valve group; said predetermined directional control valve comprises a hydraulically-operated pilot valve, a predetermined directional control valve control device for changing over said predetermined directional control valve comprises a pilot control device for outputting a pilot pressure, said merge control valve control means includes a second shuttle valve, which is adapted to detect a pilot pressure outputted from said predetermined directional control valve control device and is adapted to output said pilot pressure as a pressure signal for changing over said merge control valve, and a second pilot line communicating said second shuttle valve with a drive portion of said merge control valve.