Patent ID: 7290390

Claim:
A travel control device for excavators, comprising: at least one main fluid pump ( 1 , 2 ) and an auxiliary pump ( 4 ) each for discharging a hydraulic flow; left and right travel motors ( 12 , 14 ) driven by the hydraulic flow of the main fluid pump ( 1 , 2 ) and respectively provided with speed changing mechanisms ( 13 , 15 ); travel control spools ( 16 , 18 ) for controlling the hydraulic flow to the left and right travel motors ( 12 , 14 ); manual travel control devices ( 20 , 22 ) for receiving the hydraulic flow from the auxiliary pump ( 4 ) and supplying a travel control signal pressure to the travel control spools ( 16 , 18 ); a high speed shifting valve ( 26 ) provided on a high speed signal line ( 24 ) interconnecting the auxiliary pump ( 4 ) and the speed changing mechanisms ( 13 , 15 ) for cutting off or transmitting a high speed signal pressure to the speed changing mechanisms ( 13 , 15 ); a travel signal detection means ( 32 ) for detecting the travel control signal pressure outputted from the manual travel control devices ( 20 , 22 ); and a shutoff valve ( 28 ) provided on the high speed signal line ( 24 ) in a serial relationship with the high speed shifting valve ( 26 ) for closing the high speed signal line ( 24 ) to keep the speed changing mechanisms ( 13 , 15 ) in a low speed condition if the travel control signal pressure supplied from the travel signal detection means ( 32 ) is no greater than a predetermined pressure value and for opening the high speed signal line ( 24 ) to keep the speed changing mechanisms ( 13 , 15 ) in a high speed condition if the travel control signal pressure supplied from the travel signal detection means ( 32 ) exceeds the predetermined pressure value.