Apparatus for suppressing quaky movements of mobile cranes

Abstract

An apparatus for damping quaky movements of a mobile type crane includes the prohibition of the formation of a closed damping circuit through the opposing oil chambers of a boom uplifting cylinder in working mode or a crane operation in travel mode of the crane, enhancing safety in crane operation while ensuring effective quake damping action in vehicle travel. The apparatus includes a vehicle body supported on driven wheels; a boom pivotally supported on the vehicle body through a hydraulic cylinder for pivoting movements about a horizontal shaft; main hydraulic pumps connected through a transmission mechanism to an engine mounted on the vehicle body and switchable between on- and off-positions; a direction control valve for selectively supplying and draining the discharge oil pressures of the main pumps to and from a first load-holding main oil chamber and an opposing second oil chamber of the cylinder; a counter-balancing valve provided between the cylinder and directionh control valve; an accumulator provided between the cylinder and counter-balancing valve for suppressing quaky movements of the vehicle body; a mode selector means for switching the mode of operation between a vehicle travel mode forming a closed circuit through the first and second oil chambers and in communication with the accumulator, and a working mode cancelling the closed circuit and supplying and draining oil pressures separately to and from the first and second oil chambers; and a controller adapted to permit a switch to the travel mode position of the travel mode selector only when the main pumps are in an off state.