Patent ID: 9506220
Filing Date: 2016-11-29
CPC Classification: E02F,F15B

Claim Text:
1. A slewing-type working machine comprising: a base carrier; an upper slewing body mounted on the base carrier so as to be capable of being slewed; a hydraulic motor including first and second ports and receiving supply of hydraulic fluid from one of the first and second ports and discharges the hydraulic fluid from the other one of the first and second ports, thereby slewing the upper slewing body; a hydraulic pump discharging the hydraulic fluid supplied to the hydraulic motor; a slewing operation device including an operating member to which an operation is applied to input a command for the slewing and outputting an operation signal corresponding to the operation applied to the operating member; a control valve which is operated so as to control supply of hydraulic fluid to the hydraulic motor and discharge of hydraulic fluid from the hydraulic motor, based on the operation signal of the slewing operation device; a first pipe-line connecting the first port of the hydraulic motor to the control valve; a second pipe-line connecting the second port of the hydraulic motor to the control valve; a communication switching device provided between both of first and second pipe-lines and a tank to be switched among a state of cutting off both of the first and second pipe-lines from the tank, a state of bringing the first pipe-line into communication with the tank while cutting off the second pipe-line from the tank, and a state of bringing the second pipe-line into communication with the tank while cutting off the first pipe-line from the tank; and a switching command section adapted to generate a command signal based on the operation signal output from the slewing operation device and input the command signal to the communication switching device to switching the states, so as to cause the communication switching device to bring, when the upper slewing body is slewed by the hydraulic motor, only a pipe-line that is one of the first and second pipe-lines and corresponds to a pipe line on the discharge side of the hydraulic motor into communication with the tank, while bypassing the control valve, wherein the switching command section is a controller adapted to judge whether the upper slewing body is being driven for slewing, or decelerated, or in a stopped state and adapted to input the command signal to the communication switching device to switching the states, so as to cause the communication switching device to bring, when the control valve is switched to the first slewing position or the second slewing position and the controller judges that the upper slewing body is driven for slewing by the hydraulic motor, only a pipe-line that is one of the first and second pipe-lines and corresponds to a pipe-line through which the hydraulic fluid discharged from the hydraulic motor is allowed to be returned to the tank by the control valve into communication with the tank, while bypassing the control valve.