Patent ID: 8104947

Claim:
A concrete agitating drum driving device, comprising: a hydraulic motor mechanically connected to a concrete agitating drum; a variable capacity hydraulic pump driven by a combustion engine to drive the hydraulic motor to rotate by supplying pressurized working oil, the variable capacity hydraulic pump comprising a discharge passage to which the variable capacity hydraulic pump discharges the pressurized working oil which is to be supplied to the hydraulic motor; a mechanism which varies a capacity of the variable capacity hydraulic pump to maintain a pump discharge flow rate of the pressurized working oil discharged into the discharge passage by the variable capacity hydraulic pump constant; a charge pump which rotates in synchronization with the variable capacity hydraulic pump and discharges working oil which is to be suctioned by the variable capacity hydraulic pump; and a valve which narrows a flow cross-sectional area of the pressurized working oil supplied from the discharge passage to the hydraulic motor as a discharge pressure of the charge pump decreases.