Patent ID: 8438846

Claim:
A hydraulic drive apparatus which drives a variable displacement hydraulic motor by a pressure oil discharged from a variable displacement hydraulic pump and outputs a driving force of the hydraulic motor to outside, the hydraulic drive apparatus comprising: a torque upper limit setting unit which sets an upper limit of an output torque with respect to the hydraulic motor; a rotation number upper limit setting unit which sets an upper limit of the rotation number with respect to the hydraulic motor; and a control unit which sets a maximum capacity limit value of the hydraulic motor in accordance with the upper limit of the output torque, sets a minimum capacity limit value of the hydraulic motor in accordance with the upper limit of the rotation number, and sets a maximum capacity limit value of the hydraulic pump in accordance with the upper limit of the output torque and the upper limit of the rotation number, when the upper limit of the output torque is set by the torque upper limit setting unit and when the upper limit of the rotation number is set by the rotation number upper limit setting unit; (a) when the upper limit of the rotation number with respect to the hydraulic motor set by the rotation number upper limit setting unit exceeds an upper limit of the rotation number which is defined by the maximum capacity limit value of the hydraulic motor, the control unit sets the capacity limit value of the hydraulic motor as the minimum capacity limit value, the capacity limit value corresponding to the upper limit of the rotation number with respect to the hydraulic motor and the upper limit of the rotation number being set by rotation number upper limit setting unit, and (b) when the upper limit of the rotation number with respect to the hydraulic motor set by the rotation number upper limit setting unit does not exceed the upper limit of the rotation number which is defined by the maximum capacity limit value of the hydraulic motor, the control unit sets the maximum capacity limit value of the hydraulic motor as the minimum capacity limit value of the hydraulic motor, and wherein, in a case of (b), the capacity limit value of the hydraulic pump is set as the maximum capacity limit value of the hydraulic pump, the capacity limit value corresponding to the upper limit of the rotation number with respect to the hydraulic motor and the upper limit of the rotation number being set by the rotation number upper limit setting unit.