Patent ID: 8136271

Claim:
A hydraulic unit, comprising: a variable displacement pump; an electric motor having a controllable rotational speed, for driving the variable displacement pump; and a flow rate controller configured to switch among multiple modes of operation, including a first mode of operation in which a flow rate is adjusted by controlling the rotational speed of the electric motor while maintaining a displacement of the variable displacement pump at a maximum value, a second mode of operation in which the flow rate is adjusted by changing the displacement of the variable displacement pump while maintaining the rotational speed of the electric motor at a minimum value lower than the lowest rotational speed used in the first mode of operation, and a third mode of operation in which, in a range where a discharge pressure of the variable displacement pump is larger than that in a state where the displacement of the variable displacement pump is at the maximum value, and the electric motor is at a maximum shaft torque, the flow rate is adjusted by changing the rotational speed of the electric motor in a range larger than the minimum rotational speed, while maintaining the displacement of the variable displacement pump at an allowable maximum value corresponding to the discharge pressure of the variable displacement pump in a state where the electric motor is at the maximum shaft torque.