Patent ID: 7533527
Filing Date: 2009-05-19
Classification: B60W,E02F,F04B

Abstract:
1. A hydraulic drive device for a work machine, comprising: an engine; a hydraulic pump driven by the engine; a hydraulic actuator operated by pressure oil discharged from the hydraulic pump; working condition identifying means for identifying working conditions; engine controlling means for controlling output torque of the engine; and hydraulic pump controlling means for controlling absorption torque of the hydraulic pump, wherein when the working condition identifying means identifies a first working condition of the working conditions, the engine controlling means controls the output torque of the engine to achieve a first engine output torque characteristic corresponding to the first working condition, and the hydraulic pump controlling means controls the absorption torque of the hydraulic pump so as to match the output torque of the engine that substantially corresponds to an engine speed at which output of the engine reaches a maximum when the first engine output torque characteristic is set with the absorption torque of the hydraulic pump that corresponds to said engine speed, wherein when the working condition identifying means identifies a different working condition of the working conditions, the engine controlling means controls the output torque of the engine to achieve a different engine output torque characteristic corresponding to the different working condition, and the hydraulic pump controlling means controls the absorption torque of the hydraulic pump so as to match the output torque of the engine that substantially corresponds to an engine speed at which output of the engine reaches a maximum when the different engine output torque characteristic is set with the absorption torque of the hydraulic pump that corresponds to said engine speed, and wherein when the working condition identifying means determines that the working condition has changed from the first working condition to the different working condition, the engine controlling means changes the engine output torque characteristic from the first one to the different one, and the hydraulic pump controlling means changes the hydraulic pump absorption torque characteristic from the first one to the different one.