Apparatus for controlling hydrualic pump

An apparatus for controlling a variable displacement hydraulic pump including an engine as a driving power source, said engine having a constant horsepower characteristic at a predetermined revolution range, comprising;

• means for detecting the number of revolutions of the engine,
• means for setting a target pump absorption torque T.sub.P in
• means for detecting a pressure of hydraulic oil delivered from said pump,
• means for detecting that the engine is excessively heated,
• means for indicating a plurality of operation modes corresponding to an intensity of load,
• means for setting a plurality of pump absorption horsepower characteristics corresponding to said operation modes and setting a pump absorption horsepower characteristic relative to an operational mode for a light intensity of load in place of the existent pump absorption horsepower characteristic which is set for case where it is detected that the engine is excessively heated,
• means for looking for an inclination angle command relative to a swash plate in the pump so as to obtain an absorption horsepower which conforms to said set absorption horsepower characteristic with reference to the set absorption horsepower characteristic, the number of revolutions of the engine and said pressure of hydraulic oil delivered from the engine,
• means for reducing the number of revolutions of the engine to a predetermined number of revolutions when it is detected that the engine is excessively heated, and
• means for controlling said swash plate so as to allow an inclination angle of the swash plate in the pump to accordance with the following equation,
• T.sub.P =T.sub.E (N.sub.c)+(N-N.sub.c)
• where
• TE (N.sub.c) ;
• rated torque characteristic of the engine at a predetermined revolution number range
• K ;
• constant
• N ;
• number of revolutions of the engine
• N.sub.c ;
• target number of revolutions of the engine
• means for controlling a swash plate in the pump so as to obtain an absorption torque with reference to said target torque absorption torque and a pressure of hydraulic oil delivered from the pump, and
• means for reducing said target number of revolutions of the engine under a condition that an inclination angle of said swash plate is smaller than a preset angle.