Patent ID: 7281373

Claim:
A fluid pump control device for wheel loaders, comprising: an engine ( 8 ) for driving an axle through a transmission ( 9 ); a main pump (P 1 ) driven by the engine ( 8 ) for supplying a hydraulic flow to front working implements; a variable-displacement steering pump (P 2 ) driven by the engine ( 8 ) for discharging a hydraulic flow to be supplied to a steering device ( 7 ) or to be merged with the hydraulic flow of the main pump (P 1 ) and then supplied to the front working implements, the steering pump (P 2 ) including a swash plate ( 13 ) and a pump regulator ( 14 ) for regulating an inclination angle of the swash plate ( 13 ) to vary the fluid quantity discharged by the steering pump (P 2 ); an auxiliary pump (P 3 ) driven by the engine ( 8 ) for supplying a hydraulic flow to a working implement control valve ( 1 ) and a brake device ( 12 ); an electronic proportional control valve ( 17 ) provided on a discharge quantity control signal line ( 16 ) for variably controlling a pilot pressure conveyed the pump regulator ( 14 ), the discharge quantity control signal line ( 16 ) bifurcated from a pilot signal line ( 19 ) of a joystick valve ( 15 ) and connected to the pump regulator ( 14 ); a hydraulic load detection means ( 4 ) for detecting a real hydraulic load (Px) based on the fluid pressure of the hydraulic flow discharged by the main pump (P 1 ); an engine revolution detection means ( 10 ) for detecting the number of revolution (N 1 ) of the engine ( 8 ); a transmission revolution detection means ( 11 ) for detecting the number of output shaft revolution (N 2 ) of the transmission ( 9 ); and a controller ( 20 ) for calculating the ratio of the transmission output shaft revolution number (N 2 ) to the engine revolution number (N 1 ) to find a real travel load (La), calculating the ratio of the real travel load (La) to a predetermined maximum travel load (Lmax) to find a travel load ratio (Rt), calculating the ratio of the real hydraulic load (Px) to a predetermined maximum hydraulic load (Pmax) to find a hydraulic load ratio (Rp), controlling the electronic proportional control valve ( 17 ) in such a manner as to reduce the fluid discharge quantity of the steering pump (P 2 ) if the travel load ratio (Rt) exceeds a predetermined reference travel load value and if the hydraulic load ratio (Rp) is greater than a predetermined reference hydraulic load value, and controlling the electronic proportional control valve ( 17 ) in such a manner as to maximize the fluid discharge quantity of the steering pump (P 2 ) if one of the travel load ratio (Rt) and the hydraulic load ratio (Rp) fails to reach the corresponding reference value.