Fluid pump control device for wheel loaders

A fluid pump control device for wheel loaders, comprising:

• an engine (8) for driving an axle through a transmission (9);
• a main pump (P1) driven by the engine (8) for supplying a hydraulic flow to front working implements;
• a variable-displacement steering pump (P2) 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 (P1) and then supplied to the front working implements, the steering pump (P2) 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 (P2);
• an auxiliary pump (P3) 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 (P1);
• an engine revolution detection means (10) for detecting the number of revolution (N1) of the engine (8);
• a transmission revolution detection means (11) for detecting the number of output shaft revolution (N2) of the transmission (9);
• and
• a controller (20) for calculating the ratio of the transmission output shaft revolution number (N2) to the engine revolution number (N1) 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 (P2) 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 (P2) if one of the travel load ratio (Rt) and the hydraulic load ratio (Rp) fails to reach the corresponding reference value.