The cooling system with two fans is generally driven by electrical motors in the small cars. Compared with the traditional cars, heavy duty trucks have the larger heat dissipation power of cooling system. The motors power consumption of dual fans will be larger and the two electrical motors will occupy a large space in the engine cabin. Hydrostatic drive refers to the cooling fan is driven by hydraulic motor, but it has the low transmission efficiency. According to the engine water temperature value and the actual working status of the hydraulic system, the actual speed of cooling fan can be controlled by the computer, which guarantees the normal working water temperature of the engine. Hydrostatic drive is generally applied to heavy vehicles, engineering machinery and excavators as driving source of cooling fan which contains the advantages of large output power, overload protection, continuous speed regulation and flexible space arrangements. Integrating the characteristics of the driving modes with the hydraulic motor and electrical motor, the two motors of cooling fan can adopt cooperative operation using both driving modes. In the situation of low heat dissipation power, the cooling fan only can be driven by electrical motor, and two motors work cooperatively when the engine have the high heat dissipation power. By means of establishing the fuzzy control strategy, the rotary speed of two motors can be adjusted according to the real-time engine water temperature variation. Compared with the conventional PID control, the fuzzy control can avoid overshoot and improve temperature control precision. Owning to the overflow loss of hydraulic valve, the performance analysis of two driving modes with two hydraulic motors and the dual electro-hydraulic motors will have a comparison. The results prove that the power consumption of pure hydraulic system is 5.3kW while the power consumption using dual electro-hydraulic motors is 3.5kW, so that the power consumption saves 34% on average.
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