Development of Control System for Electrical Radiator Fan using Dual Sensor & Microprocessor Based Electronic Unit

Use of Electrically powered radiator cooling fan with bimetal thermoswitch control is common in automobiles. Switching the electric fan ON and OFF at the desired cooling system temperatures is the biggest challenge faced by the system designers. This is due to poor response of the thermo-switch at different temperature rise rates (°C / min) of the cooling system. The thermal inertia characteristics of the bimetal sensors govern the effectiveness of such control systems.

Control by use of traditional bimetallic strip based thermo-switch works effectively only when the system temperature rise rates (°C / min) is within a specified band. This results in overheating of the cooling system. This leads to design change for increased cooling capacity, which has a large impact on material cost increase & sometimes creates issues in packaging of engine cooling system components.

This paper describes a radiator fan control system consisting of a dual sensor in place of existing bimetal strip thermoswitch and a microprocessor based electronic control unit. This unit caters to the different rate of rise of the engine temperatures (°C / min) owing to various vehicle speeds at different road load conditions.

This has resulted in optimising the size of radiator & reduction in load on vehicle electrical system.