Electric fan working principle
The engine may not require forced air from the fan during initial operation or at low coolant temperatures, or when the vehicle is traveling at high speed and ambient airflow through the radiator provides sufficient cooling. To ensure reliable control, the electric fan is operated based on a coolant temperature sensor. Using an electric fan improves engine warm-up characteristics, reduces fuel consumption, and lowers fan noise. Generally, the electric fan should not operate at idle.
The electric fan assembly typically consists of the motor, a cutout relay, and a coolant temperature switch. When the coolant temperature is below 93 C, the coolant temperature switch closes the cutout relay circuit; the relay coil pulls the contact open so that the motor is de-energized and the fan does not run. When the coolant temperature exceeds 93 C, the coolant temperature switch opens; no current flows through the relay coil, the contact closes, the fan motor is energized, and the fan runs to deliver air.
Hydraulic torque converter fan operation
This temperature-controlled hydraulic torque converter fan adjusts fan speed according to the temperature of the air passing through the radiator. At low temperatures the fan runs slowly, improving engine warm-up and reducing noise; as engine temperature rises, fan speed increases to accelerate cooling.
The hydraulic torque converter fan includes a torque converter rotor at its front. The converter cover and housing are fastened to the fan by screws. The main torque converter shaft is supported by bearings and connected to the converter cover. Both the reservoir chamber and the working chamber of the converter are filled with silicone fluid, separated by a partition plate. The partition plate has oil and return holes that are opened and closed by a bimetallic strip. In addition, a communication hole around the rotor housing connects the reservoir chamber and the working chamber.
(1) When the air temperature through the radiator is below 60 C, the bimetallic strip contracts and closes the return oil hole in the partition plate. As the converter rotor shaft rotates, the toothed surface around the rotor pumps silicone fluid from the working chamber through the communication hole into the reservoir, reducing the fluid in the working chamber and increasing slip. For example, if the fan pulley speed is 4000 rpm, the fan speed may be only 800 rpm.
(2) When the air temperature through the radiator exceeds 60 C, the bimetallic strip expands and opens the return oil hole. Under centrifugal force, silicone fluid flows back through the return hole into the working chamber, increasing the fluid volume, reducing slip, and raising fan speed. For example, if the fan pulley speed is 4000 rpm, the fan speed may be 2000 rpm. Because this type of fan speed control depends on the amount of silicone fluid inside the torque converter, any fluid leakage that reduces the working-chamber oil will lower fan speed and can lead to engine overheating.
Silicone oil fan clutch operation
The silicone oil fan clutch transmits torque using silicone fluid as the medium, leveraging the fluid's high viscosity. It uses the temperature of the air behind the radiator and an automatic temperature sensor to engage or disengage the clutch. At low temperatures the silicone fluid does not flow, the fan clutch is disengaged, and the fan runs slowly or idles. At high temperatures the silicone fluid becomes viscous and the clutch engages, causing the fan and water-pump shaft to rotate together to help regulate engine temperature.
The temperature-sensing elements in silicone oil fan clutches are typically bimetallic helical spring sensors. Operation proceeds as follows:
(1) When the air temperature through the radiator rises, the bimetallic sensor deforms from heat, forcing the valve shaft to rotate and opening the inlet oil hole on the driven plate. Silicone fluid stored between the driven plate and the front cover flows into the working chamber between the drive and driven plates, engaging the clutch and increasing fan speed. Higher air temperatures open the inlet hole more, which increases fan speed.
(2) When the air temperature through the radiator falls, the bimetallic sensor returns to its original shape and the valve closes the inlet hole. Under centrifugal force, silicone fluid returns from the working chamber to the reservoir through the return hole, the clutch disengages, and fan speed drops to a low level.
