LO 11-7 Identify and describe the types, features, and applications of cooling fans

Fans and Fan Drives

Engine fans are designed to increase airflow across the radiator, which improves the effectiveness of heat removal from coolant by the radiator, air charge cooler, A/C condenser, and other accessory coolers located in front of the radiator. The number of blades, as well as the fan speed and fan pitch, determines the volume of air moved by the fan Figure 60. Mechanical engine power coupled through drive belts is used to rotate fans, but electric fans can also be used Figure 61. For most on-highway vehicles, engine fans pull air through the radiator in the same direction as airflow when traveling in a forward direction. When the vehicle is traveling, its movement usually creates enough airflow, and the fan is not required. At low-speed operation and at idle, air movement is often inadequate, and the fan is required by the cooling system and to move air across the A/C condenser and any other front-mounted heat exchangers. To reduce the parasitic loss of power from the engine, which is often more than 25 horsepower (hp; 19 kilowatts [kW]) on some HD fans, a fan drive mechanism is used to decouple the fan from the engine or to regulate its speed when high fan airflow is not required.

FIGURE 11-60: A conventional fiberglass engine fan and variable-speed, viscous-type fan clutch. Fins on the fan clutch absorb heat from the radiator to make the fan drive more temperature sensitive.

FIGURE 11-61: Without an engine, electric cooling fans are needed by this battery electric vehicle to increase airflow across the radiator.