Comparison of Modulated (Viscous) versus On-Off Fan Clutches

Both the advent of the energy crisis and the regulation of noise levels are making fan drives highly desirable for heavy truck applications. This paper evaluates the reduction of power drain and fan noise for two types of fan drives generally available today: the on-off air-activated clutch and the modulated viscous drive. In addition, the principles of operation, life, and application considerations are discussed.