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The Impact of Torque on Fan Clutch Performance


August 7, 2018

How Torque Applies to Fan Clutches

A fan clutch must apply a certain amount of torque to rotating components in order to engage the fan, overcome the resistance to turn it, and keep it spinning. The resistance of the fan, to the fan clutch, increases in relation to the size of the fan, the number and pitch of the blades and the RPMs of the engine. On a typical on/off or two-speed fan clutch, engagement is managed by spring pressure and friction material which, together with design, control the speed and nature (abrupt or smooth transition/ramp up) of the engagement. To optimize fan clutch service life, it is important that its torque capacity be appropriate to the application and that it be applied in such a manner as to achieve a smooth engagement. Excessive torque, applied abruptly, can damage belts, tensioners, cooling fans and fan clutches and thereby shorten service life. (See Figure A).

Figure A: To get up to speed quickly and theoretically reduce the stress on the bearing by the friction disk, an excessive amount of torque is applied by the competitive fan clutch, putting high stress on all cooling (including the bearing) and other components.

Horton has worked directly with OEM engineers, for many years, to determine just the right amount of torque for an application.

Fan Clutch Design Can Impact Torque

Some competitive fan clutches use a cone-shaped friction liner design which has less tolerance for wear than Horton’s multi-spring clutch pack and durable friction liner. Thus, to offset the wear factor, these competitive clutches apply higher torque to achieve a quick though harsh engagement. The latter leads to potential damage described earlier. Horton’s design, however, can tolerate small amounts of slippage without excessive wear, so torque does not have to be unnecessarily high. The added benefit is a smooth ramp up with less strain on belts, tensioners, clutch and fan.

Competitors sometimes claim that excess slippage causes incrementally more heat, and that heat leads directly to bearing failures. While heat may be inimical to service life, depending on the bearing, the excessive torque they use to theoretically decrease heat stresses belts and tensioners, notwithstanding the bearings. Often, the belts and tensioners go first because of high belt loading at time of engagement (See Figure B). Application-specific torque and a smooth ramp up are always better for an application, and things like heat can be dealt with through first-rate engineering design and materials.

Figure B: Horton laboratory and field tests confirm that abrupt fan engagements result in extreme belt loads and fan clutch component failure, especially if clutch is oversized for the requirements of the application.

Horton’s Solution for Optimizing Fan Clutch Life

Take Aways

  1. Excessive torque, applied abruptly, can damage belts, tensioners, the fan and the fan clutch.
  2. The right amount of torque for the application provides more reliable operation and longer service life.
  3. Horton works closely with OEM engineers to determine the precise amount of torque for each specific application.
  4. The torque levels specified for an application are proven in rigorous lab and field testing
  5. The largest and fastest heavy-duty truck engine fans (in high-volume production) require only 2,300 in.-lbs. [260 N-m] of torque. At 2,400 in.-lbs [271 N-m] the Horton DM Advantage® fan clutch provides the right amount of torque for this application. Horton engineering works directly with OEMs, to determine the torque capacity, for applications requiring higher or other application-specific torque requirements.
  6. Horton knows how fans perform because it is the industry’s largest designer and manufacturer of cooling fans and fan drives.
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