Fan Drives

Fan Drive or Fan Clutch

Fan Drive (or Fan Clutch)

The purpose of the fan clutch, with an attached fan, is to help keep engines within set operating temperature parameters, usually defined by the manufacturer. The temperature sensing can be accomplished by a bi-metallic sensory system or by an electronic control. The two terms, “fan clutch” and “fan drive,” are interchangeable.

While the fan drive is driven off the engine, it is designed to “freewheel” when not engaged and engage (using the engine as the prime mover) as engine temperature increases. There are three basic types of fan drives, each with advantages in terms of features and price: on/off, two-speed and variable-speed.

On/Off Fan Clutch
DM Advantage On/Off

On/Off Fan Clutch

The basic operation of the on/off fan drive is it engages when the temperature of the engine reaches a set point. It will remain engaged until the temperature is reduced back to its optimum range—hence “on” and “off.”

The on/off drive is the simplest of the three types and typically the least expensive. They are usually designated for over the road and long haul Class 5-8 trucks, buses and some off-highway applications. It is important to specify a fan drive to the application when possible because the on/off model could be running continually if associated with the wrong application. As a general rule, the fan clutch should not be engaged more than ten percent of the time. While constant operation is fine (other than reduced life span), the fact that it is putting a load on the engine increases fuel consumption — plus it’s noisier if it’s constantly running. Last, horsepower devoted to operating the drive reduces available horsepower to the work.

Horton offers a variety of on/off models to accommodate both on- and off-highway needs. These include the DM Advantage®, EC450/EC600, HT/S Advantage and HT650.

Two-Speed Fan Clutch
DM Advantage Two-Speed

Two-Speed Fan Clutch

In an application where the fan would need to run more than 10 percent of the time to keep the engine cool, the two-speed fan would be a good choice. The two-speed drive is capable of switching from a lower, eddy-current mode to a higher, spring-actuated mode (higher speed) for optimum cooling. It’s ideal for the heavy-duty vocational market but also for some on-highway applications. Typical applications might include garbage trucks, rear-engine cement trucks, dump trucks, etc. Generally, it works well on applications that are not constantly moving or at idle, such that no ram air is flowing across the engine. The concept of the two-speed fan drive is to reduce the number of fan clutch engagements. Accordingly, the two-speed will reduce fuel consumption, produce less noise and make more horsepower available for work in eddy-current mode.

The two-speed drive is typically more expensive than the on/off fan drive but is the preferred drive to specify in select applications. It also offers fast warm ups in cold weather, less liner wear due to less cycling and longer life.

Horton offers several two-speed fan drives for on- and off-highway applications including: DM Advantage® and Arctis.

Variable-Speed Fan Drive

Variable-Speed Fan Drive

Variable-speed fan drives are usually “viscous” or fluid couplings. In general, the variable-speed fan drive operates according to the cooling demands required to keep the engine at optimum operating temperature. When less cooling is needed, it operates at a low off speed allowing faster warm ups, increased cab heat, significant noise reduction, increased available horsepower and less fuel consumption. When more cooling is required, it ramps up to a higher speed quickly, smoothly and with reduced stress on both drive, engine and adjacent components. It’s also maintenance free (no liner) and helps OEMs meet Tier 4 requirements. The variable-speed operation also helps reduce fan abrasions from dirt, rocks and other debris as it has the capacity to operate at lower speeds and may cycle less often and for shorter periods.

Variable-speed fan drives are available in many sizes for a variety of applications including medium- and heavy-duty trucks, vocational trucks, buses, specialty on-highway vehicles, and many off-road applications.

Horton offers several variable-speed fan drive models for both on- and off-highway needs including: RCV250, RCV1000, RCV2000, LCV40, LCV80, LCV220, VS Directly Controlled and VS Air Sensing.