While on/off fan drives have been the preferred solution for their durability and fuel efficiency in over-the-road applications, BorgWarner's new DuroSpeed two-speed fan drive was developed for more severe service applications, such as vocational and off-highway truck applications (cement mixers, dump trucks, construction trucks, mining trucks, refuse trucks, etc.), and such applications “have very different cooling needs than line haul trucks," said Daniel Paterra, President and General Manager, BorgWarner Thermal Systems.

That said, the DuroSpeed fan drive is, in fact, based off the company’s Kysor on/off fan drive, with the addition of two components.

When used in severe-duty applications, on/off fan drives continually engage and disengage. When disengaged, engine temperatures rise quickly, causing the clutch to engage repeatedly.

In contrast, the pneumatically actuated DuroSpeed two-speed drive uses an eddy current to give it an elevated disengage fan speed (~500 rpm) to prevent engine temperatures from rising too quickly. This gives vocational trucks additional cooling without having to engage the fan.

Because the DuroSpeed fan drive engages and disengages less often, clutch life increases, noise decreases, dust buildup in the radiator is minimized, and more horsepower is available, allowing the vehicle to achieve higher work output. If more cooling is required, then the fan uses a friction material to fully lock up so the fan spins at full speed, cooling the engine down.

An on/off drive is traditionally designed to have a minimum disengage speed of about ~100 rpm, a figure that should be as low as possible so that minimum energy is taken away from the engine. If the engine needs cooling, the fan fully engages in the same exact manner as the DuroSpeed drive to cool the engine (friction lockup). The goal with line haul trucks is to keep the fan off as much as possible to maximize fuel economy. As a BorgWarner spokesperson told SAE Magazines, “It is not wise to use two-speed fan drives on line haul applications as this is a loss of fuel economy. Higher fan speed robs energy from the engine when there is no real additional cooling needed on the engine.”

That begs the question that if a two-speed fan drive works better than an on/off fan drive for off-highway duty cycles, wouldn’t a variable-speed fan drive work best? According to the spokesperson, “Our variable-speed fan drive has been available since the late 90s and targets this market as well. The advantage that the DuroSpeed drive has is when there are several truck models, with low volumes. The DuroSpeed drive can be applied to these low volumes easier. Variable speed in the end is a more elegant solution, but can take a little more development.”

However, according to BorgWarner, even as it “proceeded to lead the market in variable-speed fan drive technology, the industry continued to show a strong desire for a version of the current popular friction clutch, but with the ability to decrease engagements by carrying enough disengaged fan speed to meet a large portion of cooling requirements—particularity in severe service applications where fan engagements are more frequent. BorgWarner responded by creating the DuroSpeed fan drive. Applications that require the fan drive to engage frequently at medium to high engine speeds will benefit from the DuroSpeed fan drive.”

Compared with competitive models, the DuroSpeed fan drive has no spinning air connections to wear, inspect, or service, and is designed to operate at lower temperatures.

“Our testing shows the DuroSpeed fan drive's flux ring design enables this clutch to run 70°F cooler than competitive offerings,” said Paterra. “The cooler internal operating temperature increases bearing and liner durability, allowing nearly twice as many engagements over its lifetime."

Weighing 5-10 lb (2.3-4.5 kg) less and using 11 fewer components than comparable units, the DuroSpeed fan drive also helps deliver better fuel economy. According to the spokesperson, “the weight savings comes strictly from fewer components and the unique flux ring design, which was engineered to be as small and light as possible while rejecting the heat away from the fan clutch as effectively as possible.”

The flux ring is made up of a steel mounting ring, with over-molded aluminum cooling fins. Based on how it is mounted, located between the pulley face and the clutch, the steel mounting ring helps transfer the heat away from the internal components of the clutch, such as bearings, seals, and the friction liner interface. Then, the aluminum cooling fins, which are molded around the steel ring, help transfer that heat to the surrounding air. The flux ring is designed to work like a fan itself, pumping air past the cooling fins, giving it improved cooling capability.

To reduce complexity and minimize upgrade costs, BorgWarner's modular design of the DuroSpeed fan drive uses the same clutch unit for all applications. Any Kysor on/off fan drive can be easily retrofitted to a DuroSpeed fan drive with a conversion kit.

Initially driven by customer demand, mainly in North and South America, the design process for the DuroSpeed fan drive was completed at BorgWarner’s Technical Center in Marshall, MI. It is expected to first launch through aftermarket channels in late April, and the company is working with OEMs directly for its launch.