More APU choices from Kohler: two new auxiliary power units target heavy-duty truck fleets, owner-operators; air- and liquid-cooled engine options

Diesel Progress North American Edition, May, 2008 by Mike Brezonick

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Continuing its advance into the heavy-duty truck markets, Kohler Power Systems has introduced two new auxiliary power units (APU) targeting heavy-duty sleeper cabs. The 3APU-HC is designed to provide power to keep the truck's main batteries charged and accommodate in-cab electrical loads as well as provide cab heating and cooling. The 7APU is a more conventional generator set system engineered to deliver electrical output to operate vehicle climate control systems and meet hotel electrical load demands, the company said.

Both of the new APUs were unveiled at the recent Mid-America Trucking Show in Louisville, Ky.

"These are totally new products from Kohler," said Stacy Peshkopia, senior product manager--mobile products at Kohler Power Systems. "We have gone in a different direction with these two products to give our customers more options.

"The 3APU-HC is really more of a heat pump that will keep the truck's battery charged and power basic needs, while the 7APU accommodates more intense power demands. Both are stand-alone units that do not intrude into any of the truck's systems."

The 3APU-HC is powered by a single-cylinder, 0.349 L, air-cooled diesel engine that is rated 4.7 hp at 2550 rpm and meets the U.S. EPA's Tier 2 emissions standards for small engines. It is built by Lombardini, the Italian engine manufacturer that was acquired by Kohler Co. last year.

A 55 amp Mecc Alte alternator is belt driven off the APU engine and is designed to keep the vehicle batteries charged. All of the cab's electrical loads can then be run off the main batteries, Kohler said, without fear of depleting the batteries unduly.

The 3APU-HC is designed to save space and weight and is 15 in. wide, 24 in. high and 28 in. deep from the frame rail, with a dry weight of 240 lb., not counting mounting brackets. The enclosure utilizes sound attenuating insulation to reduce noise emissions to less than 68 dB(A), according to the company.

The APU engine also drives a compressor that works with separate evaporator and condenser components to provide 12,000 Btu/hour of air conditioning and 10,000 Btu/hour of heat. The evaporator is a 22.44 in. wide by 14.5 in. high by 6.25 in. deep wall-mounted unit that incorporates four airflow cups that Kohler said distributes heating and cooling evenly throughout the truck cabin. Mounting it on the wall also flees up storage space, the company said. "Because no components are required to be mounted under the bunk, the Kohler 3APU-HC is a space saver for today's trucks," Peshkopia noted.

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The wall-mounted evaporator unit also incorporates temperature control, in-cab stop/start controls and an hourmeter.

The condenser unit, which is typically mounted outside on the back of the truck cab, is also designed to be compact, with dimensions of 26.56 in. long, 15.16 in. high and 5.5 in. deep.

All of the primary service points--oil dipstick, oil filter, air cleaner and fuel filter--are positioned on one side of the APU and standard oil drain intervals are 500 hours, the company said.

The Kohler 7APU is a diesel-driven gen-set that delivers 6.5 kW of electricity, which is enough to operate a typical 14,000 Btu air conditioner or heater, as well as handle hotel electrical loads. The heart of the unit is a two-cylinder, 0.686 L liquid-cooled diesel engine that drives a brushless alternator through a poly V-belt system with automatic belt tensioner. The mechanically controlled engine has a bore and stroke of 75 x 77.6 mm. and incorpo rates a cast-iron block, indirect injection and a glow plug system for engine preheating in cold temperature.

Maximum output at the rated speed of 3600 rpm is 17 hp, but for the APU application, the engine operates at 2600 rpm. Fuel consumption is 0.3 gph at typical load, Kohler said.

The engine meets EPA Tier 4 emissions standards for small engines, and Kohler said it is also in the final stages of vendor selection for a diesel particulate filter that will pave the way for the APU to operate in California.

An integral three-pass radiator provides engine cooling, and no tie-in with the truck's cooling circuit is required. "When we were designing these units, that was one of the main considerations," said Peshkopia. "When we spoke with the owner-operators and fleet managers, they were insistent that tapping anything into their engine would void their warranty--so we took that into consideration.

"When you are using the truck's cooling system, that is always a concern. Obviously we wanted to engineer APUs that complement their $130,000 truck, not work against it."

Liquid cooling also helps reduce noise emissions, which are rated at under 71 dB(A). Other noise-reduction features on both APUs include an enclosed super-quiet muffler, the use of insulation material on many of the interior surfaces of the enclosure and a four-point mounting isolation system.

Serviceability is enhanced by singleside access to the air cleaner, fuel filter and lube oil system. Like its smaller sibling, the 7APU has a standard oil change interval of 500 hours.