Behr puts the cooling touch on Kenworth T680 cabin

  • 25-Jul-2012 03:47 EDT
T680 INT.jpg

The Kenworth T680's windshield is 50% larger than the predecessor, but the HVAC system's defrost capability uses a high performing heater core and a specifically tuned set of ducts and turning vanes that were "developed through CFD simulations to reach the farthest points on the windshield," according to Behr's John Tepas.


“With this product, we surveyed more customers than we had ever done in the past,” Doug Caley, Engineering Manager for the Kenworth Truck Co., told SAE Magazines at a Detroit media briefing on June 19 that focused on the Kenworth T680’s thermal management system.

In addition to analyzing in-field data, the T680 team sought detailed feedback from dealers, fleet operators, and drivers.

John Tepas, Vice President of Engineering for Behr America, the system supplier of the truck’s thermal management system, said that comments from drivers and others provided a framework for the HVAC system’s product development team.

“One of the key things we focused on was system reliability,” Tepas told SAE.

With fleet owners and operators earning money on every delivery, downtime for HVAC repairs can sour the financial sheet. So with a primary goal of designing a more robust HVAC system, engineers opted for new sealing technologies. The team also scrutinized existing production processes at three Kenworth assembly plants in the U.S. and Mexico, a Peterbilt plant in the U.S., and a Paccar plant in Canada to pinpoint possible trouble spots. (Kenworth and Peterbilt are Paccar Companies.)

The review prompted an array of specific quality checks on the refrigerant handling lines and the component assembly lines.

“We’re also doing additional leak checks during component manufacturing to assure that the units are built correctly. And we’re using very specific hardware tools and torque measuring methods at the truck assembly plants to assure that the HVAC system is leak-free and properly filled,” Tepas explained.

Newly developed proprietary software can determine when certain compressor operating conditions exist—such as a low refrigerant charge or excessive clutch cycles—that could cause premature system failures. Dealer service technicians will get a ripple benefit from the T680’s new software technology.

“We took advantage of the additional computing power to add diagnostic capability, which will allow for quicker and easier service,” Tepas said.

Behr engineers also leveraged their knowledge from designing and developing HVAC systems for light passenger vehicles.

“We used automotive heat exchangers in the Kenworth T680. The aluminum heat exchanger is more akin to an automotive-style construction. But this heater core was engineered with a specially designed coolant system that can withstand the cycles and flow rates associated with larger engines and longer duty cycles,” said Tepas.

Similar to various passenger car applications, the HVAC evaporator uses BehrOxal treatment for corrosion protection and to help prevent system start-up odor.

One of the big development aids for Behr was the supplier’s climatic wind tunnel in Troy, MI. The chamber enabled engineers to replicate all sorts of conditions. For instance, engineers were able to conduct defrost tests with thick layers of ice on the Kenworth T680’s mammoth windshield, which is 50% larger than its predecessor.

Behr engineers also used the wind tunnel to run automatic temperature control calibrations, dramatically reducing the amount of time spent road testing the HVAC system. And during the HVAC system’s design phase, engineers frequently used the wind-tunnel environment to pinpoint potential oil pooling areas.

“By making design modifications, we were able to eliminate the problematic spots where oil might get trapped. The final production design assures proper lubrication back to the compressor, even in extremely low temperatures or other challenging operating conditions,” Tepas explained.

In developing the HVAC’s automatic temperature control, engineers had to consider the sun’s position at dawn and at sundown as well as instances when the truck would pass under a cloud or travel through a tunnel. These and other transient conditions needed to occur in testing situations to ensure that the HVAC system would react as predicted.

“With the Kenworth T680 program, we used the wind tunnel more extensively than on any previous development project. A primary reason the wind tunnel was used so frequently was because we needed to improve our confidence in the operation of the new control algorithms for the HVAC’s automatic temperature control system,” Tepas said.

In addition to being the system supplier for the HVAC unit, Behr is providing its radiators, EGR coolers, and charge air coolers for the engine cooling modules.

According to Dr. Thomas Mersch, Behr’s Chief Engineer of Truck Engine Cooling, Behr’s customized cooling modules are delivered in-line sequence for all vehicle builds.

“The fact that Behr is the supplier for both the HVAC system and the engine cooling modules provides an optimized interface between the two cooling circuits in the Kenworth T680,” said Mersch.

Production of the T680 began this past May at Kenworth’s Chillicothe, OH, plant.

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