Peterbilt Motors Company just unveiled its 2006 lineup of Class 8 conventional trucks and tractors, representing one of the most significant product development investments in its history. Featuring new technologies and operating environments, the new lineup includes an HVAC air distribution system that has been completely redesigned for improved performance.
Conceived by Peterbilt’s Senior Project Engineer Wade Walterscheid and Project Engineer Terry Manuel, the patent-pending design teetered between success and failure on one millimeter of tolerance between an injection molded rotating canister and its housing. “It was a fairly high risk design that Peterbilt developed in spite of a similar industry attempt that failed due to the high tolerances required,” says Walterscheid. “Peterbilt believes in purposeful innovation, and this system promised a 20 percent boost to the HVAC airflow without touching the main unit or the fan assembly. Our engineering staff and Mack Molding made a commitment to get the job done right.”
Already a current supplier, Mack Molding’s southern operations was chosen to furnish four injection molded parts for the new 2006 Models’ HVAC system — the upper (rust colored) and lower(gray) housings, rotating mode cylinder (internal) and an air transition part (purple), as well as some 16 additional interior trim components. “Supplier selection is one of the most important management decisions made early on in a program, and this engineering project was the second largest in Peterbilt’s history in terms of capital investment,” says Walterscheid. “Peterbilt considered it paramount that the best possible avenues be taken to guarantee success, and requested that Modine Manufacturing, our system supplier, select Mack for the HVAC injection molding. Mack was able to commit dedicated resources and had the capacity needed to meet our aggressive schedules and production requirements.”
Up for the challenge
“The overall mode housing design is as simplistic as one can imagine, but caused Mack’s molded components to push the limits of materials and manufacturing processes,” says Walterscheid. Specifically, the challenges included:
- extremely precise clearance (less than 1mm) between the rotating mode cylinder and inside diameter of the assembled scroll housing
- sufficient dimensional stability to deliver very flat parts on a consistent basis that could withstand extreme weather variables
- tooling design that would provide consistent material flow
- narrow timeframe to meet schedule for winter weather testing.
Starting with the material, Mack recommended a custom engineered polycarbonate resin from LNP with a unique blend of glass fiber and glass bead for dimensional stability. “The material had to be able to withstand extreme temperature ranges, from -60 to 120 degrees Fahrenheit, as well as chemical resistance, salt spray, electromagnetic susceptibility and more,” says Ken Kincaid, technical engineering manager at Mack’s southern operations. “Peterbilt subjected the HVAC and other main truck systems to extreme conditions with the vehicle loaded and at road speed in Death Valley, Calif., in the summer and above the Arctic Circle in the winter. Under both temperature extremes, this material withstood the test.”
Tooling was also critical to maintain dimensional accuracy and consistency. Mack worked with Delta Mold, Charlotte, N.C., to design a family tool that molds both the upper and lower scroll housings in one shot. “Strategically placed gating was crucial to allow for improved material flow to accommodate the tight tolerance requirements,” says Steve Butler, Mack business unit director. “We got first parts off steel tools in 10 weeks to meet Peterbilt’s timeframe for cold weather testing, which was critical to approving the new system for the 2006 lineup.”
Even earlier, Mack Prototype, the company’s prototyping division in Gardner, Mass., molded first parts for airflow and volume testing. Mack Prototype built SLA masters of all four parts, as well as RTV rubber molds for producing polyurethane prototypes.
“The final challenge was presented by the design of the rotating mode cylinder itself, which is extremely complicated for a molded part,” says Kincaid. “Because of its deep ribs and one-piece part design, it has to be rotated 40 degrees and ejected off the tool. That’s a very unorthodox part removal method, but we’ve developed a system to handle it.”
In the end
Peterbilt’s new design greatly reduced part count, boosted performance and improved climate control. The results are dramatic:
- 20 percent increase in air flow
- 400 percent improvement in side-window defrost efficiency
- enhanced look and feel with upgraded dash-mounted controls
- more precise temperature management via digital technology
- all-around improvement in assembly ease, reliability and air flow consistency from cab to cab
- overall cost reduction.
“With Mack’s experience in processing and expertise in refinement, the end products are perhaps the finest and most precise components ever produced for a vehicle air distribution system,” says Walterscheid. The HVAC system, along with the new interior and complete 2006 lineup were rolled out at the 2005 Mid-America Truck Show this spring. “The new interior is very luxurious, has excellent fit and finish, and includes improvements like the new HVAC system that give customers added incentive to make Peterbilt their vehicle of choice,” adds Walterscheid. “We’ve definitely raised the bar.”
Contacts: Ken Kincaid, Mack Technical Engineering Mgr
Steve Butler, Mack Business Unit Director
Wade Walterscheid, Peterbilt Senior Project Engineer
Peterbilt Motors Company, a division of PACCAR inc. (Nasdaq: PCAR), manufactures premium quality trucks for a wide range of markets, including over-the-road, construction, municipal and medium-duty. Based in Denton, Texas, Peterbilt combines classic styling, innovative design and superior-quality features in a custom-engineered truck that stands as the “Class” of the industry. For more information, visit http://www.peterbilt.com.