Curt Tamandl will tell you that chassis engineering for Class 8 tractors has become a very complex balancing act, largely because of the demands being placed on what he calls the critical “bones” of the modern truck are often contradictory.
“We look at the chassis as the backbone of the truck,” says Tamandl, manager of product development for the chassis department at Mack Trucks Inc.: “It's [where] we hang everything else — the cab, engine, transmission, axles, tires, etc. — so any changes you make to the chassis have a significant impact on the overall vehicle.
“Take what I call ‘exotic’ materials that give you lower weight and increased durability: You can't use them because they raise the cost of a vehicle too much. That's why balancing all of the elements involved — cost, weight, durability, etc. — is so critical today.”
He points to the development of Mack's new Advantage chassis for its highway tractors as an example of working to get everything the customer wants into an affordable chassis package.
“What we did is spread out and reduce the load stress on key parts of the chassis, so we could reduce the weight of the chassis without the need to involve exotic materials in the design,” he explains. “This is a lot harder to do these days as the duty cycle of trucks keeps getting harsher, the amount of payload they carry gets higher, and more stress is created for the chassis to handle. Optimizing the chassis components to deal with all of that cost effectively over the lifecycle of the vehicle makes it a real challenge.
“Different components react differently when they are put together,” Tamandl continues. “We have this whole range of components customers get to choose from when they spec their vehicles. So we have to do a lot of analytical testing as we design the chassis.”
In addition, chassis are subject to a number of operational stresses. “A day-cab tractor working in the city, for example, is going to be making a lot of stops, starts and turns. So you're going to get a lot more vibration and stress working through the chassis,” Tamandl says. “With a longhaul sleeper tractor, you don't have nearly the same amount of turning and twisting, but there's more exposure to rough weather and harsh conditions, such as mountain driving. Yet the chassis you design has to handle those two very different operational patterns.”
To meet these sometimes opposing demands, chassis engineers are focusing on critical design areas. One is “resistance bending moment,” or RBM, which is a measure of chassis strength. Another is the chassis' role in cooling today's hotter low-emission engines. Tamandl points to the offset design of Mack's Advantage chassis, with its improved airflow, as well as the addition of a larger cooling module. Two additional areas of concern for chassis designers are improving ride and handling, and reducing noise inside the cab.
Time is one of the biggest challenges facing chassis engineers. “The amount of engineering we're being called upon to do is increasing rapidly, yet the time windows to deliver finished products are much smaller,” Tamandl explains. “As an engineer, you want to change everything from the ground up.” But that's not realistic in today's fast-paced environment. Engineers have to be able to take an existing base and focus on changing key areas to meet new demands. “It's all about adapting products to fit future needs,” he relates.
Tamandl says this engineering strategy is being played out at Mack in a number of interesting ways. Instead of having separate architectures for vocational and highway chassis, for example, engineers are creating one package to meet the needs of both applications.
“Now you have a chassis that's easier to maintain and build off of for specific niches,” he says. “It also allows us to reduce development time on the engineering side, shrinking the product development cycle. In the past, it took 15 years to change [a product] and adapt it to new market needs. We've shrunk that to between 5 and 10 years. That [speed] becomes really important when you're dealing with issues such as how new emission regulations affect engine design, cooling needs, etc.”