Long taken for granted, the truck chassis has come under greater scrutiny recently, as emission control regulations, driver ergonomics, and the demand for enhanced efficiency and capability make commercial vehicle designs ever more complicated.
“As long as customers get the performance they expect from their vehicles, the chassis sort of disappears into the ether as it were — t doesn't get a lot of attention,” says Landon Grogan, program manager for Sterling Truck Corp.
“But the chassis plays a critical role in making a truck more flexible and efficient for the customer,” he says. “So when we make changes to the chassis, we have to do so in a way that takes nothing away from the capability customers expect from their truck.”
Grogan points to Sterling's new HX chassis for the OEM's A-Line and L-Line trucks, as an example of how chassis are being overhauled in the face of changing regulatory and market conditions.
“The main issue driving chassis design today is to get more strength with less weight,” says Grogan. However, the 2004 low-emission engines weigh more, cost more and generally require much more cooling, so truck OEMs had to make lots of chassis changes to help minimize those impacts, while also giving customers more options in terms of component mounting, axle configurations, etc.
“The '04 engine issue put the spotlight on the need to do some really radical things when it came to the chassis,” says Grogan. “We had a chance to look at ride quality…weight savings, better frame/component integration, and other issues.”
For example, Sterling developed a new chassis grid system called “OptiLock.” It's based on a frame-hole layout process that provides pre-determined rows of potential chassis hole locations spaced about two inches apart, center to center. All chassis component-mounting holes comply with the grid pattern, allowing for a more consistent mounting process.
“What we're doing is moving the component-mounting effort to a different point in the production process,” Grogan explains. “We're doing a lot more work on the front end of the design effort, but it allows us to automate the actual frame-punching process on the production line. That makes the manufacturing process easier and allows for much more flexibility downstream for both the OEM and the customer.”
OptiLock also enables Sterling to pre-punch body and equipment mounting holes in the grid area for customers, saving them time during body installation.
Another issue deals with keeping a “clean back of cab” so vocational customers in particular don't have to do a lot of body modifications in order to attach equipment to the cab. This issue is complicated by the requirements of at least one new low-emission engine model.
“With Caterpillar's ACERT engine…you need a heavier muffler to handle the aftertreatment system,” explains Grogan. “That means some fleets will have to move to a dual exhaust stack set-up instead of the single exhaust they used before.” This, in turn, changes how the exhaust system gets routed through the chassis.
The demand for a more comfortable ride is also affecting chassis design, specifically in terms of suspension offerings. Yet improvements in ride quality cannot come at the expensive of vehicle capability, says Grogan. “Ride quality is a big issue in terms of driver ergonomics and it's an area of continual challenge as trucks more and more are emulating ride enhancements developed for automobiles.”
Consequently, the HX's front suspensions now include both taper- and multi-leaf spring design options. “The taper-leaf springs gives the truck more front-end weight capacity,” says Grogan. “Not only must they manage the heavier engines and beefed-up cooling packages, they also must still allow for the addition of snowplows and other front-end equipment.”
He notes that all of these changes represent just the first of what could be many chassis redesign efforts in the coming years. “There's so much change going on at the front of the vehicle that design activity along the length of the chassis has gone way up,” Grogan says. “It'll never cease to be interesting.”