Creating a system of components that function as a single, smooth-shifting unit has always been the ultimate goal of drivetrain integration.
Achieving this has been complicated by the fact that components are often made by different companies, making it difficult to get the most engine power with the best fuel economy across all trucking applications.
Add in the government mandate for stricter diesel emissions and the job of driveline integration job becomes even tougher.
As a result, two distinct pathways to drivetrain integration are developing: a vertical approach and a systems approach. In the former, truck OEMs primarily use in-house components to build drivetrains, giving them more control over how the individual parts fit and work together as single package. In the systems approach, suppliers spec and package individual parts, in turn providing a single, integrated drivetrain to truck manufacturers.
No matter how drivetrain integration is achieved, however, the goals are the same: reduce emissions, make better use of space on the chassis, and maximize fuel economy, performance and reliability across multiple truck applications.
According to Charlie Allen, national service director for Arvin — Meritor, “A lot of what's going on in terms of drivetrain integration today goes to the fact that as vehicles approach 2007, more complex technologies are involved and the wide open space we used to have on the chassis is no longer there.” Stricter emissions regulations also mean “tough [performance] choices, so drivetrain spec'-ing is becoming much more important,” he adds.
Viewing the drivetrain as a single package, rather than a collection of mix-and-match components, should fuel engineering efforts in the future, says Matt Baus, chief engineer for powertrains at International Truck & Engine Corp.
“It's about optimizing the whole package — trading off between the strengths of each component within the drivetrain,” he explains. “The key is to gear the entire drivetrain for specific operations, getting the optimum configuration for mountainous terrain or on- and off-road applications so each gets the best reliability and fuel economy possible.”
The integrated drivetrain concept can also help OEMs in their efforts to compensate for fuel economy and vehicle performance degradation resulting from '07 technology needs, adds Baus. “We can take advantage of situations within '07 compliance that we previously might have viewed as problems,” Baus notes. “For example, the larger cooling systems we're using to handle the higher heat rejection produced by '07 engines give us a way to get additional cooling to the drivetrain as well. A more capable cooling system thus offers us more room in the duty cycle to get the same or better fuel economy in some truck applications.”
Gary Ganaway, director of system and product strategy for ArvinMeritor, notes that for a fleet to survive in these days of high fuel costs and tight emission rules, it must spec a drivetrain package that will give its vehicles the best performance and fuel efficiency possible for its particular operating environment. That's why optimization is becoming a key design focus for drivetrain component manufacturers going forward.
“You can't just look at everything separately anymore,” he says.
“The engine, the transmission, the axles — even the tires — all impact performance and fuel economy, and by extension drivetrain efficiency. Under-inflated tires, for example, can cost you upwards of 1% in terms of fuel economy — and also reduces the efficiency of the drivetrain itself.”
Preston Feight, director of product planning at Kenworth, says optimization revolves around developing the lowest-cost drivetrain combination possible that in turn yields the best operational reliability and best fuel economy possible.
While drivetrain optimization is certainly not a new concept, the technology required to meet '07 and '10 emission rules is generating new interest. “The emissions-reduction issue is acting as a catalyst to bring new technology and opportunity to drivetrain components,” Feight says.
Dimitri Kazarinoff, director of global marketing for Eaton Corp.'s truck group and Roadranger, cites the increased use of automated transmissions and the explosion of electronic controls in drivetrain components as two additional factors behind optimization efforts.
“More electronics and more computing power mean all the components that make up the commercial truck drivetrain now talk with each other and the engine better,” he explains. “With all the computing power available now, the opportunity for optimization is much greater.”
Kazarinoff points out that automated transmissions —both fully automatic units and automated mechanicals where only minimal manual shifting is required — can really help an integrated drivetrain achieve better fuel economy, since a computer makes all the shifting decisions based on precisely calculated algorithms, rather than the feelings of the driver.
The move to more fully integrated drivetrains, however, does not mean that fleets no longer have choices. “Trucking isn't homogenous enough to support just one or two drivetrain packages,” says Kenworth's Feight. “We'd risk choosing a technology approach that's too narrowly focused [and] doesn't give the customer all the capabilities they need.”
However, David McKenna, marketing manager for engines, transmissions and axles at Mack Trucks, cautions that choices will be more limited in the future.
“Customers have always demanded that we as OEMs supply them with what they want in terms of truck components, especially when it comes to drivetrains,” he says. “But as we move forward through '07 and '10 emissions changes, we won't be able to offer some of the things we offered in the past due to the restrictions emission controls place on us.”
For the future, getting drivetrain components to function in a mutually supportive relationship is what Kenworth's Feight says should give fleets the best fuel economy, reliability and drivability possible.
“It's part of a holistic design process. The point is not to force drivetrain components to go together, nor to have plug-and-play drivetrain construction,” he explains. “You want to be able to sit down with a fleet to select the best mix of components — from the transmission down to the tires —that will give them the best fuel economy and performance for their particular [operating] conditions.”
Mack's McKenna believes that these technological advances will create two circumstances: fewer spec'ing choices in some areas, yet more drivetrain capability overall.
Ironically, that narrowing of component choice has a substantial upside for fleets — drivetrain packages that are far more highly tuned to offer the best performance and fuel efficiency possible.
“It's a function of what's happening on the engine side of our business to a degree,” says McKenna. “At one point in time, we offered every engine available on the market. But now … we don't offer as many … and that's being narrowed further by emission control needs. That in turn limits drivetrain selection to what will best fit those engine power outputs.”
“We've spent years engineering drivetrain components to meet engine outputs… dialing into the engine's ‘sweet spot’ in terms of transmission shift points and rear axle gear ratios to vastly improve performance and fuel economy at the same time,” McKenna notes.
Points for the package
In developing drivetrain components that function as a single, seamless unit, engineers say it's critical to keep several key points in mind.
- FUEL ECONOMY
“We expect better integrated drivertains can help here,” says Matt Baus, chief engineer for powertrains at International Truck & Engine Corp. Moving to direct drive transmission formats, for example, could save three-quarters of a percent in fuel economy. Even axle alignment and tire inflation have a much greater impact on fuel economy today within the context of an integrated drivetrain, says David McKenna, marketing manager for engines, transmissions and axles at Mack Trucks: “If your axles are out of alignment, you can lose 1% to 2% in fuel economy. If just two of your tires are under-inflated by 20%, that's another 1% to 2% fuel efficiency loss.”
“This is always a big part of drivetrain engineering, because reliability and durability have a direct impact on vehicle productivity and uptime,” McKenna points out.
- VEHICLE PERFORMANCE
Better integration leads to creation of specific drivetrain packages for a wider range of truck applications, says Baus. “We need to offer rear axles that provide the right GVW capacity for the customer, while also making sure the right gear ratios, mounting style and suspension are in place so fuel economy and performance don't suffer.”
- EMISSIONS COMPLIANCE
Drivetrains must function within the confines of 2007 and 2010 emissions regulations. “But the goal is to be as transparent as possible, so customers don't have to operate their equipment any differently,” says Baus.