Electrification’s Impact on Commercial-Vehicle Chassis Design
Transition to EV propulsion is causing a simultaneous shift in design considerations for commercial-truck OEMs.
Electrification in the commercial and off-highway truck sectors is ramping up at an increasingly rapid pace. This fundamental change in propulsion will be one of the most significant shifts in the industry’s history and is having ripple effects on various aspects of chassis design, validation and reliability. Making matters more complicated is the lack of fully defined standards in the segment. This issue was discussed at length by a panel at SAE’s 2022 COMVEC conference in Indianapolis, Indiana.
The panel was moderated by Amrut A. Patki, director product group RCB & steering column at Bendix Commercial Vehicle Systems. The panelists were Colm Bloomer, manager of systems and attributes at Ricardo North America, Somnath Ghorad, director of durability simulation and development at Nikola Motor Corporation, Collin B. Milliken, director of chassis engineering at Navistar and James Turney, director of chassis engineering for Daimler Trucks North America.
The session explored the views and experiences of these OEMs regarding the implementation of electric and other zero-emission powertrains on various aspects of chassis design, such as impact safety, packaging and validation.
A clean slate
One of the most significant challenges electrification presents for commercial vehicle OEMs is designing a chassis with very little legacy knowledge. “For years, SAE and OEMs have worked to develop all the standards that we use to nurture and build new chassis and go to the next level of design,” said Patki. “And here comes electrification!
“There are no standards established, there is no background by which we can know things like how do these systems integrate?” he continued. “What happens if you add the battery pack at one level of design versus another? What kind of resonance you are going to be at on a chassis that has no traditional engine? What happens with the frequencies for all the algorithms from the past when conditions are changing on the chassis? Do they still apply?”
All these issues pose a huge question mark for OEMs and how they are going to move to the next level of implementation for electrified chassis. “Our legacy ICE designs have been fairly standard over the years,” said Ricardo’s Bloomer. “But batteries are coming in all shapes and sizes and OEMs want to put them in different parts of the vehicle. This is also true of hydrogen fuel-cell vehicles. So, a lot of standardization needs to happen in order for us to effectively move to the next step of design for a cost-effective modular frame.”
While many OEMs are updating legacy chassis to more quickly and cost-effectively retrofit EV and fuel-cell powertrains, that route is not without its own difficulties. “Previously, our frames were all designed around an ICE powertrain,” said Bloomer. “But there’s definitely some challenges and opportunities for optimizing them around an EV powertrain.”
Bloomer went on to describe some of the challenges he and his team at Ricardo have seen for updating an ICE frame design for an electrified driveline. “For one thing, the frame now becomes a protecting element for portions of the powertrain, such as sensitive electrical components like fuel cells and batteries. Some batteries have a high-integrity structure, while others are very lightweight. So, the frame is not just a mounting point, but also protecting the power source from impacts, partial deflection inputs and vibration.”
Bloomer also described some of the issues that eAxles can present in chassis development. “eAxles lead to a significant increase in unsprung mass,” he said. This not only affects the ride quality, but you’re also putting a lot of sensitive electronics on the unsprung mass, which can present a durability challenge.”
There are other integration issues, he said, for eAxles: “You also have to consider the interaction between the driveline at the park brake. Do you want those to work together? Do you need just one or the other or both? So you have to find the solution there with very different axle architecture.”
Bloomer also detailed some of the challenges and opportunities that high-voltage systems offer for brake and steering integration. “Going to high-voltage components enables electromechanical steering and brakes, which can be much more package-efficient and integrated into the frame. This can translate to both heavy- and light-duty commercial vehicles. Steer-by-wire is also a potential solution for modularity between designs thanks to these higher voltage systems.”
Modern problems, modern solutions
Despite the challenges and disruption electrification is causing in the commercial truck sector, it also is opening opportunities for new ideas and designs that before may not have been possible. “For certain lighter vehicle classes, you have the opportunity to go for automotive-style suspension architectures such as independent suspension,” said Bloomer. “This provides clear advantages in ride and handling. An electric driveline also becomes part of the sprung mass in this instance, which provides durability advantages.”
The upcoming shift in traditional powertrains reportedly is creating certain supply-chain challenges, particularly for hydraulic brakes. “These vehicles come in roughly between what is currently available for lighter-duty hydraulic brakes and heavy truck air brakes,” Bloomer said. “There’s not many suppliers for hydraulic brake components on the scale these trucks will require, so we can see this as a particular challenge.”
Daimler’s Turney also described the shift in mentality that OEMs have undergone in order to address EV powertrain integration. “We have to reconsider every aspect of vehicle design,” he said. “We (now) have to cool a battery and a lot of other things, plus we have an HVAC system that doesn’t have an engine. It’s a totally new approach. We have to keep an open mind throughout the design process and ask if what we’re doing is actually the best way to integrate an alternative powertrain.”