BEV-Agnostic’ Systems Require Attention

Batteries and motors get most of the spotlight, but electrification may significantly impact the engineering of steering, braking and suspension, too.

The Hyundai Mobis e-corner system allows wheels to be articulated 90 degrees from straight, allowing for unheard of maneuvering in small areas. (Hyundai Mobis)

Much has been written about battery-electric propulsion’s impact on the automotive ecosystem. The level of change moves much past an overhaul to a complete re-imagination. While it can be difficult to categorize different system areas into neat buckets driven by the impact of BEV propulsion, no doubt that there are at least five major systems negatively impacted. Known as “BEV-negative” systems: internal-combustion engines, “traditional” transmissions, driveline systems, fuel and exhaust. They all face significant upheaval from a refocus on alternative systems and carryover of components, when possible, with BEV volumes rising.

Michael Robinet

Executive Director, Consulting,

S&P Global Mobility

SAE Foundation Trustee

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Beyond the BEV-negative systems, there is a handful of other system areas significantly impacted as our world changes. Depending on your perspective – and while many may characterize the control/chassis systems of braking, steering and suspension as “BEV-agnostic” systems (still required, though altering significantly) – there are risks and opportunities in these areas as the industry adapts. Let’s tackle each from a 30,000-foot perspective.

Braking: Two main technical factors underscore electrification’s impact on braking. The shift of the center of mass lower in the vehicle (because of the battery pack) and the increase in vehicle mass alters demands on the braking system. Possibly more important is the ability for speed to be scrubbed off through propulsion-system regeneration/energy capture. This ability to slow the vehicle through recapturing energy back into storage systems is a game-changer.

Many BEVs now have reduced requirements for a 4-wheel-disc braking system as a significant portion of deceleration typically can be recaptured by the new drivetrain. In absence of vacuum supplied from traditional ICE engines, electro-hydraulic actuation systems increasingly are the norm. In the future, the elimination of rear braking is a very real possibility. Braking systems will be a focal point as BEVs become more prevalent.

Steering: OEMs have sought for decades to alter/eliminate the mechanical link between driver and steered wheels, the goals being improved control, weight reduction and packaging freedom. While the technology exists for a purely electronic connection, there always is the issue of redundancy from a safety perspective. The integration of SAE Level 2 ADAS systems (lane-keeping and lane-changing capabilities) demonstrates that electronic-input capability is here. With improved power availability as BEV propulsion proliferates, new challenges arise. For example, steering shafts previously requiring one bend now may require two to reach the steering rack, as altering the battery box is not an option. But in the future, steering may be controlled and actuated at each wheel hub for ultimate packaging flexibility. BEVs and automated driving have opened many possibilities for future steering systems.

Suspension: packaging and greater power availability have opened possibilities for changes in suspension technology. The major shift has been the integration of air suspension – enabling lower hood heights, the ability to reduce ground clearance at speed to improve aerodynamics (critical for BEVs) and the ability for drivers to customize ride dynamics. Long viewed as a niche technology, air suspension has opened new possibilities. But at the core of future changes in suspension will be cost and packaging. Traditional spring and strut structures still are most prevalent, though packaging constraints from battery housings and increased vehicle mass will offer new challenges for traditional systems.

Of the three systems outlined, braking has certainly taken the lead of late as BEV propulsion drives more immediate decisions. Steering and suspension systems are changing, though on their own timeline – dependent on consumer needs and affordability.