Regenerative braking isn’t new. It has been utilized in hybrid and all-electric passenger vehicles for over 20 years, but it has yet to gain significant traction in heavy-duty commercial vehicles. Some lingering technological challenges are delaying universal application, even though adopting regenerative braking on trailer units promises significant practical and environmental benefits.
Electric tractors that rely on regenerative braking for power have been manufactured, like the Volvo VNR Electric or the Peterbilt 579 Electric. However, widespread or long-distance use has one huge obstacle: the large battery capacity that would be needed to power these large vehicles and meet required operating ranges (while hauling tens of thousands of pounds) is challenging both technically and economically.
While battery technology continues to advance, there’s another question that deserves an answer: Could we see regenerative braking become a reality on trailers as well?
“Energy efficiency does not have to be a subject for trucks and tractors only,” says Chris Lee, Vice President of Engineering at Great Dane. “The complete road train must be considered, since trailers take a share of vehicle power by driving resistances, parasitic losses, auxiliary devices, and energy conversion to heat by friction brakes. It is, therefore, a plausible step to consider the electrification of trailers as a contributor to energy efficiency. Regenerative braking is readily utilized for EVs today but has not been actively pursued for trailer applications.”
Benefits and Opportunities from Regenerative Braking
There are numerous benefits to incorporating regenerative braking on trailer units. The energy captured and stored in batteries or capacitors onboard the trailer can be used as either supplementary power to increase an electric truck’s range or to power onboard auxiliary units. Other benefits include increasing braking efficiency, CO2 emission reduction, and even noise reduction.
Regenerative braking delivers extra benefits when trailers travel downhill or brake frequently. “Energy recovery is the primary benefit of regenerative braking, although the amount of recoverable energy is highly variable depending on application and terrain,” says John Bennett, Vice President and Chief Technology Officer at Meritor. “The stored energy can potentially be used for propulsion assistance, powering an electric TRU, power for hoteling, autonomous parking, and power for liftgates.”
Manufacturers like ConMet are excited about the possibilities regenerative braking offers as well. “We see significant opportunity for the use of this energy to operate other systems such as liftgates or electric lift trucks on the trailer as well as powering refrigeration and/or to provide propulsion, ultimately improving overall vehicle fuel efficiency,” says Caleb Lander, electrification product manager at ConMet.
According to Patrick Kealy, North America OEM Trailer Business Leader for the Commercial Vehicle Control Systems Division at ZF, benefits of regenerative braking can also include traction support in ice, snow, and off-road surfaces; as well as the ability to provide an additional power supply for auxiliary devices like sensing, detection, and communication systems.
Challenges in the Way of Widespread Implementation
There are some obstacles to incorporating regenerative braking.
“A regenerative braking system requires an electronically controlled braking system (EBS), which is widely used in other regions but not yet in North America,” says ZF’s Kealy. “Current U.S. brake regulations will need to be adapted to support EBS implementation. But we are hopeful that this will be resolved since EBS is an important feature for enabling automation, too.”
ConMet’s Lander points out that the constantly evolving technology associated with electrification can potentially make planning ahead difficult. “Electrification technology, especially in batteries, is constantly changing and improving,” he said. “Due to the pace of change, careful consideration must be made when selecting the right technology and suppliers for systems that will be deployed for 10 years or more.”
Reliability is another consideration. “We all know the underside of a trailer is an extremely challenging environment for electronics to survive, especially for the expected asset life cycle,” notes Thermo King’s Hubbard. “But we see axle OEMs making good progress on electrification of straight trucks and believe that durable components will eventually be available.
“Regenerative brakes are not currently able to eliminate traditional braking systems, and they will need to avoid interfering with ABS and stability control systems. Brake system integration will have to be addressed between the axle generator and the brake controller OEMs.”
Matt Gold, Director of Sales for Hyliion, notes that another obstacle to implementation is capturing enough energy without negatively impacting the fuel economy of the trailer. “It’s challenging to capture and store sufficient energy to supply enough electric power to either provide additional power via an e-axle, or to power trailer technologies like PTO, reefers, or lift equipment,” he says. “For most fleets, they are looking for an ROI that fits into a two- to three-year period, which is driven by the cost of the technology and life of the trailer.”
Compatibility is another thing to keep an eye on, notes Great Dane’s Lee. “The battery and motors need to be the right size and type to match the regen rate/C- rate. This may have a direct impact on the cost and life of the entire system. The packaging of regenerative braking components and installation on the trailer body must be structurally compatible to ensure trailer fatigue life and longevity. Large structures mounted in the trailer belly area may cause undue fatigue and stress on trailer rails and roof, causing premature failure.”
Additionally, Lee points out, your fleet’s safety and maintenance protocols will have to be updated to account for the new technology.
Regenerative Braking is the Future
Implementing regenerative braking for trailers will be a challenge—but with so many manufacturers researching, testing, and exploring, it’s closer to reality than ever. When the technology is ready, the benefits will be felt industrywide.