Electric vehicles regenerative braking

While saving energy, regenerative braking systems in electric vehicles have a second advantage — unlike conventional friction brakes, they don’t give off harmful airborne particles

Mother Nature does not waste energy. A great example is the breathing mechanism of kangaroos. When kangaroos are stationary they breathe like most animals, using muscles and energy to both inhale and exhale. Once on the move though, kangaroos can forget about respiration. That’s because as they leave the ground in their hopping gait their torsos stretch open and air is pulled involuntarily into their lungs. When they land, their torsos compress, and inner organs move up to push air out of the lungs.

Imagine machines that utilize energy on both their positive and negative activities.

Slowing down and stopping are perceived as the negative experience of transportation

Separate mechanisms

For most of the 130-odd-year history of the automobile, each vehicle has had an intricate series of mechanisms to move itself and an entirely different series of mechanisms to stop itself. In theory these mechanisms are not only separate, they are antagonistic. Slowing down and stopping are perceived as the negative experience of transportation. It is difficult to get excited about applying friction to a rotating disc or drum brake. This indifference to deceleration might have been best coined by Ettore Bugatti, who designed and built some of the most exotic vehicles of his era. When challenged on the point that the efficacy of the brakes on his cars was nowhere near on par with the cars’ performance, he responded: “I make cars to go; not to stop.”

Back in the 1990s a group of engineers from Volkswagen experimented with the concept of harvesting kinetic energy produced as a vehicle decelerates, and then using it to assist in acceleration. There were running prototypes of existing VW gasoline and diesel-powered models that were equipped with a separate flywheel mechanism. Stepping on the brake pedal engaged the flywheel to the motion of the car’s wheels. The accelerating flywheel drew its kinetic energy from the car’s wheels causing the car to slow down. A clutch-like device allowed the flywheel to continue to rotate once the car came to a complete stop. When it was time for the car to accelerate the flywheel reconnected to the cars wheels, transferred its rotating energy back into them, thereby assisting in a more energy-efficient acceleration. The concept never saw production but was soon followed by one that has: regenerative braking.

Substantial advantage

If there is a single most “Zen-elegant/kangaroo breathing” element of an electric vehicle it has to be its regenerative braking system. Even if it was the only advantage of an EV it would be substantial. Electric vehicles manage to harvest kinetic energy under deceleration without heavy or complex add-ons, store it as potential energy in a battery, and then use it when needed as kinetic energy to accelerate. The same electric motor that powers the vehicle works in reverse in a frictionless process. Not only does the car slow down, the potential travel range of the vehicle is extended.

Electric cars have two braking systems — standard friction and regenerative. I like to refer to the latter, which does not actually include a brake mechanism, as a Regenerative Deceleration System (RDS). The prudent left foot (or left hand) of an EV driver employing the RDS can limit the use of the EV’s friction brakes to emergency situations only. Less brake wear and service costs are substantial benefits, but there is another big advantage of diminished friction brake usage: reduction of particulate pollution. 

In 2014, a study by the Environmental Science Pollution Research Institute, reporting to the European Commission, Joint Research Centre for Sustainable Transport concluded: “Exhaust and non-exhaust sources contribute almost equally to total traffic-related PM10 [a widely monitored size of particulate] emissions. Brake wear has been recognized as one of the most important non-exhaust traffic-related source, with its relative contribution to non-exhaust traffic-related emissions ranging between 16 and 55%, and to total traffic-related PM10 emissions between 11 and 21%.”

Toxic aerosol

Those metallic particles are particularly harmful when they interact with other airborne particulates, as a study by the Georgia Institute of Technology, funded by the U.S. National Science Foundation (a branch of the Environmental Protection Agency), revealed. It found that metals such as “copper, iron, and manganese interact with acidic surface-rich particles already in the air to produce a toxic aerosol.”

EV drivers can significantly reduce the particulate toxins released into the atmosphere by finessing the regenerative deceleration factor over the friction brakes.

A vehicle descending down a mountainside highway will need to have its speed limited. An internal combustion engine car grinds down its expensive discs, releasing nasty metallic particles into the atmosphere and wasting fuel, unless their engine turns itself off. As well, the longer the road the more prone friction brakes are to fade in terms of their effectiveness. But an EV’s regenerative deceleration properties can keep the car under control without heat, nasty particles or stress. And all the while, the car’s conventional friction brakes sit at the ready in case a moose pops out of the woods or an ICE vehicle ahead of it locks up in panic. The proactive skill of harvesting energy back into a battery may amuse (dare I say challenge) the pilot of an EV.

Which of the two cars do you think Mother Nature would choose to ride in?

A video by Bosch Mobility Solutions explaining regenerative braking.
Peter Vella photo

Peter Vella calls himself a car nut with a conscience, and has found his enthusiasm for things mobile revitalized by the electric vehicle movement. He travels extensively to most any electric vehicle symposium, international car show or car museum he can get to.