What is regenerative braking?

To Warren Brown, Washington Post, automotive journalist,

Dear Warren,

I read your chat on March 13 and was impressed. I didnt realize you had so many enthusiastic geeks reading your discussion. Its heartening to see so many people trying to get the correct definition for an advanced technology issue. Who knows, maybe the space program does have a chance!

Oh hey, did you watch the Keplar launch on NASA TV? There was a commentator, Stephen Agid, that was great. At one point he said, “engine out: expected” Stretch and I were laughing our heads off. We went around the house the rest of the night emulating his baritone voice, “engine out: expected”. You know youre a true geek when you watch the NASA TV and you want to start a fan club and make Agid as famous as the Obama girl.

I regress. Sorry, back to regenerative braking.

Some of what was happening in your discussion started back in the days of Sesame Street. Yep, the television show that is loved by adults and children alike. The show knows that in order to keep a young childs attention you have to keep it simple stupid (KISS). The attention span is about nine seconds and in those nine seconds you have to educate and entertain, otherwise the child goes running into the kitchen wanting something from Mommy.

Things havent changed that much for most people. With this ever crowded world of ours a journalist gets about a paragraph, maybe two, before the reader decides to move on. Hence the reason for the confusion about how to describe regenerative braking. We try to make it easy to understand for the masses, so that they stay interested. Instead of talking about braking load, we call it heat.

Most people understand heat, they havent a clue what kinetic energy is. The marketing/public relations folks understand the same about many journalists. Even Stephen Ellis, Manager of Fuel Cell Vehicles and Marketing, American Honda Motor Company,says he remembers referring to energy as heat in the early days. Either we dont understand it fully, or we need to explain it to our readers simply. For what ever reason, in the beginning that is how regenerative braking was explained.

I have talked to many engineers at all the manufacturing groups this week.

Here is the geek answer:

The hybrids on the road today regenerate by using an electric motor as a generator when braking. This is sometimes referred to as turning the motor/generator into a generator and the rotational energy of the front wheels is used to generate electricity.

Often, the motor and generator are the same unit, located in the engine compartment or as part of the transmission. This large “generator” absorbs a lot of kinetic energy as it induces current to flow in a magnetic field, slowing the car.

regen_braking What is regenerative braking? Automobiles and Energy electric vehicles (EV) electricity Emissions Environment Plugin-electric vehicles Technology
Here the engine is turning the generator to charge the battery while the vehicle is stationary.

The electricity produced by slowing down has to go somewhere, so it is used to charge up the battery. Subsequently, the battery provides electricity to power the electric motor during acceleration. This electrical regeneration reduces (and sometimes eliminates) the braking load (heat) at the wheel.

Motion of the front wheel spins the Traction Motor to charge the HV battery.

Because there is less friction at the brakes, the brakes dont need to be replaced as often, meaning less expense to the owner.

You can see why regenerative braking is not described as I have above.

I have lost half your audience. Their eyes have glazed over and they are looking for the end of the story.

Knowledge is a subconscious transference, one tries to make sense of the unknown by relating it to information they already have stored somewhere in their brain. If you were to use running as an example, even a person who doesnt run can imagine that their feet get hot when running up and down a hill. They can imagine that there is wasted energy in movement.

Here is a non-geek answer:

regen_braking_graph What is regenerative braking? Automobiles and Energy electric vehicles (EV) electricity Emissions Environment Plugin-electric vehicles Technology
Most of the light to moderate braking energy can now be recaptured as electricity that goes to the battery.
As you can see, most of the light to moderate braking energy can now be recaptured as electricity that goes to the battery. Think of regenerative braking this way:

– A runner knows they are expending energy even when they are running downhill.

– The runner still has to expend energy to control ones body even running downhill.

– The runner can not capture any kinetic energy running downhill like a regenerative braking system.

But wouldnt it be great if there was a system that could capture wasted energy while running, and at somewhere around mile 22 of a marathon, that energy would kick in?

Engineers have found a way to capture that electricity via the motor/generator, so that you can use it later. That is regenerative braking. Some of your geeks will see this explanation as inaccurate, or too simple, but I think the lay person that reads it will get more of a feel of what regenerative energy is.

As you have heard me say before, Warren, were a brilliant nation – we have the ability, the science and the technology to be self-sufficient. Now we need the will.

I hope this helps

Love ya Warbro

or as they say in NASA lingo:

engine out – expected.

About the Author:

Lou Ann Hammond is the CEO of Carlist and Driving the Nation. She is the co-host of Real Wheels Washington Post carchat every Friday morning and is the Automotive, energy correspondent for The John Batchelor Show and a Contributor to Automotive Electronics magazine headquartered in Korea. Hammond is a member of the North American Car and Truck of the Year (NACTOY), Women's World Car of the Year (WWCOTY), and the Concept Car of the Year.