Just as the Chevy Volt uses an electric motor to propel you forward, it uses the same motor to help slow you down. When you either lift your foot from the accelerator or press on the brake pedal, the main drive motor temporarily operates as a generator, working to partially recharge the battery bank. In this mode, the motor produces a drag on the front wheels, slowing the car, though not to a complete stop. As the car slows, the effect of the regenerative braking fades out and the friction brakes take you the rest of the way to a full stop.
GM tuned the Volt's control software so that the car drives like a snappy gas-powered car with an automatic transmission. If you want your Volt to drive more like a sports car with a manual transmission, do the following:
Take off and get up to a reasonable speed.
Shift the transmission selector to the Low setting. This engages electric motor braking when you’re coasting.
Press the dashboard Sport mode button. This will give you a bit more zip at higher RPMs.
Now take your foot off the gas pedal.
The 2012 Chevy Volt
The Low setting makes the Volt's regenerative braking considerably more aggressive, like driving a manual transmission car in second or third gear. You'll slow down quickly without needing to tap the brake pedal, though you'll still need to do that to come to a complete stop. Doesn't that feel more like you're driving a sports car?
How Well Does It Work?
Just how efficient is the Volt's regenerative braking system, and how well does it work? You know the answer to that: it depends.
GM used the Environmental Protection Agency's City Driving Cycle Federal Test Procedure (FTP) to rate the Volt's All Electric Range (AER). The maximum regenerative deceleration achieved during these tests was 0.315g, at which point the efficiency of the regenerative braking system was just under 75 percent. As the car slows down, the efficiency drops rapidly below 0.1g, at which point you're increasingly reliant on the friction brakes. At higher speeds, the effect of regenerative braking is outweighed by wind drag and tire friction.
The Volt battery pack has active liquid cooling. the battery fire you refer to was due to loss of coolant and it happened 3 weeks after it was crushed (and would not have occured at all had protocol been observed). I am not concerned in the LEAST about the safety of the battery. I am much more concerned about the 9 gallons of hydrocarbon incendiary fuel sitting in the tank.
I am assuming that the battery explosion you were injured in was a FLA battery? the main by products of over-charging a lead-acid battery are heat and hydrogen. not a really good combination.
"Normal" brakes get hot because all of the braking energy is friction generated heat. regenerative braking uses the drag created when a motor is turned into a generator. If you've ever ridden a bicycle with a tire generator on it, then switched on the lights and felt the increased drag you would know exactly what I mean.
In the VOlt, the battery and battery charging electronics are all actively liquid cooled, so yes, the engineers thought of it.
Point one: You are mistaken. The Volt does NOT try to keep the battery full. It depletes to the switchover point and then maintains that level, having used approximately 60% of the 16 kWh capacity. there is plenty of headroom to absorb regenerative braking charge.
Point two: again mistaken: You said "Regeneration is most effective in city driving and only when the car is driven agressively. Fast and hard acceleration takes from the battery leaving room to regenerate. This is why the Prias and Volt have good MPG numbers for the city driving circuit."
This is incorrect. regeneration is best when NOT driven aggressively because the harder you brake the more you get into the friction brakes and bleed off the energy as heat. additionally, the Volt does not try to keep the battery full. It is not a hybrid in the same ilk as a Prius that tries to maintain a full battery. it is pure electric until the charge is dropped by 10 kWh and then that battery level is maintained.
You are off the mark on why Prius and Volt get good fuel economy in the city: they are extremely efficient at low speeds and stop-start compared to straight ICE vehicles because electric motors deliver maximum torque instantly, hence good acceleration with very low power off the line, and then recapture of electricity on braking
The Volt has an incredibly sophisticated charge and climate management system: one that continually monitors the 288 cells several times a second and balances the individual charge as the battery is being recharged. In addition, the battery pack has an ACTIVE liquid climate control system to hold the battery temperature within a specific optimal temperature range.
When driving the Volt in D, the accelerator pedal "lift-off" feel is indistinguishable from driving an ICE vehicle with an automatic transmission when you lift your foot. It coasts! However, in L it feels like you downshifted to 2nd or 3rd (in a 3 speed or 4 speed tranny)
Bill, the Volt, like the Prius, has a dual braking system. Under most conditions, you are using regenerative braking, but in panic stops and below about 5 mph it switches to the friction brakes. With 10,300 miles on mine, the friction brake rotors still have the factory machining marks. The batteries are not a waste concern: they are expected to be able to power the cars reliably for a decade or more, and after their capacity falls below 70% of nominal they are going to be repurposed as storage devices for solar, wind, and Smart Grid systems. after they are no longer useful for these purposes (~40 years) the materials are 95% recyclable.
The regen braking does not deliver enough energy to the battery to overcharge it. There is a kWh used meter on the display, and I have seen the displayed number decrease in long downhill coasting, but only 1 to 3 TENTHS of a kWh. It is conceivable that you could pick up a lot more in a long drop on mountainous roads, but unless you started at the top with a full charge it is not likely that you would knock on the charge-limiter.
The Volt depletes ~10 kWh of charge before the ICE generator kicks in, and it does not REcharge the battery, it simply maintains the battery at the level it is at when switchover occurs
I found quite the opposite. I traded my 2006 Cadillac CTS for a 2012 Chevy Volt 7 months ago. I have put 10,300 miles on it since then, and in D the effect seems to be almost no drag at all compared to the Caddy with an automatic tranny. In L it definitely feels like driving a manual tranny car.
Great article! Coming from the off-highway electric machine world, regen braking has been part of my world for a long time. It's good to see it being used in the "closed system" of the new electric cars.
Great article, John. There's never a feel of "free-wheeling" when you let your foot off the Volt's accelerator. There's always a slight feeling of drag.
Using almost 200 light-emitting diodes in the front and back of the new 2014 CTS, Cadillac designers are showing how LEDs can change the character of a vehicle.
We looked at a number of sources to determine this year's greenest cars, from KBB to automotive trade magazines to environmental organizations. These 14 cars emerged as being great at either stretching fuel or reducing carbon footprint.
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 3
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
A quick look into the merger of two powerhouse 3D printing OEMs and the new leader in rapid prototyping solutions, Stratasys. The industrial revolution is now led by 3D printing and engineers are given the opportunity to fully maximize their design capabilities, reduce their time-to-market and functionally test prototypes cheaper, faster and easier. Bruce Bradshaw, Director of Marketing in North America, will explore the large product offering and variety of materials that will help CAD designers articulate their product design with actual, physical prototypes. This broadcast will dive deep into technical information including application specific stories from real world customers and their experiences with 3D printing. 3D Printing is
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
3 
