Capacitors To Kill Friction Brakes In Electric, Hybrid Cars?

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Mazda i-ELOOP capacitor-based regenerative braking technology

Mazda i-ELOOP capacitor-based regenerative braking technology

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Drivers of hybrid and electric vehicles will be used to the feel of regenerative braking.

As you brake, or even lift off the accelerator pedal in some electric vehicles, kinetic energy from the car's motion is captured by the electric motor, which when not being driven turns into a generator. This power is then stored in the batteries.

The effectiveness of this is limited by how quickly the battery can store generated energy - not enough to warrant the absence of friction brakes. A new supercapacitor could be about to change this.

Unlike batteries, which store energy chemically, capacitors store energy in an electric field. They can store this energy - and discharge it - very quickly.

A new flexible, solid-state supercapacitor, writes Physorg, could be used to store energy much quicker than a battery could, allowing the electric motor, or electromagnetic brakes, to entirely supplant friction brakes. That means far less kinetic energy is wasted as heat, improving efficiency.

There are plenty of potential benefits. Not only is the system more efficient in terms of energy use, but for drivers, brake feel would improve - there'd no longer be the feeling of two separate braking forces doing their thing.

Potentially, there's a weight saving too. Friction brakes and their associated components are relatively heavy, and much of that weight is rotating with the wheels. Engineers call it unsprung mass, and the less unsprung mass, the better. Handling improves, ride quality improves, performance improves.

The supercapacitor being explored by researchers at the University of Minnesota and University of North Texas uses carbon nanotube-coated cotton paper and is completely solid-state. That means it isn't as bulky as current supercapacitors, which use a hazardous liquid electrolyte that needs protecting.

It's thin, light, and flexible, which would allow it to be used anywhere in the car, with zero impact on packaging.

The design is still in early stages - contrary to one of the main benefits of capacitors, they've found the new supercapacitor to have high resistance and charge slowly, but this is a feature the teams think can be improved upon.

It may be some time before all our braking is done without traditional friction brakes (at the very least, friction brakes are still useful as a backup system) but it could soon be supercapacitors, rather than batteries, that are used to recover braking energy in electric cars.
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Comments (13)
  1. Despite charging quickly, supercapacitors may also charge the main battery at this component's speed.
    I mean, while capturing the kinectic energy, when not braking, the energy can be returned to the battery, at it's speed, I suppose.

  2. So if you remove the friction brakes, what happens when the capacitor is at capacity and you still need to stop?

  3. I saw an article that shows the suppliers are working on a large resistive heater (heat dump) for just such a purpose. But I do wonder, can regen brakes really work for hard stop or at slow speeds?

  4. What has a supercapacitor to do with eliminating the need for friction breaking? They only store the energy generated by the breaking process, the stopping power would have to come from the electric motor which AFAIK would generate it regardless of the presence of devices to capture all the energy generated in the process.

  5. I doubt that friction brakes can be eliminated completely especially in a panic stop where you have to slam on the brakes. However I do like the idea of being able to recover more of that energy that would normally be wasted as heat/friction. I am happy to hear that some of the research is being done at my alma mater the U of MN. I am surprised that more EV manufactures are not using the new energy generating shock absorbers that are being developed. I wonder how much additional range they could add to an EV.

  6. Right, where is that technology at? It has been more than 2 years since prototypes went into test trucks. GCR staff, any interest in finding out what happened to regen shock absorbers and writing it up?

  7. Thanks for the reminder John, Mark - I'll look into it.

  8. Alright if you eliminate friction brakes and their associated unsprung weight penalty as the article states what is going to take their place? You would need wheel motors to produce the electricity for the capacitor and this would negate any weight benefits.Alternatively you would need front and aft motors driving two wheels each again a weight penality albeit sprung weight.Point is each of the four wheels has to produce electricity via a generator to be routed to the capacitor, a fact completely overlooked in this article.

  9. no friction brakes at all?? how will this work? slowing down much faster does not mean stop does it? will this insure all accidents happen at less than 5 mph?

  10. Is this tech compatible with the need for anti-lock brakes and stability control?

  11. Dear Sir:
    Here is some information regarding a new patent which embodies a super efficient but economical KERS system, with application to most rolling vehicles, which utilizes a flywheel for recovered energy storage and an eddycurrent functioned clutch coupled to a gear transmission to provide IVT energy management between the vehicle and the flywheel at efficiency of 95%.

    I own this new patent and am soliciting interest. Importantly, there are no measures by which this technology does not surpass present battery hybrids as well as mechanical systems such as those using mechanical variable transmissions (CVT).

    Although this patent is recently issued, it utilizes well proven technology; albeit in a new way.

  12. This super capacitor idea in limited by the time rate of generation of electricity built into the vehicle's motor/generator. It would evidently have to be very large to be able to supplant the friction brake capabilities. In addition, the system would have to be distributed to all four wheels in order to obtain equivalent contact friction with the road. There are additional cautionary factors to be considered as well.
    There are usually many pitfalls when one runs with new science.

  13. (There are usually many pitfalls when one runs with new science.}
    I suppose this applies to your patent as well?

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