What is recoverable energy?

[klippe]

Hi All,

First Post

Just want to start by saying what an awesome site this is. I have been trying to find a technical-minded forum for ages, seems my search is over!

Now to all you brain-boxes out there....

I hear the term 'recoverable energy' being banded around in F1 circles all the time. I am not really sure what it's all about.

I have heard something along the line of teams using heat couplers on the brake systems to help generate electricity to power various things (or help power various things). Was this indeed happening or am I dreaming?

Also what other 'recoverable energy' is gathered? And how?

I hope this hasn't been addressed before, I did do a search and found it referred to in posts, but not really ever explained.

Thanks,

Cliff

[Guest]

The recoverable energy being referred to is the kinetic energy present in all the rotating equipment.
Most vehicles that make use of recoverable energy have alternators/DC generators attached to the transmission downstream of the clutch. Under normal running or accelerating the generators' field is NOT energised, so it just spins freely. Under braking, the generators' field is energised such that the torque acting via the transmission on the wheels aids braking. The torque driving the generator produces electrical current, which can be put to use elsewhere in the vehicle. i.e. there is a flow of energy from the kinetic energy stored in the rotating equipment to electrical energy which is then stored in batteries or used by other systems.

I'm not sure about "heat couplers" - to my mind any heat generated at the brakes just gets dissipated to the atmosphere. It may be possible to use reverse thermocouples to turn some of the heat into current, but these would have to be in contact with the brake discs, which would cause issues.
That being said, if one used the radiators as a heat source and could get the other end of the thermocouple into a cooler area, the temperature difference would generate a voltage which could be used to power some of the electronics - there would be issues with regulating the voltage magnitude as the temperature difference fluctuated.

Regenerative braking is used very successfully on hybrid cars (Toyota Prius etc) because these already have electric motors attached to the wheels. By switching the polarity of the magnetic field, the motor becomes a generator. On an f1 car, a motor/generator attached to a wheel becomes

[ReubenG]

another addition to the rotational inertia of the system, which reduces the acceleration of the system. Also the generators would require cooling, so there is the problem of ducting air them, which increases drag on the vehicle.

It's been a fairly long post, but I've had many arguments about the benefits of energy recovery systems on racing vehicles. Be fun to see where this one goes.

Forgot to sign in before starting the post before this one.

[klippe]

Thanks RuebenG,

Yeah sorry, I meant "thermocouples" not 'heat couplers" (hehe).

I had thought that recoverable energy was mainly used for electrical purposes - thanks for the explanation.

Anyone else out there have more info on this?

Oh, one other thing, I didn't think that thermocouples had to be attached to the actual discs, I would have thought the heat in the general area of the braking system would have been enough to sufficiently heat them (at least enough to generate some current). Obviously they have to be mounted somewhere, and I guess anything around that area's going to be pretty hot anyway......such as mounting on the surface of the calipers?

Thanks again,

Cliff

[riff_raff]

Cliff,

Energy storage/recovery systems (flywheels, hydraulic accumulators, etc.) on F1 cars are illegal. On the other hand, maintaining maximum speed (or inertia) through a corner is a goal that all F1 designers seek to achieve.

As for F1 brake rotor temps, they are extremely high- in excess of 1400degF. The brake rotors and pads are both made of carbon/carbon composite and wear equally during their useful life. Carbon/carbon rotors/pads have a very unique property in that its' Mu value (coefficient of friction) increases with temperature. I'm sure you've seen an F1 car braking hard into a corner with the brake rotors glowing white hot. The hotter they get, the better they grip. All other brake materials' Mu value (ie. cast iron rotors) decrease with increasing temps. Thus the classic "brake fade" condition.

Carbon/carbon brakes also have the added benefit of low density and high stiffness modulus. They weigh about 25% of a comparable metal rotor, thus reducing unsprung weight. Carbon/carbon also reduces polar moment of inertia for things like clutches.

The drawback of carbon/carbon brakes and clutches is that they tend to have an "on/off" friction characteristic, with no in-between. That is why you see even professional race drivers sometimes stall their engines when leaving the pits. Also, since carbon/carbon brakes need to run so hot, they can cause thermal problems for all of the surrounding components like wheels, uprights, calipers, tires, etc.

In the olden days, brake rotor temps were analysed using thermal paints. Nowadays, I think they are monitored real-time using infrared.

Regards,
Terry