When will serve the disc brakes?

[ClaBerCla]

The electric motor in the Volt will serve as a motor to move the car and as a generator to stop or slow down the car.
But when will serve the disc brakes? Are they only a brake backup?
And as the electric motor will activate only the front wheels, does that mean that only front wheels will serve when the brake pedal is depressed?
And if we use the brakes on a slippery road and that the electric motor become a generator and only front wheels serve to slow down the car, will we lose control of the car?

[capn]

the regenerative brakes can only do so much so they are complimentary towards the hydraulic brakes.

[Altazi]

The electric motor in the Volt will serve as a motor to move the car and as a generator to stop or slow down the car.
But when will serve the disc brakes? Are they only a brake backup?
And as the electric motor will activate only the front wheels, does that mean that only front wheels will serve when the brake pedal is depressed?
And if we use the brakes on a slippery road and that the electric motor become a generator and only front wheels serve to slow down the car, will we lose control of the car?

I bet they figured this out already. Engineers are clever!

[kubel]

They got this down during the 90's. Cars like the EV1 and RAV4-EV had regenerative braking, with 4-wheel brakes. The electric motor can reclaim the energy when the car is braking from the drive wheels only. But brakes are still applied to all wheels just like in a normal car.

Think of it like using the engine to help brake your car you have now. You upshift, let out the clutch and the gas, and use the engine to slow your car down while you also apply brakes at the same time. In an EV, the car is basically doing the same thing, except the motor is reclaiming that energy instead of just wasting it.

The most ideal solution would be to use independent motors powering each wheel with each wheel also having brakes. That way you could use the motors for traction control in addition to drive and regenerative braking. But I'm expecting the Volt to have 4 disk brakes (or two front disk and two rear drums) with the front wheels supplying power and regenerative braking from one motor.

[ClaBerCla]

Thank you. Your explanation is very good. Instead to lose energy with standard rear brakes, GM could add generator at these weels and recover more energy to the batteries using also rear brakes.

[willdryden]

Thank you. Your explanation is very good. Instead to lose energy with standard rear brakes, GM could add generator at these weels and recover more energy to the batteries using also rear brakes.

You can only charge the batteries so quickly or they overheat. That is why 100% regen breaking is not desirabe. If you want to buffer the power in ultracaps, then it can be done.

[ClaBerCla]

I think that new lithium-ion nanophosphate batteries could be full charged in only three minutes. So, you could go at electric station service, plugin our Volt, take a coffee and go. Batteries technology research is currently exponential and possibilities are great.
So with this kind of battery the energy could be recovered using the four wheels instead only front wheels.

[Guy Incognito]

But when will serve the disc brakes? Are they only a brake backup?

The friction brakes will be the primary form of braking in conjunction with regenerative braking. Regenerative braking reduces wear on the friction brakes, extending their life.

And as the electric motor will activate only the front wheels, does that mean that only front wheels will serve when the brake pedal is depressed?

When braking, the friction brakes on all four wheels will engage in addition to the regenerative brakes.

[Engineer_101]

There are several issues that govern the function of the regenerative braking -

1. The battery has to be receptive to the energy being forced into it. This will be dependant on the State of Charge (SOC). A 100% charged battery will not be receptive to additional energy input. Regenerative braking can occur if there is a resistor or other energy dump, or means of energy storage. The energy that can be dumped will be limited by the I^2 R that can be put into the braking resistor.
2. The traction drive motor, working as a generator, will have a point where energy will have to be added into the motor armature to cause the rotor torque that resists the rotation of the axle. There will be a point when the rotational speed of the motor/generator shaft will not provide stopping torque to the wheel. The friction service brake will have to do the final stop.
3. The drive electronics will have a limit to the amount of magnetic flux that can be induced into the rotor, and still have recoverable power from the motor/generator. This is the point when the energy captured from the decelerating vehicle will not provide a net gain. The service brakes will have to provide the final stop.
4. "Hill holding" with a "plugged" induction motor is not a good idea. Makes the electronics and the traction motor heat up, without airflow.

Great discussion. Keep it going.

Go Volt!