Could an EV manage without normal brakes completely?

[Frimley111R]

I know that many/most use regenerative braking but they also use normal brakes. However, in my younger days of racing electric radio controlled cars, they had so much power that they could brake/stop the wheels completely, in the same way hydraulic brakes do. Could an EV have enough power to do the same? The brake pedal could be used as it is now but it just uses the electric motor.

[Falconer]

Frimley111R said:

I know that many/most use regenerative braking but they also use normal brakes. However, in my younger days of racing electric radio controlled cars, they had so much power that they could brake/stop the wheels completely, in the same way hydraulic brakes do. Could an EV have enough power to do the same? The brake pedal could be used as it is now but it just uses the electric motor.

I had an Outlander PHEV. In normal driving you could leave the foot brake alone (although on early models this did not activate the brake lights). It had 5 levels of regen braking, 5 was quite hard but not emergency stop .I was never brave enough to try coming to a complete stop.

[uknick]

My 2014 i3 will stop the car completely without brakes; obviously you have to lift off with enough distance left to let it do its job.

However, when the batteries are cold or at 100% charge the regen is a lot less so you do need to use the brakes to stop.

[Dave Hedgehog]

Frimley111R said:

I know that many/most use regenerative braking but they also use normal brakes. However, in my younger days of racing electric radio controlled cars, they had so much power that they could brake/stop the wheels completely, in the same way hydraulic brakes do. Could an EV have enough power to do the same? The brake pedal could be used as it is now but it just uses the electric motor.

with no emergency situations it is totally possible to drive a model 3 and never use the brake at all, even in london rush hour traffic. Lifting acts like strong engine braking and you can vary it with the throttle

some EVs use the top part of the brake pedal to activate regen braking with no physical braking, its bloody horrible to drive. Tesla have one foot braking / regen to perfection

Regen braking is not strong enough to do emergency stop levels of braking on 2 tonne cars (above 0.5g)

Edited by Dave Hedgehog on Wednesday 25th March 10:59

[Jakg]

Practically, maybe, but theoretically - no.

Energy cannot be created or destroyed.

Normal brakes convert speed into heat.

Regen converts the speed into electrical current that goes into the battery. But when the battery is full - then what?

[uknick]

Jakg said:

Practically, maybe, but theoretically - no.


Regen converts the speed into electrical current that goes into the battery. But when the battery is full - then what?

It doesn't work very well, if at all.

[George Smiley]

Dave Hedgehog said:

with no emergency situations it is totally possible to drive a model 3 and never use the brake at all, even in london rush hour traffic. Lifting acts like strong engine braking and you can vary it with the throttle

some EVs use the top part of the brake pedal to activate regen braking with no physical braking, its bloody horrible to drive. Tesla have one foot braking / regen to perfection

Regen braking is not strong enough to do emergency stop levels of braking on 2 tonne cars (above 0.5g)

Edited by Dave Hedgehog on Wednesday 25th March 10:59

I'd say 90% of my driving uses no brakes now but there are occasions where necessary, also regen brakes allow some freewheel after acceleration so the effect is not always consistent. I love the 3, the fact it has a proper 2nd brake circuit rather than regen on the pedal makes it so much smoother

The entire experience has sullied my fun of driving my older classics, the way you can use regen braking into corners is a revelation and trumps left foot heroics

[donkmeister]

I was hoping to do some actual maths with numbers from a current cooking version petrol hatchback, but a quick google does't yield the stopping distances for the cars I was looking at (e.g. Focus Ecoboost 125).

In short. A modern cooking version hatchback will do 0-60mph in around 10 seconds with 125bhp. However, it will also stop from 60-0 in around 3 seconds. The brakes are equivalent to around 5-600bhp. (sidenote, the big brakes fitted to hot versions of cars are 95% down to marketing, and 5% down to the minority of people who will actually push the car hard enough for fade to be an issue).

So, an EV might be able to "make do" with motor braking only, provided it was able to produce enough regen or reverse power to achieve this sort of braking power. Of course, you would need to prove that it was as reliable as a dual-circuit braking system. There are precedents for this sort of paradigm-shift, e.g. the SBC braking system that Mercedes were pushing in the early-00's, or when Boeing had the 777 twin-engined aircraft cleared for transpacific use.

[ds666]

Dave Hedgehog said:

Frimley111R said:

some EVs use the top part of the brake pedal to activate regen braking with no physical braking, its bloody horrible to drive.

Edited by Dave Hedgehog on Wednesday 25th March 10:59

Audi Etron brakes do as you comment and the pedal feel is really good . I do wish , however , it was much more "one-pedal " than they've made it .

Funny how all the Tesla people moan about i-pace brakes , then comment about how they drive without using them ....

[SWoll]

uknick said:

Jakg said:

Practically, maybe, but theoretically - no.


Regen converts the speed into electrical current that goes into the battery. But when the battery is full - then what?

It doesn't work very well, if at all.

Hence recommended to only charge to 95% even for long trips.

One pedal great for everyday driving but the physical brakes still get plenty of use on our Model 3.

[98elise]

Theoretically I don't see why not. A motor can be controlled very accurately.

Practically though I suspect that a car needs some sort of mechanical brakes to satisfy regulations. If the motor or battery failed you would lose power and braking.

[granada203028]

Yes a typical EV still has the potential to stop much quicker than it can accelerate, limited only by tyre adhesion.

So motor/power electronics are not sized large enough for an emergency stop from speed situation and would not likely be considered reliable enough anyway.

A further issue with the friction brakes though is if they get little routine use then they can be subject to deterioration, particularly if over sized. Presumably Teslas et all with big brake packages include advice to use them heavily periodically to ensure they work properly, don't develop judder etc.

My Leaf failed its MOT a few years ago on corroded front discs where they were not cleaning up adequately. I've noticed a recent intermittent grabbing though it has just passed its MOT OK.

[George Smiley]

Indeed if a maglev can decelerate then a car can, but you want redundancy built in.

I'd imagine they use non ferrous to help alleviate the issue from lack of use and possibly have automatic application to clean them up.

[Durzel]

i3 decelerates fairly briskly if you take your foot off the accelerator, but if you're going downhill or have built up a head of steam the distance travelled before coming to a complete stop is quite far. To some extent part of the fun (?) of driving it is trying to anticipate the distance required as much as possible.

It would be seriously dangerous to not have a brake though. If something/someone does something unexpected in front of you then you still need the ability to do an emergency stop, or brake hard.

[Evanivitch]

Yes, you could brake on just regen, even an emergency stop.

But the current designs are limited by motor and battery preservation. If you uprated the battery and used a capacitor or load dump instead of the battery then you could have as much regenerative braking as you like.

[98elise]

Durzel said:

i3 decelerates fairly briskly if you take your foot off the accelerator, but if you're going downhill or have built up a head of steam the distance travelled before coming to a complete stop is quite far. To some extent part of the fun (?) of driving it is trying to anticipate the distance required as much as possible.

It would be seriously dangerous to not have a brake though. If something/someone does something unexpected in front of you then you still need the ability to do an emergency stop, or brake hard.

You're missing the point. The OP was asking if the motors could supply the braking, not just through regeneration. The motor can apply any torque you want, both backwards and forwards. It can replicate any braking situation. If you really wanted to you could spin the wheels backwards while the car was traveling forwards.

It's not a question of removing the brakes from a current car, it's a theoretical questions.

Edited by 98elise on Sunday 29th March 08:31

[Boxbrownie]

uknick said:

My 2014 i3 will stop the car completely without brakes; obviously you have to lift off with enough distance left to let it do its job.

However, when the batteries are cold or at 100% charge the regen is a lot less so you do need to use the brakes to stop.

I wonder if your i3 hasn’t been software updated, our i3 2017MY REX even with a full charge will stop to a halt the same as when battery is depleted, the i3 uses the brakes to “replicate” regen when the battery is 100% so as to keep the driving characteristics the same.

[Heres Johnny]

Jakg said:

Practically, maybe, but theoretically - no.

Energy cannot be created or destroyed.

Normal brakes convert speed into heat.

Regen converts the speed into electrical current that goes into the battery. But when the battery is full - then what?

This really - so not really practical

[Heres Johnny]

Boxbrownie said:

uknick said:

My 2014 i3 will stop the car completely without brakes; obviously you have to lift off with enough distance left to let it do its job.

However, when the batteries are cold or at 100% charge the regen is a lot less so you do need to use the brakes to stop.

I wonder if your i3 hasn’t been software updated, our i3 2017MY REX even with a full charge will stop to a halt the same as when battery is depleted, the i3 uses the brakes to “replicate” regen when the battery is 100% so as to keep the driving characteristics the same.

I suspect you have a bigger battery and can handle a higher charge rate which equates to the level of regen

[Evanivitch]

Heres Johnny said:

Jakg said:

Practically, maybe, but theoretically - no.

Energy cannot be created or destroyed.

Normal brakes convert speed into heat.

Regen converts the speed into electrical current that goes into the battery. But when the battery is full - then what?

This really - so not really practical

Easily done with a load dump unit, loads of regen systems use them. Wouldn't have to be huge for the short spike seen. Or a capacitor.