EV Brakes - do we need to go back in time?
Discussion
Quattr04. said:
I imagine this is why several ground up EVs have already done so, the VAG range for example
What car is it out of interest? A ground UP EV or a ICE model fitted with a EV motor?
Its an MG ZS, can't imagine they've change the brakes from the ICE variant.What car is it out of interest? A ground UP EV or a ICE model fitted with a EV motor?
I didnt realise any EV came with drums
andburg said:
Wife's car just back from service, advised rear brake disk inner edges have slight corrosion and that she should drive with regen turned down for a bit to help clean them up.
Given you should regen as much as possible is it time to go back to drum brakes at the rear?
I think EVs are a bit of a learning curve. Regen isn't necessary if 100% charged so is when it's worth adjusting your driving style a bit and use the brakes a bit. Given you should regen as much as possible is it time to go back to drum brakes at the rear?
My rear brakes are fine after 6 years and 85k miles. I've got fixed regen so adjust my driving so I use the brakes often but not much at all IYSWIM.
Quattr04. said:
I imagine this is why several ground up EVs have already done so, the VAG range for example
What car is it out of interest? A ground UP EV or a ICE model fitted with a EV motor?
VAG does because their platform is largely RWD which means the regen on the rear makes disks almost completely pointless.What car is it out of interest? A ground UP EV or a ICE model fitted with a EV motor?
Rear corrosion is definitely an issue on many EVs.
Zero Fuchs said:
I think EVs are a bit of a learning curve. Regen isn't necessary if 100% charged so is when it's worth adjusting your driving style a bit and use the brakes a bit.
My rear brakes are fine after 6 years and 85k miles. I've got fixed regen so adjust my driving so I use the brakes often but not much at all IYSWIM.
You do the miles to keep them clean. Shes 3 years and 15k miles in with 5% pad wearMy rear brakes are fine after 6 years and 85k miles. I've got fixed regen so adjust my driving so I use the brakes often but not much at all IYSWIM.
andburg said:
Zero Fuchs said:
I think EVs are a bit of a learning curve. Regen isn't necessary if 100% charged so is when it's worth adjusting your driving style a bit and use the brakes a bit.
My rear brakes are fine after 6 years and 85k miles. I've got fixed regen so adjust my driving so I use the brakes often but not much at all IYSWIM.
You do the miles to keep them clean. Shes 3 years and 15k miles in with 5% pad wearMy rear brakes are fine after 6 years and 85k miles. I've got fixed regen so adjust my driving so I use the brakes often but not much at all IYSWIM.
For context I only changed my front pads/discs after 75k so gives an idea of how much use they had. My rears still have 50% left on them and the discs are fine.
budgie smuggler said:
Since the braking is managed in software anyway, they could probably add a bit of code to use the physical brakes every X miles or once per drive or whatever.
My Octavia (and probably a lot of other cars) does something similar to keep the discs clear of water when it's raining.
Kia already has this.My Octavia (and probably a lot of other cars) does something similar to keep the discs clear of water when it's raining.
Bear in mind that regen setting doesn't really affect brake wear, whether disc or drum - the blending of regen and physical braking means even if on low regen and using the brake pedal, it's mostly regen rather than pad in disc unless braking very hard.
The exception is, as mentioned above, when the car is 100% charged when the physical brakes work much more.
And the best setting on the open road is low regen which allows coasting as this is the most efficient us of energy. High regen only generally more efficient in stop start city driving.
The exception is, as mentioned above, when the car is 100% charged when the physical brakes work much more.
And the best setting on the open road is low regen which allows coasting as this is the most efficient us of energy. High regen only generally more efficient in stop start city driving.
Evanivitch said:
budgie smuggler said:
Since the braking is managed in software anyway, they could probably add a bit of code to use the physical brakes every X miles or once per drive or whatever.
My Octavia (and probably a lot of other cars) does something similar to keep the discs clear of water when it's raining.
Kia already has this.My Octavia (and probably a lot of other cars) does something similar to keep the discs clear of water when it's raining.
We find a lot of EV's have badly rusted discs - Tesla being the worst, Leafs and Zoes have drums, however its not just EV's, JLR cars all suffer from badly rusted discs - Disco Sports being the worst - 6k being the lowest, followed by anything VAG.
Drums - VW cannot do these right either, always sticking and usually ending up with leaking cylinders
Drums - VW cannot do these right either, always sticking and usually ending up with leaking cylinders
Discombobulate said:
Bear in mind that regen setting doesn't really affect brake wear, whether disc or drum - the blending of regen and physical braking means even if on low regen and using the brake pedal, it's mostly regen rather than pad in disc unless braking very hard.
The exception is, as mentioned above, when the car is 100% charged when the physical brakes work much more.
And the best setting on the open road is low regen which allows coasting as this is the most efficient us of energy. High regen only generally more efficient in stop start city driving.
Brake in neutral also works on several cars.The exception is, as mentioned above, when the car is 100% charged when the physical brakes work much more.
And the best setting on the open road is low regen which allows coasting as this is the most efficient us of energy. High regen only generally more efficient in stop start city driving.
Discombobulate said:
Bear in mind that regen setting doesn't really affect brake wear, whether disc or drum - the blending of regen and physical braking means even if on low regen and using the brake pedal, it's mostly regen rather than pad in disc unless braking very hard.
The exception is, as mentioned above, when the car is 100% charged when the physical brakes work much more.
And the best setting on the open road is low regen which allows coasting as this is the most efficient us of energy. High regen only generally more efficient in stop start city driving.
One of the exceptions is Hyundai I5: regen level 0 will switch off the regeneration completely for a while. The exception is, as mentioned above, when the car is 100% charged when the physical brakes work much more.
And the best setting on the open road is low regen which allows coasting as this is the most efficient us of energy. High regen only generally more efficient in stop start city driving.
I have a calendar reminder every two weeks to clean the brakes. I usually use the highest "normal" regeneration (below one pedal mode), which is enough for 10% downhills. So in normal driving the discs won't get used unless someone screws up.
Incidentally, high regen and coasting are not mutually exclusive (with a bit of focus and familiarisation). "Why bother?" is probably another discussion.
Frimley111R said:
I wonder how long before they get rid of brakes. The motor can be stopped by reversing the current so why not just do that?
The kinetic energy has to go somewhere, normally it's converted to heat in the discs and pads.If your only means of stopping the car is regen, then what are you going to do if say the battery is 100% charged or the motor/drive develops an open circuit fault?
Braking resistors are used for this purpose for example in the rail sector where electric motors are used for traction, so it's possible that with enough redundancy between say the front and rear axles that you could certify an emergency braking system based on large ceramic resistors.
The kinetic energy becomes heat in these resistors, so they will only be able to cope with a certain number of stops an hour, and especially so for high speed stops.
Short-circuiting the motor/s might also work as this manifests as heat in the motor's copper and iron, which can be removed by the cooling circuit.
One of the problems with all electrical based braking systems is that P= V^2/R so the braking power increases with the square of the motor's voltage for a fixed resistance, whereas to brake at constant g deceleration requires a linear reduction in power relative to road speed, and motor voltage also tends to vary linearly with speed. In other words, you won't get constant g deceleration with a fixed resistance, unless the motor voltage is actively controlled to be non-linear with speed.
Front discs are probably the simplest option...
GT9 said:
The kinetic energy has to go somewhere, normally it's converted to heat in the discs and pads.
If your only means of stopping the car is regen, then what are you going to do if say the battery is 100% charged or the motor/drive develops an open circuit fault?
Based on personal experience, charging the battery much above 85% at the parking lot up Mount Etna would mean the loss of regen brakes before sea level. Maybe a less obvious scenario to prepare for than a full battery?If your only means of stopping the car is regen, then what are you going to do if say the battery is 100% charged or the motor/drive develops an open circuit fault?
Frimley111R said:
I wonder how long before they get rid of brakes. The motor can be stopped by reversing the current so why not just do that?
I think Mercedes proposed a disc brake that is internal to the motor. So no brakes on the wheels, but one per driven axle as part of the motor assembly. Presumably only needed for parking on slopes and additional friction brakes when you really need to stop in a hurry.Regen probably can't stop you as fast as a set of friction brakes. If your motor is 200kW then you only have that much power in the opposite direction (and usually less). You also don't get regen or don't get full effect regen at very high SOC because there is no where for it to go.
I think if you worked out for an 1800kg car stopping from 60mph at 1g deceleration the peak power dissipated is something around 370 kW with the average over the whole stop being about 180kW. The motor is only going to give you its peak power at higher speeds, its going to give you very little at slow speed. So we do still need friction brakes and we should have them as fall-back anyway but do we require a big disc and calliper for each wheel?
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