Electric Car Experiences

[coppice]

With all these EVs that make minimal use of their disc brakes, do people find rusting and seizing problems? Many ICE cars have tried to minimise the use of their rear brakes, by a variety of mechanisms, like pressure valves in the rear brake hydraulic lines. The results have typically been that light footed drivers make no use of their rear brakes at all, and they rust and seize up.

[NiHaoMike]

With all these EVs that make minimal use of their disc brakes, do people find rusting and seizing problems? Many ICE cars have tried to minimise the use of their rear brakes, by a variety of mechanisms, like pressure valves in the rear brake hydraulic lines. The results have typically been that light footed drivers make no use of their rear brakes at all, and they rust and seize up.

Parking brakes typically operate the rear brakes, so they would get cycled.

[SilverSolder]

With all these EVs that make minimal use of their disc brakes, do people find rusting and seizing problems? Many ICE cars have tried to minimise the use of their rear brakes, by a variety of mechanisms, like pressure valves in the rear brake hydraulic lines. The results have typically been that light footed drivers make no use of their rear brakes at all, and they rust and seize up.

I've noticed that even on my hybrid car, the front brakes last much longer than ICE cars.  (I owned the same vehicle as ICE and Hybrid, so I know it's the only difference!)   This means corrosion can become a problem.

The rear brakes hardly wear at all, the only reason to change them is corrosion.


The way around it is to buy the highest quality coated rotors, etc. - that way, you get a good service life out of them.  I have good results with Bosch brake parts - high quality without being stupid expensive.  Don't try the cheap fast rusting parts, they only work well on ICE vehicles that are used constantly in a benign climate!

[DougSpindler]

Just tried an experiment with my Volt.  According to Volt's Energy meter on the dash, when coasting (foot off the accelerator and the break), it show regen breaking is occurring and the energy is flowing to the battery.

When using the brake pedal going down a hill, if I lightly apply the breaks energy is flowing to the batteries.  As I apply more pressure on the brakes regen braking continues. I would expect to reach a point where the regen system is maxed out and the brake pads take over.  Couldn't really find that spot.

Lesson I learned from my little experiment is can't tell when regen braking is maxed out and the brake pads take over.

[coppice]

With all these EVs that make minimal use of their disc brakes, do people find rusting and seizing problems? Many ICE cars have tried to minimise the use of their rear brakes, by a variety of mechanisms, like pressure valves in the rear brake hydraulic lines. The results have typically been that light footed drivers make no use of their rear brakes at all, and they rust and seize up.

Parking brakes typically operate the rear brakes, so they would get cycled.

Who uses the parking brake regularly in an automatic (yes, I know, people who live on a steep slope)? Parking brakes are not used in motion, and the mechanism for parking is often completely separate from the mechanism for foot braking. So, using the parking break doesn't keep cleaning corrosion of the discs, and may not exercise the hydraulic mechanism.

[tom66]

The discs on my GTE hybrid frequently show rust.  I do make sure to use the physical brakes from time to time to keep them clean now, as I had to replace the discs and pads all around at 69,000 miles / 5 years as all discs had signs of corrosion. 
 
Teslas seem to have a brake wipe function which seemlessly applies braking torque periodically, while adjusting drive motor torque to compensate.  Presumably this keeps the discs free of contamination/water.  Not sure if other vehicles use this too.  I wonder what the net effect on range is but it probably doesn't require much energy to keep the discs clear of surface contaminants.

Park brake on my car is electronic and just actuates the rear calipers with a cable actuation.  As far as I can tell it is essentially an electric "hand brake", pulling the braking cable with an electronic actuator instead of the approach which some cars use which is to have a separate motor/brake caliper on the rear discs.

In 'D' mode (coast/drive instead of regen/drive) the car still regenerates energy, but does this when heading downhill only.  In other words, if it can recuperate some energy but maintain your speed, it will do so (although it's not true cruise control, it appears to make some pessimistic assumptions about drag and weight and tends to accelerate a little more than coast.)  Disappointingly, I found this is deleted from e-Golf and ID3;  I've found it quite useful when driving on the motorway.  Of course, you can still use ACC if you want but that's not always appropriate in inclement weather.

[SilverSolder]

I like the Tesla "auto brake disc clean" idea.  Basically, it seems it is good for the brakes to get hot once in a while.   If you live in a hilly area, this is likely to be less of a problem than if you are always driving in slow traffic and coasting to stops.  Obviously an old school ICE car is much less likely to have problems like this, but you can still see how "careful" drivers (e.g. Mrs. SilverSolder) gets much worse brake rust issues than more ahem, "sporty" drivers (cough). 

[DougSpindler]

What difference does it make if the rotors get some corrasion/rust on them? First application of the brakes would remove the corrasion.

[coppice]

What difference does it make if the rotors get some corrasion/rust on them? First application of the brakes would remove the corrasion.

Two problems there. One is the corrosion on a rarely unused rotor can get very deep (been there. done that.). The other is if your first use in ages is an emergency stop, you don't want the stop extended as you scrub off the rust and finally get a good grip.

As I said earlier, its not just the rotor that is an issue. In ICE cars where the rear brakes are only used for heavy braking there is a history of light footed drivers having the breaking mechanisms seize.

[DougSpindler]

What difference does it make if the rotors get some corrasion/rust on them? First application of the brakes would remove the corrasion.

Two problems there. One is the corrosion on a rarely unused rotor can get very deep (been there. done that.). The other is if your first use in ages is an emergency stop, you don't want the stop extended as you scrub off the rust and finally get a good grip.

As I said earlier, its not just the rotor that is an issue. In ICE cars where the rear brakes are only used for heavy braking there is a history of light footed drivers having the breaking mechanisms seize.

Still not following you.  What difference does it make if the corrasion is deep?  The pads will wear to the new shape.

Hard to believe the first breaking one has to make is an emergency stop when exiting a garage or a parking space.  One or two applications of the brakes remove the corrosion.

[SilverSolder]

On many modern cars, the rotors have become part of the "male jewelry" and clearly visible inside the alloy wheels -  So you don't want these things to look bad.   

After rain come the puddles that you drive through...  if the rotors aren't warm, the spray water never "boils off" and you end up parking the vehicle with wet rotors = guaranteed rust.

On an EV with high regen ability, it is quite conceivable that the friction brakes barely get used at all, if the driver is very "smooth" and the environment doesn't have hills - would be interesting to measure the rotor temperatures after a drive!   Somehow, I think the rotors on a V8 musclecar might be warmer after a drive than the rotors on a HEV or EV!

That said, even an ICE car could use this kind of system, for the rear brakes only (and parking brakes!).  One benefit of electric/electronic parking brakes is that they actually get used (by the computer, not the driver) so they are less likely to seize.  Of course, a human driver that actually uses the hand brake daily is unlikely to have big issues with this either...   but rust never sleeps...

[tom66]

The rotors on my car are almost always cool to the touch on longer trips. 

When on "hill hold"/"auto hold" my car doesn't seem to use the parking brake, for whatever reason.  It just holds the regular braking circuit on using the iBooster.  You can manually actuate the parking brake which the car will turn off automatically when you set off, seemlessly.  So I've no idea why it doesn't do this, perhaps they are concerned about the reliability of frequently driving the brake calipers with the park brake actuator?

[SilverSolder]

Try measuring them after 1 stop from 50mph...   They will have soaked up a noticeable amount of energy.

[maginnovision]

I like the Tesla "auto brake disc clean" idea.  Basically, it seems it is good for the brakes to get hot once in a while.   If you live in a hilly area, this is likely to be less of a problem than if you are always driving in slow traffic and coasting to stops.  Obviously an old school ICE car is much less likely to have problems like this, but you can still see how "careful" drivers (e.g. Mrs. SilverSolder) gets much worse brake rust issues than more ahem, "sporty" drivers (cough). 

A lot of cars scrub the rotors during driving. It's a pretty old idea. Also rust on the rotors doesn't matter because virtually any braking will clean it up. Your bigger issue would be seizing calipers but as long as maintenance is done regularly it also shouldn't be an issue.

[SilverSolder]

I like the Tesla "auto brake disc clean" idea.  Basically, it seems it is good for the brakes to get hot once in a while.   If you live in a hilly area, this is likely to be less of a problem than if you are always driving in slow traffic and coasting to stops.  Obviously an old school ICE car is much less likely to have problems like this, but you can still see how "careful" drivers (e.g. Mrs. SilverSolder) gets much worse brake rust issues than more ahem, "sporty" drivers (cough). 

A lot of cars scrub the rotors during driving. It's a pretty old idea. Also rust on the rotors doesn't matter because virtually any braking will clean it up. Your bigger issue would be seizing calipers but as long as maintenance is done regularly it also shouldn't be an issue.

If you live in a cold, salted roads climate, and you have a "stable" of older cars, you begin to appreciate well made rotors over the "cast crap" ones...  the good ones will last 2x or 3x the life of the bad ones, and the worst ones...  the worst ones I've had, actually rusted to near uselessness in one year!

I'm a big fan of the Bosch coated rotors, they really last well out of the (many) brands I have tried, and don't cost much more than the "cast crap".

[coppice]

A lot of cars scrub the rotors during driving. It's a pretty old idea. Also rust on the rotors doesn't matter because virtually any braking will clean it up. Your bigger issue would be seizing calipers but as long as maintenance is done regularly it also shouldn't be an issue.

If that has been your experience I assume you live in a dry climate. Its not the experience many of us have. Its quite common for rust to build up faster than braking can clean it off if the car is not used heavily.

[Circlotron]

It will be with the exhaust valves open.  Compressing air 9:1 generates a lot of heat taking energy out of the system.

Doesn't letting that air expand absorb most of that same heat? Obviously this is not 100% efficient but nothing is. With the valves open there will be pumping losses due to the restrictions, with the valves closed there will be increased friction losses due to the greater mechanical forces on the pistons and crank but some of the energy used compressing the air will be recovered as the air expands.

Yep, some of the energy expended in compressing the air on the upstroke will be recovered on the downstroke. Proof of this is diesel engines in large trucks that have an exhaust brake. The details vary, but many have an arrangement where the exhaust valve is opened at the very top of the 22:1 compression stroke and the compressed air and associated energy simply roars out, hence the characteristic sound made when the exhaust brake is used. I've read that the exhaust brake when activated can absorb roughly the same amount of horsepower that the engine can produce. So logically, if the compressed air is retained and allowed to expand on the downstroke, much of the energy in the compressed air is recovered.

[ahbushnell]

Just tried an experiment with my Volt.  According to Volt's Energy meter on the dash, when coasting (foot off the accelerator and the break), it show regen breaking is occurring and the energy is flowing to the battery.

When using the brake pedal going down a hill, if I lightly apply the breaks energy is flowing to the batteries.  As I apply more pressure on the brakes regen braking continues. I would expect to reach a point where the regen system is maxed out and the brake pads take over.  Couldn't really find that spot.

Lesson I learned from my little experiment is can't tell when regen braking is maxed out and the brake pads take over.

On my PHEV outlander when the battery is fully charged you can really feel the difference in braking.  The regen is minimal. 

Try it on your volt. 

[DougSpindler]

Just tried it in my Volt and you are right. When the battery is fully charged regen braking can have you sailing through red lights if you are thinking about it. 

[coppice]

Just tried it in my Volt and you are right. When the battery is fully charged regen braking can have you sailing through red lights if you are thinking about it.

The Volt doesn't seem very sophisticated. The computers don't seem to dynamically work the disc brakes and regenerative braking for optimal results. More recent cars seem to take the driver's foot input and apply braking in a reasonably optimal manner. If the battery is full you still get the same braking effect, but it is achieved inefficiently through the disc pads. Obviously, if the car is set up to give regenerative braking just by lifting your foot from the accelerator, there isn't a lot the car can do about that when the battery is full. I don't think anyone is apply disc braking just on a raised foot, so you will feel an obvious difference when you raise your foot.

[DougSpindler]

This is for the Volt.  When the battery is fully charged and the regen braking paddle on the steering wheel is used the regen braking is unpredictable.  Sometimes when you pull on the paddle there is almost no braking.  Must be when the battery is fully charged? Other times it seems like there is some heavier braking, but then it lets up.  This making me think the braking is heavier until the battery reaches “full charge” and then there is no regen braking.

I use the regen braking paddle when I drive.  When I leave my house I travel downhill and have to stop at two stop signs. There are times I forget the battery is at full charge and the regen braking doesn’t do mush and I have to slam on the brakes.  Other times there is regen braking and then in the middle of slowing down the regen braking all of a sudden stop which means again I have to slam on the brakes.

This is actually somewhat dangerous as when regen braking will brake and when it won’t is unpredictable.

[tom66]

Having driven at least 10 EVs in various forms, I can't think of any one that applies brakes to emulate regen on the accelerator pedal alone.  Whereas they do tend to all, bar the MG ZS EV, emulate similar braking performance on the brake pedal regardless of regen being available or not.

[DougSpindler]

Having driven at least 10 EVs in various forms, I can't think of any one that applies brakes to emulate regen on the accelerator pedal alone.  Whereas they do tend to all, bar the MG ZS EV, emulate similar braking performance on the brake pedal regardless of regen being available or not.

You must not have driven the BMW, then.  There are videos of people driving the BMW in cities such as London and show how they can drive and never use the brakes.  If you take you foot off the accelerator the car brakes.


https://youtu.be/WjkYcnsXK7U

[tom66]

Yes, but that's regen braking

What I mean is I don't think any car I've ever driven emulates braking on the accelerator pedal alone - i.e. the physical brakes are only actuated by the brake pedal (or adaptive cruise control and emergency stop functions, if fitted.)  The regen availability therefore depends on battery SoC, so drivers need to be aware of that if they depend on the accelerator only braking.

[coppice]

Yes, but that's regen braking

What I mean is I don't think any car I've ever driven emulates braking on the accelerator pedal alone - i.e. the physical brakes are only actuated by the brake pedal (or adaptive cruise control and emergency stop functions, if fitted.)  The regen availability therefore depends on battery SoC, so drivers need to be aware of that if they depend on the accelerator only braking.

I've seen video of a second gen Leaf in one pedal driving mode stop on a gentle incline just by raising the driver's foot. Maybe the car does almost all its stopping using regen, but it appears to use the disc brakes to finally stop in a well controlled manner and hold its position. Having the computers use the disc brakes automatically for various driver assist functions - adaptive cruise, hill start assist, etc - is becoming normal on ICE cars. I'd be surprised if nobody is using this to augment regenerative braking in an electric car.