MG4 Rear Brake Discs corroded, 3700 miles in, + bonus other issues

stevegus said:
Emergency stops done how? I dont think you are really thinking this through.

Ice and snow?
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Regen and regen. You’re being too narrow minded. The stopping power from reversing a motor can be immense

It’s usually relatively easy to find ways why changes might not work, but a little more challenging looking at how they might happen.
It’s by exploring new ways and ideas and expanding technology that we develop.

We are obviously not at the point where conventional friction brakes could be removed from cars.
Yes, there are several technical challenges that will need to be overcome, as well as the obvious commercial ones.

We are already at the stage where friction braking is used much less on EV’s and in some cases with one pedal driving not used at all on some journeys. Friction brakes are consequently seizing and rusting due to lack of use. Drum brakes have started appearing on some cars too.

So, it would seem a logical progression that conventional friction braking will change and developing the regenerative technology/using the braking power of electric motors, would seem a good place to look.
How in detail this might work, I don’t have the technical background to say other than to comment at a high level.

But to me, the idea that we will eventually move away from the now dated braking systems to a system that fits better with electric cars is a sound one.

PeteC said:
I can only think of two means of slowing - the friction brakes and regen. If you are thinking of footbrake and handbrake as two methods, surely they both use the friction brakes?
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I was responding to post #34 that suggested a car must have two forms of braking and suggested handbrake and foot brake as 2 (I’m not sure if this is true as I haven’t checked). Yes, there are currently only two methods of braking friction and regen.
 
When the battery is full and there is no chance of regen slowing the car, it could be possible for the car to apply battery power in the reverse direction of the motor to slow the car. The friction brakes could be removed from a purely technology perspective, but there’s something reassuring about pressure on the pedal physically applying pads to discs.
 
So cocijo

How are you doing these emergency stops with just regen from a rear axle?

Most braking effects is from the front where there are no motors.

So the option is

Fit cheap as chips disc brakes

Or

Have two motors. A braking ballast resistor in case the battery is full. Not simple not cheap
 
stevegus said:
So cocijo

How are you doing these emergency stops with just regen from a rear axle?

Most braking effects is from the front where there are no motors.

So the option is

Fit cheap as chips disc brakes

Or

Have two motors. A braking ballast resistor in case the battery is full. Not simple not cheap
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I’m talking generically, and hypothesising about potential changes and improvements, not just about the MG4.
You seem to have made your mind up that it won’t work and explored all of the options that anyone will ever think of, so let’s just stay with friction brakes forever.
It’s far less taxing than coming up with ideas, suggested improvements and new solutions.
 
I was thinking (dangerous) that the conventional brake callipers on a none drive axle might eventually be replaced with an electromagnet that also uses a rotating disc but without any physical contact.
 
Cocijo said:
I was thinking (dangerous) that the conventional brake callipers on a none drive axle might eventually be replaced with an electromagnet that also uses a rotating disc but without any physical contact.
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Electromagnetic brakes have existed on coaches for many years. Telma. Doesn’t replace the conventional brakes of course but good for when prolonged periods of gentle braking needed.
 
Yes - and there’s the Jake brake on commercials that uses the engine compression to slow the vehicle (ICE of course).
I think that the big advantage with using something like a Telma equivalent on an EV is that there is already the battery pack and regen braking infrastructure to further support it’s use.
 
Macadoodle said:
They should have copied VW and fitted drums to the rear. They last forever, are better for unsprung weight and wouldn't even be noticeable behind the aero covers.
Rear discs on a RWD EV are mostly redundant.
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Better still have a transmission brake like they used to have on Land Rovers to reduce the unsprung weight even further.
 
Macadoodle said:
They should have copied VW and fitted drums to the rear. They last forever, are better for unsprung weight and wouldn't even be noticeable behind the aero covers.
Rear discs on a RWD EV are mostly redundant.
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Absolutely this.
But people feel cheated by drums and want to see discs.
Drums are MUCH better suited to the light use an EV gives it’s rear brakes.
Proper thinking from VW.
 
siteguru said:
In which case what @Cocijo proposes could never work - friction brakes will always be needed as there is no regen when the battery is full. The alternative is to only allow the battery to charge to, say, 90% in order for there to be capacity for regen to flow in to. But that would then play havoc with WLTP and range figures.

One could argue that they're also needed when parked up, but in theory the motor could be locked in place to hold the car still.
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Supercapacitors will do the job. An inboard disc would still be needed for emergency backup in case of total electrical system failure. Variable road friction (ice/snow/diesel) are best managed by computer traction control.
Stainless (steel) is often used for discs these days, but careful matching to pad material is required. Carbon steel discs will all corrode - esp in winter with road salt - and the pitting will be more noticeable on ev's that often are only infrequently using their friction brakes (did this this-morning after a 100% charge, the rust was very quickly rubbed off). Obs an ice vehicle will likely have clean discs, unless the operator's pretty hot on downshifting...

p.s. even 'stainless' corrodes with salt and water spray. And there are shedloads of 'stainless' grades; caveat emptor!
 
bowfer said:
Absolutely this.
But people feel cheated by drums and want to see discs.
Drums are MUCH better suited to the light use an EV gives it’s rear brakes.
Proper thinking from VW.
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make the drums internal and the unsprung weight is reduced, too...
 
Why are drums better on the rear of EV’s?
 
nbenn said:
Does braking still regen up to a point though? I use low regen most of the time as I prefer it as the feels smoother to run. I do see regen go up when I'm braking though..
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I'm with you on this , more efficient to let the car roll using energy you have already put in than to have strong regen turning some of that energy into heat.
 
Cocijo said:
Why are drums better on the rear of EV’s?
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Its already been discussed that discs only get light use on an EV and that a lot of the braking is by regen.

Most braking effort goes to the front brakes which is why most modern cars at least have discs on that axle.

Its not unusual to see small and midsized cars and SUVs have disks on the rear as they are fairly lightweight and dont NEED disks on the back.

With the MG4 the rear axle takes the regen. So what braking effort is there, is mostly taken up by the regen.

So the discs are doing next to nothing and get corroded as some are reporting.

Sooooo

Put the less efficient drums on the back. They are enclosed, and you dont get unsightly corrosion.
 

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