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

[Lovemyev]

The ZS EV Gen2 has weaker Regen strength over the Gen1 with BMS update, but a small plus side, is that the brake disc’s stay brighter longer .
Roundabouts and swings I guess !.

 

[Ian Key]

Re the brakes not being used, I did 55k miles in my BMW i3 which has strong regen, true 1 pedal driving. Every time I had the car serviced they commented that there was minimal wear on the brake pads front and rear, as expected, yet the discs were in great shape. They didn’t look anything special or expensive to me.

Probably a better quality of steel.

 

[PristDean]

Probably a better quality of steel.

Agree, I had a Alfa Romeo once and had the discs and pads changed. After about 3000 miles all the discs were corroded. Straight back to the garage who fitted them who cited poor quality discs and replaced for me.
So if this is a problem on the MG4, better quality discs needed

 

[Alb]

I think there is something in the quality argument.
By way of comparison, here's a pair of pics showing the rear disks on my MG5 at 2 months old compared with my Ford Focus at 9 years old:

 

[Cocijo]

We are not that far away from being able to completely remove friction brakes from an EV. Yes It might be a controversial comment, but with developments in regen and the amount of retardation this can produce, friction brakes are becoming more and more unnecessary. They are really a legacy from ICE cars.
A soon as the regen technology develops a little more and it becomes commercial viable we will see them disappear.

 

[siteguru]

Batteries would have to be specified with a much larger buffer for that to be the case ... if you've charged to 100% (usable) then there's nowhere for the regen to go - especially on the SE SR which only has a 0.2kWh buffer.

 

[Ayoull]

Batteries would have to be specified with a much larger buffer for that to be the case ... if you've charged to 100% (usable) then there's nowhere for the regen to go - especially on the SE SR which only has a 0.2kWh buffer.

The over provisioning of batteries is for degredation management not for a regen buffer.

 

[siteguru]

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.

 

[Cocijo]

The devil is in the detail - but couldn’t the majority of the kinetic energy transfer be used to slow the car if needed not charge the battery? If retardation wasn’t needed then no regen if HV was full.

 

[Ayoull]

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.

You could utilise a capacitor and bleed resistor bank to dissipate any generated energy but you're relying on contactors engaging and disengaging when the HV battery level reaches levels where regen will work to charge it, and also that your bleed resistor has discharged the capacitor enough to allow for the motor to effectively slow down the car, starts getting more complex, where as with brakes, simpler the better is the best approach for safety.

 

[siteguru]

The devil is in the detail - but couldn’t the majority of the kinetic energy transfer be used to slow the car if needed not charge the battery? If retardation wasn’t needed then no regen if HV was full.

In order to slow the vehicle the motor must switch to being a generator - that generator must have a load for the generated energy to flow in to. That's how it works ... and that's why its official name is KERS - Kinetic Energy Recovery System; motion is converted into power, which causes retardation of the vehicle. If there's nowhere for the recovered energy to flow to then the generator effectively shuts down, thus no retardation.

 

[Cocijo]

I don’t think that the challenges are insurmountable. There is definitely a technical solution - if it’s viable commercially at this moment is questionable
Having two completely different methods of braking will not be around on EV’s forever. Just think what weight savings could be made for example - no brake lines, cylinders, discs, callipers. I guess friction brakes will stick around as the cheaper option for now though. The fail safe and full functionality needs to be proven for regen first.
I think some trains have also made great progress using regen braking.

 

[Ayoull]

I don’t think that the challenges are insurmountable. There is definitely a technical solution - if it’s viable commercially at this moment is questionable
Having two completely different methods of braking will not be around on EV’s forever. Just think what weight savings could be made for example - no brake lines, cylinders, discs, callipers. I guess friction brakes will stick around as the cheaper option for now though. The fail safe and full functionality needs to be proven for regen first.
I think some trains have also made great progress using regen braking.

Very different in trains though as the reverse power flow produced is fed into a fixed distribution network which is used to power other vehicles on the line.

 

[BugEyed]

The law currently requires two separate means of braking, which is normally the foot brake and the hand brake (or Emergency brake for our US members). No chance that this would change nor would braking on one axle only be allowed.

 

[Lovemyev]

With regards the quality of the OEM factory disc's, we are a bit stuck with them for now, until some of the third party suppliers are able to provide alternative products.
Here is a company who apply a anti-corrosion treatment to their disc's :-
"Comline range feature a specialised anti-corrosion coating. This coating is applied to all areas of the disc, including the hub and friction surface, to a maximum thickness of 25 microns, ensuring effective rust protection and premium aesthetics.
To achieve this premium finish, each Comline disc is subjected to a nine-stage process that adheres the advanced formulation coating to the precisely manufactured disc. Corrosion resistance is guaranteed by extensive salt spray testing up to 240 hours."
A lot of the trade have had good results from using these disc's.
Of course the ZS is not covered - Yet !.

https://www.comline.uk.com/products/brake-discs

 

[Miscreant]

With regards the quality of the OEM factory disc's, we are a bit stuck with them for now, until some of the third party suppliers are able to provide alternative products.
Here is a company who apply a anti-corrosion treatment to their disc's :-
"Comline range feature a specialised anti-corrosion coating. This coating is applied to all areas of the disc, including the hub and friction surface, to a maximum thickness of 25 microns, ensuring effective rust protection and premium aesthetics.
To achieve this premium finish, each Comline disc is subjected to a nine-stage process that adheres the advanced formulation coating to the precisely manufactured disc. Corrosion resistance is guaranteed by extensive salt spray testing up to 240 hours."
A lot of the trade have had good results from using these disc's.
Of course the ZS is not covered - Yet !.

https://www.comline.uk.com/products/brake-discs

Surely the anti-corrosion coating is only for storage. A 25 micron layer on the friction surface will be ablated almost immediately on contact with the brake pads and then you are at bare metal from that point.

 

[Robf]

In order to slow the vehicle the motor must switch to being a generator - that generator must have a load for the generated energy to flow in to. That's how it works ... and that's why its official name is KERS - Kinetic Energy Recovery System; motion is converted into power, which causes retardation of the vehicle. If there's nowhere for the recovered energy to flow to then the generator effectively shuts down, thus no retardation.

Couldn,t you connect it up to the front passenger seat and make it live, you know, the one the wife usually sits in

 

[Cocijo]

The law currently requires two separate means of braking, which is normally the foot brake and the hand brake (or Emergency brake for our US members). No chance that this would change nor would braking on one axle only be allowed.

EV’s have 3 means of braking - so remove the friction brakes!

 

[Lovemyev]

Surely the anti-corrosion coating is only for storage. A 25 micron layer on the friction surface will be ablated almost immediately on contact with the brake pads and then you are at bare metal from that point.

This is very true of course, but the centre hub and the non contact points of the inner and outer disc face surface, where to fiction pad does not come in contact are still treated.
This helps prevent rust / scale and a thick crust building up on these, non contact points.
Also, I believe the steel used in these disc's are of a better quality as well.
I watched a video where these disc's had been used, be somebody in the trade to replace some OEM corroded disc's on a VW Passat - I think it was ??.
Then about 9 months latter the guy made another video which involved removing the road wheels again, the first thing he pointed out was no rust had formed on any part of the disc's / rotors.

 

[stevegus]

We are not that far away from being able to completely remove friction brakes from an EV. Yes It might be a controversial comment, but with developments in regen and the amount of retardation this can produce, friction brakes are becoming more and more unnecessary. They are really a legacy from ICE cars.
A soon as the regen technology develops a little more and it becomes commercial viable we will see them disappear.

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

Ice and snow?