Brakes and ABS on the MG4

[mg4mc]

The 4 does not appear to have a conventional separate ABS system as we know it. Everything goes through the IBS (Intelligent Brake System) including the wheel speed sensors. The only way I can see it achieves ABS (and traction control) is by activating a pair of inlet and relief valves on each wheel cylinder hydraulic circuit. The IBS is what enables the brake-by-wire required for the regen and one pedal driving and is of course bus linked to lots of other modules, so who knows how it works!

 

[Deleted member 14300]

Would this mean the brake pedals are electronic devices and not direct to the servo / master cylinder?

 

[mg4mc]

Would this mean the brake pedals are electronic devices and not direct to the servo / master cylinder?

No, the pedal is connected to the master cylinder, but the master cylinder is not normally* connected to the wheel cylinders. It is connected to a simulator and pressure sensor. The IBS then controls the brakes via a motor and hydraulic pump.

* The master cylinder is connected to the wheel cylinders if the the IBS detects a fault in the system, or there is a total power loss.

 

[Deleted member 14300]

No, the pedal is connected to the master cylinder, but the master cylinder is not normally* connected to the wheel cylinders. It is connected to a simulator and pressure sensor. The IBS then controls the brakes via a motor and hydraulic pump.

* The master cylinder is connected to the wheel cylinders if the the IBS detects a fault in the system, or there is a total power loss.

Makes sense then. The brakes weren't as keen let's say.

 

[mg4mc]

It also means the normal vacuum servo is not required either. I guess the "emergency" braking will need a hefty pedal push!

 

[Rolfe]

No, the pedal is connected to the master cylinder, but the master cylinder is not normally* connected to the wheel cylinders. It is connected to a simulator and pressure sensor. The IBS then controls the brakes via a motor and hydraulic pump.

* The master cylinder is connected to the wheel cylinders if the the IBS detects a fault in the system, or there is a total power loss.

Hear the word of the Lord!

 

[GaryMG4]

I guess that explains how eco mode deadens the effect of the brake pedal. Total madness, why would you want that and how does it make it more 'eco',

 

[tsedge]

I guess that explains how eco mode deadens the effect of the brake pedal. Total madness, why would you want that and how does it make it more 'eco',

Presumably it promotes smoother driving or somesuch.

 

[Deleted member 14300]

Makes sense on the ability to alter pedal feel then. I expected something on the throttle pedal, but brakes?
I will say driving with the camera blind I had to haul ass quick and the brakes worked, but like you'd expect on a non abs car. This has to be the most ludicrous design I've ever seen in years. I've been under the bonnet to top washer fluid up and it's correct, no vacuum servo, just a distribution unit on the bulkhead. Bet bleeding them would be fun.

 

[olliewebb]

Makes sense on the ability to alter pedal feel then. I expected something on the throttle pedal, but brakes?
I will say driving with the camera blind I had to haul ass quick and the brakes worked, but like you'd expect on a non abs car. This has to be the most ludicrous design I've ever seen in years. I've been under the bonnet to top washer fluid up and it's correct, no vacuum servo, just a distribution unit on the bulkhead. Bet bleeding them would be fun.

I doubt bleeding will be that much of a pain, given most cars now you just pressure bleed them from the reservoir end any way. Even your local back street garage isn’t going to manually bleed your brakes.

 

[leonkernan]

Can we take the brake talk to a separate thread? It‘s nothing to do with the engineering menu topic.

 

[Rolfe]

Your wish is my command.

 

[mg4mc]

I doubt bleeding will be that much of a pain, given most cars now you just pressure bleed them from the reservoir end any way. Even your local back street garage isn’t going to manually bleed your brakes.

Well, the problem is unlike "standard" brake systems where it was pretty much a single path from the master cylinder, through ABS to the wheel cylinder. The MG4 has multiple paths which are opened and closed with valves as required, plus a circuit round the simulator, and a pump.

 

[olliewebb]

Well, the problem is unlike "standard" brake systems where it was pretty much a single path from the master cylinder, through ABS to the wheel cylinder. The MG4 has multiple paths which are opened and closed with valves as required, plus a circuit round the simulator, and a pump.

View attachment 21530

Tut tut, the post above specifically forbade this!

 

[mg4mc]

What? This is the new brake and ABS thread!

 

[olliewebb]

What? This is the new brake and ABS thread!

Yeah but the mods here are scruffy and don’t tidy stuff up.

 

[Rolfe]

Tell me what needs moved and I'll do it...

Sigh. You can't please everyone.

 

[siteguru]

Don't worry ... @olliewebb is just observing that @leonkernan's post is no longer relevant now that you have spun those posts off into this new thread. He's just being unnecessarily picky.

 

[Rolfe]

Well, I could have deleted it, but I thought it was informative, for anyone who was wondering what happened.