Interesting/worrying story from Scotland - ZS with no brakes.

Of course, without a doubt, especially if a police vehicle had to be rammed into to stop it. A short time after the Brian Morrison incident there was a runaway Jaguar I-Pace on the M62, again the police were involved in this terrifying ordeal. That driver was arrested and spent a couple of nights in the cells before prosecution.
Some time ago, I would agree. However, since the Post Office scandal, the Infected Blood scandal and many police scandals, I find nothing is "without doubt" nowadays.
Like many others, I watched as more and more Sub-postmasters were prosecuted when it was perfectly obvious there was something seriously wrong....
 
I assume this is a reply to me?

The brakes are available in full effect but you have to push harder in ECO mode to get that effect. It just modulates the curve of effectiveness of the pedal, it doesn't change the maximum braking available.

Anyway, this is how it works, however surprising it may be.
I liken it to having a bit of bungee cord in the brake and accelerator linkages. You have to take the stretch out before you get full effect.
 
Some time ago, I would agree. However, since the Post Office scandal, the Infected Blood scandal and many police scandals, I find nothing is "without doubt" nowadays.
Like many others, I watched as more and more Sub-postmasters were prosecuted when it was perfectly obvious there was something seriously wrong....
There is an essential difference here though, the Post Office situation was a cover up by the government and Post Office executives i.e. the ones that would get into trouble if it surfaced which of course it did.
The DVSA have no need to cover anything up here, nor have the government, they have no need to cover their backsides so why would they try?
 
Well the government oversee the regulations pertaining to vehicle safety, in the same way they oversee the rules that apply to the post office. But that's not really the point: what I'm saying is that when something is not done it does not mean nothing NEEDS to be done, because companies, authorities and even regulators are unbelievably sloppy.
 
The MG4 (which is what @tsedge has) does not have a servo, it has a computer-controlled pump that does the actual braking, the pedal is not normally directly connected to the brakes themselves.
Sorry for the late reply.

I'm 99% sure that MG (any current model) does not do brake by wire. There is a vacuum pump as in all EVs that provides vacuum for the brake assist. For Adaptive Cruise Control and Automatic Emergency Braking to operate the mechanical brakes, there must be some other mechanism that effectively "applies the brakes", but that will be something that provably does not reduce pressure from pressing the brake pedal. Unless you have amazing and expensive approvals, pressing the brake pedal has to operate the friction brakes through hydraulic pressure with a dual redundant system.
 
Sorry for the late reply.

I'm 99% sure that MG (any current model) does not do brake by wire. There is a vacuum pump as in all EVs that provides vacuum for the brake assist. For Adaptive Cruise Control and Automatic Emergency Braking to operate the mechanical brakes, there must be some other mechanism that effectively "applies the brakes", but that will be something that provably does not reduce pressure from pressing the brake pedal. Unless you have amazing and expensive approvals, pressing the brake pedal has to operate the friction brakes through hydraulic pressure with a dual redundant system.
Check out the link I posted in #365* and you'll see how it actually works, it isn't a conventional system and nor are a lot of other EVs.

* Leads to this post with a hydraulic circuit.
 
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Check out the link I posted in #365 and you'll see how it actually works, it isn't a conventional system and nor are a lot of other EVs.
A couple of points:
1) The braking system isnt in question here, allegedly the vehicle accelerated quickly
2) According to MG, the braking system on the MG4 is "Continental Braking System"
Having had a look around cyberspace, all of the systems be it IBS or CBS etc have a backup that the pedal pressure can get to the callipers in the event of a system failure. Braking would still occur.
 
A couple of points:
1) The braking system isnt in question here, allegedly the vehicle accelerated quickly
2) According to MG, the braking system on the MG4 is "Continental Braking System"
Having had a look around cyberspace, all of the systems be it IBS or CBS etc have a backup that the pedal pressure can get to the callipers in the event of a system failure. Braking would still occur.
Yes, I was responding to Coulomb's post about the braking system.

Of course it is designed to fail-safe, everything safety critical is. The question is does the design work properly under all circumstances?

There have been plenty of fail safe or backup systems that have failed on aircraft, for example, where money is no object. Do we trust low cost car manufacturer's design and engineering?
 
I'm not going to read through 20 pages of comments, so this simple point might/probably has already been made. The Construction & Use regulations set out the rules for braking systems. There must be at least two independent mechanical / hydraulic braking systems in addition to the handbrake. This is almost always done by a split system where if a fault develops in one half, the other half still works.

Unless the brake master cylinder is torn out of the car (in which case you have a much bigger problem), there should be no way that there is a total loss of hydraulic braking. If power assistance fails, you would have to press the brake pedal MUCH harder, but the brakes still work. If you do somehow have total hydraulic failure, the car still has a secondary system (normally the handbrake/parking brake/emergency brake) which has to be capable of bringing the car to a halt. And ‘bringing to a halt' includes circumstances where the means of providing motion remains engaged.

"The braking system shall be so designed that in the event of failure of any part (other than a fixed member or a brake shoe anchor pin) through or by means of which the force necessary to apply the brakes is transmitted, there shall still be available for application by the driver brakes sufficient under the most adverse conditions to bring the vehicle to rest within a reasonable distance."

 
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One problem I see with the current brake-by-wire systems such as used by the MG4 is that they fail-safe if power is lost (the change-over valves require power to switch the hydraulic circuits from the pedal to the computer controlled pump); or the computer detects a problem.

But what happens if the control computer hangs? Of course computers never have bugs, hang, or get hit by cosmic rays etc!

That is why true fail-safe systems have three or more computers (and sensors) and use majority voting to detect problems.

It's all speculation by all of us of course unless someone here worked on the system design or has access to internal information.
 
Check out the link I posted in #365* and you'll see how it actually works...

Thanks, but all I see is a hydraulic circuit diagram (as opposed to an electrical, or even a system level diagram). I see a standard hydraulic system with some valves that allows a "simulator" to simulate pressing the pedal. The electric motor there operates only the rear brakes; it may be just the electric handbrake. [ Edit: as pointed out a few posts down, the electric motor likely operates alk four wheels. But that doesn't change my arguments. ]

One problem I see with the current brake-by-wire systems such as used by the MG4 is that...

So sorry, I still see no evidence of brake by wire.

But what happens if the control computer hangs?
Then you have to have a completely redundant system that can take over instantly when the first one is detected as not working. That's one reason why so few passenger vehicles have steer by wire, and why the Tesla Cybertruck is considered so advanced for 1) having designed such a system that is suitable for mass production, and 2) getting it though the long regulatory process while the design was still secret, at least from the general public.

This sort of innovation is unlikely to come from the likes of SAIC/MG, in my opinion. Even Tesla, who have the ability to turn the impossible into the merely late, aren't attempting brake by wire as yet, as far as I know.

But perhaps my use of the term "by wire" is wrong; if so, please show me.
 
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Thanks, but all I see is a hydraulic circuit diagram (as opposed to an electrical, or even a system level diagram). I see a standard hydraulic system with some valves that allows a "simulator" to simulate pressing the pedal. The electric motor there operates only the rear brakes; it may be just the electric handbrake.



So sorry, I still see no evidence of brake by wire.


Then you have to have a completely redundant system that can take over instantly when the first one is detected as not working. That's one reason why so few passenger vehicles have steer by wire, and why the Tesla Cybertruck is considered so advanced for 1) having designed such a system that is suitable for mass production, and 2) getting it though the long regulatory process while the design was still secret, at least from the general public.

This sort of innovation is unlikely to come from the likes of SAIC/MG, in my opinion. Even Tesla, who have the ability to turn the impossible into the merely late, aren't attempting brake by wire as yet, as far as I know.

But perhaps my use of the term "by wire" is wrong; if so, please show me.
Exactly -

"there shall still be available for application by the driver brakes sufficient under the most adverse conditions to bring the vehicle to rest within a reasonable distance."

However the MG4 braking system works, however complex it is made and however many computers are involved, however many potential errors could be incorporated in the engineering of the MG4 braking system, the basic fact remains that there MUST be a fail-safe system of stopping every car.

The origin of this thread was a story about someone in a 'runaway' car which they couldn't shut down and whose brakes wouldn't work. But any vehicle sold in the UK has to go through type approval / homologation to make sure it complies with the Construction and Use regulations, so total brake failure should NEVER happen.

We've had suggestions of negligence in government, but ask yourself whether EVERYONE in the system of regulatory compliance was negligent or complicit in some complex conspiracy to allow dangerous vehicles to be sold. Really? And we're the EV community which continually complains about stupid conspiratorial stories from the 'haters'?

If there’s any truth to the story, society cannot allow runaway cars to be used on our roads. So let's get every MG4 subject to an emergency recall and taken off the road until MG acknowledges that a problem exists, a solution is found, and they are all modified.

Hmmm ….

Otherwise, let's just accept that this story is hogwash!
 
Thanks, but all I see is a hydraulic circuit diagram (as opposed to an electrical, or even a system level diagram). I see a standard hydraulic system with some valves that allows a "simulator" to simulate pressing the pedal. The electric motor there operates only the rear brakes; it may be just the electric handbrake.



So sorry, I still see no evidence of brake by wire.


Then you have to have a completely redundant system that can take over instantly when the first one is detected as not working. That's one reason why so few passenger vehicles have steer by wire, and why the Tesla Cybertruck is considered so advanced for 1) having designed such a system that is suitable for mass production, and 2) getting it though the long regulatory process while the design was still secret, at least from the general public.

This sort of innovation is unlikely to come from the likes of SAIC/MG, in my opinion. Even Tesla, who have the ability to turn the impossible into the merely late, aren't attempting brake by wire as yet, as far as I know.

But perhaps my use of the term "by wire" is wrong; if so, please show me.
Then you haven't understood the diagram correctly, the motor/pump is connected to all four wheel cylinders. The posts from me above the diagram explain the basic operation. Have a look, there is no brake servo in your MG4, it is all computer controlled.
 
Then you haven't understood the diagram correctly, the motor/pump is connected to all four wheel cylinders. The posts from me above the diagram explain the basic operation. Have a look, there is no brake servo in your MG4, it is all computer controlled.
It is NOT all computer controlled. With 12v disconnected and parking brake released, the hydraulic brakes will still work from the pedal (without any assistance so will be heavier than normal). You see it here from the diagram posted earlier the hydraulic route from the mater cylinder to all 4 wheels.
mg4brk.PNG

When not receiving a control signal from the brake by wire system all of the valkves are in the positions shown i.e. de energised.
When the brake by wire system is functioning it will energise the valves that it needs to perform the braking as programmed.
It is true that computers can and do go wrong, I am absolutely certain, in this mission critical role the computer will have a watchdog running. The watchdog is a small circuit that will need communications from the computer typically at 1 kHz or more. In the event of none communication (computer hung / frozen / crashed) the outputs will be disabled, a fault logged and the driver alerted to the issue.
 
Before everyone disappears down a rabbit hole, a reminder that this thread is about perceived braking issues on the ZSEV and this does not have the same braking system as an MG4.
Discussion of how the MG4 system works is nonetheless very interesting so by all means raise a new thread on it in the MG4 area (y)
 
Before everyone disappears down a rabbit hole, a reminder that this thread is about perceived braking issues on the ZSEV and this does not have the same braking system as an MG4.
Very true and it wasnt about braking on the ZSEV either, it was about runaway acceleration?

Discussion of how the MG4 system works is nonetheless very interesting so by all means raise a new thread on it in the MG4 area (y)
Maybe split the latter part of this thread off into the MG4 section?
 
Well my comment is common to both.
I'm very pleased that the rumour of total fly-by-wire has been scotched. A great relief.
Secondly, the only way to make a brake system truly fail- safe is to have all, or at least most, of the brakes coming on full in the event of a loss of fluid in the hydraulic system. This is the practise used in trucks. This is only not required in completely separate dual-circuit systems as used in most cars. One hopes that is still being maintained.
 
It is NOT all computer controlled. With 12v disconnected and parking brake released, the hydraulic brakes will still work from the pedal (without any assistance so will be heavier than normal).
Which is what I said in my referenced posts ?‍♂️

Obviously it is not computer controlled if you have lost all 12V power, and in that case the changeover valves failsafe as you show.
 
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Before everyone disappears down a rabbit hole, a reminder that this thread is about perceived braking issues on the ZSEV and this does not have the same braking system as an MG4.
Discussion of how the MG4 system works is nonetheless very interesting so by all means raise a new thread on it in the MG4 area (y)
My understanding is that the two systems are basically the same, even if the MG4 version is a later design. Do you have evidence to the contrary? Genuinely curious.

Well my comment is common to both.
I'm very pleased that the rumour of total fly-by-wire has been scotched. A great relief.
Secondly, the only way to make a brake system truly fail- safe is to have all, or at least most, of the brakes coming on full in the event of a loss of fluid in the hydraulic system. This is the practise used in trucks. This is only not required in completely separate dual-circuit systems as used in most cars. One hopes that is still being maintained.
We need to stop talking about two extremes here: these systems are neither passive conventional braking systems nor are they drive-by-wire.

They are a mixture of a computer controlled blended braking system (regen and brakes) with fault/power loss failover to an unassisted manual set up - one that in many cases would still catch out an unprepared driver used to assisted brakes.

It is possible there are fault scenarios that are not identified correctly by the computer and it is largely software controlled, so it is at potential risk of bugs. MG does not have a good track record on software bugs and strange system behaviours.

It seems we have two camps:
a) These systems are 100% failsafe and every problem reported is user error or fabrication (or pedal obstruction).
b) There's enough people reporting this to cast doubt on whether it is 100% failsafe.

At this point I think we are going around in circles, so I'll bow out.
 
We need to stop talking about two extremes here: these systems are neither passive conventional braking systems nor are they drive-by-wire.

They are a mixture of a computer controlled blended braking system (regen and brakes) with fault/power loss failover to an unassisted manual set up - one that in many cases would still catch out an unprepared driver used to assisted brakes.

It is possible there are fault scenarios that are not identified correctly by the computer and it is largely software controlled, so it is at potential risk of bugs. MG does not have a good track record on software bugs and strange system behaviours.

It seems we have two camps:
a) These systems are 100% failsafe and every problem reported is user error or fabrication (or pedal obstruction).
b) There's enough people reporting this to cast doubt on whether it is 100% failsafe.

At this point I think we are going around in circles, so I'll bow out.

I'm still calling pedal error.
 
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