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

[Surfdog]

"it's on the BBC so it must be true."

And just like the BBC the it looks like the mental health card has been played to avoid answering any questions or giving further explanation.

 

[RobinH]

Just on the subject of "it's on the BBC so it must be true."

The BBC is in the entertainment business, and BBC news is no exception.
If you have insight into a major story you soon realise how few relevant, cross-checked facts they actually report and how much is just opinion and padding.
They are better than most but today's constant demand for content means the bar is set very, very low.

 

[johnb80]

You are correct that it may be a much slower speed event than reported, but on the rest I do not agree, johnb80.

That is entirely your perogative and I dont mind at all that youre wrong!

If there is a system to "increase a little or decrease a little" the hydraulic pressure, if that system fails then virtually anything can happen,

Nope, it's easy to have a modulator on the brake lines, essentially pistons in a bore. If the pistons move down the pressure is reduced if they move up the pressure is increased. They would not all fail at the same time dumping all of the hydraulic fluid.

it has failed and is out of control. The brake pedal sensor could well be a pressure switch, certainly in older cars it would be very likely, or it could be that the car was "dribbling" as they do at low speed with no accelerator input.

Why would they use a pressure switch as opposed to a simple mechanical switch on the pedal. The pressure switch is more expensive, harder to adjust, less reliable.

And what does "they don't design brake systems that way" mean?

Would you believe, they dont design brake systems this way You said any system that can adjust the pressure in a brake is a point of failure. I'm merely pointing out that with modern designs this is all taken into account.

The only way to avoid this scenario is to design a "fail-safe" brake system which would mean the brakes failing in "fully on" mode, as with lorries and buses.

Well you'd be wrong there, the design is such that the brake pedal will always transmit pressure to the callipers / pistons. In the event of a leak on one circuit the other circuit will still give some brake functionality.

There is no evidence that such a design has been incorporated.

Because it hasnt, it's not necessary for cars.

The MG ZS EV uses a Bosch electric steering system and therefore COULD be using the Bosch brake I Booster system.
Below is a link to the Bosch web site, for anybody is interested in how the brakes are assisted in an electric car.
Half way down the page there is short video explaining / demonstrating how the system operates.
Vacuum is supplied by an electric motor that is constantly producing a vacuum to keep the servo reservoir top up.
The Tesla system works in a similar way.
Not too dissimilar to the servo unit used in an ICE car, but it this case the vacuum is provided by ICE.
When the reservoir is filled, even if the electric motor looses power, there should be enough stored vacuum to bring the car to a stop.

iBooster

The iBooster is a vacuum-independent and electromechanical brake booster.

www.bosch-mobility.com

Even if there is no vacuum, servo assisted brakes still work just with a heavier pedal load.

 

[mg4mc]

Even if there is no vacuum, servo assisted brakes still work just with a heavier pedal load.

Well yes, but when did you last drive a car without power assistance? I last did it earlier this year and you end up nearly bending the steering wheel to bring it to a halt when the car is coasting. I'd like to see anyone do it against an EV motor that is trying to maintain the same speed.

 

[DisterBertieBear]

Well yes, but when did you last drive a car without power assistance? I last did it earlier this year and you end up nearly bending the steering wheel to bring it to a halt when the car is coasting. I'd like to see anyone do it against an EV motor that is trying to maintain the same speed.

So explain why the servo failed, and yet the car slowed down to 15mph on a roundabout, even though the MG ZS is notorious for using the brakes to slow on ACC and not regen?

I get it that steering wheels without power assist are a pain, and brakes might be spongey and hard but this is a remarkably selective and yet imprecise electrical failure that prevents ACC going off, steering assist being fine and 2 ton of vehicle is slowed so much it takes no damage when a police van brakes in front of it (but somehow the emergency braking system is off, or somehow it works on this scenario).

It's like swiss cheese.

 

[mg4mc]

Dunno, I haven't examined the car or seen diagnostic logs. I do know there are a lot of absolute opinions on this thread with little to no evidence one way or other.

However plausible or not the story is, there are probably more failure paths in a modern cars computer systems than you can shake a stick at.

 

[johnb80]

Well yes, but when did you last drive a car without power assistance? I last did it earlier this year and you end up nearly bending the steering wheel to bring it to a halt when the car is coasting. I'd like to see anyone do it against an EV motor that is trying to maintain the same speed.

Quite recently by coincidence

Yes the brakes are heavy BUT when you’re in panic mode you have immense strength. In addition, it was only doing 15 mph.

Dunno, I haven't examined the car or seen diagnostic logs. I do know there are a lot of absolute opinions on this thread with little to no evidence one way or other.

Yep, the only evidence is what the driver has given us but that can be assessed against experience and knowledge of vehicle systems. Holes in the story were immediately apparent.

However plausible or not the story is, there are probably more failure paths in a modern cars computer systems than you can shake a stick at.

Really? The ECU’s have loads of monitoring and protection systems built in. As an example the throttle is an electrical signal as opposed to a physical Bowden cable in the past. With the Bowden cable if it corrodes or becomes sticky nothing happens other than the engine can be stuck at a throttle setting. On the modern drive by wire systems not one but two signals come from the throttle pedal. If the ECU detects the signals are not identical the ECU will go into a limp home safety mode and will log implausible signal. This type of programming and monitoring is done on most if not all sensors.
So, in terms of failure paths there may be more of them but they’re monitored more closely and the system would cope in a safe manner

 

[Lovemyev]

Even if there is no vacuum, servo assisted brakes still work just with a heavier pedal load.

Yes John I do agree and understand this fully.
I was just making the point that IF the electric motor failed or it suffered a total lost of power, the drivers initial press of the footbrake would act almost as normal.
But any further subsequent pressure applied would result in huge decline in the stopping ability of the car, as the vacuum reservoir has now become pretty much depleted.
Bringing the car to a stop with no assistance from the brake servo, is very similar to trying to steer a car when the power assisted steering is not in operation.
The human effort required in order to make an impact, would require the arm and leg strength of superman, in order to make some impact.
We all have become very use to having the great features of power assisted systems now.
Having recovered a number of cars that has no assistance systems working, even getting a car onto a trailer is a bit of a challenge .

 

[timp]

Without the power assistance the foot brake is pretty ineffective.

In the MG4 you can use the EPB as an emergency brake in this situation by holding the EPB button up - not releasing it like you would do normally. Not sure if the ZS had this as well.

There would not be much damage if the ZS and the van were doing the same speed then the van slowed after contact was made.

Hi. Is the EPB button the central one with R N D which you press to engage handbrake? Tia

 

[kin]

Well yes, but when did you last drive a car without power assistance? I last did it earlier this year and you end up nearly bending the steering wheel to bring it to a halt when the car is coasting. I'd like to see anyone do it against an EV motor that is trying to maintain the same speed.

Ok it kind of make sense now, if the ZS lost servo assistant, the brake pedal would be very stiff and hard to press, if the driver was inexperienced, he would have panicked and assumed brake failure??

 

[bimbamboodle]

All I know is that this afternoon I drove past a secondary school in an identical car to the one that was on the news yesterday and a bunch of lads thought it was hilarious to point me out, maybe they were just impressed that I had the car under control?!

 

[scoobeesnac]

According to the news report he has mobility issues, so maybe could not press the brakes hard enough. Fwiw

 

[dspencer12345]

Is it me, or is the picture of @MGZS nothing like the picture on the news?! I think that post might be fake, particularly given there have been no further posts since.
I'm sure we'd all love to hear from the real driver to try to understand the full circumstances of what happened.
1) what did the policeman do that deactivated the vehicle?
2) which 9 warning lights came on?
3) where's the car now? With MG?

Based on the news report it all sounds very unlikely, but then sometimes multiple faults can occur simultaneously. Just bad luck?!

 

[rjb1970]

Is it me, or is the picture of @MGZS nothing like the picture on the news?! I think that post might be fake, particularly given there have been no further posts since.
I'm sure we'd all love to hear from the real driver to try to understand the full circumstances of what happened.
1) what did the policeman do that deactivated the vehicle?
2) which 9 warning lights came on?
3) where's the car now? With MG?

Based on the news report it all sounds very unlikely, but then sometimes multiple faults can occur simultaneously. Just bad luck?!

As I've mentioned earlier in this thread, I used to know him. The picture here is still him, but not a recent picture. Why he wouldn't use his Facebook picture or something more recent is beyond me.

 

[Surfdog]

Is it me, or is the picture of @MGZS nothing like the picture on the news?! I think that post might be fake, particularly given there have been no further posts since.
I'm sure we'd all love to hear from the real driver to try to understand the full circumstances of what happened.
1) what did the policeman do that deactivated the vehicle?
2) which 9 warning lights came on?
3) where's the car now? With MG?

Based on the news report it all sounds very unlikely, but then sometimes multiple faults can occur simultaneously. Just bad luck?!

You're right. The avatar for @MGZS is not the same guy who features in the news articles and on his Facebook profile. So @MGZS is probably fake or maybe the real guy using another individuals picture. This gets more intriguing by the hour.

 

[rjb1970]

You're right. The avatar for @MGZS is not the same guy who features in the news articles and on his Facebook profile. So @MGZS is probably fake or maybe the real guy using another individuals picture. This gets more intriguing by the hour.

It is the same guy, but the picture here is about 15 years old!

 

[Scoobydoo]

Man 'kidnapped' by his runaway EV rammed off the road by police

The motorist from Glasgow couldn't get his EV to brake. Instead, he was trapped in his moving vehicle until police were forced to take drastic action.

www.euronews.com

This story is growing arms and legs.

 

[dspencer12345]

As I've mentioned earlier in this thread, I used to know him. The picture here is still him, but not a recent picture. Why he wouldn't use his Facebook picture or something more recent is beyond me.

Saw your post, which was very interesting. I still wonder if the thread post is fake though. You've posted 45 times and I've posted 28, yet neither of us feel the need to create an avatar. Yet this user comes on and creates one straight away with his first post?

 

[rjb1970]

Saw your post, which was very interesting. I still wonder if the thread post is fake though. You've posted 45 times and I've posted 28, yet neither of us feel the need to create an avatar. Yet this user comes on and creates one straight away with his first post?

Curiouser and curiouser!

 

[Coulomb]

Yet this user comes on and creates one straight away with his first post?

I would not read too much into that little factoid.

Edit: However, I'll admit that the 15 years old image (if true) is weird. It does suggest wanting to garner sympathy.