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ibooster braking system logic issue [and discussion around brake failure claim in shanghai]

Tam

Well-Known Member
Nov 25, 2012
8,778
7,602
Visalia, CA
The accident happened in a "national highway" in China, which is not like US highway. There are traffic lights a few miles apart, truck/semi driving at 40-50 mph (sometimes in the left lane). Cars want to move fast would need to maneuver in traffic. I would not be surprised the driver brakes more than 40 times in 30-minute log, if he is a aggresive driver.

He might be an aggressive driver and a frequent braker but not an aggressive braker.

As posted previously,

When the car accelerated to 118 km/hr (74MPH) and only 6 seconds before the collision, the force from the brake pedal was too light: Only 0.3 bar out of 140.7 bar.

That didn't mean it didn't slow down. It did but just a tiny bit: 116 km/hr (72MPH) and it's only 4 seconds before the collision.

He did apply additional force from 4.5 to 12.3 bar (still too light out of 140.7 bar) and resulted in the speed reduction to 94 km/hr (58MPH) just 2 seconds before the collision.

Just about 1 second before the collision, he did apply additional force 92.7 bar) and resulted in the speed reduction to 74 km/hr (45MPH).

Luckily in that split 1 second, the AEB (Automatic Emergency Brake) was helping to get the force of applying the braking pedal to all the way 140.7 bar and resulted in the slow speed of 48.5 km/hr (30MPH).
 

Electric Dream

Pilots the Millennium Milkfloat
Jul 21, 2016
1,682
2,759
UK
Something I think that's worth mentioning is that a pressure of 140 bar is braking VERY hard and I doubt most drivers would even be able to press the pedal hard enough to get to that pressure.

Even driving on track, anything over 100 bar is unusual unless braking from high speed into a very slow corner, but even then the aim is not to trigger the ABS because as we know that will increase the braking distance, so very hard braking on track (with road legal tyres) is often something like 80-100 bar. Drivers who have never been on track won't even think they can brake as hard as that without the car doing something unpredicatable. I see this all the time with new track drivers. They have to re-calibrate their thinking of what is 'hard braking'.

With a Model 3 Performance in track mode, the brake pressure is recorded in a .CSV file along with other data, so we can analyse the driving after the event. Looking at brake pressure data, it's very common to see that 0.3 bar figure every now and then while the accelerator is being pressed but the brake pedal isn't. It's also common to see readings in the 0.3-2.0 bar region mid-corner without the driver pressing the brake pedal. Whether that's torque vectoring or just some anomoly I can't say for sure, but it happens. So, any brake pressure readings below 2 bar can usually be ignored as a driver input. Even very light braking is well over the 2 bar figure.

I'd say the 92.7 bar reading 1 second before the collision is the driver pressing the pedal as hard as he could and probably harder than he ever did before in that car. It was still too little too late.
 

Big Earl

bnkwupt
Jul 12, 2017
5,296
9,758
Springfield, VA
I just tried it out on my 2018 Tesla Model 3 Long Range and although there are audio and visual alarms, they don't interfere with driving with two feet and with two pedals depressed at the same time.

I would not recommend it but for those who are addicted to two pedals depressed at the same time, I can see how they like it in Model 3. They can regulate the speed with the brake pedal and not just the accelerator pedal all at the same time. It becomes an art which again, I do not endorse.

It's possible to fine-tune the art so instead of lifting the accelerator pedal frequently, they can adjust the brake pedal pressure 40 times per 30 minutes.

I would say that takes practice, especially I have to ignore the alarms. But they are not really loud so it's not that distracting at all.


Hi Tam,

Your video demonstrates exactly what I was talking about. When you have your foot on the accelerator and you put your other foot on the brake pedal, the car warns you and immediately removes propulsion power, as shown by the power indicator displaying no positive or negative power. The car is coasting even though you have your foot fully (or close to it) on the accelerator.

Here is my video from last year:

I think the confusion comes from me originally stating that it was impossible to two-foot drive the Model 3, which is technically incorrect. It is possible, as we've both shown. I guess my point was that it isn't unsafe and the brake pedal overrides the accelerator pedal, which demonstrates that the car can always be stopped using the brake pedal, even if the accelerator gets jammed on the floor.
 

Gasaraki

Active Member
Oct 21, 2019
1,668
1,070
Syracuse, NY
At least 4 points to add.

1、Ms. Zhang's case is not the only one.
She is in fact the one who starts a war against Tesla in public. Almost every fews days there will be one Tesla accident declaring to encounter brake malfunction and SUA. Check regularly the
Chinese Tweet-like platform Weibo will easily prove.
2、Once reported, any possible design defect should be investigated completely, no matter whether it exists or not and how small the possibility is.
3、Even if other brands may suffer more accidents, if they are clearly proved to be drivers' faluts, then the brand is not responsible. However, for Tesla, it's not the case. Obviously, the public are not fully convinced that all these accidents are drivers' faults.
4、One step back, even if Tesla's braking system gets eventually proved to be bug-free, Tesla may also needs to reflect after so many cases, whether its operation logic needs further improvement.
-I'm sorry but but after visiting China, I could tell people in China are bad drivers. Way worst than US drivers. Drivers in China think rules, signs, or lines are just options, no need to follow them. People in the US are dumb also, hitting the accelerator and blaming the brake system. Happens all the time here in the US.
-Brakes do fail on ICE cars also. Doesn't mean there are systematic issues. Plus the physical brakes are not even made by Tesla. Brembo and Bosch have been doing brakes for a long time. They are not amateurs.
-The data recorder and the government already said that the driver's at fault. What other proof would it take?
 

Gasaraki

Active Member
Oct 21, 2019
1,668
1,070
Syracuse, NY
How do you search for these ODIs? Is there a place on nhtsa.gov where I can search specifically for investigations into Teslas? (Or Toyotas, or...).

I read most of the ODI document that you linked to. More than 50%, but I confess I skimmed a bit.

My very high level summary of that: the reports that they investigated did not show any brake malfunction, if anything they showed drivers accidentally mashing the accelerator when they perhaps meant to mash the brake pedal; and Belt's papers are best ignored.

That does not sound to me like a malfunction of the car.

But I have to wonder: could some people have muscle memory for bringing a car to a stop that consists of "use brake to stop the car, then press harder for full stop", and that causes them to occasionally mess up on cars with aggressive regen: the car mostly comes to a stop via regen, but if the foot is still over the accelerator (while regen is slowing the car), and then without thinking the next step is "mash the pedal to come to full stop" and they do that without moving the foot to the brake pedal? I haven't done this, but I have noticed that now when I'm coming to a red light or stop sign that frequently my foot is hovering over the accelerator, not the brake.

Also, not all hybrids do regen only via brake pedal. On my wife's 2020 Honda Insight there is regen when you take your foot off the accelerator, and paddles behind the steering wheel to let you adjust that regen up/down. And regen will be used when going downhill to attempt to keep at the set adaptive cruise speed, but it won't fade in the brakes to maintain speed.
Sure that's how unintended accelerations happen, people setting on the accelerator thinking it's the brake. That is why I blame bad drivers.

When you are slowing to a stop, your foot should always be over the brake petal, even if you never plan on using the brake petal. Anytime you are no pressing down on the accelerator, your foot should be over the brake petal.
 

Tam

Well-Known Member
Nov 25, 2012
8,778
7,602
Visalia, CA
....It is possible, as we've both shown. I guess my point was that it isn't unsafe and the brake pedal overrides the accelerator pedal, which demonstrates that the car can always be stopped using the brake pedal, even if the accelerator gets jammed on the floor...
Exactly, good points! Just because it is possible for a driver to jump to the back seat and let the Tesla drive itself that doesn't mean it's safe.

Same with driving with 2 feet and I don't think it's safe either.
 

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