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Old 8th July 2014, 17:26   #1
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Default The End of Left-Foot Braking? BTO - Brake Throttle Override

A 911 call made from the car:
"We're in a Lexus ... and we're going north on highway 125 and our accelerator is stuck ... there's no brakes ... hold on and pray ..." The call ends with the sound of it crashing, prosecutors said. (link)

We've all heard the horror stories of cars uncontrollably charging down the freeway, like they had a mind of their own. All the drivers claim they were pressing the brakes but nothing was happening, and the car continued to accelerate.

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So, what's the problem?
  • Is this happening because the floor-mats have slid forward and are depressing the accelerator?
  • Are the drivers accidentally pressing the wrong pedal in a panic?
  • Is there a bug in the ECU firmware?
  • Are the accelerator mechanisms or sensors faulty?

Whatever the reason, many lives and billions of dollars have been lost as a result of these problems.


What's the solution?

Something had to be done to stop this from happening in the future. Even if the problem was purely due to human error, there should be an engineering solution to prevent the problem.

Last edited by Rehaan : 8th July 2014 at 17:55.
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Old 8th July 2014, 17:27   #2
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Lets Change Scenes:

A few pistonheads are throwing a Lotus Elise around Spa Circuit in Belgium.

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As they approach a downhill left-hander in 4th gear, they left-foot brake a little, straighten up, and get back on the power.
But there's no power!

Instead, an orange spanner symbol has shown up on the instrument cluster.
The Elise is in limp mode.

After a few minutes, the error icon disappeared and the car recovers.
They can put the power down again.

But alas, same corner, same sequence of events.
Back in limp mode!

Some sort of ECU problem, they assume.
They write to Lotus.


Now here's the interesting part...

You'll see how Lotus' reply ties both the above stories together:
“What you experienced to put the car in limp-home mode is what we refer to as ‘BTO’ (Brake Throttle Override) which is a feature that helps to address a UA (Unintended Acceleration) in trapped accelerator pedal situations. As reported in the press and to NHTSA, most vehicle manufacturers, including Lotus, have already adopted brake-throttle override or will be incorporating it into all vehicle designs over the next few model years.” [Not just those equipped with Toyota engines…]
- source

So basically, if the ECU notices that you're pressing both, the brake and the accelerator, it gives the brake preference and completely ignores the accelerator input.

In other words, expect cars to become more safe on the roads, and less fun on the racetrack.

Bye-bye left-foot braking!

Last edited by Rehaan : 8th July 2014 at 18:01.
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Old 8th July 2014, 20:33   #3
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Generally, driver pedal inputs === driver intention.

Brake pedal + Accelerator pedal === Control Units confused (workarounds possible).

It's a safety feature, but there is plenty to play around with the accelerator pedal characteristics. Road cars will have limitations, luckily out test cars do not.

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Old 8th July 2014, 21:07   #4
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Not so, good news for the enthusiasts. However, considering the number of people who actually Left-Foot-Brake vs Accidents avoided, this new feature makes sense.

Hopefully, it evolves..
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Old 8th July 2014, 22:10   #5
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

So, is this something expected from Y201X and beyond? I am sure no such device exists in the mass market 200X vintage - which most of India drives today.
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Old 8th July 2014, 22:37   #6
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Quote:
Originally Posted by Rehaan View Post
A 911 call made from the car: [indent]"We're in a Lexus ... and we're going north on highway 125 and our accelerator is stuck ... there's no brakes ... hold on and pray ..." The call ends with the sound of it crashing, prosecutors said.
Still doesn't cover the quoted case, right? The caller said there were no brakes too.

Anyway, still I would say something is better than nothing, specially when it can save lives. Would be nice to have an override for it though, only for track days!

Quote:
Originally Posted by Rehaan View Post
So basically, if the ECU notices that you're pressing both, the brake and the accelerator, it gives the brake preference and completely ignores the accelerator input.
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Old 8th July 2014, 22:55   #7
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

This would certainly help when panic braking and your foot presses both accelerator and brake pedals.

On the track, you could simply disconnect the brake switch and enjoy left foot braking.

Regarding throttle stuck open, one can pop the transmission into neutral, coast to the road side and turn off the engine, right? Would work for an automatic too.
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Old 8th July 2014, 23:39   #8
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Lol. Guys you won't believe it but my Indigo Marina has it. Haha. Now I know what it is but initially I had not realised it and had thought it to be an ECU quirk. I had chanced upon it by accident. After driving through some water deep enough to submerge my tyres, I was doing left foot braking along with throttle to dry up the disks quickly and realise that the car has gone into limp home mode and throttle was not responding. I re did the test a few more time on different occasions and it happened each and every time.
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Old 9th July 2014, 00:39   #9
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Quote:
Originally Posted by bravo6 View Post
Regarding throttle stuck open, one can pop the transmission into neutral, coast to the road side and turn off the engine, right? Would work for an automatic too.
OT - Reading the Lexus' incidence in the OP I got so blinded by it that such a simple thing (of shifting to neutral in such a case) didn't strike me

Even the Lexus guy could have shifted to neutral and coasted to a halt right?

Coming to the topic, I find it a welcome addition. It will help reduce those accidents where, because of getting frightened people slam both their feet on the A & B pedals..

Let us wait and watch how this is accepted worldwide and how better does it get over time..

-Bhargav
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Old 9th July 2014, 09:05   #10
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Quote:
Originally Posted by joybhowmik View Post
I am sure no such device exists in the mass market 200X vintage - which most of India drives today.
Apparently the DSG equipped cars have something similar built in -- but I'm guessing that is mostly to save the clutch from extreme wear.

Quote:
Originally Posted by amitoj View Post
Still doesn't cover the quoted case, right? The caller said there were no brakes too.
A lot of times when someone is doing something wrong (especially in a frenzy), they think they are doing one thing, but they are actually doing something else. Who knows what was actually happening.

However, i think this would cover the quoted case, as there is a high chance that the throttle was stuck open for whatever reason.

If I'm not mistaken, brake specs do say that they should be able to overpower the engine (i don't remember the specifics - but for example, FSAE rules say the racecar should be able to lock all 4 wheels whilst traveling at xxx mph). However, in panic situations, there can be a very high human error factor.

Quote:
Originally Posted by bravo6 View Post
Regarding throttle stuck open, one can pop the transmission into neutral, coast to the road side and turn off the engine, right? Would work for an automatic too.
Yes, but once again, who knows how fast these things happened and what the technical knowledge of the driver/s was. It's easy to think of these things when sitting behind a computer screen, but in reality there are several other things running through your mind when it actually happens.

Quote:
Originally Posted by wanderernomad View Post
Lol. Guys you won't believe it but my Indigo Marina has it.
Hah! Nice find. Guess this solved a mystery for you then

cya
R

Last edited by Rehaan : 9th July 2014 at 09:07.
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Old 9th July 2014, 09:08   #11
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

How then do we start and move a vehicle in a downward slope?I prefer to double pedal brake and clutch and then Slowly accelerate to prevent backward
Slide.
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Old 9th July 2014, 09:33   #12
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

@josephnishanth handbrake

@Rehaan yup, this will be of immense help to people in such an unnerving emergency.
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Old 9th July 2014, 10:37   #13
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Default re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Here's a more detailed story on this Toyota stuck pedal thing:

http://www.thetruthaboutcars.com/201...fective-gm-ig/

Doesn't make for a pretty story.

As others pointed out, it seems odd that the brakes were not working. I would think that even with a stuck throttle stomping on the brakes would slow you down. I can't really think of any reason why the stuck throttle pedal would affect braking. Even though initially it was related to a floormat it would have to be some thick mat before it would hinder the brake pedal coming down.

Jeroen

Last edited by GTO : 9th July 2014 at 11:44. Reason: Typo
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Old 9th July 2014, 13:38   #14
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Default Re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Comprehensive and informative article on Brake Throttle Override systems prevalent in the automotive world. Nice read.

http://www.thecarconnection.com/news...e-new-standard

Source: The Car Connection

Also it seems the NHTSA in the USA has mandated that Brake throttle override systems be fitted in all new vehicles henceforth. Detailed document attached.

It does not seem too difficult to incorporate this function. Was speaking to my friend who is a vehicle embedded systems / electronics guy and he was saying it involves some fairly simple logic and programming between the ECU and the throttle pedal sensors. Nowadays almost all modern cars have electronic throttle controls so it is all the more convenient to integrate.

Hopefully some OEM will introduce this in India specially for their AMT/AT models - it can actually be a marketing USP.

Is anyone aware what is the current status of BTO functions w.r.t. the VW's & Audi's DSG's/CVT's respectively? Do we get it in our country?
Attached Files
File Type: pdf FMVSS_124_BTO_NPRM_Final.pdf (334.0 KB, 207 views)

Last edited by arjab : 9th July 2014 at 13:46.
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Old 9th July 2014, 13:56   #15
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Default Re: The End of Left-Foot Braking? BTO - Brake Throttle Override

Quote:
Originally Posted by bravo6 View Post
Regarding throttle stuck open, one can pop the transmission into neutral, coast to the road side and turn off the engine, right? Would work for an automatic too.
In case of manual, would it not be wise to use Engine braking? Shifting down to first gear may be and then re-engaging the clutch? Stopping from high speeds using coasting could take some time.

Anyways, in case of such situations, the first response is panic. So always better to have a fail safe.
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