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RE: Race condition...

Hi Ian


See this




from an engineer who used to work at Ford in around the same era that I was working in automotive. The key phrase he uses is


The system level error that Toyota made is not letting a brake signal override a throttle signal.


Although not common over here in the UK because of our penchant for stick shift (manual gearboxes), most cars in the US have automatic gearboxes and cruise control. One of the standard signals to cruise control is the brake signal to disengage it.



Tony Gore

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From: Ian East [mailto:ian.east@xxxxxxxxxxxx]
Sent: 19 March 2010 18:39
To: Tony Gore
Cc: Jones, Chris C (UK Warton); occam-com@xxxxxxxxxx
Subject: Re: Race condition...



On 19 Mar 2010, at 17:55, Tony Gore wrote:

Not on this one, but the original Toyota accelerator problem does appear to have been a poor piece of software. It is normal when writing an engine controller to take account of other inputs. Thus, if the brake is pressed (in my days, detected by the same switch that puts the brake light on) then you cut the fuel injection down to a small level to sustain combustion and keep the engine ticking over and this also helps keep emissions down.

This makes the brake light switch into a safety-critical component!

In the case of Toyota, they do not appear to have done this, or if they have, the conflict between the signals has been mismanaged. This is why the engine can have full throttle and is not overridden by the brake. Modern engines (especially in US cars) are more powerful than the brakes, and this is why people are finding it impossible to stop the car in some circumstances.


Is it not the case that the accelerator pedal is now used as a "speed control", telling the fuel management system the acceleration the driver wants?

If so, the software will simply ramp up the power when the brake is applied, assuming it is unaware (or takes no account) of that.


Can it really be that simple?





Ian East

Open Channel Publishing Ltd.

(Reg. in England, Company Number 6818450)