|
Hi Ian See this http://www.edn.com/blog/1700000170/post/1760052976.html?nid=3351&rid=8414203 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 email tony@xxxxxxxxxxxx From: Ian East [mailto:ian.east@xxxxxxxxxxxx] 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 Ian East Open Channel Publishing Ltd. (Reg. in England, Company Number 6818450) |