[SystemSafety] Another runaway car

[Bernd Sieker]

On 14.02.13 14:38, michael.ellims at tesco.net wrote:
>
> You should be able to turn off the ignition at any time, there is usually a relay for the fuel pump however if it’s software controlled...

In Germany there is a requirement that the engine must not be able to 
run unless the key is in the ignition and rotated to the "running" 
position, but I don't know if there is still a requirement that it be a 
direct mechanical/electromechanical (relay) link to an ignition (petrol) 
or injection (diesel) shutoff. If it's software-controlled ... who knows?

>
> Failing that, the vehicle can be put into neutral, that’s almost always a mechanical shift unless you have paddles on the steering wheel. Then I have no idea.

If the gear is under (torque) load, it may not be easy to force a manual 
gearbox into neutral, although it may be possible with brute force. But, 
as below, if this was a specially adapted vehicle for a disabled driver, 
it was probably an automatic transmission, where Neutral may be 
electronically disabled above a certain speed (and, of course, no 
mechanical clutch pedal, either).

>
> The service brakes should be able to overpower the engine, esp. at high speed as the torque at the wheels is lower (i.e. high gear) and the front brakes should be able to apply >> 3000Nm per wheel on a vehicle that size. Note it shouldn’t matter if the throttle is open as regulations require an energy reserve to allow the brakes to be applied 9 times with no engine power. However if you keep using that up - then no power brakes.

I agree. The problem arises if the brakes are (a) overheated from 
several half-hearted braking attempts or (b) there is insufficient 
suction, if braking assistance is vacuum-powered, and the vacuum is 
taken from the intake manifold: At fully open throttle there is very 
little "vacuum".

Many modern petrol (and all diesel) engines use a mechanically driven 
suction pump. In that case even at full throttle there should be enough 
"vacuum" for the power brakes. Unassisted brakes should in theory be 
always available, but may require force beyond the driver's capabilities 
in some cases.

Will be interesting to follow this.


Bernd