My understanding: Engine brake uses engine friction to damp the vehicle momentum. If one wishes to apply engine brake to assist manual gearshift,(activate engine brake, rpm dies, shift to lower gear), will this result in engine stall?

With modern day trucks,I understand idle governor takes care if rpm falls.
However, in below sequence
     1)activate engine brake-->Vehicle drives engine-->rpm reduces slowly
     2)clutch pedal pressed-->nothing drives engine
     3)gear shift done
     4)clutch pedal released.Here my guess is,
based on the various factors such as
     a)duration of clutch press,
     b)previous gear and current gear,
     c)based on vehicle momentum,
     d)due to sudden loading,
engine might stall and this may not be recovered with governor. So,
     a)Is there a possibility of engine stall in above scenario?
     b)Is it not safe to have engine brake active during gear shift?


No,engine control unit will prevent engine stall if cluch pedal is pressed during engine brake activation. There is a small switch on top of clutch pedal in modern vehicles.This will be used to sense clutch pedal press. Truck control unit senses clutch pedal press and deactivates engine brake. An example can be seen here:

Clutch pedal switch from Askthemechanic.co.uk

When clutch pedal is pressed, switch opens and engine brake is automatically deactivated by truck electronic control unit. Switch is designed as "normally open,close when pressed".So,if switch becomes faulty, engine brake doesn't work as Truck control unit senses clutch pedal pressed condition.

  • Does it mean "engine might stall if above condition is not taken care by engine control unit OR if there is no engine control unit"? – niko Feb 6 '16 at 3:52

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