Hill Start Assist is a feature that's used to prevent a vehicle from rolling downhill as you're about to drive off or
move from a standstill on an incline.
How it works is by automatically keeping the brakes applied for a few seconds
after you've released the brake pedal to give you time to comfortably drive off without worrying about the vehicle rolling
The amount of time the brakes are kept applied after you've released the brake pedal varies between vehicles but two
to three seconds seem to the popular timeframe.
For hill start assist to work effectively and not be an annoyance the system must detect whether the vehicle is
stationary on an incline or on a level surface as the feature will be annoying if it holds the vehicle on a level surface.
The system uses several sensors and variables such as incline detection, engine speed sensors and pedal position sensors
i.e. accelerator, brake (and clutch if necessary) to function.
Engine speed, vehicle speed or wheel speed sensors will alert whichever ECU
that operates the hill start assist that the vehicle came to a stop.
Whilst stationary the incline detection will send information to the ECU that the vehicle is on a hill and also how
steep the incline is so it knows that assistance is needed soon.
The pedal position sensors indicate to the ECU your intention to move or drive off and it instantly maintains the braking
force for a few predetermined seconds but you can pull off before that.
If the predetermined time is three seconds but the system notices from your input of the accelerator pedal that you can
safely drive off in half or quarter of that time it will release the brakes allowing you to drive off instead of waiting for the
The system should also release the brakes relatively slowly to avoid the vehicle suddenly jerking as it starts to move as
the engine would have a slightly higher revs as opposed to an unaided pull off in normal conditions.
Hill start assist should function just as effectively whether the vehicle has been parked on a hill for the past five days
and is now about to pull off or has been stationary on the hill for five seconds in stop and go traffic and it'll work whether
you're about to drive uphill or reverse uphill.
It will also be very useful on vehicles with a manual transmission as it eliminates
the need for riding the clutch or using the parking brake to pull off.
Hill start assist is now common on many types of vehicles and is among the many electronically controlled driver assistance