Basics of Automotive Electronics: Engine Start-Stop System

Engine Start-Stop functionality is basically turning-off the engine when the vehicle is not moving for a certain pre-defined duration (ex situations - while waiting in the road signals, or during traffic jam situations) to save the fuel.

Vehicle will be started automatically by pressing clutch or accelerator pedal, without the need for cranking again.

Passenger safety and comfort are considered before going to engine auto-stop or auto-start of the engine.

Auto-Stop of the Engine

Auto-Stop of the engine will be initiated if all of the below conditions are satisfied.

Acceleration pedal is not being pressed.
Vehicle speed is lesser than threshold.
Clutch is not pressed.
Gear is in Neutral.
Brake is pressed (non-MT)

Auto-Stop Release Conditions
Once the auto-stop request has been detected, following are the conditions to allow the stop to happen.
If any one of the below conditions are not satisfied, auto-stop will be inhibited.

Gear should not be in Reverse.
No fault in Gearbox start-stop request signal.
SOC, SOH, SOF and battery temperature are within the calibrated thresholds, which are determined by IBS.
AC switch is ON and cabin temperature is less than threshold.
Coolant temperature is less than threshold.
Brake booster pressure is greater than threshold.
Engine speed is lesser than threshold.
Minimum waiting time for engine stop after the engine was started last.
Minimum velocity the vehicle should reach for the engine stop, after the engine was started last.
Minimum engine speed the vehicle should reach for the engine stop after the engine was started last.
If slow movement of vehicle is detected, then it is considered as traffic jam situation, and auto-stop will be inhibited.
If panic braking is detected, then auto-stop of the vehicle will be disabled. (Panic braking is detected based on the time for the vehicle to come to halt from the current speed. If the vehicle comes to halt before the remaining brake duration timer reaches zero, then it is considered as panic braking)

Auto-Start of the Engine

Engine will start automatically if any of the below conditions are satisfied.

Driver requests

If accelerator pedal is pressed more than the calibrated threshold
If clutch is pressed 10% and there is no fault in the 10% clutch signal Or Clutch is pressed 90% (In MT)
If Brake pedal is active (In AT/CVT)

System requests

If AC switch is ON and cabin is becoming hotter/cooler than set temperature.
If coolant temperature is greater than threshold.
Re-check whether engine stop is passed status.
Certain time is elapsed after engine is stopped successfully.If SOC, SOH, SOF and battery temperature fall outside the calibrated thresholds, which are determined by Intelligent Battery Sensor(IBS)
If the brake booster pressure falls OR if there is any error in the brake booster pressure sensor
Vehicle is moving and speed is more than calibrated threshold.

Driver presence is determined based on Cranking input, Accelerator pedal, clutch and brake inputs.

Auto-Start Release Conditions
Once the auto-start request has been detected, following are the conditions to allow the start to happen.
If any one of the below conditions are not satisfied, auto-start will be inhibited.

Driver releases

Gear should be in Neutral position.
Clutch should be pressed 90% - to ensure the drivetrain open.

System Releases

Driver presence is detected.
Driver door is closed.
Driver seat belt is closed.
Hood is closed.
If SOC, SOH, SOF and battery temperature are within the calibrated thresholds, which are determined by IBS
Start enable from thermal systems.
Start enable from CoEng
Brake pedal should be pressed during start in non-MT vehicles.
If first engine auto-start is successful.
If number of engine start aborts are greater than the calibrated count