Stop/Start System Description and Operation: Notes

The Stop/Start System is used to improve fuel efficiency in stop/start driving. The vehicle automatically shuts off the engine in appropriate conditions, at a traffic light for example, resulting in zero tail pipe emissions and saving fuel which otherwise is used idling the engine when stationary. The engine restarts when the driver is ready to move away.

When the driver prepares to move away (by releasing the brake pedal and/or depressing the accelerator pedal), the engine will start; it takes approximately 400 ms for the engine to restart from the time the brake pedal transition initiates this activity.

To support the increased number of engine starts, the starter motor is upgraded with a high performance electric motor and a stronger pinion engagement mechanism with reduced noise levels.

There is a battery sensor module connected to the battery which continually monitors the battery charging current, and voltage. This module communicates to the body control module (BCM) via LIN serial data. The engine control module (ECM) receives the voltage and current information from the BCM via high speed serial data and this is used to determine if the battery state of charge (SOC) as calculated in the ECM by the Battery State Estimation (BSE) system, is sufficient to support a Stop/Start condition. The ECM has access to independent sensing systems to verify the information received from the battery sensor module via the BCM is correct. These sensing systems include an analog current sensor wired directly to the ECM and battery voltage sensing via the Run/Crank input to the ECM. This system also utilizes a dual battery configuration which includes the primary 12V battery as well as an auxiliary 12V battery. The auxiliary battery is used to power vehicle loads, except the starter, during stop/start cranking events.

For the engine to shutdown, the vehicle must be below 5 km/h (3 MPH), with the brake pedal depressed to keep the vehicle at rest. To restart, the driver releases the brake pedal and the starter motor engages the engine, and the vehicle is ready to drive away. When the engine has been shut down by the Stop/Start System, the tachometer needle will rest at the Autostop indicator icon (500 RPM point) indicating the engine has been shut down by the Stop/Start System.

When the Stop/Start System has shut down the engine, and the ambient temperature is below 15°C (59°F), the ECM will activate the Stop/Start auxiliary relay which controls the electric engine coolant cabin heater pump motor to continually circulate the engine coolant through the engine and heater core while the engine is off. This is to ensure the engine and passenger compartment temperature is maintained while off. Once the Stop/Start System has restarted the engine, the ECM will turn off the electric coolant pump motor, thus allowing the engine's internal coolant pump to circulate the engine coolant. The Stop/Start System is automatically activated each time the ignition switch is turned on.

Courtesy of GENERAL MOTORS COMPANY