Stop/Start System Description and Operation: Notes
Ultracapacitors should not be opened, disassembled, crushed, burned, charged over 5V, or exposed to high temperatures greater than 81.6°C (179°F). Ultracapacitors contain acetonitrile. If ultracapacitor leaks or ruptures it will emit flammable liquid and vapor with an aromatic ether-like odor. Harmful if inhaled or absorbed through the skin. Causes respiratory tract, eye, and skin irritation. May be harmful if swallowed. Can cause target organ damage. Arcing may also occur when charged and shorted, resulting in molten metal splattering and arc-flash hazards. To reduce the risk of personal injury and/or vehicle damage:
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The Stop/Start System is used to improve fuel efficiency in stop/start driving. The vehicle automatically shuts down 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 instantly restarts when the driver is ready to move away.
The purpose of the capacitor Stop/Start System is to provide an added boost of voltage during an autostart to prevent low voltage to vehicle modules and to provide a higher voltage to the starter motor to aid in a quicker and smoother engine restart. The capacitor Stop/Start System also provides an added boost of voltage during other engine starts.
The capacitor Stop/Start System consists of a stop/start capacitor and a stop/start capacitor control module. The stop/start capacitor consists of two capacitors in series and is located in the negative battery cable. Upon engine starting, the module charges the capacitor to a voltage in the range of 3.2 - 4.5 V (varies depending on vehicle engine). After ignition off, the capacitor voltage drops down to approximately 3.5 V in order to run a self-test. In normal operating mode, the module connects the battery to chassis ground. During an autostart, the module opens the switch to ground and closes the switch to the capacitor to provide a boost in voltage to the vehicle's complete electrical system.
The module monitors the capacitor temperature using a thermistor. It also monitors the voltage of the stop/start capacitor as well as the voltage between the two capacitors in series to ensure proper load balancing and to prevent overcharging. The voltage between the two capacitors should always be one-half the voltage of the total capacitor.
The Stop/Start system can reduce fuel consumption and carbon dioxide (CO2) emissions by up to 5% in mixed driving conditions. In an urban environment and in heavy traffic with frequent stops the savings may increase to as much as 10%.
There are also sophisticated controls in place to help ensure the Stop/Start System does not compromise the needs of either the driver or vehicle. For the engine to shutdown the vehicle must be below 5 km/h (3 MPH). In a vehicle with a manual transmission, the manual transmission must be in neutral and the clutch pedal fully released. To restart, the driver simply depresses the clutch pedal and the enhanced starter motor engages the engine, ready for when first gear is selected. For the engine to shutdown in an automatic transmission, the selector lever must be in position D, and brake pedal depressed. To restart, the driver simply releases the brake pedal and the enhanced starter motor engages the engine. When the engine has been shut down by the Stop/Start System, the tachometer needle will point at the Autostop (500 RPM point) indicating the engine has been shut down by the Stop/Start System.
To ensure neither the needs of the driver or vehicle are compromised the engine will not shut down in the following circumstances:
- Ambient and coolant temperature correlation does not match specified values.
- Ambient temperature is less than -10°C (14°F)
- Battery temperature is less than 0°C (32°F) or greater than 55°C (131°F)
- Driver seat belt is not fastened and the drivers door is not fully closed (not applicable to vehicles in North America)
- Clutch or accelerator pedal is pressed
- HVAC system demand is high
- HVAC defrost has been selected
- Battery charge is low
Likewise the engine will automatically restart if:
- Driver door opened and driver seat belt unbuckled (not applicable to vehicles in North America)
- Engine hood opened
- Battery charge is low
- HVAC demand increases
- Vehicle speed increases
- Brake booster vacuum has been reduced
- Engine coolant temperature is greater than 125°C (257°F)
- Autostopmode turned OFF by driver
- Autostop time exceeded 2 min
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 pump motor to continually circulate the engine coolant through the engine 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 engines internal coolant pump to circulate the engine coolant. The Stop/Start System is automatically activated each time the ignition switch is turned on, although there is an Autostop Switch to disable the system, if the driver so desires.