Stop-Start Hybrid
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Stop/Start "hybrids" are not true hybrids since electricity from the battery is not used to propel the vehicle. However, the Stop/Start feature is an important energy-saving advancement towards greater fuel economy, not only for conventional gasoline and diesel powered vehicles, but also mild hybrid vehicles.
Stop/Start technology conserves energy by shutting off the engine (gasoline or diesel fueled) when the vehicle is at rest. This mainly occurs at traffic lights and railway crossings, although smarter systems will enable this technology to work in "stop and go" commuting scenarios. When the traffic light goes green or the train passes, Stop/Start systems automatically re-start when the driver lifts off the brake pedal (with the transmission still in forward gear) or when the accelerator pedal is pushed downward.
European market BMWs will be equipped with a stop-start feature that turns off their gasoline or diesel engined vehicles when the car comes to a stop sometime around 2007. The same system will be available for European market MINI Coopers. BMW's Stop/Start uses a specially modified starter, used in place of a belt-driven alternator, combined with a heavy duty battery. An intelligent belt tensioner enables dual Stop/Start and generator modes of operation. The new alternator system BMW has called Brake Energy Recuperation makes better use of the energy generated by the car's charging system. When the driver applies the brakes, a sensor alerts the specialized starter to produce a short blast of electricity to bring the battery up to a 90 percent charge. When the driver accelerates, the specialized starter is allowed to spin (no drag placed on the engine). When the vehicle comes to a standstill at traffic lights or in congestion, the combustion engine can be switched off and then restarted automatically and almost imperceptibly. The engine restarts immediately when the driver lifts their foot off the brake pedal. BMW calls this offering a "micro hybrid". Utilizing the existing 14-volt on-board power supply, in conjunction with an energy management system, this can yield fuel savings of up to six percent based on the New European Driving Cycle (NEDC).
Citroën launched the first mass-market vehicle Stop and Start technology. The C3 Stop & Start combined an automated gearbox and an electronically controlled reversible alternator for the 2005 model year. When the driver applies the brakes to stop the car, the engine cuts out while the car makes a complete stop. A green "eco" indicator appears on the instrument cluster. The engine remains on standby until the driver keeps a foot on the brake pedal. After the brake pedal is released, the engine starts again automatically and if the accelerator pedal gets pressed down, the clutch engages on the SensoDrive® gearbox. The system can even be deactivated at any time by switching on the "eco off" button on the dash.
The strong suit of this Start/Stop "hybrid" system technology is urban cycle fuel economy. Fuel efficiency can be improved by as much as 8%-10%, depending on the vehicle and system. In practice, far greater savings are possible when driving in stop and go urban traffic. The feature is being evaluated for North America, although Stop/Start may not be suitable for hot climates, since the air conditioning compressor (in conventional engined cars) stops working once the engine ignition is off.
