For a jointly developed starter-alternator that resulted in 55 patent applications, Valeo and PSA Peugeot Citroën received the first "Engineers of the Year” in the sustainable development category. The award was bestowed by “Usine Nouvelle,” “Industries et Technologies,” and the National Council of French Engineers and Scientists (CNSIF).
PSA Peugeot Citroën's Automotive Research and Innovation Department began work in October 1998 on environmentally friendly powertrain technologies. Tests demonstrated that in built-up areas, vehicles are stationary for an average of 35 percent of driving time. Switching a motor to standby mode when the vehicle is at a standstill is effective in reducing CO2 emissions, but previous efforts to develop such a capability resulted in unacceptably slow engine re-start times, excessive starter noise, and insufficient reliability.
Valeo, which had supplied alternators and starters to the PSA Peugeot Citroën Group, proposed a belt-driven reversible starter-alternator that uses the alternator to start the engine and thus eliminates the need for a conventional starter motor.
A collaborative effort by the two firms involving 60 people resulted in a system PSA Peugeot Citroën calls Stop & Start and Valeo calls StARS. Valeo designed the electrical machine and the power and control electronics, while PSA Peugeot Citroën focused on control strategies, human-machine interfaces and finding a belt-driven solution to link the alternator and the crankshaft.
Design goals included noise- and vibration-free engine starting and stopping; instant engine re-start at the slightest signal from the driver; optimized reductions in fuel consumption and CO2 emissions, and automated control of the Stop & Start function for driver-friendly operation.
Valeo Chairman and Chief Executive Officer Thierry Morin says the Stop & Start function turns the engine off automatically when the vehicle comes to a standstill and restarts the engine instantly and silently as soon as the driver releases the brake pedal or accelerates. Drivers are not required to alter their usual driving habits. Depending on the vehicle and the engine, the Stop & Start system provides fuel savings of around 10 percent for city driving and six percent in standard combined cycles.
Deployed in vehicles with a 12V power network and a conventional battery, the function uses electronics to allow the alternator to take over the functions of the starter motor. In inverter mode, the reversible starter-alternator transforms 12V direct current from the battery into three-phase current to supply the alternator-starter motor. In rectifier mode, the starter-alternator generates the electricity required for the vehicle, providing intelligent control of the drain current, outputs as high as 180 amps, and an efficiency gain of up to 15 percent, according to Valeo.
The reversible starter-alternator's electronic management module communicates with all other body controllers in the vehicle with no modifications necessary. The engine starts silently thanks to the accessory belt, which is enabled by a special material and hydraulic damping of the tensioner.
Gasoline and diesel engine fuel injection strategies developed for Stop & Start ensure that restart is instantaneous (400 milliseconds, i.e. twice as fast as a conventional starter motor) and pollution-free, the latter benefit due to an accelerated temperature rise in catalytic converters, particle filters, and other pollution control devices.
The Citroën C3 Stop & Start is the first vehicle to be equipped with the StARS system. Valeo has begun development efforts with Ford, Hyundai and other automakers. This system will be used for larger engines in the short term, according to Morin, but will become more compact and offer new functions leading to further fuel savings and even lower emissions.
Morin notes that in addition to the improved fuel consumption and lower CO2 emissions provided by automatic engine cut-off, drivers and the environment both benefit from total silence whenever vehicles are at a standstill.