Valeo StARS + X Hybrid Start-Stop System

Micro hybrids with only engine stop-start capability can reduce fuel consumption by 4 to 5 percent, according to the Valeo Group, which offers its Starter-Alternator Reversible System (StARS). Now that the company is adding a regenerative braking capability, StARS +X, could potentially increase this to a 10 to 15 percent reduction. Valeo has measured reductions of up to 25 percent in real-world testing in congested Paris traffic.

The belt-driven StARS, as used on the European-market Citroen C2 and C3 Stop&Start, turns the engine off as the vehicle comes to a stop, and almost silently restarts the engine in just 400 milliseconds when a driver takes his foot off the brake pedal. The system features a reversible alternator that acts as a standard alternator.  It is driven by the engine to charge the battery and as a starter motor driven by the battery. A driver can deactivate the system via a button on the dash. The StARS system delivers about 42 mpg U.S. mpg on a combined cycle and reduces CO2 emissions by about 10 percent compared to a regular gasoline C2.

Regenerative braking capability in the StARS + X is achieved with the aid of supercapacitors that store electrical energy recovered during braking. Valeo is investigating different size supercapacitor powerpacks, including 6, 10, and 12 cell variants, to support a range of powertrains and internal space constraints. These powerpacks must last for the lifetime of the vehicle, be reliable in the harsh engine compartment environment near to the hot engine, and be safe and environmentally friendly. Valeo is specifying 600,000 stop-starts, 1 million regeneration events, and 200,000 boost events for the system.

Testing is being conducted in partnership with INRETS, the French National Institute for Transport and Safety Research.