|Configuration of the StARS + X system with start-stop and regenerative braking. Click to enlarge.
Valeo is developing a supercapacitor-based extension to its award-winning StARS stop-start system (earlier post) to support regenerative braking and thus enable a greater reduction in fuel consumption than is possible with the stop-start system alone.
By itself, the start-stop system delivers a reduction in fuel consumption of 4-5% (although Valeo has measured reductions of up to 25% in real-world testing in congested traffic in Paris). The new StARS + X system with regenerative braking can deliver a 10-15% reduction, according to Valeo.
The StARS + X system uses a slightly different architecture with different motor for starting and regen, and support for voltage between 14V and 30V. The floating voltage enables extended torque for diesel or large engine cold cranking, 4 kW generation for regenerative braking and extra power supplies for peak loads.
Valeo is working with multiple supercapacitor technologies with capacitance values of 200 farads with nominal voltage between 20V and 30V, depending upon the technology. The company is using different size powerpacks—12-, 10- and 6-cell—to support a range of powertrains and internal space constraints.
The powerpacks must last for the lifetime of the vehicle, deliver reliability in the harsh thermal environment created by being close to the 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 in partnership with INRETS (French National Institute for Transport and Safety Research) on the new systems is currently underway. The main goal of the current testing is to observe the failure of the cells.