The Citroen C3 is first the European production vehicle to offer Stop-Start via a 14-volt belt-driven starter-alternator in a market that is becoming increasingly concerned with CO2 emissions and fuel economy. The beauty of the starter-alternator is that it completely eliminates the need for a starter motor (in smaller vehicles) by virtue of a dual-function alternator-type device.

The starter-alternator is similar in appearance to an alternator, and supplier Valeo has developed the concept over a number years by adding power electronics to enable it to function as both an alternator and a starter motor via the same ancillary drive belt. Starting is much quieter and quicker (<0.4mS in normal conditions) and this enables the engine to be shut down and restarted automatically whenever the vehicle is temporarily stationary (more than a third of the time in Paris traffic). Citroen claims overall fuel economy improvements of 6-10%, depending on the drive cycle.
 
PSA Peugeot Citroen will extend Stop-Start technology to other group models, including the Peugeot brand, and roll-out is expected to be so rapid that Jean-Marie Folz says over 50,000 such vehicles will be on the road by the end of 2005. In all cases, the company will offer the technology in conjunction with its Sensodrive automated manual gearbox for maximum ease of driving; "combining it with the Sensodrive gearbox makes it very easy to use and very convenient, with good driveability in every application," explains PSA spokesman Jean-Francois Huere.

First applications will be with a 1.4 or 1.6 litre gasoline engine but the group has also engineered Stop-Start to suit its other Sensodrive option; the 1.4 litre HDi diesel engine.

Valeo's starter-alternator, with one-piece connector for the three-phase electronics

Valeo's winning of this contract and PSA's application is good news for starter-alternator technology in general. Suppliers such as Delphi, Denso and Visteon have developed their own versions of the technology (including 42-volt versions). Already Denso has its 42-volt belt starter-alternator in production, but only for the Japanese-market Crown luxury saloon, chiefly for its Stop-Start and higher generating capacity.

Visteon previewed its proof-of-concept SpeedStart12 starter-alternator in London late last year on a 1.8 litre Ford Mondeo. The Visteon system is a more costly, water-cooled, device, which, unlike Valeo's current system, incorporates its power electronics within the body of the device. The output of SpeedStart12 is also greater, with up to 3.0kW of electrical generating capacity and 2.1kW of hot-starting power - good enough to start 3.0 litre gasoline engines. The Visteon unit's efficiency is high in comparison to conventional alternator designs, explains spokesman Martin West, due to its advanced power electronics; "we have in excess of 80% average efficiency, and we're proving that on the test bench as well." Visteon is currently road-testing development versions of SpeedStart12 in a larger 2.0 litre European vehicle, and the company estimates that its system will see its first OEM application in 2007.

Visteon's SpeedStart12starter-alternator uses a drive-belt co-developed with Gates

Gilles Michel, PSA Peugeot Citroen's Executive Vice president, Platforms, Engineering and Purchasing, explains that Stop-Start is an example of "a first level hybrid available on a large scale." More advanced versions of the belt starter-alternator will in future also provide some degree of engine torque assist, allowing for mild hybrid operation and possibly brake energy recovery. Delphi, which initially planned to produce belt-drive starter-alternators, has changed its plan, instead now acting as a consultant on the technology, rather than producing the devices itself; "Delphi does not consider itself to be acting in the generator (alternator) business, but will still position itself in the Stop-Start products as an electronics and systems expert. On a case-to-case base, we will position ourselves either as a Tier I supplier or as a Tier 2," says a spokesman. Essentially, this means that Delphi is no longer a manufacturer of generators but does have the software and systems expertise to implement Stop-Start.

Mark Wilkinson