PARIS – PSA Peugeot Citroen plans to sell 1 million vehicles equipped with its new stop/start system attached to its 1.4L and 1.6L diesels in the next 30 months.

Christian Chapelle, managing director-powertrains and chassis, says the auto maker is the first to use the fan belt and a diesel engine in a stop/start system. The result is a silent, 400 millisecond restart that drivers won’t notice.

PSA spent €300 million ($360 million) to develop the stop/start system, part of its €1 billion ($1.2 billion) investment in remaking its engines to meet the Euro 5 emission rules.

The auto maker’s stop/start diesel, called e-HDi, will cut carbon-dioxide emissions by 5 g/km in the European combined driving cycle. Because cars fitted with stop/start also will have Michelin SA low-rolling resistance tires, low viscosity oil and optimized gear ratios, the total gain for the customer will be 10 g/km.

A vehicle dropping from 129 g/km to 119 g/km would boost mileage from 49 mpg to 53 mpg (4.8 L/100 km to 4.4 L/100 km).

Customers will pay “several hundred euros more” for the stop/start system, says Jean-Marc Gales, managing director of the Peugeot and Citroen brands.

Citroen will launch the technology this fall in the C4, C4 Picasso and C5, and Peugeot will apply the system next year in the 308 and the replacement for the 407.

Progressively, stop/start will be offered across PSA’s range of vehicles. In 2013, as the Euro 6 rules approach, it will be added to the 2.0L diesel and gasoline engines.

Fuel savings will be as high as 15% in city driving, where cars are stopped at lights or in traffic jams 30% of the time, Gales says.

The energy used to start a diesel is the same used to idle for 3 seconds, so fuel is saved every time the engine is stopped more than 3 seconds. PSA says the 30% figure and that of an average stop at 15 seconds are based on studies in Paris.

Good mileage is a key element of PSA’s marketing approach, and last year the auto maker sold 757,000 cars emitting 120 g/km or less. The goal for 2012 is 1 million, Gales says, with 30% of the company’s diesels having e-HDi engines.

Citroen first introduced stop/start in Europe in 2004 on1.4L gasoline engines. The auto maker chose to put the second generation on its most-popular diesels for the maximum effect in lowering its corporate average fuel economy, Chapelle says.

PSA and Fiat Automobiles SpA have the best averages in Europe now, but PSA’s cars are the most-efficient when average weight is considered. To meet its goal of 128 g/km in 2015, PSA has to show an 8% improvement from its 2008 average, the smallest change required of any auto maker in Europe.

The stop/start system will be available on PSA’s manual and automated-manual transmissions.

The control systems for the two are somewhat different. The strategy for the roboticized semiautomatic automated-manual transmissions is based on maximum CO2 savings, while with the manuals it’s aimed at being imperceptible for drivers.

In the semiautomatic, the engine is stopped only when deceleration reaches 5 mph (8 km/h) and the driver is braking. A control unit for the transmission decides when to switch gears downward, as cutting out the engine at higher speeds could cause problems.

Stop/start with the manual kicks in when the driver pushes in the clutch or puts the gearshift in neutral as the car decelerates toward a stoplight, allowing the engine to stop at 12 mph (20 km/h). If the driver is coasting downhill in neutral, or with the clutch in, the engine will restart at 35 mph (22 km/h).

The software also considers other situations. Hard braking that requires a lot of hydraulic pressure will restart the engine. In deceleration at high speeds where the engine is effectively braking the car, the alternator produces energy to recharge the battery.

Valeo SA developed the alternator-motor at the heart of the system. It delivers 3 hp (2.2 kW) of energy to turn the engine over and restart it in 0.4 seconds.

The supplier furnished the first-generation system to Citroen, and for the second generation, it has packaged the power electronics and the electronic control unit on the alternator itself.

Valeo received €140 million ($169 million) from the French government to develop this technology and another that would operate valves with electricity, instead of mechanically. A company spokesman declines to say how much of that was devoted to the stop/start system.

PSA deployed 500 engineers to work on the stop/start system over 36 months of development and filed 30 patents protecting its new technologies.

The auto maker says its system is good for 600,000 restarts, compared with competitors using a beefed-up starter good for only 200,000 to 300,000 restarts. An ordinary starter is designed for 50,000 to 60,000 starts during the typical lifetime of a car.

PSA says Volkswagen AG, Toyota Motor Corp., Fiat, BMW AG, Kia Motors Corp., Mazda Motor Corp. and the Land Rover brand all have chosen the more durable starter motors. Only Daimler AG uses a similar method based on an alternator and fan belt.

PSA’s system starts a diesel twice as fast as the initial start with a key, the auto maker says, and 40% faster than a beefed-up starter. It also is quieter and causes less vibration than the starter approach.

That’s because turning the engine over with the fan belt, furnished by Gates Corp., is smoother than turning over the flywheel with the starter motor.

Several elements on the 1.4L and 1.6L engines were adapted for the stop/start system. The turbocharger requires specific lubrication; the fuel pump for the common rail is reinforced; and the dual-mass flywheel is adapted to limit noise, vibration and harshness during stop/start transitions.

The 12-volt lead-acid battery holds 70 Ah of electricity, but alone it would not provide the energy PSA required. The power to turn over the diesel was found by adding a 5-volt super capacitor from Continental AG, and the battery could be designed for its energy capacity instead of power output.

Transferring responsibility for restarting to the capacitors also means the 12-volt network in the car is not affected by the restarts. Typically, cranking a cold engine, for example, dims the headlights because of the energy drained off to the starter.

PSA’s stop/start system can be used from -13° F to +85º F (-5º C to +30º C). The engine stays on when the engine bay is colder or hotter, which helps keep the interior comfortable by warming it faster or keeping the air conditioner on.