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Clever cars cut emissions

By Paul Hudson for CNN

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LONDON, England (CNN) -- If you're stuck in traffic, what's the use of leaving your engine running?

This was the thinking behind a novel approach to achieving the twin aims of reducing fuel use while simultaneously improving air quality on our streets.

Despite the huge strides in petrol and diesel engine efficiency, internal combustion engines are at their most efficient at steady engine speeds. Fine on the open highway, but all but impossible to achieve in urban areas, particularly large towns and cities where mobility is at a premium.

The new, three-door version of the BMW 1-series, on sale next month, employs a feature that cuts the engine when it's not required. The system can be used in conjunction with both petrol and diesel engines.

Co-developed by BMW and German electronics giant Bosch, the Smart Electronic stop-start system cuts the engine in traffic jams or at traffic lights.

Standard on all manual transmission models (except the 130i), the Automatic Start-Stop function automatically switches the engine off when the vehicle is stationary and the driver puts the car into neutral. To restart the driver only need engage the clutch before pulling away in the normal manner. The system can be switched off if required.

"This technology reduces fuel consumption significantly, especially in city center driving," said Dr. Volkmar Denner, member of the Bosch board of management. "The system will help to reduce CO2 emissions further in the future."

The technology has gone into production at BMW from this month on the 1 Series. Bosch supplies the key components for this system, including a starter that has been developed specifically for this application.

Like all the best ideas, it's unobtrusive in operation -- the only time the driver is aware of it is when there's silence. The engine is programmed to switch off whenever the car's battery of sensors detect it's at a halt, then automatically starting it again when the driver depresses the clutch pedal prior to moving away.

And it works. As part of the EC official fuel consumption test that every car on sale in the EU has to undergo, the urban component of the New European Driving Cycle (NEDC), calls for twelve 15-second stops over seven kilometers, replicating an average urban journey.

Tests by Bosch using a route conforming to the NEDC model have found that stopping the engine at these stops reduces fuel consumption and CO2 emissions by up to eight per cent, depending on the vehicle. If the stops last longer, as frequently happens at large junctions, rail crossings etc, the actual savings on CO2 emissions and fuel can be significantly higher.

The technology required the development of a specially designed starter motor, the Smart Starter Motor. Bosch already produces the battery sensor required to detect the battery's current state of charge and to communicate this information via the energy management system.

Incorporating the stop-start technology requires no other change to the BMW's drivetrain or the engine, delivering a substantial cost saving as well as the aforementioned environmental benefits.

Potential drawbacks include an increased risk of starter failure, since it will be working so much more often that a conventional item. That has obviously been taken into account for this application -- there's an improved electric motor and stronger pinion-engaging mechanism. Anyway, the failure rate of modern ancillary components is so low as to be negligible, certainly not outweighing the potential fuel savings to the driver.

But this is not new technology, merely a refinement of existing systems. French manufacturer Citroën was the first to market with this type of set-up, fitted to its C2 and C3 superminis. It discovered during reliability trials that, in typical customer use, cars are standing still 30 per cent of the time. This means that, in addition to improved fuel economy and lower

CO2 emissions, customers and the urban environment will also benefit from the fact that the cars are completely quiet during those periods when they are not moving It is a similar application, with the engine cutting out when the car is stopped and idling (at red traffic lights, for deliveries, in traffic jams, etc), then instantly restarting as soon as the driver touches the accelerator -- Citroën claims it takes place in just 400 milliseconds.

The PSA Peugeot-Citroën system is combined with a clutchless, semi-automatic transmission, unlike the manual BMW. The French had some difficulty overcoming the differences in refinement between petrol and diesel engines, so the production Stop & Start model was only avilable with a petrol engine.

Neverless, the Stop & Start system is claimed to reduce fuel consumption by up to 10 per cent during urban driving, and by six per cent in the standard EU Combined economy cycle.

This technology employs a reversible alternator that acts as a standard alternator one minute (driven by the engine to charge the battery) but, when required, then acts as a starter motor, driven by the battery to re-start the engine. For those who might be suspicious of such technology, the system can be easily deactivated via a button on the dashboard.

BMW is not renowned for its fuel-saving measures, but the new 1-series and revised 5-series saloon (sedan) and estate (wagon) incorporate a number of innovations to improve economy. Brake Energy Regeneration (iGR) uses an Intelligent Alternator Control (IAC) and an Absorbent Glass Mat battery to recycle energy the would be normally lost by braking.

This is achieved as the IAC reduces drag on the engine by only engaging when required to charge the battery when required, whereas a traditional alternator is always drawing power from the engine.

Additionally, the energy generated by the engine on over-run (under braking or descending a hill) is utilized by the IAC to charge the battery. Such is the sophistication of modern electronics that this accounts for a three per cent saving in total fuel usage.

Electric power steering results in a 90 per cent energy saving compared to a conventional mechanical hydraulic steering system. Power assistance is provided by an electric motor that works only when required, such as turning a corner. Other fuel saving measures include to various ancillary devices, such as the air-conditioning power supply being disconnected from the drivetrain when not in use.

Economy is further improved by flaps behind the grille, which close for improved aerodynamic efficiency should the engine require less airflow. The feature also improves cold-starting times.

In the short term, manufacturers will concentrate on things such as this to reduce fuel consumption and CO2 emissions.

There is likely to be wider adoption of bio-fuels grown from sustainable crops, with more efficient computerized transmissions making each gallon last longer.

In the longer term, the hydrogen fuel cell remains the most likely post-fossil fuel motive source.

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