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Engines that combine the best thermal efficiencies of petrol and diesel units mated to non-conventional gearboxes like Volkswagen's dual clutch design - that's what carmakers are working on to help cut CO2 emissions.
The development of hydrogen fuel-cell systems to replace combustion engines has hurried along over the past few years, but the prohibitive cost of setting up hydrogen refuelling stations is a key barrier to the fuel's widespread use.
Petrol and diesel engines - in many cases mated to electric hybrid systems - will be with us for a long time yet. The task facing carmakers is to make more efficient use of both fuels.
VW sees a future in engines that combine the best qualities of petrol and diesel units.
"With the issues of pollution mostly solved, CO2 now dominates the environmental debate," said Jurgen Leohold, VW's executive director for group research. "A critical question is where does the energy come from in the future."
The German carmaker unveiled at a future technology conference in Europe two low-emissions engine projects it sees as energy-savers.
One is a diesel engine that uses the homogenous air-fuel mixing style of a petrol engine. The result, says the company, is a fuel-sipping powertrain with low CO2 and virtually no soot, which is a problem with conventional diesels. VW calls this the "combined combustion system" and says it could be road-ready within a decade.
The other is a petrol engine that can switch to diesel-like compression ignition mode. This strategy is to combine the cleaner exhaust properties of petrol engines and the better fuel economy of diesels. VW calls it "petrol compression ignition". It did not say when the technology would be ready for the road.
Both VW engine concepts offer the promise of higher fuel economy and lower emissions. They would also work with the existing refuelling infrastructure, unlike hydrogen.
But there are drawbacks. The combined combustion system works best with synthetic and biomass fuels, but the production and availability of those fuels is limited - and they are expensive.
The petrol compression ignition engine requires sophisticated controls to closely manage the air-fuel mixture and cylinder temperature.
Also, the diesel mode is available only in low speed and cruising conditions. When the engine reverts to conventional spark-ignition mode for starting and at higher speeds, fuel economy falls.
There is another downside - both engines would be largely limited to the low-speed, low-load driving of a city environment.
Other carmakers are working with engine strategies such as homogeneous combustion, variable valve timing and lift, or adjusting compression ratios. But VW thinks still more gains are possible from existing technology.
The goal of all these efforts is to improve fuel economy and cut emissions while avoiding the cost and weight penalties of hybrid powertrains and fuel cells.
Despite the advanced concepts, VW has developed a hybrid powertrain to go into production within the next couple of years, and is working on a fuel-cell powertrain.
European lawmakers want CO2 emissions cut to 120 grams per kilometre by 2012. Average emissions for Europe's car fleet are currently about 160g/km.
There are only a handful of cars in New Zealand that meet or better 160g/km, among them the Honda Jazz, Fiat Punto, VW Polo and Kia Picanto. Those cars that better 120g/km are petrol/electric hybrids, the Honda Civic and Toyota Prius, and DaimlerChrysler's petrol-powered Smart ForTwo coupe.
Prospects are improving for non-conventional transmissions as engineers search for new ways to boost fuel efficiency and slash CO2 emissions.
Ford and transmission specialist Getrag have developed a transmission called the Powershift System.
"This offers the driver the control of a conventional manual transmission and the smooth and effortless two-pedal operation of an automatic," says Ford of Europe chief Lewis Booth.
The system provides a 10 per cent fuel saving compared with existing automatic transmissions.
The need to combine fuel efficiencies with sportiness and comfort at a competitive cost is giving independent European developers such as Zeroshift, Torotrak and Antonov new opportunities. Many of their ideas are being evaluated by major carmakers.
Several new transmission types are now available. Among them are continuously variable transmissions (CVTs), automated manual transmissions (AMTs) and dual-clutch transmissions (DCTs).
Made by Borg Warner and pioneered by Volkswagen and Audi, the DCT claims to combine the advantages of both the manual's sporty driving and good economy and the auto's smoothness and automatic operation. It is used by VW and Audi in New Zealand. VW calls it DSG - direct shift gearbox.
The six-speed unit is proving so efficient that competitors such as Ford are rushing to launch similar systems. VW will add a seven-speed version for smaller vehicles in some markets.
The British Zeroshift system is essentially a replacement for current synchromesh systems. Zeroshift's interlocking ring mechanisms reduce the effort to shift gears.
This allows low-cost electric actuators to automate the process and means improved acceleration, greater fuel economy and increased comfort, says the company.
Netherlands-based Antonov uses two three-speed planetary gear modules on parallel shafts to provide six effective forward ratios, plus reverse.
It says its efficiency gains over conventional automatics come largely through the use of a mulitplate wet clutch in one of the planetary modules as the launch device.
Antonov claims this clutch and a second unit in the other gearset allows direct switches between any two gears when in automatic mode.
The unit is as small as many five-speed manuals, an advantage for front-drive applications.
Torotrak, based in the north of England, calls its system an infinitely variable transmission. It changes ratios by adjusting where a set of rollers makes contact with two parallel bowl-like plates, or toroids.
One is the driving plate connected to the engine, the other the driven plate leading to the wheels. If the rollers contact the driving plate on its inner radius and the driven plate on its outermost radius, it creates a low gear ratio suitable for starts from rest.
If the rotors then swivel to contact the outside of the driving plate and the inside of the driven plate, it creates a high-gear ratio for cruising.
A special traction fluid ensures the rollers grip the plates strongly without great pressure.
Torotrak claims the ability to create very high ratios allows its demonstrator, a four-wheel-drive Ford Explorer, to cruise at 120km/h with engine speed of 1000rpm.
