It took Toyota around 25 years to perfect hybrid technology and launch it on a series production car. The technology has since migrated into Toyota’s bigger cars (such as the GS and LS executive saloons) with the electric motors hooked up to beefy V6 and V8 engines.

European carmakers, however, have come up with another plan. They are poised to use simplified hybrid technology to allow them to radically downsize the typical engine in larger cars, improving fuel economy and reducing Co2 emissions and pollution.

Such systems are penciled in for future BMWs (including the next 5-series and 3-series) but Saab sources have told Autocar about the system they are planning for an upcoming version of the new 9-5.

Despite being an executive-size machine, the company is developing a 9-5 powered by a tiny turbocharged 1.4-litre petrol engine. This engine will be backed up during periods of acceleration by an electric motor sandwiched between the engine and transmission.

The electric motor will come on stream when the driver is pulling away or accelerating. The big advantage of an electric motor is that it offers high levels of torque as soon as it starts turning.

However, when the car is cruising the 130bhp 1.4-litre engine has more than adequate power on its own, so the electric motor can act as dynamo, re-charging the on-board battery. Because the hybrid assist is only used in short bursts, the car’s battery pack can quite small and - crucially - relatively cheap.

The upshot should be diesel-matching economy, petrol refinement, lower pollutant levels and impressive acceleration.

Another reason we’ll be seeing more of these systems is because a diesel engine that meets the upcoming EU6 pollution regulations is very expensive to produce because of the pollution-trapping kit required.

Pairing up a cheap, simple small petrol engine with an electric motor/generator and a small battery pack may not be much more expensive. And it should - thanks to the fat torque curve - do a decent impression of a V6 (or even V8) engine.

It will also be very clean in terms of pollution and ideal for the burgeoning number of ‘low-pollution zones’ being rolled out across continental Europe and the US.

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