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Volkswagen Group and Porsche are preparing hybrid SUVs for next year. The first generation of the parallel-hybrid drivetrains will use 3.6-litre gasoline direct injection engines, electric motors and nickel metal hydride batteries to boost efficiency by 15 per cent.

The VW Touareg, Audi Q7 and Porsche Cayenne are based on the same platform. The OEMs worked together on the basic system with suppliers Bosch and Continental, but engineers are carrying out application engineering for the three vehicles independently.

The SUVs will be the OEMs’ first full hybrids. Their size makes packaging easier. As the size of the systems reduces, applications in smaller cars are likely.

The four-wheel drive vehicles’ improved fuel economy should also be good marketing as pressure on the German OEMs to cut CO2 emissions continues. The Porsche Cayenne will achieve 9.8l/100km, instead of 12.9l/100km in the standard 3.6-litre version.

The hybrid Audi Q7 should do slightly better. Audi powertrain electronics manager Josef Bast said: “It currently achieves fuel economy of 9.8l/100km; Audi engineers hope to improve the fuel consumption slightly.”

The standard version achieves 12.7l/100km.

The V6 has an output of 206kW (280hp) and peak torque of 375Nm. The electric motor sits between the engine and the torque converter. It adds up to 285Nm of extra torque and 34kW of power. It measures 330mm and is 55mm long and the complete module weighs 40kg.

An electrically actuated clutch links the motor with the engine, so the car can drive with batteries, engine or both. A lot of Bast’s work is to ensure the transition between the modes is smooth. “We have to make sure that customers don’t feel any hesitation or change in acceleration,” said Bast.

Audi does this by briefly opening the torque converter lockup clutch, adapting the clutch point and increasing the motor’s torque.

The 38kW battery pack sits in the spare wheel well. It weighs 69kg and measures 347mm x 633mm x 291mm. It comprises 240 cells generating 288 volts. “Our engineering goal is for it to last more than ten years and 300,000km,” said Bast.

A lithium ion pack would weigh around 20 per cent less, but Bast does not expect Audi to introduce the technology before 2010.

The SUVs have a separate climate control system for the rear seats that also cools the battery – an important part of the pack’s durability. The battery’s internal resistance generates heat when it charges and discharges. If this is not dissipated, it affects the cells’ chemical makeup.

Three driving modes are possible. The V6 and the motor can work on their own or the vehicle can combine both. The motor can be used for speeds up to 50km/h. The battery can drive the SUV for up to 2km in pure electric mode.