2011 Volkswagen Touareg Hybrid

Press release

With its low combined fuel consumption of 8.2 l/100 km, the all-wheel drive Touareg Hybrid sets new standards among genuine SUVs with petrol engines. CO2 emissions are
equally low: 193 g/km. The Hybrid drive, the new top engine choice, combines the power of a classic eight-cylinder engine with the fuel economy of a six or four-cylinder engine. Therefore, it is replacing the previous V8 petrol engines in Europe and America, continuing the success ful Volkswagen strategy of downsizing. Naturally, the Touareg Hybrid fulfils requirements of the Euro-5 emissions standard in Europe and ULEV2 in the USA. The SUV reaches a top speed of 240 km/h and accelerates to 100 km/h in just 6.5 seconds.

The drive unit of the Touareg Hybrid primarily consists of a supercharged V6 TSI (direct-injection petrol engine with 245 kW /333 PS), an 8-speed automatic transmission customised for hybrid, towing vehicle and off-road use, including torque converter, final drive units and centre differential, as well as the Hybrid Module integrated between the internal combustion engine and automatic transmission. This module – the “heart of the hybrid” – contains an E-motor (34.3 kW /46 PS) and a disengagement clutch. The Hybrid Module has a diameter of 400 millimetres, is only 145 millimetres long and weighs just 55 kilograms.

When the V6 TSI and E-motor work simultaneously at full power (boos ting), a system power output of up to 279 kW /380 PS and maximum torque of 580 Newton-metres are delivered.

The drive energy for the E-motor is stored in a Nickel Metal-Hydride (Ni-MH) battery at the rear of the Touareg, stated more precisely in the spare wheel recess. With its nominal voltage of 288 Volt, the battery has an energy capacity of 1.7 kilowatt-hours (kWh) and a peak output power of 38 kW. The energy stored in the battery is sufficient to drive the Touareg over a distance of about two kilometres and up to a speed of 50 km/h in pure electric mode. The interplay of the individual system components is “co-ordinated” by a Hybrid Manager.

Parallel hybrid ideal for SUV use

Volkswagen deliberately chose a parallel hybrid drive configuration for the Touareg. In contrast to other possible hybrid systems, it assures excel lent off-road performance and unlimited continuous climbing abili ty. In addition, with its maximum trailer payload of up to 3.5 tonnes, the Touareg is also an ideal towing vehicle in the hybrid version. More over, the parallel hybrid is more efficient than alternative hybrid concepts on long-distance and motorway journeys.

Compared to a conventional SUV of the same size and power, the hybrid concept delivers fuel savings of up to 25 percent in city driving. In combined mode driving – a mix of city, highway and motorway drives – development engineers calculate an average saving of 17 percent. Essen tially, four parameters were exploited to achieve this fuel efficien cy on the Touareg Hybrid: Electric driving: Emission-free driving (as described, up to 50 km/h) by pure electric power reduces petrol consumption. In this case, the V6 TSI is not only shut off, but is also disengaged from the 8-speed automatic by a disengagement clutch to avoid drag torque losses.

Coasting: As soon as the driver releases the accelerator pedal, the V6 TSI is disengaged from the transmission. This is even possible at higher speeds (up to 160 km/h), i.e. on the motorway as well. The Touareg “rolls” significantly longer, since drag torque losses are eliminated. When drivers adopt an anticipatory style of driving, this has a direct positive impact on fuel economy.

Regenerative braking: During braking, the E-Motor − now operating as a generator – recovers kinetic energy, which is then stored in the highvoltage battery (NiMH battery).

Stop-Start system: All V6 versions of the new Touareg are equipped with a standard Stop-Start system – and naturally this also includesthe Touareg Hybrid. The Stop-Start system integrated in the powertrain improves fuel economy, especially in urban areas and stop-andgo traffic.

The Hybrid Manager – the brain that directs the drive sources The individual components are networked by a Hybrid Manager. Integra ted in the engine controller, it communicates via the CAN bus lines with units such as the automatic transmission, high-voltage battery and the so-called power electronics. The latter manages the energy flow between the electric motor and the high-voltage battery. Besides a pulse-controlled inverter to control the E-motor, the power electronics also contains a DC/DC converter. It is responsible for supply ing the 12V electrical system from the E-motor or the highvoltage battery.

Depending on the charge state of the battery, vehicle speed and other vehicle-specific parameters, the Hybrid Manager automatically ana lyses and chooses the ideal operating strategy – in fractions of a second.

This operating strategy is a key component of the software for control ling the powertrain. Because it networks the systems to optimise utilisation of the electrical energy available in the battery for maximum possible efficiency. This is anything but trivial. In contrast to the fuel tank, the electrical energy storage device – the battery – is not only discharged while driving; it is charged too. So, optimal operation of the Touareg Hybrid involves many short phases of use and storage of electri cal ener gy and therefore continually alternating operating modes.

E-motor brings the V6 TSI back in motion

Whenever the V6 TSI is not needed to operate the Touareg, the disengagement clutch in the Hybrid Module disengages, and the motor is shut off – without the driver noticing. If the operating mode is switched again, and the V6 TSI is then re-started, this too is imper ceptible to the driver. And that is how it should be. Because the quali ty with which the sixcylinder is started during the drive affects the impression of the overall vehicle’s comfort. Essentially, the operating strategy’s engine start request is based on feedback from electric driving or braking regeneration. The control system then initiates – in fractions of a second – an energy flow sequence in which the re-start is coordinated as a kind of drive technology “handshake” between the V6 TSI, disengagement clutch, E-motor and transmission.

And this is how the V6 is re-started: If there is an engine start request, the torque converter lockup clutch of the automatic is made to slip, and the speed of the E-motor is increased to the target value specified by the transmission control module. Only then does the engine controller get the enable to activate the disengagement clutch. As the clutch starts to engage, the V6 TSI is “push started” by the E-motor and is started by an enable of fuel injection and ignition. Then the disengagement clutch is disengaged again, so that the combustion engine can run up to its target speed nearly load-free. The E-motor’s torque is increased to the momentary torque transmitted by the disengagement clutch during the “push start” process, and after the combustion engine is started, E- motor torque is reduced as the combustion engine’s torque rises. This is how the transmission’s input torque and associated wheel torque are maintained at the target value desired by the driver. When the speeds of the E-motor and V6 TSI match, the disengagement clutch and then the torque converter lockup clutch are re-engaged.

This starting sequence, always run the same way, can now be scaled between a comfort-oriented and dynamics-oriented range by the Hybrid Manager, which varies the duration of the individual subprocesses. This is how the different driver inputs − detected from accelera tor pedal activations − are put into effect.

Kinetic energy is ideal for charging the battery

Incidentally, the recovery of braking energy – or regenerative braking – represents one of the best types of battery charging in terms of its effect on overall fuel economy. It is even more energy-efficient to directly maximise the kinetic energy of the coasting vehicle by minimising drag torque in the drivetrain. To do this, the V6 TSI is decoupled from the drivetrain and shut off during coasting (or “sailing”) by opening the disengagement clutch, so that its drag losses do not affect the vehicle’s overall efficiency. The energy-generating torque of the E-motor is regula ted to just cover the power needs of auxiliary consumers.

As already mentioned, this coasting mode is essentially possible up to vehicle speeds of 160 km/h. If the driver brakes the Touareg by pressing the brake pedal, the motion of the E-motor, now acting as a generator, is converted into electrical energy and is stored in the highvoltage battery. It is then available for the next acceleration phase. Yet, even the best electronic control of the hybrid components is only effective if the drive sources are operating efficiently. It is the V6 TSI that guarantees this efficiency on the new Touareg Hybrid.

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