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Power Train
Bosch full hybrid concept in detail
June 08, 2010 | Christoph Hammerschmidt | 222900883
These days, the hybrid versions of the Volkswagen
Touareg and Porsche Cayenne S launch serial
production. Developed in close cooperation with
electronics supplier Robert Bosch GmbH, they are
the world's first parallel full hybrids to enter series
production. Here is an in-depth article on the HEV
technology implemented in these vehicles.
Modern control technology manages the interaction between the vehicle's internal
combustion engine and electric motor without requiring a mechanical power splitting
device. “One of the main advantages of our system lies in its simple design,” says Oliver
Schlesiger. As a Bosch customer project manager, the engineer has been working on a
new interpretation of the hybrid drive since 2007. His two customers, Volkswagen and
Porsche, launched the result in April 2010. The VW Touareg Hybrid and the Porsche
Cayenne S Hybrid are the world's first parallel full hybrids – and Bosch has contributed
the key hybrid drive components.
Hybrid vehicles basically combine an internal combustion engine with an electric motor.
The Volkswagen Touareg and the Porsche Cayenne are full hybrids – as opposed to
mild hybrids – which means they can be driven short distances on electric power alone.
By choosing to create a common SUV platform, the two automakers have chosen a
parallel hybrid system from Bosch – and that has made a whole world of difference. It
essentially involves replacing run-of-the-mill mechanics with intelligence: instead of
using a planetary gear unit as a power splitting device, control technology is employed
to split the torque between the electric motor and the internal combustion engine. That
cuts down costs and complexity. “Another key issue is the fact that our electric motor is
practically self-sufficient. You can drive on electric power alone at any time by simply
disengaging the clutch and shutting down the combustion engine,” Schlesiger says.
Smooth engagement is especially important when the electric motor hands over to the
internal combustion engine, when both sources work together, or when the combustion
motor temporarily shuts down. In the parallel full hybrids developed by Volkswagen and
Porsche, this is all performed automatically. “The system works on the basis of how
much torque the driver is asking for,” says Dr. Matthias Küsell, head of hybrid
development at Bosch. In other words, the control unit interprets the driver's wishes by
monitoring the pressure on the gas pedal. Depending on whether the driver is gently
accelerating in city traffic, picking up speed on a clear road, going full speed down an
open road or freeway, or simply sitting back and cruising along, the hybrid control unit
translates the pressure applied to the gas pedal into electric-powered, hybrid, or
combustion engine-powered driving. At the same time, it monitors the pressure applied
to the brake pedal to determine how much brake torque should be set by the electric
motor. "
Drivers would quickly get frustrated with hybrid cars if the switch between the different
drive systems was noticeable. So jolting and jarring are definitely a no-no. But how do
engineers manage to synchronize the Cayenne and Touareg V6 engine with the Bosch
electric motor down to a precision of just a few milliseconds? More to the point: how do
the developers get a 245-kilowatt (333-hp) direct injection engine providing up to 440
Newton meters of torque to seamlessly blend together with the electric motor's rating of
34 kilowatts (47 hp) and 300 Newton meters? The trick lies in measuring, controlling,
and regulating – in other words, in maintaining perfect interaction between sensor
systems, control technology, and actuators.
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