While the automotive industry remains fixated on 3.0-L cars (3.0 L meaning fuel consumption of 3.0 L/100 km), Bosch is focusing on 5.0 liters—which describes the package-volume target for a power electronics unit developed by the company for a production parallel-hybrid vehicle.
Bosch's power electronics unit in the 2011 Porsche Cayenne S and Volkswagen Touareg parallel hybrids consumes 10 L of package volume, which itself is 33% smaller than previous units, company engineers claim. It has done so without compromising performance.
“Our aim is to get the next-generation version down to 5.0 liters,” said Matthias Küsell, Bosch’s Head of Development and Customer Projects, Hybrid and Electric Vehicles. The power electronics, which include an inverter, are a core component that provide an interface between the vehicle's high-voltage electric drive and its 12-V electrical system.
For the new Porsche and VW models, Bosch supplies the power electronics, electric motor, and the Motronic control unit. The Motronic ECU governs actuation of the electric motor, the gasoline engine, or the two in parallel. Bosch also supplies an integrated motor generator (IMG).
The liquid-cooled electric motor is rated at 34 kW and 300 N·m (221 lb·ft) and has a separate clutch. The hybrid module is positioned between the vehicles' supercharged 3.0-L V6 rated at 245 kW (328 hp) and 440 N·m (324 lb·ft) and Aisin-supplied eight-speed automatic transmission used by both brands. The module’s diameter and length measure 30 x 14.5 cm (11.8 x 5.7 in), respectively.
Both Porsche and VW hybrids can cruise at 50-60 km/h (31-37 mph) on electric power only, the companies claim. A Sanyo 288-V nickel-metal hydride (NiMH) battery with a capacity of 1.7 kW·h is fitted.
Bosch states that lifting off the accelerator pedal at speeds up to about 160 km/h (99 mph) activates “sailing mode”—the ICE shuts down while all necessary systems are maintained. When braking, the hybrid control unit monitors brake pedal pressure to decide what braking torque should be electrically set by the IMG; ABS and electronic stability program (ESP) always take precedent.
When necessary for maximum acceleration, a power-boost mode enhances total output to 279 kW (374 hp) and 580 N·m (428 lb·ft).
Claimed EU cycle fuel consumption is 8.2 L/100 km and CO2 emissions of 193 g/km. The cars meet ULEV 2 and Euro5 standards.
As usual with hybrid vehicles, Bosch faced the need to achieve acceptably smooth transition between electric, hybrid, and ICE power. To do so, the control unit receives data from the ICE, electric motor, battery, clutch, and other components, explained Küsell.
The unit uses the data flow to analyze and control powertrain interaction, with an adaptive clutch operating to smooth transitions. Its ability to ensure electric motor and ICE are turning at the same speed when transferring torque is a core aspect of parallel-hybrid technology.
An additional CAN bus interface is used to exchange data with relevant hybrid components, including the rate of individual injections of fuel.