Automotive Intelligence - the web for automotive professionals and car enthusiasts
February 26, 2009
The Cayenne S Hybrid uses a supercharged Audi 3.0-liter V6 engine with Direct Fuel Injection (DFI), 333 horsepower and 324 lb-ft of torque from 2,900 to 5,300 rpm. It is mated with 52-horsepower three-phase synchronous electric motor that produces up to 221 lb-ft of torque and also acts as an alternator, and the combined power units are joined to an eight-speed automatic transmission. Also on board is a 154-lb. no-maintenance 38 kW nickel metal hydride (NiMH) battery. Measuring 13.7" x 24.9" x 11.5", it fits in the spare tire well, thus not compromising luggage capacity.
The Hybrid Manager is the Cayenne S Hybrid's "Heart"
The heart of these technologies is the powerful Hybrid Manager, which requires some 20,000 data parameters to operate (compared to a conventional engine control unit that operates on less than one-third of the data). Since a parallel full hybrid operates in three classic hybrid modes - power generated by the combustion engine and electric motor, power generated by the combustion engine only, and power generated by the electric motor only - the Hybrid Manager's main function is to seamlessly coordinate these modes to deliver optimal performance and efficiency.
With a clutch being the key connection between the combustion engine and the electric motor, the Hybrid Manager has the tough job of providing smooth but quick switching among the three hybrid modes without delay or a noticeable transition felt by the driver and passengers. For example, the Cayenne S Hybrid can motor along solely on electric power for up to 1.2 miles with the combustion engine off, and the Hybrid Manager will fire up the engine as soon as the driver presses the accelerator, increase engine speed appropriately and engage the clutch to transfer power to the transmission without the driver or passengers noticing what is happening. And, it does this within just 300 milliseconds.
When driving with just the combustion engine, the Hybrid Manager also will ensure the engine is operating as efficiently as possible in reference to its load. It switches the electric motor to an alternator mode, so the fuel consumed by the combustion engine not only efficiently powers the Cayenne but also generates electricity that can be 'parked' in the NiMH battery. Finally, when the driver presses the brake pedal, the Hybrid Manager feeds as much energy as possible from the electric motor (again running as an alternator) to the battery.
The Cayenne S Hybrid also has electrically driven ancillary components such as the air conditioning compressor and the power steering pump.
Unlike conventional Cayenne SUVs, the Cayenne S Hybrid uses an eight-speed automatic unit. Porsche engineers added to the conventional transmission oil pump a new electrical drive pump to shift gears smoothly and efficiently also in electric mode. Top speed comes in sixth gear, and the two higher gears serve to further reduce engine speed to enhance fuel economy. Eighth gear, for example, enables the driver to 'coast' along without the combustion engine at speeds up to 86 mph.
Porsche expects the Cayenne S Hybrid to consume less than nine liters of fuel per 100 kilometers in the New European Driving Cycle. EPA fuel economy figures are not yet available.
A similar hybrid system will find its way into the new Porsche Panamera(R) four-door gran turismo sometime following Porsche's fourth model line debut in late summer 2009.
(Feb 20, 2009)