Super Sports Hybrid From Porsche
Porsche sprang a major surprise on the commentators and the crowds at the 2010
Geneva auto show with its 918 Spyder. Few had anticipated a new design from the
elite German sports car maker, just recently drawn into the orbit of Europe’s
leading automaker, the Volkswagen group. Fewer still could believe that a car
with such racing allure and strong links to the Carrera GT super car could pack
such a powerful punch yet promise astonishing fuel economy and a
headline-grabbing CO2 output of just 70 g/km.
The simple figures do indeed seem scarcely credible, even for a lightweight, two-seater sports car: an installed horsepower total of well over 700, giving 0-100 km/h acceleration in 3.2 seconds; a top speed of over 320 km/h, and the proven ability to lap the challenging Nurburgring in seven and a half minutes – even faster than the V-10 engine Carrera GT. Most difficult of all to grasp, however, is the claim that the 918 Spyder’s CO2 emissions, when tested on the standard EU cycle, are just 70 g/km.
The secret, as is so often the case in contemporary design studies, lies in the judicious use of electric power and energy recuperation, and in the clever strategies for blending the most appropriate types of power to achieve a wide spread of seemingly incompatible performance targets.
For outright against-the-clock acceleration in an open-road or racetrack environment, the 3.4 liter gasoline V-8 mounted behind the driver and powering the rear wheels through Porsche’s own seven-speed PDK dual clutch transmission provides a generous 500 hp – more than enough to provide the light (1490 kg) Spyder with startling acceleration and top speed.
However, this power train on its own would not be able to yield the low consumption values that next-generation sports cars will require in order to regain social acceptability. Some form of hybridization or electric drive is now de rigueur if a top premium model is to pass with a clear conscience through congested cities and quiet villages.
Sports car expert Porsche’s method for adding this hybrid dimension has been to configure its electrification to do double duty – not just saving tailpipe emissions, but boosting performance beyond what would be possible with exclusively gasoline power. This latter point will not be lost on those wealthy enthusiasts able to afford extreme sports cars. Indeed, if the thinking behind the 918 finds its way into Porsche’s core production models, this car could be seen as emblematic of a new breed of sports cars that are lean, intelligent, and friendly in their disposition – in contrast to the brute force twelve- and sixteen-cylinder super cars that currently exemplify high performance.
Electric motors with a combined output of 160 kW (218 hp) handle power delivery from the lithium ion battery packaged between the cockpit and the mid-mounted engine. The rear motor is packaged inside the Porsche PDK dual clutch transmission feeding power to the rear wheels, in a clear indication that hybridization of Porsche sports cars with the same rear engine and DCT layout is a real possibility.
Porsche has given only sketchy details of the motor unit powering the front axle, stating only that it has a fixed gear ratio. The implication is that it must be able to cover a wide rpm span, but no mention is made of a differential, which would be essential if a single motor drove both wheels. More likely, perhaps, is that the electric drive unit conceals twin motors, just as on the 911 GT3 Hybrid, allowing the driveshafts to run at different speeds when negotiating a corner.
Of equal interest to the mechanical setup is the control system overseeing its operation. Four different modes are available to the driver, selected via a button on the steering wheel. E-Drive runs the 918 under pure battery power, enjoying zero emissions and a range of 25 km. Hybrid mode brings the gasoline engine as well as the electric motors into play and, says Porsche, offers a range of characteristics “... from particularly fuel efficient all the way to extra powerful.”
Sport Hybrid mode pushes the emphasis towards performance, bringing torque vectoring and a rearward bias to the drive to improve handling dynamics. Finally, in Race Hybrid mode, finally, all systems focus on maximum performance. There is even an E-boost capability to feed in extra electrical power for push-to-pass overtaking maneuvers on the track.
If Porsche’s claims are borne out – and the company has a good history of delivering on what it promises -- the 918 Spyder will come to be seen as the ambassador for a fresh generation of eco-conscious extreme sports cars making intelligent use of hybrid power and advanced transmission technology to provide the best of both worlds.
| Porsche 918 Spyder Concept | |
|---|---|
| Gasoline engine | 3.4 liter V-8, 500 hp |
| Electric motors | 160 kW total |
| Transmission | Porsche PDK dual clutch 7-speed |
| Drive | Front: electric Rear: electric, gasoline |
| Acceleration 0-100 km/h | 3.2 sec |
| Maximum speed | 320+ km/h |
| CO2 emissions, NEDC cycle | 70 g/km |
| Availability | Show concept only |
Story Filed: 5/03/2010
By Tony Lewin, managing editor DCTfacts.com