Automotive manufacturers are adopting numerous technologies to improve fuel economy and reduce emissions, but most of this effort is concentrated on mass-produced cars. However, as Paul Stevens reports, manufacturers of supercars are now investigating hybrid and other 'green' technologies.
Previously within the Automotive Design section of European Design Engineer we have covered various technologies that are contributing - or have the potential to contribute - to cars that are more environmentally-friendly. Generally these technologies are to be found in small 'city cars' or family cars, which, to be honest, are not always very exciting.
When it comes to supercars, however, manufacturers have remained focused primarily on performance and handling, with lightweight materials such as carbon-fibre composites, titanium and magnesium being used with a view to reducing weight and increasing performance, rather than for cutting greenhouse gas emissions (though this and improved fuel economy are, nevertheless, welcome benefits). Visitors to this year's Geneva Motor Show might, therefore, have been surprised to see two concept supercars with distinctly 'green' credentials. Both Ferrari and Porsche displayed hybrid vehicles and made statements about the use of environmentally-friendly technologies in the future.
After the success of the Ferrari 458 Italia, which is said to have class-leading carbon dioxide emissions 307 g/km and a specific power output 127 HP/litre, Ferrari had two 'green' exhibits. The first of these was a Stop & Start system installed in the Ferrari California, and the second was the Hy-Kers vettura laboratorio (experimental vehicle).
Introduced on the Ferrari California from March 2010, the Stop & Start system cuts fuel consumption and CO2 emissions by 6 per cent to 280 g/km in the ECE + EUDC combined cycle. The system operates in just 230 milliseconds, which is so fast that the driver barely notices the engine restarting.
More striking, however, was the green-painted Hy-Kers vettura laboratorio that aims to reduce CO2 emissions by 35 per cent on the combined cycle (ECE + EUDC). This car is based on the 599 GTB Fiorano but, importantly, the company says that the technology may one day be fitted to all future 8- and 12-cylinder Ferraris. Thanks to ongoing research combined with experience gained in Formula 1, Ferrari believes that the technology enhances the cars' sporty character and driver involvement (Fig. 1).
One of the principle objectives of the project is ensuring that Ferrari will be in a position to comply with future CO2 emissions standards, particularly in terms of the urban cycle. City driving is traditionally where sports cars perform badly in terms of emissions, as their engines are designed for maximum efficiency and performance at high speeds.
Despite its hybrid technology, the Hy-Kers car's weight distribution remains unchanged because the flat lithium-ion batteries are located below the floorpan of the car. Indeed, the car actually benefits from a lower centre of gravity, and interior and luggage space are unaffected.
Maranello's engineers also employed Ferrari's track experience in the design, engineering and manufacture of the innovative electric motor that produces over 100 HP (Ferrari's goal was to offset every kilogramme increase in weight by raising overall power output by 1 HP). In operation, the motor cuts in during acceleration to give an instantaneous torque boost, with torque control being a function of grip, gear and accelerator pedal position. Depending on the vehicle speed and engine load - for example, in town driving - the hybrid system can function as a fully-electric drive train.
Weighing about 40 kg, the compact, three-phase, high-voltage electric motor is coupled to the rear of the dual-clutch, seven-speed F1 transmission. It operates through one of the transmission's two clutches and engages one of the two gearbox primary shafts.
Under braking, the electric drive unit acts as a generator to recharge the batteries. This phase is controlled by a dedicated electronics module that was developed using the knowledge gained in F1 and, as well as managing the power supply and recharging the batteries, the module also powers the engine's ancillaries via a generator mounted on the V12 engine.
Also shown at Geneva was the Porsche 918 Spyder concept car, alongside the company's new Cayenne S Hybrid production car and the 911 GT3 R Hybrid race car. Moreover, since the Geneva unveiling, the Supervisory Board of Porsche has agreed to series development of the 918 Spyder in Weissach (Fig. 2). The Concept Study of the 918 Spyder indicates that CO2 emissions will be just 70 g/km, with fuel consumption being of 3.0 litres per 100 km (94.1 mpg) on the NEDC (New European Driving Cycle), yet acceleration from 0-100 km/h (62 mph) takes just under 3.2 seconds and the top speed is more than 320 km/h (198 mph).
Porsche says its 918 Spyder combines Porsche Intelligent Performance technology, knowledge gained through motorsport, and classic but modern design. The open two-seater is powered by a high-speed V8 developing more than 500 BHP; in addition, electric motors on the front and rear axles deliver a further 218 BHP (160 kW). The V8 engine is positioned in front of the rear axle, with power transmitted to the wheels by a seven-speed, double-clutch transmission that also feeds power from the electric drive system to the rear axle. Electric drive is transmitted to the front wheels via a fixed transmission ratio.
Electrical energy is storied in a liquid-cooled lithium-ion battery positioned behind the passenger cell. Being a 'plug-in' hybrid, the car's battery can be charged from a regular electrical outlet. A regenerative braking system also converts the car's kinetic energy into electrical energy to recharge the battery.
Inside, the driver is presented with three dials for road speed, engine speed and energy management. More striking, however, is the centre console that houses a touch-sensitive surface for control of the car's functions, serving to reduce the number of visible controls and maintain the principle of direct operation (Fig. 3). A button on the steering wheel enables the driver to select from four different running modes, ranging from E-Drive mode in which the car uses electric power alone, though Race Hybrid mode in which the drive systems are focused on performance. There is also a push-to-pass button that provides additional torque from the electric drive system for faster acceleration, referred to by Porsche as E-boosting.
While the 918 Spyder is only due to be manufactured in small numbers, the Cayenne S Hybrid is a production car with a sophisticated parallel full hybrid drive-train that is said to combine the sporting performance of an eight-cylinder engine with the economy of a six-cylinder and a new 'sailing mode' for even lower fuel consumption. The Cayenne also features an Auto Start Stop function. With CO2 emissions of 193 g/km from its 333 HP supercharged 3.0-litre V6 engine, the Cayenne S Hybrid is the cleanest production Porsche. As well as the petrol engine, there is a 34 kW (47 HP) electric motor to help improve economy and performance, with a separator clutch that connects the two drive units.
For rapid acceleration from standstill, the electric motor can provide additional thrust through its 'boosting' effect. Intelligent management of the separator clutch makes for an inconspicuous transition among the hybrid-specific driving modes, and one which is said to be comfortable and quick for the driver. At the same time, the petrol engine may be completely switched off at speeds of up to 156 km/h (97 mph), being fully disengaged from the drive train when no further power is required. In this 'sailing mode' the drag forces exerted by the petrol engine are eliminated to improve fuel consumption.
With a long history in motorsport, it is not surprising that Porsche also used the Geneva Motor Show to display its innovative 911 GT3 R Hybrid. This car's rear-mounted 480 HP petrol engine is supplemented by two 60 kW electric motors powering the front axle. Under braking, the 911 GT3 R Hybrid converts kinetic energy into electrical energy and stores it in a flywheel such that it may be released at the driver's command to boost acceleration.
Not long after the Geneva show, the 911 GT3 R Hybrid was entered in the NŸrburgring 24 Hours race (Fig. 4). Unfortunately the car had to retire after 22 hours and 15 minutes due to a problem with its conventional petrol engine.
Also shown at Geneva was the Lotus Evora 414E Hybrid concept car, a high-performance technology demonstrator with a plug-in series hybrid drive system. This car's range-extended electric drive consists of two electric motors driving each of the rear wheels independently via a single-speed geartrain that is integrated within a common transmission housing, enabling torque vectoring for stability control of the vehicle. The motors each provide 152 kW (204 HP) of power and 400 Nm of torque. Electrical energy is stored in a lithium polymer battery mounted in the centre of the vehicle. Additional range is provided by the 1.2 litre, three-cylinder Lotus Range Extender engine that is optimised for operation at 3500 RPM for generating electric power in series hybrid vehicles (Fig. 5).
Interestingly, the Evora 414E Hybrid also showcases a new technology from Lotus Engineering, namely a sports mode that simulates a seven-speed, paddle-shift transmission that combines driver involvement for a hybrid sports car and optimised energy recuperation. For everyday commuting journeys, up to 35 miles can be travelled using battery power, with the battery being recharged overnight using a conventional domestic mains supply.
Most people reading this are more likely to plug in an electric lawnmower than a hybrid supercar. But it is heartening to know that engineers are striving towards high-performance cars that are cheaper and cleaner to run.