Jaguar Introduces C-X75 Gas Micro-turbine Extended Range Electric Vehicle Concept
30 September 2010
|The C-X75. Click to enlarge.|
Jaguar has unveiled the C-X75 concept, an extended range electric vehicle that uses twin gas micro-turbines from Bladon Jets to power two switched reluctance generators from SR Drives. (Earlier post.) Traction is provided by four 145 kW (195 bhp), 400 N·m (295 lb-ft) traction motors at each wheel for total drive power of 580 kW/780 bhp.
The plug-in, electric drive supercar has an all-electric range of 110 km (68 miles) plus a potential top speed of 330 km/h (205 mph), acceleration from 0-100 km/h (62 mph) in 3.4 seconds, and 80-145 km/h (50-90 mph) in 2.3 seconds. Active aerodynamics allow for a simple fuselage section that remains stable at very high speeds. The plug-in will produce 28 grams of CO2 per kilometer on the EU test cycle, according to Jaguar.
The mid-mounted 70 kW (94 bhp) micro gas-turbines can generate a combined 140 kW (188 bhp) to charge the batteries and extend the range of the car to 900 km (560 miles)—or, when in Track mode, provide supplementary power directly to the electric motors. The four electric motors provide torque-vectored, all-wheel drive traction and grip, which Jaguar deems essential in a car that produces 1,600 N·m (1,180 lb-ft) of torque.
The single-speed transmission has a final drive ratio of 3.1:1.
|C-X75 powertrain. Click to enlarge.||C-X75 airflow. Click to enlarge.|
The driver and passenger are seated ahead of a sealed airbox that houses the micro gas-turbines. The seats are fixed to the bulkhead as in a single-seater racing car, and air to feed the turbines passes smoothly around them via channels in the structure of the body. With the seats anchored in place, the steering wheel, controls, main binnacle and pedal box all adjust towards the driver.
|Micro-turbine genset diagram. Click to enlarge.|
Micro-turbines. UK-based Bladon Jets achieved a recent breakthrough in producing the multi-stage axial flow compressors—the technology used on all large gas turbines—on a miniaturized scale and to very high tolerances. This increased the compression and efficiency of micro gas-turbines to the point at which they can be viewed as a realistic power source. Each of the micro gas-turbines weighs just 35 kg and produces 70 kW of power at a constant 80,000 rpm.
Because the exhaust gases form part of the active aerodynamic package, Jaguar has utilized a specialized zirconia-molybdenum coating. This advanced heat-resistant coating is regularly used in Formula One cars and is applied in a plasma spray to the carbon-fiber diffuser to protect it from the exhaust gases.
Turbines offer a number of advantages over a reciprocating piston engine when powering range-extending generators, Jaguar says. With fewer moving parts and air bearings, turbines do not need oil lubrication or water-cooling systems, all of which offers considerable weight-saving benefits. They can also be run on a range of fuels including diesel, biofuels, compressed natural gas and liquid petroleum gas.
Turbines reach their optimum operating speed and temperature in seconds and so can be used in short bursts to top up the batteries without compromising fuel consumption or life-cycle. Coupled to two switched reluctance generators supplied by SR Drives, the turbines operate either in sequence or together, depending on energy needs, to charge the batteries—or provide power directly to the electric motors—as dictated by the propulsion system supervisory system.
Active aerodynamics. Jaguar is already aiming to reduce the drag coefficient of its future models in order to increase fuel efficiency. The C-X75 presented the additional challenge of managing the high volume of air required by the turbines. To achieve this active aerodynamics have been utilized for the first time on a Jaguar.
By opening the front grille and brake cooling vents only when necessary, Jaguar has increased the design’s aerodynamic efficiency. At the rear corners of the car vertical control surfaces automatically engage at higher speeds to direct airflow aft of the rear wheels for increased stability and efficiency.
The carbon-fibre rear diffuser, a crucial element in guiding airflow under the car and creating downforce includes an active airfoil, which is lowered automatically as speed increases. Vanes in the exhaust ports then alter the directional flow of the gases to further increase the effectiveness of the Venturi tunnel.
The C-X75 has a drag coefficient of 0.32 Cd and active downforce created through the use of an underbody Venturi. The underbody Venturi and directional exhaust gas control kept the car as sleek, compact and low as possible while still generating large amounts of grip and downforce. Indeed, the movement of air itself was one of the principal drivers behind many of the design cues that were incorporated into the bodywork.
We wanted to emphasize how the air makes its way not just over the car but is also channelled into the rear airbox. When operating at 80,000 rpm, each gas-turbine requires 35,000 liters of air a minute which means we needed a series of carefully honed intakes.—Principal designer Matt Beaven
Advanced lightweight aluminium construction techniques provide weight-saving and economy benefits. Additionally, up to 50% of the metal content is recycled.
Batteries. Battery technology is currently the greatest limiting factor in the development of high-performance electric vehicles with a realistic range. Jaguar says its engineers are currently carrying out research with leading battery suppliers into the next generation of power cells in order to find the best compromise between energy and power densities. The batteries used in the C-X75 are of a composition which offers benefits in terms of weight, lifecycle, energy density and safety.
Braking. The C-X75 is fitted with the brakes used on the supercharged XFR which in 2009 became the fastest Jaguar ever, achieving 363 km/h (226 mph) at the Bonneville Salt Flats in Utah. In this application, regenerative braking technology on all four wheels helps recharge the batteries during driving. The 380 mm internally ventilated front discs and 345 mm rears are covered by polished alloy wheels of 21 and 22 inches wrapped in bespoke hand-cut Pirelli rubber measuring 265/30 ZR21 and 365/25 ZR22 front and rear respectively.
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