Techrules, a new China-based automotive R&D company, made its global debut at the 2016 Geneva International Motor Show with the unveiling of a Turbine-Recharging Electric Vehicle (TREV) series hybrid system applied in a 6-motor, all-wheel drive supercar concept.
TREV is a range extender system that uses a micro-turbine (fueled either by liquid or gaseous fuels) to generate electricity that charges a battery pack. The battery powers the motors that drive the wheels. In 2010, Jaguar introduced a similar concept, the C-X75 extended range electric vehicle that used twin gas micro-turbines from Bladon Jets to power two switched reluctance generators from SR Drives. (Earlier post.)
|Techrules AT96 (liquid fueled) TREV supercar on the track. Click to enlarge.|
Techrules said that its newly developed battery management technologies enable superior charging efficiency. The high efficiency of the TREV range extender results in a requirement for fewer batteries, saving weight and space.
Techrules started testing a development prototype of the TREV supercar last month at the Silverstone race circuit in the UK.
Performance specs for the TREV include peak power of 768 kW (1,030 bhp), with a projected 0 - 100 km/h time of 2.5 seconds, 350 km/h (217 mph) restricted top speed). Projections, based on initial testing, indicate that the range of a future production supercar under battery power alone will be up to 150 km (93 miles).
Where charging points are unavailable TREV technology can recharge batteries anywhere, either while underway or when parked. It is envisioned that this parked recharging process could be completed unsupervised—overnight for example.
Maximum range—based on the battery configuration in the concept supercar presented at Geneva—is projected to be more than 2,000 km (1,243 miles) from 80 liters (21 gallons) of aviation kerosene—or a fuel with equivalent calorific value—in urban driving conditions.
There is no direct electrical feed from the generator to the electric traction motors: the TREV system is purely a series hybrid range extender system.
Air drawn into the micro turbine is passed through a heat exchanger where heat from the exhaust air is transferred to the cold intake air after it has been compressed. Ignition of the compressed and heated fuel-air mixture generates energy which is channelled at very high speeds to turn the turbine vanes. As this hot exhaust gas is expelled, it passes through the heat exchanger to ensure the heat energy is recuperated and transferred to cold intake air.
Because turbines have always been a very inefficient way to convert chemical energy into useful wheel turning mechanical energy, only a few have tried to use a turbine in the powertrain system, and none have ever succeeded commercially. But, with electric vehicles, an electric motor is used to drive the wheels, which effectively frees the combustion engine to exclusively convert chemical energy into mechanical energy and finally into electric energy. This is a major breakthrough, making it possible for us to use the highly efficient turbine engine as a superb range extender on our vehicles.—Techrules Chief Technology Officer, Matthew Jin
The turbine shaft powers a generator that produces electricity to charge the battery cells. In Techrules’ TREV configuration, the turbine and the generator share the same shaft and rotate at the same speed: over 96,000 revolutions per minute.The turbine produces 36 kW. Of this output, 30 kW powers the generator, with 6 kW directly powering auxiliary equipment such as the inverters. The 30 kW electrical output from the generator is used to charge the battery pack.
The total weight of the TREV range extender system (micro-turbine, inverters, fuel pumps, air pumps, and generator, but excluding batteries and motors) is approximately 100 kg (220 lbs).
The TREV system incorporates several new technologies that make it approximately 50% more efficient than range extender systems using gasoline engines, Techrules said.
The high rotational speeds that the shaft requires in order to draw in the required volume of air means that achieving low friction is paramount to the efficiency of the TREV system.
Techrules employs air bearing technology—a high pressure feed of compressed air—instead of a traditional oil lubricant film to separate the shaft from the bearing. This results in fewer frictional energy losses, since it eliminates parasitic losses of a mechanical bearing. The use of an air bearing system is not unique, but how Techrules uses the air bearing involves innovations.
Of particular note is that the air bearing is also supported by a magnetic field that allows for precise adjustment of the high speed shaft. Both bearing solutions work together to maintain stability. The magnetic bearing allows a far greater clearance between the shaft and its wall lining, which delivers significant advantages for the long-term durability of the system.
This is an especially important consideration in automotive applications of turbine systems because—unlike in stable power generation conditions—the entire assembly must be able to be capable of withstanding volatile operating conditions that result from, for example, vertical shocks from uneven road surfaces and lateral forces in cornering. Techrules’ hybrid bearing system is also more economic to produce, because the built-in extra clearance space reduces the extreme tolerances usually required.
In addition, a new design of internal foil—an intrinsic component within an air bearing—is used for the bearing liner that supports the air pressure and flow. It is made of a new compound material that gives it superior durability. Of equal importance is that the new foil enables the mass production of the bearing liner at the required production tolerances to be achieved at a high volume scale at low cost.
Techrules has also introduced a new and innovative heat exchanger design that is more thermally efficient than conventional designs. A new material has been introduced in the hybrid heat exchanger which greatly increases the efficiency of heat recuperation from the exhaust gases.
New charge balancing strategy. The TREV system employs an innovative smart battery management system that optimizes the efficiency of battery charging and power balancing between battery cells.
In a conventional lithium-ion battery management system, to avoid cells being damaged by overcharging, the cells—which each charge at a slightly different rate—must be balanced as they charge. This balancing is conventionally achieved by actively discharging the cells that are charging more quickly in order to enable the other cells to catch up. This process sees a proportion of energy wasted during the charging process and increases the time required to charge all cells fully.
To address the shortcomings with this standard industry practice, Techrules’ battery balancing system harnesses the excess voltage in cells that are charging more quickly, sharing their charge with slower-charging neighboring cells to achieve the required balance. As a result, the entire pack charges more quickly, and there is no energy wasted in actively discharging the best-performing cells, the company says.
Power-dense cells. The TREV system uses readily available cylindrical 18650 Lithium-Manganese-Oxide battery cells. Techrules is focusing its capabilities on the efficiency of the battery management rather than the battery chemistry itself. Its insight and smart battery management system will be applicable to any future, higher capacity battery technology.
Because the TREV system incorporates a series hybrid range extender, Techrules is prioritizing power density ahead of energy density.
With a common core architecture, the TREV system can be tailored to run on one of a variety of fuels. This means that the configuration of the TREV system can be matched to the fuel which is already prevalent in a specific market with a comprehensive supply and distribution infrastructure. As a result, adoption of the TREV system by the fuel supply industry, vehicle manufacturers and consumers requires no major investment in new networks. The TREV system’s turbine has been tested in various guises, with alternative versions running natural gas, biogas, diesel, gasoline and aviation kerosene.
The two concepts. Techrules is showcasing its TREV technology at the 2016 Geneva International Motor Show in a two-seater all-wheel drive concept supercar. The turbine generator is carried behind the passenger cabin and in front of the rear wheels, making the concept a mid-engined extended-range electric vehicle.
It is presented in two designs, the AT96 and GT96. These designs—each offering an alternative configuration of the TREV system—are two variations of a vision of how turbine-recharging supercars might look when the technology enters production in China’s first supercar.
AT refers to Aviation Turbine, indicating that the turbine is configured to run on a liquid fuel such as aviation kerosene, diesel and gasoline. The AT96 is a vision of a track-focused version of the supercar and features management large rear wing, which provides both straight-line stability as well as downforce to aid high speed cornering. The GT96 (gas turbine) is designed to run on a gaseous fuel such as biogas and natural gas and is styled as a road-going hypercar.
The supercar also incorporates plug-in charging capability for markets where public or residential off-street parking charging networks are in place.
A first supercar development prototype based on the AT96 aviation turbine configuration has been produced by Techrules’ specialist vehicle engineering partners in Italy and the UK.Initial testing began in February 2016 at the iconic Silverstone race circuit in the UK.
At the heart of the concept is a carbon-fiber monocoque to provide exceptional torsional rigidity and passenger safety. The body structure is also lightweight carbon fiber, including the dihedral doors.
The rear subframe carries the primary range extender components, including the micro turbine generator and direct ancillary systems, as well as the cooling systems for the electric traction motors and battery pack, and the rear motors and inverters.
Under the carbon-fibre body, a longitudinal T-shaped battery back runs down a central spine of the car, providing the same appearance in the passenger cabin as a transmission tunnel would in a front-engine, rear wheel drive car. The battery pack is liquid cooled to maintain an optimal operating temperature for the cells.
The battery pack comprises 2,376 individual 18650 cylindrical cells that use Lithium-Manganese-Oxide chemistry chemistry with a capacity of 20 kWh usable and with a voltage of 720 V. Thanks to its smart battery management system, the battery pack can be charged by the turbine generator in approximately 40 minutes.
The supercar concept is driven by six electric traction motors, each weighing 13 kg and each one of which is coupled to its own dedicated inverter. Each front wheel is driven by a single motor, while each rear wheel is driven by a pair of motors.
The primary advantage of using two smaller motors instead of a single larger motor for each rear wheel is packaging efficiency and simpler mounting to the monocoque, Techrules said.
This six-motor layout with independent power feeding each wheel provides an ideal configuration for torque vectoring which is managed by an electronic control unit. Four-way torque vectoring guarantees maximum cornering stability at high speed and eliminates the requirement for complex and heavy mechanical differentials.
With such power and speed available from the accelerator pedal, so is there due consideration for high performance stopping power. Rapid retardation is achieved with 405 mm ventilated discs with six-piston calipers at the front, and 380 mm ventilated discs with four-piston calipers at the rear.
Techrules is a subsidiary of Txr-S, a research and development company which has other subsidiaries operating in the fields of new materials development, biogas production and aerospace.
Techrules plans to begin series production of TREV technology in a low volume supercar of its own design within a couple of years. It then plans to begin production of higher volume city cars a few years later.