Hybridized Transmission Reduces Supercar Emissions

U.K. high-performance sports-car transmission specialist Xtrac develops a hybridized automated manual transmission (H-AMT) that will allow luxury supercars to meet the 95 g/km carbon-dioxide emissions requirement being introduced by European legislators in 2020.

Xtrac Automotive and Engineering Business General Manager Clive Woolmer and principal engineer Chris Cholmeley recently presented details of the new transmission at the 11th International CTi Symposium and Exhibition in Berlin.

The prototype-ready gearbox, designated 1010, is aimed at auto makers competing in the high-growth sector of premium-luxury cars, which includes limousines as well as supercars.

For the 1010 hybrid gearbox, Xtrac partnered with Magneti Marelli for the bespoke electro-hydraulic actuation system, transmission control unit, electric motor and inverter and system software. The design includes individual actuators on each selector fork, and a 60kW (78-hp) continuous 120kW (156-hp) peak-output electric motor.

Cholmeley says the product lifecycles of premium-luxury supercars typically are longer than mainstream cars due to significantly lower production volumes and the need to amortize high development costs.

“With the 2020 CO2 requirement now very much on the horizon, the next generation of supercars must respond to the emissions challenge, but at the same time not lose any of their brand and product appeal,” he says.

Xtrac believes its distinctive transverse-transmission configuration lends itself particularly well to hybridization and offers a solution to the supercar sector’s preference for retaining high-power multi-cylinder engines while meeting 2020 emissions targets.

The 1010 hybrid transmission’s total weight of 76 lbs (168 kg) is made up of 55 lbs. (120 kg) for the gearbox and 22 lbs. (48 kg) for the motor and hybrid components. The company says this represents up to a 20% weight savings over a comparably sized hybridized dual-clutch transmission.

The gearbox can handle engine-torque capacities ranging from 590 to 738 lb.-ft. (800 to 1,000 Nm), depending on vehicle gross weight and the particular application.

The speed range is set just below 95 mph (150 km/h), covering most European maximum speed limits except for the unrestricted German autobahn. The restriction allows torque infill up to fourth gear during high-performance acceleration and in all gears up to the threshold speed during low-speed driving.

Torque infill is the application of additional torque through the transmission to the road wheels during the period of a gear change, where in a conventional transmission the torque is interrupted to allow the shift to complete.

Developed as an alternative to heavier and more complex DCTs, the Xtrac 1010 H-AMT has a lower total parts count and overall mass compared with a hybrid DCT by focusing on optimized packaging, weight reduction and cost efficiency.

The modular design meets a number of sports-car driveline architectures, including front-engine longitudinal powertrain layouts.

For increased efficiency the 7-speed gearbox offers multiple modes of internal-combustion engine and electric motor-generator operation and an overall ratio spread of almost 6:1, which is higher than many other transmissions in the sector.

Xtrac believes parallel-hybrid-electric vehicles can best satisfy the 2020 CO2-reduction targets.

Woolmer says in a statement Xtrac is positioned to work both with leading race teams and high-performance supercar manufacturers to ensure the technology-transfer potential between the automotive and motorsport industries is fully exploited.

“The premium-luxury-car sector is predominantly filled with high-performance mid-engine sports cars, coupes, roadsters and luxury-limousine derivatives,” he says.

“The sector is enjoying strong sales growth, especially in Asian markets, but the very nature of their high-power output means they are currently the worst-performing vehicles in terms of fuel consumption and emissions.

“We believe we now have a viable and cost-effective transmission solution for these vehicles.”

Xtrac’s global headquarters is in Berkshire, with additional facilities in North America.