New Efficient Supercharger with Variable Drive for Downsized Gasoline Engines

Rotrak, the new 50:50 joint-venture between traction drive specialist Torotrak plc and centrifugal supercharger company Rotrex AS, will present a highly efficient supercharger system in a paper at the 15th Supercharging Conference in Dresden on 24 September. The joint venture company combines a Rotrex supercharger with a Torotrak full-toroidal traction drive to produce a mechanical supercharger system that overcomes the problems inherent in conventional supercharger and turbocharger systems.

Turbo lag can become increasingly intrusive as engines get smaller. Superchargers are mechanically geared to enhance performance at either low or high engine speeds. The Rotrak solution overcomes this constraint by connecting the supercharger to the engine by a compact variable drive, allowing efficient operation across the whole engine speed range.

The need to reduce CO2 emissions is leading to downsized engines, heavily boosted by turbo- or supercharging. But while these engines easily reach high peak power and torque figures, they struggle to provide the required low-speed response. A fully integrated centrifugal compressor connected to the engine via a variable drive will achieve a unique combination of low- and high-speed performance with a highly cost-effective system.

—Torotrak engineering manager David Burtt, co-author of the paper

Gasoline engines are typically less expensive than diesels for the same application but have higher exhaust temperatures, making advanced turbocharging more difficult.

Independent analysis has estimated that the world market for pressure-charged gasoline engines will grow from 2.5 million today to 12 million by 2016. The emergence of a practical and cost-effective way to supercharge small gasoline engines could have significant market impact.

—David Burtt

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