Supercharger system is driven via variable-speed mechanical drive

Paul Boughton

Rotrak presented a novel supercharger system in a paper at the 15th Supercharging Conference in Dresden on 24 September 2010. The joint venture company combines a Rotrex supercharger with a Torotrak full-toroidal traction drive in a mechanical supercharger system that overcomes the problems inherent in conventional supercharger and turbocharger systems.
With a turbo, the delay in response, called lag, becomes increasingly intrusive as engines get smaller. Superchargers are mechanically geared to enhance performance at either low or high engine speeds. The Rotrak alternative overcomes this constraint by connecting the supercharger to the engine via a compact variable drive, enabling efficient operation across the whole engine speed range.
Torotrak engineering manager David Burtt, co-author of the paper, explains: "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."
Gasoline engines are typically much cheaper than diesels for the same application but have higher exhaust temperatures, making advanced turbocharging more difficult.
Burtt states: "Independent analysis has estimated that the world market for pressure-charged gasoline engines will grow from 2.5million today to 12million by 2016. The emergence of a practical and cost-effective way to supercharge small gasoline engines could have significant market impact."
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