Vehicle manufacturers are moving aggressively to downsize their engines in order to achieve substantial efficiency gains with reductions in fuel consumption and CO₂ emissions. As engines get smaller, one challenge becomes boosting performance across the entire speed-range to provide large-engine responsiveness and to make sure that driving remains enjoyable.

A conventional turbocharger struggles at low speed, particularly in these smaller engines. Better low-speed boost can be achieved but it is complex and costly, the firms note. Supercharging is the main alternative, but the fixed ratio between engine and supercharger speeds means that if boost is optimized for low-end response, then energy is wasted at higher engine revs.

The Rotrex supercharger traction drive uses an elastic annulus with a small pre-span to secure contact between the roller planets and the sun shaft with a reasonable force; the traction drive transmits power through traction forces between the rolling elements. The patented “ramp effect” increases efficiency and reliability in the transmission by regulating the torque transfer capability on demand through self-adjusting planet geometry.

To enhance performance, the Rotrex traction drive uses a special traction fluid. These fluids are a new family of synthetic hydrocarbon oils and greases offering a series of unique performance advantages. Developed specially for its use in Rotrex superchargers, the SX100 fluid momentarily increases viscosity under high surface pressure, enhancing the traction drive performance by securing the optimum friction between rolling elements while cooling and protecting the system.

This traction drive, combined with the latest technology in centrifugal compression, characterized by high adiabatic efficiency and low noise, results in a compact, efficient, low noise and reliable unit, Rotrex says.

Rotrex’ standard product range consists of the C15, C30 and C38 families. The company is currently developing an extremely compact traction drive platform, the Rotrex C8, which will specifically address compact applications, and is due out in the latter part of this year.

Torotrak and Rotrex are ideally positioned as partners for the development of variable drive supercharging systems. For some time we have been looking for a scalable, efficient and durable technology to provide a variable drive capability for our centrifugal compressors and our studies have confirmed that Torotrak is the clear leader in this field.

—Rotrex managing director Lars Kristiansen

Adding Torotrak’s scalable variable speed traction drive to Rotrex’s technology will overcome many of the compromises that affect current pressure-charging systems.

—Torotrak CEO Dick Elsy

Independent analysts estimate that the market for pressure-charged gasoline engines will grow from the current global level of 2.5 million units per year to 12 million by 2016. The more established market for diesel pressure-charging is predicted to grow from 10.5 million to 16.1 million units in the same period.

Torotrak designs and develops Continuously Variable (CVT) and Infinitely Variable (IVT) transmissions which deliver high levels of performance, functionality and refinement along with improved fuel economy and reduced emissions. Torotrak develops main drive transmissions as well as variable ratio transmissions for application in flywheel-based mechanical hybrid systems and for use as auxiliary drives.

In the past three years Torotrak has undergone a period of intensive business and technology development in pursuit of a multi-market strategy. It has secured a number of world-class licensees and is working with them on programs with the potential for volume manufacture, primarily in main-drive transmission applications. These include one of Europe’s most successful truck and bus manufacturers and Allison Transmission Inc.