Supercharged route to powerful, smaller car engines

A variable-speed supercharger being developed in the

could facilitate the next generation of downsized engines with the performance of larger units, its designer claims.

Reducing engine size is one of the best ways for European carmakers to cut CO2 emissions. But while existing pressure charging techniques such as the use of turbochargers can give downsized engines good performance at high engine speeds, lower speed performance is somewhat compromised, and downsized engines are not always appealing to consumers.

Luke Barker, technical director at Milton Keynes-based Integral Powertrain, explained that the most common form of pressure charging in a downsized engine is via a turbocharger which takes its power from exhaust gases. The problem with a turbocharger is that the delay while exhaust flow builds to a point where effective boost can be delivered is exacerbated in downsized engines.

‘In a turbocharged engine you only get half the peak acceleration to start with and it feels very laggy,’ he said.

Barker said users of downsized engines typically compensate for this by driving the engines in a higher speed range and using a lower gear, defeating the object of downsizing.

‘You downsize to do less frictional and pumping work, but by driving in a higher speed range you completely lose the benefits,’ he said.

Integral Powertrain’s Supergen system is a mechanically driven supercharger that uses a centrifugal compressor — the type used by most turbochargers.

Traditionally, centrifugal compressors have provided poor low-speed performance, but while Supergen takes most of its power from a physical link to the vehicle’s engine, electrical energy from the vehicle’s generator powers an advanced gearing system that varies the compressor speed.

By removing the fixed link between engine and compressor speeds, the compressor is able to run at the optimum speed for the conditions. An additional advantage, said Barker, is that it will be a relatively straightforward process for carmakers to incorporate the technology into existing engine designs.

It is currently at the simulation phase and the company is discussing the development of a full prototype with a number of OEMs.

Barker said he expects the technology to enter series production in around three years.