V-Charge forced-induction performance predictions validated 25 July 2012

Testing on a development vehicle has confirmed that Torotrak's innovative V-Charge variable-drive supercharger slashes time-to-torque by up to 70%, compared with current single turbocharger technologies.

The firms' new pressure charger is said to combine the best of supercharging with the best of turbo-charging.

Torotrak product director Andrew de Freitas says that testing has shown the system to be capable of boosting torque from zero to 95% in less than 400msec at any engine speed – around one third the time required by the latest generation of heavily-downsized small turbocharged engines in the critical low-speed range.

He claims the results prove that V-Charge currently provides the only cost-effective route to affordable downsized engines that combine low CO2 with the driveability of a larger, naturally-aspirated engine.

"Engine downsizing is the dominant industry trend for reducing emissions, but with today's technologies there is a compromise between cost and performance," reasons de Freitas.

"In a downsizing application, a single turbo will deliver the required CO2 reduction, but at the expense of significant areas of driveability. A more sophisticated boosting system provides good driveability but with the cost and engineering issues that come with complex technologies," he continues.

"Our test results, and the comments of specialists who have driven the development vehicle, confirm that V-Charge will deliver class-leading driveability at an affordable price."

Torotrak says that V-Charge gets around engineering and cost problems associated with conventional technologies by using a small, high-efficiency impeller, similar to a conventional turbo, but driven via its 'compact variable drive' – a gearless variable speed transmission that can change ratio from 0.4 to 2.5 within 250msec.

This allows high boost to be provided on-demand at low engine speeds, giving instant throttle response, without the inefficiency of providing too much boost at higher engine speeds.

Although initially aimed at petrol passenger car engines, because that's where the opportunity is greatest, Torotrak says there is no reason why its V-Charge shouldn't be applied to diesel engines, even for large commercial vehicles, as the concept is scalable.

While heavy-duty commercial vehicles may not have a need for the instant pick-up that V-Charge provides, there may well be opportunities on vehicles for pick-and-drop type applications.

V-Charge may also allow further optimisation of combustion strategy that could help that duty cycle. And there is another point: the back pressure caused by increasing amounts of after-treatment on the run-up to Euro 6 is causing increasing concern amongst engine designers, who may well welcome the concept of taking the turbo out of the exhaust stream.

The build and vehicle integration of V-Charge was carried-out by Torotrak's engineering team at the company's UK technical centre.

Initial design simulations were confirmed over 12 months of development and rig testing.

Before installing the system in a 1.1 litre Renault Clio, the company's calibration specialists mapped the performance of the standard turbocharger installation so that it could be electronically simulated, allowing realistic back-to-back comparisons with V-Charge at the flick of a switch.

Brian Tinham

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Torotrak (Development) Ltd

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