Fast torque

There have been many variations on the forced induction method of turbo charging, each with its own pros and cons. But Visteon in the UK has developed a system that seems to have incorporated the best features of all current designs.

A traditional supercharger can be considered to be an air compressor that forces an extremely dense air/fuel mixture into a combustion chamber. Indeed, that same definition could be applied to a turbocharger, too.

In a supercharger, a belt connected to the engine’s crankshaft drives the impellers of the supercharger. The spinning of the impellers compresses the intake air and creates boost.

In a turbocharged engine, impellers also act on the intake charge to create boost. In this case, however, the impellers are driven by gasses flowing through the exhaust header. That means that the amount of boost created by a turbo depends on exhaust flow, so turbocharged engines do not provide as much boost at low RPM s they do at higher RPM. This is often called ‘turbo lag,’ because of the time taken for the turbo to build boost and create horsepower. Supercharged engines do not suffer from this ‘lag’ because, as long as the engine is running, the supercharger is spinning and creating boost.

Now, a new system from Visteon, dubbed the Torque Enhancement System (VTES) seems to have incorporated the best features of all current designs. Better yet, it can be applied to existing engine designs with little or no modification of the engine compartment.

‘Conventional turbo charging is an efficient boosting device. It uses what would otherwise be wasted exhaust energy. The only problem is response lag – you put your foot down, wait for a while for the exhaust gas to spool up before you get your boost. Variable nozzle turbos go some way towards helping turbo lag but not all the way. They also can’t stand the high exhaust gas temperatures of gasoline engines,’ explains Guy Morris, senior manager, advanced powertrain systems at Visteon.

The supercharging alternative tends to be inefficient. As well as noise and vibration problems, there are problems with parasitic losses with the compression device and the belt drive. The belt drive also causes packaging issues in the engine compartment.

So how about an electrically assisted turbo charger? That’s what the Visteon team have essentially developed with the VTES system – an integrated air management system, at the heart of which is an electronically controlled electric compressor.

The VTES system comprises an electronically controlled on-demand electric air compressor, an air induction system, and control electronics that can be integrated under the bonnet into the existing geometry of the air intake and battery space without the need to redesign the engine or make major changes to the vehicle assembly process.

The VTES only operates close to, or at, wide open throttle for vehicle acceleration, and, when not required, the motor compressor is bypassed and air enters the engine normally.

There are two main applications for VTES. First, when used in naturally aspirated gasoline engines, it improves the torque profile which can be used to improve engine performance or allow the vehicle dynamics to be changed through re-gearing, or downsizing – putting a smaller engine in a larger vehicle. Secondly, in turbocharged engines, it can enhance performance by improving the low end torque for driveability and eliminating turbo lag.

Potential customers have not been disclosed but demonstration cars based on Fiat and Renault cars have been demonstrated.

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