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Torque sensor aids supercharger research at Imperial College

04 December 2013

Ultra Boost, a three year project partially funded by the Technology Strategy Board, is aiming to develop a supercharged petrol engine with the same power output and only 35 percent of the exhaust emissions of a current five-litre V8 engine that is only half the size.

With the number of cars, vans and light trucks on the roads expected to double in the next 25 years, there is considerable research in progress aimed at developing new techniques to increase the efficiency and reduce the carbon footprint of existing low carbon vehicles.

Currently, less than one in every thousand of the vehicles on the UK roads are pure electric or hybrid versions, with the other nine hundred and ninety nine being powered by an internal combustion engine, either petrol or diesel fuelled.

As part of the Ultra Boost project, a research team at Imperial College London is developing a new supercharger test rig with the aim of assessing the performance of various boosting components and eventually allow smaller, more fuel efficient engines to replace larger, less environmentally friendly types. 

A key component of the system that monitors the efficiency of the supercharger is a Kistler Smart torque sensor, which is characterised by its ability to operate precisely and reliably at high speeds. The key to obtaining accurate, repeatable data is the precise monitoring of all the parameters relating to rig performance, as Imperial's Dr Alessandro Romagnoli explains:

“To measure the supercharger performance, we needed to replicate the same layout as the engine. The supercharger is driven by an electric motor which, by a system of gears with different ratios, runs the supercharger up to 24,000 rpm providing up to 50Nm.

"The Kistler Smart torque sensor is located in one shaft [replicating the engine crankshaft] and by measuring the power supplied by the electric motor and the power consumed by the supercharger it is possible to calculate the supercharger efficiency - there being little point in developing a system that absorbs a significant proportion of the total power output of the engine, especially when the system is running light.”

The Kistler Type 4502A series sensor used in the Imperial application operates on the strain gauge principle and supplies an analogue output signal of 0-5Vdc, via a contactless method.

The unit is also available with integrated rotational angle/speed measurement, capability, the rotational angle signal with two tracks of each 360 pulses per revolution being available as a TTL signal. In the case of the Type 4501A series, power is supplied, and the measuring signal is transferred between the rotating shaft and the case, via high-grade, durable slip rings.

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