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A Torqsense transducer from Sensor Technology is a key part of a test rig designed by Powertrain Technologies to accurately measure small changes in drive torque.

Powertrain Technologies was asked to design an intelligent lubrication system and to analyse its effects on engine friction and parasitic losses.

The company built a highly specialised test rig for the project.

The engine being tested was a current production diesel and the test bed was configured for motored friction tests with a 6,000rpm 32kW electric motor driving the engine.

Andrew Barnes, a director at Powertrain, said: ‘We completely redesigned the engine lubrication system and installed a bank of five computer controlled oil pumps.

‘Each is capable of supplying individual parts of the engine with oil under conditions unique to that part of the engine and sensitive to the engine operating conditions.’ The idea was to completely profile the performance of the engine under various lubrication conditions and to derive optimum configurations of the intelligent systems for best performance.

‘Both petrol and diesel engines run far cleaner than they did 20 or 30 years ago,’ added Barnes.

‘However, the need to operate efficiently under a wide range speeds and loads and environmental conditions from -40C to + 40C remains the Achilles heel.

‘Intelligent lubrication has the potential to improve performance no end, although quantifying the best configuration is tough.’ He went on to say that the torque sensor is critical to the project since the object of the exercise is to measure the effect on friction of a range of different oil supply strategies and oil types.

Thus the changes in friction are represented by a change in the motored drive torque of the engine.

Torqsense sensors are particularly appropriate for development work because they are wireless.

‘It is a fit-and-forget, non-contact, digital sensor,’ said Tony Ingham of Sensor Technology.

‘There is no need for wiring up slip rings for each new measurement and good accuracies are obtained using digital outputs.’ Torqsense senses and measures the radio frequency (RF) waves generated by two Surface Acoustic Wave devices (SAWs) fixed onto a rotating shaft and converts them to a torque measurement using two tiny SAWs made of ceramic piezoelectric material with frequency resonating combs laid down on their surface.

The SAWs are fixed onto the drive shaft at 90deg to one another.

As the torque increases the combs expand or contract proportionally to the torque being applied.

In effect the combs act similarly to strain gauges, but instead measure changes in resonant frequency.

The adjacent RF pick-up emits radio waves towards the SAWs as well as collecting the reflected resonant changes and it’s this change in frequency of the reflected waves that identifies the applied torque.

Powertrain’s research has now progressed to the next stage in which the test rig is forsaken and the engine installed in a car to quantify the effect on fuel economy.

Sensor Technology

Sensor Technology are manufacturers of TORQSENSE Transducers, the world’s first low cost non-contact rotary torque transducers designed for OEM applications. Rotary torque measurement has always been difficult and expensive.

The patented method uses a surface acoustic wave device as a frequency dependent strain gauge and measures the change in resonant frequency caused by the applied strain in the shaft.

The signal is transmitted via an RF couple from the rotating shaft to a fixed pick-up.

By using a frequency-based device, the signal bandwidth is increased, and the problem of electronic interference common with analogue signals is eliminated. The torque sensors are designed to operate direct from a PLC or a PC.

They require minimum length of shaft, have low inertia, no physical contact between shaft and housing, wide bandwidth, high resolution and accuracy resolution to better than one part in a million, and excellent noise immunity.

The technology lends itself to design of OEM transducers for specific customer applications. Applications include automotive, manufacturing machines, condition monitoring where knowledge of torque is critical, torque control of tightening procedures, and monitoring of viscosity during mixing where consistency is required. The technology replaces existing types of rotary torque sensors by providing better performance at a lower price.

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