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An Innovative Torque Sensor Is Helping To Reduce Engine Emissions

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With engine efficiency under the spotlight like never
before, automotive companies are exploring all avenues for improving
performance. And because engines have a rotating power output, torque is the
key measurement.

Car engines are the bett noir of the environmental lobby.
There is no doubt that they are major contributors to carbon build up. But
equally they are fundamental to modern life. A true replacement is decades
away, so we have to make them as efficient as possible.

Engine lubrication systems are essentially dumb. They have a
simple mechanical pump which has been sized to ensure an adequate supply of oil
in the worst operating condition. This
is typically a hot engine at idle. The pump is thus hugely oversized for most
of the rest of the speed range and, as a consequence, nearly 60% of its output
is dumped straight back into the sump via the relief valve. It will also
deliver the same amount of oil to every part of the engine regardless of what
that system might actually need. The pump is also insensitive to engine load
and thus the bearings will receive the same oil supply at a given speed
regardless of the load. This is a very inefficient system.

In addition the pump forces nearly a ton of oil per hour
through the filter, and when the oil is cold this takes a huge amount of
energy.

With this in mind a major UK company asked Powertrain
Technologies Ltd in Snetterton, Norfolk, to design an intelligent lubrication
system and to analyse its effects on engine friction and parasitic losses. They
built a highly specialised test rig for the project and since accuracy in
measuring small changes in drive torque reliably and repeatably was a critical
requirement a key part of the rig is a TorqSense transducer from Sensor
Technology in Banbury.

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 explains: “We
completely re-designed the engine lubrication system and installed a bank of
five computer controlled oil pumps (to our own design). 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 (for
example we can supply the head with oil at pressures different to the block and
supply the bearings with more oil when the engine is under high load).”

The idea is 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,” says Andrew. “However the need to operate efficiently
under a wide range speeds and loads and environmental conditions from -40
degrees C to + 40 degrees C remains the Achilles Heel. Intelligent lubrication
has the potential to improve performance no end, although quantifying the best
configuration is painstaking work.”

He goes on to explain 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's a fit-and-forget,
non-contact, digital sensor,” says Tony Ingham of Sensor Technology, “meaning
you don't have to fiddle around wiring up slip rings for each new measurement
and together with digital outputs good accuracies can be obtained. The adjacent
RF pickup emits radio waves towards the SAW's as well as collecting the
reflected resonant changes and it this change in frequency of the reflected
waves that identifies the applied torqueed.”

TorqSense effectively senses and measures the radio
frequency, RF, waves generated by two Surface Acoustic Wave devices or SAW's
fixed onto a rotating shaft and converts them to a torque measurement using two
tiny SAW's made of ceramic piezoelectric material with frequency resonating
combs laid down on their surface. The SAW's are fixed onto the drive shaft at
90degrees 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 pickup emits radio waves towards the SAW's as well as collecting
the reflected resonant changes and its 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.

“It's now a matter of driving it under all sorts of
conditions on a mixture of test tracks and rolling roads to build up profiles
of fuel consumption, says Andrew.


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