Sensor Technology Ltd. - PRODUCT NEWS
Reducing Engine Friction.
An innovative torque sensor is helping to reduce engine emissions and
improve economy as part of a project to develop an intelligent lubrication
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
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
TorqSense sensors are particularly appropriate for development work because
they are wireless. Its a fit-and-forget, non-contact, digital
sensor, says Tony Ingham of Sensor Technology, meaning you dont
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 SAWs 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 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
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
The adjacent RF pickup emits radio waves towards the SAWs 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.
Its 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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