TorqSense aids development of intelligent lubrication

Automotive companies are exploring numerous ways to improving performance and engine efficiency. And because engines have a rotating power output, torque is a key measurement.

Traditional engine lubrication systems have a simple mechanical pump that is sized to ensure an adequate supply of oil in the worst operating conditions - which is typically a hot engine at idle. The pump is therefore grossly oversized for most of the rest of the speed range and, as a consequence, nearly 60 per cent 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 those components might actually need. Furthermore, the pump is insensitive to engine load, so the bearings receive the same oil supply at a given speed regardless of the load. Overall, this is a very inefficient system.

In addition, the pump flows nearly one ton of oil per hour through the filter and, when the oil is cold, this consumes a large amount of energy.

In search of intelligent lubrication

With this in mind, a major UK company asked Powertrain Technologies Ltd in Snetterton, Norfolk, to design an intelligent lubrication system and analyse its effects on engine friction and parasitic losses. Powertrain Technologies built a 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.

The engine under test was a current production diesel and the test bed was configured for motored friction tests with a 6000rpm 32kW electric motor driving the engine.

Andrew Barnes, a director at Powertrain, explains: "We completely redesigned 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 profile the performance of the engine under various lubrication conditions and derive optimum configurations for the intelligent systems for best performance.

Barnes continues: "Both petrol and diesel engines run far cleaner than they did 20 or 30 years ago. However the need to operate efficiently under a wide range speeds and loads and environmental conditions from -40 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. Consequently the changes in friction are represented by a change in the motored drive torque of the engine.

Non-contact torque measurement

TorqSense sensors are particularly appropriate for development work because they are wireless. Tony Ingham of Sensor Technology says: "It is a fit-and-forget, non-contact, digital sensor, meaning you do not have to fiddle around wiring up slip rings for each new measurement and, together with digital outputs, good accuracies can be obtained."

TorqSense devices effectively sense and measure the RF (radio frequency) waves generated by two Surface Acoustic Wave (SAW) devices 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 on their surface. The SAWs are fixed onto the drive shaft at 90 degrees 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 SAWs as well as collecting the reflected resonant changes and it is this change in frequency of the reflected waves that identifies the applied torque.

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

Barnes comments: "It is 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."

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