Displacement measurement for engine optimisation
Modern internal combustion engines are tuned to provide high performance while still remaining kind to the environment. In this respect, the interaction of the various components is playing an ever more important role. Monitoring this interaction on the running engine presents a challenge. Enormous pressures and temperatures prevail, there are many moving parts and there is almost no way that a sensor can be integrated.
Only a few sensors are able to meet these challenges. Micro-Epsilon from Ortenburg has for many years proved itself as a dependable supplier of measurement technology for engine development. And so, in interesting development projects new ways are continuously being found to improve the efficiency of internal combustion engines. The sensors that are considered for this application are based on the eddy current principle. In this method, a coil conducts a constant alternating current, forming a magnetic field around the coil. If an electrically conducting object is present in this magnetic field, eddy currents are produced in it. They act against the excitation magnetic field and influence the coil impedance. This measured quantity can be used for further processing.
Eddy current sensors from Micro-Epsilon measure displacement, distance, position and spacing with sub-micrometer accuracy. These sensors have been used for many years in numerous applications on internal combustion engines. Special miniature eddy current sensors have been produced, the smallest having an external diameter of only 2 mm. This demonstrates that the company supplies the world´s smallest eddy current sensor. The distance between the controller and sensor can be extended to 15 m. As a result, the controller can be mounted in the passenger compartment during measurement. In addition, the operating controls for the controller are located within the housing. This means that the controller is fully sealed and resistant to oil, water and dirt.
The number of applications is continually rising. For example, the lateral movement of the pistons can be determined, the movement of the crankshaft acquired, the bearing gap on the drive shaft can be measured and the expansion of the cylinder head gasket can also be monitored.
In addition to the engine, other important components can be monitored. For example, Micro-Epsilon has developed a special sensor for measuring the speed of the turbocharger.
Turbochargers are particularly interesting at the moment, because they are to be found in each diesel vehicle. Apart from the angle of the guide vanes, the speed of the vanes on the turbine wheel is important for the performance of the turbocharger. So the rotation of the vanes is measured on the face side. Due to the increasing material stresses and speeds, titanium vanes are being used more and more, which presents a challenge in terms of measurement technology.
This is because eddy current sensors cannot be used on titanium. Titanium is a very poor electrical conductor and the speeds vary from 200 to 400,000 rpm. Consequently, it is extremely difficult to measure the speed. However, using special linearisation and an advanced electronic system, Micro-Epsilon is able to precisely measure this speed over the whole speed range.