Scuffing detection of TU3 cam-follower contacts by electrostatic charge condition monitoring

The increasing costs associated with lubricant development and qualification has driven the need for condition monitoring techniques to be deployed on test engines to maximise information gained from expensive testing programmes. This paper discusses the results from a motorised TU3 engine with electrostatic sensors focused on the cams. System characterisation tests and an oil starvation test were used to decouple charge mechanisms associated with a lubricated wear test, accelerated through the use of carbon black. Cross-correlation of various charge signal processing techniques, scanning electron microscopy and profilometry revealed that tribocharging dominated during running-in/mild wear and contact potential difference (CPD) dominated during the progression of severe adhesive wear. Tribocharging (the charge generated by a low conductivity fluid) has been shown to be affected by oil temperature, cam rotation speed and the presence of charged species within the lubricant. Contact potential differences was principally generated by the work function difference between oxidised and nascent regions associated with adhesive wear on the cam surface. Electrostatic monitoring which is sensitive to lubricant chemistry and wear, and can be implemented in an industry standard engine, has great potential for the lubricant industry.