Fretting tests on connector terminals

Sammanfattning: Fretting is a complex set of mechanical and electrical mechanics that occurs at the contact surface between two vibrating objects. It is widely present in electrical connectors close to combustion engines due to the constant exposure to vibrations. Fretting is an extensive problem in the automotive industry but little research is done. In this thesis, a connector attached to a high pressure fuel pump that is present in several cars made by Volvo Car Corporation is analysed. The goal is to investigate the design properties of the connector and evaluate if laser vibrometry is a valid method for connector vibration measurement. Fretting has previously been observed to correlate with the relative displacement between the male and female connector terminals. Accelerometers are widely used to measure acceleration and displacement of various components of the engine, but to measure directly on the terminals inside the connector is impossible. To instead use lasers to measure the relative displacement could prove to be an effective way of predicting fretting damage. The connector is analysed in a vibration laboratory where it and the pump it is connected to is mounted to a fixture. This way the vibration schedule can be designed and controlled with accuracy. To have a frame of reference when designing and analysing the results of this test, a real engine vibration test is first analysed. In this test, the connector is attached to the engine in the same way as in production cars. The engine is then run from idle to full throttle and the vibrations in the connector is measured. It is found that the measurement of the terminal relative displacement is much more accurate when using lasers instead of accelerometers. The result of using the accelerometer showed a misleading result. The relative displacement was up to five times higher and three times lower than the true displacement, measured with the lasers. A method to predict fretting damage can be developed using laser vibrometry. The thesis also present suggestions on details in the connectors that are beneficial from a fretting point of view.