An investigation into the engagement characteristics of an automotive dry friction clutch

The object of this research was to investigate the period of time during which the clutch plates of a motor vehicle are engaged to effect a start from rest. The problem was approached from two sides, firstly a mathematical model has been produced in the form of a digital computer program. Secondly, practical investigations were undertaken in order to shed more light upon certain problem areas highlighted whilst developing the mathematical model. Finally the two types of investigations were combined to give a more realistic model of the engagement period than any that had previously been published. The mathematical model allowed parametric studies of the clutch to be made giving details of slip time, speeds, clamp load, friction level, heat generated and the one dimensional temperature distribution through one half of the clutch assembly. Two methods for the solution of the temperature distribution problem were used in order to give a cross check during the development of the mathematical model. Stability of the two methods has been investigated and limits suggested which if adhered to prevent instability errors occurring. Practical work on a test rig was carried out in order to investigate the variation of friction levels during the engagement period and also the temperatures reached. A test vehicle was instrumented to find out how the general public operated the clutch in service and how their operation varied with test conditions i.e. gradients and traffic conditions. Finally a computer controlled test rig comprising of an engine, clutch with e1ectro-hydraulic ram operation and inertia flywheel was developed. This rig was completely automatic and could be used to simulate different engagement rates, gradients and, if inertia were added or subtracted, different vehicles. The result has been that a useful tool, in the form of an easily used computer program has been developed, the limitations of which have been investigated. Also, a test facility has been developed which can be programmed to simulate in vehicle use. The model and test rig produced lend themselves to extension to further work in the area of clutch and transmission vibrations, especially clutch judder.