The use of a two stage dimensional variation analysis model to simulate the action of a hydraulic tappet adjustor in a car engine valve train system

Dimensional variation analysis (DVA) models have been used in the manufacturing industry for over 20 years to predict how minor variations in the size, shape and location of the components parts is likely to propagate throughout and affect the overall dimensions, operation and performance of a complete mechanical system. This paper is one of in series of four papers that describe how different techniques can be utilised to aid the creation and application of DVA models. This paper explains the development and use of a two stage DVA model to simulate the action of a hydraulic tappet adjuster and dimensional interdependence that exists between the adjustment of a hydraulic tappet and the actuation (opening & closing) of the cylinder valve. The three other papers cover the use of kinematic constraint maps to prepare the structure of a DVA model; the use of virtual fixtures, jigs and gauges to achieve the necessary component location and the required variation measurements, and the use of 3D plots to display large numbers of DVA results as a single 3D shape. A hydraulic tappet adjustor performs two functions; it is part of the valve train system that actuates (opens & closes) the cylinder valve and it also self adjusts to take up any free play in the valve train system. These two functions, tappet adjustment and valve actuation, are separate operations that occur at different times during the valve train operating cycle and so need to be modelled as different configurations in a DVA model. In a conventional multiple configuration DVA model, each configuration has to be fully constrained and mathematically closed independently of any other model configuration. This requirement makes it difficult to include the interdependence between tappet adjustment and valve actuation. The two stage approach overcomes this limitation by allowing the output variation from the tappet setting configuration to be carried over into the valve actuation configuration and can thereby fully account for the interdependence between the two operations