The analysis of an engine with a variable valve train

The stress collective of a high performance petrol engine in its application as a passenger car drive is characterised by high partial load proportions. If the load control of the petrol engine is achieved through throttling under these lower load range operating conditions, there are very high gas exchange losses (throttling losses), resulting thereby in a specifically poor, system-dependent partial load consumption. Recently increasing efforts have been undertaken with different systems, such as cylinder disconnection, multi-valve technique, channel disconnection, camshaft adjustment or the variable valve train, to lower the emission and the fuel consumption while enhancing specific engine performance at the same time. Through thermodynamic analyses, the engine improvement potential is demonstrated with the help of the variable valve timing system on the basis of test results from a single-cylinder unit concerning fuel consumption and performance. This paper provides further details on different methods of technical implementation of variable valve gears, the pros and cons of the systems as compared to an engine with a conventional valve system and the thermodynamic or specific flow-related features of the engines with variable valve impulse. Of special interest here is the analysis of throttle-free load via an advanced variable intake close and maximum stroke reduktion. The test unit is a single-cylinder engine, the variation of the different valve timing is realised with the help of a hydraulically actuated computer-controlled unit. The tools applied to analyse the engines were a combustion and load change analysis as well as a three-dimensional flow calculation.