Application of NVH Techniques to Engine Production Line Test

A major manufacturer of small engines has recently implemented cold and hot start tests on the assembly lines of one of its engines. The cold start test refers to the test in which the engine is motored for a short time. Since this is a motored test, with no combustion occurring in the cylinder, the objective of this test is the detection of manufacturing and assembly defects. Next the engine undergoes a hot start test, in which fuel and air are supplied and the engine is started under a predefined load condition. This is a test performed to verify the performance of the engine under the application conditions. In both tests, typically multiple parameters are measured and extracted to assess the mechanical and thermal performance of the engine. Since noise level and sound quality of small engines have become major concerns for application manufacturers and end-users, an investigation was performed to assess the feasibility of including NVH parameters in the test criteria. Furthermore, some of the NVH parameters can be used to improve and refine the detection of mechanical defects in the cold start test and to detect abnormal combustion phenomena (knock, misfire) in the hot start test. This paper will describe the process and the tools used in the investigation along with all testing, signal processing and correlation methods. Conclusions related to the usefulness and feasibility of NVH parameters and to the efficiency of the test stands will also be presented.