Model Verification of CAE with NVH-test Acting on Downsized Car Engines 2019-01-1550

Today’s trend of downsized internal combustion engine development for cars is characterized with; high torque, low engine speed, low weight, high degree of cyclic irregularity, low excitation frequency due to fewer cylinders active e.g. 4-cylinder or less. Torque output 100 Nm at low engine speed 1000 rpm has become normal. This implies in respect of vibrations that it is important to control engine suspension rigid body modes e.g. roll yaw and pith ones. The rigid body modes frequencies should be low so they cannot be reached and induced by the low exciting harmonics of cylinder pressure and mass forces for low engine speeds or idling. Crucial is the rigid body modes in relation to the excitation forces. It is also important to control the overall flexible vibration modes. Our purpose is to describe the method to optimize the powertrain suspension, beginning with modeling/simulation and ending with verifying the vibration level on a real running engine i.e. a Volvo Cars in-line 4-cylinder VEA diesel engine in a test rig/cell. As a method a mathematical CAE model was created in simulation software EXCITE in order to handle the vibration phenomenon as a first step. After that measurements of vibrations, torque and cylinder pressure traces were done simultaneously with NVH testing tool DEWESoft. Also impact test with a modal hammer has been done in order to find rigid body mode frequencies. The measured cylinder pressure were then applied as input to the simulation model in order to have consistent input load between test and simulation. Correlation CAE vs NVH-test was done with crank angle based vibrations signals and match was very good. We found that the crank shaft no uniformity is a very god measure of the resulting external forces which control the engine vibrations e.g. rigid body modes.