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
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
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.