A structural study of the cylinder block was made using a 4-cylinder, 1,800 cc gasoline engine with an aim toward reducing engine noise. First, we studied the relationship between cylinder block vibration and radiated noise, and also the principal component modes of noise and vibration.
From the results obtained, it became clear that engine noise could be reduced by suppressing the basic natural vibration of the cylinder block.
Then, alternative shapes of engine blocks were examined in an attempt to reduce noise with a minimal change in present production facilities and engine weight, using the finite element method.
The trial cylinder block was built into an engine after examination by the impulse excitation method and holography. As the result of testing it in running condition, we were able to reduce the noise of the engine proper 2.5db-A with a weight increase of about 3 percent.