Control of ‘Piston Stick Slip Noise’ in a 4-Cylinder Gasoline Engine 870991

Practical methods of reducing a “Diesel Sounding Knock” at idle conditions, in a 4 cylinder, 2.2 liter, gasoline engine were investigated. A peak noise averaging method was used to determine the effect of accumulated mileage and sensitivity to various friction modifiers and lubricants. Piston parameters were also optimized and, with a friction modifier, produced a 10 dB average peak noise level reduction. Data relating the average peak noise levels to accumulated mileage and percent concentration of a friction modifier were obtained and time history recordings documenting the peak noise level changes were made. The results of the testing confirm published findings on “Diesel Sounding Knock” and support a “Piston Stick Slip” theory as the noise generation mechanism.