Both ride comfort and noise level inside the cabin are critical factors in assessment of quality of a passenger car and are gaining increasing importance in chassis development. The customer preferences toward the ride comfort, which rise consistently, are mainly responsible for this. Many researches have been done and are still going on to resolve the noise and vibration problem at the initial design stage. In practice, however, a great portion of the ride comfort and noise problems of a car is improved at the final tuning work that is performed mainly on the suspension system underneath the car body. One difficulty with the current tuning technique is that it is very time consuming due to the great dependence on subjective assessment in finding primary reasons of the noise and vibration problems.
Various motions or vibrations of a car body suspended from ground are originated by the operational forces transmitted onto the car body through bushing attachments, which should be very closely correlated to the ride comfort and the noise level inside the cabin. Hence, identification of distributional characteristics over the car body of the operational transmission forces through such resilient elements could provide objective reference materials for improvement of the ride quality and greatly reduce the trial and errors in the final tuning stage dealing with noise and vibration problems.
Since direct measurement of the operational transmission forces by installing custom-made force sensors at the bushing joints in the three principal directions is extremely difficult and cost ineffective, a technique of using rubber bushing itself as a sensor is employed in this research for the identification of transmission forces. The method starts from an idea that the transmission forces can be related to deformation of the rubber bushing multiplied by complex stiffness of the bushing. The deformation of the rubber bushing can be obtained by estimating relative accelerations across the bushing from the absolute vibration signals measured at various points of the rigid link and the car body connected to the bushing and by double integrating the relative accelerations. The identification of operational forces generated mainly due to the motions of a unsprung mass and the bushing properties in the frequency range over 5 to 200 Hz were the object of this paper.
Several useful results are shown by applying the proposed method to a rear suspension system of a passenger car under driving conditions. Some problems and solutions are analyzed by focusing on the possible improvements and the limitations in the force estimation.