Influence of Passenger Car Suspension Design on Carbody Roll and on Wheel Unloading on Curves at Unbalance Speeds

Analytical results indicate that there is a wide variation in roll and lateral behavior on curves at unbalance speeds, for passenger car suspensions in use today. This paper categorizes passenger car types and analyzes behavior under the action of quasi-static lateral forces such as can occur on curves. Understanding this behavior can be important in providing guidelines for developing new designs that operate at relatively high unbalance speeds while still retaining safe operation, good ride quality and other performance related to suspension system design. The approach taken is to develop equations of motion in terms of the physical parameters that must be known in order to determine carbody roll and lateral motions due to lateral loads and laterally offset component weights. These equations are then rearranged in terms of parameters that characterize quasistatic and dynamic performance in a form that facilitates making general statements about the comparative influence of categories of cars on carbody roll and lateral motions, and the resultant increase in wheel unloading, as functions of lateral load. Results are presented for ranges of cars in each category. Roll and lateral motions of existing designs can be estimated by using the physical parameters of the existing design to calculate the parameters used in the equations presented in the paper and then using those equations to calculate estimates of the roll and lateral motions. For contemplated new designs either physical parameters can be selected and motions calculated, or values of the parameters used in the equations presented in the paper that result in desirable levels of roll and lateral motions can be used as trial values for initial and later iterations of the design. The analytical approach has been subjected to limited correlation with static lean test results with good agreement found.