Seal friction characteristics of a hydro-pneumatic suspension strut

Abstract

Hydro-pneumatic suspensions (HPS), due to their compact design and superior ride and handling performance potentials, are increasingly being implemented in commercial vehicles. Such struts may require relatively high friction due to seals, which could affect vehicle ride performance in adverse manner. The friction, however, has been either ignored or idealized as Coulomb force in vast majority of the reported studies. In this study, the nonlinear friction property of a simple and low-cost design of a HPS are characterized experimentally and analytically. Laboratory measurements were conducted to characterize seal friction within the HPS strut as a function of the fluid pressure, and strut velocity and total force under nearly constant temperature. An analytical model of the seal friction is developed as a function of the strut velocity considering the Stribeck effect and the hysteresis. The results suggested that the proposed friction model could provide reasonably good prediction of the seal friction within the HPS strut over the considered frequency and stroke ranges. A lower stroke of the HPS strut revealed relatively less stiction force of the seals but greater hysteresis transition velocity, which contributed to wider hysteresis due to seal friction. The experimental results also suggested asymmetric seal friction-velocity relationship to some extent, which could be attributed to the seals' asymmetric design and nonlinear elastic properties.