Journal of Applied Sciences1812-56541812-5662Asian Network for Scientific Information10.3923/jas.2015.1127.1132ShavalipourAghilMohamed HarisSallehuddinMohd NopiahZulkifli82015158The suspension system plays an important role in ensuring the safety and comfort of passengers in a vehicle. Conflicting requirements for ride smoothness and road holding ability means trade offs are often necessary to achieve satisfactory performance on both specifications. Active suspension systems have been introduced to provide greater flexibility in addressing such conflicting requirements. In active suspensions, the controller design influences the system performance and hence, much effort has been put into formulating its optimal design. The Linear Quadratic Regulator (LQR) is one such optimal control scheme that has been used in active suspension systems. Conventionally, LQR controller gains are tuned through numerical computation based on a nominal system model with constant parameter values. In actual situations, parameter variations would occur for one reason or another. In this study, the effects of sprung mass variations on active suspension under LQR control is studied. A method for LQR control design for an active suspension system using symbolic computation and the concepts of the sum of roots and Grobner bases is presented. This method enables the controller gain to be tuned whilst the sprung mass is retained as a symbolic parameter.]]>Anai, H., S. Hara, M. Kanno and K. Yokoyama,2009Bini, D.A., B. Iannazzo and B. Meini,2012Boyd, S., L. El Ghaoui, E. Feron and V. Balakrishnan,1994Camino, J.F., D. Zampieri, R.H.C. Takahashi and P.L.D. Peres,19972 and LQR active suspension control schemes with uncertain parameters: A comparison.]]>Chen, S., R. He, H. Liu and M. Yao,2012Choi, S.B. and W.K. Kim,2000Gao, H., J. Lam and C. Wang,2006Gordon, T.J. and R.S. Sharp,1998Hrovat, D.,1997Kanno, M., S. Hara and H. Anai,2011H_{2} control based on symbolic-numeric hybrid optimization.]]>Karnopp, D.,1975Nagai, M., A. Moran, Y. Tamura and S. Koizumi,1997Naude, A.F. and J.A. Snyman,2003Rao, M.V.C. and V. Prahlad,1997Ryu, S., Y. Park and M. Suh,2011Scheibe, F. and M.C. Smith,2009Tamboli, J.A. and S.G. Joshi,1999Wang, H.X. and H.S. Zhang,2010∞ preview control.]]>Wo, S., Y. Zou, Q. Chen and S. Xu,2009Zaremba, A., R. Hampo and D. Hrovat,1997Zhou, K., J.C. Doyle and K. Glover,1996Zhou, R., A. Zolotas and R. Goodall,2011