Pramanik et al. 2012. Int. J. Vehicle Structures & Systems, 4(2), 64-68 International Journal of Vehicle Structures & Systems Available online at www.ijvss.maftree.org ISSN: 0975-3060 (Print), 0975-3540 (Online) doi: 10.4273/ijvss.4.2.05 © 2012. MechAero Foundation for Technical Research & Education Excellence 64 Comparative Study of Steering Mechanisms for Large Wheelbase Vehicles S. Pramanik a , R.B. Ingle b and A.A. Latey c a Dept. of Mechanical Engg., College of Military Engineering, Pune, India. Corresponding Author, Email: santiranjan_pramanik@rediffmail.com b Dept. of Mechanical Engg., Cummins College of Engg. for Women, Pune, India. Email: rbingle2002@yahoo.com c Dept. of Mechanical Engg., College of Engineering, Pune, India. Email: aal.mech@coep.ac.in ABSTRACT: This paper presents an optimum synthesis of Ackermann, rack and pinion and centre lever steering mechanisms using Hookes and Jeeves optimization. The objective function of the optimisation comprises of steering error. The length of the steering arm has been assumed as one-fifth of the wheel track for all cases. The steering error, transmission angle and mechanical advantages of these steering mechanisms have been compared. It has been found that the rack and pinion steering mechanism produces the least steering error. The transmission angle and mechanical advantage of the centre lever steering mechanism are most favourable. A suggestion has been made to replace the existing Ackermann steering mechanism for long wheelbase vehicles by a central outrigger type leading rack and pinion steering mechanism. KEYWORDS: Ackermann steering; Rack and pinion steering; Centre-lever steering; Hooke and Jeeves optimization; Steering error; Transmission angle; Mechanical advantage CITATION: S. Pramanik, R.B. Ingle and A.A. Latey. 2012. Comparative Study of Steering Mechanisms for Large Wheelbase Vehicles, Int. J. Vehicle Structures & Systems, 4(2), 64-68. doi:10.4273/ijvss.4.2.05 1. Introduction A lot of attention has been paid to the steering mechanism for four wheel vehicles by the researchers for its optimization. Fahey and Huston [1] have suggested an eight-member mechanism for automotive steering with seven precision points in the entire range of rotation. They have modified an Ackermann steering mechanism and shown a reduction in the steering error greatly and the divergent end behaviour of the steering error curve modification. They have concluded that the motion of inside wheel was stiffened as the outside wheel was quickened nearing the end range and there by the steering error was reduced. Simionescu and Beale [2] have considered Ackermann steering mechanism and presented design charts from which the parameters could be selected to achieve an optimum steering mechanism. Simionescu and Smith [3] have optimized rack-and- pinion steering mechanisms and have plotted the design charts. These charts aid automotive engineers in the early stages of conceiving a new steering mechanism. Simionescu and Smith [4] have optimized a centre-lever steering mechanism using Brent algorithm. They have presented the design charts which considerably eased the work of the engineer in determining the optimum geometry of a centre-lever steering mechanism. Pramanik [5] has synthesized a centre-lever steering mechanism for automobiles using precision point method. He considered three design parameters and five precision points. The procedure has led to a set of nonlinear algebraic equations with three unknowns. Newton-Raphson method has been used to solve these equations. The maximum steering error is 0.3 degree in a range of 61 degree rotation of the inner wheel. Hanzaki et al [6] have performed combined kinematic and sensitivity optimization of a rack and pinion steering mechanism. They have found that the optimized kinematic error is very sensitive to the variations of the linkage parameters. In the present work optimal synthesis has been carried out for all three types of steering mechanisms using Hooke and Jeeves optimization method [7] and their performances have been compared. On the basis of this comparison, a suggestion has been made for better alternative steering mechanism for long wheelbase vehicles. 2. Ackermann steering mechanism An Ackermann steering mechanism ABCD has been shown in Fig.1. The links AB and CD are equal in length and are equally inclined to the link AD for straight-ahead motion of the vehicle. For a right turn, the link AB is