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  • Topic: Steering, Vehicle dynamics, Wheel
  • Pages : 17 (5626 words )
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  • Published : September 13, 2013
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DEVELOPMENT OF FOUR WHEEL STEERING SYSTEM FOR A CAR
K. Lohith1, Dr. S. R. Shankapal2, M. H. Monish Gowda3 1- M. Sc. [Engg.] Student, 2-President, 3- Assistant professor Automotive and Aeronautical Engineering Department, M. S. Ramaiah School of Advanced Studies, Bangalore – 58.

Abstract
Production cars are designed to understeer and rarely do they oversteer. If a car could automatically compensate for an understeer/oversteer problem, the driver would enjoy nearly neutral steering under varying operating conditions. Four-wheel steering is a serious effort on the part of automotive design engineers to provide near-neutral steering. Also in situations like low speed cornering, vehicle parking and driving in city conditions with heavy traffic in tight spaces, driving would be very difficult due to vehicle’s larger wheelbase and track width. Hence there is a requirement of a mechanism which result in less turning radius and it can be achieved by implementing four wheel steering mechanism instead of regular two wheel steering. In this project Maruti Suzuki 800 is considered as a benchmark vehicle. The main aim of this project is to turn the rear wheels out of phase to the front wheels. In order to achieve this, a mechanism which consists of two bevel gears and intermediate shaft which transmit 100% torque as well turns rear wheels in out of phase was developed. The mechanism was modelled using CATIA and the motion simulation was done using ADAMS. A physical prototype was realised. The prototype was tested for its cornering ability through constant radius test and was found 50% reduction in turning radius and the vehicle was operated at low speed of 10 kmph. Nomenclature L R a2 δif δof δir δif R1 Wf W C1 C2 wf wr δ δi δo Wheelbase (mm) Turning radius (mm) Distance of CG from rear axle (mm) Inner angle of front tire (degree) Outer angle of front tire (degree) Inner angle of rear tire (degree) Outer angle of rear tire (degree) Distance between instantaneous centre and the axis of the vehicle (mm) Load on front axle (kg) Total weight of car (kg) Distance of instantaneous centre from front axle axis (mm) Distance of instantaneous centre from rear axle axis (mm) Front track width (mm) Rear track width (mm) Total steering angle of the vehicle (degree) Total inner angle of the vehicle (degree) Total outer angle of the vehicle (degree) By changing the direction of the rear wheels there is reduction in turning radius of the vehicle which is efficient in parking, low speed cornering and high speed lane change. In city driving conditions the vehicle with higher wheelbase and track width face problems of turning as the space is confined, the same problem is faced in low speed cornering. Usually customers pick the vehicle with higher wheelbase and track width for their comfort and face these problems, so to overcome this problem a concept of four wheel steering can be adopted in the vehicle. Four wheel steering reduces the turning radius of the vehicle which is effective in confined space, in this project four wheel steering is adopted for the existing vehicle and turning radius is reduced without changing the dimension of the vehicle.

2. BACKGROUND THEORY
The most effective type of steering, this type has all the four wheels of the vehicle used for steering purpose. In a typical front wheel steering system the rear wheels do not turn in the direction of the curve and thus curb on the efficiency of the steering. Normally this system is not been the preferred choice due to complexity of conventional mechanical four wheel steering systems. However, a few cars like the Honda Prelude, Nissan Skyline GT-R have been available with four wheel steering systems, where the rear wheels turn by an angle to aid the front wheels in steering. However, these systems had the rear wheels steered by only 2 or 3 degrees, as their main aim was to assist the front wheels rather than steer by themselves. With advances in technology, modern four wheel...
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