Four Wheel Steering Project Report

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PROBLEM DEFINITION

Nowadays all vehicles uses two wheel steering system, but the efficiency of the two wheel steering (2WS) vehicle is proven that it is still low compared to the four wheel steering (4WS) system car. So, this project is base on how to prove that the 4WS is better than 2WS in terms of turning radius 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 conhuditions 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.
 

 INTRODUCTION

Four wheel steering is a method developed in automobile industry for the effective turning of the vehicle and to increase the manuverbility. 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. In four wheel steering the rear wheels turn with the front wheels thus increasing the
efficiency of the vehicle. The direction of steering the rear wheels relative to the front wheels depends on the operating conditions. At low speed wheel movement is pronounced, so that rear wheels are steered in the opposite direction to that of front wheels. At high speed, when steering adjustments are subtle, the front wheels and the rear wheels turn in the same direction. 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.

WORKING PRINCIPLE

 
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 our 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 steering systems boast of fully electronic steer-by-wire systems, equal steer angles for front and rear wheels, Usually in vehicles during turning, the tires are subject to the forces of grip, momentum, and steering
input when making a movement other than straight ahead driving. These forces compete with each other during steering manoeuvres. With a front-steered vehicle, the rear end is always trying to catch up to the directional changes of the front wheels. This causes the vehicle to sway. When turning, the driver is putting into motion a complex series of forces. Each of these must be balanced against the others. The tires are subjected to road grip and slip angle. Grip holds the car’s wheels to he road, and momentum moves the car straight ahead. Steering input causes the front wheels to turn.

APPLICATION OF FOUR WHEEL STEERING

  • Parallel parking
  • Zero steer can significantly ease the parking process due to its extremely short turning footprint. This is exemplified by the parallel parking scenario which is common in foreign countries and is pretty relevant to our cities. Here a car has to park itself
  • between the two other cars parked on the service lane.
  • High speed lane changing
  • Another driving maneuver that frequently becomes cumbersome and even dangerous is changing lanes at fairly high speed. Although this is less steering sensitive this does require a lot of concentration from the driver since he has to judge the space and vehicles behind
  • them. The vehicle with arrows is the model under study. As can be seen from the figure the vehicle can turn with hardly any space requirement with a single steering action and also resume without any corrective inputs. Thus it also acts as a driver aid helping relatively
  • inexperienced drivers make quick lane changes even athigh speeds.
  • The manufactured the first four wheel steering car and it defines four wheel steering as the effect of the 4WS mechanism acting in this way was non-linear steering.
 

ADVANTAGES.

1)      It reduces the turning radius.
2)      Such simple that an unskilled driver .
3)      Very useful in heavy traffic of metro cities.
4)     Steering angles position of instantaneous centre for turning radius 4.4m. parking of car in a less space is makes very simple.

 

 

DISADVANTAGES.

1)      Initial cost is high.
2)      It increases the crabbing effect while driving.
3)      It cannot be applied without power steering.

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