Four Wheel Steering System.

Presentation on Four Wheel Steering System

1. Four wheel steering System: Done by:- Md.Mudassir khan IV year Mechanical 13H11A0337

2. Contents: Contents Introduction Steering system Working principle Types of 4 wheel steering system Functions of steering system Advantages Disadvantages Applications Conclusions

3. Abstract:                The purpose of this report is to discuss about 4 wheel steering system and its’ mechanism.  Here we discuss the 4 wheel system mechanism which we have made as a project. First we gave an introduction about the 4WS ,then we briefly discuss about different types of 4WS mechanism and their functioning. We briefly describe our  project. Its’ design, working methodology,  working mechanism, cost analysis. Then there are some applications of this mechanism for which this system is now being used widely. After  that some advantages and disadvantages of 4WS are pointed out one by one with description.

4. Introduction: 4 wheel steering is a method developed in automobile industry for the effective turning of the vehicle and to increase the maneuverability. 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.

5. Steering system: Steering is the collection of components and linkages which allow a vehicle to follow the desired course. To get the desire output, input is given by a function which is called steering wheel. The most conventional steering arrangement  is to turn the front wheels using a hand operated steering wheel which is positioned in front of the driver via the steering column, which may contain universal joints  to allow it to deviate somewhat from a straight line. Other arrangements are sometimes found on different types of vehicles for example, a tiller or rear wheel steering. Tracked vehicles such as bulldozers and tanks usually employ differential steering that is, the tracks are made to move at different speeds or even in opposite directions, using clutches and brakes, to bring about a change of direction As we are discussing about car steering system so there are various types of steering system based on the movement of wheels. I. 2 Wheel Steering. ii. 4 Wheel Steering. iii. Power Steering. iv. Speed Sensitive Steering.

6. WORKING PRINCIPLE: When the steering is steered the power is transferred to the front steering gear box, and a bevel gear arrangement is made to transfer the power to the rear steering gear box. Bevel gear is used to transmit the rotary motion perpendicularly, so the one bevel gear is introduced in the front steering rod. Other bevel gear is connected to the transfer rod. Two supports are used to support the transfer rod. Transfer rod is connected to the rear steering gear box. Rear steering gear box is fixed to the car body by bolts and nuts and the ends of the steering box are connected to the rear wheel hub where the tyres are mounted. As the steering is steered the rear wheels also turn by the arrangements made and the rear wheel turn in the opposite direction.

7. TYPES OF STEERING SYSYEM: There are mainly 3 types of 4WS mechanism Mechanical 4 Wheel System. Hydraulic 4 Wheel System. Electro Hydraulic 4 Wheel System.

8. Mechanical 4WS System: In a straight mechanical type of 4WS two steering gears are used one for the front and the other for the rear wheels. A steel shaft connects the two steering gearboxes and terminates at an eccentric shaft that is fitted with an offset pin. This pin engages a second offset pin that fits into a planetary gear. The planetary gear meshes with the matching teeth of an internal gear that is secured in a fixed position to the gearbox housing. This means that the planetary gear can rotate but the internal gear cannot. The eccentric pin of the planetary gear fits into a hole in a slider for the steering gear.

9. Hydraulic 4WS System: The rear wheels turn only in the same direction as the front wheels. They also turn no more than 11/2 degrees. The system only activates at speeds above 30 mph (50 km/h) and does not operate when the vehicle moves in reverse. A two way hydraulic cylinder mounted on the rear stub frame turn the wheels. Fluid for this cylinder is supplied by a rear steering pump that is driven by the differential. The pump only operates when the front wheels are turning. A tank in the engine compartment supplies the rear steering pump with fluid.

10. Electro Hydraulic 4WS: In this design, a speed sensor and steering wheel angle sensor feed information to the electronic control unit (ECU). By processing the information received the ECU commands the hydraulic system steer the rear wheels. At low road speed, the rear wheels of this system are not considered a dynamic factor in the steering process. At moderate road speeds, the rear wheels are steered momentarily counter 45 phase, through neutral, then in phase with the front wheels. At high road speeds, the rear wheels turns only in phase with the front wheels. The ECU must know not only road speed, but also how much and quickly the steering wheel is turned. 

11. FUNCTIONS OF THE STEERING SYSTEM: To control the angular motion the wheels and thus the direction of motion of the vehicle. To provide directional stability of the vehicle while going straight ahead. To facilitate straight ahead condition of the vehicle after completing a turn. The road irregularities must be damped to the maximum possible extent. This should co-exist with the road feel for the driver so that he can feel the road condition without experiencing the effects of moving over it. To minimize tyre wear and increase the life of the tyres.

12. Advantages: Superior cornering stability Improved steering response and precision High speed straight line stability Improved rapid lane changing maneuvers Smaller turning radius

13. Disadvantages: Expensive Construction Complex Mechanism Higher Maintenance Cost

14. Applications: Parking Junctions Slippery surfaces Turning On Narrow Road U - turn

15. Conclusions: Advantageous to 2WS Complex and expensive Cost may drop as the system becomes common