MODERN STEERING SYSTEMS

 MODERN STEERING SYSTEMS

 

 FOUR WHEEL STEERING:

                There are three types of 4 wheels steering system 

1.     Mechanical 4wS
2.     Hydraulic 4ws 
3.     Electra-hydraulic 4ws

        

The concept of four wheel steering is hardly and relatively new as four wheel drive    Admittedly those systems were custom, typically controlled and separately controlled from the front wheels.

                                                                                                                  The first production four wheels steering for the average, American automobile consumer was offered 20 years ago. On the 1988, this system was entirely self contained, automatic and mechanical: no electronic, no speed sensors, no computers, no hydraulic, just two racks and a rod between them.

Four wheel steering (4ws) is also called the rear wheels steering or all wheel steering.The (4ws) four wheel steering should not be confused with four wheel drive. 4ws system improves handling and helps the vehicle at lighter turns. The front wheels do the actual steering work. The rear wheel turning is generally limited a 5⁰ to 20 ⁰ during an opposite duration turn. During the same direction turn rear wheel steering is limited the about 1⁰ to 1.5 ⁰. In a (4ws) system, the front and rear wheels steer towards same direction which is said to be in-phase at high speed, where as the front and rear wheels turn in an opposite direction at slow speed which is called anti- phase or opposite phase and it is produced at a sharper turn and tighter turn.

Steering system allows the driver to control the direction of the vehicle travel. This is made possible by linkage that connects the steering wheel to the steerable wheels and tires. The steering system may be either manual or power .When the energy source for the steering system is the force, the drives applies to the steering wheel, then the vehicle has manual steering .Power steering used a hydraulic pump or in motor to assist the driver effects. In the modern age most of the vehicles are manufacture with a power steering mechanism.

The operation is same for both manual and power steering .As the drive turns the steering where the movement is carried to the steering gear. It chains the rotary matron of the steering wheel, in to straight line or linear motion. The linear motion acts through steering linkage /tie rod attached to the steering knuckle .arms or steering arms. The steering knuckle then turns the wheels in to left or right side.

 ADVANTAGE OF FOUR WHEEL STEERING:

• The vehicle's cornering behavior becomes more stable and controllable at high speedsas well as on wet or slippery road surfaces.                                     
•  The vehicle's response to steering input becomes quicker and more precise throughout the vehicle's entire speed range.The vehicle's straight-line stability at high speeds is improved. 
• Negative effects of road irregularities and crosswinds on the vehicle's stability are minimized.Stability in lane changing at high speeds is improved. 
• The vehicle is less likely to going a spin even in situations in which the driver must make a sudden and relatively large change of direction. 
• By steering the rear wheels in the direction opposite the front wheels at low speeds,the vehicle's turning circle is greatly reduced. 
• Therefore, vehicle maneuvering on narrow-roads and during parking becomes easier.

APPLICATION OF FOUR WHEEL STEERING:

It is used for easy parking of four wheelers, and can be implemented in monster trucks, large farm vehicles and trucks. Etc..

FAIL OF SAFETY MEASURES:

• All 4WS systems have fail-safe measures. For example, with the elector-hydraulic setup, the system automatically counteracts possible causes of failure: both electronic and hydraulic, and converts the entire steering system to a conventional two-wheel steering type. 
• Specifically, if a hydraulic defect should reduce pressure level (by a movement malfunction or a broken driving belt), the rear-wheel-steering mechanism is automatically locked in a neutral position, activating a low-level warning light.
• In the event of an electrical failure, it would be detected by a self-diagnostic circuit integrated in the four wheel-steering control unit.
•  The control unit stimulates a solenoid valve, which neutralizes hydraulic pressure, thereby alternating the system to two-wheel steering.
•  The failure would be indicated by the system's warning light in the main instrument display
• .On any 4WS system, there must be near-perfect compliance between the position of the steering wheel, the position of the front wheels, and the position of the rear wheels. It is usually recommended that the car be driven about 20 feet (6 meters) in a dead-straight line.
•  Then, the position of the front/rear wheels is checked with respect to steering wheel position.
•  The base reference point is a strip of masking tape on the steering wheel hub and the steering column.When the wheel is positioned dead center, draw a line down the tape. 
• Run the car a short distance straight ahead to see if the reference line holds. If not, corrections are needed,such as repositioning the steering wheel. Even severe imbalance of a rear wheel on a speed sensitive 4WS system can cause problems and make basic troubleshooting a bit frustrating.

 ZERO STEERING:

               Zero steering are those which has a minimum steering radius that is equal to zero,which rotates about its own some of the jeeps comes with this type of steering.you can see in this picture that the turning radius is zero and this is known as zero steering.

A jeep named hurricane has this type of steering..

JEEP HURRICANE STEERING:

                               

The Hurricane's steering system is a marvel of engineering all by itself. There are multiple steering modes using four-wheel independent steering. That means that each wheel can turn separately from the others.                               

In standard steering mode, the rear wheels turn in the opposite direction to the front wheels, which tightens the turning radius and makes for more accurate steering.

                                                                                           PHOTO COURTESY: DIAMLER CHRYSLER

In a second mode, the rear wheels turn in the same direction as the front wheels, meaning the Hurricane can "crab-steer" -- move to the side without changing the direction that it faces.

A third mode, utilizing the "T-Box Zero Steer" mechanism, allows all four wheels to "toe-in" and changes the drive direction to each wheel so that they alternate. The result? The Jeep Hurricane has a turning radius of zero. The Hurricane can actually rotate in place.

The cars with four wheel steering differ from that of ordinary one as shown in the image above.