The Four-wheel steering system is also called as Quadra Steering System, Rear wheel steering, All wheel steering or Quadrasteer. It is developed by Delphi of General Motors to use in vehicles. This system provides a driver to actively steer the rear wheels during turning maneuvers.
Generally, all steering systems are developed to respond driver while driving. It allows the driver to guide the vehicle on the road to turn it right or left as desired.
But,
In quadra steering system we can steer front wheels and rear wheels of vehicles at the same time. In this system, both front and rear wheels steered in the same direction and are parallel to each other.
This steering system reduces the space required for turning the vehicle as compared to that of the two-wheel steering system.
The Quadra steer steering system offers a 21% reduction rate in turning radius. So if a vehicle is capable of making a U-turn in a 25ft space, Quadra steer system allows the driver to do it in about 20ft.
The present 4WS four-wheel steering system works with the help of mechanical linkages. The system uses a manual manipulator to control and direct the articulation (left and right turning) of rear wheels.
Types of the steering system
For turning of the vehicle, there are two types of steering system used:
Conventional Steering System
Four Wheel Steering System
1. Conventional Steering System
The conventional steering system allows is to turn the front wheels by using a hand-operated steering wheel, which is in front of the driver.
That means during the steering of the vehicle, only the front wheels are steered towards the right or left direction according to the requirement, And the rear wheels are followers of front wheels in this system.
2. Four Wheel Steering System [Quadra Steering System]
Quadra steering system is employed by some vehicles to improve the steering response. It increases vehicle stability while driving at high speed. And it also helps to decrease turning radius at low speed.
This type of system is dependent on vehicle speed and it will read from various sensors.
When the vehicle is running at high speed all four wheels will turn the same direction to have greater stability.
On the highway to merge lane, you turn the wheel a little bit all four wheels will turn that direction and you’ll have a nice smooth stable merger. At the low-speed wheel, the movement is pronounced, so that rear wheels are steered in the opposite direction to that of front wheels.
It also simplifies the position of the car in parking situations in a limited space.
Since the rear wheels are made to follow the path of front wheels, the rear of a four-wheel system car does not turn in the normal way. Thus the risk of hitting any barrier is reduced.
In a 4WS system, the control of drive angle at the front and rear wheels is most essential.
There is completely free steering in four wheels. and need to turn in an unconventional direction to ensure that the vehicle rotates on its own axis. Such systems need precise calculation from the servo motor. so that real-time feedback can be ensured that all three steering modes work.
The only problem with this layout is that conventional rack-and-pinion steering with pitman’s arms will not be suitable since the two front wheels are steered in opposite directions.
PHASES OF QUADRA STEERING SYSTEM
The steering systems work on the following three phases:
Negative Phase
Positive Phase
Neutral Phase
This phase helps vehicles to steered into tighter parking spaces. It makes the vehicle more efficient and stable on cornering, easier and safer lanes change when on highways.
While driving at lower speeds, rear wheel turns in the opposite direction from the front wheel. This is a negative phase.
At a moderate speed, the rear wheel remains straight or neutral.
At a higher speed, the rear wheel is in a positive phase turning in the same direction as the front wheels.
1. Negative Phase
In the negative phase, both front and rear axles move in the opposite direction relative to each other. As both axles move in different direction directions the radius of curvature while turning reduces. This means that the vehicle will need less space for parking and it will be helpful in places where traffic and parking are a major problem.
2. Neutral Phase
In the neutral phase, only the front wheels either runs in the right or left direction and the rear wheel are the followers of the front wheels. This is the drive we see in all the four wheels in everyday’s life. It is usually used at medium speed.
3. Positive Phase
In the positive phase, both the axle front and rear move in the same direction relative to each other.
This motion of both the front and rear axle helps the quadra steering system capable vehicle to change the lane during highway driving. It is generally applied at a higher speed.
Compared the Four Wheel steering system to Conventional Steering System:
The car is more efficient and stable on the cornering.
Better steering response and precision high-speed straight-line stability.
Significant improvements in fast, easy, safe lane changing the drive.
Smaller turning corners and tight space drive at low speed.
Risk of hitting any barrier is greatly reduced.
Feature Aspects of 4WS
This innovative feature of steering system makes drive all wheels using a single steering actuator.
By successfully implementing this feature will allow for the development of a four-wheel, steered power base with maximum flexibility, uncompromised static stability, front wheel and rear-wheel tracking, and excellent obstacle climbing capability.
The advanced system of the 4WS will work with the help or microprocessors. This system utilizes an onboard computer to control and direct the turning left and right of the rear wheels.
Conclusion
The four-wheel steering is more advantageous over the conventional two-wheel steering system. The 4WS provide cornering capability, straight-line stability, very responsive steering, lane changing and low-speed drive.
These systems are very complex and expensive. Currently, the cost of four-wheel steering system vehicle is more than conventional two steering system.
Four-wheel steering is increasing in popularity and it is likely to come in more and more new vehicles. As the system becomes more common in the vehicle, the price of four-wheel steering systems will be dropped.
That’s it, thanks for reading if you have a question on “four wheel steering system” ask in the comments. If you like this article please share with your friends.
Saif M. is a Mechanical Engineer by profession. He completed his engineering studies in 2014 and is currently working in a large firm as Mechanical Engineer. He is also an author and editor at www.theengineerspost.com
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