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ABSTRACT
The most conventional and general steering arrangement is to turn the front wheels using a hand– operated steering wheel which is positioned in front of the Driver. Usually during the steering of the vehicle, only the front wheels are steered towards right or left according to the requirement and the rear wheels are mere followers of the front wheels in this system. In this paper, both front wheel and rear wheels can be steered according to speed other vehicle and space available for turning.
A Four wheel steering system also known as Quadra steering system. Four wheel steering is system that gives full size vehicles greater ease while driving at low speed, and improves stability, handling and control at higher speed. Quadra steering system works in following three phases Negative phase, Neutral phase, Positive phase. It enables the car to be steered into parking spaces. It also makes the car is stable at high speed. It makes the car more efficient and stable on cornering, easier and safer lanes change in highways.
The steering system allows the driver to guide the moving vehicle on the road and turn it right or left as desired to take turn at low speed as well as high speed. In this type of steering system, we can steer a front wheel, as well as the rear wheel of the vehicles simultaneously. Four wheel steering system has got cornering capability, steering response, straight line stability, lane changing and low speed maneuverability. Quadra steering system has main aim that it offers reduction of turning radius so that vehicle should not require greater efforts on the part of the driver.The Quadra steer steering system offers a 21% reduction in turning radius. So if a vehicle is capable of making a U-turn in a 25-foot space, Quadra steer allows the driver to do it in about 20 feet.
INTRODUCTION
A German scientist Daimler-Benz, for the first time developed four-wheel drive or four-wheel steering vehicles for the forest service. Their rear wheels were designed to turn in opposite direction to the front wheel so that the vehicle could make sharp turns.
In the year 1978, it was modified by the Japanese scientist “Furukawa”. According to him, “all the wheels should turn in the same direction at high speeds & in opposite direction at the lower speeds”. Later, it was studied at Oguchi's laboratory at Shibaura Institute of Technology, led by the professor Oguchi.
Accordingly, a new mechanism had to be developed by combining an electronic control device and variable gear-ratio mechanism. "When the 4WS system was in development," Furukawa said, "I truly believed that I was creating a technology.But when I look back at it now, perhaps it was the 4WS technology that was nurturing me." "It was the desire to bring what we believed to the world, and to see it accepted by users," Furukawa explained. "That's the thing that made in our process work." The 4WS system undeniably established a new standard in driving performance, but without a doubt it did something more. It brought creative minds together in a solution that would one day benefit the automotive world.
In four wheel steering system the direction of steering the rear wheels relative to the front wheels depends on the operating conditions. As the low speed of vehicle while maneuvering or taking the turn the rear wheel turn at opposite direction to the front wheel and for high speed of vehicle while taking the turn the rear wheel takes same turn as of front wheel direction. It improves handling and helps the vehicle make tighter turns. This system is used to minimize the turning radius. In most active four-wheel steering systems, the rear wheels are steered by a computer and actuators. The rear wheels generally cannot turn as far as the front wheels.
LITERATURE REVIEW
New generation of active steering systems distinguishes a need of steering of rear wheels for the reason of directional stability from a need of steering of rear wheels for the reason of cornering at slow speed.. The aim of 4WS system is a better stability during overtaking maneuvers, reduction of vehicle oscillation around its vertical axis, improvement of active safety. And study of 2 wheel steering system, study of 4 wheel steering system, comparing both 2WS and 4WS to find difference in turning radius in between them is done by Mr. Sachin saxena.
1. R.C. Singh (2014)
a. From International Conference of Advance Research and Innovation (ICARI-2014)
b. Objective: study about 4WS steering system, and rear wheel control in 4WS system
c. Result:The aim of 4WS system is a better stability during overtaking maneuvers, reduction of vehicle oscillation around its vertical axis, improvement of active safety.
2. Sachin Saxena (2014)
a. From International Journal of Mechanical and Robotics Research (IJMERR 2014)
b. Objective: study of 2 wheel steering system, study of 4 wheel steering system, comparing both 2WS and 4WS to find difference in turning radius.
c. Result: 4 wheel steering system has more advantages than 2 wheel steering system. Turning radius of 4 wheel steering system is smaller than 2 wheel steering system.
3. Dr. V.V. Pratibha Bharti (2015)
a. From International Journal of Emerging Technology and Innovative Engineering (IJETIE 2015)
b. Objective: History of four wheel steering, components and process involve in 4 wheel steering
c. Result: 4WS is basically come from germane, 4WS has three modes.
4. Mr. Krishna Bevinkatti (2015)
a. From International Journal of Emerging Technology and Innovative Engineering (IJETIE 2015
b. Objective: study about 4 wheel steering, its specificationsand cornering ability.
c. Result: 4 wheel steering system is more sensible during narrow roads and during cornering. Due to smaller turning radius the parking and un parking of vehicle is easily performed.
5. Mr. Manish K. Mistry (2014)
a. From Technical Journals India (2014)
b. Objective: parts of 4 wheel steering system, its specifications.
c. Results: reduction in turning radius, better cornering, zero steer mode can also be implemented.
WHAT IS QUADRA STEERING..?
Steering is the term applied to the collection of components, linkages, etc. which will allow a vehicle to follow the desired course. 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.
In four wheel steering system all four wheels are to be steered according to the steer perform to drive towards left or right. Four-wheel steering, 4WS, also called rear-wheel steering or all-wheel steering, provides a means to actively steer the rear wheels during turning maneuvers. It should not be confused with four-wheel drive in which all four wheels of a vehicle are powered. It improves handling and helps the vehicle make tighter turns.
Production-built cars tend to under steer or, in few instances, over steer. If a car could automatically compensate for an under steer or over steer problem, the driver would enjoy nearly neutral steering under varying conditions. In most active four wheel steering system, the rear wheels are steered by a computer and actuators, the rear wheels generally cannot turn as far as the front wheels. Some systems including Delphi’s Quadra steer and the system in Honda’s Prelude line allow the rear wheels to be steered in the opposite direction as the front wheels during low speeds. This allows the vehicle to turn in a significantly smaller radius sometimes critical for large tucks or tractors and vehicles with trailers.
WHY TO USE QUADRA STEERING
If we understand the concept of steering then we come to know that during steering the tires are subject to theforces of grip, momentum, and steering input when making a movement other than straight-ahead driving. These forces compete with each other during steering maneuvers. 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. As a normal part of operating a vehicle, the driver learns to adjust to these forces without thinking about them.
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 the road, and momentum moves the car straight ahead. Steering inputcauses the front wheels to turn. The car momentarily resists the turning motion, causing a tire slip angle to form. Once the vehicle begins to respond to the steering input, cornering forces are generated. The vehicle sways as the rear wheels attempt to keep up with the cornering forces already generated by the front tires. This is referred to as rear-end lag, because there is a time delay between steering input and vehicle reaction.
When the front wheels are turned back to a straight -ahead position, the vehicle must again try to adjust by reversing the same forces developed by the turn. As the steering is turned, the vehicle body sways as the rear wheels again try to keep up with the cornering forces generated by the front wheels.
DIFFERENT STEERING MECHANISMS
There are two steering mechanisms, which are as follows:
1. Ackerman’s Steering Mechanism
2. Davis Steering Mechanism
1. Ackerman’s Steering Mechanism:
Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radii. It was invented by the German Carriage Builder "Lankensperger" in 1817, then patented by his agent in England Rudolph Ackermann (1764– 1834) in 1818.
The intention of Ackermann geometry is to avoid the need for tyres to slip sideways when following the path around a curve. The geometrical solution to this is for all wheels to have their axles arranged as radii of a circle with a common center point. As the rear wheels are fixed, this center point must be on a line extended from the rear axle. Intersecting the axes of the front wheels on this line as well requires that the inside front wheel is turned, when steering, through a greater angle than the outside wheel. Rather than the preceding "turntable" steering, where both front wheels turned around a common pivot, each wheel gained its own pivot, close to its own hub. A linkage between these Hubs moved the two wheels together, and by careful arrangement of the linkage dimensions the Ackermann geometry could be approximated. This was achieved by making the linkage nota simple parallelogram, but by making the length of the track rod shorter than that of the axle, so that the steering arms of the hubs appeared to "toe out".
As the steering moved, the wheels turned according to Ackermann, with the inner wheel turning further. If the track rod is placed ahead of the axle, it should instead be longer in comparison, thus preserving this same "toe out".A simple approximation to perfect Ackermann steering geometry may be generated by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the center of the rear axle. The steering pivot points are joined by a rigid bar called the tie rod which can also be part of the steering mechanism, in the form of a rack and pinion for instance. With perfect Ackermann, at any angle of steering, the center point of all of the circles traced by all wheels will lie at a common point. Note that this may be difficult arrangement in practice with simple linkages, and designers are advised to draw or analyze their steering systems over the full range of steering angles. Modern cars do not use pureAckermann steering, partly because it ignores important dynamic and compliant effects, but the principle is sound for low speed maneuvers. Some race cars use reverseAckermann geometry to compensate for the large difference in slip angle between the inner and outer front tyres while cornering at high speed. The use of such geometry helps reduce tyre temperatures during high-speed cornering but compromises performance in low speed maneuvers.
2. Davis Steering Mechanism:
The Davis steering mechanism consists of a cross link KL sliding parallel to another link AB and is connected to the stub axles of the two front wheels by means of two similar bell crank levers ACK and DBK pivoted at A and B respectively. The cross link KL slides insides in the bearing and carries pins at its end K and L. The slide blocks are pivoted on these pins and move with the turning of bell crank levers as the steering wheel is when the vehicle is running straight, the gear set to in its mid-position. The short arms AK and BL are inclined an angle 90+α to their stub axles AC and BD. The correct steering depends upon a suitable selection of cross-arm angle α, and is given by
Tanα = b / 2l
Where
b = AB = distance between the pivots of front axles.
l = wheel base.
The range of b / l is 0.4 to 0.5 hence angle α lies between 11.3 and 14.10.
DIFFERENT TYPES OF QUADRA STEERING SYSTEMS
1. Mechanical 4WS System
2. Hydraulic 4WS System
3. Electro/Hydraulic 4WS system
1. 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 planetary gear fits into a hole in a slider for steering gear.
A 120-degree turn of the steering wheel rotates the planetary gear to move the slider in same direction that the front wheels are headed. Further action of steering wheel past the 120 degree point, causes the rear wheel to straightening out due to double crank action and rotation of the planetary gear. Turning the steering wheel to a greater angle, about 230 degree, finds the rearwheel in a neutral position regarding a front wheels. Further rotation of the steering wheel results in rear wheel going counter phase with regard to the front wheels. About 2.3 degrees maximum counter phase steering is possible.
Mechanical 4WS is steering angle sensitive. It is not sensitive to vehicle road speed.
Hydraulic 4WS System:
The hydraulic 4 wheel steering system is simple in design, both in components and operation. 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 50 km/hr. and does not operate when 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 fluids.
When the steering wheel is turned, the front steering pump sends fluid under pressure to the rotary valve in the front rack and pinion unit. This forces fluid into the front power cylinder, and the front wheels turn in the direction steered. The fluid pressure varies with the turning of the steering wheel. The faster and farther the steering wheel is turned, the greater the fluid pressure.
The fluid is also fed under the same pressure to the control valve where it opens a spool valve in the control valve housing. As the spool valves moves, it allows fluid from the rear steering pump to move through and operate the rear power cylinder. The higher the pressure on the spool, the farther it moves. The farther it moves, the more fluid it allows through to move the rear wheels. As mentioned earlier, this system limits the rear wheel movement to 11/2 degrees in either the left or right direction.
MODES OF 4WS SYSTEM:
There are three modes of 4WS system, such as
• Negative mode:
The negative mode or negative phase is used for low speed maneuvers up to 50 km/hr. this is where the rear wheels turn opposite to front wheels. This phase is limited to maximum of 12 degrees rotation at slow speeds and gradually decreases to zero degree. Ref. fig. A.
• Positive mode:
The positive phase begins after 50km/hr. and is used when the rear wheels turn in the same direction as the front wheels. This is limited to a maximum arc of 5 degrees and decreases with speed. When transmission is in ‘park’, rear wheel steering is limited to five degrees to avoid excessive tire wear. Ref. fig. C.
COMPARISON WITH 2WS SYSTEM
• Car more efficient and stable on cornering.
• Improved steering responsiveness and precision.
• High speed straight line stability.
• Notable improvement in rapid, easier, safer lane changing maneuvers.
• Smaller turning radius and tight space maneuverability at low speed.
• Relative Wheel Angles and their Control.
• Risk of hitting an obstacle is greatly reduced
• Turning radius of 4WS steering is 5.14 ft. while for 2WS steering it is 14.70 ft.
FUTURE ASPECTS
An innovative feature of this steering linkage design is its ability to drive all four Wheels using a single steering actuator. Its successful implementation will allow for the development of a four-wheel, steered power base with maximum maneuverability, uncompromised static stability, front- and rear wheel tracking, and optimum obstacle climbing capability.
The advanced system of “Four wheel steering” will work electronically with the help or microprocessors.
The system will utilize an onboard computer to control and direct the turning left and right of the rear wheels.
PRODUCTION CARS WITH ACTIVE FOUR WHEEL STEERING
1. BMW 850CSi (optional)
2. Efini MS-9 (high and low speed)
3. GMC Sierra (2002) (high and low speed)
4. Honda Accord (1991) (high and low speed, mechanical)
5. Infiniti M45 (option on Sport models) (2006-Present)
6. Infiniti Q45t (1989-1994) (high speed only)
7. Mitsubishi Galant/Sigma (high speed only)
8. Mitsubishi GTO (also sold as the Mitsubishi 3000GT and the Dodge Stealth) (high speed only)
9. Lamborghini 2016 this is the latest in all above
10. Audi Q7
11. Jeep hurricane (it also work by steer by wire)
12. Porsche GT3
13. Renault Laguna
14. GM Silverado
15. GM sierra
16. Suburbon and Yukon
ADVANTAGES & DISADVANTAGES
ADVANTAGES:
1. Computer-controlled Quadra steer can be switched on and off and has an effective trailer towing mode.
2. A computer determines how much and in which direction the rear wheels should move, and whether the rear wheels should turn the same direction as the front wheels or in the opposite direction. The movement is variable up to a couple of inches.
3. At slow speeds, the rear wheels move the opposite direction of the front wheels. This makes for easier parking and maneuvering.
4. At highway speeds, the rear wheels move in the same direction as the front wheels for easier lane changing. If you’re pulling a trailer you’ll really appreciate this feature, since it allows your vehicle to change lanes without the snaking-effect you’d normally experience.
DISADVANTAGES:
1. Significantly increase in work load for front tyres.
2. Large amount of left/right weight transfer seen in 4ws vehicle.
3. Uneven tyres wear of front and rear wheels.
APPLICATIONS OF 4WS
1. Parallel parking: Due to smaller turning radius the parking and imparking of vehicle is easily performed towards the right or left side.
2. High speed lane changing: In this is less steering sensitive this does require a lot of concentration from driver since he has to judge the space and vehicles behind them.
3. Slippery road surfaces: Due to the rear wheel steering operation on low friction surfaces occurs hence vehicle direction easier to control.
4. Narrow Roads: Due to rear wheel steering on narrow roads with tight bends, counter phase steering reduces the turning radius.
5. U-Turns: By minimizing the vehicle’s turning radius and counter phase steering of rear wheels enables U-Turns to be performed on narrow roads.
CONCLUSION
Four wheel steering is a relatively new technology, that imposes maneuverability in cars, trucks and trailers .in standard two wheels steering vehicles, the rear set of wheels are always directed forward therefore and do not play an active role in controlling the steering in four wheel steering system the rear wheel can turn left and right . To keep the driving controls as simple as possible. The aim of 4WS system is a better stability during overtaking maneuvers, reduction of vehicle oscillation around its vertical axis, reduced sensibility to lateral wind, neutral behavior during cornering, etc., i.e. improvement of active safety.
Even though it is advantageous over the conventional two-wheel steering system, 4WS is complex and expensive. Currently the cost of a vehicle with four wheel steering is more. Thus the four-wheel steering system has got cornering capability, steering at for a vehicle with the conventional two wheel steering. Four wheel steering is growing in popularity and it is likely to come in more and more new vehicles.