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ABSTRACT
The basic aim of steering is to ensure that the wheels are pointing in the desired
directions. This is typically ...
1. INTRODUCTION
The most conventional steering arrangement is to turn the front wheels using a
hand–operated steering whee...
Figure-1.1 Steering gear
There are 2 basic types of steering boxes - those with rack-and-pinion gearing, and
those with wo...
To allow heavy transport vehicles to carry extra weight, two steering axles may be
used. They’re connected by a link to a ...
2. WHEELED VEHICLE STEERING
2.1 Basic geometry
The basic aim of steering is to ensure that the wheels are pointing in the ...
Figure 2.1.1 Ackermann Steering mechanism
Older designs use two main principles: the worm and sector design and the screw
...
The recirculating ball mechanism has the advantage of a much greater mechanical
advantage, so that it was found on larger,...
Figure 2.1.2 Ackermann steering geometry
2.2 Power Steering
Power steering helps the driver of a vehicle to steer by direc...
power steering motor only needs to provide assistance when the steering wheel is
turned, whereas the hydraulic pump must r...
perceive that motoristsmight need to make large steeringinputs while manoeuvring
for parking, but not while traveling at h...
it set a record breaking time of 10:47.77.[3] The car would go on to victory in the
1989 and 1990 Paris-Dakar Rally, again...
3. PRINCIPLE OF STEERING
The steering system must provide control over the direction of travel of the vehicle;
good maneuv...
The steering box converts the rotary motion of the steering wheel, to the linear
motion needed to steer the vehicle. It al...
4 TYPES OF STEERING SYSTEM
4.1. Rack & Pinion Steering System
Many modern cars use rack and pinion steering mechanisms, wh...
Figure 4.2.1 Components of rack and pinion steering system
The primary components of the rack and pinion steering system a...
Pinion:- The pinion is connected to the steering column. As the driver turns the
steering wheel, the forces are transferre...
Figure 4.2.4 Gear
Inner Ball Joint Or Socket:- The inner ball joint is attached to the tie-rod, to
allow for suspension mo...
rod ends are left or right hand threaded. This allows toe-in or toe-out to be adjusted
to the manufacturer's specification...
Figure 4.2.1 Recirculating ball
Mechanism:-
The recirculating ball steering mechanism contains a worm gear inside a block ...
The primary components of the recirculating ball and nut steering system are:
1. Pitman Arm Shaft
2. Idler Arm
3. Track Ro...
Idler Arm:- The idler arm is attached to the chassis and is positioned parallel to the
pitman arm.
Figure 4.2.3 Idler arm
Track Rod or Centre Link:- The track rod connects the pitman arm shaft to the
idler arm shaft. In this way any movement in...
Figure 4.2.5 Tracker rod
Tie Rod End:- Tie rod ends are attached to the tie-rodshaft. These pivot as the rack
is extended ...
Adjustment Sleeve:- The adjustment sleeve connects the tie-rod to the tie-rod end.
It provides the adjustment point for to...
Figure 4.3.1 Four wheel steering
With heavier vehicles, increased use of front-wheel drive, and wider, low-profile
tyres, ...
5. STEERING MECHANISMS
1. Ackermann steering geometry
2. Davis steering geometry
5.1. Ackermann steering geometry
It is a ...
Figure 5.1.1 Ackermann steering
Modern cars do not use pure Ackermann steering, partly because it ignores
important dynami...
Figure 5.1.2 Rack pinion gear
The Ackerman Steering Principle defines the geometry that is applied to four wheel
drive to ...
As the rear wheels are fixed, this centre point must be on a line extended from the
rear axle.
Intersecting the axes of th...
6. STEERING RATIO
Steering ratio refers to the ratio between the turn of the steering wheel (in degrees)
or handlebars and...
but it will be harder to turn the steeringwheel. Larger and heavier vehicles will often
have a higher steering ratio, whic...
Figure 6.1.2 Steering effort characteristics
6.2. Turning circles
Figure 6.2.1 Turning circle
7. CONCLUSION
With the world’s highest growth rate for passenger vehicle production, the Chinese
automotive market crossed...
7. FUTURE SCOPE
You can expect to see several innovations that will improve fuel economy. One of
the coolest ideas on the ...
8. REFRENCES
1. http://www.hemmings.com/hmn/stories/2010/07/01/hmn_feature20.html
2. http://www.cnet.com/videos/top-5-citr...
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Steering system project report

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Steering system project report

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Steering system project report

  1. 1. ABSTRACT The basic aim of steering is to ensure that the wheels are pointing in the desired directions. This is typically achieved by a series of linkages, rods, pivots and gears. One of the fundamental concepts is that of caster angle – each wheel is steeredwith a pivot point ahead of the wheel; this makes the steering tend to be self-centring towards the direction of travel. When the driver turns the steering wheel, a shaft from the steering column turns a steering gear. The steering gear moves tie rods that connect to the front wheels. The tie rods move the front wheels to turn the vehicle right or left. The steering system must provide control over the direction of travel of the vehicle; good maneuverability for parking the vehicle; smooth recovery from turns, as the driver releases the steering wheel; and minimum transmission of road shocks from the road surface. The steering system provides control over direction of travel, good manoeuvrability, smooth recovery from turns, and minimum transmission of road shocks.
  2. 2. 1. INTRODUCTION 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 (which may also be part of the collapsible steering column design), to allow it to deviate somewhat from a straight line. Other arrangements are sometimesfound 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 course or direction. The direction of motion of a motor vehicle is controlled by a steering system. A basic steering system has 3 main parts: A steering box connected to the steering wheel. The linkage connecting the steering box to the wheel assemblies at the front wheels. And front suspension parts to let the wheel assemblies pivot. When the driver turns the steering wheel, a shaft from the steering column turns a steering gear. The steering gear moves tie rods that connect to the front wheels. The tie rods move the front wheels to turn the vehicle right or left. Steering is the collection of components, linkages, etc. which allow a vessel (ship, boat) or vehicle (car, motorcycle, bicycle) to follow the desired course. An exception is the case of rail transport by which rail tracks combined together with railroad switches (and also known as 'points' in British English) provide the steering function. The primary purpose of the steering system is to allow the driver to guide the vehicle.
  3. 3. Figure-1.1 Steering gear There are 2 basic types of steering boxes - those with rack-and-pinion gearing, and those with worm gearing. In both cases, the gearing in the steering box makes it easier for the driver to turn the steering wheel, and hence, the wheels. A rack-and-pinion steering system has a steering wheel, a main-shaft, universal joints, and an intermediate shaft. When the steering is turned, movement is transferred by the shafts to the pinion. The pinion is meshed with the teeth of the rack, so pinion rotation moves the rack from side to side. This type of steering is used on passenger vehicles because it is light, and direct. This steering system has worm gearing. It provides a gear reduction, and a 90 degree change in direction. It has more parts and joints than the rack type, but it is more robust, and may be used on heavier vehicles.
  4. 4. To allow heavy transport vehicles to carry extra weight, two steering axles may be used. They’re connected by a link to a common steering box. These vehicles are called tandem, or twin-steered vehicles. Some passenger vehicles also steer the rear wheels slightly. This gives improved manoeuvrability. The system is known as 4-wheel steering. It can be controlled mechanically, through a direct connection, between the front and rear steering boxes. Or it can be computer-controlled. With heavier vehicles, increased use of front-wheel-drive, and wider, low-profile tyres, more steering effort is needed, so power steering is used. An engine-driven hydraulic pump provides pressure that helps the driver steer the vehicle. The power steering system is designed so that the vehicle can still be controlled, even if the engine or the power steering system, fails.
  5. 5. 2. WHEELED VEHICLE STEERING 2.1 Basic geometry The basic aim of steering is to ensure that the wheels are pointing in the desired directions. This is typically achieved by a series of linkages, rods, pivots and gears. One of the fundamental concepts is that of caster angle – each wheel is steeredwith a pivot point ahead of the wheel; this makes the steering tend to be self-centring towards the direction of travel. The steering linkages connecting the steering box and the wheels usually conform to a variation of Ackermann steering geometry, to account for the fact that in a turn, the inner wheel is actually travelling a path of smaller radius than the outer wheel, so that the degree of toe suitable for driving in a straight path is not suitable for turns. The angle the wheels make with the vertical plane also influences steering dynamics (camber angle) as do the tires. Many modern cars use rack and pinion steering mechanisms, where the steering wheel turns the pinion gear; the pinion moves the rack, which is a linear gear that meshes with the pinion, converting circular motion into linear motion along the transverse axis of the car (side to side motion). This motion applies steering torque to the swivel pin ball joints that replaced previously used kingpins of the stub axle of the steered wheels via tie rods and a short lever arm called the steering arm. The rack and pinion design has the advantages of a large degree of feedback and direct steering "feel". A disadvantage is that it is not adjustable, so that when it does wear and develop lash, the only cure is replacement. BMW began to use rack and pinion steering systems in the 1930s, and many other European manufacturers adopted the technology. American automakers adopted rack and pinion steering beginning with the 1974 Ford Pinto.[1]
  6. 6. Figure 2.1.1 Ackermann Steering mechanism Older designs use two main principles: the worm and sector design and the screw and nut. Both types were enhanced by reducing the friction; for screw and nut it is the recirculating ball mechanism, which is still found on trucks and utility vehicles. The steering column turns a large screw which meshes with nut by recirculating balls. The nut moves a sectorof a gear, causing it to rotate about its axis as the screw is turned; an arm attached to the axis of the sector moves the Pitman arm, which is connected to the steering linkage and thus steers the wheels. The recirculating ball version of this apparatus reduces the considerable friction by placing large ball bearings between the screw and the nut; at either end of the apparatus the balls exit from between the two pieces into a channel internal to the box which connects them with the other end of the apparatus, thus they are "recirculated".
  7. 7. The recirculating ball mechanism has the advantage of a much greater mechanical advantage, so that it was found on larger, heavier vehicles while the rack and pinion was originally limited to smaller and lighter ones; due to the almost universal adoption of power steering, however, this is no longer an important advantage, leading to the increasing use of rack and pinion on newer cars. The recirculating ball design also has a perceptible lash, or "dead spot" on center, where a minute turn of the steering wheel in either direction does not move the steering apparatus; this is easily adjustable via a screw on the end of the steering box to account for wear, but it cannot be entirely eliminated because it will create excessive internal forces at other positions and the mechanism will wear very rapidly. This design is still in use in trucks and other large vehicles, where rapidity of steering and direct feel are less important than robustness, maintainability, and mechanical advantage. The worm and sector was an older design, used for example in Willys and Chrysler vehicles, and the Ford Falcon (1960's). To reduce friction, the sector is replaced by a roller or rotating pins on the rocker shaft arm. Other systems for steering exist, but are uncommon on road vehicles. Children's toys and go-karts often use a very direct linkage in the form of a bell crank (also commonly known as a Pitman arm) attached directly between the steering column and the steering arms, and the use of cable-operated steering linkages (e.g. the capstan and bowstring mechanism) is also found on some home-built vehicles such as soapbox cars and recumbent tricycles.
  8. 8. Figure 2.1.2 Ackermann steering geometry 2.2 Power Steering Power steering helps the driver of a vehicle to steer by directing some of the its power to assist in swiveling the steered road wheels about their steering axes. As vehicles have become heavier and switched to front wheel drive, particularly using negative offset geometry, along with increases in tire width and diameter, the effort needed to turn the wheels about their steering axis has increased, often to the point where major physical exertion would be needed were it not for power assistance. To alleviate this auto makers have developed power steering systems, or more correctly power-assisted steering, since on road-going vehicles there has to be a mechanical linkage as a fail-safe. There are two types of power steering systems: hydraulic and electric/electronic. A hydraulic-electric hybrid system is also possible. A hydraulic power steering (HPS) uses hydraulic pressure supplied by an engine- driven pump to assist the motion of turning the steering wheel. Electric power steering (EPS) is more efficient than hydraulic power steering, since the electric
  9. 9. power steering motor only needs to provide assistance when the steering wheel is turned, whereas the hydraulic pump must run constantly. In EPS, the amount of assistance is easily tunable to the vehicle type, road speed, and even driver preference. An added benefit is the elimination of environmental hazard posed by leakage and disposal of hydraulic power steering fluid. In addition, electrical assistance is not lost when the engine fails or stalls, whereas hydraulic assistance stops working if the engine stops, making the steering doubly heavy as the driver must now turn not only the very heavy steering—without any help—but also the power-assistance system itself. Figure 2.2.2 Power steering 2.3 Speed Sensitive Steering An outgrowth of power steering is speed sensitive steering, where the steering is heavily assisted at low speed and lightly assisted at high speed. Auto makers
  10. 10. perceive that motoristsmight need to make large steeringinputs while manoeuvring for parking, but not while traveling at high speed. The first vehicle with this feature was the Citroën SM with its Diravi layout, although rather than altering the amount of assistance as in modern power steering systems, it altered the pressure on a centring cam which made the steering wheel try to "spring" back to the straight- ahead position. Modern speed-sensitive power steering systems reduce the mechanical or electrical assistance as the vehicle speed increases, giving a more direct feel. This feature is gradually becoming more common. 2.4 Four Wheel Steering In an active four-wheel steering system, all four wheels turn at the same time when the driver steers. In most active four-wheel steering systems, the rear wheels are steeredby a computer and actuators. The rear wheels generally cannot turn as far as the front wheels. There can be controls to switch off the rear steer and options to steer only the rear wheels independently of the front wheels. At low speed (e.g. parking) the rear wheels turn opposite of the front wheels, reducing the turning radius by up to twenty-five percent, sometimes critical for large trucks or tractors and vehicles with trailers, while at higher speeds both front and rear wheels turn alike (electronically controlled), so that the vehicle may change position with less yaw, enhancing straight-line stability. The "snaking effect" experienced during motorway drives while towing a travel trailer is thus largely nullified.[dubious – discuss] Four-wheel steering found its most widespread use in monster trucks, where manoeuvrability in small arenas is critical, and it is also popular in large farm vehicles and trucks. Some of the modern European Intercity buses also utilize four-wheel steering to assist manoeuvrability in bus terminals, and also to improve road stability. The first rally vehicle to use the technology was the Peugeot 405 Turbo 16. Its debut was at the 1988 Pikes Peak International Hill Climb, where
  11. 11. it set a record breaking time of 10:47.77.[3] The car would go on to victory in the 1989 and 1990 Paris-Dakar Rally, again driven by Ari Virtanen. Previously, Honda had four-wheel steering as an option in their 1987– 2001 Prelude and Honda Ascot Innova models (1992–1996). Mazdaalso offered four-wheel steering on the 626 and MX6 in 1988. General Motors offered Delphi's Quadrasteer in their consumer Silverado/Sierra and Suburban/Yukon. However, only 16,500 vehicles were sold with this system from its introduction in 2002 through 2004. Due to this low demand, GM discontinued the technology at the end of the 2005 model year.[4] Nissan/Infiniti offer several versions of their HICAS system as standard or as an option in much of their line-up. A new "Active Drive" system is introduced on the 2008 version of the Renault line. It was designed as one of several measures to increase security and stability. The Active Drive should lower the effectsof under steer and decrease the chances of spinning by diverting part of the G-forces generated in a turn from the front to the rear tires. At low speeds the turning circle can be tightened so parking and maneuvering is easier. Figure 2.4.1 Four wheel steering
  12. 12. 3. PRINCIPLE OF STEERING The steering system must provide control over the direction of travel of the vehicle; good maneuverability for parking the vehicle; smooth recovery from turns, as the driver releases the steering wheel; and minimum transmission of road shocks from the road surface. The steeringsystem provides control over direction of travel, good manoeuvrability, smooth recovery from turns, and minimum transmission of road shocks. Figure 3.1 Steering digram The effort by the driver is transferred from the steering wheel, down the steering column, to a steering box.
  13. 13. The steering box converts the rotary motion of the steering wheel, to the linear motion needed to steer the vehicle. It also gives the driver a mechanical advantage. The linear motion from the steering box is then transferred by tie-rods, to the steering arms at the front wheels. The tie rods have ball joints that allow steering movement, and movement of the suspension. The steering-arm ball-joints are arranged so that movement in the suspension does not affect steering operation.
  14. 14. 4 TYPES OF STEERING SYSTEM 4.1. Rack & Pinion Steering System Many modern cars use rack and pinion steering mechanisms, where the steering wheel turns the pinion gear; the pinion moves the rack, which is a linear gear that meshes with the pinion, converting circular motion into linear motion along the transverse axis of the car (side to side motion). This motion applies steering torque to the swivel pin ball joints that replaced previously used kingpins of the stub axle of the steered wheels via tie rods and a short lever arm called the steering arm. The rack and pinion design has the advantages of a large degree of feedback and direct steering "feel". A disadvantage is that it is not adjustable, so that when it does wear and develop lash, the only cure is replacement.
  15. 15. Figure 4.2.1 Components of rack and pinion steering system The primary components of the rack and pinion steering system are: 1. Rubber Bellows 2. Pinion 3. Rack 4. Inner Ball Joint 5. Tie Rod Rubber Bellows:- This rubber bellows is attached to the Rack and Pinion housing. It protects the inner joints from dirt and contaminants. In addition, it retains the grease lubricant inside the rack and pinion housing. There is an identical bellows on the other end of the rack for the opposite side connection. Figure 4.2.2 Steering Gear
  16. 16. Pinion:- The pinion is connected to the steering column. As the driver turns the steering wheel, the forces are transferred to the pinion and it then causes the rack to move in either direction. This is achieved by having the pinion in constant mesh with the rack. Figure 4.2.3 Clashing gears Rack:- The rack slides in the housing and is moved by the action of the meshed pinion into the teeth of the rack. It normally has an adjustable bush opposite the pinion to control their meshing, and a nylon bush at the other end.
  17. 17. Figure 4.2.4 Gear Inner Ball Joint Or Socket:- The inner ball joint is attached to the tie-rod, to allow for suspension movement and slight changes in steering angles. Figure 4.2.4 Steering rod viewed Tie Rod:- A tie rod end is attached to the tie-rod shaft. These pivot as the rack is extended or retracted when the vehicle is negotiating turns. Some tie-rods and tie-
  18. 18. rod ends are left or right hand threaded. This allows toe-in or toe-out to be adjusted to the manufacturer's specifications. Figure 4.2.5 Tie rod 4.2. Recirculating Ball type Recirculatingball,also known as recirculatingball and nut or worm and sector, is a steering mechanism commonly found in older automobiles, and some trucks. Most newer cars use the more economical rack and pinion steeringinstead, but some manufacturers (including Chrysler and General Motors) still use this technology in some models; e.g., the Jeep Wrangler and the Crossfire for the durability and strength inherent in the design.
  19. 19. Figure 4.2.1 Recirculating ball Mechanism:- The recirculating ball steering mechanism contains a worm gear inside a block with a threaded hole in it; this block has gear teeth cut into the outside to engage the sector shaft (also called a sector gear) which moves the Pitman arm. The steering wheel connects to a shaft, which rotates the worm gear inside of the block. Instead of twisting further into the block, the worm gear is fixed so that when it spins, it moves the block, which transmits the motion through the gear to the pitman arm, causing the roadwheels to turn.
  20. 20. The primary components of the recirculating ball and nut steering system are: 1. Pitman Arm Shaft 2. Idler Arm 3. Track Rod Or Centre Link 4. Tie Rod 5. Tie Rod End 6. Adsutment Sleeve Pitman Arm Shaft:- The pitman arm shaft is attached to the steeringbox by a spline and nut. As the driver turns the steering wheel, the steering box mechanism moves the steering linkages via the pitman arm shaft either left or right, depending on the direction in which the steering wheel is turned. The steering box provides the change of angle at 90° to the steering linkage.
  21. 21. Idler Arm:- The idler arm is attached to the chassis and is positioned parallel to the pitman arm. Figure 4.2.3 Idler arm
  22. 22. Track Rod or Centre Link:- The track rod connects the pitman arm shaft to the idler arm shaft. In this way any movement in the pitman arm shaft is directlyapplied to the idler arm shaft. Figure 4.2.4 Tracker rod Tie Rod:- The tie rods connect the track rod to the steering arms that are located on the steering knuckles. Thus all movement from the pitman arm shaft is relayed directly to the front wheels, which steer the vehicle.
  23. 23. Figure 4.2.5 Tracker rod Tie Rod End:- Tie rod ends are attached to the tie-rodshaft. These pivot as the rack is extended or retracted when the vehicle is negotiating turns. Tie-rods and tie-rod ends are left or right hand threaded. Figure 4.2.6 Tie rod end
  24. 24. Adjustment Sleeve:- The adjustment sleeve connects the tie-rod to the tie-rod end. It provides the adjustment point for toe-in or toe-out, depending on the manufacturers' specifications. Figure 4.2.7 Adjustment sleeve 4.3. Four Wheel Steering System Some cars have four-wheel steering. This can be computer controlledor it can be mechanical, through a direct connection between the front and rear steering boxes, or it can be computer-controlled, or the rear wheels can be mounted on special, compliant mounts. As cornering forces are applied to them, they alter the steering angles.
  25. 25. Figure 4.3.1 Four wheel steering With heavier vehicles, increased use of front-wheel drive, and wider, low-profile tyres, more steering effort is needed, so power assistance is used. A hydraulic pump is driven from the engine, to provide pressure to help the driver. The power steering system is designed so that even if the engine or the power steeringsystem fails, the vehicle can still be controlled. However, much more driver effort is required. The relationships between the steering system, the wheel positions, and the suspension system, form what is called the steering geometry. These relationships must always stay within manufacturer specifications.
  26. 26. 5. STEERING MECHANISMS 1. Ackermann steering geometry 2. Davis steering geometry 5.1. Ackermann steering geometry It 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 radius. It was invented by the German Carriage Builder Georg Lankensperger in Munich in 1817, then patented by his agent in England, Rudolph Ackermann (1764–1834) in 1818 for horse drawn carriages. Erasmus Darwin may have a prior claim as the inventor dating from 1758. 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 centre of the rear axle. The steeringpivot points are joined by a rigid bar called the tie rod which can also be part of the steeringmechanism, in the form of a rack and pinion for instance. With perfect Ackermann, at any angle of steering, the centre point of all of the circles traced by all wheels will lie at a common point. Note that this may be difficult to arrange in practice with simple linkages, and designers are advised to draw or analyze their steering systems over the full range of steering angles.
  27. 27. Figure 5.1.1 Ackermann steering Modern cars do not use pure Ackermann steering, partly because it ignores important dynamic and compliant effects, but the principle is sound for low speed manoeuvres. Some race cars use reverse Ackermann 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.
  28. 28. Figure 5.1.2 Rack pinion gear The Ackerman Steering Principle defines the geometry that is applied to four wheel drive to enable the correct turning angle of the steeringwheels to be generated when negotiating a corner or a curve.An Ackermann steering gear has only turning pairs and thus is preferred. Its drawback is that it fulfils the fundamental equation of correct gearing at the middle and the two extreme position and not in all positions. With perfect Ackermann, at any angle of steering, the centre point of all of the circles traced by all wheels will lie at a common point. 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 centre point.
  29. 29. As the rear wheels are fixed, this centre 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.The principle of Ackerman Steering is the relationship between the front inside tire and front outside tire in a corner or curve. 5.2. Davis Steering Geometry A Davis steeringgear has sliding pairs which means more frictionand easy wearing. The gear fulfils the fundamental equation of gearing in all the positions. However, due to easy wearing it becomes inaccurate after some time. This is the reason why this type of steering mechaism are now absolute these days and are not used in offroad vehicles as they are more prone to wear and tear. Figure 5.2.1 Davis steering mechanism It is recommended not to go for devis steering arrangement though it has accurate mechanism and is mathematically better than ackerman but it should noted that its availability is less and also it gets wear easily due to sliding pair.
  30. 30. 6. STEERING RATIO Steering ratio refers to the ratio between the turn of the steering wheel (in degrees) or handlebars and the turn of the wheels (in degrees). The steering ratio, is the amount of degrees you have to turn the steering wheel, for the wheels to turn an amount of degrees. In motorcycles and bicycles, the steering ratio is always 1:1, because the steering wheel will always follow the wheel. x:y means that you have turn the steering wheel x degree(s), for the wheel(s) to turn y degree(s). In most passenger cars, the ratio is between 12:1 and 20:1. Example: If one complete turn of the steering wheel, 360 degrees, causes the wheels to turn 24 degrees, the ratio is then 360:24 = 15:1 (360/24=15). Figure 6.1.1 Steering Ratio Graph A higher steering ratio means that you have to turn the steering wheel more, to get the wheels turning, but it will be easier to turn the steering wheel. A lower steering ratio means that you have to turn the steering wheel less, to get the wheels turning,
  31. 31. but it will be harder to turn the steeringwheel. Larger and heavier vehicles will often have a higher steering ratio, which will make the steering wheel easier to turn. If a truck had a low steering ratio, it would be very hard to turn the steering wheel. In normal and lighter cars, the wheels become easier to turn, so the steering ratio doesn't have to be as high. In race cars the ratio becomes really low, because you want the vehicle to respond a lot quicker than in normal cars. The steering wheel will also become a lot harder to turn. 6.1. Variable Ratio Steering A variable-ratio steering, is a system that uses different ratios on the rack, in a rack and pinion steering system. At the center of the rack, the space between the teeth are smaller and the space becomes larger as the pinion moves down the rack. In the middle of the rack you'll have a higher ratio and the ratio becomes lower as you turn the steering wheel towards lock. This makes the steering less sensitive, when the steering wheel is close to its center position and makes it harder for the driver to oversteer at high speeds. As you turn the steering wheel towards lock, the wheels begins to react more to your steering input.
  32. 32. Figure 6.1.2 Steering effort characteristics 6.2. Turning circles Figure 6.2.1 Turning circle
  33. 33. 7. CONCLUSION With the world’s highest growth rate for passenger vehicle production, the Chinese automotive market crossed production volume of 3.8 million units in 2005. It is expected that China will surpass Japan and become the world’s second-largest automotive market by 2010, trailing only the United States. The Chinese automotive market is one of the most dynamic markets, not only for its high growth rate, but also for the advanced technologies applied. For example, one of the most advanced steering technologies, electric power steering (EPS), is expected to emerge strongly and win a large market share during the next decade. Pitman arm mechanisms have a steering 'box' where the shaft from the steering wheel comes in and a lever arm comes out - the pitman arm. This pitman arm is linked to the track rod or centre link, which is supported by idler arms. The tie rods connect to the track rod. There are a large number of variations of the actual mechanical linkage from direct-link where the pitman arm is connected directly to the track rod, to compound linkages where it is connected to one end of the steering system or the track rod via other rods. The example here shows a compound link (left). Most of the steering box mechanisms that drive the pitman arm have a 'dead spot' in the centre of the steering where you can turn the steering wheel a slight amount before the front wheels start to turn. This slack can normally be adjusted with a screw mechanism but it can't ever be eliminated. The traditional advantage of these systems is that they give bigger mechanical advantage and thus work well on heavier vehicles. With the advent of power steering, that has become a moot point and the steering system design is now more to do with mechanical design, price and weight. The following are the four basic types of steering box used in pitman arm systems.
  34. 34. 7. FUTURE SCOPE You can expect to see several innovations that will improve fuel economy. One of the coolest ideas on the drawing board is the "steer-by-wire" or "drive-by-wire" system. These systems would completely eliminate the mechanical connection between the steering wheel and the steering, replacing it with a purely electronic control system. Essentially, the steering wheel would work like the one you can buy for your home computer to play games. It would contain sensors that tell the car what the driver is doing with the wheel, and have some motors in it to provide the driver with feedback on what the car is doing. The output of these sensors would be used to control a motorized steering system. This would free up space in the engine compartment by eliminating the steering shaft. It would also reduce vibration inside the car. General Motors has introduced a concept car, the Hy-wire, that features this type of driving system. One of the most exciting things about the drive-by-wire system in the GM Hy-wire is that you can fine-tune vehicle handling without changing anything in the car's mechanical components -- all it takes to adjust the steering is some new computer software. In future drive-by-wire vehicles, you will most likely be able to configure the controlsexactly to your liking by pressing a few buttons, just like you might adjust the seat position in a car today. It would also be possible in this sort of system to store distinct control preferences for each driver in the family.
  35. 35. 8. REFRENCES 1. http://www.hemmings.com/hmn/stories/2010/07/01/hmn_feature20.html 2. http://www.cnet.com/videos/top-5-citroen-sm-innovations-that-saw-the-future/ 3. "1988 Peugeot 405 T16 GR Pikes Peak". Retrieved 16 March 2015. 4. Murphy, Tom; Corbett, Brian (2005-03-01). "Quadrasteer Off Course". Wards Auto World. Retrieved 2010-06-11. 5. https://www.audi- mediaservices.com/publish/ms/content/en/public/pressemitteilungen/2014/12/12/t he_new_audi_q7__.html The new Audi Q7 – Sportiness, efficiency, premium comfort 6. "2009 BMW 750Li and 750i Technology - Inside the 2009 BMW 7 Series". Motor Trend. Retrieved 2011-11-13. 7. Johnson, Erik (June 2007). "2008 Infiniti G37 Sport Coupe - Suspension, Handling, and Four-Wheel Steering". 8. http://www.porsche.com/usa/models/911/911-turbo/chassis/rear-axles-steering/ 9. http://www.porsche.com/usa/models/911/911-turbo-s/chassis/rear-axles-steering/ 10. http://www.carscoops.com/2014/10/new-renault-espace-comes-with-four.html 11. http://www.autoevolution.com/news/2016-renault-megane-brings-four-wheel- steering-87-inch-touchscreen-to-frankfurt-live-photos-99958.html 12. http://en-voiture.blog.leparisien.fr/archive/2015/12/03/essai-renault-talisman- amulette-16276.html 13. "Toyota Camry Catalog".

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