Fabrication Of Four Wheel Steering Mechanism.docx

FABRICATION OF FOUR WHEEL STEERING MECHANISM Abstract Nowadays, the every vehicle existed mostly still using the two wheel steering system to control the movement of the vehicle whether it is front wheel drive, rear wheel drive or all wheel drive. But due to the awareness of safety, four wheel steering vehicles are being used increasingly due to high performance and stability that they bring to the vehicles. In this report, the performance of four wheels steered vehicle model is considered which is optimally controlled during a lane change maneuver in three type of condition which is low speed maneuver, medium speed maneuver and high speed maneuver. Four-Wheel Steering – Rear Wheels Control. For parking and low-speed maneuvers, the rear Wheel steer in the opposite direction of the front wheels, allowing much sharper turns. At higher speeds, the rest wheels steer in the same direction as the front wheels. The result is more stability and less body lean during fast lane changes and turns because the front wheels don’t have to drag nonsteering rear wheels onto the path.

1. INTRODUCTION

Steering is the term applied to the collection of components, linkages, etc. which will allow a vessel (ship, boat) or vehicle (car, motorcycle and bicycles) to follow the desired course. 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 vehicle are powered.

Four wheel steering is a method developed in automobile industry for the effective turning of the vehicle, increase the maneuverability and reduce the drivers steering effort. In city driving conditions, the vehicle with higher track width and wheelbase face problems of turning as the space is confined the same problem is faced in low speed cornering. The turning radius is reduced in the four wheel steering of the vehicle which is effective in confined space, in this project turning radius is reduced without changing the dimension of the vehicles.

In situations like vehicle parking, low speed cornering and driving in city conditions with heavy traffic in tight spaces, driving is very difficult due to vehicle’s larger track width and wheelbase. When both the front and rear wheels steer toward the same direction, they are said to be in-phase and this produces a kind of sideways movement of the car at low speeds. When the front and rear wheels are steered in opposite direction, this is called anti-phase, counter-phase or opposite-phase and it produces a sharper, tighter turn.

Hence, there is a requirement of a mechanism which result in less turning radius and it can be achieved by implementing four wheel steering.

2. PRINCIPLE The steering mechanism consists of rack and pinion arrangements which are used to turn the wheels in the front. And a bevel gear arrangement is made just after the steering and power is transmitted through the transfer shaft to the gear box assembly. Then power is transmitted to the rear wheels. Layout/Operation of the system: Two subsystems: Rack and pinion for front and rear, identical geometry and components. Steering column is fitted with 3 bevel gears meshes and transmits power to front and rear rack and pinion. As steering wheel is turned the entire rotation is transferred to front rack and pinion and only half of the rotation is transferred to rear rack and pinion. 1. Ackermann steering mechanism Ackermann steering mechanism is a geometric arrangement of linkages in the steering of vehicle designed to solve the problem of wheels on the inside and outside of a turn needing of different radii. 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 circles with a common centre point. 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.

2. Steering ratio The steering ratio is the ratio of number of degrees of turn of the steering wheel to the number of degrees the wheels turn. In cars, the ratio is between 12:1 and 20:1. For 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. A higher steering ratio means that the steering wheel is turned more to get the wheels turning, but it will be easier to turn the steering wheel. A lower steering ratio means that the steering wheel is turned less to get the wheels turning, but it will harder to turn the steering wheel. Larger and heavier vehicles will often have a higher steering ratio. 3. Turning radius The turning radius of a vehicle is the radius of the smallest circular turn (i.e. U-turn) that the vehicle is capable of making. There is no hard and fast formula to calculate the turning circle but an approximate value can be obtained using the formula: Turning circle radius = Track/2 + Wheel base/sin (Average steer angle)

Fig2.3: Turning radius view

4. Steering geometry Steering geometry is the geometric arrangement of the parts of a steering system and the value of the lengths and angles within it. Steering geometry changes due to bumps in the road may cause the front wheels to steer in a different direction together or independent of each other. Combined with the cars improved steering geometry, a wide wheel and large footprint will notably improve handling and grip. 3. BACKGROUND THEORY The most effective type of steering, this type has all the four wheels of the vehicle used for steering purpose. 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. Normally this system is not been the preferred choice due to complexity of conventional mechanical four wheel steering systems. However, a few cars like the Honda Prelude, Nissan Skyline GT-R have been available with four wheel steering systems, where the rear wheels turn by an angle to aid the front wheels in steering. However, these systems had the rear wheels steered by only 2 or 3 degrees, as their main aim was to assist the front wheels rather than steer by themselves. With advances in technology, modern four wheel steering systems boast of fully electronic steer-by-wire systems, equal steer angles for front and rear wheels, and sensors to monitor the vehicle dynamics and adjust the steer angles in real time. Although such a complex four wheel steering model has not been created for production purposes, a number of experimental concepts with some of these technologies have been built and tested successfully. Usually in vehicles during turning, the tires are subject to the forces of grip, momentum, and steering input when making a movement other than straight ahead driving. These forces compete with each other during steering manoeuvres. 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. 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 input causes 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. 4. THE CONCEPTS The Four Wheel Steering System consists of rack and pinion mechanism assisted by bevel gears of which is connected to front pinion, steering rod in which input is given by the driver and another will be connected to rear pinion. Rear wheel system consists of two racks with two pinions. One of the racks will be in front of the rear wheel axis and the other will be at the front axis. Also at any point in the system, one of the rack & pinion assembly will be engaged with the other being disengaged. At lower speeds, the pinion will be in contact with rear rack so as to keep the wheels motion out of phase while for higher speeds pinion will be in contact with front rack of rear steering system, giving in phase motion to wheels. This position of the rear pinion on the rack is controlled by a steering mechanism. The angle turned by rear wheels will not be as high as that of front wheels because the function of rear steering system is to assist the motion of front wheels and not provide its own direction. This change of angle is obtained by changing gear ratio of rack and pinion.

Fig4.1: Conceptual model

5. 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. Condition for True Rolling While tackling a turn, the condition of perfect rolling motion will be satisfied if all the four wheel axes when projected at one point called the instantaneous centre, and when the following equation is satisfied: Cot Ø – cot θ = c / b

Fig.5.1: True rolling condition

Slow and High Speed Modes

At Slow Speeds rear wheels turn in direction opposite to that of front wheels. This mode is used for navigating through hilly areas and in congested city where better cornering is required for U turn and tight streets with low turning circle which can be reduced as shown in Fig 2.

Fig.5.2: Slow Speed At High Speeds, turning the rear wheels through an angle opposite to front wheels might lead to vehicle instability and is thus unsuitable. Hence the rear wheels are turned in the same direction of front wheels in four-wheel steering systems. This is shown in Fig 3.

Fig.5.3: High Speed



In-Phase and Counter-Phase Steering

Fig.5.4:In-phase and counter

Phase steering

 The 4WS system performs two distinct operations: in- phase steering, whereby the rear wheels are turned in the same direction as the front wheels, and counter phase steering, whereby the rear wheels are turned in the opposite direction. The 4WS system is effective in the following situations:

 Lane Changes

 Gentle Curves  Junctions  Narrow Roads

 U-Turns  Parallel Parking

Fig.5.5: Car in various modes

U-Turns By minimizing the vehicle’s turning radius, counter-phase steering of the rear wheels enables U-turns to be performed easily on narrow roads. High Speed Lane Changing Another driving maneuver that frequently becomes cumbersome and even dangerous is changing lanes at fairly high speeds. Although this is less steering intensive, this does not require a lot concentration from the driver since he has to judge the space and vehicles behind him. Here is how crab mode can simplify this action. Parallel Parking Zero steer can significantly ease the parking process, due to its extremely short turning footprint. This is exemplified by the parallel parking scenario, which is common in foreign countries and is pretty relevant to our cities. Here, a car has to park it between two other cars parked on the service lane. This maneuver requires a three-way movement of the vehicle and consequently heavy steering inputs. Moreover, to successfully park the vehicle without incurring any damage, at least 1.75 times the length of the car must be available for parking for a two-wheel steered car.

6. METHODOLOGY OF FOUR WHEEL STEERING There are three types of production of four-wheel steering systems: 1. Mechanical 4WS system 2. Hydraulic 4WS system 3. Electro-hydraulic 4WS system 6.1 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 the planetary gear fits into a hole in a slider for the steering gear. A 120degree turn of the steering wheel rotates the planetary gear to move the slider in the same direction that the front wheels are headed. Proportionately, the rear wheels turn the steering wheel about 1.5 to 10 degrees. Further rotation of the steering wheel, past the 120degree point, causes the rear wheels to start straightening out due to the double-crank action (two eccentric pins) and rotation of the planetary gear. Turning the steering wheel to a greater angle about 230 degrees, finds the rear wheels in a neutral position regarding the front wheels. Further rotation of the steering wheel results in the rear wheels going counter phase with regard to the front wheels. About 5.3 degrees maximum counter phase rear steering is possible. Mechanical 4WS is steering angle sensitive.

Fig.6.1:Mechanical4WSsystem 2 Hydraulic 4WS system In the hydraulic four-wheel-steering system, the rear wheel turns only in the same direction as the front wheels. This system limits rear wheel movement to 5.5 degrees in either the left or right direction. 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. 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 valve 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.

Fig.6.2: Hydraulic 4WS system

6.3 Electro- hydraulic 4WS system In this system, 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 to steer the rear wheels. At low speed, the rear wheels of this system are not considered a dynamic factor in the steering process. At moderate speeds, the rear wheels are steered momentarily counter 45 phase, through neutral, then in phase with the front wheels. At high speeds, the rear wheel 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. These three factors - road speed, amount of steering wheel turn, and the quickness of the steering wheel turn - are interpreted by the ECU to maintain continuous and desired steer angle of the rear wheels. The yoke is a major mechanical component of this electro-hydraulic design. The position of the control yoke varies with vehicle road speed. The stepper motor moves the control yoke. A swing arm is attached to the control yoke. The position of the yoke determines the arc of the swing rod. The arc of the swing arm is transmitted through a control arm that passes through a large bevel gear. Stepper motor action eventually causes a push-or-pull movement of its output shaft to steer the rear wheels up to a maximum of 5 degrees in either direction. The electronically controlled, 4WS system regulates the angle and direction of the rear wheels in response to speed and driver's steering. This speedsensing system optimizes the vehicle's dynamic characteristics, thereby producing enhanced stability.

Fig.6.3: Electro hydraulic 4WS 7. IMPORTANT MATERIALS REQUIRED

7.1

Bevel gear:

Bevel gears are gears where the axes of the two shafts intersect and the tooth-bearing faces of the gears themselves are conically shaped. Bevel gears are most often mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well. The pitch surface of bevel gears is a cone.

Fig.7.1: Bevel gear

7.2

Ball bearing:

A bearing is a machine element that constrains relative motion to only the desired motion, and reduces friction between moving parts. The design of the bearing may, for example, provide for free linear movement of the moving part or for free rotation around a fixed axis; or, it may prevent a motion by controlling the vectors of normal forces that bear on the moving parts. Most bearings facilitate the desired motion by minimizing friction

Fig.7.2: Ball bearing

7.3 Tire: A tire (British tyre) is a ring of material that covers the rim of a wheel. Most road vehicles and many other vehicles use rubber tires. Tires help vehicles to move smoothly. Tires need to be changed after their treads wear away. Driving with worn tires is very dangerous. It can cause the tire to explode and the driver to lose control. Tires are made of different types of rubber. Tires made of harder rubber are made for long lasting performance, like long-distance truck carriers. They come in different sizes and have different tread patterns. There are many different sizes of tires. On car and truck tires, they are marked with 3 numbers and might look like: 225/60R16. Example Tire size: 225/60R16 Tire width = 225mm Sidewall height = 135mm (225 * .60 = 135) Wheel diameter = 16 inches

Fig.7.3: Tire

7.4 Wheel hub or Spindle:

fig7.4: Wheel hub

7.5 Nuts and bolts: A nut is a type of fastener with a threaded hole. Nuts are almost always used in conjunction with a mating bolt to fasten multiple parts together. The two partners are kept together by a combination of their threads' friction (with slight elastic deformation), a slight stretching of the bolt, and compression of the parts to be held together. A bolt is a form of threaded fastener with an external male thread.

Fig.7.5: nuts and bolts

7.6 Drive shaft: A drive shaft, driveshaft, driving shaft, propeller shaft is a mechanical component for transmitting torque and rotation, usually used to connect other components of a drive train that cannot be connected directly because of distance or the need to allow for relative movement between them. As torque carriers, drive shafts are subject to torsion and shear stress, equivalent to the difference between the input torque and the load. They must therefore be strong enough to bear the stress, whilst avoiding too much additional weight as that would in turn increase their inertia.

Fig.7.6: Drive shaft

7.7

Steering:

Steering is the collection of components, linkages, etc. which allows any vehicle (car, motorcycle, bicycle) to follow the desired course. The primary purpose of the steering system is to allow the driver to guide the vehicle. Four-wheel steering is a system employed by some vehicles to improve steering response, increase vehicle stability while maneuvering at high speed, or to decrease turning radius at low speed.

fig.7.7: Steering 7.8

Chain:

A chain is typically made of metal. A chain may consist of two or more links. Those designed for transferring power in machines have links designed to mesh with the teeth of the sprockets of the machine, and are flexible in only one dimension. They are known as roller chains, though there are also non-roller chains such as block chain.

Fig.7.8: chains

8. PHASES OF QUADRA STEERING SYSTEM In this type of steering system, we can steer a front wheel, as well as the rear wheel of the vehicles simultaneously. This steering mainly includes two types of steering: Front wheels and rear wheels are steered in the same direction and are parallel to each other. This type of system is very useful during lane changing. Front wheels are steered in the direction opposite to that of the rear wheel. This steering system reduces the space required by the vehicle during turning as compared to that of the two wheel steering system. The present “Four Wheel Steering” works mechanically with help of linkages. The system utilizes a manual manipulator to control and direct the articulation (left and right turning) of rear wheels. The system operates in three phases: Negative, Neutral and Positive. At lower speeds, rear wheel turns in opposite direction from the front wheel. This is negative phase. At moderate speed, the rear wheel remains straight or neutral. At higher speed, the rear wheel are in the positive phase turning in the same direction as the front wheels. 8.1

Negative Phase

In this drive the axles both the front and the rear move in opposite direction relative to each other. This drive is mainly used during parking of the vehicle. As both the axle move in different directions the radius of curvature while turning reduces. This means the vehicle will require less space for parking and this will be helpful in places where traffic and parking is a major problem.

Fig8.1: Negative phase

8.2

Neutral Phase

In this drive only the front axle moves either in clockwise or anticlockwise direction and the rear wheel being unmoved. This is the drive that we see in day to day life in all the four wheelers. It is generally used at moderate speed.

Fig.8.2 neutral phase 8.3

Positive Phase

As the name suggest, in this drive both the axle viz. front and rear move in same direction relative to the each other. This motion of both the front and the rear axle helps Quadra steering system enabled vehicle to change the lane during highway driving. It is generally applied at higher speed.

Fig.8.3: positive phase

9. TYPES OF STEER Balancing of vehicle is very important and it can be achieved in different ways i.e. under-steer, over-steer and neutral-steer. 9.1 Under-Steer Under steer is so called because when the slip angle of front wheels is greater than slip angle of rear wheels. The diagram for the under steer is given below, from the diagram the explanation is made out clear very well.

Fig.9.1: Under steer 9.2 Over-Steer Over steer is defined when the slip angle of front wheels lesser than the slip angle of rear wheels.

Fig.9.2: Over steer

9.3 Neutral-steer or Counter-steering Counter-steering can defined as when the slip angle of front wheels is equal to slip angle of rear wheels.

Fig.9.3: Neutral steer 10. OPERATIONS 10.1

Welding:

Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing fusion, which is distinct from lower temperature metal-joining techniques such as brazing and soldering, which do not melt the base metal. In addition to melting the base metal, a filler material is typically added to the joint to form a pool of molten material (the weld pool) that cools to form a joint that is usually stronger than the base material. Pressure may also be used in conjunction with heat, or by itself, to produce a weld. We used GMAW for welding operation purpose. Gas Metal Arc Welding (GMAW) – commonly termed MIG (metal, inert gas), uses a wire feeding gun that feeds wire at an adjustable speed and flows an argon-based shielding gas or a mix of argon and carbon dioxide (CO2) over the weld puddle to protect it from atmospheric contamination.

Fig.10.1: Operations of Welding

10.2 Cutting: Cutting is the separation of a physical object, into two or more portions, through the application of an acutely directed force. Cutting is a compressive and shearing phenomenon, and occurs only when the total stress generated by the cutting implement exceeds the ultimate strength of the material of the object being cut. Cutting has been at the core of manufacturing throughout history. For metals many methods are used and can be grouped by the physical phenomenon used.

Fig10.2: Operations of Cutting

10.3 Grinding: A grinding machine, often shortened to grinder, is any of various power tools or machine tools used for grinding, which is a type of machining using an abrasive wheel as the cutting tool. Each grain of abrasive on the wheel's surface cuts a small chip from the work piece via shear deformation. Grinding is used to finish work piece that must show high surface quality (e.g., low surface roughness) and high accuracy of shape and dimension. As the accuracy in dimensions in grinding is of the order of 0.000025 mm, in most applications it tends to be a finishing operation and removes comparatively little metal, about 0.25 to 0.50 mm depth. However, there are some roughing applications in which grinding removes high volumes of metal quite rapidly. Thus, grinding is a diverse field.

Fig10.3: Operation of Grinding

10.4 Drilling:

Drilling is a cutting process that uses a drill bit to cut a hole of circular cross section in solid materials. The drill bit is usually a rotary cutting tool, often multipoint. The bit is pressed against the work piece and rotated at rates from hundreds to thousands of revolutions per minute. This forces the cutting edge against the work piece, cutting off chips (swarf) from the hole as it is drilled. In rock drilling, the hole is usually not made through a circular cutting motion, though the bit is usually rotated. Instead, the hole is usually made by hammering a drill bit into the hole with quickly repeated short movements. The hammering action can be performed from outside of the hole (top-hammer drill) or within the hole (down-the-hole drill, DTH). Drills used for horizontal drilling are called drifter drills.

Fig.10.4: Operation of Drilling

11. DESIGN OF FRAME

For building of prototype model, the designed model is considered along with that a frame is built to support the steering, suspension and seat. The frame is designed considering the wheelbase and track width of Maruti Suzuki 800 and also it has to support for the suspension part as the suspension is welded to the frame, seat is also welded to the frame, the support structure for steering column and rack body is welded to the frame. The frame also takes the road load and load of the driver, so considering all the factors the frame is designed and developed.

35 cm

65c

140cm Fig.11.1: Design of Frame

14. COST AND DESIGN ANALYSIS Compone nts

Dimensions ( cm )

Quantity

Cost Rs.

Frame

Length: 52*120

1

1200

Sprocket

Pitch:0.5

4

200

Outer diameter:7.5 Inner diameter:2.2 Width:0.125 No. Of teeth:18 Chain

Length: 45

6

400

Bearing

Outer diameter:2.0

10

2500

1

180

Inner diameter:4.1 Outer diameter:2.5 Inner diameter:5.3 Spindle hub

Diameter:2.0

4

2400

Steering

Diameter:

1

600

Knuckle arms

Length: 40

1

500

Nuts

Length:11

16

160

8

80

16

80

8

40

Diameter:1.1 Length:10.5 Diameter:1.1 Bolts

Outer diameter:2.0 Inner diameter:1.1 Outer diameter:2.0 Inner diameter: 1.1

Bevel gears

Outer diameter:9

2

400

4

2800

6

300

4

600

2

3000

1

400

Inner diameter:3.2 No. Of teeth:10 Module:0.6 Face width:5 Wheel

Outer diameter: 48 Inner diameter: 40

Rack

Length: 45 Face width:0.5

Pedals Drive shaft

Length:25 Diameter:2.2

Rear shaft

Outer diameter:3.2 Inner diameter:2.6 Face width:96

Sheet metal

450

Paint Drill bit

Diameter: 10 mm

1

500

2

400

Lubrication

150

Total material cost

17340/-

Transportation cost Total cost

-

1500 18900/᷈-

COMPARISON 

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

Fig.15.1:

comparison between 4WS and 2WS

Bevel Gears Bevel gears are useful when the direction of a shaft's rotation needs to be changed. They are usually mounted on shafts that are 90 degrees apart, but can be designed to work at other angles as well. The teeth on bevel gears can be straight, spiral or hypoid. Straight bevel gear teeth actually have the same problem as straight spur gear teeth -- as each tooth engages, it impacts the corresponding tooth all at once.

Photo courtesy Emerson Power Transmission Corp. Figure 5. Bevel gears

Just like with spur gears, the solution to this problem is to curve the gear teeth. These spiral teeth engage just like helical teeth: the contact starts at one end of the gear and progressively spreads across the whole tooth.

Photo courtesy Emerson Power Transmission Corp. Figure 6. Spiral bevel gears

On straight and spiral bevel gears, the shafts must be perpendicular to each other, but they must also be in the same plane. If you were to extend the two shafts past the gears, they would intersect. The hypoid gear, on the other hand, can engage with the axes in different planes.

Figure 7. Hypoid bevel gears in a car differential

This feature is used in many car differentials. The ring gear of the differential and the input pinion gear are both hypoid. This allows the input pinion to be mounted lower than the axis of the ring gear. Figure 7 shows the input pinion engaging the ring gear of the differential. Since the driveshaft of the car is connected to the input pinion, this also lowers the driveshaft. This means that the driveshaft doesn't intrude into the passenger compartment of the car as much, making more room for people and cargo.

Spur Gears

PHOTO COURTESY EMERSON POWER TRANSMISSION CORP. Figure 2. Spur gears Spur gears are the most common type of gears. They have straight teeth, and are mounted on parallel shafts. Sometimes, many spur gears are used at once to create very large gear reductions. Spur gears are used in many devices that you can see all over HowStuffWorks, like the electric screwdriver, dancing monster, oscillating sprinkler, windup alarm clock, washing machine and clothes dryer. But you won't find many in your car. This is because the spur gear can be really loud. Each time a gear tooth engages a tooth on the other gear, the teeth collide, and this impact makes a noise. It also increases the stress on the gear teeth. To reduce the noise and stress in the gears, most of the gears in your car are helical.

Basics

Figure 1. Animation of peg wheel gear On any gear, the ratio is determined by the distances from the center of the gear to the point of contact. For instance, in a device with two gears, if one gear is twice the diameter of the other, the ratio would be 2:1. One of the most primitive types of gears we could look at would be a wheel with wooden pegs sticking out of it. The problem with this type of gear is that the distance from the center of each gear to the point of contact changes as the gears rotate. This means that the gear ratio changes as the gear turns, meaning that the output speed also changes. If you used a gear like this in your car, it would be impossible to maintain a constant speed -- you would be accelerating and decelerating constantly. Many modern gears use a special tooth profile called an involute. This profile has the very important property of maintaining a constant speed ratio between the two gears. Like the peg wheel above, the contact point moves; but the shape of the involute gear tooth compensates for this movement. See this section for details. Now let's take a look at some of the different types of gears. Details on Involute Gear Profiles

Figure 10. Animation of involute gear On an involute profile gear tooth, the contact point starts closer to one gear, and as the gear spins, the contact point moves away from that gear and toward the other. If you were to follow the contact point, it would describe a straight line that starts near one gear and ends up near the other. This means that the radius of the contact point gets larger as the teeth engage.

The pitch diameter is the effective contact diameter. Since the contact diameter is not constant, the pitch diameter is really the average contact distance. As the teeth first start to engage, the top gear tooth contacts the bottom gear tooth inside the pitch diameter. But notice that the part of the top gear tooth that contacts the bottom gear tooth is very skinny at this point. As the gears turn, the contact point slides up onto the thicker part of the top gear tooth. This pushes the top gear ahead, so it compensates for the slightly smaller contact diameter. As the teeth continue to rotate, the contact point moves even further away, going outside the pitch diameter -- but the profile of the bottom tooth compensates for this movement. The contact point starts to slide onto the skinny part of the bottom tooth, subtracting a little bit of velocity from the top gear to compensate for the increased diameter of contact. The end result is that even though the contact point diameter changes continually, the speed remains the same. So an involute profile gear tooth produces a constant ratio of rotational speed.

Rack and Pinion Drive System: A rack and pinion drive system consists of a rack (or a “linear gear”) and a pinion (or “circular gear”). The teeth of a rack and pinion drive can be straight or helical, although helical teeth are often used due to their higher load capacity and quieter operation. For a rack and pinion drive system, the maximum force that can be transmitted is largely determined by the tooth pitch and the size of the pinion. These systems are well-established linear drive mechanisms, providing high-speed travel over extremely long lengths. They are frequently used in large gantry systems for material handling, machining, welding and assembly, especially in the automotive, machine tool, and packaging industries.

An example of a typical straight-toothed rack and pinion showing the linear rack and the pinion gear. (Image via Cross and Morse) Rack and pinions can be constructed in nearly unlimited lengths. Rack sections can be joined endlessly, although the guide mechanism (a profiled rail or cam roller, for example) can be the limiting factor in maximum stroke length. Rack and pinion systems can operate in one of two ways: with the pinion (including gearbox and motor) moving and the rack stationary, or with the pinion assembly stationary and the rack moving. Rack and pinion drive systems do have backlash, due to the meshing of gear teeth. But high precision helical rack and pinion systems have tooth pitch errors in the single-micron range. It’s also possible to preload a rack and pinion system to prevent backlash. Lubrication is critical for rack-and-pinion systems due to the metal-on-metal contact combined with the tight clearances between gear teeth. Automatic lubrication systems are recommended for use with rack and pinions to ensure proper lubrication and avoid reduced performance or even failure.

ELECTRIC ARC WELDING:

Electric arc welding is performed between cylinder and bottom flange. In electrical arc welding, the intense heat of electric arc is used to fuse the parts being joined. In most arc welding processes, the arc is struck between electrode and work piece, and is referred as direct arc. The arc struck between non-consumable electrodes adjacent to the parts being joined is called indirect arc. In this case, the heat is transferred to metal by radiation. This method is rarely used because of low thermal efficiency. Electric arc welding is preferred over gas welding, because the speed and ease with which welds may be made. Electric welding equipment is more expensive, but operating cost is lower.

Principle of arc welding: The principle of arc welding is based upon the formation of an electric arc between consumable electrode (bare or coated) or non-consumable electrode and the base metal. The heat of the arc is concentrated at the point of welding, and as a result, it melts the electrode (consumable electrode) and the base metal. When the weld metal solidifies, a sound joint is formed. When the metal solidifies, the slag gets deposited on its surface as it is lighter than metal, and the weld metal is allowed to cool gradually and slowly. The slag deposited over the weld is removed by chipping. The electric arc is produced when the current flows across the air gap between the end of metal electrode and the work surface. This arc is strong stable electric discharge occurring in the air gap between an electrode and the work. The temperature of this arc is about 3600C which can melt and fuse the metal very quickly to produce joint. The temperature of the arc at the centre is around 6500C. Only 60 to 70% of the heat is utilised in arc welding to heat up and melt the metal. The remaining 40 to 30% is dissipated into surroundings.

FIG 3.23- ELECTRIC ARC WELDING Metal arc welding is the most common type of arc welding and it is normally a manual operation. Therefore it is usually referred as Manual Metal Arc Welding (MMAW). It uses consumable metal electrodes. The arc is produced with low voltage (20-80V) but with very high current (80500amps). The electric circuit consistsa.c or d.c power source, and from the power source welding current is conveyed to work through electrode, electrode holder and welding leads. The circuit is completed by sinking the arc i.e., making the contact between electrode and work. The operator maintains arc at required intensity.

ARC WELDING The sequences of steps involved in arc welding operation are: 1. Preparation of edges, 2. Holding the work piece in a fixture, 3. Striking the arc, and 4. Welding the joint Before welding, the edges of the work pieces are suitably prepared, and the joint area is cleaned with the wire brush. This ensures sound joint. The parent metals are held in a fixture and welding leads are properly connected to power source. The arc is struck by scratching the tip of electrode on the parent metal. As the electrode tip makes contact, the current flows and then as it is drawn away an arc is formed across the gap. Arc can also be struck by tapping down the electrode to make contact with work piece and is then raised to maintain a constant gap across which an arc is formed. During the welding, the electrode is given the following motions. i.

The electrode is fed downwards, and it should be controlled properly to maintain constant gap (2-4mm)

ii.

The electrode is moved slowly along the joint.

iii.

The electrode tip is given an oscillating movement across the (weaving motion) weld to maintain proper bead width and secure good penetration of the weld. The width of weave should not be greater than 3 times the diameter of the electrode.

In multi-pass welding, slag coated on the bead after the first pass should be chipped off and cleaned by wire brush before the start of the second pass. The procedure is followed for the subsequent passes. In most cases, after welding, the part must be heat-treated to change the size of the grain in the weld bead and the surrounding area. Selection of electrodes: Type of electrode used depends upon: i.

The type of metal to be welded

ii.

The position in which the weld is to be done

iii.

The power source

iv.

Polarity, in case of D.C

v.

Thickness of the base metal

vi.

Expected properties of the welded joint.

Bare electrodes are used for welding low carbon steel or wrought iron. They are also mostly used in submerged arc welding. Coated electrodes are employed for welding high carbon steels, alloy steels and non-ferrous metals and their alloys. It is best to follow the recommendations of manufacturers for using electrodes for different work. Advantages and limitations of arc welding: Arc welding offer the following advantages: 1. Metal arc welding is faster and lower in cost than gas welding. 2. The process is a quite versatile, and welds can be made in any position. 3. Suitable for wide range of metals (ferrous and non-ferrous) and their alloys. 4. Less sensitive to weld than other processes.

However, the arc welding process has the following limitations: 1. The process is not suitable for thin sections. 2. The process is not suitable for mechanisation. 3. Electrode replacement is necessary for long joints. 4. Not suitable for heavy fabrications because less metal is deposited per hour. 5. Failure to remove the slag when run is interrupted leads to slag inclusions in the weld. Applications: The Manual Metal Arc Welding (MMAW) has a wider field of applications. It is employed for fabrication of pressure vessels, ships, structural steel work, and joints in pipe work, construction and repair of machine parts. This process can also be used for hard facing and repairs of the broken parts.

ADVANTAGES

1. Superior cornering stability: The vehicle cornering behaviour becomes more stable and controllable at high speed as well as on wet slippering road surfaces. 2. Improved steering response and precision: The vehicle response to steering input becomes quicker and more precise throughout the vehicle enter speed range. 3. High speed straight line stability: The vehicle’s straight –line stability at high speed is improved. Negative effects of road irregularities and crosswinds on the vehicles stability are minimized. 4. Improved rapid lane-changing maneuvers: This is stability in lane changing at high speed is improved. In high speed type operation become easier. The vehicle is less likely to go into a spin even in situations in which the driver must make a sudden and relatively large change of direction. 5. Smaller turning radius: By steering the rear wheels in the duration opposite the front wheels at low speed, the vehicle’s turning circle is greatly reduced. Therefore, vehicle maneuvering on narrow roads and during parking become easier. 6. Controlling: Computer-controlled Quadra steer can be switched on and off and has an effective trailer towing mode.

DISADVANTAGES

1. The 4ws, due to construction of many new components, the system becomes more expensive. 2. The system includes as many components (especially electronically) there is always a chance to get any of the part inactive, thus the system become in operative. 3. The system is not stable at high speed gets overpowered and topple in some cases. 4.

Pump and sensors should be checked regularly to avoid its failure.

18. FUTURE SCOPE An innovative feature of this steering linkage design is its ability to drive all four Wheels using a single steering actuator. Having studied how 4WS has an effect on the vehicles stability and driver maneuverability, we now look at what the future will present us with. It’s 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.

APPLICATION 1. Gentle curve: on gentle curves, in phase steering of the rear wheels improves the vehicle stability.

2. Parking: during a parking a vehicles driver typically turns the steering wheels through a large angle to achieve a small turning radius. By counter phase steering of the rear wheels, 4ws system realizes a smaller radius then is possible with 2ws. As a result vehicle is turned in small radius at parking.

3. Junctions: on a cross roads or other junction where roads intersect at 90 degree or tighter angles, counter phase steering of the rear wheels causes the front and rear wheels to follow more-or-less path. As a result the vehicle can be turned easily at a function. 4. Slippery road surfaces: during steering operation on snow, icy, muddy and other low friction surfaces, steering of the rear wheels suppress sideways drift of the vehicles rear end. As a result the vehicles direction is easier to control. 5. U-turns: by minimizing the vehicles turning radius, counter phase steering of the rear wheels enables U-turns to be performed easily on narrow roads.

20. CONCLUSION This paper focused on a steering mechanism which offers feasible solutions to a number of current maneuvering limitations. Different mechanisms were adopted by trial and error method in order to facilitate the engagement of the wheels in the required direction, and the most convenient method was adopted. Thus the four-wheel steering system is a relatively new technology that imposes cornering capability, steering response, straight-line stability, lane changing and low-speed maneuverability in cars, trucks and trailers.

The aim of 4WS system is a better stability during overtaking manoeuvres, reduction of vehicle oscillation around its vertical axis, reduced sensibility to lateral wind, neutral behaviour during cornering, 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 than that for a vehicle with the conventional two wheel steering. Four wheel steering is growing in popularity and it is likely to have with all vehicles. As the systems takes over market the cost of four wheel steering will fall down.

REFERENCES 1. K. Lohith, Dr. S.R. Shankapal, M.H. Monish Gowda, “DEVELOPMENT OF FOUR WHEEL STEERING SYSTEM FOR A CAR”. 2. DILIP S. CHOUDHARY, “FOUR WHEEL STEERING SYSTEM”. International Journal of Mechanical Engineering and Robotic Research”.

Volume: 3 Issue: 4, ISSN 2278-0149 3. K.Lohith, Dr. S.R. shankapal, M.H. Monish Gowda, “ Development of Four Wheel Steering system for a Car” vol. 12, pg. 90-97, Issue 1, April 2013. 4.

V. B. Bhandari “ Design of Machine Elements” McGraw Hill Education

India Pvt. Ltd., vol. 3, 11th Edition, 2013. 5. Abhinav Tikley, Mayur Khangan, “FOUR WHEEL STEERING- A REVIEW”. International Journal of Research In Science And Engineering. volume: 1 Issue: 3 e-ISSN: 2394-8299, p-ISSN: 2394-8280

6.

Arun Singh, Abhishek Kumar, Rajiv Chaudhary, R.C Singh. “Study of Four Wheel Steering System to Reduce Turning Radius and Increase Stability”. International Conference of Advance Research And Innovation ISBN 978-93-5156-328-0

7. Saket Bhishikar, Vatsal Gudhka, Neel Dalal, Paarth Mehta. “Design and Simulation of 4 Wheel Steering system”. International Journal of Engineering and Innovative Technology (IJEIT) Volume 3, Issue 12, June 2014 ISSN: 22773754 8. Kripal singh volume 1 and 2 Automobile Engineering