steering system somnath

7/29/2019 Steering System Somnath

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Dept. of Mechanical Engineering

STEERING SYSTEM

The function of steering is to steer the front wheel in response to driver command inputs in order

to provide overall directional control of the vehicle. The factors kept in mind while designing thesteering system were

Simplicity Safety Requiring minimum steer effort Economical

Steering geometry

Ackerman

The Ackerman Steering Principle defines the geometry that is applied to all vehicles (two or four

wheel drive) to enable the correct turning angle of the steering wheels to be generated when

negotiating a corner or a curve.

When a car is travelling around a corner (the red lines represent the path that the wheels follow)the inside wheels of the car follow a smaller diameter circle than the outside wheels.

If both the wheels were turned by the same amount, the inside wheel would scrub (effectively

sliding sideways) and lessen the effectiveness of the steering. This tire scrubbing, which also

creates unwanted heat and wear in the tire, can be eliminated by turning the inside wheel at a

greater angle than the outside one.


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The difference in the angles of the inside and outside wheels may be better understood by

studying the diagram, where we have marked the inside and outside radius that each of the tires

passes through. The Inside Radius (Ri) and the Outside Radius (Ro) are dependent on a number

of factors including the car width and the tightness of the corner the car is intended to pass

through. Aligning both wheels in the proper direction of travel creates consistent steering without

undue wear and heat being generated in either of the tires.

Steering Arm Angles

Creating mis-alignment of the wheels is achieved by a combination of the angle and the length of

the steering arms. Below a few diagrams are shown that give examples using parallel and angled

steering arms to demonstrate why there is a need for using the Ackerman Steering Principle.

Parallel Steering Arms

The steering arms in the diagram to the left are straight and parallel to the sides of the vehicle,

which would create a situation where equal movement of the steering servo would produce equal

angular movement of the wheels.

As the steering arm pivot point (A) is vertically aligned with the king pin pivot point (B) when

the wheel is pointing straight ahead, the same amount of movement to the Left or to the Right

moves the steering arm pivot point the same vertical distance forward of its starting point.

Angled Steering Arms


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The steering arms in the image to the left are angled inwards to create a means for the wheel

angles to change at a different rate. This is the basis of the Ackerman Steering Principle and

creates this unequal angular movement of the wheels.

As the steering arms are angled, the pivot point (A) is not vertically aligned and is, in a straight

ahead position, part way round the circle. Because of this, a Right movement of the steering arm

will cause the pivot point to move a greater distance in the forward direction than a Left

movement of the steering arm.

An important point worth noting is that this unequal angular movement is exponential, that is,

the more you turn the wheel the greater the angular difference between the wheels - otherwise

both the wheels would never point forward when the car is not turning.

Low Lateral Acceleration

At low speeds when the tires have minimal tire shear losses on dry, clean pavement, the true

Ackermann steering geometry is beneficial as the tires are in almost a perfect situation of minute

slip angle. Parallel or reverse Ackermann in this scenario would push (or under steer) the front of

the car away from the desired path. In both situations, the inside tire contributes to this push

similarly to a centrifugal force.

High Lateral Acceleration

At high lateral accelerations, true Ackermann becomes disadvantageous as loads on the outside

wheel increase and the greater slip angle of the inside tire creates higher tire temperatures and

slows down the car due to tire drag. The inside tire has also surpassed the maximum slip angle of

grip assuming the outer tire is already at the optimum slip angle. Parallel or reverse setups are


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more advantageous in this situation as both the inside and outside tires still have lateral grip.

Reverse Ackermann steering can even be more beneficial than the parallel Ackermann geometry

since the outside tire (which currently has more load due to weight transfer) is at the optimum

slip angle and the inside is at a lower slip angle with less grip. This in turn allows the inside tire

to have grip but less than the outside tire, decreasing the effects of under steer.

100% Ackermann is when both the wheels are travelling in concentric circles while 0% is for

travelling in equal circles. Forward Ackermann geometry with 60% Ackermann was chosen

for our BAJA vehicle.

Reasons for the choice:

It creates an additional drag force that helps yaw the car. The second is that the slip angle of maximum lateral force changes with vertical load,

so to extract maximum lateral force, the outside wheel needs to be a different amount

than the inner.

CamberCamber is the angle of the wheel relative to vertical, as viewed from the front or the

rear of the car. If the wheel leans in towards the chassis, it has negative camber; if itleans away from the car, it has positive camber. The cornering force that a tire can

develop is highly dependent on its angle relative to the road surface, and so wheel

camber has a major effect on the road holding of a car. The camber angle taken for

Baja car is typically around neg. 1/2 degree as tire develops its maximum cornering

force at such a small negative camber angle. This fact is due to the contribution of

camber thrust, which is an additional lateral force generated by elastic deformation as

the tread rubber pulls through the tire/road interface (the contact patch).


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Caster

Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as

viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned

farther rearward than the bottom pivot), then the caster is positive; if it's tilted forward, then the

caster is negative.

Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is

used to enhance straight-line stability.

Due to many design considerations, it is desirable to have the steering axis of a car's wheel right

at the wheel hub. If the steering axis were to be set vertical with this layout, the axis would be

coincident with the tire contact patch. The trail would be zero, and no castering would be

generated. The wheel would be essentially free to spin about the patch (actually, the tire itself

generates a bit of a castering effect due to a phenomenon known as "pneumatic trail," but this

effect is much smaller than that created by mechanical castering, so we'll ignore it here).

Fortunately, it is possible to create castering by tilting the steering axis in the positive direction.With such an arrangement, the steering axis intersects the ground at a point in front of the tire

contact patch, and thus the same effect as seen in the shopping cart casters is achieved.

The tilted steering axis has another important effect on suspension geometry. Since the wheel

rotates about a tilted axis, the wheel gains camber as it is turned. This effect is best visualized by


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imagining the unrealistically extreme case where the steering axis would be horizontal-as the

steering wheel is turned, the road wheel would simply change camber rather than direction. This

effect causes the outside wheel in a turn to gain negative camber, while the inside wheel gains

positive camber. These camber changes are generally favorable for cornering, although it is

possible to overdo it.

Most cars are not particularly sensitive to caster settings. Nevertheless, it is important to ensure

that the caster is the same on both sides of the car to avoid the tendency to pull to one side. While

greater caster angles serve to improve straight-line stability, they also cause an increase in

steering effort. Three to five degrees of positive caster is the typical range of settings, with lower

angles being used on heavier vehicles to keep the steering effort reasonable.

.

Toe in/Toe outWhen a pair of wheels is set so that their leading edges are pointed slightly towards each other,

the wheel pair is said to have toe-in. If the leading edges point away from each other, the pair is

said to have toe-out. The amount of toe can be expressed in degrees as the angle to which the

wheels are out of parallel, or more commonly, as the difference between the track widths as

measured at the leading and trailing edges of the tires or wheels. Toe settings affect three major

areas of performance: tire wear, straight-line stability and corner entry handling characteristics.

For minimum tire wear and power loss, the wheels on a given axle of a car should point directly

ahead when the car is running in a straight line. Excessive toe-in or toe-out causes the tires to


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scrub, since they are always turned relative to the direction of travel. Too much toe-in causes

accelerated wear at the outboard edges of the tires, while too much toe-out causes wear at the

inboard edges.

In our Baja vehicle we use Toe in of 3-4mm.The reasons for the choice is:

Toe in unlike Toe out (which encourages initiation of turn) provides straight line stability. With

the steering wheel centered, toe-in causes the wheels to tend to roll along paths that intersect

each other. Under this condition, the wheels are at odds with each other, and no turn results. Also

when pushed down the road, a non-driven wheel will tend to toe itself out especially in rear-drive

cars. Thus, toe in helps in providing stability while going down the road.

The basic types of steering systems used are described below-


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1. RACK ANS PINION STEERING

As the name implies, rack-and-pinion steering consists of two major components -- a rack and a

pinion. The rack -- also known as a steering rack -- is a long piece of metal that is flat on at least

one side. The flat side contains teeth running the length of the rack. The teeth are cutperpendicular to the edges of the rack, meaning they run side by side from one end of the rack to

the other.

The other major component, the pinion -- more correctly, the pinion shaft -- is a round rod that

also has teeth on it, although these teeth run parallel to the length of the shaft, not lengthwise as

on the rack. The pinion shaft comes into the rack at a ninety-degree angle, held in place by a

collar, and the teeth on the pinion mesh with the teeth on the rack. The pinion is connected

directly to the steering column, so when the steering wheel is turned to the left, for instance, the

pinion rotates counter-clockwise (from the driver's perspective). Simply put, the rotary motion of

the pinion is changed to transverse motion by the rack. The rack moves to the right, making the

wheels go left. The car turns left.

Rack and pinion steering mechanisms have the following advantages


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Advantages:

Simple construction

Economical and uncomplicated to manufacture

Easy to operate due to good degree of efficiency

Contact between steering rack and pinion is free of play and even internal damping is

maintained

Tie rods can be joined directly to the steering rack

Minimal steering elasticity compliance

compact (the reason why this type of steering is fitted in all European and Japanese front -wheel

drive vehicles)

The idler arm (including bearing) and the intermediate rod are no longer needed

Easy to limit steering racktravel and therefore the steering angle

2. PITMAN ARM TYPE

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.


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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 startto 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.

a)Worm and sector

In this type of steering box, the end of the shaft from the steering wheel has a worm gear

attached to it. It meshes directly with a sector gear (so called because it's a section of a full gear

wheel). When the steering wheel is turned, the shaft turns the worm gear, and the sector gear

pivots around its axis as its teeth are moved along the worm gear. The sector gear is mounted on

the cross shaft which passes through the steering box and out the bottom where it is splined, and

the the pitman arm is attached to the splines. When the sector gear turns, it turns the cross shaft,
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which turns the pitman arm, giving the output motion that is fed into the mechanical linkage on

the track rod. The following diagram shows the active components that are present inside the

worm and sector steering box. The box itself is sealed and filled with grease.

Worm and roller

The worm and roller steering box is similar in design to the worm and sector box. The difference

here is that instead of having a sector gear that meshes with the worm gear, there is a roller

instead. The roller is mounted on a roller bearing shaft and is held captive on the end of the cross

shaft. As the worm gear turns, the roller is forced to move along it but because it is held captive

on the cross shaft, it twists the cross shaft. Typically in these designs, the worm gear is actually

an hourglass shape so that it is wider at the ends. Without the hourglass shape, the roller might

disengage from it at the extents of its travel.

Worm and nut or recirculating ball

This is by far the most common type of steering box for pitman arm systems. In a recirculating

ball steering box, the worm drive has many more turns on it with a finer pitch. A box or nut is

clamped over the worm drive that contains dozens of ball bearings. These loop around the worm

drive and then out into a recirculating channel within the nut where they are fed back into the
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worm drive again. Hence recirculating. As the steering wheel is turned, the worm drive turns and

forces the ball bearings to press against the channel inside the nut. This forces the nut to move

along the worm drive. The nut itself has a couple of gear teeth cast into the outside of it and these

mesh with the teeth on a sector gear which is attached to the cross shaft just like in the worm and

sector mechanism. This system has much less free play or slack in it than the other designs,

hence why it's used the most. The example below shows a recirculating ball mechanism with the

nut shown in cutaway so you can see the ball bearings and the recirculation channel.

Cam and lever

Cam and lever steering boxes are very similar to worm and sector steering boxes. The worm

drive is known as a cam and has a much shallower pitch and the sector gear is replaced with two

studs that sit in the cam channels. As the worm gear is turned, the studs slide along the cam

channels which forces the cross shaft to rotate, turning the pitman arm. One of the design

features of this style is that it turns the cross shaft 90 to the normal so it exits through the side of

the steering box instead of the bottom. This can result in a very compact design when necessary.
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3. RECIRCULATING BALL TYPE STEERING MECHANISM

The recirculating-ball steering gear contains a worm gear. You can image the gear in two parts.

The first part is a block of metal with a threaded hole in it. This block has gear teeth cut into the

outside of it, which engage a gear that moves the pitman arm. The steering wheel connects to a

threaded rod, similar to a bolt that sticks into the hole in the block. When the steering wheel

turns, it turns the bolt. Instead of twisting further into the block the way a regular bolt would, this

bolt is held fixed so that when it spins, it moves the block, which moves the gear that turns the

wheels.

Instead of the bolt directly engaging the threads in the block, all of the threads are filled with ball

bearings that recirculate through the gear as it turns. The balls actually serve two purposes: First,

they reduce friction and wear in the gear; second, they reduce slop in the gear. Slop would be felt

when you change the direction of the steering wheel -- without the balls in the steering gear, the

teeth would come out of contact with each other for a moment, making the steering wheel feel

loose.


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THE STEERING MECHANISM MOST SUITABLE FOR OUR VEHICLEWe are planning on implementing the rack and pinion mechanism because it is comparatively

easier to manufacture and the most cost effective. Apart from this, it has the least number of

parts hence requires less maintenance. An additional advantage is that a variable ratio steering

can be designed which has been detailed below.

STEERING RATIOSThe steering ratio is the ratio of how far you turn the steering wheel to how far the wheels turn.

For instance, if one complete revolution (360 degrees) of the steering wheel results in the wheels

of the car turning 20 degrees, then the steering ratio is 360 divided by 20, or 18:1. A higher ratio

means that you have to turn the steering wheel more to get the wheels to turn a given distance.

However, less effort is required because of the higher gear ratio.

Generally, lighter, sportier cars have lower steering ratios than larger cars and trucks. The lower

ratio gives the steering a quicker response -- you don't have to turn the steering wheel as much to

get the wheels to turn a given distance -- which is a desirable trait in sports cars. These smaller

cars are light enough that even with the lower ratio, the effort required to turn the steering wheel

is not excessive.

VARIABLE STEERING RATIOSSome cars have variable-ratio steering, which uses a rack-and-pinion gear set that has a different

tooth pitch (number of teeth per inch) in the centre than it has on the outside. This makes the car

respond quickly when starting a turn (the rack is near the centre), and also reduces effort near the

wheels turning limits.

Advantages of variable ratio steering

1. In high speed driving, increased lateral acceleration as a result of high downforce and higher

normal loads acting on the tyres result in increased loads on the steering rack. By employing a

variable ratio a reduction in steering torque can be achieved.


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2. Variable ratio can also be used to tune the yaw gain or sensitivity of the vehicle to steering

inputs. A high yaw gain makes the vehicle feel very nervous in high speed corners where the

smallest steering wheel input results in what feels like an excessive response.

3. In electric power steering systems variable ratios allow the designer to balance the power

requirements of the system.

4. Variable ratio rack and pinion systems eliminate the compromises that constant ratio systems

have by allowing the designer to utilise a best fit approach for tuning the vehicle response over a

wide range of driving conditions.

The steering ratio opted for our BAJA vehicle is 12:1 in support of the following reasons-

1. Moderate steering effort-The steering effort increases with reduction in steering ratio. The

above ratio selected offers moderate steering effort required during cornering.

2. Lesser no. of lock to lock turns- With the above steering ratio, the no. of lock to lock turns of

steering wheel is reduced. During cornering, the driver has to turn the steering wheel in lesser

amount.

Since variable steering ratios offer a much greater advantage over constant steering ratio we are

trying to look for manufacturers who can supply readymade rack and pinion ratios with desired

ratios. Nevo Developments and Sona Koyo steering systems,Gurgaon have been contacted with

regards to the requirement. A response is awaited.


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POWER STEERING

Part of the rack contains a cylinder with a piston in the middle. The piston is connected to the

rack. There are two fluid ports, one on either side of the piston. Supplying higher-pressure fluid

to one side of the piston forces the piston to move, which in turn moves the rack, providing the

power assist.

Power steering helps drivers steer vehicles by augmenting steering effort of the steering wheel.

Hydraulic or electric actuators add controlled energy to the steering mechanism, so the driver

needs to provide only modest effort regardless of conditions. Power steering helps considerably

when a vehicle is stopped or moving slowly. Also, power steering provides some feedback of

forces acting on the front wheels to give an ongoing sense of how the wheels are interacting with

the road; this is typically called "rad feel".

Representative power steering systems for cars augment steering effort via an actuator, a

hydraulic cylinder, which is part of a servo system. These systems have a direct mechanical

connection between the steering wheel and the linkage that steers the wheels. This means that

power-steering system failure (to augment effort) still permits the vehicle to be steered using

manual effort alone.


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ELECTRIC POWER STEERINGA steering sensor is located on the input shaft where it is bolted to the gearbox housing.

The sensor performs two different functions: Firstly as a torque sensor, it converts steering

torque input and direction into voltage signals for the ECU to monitor and convert into a binary

code, and secondly as a rotation sensor, which converts the rotation speed and direction into

voltage signals for the ECU to monitor and convert into a binary code.

An interfaced ECU circuit that shares the same housing converts the signals from the torque and

rotation sensors into signals that the ECU can process and provide an active output.

The microprocessor control unit analyzes inputs from the steering sensor as well as the vehicles

speed sensor. The sensor inputs are then compared to determine how much power assist is

required according to the forces capability map data stored in the ECUs memory. This map

data is pre-programmed by the manufacturer.

The ECU then emits the appropriate command to the power unit or current controller, which

supplies the electric motor with the necessary current to activate. The motor then pushes the rack

either to the right or left. Direction of rack movement is dependent on which way the voltage

flows; reversing the current flow reverses directional rotation of the motor. Increasing current to

the motor increases the amount of power assist.

The electric power assistance system has three operating modes:

1. In normal control mode left or right power assist is provided in response to input from the

torque and rotation sensors inputs.

2. The return control mode is used to assist steering return after completing a turn.

3. The damper control mode changes the vehicle speed to improve road feel and dampen

kickback.

If the steering wheel is turned and held in the full-lock position and steering assist reaches

maximum, the control unit reduces current to the electric motor to prevent an overload situation

that might damage the motor. The control unit is also designed to protect the motor against

voltage surges from a faulty alternator or charging problem.


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The electronic steering control unit is capable of self-diagnosing faults by monitoring the

systems inputs, outputs, and the driving current of the electric motor. If a problem occurs, the

control unit turns the system off by actuating a fail-safe relay in the power unit.

This eliminates all power assist, causing the system to revert back to manual steering. An in-dash

EPS warning light is also illuminated to alert the driver.

TYPES OF EPS

1. COLUMN ASSIST TYPE-The power assist unit, controller and torque sensor are attached to the steering column.

-This system is compact and easy to mount on the vehicle.

-This power assist system can be applied to fixed steering columns, tilt-type steering columns

and other column types.


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2. PINION ASSIST TYPE

-The power assist unit is attached to the steering gear's pinion shaft.

-The power assist unit is outside the vehicle's passenger compartment, allowing assist torque to

be increased greatly without raising interior noise.

-Combined with a variable-ratio steering gear, this system can suffice with a compact motor and

offer superior handling characteristics.

3. RACK ASSIST TYPE

-The power assist unit is attached to the steering gear rack.

-The power assist unit can be located freely on the rack, allowing great flexibility in layout

design.

-The power assist unit's high reduction gear ratio enables very low inertia and superior driving

feeling.

4. DIRECT DRIVE TYPE

-The steering gear rack and power assist unit form a single unit.

-The steering system is compact and fits easily in the engine compartment layout.

-The direct provision of assistance to the rack enables low friction and inertia, and in turn ideal

steering feeling.


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VEHICLE DYNAMICS

UNDERSTEER

Understeer is so called because the car steers less than what is wanted. Understeer can be

brought on by all manner of chassis, suspension and speed issues but essentially it means that the

car is losing grip on the front wheels. Typically it happens as brakes are applied and the weight is

transferred to the front of the car. At this point the mechanical grip of the front tyres can simply

be overpowered and they start to lose grip (for example on a wet or greasy road surface). The

end result is that the car will start to take the corner very wide. In racing, that normally involves

going off the outside of the corner into a catch area or on to the grass. In normal driving, it means

crashing at the outside of the corner. Getting out of understeer can involve letting off the throttle

in front-wheel-drive vehicles (to try to give the tyres chance to grip) or getting on the throttle inrear-wheel-drive vehicles (to try to bring the back end around).

OVERSTEER

Oversteer is the opposite of understeer. With oversteer, the car goes where it's pointed far too

efficiently and ends up diving into the corner much more quickly than expected. Oversteer is

brought on by the car losing grip on the rear wheels as the weight is transferred off them under

braking, resulting in the rear kicking out in the corner. Without counter-steering, the end result inracing is that the car will spin and end up going off the inside of the corner backwards. In normal

driving, it means spinning the car and ending up pointing back the way it came.


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BUMP STEER

It is defined as the tendency of a wheel to steer as it moves upwards into jounce. It is typically

measured in degrees per meter or degrees per foot. Bump steer in many stock vehicles is

usually noticed by lowering the ride height, changing the suspension geometry. This is mainly

due to the tie rod not moving in the same arc motion as the control arm (upper or lower

depending on suspension type). The examples below will further explain bump steer.

Example #1: Bump Steer Scenario

The picture displays the FRONT RIGHT section of a typical Formula SAE chassis. As can be

seen, there are two A-arms and a stationary steering rack (silver bar) with a tie rod. This will

represent the situation of a driver with no steering input (zero degrees of steering angle). The

tie rod as well as the A-arms are connected to the upright which hold the wheel hub, brake

rotor, caliper, wheel, and tire.
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Initially the vehicle has no toe in or out and is traveling in a straight line. All seems well as the

driver holds the wheel steady with no input over the smooth pavement road.
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Suddenly the driver hits a pothole compressing the front suspension. As can be seen, the front tire

immediately toes in making the vehicle less predictable and unstable. The steering can also feel a bit

light and loose under bump steer. The same issue can occur with hard braking which would

compress the front suspension due to forward weight transfer. As seen below, due to the high

difference in angle and length of the tie rod, the arc motion is completely off when compared to the

upper A-arm. As the upper A-arm loses its lateral (left to right) displacement under jounce, the tie

rod gains lateral distance pushing the upright out toeing in the front suspension.

Example #2: Scenario without Bump Steer
https://eee.uci.edu/wiki/index.php/File:Neutral_Steer_Iso.JPGhttps://eee.uci.edu/wiki/index.php/File:Bump_Steer_Front.JPGhttps://eee.uci.edu/wiki/index.php/File:Neutral_Steer_Iso.JPGhttps://eee.uci.edu/wiki/index.php/File:Bump_Steer_Front.JPGhttps://eee.uci.edu/wiki/index.php/File:Neutral_Steer_Iso.JPGhttps://eee.uci.edu/wiki/index.php/File:Bump_Steer_Front.JPGhttps://eee.uci.edu/wiki/index.php/File:Neutral_Steer_Iso.JPGhttps://eee.uci.edu/wiki/index.php/File:Bump_Steer_Front.JPGhttps://eee.uci.edu/wiki/index.php/File:Neutral_Steer_Iso.JPGhttps://eee.uci.edu/wiki/index.php/File:Bump_Steer_Front.JPGhttps://eee.uci.edu/wiki/index.php/File:Neutral_Steer_Iso.JPGhttps://eee.uci.edu/wiki/index.php/File:Bump_Steer_Front.JPGhttps://eee.uci.edu/wiki/index.php/File:Neutral_Steer_Iso.JPGhttps://eee.uci.edu/wiki/index.php/File:Bump_Steer_Front.JPG


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CALCULATIONS:-

Steering ratio- 12:1

Track- 60 inches

Wheel base- 58 inches

Maximum steering angle-

Inner front wheel- 40 deg. +/- 2 deg.

Outer front wheel- 28 deg. +/- 2 deg.

Lock to lock- 2.26 turns.

Ackermann %=60%

Turning circle radius- using the formula listed above we get it close to 11.2 feet.

Rack travel- 2.67 inches per turn

Lateral rack movement- 6.675 inches.


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ContentsSteering geometry ......................................................................................................................................................... 1

Ackerman .................................................................................................................................................................. 1

Steering Arm Angles .................................................................................................................................................. 2

Parallel Steering Arms ............................................................................................................................................... 2

Angled Steering Arms ................................................................................................................................................ 2

Low Lateral Acceleration ........................................................................................................................................... 3

High Lateral Acceleration .......................................................................................................................................... 3

Reasons for the choice: ............................................................................................................................................. 4

1. RACK ANS PINION STEERING ..................................................................................................................................... 8

2. PITMAN ARM TYPE .................................................................................................................................................... 9

a)Worm and sector ................................................................................................................................................. 10

Worm and roller ...................................................................................................................................................... 11

Worm and nut or recirculating ball ......................................................................................................................... 11

Cam and lever ......................................................................................................................................................... 12

3. RECIRCULATING BALL TYPE STEERING MECHANISM ............................................................................................... 13

THE STEERING MECHANISM MOST SUITABLE FOR OUR VEHICLE ............................................................................... 14

STEERING RATIOS ........................................................................................................................................................ 14

VARIABLE STEERING RATIOS ........................................................................................................................................ 14

POWER STEERING ........................................................................................................................................................ 16

ELECTRIC POWER STEERING ........................................................................................................................................ 17

TYPES OF EPS ............................................................................................................................................................... 18

1. COLUMN ASSIST TYPE ......................................................................................................................................... 18

2. PINION ASSIST TYPE............................................................................................................................................. 19

3. RACK ASSIST TYPE ................................................................................................................................................ 19

4. DIRECT DRIVE TYPE ............................................................................................................................................. 19

VEHICLE DYNAMICS ..................................................................................................................................................... 20

UNDERSTEER ........................................................................................................................................................... 20

OVERSTEER .............................................................................................................................................................. 20

BUMP STEER ............................................................................................................................................................ 21

Example #1: Bump Steer Scenario .......................................................................................................................... 21

Example #2: Scenario without Bump Steer ............................................................................................................. 23

CALCULATIONS:- .......................................................................................................................................................... 24


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steering system somnath

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