A PROJECT REPORT ON STEERING CONTROL BY WIRE Submitted in partial fulfillment of the requirements for the award of the degree Of Bachelor of Technology In Department of Mechanical Engineering

Submitted By: - Submitted To:-Omprakash Anil Kumar MahawarLakhmindra singh (Head Of Department)Rahul yadav Department of MEManish Sharma AIET, AlwarME, Final Year (8th Sem)

ALWAR INSTUTUTE OF ENGINEERING &TECHNOLOGY, MIAALWAR-301030 (RAJ.), INDIAMAY, 2015A PROJECT REPORTOnSTEERING CONTROL BY WIRE Submitted in partial fulfillment of the requirements for the award of the degreeofBachelor of TechnologyInDepartment of Mechanical Engineering

Submitted By: - Under the guidance of:- Omprakash M.r Subhash SharmaLakhmindra singh(Asst. Professor)Rahul yadavMechanical Departmant of ManishAIET( Alwar)Final Year (8th Sem.) ALWAR INSTUTUTE OF ENGINEERING &TECHNOLOGY, MIAALWAR-301030 (RAJ.), INDIAMAY, 2015

CERTIFICATEThis is to certify the following students have successfully complete project work on STEERING CONTROL BY WIREhas been submitted to the Rajasthan Technical University, Kota insubmitted in partial fulfillment of the requirements for the award of the degree of Bachelor of Technology in Mechanical Engineering by Omprakash (11EAEME743),Lakhmindra (11EAEME733),Manish Sharma (11EAEME736), Rahul yadav(11EAEME747),

Mr. Subhash sharma Mr. Anil Kumar MahawarPROJECT GUIDE H.O.DDepartment of ME Department of ME AIET, Alwar AIET, Alwar

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CANDIDATES DECLARATIONWe here by declare that the work of project Steering Control By Wire is being presented in the partial fullfillment of the requriment for the award of Bachelor of Technology in Mechanical Engineering to Alwar Institute of Engineering & Technology, Alwar, Affiliated to Rajasthan Technical University,Kota is an authentic record of our work carried out during VIIIsemester under the supervision of our guide Mr. Subhash Sharma Associate Professor, Department of Mechnical Engineering, Alwar Institute of Engineering & Technology, Alwar .

The matter embodied in this report has not been submitted by us for the award of any other degree or diploma.

Date:Omprakash (11EAEME743) Lakhmindra(11EAEME733) Rahul yadav (11 EAEME 747) Manish Sharma (11EAEME736)

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ABSTRACTBy-wire is the generic term used to denote control systems that depend on a communications network to connect their components, rather than the more traditional mechanical or hydraulic linkages. Steer by Wire system eliminates the mechanical connection between the driver and the vehicle front tyres. Instead, actuators are positioned at the corners of the vehicle and receive inputs from the control module to turn the wheels accordingly. A distributed control system made up of a network of controllers electrically transmits the road feel back to the steering wheel and the amount of steering wheel turn to the control system. The road feel is recreated by the use of an electric motor to provide feedback to the driver steering wheel. This is similar to the force-feedback steering wheel from the video gaming industry.

In the project our main aim has been to remove the mechanical linkage between the steering system and the steering wheel. Which is the essence of any system. We were able to do so with the use of synchro-transmitter and receiver.

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ACKNOWLEDGEMENT

I wish to express my sincere gratitude to all the members of Department of Mechanical Engineering for their constant encouragement, supervision, suggestion and advice throughout my Project work .I acknowledge my gratitude to my family members for their unconditional support and whole hearted blessings to accomplish this task.A word of thank is due to my friends who stood by me and always helped me to take the best foot forward and all the Faculty and staff members of my college. I acknowledge all who helped me at each and every step, where their support was required.We want to give special thanks to Subhash sharma Sir for Guide us.Lastly, I thank almighty God whose constant blessing has given me strength and patience to bring this work into its present form.

Date:- Place: - MIA, Alwar Omprakash (11EAEME743) Lakhmindra(11EAEME733) Rahul yadav (11 EAEME 747)

(ii) Manish Sharma (11EAEME736)

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TABLE OF CONTENT

Certificate ..... i Candidates declaration iiAbstract.iiiAcknowledgement .. iv Table of content ...vList of figure ....vi-vii CHAPETR:-1 INTRODUCTION 1-14

1.1 STEERING SYSTEM OVERVIEW 1-6 1.2 VARIOUS KINDS OF STEERING SYSTEMS 6-14 CHAPTER:-2 LITERATURE REVIEW . 14-30

2.1 SYNCHRO TRANSMITTER /RECEIVER 14-23 2.2 STEER BY WIRE 24-30

CHAPTER:-3FEBRICATION AND RESULT.... 31-32

CHAPTER:-4 CONCLUSION AND FUTURE WORK..33

CHAPTER:-5 REFERENCE34

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List of Figure

SR.NOFIGUREPAGE NO.

1Correct steering geometry2

2Ackerman Mechanism4

3Details of Ackerman Mechanism4

4Basic rack and Pinion Components6

5Rack housing assembly7

6Cross sectional view of recirculating ball steering8

7Ball screw9

8Rotary vane pump10

9Spool Valve11

10General assembly of EPS12

11Layout13

12Slider Movement14

13Angular position and winding operation of synchro when phase angle of S2 when rotor is in 00 and 1 800.

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14Angular position and winding operation of synchro when phase angle of S2 with rotor is 90016

15Computed Graph18

16Angular position and connecting diagram of synchrowhen both rotors are in phase

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17Electrical Circuit20

18Transmitter Receiver Connections21

19Inside of a synchro motor22

20Working of the brush type synchronous motors.23

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SR.NOFIGUREPAGE NO.

21Block diagram of Steer by Wire24

22Basic Layout27

23Fail Safe Unit28

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INTRODUCTION

1.1STEERING SYSTEM OVERVIEW:-

Primary function of the steering system is to achieve angular motion of the front wheels is to negotiate a turn. Steering is one of the most critical safety factors in vehicle control. It enables an input provided by the driver in the form of a torque to correspondingly control the orientation of the vehicles moving wheels, and hence, direction of motion of the vehicle. The usual approach to accomplish this task is through linkage and steering gear, which converts rotary motion of steering wheel into angular motion of front road wheels. During the developments of vehicles over the past century, various approaches have evolved relating to the steering system. During the development of vehicles over the past century, various approaches have evolved relating to the steering system.

1.1.1Condition for correct steering--

The perfect steering is achieved when all four wheels are rolling perfectly without slipping. While taking a turn the condition for perfect rolling is satisfied if the axes of the front wheel meet the axes of the rear wheels at one point, when produced. This point is the instantaneous center of the vehicle. It is seen that the inside tyre has to turn through a greater angle than the outer wheel. The diameter of the smallest circle, which the outer wheel can turn and which is obtained when the wheels are at heir extreme positions, is known as the turning circle.

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cyWheel trackWheel base b

Fig. 1 Correct steering geometry

Cot = (y+c) / b( = angle of outside lock)

= y / b + c/b = cot + c/b( = angle of inside lock)

cot - cot = c/b Eqn. (1.1) represent the basic condition for perfect rolling of all wheels.

Further, the turning circle radii for different wheels can be written as

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1.) For the inner front wheel:

RIF =b/sin - (a-c) /2

2.) For the outer front wheel:

ROF = b/sin + (a-c) / 2

3.) For the inner rear wheel:

RIR = b / tan - (a-c)/2

4.) For the outer front wheel:

ROR = b/tan + (a-c) /2

In the above equation a = wheel track

1.1.2Steering mechanism--

The Ackerman steering mechanism is university used because of its simplicity.

Ackerman Mechanism

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Fig. 2 Ackerman Mechanism

Fig. 3 Details of Ackerman Mechanism

Links RA and SB are integral with the stub axles. The links are connected with each other through track rod AB. When the vehicle is in straight ahead position these links make equal angles with the centerlines of the car. The dotted lines indicate the position of the car when the car is turning left. Let

I = length of track rodr = lengths of links RA and SB

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Then referring to Fig. 3 and neglecting obliquity of the track rod in the turned position movement of A and B in the horizontal direction may be taken to be the same (each equal to x).

Then

Sin ( - ) = (y + x) /r

Sin (- ) = (Y-X) / r

The mechanism gives only three positions for correct steering: one when = 0 and the other two corresponding to turn to right or left (at fixed turning angle). However at other turning angles it give close approximation to the ideal conditions. Further it ha the advantage of applying pivots and no sliding constraints, due to which reason its maintenance is easier. Any small deflection from true rolling angles can be readily corrected by the tyres sidewall flexibility and tread distortion.

1.1.3Function of steering system--

1) To convert rotary motion of the steering wheel into angular motion of front wheels to negotiate a turn.

2) To provide directional stability of the vehicles when going straight ahead.

3) To provide perfect steering condition i.e. perfect rolling motion of road wheels at all times.

4) To facilitate straight ahead recovery after completing a turn.

5) To minimize tyre wear.

On most cars, it takes three to four complete revolutions of the steering wheel to make the wheels turn from lock to lock (from far left to far right).

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The steering ratio is the ratio of the angle turned by the steering wheel to the angle turned by the wheels. 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: one doesnt 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.

Some cars have variable-ratio steering, which uses a rack and pinion gearset that has a different tooth pitch (number of teeth per inch) in the center than it has on the outside. This makes the car respond quickly when starting a turn (the rack is near the center), and also reduces effort near the wheels turning limits.

1.1.4ARIOUS KINDS OF STEERING SYSTEMS:-

1.1.1Mechanical system:-

(1.2.1.a)Rack and Pinion:-The rack- and-pinion steering gear was first developed for compact cars in which the engine compartment space was limited. The rack-and-pinion system is very successful in small to mid sized cars and compacts.

Fig.4 Basic rack and Pinion Components 6 The basic parts of a rack-and-pinion steering gear are shown in fig.4. The steering wheel and steering shaft are connected to a pinion gear. The pinion gear is in mesh with a straight bar that has gear teeth cut into one side. The toothed bar is called a rack. When the driver turns the steering wheel, the pinion gear turns, causing the rack to move. This movement, in turn, is connected to a linkage that moves the front wheels.

The rack-and-pinion gear is mounted in a rack housing assembly. The steering linkage consists of two inner the tie rods and two tie rod ends. The inner tie rod ends are attached to the steering rack ends. The outer tie rod ends are attached to the suspension arms on the steering knuckles. Rubber boots are used to cover and protect the inner tie rod assemblies from road splash.

Fig. 5 Rack housing assembly

1.2.1.b)Recirculating Ball and nutThe larger and heavier the car, the more difficult it is to steer. Larger car are equipped with a recirculating ball type steering gear. This type of steering gear is very low in friction and provides a good mechanical advantage for a heavy vehicle.

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Fig.6 Cross sectional view of recirculating ball steeringThe recirculating ball and nut steering gear consists of several parts contained in steering gear housing. The steering gear shaft is connected to the steering wheel either directly or through some type of flexible joint. There is a worm gear on the end of the steering gear shaft. A cross (pitman) shaft is mounted in the housing in a position 90 degrees to the worm gear. A ball nut rides on the worm gear and a gear on the cross (pitman) shaft, called the cross shaft sector, is engaged with this nut.

The sliding ball nut has tapered teeth cut on one face that mate with teeth on the sector. As the steering wheel is rotated, the nut is moved up or down on the worm. Because teeth on the nut are meshed with the teeth on the sector, the movement of the nut causes the sector shaft to rotate and swing the steering linkage connected to it.The recirculating ball construction results in a friction-free contact between the nut and the worm. When the steering wheel is turned to the left, the ball bearings roll between the worm and the nut and work their way upward in the worm groove. When the ball bearings reach the top of the nut, they enter two ball guides and are directed downward into the worm groove at a lower point. When the steering wheel is turned to the right, the ball bearings circulate in the opposite direction.

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Fig.7 Ball screw

1.1.5Power steering:-

In this system, a separate pump is driven to generate a continuous flow of hydraulic fluid that, in turn, is applied to the steering mechanism to adjust the desired orientation of the wheels. The hydraulic fluid is controlled by a high-precision value, which is progressively opened or closed in correspondence to torque applied to the steering wheel. The hydraulic system can be subdivided into engine-driven pump and electric motor driven pump.

(1.2.2.a)Engine-driven pump:-In this system, the internal combustion engine of the vehicle continuously powers the hydraulic pump. This has been the dominant approach for the last 50 years.

(1.2.2.b)Electric motor driven pump:-In this system, a separate, electronically controlled electric motor is employed to power a hydraulic pump on an on-demand basis. This design approach potentially provides improvements in system efficiencies, packaging flexibility and the customization of performance characteristics achieved through the controlling software. Due to these advantages, it is expected that this design will gain continual acceptance in new-model vehicles.

Pump:-The hydraulic power for the steering is provided by a rotary-vane pump. This pump is driven by the cars engine via a belt and pulley. It contains a set of retractable vanes that spin inside an oval chamber.

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Fig.8 Rotary vane pump

As the vanes spin, they pull hydraulic fluid from the return line at low pressure and force it into the outlet at high pressure. The amount of flow provided by the pump depends on the cars engine speed. The pump must be designed to provide adequate flow when the engine is idling. As a result, the pump moves much more fluid than necessary when the engine is running at faster speeds.

The pump contains a pressure-relief value to make sure that that pressure does not get too high, especially at high engine speeds when so much fluid is being pumped.

Rotary Value::A power steering system should assist the driver only when he is exerting force on the steering wheel (such as when starting a turn). When the driver is not exerting force (such as when driving in a straight line), the system shouldnt provide any assist. The device that senses the force on the steering wheel is called the rotary valve.

The key to the rotary valve is a torsion bar. The torsion bar is a thin rod of metal that twists when torque is applied to it. The top of the bar is connected to the steering wheel, and the bottom of the bar is connected to the pinion or worm gear (which turns the wheels), so the amount of torque in the torsion bar is equal to the amount of torque the driver is using to turn the wheels. The more torque the driver uses to turn the wheels, the more the bar twists.

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Fig.9 Spool Valve

The input from the steering shaft forms the inner part of a spool-value assembly. It also connects to the top end of the torsion bar. The bottom of the torsion bar connects to the outer part of the spool valve. The torsion bar also turns the output of the steering gear, connecting to either the pinion gear or the worm gear depending on which type of steering the car has.

As the bar twists, it rotates the inside of the spool valve relative to the outside. Since the inner part of the spool valve is also connected to the steering shaft (and therefore to the steering wheel), the amount of rotation between the inner and outer parts of the spool valve depends on how much torque the driver applies to the steering wheel.

1.1.6ELECTRONIC POWER STEERING(EPS)::

In a full electric system, a separate, integrally mounted electrical motor provides the assist power. The system is made up of: a steering column, a gear assist mechanism attached to this column, a brush less DC motor, a controller and a sensor within assist housing. The rack and pinion set up described in the manual system is also shown. This system provides assist to the driver by measuring the drivers torque with a torque sensor and sends a proportional signal to the controller. The controller also receives steering position information from the position sensor that is collocated with the torque sensor. The torque and position information is processed in the controller and an assist command is generated. Other sensory inputs that are received by the controller, such as the vehicle speed, can modulate this assist signal. The final command is given to the motor, which provides the torque to the assist mechanism. The entire assist mechanism is powered by the battery supply.11Electric power steering (EPS) is mechanically simpler than a hydraulic system, meaning that it should be more reliable. The EPS system is also designed to provide good road feel and responsiveness.

EPS Operation: -The operating principle of the EPS is basically the same as hydraulic power steering except for the following:

1. A torque sensor is used in place of the valve body unit.2. An electric assist motor is used in place of the hydraulic power cylinder.3. An Electronic Power Steering control unit is added.

Fig.10 General assembly of EPS

1.2.3.a)Mechanical Construction--

The rack is unusual in that it is mounted high on the rear engine bulkhead, and that the tie rods engage the rack in the center. The high mount location is used for crash safety, as it keeps these components out of the insights crumple zone.

The tie rods are aluminum, and they connect to an Ackerman arm that is mounted to the struts just below the spring seat.

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Fig.11 Layout

1.2.3.b)Electronic Construction--

The EPS control unit is mounted inside the car on the right side bulkhead, underneath the dash. It receives input from the vehicle speed sensor and torque sensor mounted on the steering pinion shaft.

The pinion shaft engages the pinion gear via a torsion bar, which twists slightly when there is a high amount of steering resistance. The amount of twist is in proportion to both the amount of resistance to wheel turning, and to the steering force applied. A pin on the torsion bar engages a diagonal slot in the sensor core, which moves up or down depending on the amount of torsion bar twist, and the direction of rotation. Two coils surrounding the core detect both the amount, and the direction of movement.

Using this information, the EPS Control unit determines both the amount of steering assist required, and the direction. It then supplies current to the motor for steering assist. The amount of assist is also modified in proportion to vehicle speed to maintain good steering feel.

1.2.3.c)Torque Sensor--

The torque sensor is a device to detect steering turning direction and read resistance. The sensing section of the torque sensor consists of two coils and a core (slider). The steering input shaft and pinion gear are connected via a torsion bar. The slider is engaged with pinion gear in a way that it turns together with the pinion gear but can move vertically. A guide pin is provided on the input shaft and the pin is in a slant groove on the slider.13When road resistance is low, the steering input shaft, pinion gear and slider turn together without the sliders vertical movement.

When road resistance is high, the torsion bar twists and causes a difference of steering angle between the input shaft and pinion gear. In other words, the turning angle of the guide pin and slider differ, and the guide pin forces the slider to move upward or downward.

Fig.12 Slider Movement

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LITERATURE REVIEW

SYNCHRO TRANSMITTER /RECEIVER::2.1.1Introduction--The synchro transmitter/receiver unit is designed for remote transmission of position in ac servomechanism. These are also called as torque transmitter and receiver. The unit has pair of transmitter receiver synchro motor, powered by an isolated 60 v ac inbuilt supply. Sockets are brought upon the panel to make connections with attenuated compensated output in ratio of 1: 10 for waveform observation. The synchro pair is well mounted on the project table.The Synchro:The synchros are small motors, which are used, for remote transmission of shaft angular position in ac servomechanism in ac servomechanism in ac servo system. The basic structure of synchro is wound rotor and wound stator the windings are mutually coupled in such away that it gives substantially sinusoidal variation as a function of shaft angular position. The signal transmission unit is mechanically coupled with another synchro motor called control transformer. Displacement of transmitter unit develops an output error voltage that is in proportion to the misalignment between both shafts. If the receiving end has no rotation then it will generate error voltage, which is amplified and sent to the servomotor to recorrect the position. The synchro has major advantage over potentiometer error detector as:

There is no wear from rotation except non-critical wear at slip ring.

The operating speed can be much higher than pot.

Synchro has full 360 rotation with no electrical break.

The system is highly reliable and possible of multi speed operation.

Resolution is better since no stepping effect.

There are some demerits also present

Linearity is not much better than modern servo potentiometers.

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(2.1.1.a)Basic theory: -The synchro transmitter has dumbbell shaped magnetic structure having primary winding upon rotor, which is connected with the reference voltage Vr, through asset of slip rings and brushes. The secondary windings are wound in slotted stator are distributed from its periphery. In schematic the windings are shown as 3- phase configuration but only single-phase voltage appears across them. The magnitude and polarity of these voltage/phases depends upon the angular position of the rotor.

In fig.13 when rotor and winding S2 are in such position that magnetic meridian are in parallel axis, maximum flux developed in S2 and smaller in S1 and S3. The phase angle between S2 and other windings is out of phase. The effect of it is that voltage developed in S2 has maximum amplitude, which has same polarity as of the rotor.

Fig. 13 Angular position and winding operation of synchro when phase angle of S2 when rotor is in 00 and 1 800.

Fig.14 Angular position and winding operation of synchro when phase angle of S2 with rotor is 900

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In fig.14, similar configuration is shown with rotor positioned at 90 of S2 winding which has perpendicular magnetic meridian. The voltage induced in S2 will be minimum in this case and maximum in S1.

Let

V S1n = KVr sin (ct) cos ( + 240)

V S2n = KVr sin (ct) cos ()

V S3n = KVr sin (ct) cos ( + 120) The terminal voltages across the stator coils are:

V 23 = KVr sin (ct) sin ( + 240)

V 31 = 3 KVr sin (ct) sin ()

V 12 = KVr sin (ct) sin ( + 120)

Where Vr sin ct is the reference voltage, is the respective angle in degrees

V 31 = V S3n V S1n,

V 23 = V S2n V S3n,

V 12 = V S1n V S2n,

K is a constant.

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In fig 15, a transmitting angle is drawn showing different phase angles between different windings in reference of rotor phase and voltage magnitude and its corresponding angle.In remote control system sometimes it is required to transmit angular position of a shaft following the motion of another shafts located at a distance. It is possible to transmit the position knowledge through mechanical system but it is not efficient nor is it economical. Electromechanical systems are very useful for the purpose in which shaft angular position is converted into electrical signal and transmitted through cable and received at the monitor end by similar system. The synchro transmitter/receiver is used in feedback system in servo system for acknowledgement.

Stator Terminal Voltage / phase w.r.t Vr

Stator Terminal Voltage difference / phase w.r.t Vr

Fig.15 Computed Graph

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2.1.1.b)The Synchro Transmitter / Receiver: -The synchro transmitter is constructed like two pole alternator in which rotor coil is wound on laminated core. The ends of the coil brought out through slip rings and brushes for electrical connections and designated as R1, R2. The stator portion has three coils, which are spaced 120 apart of rotor magnetic meridian. The ends of each coil are connected internally and starts are bought out for electrical connections as S1, S2, S3. The receiver motor is similar to transmitter.

2.1.1.c)The transmitter/ receiver system: -In fig 16 connections between transmitter and receiver is shown. The rotor of transmitter is excited with the AC line and the same is fed to the receiver rotor. The stators of both are connected in synchronism; S1 with S1, S2 with S2 and S3 with S3. In this configuration the rotor of receiver follows the

also be understood as, let transmitter may be a generator G and receiver may be motor M. the generated voltage / phase which are related to rotor angular position is coupled electrically with M in similar phase. It develops proportional torque, which forces M rotor to make equilibrium with the generator rotor positioning.

R2R1S3S2S1R2R1

Fig. 16 Angular position and connecting diagram of synchrowhen both rotors are in phase

I18n this condition no current flows in stator winding when the Tx rotor moves to other position this voltage distribution is disturbed. The imbalance in voltage develops a torque that tends to move the receiver rotor to follow to the new position. When it reaches T x, the induced current is nulled again. In this way the Tx - Rx pair serves to transmit the information of angular position of Tx to remotely situated Rx.

2.1.2 SYNCHRONIZING MOTORS INSTRUMENTATION::

Remote indication or control may be obtained by the use of self-synchronizing motors, called synchro equipment. Synchro equipment consists of synchro units, which electrically govern or follow the position of a mechanical indicator or device. An electrical synchro has two distinct advantages over mechanical indicators: (1) greater accuracy, and (2) simpler routing of remote indication.

There are five basic types of synchro, which are designated according to their function. The basic types are: transmitters, differential transmitters, receivers, differential receivers, and control transformers. If the power

required to operate a device is higher than the power available from a synchro, power amplification is required. Servomechanism is a term, which refers to a variety of power-amplifiers.

The transmitter, or synchro generator, consists of a rotor with a single winding and a stator with three windings placed 120 degrees apart. When the mechanical device moves, the mechanically attached rotor moves. The rotor induces a voltage in each of the stator windings based on the rotors angular position. Since the rotor is attached to the mechanical device, the induced voltage represents the position of the attached mechanical device. The voltage produced by each of the windings is utilized to control the receiving synchro position.

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Fig. 17 Electrical Circuit

The receiver, or synchro motor, is electrically similar to the synchro generator. The synchro receiver uses the voltage generated by each of the synchro generator windings to position the receiver rotor. Since the transmitter and receiver are electrically similar, the angular position of the receiver rotor corresponds to that of the synchro transmitter rotor. The receiver differs mechanically from the transmitter in that it incorporates a damping device to prevent hunting. Hunting refers to the overshoot and undershoot that occur as the receiving device tries to match the sending device. Without the damping device, the receiver would go past the desired point slightly, and then return past the desired point slightly in the other direction. This would continue, by smaller amounts each time, until the receiver came to rest at the desired position. The damper prevents hunting by feeding some of the signal back, thus slowing down the approach to the desired point.

Differential synchros are used with transmitter and receiver synchros to insert a second signal. The angular positions of the transmitter and the differential synchros are compared, and the difference or sum is transmitted to the receiver. This set up can be used to provide a feedback signal to slow the response time of the receiver, thus providing a smooth receiver motion.

Control transformer synchros are used when only a voltage indication of angular position is desired. It is similar in construction to an ordinary synchro except that the rotor windings are used only to generate a voltage, which is known as an error voltage.

20The rotor windings of a control transformer synchro are wound with many turns of fine wire to produce high impedance. Since the rotor is not fed excitation voltage, the current drawn by the stator windings would be high if they were the same as an ordinary synchro; therefore, they are also wound with many turns of fine wire to prevent excessive current. During normal operation, the output of a control transformer synchro is nearly zero (nulled) when its angular position is the same as that of the transmitter. A simple synchro system, consisting of one synchro transmitter (or generator) connected to one synchro receiver (or motor), is shown in Figure 18.

115V 60~AC SupplyReceiverTransmitterR2R1R2R1S3S2S1S3S2S1

Fig. 18 Transmitter Receiver Connections

When the transmitters shaft is turned; the synchro receivers shaft turns such that its electrical position is the same as the transmitters. What this means is that when the transmitter is turned to electrical zero, the synchro receiver also turns to zero. If the transmitter is disconnected from the synchro receiver and then reconnected, its shaft will turn to correspond to the position of the transmitter shaft.

2.1.3CHARACTERISTICS OF SYNCHRONOUS MOTORS:: It has a three- phase stator similar to that of an induction motor. Medium voltage stators are often used.

It has a wound rotor (rotating field) that has the same number of poles as the stator, and is supplied by an external source of direct current (DC). Both brush-type and blushless exciters are used to supply the DC field current to the rotor. The rotor current establishes a north /south magnetic pole relationship in the rotor poles enabling the rotor to lock-in-step with the rotating stator flux.

It starts as an induction motor. The synchronous motor rotor also has a squirrel-cage winding, known as an Amortisseur winding, which produces torque for motor starting.

2.1.4PRINCIPLE AND OPERATION:: The squirrel-cage Amortisseur winding in the rotor produces Starting Torque and Accelerating Torque to bring the synchronous motor up to speed.

21 When the motor speed reaches approximately 97% of nameplate RPM, the DC field current is applied to the rotor producing Pull-in Torque and the rotor will pull-in-step and synchronize with the rotating flux field in the stator. The motor will run at synchronous speed and produce Synchronous Torque. After synchronization, the pull-out Torque cannot be exceeded or the motor will pull out-of-step. Occasionally, if the overload is momentary, the motor will slip-a-pole and resynchronize. Pullout protection must be provided otherwise the motor will run as an induction motor drawing high current with the possibility of severe motor damage.

Fig.19 Inside of a synchro motor

2.1.5ADVANTAGES OF SYNCHRONOUS MOTORS::

The initial cost of a synchronous motor is more than that of a conventional AC induction motor due to the expense of the wound rotor and synchronizing circuitry. These initial costs are often offset by:

Precise speed regulation makes the synchronous motor an ideal choice for certain industrial processes and as a prime mover for generators.

Synchronous motors have speed/torque characteristics, which are ideally suited for direct drive of large horsepower, low-rpm loads such as reciprocating compressors.

Synchronous motors operate at an improved power factor, thereby improving overall system power factor and eliminating or reducing utility power factor penalties. An improved power factor also reduces the system voltage drop and the voltage drop at the motor terminals.22

Fig.20 Working of the brush type synchronous motors.

2.1.6 STEER BY WIRE:-

2.1.7 Introduction:-

Steer by wire systems provide many benefits in terms of functionality, and at the same time present significant challenges too. Chief among them is to make sure that an acceptable steering feel is achieved.

In this particular architecture, the sensed road wheel (RW) force is used to command the hand wheel (HW) system to provide a resistive torque for the driver. Similarly, the steering wheel position is used to command the RW system to move road wheels to the desired position. Thus, two control system loops are being closed: the HW force feedback loop and the RW position feedback loop. The commanding signals for both of these loops passes through and is modified within the Master Controller.

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Fig.21 Block diagram of Steer by Wire

The elimination of the mechanical link between the subsystems can result in abnormal steering system performance.

Steering system performance is defined by two important attributes, steering feel and steering response. An additional performance quality of a steering system that will be discussed is termed free control. Free control describes the steering system behaviour for the case of the drivers hands removed from the steering wheel. The coupled interaction of the HW and RW subsystems can greatly influence the nature of the free control response of a steer-by-wire system. The term steering feel is commonly used as a universal phrase for describing the torque that the driver feels in relation to the position of the steering wheel and the motion of the vehicle. It refers to various conditions such as on-center (vehicle travelling nearly straight), offcenter, and static steer (i.e. turning of the steering wheel with a stationary vehicle); Steering responsiveness for a steer-by-wire system presents unique challenges for road wheel position control. Chief among those challenges is the significant variation of the steering loads experienced.In actuators are positioned in the steering system of the vehicle and receive inputs from the control module to turn the wheels accordingly. This technology was originally used in the aerospace industry. A distributed control system made up of a network of controllers electrically transmits the road feel back to the steering wheel and the amount of steering wheel turn to the control system. The road feel is recreated by the use of an electric motor to provide feedback to the drivers steering wheel.24

2.1.8 Advantages of the system are--

Increasing vehicle packaging flexibility:

The removal of the mechanic linkage between the steering wheel and the wheels make left hand and right hand drive equipment implementations easy.

Simplifies vehicle assembly:

No need for the steering column, hydraulic system, rack and pinion, which significantly lightens the vehicle.

Increase vehicle efficiency:-

The vehicle carries less weight

Power requirement is low compared to the conventional hydraulic system. The only power required is for driving the electric motors.

No intrusion of the steering column in case of an accident:

Crash performances are being conducted by leading car manufacturers such as BMW and proved less damaging impact to the driver in the absence of a steering column

Variable steering gear ratio:

The number of turns of the steering wheel block to block can be adjusted.

Automated Highway System:

AHS use magnets embedded in the highway, magnetic sensors in the vehicle monitor the vehicles course, while an intricate electronic control system regulates vehicle speed and directions of travel.Basis for advance vehicle control: Control algorithms such as assist, align and damping can be updated.25

Fig.22 Basic Layout

Such system designs have yet to prove themselves sufficiently reliable and safe to prevent dangerous auto-steer events. Auto steer denotes an uncontrolled steering event neither commanded nor stoppable by the drive due to a catastrophic failure in the electronic hardware or software. Due to the lack of direct linkage with the wheels, in the event of power failure or software corruption, the driver has no control over the vehicle. In the automotive industry the lead-time for an entirely new model is approximately five years. A research is currently being conducted by a consortium of leading vehicle manufacturers, including Daimler Chrysler, Fiat, Ford, Bosch, to push for a fault tolerant drive by wire system.

To introduce the fault tolerant system into the market, several standards and requirements regarding to safety and its manufacturability have to be addressed. Furthermore, cost of production, reliability, system modularity and maintainability also come into consideration

26.2.1.9 Technical Requirements of the system::

A very basic requirement of the system is that it must be as good as its current counterparts. Ultimately, the steering system must respond at all time as long as the vehicle is in motion whether the engine is running or not. As mentioned before, it needs to provide the driver with tactile feedback informing the driver of the road condition. The steering geometry must be self-centring, self-stabilizing and not exhibit over-sensitive or under-sensitive steering at both low and high speeds. When the vehicle is stationary,

steering system should provide assist to overcome the friction between the tyres and the road surface. This requirement is designed for easy manoeuvre of the vehicle existing the parking lot. In conventional vehicles, the maximum angle of the front tyres is approximately 40. At the steering wheel, turning from one lock to the other usually takes 3.5 rotations (630 from center to block). When translating this to the system, the resolution at the steering wheel should be less than 1, to reduce the error between the command at the steering wheel and the wheels to less than 0.1. The driver should be given the capability to rotate the steering angle at a velocity of 40 per second (0.7 rad/ s). This value varies however, depending on the assist algorithm. One of the advantages of the system is the ease in which the steering feel can be altered, that is varying between the tight, sporty steering system and a smooth, luxurious one. This should be made possible by simply down loading a new program into the controller accustomed to the individual drivers. Safety is one of the most important issues of the vehicle steering system. Such new system can only be successful, if it can be proved that it is as safe as the mechanical systems. In case of a fault, either in hardware or software:

1) The steering wheel must not be blocked: the driver always must be able to control the car

2) The steering wheel must not move unintentionally, pretending a steering command

3) The force feedback must not break down: the driver always must feel the reacting forces of the road currently, to guarantee the safe operation of the actuator the concepts of redundancy is developed. This is depicted in figure 23.

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Fig.23 Fail Safe Unit The steering actuator node consists of two or more fail silent units. The term fail-silent means that each unit is either operating correctly or it is completely silent towards the bus channels and towards its actuators. The fail-silent units performing the same operations from the fault tolerant unit (FTU). It is also important that each FSU has its own power supply, thus capable of toleration single power failure. A design of such system proposed by for the steering actuator divides the inverter into three single-phase bridges that supply one phase of an induction motor each. Thus, the three phases are decoupled electrically. In usual operation mode, the machine is driven with symmetrical phase currents. In case of a fault, the affected phase is turned off and the desired torque is delivered by the remaining two phases.

2.1.10Communication System::

The drive by wire technology relies on the implementation of distributed controllers; communication system forms the backbone of this type of design. Controller Area Network (CAN), developed by Bosch GmBH, originally designed for intra-vehicular communication has found its uses in the drive by wire industry. The arbitration mechanism of this communications protocol ensures, that all messages are transferred according to the priority of their identifiers; messages with the highest priority will not be disturbed. However, even at maximum busload, the transmission of all safety related messages must be guaranteed and the system must be able to determine the point of time when the message will be transmitted with high precision. For these reasons, researchers of the drive by wire system are looking into time-triggered communication. Time-triggered operation of the communication system means that any activity is determined by a globally synchronized time. Sending and receiving information between the nodes depend on a predefined time schedule. The improvements of the time-triggered communication system are:

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Separation of data processing and communication tasks with in a node.

Support for global clock

No bandwidth limitations imposed by the protocol itself

Simplicity and predictability

TTP/C (TimeTriggered Protocol, Class C) protocol developed by the Technical University in Vienna is also being introduced. This protocol operates according to the TDMA (Time Division Multiple Access) principle. Each node connected to the bus has a pre-allocated time spot in which it sends a message on the bus. The length of these time slots may be different nodes but is fixed before the system is but into operation. Thus, the TDMA round, in which all nodes send one message each, is a fundamental concept of TTP/C. Communication among the nodes is not considered in this project.

2.1.11Force feedback steering::In essence, many decisions made by the driver today are by actually feeling the road via the mechanical link to the wheels. For example, bumpy roads make the wheel to vibrate that can be felt by the drive via the steering wheel. Drivers also have a tactile feedback of the vehicular dynamics such as slip angle and aligning moment. From a safety standpoint steering linearity helps drivers to appreciate that condition of the road surface. By removing the mechanical link and replacing with wires, these vibrations and bumps are lost. In attempt to recreate the driving sensation, it is essential to emulate the steering feel from all of the inputs of the car. These inputs can come from the wheels, suspension and chassis thus, giving the driver feedback on the condition of the road. The idea of force feedback steering has already been developed in the video gaming industry. Real vehicles, undoubtedly, require a more rugged technology compared to their on-screen counterpart and need an active system control constantly changing in response to the condition of the car. Thus, adaptive control is required. A poorly designed feedback system may have almost no relationship between the hand wheel torque applied by the driver and the actual require steering force imposed by the tyre/ road.

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2.1.12Free Control::

As was mentioned before, the term Free Control, refers to the response of the wheel after an initial condition is given to the wheel. The subsequent response would be free of driver inputs. For example, if the HW is released from a turned position, how the wheel comes back to center determines whether or not the Free Control behaviour is good or bad. Or when the wheel is given a quick jerk (and release), the ensuing response is called the free control response. In either case a quick return to center with minimal overshoot is

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FABRICATION

FABRICATION OF MODEL:-

A working model of the Steer by Wire system has been fabricated for demonstrating the concept.

Actual Steer by Wire system requires torque sensors and position sensors. These sensors are unavailable in India. Importing these is not a viable proposition due to the constraints of cost and availability.

Two different options were considered to make the model of the steer by wire system. The first option was to use photocells/photo detectors to detect the positions of the steering and use this position reference to turn the wheels. The other option was to use the synchro motor. Under these constraints it was decided to make a model of Steer by Wire system using synchro transmitter receiver. The synchro transmitter / receiver was used because the other method offered very poor resolution.

Set up:

The main components of the set up are synchro transmitter / receiver and Ackerman steering mechanism. The synchro system consists of transmitter and receiver as explained earlier and works on 110V AC. For this purpose a transformer is provided to step down the voltage from 220V to 110v.

The Ackerman steering mechanism was made from aluminum channels due to their lightweight construction and relative strength.

The motor is coupled with the steering mechanism through a M.S coupling.

The synchro transmitter is fitted with a cast Aluminum steering wheel fabricated in the workshop.

The whole set up is mounted on a table made of iron angles 30 30 inches and 30 inches in height, also fabricated in the workshop.

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RESULT AND DISCUSSION

The main aim of the project was to make steer by wire Systems. We were not able to make actual Steer by Wire System because of the non-availability of sensors.

We have made a model of the steer by wire system to demonstrate the concept. We used the synchro transmitter / receiver to demonstrate the concept of steer by wire.

Actual steer by wire systems would require large amount of testing to be done before they can be introduced into the real world, to ensure safety and reliability. Also large-scale production is required to bring the costs of the steer by wire system down.

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CONCLUSION

Our project has given us the insight into how driving will be revolutionized in the future, once the Steer by wire system is embedded into vehicles of everyday use. It is a step towards the realization of a smart car, wherein the computer in the car is able to take all the decisions with minimal human interference. It is the system, which will not only make driving a pleasure, but also will also provide greater accuracy and control over driving.

However this advantage does not necessarily accelerate the introduction of this system into the vehicles. It still requires a great deal of research and development and sophisticated instruments for its manufacturing. Though it is being introduced in some high-end cars it will take some time for the benefits of steer by wire system to reach common man.

Through our project we were able to show the principle of steer by wire using synchronous motors but on a much smaller scale than we had planned at the start of our project. The main problem that we faced was to transfer the road feel back to the driver; but synchronous motors do not have this drawback.

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REFERENCES

1.Erich Chou, Steer By Wire, Final Thesis, University of Queensland.

2. Sanket Amberkar, Farhad Bolourchi Jon Demerly and Scott Millsap, Control System Methodology for steer by wire systems, September 1998, SAE Technical Paper.

3. Dr. Jim Farelly, Control System methodology for steer by wire, August 2000, TRW Coneckt Technical center.

4. Steer by Wire System, External Presentation, Dec 2004, Delphi corp.

5. E. Bakker, H.B. Pacejka, L.Lidner, Diagnostic Development For an Electric Power Steering System, January 2002, SAE Technical paper.

6. http: / / homepages.cae.wisc.edu / vehicle / tech- report /2003 witechpaper.pdf Steering mechanisms and related forces in them.

7. http: //luuk.s4all.nl/ring / bmw nordschleife.pdf, Steer by Wire concepts.

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