Force Analysis of Steering Mechanism of a Car

TERM PAPER MEC-302 TOPIC:- Force analysis of steering mechanism of a car

Submitted by:

Submitted to:

Mazharul haque

Mr.Jaspreet Singh

B.tech (ME) Roll No:-RB4912A18 Reg.No:-10907347

ACKNOWLEDGEMENT I take this opportunity to present my votes of thanks to all those guidepost who really acted as lightening pillars to enlighten our way throughout this project that has led to successful and satisfactory s atisfactory completion of this study. We are really grateful to our HOD for providing us with an opportunity to undertake this project in this university and providing us with all the facilities. We are highly thankful to Mr.JASPREET SINGH for his active support valuable time and advice whole hearted guidance guidance sincere cooperation and pains taking involvement during the study and in completing the assignment of preparing the said project within the time stipulated. Lastly We are thankful to all those, particularly the various friends , who have been instrumental in creating proper, healthy and conductive environment and including new and fresh innovative ideas for us during the project, their help, it would have been extremely difficult for us to prepare the project in a time bound framework.

Mazharul haque

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Introduction Fundamental condition for true rolling and correct steering angle Component of steering system: power steering Principles of the Power steering There are two kinds power steering currently in use speed Sensitive Steering Four-wheel steering Application Rack and pinion steering mechanism References

1.INTRODUCTION: The most conventional steering arrangement is t o turn t he front wheels using a hand and operated steerin steering g wheel which which is positioned positioned in front of the driver driver via the steering steering co c o lumn lu mn w hic hi c h may contain universal joints which may also be part of the collapsible steering column design to allow it to deviate somewhat from a straight line. Other arrangements are sometimes found on different types of vehicles for example a tiller or rear wheel steering. Tracked vehicles such as tanks usually employ differential steering that is the tracks are made to move at different speeds or even in opposite directions to bring about a change of course. (a) Rack and pinion recirculation ball worm and sector. (b)Rack and pinion animation. (c)Rack and pinion unit mounted in the cockpit of an ariel atom sports car chassis.For most high volume production, this is usually mounted on the other side of this panel. Many modern use rack and pinion steering mechanisms where the steering wheel turns the pinion gear the pinion moves the rack which is a linear gear that meshes with the pinion converting circular motion into linear motion along the transverse axis of the car side to side motion. This motion applies steering torque to the swivel pin ball joints that replaced previously used kingpins of the stub axle of the steered wheels via tie rods and a short lever arm called the steering arm. The rack and pinion design has the advantages of a large degree of feed and direct steering feel.A disadvantage is that it is not adjustable so that when it does wear and develop lash the only cure is replacement. so that when it does older designs often use the recirculation ball mechanism which is still found on trucks and utility vehicles. This is a variation on the older worm and sector design the steering column turns a large screw the worm gear which meshes with a sector of a gear causing it to rotate about its axis as the worm gear is turned an arm attached to the axis of the sector moves the pitman arm which is connected to the steering linkage and thus steers the wheels. The recirculation ball version of this apparatus reduces the considerable friction by placing large ball bearings between the teeth of the worm and those of the screw at either end of the apparatus the balls exit from between the two pieces into a channel internal to the box which connects them with the other end of the apparatus thus they are recalculated.The recalculating ball mechanism has the advantage of a much greater mechanical advantage so that it was found on larger heavier vehicles while the rack and pinion was originally limited to smaller and lighter ones due to the almost universal adoption of power steering however this is no longer an important a d va nt a g e l e a d i n g t o t he incr increa easi sin ng use use of rack rack and and pini pinion on on newer ewer cars cars..

Fig:1(steering mechanism of car)

2.Fundamental condition for true rolling and correct steering angle : The perfect steering is achieved when all the four wheels are rolling perfectly under all conditions of running. While taking turns, the condition of perfect rolling is satisfied if the axes of the front wheels when produced meet the rear wheel axis at one point. Then this point is the instantaneous centre of the vehicle. It is seen that the inside wheel is required to turn though a greater angle than the outer wheel. The larger the steering angle, the smaller is the turning circle. There is however a maximum to which we can go as regards the steering angle. It has been found that steering angle of the inner wheel can have a maximum value of about 440. The extreme positions on either side are called lock positions. The diameter of the smallest circle which the outer front wheel of the car can

. traverse and obtained when the wheels arc at their extreme positions is known as the turning circle.

3.Component of steering system:

4.Power steering: a portion of the vehicle's power to traverse the axis axis of one or more more of the road wheels. As vehicles have become heavier and switched to front wheel drive particularly using negative offset geometry along with increases in tire width and diameter Power steering assists the driver of an automobile in steering by d ir ec t in g the effort effort needed to turn the steering steering wheel manually manually has has increased increased often to the point where major physical exertion is required. To alleviate this auto makers have developed power steering systems or more correctly power assisted steering on road going vehicles there has to be a mechanical linkage as a failsafe. There are two types of power steering systems hydraulic and electric and electronic. A hydraulic electric hybrid system is also possible.A hydraulic power steering uses hydraulic pressure supplied by an engine-driven pump to assist the motion of turning the steering wheel. Electric power steering esp is more efficient than the hydraulic power steering since the electric power steering motor only needs to provide assistance when the steering wheel is turned whereas the hydraulic pump must run constantly. In esp the assist level is easily tunable to the vehicle type road speed and even driver preference. An added benefit is the elimination of environmental hazard posed by leakage and disposal of hydraulic power steering fluid. Also in the event of the engine cutting out assist will not be lost where as hydraulic will stop working as well as making the steering doubly heavy as the driver.

Fig:2(power steering)

5.Principles of the Power steering direction Power steering has two types of device for steering effort one type is a hydraulic device utilizing engine power. The other type utilizes an electric motor. For the former the engines used to drive a pump. For the latter an independent electric motor in the front luggage compartment is used the pump. Both develop fluid pressure and this pressure acts on a piston within the power cylinder so that the pinion assists the rack effort. The amount of this assistance depends on the extent of pressure acting on the piston. Therefore if more steering force is required the pressure

must be raised. The variation in the fluid pressure is accomplished by a control valve which is linked to the steering main shaft. a)Neutral (Straight ahead) position: Fluid from the pump is sent to the control valve. If the control valve is in the neutral position all the fluid will flow pass through the control valve into the relief port and back to the pump. At this time hardly any pressure is created and because the pressure on the cylinder piston is equal on both sides the piston will not move in either.

b) While turning: When the steering main shaft is turned in either direction the control valve also moves closing one of the fluid passages. The other passage then opens wider causing a change in fluid flow volume and at the same time pressure is created. Consequently a pressure difference occurs between both sides of the piston and the piston moves in the direction of the lower pressure so that the fluid in that cylinder is forced back to the pump through the control .

6.There are two kinds power p ower steering currently in use: use :

a)Integral power steering. The system consists of solid cylinder on which two grooves have been cut known as valve spool which slides closely within the hole in the valve housing. The housing has three internal grooves the central groove is connected to the pump and two a tends are connected to the reservoir. The two additional openings from the internal collars are connected to the two sides of the cylinder as shown in the figure. When the valve spool is in the position shown in the figure then the pump delivers the oil in the central part of the housing and then delivers back to the reservoir by the passages shown by the arrows. In this position there will be no oil pressure in the cylinder and there is no tendency for the piston to slide in any direction. Thus there is no steering action and vehicle moves straight a head.

Fig:3(internal power steering) b) Linkage booster power steering: In this type power assistance is applied directly to the steering linkage. The power cylinder consists of piston and the piston rod is extended out on the right and is fixed to the frame member. The relay rod is linked with the cylinder housing.In the neutral position the spool valve is held in the centre position by the centering springs. In this position oil from pump flows to both sides of the piston in the power cylinder at equal pressure and then there will not be displacement in the power cylinder thus there will no steering action. In this position the vehicle moves straight ahead on the road.

Fig:4( Linkage booster power steering) Again when the steering wheel is turned anticlockwise as shown then the ball of the pitman arm shifts the valve spool towards right side. Due to this shifting the oil from pump flows in the valve section of the unit through the ports. Then the oil through feed line flows into the right hand side of the power cylinder. The high pressure oil inside the cylinder forces it to move to the right which results to turn the stub axles to the left side.For the right side of the vehicle this operation of the system is reversed to it.

7.speed Sensitive Steering:

An outgrowth of power steering is speed sensitive steering where the steering is heavily assisted at low speed and lightly assisted at high speed. The auto makers perceive that motorists might need to make large steering inputs while maneuvering for parking but not while traveling at high speed. The first vehicle with this feature was the citron with its diravi layout citation needed although rather than altering the amount of assistance as in modern power steering systems it alte altere red d the the press ressu ure on a cente enteri rin ng cam w h ic h ma de t he st ee r in g w he e l t r y t o sp r in g back to the straight a head position.Modern speed sensitive power steering systems reduce the mechanical or electrical assistance as the vehicle speed increases giving a more direct feel. This feature is gradually becoming more common.

Fig:5(speed sensitive steering)

8.Four-wheel steering: Four wheel steering or all wheel steering is a system employed by some vehicles to improve steering response increase vehicle vehicle stability while maneuvering at high speed or to decrease turning radius at low speed.In most active four-wheel steering systems the rear wheels are steered by a computer and actuators. The rear wheels generally cannot turn as far as the front wheels. Some systems including delphi and the system in Hondas Prelude line allow the rear wheels to be steered in the opposite direction as the front wheels during low speeds. This allows the vehicle to turn in a significantly smaller radius sometimes critical for large or tractors and vehicles with trailers.Many modern vehicles offer a form of   passive rear steering to counteract normal vehicle tendencies. For example Subaru used a passive steering system to correct for the rear wheels tendency to toe out. On many vehicles when cornering the rear wheels tend to steer slightly to the outside of a turn which can reduce stability. The passive steering system uses the lateral forces generated in a turn through suspension geometry and the bushing to correct this tendency and steer the wheels slightly to the inside of the corner. This improves the stability of  the car through the turn. This effect is called compliance under steer and it or its opposite is present on all suspensions. Typical methods of achieving compliance understeer are to use a Watts Link on a live rear axle or the use of toe control bushings on a twist beam suspension. On an independent rear suspension it is normally achieved by changing the rates of the rubber bushings in the suspension. Some suspensions will always have compliance oversteer due to geometry such as hotchkiss live axles or a semi trailing arm.Passive rear wheel steering is not a new concept as it has been in use for many years although not always recognized as such. For

example Jaguar independent rear suspension incorporated a small amount of passive rear wheel steering since 1961.

Fig:6( rear steering angle)

9. Application

In an active four-wheel steering system all four wheels turn at the same time when the driver steers. There can be controls to switch off the rear steer and options to steer only the rear wheel independent of the front wheels. At slow speeds eg. parking the rear wheels turn opposite of the front wheels reducing the turning radius by up to twenty five percent while at higher speeds both front and rear wheels turn alike electronically controlled so that the vehicle may change position with less yaw enhancing straight line stability. The Snaking effect experienced during motorway drives while towing a travel trailer is thus largely nullified. Four wheel steering found its most widespread use in monster trucks where maneuverability in small arenas is critical and it is also popular in large farm vehicles and trucks. Some of the modern European Intercity buses also utilize four wheel steering to assist maneuverability in bus terminals, and also to improve road stability. General Motors offers Delphis Quadrasteer in their consumer silverado sierra and suburban yukon. However only 16500 vehicles have been sold with this system since its introduction in 2002 through 2004. Due to this low demand gm discontinued the technology at the end of the . 2005 model year Previously honda had four wheel steering as an option in their 1987-2000 Prelude and Mazda also offered four wheel steering on the 626 and mx in 1988. A new active drive system is introduced on the 2008 version of the renault laguna line. It was designed as one of several measures to increase security and stability. The active drive should lower the effects of under steer and decrease the chances of spinning by diverting part of the gforces generated in a turn from the front to the rear tires. At low speeds the turning circle can be tightened so parking and maneuvering is easier.

10.Rack and pinion steering mechanism: mechanism : It is very simple and common type mechanism the system is shown in simplified sketch.This type is very well suitable in an independent suspension system. The system consists of a rack  housed in a tubular casing. The casing is supported on the frame near its ends. The ends of the rack are connected to the track rods with the help of ball and socket joints. The pinion shaft is carried in the plain bearings housed in casing. The pinion is meshed with the rack and the clearance is adjusted with the adjusting screw. When the pinion is given rotary motion with the steering wheel then the rack slides in either sides. This sliding motion of the rack is used through the track rods to turn the wheels in desired side.

Fig:7(Rack and pinion steering mechanism )

 References: 1. www.2 car pros.com/articles/how- car  car- steering  steering-works  carbibles.com/   steering_bible.html - Cached - Similar 2. www. car  scribd .com/doc/23430592/  Steering - Cached - Similar 3. www. scribd  .com/doc/23430592/ Steering