- - Presented ByPresented By

Karthik.sKarthik.s

(1ac08me025)(1ac08me025)Dept. of mechanical engineeringDept. of mechanical engineering

Alpha college of engineeringAlpha college of engineering

Power steering in automobiles

The fundamental purpose of steering is to achieve The fundamental purpose of steering is to achieve

angular motion of the front wheels to negotiate a angular motion of the front wheels to negotiate a turn.turn.

This can be achieved manually, where only the force This can be achieved manually, where only the force exerted by the driver is used to turn the wheels. exerted by the driver is used to turn the wheels.

Manual steering is enough for smaller vehicles, Manual steering is enough for smaller vehicles, however large amount of torque is required to be however large amount of torque is required to be applied by the driver for steering of medium and applied by the driver for steering of medium and heavy vehicles. This cannot be done manually and heavy vehicles. This cannot be done manually and requires external assistance.requires external assistance.

Power steering system provides automatic assistance Power steering system provides automatic assistance to the turning effort applied to the manual steering to the turning effort applied to the manual steering system, and makes driving easier for the driver.system, and makes driving easier for the driver.

ABSTRACTt

Steering actionSteering action: When a driver turns the : When a driver turns the steering wheel, the mechanical action rotates steering wheel, the mechanical action rotates a steering shaft inside the steering column. a steering shaft inside the steering column. Depending on the steering mechanism, gears Depending on the steering mechanism, gears or other devices convert the rotating motion or other devices convert the rotating motion of the steering wheel into a horizontal force of the steering wheel into a horizontal force that turns the wheels. Most steering systems that turns the wheels. Most steering systems link the front wheels together by means of a link the front wheels together by means of a tie-rod. The tie-rod insures that the turning of tie-rod. The tie-rod insures that the turning of one wheel is matched by a corresponding turn one wheel is matched by a corresponding turn in the other.in the other.

INTRODUCTION

When you turn your car, your front When you turn your car, your front

wheels are not pointing in the same wheels are not pointing in the same direction. For a car to turn smoothly, each direction. For a car to turn smoothly, each wheel must follow a different circle. Since the wheel must follow a different circle. Since the inside wheel is following a circle with a inside wheel is following a circle with a smaller radius, it is actually making a tighter smaller radius, it is actually making a tighter turn than the outside wheel. If you draw a turn than the outside wheel. If you draw a line perpendicular to each wheel, the lines line perpendicular to each wheel, the lines will intersect at the center point of the turn. will intersect at the center point of the turn. The geometry of the steering linkage makes The geometry of the steering linkage makes the inside wheel turn more than the outside the inside wheel turn more than the outside wheel. wheel.

Effective steering of any automobile Effective steering of any automobile depends various factors :depends various factors :

1. Steering geometry1. Steering geometry 2. Steering linkages2. Steering linkages 3. Wheel alignment3. Wheel alignment 4. Suspension system.4. Suspension system. Good steering system is characterized by:Good steering system is characterized by: 1. The accuracy of steering mechanism.1. The accuracy of steering mechanism. 2. The ease with which it can be 2. The ease with which it can be

handled.handled. 3. The directional stability it provides.3. The directional stability it provides.

The amount of torque to be applied by the driver for The amount of torque to be applied by the driver for steering of varies with the size of the vehicle. This steering of varies with the size of the vehicle. This value is very large for medium and heavy vehicles. To value is very large for medium and heavy vehicles. To cope with this the power steering was introduced.cope with this the power steering was introduced.

Power steering is a system for reducing the steering Power steering is a system for reducing the steering effort on cars by using an external power source to effort on cars by using an external power source to assist in turning the wheels. Power steering was assist in turning the wheels. Power steering was invented in the 1920’s, and the first commercially invented in the 1920’s, and the first commercially available power steering system on the 1951 Chrysler available power steering system on the 1951 Chrysler Imperial under the name Hydraguide.Imperial under the name Hydraguide.

ELECTRIC SYSTEMSELECTRIC SYSTEMS:: More modern systems, use completely electric More modern systems, use completely electric

components. Sensors detect the motion and components. Sensors detect the motion and torque of the steering column and a computer torque of the steering column and a computer applies assistive power via electric motors.applies assistive power via electric motors.

1. 1. Column-assist type-Column-assist type- The power assist The power assist unit, controller and torque sensor are attached to unit, controller and torque sensor are attached to the steering column.the steering column.-This system is compact and easy to mount on the -This system is compact and easy to mount on the vehicle.vehicle.

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

3. 3. Direct-drive type-Direct-drive type- The steering gear rack The steering gear rack and power assist unit form a single unit.and power assist unit form a single unit.-The steering system is compact and fits easily in -The steering system is compact and fits easily in the engine compartment layout.the engine compartment layout.-The direct provision of assistance to the rack -The direct provision of assistance to the rack enables low friction and inertia, and in turn ideal enables low friction and inertia, and in turn ideal steering feeling. steering feeling.

4. 4. Rack-assist type-Rack-assist type- The power assist unit is The power assist unit is attached to the steering gear rack. The power attached to the steering gear rack. The power assist unit can be located freely on the rack, assist unit can be located freely on the rack, allowing great flexibility in layout design.allowing great flexibility in layout design.

TYPES OF POWER STEERING

HYDRAULIC SYSTEMS:HYDRAULIC SYSTEMS: -This system offers both high power and a -This system offers both high power and a

smooth steering feeling.smooth steering feeling.-Application on a wide range of vehicles from -Application on a wide range of vehicles from compact cars to trucks is possible.compact cars to trucks is possible.-Electronic control by computer enables -Electronic control by computer enables performance corresponding to vehicle speed and performance corresponding to vehicle speed and an ideal steering feeling.an ideal steering feeling.

ELECTRO-HYDRAULIC SYSTEMS: ELECTRO-HYDRAULIC SYSTEMS: -Microcomputer control of the electric motor -Microcomputer control of the electric motor

driving the pump allows this hydraulic power driving the pump allows this hydraulic power steering system to achieve great energy savingssteering system to achieve great energy savings

-The motor, pump, reservoir and controller -The motor, pump, reservoir and controller compose a single unit, making installation easy compose a single unit, making installation easy and nearly eliminating the need for tubing and nearly eliminating the need for tubing adjustments after attachment.adjustments after attachment.

-The hydraulic pump is driven by a high--The hydraulic pump is driven by a high-performance brushless motor, enabling both performance brushless motor, enabling both energy savings and a quick response energy savings and a quick response

COMPONENTS OF POWER STEERING

PumpPump Rotary Rotary valvevalve Steering Steering gearsgears LinkagesLinkages

PUMP:PUMP:

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

ROTARY ROTARY VALVE :VALVE :

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

The steering gear converts the turning motion of The steering gear converts the turning motion of the steering wheel into the to-and-fro motion of the steering wheel into the to-and-fro motion of the link rod of the steering linkage. Moreover, it the link rod of the steering linkage. Moreover, it also provides the necessary leverage so that the also provides the necessary leverage so that the driver is able to steer the vehicle without fatigue.driver is able to steer the vehicle without fatigue.

There are many types and of steering gears in There are many types and of steering gears in use for automobiles. However, only a few use for automobiles. However, only a few important ones out of them are discussed here. important ones out of them are discussed here. The working of other types is also similar.The working of other types is also similar.

1.1. Worm and wheel steering gearWorm and wheel steering gear2.2. Cam and double roller steering gearCam and double roller steering gear3.3. Worm and nut steering gearWorm and nut steering gear4.4. Re-circulating ball type steering gearRe-circulating ball type steering gear5.5. Rack and pinion steering gearRack and pinion steering gear

STEERING GEARSSTEERING GEARS

STEERING LINKAGESSTEERING LINKAGES Steering linkages depends upon the type of the Steering linkages depends upon the type of the

vehicle, whether it is a car which has independent vehicle, whether it is a car which has independent front suspension or a commercial vehicle having front suspension or a commercial vehicle having generally a rigid axle type front suspension.generally a rigid axle type front suspension.Steering linkage for vehicle with Steering linkage for vehicle with

rigid axle front suspensionrigid axle front suspension Steering linkage for vehicle with Steering linkage for vehicle with independent front suspensionindependent front suspension

MANUAL RACK AND PINION STEERING SYSTEM:MANUAL RACK AND PINION STEERING SYSTEM:

MANUAL RE-CIRCULATING BALL STEERING SYSTEM:MANUAL RE-CIRCULATING BALL STEERING SYSTEM:

MANUAL STEERING SYSTEMSMANUAL STEERING SYSTEMS

HYDRAULIC POWER STEERING SYSTEM:HYDRAULIC POWER STEERING SYSTEM: Power Rack-and-pinion :Power Rack-and-pinion : When the rack-and-pinion is in a power-When the rack-and-pinion is in a power-

steering system, the rack has a slightly different steering system, the rack has a slightly different design. Part of the rack contains a cylinder with a design. Part of the rack contains a cylinder with a piston in the middle. The piston is connected to piston in the middle. The piston is connected to the rack. There are two fluid ports, one on either the rack. There are two fluid ports, one on either side of the piston. Supplying higher-pressure fluid side of the piston. Supplying higher-pressure fluid to one side of the piston forces the piston to to one side of the piston forces the piston to move, which in turn moves the rack, providing the move, which in turn moves the rack, providing the power assist.power assist.

POWER ASSISTED STEERING SYSTEMSPOWER ASSISTED STEERING SYSTEMS

Recirculating ball power steering:Recirculating ball power steering: Power steering for the recirculating ball Power steering for the recirculating ball

type steering system consists of a pump, fluid type steering system consists of a pump, fluid reservoir, pressure and return hoses and steering reservoir, pressure and return hoses and steering gear. The pump, which is driven by an accessory gear. The pump, which is driven by an accessory drive belt, consists of an impeller, pressure valve, drive belt, consists of an impeller, pressure valve, and fluid reservoir. Pump pressure builds only and fluid reservoir. Pump pressure builds only when the engine is running. The pump impeller when the engine is running. The pump impeller turns, picking up hydraulic fluid from the reservoir turns, picking up hydraulic fluid from the reservoir and feeding it to the steering gear under pressure and feeding it to the steering gear under pressure through the pressure line. The fluid is then through the pressure line. The fluid is then returned to the fluid reservoir through the non-returned to the fluid reservoir through the non-pressurized return line.pressurized return line.

ELECTRIC POWER STEERING:ELECTRIC POWER STEERING: Automotive manufacturers are now-a-days Automotive manufacturers are now-a-days

moving to Electric Power Steering (EPS) to provide moving to Electric Power Steering (EPS) to provide the convenience of steering assist without the cost the convenience of steering assist without the cost in engine size and fuel consumption.in engine size and fuel consumption.

EPS is also a cheaper and more flexible EPS is also a cheaper and more flexible solution than a hydraulic pump. Besides providing solution than a hydraulic pump. Besides providing a five percent improvement in fuel efficiency, EPS a five percent improvement in fuel efficiency, EPS is lighter (4 Kg to 6 Kg or 8 lbs to 13 lbs), and is lighter (4 Kg to 6 Kg or 8 lbs to 13 lbs), and mechanically simpler (no pump, fan belt, fluid mechanically simpler (no pump, fan belt, fluid reservoir). The same EPS system can provide high-reservoir). The same EPS system can provide high-performance driving for a sports car and smooth, performance driving for a sports car and smooth, safety-assisted steering for the family sedan safety-assisted steering for the family sedan simply by changing the controller's software. simply by changing the controller's software. 

ELECTRO-HYDRAULIC POWER STEERING :

So called "hybrid" systems use the same hydraulic So called "hybrid" systems use the same hydraulic assist technology as standard systems, with the assist technology as standard systems, with the hydraulic pressure being provided by an electric hydraulic pressure being provided by an electric motor instead of a belt driven one.motor instead of a belt driven one.

ADVANCED STEERING SYSTEMS

Variable ratio rack and pinion Variable ratio rack and pinion steering systemsteering system Electric power steeringElectric power steering Speed sensitive steeringSpeed sensitive steering Four wheel steeringFour wheel steering

A sub-species of four wheel A sub-species of four wheel steering is the Articulated steering. steering is the Articulated steering. Articulated steering is a system by Articulated steering is a system by which a four wheel drive vehicle is which a four wheel drive vehicle is split into front and rear halves which split into front and rear halves which are connected by a vertical hinge. The are connected by a vertical hinge. The front and rear halves are connected front and rear halves are connected with one or more hydraulic cylinders with one or more hydraulic cylinders that change the angle between the that change the angle between the halves, including the front and rear halves, including the front and rear axles and wheels, thus steering the axles and wheels, thus steering the vehicle. This system does not use vehicle. This system does not use steering arms, king pins, tie rods, etc. steering arms, king pins, tie rods, etc. as does four wheel steering. If the as does four wheel steering. If the vertical hinge is placed equidistant vertical hinge is placed equidistant between the two axles, it also between the two axles, it also eliminates the need for a central eliminates the need for a central differential, as both front and rear differential, as both front and rear axles will follow the same path, and axles will follow the same path, and thus rotate at the same speed.thus rotate at the same speed.

A front loader with articulated steering.

There are controls to switch off the rear steer and options There are controls to switch off the rear steer and options to steer only the rear wheel independent of the front to steer only the rear wheel independent of the front wheels. At slow speeds (wheels. At slow speeds (e.g.e.g. parking) the rear wheels turn parking) the rear wheels turn opposite to that of the front wheels, reducing the turning opposite to that of the front wheels, reducing the turning radius by up to twenty-five percent, while at higher radius by up to twenty-five percent, while at higher speeds both front and rear wheels turn alike speeds both front and rear wheels turn alike (electronically controlled), so that the vehicle may change (electronically controlled), so that the vehicle may change position with less yaw, enhancing straight-line stability. position with less yaw, enhancing straight-line stability.

Some vehicles now offer a form of "passive" four wheel Some vehicles now offer a form of "passive" four wheel steering, where the bushings by which the rear steering, where the bushings by which the rear suspension attaches to the automobile are designed to suspension attaches to the automobile are designed to compress in a precise direction under the forces of compress in a precise direction under the forces of steering, thus slightly altering the rear suspension steering, thus slightly altering the rear suspension geometry in such a manner as to enhance stability.geometry in such a manner as to enhance stability.

One of the coolest innovations in recent times is the One of the coolest innovations in recent times is the “Steer-by-wire”. These systems would completely “Steer-by-wire”. These systems would completely eliminate the mechanical connection between the steering eliminate the mechanical connection between the steering wheel and the steering, replacing it with a purely wheel and the steering, replacing it with a purely electronic control system.electronic control system.

RECENT DEVELOPMENTSRECENT DEVELOPMENTS

Over the years, power steering has become a standard equipment item Over the years, power steering has become a standard equipment item on many automobiles. The demand for this system has caused power on many automobiles. The demand for this system has caused power steering to be installed on over 90% of all domestic new car production. steering to be installed on over 90% of all domestic new car production.

Not only in domestic cars but EPS has found a widespread application Not only in domestic cars but EPS has found a widespread application in F-1 races and in sport cars. Due to a hunger for more speed and in F-1 races and in sport cars. Due to a hunger for more speed and power it was but necessary to bring this change in the design or be power it was but necessary to bring this change in the design or be willing to sacrifice the stability factor.willing to sacrifice the stability factor. This variation in design helped in This variation in design helped in achieving a better stability and maneuverability in sport cars.achieving a better stability and maneuverability in sport cars.

Though there is a continuous quest to achieve better steering system Though there is a continuous quest to achieve better steering system designs, an engineers work is only half done since there are still designs, an engineers work is only half done since there are still concerns such as flow and pressure regulation, reduction of pump flow concerns such as flow and pressure regulation, reduction of pump flow ripples, sizing of your system, optimization of your network ripples, sizing of your system, optimization of your network architecture, noise and vibrations in the supply line, losses in lines, architecture, noise and vibrations in the supply line, losses in lines, electric parts dynamics and performance, development of new control electric parts dynamics and performance, development of new control strategies for electrical or electro-hydraulic steering systems, off-line strategies for electrical or electro-hydraulic steering systems, off-line tests of the control strategies, reduction of energy consumption, tests of the control strategies, reduction of energy consumption, increase of efficiency, peak torque prediction at the wheel due to increase of efficiency, peak torque prediction at the wheel due to electrical stop strategies, velocity dependant assistance law electrical stop strategies, velocity dependant assistance law optimization, coupling between the front suspension and the hydraulic optimization, coupling between the front suspension and the hydraulic or electrical steering systems.or electrical steering systems.

Therefore optimization of steering systems is a continual improvement Therefore optimization of steering systems is a continual improvement process. process.

CONCLUSIONSCONCLUSIONS

Automobile engineering by Kirpal Singh www.howstuffworks.com www.wikipedia.com www.Autozone.com/suspension and steering.htm www.cartrackers.com/auto_glossary/s www.madsci.org www.showa1.com/en/products/4rs/pdf/power_s.pdf

REFERENCESREFERENCES

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