alishan ppt
TRANSCRIPT
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Primary function of the steering system is to achieveangular motion of the front wheels to negotiate the turn.
Secondary functions of steering system are:
1. To provide directional stability to the vehicle goingstraight ahead.
2. To provide perfect steering condition,
i.e. perfect rolling motion of road wheels at all times.
3. To facilitate straight ahead recovery after completing aturn.
4. To minimize tier wear.
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The requirements of a good steering system are:
1. The steering mechanism should be very accurateand easy to handle.
2. The effort required to steer should be minimaland must not be tiresome to the driver.
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1. Steering wheel and column,
2. A manual gearbox and pitman arm or a rack andpinion assembly,
3. Linkages; steering knuckles and ball joints; and 4. The wheel spindle assemblies.
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Power steering systems add a hydraulic pump; fluidreservoir; hoses; lines; and either a power assist unitmounted on, or integral with, a power steering-gear-assembly.
There are several different manual steering gearsin current use. The "rack and pinion" type is the choiceof most manufacturers. The "recirculating ball" type isa past favorite because the balls act as a rolling threadbetween the wormshaft and the ball nut.
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The steering linkage is made of interconnected partswhich move every time the steering wheel is turned.The rotating movement of the steering columnactivates mechanisms inside the steering box. Tie rodends, which join the key parts, pass on the steeringwheel's motion no matter what the angle of the linkageor the vibration from the road.
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For a car to turn smoothly, each wheel must follow a different circle.Since the inside wheel is following a circle with a smaller radius, it isactually making a tighter turn than the outside wheel.
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Energy absorbing steering column
Tilt wheel steering column
.Tilt and telescopic steering column
Steering column with anti-theft lock
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The different types of mechanical steerings used inmodern cars are :
RACK AND PINION STEERING
RECIRCULATING BALL BEARING MANUAL WORM AND SECTOR STEERING
WORM AND TAPERED PEG STEERING
MANUAL WORM AND ROLLER STEERING
WORM AND WHEEL STEERING
WORM AND NUT STEERING
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Rack-and-pinion steering is quickly becoming themost common type of steering on cars, small trucksand SUVs. It is actually a pretty simple mechanism. Arack-and-pinion gear set is enclosed in a metal tube,with each end of the rack protruding from the tube. Arod, called a tie rod, connects to each end of the rack.
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Recirculating-ball steering is used on many trucks andSUVs (sport utility vehicle) today. The linkages thatturns the wheels is slightly different than on a rack andpinion system. The recirculating ball steering gearcontains aworm gear. You can imagine the gear in twoparts. The first part is a block of metal with a threadedhole in it.
http://auto.howstuffworks.com/gear5.htmhttp://auto.howstuffworks.com/gear5.htm -
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The manual worm and sector steering gear assemblyuses a steering shaft with a three-turn worm gearsupported and straddled by ball bearing assemblies.The worm meshes with a 14-tooth sector attached tothe top end of the pitman arm shaft. In operation, aturn of the steering wheel causes the worm gear torotate the sector and the pitman arm shaft. Thismovement is transmitted to the pitman arm and
throughout the steering train to the wheel spindles.
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The manual worm and tapered peg steering gear has athree-turn worm gear at the lower end of the steeringshaft supported by ball bearing assemblies. Thepitman shaft has a lever end with a tapered peg that
rides in the worm grooves. When the movement of thesteering wheel revolves the worm gear, it causes thetapered peg to follow the worm gear grooves.Movement of the peg moves the lever on the pitman
shaft, which in turn moves the pitman arm and thesteering linkage.
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Various manufacturers use the manual worm androller steering gear. This steering gear has a three-turnworm gear at the lower end of the steering shaft.Instead of a sector or tapered peg on the pitman arm
shaft, the gearbox has a roller assembly (usually withtwo roller teeth) that engages the worm gear.
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The movement of the steering wheel turns the worm,which in turn drives the worm wheel. Attached to thewheel spindle rigidly is drop arm, so that a rotation ofsteering wheel corresponds to a linear motion of the
drop arm end, which is connected to the link rod ashas already been discussed.
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Here the steering wheel rotation rotates theworm, which in turn moves the nut along itslength. This cause the drop arm end to movelinearly, further moving the link rod and thus
steering the wheel.
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POWER RACK AND PINION STEERING
POWER RECIRCULATING BALL BEARINGSTEERING
HYDRAULIC POWER STEERING ELECTROHYDRAULIC POWER STEERING
ELECTRIC POWER STEERING
ACTIVE STEERING
STEER BY WIRE
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POWER RACK AND PINION
When the rack-and-pinion is in a power-steering system, the rack has a slightly different design
as shown in figure no. 4.
FIGURE 4. POWER RACK AND PINION STEERING ASSEMBLY
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.
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POWER RECIRCULATING BALL BEARING SYSTEM
Power steering in a recirculating-ball system workssimilarly to a rack-and-pinion system. Supplying higher-pressure fluid (fluid is always a oil) to one side of the block
provides assist.HYDRAULIC POWER STEERING SYSTEM
The hydraulic power steering system today is the mostused steering system. It is based on the components of the
mechanical steering system, in addition there is a hydraulicsystem, usually consisting of hydro pump with V-belt drive,hydraulic lines, oil reservoir and steering valve.
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ELECTRO-HYDRAULIC POWER STEERING SYSTEM
The electro-hydraulic power steering
system (Fig. 6) is based on the rack-and-
pinion hydraulic power steering and its
essential new feature is an electrically drivenhydraulic pump, which substitutes the
steering pump driven so far by the vehicle
engine.
FIGURE 6.ELECTROHYDRAULIC POWER
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ELECTRIC POWER STEERING SYSTEM
The electric power steering system (Fig. 7) combines a mechanical steering system with an
electronically controlled electric motor to a dry power steering. The hydraulic system, which so
far delivered the steering boost, is substituted by an electrical system. For this, a torque sensor
measures the steering wheel torque and an electronic control unit calculates the necessary servo
torque.
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The components involved in the electrical powersteering are besides the mechanical steeringcomponents:Electric motor,
Electronic control unit,
Power electronics,
Steering wheel torque sensor and
CAN data bus to other systems
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FUNCTIONAL DESCRIPTION OF ELECTRICAL STEERING SYSTEMS
FIGURE 8. SYSTEM STRUCTURES OF SAFE ELECTRICAL STEERING SYSTEMS
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SAFETY FEATURES
Detecting and evaluating all electrical failuresaccomplish the systems fail-safe behaviour concerningelectrical faults. In case of major electrical faults theelectrical power steering system is switched off
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BMW Active Steering
BMW's Active Steering, a true breakthrough insteering technology, supports the driver at all speeds,particularly in the lower and medium speed rangewhere dynamic steering offers a genuine increase indriving pleasure.
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STEER BY WIRE SYSTEMS The main feature of future steering systems is the missing
direct mechanical link between steering wheel and steeredwheels. With such a steer-by-wire steering system (Fig.11)
the missing steering columns function must be reproducedin both directions of action. In forward direction the angleset by the driver at the steering wheel is measured by asteering angle sensor and transferred with the suitablesteering ratio to the wheels. In reverse direction the
steering torque occurring at the wheels is picked up via atorque sensor and attenuated respectively, modified fedback to the driver as a counter torque on the steering
wheel.
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FIGURE 11.SBW EXPLANATORY SKETCH
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Further Advantages Improvement of steering comfort. Road disturbance is first
evaluated and assessed by the system; only useful information isfed to the driver.
Improvement of steering comfort. Road disturbance is first
evaluated and assessed by the system; only useful information isfed to the driver. Steering wheel return torques and steering ratio can be
adjusted variably by software; thus rendering the steering systemadaptable to any target group and driving situation without anyneed to redesign.
Reduction of injury risk in an accident by missing steeringcolumn.
Steering behaviour (understeering, oversteering, self-steeringproperties) can be matched by software
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CONCLUSION This contribution presented various types of electrical
steering systems and their safety aspects. The electrohydraulic power steering does no longer operate the
hydraulic pump via a V-belt drive from the internalcombustion engine. Rather, an electric motor is used,yielding energy savings and flexibility of installation.
Electrical power steering pursues this trend and
offers additional advantages since no hydraulic systemis required. A steer-by-wire system with hydraulicbackup and a purely electrical system were discussed.
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The transition to purely electrical steering systems will proceed step bystep, both for safety reasons and acceptance by the customer. The path
will lead from electrical power steering via a steer-by-wire system witha hydraulic or mechanical backup towards purely electrical steer-by-
wire systems.
REFERENCES Internet : Automotive Engineering International Online, Delphi
AutomotiveSystems;
Joseph, Heitner. Automotive Mechanics, CBS Publishers andDistribution.
Narang G.B.S. Automobile Engineering, S. Chand and Company Ltd. Crouse, W.H. Automotive Mechanics, T ATA McGraw Hill Publishing
Company Ltd.
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