Motor Grader

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Motor Grader

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Transcript of Motor Grader

Page 1: Motor Grader

Motor Grader

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Introduction Motor Grader are motor vehicles

equipped with a long front frame on which work equipment such as blade and scarifier are mounted.

Motor graders are construction machines basically designed for road recovering through such operations as cutting the road surface flat, digging side gutters etc.

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General Locations

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Land Grading Land Grading To level finish the scraped or

turned up ground, drive the machine in 1st or 2nd.

The blade will be kept at a given level and propulsion angle of approx. 60 degree.

The scraping angle is set at the standard angle of 35 degree.

Take care not to run over the banking to avoid the machine pitching.

Otherwise uneven scraping of the road face occurs and traction power will be decreased.

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Repairing of gravel road

Lower the blades so that it can just touches the surface of the road and drive in 1st or 2nd gear.

Traveling in too fast speed may cause rough finishing of the road.

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Snow removing In case of fresh snow, set

the blade at appropriate propulsion angle and the drive the machine in 3rd or 4th gear as to throw aside the snow.

In case of thick layer of snow, drive the machine in 1st or 2nd.Take enough care to obstacles covered under snow.

The scarifier can also be used for turning up the snow.

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Scarifying ( Optional ) The scarifier is attached

to break up ground surfaces which is too hard to penetrate by blade.

The scarifier operation should be driven in 1st or 2nd gear.

If the number of teeth is too many to penetrate for the teeth deep in to the ground then reduce the no. of teeth.

The number of scarifier teeth must be 5 or more.

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Mixing The blade of the grader

is available for mixing up road construction materials by its rolling function.

The grader should be driven in 2nd or 3rd speed range with the blade forward tilted and slightly angled.

Too great volume of mixing materials may be prevent sufficient rolling of them.

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Spreading In this operation

operation, the most suitable speed is 2nd or 3rd with the blade sliding.

Avoid changing its traveling direction unnecessarily otherwise the flattened surface will be disturbed by the rear wheel.

Be careful that the materials are spread to an adequate thickness.

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Ditching The operation should be in

1st or 2nd speed. The blade must be

positioned in such a manner that the dug soil is inside the rear wheel.

Also be careful to removed the earth heaped up under the chassis before it reaches the bottom of the machine.

Lean the front wheel, correspondingly to the tilt of the machine.

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Bank Cutting Adjust the blade to

the bank cutting position at the first speed range.

To allow the grader to run straight, lean the front wheel adequately for the tilt of the blade.

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STRUCTURAL

FEATURES

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Structural features The main job application of

motor grader is to flatten road surfaces by use of their blades.

A motor grader is designed such a way that the shaking of the blades caused by pitching or rolling will be minimum.

The work equipment like blade and scarifier are provided forward the operator’s seat.

All power train components, including transmission, are arranged under or behind the operator’s compartment.

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Design features When cutting rough road surface, motor

grader, specially its front wheel, is subject to vertical movements according to the roughness of road surface.

The movement are transmitted through the machine to the blade which is suspended from frame.

To minimize the blade shaking, motor grader are provided with the different design features.

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Long wheelbase Pitching – a

vehicle with a long wheelbase is subject to during travel on a bumpy road.

It is smaller than that to which vehicles with a shorter wheelbase are subject.

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Blade mounted @ center of machine

A front mounted blade such as bulldozer blade is subject to considerably large shakes when the machine runs over obstacles.

But the motor grader blade is shaken within the range of only about quarter of the bulldozer blade.

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Front axle swing from center pin

The front axle is constructed such that the axle swings on the center pin when either wheel falls into hole or rides over the obstacle.

Since the frame is subjected to pitching not rolling, the blade is subject to a slight vertical movement only.

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Rear Wheel arranged in tandem

Two rear wheels on each side of the machine are arranged in tandem at rear axle.

As a result two wheels swing as a unit along with the rear axle while each wheel acts as a traction wheel individually.

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Leaning mechanism The front wheels of a

motor grader tend to slip when the grader is traveling forward with a biased blade load.

Forward traveling of the grader can be maintained by leaning the front wheels toward the direction opposite to the slip page.

Leaning angle will depend on the load on the blade.

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No differential is employed

As motor graders are usually operated on very bumpy roads or on rough ground, The emphasis in traveling performance is placed on straight traveling capability.

For this purpose, driving power is directly transmitted to the rear axle without use differential.

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CLASSIFICATIONS

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Blade Angle : As the blade length is determined on the basis of wheelbase, engine, horsepower,machine weight, etc, the capacity of a grader is roughly estimated by comparing the length of its blade.

Work equipment control system : The mechanical system which transmits engine rotation to work equipment through mechanical linkage.The other is the hydraulic system which uses a hydraulic pump driven by the engine to actuate the system.

Drive wheel type : Most motor graders are of rear wheel drive, front wheel steering type.The rear wheel are usually arranged in tandem, except for some small sized grader which are provided with single rear wheel on each side of the machine.

Others : Some motor graders employ torque converters ( instead of friction clutches ) for easy driving.Articulated motor graders have a front frame hinged to the rear portion to reduce turning radius.

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TERMINOLOGY

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Maximum tractive force : Actual measurement of maximum tractive force may vary somewhat depending on condition of road on which the machine is tested.When a value derived by calculation from engine torque exceeds 80% of drive wheel load,the 80% drive wheel load is started as the maximum tractive force.

Gradeability : The maximum angle of an uphill on which the motor grader can travel without stopping.

Minimum turning radius : The minimum radius of a circle within which the motor grader can be turned around when measured at the center of a fully leaned outside from tire.

Maximum safety angle : The allowable angle of inclination within which the motor grader can be tilted to right or left.

Drawbar : Also called the blade drawbar. Sometimes called the A – frame or T- frame depending on its shape.

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Blade base : The distance between blade placed at right angles to the machine center lines and center of front axle.The longer the blade base, the larger the blade pressure.

Blade side shift : Two types of blade shift are employed : One moves the blade and circle together along an arch of a circle around the drawbar front end.In the other moves only the blade side wards while the circle is left stopped.The later is the favorable method for the blade side shift using an exclusive hydraulic cylinder.

Bank cut and reversed bank cut : Bank cut is the side slope cutting during which removed earth is pushed downward by the blade.

Reverse bank cut is when earth removed by the side slope cutting is pushed upward by the blade.

Leaning : The front wheel are leaned towards right or left to reduce the turning radius of the motor grader or to prevent wheels from slipping sideward.

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Steering Booster The front wheel

steering force increases with the increase of machine weight.

The steering booster lightens steering force by aid of hydraulic system

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POWER TRAIN

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A rear engine and rear drive wheel system is the most popular for motor grader.

A power train composed of engine,clutch, transmission and reduction gears is mounted as a unit on rear side.

The speed of rotation of transmission output shaft has reduce in the reduction gear unit.

The tandem drive,a unique device employed on most motor graders, minimizes pitching.This unit also acts as the reduction gears.

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FINAL DRIVE The final drive connects

the transmission to right and left tandem drive.

Unlike ordinary vehicles, motor grader have no differential.

To assure straight forward traveling of motor graders which are mainly operated in bumpy roads, they are not provided with differential.

This makes motor graders difficult to turn along sharp curves.

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TANDEM DRIVE It receives driving power from

the final drive and delivers to the rear wheels to rotate them at a reduce speed.

It minimized vertical movement of the blade when the grader travels on rough ground so that ground surface is leveled flat.

The tandem drive is designed so that is able to swing on rear axle.

It allows all rear wheels to keep proper ground contact even when any wheels fall in to a hole.

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Structure of Tandem drive

Out of four rear wheel, two mounted side by side on right tandem and two mounted on the left tandem drive case.

Each tandem drive case includes its own gearing which transmit rotation of rear axle to each wheel.

The tandem case is supported at its centre bearing on the end surface of rear axle case.

Rotation of rear axle is transmitted to each wheel through two stage reduction gearing.

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WHEELS Motor graders are

provided with rear wheel for driving and the front wheel for steering.

Low pressure tires of 2.0 to 4.0 kg/sq.cm.air pressure are commonly used for motor graders.This will provide large tractive force with minimum slippage.

Tires are provided with traction type tread pattern which is optimum for suspending the machine on muddy ground and producing large tractive force.

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Mounting of tires Front and rear tire are

mounted so that tire pattern on front tire is opposite to that of rear tire.

The direction of installation of front tires is determined to assure reliable steering.

The direction of installation of rear tires is determined to obtained production of

sufficient tractive force.

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Tire Specification Generally tire sizes are

shown as follows : 14.00 - 24 - 10 PRWidth Rim O.D Strength of tire ( inch ) ( inch ) ( ply rating )

10 PR indicates that the strength of subject tire corresponds to the strength of a tire fabricated with 10 sheets of cotton cord.The larger the numeral preceeding PR, the stronger the tire.

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BRAKE

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Function of Brake

Motor grader are provided with two individually controlled brake systems : Service brake ( or foot brake ) and parking brake ( or hand brake ).

Brake pedal is connected to the master cylinder piston through the push rod.

When the pedal depressed the oil from master cylinder will press the piston of wheel cylinder.

Each wheel cylinder acts to expand brake shoes inside the drum.

The brake drum mounted on each of four rear wheels includes internal expanding type brake shoes which cause friction force to brake the drum rotation.

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Dual Braking Circuit

The service brake system uses the dual braking circuits ( or dual brake oil piping structure ) for ensuring independent operation of service brake of each side of machine.

If either service brake oil pipe for left or right rear wheel is damaged,the safety valve will stop feeding oil to the leaky pipe.

This feature will help to supply oil to the other circuit of wheel cylinders on the opposite of the machine.

The brake lamp switch provided in the master cylinder outlet port turns on the brake lamp with increase of oil pressure resulting from depression of brake pedal.

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Parking Brake

The parking is used when a motor grader is left parked or when starting on an upgrade.

It is applied by pulling the hand brake lever towards the operator’s seat

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STEERING SYSTEM

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Salient feature The front wheel axle is

fitted to the frame with a pin at the centre of axle.No chassis spring is provided.

The leaning mechanism is provided for preventing the front wheels from slipping sideward and for minimize the turning radius.

Some graders are equipped with the steering booster which ensure light and smooth operation.

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Steering Booster The booster is provided for

lightening the steering hand wheel operating force.

Although the hand wheel torque is multiplied by the steering gear box, torque multiplication ratio can not be excessively increased since the resulting reduction ratio of the steering gearing prevents quick steering of the machine.

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Leaning Mechanism

Leaning mechanism is used for tilting the front wheels to right and left to prevents wheels for sleeping and keeps machine in straight travel.

When a motor grader is operated for road leveling, its blade is usually angled from the machine centre line which causes a slide slip force on the wheel.

Under this circumstances, the front wheel which supports only the light weights of the front frame, are liable to slip.

It will cause the machine to turn from the straight forward traveling motion.

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Leaning Mechanism Contd….. Leaning of the front wheel

is necessary to prevent the front wheel from slipping.

Sideslip force (A) caused by angling of the blade is cancelled by the opposite force(B) resulting from leaning of the front wheel.

The leaning mechanism allows the machine to turn in a reduce turning radius.

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Leaning Mechanism Construction Contd….

A hydraulic leaning cylinder is installed on the front axle.

This cylinder is controlled by the leaning controlled lever in the operator’s compartment.

When the leaning cylinder piston rod is extended, the right wheel knuckle bracket connected to the piston end and the left wheel knuckle bucket linked to the right knuckle through the leaning rod are leaned to the right.

When the cylinder rod is retracted, both right and left wheels are leaned to the left which causes both right and left wheels to tilt to the right.

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WORK EQUIPMENT

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Blade The blade which is the

main work equipment of motor grader is mounted under the frame at the middle of the wheel of the wheel base between front and rear axle.

The blade system consists of drawbar,circle and blade.

Several types of blade control mechanism are there for different blade application.

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Blade Lifting Mechanism

The blade is fitted to the drawbar through the circle.

The drawbar fitted to the frame through the ball stud at the front end of the drawbar and through two blade lift cylinders and a circle side shift cylinder at the rear end.

Ground cutting depth is adjusted equally extending or retracting two lift cylinders rod.

Blade rotating mechanism consists of hydraulic motor and circle reverse gear.

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Circle reverse gear Rotation obtained by the

hydraulic motor, which is driven by oil is too high in speed and too low in torque.

This is compensated by the circle reverse gear mounted on the drawbar.

Rotation of the hydraulic motor is reduce by the worm gear in the circle reverse gear .

Rotation of the worm wheel is transmitted to the circle through pin roller.

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Blade side shift mechanism

The blade side shift cylinder horizontally mounted on the back of blade is controlled by the control lever in the operator’s cabin.

Retracting or expanding the blade side shift cylinder rod causes the blade to move sidewise, so that any desire protrusion, right or left of the blade from the circle can be obtained.

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Circle side shift mechanism

The circle side shift cylinder located behind the blade lift cylinders is fitted to the frame through the slide block.

The piston rod end of this slanting cylinder is joined to the rear end of the drawbar to move the drawbar sideward with retraction or extension of piston rod.

The circle fitted to the drawbar follows the movement of drawbar.

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Circle The circle is a

large sized internal ring gear made of cast steel.

It is suspended from the drawbar and is turned with rotation of the pin roller of the circle reverse gear.

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Scarifier The scarifier is used for

breaking hard ground prior to cutting of ground surface with the blade.

The scarifier lifting cylinder is mounted on the front side of the frame.

When the cylinder piston rod is retracted, movement is transmitted through the arm shaft and arms to the right and left lifting links and the scarifier is lifted.

When the cylinder piston is extended the scarifier is lowered.

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Scarifier block The scarifier block is

suspended at each side from the frame with the scarifier drawbar and the lifting link.

The length of the teeth can be adjusted in two or three stages.

If cutting of ground is found difficult with the existing nos. of teeth, then number of teeth may be reduce to increase the breaking force in each teeth.

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