3 gear trains(1)

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ME‐205 : Element of machine dynamics and design

Dr. Muhammad WasifAssistant Professor – I.M.D.

Ph.D. (CAD/CAM – Canada), M.Engg. (Mfg. Engg. – NEDUET), B.E. (Mech. Engg. – NED UET). Member ASME and PEC

Room : 1st on LHS of main corridor, ground floor – IM Building

Machine dynamics : Gear Trains

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Gear Drives• Are more efficient and durable than the flexible power drives.

• Due to different designs of gears, these can used to transmit

torque and angular velocity in a wide variety of applications.

• Due to no slippage between two gear, power loss in the gear

drives are negligible.

• Gear drives are used for precise velocity ratios and high

power transmission applications.

• These are used in compact machines with less center

distances.

2ME‐205, Elements of Machine design and dynamics, conducted by Dr. Muhammad Wasif (Asst. Professor ‐ IMD, NEDUET)

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Gear Drives ‐ Limitation• Machining of gears are much costlier than the

manufacturing of flexible power drives.

• It requires proper method of lubrication, for longer

life and efficient operation.

• Machining error and misalignment cause the noise

and vibrations, which result in failure of the gear

drives.


Classification of Gear Drives


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Classification of Gear Drives


Differential of engine

Wind turbine Engine Transmission

Opposite direction Same direction Linear direction

Gear Drives for Parallel Shafts


Spur Gears

• Lengthwise teeth direction is parallel to the gear

rotation axis (uniform cross section).

• Easy to machine,

• High quality gears can be produces.

• Available in different types of tooth design and pressure angles.

In a gear pair, gears exerts only thrust force on each other.

Applications : Watches, toys, transmission drives etc.

Spur Gears

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Gear Drives for Parallel Shafts


Helical Gears

• Teeth lengthwise direction is oblique to the

gear rotation axis (increase length of teeth)

• Carry more load due to long teeth.

• Gear pair exert axial as well as thrust fore to

each other.

• Can also be used for non‐parallel shafts.

• These gears are more expensive than the spur

gear and slightly less efficient.

• Applications : Transmission of car, motorcycle.

Helical Gears


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Gear Drives for Non‐Parallel Shafts


Bevel Gears

• Are used for non‐parallel, intersecting and non‐

intersecting shafts.

• Straight, zerol and spiral bevel gears are different

types of bevel gear, based on different curvatures

of teeth.

• Spiral bevel gears are more durable, produce less

vibration, due to gradual contact b/w curved

teeth.

• Hypoid gear is a special type of spiral bevel gear

with pinion at an offset.

Straight Bevel Gears

Spiral Bevel Gears



Bevel Gears

• Spiral bevel gears provide high reduction ratio.

• Have high contact ratio with less noise, than the

straight or zerol bevel gears.

• Spiral bevel gears are more expensive and

machined by complex machine tools.

• Applications : Vehicle transmission, choppers.

Miter Gears

• Special type of bevel gear used for 90 degree

shaft with 1:1 velocity ratio.

Miter Gears

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Worm Gears

• Worm is a shank having at least one complete

tooth (thread), which drives the wheel having teeth

in helical direction, to be driven by a worm.

• Provides high reduction ratio

• Worm pair rotates in one direction and restrict the

rotation in opposite direction. i.e. worm drives the

wheel, wheel cannot drive a worm, therefore, it

locks the mechanism in one direction.

• Noiseless operation.

• Applications : chain block, speed reducer.

Worm Gears


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Gear Nomenclature


Pitch Point

• The basic requirement of gear‐tooth geometry is the provide the velocity ratios exactly constant.

• The action of a pair of gear teeth satisfying this requirement is termed conjugate gear‐tooth action.

• Law of gearing states;

“As the gears rotate, the common normal to the surfaces at the point of contact must always intersect the line of centers at the same point P, called the pitch point.”

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Gear Nomenclature


Pitch Circles

• A Circle passing through the pitch point,with the center at the rotation axis of thegear is called pitch circle.

• A gear with larger pitch circle is calledmember gear, whereas, other gear withsmaller pitch circle is called pinion. Nomatter which one is driver or driven.

• The velocity ratio and center distance are;

. .

0.5 =

Where, p=pinion, g=gear, =angular velocity

d=pitch diameter, r=pitch radius.

Gear Nomenclature


Pressure Angle

• Circle passing through the pitchpoint, with the center at the rotationaxis of the gear is called pitch circle.

• The gear with larger pitch circle iscalled member gear, whereas, gearwith smaller pitch circle is calledpinion. No matter which one is driveror driven.

• The velocity ratio between two gearis;

. .

Where, p=pinion, g=gear, =angularvelocity

d i h di f h

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Gear Nomenclature


• For a 3D spur gear, pitch cylinder isconsidered, which is formed by pitch circlepulled about the rotation axis of the gear.

• The tooth surface above the pitch cylinderis called “face”, whereas, tooth surfacebelow the cylinder is called ” flank”.

• Circular pitch (p) : Distance measured onthe circumference of the pitch circle froma point of one tooth to the correspondingpoint on the next tooth.

• Pressure angle () : It is the angle betweenthe common normal to two gear teeth atthe point of contact and the commontangent at the pitch point.

Gear Nomenclature


Profile

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Gear Nomenclature


• For a 3D spur gear, pitch cylinder isconsidered, which is formed by pitch circlepulled about the rotation axis of the gear.

• The tooth surface above the pitch cylinderis called “face”, whereas, tooth surfacebelow the cylinder is called ” flank”.

• Circular pitch (p) : Distance measured onthe circumference of the pitch circle froma point of one tooth to the correspondingpoint on the next tooth.

∙ ∙

• Diametral pitch (P) : No. of teeth per inch.

Gear Nomenclature


• Module (m) : Pitch diameter in mm.1

• Addendum : It is the radial distance of a toothfrom the pitch circle to the top of the tooth.

• Dedendum : It is the radial distance of a toothfrom the pitch circle to the bottom of thetooth.

• Addendum circle : It is the circle drawnthrough the top of the teeth and is concentricwith the pitch circle.

• Dedendum circle : It is the circle drawnthrough the bottom of the teeth. It is alsocalled root circle.

• Total depth : It is the radial distance between the addendum and the dedendum circle of a

• gear.

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Gear Nomenclature


• Clearance : It is the radial distance fromthe top of the tooth to the bottom of thetooth, in a meshing gear.

• Working depth. It is radial distance fromthe addendum circle to the clearancecircle. It is equal to the sum of theaddendum of the two meshing gears.

• Tooth thickness : It is the width of thetooth measured along the pitch circle.

• Tooth space : It is the width of space between the two adjacent teeth measured along the pitch circle.

• Backlash : It is the difference between the tooth space and the tooth thickness, as measured on the pitch circle.

Gear Nomenclature


• Top land : It is the surface of the top of thetooth.

• Face width : It is the width of the geartooth measured parallel to the axis ofrotation.

• Profile : It is the curve formed by the faceand flank of the tooth.

• Fillet radius : It is the radius that connectsthe root circle to the profile of the tooth.

• Path of contact : It is the path traced bythe point of contact of two teeth from thebeginning to the end of engagement.

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Refernces

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• R.S. Khurmi, G.K. Gupta, 2005, A text book of machine design, New Dehli‐ India, EURASIA PUBLISHING HOUSE.

• R. G. Budynass, J.K. Nisbett, 2005, Shigley’s Mechanical Engineering Deisgn, New York –USA, McGraw Hill.

• R.C. Juvinall, K.M. Marshek, 2012, Fundamental of Machine Componenet Design, NJ, John Willey and Sons.

• http://www.mae.ncsu.edu/eischen/

• http://www.khkgears.co.jp/en/gear_technology/pdf/gearabc_b.pdfB. J. Hamrock

• http://www.xtek.com/pdf/wp‐gear‐terminology.pdf

• http://www.khkgears.co.jp/en/gear_technology/pdf/gearabc_b.pdf

3 gear trains(1)

Engineering

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