Universal College Of Engineering & Technology

MECH: F-1 SUBJECT: KINEMATICS OF MECHANICS

• RESPECTED FACULTY- VATSAL SHAH

BHALODIA KRUNAL

130460119007

BHATT KALPESH J.130460119009

BHANDARI

RAJ H.

130460119

008

BELANI HARSH

130460119006

ACHARYA BHUSAN

130460119013

AHIR

RAVI

13046011

9001

GEARS-

CONTENT

Introduction Of Gears

Classification Of Gears According To Toothed Wheels

Classification Of Gears

Planetary (OR Epicyclic) Gears

Nomenclature Of Gear Teeth

Advantages & Disadvantages

Gear Box Design

Introduction Gears are used to transmit motion from one shaft to another or between shaft and a slide. This is achieved by successfully engaging teeth. Gears used no intermediate links or connector and transmit the motion by direct contact. The surface of two bodies make a tangential contact. The two bodies have either a rolling or a sliding motion along the tangent at the point of contact.

CLASSIFICATION OF GEARS ACCORDING TO TOOTHED WHEELS1) ACCORDING TO THE POSITION OF AXES OF THE SHAFTS:i. Parallelii. Intersectingiii. Non-Intersecting & Non-Parallel

2) ACCORDING TO THE PERIPHERAL VELOCITY OF THE GEARS: i. Low velocityii. Medium velocityiii. High velocity

3) ACCORDING TO THE TYPE OF GEARING:

i. External gearingii. Internal gearingiii. Rack & Pinion

4) ACCORDING TO THE POSITION OF TEETH ON THE GEAR SURFACE:

i. Straight ii. Inclinediii. Curved

CLASSIFICATION OF GEARS:

Fig.:-Various Types Of Gears

SPUR GEARS• GENERAL: Spur gears are the most commonly used

gear type. They are characterized by teeth which are:

-- perpendicular to the face of the gear. Spur gears

are by far the most commonly available, and are

generally the least expensive. The basic descriptive

geometry for a spur gear is shown in the figure below.

• LIMITATIONS: Spur gears generally cannot be used

when a direction change between the two shafts is

required.

• ADVANTAGES: Spur gears are easy to find,

inexpensive, and efficient.

Fig.:- Gear Box Of Motor Cycle Using Spur Gears

HELICAL GEARS• GENERAL: Helical gears are similar to the spur

gear except that the teeth are at an angle to the shaft,

rather than parallel to it as in a spur gear. The

resulting teeth are longer than the teeth on a spur gear

of equivalent pitch diameter. The longer teeth cause

helical gears to have the following differences from

spur gears of the same size:

• Tooth strength is greater because the teeth are longer,

• Greater surface contact on the teeth allows a helical

gear to carry more load than a spur gear,

• The longer surface of contact reduces the efficiency

of a helical gear relative to a spur gear.

Fig.:-Helical Gear

• Helical gears may be used to mesh two shafts that are not parallel,

although they are still primarily use in parallel shaft applications. A

special application in which helical gears are used is a crossed gear mesh,

in which the two shafts are perpendicular to each other: The basic

descriptive geometry for a helical gear is essentially the same as that of

the spur gear, except that the helix angle must be added as a parameter.

• LIMITATIONS: Helical gears have the major disadvantage that they

are expensive and much more difficult to find. Helical gears are also

slightly less efficient than a spur gear of the same size (see above).

• ADVANTAGES: Helical gears can be used on non parallel and even

perpendicular shafts, and can carry higher loads than can spur gears.

• To avoid axial thrust, two helical gears of opposite hand can be mounted side by side, to cancel resulting thrust forces

• Herringbone gears are mostly used on heavy machinery.

• Axial Thrust is a force that is generated in an axial direction which is along the shaft.

HERRINGBONE GEAR“DOUBLE HELICAL GEARS”

BEVEL GEARS• GENERAL: Bevel gears are primarily used to transfer

power between intersecting shafts. The teeth of these gears are

formed on a conical surface. Standard bevel gears have teeth

which are cut straight and are all parallel to the line pointing the

apex of the cone on which the teeth are based. Spiral bevel gears

are also available which have teeth that form arcs. Hypocycloid

bevel gears are a special type of spiral gear that will allow non-

intersecting, non-parallel shafts to mesh. Straight tool bevel gears

are generally considered the best choice for systems with speeds

lower than 1000 feet per minute: they commonly become noisy

above this point.

• LIMITATIONS: Limited availability. Cannot be used for

parallel shafts. Can become noisy at high speeds.

• ADVANTAGES: Excellent choice for intersecting shaft

systems.

Fig.:-Straight Bevel Gears Fig.:-Spiral Bevel Gear

WORM & WORM GEARS• GENERAL: Worm gears are special gears that resemble

screws, and can be used to drive spur gears or helical

gears.Worm gears, like helical gears, allow two non-

intersecting 'skew' shafts to mesh. Normally, the two shafts

are at right angles to each other. A worm gear is equivalent to

a V-type screw thread. Another way of looking at a worm

gear is that it is a helical gear with a very high helix angle.

Worm gears are normally used when a high gear ratio is

desired, or again when the shafts are perpendicular to each

other. One very important feature of worm gear meshes that

is often of use is their irreversibility : when a worm gear is

turned, the meshing spur gear will turn, but turning the spur

gear will not turn the worm gear. The resulting mesh is 'self

locking', and is useful in racheting mechanisms.

Fig.:-Worm & Worm Gear

• Worm gears are normally used when a high gear ratio is desired, or again

when the shafts are perpendicular to each other. One very important feature

of worm gear meshes that is often of use is their irreversibility : when a

worm gear is turned, the meshing spur gear will turn, but turning the spur

gear will not turn the worm gear. The resulting mesh is 'self locking', and is

useful in racheting mechanisms.

• LIMITATIONS: Low efficiency. The worm drives the drive gear

primarily with slipping motion, thus there are high friction losses.

• ADVANTAGES: Will tolerate large loads and high speed ratios. Meshes

are self locking (which can be either an advantage or a disadvantage).

Rack & Pinion gears• GENERAL: Rack and pinion is a type of linear actuator

that comprises a pair of gears which convert rotational motion into linear motion. The circular pinion engages teeth on a linear "gear" bar–the rack. Rotational motion applied to the pinion will cause the rack to move to the side, up to the limit of its travel. For example, in a rack railway, the rotation of a pinion mounted on a locomotive or a railcar engages a rack between the rails and pulls a train along a steep slope.

• The rack and pinion arrangement is commonly found in the steering mechanism of cars or other wheeled, steered vehicles. This arrangement provides a lesser mechanical advantage than other mechanisms such as recirculating ball, but much less backlash and greater feedback, or steering "feel".

• Enclosed steering rack in an automobileFor every pair of conjugate involute profile, there is a basic rack. This basic rack is the profile of the conjugate gear of infinite pitch radius.

Fig.:-Lathe carriage drive mechanism showing rack and pinion arrangement.

Fig.:- Helical tooth rack and pinion

Fig.:- Spur tooth rack and pinion

Planetary (or Epicyclic) Gears

• Gears whose centers can move.• Used to achieve large speed reductions in compact space.• Can achieve different reduction ratios by holding different combinations of gears fixed.• Used in automatic transmissions of cars.

Fig.:-Planetary OR Epicyclic Gear

Planet

Carrier

Input shaft

Sun gear

Ring gear

Components Of A Planetary Gear

• They have higher gear ratios. • They are popular for automatic transmissions in automobiles. • They are also used in bicycles for controlling power of pedaling automatically or manually. • They are also used for power train between internal combustion engine and an electric motor.

A Variant Of A Planetary Gear

NOMENCLATURE OF GEAR TEETH

Pitch circle gear diam.

Fillet radiusClearance

Base Circle

TERMINOLOGY• 1. Pitch Circle : - It is an imaginary circle which by pure rolling action, would give

the same motion as the actual gear.

• 2. Pitch Circle Diameter : - It is the diameter of the pitch circle.

• 3. Pitch Point : - It is a common point of contact between two pitch circles.

• 4. Pitch surface : - The surface of the imaginary rolling cylinder (cone, etc.) that the toothed gear may be considered to replace.

• 5. Addendum circle : - A circle bounding the ends of the teeth, in a right section of the gear.

• 6. Root or Deddendum circle : - The circle bounding the spaces between the teeth, in a right section of the gear.

• 7. Addendum : - The radial distance between the pitch circle and the addendum circle.

• 8. Deddendum : - The radial distance between the pitch circle and the root circle.

• 11. Flank of a tooth : - The part of the tooth surface lying inside the pitch surface.

• 12. Circular thickness ( also called the tooth thickness ) :- The thickness of the tooth measured on the pitch circle. It is the length of an arc and not the length of a straight line.

• 13. Tooth space : - The distance between adjacent teeth measured on the pitch circle.

• 14. Backlash : - The difference between the circle thickness of one gear and the tooth space of the mating gear.

Backlash = Space width – Tooth thickness• 15. Circular pitch (Pc) : - The width of a tooth and a space, measured on the

pitch circle or it is the distance measured on the circumference of the pitch circle from a point of one tooth to the corresponding point on the next tooth.

• 16. Diametral pitch (Pd) : - The number of teeth of a gear per inch of its pitch diameter. A toothed gear must have an integral number of teeth. The circular pitch, therefore, equals the pitch circumference divided by the number of teeth. The diametral pitch is, by definition, the number of teeth divided by the pitch diameter.

• 17. Module (m) : - Pitch diameter divided by number of teeth. The pitch diameter is usually specified in inches or millimetres; in the former case the module is the inverse of diametral pitch.

ADVANTAGES:1. It transmit exact velocity ratio.2. It has high efficiency.3. It has reliable service.4. It may be used to transmit large power.

DISADVANTAGES:5. The manufacture of gears requires special

tools and equipments.6. The error in cutting teeth may cause

vibration & noise during operation.

Types Features and Precision

Rating

Applications Comments Regarding Precision

Spur Parallel Shafting. High speeds and loads highest efficiency Precision Rating is excellent.

Applicable to all types of trains and a wide range of velocity ratios.

Simplest tooth elements offering maximum precision. First choice, recommended for all the gear meshes, except where very high speeds and loads or special features of other types, such as right angle drive, cannot be avoided.

Helical Parallel Shafting. Very high speeds and loads. Efficiency slightly less than spur mesh. Precision Rating is good.

Most applicable to high speeds and loads; also used whenever spurs are used.

Equivalent quality to spurs, except for complication of helix angle. Recommended for all high-speed and high-load meshes. Axial thrust component must be accommodated.

Bevel Intersecting shafts, High speeds, High loads. Precision Rating is fair to good.

Suitable for 1:1 and higher velocity ratios and for right-angle meshes (and other angles)

Good choice for right angle drive, particularly low ratios. However complicated both form and fabrication limits achievement of precision. Should be located at one of the less critical meshes of the train.

Worm & Worm Right-angle skew shafts, High velocity ratio, High speeds and loads, Low efficiency, Most designs nonreversible. Precision rating is fair to good.

High velocity ratio Angular meshes High loads.

Worm can be made to high precision, but worm gear has inherent limitations. To be considered for average precision meshes, but can be of high precision with care. Best choice for combination high velocity ratio and right-angle drive.

Types Features and Precision Rating

Applications Comments Regarding Precision

Specials - Face, Spiroid, Helicon,Beveloid.

Intersecting and skew shafts. Modest speeds and loads. Precision Rating is fair to good

Special cases To be avoided as precision meshes. Significant non-conjugate action with departure from nominal center distance and shaft angles. Fabrication needs special equipment and inspection is limited.

GEAR BOX DESIGN

GEAR BOX

Synchronizers

Stick shift

The gear box is in first gear, second gear

THANK YOU..