Gear drive system in detail as per theory of machine syllabus

1. Gear Drive System:-

2. Gears are toothed wheel which transmit the power and motion from one
shaft to another by means of successive engagement of teeth.
A. On the basis Shaft are parallel to each other, two types of gears are mounted
on the shaft to transmit the power :
i. Spur Gear
ii. Helical Gear.
iii. Rack and pinion Gear
B. On the basis of Shafts are non intersecting and non parallel and non coplanar
then power transmitting gears are:
i. Spiral Gear
ii. Worm and Worm Wheel
Types of Gears:

3. Advantages
1.It transmits exact velocity ratio.
2.It may be used to transmit large power.
3.It has high efficiency.
4.It has reliable service.
5.It has compact layout.
Disadvantages
1.The manufacture of gears require special tools and
equipment.
2.The error in cutting teeth may cause vibrations and
noise during operation.

4. Spur gears are cylindrical and have straight
teeth, and are mounted on parallel shafts.
Used to transmit the rotary motion between
two shaft which are parallel.
It is used at once to create very large gear
reductions
Larger gear: Driven gear- Spur gear / wheel.
Smaller gear: Driver Gear: Pinion.
Motion of the two gears are always opposite to
each other.
1.SPUR GEARS:

6. (i) Easy to manufacture.
(ii) Simple and Cheaper among all types of gears.
(iii)The spur gears do not create axial load or thrust on the
shaft and the bearings.
(iv) The spur gears are interchangeable.

7. (i) The contact between the two meshing teeth is sudden line contact.
Due to sudden line contact, the operation of spur gear pair is noisy.
(ii)The spur gears are not suitable for high speed applications.
(iii)The power transmitting capacity of spur gear pair is lower than the
helical gear pair.
(i) The spur gears are used in automobile gear boxes, machine
tool gear boxes, industrial gear boxes, etc.
(ii)The spur gears are mainly used for low speed applications.

8.  The teeth on helical gears are cut at
an angle to the face of the gear.
When two teeth on a helical gear
system engage, the contact starts at
one end of the tooth and
gradually spreads as the gears
rotate, until the two teeth are in full
engagement.

9. This gradual engagement makes helical gears operate
much more smoothly and quietly than spur gears. For
this reason, helical gears are used in almost all car
Transmission
Because of the angle of the teeth on helical gears, they
create a thrust load on the gear when they mesh.
Devices that use helical gears have bearings that can
support this thrust load.
 Helical Gear:

10. Fig. Helical Gear:

11.  Advantages of helical gears:
(i)The engagement is gradual, and hence the operation
is smooth and silent.
(ii)Suitable for high speed application.
(iii)The power transmitting capacity of helical gear pair
is higher than that of identical spur gear pair.
(iv)The efficiency of helical gear pair is high (96% to
99%).

12.  Limitations of helical gears:
(i)The helical gears are difficult to manufacture as
compared to spur gears.
(ii)The helical gears are costlier than the spur gears
(iii)The helical gears create axial load or thrust on the
shaft and the bearings.

13. Applications of helical gears
(i)The helical gears are used in high speed stages of
automobile gear boxes, machine tool gear boxes,
industrial gear boxes, etc.
(ii)The helical gears are used in high speed application like
steam and gas turbines.

14.  Rack and pinion gears are used to convert rotation (From the pinion)
into linear motion (of the rack). A perfect example of this is the
steering system on many cars. The steering wheel rotates a gear
which engages the rack. As the gear turns, it slides the rack either to
the right or left, depending on which way you turn the wheel. Rack
and pinion gears are also used in some scales to turn the dial that
displays your weight.

15. Bevel gears are useful when the
direction of a shaft's rotation
needs to be changed. They are
usually mounted on shafts that
are 90 degrees apart, but can be
designed to work at other
angles as well
The teeth on bevel gears can be straight, spiral or hypoid.
Straight bevel gear teeth actually have the same problem as
straight spur gear teeth -- as each tooth engages, it impacts the
corresponding tooth all at once.

16. Spiral Bevel Gear
These spiral teeth engage just like helical teeth
: the contact starts at one end of gear and
progressively spreads across the whole teeth

17.  Advantages of bevel gears:
(i) The bevel gears can transmit the power/motion
between two shafts which are at right angles.
(ii) The efficiency of bevel gear pair is high (95% to
98%).
(iii) The arrangement is very compact.

18.  Limitations of bevel gears
(i) The bevel gears are difficult to manufacture.
(ii)The cost of bevel gears is higher than spur and helical
gears.
(iii)The bevel gears are non-interchangeable
 Applications of bevel gears
(i)The bevel gears are used in differential gear box of
automobiles.
(ii)They are also used in industrial gear boxes where the
input and output shafts are required at right angles.

19.  Many worm gears have an interesting
property that no other gear set has: the
worm can easily turn the gear, but the gear
cannot turn the worm. This is because the
angle on the worm is so shallow that when
the gear tries to spin it, the friction
between the gear and the worm holds the
worm in place.
 This feature is useful for machines such as
conveyor systems, in which the locking
feature can act as a brake for the conveyor
when the motor is not turning
5.Worm gears:

20. Advantages of worm gears
(i) The worm gear drives are compact as
compared to spur, helical, or bevel gear
drives.
(ii) They can be used for high reduction
ratios, as high as 70:1 in small space
(iii)The operation of worm gear drive is
smooth
and silent.
(iv)The provision of self locking can also
be made.
(V) Tooth engagement occurs without
shock hence operation in quieter.

21.  Limitations of worm gear drives:
The efficiency of worm gear drive is low (45% to 95%). The
efficiency of worm gear drive decreases with increase in
reduction ratio. For the reduction ratio of 70:1, the efficiency is in the range of
45% to 50%.
1. In worm gear drive, due to frictional losses, considerable
amount of heat is generated. Therefore, effective cooling is
necessary.
2. The power transmitting capacity of the worm gear drive is comparatively
low.
3. The worm gear pair is costly as compared to other gear pairs.
4. The worm as well as worm gears are difficult to manufacture.
5. The worm gears are non-interchangeable.

22. Applications of worm gear drives
1. The worm gear drives are used in lifting or hoisting devices,
cranes, lifts, conveyors, etc.
2. They are used in all applications where high reduction ratio
is required.
3. The other gears used for connecting two non intersecting
and perpendicular axes.
4. shafts are hypoid bevel gears, skew bevel gears and
spiral or crossed helical gears.

23. Difference between Spur Gear and Helical
Gear:

24. Difference between Spur gear and Bevel Gear:

25.  Difference between Spur Gear and Worm and Worm Wheel:

26. Also from similar triangles O1MP and O2NP,
Therefore in order to have a constant angular velocity ratio for all
positions of the wheels, the point P must be the fixed point (called pitch
point) for the two wheels. In other words, the common normal at the
point of contact between a pair of teeth must always pass through the
pitch point. This is the fundamental condition which must be satisfied
while designing the profiles for the teeth of gear wheels. It is also known
as law of gearing.

27. Gear Terminology:

30. A gear train is two or more gear working together by meshing
their teeth and turning each other in a system to generate power
and speed. It reduces speed and increases torque. To create large
gear ratio, gears are connected together to form gear trains

35. When the axes of the first gear (i.e. first driver) and the
last gear (i.e. last driven or follower) are co-axial, then
the gear train is known as reverted gear train.
Let T1 = Number of teeth on gear 1,
r1 = Pitch circle radius of gear 1, and
N1 = Speed of gear 1 in r.p.m.
Similarly, T2, T3, T4 = Number of teeth on respective
gears,
r2, r3, r4 = Pitch circle radii of respective gears, and
N2, N3, N4 = Speed of respective gears in r.p.m.

38.  The rope drives are widely used where a large amount of power is to be transmitted, from
one pulley to another, over a considerable distance.
 The rope drives use the following two types of ropes:
 1.Fibre ropes, and 2.
 Advantages of Rope Drives:
 The fibre rope drives have the following advantages:
 1. They give smooth, steady and quiet service.
 2. They are little affected by out door conditions.
 3. The shafts may be out of strict alignment.
 4. The power may be taken off in any direction and in fractional parts of the whole
amount.
 5. They give high mechanical efficiency
 Wire ropes.