This post covers the unit wise important 2 marks questions with answers for the subject of Design of Transmission systems, Make it for your reference to study at the examination.
ANNA UNIVERSITY,CHENNAI
DEPARTMENT OF MECHANICAL ENGINEERING
SIXTH
SEMESTER / III YEAR
ME6601 – DESIGN OF TRANSMISSION SYSTEM
PART-A
1. How is a Wire rope
specified?
Ans: They are
specified by the no. of strands & the no. of wires in each strand.
2. Sketch the cross
section of a V-belt and label its important parts.
Ans: Refer pg. no.
2.1 Dots by V.Jayakumar
3. Why is the face of a
pulley crowned?
Ans: The crowning
tends to keep the belt in centre on a pulley rim while in motion.
4. What are the five parts
of roller chain?
Ans: Pin link,
Roller link, Pins, Bushes & Roller
5. Give the relationship
of ratio of tensions in a V-belt drive.
Ans: T1/T2
= e μα.cosecβ
6. What is a silent chain?
In what situations, silent chains are preferred?
Ans: i ) Inverted
tooth chains are called silent chains because of their relatively quiet
operation.
ii)
They are preferred for high-power, high speed & smooth operation.
7. Define maximum tension
in a belt.
Ans: Tension on
tight side of the belt + Centrifugal tension
8. Give the condition for
maximum power transmission in terms of centrifugal tension in case of belt
drive.
Ans: The power
transmitted shall be maximum when the centrifugal tension (Tc) is
one third of the maximum belt tension (T).
9. Why tight side of the
flat belt should be at the bottom side of the pulley?
Ans: Because the
driving pulley pulls the belt from bottom side and delivers it to the upper
side. So it is obvious that the bottom side of the belt is tight.
10.
What is meant by ‘chordal action of chain’?
Ans: When chain
passes over the sprocket, it moves as a series of chords instead of a
continuous arc as in the case of a belt drive. It results in varying speed of
the chain drive. This phenomenon is known as chordal action.
UNIT -II
PART-A
1. Mention a few gear
materials.
Ans:
Metallic
gears – steel, cast iron
Non-Metallic gears – wood, compressed
paper & synthetic resins
2. State an advantage and
disadvantage of helical gear.
Ans: Advantage:
Produce less noise than spur gears
Dis Advantage: Subjected to axial thrust
loads
3. Why is tangential component
of gear tooth force called useful component?
Ans: Because it
transmits power.
4. Compare the contact
between mating teeth of spur and helical gears.
Ans: i) In spur
gears the line of contact is parallel to the axis of rotation. The total length
of contact line is equal to the face width.
ii)
In helical gears the line of contact is diagonal across the face of the tooth.
The total length of contact line is greater than the face width. This lowers
the unit loading & increases load carrying capacity.
5. What is backlash in
gears?
Ans: It is the
difference between the tooth space and the tooth thickness along the pitch circle.
6. What is the advantage
of helical gear over spur gear?
Ans: i) Helical
gears produce less noise than spur gears.
ii)
Helical gears have a greater load capacity than equivalent spur gears.
7. Why is a gear tooth
subjected to dynamic loading?
Ans: Inaccuracies
of tooth spacing, Irregularities in
tooth profiles, Misalignment between bearings.
8. State the law of
gearing or conditions of correct gearing.
Ans: It states that
for obtaining a constant velocity ratio, at any instant of teeth the common
normal at each of contact should always pass through a pitch point, situated on
the line joining the centres of rotation of the pair of mating parts.
9. What are the commonly
used gear tooth profiles?
Ans: Involute &
Cycloidal
10.
State
about herring bone gear.
Ans: The double
helical gears connecting two parallel shafts are known as herringbone gears.
They are used in heavy machinery and gear boxes.
UNIT -III
PART-A
1. When do we employ
crossed helical gear?
Ans: A pair of
crossed-helical gears also known as spiral gears are used to connect and
transmit motion between two non-parallel and non- intersecting shafts. As the
contact between the mating teeth is always a point, these gears are suitable
only for transmitting a small amount of power.
2. Mention two
characteristics of hypoid gear.
Ans: They are
similar in appearance to spiral-bevel gears. Their pitch surfaces are
hyperboloids rather than cones. Axis of pinion is offset from the axis of the
gear.
3. What are the various
forces acting on a bevel gear?
Ans:Tangential
force, Axial force & Radial force
4. Usually worm is made of
hard material and worm gear is made of softer material – justify.
Ans: A material
strength is set so that an amount of wear of the worm becomes larger that of
the worm wheel.
5. When is bevel gear
preferred?
Ans: They are used
to transmit power between two intersecting shafts.
6. Calculate the angle
between the shafts of a crossed helical gears made of two right handed helical
gears of 15˚ helix angle each.
Ans:Shaft angle, Ө =
β1 + β2 = 2β = 2 (15˚) = 30˚
7. State the use of bevel
gears.
Ans: They are used
to transmit power between two intersecting shafts.
8. State the advantage of
worm gear drive in weight lifting machine.
Ans:The worm gear
drives are irreversible. It means that the motion cannot be transmitted from
worm wheel to the worm. This property of irreversible is advantageous in load
hoisting applications like cranes and lifts.
9. Why is the crossed helical
gear drive not used for power transmission?
Ans:As the contact
between the mating teeth of crossed helical gears is always a point, these
gears are suitable only for transmitting a small amount of power. That’s why
mostly these gears are not used for power transmission.
10.
Why is the efficiency of a worm gear drive
comparatively low?
Ans: Because of power
loss due to friction caused by sliding.
UNIT -IV
PART-A
1.
What
are the points to be considered while designing a sliding mesh type of
multi-speed gear box?
Ans: i) The
transmission ratio in a gear box is limited by ¼ < i < 2
ii)
Speed ratio of any stage should not be greater than 8.
2.
Which
type of gear is used in constant mesh gear box? Justify.
Ans: Helical gears
are used in constant mesh gear boxes to provide quieter and smooth operation.
3.
Compare
sliding mesh and synchromesh gear box.
Ans: sliding mesh gear box: It derives its
name from the fact that the meshing of the gears take place by sliding of gears
on each other. With sliding mesh gear box, double de-clutching is necessary to
bring the two sets of dog teeth to the same speed so that they can be slid into
engagement quietly.
synchromesh gear box:
To eliminate the need to de-clutch, the synchromesh gear box was introduced.
The basic gear box is laid out in the same manner as the constant mesh, but
with the addition of a cone clutch fitted between the dog and gear members.
4.
Where
is multi-speed gear boxes employed?
Ans: They are
employed wherever the variable spindle speeds are necessary.
5.
Name
the series in which speeds are arranged in multi-speed gear boxes.
Ans: Basic series of
preferred numbers are R5, R10, R20, R40 & R80.
6.
List
six standard speeds starting from 18 rpm with a step ratio 1.4.
Ans: For the step ratio Φ = 1.4, the R20 series,
the standard speeds are 18, 20, 22.4, 25, 28 & 31.5 rpm.
7.
Sketch
the kinematic layout of gears for 3 speeds between two shafts.
Ans: Refer pg.no:
9.11 Dots by V.Jayakumar
8.
Differentiate
ray diagram and structural diagram.
Ans: Ray diagram is
a graphical representation of the structural formula.
Structural
diagram is a kinematic layout that shows the arrangement of gears in a gear
box.
9.
List
out the basic rules to be followed for optimum gear box design.
Ans: i) The
transmission ratio in a gear box is limited by ¼ < =i < 2
ii)
Speed ratio of any stage should not be greater than 8.
10.
What is
step ratio? Name the series in which speeds of multi-speed gear box are
arranged.
Ans: When the
spindle speeds are arranged in geometric progression, then the ratio between
the two adjacent speeds is known as speed ratio.
Basic
series are R5, R10, R20 & R40.
UNIT -V
PART-A
1.
Name
the profile of cam that gives no jerk.
Ans: Circle –arc cam gives no jerk. Because the
derivative of acceleration of cam is zero.
2.
Give
the reasons for left and right shoes of the internal expansion brakes having
different actuating forces.
Ans: Depending upon the direction of the drum
rotation, one shoe would be a leading shoe and another shoe is a trailing shoe.
The leading shoe is self energizing whereas the trailing shoe is not. In the
leading shoe, the friction force helps the applied force and hence more
actuating force than the trailing force.
3.
What
are the effects of temperature rise in clutches?
Ans: i) Excessive
surface temperature results in premature clutch failure.
ii) May cause the individual plates to be welded
together in metal clutches.
iii)
May cause excessive wear in non-metal clutches.
4.
What
is the significance of pressure angle in cam design?
Ans: The pressure
angle is very important in cam design as it represents steepness of the cam
profile. If the pressure angle is too large, a reciprocating follower will jam
in its bearings.
5.
State
the advantage of cam mechanisms.
Ans: Cams are used
for transmitting desired motion to a follower by direct contact. Cam mechanisms
are used in the operation of IC engine valves.
6.
How
the ‘uniform rate of wear ‘assumption is valid for clutches?
Ans: In clutches,
the value of normal pressure, axial load for the given clutch is limited by the
rate of wear that can be tolerated in the brake linings. Moreover , the
assumption of uniform rate wear gives a lower calculated clutch capacity than
the assumption of uniform pressure. Hence clutches are usually designed on the
basis of uniform wear.
7.
Name
four profiles normally used in cams.
Ans: Uniform
velocity, Simple harmonic motion, Uniform acceleration & retardation,
Cycloidal motion.
8.
Under
what condition of a clutch, uniform rate of wear assumption is more valid?
Ans: If the clutch is old one.
9.
When
do we use multiple disk clutches?
Ans: It is used when
large amount of torque is to be transmitted. In a multiplate clutch, the number
of frictional linings and the metal plates are increased which increases the
capacity of the clutch to transmit torque.
10.
Differentiate
between self-energizing and self-locking brakes.
Ans: When the
frictional force is sufficient enough to apply the brake with no external
force, then the brake is said to be self-locking
brake.
When
the frictional force helps in applying the brake, then the brake is said to be self-energised brake.
