CPS Question and answers

List the inversions for double slider crank mechanism.​

Inversions of Double Slider Crank Chain :

1. Elliptical trammels.

2. Scotch yoke mechanism.

3. Oldham’s coupling.

Define centripetal and tangential acceleration.

Centripetal acceleration:

The centripetal acceleration is the rate of change of tangential velocity. When an object is moving with uniform acceleration in circular direction, it is said to be experiencing the centripetal acceleration.

Tangential acceleration:

Tangential acceleration is a measure of how the tangential velocity of a point at a certain radius changes with time. Tangential acceleration is just like linear acceleration, but it’s particular to the tangential direction, which is relevant to circular motion.

Define following terms with respect to cam and follower :

(i) Prime circle

(ii) Pitch circle

(iii) Pressure angle

(iv) Trace point

 

i. Prime circle: It is the smallest circle that can be drawn from the centre of the cam and tangent to the pitch curve. For a knife edge and a flat face follower, the prime circle and the base circle are identical. For a roller follower, the prime circle is larger than the base circle by the radius of the roller.

ii. Pitch circle: It is a circle drawn from the centre of the cam through the pitch points.

iii. Pressure angle: It is the angle between the direction of the follower motion and a normal to the pitch curve. This angle is very important in designing a cam profile. If the pressure angle is too large, a reciprocating follower will jam in its bearings.

iv. Trace point: It is a reference point on the follower and is used to generate the pitch curve. In case of knife edge follower, the knife edge represents the trace point and the pitch curve corresponds to the cam profile. In a roller follower, the centre of the roller represents the trace point.

Define self-energizing and self-locking brake. 

Self energizing & Self Locking brake

Rn x X = PL + μaRn

Rn = Normal reaction, P = Applied force, L = lever length

X = Distance of block from hinge, μ= coefficient of friction, a = distance of drum from hinge

In the above equation when frictional force adds to the breaking torque. In other words, the frictional torque and braking torque are in the same direction its a self locking brake.

In the above equation when X < μa, P becomes negative

Hence, P is not required for braking and brake gets applied on its own. It is called as self energizing brake.

List the methods to reduce the slip in belt and pulley.

Methods to reduce the slip in belt and pulley:

1. Vertical belt drive should be avoided.

2. In horizontal belt drive the upper side should be kept as loose side.

What are the limitations of shoe brake ?

Limitations of a shoe brake :

1. Heavy side thrust causes bending of the shaft.

2. More wear & tear as the contact surface is large.

State effects of imbalance in machine.

Effects of imbalance in machine

1. Imbalance imparts vibratory motion to the frame of the machine.

2. Produces noise which leads to human discomfort.

3. Detrimental effects on the machine performance & structural integrity of the machine foundation.

State law of gearing.

Gearing law (Law of gearing) :

Gearing law states that, "The law of gearing states that the angular velocity ratio of all Gears of a meshed gear system must remain constant also the common normal at the point of contact must pass through the pitch point."

Gearing law illustration

As illustrated in above animation the common normal at the point of contact passes through the pitch point. Gearing law must be followed in order to two gears transmit motion form one to another.

In order to have a constant angular velocity ratio for all positions of the wheels, it is must that the point P must be the fixed point (called pitch point) for the two wheels. In other words it can be said that , the common normal at the point of contact between a pair of teeth should always pass through the pitch point for  proper working.

This is the fundamental condition which must be satisfied while designing the profiles for the teeth of gear wheels, it is also known as the law of gearing.

Gearing law explination with diagram

State the function of flywheel in I.C. Engine.

A flywheel used in machines serves as a reservoir, which stores energy during the period when the supply of energy is more than the requirement, and releases it during the period when the requirement of energy is more than the supply. In other words, a flywheel controls the speed variations caused by the fluctuation of the engine turning moment during each cycle of operation.

Compare brakes and dynamometers. (any two points)

Compare Brakes & Dynamometers: A dynamometer is a mechanical device used to indirectly measure the power output of a prime mover like an engine or a motor. Examples: hydraulic brake dynamometer, eddy current dynamometer, prony brake dynamometer. A brake is a mechanical device usually found in automobiles that helps in decelerating a vehicle and brings it to a complete stop. Examples: internal expanding shoe brake, single and double shoe brake, simple and differential band brake.

(a) Define : (i) Spherical pair (ii) Higher pair

a) Single plate clutch b) Multi plate clutch c) Cone clutch d) Centrifugal clutch

ii) Classification of follower:

What do you mean by crowning of pulleys in flat belt drive ? State its use.

1. As no slip takes place, hence, perfect velocity ratio is obtained (Positive drive). 2. Chain drive gives high transmission efficiency (up to 98 %). 3. Chain drive may be used when the distance between the shafts is less. 4. Chain is made up of metal which would occupy less space as compared with belt or rope drive. 5. Ability to transmit power to several shafts by one chain. 6. Load on the shaft is less and long life.

Define fluctuation of speed and fluctuation of energy in case of flywheel.

Fluctuation of speed: It is the difference between the maximum and minimum speed of Flywheel. Fluctuation of speed = (N1 – N2) rpm N1 – maximum speed, N2 -- minimum speed Fluctuation of energy: It is the difference between the maximum and minimum energy of Flywheel. Maximum energy of Flywheel I ω1 2 Minimum energy of Flywheel = I ω2 2 Fluctuation of energy = I (ω1 2 - ω2 2 ) in N-m or J I – moment of inertia of flywheel = mk2 where, m – mass of the flywheel, kg and k - radius of gyration of flywheel, m2 ω1 – Maximum Angular velocity, rad/sec ω2 – Minimum Angular velocity, rad/sec

State the adverse effect of imbalance of rotating elements of machine.

The process of providing the second mass in order to counter act the effect of the centrifugal force of the disturbing mass is called balancing. In order to prevent the bad effect of centrifugal force of disturbing mass, another mass (balancing) is attached to the opposite side of the shaft at such a position, so as to balance the effect of centrifugal force of disturbing mass. This is done in such a way that the centrifugal forces of both the masses are made equal and opposite. Methods of balancing:  Balancing of rotating masses 1) Balancing of a single rotating mass by a single rotating mass in the same plane 2) Balancing of a single rotating mass by two masses rotating in the different planes * Disturbing mass lies in a plane between the planes of balancing masses * Disturbing mass lies in a plane on one end of the planes of balancing masses 3) Balancing of different masses rotating in the same plane 4) Balancing of different masses rotating in the different planes  Balancing of reciprocating masses

Define (i) Pressure angle (ii) Pitch point related to cam.

(i) Pressure angle: It is the angle between the direction of the follower motion and a normal to  the pitch curve. This angle is very important in designing a cam profile. If the pressure angel is too large, a reciprocating follower will jam in its bearing.
(ii) Pitch point: It is point on pitch curve having the maximum pressure angle.

Define:
(i) Coefficient of fluctuation of speed.
(ii) Coefficient of fluctuation of energy.

(i) Coefficient of fluctuation of speed: Coefficient of fluctuation of speed is defined as the  ratio of the maximum fluctuation of speed to the mean speed. It is denoted by C s.
Mathematically,
C s = (N 1 – N 2 ) /N
Where, N 1 = maximum speed in rpm;

N 2 =minimum speed in rpm; N = mean speed in rpm

(ii) Coefficient of fluctuation of energy: Coefficient of fluctuation of energy may be defined as the ratio of the maximum fluctuation of energy to the work done per cycle. It is denoted by Ce.
Mathematically,
Ce = Maximum fluctuation of energy/ Work done per cycle.

Draw line diagram of porter governor

Why is balancing of rotating parts necessary for high speed engines?

The high speed of engines and other machines is a common phenomenon now-a-days. It
is, therefore, very essential that all the rotating and reciprocating parts should be completely
balanced as far as possible. If these parts are not properly balanced, the dynamic forces are set
up. These forces not only increase the loads on bearings and stresses in the various members, but
also produce unpleasant and even dangerous vibrations. The balancing of unbalanced forces is
caused by rotating masses, in order to minimize pressure on the main bearings when an engine is
running.

Name different mechanisms generated from a single slider crank chain.

Different mechanism generated by single slider crank chain mechanism. 

a) Reciprocating engine, Reciprocating compressor

b) Whitworth quick return mechanism, Rotary engine,

c) Slotted crank mechanism, Oscillatory engine

d) Hand pump, pendulum pump or Bull engine

Define slip and creep in case of belt drive.

Slip --- Slip is defined as insufficient frictional grip between pulley (driver/driven) and belt. Slip is the difference between the linear velocities of pulley (driver/driven) and belt.

Creep ----- Uneven extensions and contractions of the belt when it passes from tight side to slack side. There is relative motion between belt and pulley surface, this phenomenon is called creep of belt.

State the effect of centrifugal tension on power transmission.

Effect of centrifugal tension on power transmission:

As the belt passes over the pulley with high velocity, centrifugal force is produced on the belt, which tends to act on the belt. This force tries to move the belt away from the pulley.

This force is given by,

T_C = m x V²

There is no effect of centrifugal tension on power transmitted.

State the adverse effect of imbalance of rotating elements of machine.

Adverse effect of imbalance of rotating elements:

a) Vibration, noise and discomfort,

b) Machine accuracy get disturbed,

c) Power losses,

d) More maintenance

Enlist the different type of follower motion.

Motion of the Follower :

1. Uniform velocity,                                                             2. Simple harmonic motion,

3. Uniform acceleration and retardation, and             4. Cycloidal motion.

State four conditions under which the ‘V’ belt drive is selected.

Conditions for ‘V’ Belt drive selection :

 1. Great amount of Power to be transmitted,

2. Requirement of the high velocity ratio (maximum 10).

3. Small Centre distance between the shafts

4. Positive drive requirement

5. Compact Space

State four applications of flywheel.

Applications of flywheel : Used in Internal combustion engines, press machines, mills, punching machines.

Why is balancing of rotating parts necessary for high speed engines ?

The high speed of engines and other machines is a common phenomenon now-a-days. It is, therefore, very essential that all the rotating and reciprocating parts should be completely balanced as far as possible. If these parts are not properly balanced, the dynamic forces are set up.

These forces not only increase the loads on bearings and stresses in the various members, but also produce unpleasant and even dangerous vibrations. The balancing of unbalanced forces is caused by rotating masses, in order to minimize pressure on the main bearings when an engine is running.

State any two types of motion of the follower.

 

The follower during its travel may have one of the following motions.

1. Uniform velocity,

2. Simple harmonic motion,

3. Uniform acceleration and retardation,

4. Cycloidal motion.

State any two advantages of V belt drive over flat belt drive.

Advantages -1. The V-belt drive gives compactness due to the small distance between the centres of pulleys.

2. The drive is positive, because the slip between the belt and the pulley groove is negligible.

3. Since the V-belts are made endless and there is no joint trouble, therefore the drive is smooth.

4. It provides longer life of 3 to 5 years.

5. It can be easily installed and removed.

6. The operation of the belt and pulley is quiet.

7. The belts have the ability to cushion the shock when machines are started.

8. The high velocity ratio (maximum 10) may be obtained.

9. The wedging action of the belt in the groove gives high value of limiting ratio of tensions. Therefore the power transmitted by V-belts is more than flat belts for the same coefficient of friction, arc of contact and allowable tension in the belts.

10. The V-belt may be operated in either direction with tight side of the belt at the top or bottom. The centre line may be horizontal, vertical or inclined.

Define stability and hunting of governor.​

Stability of governor : 

A governor is said to be stable when for every speed within the working range there is a definite configuration i.e. there is only one radius of rotation of the governor balls at which the governor is in equilibrium. For a stable governor, if the equilibrium speed increases, the radius of governor balls must also increase.

Hunting of governor :

A governor is said to be hunt if the speed of the engine fluctuates continuously above and below the mean speed. This is caused by a too sensitive governor which changes the fuel supply by a large amount when a small change in the speed of rotation takes place.

State any two adverse effects of imbalance.​

All the rotating and reciprocating parts should be completely balanced as far as possible. If these parts are not properly balanced,

The dynamic forces are set up.

These forces increase the loads on bearings and stresses in the various members.

Also produce unpleasant and even dangerous vibrations.

What is the necessity of clutch? State its types.

Necessity: A clutch is necessary for the transmission of power of shafts and machines which must be started and stopped frequently. Its application is also found in cases in which power is to be delivered to machines partially or fully loaded. The force of friction is used to start the driven shaft from rest and gradually brings it up to the proper speed without excessive slipping of the friction surfaces.

In automobiles, friction clutch is used to connect the engine to the driven shaft. It may be noted that -

1. The contact surfaces should develop a frictional force that may pick up and hold the load with reasonably low pressure between the contact surfaces.

2. The heat of friction should be rapidly dissipated and tendency to grab should be at a minimum.

3. The surfaces should be backed by a material stiff enough to ensure a reasonably uniform distribution of pressure.

Types :

1. Disc or plate clutches (single disc or multiple disc clutch),

2. Cone clutches, and

3. Centrifugal clutches.