“Develop success from failures. Discouragement and failure are two of the surest stepping stones to success.”
Semester – 3rd Sub – B.M.E Branch – Printing Technology
ASSIGNMENT – 1
Q.1 Define carburettor with the help of neat diagram? Ans. A device for atomising and vaporising the fuel and mixing it in different proportions under all conditions of load in the engine cylinder is known as carburettor.
Carburettor is used where spirit fuel like petrol or alcohol is used.
The process of breaking up and mixing gasoline with air in required proportion is called carburetion.
Construction and principle of operation: A simple carburettor consists of the following main components:
(i) Float chamber: It has for the storage of petrol. The arrangement is such that when the oil reaches the required level, the needle valve closes the intake passage and the supply of fuel to the chamber is cut off. When the level of petrol falls, the float also goes down thus opening the intake passage again; more petrol enters the chamber. The function of float chamber is to maintain a definite level of petrol.
Q.2 What is a gear train? Distinguish between simple gear train and compound gear train?
Ans. A gear train is any combination of gear wheels by means of which motion is transmitted from one shaft to another shaft.
(i) Simple gear train: In this gear train, each shaft carries one gear wheel only. With the exception of the first and the last gear wheel in the train, each wheel acts both as a following and driven.
So, if N₄ / N₁ = T₁ / T₄ (N = speed, T = No. of teeth in each gear)
That means the ratio of the speed of revolution per minute of gear wheels 1 and 4 is inversely proportional to the ratio of the number of teeth on them.
(ii) Compound gear train: In this gear train each shaft except the first and the last ones carries two gears wheels. Such a train is used when the velocity ratio is very large and one of the wheels of a simple gear train needs to be so small it would not be practically satisfactory to make and use it in that situation.
So, N₄ / N₁ = (T₁ / T₂) × (T₃ / T₄)
Thus, the velocity ratio of a compound gear train is therefore given by the ratio: = Product of numbers of teeth on drivers/ Product of number of teeth on followers.
Q.3 What is the working principal of belt drive? compare flat belt and drive with a v-belt drive?
(a) Belts are most common means of transmitting power from one shaft to another shaft. The shaft from which motion is transmitted is known as driving shaft and its pully as driven or driven shaft. The transmission of power is caused by the frictional grip between the contact surface of the pulleys and the belt.
Flat belt drive
V-belt drive
Q.4 In a simple gear train the gear wheels 1, 2, 3 and 4 have 40, 50, 80 teeth respectively. If the speed of wheel 1 is the RPM (Rotation per minute) calculate.
(a) R.P.M of the fourth wheel ⇒ The speed of fourth wheel:
We have, N₄ = ? r.p.m, T₁ = 80, T₄ = 40 velocity ratio (V.R) of the train = N₁ / N₄ = T₁ / T₄
⇒ N₁ / N₄ = 80 / 40 ∴ (given T₁ = 80, T₄ = 40)
⇒ 2 = N₁ / N₄ ⇒ N₄ = 60 r.p.m
The speed of fourth wheel = 60 r.p.m
(ii) V.R of the simple gear train. ⇒ V.R of the simple gear train = N₄ / N₁ = T₁ / T₄
= 80 / 40 = 2 = 1/2 Ans
Q.6 Write short Note:
(a) Magneto Ignition: A small electric generator containing a permanent magnet and used to provide high-voltage pulleys especially (formerly in the ignition system of internal combustion engine. An ignition magneto, that provided current for the ignition system of a spark ignition engine such a petrol engine. It is called magneto ignition.
(b) Lubrication of I.C engine: It is quite a hard fact that when two parts are in moving contact with each other, heat will be produced due to friction. The heat produced due to friction reduce the power transmission and cause great wear and tear of the engine parts. To minimise the friction and cool down the bearing surfaces lubricant such as oil or grease is introduced between the contact surface. This process is known as lubrication. Thus, lubrication is necessary to reduce heat produced by friction.
(c) Spark ignition engine: Spark ignition engine is also called petrol engine. In this engine have a spark plug used to ignition the mixture of air and petrol. In this engines when the piston reaches the T.D.C. It being moved down. The inlet valve opens and exhaust valve closed and a fresh mixture of air and petrol sucked inside the engine cylinder. When the mixture is compressed by the piston the mixture has very high charge. After that the spark plug produced a spark and the mixture is ignition a very high rate of heat is produced and the heat is converted into mechanical energy. So now engine is ready to work. That why petrol engine is also called ignition engine. It is the spark ignition engine.
Q.7 In a simple gear train of wheel having 4 wheels, the speed of 1st, 2nd, 3rd & 4th respectively are 300 rpm, 250 rpm, 200 rpm & 150 rpm.
Determine the V.R. Also determine the diameter of 1st wheel if the diameter of 4th wheel is 36 cm.
Given: N₁ = 300 rpm N₂ = 250 rpm N₃ = 200 rpm N₄ = 150 rpm
V.R = Speed of last wheel / Speed of first wheel = 150 / 300 = 1/2
Also given: Diameter of 4th wheel = 36 cm Diameter of 1st wheel = D₁
V.R = D₄ / D₁
1/2 = 36 / D₁
⇒ 2 × 36 = D₁ ⇒ D₁ = 72 / 3 = 24 cm