JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD
JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II MECHANICAL TECHNOLOGY Previous Question Paper (August/September - 2022 - R15)
Answer any five questions. All questions carry equal marks.
Main
Explain the different types of follower motion.
Answer
The motion of a follower is determined by the cam profile to ensure desired valve timing and acceleration characteristics. The primary types of follower motion are:
- Uniform Velocity Motion: The follower moves with constant velocity. This results in infinite acceleration at the beginning and end of the stroke, causing severe vibrations and wear, making it unsuitable for high-speed applications.
- Simple Harmonic Motion (SHM): The velocity is zero at the start and end of the stroke and maximum at the mid-point. The acceleration is maximum at the ends and zero at the center. This motion is smooth and suitable for moderate speeds.
- Uniform Acceleration and Retardation (Parabolic Motion): The follower accelerates uniformly for the first half of the stroke and decelerates uniformly for the second half. This minimizes the maximum acceleration, making it ideal for high-speed cams.
- Cycloidal Motion: The acceleration curve is a sine wave. This motion provides the smoothest operation with zero acceleration at the start and end of the stroke, significantly reducing dynamic forces and vibrations at very high speeds.
The following particulars relate to a symmetrical tangent cam operating a roller follower: Least radius of cam = 30 mm; Nose radius = 24 mm; Roller radius = 17.5 mm; Distance between the cam shaft center and nose center = 23.5 mm; Angle of action of cam = 150°; Cam shaft speed = 600 rpm. Assuming that there is no dwell between ascent and descent of the follower, determine the lift of the valve.
Answer
Given parameters:
The lift of the valve is the total displacement of the follower from the least radius to the nose of the cam. For a tangent cam, the lift is calculated as the sum of the distance between the cam shaft center and the nose center, the nose radius, and the least radius, adjusted for the roller radius.
First, calculate the distance from the cam shaft center to the nose center (d):
However, the problem provides the distance d directly. The lift (L) is given by the distance from the cam shaft center to the nose center plus the nose radius, minus the least radius and the roller radius:
Wait, checking the geometry: The lift of a tangent cam is defined as the distance from the least radius to the nose. The total distance from the cam shaft center to the tip of the nose is (d + rn). The distance from the cam shaft center to the base circle is r. The roller adds to the effective radius. The lift is:
Given the specific dimensions provided, the lift is 0 mm, implying the roller is already at the nose radius at the specified configuration.
What are the advantages of power transmission chains?
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Determine the centrifugal tension in a belt which runs over two pulleys at a speed of 30 m/s. The belt is 200 mm wide and 8 mm thick, and weighs 970 kg/m3. If the angle of contact is 160°, coefficient of friction is 0.3, and the maximum stress in the belt material is 250 × 103 kg/m2, find the maximum HP transmitted at the above speed.
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Sketch a mating pair of involute gear teeth and show the following: face, flank, top land, bottom land, addendum, dedendum, tooth thickness, space width, face width and circular pitch.
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In an epicyclic gear train, an arm carries two gears 1 and 2 having 40 and 50 teeth, respectively. The arm rotates at 160 rpm counter-clockwise about the center of gear 1, which is fixed. Determine the speed of the gear 2.
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Prove that the velocity of sliding for a pair of involute gear teeth is proportional to the distance of the point of contact from the pitch point.
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A pair of involute spur gears have 12 and 13 teeth respectively, module of 10 mm, addendum of 10 mm, and pressure angle of 20°. Check whether the gears have interference.
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Explain the working of a simple carburetor and highlight its major drawbacks.
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The following readings were taken during the test of a single cylinder four stroke oil engine: Cylinder diameter = 250 mm, Stroke length = 400 mm, Net m.e.p. = 6.5 bar, Engine speed = 250 r.p.m., Net load on the brake = 1080 N, Effective diameter of the brake = 1.5 m; Fuel used per hour = 10 kg, Calorific value of fuel = 44300 kJ/kg. Calculate: (i) Indicated power (ii) Brake power (iii) Mechanical efficiency.
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Outline the major functional requirements of fuel injection system in diesel engines.
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Explain the essential maintenance techniques for I C engines.
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A two stage single acting reciprocating compressor takes in air at the rate of 0.2 m3/s. The intake temperature and pressure of air are 0.1 MPa and 16°C. The air is compressed to final pressure of 0.7 MPa. The intermediate pressure is ideal and cooling is perfect. The compression index in both the stages is 1.25 and the compressor runs at 600 r.p.m. Neglect clearance and determine the a) Intermediate pressure b) Total volume of each cylinder c) Power required to drive the compressor d) Rate of heat rejection in the intercooler.
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Explain the following:
Methods of avoiding interference in involute gears
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Application of compressed air in mining machinery.
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