VI- Semester Diploma Examination

Course Title: Automotive Mechanics

Time: 3 Hours]                                                                                               [Max     Marks:     100

Note: Answer any SIX from Part A and any SEVEN from Part B

PART-A                                                                                                                        6x5=30 marks

1.       3. A petrol engine working on Otto cycle has a clearance volume of 20% of the stroke volume. The engine consumes 8.17 liters of petrol per hour when developing 23.5 kW i.p. The specific gravity of petrol is 0.76 and its heating value is 43,900 kJ / kg. Determine the indicated thermal efficiency of the engine. Take γ=1.4 for air

1.       Explain any one dynamometer with a neat sketch

2.       Explain with equation the torque transmitted through the clutch.

3.       List different terms involved in terminology of spur gear

4.       Define: Speed ratio, Gear ratio and diametrical Pitch

5.       Explain Ackerman steering mechanism.

6.       List the requirements of braking

7.       Explain the brake fade

8.       Find the rpm of the engine when the vehicle is moving at 60 Kph in top gear. Take the rear axle reduction to be 4.2:1 and the diameter of the wheels as 500mm

PART-B                                                                                                                 7x10=70 marks

1. The following readins were noted for a 4-cylinder, 4-stroke engine:

Diameter= 101 mm.

Stroke= 114 mm.

Speed= 1600 r.p.m.

Fuel consumption= 0.204 kg/min.

Heating value of fuel= 41800 kJ / kg

Difference in tension on either side of brake pulley= 378N

Brake circumference = 3.35m

Assume a mechanical efficiency =83%, calculate

I) Brake thermal efficiency II). Indicated thermal efficiency

III). Mean effective pressure of cylinder. IV). Petrol consumption per b.kWh.

2. An eight-cylinder automobile engine of 85.7 mm bore and stroke 82.5mm and with a compression ratio of 7:1 is tested on dynamometer which has an arm of 0.5335 m, long the dynamometer scale reading 400N and the speed of the engine 4000 r.p.m. During the ten minutes run the fuel consumption was 4.55 kg of gasoline the heating value of fuel was 45980kJ/kg. The quantity of air supplied was 5.44 kg/min at a pressure of 10x104 Pa and at temperature of 293k.find the following

(a)BP developed

(b) The b.m.e.p. (c) the b.s.f.c.,

(d) The brake thermal efficiency,

(f) The volumetric efficiency, (g) the air consumption, (g) The air-fuel ratio.

3.      A plate clutch has three discs on the driving shaft and two discs on the driven shaft, providing four pairs of contact surfaces. The outside diameter of the contact surfaces is 240 mm and inside diameter 120 mm. Take µ = 0.3, find the total spring load pressing the plates together to transmit 23 kW power at 1575 revolution per minute. If there are 6 springs each of stiffness 13 kN/m each of the contact surfaces has worn away by 1.25 mm, find the maximum power that can be transmitted, assuming uniform wear.

4.      In a constant mesh gearbox the clutch shaft pinion has 14 teeth and a lay shaft gear has 32 teeth. The number of teeth in the lay shaft gear wheels is 16, 19 and 21. The differential drive pinion has 14 teeth and crown pinion has 62 teeth. The road wheel diameter is 0.65 m. If the engine is running at a constant speed of 3200 rpm, find the various speeds of the vehicle in respective gears.

The distance L between the pivots of a car is 1.27 m. The knuckle arms are 0.165 m long. The angle between the knuckle arm and the longitudinal axis of the car in the straight ahead position is 20°. The 3.      track is 1.42 m and L is 45% of the wheelbase. Find the radius of the path near side front wheel for correct steering to the right.

4.      In a shoe-brake with leading and trailing shoes, the total actuating force of 471 N acts at a distance of0.15 m from the pivot of the shoes which is 0.075 rn from the axis of the drum of radius 0.09 m? The shoes have symmetrical lining with coefficient of friction 0.45. If the effective radius of the friction force is 0.1 m, calculate the total braking torque, when

(a) The actuating mechanism gives equal forces to the shoes; (b) when the actuating mechanism gives the shoes equal displacement

5.      A bus weighing 124587 N is to be kept at a constant speed of 32 km/hr when going down a 3 km long slope (tan ϴ = 0.1). Suggest if the brakes should be used in this operation. If there are brakes on all four wheels and if the weight is shared equally by the wheels, calculate the heat dissipated at each brake when the brakes are used to control and limit the speed to 32 km/hr.

6.      For a motor vehicle, the rolling resistance is given by, 13.6 + 0.6965 V and the air resistance by the expression 0.0827 V2 the resistance being in N and V the speed in km/hr. If the transmission efficiency is 88%, calculate the required for a top speed of 128 km/hr assuming that the engine torque at 48 km/hr in top gear is 25% more than that at 128 km/hr and that the vehicle inertia corresponds to a weight of 17805N; calculate the acceleration in m/s2 at 48 km/hr.

7.      A car of weight 13341.6 N is to be provided with an engine. The gear ratio is 3.8: 1, the wheels are 0.61 m diameter and a transmission efficiency of 92% may be assumed. The rolling resistance on good macadam road is 13 N per 1000 N of weight and air resistance is equal to 0.06023 V2, where V is the forward speed in km per hour. The total inertia of the car may be assumed to be equivalent to a weight of 17795.3 N. The car has to have a maximum acceleration of 0.76 m/s2 at 56 km/hr. Calculate(i) the engine speed at 56 km/hr ;(ii) the engine power which is needed at the above speed ;(iii) the load which the car can pull on level in a trailer if the trailer weighs 4448.8 N at 54 km/hr.

8.      a) List and explain the resistances offered against the movement of vehicle.

        b) Deduce the relationship between engine revolutions and vehicle speed 


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