Q1) What is automobile engineering. Discuss the general configuration of an Automobile?

A1) Automobile engineering is a branch of engineering dealing with the working components of automobiles and various types of methods to propel them. It can be defined as a vehicle which come into motion by itself with the use of engine and various components.

Examples: Van, jeep, scooter, truck, car, etc.

General Configuration of an Automobile

Fig: General configuration of an automobile.

The automobile consists of three important components:

Q2) Discuss the classification of an automobile with the help of suitable examples.

A2) The classification of an automobile in different basis are described as below: -

Classification of automobiles:

On Load basis:

–        like lorry, container trucks, etc.

–        like omni, tempo, etc.

–        like van, bus, car, etc.

On Wheel basis:

•         II wheeler

–        like: bike, scooters, scooties, etc.

•         III wheeler

–        like: tempo, auto rickshaw, etc.

•         IV wheeler

–        like: SUV, etc.

•         VI wheeler vehicle

–        like: container trucks, vehicle carrying trucks, etc.

On Fuel basis:

•         Petrol

–        like: bike, scooty, etc.

•         Diesel

–        like: buses, etc.

•         Electric

–        like: electric bike or scooty or car, etc.

•         Gas

•         e.g., CNG and LPG vehicles,

On Body basis:

•         Sedan with two and four doors

•         Van

•         Special purpose vehicle like ambulance, etc.

On Transmission basis:

On Engine Position basis:

–        like:  mostly all cars and trucks in India. 

Q3) Explain the important functions of an engine in an automobile?

A3) The various functions of an engine are as follow:

Fig: Working of a 4 – stroke SI engine.

Q4) Write short note on Frame/chassis of the vehicle.

A4)

Fig: Chassis or frame of a car.

Q5) Describe the Transmission System and its important elements?

A5) This system transfers the power from the engine to the wheels. The important function of this system is:

In manual transmission system, there is a clutch, gear box, a propeller shaft and final drive.

Gear Box:

Fig: Working of a gearbox (constant mesh)

Clutch:

•         The main function of the clutches is allowing the rider/driver to engage /disengage the engine and transmission.

•         As clutch gets engaged, power from the engine flows to the transmission through these clutches.

•         When there is a need for gear changing while movement, it allows temporary decoupling of engine with the wheels ensuring gears are shifted.

Fig: Single plate clutch

Q6) Write the important features of Final Drive?

A6) The important features are:

•         Final drive is the final stage in transmitting power from the engine to the wheels.

•         It also diminishes the speed of the drive shaft in comparison to wheels.

•         Final drive It also turns the propeller shaft drive 90 degree to drive the wheels.

•         This shaft comprises of small bevel pinion meshing with crown wheel. These crowning wheels provide rotary motion to rear axles.

•         There are two types of final drive, i.e., gear type and chain type.

Fig: Final drive and differential gearbox.

Q7) Explain the function and requirements of Braking System?

A7) The functions of a Braking system are:

•         The function of vehicle brake system is to halt or limit the speed of the vehicle or to prevent the movement when in immobile position.

•         All BSs use frictional force for their movement. Friction is the force that opposes the relative motion of the bodies which are in intimate contact with another and it constantly acts opposite to the moving force.

The following are the requirements that should be satisfied by the brakes:

Fig: Braking system and hydraulic lines of an automobile.

Q8) What is Steering System? Explain with the help of a suitable figure.

A8)

•         The steering wheel is placed at the driver seat in front of cabin. It is joined to the wheels to gives the steering control.

•         The main aim of the this is to provide angular motion to front side tyres so that automobile can move right/left.

•         It also provides directional stability to vehicle

In present time, some automobiles also work on power steering system. This system uses fluid pressure to decrease the steering effort.

Fig: Steering system.

Q9) Explain the Suspension System with the help of diagram.

A9) Suspension System

•         Suspension consists of different tyres, springs, shock absorbers and linkages that connects a vehicle to its wheels allowing a relative motion between the two. These systems must support ride quality and vehicle holding on the road.

•         Main function of the suspension system is to isolate the body of the vehicle from shocks and vibrations generated due to irregularities on the surface of roads.

•         The suspension system can be dependent or independent suspension system.

.

A suspension system also maintains the stability of the vehicle in pitching or rolling when the automobile is in motion

Fig: Suspension system.

Q10) Describe Power -Torque Characteristics with the help of a plot?

A10)

Fig: P & T Curve.

Torque:

It is defined as the force on a given point, which is exerted on the radius from that point. The S.I. Unit of torque is Newton - metre, while the S.I. Unit for WORK is Joule.

Power

Power is defined as the rate of doing work. Its S.I. Unit is Watt.

Power (in kW) = Torque x Speed / 9.5488

Torque is the basically the ability of doing work, while the power is how swiftly any task can be completed i.e., the power is the torque applied in a certain amount of time.

Rate of doing work is measured in Horsepower (HP). Statistically, HP is torque multiplied by rpm.

HP = T x rpm/5252

Where HP is horsepower, T is torque in pound-feet, rpm is rate of engine rotation in min, and 5252 is a constant that makes the unit’s jibe.

As such for making more power

i. more torque needs to be generated

Ii. engine must rotate at higher rpm

Iii. Both

P-T curve shows the relationship between power and torque at different engine speed. It helps in designing of an engine.

For designing an engine, optimal power curve is plotted for that particular application. After that from the design information, torque curve is plotted which will produce the desired power that is required (power curve). By evaluation of torque requirements against break mean effective pressure values you can determine the rationality of the aimed power curve.

As seen from the curve, the torque peak more often occurs at a significantly lower speed (rpm) than peak power peak. This is because the torque curve does not drop o (%-wise) as quickly as the speed is increasing (%-wise). In case of racing engines, to produce maximum avg power within the required speed (rpm) band it is desirable to operate the engine well beyond the power peak

Nonetheless, for engines operating in a relatively narrow speed band, i.e., aircraft, it is general requirement that the engine should generate maximum power at the maximum speed (RPM) which requires the peak torque to be nearly close to maximum speed (RPM).

Q11) How power can be measure? Explain the power required to run the pump.

A11) Measuring power

A dynamometer is a device which measure the power produced by an engine. It involves the use of different equipment like generator, an absorber generally eddies current type, water brake and other well-regulated equipment’s proficient of grossing power.

The control system of the dynamo (comprising of above-mentioned units) with the help of absorber calculate the exact the amount of torque produced by the engine at that instant, and then computes the RPM of the shaft. From these measurements, the power is calculated.

It then applies various factors (air temperature, barometric pressure, relative humidity) to correct the observed power to a value that would be measured under standard atmospheric conditions, called true power.

Pump running power

In the course of working with many different engine projects, we often hear the suggestion that engine power can be increased by using a "better" oil pump. An "improved" oil pump has higher pumping efficiency, and can, therefore, provide the required flow at the required pressure while consuming less power from the crankshaft to do so. It is true, the magnitude of the correction number is surprisingly small

Q12) What is the difference between Rolling and Air Resistance?

A12) Difference is discussed below:

Rolling Resistance

Fig: Direction of friction when force is applied on a wheel.

Rolling resistance of a vehicle is proportional to the component of weight normal to the surface of travel.

Where:

P = power (kW) 

Crr = coefficient of rolling resistance

M = mass (kg)

V= velocity

g= acceleration due to gravity

Frr= Rolling Resistance

Air Resistance

Fig: Air drag simulation on a car body

Variation of Air resistance and Rolling Resistance with speed

Fig: Variation of Fa and Fr with N.

Rolling and air resistance both increase with increase in vehicle speed leading to overall increase in total resistance.

Q13) What is Gradient Resistance and why it is important?

A13)

Fig: Distribution of Forces.

Significance

As the vehicle travels to move upward on a hill, weight component works in a direction opposite direction of motion and if some sort of energy is not provided to overcome this motion, the vehicle tends to slow down and move backwards.

If the vehicle is moving in upward direction at an angle(slope) θ

Weight of the vehicle (W) has 2 components:

The component parallel to surface on which vehicle is moving restrict the motion.

GR= W·Sin θ

Q14) Discuss Traction and Tractive Effort of an automobile.

A14) Traction of a vehicle is defined as the friction between a drive wheel and the surface it moves upon.

Q15) Show the different forces acting on the vehicle with a figure.

A15) The forces are shown below:

Fig: Types of forces in automobile.

Q16) How gear ratio can be determined?

A16) Gear Ratio Determination

Fig: A compound gear train.

The gear ratio can be calculated by dividing the number of teeth of the driving gear by the number of teeth of the driven gear or by dividing the output speed by the input speed.

Q17) A pair of gear A and gear B is in mesh, the gear A is driving and gear B is driven and both the gears have following arbitraries-

Gear A-

Number of teethes- 30

Diameter of gear- 20 cm

Angular velocity- 67cm/sec

Torque- 10 kg-cm

Gear B-

Number of teethes- 40

Diameter of gear- 27 cm

Angular velocity- 50cm/sec

Torque- 13.5 kg-cm

Find the gear ratio using all arbitraries.

A17) The gear ratio G can be calculated using all the arbitraries-

(i) Number of teethes-

Gear ratio (G) = 40/30

= 1.33~1.35

(ii) Diameter of gears-

Gear ratio (G) = 27/20

=1.35

(iii) Angular velocity-

Gear ratio (G) = 67/50

=1.34~1.35

(iv) Torque of gears

Gear ratio = 13.5/10

= 1.35

Q18) What are the different resistance encountered by a vehicle? Which factors influence them?

A18) The different resistances are:

Total Vehicular Resistance at Constant Velocity

TR= RR+AR (vehicle have constant velocity on level road)

TR= RR+AR + GR (vehicle have constant velocity on gradient)

AR = air resistance [N]

RR = rolling resistance [N]

GR = gradient resistance [N]

TR = total resistance [N]

The different factors influencing these resistances are:

Rolling resistance is affected by:

• Resistance due to deformation of wheel (90%)

• Tyre penetration and surface compression (4%)

• Slippage of tyre and Air circulation nearing wheel (6%)

• Others factors are: tyre width, diameter, temperature, material and design, inflation pressure and construction.

Air resistance comes into play when an object is passing through the air. Depending on the velocity of the moving vehicle, its area and shape, the resistance varies. Height, temperature, and humidity changes the density of air and, accordingly, its resistance.

The quicker a vehicle moves and larger its area, the higher the air resistance. Flying is a simple illustration where this air resistance can easily be seen. Parachutes fly in air since the surface area is adequately large to create optimum resistance that is required for pushing in upward direction.

Gradient resistance is affected by steepness of the surface, slope of the surface and the weight of the vehicle.