Constructional Details MCQ Quiz - Objective Question with Answer for Constructional Details - Download Free PDF

Explanation:

Wheel alignment:

• Wheel alignment is the positioning of the front wheel and steering mechanism to:
  • minimize tyre wear
  • reduce the driver’s effort to turn the vehicle
  • achieve self-centring after turning
  • achieve directional stability of the vehicle while running straight ahead.

Front-wheel alignment depends upon the following:

• Camber
• Castor
• Kingpin inclination
• Toe-in and Toe-out

Combined angle:

• The combined angle or included angle (1) is the angle between the vertical plane of the wheel centre line (2) and the kingpin centre line (3) called the steering axis.
• The combined angle is the sum of camber and kingpin inclination called steering axis inclination.

Kingpin inclination:

• Kingpins are mounted in such a way that they tilt inward.
• The angle between the centre line of the kingpin and the vertical line is called kingpin inclination.

Purpose of kingpin inclination:

• It provides directional stability along with the castor angle.
• It helps in the self-centring of wheels after negotiating a turn.

Camber:

• The inward or outward tilt of a wheel from the vertical is termed camber.
• The angle between the vertical line (1) from the central point of the tyre and the central line (2) of the tyre is known as the camber angle (3).
• When the wheels are tilted outward at the top it is called positive camber, and if tilted inward at the top, it is called negative camber.
• An equal camber angle is provided on both front wheels.
• With the positive camber wheels becoming vertical under load the tyre will have full contact with the road.
• If the positive camber is excessive then the tyre’s outer edge will wear out faster.
• If the negative camber is excessive the tyre’s inner edge will wear out faster.
• Unequal camber on both front wheels will result in wheel shimming at low speed (abnormal vibration).

Explanation:

Propeller shaft:

• The propeller shaft connects the gearbox and final drive.
• The pinion shaft of the differential is connected to the propeller shaft.
• One universal joint is used between the propeller shaft and the pinion shaft of the differential.
• Another universal joint with one slip joint is also used between the propeller shaft and the gearbox.
• The propeller shaft rotates at high speed and bears a heavy torque.
• So it is made of a strong steel tube.
• In some vehicles, a solid propeller shaft is also used.
• Vehicles having a larger wheelbase use two propeller shafts.
• Whenever the distance between the gearbox and rear axle is very large (example-passenger buses) more than one propeller shaft is used for torque transmission.
• The Centre support bearing is used to connect the two propeller shafts.
• A two-piece propeller shaft requires a center support bearing.
• If there is a large wheelbase, a long propeller shaft is needed.
• So a two-piece propeller shaft is used in such cases with a center support bearing.
• By incorporating this there is no sag or whirl. 

Explanation:

Clutch:

• A Clutch is a machine member used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped at will, without stopping the driving shaft.
• The clutch is located between the gearbox and the engine.
• The function of a clutch is to engage and disengage the power between the engine and gearbox.
• A clutch thus provides an interruptible connection between two rotating shafts.
• Clutches allow a high inertia load to be stated with small power.
• A popularly known application of clutch is in automotive vehicles where it is used to connect the engine and the gearbox.
• Here the clutch enables the crank and starts the engine disengaging the transmission and changing the gear to alter the torque on the wheels.
• Clutches are also used extensively in production machinery of all types.

Clutches must be designed principally to satisfy four requirements:

• The necessary actuation force should not be excessive.
• The coefficient of friction should be constant.
• The energy convened to heat must be dissipated.
• Wear must be limited to provide a reasonable clutch life.

 

Explanation:

Camshaft:

• The camshaft is used to convert the rotary motion into reciprocating motion with the help of the cam lobe.
• This reciprocating motion is transmitted to the valve through the tappet, push-rod, and rocker levers.
• The camshaft is driven by the crankshaft and it rotates at half the speed of the crankshaft since each valve opens once in every two revolutions of the crankshaft.
• The camshaft also drives the oil pump shaft. In petrol engines, the fuel pump and the distributor get their drive from the camshaft.

Construction of the camshaft:

• The camshaft (2) is either forged or cast with the cam lobes (1) one for each valve.
• The camshaft has a series of support bearings along its length.
• The cam surface is hardened for longer life. In some engines, the axis of the tappet/lifter (3) is slightly offset from the axis of the cam lobe (1).
• This offset gives a little rotation to the tappet/lifter when it moves up. So the bottom of the tappet/lifter (3) wears out uniformly.
• The lifter/tappet (3) rests on the cam lobe (1).
• The lifter (3) remains in its position on the base circle (4).
• When the cam rotates the lobe lifts the lifter (3).

Material for camshaft:

• Forged alloy steel

 

Explanation:

Gearbox (Manual transmission):

• A gearbox is used to get different torques and speeds which are required to overcome the following resistances.
  • Road resistance
  • Air resistance
  • Gradient resistance
  • Load on vehicle
• By engaging different gears, engine torque is increased while speed is decreased.
• In the top gear the r.p.m and torque of the engine and gearbox remain the same.

Types of gearboxes:

• Sliding mesh gearbox
• Constant mesh gearbox
• Synchromesh gearbox

Sliding mesh gearbox:

• In this gearbox, the gears are mounted directly on the main shaft (1).
• The gear slides on the main shaft with the help of the shifter yoke mechanism (7) to engage with the countershaft (2) gear.
• The gears on the clutch shaft (3) and countershaft (2) are fixed.
• The idler gear is always in mesh with the countershaft’s gear.
• To achieve reverse speed, the main shaft (1) gear is slided on the main shaft, to engage with the idler gear (4).
• To slide the gear on the shaft the shifter forks (7) directly sit on the main shaft’s (1) gear.
• The shifter forks are connected to the gear shift lever through the selector rods 8).
• In this type of gearbox, spur gears are always used, because the gear is slided on the shaft to engage with the countershaft gear.

 

The valve face angle is usually kept at 30° or 45° according to match with the seat angle to avoid leakage. The main function of valves is to open and close the inlet and exhaust passages of the cylinder.

Types of valves:

• Poppet-valves
• Rotary valves
• Reed valves
• Sleeve valves

Crankshaft have drilled oil passages through which oil flows from the main bearing to the connecting road bearings. Balancing of crank shaft is achieved by removing material in the crank web or adding weight to the shaft between centres in a special balancing machine.

Explanation:

Clutch:

• A Clutch is a machine member used to connect the driving shaft to a driven shaft, so that the driven shaft may be started or stopped at will, without stopping the driving shaft.
• The function of a clutch is to engage and disengage the power between the engine and gearbox.
• A clutch thus provides an interruptible connection between two rotating shafts.
• Clutches allow a high inertia load to be stated with small power.
• A popularly known application of clutch is in automotive vehicles where it is used to connect the engine and the gearbox.
• Here the clutch enables the crank and starts the engine disengaging the transmission and changing the gear to alter the torque on the wheels.
• Clutches are also used extensively in production machinery of all types.

Clutches must be designed principally to satisfy four requirements:

• The necessary actuation force should not be excessive.
• The coefficient of friction should be constant.
• The energy convened to heat must be dissipated.
• Wear must be limited to provide a reasonable clutch life.

The cylinder head is made of a single casting. It is bolted on the top of the cylinder block. It has passage for oil and water circulation. It also accommodates valves, spark plugs and heater plug.

Material: Cast iron, aluminium alloys

Types of cylinder head: According to valve arrangement, there are four types of cylinder heads.

• I head engine

• L head engine

• F head engine

• T head engine

The small end of connecting rod is fitted with a phosphor bronze bush and the small end is joined to the piston by a means of a piston pin passing through this bush.

On the other hand, precision bearings are used for camshaft fitted by press fit. These bushings are designed for radial load only.

Piston rings: There are two types of piston rings

1. Compression rings: These rings effectively seal the compression pressure and the leakage of the combustion gases. These are fitted in the top grooves. They also transfer heat from the piston to the cylinder walls. These rings vary in their cross-section. The following types of compression rings are used

• Rectangular Rings
• Taper-faced rings
• Barrel-faced rings
• Inside bevel rings
• Keystone rings

2. Oil control rings: The main purpose of an oil ring is to scrape the excess oil from the liner and drain it back to the oil sump during the downward movement of the piston. It prevents the oil from reaching the combustion chamber.

• The cam surface is hardened for longer life
• A camshaft is made of forged alloy steel
• The camshaft gets the drive from the crankshaft and rotates at half the crankshaft speed since each valve opens once in every two revolutions of the crankshaft

Requirements of a piston:

A piston should be:

• Able to withstand high temperature and pressure of combustion
• A good conductor of heat
• Light enough to minimise the inertia load

Pistons are made of cast iron, cast steel or aluminium alloy. Aluminium alloys are now most commonly used as they are lighter in weight and are good conductors of heat.

The piston pin or gudgeon pin connects the piston with the connecting road. It should be strong enough to transmit power and withstand pressure of combustion. Piston pins are made hollow to reduce inertia load due to the reciprocating motion.

Types of piston pins

• Fully floating piston pins
• Semi-floating piston pins
• Set screw type piston pins

Clutch is used to connect and disconnect transmission of power from the engine flywheel to the gearbox drive shaft.

Clutch is used to connect and disconnect transmission of power from the engine flywheel to the gearbox drive shaft.

Clutch consists of driven and driving shafts. A clutch cover is mounted on the flywheel by a set of screws. A pressure plate presses the clutch plate against the flywheel by the pressure of springs. The clutch plate hub is splined on the gearbox drive shaft. The clutch plate rotates along with flywheel and power is transmitted to the drive shaft. When the clutch pedal is pressed, the release bearing pushes the thrust plate through the linkages.