The Internal Combustion Engine (IC Engine) is a heat engine that converts chemical energy of fuel into mechanical energy.
Chemical energy of a fuel is first converted into thermal energy by means of combustion with air inside the engine. This thermal energy is again converted into useful work through mechanical mechanism of the engine.
Most of the IC Engines are reciprocating engines having piston that reciprocate back and forth in cylinders within the engine.
*IC ENGINE COMPONENTS:
The main components of a four stroke cycle engine are cylinder, piston, connecting rod, piston rings, cam shaft, crank shaft, inlet and outlet valves, fuel injector, cylinder head, push rod, cam follower, valve spring, big end bearing, etc.,.
The IC Engine used in heavy vehicles like bus is six cylinder four stroke diesel engine.
The piston reciprocates inside the cylinder. Piston rings are inserted in the circumferential grooves of the piston. The cylinder and cylinder head are bolted together.
The reciprocating motion of the piston is converted into rotary motion of the crankshaft by means of a connecting rod and crank. The small end of the connecting rod is connected to the piston by a gudgeon pin or piston pin. The big end of the connecting rod is connected to the crank pin.
*Cylinder Block:
*It is the main body of an engine which contains cylinders.
*The piston reciprocates inside the cylinder to develop power.
*The cylinders are accurately finished to accommodate pistons.
*During combustion, high pressure and temperature will be developed inside the cylinder.
*It is made of grey cast iron.
*The cylinder block is provided with water jackets for circulation of cooling water in water cooled IC Engines.
Reconditioning:
*Reconditioning of cylinder block (or) an engine is needed above running over 5 lakhs kilometer. In cylinder block, diameter of cylinder is checked for locality. If needed boring is done.
Cylinder Head:
*The cylinder head is bolted to the top of the cylinder block. It houses the inlet and exhaust valves through which the charge is taken inside of the cylinder and burnt gases are exhausted to the atmosphere from the cylinder. It also contains fuel injector and cooling water jacket. The materials used for cylinder heads are cast iron.
Crank Case:
*It may be cast integral with the cylinder block.
*It supports the crankshaft and camshaft with the help of bearings.
*It is also made of cast iron.
Oil Sump or Oil Pan:
*Oil Sump is fitted at the bottom of crankcase by using gasket.
*It contains lubricating oil.
*A drain plug is provided to the oil sump to drain out the oil.
*It is made up of pressed steel sheet.
Reconditioning:
*Oil Sump is checked for cracks to avoid leakage.
Piston:
*It is a cylindrical shaped mass that reciprocates inside the cylinder.
*The top of the piston is called as crown and sides are called as skirt.
*It has grooves to hold piston rings and oil ring.
*It is opened at the bottom end and closed at the top.
*Piston is made of cast iron, aluminium alloy, cast steel.
*The firing order for HINO Engines which are used in BS1, BS2, BS3 are 1-4-2-6-3-5
*The main function of the piston are
*To transmit the force by explosion to the crankshaft.
*To form a seal, so that the high pressure gases in the combustion chamber do not escape into the cylinder.
*To serve as a guide and a bearing for small end of the connecting rod.
Reconditioning:
*Check for cracks in piston and make another groove on the top.
*Grooves are to stop the pressure leakage.
Piston Rings:
Fig.2.4. Compression Ring and Oil Ring
*They are used to maintain air tight sealing between piston and cylinder to prevent gas leakages.
*Piston rings are fitted in the grooves which are provided in the top portion of the piston skirt.
*There are two types of piston rings used in a piston. They are
Compression Ring:
*These rings provide an effective seal for the high pressure gases inside the cylinder. Each piston is provided at least with two compression rings.
Oil Ring:
*These rings wipe off the excess oil from the cylinder walls. It also returns this excess oil to the oil sump through the slots provided on the rings. Piston rings are generally coated with Chromium or Cadmium.
Connecting Rod:
*It is used to connect the piston and crankshaft with the help of bearing.
*It is usually in I-Section.
*Its small end is connected with the piston by the piston pin and its big end is connected to the crank by the crank pin.
Crankshaft:
*It is used to convert reciprocating motion of the piston into rotary motion. The crankshaft can be held in position by the main bearings.
*Flywheel is mounted at the rear end of the crankshaft.
Counter Weights are provided to keep the system in perfect balance.
Reconditioning:
*For HINO Engine, standard diameter for connecting rod journals is 61.95 mm. In reconditioning, it can be reduced upto 60.95 mm by (0.25+0.25+0.25+0.25) four times.
*Fillet radius also reduced. This process is done by special grinding machine.
*The cracks are checked by using ultraviolet ray machine.
Camshaft:
*It is used to convert the rotary motion of the camshaft into linear motion of the follower.
*It operates the inlet and exhaust valves through rocker arms.
*It has so many cams as the number of valves in an engine.
*It is rotated at half of the speed of the crankshaft.
Engine Valves:
*Valves are used for closing and opening passage of the cylinder.
*There are two valves in an engine cylinder namely inlet and exhaust valves.
*Valves are operated by cam and rocker arm mechanism.
*Inlet Valves are larger than the Exhaust Valve.
*Valve face angle is generally kept 45⁰ or 30⁰.
COOLING SYSTEM:
*Cooling system reduces the heat of the engine.
Coolant:
*Coolant is an oil based liquid used in the water cooling system
*It acts as a cooling medium.
Radiator:
*Water cooling system is called as Radiator. In this system engine cylinders are surrounded by water jackets through which the cooling liquid flows.
Heat transferred from the cylinder walls into liquid. The liquid goes to the radiator where the liquid losses its heat by the air.
Reconditioning:
*While reconditioning the leakage should be checked.
*If any leakage that should be welded or the tube should be blocked.
Water pump:
*A pump is necessary for the forced circulation of engine cooling System.
The pump is mounted at the front end of the engine and is driven by crank-shaft through a ‘V’ belt.
LUBRICATION SYSTEM:
For the friction free running of inner part of the engine, lubrication system plays a vital role. If friction increases the temperature of the engine also increases. So, the lubrication system is installed. There are two types of lubrication system. They are as follows:
Splash System:
A Scoop is made in the lowest pall of the connecting rod and oil is stored in the oil pump.
Pressure System:
In pressure system, an oil pump takes oil from the pump through a strainer and delivers through the strainer and filter to the main oil gallery at a pressure of 200 to 400 kPa.
FUEL SUPPLY SYSTEM:
The fuel supply is done through fuel injection pump.
Fuel Injection Pump:
The function of the fuel injection pump is to deliver accurately metered quantity of fuel under high pressures at the correct sequence, to the injector(nozzle) fitted on the each cylinder. The injection pressure generally employed in case of automotive fuel injection range from 7 to 30 MPa. In some systems injection pressures can be as high as 200mpa
Reconditioning:
The filters are thoroughly cleaned. If any wear the filter should be changed.
The casing should be checked for any cracks.
Fuel Injector:
This is also known as nozzle, atomizer or fuel valve. Its function is to inject fuel in the cylinder in properly atomized form and in proper quantity.
STORAGE BATTERIES:
Storage battery is perhaps the most important comport of the on tire electrical system of a vehicle.
It gives power to the starting motor. Also it gives power to all electrical system when engine is in off condition. The different parts in the batteries are as follows:
Container
Separators
Cell covers
Electrolyte (dil.H2SO4)
In buses, two 12V Batteries are connected in series to get 24V.
Reconditioning:
By adding electrolyte in an exact dilute condition and check the separator condition and plate’s effectiveness.
STARTING MOTOR (SELF-MOTOR):
Starting motor used to give initial rotating moment to the fly wheel. Thus engine gets started.
When given positive and negative of battery actuates the armature, the armature starts rotating and when self-button is pressed, there is signal along the solenoid section which indulge in proper & horizontal motor until the time of the button release time.
When the flywheel starts rotating, the pinion from the self-motor disengage from the flywheel.
ALTERNATOR:
Alternator gets rotary moment from crank-shaft by means of ‘V’ belt.
It gives current to electrical system while engine running.
The battery charged with the current from alternator.
Alternator is a device which is used to convert mechanical energy to electrical energy where DC to AC Conversion takes place.
When the self button is pressed the self-motor starts which gives a slight rotation to the flywheel which in turn connected to the crankshaft of the engine gets rotated.
So the alternator at 1 side gets rotated & produces the DC out.
TRANSMISSION SYSTEMS:
Clutch:
Clutch is a mechanical arrangement which is used to engage and disengage the drive shaft and driven shaft.
Parts:
Fly wheel
Pressure plate
Clutch plate
Clutch spring
Reconditioning:
The pressure plate fingers are chance to get wear. So by grinding or metal adding the same depth is maintained in all fingers.
Clutch plate liners are changed.
Gear box:
When the gear is changed through the gear lever, it transmits the motion to the gear box through linkages.
According to the change in gear, the corresponding sliding dog moves and attach with the gear.
Now the speed ratio changes and correct torque will be gained through the gear box.
The main functions are
At low speeds, the torque produced by engine is very small, which increases with increase of speed peaks at some optimum speed and starts decreasing beyond that.
The transmission also provides a neutral position.
It gives reverse rotation.
Types:
Sliding mesh gear box
Synchromesh gear box
Constant mesh gear box
Reconditioning:
Check all the teeth if there is any broken teeth.
Check the bearing.
Check main shaft teeth.
If any breakages that should be changed.
Propeller Shaft:
This shaft is transmits the drive from the transmission to the level pinion or worm of final drive in front engine, rear drive vehicles and from the transfer box to the front and rear axles in all wheel drive vehicles.
Parts:
Shaft
Universal joints
Slip joint
Reconditioning:
The universal joint cross kits should be changed.
Bending of shafts should be checked failure bearings should be change.
FRONT AXLE AND STEERING:
Primary function of the steering is to achieve angular motion of the front wheels to negotiate a turn.
Front axle is a dead axle, in four wheel drive vehicles it is live axle.
In right side of the front wheel, the Track Liner is connected. It is connected
Bet
ween the sub-axle and the steering.
Tie Rod is one of the mechanical linkage which is connected above the front axle, which is used to turn the front set of wheels, when right wheel is turned by the action of steering.
Reconditioning:
In power steering system teeth of the steering gears should be changed
There should be checks for leakages.
In ordinary rotary valve type steering systems, rotary balls should be changed
The bearing guide should be checked.
King pin should be checked for any deformation which connects the front axle with the sub axle.
Socket is cleaned and the tooth is checked.
BRAKES:
The brakes are used to stop the vehicle which in motion
When the driver applies the brake, the brake lever actuate the leak valve.
It actuate the air cylinder.
The compressed air from the air cylinder is passed to the brake chamber.
In Brake Chamber, by the pressure of compressed air, the diaphragm is pushed against the concentric spring force.
Now, the push and pull rod extends from the brake chamber which is connected with the slock adjuster.
The slock adjuster actuate the brake shoe to expand towards outer which is kept inside the wheel drum. Thus the air brake is applied.
Hand Brake or Parking Brake is only available on the rear set of wheels.
Reconditioning:
Brake shoe checked for shearing and cracks.
The retracting spring thickness should be checked.
Brake lining is changed as per the condition of wear.
DIFFERENTIAL ARRANGEMENT:
When the bus is taking a turn, the outer wheels will have to travel greater distance compared to the inner wheels in the same time.
The differential should reduce the speed of inner wheels and increase the speed of outer wheels when taking turns.
This arrangement is kept in the rear axle. Propeller Shaft drive the differential gear.
Parts:
Crown Wheel
Bevel Pinion
Sun Gear (2 nos)
Star Gear (4 nos)
Cross or cage
Reconditioning Advantages:
It increases the life of the vehicle.
It reduces the cost.
It is a well economic process.
Cost of operation is less.
TYRE REBUTTONING:
The tyre which is weared is re-button in this section.
Initially the tyre is undergone Buffing Process.
New Tyre - 21⁰ angle
1st Re-buttoning Tyre - 20⁰ angle
2nd Re-buttoning Tyre - 19⁰ angle
Radial Tyre - 22⁰ angle
Next, the Bonding Vulcanizing Cement is coated over tier.
Bonding Gum is used to join the button sheet and weared tier.
Then, it is covered by a protective cloth and enclosed in an envelope.
Then tyre is boarded into a pressure chamber which is maintained above 125⁰ C for 2 hours.
After 2 hours, the tyre is taken from the chamber which is re-buttoned.
