CHAPTER 1

INTRODUCTION

The main objective of an engineering course is to implement the knowledge in to

practical application and analysing the skill in technical subjects. As far as mechanical

engineering is considered it is very important to have practical knowledge along with

theoretical knowledge. It is hard to achieve such practical experience, only availing the

resources and practical classes of our college. Also, it is impossible to provide such a

platform in college. So we decided to undergo an in-plant training at KSRTC Regional

Workshop, where most of the repairing and maintenance works of KSRTC buses are

done. KSRTC has been one of the most successful establishment of Kerala government

undertaking. Begun in the late 1960’s it has been providing excellent service to the people

both within the state and the neighboring states. The KSRTC has buses like ordinary,

limited stop, fast and superfast buses, super deluxe, which caters to the different sections

of the society.

The KSRTC has five Regional workshops. They are at Pappanamcode,

Mavelikkara, Aluva, Edapal and Kozhikode, other than the local garages available at all

important bus stands. These Regional workshops do the yearly overhauling of the buses

and the buses which are heavily damaged due to accidents.

This is the report of in-plant training done at KSRTC Regional Workshop,

Mavelikkara, Kerala, dated from 28th June 2014 to 7th July 2014.

CHAPTER 2

MAINTENANCE SECTIONS

The regional workshop consists of different sections for the smooth and easy

maintenance of the buses. The different sections and their activities are explained below.

2.1 ENGINE ASSEMBLY SECTION

The internal combustion engine is an integral part of a vehicle in which

combustion of fuel {generally, fossil fuel} occurs with an oxidizer (usually air) in a

combustion chamber. In an internal combustion engine, the expansion of the high

pressure gases which are produced during the combustion process occurs. During this

process force is applied to components of the engine such as the pistons or turbine blades

or nozzle, and by moving it over a distance results in generation of useful mechanical

energy.

In KSRTC buses we generally use 4 and 6 cylinder engines of TATA and

LEYLAND. Here, we were able to observe much about the engine parts, its working and

functions and also the repairing methods adopted. Cylinder block from the dismantled

engine is cleaned and then boring and honing is done to remove wear. The valve is grinded

to proper finish and valve seat is lapped. The damaged piston is replaced by a new one.

The weared crankshaft is ground so that ovality and taper are within permissible limits.

Crank shaft is coated with recommended lubricant. Figure 2.1 shows an engine and its

crankshaft with connecting rods.

Fig. 2.1 Enigne and engine components of a KSRTC bus.

2.2 GEAR BOX SECTION

A machine consists of a power source and a transmission system, which provides

controlled application of power. Merriam-Webster defines transmission as an assembly

of parts including the speed-changing gears and the propeller shaft by which the power is

transmitted from an engine to a live axle. The most common use is in motor vehicles,

where the transmission adapts the output at the internal combustion engine to drive

wheels. Such engines need to operate at a relatively high rotational speed, which is

inappropriate for starting, stopping and slower travel. The transmission reduces the high

engine speed to the slower wheel speed, increasing torque in process.

Fig. 2.2 Synchromesh gear box.

Most modern manual-transmission vehicles are fitted with a synchromesh

gearbox, as shown in the Figure 2.2. Transmission gears are always in mesh and rotating,

but gears on one shaft can freely rotate or be locked to the shaft. The locking mechanism

for gear consists of a collar (or dog collar) on the shaft which is able to slide sideways so

that teeth on its inner surface bridge two circular rings with teeth on their outer

circumference: one attached to the gear, one to the shaft. When the rings are bridged by

the collar, the particular gear rotationally locked to the shaft determines the output speed

of the transmission. The gearshift lever manipulates the collar using a set of linkages,

arranged such that one collar may be permitted to lock only one gear at any one time; and

while shifting gear, the locking collar from one gear is disengaged before another one is

engaged. One collar often serves for two gears: sliding in one direction selects one

transmission sped, in the other direction selects another. In the overhauling of gear box,

the teeth of all gears and the needle bearing are checked. The dog clutch and the sleeve

are checked for pitted teeth and the splines are checked for wear. If the wear is more, they

are replaced with new ones and assembled back.

2.3 PROPELLER SHAFT SECTION

A drive shaft or propeller shaft (prop shaft) or Cardan shaft is a mechanical

component for transmitting torque and rotation, usually used to connect other components

of a drive train that cannot be connected directly because of distance or the need to allow

for relative movement between them.

Fig. 2.3 Propeller Shaft.

Drive shafts are carriers of torque: they are subjected to torsion and shear stress,

equivalent to the difference between the input torque and the load .They must therefore

be strong enough to withstand or bear the stress, while avoiding too much additional

weight as that would turn increase their inertia. Figure 2.3 shows in detail the parts of a

propeller shaft. All the buses of KSRTC have a clutch and a gearbox mounted directly on

engine with a drive shaft leading to a final drive in the rear axle. Universal joint couplings

are used to connect the two shafts. Overhauling of propeller shaft consists of checking

the propeller shaft for bends and it is straightened out using hydraulic press.

2.4 SMALL UNIT SECTION

Small unit section consists of reassembling of clutch, air brake compressor, DD

unit, air drier.

2.4.1 Air Brake Unit

Compressed air brake system is typically used in KSRTC buses. The system

consist of service brakes, parking brakes, a control pedal on engine driven air compressor

and a compressed air storage tank. For the parking brake there is a disk or drum brake

arrangement which is designed to keep in the applied position by spring pressure.

Fig. 2.4 Air Brake System.

Air pressure must be produced to release these spring pressure parking brakes.

For the service brakes (the ones used while driving to slow or stop) to be applied, the

brake pedal is pushed, routing the air under pressure (approximately 100-125 Pa) to the

brake chamber, causing the brake to reduce wheel speed. Most types of truck air brakes

are drum units, though there is an increasing trend towards the use of disc brakes in this

application. The air compressor draws filtered air from the atmosphere and forces into

high-pressure reservoirs at around 120 psi. Most heavy vehicles have a gauge within the

driver's view, indicating the availability of air pressure for safe vehicle operation, often

including warning tones or lights. Setting of the parking/emergency brake releases the

pressurized air pressure in the lines between the compressed air storage tank and the

brakes. Thus actuating the (spring brake) parking brake hardware. An air pressure failure

at any point would apply full spring brake pressure immediately.

2.4.2 Clutch Unit

A clutch is a mechanism which enables the rotary motion of one shaft to be

transmitted, when desired, to a second shaft, the axis of which is coincident with that of

the first.

Fig. 2.5 Clutch.

Clutches are used whenever the transmission of power or motion needs to be

controlled either in amount or over time (e.g. electric screwdrivers limit how much torque

is transmitted through use of a clutch, clutches control whether automobiles transmit

engine power to the wheels).

In the simplest application, clutches are employed in devices which have two

rotating shafts (drive shaft or line shaft). In these devices, one shaft is typically attached

to a motor or other power unit (the driving member) while the other shaft (the driven

member) provides output power for work to be done. Overhauling of clutch assembly

includes checking for wear of the clutch lining wear, length of the springs, and cracks in

the clutch plate steel disc. Pressure plate is checked for heat damages, cracks and flatness.

The replacement of the springs, disc and clutch lining are done if necessary and

assembled.

2.4.3 Front Axle Unit

This is the assembly that support the vehicle on the front side. There is no power

transmitted to the front axle. The main parts of the front axle are s cam, roller, hub, carrier

plate, bearings, air chamber, stack adjuster, lay lender, brake drum, break shoes etc. The

steering action comes to one tire and as the tires are interconnected, both works

simultaneously.

The braking action occurs with help of air pressure since it is air brakes. As the

brake pedal is pressed on the valve, s cam rotates, the brake shoes expand and touches the

brake drum, thus the braking action works. Figure 2.6 shows the inspection of a front axle

for damages.

Fig. 2.6 Front Axle System.

2.5 DIFFERENTIAL SECTION

A differential is a device, employing gears, through which it transmits torque and

rotation. Except in some special purpose differentials, there are no other limitations on

the rotational speeds of the shafts. In automobiles and other wheeled vehicles, a

differential allows the driven road wheels to rotate at different speeds. This is necessary

when the vehicle turns, making the wheel that is travelling around the outside of the

turning curve roll faster than the other. If the engine is running of a constant speed, the

rotational speed of each driving wheel can vary, but the sum (or average) of the two

wheels speeds cannot change. An increase in the speed of one wheel must be balanced by

an equal decrease in the speed of the other.

In the overhauling of differential each tooth is inspected minutely for any pitting

or broken teeth on crown wheel pinion, sun and star pinion. Then they are checked for

the back lash of the sun pinion with star pinion.

Fig. 2.7 Differential gear.

2.6 FUEL INJECTION SECTION

Fuel injection system consists of fuel tank, fuel feed pump, fuel injection pump,

fuel filter, fuel injection nozzle and a governor. Pump is the device that pumps fuel into

the cylinders of a diesel engine. Traditionally, the pump is driven indirectly from

crankshaft by gears, chains or a toothed belt (often the timing belt) that also drives the

camshaft. It rotates at half crankshaft speed in a conventional four-stroke engine. Its

timing is such that the fuel is injected only very slightly before top dead centre of that

cylinder's Compression stroke. In some systems injection pressures can be as high as 200

MPa. Earlier diesel pumps used an in line layout with a series of cam operated injection

cylinders in a line, rather like a miniature inline engine. The pistons have a constant stroke

volume, and injection volume (i.e., throttling) is controlled by rotating the cylinders

against a cut-off port that aligns with a helical slot in the cylinder. When all the cylinders

are rotated at once, they simultaneously vary their injection volume to produce more or

less power from the engine. Figure 2.8 shows a diesel fuel pump. The injection pump

must give equal quantity of fuel to all cylinders and the supply should commence and

stop at fixed degree of crank angle both of which are checked and adjusted on the injection

pump test bench.

Fig. 2.8 Diesel Fuel Pump

Fuel filter is necessary to supply clean fuel which needs to be replaced at regular

intervals. Facilities have been provided for suitable testing of the injectors which includes;

Leak off test: The injector tester is worked up to build a pressure of 150 atm, which is

kept for 10 seconds (without spraying). In case there is a drop in pressure, the body seat

and the needle is lapped.

Spray test: The injector is fixed up as done earlier and pressure gauge is disconnected by

closing the valve. The tester is worked up four times and a second and the spray pattern

is noted. If the spray pattern is in the form of a stream or jet, the needle and the nozzle

body seat requires grinding.

2.7 ELECTRICAL SECTION

Electrical section includes the engine starter. As the key is inserted, the circuit

activates, that is the solenoid coil magnetize, pinion comes in contact with fly wheel. As

the starting motor rotates, the fly wheel and the pistons reciprocates, thus the engine starts

working. After the engine starts, the motor stops working. Another machinery in the

electrical section is the alternator, which is used for charging the batteries. The alternator

has two parts, they are stator and rotor. The parts of starter are stator and armature.

2.8 STEERING SECTION

The main parts of steering section are sector arm, bearing, oil and roller shaft. In

Tata vehicles, 74 rollers are used whereas in Leyland only 42 rollers are used. They won't

have play on the shaft. There exists two types of steering wheels. They are power and

ordinary steering wheels.

Fig. 2.9 Steering System.

2.9 SUSPENSION SECTION

The suspension system mainly used in the KSRTC buses are leaf spring

suspension system. The semi-elliptic leaf springs are the almost universally used for the

suspension in heavy commercial vehicles. The spring consists of number of leaves called

blades. The blades vary in length. The lengthiest blade with eyes on its end is called the

master leaf. All the blades are bound together by means of steel straps. Figure 2.10 shows

a leaf spring suspension system.

Fig. 2.10 Suspension system.

After prolonged use or over loading, spring assembly gets flattened or one or two

of its leaves gets broken. The center bolt is then removed and the broken leaf is dismantled

and replaced with the new one. The rubber bushes, which are used to hinge the suspension

systems to the chassis, are greased and are replaced if these are worn out.

2.10 BODY BUILDING SECTION

At Mavelikkara KSRTC regional workshop, there are two building sections;

1. New body building section

2. Old body building section

Automobile body building is an important activity. The chassis is supplied by

automobile manufacturers, and body is built by automobile body builders. Bus bodywork

is usually geared to short trips, with many transit features. Coach bodywork is for longer

distance trips, with luggage racks and under-floor lockers. Other facilities may include

toilets and televisions.

Here it mainly deals with accident cases, i.e. buses which are damaged due to

accidents. In extreme accidents, body building of damaged bus is similar to new body

building. The patch works of the buses are being done here. New buses are also built here.

Welding, riveting, sheet metal works, painting works etc. are done.

Fig. 2.11 New chassis for body work. Fig. 2.12 After body work completion.

CHAPTER 3

CONCLUSION

By this industrial training program we were able to know the functions and

operations of different parts of an automobile and we were familiarized with the tools

used for different operations.

We saw all the inner parts and repair works of KSRTC buses and the making of a

bus from chassis to its completed form. Also this training helped us to practice the theories

we studied in our syllabus. This was the best chance we ever had, to do some practical

with experienced workers in a live workshop and to see the internal parts of engines,

gearbox and other parts. So, this training program was very helpful for us in studying

about the public transportation buses of Kerala and to experience the processes involved

in repair and manufacture of those buses. By this we gained a lot of practical knowledge

which we hope will help in our studies and our future jobs.