3. Unit – I Tractors
Classification of tractors - Tractor engines – construction of engine
blocks, cylinder head and Crankcase - features of cylinder, piston,
connecting rod and crankshaft – firing order Combustion chambers.
5. Tractor
• Self propelled power unit having wheels or tracks for operating
agricultural implements and machines including trailers.
• Used as a prime mover for active tools and stationary farm
machinery through power-take off (PTO) or belt pulley
6. Development of Tractor
1890 : Tractor engine invented by George Harris of Chicago, and used the
world first tractor
1915-19: PTO – Power take off was introduced in tractor
1920-24 : All purpose tractor developed
1936-37 : Diesel engine and pneumatic tyres were used for tractors
1950-60 : Large scale manufacturing of diesel tractors
1937-41 : Hydraulic system and three point linkage developed
7. Development of Tractor
1960-61 : Tractor manufacturing started in India by first manufacturer M/s.
Eicher Good Earth.
1962-70 : Manufacturers like Tractor and Farm equipment, Hindustan
tractors, Escorts tractors, and International harvesters started work
during this period .
1971: Escort tractor limited started producing Ford Tractor
1973 :Manufacturing of HMT tractors started
1981: Auto tractors were developed
1982: Universal tractors were established
1983-08 : GTCL tractors, Bajaj, Mahindra, Swaraja, Hindustan, Sonalika,
Johndeer, PTL, VST and many other companies started
manufacturing tractor in India.
8. Selection of Tractors
Land holding
Under a single cropping pattern, it is normally recommended to consider
1 hp for every 2 hectare of land. In other words , one tractor 20-25 hp is
suitable for 40 hectare farm
Cropping pattern
Generally 1.5 hectare/hp has been recommended where adequate
irrigation facility are available and more than one crop is taken. So a 30-
35 hp tractor is suitable for 40 hectare of land
9. Selection of tractors
Soil condition
A tractor with less wheel base , higher ground clearance and low overall
weight may work successfully in lighter soils buy will not be able to give
sufficient depth in black cotton soils
Climatic condition
For very hot zone and desert area , air cooled engines are preferred over
water cooled engines. Similarly for higher altitude air cooled engines are
preferred because water cooled engines are liable to be frozen at high
altitudes
10. Selection of Tractors
Repair facilities
It should be ensured that the tractor to be purchased has a dealer at
near by place with all the technical skills for repair and maintenance of
the machine.
Running cost
Tractors with less specific fuel consumption should be preferred over
others so that the running cost may be less.
11. Selection of Tractor
Greater clearance, both vertical and horizontal.
Adaptation to the usual row-widths.
Quick – short turning ability
Convenient and easy handling.
Quick and easy attachment.
Essential accessories such as hydraulic controls. Three point linkage
and PTO.
12. Control Board of a Tractor
Ignition switch: When the ignition switch is on, the electric current flows
in the electrical circuit.
Throttle lever: This lever is for increasing or decreasing the speed of the
engine.
13. Control Board of a Tractor
Decompression lever: This lever releases compression pressure from
the combustion chamber of the engine and helps to stop the engine.
Oil pressure indicator: This indicates the lubricating oil pressure in the
system.
Water temperature gauge: This indicates the temperature of water of
the cooling system
14. Classification of tractors
Based on type of construction
(a)Riding type tractors – Tractors in which a driver can sit and drive e.g.,
General purpose four wheel tractors.
(b) Walking type tractors – Tractors with which the operator walks
along e.g., garden tractors, power tillers.
15. Based on type of drive
Track type tractors
In this type of tractors, instead of wheels; one track is fitted on either side.
This track gets drive from the sprocket run by rear axle shaft.
To steer the tractor, there is not steering gear fitted.
The tractor is steered by applying brakes to one side of the track with the
other track moving.
These are used for bulldozing or land clearing work.
Classification of tractors
16. Wheel type of tractors
Two-wheel tractors
Ssed for small farms, hilly area and gardening purposes and are called power
tillers.
Three-wheel tractors
Had single or dual wheel fitted at the front end in the centre.
Four-wheel tractors
Known as all purpose tractors. On the basis of available power, these have
been classified as
Small tractors – 15 to 25 hp, Medium tractors – 25 to 45 hp.
Large tractors – more than 45 hp.
Classification of tractors
18. Based on purpose:
Utility tractors
Designed for ploughing driving any other equipment through its P.T.O.
drive.
All purpose tractor
Used for agricultural purposes such as ploughing, harrowing, leveling,
pulling, seed drill, operating threshers, and pumps through its P.T.O.
These are provided with three point linkages.
Classification of tractors
21. Functionality OS
Orchard type tractors
Used in orchards. These are made very high in height so that driver
while sitting on the seat, the operations on the trees could be
performed.
Garden tractors
Range of 1 to 10 hp and are very small in construction. These are
mostly used for kitchen or vegetable gardens.
Earth Moving tractor
Heavy in weight and strongly built available both is tract and tyre
type.
Used in dams, quarries and other constructional works.
22. Classification of tractors
Rotary Tillers
Walking type of tractors and are used in small fields or on hills where fields
are very small and are at different levels where ordinary tractors cannot
work efficiently.
Tined blades are fitted to the tillers to prepare the seedbeds quite
effectively by pulvlerizing the soil.
These are also used in rice fields for puddling and other operations.
25. Components of tractor engines
Clutch
Clutch is a device, used to connect and disconnect the tractor engine
from the transmission gears and drive wheels.
Clutch transmits power by means of friction between driving members
and driven members
Power transmission
Transmission is a speed reducing mechanism, equipped with several
gears. It may be called a sequence of gears and shafts, through which
the engine power is transmitted to the tractor wheels.
27. Transmission gears
A tractor runs at high speed, but the rear wheel of the tractor
requires power at low speed and high torque.
Differential lock
Differential lock is a device to join both half axles of the tractor so
that even if one wheel is less resistance , the tractor comes out of the
mud etc. as both wheels move with the same speed and apply equal
traction.
Components
29. Final drive
Final drive is a gear reduction unit in the power trains between
differentials and drive wheels. Final drive transmits the power finally to
the rear axle and the wheels. The tractor rear wheels are not directly
attached to the half shafts but the drive is taken through a pair of spur
gears
Steering mechanism
The system, governing the angular movement of front wheels of a tractor
is called steering system.
Components..
32. Hydraulic control system
oIt is a mechanism in a tractor to raise , hold or lower the mounted
implement or semi-mounted equipment's by hydraulic means.
oAll tractors are equipped with hydraulic control system for operating
three point hitch of the tractor.
oThe working principle of hydraulic system is based on pascal's law. This
law states that the pressure applied to an enclosed fluid is transmitted
equally in all directions. Small force acting on small area can produce
higher force on a surface of larger area
Components..
34. It is a part of tractor transmission system.
It consists of a shaft, a shield and a cover.
The shaft is externally splined to transmit tortional power to another
machine.
A rigid guard fitted on a tractor covers the power-take-off shaft as a safety
device
This guard is called power take-off shield. Agricultural machines are
coupled with this shaft at the rear part of the tractor.
In order to operate 1000 rpm drive machine, a new standard has been
developed. Modern tractors are provided with pto speed of 1000±10 rpm.
Power take off
36. A hook
o It is provided for hitching of trailers, and other stationery machines
operated by tractor like thresher, winnower etc.
o It is provided at the back of the tractor.
Brakes
Brake is used to stop or slow down the motion of the tractor. It is mounted on
the driving axle and operated by two independent pedals.
Outlets of a tractor
37. Power outlets:
The tractor power is made available for use through hydraulic lift,
drawbar hitch, belt pulley & PTO shaft.
Outlets of a Tractor
38. Three point linkage
o It is a combination of three links, one is upper link and two are lower
links, the links articulated to the tractor and the implements at their
ends in order to connect the implement to the tractor.
o All the tractor drawn implement are attached to this and hydraulic
control is also provided for three point linkage.
Three point linkage
40. Belt pulley
A pulley is provided with PTO shaft for some of the tractors
through which rotary power output can be tapped for operating
stationery machines.
Outlets of a tractor
41. Wheelbase:
Wheel base is the horizontal distance between the front and rear wheels of
a tractor, measured at the ground contact.
Ground clearance:
It is the height of the lowest point of die tractor from the ground surface,
the tractor being loaded to its maximum permissible weight.
Track:
Track is the distance between the two wheels of the tractor on the same
axle, measured at the point of ground contact.
Important terms in tractor
42. Turning space:
It is the diameter of the smallest circle, described by the outermost
point of the tractor, while moving at a speed, not exceeding 2 km/hr
with the steering wheels in full lock.
Cage wheel:
It is a wheel or an attachment to a wheel with spaced cross bars for
improving the traction of the tractor in a wet field. It is generally used
in paddy fields.
Important terms in tractor
43. o The heat engine is a device in which heat energy of fuel after burning it
properly is used to convert it into mechanical energy (mechanical
work). The heat engine is an equipment which generates thermal
energy and transforms it into mechanical energy. The heat energy is
produced by the combustion of fuel.
Tractor Engines
44. o In this type of engine the fuel is burnt outside the engine cylinder, in a
device called boiler to produce hot gas or steam, which is used in the
engine cylinder to develop the mechanical work.
o The thermal efficiency of external combustion engine is usually in the
range of 15 to 20%, which is very low compared to the internal
combustion engine.
External Combustion Engine
46. o In this type of engine the burning or combustion of the fuel takes place
inside the engine cylinder. There are two ways in which combustion
takes place in the cylinder:
i) By rapid explosion of air-fuel mixture within the cylinder, when it is
ignited by a spark, is called constant volume combustion (C.V.C.).
ii) Combustion takes place by slow burning when the fuel is injected into
highly compressed heated air contained in the cylinder. This is called
constant pressure combustion (C.P.C.), because when the combustion
takes place, the pressure in the cylinder is almost constant.
The power is developed during the power stroke.
Internal Combustion Engine
47. o Most of the engines used in tractors, automobiles, combine harvesters,
oil engines and traction vehicles are of this type.
o The thermal efficiency of internal combustion engine is about 40%.
Internal Combustion Engine
48. Swept volume
o Volume that the piston displaces during its movement from BDC to
TDC
Compression ratio
o The compression ratio (CR) of an engine is a measure of how much the
air/air-fuel mixture is compressed in the cylinder.
IC Engines Terminology
49. Clearance volume.
o Volume of air when the piston is at BDC divided by its volume of air
when the piston is at TDC. The volume above the piston is called
clearance volume.
IC Engines Terminology
50. o Cylinder
o Cylinder head
o Cylinder liner
o Piston
o Piston Rings
o Piston Pin
o Connecting Rod
o Crankshaft
o Engine Bearings
o Valves
Constructional features of IC engine
51. o Bottom dead centre
o Top dead centre
o Scavenging
o Camshaft
o Flywheel
o Crankcase
Constructional features of IC engine
54. Cylinder
o It is a part of the engine which confines the expanding gases and forms
the combustion space.
o It provides space in which piston operates to suck the air or air-fuel
mixture.
o The piston compresses the charge and the gas is allowed to expand in the
cylinder, transmitting power for useful work.
o Cylinders are usually made of high grade cast iron.
Components of an IC Engine…
55. Cylinder block:
It is the solid casting body which includes the cylinder and water jackets
(cooling fins in the air cooled engines).
Cylinder head:
It is a detachable portion of an engine which covers the cylinder and
includes the combustion chamber, spark plugs or injector and valves
Components of an IC Engine…
57. Cylinder liner or sleeve
It is a cylindrical lining either wet or dry type which is inserted in the
cylinder block in which the piston slides.
Piston
o It is a cylindrical part closed at one end which maintains a close sliding
fit in the engine cylinder.
o It is connected to the connecting rod by a piston pin.
o The force of the expanding gases against the closed end of the
piston, forces the piston down in the cylinder.
Components of an IC Engine…
58. o This causes the connecting rod to rotate the crankshaft .
o Cast iron is chosen due to its high compressive strength.
Components of an IC Engine…
59. Piston ring
o It is a split expansion ring, placed in the groove of the piston.
o They are usually made of cast iron or pressed steel alloy.
The function of the ring are as follows
o It forms a gas tight combustion chamber for all positions of piston.
o It reduces contact area between cylinder wall and piston wall
preventing friction losses and excessive wear.
o It controls the cylinder lubrication.
o It transmits the heat away from the piston to the cylinder walls.
Components of an IC Engine…
61. Compression ring
o Compression rings are usually plain, single piece and are always placed
in the grooves of the piston nearest to the piston head.
o They prevent leakage of gases from the cylinder and helps increasing
compression pressure inside the cylinder.
Oil ring:
o Oil rings are grooved or slotted and are located either in lowest groove
above the piston pin or in a groove above the piston skirt.
o They control the distribution of lubrication oil in the cylinder and the
piston
Components of an IC Engine…
62. Piston Pin
o It is also called wrist pin or gudgeon pin. Piston pin is used to join the
connecting rod to the piston
o It provides a flexible or hinge like connection between the piston and
the connecting rod. It is usually made of case hardened alloy steel.
Components of an IC Engine…
63. Connecting rod
o It is special type of rod, small end of which is attached to the piston
and the larger end to the crankshaft.
o It transmits the power of combustion to the crankshaft
and makes it rotate continuously.
o It is usually made of drop forged steel.
o Its small end is fitted with bronze busing and
big end is provided with split bearings.
Components of an IC Engine…
64. Crankshaft
o It is the main shaft of an engine which converts the reciprocating
motion of the piston into rotary motion of the flywheel.
o The crankshaft is made of drop forged steel or cast steel.
o Crankshaft is provided with counter weights throughout its
length to have counter balance of the unit.
o Split shell bearings are used as main bearings of the crankshaft.
Crankshaft is subjected to bending as well as twisting from the
connecting rod end
Components of an IC Engine…
66. Cam Shaft
o It is a shaft which raises and lowers the inlet and exhaust valves at
proper time.
o Camshaft is driven by crankshaft by means of gears, chains or
sprockets. The speed of the camshaft is exactly half the speed of the
crankshaft in four stroke engine.
o Camshaft operates the ignition timing mechanism, lubricating oil pump
and fuel pump.
o It is mounted in the crankcase, parallel to the crankshaft.
Components of an IC Engine…
69. Crankcase :
o The crankcase is that part of the engine which supports and encloses the
crankshaft and camshaft.
o It provides a reservoir for the lubricating oil of the engine.
o It also serves as a mounting unit for accessories as like oil pump, oil
filter, dynamo, self motor and other components.
o The upper portion of the crankcase is usually integral with cylinder
block.
o The lower part of the crankcase is commonly called oil pan and is
usually made of cast iron or cast aluminum
Components of an IC Engine…
71. Flywheel
o Flywheel is made of cast iron.
The main functions of the flywheel are as follows:
o It stores energy during power stroke and returns back the same energy
during the idle strokes, providing an uniform rotary motion by virtue of
its inertia.
o The rear surface of the flywheel serves as one of the pressure surfaces
for the clutch plate.
o Engine timing marks are usually stamped on the flywheel, which helps
in adjusting the timing of the engine
Components of an IC Engine…
74. Inlet manifold
o It is that part of the engine through which air or air-fuel mixture enters
into the engine cylinder.
o It is fitted by the side of the cylinder head.
Exhaust manifold :
o It is that part of the engine through which exhaust gases go out of the
engine cylinder.
o It is capable of withstanding high temperature of burnt gases. It is fitted
by the side of the cylinder head.
Components of an IC Engine…
76. Pushrod
Pushrod is used when the camshaft is situated at the bottom end of
cylinder.
It carries the camshaft motion to the valves which are situated at the
cylinder head.
Components of an IC Engine…
80. Suction Stroke
o When the piston travels from TDC to BDC with the intake valve
open and exhaust valve closed.
o The downward motion of the piston increases the volume in the
combustion chamber which in turn creates a vacuum.
o The resulting pressure differential through the intake system
from atmospheric pressure on the outside to the vacuum on the
inside causes air to be pushed into the cylinder.
81. Second stroke : Compression stroke
o At the end of suction stroke, when the piston reaches BDC, the intake
valve gets fully closed and the piston travels upward back to TDC with
both the valves (inlet and outlet) closed.
o The air is compressed and compression is to higher pressures and
temperature. Late in the compression strike fuel is injected directly into
the combustion chamber when it mixes with very hot air.
o This causes the fuel to evaporate and self ignite, causing combustion to
start. Combustion is fully developed by TDC and continues at about
constant pressure until the fuel injection is complete and the piston has
started towards BDC.
82. Third stroke : Power stroke
o It is known as the expansion stroke when the piston moves again
downward from TDC with the pressure being generated by the fuel
burnt having both the valves fully closed.
o As the piston travels from TDC to BDC, cylinder volume is again
increased causing pressure and temperature drop.
o Late in the power stroke, the exhaust valve is opened and exhaust blow
down occurs.
o The pressure and temperature in the cylinder are still high relative to the
surroundings at this point and a pressure differential is created through
the exhaust system when the piston is near BDC.
83. Power stroke & Exhaust Stroke
o Opening the exhaust valve before the piston reaches BDC, reduces the
work obtained during the power stroke but is required because of the
finite time needed for exhaust blow down.
Exhaust Stroke
o The piston reaches BDC during the power stroke, the cylinder is still
full of exhaust gases.
o With the exhaust valve remaining open, the piston now travels upward
to make the gases move out of the cylinder into the exhaust system,
leaving only that amount of exhaust gasses which are trapped in the
clearance volume when the piston reaches TDC.
84. Exhaust stroke
o Near the end of exhaust stroke, the intake valve starts to open, so that
it is fully open by TDC to start the new intake stroke in the next cycle.
o Near TDC exhaust valve starts to close and finally is fully closed
sometime at TDC. This period when both intake valve and exhaust
valve are open is called valve overlap.
89. Firing order
o The order in which various cylinders of a multi-cylinder engine fire is
called the firing order.
o The firing order is the sequence of power delivery of each cylinder in a
multi-cylinder reciprocating engine.
o The firing order of an engine is the sequence in which the power event
occurs in the different cylinders.
o The firing order is designed to provide for balance and to eliminate
vibration to the greatest extent possible.
90. Need of firing order in a multi cylinder engine
o It is desirable to have the power impulses equally spaced and from the
point of view of balancing.
o If all cylinders fired at once, power distribution would be very jerky, so
the engine is set up to have the cylinders firing in sequence for a
smoother power delivery.
o If the pistons move in a certain rhythm, then they have to receive their
sparks in a certain rhythm too, due to this engine will run smoothly.
91. Firing order
The optimum firing order of an engine ensures
o Reduced Engine vibrations
o Better – engine cooling and
o Decreased backpressure.
Purpose of Firing Order
o Engine vibrations
o Engine cooling
o Development of back-pressure.
o Engine balancing
o Even flow of power.
92. Designing Parameters of Firing Order
o Number of Cylinders,
o Torsional vibrations,
o Heat distribution,
o Arrangement of cylinders,
o Crankshaft Alignment.
