Tractor ( Traction + Motor ) is a self-propelled power unit having wheels or tracks for operating agricultural implements and machines including trailers. Tractor engine is used as a prime mover for active tools and stationary farm machinery through power-take off (PTO) or belt pulley.
TRACTOR DEVELOPMENT
Wheel tractors
The present tractor is the result of gradual development of machine in different stages. History of tractor development is given below.
1890- The word tractor appeared first on record in a patent issued on a tractor or traction engine invented by George H. Harris of Chicago
1906- Successful gasoline tractor was introduced by Charles w. Hart and Charles H. Parr of Charles City, Iowa
1908- First Winnipeg tractor trails were held
1911- First tractor demonstration was held at Omaha ( Nebraska)
1915-1919- Power take off was introduced
1920-1924- All purpose was developed
1936- 1937 – Diesel engine was used in tractor and pneumatic tires were introduced
1950-1960- Manufacturing of diesel tractors on extensive basis throughout the world was taken up
1960-1961 – Tractor manufacturing was started in India by first manufacturer M/s Eicher Good Earth
1962-1970 – Manufacturers like Tractor and Farm Equipment , Madras , Hindustan tractors at Baroda, Escorts Tractors at Faridabad and International Harvester in Bombay started work during this period
1971- Escorts Tractor Ltd. Started producing Ford Tractors
1973- Manufacture of HMT Tractor was started
1974- Manufacture of Pitti and Kirlosker Tractor was started
1975- Harsha Tractors was established
1981- Auto tractors were started
1982- Universal Tractors was established
1983-2003- GTCL tractors, M.M Tractors, Sonalika, VST, L&T, Bajaj Tractors were produced
CLASSIFICATION OF TRACTORS
Tractors can be classified into three classes on the basis of structural design
1.Wheel tractor
2.Crawler tractor
3.Walking type tractor
Wheel tractor
Tractors having three or four pneumatic wheels are called wheel tractors. Four wheel tractors are popular everywhere.
Three /Four wheel tractor
Crawler tractor
This type is also called Track type tractor or Chain type tractor. In such tractors, there is endless chain or track in place of pneumatic wheels.
Power tiller
Power tiller is a walking type tractor. This tractor is usually fitted with two wheels only. The direction of travel and its controls for field operation is performed by the operator, walking behind the tractor.
Classification of wheel tractors
On the basis of purpose, wheeled tractors are classified into three groups
1. General purpose tractor
2. Row crop tractor
3. Special purpose tractor
1. General purpose Tractors
It is used for major farm operations such as ploughing, sowing, harvesting and transporting works. Such tractors have i) low ground clearance ii)Increased engine power iii) good adhesion and iv) wide tyre.
2. Row crop Tractors
It is used for row crop cultivation. Such tractor is provided with replaceable driving wheels of different tread widths. It has high ground clearance to save damage of crops. Wide wheel track can be adjusted to suit inter row distance.
It is used for definite jobs like cotton fields, marshy lands, hill sides, garden etc. special designs are there for special purpose tractor.
Eg. a) Tractor with winch unit b) multi drive tractor c) tractor for golf grounds etc.
Selection of tractors depend up on following factors
1. 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
2. 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.
3. 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
4. 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
5. 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.
6. Running cost: Tractors with less specific fuel consumption should be preferred over others so that the running cost may be less.
7. Initial cost and resale value: While keeping the resale value in mind , the initial cost should not be very high, otherwise higher amount of interest have to be paid
8. Test report: Test report of tractors released from farm machinery testing stations should be consulted for guidance
WHEEL TRACTOR COMPONENTS
1. I.C Engine
2. Clutch
3. Transmission gears
4. Differential unit
5. Final drive
6. Real wheel
7. Front wheels
8. Steering mechanism
9. Hydraulic control and hitch system
10. Brakes
11. Power-take-off unit
12. Tractor pulley
13. Draw bar and
14. Control panel
1. I.C engine
Internal combustion of suitable horse power is used as a prime mover in a tractor. Engines ranging from 8 to 200 hp are used in agricultural tractors. In India , four wheel tractors for agricultural operations are fitted with 25-80 hp. Walking type tractors are fitted with 8-12 hp engines
2. 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
Necessity of clutch in a tractor
👉 Engine needs cranking by any suitable device. For easy cranking, the engine is disconnected from the rest of the transmission unit by the clutch. After starting the starting the engine, the clutch is engaged to transmit the power from engine to gear box.
👉 In order to change the gears, the gear box must be kept free from engine power, otherwise the gear teeth will be damaged and engagement of gears will be difficult. This work is done by clutch.
👉 When the belt pulley of the tractor works in the field it needs to be stopped with out stopping the engine. This is done by a clutch.
3. Power Transmission system of a tractor
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. The system consists of various devices, which cause forward and backward movement of tractor to suit different field conditions. The complete path of power from engine to wheel is called power train
👉 Functions of power transmission system
1. To transmit power from the engine to the rear wheels of the tractor
2. To make reduced speed available, to rear wheels of the tractor
3. To alter the ratio of wheel speed and engine speed in order to suit the field conditions
4. To transmit power through right angle drive, because the crankshaft and rear axle are normally at right angles to each other.
👉 The power transmission system consists of :
1. Clutch
2. Transmission gears
3. Differential
4. Final drive
5. Rear axle
6. Rear wheels
4. Transmission gears
A tractor runs at high speed, but the rear wheel of the tractor requires power at low speed and high torque. That’s why it becomes essential to reduce the engine speeed and increase the torque available at the rear wheel of the tractor because
If engine power is constant, it is obvious that for higher torque at wheels , low speed is required and vice versa. So gear box is fitted between engine and rear wheels for variable speed and torque.
5. Differential unit
Differential unit is a special arrangement of gears to permit one of the rear wheels of the tractor to rotate slower or faster than the other. While turning the tractor on a curved path, the inner wheel has to travel lesser distance than the outer wheel. The inner wheel requires lesser power than the outer wheel. This condition is fulfilled by differential unit, which permits one of the rear wheels of the tractor to move faster than the other at a turning point.
👉 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.
7. Steering mechanism
The system, governing the angular movement of front wheels of a tractor is called steering system. This system minimizes the efforts of the operator in turning the front wheels with the application of leverages.
The different components of steering system are
i)steering wheel
ii) steering shaft
iii)steering gear
iv) drag link
v)steering arm
vi) tie rod
vii) king pin
When the operator turns the steering wheel, the motion is transmitted through the steering shaft to the angular motion of the pitman arm through a set of gears. The angular movement of the pitman arm is further transmitted to the steering arm through drag link and tie rods. Steering arm are keyed to the respective king pins which are integral part of the stub axle on which wheels are mounted. The movement of steering arm affects the movement of front wheel
8. Hydraulic control system
It is a mechanism in a tractor to raise , hold or lower the mounted implement or semi- mounted equipments by hydraulic means. All tractors are equipped with hydraulic control system for operating three point hitch of the tractor. Hydraulic system works on PASCAL’s Law which states that pressure applied to an enclosed fluid is transmitted equally in all directions.
👉 Basic components of hydraulic system
1. Hydraulic pump
2. Hydraulic cylinder and piston
3. Hydraulic tank
4. Control valve
5. Safety valve
6. Hose pipe and fittings
7. Lifting arms
The hydraulic pump draws up oil from the oil reservoir and sends it to the control valve under high pressure. From the control valve, the oil goes to the hydraulic cylinder to operate the piston, which in turn, raises the arms. The implements attached with the arms are lifted up.
9. 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. Each pedal can be operated independently to assist the turning of tractor during field work or locked together by means of a lock.
👉 Types of brakes –
a) Mechanical brake
b) hydraulic brake
10. Power take off
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. The guard is called power take off shield.
