Tractors

Modern tractor

Tractor is machine for driving, trailing and pushing other machines which does not have their own power supply or cannot move by themselves Usually the tractor is known as a machine appropriated to tow other machines or objects. In Great Britain and India tractor is usually named farm tractor, and a word tractor is used to indicate other type of vehicles. In Canada and USA this word indicates road tractor. Word tractor originates from Latin word trahere which means to pull. In history of the tractor word, it is supposed that the steam engines were called traction engines and that the word tractor was result of merging the word traction and motor in the word tractor.

First mechanized farms in 1800's and early 1900's used steam tractors. They were built around steam engine, which was not safe. They could explode or clinch their drivers with the belt drove attachments. In 1982 John Froelich built first practicable tractor with gasoline engine in Clayton County (Iowa, SAD). Only two of them were sold. First successful design was made by Waterloo Gasoline Traction Engine Company in 1911. In Great Britain first tractor was sold in 1897. It was an oil powered Safety Oil Traction engine made by Hornsby-Ackroyd. First successfully designed tractor was Dan Albone's Ivel tractor with three wheels in 1902. In 1908 Soundersons of Bedford introduced four wheel designs and became the biggest tractor manufacturer outside the USA. Although tractors were not so popular at first, after 1910 those gasoline machines became more and more popular because they became smaller and cheaper. Henry Ford introduced Fordson in 1917, the first mass produced tractor. It was produced in the USA, Irleand, England and Russia and by the end of 1923 it occupied 77 percent of USA market. Fordson was splited in blocks, and it used engine block to keep whole machine together. Till 1920 internal combustion gasoline engines became standard for tractors manufacturing. Classical tractor can be described as a vehicle with two big drive wheels on the shaft beneath and slightly behind driver's seat (seat and steering wheel are in the middle of tractor) and engine in front of the driver, and with two adjustable wheels under the engine. Basic design stayed unmodified nowadays, with added cabin for driver's safety and comfort.

Modern tractors usually have the five foot pedals for various operations. Pedal on the left side is clutch. Driver will push down this pedal to disengage the transmission for shifting gears or to stop the tractor. Two pedals on the right side is brakes. Left pedal stop the left rear wheel and right do the same with the right rear wheel. Independent left and right brake increase tractors steering when only rear drive wheels are used. This is useful for maneuver on the small area. Independent brakes are also useful in the mud and soft land to control a wheel to slip. To stop the tractor, driver should push down both pedals at the same time. On tractors with additional front wheel drive, this operation often lock differential on all wheels and it helps to stop the tractor when driving on the road. Fourth pedal is under the seat and it is used to block back differential when wheels slip. Differential allow outward wheel to turn faster than inward wheel in turning. But, when working on the soft soil, the same mechanism would allow one wheel to slip, thus preventing traction on the other wheel. The differential block will override this mechanism and it would provide the same traction on the both wheels. Unblocking differential is very important and it is often done by pushing the pedal one more time. This is important because tractor would not be able to turn when differential is blocked. Fifth pedal is on the right side and it is used as a foot throttle. Unlike cars, tractor's throttle can be controlled by hand, and this option is used to hold the constant speed when working. Also, this is used to provide constant power to tractor's attachments by shaft or by belt. Foot throttle is used to give car's characteristics to tractor when drive on the road. In Great Britain it is mandatory to use foot throttle when driving on the road. Some tractors, especially tractors for working with row crops, have pedal for reducing throttle (when you push it the throttle is reduced). This pedal is used to slow down the tractor's engine speed on the end of the crop row in the field - working speed is set by the hand throttle and when driver want to slow down to turn the tractor back he simply push this pedal, turn back and release the pedal (this is much better than setting hand throttle twice on every turn).

Modern tractors use large diesel engines, powered from 18 to 575 HP (15 to 480 KW). Tractors are generally classified by drive on tractors with two wheels drive, tractors with two wheels drive aided with front wheels, tractors with four wheels drive (usually with articulated steering) and tractors with tracks (with power on two or four rubber tracks). Variants of classical design includes smaller lawn tractors and theirs relative's garden tractors, with output power from 10 to 25 HP, which are used for smaller tasks on farms and gardens. Their's size and speed (when on the road) demand great attention of other traffic participants.

PTO

Most of the tractors have an ability to transmit their power to the other machines like balers, mowers or cutters. First tractors used belt wrapped around the flywheel to power stationary machines. Modern tractors use power take off (PTO) shaft to transmit rotary power to the stationary or pulled equipment. Almost all modern tractors can provide hydraulic fluid and electrical power. Most of the tractors use manual transmission. They have several sets of gear rations divided into speeds. To change the ration it is often necessary to stop the tractor. Rations have different range of speeds which provide driving from one km/h for land work to 40 km/h for road use. For reverse driving usually it is not necessary to change gear, but simply select a lever. Almost all tractors require a clutch to be pressed when shift between gears, but many modern tractors eliminated this requirement by using power shifting introduced in 1960 or by using modern continuous variable transmission. This allows operators easier control over working speed than throttle alone. Small, controlled speed is needed when using tractors in the field or for other operations, but it is not appropriate and can be dangerous for public roads. Therefore some countries introduced legislation to prevent driving tractors on the public roads. Some modern tractors, like JCB Fastrac can be driven up to 80 km/h.

Modern tractors have rollover protection system (ROPS) to protect operators from squeezing. This is important for tractors without cab where driver is protected with steel bar over the seat. For tractors with cab, protection bar is part of the cab. Especially dangerous are tractors with front wheels which are close to one another (tractors for row-crops) because they can easily rollover. New Zeland was the first country which demanded this protection by legislation in 1960.

Tree-point hitch

Attachments for tractors can be mounted on the back side of the tractor using three point hitch or by using draw bar. Three point hitch was patented by Harry Ferguson in 1926, but in 1960 it became standard (due to patent law). Attachments mounted on the three point hitch can be lifted or lowered by hydraulics using the control lever. Attachment mounted on the three point hitch is usually fully relay on tractor. Even faster way to mount attachment on the tractor is using quick hitch which is mounted on the three point hitch.