A tractor is a vehicle designed to provide a high tractive effort
(pulling force) at slow speeds, in order to haul a trailer or machinery
used in agriculture or construction. The term tractor is derived from the Latin trahere, which means "to pull."
Most commonly, the word "tractor" is used to describe the distinctive
farm vehicle. The farm tractor is used for pulling or pushing
agricultural machinery or trailers, for plowing, tilling, disking,
harrowing, planting, and similar tasks. In Canada and the United States,
the word is also used to refer to a road tractor. Other common uses of
the term include the lawn tractor and the power unit of a semi-trailer
truck.
Farm tractor
History
The first powered farm implements in the early 1800s were portable
engines—steam engines on wheels that could be used to drive mechanical
farm machinery by way of a flexible belt. Around 1850, the first
traction engines were developed from them and were widely adopted for
agricultural use. Where soil conditions permitted, as in the U.S., steam
tractors were used to direct-haul plows, but in the UK, plowing engines
were used for cable-hauled plowing instead. Steam-powered agricultural
engines remained in use well into the twentieth century, until reliable
internal combustion engines were developed.
In 1892, John Froelich built the first practical gasoline-powered
tractor in Clayton County, Iowa, but only two were sold. It was not
until 1911, when the Twin City Traction Engine Company developed the
design, that it became successful.
In Britain, the first recorded tractor sale was the oil-burning
Hornsby-Ackroyd Patent Safety Oil Traction engine, in 1897. However, the
first commercially successful design was Dan Albone's three-wheel Ivel
tractor of 1902. In 1908, Saundersons of Bedford introduced a four-wheel
design, and went on to become the largest tractor manufacturer outside
the U.S.
While unpopular at first, these gasoline-powered machines began to catch
on in the 1910s, when they became smaller and more affordable. Henry
Ford introduced the Fordson, the first mass-produced tractor, in 1917.
Built in the U.S., Ireland, England, and Russia, Fordson had 77 percent
of the U.S. market by 1923. The Fordson dispensed with a frame, using
the strength of the engine block to hold the machine together. By the
1920s, tractors with a gasoline-powered internal combustion engine had
become the norm.
The classic farm tractor is a simple open vehicle, with two very large
driving wheels on an axle below and slightly behind a single seat. The
seat and steering wheel consequently are in the center of the vehicle.
The engine is placed in front of the driver, with two steerable wheels
below the engine compartment. This basic design remained unchanged for a
number of years, but all modern models are fitted with enclosed cabs,
for reasons of operator safety and comfort.
Originally, plows and other equipment were connected via a draw-bar, or a
proprietary connecting system; prior to Harry Ferguson patenting the
three-point hitch. Recently, Bobcat's patent on its front loader
connection expired, and compact tractors are now being outfitted with
quick-connect attachments for their front-end loaders.
Operation
Modern farm tractors usually have five foot-pedals for the operator on
the floor of the tractor. The pedal on the left is the clutch. The
operator presses on this pedal to disengage the transmission for either
shifting gears or stopping the tractor. Two of the pedals on the right
are the brakes. The left brake pedal stops the left rear wheel and the
right brake pedal does the same with the right side. This independent
left and right wheel braking augments the steering of the tractor when
only the two rear wheels are driven. This is usually done when it is
necessary to make a tight turn. The split brake pedal is also used in
mud or soft dirt to control a tire that spins due to loss of traction.
The operator presses both pedals together to stop the tractor. For
tractors with additional front-wheel drive, this operation often engages
the 4-wheel locking differential to help stop the tractor when
traveling at road speeds.
A fifth pedal just in front of the seat operates the rear differential
lock (diff lock) which prevents wheelslip. The differential allows the
outside wheel to travel faster than the inside one during a turn.
However, in traction conditions on a soft surface the same mechanism
could allow one wheel to slip, thus preventing traction to the other
wheel. The diff lock overrides this, causing both wheels to supply equal
traction. Care must be taken to unlock the differential, usually by
hitting the pedal a second time, before turning, since the tractor
cannot perform a turn with the diff lock engaged.
The pedal furthest to the right is the foot throttle. Unlike the setup
in automobiles, it can also be controlled from a hand-operated lever
("hand throttle"). This helps provide a constant speed during field
work. It also helps provide continuous power for stationary tractors
that are operating an implement by shaft or belt. The foot throttle
gives the operator more automobile-like control over the speed of the
tractor for road work. This is a feature of more recent tractors; older
tractors often did not have this feature. In the UK, it is mandatory to
use the foot pedal to control engine speed while traveling on the road.
Some tractors, especially those designed for row-crop work, have a
"de-accelerator" pedal, which operates in the reverse fashion to an
automobile throttle, in that the pedal is pushed down to slow the
engine. This is to allow fine control over the speed of the tractor when
maneuvering at the end of crop rows in fields—the operating speed of
the engine is set using the hand throttle, and if the operator wishes to
slow the tractor to turn, he simply has to press the pedal, turn, and
release it once the turn is completed, rather than having to alter the
setting of the hand throttle twice during the maneuver.
Power and transmission
Modern farm tractors employ large diesel engines, which range in power
output from 18 to 575 horsepower (15 to 480 kW). Tractors can be
generally classified as two-wheel drive, two-wheel drive with front
wheel assist, four-wheel drive (often with articulated steering), or
track tractors (with either two or four powered rubber tracks).
Variations of the classic style include the diminutive lawn tractors and their more capable and ruggedly constructed cousins, garden tractors,
that range from about 10 to 25 horsepower (7.5-18.6 kW) and are used
for smaller farm tasks and mowing grass and landscaping. Their
size—especially with modern tractors—and the slower speeds are reasons
motorists are urged to use caution when encountering a tractor on the
road.
Most tractors have a means to transfer power to another machine, such as
a baler, slasher, or mower. Early tractors used belts wrapped around a
flywheel to power stationary equipment. Modern tractors use a power
take-off (PTO) shaft to provide rotary power to machinery that may be
stationary or pulled. Almost all modern tractors can also provide
external hydraulic fluid and electrical power.
Most farm tractors use a manual transmission. They have several sets of
gear ratios divided into speeds. In order to change the ratio, it is
usually necessary to stop the tractor. Between them they provide a range
of speeds from less than one mile per hour suitable for working the
land, up to about 25 miles per hour (40 km/h) for road use. Furthermore,
it is usually not necessary to change gear in order to reverse, one
simply selects a lever. Older tractors usually require that the operator
depress the clutch in order to shift between gears (a limitation of
straight-cut gears in the gearbox), but many modern tractors have
eliminated this requirement with the introduction of technologies such
as power shifting in the 1960s, and more modern continuously variable
transmissions. This allows the operator more and easier control over
working speed than the throttle alone could provide.
Slow, controllable speeds are necessary for most operations that are
performed with a tractor. They help give the farmer a larger degree of
control in certain situations, such as field work. However, when
traveling on public roads, the slow operating speeds can cause problems,
such as long lines or tailbacks, which can delay or aggravate other
road users. To alleviate conditions, some countries (for example, the
Netherlands) employ a road sign on some roads that means "no farm
tractors." Some modern tractors, such as the JCB Fastrac, are now capable of the much more tolerable road speeds of around 50 mph (80 km/h).
Safety
Agriculture in the United States is one of the most hazardous
industries, surpassed only by mining and construction. No other farm
machine is so identified with the hazards of production agriculture as
the tractor. Tractor-related injuries account for approximately 32
percent of the fatal and 6 percent of the non-fatal injuries in
agriculture. Over 50 percent of these are attributed to tractor
overturns.
The modern tractor has a roll over protection structure (ROPS) to
prevent an operator from being crushed if the tractor overturns. The
ROPS and seat belt, when worn, are the two most important safety devices
to protect operators from death during tractor overturns.
It is important to remember that the ROPS does not prevent tractor
overturns. Rather, it prevents the operator from being crushed during an
overturn. This is especially important in open-air tractors, where the
ROPS is a steel beam that extends above the operator's seat. For
tractors with operator cabs, the ROPS is part of the cab's frame. An
ROPS with an enclosed cab further reduces the likelihood of serious
injury because the operator is protected by the cab's sides and windows.
Before tractors were required to have ROPS (before the 1960s), some
farmers died when their tractors rolled over them. Row-crop tractors,
before ROPS, were particularly dangerous because of their "tricycle"
design with the two front wheels spaced close together and angled inward
toward the ground. Some farmers were killed by rollovers while
operating tractors along steep slopes. Others were killed while
attempting to tow or pull an excessive load from above axle height, or
when cold weather caused the tires to freeze down, in both cases causing
the tractor to pivot around the rear axle.
For the ROPS to work as designed, the operator must stay within the
protective frame of the ROPS. This means the operator must wear the seat
belt. Not wearing the seat belt may defeat the primary purpose of the
ROPS.
Applications
Farm implements can be attached to the rear of a tractor by either a
drawbar or three-point hitch. The latter, invented by Harry Ferguson,
has been standard since the 1960s. Equipment attached to the three-point
hitch can be raised or lowered hydraulically with a control lever. The
equipment attached to the three-point hitch is usually completely
supported by the tractor. Another way to attach an implement is via a
Quick Hitch, which is attached to the three-point hitch. This enables a
single person to attach an implement quicker, and it puts the person in
less danger when attaching the implement.
Some farm-type tractors are found in places other than farms: In the
gardening departments of large universities, in public parks, and at
highway construction sites, where the tractor may have blowtorch
cylinders strapped to its sides and a pneumatic drill air compressor
permanently fastened over its power take-off. These are often fitted
with grass (turf) tires, which are less damaging on soft surfaces than
agricultural tires.
Precision agriculture
Space technology has found its way down to agriculture in the form of GPS devices and robust, on board computers installed as optional features
on farm tractors. These technologies are used in modern, precision
farming techniques. The spin-offs from the space race have actually
facilitated automation in plowing and the use of autosteer system drones
on tractors that are manned but steered only at the end of a row. The
idea is to avoid overlap, use less fuel, and not leave streaks when
performing jobs such as cultivating.
Compact Utility Tractor
A Compact Utility Tractor (or CUT) is a smaller version of an
agricultural tractor, designed primarily for landscaping and estate
management type tasks rather than for planting and harvesting on a
commercial scale. Typical CUTs range from 20 to 50 horsepower (15-37 kW)
with available power take off (PTO) horsepower ranging from 15 to 45 hp
(11-34 kW). CUTs (especially those below 40 horsepower (30 kW)) are
often equipped with both a mid-mounted PTO and a standard rear PTO. The
mid-mounted PTO shaft typically rotates at/near 2000 rpm and is
typically used to power such implements as mid-mount finish mower, a
front-mounted snow blower, or front-mounted rotary broom. The rear PTO
is standardized at 540 rpm for the North American markets, but in some
parts of the world a dual 540/1000 rpm PTO is standard, and implements
are available for either standard in those markets.
One of the most common attachments for a compact utility tractor is the
front end loader or FEL. Like the larger agricultural tractors, a CUT
has an adjustable three-point hitch with hydraulic controls. Typically, a
CUT has a four-wheel drive (more correctly, a four-wheel assist).
Modern Compact Utility Tractors often feature a Hydrostatic
transmission, but many variants of gear drive transmissions are also
available, from low-priced, simple gear transmissions to synchronized
transmissions to advanced, glide-shift transmissions. All modern CUTs
feature a government mandated roll over protection structure (ROPS) just
like agricultural tractors. Although less common, compact backhoes may
be attached to compact utility tractors.
Compact utility tractors require special smaller implements than
full-sized agricultural tractors. Common implements include the box
blade, grader blade, landscape rake, post hole digger (or post hole
auger), rotary cutter (also called a slasher or a brush hog), a mid- or
rear-mount finish mower, broadcast seeder, subsoiler, and rototiller (or
rotary tiller). In colder climates, a rear-mounted snow blower is very
common. There are many more implement brands than there are tractor
brands offering CUT owners a wide selection to choose from.
For small-scale farming or large-scale gardening, there are some plating
and harvesting implements sized for CUTs. One and two row planting
units are commonly available, as are cultivators, sprayers, and
different types of seeders (slit, rotary, and drop).
Backhoe loader
The most common variation of the classic farm tractor is the hoe, also called a hoe loader or backhoe loader.
As the name implies, it has a loader assembly in the front and a
backhoe in the back. Backhoes attach to a 3-point hitch on farm or
industrial tractors. Industrial tractors are often heavier in
construction, particularly with regards to the use of a steel grill for
protection from rocks and the use of construction tires. When the
backhoe is permanently attached, the machine usually has a seat that can
swivel to the rear to face the hoe controls. Removable backhoe
attachments almost always have a separate seat on the attachment.
Backhoe loaders are very common and can be used for a wide variety of
tasks: Construction, small demolitions, light transportation of building
materials, powering building equipment, digging holes, loading trucks,
breaking asphalt, and paving roads. Some buckets have a retractable
bottom, enabling them to empty their load more quickly and efficiently.
Buckets with retractable bottoms are also often used for grading and
scratching off sand. The front assembly may be a removable attachment or
permanently mounted. Often the bucket can be replaced with other
devices or tools.
Their relatively small frame and precise control make backhoe loaders
very useful and common in urban engineering projects such as
construction and repairs in areas too small for larger equipment. Their
versatility and compact size make them one of the most popular urban
construction vehicles.
Engineering tractors
The durability and engine power of tractors made them highly suitable
for engineering tasks. Tractors can be fitted with engineering tools
such as a dozer blade, bucket, hoe, or ripper. When fitted with
engineering tools, the tractor is called an engineering vehicle.
A bulldozer is a track-type tractor attached with a blade in the front
and a rope-winch behind. Bulldozers are very powerful tractors and have
excellent ground-hold, as they are built to push or drag things along
the ground.
Bulldozers have been further modified over time to produce new machines
that are capable of working in ways that the original bulldozer could
not. One example is the manufacture of loader tractors, in which the
blade was replaced by a large-volume bucket and hydraulic-powered arms
that can raise and lower the bucket, thus making it useful for scooping
up earth, rock, and similar loose material to load it into trucks.
Alternatively, the bulldozer may be fitted with a pallet fork or a bale
grappler.
Other modifications to the original bulldozer include making the machine
smaller, so that it can operate in small work areas where movements are
limited. There are also tiny-wheeled loaders, officially called
Skid-steer loaders but nicknamed "Bobcat" after the original
manufacturer, which are particularly suited for small excavation
projects in confined areas.
Garden tractors
Garden tractors (also called mini tractors) are small, light, and simple
tractors designed for use in domestic gardens. They are usually
designed for cutting grass, being fitted with horizontal rotary cutting
decks.
The distinction between a garden tractor and a ride-on lawnmower is
often hard to make. Generally, a garden tractor has a more sturdy build,
with stronger frames, axles, and transmissions. Garden tractors are
generally capable of mounting other implements such as harrows,
cultivators/rotavators, sweepers, rollers and dozer-blades. Like ride-on
mowers, garden tractors generally have a horizontally mounted engine
with a belt-drive to a transaxle-type transmission (usually of 4- or
5-speeds, although some may also have two-speed reduction gearboxes or
hydraulic gearboxes). The engine is generally a 1- or 2-cylinder
gasoline (petrol) engine, although diesel engine models are also available, especially in Europe.
In the U.S., the term riding lawn mower today refers to mid- or
rear-engined machines. Front-engined tractor layout machines designed
primarily for cutting grass and light towing are called lawn tractors,
and heavy-duty lawn tractors, often shaft driven, are garden tractors.
The primary difference between a lawn tractor and a garden tractor are
the frame weight, the rear wheels (garden tractors almost always have
multiple mounting bolts, while most lawn tractors have a single bolt or
clip on the hub), and the ability to use ground engaging equipment such
as plows or disk-harrows.
EPA tractor
During World War II, a shortage of tractors in Sweden led to the invention of a new type of tractor called the EPA tractor.
(EPA was a chain of discount stores and the name was often used to
signify something of lower quality.) An EPA tractor was simply an
automobile, truck, or lorry, with the passenger space cut off behind the
front seats, equipped with two gearboxes in a row. When an older car
with a ladder frame was modified in this manner, the result was not
dissimilar to a tractor and could be used as one.
After the war, it remained popular, not as a farm vehicle but as a way
for young people without a driver's license to own something similar to a
car. Since it was legally considered a tractor, it could be driven by
people from 16 years of age and only required a tractor license.
Eventually, the legal loophole was closed and no new EPA tractors were
allowed to be made, but the remaining ones were still legal—leading to
inflated prices and protests from people who preferred EPA tractors to
ordinary cars.
On March 31, 1975, a similar type of vehicle was introduced, the A tractor, from arbetstraktor
(work tractor). The main difference is that an A tractor has a top
speed of 30 km/h. This is usually done by fitting two gearboxes in a row
and not using one of them. For a long time, the Volvo Duett was the
primary choice for conversion to an EPA or A tractor, but since supplies
have dried up, other cars have been used.
Other types of tractors
The term tractor (U.S. and Canada) or tractor unit (UK) is also applied to:
Road tractors, tractor units, or traction heads.
Heavy-duty vehicles with large engines and several axles. The majority
of these tractors are designed to pull long semi-trailers, most often
for the transport of freight of some kind over a significant distance
(as in semi-trailer truck). In England this type of "tractor" is often
called an "artic cab" and is connected to the trailer with a fifth wheel
coupling. A minority is the ballast tractor, whose load is hauled from a
drawbar. Locomotive tractors (engines) or Rail car movers The
amalgamation of machines, electrical generators, controls and devices
that comprise the traction component of railway vehicles Artillery
tractors Vehicles used to tow artillery pieces of varying weights.
Other uses of the word
In aerospace
In aircraft, a tractor configuration refers to the propellers being in front of the fuselage or wing. Conversely, if to the rear, it is a called a pusher configuration.
NASA and other space agencies use very large tractors to ferry launch
vehicles, such as booster rockets and space shuttles, from their hangars
to (and, in rare cases, from) the launchpad.
In computers
A tractor is also the part of a computer printer that pulls paper into
the device or pushes it along. This usually takes the form of a pair of
toothed gears that mesh with holes punched near the edges of the paper,
or a belt or wheel with rubber or other high-friction surface that makes
contact with the paper.
In downhole oil-well data logging
A tractor is a device which is used for conveying advanced instruments
into well holes for measurement and data logging purposes. The device is
driven through cased or open well holes by wheels, chains, or tractor
belts, and usually consists of a shell housing, an engine (electric or
fluid-driven), a driving mechanism/transmission, measuring equipment,
and interface with the surface.