Power Applications:
The power produced by the engine must be transmitted to the implement or equipment in order to do the actual work intended for the equipment. This may be accomplished via a drawbar or hitch system if the implement is to be towed or otherwise pulled through the tractive power of the engine, or via a pulley or power take-off system if the implement is stationary, or a combination of the two.
Drawbars:
Until the 1950s, plows and other tillage equipment usually were connected to the tractor via a drawbar, or a proprietary connecting system. The classic drawbar is simply a steel bar attached to the tractor (or in some cases, as in the early Fordsons, cast as part of the rear transmission housing) to which the hitch of the implement was attached with a pin or by a loop and clevis. The implement could be readily attached and removed, allowing the tractor to be used for other purposes on a daily basis. If the tractor was equipped with a swinging drawbar, the drawbar could be set at the center or offset from center to allow the tractor to run outside the path of the implement.
The drawbar system necessitated that the implement have its own running gear (usually wheels) and in the case of a plow, chisel cultivator or harrow, some sort of lift mechanism to raise it out of the ground at turns or for transport. Drawbars necessarily posed a rollover risk depending on how the tractive torque was applied. The Fordson tractors (of which more units were produced and placed in service than any other farm tractor) was extremely prone to roll over backwards due to an excessively short wheelbase. The linkage between the implement and the tractor usually had some slack which could lead to jerky starts and greater wear and tear on the tractor and the equipment.
Drawbars were appropriate to the dawn of mechanization, because they were very simple in concept and because as the tractor replaced the horse, existing horse-drawn implements usually already had running gear. As the history of mechanization progressed, however, the advantages of other hitching systems became apparent, leading to new developments. Depending on the function for which a tractor is used, however, the drawbar is still one of the usual means of attaching an implement to a tractor.
Fixed mounts:
Some tractor manufacturers produced matching equipment that could be directly mounted on the tractor. Examples included front-end loaders, belly mowers, row crop cultivators, corn pickers and corn planters. In most cases, these fixed mounts were proprietary and unique to each make of tractor, so that an implement produced by John Deere, for example, could not be attached to a Minneapolis Moline tractor. Another disadvantage was that mounting usually required some time and labor, resulting in the implement being semi-permanently attached with bolts or other mounting hardware. Usually it was impractical to remove the implement and reinstall it on a day-to-day basis. As a result, the tractor was unavailable for other uses and dedicated to a single use for an appreciable period of time. An implement generally would be mounted at the beginning of its season of use (such as tillage, planting or harvesting) and removed only when the likely use season had ended.
Three-point hitches and quick hitches:
The drawbar system was virtually the exclusive method of attaching implements (other than direct attachment to the tractor) before Harry Ferguson developed the three-point hitch. 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 put the person in less danger when attaching the implement.The three-point hitch revolutionized farm tractors and their implements. Almost every tractor today features Ferguson’s 3 point linkage or a derivative of it. The three-point hitch allows for easy attachment and detachment of implements while allowing the implement to function as a part of the tractor almost as if it were attached by a fixed mount. Previously, when the implement hit an obstacle the towing link would break or the tractor could flip over. Ferguson’s genius was to combine a connection via two lower and one upper lift arms that were connected to a hydraulic lifting ram. The ram was in turn connected to the upper of the 3 links so that increased drag (as when a plough hits a rock) caused the hydraulics to lift the implement until the obstacle was passed.
Other manufacturers copied Ferguson’s invention, or developed variations of it. For example, International Harvestor’s Farmall tractors had a two-point “Fast Hitch” and John Deere had a power lift that was similar but not as flexible as the Ferguson invention. Recently, Bobcat’s patent on its front loader connection (inspired by these earlier systems) has expired; and compact tractors are now being outfitted with quick-connect attachments for their front-end loaders.
Power take-off systems and hydraulics:
In addition to towing an implement or supplying tractive power through the wheels, most tractors have a means to transfer power to another machine such as a baler, swather, or mower. Unless it functions solely by pulling it through or over the ground, a towed implement needs its own power source (such as a baler or combine with a separate engine) or else a means of transmitting power from the tractor to the mechanical operations of the equipment.
Early tractors used belts or cables wrapped around the flywheel or a separate belt pulley to power stationary equipment, such as a threshing machine, buzz saw, silage blower, or stationary baler. In most cases, it was not practical for the tractor and equipment to move with a flexible belt or cable between them, so this system necessitated that the tractor remain in one location with the work brought to the equipment, or that the tractor be relocated at each turn and the power set-up reapplied (as in cable-drawn plowing systems used in early steam tractor operations).
Modern tractors use a power take-off (PTO) shaft to provide rotary power to machinery that may be stationary or pulled. The PTO shaft generally is at the rear of the tractor, and can be connected to an implement that is either towed by a drawbar or a three-point hitch. This eliminates the need for a separate implement-mounted power source, which is almost never seen in modern farm equipment.
There are three basic types of PTO control on a farm tractor:
Transmission
The simpliest, and earliest, form of PTO is the transmission PTO. The PTO shaft is directly connected to the tractor’s transmission. The PTO is only working when the tractor’s clutch is relased, so if you take the tractor out of gear while slowing down the PTO will stop working. This is a disadvantage in applications such as mowing.An overrunning clutch is often needed with a transmission PTO. Without it, the driven equipment (such as mower blades) will put a force on the PTO shaft, and then the transmssion, due to inertia. The equipment will “drive” the tractor, and you will still move after using the tractor’s transmission clutch. An overrunning clutch prevents this from happening by allowing the PTO shaft to freely spin in one direction. In more recent models, this is built into the tractor. In older tractors, it is an extra piece of equipment mounted on the PTO shaft.
An overrunning PTO clutch is a device that allows a tractor’s power take-off (PTO) shaft to be driven in one direction, but to spin freely (freewheel) in the other direction. The ratchet mechanism in an overrunning clutch is similar to the freewheel hub on a bicycle. The frewheel action of the overrunning clutch prevent equipment from “driving” the tractor through its PTO shaft.A typical example is a rotary mower (sometimes called a “bush hog”) that is being operated behind a tractor with a transmission PTO. When the operator pushes the clutch to slow the tractor, the inertia of the spinning mower blades put a force onto the PTO shaft. This force drives the tractor forward, causing an unsafe situation. overrunning clutch quick couplerSome tractors with transmission-linked PTO shafts have an internal overrunning PTO clutch provided by the manufacturer. For those tractors that lack the cluch, there are a number of companies that built after-market overrunning clutch mechanisms. A typical device is a quick-coupler that snaps onto tractor’s PTO shaft, between the tractor and the equipment.
Live (two-stage clutch)
A live PTO works with the use of a two-stage clutch. Pressing the clutch half-way will disengage the transmission while pressing it fully will disengage the transmission and the PTO. This allows the operator to slow down or change gears while the PTO is still operating.
Independent
An independent PTO means that the PTO shaft is controlled with a separate clutch. As with a live PTO, this allows for full control over the tractor while separately controlling the PTO. There are two major types of independent PTO; mechanical and hydraulic. A mechanical-independent PTO uses a separate on-off selector, in addition to the PTO control lever. Often the tractor must be stopped or off to change this selector position. A hydraulic-independent PTO uses a single selector.
Virtually all modern tractors can also provide external hydraulic fluid and electrical power to the equipment they are towing, either by hoses or wires.
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