Three-point hitch
From Wikipedia, the free encyclopedia
The three-point hitch most often refers to the way ploughs and other implements are attached to an agricultural tractor. Three point attachment is the simplest and the only statically definite way of joining two bodies in engineering. Harry Ferguson patented the three-point hitch for agricultural tractors in Britain in 1926. His credit does not lie in invention of the device, but in realization of the importance of rigid attachment of the plough to the tractor. The three-point hitch was not standardized until 1960. The implements can be either hooked on to the hitches of the tractor, as well as implements that are pulled and are connected to the hitches. The three points resemble either a triangle, or the letter A.
[edit] Components
The three-point hitch is made up of several components working together. These include the tractor's hydraulic system, attaching points, the lifting arms, and stabilizers.
Three-point hitches are composed of three movable arms. The two outer arms - the hitch lifting arms - are controlled by the hydraulic system, and provide lifting, lowering, and even tilting to the arms. The center arm - called the top link - is movable, but is usually not powered by the tractor's hydraulic system. Each arm has an attachment device to connect implements to the hitch.
Each hitch has attachment holes for attaching implements, and the implement has posts that fit through the holes. The implement is secured by placing a pin on the ends of the posts.
The hitch lifting arms are powered by the tractor's own hydraulic system. The hydraulic system is controlled by the operator, and usually a variety of settings are available.
There are several different hitch systems, called categories. Category Zero hitches are used with small farm or garden tractors. Category III hitches are found on the larger farm tractors, or those above 90hp.
[edit] History
Before the 1960s, each manufacturer used their own systems for hitching, or attaching their implements to their tractors. Farmers would have to purchase the same brand implements as their tractor to be able to correctly hook up the implement. A number of adaptation kits - which were clumsy and often unsafe - had to be used if a farmer needed to use a different brand implement with the tractor.
Eventually, tractor and implement manufacturers agreed on one standard system to hitch tractors to implements. As patents on technology expired, the manufacturers were able to refine the system, and nearly all the manufacturers have adopted what would become the three-point hitch system.
