Three-point Linkage

The three-point hitch also called three-point linkage most often refers to the way ploughs and other implements are attached to an agricultural tractor. Three point attachment is a simple way of joining any implement to the tractor. The implements can be attached on to the tractor by one operator, as well as implements that are pulled they can be lifted up for transport. The three points resemble either a triangle, or the letter A. Its versatility and simplicity has made it an industry standard.

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 adjustable, but is usually not powered by the tractor's hydraulic system, but is two threaded ends woth ball swivels joined by a theaded sleeve, that rotates to adjust its lenght. Each arm has a swivel ball with a large pin hole to attachment the device to pegs on the implements so it is "hitched up". A remotely adjustable top-Link is used in some applications that has a a hyraulic ram in the middle.

Each hitch has attachment holes for attaching implements, and the implement has pegs that fit through the holes. The implement is secured by placing a retainer "R" pin Through a hole in the ends of the pegs.

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.

The primary benefit of the three point hitch system is to transfer the weight of an implement to the rear wheels of a tractor. They also allow tighter turns by lifting some implements off the ground at the Headland and for transport between fields.

History

Harry Ferguson patented the three-point 'linkage' 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. He is also attributed with several innovations to this device (e.g. hydraulic lift) which made this system workable, effective, and desirable to the point of using it on mass marketed tractors (e.g. the Ford 9N).

Before the 1960s, each manufacturer used their own systems for hitching, or attaching their implements to their tractors. Commonplace was the two-point hitch system which could not effectively be used for lifting many implements. At this time, farmers would have to purchase the same brand implements as their tractor to be able to correctly hook up the implement. If a farmer needed to use a different brand implement with the tractor an adapter kit - which were typically clumsy, ill-fitting, or unsafe - had to be utilised.

In the 1960s, tractor and implement manufacturers would eventually agree on the three-point hitch as the one standard system to hitch implements to tractors. As patents on technology expired, the manufacturers were able to refine the system and create useful modifications. Now, nearly all manufacturers have adopted some standardized form of the modern three-point hitch system; many companies also offer safe adapter kits for converting the non-standard hitch systems to the three-point hitch system.

See also

• Power take-off
• Top Link
• Mounted Implement

External links

• The inventor, Harry Ferguson
• Three-point linkage model
• Massey-Ferguson Tractor Site
• Explanation of the categories
• Additional explanation of categories