Three-point hitch

The three-point hitch (British English: three-point linkage) 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. 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. Its utility 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 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.

The primary benefit of the three point hitch system is to transfer the weight and stress of an implement to the rear wheels of a tractor.

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 adaptation kit - which were typically clumsy, ill-fitting, or unsafe - had to be installed.

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 [ [http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=4969 ISO 730-1] ] form of the modern three-point hitch system; many companies also offer safe adaptation fits for converting the non-standard hitch systems to the three-point hitch system.

ee also

* Overrunning clutch
* Power take-off

External links

* [http://www.ulsterhistory.co.uk/harryferguson.htm The inventor, Harry Ferguson]
* [http://www.ferguson-museum.co.uk/3_point.htm Three-point linkage model]
* [http://www.masseyferguson.com/ Massey-Ferguson Tractor Site]
* [http://www.tractordata.com/threepoint.html Explanation of the categories]
* [http://www.tractor-outlet.com/tohitch.html Additional explanation of categories]