What is a Three-point Hitch?
The three-point hitch (also referred to as three-point linkage) is a type of hitch for attaching plows and other implements to either an industrial or agricultural tractor.
A three-point hitch looks like a triangle. It attaches the implement to the tractor. Once the implement is attached, it is fixed in place with respect to the tractor and the arm position of the hitch.
Your tractor will carry some (or all) of the implement’s weight.
The other mechanism for attaching a load is through a drawbar. This is a single point, pivoting attachment where the implement or trailer is not in a fixed position with respect to the tractor.
The primary benefit of the three-point hitch system is to transfer the weight and resistance of an implement to the tractor’s drive wheels. This gives the tractor more traction than it would otherwise have, given the same weight, power, and fuel consumption.
Features
The three-point hitch is comprised of several systems that work in sync.
These include the tractor's attaching points, lifting arms, stabilizers, and hydraulic system.
Three-point hitches are made up of three movable arms.
The two lower arms (the hitch lifting arms) are controlled by the hydraulic system. They provide lifting, lowering, and even tilting to the arms. The upper center arm (the top link) can be moved, but it is not usually powered by the tractor's hydraulic system.
Each arm has an attachment device to connect implements to the hitch and each hitch has attachment holes for attaching the implements. The implement has posts that fit through the holes.
Implements are 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, through a host of settings.
A draft control mechanism is often present in today’s modern three-point hitch systems. The draft of the implement and the amount of force it is taking to pull the implement are sensed on the top link. The hydraulic system automatically raises the arms slightly when the draft increases and lowers the arms when the draft decreases.
Size Categories
There are five different hitch sizes, called categories, or classes. The higher category hitches have sturdier lift arms and larger connector pins. There is some flexibility in the tractor HP at which one category hitch ends and the next begins.
Here they are:
Category 0: Up to 20 hp (15kW)
Category 1: 20 to 45 hp (15 to 34 kW)
Category 2: 40 to 100 hp (30 to 75 kW)
Category 3: 80 to 225 hp (60 to 168 kW)
Category 4: 180+ hp (130 kW)
(The higher category hitches have larger connector pins and sturdier lift arms.)
Three-point Hitch 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 realisation 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-Ferguson 9N). The hydraulically operated and controlled three point hitch utilized the draft of the mounted tool to moderate the depth of the tool and therefore the load on the tractor.
Before the 1940s, 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 standardised[1] form of the modern three-point hitch system; many companies also offer safe adaptation kits for converting the non-standard hitch systems to the three-point hitch system.