Three-point linkage
A three-point power lift , also known as three-point hydraulics, is a hydraulic device on tractors to couple and lift attachments (work equipment ).
The component, also known for short as three-point or hydraulic system, is often found on the rear of a tractor ( rear linkage ). Attached to the front of the tractor is referred to as a front linkage . The downward movement occurs either hydraulically or, in the case of simpler systems, through the weight of its own elements (lower links) or the attachments. The system is called three-point because the implements are attached to the tractor at three points.
construction
Two levers are mounted lengthways at the rear of the tractor . They are called lower links, the free ends of which form the two lower points of the three-point hitch. The lower links are attached to the tractor with horizontal shafts or bolts oriented transversely to the direction of travel . The field devices are coupled to the free ends of the lower links. The weight of the devices can be transferred to the drive axle , which increases the traction and thus the tractive power of the tractor. The lower links are raised either directly or via a lever system with a hydraulic cylinder . On larger tractors, one hydraulic cylinder is used per lower link. This increases the lifting force. Single or double-acting hydraulic cylinders are used. With single-acting hydraulic cylinders, only the weight of the attachment is borne. Double-acting hydraulic cylinders have the advantage that, in addition to being carried, pressure can also be exerted on the attachment.
Another lever is attached in the middle further above the lower link. It is known as the top link and enables the inclination of the attachment to be adjusted. The rearward-facing end is the third point on a three-point hitch. The top link is designed as a threaded spindle that can be lengthened or shortened without dismantling. In the case of heavier tractors and field devices, the length can be adjusted using double-acting hydraulic cylinders, even under load.
The suspension points of the upper and lower links are often designed as catch hooks . This enables the attachments to be connected more quickly without the need for assistants who, for. B. the lower links must lead laterally on the bolts.
The attachment has a so-called "A-frame"; the hooks are attached to it. When it is lifted into the transport position, the attachment is tilted in the direction of the tractor by the kinematics of the linkage of unequal length, thus shifting the attachment's center of gravity to the standing surface of the vehicle. This achieves the driving stability of the tractor that is desired for road transport.
function
With the hydraulic three-point suspension, the field devices
- transport stably and safely
- Easily and quickly put into working position in the field
- set to a certain working depth and automatically and precisely regulate it when working the soil.
Advantages of an automatic hoist control :
- Depending on the pre-setting of the hydraulics, the weight of the field device improves the traction on the rear wheels of the tractor.
- There is more pressure on the rear wheels, which reduces slip and thus tire wear.
- The front axle is not raised, even with high tractive forces. The result is better controllability.
- With all-wheel drive , the traction of all wheels can be used.
- Relief of the driver
- Better quality of work due to constant device position.
- Less wear and tear on the three-point linkage and work equipment.
Depending on the set working depth and the nature of the ground, different forces act on the upper and lower links. The handlebars transmit the push and pull forces required to control the hydraulics. If only the forces or the movements of the upper link are taken into account, one speaks of "upper link controlled". "Lower link-controlled" is the term used to describe hoist controls in which the control signals are picked up on the lower link.
The control of the hydraulic cylinders is regulated according to the following scheme:
- more draw resistance = the hoist lifts the plow on
- less pulling resistance = the lifting mechanism lowers the plow.
Depending on the type of implementation of compressive and tensile forces in control signals, a distinction is made between the following systems:
MHR
- Mechanical hoist control. The upper or lower links act on the levers of the lifting mechanism via a linkage. The MHR is the oldest form of tension control.
SHR
- Fully hydraulic hoist control. The linkages act directly on a hydraulic control valve that controls the actuation of the hydraulic cylinders. The SHR was introduced to the market by Case-IH in 1983.
- The 3-point hydraulic control system was introduced by Massey Ferguson in 1956 with the FE35.
EHR
- With the electronic hoist control, the movements and forces on the suspension are recorded electronically. The handlebars are attached to the tractor with force measuring bolts. There are two magnet coils in the bolt . The primary coil is energized. The force changes the magnetic properties of the material and a voltage is generated in the secondary coil . An electronic control unit uses this voltage to calculate the load status. The exact height can be determined and adjusted with a position sensor on the three-point hitch.
Electronic control is generally more sensitive and faster than mechanical control. The elimination of mechanical components means that electronic hoist control is low-wear and less maintenance-intensive. The EHR is standard on modern tractors. The hoist control can control depending on the pulling force or depending on the position. A mixture of both types of regulation is also possible.
- Traction control
- The tensile force on the rods is tapped as a parameter for the control. The draft-dependent control is generally only used for plowing.
- Position regulation
- The lifting mechanism is controlled according to its relative height change to the tractor. The attachment is held at a fixed height. Location control is used, for example, for fertilizer spreaders .
- Float position
- Float position means no regulation. The hydraulic cylinders are released for hydraulic return. The attachments can move freely up and down. In the floating position, the working height is set by means of support wheels on the attachment. Use, for example, in seed drills .
Additional functions can also be implemented through the use of electronics.
- Setting different transport heights for different devices.
- Vibration dampening during transport.
- Float position with electronically limited end points.
- Drive slip control
- Programmable work sequences - e.g. B. automatic lifting and lowering for turning the reversible plow at the headland
- Control of the working position and programmed work sequences with the help of GPS navigation data.
On the lower links when necessary one may Ackerschiene be attached. In old tractors without a three-point system, the drawbar was rigidly connected to the tractor.
Quick coupler and dimensions
The three-point fastenings are standardized today and equipped with quick couplers. These are divided into categories 1 to 4 depending on the PTO output. There is also category 0 for small municipal tractors. The categories are defined as follows:
| category | 0 | 1 | 2 | 3 | 4L | 4H |
|---|---|---|---|---|---|---|
| PTO power at rated engine speed | up to 15 kW | up to 48 kW | up to 92 kW | 80-185 kW | 150-350 kW | 150-350 kW |
| Upper coupling point | ||||||
| Ball diameter top link | 50 mm | 60 mm | ||||
| Ball width top link (max.) | 44 mm | 51 mm | 51 mm | 64 mm | 64 mm | |
| Pin diameter top link (tolerance) | 5/8 " | 19 mm (0; −0.08) | 25.5 mm (0; −0.13) | 32 mm (0; −0.2) | 45 mm (0; −0.8) | 45 mm (0; −0.8) |
| clear distance between safety pins on the upper link pin (min) | 76 mm | 93 mm | 102 mm | 140 mm | 140 mm | |
| Lower coupling points | ||||||
| Ball diameter lower link | 44 mm | 56 mm | 64 mm | |||
| Ball width lower link (tolerance) | 35 mm (0; −0.2) | 45 mm (0; −0.2) | 45 mm (0; −0.2) | 57.5 mm (0; −0.5) | 57.5 mm (0; −0.5) | |
| Pin diameter lower link (tolerance) | 5/8 " | 22.4 mm (+0.25; 0) | 27.7 mm (+0.3,0) | 37.4 mm (+0.35; 0) | 51.0 mm (+0.5; 0) | 51.0 mm (+0.5; 0) |
| Distance from the center of the lower link to the longitudinal center plane of the tractor | approx. 10 " | 359 mm | 435 mm | 505 mm | 610 or 612 mm | 610 or 612 mm |
| Lateral deviation of the lower links from the middle position (min.) | 100 mm | 125 mm | 125 mm | 130 mm | 130 mm | |
| Distance from the PTO end to the center of the lower coupling point with horizontal lower link | 500-575 mm | 550-625 mm | 575-675 mm | 575-675 mm | 610-670 mm | |
history
The inventor of the three-point hitch is Irish Harry Ferguson . In 1918 he was commissioned by the British Agriculture Authority to improve the efficiency of food production by developing agricultural equipment.
In 1928 he planned the prototype of a new trailer system. The aim should be to transfer some of the weight of the attachments to the tractor in order to better utilize the power of a light tractor. From the duplex hitch he developed the three-point hitch . In order to be able to effectively demonstrate his idea to future manufacturers, he planned to construct his own tractor. He used gear parts from David Brown and a Hercules engine that came from the USA.
In 1933 Ferguson unveiled the world's first three-point hydraulic tractor, the Black Tractor , in its Belfast workshop . The name was derived from its black paintwork. The Black Tractor is now in the Science Museum in London . In the following years he merged with the English tractor manufacturer David Brown . In 1936 the first series tractor with the Ferguson system, the Ferguson Brown Type A, appeared .
In 1938 Ferguson merged with the American automobile and tractor manufacturer Henry Ford . In 1938 the first Ford tractor with the three-point hitch also appeared, the type 9N .
Ferguson separated from Ford after a lengthy dispute in 1947. He then built tractors from 1947 to 1953. In 1953 he sold his factory to the Canadian agricultural machinery manufacturer Massey-Harris . From this came Massey Ferguson .
In 1979, with an articulated tractor from Massey-Ferguson, an electronic hitch control (EHR) from Bosch was brought to series production for the first time .
Agricultural historical impact
Three-point hydraulics had a lasting impact on agriculture in the 20th century. Their introduction made intensive, rational, labor-saving soil cultivation possible.
Individual evidence
- ↑ DIN ISO 730-1 Agricultural machinery and tractors - Rear three-point linkage - Part 1: Categories 1, 2, 3 and 4 (ISO 730-1: 1994) Edition: 1997-05 standard
- ↑ TractorData.com: Three-Point Hitch.
- ↑ a b masseyferguson.at: MF history - the founders. ( Memento of the original from February 28, 2008 in the Internet Archive ) Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ winci.de: Bosch-Rexroth EHR - Electronic hoist control for agricultural machinery. ( Memento of the original from October 31, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
