The agricultural hitch, an evolution technology
Although with some difficulty, the transition continues in towing systems from the historical CUNA hitch to the most modern CE hitch. In any case, the devices provided nowadays, offer a considerably higher safety level, both in the coupling and in the transfer phase
The traditional (and historical) way to couple the tractor with the equipment is undoubtedly the trailed one, where the tractor is coupled with a hitch, said tow. In countries where mechanization is not yet particularly sophisticated, this is the only solution to couple tractor and machinery. Moreover, a good alternative (which has been available for a long time and now provided on all modern tractors) concerns the carried coupling, where the link is the three-point hitch operated by the hydraulic lift. The agricultural trailers, and all machinery operated by them, are then connected to the towing hitch with a rudder, which in the mobile version allows a limited oscillation in the horizontal and vertical planes and ends with an “eye hitch”, that is, a very sturdy ring in which the engagement is obtained through a special pin.
Approval
Since the said connection between the hitch and the eye hitch, through the pin, is the only element that connects two means that can reach both several tons, it is quite obvious that operational safety must reach the highest levels, also because these trains travels do not only occur on paved roads open to traffic but also (and sometimes above all) on particularly uneven surfaces as are often interpodal and forest roads. Therefore, the sizes of both the towing hitch and the rudder tail eye hitch are strictly standardized, that is to say that there are a set of precise minimum requirements to be met, verified by independent notified bodies, which, on the basis of standards, perform severe prototype approval tests, which must be followed by a series production identical to the tested model.
As NC338-02 says, a rule of the CUNA (Vehicle Unification Technique Commission), the Implementing Regulation of the New Road Code prescribes the obligation of the hitch (or of the eye hitch) equipment for those agricultural machinery intended for a trailed coupling, which must be equipped with devices classified in categories (identified by a letter, sometimes followed by a digit) substantially different depending on the maximum towable mass and the maximum allowable vertical load on the hitch.
So far for national standardization. However, the need for EU freedom of movement has long posed a problem of unification at European level, with the consequent need to introduce and disseminate the so-called “EC hitch”. To define the standard of the latter was primarily the Directive 89/173/EC, which was followed by other Directives, on the same subject, that gradually adapted the issue to technical progress. Unfortunately, the Community legislation has provided significantly different types of hitchs from the one defined by CUNA, forcing manufacturers to offer different product lines for different markets. In order to obtain the approval, the hitchs (as well as the eye hitches) are in any case subjected to a series of horizontal and vertical loads, defined according to their declared performance, and taking into account an appropriate margin of safety. In order to prove the suitability of the device, the hitchs and the eye hitches include on their structure the details of the approval mark which, in addition to the identification data of the approval, contain alphanumeric symbols indicating the performance of the device. For a hitch, say, for example:
DGM GA xxxx 6 t V0,5
Means:
DGM = General Direction of Motorization
GA = Agricultural Hitch
xxxx = Identification of the approval
6 t = Maximum towable mass: 6 tonnes
V 0,5 = Load Maximum permitted vertical: 0,5 tonnes (500 kg)
Types and Adjustments
It is therefore important to know the coupling possibilities of each tractor according to the fitted hitch (or hitchs), and do not exceed, considering also that in addition to a horizontal, natural towing effort, some types of hitchs must also bear vertical loads due to the connection to trailers (and operators thereof) which, by their construction, “discharge” part of their weight on the eye hitch, therefore, on the towing hitch. This is especially the case with trailers with a single axle or several axes close to each other and placed in an asymmetrical position at the back of the loading platform, which then draws a part of their weight on the eye hitch. Due to the need for coupling with a wide variety of very different equipment, the hitchs are conceived differently from those mounted on other industrial vehicles (such as lorries) and therefore require positioning at different heights from the ground, especially to minimize the risk of excessive lightening of the tractor’s front axle, with the risk of reduced sensitivity in the vehicle direction or even of roll-over for rear up. Therefore, in order to work safely, it is essential to keep a pull line as horizontally as possible, but above all, with the hitching point at the lowest position. Other standards have then defined what the balance conditions must be, to ensure sufficient safety when towing equipment to the tractor. Basically, the main principle is to adjust the height of the hitch so that in any condition at least 20% of the weight of the tractor is kept on the wheels of the steering axle (ie the front axle), also optionally with the addition of dedicated cantilever ballasts.
To best meet these requirements, almost all coded categories of agricultural hitchs can be adjusted in height thanks to the so-called hitch holder which is usually secured by two or more sturdy pins in different positions on the base frame, which is fitted to the rear of the tractor.
Except for the only category A hitch, which is basically a hinged bar in the ventral part of the tractor, is normally supported at the end by two perforated plates with respect to which it can be locked in an offset position. Practically, with this hitch it is possible to make the machinery advance laterally, at the tractor side, thus avoiding having its tires passing on the tracks already made by the tractor’s wheels (or tracks), so as to reduce the localized intensity of soil compaction.
The security aspect
The most important part of the whole set is the hitch castle, that is to say, the part on which the operator intervenes most often, both to adjust its position vertically, and, particularly, to hitch or disconnect the connected tools. The latter operation, as well as the similar of fixing and disconnecting of equipment attached through the three point linkage, still causes numerous injuries and has therefore been further developed to make (semi) automatic the sequence of movements to be performed, possibly without the need for an operator close to the device. In detail, with the classic CUNA hitch, the connection between the towing hitch and the terminal eye hitch of the rudder, is made with a sturdy pin, which must be placed usually by a ground operator standing near the two vehicles. In case of sudden movements, in its retraction operation, the tractor could hit the ground unit, sending it against the equipment. This is the reason why devices have been introduced for a long time to facilitate this action, which is based on the remote handling of the pin, so as to disengage and then engage the eye hitch with leverages that can be operated from the driving seat. At the same time, some solutions have been developed to make it safer and especially less difficult the vertical adjustment of the “hitch castle”, by means of so-called “sliders”, sliding slides equipped with retractable pins with spring mechanisms (which can be operated by levers or handles), which sliding vertically into two tracks of the main frame of the hitch allow quick and easy alignment of the height of the line.
The market
As far as towing systems are concerned, Italian manufacturers figure prominently, offering a range of products suitable for both the typical Italian CUNA hitch and the European one. Without pretending to be exhaustive we can mention CBM from Modena, V. Orlandi from Flero (BS), Aries from Montone (PG) and Malesani from San Bonifacio (VR).
Fully automated systems
In addition to remote control systems for the coupling towed equipment, which still involves the direct action of the tractor driver, recently some fully automated solutions have been developed, which, with the help of sensors and electronics are able to perform the action in a “safe shot” mode, ie in a more efficient and faster way.
For example, Irish Dromone has developed a “pick-up hitch”, a device based on an extensible and retractable bar, hinged to the bottom of the tractor, which can be tilted mechanically or hydraulically in the vertical plane, so as to favour the coupling action of the device placed at the end of the towed machinery. To best couple with the equipment, the main bar can accommodate several terminal devices, such as the classic tow bar, or grapple, or ball hitchs. This action is carried out by extending and lowering the main bar by pulling back the tractor until the coupling device is matched with the towed coupling device, and then repeating the sequence in reverse order, which nevertheless provides for a final safety lock.
For towed equipment equipped with mechanically operated working parts, which therefore also need to be connected to the power take-off of the tractor via the pivot shaft, John Deere has developed the Autoconnect, an innovative device awarded during the SIM last edition in Paris. Practically, by simply positioning the tractor and the machinery (electronically assisted) the entire coupling phase is handled automatically, with the noteworthy advantage that not only fixing the hitch but also the shaft does not require operator intervention on the ground.
