Tractors with steel tracks
Italy is one of the main producers of 'classic' tracked agricultural tractors, i.e. those fitted with steel tracks. In fact, due in part to the orography of the land and the characteristics of Italy's agricultural soils, there is a constant demand for these tractors, which is met by Italian manufacturers. The current models, "heirs" of the glorious track models of the post-war period, offer good performance, an excellent level of technology and a clear improvement in driver comfort
The first crawler tractor in history, the Cleveland Cletrac Model H, was designed and built in the USA in 1917. It was equipped with a 4-cylinder, 20 Hp, endothermic engine that ran on petrol or paraffin. In Europe, the progenitor of the tracked tractors was the English Blackstone Track Tractor, marketed from 1919. It was equipped with a 3-cylinder engine that ran on kerosene or paraffin and expressed about 25 Hp. The first Italian track tractor was the Fiat 700 C, produced in 1932. It had a 30 Hp petrol engine and was a success, partly due to the interest from the army, which saw the new tractor as a viable alternative for moving mountain artillery instead of mules. A smaller version (the Fiat 708 C, with an engine of only 20 Hp) was used in the military campaigns in Somalia and Libya. In 1939, at the height of the autarkic era, a tracked tractor made history: the Fiat model "40", also known as the "Boghetto" after the name of the engine's designer, Prof. Fortunato Boghetto from Valdobbiadene (TV). Its main feature, which made it a cutting edge vehicle at the time (and even today...) was that the 40 Hp engine was multi-fuel, i.e. capable of burning anything flammable that was available: alcohol, petrol, naphtha, diesel, petroleum, palm oil, castor oil, animal oil, etc. In fact, it was a multi-fuel engine that could be used for all types of combustion. It was a low-compression Otto cycle engine with a cylindrical combustion chamber with a biconical inlet arranged eccentrically and inclined compared to the cylinder’s axis, almost as if to simulate a Venturi tube. The fuel system was completed by an injector and spark plug. With this configuration, the engine always worked with full air intake and the fuel was dosed so that, near the spark plug, the mixture was always rich enough to allow ignition. This ensured that the engine ran smoothly and with low fuel consumption. At the end of the war, with the spread of diesel engines, the Boghetto engine was, as they say, 'retired'.
This was the beginning of the golden age of Italian tracked tractors, whose spread was decisively favoured by the shape of Italian agricultural land, 35% of which is classified as mountainous, 43% as hilly and the remaining 22% as flat, with soils that are often clayey and tenacious. Among other things, a typically Italian custom, at least until the late 1970s, was ploughing at a depth of 50-60 cm. The wheeled tractors of the time were not yet as stationary and stable on slopes as the tracked ones; this meant that these machines became so widespread in our countryside that, in order to meet the farmers’ demand. Between 1930 and 1970 more than 30 manufacturers were active in Italy, with more than a hundred models of tracked machines adaptable to every production situation.
Nowadays, the number of national manufacturers of tracked tractors is much smaller, but the demand for these machines has never ceased: indeed, as much as 9% of the tractors registered in 2019 were classic tracked tractors (i.e. with steel skids), making Italy one of the countries in the world that makes the most use of these machines.
From a technical point of view, thanks to their large surface area on the ground and their high power-to-weight ratio, classic crawler tractors have excellent grip and therefore high tractive force. In addition, they float well on the ground (with an average pressure of just 0.25-0.50 kg/cm2), thus limiting soil compaction, and have excellent transverse stability thanks to their low centre of gravity, small size compared to a wheeled tractor of the same power and small turning radius (in fact, they can turn on themselves by pivoting on the inner track).
The disadvantages of these machines include their lower ergonomic level compared to wheeled models (although this aspect has been significantly improved in recent years), their poor suitability for carrying out certain operations (e.g. haymaking, crop care, transport), their slow speed and the need, if public roads are to be used, to fit the skids with special top plates, bearing in mind that the maximum speed allowed by the Highway Code is only 15 km/h. As a result, these machines are by their very nature not very multifunctional; however, they prove to be providential in cases where high traction forces and excellent stability are required, especially on slopes and in heavy terrain.
Today's classic crawler tractors have great constructional features which, although to a lesser extent than wheeled models, achieve a high level of technology without revolutionising their architecture.
In terms of engines, classic crawler tractors do not have a wide range of power ratings available on the market. They range from 74 to 113 Hp with three- or four-cylinder engines equipped with common rail injection and turbochargers. The torque reserve is interesting: in some models it can be as high as 46%, highlighting brilliant engines that respond quickly to changes in load. The transmission is mechanical with shuttle, and can have up to 16 forward and 16 reverse gears. This allows work to be carried out both at very low speeds (around 300 m/h) and at the maximum permitted speed of 15 km/h.
In addition to the classic 540 rpm and 540 ECO modes, the mechanical power take-off can also be operated at 1,000 rpm and even synchronised with the forward speed for coupling to trailers equipped with a drive axle. As a rule, engagement is carried out via an electro-hydraulic control unit.
The primary clutch is usually a single-disc or double-disc dry clutch, which can be operated either by means of a lever or, more recently, by means of a foot pedal.
Modern machines, unlike the older generation, are equipped with a high-performance hydraulic circuit, with a large number of distributors available (3 to 5, double-acting). The pump flow rate is between 38 and 50 l/min depending on the model. This allows efficient operation of both the coupled operating machines and a dozer.
Steering is carried out by means of oil-bath clutches, known as "steering clutches", which, once activated, progressively reduce the transmission of motion to the drive wheels they control to zero. This solution allows the track to be stopped immediately on the side towards which it is intended to be steered. It should be noted that, in order to reduce the turning radius of the vehicle, the corresponding brake must also be applied in addition to the clutch. Steering clutches can be operated hydrostatically, either by a pair of levers positioned in front of the operator or, in the case of New Holland tractors, by the Steering-O-Matic™ lever, a clutch-type control located in the centre of the dashboard. In this case, steering is done by moving the lever to the left or right with one hand, tilting it to one side activates only the steering clutches and directional corrections and, when the lever is moved to its end position, the brakes are also activated for tight manoeuvres.
Safety and comfort
In terms of safety, classic crawlers can be equipped with a folding bow, a four-post frame or a cab, all of which have been ROPS-approved for more than 25 years. The cab can be equipped with air conditioning and heating systems and dust filters.
The driver's seat has undergone significant updates compared to the older generation models: instead of the "rustic" padded bench, there are now mechanical or air-suspended seats, while the platform is suspended on silent blocks, significantly increasing vibration comfort. We should not forget that the tracked tractor is still a very rigid machine, which tends to return more vibrations to the driver due to the movement of the steel tracks, and that steering, especially when tight, can cause much greater stress to the musculoskeletal system than a wheeled tractor.
From the point of view of size, there are basically three different versions of crawler tractors on the market: the standard open field version, the "vineyard/fruit" version with a narrow track for easy inter-row operation and the mountain version, with a wide track to minimise the risk of tipping.
The rubber track
Finally, the most recent innovations introduced on this particular type of tractor are worth mentioning, namely rubber tracks and natural gas fuel.
In the first case, the steel chains and plates are replaced by rubber belts with herringbone treads reinforced internally by steel cables arranged in a spiral. With this solution, it is possible to circulate freely on public roads, and it is possible to make tighter turns than with traditional track systems, while reducing damage to the topsoil. In addition, vibration comfort is much better.
Methane is an innovation with ancient roots, as the Fiat 40 'Boghetto' could be powered by gas with just a few modifications.
The most important innovation today is the possibility of self-producing methane on the farm by means of anaerobic digestion of agricultural residues. This leads to significant savings in operating costs and a drastic reduction in overall emissions, making the tractor an increasingly environmentally sustainable vehicle.