The specialized tractors: a cutting-edge segment
The sector of tractors for specialized crops has always been "made in Italy". It is a segment that Italian manufacturers still lead, even if some foreign firms with technologically competitive products have come to the fore in the last few years. The particular uses for which these machines are intended impose different characteristics compared to traditional tractors in terms of design, of the engine aspects and of the driving position
The specialized tractors sector is, no doubt, very rich of different design solutions; it is an important aspect, which allows each winery, fruit, horticultural or floriculture farm to have machines “cut” to perfection for their operational reality.
For specialists, the most difficult challenges to overcome involve both transit and maneuvering, often to be carried out in spaces reduced to a minimum, while the requests in terms of mechanical and hydraulic power (and therefore the overall dimensions of the vehicle) are constantly increasing. A further (all-Italian) problem is the setting of vineyards and orchards, often planted on steep slopes, sometimes so far as to make it impossible to work with the usual wheeled models.
The management of a winery or fruit farm is rather complex, and it becomes even harder in the case of large mixed areas, with plains and slopes, with different planting heights; the choice of the most appropriate tractors corresponds therefore to major savings, in terms of working time and fuel consumption. On the other hand, considering that the average duration of the farm tractor in Italy is about 25 years when acquiring a new model, it is important to take into account the company possible future developments and of the related equipment to be combined with the tractor.
The classic specialized (similar to the open field models) are undoubtedly better suited for working on the flat and moderately sloping terrain, while on important slopes it is safer to opt for the so-called “isodiametric”, which (as the term suggests) have all the wheels of equal diameter, with the engine that is usually cantilevered compared with the front axle. With this solution, the weight distribution of the tractor alone is on average of 60% on the front and 40% on the rear, a characteristic that makes these machines very stable when driving up and down the slope.
Isodiametrics are normally more compact than the traditional specialized ones but have a lower propensity to pull and lift heavy equipment. Also, the location of the controls appears to be usually less ergonomic, however, the disadvantage is compensated by the frequent availability of the reversible guide, very useful for the execution of certain operations. However, if the slopes are really challenging, the only solution to work safely is the specialized crawler, which despite offering a lower level of comfort and creating many problems when transiting on public roads, they can boast a much higher stability than the so-called “rubber-tired” ones.
Engine and transmission
Manufacturers sometimes offer 3 and 4-cylinder solutions with the same power: in this case, it is good to keep in mind that lower fractionation characterizes short-wheelbase machines, in favor of maneuverability, but at the same time it decreases both the traction capacity, because of less grip weight, and the stability when riding uphill.
There are many variables for transmission to be taken into account: starting from simple all mechanical solutions, to get to two or three ratios under load, up to continuously variable transmission, both typical hydrostatic, and equipped with the most modern and efficient diagram with mechanical-hydraulic split-power.
With the mechanical solution, even more, if “poor” (i.e. characterized by few ratios) it is more difficult to identify the right gear, but at the same time, you get the best return, around 90%. Starting from this basic configuration, every evolution, like the addition of ratios that can be operated under load or the hydraulic reverser, undoubtedly increase the comfort and safety in use, but they oblige to insert clutches in an oil bath, which involve unavoidable additional power absorption, which among other things must always be taken into account, even when these components are not involved in the transmission of motion. For example, with the engine at full speed, every wet clutch requires an average power requirement of about 3-4 Hp.
The hydraulic transmissions lead to an undeniable increasing in the driving comfort, which has been obtained however at the expense of performance; in fact, it is necessary to consider that, on average, 25-30% of the power that this transmission manages is wasted as heat. Vice versa, for the “split-power” versions, i.e. those that use the mechanical-hydraulic branching (it is a frequently adopted solution in recent years), the dissipation rate is a function of the conditions of use, in practice the percentage of power that is hydraulically and mechanically “passing”. In fact, variable performances are obtained between the two conditions mentioned above, i.e. between 70-75% and 90%.
The driving position
A further important aspect to be carefully considered on specialized tractors concerns the driving position, above all in terms of liveability, comfort, and ergonomics, as well as the automation of the management of the machine and the equipment thanks to modern electronics. In this sector, there are huge differences between the uncovered driver seats accompanied by a simple platform compared to the latest generation cabins, air-conditioned and soundproofed.
On the other hand, it is important to note that optional features such as automatic management of the power take-off depending on the position of the lift, the insertion of the front wheel drive and the locking of the differentials, as well as the possibility of electronically adjusting the hydraulic flow (in terms of flow rates, timing and priorities) are functions which, although not negligible, allow a considerable increase in labor productivity, without substantially compromising the overall performance of the machine.
For specialized tractors, autonomy is an important parameter, given that models at the top of the segment have now engines exceeding 110 Hp; if they are working at full load (for example with a very demanding pneumatic ripper or atomizer) they consume almost 20 l/h of diesel, which requires large tanks to ensure an acceptable autonomy level. Making space where it is particularly low is a remarkable effort. A similar problem concerns the combustion air filter and any protections for a quick cleaning of the radiators, all parameters that have a rather significant influence on productivity.
It is a fundamental aspect, given that more and more often the equipment for specialized crops is hydraulically operated. Therefore, the actual flow rate of oil that can be taken, the capacity to cool it with the radiator pack, and the number and location of the hydraulic distributors, not only rear but also ventral and frontal.
The availability of an additional independent hydraulic system for the hydro guide, the electro-hydraulic drives and the possible forced lubrication of the transmission is important because it ensures smoother operation of the steering even with the engine idling or during simultaneous operation of the actuators connected to the primary circuit. Still from the hydraulic point of view, it is also necessary to evaluate the prompt recognition and correct positioning of the control levers of the distributors, even better if replaced by a single “joystick”, perhaps programmable in its functions, so as not to have to install in cabin some accessory controllers dedicated to the units.
As seen above, a tractor has a useful life higher than that of a car, therefore, the best operational conditions are assured only if you can rely on an efficient and, possibly, also economic. assistance center next to the farm. The importance of this aspect is often higher than everything has been set out before. Indeed, a prolonged standstill can even jeopardize the season, especially if it is a complex and technologically advanced tractor, given that such a machine cannot always be replaced with other simple models, even only for the specific coupling needs of the very modern units of the farm.
A need increasingly felt in the modern fruit-viticulture, but on which the manufacturers are still working, is to have tractors equipped with optoelectronic devices for automatic alignment along the row, which are not to be confused with the most complex and expensive automatic driving systems using satellite technologies. The optoelectronic sensors are much simpler and cheaper and already come with some modern wagons collecting fruit or equipment for the topping of the canopy.
Finally, there is also the ISObus, an “accessory” whose cost is currently not irrelevant, fully compatible now only with limited equipment. However, it should be kept in mind that ISObus compatible machines will spread a lot in the next two decades, so with the tractor purchased today still operating. It is also true that the ISObus of first or second generation can be implemented through after-market solutions, but the third generation one (the only one that allows the equipment to “dialogue” with the tractor, setting, for example, the desired feed speed and/or the power take-off rotation speed, as well as the desired hydraulic flow rate) is a native solution, which cannot be installed at a later time.