Full maneuverability between rows
In specialized crops, the need to work without operational limitations implies the availability of highly evolved tractors in terms of steering devices. An overview of the original and partly new solutions available on the market
peculiar characteristic of the vineyard and orchard tractors, which are also profitably used in the horticultural and nursery sector and the maintenance of green areas, is undoubtedly their compactness, i.e., the limited overall dimensions both in length and, above all, in width. In fact, technically, this machinery is also called "narrow track". Technical progress has led to such a continuous and remarkable evolution of specialized tractors that in some cases - as for example in the case of the hydraulic system - performance is now even better than that of open field models with the same engine power.
However, there is one essential requirement that specialized tractors must emphasize beyond measure: maneuverability, that is, the ability to move in highly confined spaces in an agile and fast manner, especially when towing equipment that is already rather bulky in itself, such as sprayers or towed manure spreaders.
Consequently, in addition to the reduced dimensions, which have entailed a formidable technical challenge to contain a large number of devices and equipment in minimum volumes, all the numerous manufacturers of specialized tractors, primarily Italian, such as the CNH group, the SDF group, the ARGO group, Antonio Carraro, the BCS group, Carraro SpA, etc., have been working for some time now to enhance the steering capabilities of their machinery, especially to improve the passage between rows, especially as regards the exit and entry into the inter-row space. To this end, various technical solutions have been identified, some of which are quite different from each other and some of which are absolutely new in the tractor field, but all of which share the objective of reducing the minimum turning radius as much as possible. What follows is a brief overview of what the market currently offers, with particular reference to the most recently launched technologies.
New Holland SuperSteer
New Holland tractors equipped with SuperSteer have been on the market for a few years now. The front axle is placed in a particularly forward position with respect to the engine compartment. An extensive overall steering angle (up to 76°) can be achieved, thanks also to the relative rotational movement of the axle itself, in addition to the normal movement of the wheels. Besides reduced turning radius, this obviously also entails an increase in the machine's wheelbase, so that - according to the manufacturer - with SuperSteer, front-mounted implements return more quickly to their working configuration after steering. In addition, the weight on the axles is better distributed with an increase on the front axle so that the amount of front ballasting can be reduced when working with heavy rear implements.
Again to reduce the turning radius on its 4-wheel drive models, the Japanese company Kubota has adopted the solution of increasing the rotation speed of the front wheels. Basically, employing a "hi-lo" gearbox and dedicated oil-bath multidisc clutches, when the steering angle of the inner wheel exceeds 30°, the peripheral speed automatically increases by 1.7-1.9 times (depending on the model). This enables the machine to "close" the curve sooner, with obvious advantages for headland turns and repeated turning operations in tight spaces. This results in a reduction in working time as well as in fuel and stress for the driver, who is spared repeated (and tedious) operations. In the long run, the wear factor is not to be neglected either, as in this case, it has less impact on all the mechanical parts involved. A further advantage is the increased contribution of the front axle to the overall traction, a condition that can be valuable, for example, when leaving the rows with heavy towing and wet soil. According to Kubota designers, the reduction in turning radius achieved is 18-20%. This is similar to what could be achieved by locking the inner wheel with the brake but with a much better respect for
As far as the steering is concerned, in the past, two alternative solutions have been proposed in specialized isodiametric tractors: two front steering wheels or the insertion of a central joint in the tractor body. The two technical types still coexist on the market, but for some years, BCS has been proposing the Dualsteer, a double steering system that combines the central joint of the body with the steering of the front wheels, for a total angle of 70°. According to the manufacturer, this option adds up the advantages of the two solutions: the reduction (or elimination) of additional maneuvers on the headland means minor damage to the ground and obvious time savings and improved operating comfort. Moreover, when turning on slopes, an optimal distribution of traction between the inner and outer wheels is guaranteed and high stability (provided by the steering wheels) to the benefit of the operator's safety.
With the Dualsteer, the steering proportionality of the two steering devices is managed by the hydraulic circuit and a dedicated mechanical synchronization link which also ensures progressive steering.
The benefit is tangible: BCS Volcan isodiametric tractors with Dualsteer and 280/70R18 tires have a minimum turning radius of 2.20 m (compared to 3.24 m with only the front steerable wheels and 2.70 m when the central joint is mounted). This means that it is often possible to leave an inter-row area and access the one immediately adjacent without any steering operations.
SDF Active Steer
Although not totally new (as it has already been applied in other automotive sectors), the 4-wheel steering solution on a specialized tractor was implemented for the first time on the Same Frutteto range by the Same Deutz-Fahr group, which called it 4WS. This solution does not entail an increase in track width or wheelbase (and therefore in overall dimensions), nor does it entail any change in the distribution of weights on the axles compared to the same machine in its traditional configuration.
With the 4WS, the rear wheels can reach a steering angle of ±20°; their position is constantly monitored by an electronic control unit that manages 3 different operating modes, which can be selected alternatively:
- steering of the rear wheels in counter-phase with respect to the front ones, to reduce the turning radius by up to 28%;
- “crab" mode, used for repeated operations in the farm, for example, when handling materials with the front loader or when loading/unloading packaged products. It can also be used to effectively counteract sliding downhill in the case of turnpike operations (i.e., following the slope line). In the latter case, the steering angle can be manually set to the desired value and then locked;
- delayed mode through which the rear-wheel steering remains proportional to that of the front wheels but is carried out with a slight delay. This allows the equipment being towed to travel along the same curve as the tractor without dangerously "tightening" the trajectory.
Lintrac 4-wheel steering
Using the experience gained in designing and producing vehicles for other sectors, such as the Unitrac Transporter for municipal activities, the Austrian company Lindner has developed a steerable rear axle for its Lintrac agricultural tractor range. For this purpose, it has used hydraulic steering rods made of special alloy for a maximum angle of 20°, to which the front axle is combined, which reaches a maximum steering angle of 52°. The range also includes the Lintrac 90 Vineyards model, which, while not officially falling into the category of narrow-track tractors, thanks to the solution described, has a minimum turning radius of 3.5 m. with a combination of 420/65-R20 tires on the front and 480/70-R28 on the rear. Obviously, “crab” steering can also be activated.
Maximum maneuverability also in the farm
The best maneuverability of self-propelled agricultural vehicles is particularly significant on the farm, where it is often necessary to move in narrow spaces with sometimes bulky vehicles.
Therefore, the 4-wheel steering solution has always been practically an obligation for telescopic handlers for agricultural use, destined to operate exclusively (or almost exclusively) between farm buildings. This has long been the case for one of the leading international telehandler manufacturers, Merlo SpA of S. Defendente di Cervasca (CN), which offers its entire range dedicated to the agricultural sector with this feature, available in three modes (two-wheel steering, 4-wheel steering, crab steering).
The same applies, but in an even more demanding way, to self-propelled mulcher-mixer wagons, whose models with the highest operating capacity often have very considerable overall dimensions. For some years now, Faresin Industries of Breganze (VI) has been producing ranges of 4-wheel drive chopping-mixing wagons which also make use of 3 different steering modes, i.e., only the front wheels (suitable for transfers), 4-wheel steering (for a 15% reduction in the turning radius) and crab steering (for combined forward and sideways movement).