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The self-propelled agricultural machinery levelling on slope

In order to ensure the necessary stability when working on sloping terrain, combine harvesters, grape harvesters and other implements, especially the self-propelled versions, have adopted various technical solutions to ensure an adequate level of safety against tipping, but also better quality of work

by Domenico Pessina
March - April 2023 | Back

The orographic distribution of the Italian territory (ISTAT data) is made up of plains for only about 23% of its surface, while 42% is hills and 35% is mountains. It is therefore clear that a considerable part of the cultivable area is not flat, and that indeed some crops where our country is a leader, such as wine grapes, are cultivated largely on more or less sloping land. Therefore, the mechanisation of the sloping areas had to develop machinery over time, primarily self-propelled machines, with devices to improve their stability when they had to work in slopeways downhill ploughing (i.e. in the line of maximum slope), or in contour ploughing (i.e. in relation to the contour lines), without of course neglecting the countless intermediate situations.

Self-levelling combines

Undoubtedly, the agricultural machine on which levelling technology, regarding the entire vehicle body and/or one or more internal parts, has been most developed in recent decades is the combine harvester. The need to harvest cereal grains even on more or less steeply sloping terrain has led to the emergence of various technical solutions in Italy and to some specialised manufacturers developing levelling kits for these self-propelled implements.

It is necessary, however, to distinguish the different mechanical systems that have been applied to the front and rear axles to ensure the levelling of the machine body and at the same time the best grip of the wheels on the ground, an essential factor for safe progress even on steep slopes.

On combine harvesters, traction is always provided by the front wheels (of large diameter). The transmission of motion is usually mechanical, to ensure the best efficiency in power transfer. In an increasing number of cases, the rear axle, which is the steered axle and has tyres of a much smaller diameter, can also be provided with traction, although the transmission of motion is typically hydraulic, by means of motors applied directly to the wheels.


Transverse and longitudinal levelling

If the need is to keep the machine body horizontal when working along level lines, the front wheels can be offset basically with two different technical choices, namely by means of cascading and rotating final drives, which can compensate for slopes of up to 18-20%. On the other hand, for greater slopes (up to 40%), articulated parallelogram structures and hydraulic compensation cylinders are used, while motion to the wheels is transmitted via sturdy cardan shafts.

On the other hand, when travelling in retracting mode, it is necessary to level the machine according to the direction of travel. In this case, the rear axle, again with a typical articulated quadrilateral structure and the ever-present pair of hydraulic cylinders, intervenes and takes care of the consequent needs. It should be noted that performance is significantly different when working uphill rather than downhill: typically, slopes of up to 30% and 10% respectively can be compensated for.

Obviously, to increase harvesting efficiency, the combine can also be driven on mixed paths, i.e. at an angle to the slope. In this case, the best result is obtained with double levelling and with devices that make automatic adjustment of the constant horizontality of the vehicle; this is done by a dedicated control unit, assisted by a series of inclinometers.


Levelling of working devices and parts

Naturally, the cutter bar of the combine must faithfully follow the slope and undulations of the terrain in order to effectively harvest the entire grain, minimising losses during harvesting. For this, the machine body can vary its inclination with respect to the ground. This leads to a shift in the internal flow of product (especially when working with a turner), with its concentration only on a part of the area dedicated to working that individual part. This is a potential problem that can affect the elevator channel, the beater-counter-beater complex, after-beaters, straw walkers (when present), and sieves. All this can compromise threshing efficiency and subsequently also the cleanliness of the crop. Therefore, in order to further improve combine performance, all major manufacturers have developed mechanisms to internally level these parts.

In this regard, New Holland provides on some of its models the Smart Sieve, a hydraulic system that on transversal slopes (up to 25%) swings the sieve to ensure that the grain is distributed more evenly over the entire available surface area, while the Opti-Fan has been introduced for work on longitudinal slopes, by increasing the air flow of the fan on the downhill side and reducing it on the uphill side, to compensate for the natural downhill sliding of the grain by gravity.

The high-end New Holland models are fitted with a true self-levelling sieve, hinged to the frame via a central pivot, which makes it possible to compensate for transverse slopes of up to 17%.

Claas, on the other hand, has introduced an interesting solution on hybrid machines to compensate for work on transverse slopes, when the crop tends to move towards the lowest rotor area. In practice, this involves the automatic partial closure of the downstream grids, thereby reducing the fall of the caryopses in that area. In the AGCO Group and John Deere models, action is taken on the ventilation of the sieves. John Deere, in particular, has introduced ATA (Active Terrain Adjustment), which adjusts the intensity of the ventilation to the slope, and simultaneously modulates the opening of the lower and upper sieves according to the characteristics of the grain being harvested. Finally, it should be noted that levelling systems for the entire machine body and one or more internal parts can co-exist, further improving performance.


Grape Harvesters

Since, at least in Italy, many vineyards are planted on sloping terrain, sometimes even on steep slopes, for the mechanical harvesting of wine grapes, both towed and, above all, self-propelled grape harvesters have been self-levelling for some time now. These machines are fully hydraulically operated, both for the working parts and the traction of the vehicle, so the technical choice for levelling could only be in line with this general orientation. In practice, the 4 wheels (driven, among other things, by directly installed hydraulic motors) are mounted on as many sturdy hydraulic cylinders which, thanks to dedicated sensors and the ever-present control unit, keep the machine body as horizontal as possible, both in turning and (as far as possible) retracting work. Given the often large dimensions of self-propelled models, the excursions of these cylinders can reach up to about 700 mm, compensating for transversal slopes of up to 30-35% and longitudinal slopes of 12% uphill and 8% downhill.

A bit of history...

The issue of seeking the highest level of machinery safety when working on slopes has been addressed for some time, but there is no doubt that technological progress has recently brought a great deal of help in effectively resolving the most critical situations, both from the point of view of the stability of the tractor-equipment yard, and from that of the quality of work of large self-propelled operating machines, such as combine harvesters and grape harvesters.

At the beginning of the 1950s, that is, at the beginning of the period that was characterised by the so-called 'green revolution' (or, more modernly, 'agriculture 2.0'), the issue was tackled in an active manner, i.e. by trying to prevent the progressive loss of stability and the resulting incipient overturning of the tractor with a series visual and audible alerts when a dangerous slope was reached, monitored by appropriate sensors. At the time, a common measure was to disconnect the drive from the wheels, or even switch off the engine. Special lateral struts were also installed which, in the unfortunate event of a rollover, could be quickly ejected from the tractor body and, by resting on the ground or embedding themselves in it, would be able to block the rotation of the vehicle.

An original solution, which was ahead of its time, was to equip the tractor with final reduction gears in cascade, whose rotation (obviously within certain limits) could keep the body of the vehicle horizontal even when driving on sloping surfaces.

Unfortunately, many reasons, such as the poor precision of the countermeasure, the ineffectiveness of the warning signals (underestimated by drivers), the insufficient reliability of the mechanisms and, last but not least, the high cost of these systems and devices, soon caused the rapid abandonment of all devised solutions.

Consequently, particularly for tractors, manufacturers quickly moved on to the application of a passive safety concept, i.e. not to prevent the rollover happening, but to protect the driver from its harmful consequences through the installation of a ROPS (Roll Over Protective Structure) around the driver's seat, supplemented by a lap belt built into the driver's seat, so as to effectively hold him within a certain 'survival volume' guaranteed by the tightness of the safety structure. In practice, the principle had the same purpose as the airbag fitted a year later to vehicles intended for road use, i.e. not to intervene in the occurrence of the accident, but to limit its consequences for the driver (and, in the case of airbags, also for any passengers).

The Galileo cab of Same Deutz-Fahr

Proposed by SDF more than 20 years ago on its Same and Lamborghini brand models in the 160-200 Hp range, the tractor cab self-levelling system was implemented by means of 4 hydraulic cylinders fed by the tractor's main circuit, inserted in addition to the traditional silent-blocks. By limiting the transmission of high-frequency vibrations from the engine and transmission, the anti-vibration blocks prevented the cab from becoming a dangerous resonance chamber.

This system, which could compensate for a significant difference in height between the tractor body and the cab (both longitudinal and transversal, thanks to the 230 mm of travel of the hydraulic cylinder rods, corresponding to more than 14°, or more than 25% of slope), was originally designed for ergonomic purposes. This not only maintained a correct operator posture when ploughing within the furrow, for which these models, with their high power for the time, were particularly intended, but also to protect the driver's health in all operations on sloping terrain.

The levelling was maintained with a more than acceptable readiness, but at the cost of a rather demanding absorption of power in the form of hydraulics and an increase in the running costs of the vehicle.

The electronic slope-monitoring circuit was supplemented by specific alerts when specific danger thresholds for tractor overturning were reached. These risk situations could not be correctly detected by the operator as he was constantly held in a horizozontal position.

A further 'visionary' innovation, which was ahead of its time and would be taken up much later, was the installation of a driver's cab completely decoupled from the engine compartment, with obvious advantages in terms of reduced vibration, noise and heat transmission.


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