Heavy vehicle intended to draw machinery

IS 2 380 441 Τ3

DESCRIPTION

Heavy vehicle designed to tow a machine.

The present invention relates to a heavy vehicle intended to drag a machine, such as an agricultural tractor intended to drag a working tool from the ground.

Although not limited to this application, the invention will be described more particularly with reference to an agricultural tractor.

Under certain running conditions, it is found that, when the driven tool exerts a non-negligible force of resistance to advance, for example under the effect of penetration into the ground of an element of said tool such as a disc, the tractor exhibits rebound-type jumping phenomena that, at first, cause comfort problems for the driver, and therefore a greater penalty on the driver's work and that can lead to tractor advance problems, becoming insufficient contact durations to authorize friction necessary for the tractor to advance on the ground, and therefore a loss of efficiency of the cited tractor by degradation of the adhesion of the tire on the considered ground.

These bouncing or jumping phenomena are characterized by intermittent or almost entertaining oscillations of the rolling assembly at low frequencies usually between 0.5 Hz and 4 Hz and are known as "power hop".

The solutions currently implemented by users consist of overloading the tractor and / or adapting the inflation pressure of the tractor tires empirically or according to step-by-step methods proposed by vehicle manufacturers or tire manufacturers. These pressure or test settings of the tractor are, on the one hand, a waste of time for the user and, furthermore, they affect the performance of the vehicle since the recommended optimum settings are not respected. Pressures that are too high can, for example, cause more significant compaction on soft soils and greater resistance to advance.

The numerous investigations carried out by the applicant that refer to modifications of the tires and especially of the meridian profiles of the tread, the meridian profiles of carcass reinforcement, the reinforcement materials of the carcass and crown, the modifications of designs and dimensions of sculpture blocks, have not currently provided the expected improvements, because these modifications do not act or act little on the phenomenon such as the one described above.

As regards the usual design of agricultural machine tires, the carcass reinforcement, anchored in each bead, is made up of at least one layer of textile and / or metallic reinforcing elements, the aforementioned elements being substantially parallel to each other. in the layer and being able to be substantially radial and / or frankly crossed from one fabric to the next, forming equal or unequal angles with the circumferential direction. The carcass reinforcement usually has superimposed a crown reinforcement composed of at least two working crown fabrics of reinforcing elements that can be textile or metallic, but crossed from one layer to the next, forming small angles with the circumferential direction. The tread of the tire in question is made up of rubber blocks or bars, inclined with respect to the circumferential direction at a generally high angle, and generally circumferentially separated from each other by gaps that have a width (measured in the circumferential direction) greater than the average width of the bars. Said bars can be symmetrical to each other with respect to the equatorial plane, being axially continuous or, as in most cases, axially discontinuous. The rod ends axially close to the equatorial plane are then in most cases circumferentially offset from one another, while exhibiting what is commonly called a herringbone pattern.

In patent FR 1 046 427, the applicant has described, for example, carcass reinforcements in which the directions of the reinforcing elements of the fabric or of the fabrics on one side are substantially symmetrical, with respect to the equatorial plane of the tire, the directions of the reinforcing elements of said fabrics on the other side. As has been shown and explained, fabric is to be understood as either a continuous fabric axially from bead to bead, or semi-fabrics anchored in each bead to an annular bead reinforcing element but whose radially upper extremities are distant from each other. and the equatorial plane.

Patent US 3 108 628 still teaches, with a view to giving the tire good stability under transverse stresses, to complete the radial carcass reinforcement by so-called stabilization semitones and formed by reinforcing elements inclined with respect to the circumferential direction, those mentioned overlapping Half them on the crown for most of the axial width of the tread so that the reinforcing elements intersect.

Patent FR 1 259 199 also shows and describes a directional carcass reinforcement composed of two half-sides of reinforcing elements inclined with respect to the circumferential direction in such a way that they overlap at the crown of the tire to form a cross reinforcement.

IS 2 380 441 Τ3

Other documents describe solutions that are not pneumatic but linked to the vehicle and / or the towed tool to alleviate this rebound problem.

Document US 6,260,873 describes a device interposed between a tractor and a trailed tool to absorb the stresses that can intervene between the tractor and the tool.

Document US 20050269796 describes an optimized suspension system for agricultural tractors that makes it possible to limit this phenomenon of power hop.

The different solutions already proposed do not make it possible to guarantee an efficiency on all types of soils or else they only make it possible to attenuate more or less permanently the damping of these rebound phenomena, to the detriment of other desired properties of the vehicle.

In their studies, the inventors have been given the mission of improving the behavior of heavy vehicles such as tractors designed to tow a machine and especially of reaching heavy vehicles that do not present or that present few phenomena of rebounding or jumping of the power hop type. characterized by low-frequency oscillations of the rolling assembly between 0.5 Hz and 4 Hz, whatever the nature of the terrain on which the vehicle circulates when it is dragging the machine and without specific intervention on the vehicle such as a modification of the inflation pressures or a particular ballast of the vehicle.

This objective has been achieved according to the invention by a heavy vehicle comprising at least four assembled assemblies, each consisting of a wheel and a tire, intended to drive a machine, characterized in that the properties of the vehicle verify the relationship:

<img file="ES2380441T3_D0001.tif" />

\ 7 with p '= p / L, where p is the turning radius of the vehicle, expressed in meters, and where L is the wheelbase of the vehicle, also expressed in meters, that is, the distance projected on the ground between the front wheel axle and rear wheel axle of the vehicle, p 'is expressed without units. The turning radius p is determined by the relation p = lv / m, where Iv is the vehicle's pitching moment of inertia with respect to a transverse axis (parallel to the axes of the wheels) and passing through the center of gravity of the vehicle. vehicle, which is expressed in kg.m², and m being the mass of the vehicle expressed in kg.

k expresses the ratio of the total vertical stiffness ki under the front wheel axle to the sum of the total vertical stiffnesses (ki + k2) under the vehicle's front and rear wheel axles, ki and k2 respectively expressing the stiffnesses vertical under the front wheel axle and under the rear wheel axle. The total vertical stiffness under a wheel axle is the result of the vertical stiffness of the tires and the vertical stiffness induced by the ground under each of the tires of said wheel axle. The vertical stiffness of the tire is the stiffness of the tire itself, that is, the measurement on a flat, non-deformable ground.

δ expresses the relationship between the displacement of the center of gravity towards the front and the distance L between the axles of the wheels of the vehicle, the displacement of the center of gravity towards the front being defined from a position of the center of gravity according to which ki.Li = k2.L2, with Li and L2 respectively expressing the projected distances on the ground between, on the one hand, the center of gravity and the front wheel axle and, on the other, the rear wheel axle.

h 'is the ratio between the height of the traction line with respect to a ground that forms a horizontal plane, the vehicle and the machine being pulled in working position being arranged on said ground that forms a horizontal plane, and the distance L between axles of vehicle wheels. In the sense of the invention, the floor that forms a horizontal plane is a rigid floor, which means that the heavy vehicle and the towed machine do not create tracks in said plane during the measurement of the considered height.

μ is the relationship between the longitudinal component of the resistance force applied by the machine pulled on the vehicle, and the weight of the vehicle.

As can be seen from the foregoing, the parameters p ', k, δ, h' and μ are expressed without units.

The measurements of these different characteristics can be carried out according to any means known to the person skilled in the art, even by modeling tools.

IS 2 380 441 Τ3

The distance L between wheel axles is measurable, for example, by projection onto the ground of the wheel axle axles. The longitudinal position of the vehicle's center of gravity can be deduced from measurements of wheel axle loads.

The mass m of the vehicle is determined, for example, by weighing the entire tractor (chassis and mounted assemblies).

The pitching moment of inertia lv can be evaluated experimentally by placing the tractor on a platform, the transverse axis of the tractor and the oscillation axis of the platform being aligned. The moment of inertia can also be measured by proceeding as before in each of the subparts that make up the tractor assembly, and then by mathematical calculation (Huygens theorem). The pitch moment of inertia can also be quantified by numerical calculation, especially using computer aided calculation (CAO) tools.

Having the quantities L, me lv, the value of p 'is obtained by calculation as explained above:

<img file="ES2380441T3_D0002.tif" />

The term k can be estimated from the total stiffnesses under the wheel axles: k = kl / / (k1 + k 2) where ki is the total stiffness under the wheel axle i with i = 1 for the wheel axle front ei = 2 for the rear wheel axle. ki is the vertical stiffness of the set made up of the tire and the ground on which the tire rolls. The stiffness of the set of tires on the wheel axle i is designated by kip (the tires operating in parallel, their own stiffnesses kipj are added to give kip). The stiffness kipj of the tire j of the wheel axle i is the ratio between the increase in load that it supports and the decrease in the height of the center of the wheel, the tire resting on a flat, non-deformable and horizontal ground and initially supporting, with the other tires on the same wheel axle i, the load on said wheel axle. The stiffness is then usually expressed in N / m (Newton per meter). The stiffness kisj of the ground on which said tire j of the wheel axle i rolls is the ratio between an increase in load applied by said tire during its passage and the variation of the depth of rolling then created. The stiffness kisj, therefore, is also usually expressed in N / m. In the case of running on soft ground, the tires of the front wheel axle compact the ground during their passage, so that the stiffness of the ground under the rear wheel axle increases with respect to the stiffness under the front wheel axle. In a practical way, the total stiffness under the wheel axle is calculated by the formula ki =

<td colspan="2"></td><td> -1</td><td colspan="2">r 3-1Ί</td>

<td></td><td>Σ ^kiPj</td><td> +</td><td>Σ ^ki%</td><td></td>

<td></td><td>lj 0</td><td></td><td>l^j 0</td><td></td>

Or, the relationship between the variation in the load applied by the tires on the ground and the resulting decrease in altitude of the wheel axle is directly measured.

The inventors have been able to show that if the set of vehicle characteristics satisfy the aforementioned relationship, the occurrences of rebound or power hop phenomena decrease significantly, or are even non-existent, especially depending on the terrain on which the vehicle circulates.

According to a first embodiment of a vehicle according to the invention, p 'verifies the ratio p'&gt; 0.525. Said p 'value effectively allows for the reduction of power hop phenomena, allowing the aforementioned p' value to satisfy the aforementioned relationship. Since p 'is proportional to the turning radius p of the vehicle, the value of p' can be modified as a function of the design of the vehicle and especially by a choice of distribution of the masses of the constituent elements of the vehicle. Compared to a conventional vehicle, this embodiment of the invention will consist in moving the constituent masses of the vehicle away from its center of gravity in order to increase its turning radius.

According to another embodiment of a vehicle according to the invention, p 'verifies the relationship: p' &lt;0.395. Said value of p 'allows, as previously, to favor the decrease of the phenomena of power hop, allowing the mentioned value of p' to satisfy the relationship stated above. Since p 'is proportional to the turning radius p of the vehicle, the value of p' can be modified as a function of the design of the vehicle and especially by a choice of distribution of the masses of the constituent elements of the vehicle. Contrary to the embodiment presented above, when purchased with a typical vehicle, this embodiment of the invention will consist of centering the constituent masses of the vehicle around its center of gravity in a plane containing the vertical and forward directions of the vehicle in order to decrease your turning radius. These masses, on the other hand, can be distributed according to the transverse direction of the vehicle.

IS 2 380 441 Τ3

According to one or the other of these embodiments of a vehicle according to the invention, the variation of the p 'value makes it possible to modify the first element (p k. (1 - k)) of the relationship or inequality presented above and in both cases it allows satisfying the aforementioned relationship.

An advantageous variant of the invention provides that the height of the side of the tires that equip the rear wheel axle of the vehicle is at least 15% lower than the height of the side of the tires that equip the front wheel axle of the vehicle.

The height of the side of a tire has a direct effect on the stiffness of the tire during use with a given pressure and load of said tire. A side height difference between the tires that equip the rear wheel axle of the vehicle and the tires that equip the front wheel axle of the vehicle as proposed according to this variant of the invention will contribute to modifying the value δ which is proportional to the displacement of the center of gravity towards the front, with respect to a reference position of the center of gravity according to which ki.li = k₂.l₂. By driving the proposed sidewall height difference according to this variant of the invention at heights of the sidewalls of the rear tires lower than those of the front tires, the stiffness of the rear tires increases with respect to that of the front tires and therefore the center of gravity is shifted towards the front with respect to the reference position of the center of gravity, due to the displacement of said reference position towards the rear of the vehicle when the rear tires are stiffened with respect to the front tires.

The difference in value of at least 15% between the side heights of the tires that equip the rear wheel axle of the vehicle, and of the tires that equip the front wheel axle of the vehicle, the side heights of the tires being that equipped to the rear axle of the vehicle's lower wheels, allows to set the value of the second element

hm 2 of the relationship or inequality presented above at a level high enough for the mentioned inequality to be verified.

Below a 15% deviation between the side heights of the tires that equip the rear wheel axle of the vehicle and of the tires that equip the front wheel axle of the vehicle, the influence on the occurrence of rebound phenomena is insufficient. .

In the case of a vehicle equipped with tires of identical outer diameter for the tires that equip the rear wheel axle of the vehicle and for the tires that equip the front wheel axle of the vehicle, the tires that equip the rear wheel axle have sides smaller in height than the tires that equip the front wheel axle; the aforementioned tires are therefore different.

In the case of a vehicle equipped with tires of different outer diameters from one wheel axle to the other, the outer diameter of the tires that equip the rear wheel axle of the vehicle is preferably less than the outer diameter of the tires that equip the rear wheel axle. front wheels of the vehicle.

According to another variant of the invention, the side height of the tires that equip the rear wheel axle of the vehicle is at least 15% higher than the side height of the tires that equip the front wheel axle of the vehicle and the axial width of the treads of the tires that equip the front wheel axle of the vehicle is at least equal to the axial width of the treads of the tires that equip the rear wheel axle of the vehicle.

The axial or transverse direction of a tire is parallel to the axis of rotation of said tire.

When the vehicle is equipped with twin or triple mounts, in the sense of the invention, the axial width of the treads of the tires that equip a wheel axle is understood as the sum of the axial widths of the set of tires that equip the aforementioned wheel axle.

The difference in value of at least 15% between the side heights of the tires that equip the rear wheel axle of the vehicle and of the tires that equip the front wheel axle of the vehicle, the side heights of the tires being that the rear axle is equipped with upper vehicle wheels, Combined with axial widths of the tire treads that equip the front wheel axle of the vehicle greater than or equal to the axial widths of the treads of the tires that equip the rear wheel axle of the vehicle, they help to increase the value of the second element tion or inequality presented above.

of rela5

IS 2 380 441 Τ3

Studies have shown that the mere difference of at least 15% between the side heights when the sidewalls of the tires that equip the rear wheel axle of the vehicle are greater is not enough to fight effectively in any circumstances against the phenomena. of power hop. Indeed, the increase in the value of the second element of the ratio or inequality then also requires that the axial widths of the treads of the tires that equip the front wheel axle of the vehicle are greater than or equal to the axial widths of the bands. tread of the tires that equip the rear wheel axle of the vehicle. The insufficiency of the difference in side heights, taken in isolation, can be explained especially by the limitation of the increase in total stiffness under the front wheel axle caused by the flexibility of the uncompacted soil during the passage of the tires that equip the axle. front wheels of the vehicle, the aforementioned vehicle moving forward.

The increase in the axial widths of the treads of the tires that equip the front wheel axle with respect to the axial widths of the treads of the tires that equip the rear wheel axle, especially compared to common vehicles, makes it possible to increase the rigidity of the ground with respect to the tires that equip the front wheel axle of the vehicle; By increasing the surface in contact with the ground of said tires, the stiffness of the ground perceived by the front wheel axle of the vehicle increases and contributes to the increase in total stiffness under the front wheel axle.

The invention still proposes, advantageously, that the distance L between the axles of the wheels of the vehicle verifies the relationship: L&gt; 1.1 x (m / d)^1/3, corresponding to a mean density value equal to 300 kg / m³ yma the mass of the vehicle, expressed in kg.

Such values ​​of distance L between wheels allow to contribute to decrease the value of the third element of the relation or inequality presented above, reducing the value of h '.

Studies have shown that such unusual wheelbase values ​​for tractor-type vehicles effectively favor the disappearance of power hop phenomena compared to tractors with a more common wheelbase and run-in under the same conditions.

The different embodiments and / or variants of the invention, presented above, are particularly more adapted to the case of an agricultural tractor that pulls a working tool from the ground that causes a high resistance to advance such as a disc rotator.

Other details and advantageous characteristics of the invention will be deduced from the following description of an embodiment of the invention with reference to Figures 1 and 2, which represent:

- figure 1, a schematic representation of a vehicle according to a first embodiment of the invention,

FIG. 2, a schematic representation of a vehicle according to a second embodiment of the invention.

Figures are not represented to scale to simplify understanding.

In figure 1, the schematized vehicle is an agricultural tractor 3 of the 4-wheel-drive type provided with an engine with a power of 125 kW and an unladen mass equal to 8660 kg. Tractor 1 is equipped on the front wheel axle with tires 1 of size 500 / 65R34 which therefore comprise sides with a height h-ι equal to 325 mm (500 x 0.65) and on the rear wheel axle. sero with tires 2 of measures 480 / 80R46 Agribib that therefore include sides that have a height h2 equal to 384 mm (480 x 0.80).

The sides of the tires 2 that equip the rear wheel axle are therefore 18.2% larger than the sides of the tires 1 that equip the front wheel axle.

Furthermore, according to the invention, the tires 1 that equip the front wheel axle have a tread width equal to 450 mm, greater than the tread width of the tires 2 that equip the wheel axle rear, in turn equal to 432 mm.

Tests have shown that a typical tractor equipped according to the description in figure 1 makes it possible to reduce the occurrence of power hop phenomena on certain types of terrain compared to the same reference tractor more commonly equipped with tires whose bands tread are wider at the rear wheel axle.

In the case of the tractor equipped with tires according to the invention and in the case of the reference tractor, the tractor and the towed machine were identical and circulated on identical ground. The towed machine was a tine cultivator.

IS 2 380 441 Τ3

The tests have been carried out at different tire inflation pressures, especially to explore the inflation pressures found in farmers and take into account all the situations in which the power hop phenomenon may appear.

The tests have been carried out on wheat stubble with one or two passes through the same place to reproduce real actions of the farmer, the second pass having as an objective to finish burying the undesirable vegetation.

The results have shown that the invention effectively makes it possible to limit or even eliminate this phenomenon of power hop in certain particular cases. Indeed, whatever the driving conditions, it is observed that, with respect to the reference tractor, the tractor according to the invention allows acceptable comfort and traction conditions when the reference tractor presents unacceptable comfort for the driver, or an unacceptable lack of traction due to the phenomenon of power hop.

Modeling techniques have also made it possible to show that different tractor conditions could still contribute to making power hop phenomena disappear.

A first conception has consisted in concentrating the masses of the tractor around the center of gravity to arrive at a value of p 'equal to 0.38. The value of p 'calculated for the tractor in figure 1 is equal to 0.43, where the mass of the tractor is equal to 18321 kg, its moment of inertia equal to 14400 kg.m² and its distance between axes equal to 3 m.

The tests carried out by modeling have shown that a vehicle of this type, with a value of p 'equal to 0.38, equipped with tires according to the description in figure 1, does not present almost any phenomenon of power hop whatever the type. nature and type of terrain on which the vehicle circulates.

A second conception has consisted on the contrary in moving the masses of the tractor away from its center of gravity to obtain a value of p 'equal to 0.55.

The tests carried out by modeling have shown, as in the case of the first conception, that a vehicle of this type, with a value of p 'equal to 0.55, equipped with tires according to the description in figure 1, does not It presents almost no phenomenon of the power hop type whatever the nature and type of terrain on which the vehicle circulates.

FIG. 2 represents a vehicle 23, the tires 21, 22 of which have the same outer diameters. The 21 tires that equip the front wheel axle are measures 710 / 70R38 in twin mount (4 tires on the wheel axle) and the 22 tires that equip the rear wheel axle are measures 710 / 40R54 in twin mount (4 tires on the wheel axle).

The sides of the 21 tires that equip the front wheel axle have a height h21 equal to 497 mm (710 x 0.70) and the sides of the 22 tires that equip the rear wheel axle have a height h22 equal to 284 mm (710 x 0.40).

The sides of the tires 22 that equip the rear wheel axle are therefore 43% smaller than the sides of the tires 21 that equip the front wheel axle.

The tests carried out, similar to those described with reference to figure 1, with a vehicle comprising tires that all have identical outer diameters and in accordance with the description of figure 2 have shown a decrease in the appearance of power hop phenomena on certain types of terrain compared to the same vehicle more commonly equipped with totally identical tires.

The modeling techniques have also made it possible to show that different conceptions of the vehicle, similar to the two conceptions presented referring to figure 1, could still contribute to making the phenomena of power hop disappear for a vehicle such as that described in the case of the Figure 2, whatever the type of terrain.