Assembly comprising a chassis for a variable-track machinery equipment such as a sprayer-type agricultural machinery equipment or a straddle machinery equipment

Abstract

The present invention relates to an assembly which includes: a chassis for a mobile land vehicle, in particular an agricultural or public works vehicle; at least two half-crossmembers (21) mounted telescopically on the chassis; wheel mountings (27) pivotably mounted on each one of said half-crossmembers; steered wheels rotatably mounted on said mountings; and a device for controlling the direction of the wheels. The assembly is characterized in that it includes means (39, 41, 47) designed, for a certain position of two half-crossmembers, to increase, upon the pivoting of the wheels, the opening of the said wheels relative to the opening of the wheels resulting from the same pivoting and another position of the two half-crossmembers.

Claims

1. An assembly comprising: a chassis for a movable terrestrial machinery equipment; at least two half-crossmembers telescopically mounted on the chassis between a retracted position and an extended position; wheels supports pivotally mounted on each one of said half-crossmembers; steerable wheels rotatably mounted on said supports and connected to each other by an axle; a device for piloting the steering of the wheels; and a mechanical or electro-hydraulic or electro-electric component configured to enlarge or reduce the angle between the wheels of the same axle for a certain pivoting of said wheels and for a certain position of said half-crossmembers, in comparison with the angle obtained between said wheels, for the same pivoting of said wheels and for another position of said half-crossmembers, said enlargement or reduction of the angle being directly dependent of the distance between the wheels.

2. The assembly according to claim 1, wherein the device for piloting the steering of the wheels comprises steering cylinders interposed between the chassis and the wheels supports, wherein said component shaped so as to enlarge or reduce the angle between the wheels of the same axle for a certain pivoting of said wheels and for a certain position of said half-crossmembers, in comparison with the angle obtained between said wheels, for the same pivoting of said wheels, and for another position of said half-crossmembers, said enlargement or reduction of the angle being directly dependent of the distance between the wheels, comprise a mechanical component for displacing an attachment point of each steering cylinder during an extension of the half-crossmembers relative to the chassis.

3. The assembly according to claim 2, wherein the attachment point of each cylinder cooperates with at least one ramp/glider system shaped so as to constrain the attachment point of each cylinder to be displaced in a glider.

4. The assembly according to claim 3, wherein the means for displacing the attachment point of each cylinder comprise, at least one submount mounted on a half-crossmember and comprising said glider shaped so as to cooperate with the attachment point of each cylinder, or, the at least one ramp mounted on a crossmember support secured to the chassis, said ramp being shaped so as to constrain the displacement of the attachment point of the cylinder in said glider during a displacement of said half-crossmembers.

5. The assembly according to claim 4, wherein at least one of said ramps extends substantially from a central portion of the crossmember support toward an end portion of said support.

6. The assembly according to claim 4, wherein the at least one ramp is tilted with respect to an axis of displacement of the half-crossmembers.

7. The assembly according to claim 4, wherein the glider is shaped so as to enable a rotational-translational and/or linear motion of the attachment point of the cylinder.

8. The assembly according to claim 3, wherein the half-crossmember comprises a setting component configured for setting the inclination of the at least one ramp with respect to said half-crossmember.

9. The assembly according to claim 1, wherein the component configured to enlarge or reduce the angle between the wheels of the same axle for a certain pivoting of said wheels and for a certain position of said half-crossmembers, in comparison with the angle obtained between said wheels, for the same pivoting of said wheels and for another position of said half-crossmembers, said enlargement or reduction of the angle being directly dependent of the distance between the wheels, comprise at least one electro-hydraulic device.

10. The assembly according to claim 9, wherein the device for piloting the steering of the wheels comprises steering cylinders interposed between the chassis and the wheels supports, characterized in that the electro-hydraulic device comprises: an acquiring component configured for acquiring the position of the wheels and the track width of the machinery equipment; at least one supervisor comprising at least one calculator connected to said acquisition component; at least one box for regulating the hydraulic pressure introduced into the steering cylinders.

11. The assembly according to claim 10, wherein the acquiring component comprises: at least one steering sensor adapted for determining the pivot angle of at least one wheel; at least one track sensor adapted for determining the track width of the machinery equipment.

12. The assembly according to claim 10, wherein the box for regulating the hydraulic pressure introduced into the steering cylinders defines a closed-loop circuit with one of said steering cylinders.

13. The assembly according to claim 10, wherein the box is connected to a steering control device of the machinery equipment and is adapted for piloting the extension of said cylinders.

14. The assembly according to claim 10, wherein the box comprises at least one electrical control valve adapted for enabling the introduction of a fluid so as to increase or decrease the extension of the steering cylinders.

15. The assembly according to claim 1, wherein the component configured to enlarge or reduce the angle between the wheels of the same axle for a certain pivoting of said wheels and for a certain position of said half-crossmembers, in comparison with the angle obtained between said wheels, for the same pivoting of said wheels and for another position of said half-crossmembers, said enlargement or reduction of the angle being directly dependent of the distance between the wheels, comprise at least one electro-electric device.

16. A self-propelled or trailed movable terrestrial variable-track machinery equipment with at least two steerable wheels, comprising at least one assembly according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features, objects and advantages of the present invention, will appear upon reading the detailed description that follows, according to the embodiments given as non-limiting examples, and with reference to the appended drawings in which:

(2) FIGS. 1 to 6 relate to a variable-track machinery equipment according to the prior art:

(3) FIG. 1 schematically represents a variable-track machinery equipment in the retracted position in a rectilinear displacement;

(4) FIG. 2 schematically represents the same machinery equipment in a cornering situation, wherein the Ackermann steering geometry has been traced;

(5) FIG. 3 is a representation similar to that of FIG. 1, wherein the Ackermann steering geometry has been traced;

(6) FIG. 4 represents, in a cornering situation, the variable-track machinery equipment in the extended position, wherein the Ackermann steering geometry has been traced;

(7) FIG. 5 represents a four-wheel-steered variable-track machinery equipment in the retracted position and in a cornering situation, wherein the Ackermann steering geometry has been traced;

(8) FIG. 6 is a representation similar to that of FIG. 5, the machinery equipment being configured in the extended position;

(9) FIG. 7 illustrates a simplified view of a chassis for a variable-track machinery equipment equipped with an assembly according to a first embodiment of the invention;

(10) FIG. 8 is an enlarged simplified view of the area VIII of FIG. 7;

(11) FIG. 9 schematically represents a top view of a half-crossmember in the retracted position mounted on the crossmember support, for a two-wheel-steered vehicle;

(12) FIG. 10 is a view similar to that of FIG. 9, the half-crossmember being represented in the extended position;

(13) FIG. 11 is a simplified view similar to that of FIG. 8, the half-crossmember being represented in the extended position;

(14) FIG. 12 schematically represents, in a cornering situation, the two-wheel-steered variable-track machinery equipment in the extended position, equipped with an assembly according to the first embodiment of the invention, wherein the steering angle correction is represented;

(15) FIG. 13 schematically represents a top view of a half-crossmember in the retracted position mounted on the crossmember support, for a four-wheel-steered vehicle;

(16) FIG. 14 is a view similar to that of FIG. 13, the half-crossmember being represented in the extended position;

(17) FIG. 15 is a view similar to that of FIG. 12, the represented machinery equipment being a four-wheel-steered vehicle;

(18) FIG. 16 schematically represents a four-wheel-steered vehicle equipped with an assembly according to a second embodiment of the invention; and

(19) FIG. 17 represents a four-wheel-steered vehicle equipped with an assembly according to a third embodiment of the invention.

DETAILED DESCRIPTION

(20) In all figures, identical or similar references refer to identical or similar members or sets of members.

(21) Referring to FIG. 7, illustrating a half-crossmember 21 according to the invention, telescopically mounted on a crossmember support 23 secured to a chassis 24.

(22) The cross-member support 23 is mounted on the chassis 24 while keeping its suspension degrees of freedom, the chassis 24 may be a movable terrestrial machinery equipment (not represented) such as, for example, a sprayer-type agricultural machinery equipment, a straddle machinery equipment, a construction machinery equipment or any other type.

(23) Two half-crossmembers (only the half-crossmember intended to support the right front wheel is represented in a simplified manner) are mounted on the crossmember support 23, symmetrically positioned with respect to the longitudinal axis 25 of the chassis.

(24) The end portion 26 of each half-crossmember 21 receives a wheel support 27 intended to support a wheel (not represented) rotatably mounted on the shaft 29.

(25) Referring to FIG. 8, illustrating, in a simplified manner for more clarity, the half-crossmember 21 in a retracted position, mounted on the crossmember support 23.

(26) The wheel support 27 comprises a steering knuckle assembly 31 pivotally mounted about a substantially vertical pivot axis 32. Pivoting of the steering knuckle assembly 31 is achieved via a steering cylinder 33, the rod end of which is connected to a steering tie rod 35 secured to said steering knuckle assembly.

(27) The steering cylinders constitute a device for piloting the steering of the wheels. Of course, such a device may be constituted by any other means known by those skilled in the art.

(28) The steering cylinders 33 are typically constituted by double-acting cylinders, connected to a conventional steering control device (not represented) comprising a hydraulic pump activated by the rotation of the steering wheel from the driver's cab and delivering a fluid at either side of the piston of the cylinder, depending on the direction of rotation of the steering wheel.

(29) Each half-crossmember 21 is further movable in translation relative to the crossmember support along an axis of displacement 37. The displacement of each half-crossmember allows switching the machinery equipment alternately between a retracted position and an extended position.

(30) When the machinery equipment is in the retracted position, the track width is, for example, equal to about 1.8 meters, and the machinery equipment is particularly adapted for rolling on all tracks of the roadway.

(31) When in an extended position, the machinery equipment presents, for example, a track width equal to about 3.2 meters, thereby enhancing the stability of the machinery equipment on irregular surfaces such as, for example, those of fields to be sprayed on.

(32) Switching between these positions is achieved in a known manner via cylinders comprising an attachment point secured to the crossmember support and the end of each rod of which is connected to each half-crossmember. By activating the cylinders, the half-crossmembers switch from their retracted position into their extended position. This arrangement is well known by those skilled in the art and hence, it will not be described further in the following description.

(33) According to the invention, a submount 39 is fastened on each one of the half-crossmembers 21, on which is inscribed a slot, equivalent to a glider 41, with a substantially circular profile and the dimensions of which are shaped so as to receive an attachment point 43 of the steering cylinder 33.

(34) Referring now to FIG. 9, schematically representing a top view of the crossmember support 23 and the half-crossmember 21 in the retracted position, which position corresponds to the position that has just been illustrated.

(35) In such a position, the attachment point 43 of the cylinder 33 is in abutment against the front end 45 of the glider 41.

(36) The crossmember support 23 receives a ramp 47 connected to said support by a holding device 48. The ramp 47 extends substantially from a central portion 49 of said support located substantially at the level of the longitudinal axis of the chassis (to the left of the crossmember support 23 in FIG. 9) toward an end portion 51 of said support (to the right of the crossmember support). Furthermore, the ramp 47 is tilted with respect to the axis of displacement 37 of the half-crossmembers, and is shaped so as to enable sliding of the attachment point of the cylinder along said ramp.

(37) The arrangement of the glider 41, the ramp 47 and the steering cylinder 33 is such that during a displacement from a retracted position to an extended position represented in FIGS. 10 and 11, the ramp 47 constrains the attachment point 43 of the cylinder to be displaced along the glider 41, from the front end 45 of said glider back to the rear end 53 of the glider.

(38) To this end, the submount 39 and the ramp 47 constitute means for displacing the attachment point of each steering cylinder during an extension of the half-crossmembers relative to the chassis.

(39) In such an extended position, the angle formed between the cylinder 33 and the steering tie rod 35 is reduced in comparison with the angle obtained in the previously described retracted position, represented in FIG. 9.

(40) By reducing the angle between the cylinder and the steering tie rod when the track width is enlarged, that is to say by bringing the attachment point 43 of the cylinder close to the half-crossmember 21, without modifying the inclination of said steering tie rod in a rectilinear operation situation, the same cylinder stroke results in a more significant inclination of said steering tie rod, in comparison with the inclination of the steering tie rod obtained for the same cylinder stroke in a retracted position.

(41) In other words, when the wheels pivot in a cornering situation, and with the half-crossmembers 21 in an extended position, the opening angle between the steered wheels (visible in FIG. 12), which corresponds to the angle formed by the steered wheels in a cornering situation, is substantially enlarged in comparison with the relative opening of said wheels obtained when the wheels pivot, with the half-crossmembers in the retracted position.

(42) The fact that a larger angular opening between the wheels is allowed when the track width is enlarged results in a displacement of the Ackermann point substantially along the axis passing through the shafts of the rear wheels, as illustrated in FIG. 12, schematically representing a machinery equipment 1 in the extended position, for example for a 3-meter track width.

(43) In this Figure have been traced the Ackermann steering geometry A, obtained without any device for correcting the attachment point of the cylinder based on the track width, and the Ackermann steering geometry B that is obtained with the means according to the invention intended to displace the attachment point of the cylinders, when the steered wheels of the machinery equipment pivot to the right.

(44) Referring to the steering geometry A, the instantaneous center of rotation ICR.sub.A, at the intersection of the line (d.sub.D) perpendicular to the right front wheel 3.sub.D and passing through its center, with the line (d.sub.G) perpendicular to the left front wheel 3.sub.G and passing through its center, is located to the rear of the axis (d.sub.5) passing through the center of the rear wheels 7.sub.G, 7.sub.D.

(45) According to the steering geometry B, obtained thanks to the assembly according to the invention, the right front wheel has pivoted through a larger angle in comparison with the right front wheel of the steering geometry A, and this for the same cylinder stroke. By enlarging the relative opening of the steered wheels when the track width is enlarged, the instantaneous center of rotation ICR.sub.B is aligned on the axis (d.sub.5), thereby allowing approaching the non-slip conditions and significantly limiting the shifting phenomenon.

(46) Referring now to FIG. 13, schematically illustrating an embodiment of the means for displacing the attachment point of the cylinder when the vehicle is equipped with means for switching alternately from a two-wheel-drive configuration into a four-wheel drive configuration.

(47) FIG. 13 schematically represents a top view of the half-crossmember 21 in the retracted position.

(48) The holding device 48 (visible in FIGS. 9 and 10) between the crossmember support 23 and the ramp 47 has been replaced with a cylinder 55, thereby allowing modifying the inclination of said ramp when switching from a two-wheel-steered configuration into a four-wheel-steered configuration, which is conventionally carried out from the driver's cab.

(49) When switching into a four-wheel-steered configuration, the angle between the ramp 47 and the crossmember support 23 has been reduced in comparison with the angle formed for a two-wheel-steered configuration, which results in a displacement of the attachment point 43 of the cylinder 33 in the glider 41 supported by the submount 39.

(50) The glider 41 is shaped, on the one hand, so as to displace the attachment point 43 of the cylinder 33 to the left of the half-crossmember 21, when switching from a two-wheel-steered configuration into a four-wheel-steered configuration, and on the other hand, so as to enable a rotational-translational motion of the attachment point 43 of the cylinder 33, when switching from a retracted position into an extended position of the machinery equipment.

(51) By providing for a displacement of the attachment point of the cylinder to the left of the half-crossmember, when switching from a two-wheel-steered configuration into a four-wheel-steered configuration, the angle between the steering tie rod 35 and the cylinder 33 is reduced, for the same cylinder stroke, in comparison with the angle obtained with a two-wheel-steered vehicle.

(52) Thus, for a four-wheel-steered vehicle, the magnitude of pivoting of the steering tie rod 35 is increased for a cylinder stroke 33 identical to that obtained with a two-wheel-steered vehicle.

(53) Of course, the cylinder 33 may be replaced with any means allowing setting the inclination of the ramp with respect to the half-crossmember and known by those skilled in the art, such as for example a linkage system.

(54) As before, and as illustrated in FIG. 14 schematically representing a top view of the half-crossmember 21 in the extended position, the angle formed between the cylinder 33 and the steering tie rod 35 is reduced in comparison with the angle obtained in the previously described retracted position, represented in FIG. 13. By reducing this angle in this manner, the attachment point 43 of the cylinder 33 is brought close to the half-crossmember 21 without modifying the inclination of the steering tie rod 35 in a rectilinear operation situation. Thus, the same cylinder stroke results in a more significant inclination of the steering tie rod 35 when the machinery equipment is in the extended position, in comparison with the inclination obtained for the same cylinder stroke in the retracted position.

(55) In other words, when the wheels pivot in a cornering situation, and with the half-crossmembers 21 in an extended position, the opening angle between the steered wheels is substantially enlarged in comparison with the relative opening of said wheels obtained when the wheels pivot, with the half-crossmembers in the retracted position.

(56) Referring now to FIG. 15 illustrating, as in FIG. 12, the Ackermann steering geometry A obtained without any device for correcting the attachment point of the cylinder based on the track width, and the Ackermann steering geometry B obtained with the means according to the invention intended to displace the attachment point of the cylinders, during a right turn, for a four-wheel-steered vehicle.

(57) Referring to the steering geometry A, the instantaneous center of rotation ICR.sub.A(AV), at the intersection of the line (d.sub.D).sub.AV perpendicular to the right front wheel 3.sub.D and passing through its center, with the line (d.sub.G).sub.AV perpendicular to the left front wheel 3.sub.G and passing through its center, is located to the rear of the transverse middle axis 10 of the machinery equipment, whereas the instantaneous center of rotation ICR.sub.A(AR), at the intersection of the line (d.sub.D).sub.AR perpendicular to the right rear wheel 7.sub.D and passing through its center, with the line (d.sub.G).sub.AR perpendicular to the left rear wheel 7.sub.G and passing through its center, is located to the front of the transverse middle axis 10 of the machinery equipment.

(58) According to the steering geometry B, obtained thanks to the assembly according to the invention, the right front wheel 3.sub.D has pivoted through a larger angle in comparison with the right front wheel of the steering geometry A, and this for the same cylinder stroke. Similarly, the right rear wheel 7.sub.D has also pivoted through a larger angle in comparison with the right rear wheel of the steering geometry A.

(59) By enlarging the relative opening of the steered wheels, corresponding to an enlargement of the angles .sub.AV and .sub.AR when the track width is enlarged, the instantaneous center of rotation ICR.sub.B of the four steered wheels is substantially aligned on the transverse middle axis 10, thereby allowing approaching the non-slip conditions and significantly limiting the shifting phenomenon.

(60) Referring now to FIG. 16, schematically illustrating a four-wheel-steered machinery equipment equipped with an assembly according to a second embodiment of the invention.

(61) As before, the machinery equipment 1 comprises a front axle 2 at the ends of which are mounted two steered front wheels 3.sub.G, 3.sub.D and a rear axle 5 at the ends of which are mounted two rear wheels 7.sub.G, 7.sub.D which may be steerable or not.

(62) Of course, the front wheels may also be non-steerable and, in this case, only the rear wheels are steerable.

(63) The machinery equipment 1 comprises four half-crossmembers 210 telescopically mounted on crossmember supports 230 secured to the chassis 24 and positioned at the front axle 2 and at the rear axle 5.

(64) As before, the end portion 260 of each half-crossmember 210 receives a wheel support (not represented) comprising a steering knuckle assembly pivotally mounted about a substantially vertical pivot axis, pivoting of the steering knuckle assembly being achieved via steering cylinders 330, the rod end of which is connected to a steering tie rod 350 secured to the steering knuckle assembly.

(65) The steering cylinders 330, typically constituted by double-acting cylinders, are connected to a conventional steering control device 601 of the Orbitrol type, comprising a hydraulic pump P activated by the rotation of the steering wheel from the driver's cab and delivering a fluid at either side of the piston of the cylinder, depending on the direction of rotation of the steering wheel, and a tank T for fluid recovery.

(66) Each half-crossmember 210 is further movable in translation relative to the crossmember support along an axis of displacement 370. The displacement of each half-crossmember allows making the machinery equipment switch alternately between a retracted position and an extended position.

(67) Switching between these positions is achieved in a known manner via track cylinders 603 comprising an attachment point 605 secured to the crossmember support 230 and the end 607 of each rod of which is connected to each half-crossmember 210. In a known manner, by activating the cylinders, the half-crossmembers switch from their retracted position into their extended position.

(68) The steering control device 601 controls the rotation of the steered wheels by introducing a pressurized fluid into the steering cylinders 330. For this purpose, each steering cylinder is connected to two check valves 609, 611.

(69) The front wheels 3.sub.D and 3.sub.G are steerable and the rear wheels 7.sub.D and 7.sub.G are made steerable or non-steerable via a set of slide valves 613.

(70) As example, in order to perform a right turn, the steering control device 601 sends a pressurized fluid in a conduit 615a and in a conduit 615b. The fluid passes through the check valve 609 and then penetrates into the orifice 617 of the steering cylinder 330 connected to the right front wheel, which results in a displacement of the rod of the cylinder in the direction of the arrow F1, and concurrently resulting in a clockwise pivoting of the steering tie rod 350 and the rotation of the right front wheel 3.sub.D to the right.

(71) Indeed, when the fluid reaches the check valve 609, a volume of this pressurized fluid passes through the bridge 619, thereby unlocking the check valve 611 and allowing the fluid coming out of the cylinder 330 to flow in a conduit 621 until reaching the check valve 611 connected to the steering cylinder 330 of the left front wheel. A certain volume of the pressurized fluid penetrates in the check valve 611 and a certain volume of fluid passes through the bridge 623.

(72) The volume of fluid that penetrates in the check valve 611 enters into the orifice 625 of the steering cylinder 330 connected to the left front wheel 3.sub.G, resulting in the displacement of the rod of the cylinder in the direction as represented by the arrow F2. Such a displacement of the cylinder rod results in a pivoting of the corresponding steering tie rod 350, and concurrently the rotation of the left front wheel 3.sub.G to the right.

(73) The volume of fluid that has passed through the bridge 623 unlocks the check valve 609 thereby allowing the fluid coming out of the left cylinder 330 to flow toward the tank T of the steering control device 601, via the conduit 627, so that the hydraulic circuit is a closed-loop circuit.

(74) The conduit 615 is, in turn, connected to the slide valves 613. The valves 613 are electronically (or electrically) controlled so as to allow for three steering modes of the machinery equipment: two steered front wheels, four steered wheels in a crab fashion (in a cornering situation, the wheels are along the same direction), four steered wheels in a coordinated fashion (in a cornering situation, the two steered rear wheels turn in the reverse direction as the steered front wheels).

(75) For a displacement of the machinery equipment in the four-wheel-steered mode in a coordinated fashion, a signal is sent from the driver's cab to an electrical control valve 631 thereby activating the valve 633. The fluid that is displacing in the conduit 615b as the command for displacing the machinery equipment to the right is sent then passes through the valve 633 and circulates in a conduit 635 feeding the steering cylinder 330 of the right rear wheel 7.sub.D via a check valve 609.

(76) The fluid penetrates into the orifice 637 of the cylinder 330, thereby displacing the rod of the cylinder in the direction of the arrow F3, which results in a counterclockwise pivoting of the steering tie rod 350 of the right rear wheel 7.sub.D, and the rotation of said wheel to the left.

(77) The left rear wheel 7.sub.G is also turned to the left thanks to the action of the pressurized fluid which passes through the bridge 639 thereby unlocking the check valve 611 and allowing the fluid coming out of the cylinder 330 to flow in the conduit 641 feeding the steering cylinder 330 of the left rear wheel, via the check valve 611.

(78) A portion of the volume of fluid arriving via the conduit 641 is actually sent in the check valve 611. By passing through the bridge 645, the other portion of the volume of fluid unlocks the check valve 609 thereby allowing the fluid coming out of the cylinder 330 to return in the tank T of the steering control device 601.

(79) The preceding description relates to the coordinated operation of the machinery equipment in the four-wheel-steered mode, that is to say that the front wheels and the rear wheels turn in opposite directions when the machinery equipment is turning.

(80) In order to enable a displacement of the machinery equipment in the four-wheel drive mode in a crab fashion, an electric signal is sent to the electrical control device 649 in order to activate the valve 647, thereby enabling a displacement of the fluid from the conduit 615b toward the conduit 643 and the introduction of the fluid into the corresponding orifice of the steering cylinder 330, which results in a rotation of the left rear wheel to the right during a right turn.

(81) Switching from a four-wheel-steered mode into the two-wheel-steered mode is achieved by restoring the valves 633 and 647 into their original position. In such a configuration, the fluid sent by the steering control device 601 in the right or left conduit is blocked at the slide valves 613 and does not reach the rear wheels.

(82) According to the invention, for a certain position of the two half-crossmembers, the assembly comprises means shaped so as to enlarge or reduce the relative opening of the wheels as they pivot, in comparison with the relative opening of the wheels obtained for the same pivoting and with another position of the two half-crossmembers.

(83) According to this second embodiment of the invention, these means comprise an electro-hydraulic device.

(84) These means comprise electronic means which control a BTAP box 651 for regulating the hydraulic pressure introduced into the steering cylinders.

(85) Each steering cylinder is connected to the regulation box 651, which is, in turn, connected to the pump P and to the tank T of the steering control device 601.

(86) The regulation box 651 is controlled by a digital supervisor (not represented) further comprising at least one calculator.

(87) The entire device is equipped with means for acquiring the position of the wheels and the track width of the machinery equipment.

(88) By means for acquiring the position of the wheels, it is referred to any device adapted for determining the pivot angle of a wheel of the machinery equipment at a given time. To this end, such a device may be adapted for collecting the position of the wheel, that is to say its pivot angle with respect to a reference position, or collecting the value of the stroke of a steering cylinder secured to the steering tie rod of a wheel, in order to deduce the pivot angle of the wheel therefrom.

(89) By means for acquiring the track width, it is referred to any device adapted for collecting the track width that the machinery equipment presents at a given time.

(90) More specifically and as example, the track cylinder 603 is connected to a track sensor adapted for assessing the track width of the machinery equipment, whereas the steering cylinder 330 is connected to a steering sensor adapted for collecting the position of the wheel. The position sensor collects either the angle of rotation of the wheel or the distance covered by the rod of the steering cylinder 330.

(91) The digital supervisor defines the necessary angular correction to be brought to one or more of the steered wheels in order to approach the Ackermann steering geometry.

(92) Afterwards, the digital calculator of the supervisor sends a command to the regulation box 651 so as to control the introduction of a fluid into either one of the two orifices of the steering cylinder 330 in order to enlarge or reduce the stroke of the rod of the cylinder and consequently act on the angle of rotation of a wheel.

(93) For this purpose, for a given track width and for a given angle of the so-called master wheel, the so-called piloted wheel must present a certain angle of rotation in order to comply with the Ackermann steering geometry.

(94) In the case of a right turn with the machinery equipment in the four-wheel-steered position and operating in a coordinated fashion, the fluid is sent in the steering cylinders 330 which activate the right front wheel 3.sub.D and the right rear wheel 7.sub.D as previously explained in the description.

(95) The digital calculator of the supervisor receives the information from the track and steering sensors. The calculator compares the values of the angle of each master wheel (for example, the right front wheel and the right rear wheel, respectively) and the angle of each piloted wheel (for example, the left front wheel and the left rear wheel, respectively) to the theoretical values of the angle expected for the left front wheel and left rear wheel, for a given track width.

(96) For this purpose, the calculator is provided with abacuses informing on the angle of rotation that the piloted wheel has to present in order to approach as close as possible the Ackermann steering geometry, for a given track width and for a given angle of the master wheel.

(97) In the case where an enlargement of the angle of the left front wheel (the piloted wheel) is, for example, necessary in order to approach the Ackermann steering geometry, which case is considered when switching from an extended position of the two half-crossmembers into a retracted position of the two half-crossmembers, the supervisor controls the regulation box 651 connected to the left front wheel 3.sub.G. An electric signal is then sent to the electrical control valve 653 which results in an introduction of the fluid into the pathway B through the conduit 655 connected to the orifice 625 of the steering cylinder 330 of the left front wheel, thereby enabling an extension of the stroke of the cylinder, and thus an enlargement of the angle of rotation of the wheel in comparison with the angle initially obtained for a larger track width.

(98) In the case where a reduction of the angle of the left front wheel is necessary in order to approach the Ackermann steering geometry, which case is considered when switching from a retracted position of the two half-crossmembers into an extended position of the two half-crossmembers, the supervisor controls the regulation box 651 connected to the left front wheel 3.sub.G and an electric signal is sent to the electrical control valve 657 which results in an introduction of the fluid into the pathway A through the conduit 659 connected to the orifice 661 of the steering cylinder 330 of the left front wheel, thereby enabling a reduction of the stroke of the cylinder, and thus a reduction of the angle of rotation of the wheel in comparison with the angle initially obtained for a smaller track width.

(99) The regulation box 651 forms with the steering cylinder 330 a closed-loop circuit, that is to say that a first orifice of the cylinder receives the pressurized fluid thanks to the pump P of the steering control device 601 to which the regulation box is connected, and a second orifice of the steering cylinder is connected to said regulation box which is also connected to the tank T of the steering control device, in order to evacuate the fluid introduced into the cylinder.

(100) The preceding description refers to an electro-hydraulic device. Of course, this device may be replaced with an electro-pneumatic device, or still with an electro-electric device. As example, in the case of an electro-electric device, the steering and/or track cylinders, to which the present description refers, consist of electric cylinders, as illustrated in FIG. 17.

(101) Thanks to the present invention, we remain close to the Ackermann steering geometry regardless of the retained track width. Furthermore, compliance with the Ackermann steering geometry is achieved thanks to a device which is easy to mount on any type of movable terrestrial variable-track machinery equipment whether with two or with four steerable wheels.

(102) According to the first embodiment of the assembly according to the invention, the displacement of the half-crossmembers alternately between a retracted position and an extended position results, mechanically, simultaneously and instantaneously, in the displacement of the attachment point of the cylinders, thereby suppressing the prior step of setting up the inclination of the steering tie rods.

(103) According to the second embodiment, we approach the Ackermann steering geometry regardless of the track width applied to the machinery equipment, thanks to an electronically-piloted hydraulic device. Alternatively, this device may be pneumatic or electric.

(104) It goes without saying that the invention is not limited to the sole embodiments of this assembly, described above only but as illustrative examples, but it encompasses, on the contrary, all variants thereof. To this end, for example, the assembly previously described with reference to the first embodiment of the invention may be advantageously coupled with an electronic control device, thereby allowing increasing the accuracy of the positioning of the attachment point of the cylinder in the glider.