The present invention relates to a track system for a tracked work vehicle, such as a construction equipment vehicle or a military tracked vehicle or an agricultural vehicle, e.g. a combined harvester or the like.

BACKGROUND OF THE INVENTION

A tracked work vehicle is provided with a suspension in order to increase adhesion and traction performances on soft grounds, such as grounds affected by a relatively high degree of humidity or grounds having a relatively high quantity of sand.

A rubber tracked vehicle is preferred to satisfy the need for a relatively high speed on paved streets, e.g. during a travel of the work vehicle to and from a construction site or a cultivated field. Furthermore, a rubber track tends to be relatively less expensive than other tracks.

The suspension is normally an undercarriage suspension and provides the highest traction performances when the track adheres the ground. Sometimes the surface layer of the ground is not uniform and bodies made of a hard material are found on or immediately below the surface of the ground, such as rocks, spare metallic construction materials such as tubes or the like.

When encountering such an obstacle, it is important to find a compromise between stiffness and kinematic compliance for the design of the track-supporting idlers, rollers and structure of the suspension. Otherwise the track, in particular the rubber track, may undergo excessive wear. In particular it is important that the rollers are sufficiently constrained to provide proper support to the track when the ground is uniformly soft and are mobile enough to retract only in the near surroundings of a hard body on the ground surface. In both instances the scope is to keep or improve traction performances and, at the same time, lower the wear of the track.

SUMMARY OF THE INVENTION

The scope of the present invention is achieved by a rubber tracked work vehicle according to claim 1. According to a preferred embodiment, intermediate rocker is connected to the undercarriage beam via the first and the second rockers.

According to another preferred embodiment the elastic or visco-elastic connection is a bushing.

According to another preferred embodiment at least one roller wheel comprises a first and a second wheel, and a shaft to connect first and second wheels, the shaft being pivotally attached to a relevant rocker.

According to the invention, an existing tracked vehicle is retrofittable or can be provided with a linkage according to the present invention during a periodic maintenance.

Additional features of the invention are disclosed in the description and the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, the latter will further be disclosed with reference to the accompanying figures in which:

Figure 1 shows a work vehicle that can be equipped with the present invention;

Figure 2 is a sketch of a linkage for the vehicle of figure 1 ;

Figure 3 is a bottom enlarged perspective view of an embodiment of the linkage of figure 2. Some elements are cancelled for clarity's sake; and

Figure 4 is a lateral enlarged perspective view of figure 3.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 refers, as a whole, to a work vehicle 1 comprising a frame 2 and at least two rubber tracked, preferably four, track systems 3 attached to frame 2.

Frame 2 can be a rigid frame and in this case the vehicle may be provided with steering wheels (not shown); or a hinged frame having a front part 4, a rear part 5 hinged to front part 4 about axis A and a steering unit (not shown), preferably a hydraulic steering unit comprising linear actuators, to control the relative angular position of front part 4 with respect to rear part 5 about axis A. Each track system 3 comprises a rubber track 6, a drive wheel 7 extending from a differential (not shown) for driving track 6 and an undercarriage 8 pivoting with respect to frame 2. Undercarriage 8 comprises a front idler wheel 9, a rear idler wheel 10 about which track 6 is wrapped, roller wheels 1 1 , 12, 13 for guiding track 6, all of which are supported by an undercarriage beam 14, which extends fore-and-aft, and to which wheels 1 1 , 12, 9 and 10 are coupled. While the "front idler wheel," "rear idler wheel," "roller wheel" are singular terms, a plurality of wheels may be provided at each relative position in side-to-side orientation, such as in this embodiment. Advantageously, in order to provide a better contact surface with rubber track 6, at least wheels 1 1 , 12, 13, 9 and 10 are twin wheels, i.e. each wheel comprises two wheels coupled side-to-side.

In particular undercarriage beam 14 is connected to frame 2 in order to tilt in a plane parallel to axis A and oriented fore-and-aft when vehicle 1 travels along a straight path. Preferably undercarriage beam 14 is hinged to frame 2 in order to tilt for a maximum of 15 degrees with respect to a neutral position shown in figure 1. Instead drive wheel 7 is fixed to frame 2.

Each track system 3 further comprises a tilting linkage 15 to connect roller wheels 1 1 , 12, 13 to undercarriage beam 14 in order to provide one or more degrees of freedom to such rollers with respect to beam 14. In particular, linkage 15 comprises a rigid rocker 20, 21 , 22 connected to a respective roller wheel 1 1 , 12, 13. Rigid rockers 20, 22 are respectively adjacent to idler 9 and idler 10 and hinged to beam 14. Rocker 21 is longitudinally placed between rockers 20, 22 and is connected to beam 14 via rockers 20, 22. Therefore intermediate rocker 21 is floating with respect to beam 14.

In addition, track system 3 comprises at least one elastic or visco-elastic connection 23 to connect rockers 20, 22 to rocker 21 in such a way that an upwards motion of a leading roller, e.g. roller wheel 1 1 during climbing an obstacle 24, applies a downwards action on both trailing rollers 12 and 13, such action being transmitted through the elastic or visco-elastic connections 23. Such functioning is obtained via the floating connection of intermediate rocker 21 to beam 14, which is operated only via rockers 20, 22. In view of the required effect, the distance and relative position of each hinge and center of roller wheels 1 1 , 12, 13 within linkage 15 provides a different distribution of forces on rollers. Preferably, the position of roller wheels 1 1 , 12, 13 before mounting of track 6 is such to increase the tension of the track after mounting of the latter about drive wheel 7 and idler wheels 9, 10. Furthermore, the connection can be either passive, i.e. including a spring and a damper that are pre-set during assembly or by the user before a specific mission of vehicle 1 , or active, i.e. including actuators to change the spring modulus or stiffness and/or the damping of the connection when vehicle 1 is working.

Preferably, the connection is visco-elastic and comprises inserts, e.g. a pack of discs, or bushings of a rubber material possibly reinforced either by particles or fibres or by one or more woven or non-woven layers. Rubber inserts or bushings are loaded to transfer the target action by either compression or shear or a combination of the two.

According to the functional sketch of figure 2, each rocker 20, 22 comprises a first end portion 25 carrying a relative roller 1 1 , 13 and a second end portion 26 projecting on an opposite side of the first end portion with respect to a hinge 27 for connection of the rocker to undercarriage beam 14. Rockers 20, 22 are specular with respect to intermediate rocker 21 (figure 2) so that rollers 1 1 , 13 are opposite to respective hinge 27 with respect to intermediate rocker 21. Intermediate rocker 21 is preferably symmetrical with respect to a plan comprising the axis of roller 12 but other configurations are possible. According to the present embodiment connections 23 apply the respective loads on points that are symmetrical with respect to the plane comprising the axis of roller 12.

When roller 12 is leading roller, obstacle 24 lifts intermediate rocker 21 and this causes both rockers 20, 22 to push down the respective trailing rollers 1 1 , 13.

According to a preferred embodiment of the invention (figure 3), rockers 20, 21 , 22 are located below the undercarriage beam 14 and hinges 27 for connection with rockers 20, 22 are defined by stirrups 28 extending from beam 14 towards the ground opposite to driving wheel 7. Furthermore, rockers 20, 21 , 22 are hinged one to the other. To do so, first and second end portions 25, 26 of rockers 20, 22 define an angle between 90° and 180° and hinge 27 is located in a vertex portion 29 of rockers 20, 22 formed between first and second end portions 25, 26.

Furthermore the elastic or visco-elastic connection 23 is located below undercarriage beam 14 and comprises a rubber bushing mounted in hinge 31 for connection between two adjacent rockers 20, 21 , 22. Preferably, the shape of rockers 20, 21 , 22 and the position of hinges 27 and 31 is such to provide a kinematically fixed configuration when loaded on a geometric plane. This means that, if the rubber bushing 23 were substituted by a rigid body, rollers 1 1 , 12, 13 and rockers 20, 21 , 22 could not move one with respect to the other. In such a condition, the provision of rubber bushings 23 in hinges 31 and optionally also in hinges 27 provides, by means of compression of the bushings depending on the obstacles encountered by track 6, relatives degrees of freedom between rockers 20, 21 , 22 and, accordingly, between rollers 1 1 , 12, 13. Such configuration therefore provides kinematic liability only in view of the fact that rubber bushings 23 are deformable. This results in a relatively stiff configuration of the suspension, i.e. the combination of tilting supports and elastic or visco-elastic connection.

As a further feature shown in the drawings, rollers 1 1 , 12, 13 comprise a first and a second wheel 60, 61 rigidly connected one to the other by a shaft 62. Each shaft 62 is pivotably attached to first end portion 25 of the relative rocker 20, 22 or to rocker 21 , preferably in the plane of symmetry, in order to provide a rotational degree of freedom about an axis A that is co-planar to a mid-plane of track 6 and/or of shaft 62.

Preferably (figure 4), pivoting axis of shaft 62 is defined by a pin (not shown), in particular a screwable pin, attached in a dedicated seat within first end portion 25. Shaft 62 is attached to the pin. In order to restore a neutral position, i.e. a position wherein shaft 62 is substantially parallel to axes of drive wheel 7 and idler wheels 9, 10, a resilient element (not shown) acts on shaft 62. Preferably resilient element is housed at least in part or wholly within first end portion 25. According to one embodiment, the resilient element comprises rubber bushings, or a pack of rubber discs or the like and is coaxial to shaft 62.

It is preferable that elastic or visco-elastic connection 23 is designed such that, when travelling on a paved street, at least front idler wheel 9, preferably also idler wheel 10, are lifted from the paved surface. Without a prejudice to the stability of the work vehicle, this decreases wear on rubber track 6.

The advantages of an undercarriage suspension according to the present invention are the following.

The provision of rockers connected one to the other by elastic or visco-elastic connections provides the combined effect of increasing effectiveness to overcome obstacles and, at the same time, reduce the wear of the track. Indeed a controlled compliance of the rollers is such to avoid tension peaks within the track when the ground is rough or non-homogeneous. This is in particular true where the linkage 15 is such to provide that both trailing rollers 12, 13 a load that presses track 6 down when leading roller 1 1 climbs obstacle 24.

Connections 23 located below undercarriage beam 14 provide the lowest possible impact on undercarriage beam.

It is clear that changes and variations are applicable to the work vehicle according to the present invention without departing from the scope of protection as defined in the attached claims.

For example, track 6 can be arranged along a triangular path, as shown e.g. in figure 1 , or along other paths. This may increase or reduce the number of idler wheels with respect to the embodiments discussed in the preceding paragraphs.

When at least three rollers are provided to guide track 6, two rollers may be attached to a single intermediate rocker such as e.g. a walking beam, in order to rigidly tilt one with respect to the other when track 6 runs on an obstacle 23.

It is possible to retrofit existing work vehicles with a kit comprising at least the undercarriage beam 14, rockers 20, 21 , 22 and connection 23.

According to a further not shown embodiment connection 23 is a rubber block, preferably a reinforced rubber block, defining a deformable spacer between adjacent rockers 20, 21 , 22 according to the sketch of figure 2. The rubber block is compressed when adjacent rockers rotate in opposite angular directions. In order to provide proper absorption and/or load resistance, the rubber block shall have suitable dimensions.

The rubber block is located below undercarriage beam 14 and is preferably carried by the relevant rockers 20, 21 , 22. Conveniently the rubber block is interference fitted between second end portions 26 an intermediate rocker 21 in order to provide, after mounting, a tensioning action on track 6. The rubber block is preferably attached to one of the adjacent rockers and abuts without being attached to the other of the adjacent rockers. It is possible that connection 23 be a link comprising a single elastic or visco-elastic element, in particular a linear single elastic or visco-elastic element or damper.

As an alternative, connection 23 comprises a rubber block compressed by rockers 20, 22.