EP2825397A2

EP2825397A2 - Tyre for a vehicle

Info

Publication number: EP2825397A2
Application number: EP13760337.9A
Authority: EP
Inventors: Toivo PITKÄNEN
Original assignee: MECLIMB Oy
Current assignee: MECLIMB Oy
Priority date: 2012-03-12
Filing date: 2013-03-11
Publication date: 2015-01-21
Also published as: EP2825402A1; EP2825402A4; WO2013135955A2; EP2825397A4; FI125664B; WO2013135955A3; FI20125267A; WO2013135954A1

Abstract

The object of the invention is a tyre for a vehicle, which tyre comprises at least a surface layer (22) as well as an air space (20) and which tyre is configured to be disposed on the rim (13) of a wheel rim. The air space (20) is composed of a plurality of air channels (24) side by side, which are separated from each other with an essentially flexible wall material (25).

Description

TYRE FOR A VEHICLE

The object of the invention is a tyre for a vehicle as defined in the preamble of claim 1.

The tyre according to the invention is particularly suited to vehicles intended to move in off-road terrain. In these types of vehicles, such as in e.g. various power tools and forest machinery, the properties of the wheels and tyres and the suspension solutions of the wheels are important, because they essentially affect how the vehicle travels in possible rough terrain. The grip between the tyres and the underlying surface must be good so that the tyres do not slip in bad terrain. In addition, the wheels and tyres must also be suited to moving on an uneven underlying surface and passing over various obstructions, in which case the suspension of the wheels is of critical importance. The biggest problem in off-road driving is known to be slipping of the wheels and passing over various obstructions, which considerably hampers moving in off-road terrain. Another problem is the tyre structures according to prior art, in which tyres a stiff frame must be used for achieving sufficient counterforce to the force produced by carrying a load and by an obstruction. This counterforce is produced almost entirely from a rise in the air pressure of the tyre and the air pressure is directed at the whole area of the inner part of the tyre. In order for the deformation of the surface of the tyre to remain within reasonable bounds, a stiff structure and high air pressure must be used, which properties in turn stiffen the adaptabil- ity of the contact surface. A tyre thus comprises only two load-bearing structures, i.e. the sides of the tyre.

The aim of this invention is to eliminate the aforementioned drawbacks and to achieve a tyre for a vehicle, by the aid of which, inter alia, the locomotion of various off-road vehi- cles in rough terrain is facilitated. The vehicle tyre according to the invention is characterized by what is disclosed in the characterization part of claim 1. Other embodiments of the invention are characterized by what is disclosed in the other claims.

One advantage of the solution according to the invention is the improved grip of tyres and the ability to pass over obstructions in, inter alia, vehicles being driven in rough terrain, such as in various power tools and forest machinery. From this follows the advantage that locomotion with off-road vehicles in difficult terrain becomes easier and it is possible to access more difficult locations with them. One advantage of the solution is also that by means of it tyres of different sizes and possessing different flexing properties and^■ load-bearing properties can be fabricated easily, because the bearing force of the tyre comes from many points of the contact surface of a hose filled with air. In this case, the force produced by one contact patch does not really raise the internal pressure. At the same time the ability of the contact patch to flex is retained, i.e. it is able to grip better. Another advantage is that the tyres can be made to be very lightweight and low-profile and the lateral stiffness of the tyre is extremely large.

In the following, the invention will be described in more detail by the aid of some examples of its embodiment with reference to the attached drawings, wherein Fig. 1 presents a simplified and diagrammatic ^" view obliquely from the side and top of one tyre according to the invention,

Fig . 2 presents a magnified, diagrammatic and simplified view of a part of the cross -sect ion of the tyre ac- cording to Fig. 1, presents a diagrammatic and simplified view of a part of a cross-section of one second tyre according to the invention,

presents a sectioned part of one surface layer of a tyre according to the invention,

presents an oblique top view of the surface layer of a tyre according to Fig. 4,

presents an oblique view from the side and top of one suspension arrangement for a wheel of a vehicle, provided with a tyre according to the invention, in which suspension arrangement one wheel is removed for the sake of graphical clarity,

presents a rear view of one suspension arrangement according to Fig. 6 for a wheel of a vehicle, in which suspension arrangement both wheels of one axle system are presented when cross-sectioned, presents a diagrammatic and simplified side view of the principle of a suspension arrangement for the wheel of a vehicle presented in Figs. 6 and 7, and presents a diagrammatic, simplified and oblique rear view of the principle of a suspension arrangement according to Figs. 6-8 for a wheel of a vehicle in different operating situations. Figs. 1 and 2 present a simplified and diagrammatic view of one tyre according to the invention, and Fig. 3 presents a diagrammatic and ^'simplified view of a part of a cross-section of one second tyre according to the invention. The tyre is extremely low profile and its flexible part is constructed on the outer surface of the rim 13 of a thin e.g. metal wheel rim disc, such as a wheel rim, in such a way that the tyre comprises at least e.g. a metal wheel rim part and an air- filled flexible part comprising a flexible material, e.g. rubber, on its outer rim. On the second edge, preferably the outer edge, or near it, of the inner surface of the rim 13 of the wheel rim is a shallow reinforcing ring 13b, with fixing lugs 16, extending towards the center axis of the rim of the wheel rim 13, to which fixing lugs the center part 13a of the wheel rim presented in Fig. 7, with the hub of the wheel, is fixed by the aid of fixing holes 17 and suitable fastening means, such as fixing bolts.

The flexible part of the tyre according to the invention comprises at least a surface layer 22, in which is a suitable tread pattern, and an air space 20, in which are air ducts 24 and a wall 25 between them of essentially flexible material separating the air ducts 24 from each other. The air space 20 is composed e.g. of air hoses 27 that are side-by-side under the surface layer 22, which air hoses are fitted e.g. by vul- canizing onto the outer surface of the rim 13 of the wheel rim. In this case the wall 25 of flexible material comprises two walls of air hoses 27 that are side-by-side and against each other, though some other suitable filler material can additionally be between the hoses.

Closest to the outer surface of the rim 13 of the wheel rim is a thin layer 18 of adhesion-improving agent, such as an adhesive rubber layer, which can also be e.g. of raw rubber, which is brushed onto the outer surface of the rim 13 of the wheel rim. This rubber layer is configured to function also as a flexing agent. The outer edge of the rim 13 of the wheel rim is also preferably turned slightly upwards, which fold supports, either directly or via a filler, the edgemost turns of the layer formed from the air hoses 27 or from correspond- ing air-duct structures.

On the outer surface of the layer 18 of adhesion-improving agent is a thin binder layer 19 of fabric netting or corresponding material, which is configured to bind the air-duct structures, such as air hoses 27, of the air space 20 to each other and to support the air hoses 27. The binder layer 19 is folded onto the edgemost air hoses 27 on the side edges of the tyre. The adhesion between the air hoses 27 and the adhesion of the air hoses 27 to the outer surface of the rim 13 of the wheel rim is configured at the same time to evenly support the rim 13 of the wheel rim essentially for the whole width of the rim 13 of the wheel rim. Preferably a reinforcement layer 21, e.g. a cross-wound textile fiber layer, the whole width of the tyre is further on top of the air hoses 27 or other air-duct structure. Further, the topmost layer is the surface layer 22, which can be e.g. of treaded rubber on its outer surface. The surface layer 22 binds all the surface structures of the tyre together and also, if necessary, closes off the surplus gaps in the air space 20, e.g. the gaps between air hoses 27.

The profile ratio of the tyre can be freely selected determined by the diameter and shape of the air ducts 24, or also by the number of air duct layers one on top of another. The diameter of an air hose 27 functioning as an air duct 24 is suitably e.g. between 10-100 mm, preferably however smaller than 50 mm. The shape of the cross-section of an air duct 24 can be e.g. round, rectangular or elliptical. The air ducts 24 of the air space 20 are preferably composed of e.g. a structure comprising one air hose 27, which is wound into a spiral on the outer surface of the rim 13 of the wheel rim in such a way that each adjacent layer is either right next to each other or material is suitably disposed between adjacent layers. Thus there can be wedge-shaped rubber filling, such as pins both above and below, between air-hose coils or air ducts 24, or flat gripping rubbers can be between them. The harder points between the air ducts 24 remain raised when the points filled with air flex. In this way the grip of the tyre can be improved. At the end of the edgemost air-duct coil on the outer edge of the tyre, i.e. at the end of e.g. the air-hose coil, is an air valve 23 for filling the air ducts 24. The ends of the air hose 27 can be cut orthogonally or obliquely. A preferred structure also comprises additional reinforcements of the edgemost, i.e. outermost, hose coil, for which additional reinforcement fabric of ribbon type or of twisted cord type can be used. Additional reinforcements are advantageous in case e.g. the wheel 1 grazes a sharp stone or other obstruction when it is moving in the terrain.

With the longitudinal or obliquely transverse alignment of the topmost bearing fabric layer 22, the flex properties of the tyre can be influenced. Saturation of the internal fibers of all the fabrics with rubber is ensured either with rubber cements or with dissolved raw rubber. The cord-like outermost fabric layer 22 bears the load and determines the flex properties. The coil density and cord thickness affect the stiffness. This outermost fabric layer 22 keeps the tyre in its shape just as in a radial tyre.

Figs. 4 and 5 present one surface layer 22 of a tyre according to the invention. The thickness of the surface rubber is suitably e.g. approx. 10 mm, most of which thickness, is cut into the tread pattern of the tyre. The tread pattern is composed e.g. of protrusions 26a of essentially rectangular shape, the rows formed by which are between the air-hose coils. Between the protrusions 26a is a shallower point 26b. The orthogonal longitudinal and transverse square-shaped protrusion pattern holds well in the traction direction and in the lateral direction. The stress level of the tyre is, depending on the operation, of a totally different class compared to prior-art tyre structures. With the structure ac- cording to the invention lightweight tyres can be fabricated, in which case operation is faster and energy consumption decreases .

Fig. 6 presents one suspension arrangement for a wheel 1 of a vehicle provided with a tyre according to the invention at the point of one axle system and seen obliquely from the side and from above. The suspension arms 2 of the wheels 1 are pivoted at their first ends to a coupling part 3 of the suspension by the aid of a joint 12. The suspension arms 2 are comprised of two parts. In its initial position, when the vehicle is e.g. on a flat underlying surface, the first parts, i.e. the frame parts 2a, of the suspension arms 2, which parts are fixed at their first ends in a pivoted manner to the coupling part 3 of the axle system, point from the cou- pling part 3 straight to the side and sloping slightly downwards from the horizontal plane, after which there is an angle in the frame parts 2a and the direction of the frame parts 2a changes to sloping slightly upwards. A second part of the suspension arm 2 is fixed at its first end to the second end of the frame part 2a, i.e. said second part being a suspension rod part 2b of essentially a roughly semicircular shape or of a corresponding angularly shaped structure, which is a curved part of essentially semicircular shape pointing forwards in the direction of travel of the vehicle, which part is disposed, as viewed from the front of the vehicle, in an oblique position in such a way that the higher first end of the suspension rod part 2b is closer to the longitudinal center line of the vehicle than the lower second end of the suspension rod part 2b, which second end is also always inside the rim 13 of the wheel rim of the wheel 1 and to which second end of the suspension rod part 2b the wheel 1 is arranged to be fixed. The bottom part of the suspension rod part 2b of the suspension arm 2 comprises fixing lugs 4 and 5 for hinging the suspension of the wheel 1. Both fixing lugs 4 and 5 are arranged to extend from their free end to inside the rim 13 of the wheel rim of the wheel 1.

To the fixing lugs 4 and 5 is connected at its bottom part, e.g. by the aid of the ball joint 7 as well as by the aid of the ball joints 8 and 9 and the plate-shaped coupling part 10, a suspension element 6 of the wheel 1. The coupling part 10 is connected to the fixing lug 4 by the aid of the ball joint 8 and to the suspension element 6 by the aid of the ball joint 9. A motor 11, which is e.g. a hydraulic motor, functioning as a hub motor is also fixed to the suspension element 6. The suspension element 6 and the motor 11 together form the bearings of the wheel 1. To each wheel 1 is connected its own motor 11, fixed to the center part 13a of the wheel rim.

The suspension element 6 of the wheel 1 and at the same time also the wheel 1 are arranged to turn and to incline within the limits permitted by the movement of the ball joints 7, 8 and 9 and of the coupling part 10. Thanks to suitable shaping of the suspension arm 2 and suitable pivoting of the suspension element 6, i.e. to suitable adjustment settings, the wheel 1 can turn and incline into different positions at rather large angles without the suspension arm 2 or suspen- sion element 6 hitting the inside surface of the rim 13 of the wheel rim of the wheel 1. The suspension arm 2 is arranged to turn at its first end around the joint 12 in relation to the coupling part 3, in which case the wheel 1 can also move up and down in the vertical direction. Thanks to this type of suspension arrangement the wheels 1 follow different difficult shapes of the terrain and obstructions very well, when driving with the vehicle in off-road terrain.

The center axes of the first ball joint 7 and of the second ball joint 8 are always on the same straight line as each other, which line is called the caster line CL, but the position of the third ball joint 9 with respect to the aforementioned straight line and to the second ball joint 8 changes according to the turning and inclining of the wheel. Thus the ball joint 9 rotates in a conical pendulum manner around the straight line formed by the ball joints 7 and 8, i.e. around the caster line CL . Thanks to the shape, placement and dimensioning of the support structure of the axle system, i.e. to the adjustment settings, the fixing of the wheel 1 turns and inclines into different positions with the ball joint 7 as the center point, i.e., in relation to the ball joint 7. The ball joints 7 and 8 are arranged to distribute the load acting on the wheel 1 according to their leverage ratio, which load on a flat underlying surface in an idle state is essen- tially one-half on both joints 7 and 8, in which case the ball joints 7 and 8 distribute the load roughly half and half. As viewed from the side of the wheel 1, the ball joints 8 and 9 are on a first side of the vertical center line of the wheel passing via the hub of the wheel 1, i.e. on the rear side of the aforementioned center line in the direction of travel of the vehicle, and the ball joint 7 is on the second side of the vertical center line of the wheel passing via the hub of the wheel 1, i.e. on the front side of the aforementioned center line in the direction of travel of the vehi- cle .

The shock absorbers 14 and 15 also function as inclination dampers and both stabilize and damp inclining movements and turning movements of the wheel. The axle system with wheels 1 is connected to the vehicle with a coupling part 3. There can be e.g. two, three or four essentially similar axle systems consecutively in a vehicle.

Fig. 7 presents the axle system according to Fig. 6 as viewed from the rear in the direction of travel of the vehicle in such a way that both wheels 1 of the axle system are presented cross-sectioned. For the sake of clarity the special structure of the tyres, which has already been explained in Figs. 1-4, is not presented in the sections of the wheels 1. The axle system and wheels 1 are in their initial position in an idle state and on an essentially flat underlying surface. Fig. 7 shows the inclined position of the suspension rod parts 2b of the suspension arms 2 well, in which position the suspension rod part 2b is in a sloping position in such a way that the bottom end of the suspension rod part 2b is inside the rim 13 of the wheel rim of the wheel 1 below the axis of rotation of the wheel 1 and below both the motor 11 and suspension element 6. In addition, Fig. 7 clearly shows that the tyre profile is very low, which enables good tyre grip and good traveling properties in off-road terrain.

Figs. 8 and 9 present in a diagrammatic and simplified manner the principle of a suspension arrangement for a wheel 1 of a vehicle provided with the tyre according to the invention presented by Figs. 6 and 7. All the axle lines, in relation to which the various functions occur when the vehicle moves, travel through the center point of the first ball joint 7. The wheel 1 rotates, by the aid of the motor 11 functioning as a hub motor, around its own center axis, i.e. around its axis of rotation, but functions in a new way around exactly the ball joint 7. The ball joints 7-9 comprise a spherical inner part, and casings functioning as coupling means around it. Thus the ball joints 7-9 can function between two different structural elements.

The suspension arrangement presented has essentially three basic settings, namely; the location, the caster line setting, and the steering angle. There is one basic setting between the ball joints 7 and 8, which is called the caster line CL . Correspondingly, the steering line SL is configured between the ball joints 7 and 9. In addition, a third line is the steering axis line SA, around which line the lateral steering of the wheel 1 occurs. The position of the wheel 1 in relation to the position of the vehicle follows the posi- tions of the caster line CL and of the steering line SL in the different phases of movement of the vehicle. Only the caster line CL is fixed and continuously follows the trajectory of the suspension arm 2 and of the suspension rod part 2b and the change in position resulting from it. The ball parts of the ball joints 7 and 9 are fixed to the suspension element 6 and the whole structure is suspended on the hub of a wheel 1 provided with a tyre according to the invention. The ball part of the ball joint 8 is attached to the fixing lug 4 of the suspension rod part 2b of the suspension arm 2. Correspondingly, the casing parts functioning as the coupling means of the ball joints 8 and 9 are attached to the coupling part 10. The forces from the suspension arm- 2 are exerted on the wheel 1 via the ball joints 7 and 8, and the ball joint 9 functions according to the situation. Correspondingly, the forces from the wheel 1 are exerted on the suspension arm 2 via the ball joints 7 and 9, in which case the ball joint 9 also functions as a reacting part, which the ball joint 8 steers . In the suspension arrangement of the wheel, the center of mass shifts forwards and backwards in the area between the arrow A presented in Fig. 8. The center of mass shifts forwards either from the collision movement caused by the obstruction 0 or as a result of the increased resistance. The value of the countermoment then exceeds the effect of the weight acting on the ball joints 8 and 9. Since the operation of the suspension arrangement changes as a result of a change in where the weight acts and a change in leverage ratios, the operation of the suspension arrangement, its rigidity, reac- tion speed and the steerability of the wheel 1 can be ad- justed by changing the position of the ball joints 7-9 in relation to each other and to the hub of the wheel 1. In this case the directing of the weight onto the ball joints 7-9 changes, and the position of the lines CL and SL with respect to the contact patch between the wheel 1 and the underlying surface also changes.

One adjustment item is the caster line CL. In normal use the position of the ball joints 7-9 and the caster line CL are e.g. in, or near, the locations presented by Figs. 8 and 9. The basic setting of the caster line CL is an angle towards the drive direction. This angle is e.g. rising towards the front compared to the horizontal plane, in which case a positive angle of incidence is in question.

One adjustment item is the steering line SL and its angle of incidence. The wheel 1 operates according to the forces produced by the angles of incidence and the underlying drive surface. It reacts only to the forces produced by the under- lying drive surface according to the leverage ratios. When passing over an obstruction, the wheel 1 does not try to repel an obstruction, but instead steers towards it, even if the obstruction were on either side of the wheel. By inclining, the wheel 1 obtains a larger and better grip from the obstruction. The wheel can pass over smaller obstructions just by inclining, without it affecting the height position of the ball joint 7. Thanks to the structure of the suspension arrangement, the wheel 1 always follows the trajectory of the ball joint 7, also when locked in inclining, in which case it also steers itself. With very large steering angles the ball joint 7 rises up to even the height of the front edge of the wheel 1 and the center of mass rises along with it. This results in an ability to pass over large obstructions, which is impossible for a rigid wheel. Combined in in- clination and steering, the wheel damps all the forces and also restrains longitudinal forces. It is exactly the change in relative speed caused by the path of movement that evens out longitudinal forces. Correspondingly, the inclination and steering of the wheel, as well as the special structure of the tyre, restrain lateral forces. Thus the wheel harms nature very little and leaves only minor traces, if any, on its underlying surface.

The ball joints 7 and 8 are, as viewed from the top, prefera- bly on the center line of the wheel 1 in the width direction of the wheel 1. In this case also the caster line CL is on the center line of the wheel 1 in the width direction of the wheel 1. In the idle state the lines CL and SL are parallel with each other when viewed exactly from above. The contact patch of the wheel 1 -with its underlying surface is midway between the ball joints 7 and 8 in the direction of travel of the vehicle. If the wheel 1 encounters an obstruction, for instance on the right-hand side of the aforementioned center line, it produces torsion, which shifts the ball joint 9 to the left-hand side of the center line. The wheel 1 then steers to the right. Simultaneously the wheel 1 is able to incline and steer towards the obstruction. When the ball joint 9 is on the top of the circle presented in Fig. 9 with a dot-and-dash line, the steering of the wheel 1 is fast. On the sides of the circle, e.g. in position 9a, on the other hand, the flex rearwards is fast.

In the structure according to the invention the center of mass in the height direction is on the caster line CL between the ball joints 7 and 8. For this reason a tyre with as low a profile as possible is needed. At the same time the center of mass being exerted from the vehicle shifts from the hub of the wheel 1 to near the surface of the underlying drive surface. It is exactly this property that is a complete paradigm shift compared to solutions according to prior art. When passing over an obstruction the weight acting on the wheel must be levered over the obstruction. The higher the obstruction, the more additional force is needed. This is exactly the greatest drawback of structures according to prior art. The center of mass does not shift and the contact patch moves away from the center line. The ability to grip is always lost if the speed is not sufficient to pass over the obstruction. Additional force in this case only increases the slip of the wheel .

In the preceding the operation of the suspension arrangement of a vehicle according to the invention has been explained simplifying the operation in such a way that it is presented as the extreme positions of individual movements. In prac- tice, all the rolling and inclining movements are involved at the same time in the operation of a wheel 1. In this case the axle system automatically seeks the positions according the easiest way of traveling and the surface of the low-profile tyre always seeks its way optimally for the direction of un- derlying travel surface, in which case the loading force is always in the normal direction of its support surface. In this case the best possible advantage is obtained from the low-profile tyre structure according to the invention and from its adaptability.

The so-called neutral contact enabled by the new tyre structure according to the invention and by the suspension solution presented results from the self-steerability of the wheel 1. The ball joints 7 and 8 are attached to the suspen- sion arm 2 and the ball joint 9 is attached to the suspension element 6 of a motor 11 functioning as a hub motor. The aforementioned neutral contact always keeps the contact as close to static friction as is generally possible. Inclination of the wheel 1, on the other hand, distributes the sur- face pressure in the contact patch and always takes a larger contact surface than old structures. The wheel 1 does this fully on the terms of the underlying drive surface, whereas the suspension structure of a wheel according to prior art operates only on the terms of the suspension of the wheel. The tyre according to the invention is able to adapt to small unevennesses in the underlying drive surface because it does not have a solid and stiff bearing structure. The carrying capacity is based on many tubular parts, which together form the load-bearing capability.

There are two factors acting together in the tyre according to the invention, which factors affect the load-bearing capability and flexing of the tyre. The air part comprised of air ducts 24 flexes inwards and the rubber parts on the sides of the air ducts 24 then bear an ever-increasing weight. The surface of the tyre at the point of the air part of an air duct 24 flexes inwards, in which case the stiffer point of the rubber part that is the wall 25 takes grip from both sides of the air part . In an idle state the surface of the tyre is therefore in a zero-state, but the contact of the tyre when it rotates is able to take grip from above and below the idle state of the contact surface. The return of the flex of the air part also cleans the tread of the tyre more effectively than in structures according to prior art.

It is obvious to the person skilled in the art that the invention is not limited solely to the example described above, but that it may be varied within the scope of the claims presented below. Thus for example the structure of the tyre can differ to what is presented above. There can be more different rubber layers and reinforcement layers, and they can be different. In addition, the air hoses can be, instead of one spirally wound hose, a number of hoses or ducts side by side, which are, with regard to their air parts, either connected to each other or separate from each other, and which each have their own valve or they have a valve shared between them .

Claims

1. Tyre for a vehicle, which tyre comprises at least a surface layer (22) as well as an air space (20) and which tyre is configured to be disposed on the rim (13) of a wheel rim, characterized in that the air space (20) is composed of a plurality of air channels (24) side-by-side, which are separated from each other with an essentially flexible wall material (25) .

2. Tyre according to claim 1, characterized in that the air parts of the air ducts (24) are connected to each other and they all have a common valve (23) for filling the air ducts (24) with air or with another filling agent.

3. Tyre according to claim 1 or 2, characterized in that the air ducts^' "(24) are composed of one air hose (27), which is wound into a spiral onto the outer surface of the rim (13) of the wheel rim of the tyre.

4. Tyre according to claim 1, 2 or 3, characterized in that suitably disposed between adjacent air ducts (24) is material that is stiffer than the wall between the air ducts (24), such as wedge-shaped rubber filling or rubber pins (26a), which stiffer material is configured to remain raised when the points filled with air flex.

5^'·. Tyre according to any of the preceding claims, characterized in that the diameter of the air ducts (24) of the tyre is between 10-100 mm, preferably e.g. smaller than 50 mm.

6. Tyre according to any of the preceding claims, characterized in that the tyre belongs as a part of a wheel (1), which is fixed to an axle system provided with suspension arms (2), the wheel (1) at both ends of which axle system being sup- ported on the suspension arm (2) from below the axis of rotation of the wheel (1) by at least three joints (7-9), of which the center axes of the first joint (7) and of the second joint (8) are always on the same straight line (CL) as each other and the position of which third joint (9) with respect to the aforementioned straight line (CL) and to the second joint (8) is arranged to change according to the turning and/or inclining of the wheel (1) .