This invention relates to a wheel construction and more particularly but not exclusively to a wheel construction for agricultural vehicles or light construction machines or the like.

Wheel constructions for agricultural vehicles and the like off-road vehicles, are known which include a circular wheel rim which provides respective axialfy inner and outer flanges which each provide a seat for a tyre bead of a floatation tyre which is fitted to a radially outer, or "tyre side" of the rim. In the example of US-A-5560686, such a wheel construction is disclosed which further includes a disc by means of which the wheel is securabte to a hub of the vehicle, the disc being connected to a radially inner side of the rim and the disc and rim being separable. This invention is though applicable to wheels in which the rim and disc are permanently connected together e.g. by welding.

In this specification, by "floatation tyre" we mean a wide (axialiy long) tyre which spreads loads thus reducing, e.g. soil, compaction, when the vehicle is driven on a non-road surface.

Agricultural vehicle wheel constructions are known which include a wheel rim with axialiy inner and outer portions which each provide a tyre bead seat flange, and an adjoining frusto-conicai connecting surface which extends axiaϋy towards the mid-portion where there is central well. The tyre bead seat flange, and typically at least a part of the connecting surface, together provide a seat for the tyre. The connecting surface adjoins a circumferentially extending side part, which side part extends to and adjoins the mid-portion of the rim.

It has been found that with such existing rims, the service iife of the rims may be insufficient because structural stresses which occur in the area where the side parts adjoin the mid-region, can lead to premature failures of the rims.

According to one aspect of the present invention we provide a wheel construction according to claim 1.

The present invention enables the structural stresses which occur in the area where the side part of the at least one of the inner and outer portions adjoins the mid-region to be decreased, and this has been found to lead to structural failures in this area to be at least reduced. This enables the service life of the rim to be increased compared with prior proposals, and moreover, the thickness of the rim material can be reduced without compromising the structural integrity of the rim, thus reducing weight and the cost of production.

In a preferred embodiment the first concave surface of the curved region is located radially outwardly of the second concave surface and the third concave surface is located radially inwardly of the second concave surface, the third concave surface continuously adjoining the mid-region and the first concave surface continuously adjoining the frusto-conicai region.

Between the first and second concave surfaces there may be a convex formation, and between the second and third concave surfaces there may be a further convex formation, all when viewed from the tyre side of the rim. The convex formation between the first and second concave surfaces preferably continuously melds with the adjacent first and second concave surfaces, and the further convex formation between the second and third concave surfaces may continuously meld with the adjacent second and third concave surfaces. Thus a continuously undulating curved region is provided.

The second and third concave surfaces and the further convex formation between the second and third curved surfaces may each have a local respectively internal and external radius of between 6mm and 14mm, and preferably of about 10mm.

The first concave surface, and the convex formation between the first and second concave surfaces may each have a local respectively internal and externa! radius of between 8mm and 16mm, and preferably of about 12mm,

The frusto-conical region of the side part may subtend an angle of between 15° and 50°, preferably an angle of about 36° to a plane which is perpendicular to the wheel axis.

Preferably the wheel rim is symmetrical about a central plane of the mid-region which is perpendicular to the wheel axis.

The external loca! radius at the radiussed surface where the frusto-conical region of the side part and the connecting surface continuously meld may be between 5.5mm and 13mm.

The frusto-conical connecting surface of the at least one of the inner and outer portions may subtend an angle to a plane which is perpendicular to the wheel axis, of greater than 75 ^C and preferably in the order of 85° or even 95°.

To add rigidity to the construction, if desired the flange of the at least one of the inner and outer portions may extend radially outwardly of the end of maximum radius of the frusto-conical connecting surface to a curved flange surface where the radius of the respective radially inner or outer portion is a maximum, by a distance of at least 12mm. A termination position of the flange may be located more than two-thirds of the distance between the end of maximum radius of the frusto-conical connecting surface and the curved fiange surface.

Embodiments of the invention will now be described with reference to the accompanying drawings in which:

FIGURE 1 is an illustrative axial end view of a wheel for an agricultural or light construction vehicle, in accordance with the present invention;

FIGURE 2 is a cut away perspective view on l-l of figure 1 of part of the wheel, showing the general wheel construction;

FIGURE 3 is a detaiied sectional view of an axially outer portion of a wheel construction in accordance with the present invention, enlarged for clarity.

Referring to figures 1 and 2 there is shown a wheel construction 10 which includes a wheel rim 11 which in use, at a tyre side 12 of the rim 11 receives a tyre 14. The position of the tyre 14 is indicated oniy in figure 3.

The rim 11 is circular and in this case is generally symmetrical, having axially inner 16 and axially outer 15 portions, and a mid-portion 18 between the axially inner and outer portions 15, 16.

Each axiafly inner and outer portion 16, 15 provides a fiange 22, a frusto- conical connecting surface 23, and side parts 19, 20 between the mid portion 18 and each respective connecting surface 23.

Each flange 22 and an adjacent part of the connecting surface 23 in use, provide a seat for a bead of the tyre 14. The rim 11 has secured, reieasabiy or permanently, at the inner radial side opposite the tyre receiving side 12, a disc 13 by means of which the wheel 10 is mountable on a hub 17, by means of a plurality of fasteners 21. In use, the wheel 10 rotates with the hub 17 about a wheel axis A.

It has been found that with prior art proposals, as the wheel rim 11 is formed, typically by a coid forming or pressing operation, the areas where the side parts 19, 20 adjoin the mid-portion 18 are formed with structural stresses which can lead to premature failure of the wheel rim 11 in this area. Also, with some prior proposals, the flanges 22 at the axia! ends of the wheel construction 10 which provide the tyre 14 bead seats, have been found to be insufficiently substantial.

The configuration of the axiaily outermost portion 15 of the rim 11 i.e. the portion of the rim 11 which is use is axiaily outermost of the vehicle on which the wheel 10 of the invention is mounted, will now be described in detail, with additional reference to figure 3.

The generally frusto-conical connecting surface 23 has an axial end 24 of greatest radius and an axial end 25 of least radius, the connecting surface 23, at its axiai end 24 of greatest radius, adjoins the flange 22, and the connecting surface 23 extends radially inwardly of the rim 11 towards the mid-portion 18. The axiai end 25 of the frusto-conical connecting surface 23 of least radius adjoins, by a circumferentially extending radiussed surface 26, the adjacent side part 19.

In another embodiment, if desired, instead of the radiussed surface 26, the connecting surface 23 and the side part 19 may be adjoined by a convex hump which may extend radialiy outwardly of the wheel axis A beyond the end The mid-portion 18 includes a circumferential well where the radius of the wheel rim 11 is a minimum.

Referring now to figure 3 the side part 19 includes both a frusto-conica! region 28 and a curved region 40. By providing the side part 19 particularly the curved region 40, in accordance with the invention, the stresses present in the area between the frusta-conical region 28 and the mid region 18 are avoided during manufacture thus improving the service life of the wheel 10.

The frusto-conical region 28 subtends an angle B of about 36° to a plane P which extends perpendicularly to the wheel axis A but the frusto-conica! region 28 may in other examples, typically subtend an angle of between 15° and 50°.

The curved region 40 adjoins an end 29 of least radius of the frusto-conica! region 28 of the side part 19. The curved region 40 is provided by a first circumferentialiy extending concave surface 41 , and a second circumferentiaiiy extending concave surface 42 and a third circumferentialiy extending concave surface 43, (ail when viewed from the tyre side 12 of the rim 11 ). The first and second concave surfaces 41 , 42 are axially separated in this example, by a convex formation 44 and the second and third concave surfaces 42, 43 are axialiy separated by a further convex formation 45 {all when viewed from the tyre side 12 of the rim 11 ).

In this example, the first concave surface 41 of the curved region 40 is iocated radially outwardly (relative to the wheel axis A) of the second and third concave surface, 42, 43 and the third concave surface 43 is located radially inwardly of the first and second concave surfaces 41 , 42 so that the second concave surface 42 is between the first and third concave surfaces 41 , 43. The third concave surface 43 continuously adjoins the mid-region 18. The convex formation 44 between the first and second concave surfaces 41 , 42 continuously melds with the adjacent first and second concave surfaces 41 , 42 and the further convex formation 45 continuous melds with the adjustment second and third convex surfaces 42, 43 so that the curved region 40 is continuously undulating, although if desired, there may be a frusto-conicai or cylindrical region between the convex formation 44 and one or other of the concave surfaces 41 , 42, and/or between the further convex formation 45 and one or other of the second and third concave surfaces 42, 43.

Through this specification, by "ioca!" radius we mean the actual radius of the surface rather than the radial distance of the surface from the wheel axis.

In the example of figure 3, the second and third concave surfaces 42, 43 and the further convex formation 45 between them, each are of a local respective internal and external radius R1 , R2, R3, of about 10mm, but in any event preferably of between 6mm and 14mm. The radii R1 , R2, R3 need not all be the same, as in the example, but at least one of the second and third concave surfaces 42, 43 may have a local radius different to the other or to the further convex formation 45 as desired.

Further, in the example of figure 3, the first concave surface 41 and the convex surface 44 between the first and second concave surfaces 41 , 42 are of a local respective internal and external radius R4, R5 respectively, of about 12mm, but in any event of preferably between 8mm and 16mm. The radii R4 and R5 need not be the same, as in the example.

In another example, ali of the radii R1, R2, R3, R4 and R5 of the curved surfaces of the curved region 40 of the side part 19, may al! be the same, or may all be different, or any or some of them may be the same, The radiussed surface 26 of the outer portion 15 of the rim 11 in the example, may have a local radius Rδ of between 5.5mm and 13.5mm and desirably of about 9.5mm.

The frusto-conicai connecting surface 23 of the outer portion 15 may subtend an angle C to the plane P which is perpendicular to the wheel axis A, of greater than 75°, e.g. 85° or 95° as in the example shown so that the cone angle of the frusto-conicai connecting surface 23 may be about 10°.

In the wheel construction 10 of the example the flanges 22 of the inner and outer portions 15, 16 each terminate at a respective position 30 outwardly radially relative to the wheel axis A of the frusto-conicai connecting surface 23. The flange 22 extends radially outwardly of the end 24 of maximum radius of the frusto-conicai connecting surface 23 to a curved flange surface 36 where the wheel rim 11 is of maximum radius, of a distance of at least 12mm and the termination positions 30 of the flanges are preferably located not more than two-thirds of the distance between the end 24 of maximum radius of the frusto- conicai connecting surface 23 and the curved flange surface 36, Thus the flanges 22 are more substantial than in prior art proposal and add additional stiffness at the axial ends of the rim 11 , as well as adding stiffness to the rim 11 generally. In the example, the convex curved flange surface 36 of each flange 22, when viewed from the tyre side 12 of the rim 11 , has a local radius of about 12.7mm, and where the flange 22 adjoins the end 24 of maximum radius of the frusto-conicai connecting surface 23, there is a local internal radius R7 in the order of 8mm.

By adopting the present invention, a rim 11 is provided in which the material thickness of the rim 11 can be reduced compared with comparable rims which do not incorporate the invention. Various modifications are possible without departing from the scope of the invention.

In the example shown in the figures 1 , 2 and 4, the rim 11 is symmetrica! about a central plane of the mid region 18 which is perpendicular to the wheel axis A and coincident with line l-l in figure 1. in another example the wheel 10 may be asymmetricai and only one of the side parts 19, 20 of the wheel 10 may have the profile of the invention.

Although the wheel construction described is that of a floatation wheel for use on an agricultural vehicle such as a tractor, or a light construction vehicle such as an excavating and/or loading machine, the invention may be applied to another wheei construction.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.