Description

Technical Field

The present invention relates to a wheel rim for an agricultural vehicle, more particularly to a wheel rim for an agricultural tractor.

Prior Art

A wheel rim for a vehicle includes a metal body, made for instance of stamped steel. A wheel rim essentially has a central region for fixing the rim to one of the hubs of a vehicle and a region peripherally located in radial direction relative to the rim rotation axis and to the central region, where the tyre seat is defined.

Said seat includes an annular channel laterally delimited by a pair of circumferential edges radially extending relative to the rim rotation axis. The circumferential edges delimit the channel and prevent the tyre from slipping out of the seat provided in the rim body. The cross-section of the channel for the tyre, i.e. the section taken along a plane parallel to the rim rotation axis, generally has a half-circular profile. Moreover, the channel depth increases from the periphery to the centre of the channel. Thus, the channel profile has a central channel portion where the channel depth is maximum. According to the prior art, the channel profile may be symmetrical or asymmetrical relative to said central channel portion and may include, from the periphery, i.e. from the edge, to the centre, portions or levels at progressively decreasing depths.

Fig. 1 schematically shows, in the portion at the right of the central plane ("P"), one half of an annular channel (13a) of a first wheel rim (11a) of known type for agricultural vehicles. The rim includes a rim body having a central region for fixing the rim to the hub and a peripheral region (9b). The channel (13a) is of conventional type, i.e. it is made in accordance with the prior art, for an agricultural vehicle, for instance an agricultural tractor. As it can be appreciated, the profile of the channel (13a) includes, from the periphery, i.e. the edge (15a), to the centre, a first portion (17a) adjacent to the edge (15a), a second portion (19a), or intermediate portion, with greater depth than the first portion (17a), and a third portion (21a), corresponding to the central portion of the channel (13a). The central portion (21a) has a greater depth than the second portion (19a) and, consequently, than the first portion (17a). Connecting regions (23a, 25a, 27a) are provided between the peripheral edge (15a) and the first peripheral portion (17a), between said first portion (17a) and the second portion (19a), and between said second portion (19a) and the central portion (21a), respectively. The first portion (17a), the second portion (19a) and the central portion (21a) are parallel to the rim rotation axis.

Always in accordance with the prior art, this exemplary profile of the channel (13a) is symmetrical with respect to the central plane ("P") and thus repeats identical on the opposite side of the body of the wheel rim (11a). The first portion (17a) is arranged to receive the tyre bead when the tyre is mounted in a working configuration on the rim (11a) for the use of the vehicle the wheel rim (11a) is associated with.

Still referring to Fig. 1, there is schematically shown, in the portion at the left of the central plane ("P"), one half of an annular channel (13b) of a second wheel rim (l ib) of known type, including a rim body having a central region for fixing the rim to the hub and a peripheral region (9b). An annular channel (13b) for the tyre is defined in the peripheral region (9b) and is delimited by outer edges (15b) radially extending relative to the rim (1 lb) and arranged to prevent the tyre from slipping out of the rim. Said annular channel (13b) has a profile having an increasing depth from the periphery to the centre. More particularly, from the periphery of the rim (l ib), i.e. from each outer edge (15b), to the centre of the rim (l ib), parallel to the rim rotation axis, there are defined a peripheral portion (17b), arranged to receive the tyre bead when the tyre is mounted in a working configuration on the body of the rim (1 lb), and a central portion (21b). The central portion (21b) has a greater depth than the peripheral portion (17b). Moreover, a connecting portion having an increasing depth from the peripheral portion (17b) to the central portion (21b) and including a plurality of inclined annular surfaces (29b, 31b, 33b, 35b) is provided between the peripheral portion (17b) and the central portion (21b). This second embodiment in accordance with the prior art has been proposed in the past in order to make smoother and more gradual the passage of the tyre beads from the configuration in which they rest on the central portion (21b) to the configuration in which they rest on the peripheral portion (17b) when the tyre is inflated during installation.

As it will become apparent from the following description, both prior art solutions described above have a number of drawbacks,

As known, the bead of a tyre, in particular an agricultural tyre, for instance for an agricultural tractor, includes a layer of rubberised cloth that prevents wear caused by tyre rubbing against the rim edge and ensures the friction necessary for preventing the tyre rotation on the rim while the vehicle is travelling.

Moreover, as known, the beads of the tyres, in particular the tyres intended for use in agricultural vehicles, are internally equipped with a so-called bead wire. The bead wire generally includes a steel rib or band placed in the bead, the purpose of which is positioning the tyre on the rim body and keeping it in position, preventing the tyre from possibly slipping out.

The proper positioning of the beads of an agricultural tyre in a rim of such kind takes place by inflating the tyre at high pressure, typically 2.5 bars. Such an operation is performed starting from a configuration in which the flat tyre is received in the channel (13a; 13b) of the rim (11a; 1 lb). By operating in this way, the tyre beads, that initially rest on the central portion (21a; 21b) of the profile of the rim (11a; l ib), are submitted to a thrust from the inside of the tyre, which thrust is arranged to space apart the beads from each other and to make them rest on the first peripheral portion (17a, 17b), in abutment against the edges (15a, 15b) of the rim (11a; l ib). While passing from the rest condition to the condition in abutment against the peripheral edges (15a, 15b), the tyre beads are submitted to a transverse thrust of high intensity. Indeed, such a thrust must overcome the elastic resistance opposed by the tyre structure, which opposes the transversal and radial expansion of the same tyre. This elastic resistance is moreover accentuated because, with respect to the rotation axis of the rim (11a; 1 lb), substantially corresponding to the central axis of the tyre, the peripheral portion (17a, 17b) has a greater radius than the central portion (21a; 21b), and because the regions (23a, 25a, 27a; 31b, 33b, 35b) of the profile of the channel (13a; 13b) of the rim (11a; l ib) connecting the portions at different depths define wide angles, typically close to 90°, with the planes of the respective portions (17a, 19a, 21a; 29b, 31b, 33b, 35b) at increasing depths. Due to such reasons, during the mounting phase of the tyre, in particular during the step in which the beads are positioned into the respective peripheral seats, carried out with a pressure increase inside the tyre, the tyre beads can undergo damages and even breakages. Such damages can affect the covering structure of the beads and also the internal bead wire.

Under such undesirable situations, the tyre is therefore irreparably damaged and is to be replaced.

A further, but not the last drawback of the prior art is the risk that the tyre bursts, due to the strong pressure increase in the mounting step described above and to the above- mentioned opposition of the tyre structure to warp itself and to become positioned with its beads on the peripheral portions of the rim channel.

The present invention aims at overcoming the drawbacks of the prior art and in particular at solving the problem of how to avoid damage and breakage of the beads and the bead wire when the tyre is being mounted on the rim of an agricultural vehicle. Another object of the invention is to provide a profile for a wheel rim of the aforesaid kind, which can be formed both during manufacturing of a rim and during modification of existing rims having profiles in accordance with the prior art.

A further, but not the last object of the invention is to provide a wheel rim that can be industrially produced with limited costs.

Description of the invention

The above and other objects are achieved by the wheel rim for an agricultural vehicle as claimed in the appended claims.

The wheel rim for an agricultural vehicle according to the invention includes a rim body having a central region for fixing the rim to the hub and a peripheral region in which an annular channel for the tyre is defined. The annular channel is delimited by outer edges that radially extend relative to the central region and are therefore arranged to prevent the tyre from slipping out of the rim. The annular channel has a cross-section, i.e. a section taken along a plane parallel with the rim rotation axis, having an increasing depth from the periphery of the channel to the centre of the channel. Moreover, the channel is preferably symmetrical relative to a median plane perpendicular to the rim rotation axis and passing through the centre of the channel.

A peripheral portion and a central portion are defined in the channel, from the periphery of the channel, i.e. from the outer edges, to the centre, parallel to the rim rotation axis. The peripheral portion is arranged to receive the tyre bead when said tyre is mounted in a working configuration on the rim body. Preferably, the peripheral portion and the central portion are cylindrical and are parallel to the rim rotation axis.

According to the invention, a conical connecting portion defining a corresponding conical annular connecting surface is provided in the channel between the peripheral portion and the central portion, which surface is inclined so that the depth of the channel linearly increases from the peripheral portion to the central portion. The connecting portion is connected without interruptions to the central portion and the peripheral portion.

Preferably, according to the invention, the peripheral and central portions define corresponding cylindrical surfaces parallel to the rim rotation axis and form angles ranging from 20° to 60° and, more preferably, angles of 30°, with the connecting surface defined by the connecting portion.

In accordance with a particular embodiment of the invention, the wheel rim includes a channel having a first level of depth, or of distance from the rim rotation axis, wherein said first level corresponds to a peripheral portion defining an annular surface substantially parallel to the rim rotation axis, a second level of depth, or of distance from the rim rotation axis, wherein said second level corresponds to the central portion defining an annular surface substantially parallel to the rim rotation axis, and a surface defined by the connecting portion and connecting the annular surface of the peripheral portion to the annular surface of the central portion, without interruption. According to the invention, the profile of at least one half of the rim channel only comprises said two annular surfaces and said intermediate connecting surface.

Advantageously, thanks to the arrangement claimed, the smooth and gradual passage of the tyre beads from the condition in which they rest on the central portion to the condition in which they rest on the peripheral portion when the tyre is being inflated during the mounting step is made easier.

In accordance with a preferred embodiment of the invention, the conical connecting portion has a surface inclined relative to a plane perpendicular to the rim rotation axis by an angle ranging from 40° to 80°. Preferably, said angle is of about 60°.

The wheel rim according to the invention can preferably be made as an integral body, for instance of stamped metal sheet, or can be made of several pieces fastened together by known fastening means. The wheel rim according to the invention can be obtained by mechanical deformation from a rim body of known type, or by applying an insert on a rim body of known type.

Advantageously, by applying said insert, the invention can therefore be applied to wheel rims for agricultural vehicle, for instance agricultural tractors, of known type and already existing in commerce.

A further, but not the last advantage of the invention is that the profile of the rim according to the invention allows a saving in compressed air during tyre installation. Indeed, thanks to the channel profile according to the invention, the tyre adheres to the rim and becomes positioned in the proper position more quickly than in the prior art rims and at a lower pressure. Use of a lower pressure further allows considerably reducing the risk of damaging the tyre bead during the mounting step. Always thanks to the lower inflating pressure during tyre installation, the operation is also safer for the operator, since the risk that the tyre bursts or breaks is reduced. According to the invention, the maximum inflating pressure required to achieve the proper accommodation of the tyre bead on the rim is kept lower than in the prior art and is typically below 1.2 - 1.3 bars.

Some preferred embodiments of the invention will be provided by way of non- limiting examples with reference to the accompanying drawings, in which: - Fig. 1 shows, in the right-hand and left-hand portions, respectively, cross-sectional partial views of a first and a second wheel rim in accordance with the prior art;

- Fig. 2A is a cross-sectional partial view of a wheel rim in accordance with a preferred embodiment of the invention, where the channel profile according to the invention is superimposed to the first example of the prior art;

- Fig. 2B is a cross-sectional partial view of a wheel rim in accordance with a preferred embodiment of the invention;

- Fig. 3 is a cross-sectional partial view of a wheel rim in accordance with a second embodiment of the invention.

In all figures, the same reference numerals have been used to denote equal or functionally equivalent components. Moreover, the figures show a first half of the channel relative to a plane perpendicular to the rotation axis and passing through the centre of the channel, the second half, not illustrated, being preferably the mirror image of the first half. Description of some preferred embodiments

Referring to Figs. 2A and 2B, the wheel rim according to the invention has been denoted in the whole with reference numeral 111. Rim 111 includes a central region for fixing the rim to one of the hubs of the vehicle the rim is associated with. Said central region is not shown since it can be made according to techniques known to the skilled in the art. Rim 111 further includes a peripheral region 109 in which an annular channel 113 for a tyre arranged to be associated with rim 111 is defined. Channel 113 circumferentially extends around the central region of rim 111.

Channel 113 is delimited by outer circumferential edges 115 radially extending relative to the central region of rim 111. Edges 115 are arranged to prevent the tyre from slipping out of rim 111. Annular channel 113 has a profile or cross-sectional shape with variable depth. According to the invention, a peripheral portion 117, arranged to receive the tyre bead when the tyre is mounted in a working configuration on rim 111, and a central portion 121 are defined in channel 113 from the periphery of the channel, i.e. from outer edges 115, to the centre of channel 113 and parallel to rotation axis "S" of the rim. The peripheral portion and the central portion define corresponding cylindrical surfaces substantially parallel to rotation axis "S" of the rim. Further, channel 113 has a greater depth in correspondence of central portion 121 than in correspondence of peripheral portion 117. Consequently, the distance from axis "S" of the cylindrical surface defined by peripheral portion 117 will be greater than the distance from axis "S" of the cylindrical surface defined by central portion 121. Advantageously, according to the invention, a conical connecting portion 137 is provided between peripheral portion 117 and central portion 121. Connecting portion 137 defines a corresponding inclined conical annular surface 139, so that channel 113 has a depth linearly increasing from peripheral portion 117 to central portion 121. Connecting portion 137 is moreover connected to central portion 121 and peripheral portion 117.

Referring to the preferred embodiment depicted in Figs. 2A and 2B, conical connecting portion 137 is inclined by an angle a of about 60° relative to plane "P" perpendicular to the rim rotation axis. According to the invention, said angle a preferably ranges from 40° to 80°.

According to this embodiment of the invention, peripheral and central portions 117 and 121 define corresponding cylindrical surfaces parallel to rotation axis "S" of the rim and form angles β, γ ranging from 20° to 60° and, more preferably, angles of 30°, with connecting surface 139 defined by connecting portion 137.

Advantageously, thanks to the provision of such an inclined conical connecting portion 137, the smooth and gradual passage of the tyre beads from the configuration in which they rest on central portion 121 of the rim to the configuration in which they rest on the peripheral portion 117 is determined when the tyre is inflated. Moreover, advantageously, the pressure required to cause the proper accommodation of the tyre beads on peripheral portions 117 is lower than that required in case of the prior art rims, with a consequent reduction in the risk that the tyre bursts.

According to the invention, inclined connecting portion 137 is unique, that is it extends without interruptions and with a constant slope between peripheral portion 117 and central portion 121.

In the embodiment illustrated, peripheral and central portions 117 and 121 are parallel to rotation axis "S" of rim 111.

According to the invention, conical connecting portion 137 can be formed either ex novo, i.e. when making a new wheel rim 111, or even on an existing conventional wheel rim. In the latter case, the rim is submitted to an operation of mechanical deformation of the region of the profile of channel 113. In the alternative, in order to achieve the desired profile, it is also possible to apply an additional element or insert, made of metal or another material, such as plastics or silicone, on a conventional rim, for instance a rim made in accordance with one of the prior art embodiments shown in Fig. 1. Such an additional element, distinct from the rim, can be secured, preferably in permanent manner, to the body of the wheel rim, for instance by soldering, gluing, riveting or other known means.

In this respect, referring to Fig. 3, a wheel rim 111' is shown, including a connecting region 143 of the profile of channel 113' located between portions 117, 121 at different depths, at the periphery and the centre of the channel, respectively. As it can be appreciated from the Figure, connecting region 143 forms accentuated angles, close to 90°, with the planes of the corresponding adjoining portions 117, 121 at different depths. In accordance with this embodiment of the invention, an element 151 is applied on wheel rim 111' in correspondence of connecting region 143. Said element 151 can be preferably made of plastics or silicone and, as it can be appreciated from the Figure, once it has been applied on connecting region 143, it forms a corresponding conical connecting portion 137 defining a corresponding conical annular connecting surface 139, so that the depth of channel 113' linearly increases from peripheral portion 117 to central portion 121.

Advantageously, according to the invention, element 151 has a substantially triangular or trapezoidal cross-sectional shape, and it is preferably made of a deformable material, e.g. silicone or plastics, so that it can fit the profile of connecting region 143. Element 151 can be made as a continuous ribbon whose length is substantially the same as that of the circumference of rim 111' in correspondence of connecting region 143. In a variant of this embodiment, element 151 can be made by a plurality of arc-shaped sections, having e.g. an extension ranging from 10° to 15°, and in this case conical connecting portion 137 is thus obtained by applying a plurality of sections 151a... l51i... 151n on rim 111' in correspondence of connecting region 143. In this variant, sections 151a...15 li... 151n may be applied so as to be adjacent to each other, without interruptions, or by leaving gaps lacking element 151 and having such an angular extension that they do not affect the attainment of the advantageous results of the invention, for instance an extension ranging from 1 to 5°.

The wheel rim as described can undergo several changes and modifications, falling within the same inventive principle.