GB1591076A

GB1591076A - Pneumatic tyre cover

Info

Publication number: GB1591076A
Application number: GB1358678A
Authority: GB
Original assignee: Sirio SpA
Current assignee: Sirio SpA
Priority date: 1977-04-07
Filing date: 1978-04-06
Publication date: 1981-06-10
Also published as: ATA245078A; AT360351B; DE2813954A1; FR2386422A1; IT1074850B

Description

(54) PNEUMATIC TYRE COVER (71) We, SIRIO S.P.A., an Italian joint stock company, of Via Andrea da Isernia, 20, Napoli, Italy, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to tyre covers without internal reinforcement, suitable for vehicles of any kind.

As is known, conventional tyre covers containing internal reinforcement elements require difficult and complicated manufacturing processes. Consequently in recent years much study and research has been devoted to tyres having injection-moulded or cast bodies without internal reinforcement, produced from polyurethane elastomers, which have exceptional mechanical strength.

Such tyres are much less expensive than conventional tyres and the method and apparatus for producing them is simplified, with a consequent reduction in capital investment.

Tyres without reinforcement elements have a high degree of uniformity and they are therefore potentially better able than conventional tyres to ensure uniform running of a vehicle on which they are fitted.

This desirable result has not, however, hitherto been achieved, due to various problems which have remained unresolved. Among these problems are overheating of the tyres, leading to expansion of the tyres under working conditions, unsatisfactory watertightness, especially on wet terrain, and finally poor running stability of the vehicle.

An object of the present invention is to overcome these disadvantages, or at least significantly to reduce their effect.

The material of the tread of the tyre cover of this invention is different from that of the tyre body, and the body has a special form.

According to one aspect of the present invention there is provided a tyre cover comprising a body and a tread carried by the body, the body having beads with internal bead wires which are adapted to fit a wheel rim, wherein: (i) the tread is deprived of any reinforcement and is made of an elastomeric material with a base of isoprene rubber and/or butadiene-styrene rubber which, after vulcanisation, has properties of hysteresis and hardness inferior to that of the material which constitutes the tyre body; (ii) the tyre body is made of an e]astomeric material with a base of polyurethane, the bead wires being the sole internal reinforcements; (iii) the tyre body has ratio H/C between 0.40 and 0.50, where H is the maximum cross-sectional height of the body measured from the bead edge, and C is the maximum transverse width of said tyre body when fitted to a wheel rim and inflated; and (iv) the tyre body when fitted to a wheel rim and inflated has a cross-sectional profile which is semi-circular along the medial line of mean thickness, said body being adapted to fit a wheel rim of width L, the value of which is at least equal to 2H so that the maximum transverse width C of the tyre is located at the same level as the bead wires and the ratio L/C has a value of 1.

In accordance with another aspect of the present invention there is provided a tyre cover comprising a body and a tread carried by the body, the body having beads with internal bead wires which are adapted to fit a wheel rim, wherein: (i) the tread is made of an elastomeric material with a base of isoprene rubber and/or butadiene-styrene rubber which after vulcanisation, has properties of hysteresis and hardness inferior to that of the material which constitutes the tyre body; (ii) the tyre body is made of an elastomeric material with a base of polyurethane, the bead wires being the sole internal reinforcements; (iii) the tyre body has ratio H/C between 0.35 and 0.60, where H is the maximum cross-sectional height of the body measured from the bead edge, and C is the maximum transverse width of said tyre bcdy when fitted to a wheel rim and inflated; and (iv) the cross-sectional profile of the tyre body when fitted to a wheel rim and inflated is such that its maximum width C is located in an intermediate position between the line joining the bead wires and the outermost radial point and the said body when fitted to a wheel rim of width L has a ratio L/C which is less than 1.

According to a further aspect of the invention there is provided a tyre cover comprising a body and a tread carried by the body, the body having beads with internal bead wires which are adapted to fit a wheel rim, wherein: (i) the tread is made of an elastomeric material with a base of isoprene rubber and/or butadiene-styrene rubber which, after vulcanisation, has properties of hysteresis and hardness inferior to that of the material which constitutes the tyre body; (ii) the tyre body is made of an elastomeric material with a base of polyurethane, the bead wires being the sole internal reinforcements; (iii) the tyre body has ratio H/C between 0.35 and 0.60, where H is the maximum cross-sectional height of the body measured from the bead edge, and C is the maximum transverse width of said tyre body when fitted to a wheel rim and inflated; and (iv) the body after moulding has a cross sectional profile, with an outwardly concave peripheral part adapted to receive the tread, the centre of said concave part coinciding with the plane of symmetry of the said tyre body.

According to the invention there is also provided a method for the production of a vehicle tyre comprising a tyre thread of an elastomeric material with a base of isoprene rubber and/or butadiene-styrene rubber and a tyre body of elastomeric material with a base of polyurethane, with bead wires as the sole internal reinforcement, wherein the tyre body is first moulded and the tread is manufactured separately and vulcanised, and then adhered firmly to the body by means of suitable adhesives which are then vulcanised. The tread may be deposited, injected or moulded onto the preformed body and then vulcanised.

A tread formed from conventional elastomer, as in the tyre of this invention, has high resistance to wear and makes possible good road holding on both dry and wet surfaces.

The tyre body may be made, with the help of suitable moulds, by means of injection moulding or casting methods.

The appearance of the tyre body is greatly flattened and the best results are obtained with H/C ratio values, as defined above, between 0.40 and 0.50.

There are two preferred characteristic forms for the cross-sectional profile of the tyre body.

According to one embodiment, called for simplicity "T form", the body is fitted to a wheel rim of width L, such that the ratio L/C has a value less than 1, and preferably between 0.70 and 0.95. In this embodiment the "chord" C, that is, the maximum transverse width of the body when fitted to the rim and inflated, is located an intermediate height between that of the line adjoining the centres of the bead wires and the radially outermost point of the tyre body.

In manufacturing tyres of the "T form" the shape of the mould used may be such as to confer on the peripheral part of the tyre body which receives the tread an outwardfacing concavity the centre of which coincides with the plane of symmetry of the tyre body.

In other words, the peripheral part of the tyre body has an outer diameter in its centre less than the diameters of the two adjacent symmetrical lateral areas or shoulders of the peripheral part.

It should be pointed out that the concavity of the "T form" tyre body is transformed into an outward convexity when the body is fitted to a wheel rim and inflated.

This shaping of the moulded tyre body affords unexpectedly useful results, and counteracts the tendency for the tyre cover to adopt a cross sectional profile which is excessively convex outwards when inflated.

This in turn prevents the tread, which is eventually superimposed on the tyre body, from assuming an excessive curvature.

The "T form" tyre can be fitted to con ventional wheel rims.

According to another embodiment & f the invention, called for simplicity "S form" the tyre cover is adapted to be fitted to a wheel rim which is wider than usual, having a width L equal to or greater than 2tri. In this embodiment the ratio L/C is equal to 1, since the maximum width C practically coincides with the line joining the centres of the bead wires, and the medial line of mean thickness of the cross section cf the tyre body has an arcuate or even semi-circular profile.

The "S form" tyre has considerably improved transverse stability, wheel rims of a special construction being needed to lock the tyre beads.

The invention will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which: Figure 1 shows in cross section a tyre cover according to a first embodiment of the invention; Figure 2 is a cross section of a tyre cover according to a second embodiment of the invention, both the first and second embodiments being shown fitted to a wheel rim and inflated; Figure 3 is a cross section of the body of the tyre cover illustrated in Figure 1, without its tread, and uninflated before being fitted to a wheel rim, and Figure 4 is a cross section of the body of the tyre cover illustrated in Figure 2, without its tread, in an uninflated condition before being fitted to a wheel rim.

Figures 1 and 2 each show a tyre cover having a tread 1 of a conventional type made of a rubber mixture adhered to a body 2 of polyurethane. The body 2 has beads, reinforced by bead wires 3, fitted to a wheel rim 4.

The tread 1 is made from an elastomeric material with a base of isoprene rubber and/or butadiene-styrol rubber which after vulcanisation has hardness and hysteresis properties inferior to the material of the body 2.

In both Figures 1 and 2 the letters shown have the following significance: H is the maximum cross-sectional height of the tyre body 2 without the tread 1; C the maximum transverse width of the tyre tread 1, also known as the "chord"; B-B' is a line joining the centres of the two bead wires 3; A-A' is a line passing through the bearing surfaces of the beads on the wheel rim 4; X-X' is the plane of symmetry of the tyre; K is the summit point of the tyre body.

In the embodiment of Figure 1, having a so-called "T form", the indicated dimensions are as follows: H = 60 mm, C = 134 mm, H/C = 0.447, L = 114 mm, L/C = 0.85. In this embodiment the maximum width C of the tyre body is situated at a level substantially equal to half the crosssectional height H.

In the embodiment of Figure 2, having a so-called "S form", the indicated dimensions are as follows: H = 70 mm, C = 172 mm, H/C = 0.407, L = 152 mm. In this embodiment the maximum width C of the tyre body is situated at the height of the line B-B' joining the centres of the bead wires 3. The ratio L/H is in this case greater than 2.

In Figure 2 the curve traced in dashes is the medial line of the cross sectional profile of the tyre body, this line being substantially semi-circular.

Figure 3 shows the cross-sectional profile of the body of the "T:form" tyre of Figure 1, without its tread, and in an uninflated condition, as it appears after manufacture, for example in a moulding process.

It will be seen that the tyre cross-section has an outwardly concave central portion the centre of which, K, is situated nearer the axis of rotation of the tyre than the peripheral parts of the tread-bearing regions or shoulders of the tyre body. It will also be noted that the thickness of the tyre body has a minimum value S at the height of the chord CS corresponding to the maximum width of the tyre and a maximum value S' on the centreline in correspondence with the point K. Thus where the tyre body of Figure 3 is intersected by the plane of symmetry X-X' it has a thickness greater than that of other parts of the body, except, of course, for the beads of the tyre.

This lack of uniformity in thickness is established both by calculation and through practical experience based on the characteristics of the selected material for the tyre body, with the object of endowing the inflated tyre with the desired profile.

Figure 4 shows the cross-sectional profile of the "S form" tyre body of Figure 2,.

shown without its tread and uninflated, as it appears after manufacture by moulding or some other chosen method.

In this case the profile of the uninflated tyre does not differ substantially from that of the tyre when inflated, except for the proportionally smaller dimensions of the uninflated tyre. The differences between the dimensions of the inflated and the uninflated tyre are equal to the amount of dilation undergone by the material of the tyre body due to the tensions which result when the tyre is inflated. Thus the maximum width CS and maximum cross section height HS of the uninflated tyre will be less than the corresponding dimensions C and S of the inflated tyre body shown in Figure 2. Similarly, the outside width MM' and the inside width NN' of the uninflated tyre body in Figure 4 are less than the corresponding dimensions C and S of the inflated tyre body shown in Figure 2. Similarly, the outside width MM' and the inside width NN' of the uninflated tyre body in Figure 4 are less than the corresponding dimensions of the inflated tyre shown in Figure 2.

A similar comparison can be made between the uninflated tyre body of Figure 3 and the corresponding inflated tyre body in Figure 1, bearing in mind the different profiles imposed during production for the purpose of endowing the tyre body with the desired profile.

WHAT WE CLAIM ZS:- 1. A tyre cover comprising a body and a tread carried by the body, the body having beads with internal bead wires which are adapted to fit a wheel rim, wherein: (i) the tread is deprived of any reinforcement and is made of an elastomeric material with a base of isoprene rubber and/or butadiene-styrene rubber which, after vulcanisation, has properties of hysteresis and hardness inferior to that of the material which constitutes the tyre body; (ii) the tyre body is made of an elastomeric material with a base of polyurethane, the bead wires being the sole internal reinforcements; (iii) the tyre body has ratio H/C between 0.40 and 0.50, where H is the maximum cross-sectional height of the body measured

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the tyre cover illustrated in Figure 2, without its tread, in an uninflated condition before being fitted to a wheel rim. Figures 1 and 2 each show a tyre cover having a tread 1 of a conventional type made of a rubber mixture adhered to a body 2 of polyurethane. The body 2 has beads, reinforced by bead wires 3, fitted to a wheel rim 4. The tread 1 is made from an elastomeric material with a base of isoprene rubber and/or butadiene-styrol rubber which after vulcanisation has hardness and hysteresis properties inferior to the material of the body 2. In both Figures 1 and 2 the letters shown have the following significance: H is the maximum cross-sectional height of the tyre body 2 without the tread 1; C the maximum transverse width of the tyre tread 1, also known as the "chord"; B-B' is a line joining the centres of the two bead wires 3; A-A' is a line passing through the bearing surfaces of the beads on the wheel rim 4; X-X' is the plane of symmetry of the tyre; K is the summit point of the tyre body. In the embodiment of Figure 1, having a so-called "T form", the indicated dimensions are as follows: H = 60 mm, C = 134 mm, H/C = 0.447, L = 114 mm, L/C = 0.85. In this embodiment the maximum width C of the tyre body is situated at a level substantially equal to half the crosssectional height H. In the embodiment of Figure 2, having a so-called "S form", the indicated dimensions are as follows: H = 70 mm, C = 172 mm, H/C = 0.407, L = 152 mm. In this embodiment the maximum width C of the tyre body is situated at the height of the line B-B' joining the centres of the bead wires 3. The ratio L/H is in this case greater than 2. In Figure 2 the curve traced in dashes is the medial line of the cross sectional profile of the tyre body, this line being substantially semi-circular. Figure 3 shows the cross-sectional profile of the body of the "T:form" tyre of Figure 1, without its tread, and in an uninflated condition, as it appears after manufacture, for example in a moulding process. It will be seen that the tyre cross-section has an outwardly concave central portion the centre of which, K, is situated nearer the axis of rotation of the tyre than the peripheral parts of the tread-bearing regions or shoulders of the tyre body. It will also be noted that the thickness of the tyre body has a minimum value S at the height of the chord CS corresponding to the maximum width of the tyre and a maximum value S' on the centreline in correspondence with the point K. Thus where the tyre body of Figure 3 is intersected by the plane of symmetry X-X' it has a thickness greater than that of other parts of the body, except, of course, for the beads of the tyre. This lack of uniformity in thickness is established both by calculation and through practical experience based on the characteristics of the selected material for the tyre body, with the object of endowing the inflated tyre with the desired profile. Figure 4 shows the cross-sectional profile of the "S form" tyre body of Figure 2,. shown without its tread and uninflated, as it appears after manufacture by moulding or some other chosen method. In this case the profile of the uninflated tyre does not differ substantially from that of the tyre when inflated, except for the proportionally smaller dimensions of the uninflated tyre. The differences between the dimensions of the inflated and the uninflated tyre are equal to the amount of dilation undergone by the material of the tyre body due to the tensions which result when the tyre is inflated. Thus the maximum width CS and maximum cross section height HS of the uninflated tyre will be less than the corresponding dimensions C and S of the inflated tyre body shown in Figure 2. Similarly, the outside width MM' and the inside width NN' of the uninflated tyre body in Figure 4 are less than the corresponding dimensions C and S of the inflated tyre body shown in Figure 2. Similarly, the outside width MM' and the inside width NN' of the uninflated tyre body in Figure 4 are less than the corresponding dimensions of the inflated tyre shown in Figure 2. A similar comparison can be made between the uninflated tyre body of Figure 3 and the corresponding inflated tyre body in Figure 1, bearing in mind the different profiles imposed during production for the purpose of endowing the tyre body with the desired profile. WHAT WE CLAIM ZS:-

1. A tyre cover comprising a body and a tread carried by the body, the body having beads with internal bead wires which are adapted to fit a wheel rim, wherein: (i) the tread is deprived of any reinforcement and is made of an elastomeric material with a base of isoprene rubber and/or butadiene-styrene rubber which, after vulcanisation, has properties of hysteresis and hardness inferior to that of the material which constitutes the tyre body; (ii) the tyre body is made of an elastomeric material with a base of polyurethane, the bead wires being the sole internal reinforcements; (iii) the tyre body has ratio H/C between 0.40 and 0.50, where H is the maximum cross-sectional height of the body measured

from the bead edge, and C is the maximum transverse width of said tyre body when fitted to a wheel rim and inflated; and (iv) the tyre body when fitted to a wheel rim and inflated has a cross-sectional profile which is semi-circular along the medial line of mean thickness, said body being adapted to fit a wheel rim of width L, the value of which is at least equal to 2H so that the maximum transverse width C of the tyre is located at the same level as the bead wires and the ratio L/C has a value of 1.

2. A tyre cover comprising a body and a tread carried by the body, the body having beads with internal bead wires which are adapted to fit a wheel rim, wherein: (i) the tread is made of an elastomeric material with a base of isoprene rubber and/or butadiene-styrene rubber which, after vulcanisation, has properties of hysteresis and hardness inferior to that of the material which constitutes the tyre body; (ii) the tyre body is made of an elastomeric material with a base of polyurethane, the bead wires being the sole internal reinforcements; (iii) the tyre body has ratio H/C between 0.35 and 0.60, where H is the maximum cross-sectional height of the body measured from the bead edge, and C is the maximum transverse width of said tyre body when fitted to a wheel rim and inflated; and (iv) the cross-sectional profile of the tyre body when fitted to a wheel rim and inflated is such that its maximum width C is located in an intermediate position between the line joining the bead wires and the outermost radial point and the said body when fitted to a wheel rim of width L has a ratio L/C which is less than 1.

3. A tyre cover as claimed in claim 2, in which said ratio H/C has a value between 0.40 and 0.50.

4. A tyre cover as claimed in claim 2 or 3, in which the ratio L/C is between 0.70 and 0.95.

5. A tyre cover as claimed in claim 2, 3 or 4, wherein the body after moulding has a cross-sectional profile, excluding the tread, with an outwardly concave peripheral part adapted to receive the tread, the centre of said concave part coinciding with the plane of symmetry of the said tyre body.

6. A tyre cover comprising a body and a tread carried by the body, the body having beads with internal bead wires which are adapted to fit a wheel rim, wherein: (i) the tread is made of an elastomeric material with a base of isoprene rubber and/or butadiene-styrene rubber which, after vulcanisation, has properties of hysteresis and hardness inferior to that of the material which constitutes the tyre body; (ii) the tyre body is made of an elastomeric material with a base of polyurethane, the bead wires being the sole internal reinforcements; (iii) the tyre body has ratio H/C between 0.35 and 0.60 where H is the maximum cross-sectional height of the body measured from the bead edge, and C is the maximum transverse width of said tyre body when fitted to a wheel rim and inflated; and (iv) the body after moulding has a crosssectional profile, with an outwardly concave peripheral part adapted to receive the tread, the centre of said concave part coinciding with the plane of symmetry of the said tyre body.

7. A tyre as claimed in claim 5 or 6, wherein the body has, in its region intersected by the plane of symmetry of the tyre body, a thickness which is exceeded only at the beads of the tyre.

8. A method for the production of a vehicle tyre comprising a tyre tread of an elastomeric material with a base of isoprene rubber and/or butadiene-styrene rubber and a tyre body of elastomeric material with a base of polyurethane, with bead wires as the sole internal reinforcement, wherein the tyre body is first moulded and the tread is manufactured separately and vulcanised, and then adhered firmly to the body by means of suitable adhesives which are then vulcanised.

9. A method as claimed in claim 8, wherein the tread is deposited upon the preformed tyre body and then vulcanised.

10. A tyre cover substantially as herein described with reference to and as shown in Figures 1 and 3 or Figures 2 and 4 of the accompanying drawings.