Vehicle tyre

Abstract: A tyre for a vehicle having at least one wheel at each corner, the tyre comprising a ground contacting tread (1) extending axially between first and second edge regions (IE,OE) and having tread grooves (2,10,11) formed therein, characterised in that in the first axial edge region (IE) of the tread the tread grooves are aligned substantially in the tyre circumferential direction and in the second axial edge region (OE) of the tread the grooves are aligned substantially in the tyre axial direction and in a third axial region (CR) of the tread axially between the first (IE) and second edge (OE) regions the alignment of the grooves changes progressively from circumferential to axial.

Description: This invention relates to tyres for vehicles which generally have at least one wheel at each corner such as passenger cars, vans, trucks or buses. In common with most other types of tyres, in order for this tyre to perform well under all conditions it is usual for the ground contacting tread region of the tyre to be provided with relatively deep grooves in the surface. In wet conditions such grooves assist in clearing water from the contact area between the tyre tread and the road surface and thus help to retain steering control of the vehicle by preventing aquaplaning. In other conditions such as snow and ice or in off-road applications such grooves provide edges which assist in the transmission of traction forces. However the provision of such grooves effectively weakens the tyre tread and renders it more prone to wear. This occurs because such grooves divide the tread into discrete elements such as ribs and blocks which individually are more susceptible to deformation and movement in the tyre/ground contact region due to the tractive forces transmitted therein resulting in abrasion of the rubber against the road surface. DE-A-3 726 593 shows a tyre which comprises the features of the preamble of claim 1. In making the present invention, the inventors studied the alignment of the grooves in the tread of such tyres and determined that it was possible to arrange these so as to minimise wear of the tread rubber. Accordingly it is an object of the present invention to provide a tyre for a four wheeled vehicle which is improved in tread wear. According to one aspect of the present invention a tyre for a vehicle having at least one wheel at each corner comprises a ground contacting tread extending axially between first and second edge regions and having tread grooves formed therein, wherein in the first axial edge region of the tread the tread grooves are aligned substantially in the tyre circumferential direction, characterised in that in the second axial edge region of the tread the grooves are aligned substantially in the tyre axial direction and in a third axial region of the tread axially between the first and second edge regions the alignment of the grooves changes progressively from circumferential to axial. According to another aspect the invention provides a method of determining the required tread groove angle to form the tread pattern of a tyre for a four-wheeled vehicle to give optimum tread wear comprising at successive axial points across the tread from the centre to the tread edge aligning the tread groove in the direction of the resultant force acting on the tread at that axial point when the point is in the tyre/road contact region. Further aspects of the invention will become apparent from the following description by way of example only of embodiments of the invention in conjunction with the following drawings in which:- Figure 1 shows a schematic view of a tyre in accordance with the invention; Figure 2 shows a schematic plan view of the tyre of Figure 1 mounted on a vehicle in accordance with another aspect of the invention; Figure 3 shows a schematic plan view of another tyre of the invention mounted on a vehicle; Figure 4 is a schematic diagram showing discontinuous tread grooves in accordance with the invention; and Figure 5 is a schematic diagram showing another pattern of discontinuous tread grooves according to the invention. Figure 1 shows a front view of a tyre according to a first embodiment of the invention comprising a tyre tread 1 having tread grooves 2 formed therein. The tread grooves 2 extend axially across the entire width of the tread between axial edge regions OE and IE through the central tread region CR. In the outer axial edge region OE of the tread the alignment of the grooves is substantially axial whereas in the inner axial edge region IE the grooves are aligned substantially in the tyre circumferential direction. In the central region CR of the tyre between the outer and inner edge regions OE and IE respectively the alignment of the tread grooves 2 changes progressively from axial to circumferential as shown. Thus to summarise the alignment of grooves according to the invention, the angle  of the groove to the circumferential direction of the tyre at any axial point or position P displaced by distance d from the tyre inner edge IE increases with increasing d wherein 0°≤≤90° and 0≤d≤ tread width TW. Thus in accordance with the present invention the tyre is provided with tread grooves 2 having the configuration shown in Figure 1. For the purposes of providing a generally optimised groove alignment such as depicted in Figure 1, the inventors have found that a cosecant curve gives a configuration which reduces tread groove wear. The cosecant curve is implemented on the tyre tread as y= cosecant (x) wherein y is the circumferential tyre direction and x is the axial direction. According to another aspect the invention provides the tyre mounted on a vehicle. As shown in the schematic diagram of Figure 2, the tyre of Figure 1 is mounted on the vehicle so that the tyre inner edge region IE is closest to the vehicle longitudinal centreline represented by VCL. Thus it can be seen from Figure 2 that in order to derive the optimum improved tread groove wear from the tyre of Figure 1, it is intended that the present tyres be fitted as orientated pairs to the steerable front axle FA and the rear axle RA. The specific orientation shown in Figure 2 wherein the front tyre pair is orientated oppositely to the rear tyre pair would be particularly suited to a rear wheel driven vehicle in which due to load transfer characteristics the acceleration forces act predominantly through the rear wheels whilst the braking forces act predominantly through the front wheels. In the case of other types of vehicle or where such directional tyre fitment is undesirable, an alternative embodiment of the present invention shown in Figure 3 may be employed. As can be seen in Figure 3 the tyre 3 has two patterns of tread grooves, one pattern of grooves 4 and another pattern of grooves 5 which curve in opposite circumferential direction as they progress axially inwardly. Whilst only the pattern of grooves 4 will have the optimum alignment for braking and the pattern of grooves 5 will have the optimum alignment for acceleration, overall the combination of grooves shown retain to a large degree the beneficial reduced tread wear attributable to the invention. Whilst the aforementioned tread grooves as shown and described as continuous across the axial width of the tread they may be discontinuous in which event each groove section be it straight or curved is aligned according to the invention. Example of discontinuous groove patterns are shown in the schematic diagrams Figure 4 and Figure 5. Thus these discontinuous patterns comprise individual groove sections 10a-10f and 11a-11f respectively. The tread may also comprise longitudinal tread grooves. The invention also provides a method of determining the required tread groove angle or alignment to form the tread pattern having optimum, i.e. minimum, tread wear. This method comprises at successive axial points across the tread from one edge to the other edge aligning the tread groove in the same direction as the resultant typical slippage of the tread when the axial point concerned is within or at the centre of the tread/road contact region. Thus in accordance with the invention whilst there may be determined a groove alignment pattern which can reduce tread wear for each class or type of tyre the optimum alignment pattern giving the maximum benefit will vary dependent on the manner of use of the tyre, i.e. the type of driving of the vehicle, which ultimately determines the degree and direction of tread slippage. This method may be implemented either by calculation or by practical determination. For the method by calculation it has been found expedient to determine the direction of the resultant force acting on the tread at a particular axial point in the contact region and aligning the groove substantially in the same direction. In the practical implementation of the method the tyre, preferably an unused tyre, is provided with an array of small holes, preferably circular in shape at the tyre surface, to provide a hole at each axial position across the tread surface. The tyre is then run on the vehicle under all driving conditions to initiate wearing of the tread over its entire width. The tread wear will become apparent with the appearance of a pattern of wear emanating in a particular direction from each small hole according to the axial position of the hole. Subsequently the tread groove pattern can be formed or cut into the tread of another tyre by aligning the tread groove at any particular axial position in the same direction as the wear pattern emanating from the hole at that position on the worn tyre. Whilst the above-described embodiments have a substantially continuous tread surface between circumferentially adjacent tread grooves of the invention other embodiments may have other tread grooves or sipes as common in the art. Also whilst the above-described embodiments have the groove angles or alignments at the inner edge IE and outer edge OE at 0° and 90° respectively to the tyre circumferential direction other angles such as 10° and 80° respectively can be used which will retain to a large degree the advantage of reduced tread wear according to the invention.

Claims: A tyre for a vehicle having at least one wheel at each corner, the tyre comprising a ground contacting tread (1) extending axially between first and second edge regions (IE,OE) and having tread grooves (2,10,11) formed therein, wherein in the first axial edge region (IE) of the tread the tread grooves are aligned substantially in the tyre circumferential direction, characterised in that in the second axial edge region (OE) of the tread the grooves are aligned substantially in the tyre axial direction and in a third axial region (CR) of the tread axially between the first (IE) and second edge (OE) regions the alignment of the grooves changes progressively from circumferential to axial. A tyre according to claim 1, characterised in that the grooves (2) extend continuously from the first axial edge region (IE) to the second axial edge region (OE). A tyre according to claim 1 or claim 2, characterised in that the first axial edge region (IE) of the tyre is disposed nearest to the vehicle longitudinal centreline (VCL). A method of determining the required tread groove angle to form the tread pattern of a tyre for a vehicle having a wheel at each corner to give optimum tread wear comprising at successive axial points across the tread from the centre to the tread edge aligning the tread groove substantially in the direction of the resultant force acting on the tread at that axial point when the point is in the tyre/road contact region. A method in accordance with claim 4, comprising forming small holes in the tread surface at successive axial positions across the tread from the centre to the edge, running the tyre on the vehicle to initiate a pattern of wear emanating from each small hole, and forming tread grooves in the surface of a subsequent tyre such that at any particular axial point the tread groove is aligned in the same direction as the pattern of wear emanating from the small hole formed at that point on the worn tyre. A method according to claim 5, wherein the small holes are circular in shape at the tyre surface.

Inventors: JACKSON MICHAEL, STEPHENS PAUL, WATKINS DAVID ROBERT, JACKSON, MICHAEL, STEPHENS, PAUL, WATKINS, DAVID ROBERT
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1998
Main classification: B60C11
IPC codes: B60C11, B60C19, B60C5