Pneumatic tyre

Abstract: A radial tyre having bread regions comprising bead clinch and bead seat has between two and ten circumferentially extending ribs projecting outward of the bead outer surface. The tyre has improved uniformity when mounted on the wheelrim.

Description: This invention relates to a pneumatic tyre of the type having a radial construction. Advances in the design of vehicle suspensions have produced improvements in vehicle ride comfort which necessitate ever better uniformity in the tyres, particularly in relation to Radial Run-Out (RRO), Lateral Run Out (LRO) and Radial Force Variation (RFV) of the tyre. The reasons for these uniformity variations in tyres are complex but result basically from the tyre construction and fabrication methods. Most tyre components are made in long continuous lengths in which cross-sectional variations may be minimised, however in the tyre building process these are cut into discrete lengths and jointed to form the uncured toroidal tyre carcass. Such joints may be overlap joints or butt joints. Fabric reinforced components are normally overlapped at the joint whereas steel reinforced components are usually butted. Non-reinforced rubber components such as the tread, sidewall and clinch components are usually butted with an overlapping scarf joint. Thus component joints may have an excess of material or in the case of rubber components a scarcity of material dependent on the tolerance of the cut length. Studies by the inventors have shown that the seating pressure between the tyre and wheelrim is directly related to tyre non-uniformity manifest as variations in radial and lateral forces such as may be produced by joints in major component such as tread or breaker ply strips. Additionally component joints in the bead regions themselves may cause variation in the proper seating of the bead on the wheelrim to the further detriment of uniformity. A tyre having ridges on the bead base, in accordance with the preamble of claim 1, to improve resistance to coming off the wheelrim is known for example from JP-A-07069010. Accordingly it is an object of the present invention to provide a tyre having improved uniformity when mounted on a wheelrim. According to the present invention a radial tyre comprising a tyre carcass comprising a strip of circumferentially extending material jointed at the ends and comprising reinforcing cords extending between two bead regions and enclosed therein by wrapping around a circumferentially extending inextensible bead core, the axially outer surface of each bead region comprising a bead seat radially inward of the bead core for seating onto the bead seat of a wheelrim terminating at a bead toe at the axial inward end of the bead seat, a bead clinch extending substantially radially outwardly and located axially outwardly of the bead core and bead heel extending between the radially inward end of the bead clinch and the axially outward end of the bead seat, the bead regions having a bead base width being the axial distance between the bead toe and a bead heel point, each bead region having between two and ten circumferentially extending ribs each projecting outward of the outer surface, characterised in that the rib surface lying between the base edges is one continuous surface having no edges and the rib surface in cross-section comprises an arc and a straight line meeting tangentially between base edges. Preferably the ribs are continuous around the circumference of the tyre bead. The ribs preferably project outward from the bead region outer surface by a distance which is not greater than 8%, or more preferably 3%, of the bead base width. Also preferably the ribs have a maximum width of between 5 arid 15%, or most preferably 10%, of the bead base width. The ribs may have their maximum width across the base and may have their maximum projecting distance at a single point on the rib surface lying nearest the edge of the rib nearest the bead toe. The tyre may have ribs on the bead base and may have ribs on the bead heel. Further aspects of the invention will become apparent from the following description, by way of example only, of one embodiment in conjunction with the following drawings in which: Figure 1 shows a schematic diagram of a cross-section of one half of a radial tyre for a passenger vehicle according to the invention; Figure 2 is a schematic diagram of the bead region of the tyre of Figure 1; Figure 3 is a schematic cross-sectional diagram of the bead region of the tyre of Figure 1 showing the constructions of the theoretical bead heel point; Figure 4 is a schematic cross-sectional diagram of a rib of the bead region of the tyre of Figures 1-3; Figure 5 is a schematic cross-sectional diagram of the bead region of a truck tyre; and Figure 6 is a cross-sectional diagram of a motorcycle tyre bead region. Figure 1 shows the construction of a 165R13 size passenger vehicle tyre according to the present invention. The tyre construction comprises a single reinforcing ply 1 extending through a tread region 3 to bead regions 2 wherein it is anchored by being turned up around an inextensible bead core 4 from the axially inside to the outside to form ply turn-ups 5. In each bead region 2 a tapering hard rubber apex 6 is disposed radially outward of the bead core 4 and between the ply 1 and the ply turn-up 5 to stiffen the bead region 2. On the axially outer side of the ply turn-up 5 is disposed a rubber clinch strip 7 to prevent chafing against the flange of the wheel rim. The ground contacting tread region 3 of the tyre has a patterned rubber tread 8 and a reinforcing breaker 9 disposed radially inward to the tread 8 and outward of the ply 1. On the inside of the tyre is an innerlining 10 comprising a rubber of high impermeability to air and moisture for the purpose of retaining the inflation air. Between the tread region 3 and the bead regions 2 the ply 1 passes through sidewall regions 11 and is protected by a sidewall rubber 12. With the exception of the bead core 4 all of the above-mentioned components of the tyre are normally prepared in continuous lengths, but to the required circumferential length and assembled in a particular order by wrapping around a former and bringing the two cut ends together to form a joint of one of the above-mentioned types. Figures 2 and 3 show detail of the bead region 2 of the tyre of Figure 1. Thus the outside of the bead region 2 comprises a double tapered bead seat BS, for seating on a wheelrim, lying radially inside the bead coil 4, a bead clinch BC lying axially outward of the bead coil and extending substantially radially outwardly and between the bead seat BS and bead clinch BC a curved bead heel BH. The double tapered bead sear BS comprises an axially outer first taper portion BS1 inclined at a relatively small angle ∝ 1 to the tyre axial direction and an axially inner second taper portion BS2 inclined at a larger angle ∝ 2 . The bead region has a bead base width (or J dimension) of 14mm being the axial distance between the bead toe BT at the axially inner end of the bead seat BS and the theoretical bead heel point BHP, which is a notional point on the designated diameter BD vertically below the vertical portion of the tyre bead clinch BC or vertically below the point of inflexion of the bead clinch BC. The bead region 2 has six ribs R1-R6 projecting from the outer surface of the bead and extending circumferentially around the entire circumference of the tyre. In this embodiment three ribs R1-R3 are provided on the bead heel BH and three ribs R4-R6 are provided on the bead seat BS. As shown in Figure 4 each rib has a maximum width RW measured along the bead surface between the axially outer and inner base edges OE and IE respectively of 1.4mm. The outer surface of the rib between the base edges OE and IE is a single surface without edges having a contour defined by a circular arc of radius 0.4mm and a straight line meeting tangentially. Accordingly the rib has a maximum projecting distance PD of 0.4mm at a single point MP which is nearest to the axially inner base IE, that is the distance MD of the point MP of the maximum projecting distance PD from the axially inner base edge IE is less than half of the rib width RW. In this embodiment the six ribs R1-R6 are equally spaced apart along the bead outer surface. In order to illustrate the invention a batch of twenty experimental tyres in accordance with the invention and a batch of twenty standard tyres for comparison were prepared. For this initially a batch of forty green tyre cases were assembled by the same operator using the same building machine and tyre components from the same batch. Twenty of these uncured cases were moulded in a 165R13 size mould in which the mould bead rings had been modified to have six grooves having position and shape complementary to the six ribs R1-R6 shown in Figure 2. The remaining twenty uncured cases were moulded consecutively in the same mould in which the modified bead rings had been replaced by standard bead rings having a single circumferentially continuous groove of 0.4mm radius and 0.3mm depth located in the bead heel region to provide conventional line venting of the tyre bead. The experimental and standard tyres were tested for uniformity by mounting the tyre on a 'true' wheelrim of a scheduled size having negligible run-out and inflating the tyre to its schedule pressure than measuring the properties of Lateral Force Variation (LFV), and Radial Run Out (RRO) of the unit. The results of these tests are given in Table 1 which shows the averages of twenty tyres. Thus Table 1 shows the composite value which is the peak to peak difference between the maximum and minimum value of the property being measured during one revolution of the tyre and the first harmonic value which is the peak to peak amplitude of the sine wave representing that measurement for one revolution of the tyre. The Lateral Force Variation (LFV) tests were performed in both forward and reverse rotation direction. Uniformity Test Experimental Tyre Standard Tyre Composite First Harmonic Composite First Harmonic LFV Forward 45.80 35.95 62.50 51.45 (N) Reverse 74.60 59.80 80.60 70.15 RFV Forward (N) 62.45 32.15 70.05 45.6 RRO (mm) 0.753 0.3 0.91 0.4 Accordingly it can be seen that in every test the experimental tyres recorded a lower value indicating better uniformity than the standard tyre. Overall the experimental tyres exhibited significant levels of 17%, 25% and 20% improvements in Lateral Force Variation (IFV), Radial Force Variation (RFV) and Radial Run Out (RRO) respectively. Shown in Figure 5 the outside of the bead region 2 of a truck tyre comprises a double tapered bead seat BS, for seating on a wheelrim, lying radially inside the bead coil 4, a bead clinch BC lying axially outward of the bead coil and extending substantially radially outwardly and between the bead seat BS and bead clinch BC a curved bead heel BH. The bead region 2 is provided with ten ribs R1-R10 projecting from the outer surface of the bead and extending circumferentially around the entire circumference of the tyre. In this embodiment three ribs R1-R3 are provided on the bead heel BH and seven ribs R4-R10 are provided on the bead seat BS. The shape, dimensions and positioning of these ribs R1-R10 are in accordance with the preferred dimensions set forth above. Figure 6 shows the bead of a motorcycle tyre having two such circumferentially extending ribs R21 and R22, provided one each in the bead heel and bead seat regions respectively. Tyres having the beads illustrated in Figures 5 and 6 have been extensively tested in comparison to similar conventional tyres and have shown improved levels of uniformity.

Claims: A radial tyre comprising a tyre carcass (1) comprising a strip of circumferentially extending material jointed at the ends and comprising reinforcing cords extending between two bead regions (2) and enclosed therein by wrapping around a circumferentially extending inextensible bead core (4), the axially outer surface of each bead region (2) comprising a bead seat (BS) radially inward of the bead core (4) for seating onto the bead seat of a wheelrim terminating at a bead toe (BT) at the axial inward end of the bead seat (BS), a bead clinch (BC) extending substantially radially outwardly and located axially outwardly of the bead core (4) and bead heel (BH) extending between the radially inward end of the bead clinch (BC) and the axially outward end of the bead seat (BS), the bead regions (2) having a bead base width (J) being the axial distance between the bead toe (BT) and a bead heel point (BHP), each bead region (2) having between two and ten circumferentially extending ribs (R1-R10) each projecting outward of the outer surface, characterised in that the rib surface lying between the base edges (OE,IE) is one continuous surface having no edges and the rib surface in cross-section consists of an arc and a straight line meeting tangentially between base edges (IE,OE). A tyre according to claim 1, characterised in that the ribs (R1,R10) extend continuously around the circumference of the tyre bead. A tyre according to either of claims 1 or 2, characterised in that the ribs (R1-R10) project outwardly from the bead region outer surface by a projecting distance (PD) which is not greater than 8% of the bead base width (J). A tyre according to claim 1 or 2, characterised in that the ribs (R1-R10) project outward from the bead region (2) outer surface by a projecting distance (PD) which is not greater than 3% of the bead base width (J). A tyre according to any of claims 1 to 4, characterised in that the ribs (R1-R10) have a maximum cross-sectional width (RW) which is in the range of 5-15% of the bead base width (J). A tyre according to any of claims 1 to 4, characterised in that the ribs (R1-R10) have a maximum cross-sectional width (RW) which is 10% of the bead base width (J). A tyre according to any of claims 1 to 6, characterised in that the maximum cross-sectional width (RW) of the ribs (R1-R10) is across the base of the rib where the rib contacts the outer surface of the bead region (2). A tyre according to any of claims 1 to 7, characterised in that the maximum projecting distance (PD) of the ribs (R1-R10) is located at a single point (MP) on the rib cross-section. A tyre according to claim 8, characterised in that the point (MP) of maximum projecting distance (PD) of each rib (R1-R10) lies nearer to the axially inner base edge (IE) than the axially outer base edge (OE). A tyre according to claim 1, characterised by six ribs (R1-R6). A tyre according to any of claims 1 to 9, characterised in that three ribs (R4-R6) are provided on the bead seat (BS). A tyre according to claim 11, characterised in that the ribs (R4-R6) are equally spaced apart on the bead seat (BS). A tyre according to any of claims 1 to 12, characterised in that the tyre has three ribs (R1-R3) provided on the bead heel (BH). A tyre according to claim 13, characterised in that the ribs (R1-R3) are equally spaced apart on the bead heel. A tyre according to any of claims 1 to 14, characterised in that the ribs (R1-R10) are equally spaced apart on the bead region.

Inventors: TURLEY JOHN ANTHONY, WILLIAMS ARTHUR ROGER, TURLEY, JOHN ANTHONY, WILLIAMS, ARTHUR ROGER
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1996
Main classification: B60C15
IPC codes: B60C15, B60C5