Pneumatic tyre and method of manufacturing the same

Abstract: A pneumatic tyre and a method of manufacturing the tyre are disclosed, wherein the tyre comprises a carcass ply (6) turned up around a bead core (5) in each bead portion (9), and a rubber bead filler disposed between the turnup portion (6B) and main portion (6A) of the carcass ply (6) and extending radially outwardly from the bead core (5) beyond the maximum section width point (K) of the tyre, the bead filler comprising a radially inner part (9) made of a bead apex rubber tapering radially outwardly from the bead core (5) and a radially outer part (10) made of a strip of hard rubber having a substantially constant thickness (T) and a JIS-A hardness of 75 to 95 degrees, the radially outer end (10b) of the bead apex rubber (9) being lower than the radially outer end of a flange of a standard rim.

Description: The present invention relates to a pneumatic tyre and a method of manufacturing the tyre, more particularly to an improvement concerning a bead filler being capable of improving the production efficiency without deteriorating the steering stability. In general, as shown in Fig.9, in order to reinforce the bead portions (a) and the lower sidewall portion of a pneumatic tyre, especially a radial tyre, a bead filler (d) made of a great mass of hard rubber is disposed between a turnup portion (b2) and main portion (b1) of the carcass (b). Such a tyre is usually manufactured by using a tyre building drum, and as shown in Fig.10 the thick bead filler (d) necessitates a moderate bending action onto the carcass (b) wound around the tyre building drum so as not to deform or crack the filler. Thus, it is difficult to increase production efficiency. EP-A-0 780 248 discloses a tyre according to the preamble of claim 1. Although this known tyre enables straight forward manufacture, while at the same time enhancing the steering capability and reducing the weight of the tyre as compared with known tyres of the same type, the production efficiency and the steering stability are still not optimal. It is an object of the present invention to provide a pneumatic tyre and a method of manufacture therefor in which, by employing a bead filler made up of two separate rubber materials connected at a certain height, the production efficiency can be improved without deteriorating the steering stability. This object is achieved by the features of claim 1. According to another aspect of the present invention, a method of manufacturing the pneumatic tyre comprises the steps of winding a carcass ply around a cylindrical surface of a tyre building drum so that the edges of the carcass ply protrude from the edges of the cylindrical surface, decreasing the diameter of the protruding portions of the wound carcass ply relatively to the main portion, setting an annular bead core around each of the protruding portions and a bead apex rubber on the radially outer side of the bead core, the bead apex rubber having a radially outer end place at substantially the same radial position of the edge of the cylindrical surface or radially inwards thereof, winding a strip of hard rubber around the main portion of the carcass ply so as to contact with the bead apex rubber, and turning up the protruding portions of the carcass ply around the bead cores. Embodiments of the present invention will now be described in detail in conjunction with the accompanying drawings, in which: Fig.1 is a cross sectional view of a tyre according to the present invention; Fig.2 is an enlarged cross sectional view of the bead portion thereof; Figs.3, 4 and 5 are cross sectional views showing modifications of the bead filler; Fig.6 is a cross sectional view of a test tyre; Figs.7(A) to (C) are schematic cross sectional views for explaining a method of manufacturing the tyre according to the present invention; Figs.8(A) to (C) are cross sectional views showing modifications of the bead filler; Fig.9 is a cross sectional view of a test tyre having a conventional bead filler; and Fig.10 is a schematic cross sectional for explaining a problem in making the tyre having the conventional bead filler. In the figures, a pneumatic tyre 1 according to the present invention is a radial tyre for passenger cars. The tyre 1 comprises a tread portion 2, a pair of sidewall portions 3, a pair of bead portions 4 each with a bead core 5 therein, a carcass 6 extending between the bead portions 4, and a belt 7 disposed radially outside the carcass 6 in the tread portion 2. The carcass 6 comprises at least one ply of cords arranged radially at an angle of 70 to 90 degrees with respect to the tyre equator C and extending between the bead portions 4 through the tread portion 2 and sidewall portions 3 and turned up around the bead cores 5 from the axially inside to outside of the tyre to form a pair of turnup portions 6B and a main portion 6A. For the carcass cords, organic fibre cords, e.g. polyester, nylon, aromatic polyamide and the like are suitably used. The carcass in this example is composed of a single ply of cords arranged at substantially 90 degrees with respect to the tyre equator C. The belt 7 comprises the usual two crossed breaker plies 7a and 7b of parallel cords laid at an angle of 10 to 30 degrees with respect to the tyre equator C. For the belt cords, steel cords and organic fibre cords, e.g. aromatic polyamide, nylon, polyester and the like can be used. In this embodiment, the belt is composed of two plies of steel cords. Each bead portion 4 is provided between the turnup portion 6B and main portion 6A of the carcass 6 with a rubber bead filler. The bead filler extends continuously radially outwardly from the bead core 5 beyond the maximum section width point K of the tyre. The bead filler comprises a radially inner part tapering radially outwardly from the radially outside of the bead core 5 and a radially outer part having a substantially constant thickness T. The radially inner part is made of a bead apex rubber 9, and the radially outer part is made of a strip of hard rubber 10 separate from the bead apex rubber 9. The bead apex rubber 9 is a hard rubber having a JIS-A hardness of 75 to 95 degrees and the sectional shape thereof is substantially triangular. The radially outer extreme end thereof is positioned at a height H1 in a range of less than the height HR of the radially outer end of the flange R1 of a standard rim R, each height measured from the bead base line L. Here, the standard rim is the "standard rim" specified in JATMA, the "Measuring Rim" in ETRTO, the "Design Rim" in TRA or the like. The hard rubber 10 of the radially outer constant-thickness part has a JIS-A hardness of 75 to 95 degrees. The hardness of the rubber 10 differs from that of the rubber 9. But it is possible that they are the same hardness. In this example, the radially inner and outer parts 9 and 10 are made of different rubber compounds, but it is also possible that these parts are the same compound. The radially inner end of the hard rubber strip 10 is spliced with the radially outer end of the bead apex rubber 9. The changing point from the tapering part to the constant-width part is positioned radially inwards of the radially outer end of the flange R1 of the standard rim R. The radially outer constant-thickness part 10 extends along the axially outer surface of the carcass main portion 6A beyond the maximum tyre section width point K and preferably has a substantially constant thickness T in the range of from 0.3 to 2.0 mm except for the edges 10a, 10b. In this embodiment, the radially outer constant-thickness part 10 has a radially outer end 10a. The end 10a may be positioned near the maximum section width point K as shown in Fig.1, or higher at the middle between the maximum section width point K and the belt edge 7e as shown in Fig.3, or between the belt 7 and the carcass 6 as shown in Fig.4. Further, as shown in Fig.5 as another embodiment, it is possible to form the radially outer constant-thickness part 10 as having no radial outer end. That is, the constant-thickness part 10 extends continuously from one of the bead portions 4 to the other. If the hardness of the radially outer constant-thickness part 10 is less than 75 degrees, it is insufficient to improve the steering stability. If more than 95 degrees, the ride comfort is greatly deteriorated. If the thickness T is more than 2.0 mm, the ride comfort deteriorates and the tyre weight unfavourably increases. If less than 0.3 mm, the lateral stiffness of the tyre is low and the steering stability is greatly decreased. In this embodiment, the radially inner edge 10b of the rubber strip 10 is disposed on the axially outer side of the radially outer end portion of the bead apex 9 as shown in Fig.2. But it is also possible to dispose the edge 10b on the axially inside of the radially outer end portion of the bead apex 9 as shown in Fig.8(A). Further, the rubber strip 10 can be extended to the bead core 5 or the vicinity thereof as shown in Figs.8(B) and 8(C). Figs.7(A) to 7(C) shown part of the steps of a method of manufacturing the above-mentioned pneumatic tyre 1. For example, the method comprises the steps of applying an inner liner rubber 21 on to a cylindrical outer surface of a tyre building drum 20. Winding a carcass ply 6 around the cylindrical outer surface of the tyre building drum 20 so that the edges of the carcass ply 6 protrude from the edges of the cylindrical outer surface. Decreasing the diameter of the protruding portions 23 of the wound carcass ply 6 relatively to the diameter of the main portion, setting a bead core 5 and a bead apex rubber 9 around each of the protruding portions 23. The bead apex rubber 9 is fixed on the radially outer side of the bead core 5 in advance and is fitted as an annular assembly 22. The bead apex rubber 9 has such a height that the radially outer end thereof is positioned at substantially same radial height as the edge of the cylindrical outer surface of the tyre building drum 20 or lower. A strip of hard rubber 10 is then wound around the carcass ply 6 so that the axially outer edge of the wound strip 10 contacts with the bead apex 9, and the protruding portions 23 are turned up around the bead core 5 so as to wrap the assembly 22. Finally the carcass is expanded into a toroidal shape, applying sidewall rubber on both sides of the carcass, setting a tread ring radially outside the carcass, and vulcanising the green tyre in a mould. Incidentally, in respect of the order of the step of setting the assembly 22 and the step of winding the hard rubber strip 10, these steps are interchangeable with each other according to the relative position of the hard rubber strip edge 10b to the bead apex. For example, in case of Fig.2 or Fig.8(C), the assembly setting step may be carried out first. In case of Fig.8(A) or Fig.8(B), the strip winding step may be first. Comparison Test Test tyres of size 155SR13 having specifications shown in Table 1 were made and tested for steering stability, ride comfort and production efficiency. A) Steering stability test and Ride comfort test A test car provided with test tyres was run in a dry test course and the ride comfort and steering stability were evaluated into ten ranks by the test driver's feelings, wherein the higher the rank, the better the performance. Wheel rim: 4.5X13 standard rim Inner pressure: 2.0 kgf/sq.cm Test car: 1000cc FF passenger car B) Production efficiency test The time required for making the tyre in a certain production line was measured. In the table, the reciprocals are indicated by an index based on Ref.1 being 100. Thus, the larger the value, the better the production efficiency.

Claims: A pneumatic tyre comprising a carcass ply (6) extending between bead portions (4) through a tread portion (2) and sidewall portions (3) and turned up around a bead core (5) in each said bead portion (4) to form a pair of turnup portions (6B) and a main portion (6A) therebetween, a rubber bead filler disposed between the turnup portion (6B) and main portion (6A) of the carcass ply (6) in each said bead portion (4), said rubber bead filler continuously extending radially outwardly from the bead core (5) beyond the maximum section width point (K) of the tyre, said rubber bead filler comprising a radially inner part (9) tapering radially outwardly from the bead core and a radially outer part (10) having a substantially constant thickness (T), characterised by said radially outer part (10) having a JIS-A hardness of 75 to 95 degrees and in that the radially inner tapering part (9) is made of a bead apex rubber, and the radially outer constant-thickness part (10) is made of a strip of hard rubber spliced with the bead apex rubber, and the radially outer end (10b) of the bead apex rubber (9) is lower than the radially outer end of a flange of a standard rim. A pneumatic tyre according to claim 1, characterised in that the rubber bead filler has a radially outer end (10a) positioned between the maximum section width point (K) and an axial edge (7e) of a tread reinforcing belt (7) disposed in the tread portion (2). A pneumatic tyre according to claim 1, characterised in that said rubber bead filler has a radially outer end (10a) positioned beneath a tread reinforcing belt (7) disposed in the tread portion (2). A pneumatic tyre according to claim 1, characterised in that the radially outer constant-thickness part (10) extends continuously from one bead portion to the other whereby the rubber bead filler has no radially outer end. A method of manufacturing the pneumatic tyre as set forth in any of claims 1 to 4, comprising the steps of winding a carcass ply (6) around a cylindrical surface of a tyre building drum (20) so that the edges of the carcass ply (6) protrude from the edges of the cylindrical surface, decreasing the diameter of the protruding portions (23) of the wound carcass ply relatively to the main portion, setting an annular bead core (5) around each of the protruding portions and a bead apex rubber (9) on the radially outer side of the bead core (5), the bead apex rubber (9) having a radially outer end (10b) placed at substantially the same radial position of the edge of the cylindrical surface or radially inwards thereof, winding a strip of hard rubber (10) around the main portion of the carcass ply (6) so as to contact with the bead apex rubber, and turning up the protruding portions (23) of the carcass ply around the bead cores.

Inventors: SUZUKI KAZUYA, SUZUKI, KAZUYA
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1998
Main classification: B60C15
IPC codes: B60C15, B60C13, B29D30, B60C9