PNEUMATIC TIRE INCLUDING BELT AND CIRCUMFERENTIAL RIBS

Abstract: The present invention provides a tire (T) comprising a tread portion having a tread design pattern including circumferentially continuous ribs: lateral ribs (1) and other ribs (2). The tread portion is reinforced by a carcass having at least a ply (5), and by a belt having at least two working plies (61, 62). The working plies (61, 62) extend transversely beneath all the ribs, and extend beyond a limit line (7). The thickness (Ti) of the tread between the radially innermost part of the carcass ply (5) and the radially external surface (10) does not depart from the thickness (Tc) at the middle point by more than 10 %. The tire tread portion is molded so that the radially external surface of the lateral and other ribs defines a transverse profile that is substantially flat.

Description: PNEUMATIC TIRE INCLUDING BELT AND CIRCUMFERENTIAL RIBS Background of the Invention This invention relates to vehicle tires, and more particularly to heavy duty truck tires specially designed to be used for long haul trucking operations. An object of the invention is to provide to the driver a more comfortable drive. Another object of the invention is to improve the handling of the tire. More specifically, an object of the invention is to address the problem of deterioration of the comfort and of handling that in certain circumstances has proved to be caused by the tire after the tire has been in use for a number of miles. It may happen that the rolling comfort or the handling becomes unacceptable to the driver at a relatively low mileage such that the tire must be removed well before the end of its normal service life. The problem of bad evolution of comfort is occurring especially in front steer axle tires, in long haul services (i.e. tires which for most of the time do not pass on the road a torque as significant as the driven wheels -no driving torque, the braking operations do not count for a significant part of the service life-). Summary of the Invention According to the present invention, the comfort and handling of the tire is addressed by providing a pneumatic tire comprising a tread portion • having a tread design pattern including : •+ a lateral, circumferentially continuous rib located at each side of the tread, and including a plurality of other circumferentially continuous ribs located between the two lateral ribs, said lateral ribs having a radially external surface for contacting the road and having lateral flanges defining at least in part circumferential continuous grooves located between the ribs, at least the axially outer lateral flange of said lateral ribs being radially outwardly terminated by a junction separating said radially external surface and said axially outer lateral flange of said lateral ribs, -► on each side, a protective cover located axially outwardly of said lateral ribs, • said tread portion being reinforced by a carcass having at least a ply, and reinforced by a belt having at least two working plies extending transversally beneath all said ribs, said working plies including parallel cords arranged at an angle in the range of 10°-30°, and said working plies having an end on both sides of the tread, • said end of said working plies being located axially outwards of a limit line, said limit line being perpendicular to a tread reference line, said tread reference line being the virtual line parallel to the axis of the tire and in contact with the radially outermost point of the radially external surface, • the thickness T; of the tread between the radially innermost part of said carcass and said radially external surface, measured perpendicularly to said tread reference line, does not depart from the thickness T c at the middle point by more than 10%, the radially external surface of said tire tread portion having a transverse radius of curvature greater than 1500 mm, when the tire in mounted on a predefined rim and not inflated. Description of the Drawings The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings showing two examples of the invention: Figure 1 is a fragmentary plan view of a first variation of a tire featuring this invention; and Figure 2 is a fragmentary plan view of a second variation of a tire featuring this invention. Detailed Description of the Preferred Embodiment of the Invention One variation of the preferred embodiment of the tire T of the present invention is shown in Fig. 1 and another variation thereof is shown in Fig. 2. Turning to common features of the two variations, the tire T has a tread portion having a tread design pattern. The invention is related to a typical tread design pattern having proved being suited for front axle tires used in long haul. That tread design pattern comprises essentially parallel ribs separated by parallel grooves. Those parallel ribs here include, located on each respective side of the tread, a lateral rib 1 that is circumferentially continuous, i.e. not divided into a plurality of blocks. This basic tread pattern unit is repeated laterally, with or without changes of actual shape, so that the tread includes a plurality of other ribs 2, located between the two lateral ribs 1 and also being circumferentially continuous. Each lateral rib 1 and other ribs 2 has a radially external surface 10. Each of the lateral rib 1 and the other ribs 2 are limited laterally by flanges 11, 12 defining at least in part and two by two circumferential continuous grooves 13. In the embodiments illustrating the invention, at least the axially outer lateral flange 11 of the lateral rib 1 is radially outwardly terminated by a junction interconnecting the radially external surface 10 and the axially outer lateral flange 11. In the described embodiment, the junction is an edge 14. In the two variations of the embodiment, all of the lateral ribs 1 and other ribs 2 are bordered laterally by edges forming a sharp angle. The axially outer lateral flange 11 of lateral rib 1 and the radially external surface 10 of the lateral rib 1, as viewed in a radial section like the one of figures 1 and 2, define an angle α ranging between 90° and 110°. In other words, the axially outer lateral flange 11 of lateral rib 1 and the radially external surface 10 of the lateral rib 1, as viewed in a radial section like the one of figures 1 and 2, define a sharp angle. The tire T is reinforced by a carcass comprising at least one carcass ply 5 and by a belt. The belt, as shown in the figures, includes two working plies 61, 62, and a protective ply 63. The means to realize the so-called working plies and protective ply are well known in the art. Thus, further details are not given in the present disclosure. It is enough to recall that the working plies generally are made essentially of inextensible parallel cords arranged at an angle in the range of 15°-30°, and that a protective ply is generally a ply which can be more extendible. Also it is enough to recall that the belt could also include other reinforcing means like cords arranged at a zero angle with respect to the mid circumferential plane of the tire T, also called "jointless reinforcing ply or plies", having cord or cords substantially parallel to the mid circumferential plane of the tire T (a plane perpendicular to the axis of the tire T), that latter reinforcement being useful namely to keep unchanged after breaking in the shape and properties of the tire T. All the lateral and other ribs 1, 2 have a radially external surface 10 for contacting the road. Assuming that the surface of the road is flat (bearing in mind that the tire T of the invention is designed for long haul applications, this assumption is close to reality) the radially external surface 10 will be urged to become flat during rolling. According to an aspect of the invention, the belt and more generally the tread portion as a whole is so designed as to achieve a normal stress perpendicular to radially external surface 10 in the tread as even or uniform as possible in a loaded static condition of the tire T. One could suppose that uniform normal stresses will also be experienced during dynamic rolling of the tire T and that such conditions will enhance the comfort and handling of the tire T. According to a feature of the invention, the belt, more precisely at least the working plies 61, 62 of the belt, extend beneath all the lateral ribs 1 and other ribs 2 for providing an equal support thereof. In other words, with reference to the drawings, the ends 610, 620 of the working plies 61, 62 is extended beyond a limit line 7 (shown in dotted line). The limit line 7 is defined by a perpendicular to a tread reference line 8. The tread reference line 8, as viewed in a radial section of the tire T like the one shown in figures 1 and 2, is the imaginary line parallel to the axis of the tire T and in contact with the radially outermost point of the radially external surface 10. A second condition that the limit line 7 has to fulfill is to pass through the edge 14 of the lateral rib 1. It is to be noticed that the tire T tread portion is molded so that the radially external surface 10 of the lateral and other ribs defines a transverse profile which is close to a cylinder when the tire T in mounted on a predefined rim and non inflated. The transverse radius of curvature R is the range of 1,500 mm to an infinite value. Advantageously, the transverse radius of curvature is greater than 5,000 mm. For instance, the two variations show a transverse radius of curvature R reaching 20,000 mm. With reference to the drawings, one see that the thickness T s of the tread is pointed out at different location: thickness Ti at the axially outer border of lateral rib 1, thickness T 2 for respective adjacent other rib 2, and thickness T c in the middle of the tire T (thickness measured at the mid circumferential plane, i.e. the plane perpendicular to the tire's axis of rotation and passing through the center of its tread). The thickness Tj is measured between the radially innermost part of the carcass ply 5 and the radially external surface 10. The thickness T s is measured perpendicularly to the tread reference line 8. The portion of the tread measured by the thickness T j includes reinforcing members of the belt, the rubber compounds and the carcass ply. If the carcass includes more than a single carcass ply, the thickness is measured from the radially innermost part of the radially innermost ply. It is thereby established a reference referred to in general by "the radially innermost part of the carcass". According to another feature of the invention, the thickness T i; in any point between the middle of the tire tread and the axially outermost part of the lateral rib 1, does not depart from the thickness T c at the middle point by more than 10%, and preferably not more than 8%. In any case, the thickness is greater than 20 mm, as it is a tire T for heavy truck. The following table is an example of thickness Tj taken on a tire T according to the invention. In this tire T, the difference of thickness is - — : = 5.9% , thus less than 8%. 27 The onset of unacceptable comfort or unacceptable handling, or the rate of deterioration thereof if any, is thus kept within limits that are by far more compatible with the normal service life of the tire T, thereby avoiding the removal of the tire T well before that the height of the ribs has decreased up to the preset wearing limit. On each side of the tread, a protective cover is located axially outwardly of the lateral ribs. The two examples illustrating the invention differ by the embodiment of the cover. The cover on figure 1 is a narrow shoulder rib 3. Standard tread rubber materials can be used for the shoulder rib 3 as for lateral ribs 1 and other ribs 2. The shoulder rib 3 is laterally recessed from the lateral rib 1 by a narrow groove 31. In other words, the surface 30 of the shoulder rib 3 is recessed with respect to the radially external surface 10 of the lateral rib 1. According to the need to protect the extended belt of the invention, a preferred width of the shoulder rib 3 is in a range of about 10 millimeters to about 20 millimeters. The dimensions and geometry of the shoulder rib 3 are selected such that, during normal running of the tire T, experiences different stresses than lateral ribs 1 and other ribs 2. This feature helps to maintain a sharp edge 14 on the lateral ribs 1. In the particular geometry of the shoulder rib 3, the radial height of the shoulder rib 3 is below the radially external surface 10 by a distance in the range of 1 mm to 2 mm. Figure 2 shows another cover which is not a wearing part of the tread and has no contribution whatsoever to sustain the load. Its function merely is to protect the ends 610, 620 of the working plies 61, 62 and the end 630 of the protective ply 63. The protective cover is a rubber product 4 having an axially inner end joined with the bottom of the axially outer lateral flange 11. In other words, the radially outer surface 40 of the rubber product 4 is approximately even with the bottom of the grooves 13. This variation may be used to improve cooling of the shoulder part if the help of the shoulder rib appears not being needed. To be more general, the protective cover could have any radial height between the limits set forth by the above variations illustrating the invention. The protective cover could be made even with the radially external surface 10, and in that case one would use another rubber material than the one of main part of the tread: the rubber material of the protective cover would ideally be less hysteretic than the rubber material of the lateral ribs 1 and the other ribs 2. In the two variations of the preferred embodiment, the carcass is a radial carcass. The tire T is designed to be mounted on a rim the shape and dimensions of which is defined by well established standards (See e.g. "The Tire and Rim Association, Inc." or "The European Tire & Rim Technical Organization"). According to the well known way of designing tires, a tire T of a preselected size is designed to work on one or a couple of desired rim sizes selected among the above mentioned standards. The tire T also is designed to work at a so-called "nominal inflation pressure". In the described embodiment, the carcass is designed to assume, if the tire T is mounted on the specific rim and inflated at the nominal inflation pressure, a natural shape of equilibrium in the sidewalls. In the tread area, the carcass is adhered on the belt and works as a unit with the working plies; the carcass tends to assume a cylindrical shape. In the shoulder portion, beyond the protective cover, the carcass is connected to that part having a cylindrical shape (into the tread portion) and to that part having a natural shape of equilibrium (in the sidewalls) in a manner as progressive and smooth as possible.

Claims: Claims What is claimed: 1. A pneumatic tire comprising a tread portion • having a tread design pattern including : ■ ♦ a lateral, circumferentially continuous rib located at each side of the tread, and including a plurality of other circumferentially continuous ribs located between the two lateral ribs, said lateral ribs having a radially external surface for contacting the road and having lateral flanges defining at least in part circumferential continuous grooves located between the ribs, at least the axially outer lateral flange of said lateral ribs being radially outwardly terminated by a junction separating said radially external surface and said axially outer lateral flange of said lateral ribs, ■ ♦ on each side, a protective cover located axially outwardly of said lateral ribs, • said tread portion being reinforced by a carcass having at least a ply, and reinforced by a belt having at least two working plies extending transversally beneath all said ribs, said working plies including parallel cords arranged at an angle in the range of 10°-30°, and said working plies having an end on both sides of the tread, • said end of said working plies being located axially outwards of a limit line, said limit line being perpendicular to a tread reference line, said tread reference line being the virtual line parallel to the axis of the tire and in contact with the radially outermost point of the radially external surface, • the thickness Tj of the tread between the radially innermost part of said carcass and said radially external surface, measured perpendicularly to said tread reference line, does not depart from the thickness T c at the middle point by more than 10%, the radially external surface of said tire tread portion having a transverse radius of curvature greater than 1500 mm, when the tire in mounted on a predefined rim and not inflated. 2. A tire according to claim 1, wherein said transverse radius of curvature is greater than 5,000 mm. 3. A tire according to claim 1, wherein said transverse radius of curvature is about 20,000 mm. 4. A tire according to claim 1, wherein said thickness is greater than 20 mm. 5. A tire according to claim 1, wherein said protective rib has a radially external surface which is radially inside of sail external surface of said lateral ribs. 6. A tire according to claim 5, wherein the protective cover is a shoulder rib whose radial height is below the external surface of said lateral rib of a distance in the range of 1 mm to 2 mm. 7. A tire according to claim 1, wherein the rubber material of the protective cover is less hysteretic than the rubber material of the tread. 8. A tire according to claim 1, wherein the junction is an edge. AMENDED CLAIMS [received by the International Bureau on 1 December 1998 (01.12.98); original claims 1-8 replaced by new claims 1-11 (3 pages)] 1. A pneumatic tire having a tread portion with a selected tread design pattern: said tread portion having circumferentially extending lateral rib at each outer side of said tread portion, a plurality of circumferentially extending other ribs located between said lateral ribs, each of said ribs having a circumferentially extending outer surface and outer lateral flanges defining a plurality of grooves separating said ribs, outer limits of ai least said outer lateral flanges of said lateral ribs forming a juncture with said outer surface; a carcass having a belt with at least a pair of working plies reinforcing said tread portion, said working plies extending transversely beneath said ribs with opposed end portions thereof being located outwardly of said tread portion; a protective cover formed axially outward of each of said lateral ribs and end portions and radially outward of each of said end portions; a tread reference line extending parallel of the tire axis and in lateral contact with said outer surface, a first limit line extending perpendicular of said tread reference line and through said juncture, a second limit line extending perpendicular of said tread reference line and along said mid circumferential plane; said tread having a thickness measured between a radially innermost part of said carcass and said outer surface along said first and second limit lines , said thickness being constant within 10% between said limit lines; and, said outer surface having a transverse radius of curvature greater than 2500 mm with the tire mounted on a pre-defined rim and uninflated. 2. The tire according to claim 1 wherein said cords are parallel and are arranged at an angle of between 10° and 30°. 3. The tire according to claim 1 wherein said radius of curvature is greater than 5000 mm. 4. The tire accordingly to claim 1 wherein said thickness is greater than 20 mm. S. The tire according to claim 1 wherein said protective cover includes a shoulder rib having a radial height below said tread reference line by between about 1 mm to 2 mm. 6. The tire according to claim 1 wherein said protective cover extends axially outward from said outer lateral surface of said lateral ribs beyond said end portions of said working plies. 7. The tire of claim 1 wherein said outer lateral flanges of said lateral ribs and said outer surface define an angle between 90" and 110" at said junction. 8. The tire of claim 1 wherein said junction is angular. 9. The tire of claim 1 wherein rubber material forming said protective portion is less hysteretic that rubber material forming the remainder of said tire. 10. The tire of claim 1 wherein each said protective cover includes a radially outer surface, said radially outer surface of said protective cover being approximately axially aligned with the bottom of said groove. 11. A pneumatic tire having a tread portion with a selected tread design pattern: said tread portion having a circumferentially extending lateral rib at each outer side of said tread portion, a plurality of circumferentially extending other ribs located between said lateral ribs, each of said ribs having a circumferentially extending outer surface and outer lateral flanges defining a plurality of grooves separating said ribs, outer limits of at least said outer lateral flanges of said lateral ribs forming a juncture with said outer surface; a carcass having a belt with at least a pair of working plies reinforcing said tread portion, said working plies extending transversely beneath said ribs with opposed end portions thereof being located outwardly of said tread portion; a protective cover formed axially outward of each of said lateral ribs and end portions and radially outward of each of said end portions; a tread reference line extending parallel of the tire axis, a first limit line extending perpendicular of said tread reference line and through said juncture , a second limit line extending perpendicular of said tread reference line and along said mid circumferential plane; said tread having a thickness of no less than 20 mm measured between a radially innermost part of said carcass and said outer surface along said first and second limit lines said thickness being constant within between 8% and 10% between said limit lines; and, said outer surface having a transverse radius of curvature of approximately 5,000 mm; wherein, said outer surfaces of said lateral and said other ribs are contacted by said tread reference line. -1.1 -

Inventors: RADULESCU ROBERT CIPRIAN, RADULESCU, ROBERT, CIPRIAN
Applicants: MICHELIN RECH TECH, RADULESCU ROBERT CIPRIAN, MICHELIN RECHERCHE ET TECHNIQUE S.A., RADULESCU, ROBERT, CIPRIAN
Application year: 1998
Main classification: B60C3
IPC codes: B60C9, B60C11