Patent Application
20060137794
The present invention relates generally to pneumatic tires, and more particularly to an improved tire tread design using tie bars.
Conventional tire designs utilize treads with circumferentially and laterally extending grooves that divide the tire tread into a plurality of block elements. The grooves expel water from beneath the tread to prevent hydroplaning and also to provide improved traction in snow, mud, and wet road conditions. In some designs, however, small tread blocks can reduce tire stiffness, thereby affecting performance and causing irregular wear of the tread. One solution to this problem has been to reinforce small tread blocks by connecting them to adjacent tread blocks with tie bars. The tie bars are typically formed in the bottom of the groove and do not extend all the way to the top of the tread blocks.
While tie bars help to improve handling and reduce irregular wear, the location of tie bars in the bottoms of the grooves does not provide optimal performance. Specifically, this tie bar configuration does not reinforce the upper ends of the tread blocks where it is needed, and thereby provides only a limited increase in stiffness when the tire is new. Having tie bars in the bottoms of the grooves also tends to cause excessive stiffness of the tread blocks as the tire becomes worn from use. Moreover, the location of tie bars in the bottoms of grooves inhibits the water expelling function of the grooves.
A need therefore exists for an improved tire tread design which overcomes these and other drawbacks of the prior art.
The present invention provides a tire design having tread blocks that are reinforced by tie bars which extend between upper portions of the tread blocks to provide increased stiffness when the tire is new. The tie bars are diminished as the tread wears and therefore do not contribute to increased tread stiffness during the life of the tire. In one embodiment, the tread blocks are defined by circumferential and lateral grooves formed into the outer surface of the tire. The tire includes at least one tie bar extending between at least two of the tread blocks. The tie bar extends across at least one of the circumferential and lateral grooves and is spaced from the groove bottom surface. Accordingly, the tie bar is worn away with the tread block as the tire wears. Moreover, because the tie bar does not extend to the groove bottom surface, the tie bar of the present invention does not inhibit the grooves from expelling water outwardly of the tire tread.
In another embodiment, a tire according to the present invention is formed in a mold having at least one first molding member for forming the tread, and at least a second molding member for forming the tie bar. The second molding member is separable from the first molding member such that the first and second molding members may be separately removed from the formed tire. The second molding member includes a groove-engaging portion that extends to the formed groove bottom surface such that the formed tie bar is spaced from the formed groove bottom surface. In another embodiment, the second molding member is resiliently coupled to the first molding member such that when the first molding member is removed from the formed tire, the resilient coupling facilitates automatic removal of the second molding member from the formed tire.
The features and objectives of the present invention will become more readily apparent from the following Detailed Description taken in conjunction with the accompanying drawings.
Definitions
“Axial” and “axially” refer to lines or directions that are parallel to the axis of rotation of the tire.
“Block element” and “tread block” refer to tread elements defined by a circumferential groove or shoulder and a pair of lateral extending grooves.
“Circumferential” means lines or directions extending along the perimeter of the surface of the annular tread, perpendicular to the axial direction.
“Groove” means an elongated void area in a tread that may extend circumferentially or laterally about the tread in a straight, curved, or zigzag manner. Circumferentially and laterally extending grooves sometimes have common portions. The “groove width” is equal to the tread surface area occupied by a groove or groove portion (the width of which is in question) divided by the length of such groove or groove portion; thus, the groove width is its average width over its length. Grooves may have varying depths in a tire. The depth of a groove may vary around the circumference of the tread, or the depth of one groove may be constant but vary from the depth of another groove in the tire.
“Lateral” means an axial direction.
“Radial” and “radially” refer to directions radially toward or away from the axis of rotation of the tire.
“Tie bar” refers to an extra thickness of rubber, conventionally at the bottom of a groove such that, in the locations where the extra rubber is present, the groove depth is less than the groove depth at all other locations. Tie bars stabilize a tread block by limiting the independent movement of two tread blocks that are separated by grooves.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.
The tie bars 40 extend in directions toward the groove bottom surface 36, but are spaced from the groove bottom surface 36. In one embodiment, the spaces between the tie bars 40 and the groove bottom surface 36 provide passageways through which water may be directed outwardly of the tread 12. The tie bars 40 may extend from the outer surface 34 of the tire 10, or they may be spaced a distance S from the outer surface 34 of the tire, as depicted by tie bar 40c shown in
As depicted in
Referring now to
As best depicted in
After the tread blocks 38, and the tie bars 40 have been formed, the mold 50 is opened to permit removal of the formed tire 10. As the mold 50 opens, the first molding member 52 is removed from the formed tire, as depicted in
In another aspect of the invention, a method of making a tire 10 utilizing, for example, a mold 50, 50a as described above, includes forming a tire tread 12 having a plurality of circumferential and lateral grooves 30, 32 which define a plurality of tread blocks 38 in the tire tread 12, and forming at least one tie bar 40 between at least two of the tread blocks 38 such that the tie bar 40 extends across at least one of the circumferential and lateral grooves 30, 32, and is spaced from a respective groove bottom surface 36 defined by the circumferential and lateral grooves 30, 32. In another embodiment, the method includes molding the tire tread 12 with the first molding member 52, forming the tie bar 40 with the second molding member 56 which is separable from the first molding member 52, removing the first molding member 52 from the formed tire 10, and removing the second molding member 56 from the formed tire 10.
While the present invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of Applicant's general inventive concept.
