A CONVERTIBLE TREAD FOR A RADIAL TRUCK OR TRAILER TIRE

Abstract: A radial ply pneumatic tire (10) for trucks or trailers has a tread (12) with at least three longitudinal grooves (20, 22) extending circumferentially to divide the tread (12) into at least four parts and lateral grooves (30, 31, 32, 33, 34) extending across the at least four parts of the tread to form at least four rows (1, 2, 3, 4 and 5) of circumferentially separated blocks (40). The longitudinal grooves (30, 31, 33, 34) have average widths of W1 for a depth extending between the radially outer surface (42) of the blocks (40) to less than 60 % of the tread depth (D) thereafter the average width of the longitudinal groove narrows to less than 50 % of W1. The lateral grooves (22) in each shoulder row (15) extend to a depth of less than 60 % of the tread depth (D). The lateral grooves in the central rows (2, 3 and 4) have an average length of L1 between the radially outer surface (42) of the tread blocks (40) to a depth of less than 60 % of the total depth (D), thereafter the average length increases from L1 between the radially outer surface (42) of the tread blocks (40) to a depth of a less than 60 % of the total depth (D), thereafter the average length increases from L1 to greater than L1, preferably to L1, plus at least 50 % W1. Most preferably, the lateral groove in the central region (2, 3 and 4) also narrows to less than 80 % of averaged width W2 of the lateral grooves. The tire (10) when new provides a tread (12) for the drive axle position, and when less than 60 % worn the tread pattern changes to one ideally suited for the trailer wheel position.

Description: A CONVERTIBLE TREAD FOR A RADIAL TRUCK OR TRAILER TIRE Technical Field This invention relates to the field of heavy duty radial pneumatic tires for trucks and truck trailers. Background Art In many areas of the world, heavy duty vehicles such as trucks must have superior traction performance on the drive axle positions of the vehicle. Tires having sufficiently aggressive tread patterns with block element type tread patterns seem to provide the best traction performance. As the tread becomes about half worn these block elements can lose some of their traction capability or performance. Ideally, the drive axle tires would be replaced at that time. Unfortunately, for the vehicle owner this means that the tread still had a useful half life remaining if it could be used in a less traction sensitive wheel position. Unfortunately, the original tread pattern when worn was not conducive to such applications such as trailer tires. The need was apparent that tread patterns must change or convert when worn partially to a different pattern if they were to be successfully used in other wheel positions. The use of convertible truck tires which start out having one block type tread pattern and as the tire reached a certain level of wear changed to a rib type tire was taught in U.S. Patent 4,223,712 wherein less than full depth inclined transverse grooves would disappear after the tire was 30% to 70% worn. A later U.S. Patent 4,732, 195 issued March 22, 1988, which taught that the transverse grooves should disappear toward the axially outside of the tread so that the separated blocks change into continuous ribs from the axially outside to the inside of the tread in sequence as the tread wears. In U.S. Patent 4,854,384 issued August 8, 1989, taught a block type tread pattern which is also converted to a rib type tire when the tire is worn in the range of 35 % to 75 % of the maximum depth. The tread has a plurality of circumferentially continuous zig-zag and straight grooves which have a total width equals to 15-35 % of the entire tread width when the tire is new and 10-25 % of the entire tread width when the tire is worn and the transverse grooves completely disappearing to form a rib pattern consisting solely of zig-zag longitudinal grooves. In these patents the tread pattern simply was converted from block elements to ribs by the loss of the transverse groove. These rib type tires generally will exhibit uniform wear and can be used where traction must be achieved by zig-zagging the longitudinal grooves. Historically, such tires have relatively poor braking traction when used on wet or snowy roads. The present invention in a unique way converts a block element tread pattern for drive axles of trucks when the tire is half worn to a combination of shoulder ribs and central rows of larger block elements which can exhibit substantially superior wet traction capability than the prior art ribbed type tires. Disclosure of the Invention A radial ply pneumatic tire 10 for trucks or trailers having a tread 12 with at least three longitudinal grooves 20,22 extend circumferentially to divide the tread 12 into at least four parts is disclosed, more preferably 5 parts divided by four longitudinal grooves 20,22. The tread 12 has lateral grooves 30,31 ,32,33,34 extending across the at least four parts of the tread 12 to form at least four rows 1 ,2,3,4,5 of circumferentially separated blocks 40 including two shoulder rows 1 ,5 and at least two, preferably three central rows 2,3,4. Each block 40 has a radially outer surface 42. The longitudinal grooves 20,22 have an average width W, between the radially outer surface 42 of the tread blocks 40 extending to a depth of less than 60 % of the total tread depth D thereafter the average width of the longitudinal grooves 20,22 narrows to less than 50% of W j and the lateral grooves 30,34 in each shoulder row extends to a depth of less than 60% of the total tread depth. The lateral grooves in the central rows 31 ,32,33 have an average length of L j between the radially outer surface 42 of the tread blocks 40 to a depth of less than 60% of the total depth D, thereafter the lateral grooves 31 ,32,33 average length increases to greater than L preferably to L, + 50% of Wι in length. The average groove width of the lateral grooves 31 ,32,33 in the central rows equals W 2 , the width W 2 being measured between the radially outer surface 42 of the block 40 to a depth of less than 60% of the total depth D, thereafter the lateral grooves narrow to an average width of less than 80% of W 2 for the remainder of the groove depth, preferably less than 50% of W 2 . These changes in average groove widths W, and W 2 of the longitudinal 20,22 and the central row lateral grooves 31 ,32,33 to less than 50% W, and less than 80% W 2 respectively preferably occurs at the same depth. Furthermore, it is preferred that the lateral grooves 30,34 in the shoulder rows 1 ,5 cease at the same depth wherein the longitudinal and the lateral grooves narrow. It is further believed important that the longitudinal and lateral grooves change average width at 40% or more of the total depth D of the tread 12. In the preferred embodiment tire each block element has at least one size 50,51 ,52,53 and a portion of the sipe 50,51 ,52,53 remains in the tread 12 after the width of the longitudinal 20,22 and lateral grooves 31 ,32,33 narrows due to the tire 10 being worn. The tire 10 when new preferably has a net-to-gross ratio of less than 70% which increases by at least 10% at the depth of the tread where the average groove widths narrow, preferably increasing by almost 20% . Definitions "Aspect ratio" of the tire means the ratio of its section height (SH) to its section width (SW) multiplied by 100% for expression as a percentage. "Asymmetric tread" means a tread that has a tread pattern not symmetrical about the centerplane or equatorial plane EP of the tire. "Circumferential" means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction. "Equatorial plane (EP)" means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread. "Footprint" means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure. "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 tread surface are 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 be of 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. If such narrow or wide grooves are of substantially reduced depth as compared to wide circumferential grooves which they interconnect, they are regarded as forming "tie bars" tending to maintain a rib¬ like character in the tread region involved. "Inboard side" means the side of the tire nearest the vehicle when the tire is mounted on a wheel and the wheel is mounted on the vehicle. "Lateral" means an axial direction. "Net contact area" means the total area of ground contacting elements between defined boundary edges divided by the gross area between the boundary edges as measured around the entire circumference of the tread. "Net-to-gross ratio" means the total area of ground contacting tread elements between the lateral edges around the entire circumference of the tread divided by the gross area of the entire tread between the lateral edges. "Non-directional tread" means a tread that has no preferred direction of forward travel and is not required to be positioned on a vehicle in a specific wheel position or positions to ensure that the tread pattern is aligned with the preferred direction of travel. Conversely, a directional tread pattern has a preferred direction of travel requiring specific wheel positioning. "Axial" and "axially" means lines or directions that are parallel to the axis of rotation of the tire. "Outboard side" means the side of the tire farthest away from the vehicle when the tire is mounted on a wheel and the wheel is mounted on the vehicle. "Radial" and "radially" means directions radially toward or away from the axis of rotation of the tire. "Rib" means a circumferentially extending strip of rubber on the tread which is defined by at least one circumferential groove and either a second such groove or a lateral edge, the strip being laterally undivided by full-depth grooves. "Sipe" means small slots molded into the tread elements of the tire that subdivide the tread surface and improve traction. "Tread element" or "traction element" means a rib or a block element. Brief Description of Drawings Fig. 1 is developed fragmentary plan view of a preferred embodiment tire having a block type tread pattern according to the invention. Fig. 2 is a plan view of the tire of Fig. 1 after tread wear has caused the conversion of the tread pattern to the two shoulder ribs with central rows of enlarged blocks. Figs. 3-7 are cross sectional views taken of the various longitudinal and lateral grooves. Detailed Description of the Invention With reference to Fig. 1 there is shown a fragmentary plan view of the preferred embodiment tire 10. The tire 10 has a tread 12 having at least three longitudinal groove 20,22 dividing the tread into at least four parts. As illustrated the tread 12 of the preferred tire has four such longitudinal grooves 20,22 dividing the tread into five parts. The tread has a plurality of lateral grooves 30,31 ,32,33,34 extending across each part and dividing the parts forming at least four, as illustrated five rows 1 ,2,3,4,5 of circumferentially separated blocks 40. Each block 40 has at least one sipe 50,51 ,52,53. Several of the transverse grooves 30,31 ,33 and 34 have a sipe 55. Numerous short lateral sipes 54 are closely spaced and positioned on a radially inner portion of the block elements 40 adjacent shoulder grooves 22. A plurality of stone penetration protectors 60 are shown extending from the base of the circumferential grooves 20,22. these features help protect the tire from having small stones or rocks from penetrating through the base of the groove 20,22, and thus exposing the reinforcing belt structure. As illustrated, the longitudinal grooves 20,22 are straight and as shown in cross sectional views of Figs. 3 and 4 have full depths D (excluding tread wear indicators and the stone penetration protectors 60). The full depth D is commonly referred to as the non-skid depth of the tread. Each groove 20,22 has an average width Wi between the radially outer surface 42 of the adjacent tread block 40 to a depth less than 60% of the total depth D. Thereafter, the width of te grooves 20,22 substantially narrow to a width of less than 50% of W, as shown about 30% of W j . With reference to the cross sectional views of Figs. 4-6, the cross sectional shape of the various lateral grooves 30,31 ,32,33,34 are shown. In each case, the transverse groove has an average width designated W 2 which is measured between the radially outer surfaces 42 of the adjacent blocks 40 to a depth of less than 60% of the depth D. In the shoulder rows 1 and 5 the lateral grooves stop at the depth of less than 60% of the .depth D. As shown these grooves extend radially inward from the tread surface at least 40% of D. Beyond that depth the groove ceases and the shoulder rows become solid shoulder ribs. With reference to the blocks 40 of the central rows 2,3 and 4, the lateral grooves 31,32,33 each has an average groove width designated W 2 , W 2 being between the radially outer surface 42 of the block 40 to a depth of less than 60% of D and preferably to a depth of at least 40% of D. Thereafter, a majority of the lateral grooves 31 ,32,33 preferably all the lateral grooves narrow to a width less than W 2 for its respective lateral groove, more preferably narrowing by about 80% less than the original W 2 By measuring along the radially outer surface 42 of each block 40 adjacent to a particular lateral groove one can determine the average length of the lateral groove, each such average length being designated L j . As the tread 12 wears to a location wherein the longitudinal grooves 20,22 narrow the lateral grooves in the central rows 2,3 and 4 actually increase in length. As shown in Fig. 2 the length increases from L, to a length of L j + greater than or equal to 50% of W, . As shown each lateral groove 31 ,32,33 increased by an amount equal to about 2/3 of W t in the central rows. Further inspection of Fig. 2 shows that the net-to-gross ratio of the preferred tire increased to about 85 % from the original or new tire net-to-gross ratio of about 68 % . It is believed that the new tire net-to-gross ratio should be at or below 70 % and after wearing down the tread depth to between 40% and 60% of D, the narrowing or elimination of the grooves should result in at least a 10% preferably 15 % or more increase in the net-to-gross contact ratio. This increase in tread rubber in contact with the road surface greatly retards the rate of tread wear. The fact that the lateral grooves 31 ,32,33 in the central rows are effectively much longer means that the tractive efficiency is also maintained at a higher rate than the early mentioned prior art rib type tires. Furthermore, the wet traction performance of the inventive tire is enhanced by the combination of the long lateral grooves and the straight longitudinal grooves. The use of straight longitudinal grooves 20,22 along with a plurality of blocks having lengthened lateral grooves markedly increasing the tractive performance of the worn tire. The generous use of lower level sipes 54, and 55 along with maintaining portions of sipes 51,52,53 also positively contribute to traction performance. The sipes 54 are as shown in dashed lines of cross sectional view 3. The sipes originate in the area of the groove walls adjacent the circumferential groove 22. The sipes are at or slightly below the intersection of the groove wall and the radially outer surface 42 of the block element 40 and extend radially inwardly to a location at, or slightly above, the base of the groove, preferably above the base of the groove or above the stone penetration protectors 60. As the tread 12 wears these sipes 54, which are originally partially hidden in the grooves 22, are exposed. When the tread reaches the transition point of wear, the sipes 54 are then fully laterally exposed and they become functionally important. At that level of tread wear the tire tread is converted to a pattern useful on free rolling axles of vehicles such as trailers. These sipes 54 help in retarding the initiation of riverwear that is a common occurrence in the block s or ribs of such tires in the location designated in rows 2 and 4 at the axially outer portions adjacent grooves 22. Although the block elements 40 of Fig. 1 and Fig. 2 are shown almost aligned in a circumferential direction. It is believed that it may be desirable to stagger the rows 1 ,2,3,4,5 so that the axially adjacent blocks are more circumferentially offset. Another important feature of this invention is the groove 24 shown in Fig. 1 as a line 24. As the tread wears this narrow straight circumferential groove which is initially not readily observable when the drive axle tread pattern is fully worn, that is as shown in Fig. 2, the 40% to 60% worn condition earlier discussed. At that level of wear the trailer pattern is fully exposed as well as this narrow groove 24. This narrow groove functions as a pressure distribution groove which helps reduce or eliminate the occurrence of chamfer wear common in the free rolling axle position of tires used on truck trailers. Another important feature is that each of the lateral grooves have their first and second ends 30A,30B, 31A,31B,32A,32B,33A,33B,34A,34B oriented perpendicular to the longitudinal direction and having one or more straight inclined portion oriented about 45 ° or more relative to the longitudinal direction this configuration insures that a large portion of the lateral grooves are perpendicularly oriented to the direction of forward travel. This greatly improves wet and dry braking traction. As can be appreciated from the above description, this tire according to the invention does not compromise the traction performance of the shoulder ribs and central block type pattern in the 60% worn condition. Great attention has been given to enhancing both the traction and the wear properties of the worn tread. The conversion for one aggressive drive axle type tread to a trailer type tread having an aggressive combination of shoulder ribs and enlarged central row blocks makes the tire according to the present invention superior to those of the prior art.

Claims: CLAIMS 1. A radial ply pneumatic tire for trucks and trailers having a tread with a total depth D at least three longitudinal grooves extending circumferentiaUy to divide the tread into at least four parts, lateral grooves extending across the at least four parts of the tread to form at least four rows of circumferentially separated blocks including two shoulder rows and at least three central rows, each block having a radially outer surface, the tire characterized by: the longitudinal grooves having an average width W, between the radially outer surface of the adjacent tread blocks extending to a depth of less than 60% of the total tread depth thereafter the average width of the longitudinal grooves narrows to less than 50% of W, and the lateral grooves in each shoulder row extend to a depth of less than 60% of the total tread depth D and the lateral grooves in the central rows having an average length of L j between the radially outer surfaces of the adjacent tread blocks to a depth of less than 60% of the total depth D thereafter the average length increases from L, to greater than L,. 2. The radial ply pneumatic tire for trucks and trailers of claim 1 wherein the lateral grooves in the central rows have an average width W 2 between the adjacent radially outer surface of the tread blocks to a depth of less than 60 % of the total depth D thereafter the lateral grooves narrows to an average width of less than 80% of W for the remainder of the groove depth. 3. The radial ply pneumatic tire for trucks and trailers of claim 1 wherein the changes in widths W, and W 2 of the longitudinal grooves and the central row lateral grooves to less than 50% W, and less than 80% W 2 , respectively occurs at the same radial depth. 4. The radial ply pneumatic tire for trucks and trailers of claim 3 wherein the lateral grooves in the shoulder rows cease at the same depth wherein the longitudinal and lateral grooves narrow. 5. The radial ply pneumatic tire for trucks and trailers of claim 2 wherein the longitudinal and lateral grooves change average width at 40% or more of the total depth of the tread. 6. The radial ply pneumatic tire for trucks and trailers of claim 2 wherein the tire has an initial net-to-gross ratio of less than 70% which increases by at least 10% at the depth of the tread where the groove widths narrow. 7. The radial ply pneumatic tire for trucks and trailers of claim 1 wherein the length of the lateral grooves L j increases to the sum of L s + greater than or equal to 50% W, . 8. The radial ply pneumatic tire for trucks and trailers of claim 1 wherein each block element has at least one sipe, a portion of the sipe remains in the tread after the average width of the longitudinal and lateral grooves narrows due to the tire being worn. 9. The radial ply pneumatic tire for trucks and trailers of claim 1 where the central rows lateral grooves in the 60% or more worn condition are oriented generally peφendicular to the direction of travel over about half of their length. 10. The radial ply pneumatic tire for trucks and trailers of claim 1 wherein the longitudinal grooves axially inward and adjacent to the shoulder row have groove walls having numerous lateral extending sipes that appear as the tread wears. 11. The radial ply pneumatic tire for trucks and trailers of claim 1 wherein at a location axially outward of the shoulder row of blocks and radially inward thereof lies a narrow circumferentially straight groove that appears as the tread wears.

Inventors: SCHUSTER DANIEL EDWARD, SERICH JOHN JAMES, SCHUSTER, DANIEL, EDWARD, SERICH, JOHN, JAMES
Applicants: GOODYEAR TIRE & RUBBER, SCHUSTER DANIEL EDWARD, SERICH JOHN JAMES, SCHUSTER, DANIEL, EDWARD, SERICH, JOHN, JAMES, THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 1996
Main classification: B60C11
IPC codes: B60C11