CA2006573C

CA2006573C - Pneumatic tire with sidewall protrusions for enhanced operation on snow covered terrain

Info

Publication number: CA2006573C
Application number: CA002006573A
Authority: CA
Inventors: Kiyoshi Ochiai; Kazuki Numata
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 1989-01-07
Filing date: 1989-12-22
Publication date: 1999-12-07
Anticipated expiration: 2009-12-22
Also published as: JPH02182503A; JPH0764166B2; DE4000339C2; CA2006573A1; DE4000339A1

Abstract

A pneumatic tire is provided having improved road grip performance on snowy roads. The pneumatic tire incudes a tread portion, and a pair of sidewall portions extending radially-inwardly from an associated tread edge to an associated bead portion. The tread portion includes primary, circumferentially-extending main grooves which are disposed on each associated side of the equator of the tire, and lateral grooves extending from the main grooves to the tread edges to open at the axially-outer end thereof at the face of the sidewall portion. This structure forms, in each shoulder region, a row of shoulder blocks which are arranged circumferentially of the tire along each tread edge. The face of the tread portion includes indentations, and each face of the sidewall portions includes associated protrusions. A pair of the indentations and the protrusions make up a gripping means. Each indentation extends both radially-inwardly from the surface of the tread portion and axially-inwardly from the face of the sidewall, thereby to extend from the tread edge to a point which is axially-inward thereof. The axially-outer end thereof is open at the face of the sidewall, and the axially-inner end terminates an axial distance inwardly of the tread edge at the top of the shoulder block.

Description

(a) TITLE OF THE INVENTION
PNEUMATIC TIRE WITH SIDEWALL PROTRUSIONS FOR ENHANCED
OPERATION ON SNOW COVERED TERRAIN
(b) TECHNICAL FIELD TO WHICH THE INVENTION RELATES
The present invention relates to a pneumatic tire having improved road grip performance on snowy roads.
(c) BACKGROUND ART
Hitherto, many efforts have been made to improve road grip performance of snow tires on snowy roads, e.g., traction performance and breaking performance.
Among such efforts were providing blocks on the tread, providing sipes on the tread elements, and varying these shapes thereof, etc. Such efforts were generally devoted to designing a tread pattern, in other words, to designing a tread structure at the tread face. However, a further improvement in the road grip performance is required.
(d) DESCRIPTION OF THE INVENTION
An object of one aspect of the present invention is therefore to provide a pneumatic tire having improved road grip performance on snowy roads, which is formed according to a new conception of the road grip such that a further gripping force can be obtained by providing gripping means in the so-called "buttress"
parts as well as the tread face.
The present invention was made after noting the fact that the radially-outermost part of the tire sidewall, which is generally called the tire buttress part, contacts with the sidewall of a rut when running on a snowy road, in particular, one which is covered by packed snow.
According to one aspect of the present invention, a pneumatic tire is provided including a tread portion, and a pair of sidewall portions extending radially-inwardly from an associated tread edge to an associated bead portion, wherein the tread portion includes primary, circumferentially-extending main grooves which are disposed on each associated side of the equator of the tire, and lateral grooves extending from the main grooves to the tread edges to open at the axially-outer end thereof at the face of the sidewall portion, thereby forming, in each shoulder region, a row of shoulder blocks which is arranged circumferentially of the tire along each tread edges, wherein the face of the tread portion includes indentations, and each face of the sidewall portions includes associated protrusions, whereby a pair of the indentations and the protrusions make up a gripping means, and wherein each indentation extends both radially-inwardly from the surface of the tread portion and axially-inwardly from the face of the sidewall, thereby to extend from the tread edge to a point which is axially-inward thereof, the axially outer end thereof being open at the face of the sidewall, and the axially-inner end terminating an axial distance inwardly of the tread edge at the top of the shoulder block.
By one variant of this aspect of the invention, the number of the shoulder blocks in each row is in the range of 25 to 60.
By another variant of this aspect of the invention or of variants thereof, the face of the tread portion which is occupied by the shoulder blocks is between and 75 % , whereby the total area of the tops of the shoulder blocks is 0.45 to 0.75 times the area of the face of the tread portion if no tread grooves were to be formed.
By another variant of this aspect of the invention or of variants thereof, the edges of each shoulder block are respectively formed in a zigzag or stepwise configuration, whereby the performance of the shoulder block to engage with snow or ice is effectively improved.
By yet another variant of this aspect of the invention or of variants thereof, the axial distance from the equator of the tire to each indentation at the face of the tread portion is 0.460 to 0.4975 times the width of the tread portion between the tread edges. By one variation thereof, the axial distance is between 1.5 and 8 mm.
By a further variant of this aspect of the invention or of variants thereof, each protrusion extends radially-inwardly from a position inwardly of the face of the tread portion to beyond a position which is 15 % of the distance of the lateral groove depth from the face of the tread portion.

2006573 v By still a further variant of this aspect of the invention or of variants thereof, each indentation has a bottom extending between the top and the axially-outer side of the shoulder block, and the bottom is inclined at an angle of 35 ° to 55 ° to the equatorial plane of the tire. By one variation thereof, the inclination is 40°.
By yet a further variant of this aspect of the invention or of variants thereof, each protrusion extends radially-outer surface which is inclined at an angle of 35 ° to 55 ° to the equatorial plane of the tire.
By a still further variant of this aspect of the invention or of variants thereof, each protrusion has a radially-inner surface, the inner edge of which being joined to the face of the sidewall portion, an axially-outer surface thereof extending parallel with the face of the sidewall portion between the radially-outer surface and the radially-inner surface, and having side surfaces at a right angle thereto.
By still another variant of this aspect of the invention or of variants thereof, the projecting amount of the protrusion constituting the distance which is measured axially from the tread edge to the circumferential edge is not less than 0.01 times the tread width between the tread edges.
By a still further variant of this aspect of the invention or of variants thereof, two angled edges are formed in a region around each tread edge by each indentation, and wherein two angled edges are formed radially-inwardly of the tread edge by each protrusion. By one variation thereof, the gripping means is provided by four angled edges which provide a road grip. By another variation thereof, five gripping means are formed on each shoulder block, and four angled edges are provided on each shoulder block.
(e) DESCRIPTION OF THE FIGURES
In the accompanying drawings:
Fig. 1 is a partial plan view showing an embodiment of one aspect of the present invention.
Fig. 2 is a sectional view thereof;
Fig. 3 is a perspective view showing a shoulder block thereof;

a 2006573 Fig. 4 is a sectional view of the shoulder block;
Fig. 5 is a graph showing the relationship between braking distance in index and the axial distance from the equator of the tire to the indentation at the tread face;
Fig. 6 is a graph showing the relationship between braking distance in index and the amount of the protrusion;
Fig. 7 is a graph showing the relationship between heel and toe wear and the above-mentioned axial distance;
Figs. 8 and 9 are perspective views each showing embodiments of other aspects of the present invention.
(t~ AT LEAST ONE MODE FOR CARRYING OUT THE INVENTION
In Figs. 1 - 4, a pneumatic tire 1 has a tread portion 2, and a pair of sidewall portions extending radially-inwardly one from each tread edge to a bead portion (not shown). The tire is provided with a block pattern in the tread portion as shown in Fig. 1.
The tread portion is provided with circumferentially-extending main grooves G2 disposed one on each side of the tire equator CO, and lateral grooves K
extending from the main grooves G2 to the tread edges T to open the axially outer end thereof at the sidewall face 3, thereby forming, in each shoulder region, a row US of shoulder blocks BS which are arranged circumferentially of the tire along each tread edge T.
Further the tread portion in this embodiment is provided, between the above-mentioned main grooves G2, with circumferentially-extending main grooves G1 and with lateral grooves, so as to form a row UC of central blocks BC which is arranged circumferentially on the centre line of the tread or the equator CO, and a row UM of middle blocks BM which is arranged circumferentially between the central block row UC and each of the shoulder block rows US.
The number of the shoulder blocks in each row UC, UM, US is preferably set in the range of 25 to 60.

Further, the occupation of the tread face by the above-mentioned shoulder blocks BC, BM and BS is arranged between 45 % and 75 % , that is, the total area SA
of the tops of the shoulder blocks BC, BM and BS is 0.45 to 0.75 times the area S of the tread face obtained, assuming that no tread groove is formed. When the SANS

5 ratio is more than 0.75, while the wear resistance is improved, the traction performance is impaired. On the other hand, when the SANS ratio is less than 0.45, wear resistance is greatly reduced.
The edges S 1 and S2 of each shoulder block BC, BM and BS, in particular side edges 52, are respectively formed in a zigzag or stepwise configuration as shown in Fig. 1, whereby the performance of the shoulder block to engage with or to scratch the snow and ice is effectively improved.
The tread face is provided with indentations 10, and each sidewall face 3 is provided protrusions 11 pairing with the respective indentations. A pair of an indentation and a protrusion make up a gripping means 7. A plurality of gripping means, in this embodiment, five gripping means, is formed on each shoulder block BS.
The indentation sinks both radially-inwardly from the tread surface and axially-inwardly from the sidewall face 3. In other words, the indentation extends from the tread edge T to a point 9 which is axially-inward thereof. The axially-outer end thereof is opened at the sidewall face 3, and the axially-inner end is terminated an axial distance 11 inward of the tread edge at the top of the shoulder block BS.
The distance L of the point 9 from the tire equator CO must be 0.46 to 0.4975 times the tread width WT between the tread edges T, and generally and preferably, the distance 11 is set in the range between 1.5 mm and 8 mm.
The indentation shown in Figs. 1 - 4 is provided with an inclined bottom l0A
extending from the tread face to sidewall face 3 at an angle (theta) of 40 ° .
The protrusion 11 projects axially-outwardly from the sidewall face 3 by a distance 12. The radially-outer surface 11A thereof is located radially-inwardly of the bottom 10A. In this embodiment, the surface 11A is inclined at the same angle as the bottom 10A, which is 40° in this example.

2006573 v~

Further, the protrusion has a radially-inner surface, the inner edge of which is joined to the sidewall face 3, an axially-outer surface 11B extending parallel with the sidewall face 3 between the radially-outer surface and the radially-inner surface, and side surfaces 11C at a right angle thereto.
The distance 12 measured axially from the tread edge T to the circumferential edge lla between the surfaces 11A and 11B, that is, the projecting amount of the protrusion, is not less than 0.01 times the tread width WT between the tread edges.
Accordingly, as shown in Figs. 3 and 4, in a region around each tread edge, two angled edges l0a are formed by each indentation 10, and two angled edges l la radially-inward of the tread edge T are formed by each protrusion 11. The edges l0a and lla can engage with the base and sidewall of the rut respectively, with shaving or scratching the snow to generate traction or breaking force. Thus, the gripping means can provide four angled edges which provide a road grip. In this embodiment, since five gripping means are formed on each shoulder block, forty angled edges are provided on every shoulder block.
In Fig. 4, the line X is a 15 % wear line, that is, an imaginary line drawn at 15 % distance of the lateral groove depth H from the tread face. In this embodiment, the main groove depth is equal to the lateral groove depth. The protrusion 11 preferably extends radially-inwardly beyond the line X so as to have a part 12 inwardly thereof which projects from the sidewall face 3, thereby maintaining the road grip performance through the tire wear life.
Figs. 5 and 7 show the results of various tests, wherein test tires of size 10.00 R 20 (Tread width WT=200 mm) having the tread pattern shown in Fig. 1 were prepared.
Fig. 5 shows the relationship between the above-mentioned distance L and braking distance on a road covered by flatly packed snow. In the tests, the distance L
was varied, while the distance 12 was kept constant at O.O1WT (=2.0 mm). The test tires of each distance L were mounted on all the wheels of a 2-D4 type truck.
Fig. 8 shows the relationship between the above-mentioned distance 12 and braking distance on a road covered by rutted packed snow. In the tests, the distance ._ 2008573 ry 12 was varied, while the distance L was kept constant at 0.48WT (=96mm). The test tires of each distance 12 were mounted on all the wheels of a 2-D4 type truck.
Fig. 7 shows the relationship between the above-mentioned distance L and heel & toe wear around the edges l0a of the indentations after a field test of 30,OOOkm running. In the tests, the distance L was varied, while the distance 12 was kept constant at O.O1WT (=2.Omm). The test tires of each distance L were mounted on the front wheels of a 2-D4 type truck.
As shown in Fig. 5, when the distance L was more than 0.4975WT, the road grip performance deteriorated. Also, as shown in Fig. 6, when the distance 12 was less than 0.01 WT, the road grip performance deteriorated. On the other hand, as shown in Fig. 7, when the distance L was less than 0.46WT, the wear resistance was impaired.
In Fig. 8, the gripping means 7 is substantially the same as that as explained above with the exception that the circumferential width of the protrusion 11 is larger than the indentation 10, while the protrusions are formed in a same width in Figs. 1-4.
In Fig. 9, the protrusion 11 is formed of the same width as the indentation 10, but the bottom l0A of the indentation which connects to the inclined radially outer surface 11A of the protrusion, is parallel with the tread face.
As explained above, in aspects of the present invention, the tire is provided with indentations and protrusions in the tire shoulder region. Accordingly, when running on a packed snow road, in addition to the engaging force between the tread and the base of the rut, an engaging force is further produced between the tire sidewalk and the rut sidewalk. As the result, the road grip performance can be effectively improved to upgrade the running performance on that snowy road.
Further, by regulating the axial extent of the indentation and the radial extent of the protrusion as mentioned above, the grip performance is maintained through the wear life of the tire without generating uneven wear.
,<

Claims

1. A pneumatic tire including a tread portion, and a pair of sidewall portions extending radially-inwardly from an associated tread edge to an associated bead portion, wherein:
(a) said tread portion includes primary, circumferentially-extending main grooves which are disposed on each associated side of the equator of said tire, and lateral grooves extending from said main grooves to the tread edges to open at the axially-outer end thereof at the face of said sidewall portion, thereby forming, in each shoulder region, a row of shoulder blocks which are arranged circumferentially of said tire along each tread edge;
(b) the face of said tread portion includes indentations, and each face of said sidewall portions includes associated protrusions, whereby a pair of said indentations and said protrusions make up a gripping means; and (c) each indentation extends both radially-inwardly from the surface of said tread portion and axially-inwardly from the face of said sidewalk thereby to extend from said tread edge to a point which is axially-inward thereof, the axially outer end thereof being open at said face of said sidewall, and the axially-inner end terminating an axial distance inwardly of said tread edge at the top of said shoulder block.

2. The pneumatic tire as claimed in claim 1, wherein the number of said shoulder blocks in each row is in the range of 25 to 60.

3. The pneumatic tire as claimed in claim 1 or claim 2, wherein said face of said tread portion which is occupied by said shoulder blocks is between 45 % and 75 % , whereby the total area of the tops of said shoulder blocks is 0.45 to 0.75 times the area of the said face of said tread portion if no tread grooves were to be formed.

4. The pneumatic tire as claimed in claim 1, claim 2 or claim 3, wherein the edges of each shoulder block are respectively formed in a zigzag or stepwise configuration, whereby the performance of the shoulder block to engage with snow or ice is effectively improved.

5. The pneumatic tire as claimed in claims 1 to 4, wherein the axial distance from the equator of said tire to each indentation at said face of said tread portion is 0.460 to 0.4975 times the width of said tread portion between said tread edges.

6. The pneumatic tire as claimed in claim 5, wherein said axial distance is between 1.5 and 8 mm.

7. The pneumatic tire as claimed in claims 1 to 6, wherein each protrusion extends radially-inwardly from a position inwardly of said face of said tread portion to beyond a position which is 15 % of the distance of the lateral groove depth from said face of said tread portion.

8. The pneumatic tire as claimed in claims 1 to 7, wherein each indentation has a bottom extending between said top and the axially-outer side of said shoulder block, and wherein said bottom is inclined at an angle of 35 °
to 55 ° to the equatorial plane of said tire.

9. The pneumatic tire as claimed in claim 8, wherein said bottom is inclined at an angle of 40°.

10. The pneumatic tire as claimed in claims 1 to 9, wherein each protrusion has a radially-outer surface which is inclined at an angle of 35 ° to 55 ° to the equatorial plane of the tire.

11. The pneumatic tire as claimed in claims 1 to 10, wherein each protrusion has a radially-inner surface, the inner edge of which being joined to said face of said sidewall portion, an axially-outer surface thereof extending parallel with said face of said sidewall portion between said radially-outer surface and said radially-inner surface, and having side surfaces at a right angle thereto.

12. The pneumatic tire as claimed in claims 1 to 11, wherein the projecting amount of said protrusion constituting the distance which is measured axially from said tread edge to a circumferential edge is not less than 0.01 times the tread width between said tread edges.

13. The pneumatic tire as claimed in claim 1 to 12, wherein two angled edges are formed in a region around each tread edge by each indentation, and wherein two angled edges are formed radially-inwardly of said tread edge by each protrusion.

14. The pneumatic tire as claimed in claim 13, wherein gripping means is provided by four angled edges which provide a road grip.

15. The pneumatic tire as claimed in claim 14, wherein five gripping means are formed on each shoulder block, and wherein four angled edges are provided on each shoulder block.