HEAVY DUTY PNEUMATIC TYRE

Abstract: A heavy duty pneumatic tyre having a tread pattern com­ prising at least one circumferential continuous groove (G) characterised by a series of spaced apart platforms (3) on a sidewall (2) of the groove (G) the platforms (3) and groove (G) being dimensional such that 0.2≦ 11/L1 ≦ 0.7,0 ≦ 12/L2 ≦ 0.4 and 0.2 ≦ H/D ≦ 1.0 where 11 is the width of the platforms (3) at the base of the groove (G), L1 is the width of the base of the circumferential groove discounting the platform (3), 12 is the width of the top of the platforms (3), L2 is the width of the top of the groove (G) at the tread surface, H is the radial height of the platforms (3) for the groove base and D is the groove depth. The resultant pattern has the properties of greatly redu­ ced stone trapping, improved rejection of stones and also provides the required good wet grip and wear properties throughout the life of the tyre tread.

Description: This invention relates to heavy duty pneumatic tyres and particularly to the tread patterns of such tyres. In general, the tyres for heavy vehicles are provided in the tread with zig-zag or straight circumferential grooves extending circumferentially to provide drainage and handling stability. Such circumferential grooves tend to pick up stones and this is a severe problem for tyres used in stoney conditions. When stone-pick up has occurred, it is difficult to discharge the stone from the groove because of the strong restraining force of the groove. As a result, the stone is then pressed into the rubber of the groove on every subsequent rotation of the tyre and this often causes severe damage. As countermeasures to stone pick-up, it has been proposed to widen the circumferential grooves or to provide steeply sloped sidewalls for the circumferential grooves so that the stone pick-up is lessened and discharged from the groove is promoted. Those countermeasures, however, have drawbacks. In the former, the wet grip and wear resistance are decreased and in the latter the wet grip property is decreased due to the groove width becoming substantially less as the tyre wears. A tyre according to the preamble of claim 1 is known, e.g. from DE-A-2921377. In this known tyre the width of the platforms at the base of the circumferential groove is about 0.5 times the width of the base of the circumferential groove discounting the platform, the width of the top of the platforms is 0.5 times the width of the top of the circumferential groove at the tread surface, the radial height of the platforms from the groove base is about 0.5 times the depth of the circumferential groove. It is an object of the present invention to provide a heavy duty pneumatic tyre which avoids the stone trapping and retaining problem without loss of wet grip and wear resistance. According to the present invention a heavy duty pneumatic tyre comprises a tread provided with two circumferential continuous grooves located one on each side of the tyre equator and provided with a series of spaced apart platforms said platforms in each circumferential groove being disposed on at least one of the groove sidewalls, characterised by the width of the platforms at the base of the circumferential groove being 0.2 to 0.7 times the width of the base of the circumferential groove discounting the platform, the width of the top of the platforms being 0 to 0.4 times the width of the top of the circumferential groove at the tread surface, the radial height of the platforms from the groove base being 0.2 to 1.0 times the depth of the circumferential groove, the total area of the platforms in each circumferential groove viewed radially inwards of the tyre being in the range of from 20% to 60% of the total groove base area of the circumferential groove, the angle of the sidewall of the platforms to the radial direction being larger than the angle of the opposite axially outer groove sidewall to the radial direction, and the angle of the axially inner groove sidewall to the radial direction being larger than the angle of the axially outer groove sidewall to the radial direction. Fig. 1 is a plan view of a tyre tread showing one embodiment of the present invention; Fig. 2 is a cross section view taken along the line A-A of Fig. 2; Figs. 3 to 6 are plan views of alternative tread patterns; Fig. 7(a) to (d) are cross sectional views of the circumferential grooves of prior art tread patterns. Fig. 8(a) to (d) are cross sectional views of the circumferential grooves corresponding to embodiments 1 to 4 of this invention. In Figs. 1 and 2 a heavy duty pneumatic tyre 1 is provided in the tread T thereof with a plurality of circumferential grooves G1, G2 and G3 each extending in a zig-zag fashion around the circumferential direction of the tyre. Each circumferential groove G1 and G2 is provided on the axially inner sides of the groove sidewalls 2 with platforms 3. The platforms are short in length and spaced apart around the circumferential direction. The two circumferential grooves G1 and G2 are positioned one on each side of the central circumferential groove G3 which is positioned along the centre line of the tread T. Each of the grooves G1 and G2 is wider than the groove G3. Hereinafter, the above mentioned circumferential grooves G1 and G2 will be referred to as circumferential grooves G. Each platform 3, in this embodiment extends down the groove G, radially of the tyre from a point below the tread surface 4 to the bottom of the circumferential groove G. The platform 3 is dimensional such that the ratio ℓ1/L1 of the base width ℓ1 of the platform 3 at the bottom of the groove to the width L1 of the bottom of the circumferential groove G is between 0.2 and 0.7. Furthermore, the ratio ℓ2/L2 of the width ℓ2 of the platform 3 at the top to the width 12 of the circumferential groove, is less than 0.4. Next the ratio H/D of the height H of the platform 3 to the depth D of the circumferential groove G is more than 0.2. Next the sum total of the surface areas of the platforms within each circumferential groove is in the range of 20% to 60% of the total groove base area of the circumferential groove. The results of these dimensional limitations is to prevent stone damage at the base of the groove by largely ejcting stones which enter the grooves G1 and G2. It is also believed that initial stone pick-up is reduced. The ratio ℓ1/L1 provides this effect without reducing the groove volume and thus the drainage properties, which would be the case if ℓ1/L1 was substantially greater than 0.7. Similarly the choice of ℓ2/L2 again provides groove volume. In addition to these main features further dimensional features may be provided to improve still further the effectiveness of the invention. The inclination angle α of the sidewall 3a of the platform 3 to the radial direction of the tyre is 1.3 times the inclination β of the opposite outside groove sidewall; and the inclination angle γ of the inside groove sidewall is larger than the inclination angle β of the outside groove sidewall. Further embodiments are shown in Figs 3 to 6 and these vary as follows:- In Fig.3 the platforms 3 are provided on both sidewalls of the central circumferential groove G3. In Fig.4 other independent platforms 8 are provided between the platforms 3 in the circumferential grooves G1 and G2. In Fig.5 the platforms 3 are provided on both the opposite groove sidewalls of each circumferential groove G1 and G2, and further, the grooves G1 and G2 are provided with other independent platforms 8. To show the effectiveness of the invention four embodiments were tested in comparison with four tyres of the prior art design, called here comparative examples 1 - 4. Each test tyre had the same width circumferential groove G but each groove G had the different sectional shape shown in each case in Fig.7(a) to (d) and Fig.8(a) to (d). Figs 7a to 7d being the prior art comparative example and Figs 8a) to 8d) the embodiments of the present invention. The measured results are set out in Table 2 wherein the number of picked up stones is defined by an index on the assumption that the comparative example 1 is 100, and the smaller the value, the better the prevention of stone pick-up. As can be seen from the test results the embodiments of the invention all had substantially improved stone trapping properties. This is due to less stones being picked up and to a more effective discharge of stones. The result is a reduction in expected tyre damage caused by stones and this affect has been shown to be obtained.

Claims: A heavy duty pneumatic tyre having a tread (T) provided with two circumferential continuous grooves (G1,G2) located one on each side of the tyre equator and provided with a series of spaced apart platforms (3), said platforms (3) in each circumferential groove (G1,G2) being disposed on at least one of the groove sidewalls (2), characterised by width (ℓ1) of the platforms (3) at the base of the circumferential groove (G₁,G₂) being 0.2 to 0.7 times the width (L1) of the base of the circumferential groove discounting the platform, the width (ℓ2) of the top of the platforms (3) being 0 to 0.4 times the width (L2) of the top of the circumferential groove at the tread surface (4), the radial height (H) of the platforms (3) from the groove base being 0.2 to 1.0 times the depth (D) of the circumferential groove, the total area of the platforms ( 3) in each circumferential groove (G1,G2) viewed radially inwards of the tyre being in the range of from 20% to 60% of the total groove base area of the circumferential groove, the angle (α) of the sidewall (3a) of the platforms (3) to the radial direction being larger than the angle (β) of the opposite axially outer groove sidewall to the radial direction, and the angle (γ) of the axially inner groove sidewall (2) to the radial direction being larger than the angle (β) of the axially outer groove sidewall to the radial direction. A tyre according to Claim 1 characterised by the tread being provided with a central groove (G3) without platforms (3). A tyre according to either of Claims 1 or 2 characterised by the circumferential grooves (G1,G2) being of zigzag configuration around the circumference of the tyre. A tyre according to claim 3 characterised by the circumferential grooves (G1,G2) being provided only at salient points of the axially inner groove sidewall with the platforms (3).

Inventors: KOYAMA, TOSHIO, OCHIAI, KIYOSHI
Applicants: SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1986
Main classification: B60C11
IPC codes: B60C11