GB2136743A

GB2136743A - Tread patterns for radial tyres

Info

Publication number: GB2136743A
Application number: GB8405700A
Authority: GB
Inventors: Christian Paech
Original assignee: FUERSTENWALDE REIFEN VEB K
Current assignee: FUERSTENWALDE REIFEN VEB K
Priority date: 1983-03-11
Filing date: 1984-03-05
Publication date: 1984-09-26
Also published as: GB2136743B; DD215045A1; SE8401333L; DD215045B1; GB8405700D0; BE899109A; SE8401333D0; NL8304245A; DE3342584A1; NO840911L

Abstract

The angle which the grooves make with a circumferential plane changes progressively (e.g. following an arc of radius R) from 80 DEG -90 DEG at the edge of the pattern to 0 DEG -10 DEG at the zenith. A groove may comprise portions of alternating direction. A separate central groove may be provided. The pattern, for car or lorry radial tyres with a cross-sectional ratio of 0.65:1 to 0.82:1, minimises shear stresses caused by flattening. <IMAGE>

Description

SPECIFICATION Improvements in or relating to radial tyres The invention relates to radial tyres with profiled treads and preferably with a cross sectional ratio within a ratio range of 0.65:1 to 0.82:1 especiallyfor passenger cars and lorries.

During travel the tyre transmits all the forces between the vehicle and the road surface. According to the momentary operating conditions on the one hand and the geometric-physical parameters of the tyre construction and profile on the other hand stresses which vary from one point to the next as regards their magnitude and direction are formed in the zone of contact between tyre and road.

It follows that the maximum frictional coefficient > obtainable between the rubber particles and the road surface is utilized to a varying extent from one point of the contact surface to another and also proves inadequate at certain places in the border zone. This means that the theoretically possible maximum frictional coefficient ij between the rubber particles and the road surface cannot in practice be achieved in a tyre.

The local variations in the stresses formed in the contact zone are caused: (I) by the driving, braking and lateral steering forces to be transmitted; (II) by the gometrical displacements and changes of curvature caused in the head of the tyre by the flattening undergone by the tyre when running; (III) by the creep of the visco-elastic rubber material subjected to pressure.

As follows from the description of the prior art and the characteristics of the known technical solutions, systems are customary in which transverse and longitudinal grooves or curved structures are provided for the contact surface of pneumatic tyres.

Their usual purposes are to ensure firm adhesion to dry and wet road surfaces, high resistance to abraison, comparatively noiseless running etc.

Far too little consideration has hitherto been given to the shear stresses acting in the contact surface and caused by flattening.

In a known profile (Offenlegungsschrift 27 10 825) the grooves are curved in the same way as a bird's wings, the curves possibly being in accordance with an elliptical equation. The purpose of the invention disclosed therein is to ensure that in a tyre with a belt-like reinforcement of the contact the oblique traction effect will be largely eliminated, providing a tyre which will run extremely smoothly, suffer very little wear and have a high drainage capacity against aquaplaning.

This profile is not the most satisfatory for the purpose of avoiding the shear stresses caused in the contact surface by flattening.

A further known contact strip (Offenlegungsschrift 24 32 363) is made up of profiled blocks with largely circular and equal central inertia ellipses.

The foregoing is said to offer the advantage of greater resistance to abrasion and of greater transmissible forces. Such a system of profiled blocks, however, takes no account whatever of the effect of the stresses caused by flattening and therefore cannot be successfully used except with tyres having a very low H:B ratio.

A contact strip hasalsobeen described (Ger. Dem.

Rep. Pat Specification 124109) which consists of three rows of similar profiled elements, the transverse grooves situated between the profiled blocks being interconnected in pairs by means of narrow recesses. In these positions profiled blocks are intended to support or serrate with one another in the event of deformation from extraneous forces, thus ensuring uniform contact pressure, firm adhesion, ample water displacement capacity, high stability in travel around bends and also a uniform degree of wear. This system likewise leaves out of account the influence of the stresses caused by flattening.

In a further profiled system described (Offenle gungsschrift30 17 268) profiled blocks positioned transversally to the direction of travel vary in their angle in relation to the peripheral direction in such a way that this angle preferably amounts to 70-80" from the edge of the contact surface but to 35-40" in the middle. The said invention, expressly intended for use with radial tyres for lorries only, represents an attampt to solve the aforementioned problems, in which, however, it has not proved completely successful.

The solution covered by Offenlegungsschrift 21 07 570 describes an asymmetrical profile formed from curved groove structures and having good drainage capacity against aquaplaning. Its lack of symmetry, however, makes it completely unsuitable for the purpose of reducing the stresses due to flattening.

The purpose of the present invention is to develop a radial tyre having an improved tread profile and of increased practical value.

In particular, it is intended to increase traffic safety under road conditions which vary seasonally and to reduce abrasion and resistance to rolling.

The purpose of the invention is to develop a radial tyre, with a suitable tread profile, in which shear stresses caused in the contact surface by flattening will be reduced to a minimum, so that a greater part of the maximum possible friction coefficient between the rubber element and the road surface will be available for the transmission of driving, braking and lateral steering forces.

According to the present invention there is provided a radial tyre having a profiled tread wherein respect of the peripheral direction of the tyre profiled grooves in the zenith of the tread are positioned at an angle of 0 to 10O and profiled grooves at the edge of the tread in respect of the peripheral direction of the tyre and remote from the zenith of the tread are positioned at angle of 90 to 80 , the change in direction from the said edge to the zenith being progressive. Preferably the cross-sectional ratio of the profiled tread is within a ratio range of 0.65:1 to 0.82:1.

Desirably the change in direction of the profiled grooves from the said edge to the zenith is substantially continuous, for instance the said change in direction may take the form of a circular arc arrangement with a radius corresponding to half the width of the tread or not differing from half the width of the tread by more than 10%.

The progressive change in the direction of the profiled grooves may be obtained by arranging for the ratio between straight profiled grooves positioned transversally and to the peripheral direction of the tyre to straight profiled grooves positioned longitudinally thereto to be such that the resulting direction always corresponds to the direction of the tangent to the appropriate circular arc or does not differtherefrom by more than 1 OP/o.

Preferabiy profiled blocks or block formations resulting from the arrangement of the profiled grooves may be so arranged that their area is not less than 2% of the square of the width of the tread.

Expediently the peripheral surface of a said profiled block does not differ by more than 35% from the circumference of a circle which has the same area as the profiled block.

An advantageous form of radial tyre embodying the invention is one wherein for longitudinally orientated profiled grooves the average of the two flank angles, in relation to the perpendicular to the rotation axis of the tyre, is greater than the angle between the line which in the position of a said longitudinally orientated profiled groove is perpendicular to the curved contact surface and the perpen diculartothe rotation axis of the tyre.

By way of example embodiments of the present invention will be explained and described with reference to the accompanying diagrammatic drawings, wherein: Figure 1 which is a plan view of the tread (tread configuration not shown), shows by the presence of various arrows stresses caused in the tread of a radial tyre byflattening of the tyre, explanatory longitude and transverse shear diagrams also constituting part of Figure 1; Figure 2 which is a view of a profiled block of a tread of a radial tyre, indicates by its distribution of arrows compensation stresses (creep) caused in a pressure-loaded profiled block by flattening of the block of the tyre tread;; Figures3a,t,c,d,e, are plan views of various forms of treads of radial tyres and are illustrative of the invention, the the Figures showing various arrangements of profiled grooves within the tyre tread surface; Figure 4 is a section through part of a wall of a radial tyre illustrative of the invention, showing a profiled longitudinal groove relative to the tyre contact surface; Figure 5 is a plan view of a radial tyre having another form of profiled tread surface illustrative of the invention, and Figures 6a and bare plan views of radial tyres having further forms of profiled tread surface illustrative of the invention.

The local friction loading ,u prevailing in the type tread or contact surface is derived from the locally effective shear stresses relating to the normal stress (pressure on ground) prevailing at this point. The local shear stress is the resultant of the three components already mentioned.

With the invention, an increase in the part played by shear stresses in the transmission of driving, braking and lateral steering forces is possible by reducing to a minimum, through the selection of a particular profile, the shear stresses 5,6,7 and 8 shown in Figures 1 and 2 and caused by flattening. 5 denotes the shear stress caused on the edge of tread by flattening; 6 denotes the shear stress caused between the edge of the zenith of the tread by flattening; 7 denotes shear stress caused in the zenith of the tread by flattening and 8 denotes compensation stress of a pressure loaded profiled block of the tread.As the transmission of force in the case of rubber is caused by slip and the abrasive sliding of the profiled elements already starts when the friction loading is still very slight, any reduction in the stress due to the flattening at the same time results in reduced wear on the profiled elements.

In addition deformation and abrasion due to stresses cause a loss of energy and thus contribute to the resistance of the tyre to rolling, so that the solution provided bythe invention for this problem likewise involves a reduction in the said resistance.

It may be seen from Figure 1 that as a general principle the magnitude and direction of the shear stresses 5,6 and 7, shown schematically, and taking place inside the boundary line of contact surface A as a result of flattening, act in such a way that they are directed from the contact surface towards the middle and are at their maximum on the edge.

In orderto characterise the system more specifically the longitudinal shear diagram of Figure 1 shows the longitudinal shear L due to flattening along a peripheral portion, i.e. the zenith line 3 of contact surface of the tyre, and the transverse shear Q due to flattening along a line 4 along the cross-section in the middle of the contact surface.

For the shear stresses acting along a peripheral line 1 on the edge of the contact surface are thus found to take a predominant resultant direction of about 90 in respect of the zenith line 3, while the predominant resultant direction of the shear stresses acting along the zenith line 3 of contact surface forms an angle of 0'in respect of the zenith line.

The compensation stresses 8 of the pressureloaded profiled blocks, shown in Figure 2, are almost independent of the stresses shown in Figure 1 and are caused by a change in the curvature of the contact strip and repercussions of the deformed lateral wail. These compensation stresses only act at the edge of the profiled block and subject the highly loaded edge zone 9 of the said profile block, shown Figure 2, to extreme friction and abrasion, since the normal stress in this zone decreases considerably at the same time.

The invention utilizes this realization and process that the direction of the profiled grooves to be worked into the contact surface in accordance with Figure 3 should be selected to ensure that the direction of the profiled grooves agrees with the predominant resultant direction of the shear stresses 5,6 and 7 caused by flattening andthatfurthermore the surface area 10 of the profiled block is as possible in relation to its periphery 11.

In the invention therefore, the arc-shaped profiled grooves 12 and 13 and the straight transverse grooves 16 and 20, as may be seen from Figures 3a,b,c,d and are designed that from the edge of the contact surface they take a direction of 90 in relation to the zenith line 3 or do not deviate from the said angle by more than 10 . The grooves 20 are straight transverse grooves inclined 89"-80" in relation to the peripheral direction of the tyre. The angle also hanges its direction continuously, e.g. as shown in Figure 3a, along a circular arc of which the radius R is equal to half the contact surface width B or does not deviate therefrom by more than 10%, so that in the zenith of the contact surface the angle between the direction taken by the profiled groove and the zenith line is within the range 0-10%.

It has been found to be a special advantage if the profiled groove does not solely follow the circular arc 12 but changes its direction alternately along the portions 12, 13 and 14 of the arc, as this improves the stabiiity of the formation of the profiled block in the zone ofthe peripheral line 2 between edge and zenith of contact surface.

It is also an advantage if the profiled grooves running from the edges to the middle in the zenith of the contact surface are not interconnected, so that a continuous middle rib 21 is formed for the purpose of absorbing the longitudinal shear stress 7,L. A further suitable means of ensuring the continuous change in the direction of the profiled grooves is shown in Figure 3b, the ratio of transversally positioned straight grooves 15, 16, and longitudinally positioned profiled grooves 17, 18, 19, being altered in such a way that the resulting direction always corresponds to the direction taken by the tangent on the circular arc in the particularly longitudinal portion concerned or does not deviate therefrom by more than 10 .

To ensure further properties, such as comparatively noiseless running, the profiled grooves 20, 22, 23, 24, arranged transversally and longitudinally may deviate by up to 100 from the axial and peripheral direction respectively, c.f. Figures 3c,d,e. The straight longitudinal grooves are inclined at 1 - 10 in relation to the peripheral direction of the tyre.

In order to reduce the compensation stresses of the profiled blocks 25 and 26 and profiled block formations 27 consisting of two profiled blocks connected together it is of advantage for the profiled blocks resulting from the arrangement of the profiled grooves, as shown in Figure 2, to have a periphery 11 which does not deviate by more than 35% from the circumference of a circle which has the same area 10 as the profiled block produced in practice.

Steps must also be taken to ensure that isolated profiled blocks 25, and 26 have a minimum area 10 which does not fall below 2% of the square of the width B of the contact surface.

As the selection of the profile for the contact surface of the tyre involves a number of further requirements which will not be discussed in detail in the present context, it should be pointed out that in addition to the variant shown in Figure 3a the variants in Figures 3c and e also prove particularly advantageous for the selection of the profiles.

A further detail, known per se, is shown in Figure 4.

In conjunction with the arrangement of the profiled grooves in accordance with the invention the shear stresses caused by flattening can be additionally reduced if in the case of longitudinally orientated profile grooves 28 the average of the flank angles 29 and 30, in relation to the perpendicular rotation axis of the tyre 31, is greater than the angle between the line 32 which is perpendicular to the curved contact surface at the point where the longitudinally orientated profile groove is provided and the perpendicular to the roation axis of the tyre. The flank angle 29 or 30 is the angle formed by the flank of a profiled block in relation to the imaginary median line between two adjacent flanks.

Figure 5 shows an advantageous version of the variant of the invention illustrated in Figure 3a.

Section a of Figure 5 represents the basic principle of the arrangement of the profiled grooves. The profiled grooves are produced by adjacent circular arc pieces 12,13 and 14with a radius R, as a result of which the direction taken by the profiled groove changes continuously, in accordance with the invention, from the edge of the contact surface to the zenith.

The resulting profiled block formation 27 is connected in the zenith of the contact surface with the middle rib 21, cf. Figure 3b. If a middle groove 33 is worked into the zenith, then longitudinal ribs 36, situated near the zenith, are to be provided, to absorb the shear stresses acting in the peripheral direction.

Th width of the profiled grooves and the length of the short profiled grooves 34 are selected to ensure that the ratio of the positive area of the profile to the overall area will be between 0.65 and 0.75, preferably about 0.7. As a profile is constructed on the optimum lines from the point of view of the stresses, a negative profile part 30% can be achieved, resulting in a high-degree of protection against aquaplaning and at the same time in very limited abrasion intensity.

Further possible designs for profiles are shown in Figures Sc and d. If isolated profile blocks 25 are provided, however, then the area of a profiled block of this kind should be equal to at least 2% of the square of the width of the contact surface.

A likewise advantageous embodiment of the invention is shown in Figures 6a and b. The explanations given in connection with Figures 3 and 5 apply in principle hereagain, although in this case straight profiled grooves are adopted.

The wide transverse grooves 20 are increasingly connected, from the shoulder to the middle of the contact surface, by equally wide longitudinal grooves 17,18,19,22,23 and 24, so that compact profiled blocks or profiled block formations 25,26,27 are produced which ensure a high-degree of traffic safety under the road conditions which vary from season to season and also a greatly reduced degree of abrasion.

Particular properties achieved by this system are as follows: very short braking paths, both on dry and on wet road surfaces; A high-degree of protection against aquaplaning; high lateral steering forces in travel around bends.

According to Figure 6a the length of the profiled groove orientated in the peripheral direction, increases from 34 to 17, 18 and 19, resulting in the continuous change in direction. This result is also obtained in Figure 6b by means of the arrangement adopted for the grooves 22,23 and 24.

To reduce the compensation voltages caused by the pressure loading it is of advantage for the corners 35 of profiled blocks to be rounded. The longitudinal grooves 18 and 19 in Figure 6a are offset stepwise in order to ensure uniform rigidity in the head of the tyre. This "stepped offset" increases the good traction (short braking paths) resulting from the arrangement of the profiled grooves in accordance with the invention, where the road surface is wet, subject to winter conditions or "loose".

Needless to say, fine laminations should preferably be introduced into the profiles shown in Figures 5 and 6 in order to enable the tyres to grip the road more firmly in wet weather.

Claims

1. A radial tyre having a profiled tread wherein in respect of the peripheral direction of the tyre profiled grooves in the zenith of the tread are positioned at an angle of O" to 10 and profiled grooves at the edge of the tread in respect of the peripheral direction of the tyre and remote from the zenith of the tread are positioned at angle of 90 to 80 , the change in direction from the said edge to the zenith being progressive.

2. A radial tyre according to Claim 1, wherein the cross-sectional ratio of the profiled tread is within a ration range of 0.65:1 to 0.82:1.

3. A radial tyre according to Claim 1 or Claim 2, wherein the change in direction of the profiled grooves from the said edge to the zenith is substantially continuous.

4. A radial tyre according to Claim 3, wherein the said change in direction takes the form of a circular arc arrangement with a radius corresponding to half the width of the tread or not differing from half the width of the tread by more than 10%.

5. A radial tyre according to any preceding claim, wherein the progressive change in the direction of the profiled grooves has been obtained by arranging for the ratio between straight profiled grooves positioned tranversally to the peripheral direction of the tyre to straight profiled grooves positioned longitudinally thereto to be such that the resulting direction always corresponds to the direction of the tangent to the appropriate circular arc or does not differtherefrom by more than 10%.

6. A radial tyre according to any preceding claim, wherein profiled blocks or block formations resulting from the arrangement of the profiled grooves are so arranged that their area is not less than 2% of the square of the width of the tread.

7. A radial tyre according to Claim 6, wherein the peripheral surface of a said profiled block does not differ by more than 35% from the circumference of a circle which has the same area as the profiled block.

8. A radial tyre according to any preceeding claim, wherein for longitudinally orientated profiled grooves the average of the two flank angles, in relation to the perpendicular to the rotation axis of the tyre, is greater than the angle between the line which in the position of a said longitudinally orientated profiled groove is perpendicular to the curved contact surface and the perpendicular to the rotation axis of the tyre.

9. A radial tyre substantially as herein described with reference to any one or more the accompanying drawings.