GB2268453A - Partially randomised tyre treads. - Google Patents

Abstract

A method for the design and manufacture of tyre treads uses partially randomised tyre tread patterns in place of the regularly-repeated tread patterns of conventional tyres. The patterns of tyre treads (1 of Fig. 1) of vehicle tyres are partially randomised to create patterns and thereby enable manufacture of tyres in which the tread pattern is not repeated regularly around the circumference of the tyre. Such partially randomised tyre treads produce less recognisable noise against road surfaces, increased road grip in conjunction with ABS braking systems, and opportunities of increased traction in heavy earth moving equipment. Examples of new designs and techniques are demonstrated for bicycle tyres, motor vehicle tyres and industrial equipment tyres in Figs. 2-13. <IMAGE>

Description

PARTIALLY RANDOMISED TYRE TREADS This invention relates to a method for improving the manufacture of treads on tyres. This is achieved by making limited random variations to the highly-repetitive patterns which are conventionally used in a tyre-tread, thereby reducing the perceived tyre noise and improving grip in many critical circumstances.

It is well-known to manufacture tyres for vehicles. These may be of solid or pneumatic type.

Frequently a tread pattern is included on the surfaces most likely to come into contact with the surface of the ground. The tread is normally included as a moulded pattern, or by moulding in rigid material such as metal wire. The purpose of the tread is principally to improve the coefficient of friction or grip between the tyre and the ground surface. It is normal for the tread pattern to be repeated many times around the circumference. This may be described as giving the curved tyre surface a pattern which is repeated regularly about an axis of rotational symmetry passing through the spindle upon which the wheel rotates. The pattern is normally but not necessarily seen as consisting of grooves forming a patterned surface of intersecting straight lines when viewed from a point vertically above the circumference of the tyre.The pattern used is often claimed to have been chosen to give a particularly good performance under certain circumstances, such, as, for example, when squeezing water from between the tyre surface and a wet road surface at higher vehicle speeds.

Such a regularly repeated pattern suffers from two disadvantages. First, it produces a sound which the human ear detects as a whine, or hum, corresponding to a musical frequency. This is due to the fact that the tread generates, at a given speed, a regular series of striking contacts with a road surface. Second, the tyre tread pattern is optimised in tests to suit a particular road surface or a particular weather condition. But this regular tyre pattern cannot be optimised, once and for all, to suit all variations of condition which a tyre will meet during its normal lifetime.

It is more recently well-known to design the braking systems of motor vehicles, including aircraft, so that when a wheel surface skids and no longer allows the wheel to revolve, the braking system relaxes forces to allow the wheel to revolve until the coefficient of static friction has risen above the coefficient of sliding friction. This slip-stick pattern of braking forces is repeated. This braking equipment may be thought of as searching for optimum friction or optimum braking effect. One form is commonly described as ABS braking when applied to motor vehicles.

According to the present invention there is provided a method for improving the manufacture of treads on tyres by which the shape of tread patterns are not repeated at regular intervals around the circumference of a tyre but are varied to create new partially randomised tread patterns, thereby reducing both of the disadvantages referred to in the introduction above.The mathematical variations need not be limited to a particular formula, but may be generated within limits by use of random changes in angles, random changes in height or depth of tread above or below the average diameter of the tyre, random changes in node points on a surface matrix or any combination of such parameters which lead to the definition of a three dimensional surfaces In addition according to the present invention there is provided a method for improving the manufacture of treads on tyres whereby there is the simultaneous possibility of a synergistic advantage when used in association with advanced braking mechanisms. According to the present invention the tread pattern of existing or future regularly-repeated tread patterns are modified by partial randomisation of the pattern of the pattern to avoid the regular repetition around the circumference.The term partial randomisation is used to make clear that total randomisation is impossible, because the randomisation must lie within bounds, for there are bounds to the overall size of a tyre, there are bounds to the fraction of the total surface of the tyre which may usefully contact the road surface, and bounds to which the surface may protrude in a diametral direction from the average diameter of the tyre, and bounds by which out-of-balance forces may be difficult to correct with normal wheelbalancing techniques. According to the present invention significant gains can be achieved by partial randomisation within such practical bounds.

Specific embodiments of the invention will be described by way of examples with reference to the accompanying drawings in which: Figure 1 shows in perspective a typical vehicle tyre.

Figure 2 shows the projection onto a plane surface of the pattern of a bicycle tyre tread developed by rolling a tyre under light load upon a flat surfaces Figure 3 shows in similar manner a tread pattern derived from the pattern shown in Figure 2 by partial randomisation.

Figure 4 represents the projection onto a plane surface of a very simple tread pattern of a motor vehicle tyre.

Figure 5 represents the projection onto a plane surface of a tyre tread derived from the pattern shown in Figure 4 by partial randomisation.

Figure 6 represents the projection onto a plane surface of a tyre tread also derived from Figure 4 by a different partial randomisation.

Figure 7 represents the projection onto a plane surface of another regularly - patterned tyre tread.

Figure 8 represents the projection onto a plane surface of a tyre tread derived from Figure 7 by partial randomisation.

Figure 9 represents the projection onto a plane surface of another regularly-patterned tyre tread.

Figure 10 represents a partially-randomised tyre pattern derived from that of Figure 9.

Figure 11 represents the projection onto a plane surface of a regularly-patterned tyre tread used by heavy equipment.

Figures 11, 12 represent two different partially randomised tyre patterns derived from Figure 10.

A first specific embodiment of the invention will now be described by way of example with reference to the drawings. A conventional pneumatic tyre is shown in perspective in Fig. 1. It consists of a moulded rubber shape 1 in which the sidewalls 2 have an essentially plain surface, and the outer circumferential surface 3 makes contact with the road surface. The circumferential surface 3 has a moulded pattern of tread 4, indicated in Fig. 1 by a hatched surface. The overall size of such a tyre may vary greatly depending upon the size of the vehicle for which it is intended, and the purpose and task of the vehicle and tyre in combination. Fig. 2 shows the projection onto a plane surface of the very simple pattern developed from a bicycle tyre by rolling it under light load over a flat surface.The tyre surface itself carried raised cylindrical shapes with flat tops and axes vertical to the general tyre surface. The relative positions of the axes of the cylinders are on the developed plane surface of Fig 2 as circles 6 whose centres form a hexagonal pattern. This pattern is repeated around the total circumference of the tyre. By partial randomisation a new tyre design represented in Fig 3 is created by using the following partial randomisation rule.

The centre of each individual tread circle is translated from its original position in one of four directions along the axes of the hexagonal pattern - up and to the left, or up and to the right, or down and to the left, or down and to the right. In each case the direction of translation is decided by a random method - the throw of a dice using sides 1,2,3 and 4. The direction so determined is shown by arrows 7 in Fig 2. The distance of each individual translation is also decided by a random method - the throw of a second dice using sides 1,2,3,4 and 5 to determine a translation distance of 1,2,3,4 or 5 millimetres. The resulting tread design shown for part of the circumference is represented in Fig 3. The design can obviously be continued using the same random method to cover the complete circumference of a tyre, and can be used to manufacture a modified mould to produce a new advantageous design of tyre. The sound made by such a tyre rolling on a smooth surface will produce noise which is less regular in pattern and more closely resembling random or white noise which the human ear discerns as producing less whine or hum.

A second specific embodiment of the invention will now be described by way of example by reference to the accompanying drawings. Fig 4 shows the projection onto a plane surface of a simple pattern of a tread of a motor tyre. It has a regular repeat pattern, in which the dark areas 8 indicate grooves in the tyre surface. By partial randomisation the pattern is modified to create a new design indicated in Fig 5. The partial randomisation was made by using the following rule.

Each inverted V-shaped groove 9 in the left-hand column 1 2 and the corresponding V-shaped groove in the right-hand column 13 of Fig. 4 were together moved up on an even dice-throw or down on an odd dice-throw, by a distance of 1,2,3,4 or 5 units of distance determined by a second dice-throw using the scale of 10 units shown at 15. A different pattern derived by partial randomisation from Fig. 4 is shown at Fig. 6. In this case only the left-hand column 1 2 of Fig. 4 was used, together with the partial randomisation rule that each inverted V-groove of the pattern in column 16 of Fig. 6 was derived from an inverted V-groove of column 12 by moving it up on an even dice-throw or down on an odd dice-throw by a distance of 1,2, or 3 units of distance determined by a second dice-throw.Similarly the grooves of the right-hand column 17 of Fig 6 were independently moved to different positions. Careful comparison of Fig. 5 with Fig. 6 exemplifies two further facts. If the rule of producing the design of Fig; 5 were continued around the whole circumference of a tyre it is highly probable that grooves would overlap in the pattern at some points because moves of 5 units of distance in opposite directions for adjacent grooves would equal 10 units of distance, the original spacings of Fig. 4. The rule used to derive Fig. 6 limits translations of distance to 3 units instead of 5 units. In Fig. 6 grooves 19 and 20 are alongside each other (by chance) although translated from their original position of groove 21 of Fig. 4.

Nevertheless the sound made as the high points of the tread of Fig. 6 on a rolling tyre strike a road surface will be irregular and will not produce the regular frequency associated with whine or hum, and will be heard more like a whisper. At the same time the varied spacings increase the probability of some part of the tyre circumference finding a good grip under the influence of ABS or similar braking systems on a variety of ground surfaces.

A third embodiment of the invention will now be described by way of example with reference to the accompanying drawings. At Fig. 7 is shown a regular pattern of points, or nodes 30 from which could be derived a regular repeat pattern of tread grooves around a tyre. A partially randomised pattern of nodes can be created with the object of presenting grooves at different angles to the direction of travel of a rolling tyre. In this example the nodes were moved from their regular positions according to a rule that nodes in columns 31 and 34 were moved up on an even dicethrow or down on an odd dice-throw by 1 to 1 2 units of distance determined by a dodecahedral dice. A result is shown as Fig. 8. Such patterns could be incorporated and extended over the complete road surface of a tyre and should be advantageous to tyres on vehicles braking while cornering at speed.

A fourth embodiment of the invention will now be described by way of example by reference to the accompanying drawings. At Fig. 9 is shown a square matrix of point nodes 40. A partial randomisation of the node positions is obtained by using two dice. The first determines the direction of translation 41 of a node, 1 = up, 2 = down, 3 = left, 4 = right; the second determines the extent of the translation of the node, numbers corresponding to distance units of 1 to 5 respectively. Fig. 10 shows such a partially randomised derivation of the original square matrix with nodes connected by straight lines 42. The position of the original square matrix pattern of straight lines is shown as dotted lines 43.The position of the nodes exemplified by Fig. 10 may in turn be used to define, for example the centres of circles of fixed or partially randomised diameter or the origins of ellipses with partially randomised varying sizes and directions of principal axes. The areas defined by nodes such as those in Fig. 10, for example those shown at 44,45,46,47 may be used to contain regular or partially randomised patterns each of which has been chosen to optimise performance for a particular weather or road or load condition of more conventional tyre treads, thereby allowing modern braking or power drive systems to detect and use the most advantageous areas of tread encountered in any particular operational circumstance.

A fifth embodiment of the invention will now be described by way of example with reference to the accompanying drawings. Fig. 11 shows, as hatched areas 51, raised bars of a tread typically used for earth-moving machinery, mechanical diggers, and agricultural tractors, where power and wheel grip are of paramount importance. These are frequently used on very rough terrain. Nodes 52 are used to indicate position, and arrows 53 are used to indicate the direction in which the position of the bars is altered by partial randomisation using a table of random numbers. An even number indicated a random decision to translate in an upward direction, or an odd number indicated a random decision to translate in a downward direction.Similarly the next part of the random number table determined a distance of translation of 1 unit for an odd number or 2 units for an even number, taken from the scale 54. The pattern so determined is shown in Fig. 12. This method of partial randomisation can be continued around the whole circumference as in earlier examples. The pattern so produced allows grip to be found, for example, over a surface of varied sizes of large stones. This pattern allows also that large areas, for example area 55, offer the opportunity of greater grip on soft fine ground where the larger area defines a larger shear force between tyre and ground, before grip fails by shear in the ground material. The pattern shown in Fig. 13 was developed from Fig. 11 by the even up, odd down rule (without reference to the arrows of Fig. 11), but dice sides 1,2,3 defining the number of half-units of translation from the scale 54. The derivations represented by Fig. 12 and Fig. 13 are, of course, different by virtue of the partial randomness of their creation, but are quite different in another sense. The partial randomisation exemplified by Fig. 13 had smaller bounds, namely a limit of translation of 1 Y2 units. This prevented overlapping of the bars. Although bars could lie adjacent to each other as at 57, bars could not coincide as at 56 in Fig 12, leading to the elimination of a bar. This comparison is a further example of why randomisation must be partial, and why complete randomisation of a pattern without limits has no meaning.

A sixth embodiment of the invention will now be described by way of example. A tyre tread pattern need not be partially randomised using the same partial randomisation throughout its circumference, but may use different partial randomisation rules, for example, for seven different parts of the circumference. Such a pattern allows research upon tyre grip to be carried out in conjunction with ABS braking and synchronised flash photography to compare grip of the seven different patterns in one experiment. The same principle may be used to compare non-randomised patterns with partially randomised patterns. Furthermore it will be advantageous to use one set of partial randomisation rules to produce tread pattern near the sides of the tread surface, and a different set or sets of partial randomisation rules for the central parts of the tread surfaces.

A seventh embodiment of the invention will now be described by way of example. Any pattern upon a tyre surface as displayed upon a plane projection may have any particular part of the pattern moulded into the tyre surface to any depth chosen at random within limits, or have solid materials incorporated at any point on the surface or at any depth above or below the surface, chosen at random within limits.

Claims (17)

1. Tyre treads having any partially randomised patterns which are not repeated regularly around the tread surface of a tyre.

2. A method for the design and manufacture of partially randomised tyre treads, as claimed in Claim 1, by use of random modifications to any regularly-repeated pattern of tyre tread.

3. A method for the design and manufacture of treads on tyres, as claimed in Claims 1 and 2, by which the shape of the tread patterns are not repeated at regular intervals around the circumference of a tyre, but are varied to create new partially randomised tread patterns.

4. A method for the design and manufacture of treads on tyres, as claimed in any preceding claim, by which the tread pattern of existing or future regularly-repeated tread patterns are modified by partial randomisation of the pattern to avoid the regular repetition over the tyre tread surface.

5. A bicycle tyre tread pattern, as claimed in Claims 1-4, which is derived from a regular hexagonal pattern of circles by partial randomisation using random decisions to translate the centres of the circles in one of four directions by distances chosen at random within limits.

6. A motor vehicle tyre tread pattern, as claimed in Claims 1-4, which is derived from a regular pattern by a partially randomised translation of pattern units in a circumferential direction.

7. A motor vehicle tyre tread pattern, as claimed in Claims 1-4, which is derived from a regular pattern of node points by partially randomised translation of those node points to different positions on the tyre surface.

8. A motor vehicle tyre tread pattern, as claimed in Claims 1-4 and 7, which is derived from a regular pattern of node points by partial randomisation to define areas within which different regular or partially randomised patterns are created.

9. Heavy vehicle tyre tread patterns, as claimed in Claims 1-4, 7,8, which are derived from regular patterns by partial randomisation to create a variety of surface areas with the objective of improving traction.

10. The use of any geometrical set of measurements, including distances, angles, centres of circles, circumferences, points, nodes, principal axes of ellipses, vectors, mathematical formulae which together describe a surface in three dimensions, as the basis for limited random variation of shapes of tyre surfaces to create any three-dimensional tyre treads of irregular pattern, as claimed in any preceding claim.

11. The use of any method of generating random numbers, including coins, dice, tables of random numbers, gaming machines or computer programmes to design and manufacture partially randomised tyre treads as claimed in any preceding claim.

12. The use of any of the methods of design and manufacture, as claimed in any preceding claim, to produce partially randomised tyre treads of unlimited complexity.

13. The use of the methods of design and manufacture as claimed in any preceding claim to produce partially randomised tyre treads using different partial randomisation rules to create different patterns in different parts of the tread surfaces.

14. The use of the methods of design and manufacture as claimed in any preceding claim to create partially randomised tread patterns to reduce the perceived tyre noise associated with regular tyre tread patterns.

15. The use of the methods of design and manufacture as claimed in any preceding claim, to create partially randomised tread patterns intended to increase tyre grip in association with ABS or other reactive braking systems.

1 6. The use of the methods of design and manufacture, as claimed in any preceding claim to create partially randomised tread patterns intended to improve the traction performance of heavy vehicles.

17. The use of the methods of design and manufacture as claimed in any preceding claim to include the raising or lowering of moulded surface above or below the average radius of the tyre tread surface.

1 8. The use of the methods of design and manufacture as claimed in any preceding claim to determine the position of the incorporation of other materials into the tyre tread structure.