Patent Description:
In snowy conditions, snow collects in the grooves of a tyre during rolling. During acceleration or cornering, the snow can slide within the groove. This means that the sliding snow provides very little grip on the snow on the road surface. Hitherto it has been desirable to keep the grooves clear so that water can drain from the grooves easily in wet conditions.

<CIT> discloses a tyre with protrusions located on the bottom wall of a groove in the tyre tread. The protrusions are intended to improve grip on snow without greatly affecting water flow. <CIT> discloses a tyre with a device in a groove to prevent the snow entering the groove. However, these arrangements leave room for improvement. Attention is also drawn to the disclosures of <CIT>, <CIT>, <CIT> and <CIT>.

The present invention aims to mitigate at least one problem of the prior art.

The present invention provides a tyre as claimed in claim <NUM>.

The first surface acts to trap snow flowing from the first side, and the second surface acts to allow water to flow smoothly round the snow trapping device. The snow trapped by the first surface has two effects: firstly, some of the snow sliding in the groove encounters the first surface which stops the snow sliding any further; secondly, other of the snow, which is above the snow trapping device, does not encounter the first surface but is subject shear stress from the snow that has been trapped. The shear stress slows the sliding of that portion of snow. The overall effect is to slow down the whole pack of snow which improves snow compression and overall grip.

Prior art snow trapping devices tend to cause flow separation and recirculation downstream of the device, which results in increased hydrodynamic drag and flow losses and reduced water drainage. In contrast, in the present invention, the passageway for water through the device reduces flow separation and recirculation downstream of the device, thereby improving water flow and drainage. Specifically, the water flow encountering the device is divided into two main flows. One is channelled inside the passageway, and the other flows over the snow trapping device. The flow channelled inside the passageway creates a water pressure gradient which reduces creation of the recirculation region.

<CIT> discloses a tyre with device in a groove to prevent snow entering the groove. The device is positioned in a circumferential direction groove and a width direction groove at the point where the two grooves cross each other. According to <FIG>, only a small portion of the device is positioned between the side walls of either groove, and most is positioned at the intersection of the grooves. This means that the device blocks water flow along both intersecting grooves. In contrast, the device of the present invention does not block the water flow so much. By providing that at least half of the device is positioned between the side walls of the groove in a plan view of the tread, water drainage is improved because less of the intersection between two grooves is blocked.

In addition, during cornering, for example, it can be desirable for snow to be diverted into circumferential grooves from intersecting grooves to increase the amount of snow trapped and therefore snow-snow grip. Since the device of <CIT> blocks most of the intersection point, the amount of snow that can be diverted will be limited. In contrast, in the present invention, the device, or snow trapped by the device in the groove, can divert more snow into an intersecting groove at the intersection point, thereby improving grip on snow.

Alternatively, in the present invention, the feature that the snow trapping device extends at most halfway across the area of the groove may be provided. This feature provides improved water drainage in comparison to the prior art, for the following reasons. In <CIT>, the device extends more than halfway across the area of the groove from the bottom wall of the groove. This means the device provides a large blocking effect on water flowing in the groove, which reduces drainage. In contrast, by the snow trapping device extending at most <NUM>% of the way across the area of the groove, the device does not block so much of the area of the groove, which improves water drainage.

When the snow trapping device passes through the contact patch of the tyre, the parts which overlap are joined to or in contact with each other so that the passageway is formed between the joining or contact point and the bottom wall of the groove. In this way, an "outer" joining or contact point may be formed.

The joining or contact point may be formed at the apex of the snow trapping device. Preferably, a sipe is provided at the contact point which allows the parts to contact each other. The sipe opens when the snow trapping device is outside the contact patch, and closes when the snow trapping device enters the contact patch.

The sipe may be at the apex of the snow trapping device.

Alternatively, the parts which overlap may be joined to each other by being integrally formed at the joining point.

Preferably, the parts which overlap are joined to each other so that a joining point is formed between the passageway and the bottom wall of the groove. In this way, an "inner" joining point may be formed. To achieve this, the parts may be integrally formed at the "inner" contact point.

It is preferable that the parts of the device which overlap in the groove longitudinal direction are integrally formed.

Preferably, the parts of the device which overlap in the groove longitudinal direction extend along the groove longitudinal direction from the same start point, and preferably to the same end point.

The passageway comprises a hole in the device.

Preferably, a maximum dimension of the hole orthogonal to the groove longitudinal direction is less than half the depth of the snow trapping device. For example, a maximum dimension of the hole may be preferably less than <NUM>, when for example the depth of the snow trapping device is <NUM> and, for example, the depth of the groove is <NUM>. This helps to prevent snow passing through the hole.

The hole may be circular in cross-section.

The passageway comprises a sipe. In the present specification, a sipe is a groove that closes when it passes through the contact patch of the tyre.

According to the invention, the sipe is formed outside the hole in a tyre radial direction, and adjoins the hole. The sipe helps to simplify the manufacturing process by allowing the hole to be formed more easily during moulding of the tyre.

Preferably, in tread plan view, the passageway is substantially parallel with the groove longitudinal direction. Preferably, in a cross-sectional view along the groove longitudinal direction, the passageway is substantially parallel with the groove longitudinal direction. When the passageway is substantially parallel with the groove longitudinal direction in these two views, the passageway follows the flow streamline, which reduces resistance to flow.

Preferably, the passageway comprises a hole formed in the second surface. Preferably, the passageway comprises a hole formed the first surface.

The passageway may have a substantially constant cross-sectional area along its length.

Preferably, the snow trapping device is attached to a bottom wall and a side wall of the groove.

In one aspect of the present invention, the snow trapping device is attached to both a bottom wall and a side wall of the groove.

The fact that the snow trapping device is attached to both a bottom wall and a side wall of the groove means that the device is securely attached and is less likely to become detached from the groove than in the prior art. For example, in <CIT> the protrusions are only attached to the bottom wall of the groove.

Preferably, the snow trapping device is attached to both side walls of the groove.

Preferably, the second surface is inclined by less than <NUM>°, more preferably less than <NUM>°, with respect to the bottom wall of the groove. This avoids abrupt changes of direction of the water flow to provide a smooth flow.

Preferably, the second surface directs water flowing from the second side outwards in a tyre radial direction.

Preferably, the second (inclined) surface directs water flowing from the second side away from the bottom wall of the groove.

Preferably, at least half of the first (snow trapping) surface of the device (which may be in more than one part) when viewed along the groove width direction does not face outwards in the tyre radial direction. This means the snow is not directed outwards in the tyre radial direction and is trapped more effectively.

It is preferable that the apex of the snow trapping device extends from one side wall to the other at a constant height.

Preferably, the first (snow trapping) surface extends in a direction which is substantially parallel to the groove width direction. This helps to trap snow more effectively.

Preferably, the first (snow trapping) surface extends at a right angle to the bottom wall and/or a side wall of the groove. This helps to trap snow more effectively.

Preferably, the first surface is planar.

Preferably, the first (snow trapping) surface which is planar is normal to the groove longitudinal direction.

Preferably, the second surface is planar.

Preferably, the groove is a width direction groove. Here, "width direction groove" means the groove extends in the width direction, but does not need to extend exactly parallel to the width direction.

When the groove is a width direction groove, the snow trapping device improves grip during cornering, when the snow tries to slide in the tyre width direction.

Preferably, the groove is provided in the tyre shoulder region. "Tyre shoulder region" means the region between the tread end and a point halfway to the tyre equatorial plane from the tread end.

Preferably, the tyre is a pneumatic tyre. Preferably, the tyre is a snow tyre or an allseason tyre. Preferably, in a plan view of the tread, the tyre has a V-shaped groove, and the snow trapping device is located in the V-shaped groove.

Preferably, the first side is the outside in the tyre width direction. Hence the second side is the inside in the tyre width direction. "Outside" means outside with respect to the tyre equatorial plane.

When the first side is the outside in the tyre width direction, and hence the second side is the inside in the tyre width direction, the second surface allows water to flow smoothly round the snow trapping device towards the outside with respect to the tyre equatorial plane. This is the predominant flow direction of water drainage in the width direction grooves.

Preferably, the depth of the snow trapping device is at least <NUM>% or at least <NUM>% of the depth of the groove. Preferably, when viewed in the groove longitudinal direction, the snow trapping device occupies at least <NUM>% or at least <NUM>% of the area of the groove. With these two features, a minimum level of snow trapping can be achieved.

Preferably, when viewed in the groove longitudinal direction, the device occupies at most <NUM>% of the area of the groove, more preferably at most <NUM>%, more preferably at most <NUM>%.

Preferably, when viewed in the groove longitudinal direction, the device extends at most halfway across the area of the groove from the bottom wall of the groove. In <CIT>, the device extends more than halfway across the area of the groove from the bottom wall of the groove. This means the device provides a large blocking effect on water flowing in the groove, which reduces drainage. In the preferred embodiment of the present invention, in contrast, by the snow trapping device extending at most <NUM>% of the way across the area of the groove, the device does not block so much of the area of the groove, which improves water drainage.

More preferably, the device extends across at most at most <NUM>% of the way across the area of the groove from the bottom wall of the groove, more preferably at most <NUM>%.

According to the invention, the depth of the device is at most <NUM>% of the depth of the groove, mere preferably at most <NUM>%, more preferably at most <NUM>%.

When the device occupies or extends across less of the area of the groove in this way, the device provides less hindrance to the flow of water along the groove. Also, restricting the depth of the device helps to improve fatigue resistance and wear resistance. This is because the device is less likely to contact the road surface during running.

Preferably, a maximum dimension of the passageway orthogonal to the groove longitudinal direction is less than half the depth of the snow trapping device. For example, a maximum dimension of the passageway may be preferably less than <NUM>, when for example the depth of the snow trapping device is <NUM> and, for example, the depth of the groove is <NUM>. This helps to prevent snow passing through the passageway.

A preferred embodiment of the present invention will now be described, purely by way of example, with reference to the drawings in which:.

Referring to <FIG>, a portion of a tyre tread <NUM> is shown. The tread <NUM> has a groove (lug) <NUM> having a snow trapping device in the form of a dam <NUM> in it. In the present embodiment, the snow trapping device <NUM> is adjacent to, and attached to, a bottom wall <NUM> of the groove <NUM>, as well as being adjacent to and attached to a left-hand side wall <NUM> and a right-hand side wall <NUM> of the groove <NUM>.

The groove <NUM> and snow trapping device <NUM> are shown when they are not in the contact patch of the tyre.

The dam <NUM> has a first, snow trapping surface <NUM> facing a first side in the groove longitudinal direction. In <FIG>, the first side of the dam <NUM> is towards the top of <FIG>. The first, snow trapping surface <NUM> is configured to trap snow flowing from the first side in the groove longitudinal direction.

The dam <NUM> has a second, inclined surface <NUM> facing a second side in the groove longitudinal direction which is opposite to the first side. In <FIG>, the second side of the dam <NUM> is towards the bottom of <FIG>. The second, inclined surface <NUM> is inclined so as to direct water flowing from the second side away from the wall to which the snow trapping device is adjacent. In the present embodiment, the surface <NUM> is inclined with respect to the bottom wall <NUM> of the groove <NUM>, and directs the flow of water away from the bottom wall <NUM>. The surface <NUM> does not direct the flow of water away from the side walls <NUM> and <NUM> of the groove <NUM>.

It can be seen from <FIG> that the dam <NUM> has a left-hand part <NUM> and a right-hand part <NUM>. In the present embodiment, the parts <NUM> and <NUM> are integrally formed, but this is not essential. In <FIG>, the parts <NUM> and <NUM> are divided by a dotted line. The parts <NUM> and <NUM> overlap along the groove longitudinal direction so as to form a passageway <NUM> for water through the dam <NUM> in the groove longitudinal direction.

It is also shown in <FIG> that the whole of the dam <NUM> is positioned between the side walls <NUM> and <NUM> of the groove <NUM>.

In the present embodiment, the passageway <NUM> comprises a hole <NUM> and a sipe <NUM> which pass through the middle of the dam <NUM> in the groove width direction. The hole <NUM> adjoins the sipe <NUM>, and the hole <NUM> is nearer to the bottom wall <NUM> of the groove <NUM> than the sipe <NUM>. The hole <NUM> passes through the inclined surface <NUM> and the snow trapping surface <NUM>, and the axis of the hole <NUM> is parallel to the groove longitudinal direction. The sipe <NUM> also passes through the inclined surface <NUM> and the snow trapping surface <NUM>. The sipe <NUM> may simplify the manufacturing process by allowing the hole <NUM> to be formed more easily during moulding of the tyre. The sipe <NUM> is sized to close when it passes through the contact patch of the tyre, which prevents loss of flow rate. This closing is due to the block barrelling effect. At that time, the passageway <NUM> consists of just the hole <NUM>.

In particular, when the dam <NUM> passes through the contact patch of the tyre, the sipe <NUM> closes so that the parts <NUM> and <NUM> contact each other. This means that the passageway <NUM> consists of just the hole <NUM>, which is formed between the contact point and the bottom wall <NUM>.

The snow trapping surface <NUM> is planar, with the plane being normal to the groove longitudinal direction. This provides a blunt end of the dam <NUM> with which to trap snow. The surface <NUM> extends from the bottom wall <NUM> of the groove <NUM>, and also, in the present embodiment, from the left side wall <NUM> to the right side wall <NUM>.

The inclined surface <NUM> is planar and is inclined with respect to the bottom wall <NUM> of the groove <NUM>. The surface <NUM> acts as ramp to lift water up and over the dam <NUM> in a smooth flow. The angle of inclination of the surface <NUM> is preferably less than <NUM>°, more preferably less than <NUM>°, to avoid abrupt changes of direction of the water flow and to provide a smooth flow.

The passageway <NUM> allows water to flow through the dam <NUM> and acts to reduce flow separation and recirculation downstream of the dam <NUM> (in particular, downstream of the snow trapping surface <NUM>).

Referring to <FIG>, the tyre is a snow tyre with several sipes provided in each tread block. The tyre has a configuration of V-shaped grooves characteristic of a unidirectional tyre. The angle of the grooves making up the V shape, with respect to the tyre width direction, changes from small to large from the shoulder region to the centre region of the tyre. Hence the angle is larger near the tyre equatorial plane.

It can be seen from the tread plan view in <FIG> that the dam <NUM> is positioned approximately in the middle in the groove longitudinal direction of the groove section in which it is located. The groove section extends from the tread end to the intersection with a groove (circumferential groove <NUM>) running in the tyre circumferential direction. This groove section has a relatively small angle with respect to the tyre width direction. Therefore, snow slides particularly in this groove section during cornering. The contact patch <NUM> is also shown in <FIG> with a dotted line.

In the present embodiment, the dam <NUM> is provided only in the shoulder regions of the tyre, and only in tyre width direction grooves. However, this is not essential, and the dam <NUM> may be provided elsewhere in addition or alternatively, possibly in grooves other than tyre width direction grooves.

Referring again to <FIG>, the cross-sectional view along line A-A' shows the inside of the dam <NUM>. The hole <NUM> is shown, but the sipe <NUM> is not. DG denotes the depth of the groove <NUM>, and DD the depth of the dam <NUM>. The depth DD of the dam <NUM> is, in the present embodiment, about <NUM>% of the depth DG of the groove <NUM>. Accordingly, in the present embodiment, when viewed in the groove longitudinal direction, the dam <NUM> extends about a quarter of the way across the area of the groove <NUM> from the bottom wall <NUM>. In the present embodiment, the dam <NUM> occupies about <NUM>% of the volume of the groove section. As shown, the dam <NUM> forms a right-angled triangle in cross-section.

<FIG> illustrates schematically the snow performance of the tyre of the preferred embodiment, in comparison to a tyre without a snow trapping device.

In the upper view of <FIG>, snow flowing along the groove <NUM> from right to left encounters the dam <NUM>. The depth of the dam <NUM> is less than the depth of the groove <NUM>. The lower layer of snow encounters the snow trapping surface <NUM> which prevents the snow flowing any further. The upper layer of snow does not encounter the surface <NUM>, but nevertheless its flow is slowed because of the shear force from the lower layer of snow which has been trapped by surface <NUM>.

In the lower view of <FIG>, in contrast, the snow can flow unimpeded along the groove.

<FIG> illustrates schematically the wet performance of the tyre of the preferred embodiment.

In <FIG>, water flowing along the groove <NUM> from left to right encounters the dam <NUM> and in particular the inclined surface <NUM>. The surface <NUM> directs the flow upwards and away from the bottom wall <NUM> of the groove <NUM>. Some of the water then flows through the hole <NUM> parallel to the groove longitudinal direction. The majority of the water continues up the inclined surface <NUM> and over the top of the dam <NUM> and then down towards the bottom wall <NUM> of the groove <NUM>. A recirculation region <NUM> is shown downstream of the snow trapping surface <NUM>. The flows of water meet in this recirculation region <NUM>, and the flow which has passed through the hole <NUM> reduces the size of the recirculation region in comparison to the case where there is no flow through the dam <NUM>. This reduces flow losses and improves water drainage from the tyre.

Computer simulations were carried out to model the snow and wet performance of the tyre according to the preferred embodiment of the present invention but without the passageway <NUM>. The simulations for the snow performance modelled the tyre turning <NUM>° during cornering. The results of the simulations for the snow performance are shown in <FIG>.

<FIG> shows the snow density on the tyre tread of a tyre without a snow trapping device, and <FIG> shows the snow density on the tyre tread of a tyre with a snow trapping device according to the embodiment of <FIG>.

In <FIG>, contour lines join points of equal snow density. In <FIG>, the area inside the dashed boxes contains the dams <NUM>, and these areas have a low density where the dams <NUM> are, but have areas of higher snow density around the dams <NUM> than the corresponding areas in <FIG>. In <FIG>, the shape of the contour lines shows that the snow density is high in the circumferential groove <NUM> as well as in the adjacent tyre width direction groove. By comparing <FIG>, it can be seen that the snow density in the circumferential groove <NUM> in <FIG> is higher than in the corresponding area in <FIG>.

The results show an increase of about <NUM>% in lateral force when the dams <NUM> are present in comparison to the case where they are not.

The results also showed an increase in the amount of snow flowing into the circumferential direction grooves intersecting the groove section in which the dam <NUM> is located. This contributed to an improvement in grip in the snow. The flow into these circumferential grooves has the following mechanism. During cornering, snow in the contact patch is subject to a force with a component in the width direction of the tyre but also with a component in the circumferential direction. (During traction, the circumferential component is upwards in <FIG>, and left to right in <FIG>). The component in the circumferential direction causes the snow to flow towards the groove section in which the dam <NUM> is located. However, the snow trapped by the dam <NUM> causes the snow from the contact patch to be diverted into the circumferential groove <NUM>. This increases the snow density in the circumferential groove <NUM> and the snow gripping effect.

As for wet performance, the simulations did not show any significant change in performance due to the presence of the dams <NUM>. However, the simulations were carried out with the assumption that the flow was both inviscid and laminar, because of the technical limitations of the simulation equipment. In reality, it is known that the recirculation region downstream of the dam <NUM> will be mainly due to viscous and turbulence effects. Therefore, it is to be expected that, in reality, the wet performance will be significantly worse than the simulations show, and also that the presence of the passageway <NUM> will beneficial to counteract the recirculation.

An explanation of the preferred dimensions of the features of the snow trapping device (dam) <NUM> will be made with reference to <FIG>. The dimensions are as follows:.

The dimensions DD and L mentioned above were used in the simulations, but WS and WH were not (because no passageway <NUM> was modelled in the simulations).

Claim 1:
A tyre comprising:
a tread (<NUM>) with a groove (<NUM>), the groove (<NUM>) having a snow trapping device (<NUM>) in it attached to a bottom wall (<NUM>) of the groove (<NUM>), the snow trapping device (<NUM>) having a first surface (<NUM>) facing a first side in the groove longitudinal direction, the first surface (<NUM>) being configured to trap snow flowing from the first side in the groove longitudinal direction, and the device (<NUM>) having a second surface (<NUM>) facing a second side in the groove longitudinal direction which is opposite to the first side, the second surface (<NUM>) being inclined so as to direct water flowing from the second side away from the bottom wall (<NUM>) of the groove (<NUM>),
wherein parts (<NUM>, <NUM>) of the device (<NUM>) overlap along the groove longitudinal direction so as to form a passageway (<NUM>) for water through the device (<NUM>) in the groove longitudinal direction,
wherein, in a plan view of the tread (<NUM>), the whole of the device (<NUM>) is positioned between the side walls (<NUM>, <NUM>) of the groove (<NUM>),
wherein, when the snow trapping device (<NUM>) passes through the contact patch of the tyre, the parts (<NUM>, <NUM>) which overlap are joined to or in contact with each other so that the passageway (<NUM>) is formed between a joining or contact point and the bottom wall (<NUM>) of the groove (<NUM>),
characterized in that the passageway (<NUM>) comprises a sipe (<NUM>), and a hole (<NUM>) in the device (<NUM>), the sipe (<NUM>) being formed outside the hole (<NUM>) in a tyre radial direction and adjoining the hole (<NUM>), and
wherein the depth of the snow trapping device (<NUM>) is at most <NUM>% of the depth of the groove (<NUM>), wherein the depth is measured from the bottom wall (<NUM>) of the groove (<NUM>).