Patent Application
20180244111
This invention relates generally to a tire tread. More specifically, this invention relates to tire treads for heavy trucks, in particular tire treads for free-rolling wheels thereof (so called steer positions and trailer positions), especially tire treads for steer positions.
Tire treads generally extend about the outer circumference of a tire to operate as the intermediary between the tire and a surface upon which it travels (the operating surface). Contact between the tire tread and the operating surface occurs along a footprint of the tire. Tire treads provide grip to resist tire slip that may result during tire acceleration, braking, and/or cornering. Tire treads may also include tread elements, such as ribs or lugs, and tread features, such as grooves and sipes, each of which may assist in providing target tire performance when a tire is operating under particular conditions. The tread pattern generally includes repetitions of identical sub-patterns, the length of such sub-pattern being referred to as the “pitch”. Each rib (seen in isolation) may have its own pitch and this pitch may be different from the pitch of the full tread including all tread elements and features.
One common problem faced by tire manufacturers is how to increase the wear resistance.
A solution is to increase the ratio of the tread surface being in contact with the operating surface. This ratio is known as the Contact Surface Ratio (CSR). Increasing the CSR is known to be beneficial for wear life. However, increasing the CSR is also known for harming the wet braking adherence performance of the tread. Wet braking adherence performance is a very important element that must not only be obtained with an unworn tread but also throughout the useful life of the tread as it progressively wears out.
Irregular wear is also a great concern as it can provoke vibrations becoming sensible by the driver in the steering wheel or produce a poor looking wear pattern, both of which leading to the tire being often removed from service at an early stage of its wear life.
Therefore, to further increase the wear performance of tires it may be desirous to propose a novel way to design a tire tread that would not result in compromising its wet braking performance or its resistance to irregular wear.
The invention provides for a heavy truck tire tread having a longitudinal direction, a lateral direction and a thickness direction, said tread having a ground-engaging contact surface and comprising at least four main longitudinal grooves defining at least five main longitudinal ribs, the at least four main longitudinal grooves comprising at least one and not more than three open grooves and at least two partially hidden grooves, each of said at least two partially hidden grooves comprising openings to the ground-engaging contact surface and an undersurface channel that is connected to the openings by ducts extending substantially in the thickness direction, longitudinal sipes extending substantially along the longitudinal direction connecting successive openings to the channel, said tread comprising at least two non-shoulder main ribs, said at least two non-shoulder main ribs comprising lateral sipes extending in the lateral direction, the tread comprising at least 120 of said lateral sipes, wherein for each partially hidden groove:
Preferably, the total surface area of all openings is less than 100 cm2.
Preferably, the average section area of all ducts having a mean section area of at least 5 mm2 is less than 100 mm2.
Preferably, the ratio between an average height of said lateral sipes and a tread depth is greater than 0.33.
Preferably, the ratio between the average height of said lateral sipes and the tread depth is greater than 0.5 and wherein the tread comprises at least 300 of said lateral sipes.
Preferably, the ratio between the average section area of all said ducts having a mean section area of at least 5 mm2 and the average section area of the longitudinal channel is less than 1.
Preferably, each partially hidden groove comprises at least 100 openings to the ground-engaging contact surface (more preferably, at least 200).
Preferably, said lateral sipes are connected to the ducts.
Preferably, each of said ducts has at least one lateral edge sipes.
Preferably, said longitudinal sipes are undulated along the longitudinal direction of the tread.
Preferably, said lateral sipes are undulated along the lateral direction of the tread.
Preferably, said lateral and longitudinal sipes are undulated along the thickness direction of the tread.
Preferably, the tread pattern is directional.
Preferably, said lateral sipes are inclined relative to the lateral direction.
Preferably, said lateral sipes are inclined relative to the thickness direction.
The invention also provides for a heavy truck tire comprising such a tread.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more detailed descriptions of a particular embodiment of the invention.
Reference will now be made in detail to an embodiment of the invention, example of which is illustrated in the drawings. This example is provided by way of explanation of the invention.
As shown in
The tread 2 has a contact surface CS for engaging the operating surface on which the tire is rolling and the tire has sidewalls SW.
The tread has a longitudinal direction (also referred to as the circumferential direction), a lateral direction (also referred to as the axial or transverse direction) and a thickness direction (also referred to as the tread depth direction).
The tread has four main longitudinal grooves 3, 4, 5 and 6 going continuously around the circumference of the tire. Between tread shoulders 7 and 8, the four main longitudinal grooves define five main ribs 9, 10, 11, 12 and 13.
As better visible form the section view of
The main grooves 3 and 6 closest to the tread shoulders will now be referred to as the “shoulder grooves”. The main grooves 4 and 5 located in the center of the tread will now be referred to as the “intermediate grooves”.
The main ribs 9 and 13 between shoulders and shoulder grooves will now be referred to as the “shoulder ribs”. The main ribs 10 and 12 between shoulder grooves and intermediate grooves will now be referred to as the “intermediate ribs”. The rib 11 between the two intermediate grooves 4 and 5 will now be referred to as the “center rib”. In a tread having six main ribs (and not five as in the described embodiment), there would be two center ribs, one on either side of a center groove.
As better visible on the combination of
According to the invention, the tread has at least one and not more than three open grooves and at least two partially hidden grooves.
In an embodiment of the invention and as represented in the drawings, the two shoulder grooves 3 and 6 are open grooves and the two intermediate grooves 4 and 5 are partially hidden grooves.
In the partially hidden grooves 4 and 5, openings 41 and 51 in the contact surface CS connect respectively with undersurface channels 42 and 52 via ducts 43 extending in the thickness direction of the tread.
It is apparent especially from
In the embodiment of
The undersurface channels 42 and 52 are 5 mm wide and 7 mm high in average, their average section area being 31 mm2.
In this embodiment, the section area of the ducts is much smaller than the section area of the channels, the ratio between the section area of the ducts and the section area of the longitudinal channel is about 0.4. If the ducts have variable sections along their length and different sizes between, this ratio must be calculated using the average section area of those ducts having a mean section area of at least 5 mm2, excluding smaller ones from the average. Similarly if the channel has a variable section area along its length, it has to be averaged over its full length.
The drawings showing only one embodiment with cylindrical ducts, it is understood that ducts may have a different size or shape (the openings being for instance substantially rectangular with the longer side in the longitudinal direction) and the ducts may be in a different number. For instance, another embodiment of the invention would have a lower number of ducts, the ducts having a greater section area.
Longitudinal sipes 44 and 54 connect their respective channel and ducts to the contact surface CS as best visible from
The intermediate ribs 10 and 12 have lateral sipes 105 and 125 extending across them. Those sipes may be more or less high but preferably (as shown in dotted lines on
The ratio between the average height of said lateral sipes and the tread depth is about 0.65 in this embodiment. There are 120 lateral sipes for each intermediate rib in this embodiment.
As shown on
The center rib 11 also has similar lateral sipes 115 and in the same number as in an intermediate rib. Those sipes are not inclined relative to the lateral direction in order for the tread to keep a substantially symmetric pattern. The full tread has therefore a total of 360 lateral sipes.
The shoulder ribs 9 and 13 may have engravings 91 and 131. Those engravings are preferably very shallow to keep the shoulder ribs as solid as possible.
Narrow lateral edge sipes (so-called micro-sipes) 92, 93, 103 are molded along both edges of the shoulder ribs 9 and 13 and on the facing edges of the intermediate ribs 10 and 12. Similar lateral edge sipes 45 and 46 are connected to the ducts 43.
Starting from the contact surface CS, lateral sipes and micro-sipes may be inclined by a small angle from the tread thickness direction toward the entrance of the footprint (that is to say in the rotation direction of the tire, see arrows on the shoulders of the tread). This angle is between 5° and 25°, for instance 12°.
As visible on
As visible on the drawings, the tread pattern is directional, meaning that the tire has to be mounted in a given direction to perform consistently. The preferred rolling direction is generally indicated by arrows molded on the shoulders of the tread.
It should be understood from the foregoing description that various modifications and changes may be made to the embodiments of the present invention without departing from its true spirit. The foregoing description is provided for the purpose of illustration only and should not be construed in a limiting sense. Only the language of the following claims should limit the scope of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/US2015/048468 | Sep 2015 | US | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US16/46976 | 8/15/2016 | WO | 00 |
