BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a boot whose upper is mounted on a multi-layered bottom assembly having a wearable layer on which an intermediate layer, or “core layer,” having predetermined characteristics of rigidity in torsion and bending, is directly fixed. More particularly, the invention relates to an intercalary layer which makes it possible to dampen the shocks between the upper and the “core layer.”

[0003] 2. Description of Background and Relevant Information

[0004] Boots of the aforementioned type are known, for example, from the published patent applications EP 0 887 027, EP 0 748 596, WO 96/04811, as well as from patent document EP 0 548 475. In these boots, the bottom assembly, as opposed to the upper, includes all of the elements that constitute the bottom of the boot and are positioned between the foot and the ground.

[0005] According to these documents, the bottom assembly of the boot has a plurality of layers, including a wearable layer adapted to come into contact with the ground, and on which an intermediate layer, or “core layer,” provided with characteristics of torsional rigidity and bending and forming the bottom of these boots, is directly fixed. Complementarily, an upper layer, referred to as the comfort layer, is placed on the core layer and it functions to dampen the shocks upon each impact of the bottom assembly on the ground, and especially during the passive phase of the foot movement in which the vertical component of the ground reaction forces can reach values that are equal to several times the user's body weight, during a very brief period of time on the order of 20-30 milliseconds.

[0006] For these reasons, the upper comfort layer of these boots, and the generality of known sports boots, except those adapted for sprinting, is characterized by a substantial thickness that is measured in multiple millimeters, and by its ability to deform elastically, especially to compress itself. Thus, the constituent material of the comfort layer is generally characterized by a Shore A hardness that is almost always greater than 35. The treatment of the shock from the impact is therefore generally achieved due to the resistance and great elastic deformation capacity of this comfort layer which, in fact, offers a certain braking distance to bring the foot vertical positioning speed, which is on the order of 1 meter/second, to zero. Moreover, since the comfort layer is inserted between the foot and the core layer, risks of interference of this core layer with comfort are avoided, which is not the case with most bottom assemblies where the comfort layer is located between the wearable layer and the core layer.

[0007] More specifically, the boots described in the documents EP 0 548 475, EP 0 887 027, and WO 96/04811 include bottom assemblies that successively have a wearable layer, a core layer, and a shock-absorbing comfort layer over almost the entire zone corresponding to the plantar surface with, at least for the shock-absorbing comfort layer, a decreasing variation in thickness from the heel to the tip of the bottom assembly. On the other hand, according to the document EP 0 748 596, the shock-absorbing comfort layer is limited to the heel zone and is housed in a recess provided in the core layer.

[0008] These different arrangements and distributions of the shock-absorbing layer between the heel and the tip of the bottom assembly aim at providing a shock absorption, through elastic deformation, localized only in the areas where the shocks resulting from the contact with the ground are the most intense and the most frequent. Thus, a reliable support and a certain stability over the largest possible surface of the bottom assembly are preserved, which is favorable to the support of the foot during movement thereof, especially when shock absorption ceases during the propulsion phase.

[0009] By way of example, these multi-layered bottom assemblies having a variable distribution of the comfort layer, in correspondence with the plantar surface zone are capable of providing, through elastic deformation of a certain amplitude of their comfort layer, a dampening of the intensity of the shocks transmitted to the foot on impact, which is on the order of 30-50% at the heel, which satisfies the notion of comfort, and on the order of 10% on the tip of the bottom assembly, which satisfies the notion of performance-efficiency. In fact, these bottom assemblies have a resonance frequency that can vary between the heel and forefoot zones, as a function of the most frequent localization of the most intense shocks.

[0010] The aforementioned multi-layered bottom assemblies are therefore generally satisfactory for the shock treatment, because they offer a good compromise which provides comfort, load distribution and stability during propulsion.

[0011] However, due precisely to the variation in their resonance frequency, from the heel to the forefoot, they are capable of amplifying an impulse, such as a shock applied to a given area, instead of absorbing it, if that impulse biases them at a frequency that is close to their resonance frequency in that area. A direct consequence from this type of vibrating phenomena is the propagation of shockwaves in the user's foot and the occurrence of micro-vibrations in the foot/boot interface, especially on impact of the heel on the ground at the end of the braking course, and during the propulsion phase at the forefoot beneath the metatarsal heads where pressure increases substantially.

[0012] To dampen these vibrating phenomena that disturb the proprioceptive system of the boot user and cause micro-traumas, additional shock-absorbing elements are often introduced into the boot a posteriori, and are arranged between its bottom assembly and the user's foot. By way of example, one can cite the internal soles and heel pieces that are often commercially available as boot accessories for treating “the shockwave.” In any event, insofar as these soles and heel pieces are satisfactory in the shock wave treatment, they have proven to be a hybrid solution. Indeed, on the one hand, they modify the initial fitting volume of the boot, as well as the foot seating, particularly in the rear-to-front direction, especially with respect to the heel pieces, and, on the other hand, they provide the boot with a heterogeneous character.

SUMMARY OF THE INVENTION

[0013] An object of the present invention is to overcome the various disadvantages of the aforementioned boots for the shockwave treatment, and especially to absorb the micro-vibrations that can occur by resonance effect, while retaining the advantages provided by the multi-layered bottom assemblies in which the core layer is fixed directly on the wearable layer.

[0014] To this end, a particular object of the invention is precisely not to substantially increase the thickness of the bottom assembly, despite the use, in the foot/bottom assembly interface, of a shock-absorbing layer adapted to serve as a dynamic screen, due to its “elastic deformation” capacity, for the micro-vibrations which are characterized by a very quick periodical displacement of very small amplitude, and which can occur by resonance effect during the shock from the impact, especially when shock absorption ceases.

[0015] Another object is to respect the natural foot movement, such that this shock-absorbing layer does not require any substantial expenditure of supplemental energy to deform the bottom assembly when the user's foot bends, during the propulsion phase in the area of the forefoot, for example, and does not alter the stability.

[0016] Yet another object of the invention is to propose a homogeneous multi-layered bottom assembly structure which, provided with a layer for absorbing the micro-vibrations, can be variable in order to meet the various needs for shock absorption in amplitude and frequency, according to the intended use of the boot, for example, a foot-race, walking, hiking, team sports such as soccer, rugby, etc. In this sense, the dampening of the micro-vibrations is generally treated between the bottom assembly and the boot upper, or only over a predetermined area of the bottom assembly.

[0017] To achieve these objects, the boot, whose upper is mounted on a multi-layered bottom assembly having a wearable sole on which a core layer is fixed directly, includes a specific shock-absorbing layer for treating the micro-vibrations, in the form of a thin elastic membrane with a thickness of less than 2 millimeters, fixed on the core layer so as to function between the latter and the boot upper. This thin shock-absorbing layer or elastic membrane includes a visco-elastic material having a Shore A hardness on the order of 20-30, such that, due to its elastic deformation properties, it behaves in the manner of a dynamic screen that is particularly well adapted for dampening the micro-vibrations that are characterized by a displacement of very small amplitude and a high frequency. This integration of the elastic membrane into the multi-layered bottom assembly allows a homogeneous construction of the latter and, thus, of the boot, without causing much harm to the stability, since it only slightly increases the thickness of the bottom assembly, and therefore the relative height of the plantar surface relative to the ground.

[0018] According to an interesting embodiment, the shock-absorbing layer constituted by the elastic membrane has, on the side facing the core layer, a discontinuous surface having a multitude of points of contact that are determined by the intersecting points of a multitude of cavities open on the side facing the core layer. In this way, a portion of the energy is further dissipated-absorbed by the elastic membrane, perpendicular to the micro-vibrations.

[0019] According to one embodiment, the boot, whose bottom assembly is provided with an elastic membrane for absorbing the micro-vibrations fixed directly on the core layer, and a core layer is obtained, in the heel zone, with a vertical extension that rises along at least a portion of the boot upper, such extension forming the stiffener thereof. Advantageously, the shock-absorbing elastic membrane which is fixed on the core layer, in this example of construction, is provided to extend over the entire internal surface of the stiffener in a manner so as to be inserted completely between the upper and the core layer. The shock-absorbing elastic membrane can be associated with the core layer, fixed directly on the wearable layer, over the entire zone corresponding to the plantar surface, or only over a more restricted zone such as that of the heel or forefoot.

[0020] More specifically, according to the intended use of the boot, such as hiking, for example, the multi-layered structure of the bottom assembly can have an elastic membrane for dampening the micro-vibrations only in the forefoot zone, and a shock-absorbing layer at the heel that can be deformed-compressed over a certain distance to bring the foot vertical positioning speed to zero by dampening the intensity of the shock from the impact to the maximum. Thus designed, the boot provides the user, on the one hand, with good shock absorption at the heel, which is absolutely necessary when walking down a slope, for example, and, on the other hand, an excellent support without micro-vibrations beneath the forefoot, which contributes to stability and efficiency.

[0021] According to an advantageous embodiment of such a boot, the core layer is divided, in the heel zone and from a common attachment point located in the vicinity of the forefoot zone, into two elastic blades that are spaced apart in the direction of the bottom assembly thickness.

[0022] These two elastic blades extending from the core layer thus constitute either a shock-absorbing structure complementary to the shock-absorbing comfort layer, or a shock-absorbing structure capable of replacing this shock-absorbing layer. Preferably, an elastically deformable material is inserted between the two elastic blades of the core layer so as to provide the bottom assembly with a more homogeneous configuration and/or to increase the resistance to deformation provided by the blades.

[0023] Furthermore, according to an alternative embodiment of the core layer, the latter is obtained with at least one lateral and vertical extension which rises in the direction of the instep girth where it is connected to a device for tightening and holding the foot, this extension thereby constituting the equivalent of a tightening flap. The foot is therefore flattened against the elastic membrane that is fixed on the core layer, by direct action on the tightening flap coming from the core layer, which prevents any loss of the tightening force through the upper. The solution, which includes providing the core layer with two lateral and vertical extensions each rising along a side of the boot upper, in the direction of the instep girth where they are mutually connected to the tightening device, is preferred. Indeed, it provides a better foot retention, a more energetic tightening, and more stability, because the tightening force on the user's foot is symmetrically recovered with respect to the longitudinal axis of the bottom assembly and beginning at the core layer.

[0024] According to another embodiment of the invention, a shock-absorbing layer is fixed on the elastic membrane which is thus “sandwiched” between this comfort layer and the core layer. In such a structure of the multi-layered bottom assembly, the following can be successively identified, from the ground toward the user's foot:

[0025] a wearable layer that has predetermined properties of flexibility, adherence, and abrasion resistance capable of allowing good foot movement, good grip on the ground, as well as good wear resistance;

[0026] a core layer which, arranged directly on the wearable layer, has controlled properties of torsional rigidity and bending in order to simultaneously ensure the distribution of the shocks recorded by the wearable layer and their transfer toward the foot, while allowing good movement of the latter;

[0027] an elastic membrane which, contiguous to the core layer, is provided with dimensional and mechanical characteristics such as thinness, of less than 2 millimeters, combined with a high elasticity and a low Shore A hardness, on the order of 20-30, in order to dampen the micro-vibrations that are characterized by a displacement of very small amplitude and a high frequency; and

[0028] a shock-absorbing comfort layer which, arranged on the elastic membrane, has a thickness that is measured in multiple millimeters, on the one hand, and an elastically compressible constituent material having a Shore A hardness at least equal to 35, on the other hand. The object of the comfort layer is to provide, by deforming itself, a certain braking distance used to bring the vertical foot positioning speed to zero on impact, or a zero value, simultaneously with a maximum dampening of the intensity of the shock from the impact.