This invention relates to a footwear sole and in particular a shoe sole, which sole comprises a system of liquid-filled compartments interconnected by flow-inhibiting passages.

Patent publication No. EP-170947-A1 describes a resilient support comprising a system of liquid-filled passages of the above-mentioned kind, and in said patent publication it is mentioned that such a support is suitable for shoe soles.

During the practical embodiment of a footwear sole based on such a system of interconnected liquid-filled compartments it has been found that a surprisingly good walking comfort is obtained with a footwear sole which is characterized in that the heel, arch and toe portions of the footwear sole each comprises a separate system of liquid-filled compartments interconnected by flow-inhibiting passa¬ ges and that the system of liquid-filled compartments in the toe portion as well as the system of liquid-filled compartments in the heel portion are connected to the system of liquid-filled compart¬ ments in the arch portion through passages which are adapted so as to produce a higher resistance to liquid flow towards the arch portion than away from same.

The present invention is based on the discovery that the heel and toe portion of a footwear sole are exposed to heavier load during walking than the arch portion, and that in order to prevent stepping through in the two first-mentioned portions of the sole it is necessary to establish a higher degree of liquid flow resistance from the toe or the heel portion towards the arch portion than in the opposite direction, and that the liquid flow in the latter direction should be as high as possible in order to allow the amount of liquid in e.g. the heel portion to be restored rapidly, when the load on the heel portion is relieved and is transferred to the toe portion through the arch portion. The same applies, when the load on the toe portion is relieved and transferred to the heel portion.

The passage between the heel or toe and arch portions, respectively, is preferably provided at the edge of the sole and preferably it

comprises a valve producing said asymmetric flow resistance. Valves of this kind are well known in the art.

Owing to its simple construction and to its considerable sturdiness a particularly preferred valve consists of a bar-shaped body to which are attached radially radiating soft brushes which are longer than the radius of the passage, the free ends of the brush pointing away from the arch portion of the sole.

By placing such a valve in each of the two said passages the brushes spread out when the pressure in the toe portion or on the heel portion increases, thus increasing the resistance to liquid flow towards the arch portion. However, when the pressure in the arch portion is caused to exceed the pressure in the heel portion or the toe portion the brushes are pressed against the bar-shaped body and in this position they produce only limited resistance to the liquid flow through the passages in question.

Preferably, the liquid in the compartments have a higher viscosity than water, but the compartments may also contain pure water or aqueous media of substantially the same viscosity as water. When a relatively viscous liquid is used in said compartments it preferably consists of 80% water and 20% propylene glycol.

The invention will now be described more in detail with reference to the accompanying drawing, wherein:

Figure 1 is a horizontal-sectional view through a shoe sole accor¬ ding to the invention,

Figure 2 is an axial-sectional view through a passage connecting the heel portion with the arch portion in the shoe sole shown in Figure 1, and with a valve located within the passage,

Figure 3 is a cross-sectional view of the passage shown in Figure 2 equipped with a valve under liquid flow from the arch portion towards the heel portion, and

Figure 4 is a cross-sectional view of the passage shown in Figure 2

equipped with a valve under liquid flow from heel portion towards the arch portion.

The shoe sole shown in Figure 1 comprises a heel portion 1, an arch portion 2 and a toe portion 3. Each of these portions comprises a number of liquid-filled compartments 4 which are interconnected by narrow passages 5. The liquid-filled compartments 4 of the heel portion 1 are connected to the liquid-filled compartments 4 of the arch portion 2 through a passage 6 located at the edge of the sole. Similarly, the liquid-filled compartments 4 of the toe portion 3 are connected to the liquid-filled compartments 4 of the arch portion 2 through a further passage 7. Passages 6 and 7 are equipped with valves (not shown), which produce a considerably higher resistance to the liquid flow away from the heel portion or the toe portion than from the arch portion towards the heel or toe portion.

The valve shown in Figures 2-4 consists of a bar-shaped body 10 placed centrally in the passage 6 and having fixed thereto a large number of radially radiating soft brushes 11 which are longer than the radius of the passage and with the brushes pointing towards the heel portion.

Figure 3 shows the position of the brushes during flow of liquid from the arch portion 2 towards the heel portion 1 and Figure 4 the position of brushes during liquid flow in the opposite direction. As will appear by comparing Figures 3 and 4, the brushes produce a much higher resistance to flow towards the arch portion 2 than away from same.