Cushion structure

Abstract

A cushioning structure effective to alleviate a blood stream trouble and loads on muscles and to prevent an outbreak of trouble caused by them such as economy-class syndrome and the like is provided. The structure includes an upper elastic member 11 composed of a three-dimensional net member formed by connecting a pair of ground knitted fabrics disposed apart from each other using connecting yarn, and a spring constant in the range of initial load during a pressurizing process is set in the range of 0.1 to 20 N/mm and, at the same time, during a restoring process, a spring constant after restoring to an amount of displacement of 20 mm or less, at the latest, to 2 mm, is set to be lower than the spring constant in the range of initial load during the aforementioned pressurizing process. As a result, when a person comes into contact with a cushioning member by a sitting movement or a standing movement, temporal set in fatigue (stroke) of about several millimeters to about ten and several millimeters is created, thereby improving a feeling of fitting (compatibility) which makes a person feel comfortable, and effectively alleviate a blood stream trouble and loads on muscles.

Description

TECHNICAL FIELD

[0001] The present invention relates to a cushioning structure including a three-dimensional net member, and especially to a cushioning structure suitable for manufacturing a seat structure and the like which reduces blood stream trouble or loads on muscles.

BACKGROUND ART

[0002] In recent years, a cushioning structure using a thin net member (three-dimensional net member) which is of a three-dimensional solid structure, can display high cushioning property, has a large number of pores, and is excellent in breathability has been known. Such a three-dimensional net member is built up its three-dimensional structure by connecting a pair of ground knitted fabrics disposed apart from each other with a plenty of connecting yarns, and excellent in breathability, body pressure dispersing property, and rebounding property.

[0003] In general, when the load bearing characteristic of a cushioning member is higher than the load bearing characteristic of the muscle, and a difference in shape between the cushioning member and the muscle is large, the muscle is much deformed by a reaction force from the cushioning member (mainly a force in the normal line direction in a case of rather hard cushioning member, and mainly a force in a shear direction in case of a cushion harder than the muscle but totally the hardness being on a soft side), thereby causing the muscle to be deformed largely, and pressed, which results in bias flow of blood or increase of loads on muscles. On the contrary, when the load bearing characteristic of a cushioning member is remarkably low compared with the load bearing characteristic of the muscle, the deformation of the muscle is restrained. However, though the amount of deformation of the cushioning member is large, since the amount of depression of the cushioning member is also large, mainly shear stress serves in play, which rather increases the loads on muscles. For instance, when soft polyurethane slab foam and viscoelastic polyurethane foam are used in piles, though considerably soft load bearing characteristic can be obtained, compared with the case of using other materials, since the amount of deformation as a cushioning member is large, it has a problem of increase of loads on muscles due to shear stress, as described above.

[0004] In recent years, especially in an aircraft, outbreak instances of a trouble so-called economy-class syndrome have been reported. A blood stream trouble caused by taking the same posture for a long time in sitting on a chair having a structure of supporting the femoral region strongly to prevent backside slipping is thought to contribute to this syndrome. The aircraft industry are looking forward to a proposal of a seat structure which can reduce the outbreak of such an economy-class syndrome.

[0005] The present invention is achieved in view of the above-described points, and the object thereof is to provide a cushioning structure effective to reduce blood stream trouble, loads on muscles, and to prevent the outbreak of the economy-class syndrome and the like including the outbreak of troubles owing thereto.

DISCLOSURE OF THE INVENTION

[0006] As a result of assiduous studies to solve the above-described problems, the present inventor paid attention that when the load bearing characteristic of a cushioning member (elastic member) which comes in contact with the muscles directly or indirectly is made close to the load bearing characteristic of people's muscle, the cushioning member deforms according to the shape of the muscle, which helps to restrain large deformation of the muscle without setting the load bearing characteristic of the cushioning member softer than necessary, and is effective to prevent blood stream trouble and the like. The present inventor also paid attention that deformation of muscles at a portion protruded by the bone is also reduced in the deformation, which is effective to prevent the blood stream trouble locally. The present inventor also paid attention that amount of the deformation can be reduced, as mentioned above, by using a three-dimensional net member which can display high cushioning property even if it is thin as a cushioning member (elastic member), and increase of loads on muscles due to a shear stress created by a large deformation when a soft cushioning member is used, and in an area of small displacement, a reaction force inputted from the cushioning member into the muscle can be made small by setting the load bearing characteristic to a further softer load bearing characteristic than that during the pressurizing process.

[0007] From these aforementioned points of view, the present inventor thought that not only a three-dimensional net member is used as a cushioning member (elastic member), but also by utilizing the hysteresis loss of its load bearing characteristic, the characteristic is made close to the load bearing characteristic of a person in the pressurizing process (go-process), and made to be a softer load bearing characteristic with a small reaction force after the amount of displacement reaches a predetermined point during the restoring process (return process), thereby movement of the body can be induced. The present inventor has accomplished the present invention by thinking that through this setting of the load bearing characteristic, when the cushioning member is touched at the time of a sitting movement or a standing movement, temporal set in fatigue (stroke) under loads in the range of about several millimeters to about ten and several millimeters is generated, and when a portion of a small area protruded by the bone among the haunches portion and the like which come into contact with the cushioning member contacts with the cushioning member, the cushioning member fits quickly with little sensing of the reaction force owing to this temporal set in fatigue under loads so that a feeling of fitting (compatibility) which makes a person comfortable can be improved, thereby, the blood stream trouble and the loads on muscles can be effectively reduced.

[0008] At the same time, the present inventor has also paid attention that when the amount of stroke is made small, and the load bearing characteristic in a small load area and a small displacement area until arriving at an equilibrium point of the load is set to be soft to make the above-described temporal set in fatigue (stroke) under loads in the range of several millimeters to ten and several millimeters, though it is effective to prevent blood stream trouble as described above, when a load more than predetermined is applied and the contact angle is increased, this temporal set in fatigue under loads is felt to be bottom touch. Accordingly, in the present invention, in order to prevent such a feeling of bottom touch, another elastic member which is high in linearity and high in a feeling of a spring is arranged in two tiers or in multi-tiers in series, or is arranged to be combined in parallel.

[0009] That is, the present invention described in claim 1 is to provide a cushioning structure including an elastic member composed of a three-dimensional net member formed by connecting a pair of ground knitted fabrics disposed apart from each other using connecting yarn, wherein, as a load bearing characteristic of the cushioning structure, a spring constant during a pressurizing process is set in the range of 0.1 to 10 N/mm and, at the same time, during a restoring process, a spring constant after restoring to an amount of displacement of 20 mm or less, at the latest, to 2 mm, is set to be lower than the spring constant in the aforementioned pressurizing process.

[0010] The present invention described in claim 2 is to provide the cushioning structure according to claim 1, wherein the spring constant in the aforementioned pressurizing process is set in the range of 0.1 to 5 N/mm.

[0011] The present invention described in claim 3 is to provide the cushioning structure according to claims 1 or 2, wherein the amount of hysteresis loss between the pressurizing process and the restoring process in the load bearing characteristic is in the range of 40 N or less.

[0012] The present invention described in claim 4 is to provide the cushioning structure according to any one of claim 1 to claim 3, wherein the elastic member composed of the three-dimensional net member is configured to have a small reaction force such that as a load bearing characteristic during the pressurizing process the three-dimensional net member with a board for press of 30 mm in diameter alone, a spring constant after restoring to an amount of displacement of 20 mm or less, at the latest, to 1 mm during the restoring process is lower than the spring constant during the pressurizing process in the aforementioned whole load bearing characteristic.

[0013] The present invention described in claim 5 is to provide the cushioning structure according to claim 4, wherein the aforementioned three-dimensional net member formed in a structure having a small reaction force has a thickness in the range of 5 to 30 mm.

[0014] The present invention described in claim 6 is to provide the cushioning structure according to claim 4 or claim 5, wherein the aforementioned three-dimensional net member formed in a structure having a small reaction force is provided with concave and convex portions at least on one surface, and the elasticity of the concave portion and that of the convex portion are different from each other.

[0015] The present invention described in claim 7 is to provide the cushioning structure according to claim 6, wherein the aforementioned three-dimensional net member formed in a structure having a small reaction force has a structure in which the aforementioned convex portion is formed substantially in an arch shaped cross section between adjacent concave portions, and the elasticity in a bending direction of the convex portion having the substantially arch shaped cross section and the damping caused by friction accompanying sliding of the connecting yarn disposed in the concave portions can be utilized.

[0016] The present invention described in claim 8 is to provide the cushioning structure according to any one of claim 4 to claim 7, wherein another elastic member serving as a function to prevent the cushion from bottom touch during the pressurizing process is provided below an elastic member composed of the three-dimensional net member formed in a structure with a small reaction force.

[0017] The present invention described in claim 9 is to provide the cushioning structure according to claim 8, wherein the aforementioned another elastic member serving as a function to prevent the cushion from bottom touch is a net type elastic member, a sheet type elastic member, or a net or sheet type elastic member supported via metal springs.

[0018] The present invention described in claim 10 is to provide the cushioning structure according to claim 8 or claim 9, wherein the aforementioned another elastic member serving as a function to prevent bottom touch is disposed at a predetermined interval to the elastic member composed of a three-dimensional net member formed in a structure with a small reaction force.

[0019] The present invention described in claim 11 is to provide the cushioning structure according to any one of claim 4 to claim 9, wherein still another elastic member higher in surface stiffness than the elastic member composed of the three-dimensional net member formed in a structure with a small reaction force is layered, in addition to the elastic member composed of the three-dimensional net member formed in a structure with a small reaction force and aforementioned another elastic member serving to prevent bottom touch.

[0020] The present invention described in claim 12 is to provide the cushioning structure according to claim 11, wherein an elastic member composed of the three-dimensional net member formed in a structure with a small reaction force is laminated on the upper portion of still another elastic member described above, and another elastic member described above serving as a function to prevent bottom touch is arranged on the lower portion of still another elastic member described above at a predetermined interval.

[0021] The present invention described in claim 13 is to provide the cushioning structure according to any one of claim 1 to claim 12, wherein the cushioning structure is applied to various seat structures including a vehicle seat and a furniture chair or a mat for furniture or for seating.

[0022] The present invention described in claim 14 is to provide the cushioning structure according to claim 13, wherein the cushioning structure is applied to a seat structure for an aircraft.

BRIEF DESCRIPTION OF DRAWINGS

[0023] FIG. 1 is a view schematically showing the structure of a cushioning structure relating to a first embodiment of the present invention;

[0024] FIG. 2 is a view schematically showing the structure of a cushioning structure relating to a second embodiment of the present invention;

[0025] FIG. 3 is a view schematically showing the structure of a cushioning structure relating to a third embodiment of the present invention;

[0026] FIG. 4 is a view schematically showing the structure of a cushioning structure relating to a fourth embodiment of the present invention;

[0027] FIG. 5 is a view schematically showing the structure of a cushioning structure relating to a fifth embodiment of the present invention;

[0028] FIG. 6 is a cross sectional view showing the structure of an example of a three-dimensional net member usable in the above-described respective embodiments;

[0029] FIG. 7 is a view showing an example of one grand knitted fabric;

[0030] FIG. 8 is a view showing an example of the other grand knitted fabric;

[0031] FIG. 9A to FIG. 9E are explanatory views showing the way of various arrangement of connecting yarn;

[0032] FIG. 10 is a perspective view showing a three-dimensional net member provided with a concave and convex portion usable as an upper elastic member in the above-described respective embodiments;

[0033] FIG. 11 is a cross sectional view of the three-dimensional net member shown in FIG. 10;

[0034] FIG. 12 is a view for explaining a function of substantially arch-shaped spring elements formed in the three-dimensional net member shown in FIG. 10;

[0035] FIG. 13 is a view for explaining the function of substantially arch-shaped spring elements formed in the three-dimensional net member shown in FIG. 10;

[0036] FIG. 14 is a perspective view of another three-dimensional net member with no concave and convex portion usable as an upper elastic member in the above-described respective embodiments, which is used in test example 1;

[0037] FIG. 15 is a graph showing a relation of load to displacement characteristic of three-dimensional net members alone in experiments 1 to 4.

[0038] FIG. 16 is a graph showing a relation of load to displacement characteristic of cushioning structures relating to respective embodiments;

[0039] FIG. 17 is a graph showing a relation of load to displacement characteristic of the three-dimensional net member having the concave and convex portion when pressurized with a board for press of 30 mm in diameter;

[0040] FIG. 18 is a graph showing a relation of load to displacement characteristic of the three-dimensional net member having the concave and convex portion when pressurized with a board for press of 98 mm in diameter;

[0041] FIG. 19 is a graph showing a relation of load to displacement characteristic of the three-dimensional net member having the concave and convex portion when pressurized with a board for press of 200 mm in diameter;

[0042] FIG. 20 is a view for explaining a function of a seat cushion portion applied with the cushioning structure of the present invention;

[0043] FIG. 21 is a view for explaining a function of a seat cushion portion applied with the cushioning structure of the present invention;

[0044] FIG. 22A and FIG. 22B are views for explaining a function of a seat back portion applied with the cushioning structure of the present invention;

[0045] FIG. 23 is a view for explaining a function of the seat back portion applied with the cushioning structure of the present invention;

[0046] FIG. 24A and FIG. 24B are views for explaining characteristics of a seat applied with the cushioning structure of the present invention;

[0047] FIG. 25 is a graph showing a relation of load to displacement characteristic of the seat cushion portion applied with the cushioning structure of the present invention;

[0048] FIG. 26 is a graph showing a relation of load to displacement characteristic of the seat back portion applied with the cushioning structure of the present invention; and

[0049] FIG. 27 is a graph showing a vibration characteristic of a seat applied with the cushioning structure of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0050] Hereinafter, the present invention will be explained in further detail based on embodiments shown in the drawings. FIG. 1 is a view showing a cushioning structure 10 relating to a first embodiment. The cushioning structure 10 relating to the first embodiment is formed by disposing two elastic members 11 and 12 vertically. Between them, an upper elastic member 11 is composed of a three-dimensional net member with a concave and convex portion formed therein. For instance, when it is employed as a seat cushion of a seat structure, it is spread over and strained between confronting side frames (not shown) constituting the seat structure with a predetermined elongation percentage. It should be noted that in order to ensure that the characteristics belonging to the three-dimensional net member itself are displayed sufficiently, and to make its load bearing characteristic close to the load bearing characteristic of the muscle in a small load area during the pressurizing process and to make its reaction force small in a small displacement area during the restoring process by elastic deformation in the vertical direction and in the horizontal direction at the time of straining, it is not recommended that it be strained with a high tension but with an elongation percentage of 5% or less.

[0051] An lower elastic member 12 is formed of a net type elastic member such as Plumaflex or a sheet type elastic member. When the cushioning structure 10 is employed, for instance, in a seat structure as described above, it is supported by engaging with one end of a metal spring 15 through the metal spring 15 engaging at the other end thereof with side frames (not shown) which strains the upper elastic member 11 or with a frame member and the like disposed at a lower portion of the side frame. It is preferable that the spring characteristic created by the lower elastic member 12 and the metal spring 15 be high in linearity than that of the upper elastic member 11 composed of a three-dimensional net member, and a spring constant of 35 N to 100 N by a board for press of 98 mm in diameter when combined with the upper elastic member 11 is close to the spring constant of the muscle of the haunches. On the other hand, though the upper elastic member 11 is high in surface stiffness against pressure over a large area at a force of 20 N or less, the partial spring constant measured by pressing the concave portion and in the vicinity of the convex portions on both sides of the concave portion with a board for press of about 30 mm in diameter to about 20 mm in diameter is set to be smaller than the spring constant created by the lower elastic member 12 and the metal spring 15 because of its shape being provided with a ridge composed of concave and convex portions. Through this configuration, it creates temporal set in fatigue under loads as described above, when a protruding portion of the body comes into contact with the seat, it becomes easy to settle partially (refer to FIG. 13), and a feeling of fitting is improved.

[0052] As will be described later, the upper elastic member 11 composed of a three-dimensional net member has a thickness of about 5 mm to about 30 mm, the amount of displacement stroke in the vertical direction is small, and the load bearing characteristic in a small displacement area is extremely small and has little reaction force. Accordingly, when an applied load meets or exceeds a predetermined value, a person sitting on the cushion may feel the bottom touch. Therefore, a restoring force of the upper elastic member 11 is made up by the lower elastic member 12 having a spring characteristic high in linearity and the metal spring 15 so that the feeling of bottom touch is prevented by the elastic force in a load area where the predetermined load is exceeded.

[0053] It should be noted that it is possible to structure in a manner that the spring characteristic created by the above described lower elastic member 12 and the metal spring 15 is possessed by the lower elastic member alone composed of a net type elastic member or sheet type elastic member having surface stiffness. In other words, it is possible to use the lower elastic member alone which has a spring characteristic including the spring characteristic of the metal spring together with high surface stiffness. Needless to say, in this case, the lower elastic member is directly strained over the side frames.

[0054] Though the upper elastic member 11 and the lower elastic member 12 can be disposed to come into contact with each other when no load is applied, it is preferable to dispose them a little apart from each other when the cushion structure is employed in the seat cushion of a seat structure for instance. Through this arrangement, since the upper elastic member 11 itself has a predetermined amount of stroke till it touches the lower elastic member 12, a feeling of fitting in a small load area and a small displacement area due to deformation in the vertical direction and elongation in the horizontal direction of the upper elastic member 11 can be further improved.

[0055] FIG. 2 is a view showing one example of a cushioning structure 20 relating to a second embodiment of the present invention. In the second embodiment, the cushioning structure is formed of three layers composed of an upper elastic member 21, a lower elastic member 22 and a middle elastic member 23 disposed in the middle of both the upper and lower elastic members. The upper elastic member 21 is composed of a three-dimensional net member having concave and convex portions, and has a same function as the upper elastic member 11 relating to the above-described first embodiment. The lower elastic member 22 is composed of a net type elastic member such as Plumaflex or the like which is formed by putting, metal wires together for instance, or a sheet type elastic member such as a three-dimensional net member or the like, disposed to an appropriate frame members or the like forming, for instance, a seat structure via a metal spring 25, so that the similar function to the lower elastic member 12 relating to the above-described first embodiment is provided.

[0056] The middle elastic member 23 is composed of a three-dimensional net member, and disposed to be layered under the upper elastic member 21 between side frames of the seat cushion which forms a seat structure, for instance. The middle elastic member 23 is higher in surface stiffness than the upper elastic member 21 which is provided to display a soft load bearing characteristic as described above in a small load area, when the load area becomes a predetermined area or more, and is provided to prevent depression more than necessary, to increase a feeling of stability at the time of being seated or lying owing to a feeling of the stiffness, and at the same time, to restrain a feeling of bottom touch of the upper elastic member 21 similarly to the lower elastic member 22. Moreover, it is provided to reduce a feeling of something foreign caused by the metal spring 25 or the side frames. It should be noted that a reaction force against a seated person can be drastically reduced by disposing either the upper elastic member 21 or the middle elastic member 23, or preferably both of them so that respective side portions become free ends. This is because at the time of being seated or the like, respective side portions move upwards in the drawing (in the direction of normal line) as if to roll in the direction of rotation by the deformation accompanied by the input load, and a force in the shear direction is not generated so much, which helps to disperse the input load. Accordingly, in order to display such a function, the three-dimensional net member composing the middle elastic member 23 is disposed with a tension higher than that of the upper elastic member 21, or in order to increase tolerance in deformation (degree of freedom) and to reduce a reaction force against a person, the three-dimensional net member for the middle elastic member 23 is arranged so that the respective side portions become rotation-free ends. Further, a three-dimensional net member having the load bearing characteristic in the thickness direction is higher than that of the upper elastic member 21 or having a large deflection amount is adopted so as to feel like a spring rich in elasticity.

[0057] Further, as the middle elastic member 23, any members can be adopted provided that it can prevent unnecessarily large depression of the upper elastic member 21 and has an elastic force capable of displaying a predetermined feel of stiffness. Accordingly, it is not limited to a three-dimensional net member. For instance, a felt formed in a predetermined thickness can be used as a third embodiment shown in FIG. 3, as a middle elastic member 33. It should be noted that the structure of an upper elastic member 31 and the structure of a lower elastic member 32 supported via a metal spring 35 in a cushion structure 30 of the third embodiment shown in FIG. 3 are the same as those in the second embodiment.

[0058] FIG. 4 is a view showing a cushioning structure 40 relating to a fourth embodiment of the present invention. The cushioning structure 40 has a configuration specially suitable for using as a mat for bedding or the like and is composed of an upper elastic member 41, a middle elastic member 43, and a lower elastic member 42 piled vertically. Further, as explained in the above-described embodiments, it is preferable to dispose respective elastic members 41 to 43 without connecting respective end portions thereof, but making them as free ends, thereby enabling input load to disperse so that the reaction force against a person can be reduced. However, even in the case of connecting these respective elastic member 41 to 43 by sewing or the like, if the end portions of respective elastic member 41 to 43 are connected in a state to leave a room capable of creating similar deformation to that when they are made free ends, it becomes possible to bring a similar effect to the above-described effect due to the elasticity possessed by respective elastic members. It is needless to say that an effect of making a reaction force against a person small in quest of dispersing an input load, by making ends of respective elastic members free ends, or by connecting respective elastic member leaving a deformable room (or space), as described above, is not limited to the present embodiment but also similar to other embodiments.

[0059] The upper elastic member 41, the middle elastic member 43, and the lower elastic member 42 are all composed of a three-dimensional net member, and in this embodiment, and are structured in layer without connecting respective members to each other, which have different load bearing characteristic from each other.

[0060] The upper elastic member 41 is, similarly to the upper elastic member 11 of the first embodiment, the upper elastic member 21 of the second embodiment, and the upper elastic member 31 of the third embodiment, disposed to let the cushioning structure 40 provide a function to set its load bearing characteristic to come close to the load bearing characteristic of muscle in a pressurizing process, and to make the reaction force small in a small displacement area in a restoring process. Accordingly, the upper elastic member 41 is set to have a soft load bearing characteristic with a low spring constant. However, in FIG. 4, there is no concave and convex portion, different from those shown in FIG. 1 to FIG. 3. When a concave and convex portion is formed, since a convex portion is formed in a substantially arch-shaped cross section between adjacent concave portions, the connecting yarn between ground knitted fabrics are disposed with an inclination, the convex portion serves to form an arch-shaped spring, and the elasticity in the bending direction and the horizontal direction can be utilized. Accordingly, in a structure forming concave and convex portions, a soft spring constant that is close to the load bearing characteristic of a person, and has temporal set in fatigue characteristic under loads in which the reaction force is decreased in a fixed deformation can be easily set up.

[0061] On the other hand, in the case of no concave and convex portion being formed, when compared with the case of forming concave and convex portions, the connecting yarn is disposed between confronting ground knitted fabrics without so much inclination, and the load bearing characteristic is determined mainly by buckling strength of the connecting yarn. Therefore, when a soft load bearing characteristic like the above-mentioned first to third embodiments is given without forming a concave and convex portion, a three-dimensional net member having a feeling of a soft spring can be obtained by designing the connecting yarn to be disposed at a predetermined inclination in advance at the time of formation, or by selecting thickness and length of the connecting yarn appropriately. It should be noted that when a three-dimensional net member is set to have a soft structure with a feeling of a spring by arranging the formation structure, it can be adjusted by either any one element or a combination of any two or more elements among such an element as density of the connecting yarn arrangement, material of the connecting yarn, a stitch shape of the ground knitted fabric, a stitch size of the ground knitted fabric, material of the ground yarn composing the ground knitted fabric, a knot fixing power at a joint portion between the connecting yarn and the ground knitted fabric as well as the thickness and length of the above-described connecting yarn. Needless to say, in the case of a three-dimensional net member forming concave and convex portions, by adjusting similar elements, it is possible to obtain a structure having a feeling of various springs even the width of a concave and convex portion is similar to each other.

[0062] When a load area becomes more than a predetermined area, the middle elastic member 43 is, similar to the middle elastic members 23 and 33 relating to the above-described second and third embodiment, provided to prevent unnecessary depression of the upper elastic member 41 disposed to display a soft load bearing characteristic in a small load area, to increase a feeling of stability at the time of being seated and lying by displacement created by the free ends and by a feeling of stiffness which the elastic member itself possesses, and at the same time, to restrain a feeling of bottom touch of the upper elastic member 41 together with the lower elastic member 42. For instance, a three-dimensional net member formed to have a feeling of a spring harder than the upper elastic member 41.

[0063] The lower elastic member 42 is, similar to the lower elastic member 12, 22 and 32 of the above-described first to third embodiments, disposed to prevent a feeling of bottom touch due to its elastic force, and a three-dimensional net member provided with a spring characteristic high in linearity than that of the upper elastic member 41 is adopted.

[0064] It should be noted that as the middle elastic member 43 and the lower elastic member 42 in the fourth embodiment, it is not limited to a three-dimensional net member but it is possible to substitute them with other members having the above-described predetermined characteristics such as, for instance, felt, polyurethane foam, or the like.

[0065] FIG. 5 is a view showing a cushioning structure 50 relating to a fifth embodiment. The cushioning structure 50 has a configuration suitable for using as a mat for bedding or the like similar to the fourth embodiment, and six elastic members 51 to 56 consisting of a three-dimensional net members are structured in a vertical multilayer.

[0066] In the present embodiment, a first elastic member 51 disposed on the top portion and a sixth elastic member 56 disposed on the lowermost portion are formed of a three-dimensional net member having concave and convex portions, similarly to the upper elastic member 11 and the like of the above-described first embodiment, and has a function to set its load bearing characteristic to come close to the load bearing characteristic of muscle in a small area in the pressurizing process, and to make the reaction force small in a small displacement area in the restoring process, and a partial spring constant by a board for press of 30 mm in diameter is set to be low so as to have a soft load bearing characteristic though a feel of stiffness in a wide area is high.

[0067] Among four layers of elastic members disposed between the above-described first elastic member 51 and the sixth elastic member 56, a second elastic member 52 which is the second from the top in FIG. 5, and a fourth elastic member 54 which is the fourth from the top in FIG. 5, are provided with a function corresponding to the middle elastic member 23 in the above-described second embodiment and the like. When a load area becomes more than a predetermined area, the second elastic member 52 and the fourth elastic member 54 are provided to prevent unnecessary sink-in of the first and sixth elastic members 51 and 56 provided to display a soft load bearing characteristic in a small load area, to increase a feeling of stability at the time of being seated and lying by its feeling of stiffness, and at the same time, to restrain a reaction force to a person or a feeling of bottom touch by dispersion of the load.

[0068] On the other hand, a third elastic member 53 and a fifth elastic member 55 are provided with a spring characteristic similar to the spring characteristic created by the lower elastic member 12 and the metal spring 15 of the above-described first embodiment, and the load bearing characteristic by a board for press of 98 mm in diameter is close to the load bearing characteristic of muscles of the haunches in the area of 35 N to 100 N. It should be noted that the second to fifth elastic member 52, 53, 54 and 55 disposed between the first elastic member 51 and the sixth elastic member 56 are acceptable so far as any of them can mainly supply a feeling of stiffness and others can display mainly a high feeling of spring, so that its order of layer or the number of layers are not limited. Further, in the present embodiment, in order to enhance a load dispersion function, it is preferable to make the end portions free similarly to the fourth embodiment.

[0069] Next, a structure of a three-dimensional net member 100 used as the upper elastic member 11 in the first embodiment, the upper elastic member 21 or the middle elastic member 23 in the second embodiment, the upper elastic member 31 in the third embodiment, the upper elastic member 41, the middle elastic member 43 or the lower elastic member 42 in the fourth embodiment, and the first to sixth elastic member 51 to 56 in the fifth embodiment will be explained referring to FIG. 6 to FIG. 9. As shown in FIG. 6, the three-dimensional net member 100 is structured of a solid three-dimensional structure including a pair of ground knitted fabrics 110 and 120 disposed apart from each other and a lot of connecting yarn 130 running between the pair of ground knitted fabrics 110 and 120 to connect both.

[0070] One of the ground knitted fabrics 110 is formed with a flat knitted fabric structure (small mesh) structured with yarns made of twisted monofilaments continuous to any directions in both wale direction and course direction as shown in FIG. 7, for instance. On the other hand, the other ground knitted fabric 120 is formed in a larger stitch structure than that of the ground knitted fabric 110 including a honeycomb-like (hexagon) mesh made of twisted short filaments, as shown in FIG. 8 for instance. Needless to say, this knitted fabric structure is just an example, and it is possible to adopt knitted fabric structures other than the small mesh structure or the honey comb structure. The connecting yarns 130 are knitted between the pair of ground knitted fabrics 110 and 120 to keep a predetermined distance between one of the ground knitted fabrics 110 and the other ground knitted fabric 120 so that a predetermined stiffness is given to the three-dimensional net member 100 which is a solid mesh knitting.

[0071] The thickness or the like of the ground yarn forming the ground knitted fabrics 110 and 120 is not limited particularly, but selected from that which can provide firmness in structure required for a solid knitted fabric and being in the range not to give difficulty in a formation work. As a ground yarn, a monofilament can be used, but it is preferable to use a multifilament or a spun yarn from the point of view such as feeling, softness in surface touch and so on.

[0072] It is preferable to use a monofilament as a connecting yarn 130, and it is suitable to use the one having a thickness in the range of 167 to 1100 decitex. This is because a cushioning property having a favorable restoring force cannot be given by the multifilament, and when the thickness becomes lower than 167 decitex, it becomes difficult to obtain suitable firmness in structure. When it becomes more than 1100 decitex, it becomes too hard to obtain a suitable spring property (cushioning property). In other words, adoption of the monofilament having the above-described range as a connecting yarn 130 makes it possible to support the load of a seated person by deformation of the stitch structure composing respective ground knitted fabrics 110 and 120, and by falling down and buckling characteristic of the connecting yarn 130, and by restoring force of adjacent connecting yarn 130 giving a spring characteristic to the buckling characteristic, in other words, is possible to support by the buckling characteristic having a restoring force, so that a soft structure having a soft spring characteristic without occurring of stress concentration can be realized. It should be noted that in the case of forming concave and convex portions, since a spring element having a cross section of substantially arch shape can be formed as will be described later, it is possible to give a further softer spring characteristic.

[0073] As a material for the ground yarn or the connection fiber 130, it is not limited to some special material and, for instance, synthetic fiber or regenerated fiber such as polypropylene, polyester, polyamide, polyacrylonitrile, rayon and so on, or natural fiber such as wool, silk, cotton and so on can be cited. The above material can be used alone or can be used as any combination thereof. It is preferable to use thermoplastic polyester fibers such as polyethylene terephthalate (PET), and polybutylene terephthalate (PBT), polyamide fibers such as nylon 6 and nylon 66, polyolefine fibers such as polyethylene and polypropylene, or a combination of two or more kinds of these fibers. Incidentally, polyester fibers is suitable because of its regeneration property. It should be noted that the shape of fibers used for the ground yarn or the connecting yarn 130 is not limited, and a round cross sectional fiber, a modified cross sectional fiber and so on can be used.

[0074] As for the manner of arranging the connecting yarn 130 (pile structure), when the connecting yarns 130 connecting respective ground knitted fabrics 110 and 120 are expressed from states seen from the side, more concretely, they are classified in the types shown in FIG. 9A to FIG. 9E. FIG. 9A and FIG. 9B are a straight type in which the connecting yarns 130 are knitted almost vertically between the ground knitted fabrics 110 and 120, and between the two, FIG. 9A is the one knitted straight in the shape of the letter 8, and FIG. 9B is the one knitted simply straight. FIG. 9C to FIG. 9E are cross types in which the connecting yarns 130 are knitted to cross each other on the way between the ground knitted fabrics 110 and 120. Among these, FIG. 9C is the one knitted to cross the fibers in the shape of the letter of 8, FIG. 9D is the one knitted in a cross simply, and FIG. 9E is the one knitted two fibers together in cross (double cross). It should be noted that, as shown in FIG. 9C to FIG. 9E, when the connecting yarn 130 are disposed slantwise in a cross with each other, it is possible to give a soft spring characteristic having large compressibility while keeping a sufficient restoring force due to buckling strength of respective connecting yarn 130 compared with the pattern in which the connecting yarn 130 are disposed almost vertically between the ground knitted fabrics 110 and 120 (refer to FIG. 9A and FIG. 9B).

[0075] Here, when the above-described three-dimensional net member 100 is used as the upper elastic members 11, 21, 31 of the above-described first to third embodiments, and the first and sixth elastic members 51, 56 of the fifth embodiment, it is processed into a structure having concave portions 150 and convex portions 160, as shown in FIG. 10 and FIG. 11. More concretely, the three-dimensional net member 100 is processed so that the pair of ground knitted fabrics 110 and 120 which are disposed apart from each other at predetermined intervals along the course direction come close in the three-dimensional net member 100 to form concave portions 150, thereby forming convex portions 160 between adjacent concave portions 150 and 150.

[0076] Though the concave portion 150 can be formed from one side alone out of the pair of ground knitted fabrics 110 and 120, it can be formed from both sides as shown in FIG. 10 and FIG. 11. As a means for forming the concave portion 150 by allowing the ground knitted fabrics 110 and 120 to come close to each other, a sewing means by sewing on a machine, or further such as interposing fusion fiber between the ground knitted fabrics 110 and 120 to bond them by melting the fusion fiber, as well as by welding, or by bonding. It is preferable to use a vibration welding means among these means described above. It is because this means can prevent the welded portion to become stiff, and at the same time, the bonding strength is very high.

[0077] As above, by forming the concave portions 150, at the portions where the concave portions 150 are formed, the connecting yarns 130 disposed in those area are tend to incline or bend, and further some connecting yarns 130 move to the areas of adjacent convex portions 160 via the concave portions 150 so as to be unevenly distributed. Accordingly, in these areas, nearby connecting yarns 130 are confounded with each other when being bonded. As a result of confoundly bonding as described above, both sides of the connecting yarn 130 putting the confounded portion 130a inbetween can serve as respective independent spring elements (deforming elements) for the ground knitted fabric 110 or the ground knitted fabric 120 which are respective bonding objects of both sides. Therefore, as schematically shown in FIG. 12, the area from a confounded portion 130a where the connecting yarns 130 are confounded in a concave portion 150 to another confounded portion 130a where the connecting yarns are confounded in a neighboring concave portion 150, formed is a structure taken to be serving as a spring element having substantially an arch shaped cross section and a damping element due to friction between yarns including the ground knitting fabric 110 and the connecting yarns 130 disposed in this area.

[0078] As a result, in the three-dimensional net member having concave and convex portions, the modulus of elasticity at the concave portion 150 is different from that at the convex portion 160. When the convex portion 160 is compression-deformed due to an applied load, the buckling strength of the connecting yarn 130 becomes relatively small so that the buckling characteristic becomes hard to exhibit compared with the case of using the three-dimensional net member 100 without forming a concave and convex portion, and as shown by an imaginary line in FIG. 12, an elastic function in the bending direction of the spring element having a cross section in a substantially arch shape including the confounded connecting yarn 130 becomes relatively large. In other words, in the spring characteristic of the convex portion 160 compared with a three-dimensional net member formed in the same condition except not forming a concave and convex portion, the spring constant is small and becomes easy to start deforming from a very small load area, so that its buckling characteristic is hard to exhibit. As a result, a three-dimensional net member with a concave and convex portion becomes small in a maximum value in the amount of hysteresis loss and becomes high in linearity compared with the case without a concave and convex portion. However, in its load bearing characteristic, an ordinary three-dimensional net member shows a characteristic similar to a viscoelastic material of which restoring movement is delayed due to the hysteresis even the load becomes zero at the time of restoring, because of friction between the connecting yarns at the time of restoring of the connecting yarn 13, and in a three-dimensional net member having a concave and convex portion, the friction between yarns acts on the above-described bending elasticity to cause further increase in the friction between yarns at a concave portion. As a consequence, direction of the deformation and the like change according to an input, which allows the spring element and the damping element corresponding to the input to work.

[0079] Further, in the three-dimensional net member forming concave and convex portions, elasticity expanding and contracting in substantially perpendicular to a formation line of the concave portion 150 is given by confoundly bonding the connecting yarns 130 at the concave portion 150. Accordingly, when it is strained over seat frames or the like of a seat structure, in addition to a spring property in the bending direction by a spring element having a substantially arch-shaped cross section generated in the thickness direction, elasticity (spring property) generated in the surface direction substantially perpendicular to the bending direction comes is added by the connecting yarn forming a spring element having a substantially arch-shaped cross section, and this elongation further contributes to reduction of the spring constant. Furthermore, owing to the characteristic similar to a viscoelastic material created by the increase of the friction between yarns, the damping characteristic also gets large. Accordingly, by disposing the upper elastic member 11, the middle elastic members 23 and 33 above respective lower elastic members 12, 22, and 32 shown in the above-described first to third embodiments at respectively predetermined distances of intervals, elongation in lateral directions of respective upper elastic members 11, 21, and 31 composed of three-dimensional net members having concave and convex portions work effectively, delay characteristic of the restoring movement are revealed more remarkably, and the damping ratio also gets large.

[0080] Further, as shown in FIG. 13, when a portion protruded by a bone of the human body (corresponding nearly to a board for press having a diameter of 30 mm) comes in contact with a three-dimensional net member, the convex portions 160 on both sides of the concave portion 150 sandwiched therebetween are depressively deformed as if running away toward outside and partial temporal set in fatigue under loads is created. Then, when the portion is further applied with a load and pressed in a large area, the whole three-dimensional net member comes to support the load, and since deformation as shown in FIG. 13 appears due to the existence of such concave and convex portions, a feeling of fitting is improved in a small displacement area.

[0081] The upper elastic members 11, 21, 31 and 41 of the above-described respective embodiments and the first and sixth elastic members 51 and 56 of the fifth embodiment are provided with a soft spring characteristic, and a reaction force in the range of predetermined amount of displacement or less is made small. However, when the amounts of the upper elastic members 11, 21, 31, 41 and so on are large, shear stress starts to serve on the muscles, which leads to increase in a load on the muscles instead. Therefore, it is preferable to form respective upper elastic members 11, 21, 31, 41 and so on to have a thickness including a pair of ground knitted fabrics (the thickness of the convex portion when concave and convex portions are formed) in the range of 5 to 30 mm, lest the maximum amount of deformation should be so large.

TEST EXAMPLE

[0082] The load characteristics of individual three-dimensional net members (test example 1 to 4) usable for the upper elastic member 11 of the first embodiment shown in FIG. 1, the upper elastic member 21 of the second embodiment shown in FIG. 2, the upper elastic member 31 of the third embodiment shown in FIG. 3, the upper elastic member 41 of the fourth embodiment shown in FIG. 4, the first and sixth elastic members 51 and 56 of the fifth embodiment shown in FIG. 5 are measured. The measurement is carried out by pressing a circular board for press of 200 mm in diameter at a speed of 50 mm/minute. The results are shown in FIG. 15.

[0083] The conditions of manufacturing the three-dimensional net members used in test examples 1 to 4 are as follows. The three-dimensional net member used in test example 1 has no concave and convex portion, and is structured, as shown in FIG. 14, that space portions 210 are formed between ridge portions (band-shaped portion) 200 formed at intervals of one wale or a plurality of wales. In the space portion 210, connecting portions 220 are formed over the range of 1 to several courses so as to bridge between the adjacent ridge portions 200. All of the test examples 2 to 4 are formed with concave and convex portions as shown in FIG. 10 and FIG. 11. A manufacturing condition for a comparison example is the same as that for the test example 4 except that concave portions are not formed by vibration welding, and the compressibility is 13.2%, the compression modulus of elasticity is 98.1%.

Test Example 1

[0084] knitting machine: Double Raschel knitting machine (9 guage/2.54 cm, bed gap distance 15 mm)

[0085] wale density: 10 wale/2.54 cm

[0086] course density: 14 course/2.54 cm

[0087] finished thickness (distance between surfaces of a pair of ground knitted fabrics): 11.5 mm

[0088] ground yarn used in one ground knitted fabric: 1170 decitex/96f polyester·BCF multifilament (crimped yarn)

[0089] ground yarn used in the other ground knitted fabric: 660 decitex/192f polyester·BCF multifilament (crimped yarn)

[0090] connecting yarn: 660 decitex/1f polyester

[0091] structure of one ground knitted fabric: derivative stitch of 2 course mesh

[0092] structure of the other ground knitted fabric: queen's cord

[0093] total thickness of a stitch formed with ground yarn in one ground knitted fabric and connecting yarn: 1830 decitex, (partially 3000 decitex)

[0094] total thickness of a stitch formed with ground yarn in the other ground knitted fabric and connecting yarn: 1980 decitex

[0095] compressibility of ridge portion: 49.5%

[0096] compression modulus of elasticity of ridge portion: 98.8%

[0097] difference in compressibility between ridge portion and other portions: 5.2%

[0098] width of ridge portion: 6 wales

[0099] width of space portion: 1 wale

Test Example 2

[0100] knitting machine: Double Raschel knitting machine (9 guage/2.54 cm, bed gap distance 15 mm)

[0101] wale density: 10 wale/2.54 cm

[0102] course density: 14 course/2.54 cm

[0103] finished thickness (distance between surfaces of a pair of ground knitted fabrics): 11.5 mm

[0104] ground yarn used in one ground knitted fabric: 1170 decitex/96f polyester→BCF multifilament (crimped yarn)

[0105] ground yarn used in the other ground knitted fabric: 660 decitex/192f polyester→BCF multifilament (crimped yarn)

[0106] connecting yarn: 660 decitex/1f polyester

[0107] structure of one ground knitted fabric: derivative stitch of 2 course mesh

[0108] structure of the other ground knitted fabric: queen's cord

[0109] total thickness of a stitch formed with ground yarn in one ground knitted fabric and connecting yarn: 1830 decitex, (partially 3000 decitex)

[0110] total thickness of a stitch formed with ground yarn in the other ground knitted fabric and connecting yarn: 1980 decitex

[0111] compressibility of convex portion: 57.9%

[0112] compression modulus of elasticity of convex portion: 98.8%

[0113] difference in compressibility between convex portion and concave portion: 57.8%

[0114] vibration welding condition of concave portion: applied pressure 18.2 kgf/m2, amplitude 1.0 mm, time period 1.2 sec

[0115] width of convex portion: 5 wales

[0116] width of concave portion: 2 wales

Test Example 3

[0117] knitting machine: Double Raschel knitting machine (9 guage/2.54 cm,

[0118] bed gap distance 15 mm)

[0119] wale density: 9.8 wale/2.54 cm

[0120] course density: 12.8 course/2.54 cm

[0121] finished thickness (distance between surfaces of a pair of ground knitted fabrics): 12.05 mm

[0122] ground yarn used in one ground knitted fabric: 1170 decitex/384f

[0123] ground yarn used in the other ground knitted fabric: 560 decitex/70f

[0124] connecting yarn: 560 decitex/1f

[0125] structure of one ground knitted fabric: 1 repeat 2 course mesh

[0126] structure of the other ground knitted fabric: queen's cord

[0127] total thickness of a stitch formed with ground yarn in one ground knitted fabric and connecting yarn: 1730 decitex

[0128] total thickness of a stitch formed with ground yarn in the other ground knitted fabric and connecting yarn: 1120 decitex

[0129] compressibility of convex portion 89.1%

[0130] compression modulus of elasticity of convex portion: 100%

[0131] difference in compressibility between convex portion and concave portion: 89.0%

[0132] vibration welding condition of concave portion: applied pressure 21.7 kgf/m2, amplitude 1.0 mm, time period 1.0 sec

[0133] width of convex portion: 6 wales

[0134] width of concave portion: 2 wales

Test Example 4

[0135] knitting machine: Double Raschel knitting machine (9 guage/2.54 cm, bed gap distance 15 mm)

[0136] wale density: 9 wale/2.54 cm

[0137] course density: 13.5 course/2.54 cm

[0138] finished thickness (distance between surfaces of a pair of ground knitted fabrics): 11.5 mm

[0139] ground yarn used in one ground knitted fabric: 1170 decitex/96f

[0140] ground yarn used in the other ground knitted fabric: 660 decitex/192f

[0141] connecting yarn: 660 decitex/1f

[0142] structure of one ground knitted fabric: convex portion→1 repeat 4 course mesh, concave portion→modified W atlas

[0143] structure of the other ground knitted fabric: queen's cord

[0144] total thickness of a stitch formed with ground yarn in one ground knitted fabric and connecting yarn: 2050 decitex (partially 3220 decitex)

[0145] total thickness of a stitch formed with ground yarn in the other ground knitted fabric and connecting yarn: 1540 decitex

[0146] compressibility of convex portion: 20.0%

[0147] compression modulus of elasticity of convex portion: 94.3%

[0148] difference in compressibility between convex portion and concave portion 310: 6.8%

[0149] vibration welding condition of concave portion: applied pressure 18.2 kgf/m2, amplitude 1.0 mm, time period 1.2 sec

[0150] width of convex portion: 9 wales

[0151] width of concave portion: 3 wales

[0152] Incidentally, the compressibility and the compression modulus of elasticity are measured according to a test method based on JASO Standard M404-84 “Compressibility and Compression modulus of elasticity”. More concretely, three sheets of samples in the size of 50 mm×50 mm are prepared, and respective thickness are measured after an initial pressure of 3.5 g/cm2 (0.343 kPa) is applied on each of the samples in the thickness direction for 30 seconds. Then, the thickness of the samples are measured at the time of keeping them for 10 minutes under the pressure of 200 g/cm2 (19.6 kPa). Then, after keeping the samples for 10 minutes with the loads being removed, a pressure of 3.5 g/cm2 (0.343 kPa) is applied again for 30 seconds and the thickness is measured. The compressibility and the compression modulus of elasticity are calculated based on the following equations and expressed in an average value of three samples respectively.

Compressibility (%)={(t0−t1)/t0}×100  Equation 1

Compression modulus of elasticity (%)={(t0−t1)/(t0t1)}×100  Equation 2

[0153] Here, to indicates a thickness (mm) of the sample when a pressure of 3.5 g/cm2 (0.343 kPa) is applied, t1 indicates a thickness (mm) of the sample when a pressure of 200 g/cm2 (19.6 kPa) and t′0 indicates a thickness (mm) of the sample when a pressure of 3.5 g/cm2 (0.343 kPa) is applied again.

[0154] As is clear from FIG. 15, when the load bearing characteristic in the go-process (pressurizing process) till the upper initial load range of 200 N (about 20 kg) while using a board for press of 200 mm in diameter is observed, it is found that the spring constant in each test example is lower than that in the comparison example having low compressibility and high compression modulus of elasticity. Further, when the test example 1 which forms no concave and convex portion and the test example 2 which forms concave and convex portions are compared, the test example 2 which forms concave and convex portions shows a lower spring constant and a softer load bearing characteristic. This is because by utilizing mainly the spring property in a bending direction owing to a spring element having a substantially arch-shaped cross section, the hysteresis loss becomes small and the linearity becomes high compared with an ordinary three-dimensional net member having a high friction coefficient owing to its buckling characteristic and knot fixing strength.

[0155] In the return process (restoring process), though both are found to have spring constants lower than those in the pressurizing process due to the hysteresis loss, in the case of the comparison example, the spring constant in the restoring process even in the displacement range of 2 to 1 mm is still about 40 N/mm, and the reaction force remains till the displacement amount becomes nearly 0 mm. On the other hand, in the case of test examples 1 to 4, after the displacement amount comes to 1 mm at the latest in the restoring process, the structure is found to have a very small reaction force such that the spring constant becomes much lower than the spring constant in the pressurizing process of all the cushioning structure in each embodiment which will be described later, and becomes nearly zero. This load bearing characteristic is measured by pressing with a board for press of 200 mm in diameter at a speed of 50 mm/min. In the load bearing characteristic of a three-dimensional net member alone, it is required as described above to have a function to improve a feeling of fitting in a small displacement area by a partial displacement. Therefore, a characteristic of a spring characteristic to become nearly zero after the displacement amount of 20 mm or less comes to 1 mm in the above-described restoring process can preferably exhibit at the time of being pressed with a board for press of 30 mm in diameter at a speed of 50 mm/min (refer to FIG. 13).

[0156] (Embodiments 1 to 5)

[0157] Load bearing characteristics are measured for the whole cushioning structures relating to the first embodiment shown in FIG. 1 (embodiment 1), the second embodiment shown in FIG. 2 (embodiment 2), the third embodiment shown in FIG. 3 (embodiment 3), the fourth embodiment shown in FIG. 4 (embodiment 4), and the fifth embodiment shown in FIG. 5 (embodiment 5). It should be noted that the three-dimensional net member used for the upper elastic members 11, 21, and 31 in the embodiment 1 to 3, and the first and sixth elastic members 51 and 56 in the embodiment 5 is used in the above-described test example 2 which is strained at the elongation percentage of zero and the longitudinal direction of the convex portion is along the direction of gap between the side frames. In the embodiment 4, the elastic member adopted in the above-described test example 1 is used as the upper elastic member 41. The measurement is carried out by pressing a circular board for press of 98 mm in diameter from a surface of the three-dimensional net member to 100 N at a speed of 50 mm/minute. The result is shown in FIG. 16. Further, for the muscles of haunches of a person, the load bearing characteristic is measured similarly by pressing with a circular board for press of 98 mm in diameter and the result is shown in the same figure.

[0158] In all of respective lower elastic members 12, 22, and 32 in embodiments 1 to 3, the same Plumaflex is strained by 4 pieces of metal springs on the right and left respectively. The adopted metal spring is a coil spring having 2.6 mm in wire diameter, 54.6 mm in coil length, 16.1 mm in coil average diameter, 20 in winding number, and 0.55 N/mm in spring constant.

[0159] As is clear from FIG. 16, spring constants of the load bearing characteristic in the go-process (pressurizing process) are all in the range of 0.1 to 10 N/mm, and at the same time, the amounts of hysteresis loss are in the range of 10 to 20 N, and especially in the area of 35 to 100 N which is over the load equilibrium point, it shows a low spring constant close to the spring characteristic of muscles. Incidentally, a preferable spring constant is in the range of 0.1 to 5 N which is closer to the spring constant of muscles. The amount of hysteresis loss is preferably in the range of 10 to 20 N as a characteristic when measurement is carried out by pressing with a board for press of 98 mm in diameter as described above, but the range below 40 N is acceptable.

[0160] On the other hand, in a return process (restoring process) of the load bearing characteristic, embodiment 1, embodiment 2, and embodiment 4 show the spring constants after the displacement amounts come to about 3 to 5 mm which is before the displacement amount comes to zero or the tested samples are completely restored, becomes substantially zero which is lower than the spring constant of muscles. Further in embodiment 3 and embodiment 5, when the displacement amounts come to about 15 to 18 mm before it becomes zero or the tested samples are completely restored, the spring constant thereafter becomes substantially zero. In other words, in the load bearing characteristic of the three-dimensional net member alone in the above-described test example 2, the spring constant comes to near zero at the time of the displacement amount to be about 2 mm. However, by making it into a layered cushioning structure as in the embodiments, it is found that the range to get near zero of the spring constant is widened.

[0161] From the above, by disposing to a three-dimensional net member another elastic member to prevent bottom touch in layers, and if necessary, by arranging still another elastic member such as a metal spring, Plumaflex, or the like which is high in surface stiffness, capable of preventing a feeling of something foreign in layers, it is found that a spring constant which does not allow a seated person to feel a reaction force can be provided in an area below the predetermined displacement amount, more concretely, in an area from the displacement amount of 20 mm to 2 mm at the latest considering the data in the above-described embodiments, for instance, after the displacement amount comes to about 15 mm or less in embodiment 3. Through this arrangement, in the range of displacement from several millimeters to ten and several millimeters or so, the structure tends to bend under a small load due to the spring constant of 0.1 to 10 N/mm or less, which is close to muscles during pressurizing process, but since it causes only temporal set in fatigue due to the load with almost no inputting of the reaction force thereof, the cushioning structures in respective embodiments only give the seated person a feeling of light touch on a small contact area as in the case of coming in contact with a portion protruded by a bone of the human body, and there is no reaction force which causes a blood stream trouble or loads on muscles. Therefore, a feeling of seating with a feeling of being safe can be obtained.

[0162] (Embodiment 6)

[0163] A three-dimensional net member (embodiment 6) with concave and convex portions as shown in FIG. 10 and FIG. 11 is mounted on a plane board, and the load bearing characteristic is measured while changing the size (diameter) of a board for press. The results are shown in FIG. 17 to FIG. 19. FIG. 17 shows the case of pressurizing to 100 N with a board for press of 30 mm in diameter, FIG. 18 shows the case of pressurizing to 100 N with a board for press of 98 mm in diameter, and FIG. 19 shows the case of pressurizing to 1000 N with a board for press of 200 mm in diameter. It should be noted that all of the speed of the board for press are 50 mm/minute. Further, in all cases, similar measurement is carried out for a three-dimensional net member (for comparison) with no concave and convex portion prepared under completely the same condition as in embodiment 6 except no formation of concave and convex portion by vibration welding.

[0164] As is clear from FIG. 17, when pressurized with a board for press of 30 mm in diameter, embodiment 6 is found to be low as a whole in a load value against a displacement amount compared with the comparison example, and a displacement amount in which the spring constant during the restoring process comes to zero is found to be increased. Accordingly, it is found that it tends to displace partially, and when a protruded portion comes in contact, the reaction force at that time is small. As shown in FIG. 18, when pressurized with a board of 98 mm in diameter (corresponding to the one side size of human haunches), a load value against a displacement amount is lowered as a whole similarly, compared with the comparison example. The spring constants both in the pressurizing process and the restoring process are lowered and when compared with the comparison example, the reaction force is found to be small. However, the linearity gets higher compared with the case of pressurizing with the board of 30 mm in diameter in FIG. 17, which shows that the surface stiffness becomes high by increment of pressurized area. In the case of pressurizing with the board for press of 200 mm in diameter in FIG. 19, the linearity is similarly enhanced and the surface stiffness is increased compared with the case of the comparison example.

[0165] As above, it can be said that it becomes clear from the experiment result that by making a structure including concave and convex portions as in embodiment 6, in the case of a small contact area, the structure gives only a seated person a feeling of light contact, and creates no reaction force which may cause a blood stream trouble or loads on muscles, and in the case of a large contact area, the structure can exhibit a sufficient surface stiffness, absorbs physique differences between seated persons to give a feeling of seating with a feeling of being safe.

[0166] Here, in a case that a cushioning structure according to the present invention is applied to a sitting seat, it is preferable that at a portion coming into contact with haunches, namely at a seat cushion portion, when a portion protruded by a bone is abutted, it can create temporal set in fatigue under loads while being partially bent as shown in FIG. 20, and as shown in FIG. 21, when a load is further applied, it has a structure that can support the load with a wider area according to the size of the inputted figure (shape and size of the haunches). This is because that since there is little difference of physique in shape and size of the haunches, when a load more than predetermined is applied, it enhances its vibration absorbability by serving the spring property sufficiently. Therefore, in a seat cushion portion, similarly to each embodiment described above, it is preferable to use such a structure that on an elastic member having a small reaction force such as a three-dimensional net member with concave and convex portions, another elastic member (such as Plumaflex, a metal spring, or the like) having a spring property is disposed, or if necessary, still another elastic member having a high surface stiffness is disposed.

[0167] On the other hand, in a seat back portion, a difference in physique is exhibited more clearly than the haunches due to a skeletal structure, and a difference in a position protruded by bones is larger compared with the haunches. Accordingly, it is preferable for a cushioning structure to form a seat back portion to put emphasis on a function to absorb a difference in physique. From this point of view, the conventional cushioning structure of using a polyurethane foam is insufficient in respect of a physique difference absorbing function, because, as shown in a imaginary line in FIG. 22B, the whole cushion is bent backwards around a substantially central portion of the seat back potion so that both sides are drawn nearly to the central portion. On the contrary, when the three-dimensional net members explained in the above-described respective embodiments are used and strained at an elongation percentage of less than 5%, a structure can be obtained in which, as shown in FIG. 23, it can create a partial temporal set in fatigue under loads in a small load range and displacement area, and, as shown in FIG. 22A, even when a further load is applied on it, it can follow the skeletal structure to absorb the difference in physique, and deform while fitting to the body by a damping characteristic due to friction between yarns. Therefore, in a cushioning structure composing a seat back portion, it is recommendable to make a structure to use, for instance, a three-dimensional net member with concave and convex portions explained in the above-described respective embodiment as an elastic member and only strain it, but not to dispose other elastic members.

[0168] Through this formation, in a seat cushion portion, as shown in FIG. 24A and FIG. 24B, a cushioning structure putting emphasis mainly on a spring element can be formed, and in a seat back portion, a cushioning structure putting emphasis mainly on a damping element can be formed. Therefore, the present invention has a merit of realizing a sitting seat structure provided with such ideal functions by selecting a combination of cushioning structures easily and at low costs.

[0169] According to FIGS. 24A and 24B, for a seat cushion portion, a cushioning structure of the present invention in which Plumaflex is supported with right and left total 8 pieces of metal springs (coil spring) and a three-dimensional net member with concave and convex portions is arranged thereon is adopted (refer to FIG. 1), and for a seat back portion, only a three-dimensional net member with concave and convex portions is adopted as a cushioning structure of the present invention, to prepare a car seat and respective load bearing characteristics are measured. It should be noted that the three-dimensional net members are supported at an elongation percentage of zero.

[0170] FIG. 25 shows load bearing characteristics of the cushioning structure adopted for the seat cushion portion, in which a broken line shows a load bearing characteristic combined both of the metal springs and Plumaflex, a thin solid line shows a load bearing characteristic of the whole cushioning structure layered with three-dimensional net members, and a bold solid line shows a spring constant (k) of the whole cushioning structure. As is clear from the drawing, it is found that linearity is high and the spring characteristic contributes to a high degree because the metal springs and Plumaflex are arranged to the three-dimensional net member in layers. Incidentally, after about 8 to about 10 mm in the restoring process, the spring constant comes to nearly zero, and temporal set in fatigue under loads is generated in a small displacement area.

[0171] FIG. 26 shows a load bearing characteristic of the cushioning structure adopted for the seat back portion, namely the cushioning structure consisting of only a three-dimensional net member with concave and convex portions. Incidentally, a bold solid line shows a load bearing characteristic of the haunches. From this result, it is found that in the cushioning structure adopted for the seat back portion, hysteresis loss becomes large compared with that in the seat cushion portion, showing large contribution of the damping element. Further, it is also found that the load bearing characteristic of this cushioning structure is almost parallel to the load bearing characteristic of the haunches, and has a characteristic close to the load bearing characteristic of the muscle. Incidentally, after the displacement amount of about 20 mm in the restoring process, the spring constant is nearly zero.

[0172] Then, a person of JM96 (cushion share load: 85 kg) is seated on the above-described seats, a vibrator platform is disposed below the seat cushion portion, and acceleration transmittance against frequency (G/G) is measured. The result is shown by a broken line in FIG. 27. For comparison, a vibration characteristic of a seat using polyurethane foam is shown by a thin solid line, and a vibration characteristic of a seat using an ordinary three-dimensional net member without concave and convex portion (provided that other conditions except no concave and convex portion are the same as that for the seat of the present invention) is shown by a bold solid line.

[0173] Although if the acceleration transmittance (G/G) exceeds 2.0, it gives a bad effect to a feeling of riding comfort, but as for this point they are all restrained to a low vibration transmittance. However, compared with a seat using polyurethane foam, all of the seat using a three-dimensional net member has a slightly lower vibration transmittance, and shows a favorable characteristic.

[0174] It has been known that a factor affecting a riding comfort largely is vibration of 2 Hz or less and 5 Hz which shakes a skeletal structure itself by vibration. Accordingly, it is desirable that the resonance peak should keep away from these ranges and the acceleration transmittance of 6 to 8 Hz which makes resonance with the internal organs should be lowered. As for this point of view, when the cushioning structure of the present invention is used, the resonance peak is set between 2 Hz and 5 Hz, and the frequency is set to be lower than those of other two cushioning structures. Accordingly, the acceleration transmittance in the range of 6 Hz to 8 Hz at which the internal organ resonates is set to be remarkably lower than those of other two cushioning structures. Therefore, it is found that when the cushioning structure of the present invention is used, it is also very excellent in a point of vibration absorbency.

INDUSTRIAL AVAILABILITY

[0175] The cushioning structure of the present invention includes an elastic member composed of a three-dimensional net member formed by connecting a pair of ground knitted fabrics disposed apart from each other using connecting yarn, and a spring constant during a pressurizing process is set in the range of 0.1 to 10 N/mm and, at the same time, during a restoring process, a spring constant after restoring to an amount of displacement of 20 mm or less, at the latest, to 2 mm, is set to be lower than the spring constant during the aforementioned pressurizing process. As a result, when a person comes into contact with a cushioning member by a sitting movement or a standing movement, temporal set in fatigue under loads (stroke) of about several millimeters to about ten and several millimeters is created, thereby improving a feeling of fitting (compatibility) which makes a person feel comfortable, and effectively alleviate a blood stream trouble and loads on muscles. Therefore, when the cushioning structure of the present invention is applied especially to a seat structure of aircraft, it is effective to prevent a trouble so-called an economy-class syndrome which is caused by blood stream trouble or loads on muscles.

Claims

1. A cushioning structure including an elastic member composed of a three-dimensional net member formed by connecting a pair of ground knitted fabrics disposed apart from each other using connecting yarn,

wherein, as a load bearing characteristic of the cushioning structure, a spring constant during a pressurizing process is set in the range of 0.1 to 10 N/mm and, at the same time, during a restoring process, a spring constant after restoring to an amount of displacement of 20 mm or less, at the latest, to 2 mm, is set to be lower than the spring constant in the aforementioned pressurizing process.

2. The cushioning structure according to claim 1, wherein the spring constant in the aforementioned pressurizing process is set in the range of 0.1 to 5 N/mm.

3. The cushioning structure according to claims 1 or 2, wherein the amount of hysteresis loss between the pressurizing process and the restoring process in the load bearing characteristic is in the range of 40 N or less.

4. The cushioning structure according to any one of claim 1 to claim 3, wherein the elastic member composed of the three-dimensional net member is configured to have a small reaction force such that as a load bearing characteristic during the pressurizing process the three-dimensional net member with a board for press of 30 mm in diameter alone, a spring constant after restoring to an amount of displacement of 20 mm or less, at the latest, to 1 mm during the restoring process is lower than the spring constant during the pressurizing process in the whole load bearing characteristic.

5. The cushioning structure according to claim 4, wherein said three-dimensional net member formed in a structure having a small reaction force has a thickness in the range of 5 to 30 mm.

6. The cushioning structure according to claim 4 or claim 5, wherein said three-dimensional net member formed in a structure having a small reaction force is provided with concave and convex portions at least on one surface, and the elasticity of the concave portion and that of the convex portion are different from each other.

7 The cushioning structure according to claim 6, wherein said three-dimensional net member formed in a structure having a small reaction force has a structure in which the convex portion is formed substantially in an arch shaped cross section between adjacent concave portions, and the elasticity in a bending direction of the convex portion having the substantially arch shaped cross section and the damping caused by friction accompanying sliding of the connecting yarn disposed in the concave portions can be utilized.

8. The cushioning structure according to any one of claims 4 to 7, wherein another elastic member serving as a function to prevent the cushion from bottom touch during the pressurizing process is provided below an elastic member composed of said three-dimensional net member formed in a structure with a small reaction force.

9 The cushioning structure according to claim 8, wherein aforementioned another elastic member serving as a function to prevent the cushion from bottom touch is a net type elastic member, a sheet type elastic member, or a net or sheet type elastic member supported via metal springs.

10. The cushioning structure according to claim 8 or claim 9, wherein aforementioned another elastic member serving as a function to prevent bottom touch is disposed at a predetermined interval to the elastic member composed of a three-dimensional net member formed in a structure with a small reaction force.

11. The cushioning structure according to any one of claim 4 to claim 9, wherein still another elastic member higher in surface stiffness than the elastic member composed of the three-dimensional net member formed in a structure with a small reaction force is layered, in addition to the elastic member composed of said three-dimensional net member formed in a structure with a small reaction force and aforementioned another elastic member serving to prevent bottom touch.

12. The cushioning structure according to claim 11, wherein an elastic member composed of the three-dimensional net member formed in a structure with a small reaction force is laminated on the upper portion of still another elastic member described above, and another elastic member described above serving as a function to prevent bottom touch is arranged on the lower portion of still another elastic member described above at a predetermined interval.

13. The cushioning structure according to any one of claim 1 to claim 12, wherein the cushioning structure is applied to various seat structures including a vehicle seat and a furniture chair or a mat for furniture or for seating.

14. The cushioning structure according to claim 13, wherein the cushioning structure is applied to a seat structure for an aircraft.