WO2001024893A1

WO2001024893A1 - Wheel for inline skates and the like

Info

Publication number: WO2001024893A1
Application number: PCT/US2000/041040
Authority: WO
Inventors: Hendrik A. Van Egeraat; Jens E. Jacobbson
Original assignee: Pc Vane Inc.
Priority date: 1999-10-04
Filing date: 2000-10-02
Publication date: 2001-04-12
Also published as: AU1629601A

Abstract

Wheel for inline skates comprising a main body (1) and an inner tire (1c) that together with an outer tire (3) form a cylindrical section with a greater width (A) than thickness which veering (F1) can accept diametrical loads and a coupling flange (1b) that is considerably thinner than the width (A) of the wheel (100) which allows a veering acceptance of centric loads.

Description

WHEEL FOR INLINE SKATES AND THE LIKE

TECHNICAL FIELD:

The present invention relates to a wheel for inline skates and the like. It flexibly accepts and returns the fluctuating, alternating- and intermitting ground reaction loads, as generated during the skating motion and its -load cycle, in a motion energy preserving manner. The wheel has a main body, tire and bearing core that are made of materials which by their characteristics and geometry complement each other. They result in a unit which has defined relations between damping (motion energy absorption that is necessary to guarantee roadworthiness -avoid slipping- and protect the human body against vibrations) , resilience and spring action

(elastic action to return loads in a motion energy saving manner and vibration insulation) . The requirements on damping, resilience and spring action differ in accordance with the stage of the skating motion, its force and the wheel position (inclination) . The main body of the wheel includes a tire and a bearing core that are, by their predominantly cylindrical geometry, stiffer in the lateral diametric direction than their common considerably less thick intermediary flange . Thereby enabling a flexible spring-like deformation of the wheel to force-components that are parallel and vertical to the rotation axis at the same time. Around the tire core a resilient tire is attached that in its outer cross section resembles a double involute curve which in its sliding (enveloping) length surpasses the working length. The resilient tire high rebound (elastic response) while the wheel is within its vertical ( the wheel inclinations in between +15° and- 15°) limits and a relatively high damping (giving grip on the skating surface) when the wheel is out of its vertical limits. The fore mentioned tire core forms together with the tire a section that resembles a cylindrical cut which is wider than its thickness. The tire is anchored at the lateral sides of the wheel, concentrating the resilient action within the whole tire thickness, thereby reducing energy loss by undue molecular friction and against well defined recoil areas, in order to accept all return forces (energy) as effectively as possible.

BACKGROUND OF THE INVENTION:

While testing wheels with an intermediate flange, that in width was smaller than both the tire and the bearing core, one particular version showed a lower roller resistance than anticipated. The roller resistance of the wheel, once its axis turned under an angle of >15° in relation to the skating surface, became even lower than in known wheels. The result being more startling when one considers that the particular wheel was an economy version of which both wheel body and tire are made of thermoplastic polyurethane ' s that are known for their high damping (energy absorbing) characteristics. Immediately the question arose if the geometrical configuration, its stiffness and its form recuperation speed (the time it takes to regain its original form once loads are reduced or released) played a roll . Measurements with a servo hydraulic uniaxial tester showed that during the minute changes in the geometry of the wheel a considerable amount of energy is accumulated and returned. In other words the configuration does act as a spring and more specifically as a spring with an exponentially growing force to deformation ratio. It being it understood that said energy is the result of both radial- as well as axial load components. Said spring action will at the same time improve the vibration insulation. With these facts it became possible to pronounce the effects by adapting the configurations in such a way that a progressively growing resistance accepts deflection loads and returns those in an energy preserving manner, independent of the load direction that is relative to the skating motion, while covering the different physical user profiles in a relative small number of wheel categories. Another step in the development was to reduce the thickness of the cylindrical wall that forms the tire, in order to enhance the resilience of the configuration, while also allowing for a more economical use of the material . It was decided to omit all mechanical fastening profiling diametrical to the wheel and along its cross section which comes in contact with the ground and instead concentrate those on the side of the tire by anchoring the wear ply there. Said wear ply and main body then connect diametrically, directly and flatly onto each other over the main action radius of the wheel, resulting again in a considerable reduction of material and weight. Sought was a more flexible tire, which was achieved, but also found was that again the diametrical roller resistance decreased. The explanation being, as afterward concluded, that the outer tire and the inner tire of the wheel were flatly connected to each other without intermediary profiling, which otherwise greatly increases the contact circumference between both entities and energy absorption. Tests were made for options with profiled connecting flanges and such with different thickness, all in relation to their specific modules of elasticity and loads. In order to increase the possibility to accept and return perpendicular directed ground forces, thereby again reducing the roller resistance and/or adaptation for light/heavy persons. The result being that those constructions have little relevance to wheels with tires of polymerised urethane, but they substantially improve the wheels with tires made from thermoplastics, because they have a considerably higher specific damping and consequently worse resilient action.

The roller skating motion is primarily in the forward direction, while the motion pattern is highly individual. Some persons get good results with maximum inclinations of 10°on the lateral side of the feet while others use inclinations of about 30°, for the medial side of the foot these values are 30° respectively 60°. The motion energy is for more than 60% generated in between the inclinations -15° and +15°, while 30% is generated between +15° and +30° on the medial side of the foot and the rest 10% between +30° and +60° again on the medial side of the foot.

Inline skate wheels are in general produced and assembled from a stiff hub in a thermoplastic material such as for instance glass fibre reinforced polyurethane, which has an elasticity module of for instance 6000 N/mm² and absorbs (damps) the greater part of the motion energy it receives . The tire is predominantly made of a urethane polymer, which needs mechanically fastening (anchoring) to the hub. The tire has a very low module of elasticity < 25 N/mm² but a high rebound capacity (elastic energy return) that can be more than 75% in accordance with DIN 53512. In order to fully recuperate as much as possible of the bouncing potential of the tire shall the; -contact area with the hub not constrict the deformation potential of the tire, -bouncing-action be in the radial direction and not be confused in its direction by contact surface enlarging profiling. Furthermore is the influence of the hardness (Shore) of the tire only marginally related to its bouncing capacity and therefore the roller resistance. Materials, such as for instance polymerised urethane resins, are known to have bouncing capacity of 75% or more, within a hardness range of 50A to 90 A Shore. However in the amount of elastic action of a given tire the load/deformation is an important factor, so light persons will need a softer (low Shore hardness) tire than the ones that are more heavy in order to pass comfortably over rough surfaces. If a person is too heavy for the load/deformation characteristic of a wheel (overload) and specially the tire, the rebound characteristics and over all resilient capacity of the wheel will be severely restricted and the motion energy will be destroyed in excessive damping. Said excessive damping will result in the well-known heating of the wheel and rapid wear of the tire. If a person is too light for the load/deformation characteristics of the wheel (underload) and its tire, the rebound characteristics and over all resilient capacity of the wheel will become too high and not enough damping is created to assure road contact. Said insufficient damping will result in sliding and loss of road contact. Another factor is that the demands on load/ deformation characteristics on the resilient tire change with the inclination of the wheel. The load is greatest when the wheel rotation axis is parallel to the ground, and the lowest at the maximum inclination. Here, as in different weight, it is also important that the resilient action of the wheel and its damping are adapted to the situation and that enough damping always is created to guarantee road contact. In other words, the damping shall be low when the load is high and high when the load is low. Finally transport wheels which in appearance resemble the wheel at hand are generally known. They also have a reduced main body width in relation to the tire width, there however the comparison ends, because they are; - solely designed to accept loads diametrical to the rotation axis, - their material, by and large fibre reinforced polyamide, has elasticity modules well over 10000 N/mm² in order to give stiffness to the wheel body in order to accept permanent loads that are diametric to the rotation axis, thereby concentrating the resilient action of the wheel primarily within the tire, - have flat relatively thin rectangular tires, that are laterally locked in between flanges on the main body and diametrically on herringbone like profiles.

- From; -US 330.884 S, -US 5.310.250 US, -EP 0 714 682, -EP 0 750 926, -US 5,573,309, -US -5,823,634, -US

339.320, -US 397,390, -US WO 98/58712 (20 Junel997) and -WO 97/17116 wheels are known having a hub with bearing pockets, and holes parallel to the rotation axis, in which the tire is attached. The construction is material consuming, and therefore expensive and not cost effective. The common part of the tire and the hub constricts the resilient action of the enclosed tire material and results in a central core with such lateral stiffness that the resilient action of the wheel is concentrated in the tire material and than only in its radial direction. No efforts to guarantee an appropriate damping action of the wheel at its common inclinations have been made.

From WO 98/58712 is known a multilayer skate wheel in which cylindrical sections of different partly cured elastomeric material are flatly bonded to each other. The process is costly and complicated, does not result in material reduction, while the consecutive cylinders of material will result in a lateral stiffness of the wheel that concentrates the resilient action in the radial direction only.

Wheels having a flexible connection according EP 0 642 814 through wings, or tangentially arranged spokes US 0 330 883 in order to achieve a non rigid suspension between bearing pockets and tire will function flexibly only under loads and components thereof that are radial to the wheel . A further disadvantage is that they work like blade springs with a linear load deflection capacity only, which is virtually impossible within the given space seen the exponential changing roller-skate loads.

Wheels with gas filled bladders are known from; US 5,632,829, -US 5630891, US 5,641,365 and US 5,733,015. They are complicated to produce and maintain, the stress-to-strain relation of the tire is low, thus making the resilience greatly depending on the pressure differences which in their turn are directly related to volume changes and the ground reaction is exponentially changing in relation to weight, speed, roughness of surface etc. In the small tires at hand dramatic changes of the ground contact area are inevitable, leading to pit erosion and although the tire may accept axial forces at its periphery, the tendency will be to absorb (damp) and accompany the energy/movement rather than to return it, because of the low lateral stiffness of the tire. Similar disadvantages can be recorded for a number of other patents in which a tire core of a cellular rubber of plastic material is used.

From fore mentioned WO 97/17116 and numerous patents dealing with tandem roller skates a wheel is known of which the flexibility (elasticity) of the tire is modified by circular grooves in their sides. These grooves are made to make the sides of the tires flex easily into them in order to sustain road contact. The stiffness of the tire and capacity to achieve loads and return them is thereby sharply reduced by the very low elasticity module that is inherent to the construction .

From fore mentioned WO 97/17116 a flat or slightly curved middle rolling section that is sharper curved at the roller shoulder is known. Inclinations of the central axis out of its parallel ground position with around 60° are common in inline skating. These movements shall be projected to the tire area on an as uniform as possible contact area, giving constant grip, while avoiding dispersion of the radial wheel velocity over conflicting contact circles. The enclosed wheel will concentrate all ground contact that supersedes the angle of its slightly curved rolling section arc (which is 0° when the surface is flat) on the sharper curved shoulders and decline the contact area as well as the grip. Substantially the same, however giving a completely different result is known from US 5,310,250. Here the middle rolling section is formed by a sharp curve, while the shoulders are made by bigger curves that tangent both the wheel sides and the fore mentioned sharp curve. Again once the wheel inclines beyond the angle enclosed by the sharply curved middle roller section, all ground contact will be concentrated on the shoulders, this time however enlarging the contact area and dispersing the rotational wheel velocity over a number of contact circles, representing conflicting diameters which will inevitably result in slowing down and extra wear.

To achieve a tire form that is curved in such a way that ground contact/grip is continuous, while dispersing the velocity of the wheels on the ground surface over an as small as possible area, and avoiding conflicting wheel diameters, an involute curve was adapted. From standard engineering books constructions on involute sliding splines (involute gear) were studied and used in order to approximate a tire cross section, which has an as equal as possible road contact under all possible wheel inclinations, while avoiding the division of the rotational speed of the wheel on ground contact over a great number of different diameters. It was found that the wheels had a better grip when inclined, this could be attributed to the higher damping at the sharp edges and the flattening of the tire at its sides.

Furthermore in the above mentioned patent disclosures assumptions are made on roller resistance being related to hardness (Shore) , but again this depends nearly entirely on the material in question and its specific rebound capacity, as for example defined by DIN 53512. It is for instance known from BASF literature on ELASTURAN 6060 that it varies in rebound capacity within a narrow range between 70 and 75% over a Shore A hardness range between 50 and 90.

It has to be observed that the human body is geared to accept motion and its load components, such as shocks, vibrations, changes in motion energy (body mass vs. speed) and centrifugal forces, by damping within the coupled mass of the body and resilient muscle action in the frontal (forward) direction, to a much lesser extent backward movements, while it can hardly cope with side movements. Especially feet, lower legs, and leg joints perform poorly in relation to lateral motion loads and their vibration components. While inclining the wheel during the skating motion the ground reaction forces will result in a component that is lateral to the feet and body, this general force and its components (vibrations, shocks etc) shall than be met with extra damping within the wheel, thereby protecting the body. Coinciding and an added benefit of said extra damping is that it is also needed in order to sustain road contact at the more inclined positions.

SUMMARY OF THE INVENTION:

The present invention comprises a wheel for inline skates and the like that in a motion energy saving way accepts and accompanies the fluctuating and diverging loads inherent to the inline skating motion pattern. The wheel also serves the purpose of adapting its characteristics in regard to damping, resilience and spring action with regard to its position (inclination) and at the same time enabling a more economic and comprehensive use of materials. The wheel serves the purpose of keeping the product of load and friction over the contact area adapted to the requirements^ thereby achieving a uniform spring action of the main body and resilient bouncing capacity of the tire and all components related thereto (vibration insulation, damping, shock absorption and roller resistance) . Finally the wheel does serve the purpose of accepting the lateral (in relation to the feet and body) loads components of the ground reaction forces and the vibration/shock insulation/absorption thereof and protect the human body therefrom.

The said purpose is fulfilled with a wheel embodiment within the scope of the present claims.

BRIEF DESCRIPTION OF THE DRAWINGS:

Fig. 1 shows a three dimensional sectional view of a wheel in accordance with the invention.

Fig. 2 shows a side elevation of the device shown in fig. 1.

Fig. 3 shows a cross section I-I (see Fig. 2) of the lower half of the device shown in fig. 1 that indicates the wheel inclinations which each have their own functional requirement. Fig- 4a shows the ground reaction forces and the deformation of the tire, when the wheel is placed perpendicular, in regard to its rotational axis.

Fig. 4b shows the same configuration as in Fig. 4a, with the rotational axis is turned 15°. Fig. 4c shows the same configuration as in

Fig. 4b, with an increased ground force.

Fig. 4d shows a configuration of forces as shown in Fig. 4c, however under a general wheel inclination of 30°. Fig. 4e shows a configuration of forces as shown in Fig. 4d, however under a general wheel inclination of 45°.

Fig. 4f shows a configuration of forces as shown in Fig. 4e, however under a general wheel inclination of 60°.

Fig. 5 shows the construction of the involute curve for the outer surface cross section of the tire. Fig. 6 shows the respective slip reaction forces and their perpendicular components in relation to the centre of the flange.

Fig. 7 shows the thickness of the tire in relation to the wheel inclination.

Fig. 8 shows in diagram the development of;- the slip reaction forces, -the vertical ground load components and -the time spent at the respective wheel inclinations . Fig. 9 shows a wheel with a profiled flange and the bearing options.

DESCRIPTION OF THE INVENTION:

The preferred embodiment hereafter described is showing a wheel for roller-skates and the like which accepts and returns the fluctuating, intermitting and alternating ground reaction forces that result from cyclic motions. The wheel exists of a main body that in one piece combines a predominantly cylindrical rebound ply and tire, a bearing core and a common flange that is smaller in width than the aforementioned parts. Said main body is preferably produced in a polyurethane plastic and enables by its spring-like deformation, as well as by its resilient tire, the return of part of the directional as well as in strength varying roller-skate loads and thereby preserve motion energy. The cylindrical form of the tire also enables a fixation of the wear/rebound ply on the side of the wheel, whereby it becomes possible to concentrate the bouncing action over its main user area fully within all available tire material. The damping characteristics (protection against lateral vibrations as well as avoiding slipping) vary with the inclinations to meet the different roadworthiness requirements.

Fig. 1 shows the wheel 100. The main body 1 encloses at its core la a bearing outer ring 2. Another part of the main body 1 is the inner tire lc to which a tire 3 is attached. The bearing core la is connected to the inner tire lc over a considerably thinner flange lb. The main body 1 is built up of diametrically uniform sections in respect to the maximum user inclination G (see Fig. 3) of the wheel 100. In other words the sections la, lc and lb have no radial or geometrical stress concentration factors such as spokes, holes and other segmentations that otherwise will give different stiffness and roller resistance within the wheel. The main body 1 is preferably made of a non reinforced polyurethane plastic and has an elasticity module of for example 1200-2500 N/mm² depending on the load characteristics (body mass/velocity) of the user and their respective category. The main body 1 and its connections to either the outer tire 3 or bearing ring 2 has the following functions:

The part la of main body 1 forms over its non profiled, rebound contact surface 5 together with the tire 3 a predominantly cylindrical section, in width A bigger than thickness B. The width E of the rebound contact surface 5 is practically well included within the maximum wheel inclination as signified by the angle H (see Fig. 3) in order to concentrate the resilient action of tire 3 against surface 5. The outer tire 3 is made of a polyurethane polymer that has a resilience of up to 75% providing the right load/deformation characteristics are met . The recoil of the tire 3, when the loads are released is fully directed against the surface 5 of the inner tire lc. Tire 3 is form fast and has a reasonable adhesion to the main body 1 mechanical anchoring is done around protrusions 4 on the side of main body 1. Part la also allows for a spring like deformation F, mainly to diametric loads on the side of the wheel 100. The spring like action will represent an over compensated spring (a spring with a load characteristic that grows progressively stronger in relation to each unit of compression) , mainly because the cylindrical form A-B and the connection to flange la.

The protrusions 4 are located outside the vertical component Rp3 (see Fig. 6) of the ground reaction force Rr3 (see Fig. 6) at the wheels maximum inclination, as defined by angle Q (see fig. 3) . In roller-skating the maximum inclination of the wheel is around 60° on the medial side of the foot, measured from the original position where the rotation axis of the wheel is parallel to the skating surface. The angle G (see Fig. 3), which encloses the tire surface, represents in cross section a double involute function of angles from 15° to 75° and 75° to 15°. - The flange lb connecting inner tire la with the bearing core 2 does not behave like a stiff member, because true diametric loads will hardly occur during the skating motion and the material has a relatively low module of elasticity, which when true diametric loads occur will cause a bulbous deformation 16a and 16b (see Fig. 4B) and a relative shortening of the flange lb. However and if necessary (adapting for light persons) the diametric spring action of the flange lb will be modified in order to accept in that direction loads by profiling zones 6 and 7 in it (see Fig. 7) .

The bearing core lc locks around the bearing outer ring 2, those two parts forming a stiff unit, in relation to the flange lb.

The tire 3 is made either from a thermoplastic or polymer of polyurethane and has the form of a double involute curve H (see fig. 3), of which each half preferably covers 90° when a thermoplastic polyurethane is used and 75° (see Fig. 9) when a polymerised polyurethane is used. Each tire material has its disadvantages and advantages. The thermoplastic material

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beginning of angle Gl . From there by pushing and displacing the centre of gravity of the body, the angles G2 , G3 , G4 and G5 on the medial side of the foot are gone through. Signifying that on each foot the lateral side, signified by angle G6 , not is used. It is however customary that the wheels are exchanged between left and right foot and turned using at one time angle G7 and at another time G8. However it also signifies that in whatever position the wheel is used the area as defined by Gl and G2 will always be exposed to wear. To avoid excessive wear of tire 3 (see Fig. 1) within the angle Gl and G2 , it is important that overload of the elastic capacity of the tire 3 (see Fig. 1) in this area is avoided. It shall also be understood that therewith excessive damping, the main course to wear, is avoided.

The maximum mechanical (friction) requirements as defined by Rfl (see Fig. 4b), within said positions G1-G2 is low and will require minimal damping, excess thereof will only cause heat, wear and motion energy consumption. The correct dimensioning of the elastic capacity of the tire 3 (see Fig. 1) in the positions G2 and G4 is also very important because not only is it loaded, in whatever position the wheel is installed, but it is also loaded during around 60% of the skating motion (Tl+T2= 60% of T see Fig 8) .

Fig. 4a shows a cross section I-I (see Fig. 2) over the lower half of wheel 100 (see Fig. 1) with its rotational axis (50 see Fig. 1) parallel to the skating surface. The ground reaction force Rr (see also Fig 6 and 8) then is vertical to the rotation axis 50, which practically hardly ever will happen, because of the dynamic ground reaction forces, which are not unidirectional and vary with the roughness of the skating surface. The ground reaction forces fluctuations that are due to surface conditions are left out at this time

(except for the part covering the elastic capacity and extreme conditions that are covered in Fig.4c), because the tire has a very low modulus of elasticity. The ground reaction force Rr is the total of the body mass of the skater Fw and the (varying) push force of the skater Fd. The loads Fw+Fd are concentrated on the inside of the bearing ring 2, while the counter force Rr is concentrated at the middle of tire 3 (see Fig. 1) . In between the said forces Fw+Fd and Rr the tire core la, the flange lb, the inner tire lc and the tire 3 (see Fig. 1) are situated. Said forces will influence;- tire 3 (see Fig. 1) , that will be deformed because its volume is reduced at 14 and expanded at 13,- the tire core that will flex at 16c and 16d, - the flange lb (see Fig 1) by moving in either direction 16a or 16b. Rr is not only a static load, it also represents vibrations that are generated at the skating surface. These vibrations will be insulated from the body in relation to the elastic capacity of the tire. The greater the elastic deformation of the tire is, the more energy will be lost in damping. The tire at hand with a (theoretically) resilient (elastic) rebound capacity of 75% will therewith insulate also (theoretically) 75% of the vibrations. In the true vertical position with a relative body mass load on the wheel of 150 N, a Shore hardness of the polymer urethane tire 3 (see Fig. 1) of 80A on a asphalt surface (with a spatial frequency of 50-500 - ¹ and a vibration frequency of 400-4000 Hz) , the total deformation volumel4 will amount to 10% in relation to the activated volume as indicated by 15a and 15b, allowing for a rebound (elastic) capacity of 75% (energy return) . The rest of the energy is lost in damping; mainly material friction caused by deformation, vibration absorption and friction on the ground surface. The vibration absorption shall not be confused with the vibration insulation which is an inverted function of the damping. In other words the vibration insulation will be total (no transfer of vibrations), when no damping takes place. The resilient action of the tire 3 (see Fig. 1) within its activated part, as defined by 15a and 15b, is concentrated between the flat surface 5 (see Fig. 1) and the ground surface and both able to constantly accept and return the fluctuating deformation energy of the tire 3 (see Fig. 1), here in diametrical directions. Herewith a situation is created in which roughly 75% of the motion energy is returned.

Fig. 4b shows the load conditions for an inclination of 15°, this being either on the lateral or medial side of the feet (see Fig.3 Gl and G2) . As is inherent to roller-skating the push off force Fpl will stay perpendicular to the rotation axis, while the weight component Fwl remains perpendicular to the skating surface. The situation relates to the double push stroke, in which the wheel is placed with its rotation axis inclined on the lateral side of the feet (see Fig3 G2. ) . The wheel is then during a push stroke, in which the centre of gravity of the body is moved, that is placed vertical. After which, during a fluent motion (displacement of gravity centre) , the wheel inclining movement on the medial side of the feet takes place again covering 15° (angle G2 see Fig. 3) , before continuing (fluently) the further wheel inclination on the medial side of the feet (see Fig 3 G3 , G4 , G5) . The general load resultants Rrl and Frl have, by inclining G2 (or for that matter Gl see Fig 3), as indicated by the centre line 12 and its original position line 20, kept relatively high vertical exponents, signified by Fvl and Rvl . The horizontal component Rfl shows the minimum friction force required to avoid slipping, once the motion angle has turned the angular distance G2. Indicating therewith that the damping within tire 3 has to be increased in relation to the vertical position as shown in Fig. 4a. The friction requirement (to assure good roadworthiness) within said inclinations of -15° and +15°, are a product of the vertical load Rvl and the friction coefficient of the tire 3 and its contact area at skating surface 17. Said friction coefficient of tire 3 is adapted by reducing the elastic capacity of tire 3 by reducing its thickness and consequently augmenting its damping capacity. The algebraic solution of the different forces that work on the wheel 100 (see Fig. 1) shows that a diametric force Fdl with a perpendicular distance al has come into being exerting a moment of force on the bearing outer ring 2. Said moment of force will cause a centric veering and deformation of (primarily) the flange lb in the directions of either F2 or F3 (see Fig.l) . Said deformation can be used, even in a thermoplastic urethane, providing the torsion module and the load thereof is kept within acceptable operational limits. By the veering acceptance of the load Fdl the flange lb is instrumental in replacing the elastic overload of tire 3 that is required to generate enough friction (see also Fig. 1 F2 an F3) . Said algebraic solution of forces also discloses that at a perpendicular distance a2 a force Rdl is starting to exert a dynamic moment that will result in a veering motion of the inner tire lc at the direction of FI (see Fig. 1) , again initiating a return of energy (see also Fig. 1 FI) . Signifying that even under an inclination of 15° of the wheel 100 (see Fig. 1) a considerable amount (65% or more) of the motion energy is returned without adventuring roadworthiness. The inclination of G1-G2 (+15° or -15°) falls also within the acceptance/tolerance of the damping capacity of the coupled mass in the human body and its resilient muscle capacity. Fig. 4c shows a cross section I-I (see Fig. 2) of the lower half of the wheel 100 (see Fig. 1) under extreme load conditions, which might occur while roller- skating on deep grooved raffled tiles with a very low spatial frequency but high amplitude. The ground reaction force has a centric, component Rv2 , forming a couple that algebraicly results in a moment of force that is the result of force Fd2 and its perpendicular distance b2 diametrically (veering flange lb see also F2 and F3 Fig. 1) and a diametric component Rd2 , forming a couple that algebraic results in a moment of force that is the result of force Rd2 and its perpendicular distance b2. Said moment has not increased overtly from the moment Fdl x al (see Fig. 4b) , signifying that nearly all deformation energy is absorbed by tire 3 in elastic overload and damping. The energy return will of course reduce sharply and will in the situation shown, where the increase of deformation of tire 3 is more than 50% in relation to the deformation shown in Fig. 4b, while the load is not increased more than 20% be not more than 40%. That is in line with the rotation axis and forms therewith as a product the moment with which the bearing outer core 2 is veered within flange lb. Thereby it should be understood that the resilient capacity of the wheel not is restricted to the deformation within the tire 3 (see Fig.l) .

Fig 4d shows the load diagram, when the wheel 100 (see Fig. 1) has reached an inclination of 30° (angleG2+G3 see Fig. 3) . The centric moment of force is now equal to the product of Fd3 and perpendicular distance cl . The centric moment of force has grown considerably indicating that the veering action of flange lb in the direction F2 (see Fig. 1) has grown also. The diametric moment of force is now equal to the product of Rd3 and perpendicular distance c2. The diametric moment of force has grown considerably indicating that the veering of inner tire lc in the direction FI (see Fig. 1) has grown also. The friction requirements have grown to a force Rf3 however its vertical component Rv3 has become less, indicating that the friction coefficient of the tire 3 must grow here. To augment the friction coefficient the tire is made thinner, in order to increase damping within the tire material, which will be accompanied by a considerable amount of motion energy loss. Part of the motion energy loss will be recuperated over the veering action of inner tire lc and flange lb. Describing therewith a situation in which still 60% of the motion energy is restored. Fig. 4e shows the load diagram, when the wheel 100 (see Fig. 1) has reached an inclination of 45° (angle G2+G3+G4 see Fig. 3) The centric moment of force, the product of Fd4 and dl has grown and therewith the veering action F3 (see Fig. 1) within flange lb (see Fig 1) . The diametric moment of force, the product of Rd4 and d2 have also grown and therewith the veering action FI (see Fig. 1) of flange lc (see Fig. 1) . The friction requirement has grown to Rf4 while its vertical component Rv4 is reduced, indicating that the friction coefficient must grow again. The elastic ratio of the tire must grow again, by making the tire thinner and allow for more damping action therein.

Fig. 4f shows the load situation, when the wheel 100 (see Fig. 1) has reached an inclination of 60° (angles G2+G3+G4 and G5 see Fig. 3) which will only happen at full power output during start, curves or when higher speeds are required. The centric moment of force, the product of Fd5 and el has grown and therewith the veering action F3 (see Fig. 1) within flange lb. The diametric moment of force, the product of Rd5 and dl has also grown and therewith the veering action FI (see Fig. 1) of inner tire lc (see Fig. 1) . The friction requirement has grown to Rf5 while its vertical component Rv4 is further reduced. The tire thickness must again be reduced in order to allow for a higher elastic ratio and more damping.

Fig. 5 shows the construction of the involute curves 25 and 25* that each substitute halves of the outer cross section of the tire 3 (see Fig. 1) . Important in the construction is to define the radius r (addendum) of the base circle. Said base circle is related to halve the width of the wheel 100 (see Fig. 1) and the enveloping angle K5. The radius r will for the enveloping radius of K5 (75°) be N/cosa (52.58) (giving the length 0) /cosb (15°). In the example at hand, where K5=75° N=llmm and b=15° this will result in a radius r of; 11/0.79335/0.96593= 14,8. of the involute curve will be used at a number of inclinations spanning maximally an angle G1+G2 or G3+G4 (see Fig. 3a) having an enveloping length of 75° divided over an angle of around 60° on the medial side of the feet (Gl or G3 see Fig. 3) and around 15° on the lateral side of the feet (G2 or G4 see Fig. 3) when driving forward. During the varying inclinations the wheels, at their contact diameters a (when vertical) versus e (when maximally inclined) , vertical to the rotation axis 27 (see Fig 4a) must vary as little as possible, thereby avoiding that the rotational (radial) velocity of the wheel will be divided over contact circles that have conflicting diameters. The best results were achieved by dispersing the different inclinations of the wheel 100 (see Fig.l) over a tire 3 (see Fig. 1) that has a contact cross section that resembles an involute curve 25 respectively 25* and encompasses around 75°, being 15°over the maximal inclination that is used in roller-skating. The wheel 100 (see Fig. 1) unwinds thereby like a taut line over its involute curve 25 respectively 25*, during its inclining motion. For the construction of the involute curve it is important to have the following parameter; - the width of the wheel 100 (see Fig. 1), which in this case is 22 mm,- the maximum users inclination (length of the loaded curve) , which in this case is 60°,- the total length of the involute curve, which in this case is 75°. The diameter of the base circle then is in the true vertical position (see also friction value RfO Fig. 3b) , when the ground reaction force Rr is vertical to the rotation axis 50 (see Fig. 1) , hardly any friction is required, indicating that the damping there can be at its absolute minimum and motion energy can be returned to the maximum of the resilient material of tire 3 (see Fig 1) . The maximum resilient return of motion energy by tire 3 (see Fig. 1) is determined by the following criteria:

• The characteristics of the material used.

• The load/deformation relation, meaning that a material will have its best resilient energy return when it is not over- or for that matter under loaded.

• The contact surfaces between which the resilient action of tire material 3 (see Fig. 1) takes place are defined by the surface 5 (see Fig. 1) and the ground surface . For the inclinations of the wheel 100 (see Fig. 1) at the end of the angles G2 (-15°) and G4 (+15°) (see Fig. 3) the horizontal friction load-requirements Rfl and Rfl* (see Fig. 6) have the vertical load-components Rvl respectively Rvl* (see Fig. 6) . It becomes clear that the damping within the tire 3 (see Fig.l) will have to increase, requiring a higher load/deformation, this will be achieved by reducing the tire thickness 30 (see

Fig. 7) accordingly (to avoid slipping) . The deformation of tire 3 (see Fig 1) within the zones 15a and 15b (see Fig. 4a) is kept small in volume and thus gives a high elastic motion energy return (elastic load ratio) . The rebound capacity is limited to 75%, due to losses within the material (molecular friction) . The rebound capacity and its molecular friction loss is influenced (lowered) negatively when the bouncing areas, surrounding the volume 15, are profiled and irregular. Therefore care has been taken to make these areas (see also bouncing surface 5 Fig. 1) as flat as possible, in order to receive forces 15b and rebound forces 15a (see Fig, 4a) as diametrically opposed as possible to each other. The resilient action of the middle flange lb (see Fig. 4a) is concentrated on minute deformations in thickness 16a, 16b (see Fig. 4b) and movements of the flange la (see Fig. 4a) 16c, 16d relative to the vertically stiffer flange lb (see Fig 4a) . The minute changes store enough resilient energy for an energy return of 4-6% in the given situation. Meaning that in the given situation around 80% of the motion energy is returned by veering (spring action) .

Fig. 6 shows the forces Rr, Rvl, Rv3 , Rv4 and Rv5 that work perpendicularly on the tire at the given wheel inclination. The aforementioned forces are directly related to the elastic deformation ratio for tire 3 (see Fig. 1) at the given wheel inclinations, while they will change (decrease) for the inclination of the wheel out of the vertical. The forces Rfl, Rf3 , Rf4 and Rf5 indicate the friction requirements at the given wheel inclinations, they will change (increase) for the inclinations for the wheel out of the vertical.

Indicating once more the necessity of the increase of the friction coefficient in order to avoid slipping.

Fig. 7 shows the decrease in tire thickness along the width A (see Fig.l) of the tire, in order to give the tire different elastic ratios. The length 29 indicates the place on the wheel were full elastic capacity is possible, deformations here are calculated to a deformation maximum of 16%. The lines 30 and 30* indicate the areas were the elastic ratio is increased in order to create damping and friction, deformations here are calculated to a maximum of 22%. The lines indicate the 31 and 31* where the elastic ratio is again increased to a deformation maximum of 26%. The lines 32 and 32* indicate the areas where the elastic ratio is again increased to a deformation maximum of 30%. The lines 33 and 33* indicate the areas where the elastic ratio is again increased, this time to a maximum of 35%. The deformation areas are only related to the loaded tire part, for instance will the deformed area as defined by 15a and 15b (see Fig 1) be greater than the deformation area 19 (see Fig.4f). Fig. 8 shows in diagram:

• The vertical load components that belong to the wheel inclinations are -15° at 21, 0° at 22, +15° at 23, +30° at 24, +45° at 25 and +60° at 26 are respectively Rvl*

(equal to Rvl see Fig. 4b) Rr (see also Fig. 4a) , Rvl (see also Fig. 4b) , Rv3 (see also Fig. 4d) , Rv4 (see also Fig. 4e) and Rv5 (see also Fig. 4f) . • The friction load components that belong to the respective wheel inclinations (as mentioned above) are Rfl* (equal to Rfl see also Fig. 4b), Rf which is around 0, Rfl (see also Fig. 4b) , Rf3 (see also Fig. 4d) , Rf4 (see also Fig. 4e) and Rf5

(see also Fig. 4f) .

• The respective time spent at each moment of the roller skating action, capacity and mass of for example a skilled roller skater using a "double stroke" push is reproduced in line 30 (see Fig. 7) , signifying from point 21 to point 26, the first ground contact with the wheels 21 until the wheels leave the ground contact at the end of the push off stroke 26. The wheels are placed on the ground at an angle of -15° at 21 then the first push off is made till the rotational axis is parallel with the ground again at 22, than the next push is made till the rotational axis is inclined 60° at 26. The inclination of +15° is at 23, +30° is at 24, +45° is at 25 and +60° is at 26.

• The percentages of stroke at its inclinations is defined at line 30 over the following percentages: 30% between 21 (-15°) and 22 (0°) , 30% between 22 (0°) and 23 (+15°), 22% between 23 (+15°) and 24 (+30°) , 13% between 24 (+30°) and 25 (+45°), 5% between 25 (+45°) and 26 (+60°). Fig. 9 shows a cross section over a wheel in which the flanges are profiled at 6 and 7 in order to make them more flexible. The bearing options include ball bearings 42 and 43 fitted in an aluminium ring 40 and 41, or direct in a bearing core of the same material as the flange 45, or a profiled roller bearing 44. The tire is thinner than in the fore going example, because it is made of a thermoplastic urethane that has a high internal damping.

Claims

Claims :

1. A wheel (100), particularly for roller skates with a main body (1) , that combines a tire core (lc) and a bearing core (la) with a substantially thinner flange (lb) c h a r a c t e r i z e d in that the body can veering accept centric (Fdl , Fd2 , Fd3 , Fd4 , andFd5) and diametric (Rdl , Rd2 , Rd4 , and Rd5) loads and thereby accumulate and return motion energy.

2. A wheel (100), that has an inner tire (1) to which an outer tire (3) is attached, c h a r a c t e r i z e d in that the width (A) is greater than the thickness (B) .

3. A tire (3) of which the thickness (29, 30,30*, 31,31*, 32,32*, 33,33*) in relation to the outer surface (5) of the inner tire (lc) is altered, c h a r a c t e r i z e d in that the elastic load ratio of the tire (3) can be adapted to the inclinations (G1,G2,G3,G4 and G5) and their specific friction requirements (Rf1 , Rf2 , Rf3 , Rf4 and Rf5) .

4. A wheel (100) with an elastic tire (3) and a main body (1) centric deformation zones (F2 andbF3) and diametric deformation zones (FI) c h a r a c t e r i s e d in that motion energy is accumulated and restored by the elastic action of the tire (3) and by the spring like deformation of the inner tire lc and the flange lb.

5. A wheel (100) according to any of the claims 1-4 c h a r a c t e r i z e d in that the energy accumulating and -restoring capacity of the tire (3), that of the inner tire (lc) and that of the flange (lb) integrally complement each other.