The present invention relates to a spring element for the formation of a spring, wherein said spring element mainly consists of a resilient material and has a first and a second series of holes, whereby the spring element has a characteristic distance equal to the distance between the centre of at least one hole of the first series of holes and points on the circum- ference of holes of the second series of holes most remote from said centre.

Furthermore, the invention relates to a spring comprising one or more spring elements of this kind as well as connecting means for the connection of the spring to mutually movable objects.

Finally, the invention relates to a suspension system for a training device to receive punches, kicks etc., e. g. a punching ball, said system comprising such a spring.

In GB 613,000 a vibration insulating mounting is disclosed comprising a first and a second flexible member, mainly annular elements, which are connected between an interior and an exterior connector. The first member is permanently connected to both con- nectors, whereas the second member is permanently connected to one connector, leaving a play in relation to the other connector. In result, up to a certain motion amplitude threshold value, only the first member will flex, be compliant and/or absorbent upon mutual motion of the two connectors, whereas both members will flex, be compliant and/or absorbent when the amplitude of mutual motion exceeds the threshold value.

The suspension is particularly designed for the suspension of vibrating devices, in which the vibration amplitude may increase severely in connection with resonance, e. g. when passing certain level of RPM during starting or stopping. The method described

ensures a soft suspension, and therefore a fine vibra- tion separation at normal operation, and a more rigid suspension, and therefore a more efficient vibration absorbtion at large vibration amplitudes, e. g. in connection with resonance.

SE 119,945 discloses a device for boxing training with a punching ball suspended in springs, whereby the impact of punches to the ball is determined and the measurement result is shown by means of lights going on, whereby the number of lighting lights indicates the magnitude of the punch. The force of the springs is adjustable by means of regulators, however, since the spring constant of said springs is not increased progressively, the punching ball will be suspended comparatively rigidly, and, most likely, require the user to wear protective equipment, e. g. boxing gloves.

Moreover, the punching ball will probably make several oscillations in various directions before settling down after a swing, which is inconvenient to the user who must be careful not to get hit by the punching ball.

Finally, the recording of the deflections of the punching ball will hardly be precise as the springs are placed between the punching ball and the recording device and thus translate the oscillations of the punching ball unpredictably.

US 5,147,258 discloses a suspension for a punching ball, in which the suspension comprises a ball joint and a flexible element, e. g. a resilient hose part.

Said suspension thus has a constant rigidity that cannot be adjusted. If provided with such a suspension, the punching ball will hardly settle down soon after a swing.

US 4,974,833 discloses a training device for martial arts comprising a matting of adequate thickness to absorb punches and leave the person punching without

injuries. In certain places, said device comprises means for the determination of the amplitude of the movement of the matting when those places are hit, but not for the speed of the amplitude of the matting.

Furthermore, the compliance of the training device cannot easily be changed after its fabrication, and the device is applicable for the absorbtion of punches from one direction only.

The object of the invention is to provide a spring element for the formation of a spring, whereby the characteristic of the spring may be chosen to be nonlinear and adjustable in a simple way to meet individual needs.

To achieve this, the spring element is character- ized in being designed to be detachably connected to a number of connecting means corresponding to the number of holes, whereby a first set of connecting means is movable in relation to a second set of connecting means so that, in order to ensure mutual compliance between the two sets of connecting means, the first set of connecting means engages into the first series of holes of the spring element and the second set of connecting means into the second series of holes, and that, at least in the second series of holes, the holes are designed to leave a play between at least part of the circumference of the holes and the corresponding connecting means upon engagement.

As the holes of the second series of holes of the spring element may have a size and/or a shape prevent- ing the connecting means from touching the circumfer- ence or all of the circumference of the holes, when the characteristic distance of the element has certain magnitudes and at certain positions of the two sets of connecting means in relation to each other, said connecting means will be somewhat movable in relation

to the first set of connecting means before the spring element starts deforming.

The claims 2 and 3 relate to preferred embodiments of the two series of holes of the spring element.

If the spring element is designed as suggested in claim 4, a particularly simple and inexpensive manu- facturing process is achieved.

The embodiment referred to in claim 5 ensures an increased durability of the spring elements in as much as the holes are reinforced wherever the spring elements are exposed the most to wear and tear.

Furthermore, the object of the present invention is to provide a spring having a rigidity that can be easily adjusted, whereby the characteristic of the spring is a type allowing a spring body to settle down comparatively soon after having made an oscillation.

To meet this object, the spring comprises one or more spring elements according to the invention and has connecting means for the connection of the spring to mutually movable objects, whereby it is characterized in that a first set of connecting means engages into the first series of holes and a second set of connect- ing means engages into the second series of holes of each spring element.

In consequence, the rigidity of the spring may be altered, simply by changing the number of and/or the rigidity or the damping characteristics of the spring elements to be placed on the connecting means of the spring.

Another object of the invention is to provide a spring of the same kind, whereby the spring may, addi- tionally, be progressive, and wherein the progression of the spring is adjustable in a simple way.

To achieve this, the spring comprises two or more spring elements according to the invention, and, as an

additional characteristic feature, at least two of the spring elements have different characteristic dis- tances.

A spring comprising spring elements according to the invention of different characteristic distances allows the spring rate of the spring to be generally stepwise variable, dependable on the position of the two sets of connecting means in relation to each other.

Thus, a curve showing the spring force as a function of the mutual displacement of the first set of connecting means in relation to the second set of connecting means will present a number of breaks, or at least changes of curvature, corresponding to the number of spring elements having different characteristic distances.

Accordingly, the spring may be designed to be compara- tively soft at minor motions and more rigid at larger motions of one set of connecting means in relation to the other. The spring characteristic is adjustable upon choice of number of spring elements and their charac- teristic distances and resiliences.

The claims 8 and 9 each discloses an embodiment of the spring including spring elements, wherein the springs may be designed to have uniform characteristics as regards oscillations of the first connecting means in any direction in a plane compared to the other set of connecting means.

The disclosures of claim 10 lead to corresponding advantages as those of claim 5.

Finally, the object of the present invention is to provide a suspension system for a training device to receive punches, kicks etc., e. g. a punching ball, whereby the kinematic characteristic of the training device during or after punches or kicks may be adjusted in a simple way to meet the requirements of the user,

and wherein the kinematic characteristic is non- directional, generally in a plane.

In order to achieve this, the suspension system is characterized in that the training device is kinematically connected to a first set of movable connecting means engaging into the first series of holes of the spring elements of a spring according to the invention and that the suspension system comprises a second set of connecting means corresponding to the number of holes in the second series of holes, whereby the connecting means are mainly rigidly and stationarily suspended and engage into the second series of holes of the spring elements of the spring.

As the spring of the suspension system may com- prise spring elements having different characteristic distances, so that the spring constant varies with the position in relation to the neutral position, the suspension system may easily be adjusted to provide the training device with the progressive compliance or resistance characteristic wanted by the user or for instance a trainer.

The suspension system may for instance be adjusted to provide the training device with such a resistance characteristic that at minor swings the punch resis- tance is modest enough for a boxer to use the training device without boxing gloves, whereby, at the same time, at larger swings the punch resistance is adequate enough for him to accomplish realistically powerful and grave punches, and that accordingly the magnitude and speed of the swing reflects the impact strength of the boxer.

Since, within certain limits, the choice of resilient material enables the achievement of a desired internal friction of the spring elements, also the damping of the oscillatory movements of the training

device may to some extent be individually adjusted, so that the device settles down comparatively soon after a deflection. Accordingly, it is possible to provide the training device with a pattern of motions which to a far larger extent than in the prior art resembles the motions and punch resistance of a fighting opponent.

The claim 12 discloses a preferred embodiment of the two sets of connecting means of the suspension system.

The embodiments of the suspension system disclosed in claims 13-14 represent a suspension of the training device, wherein the suspension is nondirectional and mainly in a plane, and a precise recording of both the magnitude and the speed of the oscillations of the training device is achieved.

The disclosures of claim 15 enable data processing of the magnitude and speed of the oscillations of the training device, e. g. the presence of a display read- out, storing and/or transmission, for instance to be used in connection with systematic training programmes or competitions.

In the following, preferred embodiments of the spring element, a spring comprising spring elements as well as the suspension system, all according to the invention, are described with reference to the draw- ings, wherein: Fig. 1 schematically shows a spring element according to the invention, Fig. 2 schematically shows another embodiment of a spring element according to the invention, Fig. 3 schematically and in exploded view shows the principle of a spring or an vibration damper according to the invention having linear motions,

Fig. 4 shows a lateral view of an embodiment of a spring or an vibration damper according to the prin- ciple of Fig. 3, Fig. 5 schematically shows a torsion spring element according to the invention, Fig. 6 shows an oblique view of a third embodiment of a spring element according to the invention, Fig. 7 shows a top view of the element of Fig. 6, Fig. 8 shows a fourth embodiment of a spring element according to the invention, Fig. 9 schematically shows an anchor plate with connecting means to be used together with the spring elements of Figs. 6-8, Fig. 10 schematically shows a sectional view of part of a suspension system according to the invention foreseen for a punching ball and comprising a spring according to the invention having four spring elements according to the invention, and Fig. 11 shows the suspension system of Fig. 10 mounted on a wall and carrying a punching ball.

In Fig. 1 a spring element 21 according to the invention and designed for linear spring motions is shown. The spring element 21 has two series of holes, whereby a first series of holes consists of one circu- lar hole 24 only. The second series of holes consists of two oblong holes 22, whereby part of the holes 22 have reinforcements 23 of a rigid material along part of their circumference.

Fig. 2 shows another spring element 31 according to the invention, which is also designed for linear spring motions, whereby the first series of holes comprises two annular holes 34. The second series of holes comprises one oblong hole 32 having reinforce- ments 33 of a rigid material along part of the circum- ference.

The spring elements 21,31 may advantageously be made of rubber sheet of a uniform thickness (in Figs.

1-2 the rubber sheets extend in the plane of the paper), and the reinforcements 23,33 may for instance consist of metal shoes that are welded, vulcanized or glued into the rubber sheet.

In Figs. 3-4 it is illustrated how the spring elements 21 may be used together with three associated connecting means. Fig. 3 presents a schematic exploded drawing, whereas Fig. 4 is a lateral view of a spring or an vibration damper 59 having a linear operating motion 55,60.

In Fig. 3, three spring elements corresponding to the element 21 are referenced as 41-43. The associated connecting means all have the form of connecting rods 47-49 having a circular cross-section. The two connect- ing rods 47,48 are secured to a stationary foundation 52, in this case in form of a sheet having a cut-out 59. As implied at 53, the foundation 52 may for instance be tied to a machine frame. The third connect- ing rod 49 is secured to a movable arm 54 transmitting a to-and-fro motion 55 from a machine part or the like not shown. The arm 54 may for instance constitute a firmly connected part of a vibrating motor base that is integrated in a machine having said machine frame.

When said motor base is vibrating, e. g. when the motor is running, the vibrations 55 are transmitted through the arm 54 to the connecting rod 49 making the to-and-fro motions, shown as 50-51, whereas the con- necting rods 47-48 are stationary. During operation, the three spring elements 41-43 are placed on the connecting rods, as shown in Fig. 4. Since the holes 61-63 of the first series of holes of the spring elements have a relatively tight fit around the con- necting rod 49, the centre part of the spring elements

around the holes 61-63 is forced to follow the motions 50-51 of the connecting rod 49, and thus the motion 55 of the arm 54.

As shown in Fig. 3, the distances 44-46 in the operating directions of the spring elements, from the centre of the first hole 61-63 to the outermost edge 56-58 of one of the other holes 64-66, are different from the three spring elements 41-43. Assuming the dimensions shown in Fig. 3, in the neutral position, the edge 56 of the second hole 64 of the spring element 41 will make full contact with the connecting rod 47.

Contrary to this, there will be a minor play between the edge 57 of the second hole 65 of the spring element 42 and the rod 47 and a yet larger play between the edge 58 of the second hole 66 of the spring element 43 and the rod 47. Con-sequently, the edge 57 will not abut on the connecting rod 47 until after a certain motion of the arm 54 with the connecting rod 49 has taken place, and, likewise, the edge 58 will not abut on the rod 47 until after a somewhat larger motion of the arm 54.

In this way it is achieved that only the spring element 41 is compliant during the first part of the oscillation of the rod 49 to one of the sides 50,51, that two spring elements 41-42 are compliant during the further motion after abutment of the hole edge 57, and, that all three spring elements 41-43 are compliant after the abutment of the hole edge 58 on the connect- ing rod 47.

Assuming that the spring effect of each of the spring elements is mainly linear, the spring rate of the compound spring with the spring elements 41-43 of the vibration damper 59 (Fig. 4) will increase stepwise by three steps as the three spring elements 41-43

"engage", and, in this way, the compound spring has been made stepwise progressive.

It will be obvious to a person skilled in the art that the progression of the compound spring is adjust- able upon needs and desires by means of a reasonable choice of numbers of spring elements 41-43 and their distances 44-46. The distances 44-46 correspond to the distances 25,35 respectively, shown in Figs. 1 and 2.

All said distances are measured from the centre of at least one hole in the first series of holes 24,34,61- 63 to the outermost point 56-58 on the edge of some or all holes of the second series of holes 22,32,64-66, and, in the following, for each spring element, all those distances are referred to as the characteristic distance of same since the characteristic distance represents a measure of the distance between the con- necting means 47-49 when the spring element begins or stops springing.

In order to obtain a practical and uniform defini- tion of the characteristic distance for all spring element embodiments according to the invention, the characteristic distance is determined from the centre of the first hole but to the edge of the other hole. In consequence, the characteristic distance will deviate from the corresponding distance between the centre axes of the connecting means by 1S the thickness of a con- necting means. However, this has no practical import- ance to the definitions or the understanding of the invention.

As described in connection with Figs. 1-4, springs or vibration dampers having linear operating directions may thus be formed. When spring elements 21,31,41-43 are chosen and adjusted properly, said springs or vibration dampers may be provided with practically any spring resistance and progression wanted. Moreover,

when rubber material for the spring elements is chosen, in a way known per se, the vibration dampers may be provided with more or less internal friction, so that, within certain practical limits, the internal friction of the completed spring or vibration damper will be optional.

Provided that suitable hole diameters are chosen for the first series of holes, the rubber material of the spring elements will fit tightly around the con- necting means and thus keep themselves in place.

Nevertheless, replacement of the elements will always be possible without any ado.

Springs and vibration dampers as described herein will be applicable in numerous connections within mechanical engineering and related fields, e. g. for vibration insulating, oscillation and/or shock absorbing, damping of sudden jerks in hitches, conveyor belts etc. as well as in other corresponding applica- tions.

Fig. 5 schematically shows a spring element 71 according to the invention for the formation of a torsion spring with torsion axis 72, which is identical to the rotation symmetry axis 72 of the element 71. The spring element 71 is placed on six connecting means 73- 78, whereby three 73-75 are stationary and three 76-78 are movable in a rotation motion 79-80 around the axis 72. Apart from this, the connecting means are of the same kind as described above. The two sets of each three connecting means are, in a manner not shown, connected to bases corresponding to 52 and 54 of Figs.

3-4. Like for the characteristic distances 25,35 of Figs. 3-4, a characteristic angle 81 with corresponding properties may be defined in this case.

A person skilled in the art will appreciate the torsion springs or vibration dampers being constructed

with such elements 71 having just as various applica- tions as described above.

Figs. 6-7 show a spring element 1 according to the invention, wherein the first series of holes comprises a single circular hole 4. The second series of holes comprises several oblong holes 2 having reinforcements 3 of a rigid material along part of the circumference of the holes 2. Additionally, along the circumference of the annular hole 4 there is a reinforcement 5 of a rigid material.

As most evident from Fig. 6, the spring element 1 is mainly plane and of uniform thickness. The operating directions of the element 1 are all directions in the plane of the element 1 corresponding to the plane of the paper in Fig. 7.

The spring element 1 of Figs. 6-7 has a character- istic distance 18 equal to the largest distance between points on the edge of one of the holes 2 and the centre of the hole 4, whereby the centre of same correspond to the rotation symmetry axis 91 of the element 1. Addi- tionally, the spring element 1 of Figs. 6-7 is charac- terized in the points on the edge of the holes 2 outermost to the hole 4 being placed in a circle having a radius corresponding to the characteristic distance 18.

Fig. 9 shows a disc 6 of a rigid material pictured like in Fig. 7 and in the same scale. To the disc 6 connecting means 7 are attached, constituting the second set of connecting means. The connecting means in question are formed as connecting bolts 7 attached to the disc 6, e. g. by means of not shown nuts on each side of the disc 6. The means 7 protrude perpendicu- larly to the disc 6 and are placed along a circle having a radius equal to the characteristic distance 18 of the spring element 1.

If, for instance, the disc 6 is fixed and the spring element 1 placed with the connecting bolts 7 through the holes 2, a connecting means protruding through the hole 4 will be influenced by a spring force directed backwards towards the axis 91, no matter in what direction in the plane of the paper (Figs. 7 and 9) said connecting means is being moved. In other words, the spring element operates as a return spring which can operate in all operating directions in the plane mentioned. The disc 6 with the connecting bolts 7 is thus used quite equivalently to the base 52, the arm 54 and the connecting rods 47-49 of Figs. 3-4.

To illustrate the use of a spring based on spring elements 1, by way of example, the suspension system of a training device, e. g. a punching ball, as shown in Figs. 10-11, will be described in the following. It will be obvious to a person skilled in the art that the described use of an adjustable progressive return spring operating in one plane will have equivalent application possibilities in many other circumstances.

Fig. 10 shows a cross-section of part of a suspen- sion system comprising a spring based on four spring elements 1 (Figs. 6-7). In Fig. 10, the spring is shown in its no-load mode. The spring elements 1 are placed on top of the disc 6 so that the smallest spring element, which also has the smallest characteristic distance, is closest to the disc 6 whereas the other spring elements are placed upon successively increasing sizes.

In Fig. 11 the total suspension system 112 includ- ing the training device (the punching ball) 17 being used by a boxer 110 is shown. On a wall 111 pillars 113 are mounted imbedding a frame 114 in such a way that it is vertically displaceable and retainable at a wanted level. The frame 114 carries a ball-and-socket joint or

a swivel bearing 16, wherein a rod 20 is swivelling suspended. Additionally, the frame 114 carries the disc 6 supporting the connecting bolts 7 and the spring elements 1. The arrangement of the disc 6 including the bolts 7 and the elements 1 is shown in the inserted picture of Fig. 11. In the suspension system 112, these parts are covered by a screen 116 carrying a display unit 117 with three bar-graph-displays 118.

Although, in Fig. 11, the boxer 110 is shown wearing boxing gloves, contrary to suspension systems of prior art, the suspension system 112 according to the invention may without any ado be designed in such a way that it is safe to use without gloves for boxing training or other martial arts training. As a matter of fact, with suspension systems of prior art, hand injuries frequently arise because the punching ball is often made comparatively heavy in order to ensure sufficient inertia resistance as the spring systems of the known suspension systems are incapable of offering a realistically differentiated impact resistance varying to a wanted extent according to the oscilla- tions of the punching ball. With the spring element according to the invention this does not present a problem, and, accordingly, without any design diffi- culties, the ball may be made so light that it will not harm the athlete's hands.

As far as the embodiment of a spring consisting of the spring elements 1 according to the invention shown in Fig. 10 and the inserted picture of Fig. 11 is concerned, the characteristic distance of the spring element, which has the smallest characteristic dis- tance, is a little smaller than the radius of the circle in which the connecting bolts 7 are secured to the disc 6. Therefore, the spring element having the smallest characteristic distance (the lowest element 1

of Fig. 10 and the top element 1 of Fig. 11) must be stretched somewhat to fit around the connecting bolts 7.

As regards the embodiment according to Fig. 10, the spring element having the smallest characteristic radius is placed first on top of the disc 6 so that the means 7 protrude through the holes 2 of the second series of holes. Subsequently, the other spring elements having increasing characteristic distances are placed likewise.

The first set of connecting means which is to co- operate with the holes 4 representing the first series of holes of each spring element 1 in this case consists of one connecting means, constituted by a connecting rod 9 protruding through a hole 8 in the middle of the disc 6 as well as through the circular hole 4 of each of the spring elements 1. As far a the spring element shown in Fig. 6 is concerned, the height of the rein- forcement 5 is mainly corresponding to the thickness of the spring element, and so, after having been assembled to one spring, the spring elements 1 will be close to each other. Optionally, the reinforcement 5 may be designed higher than the thickness of the spring element so that, except at the reinforcements, the spring elements of the spring do not touch each other.

This reduces the possible wear and tear of the spring elements. In the embodiment shown, the reinforcements 5 are thicker than the spring elements thus ensuring that the spring elements do not touch each elsewhere.

The nuts 15 securing the connecting bolts 7 firmly to the disc prevent the lowest spring element 1 from touching the disc 6. As will appear, the reinforcements 3 of the smallest spring element abut to the connecting bolts 7 and, in the unloaded mode of the spring, the horizontal distance 19 between the connecting bolts 7

and the reinforcements 3 is larger as far as the other spring elements are concerned.

Furthermore, the connecting means 9 constitutes the upper end of a rod 20 protruding through the hole 8 of the disc 6 and through the first (middle) hole 4 of each of the spring elements 1. The swivel bearing 16, which is secured to the retainer 113 on the wall by means of the frame 114 (Fig. 11) having displaceable shoes 115, supports the rod 20 with the connecting means 9.

When the spring is loaded, i. e. when the rod 20 including the connecting means 9 is swung around the swivel bearing 16, the smallest spring element 1 will be the first to offer spring force or resistance. At larger oscillations of the rod 20, the edge reinforce- ments 3 of the next spring element will abut against one of the connecting bolts 7, and the spring force of the spring will subsequently be constituted by the spring forces of the two spring elements having the two smallest characteristic distances. Correspondingly, the other spring elements will be actuated at yet larger deviations of the rod 20 with the connecting means 9.

The suspension system shown in Figs. 10 and 11 comprises a device for the detection and/or recording of the magnitude and speed of the swings of the con- necting means 9, and, accordingly, the swing of the rod 20 and the punching ball 17. Preferably, next to the upper end of the connecting means 9, said device comprises a part of a mainly ball-shaped surface 11 close to the motion surface of the upper end of the connecting means 9, whereby the radius of the surface 11 is designed in such a way that the distance between the upper end of the connecting means 9 and the surface is mainly constant during the motions of the rod 20.

The motions of the connecting means 9 are recorded by means or appliances placed on the surface 11 and at the upper end of the connecting means 9, respectively.

Several transducer systems known per se are applicable, e. g. electrical slide contacts, photocells combined with light-emitting diodes, hall elements combined with surfaces magnetized in a changing pattern etc.

As far as the embodiment shown in Fig. 10 is concerned, in a preferred embodiment a magnet placed at the end of the connecting means 9 is used in connection with mainly concentric turns of electric wires 12,13, 14 is incorporated in or, respectively, placed on the ball-shaped surface 11. Motions of the connecting means 9 make the magnet 10 induce electrical impulses into the turns 12-14, and those impulses may be used to determine the magnitude and speed of the oscillations of the connecting means 9, although, however, not the direction of the oscillations.

Whenever used for a punching ball 17, the suspen- sion system is placed at the lower end of the rod 20.

As the distance between the punching ball 17 and the swivel bearing 16 as well as the distance between the swivel bearing 16 and the upper end of the connecting means 9 are known, the deflection of the upper end of the connecting means 9 will unambiguously indicate the deflection of the punching ball 17.

The concentric turns 12-14 of the electric lines are connected to a electronic detection and/or record- ing device 117 (Fig. 11), preferably comprising read- out means. The read-out means may be acoustical, e. g. a loudspeaker, and/or visual, e. g. displays, preferably comprising one or more bar-graph-displays 118. In case of a suspension system 112 and a punching ball 17, the read-out means may for instance read out determined values of the punch speed, impact magnitude (power of

impact) as well as resulting punch effectivity. The electronic detection and/or recording device may include a computer or be connected to one and may for instance be used when the punching ball is utilized in connection with tournaments.

As suggested by the presence of the connecting wire 119, a computer in the recording device 117 may be connected to other computers in similar suspension systems placed far away from the suspension system 112 shown. In this way, the performances of for instance boxers training on individual punching balls may be compared immediately during the training, whereby quite new opportunities arise how to arrange long-distance tournaments or team tournaments between athletes far away from each other, e. g. in different towns or different countries. It will be obvious to a person skilled in the art that without any ado the suspension system 112 may be provided with the rod 20 in a hori- zontal position, or it may be sitting on its own on the floor or fastened thereto.

When used together with a punching ball, the spring elements 1 may be produced of caoutchouc having a hardness of preferably 65° Shore. Advantageously, the reinforcements 3 may be identical for all the spring elements 1 even if the characteristic distances 18 of same differ.

Like the formation of the spring element 31 (Fig.

2) in relation to the spring element 21 (Fig. 1), according to the invention, as shown in Fig. 8, a spring element 100 may be used instead of the spring element 1. The spring element 100 has a first series of holes 101, which are placed circularly corresponding to the placing of the connecting bolts on the disc 6. The holes 101 preferably have a diameter more or less equal to the diameter of the bolts 7.

The second set of holes of the spring element 100 comprises one single hole 102 having a diameter larger than the diameter of the corresponding connecting means; thus, the previously mentioned play between the edge of said hole and the corresponding connecting means is obtained. The characteristic distance 104 of the spring element is measured from the centre of one of the first holes 101 to the opposite edge of the hole 102. To form a progressive spring with spring elements 100, the diameters of the holes 102 of same must be correspondingly different. The edge of the hole 102 is preferably provided with an reinforcement 103.

A spring comprising spring elements 1 according to the invention may be used for other purposes, whenever it is desired that a spring returns to its neutral position directly. Furthermore, spring elements 1 according to the invention are advantageous when several operation directions are wanted for a spring.