FR2902678A1 - Producing helicoidal springs with flat spirals, for use e.g. in automobile steering units, by joining projecting elements on flat strip helix and forming inner strip by fixing the elements - Google Patents

Abstract

Production of helicoidal springs, with flat spirals formed by inner and outer helicoidal strips connected by a transverse lattice, involves (a) forming a flat strip with separate shaped elements, projecting from the same longitudinal edge of and in the same plane as the strip, (b) helicoidally shaping by joining each projecting element to the adjacent elements to form the outer strip and (c) fixing the projecting elements to form the inner strip (parallel to the outer strip) and connecting lattice. Independent claims are included for: (1) the helicoidal springs obtained by the process; and (2) a vehicle steering unit comprising (i) a steering column rotating freely relative to a fixed support on the vehicle, where the end opposite to that connected to the vehicle wheels extends beyond the support and carries a steering wheel hub (mounted rotatably relative to the column), (ii) a steering wheel permanently fixed to the column and (iii) a helicoidal spring having its ends permanently fixed to the hub and fixed support respectively, the novel feature being that the spring is produced by the present process.

Description

METHOD FOR PRODUCING A HELICOIDAL SPRING, A HELICOIDAL SPRING

  The present invention relates to a method for producing a helical spring. It also relates to a helical spring obtained by the implementation of this method, and a steering assembly comprising such a spring. The invention finds a particularly advantageous application in the field of the production of coil springs with flat turns especially intended for steering assemblies of motor vehicles.

  In the automotive industry, a new concept, known as the Fixed Wheel Steering Wheel (VMF), or also called Fixed Center Steering Wheel (VCCF), is emerging today in the field of vehicle steering assemblies. This is to make fixed a central hub adjacent to the steering wheel, that is to say free to rotate relative to the steering wheel, so that it can receive a number of function commands such as radio, air conditioner, navigation, cruise control, ..., the aims of this Fixed Wheel Steering wheel concept being to facilitate access to these functions by commands located directly on the steering wheel of the vehicle, and to allow a non-circular shape for the airbag cushion to be more effective in case of 25 shocks.

  For this purpose, use is made of a mechanical architecture described in particular in documents FR-A-2-833915 and FR-A-2-833916, architecture based on the use of a helical spring allowing the position of the Steering wheel and steering mechanism unchanged, while integrating the transmission of electric wires and without making any changes to the basic architecture of the vehicle.

  The coil spring used to immobilize the central part of the steering wheel, s or hub, is directly fixed on the sheath of the steering column and on the safety cushion. It must be very stiff in axial torsion and very flexible in axial compression.

  In this perspective, a solution adopted consists in producing a helical spring with flat turns. "Flat coil" means a turn whose thickness, that is to say the dimension in the direction of the axis of the turns, is much smaller than the height, that is to say the dimension in a direction perpendicular to the axis, in a ratio of 1/5, or even less than 1/20, in order to increase the ratio between the two stiffnesses, the section of the spring is proposed with cuts in the sidewall, this prohibiting a continuous manufacturing such as that of conventional springs.

  In general, the helical springs are obtained by winding processes implemented respectively cold and hot. Typically, the cold winding is suitable for round wires having a diameter generally less than 7 mm and rarely up to 20 mm. The hot winding is suitable for bars with an average diameter of up to 30 mm.

  Since such processes involve very large plastic deformations of the material to form the helical spring, including deformations in directions perpendicular to the winding axis, these methods are not suitable for the manufacture of coil springs with flat turns. Thus, a method for producing a helical spring from a flat material has been developed which consists essentially of cutting in a support a periodic set of adjacent strips arranged in an elementary pattern with respect to the center of a segment of folding and making successive folds of all of said strips around the fold axes. According to another embodiment, also implemented from a flat material, a plurality of plane elementary washers of identical geometry is cut in a support. These washers are cut to be able to carry on each of them an identical axial spacing washer io washer and to assemble them, by welding, along respective junction lines resulting from the cutting of each of the elementary washers.

  Although the helical springs obtained according to this method have given fairly satisfactory results in various tests, it has nevertheless been found that the performance of these springs could be improved if it was possible to decouple the flexural stiffness of the stiffness. torsion.

  The object of the invention is to propose a method for producing a spring with flat turns capable of obtaining the desired decoupling of torsional and flexural stiffness.

  The object of the invention is achieved with a method of producing a helical spring with flat turns, formed of two helical strips, respectively inner and outer, joined together by a transverse lattice, by means of the following steps: producing a flat strip and a succession of disjoint elements of suitable shape, projecting on the same longitudinal edge of said strip and in the same plane as this strip; - helical forming of the strip so as to join each element protruding with the projecting elements which surround it, said strip being intended to form the outer helical strip of the spring; - Securing the projecting elements and contacted so as to form the inner helical band of the spring, which extends parallel to the outer helical band, and the lattice solidarisant the two helical strips between them.

  In a particular embodiment, the production of the flat strip and the projecting elements is obtained by cutting shapes in a flat support, so as to form a succession of patterns of suitable shape.

  Advantageously, the cutting of the flat strip and the projecting elements is carried out by stamping in one and the same operation. According to one characteristic, the helicoidal shaping step comprises bending the plane strip, the bending axis corresponding to the winding axis of the coils of the helical spring, and an axial deformation of said strip, of a spacing corresponding to the pitch of the spring, made 20 along the bending axis of said band.

  The present invention also relates to the following features: the step of axial deformation of the flat strip is carried out continuously, concomitantly with the step of bending said strip; The step of axial deformation of the flat strip is repeated periodically turn after turn, after each formation of a turn of angular section smaller than 360; the step of securing the projecting elements is carried out in a single final step, once the complete shaping of the outer helical band of the spring from the flat strip; - The step of securing the projecting elements is repeated periodically turns after turn, after each formation of a turn of angular section less than 360.

  Advantageously, the projecting elements are made so as to form a periodic succession of patterns along the flat strip.

  The invention also relates to a helical spring obtained by implementing the method described above. The invention also relates to a vehicle steering assembly comprising a steering column mounted free to rotate with respect to a fixed support of the vehicle, and whose end opposite to that connected to the vehicle's steering wheels extends to the fixed support and carries a steering wheel hub, rotatably mounted relative to said column, said assembly further comprising a steering wheel rigidly secured to the column, and a helical spring obtained by the method described above, said spring being interposed between the hub and the fixed support having an end rigidly secured to the hub, the opposite end being rigidly secured to the fixed support.

  Other features and advantages of the present invention will appear on reading the detailed description below, of an example of non-limiting implementation, with reference to the appended figures in which: - Figure 1 shows schematically the l vehicle steering assembly comprising a spring according to the invention; FIG. 2a is a perspective view of a section of flat turn without perforation, in the form of a flat circular ring; FIG. 2b is a perspective view of the turn section of FIG. 2a after three-dimensional forming; - Figure 2c is a top view of a flat support from which are formed the flat strip and the projecting elements by a cutting step according to the invention; - Figure 3a is a top view of a portion of a first support cut for the realization of a coil spring according to the invention; FIG. 3b is a top view of a section of flat turn made from a support as shown in FIG. 3a; FIG. 4a is a plan view of a portion of a second cut support; FIG. 4b is a plan view of a flat turn section made from a support as shown in FIG. 4a; FIG. 5a is a plan view of a portion of a third cut support; FIG. 5b is a top view of a flat turn section made from a support as shown in FIG. 5a; FIG. 6a is a plan view of a portion of a fourth cut support; FIG. 6b is a top view of a flat turn section made from a support as shown in FIG. 6a; FIG. 7a is a view from above of a portion of a fourth cut support; FIG. 7b is a top view of a flat turn section made from a support as shown in FIG. 7a; FIG. 8a is a view from above of a part of a fifth support 25 cut away; FIG. 8b is a plan view of a flat turn section made from a support as shown in FIG. 8a; FIG. 9a is a view from above of a portion of a sixth cut support; Fig. 9b is a top view of a flat turn section made from a support as shown in Fig. 9a; Fig. 10a is a top view of a portion of a seventh cut support; FIG. 10b is a view from above of a flat turn section made from a support as represented in FIG. 10a; FIG. 11 is a view from above of a flat turn section obtained by the method according to the invention; - Figures 12a and 12b show two embodiments of the fastening of the projecting elements.

  To locate the spring of the invention, Figure 1 shows schematically a vehicle steering assembly, including a motor vehicle. This assembly comprises a steering column 1 mounted free to rotate relative to a fixed support of the vehicle, such as the dashboard shown only by a sheath 2, in bearings 201, 202 integral with the sheath 2. The end 103 of this column 1 opposite to that connected to the steering wheels of the vehicle, for example by means of a rack and pinion assembly (not shown), extends beyond the fixed support 2 and carries a steering wheel hub 4 steering assembly, mounted to rotate relative to the column 1. This assembly further comprises a steering wheel 3 rigidly secured to the column 1 by a plate 6 fixed to the rim 300 of the steering wheel 3 and interposed between the fixed support 2 and the hub 4 perpendicular to the column 1.

  This steering assembly is equipped with a helical spring 5 with 25 flat turns, interposed between the hub 4 and the fixed support 2 having an end rigidly secured to the hub 4, the opposite end being rigidly secured to the fixed support 2, so that to ensure a mechanical and electrical connection between these two elements.

  The plate 6 of the steering wheel 3 is interposed between two turns 500 of the spring 5 so as to be rotatable between these turns 500 and be simultaneously moved in an axial direction during a rotation of the flywheel 3, independently of the hub 4.

  Thanks to this arrangement of the spring 5 according to the invention and the arrangement of the steering column 1 relative to the fixed support 2 of the vehicle, the rotation of the steering wheel 3 causes only the rotation of the steering column 1, but remains, at least substantially, without effect on the coil spring 5 and the hub 4 is thus kept motionless in rotation therewith. This result is obtained thanks to the high stiffness in axial torsion and the great flexibility in axial compression of the coil spring 5 according to the invention.

  A steering assembly of this type thus has the advantage of providing a fixed central hub regardless of the steering angle of the steering wheel. A helical spring with flat turns obtained by the method according to the invention is formed of a succession of flat turns.

  A flat coil 100 is shown in FIG. 2a as a circular ring sector extending in a plane, and is shown in FIG. 2b in an axially deformed state.

  From the flat part shown in FIG. 2a, a three-dimensional part is produced by axial deformation. The three-dimensional flat turn 100 shown in FIG. 2b has the same geometrical characteristics as the turn of FIG. 2a, except for the deformation which is practiced to radially space the two extreme edges 101, 102 by a corresponding axial distance D. in the spring.

  The production method according to the invention is intended to produce a helical spring with flat turns formed of two helical strips, respectively inner and outer, joined together by a transverse lattice. The spring obtained by this method thus consists of cut turns, the cutouts of shapes (or perforations) being delimited by the two opposite helical strips and the lattice.

  The method according to the invention comprises the following steps, with reference to FIG. 2c: - production of a flat strip 106 and a succession of disjoint elements 105 of suitable shape, projecting on the same edge io longitudinal of said band 106 and in the same plane as this band; - helical forming of the strip 106 so as to join each projecting element 105 with the projecting elements 105 which surround it, said strip 105 being intended to form the outer helical strip of the spring; - Securing the projecting elements 105 and brought into contact so as to form the inner helical band of the spring, extending parallel to the outer helical band, and the lattice solidarisant the two helical strips between them.

  As shown in FIGS. 3a to 10a, the projecting elements 20 form a periodic succession of patterns along the flat strip. The periodic pattern may be formed of a single projecting element, so as to have a succession of identical projecting elements distributed at equidistance, as illustrated in FIGS. 3a, 7a, 8a, 9a and 10a. The pattern may also be formed of a plurality of distinct projecting elements as illustrated in Figures 4a, 5a and 6a for a pattern of two different projecting elements.

  As represented in FIG. 2c, the flat strip 106 and the projecting elements 105 are preferably formed in a flat support 104 of generally parallelepipedal shape; said protruding elements 105 thus made of material with the flat strip 106. The flat strip 105 and the projecting elements 106 are preferably obtained by cutting shapes in the flat support 104, said shapes being represented in broken lines on the Figure 2c, so as to form a succession of patterns of suitable shape. The flat support 104 is for example obtained by cutting in a sheet-metal side, the choice of the sheet being determined by the properties of the materials and the value of the thickness targeted for the spring.

  The cutting of shapes in the support 104 can be performed by perforation, punching, precision cutting, burr-free cutting and cutting with a progressive tool. The cutting of shapes in the support 104 can be carried out in one and the same step, in particular in one and the same stamping operation.

  The method of producing the spring consists in forming in particular a flat strip whose length corresponds to the total length of the outer helical strip of the spring that is desired. The helical forming (or spiral shaping) step comprises -bending the flat strip, the bending axis corresponding to the winding axis of the coils of the coil spring; An axial deformation of this flat strip, of a spacing corresponding to the pitch of the spring, made along the bending axis of said strip.

  The axial deformation step is: - carried out continuously, concomitantly with the bending step of this band; 2902678 It - is repeated periodically turn after turn, a number of times equivalent to the number of turns, after each formation of a turn of angular section less than 360 (that is to say before having made a complete turn of spiral), so that the spring rises discontinuously, turns after turn.

  The helical shaping mentioned above is advantageously carried out by rolling in a desired pitch helix shape, for example between 3 and 6 mm. Moreover, the joining of the protruding elements 105 (initially disjoint) leading to the formation of the inner helical band of the spring, this band being continuous, may be: - made in a single final step, once the shaping is done complete the outer helical web of the spring from the flat strip; repeated periodically turns after, after each formation of a turn of angular section less than 360 (that is to say before having made a complete spiral turn), each step can be performed before the deformation step axial axis of the corresponding turn. FIGS. 3a to 10a show eight exemplary embodiments of a flat strip and projecting elements to obtain a helical spring according to the invention. Figures 3b to 10b show the sections of flat turns obtained by bending the corresponding flat strips and securing the projecting elements.

  Thus, Figure 3a shows a first embodiment of a flat support 110 cut to obtain a flat coil 110 as shown in Figure 3b; these cuts leading to the production of a flat strip 16 and 30 projecting elements (13, 14, 15) forming a succession of patterns. The succession of patterns is composed of a periodic sequence of triangles 11 formed along the flat strip 16, each triangle being delimited by: a base 13 substantially parallel to the flat strip 16; and a first 14 and a second side extending between the base 13 and the flat strip 16, these two sides joining in a point integral with said strip 16.

  The longitudinal distance between two successive points is greater than the length of the base 13 of the triangles 11. An opening 17 is formed between two successive patterns, the projecting elements being disjoint. In this way, the opening 17 is delimited by the bases 13 of the successive triangles 11; the ends of the bases 13 being bevelled so as to cooperate at their junction.

  As illustrated by the arrows C of FIG. 3a, a bending of the flat strip 16 leads to the approximation of the triangles 11, and in particular the bases 13, and thus to the closure F of the openings 17. The method comprises a step of joining the successive bases 13 and put in contact. This bending and these solidarisations make it possible to obtain a spring formed of a succession of flat turns 110 as represented in FIG. 3b. This flat turn 110 is thus composed of an inverted triangle sequence 11, 12; each triangle 12 being delimited by the band 16, by a second side 15 of a triangle 11 connected to a first side 14 of the next triangle 11.

  The bases 13 secured to each other and form the inner ring of the flat coil 110 (these solidarisations being illustrated by the reference 111 in Figure 3b), and the strip 16 forms the outer ring of this coil 110. The sides 14 and 15 form Thus, a trellis joining the two rings together. After the axial deformation step, the continuous band formed of the outer rings of the successive turns will form the outer helical band of the spring and the continuous band formed of the inner rings of the successive turns will form the inner helical band. spring.

  Figure 4a shows a second embodiment of a flat support 20 cut to obtain a flat turn as shown in Figure 4b; these cuts leading to the realization of a flat strip 26 and protruding elements (23, 24, 25, 28, 29) forming a succession of patterns. The succession of patterns is composed of a periodic sequence of rectangles 21, each rectangle being partially delimited by: the flat strip 26; a base 23 substantially parallel to the flat strip 26 and extending over part of the width of said rectangle 21; a first side 24 secured to a first end of the strip 26, said side 24 extending substantially normally to this strip 26 and having a second free end; a second side 25 corresponding to the first side 24 of the next rectangle.

  Two diagonals 28, 29 respectively connect the first end of the first side 24 to one end of the base 23, and the first end of the second side 25 to the other end of the base 23.

  Two openings 27 are provided on each successive pattern, they are delimited respectively by the free end of the first side 24 and one end of the base 23, and by the free end of the second side 25 and the other end of the base 23. ; the free ends of the first 24 and second 25 sides being beveled. A bending of the flat strip 26 leads to the bringing together of the sides 24, 25 and the bases 23 and thus to the closing of the openings 27. The method comprises a step of joining the bases 23 and sides 24, 25 successive rectangles 21; this bending and these solidarisations to obtain a spring formed of a succession of flat turns 120 as shown in Figure 4b. Thus the method comprises a step ensuring the securing 121 of the free end of the first side 24 with one end of the base 23, and the securing 122 of the free end of the second side 25 with the other end of the base 23. The bases 23 joined to the free ends of the sides 24, 25 thus form the inner ring of the turn 120.

  Figure 5a shows a third embodiment of a flat support 30 cut to obtain a flat turn as shown in Figure 5b; these cuts leading to the production of a flat strip 36 and protruding elements (32, 33, 34, 35, 38) forming a succession of patterns. The succession of patterns is composed of a periodic sequence of triangles 31 and beams 32 projecting from the strip 36. Each triangle 31 is delimited by: a base 33 substantially parallel to the flat strip 36; and - a first 34 and a second 35 extending between the base 33 and the flat strip 36, these two sides joining in a point integral with this strip 36.

  A mediator 38 extends between the middle of the base 33 and the tip of the triangle 31 corresponding to the junction of the two sides 34, 35. The beam 32 has an end secured to the band 36 and a free opposite end; the beam 32 extending substantially normally to this band 36.

  Two openings 37 are provided on each successive pattern, they are delimited by the free ends of the beams 32 and the ends of the bases 33 of the triangles 31.

  A bending of the band 36 leads to the bringing together of the bases 33 and the beams 32 and thus to the closing of the openings 37. The method comprises a step of joining the bases 33 and the successive beams 32; this bending and these solidarisations make it possible to obtain a spring formed of a succession of flat turns 130 as represented in FIG. 5b. Thus the method comprises a step ensuring the securing 131 of a first end of the base 33 with the free end of a beam 32 and the fastening 132 of a second end of the base 33 with the free end of a Next beam 32. The bases 33 joined to the free ends of the beams 32 thus form the inner ring of the turn 130.

  In these first three embodiments, the perforations in the flat supports 10, 20, 30 are of generally triangular shape.

  Figure 6a shows a fourth embodiment of a flat support 40 cut to obtain a flat turn as shown in Figure 6b; these cuts leading to the realization of a flat strip 46 and protruding elements (42, 43, 48) forming a succession of patterns. The periodic patterns formed in this fourth flat support 40 correspond to the patterns formed in the third support 30 shown in Figure 5a, the two sides 34, 35 being absent. Each pattern comprises: a first beam 48, secured at its first end of the flat strip 46 and extending normally to said strip 46, this first beam 48 corresponding to the perpendicular bisector 38 mentioned in the third embodiment of a support cut 30; a base 43, substantially parallel to the flat strip 46, integral at its center with the second end of the first beam 48; and a second beam 42 having an end secured to the flat strip 46 and a free opposite end, the second beam 42 extending substantially normally to said strip 46.

  The succession of patterns is thus composed of a periodic sequence of rectangles 41 delimited by these elements 42, 43, 46 and 48.

  Two openings 47 are provided on each successive pattern, they are delimited by the free ends of the second beams 42 and the ends of the bases 43.

  A bending of the band 46 leads to the approximation of the bases 43 and the second beams 42 and thus to the closing of the openings 47. The method comprises a step of joining the bases 43 and the second beams 42; this bending and these solidarisations to obtain a spring formed of a succession of flat turns 140 as shown in Figure 6b. Thus the method comprises a step ensuring the securing 141 of a first end of the base 33 with the free end of a second beam 42 and the junction 142 of a second end of the base 43 with the free end of a second beam 42 following. The bases 43 joined to the free ends of the second beams 42 thus form the inner crown of the turn 140.

  For the second, third and fourth embodiments respectively, the turn respectively 120, 130 and 140 comprise perforations having generally polygonal shapes, in particular trapezoidal shapes with two concentric sides (23, 26), (33, 36) , (43, 46) being respectively part of the inner and outer rings of the turn and two straight sides (24, 25), (32, 38), (42, 48) oriented along radial lines passing through the center of the turn and the AX axis of symmetry. In the second embodiment, the trapezoidal perforation comprises two diagonals 28, 29. In the third embodiment, the trapezoidal perforation comprises a single diagonal 34. In the fourth embodiment, the trapezoidal perforation comprises no diagonal.

  As an exemplary embodiment, the elements delimiting the trapezoidal perforations are formed in the sheet metal flank with a width of the order of 5 to 10 mm, and the diagonals have a substantially equivalent width or slightly smaller.

  Figures 7a to 10a show four other forms of perforations io possible in a flat support for the realization of a helical spring according to the invention, the associated turns being partially shown in Figures 7b to 10b.

  Thus, FIG. 7a shows a flat support 50 comprising perforations 51 of substantially trapezoidal shape delimited by triangular-shaped disjointed beams 52 and projecting from a flat strip 56. These triangular beams 52 each have a base 53 substantially parallel to the plane strip 56 and a point secured to said 56. The bases 53 of two successive beams 52 are not connected and thus delimit an opening 57.

  A bending of the band 56 leads to the approximation of the beams 52, and therefore of their respective bases 53, and thus to the closing of the openings 57. The method comprises a step of joining the successive bases 53, so as to obtain a formed spring flat turns 150 as shown in FIG. 7b. This turn 150 is provided with substantially trapezoidal perforations 51 whose large base 54 and the small base 55 have curved shapes approximately taking up the curve of the inner ring and the outer ring of the turn 150. In this form, the 30 large bases 54 adjacent trapezoidal perforations 51 are disposed along the outer ring of the turn 150.

  FIG. 8a shows a flat support 60 comprising perforations 61 of substantially trapezoidal shape delimited by triangular-shaped disjointed beams 62 and projecting from a flat strip 66. These triangular beams 62 each have a side 68 secured to the strip 66 and a tip opposite said side 68, integral with a base 63, of generally rectangular shape and substantially parallel to the plane strip 66. The bases 63 of two successive beams 62 are not connected and thus delimit an opening 67. i0 A bending of the band 66 leads to the approximation of the beams 62, and therefore of their respective bases 63, and thus to the closing of the openings 67. The method comprises a step of joining the successive bases 63, so as to obtain a formed spring flat turns 160 as shown in FIG. 8b. This turn 160 is provided with perforations 61 of substantially trapezoidal shape whose large base 64 and the small base 65 have curved shapes approximately taking the shape of the inner and outer crowns respectively of the turn 160. Unlike the arrangement of the perforations 51 in the turn 150, the perforations 61 of the turn 160 are arranged with their large base 64 on the side of the inner ring of the turn 160. This results in the remaining part of the material, formed of the beam 62, that it is clearly larger than the corresponding portion 52 of the turn 150.

  FIG. 9a shows a flat support 70 having substantially diamond-shaped perforations 71 delimited by disjointed beams 72 projecting from a flat strip 76. Each beam 72 has the general shape of two triangles connected by a point. The side 78, opposite to said tip, of the first triangle is integral with the band 76 and the side 73, also opposite said tip, of the second triangle is substantially parallel to the plane band 76. The sides 73 of the second triangles of two successive beams 72 are not connected and thus delimit an opening 77.

  A bending of the band 76 leads to the bringing together of the beams 72, and therefore of the sides 73 of the second successive triangles, and thus to the closing of the openings 77. The method comprises a step of securing said successive sides 73 so as to obtain a spring formed of flat turns 170 as shown in Figure 9b. This turn 170 is thus provided with perforations 71 in the shape of a diamond. The large diagonals of the lozenges 71 are oriented at least approximately in the radial direction of the turns 170.

  FIG. 10a shows a flat support 80 having substantially elliptical perforations 81 delimited by beams 82 which are disjoint and integral with the same edge of a flat strip 86. Each beam 82 has concave edges and comprises two bases, respectively 83 and 88; the first base 88 being integral with the strip 86 and the second base 83 opposite being substantially parallel to said strip 86. The second bases 83 of two successive beams 82 are not connected and thus delimit an opening 87.

  A bending of the strip 86 leads to the bringing together of the beams 82, and therefore of the second successive bases 83, and thus to closing the openings 87. The method comprises a step of joining said second successive bases 83 so as to obtain a formed spring 180 flat turns as shown in Figure 10b. This turn 180 is thus provided with elliptical perforations 81. The perforations 81 are oriented so that their large diameter is oriented substantially in the radial direction passing through the center of the turn 180.30 For all the embodiments described above, the joining of the projecting elements (corresponding to the joining of the elements defining the openings) can be achieved by any known means, in particular by welding (with a point or a weld seam), clinching, riveting, stapling ...

  As shown in FIG. 11, the obtaining of a turn 190 comprises a step of securing 191 and / or 192 of two elements, for example a base 93 and a beam 92 delimiting a perforation 91. FIG. 12a shows a beam 92. whose free end has a first protruding member 197 intended to cooperate with a recess 193 of complementary shape formed in a first base 93, obtained for example by a plastic overmolding of the projecting member 197. The end free of the beam 92 may comprise a second protruding member 197, extending in a direction opposite to the first protruding member 197, and intended to cooperate with a second base 93 successive of the first.

  Of course the projecting member 197 may be integral with the base 93 and the cavity 193 formed in the beam 92. Similarly, for the joining of two successive bases, a protruding member is integral with one end of the first base while a cavity is formed in the end facing the second base. The protruding member 197 may have a generally nonlimiting shape of an ellipse, as illustrated in FIG. 12a, or a dovetail as illustrated in FIG. 12b.

  In order to avoid the concentration of stresses, the cut-outs of the shapes in the flat support (in particular by perforation) can be made with rounded corners. In addition, the bases 13, 23, 33, 43, 53, 63, 83 and sides 73 may have a slightly curved shape, so as to coincide with a circular shape after the bending step.

  Of course the implementation example mentioned above is not limiting in nature and further details and improvements can be made to the process according to the invention, without departing from the scope of the invention where other forms cuts can be made.10

Claims (4)

  1. A method of producing a helical spring with flat turns formed of two helical strips, respectively inner and outer, joined together by a transverse lattice, by means of the following steps: - realization of a flat strip and a succession of disjoint elements of suitable shape, extending in projection on the same longitudinal edge of said strip and in the same plane as this strip; - helical forming of the strip so as to join each element in projection with the projecting elements which surround it, said strip being intended to form the outer helical strip of the spring; - Securing the projecting elements thus brought into contact so as to form the inner helical band of the spring, which extends parallel to the outer helical band, and the lattice solidarisant the two helical strips 15 between them.   2. Method according to claim 1, characterized in that the embodiment of the flat strip and the projecting elements is obtained by cutting shapes in a flat support, so as to form a succession of patterns 20 adapted form.   3. Method according to claim 2, characterized in that the cutting of the flat strip and the projecting elements is carried out by stamping in one and the same operation. 25   4. Method according to any one of the preceding claims, characterized in that the helical forming step comprises: - a bending of the flat strip, the bending axis corresponding to the winding axis of the turns of the coil spring; An axial deformation of said strip, of a spacing corresponding to the pitch of the spring, produced along the axis of bending of said strip. i0. Method according to claim 4, characterized in that the step of axial deformation of the flat strip is carried out continuously, concomitantly with the step of bending said strip. 6. Method according to claim 4, characterized in that the step of axial deformation of the flat strip is repeated periodically turn after turn, after each formation of a turn of angular section less than 360. 7. Method according to any one of the preceding claims, characterized in that the projecting elements are made so as to form a periodic succession of patterns along the flat strip. 8. Method according to any one of the preceding claims, characterized in that the step of securing the projecting elements is carried out in a single final step, once done the complete shaping of the outer helical band of the spring to from the flat strip. 9. Method according to any one of the preceding claims, characterized in that the step of joining the protruding elements is repeated periodically turn after turn, after each formation of a turn of angular section less than 360. 10. A helical spring obtained by carrying out the method according to any one of the preceding claims. 11. A vehicle steering assembly comprising a steering column (1) mounted free to rotate relative to a fixed support (2) of the vehicle, and whose end (103) opposite to that connected to the steering wheels of the vehicle extends beyond the fixed support (2) and carries a hub (4) of steering wheel, rotatably mounted relative to said column (1), said assembly further comprising a steering wheel (3) rigidly secured to the column (1), and a helical spring (5) interposed between the hub (4) and the fixed support (2) having an end rigidly secured to the hub (4), the opposite end being rigidly secured to the fixed support (2), characterized in that the helical spring (5) is in accordance with a spring according to any one of claims 9 and 10.