FR3062337A1 - METHOD FOR MANUFACTURING A GLOBIC TOOTHING WHEEL COMPRISING PARTIAL MOLDING OF THE DENTURE FOLLOWED BY A MACHINING STEP OF A CONCAVE DENTURE BOTTOM - Google Patents

Abstract

The invention relates to a method for manufacturing a wheel (1) with global teeth (2) having a central axis (XX '), said method comprising a step (a) of molding a rim (5) with preformed toothing (2A), during which a rim (5) is made by a molding operation which is centered on the central axis (XX ') and which comprises a plurality of preformed teeth (2A) which form a succession of pre-formed toothing tops (6A), each separated from each other by preformed tooth bases (3A), then a step (b) of overall cutting, during which the rim (5) is further hollowed, by cutting, starting from the preformed toothpans (3A) which result from the molding step (a), so as to create in each of said preformed teeth (3A) a concave bottom recess (11) which transforms each preformed tooth base (3A) in a bottom of toothing called "bottom end teeth" (3B) having a global profile ( 4).

Description

Holder (s): simplified.

JTEKT EUROPE Joint-stock company

O Extension request (s):

® Agent (s): CABINET GERMAIN & MAUREAU.

* 54) METHOD FOR MANUFACTURING A GLOBIC TOOTHING WHEEL INCLUDING A PARTIAL MOLDING OF THE TOOTHING FOLLOWED BY A STEP OF MACHINING A CONCAVE TOOTHING BOTTOM.

FR 3,062,337 - A1 (57) The invention relates to a method of manufacturing a wheel (1) with global toothing (2) having a central axis (XXj, said method comprising a step (a) of molding a rim (5) with preformed teeth (2A), during which a rim (5) is produced, by a molding operation, which is centered on the central axis (XXj and which comprises a plurality of preformed teeth (2A) which form a succession of preformed toothing peaks (6A), each separated from each other by preformed toothing bottoms (3A), then a step (b) of overall cutting, during which the rim (5), by cutting, from the preformed toothing (3A) which results from the molding step (a), so as to create in each of said preformed toothing (3A) a bottom recess (11 ) concave which transforms each preformed toothing (3A) into a toothing known as “final toothing” (3B) t a global profile (4).

Method for manufacturing a global toothed wheel comprising a partial molding of the toothing followed by a step of machining a concave toothing

The present invention relates to the field of manufacturing toothed wheels with global toothing, intended for various mechanisms, such as gear reducers, and more particularly intended for tangential wheel and worm gear reducers which can be used for example in within power steering systems.

The invention relates more particularly to the production of wheels with global toothing in polymer material, which combine robustness and lightness.

Global toothing has the particularity of having a concave-shaped toothing background, arranged in a portion of a torus whose central axis corresponds to that of the wheel.

Due to this concave shape, the manufacture of such wheels with a global toothing is generally long and complex.

In fact, it is known in particular to produce by molding a wheel preform, which comprises a smooth rim, known as a “raw rim”, from which one then cuts out overall teeth. Of course, the rim must therefore have a radial thickness of material which is sufficient, that is to say which is greater than the maximum height of the teeth envisaged.

However, the duration of a molding cycle closely depends on two stages: compaction and cooling.

Compaction is the operation by which the thermoplastic polymer material is kept hot under pressure in the mold cavity in order to ensure crystallization of said polymer material. In practice, the duration of compaction varies substantially linearly with the thickness of the molded material.

The purpose of cooling, which follows compacting, is to cool the molded part until it reaches a temperature low enough for said part to be sufficiently hard, and therefore not to be deformed, when it is ejected from the mold. . In practice, the cooling time varies significantly depending on the square of the thickness of the molded material.

The need to provide a rough rim with a large radial thickness therefore makes the molding cycle particularly long.

According to another known manufacturing possibility, it has been envisaged, for example in document WO-2012/152579, to directly produce a global toothing by molding, rather than by cutting.

However, such a molding requires an extremely complex tool, allowing the demoulding of the overall toothing.

Such tooling can thus in particular comprise a crown which radially delimits the mold cavity and which is divided into a large number of distinct profiled segments, each profiled segment covering a different angular sector around the axis of the wheel, and being provided with 'a portion of the toothing profile and a pouring channel.

In addition to its high cost, such tools can present certain implementation difficulties.

In particular, the installation of the profiled segments, which must be joined and maintained edges to edges to form the crown, requires time and requires particular care.

In addition, it is not excluded that imperfections at the junctions between profiled segments produce, on the teeth, surface defects, such as burrs, or geometric defects in circularity.

In addition, whatever the process used to shape the overall shape of the teeth, whether by cutting or molding, we generally create, at the intersection of the concave bottom of teeth with the upper and lower faces of the wheel , sharp angles, and therefore stress concentration zones, which can be the cause of a fatigue failure of the wheel.

The objects assigned to the invention therefore aim to remedy the aforementioned drawbacks and to propose a new method of manufacturing a global gear wheel which makes it possible to manufacture, quickly and at low cost, light and robust global gear wheels.

The objects assigned to the invention are achieved by means of a method for manufacturing a global toothed wheel having a central axis (XX '), said method being characterized in that it comprises a step (a) of molding a rim with preformed toothing, during which a rim is produced, by a molding operation, which is centered on the central axis (XX '), which surrounds said central axis (XX'), and which comprises a plurality of preformed teeth, obtained by the molding operation, said preformed teeth forming, along the circumference of the rim, a succession of preformed toothing peaks, each separated from one another by preformed toothing bases which are radially closer to the central axis (XX ') than said preformed toothing, then a step (b) of global cutting, during which the rim is further hollowed out, by cutting, penetrating into the radial thickness of the rim from the funds of preformed toothing which results from step (a) of molding, so as to create in each of said preformed toothing, a concave bottom recess which transforms each preformed toothing to a so called "final toothing" a global profile.

Advantageously, the fact of preforming teeth in the rim during the molding operation makes it possible first of all to intrinsically reduce the cycle time of said molding operation.

In fact, the presence of preformed, hollow toothing bases locally reduces the radial thickness of the rim, compared to a solid smooth rim, which makes it possible to reduce the compaction time as well as the cooling time which depend on said radial thickness, as explained above.

In addition, the preformed teeth form, during molding, cooling fins which facilitate the evacuation of heat, and consequently accelerate cooling.

In practice, the inventors have thus been able to reduce the radial thickness of the rim by around 15% to 25%, at the level of the preformed toothing, and thus reduce the cooling time by about 35%, and the duration of compaction from 15% to 20%, i.e. a total time saving per molding cycle of around 20% to 30%.

For example, the duration of the molding cycle of a wheel whose maximum radial thickness of the rim was 11 mm (at the level of preformed toothing) could thus have been lowered by 170 seconds for a smooth rim at 110 seconds for a rim with preformed toothing whose radial thickness of the preformed toothing was 9 mm.

In addition, the method according to the invention makes it possible to break down the production of the overall teeth in two stages, namely a first molding stage (a) which makes it possible to partially produce the toothing by preforming preformed teeth which are of simple shape, not overall, and in particular devoid of concave zones which would be difficult to unmold, then a cutting step (b) which makes it possible to finish the teeth by machining by giving said teeth, and more particularly to the final teeth, their desired overall shape.

The mold used to preform the teeth can therefore be of relatively simple shape, and in particular use a crown-type impression, toothed on its internal face, which is monolithic, since the shape of the preformed teeth is compatible with extraction of the wheel from the mold (that is to say a mold release) in a direction which corresponds substantially to the central axis (XX ') of the wheel.

The molding operation can therefore be carried out quickly and at a lower cost.

The cutting operation allows it to give the teeth their overall shape in a second step, after molding, and more particularly after demolding, by carrying out a resumption of machining which removes material from the rim in the funds preformed teeth, and where appropriate in the sides of said preformed teeth.

Since the teeth are already preformed, the cutting corresponds only to the global, concave part of the teeth, and therefore relates to a relatively small thickness of material.

In addition, the cutting can be carried out by means of a relatively simple tool, of the milling cutter type, the rounded shape of which corresponds directly to the shape of the desired overall profile.

The cutting operation is therefore relatively quick and inexpensive.

In addition, the cutting makes it possible to precisely control the dimensions and the shape of the teeth, as well as the circularity of the implantation of said teeth, which provides a final toothed wheel of good quality and high precision.

Thus, the invention advantageously makes it possible to combine the advantages of molding and cutting without suffering the disadvantages.

Finally, the method proposed by the invention makes it possible to form, preferably, at the base of the toothing bases, during step (a) of molding, reinforcement bosses which remain at least partially after step ( b) of cutting, and which ensure smooth transitions between the overall profile of the final toothing and the lower and upper faces of the wheel, in order to avoid concentrations of stresses.

The method according to the invention thus makes it possible to obtain, in a rapid manner and with a minimum of raw material, particularly robust global teeth wheels.

Other objects, characteristics and advantages of the invention will appear in more detail on reading the description which follows, as well as with the aid of the appended drawings, provided purely by way of non-limiting illustration, among which:

FIG. 1 illustrates, according to a view in projection from below, a wheel resulting from a step (a) of rim molding according to the invention.

FIG. 2 illustrates, according to a side projection view, the wheel of FIG. 1.

Figure 3 is a detail view of the rim of the wheel of Figure 1, and the preformed teeth.

FIG. 4 illustrates, in a detail view in longitudinal section, the preformed toothing of the wheel of FIGS. 1 to 3, with an illustration, by means of inscribed circles, of the reduction in thickness obtained by the preforming of the bottoms toothing.

FIG. 5 illustrates, in a detail view in longitudinal section, the principle of producing a global toothing in two stages according to the invention, by showing the molding zone, corresponding to the non-global preformed toothing background obtained by molding operation, and the cutting area, corresponding to the concave overall profile of the final toothing base obtained subsequently by the cutting operation.

Figure 6 illustrates, in a side projection view, the wheel of Figures 1 to 4 after step (b) of cutting.

FIG. 7 illustrates, according to a detail view in longitudinal section of the wheel of FIG. 6, the arrangement of the connection between the global profile of the toothing bottom and an axial excess thickness formed by a continuous annular reinforcement boss.

FIG. 8 illustrates, in a view from below, a variant of a wheel according to the invention, comprising reinforcement bosses fragmented into orthoradial arcs.

FIG. 9 is a detailed view of FIG. 8.

FIG. 10 illustrates, according to a detail view in longitudinal section, the wheel of FIGS. 8 and 9.

Figure 11 is a detail view of Figure 10, showing the geometry of the connection between the overall profile of the toothing bottom and the axial allowance provided by a reinforcing boss.

FIG. 12 illustrates, in a view in projection from below, another variant of a wheel according to the invention, comprising reinforcement bosses of triangular type.

FIG. 13 is a detail view of FIG. 12.

FIG. 14 illustrates, according to a detail view in longitudinal section, the wheel of FIGS. 12 and 13.

Figure 15 is a detail view of Figure 14, showing the geometry of the connection between the overall profile of the toothing background and the axial allowance provided by a reinforcement boss.

FIG. 16 illustrates, according to a detailed view in projection from below, another variant of triangular reinforcement bosses.

FIG. 17 is a detail view, in longitudinal section, of the connection between the global profile of the toothing bottom and the axial allowance provided by a reinforcement boss of FIG. 16.

FIG. 18 illustrates, according to a detailed view in projection from below, another variant of chevron reinforcement bosses.

FIG. 19 is a detailed view, in longitudinal section, of the connection between the overall profile of the toothing bottom and the axial allowance provided by a reinforcement boss of FIG. 18.

The present invention relates to a method of manufacturing a wheel 1 with global toothing 2.

Said wheel 1 has a central axis (XX '), which corresponds to the axis of rotation of wheel 1 when said wheel is in service.

By “global toothing” is meant, in a manner known per se, a toothing 2 within which the toothing bases 3 have a curved shape along the central axis (XX ′), so as to form a radial limit. concave tooth, as shown in Figures 5, 10 and 14.

More particularly, a toothing 2 is thus designated within which the toothing bottoms 3 form concave portions of a torus centered on the central axis (XX '), said concave portions thus opening onto the outside of the wheel.

The global profile 4 of each toothing 3 thus has a concave shape in an arc, which is deeper, that is to say closer radially to the central axis (XX '), in its middle than at its axial ends, that is to say a curved shape in an arc of a circle, the (fictitious) center of curvature of which is situated radially outside the wheel, beyond the material radial limit of the bottom of the teeth in question, and whose radius of curvature is here denoted R4.

Such a global toothing 2 advantageously allows a worm having a circular section substantially conjugate to the global profile 4, and disposed tangentially or substantially tangentially with respect to the wheel 1 (so as to form a so-called "left" gear whose axes do not are neither parallel nor concurrent), to mesh with said global toothing 2 on an extended contact surface.

For convenience of description, and unless otherwise indicated, the expression “axial” will denote a direction or dimension parallel to the central axis (XX ′), or even coincident with said central axis (XX ′), by “radial” a direction or a dimension perpendicular to said central axis (XX '), and by "orthoradial" a tangential direction which is contained in a plane normal to the central axis (XX') and which is perpendicular to the radius at the point considered (the radial and orthoradial directions thus forming, at a point distinct from the central axis (XX '), a Frénet coordinate system associated with the point considered).

According to the invention, the method comprises a step (a) of molding a rim 5 with preformed teeth 2A, during which a rim 5 is produced, by a molding operation, which is centered on the central axis ( XX '), which surrounds said central axis (XX'), here preferably over 360 degrees around said central axis (XX '), preferably in a generally circular shape of revolution around the central axis (XX'), and which comprises a plurality of preformed teeth 2A, obtained by the molding operation, said preformed teeth 2A forming, along the circumference of the rim 5, around the main axis (XX '), a succession of preformed tops of teeth 6A, each separated from one another by preformed toothing bottoms 3A which are radially closer to the central axis (XX ') than said preformed toothing tops 6A, as is clearly visible in FIGS. 4 and 5.

By way of illustration, circles marked C3A_min, C3A_max and C6A make it possible to respectively view the minimum radial thickness C3A_min of the rim 5 at the level of the preformed toothing 3A, the maximum radial thickness C3A_max of the rim 5 at the bottom of the rim preformed toothing 3A, and the radial thickness C6A of the rim 5 at the level of the preformed toothing tops 6A, thus showing the reduction in thickness which is obtained thanks to the presence of the preformed toothing bottoms 3A.

A preformed wheel 1 obtained by molding according to the invention is illustrated in FIGS. 1 to 3.

Preferably, during step (a) of rim molding 5, the rim 5 and the corresponding preformed teeth 2A are produced by molding a polymer material.

The rim 5 will thus be molded easily and quickly, at a lower cost, while being particularly light.

More preferably, an injection molding of a thermoplastic polymer will be carried out such as for example a Polyamide PA, in particular a Polyphthalamide PPA, a Polyethylene Terephthalate PET or a Polybutylene Terephthalate PBT, a Polyketone PK, a Polyoxymethylene POM, or a Polyphenylene Sulfone PPS .

The molding will preferably be carried out hot, that is to say at a temperature above room temperature, the mold being typically between 70 ° C and 110 ° C, and the polymer being injected at a temperature substantially between 270 ° C and 330 ° C.

As can be seen in FIGS. 1, 4, 5, 8, 10, 12, and 14, the rim 5 can, in a manner known per se, be overmolded, in radial allowance, and if necessary also in axial allowance, on a core 7 which is previously formed.

Said core 7 thus extends radially, after molding of the rim 5, between on the one hand a hub 8, centered on the central axis (XX '), and on the other hand said rim 5, to form the spokes of wheel 1.

The core 7 is preferably made of a polymer material, preferably a thermoplastic polymer.

The polymer material constituting the core 7 will preferably be more rigid than the polymer material constituting the rim 5, that is to say which will preferably have a higher Young's modulus than the Young's modulus of the material. polymer constituting the rim 5.

This difference in rigidity will keep a wheel 1 generally rigid, while giving the teeth 2 a certain flexibility which improves the quality of the engagement and the service life.

In order to give the core 7 a structure that is both light and solid, said core 7 may include ribs 9, preferably oriented substantially radially, and which can partition cells 10, as can be seen in FIGS. 1, 8 and 12.

Preferably, the core 7 will be produced by molding, prior to step (a) of molding the rim 5.

More particularly, the core 7 can be produced by overmolding on the hub 8.

The method according to the invention will thus preferably comprise successively two overmolding operations, namely a first overmolding operation during which the core 7 is produced by overmolding a first polymeric material on the hub 8, then a second operation overmolding a second polymeric material, said second overmolding step corresponding to step (a) of molding the rim 5, during which the rim 5 is produced by overmolding on the core 7 previously solidified, the rim 5 thus forming a coating layer which at least partially covers the core 7, in particular in radial excess thickness of said core 7.

According to a possible embodiment, as illustrated in FIGS. 1, 8 and 12, the hub 8 may take the form of a socket, preferably metallic, which is centered on the central axis (XX ') and intended to be engaged on a shaft used to support the wheel 1.

According to another possible embodiment, the hub 8 may be directly formed by a shaft, preferably metallic, which is centered on the central axis (XX ') and which materializes the axis of rotation of the wheel 1, so that the core 7 will then be directly molded onto said shaft.

Whatever the rim molding method 5 selected, the preformed teeth bases 3A which are produced during step (a) of rim molding 5 are not global, and more generally do not form concave depressions which are 'would open on the outside of the wheel 1, when considering said preformed toothing bottom 3A along the generating line L2 of each corresponding tooth 2.

Such a non-global arrangement, and more generally non-concave, in the direction, mainly axial or even exclusively axial, of the generating line L2, is advantageously compatible with a mold release oriented substantially along the central axis (XX '), and therefore facilitates the manufacturing and demolding of all of the preformed teeth 2A from a mold of simple shape.

According to the invention, the method then comprises, after step (a) of molding the rim 5 and of the preformed toothing 2A thereof, a step (b) of overall cutting, during which further digging the rim 5, by cutting, penetrating into the radial thickness of the rim 5 from the preformed toothing bases 3A which result from the molding step (a), so as to create in each of said preformed toothing bases 3A a concave bottom recess 11 which transforms each preformed bottom of teeth 3A into a bottom of so-called “final bottom of teeth” 3B having an overall profile 4, as is illustrated in particular in FIGS. 5, 10 and 14.

Thus, according to the invention, after having partially shaped the toothing 2, by molding a first preformed toothing 2A, provisional, which is non-global and easily demouldable, then a resumption of machining is carried out to modify this preformed toothing 2A , by removing material, at least in the preformed toothing 3A, to give the desired overall shape to the final toothing 3B and thus transform the first preformed toothing 2A, non-global, into a second final toothing 2B, global.

The teeth 2, and more particularly the final teeth 2B, designate here of course all of the meshing teeth of the wheel 1, which will come to cooperate with a wheel or a global screw of conjugate shape, and which will thus allow the wheel 1 to transmit or receive forces, and more particularly a torque around the central axis (XX ').

The overall profile 4 of each bottom recess 11, concave, advantageously corresponds to a portion of a torus, centered on the central axis (XX ').

In projection in a longitudinal section plane containing the central axis (XX '), the bottom recess 11, and consequently the overall profile 4, thus form a sort of bowl, the bowl bottom, preferably located axially substantially in a median plane of the wheel 1 which is perpendicular to the central axis (XX ') and which is located midway between the axial ends of the teeth 2B, is deeper, with respect to the outside, and more particularly is closer radially to the central axis (XX '), than the edges of said bowl located axially on either side of said bowl bottom (and more generally located on either side of the aforementioned median plane) .

The cutting operation is preferably carried out by a milling cutter, the axis of rotation of which is oriented substantially in the direction which will correspond to the axis of the global worm which it is intended to make cooperate with the wheel 1.

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Preferably, said cutter is pressed in turn into each preformed toothing bottom 3A, in a substantially radial centripetal penetration movement.

During the cutting step (b), the angular positions (in azimuth) of the teeth 2 to be cut successively are indexed in rotation about the central axis (XX '), so that the wheel is incremented at each operation of cutting an angle value equal to the pitch of toothing 2.

As such, the number and the azimuthal position, around the central axis (XX '), of the preformed teeth 2A, and more particularly of the preformed toothing tops 6A and of the corresponding preformed toothing bases 3A, are identical to the number and at the azimuthal position of the final teeth 2A, respectively of the final toothing peaks 6B and of the final toothing bottoms 3B, of the wheel 1.

As is particularly visible in FIGS. 1 to 3, the preformed teeth 2A obtained during step (a) of molding have preformed flanks 20A, 21A which are located on either side of each preformed toothing base. 3A.

Preferably, during cutting step (b), it is also then possible to dig, in addition to the bottom recess 11 which is hollowed out in the bottom of the toothing 3, 3A, concave lateral recesses in said said preformed flanks 20A, 21A, so as to obtain concave final flanks 20B, 21B, as is clearly visible in FIG. 6.

Simultaneous digging of the bottom recess 11 and the lateral recesses can be carried out by means of a curved disc cutter, which is thicker towards its axis of rotation than at its radial end.

Concave end flanks 20B, 21B will advantageously provide better contact surfaces, more extensive, to the overall screw, and will provide a more progressive engagement as well as a better overall efficiency of the reducer.

It will be noted that the cutting of concave flanks 20B, 21B also has the effect of thinning the width (orthoradial) of the teeth 2B substantially in their middle, and therefore of making the tops of the final teeth 6B locally narrower in their axially median portion than 'at their axial ends.

Furthermore, it is of course conceivable, in absolute terms, to take advantage of step (b) of cutting to improve the finish of the toothing tops 6, for example to deburr the preformed toothing tops 6A.

However, preferably, in order to limit the duration and the cost of the cutting step (b), and to save raw material, the height will not be modified during the cutting step (b). (radial) of the tops of teeth 6, so that the tops of final teeth 6B will be located at the same radius, relative to the central axis (XX '), as the tops of preformed teeth 6A.

Preferably, each preformed toothing base 3A, as it results from step (a) of rim molding, extends, along the central axis (XX '), from a first extreme abscissa X3_inf up to 'to a second extreme abscissa X3_sup, and is delimited, between said first and second extreme abscissae X3_inf, X3_sup, and before step (b) of cutting, by a tooth envelope which is generated in accordance with a generating line L2 which does not does not have, between said extreme abscissae, a concave recess towards the central axis (XX ').

The tooth envelope here corresponds to the surface of the assembly formed by the preformed toothing base 3A and the preformed toothing flanks 20A, 21A, such that said surface is geometrically generated by a translation (scanning), along the generating line L2, of a basic curve which corresponds to the cross section of the toothing (here the preformed toothing) 2A, that is to say which corresponds to the profile of the toothing considered in section in a plane normal to l 'central axis (XX').

Advantageously, the generating line L2 not being concave, and a fortiori not global, the envelope which it generates, and therefore in particular the longitudinal profile of the bottom of the preformed toothing 3A, which is parallel to said generating line L2 is also not concave, so that the imprint of the mold which materializes said envelope during step (a) of molding does not form an obstacle to extraction, that is to say to a release from the preformed toothing 2A in an orientation which corresponds substantially to the orientation of said generating line L2.

Thus, it is indeed the cutting operation which gives the final toothing 2B its overall shape, which is initially devoid of the preformed toothing 2A.

It will be noted that the generating line L2, which coincides with the deepest longitudinal course of the preformed toothing bottom 3A, thus marks, as illustrated in FIGS. 5, 10 and 14, the (radial) border between a zone of molding ("molding zone") MZ and a cutting zone ("cutting zone") CZ, ie the border between the radial height of the preformed tooth 2A which results from molding and the additional radial height of the final tooth 2B, corresponding to the radial depth of the recess 11 which is produced by cutting.

It will also be noted that the radial height of the molding zone MZ, that is to say the (radial) height of the preformed teeth 2A, preferably represents at least 20%, at least 30%, at least 40%, and preferably between 40% and 60%, for example substantially 50%, of the maximum total (radial) height of the final overall toothing 2B, that is to say of the cumulative radial heights of the molding zone MZ and of the zone of cutting CZ.

Thus, the production of the toothing 2 will be effectively distributed between the molding operation and the cutting operation.

It will be noted that the respective radial heights of the molding area MZ and of the cutting area CZ will depend in particular, for a radius R4 of given overall profile 4, on the axial thickness of the wheel 1, and more particularly on the thickness axial of the toothing 3, measured axially between the lower face 32 and the upper face 33 of the wheel 1.

Indeed, for a radius R4 of given global profile 4, and for a given preformed toothing depth 2A (that is to say for a given radial height of the molding area MZ), plus the axial thickness of the wheel 1 will be raised, the longer, as a result, the arc of circle of the global profile 4, and therefore the greater the depth proper to the global profile 4 (that is to say the radial height of the cutting zone CZ) will be important, and therefore the lower the ratio MZ / (MZ + CZ) of the radial height of the molding area MZ over the total radial height MZ + CZ.

It will be noted in this respect that the axial thickness of the wheel 1 will result from a compromise according to which an intermediate axial thickness value is chosen between on the one hand an axial thickness which is as small as possible in order to limit the overall volume of material used to form the rim 5 during step (a) of molding, and in order to reduce the molding cycle time, and on the other hand an axial thickness which is strong enough to give the feet of teeth 2 a good mechanical resistance to shocks and torques that the wheel must transmit 1.

In practice, an MZ / (MZ + CZ) ratio of the order of 50%, and for example between 40% and 60% as indicated above, will advantageously be suitable for such a compromise.

According to a preferential possibility of arrangement, the generating line L2 is rectilinear.

This simplifies in particular the structure of the mold, and makes it possible to generate, with respect to the demolding direction (generally axial), a preformed toothing 2A whose preformed toothing base 3A, considered from its first extreme abscissa X3_inf to its second abscissa X3_sup extremale, is "flat", in that it is neither concave nor convex when traversing said preformed toothing bottom 3A in a rectilinear longitudinal direction, parallel to the generating line L2, so that said bottom 3A preformed toothing is easily removable from the mold (in this direction).

It will also be noted that the generative line L2, preferably rectilinear, is preferably predominantly axial, that is to say that its directing vector comprises a majority component of axial extension L2_A, which is greater than any other components of extension , radial and / or orthoradial.

According to a first possible arrangement, the generating line L2 will be rectilinear and will include a nonzero axial component L2_A as well as a nonzero orthoradial component L2_T, so that it will form with respect to the central axis (XX ') , and in projection in a plane perpendicular to the radius of the tooth 2A considered, an angle of inclination a2 (not zero).

Thus, according to a preferred variant of the invention, the preformed teeth 2A which result from step (a) of rim molding form a rectilinear toothing which has both a non-zero axial extension component L2_A along l 'axis (XX') and a component of orthoradial extension L2_T not zero with respect to the central axis (XX '), so as to form an oblique rectilinear toothing, as illustrated in FIG. 2.

It will be noted that the inclined generating line L2, although being oblique, will then indeed be rectilinear, and not wound in a helix around the axis (XX '), so that the toothing 2 will be rectilinear and oblique, and not helical, which will facilitate its release.

When the preformed wheel 1 is removed from the mold, at the end of step (a) of rim molding, it is in fact possible to extract the preformed wheel 1 by exerting an axial thrust on said wheel 1 by means of suitable extractors.

The angle of inclination a2, here non-zero, of the preformed toothing 2A will then simply have the consequence that, when the preformed wheel 1 is ejected, said wheel 1 will turn slightly and gradually around its central axis (XX ' ) to accommodate its axial displacement relative to the mold footprint.

By convention, it can be considered that the axial extension component L2_A of the toothing 2 corresponds to the axial distance which separates the first extremal abscissa X3_inf from the preformed toothing 3A from the second extremal abscissa X3_sup of said preformed toothing 3A, while that the orthoradial extension component L2_T corresponds to the transverse deviation (orthoradial) of the generating line L2 between said extreme abscissae X3_inf, X3_sup.

Thus, we will have: tan (a2) = L2_T / L2_A.

Of course, the above-mentioned inclination a2 will also be found in the final toothing 2B, as illustrated in FIG. 6, so that one will then obtain a final toothing which is both global (due to the recess bottom 11 with global profile 4), rectilinear (because the generating line L2 is a straight line), and inclined (due to the orthoradial inclination a2 of said generating line with respect to the central axis).

Inclining the toothing 2 at an angle of inclination a2 can be advantageous for two reasons.

First of all, this makes it possible to tilt the axis of the worm, a few degrees, relative to the median plane of the wheel, and thus, in the case of a power steering system, to position the motor assistance, which drives said worm, in such a way that the overall size of the mechanism is reduced, and more generally that the size of said power steering system is reduced.

In addition, the inclination of the teeth 2 makes it possible to increase the total length of said teeth 2, in a given and limited axial space (between the axially extremal faces of each tooth), which improves the mechanical strength and the endurance of said teeth. 2.

Preferably, the angle of inclination a2 of the teeth 2, 2A, 2B, will be between 1 degree and 20 degrees, preferably between 2 degrees and 15 degrees, and may in particular be equal, according to preferred configurations, to 2 degrees or at 15 degrees.

According to a second possible arrangement, the straight line L2 may have a zero L2_T orthoradial extension component.

Thus, according to a possible variant of the invention, the preformed teeth 2A which result from step (a) of rim molding, and consequently the final teeth 2B which result therefrom, may form a toothing 2 straight (not oblique to the sense of the above, i.e. with a2 = 0).

In absolute terms, the generating line L2 could however have, despite a component of orthoradial extension L2_T zero, and in addition to a component of axial extension L2_A nonzero, a component of radial extension not zero, so that the toothing 2 would be straight, but wheel 1 is generally conical.

However, and according to a third possible arrangement, which constitutes a sub-variant of the previous one, the directing vector of the generating line L2 may exclusively comprise an axial extension component L2_A, so that said generating line L2 is parallel to the central axis (XX ').

There will thus be a right wheel 1 (not conical) with straight teeth (not oblique), which would correspond to a wheel of the type illustrated in FIGS. 2 and 6, but with a zero tilt angle: a2 = 0.

Such a variant has in particular the advantage of being easy to manufacture by means of a very simple tool (mold).

Preferably, according to a characteristic which can constitute an invention in its own right, and which could also apply, in absolute terms, to a manufacturing process where the overall toothing 2 is cut from a smooth rim without preformed teeth , during step (a) of rim molding 5, is carried out in one piece with the rim 5, and in alignment (axial) of the preformed toothing bottoms 3A, reinforcement bosses 30 which are arranged so as to project axially with respect to the (future) locations of the corresponding concave bottom recesses 11, such that said bottom recesses 11 are then made during step (b) of cutting, so that said bosses of reinforcement 30 provide, in each final tooth base 3B concerned, and as can be seen in particular in FIGS. 7, 11, 15, 17 and 19, an axial allowance 31 which extends axially beyond the overall profile 4 generated by the recess 11 concave bottom.

Preferably, reinforcement bosses 30 are provided which project axially on each side of said bottom recesses 11, so as to preferably create axial thicknesses 31 which extend axially beyond the overall profile 4 on either side. other, axially, of said global profile 4, that is to say on the two sides, upstream and downstream, of said global profile 4, along the central axis (XX '), and more precisely along the generating line L2.

For this purpose, provision is preferably made for each tooth 2, 2A, 2B, two reinforcement bosses 30, the first located downstream, towards the first extreme abscissa X3_inf, and the second located upstream, towards the second extreme abscissa X3_sup, as seen in particular in Figures 10 and 14.

Advantageously, the presence of the reinforcement bosses 30 makes it possible to extend the toothing base 3, 3A, 3B beyond the axial range occupied by the global profile 4, so as to prevent the intersection of said global profile 4 with the rim 5, and more particularly with the axially extremal face, called the "lower face" 32 of the wheel 1 and the opposite axially extremal face, called the "upper face" 33 of said wheel 1, at the axial ends of the final toothing base 3B, do not comes in the form of a sharp angle.

Thus, the reinforcement bosses 30 extend the bottom of teeth 3, 3B, projecting from the underside 32 of the wheel 1, and / or respectively projecting from the top face 33 of the wheel 1, according to an axial allowance profile. 31 which is distinct from the overall profile 4, in particular in that said axial allowance profile 31 marks a rupture with respect to the curvature of said overall profile 4, and which is connected to said overall profile 4, at an axial end of said overall profile 4, to give the final teeth base 3B a geometric shape which avoids stress concentrations.

The reinforcement bosses 30 can of course have different shapes without departing from the scope of the invention.

Thus, according to a first variant, the wheel may include a continuous annular boss 30, forming a crown which extends in one piece over 360 degrees around the central axis (XX '), so as to pass through all of the toothing 3, 3A, 3B of the wheel face 32, 33 concerned, as illustrated in FIGS. 3, 4 and 7.

Preferably, the wheel 1 may include such an annular boss 30 on each of its lower 32 and upper 33 faces.

Alternatively, the boss or bosses 30 may be angularly divided into several distinct portions around the central axis (XX ′), preferably as many individual bosses 30 as there are teeth 3, 3A, 3B, such as illustrated in Figures 8 to 19.

Each individual boss 30 will then occupy, around the central axis (XX '), an angular sector at least equal to the angular sector covered by the toothing bottom 3, 3A, 3B, and will preferably be substantially angularly centered on said bottom of teeth 3, 3A, 3B.

Preferably, all the reinforcement bosses 30 (at least on the same face 32, 33 of the wheel) will be identical, the wheel 1 thus being geometrically invariant by rotation about the central axis (XX ').

Thus, according to a second variant illustrated in Figures 8, 9, 10 and 11, the bosses 30 are substantially linear, and are in the form of arcs, substantially orthoradial, which correspond to distinct angular subdivisions of the same annular ring. .

According to a third variant illustrated in FIGS. 12, 13, 14 and 15, the bosses 30 have the shape of triangles of which a base, substantially orthoradial, is intersecting at the bottom of teeth 3, 3A, 3B, and whose apex opposite to said base points towards the central axis (XX ').

According to a fourth variant illustrated in FIGS. 16 and 17, the bosses 30 are triangular, as for the third variant, but offset radially towards the periphery of the rim 5, so that the intersection between the toothing bottom 3, 3A, 3B and the boss 30 takes place deeper in the triangle, in an area of maximum thickness of the boss 30, in order to obtain axial extra thickness 31 longer than those obtained with the third variant of FIGS. 12 to 15.

According to a fifth variant illustrated in Figures 18 to 19, the bosses 30 may each be in the form of two arcs joined in a chevron by their top, said top coinciding with the bottom of teeth 3, 3A, 3B.

Of course, the shape of the bosses 30 may be subject to variants without departing from the scope of the invention. The definition and the choice of the shape of the bosses 30 can be optimized as a function for example of simulations by calculation or of tests which will make it possible to select the shape or the dimensions which most effectively limit the stresses.

It will be noted that, whatever the variant reinforcement boss 30 chosen, the axial allowance 31 will preferably be obtained directly in its final form during step (a) of molding.

In other words, the layout of the axial excess thickness 31 will preferably correspond to the layout of the preformed toothing base 3A, such that said layout results directly from the molding operation.

To this end, the layout of the axial excess thicknesses 31 will preferably coincide with the generating line L2 which delimits the preformed toothing base 3A, and therefore with the mold imprint which makes it possible to preform the preformed teeth 2A in the rim

5.

Thus, during step (b) of cutting, it will advantageously not be necessary to carry out a specific material removal which would aim to modify the shape of the axial allowance 31, only the material removal corresponding to the realization of the 'bottom recess 11, and if necessary the recess of the flanks of teeth 20A, 21A, being necessary.

Each final toothing base 3B, which comprises on the one hand a central overall profile 4 and on the other hand two peripheral extensions in the form of two axial thickeners 31 which are connected to said central overall profile 4 at each axial end of said overall profile 4, can thus be obtained directly, simply by digging the bottom recess 11, that is to say by adding the overall profile 4 between the pre-existing axial thickeners 31, from the generating line L2 of the preformed toothing bottom 3A.

As a variant, one could of course take advantage of step (b) of cutting to touch up the shape of the axial thicknesses 31, without going beyond the ambit of the invention.

Whether the axial excess thicknesses 31 result exclusively from the molding step (a) or else from a resumption of machining carried out during the cutting step (b), said axial excess thicknesses 31 which remain after the step (b ) of cutting, with respect to the overall profile 4, thanks to the reinforcement bosses 30, each preferably preferably forms a flat axially which, with the overall profile 4 of the final back teeth 3B, and on the side of the rim 5 oriented towards the 'central axis (XX'), an angle called "connection angle" β which is an obtuse angle, as can be seen in FIGS. 7, 11, 15, 17 and 19.

Said flat is preferably substantially, or even exactly, parallel to the central axis (XX ').

By convention and for convenience of representation, the connection angle β will be considered in a sagittal plane which contains the central axis (XX ') and which passes through the intersection considered between the global profile 4 and the flat part of the axial allowance 31.

Said connection angle β will be measured between the tangent to the global profile 4 and the tangent to the flat 31, on the side of the solid material of the rim 5, that is to say on the side radially comprised between the central axis (XX ') and the limit of the back of teeth 3, 3B.

Advantageously, the fact of having an obtuse β connection angle, that is to say greater than 90 degrees, and less than 180 degrees, makes it possible to obtain a toothing which is both functional and resistant.

Indeed, a connection angle β of more than 90 degrees guarantees that the connection of the global profile 4 with the corresponding face 32, 33 of the wheel, here in this case with the reinforcement boss 30, is made in a smooth transition , without sharp angles, which avoids the concentration of stresses.

Then, insofar as the connection angle β is also less than 180 degrees, it is ensured that the axial extension 31 (the flat) remains behind the fictitious circular extension of the global profile 4, beyond the 'bottom recess 11, without interfering with said fictitious circular extension of the global profile 4, and thus leaves clear the space necessary for the passage of the global screw, in order to allow meshing without interference.

Depending in particular on the shape and the radial position of the boss 30, the profile of the axial excess thickness 31, and more particularly the flat, may correspond, axially, to part of the axial thickness E30 of the reinforcement boss 30 (FIGS. 7,11,15), preferably to a majority part (i.e. more than half) of the axial thickness E30 of the reinforcement boss 30 (FIGS. 11, FIG. 15), or to the whole of the axial thickness E30 of the reinforcement boss 30 (FIGS. 17 and 19), considered relative to the limit of the overall profile 4.

The axial allowance 31, and more particularly the corresponding flat, will preferably have, beyond the overall profile 4, an axial length strictly greater than 0.2 mm, preferably at least 0.5 mm, or even at least minus 1 mm.

More generally, the axial thickness E30 of the reinforcement boss 30 will preferably be greater than or equal to 0.5 mm, 0.6 mm, or even 1 mm, and for example between 0.5 mm and 2 mm, even between 0.5 mm and 1 mm.

Indeed, at the junction between two intersecting profiles, the stress concentrations decrease in proportion to the square of the radius of connection between said profiles.

Consequently, even a relatively small thickness E30 is sufficient to give the reinforcement boss 30 its anti-stress concentration function, without significantly increasing the size and the weight of the wheel 1, provided that said thickness E30 makes it possible to create the necessary connection radii, typically equal to or greater than 0.3 mm and for example comprised between 0.3 mm and 0.5 mm, and / or makes it possible to create a connection angle β greater than 90 degrees as indicated above.

More generally, both to avoid stress concentrations and to facilitate the manufacture of the mold and the molding operation of the rim 5, regardless of the shape of the reinforcement bosses 30 (arc of circles, triangles, rafters , etc.), said reinforcement bosses 30 preferably have rounded connections R30 with the face 32, 33 of the wheel 1 on which said bosses 30 protrude.

In a particularly preferred manner, all the radii of said rounded connections R30 are greater than 0.1 mm, preferably greater than 0.2 mm, and particularly preferably equal to or greater than 0.3 mm.

Preferably, in particular by convenience of molding the rim 5, the radii of said rounded connections R30 will be between 0.3 mm and 0.5 mm.

The thickness (axial) E30 of the reinforcement bosses 30 will preferably be equal to or greater than twice the connection radius R30 chosen, so that the reinforcement boss can have such a connection radius R30 as well at its base , at the connection with the face 32, 33 of the wheel 1 or the toothing 2, only at its apex (edge) forming the free axial end of said reinforcement boss 30.

All the transitions, concave as convex, of the reinforcement boss 30 relative to the surfaces of the wheel 1 and of the toothing 2 are therefore particularly gradual, which, here again, avoids stress concentrations.

The invention of course relates to a wheel 1 with global toothing 2 obtained by a method according to the invention, as well as a gear mechanism, for example a tangential wheel and worm gear reducer, using at least one toothed wheel 1 global according to the invention on which meshes a worm, preferably global.

The invention likewise relates to a power steering system comprising a reduction gear equipped with such a wheel 1 with global toothing 2, as well as a vehicle, and in particular a motor vehicle, equipped with such a power steering system.

Of course, the invention is not limited to the variant embodiments described in the foregoing, the person skilled in the art being in particular able to isolate or freely combine one or the other of the above characteristics with each other. or substitute an equivalent.

Claims (10)

1. A method of manufacturing a wheel (1) with global toothing (2) having a central axis (XX '), said method being characterized in that it comprises a step (a) of molding a rim (5 ) with preformed teeth (2A), during which a rim (5) is produced, by a molding operation, which is centered on the central axis (XX '), which surrounds said central axis (XX'), and which comprises a plurality of preformed teeth (2A), obtained by the molding operation, said preformed teeth (2A) forming, along the circumference of the rim, a succession of preformed toothing peaks (6A), each separated 'from one another by preformed toothing bottoms (3A) which are radially closer to the central axis (XX') than said preformed toothing tops (6A), then a step (b) of overall cutting, at during which the rim (5) is further hollowed out, by cutting, penetrating into the radial thickness of the rim from the toothing preformed (3A) which result from the molding step (a), so as to create in each of said preformed toothing (3A) a concave bottom recess (11) which transforms each preformed toothing (3A) into a back cover known as “final back cover” (3B) having a global profile (4). 2. Method according to claim 1 characterized in that each preformed toothing base (3A) as it results from step (a) of rim molding, extends along the central axis (XX ' ), from a first extreme abscissa (X3_inf) to a second extreme abscissa (X3_sup), and is delimited, between said first and second extreme abscissas, and before step (b) of cutting, by a tooth envelope which is generated in accordance with a generating line (L2) which does not have, between said extreme abscissae (X3_inf, X3_sup), a concave recess towards the central axis (XX '). 3. Method according to claim 2 characterized in that the generating line (L2) is straight. 4. Method according to one of the preceding claims characterized in that the preformed teeth (2A) which result from step (a) of rim molding form a straight toothing. 5. Method according to one of claims 1 to 3 characterized in that the preformed teeth (2A) which result from the step (a) of rim molding form a straight toothing (2A) which has both a component d 'axial extension (L2_A) not zero along the axis (XX') and a component of orthoradial extension (L2_T) not zero with respect to the central axis (XX '), so as to form an oblique rectilinear toothing . 6. Method according to any one of the preceding claims, characterized in that the preformed teeth (2A) obtained during step (a) of molding have preformed flanks (20A, 21A) which are located on either side other of each preformed toothing base (3A), and in that one also digs, during cutting step (b), concave lateral recesses in said preformed flanks so as to obtain final flanks (20B, 21B) concaves. 7. Method according to any one of the preceding claims, characterized in that, during step (a) rim molding, is carried out, in one piece with the rim (5), and in alignment preformed toothing bottoms (3A), reinforcing bosses (30) which are arranged so as to project axially with respect to the locations of the corresponding concave bottom recesses (11), preferably on each side of said bottom recesses, such that said bottom recesses (11) are then made during cutting step (b), so that said reinforcement bosses (30) provide, in each final toothing bottom (3B) concerned, an axial allowance ( 31) which extends axially beyond the global profile (4) generated by the concave bottom recess (11), preferably on either side, axially, of said global profile (4). 8. Method according to claim 7 characterized in that the axial thickeners (31) each axially form a flat, preferably substantially parallel to the central axis (XX '), flat which forms, with the overall profile (4) of the bottom final teeth (3B), and on the side of the rim oriented towards the central axis (XX '), an angle called "connection angle" (β) which is an obtuse angle. 9. Method according to claim 7 or 8 characterized in that the reinforcement bosses (30) have rounded connections (R30) with the face of the wheel on which they project, and in that all the radii of said rounded connections are greater than 0.1 mm, preferably greater than 0.2 mm, and preferably equal to or greater than 0.3 mm, and preferably between 0.3 mm and 0.5 mm. 10. Method according to any one of the preceding claims, characterized in that, during step (a) of rim molding, the rim (5) and the corresponding preformed teeth (2A) are produced by molding a polymer material. 1/3