Abstract:
The invention seeks to improve the transfer function of drive devices such as pulleys and other coupling means, and it proposes creating zones of shear in the inserted deformable material forming a decoupling element. In an embodiment, the decoupling element is made in the form of a ring ( 2 ) presenting at least one meshing face ( 21   e   , 21   i ) complementary to a corresponding meshing face ( 31, 41 ) formed on the facing support ( 3, 4 ), the meshing projections ( 2   e   , 2   i   , 3   e   , 4   i ) engaging in one another to take up power transmission torque by working in shear by being blocked against each other during rotation. The invention is applicable to all drive devices including a filtering, damping, or absorbing element, e.g. for use in the automotive industry.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to a decoupling element of deformable material, such as rubber or elastomer, for a rotary drive device such as a pulley, a wheel, etc. in a power transmission system for a compressor, alternator, starter, or any other type of accessory that needs to be driven in rotation. 
   As shown in the diagrammatic longitudinal and cross-section views of  FIGS. 1   a  and  1   b , pulleys or other rotary coupling means generally interpose a portion A of annular shape made of rubber having a section that is rectangular or shaped, between a rim B and a central hub C. By deforming in shear, between a rest position K 0  and a position K in rotation, this piece allows a certain amount of angular offset to occur, thereby performing its decoupling function, in particular as a frequency filter and damper between the exciter (arrow E) and the response (arrow R).  FIG. 1   c  shows a cross section similar to that of  FIG. 1   a  with a link insert or friction layer D. The link insert is described in U.S. Pat. No. 5,377,962 to Ochs et al. 
   The ring A is generally fixed via its inside and outside faces by overmolding or bonding to cylindrical supports made of metal or plastics material and forming respectively the inner hub and the outer rim. It is generally also appropriate to bond the ring to strength members which are themselves force-fitted between the rim and the hub. 
   That solution, as disclosed for example in patent EP 0 740 077 presents numerous drawbacks, and in particular:
         bonding requires coating and molding operations that are unsatisfactory in terms of cost and harm to the environment due to the use of adhesives and solvents;   the inserts which are generally made of metal give rise to non-negligible extra cost;   overmolding implies an additional swaging step to release differential stresses by radial deformation, and thus also leads to extra cost;   force-fitting the inserts leads to stresses in the parts; and   the system cannot be disassembled.       

   In other documents, for example patent EP 0 793 031, the ring has successive concave and convex undulations of essentially continuous curvature facing complementary shapes made on the hub and the rim. The undulations perform two functions, that of filtering without bonding and that of limiting torque. The concave and convex shapes allow the parts to slip relative to each other beyond a cutoff torque, and also to return to a driving configuration below the cutoff. 
   That type of solution leads to non-linearity in the torque exerted as angular offset increases, and thus to non-linear stiffness, which is harmful to the filtering function. To be effective filtering must be tuned to specific cutoff frequencies that differ depending on the structure of the system or the type of transmission that is to be provided. However since the system is non-linear, its resonant bandwidth is very broad and filtering is not performed correctly. 
   SUMMARY OF THE INVENTION 
   In order to remedy those drawbacks and improve the transfer function of the elastic insert, the invention proposes creating zones in which stresses act essentially in shear in the deformable material so as to implement the power transmission function alone in these zones, independently of any torque limiting effect. 
   More precisely, the invention provides a decoupling element of deformable material e.g. an elastic material such as rubber or elastomer, for interposing between the faces of two supports of a drive device having a central axis of rotation, the element being formed by a ring comprising a central core and at least two opposite faces. At least one of these faces and the facing face of the support present complementary abrupt projections suitable for meshing together, meshing of the ring creating zones at the roots of the projections where the central core substantially works in shear, these zones being regularly distributed over at least one of the faces of the ring. The central core extends from the protuberance-free continuous annular portion of the ring. 
   Under such conditions, the work of the ring is performed by reducing the radial component of the compression which would otherwise become preponderant with increasing angular offset. A linear relationship between torque and offset is then ensured, which leads to constant stiffness over a large angular range, for example a range greater than ±9°, and thus to a narrow resonant band. 
   In particular embodiments:
         the two opposite faces of the ring and the facing faces of the supports are fluted, or else only one face of the ring and the facing face of the support are fluted, the non-fluted face of the ring and the facing face of the support being bonded together, possibly via a linking insert;   the faces of the ring and of the supports that mesh are cylindrical and parallel to the axis of rotation and/or radial and perpendicular to said axis, the projections being respectively radial and/or axial;   the projections are of constant or linearly varying profile so as to facilitate unmolding and assembly by self-centering when engaging the ring on the supports;   the projections are crenellations of right section, i.e. having side flanks that are substantially perpendicular to the face of the ring on which they are formed;   the projections present side flanks of section that flares going away from said face, with a mean angle of up to 60° relative to the radius, being of trapezoidal shape, or hyperbolic shape, with suitable curvature and advantageously of tapering shape to facilitate unmolding or assembly by self-centering when engaging the free ring on the supports;   when the two opposite cylindrical faces are parallel to the axis of rotation of the ring and carry opposite radial projections, the square of the ratio of the radii of the opposite cylindrical faces is inversely equal to the ratio of the angles at the center intercepting two projections on respective faces, the opposite projections being periodically distributed in a basic pattern so as to exert shear stresses over the entire ring that are constant and that are reversible on going from one direction of rotation to the other;   the ring is split to form an opening so as to make assembly easier during insertion of the hub by expanding the ring, and during its own insertion into the rim by compressing the ring, thereby compensating for play between the parts.       

   The ring of the invention may be made by molding, by extrusion followed by cutting up or slicing into “washers”, or by injection/compression. In some cases, the material is made flat and then rolled up and cut to shape in order to make split rings. 
   The present invention comes more generally within the context of a power transmission system including a torque limiter or breaker for the purpose of stopping drive in the event of jamming, and a rotary drive device including the decoupling element. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described below in greater detail in non-limiting manner by describing embodiments with reference to the accompanying drawings, in which: 
       FIGS. 1   a ,  1   b , and  1   c  (described above) are diagrammatic section views of a prior art ring of deformable material; 
       FIGS. 2   a  and  2   b  are fragmentary section views of decoupling rings of constant profile, with teeth respectively of right profile and of flared profile, the rings being mounted between two complementary supports, and the figures illustrating diagrammatically the shear behavior of rings of the invention; 
       FIG. 3  is an exploded view of an embodiment of a drive device including a decoupling ring and supports of right and constant profile for a radial assembly; 
       FIGS. 4   a  and  4   b  are axial and longitudinal section views on A—A and B—B showing the  FIG. 3  assembly once assembled; 
       FIG. 5  is an exploded view showing a variant having a split ring; 
       FIG. 6  is an exploded view showing a variant having a ring and supports of varying profile for self-centering purposes; 
       FIG. 7  is an exploded view of an embodiment of a drive device having a ring with axial projections formed on its opposite radial faces; 
       FIGS. 8   a  and  8   b  are perspective views seen from two different angles showing an example of a ring having both radial and axial projections; 
       FIGS. 9   a  and  9   b  are axial and longitudinal section views on A—A and B—B showing a drive device of the invention including the ring of  FIGS. 8   a  and  8   b ; and 
       FIG. 10  is an exploded view of an embodiment of a drive device of the invention including a ring having radial projections in the form of cylindrical studs. 
       FIG. 11  is a diagrammatic section view of another embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown diagrammatically in the fragmentary section of  FIG. 2   a , an example of a cylindrical decoupling ring  2  of the invention comprises a continuous annular central core  1  (outlined within the ring by dashed lines in the figure) and abrupt projections  2   e ,  2   i  extending radially from the side flanks  22   a  and projecting at right angles in this example. 
   The projections respectively referenced  2   e  and  2   i  are regularly distributed in alternation respectively on the outside face  21   e  and on the inside face  21   i  of the ring in particular in order to conserve good uniformity in mass distribution. A section of ring defined by a pair of successive projections, an inside projection and an outside projection, thus forms a basic pattern which is repeated around the ring so as to form cylindrical crenellated faces. 
   The ring meshes between two supports comprising a central hub  3  and a rim  4  presenting faces  31  and  41  that face the complementary faces  21   i  and  21   i  of the ring. The rim and the hub are made of metal or of plastics material in the example shown, while the ring is made of rubber. The ring may be obtained by combining an elastomer material with a metal reinforcing insert, or a plurality of materials or a single elastomer material of different densities:
         a density for the core which is subjected to shear and which imparts stiffness;   a density for the outer projections, advantageously including textile reinforcement to reinforce contact and combat wear; and   a density for the inside projections, with textile reinforcement being optional.       

   In a second example shown diagrammatically in  FIG. 2   b , the side flanks  22   b  of the projections  20   e  and  20   i  are radially flared away from the central core  1  of the ring. The projections present an “hourglass” shape in section of trapezoidal form, with a mean flare angle α 3  that may be as much as 60°, as shown.  FIG. 11  shows projections  20   e ′ as part of ring  2 ″ that have a hyperbolic or curved shape. 
   In operation, power transmission is localized at the roots of the projections  2   e  and  2   i  and takes place for the most part in the shear zones K 1 . Because of the blocking obtained by the right or inclined side flanks, compression remains secondary. 
   In addition, the section of the projections is dimensioned by ratios appropriate for the sections in the working zones so as to limit bending and thus put the central core into compression, thereby enhancing work in shear, with work in compression becoming negligible. 
   With radial projections, the square of the ratio of the radii of the cylindrical faces  21   e  and  21   i  (R 1 /R 2 ) 2  is advantageously substantially equal to the inverse of the ratio of the angles (α 2 /α 1 ) at the center intercepting two projections  2   e  and  2   i  on respective faces. This dimensioning causes the shear stresses K 1  exerted on the ring as a whole to be made uniform and constant, said stresses being located mainly at the roots of the projections. This dimensioning also makes the shear reversible when going from one direction of rotation to the other. 
   The exploded view of  FIG. 3  and the section views of  FIGS. 4   a  and  4   b  show an example of a drive device  10  for a motor vehicle compressor. This device comprises a cylindrical decoupling ring  2  of right and constant profile together with a central hub  3  and a rim  4  forming supports with complementary profiles that are right and constant. These elements correspond to the elements shown in  FIG. 2   a  for making a radial assembly. 
   The hub  3  presents a central gear  30  for driving the shaft  50  ( FIGS. 4   a  and  4   b ) of the alternator about an axis X′X. The face  31  of the hub is provided with projections  3   e  of right and constant profile that are complementary to recesses  22   i  formed between pairs of projections  2   i  on the face  21   i  of the ring  2 . The rim  4  has a wall  42  presenting on its face  41  projections  41  and intervening recesses  44   i  for engaging respectively with the recesses  22   e  and the projections  2   e  on the face  21   e  of the ring. 
   Assembly is performed by sliding the ring between the support parts. The parts need to be finely indexed depending on the desired amount of play by using any known indexing means (optical, mechanical, etc.). 
   The height, i.e. the depth, of the fluting is a function of the power level of the torque to be transmitted, and also of their particular shape. By way of example, this height may lie in the range 1 mm to 5 mm. 
   A small amount of radial play may be retained between the parts due to manufacturing tolerances. If this is acceptable for the rim and the hub, the play can be zero with the ring then being assembled with a small amount of pressure, without that preventing disassembly. 
   Once assembled, the above assembly presents the appearance shown in axial and longitudinal section in  FIGS. 4   a  and  4   b . The rim  4  is centered by a strength member  45  mounted on a tube via bearings  46 . 
   In a variant shown in an exploded view in  FIG. 5 , the ring  2   b  is split. The opening  5  formed in this way makes assembly easier by enabling it to be opened out while the hub  3  is being inserted and by enabling it to be compressed while it is being inserted in the rim  4 , thereby enabling play between said parts to be compensated. The spreading forces exerted by the hub on the ring are compensated by the compression exerted by the rim on said ring. Once assembly is completed, no play remains between the parts. 
   In order to make split rings, the part can be molded directly or else it can be made flat by injection/compression, and then rolled up to obtain a cylindrical part having the desired opening, after which it can be dispensed by slicing. 
   In another variant, shown in exploded view in  FIG. 6 , the projections  2 ′ e  and  2 ′ i  of the ring  2 ′, and the complementary projections  3 ′ e  and  4 ′ i  respectively of the hub  3 ′ and of the rim  4 ′ have side flanks  22 ′ of right radial projection, but of axial profile that varies along the axis X′X. 
   In this example, the axial variation in the profiles is linear so as to form projections of axial profile that is trapezoidal. Under such conditions, during assembly, the short bases B 1  of the trapezoidal profiles, e.g.  2 ′ e , are placed facing the large bases B 2  of the recesses, e.g.  44 ′ i , into which they are to be engaged: self-centering adjustment then takes place between the projections and the recesses while they are being mutually engaged. The parts can then be assembled together while taking less care with indexing. Under such circumstances, molding is preferable, nevertheless extrusion is also possible with the fluting being re-machined after slicing. 
   The presence of varying profile and also of appropriate tapers also makes it easier to perform unmolding during manufacture of the ring. 
   The example shown in  FIG. 7  relates to an embodiment of the cylindrical drive device that includes a ring  200  with axial projections  202  and  203  formed on its opposite radial faces  212  and  213 . 
   In this example, the faces  212  and  213  of the ring, the face  212  of the central hub  300 , and the face  413  of the rim  400  that engage mutually are radial and perpendicular to the axis of rotation X′X. The projections  202  and  203  on the ring, the projections  302  on the hub, and the projections  403  on the rim extend axially. 
   With reference to the perspective views of  FIGS. 8   a  and  8   b , there can be seen an example of a ring  240  having projections that are both radial and axial: radial projections  24   i  and  24   e  formed on the opposite axial faces, respectively the inside face  25   i  and the outside face  25   e , are combined with axial projections  262  and  263  formed on the opposite radial faces respectively referenced  272  and  273 . Overall, this combined solution uses a quantity of material to make the projections that is equivalent to the quantity used when making radial projections or axial projections alone, given that the sections of the projections in the combined technique can be, very approximately, about half size. 
   In the example shown, the projections are right and of constant profile, however the various sections and profiles described above can also be applied to them. As before, the projections alternate around the ring so as to conserve a central core of constant thickness and a balanced distribution of masses and of shear stresses. 
   The ring  240  with combined radial and axial projections is coupled to a hub  340  and to a rim  440  presenting complementary projections  342  and  443 , as shown in the axial and longitudinal sections of  FIGS. 9   a  and  9   b . The assembly forms a drive device  11  of the invention. These figures also include elements shown in  FIGS. 4   a  and  4   b  that are equivalent respectively thereto, having the same reference symbols: the rim  440  is centered by a strength member  45  mounted on a tube via bearings  46 . 
   The exploded view of  FIG. 10  shows a variant embodiment of the drive device  12  comprising a ring  280  having radial projections in the form of cylindrical studs  282  and  283  that are respectively formed in alternation on the opposing cylindrical faces  292  and  293  of the ring  280 . The hub  380  and the rim  480  present respective notches  383  and  483  for receiving the studs. 
   The invention is not limited to the embodiments described and shown. It is possible to make the ring out of a deformable plastics material, polypropylene, polyethylene, or polyamide, or out of a composite material of the thermoplastic elastomer (TPE) type. 
   It is also possible to conserve an insert, and to use fluting for the outside face where the diameter makes it possible to retain more fluting. Meshing can be implemented on a single pair of facing faces between the ring and the rim or between the ring and the central hub, with the other pair of facing faces being bonded together.  FIG. 11  shows an insert  2 ′ having fluting  20   e ′ on its outside face to mesh with recesses on the rim  4 ′. The inner face  22   i ′ is bonded to the face  31 ′ of the central hub  3 ′. 
   The invention is applicable to any drive device including a filter, damping, or absorber element. By way of example, the accessories which are driven in rotation can be any component of an engine or of a transmission of a motor vehicle.