Abstract:
The invention relates to a one-way clutch mechanical system for a pulley-assembly of a motor vehicle alternator, having an inner element, an outer element rotatably movable relative to one another around a central axis and delimiting an annular housing between them. A one-way clutch device positioned in the annular housing and a member damping a relative rotational movement between the inner and outer elements and elements transmitting torque to the clutch device is provided. A ring rotatably secured to a first element and adjacent, along the central axis, to a damping and torque transmission member, is provided with first means for activating the member to transmit torque. A sleeve belonging to the one-way clutch device is provided with second means for activating the damping and torque transmitting member. The one-way clutch device has cams that bear against the sleeve and the second activation means has at least one raised portion.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a mechanical system with a one-way clutch, such as a pulley-assembly for a motor vehicle alternator. The invention also relates to an alternator comprising such a system configured as a one-way clutch pulley-assembly. 
       BACKGROUND OF THE INVENTION 
       [0002]    In the field of driving motor vehicle alternators, it is known to use a pulley-assembly equipped with a free wheel forming a one-way clutch device. Such a pulley-assembly makes it possible to transmit a torque between a belt that attacks a crown positioned on the outside of that assembly and an inner hub secured in rotation with the shaft of the alternator. The crown of such an assembly undergoes variations in speed and torque during use, in particular due to the acyclic nature of the engine. To smooth the speed and torque variations exerted on the pulley, it is known to use a one-way clutch (OWC) device, also called a free wheel, between the pulley and the hub. This one-way clutch device transmits a torque from the crown of the pulley-assembly to the hub, but does not transmit torque when the hub rotates faster than the outer crown. 
         [0003]    Such a pulley-assembly is sometimes called an “over running alternator decoupler” (OAD). 
         [0004]    Such a decoupler is for example known from US-A- 2011 / 065537  and comprises a ball bearing associated with a free wheel around which a torsion spring is positioned that is engaged, by its ends, with a part secured to the outer crown of the device and with a part engaged with the free wheel. This material is relatively complex and comprises a large number of parts. Furthermore, the torque transmitted from the outer crown to the free wheel via the torsion spring goes through two semi-rigid stamped parts that may deform with wear, which decreases the reliability of that material. 
         [0005]    It is also known from DE-A-10 2009 052 611 to use a free wheel formed by a spring as well as inner and outer bushes with a U-shaped and L-shaped cross-section, respectively, positioned on either side of the free wheel and a damping spring. The material thus built is bulky, and the transmission of torque goes through a skate housed at the bottom of the inner bush, which does not guarantee lasting operation over time. 
         [0006]    Comparable drawbacks arise in the one-way clutch mechanical systems used in other fields. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention aims more particularly to resolve these drawbacks by proposing a new one-way clutch mechanical system whereof the radial bulk is better controlled, that is less complex and that is more reliable than the known equipment. 
         [0008]    To that end, the invention relates to a one-way clutch mechanical system, in particular a pulley-assembly for a motor vehicle alternator, the system providing an inner element and an outer element that are movable relative to one another in rotation around a central axis and delimiting an annular housing between them, a one-way clutch device positioned in the annular housing, a damping and torque transmission member for damping a relative rotational movement between the inner and outer elements and for transmitting torque to the one-way clutch device, the member also being positioned in that annular housing. A ring, secured in rotation with a first element from among the inner and outer elements and adjacent, along the central axis, to the damping and torque transmission member, is provided with first means for activating that member to transmit torque between the inner and outer elements, and a sleeve that is rotatable relative to the first element is provided with second elements for activating the damping and torque transmitting member, in order to transmit torque between the inner and outer means. According to the invention, the sleeve belongs to the one-way clutch device, whereas the one-way clutch device comprises cams provided to bear against the sleeve and whereas the second activation means comprise at least one raised portion arranged on an edge of the sleeve oriented toward the damping and torque transmission member. 
         [0009]    Owing to the invention, the damping and torque transmission member is activated reliably, which guarantees lasting operation of the system. Furthermore, it is not necessary to design complex stamped parts to interact with the damping and torque transmission member. The positioning of the second activation means on the edge of the sleeve turned toward the damping and torque transmission member imparts good compactness to the system according to the invention. 
         [0010]    According to advantageous but optional aspects of the invention, such a mechanical system incorporates one or more of the following features, in any technically allowable combination: 
         [0011]    The ring has a U-shaped radial section with a flat bottom, and the ring has a planar annular wall forming the bottom of the U and two inner and outer cylindrical walls forming the branches of the U. 
         [0012]    The first and second activation means provides at least one raised portion arranged on a free edge of one of the cylindrical walls. 
         [0013]    The damping and torque transmission member is at least partially housed in the inner volume of the ring defined between its inner and outer cylindrical walls. 
         [0014]    The raised portion arranged on the edge of the sleeve is a shoulder designed to interact with one end of a brake spring, which constitutes the damping and torque transmission member, or a tooth intended to interact with heels belonging to a ring, which constitutes the damping and torque transmission member. 
         [0015]    The ring forms, with one of the inner and outer elements, a plain bearing for radial separation of the elements. 
         [0016]    The system includes a fitting inserted between the sleeve and the first element to control the rotational oscillations between the sleeve and the first element. 
         [0017]    The damping and torque transmission member is axially offset, relative to a one-way clutch device, along the central axis. 
         [0018]    The radial surface of the second element, from among the inner and outer elements, that defines the annular housing, is cylindrical and has a circular section and a rectilinear geometry. 
         [0019]    The first element is the outer element. Alternatively, the first element is the inner element. 
         [0020]    The damping and torque transmission member is a brake spring formed by a rod made from an elastically deformable material whereof both ends are curved to interact with the first activation means and the second activation means, respectively. 
         [0021]    The damping and torque transmission member is a ring made from an elastically deformable material and provided with heels intended to interact with the first activation means and the second activation means, respectively. 
         [0022]    The invention also relates to an alternator having a mechanical system as described above configured as a pulley-assembly with a one-way clutch. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The invention will be better understood and other advantages thereof will appear more clearly in light of the following description of five embodiments of a one-way clutch mechanical system according to its principle, provided solely as an example and done in reference to the appended drawings, in which: 
           [0024]      FIG. 1  is an axial cross-sectional block diagram of a system according to a first embodiment of the invention; 
           [0025]      FIG. 2  is a cross-sectional view along line II-II in  FIG. 1 ; 
           [0026]      FIG. 3  is an exploded perspective view, with a partial cutaway, of the system of  FIG. 1 ; 
           [0027]      FIG. 4  is an enlarged perspective view with a partial cutaway of the system of  FIG. 1  in the mounted configuration; 
           [0028]      FIGS. 5 and 6  are views similar to  FIGS. 1 and 3 , respectively, for a system according to a second embodiment of the invention; 
           [0029]      FIGS. 7 and 8  are views similar to  FIGS. 1 and 3 , respectively, for a system according to a third embodiment of the invention; 
           [0030]      FIGS. 9 and 10  are views similar to  FIGS. 1 and 3 , respectively, for a system according to a fourth embodiment of the invention; and 
           [0031]      FIGS. 11 and 12  are views similar to  FIGS. 1 and 3 , respectively, for a system according to a fifth embodiment of the invention,  FIG. 12  not, however, including a partial cutaway. 
       
    
    
       [0032]    For the clarity of the drawing, crosshatching has been incorporated only into the upper parts of  FIGS. 1 ,  5 ,  7 ,  9  and  11 . 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0033]      FIGS. 1 to 4  show a pulley-assembly  1  according to the invention and suitable for equipping a motor vehicle alternator shown in mixed lines by its driveshaft  2 , only in  FIG. 4 , for simplification purposes. 
         [0034]    The pulley-assembly  1  is centered on an axis X 1  and comprises an outer crown  10  and an inner hub  20  between which an annular housing  30  is defined that is radially delimited between an inner radial surface  12  of the crown  10  and an outer radial surface  22  of the hub  20 . 
         [0035]    The crown  10  is provided, on its outer radial surface  14 , with grooves  16  allowing it to cooperate with a notched belt  4  shown in mixed lines only in  FIG. 1 , for the clarity of the drawing. 
         [0036]    The inner hub  20  is equipped with an inner toothing  24  allowing an effective transmission of a rotational torque around the axis X 1  to the shaft  2 , which is configured in a corresponding manner and also rotates around the axis X 1 . 
         [0037]    It will be noted that the surfaces  12  and  22  are each cylindrical, with a circular base and rectilinear generatrix. These surfaces are therefore easy to produce, with a particularly attractive cost. 
         [0038]    Inside the housing  30 , a one-way clutch device or “free wheel”  40 , a ball bearing  50 , a brake spring  60  and a spacer ring  70  are positioned. 
         [0039]    The crown  10  and the hub  20  are rotatable relative to one another around the axis X 1 . 
         [0040]    The free wheel  40  makes it possible to engage the crown  10  with the hub  20  in rotation in a first direction of rotation R 1  around the central axis X 1 , and conversely, to disengage the crown  10  relative to the hub  20  in a second direction of rotation R 2  opposite the first direction of rotation R 1 . This free wheel or one-way clutch device  40  may be in accordance with the technical teaching of WO-A-2011/079963. It comprises several cams  42  guided by a cage  44  to bear, by suitable geometric surfaces, against the outer radial surface  22  of the hub  20  and against an inner radial surface  462  of the sleeve  46  that is part of the free wheel  40  and is mounted radially inside the crown  10 , respectively, with a possibility of rotation relative to that crown around the axis X 1 . 
         [0041]    The rolling bearing  50  comprises an inner ring  52 , an outer ring  54 , a row of balls  56  and a cage  58  for keeping the balls in position inside a rolling cage defined between the rings  52  and  54 . The rolling bearing  50  allows the relative rotation between the elements  10  and  20  around the axis X 1 . 
         [0042]    The spring  60  is a brake spring formed by a rod of elastically deformable material, such as steel, with turns whereof the diameter varies based on the direction of a force bringing two ends  62  and  64  of that rod that are curved radially toward the outside of the spring  60 , as shown in  FIG. 3 , closer together or further apart. 
         [0043]    The ring  70  is secured in rotation, for example glued, with the inner radial surface  12  of the crown  10 . The ring  70  axially limits the space  30  on the side opposite the rolling bearing  50 , whereas the rolling bearing  50  axially limits the space  30  on the side opposite the ring  70 . 
         [0044]    The ring  70  can be made from a synthetic material or metal. In radial cross-section relative to the axis X 1 , it is globally U-shaped with an annular bottom wall  72 , planar and perpendicular to the axis X 1 , as well as two side walls, inner  74  and outer  76 , respectively, that form the branches of the U-shaped cross-section of the ring  70  and that are each cylindrical and centered on the axis X 1 . The branches  74  and  76  have different axial widths, measured parallel to the axis X 1 . Alternatively, these lengths can be equal. 
         [0045]    The walls  74  and  76  define an inner volume  78  of the ring  70  between them in which the turns  66  of the spring  60  are partially received. 
         [0046]    In the example, the wall  76  is glued against the surface  12  of the crown  10 , while the wall  74  slidingly bears against the surface  22  of the hub  20 . 
         [0047]    The edge  762  of the wall  76  opposite the bottom  72  is equipped with a tooth  764  protruding relative to that edge in a direction parallel to the axis X 1 . That tooth  764  is intended to interact with the end  622  of the spring  60 . 
         [0048]    Furthermore, the edge  463  of the sleeve  46  turned toward the ring  70  and the spring  60  is provided with a shoulder  464  designed to interact with the end  64  of the brake spring  60 . 
         [0049]    The operation is as follows: when the crown  10  is driven by the belt  4  around the axis X 1  in the direction of rotation R 1 , the belt  10  drives the ring  70  whereof the tooth  764  exerts, on the end  62  of the spring  60 , a force in the direction of arrow F 1  in  FIG. 3 . The continuation of the rotational movement R 1  results first in rotating the spring  60  around the wall  74 , which brings the end  64  of the spring  60  into contact with the shoulder  464 . The movement of the end  64  of the spring  60  toward the shoulder  644  is shown by arrow F 2  in  FIG. 3 . The resistance opposed by the sleeve  46  against the rotation in the direction R 1  results in bringing the ends  62  and  64  closer to each other, which results in radially expanding the turns of the spring  60  around the wall  74 . This results in securing the elements  60  and  70  in rotation around the axis X 1 . 
         [0050]    The sleeve  46  then rotates in the direction of rotation R 1  and exerts, on the cams  42 , across from which it is positioned axially along the axis X 1 , a force that causes them to pivot in a configuration where those cams block each other between the surfaces  462  and  22 , to the point that they transmit the torque from the sleeve  46  to the inner hub  20 . The inner hub  20  then rotates in the direction of rotation R 1  while being supported, on one side of the device  40  along the axis X 1 , by the rolling ball bearing  50  and, on the other side, by the spacer ring  70  that forms a plain bearing with the hub  20 , at the interface between the wall  74  and the surface  22 . 
         [0051]    On the contrary, if the outer crown  10  rotates more slowly in the direction R 1  than the inner hub  20 , i.e., if the elements  10  and  20  tend to rotate relative to one another in the direction of rotation R 2 , the free wheel  40  prevents the transmission of torque between those elements, such that the inner hub  20  can rotate more quickly around the axis X 1  in the direction of rotation R 1  than the other crown  10 . In that case, the spring  60  is not radially compressed around the wall  74 , due to its interaction with the raised portions  764  and  464 , such that there is no securing in rotation between the elements  60  and  70 . 
         [0052]    Thus, the spring  60  makes it possible on the one hand to transmit the torque, between the crown  10  and the free wheel  40 , and on the other hand, to damp the jolts during acceleration of the outer crown  10  relative to the inner hub  20  in the direction of rotation R 1  because the rotational movement is only transmitted after the end  62  and  64  of that spring interact simultaneously with the raised portions  764  and  464  to drive the sleeve  46 , i.e., after the spring  60  has been elastically deformed. The spring  60  therefore makes it possible both to damp the relative rotational movement between the elements  10  and  20  upon startup and to transmit the torque in the direction of rotation R 1  of the outer crown  10  to the device  40 . 
         [0053]    Since the spring  60  and the ring  70  are axially offset relative to the device  40 , the entire radial thickness e 30  of the housing  30  is available for the clutch device  40 , which makes it possible to use cams  42 , a cage  44  [and] a sleeve  46  that are all robust. 
         [0054]    Likewise, the entire radial thickness e 30  of the housing  30  is available to house the spacer ring  70 , which can also be robust, which is important because it participates in maintaining the radial separation between the elements  10  and  20 , around the axis X 1 , while forming a radial spacer that acts as a complement to the rolling ball bearing  50 . 
         [0055]    Furthermore, since the spring  60  and the ring  70  are positioned on one side of the device  40  along the axis X 1 , while the rolling ball bearing  50  is positioned on the other side, the forces exerted on the device  40  are globally balanced, which contributes to the proper lifetime of the pulley-assembly  1 . 
         [0056]    In the second to fifth embodiments of the invention shown in  FIGS. 5  and following, elements similar to those of the first embodiment bear the same references. Hereinafter, we primarily describe what differs between these embodiments and the first. 
         [0057]    In the second embodiment of  FIGS. 5 and 6 , a trim  90  made from polytetrafluoroethylene (PTFE) is radially inserted between the outer radial surface  466  of the sleeve  46  and the inner radial surface  12  of the crown  10 . This trim  90  serves to damp the transitional phase upon torque transfer, i.e., to brake the relative rotation between the outer crown  10  and the sleeve  46 , while the spring  60  is not completely operational to transmit the torque between the elements  70  and  46 . The trim  90  increases the friction coefficient between the parts  10  and  46 , which prevents the oscillations of the parts  10  and  46  relative to one another, in rotation around the axis X 1 , when the outer crown  10  rotates more quickly than the sleeve  46  in the direction of rotation R 1 . In other words, the trim  90  introduces a sort of hysteresis into the relative movement of the parts  10  and  46  with respect to one another, for dynamic stabilization purposes and in order to avoid oscillations, as mentioned above. 
         [0058]    For the rest, this embodiment works like the first. 
         [0059]    In the third embodiment shown in  FIGS. 7 and 8 , the ring  70  is secured by its inner wall  74  to the inner sleeve  20 . The ring  70  may be glued, forcibly mounted or crimped on the inner sleeve  20 . In that case, the edge  742  of the wall  74  opposite the bottom  72  is equipped with a tooth  744  designed to interact with one end  62  of the spring  60  that is outwardly curved, i.e., opposite the axis X 1 , relative to the turns  66  of that spring. The edge  463  of the sleeve  46  oriented toward the spring  60  is, as in the first embodiment, equipped with a shoulder  464  designed to interact with the second end  64  of the spring  60 . 
         [0060]    In the event the outer crown  10  tends to rotate more quickly than the inner sleeve  20  in the direction of rotation R 1 , the inner radial surface  12  of the crown  10  acts directly on the cams  42  of the device  40  to cause those cans to switch into a torque transmitting configuration in which the cams  42  drive the sleeve  46  in the same direction, in rotation around the axis X 1 . That sleeve then, by its raised portion  464 , drives the end  64  of the sleeve  60 , which results in radially tightening the turns  66  of the spring  60  and rotating the end  62  in the same direction, which pushes on the tooth  744 , which drives the ring  70  in the same direction. Since the ring  70  is secured in rotation with the inner sleeve  20 , it then rotates that sleeve in the same direction of rotation R 1 . The contraction of the turns  66  of the spring  60  results in the rotational securing of the spring  60  and the wall  76  of the ring  70 . 
         [0061]    In case of rotation in the opposite direction, the free wheel  40  does not transmit torque, as in the first embodiment. 
         [0062]    In the fourth embodiment shown in  FIGS. 9 and 10 , a trim  90  is used as in the second embodiment, while the general architecture of the pulley-assembly  1  is close to that of the third embodiment. The trim  10  is radially inserted between the inner radial surface  462  of the sleeve  46  and the outer radial surface  22  of the hub  20 . 
         [0063]    In the first four embodiments described above, the spring  60  is not necessarily of the torsion spring type with circular turns, like that shown in the figures. It may have other turn shapes. It may for example be a “clock spring”. 
         [0064]    In the fifth embodiment shown in  FIGS. 11 and 12 , an elastomeric ring  160  is used as a member for damping the relative rotation between the elements  10  and  20  and as a torque transmission member from the crown  10  to the free wheel  40 . That ring  160  is provided with four spurs  162  that extend radially outward relative to the ring  160 , on four angular sectors regularly distributed around its central axis combined with the axis X 1  during use. The spacer ring  70  is equipped with two teeth  79  that engage between two adjacent spurs  162  of the ring  160 . On another side, the sleeve  46  is equipped with two other teeth  469  protruding relative to its edge  463  turned toward the ring  160  and designed to engage between two spurs  162  of the ring  160 , in the spaces left free by the teeth  79 . 
         [0065]    A reinforcing ring  170  is inserted between the free wheel  40  and the ring  160 , with an outer diameter smaller than the inner diameter of the teeth  469 , such that it limits the deformations of the ring  160  in an axial direction oriented toward the device  40 , without hindering the engagement between the elements  46  and  160 . 
         [0066]    During the transmission of torque between the elements  70  and  46 , which occurs in a manner comparable to that explained for the first body, the spurs  162  of the ring  160  work by shearing. The elastic nature of the material used for the ring  160  allows it to damp the relative rotation between the elements  70  and  46 , i.e., between the elements  10  and  20 . The relative rigidity of that ring also allows it to transmit the torque effectively between those elements  70  and  46 . 
         [0067]    Alternatively, in place of an elastomer, another less deformable synthetic material may be used to form the ring  160 . 
         [0068]    Alternatively, the rolling bearing  50  may be a rolling bearing with rolling bodies of a type different from a rolling ball bearing, for example a rolling bearing with rollers or needles. 
         [0069]    In all of the embodiments, the ring  70  forms a plain bearing, either with the inner hub  20 , or with the outer crown  10 . 
         [0070]    In all embodiments, the fact that the torque transmission member  60  or  160  is axially offset relative to the one way clutch  40 , along central axis X 1 , implies that along this axis, items  60  and  40 , or items  160  and  40 , do not overlap. 
         [0071]    The invention is not limited to the field of pulley-assemblies for alternators. 
         [0072]    The embodiments and alternatives discussed above may be combined to create new embodiments.