Patent Publication Number: US-2007099743-A1

Title: Clutch assembly

Description:
FIELD OF THE INVENTION  
      The present invention relates to drive trains for transmitting rotational movement from a motor to a drive element. In particular, the invention relates to “overload” clutch assemblies within such drive trains.  
     BACKGROUND  
      In many drive train applications overload relief is required. For instance, overload relief may be required to enable manual movement of a driven element without damaging the gear train Coupling and isolation between the overload protected side of a mechanism and the driven side of a mechanism can be provided by a positive engagement clutch. Such clutches are known and used in automotive applications including external mirror head drives. The applicant&#39;s patent PCT/AU02/00517 titled “POWER FOLD MECHANISM FOR DOUBLE ARM MIRRORS” discloses a clutch that is held in an engaged position by a spring force and is disengaged when the reaction forces at ramps on the clutch are great enough to overcome the spring force.  
      A problem with clutch mechanisms of the type employed in the power fold mechanism disclosed in PCT/AU02/00517 is that significant frictional force is generated between the splines and the clutch body resisting movement of the clutch body with respect to the splines.  
      It is an object of the present invention to ameliorate the aforementioned problem and to provide a simpler clutch assembly.  
      It is a further object of the invention to provide a clutch and reduction drive assembly of reduced complexity.  
      It is a further object of the invention to provide a power-folding vehicle mirror assembly having an improved clutch and reduction drive.  
     SUMMARY OF THE INVENTION  
      According to a first aspect of the invention there is provided a power-folding vehicle mirror assembly comprising: 
          a base mountable to a vehicle;     a clutch body mounted to and rotationally fixed to the base;     a sun gear slidably mounted to the base for rotation about a first axis, the sun gear biased towards engagement with the clutch body by a biasing means;     a mirror head assembly rotatably mounted to the base;     a planetary gear mounted to the mirror head assembly for rotation about a second axis, the planetary gear meshing with the sun gear; and     a motor operably connected to the planetary gear for driving the mirror head assembly around the sun gear,     wherein, upon the application of a manual breakaway force to the mirror head assembly, the planetary gear transmits a breakaway torque to the sun gear, the breakaway torque sliding the sun gear away from and out of engagement with the clutch body, thereby allowing rotation of the sun gear and mirror head assembly with respect to the base while maintaining mesh with the planetary gear.        

      Preferably the biasing means comprises a spring.  
      Preferably the assembly further comprises ramped detents on the clutch body bearing against corresponding detents on the sun gear, 
          whereby the ramped detents enable an axial force to be generated as the detents are rotationally forced against each other, the axial force working against the spring to enable the sun gear to disengage from the clutch body thereby allowing relative rotation        

      Preferably the planetary gear is a worm gear.  
      Preferably the spring comprises a disc spring.  
      Preferably the spring has a negative spring rate.  
      Preferably the first and second axes are orthogonal, the sun gear is helically formed at a first helix angle and the worm gear is helically formed at a second helix angle complimentary to the first helix angle.  
      Preferably the ramped detents are ramped so that the breakaway torque is substantially the same in either breakaway direction.  
      According to a second aspect of the invention there is provided a clutch and reduction drive assembly comprising: 
          a first gear mounted to a first body for rotation about a first axis;     a second gear meshing with the first gear, the second gear mounted to a second body for rotation about a second axis; and     a clutch mechanism having a clutch body and a clutch body receiving portion, the receiving portion mounted to or integral with the second gear, the clutch mechanism preventing relative rotation between the clutch body and the second gear in an engaged position and allowing relative rotation between the clutch body and the second gear in a disengaged position,     characterised in that the clutch mechanism is disengagable by movement of the second gear together with the receiving portion with respect to both the clutch body and the first gear while the second gear remains meshing with the first gear, the movement in a direction along the second axis of rotation.        

      Preferably the clutch mechanism is loaded by a spring.  
      Preferably the dutch mechanism further comprises ramped detents on the clutch body bearing against corresponding detents on receiving portion, 
          whereby the ramped detents enable an axial force to be generated as the detents are rotationally forced against each other, the axial force overcoming the load on the clutch mechanism provided by the spring thereby enabling the clutch mechanism to disengage.        

      Preferably the first gear is a worm gear.  
      Preferably the worm gear is driven by a motor.  
      Preferably the motor drives the worm gear through a reduction gear drive.  
      Preferably the reduction gear drive includes a further worm gear.  
      Preferably the spring comprises a disc spring.  
      Preferably the spring has a negative spring rate.  
      Preferably second gear is helically cut at an angle to match the worm gear so as to allow the first and second axes of rotation to be perpendicular to each other. Alternatively, the second gear straight cut and the first and second axes of rotation are not perpendicular to each other. With this alternative, the movement of the second gear with respect to the clutch body in a direction along the second axis does not result in rotation of the second gear about the second axis.  
      The second aspect of the invention will find many applications. For instance an embodiment of the invention may include a vehicle sub-assembly such as an external mirror. With such an embodiment one of the first and second bodies would be connected to the vehicle body and the other of the first and second bodies would be connected to a driven component. For example, the driven component could be an externally mounted mirror head that is movable from a deployed position away from the vehicle side to a parked position adjacent the vehicle side under the action of the clutch and reduction drive assembly of the invention.  
      According to a third aspect of the invention there is provided a clutch and reduction drive assembly comprising: 
          a primary frame;     a clutch body mounted to and rotational fixed to the primary frame;     a primary gear slidably and rotatably mounted to the primary frame for rotation about a first axis, the primary gear biased towards engagement with the clutch body by a biasing means;     a secondary frame rotatably mounted to the base; and     a secondary gear mounted to the secondary frame for rotation about a second axis, the secondary gear meshing with the primary gear,     wherein the primary gear is movable against the biasing means from an engaged position in which rotation with respect to the clutch body is prevented to a disengaged position in which rotation with respect to the clutch body occurs.        

      Preferably the biasing means comprises a spring, still preferably, a disc spring.  
      Preferable the assembly further comprises ramped detents on the clutch body bearing against corresponding detents on the primary gear, 
          whereby the ramped detents enable an axial force to be generated as the detents are rotationally forced against each other, the axial force working against the spring to enable the primary gear to disengage from the clutch body thereby allowing relative rotation.        

      Preferably the secondary gear is a worm gear.  
      Preferably the spring has a negative spring rate.  
      Preferably the first and second axes are orthogonal, the primary gear is helically formed at a first helix angle and the worm gear is helically formed at a second helix angle complimentary to the first helix angle.  
      A specific embodiment of the invention will now be described in some further detail with reference to and as illustrated in the accompanying figures. This embodiment is illustrative, and is not meant to be restrictive of the scope of the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION  
      A preferred embodiment of the invention is illustrated in the accompanying representations in which:  
       FIG. 1  shows a power folding external vehicle mirror assembly.  
       FIG. 2  is an exploded view of a power folding mechanism for a vehicle mirror.  
       FIG. 3  is a perspective view of a clutch body component of the assembly of  FIG. 2   
       FIG. 4  is a perspective view of a sun gear component of the assembly of  FIG. 2 .  
       FIG. 5  is a front view of the assembly of  FIG. 2 .  
       FIG. 6  is a sectionally view through the line B-B indicated on  FIG. 5 .  
       FIG. 7  is a sectional view through the line A-A as shown on  FIG. 5 .  
       FIGS. 8 and 9  are similar views to that of  FIG. 6  (inverted) showing a disengaged and engaged position of a clutch mechanism respectively.  
       FIG. 10  is a sectional view through lines c as indicated on  FIG. 5 .  
       FIG. 11  is an exploded perspective view of the assembly of  FIG. 1  with its covers removed. 
    
    
      Referring to  FIGS. 2, 5  and  6 , a clutch and reduction drive assembly according to an embodiment of the invention is shown. The clutch and reduction drive assembly comprises a first gear in the form of a drive worm  54  mounted to a first body in the form of a housing  40  for rotation about a first axis  51  (shown on  FIG. 5 ). A second gear referred to hereinafter as a drive gear  56  meshes with the drive worm  54 . The drive gear  56  is mounted to a second body by a part  79  for rotation about a second axis  57  as indicated on  FIG. 6 .  
      Depending on how the housing  40  and part  79  is mounted, rotation of the drive gear  56  about the second axis  57  may occur either when the clutch is engaged or disengaged.  
      The drive gear  56  has a dutch body receiving portion  61  integral with its upper face as is shown in  FIG. 4 . The receiving portion includes ramped detents  60  shaped to cooperate with a clutch body  64  which, in this embodiment, is integral with the part  79  as is shown in  FIG. 3 . The clutch mechanism prevents relative rotation between the clutch body  64  and the drive gear  56  in an engaged position and allows relative rotation between the clutch body  64  and the drive gear  56  in a disengaged position.  
      In other embodiments of the invention the receiving portion may be a separate component to the drive gear, and/or the dutch body may be a separate component to part  79 .  
      The clutch mechanism is loaded by a spring arrangement in the form a disc spring  70  shown in  FIGS. 2, 6 ,  8  and  9 . This spring  70  biases the drive gear  56  upward into engagement with the clutch body  64 . The ramped detents  60  enable an axial force to be generated as the detents are rotationally forced against each other. When the axial force is sufficient to overcome the load on the clutch provided by the spring  70 , the clutch mechanism disengages thereby allowing the drive gear  56  to rotate with respect to the dutch body  64  and the part  79 .  
      Referring to  FIGS. 2 and 5  it can be seen that the clutch and reduction drive assembly is driven by an electric motor  46  driving the motor worm  48  which in turn drives a motor worm driven gear  50  which is fixed to the drive worm  54 . The drive worm  54  meshes with the drive gear  56 .  
      With this embodiment of the invention, the second gear, that is the drive gear  56  is helically cut at an angle to match the worm gear  54  so as to allow the first and second axis of rotation  51  and  57  to be perpendicular to each other. With this arrangement, the drive gear  56  will advance or retard with respect to the drive worm  54  (depending on the hand of the worm) as the clutch is moved from an engaged to a disengaged position. To maintain equal disengagement torque in either rotational directions, different ramp angles on the faces of the detents  60  are used. For example, referring to  FIGS. 3 and 4 , ramps  86  and  87  are different angles, as are ramps  82  and  84  on the clutch body  64 .  
      In an alternative embodiment of the invention the drive gear  56  is straight cut and the first and second axes of rotation  51  and  57  are not perpendicular to each other. With this alternative arrangement, no advancing or retarding of the drive gear occurs, however more space is required to accommodate the drive components.  
      The disc or belleville spring  70  can be replaced with a conventional coil spring or any other biasing arrangement.  
      With the clutch assembly described above, there is no requirement for a spline on the axially moving component, in this case gear  56 . The meshing between the teeth of the gear  56  and the gear  54  replaces the need for a spline. Not only does this simplify the construction of the dutch mechanism as compared to earlier clutches, it results in a significant reduction in the frictional force that usually exists between the splined components.  
      The clutch and reduction drive assembly described above will have many applications. In automotive components such as mirrors there is a need to provide motor driven components with the ability to be manually overridden without damage of a gear train. A particular example of this is a power folding truck “wing” mirror illustrated in  FIG. 1 .  
       FIG. 1  shows an external side or “wing” mirror assembly  11  comprising a mirror head assembly  12  and two mirrors  13 . The mirror assembly  11  has a base  14  mountable to a vehicle. As shown in  FIG. 11 , upper and lower arms  15  and  16  extend from the base  14  to the head portion  12 . Each arm  15  and  16  has a clutch and reduction drive assembly mounted within a housing comprising upper and lower shells  40  and  40 ′ as shown in  FIG. 2 . Screws  25  hold the housing shells together. The housing and hence the clutch and reduction drive assembly is mounted into the arms by means of two press fit pins  26  through the housing  40  as shown in  FIGS. 2 and 11 . Referring now to  FIG. 11 , it can be seen that the clutch and reduction drive assembly is mounted to the base assembly  14  by a spigot  44  that penetrates up through the part  79 . Part  79  is keyed to prevent rotation with respect to spigot  44 . The keys  78  are shown in  FIG. 5 .  
      As can be seen in the sectional view of  FIG. 6  (taken through section lines B-B indicated in  FIG. 5 ) the housing  40  (having a lower portion  40 ′) is securely held within mirror arm  15 . Thus the axis  51  about which the drive worm  54  rotates is fixed with respect to the mirror arm  15  and the head assembly  12 . Therefore, while the clutch remains engaged, rotation of the drive worm  54  causes the housing  40  and the mirror arm  15  and head portion  12  to rotate about the drive gear axis  57 . The drive worm  54  can be considered a planetary gear as it drives around the axis  57  shown in  FIG. 6 . The gear  56 , referred to previously as drive gear  56 , will now be referred to as sun gear  56  as it is the gear about which the planetary worm gear  54  rotates as the motor  46  drives the worm gear  54 .  
      Importantly, the sun gear  56  is slideably mounted to the base  14  and is slideably movable from the position shown in  FIG. 9  downwards to the position shown in  FIG. 8 . A biasing means in the form of a disc spring  70  biases the sun gear  56  upwards into engagement with the clutch body  64  as is illustrated in  FIG. 9 . It is only where a manual breakaway force is applied to the mirror head assembly  12 , for instance by a person manually pressing against the mirror head to park it or by the mirror head impacting on a person or a fixed object, that the clutch mechanism releases to the position shown in  FIG. 8 . Release occurs upon the application of a manual breakaway force to the mirror head because the planetary worm gear  54  transmits the breakaway torque to the sun gear  56 , the breakaway torque sliding the sun gear  56  away from an outer engagement with the clutch body  56 . This occurs while maintaining mesh with the planetary gear.  
      Arm covers or shrouds  22  enclose the assembly  17  to protect it and provide an aesthetically pleasing appearance as shown in  FIG. 1 .  
      With the embodiment of the invention described above with reference to FIGS.  1  to  11 , a pair of arms  15  and  16  are provided between the base  14  and the mirror head assembly  12 . In other embodiments, distinct arms will not be present. The mirror head assembly will be directly mounted to the base for relative rotation thereto.  
      The mirror assembly  11  shown in  FIG. 1  may have a telescopically adjustable head assembly  12 . The above described invention may equally be applied to a mirror assembly  11  with or without telescopically adjustable head  12 .  
      Many other applications for the clutch and reduction drive assembly  17  described above will exist. In some applications, the first gear may not be a drive worm  54  but instead may be a spur or helically cut gear  54  (not shown). In applications where no reduction is required and only clutching is required, the first gear may have the same pitch circle diameter as the second gear (the drive gear  56 ).  
      In the embodiments described above, drive input is through the first gear (the worm  54 ) with rotation of the housing  40  about the axis  100  of spigot  44  comprising the output. The axis of rotation  100  is illustrated in  FIG. 7 . In other embodiments the drive may be reversed with the worm  54  replaced by an output helical or spur gear and input being provided by rotation of the spigot  44  and hence the clutch body  64  about the axis  100 .  
      While the present invention has been described in terms of a preferred embodiment, in order to facilitate better understanding of the invention, it should be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications within its scope.