Abstract:
A motorized tilt actuator assembly comprises one or more threaded jack screws attached to a mirror glass case and traveling along one or more threaded actuator shafts with rotation of the motor. When a jack screw reaches its limit of travel, relative movement between the actuator shaft and the glass case can occur through a slip clutch mechanism during such time as the motor continues to operate. In one embodiment, the relative movement is accommodated by a spherical actuator head rotating in a compressively spring-biased socket. In another embodiment, the relative movement is accommodated by slippage along a friction surface interposed between the actuator shaft and the motor. Manual repositioning of the mirror can be accommodated by slippage of the jack screw threads past the actuator shaft threads, or by a coarse threaded interconnection of the jack screw and the actuator shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. provisional application Ser. No. 60/319,823, filed Dec. 30, 2002, which is incorporated herein in its entirety. 

   BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The invention relates to mirrors for automotive vehicles. In one aspect, the invention relates to an improved assembly for mounting a mirror actuator jack screw to a mirror carrier for controlling the vertical and horizontal tilt of the mirror. In one embodiment, the invention relates to a slip clutch applied between each jack screw and the mirror carrier to allow slip between these components when the mirror has reached the end of travel but a drive motor continues to run. 
   2. Description of the Related Art 
   Rearview mirrors are standard equipment on automotive vehicles. Frequently, the rearview mirrors can be adjusted by the operator from inside the vehicle through a motorized tilt adjustment mechanism, or tilt actuator, mounted within a mirror system. Via a motor, or a pair of motors, the horizontal and vertical tilt of the mirror is controlled by the threaded engagement of an actuator shaft, also called a jack screw, within a drive nut for each of the horizontal and vertical axes. 
   Frequently, when the actuator shafts reach their limit of movement, the motor will continue to operate for a period of time. The threaded engagement of the jack screw and the drive nut is therefor configured with a “ratchet” mechanism to allow for relative slippage between the jack screw and the drive nut so that the motor can turn without damage to the motor or the jack screw/drive nut assembly. However, this slippage is typically accompanied by a “clicking” sound as the ratchet mechanism is engaged. This clicking sound is frequently interpreted as a performance defect or the result of poor quality, or it can be interpreted as a failure of the actuator, motivating the vehicle owner to seek maintenance that may be unnecessary. Additionally, in mirrors having a positional memory feature for returning the mirror to a preselected orientation for a particular driver, the slippage between the jack screw and the drive nut will disrupt the memory setting, necessitating the resetting of the preselected orientation for each driver using the vehicle. 
   A clutch mechanism or release mechanism is frequently incorporated into the tilt actuator to accommodate the continued turning of the motor without damage to the motor or the actuator shafts. This slip clutch is typically provided at the base of the actuator shaft, distal from the interconnection of the actuator shaft to the mirror carrier (which carries the mirror element). The actuator shaft is typically mounted to the mirror carrier in a non-rotatable manner. The slip clutch at the base of the actuator shaft can be complex, and generally requires the actuator shafts to be fixedly incorporated into the tilt actuator, thereby restricting their ready removal from the tilt actuator assembly. The complex mechanism adds cost and inhibits the ready installation and removal of the tilt actuator from the mirror system for replacement or repair. 
   SUMMARY OF INVENTION 
   A vehicular mirror system comprises a reflective element having a mounting portion thereon, an actuator operably interconnected to the reflective element for controlling the tilt of the reflective element, wherein the actuator is operable in a normal range of travel, and a clutch associated with the actuator for operation of the actuator in a first mode and a second mode, wherein in the first mode the actuator moves in a normal mode of operation and actuates the tilt of the reflective element, and wherein in the second mode the actuator is placed in an impeded mode of operation and the clutch allows the actuator to slip and prevent damage thereto. One of the mounting portion and the actuator can comprise a socket, and the other of the mounting portion and the actuator can comprise a ball. The ball can be snap-fit within the socket. 
   The ball can be non-rotatably mounted within the socket, and can comprise at least one projection, wherein the socket comprises at least one slot in register with the at least one projection. The at least one projection can be received within the at least one slot when the ball is received within the socket. A compression member can be mounted around the socket to apply a compression force on the ball. The compression member can comprise a spring wrapped around the periphery of the socket, a ring, a triangular compression ring, or a C-ring. 
   The socket can have a peripheral groove on an external surface thereof., and compression member can be disposed within the peripheral groove. The compression force can be preselected to apply a sufficient frictional force between the ball and the socket to enable the ball to rotate with respect to the socket during travel in the normal range of movement, but to slip with respect to the socket when the actuator is urged beyond the normal range of travel. 
   The actuator can comprise a first portion and a second portion, wherein the first portion is non-rotatably mounted to the mounting portion of the reflective element, and the clutch is disposed between the first and second portions to allow movement of the first portion with respect to the second portion during operation in the first mode. The clutch can allow slip between the first and second portions when the actuator is operated in the second mode. The first portion can comprise an elongated member having a first end and a second end. The first end of the first portion can be non-rotatably received by the reflective element. 
   The second end of the first portion can be received by the second portion, and the second portion can comprise an annular member having an external gear portion which is driven by a motive source. The first portion can be threadingly received by the second portion, wherein driven rotation of the second portion is transferred to the first portion during the normal range of travel. The first portion can be mounted to the second portion by the clutch which slips when the first portion is driven beyond the normal range of travel. 
   The first portion can have a first bearing surface, the second portion can have a second bearing surface, and the clutch can comprise a spring which frictionally forces the first and second bearing surfaces to travel together during movement in the normal range of travel. The spring can be selected to allow the first and second bearing surfaces to slip with respect to one another when the actuator is urged beyond the normal range of travel. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     In the drawings: 
       FIG. 1  is a perspective view of a portion of a motor vehicle comprising a mirror system with a tilt actuator and jack screw slip clutches according to the invention. 
       FIG. 2  is a front exploded view of the mirror system of  FIG. 1  illustrating the tilt actuator with jackscrews according to the invention. 
       FIG. 3  is a rear exploded view of the mirror system of  FIG. 1  illustrating a glass case with sockets for receipt of the jackscrews according to the invention. 
       FIG. 4  is a perspective view of the tilt actuator assembly of  FIG. 1  with the interior exposed to illustrate the assembly of the jackscrews. 
       FIG. 5  is a perspective view of the assembled tilt actuator assembly of  FIG. 4 . 
       FIG. 6  is a close-up side view of the jack screw of  FIG. 4 . 
       FIG. 7  is a perspective view of a portion of the glass case of  FIG. 3  illustrating the sockets for receipt of the jackscrews. 
       FIG. 8  is a sectional view taken along line  8 - 8  of  FIG. 7 . 
       FIG. 9  is a perspective view of a portion of a jack screw and a socket according to a first embodiment of the invention. 
       FIG. 10  is a sectional view taken along line  10 - 10  of  FIG. 9 . 
       FIG. 11  is a perspective view of a portion of a jack screw and a socket according to a second embodiment of the invention. 
       FIG. 12  is a sectional view taken along line  12 - 12  of  FIG. 11 . 
       FIG. 13  is a perspective view of a portion of a jack screw and a socket according to a third embodiment of the invention. 
       FIG. 14  is a sectional view taken along line  14 - 14  of  FIG. 13 . 
       FIG. 15  is a close-up perspective view of a first alternate embodiment of an assembly comprising a jackscrew and a drive gear operably connected through a clutch plate assembly. 
       FIG. 16  is a cross-sectional view of the jack screw assembly of  FIG. 15  taken along line  16 - 16 . 
       FIG. 17  is a close-up perspective view of the assembly illustrated in  FIG. 15  with the drive gear removed for clarity. 
       FIG. 18  is a close-up perspective view of a second alternate embodiment of an assembly comprising a jackscrew and a drive gear operably connected through a clutch plate assembly, with the drive gear removed for clarity. 
       FIG. 19  is a cross sectional view of the jack screw assembly of  FIG. 18  with the drive gear included taken along line  19 - 19 . 
       FIG. 20  is a perspective view of an alternate embodiment of the tilt actuator assembly of  FIG. 1  with the interior exposed to illustrate an assembly comprising a pair of actuator motors and jackscrews according to the invention. 
       FIG. 21  is an exploded view of a portion of the tilt actuator assembly of  FIGS. 2-14  illustrating an alternate embodiment of the ball and socket assembly. 
   

   DETAILED DESCRIPTION 
   As illustrated in  FIG. 1 , an embodiment of a rearview mirror system  10  according to the invention is installed on an automotive vehicle  12  on or near the front of the driver&#39;s side door. An identical mirror system can be similarly mounted to the vehicle  12  on the passenger&#39;s side. The description of the structure and operation of the mirror system presented hereinafter will be equally applicable to both mirror systems. Although the invention is described herein with respect to one or more exemplary embodiments, the exemplary embodiments of the inventive concepts described herein are not to be considered as limiting, except where the claims expressly state otherwise. 
   The rearview mirror system described herein comprises several embodiments of an actuator assembly for tilting a reflective element. The actuator assembly comprises one or more jackscrews which operate within a preselected linear range of travel to tilt the reflective element. Unrestricted operation of the actuator assembly resulting in movement of the jackscrew within the preselected linear range of travel is referred to herein as a “normal mode of operation.” Restricted operation of the actuator assembly, for example, after the jackscrew is moved to the limit of the preselected linear range of travel, or in the situation in which the jackscrew is prevented from movement within the linear range of travel due, for example, to an obstruction of the movement of the reflective element, is referred to herein as an “impeded mode of operation.” 
   As illustrated also in  FIGS. 2 and 3 , in a first embodiment of the invention, the rearview mirror system  10  comprises an enclosure  14  enclosing a reflective element assembly  16  comprising a reflective element  24  mounted to a glass case  26 , a mounting frame  22 , and a single motor tilt actuator assembly  28 , and a base assembly  18  in cooperative relationship with the mounting frame  22 , which system  10  is mounted to the vehicle  12  in a generally well-known manner, and is operably connected to a remote control device (not shown) inside the vehicle through a suitable control linkage, such as a cable or wire harness (not shown). An example of such a rearview mirror system operated by a single motor tilt actuator assembly, and the selected tilting of the reflective element assembly thereby, is illustrated and described in U.S. Patent Applications Ser. No. 60/319,411, filed Jul. 19, 2002, entitled “Single-Motor Actuator With Selectable Multiple-Output Axes And Vehicle Mirror Incorporating Same,” and Ser. No. 60/319,176, Filed Apr. 9, 2002, entitled “Single Motor Actuator With Selectable Multiple Output Axle And Vehicle Mirror Incorporating Same,” which are incorporated herein by reference. The tilt actuator assembly  28  is fixedly mounted to the mounting frame  22  in a well-known manner. The reflective element  24  is attached in a generally well-known manner to a glass case  26 , which is in turn operably connected to the tilt actuator assembly  28  for adjustment of the vertical and horizontal tilt of the reflective element  24  as hereinafter described. 
   Referring now to  FIG. 4 , the actuator case  30  comprises a base  32 , and a cover  34  having a pair of spaced-apart apertures  35  extending therethrough, defining a chamber  36  containing in cooperative relationship a motor  38 , a pair of spaced-apart, generally parallel jackscrews  46  extending through the apertures  35 , as illustrated in  FIG. 5 , a pair of worm gears  42 , a pair of drive gears  44 , and a clutch assembly  40  for controlling the delivery of torque from the motor  38  to the jackscrews  46 , to comprise a single motor mirror tilt actuator assembly  28  for selectively adjusting the vertical and horizontal tilt of the reflective element assembly  16 . Each jackscrew  46  is threadably attached in a generally well-known manner to its respective drive gear  44  so that the jackscrew  46  will translate axially inwardly (i.e. retract) and outwardly (i.e. extend) of the tilt actuator assembly  28  when the drive gear  44  is rotated. It should be noted that the tilt actuator assembly  28  is exemplary only, and tilt actuator assemblies having alternative structure and operation can be employed consistent with the inventive concepts described herein. In particular, a tilt actuator assembly comprising a first motor driving a first jackscrew for tilting the mirror about a first axis and a second motor driving a second jackscrew for tilting the mirror about a second axis can be employed. 
   As illustrated in  FIG. 6 , the jackscrews  46  are generally cylindrical, elongated members comprising a cylindrical shaft  50  having an internally threaded coaxial bore, transitioning to a narrow neck  52 , to which is attached a truncated spherical head  54 . The head  54  comprises a truncated spherical surface  58 , and a flat circular surface  56  in diametric juxtaposition to the neck  52  and defining a plane generally orthogonal to the longitudinal axis of the jackscrew  46 . 
   Referring also to  FIGS. 7 and 8 , the glass case  26  comprises a generally plate-like body comprising an obverse side  62  to which the reflective element  24  is attached, and a reverse side  60 . The reverse side  60  comprises an inner surface  64  from which a pair of spaced-apart sockets  66  extend orthogonally for cooperative register with the jackscrews  56  when the reflective element assembly  16  is operably attached to the tilt actuator assembly  28 . Each socket  66  comprises two or more juxtaposed arcuate walls  68  terminating in an arcuate outer rim  70  and separated by a pair of diametrically-opposed head grooves  78 . Two arcuate walls  68  are illustrated in  FIGS. 7 and 8 . Depending inwardly from the outer rim  70  is an inclined surface  72  forming a boss  74  having an inwardly extending annular shoulder  76 . The arcuate walls  68  and the bosses  74  defining a generally spherical head cavity  80  having a generally spherical inner surface  71  and a diameter somewhat greater than the diameter of the head  54 . Extending circumferentially around the exterior of the arcuate walls  68  is a ring groove  82 , illustrated in  FIG. 8  as adjacent the inner surface  64 . 
   Referring now to  FIGS. 9 and 10 , the head  54  of the jackscrew  46  is inserted into the socket  66  in a “ball and socket” configuration so that the spherical surface  58  is in slidable register with the spherical inner surface  71 . The head  54  will be retained in the head cavity  80  by the annular shoulders  76  but can pivot and rotate relative to the glass case  26 . In a first embodiment illustrated in  FIGS. 9 and 10 , a compression element comprising a compression spring  86  is snap fit circumferentially around the arcuate walls  68  and is adapted for providing a radially inward compressive force to the arcuate walls  68 . A portion of the compression spring  86  is received in the ring groove  82  to retain the compression spring  86  in place around the arcuate walls  68 . The compression spring  86 , the arcuate walls  68 , and the head  54  are cooperatively adapted so that friction between the spherical inner surface  71  and the spherical surface  58  will prevent the jackscrews  46  from rotating relative to the sockets  66  so that the jackscrews  46  will translate coaxially with the rotation of the drive gears  44  during a normal range of travel of the jackscrews  46  between the retracted and extended positions. However, the compression spring  86 , the arcuate walls  68 , and the head  54  are also cooperatively adapted so that, when the jackscrews  46  reach the inner or outer limits of their movement, the friction between the spherical inner surface  71  and the spherical surface  58  will be overcome and the head  54  will rotate within the head cavity  80 . The frictional force between this vertical inner surface  71  and the spherical surface  58  can be selectively adjusted by adjusting the compressive force exerted by the compression spring  86 . A compression spring  86  having a low compressive force will provide a low frictional force between this vertical inner surface  71  and the spherical surface  58 . Conversely, a compression spring  86  having a high compressive force will provide a high frictional force between the vertical inner surface  71  and the spherical surface  58 . It will be recognized that the ring groove  82  can be positioned at any location along the arcuate walls  68  between the inner surface  64  and the outer rim  70  consistent with the function of the compression element described herein. 
     FIGS. 11 and 12  illustrate a second embodiment in which the compression element is a compression ring  84  comprising a generally conventional C-shaped ring retained in a ring groove  82  and applying a radially inward compressive force to the arcuate walls  68 . A diametric plane  90  is illustrated in  FIG. 12  which lies parallel to the inner surface  64  and bisects the head  54 . In this embodiment, the ring groove  82  is preferably adjacent the arcuate outer rim  70  on the side of the plane  90  away from the inner surface  64 , which will provide a more readily controlled compressive force to the arcuate walls  68 . The compression of the arcuate walls  68  by the compression ring  84  will urge the shoulders  76  together, which will create a force on the head  54  tending to urge the head  54  into the head cavity  80 , as illustrated in  FIG. 12  by the arrow “A”. The compression ring  84 , the arcuate walls  68 , and the head  54  are cooperatively adapted so that friction between the spherical inner surface  71  and the spherical surface  58  will prevent the jackscrews  46  from rotating relative to the sockets  66  so that the jackscrews  46  will translate coaxially with the rotation of the drive gears  44  during a normal range of travel of the jackscrews  46  between the retracted and extended positions. However, the compression ring  88 , the arcuate walls  68 , and the head  54  are also cooperatively adapted so that, when the jackscrews  46  reach the inner or outer limits of their movement, the friction between the spherical inner surface  71  and the spherical surface  48  will be overcome and the head  54  will rotate within the head cavity  80 . 
     FIGS. 13 and 14  illustrate a third embodiment in which the compressive force acting radially inwardly on the arcuate walls  68  is provided by a compression triangle  88  which is similarly retained in a ring groove  82  adjacent the arcuate outer rim  70 , and operates as previously described with respect to the first and second embodiments. The compression of the arcuate walls  68  by the compression triangle  88  will urge the shoulders  76  together, which will create a force on the head  54  tending to urge the head  54  into the head cavity  80 , as illustrated in  FIG. 14  by the arrow “A” 
   In each embodiment, the truncation of the head  54  forming the flat surface  56  can be selected to provide a spherical surface  58  having a selected area, thereby providing the desired frictional resistance between the spherical surface  58  and the inner spherical surface  71 . Alternatively, the head  54  can be untruncated. As well, it is within the scope of the invention to provide the radially inward compressive force to the arcuate walls  68  through other compression elements in addition to those illustrated and described herein. 
   The jackscrews  46  are attached to the glass case  26  by snap-fitting the heads  54  into the sockets  66 . The arcuate walls  68  will be flexed radially outwardly as the head  54  is inserted into the head grooves  78 , and will flexibly return radially inwardly as the head  54  moves past the annular shoulders  76 . Depending upon the compressive force exerted on the arcuate walls  68 , the heads  54  can be inserted into the sockets  66  with or without the compression elements installed. It is anticipated that the heads  54  will typically be inserted into the sockets  66  without the compression elements installed, and that the compression elements will be installed after the heads  54  are inserted into the sockets  66 . 
     FIGS. 15 ,  16 , and  17  illustrate a second embodiment of the jackscrew slip clutch assembly. A jackscrew actuator  110  comprises a jackscrew  112 , a drive gear  122 , and clutch plate assembly  124 . The jackscrew  112  comprises an elongated hollow shaft  114  comprising an annular wall  126  and a cylindrical center shaft  154  coaxial therewith defining an annular bore  158 . The annular wall  126  terminates in a plurality of annular fingers  128  having radially inwardly-extending teeth  130  extending into the annular bore  158 . Extending circumferentially around the outer surface of the annular fingers  128  is a spring channel  132  for retaining a helical spring  134  therein. The jackscrew  112  comprises a spherical head  116  connected to the shaft  114  by a narrowed neck  120 . The head  116  is bisected by a projection, illustratively shown as a blade  118 , adapted for insertion into a mating socket and slot (not shown) in the glass case  26  as is generally well-known in the art. 
   The drive gear  122  comprises a generally cylindrical body comprising an annular wall with radially outwardly-extending teeth for operable register with a worm gear  42  as is generally well-known in the art. The drive gear  122  has a circular wall  138  displaced inwardly somewhat from one end of the drive gear  122  to form an annular ring wall  137  defining an annular rim  136 . A circular shaft aperture  140  extends coaxially through the circular wall  138 . 
   The clutch plate assembly  124  comprises an irregularly-shaped body having a planar circular clutch plate  141  defining a circular clutch face  142 . Extending coaxially from the clutch face  142  is an annular, elongated threaded shaft  144  comprising an annular wall  150  having external threads  148  and defining a center bore  146  coaxial with the circular clutch face  142 . The threads  148  are adapted for threadable register with the teeth  130  so that as the clutch plate assembly  124  is rotated about its longitudinal axis, the jackscrew  112  will translate longitudinally relative to the clutch plate assembly  124 . The annular wall  150  is received in the annular bore  158 , and the center shaft  154  is slidably received in the center bore  146 . 
   Extending coaxially opposite the circular clutch face  142  is a mounting nipple  152  which is snap-fit into a mating receptacle (not shown) in the base  32  of the actuator case  30  for rotation of the clutch plate assembly  124  about its longitudinal axis relative to the base  32 . A clutch spring  156  is a circular body comprising a plurality of upwardly-directed fingers  157  extending radially inwardly and adapted for threadable register with the threaded shaft  144 . 
   The jackscrew actuator  110  is assembled by inserting the threaded shaft  144  into the shaft aperture  140  so that the clutch face  142  is in slidable register with the annular rim  136  at the perimeter of the clutch face  142 . The clutch spring  156  is threadably installed over the threaded shaft  144  until it contacts the circular wall  138  to urge the annular rim  136  against the clutch face  142 . The contact force between the annular rim  136  and the clutch face  142  can be selectively adjusted in proportion to the degree to which the spring  156  is threaded onto the threaded shaft  144 . The jackscrew  112  is then installed by inserting the center shaft  154  into the center bore  146  and the threaded shaft  144  into the annular bore  158  so that the teeth  130  threadably engage the threads  148 . The spring  134  is received in the spring channel  132  to urge the fingers  128  radially inwardly. The assembly is then snap fit into the base  132  so that the drive gear  122  engages the worm gear  42  and the head  116  engages the glass case  26 . 
   As the drive gear  122  is rotated by the worm gear  42 , friction between the annular rim  136  and the clutch face  142  will urge the rotation of the clutch plate assembly. The threaded shaft  144  will rotate relative to the jackscrew  112 , which is prevented from rotating by the connection of the head  116  and blade  118  to the glass case  26 . Thus, the jackscrew  112  will be translated along the threaded shaft  144  to tilt the glass case  26  along an axis. If the jackscrew  112  reaches its limit of travel, the clutch plate assembly  124  will be prevented from further rotation while the drive gear  122  will continue to rotate with the rotation of the worm gear  42 . The friction force between the annular rim  136  and the clutch face  142  will be exceeded, thereby enabling the motor  38  and the drive screw  122  to continue rotating without damage to either part. Similarly, the fingers  128  can flex radially-outwardly to enable the teeth  130  to move outwardly and over the threads  148  as the drive gear  122  and the threaded shaft  144  continue to rotate in the case where the friction force between the annular rim  136  and the clutch face  142  may not be exceeded. 
   The jackscrew  112  can also translate relative to the threaded shaft  144  if sufficient force is applied to the jackscrew  112 , such as by an external impact applied to the glass case  26 . The fingers  128  are urged inwardly by the spring  134 , but can flex radially outwardly against the compressive force of the spring  134  as the teeth  130  travel past the threads  148  if sufficient force is applied to the jackscrew  112 . 
     FIGS. 18 and 19  illustrate a third embodiment of the jackscrew actuator  160  which is similar in many respects to the jackscrew actuator  110  described heretofore. The jackscrew actuator  160  comprises a shaft  162  comprising an annular wall  164  terminating in a single, radially inwardly-extending tooth-like thread  166 . The clutch plate assembly  168  comprises a circular clutch plate  169  and a threaded shaft  170  having threads  172  which threadably engage the thread  166  for longitudinal translation of the shaft  162  relative to the clutch plate assembly  168  with rotation of the clutch plate assembly  168  in a manner similar to the previously described second embodiment. If the jackscrew reaches its limit of travel, the drive gear  122  will continue to rotate while the clutch plate assembly  168  will be prevented from further rotation, and the friction between the annular rim  136  of the drive gear  122  and the clutch face  142  will be exceeded. 
   The pitch of the thread  166  and the threads  172  are adapted so that, if sufficient force is applied to the jackscrew, the threaded shaft  170  will be urged to rotate. Preferably, the pitch of the threads  172  is 12.7 mm/thread so that the shaft  162  will translate 12.7 mm with one complete rotation of the shaft  170 . If the force applied to the jackscrew is inward, i.e. a force applied to the glass case  20  tending to push the jackscrew toward the circular wall  138  of the drive gear  122 , the clutch face  142  will be urged away from the annular rim  136 , thereby enabling the clutch plate assembly  168  to rotate relative to the drive gear  122 . With this embodiment, gearing reduction is necessary so that the shaft  170  will turn more slowly, thereby slowing the linear translation of the shaft  162 . 
   Although the invention has been described with respect to a single motor mirror tilt actuator  28 , it is within the scope of the invention that the tilt actuator  28  can comprise a multiple motor tilt actuator, such as the dual motor tilt actuator assembly  100  illustrated in  FIG. 20  as comprising a first motor  102  for tilting the reflective element assembly  16  about a first axis and a second motor  104  for tilting the reflective element assembly  16  about a second axis, and assembled within a housing  106 . With the dual motor tilt actuator assembly  100 , the clutch assembly  40  is eliminated. The first motor  102  will be operatively connected to a first actuator assembly comprising a jackscrew  46 , a worm gear  42 , and a drive gear  44  as is generally well-known in the art. The second motor  104  will be similarly operatively connected to a second actuator assembly comprising a jackscrew  46 , a worm gear  42 , and a drive gear  44 . 
   Regardless of the particular embodiment, the operation of the jackscrews  46 ,  112  is generally the same in that, during the normal mode of operation, the head  54 ,  116  on each embodiment of the jackscrew  46 ,  112  does not rotate within the corresponding socket  66  (because of the compression element thereon illustrated by example with reference numerals  84 ,  86 ,  88 , or because of the engagement of the blade  118  with a mating receptacle). However, when the mirror system is placed in an impeded mode of operation, such as when the actuator assembly encounters a mechanical stop with respect to the normal range of tilting travel about either the horizontal or vertical axes, or when the reflective element assembly  16  is prevented from movement, i.e., where the motor  38  continues to run when the reflective element assembly  16  encounters a mechanical stop preventing further movement in that direction, the head  54  will then turn within the socket  66  (i.e., the friction between the head  54  and the socket  66  caused by the compression elements  84 ,  86 ,  88  is overcome by the mechanical stop encountered by the mirror carrier), or the drive gear  122  will rotate relative to the clutch plate assembly  124 , 168  (i.e., the friction between the annular rim  136  and the clutch face  142  is overcome by the mechanical stop encountered by the mirror carrier), or the shaft  114  will move along the center shaft  154 . 
     FIG. 21  illustrates an alternate embodiment of the tilt actuator assembly of  FIGS. 2-14  in which the ball and socket are switched between the reflective element assembly and the actuator assembly. Thus, the glass case  26  of the reflective element assembly  16  comprises the spherical head  54  and the shaft  50  of the jack screw  46  terminates in the socket  66 . The coupling of the spherical head  54  with the socket  66  is identical to that described above for the jack screw  46  comprising the spherical head  54  and the glass case  26  of the reflective element assembly  16  comprising the socket  66 . 
   The novel jackscrew slip clutch illustrated and described herein moves the slip clutch mechanism from the drive gear/jackscrew interface to the jackscrew/glass case interface. Significantly, the “clicking” or “ratcheting” sound of the prior art mechanism that occurs when a jackscrew reaches its limit of travel is eliminated. The slip clutch mechanism described herein also simplifies the structure for transforming torque from the drive gear into linear movement of the jackscrew. This also enables the jackscrew to be readily slidably or threadably interconnected to the drive gear by inserting the jackscrew through the aperture in the actuator case cover so that the jackscrew can be added to the tilt actuator assembly after the tilt actuator assembly has been installed in the mirror system. The simplified jackscrew slip clutch results in easier assembly of the tilt actuator and mirror assemblies, and easier removal of the tilt actuator assembly for replacement and repair. Finally, the simplified slip clutch mechanism is less costly to produce and assemble, thereby reducing the cost of the mirror system. 
   While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing disclosure and drawings without departing from the spirit of the invention which is defined in the appended claims.