Abstract:
A power actuator for automotive door latches. The actuator includes an electric motor mounted in a housing. A worm is operatively coupled to the motor for driving rotation of the worm about an axis. A worm gear, which meshes with the worm, is mounted to a tubular mount in the housing for rotation about an axis substantially orthogonal to the worm axis. A cam mounted to the worm gear engages the lever of a latch. An integral camshaft depends from the cam and extends into a central aperture on the worm gear, making the rotation axis of the two coincident. The distal end of the camshaft includes at least one resilient finger received through the aperture and in abutting contact with an opposing surface of the gear to preclude axial withdrawal of the camshaft from the wheel aperture. The power actuator uses a reduced number of components.

Description:
FIELD OF THE INVENTION 
   This invention generally relates to power actuators for vehicle latches, as for example to a power actuator for releasing a trunk latch or a power actuator for moving a lock lever between a locking and unlocking position. 
   BACKGROUND OF THE INVENTION 
   Cost is an important factor for manufacturing vehicle accessories such as motorized latch release devices. The number of parts which compose a power actuator has a bearing on the cost of the product. Heretofore, known power actuators for automotive closure latches have more parts, and thus likely higher cost, than the present invention. 
   SUMMARY OF THE INVENTION 
   A power actuator for automotive closure latches according to the preferred embodiment of the invention has a reduced number of components in comparison to comparable devices currently on the market. 
   According to one embodiment of the invention, a power actuator is provided which includes a housing having a recessed region and a tubular mount extending from the center of the recessed region. An electric motor is mounted in the housing with a worm operatively coupled to the motor for driving rotation of the worm about an axis in a first rotational direction. A worm gear, in meshing engagement with the worm, is rotatably mounted to the tubular mount for rotation about an axis substantially orthogonal to the worm axis, A camshaft is mounted on the worm gear and has a rotation axis coincident with the gear axis. The camshaft has a distal end; and an output arm affixed at the distal end of the camshaft. 
   The power actuator may be employed as a latch release device. According to this embodiment, the latch release device includes a housing having a recessed region and a tubular mount extending from the center of the recessed region. An electric motor is mounted in the housing with a worm operatively coupled to the motor for driving rotation of the worm about an axis in a first rotational direction. A worm gear, in meshing engagement with the worm, is rotatably mounted to the tubular mount for rotation about an axis substantially orthogonal to the worm axis. A cam is mounted to the worm gear by an integral depending camshaft so that the rotation axis of the camshaft is coincident with the gear axis. Preferably, at least one resilient finger is provided at the distal end of the camshaft in abutting contact with a surface of the gear facing away from the cam to preclude axial withdrawal of the camshaft from the gear aperture. The cam has a surface for engaging a latch to move the latch from a closed position to a release position as the gear rotates in a first direction from a first position to a second position when driven by the motor. 
   In a preferred embodiment of the latch release device, the worm has a small diameter worm, efficient for the overall size of the device. The combination of an output cam with a gear reduction stage results in high overall force output as well. 
   In the preferred embodiment of the latch release device, the worm gear is biased against the rotation from the first position to the second position. The ability to implement a biasing return spring provides repeatable uni-directional force output, and without such a spring, bi-directional torque/force output. 
   In a particular embodiment, the device includes electrically conductive contacts embedded into the housing as the housing is molded from plastic resin, to be in electrical contact with the motor and the same time extending to the exterior of the housing for connection to an electric power supply. The integration of an electrical connector is another example how further functionality without additional components or complexity can be obtained by means of the invention described herein. 
   The housing of the latch release device can include an injection-molded closure plate, wherein a hollow portion of the housing and the plate have opposing walls shaped to abut a housing of the motor when the hollow portion and the plate are secured together, and the plate further includes protrusions which extend into the housing interior to abut sides of the motor housing to preclude movement therepast. 
   In another preferred aspect, the closure plate and housing include a plurality of holes in communication with each other and located to permit simultaneous fastening of the housing and closure plate together and fastening of the device adjacent a latch with the cam in operable proximity thereto. This arrangement permits utilization of the same fasteners which mount the unit to a host latch or mechanism to also bind the housing components of the device together. The preferred embodiment thus provides a highly versatile, customizable, compact, low-cost mechanism for power release or locking. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Detailed embodiments of the invention are described below with reference to the accompanying drawings in which: 
       FIG. 1   a  is a perspective view of a motorized latch release device of the present invention installed on an automobile, in a closed position; 
       FIG. 1   b  is similar to  FIG. 1   a  in which the motorized latch release device is in an open position; 
       FIG. 2  is a partially exploded view taken from a vantage point similar to that of the previous figures, having the cover plate of the latch release device removed and partially exploded to reveal the electric motor and worm gear arrangement of the mechanism; 
       FIG. 3  is a more fully exploded view taken from a vantage point similar to that of the previous figures, to reveal the inner housing, worm wheel and spring for biasing the worm wheel towards the closed position, and the seating area for the motor; 
       FIG. 4  is a plan type of view of the housing, spring and worm wheel with the worm wheel in the closed position; 
       FIG. 5  is similar to  FIG. 4 , but with the worm wheel fully rotated into the open position shown in  FIG. 1 ; 
       FIG. 6  is a perspective view of the exterior of the housing opposite of that shown in  FIG. 1 ; 
       FIG. 7  is perspective view from a vantage point similar to that of  FIG. 6 , partially exploded to show the motor and cover plate; 
       FIG. 8  is a top plan view of the device, as oriented in  FIG. 1 ; 
       FIG. 9  is a bottom plan view of the device, as oriented in  FIG. 1 ; 
       FIG. 10  is a right end view elevation of the device, as oriented in  FIG. 1 ; 
       FIG. 11  is a left end view elevation of the device, as oriented in  FIG. 1 ; 
       FIG. 12  is a rear elevation of the device, as oriented in  FIG. 1 ; 
       FIG. 13  is a plan view of the worm wheel, as viewed from the left of  FIG. 7 ; and 
       FIG. 14  is a sectional elevation of the worm wheel showing the cam installed therewith. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Turning to the drawings, a motorized latch release device  20  of the present invention is shown generally in  FIGS. 1   a  and  1   b . In the figures, the device is shown installed on an automobile to permit remote-controlled trunk release by a driver. As illustrated in  FIG. 1   a , the trunk is in the closed and locked position. Latch  22 , part of a conventional trunk locking mechanism, is biased in the clockwise direction. Generally speaking, device  20  operates through rotation of an output cam  28  from a closed position shown in  FIG. 1   a  to an open position shown in  FIG. 1   b . This counterclockwise rotation (as viewed in  FIGS. 1   a  and  1   b ) forces latch  22  rightward from its closed position into a release position, as illustrated by the latch positioned in  FIG. 1   b . The output cam  28  automatically rotates back to the closed position of  FIG. 1   a  after reaching the fully open position. A detailed description of device  20  and its operation is given below. 
   As shown in  FIGS. 2 and 3 , the device includes a hollow housing  30  and a closure plate  32 . Each of these members is injection-molded as single piece of plastic in a one-step process. Integrally molded as part of the housing and affixed within the plastic are electrical connectors, described further below, for connecting an electrical motor  34  of the device to an external power supply. The housing and closure are composed of a suitable plastic, in this case a glass and mineral-reinforced nylon resin. The polymers are generally selected for high strength and stiffness, dimensional stability and resistance to temperature extremes. 
   As can be seen in  FIGS. 2 and 3 , the electric motor  34  includes an output shaft  36  which drives a worm  38  mounted to the external end of the shaft. The device includes a worm gear  40  in meshing engagement with the worm, a helical spring  42 , and a cam shaft  44  upon which the output cam  28  is mounted. As described in greater detail below, these components are arranged such that the spring biases the worm gear, and hence the output cam, in the counterclockwise direction (as viewed in  FIGS. 1   a  to  3 ), towards the closed position. The motor operates via the worm to drive the worm gear in the clockwise direction, i.e., towards the open position shown in  FIG. 1   b.    
   Electric motor  34  is a high-torque output, low cogging torque 200-series motor with integrated thermal protection, EMC protection and a knurled shaft. Such motors are available, for example, from Mabuchi Motor Co., Ltd. or Johnson Electric North American, Inc. The motor is mounted in a fixed position within the housing, being held in place by positive abutment with surfaces of the housing and closure plate. A cylindrical stub  48  (see  FIG. 7 ) of the motor is seated against a concave surface  46  of the housing. The motor housing abuts directly against first and second surfaces  50 ,  52 . On the inside of closure plate  32  are two rows of triangular protrusions  54  having facing surfaces  56  located and oriented so as to, with inner surface area  58  of the plate, abut against the motor housing. Cylindrical stub  60  is received between upstanding members  62 ,  64  of the inner housing of the device, the side surfaces of each member being in abutment to help hold the shaft end of the motor from moving to the right or left, as oriented in  FIG. 1 . The motor includes first and second openings  66 ,  68  having electrical terminals disposed therein. Contact posts  70 ,  72  are molded into the housing and received within the openings  66 ,  68  of the motor each in abutting electrical contact with a terminal of the motor. 
   The housing includes a socket  74  having first and second prongs  75   a ,  75   b  molded externally as part of the rear (as oriented in  FIG. 1 ) of the housing. Each of the prongs is electrically connected by an embedded conductor to posts  70 ,  72 . Preferably, the socket and prongs are designed to receive a standard plug for supplying electrical power to the motor of the latch release device. However, any suitable form of electrical connector will suffice. 
   Turning back to the drive mechanism for the device, the drive end of the shaft  36  extends about 1.5 cm beyond the end of cylinder  60  in which it is suitably journaled. The free end of the shaft has knurled ridges (not illustrated), parallel to the lengthwise axis of the shaft, pressed into it for a length of about 7 mm. The worm  38  is tubular, having an inner diameter slightly less than the outer diameter of shaft  36  so that receipt of the worm onto the shaft results in a snug fit sufficiently tight for the expected life of the device. The ridges on the shaft are deformed radially inward slightly during assembly of the worm onto the shaft and the ridges help to ensure that the worm is rigidly affixed to the shaft so as not to rotate with respect to the shaft during operation of the device. 
   Worm gear  40  is preferably injection molded in a single step of a homopolymer acetal selected for its low friction, high wear resistance and dimensional stability properties. Alternative materials are possible. The gear is molded to include a tubular mounting shaft  80  (see  FIG. 7 ). The shaft  80  is received into the open end of a cylindrical mount  82  that is integrally molded in the housing  30 . Shaft  80  has an external diameter of about 1 cm. The diameter of the shaft  80  and the internal diameter of the cylindrical mount  82  are closely dimensioned to each other so that there is very little play between the two pieces, but at the same time the worm gear is free to rotate with respect to the cylindrical mount  82 . The abutting surfaces are very smooth, of circular cross-section, and present minimal frictional resistance to rotational movement of the gear about the central axis of the shafts. 
   In the illustrated embodiment the outer diameter of worm gear  40  is about 2.7 cm, and the width of the wheel rim, i.e., the tooth bearing portion of the wheel, is about 1.1 cm, with the total height of wheel shaft  80  being about 1.6 cm. A stop  84  is molded as part of the worm gear. The stop  84  protrudes from the toothed rim a distance of about 4 mm and extends around the circumference of the rim a distance of about 45 degrees. This stop can be omitted in the case that full 360 degree output rotation is desired. A stop  86 , molded as part of the housing, is radially spaced from the center of mount  82  a slightly smaller distance than the radial distance between worm gear stop  84  and the center of shaft  80 . Housing stop  86  and wheel stop  84  together govern the rotational (angular) distance that the worm wheel is permitted to travel between the closed position ( FIG. 1   a ) and the open position ( FIG. 1   b ), the rotational distance being about 270°. The length of the arc on which housing stop  86  lies is about 45° and the length of the arc on which the worm wheel stop  84  lies is about 45° so that together the two stops together extend about 90° along the common circle on which they together lie. When worm gear  40  is properly mounted and occupying the closed position, abutment surface  90  of the gear stop and abutment surface  92  of the housing stop abut each other to preclude clockwise rotation of the gear. When the gear is rotated counterclockwise to the extreme open position (see  FIG. 1   b ) abutment surfaces  94  and  96  of the gear stop and housing stop, respectively, come into abutment with each other so as to preclude further counterclockwise movement of the gear. Because the combined distance of the two stops is 90° of the common circle on which the two stops lie, the rotation of the gear between the closed position and the open position totals 270°. As will be seen further below this is the rotational (angular) distance traveled by cam  28  in operation of the device in releasing the latch. 
   Worm gear  40  is biased towards the closed position by the helical spring  42 . Spring  42  is installed within the generally toroidal space located between inner surface  98  of wheel rim, the outer surface of gear shaft  80  and inner surface  100  of gear wall  102 . Located within the toroidal space is a protrusion  104  which stands out from the gear wall and serves as a catch for hooked end  106  of the spring. Protrusion  104  includes overhang  108 . By precluding axial movement of the hooked portion of the spring (as in the direction parallel to the central axis of the wheel and away from inner wall  102 ), overhang  108  aids in the installation of the spring during assembly of the device, and helps to ensure that hook  106  of the spring does not slip past the catch during operation of the device. Spring end  110  is in the shape of a hook to latch onto housing surface  96 . It is noted here that gear stop  84  is generally radially spaced outwardly of spring  42 , but that hook  110  protrudes radially outwardly from the remainder of the spring so as to latch onto surface  96 , which is itself radially located to abut surface  94  of the stop of the wheel. Clearance for travel of stop  84  past hook  110  as the wheel rotates into the closed position is provided by locating the hook in recess  112  which encircles cylindrical mount  82  and extends radially outwardly in the neighborhood of stop  86 , as illustrated in  FIG. 3 . Hook  110  is thus axially spaced from stop  84  (toward the floor of the housing) to provide for travel of stop  84  past hook  110 . 
   The spring  42  is installed so as to be under constant tension and is preferably made of spring steel or stainless steel. This results in the worm gear being constantly biased towards the closed position, i.e., in the clockwise direction as viewed in either of  FIG. 1   a  or  1   b , for example. As the gear is rotated under force provided by the motor through the worm (described in greater detail below), the tension on the spring increases. 
   The motive force of motor  34  is transferred to worm gear  40  by worm  38 . Thread  76  of the worm engages teeth  114 , which have an axial pitch and lead designed to mesh with the axial pitch and lead of the worm thread. Thus activation of motor  34  results in clockwise rotation of worm  38  (as viewed from the left in  FIG. 1   a ), which in turn causes rotation of worm gear  40  in the counterclockwise direction, as viewed in  FIG. 1   a . Activation of motor  34  by application of appropriate electrical current can be instituted as by an appropriately wired button located for access by the driver, or by an activation circuit under remote control, etc. In the position of  FIG. 4 , the torque on the worm wheel from the spring is about 330 Nmm, and the torque from the spring is about 380 Nmm when the worm wheel is in the position shown in  FIG. 5 . 
   Rotation of worm gear  40  will eventually be halted by abutment of stop surfaces  94 ,  96  when the gear has rotated through an angle of about 270° to the fully open position, as previously described. Halting the gear rotation prevents the worm from turning, and hence causes motor  34  to stall. The power supplied to the motor is cut off and the stored energy in the coiled spring causes the worm gear to rotate back to the closed position. 
   The worm gear  40  has a central aperture  116  which receives a shaft  44  attached to cam  28 . The cam and shaft are injected molded as a single piece of the same type of plastic as the worm gear. The exterior profile of the cross-section of shaft  44  matches the cross-section of central aperture  116  of the gear and the cross-sections are non-circular. Shaft  44  received into the aperture is thus fixed against rotation with respect to the axis of the worm gear. Installed shaft  44  is also centered on the central axis of the worm gear so that when the gear rotates about the axis so too does the cam shaft. It will further be noted that the engagement of surfaces of the shaft  44  and aperture serve to orient the cam for operation between the closed and open positions. 
   Cam  28  is installed as part of the device after assembly of the closure and housing, described further below. This is accomplished through tabs  150  at the free end of shaft  44 . Each tab is located at the end of finger  152 , the fingers being radially spaced apart from each other on opposite sides of the central axis of shaft  44 . Each tab includes abutment surface  154  which opposes and abuts surface  156  surrounding the central aperture of worm wheel  40 . Opposing tab surfaces  154  is surface  158  of shaft  44 , surface  158  being in abutment with surface  160  of the worm gear. Thus, for installation, cam shaft  44  is inserted through aperture  162  and into worm wheel aperture  116 . Chamfered lead surfaces  164  of the tabs abut against inner surfaces of narrowed portion  117  of aperture  116  squeezing the resilient fingers together as they pass through the narrowed passage, eventually springing apart into the installed position shown in  FIG. 14  in which surfaces  154 ,  156  abut each other, and surfaces  158 ,  160  abut each other, to affix the cam against axial movement with respect to the worm wheel. 
   The cross-sectional profile of the cam surface is wing-shaped. Translation of the rotational motion of the cam shaft  44  through the cam surface to move latch  22  from the closed position to the release position is illustrated in  FIGS. 1   a  and  1   b . As shaft  44  rotates, the cam surface area generally designated as  118  contacts latch  22 . As this rotation occurs, the radial distance (from the center of shaft  44 ) of the contact portion of the cam surface with the latch is in contact increases resulting in forced movement of the latch from the closed position towards the release position. As described above, the worm gear and affixed cam rotate until the fully open position  28   a  ( FIG. 1   b ) is reached and motor  34  stalls, which stall leads to the eventual return of the cam to the closed position. 
   The cam profile converts the output torque to a linear force pushing against a movable lever, plate or other feature to which one desires a force to be applied. This cam functions as a further gear ratio for the system, where smaller distances pushed by the full rotation of the cam are seen to result in higher applied forces by the cam. 
   It is possible that the installed device could be exposed to minor amounts of water from time to time, as when a trunk was opened during a rainstorm, etc. To lessen the possibility of damage from such exposure, a liquid flow path for such liquids is provided around the periphery of the plate closure edge. Ridge  120 , molded as part of housing  30 , and ridge  122 , molded as part of the closure plate  32  are thus shaped to abut against opposing surfaces (of the closure plate and housing, respectively) to provide a limited seal against ingress of water. Further, the ridges are spaced slightly inwardly from the extreme periphery so that a liquid flow passage  124  is defined around the periphery of the ridges. 
   Housing  30  and closure plate  32  are conveniently assembled together during manufacture of device  20  through a single assembly screw  126  received through plate aperture  128 , the screw shaft being received into housing aperture  130 . Aperture  130  is of smaller cross-section than the shaft of the screw so that the threads of the screw become embedded in the plastic wall of the housing during assembly. 
   The housing and plate have a further three pairs of communicating apertures  132 ,  134 ,  136 . These apertures are used during installation of the device onto the automobile latch by fasteners  138 ,  140 ,  142 . Areas  144 ,  146 ,  148  of the external plate surface surrounding the apertures are in positive abutting contact with surfaces of the automobile when installed. (This could equally apply to external areas of the housing surround the apertures.) In this way, when the device is installed with the remainder of the latch, compressive forces are further applied to the housing and closure by their being sandwiched between the heads of fasteners  138 ,  140 ,  142  and auto surfaces with which plate areas  144 ,  146 ,  148  are in positive abutting contact. 
   Spring  42  of the illustrated device can be omitted, which of course would free the worm wheel from biasing. In such situation, the control circuitry for the device may be modified to drive the motor in first and second directions so as to move the cam from the first to the second (nominally open to the closed) positions illustrated in  FIGS. 1   a  and  1   b , respectively, and to move the cam from the second to the first positions. The device could thus alternatively be used, for example, to positively move a latch between first and second positions, e.g., a lock lever may be moved between locked and unlocked positions. It will be appreciated that the cam or other output arm may have a different profile for different applications. 
   The illustrated embodiment has been described with particularity for the purposes of description. Those skilled in the art will appreciate that a variety of modifications may be made to the embodiment described herein without departing from the spirit of the invention.