Abstract:
A power drive for a vehicle latch assembly includes a drive chassis and an electric motor. The electric motor has a drive shaft on which a gear is mounted. The electric motor further includes an engagement feature for locating the electric motor on the drive chassis. The drive chassis includes a mount plate having a slot for receiving the drive shaft during assembly of the power drive. The drive shaft is permitted to slide down a first portion of the slot, thereby allowing the engagement feature to be received by a second portion of the slots to radially locate the electric motor on the mount plate.

Description:
REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to United Kingdom Patent Application GB 0524856.2 filed on Dec. 6, 2005.  
       BACKGROUND OF INVENTION  
       [0002]     This invention relates generally to power drives, and in particular, but not exclusively, to power drives for vehicle door latches.  
         [0003]     It is common to provide vehicle door latches with power driven functions, such as power locking/unlocking, power closure, or power release. These power driven functions are of increasing importance given the reliance on electrical control in modern vehicles and the increase in door seal loads that is required to isolate a vehicle cabin from wind and tire noise.  
         [0004]     The power driven functions are typically powered by electric motors. It is common to provide the electric motor with a preinstalled pinion gear mounted on a drive shaft. This arrangement of the electric motor and the gear will often be provided as a subassembly which is subsequently assembled into a latch mechanism. However, the space envelope available to designers of the vehicle door latch is minimal. As a result, packaging of a latch assembly presents various engineering problems.  
         [0005]     This is particularly true in packaging of the electric motor, which tends to be one of the larger components which make up the latch assembly. Furthermore, the electric motor must be retained in position on a latch chassis to a relatively high degree of tolerance to ensure that the gears driven by the electric motor do not bind or become subject to excessive wear. A known method of mounting the electric motor is to provide a mount plate with a U-shaped channel that has the same width as a mount flange. In this method, any diameter pinion gear can be used. However, the U-shaped channel does not fully retain the mount flange in the radial direction.  
         [0006]     A known solution to this problem is to provide the latch chassis with a mount plate having an aperture of greater diameter than a diameter of the pinion gear. It is then possible to pass the pinion gear through the aperture to mount the electric motor to the mount plate. The aperture retains the electric motor in the radial plane and must therefore be dimensioned to accommodate a mount flange which is built into a casing of the electric motor. This particular method of mounting therefore limits the diameter of the pinion gear, which in turn limits the design of the latch mechanism.  
         [0007]     It is an object of a preferred embodiment of the present invention to overcome, or at least mitigate, some of the problems described above.  
       BRIEF SUMMARY OF INVENTION  
       [0008]     Accordingly, the present invention provides a power drive for a vehicle latch assembly including a drive chassis and an electric motor. The electric motor includes a drive shaft on which a gear is mounted. The electric motor further includes an engagement feature for locating the electric motor on the drive chassis. The drive chassis includes a mount plate having a slot for receiving the drive shaft during assembly of the power drive. The drive shaft is permitted to slide down a first portion of the slot, thereby allowing the engagement feature to be received by a second portion of the slot to radially locate the electric motor on the mount plate.  
         [0009]     A second aspect of the present invention provides a method of assembling a power drive for a vehicle latch assembly including the steps of providing a drive chassis and an electric motor. The electric motor includes a motor body, a drive shaft on which a gear is mounted, and an engagement feature for locating the electric motor on the drive chassis. The drive chassis includes a mount plate having a slot for receiving the drive shaft. The method further includes the step of sliding the motor shaft down a first portion of the slot with the gear and the motor body in opposite sides of the mount plate until the engagement feature is aligned with a second portion of the slot. The method further includes the step of moving the electric motor towards the mount plate so the engagement feature is received by the second portion of the slot to radially locate the electric motor on the mount plate. 
     
    
     DESCRIPTION OF DRAWINGS  
       [0010]     The invention will now be described by way of example only, and with reference to the following drawings, in which:  
         [0011]      FIG. 1  is a schematic plan view of a drive assembly of the current invention;  
         [0012]      FIG. 2  is a schematic end view of the drive assembly of  FIG. 1 ;  
         [0013]      FIG. 3  is an enlarged schematic plan view of a portion of the drive assembly of  FIG. 1  showing a pinion and a mount plate in further detail;  
         [0014]      FIG. 4  is an isometric representation of the drive assembly of the current invention; and  
         [0015]      FIG. 5  is a plan view of part of an alternative embodiment of the drive assembly according to the present invention. 
     
    
     DETAILED DESCRIPTION OF INVENTION  
       [0016]      FIG. 1  illustrates a power drive assembly  10  having a drive chassis  12 , an electric motor  14  and a retention arm  16 . The power drive assembly  10  forms part of a latch assembly (not shown for clarity) which is mounted in a vehicle door, as will be described in further detail shortly.  
         [0017]     The electric motor  14  includes a motor body  18  having a rear face  20 , a front face  22 , a bottom face  24 , a top face  26  and side faces  28 A and  28 B. The front face  22  defines a protruding boss in the form of a mount flange  30  (shown in dotted lines in  FIG. 1  and more clearly in  FIG. 3 ). The mount flange  30  surrounds a drive shaft  32  on which a pinion, or gear  34 , is mounted for driving a latch assembly mechanism (not shown). The mount flange  30  has a circular cross-section.  
         [0018]     The drive chassis  12  is defined by a mount plate  36 , a base plate  38  and a support plate  40 . In this particular embodiment, the mount plate  36 , the base plate  38  and the support plate  40  are defined by separate components joined by a known method, such as bolting, riveting, welding or bonding. However, it is conceivable within the scope of the invention that these features could be provided by a single component or that the drive chassis  12  could be provided without the support plate  40 .  
         [0019]     The mount plate  36  includes an upright portion  42  and a base portion  44 . The upright portion  42  defines a slot  46  which extends from a top edge  48  of the upright portion  42  to an aperture  50 . The aperture  50  is generally circular and is dimensioned to achieve a push fit with the circular mount flange  30  of the electric motor  14  to prevent the electric motor  14  from moving radially (i.e., in a direction parallel to the upright portion  42  of the mount plate  36 ) with respect to the mount plate  36 . The base portion  44  is attached to the base plate  38  by any known manner.  
         [0020]     The retention arm  16  includes a mount portion  52 , a first portion  54  and a second portion  56 , and is of a resilient nature. The mount portion  52  is mounted by rivets (or other known attachment features) to the support plate  40 . In other embodiments, it would be conceivable that the mount portion  52  would mount directly to the base portion  44  of the mount plate  36  or directly to the base plate  38 . The first portion  54  of the retention arm  16  extends at 90 degrees to the mount portion  52  and extends along the side face  28 B of the electric motor  14 . The second portion  56  is arranged at 90 degrees to the first portion  54  and is defined by a first resilient arm  58 A and a second resilient arm  58 B. The first resilient arm  58 A is arranged above the drive shaft  32  as shown in  FIG. 2 , and the second resilient arm  58 B shown is below the drive shaft  32 .  
         [0021]     An abutment  60  is mounted to the base plate  38  to retain the first portion  54  of the retention arm  16  in position. This prevents the retention arm  16  from moving away from the side face  28 B and allows the second portion  56  of the retention arm  16  to hold the electric motor  14  firmly in position.  
         [0022]     An electrical connector  62 , shown in dotted lines in  FIGS. 1 and 2 , is arranged between the electric motor  14  and the base plate  38 . This provides an interface between a central control unit (not shown for clarity) and the electric motor  14  to control drive of the gear  34 , as will be described in further detail shortly. The electric connector  62  includes a plug (not shown for clarity) arranged on the base plate  38  and a socket (not shown for clarity) arranged on the electric motor  14 . It will be appreciated that within the scope of the invention, the plug could be arranged on the electric motor  14  and the socket arranged on the base plate  38 . In this embodiment, the electric motor  14  is mounted onto the mount plate  36  before the base plate  38  (which carries the plug) is fixed in position.  
         [0023]     The subsequent fixing of the base plate  38  to the mount plate  36  inserts the plug into the socket to form the electrical connection. In an alternative embodiment (shown in  FIG. 5 ), a connector  70  is shown in which a pair of plugs  72  are provided on the front face  22  of the electric motor  14  for engagement with a pair of sockets  74 . In this embodiment, the plug  72  moves into the socket  74  in the same direction of movement as the electric motor  14  mounting onto the mount plate  36 . While the sockets  74  are provided on the mount plate  36 , and the plugs  72  engage the sockets as the electric motor  14  is being mounted on the mount plate  36 , it is conceivable that the electric motor  14  could carry the socket  74  and the mount plate could carry the plug  72 . This embodiment allows the base plate  38  to be fixed to the mount plate  36  before mounting the electric motor  14  into the mount plate  36 . In a yet further embodiment, the socket  74  (on the electric motor  14 ) is elongate to allow the plug  12  (on the base plate  38 ) to be inserted into the socket, and the socket  74  is then moved forward about the plug  72  to allow the electric motor  14  to be mounted onto the mount plate  36  after fitting the base plate  38  in position.  
         [0024]     The retention arm  16  additionally defines a projection  64  which prevents the electric motor  14  from rotating relative to the mount plate  36  when the gear  34  is driven by the electric motor  14 .  
         [0025]     In use, the power drive assembly  10  forms part of a vehicle latch assembly, with the gear  34  being arranged to drive one of a number of power mechanisms (for example, child safety on/off, lock/unlock of the latch, or power closure of the latch). The drive chassis  12  may therefore often form part of, or even be defined by, a vehicle latch assembly chassis.  
         [0026]     On receipt of a signal from the central control unit (not shown) via the electrical connector  62 , the electric motor  14  drives the gear  34 , which in turn acts on a latch assembly gear (not shown for clarity) to achieve a change in status in the latch. The power drive assembly  10  will frequently be located in a vehicle door or a boot lid. Alternatively, it may form part of the vehicle latch assembly mounted on the vehicle body.  
         [0027]     As mentioned above in this particular embodiment, the mount flange  30  and the corresponding aperture  50  are circular shaped. In alternative embodiments conceivable within the scope of the invention, the profile of the mount flange  30  and the aperture  50  could be other than circular, for example square, oblong or some other polygonal shape. Where this is the case, a projection  64  is not required because the engagement of, for example, a square aperture  50  by the similarly polygonal (square) motor flange  30 , would prevent rotation of the electric motor  14  relative to the mount plate  36 . Furthermore, it is conceivable that the aperture  50  and the mount flange  30  are of a different shape as long as there is sufficient contact between them to retain the electric motor  14  in position.  
         [0028]     The particular configuration of features described above provides a distinct advantage in terms of assembly of the power drive assembly  10  as follows.  
         [0029]     In conventional motor and mount plate arrangements, a mount plate does not define a slot which provides access to an aperture from a top surface of the mount plate and which radially retains the motor. As a result, the largest gear diameter which can be employed with the motor being fully radially retained by the mount plate is limited by a diameter of a motor flange. With the absence of a slot, assembly of the drive assembly is achieved by passing a gear through the aperture. Because the diameter of the aperture is dictated by the diameter of the motor flange, the construction of a power drive assembly with a gear diameter that is greater than a mount flange diameter presents additional complications.  
         [0030]     However, the present invention overcomes this problem by removing the necessity of passing the gear  34  through the aperture  50 . The slot  46  allows the exposed part of drive shaft  32 , i.e., the part between the motor body  18  and the gear  34 , to be passed down the slot  46  until the drive shaft  32  is arranged approximately at a center of the aperture  50 . At this point, the electric motor  14  may be moved towards the mount plate  36  (a direction G in  FIG. 1 ) to engage the mount flange  30  in the aperture  50 .  
         [0031]     Referring now to  FIG. 3 , a diameter of the gear  34  is shown at E, and a diameter of the aperture  50  is shown at F. It will be appreciated that the diameter E is greater than the diameter F. This is achievable in the present invention because the drive shaft  32  is able to pass down the slot  46  (a diameter D of the drive shaft  32  being less than a width C of the slot  46 ).  
         [0032]     The gear  34  passes down a first side of the mount plate  36 , and the mount flange  30  of the electric motor  14  passes down the other side of the mount plate  36  to allow the drive shaft  32  to pass down the slot  46 . In the present embodiment, a depth of the mount flange  30  is less than or equal to a width A of the mount plate  36 . It therefore follows that a distance B between the mount plate  36  and the gear  34  is greater than the width A of the mount plate  36 . In an alternative embodiment, where the depth of the mount flange  30  is greater than the width A, a new distance B′ between the mount plate  36  and the gear wheel is greater than the depth of the mount flange  30 .  
         [0033]     Referring again to  FIG. 1 , the second portion  56  of the retention arm  16  acts on the rear face  20  of the electric motor  14  to retain the mount flange  30  within the aperture  50 . As discussed above, to allow the drive shaft  32  to pass down the slot  46  during assembly of the power drive assembly  10 , the mount flange  30  passes down the side of the mount plate  36  facing the front face  22  of the electric motor  14 . For this to occur, the electric motor  14  must be displaced by at least the width of the mount plate  36  in the longitudinal direction H as shown in  FIG. 1  to allow mounting of the electric motor  14  onto the mount plate  36 .  
         [0034]     Firstly, with the abutment  60  in position, the second portion  56  deflects at a junction of the second portion  56  and the first portion  54 . Secondly, when the abutment  60  is not in position, the first portion  54  is able to deflect at the junction between the first portion  54  and the mount portion  52  in addition to the deflection of the second portion  56 . It is nonetheless possible to assemble the power drive assembly  10  with the abutment  60  in place, however additional advantage is obtained by attaching the abutment  60  to the face plate  38  following the insertion of the electric motor  14  into its mounted position on the mount plate  36 .  
         [0035]     Assembly of the drive assembly is therefore achieved as follows. In a first step, the mount plate  36  and the support plate  40  are assembled by bolts, rivets, bonding or other known methods of attachment. Next, the drive shaft  32  is slid down the slot  46  until the drive shaft  32  is located at approximately a center of the aperture  50 . The electric motor  14  is then moved forward in the longitudinal direction G ( FIG. 1 ) to engage the mount flange  30  in the aperture  50 . The base plate  38  is then fixed to the mount plate  36  by a known manner at the same time as engaging the electrical connector  62 . Next, the retention arm  16  is attached to the support plate  40  or other mounting portion on the drive chassis  12 . The abutment  60  is then attached to the base plate  38  to retain the first portion  54  of the retention arm  16  in position. Finally, the projection  64  is crimped or otherwise bent over to prevent rotation of the electric motor  14  with respect to the mount plate  36 .  
         [0036]     It will be appreciated that where the electrical connector of  FIG. 5  is used, the base plate  38  can be fixed to the mount plate  36  before the electric motor  14  is mounted onto the mount plate  36 .  
         [0037]     It will also be appreciated that certain features of the mount plate  36 , the base plate  38  and the support plate  40  may be changed within the scope of the invention.  
         [0038]     Similarly, the particular dimensions of the retention arm  16  may be changed within the scope of the invention.  
         [0039]     The foregoing description is only exemplary of the principles of the invention. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than using the example embodiments which have been specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.