Abstract:
A wiper drive apparatus includes a drive gear rotated by a motor, a lead frame carried on a cover attachable to the motor or motor gear and including a circumferentially of discrete conductive traces, and a park switch bridge rotatably mounted on the cover and carrying a circumferentially of spaced contacts, each slidable over conductive traces to open and close a circuit to the drive motor as the park switch bridge is engaged by and rotated by the drive gear. Each contact is carried on a beam projecting from a circumferentially of radially extending arms forming the park switch bridge. A drive pin carried on the drive gear engages successive arms to rotate the park switch bridge 90° for each revolution of the drive gear to bring a different contact into electrical connection with the conductive traces without requiring additional tooling for the lead frame or the park switch bridge itself.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Present invention relates, in general, to vehicle windshield wipers, and, more particularly, to windshield wiper park switches. 
     2. Description of Related Art 
     In vehicle windshield wiper drive apparatus, the wipers are provided with an automatic home or park position stop device which enables a wiper blade to return to the home position regardless of when a user turns off a wiper switch during the wiping cycle. 
     In a typical wiper park switch, an electrically conductive plate is provided with electrically conductive and electrically non-conductive portions or traces. An electrical contact(s) fixed to or otherwise driven by a drive gear coupled to the wiper drive motor cooperates with the electrically conductive plate to form a switch when opens and closes an electric circuit of the wiper drive motor so that even when the user turns off the wiper switch of the vehicle during the wiper cycle, the electrically conductive plate and the contact(s) form an electric circuit which enables the wiper blade to return to the park position. The contacts are typically driven or moved by the gear between two positions, one forming a closed switch with the electrically conductive plate and the other forming an open circuit. When opening the electric circuit to the motor, the contact(s) shorts the circuit to form a dynamic brake which quickly stops the wiper arm at the park position. 
     However, prior vehicle windshield wiper drive mechanisms of this type experience several problems. First, the single park switch contact is moved into and out of contact with the conductive traces on the conductive plate many times during a wiping operation. This causes wear of the contact and requires a more robust wiper and contact design which adds to the cost of manufacturing the vehicle wiper. 
     Second, prior wiper driving apparatus with conventional park switches frequently experience chatter when snow or another obstruction is disposed over a lower portion of the vehicle windshield preventing the wiper blade from returning to the park position. In this situation, the drive gear of the wiper motor is subjected to a force which acts in a direction counter to the normal rotation direction of the drive gear. When the wiper arm contacts the snow or obstacles, forces build in the arm which reverse rotates the drive gear. Since the park switch is connected directly to the drive gear rotated by the drive motor, the park switch also reverses direction again completing a circuit to the motor. This results in so-called “chatter” wherein the wiper drive motor is sequentially energized and de-energized at a rapid rate leading to a quick rise in the motor operating temperature and/or rapid deterioration of the park switch contact. 
     Thus, it would be desirable to provide a park switch for a vehicle wiper apparatus which overcomes the above-mentioned problems encountered with previously devised wiper park switches. It would also be desirable to provide a park switch for a vehicle wiper drive apparatus which can be constructed with a minimal number of components. It would also be desirable to provide a park switch for a vehicle wiper drive apparatus which minimizes wear to the movable contacting portions of the park switch. It would also be desirable to provide a park switch for a vehicle wiper drive apparatus which prevents “chattering” even if the wiper arm strikes an accumulation of snow or other obstacles preventing the wiper arm from moving to the park position. 
     SUMMARY OF THE INVENTION 
     The present invention is a park switch bridge for use in a wiper driving system. 
     According to one aspect of the present invention, the wiper drive apparatus includes a drive motor and a drive gear disposed in a housing. A lead frame is fixed within the housing and includes a plurality of discrete, electrically conductive tracks. A park switch bridge is rotatably mounted in the housing and engagably coupled to the drive gear for rotation with rotation of the drive gear. The park switch bridge includes a plurality of spaced contacts, each contact slidable over the conductive tracks to open and close a circuit to the drive motor upon rotation of the park switch bridge. 
     A park switch bridge drive or engagement member is carried on the drive gear and engages the park switch bridge upon rotation of the drive gear. The engagement member and the park switch bridge are arranged in intersecting, rotatable paths of movement such that each revolution of the drive gear causes engagement of the drive member with the park switch bridge to rotate the park switch bridge through a predetermined arc. 
     In one aspect of the invention, the contacts extend radially from a center portion of the park switch bridge. 
     Preferably, four contacts are provided on the park switch bridge equidistantally spaced substantially 90° apart. 
     According to another aspect of the invention, each contact is resiliently carried on an arm having one end at the center portion of the park switch bridge and an opposed outer end. According to another aspect of the present invention, a beam is cantilevered from each arm and carries the contact. In one aspect, the contact is unitarily formed as an integral part of the beam from the beam material. In another aspect of the invention, the contact is in the form of a pad fixedly mounted on the beam. Each beam projects from the plane of each arm to resiliently bias the contacts into engagement with the conductive tracks on the lead frame. 
     Each arm has a planar portion extending from the center portion and a raised sidewall extending along at least a portion of the peripheral edge of the planar portion. The drive or engagement member carried on the drive gear rotatingly engages the raised sidewall on each arm to rotate the park switch bridge upon rotation of the drive gear. 
     The park switch bridge of the present invention provides several advantages over previously devised park switches used in wiper driving apparatus. The provision of a plurality of contacts, such as four circumferentially spaced contacts on the park switch bridge, reduces contact wear compared to the single contacts used in prior art park switches by distributing contact wear substantially evenly over four contacts. 
     Also, the park switch bridge of the present invention, is unidirectionally coupled to the drive pin on the drive gear for rotation in only one direction. Thus, back driving or reverse rotation of the drive gear as caused by the wiper arm contacting an accumulation of snow or other obstacles on the lower portion of the vehicle windshield preventing the wiper arm from fully reaching the park position, does not result in reverse rotation of the park switch bridge which has heretofore resulted in “chattering” or a rapid on and off application of electric power of the wiper motor leading to contact deterioration and/or motor overheating. This arrangement also prevents the park switch bridge from being stranded in an operation position due to reverse rotation. 
     The present park switch bridge, by distributing contact wear over a plurality of contacts, such as four contacts, enables the contacts to be inexpensively formed from the spring beam material itself without exceeding a beam thickness which would adversely affect the spring properties of the bridge, or risking contact wear that is greater than the base material thickness. 
     Finally, the park switch bridge of the present invention, the lead frame, the drive gear and the drive pin can be readily mirrored for opposite oriented motor designs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The various features, advantages and other uses of the present invention will become more apparent when referring to following detailed description and drawing in which: 
     FIG. 1 is an exploded, perspective view of a wiper drive apparatus having a park switch constructed in accordance of the teachings of the present invention; 
     FIG. 2 is a bottom elevational view of the drive motor gear box cover, shown in FIG.  1  and depicting the park switch bridge and lead frame according to the present invention mounted on the cover and shown in a closed circuit power position; 
     FIG. 3 is an enlarged, bottom elevational view of the park switch bridge shown in FIG. 2; 
     FIG. 4 is a cross-sectional view generally taken along line  4 — 4  in FIG. 3; 
     FIG. 5 is a bottom elevational view, similar to FIG. 2, but showing the park switch bridge in an open circuit position; and 
     FIG. 6 is a bottom elevational view showing a mirror image construction of the cover, lead frame and park switch bridge according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawing, and to FIGS. 1-5 in particular, there is depicted a wiper drive apparatus  10  for driving a vehicle windshield wiper in a conventional manner. As the wiper motor and gear box of the wiper drive apparatus  10  are conventional and do not form part of the present invention, only a brief description will be provided for the wiper motor  10  and the gear box. 
     As shown in FIG. 1, the motor  12  is mounted in a housing  14  and has a rotatable output shaft formed with or carrying a worm gear  16  at an outer end. The worm gear  16  extends through a bore in a mounting plate  18  which is secured in a receptacle  20  in a gear box housing  22 . 
     A drive gear  24  is coaxially mounted on one end of a rotatable drive shaft  26 . The drive shaft  26  is supported within the gear box housing  22  and has an opposite end fixed to a bracket  28  carrying a wiper arm pivot  30 . A wiper arm, not shown, is mounted on the pivot  30  in a conventional manner and driven in oscillation over a vehicle windshield in response to energization of the motor  12  and rotation of the drive gear  24  through meshing engagement of the drive gear  24  and the worm gear  16 . 
     A cover  32  is mounted on the gear box housing  22  to enclose the drive gear  24  within the gear box housing  22 . An output receptacle  34  is carried on or unitarily formed with the cover  32  for receiving an electrical conductor or cable and connector to transmit power and other signals through a conductive path formed or mounted within the gear box  22  and the mounting plate  18  to the motor  12 . 
     As shown in FIG. 1, a park switch bridge drive or engagement member, such as a gear drive pin  36 , for example, is fixedly mounted on the drive gear  24 , preferably by molding as part of the drive gear  24 . The gear drive pin  36  is spaced from a longitudinal axis extending through drive shaft  26  and is oriented generally parallel to the drive shaft  26  while extending toward the cover  32 . 
     In FIG. 2, the cover  32 , the drive gear  24  and the gear drive pin  36  are depicted in phantom as they overlay the bottom surface of the cover  32  in the bottom view orientation shown in FIG. 2. A lead frame  40  is fixedly mounted on the cover  32  by means of fasteners, heat staking, insert molding, etc. Preferably, the lead frame  40  is insert molded in the cover  32 . 
     As is conventional, the lead frame  40  is formed of a plurality of individual conductive traces or tracks, with five traces  42 ,  44 ,  46 ,  48  and  50  being depicted by example only. The conductive trace  42  labeled “B+” is connected to the vehicle battery. Conductive trace  44  is a park switch trace. Conductive trace  46  is connected to ground through a conductor or cable running through the receptacle  34  in the cover  32 . Conductive traces  48  and  50  carry signals for low or high speed motor operation and again are connected through a connector mounted in the receptacle  34  in the cover  32  to an external control which is responsive to the user manipulatable wiper lever or switch mounted within the interior of the vehicle. As noted above, the conductive traces  42 ,  44 ,  46 ,  48  and  50  are connected through similar conductive traces in the gear box housing  22  and the mounting plate  18  to corresponding terminals or connections on the motor  12 . 
     Generally, the conductor traces  42 ,  44 ,  46 ,  48  and  50  are over-molded with the cover  32  to allow smooth transition of the switch bridge contacts across the traces during rotation of the drive gear  24  as described hereafter. 
     A park switch bridge  54  is rotatably mounted on a hub  56  unitarily projecting from the bottom surface of the cover  32 . According to the present invention, the park switch conductive trace  44  is formed with a generally arcuate portion  43  having a circular shape which surrounds the hub  56 . The park switch conductive trace  44  also includes an elongated, strip portion  45  which extends from a notched edge of the arcuate portion  43  to an edge of the cover  32  as shown in FIGS. 2 and 5. The conductive trace  42  labeled B+also has a strip portion extending adjacent to the strip portion  45  of the park switch trace  44 . The conductor trace  42  terminates in an arcuate end portion  41  which is disposed within the notch formed in the peripheral edge of the arcuate portion  43  of the park switch conductive trace  44 . Thus, it can be seen in FIGS. 2 and 5 that the end portion  41  of the B+ conductive trace  42  which is connected to the battery power is circumferentially adjacent a portion of the park switch conductive trace  44  at the same radius from the hub  56 . 
     The conductive trace  46  which is adapted to be connected to ground in the present lead frame  40  has opposite end portions disposed adjacent to two edges of the cover  32  and a center arcuate portion which is concentric about a substantial portion of the diameter of the arcuate portion  43  of the conductive trace  44 . Similarly, the conductor traces  48  and  50  have opposite end portions and a center arcuate portion which is regularly spaced from an adjacent portion of the ground conductor trace  46 . 
     The park switch bridge  54  is, by example, formed as a one piece stamping of a suitable electrically conductive material, such as beryllium-copper alloy. The park switch bridge  54  has a starfish or cross configuration formed of a centrally located, frustoconical, hollow sleeve  58  which projects out of a solid central portion  62  of the park switch bridge  54 . 
     A plurality of arms  60 , co-planar with the solid central portion  62 , extend radially outward therefrom. Preferably, the park switch bridge  54  includes four arms  60 . The arms  40  are disposed at an angle to each other, with a 90° or perpendicular angle being illustrated by way of a preferred example. Each of the arms  60  extend from a common center portion  62  with the other arms, which center portion  62  surrounds a raised, annular lip  64  disposed concentrically above the sleeve  58 . 
     Each arm  60  may have any shape, such as a rectangular shape extending from the common center portion  62  to an outer end  66 . The side walls of each arm  60  are formed with a raised perimeter wall  68 . The perimeter wall  68  projects outwardly from a generally planar portion of each arm  60  to increase the rigidity of each arm  60  and to provide a large contact area for engagement with the gear drive pin  36  as described hereafter. By way of example only, the outer end portion of each arm  60  tapers to a generally pointed outer end  66 . 
     Each arm  60  carries an electrical contact  74  on a beam  70  extending angularly out of the plane of the arms  60 . Each beam  70 , as shown in FIG. 3, is located centrally within each arm  60  and extends from an interior end portion contiguous with the center portion  62  of the park switch bridge  54  in a cantilevered manner to the same side of the plane of the arm  60  as the sleeve  58 . 
     Generally, one beam  70  is initially integrally formed with one arm  60  and then punched, pierced, stamped or otherwise separated along three edges from the corresponding arm  60  and then bent angularly out of the plane of the arm  60  to a predetermined angle, as shown in FIG. 4, sufficient to engage the conductive traces on the cover  32 . Each beam  70  is flexible to allow for unrestricted movement of the beam  70  relative to the associated arm  60  during assembly and subsequent motor operation. 
     A contact  74  is carried on the free or outer end of each beam  70 . In one preferred aspect of the invention, each contact  74  is unitarily formed with each beam  70  and, preferably, is formed out of the beam material itself. Alternately, a separate contact pad is secured to the outer end of each beam  70  by means of a suitable fastener, such as a rivet. 
     Assembly of the park switch bridge  54  is as follows. The sleeve  58  of the park switch bridge  54  is slid over the hub  56  on the cover  32 . A self-locking retainer clip  76 , shown in FIG. 2, is then pushed over the sleeve  58  to a predetermined depth. This compresses the four beams  70  of the park switch bridge  54  and provides the necessary contact force to the beams  70  while allowing the beams  70  to have sufficient robustness to adapt to profile variations in the cover  32  and the surface of the lead frame  40  during assembly and wiper operation. 
     With the park switch bridge  54  rotatably mounted on the hub  56  of the cover  32  and the cover  32  fixably connected to the gear box housing  22 , the radially outer ends of each beam  70  will successively lie in an intersecting arcuate path with the gear drive pin  36  carried on the drive gear  24 . 
     During drive motor  12  operation, rotation of the drive gear  24  causes circumferential movement of the gear drive pin  36 . During each revolution of the drive gear  24 , the gear drive pin  36  will engage one of the arms  60  on the park switch bridge  54  as shown in FIG.  2 . Regardless of the initial position of the arms  60  on the park switch bridge  54 , at least one engagement of the gear drive pin  36  with one of the arms  60  will rotate the entire park switch bridge  54  sufficiently to bring the next circumferentially adjacent arm  60  to the position shown in FIG. 2 in which the contact  74  on the beam  70  of the arm  60  engages and forms an electrical closed circuit with the B+ conductive trace  42 . 
     As the drive gear  24  and the gear drive pin  36  rotate, the gear drive pin  36  will engage the raised perimeter wall  68  on one arm  60  of the park switch bridge  54  rotating the park switch bridge  54  90° according to the positional relationship of the park switch bridge  54  and the gear drive pin  36  shown in FIG.  2 . This brings the next arm  60  to the position shown in FIG. 2 wherein the contact  74  on the next arm  60  engages the first conductive trace  42 . 
     It will be understood that the above described rotation of the park switch bridge  54  through a 90° arc occurs during each rotation of the drive gear  24  during drive motor  12  operation. The drive gear  24  and the park switch bridge  54  form a Geneva-type arrangement wherein 360° rotation of the drive gear  24  and the drive pin  36  results in 90° rotation of the park switch bridge  54 . 
     During each 90° movement of the park switch bridge  54 , starting from the position shown in FIG. 2, the park switch bridge  54  rotates in a direction bringing the arm  60  whose contact  74  was initially engaged the first conductive trace  42  on the lead frame  40 , as shown in FIG. 2, across the park switch conductive trace  44  to the ground trace  46  as shown in FIG.  5 . Through external logic or a controller, as is conventional, the transition of the contact  74  which initially engages the first conductive B+ trace  42  across the park switch or second conductive trace  44  to the third, ground conductive trace  46  is detected in conjunction with user switching of the wiper control switch from the “on” to the “off” position. 
     In this manner, the user can turn the wiper control switch to the “off” position at any point in the wiper cycle. The park switch bridge  54  will provide power to the wiper drive motor  12  until the gear drive pin  36  is rotated into engagement with one arm  60  on the park switch bridge  54  and rotates the engaged arm  60  90° transitioning the contact  74  initially contacting the first conductive trace  42  across the second park switch conductive trace  44  to the third ground conductive trace  46 . 
     After contacting the third conductive or ground trace  46 , the vehicle controller short circuits the drive motor armature to dynamically break the drive motor  12  to an immediate stop. In the stop position, the next circumferentially spaced arm  60  on the park switch bridge  54  will have rotated partially through a 90° arc such that the next circumferentially adjacent arm  60  on the park switch bridge  54  will not have reached the position shown in FIG.  2  and its contact  74  will not be in contact with the first conductive B+ trace  42 . 
     After the next start of wiper operation, rotation of the drive gear  24  will cause the gear drive pin  36  to engage the arm  60  whose contact  74  is in engagement with the ground trace  46  and rotate the park switch bridge  54  until the next circumferentially lagging arm  60  on the park switch bridge  54  engages the first conductive trace  42  for a subsequent park switch operation. 
     It should be noted that since the gear drive pin  36  engages and rotates the park switch bridge  54  in only one direction of rotation of the drive gear  24  and the gear drive pin  36 , the drive gear  24  and gear drive pin  36  are free to rotate in an opposite direction by almost 360° as a result of external forces exerted on the drive shaft  26  and drive gear  24  as would occur when the wiper arm, when moving to the park position, strikes an accumulation of snow or an other obstacle on the lower portion of the vehicle windshield. This eliminates any “chattering” of the wiper drive motor  12  as in previously devised wiper drive apparatus. As such, the park switch bridge  54  is not damaged by any reverse rotation of the drive gear  24  or moved to a position where it remains “stranded”. 
     It should also be noted that the provision of multiple contacts  74  on the park switch bridge  54  distributes contact wear evenly over the circumferentially spaced contacts  74 . In the present example where four contacts  74  are provided on the park switch bridge  54 , wear on an individual contact  74  is reduced to ¼ of the wear that would be encountered with a conventional prior art park switch utilizing a single contact. This enables the park switch bridge  54  to be formed with an inexpensive contact  74  from the same material used to form the beam  70  without exceeding a critical beam thickness which would reduce the spring properties of the beam  70  or risking contact wear that is greater than the base material thickness of the beam  70 . 
     Another advantageous aspect of the present invention is shown in FIG.  6 . which depicts an opposite or left hand motor arrangement in which the cover  32 , although having the same shape as the cover  32  shown in the right hand motor design depicted in FIGS. 1,  2  and  5 , is nevertheless arranged for an opposite motor mounting position. However, the same park switch bridge  54  and the same lead frame  40  can be mounted on the cover  32  without requiring a second stamping tool for the lead frame  40  or a separate tool for a left hand park switch bridge  54 . This reduces component proliferation and, more significantly, reduces the cost of the wiper drive apparatus.