Abstract:
A rotary switch suitable for use as a transmission gear selection switch. The switch includes a housing and a rotor rotationally connected to the housing, the rotor being rotational about a first axis. A cam follower connected to the rotor has a cam surface substantially centered about a radial axis, the radial axis being normal to the first axis. An electrical contact carried by the rotor has a contact surface spaced from the cam surface along the radial axis.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/318,535, filed Sep. 10, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to an electrical switch, and, more particularly, to a cam follower mechanism for a rotary switch as found in a transmission selection rotary switch of a vehicle.  
         BACKGROUND OF THE INVENTION  
         [0003]    Electrical switches are well known. One common type of electrical switch is a rotary switch having a rotating shaft connected to a terminal capable of making or breaking an electrical connection with one or more other terminals. Rotary switches may convert positions into binary numbers; such switches are known as coded switches. For example, a three terminal coded switch can output a binary code equivalent to eight positions. The three terminals electrically reflecting the binary equivalent of the eight switch positions.  
           [0004]    Rotary switches contain contacts which may be non-shorting contacts, otherwise known as break-before-make contacts, which operate by breaking a preceding circuit before closing the next circuit. Converse to that, rotary switches may also have shorting contacts, which operate as make-before-break contacts. The make-before-break feature indicates that an electrical contact is made with the next position before breaking the electrical contact with the current position.  
           [0005]    Rotary switches are also known which have three ball bearings therein to provide a rotational and a detent feature within the rotary switch. Rotary switches are known to have moveable electrical contacts therein, which slide from one electrical contact on a printed circuit board or substrate to another electrical contact on the printed circuit board or substrate. The wiping action of a movable contact relative to a stationary contact within the rotary switch allows the rotary switch to connect electrical circuits subject to the rotational position of the shaft.  
           [0006]    A problem with rotary switches is that the wiping of the movable contact from one stationary contact to another stationary contact causes a migration of conductive material across a nonconductive separating material, thereby causing intermittent or shorted conditions among the stationary contacts.  
           [0007]    What is needed in the art is a break-before-make rotary switch, which doesn&#39;t short between contacts.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides an apparatus for breaking electrical contact on both a common and signal surface before making electrical contact with a second signal surface.  
           [0009]    The invention comprises, in one form thereof, a rotary switch including a housing and a rotor rotationally connected to the housing. The rotor is rotatable about a first axis. A cam follower is connected to the rotor, and has a cam surface substantially centered about a radial axis. The radial axis is normal to the first axis. An electrical contact has a contact surface spaced from the cam surface along the radial axis.  
           [0010]    The invention comprises, in another form thereof, a method of passing a signal to a common terminal. The method includes steps of providing a rotary switch having a plurality of conductors and an electrical contact connected to a cam follower, the cam follower being connected to a rotor rotatable about a first axis, and biased toward at least one of the conductors with a biasing device in a direction substantially parallel to the first axis, the electrical contact being electrically connectable with at least one of the plurality of conductors; placing an electrical signal on at least one of the plurality of conductors; and connecting the electrical signal through the electrical contact to the common terminal.  
           [0011]    The invention comprises, in yet another form thereof, a transmission gear selection switch including a housing and a rotor at least partially disposed in the housing. The rotor is rotatable about a first axis. A cam follower is connected to the rotor and is movable along a second axis, the second axis being parallel to the first axis. The cam follower is disposed to follow a path in the housing. At least one ridge is positioned along the path, oriented along a corresponding radial axis, the radial axis being normal to the first axis.  
           [0012]    An advantage of the present invention is that the rotary switch breaks both a common and a signal contact by movement of a single cam follower.  
           [0013]    Another advantage of the present invention is that a three contact conductor connects a common terminal to a signal terminal, the three contact connections providing mechanical stability to the conductor in the rotary switch.  
           [0014]    Yet another advantage is that the contact is held in electrical contact with contact sectors with a spring, thereby compensating for contact wear.  
           [0015]    Yet still another advantage is that the conductive material from one sector does not migrate to another sector since the contact is lifted from one sector and placed onto an adjacent sector.  
           [0016]    Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent, and the invention will be better understood by reference to the following description of an embodiment of the invention, taken in conjunction with the accompanying drawings, wherein:  
         [0018]    [0018]FIG. 1 is a partially sectioned top view of an embodiment of a rotary switch of the present invention;  
         [0019]    [0019]FIG. 2 is a partially sectioned side view along section line  2 - 2  of the rotary switch of FIG. 1; and  
         [0020]    [0020]FIG. 3 is an enlarged partially sectioned view along section line  3 - 3  illustrating a cam follower encountering a ridge of the rotary switch of FIGS. 1 and 2. 
     
    
       [0021]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    Referring now to the drawings, and more particularly to FIGS. 1 and 2, there is shown a rotary switch  10  in accordance with the present invention. The exemplary embodiment of switch  10  is a transmission gear selection switch  10  including a housing  12 , a cover  14 , a connector  16 , a rotor  18 , O-rings  20 , conductors  22 , cam interface ridges  24 , a biasing device such as coil spring  26 , a cam follower  28  and a contact  30 .  
         [0023]    Housing  12  includes separators  32  and O-ring retaining surface  34 . Housing  12  is integral with connector  16  both being formed from a non-conductive plastic by way of an injection molding process. Housing  12  interfaces with cover  14  to provide an environmental seal for the inner workings of rotary switch  10 . O-rings  20  provide a water and dust seal by way of the compression of cover  14  with rotor  18  and housing  12 . Conductors  22  are molded into the inner body of housing  12 , with one side of conductors  22  being exposed for electrical connection with contact  30 .  
         [0024]    Separators  32  are located between adjacent conductors  22 , and prevent electrical contact between adjacent conductors  22 . Separators  32  are also positioned along a radial axis such as radial axis R 1  or R 2 . Separators  32  are made of nonconductive material and are integral with housing  12 .  
         [0025]    O-ring retaining surface  34  is in contact with an O-ring  20  that is compressed by the presence of rotor  18  as it is positioned into housing  12  during assembly of switch  10 .  
         [0026]    Cover  14  includes O-ring retaining surface  36  and housing interface  38 . Cover  14  is made from a material that is compatible with housing  12  and is positioned to environmentally seal housing  12 . O-ring retaining surface  36  interfaces with an O-ring  20  that is compressed between O-ring retaining surface  36  and rotor  18 . Housing interface  38  interconnects with an edge of housing  12 . The contacting surfaces of housing  12  and cover  14  may be sealed using an adhesive or thermal bonding method. Cover  14  has a central opening  15  thereby allowing external access to rotor  18 .  
         [0027]    Connector  16  includes a retaining protrusion  40  and signal terminals  58 - 68  located therein. Connector  16  is formed in an integral manner with housing  12 . Connector  16  allows for a polarized connection with a corresponding plug (not shown). Retaining protrusion  40  is positioned to prevent the mating of connector  16  with an incorrectly shaped plug. Retaining protrusion  40  also serves to retain a plug (not shown) connected with connector  16 .  
         [0028]    Rotor  18  includes a D-shaped opening  42 , a shoulder  44 , a rotor arm  46 , a coil spring cavity  48  and cam retainer openings  50 . Rotor  18  is rotatable about an axis X within rotary switch  10 . A cylindrical portion of rotor  18  interfaces with O-rings  20  to seal contamination out of rotary switch  10 . D-shaped opening  42  extends through rotor  18  along axis X, and is shaped to accommodate a D-shaped shaft (not shown). The D-shaped shaft (not shown) is rotated to a desired angular position, thereby causing a rotation of rotor  18 . Shoulder  44  may be a series of fluted edges that wipe along the top of O-ring  20  to provide mechanical compression thereagainst, yet allow for tolerances in the manufacture of rotor  18  and assembly tolerances of housing  12  and cover  14 .  
         [0029]    Rotor arm  46  includes a coil spring cavity  48  and cam retainer openings  50 . Rotor arm  46  extends outward from the body of rotor  18  in a manner normal to axis X. On rotor arm  46  there are four cam retainer openings  50  to position and retain cam follower  28 . Coil spring cavity  48  is molded into a portion of rotor arm  46  to position and stabilize coil spring  26 . Coil spring cavity  48  is positioned to be in alignment with a spring recess  74  of cam follower  28 . Cam follower  28  is retained by rotor arm  46  and is moveable along axis Y, which is parallel to axis X. Cam follower  28  is positioned along a side of rotor arm  46  at a fixed radius from axis X. Cam follower  28  follows a path that is based on the location of cam follower  28  on rotor arm  46  and the rotation of rotor  18 . The path being normal to, and at a fixed radius from, axis X.  
         [0030]    Conductors  22  include contact sectors  52 , a common sector  53 , interconnection portions  54 , positioning holes  56 , signal terminals  58 ,  60 ,  64 ,  66  and  68 , and a common terminal  62 . Signal terminals  58 ,  60 ,  64 ,  66  and  68  include a high terminal  58 , a low terminal  60 , a neutral terminal  64 , a reverse terminal  66  and a park terminal  68 . Terminals  58 ,  60 ,  64 ,  66  and  68  are each electrically connected to a corresponding contact sector  52 . Contact sectors  52  lie in a plane normal to axis X at a radial distance from axis X. Contact sectors  52  are concentrically located about axis X with each contact sector  52  being a portion of an arc. The ends of adjacent contact sectors  52  are electrically isolated from each other by separators  32 . Terminal  62  is connected to common sector  53 , which is positioned close to rotor  18  in the same plane as contact sectors  52 . Terminals  58 ,  60 ,  64 ,  66  and  68  are electrically connected to corresponding contact sectors  52  by way of interconnection portions  54 . Positioning holes  56  are located to assist in the injection molding process for the positioning of conductors  22  in a mold prior to injection molding taking place.  
         [0031]    Each contact sector  52  is electrically connected to a corresponding terminal  58 ,  60 ,  64 ,  66  or  68 , and sectors  52  are separated, in a radial direction from axis X, by separators  32 . Contact sectors  52  are located a radial distance from axis X that is different than the radial distance of cam follower  28  from axis X, which are each different than the radial distance of common sector  53  from axis X. Separators  32  are part of housing  12  and are approximately level with or slightly below the surface of sectors  52 .  
         [0032]    Terminals  58 - 68  are used to transmit electrical signals that are representative of the angular position of a manually operated D-shaped shaft (not shown) inserted into rotor  18 . The position of rotor arm  46  variously electrically connects at least two of terminals  58 - 68  to each other. The signal that results from the positioning of rotor arm  46  may then be used to select the gear of an automatic transmission. The position of rotor arm  46 , is positioned by a vehicle operator, using a lever (not shown) connected to the D-shaped shaft (not shown), thereby selecting a transmission gear of high, low, neutral, reverse or park. The signal of the selected gear is electrically transmitted to common terminal  62 . High terminal  58 , low terminal  60 , neutral terminal  64 , reverse terminal  66  and park terminal  68  are so labeled and used relative to the terms for transmission gears in an automatic transmission of a vehicle. The selection of electrical signals and the passing of those signals to a common terminal by way of rotary switch  10  can encompass any electrical signal, not just those associated with an automatic transmission. Rotary switch  10  conveys a signal or conduction path from terminals  58 ,  60 ,  64 ,  66  or  68  to common terminal  62  based upon the position of contact  30 , which is determined by the rotational position of rotor  18 . The positioning of rotor  18  causes an electrical connection between a sector  52  and common terminal  62  by way of the positioning of contact  30 .  
         [0033]    Now, additionally referring to FIG. 3, there is shown cam follower  28  retained by rotor  18 . Cam follower  28  includes a cam surface  70 , contact retaining protrusions  72 , a spring recess  74 , arms  75  and retaining fingers  76 . Cam surface  70  is positioned in rotary switch  10  to encounter ridges  24  as rotor  18  is rotated. Ridges  24  extend in a radial direction from axis X along radial axis R 1  or R 2  as shown in FIG. 1 or along any other radial axis originating at axis X and normal thereto. Ridges  24  do not extend radially into the area where sectors  52  or common sector  53  are located, and thereby do not cause any interference with the movement of contact  30 . Ridges  24  have a ramped surface to co-act with cam surface  70  to lift cam follower  28  and thereby respectively break electrical connection of contacts  78  and  80  with sectors  52  and  53 . Cam surface  70  is centered about a radial axis R 3 , which is normal to axis X and axis Y.  
         [0034]    Contact  30  includes common sector contacts  78  and signal contact  80 . Common sector contacts  78  each have a contact surface  82  that is directed toward common sector  53 . Contact surfaces  82  come into sliding electrical contact with common sector  53  when cam surface  70  is not in contact with a ridge  24 . Signal contact  80  has a contact surface  84  that is directed to a contact sector  52 . Contact surface  84  comes into sliding electrical contact with a contact sector  52  when cam surface  70  is not in contact with a ridge  24 . Contact surface  84  is centered about contact plane P.  
         [0035]    Contact retaining protrusions  72  extend from the body of cam follower  28  to hold contact  30  such that contact  30  will move with cam follower  28 . Cam follower  28  is biased by spring  26  to hold contacts  78  and  80  in electrical connection with corresponding sectors  53 ,  52 , that is except for when cam surface  70  encounters ridge  24 . While coil spring  26  is shown as a biasing device, it should be understood that other structures including springs or other biasing devices can be used for biasing contacts  78  and  80  toward corresponding sectors  53 ,  52 .  
         [0036]    Arms  75  extend from the body of cam follower  28  through cam retainer openings  50  and are free to slide, thereby allowing cam follower  28  to move along the Y-axis. Retaining fingers  76  are located at an end of each respective arm  75 , thereby retaining cam follower  28  to rotor  18  and preventing spring  26  from fully extending. Spring recess  74  co-acts with coil spring cavity  48  to hold coil spring  26  in position to properly bias cam follower  28 .  
         [0037]    Signal contact  80  is centered around contact plane P as shown in FIG. 3. Axis X, axis Y, and radial axis R 3  are coplanar with contact plane P. Cam surface  70  is also centered along contact plane P such that as cam follower  28  transitions across ridge  24 , cam follower  28  is displaced along axis Y, causing contact  80  to lift from contact sector  52  proximate to the location of separator  32 , thereby breaking the electrical connection between signal contact  80  and contact sector  52 . Also as a result of cam follower  28  being displaced along axis Y, the electrical connection between common sector contacts  78  and common sector  53  is broken. The co-acting of two common sector contacts  78  along with signal contact  80  and coil spring  26  bring stability to contact  30  particularly as it slides along sectors  52  and  53 . The stability is the result of there being three physical points of contact with sectors  52  and  53 .  
         [0038]    Rotary switch  10  is mounted to an assembly and is electrically connected to a transmission control system. A D-shaped shaft (not shown) is placed into D-shaped opening  42  of rotor  18  and connected with a user operable lever. As the user operable lever is moved, rotor  18  correspondingly moves, to/from high, low, neutral, reverse and park designations. The positioning of the lever (not shown) corresponds with the electrical connections of contact sectors  52 , which establish an electrical connection to common terminal  62 , thereby providing a signal on common terminal  62  that corresponds to the physical positioning of the lever (not shown). The positioning of rotor  18  can correspond to other physical phenomenon associated with a rotational position. More or fewer contact sectors may be utilized to provide signals or grounding type control systems by way of terminals located in rotary switch  10 . In addition rotary switch  10  may be ganged in multiple layers to provide additional positional information to an automotive or other system.  
         [0039]    Variations and modifications of the foregoing are within the scope of the present invention. It is understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention. The claims are to be construed to include alternative embodiments to the extent permitted by the prior art.  
         [0040]    Various features of the invention are set forth in the following claims.