Abstract:
A switch module for connection to an electrical circuit comprises a manually actuated ON/OFF switch mechanism mounted on a molded plastic case and two or more bus bars built integrally into the structure of the case, as by an insert molding process. The bus bars project out of the case at their ends, the exposed ends serving as terminals for electrical connection with the circuit and as spring contacts within the switch mechanism. The push button switch mechanism is an improvement over prior switches, having a single spring controlling both the push button and the shorting bar, and having positive alignment of the shorting bar and bus bar ends achieved by the pre-positioning of the bus bar ends in direct lateral sliding contact with the push button sidewall and sidewall-mounted shorting bar.

Description:
FIELD OF THE INVENTION 
     This invention relates to a push button switch module for an electrical circuit of the type used in small electrical fixtures, for example automobile dome lights. More particularly the invention relates to such a switch module having integrally molded bus bar conductors and an improved push button switch mechanism. 
     BACKGROUND OF THE INVENTION 
     The term &#34;push button switch&#34; as used herein refers to a two-position, ON/OFF switch mechanism where a first press of the push button actuates the switch from OFF to ON, and a second press of the push button turns the switch back OFF. Generally, such switch mechanisms include two springs: a stronger release spring which urges the push button to a raised position corresponding to OFF; and a weaker connect spring for holding a movable contact axially against a circuit contact in the ON condition. When the button is pressed down against the release spring force, the contact is moved to a closed position against the circuit contact to complete the circuit, and a latching mechanism engages the button to hold the push button down in the ON position when the button is released. A subsequent press of the push button disengages the latch so that the release spring can return the button to its raised OFF position. These switch mechanisms also use an umbrella-like rubber contact around the movable contact to isolate it from the fixed contact when the connect spring is released. Such switches are appropriate for use in many different electrical circuit applications, and are commonly used in automotive vehicles to control electrical devices such as dome lights in the passenger compartment or rear window defoggers. 
     U.S. Pat. No. 5,380,970 (co-owned with the present application by Yazaki Corporation) discloses both a prior art switch as described above, and an improved push button switch mechanism in which the push button is retained in a guide chamber formed on a housing, the housing containing a printed circuit board with a fixed electrical contact on its upper surface. The push button has a hollow lower end with an internal sliding sleeve, the sleeve carrying an electrical contact. When the push button is pressed down into the guide chamber, the sleeve is carried down until the sleeve-mounted contact meets with the fixed contact on the circuit board to close a circuit. Latching is accomplished with a heart-shaped cam groove formed in the push button and a pin engaging the cam groove to latch the push button in the switch-closed position until the button is pressed down a second time, whereupon the latching engagement between the cam groove and the pin is released. The &#39;970 switch mechanism also requires two springs, a stronger axial release spring and a weaker axial connect spring, one to bias the push button upwardly with respect to the guide chamber and the other to bias the sleeve downwardly with respect to the push button to hold the movable contact axially against the fixed contact. The relative spring rates of the two springs must be balanced for proper switch operation. The &#39;970 switch also requires a rubber contact to isolate the movable contact from the fixed contact. 
     The switch mechanism in the &#39;970 patent &#34;accommodates a circuit board 13 including a fixed contact 12&#34; (column 3, lines 38-41). The switch is a separate assembly which must be added to and aligned with the circuit board and its contact. The use of the printed circuit board as a support for the fixed contact also adds to the expense of the switch in the &#39;970 patent by virtue of both the cost of producing the circuit board and of the additional steps required to assemble the board to the switch. Additionally, the &#39;970 switch does not make any provision for the physical mounting or installation of the switch in an operative environment. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is directed toward providing a simplified switch module fabricated from a small number of simple, relatively inexpensive parts and which, after assembly, may be plugged as a pre-assembled unit into connection with an electrical power system to serve as fixture, circuit and ON/OFF circuit-controlling switch all in one. This is generally achieved with a molded housing having integrally-formed switch housing bus bars defining the circuit, the fixture and switch terminals; a push button with a shorting bar to selectively connect or &#34;short&#34; the bus bars, and a latch mechanism for the button. 
     The invention further comprises an improved push button switch mechanism with a single axial compression spring in the housing acting on the push button to force it away from the housing to an OFF position, and a latching mechanism in the housing to selectively latch the push button in the ON state when the button is pushed and released. The push button itself carries a contact or &#34;shorting bar&#34; for side-mounted sliding contact with the fixed switch terminal contacts connected to the circuit board bus bars. This mechanism reduces the number of push button springs from two to one, and further simplifies the moving contact or &#34;shorting bar&#34; by eliminating the need for a deformable rubber piece to isolate the moving contact from the fixed bus bar contact in the OFF position. Rather than having the shorting bar spring-loaded for contact force as is often the case, fixed spring contacts on the bus bars provide the contact force. This eliminates the need for separate springs within the push button assembly. 
     The molded housing is preferably formed with a plurality of electrically conductive bus bars insert-molded into the structure of the housing. The ends of the bus bars project from the molded main housing into the integrally-molded switch housing to provide fixed contacts which can be shorted by the moving contact on the push button to close the circuit and turn the powered accessory (e.g. a dome light bulb) ON. Molding the bus bars integrally with the housing results in a reduction in the number of parts that must be assembled to form the switch module, and the completed module constitutes a unitary component that is conveniently installed in its operative environment. The terminal ends of the bus bars plug into mating power terminals to connect the switch module with its power source. 
     Another feature of the invention is the integrally molded switch housing, which contains the push button switch mechanism and the fixed contact ends of the bus bars. Molding the switch housing integrally with the main housing provides cost advantages in manufacturing of the switch module, and further provides consistently accurate positioning of the bus bar fixed contact ends and the moving contact on the push button. 
     In a preferred embodiment of the inventive switch module described herein, the bus bars project out of their enclosed positions within the main housing at points intermediate the fixed switch contact ends and the power terminal ends to provide means for mounting a powered accessory such as a light bulb. In this way the module constitutes a unitary light fixture usable, for example, as a plug-in fixture in an automobile. When installed in the vehicle, the terminal ends of the bus bars plug into mating electrical terminals to supply current to the fixture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially exploded perspective view of a switch module according to the present invention for use as a dome light fixture; 
     FIG. 2 is a perspective view of the interior of an automobile with the switch module of FIG. 1 in an exploded view with respect to its installed position; 
     FIG. 3 is a cross-sectional view taken along line 3--3 in FIG. 1, with the switch in the OFF position; 
     FIG. 4 is an enlarged partial cross-sectional view taken along line 3--3 in FIG. 1, with the switch in the ON position; 
     FIG. 5 is a partial cross-sectional view taken along line 5--5 in FIG. 4, with the switch in the OFF position; and 
     FIG. 6 is a simplified perspective view of the switch module shown in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 depicts a switch module 10 according to the present invention comprising a molded plastic housing or case 12, a switch mechanism including a push button 16, and a powered fixture 18, for example a light bulb. The illustrative embodiment of the switch module shown in FIG. 1 is adapted to be mounted in an overhead receptacle 20 within the interior of an automobile or other vehicle, as shown in FIG. 2, and when connected to the vehicle electrical power system and fitted with a translucent cover (not shown) it serves as a dome light. 
     Case 12 is molded of a dielectric plastic material and is generally rectangular in shape, having a lower panel 12a, side panels 12b, 12c, end panels 12d, 12e, and an upper panel 12f. An interior wall 24 divides case 12 into a bulb well 25 and a switch well 26, and a mounting flange 28 projects outwardly from the upper edges of side panels 12b-c. Four mounting holes 30 in flange 28 permit the switch module to be secured in its operative position within the vehicle interior with screws or bolts. 
     A switch housing 32 is molded integrally with case 12 in switch well 26, extending upwardly from lower panel 12a. Switch housing 32 comprises a centrally located rectangular guide chamber 32a open at its upper end, a contact chamber 32b (FIGS. 3-4) which swells outwardly from the side of the guide chamber facing interior case wall 24, and an opposite latch chamber 32c located between the guide chamber and end panel 12e of case 12. Cut-outs 34 (FIG. 5) are formed in opposite sides of guide chamber 32a adjacent lower panel 12a, and a semi-circular spring notch 36 is formed in the sidewall of the guide chamber facing latch chamber 32c. 
     A rectangular inner push button guide 38 is located coaxially in guide chamber 32a. Inner push button guide 38 is largely hollow, except for a spring seat 40 across its upper half, the spring seat having a circular hole and bushing 42 formed through its center. 
     Three electrically conductive bus bars 44, 46, and 48 are molded into casing panels 12a, 12d and 12f, as by an insert molding process, and are exposed only at their ends and where they form an electrical bulb fixture. Bus bar 44 has a first end bent to form a fixed spring contact 44a projecting laterally into contact chamber 32b, and a second end on the opposite end of case 12 bent downwardly to form a blade terminal 44b. Bus bar 46 has a first end bent into a fixed spring contact 46a in contact chamber 32b, and a second end forming a flat bulb contact tab 46b in bulb well 25. Bus bar 48 has a first end forming a downward blade terminal 48b next to blade terminal 44b, and a second end forming a bulb contact hoop 48a in bulb well 25. It would be advantageous to have the three bus bars 44, 46 and 48 formed from single stock and insert molded as one piece into the panels. The bus bars would be separated after the molding process. 
     Light bulb 18 is a conventional automotive lamp and is placed in operative connection with the switch module by inserting the base of the bulb through bulb contact hoop 48a and against bulb contact tab 46b. Lock nubs 50 extend from opposite sides of the bulb base and engage notches 52 in bulb contact hoop 48a to retain the bulb in position. 
     Push button 16 in switch housing 32 has a flat top surface 16a and a hollow rectangular body formed by four side walls 16b-e. A guide post 16f extends downwardly from the underside of the top surface 16a into the hollow body of push button 16. Retention tabs 54 project outwardly from the lower ends of sidewalls 16c, 16e. A shorting bar 56 is mounted on sidewall 16b essentially flush with the sidewall surface, and is made of an electrically conductive material. A heart-shaped cam mechanism 58 is formed in opposite sidewall 16d. 
     A generally L-shaped latch spring insert 60 fits into latch chamber 32c and has a lateral spring post 60a on its upper end and a pinhole 60b penetrating its sidewall adjacent post 60a. Post 60a and pinhole 60b support a torsion latch spring 62. Opposite ends of latch spring 62 are bent at right angles to form a short retention pin 62a and a longer latch pin 62b. Retention pin 62a is held in pinhole 60b, and the coiled spring body is mounted on post 60a. 
     As best seen in FIGS. 4 and 6, latch insert 60, with latch spring 62 attached, fits into latch housing 32c so that latch pin 62b extends through the radius center of the semicircular upper end of spring notch 36 into guide chamber 32a . Latch insert 60 is inserted upwardly into the housing through an opening in lower panel 12a , and detent tabs 60c (see FIG. 1) extend outwardly from the latch insert and snap over cooperating surfaces to retain the latch insert in place. 
     Push button 16 is retained for sliding movement in switch housing 32, with push button side walls 16b-e sliding between the walls of guide chamber 32a and inner push button guide 38, while push button post 16f reciprocates through hole and bushing 42 in spring seat 40. Push button retention tabs 54 snap into engagement with cut-outs 34 in the lower side walls of guide chamber 32a so that they can slide up and down in the cutouts while retaining push button 16 in switch housing 32. Push button spring 64 is held in the guide chamber between the underside of push button top surface 16a and spring seat 40 to bias the push button upwardly. Latch pin 62b of torsion spring 62 engages cam mechanism 58 in sidewall 16d of the push button. 
     Switch module 10 is turned ON and OFF by successively pressing button 16. Spring 64 biases push button 16 toward the full up position corresponding to the OFF condition (FIG. 3) of switch mechanism 10. In the OFF condition the push button sidewall stays in contact with the bus bar contacts 44a and 46a, while shorting bar 56 is positioned above spring contacts 44a and 46a to open the circuit between bus bars 44 and 46 and turn light bulb 18 off. To switch the unit ON push button 16 is pressed against the force of spring 64 to bring shorting bar 56 into circuit-closing contact with bus bar contacts 44a and 46a. When switch mechanism 10 reaches the ON position (FIG. 4), pin 62b engages cam mechanism 58 to latch push button 16 in the ON position even after pressure on the button is released. The configuration of cam mechanism 58 and its interaction with latch pin 62b is described and depicted in detail in U.S. Pat. No. 5,380,970, the disclosure of which is incorporated herein by reference. 
     To return switch mechanism 10 to the OFF position, push button 16 is again pressed against spring 64. A small amount of downward travel releases the latching engagement between pin 62b and cam mechanism 58 so that when downward force on the push button 16 is terminated, spring 64 returns the push button to its fully extended position (FIGS. 3 and 5) corresponding to the OFF condition. 
     The improved switch module and switch mechanism of the present invention result in a simplified, reliable plug-in type electrical fixture with push button operation. The simplified unitary view of FIG. 6 best shows the simplified interrelationship of the modular bus bars, switch and switch housing. By placing the terminal shorting ends of the relevant bus bars in operative engagement with the push button sidewall in the switch housing (FIG. 3), and further by virtue of their being integrally molded into the switch module housing itself, the terminal ends are pre-positioned for sure contact with the shorting bar on the push button. The close-fitting guide chamber, push button switch sidewall and switch housing further ensure consistent, reliable contact between the button-mounted shorting bar and the bus bar ends in the contact chamber portion of the switch housing. The lateral spring-contact of the bus bar terminal ends with the sidewall-mounted shorting bar eliminates the need for a second connect spring to maintain the shorting bar in contact with the bus bar terminal ends and for the associated isolating structure such as the rubber contact of the prior art. Instead, the push button latch mechanism serves double duty in holding the push button ON and in maintaining the shorting bar against the bus bar terminal ends. 
     As indicated in FIG. 2, switch module 10 is operatively installed in overhead receptacle 20 in the head liner of an automobile by means of fasteners 66 which pass through mounting holes 30. When so installed, terminals 44b, 48b connect with electrical terminals 68 which are provided in the receptacle and are connected to the automobile&#39;s electrical system. Other interior trim panels (not shown) may be positioned around switch module 10 to partially cover the case to provide a desired aesthetic appearance. 
     It is apparent from the above description that the present invention provides a push button switch module that is inexpensively and easily assembled, and that the module is conveniently installed in an operating environment by virtue of its being a pre-assembled unitary component. 
     Whereas a preferred embodiment of the invention has been illustrated and described in detail, various changes can be made in the disclosed embodiment without departing from the scope or spirit of the invention as defined in the following claims.