Pressure switch

Abstract: A pressure responsive switch having upper and lower contact assemblies with a snap acting member and an electrically conductive member sandwiched therebetween. The assemblies each includes an insulating body with a hollow center and an electrically conductive member having a contact in the center portion and extending externally of the body. The snap acting member is in constant engagement with the sandwiched conductive member and normally in engagement with the electrically conductive member of the upper assembly. When a pressure is applied which is sufficient to cause the snap acting member to snap into its second stable state, the connection thereof with the electrically conductive member in the upper contact assembly is broken and connection is made with the electrically conductive member in the lower assembly. The switch is normally closed by removing the portion of the electrically conductive member in the lower assembly which extends external.ly thereof. The switch can be provided as normally open by removing the portion of the electrically conductive member in the upper assembly which extends externally thereof. In accordance with another embodiment, the switch is provided for operation in conjunction with a printed circuit board. The switch comprises an electrically conductive contact member fixed to the board and having a contact bump and an air conducting passageway. An electrically conductive support for a flexible conductive member is secured to the board within the fixed conductive contact member, the flexible member moving into and out of engagement with the bump in response to pressure changes.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION This invention relates to a pressure switch and, more specifically, to a pressure responsive switch for mounting on a printed wiring board which is capable of operating in either the normally open or normally closed condition. BRIEF DESCRIPTION OF THE PRIOR ART It is relatively standard in the automotive art to control various functions by means of microprocessor based control units to obtain performance improvements. One such application has included the operation of the transmission system by integrating engine and transmission control. Such operation requires that the transmission control be compatible with the engine control module (ECM) and be electronically accessible with inputs and outputs. One such prior art approach has utilized solenoid valves to effect gear shifting using pressure switches in the solenoid valve assembly as a way to confirm that solenoid valve actuation and deactuation has occurred responsive to pressure change in the hydraulic fluid. This pressure change is sensed using conventional snap acting pressure responsive switches which close or open electrical circuits on the occurrence of selected pressure levels. A problem with switches of this type is that snap acting switches have a lower life expectancy than is desired. In US - A - 4,758,695, there is disclosed an attempt to minimize this problem wherein a control system is provided where a metallic diaphragm is used having significantly improved longevity. Such diaphragms are formed with a central dished portion having a pressure deflection relationship such that the diaphragm is relatively stiff, having a positive coefficient of pressure with increasing deflection up to and above a relatively narrow range of set points or calibrated pressures. Within the range of set points the effective spring rate of the diaphragm is relatively supple with only a small increase in pressure resulting in relatively larger travel of the center of the diaphragm. The diaphragms are also characterized in having significantly less hysteresis than conventional snap acting discs to minimize the build up of stresses in the diaphragm since these stresses serve to limit the longevity of the diaphragm. Among the embodiments disclosed are switches in which the diaphragms are formed with an annular flat berm portion which is received on an electrical contact member with an "O"-ring disposed on top of the berm and biased thereagainst to form a fluid pressure seal by a tubular sleeve which communicates with an hydraulic fluid pressure source. Another embodiment provides a sleeve formed in two segments with the "O"-ring sandwiched therebetween so that the sleeve itself engages the berm portion. An electrical contact rivet is placed beneath the central dished portion and connected to a suitable electrical connector. While the berm provides a convenient way to mount and seal the diaphragm, the integral interconnection between the flat berm portion and the central dished portion results in limiting the life of the diaphragm. In other embodiments, the entire diaphragm is dished and maintained on the electrical contact member by means of a thin flexible membrane which also provides a seal for the switch. However, the use of a membrane to retain the diaphragms in their respective seats limits the positioning of the stationary center contact to the low pressure side of the diaphragm (to close a circuit upon pressure increase). That is, the membrane would preclude the use of a fixed contact on the high pressure side of this diaphragm (to open a circuit upon selected pressure increase). The essential difference in relation to the claimed switch consists in that the rivet closes it's bore. The provision of a contact in an open central aperture leads to the possibility of three types of switches. A further improvement in the prior art is set forth in US-A-169,799, filed March 18, 1988, by forming the entire surface of the diaphragm into a dished configuration with the center of the diaphragm having a pressure versus deflection relationship such that for increasing pressure from 0 psig up to and beyond a plateau having a range of deflections between d1 and d2, the diaphragm has a relatively stiff effective spring rate with the center deflecting between d1 and d2 at essentially the same pressure level, the diaphragm also having a relatively narrow differential between the pressure at which the center of the diaphragm deflects between d1 and d2 on increasing pressure and the pressure at which it deflects between d2 and d1 on decreasing pressure. A contact disclosed by FR-A-1 344 563 comprises channels for fluid passage. That embodiment does not provide the advantages of a contact being disposed in only a part of an opening. In US-A-3,689,719 there is described a pressure responsive switch having a diaphragm that extends across a volume in a housing. A snap-spring backing plate is provided for the diaphragm and is clamped to the housing so as to be cantilevered from it. At a certain pressure on the diaphragm the snap-spring late changes shape suddenly and causes a contact stud on the plate to jump from connection to a first fixed contact on one side of the plate to connection to a second screw-adjustable contact on the other side of the plate. FR-A-2,492,741 shows a pressure responsive switch having a domed metal diaphragm that is pressed down to meet a central contact either directly or through a membrane by the pressure medium. The diaphragm is arranged in a cup-shaped member either on an insulating plate with the contacts on it or on an electrically conducting annular seating screwed into the cup-shaped member with the central contact set in an insulating plug in the seating. While the above noted prior art has demonstrated continual improvement in the required properties, it is the continual intent of the industry to further improve such switches. In addition, it has been found that in certain applications, such as in engine control modules (ECMs), certain ones of the switches must be normally open whereas others must be normally closed. This requirement has caused the need of an inventory of at least two different switches. It is therefore apparent that a single switch which can perform either directly or with minimum alteration as both a normally open and a normally closed switch would greatly reduce the inventory requirement. This problem is solved in accordance with the present invention. SUMMARY OF THE INVENTION According to the present invention there is provided a pressure responsive switch having an upper housing part and a lower housing part of electrically insulating material held together, with a pressure responsive snap-action disc fitted over a circular aperture on a disc seat within an outer rim wall on an electrically conducting member sandwiched between the housing parts, the upper housing part having an open central aperture therethrough aligned with the snap-action disc and the circular aperture through the electrically conducting member, the disc having a normally upwardly convex configuration that can be switched to a downwardly convex configuration by pressure applied through the aperture through the upper housing part, and electrical contact so disposed that the disc engages it in one configuration and not in the other configuration, whereby the lower housing part has an open central aperture therethrough aligned with the apertures through the upper housing part and the electrically conducting member, the upper housing part has an upper substantially plane surface with an annular groove for a sealing ring surrounding its central aperture in that upper surface, the electrically conducting member is a plate having a terminal portion projecting at the side from between the housing parts, the contact is part of an electrically conducting member having a terminal wing, the member being included at least in either the upper housing part or the lower housing part so that the contact is supported and located in a part of the open central aperture of the particular housing part and the terminal wing accessible outside that housing part, the contact being aligned to be received in the open circular aperture through the electrically conducting member. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a top view of a printed wiring board containing five pressure responsive electrical switches mounted thereon in accordance with the present invention; FIGURE 1a is a front view of the FIGURE 1 board; FIGURE 2 is a circuit diagram showing the arrangement of the switches of FIGURE 1; FIGURE 3 is an exploded cross sectional view of a pressure responsive electrical switch in accordance with the second embodiment of the present invention; FIGURE 4 is an assembled view of the embodiment of FIGURE 3; FIGURE 5 is an exploded view of a pressure responsive switch in accordance with a third embodiment of the invention in the normally closed state; FIGURE 6 is an exploded view of a pressure responsive switch as in FIGURE 5 in the normally open state; FIGURE 7 is a perspective of a lead frame insulator assembly made in accordance with the invention; FIGURE 7a is a cross-sectional view of a portion of the Figure 7 assembly showing a switch mounted thereon; and FIGURE 7b is a perspective view of a terminal pin formed integrally with the lead frame. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGURE 1, there is shown a top view of a printed wiring board 1 which is formed of electrically insulating material in a well known manner and has pressure responsive electrical switches mounted thereon. Five such electrical switches 3, 5, 7, 9 and 11 are shown. The switches are each connected to electrical conductors 13 on the board 1 via pads on the board (not shown) for contacting terminals of the switches (to be discussed hereinbelow), these conductors interconnecting with plural ones of the switches and/or with terminals 15, 17 and 19 denoted as X, Y and Z, respectively (corresponding to the X, Y and Z terminals in FIGURE 2), at the edge of the board for interface with external devices. The board 1 is secured to a hydraulic manifold, for example, a valve body or other appropriate support (not shown), whereby the upper surface of each of the pressure responsive switches 3 through 11 abuts and is in hermetic sealing relationship with a variable pressure source in the valve body whereby such pressure causes each switch to operate in accordance with the degree of pressure then present at each switch as will be explained in greater detail hereinbelow. Referring now to FIGURE 2, there is shown the electrical arrangement of the switches 3 through 11. As can be seen, the switches 3 and 9 are normally open and the switches 5, 7 and 11 are normally closed. The switches are arranged whereby circuit paths on the board 1 connect both switches 7 and 9 to switch 3 and switch 11 is connected to switch 5. A reference voltage output is provided on terminal 15 when switches 3 and 9 are closed, a reference voltage output is provided on terminal 17 when switches 3 and 7 are closed and a reference voltage output is provided on terminal 19 when switches 5 and 11 are closed. A computer or the like which is coupled to the terminals 15, 17 and 19 can provided predetermined information from the sensed signals on these terminals. For example, if the arrangement as shown in FIGURE 1 is utilized to sense pressures at five locations in an automobile transmission, this being standard in the art, the particular gear in which the transmission is operating (i.e. drive, second, third, fourth, reverse) can immediately be determined and appropriate action, if required, can be instituted therefrom. Referring now to FIGURES 3 and 4, there is shown a second embodiment of a pressure responsive switch in accordance with the invention. The switch includes an upper housing 61 having an annular groove 63 for receiving an "O"-ring or gasket of other geometrical shape 65 therein and a hollow center region 67. The groove 63 preferably has the same cross sectional shape as the gasket 65. The housing 61 is formed of electrically non-conductive plastic and includes a brass conductor 69 molded therein, the conductor having a depressed region disposed in the center region 67 to form a contact 71 and a terminal wing portion 73 extending from the contact for connection to a circuit board 1. The upper housing also includes depending legs 75 for mating with a lower housing 77. An electrically conductive stainless steel snap action disc 79 is disposed beneath the contact 71 and in contact therewith. Disposed below the disc is a disc seat 81 in the form of an electrically conductive brass member having a terminal wing portion 83 for connection to the board 1, the disc seat also having an apertured center portion 85 for allowing the disc 79 to travel therethrough to contact the contact member 87 when in the snapped position. The lower housing 77 has a hollow center region 89 for receiving the contact 87. The lower housing 77 is formed of electrically non-conductive plastic and includes a brass conductor 91 molded therein, the conductor having the contact 87 as a portion thereof and a terminal wing portion 93 extending from the contact for connection to the circuit board 1. The lower housing also includes grooves 95 for receiving the legs 75 therein whereby the disc 79 and the disc seat 81 can be secured between the upper and lower housings. The elements of the switch of FIGURES 3 and 4 are designed for automatic assembly as a normally open or a normally closed switch as will be explained hereinbelow. For a normally open pressure responsive switch, the wing 73 is not connected and the switch member stacked and secured by placing the members in the arrangement shown in FIGURES 3 and 4 and forcing the legs 75 of the upper housing into the grooves 95 of the lower housing. The circuit path is then from the circuit board to the disc seat 81 and then to the disc 79. Upon increase in pressure on the disc 79, the disc will snap to the lower position and contact the contact member 87, thereby completing the circuit to the wing 93 and then to the lead frame to complete the circuit. For a normally closed pressure responsive switch, the wing 93 from the brass conductor 91 is not connected and the switch elements are assembled in the same manner as for the normally open arrangement. The circuit path is then from the circuit board to the disc seat 81 via wing 83 and then through the disc 79 to the brass insert 69 and then via wing 73 to the circuit board. Upon increasing pressure the disc 79 will snap to the lower position and travel out of contact with the contact 71 of the conductor 69 to open the circuit. The switch components are held together by three plastic pins or legs 75 which extend from the bottom side of the upper housing 61 into the grooves 95 in the lower housing 77. The disc and disc seat are "sandwiched" between the upper and lower housings 61 and 77. The legs 75 are secured in the grooves 95 by conventional means, such as by heat staking. During the assembly of the switch, the upper contact 71 or lower contact 87 are adjusted relative to the location of the disc 79 to assure that the electrical contacts are in the proper position relative to the characteristic disc curve. The calibration of each switch assures a change in electrical continuity at a given operating pressure. Once the switches are calibrated and assembly completed, the modular switch is function tested as a complete switch assembly. This design approach is unique since the pressure switches are independent of the method used to connect groups of switches in series/parallel combinations. The modular, discrete switch can then be used in various low profile pressure switch (LPPS) application, but not be an integral component of any one particular LPPS design. As a further embodiment, as shown in FIGURE 5 for a normally closed switch, wherein all like reference numbers refer to the same or similar parts as in the switch of FIGURES 3 and 4, the switch is modified to replace the O-ring 65 with an elastomer gasket 65A of rectangular cross section seated in the groove 63A. In addition, an annular internal elastomer gasket 97 of rectangular cross section is positioned in an annular groove 96 formed in the lower portion of the upper housinq 61 surrounding the contact 71. A Kapton gasket 98 with the center region 99 thereof removed in the region over the contact 71 or 87 is positioned over the internal gasket 97 with the disc 79 contacting the Kapton gasket. The remaining structure is as shown in FIGURES 3 and 4 except that the contact and wing are not provided in the lower housing 77. A filter seat portion 100 is provided in the hollow center region 67 to accommodate, if desired, a filter to prevent large contaminants from reaching the switching area. The switch of FIGURE 5 is constructed as a normally open switch as shown in FIGURE 6, wherein all like reference numbers refer to the same or similar parts as in the switch of FIGURES 3, 4 and 5, the switch being modified as in the FIGURE 5 switch to replace the O-ring 65 with an elastomer gasket 65A of rectangular cross section seated in the groove 63A. Annular internal elastomer gasket 97 of rectangular cross section is positioned in an annular groove 96 formed in the lower portion of the upper housing 61 surrounding the contact 87 in the lower housing 77. A Kapton gasket 98 with the center region 99 thereof removed in the region over the contact 87 is positioned over the internal gasket 97 with the disc 79 contacting the Kapton gasket. The remaining structure is as shown in FIGURES 3 and 4 that the contact and wing are not provided in the upper housing 61. In this embodiment, the contact 71 will not be molded into the upper housing 61 initially. A filter seat portion 100 is provided in the hollow center region 67 to accommodate a filter, if desired, to prevent large contaminants from reaching the switching area. It should be understood that, whereas a printed wiring board is discussed hereinabove, an insert molded lead frame assembly as shown in FIGURES 7 and 7a can be substituted therefor. The lead frame assembly 108 is used to improve the integrity of the riveted functions to the electrical circuits. As seen in FIGURE 7a this assembly is made of a metal stamped circuit 110 encapsulated in a non-conductive plastic 112. This approach also eliminates the rivets at the terminal pin - to - circuit function. Instead, the pins, as shown at 114 in FIGURE 7, are formed from the circuit stamping. Further, an optional feature is an alignment pin 116 molded from the same plastic, the purpose of which is to simplify mounting in the application. These are cylindrical plastic features which allow for securing the assembly to the backplate by heat staking or similar procedures.

Claims: A pressure responsive switch having an upper housing part (61) and a lower housing part (77) of electrically insulating material held together, with a pressure responsive snap-action disc (79) fitted over a circular aperture (85) on a disc seat within an outer rim wall on an electrically conducting member (81) sandwiched between the housing parts, the upper housing part (61) having an open central aperture (67) therethrough aligned with the snap-action disc (79) and the circular aperture (85) through the electrically conducting member (81), the disc (79) having a normally upwardly convex configuration that can be switched to a downwardly convex configuration by pressure applied through the aperture (67) through the upper housing part (61), and an electrical contact (71,87) so disposed that the disc (79) engages it in one configuration and not in the other configuration, whereby the lower housing part (77) has an open central aperture (89) therethrough aligned with the open apertures (67,85) through the upper housing part and the electrically conducting member, the upper housing part (61) has an upper substantially plane surface with an annular groove (63) for a sealing ring (65) surrounding its central aperture (67) in that upper surface, the electrically conducting member (81) is a plate having a terminal portion (83) projecting at the side from between the housing parts, the contact (71,87) is part of an electrically conducting member (69,91) having a terminal wing (73,93), the member being included in at least either the upper housing part (61) or the lower housing part (77) so that the contact is supported and located in a part of the open central aperture of the particular housing part and the terminal wing accessible outside that housing part, the contact being aligned to be received in the open circular aperture (85) through the electrically conducting member (81). A switch according to claim 1 having two electrically conducting members (69,91) each having a contact (71,87) and a terminal wing (73,93), the members being respectively included in the upper and lower housing parts, so that the contacts are supported in the central apertures of the housing parts and the terminal wings are accessible outside housing, the pressure responsive snap-action disc (79) engaging the contact of one electrically conducting member in each configuration. A switch according to claim 1 or claim 2 including a diaphragm (98) of electrically insulating material between the electrically conducting plate and the upper housing part, the diaphragm having a central aperture (99) to permit the snap-action disc to engage the contact of an electrically conducting member included in the upper housing part. A switch according to claim 3 including an annular gasket (97) of an elastomeric material between the diaphragm (98) and the upper housing part (61) disposed around the central aperture therein. A switch according to any one of the preceding claims wherein the housing parts (61,77) are held together by securing means (75) comprising legs projecting from the underside of the upper housing part (61) into holes (95) through the lower housing part (77), the legs having caps formed on their ends to secure the parts together.

Inventors: CZARN DAVID A, O'BRIEN EDWARD F, SOGGE DALE R, CZARN, DAVID A., O'BRIEN, EDWARD F., SOGGE, DALE R.
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1989
Main classification: H01H35
IPC codes: H01H35