INERTIA SWITCH

Abstract: An inertia switch for a supplemental inflatable restraint system. The switch comprises a casing that is divided into two chambers by an axially movable diaphragm. In one embodiment, the diaphragm carries an electrical contact on one face and an inertial mass on the other. A pair of terminals are disposed in the path of travel of the electrical contact so that when the switch is subjected to axial deceleration force the contact is urged toward the terminals. Actual contact is made when the deceleration force equals or exceeds a predetermined deceleration characteristic. The deceleration characteristic is a function not only of the diaphragm, the electrical contact, and the mass, but also of a control orifice located in an orifice that communicates the two chambers with each other. The chambers are constructed such that air is forced from one chamber into another through the control orifice when deceleration occurs and this imparts a dampening to the motion of the diaphragm. Another embodiment for sensing deceleration places the inertial mass in the one chamber that contains the contacts. The other chamber has a thin concave-convex shape that gives the switch a low profile. The switch has a molded plastic base containing a test coil for attracting the inertial mass to test the switch. A mechanism for calibrating the switch is also included.

Description: INERTIA SWITCH BACKGROUND AND SUMMARY OF THE INVENTION This invention relates to an inertia switch. Supplemental inflatable restraint devices that are used in automobiles are activated by inertia switches. These switches sense predetermined deceleration characteristics and provide switch closure signals to the devices when such predetermined characteristics are sensed. The predetermined deceleration characteristic that creates switch closure is a function of both the magnitude of deceleration and its duration. The ability of a switch to sense a predetermined deceleration characteristic is determined by the switch design. In order to embody this design in production switches, manufacturing tolerances must be closely controlled. One known type of inertia switch that is used with supplemental inflatable restraint devices comprises a sphere that travels within a tube. The predetermined deceleration characteristic that will activate the switch is a function of several parameters. One of these parameters is the closeness of the fit of the sphere within the tube. Controlling the accuracy of this fit in production switches is a significant portion of the switch cost. The present invention relates to an inertia switch which does not utilize the tube and sphere construction and for that reason offers the potential for reducing costs associated with the production of inertia switches for supplemental inflatable restraints while still attaining a specified degree of accuracy in such switches. Briefly, one embodiment of a switch embodying principles of the invention comprises a casing containing a diaphragm• that divides the casing into two chambers. The diaphragm can move axially within the casing. An electrical contact is carried by the face of the diaphragm that bounds one chamber. Terminals are disposed in that chamber in the path of travel of the electrical contact as the diaphragm moves toward that chamber. The face of the diaphragm that is toward the other chamber carries a mass since the electrical contact may be insufficient by itself to provide enough mass for the diaphragm. The diaphragm is constructed such that the electrical contact is biased out of contact with the terminals, and this represents the off condition of the switch. In response to an axial force urging the mass, diaphragm, and electrical contact toward the terminals, the electrical contact will be forced to make contact with the terminals provided that a predetermined deceleration characteristic is exceeded. This represents the closed condition of the switch, whereby the switch provides a signal to an associated supplemental inflatable restraint system. The predetermined deceleration characteristic that causes switch closure is a function not just of the diaphragm and the mass that it carries, but also of a control orifice. The control orifice is provided in an orifice structure passing through the electrical contact, the diaphragm, and the mass, and serving to communicate each chamber to the other. The casing is constructed and arranged such that air must be forced through the control orifice as the diaphragm, the mass, and the electrical contact move toward the terminals, and accordingly, the control orifice performs a timing function that forms a part of the predetermined deceleration characteristic to which the switch is responsive. Stated another way, the requirement that air be forced through the control orifice imparts a certain dampening to the diaphragm travel. In the disclosed embodiment of the invention the control orifice is in the electrical contact. The orifice can be formed quite accurately in the electrical contact by known methods, and in this way the timing function can be economically incorporated in production switches with the required degree of accuracy. Another embodiment that is provided by the present invention is that one that is endowed with a low profile, thereby making it more compact, yet without detracting from functional and calibration capabilities. A further improvement is that an electromagnetic coil for performing a testing function can be incorporated into the inertia switch in an efficient manner. A still further improvement is that means can be incorporated to provide for the switched vacuum testing of the switch. Yet another feature is the diaphragm construction. The foregoing features, advantages, and benefits of the invention, along with others, will be seen in the ensuing description, and claims, which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view through an inertia switch embodying principles of the invention. Fig. 2 is a fragmentary view looking in the direction of arrows 2-2 in Fig. 1. Fig. 3 is a fragmentary view looking in the direction of arrows 3-3 in Fig. 1. Fig. 4 is a cross-sectional view through another embodiment of inertia switch. Fig. 5 is a cross-sectional view through a further embodiment of inertia switch. Fig. 6 is a plan view of an alternate form of diaphragm. Fig. 7 is a plan view illustrating a component part of the diaphragm of Fig. 6 by itself. Fig. 8 is an axial cross sectional view through another inertia switch embodying principles of the invention. Fig. 9 is a fragmentary sectional view taken along line 9-9 in Fig. 8. DESCRIPTION OF THE PREFERRED EMBODIMENT An inertia switch 10 comprises the following parts: a plastic base 12; a metal cover 14; a metal diaphragm 16; a metal mass 18; an electrical contact 20; a pair of electrical terminals 22, 24; an electromagnetic coil 26; and an adjustment screw 28. The axis is designated by the numeral 30. Base 12 is fabricated by molding plastic material around the body of coil 26 and intermediate portions of terminals 22, 24. Lead wires (not shown) from the body of coil 26 are connected to addition electrical terminals (not shown) so that the coil can be selectively energized from an external source for testing the inertia switch in a manner to be more fully explained in the ensuing description. Base 12 has a circular opening which is closed by cover 14. The peripheral margins of cover 14 and diaphragm 16 are also circular with the three parts 12, 14, and 16 being shaped such that in assembly the entire margin of diaphragm 16 is captured between cover 14 and base 12 in a sealed manner. This creates two internal chambers 32 and 34 on opposite sides of diaphragm 16. Diaphragm 16 has a central hole 36 which passes a very short neck 38 of mass 18. The diaphragm and mass are united in a sealed manner so that gas cannot pass between chambers 32 and 34 via the fitting of neck 38 to hole 36. The bulk of mass 18 lies within chamber 34. Diaphragm 16 is inherently biased to have a concave-convex shape that is convex toward chamber 32. Cover 14 has a similar shape that is concave toward chamber 32. Together they cooperatively define a thin concave-convex shape for chamber 32 thereby endowing the inertia switch with a low axial profile. Mass 18 is securely joined to diaphragm 16 in any suitable manner so that the two form a unit. Likewise, electrical contact 20 is securely affixed to the face of mass 18 that is opposite diaphragm 16 so that the exposed face of the contact is toward terminals 22, 24. It may be desirable for the exposed contact face to contain a thin gold plating 40 for making contact with terminals 22, 24 when the switch is actuated. The diaphragm, mass, and electrical contact are constructed to have coaxial symmetry about axis 30. Orifice means 42 is provided to establish fluid communication between chamber 32 and 34. Orifice means 42 is coaxial with axis 30 and takes the form of a control orifice 44 through contact 20 and a larger orifice 46 through mass 18. The latter orifice has a circular segment extending from the former and a frusto-conical segment extending from the circular segment. The frusto-conical segment forms a seat for the rounded distal end of calibration screw 28 that is threaded into a central circular sleeve 50 that is formed integrally with cover 14. Because the diaphragm is constructed so as to be inherently biased away from terminals 22, 24 and toward cover 14, theoretical seating contact between screw 48 and the frusto-conical section of orifice 46 would occur on a circular line of contact that is concentric with axis 30. In order to assure fluid communication past what would otherwise be an endless circular line of contact, the distal end of screw 28 contains a diametrical slot 52 such that when the screw is seated, the slot interrupts the circular line of contact between the screw and seat. The axial position of screw 28 establishes an axial distance between contact 20 and terminals 22, 24 for calibrating the switch. The inertia switch operates in the following manner. When subjected to a certain deceleration force characteristic along axis 30, the diaphragm, mass, and contact will be displaced from the position illustrated in Fig. 1 to a position where contact 20 bridges terminals 22, 24 to create electrical circuit continuity between them. The requirement that the gas (air, for example) in the ensealed chamber 34 pass through the control orifice as the volume of chamber 34 contracts, imparts damping to the motion. The switch therefore gives a switch signal via terminals 22, 24. Base 12 includes a stop 54 that limits the overtravel so that excessive flexing of terminals 22, 24 is avoided. Mass 18 is a ferromagnetic material so that it, along with the diaphragm and contact, will be displaced to the signal-giving position when coil 26 is suitably energized. This is a useful test feature. In many respects, the switch of Fig. 4 is similar to that of Fig. 1 and therefore, like reference numerals will be used to designate corresponding parts but a detailed description will be omitted in the interest of conciseness. One difference between the switch of Fig. 4 and that of Fig. 1 is that the switch of Fig. 4 also includes a nipple 60 that provides communication to chamber space 34. With the switch assembly properly installed in a vehicle, one end of a tubular hose (not shown) is fitted over the exposed exterior end of nipple 60. The opposite end of the hose leads to a switched vacuum source. When the switch that controls the communication of the vacuum source to chamber space 34 via nipple 60 is closed, vacuum is not communicated to chamber space 34. However, when it is desired to perform a test of the inertia switch, the vacuum switch is opened to communicate vacuum to chamber space 34. The pressure differential acting across the diaphragm causes the diaphragm to be displaced downwardly from the positions shown in Fig. 4 in a sufficient amount that contacts 22 and 24 are bridged by the conductive layer 40 on mass 18. The capability for testing the inertia switch via switched vacuum can be additional to the electromagnetic test capability afforded by coil 26 or it can be in substitution of the electromagnetic test capability. A further difference between the inertia switch of Fig. 4 and that of Fig. 1 is that cover 14 contains no provision for acceptance of screw 28. Proper calibration is attained by means of a diametrically precise control orifice 44 that passes completely through the mass communicating chamber spaces 32 and 34. Such a precise aperture could provide a less costly construction for the inertia switch. Technology exists for creating precision holes and an appropriate form of such technology may be employed. The embodiment of inertia switch illustrated in Fig. 5 differs from that of Fig. 4 in that the vacuum test feature provided by nipple 60 is omitted. This embodiment includes a coil spring for biasing the diaphragm in any situation where the diaphragm does not have an inherent bias or else whatever inherent bias it has, is less than desired. The spring is shown to act between mass 18 and an internal shoulder of base 12. Figs. 6 and 7 illustrate an alternate embodiment of diaphragm that comprises a two-part construction. The diaphragm comprises a webbed support member 64 that is either press-fitted or insert-molded with respect to a rubber element 66. Bias for the diaphragm may be obtained either inherently by the diaphragm construction, or alternately by inclusion of a coil spring such as the coil spring 62 of Fig. 6. Where the diaphragm has an inherent bias, such inherent bias may be imparted by the webbed support, the material being steel by way of example. Figs. 8 and 9 show an inertia switch 110 that comprises a casing 112 containing a diaphragm 114 that divides the casing into two chambers 116, 118. The face of diaphragm 114 that is toward chamber 118 carries an electrical contact 120 which is centrally disposed on that face of the diaphragm. The opposite face of the diaphragm carries a mass 122. The drawings show the switch in the off condition. Diaphragm 114 is constructed of a metal, such as stainless steel, and designed to bias the diaphragm toward chamber 116 where mass 122 is in abutment with a stop 124. When the switch is subjected to an axial deceleration tending to urge diaphragm 114 toward chamber 118, electrical contact 120 will be displaced axially by the diaphragm and into bridging contact with a pair of electrical terminals 126, 128 having interior ends disposed within chamber 118. These two terminals pass through the casing wall where they are available for connection with electrical circuitry of a supplemental inflatable restraint system to supply, when bridged by contact 120, a signal indicative of switch closure representing the inertia switch having experienced a deceleration force whose magnitude and duration equal or exceed the predetermined characteristic to which the switch is responsive. Contact 120 is an electrically conductive metal, and preferably includes a thin coating 130 of a material such as gold across the face that makes contact with terminals 126, 128. A pair of posts 132, 134 project axially from the inside of the end wall of casing 112 to form stops that abut contact 120 to arrest the displacement of the diaphragm after terminals 126, 128 have been bridged by contact 120. The two chambers 116, 118 are communicated by orifice means 136. The orifice means passes from chamber 118 centrally through electrical contact 120, through diaphragm 114 and through mass 122. To assure communication with chamber 116 where mass 122 is abutted by stop 124, holes 138 are provided in stop 124 as shown. The orifice- means 136 includes a control orifice 140 formed in electrical contact 120. The two chambers are constructed and arranged such that when the switch is subjected to axial deceleration force that displaces the diaphragm, mass, and contact toward the terminals, a pressure differential is created between the two chambers causing air to be forced through the orifice means, including the control orifice. Accordingly, the control orifice creates a means for controlling the timing of the switch closure, in other words the amount of dampening the diaphragm motion. Hence, the predetermined deceleration characteristic that will be effective to operate the switch to the closed condition is a function not only of the diaphragm, the mass, and the electrical contact but also of the control orifice. It should be understood that the drawing figures are not necessarily representative of actual proportions. The control orifice will be quite small but can be formed into the electrical contact by conventional procedures that are used to create small, but very accurate holes. These procedures can be economically conducted. The switch parts can be fabricated by conventional manufacturing processes, and the switch itself is not especially complicated. Therefore, a worthwhile improvement on manufacturing costs can be obtained without sacrificing performance characteristics of an inertia switch. Where necessary, the stop 124 can be made axially adjustable as shown, to provide a certain degree of calibration. It is also contemplated that the diaphragm can be constructed with an over-center effect, such as occurs in a conical washer, to impart the desired bias. As is well known in the design of inertia switches, switch closure depends both upon the magnitude of force applied to the switch and also the duration of force application, and that will be true for the switch of the present invention. While presently a preferred embodiment of the invention has been disclosed, it will be appreciated that principles are applicable to other embodiments.

Claims: WHAT IS CLAIMED IS: 1. Inertia switch structure comprising: a casing; a diaphragm that divides said casing into two chambers and is axially displaceable within said casing; orifice means in said structure through which a gas in one of said two chambers can be driven from said one chamber; electrical terminal means disposed in said one chamber in the path of axial displacement of said diaphragm; said two chambers, said diaphragm, and said terminal means being constructed and arranged such that in response to an axial force of predetermined magnitude and duration applied to said inertia switch structure, said diaphragm is displaced axially within said casing toward said one chamber to cause a switch signal representative of the occurrence of said axial force to be given at said terminal means; and said orifice means comprising control orifice means through which gas is driven from said one chamber as said diaphragm is being displaced toward said one chamber, said control orifice means serving to impart dampening to the motion of said diaphragm toward said terminal means. 2. An inertia switch structure as set forth in claim 1 in which said diaphragm is constructed so as to be inherently biased in the axial direction away from said terminal means. 3. An inertia switch structure as set forth in claim 2 in which said diaphragm includes a mass that is carried centrally by said diaphragm on the face thereof that is toward said other chamber, said orifice means also passing through said mass. 4. An inertia switch structure as set forth in claim 3 including a stop for engaging said mass to set a limit for the extent to which said diaphragm is biased away from said terminal means. 5. An inertia switch structure as set forth in claim 2 including means acting between said casing and said diaphragm to form a stop that limits the extent to which said diaphragm is biased away from said terminal means. 6. An inertia switch structure as set forth in claim 1 in which said orifice means is arranged to communicate said one chamber to said other chamber so that gas from said one chamber is forced through said orifice means into said other chamber as said diaphragm is axially displaced toward said terminal means. 7. An inertia switch structure as set forth in claim 1 in which said orifice means passes through said diaphragm. 8. An inertia switch structure as set forth in claim 7 wherein said control orifice means is in an electrical contact portion of said diaphragm. 9. Inertia switch structure as set forth in claim 1; said casing being cooperatively defined by a plastic base having a circular open end that is closed by a circular cover; said diaphragm having a circular peripheral margin; said cover and said base coacting to capture the entire peripheral margin of said diaphragm; at least the bulk of a mass that is attached to said diaphragm being disposed entirely within said one chamber; and said circular cover comprising a wall that is concave toward said other chamber, said diaphragm comprising a wall that is convex toward said other chamber, and said cover and said diaphragm being disposed such that said other chamber is for the most part cooperatively defined by the closely spaced apart nesting of said concave and convex walls to have a thin concave-convex shape when the inertia switch is subjected to no axial force. 10. Inertia switch structure as set forth in claim 9 including a stop to set a limit for the extent to which said diaphragm is biased away from said terminal means, said stop is adjustably disposed on said cover to engage a portion of said mass that is exposed to the stop via an aperture in said diaphragm, said portion of said mass comprising a seat on which a distal portion of said stop seats, and aperture means in said distal portion of said stop forming a portion of said orifice means when said distal portion of said stop seats on said seat. 11. Inertia switch structure as set forth in claim 9 including completely embedded in said plastic base, the body of an electromagnetic coil which, when energized, attracts said mass to cause actuation of said terminal means for electrical testing of the switch. 12. Inertia switch structure as set forth in claim 1 including means communicating said one chamber to a source of switched vacuum for causing pressure differential to be created across said diaphragm such that said electrical terminal means is operated when the switched vacuum source applies vacuum to said one chamber, whereby the switched vacuum source can be used to test the inertia switch. 13. Inertia switch structure as set forth in claim 1, said diaphragm comprising a webbed support which is covered by a material which is impermeable to the gas in said one chamber.

Inventors: COOK JOHN EDWARD, DREW KERRY, COOK, JOHN, EDWARD, DREW, KERRY
Applicants: SIEMENS AUTOMOTIVE LTD
Application year: 1990
Main classification: H01H35
IPC codes: H01H35