GB2238170A

GB2238170A - Electric switch facilitating circuit testing

Info

Publication number: GB2238170A
Application number: GB8922684A
Authority: GB
Inventors: Dan Persson
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 1989-10-09
Filing date: 1989-10-09
Publication date: 1991-05-22
Also published as: GB8922684D0

Abstract

An electric switch comprises two normally separated contactors 14, 15 (also Fig 4), means such as a conductive ball 13 biassed by spring 12 to separate the contactors or to move away from the contactors (38, 39) (Fig 5), at least one of the contactors having two terminals whereby an electric path is defined between the two terminals so as to facilitate circuit testing. A high resistance (41) may be provided between two of the terminals (Fig 6). Incorporation in a motor vehicle causes movement of the conductive ball against the spring bias under accident conditions. An air bag triggering arrangement may be provided. Reference is included to testing of alarm, safety and manufacturing control systems for example. <IMAGE>

Description

DESCRIPTION OF INVENTION Improvements in or relating to an electric switch THE PRESENT INVENTION relates to an electric switch and more particularly to an electric switch so devised as to facilitate the task of testing a circuit in which the switch is incorporated.

Many electric sites have been proposed previously, to be incorporated in electric circuits and systems. In some cases it is essential to know in advance that an electric system will really function when it is activated, and thus it is desirable to be able to test that the circuits present in the electric system are complete, to ensure that the wires are nct broken, and to ensure that all the connections are electrically sound. This could well be the case with systems such as an alarm, a safety system or a system that forms part of the control arrangement for a manufacturing process.

A problem that exists in connection with the testing of electric systems is that if an electric circuit includes a normally open switch, that circuit cannot readily be tested by a passing current through the circuit.

It has been proposed however, to provide various expedients for overcoming this particular difficulty.

It is possible, for example, to provide a high resistance connected in parallel with the switch. Thus, under ordinary conditions, the resistance will not permit sufficient current to flow to cause the circuit to operate but, when it comes to testing the circuit, a current can be applied to the circuit which will flow through the high resistance, thus enabling the circuit to be tested. Such an arrangement may be satisfactory, but in many cases a switch must, when open, totally prevent the flow of any current and, of course, the provision of a resistance in parallel with the switch will prevent the switch from working in this way.

An alternative arrangement is to provide a pair of terminals which are exposed, but which are not normally connected together, the terminals being respectively connected to the two terminals of the switch.

Then, when the circuit is te be tested the exposed terminals can be connected together in some convenient way, enabling the test current provided to the circuit to flow past the normally open switch.

The disadvantage with this arrangement is that it is necessary t provide the separate exposed terminals, and the appropriate connections must be made before the testing procedure can be completed. A disadvantage that is common to both of the arrangements described above is that the integrity of the circuit can only be tested up to the terminals of the switch, and is not possible to test the integrity of the contactors of the switch. Thus, if one of the contactors is broken and is not connected to the switch terminal, this will not be revealed utilising the prior art expedients outlined above.

The present invention seeks to provide an improved switch.

According to this invention there is provided an electric switch, the switch comprising two contactors, the contactors being normally separated from and not in electrical contact with each other, means being provided for establishing electrical contact between the contactors when the switch is to be closed, at least one of the contactors comprising an element having two terminals, the element defining an electric flow path between the two terminals, part of that flow path being adpated to be brought into electrical contact with the other contactor when the switch is closed.

Preferably each of the contactors is provided with two terminals and each of the contactors defines the said current flow path.

ConvenIently one contactor is adapted to be brought into physical contact with the other contactor when the switch is closed.

Advantageously said one contactor is biassed towards the other contactor, but is maintained spaced from the other contactor by an element which, when the switch is to be closed, move away from the said contactors to permit the first contactor to move, under its bias, into contact with the second contact.

Preferably the said element comprise an element adapted to move under inertia.

Alternatively the switch comprises two contactor elements at spaced apart positions, the contactor elements being adapted to be electrically connected by means of a movable element which moves to a position where it contacts and establishes electrical connection between the two contactors.

Preferably said movable element comprises an element adapted to move under its own inertia.

Conveniently the eLement movable under its own inertia is spring biassed to an initial position and moves, under inertia, against the spring bias.

Preferably the element comprises a metallic ball.

Conveniently the element is contaIned within a housing, the housing defining a chamber, the element being movable axially of the chamber.

Preferably the switch is mounted in a motor vehicle such that the said element will moe under inertia in order to close the switch when the vehIcle decelerates under accident conditions.

In order that the invention may be more readily understood, and se that further features there may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which, FIGURE 1 is a vertical sectional view taken through a switch intended to activate an air-ba in a motor vehicle in the event of sudden deceleration of the vehicle, FIGURE 2 is a top plan vlew of the switch of Figure 1, FIGURE 3 is a vertical sectional view taken through part of the switch of Figure 1, FIGURE a is a perspective view of the contactor elements of the switch of Figures 1 to 3, FIGURE 5 is a top plan view of a modified switch incorporating contact elements in accordance with the invention in one circuit configuration, and FIGURE 6 is a view of the.switch of Figure 5 in an alternative circuit configuration.

Referring initially to Figure 1 of the accompanying drawings, a switch assembly comprises a generally cylindrical hollow housing 1 mounted on a support plate 2 by means of a mounting screw 3 which passes through an aperture in support plate 2 and into an internally threaded bore 4 provided in the housing 1. The housing 1 defines within it an axially extending generally cylindrical chamber 5, which is closed at one end b means of a cap 6. The cap 6 comprises a disc-shaped closure 7 provided with a peripheral axially extending skirt 8, the skirt carrying an inwardly directed annular protrusion 9 adapted to snap over an annular outwardly directed flange 10 provided at the end of the part of the housing 1 defining the chamber 5. A sealing ring 11 may be provided between the cap 11 and the end of the cylindrical chamber 5.

Mounted within the cylindrical chamber 5 is a helical compression spring 12 adapted to engage the interior of the cap and to bias a metal ball 13 away from the cap, axially of the chamber, towards the right as illustrated.

Mounted at the right-hand end of the housing is a pair of contactor elements 14,15. The contactor elements are shown more clearly in Figure 4 and it can be seen that the contactor element 14 comprises a substantially "U"-shaped element which has had the two 0 parallel arms thereof bent through 90 . Thus the con- tactor element 14 presents the first vertically extending leg 16 which supports a horizontally extending forwardly directed portion 17 which merges with a transverse horizontally extending portion 18. The portion 18 supports a horizontal rearwardly extending horizontal portion 19 which is parallel with but spaced from the horizontal portion 17.The portion 19 in turn is connected to a vertical extending leg portion 20 which corresponds with and is parallel with but spaced from the leg portion 16. Contact points 21 are provided on the upper surfaces of the horizontally extending portions 17 and 19 respectively.

The contractor 15 is of a similar overall configuration, and thus agaln generally consists of a U-shaped element which has had the two parallel arms 0 thereof bent through 90 . The contactor 15 presents a first vertically extending leg portion 22 which supports a horizontally extending portion 23 which overlies the horizontal extending portion 17 of the contactor 14. In the region above the contact point 21 the horizontal extendIng portion 23 is provided with a downwardly directed kinK 24. The free end of the horizontally extending portion 23 merges into a horizontal platform 25 with an upturned forward lip.The platform 25 is connected to another horizontally extending portion 26 having a configuration equivalent to that of the horizontally extending portion 23. The portion 26 thus prevents a downwardly directed kink 27, which is located above the contact point 21 of the horizontally extending portion 19 of the contactor 1lit. The horizontal extending portion 26 of the contactor 15 is located above the horizontal extending portion 19 of the contactor 14 and is co-planar with, parallel with, but slightly spaced from the horizontal portion 23. The horizontal portion 26 is connected to a vertically extending leg portion 27 which is co-planar with, parallel with, but spaced from the leg portion 22.

The contactors are mounted in position and are separated by means of an insulating block 28. A removable cover 29 is mounted on the housing, covering up a port provided to permit the contactors to be inserted into the housing. A sealing ring 30 may be provided associated with the cover 29.

As can be seen from Figure 3 the cylindrical housing 5 is provided with axially extending inwardly directed ribs 31 which terminate at positions lying on the circle having a circumference slightly greater than the circumference of the metallic ball 13. Thus the ball 13 may move axially of the housing 1, being guided by the ribs 31, whilst still leaving an air-space 32 between the outer periphery of the ball 13 and the inner periphery of the chamber 1. Thus movement of the ball is not prevented by compression of air.

As can be seen from Figure 1 the spring 12 tends to bias the ball 13 to the right and the diameter of the ball 13 is such that when the ball is so biassed to the right the ball engages under the platform 25 on the contactor 15, thus maintaining the downwardly kinked portions 2,27 of the horizontally extending arms 23,26 separated from the contact points 21. The switch illustrated is, however, so located in a motor vehicle that if the vehicle suffers severe deceleration the ball 13, due to its inertia, tends to move to the left as illustrated in Figure 1. The movement of the ball is only prevented by means of the spring 12 and the strength of the spring is selected so that the ball 13 will not move forwardly under normal deceleration, but will only move forwardly under accident conditions.

When the ball moves forwardly the lip at the free end of the platform 25 slides across the top of the ball 13 and then the arms 23,26 of the contactor 15 pivot downwardly under an inherent spring bias, thus bringing the downwardly kinked portions 24,27 into contact with the contact points 21. Thus electrical connection is established between the contactors 14 and 15.

It is to be observed, however, that the contactors 14 and 15 may each be prdvided with two terminals. Thus the contactor 14 may be provided with terminals connected to the vertically extending leg portions 16 and 20 respectively, whereas the contactor 15 may have terminals connected to the vertically extending leg portions 22 and 27. Thus, when the circuit incorporating the switch is tested it is possible to pass a test current through the contactors of the switch. This ensures that not only is the integrity of the circuit tested up to the terminals of the switch, but also the integrity of the circuit is tested through the contactors of the switch. If any one of the four terminals connected to the two contactors of the switch is a dry" connection the test current will not flow.

It is envisaged that a switch, as described, will be incorporated in the triggering arrangement for an air-bag, in a motor vehicle, wiz Is arranged to be inflated by means of a pyrotechnic gas generating device.

Figure 5 illustrates a modified embodiment of the invention for use in an ai--bag triggering arrangement wherein a housing is provided defining a cylindrical cavity 34 closed, at one end, by means of a cap 35 (which corresponds with the cap 6 of Figure 1) the cavity containing a spring 36 which serves to bias a metallic ball 37 towards the right. Two "U"-shaped contactor elements 38,39 are provided which are located on opposite sides of the housing. In each case the two arms of the U"-shaped contactor element project to the exterior of the housing and it is the base of the "U"-sha?ed contactor element which is exposed on the interior of the housing.The contactors are so located that if the metallic ball 37 moves towards the left as illustrated in Figure 5 against the bias provided by the spring 36, then the outer periphery of the ball will touch the bases of both the contactor elements 38,39 simultaneously, thus establishing el-ectrical contact between the contactors and effectively closing the switch.

As can be seen from Figure 5 the two arms of eacn of the contactors 38 and 39 are connected to res pective terminals 4C in such a way that a test current can be caused to flow through the switch, testing the integrity of the contactors 38 and 39.

Figure 6 illustrates a modified arrangement very similar to the arrangement of Figure 5, but in this arrangement one terminal of each of the contactors 38 and 39 are connected to each other by means of a high value resistor 41, and only two terminals 40 are provided for the test current and for connection to the remainder of the circuitry. In this embodiment when the switch is "open" there is a current flow path defined by the resistor 141, but the current permitted to flow is not sufficient to trigger the air-bag, but when the ball 37 touches both of the contactors 38 and 39 the circuit is fully completed and a high current then flows.

Claims

CLAIMS:

1. An electric switch, the switch comprising two contactors, the contactors being normally separated from and not in electrical contact with each other, means being provided for establishing electrical contact between the contactors when the switch is to be closed, at least one of the contactors comprising an element having two terminals, the element defining an electric flow path between the two terminals, part of that flow path being adpated to be brought into electrical contact with the other contactor when the switch is closed.

2. A switch according to Claim 1 wherein each of the contactors is provided with two terminals and each of the contactors defines the said current flow path.

3. A switch according to any one of the preceding Claims wherein one contactor is adapted to be brought into physical contact with the other contactor when the switch is closed.

h. A switch according to Claim 3 wherein said one contactor is biassed towards the other contactor, but is maintained spaced from the other contactor by an element which, when the switch is to be closed, move away from tne said contactors to permit the first contactor to move, under its bias, into contact with the second contact.

5. A switch according to Claim 4 wherein the said element comprise an element adapted to move under inertia.

6. A switch according to Claim 1 or Claim 2 wherein the switch comprises two contactor elements at spaced apart positions, the contactor elements being adapted to be electrically connected by means of a movable element which moves to a position where it contacts and establishes electrical connection between the two contactors.

7. A switch according to Claim 6 wherein said movable element comprises an element adapted to move under its own inertia.

8. A switch according to Claim 5 or 7 wherein the element movable under its own inertia is spring biassed to an initial position and moves, under inertia, against the spring bias.

9. A switch according to Claim 5, 7 or 8 wherein the element comprises a metallic ball.

10. A switch according to Claim 5, 7, 8 or 9 wherein the element is contained within a housing, the housing defining a chamber, the element being movable axially of the chamber.

11. A switch according to any one of Claims 5 or 7 to 10 wherein the switch is mounted in a motor vehicle such that the said element will move under inertia in order to close the switch when the vehicle decelerates under accident conditions.

12. A switch substantially as herein described with reference to and as shown in Figures 1 to 4 of the accompanying drawings.

13. A switch substantially as herein described with reference to and as shown in Figures 5 and 6 of the accompanying drawings.

14. Any novel feature or combination of features disclosed herein.