GB2160017A - Electrical switches - Google Patents

Abstract

An electrical switch has two moving contacts 14 and 35. A ferromagnetic inertia body 4 leaves the restraint of the magnet 5 when the switch is subject to an acceleration above a threshold value and causes contact 14 to move from the position in which it touches the contact 35. The contact 35 is operated by a relay 31. In the particular embodiment illustrated, a contact 15 moves with the contact 14 relative to a fixed contact strip 42. Movement of the contact 14 can be prevented by a locking bar (Figures 6 to 11, not shown) during the operation of which any movement of the inertia body 4 has no effect. Alternatively, the sensitivity of the inertia switch can be decreased by applying an additional magnetic field to that of the magnet 5 to impose a greater restraint on the movement of the inertia body 4. This additional magnetic field may be created by the coil of relay 31, Figure 5 (not shown). <IMAGE>

Description

SPECIFICATION Electrical switches This invention relates to an electrical switch having at least two contacts. The switches close when one contact touches the other, and the switch is broken when the contacts move apart. It is usual for one contact to be fixed and the other contact to move in response to an electrical or mechanical stimulus relative to the fixed contact.

The present invention is concerned with a switch which is responsive to two different stimuli. Rather than provide two separate switches as described above, connected in series, the present invention provides a single switch having a fixed body, two electrical contacts each movable relative to the fixed body in response to respective stimuli to or from a position in which they touch each other.

This arrangement has the advantage that there is a saving of contacts compared to two prior art switches connected in series, which provides economy of contact material and reduces the chance of failure in operation.

In one embodiment, one contact is movable in response to the stimulus of an inertia switch, the associated contact being withdrawn from the position in which it can contact the other contact when the switch has been subjected to an acceleration exceeding a given threshold. The other contact is movable in response to the magnetic field of a relay coil.

As an optional feature of the invention described above, or as an independent invention, the switch may comprise a fixed body, two contacts movable relative to the body in response to respective stimuli to positions in which the switch is closed, one of said contacts being movable away from its said position by an actuating member when subjected to an acceleration which exceeds the attraction of a magnetic field, the second contact being movable in response to the stimulus of the magnetic field of a relay coil, the relay coil being located with respect to the actuating member such that the magnetic field generated by the relay coil modifies the magnetic field restraining the actuating member.

This has the effect of changing the sensitivity of the switch to accelerations when the relay coil is de-energised. It may be desirable to reduce the sensitivity of the switch when the switch is connected in a circuit which is to be switched off when the acceleration of a vehicle exceeds a given value as a safety measure. This safety measure is not particularly desired when the vehicle is being moved other than by means of its own engine controlled by the ignition switch. When the ignition switch is turned off, the switch of the invention will only open in response to very high accelerations, but when the vehicle is being driven under its own power, it will respond to lower accelerations. This will prevent the switch being opened, for example when the vehicle is being carried on a transporter.

An alternative method of inhibiting the movement of the appropriate contact in response to the stimulus of excessive acceleration is to provide a locking member to lock said contact in its first position, preventing its movement in response to said excessive acceleration. This locking member can be movable in response to the energisation of the relay coil to an inoperative position, so that the contact responsive to the stimulus of excessive acceleration can only be moved when the relay coil is energised. This arrangement will overcome the problems of undesired movement away from it switch-making position of the contact responsive to excessive acceleration in the circumstances outlined above.

Examples of the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a section through a switch in the plane of the acceleration to which the switch is sensitive in the closed position of the switch, Figure 2 is a transverse section through the switch of Figure 1, Figure 3 shows the switch of Figure 1 with its 'inertia' contact withdrawn, Figure 4 shows the switch of Figure 1 with its 'relay' contact withdrawn, Figure 5 is a sketch of the switch of Figure 1 with the relay relocated relative to the inertia switch components, Figure 6 shows a modification of Figure 1 by the addition of a locking bar, Figure 7 is a transverse section through the switch of Figure 6, Figures 8 and 9 show the relays of Figures 6 and 7 with the relay de-energised, Figure 10 is a perspective view of a detail of the switch of Figures 6 to 9, Figure 11 is a detail of a transverse section of the switch of Figure 7, and Figure 12 shows another embodiment of the invention.

The right hand side of the switch illustrated in Figures 1 to 4 closely resembles that of Co-pending Application 8401027 (Serial No. ), although it is not identical to it. A housing 1 accommodates an inertia mass 4 in the form of a spherical steel ball which is normally restrained by a magnet 5 in a frust-conical seat 6. The force exerted by the magnet 5 on the inertia mass 4 is such that it is overcome by the attainment of a predetermined threshold value of acceleration or deceleration acting on the device and thus on the inertia mass 4.

When this threshold value is attained, the inertia mass 4 moves upwards out of the seat 6 since the attraction of the magnet 5 is insufficient to cause the mass 4 to accelerate or decelerate with the housing.

Located above the inertia mass 4 (as seen in Figure 1) is a hinge-like assembly 8 formed by two plates 9 and 10 of electrically conductive material such as brass pivotally connected together at mutually interfitting castellated edges 11 and 12. The outer edges of the two plates, which extend parallel to the interfitting edges 11 and 12, are turned over to form movable electrical contacts 14 and 15.

The hinge-like assembly 8 is arranged to pivot between two over-centre positions on either side of a centre position. In the one over-centre position shown in Figures 1 and 2, the two plates 9 and 10 are approximately parallel with their outer edges at their maximum separation. In the other position (illustrated in Figure 3) the castellated edges 11 and 12 are moved away from the seat 6 so that the outer edges of the plates 9 and 10 move towards each other in a groove 24 (Figure 2) which accommodates the width of the turned over end portions of the plates 9 and 10 and has an enlarged centre portion to accommodate the transverse movement of the edges 11 and 12.

In the over-centre position illustrated in Figure 1, the hinge-like assembly 8 is urged towards the inertia mass 4 by a spring 26 anchored in holes in the two plates 9 and 10. The spring 26 urges the hinge-like assembly 8 in the other over-centre position towards a reset piunger 27 slidably mounted in the top 28 of the housing 1. The reset plunger 27 is surrounded by a shroud 29.

The left hand side of the switch shown in Figures 1 to 4 comprises a relay 31 having energising terminals 32 and 33 connected to a coil 34. On energisation, the coil 34 attracts the armature of a movable contact 35 to the position illustrated in Figures 1 and 2 against the bias of a return spring 36. When the coil 34 is de-energised, the spring 36 rotates the armature anti-clockwise until its base hits a stop 37.

In the position shown in Figures 1 to 3, the movable contact 35 is in a position to contact the left hand contact end 14 of plate 9 when in the first over-centre position of Figures 1 and 2. Also in this first over-centre position, the right hand contact end of plate 10 touches the fixed contact 41 which is connected to a terminal 42. The movable contact 35 is connected to the relay body terminal 43, so that in the position illustrated in Figures 1 and 2 electrical continuity is achieved between the terminals 42 and 43 through the contact 35 and plates 9 and 10.This continuity is broken either by de-energisation of the relay coil 34 which causes the movable contact 35 to move to the left as seen in Figure 4 or by the switch being subjected to such an acceleration that the inertia mass 4 is released from the attraction of the magnet 5 and strikes the underside of the plates 9 and 10, causing them to move upwardly as seen in Figure 3, thus drawing the contact ends of the plates 9 and 10 towards each other, breaking the contact with the movable contact 35 and the fixed contact 41.

The electrical connection between the movable contact 35 and the contact end of the plate 9 is subjected to the magnetic influence of the relay coil 34 and the mechanical influence of the mass 4.

No intermediate fixed contacts are provided between the movable contact 35 and the plate 9, thus saving on contact material and chance of contact failure.

In Figure 1, the magnet 5 is very much smaller than that illustrated in Co-pending Application 8401027. The magnet 5 is a rare earth magnet, which is much stronger than mixtures of aluminium, cobalt and nickel which we used in the earlier apparatus.

Although a relay coil is normally designed so that the magnetic field is concentrated in the core which attracts the armature of the movable contact, it may be arranged that the magnetic field of the coil 34 co-operates with that of the magnet 5 to influence the mass 4 according to the state of energisation of the relay. Figure 5 illustrates such an alternative arrangement with the contacts in the same relative positions as illustrated in Figure 1.

The movable member of the relay 31 to which the contact 35 is attached is now L-shaped, pivotally mounted about axis 51. When the coil 34 is deenergised, the spring 52 moves the member from the position shown in Figure 5 in full lines to the position shown in dotted lines so that the contact 35 moves away from the contact 14. In the arrangement illustrated in Figure 5 the coil 34 of the relay 31 is aligned with the magnet 5. The magnetic field generated by the coil 34 opposes that of the magnet 5 so that when the relay is energised the ball 4 will leave the seat 6 at lower acceleration values compared to when the relay is not energised.

If it is desired that the plates 9 and 10 should remain in their illustrated position while the coil 34 is de-energised, no matter what acceleration is exerted on the switch, then a mechanical lock can be applied to the plates 9 and 10. Such an arrangement is illustrated in Figures 6 to 11. The modified apparatus differs from that described with reference to Figures 1 to 4 in that the arm of contact 35 is extended beyond the contact and the extension 35a engages a locking bar 53 of insulating material which is slidable within the switch housing 1 to engage lugs 44 and 45 on the plates 9 and 10 adjacent the castellated portions 11 and 12.

With the switch in its closed position as illustrated in Figures 6 and 7, the contact 35 is in contact with the contact 14 and the locking bar 53 is moved to the right as seen in the figures. The locking bar is of U-shape having two arms 54 of unequal length, each with a locking lug 55 at its free end (see Figure 7). In this position, the lugs 55 lie clear of the lugs 44 and 45, allowing the switch to be opened when the ball 4 hits the underside of the plates 9 and 10.

When the relay 31 is de-energised, the contact 35 moves away from the contact 14 so that the components are arranged as shown in Figures 8 and 9.

The locking bar 53 moves with the contact 35 to the left so that the lugs 55 engage the lugs 44 and 45, thus preventing the plates 9 and 10 being moved from their first over-centre position to their second over-centre position if the plates 9 and 10 are struck by the ball 4. With this arrangement the switch will only be opened by an undue acceleration or deceleration when the relay is energised, although of course it will be opened by movement of contact 35 when the relay is de-energised, irrespective of any accelerations occurring.

Figures 10 and 11 show details of the Engages ment of the lug 55 with the lug 44. The locking bars 54 slide in the base of groove 24, outside the contacts 14 and 15. In the position of Figures 6 and 7, illustrated in dotted lines in Figure 10, the lug 55 is located beyond the lug 44 and does not prevent its upward movement. In the position of Figures 8 and 9, illustrated in full lines in Figure 10, the lug 55 partly overlies the lug 44 and prevents its upward movement. Figure 11 shows a cross-section through the locking bar at the lug 55, showing that the bar extends beside the lug 44 and the lug 55 extends above the lug 44.

The switch described so far resembles that of our co-pending Application 8401027. The invention is not however limited to this type of switch. For example, the switch of International Publication W079/00500 could be used and its adaptation to the present invention is illustrated in Figure 12. In that figure, a relay 31 has a coil 34 which on energisation moves a contact 35 from the position shown in dashed lines in Figure 12 to the position shown in full lines. On de-energisation, the spring 52 returns the contact 35 to the position shown in dashed lines. The other contact 14 is moved from the position shown in full lines in Figure 12 to the position shown in dashed lines when a ball 4 leaves the cup 6 and strikes an actuating arm 61.

The contact 14 is mounted on an arm 62 and the arms 61 and 62 are pivoted at 63 and connected together by a spring 64 so that they have two overcentre positions, the first as shown in full lines in Figure 12, and the second with the contact 14 shown in the dashed line position and the arm 62 aligned with the stops 65. The arm 61 is returned to its full line position by the reset button 27 connected to a shaft 66. The shaft 66 engages an Lshaped lever 67 which itself engages the spring 64.

Depression of the button 27 rotates the lever 65 clockwise and urges the spring to the right in Figure 12, moving the arms 61 and 62 from the dead centre position in which the ends of the spring are to the left of the common pivot axis 63 to the dead centre position in which they are to the right. A stop 68 limits the rotation of the arm 61 about the axis 63. Terminals 32 and 33 are connected to the coil 34 of the relay 31. Terminals 42 and 43 are the switch terminals, terminal 42 being connected to the arm 62 at the pivot axis 63 and thence to the contact 14. Terminal 43 is connected through lead 69 to the contact 35 through its mounting arm. Of course, the alignment of the magnetic fields of the coil 34 and the magnet 5, as illustrated in Figure 5 in respect of the first type of switch, can also be used with the switch of Figure 12. Similarly, the arm 61 can be locked against movement by an arm operated by the solenoid 31 as described above with reference to Figures 6 to 11.

The relay 31 can be so arranged that on energisation its magnetic field adds to the field restraining the ball 4, as an alternative to the Figure 5 arrangement.

Claims (10)

1. An electrical switch, responsive to two stimuli, having a fixed body, two electrical contacts each movable relative to the fixed body in response to respective stimuli to or from a position in which they touch each other.

2. A switch as claimed in Claim 1 comprising an inertia body movable in response to acceleration of the switch above a threshold value, one of said electrical contacts being movable in response to said movement of said inertia body.

3. A switch as claimed in Claim 1 or Claim 2 comprising a relay coil, the second of said electrical contacts being movable in response to the energization of said relay coil.

4. A switch as claimed in any one of Claims 1 to 3 comprising means to reduce the sensitivity of the movement of one of said contacts to its corresponding stimulus.

5. A switch as claimed in Claim 4 wherein said means comprises locking means to prevent the movement of said one contact.

6. A switch as claimed in Claim 4 or Claim 5 wherein said means is operable in conjunction with the movement of said other of said contacts.

7. A switch as claimed in any one of Claims 4 to 6 wherein one of said contacts has its movement affected by a magnetic field, said means comprising means to change said magnetic field.

8. A switch as claimed in Claim 7 when dependent indirectly on Claim 3, the magnetic field which affects the movement of said one contact being formed by the magnetic field of the relay coil.

9. A switch as claimed in Claim 2 or any claim dependent thereon comprising a magnet to restrain movement of said inertia body when the acceleration of the switch does not exceed the threshold value.

10. An electrical switch substantially as hereinbefore described with reference to and as illustrated in Figures 1 to 5 alone as modified by Figures 5 to 11 or in Figure 12 of the accompanying drawings.