This invenv ion relates to circuit breakers for electrical circuits, particularly the electrical circuits of motor vehicles. The primary use of the circuit breaker is to minimise the possibility of fire in a crashed motor vehicle. The circuit breaker has a secondry use which is as a security device.

In the event of a vehicle being involved in a crash there can be an earthing spark from a battery powered device, such as the ignition coil of the engine, the headlights, the windscreen wipers, the air conditioner or the like or from damaged wiring connected thereto. Such a spark could ignite petrol in liquid or vapor form released in the crash resulting in the occupants being burned and in an extreme case being killed.

The disconnection of the battery from the wiring in the motor vehicle at the instant the crash overcomes this problem. As will be understood in some crash situations the motor vehicle engine can continue to operate for a short period, perhaps only part of a revolution, but this can be sufficient for the fuel distribution system to pump petrol into the engine compartment where it can be ignited by a spark from damaged electrical equipment or wiring if this is still connected to the battery.

Broadly, the invention provides a circuit breaker to- disconnect the battery of a vehicle from apparatus

powered by the battery, said circuit breaker comprising a base part including two non-connected electrically conductive posts adapted to respectively connect directly or indirectly to a battery and to battery powered apparatus, first catch means parts on the base part, a retainer, a chamber in the retainer, second catch means parts on the retainer to co-act with the first catch means parts and releasably mount the retainer on the base part with the posts within the retainer chamber, an electrically conductive bridging member housed in the retainer chamber, curved contact surface means on said bridging member and correspondingly curved contact surface means on said posts, resilient biassing means housed in the. retainer chamber urging the curved contact surface means of the posts and the bridging member into engagement and thereby conductively connect the posts, the weight of the retainer is such that when acceleration or deceleration forces above a predetermined value are applied to the circuit breaker the first and second catch means will disengage resulting in the release of the bridging member and the interruption of the electrically conductive path between said posts.

Presently preferred forms of the invention will now be described with reference to the accompanying drawings, in which:

Fig.l is a cross-sectional elevation of one form of the circuit breaker with a first type of base to a much

enlarged scale,

Fig.2 is a sectional elevation of one form of cover for the retainer of the circuit breaker, to the same scale, Fig.3 is a cross-sectional elevation of a second type of base, to the scale of Fig.l,

Fig.4 is a plan view of the base shown in Fig.3, and Fig.5 is a schematic circuit diagram showing the circuit breaker in a typical motor vehicel electrical circuit. As illustrated in Fig.l the circuit breaker has a base 1 with two parts 2 and 3 each comprised of a lug 4 with a hole 5 therethrough whereby the parts 2 and 3 can be clamped to the ends of a cable to be interrupted by the circuit breaker. The parts 2 and 3 respectively include shells 6 and 7 which are segments of a common body which has been slit diametrically, hereinafter the parts 2 and 3 may be referred to as a part pair 2/3. The shells each comprise a lower portion 8 with a trench 9 therein and the two shells of the part pair 2/3 are held connected by a plug 10 made of insulation material with an upstanding annular rib 11 housed in the trench 9 of the part pair 2/3.

There is a counterbore 12 in the upper portion of the part pair 2/3 to form two posts 19 and housed in the counterbore 12 there is a bush 13 of insulation material with a hole therethrough and a bolt 14 passes through the bush 13 and through a hole 15 between the part pair 2/3 and through a hole 16 through the plug 10 and there is a nut 17 threaded onto the bolt 14. The

bolt serves two purposes, namely to hold the bush 13 in place and tightly in the counterbore 12 to maintain the gap 18 between the posts 19 of the shells 6 and 7 and to provide a means whereby the circuit breaker can be mounted in an operational position.

The part pair 2/3 has at its upper end an outwardly curved lip 20 engageable by a plurality of resilient fingers 21 of a weighted cap-like retainer 22 thereby to releasably hold the retainer 22 on the part pair 2/3. The retainer 22 is made of a non-conductive material, e.g. a plastic material, and includes a metal weight 23 bonded to a hub 24 for the fingers 21. There is a hole 25 through the weight 23 at its upper end in communication with a counterbore 26 in the weight 23. A bush 27 with a head 28 has a body part which is slidably mounted in the hole 25 and the movement of the bush in an inward direction is limited by the head of a screw 29 and a compression spring 30 under tension between the shoulder 31 and the bush head 28 biases the bush 27 inwardly.

The bush head 28 is seated in a recess 32 in the back face of a circular contact member 33 which has a flat top 34 and curved contact face 35. The inner surfaces 36 of the ends of the posts 19 is complementarily contoured to the curvature of the contact face 35 of the contact member 33 and the resilient bias applied by the spring 30 forces the contact face 35 into contact with the contact surface

36 thereby bridging between and forming an electrically conductive path between the posts 19 and part pair 2/3. It is to be noted that in the assembled configuration with the surfaces 35 and 36 in contact there is a clearance indicated 37 between the screw head 29 and the outer end 38 of the weighted retainer 22.

As will be understood the first and second catch means consisting of the surface 20 and the fingers 21 provides a releasable connection between the retainer 22 and the base 1. The strength of the catch means is such as to hold the retainer 22 and the part pair 2/3 connected and resist the tension applied by the spring 30. When the circuit breaker is subjected to an acceleration or a deceleration which exceeds a predetermined value (which is predetermined having regard to the weight of the retainer 22 and the strength of the spring 30) the grip between the fingers 21 and surface 20 will be overcome and the retainer 22 will dislodge from the part pair 2/3. There will be disconnection of the curved surfaces 35 and 36 and the circuit will be broken between the lugs 4.

It will be clear from the illustration and description that the mating curved surfaces 35 and 36 provide an excellent conductive path for electrical current. At the same time they provide a smooth and continuous travel path during the dislodging movement of the retainer 22 relative to the base 1 under the influence of accelerating or decelerating forces in excess of the predetermined values.

The foregoing description has dealt with the mechanical aspects of the circuit breaker. There is a preferred addition to the arrangement just described and that is a cover member indicated 39 in Fig.l in broken lines and shown in detail in Fig.2. The cover 39 has several special features all for specific purposes.

It is made of an insulating material and it is resilient, there are a number of suitable plastics material from which the cover can be made. The cover body part 50 is of concertina form allowing longitudinal expansion and contraction and it has a diameter allowing the retainer 22 to release from the posts 19. The cover has a closed end 51 and an open end 52. Internally adjacent the closed end of the cover there is an inwardly projecting flange 54 adapted to engage in the groove 55 in the retainer weight 23. At the open end 52 of the cover there is an inwardly projection flange 53 to engage under a lip 48 on the base 1.

In an assembled operative circuit breaker according to the invention the cover 39 will be under compression sufficient (in the event the retainer 22 becomes separated from the base 1) to hold the contact surfaces 35-36 apart thereby preventing any unintentioned reconnection of pasts 19. Naturally, the expansion force resulting from the forced compression of the cover 39 is not of a magnitude to cause the

separation of the retainer 22 and the base l.

The cover 39 serves several purposes. One has been disclosed above. Another is to exclude road dirt and the like from coming into contact with the surfaces 35-36. Another is to hold captive the retainer 22 (in the vent of separation from the base 1) otherwise the retainer could be lost. It is to be understood that the retainer 22 can be manually disconnected from the base 1 to serve as a security device. With the cover 39 in place and the retainer 22 uncoupled from the base 1 a thief would be baffled as to why the electrical system is immobilised.

If additional security is required the cover 39 complete with the retainer 22 can be removed and taken with the driver when he leaves the vehicle. Whilst it is optional where the circuit breaker is located a position adjacent the battery of the vehicle is favoured. If on the other hand it is the intention of the user to have the removability of the retainer as a security means the circuit breaker can be located in a non-obvious location to hide it presence from a would-be car thief.

Referring now to Figs.3 and 4 there is shown a base 1 for the circuit breaker which differs from that illustrated in Fig.l. The base includes shells 56 and 57 which are the equivalents of the shells 6 and 7 of the Fig.l embodiment. The shape of the shells 56 and 57 can be readily seen in Fig.3 and it will be noted that the body parts 8 do not have the trench 9 or the

lugs 4 but are provided with threaded holes 58 to receive bolts 59 whereby the circuit breaker can be coupled into a circuit. The body parts 8 of the shells 56 and 57 are embedded in a base part 60 made of insulation material with suitable insulation properties. In effect this is a modification of the plug 10 of Fig.l. Rather than provide the through bolt 14 of Fig.l for the purpose of mounting the circuit breaker there are lugs 61 with holes 62 therethrough to facilitate the mounting of the device.

At the top of the base 60 there is an outwardly projection circular lip 62 for the retention of a cover 39 in the manner described with reference to Fig.l.

It is to be understood that the lip 62 can be part of the posts 19 as described above with reference to Fig.l.

Fig.5 is a representative installation arrangement where the battery is identified 70, the circuit breaker of this invention is identified 71 and the circuit breaker lugs are 72 and 73 and are connected respectively to the battery negative terminal and the vehicle body as the earth connection. The terminal 74 of the circuit breaker is connected to the contact member 33 of the circuit breaker 71. The component 75 is a relay and the component 76 is the ignition switch of the vehicle electrical system. The terminal 77 of the relay 75 is connected to the terminal 74 of the circuit breaker. The terminal 78 of the relay is

connected to the positive terminal of the ignition coil 83 (or in the case of a connection to the fuel injection system for the engine to the positive terminal of that unit). The relay terminals 79 and 80 are connected to the ignition switch so that when the ignition switch 76 is turned on current flows to the relay terminals 79 and 80. The result of the ignition switch being turned on is to pass current through the coil 81 in the relay and to earth through 77, 74, 33 and 73. The energisation of the coil 83 causes the relay switch 82 to operate and current will flow through relay terminal 78 to the ignition coil 83.

In the event of the circuit breaker being activated the earth connection from relay terminal 77 to the earth connection 73 will be broken and the current flow to the engine ignition coil will be interrupted. In addition, as the circuit breaker provides the earth connection for the battery all other battery powered devices will be automatically de-powered.

The foregoing is a description of preferred features of the circuit breaker of the invention. It it is to be understood that non-inventive changes can be made to the form and/or arrangement of the various components without departing from the inventive concept as set out in the following claims.