The invention relates to a battery protection unit for attachment to a vehicle battery.

A large number of different systems to prevent or protect against the theft of motor vehicles have been known for some time, many of which are remotely controlled via a small transmitter which, as a general rule, require official approval, and with some of the systems also containing contacts or relays with the ability to block parts of the vehicle' s electrical system. Also, now that it has become more common for new vehicles to be fitted with electric fuel pumps, devices have been developed which automatically interrupt the power supply to the vehicle' s fuel pump in the event of a collision in order to reduce the risk of fire or explosion. However, the majority of the aforementioned systems are either factory-fitted or call for complicated and expensive installation in a workshop. Also, the systems are generally expensive to purchase.

Now that an increasing number of countries are introducing legislation governing the use of dipped headlights when driving during daylight hours, with the associated increasing risk of forgetting to switch off

the lights when parking, and new vehicles are generally being equipped with increasingly advanced and power-consuming electronics such as car telephones and on-board computers, etc. , it would be a distinct advantage if there were to be a small, simple device which would disconnect the battery automatically if there were a risk of it becoming discharged when parked, or if the vehicle were to be subjected to a certain level of impact or collision, and which would also have the effect of rendering theft more difficult.

An object of the present invention is to create a small, cheap, simple, multi-functional and easily installed arrangement, which is accessible to all vehicle owners and is controlled by equipment which is not necessarily subject to official approval.

The invention provides a battery protection unit for attachment to a vehicle battery, comprising first detection means for detecting an unacceptable drop in the voltage of the battery, second detection means for detecting that the vehicle has been involved in a collision, switch means for isolating the battery completely or for isolating the battery from the starter motor of the vehicle, and override means for overriding the switch means, the arrangement being such that the battery is isolated completely in the event that either the first detection means detects that the battery voltage has dropped to an unacceptable level or that the

second detection means detects that the vehicle has been involved in a collision, and that the battery can be isolated from the starter motor of the vehicle in the absence of operation of the override means. Such a unit protects the battery by preventing excessive use when the battery voltage is reduced, renders the vehicle safer by the automatic isolation of the battery in the event of involvement in a collision and also acts as an anti-theft device.

Preferably, the battery is isolated from the starter motor in the absence of operation of the override means only when a current of at least 3 amperes is attempted to be drawn from the battery. This allows operation of some other battery-powered functions of the vehicle but will not allow operation of the starter motor.

Preferably, the override means are actuable from the interior of the vehicle, more preferably by insertion of a code transmitter into the cigarette-lighter socket of the vehicle. This allows convenient operation of the override means.

The invention also provides a battery in combination with a battery protection unit as described above, and also a vehicle incorporating a battery incorporating such a battery protection unit.

An embodiment of the invention will now be described wherein;

Figure 1 shows the location of a battery protection unit according to the invention in relation to a vehicle battery;

Figure 2 is a schematic diagram of the protection unit according to the invention; and

Figure 3 illustrates an advantageous embodiment of a battery protection unit according to the invention.

A unit according to the invention consists of a small unit, which is either factory-fitted inside a vehicle battery 1, or is incorporated within an access-denying capsule 2 equipped with a lockable lid fitted and locked securely above the battery so that it covers the positive battery terminal, the current being taken from a corresponding pole 3 mounted on the outside of the capsule.

The unit comprises a main relay or a main contact 4, which can be actuated by means of a control circuit 5 present inside the capsule, which control circuit in turn comprises equipment such that it is capable of being primed so that it either opens or closes the battery circuit, or so that it is prepared to interrupt the circuit when a current in excess of, for example, 3 amperes is drawn.

The control circuit 5 is designed in such a way that it can only be actuated in response to a coded signal in the vehicle' s existing electrical system, input for example via a code transmitter 6 which is inserted into

the vehicle' s existing cigarette-lighter socket. In this way, the capsule 2 acts as an anti-theft device since the starter motor of the vehicle cannot be operated without the coded transmitter being inserted into the cigarette-lighter socket of the vehicle. Thus, even if an unauthorised person gains entry to the vehicle, the vehicle cannot be started for unauthorised removal. Any convenient way of introducing the coded signal to the electrical system would be acceptable.

The control circuit 5 also contains equipment of a kind such that, via a small voltage-sensing circuit 7, it will completely disconnect the electrical system of the vehicle in the event of the voltage of the battery falling below a desired level while the vehicle is parked. Also connected to the control circuit is an impact sensor 8, which may be installed on the capsule 2 or at some other point in the engine compartment 9 of the vehicle, and which, when it is caused to move with sufficient force, instructs the control circuit 5 to disconnect the battery circuit completely.

Thus, the vehicle is rendered safer by the automatic isolation of the battery in the event of involvement in a collision, and the battery is protected from irreparable damage by preventing excessive use when the battery voltage is reduced.

In order to permit a limited power supply to be provided to the vehicle' s automatic control and central

locking systems etc. when the main relay 4 is disconnected, ie. with the capsule in the anti-theft mode, the capsule can be equipped with a circuit 10 which by-passes the main relay 4 and runs to the external pole 3 of the capsule and incorporates an automatic fuse 11 which trips at a current consumption in excess of 3 amperes, for example. The fuse 11 will then trip if an attempt is made to start the vehicle.

It is possible, however, to provide a design of the capsule such that it does not actually operate the main relay 4 on every insertion of the code transmitter 6, but simply prepares or arms the control circuit 5 so that it will only trigger the main relay 4 so that the current is interrupted completely in the event of an unauthorised attempt at starting the vehicle being made (current consumption demand in excess of 3 amperes, for example).

A design of this kind, which is characterised in that the control circuit 5 only operates the main relay 4 in the event of an actual incident (ie. collision, voltage drop when parked, or attempted theft) offers the advantage inter alia that the service life of the main relay 4 is extended by the number of main relay operations being reduced to a minimum. A design of this kind, instead of incorporating an automatic fuse 11, is equipped with a current intensity sensing contact 12 as illustrated in Figure 3 via which contact a small

proportion of the main current is always conducted. This is achieved by dividing the main current conductor into a series of parallel smaller conductors 16, each dimensioned so as to conduct an equal proportion of the main current. One of the smaller conductors leads to the current intensity sensing contact 12 and is designed to have the same overall electrical resistance as the remaining smaller conductors 16.

This current intensity sensing contact 12 consists of a coil 14 containing a spring-loaded magnet 15 which, when the field strength on the coil is sufficiently high, for example above 3 amperes, closes the circuit to the control relay 5 which, provided that it is appropriately positioned, will then immediately trigger the main relay 4 so that the main current is interrupted.

If the capsule is constructed in accordance with this latter principle, ie. so that the main relay is only caused to interrupt the main current in the event of actual incidents, the additional advantage will be achieved in that the field coil of the main relay can be made smaller, which is desirable from the point of view of the size of the capsule, given that the driving force in the field coil in the direction in which the relay interrupts the current can be strengthened by means of a manually tensioned spring 16, in such a way that the main relay can be made to be triggered like a striker spring, for example.

As already mentioned, the capsule 2 is provided with a lockable lid which can be opened by means of a key, and the main relay is designed in such a way that, irrespective of the position of the control relay 5, it is capable of manual operation and locking in the desired position at all times by means of a rocker arm 13 or a similar arrangement. This is to ensure that the vehicle can be used even if the coded key should be lost, or if a fault has occurred in any of the component parts of the capsule.

Each capsule is controlled specifically by an encoded device belonging specifically to each capsule. This encoded device or coded key is supplied in sets of three; one to be kept as a spare in a safe place, one to be fitted inside the capsule at the time of its installation, and one to the inserted in the code transmitter 6 inside the passenger compartment of the vehicle when it is desired to arm or disarm the capsule.