The present invention relates to an isolator for vehicles, which serves to isolate the electrical systems of the vehicle from the battery in the event of an impact, so as to minimise the risk of fire. Various isolator devices for vehicles have been proposed hitherto but they have all suffered from certain drawbacks and limitations which are overcome by the isolator which we have now devised,

In accordance with this invention, there is pro- vided an electrical isolator for installation in a vehicle, comprising first contacts for connecting the live terminal of the vehicle battery to an output supplying the vehicle electrical systems, at least one sensor responsive to impact of the vehicle to trigger the isolator and open said first contacts and further to close second contacts which serve to connect said output to ground.

Thus this isolator serves an important function of changing the polarity of its output from "live" to ground in the event of an impact. Therefore not only is the vehicle battery disconnected from the vehicle electrical systems, but in addition the electrical systems are connec¬ ted to ground by the isolator. This ensures that no current can be generated by the alternator or dynamo of the vehicle by self-excitation or residual field current,

which might keep the engine running and the electrical systems supplied if the battery were merely disconnected. Also any capacitors included in the electrical systems will discharge immediately and so be prevented from being the cause of any spark (which could conceivably commence a fire). The function of grounding the isolator output has not been provided by any prior isolator devices.

Preferably the or each impact sensor is in the form of an impact strip, so as to respond to direct impact. This is a marked improvement over inertia-type sensors pro¬ posed previously, which are not always reliable in operation and are only effective in the event of a head-on crash of the vehicle. Impact strips may be mounted along the front and rear bumpers of the vehicle and along its side and door panels, so that an impact from any direction will be sensed, and whether the vehicle itself strikes another vehicle or object or whether another vehicle runs into the vehicle concerned (even if the latter is stationary).

In addition to sensors responsive to impact, sensors responsive to other hazard conditions may be pro¬ vided and arranged to trigger the isolator as referred to above. For example, sensors may be provided to sense over¬ turning, fire or overheating, and excess current flowing in the vehicle electrical systems. Also, a switch may be pro- vided on the dashboard and operated in an emergency in order to trigger the isolator.

Preferably when the vehicle engine is turned off, the isolator is disabled to ground its output terminal, e.g. using the switch on the dashboard. Then when the vehicle is to be started again, the isolator must be enabled: this may be effected by momentary actuation of a switch (e.g. a push¬ button) on the dashboard, or automatically by turning the ignition key in the ignition switch in the usual way. Also a keyboard may be provided on the dashboard, or an alter- native form of coded system (e.g. infra-red) provided requir ing a predetermined code in order to close switches within

the isolator, such that it will be enabled when the steps just mentioned are carried out. This provides effective anti-theft protection for the vehicle.

Preferably the coded switches, where provided, may be closed by keying-in a secondary code if any of the impact switches becomes damaged, so overriding these switches and allowing the isolator to be enabled and the vehicle to be driven home if it is otherwise still road- worthy after an impact. Preferably the isolator is arranged so that the vehicle headlights and hazard lights are switched on in the event of the isolator being triggered, so as to warn others of a hazard and, if the vehicle is involved in a crash at night, avoid the driver being plunged into darkness, Preferably the current overload sensor comprises a moving coil device, the current.to be monitored flowing through the coil of this device. When a current of pre¬ determined value or greater flows, such that the coil is turned through a predetermined angle against its return spring, a contact which it carries makes with a fixed con¬ tact in order to trigger the isolator.

Embodiments of this invention will now be des¬ cribed by way of examples only and with reference to the accompanying drawings, in which: FIGURE 1 is a circuit diagram of an isolator in accordance with this invention, including an optional modi¬ fication:

FIGURE 2 is a diagram of another modification applicable to the circuit of Figure 1 ; FIGURE 3 shows an impact strip form of sensor in longitudinal and cross-section;

FIGURE 4 is a longitudinal section through an overturn sensing switch which may be used with the isolator of Figures 1 or 2;

FIGURE 5 is a diagram of a current overload sensing arrangement which may be incorporated in the isolator of Figure 1 or 2, and shows also the ignition switch arrangements for the modified isolator of Figure 2; and

FIGURE 6 is a diagram of a circuit which may be used with the isolator of Figure 1 or 2 to switch on the headlights and hazard lights of the vehicle in the event of an impact. Referring to Figure 1, there is shown the electrical circuit of an automatic isolator for a vehicle. The vehicle battery is shown at B2, with its negative ter¬ minal connected to ground and its positive terminal con¬ nected to a terminal P1 of the isolator. A terminal P2 of the isolator is also connected to ground and a further ter¬ minal P3 is connected to a line L for supplying power from the battery B2 to the various electrical systems of the vehicle during normal operation of the vehicle. Preferably the isolator is mounted in the vehicle alongside the vehicle battery B2, except that coded switches S1 and S2 (when pro¬ vided), a switch S3 (preferably a push-button) and a small battery B1 are mounted at the dashboard, and actuating switches S4, S5 are distributed about the vehicle as will be described. Battery B1 may be a dry battery or a re- chargeable battery, in which case a circuit may be included for recharging it from the vehicle system. The isolator comprises a transistor T1 with its collector connected to supply terminal P1 and its emitter connected to ground terminal P2 through a relay winding W1 in series. This relay winding operates two contacts, RE1 which connects line L to ground terminal P2 when the relay is de-energised, and RE2 which connects line L to supply terminal P1 when the relay is energised. The negative side of battery B1 is con¬ nected to ground and its positive side is connectable throug switches S2 and S3 in series to the base of transistor T1.

A second transistor T2 has its collector connected to the collector of transistor T1, its emitter connected through a resistor R2 to the non-ground end of relay winding W1, and its base connected to a terminal P4 of the isolator. Terminal P4 is fed from P3 via resistor R1, a fuse F2 and coded switch S1. Terminal P4 is also connectable to ground through any one of a plurality of actuating switches S4, S5. The actuating switches S4 may include one or more impact switches, which close upon impact of the vehicle, an overturn switch which closes upon the vehicle overturning, and fire or overheat switches which close if a fire or over¬ heating condition is sensed. The actuating switch S5 _> pre¬ ferably a push-button, is mounted on the dashboard and may be used to disable the isolator when the driver leaves the vehicle, and may be used in an emergency by the driver or a passenger (e.g. should the driver collapse) to isolate the vehicle.

The operation of the isolator is as follows. If the coded switches S1, S2 are provided, the driver must key- in a predetermined code on a keyboard K provided at the dashboard in order to close both these switches. Then he must close switch S3 momentarily, which has the effect of passing current to the base of transistor T1 from battery B1 in order to render this transistor conducting momentarily, energising relay winding W1. This opens relay contacts RE1 and closes contacts RE2, firstly to connect line L to the positive terminal of the vehicle battery B2 and secondly to render transistor T2 conductive, by supplying current to its base from P3 via resistor R1, fuse F2 and switch S1. The current which flows through transistor T2 in its con¬ ductive state maintains relay winding W1 energised after transistor T1 returns to its non-conductive state upon re¬ opening of switch S3. Now that the vehicle battery is connected to the line L, current passes to the vehicle electrical systems for operation of the vehicle in the usual way.

Should any of the switches S4, S5 be closed, even momentarily, whilst the vehicle is in use, the terminal P4 will be connected to ground through whichever of switches S4, S5 closed, grounding the base of transistor T2 and immediately rendering it non-conductive and de-energising relay winding W1, opening contacts RE2 and closing contacts RE1. Thus, in response to an impact or another condition to which switches S4 are responsive, or in response to closure of the push-button S5 _» the isolator serves to isolate the supply line L from vehicle battery, and instead ground this line. In that the output terminal P3 of the isolator changes its polarity from positive to negative, all the vehicle electrical systems are grounded: this in particular prevents any current being generated by the vehicle alternator or dynamo by self-excitation or residual field current, which current could keep the engine running and the electrical systems supplied if the battery B2 were simply disconnected. Further any capacitor included in the vehicle electrical systems will discharge immediately and so cannot subsequently be the cause of any spark (which could conceivably commence a fire).

Figure 1 also shows a solenoid SF connected between line L and ground and controlling a valve at the outlet from the fuel tank. If the isolator is triggered, this solenoid is de-energised to close this solenoid- operated fuel valve.

In a modification of the isolator circuit des¬ cribed above, the battery B1 is omitted and current to the base of transistor T1 is provided through a path (shown by dotted lines in Figure 1) connected from the terminal P1 to switch S2 and comprising a fuse F1, resistor R3 and diode D1. The operation of the circuit modified in this way is the same as that described above.

Referring to Figure 2 of the drawings, in another modification of the isolator circuit, the push-

button switch S3 is omitted and the isolator is enabled by the usual ignition switch of the vehicle _* Thus, a path is provided from terminal P1 (the collector of transistor T1) to the base of transistor T1, comprising in series a diode D1, fuse F3, resistor R6, relay contacts RE3 and the (optional) coded switch S2. The junction between con¬ tacts RE3 and resistor R6 is connected through a relay winding W2 to a line I which extends to the ignition switch circuit. In this latter circuit, when the ignition key is turned to its "starter" position in the usual way, a path is completed for current to pass from the vehicle battery B2 through diode D1, fuse F3, resistor R3, winding W2 and along line I: in energising winding W2, contacts RE3 are closed to establish a current path through these contacts and switch S2 to the base of transistor T1. This transistor is rendered conductive and the operation of the isolator circuit is otherwise ^' as described with reference to Figure 1 ,

The impact switches used for switches S4 pre¬ ferably comprise impact strips for example as shown in Figure 3. This strip 10 is formed of resilient rubber or plastics with one, preferably flat, surface 11 for adhering to the vehicle, e.g. to its bumpers and side panels. Its opposite surface 12 forms a contact area for impact with other vehicles or objects, and the strip is formed with a void 13 within its body and extending over its length. In the example shown, this void is rectangular in section: its opposite surfaces are provided with opposed electrodes 14, 15. One of these electrodes is connected to ground and the other is connected to the terminal P4 of the isolator (Figure 1). Preferably impact strips such as shown in

Figure 3 are mounted along the front and rear bumpers of the vehicle and all along the door and body panels of each side of the vehicle at the same level. Then if in normal use of the vehicle an impact occurs of sufficient force against any one of the impact strips, t.he particular

impact strip concerned will be deformed at least at some point along its length, so as to bring its two electrodes 14, 15 into contact, if only momentarily. The effect of this is to trigger the isolator, as described previously with reference to Figure 1.

An example of overturn switch is shown in Figure 4. This comprises a V-shaped tube 20 housing a drop of mercury M. The two ends of the tube are closed but adjacent each end a pair of electrodes 21, 22 are provided, one electrode of each pair being connected to ground and the other to the terminal P4 of the isolator. With the switch mounted for example in a transverse plane of the vehicle, with its apex pointing downwards and its ends at a common height, then if the vehicle rolls through more than a certain angle to one side or the other, the mercury will travel up one or other limb of the tube and bridge the respective pair of electrodes 21, 22: this has the effect of triggering the isolator as described pre¬ viously. For responding to an end-to-end overturn of the vehicle, the switch would need to be mounted in a length¬ wise plane of the vehicle, or preferably two such switches are provided, one for responding to sideways rolls and the other for responding to end-to-end overturns, the angle between the two limbs of the tube of each switch being appropriate to its purpose. Instead a single switch may replace these two switches, for example comprising two generally conical members fitting one-inside-the-other . but with a spacing, having annular, opposed electrodes at their wider ends and housing the drop of mercury between them at their apices.

Figure 5 shows a current overload sensing arrangement with which the isolator of Figure 1 may be provided. A moving coil device A1 is provided with its coil connected in series in the path within the isolator leading to terminal P3. Thus the greater the current being

drawn by the vehicle electrical systems from the battery B2 through the isolator, the greater will the coil of device A1 turn about its axis within a magnetic field provided by a permanent magnet of the device. If a current of greater than a predetermined value is drawn through the moving coil, it will turn through a sufficient angle for contacts S6 to make: one of these contacts is fixed (but adjustable) and connected to the base of a transistor T4 via a resistor- R5 whilst the other of these contacts is carried by and connected to the moving coil. Thus when the contacts S6 make, current flows from the coil and to the base of tran¬ sistor T4 to render the latter conductive. Transistor T4 is connected between the point P4 of the isolator circuit (Figure 1) and ground, so that when conductive it grounds the base of transistor T2 to trigger the isolator in the same manner as described previously. Figure 5 also shows the ignition switch arrangements for the circuit of Figure 1 : the terminal P3 is connected through a transistor T3 to the ignition circuit and through a diode D2 to a movable contact KY of the ignition switch, which is also connected to the line I which extends to the winding W2 of Figure 2. The contact KY has an OFF position shown by the dotted line, but when the ignition key is turned, this moves the contact KY to make with a contact KI at one end of a base of tran- sistor T3. If the key is turned to the "starter" position, contact KY is still made with contact KI but also makes with a contact KS at one end of the solenoid RE4 for the starter motor. Current then flows from the vehicle battery positive terminal through diode D1, fuse F3, resistor contact KS and starter solenoid RE4 to ground. This current serves to energise relay W2 and close contacts RE3 _> enabling the isolator as described previously. Current then passes through the isolator to terminal P3 and through transistor T3 to the ignition circuit, transistor T3 being rendered conductive by the current passing through contacts KY, KI and resistor R4 to its base. Transistor T3 is maintained

conducting when the contact KY returns to its intermediate position once the vehicle engine has started.

Figure 6 shows a circuit which may be used with the isolator device in order that the headlights and hazard lights to be switched on in the event of the isolator being triggered. The circuit of Figure 6 also provides further anti-theft protection. A line L1 is connected directly to the positive terminal of the battery B2. Relay windings W4, W5 are connected in series with fuses F4, F5 to one side of a switch S8 and to one of two movable contacts of a switch S7: the other movable contact of switch S7 is connected through a relay winding W6 and a door switch S9 to ground. The fixed contacts of switch S7 are connected respectively through a delay circuit DE1 and directly to opposite sides of an alarm horn H1. This horn is connected in series with one of a-pair of" contacts RE6 between line L1 and ground. The other contact RE6 is connected between door switch S9 and ground. Winding W4 controls contacts RE4 in a path from fuse F4 to the headlights H2 (which for normal use are energised via diode D3). Winding W5 con¬ trols contacts RE5 in a path from fuse F5 to a hazard lights flasher unit H3 which- operates hazard lights H4 (and which for normal use are energised via a switch S10). The movable contact of switch Sδ is connected to line L from the isolator output terminal P3: its other fixed contact is connected through a flasher unit SF1 and a lamp H5 to ground.

The operation of the circuit of Figure 6 is as follows. As the driver leaves the vehicle, he will close switch S7 (which will be positioned in a secret location). Then if the vehicle is broken into by opening any door, one of a number of respective door switches S9 will be closed to energise winding W6 and close its contacts RE6, one to maintain energisation of winding W6 and the other to complete a path for energising alarm horn H1 and wind¬ ings W4, W5 to close contacts RE4 and RE5 and energise the headlights and hazard lights. If in the normal course the

driver returns to the car, he must open switch S7, then when he enables the isolator current will flow along line L and through switch S8 to cause lamp H5 on the dashboard to flash. The driver then changes over switch S8 to stop this flashing before driving away. In the event of the isolator being triggered, line L will be connected to ground as previously described: as a result, relay wind¬ ings W4 and W5 will be energised to close contacts RE4 and RE5 and energise the headlights H2 and hazard lights H4. Delay circuit DE1 provides a delay, after the driver closes switch S7, before alarm horn H1 will be energised, to enable him to leave the car and close the door before this time expires.

It will be appreciated that the isolator which has been described is an electronic device which may be mounted in a small housing for fitting alongside the vehicle battery. When the isolator is disabled, no current goes beyond its input side and its output is connected to ground. The only wires which extend from the isolator (for the purpose of enabling it) carry only very low current.