GB2057737A

GB2057737A - Anti-theft system for a motor vehicle

Info

Publication number: GB2057737A
Application number: GB8022745A
Authority: GB
Original assignee: Felten and Guilleaume AG
Current assignee: Felten and Guilleaume AG
Priority date: 1979-07-13
Filing date: 1980-07-11
Publication date: 1981-04-01
Also published as: SE8005111L; IT1133456B; SE439282B; FR2460815A1; FR2460815B1; GB2057737B; ES8105207A1; IT8012596A0; ES493337A0

Abstract

An anti-theft system for a motor vehicle comprises an electrically- powered alarm, a switching device 10 for actuating the alarm, and an electric circuit 11 connecting the switching device and the alarm. The switching device is attached to the motor vehicle, and is provided with electrical contacts 13, 17 which automatically close the electric circuit 11 when the vehicle is in an inclined position. <IMAGE>

Description

SPECIFICATION Anti-theft system for a motor vehicle This invention relates to an anti-theft system for a motor vehicle, and in particular to an anti-theft system having an electrically-powered alarm which is actuated by a switching device connected to a motor vehicle.

Anti-theft systems for motor vehicles are known that are equipped with electrical contacts which actuate the vehicle horn when an attempt is made to open the door. These known anti-theft systems are, however, only effective when unauthorised persons attempt to enter the vehicle. They do not respond upon removal of vehicle parts, particularly road wheels, which are accessible from the outside.

Anti-theft systems are also known which become effective when the vehicle is shaken.

Although these known anti-theft systems set off the alarm when an unauthorised person interferes with the outside of the vehicle, they are very sensitive and also react to external influences that have nothing to do with attempts at theft, for example, when a heavy vehicle passes close by, or when strong gusts of wind shake the parked vehicle.

The aim of the invention is to provide a simple, economical and reliable anti-theft system that responds when an attempt is made to remove the wheels from the vehicle, or to load the entire vehicle on to another and to carry it away, the system not reacting however, to innocent external influences.

The present invention provides an anti-theft system for a motor vehicle, the system comprising an electrically-powered alarm, a switching device for actuating the alarm, and an electric circuit connecting the switching device and the alarm, the switching device being attached, in use, to the motor vehicle, wherein the switching device is provided with electrical contacts which automatically close the electric circuit when the vehicle is in an inclined poSition.

This system offers the advantage that the alarm is not actuated by short-term vibrations of any kind. However, the alarm is reliably actuated when the vehicle is moved along an inclined surface onto another vehicle, or when the vehicle is tilted to one side, for example, for the purpose of removing a road wheel.

Preferably, the switching device has a housing defining a chamber which is partially filled with an electrically-conductive fluid, the electrical contacts being contactable with said fluid. A switching device of this kind can be produced in a simple and economical manner and operates reliably. It can be fitted in a very small space and at practically any position on the vehicle, and the chamber can be filled to a level that exactly suits that inclined position of the particular vehicle that is necessary for raising a wheel of the vehicle from the ground. The same switching device can, therefore, be used for all types of vehicles.

In one preferred embodiment, an electrical contact is provided in the zone of the floor of said chamber, and at least one electrical contact is provided in the upper zone of said chamber, the system being such that the floor contact is electrically connectible to the or each upper contact only by said fluid. Advantageously, the housing is made of electrically non-conductive material, a floor plate made of electrically-conductive material constituting the floor contact.Conveniently, the housing is generally cylindrical, and there are a plurality of upper contacts constituted by electricallyconductive rings, the rings being attached to the cylindrical wall of the housing and being positioned at different distances from the floor plate, and wherein the rings are connected to an electronic analysis device which is such as to actuate the alarm upon a change in the inclination of the housing. The analysis device is so designed that it determines the initial orientation of the housing when the alarm is primed, and only actuates the alarm when the orientation of the housing is changed. The rings are expediently embedded in the cylindrical wall of the housing. This prevents said fluid, which washes backwards and forwards during travel, from becoming suspended in the form of drops from the rings, and from causing unrequired contact.For the same reason, it is expedient if the side walls of the housing have inner surfaces which cannot be wetted by said fluid.

Advantageously, the housing of the switching device is a cup-shaped plastics vessel which is closed off, at its top, by a cover.

Such a vessel can be held and retained in a vertical position on the vehicle when the alarm is primed. Preferably, the cover is made of metal and constitutes the upper contact, in which case an insulated conductor passes through the cover and is connected to the floor plate. This arrangement is particularly simple and economical to produce. The constant vertical position of the housing in the vehicle can be achieved by suspending the housing on gimbals, and by means of a weight at its lower end, and the housing can be immobilised by an electro-magnetic when the alarm is primed.

In other preferred embodiment, the electrical contacts are immersible sensors which extend downwards into said chamber to differing extents, said fluid being the only means for electrically connecting the sensors. Advantageously, the housing is a cup-shaped vessel whose top is closed off by a cover, and the sensors depend from the cover into said chamber. The use of immersible sensors as contacts offers the advantage, among others, that point-contact is established at the bottom ends of the sensors, and surface leakage currents cannot occur along the inner wall of the housing when said fluid washes back from the contacts. In this arrangement, the lower end of each immersible sensor defines a certain level, up to which said fluid can rise when relatively pronounced tilting or inclination of the vehicle occurs.

Preferably, there are a plurality of groups of sensors, the sensors of each group having the same length and the sensors of the different groups having different lengths, in which case the sensors of each group are connected by a common conductor to an electronic analysis device. Conveniently, one group of sensors extends into said chamber to terminate adjacent to the floor thereof. This ensures a reliable switching action, irrespective of the side to which the housing is tilted along with the vehicle.

The housing may be cylindrical, and the sensors may be distributed on radial lines extending from the central axis of the housing. These lines may extend from the central axis of the housing in a star-like formation, and form with each other angles of 1 80', 90 or, preferably, 120 . In this case, it is advantageous if the negative terminal of the switching device is connected to one immersible sensor which extends almost to the floor of the housing. This immersible sensor can be arranged in the middle of the housing.

Advantageously, the sensors of each group are arranged at the corners of a substantially equilateral triangle. This results in great reliability in the switching action, irrespective of the direction in which the housing, along with the vehicle, is tilted.

Preferably, the sensors are arranged adjacent to the inner surface of the outer wall of the housing. This offers the advantage that the highest possible switching position is achieved, since, even when the vehicle is slightly inclined, the greatest fluctuation in fluid-level in the housing can be used for switching operation. This is because each sensor is electrically connected, via said fluid, with a diametrically-opposed sensor which leads to the negative terminal and is disposed diametrically opposite thereto.

Advantageously, said chamber is annular, the annular chamber being adjacent to the outer wall of the housing, and surrounding a cylindrical chamber which accommodates the electronic analysis device. This arrangement offers the advantage that relatively little electrically-conductive fluid is needed. It also has the advantage of accommodating the analysis device within the protection of the housing interior. A further advantage is that the leads from the immersible sensors to the analysis device are very short.

When use is made of an annular chamber, the immersible sensors are expediently distributed around a circle. Such an arrangement is easy to produce, and guarantees fluid-tight, mutually-insulated seats for the individual sensors in the cover. Moreover, the leads running to the sensors can be passed, in a fluid-tight manner, through the cover and into the inter-ior of the housing.

Preferably, the sensors are arranged in two sets, one set having sensors on both sides of a first housing axis, and the other set having sensors on both sides of a second housing axis which is perpendicular to said first housing axis, and wherein the sensors of said one set are connected to the analysis device independently of the sensors of said other set.

This makes it possible to detect different inclined positions of the vehicle separately, since the inclination of the vehicle in one of the directions does not affect the sensors for the other direction. it will generally suffice if the lower ends of each two oppositely-disposed sensors form a line in the switching system at each of the levels to be probed.

Expediently, the housing is attached, in use, to the motor vehicle in such a manner that said first housing axis is parallel to the longitudinal axis of the vehicle, and said second housing axis is parallel to the transverse axis of the vehicle. The sensors of each set may be arranged on a pair of parallel lines, the sensors being equispaced on their respective lines. In order to achieve the greatest possible uniformity in the sensitivity in the response of the anti-theft system in each possible direction in which the vehicle may tilt, the sensors of said second set are spaced apart by distances greater than those by which the sensors of said first set are spaced.

Advantageously, said chamber is divided into a plurality of chamber parts by means of walls, the walls being such that the chamber parts are in fluid communication with each other. Preferably, the walls are arranged to be immersible in said fluid, and to terminate adjacent to the floor of the housing.

The immersible walls extending into said fluid allow said fluid to rise and fall at only a moderate rate. This is because fluid can only flow between the chamber parts below the immersible walls. Splashing of said fluid is suppressed, since the surface area of the fluid is relatively small in each of the chamber parts. The immersible walls may extend as far as the cover of the housing.

Preferably, there are four walls arranged at right-angles to each other. This is particularly advantageous where the chamber is annular, as the immersible walls divide the chamber into a plurality of segmental chamber parts, each of which contains immersible sensors.

Advantageously, the housing is attached, in use, to the motor vehicle in such a manner that each of said walls is inclined to the longitudinal axis of the vehicle. Thus, maximum damping down of fluctuations in the fluid level during shaking movements is achieved both in the longitudinal and the transverse directions.

Various electrically-conductive fluids can be used, provided they are able to retain their electrically-conductive properties in the temperature range prescribed. Triphenylchloromethane or triphenylfluoromethane may be used as the electrically-conductive fluid. It is preferable, however for the fluid to contain a metal salt, and a mixture of glycerine and copper sulphate is particularly suitable. A fluid of this kind possesses a certain viscosity and flows in a relatively inert manner, so that movements in the fluid level are also relatively slow.

Several forms of switching device, for use in anti-theft.systems constructed in accordance with the invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a vertical cross-section through a first form of switching device, the switching device being in its non-operating position; Figure 2 is a vertical cross-section similar to that of Fig. 1 but showing the first form of switching device in the switching position; Figure 3 is a vertical cross-section through a second form of switching device in the switching position; Figure 4 is a vertical cross-section of a third form of switching device; Figure 5 is a cross-section taken on the line V-V of Fig. 4, the analysis device being omitted from this figure; Figure 6 is a cross-section taken on the line VI-VI of Fig. 5;; Figure 7 is a horizontal cross-section of a fourth form of switching device; Figure 8 is a cross-section taken on the line VIII-VIII of Fig. 7; Figure 9 is a horizontal cross-section of a fifth form of switching device; Figure 10 is a vertical cross-section of a sixth form of switching device; Figure 11 is a cross-section taken on the line Xl-Xl of Fig. 10; Figure 12 is a horizontal cross-section of a seventh form of switching device; Figure 13 is a cross-section taken on the line Xlll-Xlll of Fig. 12; Figure 14 is a cross-section taken on the line XIV-XIV of Fig. 12; Figure 15 is a horizontal cross-section of an eighth form of switching device; Figure 16 is a vertical cross-section of a ninth form of switching device; Figure 1 7 is a cross-section taken on the line XVII-XVII of Fig. 16; and Figure 18 is a horizontal cross-section of a tenth form of switching device.

Referring to the drawings, Figs. 1 and 2 show a first form of switching device 10 having a hollow, cylindrical housing 14, the cylindrical wall 1 5 and the floor 1 6 of which are made of an electrically non-conductive material, for example a polyethylene or polypropylene plastics material. The inside of the floor 1 6 is covered by a floor plate 1 7 of electrically conductive material, preferably copper. An insulated conductor 1 8 is soldered to the floor plate 17, the insulated conductor extending upwardly within the housing 14, and passing through a cover 1 9 to the exterior of the housing. The cover 1 9 closes off the housing 14 at its top.Like the floor plate 17, the cover 1 9 is made of copper. At the peripheral edge 20 of the housing 14, the cover 1 9 is provided with a seal 21. A seal 22 is also provided in the cover 19, the conductor 1 8 passing through the seal 22. A further conductor 1 3 is connected to the cover 1 9. The conductor 1 3 constitutes a negative terminal of an alarm circuit 11, the conductor 1 8 being the positive terminal. Of the alarm circuit 11, only the wires 1 2 and 13, leading respectively from the positive and negative terminals, are shown.

An electrically-conductive fluid 23 is provided within the housing 14. This fluid may be, for example, a mixture of glycerine and copper sulphate, triphenylchloromethane or triphenylfluoromethane.

The housing 14 is suspended on gimbals (not shown) at a suitable place in a motor vehicle in such a manner that, when the vehicle is parked, the axis of the housing 14 is vertical, as shown in Fig. 1, even if the vehicle is inclined in the longitudinal or transverse direction, for example when the vehicle is parked on a hill, or with the wheels on one side of the vehicle resting on the pavement.

The housing 14 is then secured with the alarm unit (not shown) primed and in the position illustrated in Fig. 1. This can be done, for example, with the aid of an electromagnet (not shown) fitted to the vehicle. The coil of the magnet is energised, when the alarm unit is switched on, so that the magnet holds a steel plate (not shown) which is fixed to the exterior of the housing 1 4.

If the orientation of the vehicle, and therefore the orientation of the housing 14, is then altered by, for example, raising the vehicle at one side, the housing assumes an inclined orientation as shown, for example, in Fig. 2.

Since the fluid level 24 remains horizontal, it will touch the cover 1 9 at a predetermined inclination. Then the fluid 23 makes electrical contact between the cover 1 9 and the floor plate 17, so that the circuit between the wires 1 2 and 1 3 is closed, and the alarm is set off.

The inner surface 25 of the cylindrical wall 1 5 of the housing 1 4 is such that it cannot be wetted by the fluid 23. For this purpose, the housing 1 4 can be made of a non-wetting plastics material, or the inner surface 25 of the housing can be provided with a nonwetting coating.

Fig. 3 shows a second form of switching device 10 having a hollow cylindrical housing 14 similar to that of the switching device of Figs. 1 and 2. The housing 14 is provided with a cover 41, and both the housing and the cover are made of plastics material. As with the embodiment shown in Figs. 1 and 2, the floor 1 6 of the housing 14 is covered by a copper floor plate 1 7, to which is soldered an insulated conductor 1 8 which passes to the exterior of the housing through the cover 411.

Instead of the conductor 13, however, the upper part 42 of the housing 14 of the embodiment of Fig. 3 is provided with three copper contact rings 43, 44 and 45. The rings 43, 44 and 45 are set into the inner surface of the cylindrical wall 1 5 of the housing 14, and are arranged parallel with the floor 1 6 and at a distance from each other.

The contact rings 43, 44 and 45 are connected to conductors 46, 47 and 48 respectively. The conductors 46, 47 and 48 lead to a device 49 for the digital analysis of the orientation of the housing 14. As in the embodiment of Figs. 1 and 2, the housing 14 is partly filled with a conductive fluid 23, the level of which is indicated at 24.

The housing 14 is secured at any suitable point on a motor vehicle, and e::pediently in a substantially vertical position. When the vehicle is parked with the housing axis vertical, or with the housing axis inclined, for example, as shown in Fig. 3, the fluid 23 will contact at least the lowest of the rings 43, 44 and 45.

In the example shown, the fluid 23 covers parts of the two lower contact rings 43 and 44, but the fluid level 24 does not reach the uppermost contact ring 45. When the alarm unit is primed, the electronic analysis device 49 registers this condition as the initial or zero condition.

If this initial condition is then varied by tilting the vehicle, for example by raising the vehicle at one side for the purpose of removing a road wheel, or by bringing the vehicle into an inclined position so as to move the vehicle up over a sloping surface, then, depending upon the change in the inclined position, the contact ring 44 moves out of contact with the fluid 23, or the fluid also moves into contact with the third contact ring 45. In either case, the electronic analysis device 49 receives an impulse which leads to the setting off of the alarm.

Figs. 4 to 6 illustrate a third form of switching device 10, which again has a hollow, cylindrical housing 14 similar to that of the earlier embodiments. Here, however, the housing 14 has an inner cylindrical wall 50, concentric with the outer cylindrical wall 1 5.

The two cylindrical walls 1 5 and 50 defii-r&commat; define an annular chamber 56 which accommodates electrically-conductive fluid 23. The bottom of the chamber 56 is closed by a surface 51 which forms part of the container floor 1 6. At the top, the chamber 56 is closed off by an annular cover 1 9, which fits between the outer wall 1 5 and the inner wall 50 in a fluid tight manner. Preferably, the cover 1 9 is bonded or welded to the walls 1 5 and 50, so that a fluid-tight seal is obtained.The walls 1 5 and 50, the floor 1 6 and the cover 1 9 are made of a plastics material, for example polyethylene, which cannot be wafted by the fluid 23. Immersible sensors 57, 58, 59, 60 and 61 are arranged in the annular chamber 56, the sensors depending from the cover 19, and being sealed against the cover by sealing means 21.Three each of the immersible sensors 57 to 61 are provided, and the sensors are so distributed, in a circle, around the chamber 56 that the sensors of each group 57, 58, 69, 60 and 61 form the corners 57a, 57b, 57c; 58a, 58b, 58c; 59a, 59b, 59c; 60a, 60b, 60c; and 6 a, 61b, 6lcof sub- stantially equilateral triangles, which are indicated in Fig. 5 by different kinds of broken lines. The immersible sensors 57 are all connected to a negative terminal 1 3, whereas the sensors of the groups 58, 59, 60 and 61 are connected, via conductors 46, 47, 48 and 62 respectively to an electronic analysis device 49 for the digital analysis of the orientation of the housing 14. The electronic analysis device 49 is arranged in the interior 52 of the housing 14.

The conductors 13, 46, 47, 48 and 62, which are shown only diagrammatically in Fig.

5, are in fact in the form of a printed circuit provided on a conductor plate 63 which is disposed on the cover 1 9, so that the printed conductors make electrical contact with their corresponding immersible sensors 57 to 61 held in the cover 19.

As will be seen from Fig. 6, the immersible sensors 57 are long enough to extend into the fluid 23 even when the axis of the housing 14 is vertical. The immersible sensors of the groups 58 to 61, on the other hand, are shorter, but all of the sensors of each group 58, 59, 60 and 61 respectively are of the same length, and, in each case, define a switching surface parallel to the floor 1 6. As can be seen from Fig. 6, the switching surfaces formed by the sensors 58, 59, 60 and 6 I are at different distances from the floor 1 6; which distances are, however, somewhat exaggerated in this Figure.

As shown in Fig. 4, the housing 14 is provided with a cap 66 having a peripheral dependent flange 67, which engages round a bead 65 formed at the upper edge 65 of the housing. A pressure ring 69 is provided between the top 68 of the cap 66 and the conductor plate 63, the pressure ring being of U-shaped cross-section and being made of resilient material, for example glass-fibre reinforced polypropylene. Thus, the conductor plate 63 is pressed firmly against the cover 19, so that an electrically-conductive connection is established between the conductive ends of the sensors 57 to 61 and the conductor plate 63.

The electronic analysis device 49, which is secured to the lower face of the conductor plate 63, is connected through conductors (not shown) to an alarm (not shown) for example the horn of the vehicle. These conductors pass out of the cap 66 through a central opening 72.

The switching device 10 is secured to a motor vehicle, at a suitable position that is not accessible to unauthorised persons. Preferably, the switching device 10 is arranged so that the axis of its housing 14 is vertical.

Then, when the vehicle is parked and the alarm unit is primed, the analysis device 49 ascertains the particular orientation of the vehicle, this being defined by the sensors which are immersed in the fluid 23. If the vehicle, and therefore the switching device 10, is then tilted, for example as a result of unauthorised persons raising one side of the vehicle so as to remove a road wheel, the position of the fluid level 24 changes in relation to the immersible sensors of the groups 58 to 61. For example, the fluid level 24 may change in such a way that, not only the sensors of group 58, but also those of group 59 are then contacted by the fluid 23. The analysis device 49 then closes the circuit of the alarm unit so that the alarm is set off.

Figs. 7 and 8 show a fourth form of switching device 10 whose housing 14 has a cylindrical wall 1 5 and a dished floor 1 6. An immersible sensor 57, connected to a negative terminal 13, is located in the middle of the housing 14, and extends into electricallyconductive fluid 23 which covers part of the floor 16. Other sensors 58, 59 and 60 are arranged along radial lines 75, 76, 77 and 78 extending from the central axis of the housing 14. The lines 75 to 78 form angles of 90 with each other and, in plan view, form a right-angled cross. Here again, the sensors of each group 58, 59 and 60 are connected to respective conductors 46, 47 and 48. In other respects, the switching device of Figs. 7 and 8 is similar to that of Figs.

4 to 6 and operates in a similar manner.

Fig. 9 shows a fifth form of switching device 1 0. This device is similar to that of Figs. 7 and 8 in that its housing is of the same shape as that of Figs. 7 and 8, and in that a sensor 57, connected to a negative terminal 13, is located in the middle of the housing. The remaining sensors, however, are arranged along radial lines 79, 80 and 81, which are at angles of 120 to each other.

Here again, this switching device operates in a similar manner to that of the embodiment of Figs. 4 to 6.

Figs. 1 0 and 11 illustrate a sixth form of switching device 10, this sixth form being substantially similar to that of Figs. 4 to 6. Its housing 14 is secured within a motor vehicle (not illustrated) in such a manner that, when the vehicle is standing horizontally, the axis of the housing is substantially vertical, and the direction of travel (indicated by the arrow F in Fig. 11) coincides with a horizontal axis 82 which passes through the centre-point M of the housing, and is referred to hereinafter also as the "longitudinal axis" or the "longitudinai direction". A horizontal axis passing at rightangles to the longitudinal axis 82 and through the centre-point M of the housing 14 is called the "transverse axis" or the ''transverse direction".In the example shown in Figs. 10 and 11, immersible sensors 55, 57, 58, 59, 60 and 61 are disposed in a circle within the annular chamber 56, the sensors being pressed against, and sealed within, the cover 19 with the aid of a seal 21. Four each of the sensors 55, 58, 59, 60 and 61 are provided, the sensors of each group and of these being arranged at the corners of a square. Moreover, each pair of diametrically opposed sensors of each group are connected by respective conductors 85, 87, 88, 89, 90, 91, 92, 93 and 94 to an electronic analysis device 49 which is located in the interior 52 of the housing 14. Four sensors 57 are also provided, the sensors 57 being positioned at the corners of a square and extending within the chamber 56 almost to the floor 1 6 of the housing 14.The sensors 57 are constantly immersed in the fluid 23, and are all interconnected by a conductor (not shown) which is connected to a negative terminal 1 3 of the alarm control circuit.

The immersible sensors 55, 58, 59, 60 and 61 are divided into two groups L and Q, group L being associated with the longitudinal axis 82, and group 0 being associated with the transverse axis 83. In this arrangement, the sensors 55era' 58vat 59ova' 600a and 610a are disposed at the right-hand side of the longitudinal axis 82, as viewed in the direction of travel F, and in an arc 56a of the annular chamber 56, which is delimited by radial lines 95 and 96 which extend at angles of 45 and 135 respectively to the longitudinal axis 82.The sensors 55Qb, 58Qb, 59Qb, 60Qb, and 61 Qb, belonging to the same group Q, are disposed on the left-hand side of the longitudinal axis 82, as viewed in the direction of travel F, and in an arc 56b, which is delimited by the radial lines 95 and 96 extended beyond the centre-point M.

Similarly, the sensors 55La, 58t,, 59lay 60,a, and 61,a are arranged in a forward arc 56cof the annular chamber 56, as viewed in the direction of travel F; and the sensors 55Lb, 58lib, 59lib, 60,b and 61Lh are disposed in a rear arc 56dof the annular chamber 56, as viewed in the direction of travel F.

The sensors of the group L and the sensors of the group Q are connected independently of each other to the analysis device 49. Only one of the groups L and Q can co-operate, at any given time, with the analysis device 49.

If, for example, the vehicle is raised at its left hand side, and the housing 14 is tilted about the longitudinal axis 82, then the electricallyconductive fluid 23 may reach one of the sensors Qa, for example the sensor 58Qa The sensors of the group Q then act through switching impulses on the analysis device 49, whereas the sensors of the group L do not release switching impulses when they are touched by the contact fluid.

Conversely, only the sensors of the group L participate in the switching operation if a sensor in this group is initially touched by the fluid 23, possibly because the vehicle is lifted at its front or rear end, in which case the switching device 10 would be tilted about its transverse axis 83.

Figs. 1 2 to 14 show a seventh form of switching device 10, which is a modification of the embodiment of Figs. 10 and 11. Here, the housing 14 is of rectangular cross-section, and the immersible sensors 55, 57, 58, 59, 60 and 61 are disposed adjacent to the peripheral walls of the housing. The immersible sensors road 58seal 59Ga' 60Qa and 61yea are arranged, as seen in the direction of travel F, along the right-hand longitudinal wall 98, and the immersible sensors 55Qbt 58,,, 59at, 60Qb and 61Qb are arranged along the left- hand longitudinal well 99.Similarly, the im mersible sensors 55lea' 58, " 59Lar 60, and 61 lea are located along the front transverse wall 100, and the immersible sensors 55Lbt 58Lb, 59lib' 60lib and 61,b are arranged along the rear transverse wall 101. The immersible sensor 57, connected to the negative terminal, is placed in the middle of the housing 14.

This switching device 1 0 functions in the same way as the previously described switching device shown in Figs. 10 and 11. The only difference is that the spacing 19, between the sensors SQZ, and SQa associated with the transverse direction R, is greater than the spacing d, between the sensors SLa and SLb associated with the longitudinal direction F of the vehicle.

Fig. 1 5 shows an eighth form of switching device 10 whose housing 14 has a cylindrical wall 1 5 and a cupped floor 1 6. This form of switching device is similar to that of Figs. 4 to 6 in that it has a plurality of immersible sensors. An immersible sensor 57, which connected to a negative terminal of the alarm circuit, is located in the middle of the housing 14. The other sensors, which terminate at different levels, are arranged in two rows which cross each other at right angles. One of the rows, which forms the first group L of sensors, is disposed on the longitudinal axis 82 of the housing 14, whereas the other group Q of immersible sensors is arranged along the transverse axis 83 of the housing.

The sensors S, of group L respond when the vehicle, and therefore the housing 14, is tilted about the transverse axis 83, whereas the sensors SQ of group Q respond when the vehicle is raised at one side, and is tilted about its longitudinal axis 82. The sensors of each group SQ and S, have different lengths, and, as in the other arrangements, are arranged in pairs on opposite sides of the line directed at right angles thereto. Each pair of sensors is connected to the analysis device 49. As described above in connection with earlier embodiments, either one group L or the other group Q of sensors act on the analysis device 49 when the switching device 10 is tilted with the vehicle, and the fluid 23 touches a sensor in one or other of the groups.

Figs. 1 6 and 1 7 show a ninth form of switching device which again is very similar to that shown in Figs. 10 and 11. Here again, an annular chamber 56 is divided off in the housing 14 by a cylindrical inner wall 50, the chamber 56 accommodating electrically-conductive fluid 23. Sensors 57 to 61 extend downwardly into the chamber 56 from the cover 1 9. The chamber 56 is divided by four immersible walls 102, 103, 104 and 105 into four chamber 56a, 56b, 56c, and 56d.

These immersible walls 102, 1 03, 1 04, 105 terminate at a short distance from the floor 1 6 of the housing 14, and are immersed in the electrically-conductive fluid 23, the level of which is indicated by the numeral 24. The immersible walls 102 to 105 may extend up to the cover 19; however, in the arrangement shown they terminate &commat;P at a short distance below the cover. As can be seen from Fig.

1 7, the four immersible walls 102 to 105 are arranged at angles of 90 to each other, and in such a way that they all extend at an angle of about 45 to the direction of travel, which is indicated by the arrow F.

The immersible walls 102 to 105 may be formed integrally with the walls 1 5 and 50 of the housing 14. Alternatively, they may be bonded to the walls 1 5 and 50 or secured thereto in some other way.

Each segmental chamber 56a, 56b, 56c, and 56d contains five immersible sensors 57, 58, 59, 60 and 61 of differing lengths. All the sensors 57 and 61 are press-fitted into the cover 1 9, and are sealed thereagainst by means of a seal 21. The immersible sensors 57 have the greatest length, and extend into the fluid 23 when the container axis is vertical. The sensors 57 are all connected to the negative terminal 1 3 of the alarm circuit. The immersible sensors 58, 59, 60 and 61 in each pair of diametrically opposed segmental chambers 56a, 56c, and 56b, 56d, are connected by conductors 46, 47, 48 and 62 respectively to an electronic analysis device 49 for the digital analysis of the orientation of the housing 14. The analysis device 49 disposed in the interior 52 of the housing 14. As with the embodiment of Figs. 10 and 11, the conductors 46, 47, 48 and 62 are in the form of a printed circuit provided on the surface of the cover 63.

When the vehicle is parked and the alarm unit is primed, the level 24 of the fluid 23 in the housing 14 is detected by the sensors 57 to 61. If the vehicle, and therefore the housing 14, is then tilted, the fluid 23 touches other sensors, and, after a certain time-lag, the analysis device 49 sets off the alarm. If, on the other hand, the vehicle, and therefore the housing 14, is swung backwards and forwards, then, although the fluid level 24 alters, it assumes its original position again after a certain time, so that the alarm is not set off, even though in the meantime other sensors have come into contact with the fluid.

During the above-mentioned swinging movement, the movement of the fluid 23 in the housing 14 is retarded and damped down by the immersible walls 102, 103, 104 and 105, so that a surface wave, which moves right round the annular chamber 56, and would cause a false alarm, cannot occur.

Fig. 1 8 shows a tenth form of switching device 10 having immersible sensors 56, 58, 59 and 60 arranged, in two rows crossing each other at right-angles, in a hollow, cylindrical housing 14. The housing 14 is divided into four sectors 106, 107, 108 and 109 by immersible walls 102, 103, 104 and 105 which cross each other at right-angles. The floor 1 6 of the housing 14 may be dished.

The immersible sensors 57, which are connected to the negative terminal 1 3 of the alarm circuit, are located approximately in the middle of the housing 14, and extend almost to the floor 16. Thus, in any position of the housing 14 they reach into the fluid. The sensors 58, 59 and 60 are of differing lengths, and are interconnected by respective conductors which lead to the electronic analysis device 49. Thus, the sensors 58, 59 and 60 define switching surfaces at different levels in the housing 14, which levels are reached by the fluid in the housing when the vehicle is in an inclined position. The immersible walls 102 to 105 retard and damp down the movements of the fluid.

In the above-described embodiments using immersible sensors as electrical contacts, the sensors may be replaced by contact rings or contact segments as illustrated, for example, in Fig. 3. The use of immersible sensors is, however, particularly advantageous.

Claims

1. An anti-theft system for a motor vehicle, the system comprising an electricallypowered alarm, a switching device for actuating the alarm, and an electric circuit connecting the switching device and the alarm, the switching device being attached, in use, to the motor vehicle, wherein the switching device is provided with electrical contacts which automatically close the electric circuit when the vehicle is in an inclined position.

2. An anti-theft system as claimed in Claim 1, wherein the switching device has a housing defining a chamber which is partially filled with an electrically-conductive fluid, the electrical contacts being contactable with said fluid.

3. An anti-theft system as claimed in Claim 2, wherein an electrical contact is provided in the zone of the floor of said chamber, and at least one electrical contact is provided in the upper zone of said chamber, the system being such that the floor contact is electrically connectible to the or each upper contact only by said fluid.

4. An anti-theft system as claimed in Claim 3, wherein the housing is made of electrically non-conductive material, a floor plate made of electrically-conductive material constituting the floor contact.

5. An anti-theft system as claimed in Claim 4, wherein the housing is generally cylindrical, and there are a plurality of upper contacts constituted by electrically-conductive rings, the rings being attached to the cylindrical wall of the housing and being positioned at different distances from the floor plate, and wherein the rings are connected to an electronic analysis device which is such as to actuate the alarm upon a change in the inclination of the housing.

6. An anti-theft system as claimed in any one of Claims 2 to 5, wherein the housing of the switching device is a cup-shaped plastics vessel which is closed off, at its top, by a cover.

7. An anti-theft system as claimed in Claim 6 when appendant to Claim 4, wherein the cover is made of metal and constitutes the upper contact, and wherein an insulated conductor passes through the cover and is connected to the floor plate.

8. An anti-theft system as claimed in any one of Claims 2 to 7, wherein the side walls of the housing have inner surfaces which cannot be wetted by said fluid.

9. An anti-system as claimed in any one of Claims 2 to 8, wherein said fluid is triphenylfluoromethane, triphenylchloromethane, or a mixture of glycerine and copper sulphate.

1 0. An anti-theft system as claimed in Claim 2 or in any one of Claims 6, 8 and 9 when appendant to Claim 2, wherein the electrical contacts are immersible sensors which extend downwards into said chamber to differing extents, said fluid being the only means for electrically connecting the sensors.

11. An anti-theft system as claimed in Claim 10, wherein the housing is a cupshaped vessel whose top is closed off by a cover, and wherein the sensors depend from the cover into said chamber.

1 2. An anti-theft system as claimed in Claim 11, wherein there are a plurality of groups of sensors, the sensors of each group having the same length and the sensors of the different groups having different lengths, and wherein the sensors of each group are con nected by a common conductor to an electronic analysis device.

1 3. An anti-theft system as claimed in Claim 12, wherein the housing is cylindrical and the sensors are distributed along radial lines extending from the central axis of the housing.

1 4. An anti-theft system as claimed in any one of claims 10 to 13, wherein one sensor or one group of sensors extends into said chamber to terminate adjacent to the floor thereof.

1 5. An anti-theft system as claimed in Claim 12, wherein the sensors of each group are arranged at the corners of a substantially equilateral triangle.

1 6. An anti-theft system as claimed in any one of Claims 11 to 15, wherein the sensors are arranged adjacent to the inner surface of the outer wall of the housing.

1 7. An anti-theft system as claimed in any one of Claims 10 to 1 6 wherein said chamber is annular.

1 8. An anti-theft system as claimed in Claim 1 7 when appendant to Claim 12, the annular chamber is adjacent to the outer wall of the housing, and surrounds a cylindrical chamber which accommodates the electronic analysis device.

1 9. An anti-theR system as claimed in any one of Claims 1 2 to 1 8, wherein the sensors are arranged in two sets, one set having sensors on both sides of a first housing axis, and the other set having sensors on both sides of a second housing axis which is perpendicular to said first housing axis, and wherein the sensors of said one set are connected to the analysis device independently of the sensors of said other set.

20. An anti-theft system as claimed in Claim 19, wherein the housing is attached, in use, to the motor vehicle in such a manner that said first housing axis is parallel to the longitudinal axis of the vehicle, and said second housing axis is parallel to the transverse axis of the vehicle.

21. An anti-theft system as claimed in Claim 1 9 or Claim 20, wherein the sensors of each set are arranged on a pair of parallel lines, the sensors being equispaced on their respective lines.

22. An anti-theft system as claimed in Claim 21, wherein the sensors of said second set are spaced apart by distances greater than those by which the sensors of said first set are spaced.

23. An anti-theft system as claimed in any one of Claims 2 to 22, wherein said chamber is divided into a plurality of chamber parts by means of walls, the walls being such that the chamber parts are in fluid communication with each other.

24. An anti-theft system as claimed in Claim 23, wherein the walls are arranged to be irnmersible in said fluid, and to terminate adjacent to the floor of the housing.

25. An anti-theft system as claimed in Claim 24 when appendant to Claim 11, wherein the immersible walls extend as far asthe cover of the housing.

26. An anti-theft system as claimed in any one of Claims 23 to 25, wherein there are four walls arranged at right-angles to each other.

27. An anti-theft system as claimed in Claim 26, wherein the housing is attached, in use, to the motor vehicle in such a manner that each of said walls is inclined to the longitudinal axis of the vehicle.

28. An anti-theft system for a motor vehicle substantially as hereinbefore described with reference to, and as illustrated by, Figs.

1 and 2, Fig. 3, Figs. 4 to 6, Figs. 7 and 8, Fig. 9, Figs. 10 and 11, Figs. 12 to 14, Fig.

15, Figs. 16 and 17, or Fig. 18 of the accompanying drawings.

29. A switching device for a motor vehicle anti-theft system, the switching device being substantially as herein before described with reference to, and as illustrated by, Figs. 1 and 2, Fig. 3, Figs. 4 to 6, Figs. 7 and 8, Fig. 9, Figs. 10 and 11, Figs. 12to 14, Fig. 15, Figs. 16 and 17, or Fig. 18 of the accompanying drawings.