GB2056733A

GB2056733A - Alarm system

Info

Publication number: GB2056733A
Application number: GB8026173A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-08-14
Filing date: 1980-08-12
Publication date: 1981-03-18

Abstract

An alarm system for a caravan or other vehicle having a ground- engaging leg 5 which is to be lowered to engage the ground when the vehicle is parked includes a switch formed by contacts 10, 11 which are closed when the leg is in its ground-engaging position. One of the contracts 10 is mounted on a nut 4 which is movable by a lead- screw 3 which is turned when the leg 6 is to be raised. The opening of the contacts 10, 11 on turning of the lead-screw 3 causes an alarm, e.g. a siren and/or lamp, 17 to be operated to give warning that the leg is being raised ready for the vehicle to be driven or towed away. <IMAGE>

Description

SPECIFICATION Alarm system The invention relates to an alarm system of which the object is to deter the theft of, or towing or driving away a vehicle of the kind which has supports which are lowered to engage the ground when the vehicle is parked.

The term "vehicle" is used herein in a broad sense to include motorised or towed land vehicles of both private and commerical kinds, such as caravans or articulated lorries; trailers for carrying boats or other loads or a boat itself when supported on legs on the ground or on a slip-way, quay or the like. A typical application of the alarm system provided by this invention is, however, for deterring the theft of a caravan of the kind to be towed behind a vehicle.

Mechanical locking devices associated with the towing bar of a caravan have been proposed; but these can often be removed by a determined thief and eventually become corroded and can then easily be broken.

Alarm systems can also be fitted to the doors or windows of caravans to deter a thief or vandal from breaking-in; but there is no alarm system, known to the Applicant, to deter a thief from towing-away a parked caravan.

A caravan of the kind which is to be towed by a vehicle is provided with legs, usually a pair at the rear and a pair at the front, which can be swung between inoperative positions to which they are moved to substantially horizontal positions, when the caravan is to be supported solely by its wheels when being towed or manoeuvred, and operative positions to which the legs are swung about horizontal axes downwardly to engage the ground to restrain the caravan from being moved or tipped. The legs are usually swung between their operative and inoperative positions by a linkage which is operated by a nut arranged to travel along a horizontal lead-screw which is turned by a crank-handle.Thus when a caravan has been parked, and legs are in their "down" ground-engaging positions and before the caravan can be towed away, the legs have to be raised by turning the lead-screw associated with each leg or, where a leadscrew operates a pair of leg-raising mechanisms, each pair of legs.

According to the invention, an alarm system, for a vehicle of the kind which has supports which are lowered to engage the ground when the vehicle is parked, comprises a switch to be mounted on a movable part of a ground-engaging support or the raising gear therefor and an electrical circuit, including an electrically-operable alarm, whereby the switch will be operated, when the support is moved from its ground-engaging position, and the alarm will operate.

Preferably the electrical circuit is of a kind which is inoperative to actuate the alarm when the switch is closed and which actuates the alarm when the switch opens, the switch comprising a pair of normally-closed contacts of which one is to be mounted on a stationary part of the vehicle and the other is to be mounted on a movable part of the supportraising gear or on the support itself, whereby when the support-raising gear is moved, the switch will open and cause the alarm to be actuated.

This type of electrical circuit has the advantage that where a cable or lead connects the switch contacts to a box containing the circuit itself, the cutting of the cable or lead in an attempt to immobilise the alarm will be equivalent to opening the switch and the alarm will immediately be actuated.

Desirably, the electrical circuit is of a kind which will continue to actuate the alarm until the circuit has been switched off by the use of a master switch. Conveniently the master switch is of a kind operated by using a key.

The alarm is desirably of a siren type which will emit an intermittent or warbling sound, as this is more likely to attract attention or to awaken someone who is asleep more easily than a continuous sound.

However a siren emitting a continuous sound may alternatively be employed. The alarm may additionally, or alternatively, be of a kind which will give a visual warning, for example, a flashing light or an illuminated sign on the caravan.

The electrical circuit and the alarm may be contained in a pack to be placed in a compartment of or on the caravan. The pack may contain its own battery or be provided with connection points, whereby the circuit may be connected to an external battery in the caravan or on a vehicle for towing the caravan, or to an external electricity supply.

The alarm system, as stated hereinbefore, is particularly, but not exclusively, intended to be used on a caravan. In the latter, the ground-engaging supports are legs which are pivotally mounted for swinging upwardly and downwardly about a horizontal axis by a link mechanism movable by a nut which is arranged to be moved by turning a horizontal lead-screw. The alarm system may therefore include a first member which is fixed to the nut and carries one of the contacts of the switch and a second member which is arranged to be fixed to the caravan or to the chassis thereof, the first and second members being so arranged that when the leg is in its ground-engaging position, the contacts are touching each other, the electrical circuit being of the kind which has normally-closed contacts, and the contacts will open when the nut is moved to commence to raise the associated leg.The first and second members may be plates which are provided with adjustable means to permit the contacts to be set to positions such that they are closed when the associated leg is in its ground-engaging position and will open when the nut has been moved by the lead-screw through only a desired short distance in the leg-moving sense.

The adjustable means may incorporate a clamping screw to hold the contacts in their initial closed positions but which will permit relative movement longitudinally of the leadscrew between the first and second members and hence the contacts when the nut is moved by the lead-screw to commence to raise the leg. The clamping screw prevents separation of the contacts in a direction perpendicular to the longitudinal axis of the leadscrew and so any attempt to loosen the clamping screw, when the electrical circuit has not first been switched off by the master switch, will cause the contacts to separate, and the alarm to be operated.

The invention also includes a vehicle having a ground-engaging support and an alarm system in accordance with any one of the immediately preceding seven paragraphs.

By way of example, one form of the alarm system is now illustrated in association with the leg-raising gear of a caravan with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic drawing of the leg-raising gear and the alarm system, and Figure 2 is a typical circuit diagram of the alarm.

In Fig. 1, the chassis of the caravan is indicated at 1. This supports guides 2 for a lead-screw 3 extending horizontally in the fore-and-aft direction of the caravan. The leadscrew is fitted with a nut 4 which carries a leg 5. This is pivotally attached to the nut 4 and is attached by a link 6 to a fixed pivot point 7 on the chassis 1. Turning of the lead-screw 3 by a detachable crank-handle 8 moves the nut 4 along the lead-screw and so swings the leg 5 upwardly to a horizontal position in which the lower end of the leg 5 is held clear of the ground. Such a mechanism for raising and lowering a caravan leg or a pair of legs or all the legs of the caravan is well-known.

In accordance with this invention, the nut 4 carries a plate 9 which carries a movable contact 10. This is in contact when the leg 5 is in the "down" position, as shown, with a contact 11 on a plate 12 which is clamped to the chassis 1 by a screw and a nut 13. This screw is positioned in a slot 14 in the plate 12.

The contacts are connected by conductors in a cable 15 to an electrical circuit 16, shown as a "box" in Fig. 1. The box is in the form of a pack containing, or connected to, an oscillator or siren 17. The box or pack 16 contains a battery; but may have provision, as indicated at 18 for connection to an external battery or to an external electrical supply. The external battery may be in the caravan or in a towing vehicle. The circuit includes a master switch, preferably of the kind operated by a key, and this has been indicated by the keyhole 19.

When the caravan is to be towed or manoeuvred, the master switch is opened by using the key. The leg 5, or the leg 5 and another leg or legs, is raised by using the handle 8. When the caravan is to be parked, each of the legs is lowered to the position illustrated. This, in the case of the leg 5, or legs, fitted with the alarm system, closes the contacts 10 and 11. Initially, when the plate 12 is first fitted, adjustment would have been made to ensure that the contacts 10 and 11 are just touching, the adjustment being ef fected by loosening the wing-nut 13, sliding the plate 12 and then re-tightening the wingnut 13. The main switch is closed by the key, which is removed after the leg has been lowered to their ground-engaging positions.

If an attempt is made by a thief to remove the caravan, he must first raise the legs.

When he commences to turn the handle 8 to raise the leg, or legs 5, the nut 4 will move, thereby opening the contacts 10 and 11. The circuit 16 is of a kind which will actuate the alarm 17 as soon as the contacts 10 and 11 open and is also of a kind which will continue to operate until the master switch has been operated by the key. As the thief will not have the key, he cannot stop the alarm and so he will be deterred from towing away the caravan.

The alarm used is preferably a siren which is intermittent or warbling, as this is believed to be more readily noticed than a continuous siren and is more likely to awaken a sleeping person. The alarm may also, or alternatively, include a flashing light or sign mounted on the caravan.

As the circuit is of the kind which actuates the alarm 17 on the opening of the contacts 10 and 1 1, the cutting of the cable 15 in an attempt to immobilise the alarm would be equivalent to opening the contacts and the alarm would sound, and if already sounding could not be stopped, except by using the key.

The loosening of the wing-nut 13 will also cause the contacts 10 and 11 to open by movement perpendicular to the longitudinal axis of the lead-screw 3 in a direction perpendicular to the plane of Fig. 1, and thus would cause the alarm to operate.

The "box" or pack may be mounted in any convenient position on the caravan, for example, in a casing at the rear of the caravan adjacent the tow-bar.

Although the alarm system has been described for use with a leg of a caravan, it may be used in association with any vehicle having a retractable ground-engaging leg or support, whether mounted for swinging about a horizontal axis or movable vertically, as in the stabilising leg of an articulated lorry.

Fig. 2 shows a typical circuit which is within the box 16. The circuit includes a pair of transistors TR1 and TR2. The emitter and base of transistor TR1 are connected by the conductors 15. The collector of transistor TR1 is connected to the base of transistor TR2, the transistor TR2 being connected in a circuit including the solenoid of a relay 20 which when energised causes the siren 17 to be operated. In Fig. 2, the main switch 21 which is normally closed, and can only be opened by a key inserted in and turned in the key-hole 19, energises the circuit by means of the battery 22. Assuming that the switch 21 has been closed by removal of the key from the key-hole 19 after the leg 5 has been moved to the "down" position, the contacts 10 and 11 bridge the emitter and base of the transistor TR 1 which therefore holds the transistor TR2 non-conducting. When the contacts 10 and 11 open on turning the lead-screw 3 in an attempt to raise the leg 5, the transistor Tor 1 will cause the transistor TR2 to conduct, thereby energising the solenoid of the relay 20 and operating the siren 17. The circuit containing the siren 17 and the battery 22 cannot be opened to stop the siren until the key is inserted and turned in the key-hole 19 to open the main switch 21.

Claims

1. An alarm system, for a vehicle of the kind which has supports which are lowered to engage the ground when the vehicle is parked, comprising a switch to be mounted on a movable part of a ground-engaging support or the raising gear therefor and an electrical circuit, including an electrically-operable alarm, whereby the switch will be operated, when the support is moved from its groundengaging position, and the alarm will operate.

2. An alarm system as claimed in Claim 1 in which the electrical circuit is of a kind which is inoperative to actuate the alarm when the switch is closed and which actuates the alarm when the switch opens, the switch comprising a pair of normally-closed contacts of which one is to be mounted on a stationary part of the vehicle and the other is to be mounted on a movable part of the supportraising gear or on the support itself, whereby when the support-raising gear is moved, the switch wil open and cause the alarm to be actuated.

3. An alarm system as claimed in Claim 1 or 2 in which the electrical circuit is of a kind which will continue to actuate the alarm until the circuit has been switched off by the use of a master switch.

4. An alarm system as claimed in Claim 3 in which the master switch is of a kind which is operated by using a key.

5. An alarm system as claimed in any preceding claim in which the alarm is of a siren type, which will emit an intermittent or warbling or a continuous sound.

6. An alarm system as claimed in any preceding claim in which the alarm is of a kind which will give a visual warning.

7. An alarm system as claimed in any preceding claim in which the electrical circuit and the alarm comprises a pack which includes a battery.

8. An alarm system as claimed in any one of preceding claims 1-6 in which the electrical circuit and the alarm are provided with connection points, whereby the circuit is arranged to be connected to an external battery or electricity supply.

9. An alarm system as claimed in any preceding claim for use with a caravan having ground-engaging legs which are pivotally mounted for swinging upwardly and downwardly about horizontal axis by a link mechanism movable by a nut which is arranged to be moved by turning a horizontal lead-screw, the alarm signal including a first member which is fixed to the nut and carries one of the contacts of the switch and a second member which is arranged to be fixed to the caravan or to the chassis thereof, the first and second members being so arranged that when the leg is in its ground-engaging position, the contacts are touching each other, the electrical circuit being of the kind which has normally-closed contacts, and the contacts will open when the nut is moved to commence to raise the associated leg.

10. An alarm system as claimed in Claim 9 in which the first and second members are plates which have adjustable means to permit the contacts to be set to positions such that they are closed when the associated leg is in its ground-engaging position and will open when the nut has been moved by the leadscrew through only a desired short distance in the leg-moving sense.

11. An alarm system as claimed in Claim 10 in which the adjustable means incorporates a clamping screw to hold the contacts in their initial closed positions but which will permit relative movement longitudinally of the lead-screw between the first and second members and hence the contacts when the nut is moved by the lead-screw to commence to raise the leg.

12. A vehicle having a ground-engaging support and an alarm system as claimed in any preceding paragraph.

13. An alarm system, for a vehicle having a ground-engaging support, constructed and arranged substantially as described herein and shown in the accompanying drawings.