GB2029060A - Improvements in or Relating to Vehicles with Alarms - Google Patents

Abstract

A vehicle such as a motor cycle and having an electrical system, is provided with an electronic detector 25, 26 arrangement for sounding an alarm 28 if the state of the electrical system is changed when the vehicle is parked. The detector arrangement includes a voltage detector 25 which triggers an edge-triggered monostable device 26 to actuate an astable 27 driving a transducer 28 when the electrical system state is changed. The voltage detector 25 is arranged to sense a change in impedance between the vehicle earth return and the switched terminal 15 of the electrical system ignition switch 11. A vibration detector 30 is also incorporated in the detector arrangement to trigger the monostable when subjected to vibration. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Vehicles With Alarms This invention relates to a vehicle fitted with an alarm arrangement for detecting interference with the vehicle electrical system when the vehicle has been parked, and also relates to a method of detecting interference with the electrical system of a vehicle when the vehicle has been parked.

There have been designed many kinds of devices for fitting to vehicles to sound an alarm if an attempt is made to steal the vehicle. One particularly common form of such device for use on a private automobile utilises a vibration sensor which is mounted on the vehicle in a position which is not readily accessible by a would be thief. When the detector is set for operation, vibration of the vehicle is detected by the sensor and this is arranged to trigger a relay which energises the vehicle's horn.

The above-described device functions reliably and in practice is found to be quite effective on a private motor car, but the device has several disadvantages when fitted to a motor cycle. The vibration usually is a pendulum device and so is somewhat large; it is not easy to conceal such a device on a motor cycle so that it is inaccessible when the motor cycle is parked. Moreover, the theft of motor cycles usually is performed by placing the machine in neutral, and then pushing the motor cycle to a safer place, where as much time as is required is available to start the engine and then to drive away the motor cycle. Simply cutting the battery wire-which usually is accessible-will render the alarm inoperative, and so theft of a motor cycle even fitted with such an alarm is still easy.

In an attempt to overcome this problem an alarm has been designed which is arranged to monitor the operation of several of the electrical devices of a vehicle, such as a motor cycle. For example, the operation of the ignition coil and the lights may be monitored, and when voltage is applied to either of these devices by operation of the appropriate switch, the presence of the battery voltage is detected to close a relay which causes the vehicle hooter to sound. The disadvantage of such a device is that for effective protection, many different items need simultaneously to be monitored, and the fitting of such a device to an existing vehicle electrical system then becomes somewhat complex because usually a separate wire has to be connected for each monitored item.Moreover, because when a vehicle is left with the engine turned off, usually there is at least one relatively low resistance path to the vehicle earth across the ignition circuit-such as the low oil pressure warning lamp-and this can make the detection of the application of battery voltage to the various items wired through the ignition switch most difficult. It has been found necessary to isolate each low resistance path (such as that of the low oil pressure warning lamp) by means of a diode and this of course leads to even greater complexity if the warning device is to be fitted subsequent to the manufacture of a vehicle.

It is an object of one aspect of this invention to provide a vehicle fitted with an alarm arrangement for sounding an audible alarm should the state of the electrical system of the vehicle be changed by interference therewith, but which arrangement does not suffer from the problems mentioned above especially where fitted to a motor cycle. It is a further object of another aspect of this invention to provide a method of detecting a change in the state of a vehicle electrical system, and to give an audible warning if such a change in state occurs.

Accordingly, this invention provides a vehicle having an electrical system including a storage battery and an electronic detector arrangement for sounding an alarm if the state of the electrical system is changed when the vehicle is parked, which detector arrangement includes an edgetriggered monostable device having an input which is connected to a point in the electrical system which point is at battery potential when the vehicle normally is operated but which is disconnected from the battery when the vehicle is parked, alarm means connected to the monostable device output and responsive to a pulse appearing thereat to sound an audible alarm, and means to impress a voltage between the said point and the vehicle earth return whereby a change in state of the electrical system associated with said point causes a transient voltage to appear at the monostable device input thereby triggering said audible alarm.

A vehicle electrical system normally includes an ignition circuit and a key-operated ignition switch; for such a vehicle the point to which the monostable device is connected is preferably the switched terminal of the ignition switch. On a motor cycle, because all the controls are readily accessible when the machine is parked, it is usual for all services of the electrical system except for a parking light to be wired through the ignition switch to prevent abuse. When such a motor cycle is fitted with a detector arrangement in accordance with this invention, all the electrical services except the parking light will be monitored, and if for example neutral is selected or the brakes are operated, the appropriate warning light switch will close. This will be detected by the detector arrangement to cause the alarm to sound.

By setting the sensitivity of the monostable device appropriately, the detector arrangement may respond to relatively small transients appearing at said point as a result of the state of the electrical system being changed. Moreover, the sensitivity can easily be set so as to trigger even despite the relatively low impedance path presented by a low oil pressure warning lamp the switch of which is closed when the vehicle engine is stopped. A typical sensitivity for the monostable device is for triggering to occur with an edge of the order of a few millivolts in magnitude.

Conveniently, the voltage impressing means comprises a potential divider arranged across the power supply of the detector arrangement, the divided voltage being connected to said point of the electrical system. The power supply itself may include an auxiliary battery, the detector arrangement normally drawing power from the vehicle battery but the auxiliary battery being disposed for powering the arrangement in the absence of the vehicle battery. This conveniently can be achieved by connecting both batteries to the detector arrangement each through an associated diode, the auxiliary battery being of a lower voltage than the vehicle battery whereby the diode associated with the auxiliary battery normally is reversed biassed.Such an arrangement will thus still operate to detect tampering with the vehicle electrical system in the event of removal of the vehicle battery or even of cutting the battery wire in an attempt to render the detector arrangement inactive.

The preferred form of edge-triggered monostable comprises an operational amplifier both inputs of which are resistively coupled to said point in the vehicle electrical system, but one input of which is decoupled by means of a capacitor whereby a voltage transient at said point causes a differential voltage input to the operational amplifier thereby swinging the amplifier output voltage towards that of one of the power supply rails. The time constant of the monostable device may typically be about 10 seconds.

Greater protection of the vehicle may be obtained by including in the detector arrangement a vibration detector, disposed to trigger the monostable device when subjected to vibration.

One possible form for such a vibration detector is a graphite or other resistive rod-like element to rest under gravity on a pair of contacts, movement of the rod causing a change in resistance between the pair of contacts.

To protect accessories or luggage especially in the case of a motor cycle, the detector arrangement may have a further input which when connected to the vehicle earth return does not affect the operation of the detector arrangement but which when disconnected from the vehicle earth return causes the audible alarm to sound. Preferably a length of wire is connected at one end to said further input and which can be wrapped around the luggage or accessories; the other end of the wire is then connected to the earth return and disconnection thereof to release the luggage or accessories with cause the alarm to sound.

For the case in which said point of the electrical system is the switched terminal of the ignition switch, it is preferred for the detector arrangement to sense closing of the ignition switch to energise the ignition circuit and to then inhibit operation of the alarm means.

Consequently, setting of the detector arrangement automatically will occur on turning off the ignition switch, but operation is inhibited when the vehicle is to be driven by a key-holder.

According to another aspect of this invention, there is provided a method of detecting operation of a vehicle electrical system when the vehicle is parked, in which method the impedance between a point of the electrical system and the vehicle earth return is monitored by impressing a voltage on said point and then detecting transient changes in the impressed voltage by means of an edge-triggered monostable device connected to provide an output pulse when-a transient change occurs at the input thereto, and the output pulse of the monostable device drives alarm means to given an audible indication oftampering with the electrical system, said point in the electrical system being one which is disconnected from the vehicle battery when the vehicle is parked but connected to the battery when the vehicle is operated normally.

By way of example only, one specific embodiment of vehicle electrical system and detector arrangement of this invention will now be described, reference being made to the accompanying drawings, in which: Figure 1 is a block diagram of a vehicle electrical system and detector arrangement configured in accordance with this invention; Figure 2 is a circuit diagram part of the electrical system and the voltage detector; Figures 3A to 3C illustrate three alternative forms of vibration detector for use in the arrangement of Figure 1; Figure 4 is a circuit diagram of the complete detector arrangement shown in Figure 1; and Figures 5A and 5B show two alternative forms of vibration detector for use in any of the circuits of Figures 3A to 3C.

Referring initiaiiy to Figure 1, there is shown diagrammatically part of an electrical system of a motor cycle. A storage battery 10 has its negative pole earthed to the frame of the motor cycle and the other, positive pole connected to one terminal of a key-operated ignition switch 11. The positive battery pole is also connected through a cut-out 12 to an engine driven generator 13. An ignition warning light 14 is wired across the series connection of the cut-out 12 and the ignition switch 11, so that the light 14 will glow whenever the ignition switch 11 is closed and the generator 13 is not producing sufficient voltage to close the cut-out 12.

The majority of electrical services of the motor cycle are connected to the switched terminal 1 5 of the ignition switch 11, such that these services may be operated only when the switch 11 is closed by means of the key. Such services include the ignition circuit having a coil 1 6 and contact breaker 17, a neutral indicator light 1 8 operated by means of a switch 1 9 associated with the gear change mechanism, a brake light 20 operated by means of a switch 21 associated with the footbrake and/or the hand-brake, and a low-pressure oil warning light 22 operated by means of a normally-closed switch 23, which switch 23 is opened when the engine is running and generating oil pressure above a pre-set minimum.

Other services may be wired into the circuit in a similar way and on most modern motor cycles, the majority of services are wired through the ignition switch 11, so as to prevent unauthorised operation of the services-bearing in mind the accessibility of the controls of a motor cycle when it is parked. Usually, the only service not controlled by means of the ignition switch is a parking light arrangement, as shown at 24.

The above-described electrical system is fitted with a detector arrangement in accordance with this invention, in order that unauthorised operation of any of the services connected to the switched terminal 1 5 of the ignition switch may be detected and an alarm given. The detector arrangement comprises a voltage detector 25 to which is connected an edge-triggered monostable device 26 having a time constant of about 10 seconds. The output from the monostable device drives a gated astable 27, and the output from the astable is used directly to drive an audio transducer 28. The input 29 to the voltage detector is wired directly to the switched terminal 1 5 of the ignition switch 11. In addition, the edge-triggered monostable device may be triggered by means of a signal from a vibration detector 30, attached suitably to the motor cycle frame so as to detect vibration thereof.Each of the components 25, 26, 27 and 30 are connected to a common bus 31 as well as being earthed to the motor cycle frame, the bus 31 being connected either to the positive pole of the battery 10 or to an internal battery within the detector arrangement itself. The optional connection of the bus 31 is preferably effected automatically by means of a diode gate, described below.

In operation, whenever one of the electrical services connected to the switched terminal 1 5 of the ignition switch is operated-for instance if the gear change mechanism is operated to select neutral, so as to allow the motor cycle to be pushed away, thereby closing switch 1 9 and connecting light 1 8 into circuit-the change in impedance between the switched pole 1 5 of the ignition switch and the motor cycle frame is sensed by the voltage detector 25 which provides a transient voltage pulse to the edge-triggered monostable 26, thereby energising the gated astable 27 which in turn drives the transducer 28 to emit a warning sound.

Turning now to Figure 2, there is shown the circuit diagram of the voltage detector and edgetriggered monostable device in association with the battery 10 of the motor cycle as well as the ignition switch 11 and a typical load such as switch 19 and warning light 18. Bus 31 is connected to the positive pole of the battery 10 through a diode D1, and also connected to an internal battery 32 through a further diode D2.

Battery 32 is arranged to have a lesser voltage than that normally of battery 10, so that diode D2 is reverse-biassed and current is only drawn from battery 10. Should however battery 10 be removed from circuit diode D2 may conduct, allowing battery 32 to power the detector arrangement.

The detector arrangement itself comprises a pair of resistors R1 and R2 together forming a voltage divider constituting the element 25 in Figure 1. The junction of resistors R1 and R2 is connected to the switch pole 1 5 of the ignition switch 11 and also is connected through a capacitor C1 to the edge-triggered monostable device 26. This device comprises an operational amplifier 33 (such as a 741) the inverting and non-inverting inputs of which are coupled together through a pair of similar resistors R5 and R6. The junction of resistors R5 and R6 is connected to the junction of a further pair of resistors R3 and R4 arranged as a potential divider between the bus 31 and the vehicle frame.

Also connected to the non-inverting input of the amplifier 33 is a capacitor C2, and the output from the amplifier 33 is a.c. coupled through a capacitor C3. Offset null adjustment may be effected by means of a potentiometer P1 appropriately wired to the amplifier 33.

When the circuit described above is in a steady state, with the ignition switch 11 turned off, the voltage present at the inverting and non-inverting inputs of the amplifier 33 are the same. If the impedance of the path from the switched terminal 1 5 of the ignition switch and the frame is changed, for instance by closing switch 19, a transient voltage change will occur at the junction of resistors R1 and R2. This transient is transferred through capacitor C1 to the junction of resistors R3, R4, R5 and R6, and an instantaneous negative-going change in voltage occurs at the inverting input of the amplifier 33.

The capacitor C2 however serves to hold the voltage at the non-inverting input substantially constant, so that the voltage at the inverting input falls below that at the non-inverting input. The amplifier output will thus swing towards the positive bus 31, and the positive voltage is transferred through capacitor C3 to energise the gated astable 27 (Figure 1) and sound the transducer 28.

Figures 3A to 3C show three possible forms of vibration detector circuit for use in the arrangement of Figure 1. Figure 3A shows a basic circuit, including a vibration detector element 34 connected in series with a resistor R7 to the bus 31; the output is taken from the junction of the element 34 and the resistor R7 and is fed to the monostable device to cause triggering thereof when vibration of the element 34 occurs. In the arrangement of Figure 3B, the output is buffered by means of a NAND gate wired as an inverter, the input to the gate being connected to the junction of the resistor R7 and the element 34. In Figure 3C, means are provided to adjust the sensitivity of the vibration detector.Here, the junction of resistor R7 and the element 34 is connected to the input of a NAND gate wired as an inverter through a variable pre-set potentiometer P2, the input to the NAND gate also having a capacitor C4 connected to earth.

Adjustment of the potentiometer P2 alters the threshold at which the inverter will drive the monostable device to cause the alarm to sound.

Figure 4 shows the complete circuit diagram of the detector arrangement for use in the overall arrangement of Figure 1. Components R1 to R7, C1 to C4, P1 and P2 and amplifier 33 have already been described with reference to Figures 2 and 3C, and will not be described again.

The junction of variable resistor P2 and capacitor C4 of the vibration detector arrangement is taken in the circuit of Figure 4 through a capacitor C5 and further resistor R8 to the inverting input of the amplifier 33, so that a negative voltage pulse appearing at that input (whilst capacitor C2 holds the non-inverting input at a substantially constant voltage) causes the output to swing towards the positive supply voltage.

A pair of two-input NAND gates G 1 and G2 are wired as a bistable and serve to couple the amplifier output to the astable multivibrator 27.

The bistable has a time constant of about 10 seconds, determined by capacitor CT and resistor R 13. One input of gate G 1 is connected to the output of gate G2, the other input of gate G 1 being connected to the capacitor C3 and normally being held low by resistor R9. One input of gate G2 is normally held low by means of resistor R10 and capacitor C6, but this input may be taken high by means of line 35 which is connected through to the switched terminal 1 5 of the ignition switch. As soon as that input of gate G2 goes high, further operation of the astable is inhibited.When the output of the amplifier 33 goes high, so also does the other input of gate G1, taking the output of that gate G 1 low. This is transferred through capacitor C7 to the second input of gate G2, but the output of that gate G2 remains high unless meanwhile the ignition switch has been operated thereby also taking the first input of gate G2 high as well; in this case, the output of gate G2 goes low, and the output of gate G1 is always high, irrespective of the amplifier 33 output. When the output of gate G 1 goes low, the non-inverting input of amplifier 33 also is pulled low through diode D3 and resistor R1 1, discharging capacitor C2. The second input of gate G1 may also be pulled high by means of resistor R12 and diode D4 when wire 36 is connected from earth.However, as long as wire 36 is earthed, diode D4 will be reverse-biassed and resistor R 12 will not affect the operation of gate G 1. Wire 36 is used typically to wrap around luggage or other accessories carried by the motor cycle and is then earthed; disconnecting the wire to remove the luggage or accessories will therefore actuate the alarm. The time constant of capacitor C6 and resistor R9 is about 1 minute, so that operation of the alarm remains inhibited for this time following ignition switch off.

The output transducer 28 is in the form of a moving diaphragm device and is driven by a 555 timer connected as an astable multivibrator. The output of this multivibrator is modulated by means of a further multivibrator, consisting of gates G3 and G4, appropriately connected to the 555 timer.

Turning now to Figures 5A and 5B, there are shown two alternative forms of vibration detector element 34, usable in any of the arrangements 3A and 3C. The detector element of Figure 5A comprises a glass cylinder 40 having a pair of end caps 41 and 42 fitted therewithin, the end caps being metallic and having conductors 43 and 44 attached thereto. A graphite rod 45 is located within the cylinder, so as to contact the metallic end caps. Vibration of the element 34 causes the graphite rod 45 to roll around the metallic end caps 41 and 42 and the resistance therebetween changes significantly as a consequence.

In Figure 5B there is shown an essentially similar arrangement, but here a graphite rod 46 is located within a pair of conducting wire rings 47 and 48 soldered appropriately into a printed circuit provided on a board 49. Non-conducting end stops 50 are suitably mounted to the printed circuit board, to prevent the graphite rod 46 falling out of the pair of graphite rings.

To fit the above-described detector of Figure 4 to a motor cycle, all that is necessary is for the external motor cycle battery to be connected through diode D1 to bus 31, the circuit to be earthed to the motor cycle frame, the junction of resistors R1 and R2 to be connected to the ignition switch and wire 36 to be connected to an earth, first passing the wire 36 round luggage if required. Apart from wire 36, the installation is permanent and the entire circuit should be arranged so that it is mounted rigidly and will respond to vibration of the motor cycle. To set the detector, the ignition switch 11 is opened and thereafter any change in impedance between the switched terminal 1 5 of the ignition switch and the motor cycle frame will cause the alarm to emit an audible note out of the transducer 28 until the alarm self-resets, after about 10 seconds. If the motor cycle is to be pushed away to be stolen, operation of the gears (which normally are left engaged but which must be moved to the neutral position in order to push the motor cycle) will actuate switch 1 9 and sound the alarm. Also, the vibration detector should respond to movement of the motor cycle and cause the alarm to sound.

When however the motor cycle is properly to be driven away, closing switch 11 by means of the appropriate key will disable the detector device and the alarm no longer will respond to vibration or changes in impedance between the switched terminal 15 of the ignition switch and the frame.

Claims (14)

Claims

1. A vehicle having an electrical system including a storage battery and an electronic detector arrangement for sounding an alarm if the state of the electrical system is changed when the vehicle is parked, which detector arrangement includes an edge-triggered monostable device having an input which is connected to a point in the electrical system which point is at battery potential when the vehicle normally is operated but which is disconnected from the battery when the vehicle is parked, alarm means connected to the monostable device output and responsive to a pulse appearing thereat to sound an audible alarm, and means to impress a voltage between the said point and the vehicle earth return whereby a change in state of the electrical system associated with said point causes a transient voltage to appear at the monostable device input thereby triggering said audible alarm.

2. A vehicle as claimed in Claim 1, wherein the vehicle electrical system includes an ignition circuit having an ignition switch and said point of the electrical system to which the monostable device input is connected comprises the switched terminal of the ignition switch.

3. A vehicle as claimed in Claim 1 or Claim 2, wherein the voltage impressing means comprises a potential divider arranged across the power supply of the detector arrangement, the divided voltage being connected to said point of the electrical system.

4. A vehicle as claimed in any of the preceding claims, wherein the edge-triggered monostable device comprises an operational amplifier, both inputs of which are resistively coupled to said point but one input of which is decoupled by means of a capacitor whereby a voltage transient at said point causes a differential voltage to appear on the amplifier inputs, thereby swinging the output voltage towards that of one of the power supply rails of the amplifier.

5. A vehicle as claimed in any of the preceding claims, wherein a vibration detector is included in the detector arrangement so as to trigger the monostable device if vibration is detected thereby.

6. A vehicle as claimed in Claim 5, wherein the vibration detector comprises a graphite rod resting under gravity on a pair of contacts, movement of the rod causing a change in resistance between the pair of contacts.

7. A vehicle as claimed in any of the preceding claims, wherein an auxiliary battery is included in the detector arrangement, the detector arrangement normally drawing power from the vehicle battery but the auxiliary battery being disposed so as to power the arrangement in the absence of the vehicle battery.

8. A vehicle as claimed in Claim 7, wherein the auxiliary battery and the vehicle battery are each connected to a bus of the detector arrangement through a respective diode and the auxiliary battery is of a lower voltage than the vehicle battery whereby the diode associated with the auxiliary battery normally is reverse-biassed.

9. A vehicle as claimed in any of the preceding claims, wherein the detector arrangement has a further input which when connected to the vehicle earth return does not affect the operation of the detector arrangement but which when disconnected from the vehicle earth return causes the audible alarm to sound.

10. A vehicle as claimed in any of the preceding claims, wherein connection of said point to the vehicle battery to operate the vehicle inhibits operation of the detector arrangement.

11. A vehicle having an electrical system including a storage battery and an electronic detector circuit for sounding an alarm if the state of the electrical system is changed substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

12. A method of detecting operation of a vehicle electrical system when the vehicle is parked, in which method the impedance between a point of the electrical system and the vehicle earth return is monitored by impressing a voltage on said point and there detecting transient changes in the impressed voltage by means of an edge-triggered monostable device connected to provide an output pulse when a transient change occurs at the input thereto, and the output pulse of the monostable device drives alarm means to give an uadible indication of tampering with the electrical system, said point in the electrical system being one which is disconnected from the vehicle battery when the vehicle is parked but connected to the battery when the vehicle is operated normally.

13. A method as claimed in Claim 12, in which the electrical system includes an ignition circuit having an ignition switch, and the switched terminal of the ignition switch is monitored by the monostable device.

14. A method as claimed in Claim 12 or Claim 13, in which a vibration detector is wired to the edge-triggered monostable device to trigger the device when subjected to vibration, thereby to sound the alarm.

1 5. A method of detecting operation of a vehicle electrical system when the vehicle is parked substantially as hereinbefore described with reference to the accompanying drawings.