GB2284017A - Vehicle security system - Google Patents

Abstract

A main unit 1 is operable to arm and disarm a plurality of circuit breakers 2 which can immobilise the vehicle or operate a siren in response to an emergency situation such as unauthorised entry into or starting the vehicle. The circuit breakers 2 are programmable so as to be actuated at different times after the receipt of a signal indicating an unauthorised action. The circuit breakers 2 may control a fuel injection control circuit and a fuel pump power supply circuit and a siren or sirens may also be operated. A remote control key (30, figs. 9 and 10) may control the unit 1 and the breakers 2 by coded wireless links. <IMAGE>

Description

VEHICLE SECURITY SYSTEM This invention relates to a vehicle security system which is arranged to initiate a predetermined action, such as immobilising the vehicle or emitting an audible or visible warning, in response to detection of an emergency situation, such as unauthorised entry into the vehicle.

In a particular known type of such a vehicle security system, a main control unit is hard-wired to an ignition kill which can be enabled and disabled by the main unit, that is, activated and deactivated or made responsive and unresponsive to a signal indicating an emergency situation. The ignition kill continues to break the vehicle's ignition circuit even after the main unit has been destroyed by a thief.

A disadvantage of this system is that the thief can use the control wire to trace the location of the ignition kill which can then be destroyed in order to bypass the system.

In the known security system, the ignition kill is triggered by a positive or ground signal, i.e. a logic one or zero. This leads to a further disadvantage in that the thief can trigger the ignition kill to the disabling mode by simply connecting the appropriate control wire in the main unit to the required positive or negative terminal voltage.

Another disadvantage of this known security system is that the communication between the main unit or the secondary main unit (i.e. the alarm siren) and the ignition kill is not secure. Thus a thief can simply replace the original main unit with his own main unit and disarm the whole system using his own remote control key.

A still further disadvantage of this known system is that a thief can often identify the brand of the system and the function of the wires within the vehicle, by any of three methods. Firstly, certain vehicle manufacturers employ specific brands of security system. Secondly, some vehicles having security systems display labels warning off potential thieves. However, such labels either state the brand name of the system or identify the brand by their specific design. Thirdly, the brand of system can usually be identified by the outward appearance of the remote control key. In any of these cases, the thief can purchase an identical security system and ascertain the function of the wires by studying the installation guide supplied.

It is therefore an object of the invention to provide a vehicle security system which overcomes some or all of the above disadvantages associated with such known systems.

Accordingly, the invention consists in a security system for a vehicle, said system comprising a plurality of operational units each for initiating a predetermined action in response to detection of an emergency situation and means for enabling and disabling said operational units, said operational units being programmable to initiate their respective actions at different times after the receipt by said operational units of a signal indicating an emergency situation.

The enabling and disabling means may comprise a main unit intended to be installed in the vehicle.

The main unit may communicate with the operational units via wireless links or alternatively the main unit may be hard-wired to the operational units.

Alternatively or additionally to the main unit, the enabling and disabling means may comprise a control unit remote from the vehicle, the control unit communicating with the operational units via wireless links.

At least one of the operational units may be operable to immobilise the vehicle and/or at least one may be an audible waming device.

The signal indicating an emergency situation may be provided in response to unauthorised starting of the engine of the vehicle.

Preferably, the communication between the enabling and disabling means and the operational units takes place using a coded format, such as a coded bitstream.

The invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a block circuit diagram of a vehicle security system according to a first embodiment of the invention, Figure 2 is a signal diagram showing the operation of the system shown in Figure 1, Figure 3 is a block circuit diagram of a vehicle security system according to a second embodiment of the invention, Figure 4 is a signal diagram showing the operation of the system shown in Figure 3, Figure 5 is a block circuit diagram of a vehicle security system according to a third embodiment of the invention, Figure 6 is a block circuit diagram of a vehicle security system according to a fourth embodiment of the invention, Figure 7 is a signal diagram showing the operation of the system shown in Figure 6, Figure 8 shows a vehicle incorporating a security system according to an embodiment of the invention, Figure 9 shows a vehicle incorporating a security system according to an alternative embodiment of the invention and, Figure 10 is a block circuit diagram of the system shown in Figure 9, Figure 11 shows a programmable timer for use in an operational unit according to an embodiment of the invention, Figure 12 is a block circuit diagram of a digitally controlled operational unit and Figures 1 3A and 13B form a flow chart showing the operation of the unit shown in Figure 12.

Referring now to the drawings, figure 1 shows a vehicle security system having a main unit 1 including a built-in ignition kill (not shown) and an operational unit or remote circuit breaker 2. The main unit 1 communicates with the circuit breaker 2 by means of communication media 3, which in the preferred embodiment of the invention, is a radio link. For simplicity, Figure 1 only shows one remote circuit breaker 2, but it will be appreciated that at least two circuit breakers are provided.

Referring also to figure 2, the main unit 1 contains a decision making control unit 4 which issues a command signal A to an encoder 5. The encoder 5 encodes the command signal A into a coded signal B of bit-stream or bit-string format which, where a remote control key for the security system is also provided, has no direct relationship to the securely coded signal emitted by the remote control key. In this case, the remote key and a decoder (not shown) of the main unit 1 are set to one secure address, e.g. 1100 whereas the encoder 5 and decoder 8 are set to another secure address, e.g. 2300. The signal B is supplied to a modulator 6 of the main unit 1 where it is modulated into a signal C for transmission via the communication media 3. In this example, the modulator 6 is a radio modulated transmitter and the communication media 3 is air.

The circuit breaker 2 receives the modulated signal C at a demodulator 7, which in this example is a radio receiver and which demodulates the signal C back to the coded signal B. The coded signal B consists of preset address bits inserted by the encoder 5 and message bits. A decoder 8 of the circuit breaker 2 extracts the address bits from the bit pattern received and detects whether they are matched to its own preset address. All the circuit breakers and audible waming devices or sirens are set to the same address, thus preventing their operation under the control of an unauthorised main unit replacing the original main unit 1.

The decoder 8 decodes the coded signal B back to the command signal A.

Figure 2 shows how, after receiving an enabling or "Arm" command from the main unit 1, the decoder 8 pulls a latched disarm-status line Ad low. This makes the output D of an OR gate 9 low which opens the contacts of a relay 10 and an enabled or "Armed" mode commences.

If the main unit 1 detects the entry of a thief into the vehicle during the "Armed" mode, it sends a "Break" command to the circuit breaker 2. The decoder 8 pushes a "Break" signal Ab high, thus forcing a non-retriggerable programmable one-shot timer 11 to emit a pulse of duration T, predetermined by the RC time constant of the timer 11, at its output As. During this long pulse, the signal D is high and the contacts of the relay 10 are closed. Power is thus supplied from a power supply or vehicle signal line 12 to a controlled variable 13 which may, for example, be the ignition circuit or fuel pump. At the end of the pulse on As, the OR gate output D goes low, opening the contacts of the relay 10 and thus disconnecting the power source 12 from the controlled variable 13 in order to immobilise the vehicle.

Figure 3 shows an alternative vehicle security system which detects unauthorised starting of the vehicle's engine rather than unauthorised entry into the vehicle. In this system, modified remote circuit breakers 2' (only one of which is shown) instead of the main unit 1 control the time at which immobilisation occurs.

Referring also to figure 4, to arm the system, the main unit 1 sends an "Arm" command to the circuit breaker 2'. On receipt of this command, the decoder 8' pulls the "Disarm" signal Ar low in a manner similar to the signal Ad in figure 1. The low level of Ar also enables a voltage or current sensing circuit 14 to detect a drop in the terminal voltage BT1 of the vehicle battery 15.

An unauthorised user of the vehicle must bypass the built-in ignition kill of the main unit 1 by reconnecting the starter wire in order to send electric power to the starter. The starter coil then draws a large current which causes a significant drop in the battery terminal voltage BT1. The sensing circuit 14 is calibrated to detect a drop in the battery terminal voltage BT1 which occurs when the starter draws current, ensuring that unauthorised starting of the vehicle is detected.

The output of the sensing circuit 14 is supplied to one input of an AND gate 15. Another input is provided by the inversion of the "Disarm" signal Ar.

When a battery terminal voltage drop is detected in the "Armed" mode, the output of the AND gate 15 rises and triggers the one-shot timer 11. As in f figure 1, the output As of the one-shot timer 11 is combined in an OR function with the "Disarm" signal Ar to control the relay 10 and hence the immobilisation of the vehicle. The timer output As is also supplied to a negative edge triggered programmable one-shot timer 16, which at the end of the pulse on output As, produces a long negative pulse at its output Ps which is supplied to a third input of the AND gate. Thus, if a second or subsequent disturbance in the battery terminal voltage BT1 occurs during the "Armed" mode, the sensing circuit 14 is prevented from triggering the one-shot timer 11 and closing the contacts of the relay 10.

Figure 5 shows how an alternative remote circuit breaker 2", can be connected to a siren 17. In this embodiment, the input of the OR gate 9, which in figures 1 and 3 is supplied by the "Disarm" signal Ad, is connected to the negative logic level. On the falling edge of the pulse at the output from the oneshot timer As, the contacts of the relay 10 open. Thus power is no longer supplied to the input of a negative edge triggered one-shot delay timer 18, this input being instead shunted to earth through a resistor 19. The falling voltage transition triggers the one-shot timer 18 to switch on a transistor 20 for a certain period of time. During this period, the siren 17 is switched on through the return path provided by the saturated transistor 20.

Figure 6 shows an alternative connection for a siren in which a modified circuit is incorporated into the siren 22, and the functional blocks of figure 6 are similar to those of figure 1. Referring also to figure 7, when the decoder 8 receives a "Break" command from the main unit 1, its "Break" signal output Ab is pushed high, triggering the on-delay timer 11 to generate a one-shot pulse at its output Dl.

The duration T of this pulse is predetermined by the RC time constant of the timer 11. An off -delay timer 22 is triggered by the falling edge of the pulse on Dl to generate a negative pulse at its output D2. The pulse on D2 is used to enable a siren circuit 23, causing the siren 21 to sound.

Figure 8 shows an example of a vehicle security system according to an embodiment of the invention installed in a vehicle 24. A car 24 has a main unit 1 mounted beneath the dashboard and includes a built-in ignition kill (not shown) which is connected to open-circuit the primary starter coil at 25. Two wireless circuit breakers 26, 27 are installed at different places for breaking two different electric circuits. A first circuit breaker 26 is hidden in a place convenient for disconnecting the power supply of the electronic fuel injection control circuit 28 and has a trigger time set to two minutes. A second circuit breaker 27, having a trigger time set to four minutes, is mounted within the fuel pump compartment to disconnect the power supply of the fuel pump 29.

When a thief breaks into the vehicle 24, the system enters an alarm state.

The main unit 1 sends a "Break" command to both wireless circuit breakers 26, 27, which start a countdown of their respective trigger times. Meanwhile, the ignition kill built into the main unit 1 disconnects the power supply of the starter 25.

It is relatively easy for the thief to locate the main unit 1 and reconnect the starter wire. However, he is unaware that after two minutes the vehicle is immobilised when the first circuit breaker 26 disconnects the power supply of the fuel injection circuit 28.

Even if the thief realises that the immobilisation is due to the failure of the fuel injection circuit, and he reconnects the supply wire and continues to drive the vehicle, two minutes after the first immobilisation, (i.e. after four minutes in total) the vehicle comes to a halt again when the second circuit breaker 27 disconnects the power supply of the fuel pump 29.

In practice, any number of circuit breakers within reason can be installed in a vehicle, each with a different trigger time. Since each circuit breaker operates at a different time, there is never an assurance that all the circuit breakers have been bypassed.

In the embodiments of the invention described so far, all the commands issued to the remote circuit breakers emanate from the main unit 1. The vehicle owner cannot send commands directly from a remote control key to the wireless circuit breakers, but only to the main unit 1 which communicates with the circuit breakers.

Figures 9 and 10 show a vehicle security system having a decentralised system network, in which both remote circuit breakers 26', 27' as well as the main unit 1 can receive securely coded commands directly from a remote control key 30, which comprises a command key 31, an encoder 32 and a modulator 33.

All the codes are set to the same address, e.g. 1100. However, in the coded bit-stream format, data bits may be shared by the communication paths as follows. Bit &num; I is common to the remote control key encoder 32, the decoder (not shown) and encoder 5 of the main unit 1, and the decoder 8 of each circuit breaker. Bit &num; 2 is only used in the main unit encoder 5 and the circuit breaker decoder 8. Bit &num; I is used for the arming and disarming commands and can be received by the main unit 1 and by each circuit breaker. Bit &num; 2, used for the "Break" command, can only be sent by the main unit 1.

Thus the circuit breakers 26', 27' will continue to operate under the control of the remote control key 30 even if the main unit 1 has been destroyed. It should be noted that figure 10 is functionally identical to figure 3 except for the addition of the remote control key 30.

Figure 11 shows a programmable timer which may be used with each circuit breaker. This is conventional analog one-shot timer such as type LM555 or 74us123, to which is connected an RC network comprising a variable resistor 34 and a capacitor 35. The variable resistor 34 is adjusted either during manufacture of the system or during its installation in a vehicle, in order to program the required time delay for each circuit breaker.

As an alternative to using analog programmable timers, the timing may be digitally controlled as shown in Figure 12. In this case each circuit breaker includes a microcontroller 36, which receives inputs from the demodulator 7 and the voltage or current sensing circuit 14. Switches 37, such as Dual In Line Package (DIP) switches, connected to the microcontroller, are used when installing the system to set the off-delay and on-delay times of a digital timer within the microcontroller 36. The output control 38 of the microcontroller represents the immobiliser or siren as described above.

Figures 1 3A and 1 3B show the operational steps of the microcontroller under the control of the main unit 1 or the remote control key 3. Starting from step D1, if at step D2 a signal is received from the demodulator 7, then the signal is decoded at step D3. If, at step D4, that signal is found not to be the "Arm" command, or if no signal is received, then the ignition or other vehicle circuit is enabled at step D5 and the system loops back to step D2. However, if the "Arm" command is detected, then the ignition is enabled at step D7 and a further check for signals received from the demodulator 7 is made at step D2X. If a signal is received the system returns to step D3, but if no signal is received then the voltage or current sensing circuit 14 is monitored to detect whether a given threshold has been crossed. If it has, then unauthorised starting of the vehicle has occurred and at D9 system reads the off-delay setting into the timer which starts counting down. At step D10, if the timer has run to zero then immobilisation occurs at step D12. However1 if the timer is still running, and if a signal is received from the demodulator then the system returns from step D11 to step D3.

In this way the owner of the vehicle can disarm the system before the vehicle is immobilised.

After immobilisation, at step D13 the on-delay setting is read into the timer which then starts to count down. At step D14, if the timer reaches zero then ignition is enabled again at step D15 and the system returns to step D6.

Alternatively, the system can be immediately disarmed if a signal is detected at step D16 which returns the system to step D3 in order to decode the signal.

The remote circuit breakers cannot easily be located by a thief since there are no control wires to trace them from the main unit. Also, the absence of control wires simplifies the installation of the system.

The size of the printed circuit board for the circuit of the invention is similar to that of a conventional hard-wired ignition kill. For example, each circuit breaker can have dimensions of 40mm x 70mm x 28mm including its casing and a 30A relay. If the 30A relay is placed outside of the casing, the circuit breaker can be reduced to one third of this volume. The small size of the circuit breaker facilitates its installation in a securely hidden location.

The fact that the circuit breakers communicate with the main unit in a securely coded format means that when the original main unit is replaced by an unauthorised main unit, the circuit breakers will make no response.

In addition to a plurality of circuit breakers, a siren as shown in figure 5 or figures 6 and 7 can be incorporated into the system, and programmed to operate at the same time as the vehicle is immobilised, by setting both timers to the same trigger time. The loud sound emitted by the siren increases the threat to the thief.

An elegant anti-theft system can be provided by hiding a plurality of delay-timed mini- sirens throughout the vehicle.

Whilst various embodiments of the invention have been described, modifications may be made thereto without departing from the scope of the invention as defined in the appended claims. For example, in any of the embodiments having at least one time-programmable circuit breaker, the main unit may be hardwired to the circuit breaker(s), in which case no modulator or demodulator is required. Additionally, the use of a securely coded format on the communication link between the main unit and the or each circuit breaker may be incorporated into a wired or wireless link.

Claims (13)

1. A security system for a vehicle, said system comprising a plurality of operational units each for initiating a predetermined action in response to detection of an emergency situation and means for enabling and disabling said operational units, said operational units being programmable to initiate their respective actions at different times after the receipt by said operational units of a signal indicating an emergency situation.

2. A security system according to claim 1, wherein said enabling and disabling means comprises a main unit intended to be installed in the vehicle.

3. A security system according to claim 2, wherein said main unit communicates with said operational units via wireless links.

4. A security system according to claim 2, wherein said main unit is hard-wired to said operational units.

5. A security system according to claim 2, 3 or 4, wherein said signal indicating an emergency situation is received by said operational units from said main unit in a coded format.

6. A security system according to any preceding claim, wherein said operational units are arranged to detect a signal indicating an emergency situation directly.

7. A security system according to claim 6, wherein said vehicle has an engine and said operational units are arranged to sense a voltage or current signal indicating unauthorised starting of the engine of the vehicle.

8. A security system according to any preceding claim, wherein at least one of said operational units comprises an immobiliser for immobilising the vehicle.

9. A security system according to any preceding claim, wherein at least one of said operational units comprises an audible warning device.

10. A security system according to any preceding claim, wherein each of said operational units includes an analog programmable one-shot timer for adjusting the timing of the initiation of the respective predetermined action.

11. A security system according to any one of claims 1 to 9, including a digital microcontroller for adjusting the timing of the initiation of the respective predetermined actions.

12. A security system according to claim 1, wherein said enabling and disabling means comprises a control unit remote from the vehicle, said control unit communicating directly with said operational units in a coded format via wireless links.

13. A security system substantially as described herein with reference to figures 1 and 2, or figures 3 and 4, or figure 5, or figures 6 and 7, or figure 8, or figures 9 and 10, in combination with figure 11 or figures 12, 13A and 13B of the accompanying drawings.