GB2281428A

GB2281428A - Vehicle security system.

Info

Publication number: GB2281428A
Application number: GB9317522A
Authority: GB
Inventors: Martin Schulz
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1993-08-21
Filing date: 1993-08-21
Publication date: 1995-03-01
Anticipated expiration: 2013-08-21
Also published as: DE4422892A1; GB2281428B; GB9317522D0; DE4422892C2

Description

2281428 VEHICLE SECURITY SYSTEM The present invention relates to a vehicle

security system that comprises a central control module connected to remote 5 sensing units.

It is known to provide a security system that immobilises a vehicle and/or emits a visible or audible alarm signal in response to detection of an intrusion or an attempt at breaking into the vehicle. Various sensing units are known for use in such a system, amongst them glass breakage sensors, open door sensors and passive infra-red, acoustic and microwave intrusion sensors. In many systems, several sensing units are provided all electrically connected to the same central control module. The same control module may also be connected to a remote control module that disables the security system upon receiving a coded inf ra-red signal.

The present invention is concerned with the wiring configuration for such a security system and seeks to take advantage of the relatively slow rate of data transfer between the central control module and the sensing units to minimise the number of wires required, so as to reduce system complexity and installation cost.

According to the present invention, there is provided a vehicle security system comprising a plurality of sensing units for sensing intrusion or attempted intrusion into the vehicle and a common control module connected to the sensing units for causing an alarm to be emitted in response to a signal from any sensing unit, characterised in that each sensing unit is connected to the control module by a single wire, the control module being arranged to vary the voltage on the wire in order to set the operating state of the sensing unit and each sensing unit being arranged to vary 2 the current drawn from the wire to communicate data to the control module.

It is possible either to use one wire for each respective 5 sensing unit, or to connect all the sensing units using a single wire bus. The f ormer construction is the less costly to implement as no processor is required in the sensing units to control communications over a common bus.

In the case where each sensing unit has its own respective communication wire, the sensing unit may be switched on or off by simply enabling or interrupting the voltage supply to the sensing unit. As an alternative a binary encoded signal can be transmitted by modulating the voltage on the wire.

If, for example, the sensing unit requires a 9 Volts supply for its operation, the voltage on the line may be modulated between 9 Volts and 12 Volts to transmit binary data on the wire. In this way, several sensing units may be controlled by means of a single wire bus, as coded binary data may be sent to the individual units while the power demands of all units continue to be met.

Data is transmitted f rom, the sensing unit back to the control module by current modulation. If the sensing unit takes a steady current of say 2.5 mA then this may represent a binary LOW and whenever a binary HIGH is to be sent to the control module, then a switch within the sensing unit may be operated to draw say 10 mA. By monitoring the current variation on the wire, the control module may in this way detect a receive signal. As the binary signal may include a code identifying the sensing unit, this technique may be used in a system having a single wire bus as well as one wire per sensing unit.

The invention will now be described further, by way of 3 example, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a first motor vehicle 5 security installation, and Figure 2 is a similar block diagram of an alternative motor vehicle security installation.

Both the drawings show a vehicle security system comprising a central control module 10 connected to three peripheral sensing units 12, 14 and 16 of which the unit 12 is the receiver of an RF or inf ra-red remote control unit, the unit 14 is a microwave scanner for sensing an intruder within the vehicle and the unit 16 senses glass breakage. These units are given as typical examples of sensing units that may be used in a vehicle security system. Each of these units is known per se and its operation need not therefore be described in detail within the context of the present invention. The purpose of the central control module is to arm and disarm the individual sensing units and to respond to a detection signal from a sensing unit by operating the horn, the headlights or a radio pager, so as to issue a warning of the tampering with the vehicle. once again the operation of the control module is known per se and it need not be described in detail within the present context.

The invention is concerned with the wiring connecting the central control module 10 to the sensing units 12, 14 and 16. In both the illustrated embodiments of the invention, a single wire connects each peripheral sensing unit to the central control module. The difference between the two embodiments resides in the fact that in Figure 1 three wires 18, 20, 22 are provided, each connecting the central control module to a respective one of the sensing units 12, 14, 16, 4 whereas in Figure 2 the same one wire bus 24 connects the central control module 10 to all three sensing units.

Data needs to be transmitted in both directions along each 5 of the wires 18, 20 and 22 and the wire 24. The control module needs to send signals to the peripheral sensing units 12, 14 and 16 to arm and disarm them, while the sensing units need to send back signals to the control module to indicate that they have detected a remote control signal, intrusion into the vehicle or glass breakage, as the case may be.

To enable all these data communications along a single wire conductor, so as to simplify the vehicle wiring, in the present invention the control module sends signals to each peripheral sensing unit by modulating the voltage on the wire connecting them, and each sensing unit sends data back to the control module by modulating the current drawn from the wire.

Dealing first with the embodiment of Figure 1, here in its simplest form the modulation of the voltage may consist of switching the voltage on each of the wires 18, 20 and 22 between zero, when the sensing unit is disarmed, and the full supply voltage required by the sensing unit, when the latter is to be armed. In other words, the control module can simply switch the voltage supply to each peripheral sensing unit on and off. When a sensing unit is armed but inactive (i.e. no intrusion detection) it draws a small current, for example 0.25 mA from its supply wire. When a sensing unit is active on the other hand it draws a significantly larger current. typically 10 mA, thereby enabling the control module to determine the state of the sensing unit.

To allow f or additional sensing units to be added to a system, the central module 10 must be able to recognise the new sensor. To enable this to happen, after power switch on each sensor must draw current at the 'sensing unit active' level from the module 10. When this current is detected, by the module 10, the sensing unit is connected. If the current is not detected, the sensing unit is not recognised and is not at 'connected' status. This facility can also be used for diagnostics.

In the case of the second embodiment, applying a supply voltage to the bus can once again be used to control the sensing unit, provided that the system always requires all the sensing units to be in the same state, in other words all armed or all disarmed. If it is required to operate the sensing units 12, 14 and 16 individually, then a modulated voltage may be applied to the bus 24. The mean or minimum voltage on the wire 24 will in this case be sufficient to energise all the units and the modulations superimposed on the supply voltage can be decoded by a processor in each sensing unit. Any unit can then be activated by the transmission of an encoded signal matched to an address code in the sensing unit.

When any armed unit needs to send a data signal back to the control module, it modulates the current drawn from the bus 24 in accordance with a predetermined code that can be recognised within the control module. The current is varied between 2.5 mA and 10 mA, these current values being taken to represent, for example, a binary 0 and a binary 1, respectively. Even in the case where each sensing unit is connected to the central control module by its own dedicated single wire, this form of modulation may be used to convey different data to the central control module.

6 The advantage of the embodiment shown in Figure 1 is that it does not require the use of intelligent sensing units. It also has a zero standby current when the sensor is armed. This is important eg for a microwave scanner which is only to activated after a glass breakage has been detected. It does require several wires to be connected to the central control module but it is easy to add on other sensing units on a retro fit basis.

The embodiment of Figure 2, on the other hand, may reduce wiring complexity, but here processing power is required in the sensing units to control the communication over the common bus wire 24, and this will lead to additional cost. Also the standby current is increased relative to the Figure 1 embodiment and a wake up circuit may be needed to provide the enable function. of course, communication protocols are well known for controlling the flow of serial data on a common bus and these need not be described in the present context.

7

Claims

1. A vehicle security system comprising a plurality of sensing units (12, 14, 16) for sensing intrusion or attempted intrusion into the vehicle and a common control module (10) connected to the sensing units for causing an alarm to be emitted in response to a signal from any sensing unit, characterised in that each sensing unit is connected to the control module (10) by a single wire (18, 20, 22, 24), the control module being arranged to vary the voltage on the wire in order to set the operating state of the sensing unit and each sensing unit being arranged to vary the current drawn from the wire to communicate data to the control module.

is

2. A vehicle security system as claimed in claim 1, wherein one wire (18, 20, 22) is provided for connecting each respective sensing unit (12, 14, 16) to the common control module (10).

3. A vehicle security system as claimed in claim 1, wherein a single wire bus (24) connects all the sensing units (12, 14, 16) to the common control module (10).