DE3126712A1 - "SECURITY LOCK SYSTEM" - Google Patents

Description

"Security Lock System"

The invention relates to a security locking system for the control of the operation of a device with at least one unlocking element / which must be energized by a power source in order to operate, the safety interlock system of one type has, in which a distribution device is provided for distributing power from the power source to the unlocking element, wherein further a switch device is provided for controlling the power ^ issuance via the distribution device, wherein also a Receiver unit between the switch device and the unlocking element The distribution device is switched on for further control of the übar transmitted power in response to the presence of an externally transmitted signal, and wherein a transmitting unit is provided to generate this signal.

Security locking systems are used extensively to prevent unauthorized entry of buildings from safes or other closed ones To prevent evacuation, or to prevent unauthorized use of a vehicle or the like. A very common and simple form of a security locking system consists in the use of a Lock or a switch that can only be operated when the user has a key. This is the most popular form of one Safety interlock system for electrical equipment that requires electrical power to operate. That is, it is easy and inexpensive to get one. Key switch between the To switch the power source and the device to be secured. To the operation

to enable the device, the key switch must be operated, so that power can be transferred from the power source to the device can.

The key-operated switch solution becomes almost universal used as a security system for automobiles and other vehicles. This means that a key operated switch - subsequently referred to as the "ignition lock", is placed between the battery and the ignition system of the machine. Before power from the vehicle battery that Can excite the ignition system (with which the machine can first run) · the ignition lock must be switched on. Requires the ignition switch to be switched on a key with the appropriate configuration. (Others used as an alternative Security systems are also known in addition to the ignition lock arrangement, such as the provision of locks on the doors of vehicles. )

A problem with the long-known ignition locks, especially in motor vehicles, is the relative ease with which the system can be circumvented. In a vehicle, for example, a somewhat experienced thief can easily bypass the ignition lock or the ignition system otherwise "short-circuit", after which the ignition system of the machine is energized can be.

Other safety locking systems in connection with motor vehicles and the like are generally auxiliary safety systems in addition to the Ignition lock. These auxiliary safety systems usually include warning systems (sirens, horns and the like) that are triggered when a A door, window or other area of a vehicle is broken into without the actual security system being deactivated. A time switch mechanism is often used in conjunction with the warning systems, such that they are only energized after a set period of time has elapsed, namely after entering the vehicle. This time lag enables an authorized user who knows how to put the warning system out of operation to do so after he got into the vehicle. An unauthorized user, on the other hand, would not know how to take the system out of operation (how one hopes) to be chased away once the warning system sounds. Unfortunately Such systems generally do not avoid commissioning

of the vehicle. Rather, they only produce a length that determines is to draw attention to the vehicle and its occupant.

There are also known fuel control valves intended to prevent unauthorized use of a vehicle. In general, means for actuating the fuel valve to enable fuel to be supplied from the tank of the machine via a hidden switch is provided near the driver's seat position. An authorized user of the vehicle must energize the valve before starting the vehicle. However Lsider is generally enough fuel in the carburetor and the fuel supply line between the control valve and system so that the vehicle can be started and set in motion, at least for a short distance before the effect of the closed fuel control valve is detected. Not only can this be dangerous (if, for example, the vehicle suddenly stops in the middle of the street or at any other location where a dangerous traffic situation arises, but it can also be a source of irritation even for an authorized user, if that happens forgets to activate the control valve.

Some types of security interlock systems use an electronic one wireless control. The most popular sbrm of such a system are the well-known electronic garage door openers that respond to a signal address that is transmitted from a portable transmitter to a receiver inside the garage. The receiver only speaks to a command signal generated by the transmitter. The transmitter is usually in a Vehicle and must be able to transmit a signal over a distance of at least about 30 m. Incorrect and accurate It is to be able to transmit a comma signal over this distance required that the usual RF transmission techniques in the transmitter and receiver be used. That is, a radio frequency must be used as a carrier signal to transmit the command signal from the transmitter to the receiver. The use of such an RF carrier increases manufacturing costs and the complexity of both seier and receiver unit. Furthermore, it is not uncommon for a certain type of recipient to to respond to an inapplicable command signal that is transmitted by a transmitter other than the one that is actually assigned.

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Since the receipt of a command signal is generally the only requirement to unlock the security locking system, it becomes relatively easy for an unauthorized user to _{break into} the system in this way.

Magnetically activated security systems are also known. These typically require a device that responds to I> fegnetfeider, which detects the presence of an ifegnet field. Typical examples are in LE-PS 3,569,928, IB-PS 3,885,164, US-PS 3,962,695, US-PS 4,17o, co5 and U.S. Patent 4,136,338. However, these systems all speak to some kind of magnetic force field. It is therefore very easy to use a fraudulent or unauthorized magnetic field to target the to overcome so well known safety devices.

The object of the invention is to eliminate the disadvantages of the aforementioned security systems.

According to a first aspect of the invention, the solution consists in the tferkmalen mentioned in claim 1. Another aspect of the invention is a method as defined in claim 1o.

With reference to the accompanying drawings, the
The subject of the invention is explained in detail below with the aid of examples.

Fig. 1 is a block diagram of a security interlock system as it could be used with the components of a conventional motor vehicle,
Figure 2 is a more detailed block diagram

the sending and receiving units of the system,
Fig. 3 is the electrical schematic of the transmitter according to

Fig. 2,
Fig. 4 is an electrical schematic of the receiver from

Fig. 2 and
Fig. 5 is the electrical circuit diagram of a negative

Voltage source which can be used to generate the negative actuated in the receiver of FIG
Supply voltage.

The preferred use of the security lock system is in Area of motor vehicles or comparable means of transport. Accordingly, in the following explanation of the preferred embodiment a security interlock system with which the operation of a Motor vehicle is secured. It is understood, however, that a security lock system of the type described can also be used with any other device could be used that must be secured and that controllable Lst by applying switchable power or through the use of electranechanical devices that can be controlled via switchable power. Examples of such devices that could be secured by the security interlocking system would include, but are not limited to: the doors of residential houses and similar buildings, safes, electrical installations, industrial machines and the like.

In Fig. 1 is the block diagram of a security locking system shown how it is with the components of a conventional motor vehicle could be used. The system comprises a receiver unit 12 and a transmitter unit 14. The conventional components of the motor vehicle used in conjunction with the security interlock system the vehicle battery 16, the ignition lock 18 and the ignition system 2o. A solenoid valve 22 can also be connected to the safety interlock system can be used to control the flow of fuel through a fuel line 24. The fuel line 24 feeds fuel from a fuel tank of the vehicle (not shown) to the engine (also not shown).

In a conventional spark ignition system, the power is the battery 16 is fed to the ignition system 2o via cables or wires 26 and 28. The ignition lock 18 is accordingly between the battery 16 and the ignition system 2o switched in such a way that the ignition system is controlled in a safe way 2o is controlled. A fuse 3o is also typically provided as a security measure. This fuse 3o can between Ignition lock 18 and battery 16 are installed. The safety interlock system modifies the ignition system described so far in that a receiver unit 12 connected between ignition lock 18 and ignition system 2o will. Accordingly, the ignition system 2o can only work when both the receiver unit 12 and the ignition lock 18 are activated

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. is operated.

The activation of the receiver unit 12 is shown symbolically in Fig. 1 in that the switch 19 from the B position in the Α position is shifted. A magnetically coded signal, symbolic represented by the wave-shaped arrow 32 in FIG. 1, the transmitter unit 14 is coupled to the receiver unit 12 as soon as it is desired to activate the receiver unit. A solenoid valve 22 in the fuel line 24 of the vehicle can also have a Cable 34 can be connected to the active terminal ("A" of the Switch 19) of the receiver unit 12. When the receiver unit 12 through the magnetically encoded signal 32 is activated and the ignition lock has been operated, power from the battery 16 can accordingly be used the ignition system 2o as well as the solenoid valve 22, after which the vehicle can be used.

Fig. 2 shows the block diagram of the transmission unit 14 and the

14th
Receiver unit 12. The transmitter unit comprises an encoder 40, a driver stage 42 and a transmitter coil A1. The encoder 4o is energized by a voltage from the battery C through a push button switch PB. The battery B also serves to supply the driver stage 42 with power. When the switch PB is actuated, the encoder 40 generates a signal encoded in a predetermined manner, which is fed to the driver stage 42 via the signal line 44. The driver stage 42 for its part amplifies the coded signal and transmits it to the transmission coil A1 via the signal line 46.

The coded signal generated by the encoder 4o is preferably a digitally coded signal and comprises a series of logical ones Zeros and logical ones as well as synchronization bits. A complete The coded signal can for example consist of a data pattern of 16 data bits. Frequency shift encryption can for example can also be used to appropriately encode the data bit. That is, each data bit could be 'by a fixed predetermined combination a first and second frequency are represented. For example, if the first frequency is marked by an "H" (for high frequency) and the second frequency is represented by an "L" (for low frequency), a logical one can for example be encoded as "HH", a

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logical zero as "HL" and a synchronization bit as "LL". Typically the frequency H is twice as high as L. If these differ Frequencies of the transmitter coil A1 are supplied, the various associated currents generate a magnetic field around the coil A1 in correspondence with the known principles of magnetic field generation. Accordingly, there is a coded magnetic field (symbolically represented as undulating Arrow 32) around bobbin A1 as soon as the push-button switch PB of the transmitting unit 14 is actuated.

The receiver unit 12 comprises ^, as in the block diagram of Fig. shown, a receiver coil A2, an amplifier 48, a decoder 4o, a time lock circuit 52 and a relay 54. The receiver coil A2 is advantageously positioned within the receiver unit 12 so that it is close to an edge thereof. Accordingly, if a coded If the magnetic field 32 is present, this changing magnetic field will induce a voltage in the receiver coil A2 in accordance with the known principle of electromagnetic induction. This induced voltage becomes the Amplifier 48 is supplied via signal line 56, where it is amplified and processed and fed to the decoder 5o via signal line 58. The decoder 5o compares the received signal with a preprogrammed reference signal. When the received signal is the same as the reference signal, i.e., when each bit of the received signal coincides with each bit of the preprogrammed signal, the decoder 50 produces an output signal on line 6o. The presence of this output signal on line 6o triggers the time delay switch 52. This in turn is designed so that it enables the coil L of the relay 54 to be energized.

The contacts of relay 54 are; connected so that a voltage V _B can be transmitted from the vehicle battery to the ignition system 2o and the solenoid system 22. More precisely, when the ignition lock 18 has been operated, the voltage V "is supplied from the vehicle battery 16 via the signal line 28 to the relay switches" SW1 and SW2. This voltage V_ is also applied to the coil L of the relay 54, although the coil L is only connected to ground via the time delay switch 52 as soon as this has been excited by the output signal of the decoder 50. The relay * switching contacts SWT and SW2 are designed so that they are in their rest position or "off" position, as shown in Fig. 2, as long as the

Relay coil L is not energized. When the coil L is energized, however, they are moved to their lower or working position. Accordingly, if the relay switch SW1 is in the off position, it can be seen for the configuration according to FIG. 2 that the ignition system is connected to ground via signal line 29 SW2 and signal line 62. This setting of the ignition system 2o is of course an optional feature that could easily be omitted by omitting the grounded signal line, if this is desired. It can also be seen that with the relay switch contact SW2 in the off position, the solenoid valve 22, which receives power via signal line 34, is not energized. When the relay switch contacts SW1 and SW2 have been moved to their lower working position, however, it can be seen that the battery _{voltage V 0 is} supplied to the ignition system 2o via switch contact SW1 and to the solenoid valve 22 via relay switch contact SW2. In addition, this same voltage can be fed to the time delay switch 52 via the signal line 64 via the Rslais switch contact SW1. This voltage is used to hold the time delay switch 52 in the Eiii position so that the coil L of the relay 52 remains energized as long as the ignition lock 18 has been operated.

3 shows a more detailed, but still always schematic diagram of the transmission unit 14. The encoder 4o can are preferably implemented using a commercially available integrated circuit such as the S2742 Serial circuit Data Encoder manufactured and sold by Firam American Microsystems, Inc. (AMt) and using some less discrete passives Components. This serial data encoder, denoted by U1 in FIG. 3 encoded by means of a frequency shift encrypted primary data pattern, consisting of 16 data bits. Each data bit has a length equivalent to 32 cycles of a high frequency clock. The frequency of this The clock rate is determined by external = resistors R1 and R1 and capacitor C1 connected as shown. A high frequency clock of 20 kHz is typical. A commercially available 9 V battery, shown in FIG. 3 with B can be used for the line supply of the serial data encoder U1 can be used. The push button switch PB can be switched between the battery B and the encoder U1 so that a one-time Briefly depressing the PB button activates the coding unit.

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The functional and operational characteristics of the serial data encoder in the form of the integrated circuit U1 are familiar to the person skilled in the art and need not be discussed here. Suffice it to say that the purpose of the integrated coding circuit consists in providing serial data as an output signal that can be transmitted to a receiver unit. If one of the AMI manufactured circuit S2743 used as component U1, appear this serial output data at terminal 15. As mentioned above, exist this data is made up of 16 data bits, nine of which can be selected by the user by being selectively set or left open of pins 1 to 9. The remaining seven bits are fixed for a given unit and are used to mark the beginning and end of a given coded signal, as well as for synchronization purposes.

The driver stage 42 can be implemented using a single transistor Q1 (FIG. 3). This transistor Q1 can be an NPN transistor, such as the type 2N39o4, the base of which is connected directly to terminal 15 of the coding circuit U1. The emitter of the transistor Q1 is connected to the transmitter coil A1. The current accordingly flows through coil A1 under the control of the encoded signal applied to the base of transistor Q1. A light emitting diode CR1 is connected to the collector of the transistor Q ¹ I. Accordingly, all or almost all of the current flowing through coil A1 also flows through the eight emission circuit CR1. With this configuration, CR1 provides a light indication that the encoded signal is applied to the transmitter coil A1. As mentioned above, the transmitter coil A1 generates an alternating magnetic field with frequencies that are stormed by the coding circuit U1. In the preferred embodiment, these frequencies are between 5 kHz and 10 kHz, although any other suitable frequencies could be used.

Alternatively, the driver stage 42 could be implemented by using two transistors connected in a push-pull configuration. In such a circuit arrangement, a transistor is an NPN and the other a FNP ^ transistor. The emitter and base connections of both Transistors are connected together, with the common base connection is directly at the output of the coding circuit Ü1 and the

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common emitter is typically connected to the transmitter coil A1 via a coupling capacitor. In such a case he knew NFN transistor be of type 2N3904 and the PNP transistor of type 2N3906. The primary advantage of such a push-pull arrangement or similar arrangements using a coupling capacitor between Driver stage and transmitter coil A1 is that the direct current does not flow through the transmitter coil, which leads to a waste of energy would lead.

4 shows in detail the circuit of a receiver unit 12. The alternating magnetic field generated by the transmitter unit 14 induces a signal in the receiver coil A2. This signal is from Operational amplifier U2 amplified. The output of amplifier U2 becomes then further reinforced by a voltage follower circuit, consisting from another operational amplifier U3. The operational amplifier ü2 can be a commercially available integrated circuit, for example of the type CA3130 be implemented while the operational amplifier U3 (voltage follower) by using the commercially available CA3140 operational amplifier can be realized; Both types are manufactured by RCA.

The output of the voltage follower U3 comes through a coupling capacitor C10 to a serial data decoder, in the form of an integrated circuit U4. This serial data decoder U4 is equivalent to the decoder 50 .according to Fig. 2. A commercially available serial data decoder, such as the type S2742 from AMI, can be used to implement the decoder U4 in the preferred embodiment. Such a decoder decodes the transmitted 16 bits of the encoded signal using an on-chip phase locked loop. The usual settlement procedures are also used to compare the decoded signal with an externally selected code. The connecting pins of U4 with the numbering 1 to 9 in Fig. 4 know programmed by a user to correspond to the code which has been set by the user in the coding circuit UI of FIG. Accordingly the user can put nine of the bits of the sixteen-bit code word in any one Preset the desired sequence that is only known to the user, thus ensuring the integrity and secrecy of the arrangement will.

Working and operating mode of the decoding circuit U4 are the Known to those skilled in the art and need not be explained here. Suffice it to say that when a coded signal is received by the integrated circuit U4, which corresponds to the preprogrammed reference plan, that by selective definition of the nine selectable Bits has been set, an output signal at terminal 10 appears. This output signal is the one manufactured by AMI Serial data decoder type S2742 a high voltage level. If available, this allows high-lying Spannuiigspegol Current flow from decoder U4, through both diode CR2 and the resistor RI4 to capacitor C15. The tension on the positive surface of this Accordingly, the capacitor rises with a time constant which is primarily stormed by the value of the capacitor C15 and the value of the resistor RI4. As soon as this voltage reaches a certain threshold, the timer circuit U5 is triggered. The value of this switching level is determined by the voltage divider network, formed from the resistors R17 and R 18. The capacitor C16 is a bypass capacitor switched to filter out noise related to this Threshold level.

The timer circuit U5 can be realized using a commercially available standardized timing circuit 555 available from numerous semiconductor manufacturers such as Signetics, Fairchild, National and RCA is offered. As long as the voltage at terminals 2 and 6 of U5 exceeds the specified threshold value, current can be supplied via Kleircne 3 flow to ground and thus energize the coil L of the relay 54. If the However, if voltage at terminals 2 and 6 falls below the trigger threshold level, coil L of relay 54 is de-energized.

An additional diode CR3 is between the wiper of the relay switching contact SW1 and the cathode of the diode CR2 placed. This diode CR3 enables the battery voltage V_ to be applied to the capacitor C15 is once the relay 54 is energized for the first time. A high one Voltage at terminal 17 of the decoder U4, even if it is only is a momentary pulse, it is first necessary to energize the relay 54. As mentioned above, this high voltage charges the Capacitor C15 above the threshold level, so the timer circuit

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Mf-

Trigger U 5. After triggering, U5 connects coil L of Beiais 54 to ground via diode CR5. During this period, current can flow through the coil L and thus excite the field coil by switching the relay switching contacts SW1 and SW2 into their working position or lower position. When the relay switch contact SW1 is in the working position, you can see that the battery voltage V is fed back to the capacitor C15 via diode CR3. Accordingly, C15 remains charged above the threshold level and holds relay 54 in its energized state. In this way, the relay 54 remains self-holding until the point in time that the ignition lock 18 is used to disconnect _{the Batieries voltage V n.}

It would also be possible to design the time lock circuit 50 (Fig. 2) in this way interpret that when the voltage on line 60 drops below a Trigger threshold level of the circuit 52, the relay 54 for anyway would remain energized for a predetermined period of time. This time period could. be sufficiently long that a user of the security locking system (1) could transmit a coded magnetic signal from the transmitter unit 14 to the receiver unit 12 and (2) the ignition lock 18 with the ignition key. With such a In the configuration, the order of activating the receiving unit 12 and activating the ignition key 18 could accordingly be reversed.

When the ignition lock 18 is switched off, the capacitor C15 (Fig. 4) a voltage above the trigger threshold level during a period of time primarily determined by the value of resistor R15 and des Capacitor C15. A user can therefore for a brief moment turn off the ignition lock switch 18 without having to transmit a magnetically encoded signal from the transmitter unit 14 again.

It can be seen in Fig. 4 that a Zenafc diode VRZ can be used, to regulate the battery voltage V_ to a more precise value.

When the battery voltage is V "12 V, as is the case with most Motor vehicles is common, the Zener diode VRZ, for example, from Type IN4740 or a 10 V Zener diode. This regulated Zener voltage is then used to convert the integrated circuits U2, ü3, ü4 and u5 to dine. The use of the Zener diode VRZ is optional insofar as

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than all integrated circuits even with an unregulated one Voltage source would work. The use of the Zener diode VRZ, however, offers a certain overvoltage protection for them Components. It also serves to more precisely set the threshold switching level and to define the time constants that play a role in the operation of the timer circuit U5.

The decoder circuit U4 requires a negative voltage -V as well as a positive tension to get to know work. Such a negative voltage is usually within the electrical System of a normal motor vehicle not available. Accordingly can be a negative voltage source as in the schematic diagram shown in Fig. 5, used to make the required to lead negative voltage from the positive Zener voltage VZ. The circuitry of FIG. 5 includes an oscillator having a frequency of about 100 kHz. This oscillator is realized using " inverting logic gates 70 and 72 connected in series into a common Oscillator circuit are gefejt. The capacitor C19 becomes alternating charged and discharged via resistor R20, according to the change the state of logic gates 70 and 72. Resistor R19 prevents this Discharge from C19 into the input protection circuit of gate 70, bringing the frequency of the voltage is stabilized. Logic gates 74, 76, 78 and 80 are parallel and include a buffer amplifier, the shapes and buffers the oscillator output. After buffering, the amplifier output is fed to a half-wave voltage doubling circuit, Consists of capacitors C20, C21, diodes CJE6 and CR 7 and a resistor R21. A typical value for the negative voltage thus generated assuming a positive input voltage of + 10V is in the On the order of -7 or -8V. The inverting logic gates can advantageously be integrated into a single CHOS inverter circuit Form can be realized, for example the type CD4049, which is offered in the trade by numerous semiconductor manufacturers.

The circuits of Figures 3, 4, and 5 can be readily implemented by those skilled in the art using commercially available components can be constructed based on the above description. The majority

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the capacitors and resistors in these circuits are used for biasing and stabilizing purposes, and one skilled in the art can readily interpret the values and partial circuit diagrams to be used with such components to operate the various integrated circuits and other active components. The transmitter coil A1 (FIGS. 2 and 3) can comprise approximately 350 turns of wire No. 40 on a ferrite core, for example on the commercially available core R33-050-400, manufactured by Amidan. In a similar way, the receiving coil & 2 (Fig. 2 and 3) can be realized using an amidomic ferrite core R 33-050-750, using about 350 turns of wire no. 40.

The simplicity of the transmitter unit 14 enables it to be used in a relatively to realize a small, manually portable unit. When the connector is so constructed, it can easily be placed in a shirt pocket and can accordingly be conveniently used by the authorized user Are available, similar to a common key. The battery B, which is used in connection with the transmitter unit 14, can also be a small, cheap, commercially available battery, such as a 9 V battery, model 246, made by Burgess or model 216, Manufacturing company Eveready.

The receiver unit 12 can also be of relatively compact design and hidden within a vehicle or building Place in such a way that it is nonetheless close to the entrance or the place of operation. When used in one Motor vehicle, for example, the receiver unit can be under the dashboard be placed near the driver's seat. After assembly, it is relatively easy to attach it to the ignition lock 18, the ignition system 20 and the solenoid valve 22 as well to connect to ground, as shown in FIG. With the installation instructions for the receiver unit 12 for a motor vehicle would then have to be specified:

1. Fastening the receiver unit 12 inside the vehicle near the driver's seat, preferably in a place where it is not visible is.

if

2. Determine the wiring from the ignition switch 18 to the Ignition system 20 leads (this is the signal line 28 in Fig. 1). This signal line 28 is the conductor to the coil of a conventional one Ignition system or to control an electronic Ignition system leads. This signal line typically leads orwoiso a voltage between +11 to +14 V when the ignition lock is switched on and 0 V when the ignition lock is switched off. No Connection should be made to the secondary side (high voltage side) of the ignition system. There is no other connection to be made to any one the conductor of the ignition system, including the conductor from the coil to the ignition distributor.

3. Interrupt the conductor determined in step 2 (signal line 28, FIG. 1). .

4. Determine which end of the conductor interrupted in step 3 leads via the ignition lock 18 to the battery. These are around the end that carries 12 V when the ignition switch is on. Connect the wire 27 from the receiver unit 12 to this battery-side end of wire 28.

5. Connect the wire 29, also from the receiver unit 12 came to the other end of the conductor that was cut in step 3. this is the end of the wire 28 that leads to the ignition system 20.

6. Connect wire 62 from the receiving unit to a suitable measuring point, such as the vehicle frame.

7. Connect the conductor 34 from the receiver unit 12 to one of the leads of the solenoid valve 22,

8. Connect the other lead of the solenoid valve 22 to a suitable ground point, such as the vehicle frame.

When installing the system carefully according to the installation instructions above has been installed, the transmitter unit 14 can be used to unlock the receiver unit 12 with a properly encoded signal.

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After correct unlocking allows the receiver unit 12 that the vehicle including the ignition and fuel supply system can be used in the usual way. However, if the receiving unit 12 has not been unlocked, the vehicle will not start. Moreover, even if it were in any way in Gear is set, cannot drive very long because of the fuel system would be blocked.

It is important to note that the encoded signal that is between. The transmitter and receiver unit establishing the coupling is nothing more than a specified sequence of changing magnetic fields. That that is, no high-frequency carrier signal is used to transmit the encoded signal from the transmitter unit to the receiver unit.

It is understood that the embodiment described in numerous Directions could be modified without deviating from the basic idea of the invention !.

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Claims (10)

Claims 1) Safety locking system for controlling the operation of a device that has at least one unlocking element, which is through a power source must be excited before the device can be put into operation, which safety interlocking system has a type, having a distributor for distributing power from the power source to the unlocking element, with a switch device for controlling the power distribution via the distribution device, with a Receiver unit between the switch device and the unlocking element is placed for further control of the power distribution via the distribution device in response to the presence a signal transmitted from a distance and with a transmission unit for generating this signal, characterized in that the Receiver unit (12) is designed in response to a signal (32), which is a magnetic field that is variable accordingly a predetermined coded sequence that the transmitter unit (14) is designed to generate the predetermined encoded magnetic field and that the transmitting unit or receiving unit generate or detect the predetermined coded magnetic field only when the units are close to one another are arranged. 2) System according to claim 1, characterized in that the encoded magnetic field is an alternating magnetic field which oscillates at first and second frequencies, the first and second frequencies occurring sequentially within the encoded magnetic field according to a predeterminable repetition pattern. 3) System according to claim 2, characterized in that the predeterminable Repetition pattern comprises a trinary logical sequence, with a predeterminable series of logical ones, zeros and synchronization bits, The logical ones, zeros and synchronization bits are each defined by a predeterminable combination of the first and second frequencies. 4) System according to one of claims 1 to 3, characterized in that that the device to be controlled is a vehicle, the power source being the vehicle battery (16), the unlocking element being the vehicle ignition system (20) 1st and the switch device is an ignition lock (18) with on and off positions, and that an additional unlocking element with a valve device (22) in a fuel supply line (24) of the vehicle is for controlling the flow of fuel through the supply line, the valve device being controllable by the receiver unit (12) in response to the detection of the presence of the predeterminable encoded magnetic field. 5) System according to one of claims 1 to 4, characterized in that that the receiver unit has a detection device (A2) for Sensing the presence of a changing magnetic field and generating a changing signal in response to that, wherein the changing signal has variations which follow the variations in the detected magnetic field, wherein an amplifier means (48) is provided for the amplification and shaping of the changing signal, wherein a decoder (50) is provided for determining whether the changes in the amplified and shaped changing signal occur in a pattern and sequence corresponding to one preprogrammed code and for generating an unlock signal when the preprogrammed code as in the changes of the changing Signal is detected present, and wherein a relay switch device (54) is provided which is designed to be responsive to the Said unlocking signal to enable the at least one unlocking element to be excited by the power source via the distribution device, when the relay switch device is in a first position and to block the excitation of this at least one unblocking element, when the relay switch device is in a second position. 6) System according to claim 5, characterized in that the relay switch device furthermore has a ground connection device (SW1,62) for electrically connecting the at least one unlocking element as long as the relay switch device is in the second position. 7) System according to claim 5 or 6, characterized in that the receiver unit further comprises a timing circuit (U5, Fig. 4) which is designed to switch the relay switch device in its first position during a predeterminable time period after the generation of the unlocking signal, and as well a holding device (C15, Fig. 4) for holding the relay switch device in the first position for a period of time after the switch device has been flipped into its off position. 8) System according to claim 7, characterized in that the receiver unit furthermore has a holding device (52) which is designed to be responsive to the unlocking signal for holding the relay switch device in its first position as long as the switch device is switched to its on position. 9) System according to one of claims 1 to 8, in which the transmitting unit (14) has a coding device (.40) for generating a predeterminable coded signal that is selectively coded in accordance with a Sequence changes, a driver stage (42) has a magnetic field generating device for amplifying and shaping the predeterminable coded signal (A1) has to generate a changing magnetic field with changes corresponding to the predeterminable coded signal, with a second battery (B) and with a transmission switch (PB), which is electrically connected between the second battery and the eraser, the driver stage und.die magnetic field generating device is switched to enable energizing said components by the second battery when the transmission switch has been moved to a transmission position and to keep the components de-energized as long as the transmit switch is in a non-transmit position. 10) Theft prevention method for securing a device with at least one unlocking element that must be excited by a power source so that the device can be operated, which method comprising the steps of: distributing power from the power source to the unlocking element via a power distribution network, connecting a switch in series with the distribution network, which switchably controls the transmission of power to the unlocking element, An4! close a receiver unit between the switch and the unlocking element, which receiver unit is designed so that it the transmission of power to the unlocking element can also be switched controls in response to detecting the presence of a signal, and approaching a transmitter unit to the receiver unit and Activating the transmitter unit when it is desired to energize the unlocking element, characterized by the steps of: forming the receiver unit such that it responds to a magnetic field that changes according to a specifiable coded sequence changes, the transmission unit is designed in such a way that it generates the specifiable coded changing magnetic field, when it is activated, the transmitting unit or the receiving unit only then generating the predeterminable encoded magnetic field or detect when the units are close to each other.