CN1188523A - car alarm system - Google Patents

Abstract

A charging capacitor (3) of a transponder (2) is wirelessly charged by energy signals from a transceiver (1). The level of the energy transmitted depends on the quality of the inductive transmission between the transponder (2) and the transceiver (1). Too little energy is transmitted if the exciting frequency (fE) of a transceiver oscillating circuit (6, 7) does not correspond to its resonant frequency (fR) owing to component tolerances. To ensure that the charging capacitor (3) is always quickly and properly charged, the exciting frequency (fE) is varied within a predetermined frequency range during a charging phase so that it passes in the vicinity of the resonant frequency (fR) at least once.

Description

car alarm system

The invention relates to an anti-theft system for a car, in particular to a closed system which utilizes the automatic parking signal of the car for release.

An existing anti-theft system (U.S. Patent No. 5,053,774) is configured with a portable transponder that receives an interrogation coded signal sent by a fixed transceiver, and then sends a transponder back to the transceiver. Response coded signal. The energy transmitted in the interrogation coded signal will be released by the reply coded signal. This energy is temporarily stored in an accumulator. When sufficient energy is stored in the accumulator, the coded signal is released.

If the transponder and transceiver are not well matched to each other, this can lead to a very long charging time until the accumulator is fully charged.

The object of the present invention is to provide a car anti-theft system, the accumulator of its transponder can be charged reliably and quickly, so that when receiving an inquiry code signal, a response code signal can be sent without delay (hereinafter referred to as encoded signal).

The object of the invention is achieved by the features of claim 1 . Specifically, reliable coupling between the transponder and the transceiver is achieved by varying the excitation frequency of the interrogation coded signal.

Further preferred embodiments of the invention are characterized by the features of the dependent claims.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Attached are:

Fig. 1: the block schematic diagram of circuit connection of anti-theft system of the present invention,

Figure 2a-2e: Pulse signal diagrams of the anti-theft device's transponder and radio transceiver,

Figure 3: Resonant curve of an oscillating circuit,

Fig. 4: A circuit block diagram of the first embodiment for generating an oscillation,

Fig. 5: Circuit block diagram of the second embodiment.

The car anti-theft system of the present invention has a radio transceiver 1 (Fig. 1) installed in the car, and a portable transponder 2 is installed near it, and the radio transceiver 1 and the transponder 2 are realized through the coupling of the transformer adaptation. The transceiver 1 generates an alternating field, which energy is transmitted to the transponder 2, thus charging a capacitor (charging capacitor 3) or energy store in the transponder 2. When the energy in the charging capacitor 3 is sufficient, the transponder 2 is stimulated to send back a coded signal to the transceiver.

The radio transceiver 1 includes an oscillating circuit (hereinafter referred to as an antenna oscillating circuit), which uses an oscillator 4 to excite oscillation, thereby realizing energy transmission and data return. The antenna resonant circuit here comprises at least an antenna capacitor 5 and a coil (antenna 6 ). The antenna 6 can, for example, be wound around the starter lock.

The transponder 2 has a resonant circuit (referred to below as transponder resonant circuit) comprising a coil 7 and a transponder capacitor 8 . When the antenna 6 and the coil 7 are very close to each other, inductive coupling occurs, and data transmission or energy transfer starts. This is the case, for example, when the transponder 2 is mounted on a starter key. As long as the start key is inserted into the start lock and rotated, the antenna 6 and the coil 7 are electrically coupled.

The oscillations of the antenna oscillating circuits 5, 6 are modulated by the transponder 2 to the beat of the coded message. The transponder 2 includes a switch 9, which switches the auxiliary capacitor 10 and the capacitor 8 of the transponder resonant circuits 7, 8 in accordance with the clock of the coded message. Only when the charging capacitor 3 is sufficiently charged, the switch 9 is closed according to the clock of the coded information, does the modulation process start.

The switch 9 is controlled by a response control device (transponder-IC12), which is an integrated switch circuit.

If the starter key is turned in the starter lock, the transceiver 1 generates an alternating magnetic field (energy signal) with a high magnetic field strength (FIG. 2a). The energy signal is generated for a predetermined period of time (charging phase), in this example 50 milliseconds, with an amplitude of 100 volts. Depending on the quality of the coupling between the transponder 2 and the transceiver 1, ie depending on the received field strength, the charging speed of the energy signal into the charging capacitor 3 differs (FIG. 2b).

When the transmission of the energy signal is finished, the charging capacitor 3 should continue to charge, the transponder 2 confirms that the energy signal is terminated, and the transceiver 1 then generates an alternating magnetic field with a small field strength (a few millivolts in magnitude) . The switch 9 is closed for another predetermined period of time (reading phase) according to the cadence of the encoded information, generating an encoded signal (FIG. 2c). This signal is a signal of small magnitude, eg 1 millivolt, which is maintained approximately 20 milliseconds long. The amplitude of the encoded signal continues to decrease, the charging capacitor 3 provides energy for closing the switch, and then keeps charging.

The coded signal is fed back to the antenna tank circuit 5, 6 as a result of mutual inductive coupling between the antenna 6 and the coil 7. The oscillations of the antenna resonant circuits 5, 6 are thus modulated (FIG. 2d). Since the auxiliary capacitor 10 is connected and disconnected from the transponder capacitor 8, the antenna resonant circuits 5, 6 are loaded differently and the oscillation frequency of the antenna resonant circuits 5, 6 is modulated.

Assuming that the average excitation frequency f _E of the antenna oscillating circuits 5 and 6 is 129KHz, the oscillating frequencies of the antenna oscillating circuits 5 and 6 vary between 123KHz and 134KHz according to the frequency modulation of the coded signal.

The oscillation modulation of the antenna resonators 5 , 6 is controlled by a demodulator 13 and evaluated with a control and evaluation device 14 . The modulated oscillation cycle length or frequency is detected. When the modulated oscillation frequency is lower than a limit value, for example, lower than 129KHz, a high-level modulation signal is detected, and when the frequency is higher than 129KHz, a low-level signal is measured (Fig. 2e). In this way, the coded information of the transponder 2 is demodulated according to the modulated oscillation state.

This coded information is compared in the control or evaluation unit 14 with predetermined target coded information, and when the two agree, a release signal is sent to the safety device on the vehicle.

Such a security device is, for example, a door lock or an automatic parking signal. Upon decoding and correcting the coded signal, the door lock is unlocked or the auto park annunciator is deactivated, thus allowing the vehicle motor to start operating.

The antenna oscillating circuits 5 and 6 are excited to oscillate by an oscillator 4 with an excitation variable, and the excitation frequency of the oscillation is f _E . The excitation variable of the oscillator 4 can be output voltage or output current. The oscillation frequency of the oscillator 4 is f _O . A frequency divider 15 can be added between the oscillator 4 and the antenna resonant circuits 5, 6, which divides the oscillation frequency f _O into the desired excitation frequency f _E .

A fixed oscillation of the antenna resonant circuit 5 , 6 is produced by the excitation variable, the excitation frequency of which is f _E . Each oscillating circuit has a natural frequency, or resonant frequency f _R , which is determined by the components of the oscillating circuit, namely mainly the antenna 6 and the antenna capacitor 5 . If the excitation frequency f _E of the oscillating circuit is equal to the resonant frequency f _R , the generated oscillation intensity (field strength/amplitude) is maximum (the operating point Pi of the oscillating circuit is located at the resonance point Po, see Figure 3). In this case, most of the energy is transferred into the transponder 2, so that the charging capacitor 3 can be charged very quickly.

The power balance can be clearly seen from the resonance curve (Figure 3), where the frequency f is the horizontal axis (x-axis), and the oscillation intensity I varies with the excitation variable, that is, the excitation voltage or current amplitude, on the vertical axis (y-axis) . When the excitation frequency f _E (operating point Pi) deviates from the resonant frequency f _R , the oscillation intensity I is smaller and thus less energy is transmitted to the transponder 2 . When the excitation frequency f _E =resonant frequency f _R , the operating point Po is formed. Depending on the difference between the two frequencies, the operating point corresponds to a smaller intensity (see operating point P ₁ or P ₂ ).

If the operating point lies below a predetermined duty limit 16, the field energy transmitted to the transponder 2 is minimal. Due to the transfer of too little energy, it is not possible to charge the charging capacitor 3 quickly or sufficiently. The transponder 2 no longer modulates the antenna resonant circuits 5, 6, or ceases to modulate mutually.

In this car anti-theft system, it should be noted that the excitation frequency f _E should continue to coincide with the resonant frequency f _R . Given the inherent tolerances of the components of the transceiver 1 or of the transponder 2, the resonant frequency f _R and the excitation frequency f _E may deviate from each other so that an optimum energy transfer to the transponder 2 is not possible. When the two frequencies deviate from one another by a small amount, the intensity of the transmitted alternating magnetic field (magnetic field strength) can be significantly reduced if the resonant circuit is of high quality (slender curve shown in dotted line in FIG. 3 ).

An optimal power balance can be achieved if the resonant circuit and the components of the oscillator 4 are selected in such a way that they deviate only slightly from the nominal value and always have the same performance. However, to meet these requirements, a high investment must be made. Furthermore, external influences such as fluctuations in temperature also affect circuit components, causing rapid changes in their performance. It can therefore be said that the transmission of maximum energy cannot be achieved.

According to the invention, the excitation frequency f _E is varied at least during the charging phase, so that the charging capacitor 3 is always reliably and completely charged. As soon as the transponder 2 with the starter key is turned in the starter lock, the energy of the oscillator 4 is switched on. The oscillator 4 starts to oscillate at a predetermined frequency _f0 . The excitation frequency f _E can be identical to the oscillation frequency f _O , which varies within a predetermined frequency range during the charging phase. In this way, the operating point can at least once reach an approximation of the maximum energy transfer (see FIG. 3 ), enabling sufficient charging of the charging capacitor 3 .

The excitation frequency f _E can be varied at predetermined intervals within a predetermined frequency range. For example, the excitation frequency f _E can be changed within 129KHz±3% (predetermined frequency range is 129KHz±3%), step by step at 500Hz.

The excitation frequency f _E is also continuously variable within a predetermined frequency range.

The resonant frequency f _R of the antenna resonant circuits 5 , 6 can be varied at predetermined intervals relative to each excitation frequency f _E . At each excitation frequency f _E , the antenna resonant circuits 5 , 6 switch back and forth between different impedances, so that the resonant frequency f _R varies according to this excitation frequency f _E .

Fig. 4 shows a circuit for changing the excitation frequency f _E in predetermined steps. One of the exciters 17 is activated by a clock frequency CLK. The frequency sequence controller 18 predetermines the frequency spacing at which the programmable exciter 18 is to be operated. Once the starter key is turned in the starter lock, that is, once the energy flow supply is switched on (ON/OFF signal provided by AND gate 20 in FIGS. The frequency f _E is excited.

The excitation frequency f _E can also be varied continuously by means of a voltage-controlled oscillator 4 (VCO) (see FIG. 15 ). A suitable control signal (sawtooth voltage of the sawtooth generator 21 ) is applied to the input of the oscillator 4 for this purpose.

In this embodiment, the antenna tanks 5, 6 are constrained by their components to have a resonant frequency f _R of approximately 129 KHz. The oscillation frequency f _O can be approximately 4 MHz, for example. In order that the oscillator 4 can be used to excite the resonant circuit, a 1/32 frequency divider 15 should be installed between the oscillator 4 and the antenna resonant circuits 5, 6, so that an excitation frequency f _E of approximately 129 kHz is obtained.

By varying the oscillation frequency f _O to a predetermined value, the excitation frequency f _E can be varied such that at least one operating point is achieved at which approximately the maximum energy is transmitted. Sufficient energy is then transferred to the transponder 2 and enables the charging capacitor 3 to be charged reliably and quickly.

Instead of a fixed frequency divider 15 , a digital frequency divider can be used, which separates the oscillation frequency f _O from the excitation frequency f _E . This digital crossover has an infinitely adjustable division ratio.

The control or evaluation device 14 can be realized by a microprocessor or a switching circuit with equivalent functions. The function of the demodulator 13 can also be implemented by a microprocessor. The setpoint coded information is compared with the coded information transmitted by the transponder 2, this setpoint value being stored in a memory (ROM, EEPROM) not shown in the figure.

The coded information in this transponder 2 can be stored in this memory.

It is also possible to predetermine that the excitation frequency f _E changes constantly during the charging phase, but the frequency range is not predetermined, and the excitation frequency f _E always changes until the end of the predetermined time length of the charging phase. It is also possible that there is no fixed frequency range, the frequency only changes within a time span.

In the present embodiment, the length of this charging phase is approximately 50 milliseconds, during which the excitation frequency f _E of the present invention is changing and during which the charging capacitor 3 is induced by the radio transceiver 1 Charge.

The excitation frequency f _E can also have a multiple of the predetermined frequency range, so that an operating point with a maximum oscillation intensity I can be reached several times. The predetermined frequency range and time length, and how long to send the energy signal to the transponder 2 are all related to the size of the charging capacitor 3 and the amount of energy required by the transponder 2 .

The switch 9 can be realized by an integrated switch circuit including the auxiliary capacitor 10 . This switch 9 and auxiliary capacitor 10 can also be installed in said transponder-IC 12 . An inductor can also be used instead of the auxiliary capacitor 10. What is essential for the invention is that the transponder resonant circuits 7, 8 vary according to the coded information, so that the oscillations of the antenna resonant circuits 5, 6 are modulated so that a frequency, amplitude or pulse width modulation can be achieved.

Claims (11)

1. Especially for anti-theft systems of cars, including: - a fixedly installed device (1) with an antenna (6), which forms part of the first oscillating circuit (5, 6), - a portable device (2) with a coil (7) forming part of a second oscillating circuit (7, 8) connected to an energy store (3), - an oscillator (4) oscillating at an oscillation frequency (f _O ), whose output parameter is an excitation parameter with an excitation frequency (f _E ) for exciting the first oscillation circuit (5, 6) to oscillate, this excitation frequency ( f _E ) changes within a predetermined frequency range, this change lasts for a predetermined first length of time, once the fixedly installed device (1) provides energy, the energy signal is inductively transmitted from the antenna (6) to the coil (7), The energy store (3) of the portable device (2) is thereby brought into an at least partial charging operation. 2. The anti-theft system according to claim 1, characterized in that: - a permanently installed device means a transceiver (1) installed in a motor vehicle, - portable device means a portable transponder (2) carrying coded information, this transponder (2) modulating the oscillations of the oscillating circuit (5, 6) according to its coded information for a predetermined second length of time, once an energy store is at least partially charged, which can provide energy for the transponder (2), - an analysis and evaluation device (14), which receives the oscillating signal of the oscillating circuit (5, 6), After the modulated oscillation is received by the analysis and evaluation device (14), the coded information is demodulated, and in a comparator (14), the prestored rated coded information is compared with the demodulated coded information, when the two are compared When consistent, a release signal is sent to the car safety device. 3. Anti-theft system according to claim 1, characterized in that the excitation frequency (f _E ) varies within a predetermined frequency range at predetermined intervals. 4. Anti-theft system according to claim 1, characterized in that the excitation frequency (f _E ) is continuously varied within a predetermined frequency range. 5. The anti-theft system according to claim 2, characterized in that the resonant frequencies (f _R ) of the oscillation circuits (5, 6) of the radio transceiver (1) are at predetermined intervals at each excitation frequency (f _E ) Variety. 6. The antitheft system as claimed in claim 1, characterized in that the excitation frequency (f _E ) is varied via an adjustable frequency divider (15). 7. Anti-theft system according to claim 3, characterized in that the excitation frequency (f _E ) is varied by means of an oscillator (4), the output parameters of which depend on the varied control parameters of the generator (21). 8. The anti-theft system according to claim 1, characterized in that the transponder (2) is mounted on a starter key which enables the energy input of the transceiver (1) by twisting in the starter lock. 9. Anti-theft system according to claim 1, characterized in that the excitation frequency (f _E ) changes only for a predetermined length of time after the start of the energy delivery. 10. The anti-theft system according to claim 1, characterized in that the transponder (2) is inductively coupled to the antenna (6) via a coil (7). 11. The anti-theft system according to claim 1, characterized in that the security device is a door lock or an automatic parking signal.

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