FR2778464A1 - DEVICE FOR CONTROLLING THE ANTENNA OF A SYSTEM PROVIDED IN A MOTOR VEHICLE, IN PARTICULAR A DRIVE LOCKING SYSTEM - Google Patents

Abstract

This device comprises an exciter circuit (1, 2) applying an exciter stage signal to the antenna (2, LA, CA, RA) and an analysis circuit (1, 3) detecting abnormal values of the inductance or a variation of the inductance of the antenna (LA). The antenna is arranged as a resonant circuit with an antenna coil (LA) serving as an inductor and a capacitor (CA), while the analysis circuit contains a phase comparator (3) which determines the phase shift between the signal exciter stage and the antenna resonance voltage, or a rectifier and an analog-to-digital converter, which is connected downstream thereof and which transforms the antenna resonance voltage, the antenna resonance current or part of these in a digital value, and an analysis stage connected to the output of the analog / digital converter.

Description

The present invention relates to a device for controlling an antenna,

  provided in a motor vehicle, which is a constituent part of a control system working with wireless information transmission, in particular of a

line blockage.

  Control systems working with wireless information transmission generally have an antenna circuit, containing an antenna, by means of which signals can be transmitted and / or received. In the case of a pipe blocking system, the antenna can for example be placed on the ignition lock and check the presence of an engaged ignition key

  in the lock, and / or the identification of this key.

  However, the control system can monitor other parameters, for example the position of a lock bolt in a motor vehicle lock, as disclosed in DE 198 03 187 which does not

  subject of a previous publication.

  In any event, in such systems, problems arise in many cases when the antenna of the antenna circuit is far from its set position. In this case, the risk of faulty operations or voluntary attempts at fraudulent intervention intended to control the control system, for example the blocking of the pipe, is increased. This distance from the antenna relative to its set position may occur due to accidental influences, but also due to a voluntary withdrawal of the antenna for the purpose

fraudulent intervention.

  DE 34 40 538 Cl relates to a proximity switch comprising a coil which can be influenced by the approach of electrically and / or magnetically conductive substances and forms part of an oscillating circuit which is set in oscillation by a train of pulses periodic in direct current. The process of weakening the damped oscillation produced by the excitation allows to deduce the degree of proximity of an object approaching the coil. The oscillating circuit signal is applied to a threshold value comparator which produces a rectangular output signal which is subjected to a logical combination with output signals from a generator.

window signals.

  German patent application published after examination 37 039 relates to an inductance control device in which the specimen is put into oscillations damped by means of rectangular pulses, the time which elapses until the oscillations weaken constituting a measurement for existing depreciation. The oscillation signal is presented on an oscillograph and

visually controlled.

  US 5,077,528 relates to a coil arrangement which comprises two coils which are connected in series and along which moves an object to be monitored with regard to its position. The coil plug is connected to a logic device which transforms the input signal into a single-pole rectangular signal which is applied to a sequencer. The output signals from the

  sequencer are used to control the excitation of the coils.

  The invention aims to provide a device which allows control of the antenna and thus offers increased protection against faulty operations and / or attempts at fraudulent intervention. To this end, the subject of the invention is a device for controlling the antenna of a control system provided in a motor vehicle, in particular of a pipe blocking control system, comprising an exciter circuit, used to apply an exciter stage signal at the antenna, and an analysis circuit used to detect the inductance or a variation of inductance of the antenna, which picks up a signal parameter sampled by the antenna and controls the values d abnormal inductance or variations in inductance, the antenna being arranged in a resonant circuit with an antenna coil serving as an inductance and a capacitor, while the analysis circuit either contains a phase comparator which determines the phase difference between the exciter stage signal and the antenna resonance voltage, either contains a rectifier, a converter

  analog / digital, which is connected downstream of it

  ci and which transforms the antenna resonance voltage,

  the antenna resonance current or a part thereof

  ci in a numerical value, and a connected analysis stage

  at the output of the analog / digital converter.

  The device according to the invention may also have one or more of the following features: - the exciter circuit produces a rectangular signal, - the resonance circuit is arranged in the form of a series resonant circuit, - it is provided, connected to the antenna, a voltage divider whose sampling terminal is connected to an input of the phase comparator, - the analysis stage is produced in the form of a microprocessor, - a resistance is contained in the antenna circuit and the analysis circuit determines the voltage between the terminals of this resistor which is used to measure the antenna resonance current, - a contact lock around which a coil

  antenna antenna is wound.

  In the device according to the invention, an exciter stage signal is applied to the antenna circuit and the signal produced by this antenna circuit in response to the exciter stage signal is analyzed with regard to abnormal behavior of phase and / or amplitude. The signal produced by the antenna circuit in response to the exciter stage signal normally includes, i.e. for correct positioning of the antenna, a phase variation and / or amplitude variation over time. which is located in a defined area and which, under the effect of the presence or absence of the object to be monitored, for example the ignition key, can vary in a defined manner. If, on the other hand, the transmitting / receiving antenna connected to the antenna circuit were to be moved away from its set position unexpectedly or due to fraudulent intervention, the antenna circuit and the antenna would be clearly subject to other environmental influences, so that also the antenna output signal obtained in response to the excitation stage signal would be strongly distorted. This deviation from the expected signal domain in the normal case can be detected reliably by means of the analysis circuit. This analysis circuit not only reviews the output signal of the antenna circuit, but also the excitation stage signal applied to this antenna circuit and, from there, can create limits for the position domains of phase and / or amplitude, expected in the normal case, of the response signal itself expected. If the response signal were to be outside of these ranges, it could be concluded that the antenna's position or operating capability had been disturbed and a corresponding error warning could be produced. Preferably, in the case of the invention, the excitation stage signal applied to the antenna circuit, including the antenna, is compared with the signal present on the antenna, in order to determine from there disturbances , such as position shifts or voluntary intervention attempts

fraudulent or the like.

  Thus, the motor vehicle control system arranged in accordance with the invention can reliably recognize whether the associated transmitting / receiving antenna is positioned in the manner provided, for example is suitably threaded over the ignition lock, or on the contrary by

  example was removed voluntarily.

  Preferably, the excitation stage signal is produced in the form of a rectangular signal which can be formed in a simple manner by means of a cyclic switching on and off of a switching element subjected to a determined voltage, for example of a semiconductor switch element. This rectangular exciter stage signal is transformed, by the antenna produced in the manner provided in the form of a resonant oscillating circuit, into a corresponding emission signal, normally sinusoidal. The inductance and / or the variation of inductance of the resonant oscillating circuit can be determined in a different way, namely by means of the measurement of the phase shift between the excitation stage signal and the resonant frequency signal, by means measuring the amplitude of the resonant frequency voltage and / or by measuring the current flowing in the oscillating circuit, or

parties of it.

  If the phase difference between the antenna exciter stage signal and the resulting antenna resonance voltage is monitored, the fact that the antenna of the control system, for example of the line blocking, has been moved away from the prefixed position, for example the ignition lock, can be detected using the large variation in inductance which then results. In the simplest case, the inductance measurement can be carried out only when effectively due to the operation, an activation of the antenna circuit is envisaged with a view to the emission of a corresponding signal. However, according to an advantageous development of the invention, the inductance measurement can also be carried out cyclically, at a fixed rate, even when the ignition is off. This also makes it possible to detect possible fraudulent interventions on the antenna of the control system, since the variations thereby caused normally show an evolution over time which does not occur in the absence of fraudulent intervention. Thus, incorrect positioning of the antenna and / or fraudulent interventions on this antenna can be seen automatically. At the same time, this provides protection against dismantling motor vehicle control systems, in particular systems

line blocking control.

  The device according to the invention is used in particular in the case of a driving lock control system for a motor vehicle, since the safety conditions then imposed are particularly high. However, the invention can also be used in the case of all other motor vehicle control systems comprising an antenna circuit and an antenna, in order to control

  operation of the antenna / antenna circuit.

  The invention is described below in detail using the embodiment examples and with reference to the drawings. We see: in Figure 1, an exemplary embodiment of the device according to the invention and, in Figure 2, variations in time of signals which occur in the case of the example of

  embodiment shown in Figure 1.

  The embodiment of the device according to the invention which is shown in Figure 1 contains a control device 1 which consists of a microprocessor and which provides antenna control and signal analysis. The control device 1 is connected to an antenna exciter stage 2 by means of a timing line 5 and provides this antenna exciter stage 2 with a cyclic timing signal during desired normal transmission operation and also during control intervals during which the antenna circuit, including the antenna, must be checked. From the timing signal provided on line 5, the antenna driver stage 2 produces a rectangular signal having an antenna driver stage frequency f0. The excitation stage signal supplied between terminals 7 and 8 of the antenna excitation stage 2 can be a bipolar signal comprising symmetrical rectangular half-waves of different polarities, but it can also be in the form of a signal unipolar having a duty cycle of 50%

  as shown for example in Figure 2a).

  FIG. 2a) represents the variation over time of the potential present at the output 8 of the antenna exciter stage 2. The exciter stage signal is applied, by means of a series antenna resistance RA and two lines 9 and 10, to an antenna coil LA which is arranged on a contact lock 4 (iron core associated with the antenna), for example threaded over the contact lock. The antenna oscillating circuit contains the antenna coil LA and a capacitance CA connected in series therewith, so that a series oscillating antenna circuit is formed. By its other terminal, the capacitor CA is connected to the output 8 of the antenna exciter stage 3. A voltage divider with resistors, comprising resistors R1 and R2, is connected to line 10 connecting the antenna coil LA and the capacitance CA, so that the antenna voltage is present, in a form divided in a proportional manner, on a line 11 connected to the sampling outlet situated between the resistors R1 and R2. These resistors R1 and R2 may have identical ohmic values, so that is half the

  antenna voltage which is present on line 11.

  However, the resistors R1 and R2 can also have different values which are chosen so that the amplitude level present on the line 11 is lowered, by division, to a desired value which can be treated without difficulty by the circuits of

downstream processing.

  In the case of the embodiment shown in FIG. 1, a phase comparator 3 is provided, the two inputs of which are connected to the output 8 of the antenna exciter stage (exciter stage circuit) 2 and on line 11. This phase comparator 3 may preferably consist of an electronic measurement circuit which is for example contained in a printed circuit of base station. Thus, these are the input signals represented in FIGS. 2a) and 2b) which are applied to the two inputs of the phase comparator 3, namely the excitation stage signal, rectangular and symmetrical, present on terminal 8 and the antenna voltage signal lowered by division which is present on line 11. The phase comparator 3 is connected, by means of a timing line 12, to the control device 1 and receives from the latter timing signals on which it measures the phase shift that exists between the zero crossings, which each time follow each other, of the signals applied to its two inputs (exciter stage signal and resonance voltage signal). In FIG. 2, the phase shift between the zero crossing of the exciter stage signal and the zero crossing of the antenna resonance voltage is designated by ANT. Generally, the phase shift ANT = - 90 - arctg (2Qd). Here, d = (f - fo) / fo, while Q denotes the antenna quality factor, f the antenna resonance frequency (f = 1 / (2pÈLA x CA))

  and fo the antenna exciter stage frequency.

  Thus, the OANT phase shift depends on the antenna quality factor which is itself subject to the influence of the components located in the area of the antenna coil LA and is located, during normal operation, in a domain d 'wait determined. For example, a pressed ignition key can be detected by the resulting quality factor change. If, however, the antenna coil should, for example, be removed from the ignition lock 4 and / or if fraudulent intervention attempts were to be made on the antenna, one would generally obtain very large variations in the quality factor which

  would cause 4T phase shifts all the greater.

  Indeed, the contact lock 4 plays the role of iron core for the antenna coil LA wound around it and it strongly influences the inductance. If the antenna coil LA were to be moved away from the ignition lock 4 in an unforeseen manner or due to fraudulent intervention attempts, there would be a large variation in the inductance and therefore the antenna quality factor Q with a DAT phase shift of as much

stronger.

  Thus, these large phase shifts DAT signal to the control device 11 the fact that, in the antenna circuit, including the antenna, there are disturbances (caused in an unforeseen or voluntary manner) which must be classified as operations defective. Via line 6, the control device 1 receives from the phase comparator 3 the information concerning the current measured phase shift ANT and it analyzes this, with regard to its magnitude and / or its variation over time, with a view to the detection of disturbances. In the simplest case, there is prefixed, in the control device 1, a lower limit value and / or an upper limit value of the admissible phase shift domain ANT which are determined as a function of the phase shifts occurring in a minimal manner. and / or as much as possible during normal operation. If the control device 1 detects an ANT phase shift outside of this admissible range, it analyzes this situation as being a disturbance and produces a corresponding error warning signal which is indicated by the acoustic or optical channel and / or East

  stored in memory for use by the maintenance department.

  It is also possible to carry out, even when the vehicle is stopped, the inductance measurement, which, in the embodiment shown in FIG. 1, is carried out by means of the phase shift measurement, in a prefixed time base. fixed or variable, for example 10 seconds, and thereby monitor the variation over time of the measured inductance (variation over time of the phase shift). Normally, in any event, the variation over time of the inductance should include small jumps which are due to the introduction of an ignition key in the

  lock or when removing this key from the lock.

  If it is however established that the variation in inductance over time has longer fluctuations, for example which last longer, it can be deduced therefrom the existence of attempts at fraudulent intervention and, in this case, an alarm can for example be produced. In this case, the monitoring frequency according to which the inductance measurement is carried out can also be increased, in order to be able to analyze the inductance fluctuations even better and, from there, to be able to see even more clearly.

  possible attempts at fraudulent intervention.

  When fraudulent intervention is detected, the line-locking control device can also be designed so that it must only be reinitialized by the maintenance service before normal vehicle operation is carried out. re-authorized. In place of the measurement, described above, of the phase shift between the rectangular exciter stage signal and the sinusoidal antenna resonance signal, the measurement of the inductance or of the variations of inductance can also be ensured by means of a determination of the amplitude of the resonant voltage occurring on the antenna. In this case, instead of the phase comparator 3, there is provided, connected to the line 11, a rectifier downstream of which is connected an analog / digital converter. On line 6, the output signal from the analog / digital converter is supplied to the control device 1 as amplitude information. The control device 1 in this case analyzes the amplitude information, supplied on line 6, which is used to measure the amplitude of the resonant voltage and therefore serves to determine

inductance of the antenna circuit.

  The amplitude of the resonance voltage is then obtained as follows: the excitation stage voltage UTW which is exerted on the oscillating circuit of antenna has the value UTw = UT x 4 / p, "UT" designating l voltage amplitude of the symmetrical rectangular signal which is

  supplied at the output of the antenna exciter stage 2.

  The current iA passing through the resistor RA is obtained as follows:

IA = UTW / È ZAÈ,

  in which ÈZAÈ = RA2 + WO (LA - 1 / WCA)

For wo, it comes: wo = 2pfo.

  The resonant voltage present for example on the AC capacitor has the following magnitude: UCA = (UTW / ÈZAÈ) X (1 / w0CA) To determine UCA, for example, a differential amplifier can be provided which is connected to the two terminals of the capacitor AC OR is also provided in place of the phase comparator and receives its two input signals in accordance with FIG. 1. In this case, the output signal from the differential amplifier is applied to the rectifier and to the analog / digital converter which

  have already been described above.

  Since the voltage UT and therefore the effective excitation stage voltage UTw are however generally fixed in a defined and known manner, it is also possible, for the measurement of inductance, to determine, that is to say say to apply to the control device 1 via the rectifier and the analog / digital converter, only the voltage present on the line 11, and possibly also by removing the resistors R1 and R2, the

voltage present on line 10.

  It appears from the above equations that the complex resistance of the antenna circuit depends on the inductance LA, so that from the amplitude of the resonant voltage, it is possible to deduce

the respective inductance value.

  Instead of or in addition to the phase shift and / or the measurement of the amplitude of the resonant voltage, it is also possible to analyze the antenna current for

inductance measurement.

  In this case, the resistors R1 and R2 may disappear and it is possible to connect a current transformer directly to line 9 or 10. It is also possible to measure by means of a voltage detector the voltage drop between the terminals of the resistor RA and, from this, to determine the oscillating circuit current iA which varies in time in proportion to it. The output signal from the current transformer or the voltage detector which reads the voltage on the resistor RA is also applied in this case to a rectifier which is used for rectifying the current and downstream of which an analog / digital converter is connected. The output signal of this analog / digital converter is applied to the control device for signal analysis, as is also the case for the variant previously

  described of the resonant voltage.

  Instead of direct measurement of the current of the oscillating circuit, it is also possible to measure a current directly related to it, or partial current, which passes for example through the antenna exciter stage 2. As a variant or in addition, it is also possible, for the determination of the inductance, to measure the impedance of the oscillating circuit or of a part of it. This can for example be achieved by a combination of current measurement and

  amplitude measurement previously described.

Claims (7)

  1. Antenna control device (2, LA, CA, RA) of a control system provided in a motor vehicle, in particular of a pipe blocking control system, comprising an exciter circuit (1, 2 ), used to apply an exciter stage signal to the antenna (2, LA, CA, RA), and an analysis circuit (1, 3) used to detect the inductance or a variation of inductance of l antenna (LA), which picks up a signal parameter sampled by the antenna and controls abnormal inductance values or variations in inductance, the antenna being arranged in a resonant circuit with an antenna coil (LA) serving inductance and a capacitor (CA), while the analysis circuit (1, 3) either contains a phase comparator (3) which determines the phase shift between the exciter stage signal and the antenna resonance voltage, either contains a rectifier, a converter   analog / digital, which is connected downstream of it   ci and which transforms the antenna resonance voltage,   the antenna resonance current or a part thereof   ci in a numerical value, and a connected analysis stage   at the output of the analog / digital converter.   2. Device according to claim 1, characterized in that the exciter circuit (1, 2) produces a rectangular signal.   3. Device according to claim 1, characterized in that the resonance circuit is arranged   in the form of a series resonant circuit.   4. Device according to any one of   claims 1 to 3, characterized in that it is provided,   connected to the antenna, a voltage divider (R1, R2) whose sampling terminal is connected to an input of the phase comparator (3). 5. Device according to any one of   previous claims, characterized in that   the analysis stage is carried out in the form of a microprocessor (1).   6. Device according to any one of   previous claims, characterized in that   resistance (RA) is contained in the antenna circuit and in that the analysis circuit (1) determines the voltage between the terminals of this resistance which is used for the   measurement of the antenna resonance current.   7. Device according to any one of   previous claims, characterized by a lock   contact (4) around which an antenna coil (LA) of the antenna is wound.