FR2715490A1 - Method of avoiding fraud with taximeters or tachygraphs - Google Patents

Abstract

The fraud prevention system makes use of electronic signals from the anti-lock braking system (ABS) wheel sensors (1). Two parallel cables (4,5) are connected directly to the sensor and are carried inside a mechanically protective sleeve (6) to an electronic control unit (8). The electronic control unit modifies the electronic information normally transmitted to the taximeter or tachygraph if cable and signal parameters appear modified relative to stored reference values. The cable parameter is impedance between the two wires, measured by injection of a variable voltage or current. The signal parameter is the ratio of recorded pulse-widths of the signal to the recorded pulse-widths during normal movement of the vehicle.

Description

METHOD AND DEVICE FOR AVOIDING FRAUD ON A TAXI
EQUIPPED WITH A TAXIMETER OR ON A TRUCK EQUIPPED WITH
CHRONOTACHYGRAPH
The present invention relates to a method and a device for preventing fraud on a taxi equipped with a taximeter or on a truck equipped with a tachograph, the vehicle -taxi or truck- being equipped with at least one sensor electronic at least used to operate its taximeter or tachograph.

A so-called "electronic" sensor of a motor vehicle is a transducer which tests a rotary mechanical member of the vehicle, the speed of rotation of this mechanical member being representative of the number of wheel turns effected by the vehicle, and the generally alternating electrical signal supplied by this transducer corresponding to electrical pulses representative of this number of wheel turns
Traditionally, as described for example in the patent application in France no 93.02285 filed by
Applicant on February 19, 1993, this rotary mechanical member is most often one of the pinions of the gearbox
This patent application FR-93.02285, as well as the corresponding European patent application no. 93420455.3 filed on November 17, 1993 under priority of this one, explain how it is possible to avoid fraud on the taximeter or the tachograph which receives and processes these electrical impulses by providing, among other provisions, for making inviolable by means of a mechanical shielding all the circuit included between the output of the sensor and the taximeter or the tachograph.

 This mechanical shielding makes it possible in particular to prevent the taxi driver or the trucker from being able to come and plant two needles in the two respective signal output wires of the sensor, so as to be able to connect therein a pulse generator in parallel to said sensor output.

 The fraudster often chooses in this case a pulse generator with an output impedance much lower than that of the sensor, and the pulses delivered by this generator come, as the case may be, either to suffocate the pulses delivered by the sensor and therefore to replace to them, or add to them.

 The aforementioned patent application FR-93.02285 also indicates how it is advantageously possible to mechanically shield, and therefore make inviolable, the whole of the sensor itself by means of a bell which covers the sensor and which is fixed and plumbed on the gearbox.

 However, modern vehicles are now more and more often provided with a braking system called "A.B.S" which uses an electronic sensor for each vehicle wheel. Generally, these vehicles are fitted with disc brakes on all four wheels, and consequently each electronic sensor is a proximity sensor which tests the presence of notches which are made for this purpose on the outer edge of the braking disc.

 In such a case, it is obvious that the electronic sensor intended to operate the dashboard speedometer as well as the taximeter or the tachograph is one of the A.B.S sensors already present on the vehicle. The electrical pulses which are delivered by this sensor are then applied simultaneously to the A.B.S braking system, to the speedometer of the dashboard, and to the taximeter or tachograph.

 This poses a problem if one wishes to avoid the aforementioned frauds on the taximeter or the tachograph, because it is then practically no longer conceivable to connect the sensor in question to its circuit of use by a mechanically shielded cable. This sensor is in fact located on the wheel and on a portion of it which, although not rotatable, is nevertheless subject to sporadic movements due to the articulated nature of this wheel.

 There are indeed shielded cables on the market which have a certain flexibility, but this is limited and there would in any case be a fairly fragile breaking point at the point of connection of such a shielded cable on the sensor.

 In addition, such an armored cable would pass in the immediate vicinity of the hydraulic lines and the electrical safety cables which are associated with the braking device of the wheel in question. During the articulation movements of the wheel, these hydraulic lines and these electrical safety cables would then rub against the armored cable, the movements of these various cables and lines being unable to be strictly synchronous.

 This would result in rapid wear of these hydraulic lines and electric cables, and as a result of the unacceptable risks of drilling and circuit breaks.

 The object of the invention, which aims to remedy this drawback, is to propose a method and a device which in any case makes it possible to avoid fraud on a taxi or a truck, even in the case where this taxi or this truck is equipped with an ABS braking system

It relates for this purpose to a process - and also to a device - to avoid fraud on a taxi equipped with a taximeter or on a truck equipped with a tachograph, the vehicle - taxi or truck - being equipped with at least one electronic sensor which at least is used for the taximeter or the tachograph, this process consisting
to connect directly in parallel to two or to the two electrical signal output wires of this sensor, and to trigger an electronic anti-fraud action which at least consists in modifying the electronic information normally transmitted to the taximeter or tachograph if at at least one of the internal characteristics of the active dipole then present between these two wires, and / or at least one of the characteristics of the electrical signal available between these two wires during normal movement of the vehicle, has been modified with respect to previously stored reference values .

In any case, the invention will be well understood, and its advantages and other characteristics will emerge more clearly from the following description of some exemplary embodiments, with reference to the appended schematic drawing in which
Figure 1 is a block diagram of an example
simple to carry out the invention.

Figure 2 is a block diagram of the device
characteristics test which equips the device according to
Figure 1.

Figure 3 is a particular embodiment
a characteristic test circuit for setting
of the invention.

Figure 4 shows an alternative embodiment, more
economical, of the circuit according to Figure 3.

Figure 5 is a block diagram of another form
for producing a device according to the invention.

 In FIG. 1, the reference 1 designates an electromagnetic sensor (or "electronic sensor") of the number of wheel revolutions performed by a taxi fitted with a taximeter 2 and a speedometer provided on its dashboard 3.

 Instead of a taxi, it can be a truck, and in this case the reference 2 designates the tachograph with which this truck is provided.

 In the case under consideration, the vehicle - taxi or truck - is provided with an ABS braking system, so that the sensor 1, which has the purpose of supplying electrical signals representative of the number of wheel revolutions to the dashboard speeds 3 on the one hand and to the taximeter or tachograph 2 on the other hand, is quite simply one of the sensors normally used to operate the ABS braking system

 The sensor 1 is therefore placed on a wheel of the vehicle so that, as explained above, it is difficult to think of protecting its two wires 4.5 of the electrical signal output by mechanical shielding.

 At most, according to a particular characteristic of the invention, it is possible to provide such mechanical shielding 6 from point 7 at the height of which the articulation of the wheel takes place, but in any case not between this point 7 and the sensor 1. Thanks to the mechanical shielding 6, it is possible for the fraudster to connect a possible auxiliary pulse generator only to the part of the wires 4 and 5 which is between this point 7 and the sensor 1, which greatly facilitates the visual anti-fraud check, but does not however completely prevent such fraud.

 Note that between point 7 and the taximeter or tachograph 2, the mechanical shielding of inviolability is total and it comprises, practically like the device according to FIG. 1 of the aforementioned patent application FR-93.02285, successively the section of screened cable 6, a tamper-proof screened box 8 containing electrical circuits, and another section of screened cable 22.

 By “shielded cable” is meant here, as is the case in application FR-93.O2285, an electric cable surrounded by a mechanically inviolable shield. It goes without saying that this shielding is generally also an electrical shielding of mass, but it is here of a shielding of mechanical order which it is generally question, and not of a shielding of purely electrical order.

 Like the circuit according to FIG. 1 of application FR-93.02285, the tamper-proof shielded box 8 contains an operational amplifier 9 which receives the electrical signal supplied by the sensor 1 on the two signal output wires 4 and 5, and which consequently supplies on its output wire 10 a reshaped signal which is applied, via the shielded cable 22, to the taximeter or tachograph 2. This amplifier 9 also has a role of separator, and it therefore makes it possible to possibly work on the signal present on wire 10 without the signal present on wires 4 and 5 upstream of amplifier 9 being felt.

As can be seen in FIG. 1, two other pairs of wires are connected, in the box 8, to the pair of wires 4.5 upstream of the separation and shaping amplifier 9:
a first pair of wires 11.12 coming out of the
box 8 to supply impulse signals from a
share ABS circuits (not shown) and
on the other hand the speedometer of the table of
vehicle edge'3; and
a second pair of wires 13,14 which are connected
at the two input terminals 15,16 of a device
17 internal characteristics test electronics
active dipole present between wires 4 and 5
(specifically: of sensor 1 and its charge), thus
than testing at least one of the characteristics of the
signal present between these two wires when the vehicle
drives at least a predetermined speed.

 By way of nonlimiting example, the aforementioned characteristic of the signal present between these two output wires 4,5 of the sensor 1 can advantageously be the duty cycle of the pulses deduced, after possible clipping, of the alternating or purely impulse signals supplied by the sensor 1.

 The internal characteristic of the dipole can be its impedance, preferentially taken in the very general sense, that is to say without distinguishing its resistance, its inductance, and its capacitance, but rather, as will be seen below, by noting the impulse response or frequency of this dipole.

 Nonlimiting examples of embodiment of the electronic device 17 for testing characteristics will be described below with reference to FIGS. 2 to 4.

 When the sensor 1 and the taximeter or tachograph 2 are installed on the vehicle, tests are carried out by rolling the vehicle at one or more predetermined speeds. These tests result in one or more measurements, by the device 17, of the aforementioned characteristics, and the result of these test measurements is stored in the device 17, which advantageously contains a microprocessor, or other logical calculation and control unit, such as we will see it below.

 Subsequently, the electronic device 17 compares the characteristic values which it systematically, continuously or occasionally tests, with these memorized characteristics.

 If these values are not in conformity, the electronic unit 17 emits on the one hand, on a first output wire 18, an alarm signal towards the dashboard. This alarm signal triggers maintained information, visual or audible, which materializes for example by the lighting of a preferentially very bright lamp 19 on the dashboard 3 or, even better, by the emission of a signal preferentially unsustainable sound. The electronic device 17 on the other hand emits, on a second output wire 20, a command to close a static semiconductor switch 21 which is connected between the wire 10 and the ground, so that more no impulse representative of the number of revolutions of the wheel can then reach the taximeter or tachograph 2, the complete operation of which is therefore prevented.

 In order not to mistakenly trigger these two effects in the event that a parasite accidentally comes to cause an apparently non-conforming comparison, the test circuit 17 only emits non-conformity signals on its outputs 18 and 20 if this comparison does not -conform has a recurring character, that is to say repeats several successive times in a regular manner and not accidentally. Similarly, it emits a signal of non-compliance if this comparison reveals a very significant deviation, frankly abnormal, compared to the value it should have. This is for example the case when the duty cycle of the pulses is 0.9 instead of, for example, 0.1.

 Instead of being connected to a static switch 21 which short-circuits the output of the amplifier 9, the control wire 20 can also be connected, passing through the shielded cable 22, directly to the taximeter or tachograph 2 to provide the latter the information according to which it must not take into account the counting pulses of the number of wheel turns which reach it. This information can advantageously be a train of possibly coded pulses, possibly also constituting dialogue signals between the microprocessor or equivalent logical organ contained in the test device 17, and the microprocessor or equivalent logical organ of the taximeter or tachograph 2.

 As is the case for the measurement tests carried out at the installation of the sensor 1 and the taximeter or tachograph 2, at least some of said subsequent systematic tests of characteristics (for example the duty cycle of the pulses) are carried out when the frequency of the pulses supplied by the sensor (ie in fact the speed of the vehicle) is greater than a minimum value below which the test could not validly be carried out, or not be carried out at all. Furthermore, such a test is preferably carried out for several predetermined frequencies.

 A general embodiment of the electronic test device 17 is shown in FIG. 2.

 In this device 17, the two aforementioned input wires 13,14 are connected, according to wires 23 and 24, to a circuit 25 for testing the impedance of the active dipole present between terminals 14 and 15, or in other words between the signal output terminals 26 and 27 (Figure 1) of the electronic sensor 1.

 Such an impedance test circuit 25 exists commercially in the form of an integrated circuit which is incorporated in various measuring devices such as digital multimeters.

 The electronic device 17 is equipped with a microprocessor 28, or other logic member for calculation and control.

 The impedance measurement which is carried out by the integrated circuit 25 is digitized by this integrated circuit and is transmitted to the microprocessor 25 via a link 29. On the other hand, this measurement n is preferably triggered or validated by the microprocessor 28, via a connection of control 30, only when the vehicle is stopped, that is to say in fact when the microprocessor 28 receives no series of pulses from the sensor 1, and therefore via the wires 13,14 and the circuit intermediary which will be described now.

 The signals present on the two wires 13 and 14 are also applied to an input 31 of the microprocessor 28 via successively an adjustable gain amplifier 32 whose gain is adjusted by the microprocessor 28 via a control link 33, and a comparator 34 at a reference voltage Vr, for example 0.2 volts, which supplies the input 31 of the microprocessor with a logic level "0" or "1" depending on whether the voltage applied to it on its other input 35 , at the output of amplifier 32, is lower or higher than this reference voltage.

 The signals finally applied to the input 31 are then rectangular signals whose cylindrical ratio depends, if the reference voltage Vr and the gain of the amplifier 32 are fixed, on the frequency and the amplitude of the signals delivered by the sensor 1 on its terminals 26 and 27. This duty cycle is therefore characteristic of both sensor 1 and the speed of the vehicle.

 The presence of the amplifier with adjustable gain 32 is not absolutely essential, but this amplifier is useful not only for obtaining without difficulty acceptable input levels for different speeds of movement of the vehicle, but also for being able to use the same device. 17 for a whole range of sensors.

 The microprocessor therefore receives these rectangular signals on its input 31 via a link 36, and it calculates the duty cycle.

 If the values of the impedance tested by circuit 25 and of this duty cycle do not conform to the values that it memorized during the installation of the taximeter or tachograph, and if this non-conformity is not of an accidental nature to a parasite, the microprocessor emits, as explained previously, fault signals on its output wires 18 and 20.

A simpler and improved form of embodiment of a test device 17 according to FIG. 2 is shown in
Figure 3.

 The simplification and the improvement relate here to the impedance test, which is replaced by a test of the response of the aforementioned dipole, that is to say essentially of the sensor 1, to a current demand. or in voltage which is produced by the sending, by the microprocessor 28 and via a link 37 comprising a resistor in series R, of a variable electrical signal through the active dipole present between the terminals 13 and 14, that is i.e. actually through the sensor 1.

 This electrical signal can be a repetitive impulse signal or an alternating signal, of predetermined frequency F1 greater than a minimum value Fo below which the test is not practically possible and which is determined experimentally. In this case, the test is carried out when the vehicle is at a standstill, so that the comparison according to the invention is not disturbed by the signals delivered by the sensor 1 when the vehicle is moving.

 From the potentiometric link point 38 between the resistor R and said active dipole also leaves a connection 39 to a low-pass filter 40 which functions as an integrator and which supplies on its output 41, in response to the signal it receives from the microprocessor 28 and by the potentiometric circuit constituted by resistance R and said active dipole, a voltage or a voltage ramp whose amplitude is coded in digitized signals, by means of an analog-digital converter 42.

 These digital signals, which are therefore representative of the response of said dipole to the frequency signal F1 and therefore ultimately many of the internal electrical characteristics of this dipole, are transmitted for analysis to the microprocessor 28 via a link 43.

For security, this analysis can be carried out for several frequencies F1, F2, F3., Of signals supplied by the microprocessor 28 on the link 37 instead of being it for the only frequency F1
According to another form of use of the circuit of FIG. 3, the solicitation or test trigger signal which is delivered by the microprocessor 28 on the link 37 is a fine pulse, with a duration of a few tens of microseconds for example, which is sent on this link when the vehicle is traveling at a speed lower than a predetermined speed (above which the test would not be possible due to the lack of sufficient time between two successive pulses present on wire 36), and immediately after the edge of descent of each pulse present on the wire 36, at the input 31 of the microprocessor 28. For example, this maximum speed corresponds to a frequency of the signals from the sensor which is of the order of 200 Hertz.

 The integrated signal which is then collected on the wire 41, at the output of the low-pass filter 40, is then a voltage ramp which characterizes the response of the aforementioned dipole to the sending of this fine pulse. It is this voltage ramp which is digitized by the converter 42 to be analyzed and compared by the microprocessor 28. Of course, this comparison must be completed before the rising edge of the next pulse from the sensor 1 and present on the 'entry 31.

 To fix the ideas, this fine pulse is sent by the microprocessor 28 between about ten microseconds to a few milliseconds after said falling edge of the pulse from the sensor 1.

In this way, the comparison of the internal characteristics of the dipole with those previously stored can be carried out when the vehicle is running normally. Of course, in the previous case where the comparison of these internal characteristics is carried out when the vehicle is stationary, it is also possible to apply, instead of a frequency signal F1, F2, F3,. . ., a test trigger impulse and in the same way record the impulse response, that is to say the voltage ramp, which results on the output 41 of the low-pass filter 40. This way of doing is however less advantageous than that just described, since it requires the vehicle to be stopped
The circuit according to Figure 3 can be simplified as shown in Figure 4, to overcome the presence of the analog / digital converter 42, which is a relatively expensive component.

 In this case, the signal - voltage ramp or integrated voltage - which appears on the wire 41 at the output of the low-pass filter 40 is applied to a first input of an analog comparator 44 which receives on its other input a reference voltage Vo.

 As a result, on its output wire 43, a logic level "0" or "1" which is applied to the microprocessor 28 depending on whether the voltage on the wire 21 is lower or higher than the voltage Vo. The microprocessor 28 analyzes the time difference between the moment when it emits its test signal on the link 37 and the moment when it receives a logic level "1" on its input 43. It deduces therefrom the particular response of the aforementioned dipole to this signal test, and characterizes by this response said internal electrical characteristics of this dipole.

 An interesting alternative embodiment of the device according to FIGS. 1 and 2 is shown diagrammatically in FIG. 5.

 According to this case, the signals from sensor 1 are, in exactly the same way, both applied to the circuits of A.B.S. and to the speedometer via the wires 11 and 12, to the circuit 25 for testing the internal electrical characteristics of the active dipole present between the signal wires 4 and 5 from the output of the sensor 1, this circuit 25 being always connected to the microprocessor 28 by the same links 29 and 30, and to the microprocessor 28 via the same amplifiers with adjustable gain 32 and comparator 34.

 For a clear comparison of the circuit of FIG. 5 with that according to FIGS. 1 and 2, all the common elements are, as they should be, designated by the same references.

 The circuit of FIG. 5 has neither a separation amplifier 9, nor a static relay 21, nor an alarm link 18 to the dashboard. The output signals of the sensor 1 are, as before, applied to the microprocessor 28 via the adjustable gain amplifier 32 and the comparator 34, but it is the microprocessor itself which transforms these signals into information pulses which are directly transmitted, via the output wire 10 passing through the shielded cable 22, to the microprocessor which equips the taximeter or tachograph 2.

 It goes without saying that in the event of non-compliance, and therefore detection of fraud, the signals thus transmitted to the taximeter or tachograph 2 are no longer only, or are no longer at all, signals representative of the speed signal delivered. by sensor 1, but are fraud detection information signals. As before, these latter signals prevent the correct functioning of the taximeter or tachograph 2, since the latter no longer takes into account the information supposed to represent the number of wheel revolutions, and they can also trigger a visual and / or audible alarm .

 The fraud detection information signals are very generally specific signals. They can for example be quite simply speed signals which are quite improbable for the vehicle concerned, or the like.

 It goes without saying that the invention is in no way limited to the exemplary embodiments which have just been described.

 Thus, for example, the entire circuit which is in the shielded box 8 could simply be included in the taximeter or the tachograph 2, which would not only make it possible to get rid of the shielded box 8 and the shielded cable 22, but also to confuse in a single microprocessor the microprocessor 28 and the microprocessor of the taximeter or tachograph.

 The choice of the duty cycle of the pulses as characteristic of the signal is preferential for its simplicity, but the choice is not limiting. One could for example choose as characteristic the curve of variation of the peak voltage of the electric signal supplied by this sensor as a function of the speed of the vehicle, or else its response to an acceleration or a deceleration of the vehicle, that is to say say the derivative of the frequency of the signal emitted by this sensor with respect to time if this acceleration or deceleration is abnormally rapid, for example if you go from 0 to 100 km / h in two seconds, there is necessarily fraud in sensor output wires.

 Instead of checking only one characteristic of the signal, we could also check several.

 The sensor 1 could, of course, be an electronic sensor of another type, such as for example a Hall effect sensor.

Claims (17)

 1. Method for avoiding fraud on a taxi equipped with a taximeter (2) or on a truck equipped with a tachograph (2), the vehicle - taxi or truck - being equipped with at least one electronic sensor (1) which at least is used for the taximeter or the tachograph, characterized in that it consists  to be connected directly in parallel to two or to the two wires (4,5) of the electrical signal output of this sensor (1),  and to trigger an electronic anti-fraud action (18-19, 20-21) which at least consists in modifying the electronic information normally transmitted to the taximeter or tachograph if at least one of the internal characteristics of the active dipole then present between these two wires (4,5), and / or at least one of the characteristics of the electrical signal available between these two wires (4,5) during normal movement of the vehicle, has been modified with respect to previously stored reference values.  2. Method according to claim 1, characterized in that the internal characteristic of said active dipole is its impedance  3. Method according to claim 1 or claim 2, characterized in that, to test this internal characteristic, at least one variable voltage or current is injected through this dipole, and in that the impulse response is then noted or corresponding frequency of said dipole.  4. Method according to claim 3, characterized in that at least one current or voltage pulse is thus injected through said dipole, the latter being connected to an integrator (40) to obtain said impulse response.  5. Method according to one of claims 2 to 5, characterized in that this test of the internal characteristics is carried out when the vehicle is stopped.  6. Method according to claim 4, characterized in that this current or voltage pulse is injected just after the falling edge of a rectangular signal originating from the signal delivered by the sensor (1) when the vehicle is moving, and in that this test is carried out when the vehicle is traveling at a speed lower than a predetermined speed, sufficiently low so that the time interval which separates two successive pulses from this rectangular signal is sufficient for said comparison to be carried out.  7. Method according to one of claims 1 to 6, characterized in that said characteristic of the signal present at the terminals of this dipole is the duty cycle of the pulses which correspond to the rectangular signal originating from the signal delivered by the sensor (1).  8. Method according to one of claims 1 to 7, characterized in that said characteristic of the signal is the variation curve, as a function of the speed of the vehicle, of the peak voltage of the electrical signal supplied by said sensor (1) .  9. Method according to one of claims 1 to 8, characterized in that said characteristic of the signal is the derivative with respect to time of the frequency of the signal emitted by this sensor (1), that is to say the response from the latter to an acceleration or deceleration of the vehicle.  10. Method according to one of claims 1 to 9, characterized in that. when the taximeter or tachograph (2) is installed on the vehicle, measurements of these characteristics are made and stored by rolling the vehicle at one or more predetermined speeds, and in what we then compare during the tests of characteristics which are then made to detect a possible fraud, these latter characteristics to those thus memorized at the origin, in order to determine if they are indeed in conformity with these characteristics memorized at the origin.  11. Method according to claim 10, characterized in that these characteristics thus systematically tested for detecting a possible fraud are declared non-compliant only if they have a recurring character or if they are of frankly abnormal amplitude.  12. Method according to one of claims 1 to 11, characterized in that said systematic test of the characteristics of the signal present at the terminals of this dipole is carried out when the vehicle is traveling at a speed greater than a predetermined speed.  13. Device for implementing the method according to one of claims 1 to 12, characterized in that it comprises, in a mechanically tamper-evident envelope (6,8,22), an electronic device (17) for comparing said one or more characteristics with one or more stored reference values, this device (17) being coupled to anti-fraud means (20, 21) associated with the taximeter or tachograph (2).  14. Device according to claim 13, characterized in that the entire circuit between the point (7) of articulation of the wheel which comprises this sensor (1) and said taximeter or tachograph (2), is made inviolable by means (6,8,22) mechanical protection.  15. Device according to claim 13 or claim 14, characterized in that said electronic device (17) comprises a logic control and calculation member (28) which at least carries out said comparison with reference values which it has stored . and which controls the anti-fraud means associated with the taximeter or tachograph (2).  16. Device according to claim 15, characterized in that this logic member (28) also performs at least the calculation of said one or more characteristics of the signal present at the terminals of said active dipole.  17. Device according to claim 15 or claim 16, characterized in that there is provided, for this logic member (28), an output (37) which is connected to one of the terminals (13) of said active dipole at through a resistor (R), and in that the point (38) of potentiometric junction between this resistor (R) and this dipole is connected to an input (43) of this logic member (28) via a integrator (40) and an organ (42, 44) for transforming, into digital data, the analog signal detected on the output (41) of this integrator (40).