JPH0224700B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an anti-theft device for a motor vehicle, and more particularly to a device for preventing the theft of automobile tires.

[Background Art] Anti-theft devices that use vibration detection means such as piezoelectric elements are generally provided, and since this device detects vibrations of the vehicle body, it can also detect theft of tires and issue an alarm. It is something that can be done. However, there is a problem in that even if a person hits or shakes the vehicle body, an alarm may be issued, and false alarms are likely to occur.

[Object of the Invention] The present invention has been made in view of the above points, and its main purpose is to provide a vehicle for use in automobiles that reliably detects only tire theft and prevents false alarms from occurring. An object of the present invention is to provide an anti-theft device.

[Disclosure of the Invention] In the present invention, only tire theft is detected by utilizing the fact that the frequency band of the vibration when removing a wheel nut is different from that of vibration when hitting or shaking the vehicle body. That's what I do.

The wheel nuts are particularly tightly tightened to prevent the tires from coming off while the vehicle is running, and removing the wheel nuts requires a considerable amount of force, which causes vibrations.
When this vibration is detected by a piezoelectric element, the results shown in Figure 18 are obtained when the right rear wheel is removed, and the results shown in Figure 19 are obtained when the left rear wheel is removed. . From this result, it can be seen that there are few frequency components below 1KHz when removing the wheel nut.

On the other hand, when the car body was struck once, the results shown in FIG. 20 were obtained, and when the car body was struck twice, the results shown in FIG. 21 were obtained. Here, it can be seen that the vibration components are distributed over almost the entire frequency band.

From the above results, it can be seen that the vibration that occurs when removing a wheel nut has extremely less frequency components of 1KHz or less compared to the vibration that occurs when the car body is hit. The present invention focuses on this point and attempts to detect only when the wheel nut is removed.

Embodiment 1 Hereinafter, embodiments of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing the basic configuration of the present invention. A pair of piezoelectric elements 1 are provided as vibration detection means. As shown in FIG. 2, the piezoelectric element 1 has electrodes 11a and 11b provided on both sides in the thickness direction of a piezoelectric body 10 such as piezoelectric ceramic, and one electrode 11b is held in a casing 12 so as to be able to vibrate. configured. When the casing 12 vibrates, the electrode 11b bends and the piezoelectric body 1
0, and a potential difference is generated between the electrodes 11a and 11b in accordance with the vibration. This piezoelectric element 1 is connected to a vehicle body 2 as shown in FIGS. 3 and 4.
0, one each is disposed on the left and right corresponding to the lower end of the center pillar 21. In the figure, 22 is a floorboard inside the vehicle, 23 is a front door, and 24 is a rear door. The piezoelectric element 1 is attached to the vehicle body 20 by screwing or using adhesive, as shown in FIG. Although two piezoelectric elements 1 are provided here, it is also possible to use one or many piezoelectric elements.For example, in the case of one piezoelectric element, as shown in FIG. 22, and if four are installed, as shown in Fig. 7,
It is only necessary to attach the piezoelectric element 1 to the floor plate 22 at a portion close to the piezoelectric element 5. The greater the number of piezoelectric elements 1, the higher the sensitivity, but the number may be set as necessary.

The outputs of the piezoelectric element 1 are combined by a mixing circuit 2 and amplified by an amplifier circuit 3, as shown in FIG. The output of the amplifier circuit 3 is input to a first filter 4 and a second filter 5. The first filter 4 has a frequency characteristic that allows vibration components generated when removing a wheel nut to pass through.
Low pass filter that passes 5KHz or less or 1KHz
A bandpass filter or the like is used that passes frequencies above 5KHz or below. In addition, the second filter 5 has a frequency characteristic that allows vibration components that do not occur much when removing the wheel nut to pass through, and is a band pass filter with a center frequency of 700 Hz and widths of 200 to 300 Hz on the upper and lower sides, and a band pass filter with a width of 1 KHz. A low-pass filter or the like that passes the following is used. The vibration components that have passed through these filters 4 and 5 are detected through a first detection circuit 6 and a second detection circuit 7, respectively. The outputs of both detection circuits 6 and 7 are input to a comparison/judgment circuit 8. The comparison/judgment circuit 8 compares the outputs of the detection circuits 6 and 7 with a predetermined value set in advance, and determines whether the wheel nut has been removed or whether the vehicle body 20 has simply been hit or shaken based on the comparison result. Determine. In other words, the output of the first detection circuit 6 will be larger than the predetermined value both when the wheel nut is removed and when the vehicle body 20 is struck, and when the wheel nut is removed, vibrations of 1KHz or less will be suppressed. Because it rarely occurs,
At that time, the output of the second detection circuit 7 becomes less than the predetermined value. In this manner, by comparing the magnitude of the outputs of both detection circuits 6 and 7 with a predetermined value, it is possible to determine whether the wheel nut has been removed or whether the vehicle body 20 has been struck. When the wheel nut is removed, an alarm signal is output from the comparison/judgment circuit 8, and the alarm circuit 9 is driven by this alarm signal to issue an alarm.

The comparison and determination circuit 8 will be explained in more detail. The comparison/judgment circuit 8 has the configuration shown in FIG. 8, and the signals of each part are as shown in FIG. 9. The output of the first detection circuit 6 is input to a first comparator circuit 30 that compares it with a set voltage Vref ₁ , and the output of this comparator circuit 30 is set so that the output is at L level when the input is higher than the set voltage Vref ₁ . It's getting old. The output of the comparator circuit 30 is input to the differentiating circuit 37 via the inverter circuit 32, and when the output of the comparator circuit 30 rises, a negative logic pulse with a narrow pulse width is output. This pulse is generated by the first pulse generating circuit 3.
3, the pulse generating circuit 33 outputs a negative logic pulse with a predetermined time duration T ₁ after the input signal falls, and this is passed through the inverter circuit 35 to one input terminal of the 2-input AND circuit 36. Connected. The output of the second detection circuit 7 is input to the second comparator circuit 31. Similarly to the first comparator circuit 30, the second comparator circuit 31 also compares the output of the second detection circuit 7 with the set voltage Vref ₂ , and sets the output to L level when it is higher than the set voltage Vref ₂ . ing. The output of the second comparator circuit 31 is transmitted to the second pulse generating circuit 3.
4 is input. Like the first pulse generating circuit 33, the second pulse generating circuit 34 outputs a negative logic pulse having a predetermined time width _T2 from the falling edge of the input signal. The output of the second pulse generating circuit 34 is input to the other input terminal of the two-input AND circuit 36. Here, the set time width T ₂ of the second pulse generation circuit 34 is set longer than the set time width T ₁ of the first pulse generation circuit 33 . Therefore, the output of the first detection circuit 6 is the first set voltage.
Only when Vref is equal to or higher than ₁ and the output of the second detection circuit 7 is equal to or lower than the second set voltage Vref ₂ , the output of the AND circuit 36 becomes H level.
That is, as shown in FIG. 9, when the vehicle body 20 is hit, the outputs of both detection circuits 6 and 7 are both equal to or higher than the set voltages Vref ₁ and Vref ₂ ,
The output of the inverter circuit 35 becomes H level,
Since the set time width T ₁ of the first pulse generation circuit 33 is shorter than the set time width T ₂ of the second pulse generation circuit 34, the second pulse is generated while the output of the inverter circuit 35 is at H level. The output of the circuit 34 is kept at the L level, and the output of the AND circuit 36 is kept at the L level. On the other hand, when the wheel nut is removed, the output of the second detection circuit 7 is L.
level, the output of the second pulse generating circuit 34 remains at the H level and does not change, and the output of the AND circuit 36
Both input terminals of the circuit become H level, and its output becomes H level. In this way, it is possible to reliably detect that the wheel nut has been removed. Here, since the vibration is small when there is light contact with the vehicle body 20 or when there is rain on the vehicle body 20, the outputs of the detection circuits 6 and 7 should be larger than the set voltages Vref ₁ and Vref ₂ . First, no malfunctions will occur. In the above example, two filters 4 and 5 are provided, but additional filters having different pass band characteristics may be provided.

Example 2 Although the purpose of Example 1 is achieved to some extent, the strength of the vibration detected by the piezoelectric element 1 differs depending on the tightening condition of the wheel nut and the type of wheel. Furthermore, if the vibration is weak or too strong relative to the set voltages Vref ₁ and Vref ₂ , malfunction may occur. However, even in this case, the relative relationship of the frequency distribution of vibrations is as described above, so if it is possible to detect the removal of the wheel nut in response to vibrations of various strengths, it is possible to prevent malfunctions. This can be prevented.

That is, three comparison/judgment circuits 8a, 8b, and 8c having the same configuration as the comparison/judgment circuit 8 shown in Example 1 and having different set voltages for the comparator circuits 30, 31 are provided, and each comparison/judgment circuit 8
The output of the first detection circuit 6 and the output of the second detection circuit 7 are input to a, 8b, and 8c, respectively. The set voltages of each comparison/judgment circuit 8a, 8b, 8c are Vref ₁ a, Vref ₂ a, Vref ₁ b, Vref ₂ b, Vref ₁ c, respectively.
Vref ₂ c, Vref ₁ a＜Vref ₁ b＜Vref ₁ c,
The relationship is set as Vref ₂ a < Vref ₂ b < Vref ₂ c. Further, the output terminals of each comparison/judgment circuit 8a, 8b, 8c are input to a three-input OR circuit 40, respectively.

As shown in FIG. 12, even if the strength of vibration changes, when the wheel nut is removed, the relative relationship between the strength of the output of the first detection circuit 6 and the output of the second detection circuit 7 is are the same, so when an alarm signal is output from any one of the comparison/judgment circuits 8a, 8b, and 8c, it can be determined that it is the vibration that occurred when the wheel nut was removed. Actually, in this circuit, when the wheel nut is removed, the output of at least one of the comparison judgment circuits 8a, 8b, 8c becomes H level, so the output of the OR circuit 40 becomes H level, and an alarm signal is output. be. As above,
It is possible to detect that the wheel nut has been removed regardless of the strength of the vibration. In addition, in the above example, an example was shown in which three comparison judgment circuits 8a, 8b, 8c were provided, but the comparison judgment circuits 8a, 8b, 8
It is also possible to further increase the number of c's and set the level more precisely.

Example 3 This example aims to further reduce false alarms, and is intended to further reduce false alarms.
It is fixed by six wheel nuts,
To remove the tire, you need to remove all of these.
Focusing on the fact that it takes several seconds from removing one wheel nut to removing the next wheel nut, an alarm is issued when a predetermined number of wheel nuts are removed.

That is, an alarm processing section is provided that determines whether or not to drive the alarm circuit according to the number of alarm signals output from the comparison/judgment circuit 8. As shown in FIG. 13, the alarm processing section is composed of a pair of time limit circuits 41, 42 and a counter circuit 43, and each time limit circuit 41, 42 is set to a different time constant. The counter circuit 43 outputs an alarm drive signal for driving the alarm circuit when a predetermined number of alarm signals are input. That is, when a predetermined number of wheel nuts are removed, an alarm drive signal is output. Here, the set number is smaller than the number of wheel nuts to which one tire is attached. The first time limit circuit 41 is set to output a pulse having a time width Ta longer than the time required to remove a predetermined number of wheel nuts set by the counter circuit 43, and the output pulse is The counter circuit 43 is reset when the voltage falls. The second time limit circuit 42 has a time limit that is longer than the time from when one alarm signal rises until the next alarm signal is output, that is, from when one wheel nut is removed to when the next wheel nut is removed. When the next alarm signal is input during a short time Tb, the counter circuit 43 is reset. Therefore, if a predetermined number of alarm signals set in the counter circuit 43 are input while one alarm signal is input and a pulse is output from the first time limit circuit 41, an alarm drive signal is output from the counter circuit 43. On the other hand, the time set in the first time limit circuit 41 after one alarm signal is input
If a predetermined number of alarm signals are not input within Ta, or if an alarm signal is input within the time Tb set in the second time limit circuit 42 after one alarm signal is input, it is not considered an alarm signal. The counter circuit 43 is determined to be a false noise, and the counter circuit 43 is reset so as not to output an alarm drive signal.

FIG. 14 illustrates a circuit diagram in which the set number of counter circuits 43 is three, and FIG. 15 shows the signals of each part. The first time limit circuit 41 generates a one-shot pulse at the rising edge of the output signal of the retriggerable monostable multivibrator (hereinafter abbreviated as monostable multi) 51 and the monostable multivibrator 51 which is triggered at the rising edge of the alarm signal. It consists of a one shot generation circuit 52, and a first shot generation circuit 52.
As shown in FIGS. 5a, b, and c, when the alarm signal rises, the negative logic output terminal of the monostable multi 51 remains at L level for a predetermined time Ta'. This time Ta' is the time Ta that should be set in the first time limit circuit 41.
is set to the time divided by the set number in the counter circuit 43 minus 1. That is, 1
It is set to be longer than the time required from removing one wheel nut to removing the next wheel nut. If the next alarm signal is input within this time Ta′, the trigger will be applied again, and the
The pulse is extended by Ta', and if there is no next alarm signal within this time Ta', the one-shot generating circuit 52 outputs a one-shot pulse.

The second time limit circuit 42 has a monostable multi 53 that is triggered by the rising edge of the alarm signal, and outputs an alarm signal when the alarm signal is output a predetermined time after the positive logic output terminal Q of the monostable multi 53 becomes H level. The monostable multi 53 outputs a pulse for the normal time required to remove one wheel nut and then remove the next wheel nut, that is, the above-mentioned time Tb. A time constant is set to . Also, the delay circuit 5
The time constant 4 is set to be slightly larger than the pulse width of the alarm signal. Therefore, as shown in FIG. 15 a, d, e, and f, the time period from when one alarm signal is input to when the next alarm signal is input is the time Tb set in the monostable multi 53. When it is shorter than , the delay circuit 54 outputs a pulse.

The counter circuit 43 includes a delay circuit 55 that delays the alarm signal, and a shift register 56 that outputs an alarm drive signal when a predetermined number of alarm signals are input.
The two-input OR circuit 43 is connected to the reset terminal of the shift register 56. Therefore, the alarm signal is input to the shift register 56 after being delayed by the time set by the capacitor C and the resistor R of the delay circuit 55, and when three alarm signals are input, the third output terminal Q of the shift register 56 is input. ₃ becomes H level and an alarm drive signal is output.
The input terminal of the OR circuit 57 is connected to the first time limit circuit 4.
The output ends of the first and second time limit circuits 42 are connected, and when the output of either one of the time limit circuits 41 and 42 becomes H level, the shift register 56
is now being reset. Therefore, the time from when one alarm signal is input to the shift register 56 until the next alarm signal is input is equal to or longer than the time Ta' set in the first time limit circuit 41, or If the time is less than the time Tb set in the time limit circuit 42 of No. 2, the third output terminal _Q3 of the shift register 56 does not go to the H level, and those alarm signals are judged to be noise, and the alarm drive signal is not activated. It does not output anything. By the way, the 15th
In the example shown in the figure, the time constant of the delay circuit 55 is set to be smaller than the time width of the alarm signal, so even if the alarm signal is input at an interval shorter than the time width Tb, the output of the delay circuit 55 (Fig _. ) and the signal input to the reset terminal Re of the shift register 56 overlap, so they are not counted, but the time constant of the delay circuit 55 is set to be sufficiently larger than the time width Tb of the alarm signal. Take the 16th
As shown in the figure, the output of the delay circuit 55 (indicated by _P2 in Figure 16) and the signal input to the reset terminal Re of the shift register 56 do not overlap, and this alarm signal is counted. .

Embodiment 4 In Embodiment 3, the number set in the shift register 56 was set to 3, but in this case, a person who wants to remove tires can know the set number by purchasing the device, and set the number of wheel nuts to 3. There is a problem in that the tire can be removed by repeating the process of removing a smaller number of wheel nuts, waiting for the time set by the first time limit circuit 41, and then removing the wheel nuts again. In the fourth embodiment, the user is allowed to set the number as desired so that the set number is not known.

That is, the shift register 56 has multiple output terminals.
Q ₁ , Q ₂ ...Qn, which output terminal Q ₁ , Q ₂ ,
...Whether or not the alarm drive signal is extracted from Qn can be selected using a selection switch SW.

With this configuration, a person trying to take a tire cannot know the set number of tires, and since it is not known when an alarm will be issued, the wheel nut cannot be removed, and theft of the tire is definitely prevented. can be prevented.

[Effects of the Invention] As described above, the present invention includes a vibration detection means for detecting vibrations of a vehicle body, and a first filter means whose passband is the frequency band of vibrations generated when removing a wheel nut that fixes a tire. and a second filter means whose pass band is a frequency band different from the above-mentioned frequency band; It consists of a comparison judgment means that outputs an alarm signal when the value is below a set value, and an alarm notification means that generates an alarm in response to the alarm signal. In this case, no alarm is issued, and only the theft of a tire can be reliably detected, which has the advantage of not giving rise to false alarms.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention.
Fig. 2 is a sectional view showing an example of the piezoelectric element used in the above, Fig. 3 a and b are a plan view and a side view showing the mounting position of the piezoelectric element in the above, respectively, and Fig. 4 is a sectional view showing an example of the piezoelectric element used in the above. A partial perspective view showing the mounting position of the element,
FIG. 5 is a cross-sectional view showing the mounting state of the piezoelectric element same as above, FIGS.
b is a plan view and a side view showing still another example of the mounting position of the piezoelectric element same as above, FIG. 8 is a circuit diagram showing a comparison judgment circuit used in Example 1 of the present invention, and FIG. 9 is used in the same as above. FIG. 10 is an explanatory diagram of the operation of the comparison/judgment circuit used in the second embodiment of the present invention. FIG. Figure 13 is a block diagram showing Embodiment 3 of the present invention, Figure 14 is a circuit diagram of the same, Figure 15 is a diagram explaining the operation of the same, and Figure 16 is a circuit diagram with the same circuit constants changed. FIG. 17 is a block diagram showing Embodiment 4 of the present invention. FIGS. 18 and 19 are graphs showing the frequency distribution of vibrations generated in the vehicle body when removing wheel nuts. 21 and 21 are graphs showing the frequency distribution of vibrations generated in the vehicle body when the vehicle body is hit. 1 is a piezoelectric element, 4 is a first filter circuit, 5 is a second filter circuit, 8, 8a, 8b, 8c are comparison judgment circuits, 9 is an alarm circuit, 41 is a first time limit circuit, 42 is a second 43 is a counter circuit.

Claims (1)

[Scope of Claims] 1. Vibration detection means for detecting vibrations of the vehicle body, first filter means whose passband is the frequency band of vibrations generated when removing a wheel nut that fixes a tire, and the frequency band a second filter means whose passband is a different frequency band;
a comparison determination means for outputting an alarm signal when the output level of the filter means is equal to or higher than the first set value and the output level of the second filter means is equal to or lower than the second set value; 1. An anti-theft device for an automobile, comprising an alarm notification means for generating an alarm. 2 The passband of the second filter means is 1KHz.
Claim 1 characterized in that:
Anti-theft device for automobiles as described in . 3. The anti-theft device for an automobile according to claim 1, wherein the vibration detecting means comprises a plurality of piezoelectric elements, each piezoelectric element being disposed inside the vehicle body. 4. The comparison and judgment means are each composed of a plurality of comparison and judgment circuits that compare and judge the output levels of the first filter means and the second filter means, and each of the comparison and judgment circuits has a first set value and a second setting. The anti-theft device for an automobile according to claim 1, wherein the values are different from each other. 5 The above alarm notification means issues an alarm when a predetermined number of alarm signals are input, and the time from when one alarm signal is input to when the next alarm signal is input is the total time required to fix the tire. When the first set time required to remove a wheel nut is exceeded or the second set time normally required from removing one wheel nut to removing the next wheel nut is less than the second set time, the alarm signal is restarted from the beginning. An anti-theft device for an automobile according to claim 1. 6. The anti-theft device for an automobile according to claim 5, wherein the alarm notification means is provided with selection means for arbitrarily setting the number of alarm signals required to issue an alarm.