JP2800041B2 - Vehicle burglar alarm system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a vehicle burglar alarm device that detects a change in the inclination of a vehicle in an alternating manner. A bridge-type sensor that is mounted on a vehicle and detects its inclination, and a differential amplifier that amplifies the output of the sensor, with a view to preventing interference.
An offset correction circuit that compares the output of the differential amplifier with a constant value, integrates the difference output, and uses it as a reference voltage of the differential amplifier, and an alarm that issues an alarm when the output of the differential amplifier exceeds a predetermined value. Means and initialization means for temporarily setting the integration time constant of the offset correction circuit to zero at the start of parking of the vehicle.

[Industrial applications]

The present invention relates to a vehicle burglar alarm device that detects a change in the inclination of a vehicle in an alternating manner.

Theft of a tire that jacks up a parked vehicle or theft of a vehicle itself using a tow truck can be detected by monitoring changes in the inclination of the vehicle. The inclination of the vehicle itself can be easily detected by inclination detection means such as an acceleration (G) sensor, but a change in the inclination must be detected based on the inclination at the start of parking.

The DC inclination change detecting means stores the initial inclination at the start of parking and compares it with the subsequent inclination to determine the inclination change at each time, so a memory for storing the initial inclination is required. become.

On the other hand, the AC-based gradient change detecting means differentiates the output of the tilt detecting means to determine the gradient change, and thus does not require the above-mentioned memory.

[Conventional technology]

As a device for alternatingly detecting a change in the degree of inclination of a vehicle, there is a device conventionally configured as shown in FIG. In the figure
11 is an acceleration sensor attached to the vehicle, 12 is a constant current circuit, 13 is a differential amplifier, and these constitute the inclination detecting means 10. Reference numeral 20 denotes an HPF (high-pass filter) that detects only a change in the degree of inclination from the output of the inclination detecting means 10, and 31 denotes an AC amplifier that amplifies the output.

There are various types of the acceleration sensor 11. FIG. 12 shows a state in which a permanent magnet 72 is fixed to the tip of a swingable support rod 71, and acceleration G
Thus, the displacement of the magnet 72 is detected by magnetic detecting elements (Hall elements and magnetoresistive elements) 73 and 74 having opposite polarities. In this method, the two outputs of the two magnetic detecting elements 73 and 74 are input to a differential amplifier circuit, and the difference between them is obtained, thereby canceling out the variation of the elements.

On the other hand, FIG. 13 shows a semiconductor substrate 81 which is elastically deformed, in which diffusion resistors Ra to Rd are formed in four directions to form a bridge, one end of the substrate 81 is fixed, and a weight 82 is attached to the other end.
This sensor utilizes the fact that when a stress is applied to the substrate 81 by the acceleration G, the values of the resistances Ra to Rd change due to the piezo effect.
It can be detected as a voltage generated between the two output terminals A and B.

Although the apparatus shown in FIG. 11 uses the acceleration sensor shown in FIG. 13, the sensor shown in FIG. 12 can be represented by the same equivalent circuit. The differential amplifier 13 that amplifies the minute output of the acceleration sensor 11 uses two-stage operational amplifiers A1 and A2. The HPF 20 extracts only an AC component (a change in the gradient) from the output of the gradient detecting means 10. In principle, only the coupling capacitor C is required. I have it. An AC amplifier that amplifies the output of the HPF 20 is configured using an operational amplifier A3.

When the constant current I is 5 mA, the sensitivity of the acceleration sensor 11 is
It will be about 1.35mV / 0.5G. G is the gravitational acceleration, 0.5G is 30
It corresponds to the inclination of ゜. The resolution required for vehicle theft detection is as small as 3 ° in detection angle and about 0.0523G in acceleration, so if the threshold value of the subsequent circuit is 0.5V, the amplification units 13,31
The total gain of Need some degree. Further, if the inclination is 3 ° over 30 seconds to detect a gradual jack-up, the cutoff frequency of the HPF 20 becomes 0.0016 Hz, and the time constants of C and R become extremely large.

[Problems to be solved by the invention]

As described above, when the time constants of C and R are large, when the vehicle is parked on an inclined ground, the amplifying unit 31 generates an output due to the residual charge of the capacitor C for a while from the start of parking, and during this time, the vehicle is stolen. When you meet, the undetectable problem remains. For example, if C = 100 μF and R = 1 MΩ, it takes 100 seconds or more to return to the steady state value.

If a film capacitor is used as the capacitor C, the size of the capacitor increases and the cost increases. On the other hand, when an electrolytic capacitor is used as the capacitor C, there is a disadvantage that an offset is generated due to a leakage current. For example, even if a leakage current of 0.6 μA flows through a resistor R of 1 MΩ, an offset voltage of 0.6 V is generated, and a warning means having a threshold value of 0.4 to 0.5 V malfunctions.

 The present invention seeks to improve such points.

[Means for solving the problem]

FIG. 1 is a principle view of the present invention, wherein 11 is a tilt sensor having a bridge configuration, 12 is a constant current source, 13 is a differential amplifier for amplifying a sensor output, 30 includes an AC amplifier 31, a comparator 32, and an alarm 33. Alarm means, 40 is an offset correction circuit, and S1 is initialization means (for example, a switch).

[Action]

The sensor 11 generates an output according to the inclination angle of the vehicle, and the differential amplifier 13 amplifies the output. The alarm means 30 further amplifies the differential amplified output by the amplifier 31, and the amplified output is
When the threshold value of 32 is exceeded, the alarm 33 is activated to issue a theft alarm.

In the present invention, the HPF 20 as shown in FIG. 11 is not inserted between the differential amplifier 13 and the AC amplifier 31. Instead, a differential amplifier 1
An offset correction circuit 40 for maintaining the output of No. 3 at a constant value _Vref is provided so that only the change in the tilt angle is transmitted to the AC amplifier 31 similarly to the HPF.

That is, the offset correction circuit 40 uses the comparator A4 that determines the difference between the output of the differential amplifier 13 and the constant value _Vref ,
Since the difference output is used as the reference voltage of the first stage A1 of the differential amplifier 13, the output of the differential amplifier 13 always converges to a constant value _Vref . However, since the signal component is suppressed only by the comparator A4, an integrating circuit including the capacitor C and the resistor R is provided, and only the low frequency component is negatively fed back. In this case, the high-frequency component that is not negatively fed back by the offset correction circuit 40 is transmitted to the AC amplifier 31, so that if the time constant CR of the integration circuit is selected, the same transmission characteristics as the HPF 20 in FIG. 11 can be obtained.

In addition, the offset and drift of the sensor 11 and the differential amplifier 13 are removed by the negative feedback of the low frequency component, and even if an electrolytic capacitor is used for C of the integrating circuit, the offset due to the leakage current is also absorbed.

However, when the vehicle is stopped on a slope, the differential amplification output rises steeply as shown in FIG. 2, and it takes time for the output to return to the constant value _Vref . Therefore, if the theft monitoring state is set before that, an erroneous alarm occurs because the differential amplified output remains. Therefore, in the present invention, the switch S1 is temporarily turned on by a reset signal, and both ends of the resistor R are short-circuited.
As a result, the time constant of the integrating circuit becomes zero, so that the differential amplified output instantaneously returns to _Vref , and a normal theft monitoring state is set.

〔Example〕

FIG. 3 shows a first embodiment of the present invention. In this example, an LPF (low-pass filter) 50 is added to the basic configuration of FIG. This LPF50 consists of resistors R11 and R12, capacitors C11 and C12 and an operational amplifier A5. When the vehicle is parked on a bridge or the vehicle passes by the side, it joins the vehicle from outside.
It is intended to remove the vibration of about 2H _z. Therefore, L
For example, if PF50 cuts 2 Hz or more, and cuts 0.001 Hz or less by the HPF function of the offset correction circuit 40, the transfer characteristic from the differential amplifier 13 to the amplifier 31 is 0.001 Hz to 2 Hz.
It becomes BPF (Band Pass Filter).

The switch S1 for initialization is connected to the differential amplifier 13 as in FIG.
And an inverting input of the comparator A4. The input of the offset correction circuit 40 may be the output of the differential amplifier 13, but may be branched from the output of the LPF 50 as in this example. The advantages of this method will be described with reference to the embodiment shown in FIG. 7 (intermittent driving method).

FIG. 4 is a block diagram of a second embodiment of the present invention. In this example, two sensors 11, 11 'for detecting inclinations in orthogonal directions are provided.
Are used, the changeover switches S2 and S2 'are provided so that the alarm means 30 can be shared. Symbol 11 ′, 1
2 ', 13', 40 ', 50', S1 'are symbols 11,12,13,40,5
0, a circuit having the same function as S1 is shown.

FIG. 5 is a block diagram of a third embodiment of the present invention. In this example, the configuration of FIG. 4 is further developed.
1,11 'can be shared.

FIG. 6 is an operation waveform diagram common to FIG. 4 and FIG. This example shows a state where the inclination change is detected on the first sensor 11 side and the differential amplification output gradually increases. The switches S2 and S2 'are turned on and off alternately at regular intervals.
When switching the outputs of the LPFs 50 and 50 'as shown in FIG.
The output of 0 increases following the differential amplification output as shown by the broken line. On the other hand, when the input of the LPF 50 is switched as shown in FIG. 5, the output of the LPF 50 becomes the differential amplifier during the ON period of the switch S2 '.
To take in the output of 13 ', the output of LPF 50 fluctuates as shown by the solid line in FIG. In the example shown in the figure, since the capacitors C11 and C12 are discharged during the ON period of the switch S2 ', the output of the LPF 50 decreases, and the difference between the solid line and the broken line becomes a detection error factor. In order to improve this point, the switches S2 and S2 'in FIG. 5 need to be switched at a long cycle. FIG. 6 shows an example in which the switches S2 and S2 'are switched at a short cycle of 0.5 second or less.

FIG. 7 is a block diagram of a fourth embodiment of the present invention. In this example, an intermittent drive switch S3 and an LPF output holding switch S4 are added to the configuration of FIG.

The switch S3 is turned on and off at regular intervals as shown in FIG. 8, and a current is supplied to the sensor 11 only during the on period to reduce power consumption. The sensor 11 generates an output when a current flows, and outputs 0 when no current flows. From the viewpoint of the differential amplifier 13, the change in the sensor output due to the switch S3 is not different from a normal signal change. Therefore, when the differential amplified output during the period when the switch S3 is off is input to the LPF 50, the LPF output changes according to the on / off state of the switch S3. So switch S3
The switch S4 is turned on and off in synchronization with the control to keep the output of the LPF 50. However, when the switch S3 is turned on from off, a "whiskers" are generated in the differential amplified output as shown in FIG. 8. Therefore, if the on timing of the switch S4 is slightly delayed from the switch S3 so as to cut this portion, Good.

When the switch S3 is turned off, the output of the sensor 11 becomes 0. At this time, if the input of the offset correction circuit 40 is the output of the differential amplifier 13 as shown in FIG. 1, the offset correction circuit 40 adjusts the reference voltage so as to cancel the output change (fall) of the differential amplifier 13. Change. Therefore, even if the switch S3 is turned on, the output of the differential amplifier 13 does not immediately become _Vref .
Therefore, as shown in FIG. 3, the input of the offset correction circuit 40 is obtained from the output of the LPF 50. With this configuration, the output of the LPF 50 is held at _Vref during the off-period of the switch S4 including the off-period of the switch S3.
The reference voltage of 3 does not change. LPF beyond switch S4
50 inputs may be input to the offset correction circuit 40.

FIG. 9 shows a fifth embodiment of the present invention in which the above examples are combined. In this example, two sensors 11, 11 'are used to detect the inclination in the orthogonal direction. The intermittent drive switches S3, S3 'allow current to flow from the common constant current source 12 to the sensors 11, 11' alternately. FIG. 10 shows the timing. The output holding switches S4 and S4 'of the LPFs 50 and 50' are synchronized with the operation of the switches S3 and S3 '. The reset switches S1 and S1 'are turned on when the lock SW is locked, but the timings are shifted as shown in FIG. This is in accordance with the operation of the switches S3 and S3 '. The changeover switches S2 and S2 'operate in synchronization with the switches S4 and S4'. The microcomputer 34 controls these switches. The microcomputer 34 drives the horn 33 when receiving an alarm output from the comparator 32.

〔The invention's effect〕

As described above, according to the present invention, it is possible to reliably detect a theft immediately after the start of parking in a vehicular theft alarm device that uses alternating inclination change detection means. Also,
It is possible to prevent malfunction due to external vibration and prevent the battery from running out. Moreover, since the HPF is not used, there is an advantage that there is no influence of the leakage current of the electrolytic capacitor.

[Brief description of the drawings]

1 is a principle diagram of the present invention, FIG. 2 is an operation waveform diagram of FIG. 1, FIG. 3 is a configuration diagram of a first embodiment of the present invention, and FIG. 4 is a configuration of a second embodiment of the present invention. FIG. 5, FIG. 5 is a block diagram of a third embodiment of the present invention, FIG. 6 is an operation waveform diagram of FIGS. 4 and 5, FIG. 7 is a block diagram of a fourth embodiment of the present invention, FIG. Fig. 7 is an operation waveform diagram of Fig. 7, Fig. 9 is a configuration diagram of a fifth embodiment of the present invention, Fig. 10 is an operation waveform diagram of Fig. 9, and Fig. 11 is an example of a conventional inclination change detecting device. FIG. 12 is a block diagram showing an example of an acceleration sensor, and FIG. 13 is a block diagram showing another example of an acceleration sensor. In the figure, 11 is a sensor, 12 is a constant current source, 13 is a differential amplifier, 30
Is an alarm means, 31 is an AC amplifier, 32 is a comparator, 33 is an alarm,
40 is an offset correction circuit, 50 is a low-pass filter, S1 is an initialization switch, S2 is a changeover switch, S3 is an intermittent drive switch, and S4 is an LPF output holding switch.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B60R 25/10 G08B 15/00 G08B 21/00 G08B 13/00

Claims (3)

(57) [Claims] 1. A sensor (11) mounted on a vehicle and having a bridge configuration for detecting its inclination, a differential amplifier (13) for amplifying the output of the sensor, and an output of the differential amplifier and a constant value. An offset correction circuit (40) for comparing and integrating the difference output to obtain a reference voltage of the differential amplifier; an alarm means (30) for issuing an alarm when an output of the differential amplifier exceeds a predetermined value; A burglar alarm system for a vehicle, comprising: initialization means (S1) for temporarily setting an integration time constant of an offset correction circuit to zero at the start of parking of the vehicle. 2. A vehicle according to claim 1, further comprising a low-pass filter (50) for applying only low-frequency components obtained by removing external vibrations from the output of the differential amplifier (13) to the alarm means (30). For burglar alarm. 3. The burglar alarm system for a vehicle according to claim 1, further comprising switching means (S3) for intermittently operating the sensor (11).