JPH0243240B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a loop-type vehicle sensor, and more particularly, to a loop-type vehicle sensor that can automatically tune the oscillation frequency and supply sufficient communication power to the loop coil. Regarding the sensor.

A conventional loop-type vehicle sensor configures a resonant circuit with a vehicle sensing loop coil and a capacitor connected to the loop coil, and uses the resonant circuit to configure a self-excited oscillation circuit. Vehicle sensing was performed by detecting changes in signal frequency using a separately provided tuning circuit. Furthermore, vehicle-to-vehicle communication has been performed by directly modulating the self-excited oscillation circuit with a transmission signal.

However, in the conventional type, it is necessary to match the tuning frequency of the tuned circuit to the resonant frequency of the resonant circuit including the loop coil each time the vehicle sensor is installed, and therefore, the tuning operation must be performed manually each time the vehicle sensor is installed. There was an inconvenience that it was necessary. In addition, in the conventional type, since vehicle-to-vehicle communication is performed by directly applying modulation to the self-excited oscillation circuit that includes the loop coil, there is the inconvenience that it is difficult to supply sufficient power for communication to the loop coil. It was hot.

In view of the above-mentioned problems with the conventional type, an object of the present invention is to provide a loop-type vehicle sensor in which the oscillation of the loop coil is separately excited oscillation, the oscillation frequency is gradually changed, and the oscillation frequency is fixed at a tuning point. Based on the concept, it is possible to eliminate the need to perform a tuning operation each time a vehicle sensor is installed and to be able to supply sufficient power for communication to the loop coil.

To achieve this objective, the loop-type vehicle sensor of the present invention includes: a loop coil 1 whose inductance changes depending on the proximity of a vehicle; a capacitor 3 connected in series to the loop coil and forming a resonant circuit together with the loop coil; and an input. a voltage frequency conversion circuit 6 that applies an oscillation signal with a frequency corresponding to the voltage value to be applied to the resonant circuit, and a phase difference circuit that detects the phase difference between this oscillation signal and the output signal from the resonant circuit and outputs a phase difference signal. The detection circuit 10 and the integration circuit 8 that outputs a signal obtained by integrating this phase difference signal start increasing or decreasing the output voltage by inputting a reset signal, and the phase difference signal input from the phase difference detection circuit starts to rise or fall to a predetermined value. a sawtooth wave generation circuit 9 that stops increasing or decreasing its output voltage when the voltage reaches An addition circuit 7 that adds the outputs of the signal generation circuits and outputs the result to the voltage frequency conversion circuit is provided.

In this configuration, when the output voltage of the sawtooth wave generation circuit starts to rise or fall due to the input of the reset signal, the output voltage of the adder circuit also rises or falls accordingly, and therefore the voltage frequency conversion circuit to which this is inputted also rises or falls. The frequency of the oscillation signal output by the device also increases or decreases. As a result, the phase difference signal output by the phase difference detection circuit also changes, and when this phase difference signal reaches a predetermined value (for example, 0),
The output voltage of the sawtooth wave generation circuit is fixed to the voltage at that time, and the portion of the oscillation signal output by the voltage frequency conversion circuit to which the output of the sawtooth wave generation circuit contributes is also fixed accordingly. Finally, the phase difference between the oscillation signal and the output signal from the resonant circuit is always maintained at 0 because the corresponding signal is fed back to the voltage frequency conversion circuit via the integration circuit. . Therefore, the input voltage to the voltage frequency conversion circuit is automatically corrected so that a phase difference does not occur even if the inductance of the loop coil changes due to the influence of temperature, etc., and as a result, the oscillation signal and resonance The synchronization of the circuit is maintained.

However, when the inductance of the loop coil suddenly changes due to the proximity of a vehicle, a significant phase difference appears before being corrected, so that the proximity of the vehicle is sensed. The information signal generation circuit normally outputs an information signal only when the proximity of a vehicle is sensed based on the significantly appeared phase difference, and this signal is frequency modulated to the oscillation signal of the voltage frequency conversion circuit via an adder circuit. The loop coil excited by this signal is transmitted by electromagnetic induction to the vehicle's antenna.

Therefore, in the present invention, when a loop-type vehicle detector is installed on a road, there is no need for manual tuning, and the tuning is automatically performed, and the oscillation of the loop coil is separately excited, so that sufficient Communication power is supplied to the loop coil,
Accurate vehicle-to-vehicle communication is performed with a low signal-to-noise ratio.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a ground plane.

In the figure, 1 is a loop coil whose inductance changes when the vehicle comes over it and is electromagnetically coupled to the ferrite antenna of the on-board device for communication with the on-board device; 2 is the DC resistance of the loop coil 1; 3 is a resonance capacitor connected to one end of the loop coil 1, 4 is a resistor connected to the other end of the loop coil 1 and the other end is grounded, and 5 is an output side connected to the loop coil 1 via the capacitor 3. 6 is a voltage frequency conversion circuit connected to the input side of the power amplification circuit 5. The loop coil 1 is excited by an oscillation signal from the voltage frequency conversion circuit 6. Reference numeral 7 denotes an adder circuit connected to the input side of the voltage frequency conversion circuit 6 and providing a control signal 8' to the voltage frequency conversion circuit 6. 10 is a phase comparison circuit whose input side is connected to both ends of the series circuit of the capacitor 3 and the loop coil 1; Outputs voltage according to phase difference. A level detection circuit 11 is connected to the output side of the phase comparison circuit 10 and outputs a high level signal when the output level of the phase comparison circuit 10 is equal to or higher than a predetermined value. Reference numeral 8 denotes an integrating circuit which is inserted between the output side of the phase comparator circuit 10 and the adder circuit 7 and has a large time constant. A switch 12 is inserted between the integrating circuit 8 and the phase comparing circuit 10, and is opened when the output of the level detecting circuit 11 is at a high level. Reference numeral 9 denotes a sawtooth wave generation circuit inserted between the output side of the phase comparison circuit 10 and the adder circuit 7, which outputs a voltage that starts rising or falling in response to the input of the reset signal 1'. When the output level reaches 0, the output voltage level is fixed. A one-shot circuit 14 is connected to the output side of the level detection circuit 11 and outputs a pulse signal of a constant width when the output of the level detection circuit 11 rises. 13 is one shot circuit 14
is inserted between the adder circuit 7 and the one-shot circuit 1.
4 is a parallel-to-serial conversion circuit that converts the transmission road information inputted in parallel into a series and outputs it to the addition circuit 7 while outputting a pulse signal.

FIG. 3 is a block diagram showing the on-vehicle device. In the figure, 15 is a ferrite antenna that receives a signal from the loop coil 1 of the ground plane by electromagnetic induction, 16 is an amplification circuit connected to the ferrite antenna 15 and amplifies the signal received by the ferrite antenna 15, and 17 is an amplification circuit 16. 18 is a demodulation circuit connected to the band filter 17 and demodulates the signal from which noise has been removed by the band filter 17; 19 is a demodulation circuit; 18 is connected to a serial-to-parallel conversion circuit for converting the serial data signal demodulated by the demodulation circuit 18 into a parallel data signal; 20 is connected to the serial-to-parallel conversion circuit 19;
This is a display device that displays data converted by the serial/parallel conversion circuit 19.

FIG. 5 is an overview diagram showing a state in which a vehicle sensor is actually installed on a road. Vehicle 2 equipped with an on-vehicle device 23 connected to a ferrite antenna 15
1 passes over the loop coil 1 buried in the road, data is sent from the ground machine 22 connected to the loop coil 1 to the on-vehicle machine 23.

FIG. 2 and FIG. 4 are time charts showing signal waveforms of various parts of the ground plane and the vehicle-mounted machine, respectively.

Next, the operations of the ground plane and the vehicle-mounted machine will be explained with reference to these figures.

When the ground machine having the configuration shown in FIG. 1 is installed on a road, first, when a reset signal 1' is input to the sawtooth wave generating circuit 9, the voltage of the output signal 2' of the circuit 9 gradually increases. Then, the sawtooth wave generation circuit 9
Since the output side of both is connected to the voltage frequency conversion circuit 6 via the addition circuit 7, the frequency of the signal 4' of the conversion circuit 6 also gradually increases.

Now, if the output voltage of the power amplifier circuit 5 is e〓, its frequency is ω, the capacitance of the resonant capacitor 3 is C, the value of the DC resistance 2 of the loop coil 1 is r, and the inductance of the loop coil 1 is L, then the resistance 4 terminal voltage of
E〓 is expressed by equation (1).

E〓=R/R+r+j(ωL−1/ωC)e〓 ……(1) As is clear from equation (1), when ω=ω ₀ =1/√, E〓 and e〓 are in phase. However, at frequencies other than this, the phases of E〓 and e〓 are different. Therefore, as the oscillation frequency ω of the voltage frequency conversion circuit 6 gradually increases, the output 3' of the phase comparison circuit 10 gradually decreases and becomes 0 at the point ω=1/√. When the output becomes 0, the sawtooth wave generating circuit 9 stops increasing the voltage 2' and fixes it at the voltage at this point. That is, the phase comparator circuit 6
oscillation signal is fixed.

When the vehicle comes over the loop coil 1 in this state, the inductance L of the loop coil 1 changes. If the changed inductance value is L', then ω ₀ ≠1/√', so the level of the output signal 3' of the phase comparison circuit 10 gradually increases from 0. When a certain value is exceeded, the level detection circuit 11 raises the vehicle sensing output 5'. In response to the rise of this output 5', the one shot circuit 14 outputs a pulse signal 6' with a constant width. Upon receiving this pulse signal, the parallel-to-serial conversion circuit 13 converts the parallel input road information for transmission into a serial signal and outputs a signal 7'.
The output serial data signal 7' is added to the output 2' of the sawtooth wave generation circuit 9 and the output of the integration circuit 8 in the adder circuit 7, and is added to the data signal inputted to the voltage frequency conversion circuit 6 as a signal 8'. Accordingly, the voltage frequency conversion circuit 6 applies frequency modulation to the oscillation signal. The frequency-modulated signal is amplified by a power amplification circuit 5, supplied to a loop coil 1 via a capacitor 3, and oscillated toward an on-vehicle device.

This signal is received by the on-vehicle device via the ferrite antenna 15 and amplified by the amplifier circuit 16. The amplified received signal 9' is passed through the bandpass filter 1
Noise is removed at step 7, and demodulated at demodulation circuit 18 to produce a serial data signal 10'. After this data is converted into parallel data by the serial/parallel conversion circuit 19,
It is displayed on a display device 20 inside the vehicle.

By the way, the inductance L of the loop coil 1 gradually changes due to weather changes, etc., and this change also appears as an output of the phase comparator circuit 10.
This output signal is applied to the adder circuit 7 through the switch 12, the integrating circuit 8 with a large time constant, and the voltage frequency converter circuit 6 increases or decreases the oscillation frequency ω accordingly, so that the phase comparator circuit 10 is always activated. Frequency tuning is performed so that the output is zero. However, when a vehicle is detected as described above, the change in the inductance L of the loop coil 1 is rapid, so the output of the level detection circuit 11 is turned on and the switch 12 is opened. It doesn't cost anything.

As described above, according to the present invention, when a loop-type vehicle detector is installed on a road, there is no need for manual tuning, and the tuning is automatically performed, and the oscillation of the loop coil is independently excited. Therefore, sufficient communication power can be supplied to the loop coil, so that the signal-to-noise ratio of vehicle-to-vehicle communication is improved, and accurate vehicle-to-vehicle communication can be performed.

[Brief explanation of the drawing]

Fig. 1 is a block circuit diagram showing a ground machine of a loop type vehicle sensor according to an embodiment of the present invention, Fig. 2 is a time chart showing operating waveforms of each part of the ground machine of Fig. 1, and Fig. 3 is a FIG. 4 is a block circuit diagram showing an on-vehicle device of a vehicle sensor according to an embodiment of the present invention, FIG. 4 is a time chart showing operating waveforms of each part of the on-vehicle device of FIG. 3, and FIG. 5 is an embodiment of the present invention. It is a schematic diagram showing the installation state of the loop type vehicle sensor concerning an example. 1: Loop coil, 2: DC resistance of loop coil, 3: Resonant capacitor, 4: Output resistance, 5: Power amplifier circuit, 6: Voltage frequency conversion circuit, 7: Adder circuit, 8: Integrating circuit, 9: Sawtooth wave generation circuit,
10: Phase comparison circuit, 11: Level detection circuit, 1
2: Switch, 13: Parallel-serial conversion circuit, 14: One shot circuit, 15: Ferrite antenna, 1
6: Amplification circuit, 17: Band filter, 18: Demodulation circuit, 19: Serial to parallel conversion circuit, 20: Display, 2
1: Vehicle, 22: Ground machine, 23: Vehicle-mounted machine.

Claims (1)

[Claims] 1. A loop coil 1 whose inductance changes with the proximity of a vehicle; a capacitor 3 connected in series to the loop coil and forming a resonant circuit together with the loop coil; and a capacitor 3 having a frequency corresponding to an input voltage value. A voltage frequency conversion circuit 6 that applies an oscillation signal to a resonant circuit; a phase difference detection circuit 10 that detects a phase difference between this oscillation signal and an output signal from the resonant circuit and outputs a phase difference signal; and this phase difference signal. An integrator circuit 8 outputs a signal integrated with A sawtooth wave generation circuit 9 that stops rising or falling, information signal generation circuits 13 and 14 that output information signals to be transmitted to the vehicle, and the outputs of the integration circuit, sawtooth wave generation circuit, and information signal generation circuit are added together. A loop-type vehicle sensor characterized by comprising an addition circuit 7 that outputs an output to a voltage frequency conversion circuit.