JPH06201841A - Loop-coil switch - Google Patents

Abstract

PURPOSE:To provide a loop-coil switch which does not cause any malfunction by a method wherein a high frequency is used for the loop-coil switch for vehicle detection, a sensing coil is made compact and an in-phase current which is generated in a feeder supplying a high-frequency current from an oscillator to the sensing coil is suppressed. CONSTITUTION:In a loop-coil switch, a high-frequency current is supplied to a coil 1 buried and installed in a parking position through a feeder 6 from an oscillator 5 installed away from the coil, and whether a vehicle exists or not is detected by detecting a change in a resonance frequency. In the loop-coil switch, an in-phase current element coil 9 formed by winding a feeder on a high-permeability magnetic material is inserted across the loop coil 1 and the feeder 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a loop coil switch for detecting the presence or absence of a vehicle at a predetermined parking position in a parking lot.

[0002]

2. Description of the Related Art In a parking lot, as a proximity switch for detecting whether or not there is a vehicle at each partition position, a loop coil switch which utilizes a change in resonance frequency of a sensing coil has been conventionally used. This type of vehicle detection loop coil switch has a relatively low operating frequency, from 100 KHz to
Since it is in the range of 500 KHz, it was necessary to wind the sensing coil many times and embed it. 6A and 6B are views for explaining the loop coil, FIG. 6A is a perspective view showing the shape, and FIG. 6B is a cross section taken along the line AA ′ in FIG. 6A in a buried state. Indicates. The loop coil 1 is usually formed by winding 4 to 6 turns of a winding 2 having a standard size of 1 m × 2 m, and the loop coils are embedded at a distance of 1 m or more. In the case of a flat parking lot on concrete or asphalt road surface, a groove 3 is dug on the road surface according to the coil size, a loop coil 1 is installed in it, and a filling material 4 made of epoxy mortar is filled and hardened and fixed. Such a method is taken. Therefore, not only is the construction difficult if the coil size is large, but the parking lot has a large number of turns so that only the target vehicle can detect it without interference, or if it is installed alongside the existing coil, interference will occur. It was necessary to remove the extra part of the coil.

[0003]

As described above, when the operating frequency is low, the number of turns of the coil must be increased and the length of the coil also becomes long. The only way to make it compact is to increase the frequency. In that case, the configuration of the loop coil switch is as shown in FIG. 7, and the presence or absence of the vehicle is detected by the following actions. The high-frequency current generated by the oscillator 5 passes through the capacitor C2 and is supplied to the parallel resonant circuit formed by the coil L2, the variable capacitor CV, and the impedance (reactance XL in this case) of the feeder 6 seen from the point A. This operates the equivalent circuit seen from the point A as the L component as shown in FIG.

Now, when there is no vehicle at the position of the loop coil 1 as shown in FIG. 9A, it is assumed that the frequency f1 of the parallel resonance is brought close to the frequency f0 of the oscillator 5 and the relationship of f1> f0 is adjusted. When the car arrives, the inductance of L changes due to changes in iron loss and magnetic permeability of the car 8 as shown in FIG. 9B. In most cases, the inductance tends to decrease, and the resonance frequency f1 is f as shown in the tuning characteristic diagram of FIG.
It fluctuates toward the higher frequency like 1 '. Therefore, the output of the oscillator 5 increases as much as the tank circuit f1 is detuned, and the change is detected to detect the presence or absence of the vehicle.

Here, it is often difficult to install the oscillator 5 near the buried loop coil 1 in a parking lot in terms of maintenance, and the oscillator 5 is placed separately from the loop coil 1. In that case, the connecting line connecting them becomes long,
Since the high-frequency current from the oscillator 5 is attenuated on the way, the above-mentioned feeder (coaxial cable) 6 is used as a connecting wire to prevent it. However, at this time, malfunction occurs due to leakage of high frequency current. That is, FIG.
As in 1, the high frequency current is supplied from the oscillator 5 through the feeder 6, but a part of this high frequency flows through the feeder 6 again to the oscillator 5 side as an in-phase current. This means that the virtual high frequency oscillation source 51 is generated just near the connection point between the feeder 6 and the loop coil 1, and the high frequency is radiated from other than the loop coil 1. This effect is similar to that of a dipole antenna, and is λ / 4 for the used frequency.
The maximum radiation begins at. Therefore, this high-frequency in-phase current flows through the feeder 6 to the power line for supplying power to the oscillator 5, and the switch operates only by swinging on the power line.

Because of the problems described above, the use of high frequencies for loop coil switches has not been put to practical use. The present invention has been made under the above circumstances,
An object of the present invention is to make a loop coil compact by using a high frequency for a vehicle detection loop coil switch, and to block a common-mode current generated in a feeder for supplying a high frequency current generated by an oscillator to the loop coil to stabilize the loop coil. It is to provide a loop coil switch that performs the above operation.

[0007]

When the loop coil 1 and the oscillator 5 placed separately are connected by the feeder 6, the common-mode current flowing in the feeder 6 is generated as shown in FIG. In-phase current blocking coil 9 between
Can be blocked by inserting. For that purpose, the feeder (coaxial cable) on the side of the loop coil may be wound around the high-permeability magnetic material. That is, the above object of the present invention is to provide a sensing loop coil buried under the floor of a parking position, a high-frequency oscillator installed apart from the loop coil, and a high-frequency current generated from the high-frequency oscillator to the loop coil. A loop coil switch for detecting a presence or absence of a vehicle by detecting a variation in a resonance frequency of a resonance circuit including the loop coil as an impedance in the vehicle, and the loop coil and the high frequency oscillator in the feeder. And the end portion of the feeder on the side of the loop coil is wound around a high-permeability magnetic material.

[0008]

By inserting the common-mode current blocking coil 9, the loop coil 1 and the oscillator are cut off at a high frequency, so that the common-mode current does not flow in the feeder 6 and the virtual high-frequency oscillation source 51 does not occur.

[0009]

FIG. 2 shows an embodiment of the present invention. The loop coil 1 is buried under the floor on which the vehicle 8 is placed. Further, the oscillator 5 is installed at a place distant from the loop coil 1, and the high frequency current generated here is generated by the capacitor C.
2, passing through the coil L2 and the feeder 6, and supplied to the loop coil 1 through the common-mode current blocking coil 9. And
The output of the parallel resonant circuit is detected and input as a DC signal to the detection unit 7, where it is signal-processed to detect the presence or absence of a vehicle. Here, the loop coil 1 has a frequency of 1 MHz to 15 M
30 cm square to 200 c when using high frequency of Hz
An m-square one can be used in one turn.

FIG. 3 shows the structure of the in-phase current blocking coil 9. A coaxial cable 11 as a feeder is wound around a long rod 10 made of a magnetic material having high magnetic permeability such as a ferrite rod and a dust core to form a coil. To do. Although the example of winding the feeder has been described above, a twisted pair may be used or a balun may be used. The shape of the high-permeability magnetic material is also arbitrary, and may be a flat plate or a ring.

FIG. 4 shows another example of the common mode current blocking coil. A high-permeability magnetic material (for example, Q5M made of TDK) 12 having a diameter of 10 mm and a length of 120 mm is wound 100 times with a twisted pair wire 13 having a characteristic impedance of about 75Ω with two twisted wrapping wires having a diameter of 0.32 mm (twist pitch 10 mm). Then, an inductance of about 350 μH was obtained. The reactance at a frequency of 5 MHz shows a high resistance value of 11 KΩ, and the common mode current is blocked.

In the above, the case where the high frequency oscillator is installed away from the sensing loop coil and connected by the feeder has been described. However, a duct or trough is provided in the parking lot, and the oscillator is located near the sensing loop coil. A feeder is not needed if it can be embedded in. However, even in that case, the above-described antenna action occurs in the air or the connection line along the wall connecting the oscillator and the power supply, and the interference occurs. To prevent this, the oscillator 5 buried near the loop coil 1 and the power source are connected by the shield wire 15 as shown in FIG. 5, and the common-mode current blocking coil 92 may be inserted in the connecting portion. In the figure, a two-core shielded wire is used for power supply and signal output, and the outer surface of the shield is used for grounding. These three coils may be wound by laminating three layers on one high magnetic permeability material, or may be wound by winding three wires as shown in FIG. Alternatively, each wire may be wound around three high magnetic permeability materials. However, the number of turns (inductance) of each wire must be the same.

[0013]

As described above, according to the loop coil switch of the present invention, the oscillator is separated from the loop coil by inserting the common mode current blocking coil between the sensing loop coil and the feeder. However, the common-mode current does not flow in the feeder. Therefore, the high frequency can be used safely without malfunction, and therefore the sensing loop coil only needs to make one turn in a small area, which simplifies the installation work and reduces the interference with the adjacent coil. It became easier.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic structure of the present invention.

FIG. 2 is a diagram showing an embodiment of a loop coil switch according to the present invention.

FIG. 3 is a diagram showing a structure of an in-phase current blocking coil.

FIG. 4 is a diagram showing another structure of the common-mode current blocking coil.

FIG. 5 is a diagram for explaining another example of common-mode current removal.

FIG. 6 is a diagram for explaining a conventional loop coil.

FIG. 7 is a diagram showing a configuration of a conventional loop coil switch.

FIG. 8 is an equivalent circuit diagram of FIG. 7.

FIG. 9 is a diagram for explaining the operation of the loop coil switch.

FIG. 10 is a diagram showing tuning characteristics of an oscillator.

FIG. 11 is a diagram for explaining a malfunction of the conventional loop coil switch.

[Explanation of symbols]

 1 Loop coil 2 Winding 3 Groove 4 Filler material 5 Oscillator 6 Feeder 7 Detecting unit 8 Vehicle 9, 91, 92 Common mode current blocking coil 10 Long shaft rod 11 Coaxial cable 12 High permeability magnetic material 13 Twisted pair wire 14 Power supply 15 Shield wire 51 Virtual high frequency oscillator

Claims (1)

[Claims] 1. A sensing loop coil buried under the floor of a parking position, a high-frequency oscillator installed away from the loop coil, and a feeder for supplying a high-frequency current generated by the high-frequency oscillator to the loop coil. In a vehicle detection loop coil switch for detecting the presence or absence of a vehicle by detecting a variation in a resonance frequency of a resonance circuit including the loop coil as an impedance, the feeder connects the loop coil and the high frequency oscillator. At the same time, the loop coil side end of the feeder is wound around a high magnetic permeability magnetic material.