JPH03225510A - Magnetic field detecting device for vehicle - Google Patents

Abstract

PURPOSE:To improve the magnetic field detection accuracy by selecting a current of frequency which is higher than the frequency of a magnetic field produced by an alternator during a vehicle travel among currents which are generated by coils according to AC magnetic fields produced by induction cables. CONSTITUTION:The induction cables 1 and 2 are laid on both sides of a vehicle travel path. Sensors 20a and 20b are fitted to a vehicle 100 on its right and left front sides. The magnetic field sensors 20a and 20b consist of coils 22a and 22b and capacitors 24a and 24b. The magnetic sensors 20 resonate with radio waves of frequencies specified by the inductance of the coils 22 and the capacitance of the capacitors and the currents of resonance frequencies are inputted to AC amplifiers 26. The amplified currents are supplied to BPFs 28, and the currents passed through the BPFs 28 are converted by full-wave rectification parts 30 into DC voltages. A subtracter 32 generates a signal E indicating the difference in intensity between the magnetic fields from the induction cables 1 and 2 and lateral displacement is obtained with the detection signal E.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a magnetic field detection device for a vehicle that detects an alternating magnetic field generated by an induction cable laid on a running track in order to detect lateral displacement of a vehicle. .

[Prior Art] Automated vehicles that automatically travel along a predetermined course have been known, and are used for automatic guided vehicles in factories, durability tests, and the like.

In order to realize driving along the route, this autopilot vehicle uses some method to grasp the positional relationship between the route and the own troops, and if this positional relationship deviates from the route,
The direction of travel is automatically corrected by correcting the amount of steering.

Here, as a method of grasping the position of vehicles in the direction of travel of the own army's driving course, guidance cables are placed on the driving path,
There is a method of detecting the magnetic field generated by the current flowing through the induction cable using a magnetic field detection device mounted on a vehicle.

According to this method, it is possible to constantly detect the positional deviation of the own troops relative to a predetermined course, and this information can be used to achieve automatic piloting.

A magnetic field detection device that detects the magnetic field generated by such an induction cable usually has a coil for detecting the magnetic field. That is, in normal cases, an excitation alternating current is passed through the induction cable, thereby generating an alternating magnetic field. If the coil is placed in an alternating magnetic field,
An induced current corresponding to the alternating magnetic field is induced in this coil,
The magnetic field strength can be detected based on the magnitude of this induced current.

The magnitude of the induced current generated in this coil corresponds to the distance from the induction cable to the magnetic field detection device.

Therefore, by detecting the intensity of the induced current generated in the coil, the distance from the induction cable to the coil can be detected, and lateral displacement etc. can be calculated based on this.

In addition, there are two ways to lay induction cables: the stereo method, which is laid on both sides of the track, and the single-wire method, which is laid in the center of the track, but the basic method is to use a coil to detect the magnetic field generated by the cable. The configuration is the same.

Here, regarding the measurement system using the guidance cable of such an autopilot vehicle, for example, the magazine [Automobile Technology J
Vo 1. 25. No, 7. Published in 1971,・
This is shown in the magazine ``Nissan Technical Report'' No. 22, published in December 1986, and the magazine ``Toyota Technical'' Vol. 20, No. 1, published in June 1961.

[Problems to be Solved by the Invention] In this way, by detecting the magnetic field generated by the induction cable using the coil, it is possible to grasp the position of the vehicle on the track.

However, when this magnetic field detection is actually performed, there are many cases in which a large amount of noise is added to the detection signal, and sufficiently accurate detection cannot be performed. Therefore, there is a need to reduce noise and perform accurate detection.

Therefore, the inventor conducted various detection experiments using magnetic field coils and discovered that there is noise that depends on the engine rotation speed.

That is, the detection results from the coil were measured in the absence of a magnetic field from the induction cable; however, Figures 8 (A) and (B)
) The results shown are obtained. In this example, magnetic field sensors are installed in four locations on the vehicle: front (FL), rear left (RL), front cloth (FR), and rear right (RR), and the induction cable on the right side is An alternating current of 3.3kHz and 5°0kHz is passed through the induction cable on the right side.

From the figure, the previous company's magnetic field sensor generates noise of about 15% of the detection value from a normal induction cable when the engine speed is around 2000 rpm, and the previous cloth magnetic field sensor generates noise of about 15% of the detected value from the normal induction cable when the engine speed is around 3000 rpm.
1% noise was generated.

Furthermore, when we conducted on/off experiments with electric fans, etc., it became clear that this noise, which depends on the engine speed, is affected by the on/off status of the electrical load.

That is, noise was generated when the electric fan was turned on and off, but no noise was generated when the electric fan was turned off.

Therefore, it is considered that by identifying the cause of such noise generation and eliminating it, it is possible to accurately detect the magnetic field generated from the induction cable.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic field detection device for a vehicle that suppresses noise in a magnetic field detection coil mounted on a vehicle.

[Means for Solving the Problems] A vehicle magnetic field detection device according to the present invention is mounted on a vehicle, and
This is a magnetic field detection device for a vehicle that detects an alternating magnetic field generated by an induction cable laid on a vehicle running road. The vehicle is characterized by comprising frequency selection means for selecting a current having a frequency higher than the frequency of the magnetic field generated in the alternator during running.

[Effects] The inventor presumed that this noise was caused by the magnetic field generated in the alternator installed in the vehicle, based on the fact that it was affected by the on/off state of the electrical load and depended on the engine speed. .

The frequency f of the magnetic field generated in the alternator is expressed by the following equation.

f − N 60 is the number of poles of the alternator that determines the engine speed in minutes (rpm) to the frequency in seconds (Hz
) is a conversion factor for calculating.

Then, the pulley ratio (-
7, 8) When the number of alternator poles M(12) was substituted, it matched the engine rotation speed at which the above-mentioned noise occurs. Therefore, it is considered that this noise is caused by the alternating current magnetic field generated by the rotation of the alternator.

Therefore, what is necessary is to prevent the magnetic field generated in the alternator from affecting the coil.

In this invention, the current selected in the coil is configured to select a current with a frequency higher than the frequency of the magnetic field generated in the alternator when the vehicle is running at high speed, so that the influence of the magnetic field generated in the alternator during normal running of the coil is reduced. The detection results were avoided. Therefore, the magnetic field generated by the induction cable can be detected with high accuracy.

[Example] Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 is a schematic configuration diagram showing a signal processing system of a magnetic field detection device for a vehicle according to the present invention, and guide cables 1.2 are laid on both sides of a running track.

On the other hand, two magnetic field sensors 20a and 20b are attached to the front left and right sides of the vehicle 100.

The magnetic field sensors 20a and 20b have a coil 22
a, 22b, capacitors 24a, 24b, and the output side is connected to a subtracter 3 via an AC amplifier 26a, 26b, a bandpass filter 28, and a full-wave rectifier 30a, 30b.
Connected to 2.

Therefore, the magnetic field sensor 20 resonates with the radio waves at a frequency specified by the inductance of the coil 22 and the capacitance of the capacitor, and the current at this resonant frequency is transmitted to the AC amplifier 26.
is input. Then, the AC amplifier 26 amplifies this current and supplies it to the bandpass filter 28, and the bandpass filter 28 excludes AC currents other than those having a frequency corresponding to the magnetic field generated from the induction cable 1 or 2.

Further, the current that has passed through the bandpass filter 28 is converted into a DC voltage representing the intensity of the AC current in a full-wave rectifier 30, and the magnetic field from the induction cable 1.2 detected by the magnetic field sensors 20a and 20b is generated by a subtracter 32. A signal E is obtained representing the difference in intensity.

This signal E points the center of the travel path in FIG.
m, and when the displacement toward the induction cable 1 side is assumed to be positive and the displacement toward the induction cable 2 side is assumed to be negative, it has the characteristics as shown in FIG. Therefore, the lateral displacement can be obtained using the detection signal E.

Here, in this embodiment, as shown in FIG. 3, excitation power sources 200 of 8.3 kHz and 10 kHz are connected to the induction cable 1.2, and currents of these frequencies are supplied to the induction cables 1 and 2. ing. Therefore, the resonance frequencies in the magnetic field sensor 2o are also 8.3kHz and 10kHz.
It is set to about. Therefore, the magnetic fields generated by the induction cables 1 and 2 and the current induced in the magnetic field sensor 20 also have this frequency.

Therefore, the bandpass filters 28a, 28b
C. Characteristics that allow alternating currents of 8.3 kHz and 10 kHz to pass, respectively, are adopted.

In Fig. 4, the height of the magnetic field sensor 20 is 211°5 mm.
, full wave rectifier 30 when the distance between sensors is 100 mm
shows the output of In this example, there are two magnetic field sensors, one on the front (FL) and the rear left (RL), that detect the 8.3 Hz magnetic field from the left induction cable 1, and the other that detect the 10 kHz magnetic field from the right induction cable 2. The detection results (outputs of the full-wave rectifier 30) of a total of four magnetic field sensors 20, two in the front (FR) and the rear right (RR), are shown. Further, the magnetic field sensor 20 is attached to the vehicle 10 as shown in FIG.

As is clear from the figure, large noises that depend on engine rotation occur at locations above 5000 rpm for all sensors, and at engine speeds below 5000 rpm, the maximum noise is 2 times the normal detection value.
%, which is at a negligible level. In normal driving of a car, it is rare for the engine speed to exceed 500 Or pm, and it is understood that the magnetic field sensor of this embodiment can eliminate the influence of the magnetic field radiated from the alternator.

Next, FIG. 6 shows the relationship between the engine rotation speed and the output of the gold wave rectifier 30 when the height of the magnetic field sensor 20 is 530 mm. In this example, noise of about 1096 is generated at around 3000 rpm in the magnetic field sensor 20 attached to the front (FL). Although this value of 10% is considerably improved compared to the conventional example, it is a value that cannot be ignored as noise of the magnetic field sensor 20. In addition, the magnetic field sensor 20
Depending on the type of vehicle, the installation location may be limited to places where there is a lot of noise.

In order to improve this, in this embodiment, the amount of excitation current flowing through the induction cable 1.2 is increased. That is, in the past, the excitation current was about 200 mA, but in this embodiment, the excitation current is increased to about IA.

When the amount of excitation current is increased in this way, the level of noise due to the magnetic field radiated from the alternator described above is relatively reduced, and the noise level becomes negligible. That is, in this example, by increasing the excitation current,
The noise has been reduced from the above 10% to 2% and is now at a negligible level.

On the other hand, the impedance of the induction cable 1.2 has a peak around 60 to 70 kHz, as shown in FIG.

Further, an increase in impedance means an increase in loss in the induction cables 1 and 2. Therefore, it is better for the impedance to be as low as possible in the frequency band used.

Therefore, the frequency of the induction cables 1 and 2 needs to be 30 kHz or less, at which the impedance begins to rise rapidly and the difference in impedance between sunny and rainy days becomes large. And preferably, the induction cable 1 or 2
I want to keep the overall energy loss to about 150W. For this reason, the frequency is preferably 17.5 kHz or less.

The distance of the running course in this example is 700 m.
Considering the IOW margin, the energy loss is about 15%.
0W or less means that the maximum loss per 100m of induction cable is 20W or less.

[Effects of the Invention] As explained above, according to the magnetic field detection device for a vehicle according to the present invention, the influence of the magnetic field radiated from the alternator can be suppressed to a minimum, and magnetic field detection can be performed with sufficient accuracy. .

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a magnetic field detection device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing the relationship between detection signal E and lateral displacement, and Fig. 3 is an explanation showing the arrangement of the induction cable. Figure 4 is a characteristic diagram showing the relationship between noise in the output of the magnetic field sensor and engine speed, Figure 5 is an explanatory diagram showing the mounting position of the magnetic field sensor, and Figure 6 is a characteristic diagram showing the relationship between noise in the output of the magnetic field sensor and engine rotation. FIG. 7 is a characteristic diagram showing the relationship between the impedance of the induction cable and frequency. FIG. 8 is a characteristic diagram showing the relationship between noise in the output of a conventional magnetic field sensor and engine speed. 1.2 ... Induction cable 20 ... Magnetic field sensor 22 ... Coil 24 ... Capacitor 28 ... Bandpass filter 30 ... Full-wave rectifier 100 ... Vehicle 200 ... Excitation power supply

Claims (1)

[Scope of Claims] A magnetic field detection device for a vehicle that detects an alternating magnetic field generated by an induction cable mounted on a vehicle and laid on a vehicle running path, comprising: a coil that generates a current according to the alternating magnetic field; A magnetic field detection device for a vehicle, comprising: frequency selection means for selecting, from the current generated in the coil, a current having a frequency higher than the frequency of a magnetic field generated in an alternator when the vehicle is running at high speed.