JPS63306905A - Tire air pressure detector - Google Patents

Abstract

PURPOSE:To surely detect the air pressure of a tire with ease by providing, in the tire, a loop-like conductor, and a resonance circuit where resonance frequency changes in response to an air pressure, and using the detect current value and the inductive current frequency of a loop-like conductor. CONSTITUTION:In a tire 10, a loop-like conductor 11 is provided, and a closed circuit is also formed by forming the loop-like conductor 11 in a continuous circle, and further, there is provided a resonance circuit 12 where resonance frequency changes in response to the air pressure of the tire 10. Meanwhile, on the vehicle body side near the tire 10, an oscillation exciting coil 13 is disposed so as to supply inductive current to the loop-like conductor 11 through electromagnetic coupling. In addition, in order to supply current, frequency of which is controlled, to the oscillation exciting coil 13, a sweep oscillator 14 for sweeping oscillatory frequency is provided. Further, in order to detect the inductive current of the loop-like conductor 11, a pick-up coil 15 is disposed. The respective currents of the sweep oscillator 14, and the coil 15 arranged via an amplification circuit 16 and a wave detector 17 are fed to a processor 18, thereby judging the air pressure of the tire 10.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to the configuration of a tire air pressure detection device that can monitor tire air pressure of a vehicle regardless of whether the vehicle is stopped or traveling.

[Prior Art] Conventionally, a common method for detecting tire air pressure is to connect a pressure gauge to an air injection valve of a tire, and use this pressure gauge to measure tire air pressure. Recently, a method has been announced in which a pressure sensor is built into a tire rim and the tire air pressure is measured based on the output of the pressure sensor. FIG. 6 is a diagram showing a schematic configuration of a conventional device for detecting and monitoring tire air pressure using a pressure sensor. Figure 6 shows conventional tire pressure detection. The monitoring device is installed at a predetermined position on a rim 2 for holding the tire 1 and attaching the tire 1 to a vehicle body rotation shaft (not shown) so as to penetrate through the rim 2, and is injected with air through an air valve 3. A pressure sensor 4 that detects air pressure is provided at a predetermined position IT6 on the vehicle body so as to face the pressure sensor 4 provided on the rim 2, receives and decodes the output of the pressure sensor 4, and displays the decoded result on a display device E? Transmitting/receiving device 5
and a display device 7, which is provided near the driver's seat of the vehicle and displays the tire air pressure in response to a decoded signal from the transmitting/receiving device 5. FIG. 7 is a diagram showing a schematic configuration of the pressure sensor and the transmitting/receiving device shown in FIG. 6. As shown in FIG. 7, the pressure sensor 4 is a pressure sensor made of, for example, a silicon diaphragm, which is provided so as to be in contact with the air inside the tire 1, and whose resistance value rapidly changes when the tire air pressure drops below a predetermined value. Detecting changes in resistance values of the element 41 and the pressure sensitive element 41,
Antenna (or coil) transmits a signal corresponding to its resistance value
A signal processing circuit 42 that transmits to the transmitting/receiving device 5 via 43
Equipped with. The transmitting/receiving device 5 includes a receiving section 52 that receives resistance value information of the pressure sensing element 41 transmitted from the pressure sensor 4 via an antenna (or coil) 51, and converts this resistance value information into tire pressure information, and a receiving section. A determination circuit 53 is provided that compares the air pressure information from 52 with a predetermined value and transmits the comparison result to the display section 7. Next, the operation will be explained. The pressure sensor 4 is provided integrally with the rim 2 and is provided so as to constantly monitor the air pressure within the tire 1. Further, resistance value information of the pressure sensing element 41 corresponding to the detected tire air pressure is provided from the signal processing circuit 42 to the transmitting/receiving device 5 via the antenna (or coil) 43, 51 by induction or radio frequency communication. Now, when the air pressure of the tire 1 drops below a predetermined value, the resistance value of the pressure sensing element 41 changes rapidly. The signal processing circuit 42 detects this sudden change in the resistance value of the pressure sensitive element 41 and provides the resistance value information to the transmitting/receiving bag rIt5. The transmitting/receiving device 5 converts the given resistance value information into tire pressure information at the receiving section 52 and provides it to the determination circuit 53 . The determination circuit 53 compares the given tire pressure information with a predetermined reference value, and if the tire pressure is higher than the predetermined reference value, it provides information that the tire pressure is normal to the display section 1, and indicates that the tire pressure is at the predetermined reference value. In the following cases, tire air pressure defect information is provided to the display section 7. In response to the given tire pressure information, the display unit 7 lights up a blue lamp, for example, if the tire pressure is normal;
For example, a red lamp is turned on when tire pressure abnormality information is given. [Problems to be Solved by the Invention] When measuring tire air pressure by connecting a pressure gauge to a tire's inflation valve, which has been commonly done in the past,
Abnormalities in tire air pressure (particularly pressure drops) could only be detected when the tire air pressure was measured. In addition, when measuring tire pressure with a pressure gauge, it is cumbersome to stop the vehicle and use the pressure gauge to measure it, so for example, it is not necessary to check the tire pressure before entering the expressway. It is conceivable that the vehicle will be driven on a highway during this period, and in this case there is also the problem that a drop in tire air pressure could lead to an accident. Furthermore, in the conventional tire pressure detection and monitoring device described above, the pressure sensor is embedded only in a part of the rim and rotates with the rotation of the tire, while the transmitting and receiving device is fixedly attached to a part of the vehicle body. Therefore, communication between the pressure sensor 4 serving as a detection unit and the transmitting/receiving device 5 is performed only when they are located opposite each other, and tire air pressure can only be detected intermittently. Furthermore, a binary judgment is made as to whether the detected tire air pressure is higher or lower than a predetermined reference pressure, and there is a problem in that the tire air pressure cannot be continuously monitored. Therefore, an object of the present invention is to eliminate the problems of the conventional tire pressure detection device described above, and to detect a tire pressure that can easily and continuously monitor tire pressure regardless of whether the vehicle is running or stopped. The purpose is to provide equipment. [Means for Solving the Problems] The tire air pressure detection device according to the present invention includes a loop-shaped conductor provided on the tire side wall along the circumferential direction of the tire, and a closed circuit connected to the conductor loop at both ends of the conductor. A resonant circuit is provided in which the resonant frequency changes according to the tire air pressure, and a frequency-controlled current or voltage signal is supplied to this loop conductor via electromagnetic coupling, and the signal flowing through the loop conductor is electromagnetically coupled. The tire air pressure is determined based on the detected signal value and the signal frequency. [Operation] The resonant frequency of the resonant circuit connected to the loop conductor changes depending on the tire air pressure. On the other hand, since the resonant circuit and the conductor loop constitute one closed circuit, the current value (or voltage value) flowing through the conductor loop becomes maximum when the resonant circuit resonates. Therefore, by supplying an external frequency-controlled signal to the loop conductor, detecting the current (or voltage value) flowing through the loop conductor, and observing the frequency that gives the maximum current (or voltage) value, the resonant frequency can be determined. It becomes possible to detect tire air pressure through the [Embodiments of the Invention] FIG. 2 is a schematic perspective view of a tire with some parts cut away to show an example of a specific structure of the tire according to the invention. In FIG. 2, one or more turns of the conductor 11 are provided so as to draw a loop along the circumferential direction of the side wall of the tire 10, and the conductor 11 is provided at both ends of the loop-shaped conductor 11 in a continuous manner with the conductor loop. A resonant circuit 12 is provided to form a closed circuit and whose resonant frequency changes depending on the tire air pressure. The conductor 11 and the resonant circuit 12 are embedded in the tire sidewall. The resonant circuit 12 is composed of an electrical resonant circuit (LC series resonant circuit) in which a variable capacitance element C whose capacitance changes depending on the tire air pressure and a fixed inductance L whose inductance value is fixed are connected in series. FIG. 1 is a diagram showing an example of the overall configuration of a tire air pressure detection device that is an embodiment of the present invention. In FIG. 1, the tire air pressure detection device according to the present invention is configured such that the tire lO is electromagnetically coupled to a loop conductor 11.
An excitation coil 13 is provided on the vehicle body side in close proximity to the loop conductor 11 for supplying an induced current (or voltage) to the loop conductor 11 via electromagnetic coupling. a sweep oscillator 14 capable of sweeping the oscillation frequency for supplying a controlled current (or voltage), and a sweep oscillator 14 in close proximity to the tire 10 for detecting the induced current (or voltage) flowing through the loop conductor 11. A pickup coil 15 provided to be electromagnetically coupled to the loop conductor 11, an amplifier circuit 16 that amplifies the current flowing through the pickup coil 15, and a direct current proportional to the induced current that detects the high frequency current amplified by the amplifier circuit 16. It is composed of a detector 17 that outputs a level, and a processing device 18 that receives the oscillation frequency of the sweep oscillator 14 and the output of the detector 17 and determines the air pressure of the tire 10. Next, the operation will be explained. First, an LC resonant circuit 12 is connected to the loop conductor 11 so as to be continuous with the loop conductor and form a closed circuit. The capacitance C is a variable capacitance element whose capacitance value changes depending on the air pressure of the tire 10. The resonant circuit 12 has a capacitance C
and an inductance L are connected in series to form an electrical series resonant circuit. At this time, the resonant frequency f of the resonant circuit 12. is given by fo=1/2π,/T. In the above equation, the value of the capacitance C changes depending on the tire air pressure, while the value of the inductance L is fixed, so the resonant frequency fo of the resonant circuit 12 also changes depending on the tire air pressure. On the other hand, an excitation coil 13 for supplying an induced current to the loop conductor 11 is provided on the vehicle body side. The excitation coil 13 has the above-mentioned resonance frequency f. A high frequency signal is supplied from a sweep oscillator 14 whose oscillation frequency can be varied continuously at nearby frequencies. Thereby, the excitation coil 13 induces a high frequency voltage (or current) in the loop conductor 11 via electromagnetic coupling. At this time, since the current flowing through the loop conductor 11 also flows through the resonant circuit 12, the current flowing through the resonant circuit 12 is given by dividing the induced voltage by the impedance of the circuit constituted by the resonant circuit 12 and the loop conductor 11. therefore,
The frequency of the induced voltage induced in the loop conductor is the resonance circuit 12.
The induced current flowing through the loop conductor 11 becomes maximum when the resonant frequency fo is equal to the resonance frequency fo. The induced current flowing through the loop conductor 11 is detected by the pickup coil 15. That is, since the pickup coil 15 is provided near the tire 10 so as to be electromagnetically coupled to the loop conductor 11,
Through electromagnetic coupling with the loop conductor 11, a current or voltage proportional to the current flowing through the loop conductor is generated in the pickup coil 15. Since the current (or voltage) detected by this pickup coil 15 is very small, it is supplied to an amplifier 16 and amplified there. The detector 17 detects the output of the pickup coil 15 amplified by the amplifier circuit 16 and outputs a signal at a DC level proportional to the output of the amplifier 16. The processing device 18 receives the oscillation frequency of the sweep oscillator 14 and the output of the wave detector 17 and determines the tire air pressure. When the current value flowing through the loop conductor 11 has a frequency that matches the resonance frequency fo of the resonant circuit 12, the output of the pickup coil 15 also becomes maximum. Therefore, by receiving the oscillation frequency of the sweep oscillator 14 and the maximum value of the detection output of the wave detector 17, and monitoring the oscillation frequency that gives the maximum output of the wave detector 17, the resonance frequency of the resonance circuit 12 at that time can be determined. On the other hand, this resonant frequency fo is coupled to the value of the capacitance C, which varies depending on the tire pressure, according to the above equation, making it possible to detect the tire pressure. An example of a specific operation of the now judgment will be explained. Figure 3 is a diagram showing the relationship between the oscillation frequency of the sweep oscillator and the detector output, Figure 3A is a diagram showing the relationship between the oscillation frequency of the sweep oscillator and time, and Figure 3B is a diagram showing the relationship between the oscillation frequency of the sweep oscillator and time. FIG. 3C is a diagram showing the relationship between the oscillation frequency and the detection output when the capacitance of the oscillation circuit resonant circuit becomes large. Here, Fig. 3A, 3
In FIG. B and FIG. 3C, the time axes are aligned so that the oscillation frequency and the detector output correspond to each other. Now, a case will be explained in which the capacity value of the capacity C increases as the tire air pressure increases. As the tire air pressure increases and the capacitance value of the capacitor C also increases, the resonant frequency of the resonant circuit 12 decreases, giving the maximum detection output at a relatively low oscillation frequency, as shown in FIG. 3C. On the other hand, as the tire air pressure decreases, the capacitance decreases, so the resonance frequency becomes a relatively high frequency, and as shown in FIG. 3B, the detection output becomes maximum at a relatively high oscillation frequency. Therefore, the tire air pressure can be directly detected based on the correlation between the detection output and the oscillation frequency. If an alarm circuit is connected to the processing device 18, it is possible to immediately notify the driver and give a warning if the tire pressure becomes abnormal based on the result of tire pressure detection by the processing device 18. FIG. 4 is a diagram showing an example of a specific configuration of a capacitance whose capacitance value changes depending on tire air pressure. In FIG. 4, variable capacitances C are provided facing each other with a gap 64 and springs 63a and 63b.
It consists of insulators 62a and 62b that are held together via the insulators 62a and 62b, and conductor electrodes 61a and 61b that are provided in close contact with the surfaces of the insulators 62a and 62b. Electrodes 61a, 61b
Conductor wirings 65a and 65b are connected to. In this configuration, the capacitance value changes depending on the pressure applied in the direction of the thick arrow in the figure, so when embedded in the tire side wall, the distance between the insulators 62a and 62b changes depending on the tire air pressure, and the capacitance changes accordingly. The capacitance value also changes. Note that in the above embodiment, a fixed inductance L is provided to configure the resonant circuit, but this fixed inductance is not necessarily provided, and it is possible to create an inductance by using a loop-shaped conductor with one turn or multiple turns provided in the tire part. may be configured. In addition, in the above embodiment, the resonant circuit was constructed using a variable capacitance element whose capacitance value changes in response to the tire air pressure, but instead of this, a fixed capacitance element is used and the inductance L is changed depending on the tire air pressure. A variable inductance whose inductance value changes may also be used. FIG. 5 is a diagram showing the configuration of a variable inductance element whose inductance value changes depending on tire air pressure. In FIG. 5, the variable inductance element includes a diaphragm 71 receiving tire air pressure, a magnetic body 73 connected to the diaphragm 71 via a link mechanism 72, and a magnetic body 73 connected to the diaphragm 71 via a link mechanism 72.
3, and a coil 74 whose inductance value changes depending on the position. In this configuration, the diaphragm 71
The position of the magnetic body 73 changes via the link mechanism 72. Since the inductance value of the coil 74 changes depending on the position of the magnetic body inserted therein, it is possible to realize a variable inductance element whose inductance value changes depending on the tire air pressure. Further, in the above embodiment, an LC series resonant circuit is used as the resonant circuit, but the same effects as in the above embodiment can be obtained even if an LC parallel resonant circuit is used. [Effects of the Invention] As described above, according to the present invention, a loop conductor is provided along the circumferential direction of the tire side wall portion, and a closed circuit is formed continuously with the loop conductor at both ends of the tire. A resonant circuit whose resonant frequency changes according to air pressure is provided, and a frequency-controlled current is supplied to this loop conductor via electromagnetic coupling, and the current flowing through this loop conductor is detected, and the detected current value and the induction at that time are calculated. Since the system is configured to detect tire pressure using current frequency, there is no need to connect a pressure gauge to the tire's inflation valve, making it possible to constantly monitor tire pressure regardless of whether the vehicle is running or stopped. This makes it possible to prevent accidents caused by a drop in tire air pressure. In addition, since current is supplied to the loop conductor via electromagnetic coupling and the current flowing through the loop conductor is detected, there is no need for the tire to receive a power source such as a battery, and tire air pressure detection has low power consumption. The device can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the overall configuration of a tire air pressure detection device that is an embodiment of the present invention. FIG. 2 is a diagram showing an example of a specific configuration in which a loop conductor and a resonant circuit used in the tire detection device according to the present invention are provided on a tire sidewall. FIG. 3 is a diagram showing the relationship between the frequency of the current flowing through the loop conductor and the detected current value at that time, FIG. The figure is a diagram showing an example of the detector output when the resonant frequency of the resonant circuit becomes high, and Figure 3C is a diagram showing an example of the detector output when the resonant frequency of the resonant circuit is relatively low. be. FIG. 4 is a diagram showing an example of a specific configuration of a variable capacitance element. FIG. 5 is a diagram showing an example of a specific configuration of a variable inductance element. FIG. 6 is a diagram showing an example of the configuration of a conventional tire air pressure detection device. FIG. 7 is a diagram showing the configuration of a pressure sensor and a transmitting/receiving device of the tire air pressure detection device shown in FIG. 6. In the figure, 10 is a tire, 11 is a loop-shaped conductor, and 12
is a resonant circuit, 13 is an excitation coil, 14 is a sweep oscillator, 1
5 is a pickup coil, 16 is an amplifier, 17 is a detector, 18 is a signal processing device, C is a capacitor that constitutes a resonance circuit,
L is an inductance that constitutes a resonant circuit. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Figure 1R Figure 2 Figure 3A ■ Figure 4 Figure 5

Claims (3)

[Claims] (1) A device for detecting air pressure in a vehicle tire, comprising: a conductor provided on a side wall of the tire along the circumferential direction of the tire to form a loop; and the conductor at both ends of the conductor. a resonant circuit that is provided so as to form a closed circuit continuously with the loop, and whose resonant frequency changes depending on the air pressure of the tire; a variable frequency oscillation means that generates a variable frequency signal; and electromagnetic coupling with the conductor. a guide signal supply means provided near the tire to receive a signal from the variable frequency oscillation means and generate a guide signal to the conductor through electromagnetic coupling; A signal detecting means that is provided nearby and detects an induced signal flowing through the conductor; and a determining means that determines the air pressure of the tire based on the detection signal from the signal detecting means and the oscillation frequency of the variable frequency oscillating means. , tire pressure detection device. (2) The tire air pressure detection device according to claim 1, wherein the resonant circuit includes an inductance having a predetermined inductance value and a capacitor whose capacitance value changes depending on the tire air pressure. . (3) The tire air pressure detection device according to claim 1, wherein the resonant circuit includes a capacitor having a predetermined capacitance value, and an inductance whose inductance value changes depending on the tire air pressure.