JPH0560160B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a device for converting and detecting changes in the state of a tire/rim assembly of a vehicle into electrical signals.

(Prior Art) Conventionally, systems have been developed that detect, for example, the air pressure of tires mounted on a vehicle and issue a warning to the driver. In such a tire pressure detection system, the problem is how to transmit the information detected by the tire/rim assembly to the signal processing circuit on the vehicle body side. This information transmission method includes an electromagnetic coupling coil method such as a resonant coil method or an electromagnetic induction method, a mechanical method using a limit switch, an optical method using a light emitting element and a light receiving element, an electrical method using a slip ring and a brush, and an electromagnetic method using electromagnetic waves. Although there are electromagnetic methods that utilize transmission and reception, the electromagnetic coupling method seems to be advantageous in terms of operational stability, reliability, simplicity of configuration, and maintenance. The applicant has already developed a tire internal pressure alarm device based on an electromagnetic coupling coil method as disclosed in Japanese Patent Application Laid-Open No. 53-74078, but this device has an on/off pressure sensitive switch on the tire/rim assembly side. In addition to arranging one coil that constitutes a resonant circuit including a resonant circuit, one coil connected to an oscillator and a detector is placed on the vehicle body side.・The resonant circuit on the rim assembly side is opened,
A detector detects a decrease in the absorption of electromagnetic energy by the resonant circuit, thereby detecting a decrease in tire pressure. Such a detection method is called a resonant coil method, but an electromagnetic induction method has also been proposed as an electromagnetic coupling coil method. In this method, a coupling coil connected to an on-off pressure-sensitive switch that is sensitive to the tire internal pressure is installed on the tire/rim assembly side, and a transmitting coil that emits electromagnetic waves to this coupling coil on the vehicle body side, and a transmitter coil that emits electromagnetic waves from the coupling coil. The system is equipped with a receiving coil that receives electromagnetic waves, and detects changes in tire internal pressure by detecting changes in the intensity of the electromagnetic waves transmitted from the transmitting coil to the receiving coil with a signal processing circuit connected to the receiving coil.

(Problems to be Solved by the Invention) In the conventional resonant coil type detection device described above, the coil provided on the tire/rim assembly side and the coil provided on the vehicle body side face each other only once per rotation of the tire. However, there is a drawback that, for example, when the vehicle is stopped, the condition of the tire/rim assembly cannot be detected at all times. In addition, changes in the resonance circuit due to the on/off operation of a pressure-sensitive switch installed in the resonance circuit are interpreted as changes in the degree of absorption of electromagnetic energy, so the on/off state can be determined by whether the tire internal pressure is below the limit value or not. For example, it is not possible to accurately detect the tire internal pressure itself, and the information that can be obtained is limited.

In addition, in conventional electromagnetic coupling type detection devices, the transmitting coil and the receiving coil are always opposed to the coupling coil, so the condition of the tire/rim assembly can be detected even when the vehicle is stopped. Since only the on/off state corresponding to the on/off operation of the pressure-sensitive switch connected to the coupling coil can be stably detected, the tire internal pressure itself cannot be accurately detected, and there is a drawback that little information can be obtained.

In addition, with conventional tire internal pressure detection devices, if an abnormality occurs in the device, for example, if one of the coils is disconnected, it is a fail-safe system that determines that the tire internal pressure has decreased, ensuring safety. It is difficult to distinguish between abnormalities and equipment abnormalities, which makes maintenance troublesome and may make users feel uneasy.

Further, conventional tire internal pressure detection devices generally use a normally closed on/off pressure sensitive switch, which is turned off when the pressure falls below a predetermined set pressure. On the other hand, tire temperature varies greatly depending on driving conditions, and becomes considerably high when driving at high speeds. Therefore, it is desirable to change the desired set pressure according to the temperature, but in conventional tire internal pressure detection devices, the set pressure of the sensitive switch is constant, so the tire condition cannot be accurately detected. . That is, if the set operating pressure of the pressure-sensitive switch is determined based on the tire pressure during normal driving, it will not be possible to detect a drop below the desired tire pressure during high-speed driving.

An object of the present invention is to eliminate the drawbacks of the conventional detection devices described above and to provide a tire/rim assembly condition change detection device that can accurately and stably detect changes in the condition of a tire/rim assembly. It is something to do.

(Means for Solving the Problems) The tire/rim assembly state change detection device of the present invention has a resistance value that changes on the tire/rim assembly side of a vehicle in accordance with a change in the state of the tire/rim assembly. a loop fixed substantially circumferentially on the rim; and a loop connected to the sensitive element and the loop;
A coupling circuit section having a resonant circuit whose Q characteristic changes according to the resistance value of the sensing element is provided, and on the vehicle body side, an oscillator that oscillates at a specific frequency and an oscillator that faces the loop fixed on the rim are provided. a transmitting section having a transmitting coil that is arranged as shown in FIG. A receiving section including a receiving coil and a signal processing circuit for processing the output of the receiving coil is provided, and the Q of the resonant circuit is adjusted by changing the resistance value of the sensing element in response to changes in the state of the tire/rim assembly. The present invention is characterized in that the signal processing circuit is configured to detect a change in the output of the receiving coil based on the change in the transfer characteristic between the transmitting coil and the receiving coil.

(Function) FIG. 1 is a diagram showing the basic structure of the tire/rim assembly condition change detection device of the present invention. The tire and rim assembly includes a coupling circuit having a loop 1 wound around the circumference of the rim, a resonant circuit 4 having a resonant coil 2 and a resonant capacitor 3, and a sensing element 5 connected to the resonant circuit 4. A section 6 is provided. The resistance value of the sensing element 5 changes depending on the condition of the tire/rim assembly, such as tire internal pressure and tire temperature, and the Q characteristic of the resonant circuit 4 changes in accordance with this resistance value change. become.
The present invention has a feature in that a change in the condition of the tire/rim assembly is converted into a change in the Q characteristic of the resonant circuit 4 in this manner. Furthermore, the loop 1 is connected to the resonant circuit 4 and constitutes the inductance of the resonant circuit, but it is generally advantageous to reduce the number of turns of the loop 1, so the resonant circuit 4
The inductance of is determined mostly by the resonant coil 2. However, if you increase the number of turns of loop 1,
The inductance of the loop now influences the resonant frequency, and in some cases the resonant coil 2 can be omitted.

On the vehicle body side of the vehicle, a transmitting section 9 includes a transmitting coil 7 disposed to face the loop 1 and an oscillator 8 connected to the transmitting coil 7; a receiving coil 10 disposed to face the loop 1; A receiving section 13 is provided which includes a display device 12 connected to a signal processing circuit connected thereto. The oscillator 8 is, for example, 150
It is configured to oscillate at a frequency of kHz, and this oscillation output is supplied to the transmitting coil 7 to emit electromagnetic waves of 150 kHz toward the loop 1. In this case, the resonant circuit 4 of the coupling circuit section 6 is tuned to 150kHz. If the sensing element 5 is constituted by a semiconductor pressure sensing element with good temperature characteristics whose resistance value changes almost in proportion to the tire internal pressure, the resistance value will increase when the tire internal pressure is high, and therefore the resonant circuit Although the Q value of the resonant circuit 4 becomes small, as the tire internal pressure becomes low, the resistance value becomes low, and therefore the Q value of the resonant circuit 4 becomes large. In this way, the amplitude of the resonant current induced in the resonant circuit 4 of the coupling circuit section 6 changes according to the tire internal pressure, and is therefore radiated from the loop 10 connected to the resonant circuit to the receiving coil 10. The intensity of the electromagnetic waves changes depending on the tire internal pressure.

FIG. 2 shows the tire internal pressure P on the horizontal axis and the gain G of the signal received by the receiving coil 10 on the vertical axis. As described above, since the resistance value of the sensing element 5 changes approximately in inverse proportion to the tire internal pressure P, the gain G of the output signal of the receiving coil 10 also changes approximately in inverse proportion to the tire internal pressure. Therefore, by processing the output of the receiving coil 10 in the signal processing circuit 11, the tire internal pressure P itself can be displayed on the display device 12, and the output of the receiving coil 10 can be displayed as a reference value G _R corresponding to the reference tire internal pressure P _R. By comparing this with the actual tire pressure, it is possible to issue an abnormal tire internal pressure warning. Further, for example, if a disconnection occurs between the loop 1 of the coupling circuit section 6 and the resonant circuit 4, the coupling circuit will no longer function, so that almost no signal will be transmitted from the transmitting section 9 to the receiving section 13. The output of the receiving coil 10 becomes extremely small. Therefore, the output of the receiving coil 10 is compared with a sufficiently small reference value _GS , and if the output becomes smaller than this reference value _GS , it can be determined that the circuit is abnormal.

Further, according to the present invention, since the transmitting coil 7 and the receiving coil 10 are always facing the loop 1,
The above information can be obtained even when the vehicle is stopped, improving the reliability of the device. Furthermore, if a semiconductor pressure-sensitive element with excellent temperature characteristics is used as the sensing element, accurate detection that is not affected by temperature changes can be performed.

As described above, according to the present invention, a change in the state of the tire rim assembly is converted into a change in the Q characteristic of the resonant circuit 4 by the sensing element 5 whose resistance value changes according to the change in state, and the oscillating section 9 and the receiving section 13 By changing the transmission characteristic between the two and detecting the change in the output of the receiving coil 10 based on this change, changes in the state of the tire/rim assembly can be detected accurately and stably at all times.

(Embodiment) FIG. 3 is a sectional view showing the configuration of an embodiment of the detection device of the present invention, and FIG. 4 is a diagram showing the overall configuration. Tire 21 and rim 22
A loop 23 is fixed around the inner peripheral surface of the rim 22 in order to detect the state of the assembly.
is connected to a coupling circuit unit 24 incorporating a resonant circuit and a sensitive element. This unit 24 is attached to the surface of the rim 22 that is exposed inside the tire 21. As shown in FIG.
A resonant coil 25, a resonant capacitor 26 and a sensing element 27 are provided. In this example, the sensing element 27 is constituted by a semiconductor pressure sensing element whose resistance value changes depending on pressure, and is connected in parallel with the resonant coil 25.

On the body side of the vehicle, a transmitting coil unit 28 is provided at a position facing the loop 23, and a receiving coil unit 29 is also provided at a symmetrical position with respect to the transmitting coil unit 28, also facing the loop 23. The distance between these oscillating coil unit and receiving coil unit and the loop 23 is several
mm to tens of mm. The transmitting coil provided in the transmitting coil unit 28 is connected to the oscillator 30. Also,
In the receiving coil unit 29, a receiving coil and a capacitor constitute a tuning circuit, which is connected to an amplifier 31 and a detector 32. The output of the detector 32 is supplied to a first comparator 33 to detect a decrease in the tire internal pressure, and when the pressure falls below a predetermined pressure, a signal is sent to a warning light 34 to alert the driver. The output of the detector 32 is also supplied to a second comparator 35, and when a break in the circuit is detected, a warning light 36 is turned on to warn the driver. The output of the detector 32 is further supplied to a pressure conversion circuit 37, where the absolute value of the tire internal pressure is determined and displayed on a digital display 38. In this manner, in this example, it is possible to simultaneously display an abnormal decrease in tire internal pressure, an abnormality in the detection device, and an actual measured value of tire internal pressure.

In this embodiment, the oscillation frequency of the oscillator 30 is 150k.
Hz, and the resonant frequency of the resonant circuit of the coupling circuit unit 24 and the tuning frequency of the tuned circuit of the receiving coil unit 29 are also 150 kHz. That is, the inductance of the resonant coil 25 is set to 470 μH, and the capacitance of the resonant capacitor 26 is set to 0.0025 μF. Also,
The semiconductor pressure sensitive element 27 has a characteristic that the resistance value R decreases as the pressure P increases, and the resistance value increases as the pressure decreases, but in this example, it has a nonlinear characteristic as shown in FIG. 5A. It has the following. In other words, when the pressure is below a certain level, the resistance value has an almost constant high value, and when the pressure increases beyond that, the resistance value decreases almost linearly, but when the pressure exceeds a certain level, it has an almost constant low value. It has the following. When such a pressure sensitive element 27 is used, the gain of the output obtained by receiving the signal in the receiving coil unit 29, amplifying it in the amplifier 31, and detecting it in the detector 32 will be as shown in FIG. 5B. . Therefore, if the current pressure P _R is set to the reference pressure and a warning is generated when the tire internal pressure falls below this reference pressure, the reference value of the first comparator 33 is set to the fifth
The reference value G _R in Figure B may be selected. Also, the second
If the reference value in the comparator 35 is set to the fairly low reference value G _S shown in Fig. 5B, when an abnormality occurs in the equipment due to a wire breakage, the detection output will be almost zero, and an alarm of equipment abnormality will be issued. can be generated.

6A, B, and C are graphs showing the frequency characteristics of the output of the detector 32 when the tire internal pressure is higher than or lower than the standard set pressure, and when the loop 23 is disconnected. Pressure sensitive element 2 when pressure is high
The resistance value of 7 is 6KΩ and the output is -88dB, and the resistance value when low is 50KΩ or more and the output is -78dB. Therefore, it can be seen that changes in pressure can be detected with extremely high accuracy. Furthermore, as shown in Figure 5C, in the case of a disconnection, the signal is almost zero;
Differences from those at high pressures can also be detected clearly. In addition, the frequency characteristic has a resonance point of 150KHz
It can also be seen that it is within a range of approximately ±15KHz around . Therefore, for example 50KHz, 150KHz,
There is no crosstalk even when three frequencies of 200KHz are used at the same time, and three separate pieces of information such as tire internal pressure, tire internal temperature, and tire external temperature can be detected simultaneously.

FIG. 7 is a circuit diagram showing another example of the coupling circuit unit used in the detection device of the present invention. In this example, a sensing element consisting of a series circuit of a fixed resistor 41 and an on/off pressure sensitive switch 42 is connected in parallel with the resonant coil 25 and resonant capacitor 26 of the resonant circuit connected to the loop 23. The fixed resistor 41 has a resistance value of several kilohms, and the on/off pressure sensitive switch 42 is a normally closed pressure sensitive switch.
Therefore, when the tire pressure is normal, a fixed resistor 41 with a resistance value of several kilohms is connected in parallel with the resonant coil 25, so the Q value of the resonant circuit is as shown in Fig. 5A. As a result, the gain of the output of the detector 32 becomes smaller. On the other hand, if the resistor 41 is omitted, the resonant coil 25 becomes the on/off pressure-sensitive switch 4.
2 causes a short circuit, so the detection output becomes almost zero, making it impossible to distinguish it from a case of device abnormality.

When the tire internal pressure falls below the reference value, the switch 42 is turned off and the resistor 41 is disconnected from the circuit, so that the Q value of the resonant circuit becomes high and a large detection output is obtained. In this way, an abnormality in the tire internal pressure and an abnormality in the device can be detected.

The present invention is not limited to the embodiments described above, and can be modified and modified in many ways. For example, the configuration of the coupling circuit portion is not limited to the above-described embodiment, and any configuration may be used as long as the Q characteristic of the resonant circuit changes depending on the resistance value of the sensing element. In the example shown in FIG. 8A, a sensing element consisting of a series circuit of a semiconductor pressure sensing element 54 and a fixed resistor 55 is connected in parallel with the resonant coil 52 and resonant capacitor 53 of the resonant circuit connected to the loop 51. In this example, even when using a semiconductor pressure-sensitive element 54 whose resistance value decreases significantly as pressure increases, a fixed resistor 55 of several kilohms is connected to the resonant circuit, so that the output of the receiving coil becomes excessive. It is possible to prevent the device from dropping and to detect an abnormality in the device. In the example shown in FIG. 8B, a sensing element consisting of a series circuit of a semiconductor sensing element 54 and a fixed resistor 55 is connected in parallel with the resonant coil 52, and in the example shown in FIG. 8C, a sensing element is connected in parallel with the resonant coil 52. A sensing element consisting of a series circuit of a fixed resistor 55 and an on/off pressure sensitive switch 56 is connected to. In these embodiments as well, abnormalities in the device can be detected.

Furthermore, in the above-described embodiment, a semiconductor pressure-sensitive element whose resistance value changes in response to the tire internal pressure was used as the sensing element, but an element whose resistance value changes depending on the tire temperature may also be used. Tire temperature can be detected.

(Effects of the Invention) As described above, according to the tire/rim assembly condition change detection device of the present invention, the Q characteristic of the resonant circuit connected to the loop fixed around the rim is detected by the tire/rim assembly.
The resistance value is changed by a sensing element that changes according to the state change of the rim assembly, and the change in the transfer characteristic between the transmitting part and the receiving part based on the change is detected as a change in the output of the receiving coil. , it is possible to accurately and stably detect changes in the condition of the tire/rim assembly. In addition, since the transmitting coil and receiving coil are always facing the loop, changes in the condition of the tire/rim assembly can be detected not only while the vehicle is running but also while the vehicle is stopped, which has the effect of improving reliability. It will be done. Furthermore, since it is possible to distinguish between an abnormality in the device and an abnormality due to a change in the condition of the tire/rim assembly, safer and more complete management becomes possible, and maintenance becomes easier.

Furthermore, if tire internal pressure and tire temperature are detected simultaneously, for example, it is possible to accurately warn of abnormalities in tire internal pressure while compensating for changes in tire temperature.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing the basic configuration of the tire/rim assembly state change detection device of the present invention, FIG. 2 is a graph for explaining its operation, and FIG. 3 is a circuit diagram of the detection device of the present invention. FIG. 4 is a circuit diagram showing the overall structure of the embodiment; FIGS. 5A and B and FIGS. 6A to C are graphs for explaining its operation; This figure is a circuit diagram showing a modified example of the coupling circuit unit, and FIGS. 8A to 8C are circuit diagrams showing still other examples of the coupling circuit section. 1, 23, 51... loop, 2, 25, 52...
... Resonance coil, 3, 26, 53 ... Resonance capacitor, 4 ... Resonance circuit, 5, 27 ... Sensing element, 7
... Transmission coil, 8, 30... Transmitter, 9... Receiving section, 10... Receiving coil, 11... Signal processing circuit, 12... Display device, 13... Receiving section, 24...
...Coupling circuit unit, 28... Transmitting coil unit, 29... Receiving coil unit, 41, 55...
...Fixed resistance, 42, 56...On-off pressure sensitive switch, 54...Semiconductor pressure sensitive element.

Claims (1)

[Claims] 1. On the tire/rim assembly side of the vehicle, there is a tire/rim assembly.
a sensing element whose resistance value changes in response to changes in the state of the rim assembly; a loop fixed approximately around the rim; and a loop connected to the sensing element and the loop, the Q characteristic of which changes in accordance with the resistance value of the sensing element. A coupling circuit section is provided on the vehicle body side of the vehicle, and is disposed so as to face an oscillator that oscillates at a specific frequency and a loop fixed on the rim, and that is arranged to face the oscillator that oscillates at a specific frequency and that emits the oscillated electromagnetic waves from the oscillator. a transmitting section having a transmitting coil that emits toward the loop; a receiving coil that is disposed to face the loop fixed on the rim and receives electromagnetic waves radiated from the loop; and a receiving coil that processes the output of the receiving coil. a receiving section comprising a signal processing circuit for transmitting a signal, and a Q-characteristic of the resonant circuit changes due to a change in the resistance value of the sensing element in response to a change in the state of the tire/rim assembly. 1. A state change detection device for a tire/rim assembly, characterized in that the signal processing circuit is configured to detect a change in the output of the receiving coil based on a change in the transmission characteristic between the tire and rim assembly. 2. The tire/rim assembly according to claim 1, wherein the resonant circuit is provided with a resonant coil and a resonant capacitor connected in series with the loop, and the sensing element is connected in parallel with the resonant coil. state change detection device. 3. The tire/rim assembly according to claim 1 or 2, wherein the sensing element is constituted by an element that causes a continuous change in resistance with a value of several kilohms or more in response to a change in state. State change detection device. 4 The sensing element is connected to an on/off switch and a number
3. A state change detection device for a tire/rim assembly according to claim 1 or 2, characterized in that the device is configured by connecting in series with a KΩ resistor. 5. The state change of a tire/rim assembly according to claim 1, 2, 3 or 4, wherein the sensing element is constituted by a pressure sensing element whose resistance value changes depending on the tire internal pressure. Detection device. 6. The tire/rim assembly condition change detection device according to claim 1, 2, 3, 4, or 5, wherein at least a portion of the inductance of the resonant circuit is configured by the loop.