JPH05107139A - Tire pressure warning device - Google Patents

Abstract

PURPOSE:To improve the waterproofing and vibration damping properties of an antenna used for a tire pressure warning device and, at the same time, to reduce the size and weight of the antenna. CONSTITUTION:This tire pressure warning device is provided with an antenna on the opposite side of a transmitter, the resonance frequency of which electrically changes in accordance with the output of a pressure sensor, and, by transmitting a short pulse signal to the antenna, sends an alarm by discriminating the frequency of a resonance signal from the antenna. A coil 21 contained in the antenna is covered with a plastic cap 22 and a metallic socket 23 joined with a metallic protective tube 23 protecting the wiring 24 of the coil 21 is joined with the cap 22 by caulking. The space in the cap 22 is filled up with a plastic molded body 26. Therefore, a highly reliable antenna having a simple and solid structure can be manufactured at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a device for automatically detecting a tire pressure during running of an automobile and sending an alarm to a driver's seat when the detected tire pressure is abnormal. The present invention particularly relates to an antenna of a tire pressure warning device.

[0002]

2. Description of the Related Art A pressure switch for detecting a tire pressure and an electromagnetic resonance circuit which is changed by the pressure switch are provided on the tire side, and the resonance state of the resonance circuit is wirelessly detected by a device provided on the vehicle body side. The tire pressure detecting device is disclosed in Japanese Utility Model Laid-Open No. 61-81396, Japanese Utility Model Laid-Open No. 1-14.
It is known from Japanese Patent No. 7706, Japanese Utility Model Laid-Open No. 2-116395, and the like.

Each of these prior arts is an excellent idea that the tire pressure during running can be monitored by a radio signal to detect the decrease in tire pressure early and send an alarm to the driver's seat.

[0004]

However, the technique utilizing the above-mentioned principle has been installed in an ordinary automobile with a considerably reliable device, although many application studies have been conducted. Since it is not possible to offer it at a price that can be used, it is not actually installed in a commercially available car. The main reason for this is that the transmitter that includes the sensor and electromagnetic resonance circuit that is attached to the tire is subjected to severe vibrations as the vehicle runs, so it is not possible to obtain a mechanical structure that can withstand it. In order to obtain it, it is necessary to change the structure of the wheel and so on, so that it is no longer possible to use a conventionally mass-produced wheel. In a small car, there are two axles and four tires, but in a large car, there is an axle. The number of tires is 3 and the number of tires is 10. There is a reason that a rational control circuit for centrally controlling these tires could not be obtained at a low price so that it could be easily used in a practical vehicle.

The inventors of the present invention have conducted various tests on this apparatus, and have improved the structure of a pressure sensor mounted on a tire for detecting a tire pressure and a transmitter for transmitting the detection output. This antenna is installed on the vehicle body side opposite to the tires, and it is exposed to severe environments such as water and mud as well as being subjected to severe vibrations, so a solid structure is the first condition, The second condition is that the center of gravity with respect to the mounting position should be low and the design should be as small and lightweight as possible. These two conditions are mutually contradictory conditions, and the inventors of the present application have studied from a large number of trial manufactures and tests in order to obtain a structure that satisfies both of these two conditions.

That is, an object of the present invention is to realize an antenna for a tire pressure warning device which is excellent in waterproofness, has vibration resistance, and is small and lightweight.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a pressure sensor and a transmitter whose resonance frequency changes according to the output of the pressure sensor are mounted on the tire side, and an antenna facing the transmitter and this antenna are provided. A control circuit for transmitting and receiving signals and an indicator for displaying an alarm output of the control circuit are mounted on the vehicle body side, and the control circuit transmits a short pulse signal to the antenna, and a transmission circuit for the pulse signal. In response to the resonance signal transmitted from the transmitter, a frequency discrimination circuit for discriminating the frequency of the resonance signal, and a program control circuit for transmitting the alarm output by the output of the frequency discrimination circuit. In the tire pressure warning device, the antenna includes one coil, a plastic cap covering the coil, A metal socket having an end caulked and joined to the plastic cap, the wire of the coil being inserted and the other end joined to a metal protective tube of the wire, and the metal socket and the plastic cap having the coil and the metal protective tube inside. And a joint surface between the plastic molded body and the metal socket and the plastic cap has a minimum creepage distance of 10 mm.
To 25 mm.

[0008]

[Operation] The antenna provided on the vehicle body side causes the transmitter on the tire side to receive the pulse for excitation, and
An electromagnetic wave from a transmitter, which has one coil that resonates in response to the excitation pulse and that resonates and two capacitors connected to this coil as electrical elements, is received through the coil. Therefore, the surface cannot be covered with metal and is covered with a plastic cap for protection. Also, in order to introduce electrical wiring into the coil, a socket connected to the wiring protection tube is required,
This also requires the use of a metal socket for a solid structure. By making the metal socket as light as possible and filling the inside with the plastic molded body, the plastic molded body fixes the coil and its wiring against vibration.

Tests were carried out on various materials having such a structure, and when the length of the plastic molded body in the longitudinal direction along the electric wiring was short, the penetration of water into the coil from the joint portion of the wiring with the metal protective tube. Was found to be recognized. That is, it is necessary to increase the creepage distance of the joint surface between the plastic molded body and the metal socket. However, increasing the creepage distance makes the antenna large, and therefore, as a harmony point for preventing moisture from entering and reducing the size, the joint surface between the plastic molded body and the metal socket and the plastic cap is used. It was confirmed that 10 to 25 mm was appropriate when the experiment was repeated for the shortest creepage distance.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic structure of the device of the present invention and the operating principle thereof will be described first. FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. A pressure sensor 1 for detecting the air pressure is attached to each tire. The pressure sensor 1 is a pressure switch whose contacts are closed when the tire air pressure is above a predetermined value and open when the tire air pressure falls below a predetermined value. A transmitter 2 is electrically connected to this pressure switch. This transmitter 2 is a resonant circuit. The pressure switch of the pressure sensor 1 changes the capacitance of the capacitor of the resonance circuit and changes the resonance frequency.

An antenna 3 is installed on the vehicle side so as to face each transmitter 2. The antenna 3 is provided for each tire and is connected to the control circuit 4 by electric wiring. The output of the control circuit 4 is connected to an indicator (lamp) 5 provided in the driver's seat.

FIG. 2 is a diagram for explaining the operating principle of the apparatus of this embodiment. The pressure sensor 1 is a pressure switch, and the contact 7 is closed when the tire pressure is equal to or higher than a predetermined value, but the contact 7 is opened when the tire pressure is lower than the predetermined value.
The transmitter 2 has one coil L1 and capacitors C1 and C2 connected in parallel to the coil, of which the capacitor C1 is connected via the contact 7 of the pressure switch. .. Therefore, when the tire air pressure is sufficiently high, the two capacitors C1 and C2 are connected in parallel, but when the tire air pressure is low, the capacitor C1 is disconnected and the capacitor C2 is disconnected.
Only the coil L1 is connected.

In this way, the resonance frequency of the transmitter 2 changes according to the opening / closing of the contact 7. By the way, when the contact 7 is closed and the two capacitors are in parallel, the resonance frequency is about 87 kHz, and when the capacitor C1 is disconnected, the resonance frequency is about 140 kHz.

FIG. 3 is a block diagram of the control circuit 4. Terminal 1
The antenna 3 is connected to 0. A pulse having a short width is oscillated by the oscillator 11 (in this embodiment, a pulse width of several μ).
(S, repetition time several tens of μS), amplified by the amplifier 12 and transmitted from the antenna 3 as an electromagnetic wave. When this electromagnetic wave is sensitized to the coil L1 of the transmitter 2 shown in FIG. 2, the resonance circuit composed of the coil L1 and the capacitors C1 and C2 is stimulated to continue the damped oscillation at the resonance frequency.
This resonance frequency becomes an electromagnetic wave, which is captured by the antenna 3 and input from the amplifier 13 to the frequency discriminating circuit 14. Here, the resonance frequency is detected and input to the program control circuit 15. This operation is sequentially executed for each wheel under the control of the program control circuit 15, and if any decrease in tire air pressure is detected, an alarm output is sent to the display terminal 19 and the indicator (lamp) 5 in the driver's seat is turned on. Let

The structure of the antenna used in the tire pressure warning device, which is a feature of the present invention, will be described below. FIG. 4 is a sectional view showing the configuration of the antenna in the device of the present invention.

Antenna 3 used in the apparatus of the present invention
Is one coil 21, a plastic cap 22 covering the coil 21, one end is caulked and joined to the plastic cap 22, the wire 24 of the coil 21 is inserted, and the other end is joined to the metal protection tube 25 of the wire. And a plastic molded body 26 filled inside the metal socket 23 and the plastic cap 22 between the coil 21 and the metal protective tube 25.
Including the plastic molded body 26 and the metal socket 23.
The joint surface between the plastic cap 22 and the plastic cap 22 has a short creepage distance of 10 to 25 mm.

The antenna 3 is provided on the vehicle body side, transmits an exciting pulse to the transmitter 2 on the tire side, and causes the electromagnetic wave from the transmitter 2 which resonates in response to the exciting pulse to pass through the coil L2 shown in FIG. To receive through.

As described above, since the antenna 3 receives electromagnetic waves, its surface cannot be covered with metal. So, cover the surface with a plastic cap 22,
Further, in order to introduce the electric wiring into the coil L2 as a solid structure, the metal socket 23 connected to the metal protection tube 25 for protecting the electric wiring is used so as to be fixed against vibration.

The antenna 3 is required to have a solid structure in order to be exposed to a severe environment where it is exposed to water and mud while undergoing severe vibration, but on the other hand, it is desired to be small and lightweight.
In order to satisfy such contradictory conditions, antennas of various structures including the comparative example shown in FIG. 5 were tested, and the creeping surface of the joint surface between the plastic molded body 26 and the metal socket 23 and the plastic cap 22 was examined. It has been confirmed that setting the shortest distance within the range of 10 to 25 mm can achieve miniaturization and can completely prevent water from entering the coil L2 shown in FIG. 2 from the joint portion between the wiring 24 and the metal protection tube 25. Was done.

[0020]

As described above, according to the present invention, the coil of the antenna used in the tire air pressure alarm device is covered with the plastic cap and the metal socket, and is fixed with the plastic molding, thereby achieving miniaturization and waterproofing. And the vibration resistance can be enhanced, and there is an effect that a highly reliable antenna can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation principle of the device according to the embodiment of the present invention.

FIG. 3 is a block configuration diagram of a control circuit in the device according to the embodiment of the present invention.

FIG. 4 is a cross-sectional view showing the configuration of an antenna in the device of the present invention.

FIG. 5 is a cross-sectional view showing a configuration of an antenna in the comparative device.

[Explanation of symbols]

 1 Pressure Sensor 2 Transmitter 3 Antenna 4 Control Circuit 5 Indicator (Lamp) 7 Contact 10 Terminal 11 Oscillator 12, 13 Amplifier 14 Frequency Discrimination Circuit 15 Program Control Circuit 19 Display Terminal 21 Coil 22, 32 Plastic Cap 23, 33 Metal Socket 24 Wiring 25 Metal protection tube 26 Plastic molding

Claims (1)

[Claims] 1. A pressure sensor and a transmitter whose resonance frequency changes according to the output of the pressure sensor are mounted on the tire side, an antenna facing the transmitter, and a control circuit for transmitting and receiving signals to and from the antenna. An indicator for displaying an alarm output of this control circuit is attached to the vehicle body side, and the control circuit transmits a short pulse signal to the antenna, and the transmitter transmits in response to the transmission of the pulse signal. In the tire pressure warning device, the tire pressure warning device includes a receiving circuit for receiving the resonance signal, a frequency discrimination circuit for discriminating the frequency of the resonance signal, and a program control circuit for outputting the warning output by the output of the frequency discrimination circuit. Is a coil, a plastic cap that covers the coil, and one end of the plastic A metal socket in which the wire of the coil is inserted and the other end is joined to the metal protective tube of the wire by caulking and joining to a cap, and between the coil and the metal protective tube inside the metal socket and the plastic cap. A structure including a filled plastic molded body, wherein a joint surface between the plastic molded body and the metal socket and the plastic cap has a creepage shortest distance of 10 to 25 mm. apparatus.