JPH0390407A - Detecting device for air pressure in tire - Google Patents

Abstract

PURPOSE:To improve detecting accuracy with a simple construction by detecting the position of a responsible member for centrifugal force which has a magnetic substance and makes the position of the magnetic substance rotationally movable due to centrifugal force generated by rotation of a tire through a magnetism detecting means, and judging air pressure in the tire. CONSTITUTION:A pressure detecting part 29 which is fitted to a rim 3 and air in a tire 1 is introduced in it, is provided with a casing 39 thread-mounted to the rim 3, and the flange part 47 of a bellows 45 expanding due to the inner pressure of the tire is pinchedly held by the thread-mount of the casing 39. A cap 57 fitted to the casing 39 is provided, and a globular magnet 55 as a responsible member for centrifugal force is received in the space 59 defined in the interior, and held with the bellows 45. The globular magnet 55 is constructed by molding a magnet 55a with resin 55b, and a permanent magnet 60 as a holding means is fixed on the rim 3 at the opposing position to the N-pole of the globular magnet. The condition of air pressure in the tire is judged by output of a magnetism detecting part 31 to detect the position of the magnet 55.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tire air pressure detection device for detecting tire air pressure.

[Prior art] Conventionally, as a tire air pressure detection device,
As shown in Publication No. 443 and Japanese Utility Model Application No. 59-146748, when the tire air pressure decreases, the position of the magnetic member changes, and the change in magnetic flux due to the change in the position of the magnetic member is detected by a magnetic field sensing element. By this detection, tire air pressure was detected.

[Problem to be solved by the invention]

However, in these conventional devices, detection was performed based on the proximity of one pole (for example, N pole) of the magnetic member to the magnetic field sensing element, so the magnetic field sensing element detects a change in magnetic flux due to a slight change in the position of the magnetic member. However, there was a problem in that the change in the position of the magnetic member had to be large.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a tire air pressure detection device that can increase the change in magnetic flux with a simple configuration and facilitate detection.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a magnetic body, the position of the magnetic body can be rotated by the centrifugal force generated by the rotation of the tire, and the rotation a centrifugal force responsive member having a center of gravity that is different from the center of the centrifugal force responsive member, a fixing means for switching between fixing and non-fixing of the centrifugal force responsive member depending on the air pressure of the tire, and the fixing means leaving the centrifugal force responsive member unfixed. In the state, when the centrifugal force is smaller than a predetermined value, the line connecting the center and the center of gravity of the centrifugal force responsive member is along the direction of the centrifugal force, and the direction of the vector from the center to the center of gravity is a holding means for holding the centrifugal force response member in a state opposite to the direction of centrifugal force; a detection means for detecting the position of the magnetic body; and a state of the air pressure of the tire based on the detection result of the detection means. determination means for determining, when the centrifugal force is equal to or greater than the predetermined value in a state in which the fixing means does not fix the centrifugal force responsive member, the centrifugal force responsive member is resisted by the holding force of the retaining means on the centrifugal force responsive member. The direction of the vector from the center to the center of gravity is along the direction of the centrifugal force.

Furthermore, at least a portion of the centrifugal force response member may be rotatably supported by a pivot means.

Furthermore, the holding means may be a magnet.

[Effect]

In the tire air pressure detection device configured as described above, when the centrifugal force responsive member is fixed by a fixing means according to the tire air pressure, the line connecting the center of the centrifugal force responsive member and the center of gravity is the centrifugal force generated by the rotation of the tire. It is fixed along the direction of the force, and the direction from this center to the center of gravity is opposite to the direction of the centrifugal force, and the detection means detects the position of the magnetic body, and based on the detection result. A determining means determines the state of tire air pressure.

In the case where the air pressure of the tire changes and the centrifugal force responsive member is no longer fixed by the fixing means and becomes unfixed,
When the centrifugal force generated by the rotation of the tire is smaller than a predetermined value, the centrifugal force responsive member is held by the holding means in the same state as when it was fixed. On the other hand, when the fixation by the fixing means of the centrifugal force response member is released and the centrifugal force generated by the rotation of the tire exceeds a predetermined value, the centrifugal force overcomes the holding force and the centrifugal force The responsive member is inverted. At this time, the change in magnetic flux is twice as large as the maximum change in magnetic flux in the conventional case. The detection means detects this reversal of the magnetic body, and the determination means determines the state of the tire air pressure based on the detection result.

〔Example〕

The present invention will be explained below using the drawings. FIG. 1 is a diagram showing a first embodiment of the present invention, in which the present invention is applied to a normal tire. 1 is a tire, and a rim 3 is fixed to a wheel shaft 7 with a wheel nut 5. The brake drum 9 is welded to a plate 11, and the plate 11 is fixed to the wheel axle 7 with bolts (not shown). The inner ring of the bearing 13 and the wheel shaft 7 are fixed by a NAND 15. The bearing housing 17 and the cover plate 19 are fixed to the hub 21 together with the outer ring of the bearing 13 by bolts (not shown). The lower end of the shock absorber 23 is fixed to the hub 21 with a bolt 25, and the upper end (not shown) of the shock absorber 23 is fixed to the vehicle body side.

One end of the suspension arm 27 is supported on the hub 21 by a bolt 28 so as to be rotatable about the bolt 28, and the other end (not shown) of the suspension arm 27 is supported on the vehicle body side. Reference numeral 29 denotes a pressure detection section which is a main part of this embodiment, and the details thereof will be described later. A magnetic detection section 31 detects magnetism in the pressure detection section, converts it into an electrical signal, and sends the electrical signal to the control circuit 35 via the wire harness 33. 36 is a battery, and 3rd is a switch. In FIG. 1, the inner rings of the tire 1, rim 3, wheel pad 5, wheel shaft 7, brake drum 9, plate 11, nut 15, pressure detection unit 29, and bearing 13 rotate while the vehicle is running; The part is supported by the vehicle body and does not rotate.

FIG. 2 is a detailed diagram of the vicinity of the pressure detection section 29.

Reference numeral 37 denotes one communication path provided in the rim 3, which introduces the air inside the tire 1 to the pressure detection section 29.

Reference numeral 41 indicates an O-ring, and reference numeral 43 indicates a gas kent. By screwing the casing 39, the collar 47 of the bellows 45, the O-ring 41, and the gas kent 43 are press-fixed to the rim 3, and prevent tire air from leaking to the outside. It is heavily prevented. The bellows 45 as a fixing means is made of metal and expands and contracts according to the air pressure inside the tire 1, and its detailed diagram is shown in FIGS. 3 and 4. The bellows 45 is made by welding a collar portion 47, a bellows portion 51, and a magnet holding portion 53, and has an internal air chamber 49. FIG. 3 shows a state in which the air pressure in the internal air chamber 49 is low and the bellows part 51 is contracted to the right, and FIG. 4 shows a state in which the air pressure in the internal air chamber 49 is high and the bellows part 51 is extended to the left. . Returning to FIG. 2, a spherical magnet 55 as a centrifugal force responsive member is arranged in a space 59 formed by a casing 39 made of a non-magnetic material such as aluminum and a cap 57. The cap 57 is press-fitted and fixed to the casing 39. As shown in FIG. 5, the spherical magnet 55 has one end excited to the north pole and the end symmetrical to the north pole to the south pole, and the diameter of the north pole side is small and the diameter of the south pole side is large. (heavier on the south pole side) is molded with resin 55b, which has a lighter specific gravity than the magnet 55a. The magnet holding part 53 has a conical recess at its tip, so that when the air pressure is normal and the spherical magnet 55 is sandwiched and fixed between the cap 57, the spherical magnet rotates. This is to prevent this from happening. Spherical magnet 55 in rim 3
A permanent magnet 60 serving as a holding means is adhesively fixed at a location facing the north pole of the magnet 55 , and the south pole thereof faces the spherical magnet 55 . The space 59 in FIG. 2 represents the spherical magnet 5
5, and when the magnet holding part 53 does not hold down the spherical magnet 55, there is a gap that allows the spherical magnet 55 to rotate freely, and the portion where the cap 57 and the casing 39 contact the spherical magnet 55. (5 in Figure 2)
7a, 39a) are conical.

FIG. 6 shows a detailed configuration of the magnetic detection section 3I. In FIG. 6, 61 is an aluminum alloy case, 63 is a magnetic core, and iron or non-excited ferrite is used as the magnetic material. The coil 65 has an insulated conductive wire wound around a magnetic material 63 via a resin bobbin 67, and both ends of the conductive wire are caulked together with the two wire harnesses 33 by a metal fitting crimper 69. Electrically connected with the book wiring harness. With the above configuration, the magnetic detection section 31 can detect changes in external magnetism and convert them into electrical signals.

Next, the configuration of the control circuit 35 will be explained using FIGS. 7 to 11. FIG. 7(a) is a diagram showing the overall configuration of the control circuit 35, in which the waveform shaping circuit 101 and the disconnection detection circuit 1 are shown.
03, smoothing and level determination circuit 105, vehicle speed determination circuit 1
07, an abnormality display circuit I09, and a power supply circuit 111. 7) is a circuit diagram of the control circuit 35. In FIG.

In FIG. 7), the input terminal a of the waveform shaping circuit 101
, b are connected to the wire harness 33 connected to the coil 65. The voltage at the input terminal S is fixed by a circuit including a resistor 704 and a diode 705 to a forward voltage drop of approximately 0.6 to 0.7 V at a semiconductor pn junction. On the other hand, the output voltage of the magnetic detection section 31 is applied to the a terminal with the voltage of b as a reference (for example, the output voltage of the magnetic detection section 31 is 1
In the case of ■, if point b is 0.6V, point a will be 1.6V).

The voltages at points a and b are input to the input terminals of the comparator 714 through resistors 706 and 708, respectively. The comparator 714 sets the output terminal to a high level when the voltage of the input terminal is lower than that of the input terminal, and sets the output terminal to a low level when the voltage is higher than that of the input terminal.

However, the resistor 710 adds hysteresis characteristics to the comparison voltage, making the configuration resistant to noise. The resistor 711 and capacitor 712 have the function of changing the value of this hysteresis. As shown in FIG. 8, as the input voltage changes, the lower threshold voltage V at point P,
At the moment the voltage falls below V, the lower threshold voltage V changes, and eventually settles to the upper threshold voltage V2, which appears as the effect of the resistor 710. Next, at point q, the upper threshold voltage v2 changes in the same way, although the polarity is opposite.
Even if noise is superimposed on the input signal, it has a configuration that is not easily affected. The Zener diode 707 clips at a predetermined level to protect the input terminal so that an excessive voltage is not input to the input terminal of the comparator 714.

When such a waveform shaping circuit 101 receives a signal as shown in the waveform at point a in FIG. 9 from the magnetic detection section 31, it outputs a pulse as shown in the waveform at point d.

In the retriggerable monostable multi-by-break 717, the pulse width output to the output terminal Q is set by the values of the capacitor 715 and the resistor 716.

The value of this pulse width is set to be slightly longer than the period W of the detection signal generated every time the tire rotates when the vehicle speed is the lowest V6 at which a decrease in air pressure can be detected (the spherical magnet 55 can be reversed).

Next, the operation of this embodiment having the above configuration will be explained. In Fig. 2, the air pressure inside the tire 1 is normal (
If the pressure is higher than a predetermined pressure), air pressure acts on the bellows 45 via the communication path 37, and the magnet pressing portion 53 presses the spherical magnet 55 against the cap 57. In this case, a line connecting the center C of the spherical magnet 55 and the center of gravity G is along the direction of the centrifugal force generated by the rotation of the tire.

FIG. 2(a) is a diagram schematically representing this state.

In this case, even if the tire rotates and centrifugal force is generated, when the spherical magnet 55 passes by the magnetic detection section 31, the S pole of the spherical magnet 5S always touches the magnetic detection section 31, as shown in FIG. It is located on the opposite side (the side closer to the magnetic detection section 31). As a result, when the tire rotates, a voltage shown at point a on the left side of FIG. 9 is generated in the coil 65 of the magnetic detection section 31.

In FIG. 9, when the voltage at point a exceeds the upper threshold voltage Vt at time 1+, the voltage at point d changes from high level to low level. Next, tl? At 1lJ11, the voltage at point a falls below the lower threshold voltage V. Then,
The d-point voltage changes from low level to high level. The monostable multi-by-break 717 is triggered by the rising edge of this signal. L:+, j4 operates in the same way as tl, tl, and the monostable multi-high break 717 is retriggered at t4. Here, if the vehicle speed is v0 or more, the output of the monostable multi-by-break 717 is retriggered while remaining at a high level, and starts outputting the pulse width set by the capacitor 715 and resistor 716. Similarly, proceed to L5-t.

Therefore, during that time, the output of the monostable multi-bi break 717 at point g continues to maintain a high level. Therefore, the waveform at point f is a waveform obtained by ANDing the waveforms at points d and g, as shown in FIG. Next, the waveform at point k is the result of applying the waveform at point r to a low-pass filter composed of a resistor 719 and a capacitor 720. Since the waveform at point f has a small proportion of time at low level, it maintains almost high level at the point. Therefore, the comparator 726 compares the voltages at point 2 and point f, and outputs a low level.

Then, the transistor 728 is turned off, and the light emitting diode 730 is turned off.

When the air pressure inside the tire l decreases and becomes lower than a predetermined air pressure, the bellows 45 contracts and the magnet holding part 53 no longer presses the spherical magnet 55 against the cap 57, and the spherical magnet 55 becomes free. state. Therefore, when the tire rotates and centrifugal force is generated, the vibration of the tire causes the spherical magnet 55 to rotate half a rotation, the heavy S pole of the spherical magnet 55 faces the permanent magnet 60, and the light N pole of the spherical magnet 55
The pole faces the magnetic detection section 31 . Assuming that this state is reached at time t9 in FIG. 9, the output voltage of the magnetic detection section 31 that is input to point a next will be a signal with a polarity opposite to that in the normal state because the polarity of the magnet 55 has been reversed. Get out. T. Dea
The voltage at point falls below the lower threshold voltage V, and the voltage at point d remains at a high level. At t, the voltage at point a exceeds the upper threshold voltage v2, and the voltage at point d becomes low level. Similarly, at t1□+t13, the voltage at point d changes as shown. Here, since a trigger signal slightly longer than the period W is still input to the monostable multi-bi break 717, the output point g remains at a high level. Therefore, the signal at point f is obtained by ANDing points d and g, as shown in the figure. As described above, when the air pressure decreases, the ratio of high level to low level is reversed compared to when the signal at point f is normal, and the ratio of low level increases. Then, the voltage at point k gradually decreases and settles to a low level. When the voltage falls below two points at time t, the comparator 726 sets its output to high level, turns on the transistor 728, and lights up the light emitting diode 730. A drop in air pressure is detected through the operations described above. When the vehicle stops or the vehicle speed drops below a predetermined value with this air pressure reduced, the centrifugal force that causes the heavy S pole of the spherical magnet 55 to face the permanent magnet 60 side is The attractive force between the N pole of the spherical magnet 55 becomes larger, and the spherical magnet 55
As shown in FIG. 2, the S pole thereof is in a state facing the magnetic detection section 31 (this operation is hereinafter referred to as "magnet initialization operation"). FIG. 1O shows a case where the vehicle is traveling at a predetermined speed and the speed is reduced in order to stop the vehicle under normal air pressure conditions. When the vehicle speed is above a predetermined speed, the voltage at the point is greater than the predetermined value as shown on the left side of FIG. 10, and therefore the light emitting diode 730 does not light up either. As the vehicle speed gradually decreases from time t2°, a
The interval between signals from the magnetic detection unit 31 input to the points becomes longer. When the signal at point d rises at time tzl, monostable multivibrator 717 is retriggered. The time from when the vehicle speed decreases until the next signal is input from the magnetic detection section 31 is determined by the capacitor 715 and resistor 716 described above.
If the time is longer than the W set in
Next, by inputting a signal from the magnetic detection section 31,
The output point g of the monostable multivibrator 717 falls at tzz before point d rises at t23. At the same time, NAND is performed between point g and point m, which is the output of multi-by-break 733 triggered by the signal at point g.
The output of D gate 734 rises, turning on transistor 736. Since the vehicle speed is decreasing, the signals of the other axes also change in the same way, and the point h, which is connected to the point h' of the other axis, is short-circuited to GND by a transistor. Naturally, the transistor 736 also short-circuits a point corresponding to point h on the other axis to GND. When point d rises at t2.3, the monostable multi-bi break 717 is triggered and the output Q (point q) rises.

When the q point rises, the multivibrator 733 is triggered, and the output Q (m point) falls. The NAND outputs of point q and point m are held at high level, and transistor 736 remains on. From t23, the aforementioned capacitor 71
At time t24, when a time slightly longer than W set by 5 and resistor 716 has passed, point g falls, and when the time set by capacitor 731 and resistor 732 has passed from t23, fi
f) At lz5, point m rises. Here, the setting time of multi-by break 733 is monostable multi-by break 7
Set the time to be slightly longer than the time set in step 17. t24.
At t zs, transistor 736 remains on. The signal at point d rises again at t, and both multi-by-breaks 717 and 733 are triggered. The same process is repeated thereafter, but as the vehicle speed gradually decreases, the input cycle of the signal from the magnetic detection section 31 becomes longer. Since the high level time of the monostable multivibrator 717 is set by the capacitor 715 and the resistor 716 and is constant, the output at point f gradually changes the ratio of the high level time to the low level time (duty ratio). It's getting smaller. As the time that point f is at a low level gradually increases, the level of point k begins to drop. Finally, the voltage at txt falls below the threshold level (the voltage at the ffi point), and the output of the comparator 26 attempts to become high level. However, at that point, the level of the point corresponding to point h' on the other axis has fallen at t2□, similar to the h rubel of this wheel, and the level of the h rubel cannot rise. Therefore, transistor 728 also remains off, and light emitting diode 730 remains off.

FIG. 11 shows a case where the coil 65 of the magnetic detection section 31 is disconnected while the vehicle is traveling at a predetermined speed or higher under normal air pressure conditions. Until time t31, the device operates normally as described above, so the description thereof will be omitted. t
When the sensor is disconnected or malfunctions at 31, no further signals from the magnetic detection section 31 will be input to point a.

Then, the waveform shaping output point d maintains the state of tll as it is.

The monostable multi-bi break 717 is triggered by the rising edge of point d at time t3°, and thereafter no trigger signal is input. Therefore, at t:lz when the time set by the capacitor 715 and the resistor 716 has elapsed, the output point g and the output point f of the AND gate 718 fall. After that, the point f remains at a low level, so the level of the smoothing circuit output gradually decreases, and at t33, it falls below the threshold level J+/ (voltage at point f2).
The output of comparator 726 rises. At this time, the signals on the other axes are operating normally, and the point corresponding to point h' on the other axis is trying to maintain a high level. Therefore, as shown in the figure, point h rises, transistor 728 is turned on, and light emitting diode 730 is turned on.

As described above, in this circuit configuration, the indicator lamp is turned on only when the air pressure decreases at a set vehicle speed v0 or higher, and only when the sensor is disconnected at a set vehicle speed v0 or higher.

As explained above, according to this embodiment, the spherical magnet reverses only when the tire air pressure is below a predetermined value and the vehicle speed (tire rotational speed) is above a predetermined value, so that the change in magnetic flux is greatly reduced. can do. In addition, if the tire air pressure is above a predetermined value and the bellows is fixing the spherical magnet, the line connecting the center of the spherical magnet and the center of gravity is fixed along the direction of centrifugal force. Almost no rotational torque is generated when the spherical magnet attempts to rotate due to centrifugal force, and therefore the pressing force of the bellows can be reduced. In addition, since a permanent magnet is used as a holding means, when the tire air pressure decreases and the light emitting diode 730 is turned on to warn the driver and the vehicle is stopped, the initialization of the magnet is activated. The spherical magnet 55 is in the position when the air pressure is normal, and the driver only needs to inflate the tire, and the spherical magnet 55 is pressed and fixed by the magnet holding part 53 at the position where the air pressure is normal.
The spherical magnet 55 is reset to the correct position even if the driver does not reset the spherical magnet to its initial state. In addition, when the vehicle speed is higher than a predetermined value and the coil 6 of the magnetic detection section 31
5 is disconnected, the light emitting diode 730 can be turned on to warn the driver.

In the first embodiment described above, the magnet holding part serving as the fixing means is configured to unfix the spherical magnet when the tire air pressure decreases and becomes lower than the predetermined air pressure. However, the present invention is not limited to this. First, the magnet holding portion may press and fix the spherical magnet when the air pressure becomes lower than a predetermined value.

Further, in the above-mentioned first embodiment, a bellows having a magnet holding part is used as a fixing means to sandwich and fix the spherical magnet. A convex portion may be provided to fit a rod-shaped magnet holding portion provided at the tip of the bellows.

Furthermore, as the holding means, elastic rubber or a spring may be used instead of a permanent magnet.

Next, a second embodiment of the present invention will be described using FIGS. 12 to 15. In this second embodiment, a control circuit 31 converts the change in magnetism detected by the magnetic detection unit 31 in the first embodiment into an electrical signal and then processes the electrical signal.
This embodiment differs from the first embodiment only in that a microcomputer 190 is used in place of the main part. That is, the 12th
As shown in the figure, a waveform shaping circuit 10 in the first embodiment
A microcomputer 1'90 was provided between the computer 1 and the abnormality display@route 109. The operations of the waveform shaping circuit 101 and the abnormality display circuit 109 are the same as those in the first embodiment, so a description thereof will be omitted, and the operation of the microcomputer 190 will be explained using the flowchart shown in FIG.

Figure 15(a) shows the main flow that is the center of the operation, and in the middle of this main flow, Figure 15(b)
A timer overflow interrupt as shown in FIG. 15, a capture interrupt as shown in FIG. 15(C), and a conveyor interrupt as shown in FIG. 15(d) are performed. When the switch 38 is turned on and current is supplied from the power supply 36 to the control circuit 35, a power-on reset is activated in the microcomputer 190, and step 2
Execute the program from 00. First, step 202
Initializes the microcontroller's internal registers and memory, and initializes external devices. Next, in step 204, it is determined whether the vehicle speed is equal to or higher than a set value of 70. The value of the vehicle speed is determined in step 404, which will be described later. The set value Vo is the first
As in the embodiment, when the spherical magnet 55 is not fixed (free), the spherical magnet 55 is moved by the centrifugal force of the rotation of the wheel.
is set to the vehicle speed at the moment when the S pole is reversed (the heavy S pole is in a state facing the permanent magnet 60). Here, the vehicle speed is
. If it is smaller, an empty loop will be run to avoid false positives. The vehicle speed is ■. If the error flag has become larger, the process proceeds to step 206, where it is determined whether or not the error flag (described later) for each wheel is set. If there is a wheel with an error flag set, the process proceeds to step 206.
After the process proceeds to step 10 and the light emitting diode 730 of the corresponding wheel is turned on, the process returns to step 204. If it is determined in step 206 that the error flag is not sent,
Proceeding to step 208, the corresponding light emitting diode 730
After turning off the light, the process returns to step 204. When the vehicle is running, the magnetic detection unit 31 detects the air pressure shown in FIG.
4. The signal shown in FIG. 4(a) is generated. This signal is waveform-shaped by the waveform shaping circuit 101 as shown in FIG. 13Cb) or FIG.
A capture interrupt occurs every time a signal is input to the microcomputer 190. When this capture interrupt occurs,
Capture interrupt processing starting from step 400 shown in FIG. 15(C) is executed. Since the value of the free running timer at the time when the capture interrupt occurred in step 402 is set in the capture register, step 4
After reading the value in step 02 and storing it in a predetermined memory, the process proceeds to step 404.

In step 404, the vehicle speed is determined from the difference from the value in the capture register at the time of the previous capture interrupt.

Thereafter, the process proceeds to step 404, in which it is determined whether the vehicle speed is greater than or equal to v0, as in step 204, and if it is less than or equal to Vo, nothing is done, the interrupt processing is completed, and the process returns to the main flow. If the vehicle speed is greater than vo, step 4
Proceed to 08, and from the time the capture interrupt occurs, T5
Set so that a conveyor interrupt, which will be described later, will occur after seconds. T here.

The value of is longer than the time S from when the signal after waveform shaping rises to falling when the air pressure decreases at the lowest vehicle speed at which a decrease in air pressure can be detected, and when the air pressure is normal at the maximum vehicle speed, the value after waveform shaping is Set shorter than the pulse width W of the signal (corresponding to one rotation of the tire). For example, it is good to set it to about 20 G/sec.

When the conveyor interrupt occurs, conveyor interrupt processing starting from step 500 shown in FIG. 15(d) is executed. In step 502, as in step 2.4, it is determined whether the vehicle speed is 70 or higher; if it is determined to be less than vo, the conveyor interrupt process is completed and the process returns to the main flow.

If it is determined that the value is greater than or equal to V, the process proceeds to step 504 and the value (1 or 0) of the human-powered boat is read.

In the next step 506, it is determined whether or not the value of the human-powered boat is I. If it is determined that it is not 1, the error flag corresponding to the predetermined wheel is cleared in step 508, and the process returns to the main flow. If it is determined at 506 that the value of the input vote is 1, step 510
After proceeding to and setting the error flag, return to the main flow.

The free running timer mentioned above is generally about 16 bits in the case of an 8-bit CPU, and the timer clock is 1
In the case of microseconds, it is only possible to count up to about 65 milliseconds. The wheels of a car take about 370 milliseconds to make one revolution when traveling at 20 km/h, and if one attempts to calculate the vehicle speed from the interval T2 of the signals generated by the magnetic detection unit 3, it is impossible to measure it. Therefore, the free running timer reaches its maximum count and the timer overflow interrupt, which interrupts when an overflow occurs, causes 65ξ
Measures time longer than 1 second. As shown in FIG. 15(b), in the timer overflow interrupt starting at step 300, a counter is incremented at step 302. By reading the value of this counter at a predetermined timing, the number of overflows that have occurred between the previous time and the current time can be determined based on the difference between the value and the value read last time. By using the value of this counter along with the value of the capture register when calculating the vehicle speed in step 404 during the capture interrupt, it becomes possible to measure times of 65 milliseconds or more, making it possible to detect vehicle speeds down to low vehicle speeds. .

If the vehicle stops, the signal generation from the magnetic detection unit 31 also stops, and input capture interrupts no longer occur, so vehicle speed calculations are no longer performed, and the vehicle speed data is not updated and the previous data remains. It becomes tama-tama. Therefore, in step 304, it is determined whether or not there is a capture interruption within the time for one rotation of the vehicle speed when the vehicle speed is smaller than vo. If it is determined that there is a capture interrupt, the timer overflow interrupt is completed and the process returns to the main flow. If it is determined that there is no capture interrupt, the process proceeds to step 305, where it is determined whether a capture interrupt for another wheel occurs within the time for one wheel rotation when the vehicle speed is smaller than Vo. If it is determined that a capture interruption has not occurred in any other wheel, it is assumed that the vehicle is stopped, and the process proceeds to step 306, where the vehicle speed is set to 0, and then the process returns to the main flow. If it is determined in step 305 that a capture interruption has occurred in another wheel, it is presumed that the magnetic detection unit 31 in this wheel is disconnected, and the process proceeds to step 308. In step 308, the error flag of the wheel estimated to be broken is set, and then the process returns to the main flow. By doing so, the light emitting diode 730 lights up both when the tire air pressure decreases or when a failure occurs such as a sensor disconnection.

In this embodiment, the light emitting diode 730 remains lit even when the vehicle stops.

FIG. 16 shows a third embodiment of the present invention. Incidentally, the same parts as in the first embodiment are given the same reference numerals, and the explanation thereof will be omitted. In this embodiment, the permanent magnet 60 is the cap 57
In addition, in order to ensure the contraction operation of the bellows 45, a spring 71 and a spring receiver 73 are provided to bias the cap 57 and the spring receiver 73 in the left-right direction relative to each other. The concave portion provided in the bellows 45 engages with the convex portion of the bellows 45, and the spring receiver 73 pushes the bellows 45 in the right direction. The collar portion 47 of the bellows 45 is adhesively fixed to the casing 39 with an adhesive 75. 77 is a rubber plate for maintaining airtightness.

In this embodiment having the above structure, its operation is almost the same as in the first embodiment, except that when the air pressure inside the tire 1 decreases, the bellows portion 51 of the bellows 45 is reliably moved by the spring 71. The only difference is that it shrinks. The operation of the control circuit 35 is exactly the same as in the first embodiment.

As explained above, according to this embodiment, in addition to the effects of the first embodiment, when the air pressure in the tire drops below a predetermined pressure, the bellows portion 51 of the bellows 45 reliably contracts and becomes spherical. The magnet 55 becomes rotatable.

Next, a fourth embodiment of the present invention will be described using FIGS. 17 and 18. This embodiment differs in that the pressure detection section 29 described in the first embodiment is replaced with a pressure detection section 80. This pressure detection unit 80 has 8 disk-shaped magnets as shown in FIG. 18 instead of a spherical magnet as a centrifugal force responsive member. It is molded into a disk shape. A shut portion 8 is provided on the surface of the cap 84 facing the disc-shaped magnet 81.
5 is provided, and a disc-shaped magnet 8 is connected via a sliding bearing 86.
It is rotatably inserted into a hole 87 provided in the center of the holder. The casing 88 is the same as the first embodiment, and the bellows 89 also has the point that the tip of the magnet holding part 90 for fixing the disc-shaped magnet 81 has a flat shape that is most suitable for fixing the magnet. Otherwise, it is the same as the bellows explained in the first embodiment, and its explanation will be omitted. Although not shown in this embodiment, a permanent magnet is provided at a location facing the N pole of the disc-shaped magnet 81 on the rim side, similar to the first embodiment.

In this embodiment configured as described above, its operation is almost the same as in the first to third embodiments, but the following points are different. Since it is rotatably supported by the casing 85, even if the tire rotates at high speed, the disc-shaped magnet is not pressed against the casing 88 by centrifugal force, so it has an excellent effect of ensuring rotation when the air pressure decreases. Note that when the center of gravity of the conical magnet 82 in the disc-shaped magnet 81 is not at the center of the disc-shaped magnet 81 and the tire rotates with the tire air pressure reduced and centrifugal force is generated, the disc-shaped magnet 81 The effect that the light N pole faces the magnetic detection section in reverse is the same as in the first to third embodiments.

The operation of the control circuit 35 is also exactly the same as in the first to third embodiments.

Further, even if a spherical magnet is rotatably supported on the shaft in place of the disc-shaped magnet, the same effects as described above can be obtained.

A fifth embodiment is shown in FIGS. 19-21.

This is because the disk-shaped magnet 81'' of the fourth embodiment is provided with a protrusion 81''a for preventing rotation, and the cap 84'' is attached to the protrusion 81''.
This shape is designed to fit into the disc-shaped magnet 81' when the tire pressure is normal. Reference numeral 100 denotes a spring which moves the disc-shaped magnet 81' to the right to release the rotation prevention when the tire pressure is abnormally reduced.

In this way, the right end surface of the cap 84'' and the disk-shaped magnet 81
If sufficient frictional force cannot be obtained on the left end surface of the tire, a protrusion 81'a or the like may be used to prevent rotation when the tire pressure is normal. Note that the shape of the protrusion does not have to be the two-sided shape shown in FIG. 21, but can also be a quadrilateral, a triangle, or the like.

In addition, a bottle or the like to prevent rotation may be installed in a part.

Incidentally, in all the embodiments described above, not only the bellows but also the cap may be displaced to sandwich and fix the magnet.

Alternatively, the air from the tire may be guided directly into the case without providing the magnet holding part and the bellows, and the magnet may be directly pressed against the cap by this air pressure and fixed therebetween.

Moreover, it is of course possible to arrange the present detection device inside the tire.

Furthermore, instead of a light emitting diode, a buzzer or voice may be used as the notification means, or the information may be stored in a backed-up storage means such as RAM or EEFROM.

〔Effect of the invention〕

As explained above, according to the present invention, the excellent effect of increasing the change in magnetic flux with a simple configuration and facilitating detection is achieved. Further, there is an effect that the fixing force of the fixing means can be reduced, and an effect that the centrifugal force responsive member can be reset by the holding means.

[Brief explanation of drawings]

1 to 6 are cross-sectional views showing a first embodiment of the present invention,
FIG. 7 is a circuit diagram showing the control circuit of the above embodiment, FIGS. 8 to 11 are operation explanatory diagrams showing the operation of the control circuit, and FIG.
15 to 15 are circuit diagrams, operation explanatory diagrams, and flow charts showing a second embodiment of the present invention, FIG. 16 is a sectional view showing a third embodiment of the present invention, and FIGS. 17 and 18 are diagrams showing the present invention. FIG. 19 is a sectional view showing a fifth embodiment of the present invention, and FIGS. 20 and 21 are perspective views showing the fifth embodiment. Fig. 13 Fig. 4 00 00 (b) Fig. 5 400 (C) Fig. 7 Fig. 1 2 Fig. 8 Fig. F33'li' Fig. 9 Fig. 20 Fig. 21

Claims (3)

[Claims] (1) A centrifugal force responsive member that has a magnetic material and whose position can be rotated by the centrifugal force generated by the rotation of the tire, and whose center of rotation and center of gravity are different; a fixing means for switching between fixing and non-fixing of the centrifugal force responsive member; Holding the centrifugal force responsive member in a state in which a line connecting the center and the center of gravity is along the direction of the centrifugal force, and a direction of a vector from the center to the center of gravity is opposite to the direction of the centrifugal force. means, a detection means for detecting the position of the magnetic body, and a determination means for determining the state of the air pressure of the tire based on the detection result of the detection means, wherein the fixing means holds the centrifugal force responsive member. When the centrifugal force is equal to or greater than the predetermined value in the unfixed state, the direction of the vector from the center toward the center of gravity against the holding force of the centrifugal force responsive member by the holding means is the direction of the centrifugal force. A tire pressure detection device characterized by following. (2) The tire air pressure detection device according to claim 1, wherein at least a portion of the centrifugal force response member is rotatably supported by a pivot means. (3) The tire air pressure detection device according to claim 1 or 2, wherein the holding means is a magnet.