JPH0328007A - Tire air pressure detecting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a tire air pressure sensor for detecting tire air pressure.
As in Publication No. 02, if the driver is notified when the tire air pressure falls below a predetermined pressure and the vehicle then stops to replenish the air, the plunger and rotating shaft can be secured. There is known a tire air pressure detection device that automatically returns the magnetic member.

[Problem to be solved by the invention]

However, in this conventional tire pressure detection device,
Spring for automatic return. stopper. This had the problem of requiring a return means such as an unbalanced weight, making the structure complicated. The present invention has been made in view of the above problems, and it is an object of the present invention to provide a tire pressure detection device that does not require a return means and can automatically return to the initial state when air is replenished.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a movable member that has a magnetic material and is movable by centrifugal force or vibration, and is provided on a tire, and a movable member that is provided on a tire, and a tire that has a tire air pressure. a fixing means for switching between fixing and non-fixing of the movable member according to the fixed state; a detecting means for detecting the magnetic flux of the magnetic body; and a determining means for determining whether the magnetic flux detected by the detecting means is regular. We are planning to prepare.

[Effect]

In the tire air pressure detection device configured as described above, the fixing means switches between fixing and non-fixing the movable member depending on the tire air pressure. When the fixing means fixes the movable member, the position of the magnetic body in the movable member does not change, and therefore the magnetic flux detected by the detecting means is determined to be regular by the determining means.

When the fixing means does not fix the movable member, the movable member moves due to the centrifugal force or vibration of the tire, and therefore the position of the magnetic body changes, and the magnetic flux detected by the detection means is determined by the determination means. judged to be unsuitable.

[Example] The present invention will be described below with reference to 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 axle 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 with a nut l5. The bearing housing 17 and the cover plate 19 are fixed to the hub 21 with 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 connected to the bolt 28 by a bolt 28.
The other end (not shown) of the suspension arm 27 is supported by the vehicle body side. Reference numeral 29 denotes a pressure detection section which is a main part of this embodiment, and its details will be described later. Reference numeral 31 denotes a magnetic detection section as a detection means, which detects magnetism in the pressure detection section, converts it into an electric signal, and sends the electric signal to a control circuit 35 as a determination means via a wire harness 33. 36 is a battery, and 38 is a switch. In FIG. 1, a tire 1, a rim 3, a wheel nut 5, a wheel axle 7, a brake drum 9. Plate 11, nut 15, pressure detection part 2
9 rotates while the vehicle is running, but the other parts are supported by the vehicle body and do 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.

The casing 39 is screwed onto the rim 3. 41 is an O-ring, 43 is a gasket, and the flange 47 of the bellows 45 as a fixing means is screwed onto the casing S9.
The O-ring 41 and the gasket 43 are press-fixed to the rim 3, doubly preventing the air from leaking outside.

The bellows 45 as a fixing means is made of metal and expands and contracts depending on the air pressure inside the tire 1, and its detailed diagram is shown in FIGS. 3 and 4. The bellows 45 has a collar 47
．． The bellows part 51 and the magnet holding part 53 are welded together, 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 movable member is arranged in a space 59 formed by a cap 57 and a casing 39 made of a non-magnetic material such as aluminum. cap 5
7 is press-fitted and fixed to the casing 39. Spherical magnet 5
5 is a magnet 55a molded or shaped with resin 55b. Moreover, the magnet holding part 53 has a conical recess at its tip, and 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. The space 59 in FIG. 2 is larger than the spherical magnet 55 and has a gap that allows the spherical magnet 55 to rotate freely when the magnet holding part 53 is not holding the spherical magnet 55. The portion where the casing 39 contacts the spherical magnet 55 (57a, 39a in FIG.
) has a conical shape.

FIG. 5 shows a detailed configuration of the magnetic detection section 31 as a detection means. In FIG. 5, 6l 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 includes an insulated conductive wire connected to a magnetic material 63 via a resin bobbin 67.
Both ends of the conductive wire are crimped together with the two wire harnesses 33 by metal crimps 69, and each wire harness is electrically connected to the l wire harnesses. With the above structure, the magnetic detection section 31 can detect changes in external magnetism and convert them into electrical signals.

Next, the structure of the control circuit 35 as the determination means will be explained using FIG. 6. In FIG. 6, input terminals a and b of the waveform shaping circuit 101
The wire harness 33 connected to the coil 65 is connected to. The voltage at the input terminal b is controlled by the circuit of the resistor 704 and the diode 705, so that the forward voltage drop of the semiconductor pn junction is approximately 0.6 to 0. Fixed at 7V. 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 1v).
When , point b is 0. 6 V, point a will be 1.6 V). The voltages at points a and b are applied to resistors 706 and 7, respectively.
08 to the converter 714 input terminal. The comparator 714 sets the output terminal to a no level when the voltage of the input terminal is lower than the voltage 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, resistance 710
This adds hysteresis characteristics to the comparison voltage.
It has a structure that is resistant to noise. The resistor 711 and capacitor 712 have the function of changing the value of this hysteresis. As shown in FIG. 7, the moment the input voltage changes and falls below the lower threshold voltage V, at point P, the lower threshold voltage V, changes, and eventually the resistor 710
statically settles at the upper threshold voltage Vt that appears as the effect of Next, although the polarity is opposite at point q, the upper threshold voltage v2 similarly changes, making it difficult to be affected even if noise is superimposed on the input signal. Zener diode 707 is connected to converter 71
The input terminal is protected by clipping it at a predetermined level to prevent excessive voltage from being input to the input terminal.

The power supply circuit 1l1 connects the battery 36 via the switch 38.
Even if the voltage varies, a constant voltage is supplied to the control circuit 35 using a three-terminal regulator 737 and capacitors 738 and 739 for noise removal.

Next, the operation of this embodiment having the above structure 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, when the tire rotates and the spherical magnet 55 passes the magnetic detection section 31, a voltage of a certain magnitude is generated in the coil 65 of the magnetic detection section 31.

This voltage is shaped by a waveform shaping circuit 101, the signal is input to a microcomputer 190, and after predetermined calculation processing described below is performed, a signal is sent to an abnormality display circuit 109 according to the calculation result. transistor 7
28 is turned on and off to turn on and off the light emitting diode 730.

Next, the operation of the microcomputer 190 will be explained using the flowchart shown in FIG.

FIG. 8(a) shows the main flow which is the main part of the operation, and in the middle of this main flow, the timer overflow interrupt shown in FIG. 8(b), the capture interrupt shown in FIG. 8(C), The conveyor interruption shown in FIG. 8(d) is performed. When the switch 38 is turned on and current is supplied from the power supply 36 to the control circuit 35, the microcomputer 19
Power-on reset is activated at 0, and the program is executed from step 200. First, in step 202, the registers and memory inside the microcomputer and the external devices are initialized. Next, in step 204, the vehicle speed or the set value ■
. Determine whether it is greater than or equal to. The value of the vehicle speed is determined in step 404, which will be described later. The set value v0 is the vehicle speed at which an output voltage higher than the threshold voltage V I + V * in FIG. 7 is generated. Here, if the vehicle speed is smaller than v0, an empty loop will be run to avoid misjudgment. If the vehicle speed becomes greater than v0, the process proceeds to step 206, where an error flag (described later) for each wheel is set.
If there is a wheel with an error flag set, the process proceeds to step 210, lights up the light emitting diode 730 of the corresponding wheel, and then returns to step 204. If it is determined in step 206 that the error flag is not set, the process proceeds to step 208 to turn off the corresponding light emitting diode 730, and then returns to step 204. When the vehicle is running, the magnetic detection unit 31 generates a regular (non-random) signal when the air pressure is normal, and an irregular (random) signal when the air pressure is abnormal (decreased). Waveform shaping circuit 1
The signal waveform-shaped by 01 is manually input to the real-time I/O and manual port of the microcomputer 190, and a capture interrupt is generated every time the signal is input to the microcomputer 190.

When this capture interrupt occurs, capture interrupt processing starting from step 400 shown in FIG. 8(C) is executed. Since the value of the free running timer at the time when the capture interrupt occurred is set in the capture register in step 402, the value is read in step 402 and stored in a predetermined memory, and then 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 406, 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 v0, nothing is done, the interrupt process is ended, and the process returns to the main flow. When the vehicle speed is greater than v0, the process proceeds to step 408, and is set so that a conveyor interrupt, which will be described later, occurs T seconds after the capture interrupt occurs. Here, the value of T is longer than the time S for the signal after waveform shaping to rise and fall when the air pressure decreases at the minimum vehicle speed v0 at which an air pressure drop can be detected, and when the air pressure is normal at the maximum vehicle speed. Set it shorter than the pulse width W of the signal after waveform shaping (equivalent to one rotation of the tire). For example, it is preferable to set it to about 20ξ li seconds.

When the conveyor interrupt occurs, conveyor interrupt processing starting from step 500 shown in FIG. 8(d) is executed.
In step 502, similarly to step 204, the vehicle speed is V.
. It is determined whether or not the value is greater than or equal to v0, and if it is determined that it is smaller than v0, this conveyor interrupt processing is ended and the process returns to the main flow.

If it is determined that the value is v0 or more, the process advances to step 504 and reads the input vote value (1 or O).

In the next step 506, it is determined whether the current interrupt is the first interrupt, and if it is determined that it is the lth interrupt, the determination result is YES and the process proceeds to step 522.
After the input port value read in step 504 is recorded in the microcomputer's internal memory, the interrupt processing is ended and the process returns to the main flow.

If it is determined in step 506 that the current interruption is not the l-th interruption, the determination result is NO and the process proceeds to step 508. In step 508, the input value in step 522 during the previous conveyor interrupt processing is compared with the value read in step 504 during the current conveyor interrupt processing,
If the input values this time and the previous time are different, the signal sent from the magnetic detection unit 31 is random (the bellows 45 is connected to the spherical magnet 5).
The spherical magnet 55 is not fixed, and the spherical magnet 55 is damaged due to vehicle vibration, etc.
is moving freely), the determination result is NO and the process proceeds to step 512. In step 512, an error flag indicating that the tire air pressure has decreased is set, and then the process proceeds to step 514, where the value of a conveyor interrupt counter to be described later is cleared, and the process proceeds to step 522.

In step 508, the human power value in step 522 during the previous conveyor interrupt processing is compared with the value read in step 504 during the current conveyor interrupt processing, and if the current and previous human power values are equal, Since the signal sent from the magnetic detection unit 31 is non-random (the bellows 45 fixes the spherical magnet 55, and the spherical magnet 55 cannot move freely), the determination result is YES, and the process proceeds to step 516.
Proceed to. In step 516, the conveyor interrupt counter counts the number of conveyor interrupts, and it is determined whether the counter value is greater than 10. If the counter value is 10 or less, the determination result is No. Step 51
The process advances to step 8, increments the value of the conveyor interrupt counter by one, and advances to step 522. If it is determined in step 516 that the value of the conveyor interrupt counter is greater than 10, the non-random signal has been detected 11 or more times in a row, and therefore the tire pressure is normal, and the determination result is YES. Proceed to step 520. Step 520
Then, after clearing the error flag if it is set, the process proceeds to step 522. In step 522, the current input value read in step 504 is stored in place of the previous stored value, and then the process returns 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 60 milliseconds. The wheels of a car take about 370 milliseconds to make one revolution when traveling at 20 km/h, and when trying to calculate the vehicle speed from K T z during the signal generated by the magnetic detection unit 31,
It cannot be measured. Therefore, the free-running timer reaches its maximum count and the timer overflow interrupt, which interrupts when an overflow occurs, causes 6
Measure a time of 5 seconds or more. As shown in FIG. 8(b), in the timer overflow interrupt starting at step 300, a counter is incremented at step 302. If we read the value of this counter at a given timing, we get
The difference between the value and the last time it was read tells you how many times overflow has occurred between the last time and this 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 is possible to measure a time of 65 seconds or more.
Detection is possible 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 will remain. Therefore, in step 304, the vehicle speed is ■. It is determined whether there is a capture interruption within the time it takes for the vehicle speed to rotate by l when the vehicle speed is smaller. If it is determined that there is a capture interrupt, the timer overflow interrupt is immediately terminated 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 the capture interrupt for the other wheels is determined to be the vehicle speed ■. It is determined whether the capture interrupt has occurred within the time for one rotation of the smaller wheel, and if it is determined that the capture interrupt has not occurred in other wheels, it is estimated that the vehicle is stopped, After proceeding to step 306 and setting the vehicle speed to 0, 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 this, both in the event of a decrease in tire pressure or a malfunction such as a sensor disconnection,
The light emitting diode 730 lights up. As explained above, in this embodiment, when the air pressure of the tire decreases, the magnet holding part 53 and the cap 57 no longer fix the spherical magnet 55, and the spherical magnet 55 randomly moves due to centrifugal force and vibrations of the vehicle and tires. When the driver makes a movement, the magnetic detection unit 31 detects this and determines that the air pressure has decreased.On the other hand, when the driver subsequently injects air into the tire, the spherical magnet 55 moves at an arbitrary position (no matter where the south pole points). When the vehicle is clamped and fixed by the magnet holding part 53 and the cap 57 (without knowing whether the vehicle is in the position) and the vehicle is driven when the air pressure returns to normal, the signal from the spherical magnet 55 at the position shown in FIG. 2 is no longer the same. Even in this case, when the air pressure is normal and the spherical magnet 55 is sandwiched and fixed between the magnet holding part 53 and the cap 57, the magnetic signal detected by the magnetic detection part 31 remains constant. can be,
Since it is non-random, it is possible to detect whether the tire pressure is normal or not. In this embodiment, when the air pressure decreases, the fixation of the spherical magnet 55 by the bellows 45 is released, and the spherical magnet 55 moves randomly, which is detected. Often, when the tire air pressure is normal, the bellows 45 leaves the spherical magnet 55 unfixed so that it can move randomly, and when the tire air pressure decreases, the spherical magnet is fixed and a non-random signal is detected. good.

Next, a second embodiment of the present invention will be explained using FIGS. 9 and 10. In FIG. 9, 81 is a disc-shaped magnet, and as shown in FIG. 10, it has a shaft hole 87 in its center. Further, the disc-shaped magnet 81 is molded or shaped with resin 82. 84 is a cap, 85 is a shaft portion, 86 is a bearing, 88 is a casing, 89 is a bellows, and 90 is a magnet holding portion.As in the first embodiment, the bellows 89 expands and contracts in accordance with the tire air pressure. Random or non-random signals are detected by switching between fixed and non-fixed plate magnets.

In this embodiment, the shaft portion 85, the bearing 86, the shaft six 87
Therefore, when the disc-shaped magnet 81 is not fixed, it is possible to prevent the disc-shaped magnet 81 from being pressed against the casing 88 and not moving due to the centrifugal force generated by the rotation of the tire. .

〔Effect of the invention〕

As explained above, according to the present invention, the tire air pressure is detected depending on whether the magnetic flux corresponding to the state of the movable member is regular or not. Therefore, when the tire is replenished with air, the position of the movable member is fixed. This has an excellent effect in that the judgment result of the judgment means can be automatically returned to the initial state without returning to the position. (Fixing means), 55... Spherical magnet (movable member), 55
a... Permanent magnet (magnetic material).

Claims (1)

[Scope of Claims] A movable member provided on a tire that includes a magnetic material and is movable by centrifugal force or vibration; and a fixing means that switches between fixing and non-fixing the movable member depending on the air pressure of the tire. A tire air pressure detection device comprising: a detection means for detecting the magnetic flux of the magnetic body; and a determination means for determining whether the magnetic flux detected by the detection means is regular.