JPS5926029A - Method and device for detecting change of expansion pressure of tire - 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 The present invention relates to an apparatus for automatically detecting deviations in tire inflation pressure from a desired value.

It is important to keep car tires properly inflated. When a car's tires are under-inflated, they create greater resistance and thus reduce the fuel economy obtained by the car. Also, under-inflated tires are not properly inflated. This leads to a reduction in the useful life of the tire.For these reasons, tire pressure must be checked on a regular basis to ensure correct tire inflation.

In the past, the inflation pressure of automobile tires was tested by stopping the vehicle and attaching a tire pressure gauge to each tire in turn. However, motor vehicle operators may not be aware of the disadvantages of incomplete tire inflation, may not have learned the procedures used to test tire inflation, or may not be able to perform regular tire inflation tests. People are often sloppy in performing this step, simply because they are too busy or forget. As a result, many automobiles are operated with incompletely inflated tires. It would be desirable to provide an automatic device for monitoring tire pressure so that a motor vehicle operator knows when the vehicle's tires need to be re-inflated.

Automatic tire inflation monitoring devices can also help detect flat tires. Flat tire detection has always been a trivial task, since flat tires have an immediate and significant effect on the rolling and rolling characteristics of a vehicle. But this is not necessarily the case. A new type of tire called a "run-flat" tire is now being seen being used more and more on cars.

1 Run Flat" tires are designed to support the vehicle even in the event of a significant loss of tire pressure, thereby allowing the vehicle to be driven for short distances without changing the tires. Unlike conventional tire flats, "run-flat" tire flats may not be easily recognized by motorists, so automatic devices that alert drivers to flats are helpful.

Fluid pressure (usually monitored by an in-situ pressure sensor). Communication between the pressure sensor and other non-rotating equipment is not easily accomplished. Therefore, it would be desirable if a tire inflation warning system could be devised that did not require an interface to the tire.

The present invention provides a device for automatically monitoring tire inflation (E-force) by detecting changes in the elasticity of tires installed on a vehicle. The frequency spectrum of the signal provided by each accelerometer includes a pronounced low frequency peak, the location of which is influenced by the tire elasticity and therefore by the tire inflation pressure. The signal provided by the acceleration cycle is then processed to identify the location of low frequency peaks that are correlated to changes in tire inflation pressure.

Since the tire inflation pressure monitoring device does not require an on-site pressure sensor, there is no need to combine electrical signals to and from the rotating tire.

The above and other objects and advantages of the present invention will become more readily apparent from the following detailed description and description with reference to the accompanying drawings.

FIG. 1 is a simplified 111-section elevational view of one form of a support system for a front tire of a conventional passenger vehicle.

As shown in this figure, a tire 10 is supported by a spindle 12. The spindle 12 is in turn connected to the upper control arm 1
4 and a ball joint attached by a portion of the lower control arm 16.

Opposite ends of upper control arm 14 and lower control arm 160 are pivotally mounted to the vehicle frame (not shown in FIG. 1). The frame, spindle, and upper and lower control arms form a conventional four-bar linkage.

The car has a coil spring 18 installed coaxially with the shock absorber 20.
and is knocked onto the lower control arm 16. As the tire 10 travels along an uneven or uneven road, the wheel 10 moves up and down against the bias of the spring 18. Shock absorber 20 damps spring-induced vibrations.

The frequency distribution of the acceleration experienced by the wheel 10 during normal road driving is shown in FIG. As seen in Figure 2, the support equipment' frequency response 7]? nce represents the published peak (PK) between frequencies 10tlz and 2011z1
-0 Technical Document 1 e.g. SAE Report 11 No. 680.408
As written in the number, the position of V-ri is.

It depends in part on the effective elasticity of the tire 10, which in turn depends on the inflation pressure of the tire 10. As is commonly explained in SAE Reports, the frequency of the support resonance that creates PK is a function of the square root of the tire elasticity. Therefore, if the elasticity of the tire decreases (as when the inflation pressure decreases), the resonant frequency should also decrease.

In accordance with the present invention, the relationship between inflation pressure and resonant frequency is used in a device for detecting changes in inflation pressure of conventional automobile tires. General equipment direct component parts are listed in the 6th section.
As shown in the figure. In Fig.

In , automobile 30 is shown as including four tires 32, 34, 36 and 38. Next to each tire is the respective acceleration it 40.42°44 and 4
6 is installed. Each accelerometer is mounted on a supporting component adjacent to the tire in a position and orientation such that it detects the vertical acceleration experienced by the corresponding tire. The output signal provided by 46 is applied to a microcomputer-controlled signal processor 48. A speed sensor 50 and a temperature sensor 52 also provide signals to the signal processor 48. monitor the acceleration, determine the low frequency response of each tire, and
It is determined from the resonant frequency whether the inflation pressure in any one of the tires has changed beyond the permissible limit. Although the detection of low tire pressure is discussed and explained below, the method disclosed herein may also be used to detect excessive tire pressure.

Processor 48 provides an output signal to a control display panel 54 which is open for viewing by the driver of the motor vehicle. Panel 54 includes four lights, one associated with each of the four tires. When the signal processor 48 determines that the inflatable upper blade on one or more of the tires is below the desired value, a corresponding light on the control display panel 54 is illuminated.

Processor 48 may also activate an audible alarm associated with panel 54. Panel 54 also includes manual switches used for calibrating the device. Each time the driver inflates or confirms the inflation level of the car's four tires, he depresses the calibration switch. This tells the microcomputer that the inflation pressure is now correct, and the computer then calculates the resonant frequencies of the four tires and uses the resonant frequencies as a reference that is later compared to the tire setpoint. Calibration of the device in this manner is desirable because the magnitude of the resonant peak produced by a properly inflated tire can change over time due to wear of the shock absorber, aging of the bushings associated with the support system, etc. Because there is.

Tire wear can also affect the location of resonance peaks because the elasticity of a tire can change as the tire wears.

The device operates at
It operates in two different φ modes. The two different mors are obtained because the tire temperature affects the elasticity of the tire. Thus, the change in the resonant frequency of a given one of the four tires (ma).

Changes in the tire's low-temperature inflation pressure (may be caused by changes in temperature).

In order to overcome the above-mentioned problems, some device must be provided to measure the temperature of the tire at the time the frequency measurement is taken. Unfortunately, the only direct way to measure tire temperature is to include a temperature sensor on the tire itself. However, attaching a sensor to a tire requires combining electrical signals to and from the rotating tire, a problem that is sought to be avoided by the present invention. Tire temperature is expressed as 76-tangential l''!, t
Since the problem must be avoided, the method of deduction is used. It is known that if a car is stationary and unused for a period of time, the tires will reach ambient temperature. Therefore, if a temperature sensor is included to measure the ambient temperature, its signal (also represents the tire temperature for a period of time after the vehicle begins to float).

The first activation of the device occurs during the time when the vehicle is first driven after being idle for more than a predetermined period of time, e.g. 1 o'clock (d1 or more). The resonant frequency identified by processor 48 is normalized according to ambient temperature and then compared against a resonant frequency reference obtained after the operator last pressed the calibration button on control panel 54.

After a car has been driven for a period of time, the tires are probably no longer at ambient temperature. Therefore normalization of the resonant frequency by one ambient temperature may no longer be accurate. The device therefore switches to the second mode of operation. In the second mode of operation, the measured resonant frequency is no longer compared to the resonant frequency reference used in the first mode of operation. Instead, the resonant frequencies of tires on opposite sides of the stop are compared. Thus, for example, left front tire 3
The resonant frequency of 2 is compared to the resonant frequency of the right front tire 34, while the co-I length frequency of the left rear tire 36 is compared to the resonant frequency of the right rear tire 38. Corresponding tires on opposite sides of the vehicle are mounted in a similar manner and are subjected to virtually the same environment. -Thus, if the pressure of both tires remains the same, the change in the resonance frequency of one tire is fl! !
It is expressed by the change in the tire's resonant frequency. The difference in resonant frequencies is used to identify incompletely inflated tires.

4 is a more detailed block diagram of the individual components of the housing shown in FIG. 6; FIG. As shown in FIG. 4, the output of left front (LF) acceleration/pulling 40 is directed to signal processing device 62. The signal processing device 62 performs conversion amplification and possibly 1
It includes a low pass filter with a cutoff frequency of Kllz and an instrumentation amplifier. A processing device 620 output 1c is directed to filter panchromator 4. The purpose of the filter panchromator 4 is to identify the signal power of each of a plurality of individual frequency bands so as to provide information from which the location of the frequency peak PK of FIG. 2 can be determined. In the embodiment shown in FIG. 4, the filter panchromator 4 includes four bandpass filters 66.
68, 70 and 72, and their respective inputs (or outputs of the signal processing device 62) are set to H.

Each bandpass filter is designed to pass only a very narrow range of frequencies, so that the output (σ) essentially represents only a single frequency component of the accelerometer's output signal. The center frequencies of the band characteristics of the four filters 66, 68, 70, 6 and 72 are selected to correspond to four individual frequencies within the frequency range in which the peaks affected by tire elasticity are expected to occur. There is. By measuring the output power supplied by the four filters, the second
The amplitude of the frequency spectrum in the figure is defined at four separate points near the peak PK, and the position of the peak can be determined.

If it is desired to depict a frequency spectrum with greater (or smaller) resolution, a number of filters other than four may be used.

A method is used which eliminates the need for individual filters at all.

The frequency spectrum is assembled by using a fast Fourier transform (FFT) algorithm that processes the signal in real time or in the delay regime, for example. Many FFT systems, hardware and/or software, are known in the art and readily used to process accelerometer output signals.

Filter panchromator 4 of FIG. 4 also includes 14 peak rectifier and integrator circuits 74, 76, 78 and 80, each of whose inputs are connected to the output of one respectively of four voice range filters 66.6B, 70 and 72. Each arc rectifier and integrator circuit peak rectifies the output signal provided by the corresponding bandpass filter and then derives the -r integral representing the average power of the corresponding frequency component of the accelerometer output signal. It functions to integrate the composite DC signal that changes.

The integrators associated with circuits 74, 76, 78 and 80 are reset each time a new data acquisition time begins.

Each circuit 74, 76, 78 and 81] (including the "reset" input line;
It is connected in parallel to the single reset line 82 of the illustrated embodiment. When the signal provided along reset line 82 is at a high logic level, four circuits 74, 76
．． The integrator in combination with 78 and 80 is reset to zero and remains reset until a high logic level signal is removed. When the reset signal is a low logic level, the integrator is activated and the integrator The g-peak rectified signal is integrated.

The outputs of the other six acceleration positions 42, 44 and 46 are in each case transmitted to the respective signal processors 84, 86 and 8.
8 and filter banks 90, 92 and 94. The outputs of each of the four peak rectifying and integrating circuits combined with each of the four filter panchromators 4.90° 92 and 94 are combined into a multiplexer 9.
6 is directed to the corresponding input. The multiplexer 96 is
It can be thought of as a rotary switch that can be controlled to connect any given one of its input lines to its single output line 98.

The multiplexer 96 is made by microcomputer 2 and user 100.
controlled by Microcomputer 100 can take any convenient form. It consists of a microprocessor, a read-only memory (ROM) containing a fixed program to be executed by the microprocessor, and R
A random access memory ff (RAM) should be used by the microprocessor to temporarily store data during the execution of the OM program, and at least two timers controlled by the microprocessor (hereinafter referred to as timer A and (referred to as timer B) and input/output terminals for interface connection between the microprocessor and external circuits. The microcomputer elements mentioned above are of a conventional type, but they are connected to a working microcomputer. Therefore, in order to simplify iiR,
The hardware elements of the microcomputer will not be described in further detail. The software (program) executed by the microcomputer will be explained below with reference to FIGS. 5 to 8.

Generally, a microcomputer reads the output signals provided by a plurality of filter banks and processes the combined data to determine the inflation status of the four tires. At the end of a given signal integration time 1), the microcomputer 100 provides a control signal to the multiplexer 496 so that a selected one of the filter bank output lines is automatically is connected to the output line 98 of the analog-to-digital (A/'D) converter 1020 input. The microcomputer 2 user 100 then reads the digital output signal provided by the A/D converter 1[]2 and increments the control signal provided to multiplexer #96, thus instructing the next sequential filter bank. The output line of is connected to the A/D converter 1020 input. Thus, the microcomputer 100 has %4 filter panchromatic 4
．． 90. A digital signal corresponding to the amplitude of the signal provided to the output of the plurality of integrators aligned with 92 and 94 is read out. After reading the amplitude of the signal accumulated by each integrator, microcomputer 10o provides a reset signal on reset line 82, thereby resetting all '1' of the integrators to the zero state.

Microcomputer 2 user 100 then processes the newly obtained digital information to determine from the 4v] information whether the inflation pressure in one or more tires is low.

The microcomputer 100 has a light array 104 combined with the control panel 54! ti control. The light array includes four lamps 106, 108, 110 and 112, each associated with a corresponding one of the four wheels.

As per σ) above, when the microcomputer 100 determines that a low inflation condition exists in one or more of the tires, it provides a control signal to the lamp array 104 so that the corresponding lamp is illuminated.

An audible alarm may also be sounded.

Control panel 54 also includes a calibration switch 114 that is depressed by the operator each time he reinflates the tire to the appropriate cold inflation pressure. The turns acquired by the microcomputer 100 from the four filter panchromators 4, 90, 92t6 and 94 are then stored in RAM and used thereafter as reference data to be compared with future acquired data. Microcomputer 1 until the time taken as a reference is obtained and stored in RAM.
00 has 4 lamps 106, 108, 110 and 11
Turn on and off the lights all at once.

Power is constantly applied to at least one of the microcomputer's internal timers (timer B).

Power is also constantly applied to the random access memory portion of the microcomputer so that the data stored in the memory portion is not lost each time the ignition switch is turned off.

Control device 48 also includes a signal processing device 116 that processes the output of temperature sensor 52. The output of signal processor 116 is an analog signal with an amplitude representative of the temperature of the vehicle.

The output signal is applied to the corresponding input line of multiplexer 96 and read by the microcomputer as part of its normal program operation.

Speed sensor 50 is generally a tachometer that produces a pulse train with a pulse repetition rate that is directly proportional to the rotational speed of the mechanical element connected to it. The tachometer is usually attached to the odometer cable, but may alternatively be connected to any other suitable element of the vehicle whose rotational speed is indicative of the speed of the vehicle. The output signal provided by speed sensor 50 is applied directly to a series input terminal of microcomputer 100.

FIG. 5 is a step-by-step diagram of the entire operation performed by the microcomputer 1 (JO).

Whenever the vehicle's ignition switch is turned on, power is supplied to the microcomputer unit 48 shown in FIG. As mentioned above, 'tlf, power is 1 french] A and at least 1 of the timers combined with the microcomputer.
constantly added to the pieces. When power is applied to the microcomputer, the microcomputer proceeds to an initialization routine in which it sets all internal registers to appropriate initial states and generally performs internal and external housekeeping operations. Next, proceeding to step 202, where it is connected to the reset line 82.
Since a reset signal is added to the filter panchromatic 4.
90.92 and 94 and i; [1 All A-responsible dividers that are combined are reset. Internal timer A is also reset at this time, after which this timer begins to count the integral time. The microcomputer then proceeds to step 204 where it connects input line 116 via calibration switch 114.
Examine the logical signals applied to.

If the logic signal derived from the calibration switch is at a low logic level, the calibration button is pressed down by the driver.

The microcomputer then proceeds to step 206. Stage 2
At 06, the calibration flag CAL is reset to the zero state and the four lamps associated with the light array 104 are set to flash in unison. The microcomputer then returns to step 2024, and the microcomputer then returns to step 202 until the calibration button is released.
．． Repeat the cycle to perform steps 204 and 206.

Once the calibration button is released, the logic signal on input line 116 moves to a high logic level. The microcomputer recognizes a high logic level at step 204 and jumps out of the loop to step 208. In step 208, the speed of the vehicle is determined by measuring the time interval between two consecutive pulses at the output of speed sensor 50. This measurement can be performed at any time by conventional hardware or software methods. At that time, the speed of the car is, for example, 16.1 kn/h (I 0 m) and 40.25 kn+ per hour!
The reset value can be any value between 1 and 25 meters. If the speed of the vehicle is less than the limit, the flow of 70 logs proceeds to step 210 where timer A is stopped. Since timer A is stopped, the time when the car is running at a speed lower than speed ■1 is stopped by timer A.
It is not included in the integration time measured by . The timer is stopped when the car's speed is low because normally a small amount of vertical acceleration occurs then and adds a little to the integral accumulated by the filter bank. Step 210
After stopping the timer at , the program proceeds to step 212 where the speed of the vehicle is compared to a second limit value, which in this case is zero. If the speed of the car is zero (i.e. the car is stopped), the microcomputer goes to stage 2.
14, which is shown as "Mode Timing Procedure" in FIG.

The mode timing procedure is detailed in FIGS. 6A and 6B and described below. This procedure essentially measures the length of time the car is stopped. If the car is stopped for longer than a preselected time, it is assumed that the tires have cooled to ambient temperature5.
The signal provided by the temperature sensor therefore appears to be an accurate representation of the tire temperature. If the stop time is less than this selected time, no such inference is made regarding tire temperature. Thus, the length of time the car is stopped determines what mode the device will be in when the car starts moving again. In either case, the microcomputer is activated at step 20 when the car starts moving.
Return to 2.

If the speed of the vehicle was determined in step 208 to be less than the speed v1, but is determined to be much greater than v1 in step 212, the microcomputer returns to step 204, thereby validating the iterative loop. , where it waits for the car's speed to drop to zero or rise above vl v. As mentioned above, if the speed of the car decreases to zero, the microcomputer exits the loop via step 214; when the speed of the car exceeds vl, the microcomputer exits the loop via step 216. Exit 0.

At step 216, timer A is restarted to continue timing the integration time. .

At step 218, timer A is used to determine whether the integration time, e.g.
The contents will be investigated.

This time (T1) can be, for example, about 2 minutes or longer. If timer A indicates that less than T1 has elapsed, the microcomputer returns to step 204. The microcomputer then detects when the car's speed has decreased to zero or when the length of the integral time measured by timer A is T.
Steps 204-218 are repeated until the time exceeds 1.

If it is determined at step 218 that the reading of timer A is greater than T1, the microcomputer proceeds to step 220. In step 220, the microcomputer supplies address signals to the multiplexer 96 so that the outputs of the integrators combined with the four filter panchromators 4, 90, 92 and 94 are read out in sequence. The data thus obtained is processed to find the resonant frequency of each tire. The resonant frequency is then normalized according to the measured ambient temperature. The operation performed in step 220 is the seventh
It is also shown in detail in the figure. 1 microcomputer then proceeds to step 222.

At step 222, the microcomputer starts timer B.
to examine the recorded time. Timer B is reset from time to time during mode timing hand JIA214. The time recorded by timer B represents the amount of time the vehicle has been driven since the last time the tires had a chance to cool to ambient temperature.

The time recorded in this way is T2 (for example, 5 to 10 minutes)
If it is shorter, the estimated frictional heat of the tires has not yet had a chance to warm them effectively above ambient temperature.

The tire is thus assumed to be at ambient temperature.

In this case, the resonant frequency measured on each tire, Tl1FI m compensated by the ambient temperature, can be compared with reference data stored in the memory.

To accomplish the comparison, the microcomputer
Proceed to step 24.

At step 224, the logic state of the calibration flag CAL is examined. If CAL has a logic value of O, then the calibration button was pressed just before the integrator was last reset. The new - < 6tl1 plus resonant frequency is then assumed to represent the correct tension of all four tires. If the calibration flag CAL has a logic value of 00, the microcomputer proceeds to step 226. Stage 2
At 26, the calibration flag CAL is reset to a logic value of 1 and the four lamps associated with the control and display panel 54 are turned off. (You will recall that the four lamps were set to blink in step 206.) The microcomputer then switches to step 2.
Proceeding to step 28, where the data obtained during step 220 is stored for use as reference data. The microcomputer then returns to step 202 to begin processing anew.

If it is determined in step 224 that the calibration flag has a logical value of 1, then the data obtained and processed in step 220 is not reference data. The microcomputer is at stage 23 (] hr jump, here stage 2
The data obtained at step 20 is compared with reference data subsequently stored in storage at step 228. The resonant frequency of each tire determined in step 220 is the same as that of the same tire.
1” resonant frequency. If the resonant frequency of any tire decreases beyond a preselected tolerance, it is assumed that the tire is under-inflated. The microcomputer then uniformly illuminates the Lanflare array 1040 lamps corresponding to the low tires. Thereafter, the microcomputer returns to step 202 and repeats the data acquisition and processing procedure.

If, while passing through step 222, it is determined that the vehicle has been driven for a significant period of time (more than T2 minutes) so that the tire finally has a chance to cool down to ambient temperature, then the tire is at ambient temperature IL. 2) It cannot be inferred. Thus, the data recently discharged from the tire cannot be directly compared with the reference data stored in the storage device. In this case, the microcomputer At the WZ floor 232, the data obtained from each tire (not obtained from the corresponding tire of the main vehicle on the opposite side t111) is compared with the data obtained from the corresponding tire.In other words, the left jiiJ
The resonance frequency of the tire (T-F) is the right front (RF)
Tire-C is compared to the measured resonant frequency. Similarly, the resonant frequency measured with the right-hand (RR) tire is the same as the resonant frequency measured with the left-hand (LR) tire.
; M is done.

Perhaps the opposing tires are not exactly the same, but are in similar environments, and the effect of frictional heat is less than that of the tires. Once again, any detected tire inflation deviations are represented by the uniform dots of the corresponding lamps in the lamp array 104.The microcomputer then returns to step 202 to input the data. Repeat the acquisition process.

Figure 6A shows the mode timing procedure 2 shown in Figure 5.
14 is a more detailed flowchart of the operations performed during step 14; Mode timing procedure 2, as shown in Figure 6A.
14 begins at step 300, where one of the microcomputer's timers (timer B) is reset to the O state and begins to run upwards from the O state.

Timer B then begins counting the amount of time the car is stationary. The next stage 302V? - the speed of the car) is measured and compared with the value of O. If the speed of the car is equal to zero, the procedure simply remeasures the speed and repeats the comparison step. Step 302 is thus repeated for successive times t7 until it is determined that the speed of the vehicle is no longer equal to zero, at which point the procedure proceeds to step 304. In step 304, timer B is read and the time recorded in timer B is compared with a time limit T6. Time T6 represents the amount of time it takes for the tires to return to ambient temperature while the vehicle is stationary. T6 is set equal to one hour or more, for example. If the time recorded in timer B is greater than time T3, the procedure proceeds to step 306 where timer B is reset to a value of O and begins counting anew.
Timer B then begins measuring the amount of time since the car last came to rest. The next step is step 202 in Figure 5.
Go out. However, if it is determined in step 304 that the time recorded in timer B is less than T, then hand 11fD
proceeds to step 308 where timer B is set to the value of T2 or greater. Next step, ya'! '、＋
The process returns to step α 202 in FIG.

It is recognized that the only way timer B can reach step 222 of FIG. 5 and have a value less than T2 is if the time elapsed since the timer was reset in step 306 of FIG. 6A is less than MT2. I think it will be possible. Furthermore, timer B is
It is only reset at step 306 if the vehicle has been stationary long enough for the tires to return to ambient temperature.

Steps 302, 304, 306 and 3081-1: are also performed during the initialization procedure 2000 each time power is reapplied to the 4-microcomputer.

FIG. 6B shows the form that mode timing procedure 214 may have in another embodiment of the invention.

In this alternative embodiment, step 232 of FIG. 5 is eliminated;
Instead, the procedure is for timer B to record a time longer than T2. If it is determined in step 222 (indicating that the tire is no longer considered to be at ambient temperature), then a new step 310 of the mode timing procedure is jumped to. This jump is shown in dotted lines in FIG.

The procedure of FIG. 6B is similar to that of FIG. 6A, except that step 308 has been replaced by a new step 310. Therefore, stage 3 in which the car has been stationary for less than the time T3 required for the tires to return to ambient temperature.
The decision at step 04 also causes a step jump to step 310. At step 310, the speed of the vehicle is determined by monitoring the output of the vehicle speed sensor, and the speed of the vehicle is determined to be 0.
be compared with the value of As long as the speed of the car exceeds O (
That is, as long as the car is moving), the microcomputer repeats the steps. Thus, the measurement of the tire's resonant frequency is no longer relevant.

However, when the car returns to a stationary state, the microcomputer returns to step 300.

The net effect of the change between Figures 6A and 6B is that the inflation pressure is only checked when the vehicle has just started driving after a relatively long period of inactivity.

The alternative procedure of FIG. 6B, for one reason or another,
It may be desirable in environments where it would be impossible or undesirable to cross-check data from tires on opposite sides of the vehicle.

FIG. 7 is a more detailed flowchart of the operations performed during data processing stage 2200 of FIG. Step 220 is included to read the information provided by the filter puncture associated with each tire, determine the resonant frequency of each tire from the filter puncture information, and normalize the resonant frequency so determined by temperature. . The purpose of normalization is to remove the effect of ambient temperature changes on the measured resonant frequency. For example, a resonant frequency measured at 70'F' is different than a frequency measured at an ambient temperature of 500F, but the cold inflation pressure of the tire remains constant.

The normalization procedure is that when multiplied by a multiplication factor at a certain temperature, the resonant frequency measured at that temperature is the same as that measured when the ambient temperature is the normalized value (e.g. a value like 50'li'). Infer that for each given temperature it is best to select a resonant frequency that corresponds to the frequency. A "look-up table" that correlates each temperature with a corresponding normalization multiplier is determined empirically for a given vehicle and tire combination. The normalization multiplier is equal to 1 at the normalization temperature, but may be slightly above or below 1 at other temperatures. The lookup table is stored in the solid state storage device of microcomputer 100 in FIG.

The procedure of FIG. 7 begins at step 312, in which the microcomputer controls the multiplexer to connect the output of the signal processor 116, which is combined with the temperature sensor 152, to the analog-to-digital converter 102. supply the signal. The digital output signal provided by the A/D converter is therefore representative of the ambient temperature. The signal d is read by the microcomputer and used in step 314 to recall the lookup table stored in solid state storage. The value read from the storage device becomes the correction coefficient. The correction factor represents the value by which the measured resonant frequency of the famous tire must be multiplied so that it provides the resonant frequency measured at a standardized temperature of, for example, 5 D °li''.

Instead of storing a complete lookup table, the device could store a shorter lookup table containing multipliers for more widely spaced temperatures. The microcomputer is then programmed to interpolate between the individual values stored in the table. Alternatively, a mathematical expression relating temperature to a normalized multiplicative law is derived by conventional curve-fitting methods, and this expression is stored in memory in place of the look-up table. Thus, the microcomputer can calculate the normalization multiplier simply by entering the measured temperature into this equation.

At step 316, a count variable N is set to an initial value of one. In the next step 318, the microcomputer retrieves data from the four integrators associated with the tire filter bank identified by the current value of the counting variable N.

As previously mentioned, data acquisition is performed by multiplexer 96 and A/
This is achieved by appropriate control of the D converter 102. The microcomputer then examines the data in step 320 to determine the frequency of the resonant peak. Thailand)
The resonant peak frequency of 'N is represented in FIG. 7 as fr(n). The peak frequency is 1l11 using an appropriate curve.
Find the peak of the matched curve by matching the specified data point, or simply remove the maximum value of the integrated output and infer that the peak is at the center of the corresponding filter band.
It is calculated by The procedure then proceeds to step 332 where the resonant frequency is multiplied by the correction factor determined in step 314 and the corrected temperature.

At step 324, count variable 1 is examined to determine which tire was last processed. 1q
If the value of is 4, processing of the tire data is complete and the procedure jumps to step 222 of FIG. If the value of N is not 4, the procedure continues with step 326 where I is incremented by a value of 1, and then returns to step 318.

FIG. 8 is a more detailed flow diagram of the operations performed during step 2220 of FIG. As you may recall, step 22
2 is a guess about tire temperature (when 1 is not possible,
It is provided to compare the resonance frequency data of the tires on the opposite side of the car. As shown in FIG. 8, the procedure begins at step 330, where the count variable N is reset to a value of one.

In step 332 following step 330, the error value E is calculated by subtracting the two ratios together.

The first ratio is the ratio of the measured resonant frequency of tire N (i.e., fr(N)) and the reference (memory) resonant frequency of tire N (i.e., FR(N)). The second ratio is equal to the measured resonant frequency of tire N+1 (i.e. f
r(N+1)) is the ratio of the reference (memory) resonant frequency of tire N+1 (i.e., p'R(N+1)). It is assumed that the two ratios are approximately equal, unless the inflation of one of the two tires is significantly reduced compared to the other.
Ru.

In step 334, the absolute value of the error signal E determined in step 332 is compared to a tolerance range. If the absolute value of the error signal E is greater than the permissible range, hand 1 continues with step 336. In step 6 336, the lights of the control panel 54 associated with tires N and N+1 are turned on;
This indicates that the driver must check the inflation of the two tires. However, if the absolute value of the error signal E is determined in step 334 to be less than the tolerance range, then the procedure jumps instead to step 338, where tires N and 14+1 are combined with -J 1t and 2 lights. is the turn
It will be turned off. (Unless there was an error in the previous program cycle, the lights V, L are already off when the microcomputer executes step 338.) Each step 33
After 6 and 338, the procedure continues with step 340, where the count variable J=J is compared to the value of O. If N does not have a value of 6, the procedure continues with step 342. Step 1
In step 342, count variable 11 is set to step 332~
Tires 3 and 4 are given a value of 6 so that they are processed in successive passes through 340. Step 3
Upon completion of step 42, step 332 continues.

At step 34, the count variable N actually reaches the value t of 6.
0, the microcomputer exits the procedure and continues to step 202 of FIG.

While the invention has been described with reference to one preferred embodiment, it will be appreciated that various rearrangements and changes of parts may be made within the spirit and scope of the invention as defined in the claims. think.

Thus, for example, while in the implementations described above tire inflation pressure is monitored by simply measuring the resonant frequency, more complex frequency analysis algorithms may be used instead. It has been found that the peak PK, which is affected by tire inflation pressure, changes not only in frequency but also in amplitude and width with changes in tire pressure. Two or even all six of these peak characteristics are measured, stored as a reference value, and used for future comparisons. The total comparison error is then an additive and/or multiplicative function of the errors of all six characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an automobile tire support device, FIG. 2 is a graph of the frequency spectrum of acceleration experienced by the support device of FIG. 1, and FIG. 3 is a tire of the invention showing the general layout of the individual components FIG. 4 is a schematic diagram of a pressure monitoring device; FIG. 4 is a block diagram of a circuit for processing acceleration output signals to measure changes in tire inflation pressure; FIG. 6A and 6B are detailed illustrations of two alternative embodiments for one of the blocks of the flowchart of FIG. 5; FIG. A detailed diagram of the operations performed in another of the blocks in FIG. 11, FIG. 8 is a flowchart of FIG. 5. FIG. 3 is a detailed diagram of the operations performed in another; Explanation of symbols: 30-Automobile; 32.34.36.38-Tire: 40.42.44.46-Accelerometer; 48-Microcomputer; 50-Speed sensor; 5-2-Temperature sensor; 54- Control Display Panel Agent Akira Asamura Procedural Amendment (Method) September 9, 1980 Dear Director-General of the Agency] Born in 1982, Application No. 78883 - Permanent Part 1 Patent 1. '1 Number of inventions increasing since August 30, 1982

Claims (1)

[Scope of Claims] +11 A device for detecting changes in the inflation pressure of a tire of a rotating vehicle, the device comprising: detecting the vertical acceleration that the tire receives during normal driving of the vehicle to which the tire is attached; a device for providing a signal that varies with acceleration; a device for processing the acceleration signal to derive information regarding the frequency distribution of the acceleration; and in response to the frequency distribution information, the inflation pressure of the vehicle tire is selected. and a device for measuring whether or not the amount has changed by an amount exceeding a certain amount. (2) In the detection device according to claim (1), the device responsive to the frequency distribution information measures the frequency of two resonances having positions affected by tire pressure, and 1. The detection device comprising a device for determining whether the inflation pressure of the tire is below a selected level by comparing the frequency of the resonance peak to a limit value. (3) In the detection device according to claim (1), the device for processing the accelerometer signal includes a device for determining the amplitude of at least selected frequency components of the acceleration signal. The detection device characterized by: (4) In the detection device according to claim (3), the device responsive to the frequency distribution information is responsive to the amplitude of at least selected frequency components of the acceleration signal. , comprising an apparatus for measuring the frequency of a resonant peak whose position is influenced by tire pressure and determining whether the inflation pressure of the tire of the vehicle has changed based on the resonant peak frequency. Detection device. (5) A method for detecting low inflation pressure in a rotating vehicle tire, the method comprising: detecting the vertical acceleration experienced by the tire during normal operation of the vehicle to which the tire is mounted. The detection is characterized in that it includes the steps of: measuring the amplitude of at least acceleration occurring at one frequency; and determining whether tire pressure is low based on the amplitude of at least acceleration occurring at the one frequency. Method. (6) In the detection method according to claim (5), the step of measuring the amplitude of the acceleration occurring at the one frequency is performed over at least the frequency range in which the resonance frequency of the tire of the MiJ vehicle occurs. The detection method includes the step of measuring a frequency spectrum of acceleration. (7) In the detection method according to claim (6), the step of measuring whether the tire pressure is low. The detection method comprises the step of determining whether the tire pressure is low based on one characteristic of a peak in the frequency spectrum derived from the resonant frequency of the car tire. (8) The detection method according to claim (7), wherein the 1tllll constant of the low tire pressure is based on the frequency at which the maximum amplitude of the 111th peak occurs.