JP3564771B2 - Tire pressure detector - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a tire pressure detecting device for detecting a state of a tire pressure of a vehicle.
[0002]
[Prior art]
Conventionally, as a device for detecting the state of the air pressure of a tire, a constant frequency range of a signal including a vibration frequency component of the tire is analyzed with a constant resolution to extract a resonance frequency, and a tire is extracted based on the extracted resonance frequency. (Japanese Patent Application Laid-Open No. 5-133831).
[0003]
[Problems to be solved by the invention]
Incidentally, the frequency band in which the resonance frequency included in the vibration frequency component of the tire exists varies depending on the environment in which the vehicle is placed, such as the running state of the vehicle and replacement of tires and wheels. The magnitude of the resonance varies depending on the direction in which the resonance phenomenon is detected, such as front and rear, up and down, and left and right with respect to the circumferential direction of the tire. The magnitude of the resonance also changes depending on the environment in which the vehicle is placed. If only the resonance phenomenon occurring in the above is detected, the state of the air pressure cannot be accurately detected according to the traveling state.
[0004]
Accordingly, an object of the present invention is to provide a tire air pressure detecting device that can cover a wide frequency band and can cope with the change.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a predetermined frequency range is frequency- analyzed from a signal including a vibration frequency component of a tire when a vehicle is running to extract a resonance frequency (step 10). 1 to 110), in the tire air pressure detecting device and a pneumatic detecting means (step 111) for detecting the air pressure state of the said tire on the basis of the resonance frequency determined, at operation start of the vehicle, the tire air pressure There comprising means for setting an early warning mode for early warning the driver that a low electrode (step 100), the extracting unit (step 10 1-110), the early warning mode is set When the frequency analysis in the frequency analysis is roughly set and the signal is subjected to frequency analysis, and the early warning mode is released When the early warning mode is set, the frequency of the tire is detected by the air pressure detecting means (step 111). If it is determined that the air pressure is not a very low pressure, a technical means for providing a means (step 113) for canceling the early warning mode is adopted.
[0007]
According to the second aspect of the present invention, an extracting means (201 to 208) for frequency-analyzing a predetermined frequency range from a signal including a vibration frequency component of a tire when the vehicle is running to obtain a resonance frequency; the tire air pressure detecting device and a pneumatic detecting means (step 211) for detecting the state of the tire air pressure based, with a replaceable sensing means tire or wheel detects that it has been switched (step 209), said extraction means (20 1-208) is by said switching detecting means (step 209), if the tire or wheel is detected to have been exchanged, a narrow frequency range of interest of the frequency analysis from a wide range Setting means (step 210) for setting the frequency range in which the resonance frequency exists by changing to a range. To adopt a cormorant technical means.
[0008]
Resonance The invention according to claim 3, the extracting means a predetermined frequency range of the signal containing the oscillation frequency component of a tire when the vehicle travels by frequency analysis determine the resonant frequency (Step 30 1-315), that the determined A tire pressure detecting device (step 317) for detecting the condition of the tire pressure based on the frequency, when a plurality of resonance frequencies are present, the resonance energy at each resonance frequency is mutually determined. In comparison, a resonance frequency selecting means (Step 316) for selecting a predetermined resonance frequency is provided, and the air pressure detecting means (Step 317) detects an air pressure of the tire based on the selected resonance frequency. Is adopted.
[0009]
The reference numerals in the parentheses of the above means indicate the correspondence with the specific means described in the embodiments described later.
[0010]
Operation and Effect of the Invention
According to the first or second aspect of the present invention, the above-mentioned technical means is provided, and even if the tire air pressure changes due to a factor that changes the tire air pressure, it is possible to cope with the change. Can be detected.
[0011]
Incidentally, according to the invention described in 請 Motomeko 2, by a tire or wheel is replaced, even if fluctuation frequency range exists resonant frequency, it is possible to set the frequency range exists resonant frequency .
[0012]
According to the third aspect of the present invention, since the tire pressure can be detected based on the resonance frequency selected by comparing the resonance energies at a plurality of resonance frequencies with each other, the detection accuracy can be improved. Can be.
[0013]
【Example】
First, the configuration of a tire pressure detecting device according to the present invention will be described with reference to FIG.
As shown in FIG. 1, wheel speed sensors 2 to 5 are provided corresponding to the respective tires 1a to 1d of the vehicle. Each of the wheel speed sensors 2 to 5 includes gears 2a to 5a and pickup coils 2b to 5b. The gears 2a to 5a are mounted coaxially with the rotating shafts (not shown) of the tires 1a to 1d, and are made of a disk-shaped magnetic material. The pickup coils 2b to 5b are mounted at predetermined intervals near the gears 2a to 5a, and output an AC signal having a cycle corresponding to the rotation speed of the gears 2a to 5a, ie, the tires 1a to 1d.
[0014]
AC signals output from the pickup coils 2b to 5b are input to a known electronic control device (hereinafter abbreviated as ECU) 6 including a microcomputer including a CPU, a ROM, a RAM, and the like, a waveform shaping circuit, and the like. , Predetermined signal processing including waveform shaping is performed. The result of the signal processing is input to the display unit 7, and the display unit 7 notifies the driver of the state of the air pressure of each of the tires 1a to 1d.
[0015]
The display unit 7 may independently display the state of the air pressure of each of the tires 1a to 1d, or may be provided with one warning lamp, and when the air pressure of any one of the tires becomes lower than the reference air pressure. A warning may be issued by turning on the light. Reference numeral 8 denotes a switch for inputting that a tire or a wheel has been replaced.
Since the ECU 6 performs the same processing for each of the tires 1a to 1d, the flowchart described in the following embodiment shows only the flow of the processing for one tire.
[0016]
Next, a first embodiment using the tire pressure detecting device according to the present invention having the above configuration will be described.
In general, a decrease in tire air pressure can be classified into a puncture caused by running puncture and a puncture caused by stopping the vehicle or spontaneous leakage.
In the former case, since the change in air pressure is relatively gradual, it can be sufficiently detected by using a conventional means for analyzing the resonance frequency. On the other hand, in the latter case, especially when the ignition switch is turned off and the vehicle is left for a long period of time, such as overnight to several days, the tire air pressure is extremely lower than before turning off the ignition switch. May be.
[0017]
By the way, the conventional frequency analysis means sets the frequency resolution finely to detect a strict air pressure (for example, 0.1 Hz). Therefore, the existence of a resonance phenomenon is observed over a wide frequency band, and the tire air pressure is measured. It takes a long time to detect (about 1 to 3 minutes).
Therefore, the conventional frequency analysis means cannot promptly warn the driver that the tire pressure is extremely low after turning on the ignition switch.
[0018]
In order to increase the detection speed of the tire air pressure, the processing capacity of the microcomputer may be increased, but this is not practical because it directly increases the cost.
By the way, in order to warn the driver early that the air pressure of the tire is extremely low, it is not necessary to detect the air pressure of the tire exactly. In other words, if the frequency analysis is performed with a frequency resolution coarser than the reference frequency resolution used in the conventional frequency analysis, and the total sampling time is shortened, it is possible to detect a state in which the tire pressure is extremely low in a short time. Also, there is no need to increase the processing capability of the microcomputer.
[0019]
For example, the ratio between the total sampling time and the frequency resolution is inversely proportional. For example, if the frequency resolution is roughly doubled (for example, 1 Hz → 2 Hz), the total sampling time is halved.
Hereinafter, processing until the microcomputer in the ECU 4 detects an extremely reduced air pressure will be described based on the flowchart of FIG.
[0020]
First, when the ignition is turned on, the microcomputer in the ECU 4 is initialized in step 100. Here, it is assumed that the early warning mode is set when the ignition switch is turned on. When the vehicle starts running, the wheel speed is read in step 101 to calculate the wheel speed, and the counting of the number of calculations N1 is started.
[0021]
In step 102, it is determined whether or not the number of calculations N1 is equal to or greater than n0, that is, whether or not the wheel speed data calculated by calculation is equal to or greater than n0, and it is determined that the number of calculations N1 is equal to or greater than n0. Then, in step 103, the number of calculations N1 is updated to "0", and the counting of the number of calculations and analysis N2 executed in steps 101 to 105 is started.
[0022]
Next, in step 104, it is determined whether or not the early warning mode has been set. Since the early warning mode has already been set as described above, the process proceeds to step 105, and based on the n0 wheel speed data. Frequency analysis (analysis using FFT (fast Fourier function) operation), for example, with a coarse frequency resolution of 2 Hz (normally 0.5 Hz). Here, as a result of setting the frequency resolution to 2 Hz, the frequency analysis speed is quadrupled.
[0023]
Then, in step 107, it is determined whether or not the number N2 of the series of calculations and analysis in steps 101 to 105 is equal to or more than n1, and if it is determined that the number of calculations N2 is equal to or more than n1, the process proceeds to step 108. Then, the number of operations N2 is updated to “0”.
Next, in step 109, the average value of the gain of the power spectrum as the resonance energy of each frequency component is calculated. That is, this processing reduces fluctuations in the FFT calculation result due to road surface conditions such as unevenness. Then, in step 110, the resonance frequency f in the vertical direction below the spring of the vehicle (the direction from the outer periphery of the tire toward the center of the tire) is calculated based on the average value. Next, at step 111, the air pressure p corresponding to the resonance frequency calculated at step 110 is detected. This detection is performed, for example, according to a map created based on the relationship between the unsprung resonance frequency and the tire pressure described in FIG. 11 of JP-A-5-133831.
[0024]
Next, the routine proceeds to step 112, where it is determined whether the mode is the early warning mode. Since the early warning mode has been set in step 100 as described above, the process proceeds to step 113, where it is determined whether or not the calculated air pressure p is lower than the air pressure (for example, 0.8 atm) preset as an extremely low pressure. Is determined, and if it is determined that the air pressure is smaller than the preset air pressure, a warning is displayed in step 114. On the other hand, if it is determined in step 113 that the pressure is not extremely low, the early warning mode is canceled.
[0025]
Next, the process returns to step 101, proceeds to step 106 via steps 102 to 104, and performs precision-oriented frequency analysis. In other words, the analysis is performed accurately with a fine frequency resolution of 0.5 Hz. Then, the processing of steps 107 to 110 is performed as described above. Next, the air pressure is detected in step 111, a negative determination is made in step 112, and the routine proceeds to step 115, where a normal air pressure determination is made as to whether or not the detected air pressure is lower than a preset air pressure. If it is determined that the air pressure is smaller than the air pressure (air pressure larger than the extremely low pressure), a predetermined alarm is displayed in step 114. In this case, since it is determined that the air pressure of the tire is not in the extremely low pressure state, there is no problem even if the analysis is performed with a relatively slow response.
[0026]
As described above, according to the tire pressure detecting device according to the present embodiment, the frequency resolution in the frequency analysis can be coarsened and the sampling time can be shortened, so that the tire pressure is extremely reduced. The driver can be warned early.
In this embodiment, the early warning mode is set only when the ignition is turned on. However, the stop time of the vehicle is measured, and the early warning mode is set even when the measured time exceeds a predetermined time. You may. Further, if the resolution is made coarse, there is a possibility that it is erroneously determined to be a very low pressure due to external noise. Therefore, in order to prevent this and increase the accuracy of the extremely low pressure determination, steps 101 to 114 are repeatedly performed. And a step of determining whether or not the extremely low pressure determination has been performed a predetermined number of times after step 113 can be provided.
[0027]
In the following, a description will be given of a second embodiment of a tire pressure sensing apparatus according to the present invention. In conventional frequency analysis means, when the tire or wheel is replaced with a different type and the unsprung weight changes, the frequency range in which the resonance phenomenon to be detected is greatly moved, so that the air pressure is detected by frequency analysis. May be unable to do so.
[0028]
In order to solve such a problem, it is sufficient to provide frequency analysis means corresponding to the range of the frequency to be analyzed and the frequency resolution, which can correspond to many combinations of tires and wheels. Wear technology is not a good idea because it directly leads to increased costs.
Here, it is possible to detect a wider frequency range by shortening the sampling interval, but it cannot be used because the memory capacity is limited and the number of sampling data cannot be increased.
[0029]
However, if the frequency resolution is coarsened to reduce the total sampling time, the range of frequencies to be analyzed can be expanded without increasing the memory capacity.
Therefore, the tire pressure detection device according to this embodiment first observes a wide frequency range in a state where the resolution is coarse, and after roughly specifying the frequency range where the resonance phenomenon exists, gradually increases the frequency range. It is characterized in that the resonance phenomenon to be obtained is accurately extracted while narrowing, so that the resonance phenomenon is not lost.
[0030]
Hereinafter, the processing of the microcomputer in the ECU 6 of the tire pressure detecting device having the configuration will be described with reference to the flowchart of FIG.
First, in steps 200 to 203, the same processing as steps 100 to 103 in FIG. 2 is performed. Then, in step 204, frequency analysis (FFT calculation) is performed based on the calculated n0 wheel speed data. Next, in steps 205 to 208, the same processing as steps 107 to 110 in FIG. 2 is performed. If it is detected in the switch input processing in step 209 that the tire or the wheel has been replaced, in the next step 210, a relatively coarse frequency resolution is first set.
[0031]
Then, the process returns to step 201 via steps 211 and 212, and in step 204 via steps 202 and 203, a wider frequency range is analyzed.
Next, if a frequency band in which a resonance frequency exists is detected in step 210 after steps 205 to 209, in step 210, the analysis range is changed so as to narrow down to a narrow frequency band in which the resonance frequency exists. At the same time, the frequency resolution is set finely in order to accurately extract the resonance phenomenon. The setting change of the analysis range and the frequency resolution may be performed, for example, by storing a map of the relationship between the analysis range and the frequency resolution and according to the map.
[0032]
Then, based on the changed analysis range and frequency resolution, frequency analysis is performed in step 204, and as a result of the analysis, if the calculated resonance frequency f is the desired resonance frequency in step 208, step 211 When the tire air pressure is calculated in the air pressure detection process of the above, and it is determined that the calculated air pressure is smaller than the preset air pressure, a warning is displayed in step 212.
[0033]
As described above, according to the tire air pressure detection device according to the present embodiment, even if the unsprung weight changes due to the replacement of the tire or the wheel, and the frequency range where the resonance phenomenon exists is moved, the resonance phenomenon is not detected. Since the range of the existing frequency can be found, a warning can be issued by detecting the tire pressure.
As means for detecting a frequency band in which a resonance phenomenon exists, for example, means for detecting a frequency band in which a power spectrum of a predetermined level or more is concentrated and using the frequency band as a frequency band in which a resonance phenomenon exists is used. be able to. In addition, it is also possible to configure so as to change one of the analysis range and the frequency resolution.
[0034]
In the following, a description will be given of a third embodiment of a tire pressure sensing apparatus according to the present invention. The vibration frequency information of the tire includes a resonance phenomenon caused by eccentricity or twisting of the tire in the rotational direction of the tire in the front-rear, up-down, left-right directions. The frequency bands in which these resonance phenomena exist are different from each other, and the energy of each resonance also changes according to various running states where the vehicle is placed. For example, as shown in FIG. 5A, in a certain traveling state, the resonance energy around 35 Hz is larger than that near 70 Hz, but when the traveling state changes, as shown in FIG. In some driving conditions, a phenomenon may occur in which the resonance energy around 70 Hz becomes larger than that around 35 Hz.
[0035]
Therefore, observing multiple types of resonance phenomena does not overlook resonance phenomena with a large power spectrum than observing only one type of resonance phenomena. , The detection accuracy can be improved.
The tire pressure detecting device according to this embodiment focuses on the above points, and provides a tire pressure detecting device capable of improving detection accuracy with a smaller memory capacity. Specifically, a DFT (Digital Fourier Function) operation is performed in a required frequency range at a constant resolution without using an FFT operation that performs an operation over all frequencies of the tire vibration frequency components included in the wheel speed signal. . That is, the DFT operation is an operation method in which the frequency to be analyzed and its resolution can be freely set, so that, for example, the frequency range of fv1 to fv2 where the resonance phenomenon in the vertical direction exists exists with a resolution of Δfv, The frequency range of fR1 to fR2 where the longitudinal resonance phenomenon exists can be analyzed at the same time from the same sampling data with a resolution of ΔfR.
[0036]
Hereinafter, the processing of the microcomputer in the ECU 6 of the tire pressure detecting device according to this embodiment will be described with reference to the flowchart of FIG.
Steps 301, 302 to 308 in FIG. 4 perform processing until the resonance energy is calculated by analyzing the frequency range of fv1 to fv2 with a resolution of Δfv, and steps 301, 309 to 315 define the frequency range of fR1 to fR2. The processing until the resonance energy is calculated by analyzing with a resolution of ΔfR will be described.
[0037]
First, after being initialized in step 300, the wheel speed is calculated in step 301, and counting of the number of calculations N1A and N2B is started. Here, since the number of data used in the DFT (A) calculation in step 304 is different from the number of data used in the DFT (B) calculation in step 311, the number of wheel speed calculations is defined by N1A and N2B. It is divided into two types.
[0038]
Then, in step 302, it is determined whether or not the count of the number of operations N1A is equal to or greater than n0A. If it is determined that the count is equal to or greater than n0A (for example, 256), the process proceeds to step 303, and the count of the number of operations N1A is reduced to "0". At the same time, the count of the number of times N2A of the DFT (A) calculation performed in the next step 304 is started.
[0039]
Next, in step 304, a frequency analysis by DFT (A) calculation is performed based on the calculated 256 wheel speed data. In this calculation, frequency data with a resolution of 0.5 Hz is calculated from 30 to 50 Hz. Then, in step 305, it is determined whether or not the count of the number of operations N2A is equal to or greater than n1A. If it is determined that the count is equal to or greater than n1A, the process proceeds to step 306, where the count of the number of operations N2A is updated to "0". In step 307, the average value of the calculation result of the DFT (A) is obtained.
[0040]
Then, in step 308, the resonance energy PA 1 is calculated based on the average value, and the resonance frequency fA is calculated. Here, the resonance energy is defined by, for example, the sum of power spectrum gains of each frequency in the analyzed frequency range.
On the other hand, when the determination in step 302 is performed, it is determined in step 309 whether the count of the number of operations N1B is equal to or greater than n0B, and if it is determined that the count is equal to or greater than n0B (for example, 128), the process proceeds to step 310. The count of the number of operations N1B is updated to “0”, and the counting of the number of operations N2B of DFT (B) performed in the next step 311 is started. Then, in step 311, the DFT (B) is calculated based on the calculated wheel speed. In this calculation, frequency data having a resolution of 1 Hz is calculated from 60 to 80 Hz using the total of 128 sampled data.
[0041]
Then, in step 312, it is determined whether or not the count of the number of operations N2B is equal to or greater than n1B. If it is determined that the count is equal to or greater than n1B, the process proceeds to step 313, where the count of the number of operations N2B is updated to “0”. In step 314, an average value of the calculation result of the DFT (B) is obtained. Next, in step 315, the resonance energy PB is calculated based on the average value, and the resonance frequency fB is calculated.
[0042]
Next, in step 316, the resonance energy PA calculated in step 308 and the resonance energy PB calculated in step 315 are compared with each other, and the resonance frequency having the larger resonance energy is selected. Then, in step 317, an air pressure is calculated based on the selected resonance frequency, and it is determined whether the calculated air pressure is smaller than an air pressure set in advance as an extremely low pressure, and the calculated air pressure is calculated. If it is determined that the air pressure is lower than the preset air pressure, a warning is displayed in step 318.
[0043]
As described above, according to the tire pressure detection device according to the present embodiment, even if the frequency range in which the resonance phenomenon exists moves due to the traveling speed of the vehicle, it is possible to detect the warning and detect the tire pressure by detecting the resonance phenomenon. it can. In addition, since the amount of calculation is smaller than in the case of analysis using the conventional FFT calculation, the tire pressure can be detected efficiently with a limited memory capacity.
[0044]
In this embodiment, the tire pressure is detected by using one of the two resonance phenomena, but the tire pressure is detected by performing a weighted average of the energy of the plurality of detected resonance phenomena. It can also be configured .

[0045]
In each of the above embodiments, the tire pressure is obtained from the relationship between the calculated resonance frequency and the tire pressure. However, the calculated tire frequency is calculated from the calculated resonance frequency and the initial frequency f0 which is set in advance in accordance with the normal tire pressure. And a predetermined deviation Δf (set based on the initial frequency f0 corresponding to the normal tire pressure) corresponding to the allowable lower limit value of the tire pressure. ), And when it is determined that the decrease deviation (f0−f) exceeds a predetermined deviation Δf, an alarm display may be performed.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a configuration of a tire pressure detecting device according to the present invention.
FIG. 2 is a flowchart showing processing contents of an ECU in the first embodiment.
FIG. 3 is a flowchart illustrating processing performed by an ECU according to a second embodiment.
FIG. 4 is a flowchart illustrating processing performed by an ECU according to a third embodiment.
FIG. 5 (a) is a characteristic diagram showing a relationship between a tire vibration frequency and a power spectrum in a running state (1), and FIG. 5 (b) is a graph showing a relationship between a tire vibration frequency and a power spectrum in a running state (2). FIG.
[Explanation of symbols]
1a to 1d wheels, 2 to 5 wheel speed sensors, 6 ECUs
7. Display part, 8. Switch.

Claims (3)

Extraction means for obtaining a resonance frequency by frequency analysis of a predetermined frequency range from a signal containing a vibration frequency component of a tire when the vehicle is traveling, and air pressure detection means for detecting a state of the air pressure of the tire based on the obtained resonance frequency In the tire pressure detecting device provided with
At the start of operation of the vehicle, comprising means for setting an early warning mode for early warning the driver that the tire air pressure is extremely low pressure ,
The extracting means sets the frequency resolution in the frequency analysis to be coarse when the early warning mode is set, performs the frequency analysis of the signal, and finely sets the frequency resolution when the early warning mode is released. Set to analyze the frequency of the signal,
Further, a means for canceling the early warning mode when it is determined that the air pressure of the tire detected by the air pressure detecting means is not a very low pressure when the early warning mode is set. Tire pressure detector. Extraction means for obtaining a resonance frequency by frequency analysis of a predetermined frequency range from a signal containing a vibration frequency component of a tire when the vehicle is traveling, and air pressure detection means for detecting a state of the air pressure of the tire based on the obtained resonance frequency In the tire pressure detecting device provided with
With replaceable detection means for detecting that tire or wheel is replaced,
It said extraction means, by the exchange detection unit, when the tire or wheel is detected to have been exchanged, the resonant frequency is varied in a narrow range frequency range of interest of the frequency analysis from a wide range of tire air pressure detecting device, characterized in that those comprising a setting means for setting a frequency range exists. Extraction means for obtaining a resonance frequency by frequency analysis of a predetermined frequency range from a signal containing a vibration frequency component of a tire when the vehicle is traveling, and air pressure detection means for detecting a state of the air pressure of the tire based on the obtained resonance frequency In the tire pressure detecting device provided with
When a plurality of resonance frequencies are present, a resonance frequency selection unit that compares resonance energy at each resonance frequency with each other and selects a predetermined resonance frequency is provided,
The tire pressure detection device according to claim 1, wherein the air pressure detection means detects an air pressure of the tire based on the selected resonance frequency.

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