JP3563186B2 - Tire pressure detector - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a tire pressure detecting device that detects a state of a tire pressure based on a resonance frequency of the tire.
[0002]
[Prior art]
An inexpensive and highly reliable tire pressure detecting device is disclosed in Japanese Patent Application Laid-Open No. 5-133831. In the disclosed example, a tire resonance frequency is extracted from a signal including a tire vibration frequency component, and air pressure is detected from a change in the resonance frequency.
[0003]
[Problems to be solved by the invention]
The signal including the vibration frequency component of the tire includes resonance vibration of the tire and vibration due to disturbance from a road surface or the like. When the vehicle runs, the resonance vibration of the tire appears at about 40 Hz, and the resonance frequency is obtained by performing frequency analysis (for example, FFT calculation) on the resonance vibration. As a result, the tire pressure can be detected. However, the signal has many vibrations due to disturbances from the road surface and the like, and the vibration due to the disturbances from the road surface and the like is so large as to be not negligible when compared with the intensity of the resonance vibration around 40 Hz. The detection accuracy decreases due to the influence of a large signal. Here, in order to improve the detection accuracy, the detection accuracy has been improved by increasing the number of averaging processes. However, the detection accuracy tends to be saturated and a high detection accuracy cannot be obtained.
[0004]
The present invention has been made in view of the above problems, and an object of the present invention is to eliminate the influence of disturbance from a road surface or the like and to provide a tire pressure detection device capable of accurately detecting tire pressure. To provide.
[0005]
[Means for Solving the Problems]
When a vehicle is running, the resonance vibration of the tire generally appears around 40 Hz, but the vibration intensity of the resonance signal has a maximum value at a predetermined wheel speed for each vehicle, and shows a decreasing tendency as the distance from the wheel speed increases. . More specifically, as shown in FIG. 4, the peak value of the power spectrum (signal intensity) of the resonance vibration of the vibration system including the tire exhibits a maximum value at the wheel speed V0 in the figure, The further away, the smaller. In such a case, a decrease in the peak value of the power spectrum of the resonance vibration away from the wheel speed V0 means that the vehicle is easily affected by disturbance (noise) from a road surface or the like. That is, for example, the wheel speed range of Vα to Vβ in FIG. 4 can be said to be a band in which the resonance vibration of the tire is likely to occur.
[0006]
As described above, if the vibration frequency component of the tire is detected in the wheel speed range of Vα to Vβ and the resonance frequency is calculated using only the detection result, the calculation error can be reduced. However, during normal traveling of the vehicle, the wheel speed (vehicle speed) is not constant, and the period of traveling in the wheel speed bands Vα to Vβ is only a part of the entire traveling period. Therefore, for example, in the case where the resonance frequency is detected by moving average processing of the detection result of the vibration frequency component of the tire, the number of detections (or the running time) of the vibration frequency component in the wheel speed bands Vα to Vβ is smaller than a predetermined value. In some cases, the calculation accuracy of the resonance frequency may worsen. Therefore, the present invention proposes to improve the detection accuracy by selectively using the optimum resonance frequency calculation method at each time when the vehicle is running.
[0007]
That is, the tire pressure detection device of the present invention detects the vibration frequency component of the tire when the vehicle is running, and calculates the resonance frequency of the tire using the detection result of the tire vibration frequency component. Further, the tire pressure is detected based on the calculated tire resonance frequency. At this time, a predetermined wheel speed band is set based on the wheel speed at which the peak value of the power spectrum of the resonance vibration of the vibration system including the tire exhibits the maximum value, and the number of times the tire vibration frequency component is detected in the wheel speed band Alternatively, it is determined whether the vehicle traveling time exceeds a predetermined value (determination means). When the number of times of detection of the vibration frequency component in the wheel speed band or the vehicle traveling time does not exceed a predetermined value, the resonance frequency of the tire is calculated using a detection result of an arbitrary tire vibration frequency component (first calculation means). ). When the number of times of detection of the vibration frequency component in the wheel speed band or the vehicle traveling time exceeds a predetermined value, the resonance frequency of the tire is calculated using only the detection result of the tire vibration frequency component in the wheel speed band (No. 2).
[0008]
According to the above configuration, the influence of noise such as disturbance can be efficiently eliminated by selectively using a plurality of calculation methods to determine the resonance frequency, and the tire air pressure can be accurately detected. The running speed of the vehicle means a time when the wheel speed is equal to or greater than 0, and may be replaced with the running distance of the vehicle and treated as the same.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
(First Embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
[0010]
FIG. 1 is a schematic diagram showing the overall configuration of the tire pressure detecting device according to the present embodiment. As shown in the figure, wheel rotation sensors 2a, 2b, 2c, 2d corresponding to the respective tires 1a to 1d are provided on the rotation axes (not shown) of the tires 1a, 1b, 1c, 1d of the vehicle. The sensors 2a to 2d output signals including vibration frequency components of the tires 1a to 1d. More specifically, each of the wheel speed sensors 2a to 2d includes gears 3a, 3b, 3c, 3d and pickup coils 4a, 4b, 4c, 4d. The gears 3a to 3d are coaxially attached to the rotation axes of the tires 1a to 1d, and are made of a disk-shaped magnetic material. The pickup coils 4a to 4d output AC signals having a cycle corresponding to the rotation speed of the gears 3a to 3d, that is, the tires 1a to 1d.
[0011]
AC signals output from the wheel speed sensors 2a to 2d are input to a known electronic control unit (hereinafter referred to as an ECU) 5 including a waveform shaping circuit, a CPU, a ROM, a RAM, and the like, and are subjected to a predetermined signal processing including waveform shaping. Is performed. This signal processing result is input to the display unit 6, and the display unit 6 notifies the driver of the state of the air pressure of each of the tires 1a to 1d. The display unit 6 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 turned on when the air pressure of any one of the tires becomes lower than a reference value. May be warned. In the present embodiment, the wheel speed sensors 2a to 2d are configured as means for detecting a vibration frequency component of a tire when the vehicle is running. Further, the ECU 5 constitutes a determination unit, a first calculation unit, and a second calculation unit.
[0012]
FIG. 2 is a functional block diagram showing the configuration of the ECU 5 for each operation, and its outline will be briefly described. In FIG. 2, a wheel speed calculation unit 11 shapes the waveform of an AC signal output from the wheel speed sensors 2a to 2d (pickup coils 3a to 3d) into a pulse signal, and calculates a wheel speed V based on a pulse interval and a tire diameter. [Km / h] is calculated. Note that the wheel speed V is the speed at which the tire advances in the vehicle running direction, and matches the vehicle speed (vehicle speed).
[0013]
Further, the frequency analysis unit 12 performs frequency analysis (for example, FFT calculation) on the wheel speed V calculated by the wheel speed calculation unit 11 to calculate a signal strength for each frequency. The selection unit 13 selects one calculation method from a plurality of resonance frequency calculation methods based on the number of times of detection of the vibration frequency component or the running time of the vehicle. The air pressure detector 14 calculates the resonance frequency based on the resonance frequency calculation method selected by the selector 13, and detects the tire pressure.
[0014]
Next, the operation of the tire pressure detecting device configured as described above will be described in detail focusing on the processing operation of the ECU 5. FIG. 3 is a flowchart showing a tire pressure determination routine executed by the ECU 5. Since the ECU 5 performs the same processing for each of the tires 1a to 1d, only the processing for the tire 1a is shown here.
[0015]
When the routine shown in FIG. 3 starts, in step 101, the pulse interval (rotation angle) of the pulse signal corresponding to the detection signal of the wheel speed sensor 2a is divided by the required time and multiplied by the tire diameter. To calculate the wheel speed V [km / h]. In step 102, a frequency analysis (FFT calculation) is performed on the calculated wheel speed V to obtain a signal strength for each frequency.
[0016]
On the other hand, it was confirmed from the experimental results of the present inventors that the resonance vibration of the tire generally has the following characteristics. That is, as shown in FIG. 5, the resonance vibration of the tire mainly appears at about 40 Hz. Further, as shown in FIG. 4, the signal intensity of the wheel speed V peaks at a predetermined wheel speed V0 (50 km / h in the present embodiment) and shows a decreasing tendency at a wheel speed equal to or lower than V0 or equal to or higher than V0. From this, it has been found that the resonance vibration of the tire has a correlation with the wheel speed, and there is a wheel speed band (Vα to Vβ) where resonance vibration is easily generated.
[0017]
In addition, the signal including the vibration frequency component of the tire also includes a vibration component (noise) due to disturbance from a road surface or the like. At this time, if the wheel speed V is in the wheel speed range of Vα to Vβ, the signal intensity of the wheel speed V due to the resonance vibration is sufficiently large, so that it is hardly affected by a vibration component due to disturbance from a road surface or the like. On the other hand, when the wheel speed V deviates from the wheel speed range of Vα to Vβ, the signal intensity of the wheel speed V due to the resonance vibration becomes small, so that it is greatly affected by the vibration component due to disturbance from the road surface or the like. become. At this time, the obtained resonance frequency Fk largely reflects the influence of a random signal due to disturbance vibration from a road surface or the like, so that it is difficult to obtain a stable frequency due to resonance vibration of the tire.
[0018]
In addition, the inventor has found that the characteristics of the detection error-the number of extractions differ depending on the tire resonance frequency calculation method. FIG. 6 is a diagram showing detection error-detection frequency characteristics corresponding to two types of tire resonance frequency calculation methods. FIG. 6A shows a detection error of the tire air pressure when an averaging process is performed using all the extracted frequency analysis results. FIG. 6B shows the detection of the tire air pressure when the averaging process is performed using only the frequency analysis result when the wheel speed V is between Vα and Vβ among the extracted frequency analysis results. Indicates the error. According to FIG. 6, it can be seen that the detection error is smaller in the characteristic (b) as a whole.
[0019]
However, considering the case of traveling in an average city area, the time during which the wheel speed V is between Vα and Vβ is about 50% of the whole, and therefore, as shown in FIG. The characteristic line shifts to the right. That is, when the number of detections is smaller than N0, the tire resonance frequency calculation method of (a) has a smaller detection error and a higher detection accuracy than (b). On the other hand, when the number of detections is larger than N0, the tire resonance frequency calculation method (b) has a smaller detection error and a higher detection accuracy. Therefore, by selecting an optimum tire resonance frequency calculation method at each time based on the number of detections N0, the detection error of the tire air pressure is reduced.
[0020]
FIG. 8 is a diagram in which the horizontal axis indicates the wheel speed and the vertical axis indicates the frequency of occurrence of the wheel speed when traveling in an urban area, and the frequency of occurrence is expressed as% of the total running time. Although this data is an experimental value of running in an urban area, according to this data, the frequency of running around 50 km / h is the most frequent in urban area running, and this almost matches the wheel speed range of Vα to Vβ in FIG. I understand. "N0" in FIG. 7 is set based on the vehicle speed distribution shown in FIG.
[0021]
From the above, returning to the routine of FIG. 3, in step 103, the number of times Ns in which the wheel speed V is in the wheel speed band of Vα to Vβ is counted. This number Ns is the number of times that the wheel speed V is between Vα and Vβ within a range of a predetermined number of times NX going back from the present time, and if the vehicle is traveling at a constant speed between Vα and Vβ. , Ns = NX. In the following step 104, it is determined whether or not the number Ns is greater than a predetermined number N0 (see FIG. 7, where N0 <NX), and two types of tire resonance frequencies are determined according to the positive or negative determination result in step 104. Select the calculation method for.
[0022]
That is, when the number Ns of times when the wheel speed V is in the wheel speed band of Vα to Vβ is equal to or less than the predetermined number N0, the process proceeds to step 105, and the moving average process is performed using all the frequency analysis results extracted up to that time. carry out. If the number Ns is larger than the predetermined number N0, the process proceeds to step 106, and the moving average process is performed using only the frequency analysis result when the wheel speed V is between Vα and Vβ. The average signal strength for each frequency is calculated by the averaging process in steps 105 and 106.
[0023]
Thereafter, in step 107, the frequency range is set to f1 to f2 in order to detect the resonance vibration of the tire appearing in the vicinity of 40 Hz, and the resonance frequency Fk is obtained within the range of f1 to f2. Further, in the subsequent step 108, the air pressure P is calculated based on the resonance frequency Fk detected in the step 107 from the relationship between the resonance frequency and the air pressure shown in FIG. In step 109, it is determined whether or not the obtained air pressure P is equal to or lower than a preset allowable lower limit value Pd. If the air pressure P is equal to or lower than the allowable lower limit value Pd, the process proceeds to step 110, and the display unit 6 displays To display an alarm.
[0024]
According to the embodiment described in detail above, the following effects can be obtained.
(A) By obtaining the resonance frequency Fk by selectively using a plurality of calculation methods, the influence of noise such as disturbance can be efficiently eliminated, and the tire pressure P can be detected with high accuracy.
[0025]
(B) In the present embodiment, the resonance frequency calculation method is selected based on the number of times the vibration frequency component of the tire is detected. Therefore, for example, when the vehicle is not traveling, that is, when the vibration frequency component is not detected, the number of times of detection is not counted, and unnecessary count processing is not performed. As a result, a stable calculation result can be obtained.
[0026]
(C) In the present embodiment, the resonance frequency Fk is calculated by moving average processing using only a predetermined number of latest data. Therefore, even when the tire pressure P changes suddenly, the change in the tire pressure can be sequentially obtained. Further, the memory capacity can be reduced.
[0027]
(Second embodiment)
Next, a second embodiment of the present invention will be described. However, in the configuration of the present embodiment, the description of the same components as those of the above-described first embodiment will be omitted. The following description focuses on the differences from the first embodiment.
[0028]
In the first embodiment, the tire resonance frequency calculation method is selected by determining whether or not the number of detections of the vibration frequency component when the wheel speed V is between Vα and Vβ has reached a predetermined number. However, in the second embodiment, the tire resonance frequency calculation method is selected by determining the travel time of the vehicle.
[0029]
The processing will be described below with reference to the flowchart shown in FIG. The routine shown in FIG. 10 is different only in that steps 103 and 104 in FIG. 3 in the first embodiment are replaced with steps 201 and 202. That is, in step 201, the running time Ts in which the wheel speed V is in the wheel speed range of Vα to Vβ is measured, and in the following step 202, it is determined whether or not the running time Ts is longer than the predetermined time T0. This predetermined time T0 is a time corresponding to the number of detections N0 in FIG. In addition, the processing for determining the traveling time is for determining the traveling time Ts occupying a predetermined period (> T0) which is retroactive from the present time.
[0030]
When the number of runs Ts in which the wheel speed V is in the wheel speed range of Vα to Vβ is equal to or less than the predetermined time T0, the process proceeds to step 105, and the averaging process is performed using all the frequency analysis results extracted so far. carry out. If the running time Ts is longer than the predetermined time T0, the process proceeds to step 106, where the averaging process is performed using only the frequency analysis result when the wheel speed V is between Vα and Vβ.
[0031]
In the subsequent processing, as in the first embodiment, the resonance frequency Fk is calculated, and the air pressure P is calculated from the resonance frequency Fk.
As described above, also in the second embodiment, the same operation and effect as those of the first embodiment can be obtained, and as a result, it is possible to accurately detect the tire air pressure.
[0032]
(Third embodiment)
Next, a third embodiment will be described in which a part of the first embodiment is modified and embodied. In the first embodiment, the number of detections Ns of the vibration frequency component in which the wheel speed V is between the wheel speed bands Vα to Vβ is counted, and 2 is determined according to whether the number Ns exceeds a predetermined number n0. Although one of the three resonance frequency calculation methods is selectively used, in the present embodiment, one of the three resonance frequency calculation methods is selectively used.
[0033]
That is, as shown in FIG. 11, new wheel speed bands Vγ1 to Vγ2 are provided in the range of the wheel speed bands Vα to Vβ. In this case, three types of resonance frequency calculation methods are provided according to the respective wheel speed bands, and FIG. 12 shows detection error-extraction frequency characteristics in the three types of resonance frequency calculation methods. FIG. 12A shows a detection error of the tire air pressure when an averaging process is performed using all the extracted frequency analysis results. FIG. 12B shows the detection of the tire air pressure when the averaging process is performed using only the frequency analysis result when the wheel speed V is between Vα and Vβ from the extracted frequency analysis results. Indicates the error. Further, FIG. 12 (c) shows the detection of the tire air pressure when the averaging process is performed using only the frequency analysis result when the wheel speed V is between Vγ1 and Vγ2 from the extracted frequency analysis results. Indicates the error.
[0034]
In such a case, when the number of detections is smaller than N0, the tire resonance frequency calculation method of (a) has the smallest detection error, and when the number of detections is N0 to N1, the tire resonance frequency calculation method of (b) has the smallest detection error. Further, it can be seen that when the number of detections is greater than N1, the tire resonance frequency calculation method (c) has the smallest detection error.
[0035]
FIG. 13 is a flowchart showing a part of the tire pressure determination routine in the present embodiment. This routine is a modification of part of FIG.
[0036]
According to FIG. 13, in step 103, the number of times Ns in which the wheel speed V is in the wheel speed band of Vα to Vβ is counted, and in the following step 301, the number of times Ns1 in which the wheel speed V is in the wheel speed band of Vγ1 to Vγ2 is calculated. Count. In the following step 302, it is determined whether or not the number Ns is greater than a predetermined number N0 (see FIG. 12). If Ns ≦ N0, the process proceeds to step 304, and all frequency analysis results extracted so far are used. To perform moving average processing. If Ns> N0, the process proceeds to step 303, where it is determined whether or not the number Ns1 is greater than a predetermined number N1 (see FIG. 12).
[0037]
If Ns1 ≦ N1, the process proceeds to step 305, and the moving average process is performed using only the frequency analysis result when the wheel speed V is between Vα and Vβ. If Ns1> N1, the process proceeds to step 306, and the moving average process is performed using only the frequency analysis result when the wheel speed V is between Vγ1 and Vγ2.
[0038]
As described above, also in the third embodiment, the same operation and effect as those in the first and second embodiments can be obtained, and as a result, it is possible to accurately detect the tire air pressure. In particular, in the present embodiment, a third resonance frequency calculation method in which the detection error is smaller than that of the first embodiment is set, and the resonance frequency calculation method is selected from among the three additional resonance frequency calculation methods. Since the selection is made, a more accurate detection result can be obtained.
[0039]
The present invention can be embodied in the following modes in addition to the above embodiment.
(1) In the above embodiments, the wheel speed (= vehicle speed [km / h]) is obtained from the detection results of the wheel speed sensors 2a to 2d, and the resonance frequency calculation method is selected based on the wheel speed. This may be changed. For example, the rotational speed [deg / unit time] of the tires 1a to 1d may be obtained, and the resonance frequency calculation method may be selected based on the rotational speed. In such a case, the horizontal axis in FIG. 4 indicates the rotation speed of the tire, and the process of determining a band in which resonance vibration is likely to occur is also performed based on the rotation speed.
[0040]
(2) In the second embodiment, the method of calculating the resonance frequency is selected based on the vehicle travel time, but the vehicle travel time may be changed to the vehicle travel distance.
(3) In the third embodiment, three types of resonance frequency calculation methods are set, but four or more types of calculation methods may be set.
[0041]
(4) The power spectrum in the present invention is for indicating the signal strength of the vibration frequency component, and the above-mentioned power spectrum is used even when another signal strength (energy spectrum, intensity spectrum, etc.) used in agreement with the power spectrum is used. The same operation and effect as in the embodiment can be obtained.
[Brief description of the drawings]
FIG. 1 is a configuration diagram illustrating an outline of a tire pressure detection device according to an embodiment of the invention.
FIG. 2 is a functional block diagram showing a configuration of an ECU for each operation.
FIG. 3 is a flowchart illustrating a tire air pressure determination routine according to the first embodiment.
FIG. 4 is a diagram showing a power spectrum peak of resonance vibration corresponding to a wheel speed.
FIG. 5 is a waveform diagram showing a relationship between a power spectrum of a wheel speed and a frequency.
FIG. 6 is a diagram showing a relationship between the number of times of resonance vibration detection and a detection error in two types of resonance frequency calculation methods.
FIG. 7 is a diagram showing a relationship between the number of times of detection of resonance vibration and a detection error when traveling in an urban area.
FIG. 8 is a diagram showing the relationship between the wheel speed and the frequency when traveling in an urban area.
FIG. 9 is a diagram showing a relationship between a resonance frequency and a tire pressure.
FIG. 10 is a flowchart illustrating a tire air pressure determination routine according to the second embodiment.
FIG. 11 is a diagram showing a power spectrum peak value of resonance vibration corresponding to a wheel speed.
FIG. 12 is a diagram showing a relationship between the number of times of detection of resonance vibration and a detection error when traveling in an urban area in the third embodiment.
FIG. 13 is a flowchart illustrating a tire air pressure determination routine according to a third embodiment.
[Explanation of symbols]
1a to 1d: tires, 2a to 2d: wheel speed sensors, 5: ECU as discriminating means, first calculating means, and second calculating means.

Claims (3)

While detecting the vibration frequency component of the tire when the vehicle is traveling, the resonance frequency of the tire is calculated using the detection result of the tire vibration frequency component, and further, the air pressure of the tire is calculated based on the calculated resonance frequency of the tire. A tire pressure detection device for detecting
A predetermined wheel speed band is set on the basis of the wheel speed at which the peak value of the power spectrum of the resonance vibration of the vibration system including the tire exhibits the maximum value, and the number of detection of the vibration frequency component of the tire in the wheel speed band, or the vehicle Determining means for determining whether the traveling time exceeds a predetermined value,
First calculation means for calculating a resonance frequency of the tire using a detection result of an arbitrary tire vibration frequency component when the number of times of detection of the vibration frequency component in the wheel speed band or the vehicle traveling time does not exceed a predetermined value; ,
When the number of times of detection of the vibration frequency component in the wheel speed band or the vehicle traveling time exceeds a predetermined value, a second resonance frequency of the tire is calculated using only the detection result of the tire vibration frequency component in the wheel speed band. A tire pressure detecting device comprising: The tire pressure detecting device according to claim 1, wherein the predetermined value for determining the number of times of detection of the tire vibration frequency component or the vehicle traveling time by the determination unit is set based on a distribution of wheel speeds during traveling of the vehicle. The determination means determines whether the number of detections of the vibration frequency component in the wheel speed band within a predetermined number of times or a predetermined time or whether the vehicle traveling time exceeds a predetermined value,
The tire pressure detecting device according to claim 1 or 2, wherein the first and second calculation means calculate the resonance frequency of the tire by a moving average process for a predetermined number of times or within a predetermined time.

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