JP3149624B2 - Tire pressure detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tire pressure detecting device for detecting a decrease in air pressure of a vehicle tire.

[0002]

2. Description of the Related Art Conventionally, a decompression warning device measures the characteristics of a tire, for example, internal pressure or temperature, and transmits a signal to a vehicle body. The transfer has been performed by an electric signal or wirelessly through a slip ring provided in the hub. Such systems are expensive and very unreliable, especially under conditions that are unfavorable for the vehicle and, in rare cases, tire punctures.

[0003] Theoretically, tires, especially those with breakers, have a fixed, fixed circumferential tread,
The tread is running on each wheel at the same speed as the vehicle speed on the road with respect to the vehicle concerned. A fixed length of circumference means that each wheel rotates at the same angular velocity, despite the reduced pressure in the area of contact with the ground. However, it has been found that when pressure loss occurs in the tire, the radial tire rotates at an increased angular velocity (Japanese Patent Application Laid-Open No. Sho 63-305011). As a device for detecting a reduction in air pressure of a tire, a method of detecting a reduced pressure tire of a vehicle using a change in the rotation speed of the tire has been proposed.

[0004] Such a solution makes use of a speed detector, such as a variable magnetic reluctance detector, which is already widely used in vehicles with excellent reliability and with anti-locking devices for wheels. Attractive because it can be made possible. In vehicles already equipped with such a device, this solution is additionally particularly economical. This is because, in order to do so, only supplementary logic means implanted in the computer of the anti-locking device and the above-mentioned alarm means are required.

[0005] In contrast, this solution involves a rolling radius (and thus an angular velocity) induced by the bleeding of the tire (eg with a radial casing ply).
The major difficulties due to the fact that changes in the vehicle dynamics are an order of magnitude less than those normally induced in those tires by some phenomenon of vehicle dynamics must be overcome. Such changes may occur, for example, as a result of braking or accelerating the vehicle, turning the wheels, driving the vehicle uphill or downhill, driving on uneven or curved roads. As such, the relative change in angular velocity due to 0.2 bar air bleed to normal filling pressure is on the order of 0.1%, while
Even at low speeds, for example, it was possible to measure that the relative change due to the passage of the vehicle on a curve with a radius of curvature of 30 m was about 5%.

In Japanese Unexamined Patent Publication No. Hei 4-232107, a difference in the square value of angular velocity is used in order to make it possible to overcome the error caused by the non-square angular velocity value disclosed in Japanese Unexamined Patent Publication No. 63-305011. It was proposed to. However, even when the difference in the square value of the angular velocity is used, the tire radius to be detected is subject to individual differences due to wear and the like, and is easily affected by running conditions such as turning, braking, and starting. Further, radial tires, which have become very popular in recent years, have a small amount of deformation of the tire radius due to a change in tire air pressure (for example, when the air pressure of the tire decreases by 1 kg / cm ^{2, the} amount of deformation of the tire radius is about 1 mm). For these reasons, the method of indirectly detecting a change in tire air pressure from the amount of deformation of the tire radius has a problem that sufficient detection accuracy cannot be ensured.

In Japanese Patent Application No. 3-294622, the applicant of the present invention outputs an output signal including a tire vibration frequency component when the vehicle is running, and extracts a resonance frequency from the signal including the tire vibration frequency component. The present invention has proposed a tire pressure detection device including an extraction unit and a detection unit that detects a state of the tire air pressure based on the resonance frequency. According to the above configuration, the resonance frequency is extracted from the signal including the vibration frequency component of the tire, and the state of the tire air pressure is detected based on the extracted resonance frequency.

Here, when the air pressure of the tire changes, the spring constant of the tire changes accordingly. Since the resonance frequency in the vibration frequency component of the tire changes due to the change in the spring constant of the tire, the state of the tire air pressure can be detected based on the extracted resonance frequency.

[0009]

However, in the technique for detecting the resonance frequency, the gain of the resonance signal is too small, for example, on a very well-maintained flat road surface where there is no road surface input where tire resonance occurs. It is possible that the reliability of the result is reduced. Each of the conventional detection methods has superiority in detection performance in various traveling states due to its detection principle. In these detection methods, correction coefficients for improving the detection accuracy are separately prepared, but it is very difficult to cope with various running conditions including tire change and aging by the user, and the problem to be solved is such. was there.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the present invention has been developed in order to solve the above-mentioned problems by using together with the above-mentioned means for judging the air pressure having different detection principles. An object of the present invention is to improve the overall detection accuracy of the detection device.

[0011]

According to the present invention, there is provided a tire rotating speed detecting means for detecting a signal including a rotating speed component of a plurality of tires, and a tire rotating speed signal as a specific means for solving the above-mentioned problem. From the resonance frequency,
First determining means for determining the state of the tire pressure based on the tire resonance frequency, and second tire pressure determining means for comparing the tire rotation speed signal and determining the state of the tire pressure based on the comparison result; Vehicle running state detecting means for detecting a running state of the vehicle and outputting a running state detection signal; and switching output means for switching and outputting the determination values of the first and second tire air pressure determining means according to the vehicle running state. , A tire pressure detecting device is provided.

[0012]

According to the tire pressure detecting device described above, the known tire pressure detecting device utilizing the change in the number of rotations of the tire and the tire pressure detecting device utilizing the change in the resonance frequency of the tire detect the change in the resonance frequency. Although the detection accuracy of the detecting device is reduced on a uniform road surface on which vibration is unlikely to occur, the tire rotation speed is relatively stable on such a road surface, and the detection capability can be maximized.
In addition, when the vehicle runs on a curve, in addition to the difference in the turning radius, complicated factors such as the movement of the load and the application of G in the front-back or lateral direction affect the tire rotation speed. On the other hand, when the vehicle travels on a curve, the resonance frequency of the tire is not affected by the speed difference caused by the difference in turning radius, and the resonance frequency fluctuation due to load movement or acceleration / deceleration is relatively small. It is possible to maintain the same detection accuracy as time.
Therefore, by switching and outputting each detection device according to the traveling state of the vehicle including these road surface states, it is possible to correspond to any traveling state.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a tire pressure detecting device according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a configuration diagram showing the overall configuration of the tire pressure detection device. Tire rotation speed sensors are provided for the respective tires 1a to 1d of the vehicle. The rotation speed sensor of each tire is constituted by gears 2a to 2d and pickup coils 3a to 3d. The gears 2a to 2d are mounted on the rotating shafts of the tires 1a to 1d and are made of a disk-shaped magnetic material. The pickup coils 3a to 3d are mounted near these gears 2a to 2d at predetermined intervals, and output an AC signal having a cycle corresponding to the rotation speed of the gears 2a to 2d, ie, the tires 1a to 1d. AC signals output from the pickup coils 3a to 3d are input to a known electronic control unit (ECU) 4 including a waveform shaping circuit, a ROM, a RAM, and the like, where predetermined signal processing including waveform shaping is performed. The result of this signal processing is input to the display unit 5, which displays each of the tires 1a to 1a.
The state of the air pressure of 1d may be displayed independently, or one warning lamp may be provided to illuminate when any one of the tire air pressures falls below the reference air pressure to warn the user. .

An outline of the operation of the tire pressure detecting device having the above configuration will be described first with reference to a flowchart showing the main processing of FIG. The ECU 4 performs steps 010, 050, 080, 1 for each of the tires 1a to 1d.
The processes from 50 to 170 are performed individually for four wheels, and the other steps are performed only once for four wheels. First, in step 000, the RAM is initialized and its initial value is set. In step 010, after the AC signal output from the pickup coil 3 is shaped into a pulse signal by waveform shaping, the pulse interval is divided by the time therebetween to calculate the tire rotation speed V. The tire rotation speed V usually includes many high-frequency components including a tire vibration frequency component. In step 020, the average speed VAVE is calculated from the calculated values of the rotation speeds Va to Vd of the respective tires. In step 030, a counter that counts the number of times the tire rotational speed is calculated is counted up. In addition, N1 is a counter for judging the start of calculation of the tire rotation speed, and N2 is a counter for calculating the resonance frequency. In step 040, it is determined whether or not the value of the counter N1 has reached the number of accumulations n1 for calculating the tire rotation speed.
Is performed. If the number of times of integration has not reached n1, the process proceeds to step 055 to sequentially calculate the integrated value of the integrated speed and the average speed of each tire.

In step 060, when the air pressure detection processing is completed in step 050, the counter N1 is used for the next calculation.
Then, the integrated values of the integrated speed and the average speed of each tire are cleared to zero. In the next step 070, the counter N2 is compared with a predetermined number n2 as in step 040, in order to determine the integration timing of the resonance frequency. This n2
Means the number of data for performing a frequency analysis operation (hereinafter simply referred to as an FFT operation) described later. Step 07
When it is determined that the FFT operation can be started at 0, the process proceeds to step 080, where the FFT operation is executed, and the air pressure detection process 300 based on the resonance frequency described later is performed. Step 090
Is a process for clearing the counter N2 to zero for the next detection. The next step 100 is a process 400 to be described later for estimating the running state of the vehicle from information such as the rotational speed of the tire and the resonance frequency. In step 100, the running state of the vehicle is classified into three stages of running states A, B, and C in order to determine whether the detection accuracy of the tire rotation speed or the resonance frequency is more reliable.

In the running state A, a weight is placed on the K1 side with respect to the weighting coefficients K1 and K2 of the air pressure judgment results P1 and P2 for calculating the output air pressure when the reliability of the judgment result of the tire rotation speed is higher. KA1 and KA2 are set, and the routine proceeds to step 150. When it is determined that the running state is B, the determination accuracy of the resonance frequency is more reliable. Therefore, in step 140, coefficients KB1 and KB2 in which K2 is given a weight are set, and the routine proceeds to step 150. When the traveling state is C, the determination value of the detection means of either the tire rotation speed or the resonance frequency is set to a state of low reliability, and the process proceeds to step 170, so that the display of the air pressure is not updated. Here, a predetermined display state may be displayed in step 160 to warn the user that it is difficult to determine the air pressure without proceeding to step 170.
In step 150, the air pressure P to be output is calculated using the coefficients K1 and K2 set in step 120 or 140.

If it is desired to output the judgment values of the two detecting means by switching instead of weighting, the setting coefficient KA1 =
It can be easily realized by substituting set values such as 1.0 and KA2 = 0.0. The process of step 160 is a process of updating the display circuit based on the calculated air pressure P. The next step 170 is to detect, from the judgment values of the two detecting means, a case where a change factor other than air pressure, such as aging of a tire or a suspension, or a user's replacement of a tire or a wheel has occurred, and a normal tire is detected. This is processing 500 to be described later for learning to change the rotation speed and the resonance frequency, and enables accurate detection of the air pressure even when such a fluctuation occurs. The above is the description showing the overall flow of the apparatus of the present invention, and the following describes in detail each processing.

FIG. 3 shows a process 200 for calculating the air pressure based on the tire rotation speed. In steps 220 and 230, the air pressure P1i is calculated for each tire. First, at step 210, a which is a front right tire (hereinafter referred to as an FR tire) is set to a variable i indicating each tire number. Next, at step 220, the difference DVi between the integrated value of the tire and the average speed integrated value of the front and rear left and right tires is calculated. If there are no other factors that affect the tire rotation speed such as the influence of the load movement, the turning radius, and the tire wear, since this DVi is a variation due to the air pressure, multiply the correction coefficient KG1 as shown in step 230. The amount of change in air pressure △ P1 can be calculated with. If the difference between the ΔP1 and the normal pressure P0i is obtained, the current air pressure P1i can be calculated. In step 240, the variable i is incremented and a similar determination is made for the next tire. Step 25
0 is a rear left tire (hereinafter referred to as R) in which the variable i is the last tire.
It is determined whether or not the value is d indicating the L tire). If the value is equal to or more than d, the calculation of the front and rear left and right tires is completed, and the process returns to the main process 000 from the air pressure detection process.
Here, the air pressure is determined by comparing the average rotational speed of the front and rear wheels left and right tires and each tire rotational speed, for example, the average rotational speed between diagonal tires and front and rear and left and right tires,
The detection of the air pressure may be performed by using the difference processing or the like together.

FIG. 4 shows a process 300 for detecting air pressure based on the resonance frequency.
The air pressure P2i is calculated by the processing of 0 to 370. First, at step 310, a which is an FR tire is set to a variable i indicating each tire number. Next, in step 320, an FFT operation (frequency analysis operation) is performed to obtain a frequency distribution from the n1 tire rotation speeds that are time axis data.
Next, at step 330, a counter N21 for counting the number of acquired frequency data is counted up. This is to remove specific noise generated due to the influence of the accuracy of the tire rotation speed sensor, the road surface, and the like by an averaging process. In step 340, it is determined whether or not a predetermined number of times n21 has been reached. In the case of arrival, in step 345, addition processing is performed for each frequency with respect to the frequency information, and the process proceeds to the next tire without determining the air pressure. The judgment value is held.)

If it is determined in step 340 that the number of integration times n21 at which the resonance frequency can be detected has been reached, step 35
The process proceeds to 0 to perform a process of averaging the data integrated value in the frequency domain for each frequency. Next, in step 360, a process of calculating a resonance frequency from the frequency distribution obtained by averaging is performed. Specifically, for example, gain comparison of each frequency in a frequency range set by adaptation or the like in advance is performed, and the frequency having the maximum value is set as the resonance frequency fK.
Next, the air pressure P2i is calculated by a predetermined conversion from the resonance frequency fK obtained in step 370. Specifically, FIG.
As shown in FIG. 5, the conversion map of the resonance frequency-air pressure based on the characteristics of the vehicle (including the tire) is stored in the RO of the CPU.
It can be easily realized by setting it to M or the like. Step 3
At 80, the same determination is made for the next tire by incrementing the variable i. In step 390, it is determined whether or not the variable i is d indicating the RL tire as the last tire.
Returns to 0.

FIG. 5 shows a process 400 which is an example of a method for detecting a running state. This is for detecting a road surface input and weighting the determination value of each detecting means according to the degree of roughness. First, in step 410, a predetermined band (here, a DC component as an absolute value of the tire rotation speed component) can be cut in order to extract a vibration component for determining the degree of road surface roughness from the tire rotation speed information. A high-pass filter (H, P, F) processing of the tire rotation speed is performed by a high-pass digital filter having a preset coefficient as in the following arithmetic expression. However, Ka1 to K
b2 is a constant determined by the filter cutoff frequency.

VAC (n) = Ka1 · Vi (n) + Ka2 · Vi (n−1) + Ka3 ·
Vi (n-2) + Kb1 · VAC (n-1) + Kb2 · VAC (n-2) This Vi may be obtained individually for each tire,
The average value of only the rolling tires or information on any one of the rolling tires may be used as a representative value for the purpose of removing the vibration inherent in the driving system. Next, in step 420, the average vibration width DVAC of the obtained vibration component VAC within a predetermined time is calculated, and in step 430, the average is compared with a predetermined threshold level THR1. This threshold level THR1 sets the upper limit vibration level at which the detection accuracy of the air pressure based on the tire rotation speed is superior to that of the resonance frequency. If DVAC is smaller than the threshold value, the process proceeds to step 450, where the weighting coefficient is set to the tire rotation speed. The traveling state A, which is a state for favoring the speed side, is set, and the process returns to the main processing 000.

If it is determined in step 430 that the vibration level is equal to or higher than THR1, the routine proceeds to step 440, where TH
Threshold level THR2 set to a value greater than R1
Is compared. This threshold level THR2 sets the maximum vibration level that can be detected at the resonance frequency, and on extremely bad roads that exceed a certain vibration level, the resonance frequency is mixed with the vibration noise level due to the road surface and cannot be separated. This is because it becomes difficult to detect the resonance frequency (the characteristics of the resonance frequency with respect to the road surface input level are shown in FIG. 17). Further, as is clear from the principle, the means for detecting the air pressure based on the tire rotation speed makes it impossible to compare the rotation speeds of the tires on these rough roads due to the influence of random vibration, and it is also impossible to ensure the detection accuracy (for the road surface of the tire rotation speed). The characteristics with respect to the input level are shown in FIG. 18). Therefore, when the vehicle is traveling on such an extremely rough road surface, the updating or display of the air pressure is stopped by setting the running state C in step 470. It should be noted that a rough road surface on which the resonance frequency cannot be seen is not sufficiently reduced in system performance because both the frequency and the duration thereof are sufficiently small in general road running.
If it is determined in step 440 that DVAC is smaller than THR2, the traveling state B is set in step 460 on the assumption that the accuracy of the air pressure obtained from the resonance frequency is sufficiently ensured.

FIG. 6 shows a process 500 for learning to change from two types of detected values to normal pressure in order to prevent erroneous detection of air pressure due to a change in tire rotational speed or resonance frequency due to aging or the like. . Step 510
Is a process of determining whether or not learning is to be performed in order to perform the mutual comparison between the detected values under predetermined conditions with as little disturbance noise as possible. Here, for example, a straight running state or an acceleration / deceleration degree is determined based on the rotation speed of each tire, and it is determined whether or not the vehicle is in a straight running state in which the degree of acceleration / deceleration is small. Is defined as a learning permission state. If it is determined in step 510 that the state is not the learning permission state, the process returns to the main process 000. Conversely, when the learning is permitted, first, at step 520, it is determined whether the air pressure determination value P1 based on the tire rotation speed is a normal pressure. If the air pressure is normal pressure, the process proceeds to step 530, and it is similarly determined whether the air pressure is normal pressure based on the air pressure determination result P2 based on the resonance frequency. If both of the detected pressures are normal values, it is determined that normal pressure has not occurred over time and the process returns to the main process 000.

If the determination value of the resonance frequency is different from the normal value in step 530, possible causes in the running state include a change in the flatness due to a change in the tire or the wheel, a reduction in the weight, or a suspension bush. It can be determined that the tire has changed over time or has been changed from a radial tire to a studless tire. Therefore, in step 550, the conversion map 2 for calculating the air pressure from the resonance frequency is changed. As a specific changing method, the detected air pressure value is changed by linearly changing the front and rear resonance frequencies as shown in FIG. If the detected value of the air pressure based on the tire rotation speed is not the normal pressure in step 520, it is determined in step 540 whether the detected pressure based on the resonance frequency is the normal value. Here, when the air pressure P2 indicates a normal value, it can be detected that the tire has changed due to the wear of the tire or a change in the tire diameter. In this case, the process proceeds to step 560 to change the tire diameter. Specifically, the average tire speed VAVE of the front and rear left and right tires, the tire diameter Ri (n-1) of each wheel corrected up to the previous time, and the tire rotation speed Vi are corrected for each wheel tire by the following equation. The diameter Ri (n) is calculated.

## EQU2 ## Ri (n) = Ri (n-1). (Vi / VAVE)

Since the subsequent calculation of the tire rotational speed is performed based on the newly changed Ri, it is possible to continue to detect a pure air pressure change. Step 540
If it is determined that the air pressure P2 is also not normal pressure, the process returns to the main process 000 without making any change because the decrease in air pressure and aging cannot be separated. The air pressure detection values P1 and P2 referred to here may be individually determined for each tire, or the front tires or the rear tires may be considered in consideration of the improvement in determination accuracy, aging, and the actual state of tire changes. By performing an averaging process and an AND process on, the situation such as aging can be analyzed in more detail. With the above processing, air pressure detection with improved accuracy in all aspects compared to the conventional system can be realized, and learning of the initial state, which is considered to be the biggest problem with the conventional system, can be realized without the user's hands Maintenance-free system.

Next, a second embodiment of the present invention will be described. FIG. 7 shows a method 600 for detecting the turning state as the running state and switching the air pressure detecting means. In step 610, first, a speed difference between the left and right tires generated in the turning state is calculated. In general, a speed difference occurs between the front and rear wheel tires in the turning state, so that accurate detection can be performed by calculating parameters of the front wheel tire and the rear wheel tire such as DVF and DVR. The rotation speed of each tire used here can be accurately determined by the following process if the front and rear tires are normal pressure, but if any of the tires has an abnormal air pressure, In this case, it is impossible to accurately determine the turning state because the rotation speed of the tire is affected. As a countermeasure in that case, if an abnormality in the air pressure has already been detected by the previous determination, use the tire rotation speed that has been changed in consideration of the change in the tire diameter with respect to the rotation speed of the corresponding tire. (The changing method can be dealt with by the same method as the changing method of the tire diameter described in FIG. 6).

In the next step 620, it is determined whether or not the rotational speed difference DVF of the front wheel tires is equal to or less than the rotational speed difference that appears in a turning state that is equal to or greater than a predetermined value. This threshold level THV
FA represents a rotation speed difference in a turning region in which the tire rotation speed and the resonance frequency change nonlinearly under the influence of the lateral G and the load movement, and is a constant obtained from experimental data (resonance frequency and turning radius). 20 is shown in Fig. 20. The right and left wheel difference of the tire rotation speed and the turning radius are shown in Fig. 19). Further, the constant may be switched according to the rotation speed of the tire. The same applies to each of the threshold levels described below. Where DVF is THVFA
Is exceeded, the running state C is set in step 680 on the assumption that both types of detection results are unreliable. If DVF is less than THVFA, step 630
The same determination is made for the rear wheel tire. Step 6 if both front and rear tires are below the threshold level
Proceeding to 40, the level determination of the rotational speed difference of the front wheel tires is performed again. THVF set here represents a rotation speed difference level in a substantially straight traveling state in which a difference in tire rotation speed due to turning does not occur.

In step 650, the same judgment is made on the rear wheel tires, and if the front and rear wheel tires have detected the straight running state, the judgment result of the air pressure based on the tire rotation speed can be used. Select In other turning states, the running state B is set in step 670 in order to use the detection result of the resonance frequency.
In this way, the detection result of the tire rotational speed is used when the vehicle is in a stable running state relatively close to straight traveling, and the detection result of the resonance frequency is used in the turning state where no change occurs in the resonance phenomenon. In the rapid turning state (the ratio of the actual traveling to the actual traveling is sufficiently small and does not lead to the deterioration of the detection performance), the processing for retaining the previous detection result can be realized. The other processes in the present embodiment are the same as those in the first embodiment. In addition, although the tire rotation speed information is used for the determination of the turning state this time, a separate sensor capable of directly detecting the turning state (for example, a steering wheel angle sensor or a yaw rate sensor) is used to further determine the turning state. It is also possible to improve the detection accuracy.

Next, a third embodiment of the present invention will be described. FIG. 8 shows a method 700 for detecting the acceleration / deceleration state of the rolling wheel not connected to the engine as the running state and switching the tire air pressure detecting means. First, VT0 is calculated in step 710 to obtain the current vehicle speed. Generally, in the accelerated state, no slip occurs in the rotation speed of the rolling wheel, so that the rotation speed information of the rolling wheel can be used. Further, in the deceleration state, variations in each tire drop state on a low μ road or the like are assumed, but sufficiently practical estimation accuracy can be achieved by using a predetermined deceleration guard together (provided by ABS and TRC). Further, in order to correct the rotational speed difference between the inner and outer wheel tires in the turning state, a method of averaging the rotational speeds of the left and right rolling wheels is effective. With respect to the estimated vehicle speed VT0 calculated in this manner,
By observing the time change, the acceleration / deceleration (D
VT). In step 720, the calculated DVT is compared with a predetermined constant THVT1 larger than the next threshold level. When acceleration or deceleration is performed at a predetermined level or more in the same manner as in the turning state, the resonance phenomenon fluctuates due to a change in the grounding load, so that the reliability of the detection result of the resonance frequency also decreases.

Both THVT1 and TVT are constants obtained from experimental data. In step 720, the acceleration / deceleration is THV
If it is determined that it is larger than T1, the running state is set to C in step 760, and the previous detection result is held. Otherwise, the process proceeds to step 730 and the next threshold level THV
A comparison with T2 is performed. This threshold level THVT2
Is a constant that is set to a value close to almost constant running. In such a state, the slip level of each tire is sufficiently small, and thus the accuracy of air pressure detection based on the tire rotation speed is stable.
Therefore, if the acceleration / deceleration is smaller than THVT2, the routine proceeds to step 740, and the traveling state is set to A. If the acceleration / deceleration is greater than that, the traveling state B is set in step 750 to use the detection result of the resonance phenomenon.
The threshold levels THVT1 and T2 are affected by the coefficient of friction between the road surface and the tire.
It is also possible to provide a means for detecting the state and to correct the threshold levels THVT1 and T2 based on the detection result (the effect of the acceleration of the two-wheel drive vehicle on the difference between the front and rear tires of the tire rotation speed is shown in FIG. 21). . Further, instead of the estimation calculation based on the tire speed information, a direct detection means such as a ground speed meter may be used.

Next, a fourth embodiment of the present invention will be described. FIG. 9 shows a method 800 for detecting a load shift due to a change in the attitude of the vehicle (roll, pitch, yaw) as a running state and switching the method of detecting tire pressure. In step 810, each state quantity is detected using a sensor that directly detects roll, pitch, and yaw in each running state. In step 820, first, the roll amount is compared with a predetermined constant KMRA. The threshold level is set at a level at which both the tire rotation speed and the resonance frequency fluctuate due to the load movement. If the threshold level is higher than the threshold level, the process proceeds to step 895, where the traveling state C is set and the previous detection result is held. If the roll amount is at a level lower than KMRA, a comparison is made at step 830 with a lower threshold level KMR. If the roll amount is equal to or greater than the threshold level KMR, a change in the tire rotational speed occurs due to the movement of the load, so that the reliability of the detection result based on the tire rotational speed decreases. Therefore, the process proceeds to step 880 to set the running state to B, thereby calculating a detection result with a weight placed on the resonance frequency detection result. The processing in steps 850 to 870 is processing for making the same determination as in the case of roll for pitch and yaw. If all the detection results are below the predetermined value, the running state A is set at step 890 because the change due to the load movement of the tire rotation speed is at a level that can be ignored. still,
The detection of each moment can be substituted by combining the tire rotation speed and the output of the G sensor. The ground load characteristics of the tire rotation speed and the resonance frequency are shown in FIGS.

Next, a fifth embodiment of the present invention will be described. FIG. 10 illustrates a method 900 for detecting the traveling speed of the vehicle as the traveling state and switching the method of detecting the air pressure. On an actual road surface, the road surface condition is good on a road surface that is assumed to run at a relatively high speed such as a highway,
The frequency of road surface unevenness that causes the resonance phenomenon decreases. Therefore, first, in steps 910 to 930, the road surface input and the vehicle speed used in the first and third embodiments are calculated. Step 940
Then, based on the calculated traveling speed VT0, a road surface input suitable for the current traveling state is searched. This search method can be easily realized by using a map indicating the relationship between the vehicle speed and the threshold level set in a program in advance. The threshold level at each speed can be obtained from experimental data. In step 950, the current road surface input D is set for the threshold level THR thus searched.
Compare with VAC.

If the value of DVAC is smaller than THR, the effect on the tire rotation speed is at a level where the influence on the tire rotation speed can be ignored, as in the case of the first embodiment. On the other hand, on the road surface where DVAC is equal to or higher than THR, the resonance phenomenon can be accurately grasped.
At 0, the running state B is set. In this way, a method of detecting an air pressure optimal for each traveling state is selected. Although detailed explanations are not given here, in general, when the running speed of the vehicle increases, the effect of the centrifugal force generated on the tires on the tire rotation speed becomes a level that cannot be ignored, so only the running speed is set to a predetermined threshold. Compared with the level, if the threshold value is equal to or higher than the threshold level, it is possible to set the traveling state to B and prioritize the detection result of the resonance frequency. FIG. 24 shows the effect of the centrifugal force on the tire rotation speed depending on the running speed.

Next, a sixth embodiment of the present invention will be described. FIG. 11 shows a method 10 for detecting various running conditions, performing a comprehensive evaluation of these, and switching the method of detecting air pressure.
00 is shown. In an actual vehicle, the above-mentioned traveling states rarely occur independently, and a traveling state in which various states are combined is general. There is no problem in a case where a plurality of traveling states make only one of the air pressure detecting means advantageous, but there are advantages and disadvantages in either air pressure detecting method such as turning on a good road surface, and cannot be selected unconditionally. . The present embodiment describes a method for accurately detecting the air pressure in these actual running conditions. Here, for each running state, an evaluation amount for determining which detecting means is advantageous from the degree is introduced. As the evaluation amount, the evaluation amount is sequentially corrected to the traveling states B and C from the degree of each traveling state based on the traveling state A. Specifically, for example, the initial setting value of the evaluation value is set to 0, and 1
As shown by 010, each running state is detected by the method shown in the first to fifth embodiments. Next steps 1020 to 1050
Then, a predetermined amount when the resonance frequency is advantageous is added based on each detection result.

If any one of the detection results of each state affects the resonance phenomenon, a threshold value THLB set separately is added to the evaluation value to automatically set it in the subsequent processing. I do. In step 1060, a comparison is made with the threshold level THLA for the evaluation values for which evaluation has been completed for all states. This threshold level is set as an evaluation amount in a running state in which the detection result based on the tire rotation speed has no influence. Then, the driving state B is selected only when the evaluation amount is between these two threshold levels.
Also, separately from this, priority is set for each running state from a state having a high influence on each air pressure detecting means,
It is also possible to perform the determination in that order and switch the traveling states A to C. Further, a method of continuously switching the weighting coefficients K1 and K2 to the respective air pressure detection results based on the evaluation amount without separating the traveling state into the three states may be employed, or a combination of these methods may be employed. good.

Next, a seventh embodiment of the present invention will be described. FIG. 12 shows another embodiment 1100 for learning a change in the detected value of the normal pressure (tire rotation speed, resonance frequency) generated due to aging or the like. This embodiment is based on the premise that a manual switch or the like operated by a user or the like is installed, and a device that informs the system that the tire pressure is normal when the switch is pressed is added. In step 1110, it is determined whether this change request has been transmitted to the system side. If there is no change request, the process returns to the main process 000 similar to the embodiment without making any change. If it is detected that a change request has occurred, step 1120 is performed.
It is determined whether or not the vehicle is in a changeable traveling state.

The changeable running state here is a running state in which there is no change in tires or an element affecting the resonance frequency. Such a running state is determined by the running state detecting means described in each of the above embodiments. It is determined using Step 1
If it is determined in step 120 that the vehicle is in a changeable traveling state, the process proceeds to step 1130, where the current tire rotation speed,
The detection value for the normal pressure is changed using the resonance frequency detection value as in the first embodiment. In general, the running state in which the tire diameter can be detected stably is often different from that of the resonance frequency. Therefore, a learning permission state may be individually provided and independently changed.

Next, an eighth embodiment of the present invention will be described. FIG. 13 shows a method 1200 for displaying or updating the air pressure only when the judgment results of the air pressure judgment means using the tire rotation speed and the resonance frequency match. The processing from Steps 1210 to 1290 is the same as the processing from Steps 010 to 090 in the first embodiment, and the description of the contents thereof will be omitted. In step 1293, the detected pressures P1 and P2 by the respective determination means are compared with each other. As a result of the comparison, the process proceeds to step 1295 and displays the air pressure only when the respective determination results are equal (the case where the values are within a predetermined range may be included).

Next, a ninth embodiment of the present invention will be described. FIG. 14 shows a method 130 for evaluating the stability of each of the determination results of the air pressure using the tire rotation speed and the resonance frequency and employing a determination unit having a stable determination result.
0 is shown. The processing of steps 1310 to 1390 is the same as the processing of steps 010 to 090 in the first embodiment, and a description of the contents will be omitted.
In step 1391, the stability of each detection result is evaluated. As a specific method for evaluating stability, for example, a counter is provided for each detected pressure at each detected timing, and the distribution state is observed for a predetermined time.
After a predetermined time has elapsed, an evaluation value for evaluating each air pressure distribution state is calculated. For example, the ranges of the detected air pressure and the like are defined as evaluation amounts A1 and A2. Step 1392
Let's compare the evaluation quantities. In this case, since the air pressure detection value varies, it is determined that a smaller evaluation amount is more stable. Thus, steps 1393, 1
At 394, the air pressure in the stable detection method is equal to the display air pressure P.
Is set to As the air pressure to be set in this case, it is preferable to use the average air pressure determined from the distribution state.

[0040]

The tire pressure detecting device according to the present invention has the above-described structure, and is used in combination with the tire pressure determining means having different detection principles of the tire rotation speed and the resonance frequency. It is possible to cope with all driving states including changes, and to maintain high detection accuracy. In addition, there is an excellent effect that reliability is high and there is no possibility of erroneous learning and no burden on the user.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a configuration of a first example of the present invention.

FIG. 2 is a flowchart illustrating a main process according to the first embodiment of the present invention.

FIG. 3 is a flowchart illustrating a process of calculating an air pressure based on a tire rotation speed.

FIG. 4 is a flowchart illustrating a process of determining air pressure based on a resonance frequency.

FIG. 5 is a flowchart showing a process of detecting a road surface input and weighting a determination value of each air pressure determination unit according to the degree of roughness.

FIG. 6 is a flowchart showing a process of learning a change from a detected value of two types to a normal pressure.

FIG. 7 is a flowchart illustrating a process of detecting a turning state and switching an air pressure determination unit.

FIG. 8 is a flowchart showing a process for detecting acceleration / deceleration of the vehicle body and switching the air pressure determination means.

FIG. 9 is a flowchart illustrating a process of detecting a load shift due to a change in the attitude of the vehicle and switching a determination unit of air pressure.

FIG. 10 is a flowchart showing a process of detecting the traveling speed of the vehicle and switching the air pressure determination means.

FIG. 11 is a flowchart showing a process of switching an air pressure determination unit based on comprehensive evaluation of various running states.

FIG. 12 is a flowchart showing a process of another embodiment for learning a change in the detected value of the normal pressure that occurs due to aging or the like.

FIG. 13 is a flowchart showing a process of displaying or updating the air pressure only when the detection results of the two air pressure determination units match.

FIG. 14 is a flowchart showing a process for evaluating the stability of each determination result of each air pressure and employing a determination unit having a stable determination result.

FIG. 15 is a conversion map of resonance frequency-air pressure based on the characteristics of the vehicle.

FIG. 16 is a conversion map obtained by linearly correcting the resonance frequency-air pressure conversion map in FIG. 15 with respect to the resonance frequency.

FIG. 17 is a characteristic diagram showing a relationship between a resonance frequency and a road surface input level.

FIG. 18 is a characteristic diagram showing a relationship between a tire rotation speed and a road surface input level.

FIG. 19 is a characteristic diagram showing a relationship between a left and right tire difference in tire rotation speed and a turning radius.

FIG. 20 is a characteristic diagram showing a relationship between a resonance frequency and a turning radius.

FIG. 21 is a characteristic diagram showing a relationship between acceleration and a tire rotational speed difference between front and rear tires in a two-wheel drive vehicle.

FIG. 22 is a characteristic diagram showing a relationship between a ground contact load and a tire rotation speed.

FIG. 23 is a characteristic diagram showing a relationship between a ground load and a resonance frequency.

FIG. 24 is a characteristic diagram showing an influence of a centrifugal force on a tire rotation speed depending on a traveling speed.

[Explanation of symbols]

 1a-1d ... tires, 2a-2d ... gears, 3a-3d ... pickup coils, 4 .... Electronic control unit (ECU), 5 ... display unit, 000-1395 ... steps.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-271907 (JP, A) JP-A-6-278419 (JP, A) JP-A-5-213019 (JP, A) JP-A-5-210 294118 (JP, A) JP-A-63-305011 (JP, A) "Automotive Technology Handbook"<Vol.1> Fundamentals and Theory, 1st edition, Japan Society of Automotive Engineers, December 1, 1990, p. 264-288 (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 23/00-23/08 G01L 17/00

Claims (14)

(57) [Claims] 1. A tire rotation speed detecting means for detecting a signal including rotation speed components of a plurality of tires, a resonance frequency is detected from the tire rotation speed signal, and a tire pressure state is determined based on the tire resonance frequency. A first judging means for comparing the tire rotation speed signal, a second tire pressure judging means for judging a state of the tire pressure from the comparison result, and detecting a running state of the vehicle; A tire pressure detecting device, comprising: a vehicle running state detecting means for outputting a signal; and a switching output means for switching and outputting the determination values of the first and second tire pressure determining means according to the vehicle running state. . 2. A weighting means for outputting a determination result after a predetermined weight is applied to a determination value of said first and second tire pressure determination means, and said weighting means based on a signal of said vehicle running state detection means. 2. The tire pressure detecting device according to claim 1, further comprising: weight switching means for switching the weight state. 3. The function of the switching output means is stopped based on a signal of the vehicle running state detecting means, and either the determination value of the first and second tire pressure determining means is not updated or displayed. 2. The tire pressure detecting device according to claim 1, further comprising means. 4. The tire air pressure detecting device according to claim 1, wherein said vehicle running state detecting means is means for detecting a degree of unevenness of a road surface. 5. The tire pressure detecting device according to claim 1, wherein said vehicle running state detecting means is means for detecting a straight traveling state. 6. The tire pressure detecting device according to claim 1, wherein the vehicle running state detecting means is means for detecting any one of acceleration in a front-rear direction and a lateral direction of the vehicle. 7. The vehicle running state detecting means for detecting rotation of the vehicle in any one of a roll direction, a pitch direction, and a yaw direction.
The tire pressure detecting device as described in the above. 8. The vehicle according to claim 1, wherein said vehicle running state detecting means is means for detecting a running speed of the vehicle.
4. The tire pressure detecting device according to 2 or 3. 9. A coincidence detecting means for detecting when the judgment values of the first and second tire pressure judging means coincide with each other,
2. The tire pressure detecting device according to claim 1, wherein when the coincidence is detected, the switching output means is operated to output a determination result. 10. A stability monitoring means for monitoring the stability of each determination result with respect to the determination values of said first and second air pressure determination means, wherein said switching output means outputs said stability in each running state. 2. The tire pressure detecting device according to claim 1, wherein an excellent output result of the air pressure determining means is adopted. 11. The tire pressure according to claim 1, further comprising correction means for correcting a normal value of one of the air pressure judgment means based on the judgment values of the first and second air pressure judgment means. Detection device. 12. When the determination result of the air pressure obtained from the rotation speed components of the plurality of tires as the second air pressure determination means indicates an abnormal value, the resonance frequency as the first air pressure determination means is determined. If the obtained air pressure of the corresponding tire indicates a normal value, a learning means for detecting that a constant change in the tire diameter has occurred and changing a normal pressure equivalent component of the rotational speed of the tire is provided. The tire pressure detecting device according to claim 1, wherein 13. When the determination result of the air pressure obtained from the rotational speed components of the plurality of tires as the second air pressure determination means indicates a normal value, the resonance frequency as the first air pressure determination means is determined. If the obtained tire pressure indicates an abnormal value, it is detected that any aging such as replacement of the tire or the wheel and deterioration of the suspension bush has occurred, and the normal pressure of the resonance frequency is detected. The tire pressure detecting device according to claim 1, further comprising learning means for changing a corresponding component. 14. A communication device for communicating to the system that the tire pressure is normal, and when the communication device is activated, the normal pressure equivalent component of the first and second air pressure determination devices is determined. The tire pressure detecting device according to claim 1, further comprising a learning means for changing the tire pressure.