JP3136801B2 - 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 automatically determining the type of a tire and detecting the tire pressure.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. Sho 63-30501 discloses that
Since the wheel speed fluctuates when the load radius of the tire changes according to the air pressure, a tire air pressure detecting device that detects the wheel speed of each wheel and indirectly detects the tire air pressure is disclosed.

[0003]

However, the load radius of the tire varies slightly depending on running conditions such as tire wear, cornering and braking. For this reason, there is a problem that if the load radius of the tire is used as a parameter for air pressure detection, sufficient detection accuracy cannot be ensured. In order to solve the above problem, the inventor of the present application extracts a resonance frequency in a vertical direction or a front-rear direction below a spring, and determines an air pressure determination reference value (e.g., A device for detecting the state of the tire air pressure by comparing with the corresponding resonance frequency) was invented (Japanese Patent Application No. 3-294622).

The tire pressure detecting device according to the above application is
It is excellent in that the determination of the tire pressure can be reliably performed. However, since the set air pressure determination reference value is a fixed value, there is a problem that the tire air pressure state cannot be accurately determined when the tire is replaced. The present invention has been made to solve the above problems, and has as its object to provide a tire pressure detecting device capable of automatically determining the type of a tire and detecting the state of the tire pressure with high accuracy. It is assumed that.

[0005]

In order to solve the above-mentioned problems, a tire pressure detecting device according to the present invention provides a signal including a vibration frequency component of a tire when the vehicle is running .
Wheel speed sensor that outputs a wheel speed signal according to the rotation speed
(C) extracting means for extracting a signal of a resonance frequency component of the tire from the wheel speed signal; calculating means for calculating a resonance frequency from the signal of the resonance frequency component; and a type of the tire mounted on the vehicle based on the resonance frequency. A tire type determination unit for determining the wheel weight at which a tire is mounted based on a resonance frequency; and a tire pressure drop determination value set based on a determination result of the determination unit and the tire type determination unit. And a detecting unit for comparing the set tire air pressure drop determination value with the resonance frequency to detect the state of the tire air pressure.

[0006]

According to the above construction, the vibration frequency component of the tire is included.
The resonance frequency is calculated by extracting a resonance frequency component signal from the wheel speed signal, and determining the type of the tire based on the resonance frequency and determining the weight of the wheel on which the tire is mounted. Do. Then, set the tire pressure drop judging value by both judgment results, detecting a state of the tire air pressure by comparing said resonant circumferential <br/> wave number.
Here, the resonance frequency changes according to the spring constant of the tire, which substantially depends only on the air pressure of the tire. Further, the air pressure-resonance frequency characteristic of the tire changes according to the type of the tire, and also changes depending on the weight of the wheel on which the tire is mounted. Therefore, it is possible to detect the state of the tire pressure based on the resonance frequency, the type information of the tire, and the determination of the lightness of the wheel weight.

[0007]

【Example】

(First Embodiment) A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a tire pressure detecting device. Four tires 1a to 1 attached to the vehicle
Wheel speed sensors are respectively installed corresponding to d. The wheel speed sensor is a gear-shaped pulsar 2a made of a magnetic material.
2d and pickup coils 3a to 3d. The pulsars 2a to 2d are fixed to rotating axles (not shown) of the respective tires 1a to 1d. Pickup coil 3a
3d are attached to the pulsars 2a to 2d at a predetermined interval, and output an AC signal having a cycle corresponding to the rotation of the pulsars 2a to 2d, that is, the rotation speed of each of the tires 1a to 1d.

[0008] AC signals output from the pickup coils 3a to 3d are input to the ECU 4. The ECU 4
It is composed of a CPU, a waveform shaping circuit, a ROM, a RAM and the like, and processes various signals input according to a predetermined program. Then, the processing result is input to the display unit 5, and the display unit 5 notifies the driver of the state of the air pressure of each of the tires 1a to 1d. The notification mode may specifically display the state of the air pressure of each of the tires 1a to 1d. When one of the tires has a lower air pressure than the reference air pressure by one warning lamp, A warning lamp may be turned on to give a warning.

Here, the principle of detecting the tire pressure in this embodiment will be described. When a vehicle travels on a paved asphalt road surface, the tire receives vertical and longitudinal forces due to minute irregularities on the road surface, and the tire vibrates in the vertical and longitudinal directions. The frequency characteristic of the unsprung acceleration of the vehicle at the time of the tire vibration shows peak values at points a and b as shown in FIG. Point a is the vertical resonance frequency under the spring of the vehicle, and point b is the front-rear resonance frequency under the spring of the vehicle.

[0010] When the air pressure of the tire changes, the spring constant of the tire rubber portion also changes, so that the above-described resonance frequencies in the vertical direction and the front-back direction both change. For example, as shown in FIG. 3, when the air pressure of the tire decreases, the spring constant of the tire rubber part also decreases, so that the resonance frequency in the vertical direction and the front-rear direction generally shifts to the low frequency side, and the peak value point a becomes At the point a ', the peak value b shifts to the point b'. Therefore, if at least one of the resonance frequencies in the vertical and longitudinal directions under the spring of the vehicle is extracted from the vibration frequency of the tire, it is possible to detect the state of the tire pressure based on the resonance frequency.

On the other hand, as a result of detailed studies by the present inventors, it has been found that the detection signal of the wheel speed sensor contains a vibration frequency component of a tire. That is, as a result of frequency analysis of the detection signal of the wheel speed sensor, as shown in FIG. 4, it is apparent that the peak values at the two points also decrease as the tire pressure decreases, as shown in FIG. It became. For this reason, in the present embodiment, the tire air pressure is detected by extracting the resonance frequency in the vertical direction and the longitudinal direction under the spring of the vehicle from the detection signal of the wheel speed sensor.

As described above, according to the present embodiment, the anti-skid control device (ABS), which has been increasing the number of vehicles mounted in recent years,
Since a vehicle or the like equipped with a wheel is already equipped with a wheel speed sensor for each tire, it is possible to detect the tire air pressure without adding any new sensors. In the practical range of the vehicle, the change amount of the resonance frequency is almost based on the change in the spring constant of the tire rubber portion caused by the change in the tire air pressure, and is stable without being affected by other factors such as tire wear. Air pressure detection becomes possible.

However, the above description is based on the same type of tire. If the type of tire is different even if the unsprung resonance frequency is the same, the tire air pressure is different and the determination value for determining the decrease in air pressure (the unsprung resonance frequency) ) Will also be different. For this reason, it is necessary to set a reference value for determining an abnormality in the tire air pressure according to the type of the tire to be mounted.
As a result of the study by the present inventors, it has been found that the tire pressure-unsprung resonance frequency characteristic is clearly different between a normal radial tire and a studless tire (winter tire) as shown in FIG. did.

A normal radial tire indicated by reference symbol A in FIG.
The variation range of the unsprung resonance frequency of the radial tire (hereinafter simply referred to as a radial tire) appears in a region where the resonance frequency is higher than the variation range of the unsprung resonance frequency of the studless tire indicated by B. This variation is the difference between tire manufacturers
In addition to (brand), it occurs based on the weight of the wheel on which the tire is mounted. A showing the upper limit characteristic of variation
_MAX and B _MAX are when mounted on the lightest wheel, and A _MIN and B _MIN showing the lower limit characteristics of the variation are when mounted on the heaviest wheel. This is because the unsprung resonance frequency f becomes f∝√ (k / unsprung weight).
(Where k is the tire spring constant).

[0015] Here, if the tire pressure of tires attached to the lightest wheel is lowered, the lower limit of the P _L range of air pressure alarming (kg / cm ^2), if the upper limit P _H, radial tires pneumatic reference resonant frequency (unsprung resonance frequency) f _L is f _RAL next determines a decrease of the reference resonant frequency f _L of the studless tire in the same manner becomes f _STL.
As the value of P _L in this case, for example, a minimum air pressure (1.4 kg / cm ² ) defined by JIS standards may be used.
As the value of P _H, it may be used maximum air pressure (2.5kg / cm ²⁾ defined in JIS standard. still,
The value of the tire type determination resonance frequency f _K0 (hereinafter simply referred to as resonance frequency f _K0 ) for determining whether the tire type is a radial tire or a studless tire is, as can be seen from the frequency characteristics shown in FIG. It is desirable that the resonance frequency is set to a value approximately halfway between the resonance frequency corresponding to the upper limit pressure (P _H ) of the tire and the resonance frequency corresponding to the lower limit pressure (P _L ) of the radial tire.

The signal processing of the ECU 4 for detecting that the air pressure of the tire has fallen below the predetermined air pressure and issuing an alarm will be described below with reference to the flowcharts of FIGS. Since the ECU 4 performs the same processing for each wheel, the flowchart shows only signal processing for one wheel. In addition, the processing content shows an example in which it is detected that the air pressure of the tire has dropped below the reference value, and a warning is issued to the driver.

When the ignition switch is turned on, the ECU
4 starts, in step 100, the AC signal (FIG. 8) output from the pickup coil 3 is shaped into a pulse signal, and the pulse interval is divided by a predetermined time to obtain a wheel speed v. Is calculated. As shown in FIG. 9, the wheel speed v includes many high-frequency components including a vibration frequency component of a normal tire. In the following step 110, a road surface state determination process for determining whether or not the calculated fluctuation width Δv of the wheel speed v is equal to or greater than a reference value v ₀ is performed. At this time, if it is determined that the fluctuation width Δv of the wheel speed v is equal to or greater than the reference value v ₀ , the process proceeds to step 120.

In step 120, a road length determination process is performed to determine whether or not the time ΔT during which the fluctuation width Δv of the wheel speed v is equal to or longer than the reference value v ₀ is equal to or longer than a predetermined time t ₀ . Road surface state determination processing in step 110 and step 1
The road surface length determination process of No. 20 is performed when the road surface on which the vehicle is traveling is
This is performed to determine whether or not the road surface is capable of detecting tire pressure by the detection method of the present embodiment. That is, in the present embodiment, the detection of the tire air pressure is performed based on the change in the resonance frequency included in the vibration frequency component of the tire. Therefore, if the wheel speed v fluctuates to some extent and this is not continued, the resonance frequency It is not possible to obtain sufficient data for calculating. The step 120
In the determination in, the fluctuation width Δv of the wheel speed v is equal to the reference value v
_A predetermined time Δt is set when the value becomes ₀ or more. Also, within the predetermined time Δt, the fluctuation width Δv of the wheel speed v
Is greater than or equal to the reference value v ₀ , the measurement of the time ΔT is continued.

If a negative determination is made in either step 110 or step 120, step 10
Return to 0. If both steps 110 and 120 are affirmatively determined, the process proceeds to step 130, where a frequency analysis (hereinafter, referred to as FFT) calculation is performed on the calculated wheel speed v, and the number of calculations N is integrated. FF for the wheel speed obtained when the vehicle actually travels on a general road
When the T operation is performed, the frequency characteristics usually become very random as shown in FIG. This is because the shape (size and height) of the fine irregularities existing on the road surface is completely irregular, and the frequency characteristics vary for each wheel speed data. Therefore, in the present embodiment, in order to reduce the fluctuation of the frequency characteristics as much as possible, an average value of the results of the FFT operations performed a plurality of times is obtained.

[0020] At step 140 determines whether the calculated number N of the FFT operation has reached a predetermined number n _0. If not, the processing of steps 100 to 130 is repeated. If the number of operations N has reached the predetermined number n ₀ , an averaging process is performed in the following step 150. As shown in FIG. 11, this averaging process is for obtaining the average value of each FFT operation result, and the average value of the gain of each frequency component is calculated. By this averaging process, it is possible to reduce the fluctuation of the FFT calculation result due to the road surface.

However, if only the above-mentioned averaging process is performed, the resonance frequency f _{R in} the vertical direction below the spring of the vehicle due to noise or the like.
And gain in the front-rear direction of the resonant frequency f _K is, there is a problem that necessarily become necessarily the maximum peak value as compared to the gain of the frequency in the vicinity thereof. Therefore, following the above-described averaging process, a moving average process is performed in step 160. The moving average process is carried out by determining the gain Y _n of the n th frequency by the following arithmetic expression.

[0022]

_Yn = (yn _{+ 1} + Yn _-1 ) / 2 That is, in the moving average processing, the gain Y of the n-th frequency is calculated.
_n is the (n + 1) th gain y in the previous calculation result
_{n + 1} and the gain Y of the (n-1) th frequency already calculated
_It is the average value with _n-1 . As a result, the result of the FFT operation shows a waveform that changes smoothly. FIG. 12 shows the calculation result obtained by this moving average processing.

The waveform processing here is not limited to the moving average processing, and the FFT calculation result after the averaging processing may be subjected to a low-pass filter processing, or the FFT calculation in step 130 is performed. Before performing the differential operation on the wheel speed v, the FFT operation may be performed on the result of the differential operation.

In step 170, the resonance frequency f _K (hereinafter simply referred to as resonance frequency f _K ) and the resonance frequency in the vertical direction below the vehicle are measured based on the FFT calculation result smoothed by the moving average processing. f
_R (hereinafter simply referred to as resonance frequency f _R ) (FIG. 1)
3). Subsequently, at step 180, it is determined whether or not the flag F is set to "1". It is assumed that the flag F is reset to “0” by turning off the ignition switch. Therefore, the determination in step 180 after the start of the process becomes a negative determination and proceeds to step 190.

In step 190, step 170 is performed.
It is determined whether or not the resonance frequency f _K calculated in the above is equal to or lower than the resonance frequency f _K0 for determining the type of the tire. The resonance frequency f _K calculated as shown in FIG. 5 is equal to or lower than the resonance frequency f _K0 because (1) the tire type is a radial tire and the tire air pressure is considerably low; Since immediately after, there are two cases in which the tire air pressure is considered to be almost normal and the studless tire is in a state where the tire air pressure has been reduced. Therefore, when the resonance frequency f _K is equal to or less than the resonant frequency f _K0 is by using only the resonant frequency f _K0, it can not be determined for the tire type.

However, when the air pressure of the radial tire and the studless tire shown in FIG. 14 is reduced, the wheel speed (gain) V of the resonance frequency f _R and the resonance frequency f _K is obtained.
_R, when observing the transition of V _K, resonance accordance decrease in tire air pressure in the case of radial tire (FIG. 14 (a)) the frequency f
Gain V _R and V _K of _R and the resonant frequency f _K is reversed. Therefore, by calculating the ratio of the gain (V _R / V _K), you can distinguish the case of the above two cases.

Therefore, if the resonance frequency f _K ≦ resonance frequency f _K0 in the determination processing at the step 190, step 2
Proceed to 00 gain ratio of the resonance frequency f _R and the resonance frequency f _K a (V _R / V _K) calculated is compared to the value α set in advance.
If α or less, it is determined in step 210 that the tire type is a radial tire. If it is larger than α, the routine proceeds to step 220, where the tire type is determined to be a studless tire.

Step 230 following step 210
So based on the resonance frequency f _R calculated in each of the step 170, the weight of the tire subjected to determination of (= wheel weight) m, reads the determination resonant frequency f _L corresponding to the tire pressure drop warning pressure P _L from the map.

The resonance frequency f _R is obtained by setting the tire spring constant to k,
Assuming that the unsprung mass is M, the unsprung weight is obtained by the following equation.

F _R = (1 / 2π) × {{k [(1 / m) + (1 / M)]} Since the unsprung weight M is a constant value determined by vehicle specifications, the tire spring When the constant k is constant, that is, under a certain tire pressure, the resonance frequency f _R is determined unitarily by the tire weight m. Therefore, the calculated vertical resonance frequency f _R is defined as f _RA when the weight of the tire, that is, the wheel weight is light, as f _RC when the weight is heavy, and as f _RB when the weight is intermediate (FIG. 15). A pressure-resonance frequency characteristic is obtained (FIG. 16) and set as a map in the ROM of the ECU 4. Then, the respective pressure - calculated value f _RA of the resonant frequency from the resonant frequency characteristic, f _RB, each f _RC, resonant determined corresponding to a tire pressure drop warning pressure P _L frequency f _L1,
f _L2 and f _L3 are set. If it is determined tire type as studless tire in the step 220, the same resonant determined corresponding to a tire pressure drop warning pressure P _L frequency f _L1, f _L2, f _L3 is set. The maps shown in FIGS. 15 and 16 show the case of a radial tire, but are set similarly in the case of a studless tire.

When the determination of the tire type is completed and the determination resonance frequency f _L corresponding to the tire pressure drop warning pressure P _L is read from the map, the flag F is set to “1” in step 250. In the following step 260, the calculated resonance frequency f _R is compared with the set judgment resonance frequency f _L, and if f _R ≦ f _L , the process proceeds to step 270 and the display unit 5 displays a warning to the driver. I do. If f _R > f _L , the processing of step 100 and thereafter is performed. In the second and subsequent processes, in the first process started by turning on the ignition switch, the tire type is determined, the determined resonance frequency f _L is set, and the flag F is set to “1”. Steps 250 to 250 are omitted.

[0031] In the above embodiment, the type determination of the tire, but was based on the gain ratio of the resonance frequency f _R and the longitudinal direction of the resonance frequency f _K of the computed vertical direction, the resonance frequency f _R and the resonance frequency it can be carried out on the basis of f _K magnitude relationship or deviation between the. Further, the determination of the wheel weight may be performed based on the amount of change in the peak point of the resonance frequency f _{R in} the vertical direction.

[0032]

As described above, the tire pressure detecting device of the present invention has the above-described configuration, and can automatically determine the type of the tire and can set the tire pressure determination value according to the weight of the wheel on which the tire is mounted. There is an excellent effect that the detection of the air pressure state can be performed with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a tire pressure detecting device according to the present invention.

FIG. 2 is a characteristic diagram illustrating frequency characteristics of unsprung acceleration of a vehicle.

FIG. 3 is a characteristic diagram illustrating a change in resonance frequency in a vertical direction and a front-rear direction under a spring of a vehicle with a change in tire air pressure.

FIG. 4 is an explanatory diagram illustrating a principle of detecting tire air pressure.

FIG. 5 is a characteristic diagram showing tire air pressure and unsprung resonance frequency characteristics of a radial tire and a studless tire.

FIG. 6 is a flowchart showing processing contents of an ECU.

FIG. 7 is a flowchart showing processing contents of an ECU.

FIG. 8 is a waveform diagram showing an output voltage waveform of a wheel speed sensor.

FIG. 9 is a waveform diagram showing a fluctuation state of a wheel speed v calculated based on a detection signal of a wheel speed sensor.

FIG. 10 is an FFT with respect to the wheel speed v of the waveform shown in FIG. 9;
FIG. 9 is a characteristic diagram illustrating a calculation result.

FIG. 11 is an explanatory diagram for explaining an averaging process.

FIG. 12 is a characteristic diagram illustrating an FFT calculation result after performing a moving average process.

FIG. 13 is a characteristic diagram showing a relationship between a resonance frequency and a wheel speed (gain).

FIG. 14 is a characteristic diagram illustrating a relationship between a resonance frequency and a wheel speed (gain) due to a decrease in tire air pressure.

FIG. 15 is a characteristic diagram showing a relationship between a resonance frequency and a wheel speed (gain) based on a difference in wheel weight.

FIG. 16 is a characteristic diagram showing a relationship between a tire air pressure based on a difference in wheel weight and a determination resonance frequency.

[Explanation of symbols]

 1a-1d ... tires 2a-2d ... pulsars 3a-3d ... pickup coils 4. ECU (electronic control unit) 5. display unit

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tokuda ▲ Hiromi ▲ 1-1 1-1 Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (56) References JP-A-62-149503 (JP, A) 5-138331 (JP, A) JP-A-5-221208 (JP, A) JP-A-5-229320 (JP, A) JP-A-5-254316 (JP, A) JP-A-5-294118 (JP, A A) JP-A-5-330322 (JP, A) JP-A-5-213018 (JP, A) JP-A-6-122304 (JP, A) "Automotive Technology Handbook"<firstvolume> Basic / Theory , First Edition, The Society of Automotive Engineers of Japan, December 1, 1990, pp. 264-288 (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 23/00-23/06 G01L 17 / 00

Claims (4)

(57) [Claims] 1. A wheel speed signal corresponding to a wheel rotation speed as a signal containing a vibration frequency component of a tire when the vehicle is running.
A wheel speed sensor for outputting a No., from the wheel speed signal
Extracting means for extracting a signal of a resonance frequency component of the tire ,
Calculating means for calculating the resonance frequency from the signal of the resonance frequency component; tire type determination means for determining the type of tire mounted on the vehicle based on the resonance frequency; and wheel weight of the tire mounted on the tire based on the resonance frequency. Determining means for performing the determination, setting means for setting a tire pressure drop determination value based on the determination result of the determination means and the tire type determination means, and comparing the set tire pressure drop determination value with the resonance frequency. And a detecting means for detecting a state of the air pressure of the tire. 2. The tire pressure detecting device according to claim 1, wherein the tire type determining means determines the tire type based on a calculated gain ratio between a vertical resonance frequency and a front-rear resonance frequency. apparatus. 3. The tire type determining unit according to claim 1, wherein the tire type determining unit determines the tire type based on a magnitude relationship between the calculated vertical resonance frequency and the front-rear resonance frequency or a deviation between the two. Tire pressure detector. Wherein judging means for judging the wheel weight, any one of claims 1 to 3, characterized in that to determine the seriousness of the wheel weight, based on the change amount of the peak point of the resonance frequency in the vertical direction A tire pressure detecting device according to one of the preceding claims.