JP3289384B2 - 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 tire pressure of a vehicle.

[0002]

2. Description of the Related Art Conventionally, as a device for detecting tire air pressure, a wheel speed for detecting the wheel speed of each wheel by utilizing the fact that the tire radius changes (shortens) when the tire air pressure decreases is used. There has been proposed an apparatus for indirectly detecting the tire pressure of a vehicle based on a detection signal of a sensor.

[0003]

However, the tire radius to be detected has individual differences due to wear and the like, and is easily affected by running conditions such as turning, braking, and starting. Furthermore, radial tires, which have become increasingly popular in recent years, have a small amount of deformation of the tire radius due to a change in tire pressure (for example, when the tire pressure 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.

[0004] In view of the above problems, the inventors of the present application have
Calculating the wheel speed based on a pulse signal output from the wheel speed sensor, and further performing frequency analysis such as FFT calculation on the wheel speed to extract a resonance frequency component in a vertical direction or a front-rear direction under the spring of the vehicle. By
The present inventor has found that the state of tire air pressure can be detected, and filed an application for this ("Tire Air Pressure Detecting Apparatus" Japanese Patent Application No. 3-294622).

Here, the following two methods are usually considered as a method of calculating the wheel speed. A method of calculating by fixing the number of pulses to be read (for example,
The elapsed time is obtained for each predetermined pulse).

[0006] A method of performing calculation while fixing the reading time (for example, obtaining the number of pulses during each predetermined time). When calculating the wheel speed using the above method, in order to increase the accuracy, it is better to sample and calculate the data from the wheel speed sensor for each pulse as much as possible, that is, pulse interval = sampling interval However, when the wheel speed changes, the pulse interval Δtb changes as shown in FIG. 17, so that the data sampling interval does not become constant.

The wheel speed calculated for each pulse is discrete data that is constant during the pulse interval .DELTA.tb. However, when the wheel speed is changed, FIG.
As shown in (1), when this discrete data is sampled as frequency analysis data at every sampling interval Δta (constant) of the frequency analysis, which is a post-processing, the pulse interval Δtb is changed depending on the wheel speed or the gear tooth length. There is a problem that a case where the sampling interval .DELTA.ta is too coarse occurs, and appears as noise.

On the other hand, when the wheel speed is calculated using the above method, it is necessary to calculate the wheel speed at the shortest possible sampling interval (high sampling) in order to prevent deterioration of the extraction of the resonance frequency component by the frequency analysis which is the post-processing. But,
When the wheel speed is calculated by high sampling, there is a problem that the wheel speed data for performing the frequency analysis increases and the load on the processing circuit increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is possible to easily perform frequency analysis to extract a resonance frequency component by correcting the wheel speed data calculated by the above method. It is an object of the present invention to provide a tire pressure detecting device which can be used.

[0010]

According to a first aspect of the present invention, there is provided a tire pressure detecting device comprising: a wheel speed sensor for outputting a pulse signal corresponding to a rotation speed of a wheel; Wheel speed calculating means for repeatedly calculating a wheel speed signal based on the input pulse signal; and a plurality of wheel speed signals repeatedly calculated by the wheel speed calculating means.
Correction means for correcting the noise to a continuous change amount reduced at each sampling interval, and a wheel speed signal corrected by the correction means is sampled at predetermined intervals, and a resonance frequency component contained in the wheel speed signal is sampled. It is characterized by comprising extraction means for extracting, and detection means for detecting tire air pressure based on the resonance frequency component extracted by the extraction means.

According to a second aspect of the present invention, there is provided a tire pressure detecting device.
A wheel speed sensor that outputs a pulse signal according to the rotation speed of the wheel, a wheel speed calculation unit that receives a pulse signal from the wheel speed sensor, and repeatedly calculates a wheel speed signal based on the input pulse signal; Averaging means for averaging a plurality of wheel speed signals repeatedly calculated by the wheel speed calculating means at predetermined timings; sampling the wheel speed signals averaged by the averaging means; And extracting means for detecting a tire air pressure based on the resonant frequency component extracted by the extracting means.

According to a third aspect of the present invention, in the tire pressure detecting device according to the third aspect, the wheel speed calculating means determines a wheel speed based on a pulse interval of a pulse signal input from the wheel speed sensor. The signal may be repeatedly calculated, or as set forth in claim 4, the wheel speed calculating means converts the wheel speed signal based on the number of pulses within a predetermined time of the pulse signal input from the wheel speed sensor. The calculation may be repeated.

[0013]

In the tire pressure detecting device according to the first aspect of the present invention, since the correcting means corrects the plurality of wheel speed signals to a continuous change amount at predetermined timings, the tire pressure detecting device is provided in a stepwise manner. The change in the changed wheel speed becomes smooth, and the noise component can be reduced when the extraction unit samples the corrected wheel speed signal.

[0014] According to a second aspect of the present invention, there is provided a tire pressure detecting device.
The averaging means averages the plurality of wheel speed signals at predetermined timings, so that the plurality of discrete wheel speed signal data can be converted into one highly reliable wheel speed signal data. Therefore, if this averaged wheel speed signal is used, the number of times the extraction unit samples the wheel speed signal can be reduced. Therefore,
The processing load for extracting the vibration frequency component by the extraction means can be reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing the entire configuration of the first embodiment.

As shown in FIG. 1, the tires 1a to 1a of the vehicle
A wheel speed sensor is provided corresponding to 1d. Each wheel speed sensor includes gears 2a to 2d and pickup coils 3a to 3d. Gears 2a to 2d
Are coaxially mounted on the rotating shafts (not shown) of the tires 1a to 1d and are made of a disk-shaped magnetic material. The pickup coils 3a to 3d are connected to these gears 2a to 2d
Are mounted at predetermined intervals in the vicinity of the gears 2a to 2a.
2d, that is, an AC signal having a cycle corresponding to the rotation speed of the tires 1a to 1d is output. Pickup coil 3
AC signals output from a to 3d are output from a waveform shaping circuit R
Well-known electronic control unit (ECU) consisting of OM, RAM, etc.
4 to perform predetermined signal processing including waveform shaping. The result of the signal processing 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 display unit 5 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 lit when the air pressure of any one of the tires becomes lower than the reference air pressure. Then, a warning may be issued.

Here, the principle of detecting the tire air pressure in this embodiment will be described first. When the vehicle travels on, for example, 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 acceleration under the vehicle spring when the tire vibrates is as shown in FIG. As shown in FIG. 2, the frequency characteristics of the acceleration show peak values at two points, point a is the resonance frequency in the vertical direction under the spring of the vehicle, and point b is the resonance frequency in the longitudinal direction under the spring of the vehicle. is there.

On the other hand, 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 tire air pressure decreases,
Since the spring constant of the tire rubber portion also decreases, the resonance frequencies in the vertical direction and in the front-rear direction both decrease. 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.

For this reason, in the present embodiment, the resonance frequencies in the up-down direction and the front-rear direction under the spring of the vehicle are extracted from the detection signal of the wheel speed sensor. This is because, as a result of detailed studies by the inventors, it has been found that the detection signal of the wheel speed sensor includes a tire vibration frequency component. That is, as a result of frequency analysis of the detection signal of the wheel speed sensor, it is clear that peak values are shown at two points as shown in FIG. 4, and that when the tire air pressure is reduced, the peak values at the two points are also reduced. Was.

Thus, 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. Further, in the practical range of the vehicle, since the change amount of the resonance frequency is almost based on the change of the tire spring constant caused by the change of the tire pressure, without being affected by other factors such as tire wear. Stable air pressure detection becomes possible.

FIG. 11 is a flowchart showing the processing executed by the ECU 4. The flowchart of FIG. 11 relates to the calculation of the wheel speed by the method described above. In addition, since the ECU 4 performs the same processing for each of the wheels 1a to 1d, the flowchart of FIG. 11 shows only the flow of the processing for one wheel, and in the following description, the suffix of each reference numeral is omitted. . Further, the flowchart shown in FIG. 11 shows an example in which it is particularly detected that the tire air pressure has dropped below the reference value, and a warning is issued to the driver.

Referring to FIG. 11, in step 100, after the AC signal (FIG. 5) output from the pickup coil 3 is shaped into a pulse signal, the pulse interval is divided by the time between the pulse signal and the wheel speed v. Is calculated. As shown in FIG. 6, the wheel speed v usually includes many high-frequency components including a vibration frequency component of the tire.

In step 101, the calculated wheel speed v is D / A converted. By this processing, the wheel speed is obtained as continuous data as shown in FIG. Then, at predetermined sampling intervals, sampling is performed again as a wheel speed (hereinafter, wheel speed v represents this) from the D / A converted data. By the process of step 101, a smoothing effect can be given to the wheel speed signal, and the above-described noise can be reduced.

[0024] At step 110, it is determined whether the variation width Δv of the wheel speed v obtained exceeds the reference value v _0. At this time, if it is determined that the fluctuation width Δv of the wheel speed v exceeds the reference value v ₀ , the process proceeds to step 120. In step 120, the variation width Δv of the wheel speed v is set to the reference value v
It is determined whether the time ΔT exceeding ₀ has exceeded a predetermined time t ₀ . The processing in steps 110 and 120 is performed to determine whether the road surface on which the vehicle is traveling is a road surface on which tire pressure can be detected by the detection method of this embodiment. That is, in this 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 does not continue,
Sufficient data for calculating the resonance frequency cannot be obtained. In the determination in step 120, a predetermined time Δt is set when the variation width Δv of the wheel speed v exceeds the reference value v _0, and within this predetermined time Δt, the variation width Δv of the wheel speed v is again set to the reference value v _If it exceeds ₀ , the measurement of the time ΔT is continued.

In steps 110 and 120, if both are determined to be affirmative, the routine proceeds to step 130;
Return to In step 130, a frequency analysis (FFT) calculation is performed on the calculated wheel speed, and the number of calculations N is counted. FIG. 8 shows an example of the result of performing the FFT operation.

As shown in FIG. 8, when the FFT calculation is performed on the wheel speed obtained when the vehicle actually travels on a general road, frequency characteristics usually become very random. This is because the shape (size and height) of the minute unevenness existing on the road surface is completely irregular, and therefore, the frequency characteristic varies 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. Therefore, in step 140, step 130
It is determined whether or not the number N of FFT operations in has reached a predetermined number n ₀ . When the number of calculations N has not reached the predetermined number n ₀ , the processing from step 100 to step 130 is further repeatedly executed. On the other hand, when the number of operations N has reached the predetermined number of times n ₀ , step 1
Proceeding to 50, an averaging process is performed. In this averaging process, as shown in FIG. 9, an average value of each FFT operation result is obtained, and an average value of the gain of each frequency component is calculated. By such averaging processing, FFT by road surface
It is possible to reduce the variation in the calculation result.

However, with the above-described averaging process alone, the gain of the resonance frequency in the vertical and longitudinal directions below the spring of the vehicle due to noise or the like does not always reach the maximum peak value as compared with the gain of the frequency in the vicinity thereof. There is a problem that is not limited. Therefore, in this embodiment, following the above-mentioned averaging process, the following moving average process is performed in step 160.

[0028] The moving average process is carried out by determining the gain Y _n of the n th frequency by the following arithmetic expression.

[0029]

_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. 10 shows the calculation result obtained by this moving average processing.

The waveform processing here is not limited to the above moving average processing, but may be a method of averaging the n-th gain at several points before and after n. May be filtered, or
Before performing the FFT calculation in step 130, a differential calculation of the wheel speed v is performed, and an FFT is performed on the differential calculation result.
An operation may be performed.

Next, at step 170, the resonance frequency f in the front-rear direction below the spring of the vehicle is calculated based on the FFT calculation result smoothed by the moving average processing. In step 180, determine the decrease deviation from the initial frequency f ₀ (f ₀ -f) which is set to correspond to the previously normal tire pressure, decrease the deviation of the other (f ₀ -f) and a predetermined deviation Δf Compare. The predetermined deviation Δf is determined based on an initial frequency f ₀ corresponding to a normal tire pressure as a reference, and an allowable lower limit value of the tire pressure (for example, 1.4 kg / m).
² ) is set according to. Therefore, step 18
If it is determined at 0 that the decrease deviation (f ₀ −f) exceeds the predetermined deviation Δf, it is considered that the tire air pressure has decreased below the allowable lower limit value, and the routine proceeds to step 190, where the display unit 5 indicates to the driver. Warning display.

In the above-described example, the example in which the decrease in the tire air pressure is detected based on only the resonance frequency in the front-rear direction below the spring of the vehicle has been described. Instead, only the resonance frequency in the vertical direction is detected. A decrease in tire air pressure may be detected on the basis of this, or the tire air pressure may be detected based on both the front-rear direction and the vertical resonance frequency.

Further, the relationship between the tire pressure and the resonance frequency as shown in FIG. 12 is stored and calculated as a map for each tire, instead of detecting that the tire pressure has dropped below the allowable lower limit. The tire pressure itself may be directly estimated from the resonance frequency f.

Next, a second embodiment will be described. In the second embodiment, only the step 101 of the first embodiment is different, and the other parts are the same. That is, the correction of the wheel speed calculated for each pulse interval is performed as follows.

First, the wheel speed calculated for each pulse is set as the speed a at an intermediate time between the pulse intervals, and the wheel speed v at the sampling time is obtained from the speeds before and after the sampling time. As a method of obtaining the wheel speed, a corrected wheel speed v may be obtained by performing linear interpolation using two points before and after (a1, a2) as shown in FIG. 13, or a known method such as a spline using a plurality of points. May be obtained by the function of

Further, the following configuration may be used in which the number of calculations is reduced and the load on the ECU 4 is reduced. That is, although the wheel speed is calculated for each pulse in the above description, the wheel speed is calculated only for the pulse obtained at the sampling time, and correction is similarly performed as the speed a at a time intermediate the pulse interval. is there. In this case, the correction by the linear interpolation of the two points before and after is as shown in FIG.

Next, a third embodiment will be described. The third embodiment relates to the calculation of the wheel speed by the above-described method, and only the portion of step 101 in the first embodiment described above is as shown in FIG. Hereinafter, FIG. 15 will be described.

That is, after the wheel speed data is calculated based on the pulses within a predetermined time in step 100, in step 102, each time the ECU 4 performs a sampling interval (low sampling interval) at which the FFT calculation process can be performed, the ECU 4 performs the calculation before and after that. , An averaging process is performed on a plurality of wheel speed data calculated at a high sampling interval, and the averaged wheel speed data is used as a sampling value for FFT calculation. For example, as shown in FIG. 16, the wheel speed data a1 to a5 calculated at every high sampling interval t1 are converted to the low sampling interval t1.
Averaging process is performed every two to obtain wheel speed data V (sampling value) for FFT calculation. As a result, the number of data can be reduced without deteriorating high-sampling information, and the processing load on the ECU 4 during the FFT operation can be reduced.

The processing in step 102 is not an averaging processing, but a well-known digital filter operation expression (for example,
FF using quadratic IIR, linear interpolation, moving average processing, etc.
Wheel speed data for T calculation may be obtained.

Here, in the above-described third embodiment, since the high sampling interval is kept constant, a pulse may not enter the interval when the vehicle speed is low. Therefore, when the vehicle speed is low, a variable sampling method may be adopted in which the high sampling interval is lengthened.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a first exemplary embodiment of the present invention.

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

FIG. 3 is a characteristic diagram showing a state of a change in resonance frequency in a vertical direction and a front-rear direction below a spring of a vehicle due to a change in tire air pressure.

FIG. 4 is an explanatory diagram showing a principle of detecting tire pressure according to the first embodiment.

FIG. 5 is a waveform diagram showing an output voltage waveform of a wheel speed sensor.

FIG. 6 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. 7 is an explanatory diagram of a smoothing effect by D / A conversion.

8 is a characteristic diagram illustrating a result of performing a frequency analysis operation on the wheel speed v having the waveform illustrated in FIG. 6;

FIG. 9 is an explanatory diagram for explaining an averaging process in the first embodiment.

FIG. 10 is a characteristic diagram showing a frequency analysis result after performing a moving average process in the first embodiment.

FIG. 11 is a flowchart showing the processing content of the electronic control device of the first embodiment.

FIG. 12 is a characteristic diagram showing a relationship between a tire pressure and a resonance frequency.

FIG. 13 is an explanatory diagram of wheel speed correction according to the second embodiment.

FIG. 14 is an explanatory diagram of wheel speed correction with a reduced number of calculations in the second embodiment.

FIG. 15 is a flowchart showing a difference between the processing contents of the third embodiment and the first embodiment.

FIG. 16 is an explanatory diagram for describing the processing content of step 102 in FIG. 15;

FIG. 17 is an explanatory diagram for describing a method of calculating a wheel speed while fixing the number of pulses to be read.

FIG. 18 is an explanatory diagram for explaining sampling of a wheel speed signal for frequency analysis in the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tire 2 Gear 3 Pickup coil 4 Electronic control unit (ECU) 5 Display

Continuation of the front page (56) References JP-A-62-149503 (JP, A) JP-A-62-149502 (JP, A) JP-A-5-133383 (JP, A) "Automotive Technology Handbook"<FirstVolume> Basic / Theory, First Edition, The Society of Automotive Engineers of Japan, December 1990 (58) Fields investigated (Int. Cl. ⁷ , DB name) B60C 23/00-23/08

Claims (6)

(57) [Claims] 1. A wheel speed sensor for outputting a pulse signal according to a rotation speed of a wheel, a wheel signal receiving a pulse signal from the wheel speed sensor, and repeatedly calculating a wheel speed signal based on the input pulse signal. Speed calculation means, a plurality of wheel speed signals repeatedly calculated by the wheel speed calculation means noise at predetermined sampling intervals
Correction means for correcting the reduced continuous change amount; sampling means for sampling the wheel speed signal corrected by the correction means at predetermined intervals; and extracting means for extracting a resonance frequency component included in the wheel speed signal, Detecting means for detecting tire air pressure based on the resonance frequency component extracted by the extracting means. 2. A wheel speed sensor for outputting a pulse signal corresponding to a rotation speed of a wheel, a wheel signal receiving a pulse signal from the wheel speed sensor, and repeatedly calculating a wheel speed signal based on the input pulse signal. Speed calculating means, averaging means for averaging a plurality of wheel speed signals repeatedly calculated by the wheel speed calculating means at predetermined timings, and sampling the wheel speed signals averaged by the averaging means. An extraction unit for extracting a resonance frequency component included in the wheel speed signal; and a detection unit for detecting a tire air pressure based on the resonance frequency component extracted by the extraction unit, a tire pressure detection device. 3. The tire pressure detecting device according to claim 1, wherein the wheel speed calculating means repeatedly calculates a wheel speed signal based on a pulse interval of a pulse signal input from the wheel speed sensor. . 4. The wheel speed calculating means according to claim 1, wherein said wheel speed calculating means repeatedly calculates a wheel speed signal based on the number of pulses within a predetermined time of a pulse signal input from said wheel speed sensor. Tire pressure detector. 5. The averaging means according to claim 5, wherein
The number of calculations for extracting the resonance frequency component is predetermined.
Claims that are adopted when the number of times exceeds
3. The tire pressure detection device according to 2. 6. The averaging means, wherein:
The sampling interval, which varies according to the vehicle speed,
3. Senya air pressure according to claim 2, wherein the pressure is adopted.
Detection device.