JPH08156537A - Road surface state estimating device - Google Patents

Abstract

PURPOSE: To estimate the state of a road surface by the change of the air pressure of a tire accompanying a travel in a vehicle having a pneumatic pressure detecting device. CONSTITUTION: In a road surface state estimating device 10 for a vehicle having a pneumatic pressure detecting device 16 for detecting the pneumatic pressure of a tire, a tire pneumatic pressure Pe at a point of time after the lapse of a prescribed time from the traveling start of the vehicle is estimated from the tire pneumatic pressure Po at a point of time of the traveling start and an outside temperature T, and the state of the road surface is estimated on the basis of the comparison with the estimated tire pneumatic pressure Pe with the actual tire pneumatic pressure Pa after the lapse of the prescribed time from the traveling start.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road surface condition estimating device for estimating a condition of a road surface on which a vehicle such as an automobile runs.

[0002]

2. Description of the Related Art Conventionally, various road surface condition estimating devices for estimating the condition of a road surface have been known. For example, Japanese Patent Laid-Open No. 5-170087 discloses a lateral condition in a vehicle slip control device. The first road surface friction coefficient is estimated based on the lateral acceleration of the vehicle body detected by the acceleration detecting means, and the second road surface friction coefficient is estimated based on the longitudinal acceleration of the vehicle body detected by the longitudinal acceleration detecting means. A technique for estimating a road surface state by selecting a road surface friction coefficient from the first and second road surface friction coefficients based on a set selection condition is described.

According to such a road surface state estimating technique, the road surface state when the vehicle turns or the like is compared with the case where the road surface friction coefficient is estimated based on only one of the lateral acceleration and the longitudinal acceleration of the vehicle body. It is possible to accurately estimate and more appropriately execute slip control and the like.

[0004]

However, the lateral acceleration detecting means and the longitudinal acceleration detecting means are indispensable in order to estimate the road surface state by the method as described above. Therefore, the lateral acceleration detecting means and the longitudinal acceleration detecting means are used. In the case of a vehicle not equipped with this, there is a problem that the road surface condition cannot be estimated unless these detecting means are separately incorporated. This problem also applies to other road surface state estimation techniques other than the road surface state estimation technique described in the above publication.

The present invention has been made in view of the above-mentioned problems in the conventional road surface condition estimating technique, and the main problem of the present invention is that the change in the tire air pressure due to the running of the vehicle causes the road surface condition to change. It is important to note that many different air pressure detection devices that detect different tire pressures have already been proposed, and in vehicles equipped with air pressure detection devices, the road surface condition can be estimated from changes in tire air pressure. To provide a simple road surface condition estimating device.

[0006]

According to the present invention, a main problem as described above is to provide a road surface condition estimating device for a vehicle equipped with an air pressure detecting device for detecting an air pressure of a tire. The road surface state estimating device is configured to estimate the road surface state based on the tire air pressure and the tire air pressure at a time point when a predetermined time has elapsed after the start of travel.

[0007]

In general, the air pressure of a tire rises with the increase of the traveling distance and time of the vehicle due to the friction between the tire and the road surface. For example, as shown in FIG. 4, the road surface is a wet road surface. At this time, the amount of increase in tire air pressure is smaller than when the road surface is a dry road surface. Therefore, it is possible to estimate the road surface condition, for example, whether the road surface is a dry road surface or a wet road surface, from the tire air pressure at the time when the vehicle starts to travel and the tire air pressure at the time when a predetermined time has elapsed after the start of the vehicle.

According to the structure of the present invention, the road surface condition is estimated based on the tire pressure at the start of running of the vehicle and the tire pressure at the time when a predetermined time has passed after starting the running of the vehicle. It is possible to estimate the road surface condition by effectively utilizing the detection result of the air pressure detection device without requiring such special means.

As shown in FIG. 5, when the road surface is a dry road surface, the tire air pressure at the start of running the vehicle is Po, and the tire air pressure at time t after the start of running the vehicle. Let Pe be Pd, and let Pd be the amount of increase in tire air pressure from the time when the vehicle starts traveling to the time when time t elapses.

[Equation 1] Pe = Po + Pd

The amount of increase in tire air pressure Pd varies depending on the type of tire and the running conditions of the vehicle, but the outside temperature is T, the vehicle speed is V, the rolling resistance of the tire is R, and these coefficients are K1, K2, and K3, respectively. Then, the increase amount Pd of the tire air pressure can be estimated as a function of the elapsed time t from the start of running of the vehicle, the outside temperature T, the vehicle speed V, and the rolling resistance R by the following equation 2, and the rolling resistance R is As shown in Fig. 6, the tire pressure P at the start of traveling of the vehicle
Since it can be estimated if o is known, the tire air pressure Pe at time t after the start of running the vehicle can be estimated by the following mathematical expression 3.

[0011]

## EQU00002 ## Pd = f (t) {K1.T + K2.V + K3.R}

## EQU00003 ## Pe = Po + f (t) {K1 .T + K2 .V + K3 .R}

Therefore, the tire air pressure Po at the time when the vehicle starts to travel is compared with the actual tire air pressure Pa at the time t hours after the start of running, and the estimated tire air pressure Pe and the actual tire time t at the time t from the start of the running are compared. Air pressure Pa
It is possible to estimate the road surface condition by any of the comparisons with.

[0013]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an embodiment of a road surface state estimating device according to the present invention.

In FIG. 1, the road surface condition estimating device 10 comprises a reference tire air pressure calculation block 12 and a road surface condition estimating block 14. The reference tire air pressure calculation block 12 shows a signal indicating the tire air pressure P detected by the tire air pressure detection device 16, a signal indicating the outside air temperature T detected by the temperature sensor 18, and a vehicle speed V detected by the vehicle speed sensor 20. A signal is input, and the reference tire air pressure calculation block 12 calculates the estimated tire air pressure (reference air pressure) Pe at the time when a predetermined time has elapsed from the time when the vehicle started to travel based on these parameters. A signal indicating the tire air pressure P detected by the tire air pressure detection device 16 is also input to the road surface state estimation block 14, and the road surface state estimation block 14 uses the reference air pressure Pe and the actual tire air pressure at the time when a predetermined time has elapsed from the start time of running. The road surface condition is determined by comparison with Pa.

The road surface condition estimating apparatus 10 is not shown in FIG. 1, but in practice, for example, a central processing unit (CPU).
A read only memory (ROM), a random access memory (RAM), and an input / output port device, which are connected to each other by a bidirectional common bus, and the tire pressure is set according to the routine shown in FIG. It may be a microcomputer that calculates Pe and determines the road surface condition.

The operation of the illustrated embodiment will now be described with reference to the flow chart shown in FIG. The control according to the flow chart shown in FIG. 2 is started by closing an ignition switch (not shown), the flag F is initialized to 0 prior to step 10, and the elapsed time from the start of traveling of the vehicle. t is approximately counted by a timer (not shown) as an elapsed time from the closing time of the ignition switch.

First, at step 10, it is judged whether the flag F is 0 or not. If a negative judgment is made, the routine proceeds to step 50, and if an affirmative judgment is made, the routine proceeds to step 20. In step 20, the tire air pressure P when the vehicle starts traveling by the tire air pressure detection device 16 is started.
Whether or not the detection of o has been completed is performed. If a negative determination is made, the process returns to step 10, and if a positive determination is made, the tire air pressure Po is stored in step 30 and the flag F is set. Set to 1, step 4
At 0, the rolling resistance R of the tire is calculated from the map corresponding to the graph shown in FIG.

In step 50, a signal indicating the outside air temperature T detected by the temperature sensor 18 and a signal indicating the vehicle speed V detected by the vehicle speed sensor 20 are read, and in step 60, the above-mentioned equation 1 is read. According to the reference air pressure Pe,
That is, the estimated tire air pressure Pe at that time is calculated, and in step 70 it is judged whether the deviation between the reference air pressure Pe and the air pressure Po at the start of running exceeds the reference value α (a positive constant). If the determination is negative, the process returns to step 10, and if the determination is positive, the process proceeds to step 80.

In step 80, a signal indicating the actual tire air pressure Pa detected by the tire air pressure detecting device 16 is read, and in step 90, is the actual air pressure Pa greater than or equal to the reference air pressure Pe? Whether the road surface is a dry road surface is determined in step 100 when a positive determination is made, and the road surface is a wet road surface in step 110 when a negative determination is made. It is determined that there is.

The tire air pressure detection device 16 may have any structure as long as it can detect the tire air pressure, and may be, for example, a pressure sensor for detecting the tire air pressure. The routine shown in FIG. It is preferable to estimate the tire air pressure P in accordance with.

Step 21 of the tire pressure detection routine
At 0, a signal indicating the wheel speed Vw is read, and at step 220, a signal indicating a vibration component of the wheel speed is extracted from the wheel speed signal and a frequency analysis is performed on the signal (this specification). In step 230, the data within the selection range is selected from the vibration component data of the wheel speed based on the upper limit value VwH and the lower limit value VwL of the preset data selection range in step 230. To be done.

In step 240, the number of FFT operations N performed on the data within the selection range is incremented by 1, and in step 250, the number of FFT operations N is equal to or greater than the reference value No (a positive constant integer). Is determined, and if a negative determination is made, step 210
Returning to step 260, if a positive determination is made, the process proceeds to step 260.

In step 260, the average value of the gains of the respective frequency components is calculated by calculating the average value of the results of the FFT calculations for the data selected in step 230, and in step 270. In this case, moving average processing is performed on the average value of the gain of each frequency component.
That is, the gain Yn of the nth frequency is n + 1th and n−
It is calculated according to the following equation 4 as an average value of the gains Yn + 1 and Yn-1 of the first frequency.

[0025]

## EQU4 ## Yn = (Yn + 1 + Yn-1) / 2 In step 280, the tire resonance frequency fr is calculated based on the gain after the moving average processing, and step 290
At this time, the tire air pressure P is calculated and stored based on the resonance frequency fr.

Thus, according to the illustrated embodiment, in step 30, the tire pressure P at the time when the vehicle starts to run.
o is stored, the rolling resistance R of the tire is calculated based on the air pressure Po in step 40, and the estimated tire air pressure Pe at that time is calculated in accordance with equation 1 in step 60.
Is calculated, and a positive determination is made in step 70, that is, it is determined that the time to which the road surface is a dry road surface or a wet road surface can be surely determined has elapsed from the time when the vehicle starts running. In step 80, the actual tire pressure Pa at that time is read, and in step 9
From 0 to 110, the road surface condition is determined by whether the actual air pressure Pa is equal to or higher than the reference air pressure Pe. Therefore, the road surface condition can be reliably estimated using the tire air pressure detected by the tire air pressure detection device 16.

Also according to the illustrated embodiment, step 90.
The determination of the road surface condition from 110 to 110 determines the estimated air pressure Pe and the tire air pressure Po at the time when the vehicle starts running in step 70.
Since it is performed after the deviation from the reference value α is exceeded, compared to the case where the road surface condition is determined after a certain time has elapsed from the time when the vehicle starts traveling. Therefore, it is possible to more reliably determine whether the road surface state is a dry state or a wet state.

In the illustrated embodiment, a positive determination is made in step 70, so that the deviation between the estimated tire air pressure Pe and the tire air pressure Po at the time when the vehicle starts traveling has a reference value α. Step 90 after that point
The road surface condition is determined by ˜110. However, the estimated tire air pressure Pe and the tire air pressure Po at the start of running after the time when a preset time has elapsed from the start of running of the vehicle. The road surface condition may be determined by whether or not the deviation exceeds the reference value β (a positive constant).

In the illustrated embodiment, the reference tire air pressure Pe is calculated as the estimated tire air pressure when the road surface is a dry road surface as shown in FIG. The air pressure is calculated when the road surface is a wet road surface, and the road surface condition is determined based on the estimated tire air pressure on the wet road surface by determining whether the actual tire air pressure Pa is less than or equal to the reference tire air pressure. May be.

Further, in the illustrated embodiment, it is determined whether the road surface condition is a dry condition or a wet condition. For example, a negative determination is made in step 90. In this case, by determining whether or not the outside air temperature T is equal to or higher than a predetermined reference value, it is determined whether the road surface condition is a wet road surface in a narrow sense (state wet with raindrops) or an ice and snow road surface. May be.

Although the present invention has been described above in detail with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments, and various other embodiments are also possible within the scope of the present invention. It will be apparent to those skilled in the art that

For example, in the illustrated embodiment, the tire air pressure detecting device 16 is a so-called FFT type detecting device for estimating the tire air pressure by calculating the resonance frequency of the tire based on the result of the FFT calculation. The tire air pressure detection device according to the present invention performs bandpass filter processing on a wheel speed signal, obtains a disturbance w from a filtered wheel speed signal by a disturbance observer, and estimates the tire air pressure based on this disturbance, a so-called disturbance. It may be an observer type air pressure detection device.

[0033]

As is apparent from the above description, according to the configuration of the present invention, the condition of the road surface is estimated based on the tire air pressure at the start of traveling of the vehicle and the tire air pressure at the elapse of a predetermined time after the start of traveling. Since it is configured as described above, it is possible to reliably estimate the road surface condition, particularly whether the road surface is a dry road surface or a wet road surface, by using the detection result of the air pressure detection device without requiring special means such as acceleration detection means. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a road surface state estimating device according to the present invention.

FIG. 2 is a flowchart showing a road surface state estimation routine in the embodiment shown in FIG.

FIG. 3 is a flowchart showing a tire air pressure estimation routine in the embodiment shown in FIG.

FIG. 4 is a graph showing changes in tire air pressure as the vehicle travels when the road surface is a dry road surface and when the road surface is a wet road surface.

FIG. 5 is a graph showing changes in the reference tire air pressure Pe and the actual tire air pressure Pa as the vehicle travels when the road surface is a dry road surface.

FIG. 6 is a graph showing the relationship between tire air pressure P and tire rolling resistance R.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Road surface state estimation device 12 ... Reference tire pressure calculation block 14 ... Road surface state estimation block 16 ... Tire pressure detection device 18 ... Temperature sensor 20 ... Vehicle speed sensor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Kawai, 1st Toyota-cho, Toyota-cho, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Hiroyoshi Kojima, 1st Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Hideki Ohashi 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Corporation (72) Inventor Katsuhiro Asano 1 41, Yokochi, Nagakute Town, Aichi-gun, Aichi Prefecture Toyota Central Research Institute Co., Ltd. (72) Inventor Umeno Kouji Ai Prefecture Nagachite Town, Aichi Prefecture, Oita, Nagatogi, Yokoshiro 41, No. 1, Yokota Central Research Institute Co., Ltd. (72) Inventor Shunji Naito 1-1, Showa-cho, Kariya City, Aichi Nihondenso Co., Ltd. (72) Inventor Nobuyoshi Onoki 1-1, Showa-cho, Kariya city, Aichi prefecture

Claims (1)

[Claims] 1. A road surface state estimating device for a vehicle, comprising an air pressure detecting device for detecting a tire air pressure, wherein a road surface is determined based on a tire air pressure at the start of traveling of the vehicle and a tire air pressure at a predetermined time after the start of traveling. A road surface state estimation device configured to estimate the state of the road surface.