JPH0650878A - Judgement apparatus for road-surface state - Google Patents

Abstract

PURPOSE:To judge a road-surface state in a real-time manner and accurately. CONSTITUTION:Signals from a vehicle-speed detection means 6, an open-air- temperature detection means 7 and a road-noise detection means 8 are compared with a map stored in a read-only memory 3 at a central operation processing unit 1 for an electronic control unit U, and a motion control means such as an antilock brake device or the like is controlled on the basis of a road-surface state which has been judged there. When a sound-pressure signal in a low-frequency region is smaller than a threshold value in a low-frequency region map, it is judged that a road surface is in a dry state. In addition, when the road surface is in a wet state and an open-air temperature is lower than a reference value, it is judged that the road surface is in a snow state. In addition, when the sound pressure in the low-frequency region is larger than the threshold value for the low-frequency region map, it is judged that the road surface is a (heavy) wet state, and, when it is smaller than the threshold value, it is judged that the road surface is in a (slightly) wet state.

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 judging device for judging the magnitude of a friction coefficient of a road surface on which a vehicle runs based on road noise.

[0002]

2. Description of the Related Art It is known that a water film existing on a road surface reduces a friction coefficient between the road surface and a tire and has a great influence on a braking characteristic and a cornering characteristic of a vehicle. Therefore,
Anti-lock brake device, power steering device,
In order to fully exhibit the performance of the four-wheel steering system and the like, it is necessary to accurately grasp the friction coefficient of the road surface.

Conventionally, the friction coefficient of the road surface has been determined by detecting the lateral or vertical slippage of the vehicle due to a steering angle input or a brake input, but steering or braking is performed by such a method. There is a problem that the coefficient of friction of the road surface cannot be determined in a non-steady running state.

Therefore, objects such as gravel, water drops, snow flakes, and ice chips that are rolled up from the road surface by the rotation of the tire inside the wheel house are detected by a raindrop sensor, a pressure sensor, an optical sensor, etc., and the detected amount of the object is There has been proposed a method of determining that the friction coefficient of the road surface is small when the friction coefficient is large (see Japanese Patent Laid-Open No. 1-227946).

[0005]

However, the conventional method described in the above publication has a limit in accuracy because it is difficult to identify the type of object rolled up from the road surface. Moreover, when a contact sensor such as a raindrop sensor or a pressure sensor is used, there is a problem in durability and reliability, and when an optical sensor is used, there is a problem that accuracy is deteriorated due to contamination of the light emitter and the light receiver. Becomes

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a road surface condition determining means capable of accurately determining a road surface condition in real time.

[0007]

In order to achieve the above-mentioned object, a road surface condition judging device of the present invention comprises a vehicle speed detecting means for detecting a vehicle speed, an outside air temperature detecting means for detecting an outside air temperature around the vehicle, and a road. Road noise detection means for detecting noise, sound pressure data storage means for storing in advance sound pressure data of road noise according to road surface condition, vehicle speed detection means, outside air temperature detection means, road noise detection means and sound pressure data It is characterized by further comprising: a determination unit that determines the road surface state based on the output of the storage unit.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1 and FIG. 2, the road surface condition determining device includes an electronic control unit U including a microcomputer. The electronic control unit U includes a central processing unit (CPU) 1 for performing various kinds of arithmetic processing, and a random access memory (temporary storage for temporarily storing signals from various detecting means described later and calculation results in the central processing unit 1). RAM) 2
And a read-only memory (ROM) 3 in which data such as arithmetic programs and various maps are stored in advance, and an input unit 4
And an output unit 5. The vehicle speed detection means 6 and the outside air temperature detection means 7 are connected to the input section 4 of the electronic control unit U, and the road noise detection means 8 composed of an acoustic microphone is connected via the amplifier 9 and the filter 10. Further, the output unit 5 is connected to a motion control means 11 such as an antilock brake device, a power steering device, a four-wheel steering device and the like.

A pair of left and right vehicle speed detecting means 6 are provided, and in the case of a front-wheel drive vehicle, they detect the rotational speeds of the left and right rear wheels Wr which are driven wheels. Further, the outside air temperature detecting means 7 detects the outside air temperature in the vicinity of the vehicle, and is provided at a position (for example, the upper part of the trunk) where it is unlikely to be affected by the temperature of the engine room or the temperature of the cabin. Further, the road noise detecting means 8 is provided inside the wheel house of the left and right rear wheels Wr, which are less affected by the engine noise, so that stones and water do not come into direct contact with each other.

The filter 10 is composed of a predetermined bandpass filter, and has a predetermined frequency in a high frequency region.
A predetermined frequency in the low frequency region is selectively passed.

Thus, the electronic control unit U includes the vehicle speed detecting means 6, the outside air temperature detecting means 7 and the road noise detecting means 8.
The friction coefficient of the road surface is determined in real time based on the signal input from the device and the data stored in the read-only memory 3, and the operation of the motion control means 11 is controlled based on the result.

Next, the contents of the arithmetic processing executed by the central processing unit 1 of the electronic control unit U will be described with reference to the flow charts of FIGS. 3 and 4 and the graphs of FIGS.

First, the general relationship between the road surface condition and road noise will be described with reference to the graphs of FIGS.

FIGS. 5 and 6 show how the sound pressure level in each frequency region of road noise changes with changes in vehicle speed. FIG. 5 shows a dry state and FIG. 6 shows a wet state. Each corresponds. As is clear from these graphs, the sound pressure level of road noise is higher in the wet state where water drops are splashed by the wheels than in the dry state, and in both states, the sound pressure level increases with increasing vehicle speed in most frequency regions. Pressure level is increasing.
It has been experimentally confirmed that the sound pressure level is not significantly affected by the type and size of the tire, especially in the wet state.

FIGS. 7 and 8 show the characteristics of the sound pressure level in the dry state and the sound pressure level in the wet state in the high frequency region and the low frequency region. FIG. 7 shows the vehicle speed. In the case of medium speed, FIG. 8 corresponds to the case of high vehicle speed. As is clear from these graphs, the difference between the sound pressure level in the wet state and the sound pressure level in the dry state is remarkable in the high frequency region where the frequency is 1 KHz or more (see arrow a), and the frequency is lower than 1 KHz. In the frequency domain, the difference between the sound pressure level in the wet (strong) state, that is, the state where the water film thickness is large, and the sound pressure level in the wet (weak) state, that is, the state where the water film thickness is small, are significant (arrow b). reference).

From the above, whether the road surface is in the dry state or in the wet state can be judged from the sound pressure level in the high frequency region, and when the road surface is in the wet state, the thickness of the water film can be determined. It is understood that whether the value is large or small can be determined from the sound pressure level in the low frequency region.

Next, the procedure for determining the road surface condition will be specifically described with reference to the flowcharts of FIGS. 3 and 4.

In step S1, the vehicle speed detecting means 6 detects the vehicle speed V ₀ , in step S2 the outside air temperature detecting means 7 detects the outside air temperature Tc, and in step S3 the road noise detecting means 8 detects the road noise sound pressure signal. Subsequently, in step S4, the filter 10 is acted on the sound pressure signal amplified by the amplifier 9 to extract the sound pressure signal P (Hi) at the predetermined frequency Hi in the high frequency region.

Next, in step S5, the dry state determination map SPL-Hi stored in advance in the random access memory 2 of the electronic control unit U is retrieved, and in step S6 the dry state determination map SPL-Hi and the current vehicle speed V. _The sound pressure level SPL (1) serving as the determination reference is read from ₀ . FIG. 9 shows the dry state determination map SPL-
H, which is a predetermined frequency in the high frequency region.
A threshold value for setting the sound pressure level SPL (1) corresponding to the vehicle speed V ₀ is set between the dry state characteristic and the wet state characteristic of i.

Thus, for example, when the current vehicle speed V ₀ is V ₁ , the sound pressure signal P (Hi) is below the threshold sound pressure level SPL (1), that is, in step S7. If the answer is NO, it is determined in step S8 that the road surface condition is dry.

On the other hand, if the answer to step S7 is YES and the sound pressure signal P (Hi) exceeds the sound pressure level SPL (1) above the threshold value in FIG. 9, the road surface is wet in step S9. It is determined that At this time, in the subsequent step S10, the outside air temperature Tc detected by the outside air temperature detecting means 7 is compared with a predetermined reference value Ts. If Tc ≦ Ts and the outside air temperature Tc is low, the road surface is put into a snow state in step S11. It is determined that there is.

If the answer to step S10 is YES and it is determined that the road surface is not in the snow state, step S10
The sound pressure signal amplified by the amplifier 9 at 12 is filtered by the filter 1
0 is applied to take out the sound pressure signal P (L _OW ) at the predetermined frequency L _OW in the low frequency region. Next, step S1
3 Pull the random access map for determining a wet state stored in advance in the memory 2 SPL-L _OW in, the map for determining the wet state at step S14 SPL-L _OW
And the sound pressure level SPL (2) is read from the current vehicle speed V ₀ . FIG. 10 shows the wet state determination map SPL-L.
_OW , which is a predetermined frequency in the low frequency region, L _ow
Between the characteristics of the wet (strong) state and the characteristics of the wet (weak) state in S, the sound pressure level SPL corresponding to the vehicle speed V ₀
The threshold value that gives (2) is set.

Thus, for example, when the current vehicle speed V ₀ is V ₁ , if the sound pressure signal P (L _OW ) exceeds the sound pressure level SPL (2) above the threshold, that is, Step S1
If the answer to 5 is YES, it is determined in step S16 that the road surface condition is wet with a large water film thickness (strong),
On the contrary, if the sound pressure signal P (L _OW ) is equal to or lower than the sound pressure level SPL (2) above the threshold value, that is, if the answer in step S15 is NO, the road surface condition is the water film thickness in step S17. Is determined to be a small wet (weak). The threshold value of the map used for these determinations is determined in consideration of the type and size of the tire of the vehicle.

As described above, the road surface condition is dry or snow based on the signals inputted from the vehicle speed detecting means 6, the outside air temperature detecting means 7 and the road noise detecting means 8 and the data stored in the read-only memory 3. It is possible to accurately determine in real time the left and right wheels independently in real time as to whether it is in a wet (strong) or wet (weak) state, and appropriately control the motion control means 11 based on the result.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-mentioned embodiments, and various design changes can be made.

For example, in the embodiment, two maps SPL-
Hi, using SPL-L _OW dry, snow, but to determine the respective road surface condition of wet (strong) and wet (weak), by increasing the set number of the number and the threshold of the map, or By adding a vibration sensor near the road noise detection means (such as the upper arm that supports the wheels), the dry condition can be used for concrete roads, asphalt roads,
To identify Belgian roads (cobblestone roads), gravel roads, etc., to identify wet conditions into three or more types according to the thickness of the water film, and to identify snow conditions to sherbet roads, pressure snow roads, frozen roads, etc. Is also possible.

[0028]

As described above, according to the present invention, the road noise sound pressure signal detected by the road noise detection means and the road noise sound pressure data stored in the sound pressure data storage means are detected by the vehicle speed detection means. Since the detected vehicle speed is compared with the outside air temperature detected by the outside air temperature detecting means, it is possible to accurately determine the road surface condition such as dry, wet and snow in real time. Moreover, since the road noise detecting means is a non-contact type and does not come into contact with an object rolled up from the road surface, not only the durability and reliability are improved as compared with the conventional contact-type raindrop sensor and pressure sensor, but also dirt and Since it is resistant to dirt such as water, it is possible to continuously maintain stable accuracy as compared with the conventional optical sensor.

[Brief description of drawings]

FIG. 1 is a block diagram of a control system

FIG. 2 is a diagram showing the arrangement of detectors.

FIG. 3 is a first subdivision of the flowchart.

FIG. 4 is a second partial diagram of the flowchart.

FIG. 5 is a graph showing the relationship between frequency and sound pressure level for each vehicle speed in a dry state.

FIG. 6 is a graph showing the relationship between frequency and sound pressure level for each vehicle speed in a wet state.

FIG. 7 is a graph showing the relationship between frequency and sound pressure level at low vehicle speed according to road surface condition.

FIG. 8 is a graph showing the relationship between frequency and sound pressure level at high vehicle speed according to the road surface condition.

FIG. 9 is a graph showing a dry state determination map.

FIG. 10 is a graph showing a wet state determination map.

[Explanation of symbols]

1 Central processing unit (determination means) 3 Read only memory (sound pressure data storage means) 6 Vehicle speed detection means 7 Outside air temperature detection means 8 Road noise detection means

Claims (1)

[Claims] 1. A vehicle speed detecting means (6) for detecting a vehicle speed,
An outside air temperature detecting means (7) for detecting an outside air temperature around the vehicle,
Road noise detection means for detecting road noise (8)
And a sound pressure data storage means (3) in which sound pressure data of road noise according to the road surface condition is stored in advance, the vehicle speed detection means (6), the outside air temperature detection means (7), and the road noise detection means (8). And a determination means (1) for determining the road surface state based on the output of the sound pressure data storage means (3).