JP2006035928A - Road surface state determining method and device, and road surface state determining program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for accurately determining a road surface state even if there is road surface gradient and the road surface gradient is changed, and even if a driving manner of a vehicle is different (FF/FR). <P>SOLUTION: The road surface state determining method for determining the state of the road surface on which a vehicle travels, inputs a detection value of a clinometer equipped to the vehicle, inputs rotation speed information of a wheel from a wheel rotation speed detecting means attached to the vehicle, obtains ground speed and ground acceleration along a traveling surface from the rotation speed information of driven wheels, obtains a tilting angle of the road surface from the detection value of the clinometer and the ground acceleration, obtains a slip ratio from the rotation speed information of driving wheels and the ground speed, and determines a friction coefficient and the ease of sliding between the road surface and tires during traveling by using a relationship between the slip ratio, the ground acceleration, and the tilting angle of the road surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for determining a slip ratio, a friction coefficient, and slipperiness between a road surface and a tire in a road surface state, and a road surface state determination program.

  For example, Patent Document 1 discloses a road surface state determination device that determines a friction coefficient between a road surface and a tire using rotational speed information of four wheels mounted on a vehicle. Controlling a vehicle to adapt to the current weather from position and absolute time information obtained from GPS received radio waves, weather information obtained from the outside, and outside air temperature information obtained from a vehicle-mounted sensor is, for example, Patent Document 2 is disclosed. A vehicle travel control device that supports steering and vehicle speed control based on information obtained from a navigation device is disclosed in Patent Document 3, for example. In addition, by using the moving speed information of the vehicle obtained by GPS as the absolute speed of the vehicle, the slip ratio of the driving wheel of the running vehicle is calculated, and the acceleration of the vehicle is obtained by differentiating the GPS speed information with respect to time. It is also known that there is known a technique for determining the slipperiness of the road surface during traveling from the relationship between the acceleration and the slip ratio, thereby enabling a response to four-wheel drive.

  Further, Patent Document 5 discloses that the state of the road surface is determined even at the start of turning based on the rotation start timing of the driving wheel and the driven wheel at the time of starting.

JP 2001-253334 A JP 2000-82198 A JP-A-10-119807 JP 2000-79835 A

  As described above, various inventions related to slipperiness of the road surface have been made. Among them, only Patent Document 1 discloses a method for detecting slipperiness of a vehicle in real time during normal driving. is there. Patent Document 2 estimates the slipperiness according to the weather, Patent Document 3 estimates the slipperiness by the rudder angle reaction force when steering, and Patent Document 4 indicates the slipperiness due to the difference in the rotation start timing of the front and rear wheels. In all cases, the road gradient is not considered. That is, the above-mentioned document does not disclose a technique for estimating the ease of slipping in consideration of the road surface gradient.

  Moreover, although patent document 1 is disclosing the technique which determines slipperiness most in real time, even if it is the road surface condition of the same asphalt pavement, for example, when it changes from a flat road to an uphill, the method of patent document 1 is disclosed. Then, since the running resistance changes during data accumulation for linear approximation, the relationship between the slip ratio and the acceleration changes greatly. That is, even if the slip ratio increases, the acceleration does not increase. For this reason, a correlation coefficient falls and it becomes impossible to perform linear approximation. Therefore, if the uphill has a constant slope, a state in which the road surface cannot be determined until data having the same running resistance value is collected for a while after the uphill is reached. Similarly, if the slope of the road surface continues to change, the road surface determination value cannot be obtained.

  An object of the present invention is to realize accurate road surface condition determination even when there is a gradient on a road surface without using an expensive device such as a GPS by adding road surface gradient information obtained by an inclinometer.

  A first aspect of the present invention is a road surface state determination method for determining a state of a road surface on which a vehicle is traveling, the step of inputting a detection value of an inclinometer provided in the vehicle, and a wheel attached to the vehicle From the step of inputting wheel rotation speed information from the rotation speed detection means, the step of calculating the ground speed and ground acceleration of the vehicle based on the wheel rotation speed information, the detected value of the inclinometer and the ground acceleration, A step of calculating an inclination angle, and determining a state of the road surface during traveling based on the wheel rotation speed information and the inclination angle of the road surface.

  More specifically, the ground speed and ground acceleration along the traveling surface are obtained from the rotational speed information of the driven wheel, the inclination angle of the road surface is obtained from the detected value of the inclinometer and the ground acceleration, and then the rotational speed of the driving wheel. Determining the slip ratio from the information and the ground speed, and determining the coefficient of friction between the road surface and the tire and the slipperiness using the relationship between the slip ratio, the ground acceleration, and the inclination angle of the road surface To do.

A second aspect of the present invention is a road surface state determination device that determines a state of a road surface on which a vehicle is traveling,
Means for detecting a tilt angle of the vehicle with respect to the horizontal; means for detecting a rotational speed of a wheel mounted on the vehicle; means for calculating a ground speed and a ground acceleration of the vehicle based on the wheel rotational speed information; Means for calculating an inclination angle of the road surface based on the information obtained by the means and the ground acceleration, and a friction coefficient and a slip between the road surface and the tire during traveling by the wheel rotational speed information and the inclination angle of the road surface. It is a road surface information determination apparatus including determining ease.

In a third aspect of the present invention, a computer is used to determine the state of the road surface on which the vehicle is traveling.
Memory means for storing the inclination angle of the vehicle with respect to the horizontal and the rotational speed of the wheel mounted on the vehicle;
Means for calculating the ground speed and ground acceleration of the vehicle based on the rotational speed of the wheels;
The means for calculating the inclination angle of the road surface from the inclination angle of the vehicle and the ground acceleration, and the coefficient of friction and the slipperiness between the road surface and the tire during running are determined by the wheel rotation speed information and the inclination angle of the road surface. It is a road surface condition determination program for functioning as a determination means.

  Method and apparatus for determining the slipperiness of a road surface in a running vehicle using wheel rotation speed information obtained from wheel rotation speed detection means attached to the vehicle and vehicle inclination angle information obtained by an inclinometer This makes it possible to estimate the friction coefficient and slipperiness between the road surface and tires even when the road surface changes in slope, or when driving on an uphill or downhill road surface, thereby improving vehicle performance and safety. Can be increased.

  Further, even in a tunnel where GPS radio waves do not reach, it is possible to determine road surface conditions including when the road surface slope is changing, and when traveling on an upward slope road surface and traveling on a downward slope road surface.

  A description will be given with reference to FIGS. 1, 2, and 3. The vehicle is assumed to be a front-wheel drive vehicle. In FIG. 1, M is the mass of the vehicle, G is the gravitational acceleration, θ is the gradient of the road surface, T is the rotational speed of the wheel, Tf is the rotational speed of the front wheel, Tr is the rotational speed of the rear wheel, and a is the acceleration due to the driving force. is there. Here, the wheel rotation speed is the rotation angular velocity of the wheel × the dynamic load radius of the wheel.

The force F generated by the tire is the sum of the reaction forces FT according to the μ-S characteristics generated by the slip ratio S of each wheel. The front wheel right is indicated by fr, the front wheel left is indicated by fl, the rear wheel right is indicated by rr, and the rear wheel left is indicated by rl. For two-wheel drive vehicle, the driven wheel is deemed not to slip, ground speed V _R of the vehicle,
V _R = (Trl + Trr) / 2
Slip rate is
Sfl = (Tfl−V _R ) / Tfl
Sfr = (Tfr−V _R ) / Tfr
And the driving force of the tire is
F = FTfr + FTfl
FTfr = μ-s (Sfr)
FTfl = μ-s (Sfl)
It is.

Here, the slip ratio S of the drive wheels is defined as the average of the left and right wheels S = (Sfl + Sfr) / 2
For example, the driving force F generated by the tire is a reaction force generated by the slip rate S of the driving wheel according to the μ-S characteristic.
F = 2 (μ-s (S))
It can be expressed as If the vehicle mass is M, due to the force generated by the drive wheel tire,
F = M · a
As a result, an acceleration a corresponding to

When the ground speed of the vehicle is V _R and the ground acceleration is V _R ′, the detected value of the inclinometer is the vector sum X of the gravitational acceleration G and the ground acceleration (reaction force) V _R ′ along the traveling surface of the vehicle. The direction α (FIG. 1).

Considering the influence of the weight acceleration G due to the road surface inclination angle, the relationship between the driving force F and the ground acceleration V _R ′ is that the angle information (inclination angle of the road surface) with respect to the horizontal in the moving direction is θ (the climb direction is positive). ,
F = M ・ a = M ・ V _R '+ M ・ Gsinθ
(FIG. 2). The vehicle mass M can be omitted,
a = V _R '+ Gsinθ
Therefore, if the μ-S characteristics are the same for the left and right drive wheels and can be approximated by a linear expression, the average of the slip ratio S of the drive wheels and the relationship between V _R ′ + Gsin θ can be linearly approximated by It is possible to estimate the gradient, that is, to determine slipperiness (FIG. 3).

  The slipperiness of the road surface can be estimated by comparing the magnitude of this gradient with a reference value (value during asphalt travel).

  Here, when calculating the slip ratio and the driving force, a moving average process is performed on a predetermined number of data obtained every sampling time, for example, 50 data, in order to eliminate the influence of disturbance due to road surface unevenness. In order to reduce the effect of data fluctuations without reducing the number of data, data is sampled every short sampling time, for example every several tens of ms, and the data with large fluctuations obtained in this sampling time is moving average To do. Next, in order to obtain the relationship of the linear expression of the slip ratio and the driving force, linear approximation is performed by a least square approximation method for every predetermined number, for example, 20 pieces, and this process is calculated by movement at every sampling time.

  According to the present invention, by adding the travel resistance change due to the road surface gradient to the acceleration information, it is possible to determine the slipperiness of the road surface even when traveling on a road that is not a flat road. In addition, it is possible to determine whether the road surface is slippery accurately even when traveling on an uphill road surface or on a downhill road surface. In addition, the same logic can be used for both front wheel driving and rear wheel driving.

Embodiment FIG. 6 is a block diagram of a road surface condition determination apparatus according to an embodiment of the present invention. The road surface condition determination device 10 inputs the inclination angle α from the inclinometer 1 via the input device 3 and stores it in the memory 5. Further, wheel rotational speed information is inputted from the wheel speed detecting device 2 and stored in the memory 5. The wheel rotation speed information from the wheel speed detection device 2 may be a pulse generated by the rotation of the wheel. In that case, the wheel rotation speed can be calculated from the period of the input pulses or the number of pulses at a certain time interval. The CPU 4 executes a program stored in the memory 5. In this embodiment, only one memory 5 is described, but the program may be stored in a ROM (read only memory) and the operation data may be stored in a RAM (random access memory). Further, a road surface state display device 7 that displays the determined road surface state and a vehicle drive control device 8 that uses the road surface state determination information are connected.

Next, the operation will be described. The vehicle ground speed V _R (the rotational angular speed of the driven wheel × dynamic load radius) is calculated from the data string of the rotational speed information of the driven wheel input to the memory 5. The ground acceleration V _R ′ is calculated by further differentiating the calculated ground speed V _R. The ground acceleration V _R ′ may be calculated by a difference method or an approximate expression using a higher-order differential coefficient. The road inclination angle θ is calculated from the ground acceleration V _R ′ and the inclinometer detection value α.

On the other hand, it calculates the rotational speed V _t of the drive wheel from the rotational angular velocity of the drive wheel and a given wheel dynamic load radius, the difference slip ratio of S and ground speed V _R along the drive wheel rotation speed V _t and the road surface Calculate Gravity acceleration sum V _R '+ Gsinθ by ground acceleration and road surface gradient and slip rate are sequentially calculated, and a μ-S gradient is estimated by a first-order approximation from a set of a plurality of successive accelerations and slip rates.

  The obtained estimated value is output to the road surface state display device or the vehicle drive control device.

  In the present embodiment, an example in which the inclination angle α is input from the inclinometer at an indefinite interval is described, but the inclinometer detection value may be input at a constant interval in accordance with the wheel rotation speed information input. When inputting at a fixed interval, the time interval is fixed, and the calculation is simplified.

  Furthermore, a predetermined number of moving average processes may be performed on the wheel rotation speed, the vehicle ground speed or ground acceleration, and the road surface inclination angle (angle with respect to the horizontal plane in the movement direction) read at regular time intervals. By performing the moving average process, the influence of noise can be canceled and a stable result can be obtained. In addition, there is an effect that a highly accurate road surface friction coefficient can be quickly calculated.

  By using the determined road surface friction coefficient information in an ABS (anti-lock brake system) device, a TRC (traction control) device, or the like, optimal control according to the road surface friction coefficient can be performed. Further, when it is determined that the road surface has a low friction coefficient, the driver can be alerted that the road surface is slippery.

  For example, in the ABS device, the road surface friction coefficient during traveling can be input from the road surface state determination device of the present invention, and the upper limit of the brake operation force according to the road surface friction coefficient can be set. The ABS device detects slipping (tire lock) every moment and adjusts the brake operation force in real time. By setting the upper limit of the brake operation force according to the road surface condition, It becomes possible to obtain the maximum braking force immediately before locking, and there is a possibility that safer and more reliable braking can be realized. As a result, when driving on a road surface that has started to rain, a road surface in which dust has been washed away by rain, or a snowy road surface (the slipperiness varies depending on the temperature) with studless tires, the road surface such as a frozen road or a gravel road And brake control according to tire conditions.

  In the TRC device, the road surface friction coefficient is input from the road surface condition determination device of the present invention, for example, the driving force distribution of the left and right wheels is adjusted, or the upper limit of the driving force according to the road surface friction coefficient is set to start / accelerate There is a possibility that time slip can be eliminated and more effective vehicle drive control can be realized. For example, slipping can be avoided by controlling to an appropriate driving force even on a snowy slope.

  Also, for example, if the slipperiness of wet asphalt is larger than that of the standard (the slope of the slip ratio with respect to the driving force is large), it will be judged as slippery and an alarm buzzer will sound. The driver can be alerted by turning on the.

Comparative example Example of entering a slope from a flat road on an asphalt road Vehicle: Audi A4 (front wheel drive)
Place: Sumitomo Rubber Co., Ltd. Road surface speed approaching uphill from Okayama TC suburbs: 40-50km / h 2 people inclinometer data is AD converted using a tilt sensor manufactured by Tokai Rika Co., Ltd. Entered.

  In this comparative example, the wheel rotation speed is detected by counting the number of pulses generated by the wheel rotation at a constant period. The counting cycle is 50 msec. The period for capturing the inclinometer data is made to coincide with the period for counting pulses for detecting the wheel rotation speed. The detected wheel rotation speed and inclinometer data are moving averages over a detection period of 1 second.

  The arithmetic unit used is a 3 series microcomputer manufactured by NEC Corporation, an operation clock of 16 MHz, and a working memory capacity of 760 bytes. The data capturing device and the PC are ThinkPad 240 manufactured by IBM Japan.

  FIG. 4 is a plot of acceleration-slip rate calculation values by a conventional method that does not use gradient angle information. In the conventional method that does not use the inclinometer and does not consider the road surface gradient, the relationship between the slip ratio and acceleration cannot be approximated by a linear equation on the road surface where the gradient is changing. It can be seen that there is a state where the road surface state cannot be determined because it cannot be calculated.

  On the other hand, FIG. 5 is a plot of drive acceleration-slip ratio calculation values according to the method of the present invention. As shown in FIG. 5, the slip ratio can be approximated as a linear function of the driving acceleration corrected by the road surface gradient, so that the road surface friction coefficient can always be estimated.

Comparing the slip rate according to the conventional method and the slip rate according to the method of the present invention, the graphs agree at 0.03 to 0.15 m / s ² corresponding to the portion running on a flat road, but the climbing slope From the point of approach, it is bent in FIG. 4 (the inflection point in the graph of FIG. 4), and shifted upward in a region of acceleration larger than that. Therefore, the slip ratio with respect to acceleration varies on the road surface where the gradient changes, and the road surface friction coefficient cannot be estimated. On the other hand, in the driving acceleration-slip ratio (FIG. 5) according to the method of the present invention, the slip ratio with respect to the acceleration (driving acceleration) is on a straight line from the point of approaching the gradient, so the road surface gradient varies. Even so, the road surface friction coefficient can be correctly estimated.

  In this comparative example, 20 slip ratio calculated values were used to estimate the road surface friction coefficient, so the actual lead time (time from the first data input until the road surface friction coefficient estimated value was first output) Was 2 sec. Thereafter, the road surface friction coefficient estimation value is output every 50 msec, which can be said to be effective as road surface condition determination.

  Further, effects obtained when the present invention is applied to an actual vehicle will be described below.

  In this example, the estimated value (slip rate / driving acceleration) for determining the slipperiness of the road surface for determining the slipperiness of the road surface could stably output a value of around 0.0525.

  On the other hand, the estimated value of slipperiness when the vehicle travels on a slippery road surface is 0.058 as an average value when traveling on various slippery road surfaces in Sumitomo Rubber Okayama TC. Similarly, the estimated value of slipperiness when driving on a dry asphalt road surface in Okayama TC is around 0.051, for example, when the reference value is 0.05, the estimated slipperiness exceeds 0.055. If it is determined that the vehicle is slippery and the alarm buzzer is sounded, it is possible to inform the driver that the vehicle is slippery and dangerous.

  In the traveling of the present embodiment, it is possible to continue to show that the road surface is not always slippery without generating a false alarm.

It is a figure explaining the relationship between the detected value of an inclinometer, the ground acceleration of a vehicle, and the inclination angle of a road surface. It is a figure explaining the road surface state estimation which considers the road surface gradient of this invention. It is a figure showing the relationship between a slip ratio and acceleration. It is the figure which plotted the acceleration-slip ratio calculation value by the conventional method of a comparative example. It is the figure which plotted the driving acceleration-slip ratio calculation value by the method of this invention of a comparative example. 1 is a block diagram of a road surface condition determination apparatus according to an embodiment of the present invention.

Explanation of symbols

1 Inclinometer 2 Wheel speed detection device 3 Input device 4 CPU
DESCRIPTION OF SYMBOLS 5 Memory 6 Output device 7 Road surface state display apparatus 8 Vehicle drive control apparatus 10 Road surface state determination apparatus

Claims (9)

A road surface state determination method for determining a state of a road surface on which a vehicle is traveling, the step of inputting a detection value of an inclinometer provided in the vehicle, and a wheel rotation speed from a wheel rotation speed detection means attached to the vehicle. A step of inputting information, a step of calculating a ground speed and a ground acceleration of the vehicle based on the wheel rotational speed information, and a step of calculating a slope angle of the road surface from the detected value of the inclinometer and the ground acceleration. And determining a friction coefficient and slipperiness between the running road surface and the tire based on the wheel rotation speed information and the inclination angle of the road surface. The wheel rotation speed information is a wheel rotation speed calculated from the cycle of the wheel rotation pulse of the wheel speed detection means read at predetermined time intervals and the number of pulses,
The detection value of the inclinometer is read in synchronization with the time interval of wheel rotation speed detection for calculating the wheel rotation speed, the ground speed and the ground acceleration along the traveling surface are obtained from the rotation speed information of the driven wheel, and the inclination Determining the inclination angle of the road surface from the detected value of the meter and the ground acceleration, and then determining the slip ratio from the rotational speed information of the drive wheels and the ground speed,
2. The road surface condition determination method according to claim 1, wherein a friction coefficient and slipperiness between a running road surface and a tire are determined using the relationship between the slip ratio, the ground acceleration, and the inclination angle of the road surface. 3. The road surface condition determination method according to claim 2, wherein a predetermined number of moving average processes are performed on the wheel rotation speed, the vehicle ground speed or ground acceleration, and the road surface inclination angle read at regular time intervals. A road surface state determination device for determining the state of a road surface on which a vehicle is traveling, the means for detecting the inclination angle of the vehicle with respect to the horizontal, the means for detecting the rotational speed of a wheel mounted on the vehicle, and the wheel rotation Means for calculating the ground speed and ground acceleration of the vehicle based on the speed information, means for calculating the inclination angle of the road surface based on the information obtained by the tilt detecting means and the ground acceleration, and the wheel rotational speed information; A road surface state determination device including determining a friction coefficient and slipperiness between a running road surface and a tire based on an inclination angle of the road surface. The wheel rotation speed information is a wheel rotation speed calculated from the cycle of the wheel rotation pulse of the wheel speed detection means read at predetermined time intervals and the number of pulses,
In synchronization with the time interval of wheel rotation speed detection for calculating the wheel rotation speed, the detected value of the inclinometer is read, and the ground speed and ground acceleration of the vehicle along the traveling surface are obtained from the rotational speed information of the driven wheel, Determining the inclination angle of the road surface from the detected value of the inclinometer and the ground acceleration, and then determining the slip ratio from the rotational speed information of the drive wheels and the ground speed,
The road surface condition determination device according to claim 4, wherein a friction coefficient and slipperiness between the road surface and the tire during traveling are determined using the relationship between the slip ratio, the ground acceleration, and the inclination angle of the road surface. 6. The road surface condition judging device according to claim 5, wherein a predetermined number of moving average processes are performed on the wheel rotational speed, the ground speed or ground acceleration of the vehicle, and the inclination angle of the road surface, which are read at regular time intervals. To determine the condition of the road on which the vehicle is running,
Memory means for storing the inclination angle of the vehicle with respect to the horizontal and the rotational speed of the wheel mounted on the vehicle;
Means for calculating the ground speed and ground acceleration of the vehicle based on the rotational speed of the wheels;
The means for calculating the inclination angle of the road surface from the inclination angle of the vehicle and the ground acceleration, and the coefficient of friction and the slipperiness between the road surface and the tire during running are determined by the wheel rotation speed information and the inclination angle of the road surface. A road surface state determination program for functioning as a determination unit. The wheel rotation speed information is a wheel rotation speed calculated from the cycle of the wheel rotation pulse of the wheel speed detection means read at predetermined time intervals and the number of pulses,
The detection value of the inclinometer is read in synchronization with the time interval of wheel rotation speed detection for calculating the wheel rotation speed, the ground speed and the ground acceleration along the traveling surface are obtained from the rotation speed information of the driven wheel, and the inclination Determining the inclination angle of the road surface from the detected value of the meter and the ground acceleration, and then determining the slip ratio from the rotational speed information of the drive wheels and the ground speed,
8. The road surface condition determination program according to claim 7, wherein a friction coefficient and slipperiness between a running road surface and a tire are determined using the relationship between the slip ratio, the ground acceleration, and the inclination angle of the road surface. 9. The road surface condition determination program according to claim 8, further comprising a step of applying a predetermined number of moving average processes to the wheel rotation speed, the ground speed or ground acceleration of the vehicle, and the inclination angle of the road surface calculated at regular time intervals.

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