JP2011051519A - Road surface friction coefficient calculation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To calculate a road surface friction coefficient corresponding to the condition of a road surface irrespective of the traveling state of a vehicle in a road surface friction coefficient calculation device. <P>SOLUTION: The road surface friction coefficient calculation device is equipped with: a longitudinal acceleration detection means 1 detecting longitudinal acceleration acting on the vehicle; a clocking means 2 measuring regular traveling duration in a state where the longitudinal acceleration is not detected in the vehicle; a braking/driving force imparting means 3 imparting minute braking/driving force to the vehicle for a second predetermined time when the regular traveling duration measured by the clocking means 2 becomes a first predetermined time or more; and a road surface friction coefficient calculation means 4 calculating the friction coefficient of a road surface on which the vehicle travels after the impartation of the minute braking/driving force. The clocking means 2 resets the traveling elapsed time when the friction coefficient is calculated by the road surface friction coefficient calculation means 4 and starts measuring the regular traveling duration again. The friction coefficient of the road surface is periodically calculated in every predetermined time thereby. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a road surface friction coefficient computing device that calculates a friction coefficient between a traveling road surface of a vehicle and wheels.

  Conventionally, in an automatic braking device for a vehicle, control for calculating a friction coefficient of a road surface on which the vehicle travels and adjusting a braking force according to the magnitude of the road surface friction coefficient has been performed. In general, a road surface with a smaller friction coefficient reduces the friction force and becomes more slippery, and the braking distance required to stop the vehicle also increases. Therefore, an accurate calculation of the road friction coefficient is required in the automatic braking control. .

Patent Document 1 describes a road surface friction coefficient detection device that estimates the size of a road surface friction coefficient μ based on a wheel slip ratio and a longitudinal acceleration acting on a vehicle. In this technique, a linear regression coefficient of longitudinal acceleration with respect to a slip ratio of a wheel is calculated, and the magnitude of the road surface friction coefficient is estimated using a correlation between the regression coefficient and the road surface friction coefficient.
However, this technique requires a longitudinal acceleration acting on the vehicle when estimating the road surface friction coefficient, and therefore cannot cope with a traveling state such as traveling on a flat road surface at a constant speed. That is, the response to a road surface condition that changes from moment to moment is poor, and an erroneous estimation result of the road surface friction coefficient may be used for actual control.

  In order to deal with such a problem, in the technique described in Patent Document 2, in the vehicle collision prevention apparatus for preventing a collision with a front object, a slow brake that does not lock the wheel is activated before the automatic sudden brake is activated. A configuration is disclosed in which a wheel slip ratio, wheel acceleration, and the like are sampled a plurality of times, and a road surface friction coefficient is calculated from these sampling data. In this technology, when the distance to the front object is less than or equal to the first inter-vehicle distance, the brake is operated to grasp the accurate road surface friction coefficient, and the second inter-vehicle distance is calculated using this road surface friction coefficient. When the distance to the front object is further reduced and becomes less than the second inter-vehicle distance, the automatic sudden braking is activated. With these configurations, it is supposed that automatic braking can be performed at an appropriate timing according to the road surface condition.

JP-A-2005-132187 Japanese Patent Laid-Open No. 7-17346

  However, in the technique of Patent Document 2, since the distance to the front object is an operating condition for the slow brake, there is a possibility that the road surface friction coefficient cannot be grasped in time for the automatic sudden braking to be operated. For example, when the second inter-vehicle distance is calculated using the road surface friction coefficient obtained by operating the gentle brake, if the distance to the front object is already smaller than the second inter-vehicle distance, Automatic braking cannot be performed at the correct timing. Such a problem becomes more prominent as the traveling speed of the vehicle is higher.

  In addition, since the technology of Patent Document 2 is configured to grasp the road surface friction coefficient before the operation of automatic sudden braking, there is a problem that it is difficult to apply to a system including accelerator control such as traction control and cruise control. is there. In this respect, the technique of Patent Document 2 is also poor in responsiveness to a road surface condition that changes from moment to moment, and an accurate road surface friction coefficient may not be used in actual control.

  The present invention has been made in view of such problems, and has a simple configuration, and can calculate a road surface friction coefficient corresponding to a road surface condition regardless of the traveling state of the vehicle. An object is to provide an apparatus.

  (1) In order to achieve the above object, the road surface friction coefficient computing device of the present invention is detected by a steady running state detecting means for detecting a steady running state in which longitudinal acceleration does not act on the vehicle, and the steady running state detecting means. Time measuring means for measuring the duration time of the steady running state, and when the duration time measured by the time measuring means exceeds a first predetermined time, a minute braking force or a minute driving force is applied to the vehicle at a second predetermined time. Braking driving force applying means for applying only time, and road friction coefficient calculating means for calculating a friction coefficient of a road surface on which the vehicle travels after the minute braking force or the minute driving force is applied by the braking driving force applying means. The time measuring means resets the duration time when the friction coefficient is calculated by the road surface friction coefficient calculation means, and starts measuring the duration time again.

In this case, in the steady running state, the running time is periodically counted by the timing means. Further, the braking driving force applying means periodically applies the minute braking force or the minute driving force to the wheels of the vehicle. Accordingly, the road surface friction coefficient calculation means periodically calculates the friction coefficient.
The minute braking force is a small braking force that is not perceived by the driver of the vehicle, and is a weak brake that falls within the category of alarms and notifications (for example, a deceleration of 0.25 G or less within 0.8 seconds). It is conceivable that the brake is a brake that is generated and is not considered to be brake control.

  The minute driving force is a small braking force that is not perceived by the driver of the vehicle, and is a weak accelerator that falls within the range of alarms and notifications (for example, an acceleration of 0.25 G or less is generated within 0.8 seconds). Accelerator).

  (2) The vehicle speed detecting means for detecting the vehicle speed and the wheel speed detecting means for detecting the wheel speed of the driving wheel of the vehicle are further provided, and the road surface friction coefficient calculating means is detected by the vehicle speed detecting means. It is preferable to calculate the friction coefficient based on the vehicle speed and the wheel speed detected by the wheel speed detecting means.

(3) Further, it is preferable that the road surface friction coefficient calculating means calculates the friction coefficient when the steady running state is detected by the steady running state detecting means.
That is, in the traveling state in which the longitudinal acceleration is not detected, the minute braking force or the minute driving force is periodically applied to calculate the friction coefficient, while in the traveling state in which the longitudinal acceleration is detected, the friction coefficient is calculated. The friction coefficient is calculated using the longitudinal acceleration.

  (4) Further, a wiper sensor for detecting an operation or non-operation state of a wiper device mounted on the vehicle is further provided, and the braking driving force applying means detects a change in the operation state of the wiper by the wiper sensor. It is preferable that the minute braking force or the minute driving force is applied.

  (5) Further, an illuminance sensor that detects environmental illuminance around the vehicle is further provided, and the braking driving force applying means has a change amount of the environmental illuminance detected by the illuminance sensor being a predetermined amount or more. It is preferable to apply the minute braking force or the minute driving force.

  (6) The vehicle further includes an outside air temperature sensor that detects an outside air temperature of the vehicle, and the braking driving force applying unit is configured to perform the fine braking force based on the condition relating to the outside air temperature detected by the outside air temperature sensor. Alternatively, it is preferable to apply the minute driving force.

  According to the road surface friction coefficient computing device of the present invention, even in a steady running state where the longitudinal acceleration does not act on the vehicle, the road surface friction coefficient can be calculated periodically every predetermined time, and the road surface condition changes every moment. The road surface friction coefficient corresponding to the can be calculated.

It is a block block diagram which shows the structure of the vehicle to which the road surface friction coefficient calculating apparatus which concerns on one Embodiment of this invention was applied. It is a flowchart which shows the control procedure of this road surface friction coefficient calculating apparatus. It is a time chart which shows the control content of this road surface friction coefficient calculating apparatus, (a) is a steady or unsteady driving state, (b) is a fluctuation | variation of steady driving | running | working continuation time, (c) is the application conditions of automatic braking force establishment (D) indicates whether or not an automatic braking force is applied, and (e) indicates a calculation state of a road surface friction coefficient. It is a typical side view which shows the driving | running | working state of the vehicle provided with this road surface friction coefficient calculating apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[1. overall structure]
FIG. 1 illustrates a vehicle 20 including an ECU 10 that functions as the road surface friction coefficient computing device of the present invention. The ECU 10 is an electronic control unit including a storage device (ROM, RAM, etc.) and a central processing unit (CPU) that are used for storing control programs, control maps, and the like. The block configuration shown in FIG. 1 is a visualization of the various functions of a program that is arithmetically processed in the ECU 10.

  The ECU 10 has a function of issuing a braking command to the brake ECU 6 connected to the output side, and a function of calculating a road surface friction coefficient μ. The road surface friction coefficient μ calculated here is used not only for braking control in the brake ECU 6, but also for accelerator system control such as traction control and cruise control. Note that the illustration of the electronic control unit related to the control of the accelerator system is omitted.

  The brake ECU 6 is an electronic control unit that performs control for applying a braking force to the wheels 21 provided in the vehicle 20. The wheel 21 here includes a drive wheel and a driven wheel. The brake ECU 6 performs brake system control such as damage reduction brake control, automatic braking control, ABS (anti-lock braking system) control, and VSC (vehicle stability control) control.

  Damage reduction brake control is braking control for reducing damage caused by a collision with an obstacle in front of the vehicle. In the damage reduction brake control according to the present embodiment, the distance to the front obstacle and the relative speed are detected, and a value obtained by dividing the distance by the relative speed is calculated as TTC (Time to collision). When this TTC is less than the first threshold, it is determined that there is a possibility of a collision with an obstacle, and a warning and notification are given to the driver by weak braking force, voice, and screen display. Further, when the TTC is less than the second threshold value, it is determined that a collision is unavoidable, and a strong braking force is applied to reduce the speed at the time of the collision.

  The braking command to the brake ECU 6 output by the ECU 10 is a command for applying a slight braking force that is weaker than the “weak braking force” in the damage reduction brake control and has a small deceleration for a short time. That is, it is not braking control for decelerating the vehicle 20, but braking for instantaneously generating a deceleration (longitudinal acceleration) necessary for calculating the road surface friction coefficient μ. Therefore, the magnitude of the minute braking force to be applied to the wheel 21 depends on the sensing accuracy of the parameter relating to the calculation of the road surface friction coefficient μ. In the configuration of the present embodiment, the higher the sensing accuracy of the vehicle speed sensor 11, the longitudinal acceleration sensor 12, and the driving wheel speed sensor 18, the smaller the fine braking force can be set.

A vehicle speed sensor 11, a longitudinal acceleration sensor 12, a brake stroke sensor 13, and an accelerator throttle sensor 14 are connected to the input side of the ECU 10.
The vehicle speed sensor 11 is a sensor that detects the rotational angular velocity ω _B of the driven wheel corresponding to the vehicle speed of the vehicle 20. The rotational angular velocity ω _B of the driven wheel detected here is input to the ECU 10. The longitudinal acceleration sensor 12 is a sensor that detects the longitudinal acceleration / deceleration (longitudinal acceleration G) acting on the vehicle 20. The ECU 10 receives the longitudinal acceleration G detected here. Information detected by the vehicle speed sensor 11 and the longitudinal acceleration sensor 12 is used in the ECU 10 to calculate a road surface gradient.

The brake stroke sensor 13 is a sensor that detects the depression amount B of the brake pedal by the driver. The accelerator throttle sensor 14 is a sensor that detects the depression amount A of the accelerator pedal by the driver. In the present embodiment, the depression amounts A and B detected by these sensors 13 and 14 are input to the ECU 10.
Information detected by the vehicle speed sensor 11, the longitudinal acceleration sensor 12, the brake stroke sensor 13 and the accelerator throttle sensor 14 is information used by the ECU 10 to determine whether the longitudinal acceleration G is acting on the vehicle 20. is there. That is, here, these pieces of information are used for determining the condition in which the drive wheels tend to slip or lock. In the present embodiment, a traveling state in which the longitudinal acceleration G is not applied to the vehicle 20 (that is, a state in which the longitudinal acceleration G is an acceleration / deceleration within a predetermined range including 0) is referred to as a steady traveling state. This traveling state is called an unsteady traveling state. Examples of the unsteady traveling state include traveling on an uphill road, traveling on a downhill road, brake depression, accelerator depression, and the like.

  Further, a wiper sensor 15, an illuminance sensor 16, an outside air temperature sensor 17, a driving wheel speed sensor 18 and a millimeter wave radar 19 are connected to the input side of the ECU 10. The wiper sensor 15 is a sensor that detects an operating state of a wiper provided on the windshield surface or rear glass surface of the vehicle 20. Here, information on whether or not the wiper is operating is input to the ECU 10.

  The illuminance sensor 16 is a sensor that detects the ambient illuminance around the vehicle 20 (for example, the illuminance of the vehicle body surface of the vehicle 20 or the illuminance of the traveling road surface), and the outside air temperature sensor 17 is a sensor that detects the outside air temperature of the vehicle 20. is there. Information detected by the wiper sensor 15, the illuminance sensor 16, and the outside air temperature sensor 17 is information used to determine whether or not to output a braking command to the brake ECU 6.

The driving wheel speed sensor 18 is a sensor that detects the rotational angular velocity ω _A of the driving wheel. The detected rotational angular velocity ω _A of the driving wheel is input to the ECU 10. Further, the millimeter-wave radar 19, the Doppler modulation characteristics in a reflected wave of the radio wave in the millimeter wave band, a radar sensor for detecting the distance D and the relative speed V _R to the preceding obstacle of the vehicle 20. The relative speed V _R may be calculated by performing a time differentiation process on the distance D. Here detected distance D and relative speed V _R to the obstacle is used to calculate a TTC in damage reduction brake control.

[2. Configuration of ECU]
The ECU 10 includes a steady running state detection unit 1, a time measurement unit 2, a TTC calculation unit 3, an automatic braking force application unit 4, and a road surface friction coefficient calculation unit 5.
The steady running state detection unit 1 (steady running state detection means) detects whether the vehicle 20 is in a steady running state or an unsteady running state. The steady running state is a running state in which the longitudinal acceleration G does not act on the vehicle 20. The steady running state detection unit 1 includes a road surface gradient detection unit 1a, a brake operation detection unit 1b, and an accelerator operation detection unit 1c.

The road surface gradient detection unit 1a detects a road surface gradient based on the vehicle speed V _B calculated by a road surface friction coefficient calculation unit 5 described later and the longitudinal acceleration G detected by the longitudinal acceleration sensor 12. The longitudinal acceleration G includes acceleration caused by road gradient and acceleration caused by acceleration and deceleration of the vehicle 20. Accordingly, the road surface gradient detection unit 1a obtains vehicle acceleration by differentiating the vehicle speed V _B and subtracts the vehicle acceleration from the longitudinal acceleration G. Thus, only the acceleration generated by the road surface gradient is calculated, and the road surface gradient is grasped.

The brake operation detection unit 1b detects whether or not the brake pedal is depressed based on the depression amount B of the brake pedal input from the brake stroke sensor 13. Here, when the depression amount B is equal to or greater than the predetermined depression amount B _0, it is determined that the brake pedal has been depressed enough to reduce the longitudinal acceleration G.
Similarly, the accelerator operation detection unit 1c detects whether or not the accelerator pedal is depressed based on the depression amount A of the accelerator pedal input from the accelerator throttle sensor 14. Here, when the depression amount A is equal to or greater than the predetermined depression amount A _0, it is determined that the accelerator pedal is depressed enough to increase the longitudinal acceleration G.

Further, the steady running state detection unit 1 satisfies all of the following conditions (1) to (3) based on the determination results of the road surface gradient detection unit 1a, the brake operation detection unit 1b, and the accelerator operation detection unit 1c. In this case, it is determined that the traveling state of the vehicle 20 is a steady traveling state. When at least one of the conditions (1) to (3) is not satisfied, it is determined that the traveling state of the vehicle 20 is an unsteady traveling state.
(1) The brake pedal is not depressed enough to decrease the longitudinal acceleration G. (2) The accelerator pedal is not depressed enough to increase the longitudinal acceleration G. (3) The road gradient is flat (predetermined including 0 °). Is the slope within the range)

  The time measuring unit 2 (time measuring means) is a timer counter that measures the duration of the steady running state determined by the steady running state detecting unit 1, and from the time when all of the above conditions (1) to (3) are established. Start counting. The time counted here is hereinafter referred to as steady running duration T (continuous running state duration).

Further, the time measuring unit 2 continues the steady running when the steady running duration T reaches the first predetermined time T ₁ or when the road surface friction coefficient μ is calculated by the road surface friction coefficient calculating unit 5 described later. The time T is reset, and the steady running duration T is counted again from 0. That is, in the steady running state, the timer 2 continuously counts the steady running duration T.

TTC calculating section 3, based on the distance D and the relative speed V _R to the front obstacle detected by the millimeter wave radar 19, and calculates the TTC. TTC is calculated according to Equation 1 below.
TTC = D / V _R (Formula 1)
The automatic braking force applying unit 4 (braking driving force applying means) outputs a braking command to the brake ECU 6 when the steady running duration T counted by the time measuring unit 2 reaches the first predetermined time T _1. is there. Here, a braking command for applying the minute braking force of the vehicle 20 only for the second predetermined time T ₂ is output. This braking command is, for example, within the range of warnings and notifications stipulated in the revised “Technical Guidelines for Front Obstacle Collision Reduction Braking System” (November 15, 2005, National Self-Technology No. 181). A command for weak braking (braking less than 0.25G within 0.8 seconds).

Further, the automatic braking force applying unit 4 is based on the calculation results of the TTC calculation unit 3 and the detection results of the wiper sensor 15, the illuminance sensor 16, and the outside air temperature sensor 17 regardless of the value of the steady running duration T. Then, a braking command is output to the brake ECU 6. The output condition of the braking command is a case where any one of the following conditions (4) to (7) is satisfied. These conditions (4) to (7) are called automatic braking force application conditions.
(4) The TTC is less than the first threshold. (5) The wiper operating state has changed from off to on. (6) The amount of change in environmental illuminance is greater than or equal to a predetermined amount. (7) The outside air temperature exceeds the predetermined temperature threshold. Increased or decreased temperature

  Condition (4) is the same as the TTC condition in which it is determined that there is a possibility of collision with an obstacle in the damage reduction brake control. That is, the braking control condition for warning and notification to the driver in the damage reduction brake control is used as the braking control condition for calculating the road surface friction coefficient μ. The condition (5) is a condition that is satisfied when the driver starts operating the wiper due to rain or snow. Here, the operating state of the wiper is determined as an indicator of the weather.

  Condition (6) is a condition that is satisfied when the vehicle 20 enters the tunnel or moves out of the tunnel. Here, the ambient illuminance around the vehicle 20 is determined as an index of the road surface environment. Condition (7) is a condition that is satisfied, for example, when the outside air temperature is below freezing and the rainfall changes to snowfall, or when the temperature rises and the snowfall changes to rain. Here, the outside air temperature is determined as an index of the road surface environment.

The road surface friction coefficient calculation unit 5 (road surface friction coefficient calculation means) is based on the rotational angular velocity ω _A of the driving wheel detected by the driving wheel speed sensor 18 and the rotational angular velocity ω _B of the driven wheel detected by the vehicle speed sensor 11. The friction coefficient μ of the road surface on which the vehicle 20 travels is calculated. The road surface friction coefficient calculation unit 5 includes a vehicle speed detection unit 5a and a wheel speed detection unit 5b.
The vehicle speed detector 5a calculates the vehicle speed V _B from the rotational angular speed ω _B of the driven wheel. Further, the wheel speed detection unit 5b calculates the driving wheel speed V _A from the rotational angular speed ω _A of the driving wheel. Using the driving wheel speed V _A and the vehicle speed V _B , the road surface friction coefficient calculation unit 5 calculates the road surface friction coefficient μ. A specific method for calculating the road surface friction coefficient μ is arbitrary. For example, as described in Patent Document 1, the slip ratio is estimated from the driving wheel speed V _A and the vehicle speed V _B , and the longitudinal acceleration is calculated. A primary regression coefficient K with respect to the slip ratio of the longitudinal acceleration G detected by the sensor 12 may be calculated, and the magnitude of the road surface friction coefficient μ may be determined according to the magnitude of the regression coefficient K.

The calculation conditions of the road surface friction coefficient μ in the road surface friction coefficient calculation unit 5 are as follows.
(A) Immediately after the minute braking force is applied (B) The traveling state of the vehicle 20 is an unsteady traveling state The road surface friction coefficient μ calculated here is stored in a storage device (memory) (not shown), It is output to the brake ECU 6 and an electronic control unit related to the control of the accelerator system. The road surface friction coefficient calculation unit 5 updates the value every time a new road surface friction coefficient μ is calculated and stores it in the storage device.

[3. flowchart]
The ECU 10 performs control according to the flowchart shown in FIG. This flow is repeatedly executed at a predetermined cycle set in advance. Note that the initial value of the steady running duration T is T = 0.
In step A10, conditions for applying the automatic braking force that do not depend on the value of the steady running duration T are determined. That is, the automatic braking force application unit 4 determines whether or not the above conditions (4) to (7) are satisfied. When all of these conditions (4) to (7) are not established, the process proceeds to step A20, and when at least one of the conditions is established, the process proceeds to step A50.

In step A20, the timekeeping unit 2 continues to count the steady running duration T (for example, substitute the value of T + 1 for the variable T). In step A30, steady running duration T is equal to or a first less than a predetermined time T ₁ is determined. here. Proceeds to step A40 in the case of T <T _1, the routine proceeds to step A50 in the case of T ≧ T _1.
In Step A40, the steady running state detection unit 1 determines whether or not the vehicle 20 is in a steady running state. In other words, it is determined whether or not the longitudinal acceleration G is not acting on the vehicle 20, in other words, it is determined whether or not the vehicle 20 is in a traveling state in which the road surface friction coefficient μ can be calculated. Here, if it is in the steady running state, the flow is terminated as it is, and if it is not in the steady running state, the process proceeds to Step A60.

Therefore, when the vehicle 20 is in the steady running state, unless any of the above conditions (4) to (7) is satisfied, the control contents of steps A10 to A40 are repeated, and the steady running duration time T is counted. Will continue. Thereafter, the steady running duration T is above T ₁ first predetermined time, step A50 is executed.
In step A <b> 50, the automatic braking force application unit 4 outputs a minute braking force application command to the brake ECU 6. In response to this, the brake ECU 6 performs control to apply a braking force to the wheels 21. Alarm magnitude of small braking force applied here is weak enough to fall within the scope of the notification, the duration is a second predetermined time T _2. Thereafter, in step A60, the road surface friction coefficient calculation unit 5 calculates the road surface friction coefficient μ. In the subsequent step A70, the steady travel duration T is reset to T = 0, and this flow ends.

In step A40, it is determined that the vehicle 20 is in an unsteady traveling state when climbing, descending, accelerating, or decelerating. Therefore, step A50 relating to the application of a slight braking force is skipped, In step A60, a road surface friction coefficient μ is calculated.
It is as follows when the control conditions implemented by this road surface friction coefficient calculating apparatus and the control content are put together.

[4. Action, effect]
[4-1. Control according to driving conditions]
The time chart which shows the control content by this road surface friction coefficient calculating apparatus is illustrated to Fig.3 (a)-(e). As shown in FIG. 3A, the vehicle 20 is traveling on an uphill road from time t ₀ to time t ₁ . At this time, since the vehicle 20 is in an unsteady traveling state and the longitudinal acceleration G acts on the vehicle 20, the road surface friction coefficient μ can be calculated. Accordingly, as shown in FIG. 3 (e), until time t _1, the road surface friction coefficient μ at the road surface friction coefficient calculating unit 5 is calculated from time to time, the value is updated.

When the road surface becomes flat at time t ₁ and the vehicle 20 enters a traveling state in which the longitudinal acceleration G does not occur, the steady traveling state detection unit 1 determines that the vehicle 20 is in a steady traveling state. At this time, the time counting unit 2 starts counting the steady running duration T. As shown in FIG. 3B, the steady travel duration T increases with the passage of time.
Thereafter, when the first predetermined time T ₁ from the time t ₁ is the time t ₂ has elapsed, the braking command small braking force is outputted to the brake ECU6 the automatic braking force application unit 4. Thus, as shown in FIG. 3 (d), between the time t ₂ to time t ₃ when the second predetermined time T ₂ has elapsed, small braking force is applied to the wheels 21. Since the minute braking force is a weak brake that falls within the range of warnings and notifications, the driver of the vehicle 20 does not feel uncomfortable.

At time t ₃ when the small braking force applied is made, as shown in FIG. 3 (e), the calculation of road friction coefficient μ in the road surface friction coefficient calculating unit 5 is performed, its value is stored is updated. Since the road surface friction coefficient calculation unit 5 calculates the road surface friction coefficient μ using the vehicle speed V _B detected by the vehicle speed detection unit 5a and the driving wheel speed V _A detected by the wheel speed detection unit 5b, a simple calculation is performed. An accurate road surface friction coefficient μ can be calculated with the configuration. In the time measuring unit 2, the steady running duration T is reset to T = 0, and the count is restarted.

At time t ₄ when the first predetermined time T ₁ has elapsed from time t ₃ , a braking command for a slight braking force is output from the automatic braking force applying unit 4 to the brake ECU 6 again. Thus, as shown in FIG. 3 (d), during the period from time t ₄ to time t ₅ that the second predetermined time T ₂ has elapsed, small braking force is applied to the wheels 21. At time t ₅ , the road surface friction coefficient μ is calculated, and the value is updated and stored.

Thus, not only in an unsteady running state in which the longitudinal acceleration G acts on the vehicle 20 but also in a steady running state in which the longitudinal acceleration G does not act on the vehicle 20 such as on an uphill road, downhill road, and acceleration / deceleration, the first predetermined The road surface friction coefficient μ can be calculated repeatedly at intervals of time T ₁ . Since the calculated road surface friction coefficient μ is updated and stored in the road surface friction coefficient calculation unit 5 each time, it is possible to always grasp the road surface friction coefficient μ corresponding to the road surface condition that changes every moment. it can.

  Furthermore, the road surface friction coefficient μ calculated here is used not only for brake system control such as damage reduction brake control, automatic braking control, ABS control and VSC control, but also for accelerator system control such as traction control and cruise control. Therefore, the behavior of the vehicle 20 can be controlled more accurately than in the past. In particular, this road surface friction coefficient computing device constantly updates the value of the road surface friction coefficient μ, which is effective for control where it is difficult to predict when the road surface friction coefficient μ is required, and greatly improves control accuracy. Can be made.

Since the longitudinal acceleration G acting on the vehicle 20 is detected between the time t ₀ and the time t ₁ , the road surface friction coefficient μ is calculated using the longitudinal acceleration G. Thus, in the unsteady traveling state in which the longitudinal acceleration G acts on the vehicle 20, the road surface friction coefficient μ can be calculated without applying a slight braking force to the vehicle by using the longitudinal acceleration G to the maximum extent. it can. As a result, the frequency of applying the minute braking force is reduced, and the influence on the brake life can be reduced.

On the other hand, the vehicle 20 and to the distance closer to the front of the vehicle, from the time t ₅ when the TTC calculated in TTC calculating section 3 to the time t ₆ before the first predetermined time T ₁ is elapsed is less than the first threshold value In the automatic braking force applying unit 4, the condition (4) which is one of the conditions for applying the automatic braking force is established. As a result, regardless of the value of the steady running duration T, a braking command for a slight braking force is output from the automatic braking force applying unit 4 to the brake ECU 6.

Accordingly, as shown in FIG. 3 (d), during the period from time t ₆ to time t ₇ to the second predetermined time T ₂ has elapsed, small braking force is applied to the wheels 21. At time t ₇ , the road surface friction coefficient μ is calculated and its value is updated, and the steady running duration T is reset.

[4-2. Control according to the weather]
FIG. 4 illustrates another situation where the condition for applying the automatic braking force is satisfied at the time t ₇ shown in FIG. With respect to the vehicle 20 that travels outdoors during rain during the day, when the vehicle 20 is at the position indicated by the symbol X in FIG. 4, the wiper sensor 15 detects the operating state (ON) of the wiper, and the illuminance sensor 16 Then, a slightly brighter ambient illuminance is detected. At this time, the outdoor road surface R1 is wet with rain, and the road surface friction coefficient μ is a relatively small value.

  On the other hand, when the vehicle 20 enters the tunnel 22 and the vehicle 20 is at the position indicated by the symbol Y in FIG. 4, if the driver stops the wiper, the wiper sensor 15 changes the wiper operating state. (Ie, off) is detected. At this time, the condition (5) which is one of the conditions for applying the automatic braking force is satisfied. As a result, regardless of the value of the steady running continuation time T, a braking command for a slight braking force is output from the automatic braking force applying unit 4. When a slight braking force is applied to the wheel 21, the road surface friction coefficient calculation unit 5 calculates the road surface friction coefficient μ, and the value is updated and stored. The road surface friction coefficient μ updated here is the road surface friction coefficient μ of the internal road surface R2 of the tunnel 22 and is larger than the road surface friction coefficient μ of the outdoor road surface R1.

  In this way, by applying the slight braking force and calculating the road surface friction coefficient μ using the detection information of the wiper sensor 15, the road surface friction coefficient μ is calculated in response to changes in weather and road surface conditions. be able to. In particular, it is possible to quickly grasp the road surface friction coefficient μ that decreases due to rainfall.

[4-3. Control according to the driving environment]
Moreover, since the inside of the tunnel 22 is darker than the outside, when the vehicle 20 enters the tunnel 22, the illuminance sensor 16 detects a decrease in environmental illuminance. At this time, when the condition (6), which is one of the conditions for applying the automatic braking force, is satisfied, the automatic braking force applying unit 4 outputs a braking command for the minute braking force regardless of the value of the steady travel duration T. . After the application of the slight braking force, the road surface friction coefficient μ is calculated and the value is updated and stored.

  Thus, by applying the slight braking force and calculating the road surface friction coefficient μ using the detection information of the illuminance sensor 16, the road surface friction coefficient μ can be calculated immediately in response to changes in the driving environment. it can. In particular, even when the road surface condition is different between inside and outside of the tunnel 22, the road surface friction coefficient μ of the outdoor road surface R1 and the internal road surface R2 can be quickly grasped.

[5. Others]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, the specific types of sensors connected to the input side of the ECU 10 in the above-described embodiment are arbitrary. In other words, instead of the vehicle speed sensor 11 that detects the vehicle speed V _B based on the rotational angular velocity ω _B of the driven wheel, a configuration that detects the relative speed with respect to the road surface of the vehicle 20 using a radar sensor, an ultrasonic sensor, a gyro sensor, or the like. Also good. Alternatively, instead of the driving wheel speed sensor 18 that detects the driving wheel speed V _A based on the rotational angular speed ω _A of the driving wheel, a sensor that detects the driving wheel speed V _A based on the rotational angular speed of the transmission or the differential gear. May be used.

In the above-described embodiment, three conditions for determining that the traveling state of the vehicle 20 is the steady traveling state are described. However, these conditions can be changed as appropriate. The steady running state detection unit 1 only needs to detect a running state where at least the longitudinal acceleration G does not act on the vehicle 20.
In the above-described embodiment, four conditions for applying the automatic braking force are described, but these conditions are also changed as appropriate. Regarding condition (7), various condition settings regarding the outside air temperature of the vehicle 20 are conceivable. In the above condition (7), a slight braking force is applied and the road friction coefficient μ is calculated when the outside air temperature rises or falls beyond a predetermined temperature threshold, so that it responds immediately to changes in the outside air temperature. Thus, the friction coefficient can be calculated. In particular, when the predetermined temperature threshold is set to 0 ° C., it is possible to distinguish between a wet road surface and a frozen road surface, and it is possible to quickly grasp the road surface friction coefficient μ that varies depending on the outside air temperature.

Since the road surface friction coefficient μ is correlated with the surface temperature of the road surface, an automatic braking force application condition regarding the surface temperature of the road surface may be provided.
Further, in the above-described embodiment, the braking force that generates a deceleration within 0.8 seconds and 0.25 G or less is exemplified as the minute braking force applied to the vehicle, but the magnitude of the braking force is not limited to this. Note that the control of the ECU 10 does not necessarily decelerate the vehicle 20. The magnitude of the minute braking force is preferably as small as possible so long as it does not interfere with the calculation of the road surface friction coefficient μ.

  Further, in the above-described embodiment, an example is given in which a minute braking force is applied to the wheel 21 when calculating the road surface friction coefficient μ, but a minute driving force may be applied instead of the minute braking force. In this case, the minute driving force is a driving force that is small enough not to be detected by the driver of the vehicle and has a short time and a small acceleration (for example, an accelerator that generates an acceleration of 0.25 G or less within 0.8 seconds) It is possible to do. Even in such a configuration, the road surface friction coefficient μ can be calculated using a slight longitudinal acceleration generated in the vehicle 21.

1 steady running state detection unit (steady running state detection means)
DESCRIPTION OF SYMBOLS 1a Road surface gradient detection part 1b Brake operation detection part 1c Acceleration operation detection part 2 Time measuring part (time measuring means)
3 TTC calculation unit 4 Automatic braking force applying unit (braking driving force applying means)
5 Road surface friction coefficient calculation unit (road surface friction coefficient calculation means)
5a Vehicle speed detection unit (vehicle speed detection means)
5b Wheel speed detection part (wheel speed detection means)
6 Brake ECU
10 ECU (road friction coefficient calculation device)
DESCRIPTION OF SYMBOLS 11 Vehicle speed sensor 12 Longitudinal acceleration sensor 13 Brake stroke sensor 14 Accelerator throttle sensor 15 Wiper sensor 16 Illuminance sensor 17 Outside air temperature sensor 18 Drive wheel speed sensor 19 Millimeter wave radar 20 Vehicle 21 Wheel 22 Tunnel R1 Outdoor road surface R2 Internal road surface

Claims (6)

Steady running state detecting means for detecting a steady running state in which longitudinal acceleration does not act on the vehicle;
Time measuring means for measuring the duration of the steady running state detected by the steady running state detecting means;
Braking driving force applying means for applying a minute braking force or a minute driving force to the vehicle for a second predetermined time when the duration time measured by the time measuring means is equal to or longer than the first predetermined time;
Road surface friction coefficient calculating means for calculating the friction coefficient of the road surface on which the vehicle travels after the minute braking force or the minute driving force is applied by the braking driving force applying means,
A road surface friction coefficient computing device characterized in that the time measuring means resets the duration time and starts measuring the duration time again when the friction coefficient is calculated by the road surface friction coefficient calculation means. Vehicle speed detection means for detecting the vehicle speed of the vehicle;
Wheel speed detecting means for detecting the wheel speed of the driving wheel of the vehicle,
2. The road surface friction coefficient calculating means calculates the friction coefficient based on the vehicle speed detected by the vehicle speed detecting means and the wheel speed detected by the wheel speed detecting means. The described road surface friction coefficient computing device. 3. The road surface friction coefficient calculating device according to claim 1, wherein the road surface friction coefficient calculating means calculates the friction coefficient when the steady running state is detected by the steady running state detecting means. . A wiper sensor for detecting an operation or non-operation state of a wiper device mounted on the vehicle;
The brake driving force applying means applies the minute braking force or the minute driving force when a change in the operating state of the wiper is detected by the wiper sensor. The road surface friction coefficient calculating apparatus according to any one of the preceding claims. An illuminance sensor for detecting ambient illuminance around the vehicle;
The braking driving force applying means applies the minute braking force or the minute driving force when a change amount of the environmental illuminance detected by the illuminance sensor is a predetermined amount or more. 5. The road surface friction coefficient computing device according to any one of 1 to 4. An outside air temperature sensor for detecting the outside air temperature of the vehicle;
The braking driving force applying means applies the minute braking force or the minute driving force based on a condition relating to the outside air temperature detected by the outside air temperature sensor. The road surface friction coefficient calculating apparatus according to any one of the preceding claims.

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