JPH10293073A - Detector for coefficient of friction of road surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detector, for the coefficient of friction of a road surface, by which the coefficient of friction of the running road surface for a vehicle can be detected with good accuracy. SOLUTION: On the basis of a steering angle and a vehicle speed, a target yaw rate and a target transverse acceleration (a target transverse G) are set. When an actual yaw rate is too small with reference to the target yaw rate (S 495: YES) and when an actual transverse G is not too large with reference to the target G (S 500: NO), it is judged that front-wheel tires reaches their limit (S 505, S 530: YES). On the basis of the gripping force (the front gripping force) of the front-wheel tires at their time to a load (an FR wheel load + an FL wheel load), the coefficient of friction (the estimation μ) of a toad surface is computed (S 535, S 540). In addition, when the actual yaw rate is too large with reference to the target yaw rate (S 515: YES), it is judged that rear-wheel tires reached their limit. On the basis of the ratio of the gripping force (the rear gripping force) of rear-wheel tires at this time, to a load (an FR wheel load + an FL wheel load), the estimation μ is computed (S550, S 555).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a road friction coefficient detecting device for detecting a friction coefficient of a running road surface of a vehicle.

[0002]

2. Description of the Related Art Conventionally, as this type of apparatus, as disclosed in Japanese Patent Laid-Open Publication No. 3-258652, for example, a yaw rate (yaw angular velocity) and a lateral acceleration of a vehicle body which are generated as the vehicle turns. Kinetic physical quantity, vehicle speed,
Reference data representing the magnitude of the coefficient of friction of the traveling road surface with the steering wheel angle as a variable is stored in advance, and the vehicle speed, steering wheel angle, and physical quantity of motion (yaw rate or lateral acceleration) actually detected by the sensor. There has been proposed a method in which the magnitude of the friction coefficient of the traveling road surface is determined by referring to the above-mentioned reference data on the basis of the above.

[0003]

However, in the above-mentioned conventional apparatus, the above-mentioned reference data must be set by conducting running tests in advance on various road surface conditions. Even if the reference data is prepared, it is not always possible to always obtain an accurate detection result according to the actual running state and the road surface.

Moreover, in the above-described conventional apparatus, only ambiguous determination results can be obtained when the friction coefficient of the road surface is "large", "small", or "unknown".
The value of the road surface friction coefficient cannot be accurately detected as a specific numerical value. The present invention has been made in view of such a problem, and an object of the present invention is to provide a road surface friction coefficient detecting device that can accurately detect a friction coefficient of a traveling road surface of a vehicle.

[0005]

Means for Solving the Problems and Effects of the Invention In the road friction coefficient detecting apparatus of the present invention, the grip force detecting means includes:
A grip force generated by a tire mounted on a wheel of the vehicle is detected, and a load detecting unit detects a load applied to the tire. Further, the limit determining means determines whether or not the grip force of the tire is at a limit.

When the friction coefficient calculating means determines that the grip force of the tire is at the limit by the limit determining means, the two detecting means (the grip force detecting means and the load detecting means) detect the tire force. The friction coefficient of the traveling road surface is calculated from the ratio between the grip force and the load.

That is, in the present invention, the grip force generated when the tire has reached the limit is regarded as the dynamic friction force between the tire and the road surface, and the grip force at that time and the load (vertical load) applied to the tire are considered. ) And ratio (grip force / load)
, The friction coefficient of the traveling road surface is calculated.

For this reason, according to the road surface friction coefficient detecting device of the present invention, the road surface friction coefficient is set to “large” or “small”.
Instead of such a determination, it can be accurately detected as a specific numerical value. In addition, when the device is developed, the above-described effects can be obtained without performing a development procedure of collecting data for obtaining a friction coefficient by a driving experiment.

The friction coefficient calculating means may be configured to calculate the value of the ratio as it is as a friction coefficient, or to calculate the friction coefficient by multiplying the value of the ratio by a predetermined coefficient, for example. It may be configured as follows. Further, it may be an average value within a certain period of time or a value after filter processing for preventing noise.

The limit determining means detects the steering angle and the vehicle speed of the vehicle, and based on the detected steering angle and the vehicle speed,
A target value of a physical movement amount such as a yaw rate or a lateral acceleration of a vehicle body generated along with the turning of the vehicle is calculated, an actual value of the physical movement amount is detected, and the actual value of the detected physical movement amount and the calculated target value are further calculated. When the difference from the value is larger than a predetermined value, it can be configured to determine that the grip force of the tire is at the limit.

That is, the actual turning state of the vehicle, which is grasped by the physical quantity of movement such as the yaw rate and the lateral acceleration,
If the target turning state largely deviates from the predicted turning state based on the steering angle and the vehicle speed, it is determined that the grip force of the tire is at the limit. With this configuration, it is possible to easily determine whether or not the grip force of the tire is at the limit.

On the other hand, each means constituting the road friction coefficient detecting device of the present invention may be configured to operate only on any one of the wheels provided in the vehicle.
According to the structure described in claim 3, a greater effect can be obtained. That is, in the device according to the third aspect, in the road surface friction coefficient detecting device according to the second aspect, first,
Limit determination means, based on the difference between the actual value and the target value of the physical quantity of exercise, the wheel of which the grip force of the tire is the limit,
At least whether the vehicle is a front wheel or a rear wheel is specified.

For example, the limit determining means calculates a target value of the yaw rate of the vehicle body from the actual steering angle and the vehicle speed of the vehicle, detects the actual value of the yaw rate of the vehicle body, and calculates the actual value of the yaw rate of the target value. If there is a large shortage, it can be determined that understeering has occurred in the vehicle, and the grip force of the front wheel tires is at the limit. Conversely, if the actual value of the yaw rate greatly exceeds the target value, oversteering has occurred in the vehicle, and it can be specified that the grip force of the rear wheel tires is at the limit.

According to the third aspect of the present invention, the grip force detecting means and the load detecting means detect the grip force and the load of the tire at least for the front wheels and the rear wheels of the vehicle. Further, the coefficient of friction calculating means determines the coefficient of friction of the road surface on the basis of the ratio of the gripping force and the load detected by the two detecting means to the wheel whose gripping force of the tire is determined to be the limit by the limit determining means. Is calculated. That is, for a wheel identified as having a limit on the grip force of the tire, the friction coefficient of the road surface is calculated from the ratio between the grip force of the tire and the load.

Therefore, according to the road surface friction coefficient detecting device of the third aspect, if one of the front wheel tires and the rear wheel tires of the vehicle is at a limit, the road surface friction coefficient can be detected. It is possible to increase the frequency of detecting the coefficient of friction. On the other hand, in the road surface friction coefficient detecting device of the present invention, the grip force detecting means includes a longitudinal force (force in the longitudinal direction) of the tire.
Alternatively, any one of the lateral force (lateral force) may be detected as the grip force of the tire. However, as described in claim 4, the grip force detecting means includes:
If the tire longitudinal force and lateral force are calculated based on a signal from a predetermined sensor, and the resultant force of the calculated longitudinal force and lateral force is detected as the tire grip force, the tire grip force Can be detected more accurately, and the detection accuracy of the coefficient of friction can be further improved.

The sensors used by the grip force detecting means to calculate the longitudinal force and the lateral force of the tire include a longitudinal acceleration sensor that outputs a signal corresponding to at least the longitudinal acceleration of the vehicle body, A lateral acceleration sensor that outputs a corresponding signal can be considered. Then, the grip force detecting means detects at least the longitudinal acceleration and the lateral acceleration of the vehicle body based on the signals from the respective sensors, and further detects the detected longitudinal acceleration and lateral acceleration. Based on the calculation, the longitudinal force and the lateral force of the tire may be calculated.

On the other hand, in the road friction coefficient detecting apparatus of the present invention, the load detecting means detects a load applied to the tire based on a signal from a load sensor which outputs a signal corresponding to a load applied to the wheel. However, the load detecting means may detect the longitudinal acceleration and the lateral acceleration of the vehicle body and apply the tire to the tire based on the detected longitudinal acceleration and lateral acceleration. If the load is calculated and detected, a special sensor for detecting the load becomes unnecessary.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. It is needless to say that the embodiments of the present invention are not limited to the following, and can take various forms as long as they belong to the technical scope of the present invention. In the following description, the term "wheel" also refers to a tire mounted on the wheel.

FIG. 1 is a schematic configuration diagram showing the configuration of the entire control system of a vehicle according to an embodiment to which the present invention is applied. As shown in FIG. 1, each wheel (right front wheel 2FR, left front wheel 2
FL, the right rear wheel 2RR, and the left rear wheel 2RL) are provided with wheel speed sensors 4FR, 4FL, 4RR, and 4RL, respectively, for detecting the rotational speed of the wheels (hereinafter, referred to as wheel speeds).

Further, the vehicle has a lateral G sensor 6 for outputting a signal corresponding to the lateral acceleration (hereinafter referred to as lateral G) of the vehicle body.
And a yaw rate sensor 8 that outputs a signal corresponding to the yaw rate of the vehicle body, a longitudinal G sensor 10 that outputs a signal according to the longitudinal acceleration (hereinafter referred to as longitudinal G) of the vehicle body, and steering operation operated by the driver A steering angle sensor 12 that outputs a signal corresponding to an angle (hereinafter referred to as a steering angle) and a brake switch 13 that is turned on when a driver steps on a foot brake are provided.

The signals from the sensors and switches are input to an electronic control unit (hereinafter referred to as an ECU) 14. On the other hand, each wheel 2FR, 2FL, 2RR, 2RL is provided with a toe control actuator 16FR, 16FL, 16RR, 16RL for adjusting the toe angle of the wheel, respectively.

In the description of the present embodiment,
The letters "FR", "FL", "RR", and "RL" are the right front wheel 2FR, the left front wheel 2FL, and the right rear wheel 2R, respectively.
R, which corresponds to the left rear wheel 2RL. Further, the vehicle according to the present embodiment has all the wheels 2FR and 2F.
L, 2RR, and 2RL are four-wheel drive vehicles that serve as drive wheels. Although not specifically shown, the torque output from the engine via the transmission is distributed to the drive shaft for the front wheels and the drive shaft for the rear wheels by the center differential gear. Drive shaft torque
The differential gear distributes the torque to the front wheels 2FR and 2FL, and the torque of the drive shaft for the rear wheel is distributed to each of the rear wheels 2RR and 2RL by the rear differential gear.

In the vehicle of this embodiment,
The ECU 14 detects the actual turning state of the vehicle based on the signals from the sensors, determines an ideal target turning state, and controls the toe control actuator 16FR so that the actual turning state becomes the target turning state. , 16
By controlling FL, 16RR, 16RL, each wheel 2FR, 2FL, 2R
The toe angle of R and 2RL is adjusted.

In particular, the ECU 14 operates as shown in FIG.
The four-wheel load calculation process, the lateral force calculation process of FIG. 3, the longitudinal force calculation process of FIG. 4, and the road surface μ estimation calculation process of FIGS.
By executing it periodically (for example, every 8 ms),
The friction coefficient of the road surface on which the vehicle is currently traveling is detected. Then, the toe control actuators 16FR, 16FL, 16RR, and 16RL correct the toe angle control amounts of the wheels 2FR, 2FL, 2RR, and 2RL (hereinafter, referred to as toe variable angles) in accordance with the detection results.

The processing that is sequentially performed by the ECU 14 to detect the road surface friction coefficient will now be described with reference to FIG.
This will be specifically described with reference to FIGS. Note that “constants K1 to K3”, “FR static load,
FL static load, RR static load, RL static load "," vehicle weight (vehicle weight) "," moment constant "," distance between center of gravity rear tires "," distance between center of gravity front tires "," wheel base ", and" gear ratio " Are constants based on the specifications of the vehicle, and these are RO (not shown) in the ECU 14.
M is stored in advance as data.

The ECU 14 periodically executes a detection process (not shown) to detect the lateral position of the vehicle body based on signals from the lateral G sensor 6, the yaw rate sensor 8, the longitudinal G sensor 10, and the steering angle sensor 12. The vehicle speed is detected by detecting G, yaw rate, front and rear G, and steering angle, respectively, and averaging the wheel speed detected based on signals from the wheel speed sensors 4FR, 4FL, 4RR, and 4RL. I have. Then, the lateral G, the yaw rate, and the like detected in this detection processing are described in FIGS.
It is used in the processing of FIG. 6 and FIG.

Further, in the processing described below,
Regarding the longitudinal G of the vehicle body and the longitudinal force of the wheels (tires), the deceleration direction is positive and the acceleration direction is negative, and the lateral G and yaw rate of the vehicle body and the lateral forces of the wheels (tires) are positive in the right direction and left in the right direction. The direction is negative. As for the steering angle, the angle clockwise from the center position is positive, and the angle counterclockwise from the center position is negative.

First, when the ECU 14 starts execution of the four-wheel load calculation processing of FIG. 2, in the first step (hereinafter simply referred to as “S”) 100, the ECU 14 detects the four-wheel load based on the signal from the front and rear G sensor 10. The front and rear G of the vehicle body
At 10, the input front and rear G is multiplied by a constant K1 to obtain a load fluctuation 1 which is a load fluctuation between the front and rear wheels.
(= G before and after G × constant K1) is calculated.

Next, in S120, the lateral G of the vehicle body detected based on the signal from the lateral G sensor 6 is input, and then in S13
At 0, the input lateral G is multiplied by a constant K2 to obtain a load variation 2F which is a variation in load between the left and right front wheels.
(= Horizontal G × constant K2) is calculated, and in the subsequent S140, the input lateral G is multiplied by a constant K3 to obtain
The load variation 2R (= lateral G × constant K3), which is the variation of the load between the left and right rear wheels, is calculated.

The constants K1 to K3 represent the amount of load variation per unit acceleration and are set according to the spring rate of the suspension and the vehicle weight. And then
In each of S150 to S180, based on the following formulas 1 to 4, the FR wheel load, which is the load of the right front wheel 2FR, and the left front wheel 2
The FL wheel load, which is the load of FL, the RR wheel load, which is the load of the right rear wheel 2RR, and the RL wheel load, which is the load of the left rear wheel 2RL, are calculated. Note that “FR static load”, “FL static load”, “RR static load”, “RL
The “static load” means that each wheel 2 when the vehicle is stationary horizontally
These are loads applied to FR, 2FL, 2RR, and 2RL, and are set according to the weight balance of the vehicle.

[0031]

## EQU1 ## FR wheel load = FR static load + load variation 1 + load variation 2F ... Equation 1

[0032]

## EQU2 ## FL wheel load = FL static load + load variation 1-load variation 2F Equation 2

[0033]

RR wheel load = RR static load−load fluctuation 1 + load fluctuation 2R Equation 3

[0034]

RL wheel load = RL static load−load fluctuation amount 1−load fluctuation amount 2R (Equation 4) Then, the ECU 14 determines the FR in S150 to S180.
Wheel load to RL wheel load (that is, each wheel 2FR, 2FL, 2RR,
When the load currently applied to the 2RL is calculated, the four-wheel load calculation process ends, and then the execution of the lateral force calculation process in FIG. 3 starts.

As shown in FIG. 3, when the ECU 14 starts execution of the lateral force calculation processing, first, in S200, the lateral G of the vehicle body is input, and in S210, the input lateral G is multiplied by the vehicle weight. Thus, the vehicle body lateral force (= lateral G × vehicle weight), which is the total lateral force of the entire vehicle, is calculated.

In step S220, the yaw rate of the vehicle body detected based on the signal from the yaw rate sensor 8 is input. In step S230, the yaw rate of the vehicle body is differentiated by differentiating the input yaw rate. calculate. Further, in subsequent S240, the yaw moment of the vehicle body (= yaw angular acceleration × moment constant) is calculated by multiplying the yaw angular acceleration calculated in S230 by a moment constant stored in advance.

After calculating the vehicle body lateral force and the yaw moment in this manner, in S250, the front lateral force, which is the total lateral force of the front wheels 2FR and 2FL, and the rear The rear lateral force, which is the total lateral force of the wheels 2RR and 2RL, is calculated. In the following equation, “/” indicates division. The distance between the center of gravity and the front tire is the horizontal distance between the center of gravity of the vehicle and the center of the axle of the front wheels 2FR and 2FL, and the distance between the center of gravity and the rear tire is the horizontal distance between the center of gravity of the vehicle and the center of the axle of the rear wheels 2RR and 2RL. is there.

[0038]

[Formula 5] Front lateral force = (body lateral force x center-of-gravity rear tire distance + yaw moment) / wheel base ... Equation 5

[0039]

## EQU6 ## Rear lateral force = (body lateral force × center-of-gravity front tire distance−yaw moment) / wheel base (Equation 6) After calculating the front lateral force and the rear lateral force in S250, the ECU 14 calculates the lateral force. After ending the processing, the execution of the longitudinal force calculation processing in FIG. 4 is started.

As shown in FIG. 4, when the ECU 14 starts executing the longitudinal force calculation process, first, in S300, it is determined whether or not the brake switch 13 is currently turned on.
If it is determined that the brake switch 13 is turned on, the process proceeds to S310, and the "front-rear G versus front-rear force map during foot braking" is read from the ROM. Also,
If it is determined in step S300 that the brake switch 13 has not been turned on, the process proceeds to step S320, and the "front-rear G versus front-rear force map during non-foot braking" is read from the ROM.

Here, the "front-rear G versus front-rear force map at the time of foot braking" read in S310 is a total front-rear force of the front wheels 2FR and 2FL with respect to the front-rear G when the driver steps on the foot brake. This is a data map in which a front-rear force and a total front-rear force of both rear wheels 2RR and 2RL for the front-rear G (hereinafter, rear-rear force) are also stored. The front longitudinal force with respect to the front and rear G is stored as shown in the upper left column of FIG. 5, and the rear longitudinal force with respect to the front and rear G is stored as shown in the lower left column of FIG.

As shown in the upper left and lower left columns of FIG. 5, this "front-rear G versus front-rear force map at the time of foot brake" is used.
When the front and rear G is positive (in the deceleration direction), the front longitudinal force is set to be larger than the rear longitudinal force. This is because the characteristics of the proportional valve and the like provided in the brake system are such that when the foot brake is depressed with the same force, the braking force of the front wheels 2FR, 2FL is larger than the braking force of the rear wheels 2RR, 2RL ( For example, it is set to 7: 3). Further, since the vehicle of the present embodiment is a four-wheel drive vehicle, when the front and rear G is negative (acceleration direction), both the front and rear force and the rear front and rear force are set to be negative (acceleration direction). ing.

On the other hand, the "front-rear G versus front-rear force map during non-foot braking" read in S320 includes the front front-rear force for the front-rear G when the driver does not step on the foot brake and the rear front-rear force for the front-rear G as well. Power and
It is a data map stored respectively. The front longitudinal force with respect to the front and rear G is stored as shown in the upper right column of FIG. 5, and the rear longitudinal force with respect to the front and rear G is stored as shown in the lower right column of FIG.

Since the vehicle of this embodiment is a four-wheel drive vehicle, engine braking is applied to both the front wheels 2FR, 2FL and the rear wheels 2RR, 2RL. For this reason, as shown in the upper right column and lower right column of FIG. 5, in the “front-rear G versus front-rear force map during non-foot braking”,
Both the front longitudinal force and the rear longitudinal force are set to change according to the longitudinal G. The ratio between the front and rear forces and the front and rear forces corresponding to the same front and rear G is determined by the torque distribution of the center differential gear.

Next, after executing one of the above S310 and S320, the flow shifts to S330 to input the current front and rear G of the vehicle body. In S340, the front and rear forces and the rear and front forces corresponding to the input front and rear G are read in either of the data maps (the "front-rear G vs. front-rear force map at the time of foot braking" or " Front-rear G vs. front-rear force map during non-foot braking
Is calculated by interpolation or the like based on

When the ECU 14 calculates the front longitudinal force and the rear longitudinal force in S340, the ECU 14 terminates the longitudinal force calculation process, and then starts execution of the road surface μ estimation calculation process of FIGS. I do. 6 shows the first half of the road surface μ estimation calculation process, and FIG. 7 shows the second half thereof.

As shown in FIG. 6, when the ECU 14 starts execution of the road surface μ estimation calculation processing, first in S400, the steering angle detected based on the signal from the steering angle sensor 12 is input, and in S405 The vehicle speed detected based on signals from the wheel speed sensors 4FR, 4FL, 4RR, and 4RL is input.

In step S410, a target yaw rate is calculated based on the following equation 7, and in step S415, the target yaw rate is multiplied by the vehicle speed input in step S405 to obtain a target lateral G (= target yaw rate × Vehicle speed).

[0049]

## EQU7 ## Target yaw rate = (steering angle / gear ratio × vehicle speed / wheel base) / (1 + target stability factor × vehicle speed × vehicle speed) Expression 7 The target yaw rate and the target lateral G are the actual steering angles, respectively. And the ideal yaw rate and lateral G that can be considered from the vehicle speed. The “gear ratio” in the above equation 7 is:
This is the gear ratio of the steering box of the vehicle. Therefore, the “steering angle / gear ratio” in Equation 7 is:
This shows the steering angle (toe angle) of the front wheels 2FR and 2FL generated by steering operation. Further, the “target stability factor” in Expression 7 is a constant set so that the target yaw rate calculated by Expression 7 is a value that does not cause the driver to feel uncomfortable as the behavior of the vehicle.

Thus, the target yaw rate and the target lateral G
Is calculated, in S420, the actual yaw rate is input, and in S425, the yaw rate error, which is the difference between the input actual yaw rate and the calculated target yaw rate, is calculated. This yaw rate error is calculated by subtracting the target yaw rate from the actual yaw rate as shown in FIG. 6 when the target yaw rate is positive (clockwise), as shown in FIG. When the yaw rate is negative (counterclockwise), the value is calculated by further multiplying the value obtained by subtracting the target yaw rate from the actual yaw rate by “−1” as shown in Expression 9 below. That is, regardless of the turning direction of the vehicle, if the value is positive, the actual yaw rate is too large relative to the target yaw rate. Conversely, if the value is negative, the actual yaw rate is less than the target yaw rate. Indicates too small for the yaw rate.

[0051]

[Equation 8] Yaw rate error = Yaw rate−Target yaw rate Equation 8

[0052]

## EQU9 ## Yaw rate error =-(Yaw rate-Target yaw rate) Expression 9 When the yaw rate error is calculated in this way, the next step is S4
Proceeding to 30, it is determined whether or not the calculated yaw rate error is greater than a predetermined value K4 (> 0) set to a positive value. When the yaw rate error is larger than the predetermined value K4, the process proceeds to S435, and “1” indicating that the actual yaw rate is excessive is set in the excessive yaw rate flag indicating whether or not the actual yaw rate is excessive. Conversely, if the yaw rate error is not larger than the predetermined value K4, S4
The process proceeds to 40, where “0” is set in the excessive yaw rate flag.

When the yaw rate excess flag is set to "1" or "0" in S435 or S440, the process proceeds to S445, and the predetermined value K5 (<0) in which the yaw rate error is set to a negative value. ) Is determined. If the yaw rate error is smaller than the predetermined value K5, the process proceeds to S450, and a yaw rate under-flag indicating whether or not the actual yaw rate is too low is set.
"1" indicating that the value is too small is set. Conversely,
If the yaw rate error is not smaller than the predetermined value K5, the process shifts to S455 and sets the yaw rate under-flag to "0".

When the under yaw rate flag is set to "1" or "0" in S450 or S455, the process proceeds to S460. Then, a lateral G of the vehicle body is input, and a lateral G error which is a difference between the input actual lateral G and the target lateral G calculated in S415 is calculated.

This lateral G error indicates that the target lateral G is positive (rightward).
Is calculated by subtracting the target lateral G from the actual lateral G as shown in the following Expression 10 as shown in FIG. 6, but when the target lateral G is negative (leftward), Is calculated by further multiplying the value obtained by subtracting the target lateral G from the actual lateral G by “−1” as shown in the following Expression 11. That is, similarly to the yaw rate error, if the value of the lateral G error is positive regardless of the turning direction of the vehicle, the actual lateral G is too large relative to the target lateral G, and conversely, the value is negative. Indicates that the actual lateral G is too small with respect to the target lateral G.

[0056]

## EQU10 ## Lateral G error = lateral G-target lateral G ... Equation 10

[0057]

## EQU11 ## Lateral G error =-(lateral G-target lateral G) Expression 11 When the lateral G error is calculated in this way, the process proceeds to S465, where the calculated lateral G error is set to a positive value. It is determined whether it is greater than the predetermined value K6 (> 0). If the lateral G error is larger than the predetermined value K6, S4
Proceeding to 70, "1" is set to the lateral G excess flag indicating whether or not the actual lateral G is excessive. Conversely, if the lateral G error is not greater than the predetermined value K6, the flow shifts to S475, and the lateral G excess flag is set to "0".

When the lateral G excess flag is set to "1" or "0" in S470 or S475, the process proceeds to S480, and this time, the lateral G error is set to a predetermined value K7 ( It is determined whether it is smaller than <0). If the lateral G error is smaller than the predetermined value K7, S
Proceeding to 485, the horizontal G under-flag indicating whether or not the actual horizontal G is too small is set to "1" indicating that it is too small. Conversely, if the lateral G error is not smaller than the predetermined value K7, the flow shifts to S490, where "0" is set in the lateral G under-flag flag.

When the under-G value is set to "1" or "0" in S485 or S490, the flow advances to S495 shown in FIG. 7 to determine whether the under-yaw-rate flag is "1". If it is “1”, it is determined in the following S500 whether or not the lateral G excess flag is “1”. If the excessive lateral G flag is not "1", that is, if the excessive yaw rate flag is "1" and the excessive lateral G flag is "0", the vehicle is in the understeer state and the front wheels 2FR and 2FL It is determined that the grip force of the tire of the front wheel is at the limit, and the routine proceeds to S505, where "1" indicating that the grip force of the tires of the front wheels 2FR and 2FL is at the limit is set in the front wheel limit determination flag.

On the other hand, when it is determined in S495 that the under yaw rate flag is not “1”, or when it is determined in S500 that the lateral G excessive flag is “1”,
The flow shifts to S510, where "0" is set for the front wheel limit determination flag. Then, if "1" or "0" is set to the front wheel limit flag in S505 or S510, then S
Proceeding to 515, it is determined whether the excessive yaw rate flag is “1”. If the excessive yaw rate flag is "1", it is determined that the vehicle is in an oversteer state and the grip force of the tires of the rear wheels 2RR and 2RL is at the limit, and the process proceeds to S520, where the rear wheel limit determination flag is set. , Rear wheel 2
Set "1" indicating that the grip force of the RR and 2RL tires is at the limit.

On the other hand, if it is determined in S515 that the excessive yaw rate flag is not "1", the flow shifts to S525, and "0" is set in the rear wheel limit determination flag.
When the rear wheel limit flag is set to "1" or "0" in S520 or S525, the process proceeds to S530 to determine whether the front wheel limit flag is "1".

If the front wheel limit flag is "1", the flow advances to S535 to proceed to S34 of the longitudinal force calculation process (FIG. 4).
Front longitudinal force calculated at 0 and lateral force calculation processing (Fig. 3)
From the front lateral force calculated in S250, the following equation 1
2, the front grip force, which is the total grip force of the tires of both front wheels 2FR and 2FL, is calculated. That is, the front grip force is calculated as a resultant force of the front longitudinal force and the front lateral force.

[0063]

(Equation 12)

Then, in subsequent S540, the above S535
The road surface on which the vehicle is currently traveling, based on the following equation 13, based on the front grip force calculated in the above and the FR wheel load and the FL wheel load calculated in S150 and S160 of the four-wheel load calculation process (FIG. 2). Is calculated, which is the estimated value of the friction coefficient.

[0065]

[Expression 13] Estimated μ = Front grip force / (FR wheel load + FL wheel load) Expression 13 In other words, in S540, the grip force (front grip force) generated by the tires of both front wheels 2FR and 2FL is calculated by dividing the front grip force by both front wheels. The road surface friction coefficient (estimated μ) is calculated by dividing by the load (FR wheel load + FL wheel load) applied to 2FR and 2FL.

Then, if the estimated μ is calculated in S540 as described above, or if it is determined in S530 that the front wheel limit flag is not “1”, the process proceeds to S545. In this S545, it is determined whether or not the rear wheel limit flag is “1”. If the rear wheel limit flag is “1”, the process proceeds to the next S550, and S34 of the longitudinal force calculation process (FIG. 4).
0 and the rear force calculated in FIG.
The rear grip force, which is the total grip force of the tires of the two rear wheels 2RR and 2RL, is calculated from the rear lateral force calculated in S250 and Equation 14 below. That is, the rear grip force is also calculated as the resultant force of the rear longitudinal force and the rear lateral force, similarly to the front grip force.

[0067]

[Equation 14]

Then, in the subsequent S555, the above-mentioned S550
And the RR wheel load and R calculated in S170 and S180 of the four-wheel load calculation process (FIG. 2).
From the L-wheel load, an estimated μ is calculated based on Equation 15 below.

[0069]

(Equation 15) Estimated μ = Rear grip force / (RR wheel load + RL wheel load) Expression 15 That is, in S555, tires of both rear wheels 2RR and 2RL are generated as in the case of S540 and Expression 13 described above. Grip force (rear grip force), both rear wheels 2RR, 2RL
By dividing by the load (RR wheel load + RL wheel load) applied to the vehicle, the coefficient of friction (estimated μ) of the road surface is calculated. After that, the road surface μ estimation calculation process ends.

On the other hand, if it is determined in S545 that the rear wheel limit flag is not “1”, the road μ estimation calculation processing is directly performed without performing the processing of S550 and S555 for calculating the estimated μ. To end. Note that the estimated μ calculated latest in S540 or S555 of the road surface μ estimation calculation processing is the toe control actuator 16
It is referred to by other control processing for controlling FR, 16FL, 16RR, and 16RL. In the control processing, for example, when the value of the estimated μ is smaller than a predetermined determination value,
The toe variable angles of the rear wheels 2RR and 2RL are corrected in the same direction as the steering angles of the front wheels 2FR and 2FL by an angle corresponding to the estimated μ value, further improving running stability on road surfaces with low friction coefficients. I try to make it.

On the other hand, in the present embodiment, the four-wheel load calculation processing (S100 to S180) in FIG. 2 corresponds to the load detection means, and the lateral force calculation processing (S200 to S250) in FIG. The force calculation processing (S300 to S340) and S535 and S550 in FIG. 7 correspond to grip force detection means. Then, S400 to S490 of FIG. 6 and FIG.
S495 to S530 and S545 correspond to limit determination means, and S540 and S555 in FIG. 7 correspond to friction coefficient calculation means.

As described above, the ECU 14 according to the present embodiment divides the grip force of the tire by the load applied to the tire for the wheel for which the grip force of the tire is determined to be the limit, thereby obtaining the road surface. The friction coefficient (estimated μ) is calculated (S530 to S55).
5). In other words, the grip force generated when the tire reaches the limit is regarded as the dynamic friction force between the tire and the road surface, and the ratio of the grip force to the load at that time (grip force / load) is used to calculate the coefficient of friction of the running road surface. Is calculated.

Therefore, according to the ECU 14 of the present embodiment, the friction coefficient of the road surface can be accurately detected as a specific numerical value. In addition, when the ECU 14 is developed, the above-described effect can be obtained without performing a development procedure of collecting data for obtaining a friction coefficient by a driving experiment.

Further, in the ECU 14 of this embodiment, FIG.
7, the target yaw rate and the target lateral G are calculated from the actual steering angle and the vehicle speed of the vehicle, based on the actual steering angle and the vehicle speed of the vehicle by the processing of S400 to S490 of FIG. If the yaw rate is too small with respect to the target yaw rate and the actual lateral G is not excessive with respect to the target lateral G, it is determined that the grip force of the tires of the front wheels 2FR and 2FL is at the limit. If the actual yaw rate is excessively large with respect to the target yaw rate regardless of the lateral G, it is determined that the grip force of the tires of the rear wheels 2RR and 2RL is at the limit.

When it is determined that the tires of the front wheels 2FR and 2FL are at the limit, the grip force (front grip force) and load (FR wheel load +
FL load) and the estimated μ is calculated from the ratio of the rear wheel 2
If it is determined that the RR and 2RL tires are at the limit, the grip force (rear grip force) of the rear wheels 2RR and 2RL at that time.
And the load (RR wheel load + RL wheel load) is used to calculate the estimated μ.

For this reason, it is possible to easily determine whether the grip force of the tire is at the limit or not,
If any one of the FR and 2FL tires and the rear wheel 2RR and 2RL tires reaches the limit, the latest estimated μ can be detected, and the detection frequency can be increased.

Further, in the ECU 14 of this embodiment, FIG.
4 and 7, the longitudinal force and the lateral force of the tire are calculated, and the resultant force of the calculated longitudinal force and the lateral force is detected as the grip force of the tire. I have. Therefore, the grip force of the tire can be detected more accurately, and the estimated μ
Can be further improved.

Further, in the ECU 14 of the present embodiment,
According to the processing of FIG.
Since the load applied to the tire of each wheel is calculated, it is advantageous in that a load sensor for detecting the load is not required. In the above embodiment, FIG.
S415, S460 to S490, and S500 are omitted, and only the difference between the actual yaw rate and the target yaw rate (yaw rate error) is used to determine which of the tires of the front wheels 2FR and 2FL and the tires of the rear wheels 2RR and 2RL. It may be determined that the limit has been reached.

Also, if the yaw rate is not used and only the difference between the actual lateral G and the target lateral G (lateral G error) becomes larger than a predetermined value, for example, the tires of all the wheels become tired. Judging that it is the limit, for any of the wheels,
The estimated μ may be calculated from the ratio between the grip force and the load of the tire.

On the other hand, in the above embodiment, the lateral force of the tire is calculated from the actual lateral G of the vehicle and the yaw rate by the processing of FIG. 3, and the actual longitudinal G of the vehicle is calculated by the processing of FIG.
To calculate the front-rear force of the tire from
As for the lateral force of the tire, the lateral force of each wheel with respect to the lateral G is used as a data map in the same manner as when calculating the longitudinal force.
The lateral force may be stored in the OM and the lateral force may be calculated using only the actual lateral G of the vehicle body. Incidentally, if the longitudinal force and lateral force of the tire are calculated using at least the longitudinal G and lateral G of the vehicle body, it is advantageous in that the calculation accuracy can be increased,
The longitudinal force and lateral force of the tire may be calculated based on information other than longitudinal G and lateral G.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating a configuration of an entire control system of a vehicle according to an embodiment.

FIG. 2 is a flowchart illustrating a four-wheel load calculation process executed by the ECU of FIG. 1;

FIG. 3 is a flowchart illustrating a lateral force calculation process executed by an ECU of FIG. 1;

FIG. 4 is a flowchart illustrating a longitudinal force calculation process executed by the ECU of FIG. 1;

FIG. 5 is an explanatory diagram illustrating a longitudinal G vs. longitudinal force map referred to in the longitudinal force calculation processing of FIG. 4;

FIG. 6 is a flowchart showing a first half of a road surface μ estimation calculation process executed by the ECU of FIG. 1;

FIG. 7 is a flowchart illustrating a latter half of a road surface μ estimation calculation process executed by the ECU of FIG. 1;

[Explanation of symbols]

2FR, 2FL, 2RR, 2RL ... wheel 4FR, 4FL, 4RR,
4RL Wheel speed sensor 6 Lateral G sensor 8 Yaw rate sensor 10 Front and rear G sensor 12 Steering angle sensor 13 Brake switch 14 Electronic control unit (ECU) 16FR, 16FL, 16RR, 16RL ... Toe control actuator

Claims (6)

[Claims] 1. A road surface friction coefficient detecting device that detects a friction coefficient of a running road surface of a vehicle, wherein a grip force detecting unit that detects a grip force generated by a tire mounted on a wheel of the vehicle; Load detecting means for detecting a load applied to the tire; limit determining means for determining whether or not the grip force of the tire is at a limit; and the grip determining means determines that the grip force of the tire is at a limit. In this case, there is provided a friction coefficient calculating means for calculating a friction coefficient of the traveling road surface from a ratio between a grip force of the tire and a load detected by the grip force detecting means and the load detecting means, respectively. A road surface friction coefficient detecting device, characterized in that: 2. The road friction coefficient detecting device according to claim 1, wherein the limit determining unit detects a steering angle and a vehicle speed of the vehicle, and based on the detected steering angle and the vehicle speed, determines the vehicle speed. The target value of the physical quantity of movement of the vehicle body generated with the turning of the vehicle is calculated, the actual value of the physical quantity of movement is detected, and the difference between the detected actual value of the physical quantity of movement and the calculated target value is larger than a predetermined value. The road surface friction coefficient detecting device is configured to determine that the grip force of the tire is at the limit when the tire has become larger. 3. The road surface friction coefficient detecting device according to claim 2, wherein the limit determining unit determines, based on a difference between the actual value and the target value of the physical quantity of movement, a wheel whose grip force of the tire is a limit, At least the front wheel or the rear wheel of the vehicle is configured to be specified, and the grip force detection unit and the load detection unit are configured to provide at least a front wheel and a rear wheel of the vehicle with a tire grip force. And the friction coefficient calculating means, the frictional force calculating means, for the wheel specified by the limit determining means that the grip force of the tire is the limit, the grip force detecting means and the load detecting means, Road friction coefficient detection, characterized in that the friction coefficient of the traveling road surface is calculated from the ratio between the grip force and the load detected respectively by Location. 4. The road surface friction coefficient detecting device according to claim 1, wherein the grip force detecting means calculates a longitudinal force and a lateral force of the tire based on a signal from a predetermined sensor, A road surface friction coefficient detecting device, wherein the resultant force of the calculated longitudinal force and lateral force is detected as a grip force of the tire. 5. The road surface friction coefficient detecting device according to claim 4, wherein the gripping force detecting means detects at least a longitudinal acceleration and a lateral acceleration of the vehicle body, and based on the detected longitudinal acceleration and lateral acceleration, A road surface friction coefficient detecting device, which is configured to calculate a longitudinal force and a lateral force of a tire. 6. The road friction coefficient detecting device according to claim 1, wherein the load detecting means detects longitudinal acceleration and lateral acceleration of the vehicle body, and detects the detected longitudinal acceleration and lateral acceleration. Based on acceleration,
A road surface friction coefficient detecting device, which is configured to calculate and detect a load applied to the tire.