JPH01101441A - Detecting device for road surface friction coefficient - Google Patents

Abstract

PURPOSE:To accurately detect a road surface friction coefficient corresponding to the traveling state of a vehicle by adding a time delay element for compensating the time delay of the cornering power of a front and a rear wheel behind the steering wheel operation. CONSTITUTION:A motion state detecting means 51 detects motion states of the vehicle such as the lateral acceleration ay of the gravity center of the vehicle and a steering state detecting means 37 detects steering states such as front and rear steering angles thetaF and thetaR, etc. Further, a vehicle speed detecting means 53 detects the traveling speed V of the vehicle and a storage means 31 is stored with the weight (m) of the vehicle, the distances (a) and (b) between the gravity center of the vehicle and front and rear axles, cornering power KF and KR of the front and rear wheels, and a stability factor such as the yaw inertial moment I of the vehicle. Then an arithmetic means corrects the delay of the KF and KR by a correcting element 40 to calculate a dynamic friction coefficient from an equation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a friction coefficient detection device that detects a road surface friction coefficient between a vehicle tire and a road surface, and particularly relates to a friction coefficient detection device that detects a road surface friction coefficient between a vehicle tire and a road surface. Regarding detecting coefficients.

(Prior Art) Conventionally, as a friction coefficient detection device for detecting a road surface friction coefficient between a vehicle tire and a road surface, for example, JP-A-59
As disclosed in Japanese Patent Publication No. 148769, a plurality of road surface friction coefficient values are predicted according to the steering angle of the front wheels, lateral accelerations corresponding to each of the predicted friction coefficients are calculated, and the calculated lateral By comparing the acceleration and the actually measured lateral acceleration and selecting the predicted friction coefficient corresponding to the closest value, the actual friction coefficient is estimated, and this estimated friction coefficient is used to adjust the rear wheel steering when turning. There are known methods that attempt to control the angle.

(Problem to be solved by the invention) However, in the conventional method described above, it is only assumed that the coefficient of friction is constant, and transient response characteristics such as lateral acceleration and yaw rate of the vehicle in response to steering input, that is, dynamic characteristics are equally taken into account. It has not been. Therefore, a certain degree of estimation accuracy can be secured in a state where there is no change in the steering angle of the steering wheel, that is, in a steady state such as when turning, which describes a steady state, but in reality, such a steady state is extremely rare. be.

That is, with the above-mentioned conventional method, it is not possible to derive a sufficiently reliable and highly accurate road surface friction coefficient to provide accurate turning control.

In addition, because the front wheel steering angle has a certain delay with respect to the steering wheel steering, the estimation of the road friction coefficient cannot accurately respond to changes in actual driving conditions, such as when making sharp turns. Therefore, there is also the problem that detection errors occur.

The present invention has been made in view of the above, and its purpose is to detect changes in the road surface friction coefficient during cornering, etc. by detecting the road surface friction coefficient in consideration of the dynamic characteristics of the vehicle in response to steering input. It is an object of the present invention to provide a road surface friction coefficient detection device which is useful for cornering control, etc., by detecting the friction coefficient as well as taking appropriate means that can sufficiently respond to particularly sudden changes in conditions.

(Means for Solving the Problems) To achieve the above object, the present invention provides a road surface friction coefficient detection system that detects the friction coefficient μ between the tires of a vehicle and the road surface, as shown in FIG. Targeting equipment.

The motion state detection means 51 detects the motion state of the vehicle such as the lateral acceleration aY of the center of gravity of the vehicle, and the front and rear wheel steering angles θF,
A steering state detection means 37 that detects a steering state such as OR, a vehicle speed detection means 53 that detects the running speed V of the vehicle, a weight m1 of the vehicle, a distance a between the center of gravity of the vehicle and the front and rear wheel axes,
b. Storage means 31 for storing tire cornering powers KF, KR of the front wheels and rear wheels in a standard state and stability factors of the vehicle such as the yaw moment of inertia of the vehicle, and the cornering powers KF, KR stored in the storage means 31; a correction means 40 that adds a time delay element D {D=1/ (1+τ・s)1 to the time constant τ, the motion state detection means 51, the steering state detection means 37, and the vehicle speed detection means 53. According to the output value of the correction means 40 and the storage contents of the storage means 31, the formula u=[V (m (a"Kp +b"KR) + l) derived from the basic equation of motion of the vehicle
-K1・s -m;V'(a-KF-b-KR)] a
Y/2cmKF-KR(V Cb-6F+a-6R)-
s+V'c6rnee δρ)-c-av) [2) (However, c-a+b, -KF+KR% δF=D・
The friction coefficient calculating means 41 calculates the road surface friction coefficient μ based on θF1δρ=D·θday, S is the Laplace operator).

Here, the above equations (1) and (2) are derived as follows.

That is, as shown in Fig. 4, from the balance of the forces acting on the tires when the vehicle turns, the basic equation of motion is: m-aY-2FF +2 FR(3) ■, Stiff-a-FF- 2b-PR(4)FF-μmKF
(θF-β-a-γ/V) (5) FR-p-KR
CθR-β+b・y/V) (6) However, ■(
β+γ)−aY (7) (where FF, F
R is the front wheel 2. Cornering force of rear wheel 3,
γ is the yaw rate), but the above equations (3) to (7
), FF, FR, β.

By eliminating γ, i, we get [m-1-V'-, s"+ 2 p-V (m (a"
KF+ b”KR) +1゛K)・s + 4 c”K
F-KR・p"-2p-m-V" (a-KFb-K
R)] aY = 2 μm1-V” (K F-θF +KR-9R),
s'+ 4 μ'V・KF−KR−c(b・θF+a・
θR)-s + 4 p'V'KF・KR-c (θF
-θR) [8) (where S is the Laplace operator and K-Kt=.

+ to ρ, C■a+b).

Here, the square term of S is the high frequency component of the transient response,
Since it can usually be ignored, by setting it to zero and dividing both sides of the above equation by μ, we get u = [V (m (a'KF + b'KR) +
l-K1・s-m-V'(a-KF-b-Kq)]
av/2cmKF・KR(V (b・θF+a−θR)
-8+V'(θF-θR)-c-aY)
[1] is obtained.

In the above equation (1), the cornering power KF of the front and rear wheels is expressed as
, KR time delay element is added, this time delay is due to the delay in front and rear wheel steering that occurs when steering the steering wheel, and the delay in cornering force FF and FR in response to changes in tire sideslip angle, and can be approximated as follows: , the front and rear wheel steering angles θF and θR may change with a delay with respect to steering wheel steering. Therefore, the above (θF, θR in the '2J formula)
Adding a time delay element to δF=D・θF1δR=
By using D・θR and corrected δF and δR in place of θF and θR, u= [V (m (a'KF+b'KR)+ l-K
1-5-m-V'(a-KF-b-KR) ] aY/
2 c-Kr-・KR[V (b-δF+a-δR)-
8+V'(δF-δR)-c, avl In other words, the above (2 formulas are obtained).

(Function) With the above configuration, in the present invention, when the vehicle is turning, etc., the stability factor of the vehicle stored in the storage means 31, the motion state detection means 51, the steering state detection means 37, and the vehicle speed detection means 53 can be used. Based on the vehicle's basic equation of motion, the friction coefficient calculating means 41 calculates, according to variables such as the detected lateral acceleration aYs of the vehicle center of gravity, front wheel steering angle θF1, rear wheel steering angle θR, and vehicle speed V. A road surface friction coefficient μ between the tires and the road surface corresponding to the dynamic characteristics of the vehicle is calculated. In this case, the correction means 40 calculates the cornering power KF of the front and rear wheels stored in the storage means 31.
, a time delay element is added to compensate for the time delay in steering the steering wheel of KR.

Then, the road surface friction coefficient μ value is calculated based on equation (2), which is approximately obtained by adding a time delay element to the front and rear wheel steering angles θF and θR.

Therefore, the time delay in cornering forces FF and FR of the front and rear wheels with respect to steering wheel steering is corrected, the estimation error of the road surface friction coefficient μ is reduced, and changes in accordance with the dynamic characteristics of the vehicle are accurately detected.

By utilizing the road surface friction coefficient μ derived in this way for controlling the turning movement of the vehicle, it is possible to perform stable driving even when driving, for example, in sharp turns on a snow-packed road.

(Example) Hereinafter, an example of the present invention will be described based on the drawings from FIG. 2 onwards.

FIG. 2 shows the overall configuration of a four-wheel steering system for a vehicle to which the present invention is applied, where 2 and 2 are left and right front wheels of the vehicle, and 3.3 are left and right rear wheels of the vehicle. 5 is a front wheel steering mechanism that adjusts the steering angle θF of the front wheels 2.2. The front wheel steering mechanism 5 includes front wheels 2,
A pair of left and right knuckle members 6, 6 which rotatably support 2 and are supported on the vehicle body via a joint portion 6a.
and the knuckle arm portions 6b, 6 of the knuckle members 6, 6.
A pair of left and right tie rods 8 each having one end connected to b.
．． 8, a rack shaft 9 formed by connecting the other ends of the pair of tie rods 8, 8 at both ends, and a rack shaft 9 that controls the rotation of the handle 4 via a pinion and a rack (both not shown). The main component is a steering gear mechanism 10 that converts the left and right movement of the vehicle.

In the front wheel steering mechanism 5, when the handle 4 is rotated at a constant steering angle θ, the steering gear mechanism 10
The tie rods 8, 8 are moved in the left and right direction via the rack shaft 9, and due to this movement, the knuckle members 6, 6 are rotated around the joint parts 5a, 5a, respectively.
The front wheels 2, 2 are steered at a front wheel steering angle θF corresponding to a front gear ratio Z (-θ/θF).

Furthermore, a rear wheel steering mechanism 12 is provided on the rear wheels 3, 3 side for steering the left and right rear wheels 3°3 in accordance with the steering of the front wheels 2, 2 by the front wheel steering mechanism 5. ing. The rear wheel steering mechanism 12 includes elements having the same functions as the front wheel steering mechanism 5, that is, a pair of knuckle members 13.13,
A pinion shaft 16 which has a tie rod 14, 14 and a rack shaft 15, and which engages the rack portion 15a of the rack shaft 15 with a pinion portion 16a at its tip, and a bevel gear 18 attached to the other end of the pinion shaft 16. and the bevel gear 18
The main component is a pulse motor 20 having a bevel gear 19 attached to an output shaft that meshes with the motor.

Then, when the pulse motor 20 is driven by the control unit 21 (described later) in accordance with the adjustment of the front wheel steering angle θF by the front wheel steering mechanism 5, the rotational driving force of the pulse motor 20 is applied to the two bevel gears 19, 18, and the pinion. The movement is converted into a horizontal movement of the rack shaft 15 via the portion 16a and the rack portion 15a.

Further, a power cylinder 23 is disposed on the rack shaft 15 of the rear wheel steering mechanism 12 to assist in its reciprocating movement in the vehicle width direction.
A piston 23a integrally attached to the rack shaft 15, and two hydraulic chambers 2 partitioned by the piston 23a.
3b and 23C. Moreover, the hydraulic chamber 23b,
23c communicate with the control valve 26 via hydraulic passages 24, 25, respectively. The control valve 26 is communicated via an oil supply passage 27 and an oil return passage 28 with a hydraulic pump 29 that is rotationally driven by a pump drive motor 30.

The control valve 26 controls the hydraulic chambers 23b, 23 of the power cylinder 23 depending on the rotational direction of the pinion shaft 16.
This controls the supply of masterpiece pressure to c. That is, when the rack shaft 15 is moved in the vehicle width direction via the bevel gear 18.19 and the pinion shaft 16 in order to steer the rear wheel 3.3 by the rotational driving force of the pulse motor 20, the rear wheel 3.3 3, the communication relationship between the hydraulic supply passage 27, the oil return passage 28, the i hydraulic passage 24.25, and each hydraulic chamber 23b, 23C is switched, and the hydraulic chambers 23b, 23c of the power cylinder 23 are switched. The movement of the rack shaft 15 in the vehicle width direction is supported by supplying and discharging pressure oil to the rear wheels 3, 3.
The rear wheel is steered by a predetermined rear wheel steering angle θR.

Next, 21 is a control unit that controls the pulse motor 20 and the pump drive motor 30, and signals from the following sensors 51 to 53 are input to the control unit 21. That is, 51 is a lateral force sensor as a motion state detection means for detecting a lateral acceleration aY from a force in the vehicle width direction, that is, a lateral force, acting on the vehicle body when the vehicle is turning, etc., and 52 is a lateral force sensor that is predetermined from the steering wheel steering angle θ. A steering angle sensor 53 is a steering angle sensor for detecting a front wheel steering angle θF based on a predetermined front gear ratio Z, and a vehicle speed sensor 53 is a vehicle speed detecting means for detecting a vehicle speed V based on the rotation speed of the left front wheel 2.

Then, as shown in FIG. 3, the control unit 21 controls the weight of the vehicle m1, the distance a11 between the center of gravity of the vehicle and the front wheel axle.
Distance b1 between the side center of gravity and the rear wheels; Tire cornering power KF, KR of the front and rear wheels in the standard state; stability factors of the vehicle such as the yaw moment of inertia of the vehicle; and the calculation formula for the road surface friction coefficient μ, which will be described later. The storage unit 31, which serves as a storage means for storing data necessary for control such as steering ratio characteristics, detects the switching of the external switch SW, and determines whether the side slip angle β of the vehicle is set to zero or not. a switch 32 that determines whether or not (described later) and switches the calculation formula for the road surface friction coefficient μ set in the storage unit 31 according to the result of the determination; a friction coefficient calculation unit 33 that calculates a road surface friction coefficient μ between the road surface and the tire according to the output of each of the sensors based on a calculation formula for the coefficient μ; and the friction coefficient calculation unit 33
a steering ratio characteristic selection section 34 that selects an appropriate steering characteristic from the steering characteristics stored in the storage section 31 according to the output of the steering ratio R selected by the steering ratio characteristic selection section 34; In addition to calculating the steering ratio R, that is, the rear wheel steering angle OR, based on the characteristics of
A rear wheel steering angle calculating section 35 having a function of detecting the rear wheel steering angle θR after calculating the road surface friction coefficient μ in the friction coefficient calculating section 33 receives the output of the rear wheel steering angle calculating section 35, and receives the output of the rear wheel steering angle calculating section 35, Pulse signal forming unit 3 that forms pulse signals for driving the motor 20 and pump drive motor 30
6, and a drive section MC that drives the pulse motor 20 and the pump drive 30 based on the pulse signal obtained from the pulse signal forming section 36. Here, the front and rear wheel steering angles θF are determined by the steering angle sensor 52 and the rear wheel steering angle calculating section 35.

A steering state detection means 37 is configured to detect a steering state such as OR.

As a feature of the present invention, an arithmetic expression for the road surface friction coefficient μ determined as follows is set in the storage unit 31.

That is, as shown in Fig. 4, from the balance of forces acting on the tires when the vehicle turns, the basic equations of motion (3) to (7') m-av-2Fp+2 shown below are obtained.
FR 1, Chi 2 a-FF-2b-FR FF-μmKF (θF-β-a-7/V) FR-μ・K
R(θR-β+b・γ/V) However, ■(To 1 γ)
=av, (here, FF and FR are the cornering forces of the front wheel 2 and rear wheel 3, respectively, and γ is the yaw rate), but from the above equations (3) to (7), FF, FR, β, and γ.

If we eliminate Te, we get [m-I-V''-s'+ 2-p-V (m (fKF
+ b; KR) + I-K)・s + 4 c'K r-
Kp-u'-2μmm-V' (a-K F-b-K
R)] aY” 2 μm1-V”CKF-tiF+KR・OR)-s”
+ 4 μ”V・KF−KR−C(b・θF+a・OR
)-s + 4 μ'V'KF・KR-C(θF-θR
) In other words, the above equation (8) is obtained (where S is the Laplace operator, KmKF+kR, c-a+b).

Here, the square term of S is the high frequency component of the transient response,
Since it can usually be ignored, we set it to zero, and by dividing both sides of the above equation by μ, we get u=[V 1m (a”Kp +b'KR) + 1
-K)-s -m-V'(a-KF-b-KR) ]
aY/2 C-KF-KR(V (b・θp+a-θ
R)・s+V2(θF−θR)−c−aY) In other words, the above equation (1) is obtained.

That is, the road surface friction coefficient μ is determined by vehicle speed V, heavy vehicle inertial mass m, distance a between the vehicle center of gravity and the front wheel axle, distance between the vehicle center of gravity and the rear wheel axle, and cornering of the front wheels 2 and rear wheels 3 in the standard state. It is determined from variables such as stability factors such as power KF, KR, and yaw moment of inertia (2), lateral acceleration aY at the center of gravity of the vehicle, front wheel steering angle θF, rear wheel steering angle θR, and vehicle speed V.

Here, the cornering power KF of the front and rear wheels mentioned above.

A time delay element is added to KR, but this time delay is due to the delay in front and rear wheel steering that occurs when steering the steering wheel, and the cornering force FF and FR due to changes in tire sideslip angle.
Approximately, the front and rear wheel steering angles θF and θR may change with a delay relative to the steering wheel steering. Therefore, θF, θR in the above formula (2)
A time delay element D consisting of a constant time constant τ (however, D
-1/(1+τ)), δF=D・θF, δR
By using δF and δR corrected as =D・OR in place of θF and θR, -u-[V (m (a'Kp +b'KR) +l-
K1・s −m, V”(a-KF-b-KR) ] a
Y/2 C-KF・KR (V Cb・6F+a-6R)
-s+V'C6F-OR)-c-aY) In other words, the above equation (2) is obtained.

In particular, in the case of control such as four-wheel steering where β is zero, the above equation (3) ~ (If β - 0 is set for force, a simpler formula, μ謔m−aY/2 (KF°θF+KR-OR-(av
/V') Ca-Kp-b-KR) ) 00
) or u-m-aY/2 (KF-δF+KR・OR-(a
v/V') (a-KF-b-KR))
Get GD. In this embodiment, the above-mentioned equations (1), (2), (to), and 01) are used by the switch 32 as the basic equation of motion for calculating the road surface friction coefficient μ, depending on the type of vehicle control. I'm trying to switch it up.

Actually, by transforming the above 00), GD formula, u-m-
aY/ ((KF +R-KR)(θ/Z)-(aY/
V') (a-KF-b-KR) ) 07! J or u=m-av/t (KF +R-KR) (δ
/2)-(aY/V')(a-KF-b-KR)l
03) (where δ=D・θ), it is a function of the steering wheel steering angle θ and the steering ratio R.

In the storage section 31, steering ratio characteristics to be selected by the steering ratio characteristic selection section 34 are set. That is, as shown in FIG. 6, this steering ratio characteristic basically corresponds to the steering ratio R.
is continuously changed to the opposite phase side when the vehicle speed V is low, and to the same phase side when the vehicle speed V is high, and three types of steering ratio characteristics are changed according to changes in the road surface friction coefficient μ. It is something that can be switched. For example, when the road friction coefficient μ is a standard value, the curve r2 in the figure appears, whereas when the road friction coefficient μ is relatively small, the steering ratio R shifts to the same phase side as the curve r1 in the figure. The value of the reverse vehicle speed V1 is lower than the same vehicle speed V2 of the above standard characteristics,
Conversely, when the road surface friction coefficient μ is relatively large, the vehicle speed value v3 of the phase reversal is set to the higher side, as shown by the curve r3 in the figure.

Next, FIG. 5 shows a procedure for calculating the road surface friction coefficient μ, which is performed at each predetermined sampling period in the friction coefficient calculating section 33. First, in step S1, the vehicle speed sensor 5
3. From the signals of the lateral force sensor 51, the steering angle sensor 52, and the rear wheel steering angle calculating section 35, calculate the vehicle speed v1 and the lateral acceleration a of the vehicle center of gravity.
Y s Read the steering wheel angle θ and steering ratio R, step S
In steps 2 to S4, it is determined whether the vehicle speed V, lateral acceleration a, Y, and steering angle θ are greater than or equal to predetermined set values, and if each determination is YES, the process proceeds in order, and further the steering speed of the steering wheel is determined in step S5. It is determined whether the absolute value +j+ of θ is smaller than a predetermined value 0+ (#+>0) at which the vehicle is in a sharp turning state. When the determination is YES, which is 1δ1 minus δ1, it is determined that the vehicle is in a normal running state, and the process proceeds to step S6.
The road surface friction coefficient μ is calculated based on the formula On the other hand, if the determination in step S5 is 101≧0
1 (No), it is determined that the vehicle is in a sharp turning state, and the process proceeds to step S7, where the front and rear wheel steering angles θF, θ are determined.
The values δF and δR are calculated by adding the delay element to R, and then, in step S8, the road surface friction coefficient is calculated based on the above (2) using δF and δR (or the one modified to OD formula (03)). Calculate μ.

On the other hand, if any of the determinations in steps 82 to S4 above is NOl, that is, the value of the vehicle speed V, the absolute value of the steering wheel angle θ, and the absolute value of the vehicle lateral acceleration aY are lower than the set values, the above (1) ), there is a risk that the denominator on the right side approaches zero and the error increases, so instead of calculating the road surface friction coefficient μ, the road surface friction coefficient μ estimated at the previous sampling is used in step S9. The value of is set and the process moves to step 5lll. In this step SIO, it is determined whether the road surface friction coefficient μ is negative or not.
If YES, it is unreasonable considering the characteristics of the road surface friction coefficient μ, so it is reset to μm0 in step Sl+. On the other hand, if the determination in step S7 is No (μ≧0), the process directly proceeds to step S12.

Then, in step S9, in order to perform control smoothly, μ′ − μ/(1+τ′ ・s ) (
14) (where μ' is the new integrated friction coefficient obtained by integrating μ, τ' is the integration time constant, and S is the Laplace operator)
Based on this, the road surface friction coefficient μ is integrated and the control is terminated.

Therefore, the steps 82 to S5 constitute the driving state detection means 38 that detects the driving state of the vehicle, and the cornering power KF of the front and rear wheels is stored in the storage section 31 in the step S7.

A correction means 40 is configured to add a time delay element to KR. Further, the step S6 configures the first friction coefficient calculating means 39 that calculates the road surface friction coefficient μ based on the basic equation of motion (1) of the vehicle, and the step S8 configures the first friction coefficient calculation means 39 that calculates the road surface friction coefficient μ based on the basic equation of motion (1) of the vehicle. receive the output,
The above-mentioned lateral force sensor 51° steering angle sensor 52, vehicle speed sensor 53
, according to the output values of the rear wheel steering angle calculation section 35 and the correction means 40 and the stored contents of the storage section 31, the second friction coefficient calculation means as a calculation means for calculating the road surface friction coefficient μ based on the above (2 equations). 41 are configured.

When the vehicle is turning, etc., the road surface friction coefficient calculation unit 33 receives the outputs of the sensors 51 to 53 and determines the road surface based on equation (1) or (2) derived from the basic equation of motion. When the friction coefficient μ is calculated, the steering ratio characteristic selection unit 34 selects the road surface friction coefficient μ (actually, the integrated friction coefficient μ′) calculated by the road surface friction coefficient calculation unit 33.
Depending on the magnitude of the value, one of the steering ratio characteristic curves r1 to r3 shown in FIG. 6 set in advance in the storage section 31 is selected. Accordingly, the steering ratio selected by the steering ratio selection section 34, the front wheel steering angle θF detected by the steering angle sensor 52, and the vehicle speed sensor 5
Appropriate rear wheel steering angle θ is determined according to the value of vehicle speed V detected in step 3.
R is calculated. Further, the pulse signal forming unit 36 outputs a pulse signal according to the calculated value, and the drive unit MC drives the pulse motor 20 and the pump drive motor 30 in accordance with the pulse signal. is driven to a predetermined - steering angle θR.

Therefore, in the above embodiment, when the vehicle is turning, the road surface friction coefficient μ between the tires and the road surface is the lateral acceleration aY at the center of gravity of the vehicle detected by each detection means.

Depending on the front wheel steering angle θF, rear wheel steering angle θR, and vehicle speed V, (1) or ・(
Since the calculation is performed based on the equation (1), it is possible to quickly detect changes in the road surface friction coefficient μ depending on the state of motion of the vehicle.

In addition, when the vehicle is in a predetermined condition where the running condition of the vehicle suddenly changes, such as when the vehicle is in a sharp turn, the cornering power KF of the front and rear wheels stored in the storage section 31 is changed.
, KR is added with a delay element consisting of a constant time constant τ, so that the front and rear wheel steering angle θF with respect to steering wheel steering is
, the time delay in cornering force Fp and FR caused by the time delay in θR and the delay in the tire sideslip angle change is corrected, the estimation error of the road surface friction coefficient μ is reduced, and as a result, the dynamic characteristics of the vehicle are It is possible to accurately detect the corresponding change in the road surface friction coefficient μ. By using the road surface friction coefficient μ derived in this way for controlling vehicle turning, it is possible to perform stable driving even when driving, for example, in sharp turns on a snow-packed road.

In particular, in the above embodiment, since the road surface friction coefficient μ calculated in step S9 is integrated, minute fluctuations in the road surface friction coefficient μ in the transient response are smoothed out.
This has the remarkable effect of enabling more stable turning.

In the above embodiment, the road surface friction coefficient μ value is calculated by correcting the time delay only under the predetermined conditions, but the present invention is not limited to the above embodiment, and the cornering power KF, It goes without saying that a time delay element may be added to KR.

Next, an experimental example in which the control device of the above embodiment was used to perform turning control in which β becomes zero in a JWS vehicle is shown in FIGS.
This will be explained based on FIG. Figure 7 shows how the time delay between the front and rear wheels relative to steering wheel steering, that is, the dynamic characteristics of the tires, is taken into consideration on a compacted snow road (a so-called low-μ road where the average road surface friction coefficient is estimated to be 0.2 to 0.3 μm). The upper figure in Figure 7 shows the change in the steering wheel angle θ over time, and the lower figure shows the value of the road friction coefficient μ corresponding to the change in the steering wheel angle θ. Indicates change characteristics. In addition, Figure 8 shows data when the dynamic characteristics of the tire are taken into account under the same conditions and processed as a -order lag system, and for convenience, in the same figure, a time lag element consisting of a predetermined time constant is added to θ. The figure below shows the characteristics of the change in the road surface friction coefficient μ at that time. Comparing the above two figures, we can see that the peak point of the road surface friction coefficient μ corresponding to the trough of the change in steering wheel angle θ is out of phase when the dynamic characteristics of the tires are not taken into consideration (see the top and bottom diagrams in Figure 7). ), when the dynamic characteristics of the tire are considered, the position of the valley of the change characteristic of the steering wheel steering angle θ′ and the position of the peak point of the road surface friction coefficient μ match (see the top and bottom diagrams in Figure 8), and both It can be seen that the phases match. In contrast to the lower diagram in Figure 7, the lower diagram in Figure 8 shows the road surface friction coefficient μ
The change in is gradual, especially the part where μ has a large peak. In other words, the tire characteristics actually respond to steering with the steering wheel steering angle θ with a time delay as shown in the upper diagram of FIG. It can be seen that fluctuations in the estimated value of the road surface friction coefficient μ caused by ignoring the time delay are smoothed out. Here, the steering wheel steering angle θ at which the calculation should be stopped in the above embodiment is set to a very small value, and the calculation is not actually stopped even under the predetermined conditions.

In addition, Figures 9 and 10 are similar to Figures 7 and 8 above.
Figure 9 shows the data when the value of θ, at which the calculation of the road surface friction coefficient μ is stopped, is set larger than the above value under the same driving conditions as shown in the figure. The figures are taken in consideration of the dynamic characteristics of the tire, and the upper and lower figures in each figure show the characteristics corresponding to the above-mentioned Figures 7 and 8, respectively. Comparing these,
In addition to the effect of stopping the calculation based on the above formula under a predetermined condition, the peak smoothing effect of adding a time delay element is shown.

Note that the data shown in FIGS. 7 to 10 above are obtained when the integration process is performed and the integration time constant is set to a relatively small predetermined value.

Furthermore, Fig. 11 and Fig. 12 show data obtained when turning driving was controlled on a wet concrete road (so-called medium μ road where the average road surface friction coefficient μ is estimated to be about 0.6). , when the above calculation is not canceled and the time constant of the integration process is set small as in the case of each of the above figures, and tire dynamic characteristics are not taken into account, Figure 12 shows that the calculation is canceled and the integration process is The data shown below are obtained by setting the integral time constant of the conversion process to a relatively large value and taking tire dynamic characteristics into consideration. Comparing these figures shows that in addition to the effect of increasing the integral time constant and the effect of aborting calculations, the effect of stabilizing the estimation of the road surface friction coefficient μ by treating the tire dynamic characteristics as a first-order lag system is shown, making it extremely stable. It can be seen that turning control is being performed.

Note that the application of the present invention is not limited to the control of four-wheel steering as in the embodiments described above, but is also applicable to, for example, the control of two-wheel steering. In that case, the road surface friction coefficient μ detected by the road surface friction coefficient detection device of the present invention may be used to apply it to a so-called anti-lock braking system used when driving on a road surface with a low friction coefficient. It is possible to control the braking force in response to changes in the actual road surface friction coefficient μ during cornering, etc., thereby improving the control effect.

In addition, as shown in the above example, when deriving the formula for calculating the road surface friction coefficient μ from the basic equations of motion (3) to (7) of the vehicle, the formula (1) or (2) described above, that is, the following In addition to transforming the general function p-G (s) ・av/H(s) ・θ, for example, μ-G' (s) ・γ/H(s) ・θ, the yaw rate γ and It can also be a function of the steering wheel steering angle θ. Alternatively, it can be transformed into a function of sideslip angle β and steering angle θ, such as μmG' (s) ・β/H(s) ・θ, and the values of these variables γ, θ or β, θ It is also possible to adopt a configuration in which the road surface friction coefficient μ is detected in accordance with the road surface friction coefficient μ, and a time delay element is added by the correction means 40.

(Effects of the Invention) As explained above, according to the road surface friction coefficient detection device of the present invention, driving conditions such as lateral acceleration, steering angle of wheels, vehicle speed, cornering power of front and rear wheels, etc. during turning of a vehicle can be detected. Accordingly, when calculating the road surface friction coefficient between the tires and the road surface based on the equation of motion of the vehicle, a time delay element consisting of a predetermined time constant is added to the input of the cornering power of the front and rear wheels. The time delay in estimating the road surface friction coefficient due to the time delay between the front and rear wheel steering angles relative to steering is corrected, and the road surface friction coefficient can be accurately detected and output in response to changes in vehicle driving conditions, even when driving around sharp turns. This can be used for stable vehicle turning control, etc.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention. Figure 2 and subsequent figures show embodiments of the present invention. Figure 2 is an overall configuration diagram of the vehicle, Figure 3 is a configuration diagram of the vehicle control device, and Figure 4 shows the relationship of forces that act when the vehicle turns. 5 is a flowchart showing the control in the road surface friction coefficient calculation section, FIG. 6 is a diagram showing the steering ratio characteristics to be selected set in the storage section, and FIGS. 7 to 10 are respectively Figure 7 shows the experimental data on a snow compacted road. Figure 7 shows when the calculation is not canceled and the dynamic characteristics are not taken into consideration. Figure 8 is when the calculation is not canceled and the dynamic characteristics are taken into account. Figure 9 is when the calculation is canceled and the dynamic characteristics are taken into account. Figure 10 shows the experimental results when the calculation was stopped and the dynamic characteristics were taken into account, and Figures 11 and 12 show the experimental data on the middle μ road. FIG. 11 is an experimental result diagram showing data when the calculation is not canceled and dynamic characteristics are not taken into consideration, and FIG. 12 is an experimental result diagram showing data when the calculation is canceled and the dynamic characteristics are taken into account. 31... Storage unit (storage means), 35... Rear wheel steering angle calculation unit, 37... Steering state detection means, 39... First friction coefficient calculation means, 40... Correction means, 41 ...Second
Friction coefficient calculation means (friction coefficient calculation means), 51... Lateral force sensor (motion state detection means), 52... Rudder angle sensor, 53... Vehicle speed sensor (vehicle speed detection means). Patent applicant Mazda Motor Corporation representative
Person Bengeri Mae 1) Hiroshi. Figure 2 Figure 1 Figure 6 i-phase Figure 9 Figure 7 Figure 8

Claims (1)

[Claims] (1) A road surface friction coefficient detection device that detects the friction coefficient μ between the vehicle tires and the road surface, which includes a motion state detection means that detects the motion state of the vehicle such as the lateral acceleration a_Y of the vehicle center of gravity, and Steering state detection means for detecting steering states such as wheel steering angles θ_F and θ_R; vehicle speed detection means for detecting vehicle running speed V; vehicle weight m; distances a and b between the center of gravity of the vehicle and the front and rear wheel axes. , a storage means for storing stability factors of the vehicle such as tire cornering powers K_F, K_R of the front wheels and rear wheels in a standard state and yaw moment of inertia I of the vehicle, and for the cornering powers K_F, K_R stored in the storage means. a correction means for adding a time delay element D {D=1/(1+τ・s)} consisting of a constant time constant τ; output values of the motion state detection means, steering state detection means, vehicle speed detection means and correction means; Depending on the memory contents of the storage means, the formula μ=[V{m(a^2K_F+b^2K_R)+I・K] derived from the basic equation of motion of the vehicle
}・s−m・V^2(a・K_F−b・K_R)]a_
Y/2c・K_FK_R{V(b・δ_F+a・δ_R
)・s+V^2(δ_F−δ_R)−c・a_Y} (where c=a+b, K=K_F+K_R, δ_F=
A road surface friction coefficient detection device comprising: friction coefficient calculating means for calculating a road surface friction coefficient μ based on D·θ_F, δ_R=D·θ_R, s is a Laplace operator).