JPH01101437A - Detecting device for road surface friction coefficient - Google Patents

Abstract

PURPOSE:To perform accurate detection even when variables are small by calculating the road surface friction coefficient from an arithmetic equation based upon the differential values of lateral acceleration and front and rear wheel steering angles as parameters under specific conditions where an arithmetic error increases. CONSTITUTION:A 2nd friction coefficient arithmetic means 42 is used when the traveling state of the vehicle detected by a traveling state detecting means 40 meets specific requirements wherein the arithmetic error in road surface friction coefficient mu expressed by an equation I [where (s) is a Laplacean, K=KF+KR, c=a+b, and KF and KR are the tire cornering power of the front and rear wheels] increases. Namely, the road surface friction coefficient muis calculated based upon an equation II derived from the basic motion equation of the vehicle corresponding to the differential values of variables such as the lateral acceleration ay of the gravity center of the vehicle calculated by a differential value arithmetic means 38, a front wheel steering angle deltaF, and a rear wheel steering angle deltaR, the vehicle speed V, and the stability factor of the vehicle stored in a storage means 31.

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, Japanese Patent Application Laid-Open No. 1986-
As disclosed in Japanese Patent No. 148769, a plurality of values of the road surface friction coefficient are predicted according to the steering angle of the front wheels, lateral acceleration corresponding to each of the predicted friction coefficients is calculated, and the calculated lateral acceleration is calculated. By comparing the actual lateral acceleration and selecting the predicted friction coefficient corresponding to the closest value,
There is a known system that estimates an actual friction coefficient and uses the estimated friction coefficient to control the rear wheel steering angle during cornering.

(Problems to be Solved by the Invention) However, in the conventional method described above, it is assumed that the coefficient of friction is constant, and transient responses such as lateral acceleration and yaw rate of the vehicle to steering input, that is, dynamic characteristics, are not equally considered. . 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 within a steady state, but in reality,
Such steady states are extremely rare. That is, with the above-mentioned conventional method, it is not possible to derive a sufficiently reliable road surface friction coefficient and use it for accurate turning control.

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. An object of the present invention is to provide a road surface friction coefficient detection device useful for cornering control and the like.

(Means for Solving the Problems) In order to achieve the above object, the solving means of the present invention includes a friction coefficient detection device for detecting the friction coefficient between the tires of a vehicle and the road surface, as shown in FIG. set to target.

The motion state detection means 51 detects the motion state of the vehicle such as the lateral acceleration aY of the vehicle center of gravity, and the front and rear wheel steering angles δF,
The steering state detection means 37 detects the steering state such as δR, the vehicle speed detection means 53 detects the speed V of the vehicle, the weight m1 of the vehicle, the distances a and b between the center of gravity of the vehicle and the front and rear wheel axles, and the front wheels in the standard state. and rear tire cornering power KF.

A storage means 31 for storing stability factors of the vehicle such as KR and vehicle yaw moment of inertia receives the outputs of the motion state detection means 51 and the steering state detection means 37, and detects the detected values of both the detection means 51 and 37. a differential value calculating means 38 for calculating the differential value of the driving state; a driving state detecting means 40 for detecting when the running state of the vehicle is under a special predetermined condition; is under normal conditions, the motion state detection means 5
1. Based on the output values of the steering state detection means 37 and the vehicle speed detection means 53 and the contents stored in the storage means 31, calculate the road surface friction coefficient μ based on the formula % derived from the basic equation of motion of the vehicle. Receiving the output of the first friction coefficient calculating means 41 and the running state detecting means 40,
When the running state of the vehicle is under a special predetermined condition, the value is derived from the basic equation of motion of the vehicle according to the output values of the vehicle speed detection means 53 and the differential value calculation means 38 and the stored contents of the storage means 31. The second friction coefficient calculating means 42 calculates the road surface friction coefficient μ based on the formula (%).

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 following basic equation of motion: m=a Y -2F t: + 2 FR (3) -
Chi 2 a-FF-2b-FR (4) FF-u・Kr:
CδF-β=a-γ/V) (5) FR-μm
KR (δR-B+b-r/V) (6) However,
■(β+γ) = ay [7] (here, F
F and FR are front wheels 2. The cornering force of rear wheel 3, γ is the yaw rate) is obtained using the above formula (3).
From ~(7), FF, FR, β.

By eliminating γ, 8, we get [m-1-Vis'+ 2 μmV fm (a”KF
+ b”KR) +I-K}・s + 4 c”KF-
KR・μ” −2tt−m・V” (a−Kt=−b−
KR)] aY- 2B-1-V' (KF-δF + KFZ-6R)・
s"+ 4 tl"V=KF-KR-C(b・δF+&
−δR}・s + 4 u”J”KF・KR−C(δF
−δR) (8) is obtained.

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 tt - [V (m (a'KF+b''KR) + l
-K1-5-m-V" (a-K F -b-K
R) Ko a Y /2cmK F-KR{V
Cb・6t: +a−6R}・s+V”c6r knee δR
}・c=aY) In other words, the above equation (1) is obtained.

Then, by further multiplying the numerator and denominator of the above formula by S, μ'' [V (m (a'KF+b''KR) + l-
K1-5-m-V" (a-K F -b-K R
) Ko a Y / 2 c -K F-KR
{V Cb・■F+a-6R}・8+V'(6iF-(
5R}·c-isY) (8) In other words, the above formula (2) is obtained.

(Function) With the above configuration, in the present invention, when the vehicle running state determined by the running state detecting means 40 is in the normal condition when the vehicle is turning or the like, the first friction coefficient calculating means 41 stores the The stability factor of the vehicle stored in the means 31, the lateral acceleration of the vehicle center of gravity a Y s detected by the vehicle speed detecting means 53, the motion state detecting means 51, and the steering state detecting means 37, the vehicle speed V, and the front and rear wheel steering angle δ.
Depending on variables such as F1δR, the road surface friction coefficient μ is calculated based on equation (1) derived from the basic equation of motion of the vehicle.
is calculated.

Further, when the running state of the vehicle detected by the running state detecting means 40 is under special predetermined conditions such that the calculation error of the road surface friction coefficient μ according to the above equation (1) becomes large, the second friction coefficient calculating means 42 , lateral acceleration aY of the vehicle center of gravity calculated by the differential value calculation means 38, front wheel steering angle δF,
The above-mentioned ( 2) Based on the formula, the road surface friction coefficient μ is calculated.

Therefore, it is possible to quickly detect changes in the road surface friction coefficient μ according to the dynamic characteristics of the vehicle, and also
) formula approaches zero, each detection means 37.51.53
When the driving condition is such that the detection error of is magnified and the fluctuation of the calculated value of the road surface friction coefficient μ by the first calculation means 41 becomes large, the lateral acceleration a Y % of the vehicle center of gravity increases.
Since the road surface friction coefficient μ is calculated based on equation (2), which uses the differential values of variables such as the front and rear wheel steering angles δF and δR as parameters, the calculation error does not increase even when the value of each variable is small. , the road surface friction coefficient μ is accurately calculated.

Therefore, it is possible to quickly and accurately detect changes in the road surface friction coefficient μ according to the dynamic characteristics of the vehicle, and by using the road surface friction coefficient μ derived in this way for vehicle turning control, etc. For example, stable driving can be achieved even when turning around 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 configuration of a four-wheel steering system for a vehicle to which the present invention is applied, in which reference numerals 2 and 2 indicate left and right front wheels of the vehicle, and 3° and 3 indicate left and right rear wheels of the vehicle. 5 is a front wheel steering mechanism that adjusts the steering angle δF of the front wheels 2.2. The front wheel steering mechanism 5 includes a pair of left and right knuckle members 6, 6 that rotatably support the front wheels 2.2 and are supported by the vehicle body via a joint portion 6a, and a knuckle arm portion 6b of the knuckle members 6, 6. , 6b, a pair of left and right tie rods 8°8 each having one end connected thereto, a rack shaft 9 formed by connecting the other ends of the pair of tie rods 8, 8 to each other at both ends, and a rack shaft 9 that controls the rotation of the handle 4 with a pinion. The main component is a steering gear mechanism 10 that converts the rack shaft 9 into left and right movement via a rack (none of which is shown).

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 rod 8.8 moves in the left-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 δF corresponding to a front gear ratio Z (-θ/δF).

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. It is being The rear wheel steering mechanism 12 has elements having the same functions as the front wheel steering mechanism 5, that is, a pair of knuckle members 13.13, a tie rod 14.14, and a rack shaft 15. A pinion shaft 16 that meshes with the rack portion 15a at the tip end binion portion 16a, a bevel gear 18 attached to the other end of the pinion shaft 16, and the bevel gear 1.
The main component is a pulse motor 20 having a bevel gear 19 attached to an output shaft that meshes with the pulse motor 8.

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 δF 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 communicates with a hydraulic pump 29 which is rotationally driven by a pump drive motor 30 via an oil supply passage 27 and an oil return passage 28 .

The control valve 26 controls the hydraulic chambers 23b and 2 of the power cylinder 23 depending on the direction of rotation of the vinyl and on-shaft 16.
This controls the supply of hydraulic pressure to 3C. That is, when the rack shaft 15 is moved in the vehicle width direction via the bevel gears 18, 19 and the pinion shaft 16 in order to steer the rear wheels 3, 3 by the rotational driving force of the pulse motor 20,
Depending on the steering direction of the rear wheels 3°3, the communication relationship between the hydraulic pressure supply passage 27, the hydraulic pressure return passage 28, each hydraulic passage 24, 25, and each hydraulic chamber 23b, 23C is switched, and the hydraulic pressure of the power cylinder 23 is changed. By supplying and discharging pressure oil to and from the chambers 23b and 23C, movement of the rack shaft 15 in the vehicle width direction is assisted, and the rear wheel 3
, 3 by a predetermined rear wheel steering angle δR.

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 detects a front wheel steering angle δF based on a predetermined front gear ratio Z, and a vehicle speed sensor 53 serves as a vehicle speed detecting means to detect a vehicle speed V based on the rotation speed of the left front wheel 2.

As shown in FIG. 3, the control unit 21 controls the weight m of the vehicle, the distance a between the center of gravity of the vehicle and the front and rear wheel axles,
b. For control of front and rear tire cornering powers KF and KR in standard conditions, vehicle stability factors such as the vehicle's yaw moment of inertia, the calculation formula for the road surface friction coefficient μ described later, steering ratio characteristics, etc. The storage section 31 serves as a storage means for storing necessary data, and the switching of the external switch SW is detected to determine whether or not the side slip angle β of the vehicle is controlled to be zero (described later). In addition, there is a switch 32 that switches the calculation formula for the road surface friction coefficient μ set in the storage unit 31 according to the determination result, and a switch 32 that switches the calculation formula for the road surface friction coefficient μ set in the storage unit 31 according to the determination result of the switch 32 and the selected calculation formula for the road surface friction coefficient μ. A friction coefficient calculating section 33 calculates a road surface friction coefficient μ between the road surface and the tires according to the outputs of the above-mentioned sensors, and a friction coefficient calculating section 33 calculates the road surface friction coefficient μ between the road surface and the tires according to the outputs of the above-mentioned sensors. A steering ratio characteristic selection unit 34 that selects an appropriate steering ratio characteristic from the steering ratio characteristics, and a steering ratio R based on the steering ratio R selected by the steering ratio characteristic selection unit 34.
In other words, the rear wheel steering angle calculation unit 35 has a function of calculating the rear wheel steering angle δR and detecting the rear wheel steering angle δR for calculating the road-surface friction coefficient μ in the friction coefficient calculation unit 33.
and a pulse signal forming section 36 that receives the output of the rear wheel steering angle calculating section 35 and forms pulse signals for driving the pulse motor 20 and the pump drive motor 30; The drive unit MC includes a pulse motor 20 and a drive unit MC that drives the pump drive 30 based on the received pulse signals. Here, the steering angle sensor 52 and the rear wheel steering angle calculating section 35 calculate the front and rear wheel steering angles δF.
, δR, etc. steering state detection means 37
is configured.

As a feature of the present invention, the storage unit 31 is set with an arithmetic expression for the road surface friction coefficient μ determined 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 equations of motion (3) to (7) shown below are expressed as follows: ■(/3+γ ) = av (where FF and FR are the cornering forces of front wheel 2 and rear wheel 3, respectively, and γ is the yaw rate), but
From the above formulas (3) to (7'), FF, FR, β.

By eliminating γ and i, we get [m・I−Vjs'+ 2 μmV (m (a”KF
+BiKR)+1-K}・s +4 c”KF-KR-
u'-2-B-m-V” (a-Kp-b-KR)]
aY - 2u-1-V'CKF・6F+KR4R)・s″+4
μmy・KF−KR−c(b・δ1=+a−δR}・s
+ 4 p'V''Kt:・KR-C(δF-δR) In other words, we obtain the above equation (8) (where S is the Laplace operator, K=KF +kR, c=a+b) o Here, S The square term of is a high frequency component of the transient response and can usually be ignored, so it is set to zero, and by dividing both sides of the above equation by μ, 1, CZ - [V (m (a'Kp + b'Kq )
+I-K}・s -m-V' (a=KF-b-KR)
] aY/ 2 C=KFKR{V (b・6iF+a
−6R}·s +V'(δp−δR}·c=avl In other words, the above equation (1) is obtained.

In other words, the road surface friction coefficient μ is the lateral acceleration a of the vehicle center of gravity
Ys It is determined using variables such as front wheel steering angle δF, rear wheel steering angle δR1, and vehicle speed V as parameters.

Furthermore, by multiplying the numerator and denominator of the above formula by S, μ= [V (m (a”KF+b'KR) +I-K
)・s −m−V2(a・Kt−−b−KR) ] i
hY/2 c-Kr-・KR{V Cb-6F+a4q
}・s+V” (JF6R> −c=ay) In other words, the above equation (2) is obtained.

That is, the road surface friction coefficient μ is determined using the variable V and the differential values of variables such as the lateral acceleration a'/s of the vehicle center of gravity, the front wheel steering angle δF, and the rear wheel steering angle δR.

In addition, especially in the case where control is performed to make β zero with four-wheel steering, if β - 0 is set in the above equations (3) to (7), the simpler formula % formula % (Furthermore, the above formula By multiplying the 9th denominator of the numerator on the right side by S, μ=maY/2 (Krnee aF+KR−jR−(iy
/V") Ca=KF-b-KR))
00) is obtained. In this embodiment, the switching device 32 allows
The basic equation of motion for calculating the road friction coefficient μ is:
When control is not performed so that β becomes zero, the above (1), (
In 2), when performing control such that β becomes zero, the above (9),
00) formula.

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 switches to three types of steering ratio characteristics according to changes in the road surface friction coefficient μ. It is. For example, when the road surface friction coefficient μ is a standard value, the curve r2 in the figure appears, whereas when the road surface friction coefficient μ is relatively small, the vehicle speed at which the phase of the steering state is reversed is as shown by the curve r1. The value of v1 is set to a lower side than the same vehicle speed v2 of the above standard characteristic, and conversely, when the road surface friction coefficient μ is relatively large, the vehicle speed value v3 of phase reversal is set to a higher side as shown by 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.
Ys The front wheel steering angle δF and the rear wheel steering angle δR are read, and in step S2, the differential values of aY, δF, and δR among these variables are calculated. Next, in steps 83 to S5, it is determined whether the value of vehicle speed ■ and the absolute values of front wheel steering angle δF, rear wheel steering angle δR2, and lateral acceleration aY are greater than or equal to a predetermined set value, and if the determination is YES, It is determined that the normal conditions are in place for estimating the road surface friction coefficient μ, and the process proceeds to step S6, where the above (
After calculating the road surface friction coefficient μ based on equation 1) or equation (9), the process proceeds to step 5lfl.

On the other hand, step S4. If any of the determinations in SS is NOl, that is, the absolute values of the front and rear wheel steering angles δF, δR and the lateral acceleration aY of the vehicle center of gravity are each less than the set value, then the denominator on the right side of equation (1) or (9) above is Since it approaches zero and the error increases, it is determined that there is a special predetermined condition in which the normal road surface friction coefficient μ cannot be estimated, and the process moves to step S7. In steps Sy and S6, the front and rear wheel steering angles δ are
It is determined whether the absolute values of the differential values of F and δR and the absolute values of the differential value of the lateral acceleration aY are each greater than or equal to a set value. and,
Step S7. When the determination in S8 is YES,
Proceeding in order, in step S9, variable V and variables aY, δF, δ
The above ('2V or (
Step S: Calculate the road surface friction coefficient μ based on the formula
Go to IG.

In step SIO, it is determined whether the road surface friction coefficient μ is negative or not, and if the determination is YES (μ is 0), the road surface friction coefficient μ
This is unreasonable considering the characteristics of μm0 in step So.
On the other hand, the determination in step S10 is μ≧
If the answer is NO (0), the process directly proceeds to step S+3.

Note that any of the determinations in steps S3, S7, and S8 above is NO1, that is, the value of the vehicle speed V, the front and rear wheel steering angle δF,
When the absolute value of the differential value of δR and the absolute value of the differential value of the lateral acceleration aY are each smaller than the set values, step S+
In step S2, the value of the road surface friction coefficient μ estimated in the previous sampling is set, and the process proceeds to step S13.

Then, in step S+3, in order to perform control smoothly, μ'-μ/(1+τ・S) (where μ' is the new integrated friction coefficient obtained by integrating μ, τ is the integral time constant, and S is The integrated friction coefficient μ' is calculated based on the Laplace operator) and the control is completed.

Therefore, in step S2, the outputs of the lateral force sensor (motion state detection means) 51, the steering angle sensor 52, and the rear wheel steering angle calculation unit 35 (steering state detection means 37) are received, and the detection of both detection means 37.53 is performed. A differential value calculation means 38 is configured to calculate the differential value of the value, and the steps Sa, Ss
and step S7. S8 constitutes a running state detection means 40 that determines whether the running state of the vehicle meets a predetermined condition. Further, in step S6, if the running state of the vehicle does not meet the predetermined condition, the output values of the vehicle speed sensor (vehicle speed detecting means) 53, the lateral force sensor (motion state detecting means) 51, and the steering state detecting means 37 are combined with the above-mentioned memory. In accordance with the memory contents of the means 31, a first friction coefficient calculation means 41 is configured to calculate the road surface friction coefficient μ based on the above equation (1) derived from the basic equation of motion of the vehicle, and in step S7 , when the running state of the vehicle is under a predetermined condition, the above-mentioned equation derived from the basic equation of motion of the vehicle is determined according to the output values of the vehicle speed sensor 53 and the differential value calculation means 38 and the stored contents of the storage means 31. (2)
A second friction coefficient calculation means 42 is configured to calculate the road surface friction coefficient μ based on the formula.

When the vehicle is turning, etc., the road surface friction coefficient calculating section 33 calculates the road surface based on equation (1) or (2) derived from the basic equation of motion based on the outputs of the sensors 51 to 52. 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, any one of 1 to 3 is selected for the steering ratio characteristic curve of FIG. 6, which is set in advance in the storage section 31. Next, the rear wheel steering angle calculation unit 35 calculates the steering ratio selected by the steering ratio selection unit 34, the front wheel steering angle δF detected by the steering angle sensor 52, and the vehicle speed sensor 5.
An appropriate rear wheel steering angle δ is determined according to the value of the vehicle speed V detected in step 3.
R is calculated. Further, the pulse signal forming section 36 outputs a pulse signal according to the calculated value, and the driving section MC drives the pulse motor 20 and the pump drive motor 30 according to the pulse signal, thereby driving the rear wheels 3. The steering angle is driven so that the steering angle of No. 3 becomes a predetermined steering angle δR.

Therefore, in the above embodiment, when the vehicle is turning, the road surface friction coefficient μ between the tires and the road surface is determined by the vehicle speed detected by each detection means, v1, the lateral acceleration at the center of gravity of the vehicle, a, Y, the front wheel steering angle, δF, and Since the calculation is based on equation (7) or (9) derived from the basic equation of motion with the rear wheel steering angle as a parameter, changes in the road surface friction coefficient μ according to the vehicle motion state can be calculated. can be detected promptly.

In addition, when the value of the variable V or the absolute value of each variable aY, δF, δR is small, the denominator on the right side approaches zero in the above equation (1) or (9), so the detection error of each detection means is Although the calculation error of the road surface friction coefficient μ increases,
If the driving condition is under such special predetermined conditions,
Proceeding to step S7, variable V and variables aY, δF
, and the differential value of δR as parameters (a or (to)
Since the road surface friction coefficient μ is calculated using the formula, the detection error of each detection means does not increase. Therefore, even when the value of the variable V and the absolute values of the variables av, δF, and δR are small, sufficiently reliable detection accuracy can be maintained.

Since the rear wheel steering angle is controlled according to the road surface friction coefficient μ calculated in this way, stable driving is achieved without any control delay and accurately, for example, when driving around turns on a snow-packed road. It is possible.

In particular, in the above embodiment, since the integration process is performed on the road surface friction coefficient μ calculated in step SIO, minute fluctuations in the road surface friction coefficient μ during transient response are smoothed out, resulting in more stable cornering. It has the legal effect that it can be carried out.

Note that the present invention is not limited to the case of four-wheel steering as in the above embodiment; for example, in the case of two-wheel steering, the road surface friction coefficient μ detected by the road surface friction coefficient detection device of the present invention may be used. If applied to a so-called anti-lock braking system used when driving on a road surface with a low friction coefficient, it will be possible to control the braking force in response to changes in the actual road surface friction coefficient μ during cornering, etc. It is possible to improve the control effect.

(Effects of the Invention) As explained above, according to the road surface friction coefficient detection device of the present invention, the vehicle speed, lateral acceleration, and steering of the front and rear wheels derived from the basic equation of motion of the vehicle when the vehicle is turning, etc. The road surface friction coefficient between the tires and the road surface is calculated based on a calculation formula that uses variables such as angle as parameters, and under special predetermined conditions where the denominator of the formula approaches zero, lateral acceleration, front and rear wheel steering, etc. The road surface friction coefficient is calculated based on an equation that uses the angle differential value as a parameter, so even when the value of the variable is small, the road surface friction coefficient can be accurately detected as it changes without compromising detection accuracy. This enables stable turning control of one vehicle.

[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. FIG. 5 is a flowchart showing the control in the road surface friction coefficient calculation section, and FIG. 6 is a diagram showing the steering ratio characteristics to be selected set in the storage section. 31... Storage section (storage means), 35... Rear wheel steering angle calculation section, 37... Steering state detection means, 38... Differential value calculation means, 40... Traveling state detection means, 41・・・・・・
...First friction coefficient calculation means, 42...Second friction coefficient calculation means, 51...Lateral force sensor (motion state detection means})
s2... Rudder angle sensor, 53... Vehicle speed sensor (vehicle speed detection means). Patent applicant Mazda Motor Corporation representative
Person Patent attorney front 1) Buddhist rituals 2 Figure 1 Figure 6

Claims (1)

[Claims] (1) A friction coefficient detection device that detects the friction coefficient between the vehicle tires and the road surface, which detects the lateral acceleration a_ of the vehicle center of gravity.
a motion state detection means for detecting a motion state of a vehicle such as Y;
A steering state detection means for detecting steering states such as steering angles δ_F and δ_R of the front and rear wheels, a vehicle speed detection means for detecting the speed V of the vehicle, a weight m of the vehicle, a distance a between the center of gravity of the vehicle and the front and rear wheel axes, b. 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 and the yaw moment of inertia I of the vehicle in a standard state, and outputs of the above-mentioned motion state detection means and steering state detection means; a differential value calculating means for calculating a differential value of the detected values of both the detecting means; a driving state detecting means for detecting when the driving state of the vehicle is under a special predetermined condition; and an output of the driving state detecting means. Therefore, when the running state of the vehicle is under normal conditions, the equation of motion is derived from the basic equation of motion of the vehicle according to the output values of the motion state detection means, steering state detection means, and vehicle speed detection means and the contents stored in the storage means. The formula μ=[V{m(a^2K_F+b^2K_R)+
I・K}・s−m・V^2(a・K_F−b・K_R)
]a_Y/2c・K_F・K_R{V(b・δ_F+a
・δ_R)・s+V^2(δ_F−δ_R)−c・a_
Y} (where s is the Laplace operator, K=K_F+K_R,
c=a+b), the first step calculates the road surface friction coefficient μ.
In response to the outputs of the friction coefficient calculating means and the running state detecting means, when the running state of the vehicle is under a special predetermined condition,
According to the output values of the vehicle speed detection means and the differential value calculation means and the contents stored in the storage means, the formula μ=[V{m(a^2K_F+b^2K_R)+I・K
}・s−m・V^2(a・K_F−b・K_R)]■＿
Y/2_c・K_F・K_R{V(b・■_F+a・■
_R)・s+V^2(■_F−■_R)−c・■_Y} A road surface friction coefficient detection device characterized by comprising: second friction coefficient calculation means for calculating a road surface friction coefficient μ based on the following equation.