JPH01101435A - Detecting device for road surface friction coefficient - Google Patents

Abstract

PURPOSE:To accurately perform detection by calculating the road surface friction coefficient between tires and a road surface from the motion equation of a vehicle in its turning, etc., according to differential values of variables such as lateral acceleration and steering angles of the front and rear wheels. CONSTITUTION:When the vehicle turns, a differential value arithmetic means 38 differentiates the lateral acceleration ay of at the vehicle gravity center detected by a motion state detecting means 51, the front and rear wheel steering angles deltaF and deltaR detected by a steering state detecting means 37, etc. Further, a friction coefficient arithmetic means 39 calculates the road surface friction coefficient mu between the tires and road surface corresponding to the dynamic characteristics of the vehicle from an equation [where c=a+b, K=KF+KR, (s) is a Laplacean, and KF and KR are the tire cornering power of the front and rear wheels] derived from the basic motion equation of the vehicle according to the output values of the differential value arithmetic means 38 and a vehicle speed detecting means 53 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 the actual coefficient of friction and uses the estimated coefficient of friction to control the steering angle of the rear wheels 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 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 m of the vehicle, the distances a, b, between the center of gravity of the vehicle and the front and rear wheel axes.
Tire cornering power KF of front and rear wheels in standard conditions.

A storage means 31 for storing vehicle stability factors such as KR and vehicle yaw moment of inertia receives the outputs of the motion state detection means 51 and steering state detection means 37, and detects the detected values of both detection means 37.53. 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 contents stored in the storage means 31. The friction coefficient calculating means 39 calculates the road surface friction coefficient μ based on the formula % (% formula %) (where c-a+b, KmKp +KR, s is a Laplace operator).

Here, the above equation (1) is 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-2Fp +2FR(3) ■, Qi2afFp-2b-FR(4 )FF-μmKF
(δF-β-a・γ/V') (5) FR-p-
Kq (δR-β+b・r/V) (6) However,
v(j+γ)−av (7) (where 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, PR, β.

By eliminating γ and Te, we get [m・IV's'+ 2μ・V (m (a'KF+
b'KR) +1・K)・s +4 c'KF-KR
・u''-2μ・m-V' (a-KF-b-KR)] a
v= 2 a-1-V” (KF4 F +Kn-6n)
・s + 4 u”V-KF-KR9C (b-δp+a
-δR)-s + 4 μ'V'Kp・KR-C・(δ
F-δR) (8) is obtained (S is the Laplace operator, K-KF+KR%cma+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 (m (a'Kp + b'KR) +
I-K)・s-m-V'Ca-Kr--b-KR)
] av/2cmKF-KR+V (b-δF+a
-δR)-8+V'(δF-δR) -c-a Y
l (1)' is obtained.

Then, by further multiplying the numerator and denominator of the above formula by S, u= [V (m (a'KF+b''KR)+ l-
K1・s-m-V"Ca-KF-b-KR)] MY
/2 C-KF, Kq (V Cb-jr-+a-a
t:z)・S+V'Cjt:6R)-c-my) In other words, the above equation (1) is obtained.

(Function) With the above configuration, in the present invention, when the vehicle is turning or the like, the lateral acceleration a 'I' of the vehicle center of gravity detected by the motion state detection means 51 s The longitudinal acceleration detected by the steering state detection means 37 According to the wheel steering angles δF, δR, etc., the differential value calculation means 38 calculates the differential values thereof, and further,
The friction coefficient calculation means 39 derives a coefficient from the basic equation of motion of the vehicle according to the output values of the differential value calculation means 38 and the vehicle speed detection means 53 and the stability factor of the vehicle stored in the storage means 31. Based on the above equation (1), the road surface friction coefficient μ between the tires and the road surface corresponding to the dynamic characteristics of the vehicle is calculated.

In that case, the differential values of each variable, ie, the lateral acceleration aY1 at the vehicle center of gravity, the front and rear wheel steering angles δF, δR, etc., are used as parameters for calculating the road surface friction coefficient μ, so even when the values of each variable are small, The road surface friction coefficient μ is accurately calculated without increasing calculation errors.

Therefore, it is possible to quickly 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. 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, where 2.2 is the left and right front wheels of the vehicle, and 3.3 is the left and right rear wheels. Reference numeral 5 denotes 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 member 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 at both ends, and a pinion to control the rotation of the handle 4. The main component is a steering gear mechanism 1G 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 1
0 causes the tie rods 8, 8 to move 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, and the front wheels 2. The front wheels are steered at a front wheel steering angle δF corresponding to a gear ratio of 2 (-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. 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.

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 19.1g 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 23 of the power cylinder 23 depending on the rotational direction of the pinion shaft 16.
This controls the supply of hydraulic 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 hydraulic return passage 28, each hydraulic passage 24, 25, and each hydraulic chamber 23b, 23C is switched, and the hydraulic chamber 23b, 23C of the power cylinder 23 is switched. The movement of the rack shaft 15 in the vehicle width direction is aided by supplying and discharging pressurized oil to and from the rear wheels 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 that detects the front wheel steering angle δF based on the predetermined front gear ratio 2 is a vehicle speed sensor serving as a vehicle speed detecting means that detects the 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 of the vehicle m1, the distance a between the center of gravity of the vehicle and the front and rear wheel axles,
b. 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 I, 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 calculating section 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 calculating section 33; A pulse signal forming section 36 receives the output of the steering angle calculating section 35 and forms a pulse signal for driving the pulse motor 20 and the pump drive motor 3G, and a pulse signal obtained from the pulse signal forming section 36 is processed. It is formed of a pulse motor 20 and a drive unit MC that drives the pump drive 30 based on the pump drive unit. Here, the steering angle sensor 5
2 and the rear wheel steering angle calculation unit 35, the front and rear wheel steering angles δF,
A steering state detection means 37 is configured to detect a steering state such as δR.

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 the forces acting on the tires when the vehicle turns, the basic equations of motion (3) to (7) m-aY-2FF+2F shown below are obtained.
R 1, Chi2a-FE-2b-FR FF-u・KF CδF-β-a・γ/v) FR-μ・
KR(δR-β+b-7/V) However, ■(/j+γ
) -aY (where FF and PR 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.

γ, by eliminating the children, we get [m-1-V"s"+ 2 B-V (m (a'Kp
+ b'KR) +1-Kl ・s + 4 c”K
p-KR・tt'-2B-m-V" (a-Kp-b
-Kq)]av- 2μm1-V” CKt-6F + KR・6 R)-
8+ 4 B"V・KF-KR-c (b-δF+a-
δR)-s + 4 μ'V'KF・KR-C(δF-
δR) In other words, the above equation (8) is obtained (where S is the Laplace operator, K-Kp +kRs 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 by setting it to zero and dividing both sides of the above equation by μ, we get u= [V (m (a”KF+btKR) + I・
K1-5-m-V'Ca-KF-b-KR)] aY
/2 c-Kr:KR(V (b-δp+a-δR)-
S +V' (δF-δR)-c-avl In other words, the above equation (1)' is obtained.

Then, by further multiplying the numerator and denominator of the above formula by S, u = [V (m (a'KF + b''KR) +
I-K)-s-m-V"(a-KF-b-KR)]
:aY/2cmKFKR(V (b-jp +a-6
R>・s+V (15F6R)-c-My) In other words, the above equation (1) is obtained.

That is, the road surface friction coefficient μ is the inertial mass of the vehicle, m1, the distance between the vehicle center of gravity and the front wheel axle, a1, the distance between the vehicle center of gravity and the rear wheel axle, and the cornering force K of the front wheels 2 and rear wheels 3 in the standard state. Stability factors such as Rs yaw moment of inertia and lateral acceleration a' at the vehicle center of gravity
+'s It is determined from the differential values of variables such as the front wheel steering angle δF and the rear wheel steering angle δR, as well as values such as the vehicle speed V.

In addition, especially in the case where control is performed to make β zero with four-wheel steering, if β-〇 is used in the above equations (3) to (7), the simpler formula % formula % (Furthermore, the above equation By multiplying the numerator and 2 denominators on the right side by S, μmm-Av/2 (Kr-jp +KR-jR-(A
y/V”) Ca-KF-b-Kq) )
(2) is obtained. In this embodiment, the switch 32 switches between equation (1) and equation (2) as the basic equation of motion for calculating the road surface friction coefficient μ, depending on the type of vehicle control.

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, the second steering ratio characteristic is basically 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 curve r
The phase of the steering state is reversed as shown in 1. - When the value of vehicle speed Vl is lower than the same vehicle speed v2 of the above standard characteristic, and conversely, when the road surface friction coefficient μ is relatively large, the phase is reversed as shown by curve r3 in the figure. The vehicle speed value ■3 is set on the higher side.

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 front wheel steering angle δF and the rear wheel steering angle δR, and in step S2, a'/+ δF, δR are calculated from these variables.
Calculate the differential value of . Next, in steps 83 to Ss, it is determined whether the value of the vehicle speed V, the front wheel steering angle δF, the rear wheel steering angle δ, and the absolute value of the differential value of the lateral acceleration aY are greater than or equal to a predetermined set value. If YES, the process proceeds in order, and in step S6 the road surface friction coefficient μ is calculated based on the above formula (1) or ('2J), and then the process proceeds to step S8.On the other hand, if any of the determinations in steps 83 to SS No,
In other words, the value of vehicle speed V, front wheel steering angle δF, rear wheel steering angle δR,
, if the absolute value of the differential value of the lateral acceleration av at the vehicle center of gravity is less than the respective set value, there is a risk that the denominator on the right side of equation (1) or (2) above will approach zero and the error will increase. , without calculating the road surface friction coefficient μ, the value of the road surface friction coefficient μ calculated during the previous sampling is set in step S7, and the process proceeds to step S8. In this step S8, it is determined whether the road surface friction coefficient μ is negative or not, and if the determination is YES (μ is O), it is unreasonable considering the characteristics of the road surface friction coefficient μ, so in step S9 it is set to μ−〇. On the other hand, if the determination in step S8 is No (μ≧0), the process directly proceeds to step 310.

Then, in step S1, 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 Laplace operator), the road surface friction coefficient μ is integrated, 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 outputs of both the detection means 37.53 are A differential value calculation means 38 is configured to calculate a differential value of the detected value, and in step S6, the output values of the vehicle speed sensor (vehicle speed detection means) 53 and the differential value calculation means 38 and the output values of the storage section (storage means) 31 are A friction coefficient calculation means 39 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 according to the stored contents.

When the vehicle is turning, etc., the friction coefficient calculation unit 33 calculates the road surface friction based on equation (1) or (2) derived from the basic equation of motion in response to the outputs of the sensors 51 to 52. When the coefficient μ is calculated, the steering ratio characteristic selection unit 34 selects a coefficient according to the value of the road surface friction coefficient μ (actually, the integrated friction coefficient μ′) calculated by the friction coefficient calculation unit 33. , any one of 1 to 3 is selected as the steering ratio characteristic curve of FIG.

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 front wheel steering angle δF detected by the vehicle speed sensor 53. An appropriate rear wheel steering angle δR is calculated according to the value of the vehicle 3v. 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. The wheels 3, 3 are driven so that the steering angle 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 lateral acceleration a'/s of the vehicle center of gravity detected by each detection means, the front wheel steering angle δF, and the rear wheel steering angle. Since the calculation is based on equation (1) or (2) derived from the basic equation of motion depending on the differential value of the angle δR, changes in the road surface friction coefficient μ depending on the state of motion of the vehicle can be quickly detected. can be detected. In addition,
Vehicle lateral force av.

The road surface friction coefficient μ can be detected accurately even when the front wheel steering angle δF and the rear wheel steering angle δR are smaller than predetermined values. That is, as a formula for calculating the road surface friction coefficient μ, each of the above variables a Y + δF is used as shown in formulas (1)' and (2)'.

In the case where the value of δR is used as is, each variable aY, δ
When the absolute values of F and δR are small, the denominator on the right side of equation (1)' or (2)' approaches zero, so the calculation error of the road surface friction coefficient μ due to the detection error of each detection means increases. Therefore, we stopped calculating the road surface friction coefficient μ, and
It is necessary to use the value of μ found in the previous control. In contrast, in the above embodiment, even in such a case, the denominator on the right side of equation (1) or (2) does not approach zero, and sufficiently reliable detection accuracy can be maintained. Since the rear wheel steering angle is controlled according to the coefficient of friction μ calculated in this way, stable driving can be performed without causing control delays, for example, when driving around turns on a snow-packed road. It is.

In addition, in particular, in the above embodiment, since the integration process of the road surface friction coefficient μ calculated in step SIQ is performed, minute fluctuations in the road surface friction coefficient μ during transient response are smoothed out, and more stable cornering is achieved. 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. Therefore, if applied to a so-called anti-lock brake system used when driving on a road surface with a low coefficient of friction, the actual road surface friction coefficient μ can be reduced during cornering, etc.
Brake force can be controlled in response to changes in
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 differential of variables such as lateral acceleration and steering angle of front and rear wheels is calculated based on the equation of motion of the vehicle when the vehicle is turning. The road surface friction coefficient between the tires and the road surface is calculated according to the value, 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 the 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 unit (storage means), 35... Rear wheel steering angle calculation unit, 37... Steering state detection means, 38... Differential value calculation means, 39... 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 Patent Attorney Front 1) Hiro 2 Figure 1 Figure 6 Figure 1 tj F Itm Figure 5

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;
Steering state detection means for detecting steering states such as front and rear wheel steering angles δ_F and δ_R, vehicle speed detection means for detecting vehicle speed V, vehicle weight m, and distances a and b between the center of gravity of the vehicle and the front and rear wheel axes. , 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 receiving outputs from the motion state detection means and the steering state detection means. , a differential value calculation means for calculating a differential value of the detected values of both the detection means, and a basic motion of the vehicle according to the output values of the vehicle speed detection means and the differential value calculation means and the memory contents of the storage means. The formula derived from the equation μ=[V{m(a^2K_F+b^2K_R)+I・K
}・s−m・V^2(a・K_F−b・K_R)]■＿
Y/2c・K_F・K_R{V(b・■＿F+a・■＿
Friction coefficient calculating means for calculating the road surface friction coefficient μ based on R)・s+V^2(■_F−■_R)−c・■_Y} (where c=a+b, K=K_F+K_R, s is the Laplace operator) A road surface friction coefficient detection device comprising: