JPH11321604A - Calculating method of body slip angle in vehicle behavior control and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with the direct detection of road friction coefficient and body slip angle and to improve the stability and responsiveness of vehicle behavior control by determining a virtual body slip angle and road friction coefficient by regressive calculation within a system forming a closed loop. SOLUTION: During the traveling of a vehicle, the tire slip angle α is arithmetically calculated 3, 4 from yaw rate γ, vehicle speed V, body slip angle β as initial value (or previously calculated value) and wheel steering angle δ. The cornering force Y is arithmetically calculated 5, 6 from slip angle α, and virtual body slip angle βe is arithmetically calculated 7 from each data Y, V, γ. The road surface friction coefficient is estimated from the relation of the cornering force Ye calculated from the yaw rate γ and side acceleration GY with the body slip angle βD calculated from each data γ, GY, V by a μ estimating device 10, and the virtual body slip angle βe is fed back to arithmetically calculate the slip angle α.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for calculating a vehicle body slip angle in vehicle behavior control for assisting a driver's driving operation so as to obtain higher responsiveness and stability of the vehicle. Things.

[0002]

2. Description of the Related Art There have been proposed various techniques for improving the turning performance of a vehicle by individually controlling a braking force and a driving force by front and rear or right and left wheels. The system detects a motion state amount of the vehicle body such as a yaw rate and feeds back this to control so that a desired vehicle behavior can be obtained. However,
As long as the vehicle is in contact with the ground via the tires, the vehicle's mobility is governed by the tire's mechanical properties.Especially in the area where the cornering force is saturated, the desired turning performance is based only on the vehicle state of motion. It is very difficult to control the vehicle.

[0003] The present applicant has proposed a vehicle behavior control method and a vehicle behavior control method capable of setting the responsiveness and stability of a vehicle to a desirable state even under running conditions in which the dynamic characteristics of the tire are out of the linear region. To Japanese Patent Application No. 8-1742.
No. 17 (see JP-A-10-965). This technology uses a sliding mode control (see Sliding Mode Control, published by Corona) to calculate a yawing moment that shows a favorable response to steering involving braking (or driving) even when the mechanical characteristics of the tire are in a nonlinear region. It is intended to control and generate the longitudinal force, and from the parameters of cornering force, yaw rate, and vehicle body slip angle of the front and rear wheels,
The yawing moment for realizing a preferable response is obtained by the following equation (1), and the longitudinal force of the tire to be controlled, that is, the left / right ratio of the braking force (or driving force) is determined by the equation (2). By individually controlling the longitudinal force of the left and right tires by known means (braking force control: see JP-A-7-69190, driving force control: see JP-A-7-17277), the dynamic characteristics of the tire are linear. It is intended to enhance the responsiveness and stability of the vehicle under running conditions outside the region.

[0004] _{Mz = - (L F Y F} -L R Y R) + (I / mV) · {(dY F / dt) + (dY R / dt)} + [kca / (1 + ca)] · I · _{[(Y F + Y R) /} mV-γ ] + I · (dβ / dt) · [(k + c) / (1 + ca) ] + I beta [kc / (1 + ca)] ... (1) where, Mz: driving force or braking force around the center of gravity of the yawing moment generated by, L _F: front axle - distance between centers of gravity, L _R: rear axle - distance between centers of gravity, Y _F: cornering force (lateral sum) of the front wheels, Y _R: rear wheel cornering force ( Left and right sum), m: mass of the center of gravity of the vehicle, V: vehicle speed,
Let I: yawing moment of inertia, c, a, k: constants appropriately determined, and γ: yaw rate (see FIG. 4).

[0005] _{Mz = (X R -X L)} L TR ... (2) However, L _TR: tread dimensions, X _R: before and after the force applied to the right tire, X _L: longitudinal force to be applied to the left tire

[0006]

By the way, in the above-mentioned prior art algorithm, it was assumed that at least the values of the friction coefficient μ between the tire and the road surface and the vehicle body slip angle β were known. However, μ and β
Has not been put into practical use to the extent that it can be used for mass-produced vehicles.Currently, the former is estimated based on the rotational speed difference between the drive wheel and the driven wheel, and the latter is Generally, the estimation is performed based on a vehicle state quantity that can be relatively easily detected, such as a yaw rate or a lateral acceleration. That is, according to the above prior art, the control accuracy is greatly affected by the accuracy of the estimated value that can be obtained only indirectly.

[0007] The present invention has been devised in order to solve such problems of the prior art, and its main objects are as follows.
It is an object of the present invention to provide a method and an apparatus for calculating a vehicle body slip angle in vehicle behavior control which can be controlled with practically sufficient accuracy without requiring direct detection values of a friction coefficient between a tire and a road surface and a vehicle body slip angle.

[0008]

According to the present invention, a tire slip angle is calculated from a yaw rate γ, a vehicle speed V, an initial value or a vehicle body slip angle β and a wheel steering angle δ as previously calculated values. α, a cornering force Y is calculated from at least the tire slip angle α based on the tire dynamic model, a virtual vehicle body slip angle β _e is calculated from the cornering force Y, the vehicle speed V, and the yaw rate γ, and a yaw rate and a lateral acceleration G are calculated. _Y
A cornering force Y _e calculated from a, based on the relationship between tire slip angle alpha _e calculated based on the vehicle body slip angle beta _D calculated from the yaw rate and lateral acceleration and vehicle speed, and the tire used in the equation of the tire dynamic model The friction coefficient μ between the road surfaces is estimated, and the virtual vehicle body slip angle β _e is fed back to calculate the tire slip angle α.

According to this, in the system forming the closed loop, both the virtual vehicle body slip angle value and the friction coefficient value between the tire and the road surface are regressively calculated, so that the friction coefficient between the tire and the road surface and the vehicle body slip angle are calculated. As a result, the stability and responsiveness of the vehicle behavior control can be ensured without directly obtaining the detected value.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a control algorithm of the present invention will be described in detail with reference to a flowchart shown in FIG. 1 and a block diagram shown in FIG.

First, the steering angle θ _{SW of the} steering wheel
There is converted is transmitted to the front-wheel steering device 1 and the rear wheel steering device 2 to the front wheel steering angle [delta] _F and the rear wheel steering angle [delta] _R. At this time, various vehicle state quantities (yaw rate γ, vehicle speed V, wheel steering angle δ,
The lateral acceleration G _Y ) is detected (step 1).

Next, based on the steering angle information δ and the vehicle speed information V, the tire slip angle α is obtained for the front and rear wheels by the following equation built in the tire slip angle calculators 3 and 4 (step 2).

Α _F = β _e + (L _F / V) γ-δ _F (front wheel) (3) α _R = β _e- (L _R / V) γ-δ _R (rear wheel) (4) Here, α _F : front wheel slip angle, α _R : rear wheel slip angle, β _e : virtual vehicle body slip angle, δ _F : front wheel steering angle, δ _R : rear wheel steering angle. Here, the initial values of the tire slip angle α and the virtual vehicle body slip angle β _e are both reset to 0 when the steering angle δ = 0 and the yaw rate γ = 0.

Next, the cornering force Y is determined for the front and rear wheels by substituting the tire slip angle α into Equation (5) of the tire dynamic model built in the cornering force calculators 5 and 6 (step 3).

[0015]

(Equation 1) … (5)

Here, μ: coefficient of friction between tire and road surface,
C: cornering power, W: ground load, X: longitudinal force,
And

Here, μ is a value updated with an estimated value obtained by successively calculating with a μ estimator 10 described later, with an appropriate value near 1 as an initial value, and C is preset as a function of μ and W. W is a value obtained from a corrected map, W is a value obtained by correcting a design value by longitudinal and lateral acceleration or a value obtained from an output of a load cell provided in a suspension device, and X is a value obtained by estimating from an acceleration (deceleration). , Or a value obtained from the braking fluid pressure or the engine output. The cornering force Y may be calculated without using the longitudinal force X and the contact load W as variables. In this case, although the estimation accuracy of the virtual vehicle body slip angle β _e decreases, the stability of the vehicle behavior control does not significantly decrease.

[0018] Then obtain the virtual vehicle body slip angle beta _e in virtual vehicle body slip angle computing unit 7 on the basis of the front wheel cornering force Y _F and the rear wheel cornering force Y _R calculated as described above (Step 4). Here, as shown in the following equation, first, a differential value is obtained, and this is integrated to obtain a virtual vehicle body slip angle β _e .

Dβ _e / dt = (Y _F + Y _R ) / mV-γ (6) β _e = ∫ ｛(Y _F + Y _R ) / mV-γ｝ dt (7)

By feeding back the virtual vehicle body slip angle β _e to the tire slip angle calculators 3 and 4, a practically sufficient pseudo vehicle body slip angle value can be obtained as a result. By inputting to the sliding mode calculator 8 defined by the equation (1), a yawing moment Mz serving as a basis of control for converging the vehicle body slip angle to zero is obtained (step 5). Determining the longitudinal force X _R · X _L of the right and left tires from this value (step 6), controls the vehicle 9.

On the other hand, cornering force calculators 5 and 6
Although the value of the coefficient of friction μ between the tire and the road surface used in the equation (5) of the tire dynamic model built in the tire does not impair the practical stability even if an appropriate fixed value near 1 is maintained, It has been confirmed that the higher the precision of the μ value is, the more advantageous the response is. Therefore, in the present invention, the estimated μ value is calculated based on the detected values of the vehicle speed V, the lateral acceleration G _Y, and the yaw rate γ, which are relatively easy to detect directly, and the estimated μ value is used in the processing of step 3. . Hereinafter, the operation of the μ estimator 10 for calculating the estimated μ value will be described with reference to FIGS. 3 and 5.

Here, from equation (5) of the tire dynamic model,
Vehicle body using cornering force Y calculated from
Slip angle β_eIs calculated in step 4
And is continuously executed, this β_eIs the absolute value of
Determine when the value falls below a certain small value close to 0
(Step 11). And this β_eThe absolute value of is close to 0
If the value falls below a certain small value, the lateral acceleration G_YYou
The detected value of yaw rate γ and the vehicle speed V are input to the integrator 11.
And the vehicle body slip angle β _DAsk for
(Step 12).

Β _D = ∫ ｛(G _Y / V) −γ｝ dt, T = ∫dt (8)

Here, when the absolute value of β _e becomes equal to or less than a certain small value close to 0, the calculated value of the estimated vehicle body slip angle β _D is reset, the integral calculation is started, and the steering angle change rate is calculated. When the absolute value is equal to or less than the predetermined value, β _D is calculated for an appropriate time (T = 2 to 3 seconds). By repeating this, it is possible to eliminate the inconvenience of accumulation of integration errors.

The estimated vehicle body slip angle β _D obtained in this way is used as an estimated tire slip angle calculator 12.
And estimated tire slip angle α _e by the following equation
For the front and rear wheels (step 13).

The _{α eF = β D + (L} F / V) γ-δ F ... (9-1) α eR = β D - (L R / V) γ-δ R ... (9-2)

On the other hand, only during the calculation of the estimated vehicle body slip angle β _D , the lateral acceleration G _Y and the yaw rate γ corresponding to that time are input to the estimated cornering force calculator 13, and the estimated cornering force Y _e is calculated by using the equation (Step 14).

Y_eF= 1 / 2L [mL_R・ G_Y+ I (dγ / dt)] ≒ m_F・ G_YF ... (10-1) Y_eR= 1 / 2L [mL_F・ G_Y+ I (dγ / dt)] ≒ m_R・ G_YR ... (10-2) where m_F: Mass of front axle, m_R: Mass of rear axle, G_YF:
Lateral acceleration on the front axle, G _YR: Lateral acceleration on rear axle, L:
Wheelbase (= L_R+ L_F)

The estimated cornering forces Y _eF and Y _eR of the front and rear wheels thus obtained and the estimated tire slip angles α _eF and α _eR of the front and rear wheels are input to the μ calculator 16. Here, the relation data between the estimated cornering force Y _e and the estimated tire slip angle α _e is accumulated (step 15), and if it is determined that the data is sufficient (for example, including a slip angle of 5 degrees or more), the tire The relationship between the slip angle α, the cornering force Y, and the friction coefficient μ between the tire and the road surface is obtained in advance through experiments or the like, and stored in the form of a map, and the estimated tire slip angle α _e is stored in the tire characteristic model 14 of the vehicle. Input,
μ gradually changed, for example, up to about 0 to 1.2 obtained for the left and right wheels virtual cornering force Y _d (step 16).

The virtual cornering force Y of the left and right wheels
_dF , Y _dR and the estimated cornering forces Y _eF , Y _{eR of} the left and right wheels obtained from the above relationship data are input to the comparator 15,
The μ value that minimizes the root mean square of these errors is determined (step 17), and the calculation of step 3 is performed using the optimum μ value (step 18).

The above processing is executed successively (with an appropriate cycle) during steady running without acceleration / deceleration, and the μ value used in the calculation in step 3 is updated. Can be dealt with.

The above equations (6) and (7) represent the vehicle longitudinal speed V _x
There sufficiently larger than the vehicle side slip velocity V _y, and when the change in the vehicle body longitudinal speed V _x is relatively small, but is intended to provide a vehicle body slip angle with high precision, extreme driving conditions such conditions is not satisfied In such a case, the following strict formula may be used. dV _y / dt = (Y _F + Y _R ) / m−γV _x (11) V _y = ∫ ｛[(Y _F + Y _R ) / m] −γV _x ｝ dt (12) β _e = tan ⁻¹ _{(V y / V x) ...} (13) in this case, usually, the vehicle speed since the measure by a vehicle speed sensor for detecting a rotational speed of the wheel is generally, as the vehicle body longitudinal speed V _x, of the vehicle speed sensor It is better to use the output as it is. Further, the formula (9-1), also in the vehicle speed V in (9-2), it was replaced with the vehicle longitudinal speed V _x accuracy becomes higher. FIG. 6 is a block diagram of a control system of a four-wheel-steering vehicle when such a more strict equation for estimating the vehicle body slip angle is used.

The case where the present invention is applied to a four-wheel steering vehicle has been described above, but the present invention can also be applied to a vehicle that steers only front wheels. In that case, the term relating to the rear wheel steering angle simply disappears, that is, the other components can be handled in exactly the same manner simply by setting the rear wheel steering angle to 0 (δ _R = 0).

[0034]

As described above, according to the present invention, practically sufficient responsiveness and stability can be obtained in the vehicle behavior control even if the value of the friction coefficient between the tire and the road surface is not determined in advance with high accuracy. Control can be performed, so that the system configuration can be simplified, and the manufacturing cost can be reduced. Therefore, a great effect can be obtained in promoting the practical use of a higher-performance driving operation support device.

[Brief description of the drawings]

FIG. 1 is a basic flowchart of control according to the present invention.

FIG. 2 is a block diagram of a control system of a four-wheel steering vehicle according to the present invention.

FIG. 3 is an internal block diagram of a μ estimator according to the present invention.

FIG. 4 is an explanatory diagram showing a plane motion of a vehicle.

FIG. 5 is a flowchart relating to estimation μ calculation.

FIG. 6 is a diagram similar to FIG. 2 when a more strict equation for estimating a vehicle body slip angle is used.

[Explanation of symbols]

 1.2 Steering device 3.4 Tire slip angle calculator 5.6 Cornering force calculator 7 Body slip angle calculator 8 Sliding mode calculator 9 Vehicle 10 μ estimator 11 Integrator 12 Estimated tire slip angle calculator 13 Estimated cornering Force computing unit 14 Tire characteristic model 15 Comparator 16 μ computing unit

 ──────────────────────────────────────────────────の Continuing from the front page (72) Inventor Koji Shibata 1-4-1 Chuo, Wako-shi, Saitama Pref.

Claims (2)

[Claims] 1. A process for calculating a tire slip angle α from a yaw rate γ, a vehicle speed V, an initial value or a vehicle body slip angle β and a wheel steering angle δ as previously calculated values, and a tire dynamic model from at least the tire slip angle α. Calculating the cornering force Y based on the following formula; calculating the virtual vehicle body slip angle β _e from the cornering force Y, the vehicle speed V and the yaw rate γ; and calculating the cornering force Y _e from the yaw rate and the lateral acceleration G _Y. If, based on the relationship between tire slip angle alpha _e calculated based on the vehicle body slip angle beta _D calculated from the yaw rate and lateral acceleration and the vehicle speed, the friction coefficient between the tire and the road surface used for expression of the tire dynamic model μ
And returning the virtual vehicle body slip angle β _e to the tire slip angle α calculation step, and calculating the vehicle body slip angle in vehicle behavior control. 2. A tire slip angle α based on a yaw rate γ, a vehicle speed V, a vehicle body slip angle β, and a wheel steering angle δ.
A computing unit that computes a cornering force Y based on at least the tire slip angle α based on a tire dynamic model; and computes a virtual vehicle body slip angle β _e from the cornering force Y, the vehicle speed V, and the yaw rate γ. a calculator for, the cornering force Y _e calculated from the yaw rate and the lateral acceleration G _Y, the relationship between tire slip angle alpha _e calculated based on the vehicle body slip angle beta _D calculated from the yaw rate and lateral acceleration and the vehicle speed Based on the friction coefficient μ between the tire and the road surface used in the equation of the tire dynamic model,
And an estimator for estimating the vehicle body slip angle βe in the vehicle behavior control, wherein the virtual vehicle body slip angle β _e is fed back to the tire slip angle α calculator.