JP3102104B2 - Vehicle steering angle control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering angle control device for a vehicle, and more particularly, to a control device for preventing a steering characteristic from being oversteered when the vehicle turns.

[0002]

2. Description of the Related Art As a steering angle control device for a vehicle, there is a steering angle control method as described in, for example, Transactions of the Society of Instrument and Control Engineers, Vol. 23, No. 8, "New control method for four-wheel steering vehicle".
This is a control method for optimizing the motion of the vehicle by rear wheel steering angle control, and using a reference model for setting a desired yaw rate response and the like to the steering angle input and the motion characteristics of the own vehicle, the rear wheel steering is controlled. This is a feed-forward type model adaptation or tracking control method for setting an angle.

[0003] In a four-wheel steering system, by applying the above control method, a response very close to the response of the reference model can be obtained even in a real vehicle, and the steering stability of the vehicle can be remarkably improved.

[0004]

The above technique is based on 2WS.
Compared to cars, it can contribute to adding new vehicle performance to maneuverability and stability.However, in the following aspects, it is difficult to fully demonstrate the performance, and therefore There is room for improvement.

In other words, basically, the designer is arbitrarily given the characteristics of the reference model, and therefore, for example, the steady-state gain of the reference model, which is the target of movement, is less than that of the base vehicle at low speed. It is possible to freely set the driver's intention, such as turning by inputting the steering angle, and lowering the gain at high speed to increase stability. In some cases, when the yaw rate gain is increased on the low speed side, the steering characteristic may be oversteered by performing the steering angle control. Depending on the degree of such over-steering, even if the steering wheel steering angle is constant, the steering characteristics are affected, and when the steering characteristics change during the execution of the control, it becomes difficult to drive the vehicle. If the control can be performed, it is possible to make the control more effective.

[0006] The object of the present invention is therefore to improve the above,
By providing a vehicle steering angle control device that can prevent the steering characteristic of the vehicle from changing stably even by the steering angle control, and thereby exhibit more effective control as a stable vehicle characteristic. is there.

[0007]

According to the present invention, there is provided the following vehicle steering angle control device. A steering device including a steering angle control mechanism capable of controlling at least one of a front wheel and a rear wheel, and a drive unit that drives the mechanism according to a steering angle control input such that an actual steering angle matches a control input value. Detecting means for detecting a steering angle of a steering wheel or an amount corresponding thereto, a detecting means for detecting a vehicle speed or an amount corresponding thereto, and yaw and yaw of the vehicle using outputs from these detecting means. Vehicle motion target value setting means for setting a steady-state characteristic and a transient response characteristic with respect to a steering angle input for at least one controlled variable relating to the lateral plane motion; and a motion target value set by the vehicle motion target value setting means. Steering angle calculating means for calculating a steering angle control input value of the controlled wheel so that the vehicle response of the steering wheel coincides with or follows the steering response, and instructing the steering device. A location, said vehicle motion target value setting means uses the reference model to calculate the steady-state gain target value according to the vehicle speed,
A steady gain target value setting means for setting the calculated value as a steady gain target value of the controlled variable with respect to the steering angle input; comparing the steady gain target value with a steady gain limit value set according to the vehicle speed; As a result, there is provided a steady-state gain limiter for setting a smaller one as a steady-state gain of a steady-state characteristic with respect to a steering angle input for the controlled variable set by the vehicle motion target value setting means, and turning the controlled object vehicle. A steering angle control device for a vehicle, wherein a steering characteristic of a vehicle to be controlled is prevented from changing to an oversteer characteristic side in response to a change in vehicle speed during the vehicle.

[0008]

According to the present invention, the steering apparatus steers at least one of the front wheel and the rear wheel based on a steering angle control input, and the vehicle motion target value setting means detects the steering angle or an amount corresponding thereto. Steady-state characteristics and transient characteristics with respect to a steering angle input are set for at least one controlled variable related to the yaw / lateral plane motion of the vehicle by using an output from the detecting unit and a detecting unit that detects a vehicle speed or an amount corresponding thereto. Here, regarding the setting of the steady-state characteristics, the vehicle motion target value setting means calculates a steady-state gain target value corresponding to the vehicle speed using a reference model, and uses the calculated value as a controlled variable with respect to a steering angle input. A steady gain target value setting means for setting as a steady gain target value, and comparing the steady gain target value with a steady gain limit value set according to the vehicle speed. As a result, the vehicle speed during turning of the controlled vehicle has a steady-state gain limiter having a smaller one as a steady-state gain of a steady characteristic with respect to the steering angle input for the controlled variable set by the vehicle motion target value setting means. The steering characteristic of the control target vehicle is prevented from changing to the oversteer characteristic side in response to the change of the steering angle, and the steering angle calculating means is configured to set the actual vehicle response to the movement target value set by the vehicle movement target value setting means. The steering angle control input value of the wheel to be controlled is calculated so that the control values coincide or follow, and a command is issued to the steering device.

Thus, in the steady state of the steering angle control in which the steering wheel steering angle is fixed at the time of turning the vehicle,
When the vehicle speed is changed, it is possible to prevent the steering characteristics of the vehicle from becoming oversteer characteristics by performing steering angle control in a part of the vehicle speed region, and therefore, compared to the case without the limiter. It is possible to appropriately prevent the steer characteristics from wandering, so that the driver can obtain stable vehicle characteristics without feeling uneasy. In addition, it is possible to realize the above while securing the degree of freedom of the designer. Here, regarding the setting of the steady-state characteristics in the vehicle motion target value setting means, using a reference model, a steady-state according to the vehicle speed is used. As a result of comparison between the steady gain target value obtained by calculating the gain target value on the side of the steady gain target value setting means and the steady gain limit value set according to the vehicle speed on the limiter side, the smaller one is determined as the vehicle motion. The final steady gain of the steady-state characteristic with respect to the steering angle input for the controlled variable set by the target value setting means, and the steady-state gain is limited. Since the change to the oversteer characteristic side can be prevented, a response very close to the response of the reference model can be obtained even in the actual vehicle. The advantages can be exploited in a way that maximizes this without sacrificing as much as possible.Therefore, for the reference model, the designer can arbitrarily set the stationary gain of the stationary characteristic of the reference model. On the other hand, even if the steady-state gain of the reference model is set arbitrarily as described above, it is possible to prevent the change to the oversteer characteristic side by limiting the steady-state gain for a part of the vehicle speed range as described above. Therefore, it is possible to achieve both of these while securing the degree of freedom in designing the vehicle motion target of the designer. In this case, according to the preferred embodiment of the present invention, for example, as described with reference to a comparative example of FIG. 6 described later, a part of the vehicle speed region corresponding to the hatched portion of FIG. For example, in the preferred embodiment, V = 6 m / s ~
12m / s), while preventing steady-state gain by limiting the steady-state gain, and achieving a vehicle speed region portion (for example, a vehicle speed region above the vehicle speed region exceeding the vehicle speed region portion)
For the preferred embodiment, V ≧ 12 m / s), the above-mentioned advantage of the original steering angle control using the reference model can be maintained, and the steady-state gain target value of the reference model is set so that the vehicle can be turned with a small steering angle input. In the set vehicle speed range, the steady-state gain is increased according to the characteristics of the reference model, and the steady-state gain target value of the reference model is lowered to increase stability. The desired steady-state characteristic based on the given reference model can be realized in the control target vehicle, and the steady-state gain limit is set in advance by the steady-state gain limiter according to the vehicle speed as a result of the comparison. The steady gain limit value is determined for the vehicle speed region corresponding to the vehicle speed region where the steady gain of the steady characteristic set by the vehicle motion target value setting means is set. This is a mode of limiting the gain, and when the vehicle speed is changed in the turning state, even when the steady gain is limited in the vehicle speed region, the steady gain is not increased in the vehicle speed region portion that is equal to or higher than the vehicle speed exceeding the vehicle speed region portion. The configuration is not limited by the limit value, and the steady gain target value calculated by the steady gain target value setting means using the reference model is set as the steady gain of the steady characteristic set by the vehicle motion target value setting means. As a result, the present invention can be suitably implemented, and can realize the above.
Further, according to the present invention, the steady-state gain limiter also controls the steering angle of the controlled wheel with respect to the steady-state characteristic of the reference model to be given, so that the steering angle input is kept constant during turning of the controlled vehicle to reduce the vehicle speed. The present invention is preferably configured such that a steady gain limit value according to the vehicle speed is set so as to limit the steady gain so that the turning radius of the controlled wheel does not become smaller than the turning radius at the start of the steering angle control when the wheel speed changes. In the same way, it is possible to realize the above. When the vehicle speed is lower than a first predetermined vehicle speed in a low vehicle speed range (for example, V = 6 m / s in the preferred embodiment), a non-control region in which steering angle control of a wheel to be controlled is not performed is set. A vehicle speed region equal to or higher than the first predetermined vehicle speed is set as a steering angle control target region related to the vehicle speed so as to start the steering angle control from the vehicle speed, and the first predetermined vehicle speed value in the steering angle control target region is set. And a second predetermined vehicle speed that is greater than the first predetermined vehicle speed value (for example, V = V in the preferred embodiment).
In the steering angle control in the vehicle speed region between the values of 12 m / s), the steering angle (for example, the rear wheel steering angle δ _{R in the} preferred embodiment) that is actually controlled of the controlled wheel in response to the change in the vehicle speed is changed. Quantity 0
And the steering angle of the wheel to be controlled is a target value for obtaining the steady-state characteristic of the reference model given by the steady-state gain target value setting means at the second predetermined vehicle speed. The present invention can be preferably implemented as a configuration that is equal to the amount (for example, the rear wheel steering angle amount δ _RC in the preferred embodiment), and similarly, the above can be realized. Further, the steady-state gain target value setting by the steady-state gain target value setting means is more effective in the low-speed range than in the base vehicle when it is assumed that the control steering angle of the control target wheel is fixed to zero. In order to make it possible to turn with a small steering angle input, to increase the steady-state gain target value on the low speed side of the given reference model, and to increase stability compared to the base vehicle in the high speed range, the high speed of the given reference model The present invention can be suitably implemented as setting the characteristic of the reference model so as to lower the steady-state gain target value on the side, and similarly, the above can be realized. The steering characteristic is an understeer characteristic in a vehicle speed region lower than the first predetermined vehicle speed, and the steering characteristic is an understeer characteristic in a vehicle speed region in the steering angle control target region that is equal to or higher than the second predetermined vehicle speed. The vehicle speed was changed from a turning state with a constant steering angle by limiting a steady gain by the steady gain limiter for a vehicle speed range between the first predetermined vehicle speed and the second predetermined vehicle speed in the control target region. When the vehicle speed is lower than the first predetermined vehicle speed, the vehicle speed is between the first predetermined vehicle speed and the second predetermined vehicle speed, and the vehicle speed is equal to or higher than the second predetermined vehicle speed, the steering characteristic is understeer, As a thing which prevents it from changing with oversteer and understeer,
The present invention can be suitably implemented, and similarly enables the above to be realized.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 4 show an embodiment of a steering angle control device according to the present invention, which is applied to a steering angle control system for steering rear wheels. More specifically, the embodiment apparatus shows an embodiment in a control system to which feed-forward type yaw rate model adaptive control is applied. Specifically, FIG. 1 is a hardware configuration diagram, and FIG. FIG. 3 is a block diagram of a vehicle motion target value setting section (in this example, a yaw rate target value setting section), and FIGS.

First, the hardware of FIG. 1 will be described.
Here, the applied steering angle system assumes that the front wheels are mainly steered via the steering gear according to the steering angle of the steering wheel of the vehicle, and the rear wheels of the vehicle are the rear wheel steering mechanism 1 (steering angle control mechanism). ), The steering is performed by a rear wheel steering device including the actuator drive unit 2, and the rear wheel steering angle δ
_R is controlled by the controller 3. Controller 3
Is a yaw rate target value setting unit 4 serving as a vehicle motion target value setting unit, and a rear wheel steering unit is provided so that an actual vehicle response matches or follows a motion target value (yaw rate target value) set by the target value setting unit. And a rear wheel steering angle calculation unit 5 for calculating the angle.

More specifically, a yaw rate target value setting unit 4
Receives a signal from a steering angle sensor 11 for detecting a steering angle θ of a steering wheel and a signal from a vehicle speed sensor 12 for detecting a vehicle speed V, and sets a response target value relating to yaw to a steering angle input based on these signals. Then, the rear wheel steering angle calculation unit 5 calculates a rear wheel steering angle for matching the actual vehicle yaw rate response to the yaw rate target value (controlled amount target value) set above based on the dynamic characteristics of the host vehicle. Then, the actuator drive unit 2 drives the actuator of the steering mechanism 1 such that the actual actual steering angle matches the rear wheel steering angle target value δ _RT (command value) calculated in this way. The steering angle sensor can detect the amount corresponding to the steering angle, and the vehicle speed sensor can also detect the vehicle speed equivalent. In this example, a pulse signal from a vehicle speed pulse sensor is used to read the vehicle speed V value used for the calculation.

FIG. 2 shows a feature of the present control in which, when the controlled variable is a yaw rate, a limiter section is provided for a yaw rate gain set value in advance so that the vehicle does not change in the oversteer direction due to the own vehicle characteristics. Details of an example of the contents of the yaw rate target value setting section 4 are shown as functional blocks. The setting unit 4 is represented by blocks of a linear stationary yaw rate gain target value setting unit 4a, a stationary yaw rate gain limiter 4b, a yaw rate stationary target value setting unit 4c, and a yaw rate transient characteristic target value setting unit 4d.

Linear steady-state yaw rate gain target value setting section 4a
Is a setting section for setting a first linear steady-state yaw rate gain target value G _mod . Here, the target value G _mod is given using the vehicle speed V as a parameter. More particularly, in accordance with the vehicle speed V input, stability factor A _m in the reference model, the wheel base L, using a steering gear ratio N _m, calculating a first linear steady yaw rate gain target value G _mod (mentioned formula 11 ).

The steady-state yaw rate gain limiter 4b uses a steady-state yaw rate gain amount (limit amount) G _mLIM value set in advance according to the vehicle speed V, and obtains a G _mod value obtained by calculating the G _mLIM value and the setting unit 4a. comparing, as a result, to set the small becomes better as a final steady state yaw rate gain target value G _m. The value G _mLIM is such that the steady-state characteristics of the reference model increase the vehicle speed V even when the low-pass gain of the reference model is set high so that the vehicle can turn with a smaller steering angle in the low-speed range. On the other hand, it is used to limit the steady-state gain characteristic so that it does not become less than the turning radius ratio at the start of control. More specifically, the G _mLIM value is set by the stability factor A of the own vehicle, the wheelbase L, the basic steady-state characteristics of the vehicle represented by the steering gear ratio N, and are set in advance in map data or the like in accordance with the vehicle speed V so that the turning radius does not become smaller than the turning radius at the start of the rear wheel steering angle control. (See Equations 22 and 29 below).
Here, regarding the setting of the first linear steady-state yaw rate gain target value (setting unit 4a), the designer sets the limit value G _mLIM
Irrespective of the characteristic, therefore, at low speeds, the yaw rate gain is increased relative to the base vehicle (when the rear wheel steering angle is fixed to zero), and at high speeds, It can be set freely, for example, by lowering the gain to increase the stability. However, the final steady-state yaw rate gain target value G _m
Is set so as not to exceed the G _mLIM value, and the limiter 4b sets the G
limit check using _{mL IM,} and sets the G _m corresponding to the comparison result.

The steady yaw rate target value setting section 4c is a setting section for setting a steady yaw rate target value. That is, here, the yaw rate steady target value (d / dt) φ _mo obtained by multiplying the former value by the latter value based on the steering angle θ and the steady yaw rate gain target value G _m determined by the limiter 4b is set. Is done. Yaw rate and the yaw angular acceleration target value for obtaining a yaw rate transient characteristic target value desired transient response in the setting unit _{4d (d / dt) φ m} , (d 2 / dt 2) Set the phi _m, the rear wheel steering angle calculation The section 5 performs a control steering angle calculation for realizing these target values.

As described above, the yaw rate target setting section 4, which is a vehicle motion target value setting section, uses a reference model for setting a desired response to a steering angle input, and uses a predetermined steady-state characteristic and a transient response characteristic for a steering angle input. In this case, the steady-state yaw rate gain of the controlled variable set by the target value setting section is set by the configuration of FIG. 2 so that the steer characteristic of the controlled vehicle does not become the oversteer characteristic.
In other words, no matter what the steady yaw rate gain is set by the setter, the turning radius becomes smaller as the vehicle speed V increases during turning of the vehicle, even if the steer characteristics of the own vehicle perform the rear wheel steering angle control. Try not to be.

3 and 4 are flowcharts of an example of a rear wheel steering angle control program according to the present control executed by the controller 3. is there. This program is executed in an interrupt process every fixed time ΔT. Steps 101 to 103 (FIG. 3) and steps 104 and 105 (FIG. 4) are executed as shown in FIGS.
The reference numerals attached to the corresponding parts in are also added.

In step 100, every time this step is executed, the steering angle θ and the vehicle speed V detected by the sensors 11 and 12 are read, and the rear wheel steering angle (target value) δ _RT is obtained based on these by the following calculation and the like. . That is, step 101 is a step of calculating a first constant yaw rate gain target value G _mod the designer libitum, firstly, where the _{G mod, G mod = V /} NmL (1 + AmV 2 ) ----- Compute with 11. The above is given by the input of the vehicle speed V. As described above, Am is a stability factor and Nm
Is a steering gear ratio (gear ratio), L is a wheel base, and here, for example, Nm = 11.0, Am = 3.6 × 10 ^-3
And L = 2.5 m for the wheelbase.

In the following step 102, if the limit check is satisfied, a process for limiting the steady yaw rate gain is executed. Here the contents of the made steps 200-202 such illustrated in figure, first, the calculated value G _mod
And a preset limit amount G _mLIM , G _mod ≦ G
It is checked whether it is _mLIM (step 200), and if the answer is YES and does not exceed the set limit value, the value G _mod calculated by the above equation is reset again as the final steady-state yaw rate gain target value G _m (step 201). ), scolded Zare if the target value G _m G
_mLIM is set (step 202), and the process is terminated.

Thus, here, _assuming that the limiting amount is G _mLIM , (a) When G _mod ≤ G _mLIM , G _m = G _mod ----- 12 (b) When G _mLIM <G _mod , G _m = G _mLIM ----- 13 and the steady-state yaw rate gain target value is set so as not to exceed the limit. Here, G _mLIM is a control amount previously set according to the vehicle speed V as described above, that is, G _mLIM (V), and is specifically set as described later. Note that, in the above description, the addition of (V) means that the value is a value corresponding to the vehicle speed V (the same notation below applies to this).

First, steady yaw rate (d / dt) during four-wheel steering
φ _(4WS) is expressed by the following equation. (d / dt) φ _(4WS) = {V / (1 + AV ² ) L} (θ / N−δ _R ) ----- 14 where A, L and N are the stability of the vehicle Factor,
Wheelbase, steering gear ratio. here,
In the present embodiment, the control target region for the vehicle speed V is a range that is equal to or higher than a predetermined vehicle speed in the low-speed region.
The rear wheel control is started from m / s. As described above, in this example, since the vehicle speed pulse sensor is used to read the vehicle speed V used for calculation in this example, at extremely low speeds, the calculation accuracy is greatly reduced. , The mechanical limit of the rear wheel steering angle control amount (for example, in the Nissan Super HICS system
deg or less) since such, in view of the like that there is unsuitable areas in control at low speed, and the actual after about wheel control steering angle [delta] _R initiates the rear wheel control from more than a certain vehicle speed (the actual control region The vehicle speed value in that case is V = 6m /
s. Thus, V = 6
m / s (approximately 22 km / h), rear wheel control is started, and in the region beyond that, a multiplication coefficient K (≦ 1.0) is multiplied and continuously multiplied by, for example, 12 m / s to become equal to the target value. To control.

FIG. 5 shows the contents according to the control described later, and the characteristic of the coefficient k is illustrated in (b) in the figure.

In this embodiment, V = 6 m / s
Since taking how to start the rear wheel control more, the [delta] _R in formula 14 showing the steady yaw rate at the time of four-wheel steering (time control) is provided with _{δ R = k · δ RC -----} 15 Become. Here, δ _RC in the equation is a steady-state characteristic of the reference model arbitrarily given by a designer, and a rear wheel steering angle for obtaining G _m (V) = V / NmL (1 + AmV ² ) ----- 16 Equation 16 is equivalent to Equation 11 described above. Further, in the above equation 15, the value k takes a value in the range of 0 to 1.0, and when k = 0, δ _R = 0,
When k = 1.0, δ _R = δ _RC .

From the above, first, the steady-state yaw rate (d / dt) φ _{(6 m / s)} at V = 6 m / s (in other words, k = 0 ₎ is, therefore, given by the above equation (14 ₎ , 6 (m / s) and δ _R = 0, the following equation: (d / dt) φ _{(6m / s)} = [6 / ｛(1 + A · 6 ² ) · L · N｝] · θ ---- -It is indicated by 17. Therefore, focusing on the steering characteristic of the vehicle, if the steering angle input θ is constant in the present example, if the steering angle input θ is constant in order to prevent the vehicle from becoming the oversteer characteristic by performing the rear wheel control, At
It is necessary to set the steady-state yaw rate characteristic of the reference model to be given so that the turning radius does not become smaller than the turning radius at the time of V = 6 m / s (that is, when entering the control area). On the other hand, if it is intended to ensure that the designer can arbitrarily give the characteristic, the degree of freedom in the design must be maintained.

Therefore, in the present embodiment, the steady-state gain characteristic is limited so that the steady-state property of the given reference model does not fall below the turning radius ratio at the start of the control with the increase in the vehicle speed V. For the value of G _mLIM described above used for that purpose, it is _calculated in the region of V ≧ 12 m / s and V = 12 m / s.
In each of the regions where the speed is less than m / s and the control is performed, the following settings are made.

In the case of V ≧ 12 m / s In the case of V ≧ 12 m / s, 6 / (d / dt) φ _{(6 m / s)} ≦ V / (d / dt) φm ----- 18 Therefore, the following equation is obtained by modifying the above equation 18 and using the above equation 17 therein. (d / dt) φm ≦ (V / 6) ・ (d / dt) φ _{(6m / s)} = (V / 6) ・ [6 / ｛(1 + A ・ 6 ² ) ・ L ・ N｝] ・ θ = [V / ｛(1 + A · 6 ² ) · L · N｝] · θ ----- 19 Here, (d / dt) φm <G _m · θ ----- 20 From Expression 19, the following relational expression is established. _{G m ≦ V / (1 +} A · 6 2) · L · N ----- 21 Thus, the above equation the final steady state yaw rate gain target value
So as to obtain a range of 20 is established, limiting the amount G _MLIM to limit it for G _mod value, in this _{case, G mLIM = V / {(} 1 + A · 6 2) · L · N} ---- -Set to 22.

In the case of 6 m / s <V <12 m / s In this case, it is as follows. First, the following relationships are used, respectively. That is, (d / dt) φ _(4WS) = ｛V / (1 + A · V ² ) · L｝ · (θ / N−δ _R ) according to the above Expression 14, and δ _R = δ _R in this case = (V−6) / 6 · δ _RC = k · δ _RC ----- 23 (∴0 <k <1), and the equation 20 (d / dt) φm <G _m · θ . Here, (d / dt) φ _(4ws) = (d / dt) φ _m
From Equations 14 and 20, _RC is set to the right side = right side, and by substituting δ _R = k · δ _RC and adjusting for δ _RC , the following equation is obtained. δ _RC = [(θ / N) − ｛(1 + A · V ² ) L / N｝ G _m · θ] · (1 / k) ---- 24 On the other hand, from Equations 14, 23 and 24 above , (d / dt) When determining the expression for phi _m (with replacing [delta] _R in formula 14 the right side to the [delta] _RC, those organized by applying the above equation 24 regarding its _{δ RC, (d / dt)} φ _m ), (d / dt) φ _m = [V / ｛(1 + A · V ² ) L｝] · [(1 / N) −k ｛(1 / N) − ((1 + A · V ² ) L / V) · G _m ｝] · θ ----- 25. Here, similarly, 6 / (d / dt) φ _{(6 m / s)} ≦ V / (d / d
the relationship t) phi _m, if deformation this is as follows. (d / dt) φ _m ≤ (V / 6) ・ (d / dt) φ _{(6m / s)} ----- 26 From these equations 25 and 26, in this case, [V / ｛(1 + A V ² ) L｝] · [(1 / N) −k ｛(1 / N) − ((1 + A · V ² ) L / V) · G _m ｝] · θ ≦ (V / 6) · [6 / {(1 + A · V ² ) LN}] · θ ----- 27 is derived, and if this is further arranged for G _m , the following relational expression is obtained. G _m ≦ [V / ｛(1 + A · V ² ) LN｝] · [1− (1 / k) + (1 / k) · ｛(1 + A · V ² ) / (1 + A · 6 ² )｝]- --- 28 Therefore, the limiting amount G _mLIM in this case is the value on the right side of the above equation 28, that is, G _mLIM = [V / ｛(1 + A · V ² ) LN｝] · [1 − (1 / k) + (1 / k) · ｛(1 + A · V ² ) / (1 + A · 6 ² )｝] ----- 29 is set.

As described above, in the steady yaw rate gain limiter processing, in the rear wheel steering angle control in the four-wheel steering system (4WS), the value G _mLIM is _replaced with the value of the own vehicle so that the vehicle does not have an oversteer characteristic during turning. Using the basic steady-state characteristics of the vehicle represented by the stability factor A, the wheelbase L, and the steering gear ratio, the vehicle is prepared in advance according to the vehicle speed V so that it does not become smaller than the turning radius at the start of rear wheel control. Step 10 of FIG. 3
It is applied in 2. For more information, see Step 20
0, the vehicle speed V value at that time (step 100
The G _MLIM corresponding to the input value) is read from the map data and the like in the applied to the determination, and the corresponding time is used to set the read G _MLIM value G _m value in step 202.

Note that if V = 12 m / s,
k = 1 (see Equation 23).
_mLIM (V = 12 m / s) is consistent with that of Equation 22 described above. In the case of V = 6 m / s (that is, δ _R = 0) and the case where the rear wheel control is not performed in the present embodiment in a lower speed range, there is no particular need to set, but for convenience, Shall be set. G _mLIM = (V / 6) · G _mLIM (6m / s) ----- 30

Returning to FIG. 3, the next step 103 is the steady yaw rate gain target value set in step 102.
( _Gm value set in steps 201 and 202 in FIG. 3)
The steering angle θ type G _m values obtained by comparing the steady yaw rate gain G _mod which the control quantity G _MLIM and designer libitum, calculates a yaw rate constant value. This operation is
The following equation, (d / dt) φ _mo = G _m · θ ----- 31, is used as the final steady-state yaw rate target value with the calculated value (d / dt) φ _mo .

The following step 104 (FIG. 4) is a yaw rate transient characteristic setting calculation process for causing the yaw rate to respond to the steering angle input with a first-order delay based on the time constant τ. The yaw rate and yaw angular acceleration target values are as follows. (d / dt) φ _m ,
(d ² / dt ²⁾ to set the phi _m. (d / dt) φ _m = ∫ ((d ² / dt ² ) φ _m ) dt ----- 32 (d ² / dt ² ) φ _m = ((d / dt) φ _mo- (d / dt ) φ _m ) / τ ----- 33 That is, the target yaw angular acceleration value (d ² / dt ² ) φ _m corresponding to the steering angle θ is obtained based on the primary delay system of the time constant τ, and (d ² / dt ² )
Request phi yaw rate should aim by integration of _{m (d / dt) φ m} . In the case of digital calculation, the above integration is approximated by (d / dt) φ _m = (d / dt) φ _m + ΔT · (d ² / dt ² ) φ _m ----- 34. This process is performed in a similar manner when the subsequent integration is required.

Next, at step 105, the rear wheel steering angle calculation unit 5
Is performed. Here, well-known
Based on the equation of motion of the vehicle, the rear wheel steering angle target value δ is as follows:
_RTIs calculated. That is, using the dynamic characteristics of the own vehicle,
(D / dt) φ set in step 104_m, (d^Two/ dt^Two) φ_mSatisfied
The rear wheel steering angle is calculated. First, the lateral speed V_YNitsu
The previous dV required as described below_Y/ dt product
Minutes, V_Y= ∫ (d / dt) V_Y ----- 35 (V_Y= V_Y+ ΔT ・ (d / dt) V_Y), V_YThe value is calculated, and this and (d / dt) φ_mBased on
And the front wheel sideslip angle β_FTo B_F= θ / N- (V_Y+ L_F・ (D / dt) φ_m) / V ----- 36 (L_F: Distance between front wheel and center of gravity)_FFrom front wheel cornering fo
Source C_FIs calculated by the following equation. C_F= eK_F・ Β_F ----- 37 (eK_F: Front equivalent cornering power)
The front wheel
When the cornering force is on, the target yaw
Angular acceleration (d^Two/ dt^Two) φ_mRear corner required to produce
Ning Force C _RTo C_R= ｛L_F・ C_F-(I_z・ (D^Two/ dt^Two) φ_m/ 2)｝ / L_R ----- 38 (I_z: Yaw inertia, L_R: Distance between rear wheel and center of gravity).

[0034] Thus, the inverse operation subsequent to wheel slip angle beta _R after to obtain the cornering force _{C R β R = C R /} K R ----- 39: determined by (K _R rear cornering power) Then, based on the slip angle β _R , the rear wheel steering angle δ _RT is calculated by the following equation. δ _RT = β _R + (V _Y -L _R・ (d / dt) φ _m ) / V ----- 40 And (d / dt) V _{Y to be} used in the next operation cycle
The value is calculated by the following equation: (d / dt) V _Y = (2C _F + 2C _R ) · MV · (d / dt) φ _m ---- 41 (M: vehicle mass).

Thus, in step 106, the rear wheel steering angle value δ _RT calculated as described above is set as a target value and a signal corresponding to the target value is output to the actuator drive unit 2, and the rear wheels are calculated by the rear wheel steering mechanism 1. Steer only the steering angle.

With the steering angle control as described above, even if the gain on the low-sequence side is set higher, it is possible to prevent the vehicle from having an oversteer characteristic, and the vehicle is set in the oversteer direction in advance from the own vehicle characteristic. By applying a limiter to the yaw rate gain set value so that it does not change, the steer characteristics of the vehicle do not fluctuate no matter what the steady yaw rate gain is set by the designer, so the driver does not feel uneasy and stable Vehicle characteristics can be obtained.

Hereinafter, a specific description will be given with reference to FIGS. 5 and 6 (comparative example). FIG. 5 shows a steady yaw rate gain characteristic in the case of this control ((a) in the figure), a rear wheel steering angle ratio ((c)), a turning radius ratio ((d)), and a coefficient k mentioned above. FIG. 6 shows a result as a comparative example without a limiter, and FIG.
Will be described. The comparative example here is based on the control described in "3.1 Yaw rate model adaptation control" of the above-mentioned document.

First, the vehicle to be controlled (own vehicle) has a stability factor A = 2.0 × 10 ⁻³ , a steering gear ratio N = 15, and a wheel base L = 2.5 m. At this time,
The steady yaw rate gain G _2ws (V) when the base vehicle, that is, the rear wheel steering angle is fixed to zero, is expressed as follows (FIG. 6).
(A) dot-dash line). G _2ws (V) = V / NL (1 + AV ² ) ----- 42 On the other hand, the steady gain of the reference model, which is the motion target, is basically turned at a low speed side with a smaller steering angle. For example, the following setting is made so as to be possible (that is, to increase the phase of the rear wheel reverse phase), and to increase the stability by decreasing the gain at a high speed. G _m (V) = V / N _n L (1+ A _m V ² ) N _m = 11 ----- 43 A _m = 3.6 × 10 ^-3 Steady-state gain characteristics of the reference model with this setting 6 (a) is shown in comparison with the base vehicle (2WS).

The above-mentioned reference model has a transient response characteristic of a first-order lag system having no overshoot with respect to the input of the steering angle θ as shown by the following yaw rate target value (d / dt) φ _m in the following equation. And the constant τ is given by
For example, τ = 0.05 (sec) is set so as to obtain a sufficiently agile response within a range that does not require an excessive load on the actuator. (d / dt) φ _m = G _m (V) ・ {1 / (1+ τS)} ・ θ ---------- 27 where S: derivative operator

Further, also in the case of the comparative example, the actual rear wheel steering angle control is started from V = 6 m / s, and therefore, a coefficient k having a characteristic as shown in FIG. , Δ _R =
It is assumed that the control is continuously performed so as to be equal to the target value δ _RC at V = 12 m / s by multiplying the coefficient k like k · δ _RC .

Now, a reference model is set as described above,
Further, in this example, V = 6 m / s or more is set as the actual control target area for the vehicle speed V, and the rear wheel steering angle ratio δ _R / to the front wheel steering angle δ _{F in} the steady state when the rear wheel steering angle control is performed.
Figures (c) and (d) show δ _F and the turning radius ratio R / R _O (R: actual radius, R _O : geometric theoretical radius). Further, the solid line characteristic shown in FIG. 3A represents the target yaw rate gain (= generated yaw rate gain) in this case.

Looking at the target yaw rate gain,
First, the following can be said. That is, the non-control region relating to the vehicle speed V with k = 6 m / s (k = 0, δ _R = 0)
In, the yaw rate gain is based on the base vehicle (δ _R =
0). On the other hand, in the region where the control is executed, the yaw rate gain at the low speed side is higher than that of the broken line (G _2WS ) of the base vehicle, and as a result,
It is possible to turn with a smaller steering angle input than the base vehicle, and at high speed, the gain is lowered and the stability is increased as compared to the broken line of the base vehicle, so that the aim described above is achieved. It is understood that

On the other hand, focusing on the turning radius, FIG.
As shown in the hatched portion (d), the turning radius becomes smaller as the vehicle speed V increases from V = 6 m / s at the start of the control. That is, it is shown that when the vehicle speed is increased from the constant turning state, the vehicle tends to have an oversteer characteristic in which the vehicle cuts inward from the turning R (the turning R decreases), and accordingly, the steer characteristic becomes understeer (u / s)
It can be seen that the state changes from oversteer (o / s) to understeer (u / s). So, in this case,
Despite driving with a constant steering wheel steering angle (steering wheel angle), the steering characteristics fluctuate.

On the other hand, in the present embodiment, the steady yaw rate gain limiter can prevent the steer characteristic of the vehicle to be controlled from changing to the oversteer characteristic.
The above-mentioned comparative example (broken line) shows the yaw rate gain characteristics ((a) in the figure), the rear wheel steering angle ratio ((c)), and the turning radius ratio ((d)).
As shown in the figure, even when the yaw rate gain is increased so that the vehicle can turn at a low speed with a smaller steering angle input compared to the base vehicle, the oversteer characteristic that the vehicle turns inward when the vehicle speed increases from a constant turning state Is avoided. The limiter line (two-dot chain line) in FIG.
In this example, the limiter line is V / 6 · (d / dt) φ _{(6 m / s)} , but after the control is started, the target yaw rate gain G _m (= generated yaw rate gain) after this control is limited by this. is the thing now, the results, as shown in FIG. (c), the rear wheel steering angle ratio [delta] _R / [delta] _F characteristics, wheel reverse phase after low speed side is suppressed to be much smaller than in Comparative example, Correspondingly, the steer characteristic is not the oversteer characteristic in the control of this embodiment as shown in FIG. Therefore, the steering characteristic of the vehicle changes from u / s → o / s → even though the driver is driving with the steering wheel steering angle kept constant.
It avoids the situation that changes suddenly like u / s, and does not make it difficult to drive due to it,
Stable vehicle characteristics can be obtained without giving the driver a feeling of anxiety, and the above can be achieved even if the designer sets the steady-state yaw rate gain of the reference model arbitrarily, ensuring design flexibility. In addition, it is possible to achieve both.

In the above example of the program, the limit value G
_{Although it} has been _described that _mLIM is _stored in advance as map data or the like according to the vehicle speed and is read out, a method of sequentially calculating and applying G _mLIM in real time instead of such a search process may be used. Further, the present invention is not used only for the feed-forward type yaw rate model adaptation control, and can be implemented, for example, in "3.3 D ^* model following control" of the above-mentioned document.

[0046]

According to the present invention, in a steady state of steering angle control during turning of a vehicle, when the vehicle speed is changed, the steering characteristics of the vehicle to be controlled perform steering angle control in a part of the vehicle speed region. By doing so, it is possible to prevent the oversteer characteristics from becoming oversteer characteristics, and it is possible to prevent the steer characteristics of the controlled vehicle from changing to the oversteer characteristics side even by performing the steering angle control. Since there is no change, it is possible to avoid difficulty in driving and to achieve stable vehicle characteristics, and it is also possible to achieve this while securing the degree of freedom in designing the vehicle motion target of the designer. The advantage of the steering angle control using the reference model that a response very close to the response of the reference model can be obtained even in an actual vehicle can be obtained without deteriorating as much as possible. The reference model can be arbitrarily set with respect to the reference model, and the designer can arbitrarily set the steady-state gain of the steady-state characteristic of the reference model. Even if the steady gain is set, it is possible to prevent the change to the oversteer characteristic side by limiting the steady gain for a part of the vehicle speed range, and therefore, the degree of freedom in designing the vehicle motion target of the designer is improved. It is possible to achieve these both while securing.

[Brief description of the drawings]

FIG. 1 is a hardware block diagram showing an embodiment of the apparatus of the present invention.

FIG. 2 is a block diagram showing an example of the content of a yaw rate target value setting unit of the example.

FIG. 3 is a flowchart showing an example of the control program of the same example in a divided manner, and showing a part of the flowchart.

FIG. 4 is also a diagram showing another part.

FIG. 5 is a diagram illustrating an example of a relationship between a steady yaw rate gain characteristic, a rear wheel steering angle ratio, and a turning radius ratio for explanation when control is performed by the embodiment device.

6 is a diagram showing an example of a reference model steady-state characteristic setting in a comparative example without a limiter shown in comparison with FIG. 5, and an example of a rear wheel steering angle ratio and a turning radius ratio at that time.

[Explanation of symbols]

 1 Rear wheel steering mechanism 2 Actuator drive 3 Controller 4 Yaw rate target value setting section 4a Linear steady-state yaw rate gain target value setting section 4b Steady-state yaw rate gain limiter 4c Yaw rate steady-state target value setting section 4d Yaw rate transient characteristic target value setting section 5 Rear wheel steering Angle calculator 11 Steering angle sensor 12 Vehicle speed sensor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B62D 6/00-6/06 B62D 101: 00 B62D 113: 00 B62D 137: 00

Claims (6)

(57) [Claims] 1. A steering angle control mechanism capable of controlling a steering angle of at least one of a front wheel and a rear wheel, and a drive for driving a mechanism according to a steering angle control input such that an actual steering angle matches a control input value. In a vehicle having a steering device including a part, a detecting means for detecting a steering angle of a steering wheel or an amount corresponding thereto, a detecting means for detecting a vehicle speed or an amount corresponding thereto, and an output from these detecting means. and car <br/> both exercise target value setting means to set the steady-state characteristics and transient response characteristics with respect to the steering angle input for at least one controlled amount related to yaw and lateral planar motion of the vehicle Te, said vehicle motion target value Steering angle calculating means for calculating a steering angle control input value of the controlled wheel so that the actual vehicle response matches or follows the movement target value set by the setting means and instructing the steering device; A steering angle control apparatus having a, said vehicle motion target value setting means, by using a reference model, car
Calculates a steady-state gain target value according to the speed, and steers the calculated value.
Set as the steady gain target value of the controlled variable for angle input
A steady gain target value setting means for
Steady gain control set according to the gain target value and vehicle speed
Limit, and as a result, the smaller one is
Steering for the controlled amount set by the target value setting means
Steady-state gain as steady-state gain for steady-state characteristics with respect to angular input
Changes in vehicle speed during turning of the controlled vehicle with a limiter
Contrast, the vehicle steering angle control apparatus characterized by steering characteristic of the controlled object vehicle so as to prevent the change in the oversteer characteristic side. (2) The limitation of the steady-state gain is based on the comparison result.
As a result, a steady gain limiter is set in advance according to the vehicle speed.
The set steady-state gain limit value is the vehicle motion target value setting means.
In the vehicle speed range, which is the steady gain of the steady characteristic set in the step
Limit the steady-state gain for the corresponding vehicle speed region
Is an aspect, The vehicle speed range when the vehicle speed is changed in the turning state
Even when the steady gain is limited in the
In a vehicle speed region portion that is equal to or higher than the vehicle speed exceeding the
The steady-state gain target value is not limited by the in-limit value.
The steady-state gain calculated by the setting means using the reference model
The target value is the vehicle motion target value setting means. Set by
The steady gain of the normal characteristic The vehicle steering angle control device according to claim 1, wherein
Place. (3) The stationary gain limiter is a
Controls the steering angle of the wheel to be controlled for the steady-state characteristics of the model.
Input of the steering angle when turning the controlled vehicle.
When the vehicle speed changes while keeping
Of the turning radius at the start of steering angle control
In order to limit the in-
Set limit values, The vehicle according to claim 1 or claim 2, wherein
Dual-purpose steering angle control device. (4) If the vehicle speed is lower than the first predetermined vehicle speed in the low vehicle speed range,
Set a non-control area where steering angle control of the target wheel is not performed
On the other hand, the steering angle control is started from the first predetermined vehicle speed.
The steering angle control relating to the vehicle speed is performed in a vehicle speed region equal to or higher than the first predetermined vehicle speed.
Control target area and the steering angle control target area.
The first predetermined vehicle speed value and the first predetermined vehicle speed value
In a vehicle speed range between a second predetermined vehicle speed value having
In steering angle control, the actual control target wheels are
The steering angle that is controlled at the time is continuously increased from the steering angle amount 0
And at the second predetermined vehicle speed,
Norm in which the steering angle is given by the steady gain target value setting means
Steering angle, which is the target value for obtaining the steady-state characteristics of the model, etc.
Make it easier The method according to any one of claims 1 to 3, wherein
Onboard vehicle steering angle control device. 5. A method according to claim 1, wherein said constant gain target value setting means sets a constant value.
The normal gain target value setting sets the control steering angle of the control target wheel to zero.
Low compared to the base vehicle assuming that
On the speed range side, turning with less steering angle input compared to the base vehicle
The steady state on the low speed side of the reference model given to enable
Increase the gain target value, and
Of reference models to increase stability compared to
To reduce the steady-state gain target value on the high-speed side,
5. The method according to claim 1 , wherein Dell characteristics are set.
Onboard vehicle steering angle control device. 6. In a vehicle speed range lower than the first predetermined vehicle speed,
The understeer characteristic is the understeer characteristic.
In the vehicle speed range above the second predetermined vehicle speed, A characteristic
Is an understeer characteristic, and in the steering angle control target area,
Vehicle speed between the first predetermined vehicle speed and the second predetermined vehicle speed
The steady-state gain limiter
By restricting the steering angle,
When the vehicle speed changes, the vehicle speed is lower than the first predetermined vehicle speed;
A vehicle speed between the first predetermined vehicle speed and the second predetermined vehicle speed;
And a vehicle speed equal to or higher than the second predetermined vehicle speed.
Are understeer, oversteer, and understeer
To prevent change, The vehicle according to claim 4 or claim 5, wherein
Dual-purpose steering angle control device.