JP2000302053A - Vehicle steering angle control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering angle control device for vehicle to perform a yaw rate feedback control of the steering angle within the range not going beyond the gripping limit of tire. SOLUTION: A steering angle control device for a vehicle is equipped with an auxiliary steering angle adjusting mechanism 14 installed in a transmission path of a steering angle transmitting mechanism and made adjustable for the steering angle of a steering wheel 10, an actuator 19 to drive the auxiliary steering angle adjusting mechanism, and a controlling means (controller 20) to control the actuator through yaw rate feedback control, wherein the controlling means is furnished with a presuming means to presume the limit value of cornering force and corrects the yaw rate feedback of the target steering angle so that the target figure of cornering force corresponding to the target steering angle does not exceed the limit value of cornering force.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises an auxiliary steering angle adjusting mechanism capable of increasing or decreasing the turning of a steered wheel which is steered in conjunction with the operation of a steering wheel in accordance with the amount of motion of the vehicle. The present invention relates to a vehicle steering angle control device.

[0002]

2. Description of the Related Art Conventionally, an auxiliary steering angle adjusting mechanism capable of controlling turning-up or turning-back of a steering wheel which is steered in association with steering wheel operation has been provided, and the steering wheel is controlled in accordance with various motion state amounts of a vehicle. There is known a vehicle steering angle control device which can maintain the steering angle of the vehicle at an optimum value and improve the running stability of the vehicle.
No. 454 is disclosed. The vehicle steering angle control device described in the publication includes a target steering angle of a steered wheel, a target steering angle feedforward term calculated based on a rotation angle of a steering wheel, and various vehicle motion state quantities (vehicle speed, steering wheel Rotation angle, etc.) and the target steering angle yaw rate feedback term calculated based on the deviation between the target yaw rate calculated from the target yaw rate and the detected actual yaw rate, so that the actual steering angle of the steered wheels becomes the target steering angle. By controlling the auxiliary steering angle adjustment mechanism so that
The yaw rate is dynamically fed back to correct the steering angle of the steered wheels so that the actual yaw rate approaches the target yaw rate, thereby accurately responding to the driver's request and improving the running stability of the vehicle.

[0003]

The yaw rate of the vehicle is
This is caused by a cornering force generated on the tire by steering the steered wheels. In order to increase the yaw rate, it is necessary to generate a larger cornering force. Here, the cornering force refers to a lateral force generated in a direction perpendicular to the traveling direction of the tire when a difference (slip angle) occurs between the direction of the tire and the traveling direction of the tire. The relationship between the cornering force and the slip angle generally has a relationship as shown in FIG. That is, the cornering force Cf is set to the slip angle αf until the slip angle αf reaches the vicinity of the constant value A.
When the slip angle αf reaches a fixed value A, the slip angle αf reaches a maximum value (a limit cornering force or a tire grip limit; the same applies hereinafter) and the slip angle α.
When f exceeds a certain value A, the value gradually decreases.

Therefore, in the steering angle control device described above, when the actual yaw rate does not reach the target yaw rate, and when the grip limit is not exceeded, the number of steered wheels is increased and the slip angle is increased. By generating a larger cornering force, the steering angle of the steered wheels can be corrected so as to increase the actual yaw rate and approach the target yaw rate.

[0005] However, the grip limit of the tire is determined by the friction coefficient of the running road surface. When the friction coefficient of the running road surface is low, the grip limit of the steering wheel tire becomes low, and the grip of the steering wheel becomes low. It is easy to exceed the limit.
If the grip limit is exceeded, the cornering force does not increase even if the steering wheel is turned more and the slip angle is increased, so that the actual yaw rate does not increase and may not reach the target yaw rate. In such a case, the steering wheel turning control is further performed, so that the steering wheel is unnecessarily turned excessively, which causes a reduction in the running stability of the vehicle. In addition, if the steered wheels are unnecessarily turned too much, a steering delay is likely to occur at the time of turning back and the like, leading to deterioration of the steerability of the vehicle.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-described problem. In a steering angle control device for a vehicle having an auxiliary steering angle adjusting mechanism for performing a yaw rate feedback control, the steering wheel does not exceed a grip limit of a tire of a steered wheel. An object of the present invention is to provide a device that controls a steering angle of a steered wheel within a range.

[0007]

According to one aspect of the present invention, there is provided a steering angle transmitting mechanism for steering a steered wheel in response to a rotation operation of a steering wheel.
An auxiliary steering angle adjustment mechanism that is provided in a transmission path of the steering angle transmission mechanism and that is configured to be able to further increase or return the steered wheels; an actuator that drives the auxiliary steering angle adjustment mechanism; and rotation of the steering wheel. The steering as a sum of a target steering angle feedforward term calculated based on the angle and a target steering angle yaw rate feedback term calculated based on a deviation between a target yaw rate calculated from various vehicle motion state quantities and an actual yaw rate. Control means for calculating a target steering angle of a wheel and controlling the actuator so that an actual steering angle of the steered wheel becomes the target steering angle, wherein the control means estimates a limit cornering force value. And a target cornering force feed force calculated based on a rotation angle of the steering wheel. The target cornering force value calculated as the sum of the target cornering force yaw rate feedback value calculated based on the deviation between the target yaw rate and the actual yaw rate exceeds the limit cornering force value estimated by the estimating means. The target cornering force value is corrected so that the target cornering force value does not exceed the limit cornering force value, and the target steering angle yaw rate feedback term is changed to the corrected target cornering force yaw rate feedback value. And calculating the target steering angle of the steered wheels by correcting the steering angle to a value corresponding to the following.

According to the first aspect of the present invention, the control means for calculating the target steering angle is calculated from the target steering angle feedforward term calculated based on the rotation angle of the steering wheel and various vehicle motion state quantities. In calculating the target steering angle as an addition value of the target steering angle yaw rate feedback term calculated based on the deviation between the target yaw rate and the actual yaw rate, first, the value of the target steering angle feedforward term and the target steering angle yaw rate feedback The term values are converted to corresponding target cornering force feedforward values and target cornering force yaw rate feedback values, respectively. Then, the target cornering force value calculated as the sum of the target cornering force feedforward value and the target cornering force yaw rate feedback value is:
If it exceeds the limit cornering force value (tire grip limit) estimated by the estimation means of the control means,
Only the target cornering force yaw rate feedback value is corrected so that the target cornering force value does not exceed the limit cornering force value, and the value of the target steering angle yaw rate feedback term is changed to a value corresponding to the corrected target cornering force yaw rate feedback value. The target steering angle of the steered wheel is calculated after the correction.

In this manner, the value of the yaw rate feedback term of the target steering angle of the steered wheel is calculated by correcting the value so as not to exceed the grip limit of the tire. A situation in which the vehicle is cut off too much and the running stability of the vehicle is reduced does not occur. Further, since the steered wheels are not unnecessarily turned too much, a steering delay at the time of turning back and the like is less likely to occur, which leads to an improvement in the steerability of the vehicle.

According to a second aspect of the present invention, there is provided a steering angle transmitting mechanism for steering a steered wheel in response to a rotation operation of a steering wheel, and a steering wheel provided in a transmission path of the steering angle transmitting mechanism for increasing or decreasing the number of the steered wheels. An auxiliary steering angle adjustment mechanism configured to be able to switch back, an actuator for driving the auxiliary steering angle adjustment mechanism, a target steering angle feedforward term calculated based on the rotation angle of the steering wheel, and various vehicle motion state quantities The target steering angle of the steered wheel is calculated as an added value of a target steering angle yaw rate feedback term calculated based on the deviation between the target yaw rate calculated from the actual yaw rate and the actual steering angle of the steered wheel. Control means for controlling the actuator so as to form an angle, wherein the control means controls the target steering angle yaw rate feed. Tsu when the click section have a direction value that increases off the steering wheel and a steering angle control apparatus for a vehicle, characterized in that to limit the target steering angle yaw rate feedback term to a predetermined value.

According to a second aspect of the present invention, in the first aspect, when it is difficult for the estimating means of the control means to estimate the limit cornering force (tire grip limit), the first aspect of the present invention. Is an effective alternative to

That is, when it is difficult to estimate the limit cornering force, the value of the target steering angle yaw rate feedback term of the steered wheels cannot be corrected to a range that does not exceed the tire grip limit. Therefore, when the target steering angle yaw rate feedback term has a value in the direction of increasing the number of steered wheels, the control means limits the target steering angle yaw rate feedback term to a predetermined value (for example, zero). By limiting the amount of turning of the steered wheels, unnecessary excessive turning of the steered wheels can be prevented, and the same effect as that of the first aspect can be easily obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing the connection of the whole vehicle steering angle control device according to one embodiment of the present invention. First, the mechanical configuration will be described.

In FIG. 1, reference numeral 11 denotes a steering wheel, which is integrally fixed to a steering input shaft 12. Reference numeral 15 denotes a steering output shaft, which is disposed coaxially with the steering input shaft 12, and the steering output shaft 15 and the steering input shaft 12 are connected via an auxiliary steering angle adjusting mechanism 14.

Further, the steering output shaft 15 is connected to the tie rod 1 by a rack and pinion mechanism (not shown) or the like.
6 so that the rotation of the steering output shaft 15 is converted into a lateral displacement of the tie rod 16 in FIG. Steered wheels 10 are respectively connected to both ends of the tie rod 16 via a link mechanism 17, and the steered wheels 10 are steered by the lateral displacement of the tie rod 16 in FIG.

With the above configuration, when the steering wheel 11 is rotated, the rotation is transmitted to the steering output shaft 15 via the steering input shaft 12 and the auxiliary steering angle adjusting mechanism 14, and the rotation of the steering output shaft 15 is controlled. The steering wheel 10 is steered via the link mechanism 17 by being converted into the lateral displacement of the tie rod 16. Thus, the steering input shaft 1
2, auxiliary steering angle adjustment mechanism 14, steering output shaft 1
5, the tie rod 16 and the link mechanism 17 constitute a steering angle transmission mechanism.

The auxiliary steering angle adjusting mechanism 14 is driven by a motor 19 (actuator). In the non-drive state, the rotation angle of the steering input shaft 12 and the rotation angle of the steering output shaft 15 maintain a constant correspondence relationship. By adjusting the rotation angle of the steering output shaft 15 with respect to the rotation angle, the steering wheel 10 can be turned further or turned back.

Next, a control system of the auxiliary steering angle adjusting mechanism 14 will be described. In FIG. 1, reference numeral 18 denotes a steering angle sensor for the steered wheels 10, and the steering angle sensor 18 detects an actual steering angle (vehicle motion state amount) of the steered wheels 10 and outputs a signal thereof. Reference numeral 13 denotes a steering operation angle sensor. The steering operation angle sensor 13 detects an operation angle (vehicle motion state amount) of the steering wheel 11 and outputs a signal thereof. 20 is a controller (control means),
The controller 20 receives output signals of the steering angle sensor 18 and the steering operation angle sensor 13 and output signals of a vehicle speed sensor and a yaw rate sensor (not shown), and performs a yaw rate feedback control based on these output signals to thereby maintain the running stability of the vehicle. The optimum target steering angle of the steered wheels 10 at the moment when the target steering angle can be improved is calculated. If the actual steering angle of the steered wheels 10 at that time does not match the calculated target steering angle, the motor 19 is controlled so that the actual steering angle becomes the target steering angle, and the auxiliary steering angle adjustment is performed. The mechanism 14 is driven. Auxiliary steering angle adjustment mechanism 14
Is driven, as described above, the steered wheels 10 are turned further or turned back, and the additional value control is performed so that the actual steering angles of the steered wheels 10 become the target steering angles.

Next, a specific calculation procedure of the controller 20 according to the embodiment of the present invention will be described with reference to FIG. The symbols used in FIG. 2 are defined as follows. str: Actual steering angle (rad), ya
w: actual yaw rate (rad / s), trg_yaw: target yaw rate (rad / s), vx: longitudinal vehicle speed (m / s), vy: lateral vehicle speed (m / s), δf_sen: actual steering angle (rad) , Cf_ff: target cornering force feed forward value (N), cf_f
b: target cornering force yaw rate feedback value (N), δf_fb_org: target steering angle yaw rate feedback term before correction (rad), δf_fb: target steering angle yaw rate feedback term after correction (rad), δf_ff: target steering angle feedforward term (Rad), δf: target steering angle (rad), cf: limit cornering force value (N),
mt_ang: Control motor angle (rad). In FIG. 2, in step 101, a target yaw rate trg_yaw is calculated. trg_yaw is a relational expression F_yaw (str, vx) = (F_yaw
_max (vx) / STR_MAX) · str. Where ST
R_MAX is the maximum steering rotation angle, and STR_MAX =
9.425 (rad). F_yaw_max (vx) is a function that calculates the limit yaw rate using vx as a variable. The limit yaw rate is set to be larger as the vehicle speed vx in the front-rear direction is lower and smaller as the vehicle speed vx is higher, based on the dynamic balance between the vehicle speed and the centrifugal force. You.

In step 102, a pre-correction value δf_fb_org of the target steering angle yaw rate feedback term is calculated. δf_fb_org is a relational expression F_fb (trg_yaw-yaw)
= TIRE_GAIN · (trg_yaw-yaw) Here, TIRE_GAIN is a tire steering angle conversion gain, and TIRE_GAIN
GAIN = 0.001 (sec).

In step 103, a target steering angle feedforward term δf_ff based on the rotation angle of the steering wheel 11 is calculated. δf_ff is a relational expression F_ff
It is calculated by (str) = (DF_MAX / STR_MAX) · str. Here, DF_MAX is the maximum steering angle, and DF_MAX =
0.556 (rad).

In step 104, a target cornering force value is calculated. Among the target cornering force values, a feedforward value cf_ff based on the rotation angle of the steering wheel 11 is represented by a relational expression F_cff (str) =
It is calculated by (CF_MAX / STR_MAX) · str. Where CF
_MAX is a maximum cornering force value generated on a road having a normal high friction coefficient, and CF_MAX = 120.
(N). Among the target cornering force values, the yaw rate feedback value cf_fb is calculated by a relational expression F_cfb (trg
_yaw-yaw) = CF_GAIN · (trg_yaw-yaw). Here, CF_GAIN is a cornering force conversion gain, and CF_GAIN = 44919 (N · s / rad).
Therefore, the target cornering force value is calculated as the sum of these (cf_ff + cf_fb).

Next, the routine proceeds to step 105. Step 1
In step 05, finally, the corrected value δf_fb of the target steering angle yaw rate feedback term is calculated. In preparation for the correction, first, the limit cornering force value cf is estimated. The estimation of the marginal cornering force value cf is based on the relational expression
F_cf (δf_sen, yaw, vx, vy) = (M · (vx · yaw + vx · ata)
n (vy / vx)) · lr + lz · yaw) / ((lf + lr) · (δf_sen
-atan (vy / vx)-(lf ・ yaw) / vx)). Here, M is the vehicle mass, M = 2000 (kg), lz is the moment of inertia of the vehicle, and lz = 2455 (kgf ·
m), lf is the distance from the center of gravity of the vehicle to the front wheel axle, l
f = 1.333 (m), lr is the distance from the center of gravity of the vehicle to the rear wheel axle, and lr = 1.485 (m). afterwards,
Based on the feedforward value cf_ff of the target cornering force value and the yaw rate feedback value cf_fb calculated in step 104, it is determined whether or not the target cornering force value (cf_ff + cf_fb) exceeds the limit cornering force value. Then, only the yaw rate feedback value cf_fb is corrected. Here, the reason for not correcting the feedforward value cf_ff is to give priority to the intention of the driver operating the steering wheel 11. Then, based on the corrected value of the yaw rate feedback value cf_fb, a corrected value δf_fb of the corresponding target steering angle yaw rate feedback term is calculated. Specifically, the determination is made in the following three patterns.

First, the case where cf_ff> cf, that is, the case where the feedforward value itself exceeds the limit cornering force value. Since the feedforward value cf_ff itself is not corrected as described above, in this case, the target cornering force value (cf_ff + cf_fb)
Cannot be corrected within the limit cornering force value cf, but at least the feedback value cf_fb = 0.
To reduce the target cornering force value. Therefore, the post-correction value δf_fb of the target steering angle yaw rate feedback term is set to 0.

Second, cf_ff <cf <(cf_ff + cf_f)
The case of b), that is, the case where the feedforward value is less than the limit cornering force value, but the target cornering force value which is the sum of the feedforward value and the feedback value exceeds the limit cornering force value. In this case, cf = (cf_ff + cf_fb)
The feedback value is corrected to (cf-cf_ff) so that Therefore, the corrected value of the target steering angle yaw rate feedback term δf_fb = δf_fb_org · ((cf-cf_ff) / cf
_fb).

Third, in other cases, that is, a target cornering force value (cf_ff + cf_f) which is an added value of the feed forward value cf_ff and the feedback value cf_fb.
b) does not exceed the limit cornering force value cf. In this case, since the feedback value cf_fb does not need to be corrected, the target steering angle yaw rate feedback term is not corrected, and δf_fb = δf_fb_org.

Next, proceed to step 106,
The target steering angle δf = δf_ff + δf_fb is calculated by adding the corrected value δf_fb of the target steering angle yaw rate feedback term calculated in step 05 and the value δf_ff of the target steering angle feedforward term calculated in step 103.

In the next step 107, step 106
Based on the target steering angle δf calculated in, the control motor angle mt_an
g is being calculated. The control motor angle mt_ang is calculated by the relational expression F_
It is calculated by ma (δf, str) = δf-str · GR. Here, GR is a steering gear ratio, and GR = 17. The controller 20 supplies a control signal corresponding to the control motor angle mt_ang calculated here to the motor 19,
The motor 19 drives the auxiliary steering angle transmission mechanism according to the control signal to adjust the steering angle of the steered wheels 10.

As described above, the target steering angle δ of the steered wheels 10
Since the value of the yaw rate feedback term δf_fb of f is corrected so as not to exceed the grip limit (limit cornering force value cf) of the tire, the steering wheel 10 is unnecessarily excessively cut as in the related art. As a result, a situation in which the running stability of the vehicle is reduced does not occur. Further, since the steered wheels are not unnecessarily turned too much, a steering delay at the time of turning back and the like is less likely to occur, which leads to an improvement in the steerability of the vehicle.

Next, a specific calculation procedure of the controller 20 according to an embodiment of the present invention will be described with reference to FIG. In FIG. 3, the same or equivalent parts as those in FIG. 2 are denoted by the same reference numerals as those described above, and redundant description will be omitted.

The calculation procedure shown in FIG. 3 is used when it is difficult to estimate the limit cornering force cf.
Is effective as an alternative to the calculation procedure shown in FIG.

That is, when it is difficult to estimate the limit cornering force cf, the value of the target steering angle yaw rate feedback term δf_fb_org of the steered wheels 10 cannot be corrected to a range not exceeding the tire grip limit. . Therefore, the controller 20 determines that the value of the target steering angle yaw rate feedback term δf_fb_org is
If the value of the steering wheel 10 is increased, the value of the target steering angle yaw rate feedback term δf_fb_org is limited to a predetermined value (zero in FIG. 3), and the steering wheel 10 is increased. Limit the amount. Therefore, the difference between FIG. 3 and FIG.
In addition, since there is no need to calculate the target cornering force value, there is no step 104. Second, the calculation algorithm in step 105 ′ for calculating the corrected value δf_fb of the target steering angle yaw rate feedback term is different from step 105 in FIG.

In step 105 'in FIG. 3, first, the target steering angle yaw rate feedback term δf_
It is determined whether or not the value of fb_org is a value in a direction in which the steered wheels 10 are further turned. Specifically, based on the target yaw rate trg_yaw calculated in step 101 and the target steering angle yaw rate feedback term δf_fb_org calculated in step 102, if (trg_yaw · δf_fb_org> 0), it is determined that the turning direction is the further turning direction. In this case, the corrected value δf_fb of the target steering angle yaw rate feedback term is set to 0 (predetermined value). On the other hand, if (trg_yaw · δf_fb_org <0), it is determined that the vehicle is in the return direction, and in this case, it is not necessary to correct the target steering angle yaw rate feedback term, so δf_fb = δf_fb_org.

As described above, when the value of the target steering angle yaw rate feedback term δf_fb_org is a value in the direction in which the steered wheels 10 are increased, the value of the target steering angle yaw rate feedback term δf_fb_org is determined in advance. By limiting the steering wheel 10 to a predetermined value (zero in FIG. 3) and limiting the amount of turning of the steering wheel 10 to increase, unnecessary unnecessary turning of the steering wheel 10 is prevented, and the calculation procedure shown in FIG. The same effect as that described above can be obtained.

[0036]

As described above, according to the first aspect of the present invention,
According to the invention described in the above, in the steering angle control device of the vehicle having an auxiliary steering angle adjustment mechanism that performs the yaw rate feedback control, the grip limit of the tire of the steering wheel is estimated,
It is possible to provide a device that controls the steering angle of the steered wheel within a range that does not exceed the grip limit of the tire of the steered wheel.

According to the second aspect of the present invention, in the first aspect, even when it is difficult to estimate the grip limit of the tire of the steered wheel, the yaw rate feedback control can be performed. As a result, in the case where the steering wheel is further turned and controlled, the amount of turning can be limited.

Accordingly, a situation in which the steered wheels are unnecessarily turned too much and the running stability of the vehicle is reduced does not occur. In addition, since the steered wheels are not unnecessarily turned too much, steering delays at the time of turning back and the like are less likely to occur, and the steerability of the vehicle can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a connection of an entire vehicle steering angle control device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a specific calculation procedure of the controller in one embodiment of the invention according to claim 1 of the present invention.

FIG. 3 is a flowchart showing a specific calculation procedure of the controller in one embodiment of the invention according to claim 2 of the present invention.

FIG. 4 is a graph showing a general relationship between a cornering force and a slip angle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Steering wheel 11 Steering wheel 12 Steering input shaft 14 Auxiliary steering angle adjusting mechanism 15 Steering output shaft 19 Motor (actuator) 20 Controller (control means, estimation means)

Claims (2)

[Claims] 1. A steering angle transmission mechanism for steering a steering wheel in accordance with a rotation operation of a steering wheel, and a steering wheel transmission mechanism provided in a transmission path of the steering angle transmission mechanism so as to be able to further increase or return the steering wheel. An auxiliary steering angle adjustment mechanism, an actuator for driving the auxiliary steering angle adjustment mechanism, a target steering angle feedforward term calculated based on the rotation angle of the steering wheel, and a target yaw rate calculated from various vehicle motion state quantities. The target steering angle of the steered wheel is calculated as an added value with the target steering angle yaw rate feedback term calculated based on the deviation from the actual yaw rate. The actuator is operated so that the actual steering angle of the steered wheel becomes the target steering angle. Control means for controlling the, the control means comprises estimating means for estimating the limit cornering force value, A target cornering force calculated as an addition value of a target cornering force feedforward value calculated based on the rotation angle of the steering wheel and a target cornering force yaw rate feedback value calculated based on a deviation between the target yaw rate and the actual yaw rate. When the value exceeds the limit cornering force value estimated by the estimating means, the target cornering force yaw rate feedback value is corrected so that the target cornering force value does not exceed the limit cornering force value, and the target steering angle yaw rate is corrected. A steering angle control device for a vehicle, wherein a feedback term is corrected to a value corresponding to the corrected target cornering force yaw rate feedback value to calculate a target steering angle of the steered wheels. 2. A steering angle transmitting mechanism for steering a steering wheel in accordance with a rotation operation of a steering wheel, and a steering wheel provided in a transmission path of the steering angle transmitting mechanism so that the steering wheel can be turned up or back. An auxiliary steering angle adjustment mechanism, an actuator for driving the auxiliary steering angle adjustment mechanism, a target steering angle feedforward term calculated based on the rotation angle of the steering wheel, and a target yaw rate calculated from various vehicle motion state quantities. The target steering angle of the steered wheel is calculated as an added value with the target steering angle yaw rate feedback term calculated based on the deviation from the actual yaw rate. The actuator is operated so that the actual steering angle of the steered wheel becomes the target steering angle. Control means for controlling the target steering angle yaw rate feedback term to turn off the steered wheels. A steering angle control device for a vehicle, wherein the target steering angle yaw rate feedback term is limited to a predetermined value when the value is in the increasing direction.