JP3184324B2 - Vehicle steering system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forcible steering control of a rear wheel or a front wheel according to a steering state of a vehicle.
The present invention relates to an improvement in a vehicle steering system that enhances drivability and stability of a vehicle.

[0002]

2. Description of the Related Art Conventionally, a steering apparatus for a vehicle of this type determines a steering ratio of a rear wheel according to a vehicle speed with respect to a steering angle of a front wheel corresponding to a steering operation amount. It is known that the steering control of the rear wheels is known, but with this one, it is possible to obtain the steering performance that matches the driver's intention at any vehicle speed, but on the other hand, in the initial stage when the driver operates the steering. In this state, the front wheels and the rear wheels often have the same phase, and there is a regret that the turning performance of the vehicle in the initial state is low.

For this reason, conventionally, for example, Japanese Unexamined Patent Publication No.
In the device disclosed in Japanese Patent Publication No. 268, a control target yaw rate of a vehicle is calculated based on a steering amount of a driver, and a yaw rate of the vehicle is measured, and a yaw rate of the vehicle is measured according to a deviation between the measured value of the yaw rate and the control target value. The feedback control amount is calculated, and the steering angle of the rear wheel is feedback-controlled with the feedback control amount, thereby quickly generating a yaw rate even in the initial state of the steering operation, thereby improving the turning performance of the vehicle in this initial state. Is increasing.

[0004]

However, in the above-mentioned conventional feedback control, the feedback control amount is calculated only in accordance with the deviation between the actual measured value of the yaw rate and the control target value, and the rear wheels are steered. For this reason, there is also a limit in accurately controlling the actual yaw rate to the control target value.

Therefore, for example, it is conceivable to employ state feedback control instead of the above feedback control. In this state feedback control, in addition to the yaw rate, a plurality of state variables of the vehicle, for example, the sideslip angle of the wheel, the cornering force of the front wheel and the rear wheel, and the like are estimated to grasp the motion state of the vehicle. Since the control target is controlled using the plurality of state variables of the vehicle, if the steering angle of the front wheel or the rear wheel is feedback-controlled so that the yaw rate generated in the vehicle becomes the control target value, the vehicle is always controlled. Therefore, it is possible to control the vehicle optimally for drivability and stability, for example, by generating a target yaw rate and improving the turning performance of the vehicle at the time of steering operation.

In this case, in the state feedback control, it is general that the control gain is fixedly set to an appropriate value of a certain magnitude so as to obtain a quick response to a change in the state of the vehicle. . That is, when the steering angle of the front wheels is large and the cornering force of the vehicle enters a non-linear region that is not proportional to the side slip angle of the wheels, the stability of the vehicle tends to decrease, but the control gain is large at this time. Accordingly, a large control amount is calculated, the rate of change of the steering angle of the front wheels or the rear wheels increases, and the vehicle tends to be unstable. Therefore, when the control gain of the state feedback control is fixedly set to an appropriate value, when the vehicle travels straight,
From the viewpoint of enhancing the straightness, the fixed control gain is relatively small, the control amount is small, and it is difficult to quickly correct the state change of the vehicle, and it is difficult to improve the straightness of the vehicle. Regret arises.

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to use a state feedback control for steering control of a front wheel or a rear wheel as described above, and to increase a control gain of the state feedback control for a vehicle. It is an object of the present invention to improve the straight traveling performance of the vehicle by appropriately changing the traveling state according to the traveling state.

[0008]

In order to achieve the above object, a specific solution of the invention according to claim 1 is to steer a front wheel or a rear wheel separately from a steering wheel as shown in FIG. The steering means 20 and a plurality of state variables of the vehicle, including at least the actual yaw rate of the vehicle and the estimated sideslip angle of the wheels.
Observed, so that the actual yaw rate of <br/> vehicle based on a plurality of state variables of the observed vehicle to the control target yaw rate
Calculates the target control amount for the front or rear wheel steering,
State feedback control means 30 for performing feedback control of the steering means 20 based on the target control amount . Further, a steering angle detecting means 38 for detecting a front wheel steering angle of the vehicle.
And a gain correction means 33 for largely correcting the control gain of the state feedback control means 30 when the front wheel steering angle detected by the steering angle detection means 38 is small.

According to a second aspect of the present invention, a vehicle speed detecting means for detecting a vehicle speed is provided in place of the steering angle detecting means of the first aspect of the present invention, and the vehicle speed detected by the vehicle speed detecting means is high. In some cases, the control gain of the state feedback control means 30 is largely corrected by the gain correction means 33.

[0010]

According to the above construction, in the first and second aspects of the present invention, the operating means 20 is controlled by the state feedback control means 30, and the steering angle of the front wheel or the rear wheel is state feedback controlled. The yaw rate acting on the control target value accurately matches the control target value, and a good driving characteristic of the vehicle as controlled can be obtained.

In this case, when the state of the vehicle is largely changed, such as a turning state of the vehicle in which the driver largely operates the steering wheel, the stability of the vehicle is reduced. Since the control amount is calculated to an appropriate value with the control gain of the appropriate value of the control, the change rate of the steering angle of the front wheels or the rear wheels becomes appropriate for the vehicle in the unstable state, and the vehicle becomes unstable. The frequency is reduced, and the stability of the vehicle is improved.

On the other hand, when the front wheel steering angle is small and when the vehicle speed is high, that is, when the vehicle is running straight, the control gain of the state feedback control means 30 is greatly corrected by the gain correction means 33. The amount follows the state change during the straight running with good responsiveness, and as a result, the straight running is improved.

[0013]

As described above, according to the vehicle steering system of the first and second aspects of the present invention, when the state feedback control is used as the front or rear wheel steering angle control, the control gain is increased. When the front wheel steering angle is small or the vehicle speed is high, the value is corrected to a large value, so that the state feedback control amount when the vehicle state change is large can be set to an appropriate value, and the vehicle can be effectively prevented from becoming unstable. In addition, it is possible to effectively suppress the state change during the straight running of the vehicle, and to improve the straight running performance of the vehicle.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

FIG. 2 is a schematic plan view of a vehicle steering system according to the present invention, wherein 1 is a steering wheel, 2 is left and right front wheels, 3
Is a left and right rear wheel, 10 is a front wheel steering device that steers the left and right front wheels 2 and 2 by operating the steering 1, and 20 is a left and right rear wheel 3 according to steering of the front wheels 2 and 2 by the front wheel steering device 10. 3 is a rear wheel steering device as steering means for steering the third wheel.

The front wheel steering apparatus 10 has a relay rod 11 arranged in the width direction of the vehicle body, and both ends of the rod 11 are tie rods 12, 12 and a knuckle arm 1, respectively.
It is connected to the left and right front wheels 2, 2 via 3, 13.
The relay rod 11 is provided with a rack and pinion mechanism 14 for moving the relay rod 11 right and left in conjunction with the operation of the steering wheel 1. In this configuration, the front wheels 2, 2 are steered.

On the other hand, the rear wheel steering device 20 has a relay rod 21 disposed in the width direction of the vehicle body in the same manner as described above, and both ends of the rod 21 are respectively connected via tie rods 22, 22 and knuckle arms 23, 23. And are connected to the left and right rear wheels 3,3. The relay rod 21 is provided with a centering spring 22 for urging the rod 21 to a neutral position, and a rack-and-pinion mechanism 23. The mechanism 23 includes a clutch 24, a speed reduction mechanism 25. ,
When the clutch 24 is engaged, the relay rod 21 is moved in the vehicle width direction via the rack-and-pinion mechanism 23 by rotating the motor 26 when the clutch 24 is engaged, so that the rear wheels 3 are moved to the motor 26. The steering is steered by an angle corresponding to the rotation amount.

The motor 26 is connected to the control unit 2
It is more driving control 9. The control unit 29
As shown in FIG. 3, state feedback control is internally performed based on a plurality of state variables including at least the actual yaw rate and the side slip angle of the wheels, at which the state of the vehicle can be estimated. (Hereinafter referred to as LQG control)
LQG control means 30 as a state feedback control means, a vehicle speed sensitive MAP control means 31,
It basically has a control switching means 32 for selectively switching between LQG control by the control means 30 and MAP control by the vehicle speed sensitive MAP control means 31. The vehicle speed-sensitive MAP control means 31 sets the target steering angle of the rear wheel 3 to be controlled based on a map stored in advance so that the control is stable, such that the characteristic has a relatively strong tendency to understeer according to the vehicle speed and the front wheel steering angle. As described above, the steering angle of the rear wheel 3 is controlled by the motor 26 to the target steering angle.
As shown in (1), in the cornering force characteristics of the wheel with respect to the side slip angle β of the wheel, the control is stable even in a nonlinear region where the change of the cornering force is not proportional to the side slip angle β.

As shown in FIG. 3, the control unit 29 includes a lateral acceleration sensor 35 for detecting a lateral acceleration acting on the vehicle, a yaw rate sensor 36 for detecting an actual yaw rate acting on the vehicle, and a rear wheel. A rear wheel steering angle sensor 37 for detecting the steering angle of the front wheel 2, a front wheel steering angle sensor 38 for detecting the steering angle of the front wheel 2,
A vehicle speed sensor 39 as vehicle speed detecting means for detecting the vehicle speed is input.

Next, the drive control of the motor 26 by the control unit 29 will be described with reference to the control flow of FIG. In FIG. 5, when the control timing of each set cycle is reached in step S1, the above-mentioned sensors 3
Vehicle speed Vs, front wheel steering angle Fs based on detection signals of 6 to 39
tg, rear wheel steering angle Rstg, yaw rate d レ イ / dt occurring in the vehicle, and lateral motion Yg acting on the vehicle are measured for the motion state amount of each vehicle.

In step S3, a control target yaw rate yrt of the vehicle is calculated based on the following equation.

[0022] Here, A is the stability factor, and L is the wheelbase of the vehicle.

Thereafter, the front wheel steering speed df is calculated from the following equation based on the previous value and the current value of the front wheel steering angle Fstg detected by the front wheel steering angle sensor 38 in step S4.

Df = {Fstg (n) −Fstg (n−1)} * k (k is a proportionality constant) Then, in step S5, the cornering force of the wheel is set to the linear region and the nonlinear region shown in FIG. Front wheel steering speed dfo that generates the sideslip angle βo of the wheel at the boundary of
And the absolute value | df | of the actual front wheel steering speed. As a result, when it is in the linear region of | df | <dfo, the steering angle control amount RFB of the rear wheel 3 in the LQG control is calculated in steps S6 to S11. That is,
First, in step S6, a plurality of state quantities of the vehicle and a plurality of observation quantities of the vehicle (multiple
The number of state variables is calculated and estimated. Here, the state quantities of the vehicle include the side slip angle β of the vehicle and the change speed d of the steering angle of the rear wheels.
Rstg / dt, front wheel cornering force Cff,
And four kinds of rear wheel cornering forces Cfr are estimated. As the amount of vehicle observation, six types are calculated and estimated by adding the steering angle Rstg of the rear wheels and the yaw rate dψ / dt acting on the vehicle to the four types of estimated state quantities. However, the measured values are used for the steering angle Rstg and the yaw rate d レ イ / dt of the rear wheels. Here, the estimation of the state quantity and the observed quantity of the vehicle is performed by setting the estimated state quantity of the vehicle to xob and the estimated observed quantity of the vehicle to y.
Ob is performed by an operation based on the following state equation and output equation.

Dxob / dt = Aob * xob + Bob * y + Job * RFB (n-1) yob = Cob * xob + Dob * y where Aob, Bob, Cob, Dob and Job are observer gains, and RFB is an LQG control amount. , Y
Are the measured yaw rate dψ / dt and the LQG control amount RFB value.

After that, the value of the control gain in the LQG control is determined. In step S7, the absolute value | fstg | of the front wheel steering angle is compared with the minute value fo.
In step S8, the vehicle speed Vs is compared with the high vehicle speed value Vo, and
At the time of a large steering angle of | fstg | ≧ fo or at a low vehicle speed of Vs ≦ Vo, two control gains F and FI described later are set to appropriate values Fs and FIs in step S9, while | fst
At the time of a small steering angle of g | <fo or at a high vehicle speed of Vs> Vo, at step S10, the two kinds of control gains F and FI are set to values Fl and FIl (Fl (Fl) larger than the appropriate values Fs and FIs, respectively.
s <Fl, FIs <FIl).

Then, in step S11, the left and right rear wheels 3,
LQG control amount RFB as target control amount for three steerings
Is calculated. In this calculation, first, the measured yaw rate dψ / d
t and the control target yaw rate yrt (dψ / dt−
yrt) is calculated by the equation Sig (n) = Sig (n
-1) + (dψ / dt-yrt)
The control value obtained by calculating the actual yaw rate dψ / dt of the vehicle
The LQG control amount R is set so that the target yaw rate yrt is obtained.
The FB, the integration value Sig, the estimated observable yo
b, and the two types of control gains F and FI are used to calculate the following equation: RFB = −F * yob−FI * Sig.

Thereafter, in step S12, the steering angle control amount R of the rear wheel is calculated by the LQG control amount R calculated in step S11.
FB is set (R = RFB), and in step S13, the drive of the motor 26 is controlled by the control amount R to control the steering of the left and right rear wheels 3, 3.

On the other hand, in step S5, | df | ≧ df
In the non-linear region, the steering angle control amount RMAP of the rear wheel 3 in the vehicle speed sensitive MAP control is calculated in step S14, and the proportional constant r on the map corresponding to the vehicle speed Vsp shown in the step is first calculated. Then, the MAP control amount RMAP is obtained by multiplying the calculated proportional constant r by the front wheel steering angle fstg.

Thereafter, in step S15, the steering angle control amount R of the rear wheel is calculated by the MAP control amount RM calculated in step S14.
AP is set (R = RMAP), and in step S13, the drive of the motor 26 is controlled by the control amount R (= RMAP), and the left and right rear wheels 3, 3 are steered.

Therefore, in the control flow of FIG.
Steps S6 and S11 constitute the state feedback control means 30. Also, at steps S7, S8 and S10, when the front wheel steering angle | fstg | The control gains F and FI of the state feedback control means 30 are set to appropriate values F
s, FIs to be corrected to be larger than Fl, FIl (Fs <
The gain compensating means 33 is configured to set Fl, FIs <FIl).

Therefore, in the above embodiment, the steering speed | df | of the front wheel is slower than the set value dfo (| df).
In the case of | <dfo), the cornering force of the wheel is in the linear region, and the steering angle of the rear wheels 3, 3 is LQG controlled by the LQG control means 30, so that the yaw rate of the vehicle is accurately adjusted to the control target value yrt. Under the control, the intended vehicle motion characteristics are obtained, and the driving performance of the vehicle is improved.

In such a case, when the front wheel steering angle | fstg | exceeds a set value fo and the vehicle turns, for example, the side slip angle of the wheels approaches the non-linear region of FIG. 5 and the stability of the vehicle is likely to decrease. However, at this time, since the two kinds of control gains F and FI of the LQG control are set to the predetermined appropriate values Fs and FIs, the LQG control amount RFB is also set to an appropriate value and the state of the vehicle is changed. The steering angle change rate of the rear wheels 3 also becomes an appropriate value with respect to the change, and the stability of the vehicle is properly secured.

On the other hand, when the front wheel steering angle | fstg | is smaller than the set value fo, or when the vehicle speed Vs decreases
During the above-described high-speed running, that is, when the vehicle is running straight, the two types of control gains F and FI of the LQG control are set to the predetermined values Fs and F.
LQG is set to a value Fl, FIl larger than Is.
Since the control amount RFB also becomes large accordingly, the steering angle of the rear wheel 3 quickly changes in response to a change in the state of the vehicle,
The straight running performance of the vehicle is improved.

FIG. 6 shows another embodiment. In the above-described embodiment, the rear wheels 3, 3 are controlled electrically using the rear wheel steering device 20, and the front wheels 2, 2 are electrically controlled separately from the steering. This is applied to a steering control.

That is, in the steering system shown in FIG.
The rear wheel steering device 20 shown in FIG. 1 is not provided, and the rack and
A pinion mechanism 40 and a motor 41 for driving the mechanism 40
The door is provided, which is configured to drive control by the control unit 29 of the motor 41. Other configurations are the same as those of the above-described embodiment. However, in the present embodiment, when the rear wheels are steered and the rear wheels are steered in the opposite phase to the front wheels, the front wheels are steered. Steering control to increase the angle,
In the above embodiment, when the steering control of the rear wheels is performed in the same phase, in the present embodiment, the steering control may be performed to reduce the steering angle of the front wheels.

In the above description, in the LQG control, there are six types of estimated observable amounts of the vehicle, namely, the side slip angle β of the vehicle, the change speed dRstg / dt of the steering angle of the rear wheel, and the cornering force of the front and rear wheels. Cff, Cfr, the steering angle Rstg of the rear wheels, and the yaw rate dψ /
Although the state of the vehicle was accurately observed using dt, it is sufficient to observe the state of the vehicle at least by observing the actual yaw rate of the vehicle and the estimated sideslip angle of the wheel.

[Brief description of the drawings]

FIG. 1 is a block diagram of the first embodiment of the present invention;

FIG. 2 is a diagram illustrating an overall configuration of a steering device that also steers a rear wheel of a vehicle.

FIG. 3 is a diagram showing a block configuration of steering control of a rear wheel.

FIG. 4 is a diagram showing a control flow of rear wheel steering control.

FIG. 5 is a diagram showing a cornering force characteristic with respect to a side slip angle of a wheel.

FIG. 6 is a diagram showing an overall configuration of a steering device that steers a front wheel.

[Explanation of symbols]

Reference Signs List 1 steering 3 rear wheel (wheel) 20 rear wheel steering device 26 motor 29 control unit 30 LQG control means (state feedback control means) 33 gain correction means 35 lateral acceleration sensor 36 yaw rate sensor 37 rear wheel steering angle sensor 38 front wheel steering angle sensor (Steering angle detecting means) 39 Vehicle speed sensor (vehicle speed detecting means)

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ identification code FI B62D 117: 00 137: 00 (58) Field surveyed (Int.Cl. ⁷ , DB name) B62D 6/00 B62D 7/14

Claims (2)

(57) [Claims] 1. A steering means for steering a front wheel or a rear wheel separately from a steering, at least an actual yaw rate of a vehicle and an estimated side slip angle of wheels.
Observes multiple state variables of the vehicle including
The steering of the front or rear wheels is controlled so that the actual yaw rate of the vehicle becomes the control target yaw rate based on the two state variables .
The target control amount to be calculated is calculated, and the target steering amount is calculated based on the target control amount.
A state feedback control means for feedback controlling means, and steering angle detecting means for detecting a front wheel steering angle of the vehicle, when the front-wheel steering angle detected by the steering angle detecting means is small, the control gain of the state feedback control means A steering apparatus for a vehicle, comprising: a gain correcting means for performing a large correction. 2. Steering means for steering front or rear wheels separately from steering, at least the actual yaw rate of the vehicle and the estimated sideslip angle of the wheels.
Observes multiple state variables of the vehicle including
The steering of the front or rear wheels is controlled so that the actual yaw rate of the vehicle becomes the control target yaw rate based on the two state variables .
The target control amount to be calculated is calculated, and the target steering amount is calculated based on the target control amount.
A state feedback control means for feedback controlling means, and vehicle speed detecting means for detecting a vehicle speed, when the vehicle speed is high, which is detected by the vehicle speed detecting means, and gain correction means for increasing correcting the control gain of the state feedback control means A steering device for a vehicle, comprising: