JPH0220475A - Control device for steering angle - Google Patents

Abstract

PURPOSE:To improve the traveling stability of a vehicle by composing a steering angle control device spoiling no responsibility and stability even if various constants of a control system fluctuate with the change of an external part environment. CONSTITUTION:A rear wheel steering angle arithmetic part 14 outputs the aiming steering angle of a rear wheel 5 by its operation based on the car speed detection signal V fed from a car speed sensor 13 and the steering angle detection signal thetaF fed from a steering angle sensor 12. A motor control device 15 is equipped with an interface circuit, computer, etc., operating a control signal for a motor 7 according to the aiming steering angle thetaRS fed from the rear wheel steering angle arithmetic part 14 and the signal fed from the rotary encoder 7a outputting the turning position of the motor 7. A driving circuit 16 is equipped with a pulse width modulating circuit, a power element for a left rotation and that for a right rotation, performing a pulse width modulation control according to the control signal fed from the motor control device 15.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a steering angle control device that controls the steering angle of wheels, and in particular, even when various constants of a controlled object change.
This allows the desired response to be obtained.

[Conventional technology]

The conventional steering angle control device sets the target steering angle of the wheels to θ, l1, the transfer function of the controlled object composed of the steering angle variable mechanism and the actuator to C, (S), and the feedback gain to,
If the actual steering angle of the wheels is θ and the actual steering angular velocity is θ, this can be represented by a block diagram as shown in FIG. Note that S is a Laplace operator.

That is, since the control signal input to the controlled object Gr(S) is determined according to the displacement of the actual steering angle θ from the target steering angle θl, and the actual steering angular velocity, the actual steering angle θ, can quickly converge to the target steering angle θ□.

Here, the feedback gain Kl+Kffi has been determined in consideration of various constants of the controlled object measured in advance so as to provide a control system having desired responsiveness.

[Problem to be solved by the invention]

However, due to changes in the external environment such as the outside temperature, the constants of the controlled object fluctuate from the previously measured values, and the characteristics of the controlled object become different from those at the time the control system was designed. Since responsiveness cannot be obtained, it takes time for the actual steering angle to converge to the target steering angle, resulting in an unresolved problem that the running stability of the vehicle is impaired.

Also, when designing the control system, the feedback gain KI
Even if +2 is increased and the responsiveness of the control system is thereby improved, the overshoot amount of the actual steering angle with respect to the target steering angle becomes large, which impairs the stability of the control system. In some cases, there was a risk that the steady-state deviation would not become sufficiently small no matter how long it took, and the actual rake angle would oscillate.

This invention was made by focusing on the unresolved problems of the prior art described above, and it is possible to avoid loss of responsiveness and stability even if various constants of the control system fluctuate due to changes in the external environment. The purpose of the present invention is to provide a steering angle control device that does not require a steering wheel.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a control object that includes a variable steering angle mechanism that generates a steering angle to a wheel and an actuator that drives the variable steering angle mechanism in response to a control signal. In the steering angle control device controlled by an actuator control device that calculates and outputs, the actuator control device receives a target steering angle of the wheel and inputs a specific model that exhibits a desired response, and calculates the target steering angle in parallel with this specific model. is input, a precompensator whose transfer function has the transfer function of the specific model as the numerator and the transfer function of the controlled object as the denominator, and the difference between the output of the specific model and the output point of the controlled object and the and control signal calculation means for calculating the control signal based on the output of the predistorter.

[Effect]

The difference between the output of a specific model to which the target steering angle is input and which exhibits the desired response and the output of the controlled object, and the transfer function of the specific model to which the target steering angle is input is the denominator ζ, and the transfer function of the controlled object is the numerator. Based on the output of the precompensator, the control signal calculation means calculates a control signal for the actuator.

When the control signal is supplied to the actuator, the variable steering angle mechanism driven by the actuator is driven, and a steering angle is generated in the wheels.

For example, even if various constants of the controlled object fluctuate due to changes in the external environment and a difference occurs between the output of the controlled object and the output of a specific model, a control signal corresponding to this difference is calculated by the control signal calculation means. Since feedback control is performed to correct the difference, a desired response can be obtained from the controlled object.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

1 to 4 show an embodiment of the present invention, and this is an example in which a steering angle control device according to the present invention is applied to a rear wheel steering device of a vehicle.

First, the configuration will be explained. In FIG. 1, a rear wheel that can be steered around a kingpin shaft 4a is connected to an end of a tie rod 2 (one end omitted) that forms part of the rear wheel steering system via a ball joint 3 and a knuckle arm 4. 5 are connected.

A worm 2a is integrally formed on the periphery of the tie rod 2 at approximately the center in the longitudinal direction.
, - are screwed together by a ball nut 6 that is only rotatable and prevented from moving in the axial direction.

This ball nut 6 has an assist gear 8a fixed to its outer periphery G with the same rotating shaft, and an assist gear 8a that meshes with the assist gear 8a and is fixed to the output shaft of a motor 7 for rear wheel steering as an active motor. The rotational force of the motor 7 is transmitted through a reduction gear mechanism 8 constituted by a drive gear 8b, and when the ball nut G is rotated by the rotational force of the motor 7, the ball nut G is
The tie rod 2 integrally formed with the worms 2a meshing with the wheels 1 and 6 moves in the longitudinal direction, and as a result, a steering angle is generated in the rear wheels 5.

Here, tie rod 2. A worm 2''r, a ball joint 3, a knuckle arm 4, a pole nut 6, and a speed reduction mechanism 8 constitute a rear wheel steering device 1 as a variable steering angle mechanism.

In addition, a member 9 supported by the vehicle body (not shown) and a tie opening/
A coil spring 10 that biases the tie rod 2 so that the rear wheels 5 maintain a straight-ahead state is provided between the member 2b fixed to the door 2, and a coil spring 10 that biases the tie rod 2 so that the rear wheels 5 maintain a straight-ahead state, and a coil spring 10 that biases the tie rod 2 according to the rear wheel turning speed from the moving speed portion of the tie rod 2. Shock absorber 11 that generates damping force
is interposed. In addition, another coil spring and a shock absorber are interposed near the other end of the tie rod 2 located on the right side (not shown) in FIG. 1 with the same structure as above.

A steering angle sensor 12 detects the steering angle of a front wheel steering system (not shown), which detects the rotational position of the steering wheel and outputs a steering angle detection signal θ corresponding to the steering angle.

Reference numeral 13 denotes a vehicle speed sensor that detects the vehicle speed, and for example, detects the rotational speed of the output shaft of the transmission and outputs a vehicle speed detection signal V consisting of a periodic pulse signal corresponding to the rotational speed.

14 is a steering angle detection signal θ supplied from the steering angle sensor 12.
, and the vehicle speed detection signal (2) supplied from the vehicle speed sensor 13, the target steering angle θ of the rear wheels 5 is determined.

For example, when driving at low speeds, the front wheels and rear wheels 5 are used in reverse to improve the turning performance of the vehicle, and when driving at high speeds, the front wheels and rear wheels 5 are used in reverse. A target steering angle θ1 is calculated so that the running stability of the vehicle is improved by being in the same phase.

15 includes, for example, an interface circuit, a microcomputer, etc., and receives the target steering angle θ8.15 supplied from the rear wheel steering angle calculation unit 14. This is a motor control device as an actuator control device that calculates and outputs a control signal for the motor 7 according to the detection signal supplied from the rotary encoder 7a that outputs the rotational position of the motor 7. Note that since the transmission mechanism from the motor 7 to the rear wheels 5 is considered to be a rigid body, the detection signal supplied from the rotary encoder 7a corresponds to the actual steering angle θ8 and the actual steering angular velocity υ8 of the rear wheels 5.

16 includes a power element for left rotation, a power element for right rotation, etc. of the pulse width modulation circuit 2, and the motor control device 15
This is a drive circuit that performs pulse width modulation control in response to control signals supplied from the motor 7 and drives the motor 7.

That is, when the motor control device 15 executes a predetermined calculation to calculate a control signal for the motor 7, the drive circuit 16 performs pulse width modulation control in accordance with the control signal.
Depending on the pulse width, either the left or right rotational power element supplies current to the motor 7, and as a result, a predetermined rotational force is generated in the motor 7, so as described above, the rear wheel steering device 1
is driven, and a steering angle is generated in the rear wheels 5.

FIG. 2 shows a block diagram of the control system shown in FIG. 1, in which the rear wheel steering device 1 and the motor 7 constitute a controlled object.

The motor control device 15 includes a predetermined model 15a that exhibits a response desired by the designer, an @'II compensator 15b, and a control signal calculation section 15C that calculates a control signal for a controlled object. Predistorter 15b
The target rudder angle θ8. calculated by the target rudder angle calculating section is calculated by the target rudder angle calculating section.
are supplied, and the control signal calculation unit 15c calculates the predetermined model I 5 a and the output of the precompensator 15b "!H,'/
A control signal for the control device, that is, a drive current value j of the motor 7, is calculated based on do.

The control signal calculation unit 15c outputs the output y2 of the specific model 15a.
and the signal yr from the controlled object 20 (corresponding to the actual steering angle θ2 of the rear wheels 5) (y14 yr), and the output of this adder 15d (y14 yr)
is input to the regulator 15c, the output yF of the precompensator 151), and the output H(S) of the regulator 15e (yH-YP
) and outputs a drive current value i.

Here, the equation of motion of the controlled object 20 can be expressed by the following +11 and equation (2).

......(1) However, A-Ks*p/JB-(DKRP+Kll"G/R,)/JC
=Kr/J X□-θR: Angular position (rad) of motor 7 K 3RP
= K s */ (Ni+ D□/(NeIXN@z) ”DK
R: Viscosity of shock absorber 11 (kgf-S) K,; Back electromotive force constant of motor 7 (v-s/raa) KT
: Torque constant of motor 7 (kgf-Rin/A) (kg
fl・51) J:: Moment of inertia of motor 7 JGl: Moment of inertia of drive gear 8b JG! Moment of inertia J6z of near assist gear 8a: Moment of inertia JT of ball nut 7: Mini current moment of inertia of rear wheel 5 (A) G: Gravitational acceleration (m/s') R8: Internal resistance of motor 7.

Therefore, the transfer function GP(S) of the controlled object 20 is expressed by the following equation (3).

In this way, since the transfer function CP (S) of the controlled object 20 is a quadratic lag system, the state formula and transfer function G s ( s) as shown below (41, (5
1 and (6).

The state equation and transfer function Gr(S) of 5c are as shown in the following equations (?), +81, and (9), respectively.

S2+2ξ(13nS+ωI And, the precompensator 15c has its own transfer function c y
(s) is designed to have the transfer function GM(S) of the specific model 15a in the numerator and the transfer function CP(S) of the controlled object in the denominator, so the precompensator 1Gy(S
) -G, (S)/CP(S) -・
-(91 Also, in order to minimize the steady-state deviation of the actual steering angle, the adjuster 15e in the control signal calculation unit 15e constituting the feedback loop uses a proportional It was made into an integral element.

H(S) = (Kl 10Kz,”s)
--------(10) However, K and 2 are feed pack gain constants, respectively.

Therefore, the current applied to the motor 7 can be expressed as in the following equation 00.

1 (S) −Y, (S) + H(S) (Y, (S
)-YP(S) )...all Next, the operation of the above embodiment will be explained.

3 and 4 show that the four-wheel steering vehicle described in Japanese Patent Application Laid-Open No. 61-67670 is operated by the steering angle control device explained in the above embodiment and the conventional steering angle control device shown in FIG. It shows the simulation results of the change in rear wheel steering angle (Fig. 3.4 (a)) and the change in yaw rate 1 (Fig. 3.4 (b)) under control. FIG. 4 shows the case where no parameter variation has occurred, and the case where parameter variation has occurred. In the figure, O is the trajectory of the target steering angle, 0 is the trajectory of the output from the steering angle control device of the above embodiment, and Δ
1 and 2 respectively represent output trajectories of the conventional steering angle control device.

Here, the constants used in the simulation are as follows.

Vehicle specifications> Vehicle mass: M = 125 (kg) Equivalent cornering power of front wheels: ekf = 3750 (kg f /rad) Cornering power of rear wheels: kf = 6000 (kg f /rad) Yaw inertia of vehicle Moment: Iz = 200 Ckgf-m・s) Distance from vehicle center of gravity to front axle: LF=1.0 (rn) Distance from vehicle center of gravity to rear axle: Lr-1.5 (m) Steering gear Ratio: N=20 Yawley control model> Stability factor: As=2. Ox 10-'
Time constant: r-0.05 <Specifications of controlled object> NR+=40/l 5 Nuz= 220 Ksar =1.78 Qx 1 0-”DI[ll
! = =7.222 x 1 0-', =5.
95X 1 0-2 Kt = 5.83 x], 0-”R, = 0.1
32 J = 8.160X10-' G = 9.8 Motor section model> ωE60 ξ -0,5 <Feed bank gain> Conventional: + = -J/KT (K3IP/KT-ωfi") - −
5,038, =J/nia((Dx*r+,"G/re)/J-
2ξω8) = 4°437 This example: , = 200, = 10 In addition, the staining results in Fig. 4 show that due to the rise in outside temperature, the back electromotive force constant of the motor 7 and the torque constant KT
decreases by about 10%, and the internal resistance R.

This was done on the assumption that the amount increased by about 10%.

First, the simulation results when no parameter variation occurs will be explained.

As is clear from FIG. 3, the output of the steering angle control device of this embodiment follows the target values of the rear wheel steering angle and yaw rate with good responsiveness, similar to the conventional steering angle control device, and the steady-state deviation is also small enough.

Here, if the parameters of the controlled object 20 are the same as at the time of design and its transfer function has not changed, the transfer function G (S) of the control system shown in FIG. 2 is expressed by the following equation (2). It's going to be like that.

=C, (S)...
... 0 In this way, if the parameters of the controlled object 20 do not vary, the transfer function G of the entire control system shown in FIG.
(S) is equivalent to the transfer function G)1(S) of the specific model 15a exhibiting the desired response, so this specific model 1
If 5a is designed appropriately, a control system with excellent responsiveness and stability can be realized.

Next, the simulation results when the parameters of the controlled object 20 vary as described in 7 above will be explained.

As is clear from Fig. 4, in the conventional steering angle control device,
Because the transfer function of the controlled object differs from when the control device was designed, the feedbank gain set based on the past controlled object may have an inaccurate value for the current controlled object. Therefore, the human power signal to the controlled object due to the action of the feedback loop becomes an inaccurate value, and as a result, the stability of the controlled object, that is, the driving stability and driving safety of the vehicle is impaired.

On the other hand, in the steering angle control device of this embodiment, the motor control device I
5 is the difference (ys y
Since feedback control is performed based on p), the output yP of the controlled object 20 follows the output y of the specific model 15a. As a result, suitable outputs as shown in FIG. 4 (al and fbl) can be obtained.

In addition, in the steering angle control device of this embodiment, the controlled object 2
Even when various disturbances are input to the control system, not only the parameter fluctuation of 0, the output y of the controlled object 20,
follows the output '/H of the specific model 15a, so a desired response can be obtained.

In the above embodiment, the present invention is applied to a rear wheel steering angle control device, but the present invention is not limited thereto, and can also be applied to a front wheel steering system steering angle control device.

〔Effect of the invention〕

As explained above, according to the steering angle control device of the present invention,
ff1lJ consists of a variable steering angle mechanism that generates a steering angle on the wheels and an actuator that drives this variable steering angle mechanism.
? 8. The target steering angle is a specific model that exhibits a desired response when the target steering angle of the wheels is input, and the target steering angle is input in parallel with this specific model, and the transfer function has the transfer function of the specific model in the numerator, and control for calculating the control signal based on the aforementioned complementary 1fl unit having the transfer function of the controlled object as a denominator, the difference between the output of the specific model and the output of the control target image, and the output of the predistorter; Since the actuator is controlled by an actuator control device equipped with a signal calculation means, the control characteristics in the steady state are not affected by the control characteristics, and the control characteristics can be changed, for example, when the parameters of the controlled object fluctuate due to changes in the external environment, or when the control system Since the output of the controlled object follows the output of the specific model even when various disturbances are input to the control object, there is an effect that a desired response can be obtained from the controlled object.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the entire configuration of an embodiment of the present invention, FIG. 2 is a block diagram showing the control system of this embodiment, and FIGS. 3 and 4 are diagrams showing the configuration of this embodiment and the conventional example. This is a graph showing a comparison of the results of smearing, and FIG. 3 shows the case where no parameter fluctuation has occurred in the controlled object, and FIG. 4 shows the case where parameter fluctuation has occurred in the controlled object.
Fig. 364 (.1) shows the change in the rear wheel steering angle, and Fig. 364 (b) shows the change in the yaw rate of the vehicle. FIG. 5 is a block diagram showing a conventional control system. DESCRIPTION OF SYMBOLS 1... Rear wheel steering device, 5... Rear wheel, 7... Motor (actuator), 15... Motor control device (actuator control device), 15a... Specific model, 15
b... Precompensator, 15c... Control signal calculation unit, 2
゜・・・Controlled object.

Claims (1)

[Claims] (1) A controlled object consisting of a variable steering angle mechanism that generates a steering angle to the wheels and an actuator that drives the variable steering angle mechanism according to a control signal is controlled by an actuator control device that calculates and outputs the control signal. In the steering angle control device, the actuator control device includes a specific model in which the target steering angle of the wheels is input and exhibits a desired response, and the target steering angle is input in parallel with this specific model, and the transfer function is a precompensator having a transfer function of the model as a numerator and a transfer function of the controlled object as a denominator; A steering angle control device comprising: control signal calculation means for calculating the control signal.