JP3152265B2 - Four-wheel 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 four-wheel steering system for providing an auxiliary steering angle by yaw rate feedback control during front wheel steering.

[0002]

2. Description of the Related Art Conventionally, as a four-wheel steering device for giving an auxiliary steering angle to rear wheels by yaw rate feedback control during front wheel steering, for example, a device described in Japanese Patent Application Laid-Open No. 63-192667 is known.

[0003]

However, in the conventional four-wheel steering system described above, only one delay time constant is set as a delay time constant for obtaining the target yaw rate. As shown in the yaw rate characteristic of No. 6, when the delay time constant is set to a small value in order to obtain a quick turning characteristic when turning the rudder further, the vehicle response becomes too sensitive at the time of turning back the rudder, and the actual yaw rate becomes lower. The convergence decreases.

[0004] Therefore, if the delay time constant is set to a large value in order to obtain a gentle convergence at the time of turning back the rudder, turning performance is poor when turning the rudder further.

That is, there is a problem that it is not possible to obtain a desirable yaw rate characteristic at each of the corner entrance where the rudder is turned more and the corner exit where the rudder is turned back.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problem. An object of the present invention is to provide a four-wheel steering system which provides an auxiliary steering angle by yaw rate feedback control during front wheel steering. The aim is to achieve both quick turning at the time and gentle convergence at the time of turning back the rudder.

[0007]

In order to solve the above-mentioned problems, in the four-wheel steering system according to the present invention, when the direction of change in the steering angle is the increasing direction, the delay time constant is set to a low value when the changing direction of the steering angle is increased. Sometimes a delay time constant setting means for setting a delay time constant having a high value is provided, and a target yaw rate calculation means for calculating a target yaw rate based on the target yaw rate steady value and the set delay time constant is provided.

That is, as shown in the claim correspondence diagram of FIG. 1, an auxiliary steering angle actuator a capable of giving an auxiliary steering angle to at least one of the front and rear wheels by an external command.
A vehicle speed detecting means b for detecting a vehicle speed, a steering steering angle detecting means c for detecting a steering steering angle, a yaw rate detecting means d for detecting a yaw rate, and calculating a target yaw rate steady value according to the vehicle speed and the steering angle. A target yaw rate steady value calculating means e; a steering steering angle change direction determining means f for determining whether the direction of change of the steering angle is a turning-up direction or a turning-back direction; A delay time constant setting means g which sets a low value of the delay time constant and sets a high value of the delay time constant in the reverse direction, and calculates the target yaw rate by the target yaw rate steady value and the set delay time constant. The target yaw rate calculating means h and the actual yaw rate from the yaw rate detecting means d coincide with the target yaw rate. Includes a yaw rate feedback control means i for outputting a command for controlling the auxiliary steering angle amount in the auxiliary steering angle actuator a, a.

[0009]

During front wheel steering, the target yaw rate steady value calculating means e calculates the target yaw rate steady value according to the vehicle speed from the vehicle speed detecting means b and the steering angle from the steering angle detecting means c. The direction judging means f judges whether the changing direction of the steering angle is the turning direction or the turning back direction, and the delay time constant setting means g has a low value when the changing direction of the steering angle is the turning direction. Set to a constant,
In the reverse direction, the lag time constant is set to a high value,
The target yaw rate calculating means f calculates the target yaw rate based on the target yaw rate steady-state value and the set delay time constant.

In the yaw rate feedback control means i, a command for controlling the amount of auxiliary steering angle is output to the auxiliary steering angle actuator a so that the actual target yaw rate from the yaw rate detection means d matches the calculated target yaw rate. An auxiliary steering angle is given to one of the front and rear wheels.

Therefore, for example, at the corner entrance side where the steering angle is increased by turning the steering wheel during step steering, the steering angle is set based on the low delay time constant set by the delay time constant setting means g. , A target yaw rate with a good response to the change of the vehicle speed is calculated, and the yaw rate of the vehicle rises with a good response and a quick turning property can be obtained.

On the corner exit side where the steering angle is turned back, a sufficient response delay to a change in the steering angle is obtained based on the high value of the delay time constant set by the delay time constant setting means g. And the target yaw rate is calculated, and the yaw rate of the vehicle converges gently.

[0013]

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

The configuration will be described.

FIG. 2 is an overall system diagram showing a vehicle to which the four-wheel steering system according to the embodiment of the present invention is applied.

In FIG. 2, the front wheels 1 and 2 are steered by a steering handle 3 and a mechanical link type steering mechanism 4.
Done by This includes, for example, a steering gear, a pitman arm, a relay rod, side rods 5, 6, knuckle arms 7, 8, and the like.

The steering of the rear wheels 9, 10 is performed by an electric steering device 11 (corresponding to an auxiliary steering angle actuator a). The rear wheels 9, 10 are connected by a rack shaft 12, side rods 13, 14, and knuckle arms 15, 16, and a rack tube 17 in which the rack 12 is inserted has a speed reduction mechanism 18 and a motor 19.
The motor 19 and the fail-safe solenoid 20 are provided with a vehicle speed sensor 21 (corresponding to a vehicle speed detecting means b) and a front wheel steering angle sensor 22.
Drive control is performed by a controller 26 that inputs signals from the steering angle detection means c (corresponding to the steering angle detection means c), the rear steering angle sub-sensor 23, the rear steering angle main sensor 24, and the yaw rate sensor 25 (corresponding to the yaw rate detection means d).

FIG. 3 is a sectional view showing a specific structure of the electric steering apparatus 11.

In FIG. 3, a rack tube 17 in which the rack 12 is inserted is fixed to the vehicle body via a bracket. Side rods 13 and 14 are connected to both ends of the rack 12 via ball joints 30 and 31. The reduction mechanism 18 includes a motor pinion 32 connected to the motor shaft of the motor 19, a ring gear 33 meshing with the motor pinion 32, and a rack pinion 35 fixed to the ring gear 33 and meshing with the rack gear 12a. Have been. Therefore, when the motor shaft of the motor 19 rotates, the rotation is transmitted to the motor pinion 32 → the ring gear 33 → the rack pinion 35, and the rack shaft 12 moves in the axial direction due to the engagement between the rotating rack pinion 35 and the rack gear 12a. The rear wheels 9, 10 are steered. This rear wheel 9,10
Is proportional to the amount of movement of the rack shaft 12, that is, the amount of rotation of the motor shaft.

The rack pinion 35 is provided with a rear steering angle main sensor 24 having a potentiometer structure for detecting a rear wheel steering angle based on the rotation amount.

The fail-safe solenoid 20 includes:
The lock pin 20a is provided so as to be able to advance and retreat, and when a failure occurs in the electronic control system or the like, the lock pin 20a is fitted into a lock groove 12b formed in the rack shaft 12 so that the rack shaft 12 and the rear wheels 9, 10 are moved. It is fixed at a position to maintain the neutral steering angle position.

The operation will be described.

[Rear Wheel Steering Angle Control Operation] FIG. 4 is a flowchart showing the flow of the rear wheel steering angle control operation performed by the controller 26. Each step will be described below.

In step 40, the vehicle speed V, the steering angle θ, the yaw rate sensor value ψ ′S, and the rear steering angle main sensor value δrS are read.

In step 41, a target yaw rate steady value ψ'MO as a yaw rate value per unit steering angle is calculated for each vehicle speed based on the vehicle speed V and the steering angle θ (the target yaw rate steady value calculating means e). Equivalent).

In step 42, it is determined whether or not a value obtained by multiplying the steering angle θ by the steering angle differential value θ ′ is equal to or greater than 0 (corresponding to the steering angle change direction determining means f).

That is, when θ · θ ′ ≧ 0, it is determined that the direction of change in the steering angle is a turning-up direction, and when θ · θ ′ <0, the direction of change in the steering angle is turned back. The direction is determined.

In step 43, θ · θ ′ ≧ 0,
When it is determined that the steering rudder angle change direction is the turning direction, the first-order lag time constant TO is set to TOp (<TOm) by a low value for obtaining the turning property (corresponding to the lag time constant setting means g) ).

In step 44, θ · θ ′ <0, and
When it is determined that the steering angle change direction is the return direction, the first-order lag time constant TO is set to TOm (> TOp) by a high value for obtaining convergence (corresponding to the lag time constant setting means g). ).

In step 45, the target yaw rate ψ'M is calculated by the following equation using the target yaw rate steady-state value ψ'MO and the first-order lag time constant TO set in step 43 or step 44 (target yaw rate calculation means h). Equivalent).

Ψ'M = ψ'MO / (1 + TO · S) S;
In the Laplace operator step 46, a deviation ε between the target yaw rate ψ′M and the detected yaw rate ψ ′S is calculated.

In step 47, the deviation ε is determined according to the vehicle speed V.
Are set on the basis of the map.

In step 48, the deviation ε and the proportional term K
The feedback rear wheel steering angle δrF / B is calculated by the following equation based on P and the differential term KD.

In step 49, the feedback rear wheel steering angle δrF / B in step 48 is converted to a motor rotation target value THi.

In step 50, the rear steering angle main sensor value δrS is converted to an actual motor rotation value THNO.

In step 51, the motor control current IM is calculated from the motor rotation target value THi and the motor rotation actual value THNO.

At step 52, PW is set according to the output command.
The duty ratio of M is controlled, and a motor control current IM is output.

Steps 46 to 52 correspond to the yaw rate feedback control means i.

At the time of turning, for example, at the time of turning at the time of step steering, at the corner entrance side where the steering angle is increased, the flow proceeds from step 42 to step 43 in the flowchart of FIG.
In 3, the first-order lag time constant TO is set to a low value TOp.

Then, in step 45, a target yaw rate ψ'M having a good response to a change in the steering angle is calculated based on the first-order lag time constant TO having a low value. By controlling the rear wheel steering angle so that the actual yaw rate matches M, at the corner entrance side, the actual yaw rate of the vehicle rises swiftly and quickly along the target yaw rate ψ'M as shown in FIG. Property is obtained.

On the corner exit side where the steering steering angle is turned back, the flow proceeds from step 42 to step 44 in the flowchart of FIG.
In step 44, the first-order lag time constant TO is set to a high value TOm.

In step 45, the target yaw rate ψ'M is calculated with a sufficient response delay with respect to the change in the steering angle based on the high-order first-order lag time constant TO. By controlling the rear wheel steering angle so that the actual yaw rate matches the target yaw rate ψ'M, FIG.
As shown in the figure, the actual yaw rate of the vehicle converges gently on the corner exit side.

The effect will be described.

In a four-wheel steering system in which an auxiliary steering angle is applied to the rear wheels 9 and 10 by yaw rate feedback control when the front wheels 1 and 2 are steered, when the direction of change in the steering angle is increasing, the value of the first-order lag is low. Set to the constant TO,
In the case of the turning back direction, the first-order lag time constant TO is set to a high value, and the target yaw rate ψ'M is calculated based on the target yaw rate steady-state value ψ'MO and the set first-order lag time constant TO.
A device that performs yaw rate feedback control so that the yaw rate detection value ψ'S matches this target yaw rate ψ'M. Can be.

Although the embodiment has been described with reference to the drawings, the specific configuration is not limited to the embodiment, and even if there are changes and additions without departing from the gist of the invention, the invention is included in the invention. It is.

For example, in the embodiment, the example of the four-wheel steering device using the electric actuator has been described, but the present invention can also be applied to the four-wheel steering device using the hydraulic actuator.

In the embodiment, the example in which only the rear wheels are assisted is shown. However, the present invention can be applied to a device in which both the front and rear wheels are assisted.

[0048]

As described above, according to the present invention, in a four-wheel steering system in which an auxiliary steering angle is provided by yaw rate feedback control at the time of front wheel steering, a low value is obtained when the direction of change of the steering angle is a turning direction. And a delay time constant setting means for setting the delay time constant to a high value in the reverse direction, and calculating a target yaw rate based on the target yaw rate steady value and the set delay time constant. Since the calculation means is provided, it is possible to obtain an effect that it is possible to achieve both quick turning performance when turning the rudder further and gentle convergence when turning back the rudder.

[Brief description of the drawings]

FIG. 1 is a view corresponding to a claim showing a four-wheel steering device of the present invention.

FIG. 2 is an overall system diagram showing a vehicle to which the four-wheel steering device of the embodiment is applied.

FIG. 3 is a cross-sectional view of the electric steering device of the embodiment device.

FIG. 4 is a flowchart illustrating a flow of a rear wheel steering angle control operation performed by a controller of the embodiment device.

FIG. 5 is a diagram illustrating a steering angle characteristic, a target yaw rate, and an actual yaw rate characteristic when the vehicle is turning with step steering in the embodiment.

FIG. 6 is a diagram showing a steering angle characteristic diagram, a target yaw rate, and a steering angle characteristic at the time of turning with step steering in the conventional device.
It is an actual yaw rate characteristic diagram.

[Explanation of symbols]

 a auxiliary steering angle actuator b vehicle speed detecting means c steering steering angle detecting means d yaw rate detecting means e target yaw rate steady value calculating means f steering steering angle change direction determining means g delay time constant setting means h target yaw rate calculating means i yaw rate feedback controlling means

Continuation of the front page (56) References JP-A-3-10970 (JP, A) JP-A-63-192667 (JP, A) JP-A-4-358965 (JP, A) JP-A-4-303068 (JP) JP-A-5-58315 (JP, A) JP-A-4-193684 (JP, A) JP-A-4-3499071 (JP, A) JP-A-4-303069 (JP, A) 3-213466 (JP, A) JP-A-4-166473 (JP, A) JP-A-1-172059 (JP, A) JP-A-6-278631 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B62D 6/00 B62D 7/14

Claims (1)

(57) [Claims] 1. An auxiliary steering angle actuator capable of giving an auxiliary steering angle to at least one of the front and rear wheels by an external command, a vehicle speed detecting means for detecting a vehicle speed, and a steering steering angle detecting means for detecting a steering steering angle. And yaw rate detection means for detecting a yaw rate; target yaw rate steady value calculation means for calculating a target yaw rate steady value according to the vehicle speed and the steering angle; and determining whether the direction of change in the steering angle is the increasing direction or the returning direction. Means for determining a steering angle change direction to be determined; a delay time constant set to a low value delay time constant when the direction of change of the steering angle is increasing, and to a high value delay time constant when the direction of change of the steering angle is reverse. Setting means; a target yaw rate for calculating a target yaw rate based on the target yaw rate steady value and a set delay time constant. A rate calculating means, and a yaw rate feedback control means for outputting a command for controlling an auxiliary steering angle amount to the auxiliary steering angle actuator so that the actual yaw rate from the yaw rate detecting means matches the target yaw rate. A four-wheel steering system characterized by the following.