JP2784448B2 - Integrated control system for vehicle rear wheel steering and brake control - Google Patents

Abstract

PURPOSE:To obtain stable braking control and apply an efficient brake from the start of the brake by providing an integrated control device correcting the steering ratio characteristic to the same phase side when the slip ratio of wheels reaches the steering ratio characteristic correction threshold value. CONSTITUTION:The 4WS controller 10 of a four-wheel-steered vehicle determines the rear wheel steering angle from the vehicle body speed information based on the preset steering ratio characteristic and controls the steering of rear wheels 2R via a motor 4. An ABS device 20 controlling the brake liquid pressure is provided, it calculates the slip ratio and acceleration of wheels from the wheel speed information, and it compares calculated values with the brake control start threshold value to control the brake liquid pressure. The steering ratio characteristic correction threshold value is set to the slip ratio smaller than the brake control start threshold value, and an integrated control device 30 is provided which corrects the steering ratio characteristic to the same phase side if the slip ratio of vehicles reaches this threshold value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention controls a steerable rear wheel with respect to a front wheel with a predetermined steering ratio characteristic, and sets a wheel slip ratio to a target slip ratio during braking. The present invention relates to an overall control device for rear wheel steering and brake control of a vehicle to be brake-controlled.

[Related Art and Problems] Recently, there is a four-wheel steering (so-called 4WS) vehicle capable of steering not only a front wheel but also a rear wheel. As a rear-wheel steering control method for such a four-wheel steering vehicle, There is a so-called speed-sensitive type in which the steering angle of the rear wheels with respect to the steering angle of the front wheels (that is, the steering ratio) is changed according to the speed (vehicle speed) of the vehicle. This is a relationship between a predetermined vehicle speed and a steering ratio (steering ratio characteristic).
Normally, the rear wheels are set to be steered to the same side (the same phase) as the front wheels at a high speed, and to the opposite sides (opposite phase) to the front wheels at a low speed. According to this, there is an effect that the straight running stability is improved at a high speed and a stable turning with little change in posture is possible, and a small turning is effective at a low speed.

In such a speed-sensitive type 4WS, the running characteristics of the vehicle change depending on the setting of the steering ratio characteristics, so that the steering ratio characteristics can be corrected and multiple steering ratio characteristic maps can be switched according to the driver's preference and driving conditions. It is conceivable to obtain improved running characteristics.

On the other hand, recently, many vehicles are equipped with a braking control device (anti-lock brake system: hereinafter, referred to as ABS) that controls a braking force so as to prevent the wheels from locking during braking.

ABS detects the rotation of all the wheels by a sensor, estimates the speed of the vehicle based on the rotation speed of these wheels, calculates the slip ratio of the wheels, and when braking, this slip ratio is a predetermined value with good braking efficiency. The brake fluid pressure is controlled so as to keep the wheels from locking, and specifically, the braking target vehicle speed when the vehicle is decelerated from the estimated vehicle speed at the target slip ratio with good braking efficiency is determined. When the slip ratio reaches a predetermined braking control start threshold value, braking control is performed so that the wheel speed (wheel rotational peripheral speed) matches the braking target vehicle body speed. (JP
As a result, it is possible to maintain the directional stability during braking, secure the maneuverability, and shorten the braking stop distance.

Here, the slip ratio with good braking efficiency is generally about 15 to
Although it is said to be around 20%, if the braking target vehicle speed is set using the slip ratio with the highest braking efficiency, braking can be performed satisfactorily in a straight-ahead state, but during cornering that requires cornering force ( In other words, there is a possibility that the wheel easily loses grip during braking in the steered state. That is, at the time of turning, the steering wheel is steered larger than the actual traveling direction to give a larger side slip angle to the wheel, and the component force of the grip force in the wheel rotation direction generated by the side slip angle toward the turning center direction acts as a cornering force. However, the grip force in the wheel rotation direction is reduced by the cornering force, and when the braking control is performed with the slip ratio having the highest braking efficiency as the target slip ratio as in the case of straight traveling, the grip component in the braking direction is smaller than that in the straight traveling. The wheels are easily locked.

For this reason, it is general to set the target slip ratio to a value lower than the slip ratio with the highest braking efficiency in consideration of braking during turning.

By the way, in a 4WS vehicle as described above, a large cornering force can be obtained when the rear wheels are turning to the same phase side, so that it is possible to improve the braking efficiency by increasing the target slip ratio in the braking control. It becomes possible. or,
Conversely, it is conceivable to correct the steering ratio so that the required cornering force is obtained based on the slip ratio of the wheel obtained by the ABS during turning, and in this case, the target slip ratio in the braking control is considered. Should be high from the beginning (slip ratio with the best braking efficiency).

In other words, the steering ratio characteristic of the 4WS and the braking control have a close relationship, and when the steering ratio characteristic is corrected or a plurality of steering ratio characteristic maps are switched, the steering ratio characteristic is adapted according to the applied steering ratio characteristic. It is desirable to perform the braking control by changing the target slip ratio.

However, when the steering ratio characteristic of the 4WS is configured to be automatically corrected and switched according to the driving state, and the target slip ratio of the braking control is corrected after the steering ratio characteristic is changed. If the braking operation is being performed when the steering ratio characteristic is changed, the degree of effectiveness of the brake changes due to the change in the target slip ratio accompanying the change in the steering ratio characteristic, and the feeling of braking becomes jerky. For example, if the steering ratio characteristic is corrected after the braking control is started, and the target slip ratio of the braking control is changed based on the corrected steering ratio characteristic, the braking force is initially set to the target slip ratio. It is bad because it is low, and it gradually improves as the steering ratio characteristic is corrected and the target slip ratio changes (increases). It is not only dangerous but also dangerous.

[Object of the Invention] In view of the above-mentioned circumstances, the present invention is to perform a stable braking control by changing a steering ratio characteristic in advance before a braking control and preventing a change in a target slip ratio during the braking control. It is an object of the present invention to provide a total control device for rear wheel steering and brake control of a vehicle that can perform the control.

[Constitution of the Invention] For this reason, the integrated control device for rear wheel steering and brake control of the vehicle according to the present invention performs steering control with a predetermined steering ratio characteristic of a rear wheel with respect to a front wheel based on vehicle speed information. Rear wheel steering control means for detecting the rotation of the wheels and calculating the slip ratio thereof. When the slip ratio reaches a predetermined braking control start threshold value during braking, braking is performed so that the slip ratio becomes the target slip ratio. A braking control device for controlling the operation of the device;
A steering ratio characteristic correction threshold value set to a slip ratio smaller than a braking control start threshold value in the braking control device, and when the wheel slip ratio reaches the steering ratio characteristic correction threshold value, the steering ratio characteristic of the rear wheel steering control means is increased. And a general control means for correcting the phase shift to the same phase side.

According to this, the steering ratio characteristic is corrected before the braking control is performed, and when the slip ratio reaches the braking control start threshold and the braking control is required, the steering ratio characteristic is corrected from the beginning based on the corrected steering ratio characteristic. Steering control and braking control can be performed.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a vehicle 1 provided with an overall control device for rear wheel steering and brake control of the vehicle according to the present invention,
The rear wheels 2R (2RL, 2RR) are configured to be steerable, and the 4WS controller 10 as rear wheel steering control means for steering-controlling the rear wheels 2R ... with the front wheels 2F (2FL, 2FR) at a predetermined steering ratio.
And an ABS device 20 as a braking control device, and a comprehensive control device 30 as comprehensive control means for integrally controlling the 4WS controller 10 and the ABS device 20.

In the steering mechanism of the vehicle 1, the front wheels 2F are steered by rotation of a steering wheel 3 via a gear train, and the rear wheels 2R are steered by driving a motor 4 controlled by a 4WS controller 10. It has become.

The front wheel steering mechanism is provided with a steering angle sensor 5, and steering information of the front wheels detected by the steering angle sensor 5 is input to the 4WS controller 10.

The front wheel steering information from the steering angle sensor 5 and the vehicle speed information from the vehicle speed sensor 6 are input to the 4WS controller 10, and the 4WS controller 10 determines the input information and a predetermined value to be described later. The rear wheel steering angle is determined based on the steering ratio characteristics, and the motor 4 is controlled and driven to steer the rear wheels. The rear wheel steering angle is detected by a rear wheel steering angle sensor 7 provided in the rear wheel steering mechanism and input to the 4WS controller 10 to perform feedback control.

Here, the 4WS controller 10, as shown in FIG.
Two steering ratios, a basic steering ratio characteristic indicated by A in the drawing and a corrected steering ratio characteristic indicated by B in the drawing when the basic steering ratio characteristic is corrected to a stable side (in-phase side), which are applied in a normal traveling state. Has characteristics. Switching from the basic steering ratio characteristic A to the corrected steering ratio characteristic B is performed by the integrated control device 3 based on information from the ABS device 20.
This is performed by a command from 0, and will be described later in detail.

The ABS device 20 controls the brake fluid pressure supplied to the wheel cylinders 2S provided for the respective wheels 2 so that the wheels 2 can be efficiently braked without being locked during braking.

Wheel speed information is input to the ABS device 20 from wheel speed sensors 21 provided in the vicinity of the wheels 2. The ABS device 20 controls the wheel speed as shown in FIG. As shown in the flowchart, based on the wheel speed information, the speed of each wheel (rotational peripheral speed of the wheel) and the speed of the vehicle are estimated (pseudo body speed), and the slip ratio: S and acceleration: V of each wheel are calculated. and (S11, S12, S13 and S14), the wheel slip ratio, which is the calculation: S and acceleration: respectively preset by which the braking control start threshold: compared S _{1, 1} a, either one but If the braking control start threshold has been reached, the hydraulic unit 20HU is controlled and driven to perform braking control (S15, S16 and S17).

As shown in FIG. 3, one hydraulic circuit of the hydraulic unit 20HU has a normal passage N used for normal braking, an ABS passage B used for ABS operation, and a return passage R formed by an F valve 22, A check valve 23, a magnet valve 24, a reservoir 25, a pump 26, and an accumulator 27 are used. FIG. 3 shows only one hydraulic circuit as described above. Hereinafter, description will be made based on this drawing, but a similar hydraulic circuit is configured for each wheel.

The normal passage N connects the master cylinder 28 and the wheel cylinder 2S via an F valve 22 and a magnet valve 24 in series.

The ABS passage B branches off from the normal passage N between the F valve 22 and the magnet valve 24, and the accumulator 27, the pump 26
And a reservoir 25 via a reservoir 25.

The return passage R connects the master cylinder 2M and the wheel cylinder 2S via the check valve 23, and is a passage for returning the brake fluid from the wheel cylinder 2H to the master cylinder 2M when the brake is released.

The F-valve 22 provided in the normal passage N has a so-called check valve-like function of guiding the brake fluid pressure from the master cylinder 2M to the magnet valve 24 side and preventing conduction in the reverse direction. However, in the case where the pressure is equal to or lower than a predetermined pressure, reverse conduction is also possible.

The magnet valve 24 switches the three ports based on a command (control current) from the control unit 20CU, and switches the brake fluid pressure from the master cylinder 2M to the wheel cylinder 2S between the normal passage N and the ABS passage B, or It acts to block both.

The hydraulic unit 20HU configured as described above operates as follows.

During normal braking, the magnet valve 24 is set to the normal passage N side. Thereby, the brake fluid pressure generated in the master cylinder 2M by the operation of the brake pedal BP reaches the wheel cylinder 2S as it is and performs the braking action. When the brake is released, the brake fluid returns to the master cylinder 28 via the return passage R.

At the time of braking control, by switching the magnet valve 24, the brake fluid pressure supplied to the wheel cylinder 2S can be changed to three states of pressure reduction, holding, and pressure increase.

That is, by closing the normal passage N from the normal state (illustrated state) in which the normal passage N communicates with the ABS passage B and communicating with the ABS passage B, the hydraulic pressure of the wheel cylinder 2S escapes to the reservoir 25 and is reduced. By shutting off both the ABS and the ABS passage B, the hydraulic pressure of the wheel cylinder 2S can be kept constant. If the brake fluid pressure is sufficiently stored in the accumulator 25, the brake fluid pressure stored in the accumulator 25 is applied to the wheel cylinder 2S to increase the pressure when switching to the normal passage N side. The accumulator 25 stores the brake fluid in the reservoir 25 by driving the pump 26 by the motor 28 when the pressure is reduced.

Next, braking control by the ABS device 20 will be described with reference to FIG.

Here, in the braking control by the ABS device 20, as described above, each of the wheel slip ratio: S and the acceleration: has a braking control start threshold value: S ₁ , ₁ , and either one of them has the brake control start threshold value. When it reaches, braking control is performed. One-dot chain line is the slip rate brake control start threshold from the pseudo vehicle speed: shows the vehicle speed in the case of deceleration in S ₁ (braking control start vehicle speed), the wheel speed becomes lower than the vehicle speed slip ratio: S is This means that the braking control start threshold value (slip ratio: S ₁ ) has been exceeded. In addition, the broken line in the figure indicates a braking control start threshold value of the wheel acceleration: ₁ (= −b _o ).

When the brake pedal BP is depressed for vehicle braking, the brake fluid pressure applied to the wheel cylinder 2S increases to perform a braking action, the wheel speed decreases, and the difference between the wheel speed and the vehicle speed increases (between a and b). ).

Deceleration of the wheel 2 (negative acceleration) braking control start threshold: exceeds -b _o and (below) (A point), the magnet valve 24 Te switched to the holding position for holding the brake fluid pressure (between b-c ).

The difference between the wheel speed and the vehicle speed increases, and the wheel speed falls below the braking control start vehicle speed (below the predetermined slip ratio: S)
(Point B), it is determined that the wheels 2 tend to lock,
The pressure of the wheel cylinder 2S is reduced by switching the magnet valve 24 to the pressure reducing position. Thereby, the braking action is reduced (between cd).

The brake fluid pressure decreasing by the braking action of the acceleration of the wheel 2 by relieving the braking control start threshold: When returning to -b _o (C point), and holds the brake fluid pressure Te switched to the holding position the magnet valve 24 again ( d-e).

If the wheel speed recovers and increases while maintaining the holding state and the acceleration of the wheel 2 exceeds the set value: + b20 (D
Point), it is determined that the wheel speed has sufficiently recovered, and the magnet valve 24 is switched to the pressure increasing position to increase the brake fluid pressure (e).
−f).

The acceleration of the wheel 2 is set by increasing the brake fluid pressure:
When the pressure drops to + b20 (point E), the magnet valve 24 is switched to the holding position to hold the brake fluid pressure (between f and g).

Acceleration set value of the wheel 2: + b10 falls below the braking control start threshold: to over -b _o, repeated pressure increase, a holding (between g-h).

Wheel 2 acceleration braking control start threshold: exceeds -b _o (F point), in which again repeat the cycle described above.

By the above control, the wheel 2 rotates in a state where the largest braking force is obtained between the wheel 2 and the road surface.

The same information of the slip ratio S and the acceleration of the wheels used for the braking control is input from the ABS device 20 to the integrated control device 30 that integrally controls the 4WS controller 10 and the ABS device 20. .

As shown by the broken lines in FIG. 4, the integrated control device 30 determines a predetermined amount from the braking control threshold value: S ₁ , V _{1 in the} ABS device 20 for each piece of information (wheel slip rate: S and acceleration: V). A small steering characteristic correction threshold: S _o , V _o (where S _o <S ₁ , _o < ₁ ) is set, and the wheel slip ratio: S or acceleration: V is set to the steering characteristic correction threshold: S _o , _When it reaches _o , the 4WS controller 10 is instructed to switch the steering ratio characteristic from the basic steering ratio characteristic A to the corrected steering ratio characteristic B.

That is, in a situation where the braking control is performed by the ABS device 20, 4W is performed earlier than the braking control is performed.
The steering ratio characteristic of the S controller 10 is switched from the basic steering ratio characteristic A to the corrected steering ratio characteristic B.

FIG. 5 (A) shows a flowchart of the steering ratio characteristic switching control by the general control device 30.

That is, the wheel slip ratio: S and acceleration: are read from the ABS device 20 (S1), and the respective values are compared with the steering characteristic correction threshold values: S _o , _o (S2, S3). 4WS controller 10 if the correction threshold has been reached
The steering ratio characteristic is corrected from the basic steering ratio characteristic A to the steering ratio characteristic B.
(S4).

As shown in the flowchart of FIG. 5C, the 4WS controller 10 reads the vehicle speed information from the vehicle speed sensor 6 (S21) and, based on the command of the general control device 30 (S2).
2) A steering ratio characteristic is selected (S23 or S24), and 4WS control is performed based on the selected steering ratio characteristic (S25).

[Effect of the Invention] According to the integrated control device for rear wheel steering and brake control of the vehicle according to the present invention as described above, the steering ratio characteristics can be changed in advance before the braking control. Therefore, even when the target slip ratio is changed in accordance with the change in the steering ratio characteristic, the target slip ratio is changed during the braking control and the braking force does not change, and stable braking control can be performed. Efficient braking can be performed from the start of braking.

[Brief description of the drawings]

FIG. 1 is a schematic structural view of a vehicle provided with an integrated control device for rear wheel steering and brake control according to the present invention, and FIG.
FIG. 3 is a hydraulic circuit diagram of the ABS device, FIG. 4 is a time chart showing braking control by the ABS device, FIG. 5 (A) is a control flowchart by the general control device, and FIG. Is the control flowchart of the ABS device,
(C) is a 4WS control flowchart by the 4WS controller. 1 ... vehicle 2FL, 2FR ... front wheel 2RL, 2RR ... rear wheel 10 ... 4WS controller (rear wheel steering control means) 20 ... ABS device (brake control device) 30 ... general control device (general control means)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI B62D 109: 00 (72) Inventor Takashi Nakajima 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Inventor Ken Murai 3-1 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Inside Mazda Co., Ltd. (72) Inventor Fumio Kageyama 3-1 Shinchi-chi, Fuchu-cho, Aki County, Hiroshima Prefecture Inside Mazda Co., Ltd. (56) References JP 62 JP-18368 (JP, A) JP-A-3-281483 (JP, A) JP-A-2-241877 (JP, A) JP-A-1-301471 (JP, A) JP-A-62-238171 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B62D 6/00 B62D 7/14 B60T 8/58

Claims (1)

(57) [Claims] 1. A vehicle capable of steering rear wheels, comprising: rear wheel steering control means for controlling the rear wheels with respect to the front wheels with a predetermined steering ratio characteristic based on vehicle speed information; Brake control for detecting rotation and calculating the slip ratio, and when the brake reaches a predetermined brake control start threshold during braking, braking control for controlling the operation of the braking device so that the slip ratio becomes the target slip ratio. A steering ratio characteristic correction threshold value set to a slip ratio smaller than a braking control start threshold value in the braking control device, and the rear wheel steering is performed when the slip ratio of the wheel reaches the steering ratio characteristic correction threshold value. And a comprehensive control means for correcting the steering ratio characteristic of the control means to the same phase side.