JPH03262779A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To perform precise and stable rear wheel steering control by estimating the vehicle body speed from the rotation of wheels, calculating the slip ratio of the wheels, controlling the braking force according to the calculated result, and performing the rear wheel steering control based on the estimated vehicle body speed. CONSTITUTION:The front wheel steering state and estimated vehicle body speed information from a steering angle sensor 5 are inputted to the 4WS controller 10 of a four-wheel-steered vehicle, the rear wheel steering angle is determined based on the preset steering ratio characteristic, a motor 4 is driven based on the rear wheel steering angle, and the steering of rear wheels 2R is controlled. An ABS device 20 controlling the brake liquid pressure is provided, it calculates the wheel speed and pseudo vehicle speed from the wheel speed information, it calculates the slip ratio and acceleration of each wheel, and it compares each calculated value and the brake control start threshold value to control the brake liquid pressure. The pseudo vehicle body speed determined by the above ABS control is used as the estimated vehicle body speed for the rear wheel steering control.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is directed to steering the rear wheels relative to the front wheels based on vehicle speed information and predetermined steering ratio characteristics in a vehicle in which the rear wheels can be steered. The present invention relates to a rear wheel steering device for a vehicle that performs steering control.

[Prior art and its problems] Recently, four-wheel steering (4-wheel steering), which allows steering not only the front wheels but also the rear wheels
There are so-called 4WS) vehicles, and as a rear wheel steering control method for such four-wheel steering vehicles, the steering angle of the rear wheels (i.e., the steering ratio) with respect to the steering angle of the front wheels is adjusted according to the speed of the vehicle (vehicle speed). There is something called a speed-sensitive type that changes the speed. This is a predetermined relationship between vehicle speed and steering ratio (steering ratio characteristic).
Normally, the rear wheels are set to be steered to the same side (same phase) as the front wheels at high speeds, and to the opposite side (opposite phase) to the front wheels at low speeds. This has the effect of improving straight-line stability at high speeds and enabling stable turns with little change in posture, while at low speeds it is possible to make tight turns.

The vehicle speed information necessary for this rear wheel steering control is obtained by detecting the rotation of the output shaft of the transmission with a sensor and using ti4K from the rotation speed of the output shaft obtained thereby. That is, the rotation speed of the drive wheels is determined from the rotation of the output shaft, and the vehicle body speed is obtained by multiplying the rotation speed of the drive wheels by the outer circumference of the vehicle.

However, in this way, what is obtained by calculation based on the rotation speed of the output shaft of the transmission is the circumferential speed of the driving wheels, which is different from the actual vehicle speed, and such input information (vehicle speed information) If rear wheel steering control is performed based on this, there is a problem in that it may not correspond to the actual vehicle speed.

In other words, the rotation speed of the output shaft of the transmission fluctuates widely as the engine rotation changes, and the drive wheels drive the vehicle while slipping against the road surface. The slip ratio of the lever changes depending on the road surface condition and the magnitude of the driving force (or braking force) applied to the wheels, and the rotation of the output shaft of the transmission does not necessarily correspond to the actual vehicle speed.

Therefore, the vehicle speed obtained from the rotation of the output shaft of the transmission has large fluctuations and large errors, and rear wheel steering control based on the vehicle speed with such large fluctuations or errors also becomes unstable.

For example, if sudden braking is performed from a high speed range where in-phase steering control is required and the engine rotation becomes extremely low, the steering control will be performed in the opposite phase even though the actual vehicle speed is in the high speed range. It is possible that the steering control is performed by determining that the vehicle is in a low speed range where the vehicle should be operated, and that the steering of the rear wheels relative to the steering of the front wheels suddenly changes from the same phase side to the opposite phase side.

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

ABS detects the rotation of all wheels using sensors, estimates the speed of the vehicle from the number of rotations of these wheels, calculates the slip rate of the wheels based on this estimated vehicle speed, and uses this slip rate as an indicator of braking efficiency. This system controls the brake fluid pressure to maintain it at a predetermined value to prevent the wheels from locking up, thereby maintaining directional stability during braking, ensuring maneuverability, and shortening braking and stopping distances. It is possible to aim for (Refer to Japanese Unexamined Patent Publication No. 56-135358, etc.) [Object of the Invention] In view of the above-mentioned circumstances, the present invention has been made to obtain highly accurate and stable vehicle speed information, and to obtain stable vehicle speed information according to the actual vehicle speed. An object of the present invention is to provide a rear wheel steering device for a vehicle that can perform wheel steering control.

[Structure of the Invention I &] For this reason, the rear wheel steering device for a vehicle according to the present invention estimates the vehicle speed from the rotation of the wheels and calculates the slip rate of the wheels, and based on the obtained estimated vehicle speed and slip rate. and a rear wheel steering control means for controlling the steering of the rear wheels relative to the front wheels based on vehicle speed information with a predetermined steering ratio characteristic. The estimated vehicle speed is used as vehicle speed information for the rear wheel steering control means.

According to this, it is possible to perform rear wheel steering control using a vehicle speed that is more in line with the actual vehicle speed than calculated from the rotation of the wheels, and it is possible to perform highly accurate and stable rear wheel steering control. .

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

FIG. 1 is a schematic configuration diagram of a steering mechanism of a vehicle l equipped with a vehicle rear wheel steering device according to the present invention.

The vehicle 1 has rear wheels 2R... (2RR, 2RL) configured to be steerable, and one-wire diameter wheels 2R...- and front wheels 2F...
- It is configured with a 4WS controller 10 as a rear wheel steering control means for controlling the steering at a predetermined steering ratio (2FR, 2FL), and an ABS device 20 as a braking control device.

In the steering mechanism of the vehicle 1, the front wheels 2F... are steered by rotation of the steering wheel 3 via a gear train, and the rear wheels 2R... are steered by the drive of a motor 4 controlled and driven by a 4WS controller 10. It is designed to be operated by the rudder.

The front wheel steering mechanism is equipped with a steering angle sensor 5,
The front wheel steering information detected by the steering angle sensor 5 is
The signal is input to the 4WS controller IO.

The 4WS controller 10 receives front wheel steering information from the aforementioned steering angle sensor 5 and an ABS system M which will be described in detail later.
Estimated vehicle speed (pseudo vehicle speed) information estimated and calculated from the wheel speeds is input, and the 4WS controller 1O adjusts the rear wheel speed based on this input information and predetermined steering ratio characteristics to be described later. The steering angle is determined, and the motor 4 is controlled and driven to steer the rear wheels. Note that this rear wheel steering angle is detected by a rear wheel steering angle sensor 7 provided in the rear wheel steering mechanism, and is input to the 4WS controller 10, where feedback control is performed.

Here, the rear wheel 2R... with respect to the steering angle of the front wheel 2F...
The steering angle ratio, that is, the steering ratio, is set as shown in the second diagram, and is a so-called vehicle speed sensitive type in which the steering angles are in opposite phases at low speeds and change to the same phase at a predetermined vehicle speed or higher.

The ABS device 20 controls each wheel 2 so that the brakes can be efficiently applied without locking the wheels 2 during braking.
The brake fluid pressure supplied to the wheel cylinder 2S provided in the vehicle is controlled.

Wheel speed information is input to the ABS device 20 from wheel speed sensors 21 provided near each wheel 2, and the ABS device 20 determines each wheel speed from this wheel speed information. The speed of the wheels (rotational peripheral speed of the wheels) and the speed of the vehicle (pseudo vehicle body speed) are calculated, and the slip rate and acceleration of each wheel are calculated, and the calculated acceleration and slip rate of each wheel are respectively set in advance. If either one of the brake control start thresholds has reached the brake control start threshold, the hydraulic unit 20HU is controlled and driven to perform brake control.

As shown in FIG. 3, the hydraulic unit 20HU has one hydraulic circuit that includes a normal passage N used during normal braking, an ABS passage long return passage R used during ABS operation, and an FHarz 22. Check valve 23. McNett Harz 24. Leatherha 25. pump 2
6 and an accumulator 27. As mentioned above, FIG. 3 shows only one system of hydraulic circuits, and the following explanation will be based on this figure, or similar hydraulic circuits will be constructed for each wheel.

The normal passage N connects the mask cylinder 28 and the wheel cylinder 2 through the F valve 22 and the Macnet valve 24 in series.
S is connected.

ABS passage length FHartz 22 and Macnet valve 24
It branches off from the normal passage N between the accumulators 27. Magnet valve 2 via pump 26 and laser 25
Connected to 4.

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

The F valve 22 normally installed in the passage N.

Does it have a so-called check valve function that guides the brake fluid pressure from the mask cylinder 2M to the McNet valve 24 side and prevents conduction in the reverse direction? It is possible.

The Macnet valve 24 receives a command (
The brake fluid pressure from the mask cylinder 2M to the wheel cylinder 2S is switched between the normal passage N and the ABS passage, or both of them are cut off.

The pyrotechnic unit 20HU constructed as described above operates as follows.

During normal braking, the magnet valve 24 is placed on the normal passage N side. As a result, the brake fluid pressure generated in the mask cylinder 2M by operating the brake pedal BP directly reaches the wheel cylinder 2S and performs a braking operation. When the brake is released, the brake fluid returns to the mask cylinder 28 via the return passage R.

During braking control, by switching the magnet valve 24, the brake fluid pressure supplied to the wheel cylinder 2S can be changed into three states: reduced pressure, maintained pressure, and increased pressure.

That is, the hydraulic pressure of the wheel cylinder 2S is reduced from the normal state (the state shown in the figure) in which it is in communication with the normal passage N to the hydraulic pressure of the wheel cylinder 2S by cutting off the normal passage jigN and making it communicate with the ABS passage.
The hydraulic fluid pressure in the wheel cylinder 2S is maintained constant by escaping to and reducing the pressure, and by blocking both the normal passage N and the ABS passage. Further, if sufficient brake fluid pressure is stored in the accumulator 25, when switching to the normal passage N side, the brake fluid pressure stored in the accumulator 25 is applied to the wheel cylinder 2S to increase the pressure. Incidentally, when the pressure is reduced, a pump 26 is driven by a motor 28 to store the leakage liquid in the leather lotus 5 in the accumulator 25.

The braking control by the ABS device 20 is described in the fourth example.
This is done as shown in the time chart in the figure.
As described above, the S device 20 has independent braking control start threshold values for the wheel slip rate and acceleration, and performs braking control when either one reaches this braking control start ill value. It is something. In the figure - dotted chain line, the vehicle speed when decelerating from the pseudo vehicle speed to the slip rate of the brake control start threshold (III dynamic control start vehicle speed)
When the wheel speed becomes lower than this vehicle body speed, it means that the slip ratio exceeds the brake control start threshold. In addition, the broken line in Figure 1 indicates the braking control start wi value of the wheel acceleration.

When the flake petal BP is depressed to brake the vehicle, the brake fluid pressure applied to the wheel cylinder 2S increases for braking action, and the wheel speed decreases, increasing the difference between the wheel speed and the vehicle body speed. while).

When the deceleration (negative acceleration) of the wheels 2 or the brake control start threshold exceeds (below) bo (point A), the magnetic valve 24 is switched to the holding position to maintain the brake fluid pressure (between b and c).

When the difference between the wheel speed and the vehicle body speed increases and the wheel speed falls below the braking control start vehicle speed (below the predetermined slip ratio), (
8 points), it is determined that the wheel 2 tends to lock, and the pressure in the wheel cylinder 2S is reduced by switching the magnetic valve 24 to the pressure reducing position. As a result, the braking action is relaxed (between c and d).

When the acceleration of the wheel 2 reaches or returns to the brake control start threshold knee b due to the relaxation of the braking action due to this brake fluid pressure reduction (point C), the magnet HARTZ 24 is switched to the holding position again and the brake fluid pressure is maintained ( Between de and e.

While maintaining the holding state, the wheel speed recovers/increases and the acceleration of wheel 2 exceeds the set value: +b20 (Point D)
, determines that the wheel speed has sufficiently recovered, and switches the magnetic valve 24 to the pressure increasing position to increase the brake fluid pressure (e-
between f).

The acceleration of wheel 2 is increased by increasing the brake fluid pressure or the set value +
When descending to b20 (point E), the magnetic valve 24 is switched to the holding position to maintain the brake fluid pressure (between f and g).

When the acceleration of the wheel 2 falls below the set value +blO, the pressure is increased and maintained repeatedly (between gh) until it exceeds the braking control start lII value -bo.

When the acceleration of the wheel 2 exceeds the brake control start threshold value -b, the CF point is activated and the above-mentioned cycle is repeated again.

By the above control, the wheels 2 are rotated in a state where the greatest braking force can be obtained between the wheels 2 and the road surface.

Here, the 4WS controller lO has <AB
The vehicle speed (pseudo vehicle speed) estimated based on wheel speed information obtained from the S device 20 or wheel speed sensors 21 provided in each wheel 2 is input. .

Based on the pseudo vehicle speed input from the ABS device 20, the 4WS controller 10 adjusts the steering of the rear wheels 2R, .
・Control the steering.

The pseudo vehicle speed calculated by the ABS device 20 corresponds to the actual vehicle speed and is a stable value independent of fluctuations in engine speed, so based on this, highly accurate and stable rear wheel steering control can be performed. It is something that

[Effects of the Invention] As described above, according to the rear wheel steering device for a vehicle according to the present invention, since the rear wheel steering control is performed based on the pseudo vehicle speed obtained by the brake control device, the actual This allows for stable rear wheel steering that corresponds to the vehicle speed.

Additionally, a vehicle speed sensor for rear wheel steering control is not required, making it possible to reduce costs.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of a vehicle equipped with a vehicle rear wheel steering system according to the present invention, Fig. 2 is a graph showing steering ratio characteristics with respect to vehicle speed, Fig. 3 is a hydraulic circuit diagram of the ABS system, and Fig. 4 is A
5 is a time chart showing braking control by the BS device. 1...Vehicle 2FL, 2FR...Front wheels 2RL, 2RR...Rear wheels lO...4WS controller (rear wheel steering control means) 20...ABS device (braking control device M) viscosity reading 1 Yo diagram

Claims (1)

[Scope of Claims] In a vehicle whose rear wheels can be steered, the vehicle speed is estimated from the rotation of the wheels, the slip rate of the wheels is calculated, and the braking force is calculated based on the estimated vehicle speed and slip rate obtained. and a rear wheel steering control means for controlling the steering of the rear wheels relative to the front wheels with a predetermined steering ratio characteristic based on the vehicle speed information, the estimation by the brake control device is provided. A rear wheel steering device for a vehicle, characterized in that the vehicle speed is configured to be used as vehicle speed information for the rear wheel steering control means.