JP2551288B2 - Vehicle rear 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 rear wheel steering system for a vehicle, and more particularly to a rear wheel steering system in which a steering angle ratio is variable depending on a vehicle speed.

[0002]

2. Description of the Related Art Japanese Patent Publication No. 60-44 discloses a method for variably controlling the steering angle ratio of rear wheels in response to the vehicle speed with respect to the steering angle of front wheels.
There is 185. According to this, the steering ratio is a negative value when the vehicle speed is low, the steering ratio is a positive value when the vehicle speed is high, and the steering ratio is between a negative value and a positive value depending on the vehicle speed. Is variable. That is, when the vehicle is traveling at a low speed, the rear wheels are steered in the opposite phase to the front wheels, and when the vehicle is traveling at a high speed, the rear wheels are steered in the same phase. It aims to improve the maneuverability of the vehicle and ensure the steering stability of the vehicle at high speeds.

[0003]

In such a vehicle speed-sensitive rear wheel steering system, when the vehicle speed changes abruptly when the vehicle turns, the steering angle ratio is variable according to the vehicle speed. Since the steered ratio also suddenly changes in accordance with the abrupt change in the vehicle speed during turning, the steered angle of the rear wheels changes abruptly and the traveling direction of the vehicle changes greatly. In order to solve the above-mentioned problem, the present invention aims to prevent a rapid change in the steering angle of the rear wheels by limiting the rate of change in vehicle speed for determining the steering angle ratio.

[0004]

In order to solve the above problems, a vehicle rear wheel steering system according to the present invention includes a front wheel steering mechanism for steering front wheels based on an operation of a steering wheel, and a vehicle speed detecting system for detecting a vehicle speed. vehicle speed detecting means for outputting a speed signal, the ratio of the rear wheel steering angle to front wheel steering angle on the basis of the vehicle speed signal at the time of high speed running than during low-speed travel, the in-phase side of the steering direction of the front and rear wheels becomes the same direction In a rear-wheel steering device for a vehicle, comprising: a steering-angle-ratio setting means to be set; and a rear-wheel steering mechanism that steers the rear wheels according to an operation of the steering wheel based on the set steering-angle ratio of the steering-angle ratio setting means, The rate of change of the vehicle speed is controlled to be equal to or less than the maximum acceleration allowed in the vehicle, and the vehicle speed signal set based on the restricted rate of change of the vehicle speed is set to the rear wheel steering angle by the steering angle ratio setting means. Wheel steering Characterized by comprising a vehicle speed change rate limiting means for the vehicle speed signal Me other settings ratio.

[0005]

According to the invention therefore, either the detected vehicle speed
If the rate of change of the vehicle speed obtained from the above exceeds the maximum rate of change or the minimum rate of change allowed for the vehicle , a vehicle speed signal based on the rate of change of the vehicle speed within these limit rate of change is output,
The steering angle ratio of the front and rear wheels is set based on the vehicle speed signal.
Therefore, a sudden change in the steering angle ratio of the front and rear wheels is prevented.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

A vehicle 10 shown in FIG. 2 is of a so-called front and rear wheel steering type, and a pair of left and right front wheels 1 which can be steered by a steering wheel (not shown) is provided on a front portion of the vehicle 10.
2 and 14 are provided, and the front wheels 12,
A pair of left and right rear wheels 16 and 18 that are automatically steered in association with the steering of 14 are provided. In this embodiment, the output is an output shaft 26 of the transmission 20, a rear wheel via a drive shaft 22 and differential DoSo location 24, 16, 1
A rotation sensor 28 for detecting the rotation speed of the transmission 20 is provided near the output shaft 26 of the transmission 20.

The rotation sensor 28 detects the passage of a large number of teeth formed on the outer peripheral portion of the speed detecting gear 30 fixed to the output shaft 26 as shown in FIG. 3, and corresponds to the number of passing teeth per unit time. The pulse signal PV ₀ of the selected frequency is output. As shown in FIG. 4, the pulse signal PV from the rotation sensor 28 is used.
₀ is the I / I of the arithmetic unit 34 for sequentially determining the vehicle speed V _n.
It is supplied to the O port 36 via the waveform shaper 44. The arithmetic unit 34 is a so-called microcomputer, and normally also serves as a steering angle control unit for the rear wheels, which is a vehicle speed change rate limiting unit and a steering angle ratio setting unit. Further, the rotation sensor 28, the waveform shaper 44 and the arithmetic unit 34 are vehicle speed detecting means. The arithmetic unit 34 includes a CPU, a ROM, a RAM, etc., which are connected to each other via a data bus line.
The vehicle speed V _n is calculated by processing the input signal according to the program stored in advance.

On the other hand, the vehicle 10 has front wheels 12,
14 of the front wheel steering angle sensor 46 is a steering angle detecting means is provided, the signal Esuderuta _f representing the steering angle [delta] _f of the front wheels 12, 14
Is supplied from the front wheel steering angle sensor 46 to the I / O port 36. Further, the vehicle 10 is provided with a brake pedal switch 48 for detecting the operation of the brake pedal, and a brake operation signal BR is supplied from the brake pedal switch 48 to the I / O port 36.
Further, the engine 50 is provided with an engine rotation sensor 52 for detecting the engine rotation speed and a throttle sensor 54 for detecting the throttle valve opening, and the engine rotation signal SE and the throttle signal TH are I / O port 36.

The CPU determines the steering direction and the steering angle of the rear wheels 16 and 18 with respect to the front wheels 12 and 14 based on the actual vehicle speed V _n and the steering angle δ _{f of the} front wheels from the relationship stored in advance in the ROM. , A drive signal DD for operating the rear wheel steering actuator 38 is supplied from the I / O port 36 to the D / A so that the steering direction and the steering angle can be obtained.
It is supplied to the hydraulic control device 42 via the converter 39 and the rear wheel steering amplifier 40. Accordingly, the hydraulic control device 42
A control valve provided therein is operated to supply operating oil pressure to the rear wheel steering actuator 38, and the steering angles of the rear wheels 16 and 18 are changed by the rear wheel steering actuator 38. Here, the hydraulic control device 42 and the rear wheel steering actuator 38 are a rear wheel steering mechanism.

The operation of this embodiment will be described below with reference to the flow charts of FIGS.

First, step SR1 is executed to determine whether or not it is the first cycle. If it is not the first time, step SR3 is executed without passing through step SR2,
If it is the first time, step SR2 is executed to clear each counter and flag, and then step SR3 is executed. In step SR3, the vehicle speed v ₀ (n · Δt) is calculated according to the following equation (1) based on the pulse signal PV ₀ .

V ₀ (n · Δt) = f · 2πr / G · H (1) where f is the frequency of the pulse signal PV ₀ , H is the number of teeth of the speed detecting gear 30, and G is differential. The gear ratio of the gear unit, r is the radius of the wheel.

In step SR4, the vehicle speed v calculated in step SR3 is detected in order to detect the low speed running of the vehicle 10.
₀ (n · Δt) is a predetermined small constant value V _a ,
For example, it is determined whether or not it is greater than 5 km / h. Δ
t is a vehicle speed calculation cycle, and n is an integer indicating the current cycle. If the determination in step SR4 is negative, steps SR14 and below, which will be described later, are executed. That is, the value of the vehicle speed V _n in step SR14 is replaced by the V _a, it is changed steering angle of the rear wheels based on the step SR15 this small vehicle speed V _a, and then waits for the time Δt in step SR16 After that, steps SR3 and subsequent steps are repeatedly executed. Note that in the step SR15, for example, the ROM stored relationship is used in FIG. 7, the vehicle speed V _n from the relation
With coefficient K indicating the steering angle ratio is calculated with respect to the front wheels 12, 14 of the rear wheel 16, 18 on the basis of the following equation from the subsequent input signal Sδ front wheel steering angle determined based on the _f [delta] _f and the coefficient K The rear wheel steering angle δ _r is calculated according to (2). The coefficient K indicates the steering direction by its positive or negative sign, and the steering ratio by its value. Then, the drive signal DD is supplied to the hydraulic control device 42 via the D / A converter 39 and the amplifier 40 so that the rear wheel steering angle δ _r is obtained.

Δ _r = K (V _n ) · δ _f (2)

If the determination in step SR4 is affirmative, that is, if the vehicle speed v ₀ (nΔt) is larger than a predetermined small value V _a , it is determined in step SR5 whether the wheels are spinning. To be judged. The spin of the wheel is the rotational acceleration of the wheel, that is, the difference between the vehicle speed obtained in this cycle and the vehicle speed obtained in the previous cycle [v ₀ (n · Δt) -v
₀ ((n-1) · Δt)] is a predetermined constant value α
It is judged to be greater than ₀ . This value α ₀ is determined to be a rotational acceleration equal to or less than the maximum rotational acceleration in the range where the wheel and the road surface do not slip. When the wheel spin is not detected in step SR5, step SR6 is executed to determine whether or not the wheel is locked. This judgment is based on the rotational acceleration of the wheel [v ₀ ((n
It is determined that −1) · Δt) −v ₀ (n · Δt)] is larger than a predetermined constant value β ₀ . This value β ₀ is set to a rotational acceleration equal to or higher than the minimum rotational acceleration in the range where the wheel does not slip on the road surface.

Steps SR5 and SR6 described above
If wheel lock and spin are not detected in
Is the case where the rotation of the wheels is normal.
Step SR7 is executed for this cycle
V calculated in₀(N · Δt) is the provisional vehicle speed V_n'age
Is adopted as a vehicle and step SR8 is executed.
Speed V_nIs determined. This vehicle speed V_nIs the provisional vehicle speed V
_n’And the previous vehicle speed V _n-1Is the maximum change in vehicle speed α_max・
The value obtained by adding Δt and the previous vehicle speed V_n-1Minimum change in vehicle speed
Value α_min・ From 3 types of values consisting of the value with Δt added
It is executed by selecting the interval value, and the vehicle speed V_nIs new
The selected value is updated. Maximum change value and maximum
The small change value is in the condition that the wheel and the road surface do not slip.
With the maximum change width and the minimum change width of the vehicle speed per time Δt
Yes, above α_maxAnd α_minIs the slip between the wheels and the road
Maximum and minimum vehicle acceleration in the non-occurring range
The vehicle speed V_nVehicle speed V at the time of decision_nTime Δt
Change rate is less than the maximum acceleration of the vehicle or the maximum
It can be suppressed over a small acceleration.

As a result, when the acceleration / deceleration of the vehicle is extremely high, or when the rotation sensor 28 or the speed detecting gear 30 fails, the vehicle speed v of an abnormally large value or an abnormally small value.
_{Even if 0} (n · Δt) is calculated, the rate of change of the vehicle speed V _n is limited to the actual maximum acceleration of the vehicle or less. That is, since the rate of change of the vehicle speed V _n is limited, the vehicle speed V _n
The abnormal operation of the control performed based on _n is prevented.

When the wheel spin is detected in step SR5, step SR9 is executed to determine the provisional vehicle speed V _n '(= V _n-1 + α _max · Δt), and then step SR8 and thereafter. Is executed. When the wheel lock is detected in step SR6, step SR10 is executed to execute the vehicle speed V _n (= V _{n-
After 1} ) is determined, step SR15 and subsequent steps are executed, and the steering angle of the rear wheels is controlled based on the vehicle speed V _n . As described above, when the wheel spin is detected in step SR5, the provisional vehicle speed V _n 'is limited to the maximum value (= V _n-1 + α _max · Δt) that can actually exist.
Stable rear wheel steering angle control can be obtained even during abnormal wheel rotation such as wheel spin. Further, when the wheel lock is detected in step SR6, the vehicle speed V _n is set to the vehicle speed V _n-1 adopted in the previous cycle, so that the vehicle speed becomes stable even during abnormal wheel rotation such as wheel lock. Wheel steering angle control is obtained.

After the vehicle speed V _n is determined in step SR8, step SR11 is executed to change the vehicle speed V _n to the temporary vehicle speed V _n 'that was previously determined.
Is determined to be the same as or not. If they are the same, it means a normal state. Therefore, step SR12 is executed to clear the flag F _Ta to zero, and step SR13 is executed to judge whether the vehicle speed V _n is smaller than V _a. It If this determination is affirmative, it means that the vehicle is running at a low speed, and therefore the above-described steps SR14 and below are executed, but if this determination is negative, then the steps SR15 and below are executed, so that the vehicle speed V _n determined in step SR8.
The steering angle of the rear wheels is determined based on

However, in step SR11,
When it is determined that the vehicle speed V _n determined in step SR8 is not the same as the temporary vehicle speed V _n 'determined in step SR7, the calculated vehicle speed v ₀ (n · Δt)
Is the maximum possible vehicle speed (= V _n-1 + α _max · Δ
t) to the minimum value (= V _n-1 −α _min · Δt), that is, the calculated rate of change in vehicle speed [v ₀ (n · Δt) −V _n-1 ]. Is the maximum acceleration α of the vehicle
_{Since the} abnormal state exceeds the range from _max to the minimum acceleration α _min , the abnormality in vehicle speed detection is determined by the duration of this abnormal state. That is, step SR17
After 1 is added to the content of the timer counter T _{1 at} , it is determined at step SR18 whether or not the content of the timer counter T exceeds _a predetermined constant value T _a . The constant value T _a is a value corresponding to a time of about 20 seconds, for example.

If the determination in step SR18 is negative, it is temporary due to wheel hops and the like, and therefore steps SR13 and thereafter are executed as usual. However, if the determination in step SR18 is affirmative, the speed detection gear 30 is damaged and the rotation sensor 28
Since it can be determined that the vehicle speed has been detected abnormally due to a malfunction of the vehicle, step SR19 is executed and the flag F _Ta is set to 1
And a display device (not shown) indicates that the vehicle speed has been detected abnormally.

In the subsequent step SR20, it is determined whether the vehicle 10 is turning, that is, is cornering. This determination is the front wheel steering angle [delta] _f representing the signal Esuderuta _f is performed by whether exceeds a predetermined value [delta] ₀ determined in advance. The constant value δ ₀ is, for example, a front wheel steering angle corresponding to a steering wheel operating angle of 45 degrees. When it is determined in step SR20 that the vehicle 10 is turning, step SR21 is executed and the vehicle speed V _n-1 (the vehicle speed before the vehicle speed detection abnormality or a constant value is adopted in the previous cycle. V ₀ ) is the current vehicle speed, but when it is determined that the vehicle is not turning, step SR22 is executed to set the current vehicle speed V _n to a predetermined constant vehicle speed V ₀ , for example, 100 km. It is fixed to a value of about / h. After the step SR21 or SR22 is executed steering angle of the rear wheels is running the steps SR1 5 or less is controlled. As described above, even if the vehicle speed detection abnormality occurs, the vehicle speed update is stopped when the vehicle 10 is cornering, so that the driver's unexpected change of the steering angle of the rear wheels is prevented. When the vehicle speed is abnormal and the vehicle 1
When the vehicle is not cornering at 0, the vehicle speed V _n is set to a constant vehicle speed V ₀ , so that the steering operation of the rear wheels is executed with a constant coefficient K (100) applicable to a wide range of vehicle speeds.

As described above, in this embodiment , step S
The vehicle speed V _n calculated for each cycle so as to be executed in R7 is adopted as the temporary vehicle speed V _n ′ , and step S R8,
In SR11, the rate of change of the vehicle speed V _n ′, that is, the gradient of change, is limited between the maximum acceleration α _max and the minimum acceleration α _min of the vehicle, and the process proceeds to step S R13. Step S based on _n
The steering angle control is executed at R15. Further, it is detected that there is no wheel lock or spin, and the provisional vehicle speed V _n ′
If rate of change exceeds the range that leads to minimum acceleration from the maximum acceleration of the vehicle, abnormality judgment of the vehicle speed detecting means less
Vehicle speed V _n through the step S R17 or we step S R22
When the vehicle is cornering, the constant vehicle speed is stopped from being updated, and when the vehicle is not cornering, is fixed to a constant vehicle speed. Therefore, even if a rapid change in vehicle speed is to be calculated, at the time of executing the steering angle control, at least the rate of change in vehicle speed is limited to a value between the maximum acceleration and the minimum acceleration of the vehicle. It is possible to suppress a sudden change in the steering angle.

[0025]

According to the present invention, the vehicle speed change rate to the vehicles
Because it is limited to less than acceptable maximum acceleration, abnormal operation of the control steering stability is improved can be prevented to be performed based on the vehicle speed. Further, even if an abnormal vehicle speed is detected due to a failure of the vehicle speed detecting means, the rate of change of the vehicle speed used when determining the steering angle ratio is limited, so the steered angle of the rear wheels may change rapidly. Therefore, the traveling direction of the vehicle does not change significantly.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the present invention.

FIG. 2 is an explanatory diagram of a main part of a vehicle to which the present invention is applied.

FIG. 3 is a view showing a mounting portion of a rotation sensor provided in the vehicle of FIG.

FIG. 4 is a diagram showing a configuration of an electronic control circuit of FIG.

5 is a flow chart for explaining the operation of the electronic control circuit of FIG.

FIG. 6 is a flowchart for explaining the operation of the electronic control circuit of FIG.

FIG. 7 is a diagram showing a relationship stored in advance in the electronic circuit of FIG. 4 for controlling the steering angle ratio of the rear wheels.

[Explanation of symbols]

 10 ... Vehicle 12, 14 ... Front wheel 16, 18 ... Rear wheel 20 ... Transmission 26 ... Output shaft 28 ... Rotation sensor 30 ... Speed detection gear 34 ... Calculation Device 36 ... I / O port 38 ... Rear wheel steering actuator 40 ... Rear wheel steering amplifier 44 ... Waveform shaper 46 ... Front wheel steering angle sensor 48 ... Brake pedal switch 50・ ・ ・ Engine 52 ・ ・ ・ Engine rotation sensor 54 ・ ・ ・ Throttle sensor

Claims (1)

(57) [Claims] A front wheel steering mechanism for steering the front wheel 1. A based on the operation of the steering wheel, a vehicle speed detecting means for outputting the detected vehicle speed signal <br/> the vehicle speed, for front-wheel steering angle based on the vehicle speed signal The steering angle ratio setting means for setting the ratio of the rear wheel steering angle to the same phase side in which the front and rear wheels are steered in the same direction when the vehicle is traveling at a high speed compared to when traveling at a low speed, and the steering angle ratio set by the steering angle ratio setting means. In a rear wheel steering device of a vehicle including a rear wheel steering mechanism that steers the rear wheels according to the operation of the steering wheel, the rate of change of the vehicle speed is controlled to be equal to or less than the maximum acceleration allowed in the vehicle, and a vehicle speed signal that is set based on the regulatory vehicle speed change rate, the ratio of the setting of the rear wheel steering angle to front wheel steering angle by the steering angle ratio setting means
Rear wheel steering apparatus for a vehicle characterized by comprising a vehicle speed change rate limiting means for the vehicle speed signal Me other.