JPH02274665A - Front and rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve turn performance without deteriorating stability by correcting in accordance with a steering condition a detected car speed being based on it determining steering angle ratio multiplying by it a front wheel steering angle obtaining a rear wheel steering angle steering to it a rear wheel. CONSTITUTION:In accordance with a steering condition detected by a steering condition detecting means, a car speed correction amount is determined by a correction amount determining means, and a car speed, detected by a car speed detecting means, is corrected by a car speed correcting means. A steering angle ratio determining means determines steering angle ratio (rear wheel steering angle/front wheel steering angle) being based on the corrected car speed. Next, a target steering angle determining means multiplies a front wheel steering angle, detected in a front wheel steering angle detecting means, by the determined steering angle ratio determining a rear wheel target steering angle, and a rear wheel is steered by a driving means. Thus improving turn performance without deteriorating stability, a steering condition can be reflected to a rear wheel steering angle only by a simplified control method, further by smoothing a change of the rear wheel steering angle, a steering feeling can be improved.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention determines the steering angle ratio of the front and rear wheels based on the steering angle of the front wheels and the vehicle speed, and steers the rear wheels to a target steering angle determined by the steering angle ratio. This applies to the front and rear wheel steering devices of the vehicle to be steered. Specifically, the vehicle speed, which is the basis for determining the steering angle ratio, is corrected according to the steering condition, and the steering angle of the rear wheels is given steering condition dependent characteristics. The present invention relates to a front and rear wheel steering device that improves turning performance without impairing stability during turning, which is an advantage.

(Prior art) In a vehicle that steers the rear wheels together with the front wheels, the steering phase and steering angle ratio of the front and rear wheels are determined based on the vehicle speed, and the steering direction and steering direction of the rear wheels relative to the front wheels are controlled. It is essential to do so. In general, such front and rear wheel steering devices aim to reduce the turning radius by steering the rear wheels in the opposite phase at low vehicle speeds so that the steering angle ratio increases at low vehicle speeds. In the vehicle speed range, stability is improved by steering the rear wheels in the same phase so that the steering angle ratio increases as the vehicle speed increases.

Conventionally, this type of front and rear wheel steering device has been disclosed, for example, in Japanese Patent Application Laid-open No. 1983-
The one described in Japanese Patent No. 77968 is known. The front and rear wheel steering device disclosed in Japanese Patent Application Laid-Open No. 59-77988 increases the rear wheel steering angle by 41 centimeters in response to an increase in the front wheel steering angle when the front wheel steering angle is less than a set value, and is larger than this set value. Based on the control characteristic that has an inflection point that reduces the rate of increase, the rear wheel turning angle is changed so that this inflection point changes to the smaller side of the front wheel turning angle as the vehicle speed increases. Control.

However, in the conventional front and rear wheel steering systems as described above, the inflection point of the characteristic curve of the control characteristic of the rear wheel steering angle with respect to the front wheel steering angle, that is, the control characteristic of the steering ratio, is detected when the vehicle speed is lower or lower. However, depending on the steering condition of the vehicle, the driver may feel that the vehicle's turning behavior is sluggish or unstable, depending on the initial settings. There is a problem.

Therefore, the present applicant first applied for the patent application No. 62-189.
No. 705 proposes a front and rear wheel steering device that corrects the steering angle ratio according to the steering condition, and attempts to solve the above problem. The front and rear wheel steering device of this prior application presets the control characteristics of the steering angle ratio with respect to the vehicle speed, detects the steering speed, determines a correction coefficient according to the steering speed, and uses this correction coefficient to determine the control characteristics described above. The steering angle ratio is corrected to achieve agile turning behavior that meets the driver's wishes.

(Problem to be solved by this invention) However,
In the front and rear wheel steering device according to the above-mentioned prior application, since the control characteristics themselves are corrected, various algorithms must be used for this correction to correspond to changes in vehicle speed and steering speed, and the control method is difficult. In addition, the steering angle ratio has a different convergence value depending on the steering speed, and when both the steering speed and vehicle speed change, the rear wheel turning angle becomes large. This has the drawback of causing fluctuations, resulting in a decrease in steering feel.

The invention of this application was made in view of the above-mentioned problems, and it is possible to easily control agile turning behavior according to turning conditions, that is, excellent maneuverability, without impairing turning stability, which is an advantage of front and rear wheel steering. An object of the present invention is to provide a front and rear wheel steering device that can be obtained by a method.

(Means for Solving the Problems) As shown in the configuration diagram of FIG. 1, the front and rear wheel steering device for a vehicle according to the present invention includes a vehicle speed detection means for detecting vehicle speed, and a front wheel steering device for detecting a front wheel turning angle. An angle detection means, a steering state detection means for detecting a steering state, a correction amount determining means for determining a vehicle speed correction amount in accordance with the steering state detected by the steering state detection means, and a correction amount determining means for determining a vehicle speed correction amount according to the steering state detected by the steering state detection means. a vehicle speed correction means for calculating a corrected vehicle speed by correcting the vehicle speed detected by the vehicle speed detection means based on the vehicle speed correction amount; and a vehicle speed correction means for storing a control characteristic of a steering angle ratio of the front and rear wheels with respect to the vehicle speed and according to the control characteristic. a steering angle ratio determining means for determining a steering angle ratio of the front and rear wheels based on the corrected vehicle speed determined by the steering angle ratio determining means, and a steering angle ratio determined by the steering angle ratio determining means and a front wheel rotation detected by the front wheel steering angle detecting means. and a drive means for steering the rear wheels to the rear wheel target steering angle calculated by the target steering angle determining means.

In the front and rear wheel steering device for a vehicle according to the first invention, the correction amount determining means determines the vehicle speed correction value according to the steering state, and the vehicle speed correction means subtracts the vehicle speed correction value from the detected vehicle speed to obtain the corrected vehicle speed. Further, in the front and rear wheel steering device for a vehicle according to the second invention, the correction amount determining means determines a vehicle speed correction coefficient according to the steering state, and the vehicle speed correction means multiplies the detected vehicle speed by the vehicle speed correction coefficient. Calculate the corrected vehicle speed.

(Function) According to the front and rear wheel steering device for a vehicle according to the present invention, the detected vehicle speed is corrected according to the steering condition to obtain a corrected vehicle speed;
Based on this corrected vehicle speed, a steering angle ratio is determined from a vehicle speed-steering angle ratio control characteristic stored in advance, and a rear wheel target steering angle is calculated from this steering angle ratio and front wheel steering angle. Steer the rear wheels around the corner.

Therefore, the vehicle speed, that is, the steering angle ratio determined based on the vehicle speed, can be set to a value that suits the steering conditions, and agile turning behavior can be obtained without impairing the sense of stability. In addition, this front and rear wheel steering system corrects the vehicle speed and determines the corresponding steering angle ratio from the control characteristics based on the corrected vehicle speed, so there is no need to change the control characteristics themselves, and simple methods such as table lookup can be used. In addition, the steering ratio, that is, the rear wheel steering angle, changes smoothly to prevent a decrease in steering feel.

According to the front and rear wheel steering device of the first invention, since the vehicle speed correction value determined according to the steering state is subtracted from the detected vehicle speed for correction, the steering angle ratio is significantly changed, especially in the middle vehicle speed range. This allows good steering performance to be obtained. Further, according to the front and rear wheel steering device of the second invention, since the vehicle speed is corrected by multiplying the detected vehicle speed by a correction coefficient determined according to the steering state, the steering angle ratio can be changed significantly especially in a high vehicle speed range. This allows for good steering performance at high vehicle speeds.

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

2 to 5 show a front and rear wheel steering system for a vehicle according to a first embodiment of the first invention, FIG. 2 is a schematic diagram of a steering mechanism system, FIG. 3 is a block diagram of a control system, and FIG. FIG. 4 is a flowchart of the main routine, and FIG. 5 is a flowchart of the subroutine.

In FIG. 2, reference numeral 11 denotes a steering handle, and the steering handle 11 is connected to a rack-and-binion type steering gear mechanism 13 via a steering shaft 12. The steering shaft 12 includes a steering angle sensor 1.
4. A steering speed sensor 15 and a torque sensor 4o are provided.

For example, the steering angle sensor 14 is composed of an encoder or the like and detects the rotation angle (steering angle) of the steering shaft 12, and the steering speed sensor 15 is composed of a tachometer generator or the like and detects the rotational angular velocity of the steering shaft 12 and torque The sensor 40 is composed of a differential transformer or the like that detects the relative displacement of two members connected by a torsion bar, and detects the transmission torque (steering torque) of the steering shaft 12. These sensors 12, 15° 40 are
They are connected to a controller 16, which will be described later, and output detection signals to the controller 16, and each functions as a steering state detection means that detects the steering state using a steering angle (front wheel turning angle), a steering speed, and a steering torque.

As is well known, the steering gear mechanism 13 includes a pinion gear 13 that rotates integrally with the steering shaft 12.
a and a rack 13b that meshes with the pinion gear 13a and extends in the vehicle width direction, and both ends of the rack 13b are connected to the knuckle arms 1 of the left and right front wheels 18FL and 18FR, respectively.
9FL.

It is connected to 19FR via a steering linkage consisting of tie rods 17FL, 17FR, etc. These front wheels 18FL and 18FR each have a vehicle speed sensor 20F.
L, 20FR are provided, and these vehicle speed sensors 20FL,
20FR is connected to the controller 18 via the M line and outputs a signal representing the vehicle speed.

Furthermore, as will be described later, vehicle speed sensors 20RL and 20RR are also provided for the rear wheels 18RL and 18RR, respectively, and these vehicle speed sensors 20RL and 20RR (hereinafter, vehicle speed sensors are represented by numbers without subscripts) are also connected to the controller 16. outputs a signal representing vehicle speed. It goes without saying that the above-mentioned steering angle sensor 14 is connected to the steering gear mechanism 1.
3, the moving distance of the rack 13b or the front wheel 18FL.

It can be replaced with a sensor that detects the steering angle of the 18FR, and similarly,
The steering speed sensor 15 can be replaced by a sensor that detects the moving speed of the rack 13b or a differential circuit that performs differential calculations on the output signal of the steering angle sensor 4.

21 is connected to the controller 16 and the controller 1
The output shaft of the motor 21 is connected to a rack-and-pinion steering gear mechanism 23 via a bevel gear mechanism 22. Bevel gear mechanism 2
2 has a bevel gear 22b fixed to the output shaft of the electric motor 21 and a bevel gear 22a that rotates integrally with a binion gear 23a of the steering gear mechanism 23. The steering gear mechanism 23 is the aforementioned steering gear mechanism 23.
Similarly, the binion gear 23a is connected to the electric motor 21 via the bevel gear mechanism 22, and both ends of the rack 23b are connected to the knuckle arms 19RL, 19 of the left and right rear wheels 18RL, 18RR, respectively.
It is connected to RR via a steering linkage consisting of tie rods 17RL, 17RR, etc. The rack 23b of the steering gear mechanism 23 is provided with a rear wheel steering angle sensor 24 that detects the moving distance of the rack 23b in the axial direction. The rear wheel steering angle sensor 24 includes a differential transformer and the like, is connected to the controller 16, and is connected to the rack 23.
The steering angle of the rear wheels 18RL and 18RR is detected over the moving distance b, and a signal representing the steering angle is output to the controller 16. As is well known, in the rear wheel steering angle sensor 24, an alternating current pulse signal is input from the controller 16 to the primary coil, the core is displaced together with the rack 23b, and a differential signal is output from the secondary coil. In this embodiment, the electric motor 21 is connected to the rear wheel 1.
Although it is provided exclusively for steering of 8RL and 18RR, electric motor 2
1 output to the front wheels 18FL and 18FR as well as the rear wheels 18R.
L.

It goes without saying that the present invention can also be achieved by adding a steering angle function generating mechanism to the transmission system of the steering force distributed to the rear wheels 18RR and the rear wheels 18RL and 18RR.

The controller 1B includes a control circuit 25 as shown in FIG.
and a drive circuit 26, a current sensor 28 of the drive circuit 26, which will be described later, is connected to the control circuit 25 along with the sensors 14, 15, 20, 24° 40 described above, and the electric motor 21 described above is connected to the drive circuit 26. has been done.

The control circuit 25 includes a constant voltage circuit 30, a microcomputer circuit 31, and input interface circuits 32, 3.
4, 35, 37, 41, 42, etc. The constant voltage circuit 30 is connected to a battery via a fuse or the like, and supplies constant voltage power to each circuit. The input interface circuits 32゜34.35, 37, 41.42 respectively correspond to the above-mentioned sensors 14, 20.24.28゜1.
5.40, and is also connected to the microcomputer circuit 31 via a data bus. An input interface circuit 32 connected to the steering angle sensor 14 processes the pressure signal from the steering angle sensor 14 and outputs a signal representing the steering angle and direction of the front wheels 18FL and 18FR to the microcomputer circuit 31. Similarly, the steering speed sensor 15
An input interface circuit 41 connected to the microcomputer circuit 31 includes an A/D converter and the like and converts the output signal of the steering speed sensor 15 into a digital signal representing the steering speed and outputs it to the microcomputer circuit 31. The input interface circuit 42 also has a torque sensor 40.
The output signal is converted into a digital signal representing the magnitude and direction of the steering torque, and the digital signal is output to the microcomputer circuit 31.

The interface circuit 35 connected to the rear wheel steering angle sensor 24 is composed of an oscillation circuit, a rectifier circuit, a low-pass filter, etc., and outputs an AC pulse signal to the primary coil of the rear wheel steering angle sensor 24, and also outputs a signal from the secondary coil. is formatted and output to the microcomputer circuit 31. The interface circuit 34 connected to the vehicle speed sensor 20 is composed of a waveform shaping circuit, an arithmetic circuit, etc.
Based on the output signal of 0, a signal representing the vehicle speed is output to the microcomputer circuit 31. An interface circuit 37 connected to the current sensor 28 includes an amplifier circuit, an A/D converter, etc., converts the output signal of the current sensor 28 into a digital signal, and outputs the digital signal to the microcomputer circuit 31.

Microcomputer circuit 3! is the CPU.

Equipped with ROM, RAM, clock, etc., each interface circuit 32,
34, 35, 41. The signals input from each sensor via 42 are processed to determine the direction and duty factor of the current flowing to the motor 21, and a pulse width modulation signal (PWM signal) g+ representing this duty factor is processed. h* 1
, J to the drive circuit 26.

The drive circuit 26 includes a booster circuit 38 and a gate drive circuit 3.
9, a current sensor 28, a relay circuit 41, a switch circuit 40, etc., a gate drive circuit 39 is connected to the battery, and a switch circuit 40 is connected to the battery via the relay circuit 41. The switch circuit 40 is
Four field effect transistors (FETs) Ql, Q2.
Q3゜Q4 are connected in a bridge shape, and these FETs
Ql, Q2. Q3. The gate of Q4 is connected to a gate drive circuit 39. The drains of FETQI, Q2 are connected to the battery, and the sources are connected to FETQ3. Q4 is also connected to the drain of FETQ3. The source of Q4 is grounded (one terminal of the battery) via the current sensor 28,
FET QI.

There is no electric current between the source/drain connection of Q3 and the source/drain connection of FET Q2゜Q4! An II machine 21 is connected. The boost circuit 38 boosts the voltage of the battery and outputs it to the gate drive circuit 39.
9 is a PWM input from the microcomputer circuit 31
Each F of the switch circuit 40 based on the signal pair i, j
ETQI, Q2. Q3. A drive signal is output to the gate of Q4. The current sensor 28 detects the current applied to the motor 21 and outputs a detection signal of this current to the above-mentioned interface circuit 37. Note that the switch circuit 40 is an FE
A duty factor drive signal corresponding to the PWM signal signal is input to the gate of TQI, and similarly, a PWM signal is input to the gate of FETQ2, and a PWM signal i is input to the gate of FETQ3.
The duty factor drive signal of the PWM signal j is input to the gate of the %FETQ4.

Next, the operation of this embodiment will be explained with reference to FIG.

The steering control device for this front and rear wheel steering device controls the electric motor 21 by executing a series of processes shown in the flowchart of FIG. 4 in the microcomputer circuit 31.

First, when the ignition key is operated and the key switch is placed in the ON position, the microcomputer circuit 3
Power is supplied to the first class, and the microcomputer circuit 31
is activated. In step P1, the microcomputer circuit 31 is initialized, and data stored in internal registers and the like are erased and addresses are designated. Subsequently, in step P2, initial failure diagnosis is performed according to a subroutine defined elsewhere, and the following processing is performed only when everything is functioning normally.

In step P3, the output signal S of the steering angle sensor 14 is read, and in step P4, the steering angle θF from the neutral position (θF≧
b, -θM).

This steering angle θF corresponds to the steering angle of the front wheels 18FL and 18FR because the rotation angle of the steering shaft 12 corresponds to the steering angle of the front wheels 18FL and 18FR.
L, represents the steering angle of 18FR (hereinafter referred to as front wheel steering angle).

Subsequently, in step P5, it is determined whether the front wheel steering angle θF is positive or negative, that is, the direction, and if the front wheel steering angle θF is positive, step P
6, the flag F1 is set to O, and if the front wheel steering angle θF is negative, the front wheel steering angle θF is made into a positive value (absolute value) in step Pf, and then the flag F1 is set to 1 in step P8. .

Next, in step P9, the vehicle speed V (actual vehicle speed V) is read from the output signal of each vehicle speed sensor 20, and in the following step P10, a vehicle speed correction subroutine defined elsewhere is executed to correct the vehicle speed V. As shown in FIG. 5, this vehicle speed correction subroutine reads the steering speed b2 from the output signal of the steering speed sensor 15 in step Q1, and
In step Q2, a map search is performed for the vehicle speed correction value ΔV from the data table A shown in FIG. 13 using the steering speed O1 as an address. Correct V. As is clear from the figure, the vehicle speed correction value ΔV has a characteristic that it gradually increases from a predetermined vehicle speed in the middle vehicle speed range and becomes a constant value in the high vehicle speed range. Then, in the next step pH, a map search is performed for the steering angle ratio k using the corrected vehicle speed V as an address from the data table 1 shown in FIG. As is clear from FIG. 11, this steering angle ratio has a positive value (representing the same phase) that asymptotically approaches (converges to) a predetermined value in a high vehicle speed region higher than the predetermined vehicle speed V. It has a negative value (representing an opposite phase) that converges to a predetermined value in a lower vehicle speed region. Moreover, since this steering angle ratio is determined using the vehicle speed corrected according to the steering speed S as an address, it exhibits the characteristics shown in FIG. 19 with respect to the actual vehicle speed using the steering speed Y as a parameter. In other words, when the actual vehicle speed is the same, the steering angle ratio becomes (5? rr< fJ
r2<fJ r3), exhibiting characteristics as shown by solid lines, broken lines, and chain lines, respectively. Subsequently, in step P12, the front wheel steering angle θF is multiplied by the steering angle ratio k to determine the rear wheel 18R.
The target steering angle (rear wheel target steering angle) θRT of L and 18RR is calculated. The above-mentioned vehicle speed correction value △V is obtained by searching the coefficient 6 from the data table shown in FIG. 21 using the steering speed 9r as an address, and multiplying the actual vehicle speed ■ by this coefficient ε.
It is also possible to obtain V=■・ε).

Next, in step P13, the vehicle speed V is set to a predetermined vehicle speed v
It is determined whether the vehicle speed V exceeds 0 and the vehicle speed V is a predetermined vehicle speed■.

If it exceeds step P14゜PI5. PlB processing is performed, and the vehicle speed V is the predetermined vehicle speed V. If it is below, the process of step P17° PlB, PI3 is performed. Step P
14, the value of the flag F1 is determined, and if the flag F1 is 1, the flag F3 is set to 1 in step P15, and if the flag F1 is 0, the flag F3 is set to 1 in step P16.
Set to 0. Similarly, in step P17, the value of flag F1 is determined, and if flag F1 is 1, step P
The flag F3 is set to 0 in step P18, and if the flag F1 is 0, the flag F3 is set to 1 in step P19.

In the subsequent step P20, the output signals θR1 and θR2 of the rear wheel steering angle sensor 24 are read, and in step P21, a failure diagnosis of the rear wheel steering angle sensor 24 is performed according to a subroutine defined elsewhere. In this step P21, the following process is executed only when it is diagnosed that the rear wheel steering angle sensor 24 is functioning normally. Then, step P22
, the output signal θR1θR2 of the rear wheel steering angle sensor 24
is subtracted to calculate the rear wheel steering angle θR.

Next, in step P23, it is determined whether the rear wheel steering angle θR is positive or negative, and if the rear wheel steering angle θR is positive, the flag F2 is set to 0 in step P24, and if the rear wheel steering angle θR is negative, the flag F2 is set to 0. For example, after the rear wheel steering angle θR is made into a positive value (absolute value) in step P25, the flag F2 is set to 1 in step P26.

In the next step P27, flag F2 and flag F
3 and flag F2. If the values of F3 are different, the process of step P28 is performed, and the flag F2. If F3 is the same value, the processes from step P29 to step P34 are performed. In step P28, the rear wheel target steering angle θRT
and the rear wheel steering angle θR to calculate the deviation ΔθR. Further, in step P29, the rear wheel steering angle θR is subtracted from the rear wheel target steering angle θRT to calculate the deviation ΔθR, and then, in step P30, it is determined whether the deviation ΔθR is positive or negative. This step P
30, when it is determined that the deviation ΔθR is negative, in step P31, the deviation ΔθR is made into a positive value, and then steps P32, P33. At P34, the value of flag F3 is replaced.

That is, in step P32, the value of flag F3 is determined,
If flag F3 is 0, flag F3 is replaced with 1 in step P33, and if flag F3 is 1, step P
34, the flag F3 is replaced with 0.

Next, in step P35, a map search is performed for the rear wheel steering force using the deviation ΔθR as an address from the data table 2 shown in FIG. This rear wheel steering force is generated by the electric motor 21
It represents the duty factor, that is, the current value, of the current flowing to the current, and has a dead zone of O in the low deviation region close to 0, and takes a constant value that increases as the difference (m) increases.Subsequently, in step P36, the Determine whether the wheel steering force is O or not,
If the rear wheel steering force is O, set PWM signals g, h, i, and jlc to 0, 0, and 1.1, respectively, in step P37;
Further, if the rear wheel drive force is not zero, the value of the flag F3 is determined in step P38. In this step P38, if it is determined that the flag F3 is 0, then in step P39
WM signals g, h.

1 each for i and J. If the flag F3 is determined to be 1, o, 1°D, and O are set to the PWM signals g, h, i, and j, respectively, in step P40.

Then, in step P41, the PWM signals gt h, t, j
Output. Therefore, the electric motor 21 is connected to the rear wheel 18RL.
, 18RR is energized according to the steering direction of duty factor D to steer the rear wheels 18RL and 18RR to the target steering angle, and when the current is not energized, the windings are short-circuited to perform electric braking and the rear wheels are steered. to maintain the angle at the target rudder angle. Thereafter, in step P42, failure diagnosis of the drive system such as the electric motor 21 and the switch circuit 40 is performed according to a subroutine defined elsewhere, and the series of processing from step P2 is repeated again.

As mentioned above, in the steering control device of this embodiment,
A vehicle speed correction value △V is determined according to the steering speed, this vehicle speed correction value △V is subtracted from the detected actual vehicle speed to correct the actual vehicle speed, and the steering angle ratio k is determined based on this corrected vehicle speed. The target steering angle θR is obtained by multiplying the front wheel steering angle θF by the steering angle ratio k.
Steer rear wheels 18RL and 18RR to T. For this reason, as is clear from the figure, the steering angle ratio, that is, the rear wheel 18R
The steering angle of L and 18RR changes depending on the steering speed 1)r, and when the steering speed 1) is large during in-phase steering in a high vehicle speed range, it becomes small, so that the steering angle of the driver can be adjusted without compromising stability. You can obtain agile turning performance that corresponds to your intention, that is, excellent maneuverability, and the steering speed or
If the diameter is large, it becomes large and the turning radius can be reduced.
Furthermore, the phase can be changed in the medium vehicle speed range, resulting in excellent turning performance. Since this front and rear wheel steering system subtracts and corrects the actual vehicle speed, it is possible to change the steering angle ratio k largely in the middle vehicle speed region where the value of the steering angle ratio is small and the rate of change is large, and the rear wheel steering device The steering speed has a strong influence on the turning angles of 18RL and 18RR, and the turning performance in the medium speed range can be greatly improved. In addition, in this front and rear wheel steering system, the characteristics of the steering angle ratio relative to the vehicle speed V converge to a constant value in the high and low vehicle speed ranges regardless of the steering speed, so when the vehicle speed and steering speed vary greatly. However, the steering angle of the rear wheels changes smoothly, giving you a good steering feel.

Further, according to this front and rear wheel steering device, the characteristics of the steering angle ratio relative to the vehicle speed are stored in advance in the ROM of the microcomputer circuit, and the steering angle is adjusted based on the vehicle speed corrected from the characteristics without changing the characteristics. Since the steering angle ratio is determined, the steering angle ratio can be determined using only a simple control method such as a table lookup, and the control can be simplified.

FIG. 6 shows a front and rear wheel steering device according to a second embodiment of the first invention. Note that in this second embodiment, a third embodiment described later, and each embodiment of a second invention described later, the basic configurations of the steering mechanism system and control circuit are the same as those of the previously described embodiments, so Only the vehicle speed correction subroutine corresponding to step P of the main routine shown in FIG. 4 will be explained, and the explanation of other parts will be omitted.

In this second embodiment, the steering torque is detected by the torque sensor 40, and the vehicle speed detected by the steering angle sensor 14 is corrected based on the steering torque according to the flowchart of FIG.

As shown in the figure, the vehicle speed correction is performed by reading the steering torque T from the output signal of the torque sensor 40 in step Q1, and using the steering torque T as an address in step Q2 to calculate the vehicle speed from the data table B having the characteristics shown in FIG. Correction value △■
Search the map. As is clear from the figure, this vehicle speed correction value ΔV has a characteristic of increasing as the steering torque T increases. Then, in step Q3, the actual vehicle speed V is corrected by subtracting the vehicle speed correction value △■ from the actual vehicle speed V, and then the corrected vehicle speed V is addressed at step pH of the main routine shown in FIG. The steering angle ratio k is searched up as follows, and the processing from step P12 onward is performed in the same manner as in the above-described embodiment.

In this second embodiment as well, as in the first embodiment described above, the steering angle ratio k changes as shown in FIG. Excellent turning performance can be obtained without any damage, and since the characteristics of the steering angle ratio relative to vehicle speed are not changed, the steering angle of the rear wheels can be smoothly changed, and the vehicle speed can be roughly corrected by subtraction. Therefore, in the middle vehicle speed region where the change in the steering angle ratio on the characteristic curve is large and the value is small, the steering angle ratio can be changed largely according to the steering torque, thereby improving the retrospective performance in the middle vehicle speed region.

In particular, in this second embodiment, since the steering torque corresponds proportionally to the lateral acceleration (lateral G), it is possible to further improve the turning performance during mid-low speed turns where the lateral G becomes large.

FIG. 7 shows a front and rear wheel steering device according to a third embodiment of the first invention.

In this third embodiment as well, the main routine shown in FIG. 4 described above is executed, but the vehicle speed correction subroutine in step P10 is carried out based on the flowchart shown in FIG. As shown in the figure, in step b1, this vehicle speed correction subroutine searches the vehicle speed correction value ΔV from the data table of FIG. 15 using the front wheel steering angle θF as an address, and in step Q
2, the actual vehicle speed V is corrected by subtracting the vehicle speed correction value Δ■ from the actual vehicle speed V. Then, at step pH, a map search is performed for the steering angle ratio k using the corrected vehicle speed as an address.

In this third embodiment, as in the first and second embodiments described above, the steering angle ratio k changes as shown in FIG. 20 depending on the front wheel steering angle θF, which impairs stability. It is possible to improve steering performance, especially in the medium speed range, without any problems, and it is also possible to smoothly change the steering angle of the rear wheels to improve the steering feeling.

FIG. 8 shows a front and rear wheel steering device according to a first embodiment of the second invention.

In this first embodiment, the main routine shown in FIG. 4 is executed to control the turning angle of the rear wheels, as in each of the embodiments of the first invention described above, but the vehicle speed correction in step PIO is The subroutine carries out a series of processes shown in the flowchart of FIG. As shown in the figure, the vehicle speed correction is performed by reading the steering speed S from the output signal of the steering speed sensor 15 in Step Q1, and using the steering speed S as an address in Step Q2, the vehicle speed correction coefficient α is calculated according to the data table shown in the figure. Search the map,
In step Q3, the actual vehicle speed V is multiplied by the correction coefficient α to calculate the actual vehicle speed V.
Correct. Below, in the main routine of Figure 4,
The first step uses the vehicle speed V corrected by the step pH as an address.
A map search is performed for the steering angle ratio k from the data table shown in FIG. 6, and then the processing from step P12 onwards is performed. Above step P
As shown in FIG. 2, the steering angle ratio determined at it is determined by using the steering speed bx,
0. z, bF3. tax (b, t<b 22<
fJ rs< 13 F4).

In the first embodiment of the second invention, the correction coefficient α is determined according to the steering speed S representing the steering state, and the actual vehicle speed is corrected by multiplying the actual vehicle speed by this correction coefficient α. Based on the vehicle speed determined, the steering angle ratio, that is, the steering angle of the rear wheels is determined.

Therefore, the steering angle ratio k can be changed depending on the steering speed without changing the vehicle speed characteristics, which is the basis for determining the steering angle ratio, and the steering angle ratio k can be changed depending on the steering speed without compromising stability. In addition, the steering angle of the rear wheels can be changed smoothly to improve the steering feel, and furthermore, the control can be simplified. In the first embodiment of this second invention,
Since the actual vehicle speed is corrected by multiplying the actual vehicle speed by a correction coefficient, the steering angle ratio can be strongly influenced by the steering speed even in high vehicle speed ranges where the rate of change in the steering angle ratio is small. You can improve.

FIG. 9 shows a front and rear wheel steering device according to a second embodiment of the second invention.

In this second embodiment as well, the main routine shown in FIG. 4 is executed as in each of the above-mentioned embodiments, but the vehicle speed correction in step P10 is performed according to the subroutine shown in the flowchart of FIG. As shown in the flowchart of the same figure, this vehicle speed correction subroutine starts with the torque sensor 4 in step Q1.
Read the steering torque T from the output signal of 0, and step Q
In step Q2, a map search is performed for the vehicle speed correction coefficient α from the characteristic data table E shown in FIG. 17 using the steering torque T as an address, and in step Q3, the actual vehicle speed is multiplied by the vehicle speed correction coefficient α to correct the actual vehicle speed. Then, at step pH, a map search is performed for the steering angle ratio k using the corrected vehicle speed as an address,
Hereinafter, the processes after step P12 are performed.

In this second embodiment, as in the above-mentioned embodiments, it is possible to improve the control performance, especially in the high speed range, by simple control without impairing stability, and also to improve the control performance in the high speed range. Changes in angle can be made smooth. Since the steering torque T corresponds to the lateral G, it is effective in improving the maneuverability at low and medium speeds where the lateral G increases, as described in the second embodiment of the first invention.

FIG. 10 shows a front and rear wheel steering device according to a third embodiment of the second invention.

In this third embodiment, the main routine shown in FIG. 4 is also executed, but the vehicle speed correction in step P10 is performed according to the subroutine shown in the flowchart of FIG. 10. This vehicle speed correction subroutine is executed in step Q1 as shown in the same figure.
Using the front wheel steering angle θF as an address, search the vehicle speed correction coefficient α from the data table F in FIG.
2, the actual vehicle speed V is multiplied by the vehicle speed correction coefficient α to correct the vehicle speed.

Then, in step pH of the main routine, the steering angle ratio is searched on a map using the corrected vehicle speed V as an address, and thereafter, the processes from step P12 onwards are performed.

In this third embodiment as well, the turning performance can be improved by simple control without impairing stability, and the rear wheel steering angle can be changed smoothly, thereby improving the steering feeling. In this third embodiment as well, the steering angle ratio in the high vehicle speed range can be changed greatly depending on the front wheel steering angle, and the controllability in the high vehicle speed range can be greatly improved.

In addition, in each of the embodiments of the first invention described above, the vehicle speed is corrected subtractively, but it is also possible to perform additive correction depending on the initial setting of the characteristics of the steering angle ratio relative to the vehicle speed and the correction value relative to the steering state. Similarly, in the second invention, it is possible to correct the vehicle speed not only by multiplication but also by division. Further, in the embodiments of each invention, the steering speed and the like are used as the state quantity representing the steering state, but it is also possible to use a state quantity representing the turning behavior of the vehicle, such as lateral G.

(Effects of the Invention) As described above, according to the front and rear wheel steering devices for a vehicle according to the first and second inventions, the detected vehicle speed is corrected according to the steering condition, and the steering angle is adjusted based on the corrected vehicle speed. The steering angle ratio is determined and the rear wheels are steered to the determined steering angle by multiplying the front wheel steering angle by this steering angle ratio, so the steering condition is reflected in the steering angle of the rear wheels, allowing for turning without compromising stability. In addition, the steering condition can be reflected in the rear wheel steering angle using simple control methods such as table lookup without using complicated algorithms. This has the effect of making the steering smoother and improving the steering feel.

In particular, according to the front and rear wheel steering device for a vehicle according to the first invention, since the vehicle speed is subtractively corrected, the steering angle ratio is corrected even in the middle vehicle speed region where the value of the steering angle ratio is small and the rate of change is large in relation to the vehicle speed characteristic. This can be strongly influenced by the steering condition. This is particularly effective for maintaining stability at high speeds of large vehicles (such as trucks) while increasing maneuverability at medium speeds. Further, according to the front and rear wheel steering device for a vehicle according to the second invention, since the vehicle speed is multiplied and corrected, even in a high vehicle speed region where the rate of change of the steering angle ratio is large in relation to the vehicle speed characteristic, the steering angle ratio is not affected by the steering state. can be influenced. This is particularly effective in increasing the maneuverability of vehicles (sports vehicles, etc.) whose stability has been increased through aerodynamics in a high speed range.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the present invention. 2 to 5 show a front and rear wheel steering system for a vehicle according to a first embodiment of the first invention, in which FIG. 2 is a schematic diagram of a mechanical system, FIG. 3 is a block diagram of a control system, and FIG. The figure is a flowchart of the main routine,
FIG. 5 is a flowchart of the subroutine. FIG. 6 is a flowchart of the subroutine of the second embodiment of the first invention, FIG. 7 is a flowchart of the subroutine of the third embodiment of the first invention, and FIG. 8 is a flowchart of the subroutine of the third embodiment of the second invention. FIG. 9 is a flowchart of the subroutine of the second embodiment of the second invention, and FIG. 10 is a flowchart of the subroutine of the third embodiment of the second invention. Figures 11 to 18 are data tables used for control processing, Figures 19 and 20 are reference figures, and Figure 2 is a data table used for control processing.
Figure 1 shows a data table used for control processing in another aspect. 11... Steering handle 14... Rudder angle sensor 15... Steering speed sensor 6... Controller 8... FL, FR, RL. 1... Electric motor 4... Rear wheel steering angle sensor 0... Torque sensor RR single wheel license applicant

Claims (1)

[Claims] 1. Detect the front wheel steering angle and the vehicle speed, determine the rear wheel target steering angle based on the vehicle speed and the front wheel steering angle, and adjust the rear wheel steering angle to the rear wheel target steering angle. A front and rear wheel steering device for a vehicle that steers together with the front wheels in response to steering includes a steering state detection means for detecting a steering state, and a correction amount determination unit for determining a vehicle speed correction value based on the steering state detected by the steering state detection means. means, vehicle speed correction means for calculating a corrected vehicle speed by subtracting the vehicle speed correction value determined by the correction amount determination means from the detected vehicle speed; a steering angle ratio determining means for determining a steering angle ratio of front and rear wheels based on the corrected vehicle speed determined by the vehicle speed correcting means according to control characteristics; and a steering angle ratio determined by the steering angle ratio determining means and the detected steering angle ratio. A front and rear wheel steering device for a vehicle, comprising: target steering angle determining means for calculating the target rear wheel steering angle from a front wheel steering angle. 2. Detect the front wheel steering angle and vehicle speed, determine the rear wheel target steering angle based on the vehicle speed and front wheel steering angle, and adjust the rear wheels to the rear wheel target steering angle along with the front wheels according to the steering of the steering wheel. A front and rear wheel steering device for a vehicle to be steered, comprising: a steering state detection means for detecting a steering state; a correction amount determining means for determining a vehicle speed correction coefficient based on the steering state detected by the steering state detection means; a vehicle speed correction means for calculating a corrected vehicle speed by multiplying the detected vehicle speed by the vehicle speed correction coefficient determined by the determination means; and a vehicle speed correction means for storing a control characteristic of a steering angle ratio of the front and rear wheels with respect to the vehicle speed, and correcting the vehicle speed according to the control characteristic. a steering angle ratio determining means for determining a steering angle ratio of the front and rear wheels based on the corrected vehicle speed determined by the means; and a steering angle ratio determined by the steering angle ratio determining means and the detected front wheel turning angle. A front and rear wheel steering device for a vehicle, comprising: target steering angle determining means for calculating the rear wheel target steering angle. 3. The vehicle front and rear wheel steering system according to claim 1 or 2, wherein the steering state detection means detects a steering speed as a state quantity representing a steering state. 4. The vehicle front and rear wheel steering system according to claim 1 or 2, wherein the steering state detection means detects steering torque as a state quantity representing a steering state. 5. The vehicle front and rear wheel steering device according to claim 1 or 2, wherein the steering state detection means detects a front wheel turning angle as a state quantity representing a steering state.