JPS62181963A - Four-wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve responsiveness accompanying a change of steering ratio characteristics and improve safety by providing a characteristic changeover means for rear wheel steering ratio and a changeover phase direction judging means based on the signal of said changeover means, and changing the steering ratio with good responsiveness in the same phase direction whereas only under a condition that the change of the behavior of a vehicle offers no problem. CONSTITUTION:The captioned device has a characteristic changeover means for rear wheel steering ratio, a judging means which judges the phase direction of changeover on receiving the signal of said means, a characteristic changing means which immediately carries out a change at the time of changeover in the same phase direction on receiving the signal of the judging means, and a change restricting means which carries out a change on condition that prescribed conditions are satisfied at the time of changeover in a reverse phase direction. Accordingly, depending on the phase direction of the rear wheel steering ratio change, the change of steering ratio is carried out with good responsiveness in the same phase direction, whereas only under a condition that a change of the behavior of a vehicle offers no problem in the reverse phase direction, obtaining a favorable responsiveness accompanying the steering ratio change and safety.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a four-wheel steering system for a vehicle, and more specifically, to a four-wheel steering system for a vehicle, and more specifically, a system that controls a rear wheel steering ratio based on a predetermined rear wheel steering ratio characteristic. Regarding.

(Prior Art) Some vehicles have a so-called four-wheel steering system in which both the front wheels and the rear wheels are steered.

In this four-wheel steering, the rear wheel steering ratio, that is, the ratio of the rear wheel steering angle to the front wheel steering angle, is generally controlled based on a predetermined steering ratio characteristic. It has been considered to set the steering ratio characteristic and then change the steering ratio characteristic as appropriate depending on the situation.

However, since changing the steering ratio characteristics involves a change in the behavior of the vehicle, countermeasures are required in the transient region.

In response to this, it has been proposed to provide a delay means, as seen in Japanese Unexamined Patent Publication No. 60-135369.

According to the above proposal, the speed of change in the steering ratio due to the change in the steering ratio is made slowly, and a sudden change in the behavior of the heavy vehicle is prevented.

(Problems to be Solved by the Invention) However, when the steering ratio is changed in the same phase direction, this is a control to stabilize the vehicle, and it is desirable to change the steering ratio more quickly.

On the other hand, when the steering ratio is changed in the opposite phase direction, the control is to make the behavior of the vehicle agile, and it is desirable to ensure stability from the viewpoint of control.

Therefore, the present invention takes into consideration that the requirements for control differ depending on the phase direction of the characteristic change accompanying switching of the rear wheel steering ratio characteristic, and has developed a characteristic that is more preferable from the viewpoint of ensuring vehicle safety. An object of the present invention is to provide a four-wheel steering device for a vehicle that is capable of making changes.

(L stage, action for solving the problem) That is, the present invention is based on a four-wheel steering system that controls a rear wheel steering ratio based on at least two different rear wheel steering ratio characteristics. When comparing steering the wheels in the same phase direction and steering them in the opposite phase direction, the same phase direction is a control direction that increases the stability of the vehicle, whereas the opposite phase direction is a control direction that increases the stability of the vehicle. Focusing on the fact that this is the control direction that makes the vehicle more agile, if the rear wheels are steered in the same phase direction as a result of changing the steering ratio characteristics, the steering ratio characteristics are immediately changed. On the other hand, when steering in the opposite phase direction, the steering ratio characteristics can be improved only under conditions where changes in vehicle behavior due to changes in the steering ratio characteristics are not a problem. This is a change that has been made.

Specifically, as shown in FIG. 1, a characteristic switching means for switching the rear wheel steering ratio characteristic; and receiving a signal from the characteristic switching means to determine a phase direction of switching of the rear wheel steering ratio characteristic. a determining means; and a characteristic changing means that receives a signal from the determining means and immediately changes the steering ratio characteristic when the switching of the rear wheel steering ratio characteristic is to a rear wheel steering ratio characteristic in the same phase direction. and upon receiving a signal from the determining means, when the switching of the rear wheel steering ratio characteristic is to a rear wheel steering ratio characteristic in an opposite phase direction, on the condition that a predetermined condition is satisfied, A change regulating means for changing steering ratio characteristics.

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

In Fig. 2, IR is the right front wheel, IL is the left front wheel, 2R is the right rear wheel, and 2L is the left front wheel.The left and right front wheels IR and IL are linked by a front wheel steering mechanism A, and the left and right rear wheels 2R1
2L is linked by rear wheel steering mechanism B.

In the embodiment, the front wheel steering mechanism A includes a pair of left and right knuckle arms 3R13L and a tie rod 4R14L, and a relay rod 5 that connects the pair of left and right tie rods 4R14L. A steering mechanism C is linked to the front wheel steering mechanism A, and the steering mechanism C is of a rack and pinion type in this embodiment. In other words, the rack 6 is attached to the relay rod 5.
is formed, while the pinion 7 that meshes with the rack 6 is
It is connected to a handle 9 via a shaft 8. As a result, when the handle 9 is operated to the right, the relay rod 5 is displaced to the left in FIG. The steering wheel is steered clockwise in the figure by an amount corresponding to the amount of operation displacement 9, that is, the steering angle of the steering wheel. Similarly, when the steering wheel 9 is operated to the left, the left and right front wheels IR and LL are steered to the left in accordance with this operation displacement meter.

Similarly to the front wheel steering mechanism A, the rear wheel steering mechanism B also includes a pair of left and right knuckle arms IOR, 10L and tie rods IIR, 11L, and the tie ports IIR, IIL.
In this embodiment, the rear wheel steering mechanism B includes a hydraulic power steering mechanism.

To explain this power steering mechanism, a cylinder device 13 is attached to the relay rod 12, and the cylinder 13a is fixed to the vehicle body.
A piston 13d that defines the interior of 3a into two chambers 13b and 13C.
is integrated into the relay rod 12. Two chambers 13b and 13c within this cylinder 13a are connected to a control valve 16 via piping 14 or 15. Further, pipes 18 and 19 extending from the reservoir tank 17 are connected to each of the control valves 16, and an oil pump 20 driven by an engine (not shown) is connected to the pipe 18, which serves as an oil supply pipe. The control valve 16 is of a so-called booster valve type (spool type) in which the control rod 21 is a sliding type, and the input force portion 21a of the control rod 21 is used as a moving member of a steering ratio changing device E to be described later. The output portion 21b of the control rod 21 is also integrated with the relay rod 12 of the rear wheel steering mechanism B.

In such a power steering mechanism, as is known, when the control rod 21 is displaced to the left in FIG. 2, the relay rod 12 is displaced to the left in FIG. The arms IOR and IOL rotate clockwise in FIG. 2 about their rotation centers 10R' and IOL', and the rear wheel 2R12L is steered to the right.

During this steering, oil is supplied into the chamber 13b of the cylinder device 13 according to the amount of displacement of the control rod 21 to assist in driving the relay rod 12 (boosting effect). Similarly, when the control rod 21 is displaced to the right in FIG. will be steered to the left.

The front wheel steering mechanism A also has a power steering mechanism F like the rear wheel steering mechanism B. This power steering mechanism F includes a cylinder device 65 attached to the relay rod 5 of the front wheel steering mechanism A, and the cylinder 65a is fixed to the vehicle body.
A piston 65d that defines two chambers 65b and 65c inside a is integrated with the relay rod 5. This cylinder 6
The two chambers 65b and 65c in 5a are connected to piping 66 or 67.
is connected to a rotary control valve 68 provided on the shaft 8 of the steering mechanism C. The control palflow 8 is connected to a pipe 70 extending from a branch valve 69 connected to the discharge side of the oil pump 20.
, and a pipe 71 branched from the pipe 19 are connected.

Such a power steering mechanism F boosts the operating force of the handle 9 (chamber 65b or 6 of the cylinder device 65).
5c) and transmits it to the relay rod 5.The function of such a power steering mechanism F itself is basically the same as that of the power steering mechanism described above, so no further details will be given. Further explanation will be omitted.

The steering mechanism C and the rear wheel steering mechanism B are linked via the front wheel steering mechanism A and the steering ratio changing device E.

From this steering ratio changing device E, an input rod 22 extends forward, and a binion 23 attached to the front end of the input rod 22 connects the rack 24 and 111 formed on the relay rod 5 of the front wheel steering mechanism A.
iii are combined. Note that the output lot of the steering ratio changing device E is shared by the input portion 21a of the control rod 21 in the control valve 16, as described above.

An example of the steering ratio changing device E will be explained with reference to diagram f53. In this steering ratio changing device E, the input portion 21a of the control rod 21 is held slidably in the vehicle width direction with respect to the vehicle body, and its axis of movement! ; Indicated as L1. Further, this steering ratio changing device E has a swing arm 31, and the base end of the swing arm 31 is pivotably supported by a pin 33 with respect to a boulder 32. There is. This holder 32 has a rotation axis 32a that is aligned with an orthogonal line f orthogonal to the movement axis Jomon 1 of the input section 21a.
It is rotatably held on the vehicle body around L2. The pin 33 is located at the intersection of the Jomon 1 and the Jomon 2, and extends in a direction perpendicular to the orthogonal line fL2. Therefore, the swinging arm 31 can swing freely around the pin 33, but by rotating the holder 32, the angle of inclination between the pin 33 and the moving axis The angle of inclination of the oscillating orbital surface with respect to a plane (reference plane) perpendicular to the movement axis m1 is variable.

The tip of the swing arm 31 and the input section 21a are connected by a connecting rod 34. That is, the connecting member 34 connects to the swing arm 31 via the pole joint 35.
The input section 21a is connected to the input section 21a via a pole joint 36.

Due to the connecting rod 34 as described above, the spacing between the pole joints 35 and 36 at each end of the swinging arm 31 is
It will always be held constant. Therefore, if the pole joint 35 is displaced in the left-right direction in FIG.

The input section 21a will be displaced in the left-right direction in FIG.

The swinging of the swinging arm 31 about the pin 33 is performed in response to the operational displacement of the steering mechanism C, that is, the steering angle of the steering wheel. A rotating plate 37 is connected thereto. This rotating plate 37 is rotatably held on the vehicle body so that its rotating shaft 37a is at the moving axis Jomon 1, and the connecting rod 34 is connected to the pole shaft with respect to the eccentric portion of this rotating plate 37. It is slidably penetrated through the int 38.

A bevel gear 39 connected to the input rod 22 is meshed with a rotating plate 37 made of a bevel gear.

The swing plate 37 allows the swing arm 31 to swing about the pin 33 by an amount corresponding to the steering angle of the steering wheel, but the axis of the pin 33 and the movement axis 1. If the pin 33 is tilted, the ball joint 35 will move in the left-right direction in FIG. 3, that is, along the axis of movement 1. direction, and this displacement is caused by the connecting rod 34
The signal is transmitted to the input section 21a via the input section 21a, and the input section 21a is displaced. Even if the swing angle of the swing arm 31 about the pin 33 is the same, the displacement of the pole joint 35 in the left-right direction in FIG. When the angle changes, it will be changed (steering ratio change).

In order to change the inclination angle, the rotation shaft 32a of the holder 32
A sector gear 40 as a worm wheel is attached to the worm wheel, and a worm gear 41 meshing with the sector gear 40 is rotationally driven by a stepping motor 44 as an inclination angle changing means via a pair of bevel gears 42 and 43. It has become so.

Here, the swing angle of the swing arm 31 about the pin 33 and the inclination angle of the swing arm 31 (the inclination angle of the pin 33) are the same as those of the pole joint 35 (input section 21a).
The influence of the displacement in the movement axis fL1 direction will be explained. Now, the swing angle of the swing arm 31 about the pin 33 is θ, the reference plane perpendicular to the movement axis 11 is δ, and the inclination angle that the swing orbital surface of the swing arm 31 makes with the reference plane δ is α. , the eccentric distance of the pole joint 35 from the pin 33 is r, then the axis of movement of the pole joint 3 fLt
The displacement X in the direction is X = r tan a fist5inO
Therefore, it is a function with α and θ as parameters. Therefore, if the inclination angle α is fixed at a certain value, X will be a function of θ, that is, depending on the steering wheel steering angle, and if the value of this inclination angle α is changed, even if the steering wheel angle is the same, The value of X will also change. Then, this change in the inclination angle α directly results in a change in the steering ratio.

As shown in FIG. 4, this steering ratio change is made based on a steering ratio characteristic that is set in advance using heavy speed as a parameter.
First steering ratio characteristic (hereinafter referred to as "first steering ratio characteristic")

This Nol characteristic is appropriately switched between the Nol characteristic and the No2 characteristic from the low speed side.

Here, in order to forcibly set the rear wheel 2R12L to the middle position, that is, the straight-ahead position yE;, the rear wheel power steering mechanism °D includes a pair of return springs 13e,
f is attached. Both springs 13e and 13f
The relay rods 12 for the rear wheels are moved from left and right opposite directions with equal force. Further, both oil chambers 13b and 13c of the power steering mechanism are connected to a communication passage 4.
6, and an electromagnetic on-off valve 47 is connected to the communication path 46. As a result, when the on-off valve 47 is closed, the rear wheel 2R12L is moved by the spring 13 due to the supply of hydraulic pressure to the oil chamber 13b or 13c.
e or 13f, and when the on-off valve 47 is opened to make both the oil chambers 13b and 13C at the same pressure, the rear wheels 2R12C are forced to the neutral position by the action of the springs 13e and 13f. . Of course, this spring 13e,
The biasing force 13f resists the external force received from the rear wheels 2R or 2L when turning and maintains a neutral position! It is set to a size that makes it easy to read.

Further, both swing stroke ends of the sector gear 40 driven by the stepping motor 44 are regulated by an in-phase stopper 48 and an opposite-phase stopper 49 (see FIG. 3). Then, the entire swing range of such sector gear 40 (same phase side stroke end →
The necessary rotation range of the stepping motor 44 over the opposite phase side stroke end is "
580".

In FIG. 2, 51 is a control unit composed of, for example, a microcomputer, and this control unit 51 includes:
A signal from a vehicle speed sensor 53 is input, and an ON/OFF signal from a steering ratio characteristic changeover switch 54 is input. Here, the steering ratio characteristic changeover switch (SW) 54 constitutes a characteristic switching means for changing the steering ratio characteristic, and when the switch 5W54 is set to rOF FJ, it means selection of the Nol characteristic, and when it is "ON", it means the selection of the No.2 characteristic. means selection of characteristics. Further, the control unit 51 outputs an output to the stepping motor 44 and the on-off valve 47.

Next, a first embodiment of the control contents by the control unit 51 will be explained based on the flowcharts shown in FIGS. 5 to 9. In this embodiment, the steering ratio is changed in the opposite phase direction. In this case, the vehicle speed must be in a low speed range. In addition, in this embodiment, in consideration of the possibility that the stepping motor 44 may "step out" (a deviation between the number of steppings and the corresponding actual positional relationship), the reference positioning of the stepping motor 44 is carried out at any time, that is, "motor position initialization is performed." ”. In the embodiment, this "motor position initialization" is performed by bringing the sector gear 40 into contact with the opposite phase stopper 49, and this time is the origin position with the stepping number "0", and the motor is driven from this origin position. The stepping number is the motor position i at that time.
rMPJ, and this "motor position initialization" is performed at the start of control (immediately after starting the engine),
This should be done every time the vehicle speed drops to zero. Furthermore, in the flowchart shown in this embodiment, two types of flags, "flag 1" and "flag 2", are used, and the meanings of each flag are as follows.

■Flag l "This flag is used to distinguish whether or not the motor position is being initialized. When it is 0, it means that initialization has been completed, and when it is 1, it means that initialization is in progress.

(2) Flag 2 This flag is set to rlJ when "motor position initialization" is executed once, and is used to perform "motor position initialization" only once every time the vehicle speed drops to zero from the running state. be.

Based on the above-mentioned premise, the complete details will be explained each time according to the flowcharts shown in Figs. I will explain from.

Interrupt processing l (Figure 6) The interrupt routine shown in Figure 6 is for driving the stepping motor 44 to set the steering ratio according to the vehicle speed based on the Nol characteristic or the No2 characteristic, and is set by a timer. The main routine shown in FIG. 5 is interrupted every predetermined time period (for example, every 10 m5 eC if the stepping motor 44 is to be driven at a rate of 100 steps per second). In the figure, rCPJ is the target stepping number necessary to achieve the steering ratio determined based on the N01 characteristic or No2 characteristic shown in FIG. 4, and "MP"
As mentioned above, 5 indicates the swinging position of the sector gear 40 from the origin position (the steering position of the rear wheel 2R52L) when the reverse phase side stopper 49 is set as the origin position, expressed as a stepping number.

On the premise of the above, first, in step 541, it is determined whether the target stepping number CP and the current position MP match, and if CP=MP, the rear wheels 2R12L are set to a predetermined steering ratio characteristic. In step S42, the stepping motor 4
After that, in step S43, the timer is set to the above-mentioned predetermined time in preparation for the next interrupt.

When it is determined in step 541 that CP is not equal to MP, the current supplied to the stepping motor 44 is increased (current town is canceled) in preparation for driving the stepping motor 44, and then in step S45, C
It is determined whether or not it is a POMF. And CP>M
When it is determined that it is not P, stepping motor 4
Since the current position of No. 4 is located on the same phase side with respect to the target stepping number CP, in step S46, the stepping motor 44 is driven toward the opposite phase side by l stepping. Then, in accordance with the operation of this "l stepping", the current position MP is updated by one stepping in step S47, and then the process moves to step 343. Conversely, when it is determined in step S45 that CP>MP, the stepping motor 44 is driven by one step toward the same phase in step S348, and then step S45 is determined.
The current position MP is updated in step S49, and the process moves to step S43.

Interrupt processing 2 (Fig. 7) This interrupt processing is performed because the vehicle speed sensor 53 is supposed to generate a pulse as the speedometer meter cable rotates. 5), the main routine of FIG. 5 is interrupted. The vehicle speed sensor 53 is a 1, for example, 20 pulse sensor (a sensor in which the number of pulses generated when the meter cable rotates once is 20).
Therefore, the number of pulses generated when traveling 1km is r12740 pulses. Such pulses generated by the vehicle speed sensor 53 are sequentially counted and integrated in step S51, and are stored as PCN.

Interrupt Processing 3 (Fig. 8) This interrupt processing is performed when the cumulative count pulse number explained in Interrupt Processing 2 (Fig. 7) is directly calculated from the vehicle speed (km/h).
), due to the relationship with the vehicle speed sensor 53 and the meter cable set as described above, the 28
An interrupt is made to the main routine shown in FIG. 6 every 2.575 m5eC. That is, after the PCN is directly set as the vehicle speed value (km/h) in step S52, the integrated count value PGN of step S51 in FIG. 7 is cleared in step S53.

Note that FIGS. 7 and 8 are merely examples of vehicle speed detection, and vehicle speed can be detected by any conventionally known appropriate means.

Main routine (Fig. 5) First, in step Sl, the entire system is initialized, and in step S2, CPPO2MP=5
80, flag 1=rlJ, and set the steering ratio characteristic (TNO) to the NOI characteristic. That is, setting CP=0 means forcibly performing the process from step S45 to step S46, as is clear from the explanation of FIG.
The purpose is to return the sector gear 40 to 580, that is, to perform "initialization of the motor position".
This is because if only the stamping is returned, it will definitely come into contact with the opposite phase side stopper 49 and return to the original position 1v1. Moreover, it is this N that makes the steering ratio characteristic (T N O) the NOI characteristic.

This is because one characteristic is considered to be the basic characteristic in four-wheel steering.

Thereafter, in step S3, a characteristic switching check of the steering ratio, which will be described later, is performed, and then the process proceeds to step S4, where it is determined whether flag 1 is rlJ. In this step S4, the flag l is initially set to r in step S2.
Since it is set to lJ, the process moves to step S5. In this step S5, it is determined whether or not CP=MP. If CP=MP is not the case, a loop returns from step S3 to step S5 again, and during this loop, the As the stepping motor 44 shown in FIG. 6 is driven (MP approaches "0"), CP=MP eventually becomes true. And this CP=MP
At this point, "motor position initialization" is completed, and flag 1 is set to "0" and flag 2 is set to "1".

When it is determined in step S4 that the flag l is not "l", it is determined in step S7 whether or not the current vehicle speed is zero.

In this determination, if it is determined that the vehicle speed is not zero, that is, it is determined that the vehicle is running, then in step S8, the CP
depending on the current vehicle speed, the Nol characteristic or N
It is set to a value corresponding to the steering ratio determined based on the o2 characteristic. After this, in step S9, flag l and flag 2 are both set to rQJ, and step S
Return to 3.

Further, when it is determined in step S7 that the current heavy speed is zero, in step SIO flag 2 or "
0", and when flag 2 is not rQJ, that is, when it is "1", "motor position initialization"
Since the stepping motor 44 is not driven afterwards, it is deemed unnecessary to perform this "motor position initialization" again, and the process returns to step S3. Also, step S1
0 and flag 2 is "0", the process moves to step 512 to perform "motor position initialization", and in this step Sll, CP=0, MP=58
0 flag 1=ri", and the step S4 described above is set.
, "motor position initialization" is performed through step S5.

Characteristic change check (Figure 9) As mentioned above, in this embodiment, when changing the steering ratio characteristic from No2 characteristic to Nol characteristic, that is, changing the characteristic in the opposite phase direction, the vehicle speed is at a predetermined value (VO) This is done under the following conditions. In other words, under the condition that the vehicle speed is low or zero, N
Changes are being made to the ol characteristics.

First, in step S21, the characteristic changeover switch (
After reading the ON/OFF state of SW) 54, the characteristic J change switch 54 is set to r in the next step S22.
It is determined whether or not it is oNJ, and when it is roFFJ, that is, when switching to the Nol characteristic is selected, the process moves to step S23, and this step 523
, it is determined whether the vehicle speed is less than or equal to a predetermined value (Vo). Here, if it is determined that the vehicle speed exceeds the predetermined value (Vo), the characteristic switching check is repeated without setting the steering ratio characteristic. Only when the vehicle speed becomes equal to or lower than a predetermined value (Vo) does the process proceed to step S24, and in step 324 does the steering ratio characteristic change to No.
set to the property. Accordingly, the target stepping number CP is set to the target stepping number CP based on the Nol characteristic in the opposite phase direction.

On the other hand, in step S22, the characteristic changeover switch 54 is set to ro.
When it is determined that the steering ratio characteristic is NJ, that is, when switching to the No. 2 characteristic is selected, the process immediately moves to step S25, and in step S25, the steering ratio characteristic is changed to the No. 2 characteristic.
set to the property. That is, to change to the No. 2 characteristic, which is offset to the same phase side from the No. 1 characteristic, regardless of the vehicle speed, turn the characteristic changeover switch 54 "ON".
This is done immediately in response to the selection operation of
The target stepping number CP based on the characteristics is set to 1 (arrow in FIG. 4), and the rear wheels are steered in the same phase direction.

In this way, since the change in the steering ratio characteristic in the opposite phase direction (change to the Nol characteristic) is performed when the vehicle speed is low, the change in behavior of the vehicle due to the change in the steering ratio is small. In particular, in this embodiment, since the steering ratio is set to be almost the same as the NOI and NO2 characteristics in the low speed range, there is almost no change in the behavior of the vehicle due to the change.

On the other hand, the steering ratio characteristics are changed in the same phase direction (N.

Regarding the change to No. 2 characteristic), since the change in vehicle behavior due to this change changes in the direction of stabilizing the vehicle, by changing to No. 2 characteristic in synchronization with the characteristic change,
This results in excellent responsiveness.

Figures 1O to 12 show other embodiments of the present invention, and since these embodiments are modified examples of control in the characteristic switching check (Figure f59) in the first embodiment, Controls other than (15 [iNN and FIG. 8] are assumed to be the same, and only the characteristic parts will be explained.

Second Embodiment (Fig. 10) In this embodiment, for changing the steering ratio characteristic from No2 characteristic to Nol characteristic, that is, changing the characteristic in the opposite phase direction,
This is done on the condition that the steering angle θ is less than or equal to a predetermined value (Oo). That is, the No. 2 characteristic is changed to the No. 1 characteristic under the condition that the steering wheel angle 0 is small or zero, that is, the front wheels are approximately at the neutral position. This is based on the consideration that if the steering angle θ is small, the rear wheels are also in a substantially neutral position, and the change in vehicle behavior due to the change in characteristics is slight.

First, in step S61, the characteristic changeover switch (
After reading the ON/OFF state of SW) 54, the characteristic changeover switch 54 is set to "O" in the first step S62.
If it is rOFFJ, that is, if switching to the Nol characteristic is selected, the process moves to step S63, and in step S63, the steering wheel angle 0 is read. After that, in step 564, it is determined whether or not it is less than or equal to a predetermined value (Oo). Here, if it is determined that the steering wheel steering angle 0 exceeds the predetermined value (Oo), the characteristic switching check is repeated without setting the steering ratio characteristic. Then, when the steering wheel steering angle 0 becomes less than a predetermined value (θ0),
In other words, the process moves to step 565 only when the front wheels are almost at the neutral position, and in step S65 the steering ratio characteristic is set to No.
l characteristic. In response, N.

A target stepping number CP is set based on the l characteristic.

On the other hand, in step S62, the characteristic changeover switch 54 is set to ro.
When it is determined that the steering ratio characteristic is NJ, if switching to the No. 2 characteristic is selected, the process immediately moves to step S66, and in this step S66, the steering ratio characteristic is changed to NJ.
Set to o2 characteristic. That is, when changing to the same phase direction, the steering ratio is immediately changed in response to the selection operation of turning the characteristic changeover switch 54 "ON" regardless of the steering angle θ. Accordingly, a target stepping number CP is set based on the No. 2 characteristic, and the rear wheels are steered in the same phase direction. Note that the steering wheel steering angle θ may be detected from the front wheel steering angle. It goes without saying that a detection signal representing the steering angle of 0 is input to the control unit 51.

Third Embodiment (Figures 11 and 12) In this embodiment, the change in steering ratio characteristic from No2 characteristic to Nol characteristic is carried out in a region where the amount of change in the steering ratio due to the change is small. It's Nishide. That is, when the above-mentioned Nol characteristic and No2 characteristic are set as the steering ratio characteristics, as shown in FIG. This corresponds to region 1, where the amount of change in the steering ratio due to changes in steering ratio characteristics is small, and in this region ■ and region II, there is little change in vehicle behavior even if characteristics are changed in the opposite phase direction. This is what we focused on.

Based on the above, first, in step S71, the ON/OFF state of the characteristic changeover switch (SW) 54 is read, and then in the next step S72, whether the characteristic changeover switch 54 is "ON" or not is determined. If this determination is made and rOFFN is selected, that is, if switching to the Nol characteristic is selected, the process moves to step S73. In this step S73, the current vehicle speed is read, and then in step S64, the predetermined A determination is made as to whether or not it is less than or equal to the value (Vl). Here, if it is determined that the current vehicle speed exceeds the predetermined value (Vl), it is assumed that the current vehicle speed is not within the range, and the process moves to step S74.
In step S74, it is determined whether the current vehicle speed is equal to or higher than a predetermined value (v2). Here, when the current vehicle speed is smaller than the predetermined value v2, it is assumed that the current vehicle speed is not in the region H, that is, it is in the region where the amount of change in the steering ratio due to the characteristic change is large, and the 9 steering ratio characteristics are set. The characteristic switching check is repeated. Then, when the current vehicle speed is below a predetermined value (vl) (g! area engineering), or when the current vehicle speed is above the predetermined value 72 (area II)
Only then, step S73 or step S
74 to step S75, and this step S75
The steering ratio characteristic is set to the Nol characteristic. Accordingly, the target stepping number CP based on the Nol characteristic will be set.

On the other hand, in step S72, the characteristic changeover switch 54 is set to "O".
When it is determined that "N", that is, when the change to No. 2 characteristic is selected, step S is immediately performed.
76, and in step S25, the steering ratio characteristic is set to the No. 2 characteristic.

That is, when changing the characteristics in the same phase direction, regardless of the vehicle speed, the characteristics are immediately changed in response to the selection operation of setting the characteristics changeover switch 54 to rONJ, and the No. 2 characteristics are changed accordingly. 2 (Target stepping number C
P is set, and the rear end is steered in the same phase direction.

Although the embodiments have been described above, the present invention is not limited thereto, and includes, for example, the following cases.

(2) The actuator for changing the steering ratio is not limited to the stepping motor 44, and any suitable actuator such as a DC motor may be used.

(2) When the Fill unit 51 is configured by a computer, it may be of either a digital type or an analog type.

Q) Manually operated steering ratio characteristic change switch (S
W) Instead of 54, the steering ratio characteristic may be switched using an output signal from a road surface condition detecting means, for example, a steering wheel sensor. As the characteristics in this case, the steering ratio characteristics shown in FIG. 13 will be set.

(4) As for the steering ratio characteristic, it may be possible to switch between front wheel steering and four wheel steering (Fig. 14), or
In a low speed range, the vehicle may be steered sharply in the same phase direction for convenience when parking (FIG. 15). Of course, the first
When the characteristics shown in FIGS. 4 and 15 are set, it is preferable to switch by manual operation.

(Effects of the Invention) As is clear from the above description, according to the present invention, depending on the phase direction of changing the rear wheel steering ratio, responsiveness is good in the same phase direction, and changes in vehicle behavior do not cause problems in the opposite phase direction. Since the steering ratio is changed only under certain circumstances, the responsiveness and safety associated with changing the steering ratio characteristics can be improved.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of the present invention. FIG. 2 is an overall plan view showing one embodiment of the present invention. FIG. 3 is a skeleton diagram illustrating the rear wheel steering mechanism. FIG. 4 is a characteristic diagram showing an example of steering ratio characteristics. 5 and 9 are flowcharts 1 and 9 showing a control example of the first embodiment. FIG. 10 is a flowchart showing a control example of the second embodiment. FIG. 11 is a flowchart showing a control example of the third embodiment. FIG. 12 is an explanatory diagram of area setting in the control of the third embodiment. FIG. 13 to FIG. 15 are diagrams showing modified examples of steering ratio characteristics. A: Front wheel steering mechanism B: Rear wheel steering mechanism C Ni-steering mechanism E: Steering ratio changing device IRlIL: Front wheel 2R12L: Rear wheel 9: Handle 44 Steering motor 51: Control unit 54: Characteristic changeover switch (characteristic changeover switch) Means) Figure 5 Figure 6

Claims (1)

[Claims] (1) A four-wheel steering system for a vehicle that controls a rear wheel steering ratio based on at least two different rear wheel steering ratio characteristics, comprising: a characteristic switching means for switching the rear wheel steering ratio characteristic; and the characteristic switching means. a discriminating means for receiving a signal from the discriminating means and discriminating a phase direction in which the rear wheel steering ratio characteristic is switched; a characteristic changing means for immediately changing the steering ratio characteristic when switching to a ratio characteristic; and a rear wheel steering ratio characteristic in which the switching of the rear wheel steering ratio characteristic is in an opposite phase direction in response to a signal from the determining means. 1. A four-wheel steering system for a vehicle, comprising: a change regulating means for changing a steering ratio characteristic on the condition that a predetermined condition is satisfied when switching to a four-wheel steering system for a vehicle.