JPS62152977A - Steering device for four wheel of vehicle - Google Patents

Abstract

PURPOSE:To suppress the change in the behavior of a vehicle, which is entailed by the return of rear wheels to the neutral positions thereof, by operating an oil pressure release means attached to a power steering mechanism for the rear wheels, to return the rear wheels to the neutral position thereof only when a rear wheel steering control line is defective and the vehicle is in a range of small steering. CONSTITUTION:A steering device includes a front wheel steering mechanism A, which has a power steering mechanism F and is operated by a steering mechanism C, and a rear wheel steering mechanism B, which has a power steering mechanism D and is connected to the steering mechanism C through the front wheel steering mechanism A and a steering ratio changer E. The changer E has a step motor 44 as a steering ratio adjustment means, which is regulated by a control unit 51. When a rear wheel steering control line is judged to be defective and a vehicle is judged to be in a range of small steering, a valve 47 is opened to connect both the oil pressure chambers 13b, 13c of the power steering mechanism D to each other to forcibly return rear wheels 2R, 2L to the neutral positions thereof.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a four-wheel steering system for a vehicle.

(Prior Art) Some vehicles are designed to steer both the front wheels and the rear wheels, so-called four-wheel steering, as disclosed in Japanese Unexamined Patent Publication No. 199771/1983. In order to assist with the external input necessary for rear wheel steering, there are also systems in which a hydraulic power steering mechanism is attached to the rear wheel steering mechanism, as shown in Japanese Patent Application Laid-Open No. 58-22757. Proposed.

In this four-wheel steering, the ratio of the rear wheel steering angle to the front wheel steering angle, that is, the steering ratio, is changed depending on the driving condition of the vehicle, so the steering of the rear wheels is controlled electrically. Generally, external input to the steering mechanism is provided by an electromagnetic actuator.

(Problems to be Solved by the Invention) By the way, as mentioned above, when rear wheel steering is electrically controlled, this control system may fail, for example, the actuator itself for rear wheel steering or the drive of this actuator may fail. It is conceivable that the rear wheels will not be able to be controlled properly due to a failure of the transistor for the rear wheel. How to ensure safety in the event of such a failure will be one of the challenges in implementing four-wheel steering.

Therefore, an object of the present invention is to provide a backup function to the control of rear wheel steering, assuming that the rear wheel steering is assisted by a hydraulic power steering mechanism. To provide a four-wheel steering device for a vehicle, which allows the vehicle to continue running as safely as possible even when the vehicle is in an emergency.

(Means and effects for solving the problem) In order to achieve the above-mentioned object, the present invention basically forces the rear wheels to a "neutral position", that is, the rear wheels are forced to a "neutral position", i.e., the rear wheels are turned at a position where the steering angle of the rear wheels is different from the steering angle of the front wheels. A neutral position return means for reducing the steering ratio to "zero" is provided, and the neutral position return means is activated when rear wheel control is no longer performed normally.

Then, in response to the operation of the neutral position return means, a means for releasing the hydraulic pressure of the power steering mechanism is provided so that the rear wheels can return to the neutral position without being hindered by the power steering mechanism. This is to ensure that the rear wheels are not returned to the neutral position regardless of the operating state of the mechanism (m).

In addition to this, the operation of the means for returning to the neutral position is performed only when the steering ratio is in a small steering ratio region, that is, in response to the displacement of the rear wheel steering mechanism accompanying this return, the power steering In order to prevent the booster valve 1417 from being damaged, the return to the neutral position is performed only in a small steering ratio region where the actual steering ratio is below a predetermined value.

Specifically, as shown in Figure 1, in a four-wheel steering system for a vehicle that steers both the front wheels and the rear wheels, a hydraulic system is attached to the rear wheel steering mechanism and assists in steering the rear wheels. a power steering mechanism of the type; a hydraulic release means for releasing hydraulic pressure in the power steering mechanism to enable rear wheels to be steered regardless of the operating state of the power steering mechanism; and a hydraulic release means linked to the rear wheel steering mechanism. , a neutral position return means for returning the rear wheels to a neutral position when the hydraulic pressure release means is activated; and a steering ratio detection means for detecting that the steering ratio is in a small steering ratio region below a predetermined value. and a failure detection means for detecting a failure of a control system that controls rear wheel steering; and a failure detection means that receives outputs from both of the detection means and detects when the control system is malfunctioning and is in a small steering ratio region. and a backup control means for operating the hydraulic pressure release means and bringing the rear wheels to a neutral position.

(Embodiments) Examples 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 IR1IL are linked by the front wheel steering mechanism A, and the left and right rear wheels 2R
12L 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 4R54L, 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 a pinion 7 mated with the rack 6 is connected to the 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 turn to the left, the left and right front wheels IR2IL are steered to the left in accordance with the amount of displacement of this operation.

Similarly to the front wheel steering mechanism A, the rear wheel steering mechanism B also has a pair of left and right knuckle arms l0R110L and tie rods IIR, IIL, and a tie rod 1:12 that connects the tie rods IIR1IIL. In this case, the rear wheel steering mechanism B is configured to include a hydraulic power steering mechanism. This power steering mechanism will be explained with reference to Fig. 11.
A cylinder device 13 is attached to the relay rod 12,
The cylinder 13a is fixed to the vehicle body, and the piston 13 defines the inside of the cylinder 13a into two chambers 13b and 13c.
d 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 one pipe serves as an oil supply pipe. An oil pump 20 driven by an engine (not shown) is connected to '18. The control I/roll valve 16 has a spool 16a, and the control rod 21 is a sliding type, which is a so-called booster valve type.
The input part 21a integrated with the rear wheel steering ratio a is also used as a moving member of the steering ratio changing device E, which will be described later, and the output part 21b of the control rod 21 is integrated with the relay rod 12 of the rear wheel steering a mechanism B. ing.

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 arm l0R1IOL rotates clockwise in FIG. 2 about its rotation centers lOR', 10L', 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.
It is connected to a rotary control valve 68 provided on the shirt I/8 of the steering mechanism C through the. This control valve 68 has a pipe 7 extending from a branch valve 69 connected to the discharge side of the oil pump 20.
0, and a pipe 71 branched from the pipe 19 are connected.

Such a power steering structure F doubles the operating force of the steering wheel 9 (chamber 65b or 6 of the cylinder device 65).
5c by supplying oil) and transmits it to the relay rod 5.The function of such a power steering a disaster F itself is basically the same as that of the power steering mechanism described above, so no further explanation is required. Detailed explanation will be omitted.

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

An input rod 22 extends forward from the steering ratio changing device E, and a pinion 23, which is provided several times at its front end, is engaged with a rack 24 formed on the relay rod 5 of the front wheel steering mechanism A. 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 FIG. 3, and the embodiment has substantially the same configuration as that shown in the above-mentioned Japanese Patent Application Laid-open No. 199771/1983. That is, 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 is shown as 11. Further, this steering ratio changing device E has a swinging arm 31, and the base end of the swinging arm 31 is connected to a pin 33 relative to the holder 32.
It is pivotally mounted to allow free movement. This holder 32 is
The rotation axis 32a is the moving axis edge stand 1 of the input section 21a.
It is held in the vehicle body so as to be rotatable about an orthogonal line 02 that is perpendicular to . The pin 33 is
It is located at the intersection of and sentence 2, and extends in a direction perpendicular to orthogonal edge stand 2. Therefore, the swing arm 31
is said to be able to swing freely around the pin 33, but by rotating the holder 32, the angle of inclination between this pin 33 and the movable shaft edge stand 1, that is, the swing trajectory around the pin 33 can be changed. The angle of inclination with respect to a plane (reference plane) perpendicular to the movement axis it of the plane is set to −+7.

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 3 via the ball joint I.35.
1, and is also connected to the input section 21a via a ball 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 jaw 35 is displaced in the left-right direction in FIG.
In accordance with this displacement, the input section 21a is 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 on the moving shaft edge stand 1, and the connecting rod 34 is connected to the eccentric portion of the rotating plate 37. It is slidably penetrated through the joint 38.

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

Due to such a rotating plate 37, the swinging arm 31 is caused to swing around the pin 33 by an amount corresponding to the steering angle of the steering wheel, but the axis of the pin 33 and the movable shaft edge stand 1 are If the pole joint 35 is tilted, the pole joint 35 is displaced in the left-right direction in FIG.
Through 1? The signal is transmitted to 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 looks like this. And this holder 3
The rotation angle, that is, the inclination angle of No. 2 is detected by a steering ratio lateral sensor 45, which includes a potentiometer or the like, provided to the rotation shaft 32a.

Here, the swing angle of the two linked swing arms 31 about the pin 33 and the tilt angle of the swing arm 31 (the tilt angle of the pin 33) are the same as the pole joint 35 (input section 21 a).
The influence on the displacement in one direction of the moving axis 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 flt is δ, and the inclination angle that the swing orbital surface of the swing arm 31 makes with the reference plane δ is α. , when the eccentric distance between the pin 33 of the pole joint 35 and the pin 33 is r, the displacement X of the pole joint 3 in the direction of the movement axis 11 becomes . Therefore, if we add both inclination angle α to a certain value, X becomes a function of θ, that is, it depends on the steering wheel steering angle, and if we change the value of this inclination angle α, even if the steering wheel steering 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 described above, there is a case as shown in FIG. 4 as an example of changing the steering ratio by adjusting the inclination angle. In this Figure 4, the steering ratio is changed according to the vehicle speed, and when the front wheel steering angle in Figure 4 is set to a certain value, the change in the rear wheel steering angle with respect to the front wheel steering angle is shown. FIG. 5 shows how the steering ratio changes depending on the vehicle speed.

Here, a pair of return springs 13e and 13f are attached to the rear wheel power steering mechanism in order to force the rear wheels 2R12L to a neutral position, that is, a straight-ahead driving state. Both springs 13e and 13f bias the rear wheel relay rod 12 from left and right opposite directions with equal force. The oil chambers 13b and 13c of the power steering mechanism are connected through a communication passage 46, and an electromagnetic on-off valve 47 is connected to the communication passage 46. As a result, when the on-off valve 47 is closed, the rear wheel 2R12L is steered against the spring 13e or 13f by the supply of hydraulic pressure to the oil chamber 13b or 13c, and the on-off valve 47 is opened and both oil chambers 13b and 13c are steered. When the pressure is the same as that of the spring 13e,
, 13f, the rear wheel 2R12C is forced to the neutral position. Of course, the biasing forces of the springs 13e and 13f are set to a magnitude that allows the vehicle to take a neutral position against the external force received from the rear wheels 2R or 2L during turning.

Furthermore, both swing stroke ends of the sector gear 40 driven by the stepping motor 44 are regulated by a pair of stoppers 48 and 49 (see FIG. 3). The necessary rotation range of the stepping motor 44 over the entire swing range of the sector gear 40 (from the stroke end on the same phase side to the stroke end on the opposite phase side) is r580J in terms of the number of steps.

Reference numeral 51 in FIG. 2 denotes a control unit composed of, for example, a microcomputer, and this control unit 51 includes:
In addition to the output from the steering ratio sensor 45, the vehicle speed sensor 53
The output from is now input. Further, from this control unit 51, the stepping motor 44
In addition to being output to the on-off valve 47, it is also output to an alarm device 54, which includes a lamp, a buzzer, etc., to warn that the rear wheel steering angle cannot be controlled.

Next, the content of control by the control unit 51 will be explained based on the flowcharts shown in FIGS. 6 to 10. In this embodiment, the stepping motor 44 is
In consideration of the possibility that "step-out" (deviation between the number of steppings and the corresponding actual positional relationship) may occur, the reference position adjustment, that is, "motor position initialization" is performed at any time. This "motor position initialization" involves bringing the sector gear 40 into contact with one of the stoppers 48 or 49 (in the embodiment, the stopper 49 is on the opposite phase side when each member operates in the direction of the arrow in FIG. 3). This time is set as the origin position of the stepping number "0", and the stepping number driven from this origin position is set as the motor position "MP" at that time.
``Motor position initialization'' is performed at the start of control (immediately after starting the engine) and every time the vehicle speed becomes zero. Also,
In the flowchart shown in this embodiment, "flag 1", "
Four types of flags are used: ``Flag 2,'' ``Flag E,'' and ``Flag 2WSJ.'' The meaning of each flag is as follows.

(1) Flag 1 This flag is used to distinguish whether or not "motor position initialization" is in progress. When it is "0", it means that initialization has ended, and that rlJ is being initialized.

■Flag 2 When "motor position difference initialization" is executed once, it is set to rlJ, and only once every time the vehicle speed changes from non-zero m to zero.
This is used to initialize the motor position.

■Flag E This flag is used to distinguish between normality and abnormality of the rear wheel steering angle control system, where rlJ indicates abnormality and "0" indicates normality.

■Flag 2WS This flag is used to distinguish whether or not the rear wheels 2R12L are in the small steering ratio region.When rlJ is in the small steering ratio region,
” is not in the small steering ratio region. In the embodiment, whether or not this is in the small steering ratio region is determined by any one or more of the following: the power of the steering ratio sensor 45, the number of steps of the stepping motor 44, and the vehicle speed. You can find out by combining them.

Based on the above, either the interrupt processing for the main routine as shown in FIG. This will be explained starting from Figure).

Interrupt processing 1 (Fig. 8) The interrupt routine shown in Fig. 8 is for driving the stepping motor 44, and is performed every predetermined time set by a timer (for example, the stepping motor 44 is activated at 10 times per second).
If you want to drive at a rate of 0 steps, use 10ms e c
6), an interrupt is made to the main routine of FIG. In the figure, rCPJ is the target rear wheel steering angle, that is, the target stepping number, necessary to achieve the steering ratio characteristic determined by a map with vehicle speed as a parameter, as shown in FIG. 4 (FIG. 5), for example. As described above, rMPJ indicates the swinging position of the sector gear 40 (the steering position of the rear wheels 2R12L) from the origin position when the opposite phase side stopper 49 is set as the origin position, expressed as a stepping number.

Based on the above, first, in step S41, it is determined whether or not the target stepping number CP and the current position MP match, and when 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 at the predetermined time described above in preparation for the next interrupt.

When it is determined in step S41 that CP=MP is not true, 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 P>MP. 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 as compared to the target stepping number CP, in step 346, the stepping motor 44 is driven by one step toward the opposite phase side. Then, in accordance with this "one stepping" operation, the current position MP is updated by one stepping in step S47, and then the process moves to step S43. Conversely, when it is determined in step S45 that CP>MP, in step S48 the stepping motor 44 is driven by one step toward the same phase side, and then the step S
The current position MP is updated in step S49, and the process moves to step S43.

Interrupt (Figure 9) This interrupt process is performed when the vehicle speed sensor 53 generates a pulse as the speedometer meter cable rotates. 6), the main routine of FIG. 6 is interrupted. Then, the vehicle speed sensor 53 key, for example 20
While it is considered a pulse sensor (a sensor that generates 20 pulses when the meter cable rotates once),
This meter cable can be rotated by 63 km.
It is assumed that the vehicle rotates 7 times, and therefore the number of pulses generated when traveling 1km is r12740 pulses. Such pulses generated from the vehicle speed sensor 53 are sequentially counted and integrated in step S51, and the pulses are accumulated as P CN
It is stored as T.

Interruption 3 (Fig. 10) This interrupt processing is performed by the vehicle speed sensor 53 and Due to the relationship with the meter cable, 282,575m5e
An interrupt is made to the main routine shown in FIG.

That is, after the P GNT is directly set as the vehicle speed value (km/h) in step S52, the integrated count value P CNT of step 351 in FIG. 9 is cleared in step 353.

Note that FIGS. 9 and 10 are merely examples of vehicle speed detection, and vehicle speed can be detected by any conventionally known appropriate means.

Main routine (Fig. 6) First, in step S1, the entire system is initialized, and in step S2, MP=O, CP=-
580, set flag 1 = rlJ. That is,
As is clear from the explanation of FIG.
This is to return the motor until it comes into contact with the reverse phase side stopper 49, that is, to perform "motor position initialization", and r
The reason for setting the value to 580J is that no matter what position the sector gear 40 is currently in, if it is returned by 580 steps, it will always come into contact with the opposite phase side stopper 49 and return to the original position.

Thereafter, in step S3, a system check is performed, which will be described later, and then in step S4, it is determined whether the flag E is 0, that is, whether there is an abnormality in the rear wheel steering angle control system.

In step S4, if it is determined that the flag E is "0", that is, the control system is normal, step S4 is determined.
5, it is determined whether the flag l is rlJ. In this step S5, initially, step S
Since the flag l is set to rlJ in step S2, the process moves to step S6. In this step S6, CP=MP
It is determined whether CP=MP or not, a loop returns from step S3 to step S6 again, and during this loop, the stepping motor 44 shown in FIG. 8 is driven. (MP is -58
), and eventually CP=MP becomes louder. Then, when CP=MP, "motor position initialization" is completed, MP=0, CP=O, flag l=
0, flag 2=1.

When it is determined in step S5 that the flag l is not "1", it is determined in step S8 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 S9, CP is set to a value corresponding to the vehicle speed based on the map shown in FIG. 4 (FIG. 5). . After this, in step S10, flag 1 and flag 2 are both set to rQJ, and the process returns to step S3.

Further, when it is determined in step S8 that the current vehicle speed is zero, flag 2 or "
0", and if flag 2 is not "O", that is, when it is "1", the stepping motor 44 has not been driven after "motor position initialization", so this "motor position initialization"'' is not necessary, and the process returns to step S3. Also, step S11
When it is determined that flag 2 is rQJ, the process moves to step S12 to perform "motor position initialization" (same as setting in step S2).

On the other hand, when it is determined in step S4 that the flag E is not "0", that is, it is "1", this means that there is an abnormality in the control system for steering the rear wheels, so the process moves to step S13. , it is determined whether or not the vehicle is currently in a small steering ratio region. When the steering ratio is in the small steering ratio region, the on-off valve 47 is opened in step S14 to communicate the power steering arm chambers 13b and 13c, thereby forcing the rear wheels 2R12L to the neutral position. By returning the steering ratio to zero. Then, in step S15, the alarm 54 is activated to notify the driver that an abnormality has occurred in the control system. Further, in step S16, after decreasing the current supplied to the stepping motor 44,
In step S17, all the interrupt processes shown in FIGS. 8 to 10 described above are stopped, and the control for steering the rear wheels is stopped.

Note that when it is determined in step 313 that the flag 2WS is not "1", that is, when the steering ratio is not in the small steering ratio region, the processing from step S15 onward is performed without passing through step S14. In this way, when the steering ratio is large, the rear wheels 2R12L are held as they are, but in this case, it is unavoidable to protect the booster valve 16 of the power steering mechanism. To explain this point in detail, if the steering ratio is large, the spool 16a of the booster valve 16 will be displaced to the right or left in Figure 11 to a much greater extent than when the rear wheels 2R12L are in the neutral position. will be kept as is. In this state, if the rear wheel 2R12L is forced to the neutral position, the relay rod 12, that is, the output part 21b as a cylinder that houses the spool 16a, will also be largely displaced toward the neutral position, and as a result, the spool 16a and the output The portion 21b will come into strong contact with the spool 16a from the axial direction, resulting in damage to the spool 16a. On the other hand, when the neutral position is set in the small steering ratio region, the spool 16a and the output portion 21b are prevented from coming into contact with each other from the axial direction, and no damage occurs thereto.

System Check (FIG. 7) In this embodiment, it is checked whether the stepping motor 44 is being driven normally. For this reason,
By checking the level ("high" or "low") of each contact terminal when the excitation phase (each connection terminal) of the stepping motor 44 is "all energized" and "all demagnetized", it is possible to determine whether it is normal or normal. It is designed to judge.

First, in step S21, the current flowing to the steering and repping motor 44 is increased, and the flag 2WS and the flag E are set.
Both are set to "0". Thereafter, through the processes of steps S22 to S25, all the excitation phases are turned ON (excited), and after a certain period of time has elapsed, the excitation state is monitored. If all the levels are "low" in step S25, it is determined to be normal.

When it is determined in step S25 that all of the excitation phases are at the "low" level, in steps 326 to 528, all excitation phases of the stepping motor 44 are turned off, and after waiting for one hour to elapse, the excitation state is changed. Monitor. If the results of the monitoring in step S29 are all at "high" level, it is determined to be normal. After this, it is assumed that there is no abnormality in the drive control system of the stepping motor 44, and in step S31, the excitation state of the stepping motor 44 and its supply current are reset for the drive control shown in FIG.

Here, when it is determined in step S25 that all of the transistors are not at the "low" level, it is an abnormality such as an open failure in the transistor for driving the stepping motor 44, and in this case, the process moves to step S32 and the flag is set. E is set to "1". Also, step S29
If it is determined that all of them are not at "high" level, for example, the above transistor is short-circuited, a coupler in the power supply path to the stepping motor 44 is disconnected, or the wiring is disconnected or This is considered to be an abnormal situation, such as when a short circuit has occurred, and in this case also, the process moves to step 332 and the flag E is set to "1".

After step S32, it is determined whether or not the rear wheels 2R12L are currently in the small steering ratio region (the method for this determination is as described above), and if the rear wheels 2R12L are in the small steering ratio region, step S3
4, the flag 2WS is set to "1".

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.

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

■There are various possible failures in the control system for rear wheel steering, such as failure of the input part necessary to control the steering ratio, for example, the vehicle speed sensor 53. As shown in the example, the steering ratio may be set to O only when the steering ratio is in the small steering ratio region.

5 l ■In order to forcibly return the rear wheels to the neutral position, an electromagnetic actuator such as a motor or a hydraulic actuator operated by a solenoid valve may be separately installed. In this case, the on-off valve 47 The actuator may be actuated in synchronization with the opening operation.

■The hydraulic pressure of the power steering mechanism may be released by releasing the restraint of the rear wheel steering mechanism by the power steering mechanism, for example, by releasing both chambers 13b and 13c to the reservoir tank 17. , an appropriate method may be adopted.

(Effects of the Invention) As is clear from the above description, even if the control system for rear wheel steering fails, the present invention forcibly returns the rear wheels to the neutral position to ensure safe driving. It becomes possible to continue.

In particular, the return to the neutral position described above is performed only when the rear wheels are steered to a small steering ratio region, so that the booster valve of the power steering mechanism attached to the rear wheel steering returns to the neutral position. It is possible to effectively prevent damage caused by the return of the

[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 wooden invention. FIG. 3 is a Scurtleton diagram showing the rear wheel steering mechanism. FIG. 4 and FIG. 5 are graphs showing an example of steering ratio characteristics. 6 to 10 are flowcharts showing control examples according to the tree invention. FIG. 11 is a sectional view of the power steering mechanism. A: Front wheel steering mechanism B: Rear wheel steering mechanism C steering mechanism D: Power steering a structure E: Steering ratio changing device IR, IL: Front wheel 2R12L: Rear wheel 9: Handle 13 Niji cylinder device 13b, 13c: Oil chamber 13e, 13f: return spring 44 tipping motor 45: steering ratio sensor 46: communication path 47: on-off valve 51: control unit Fig. 1

Claims (1)

[Claims] (1) A four-wheel steering system for a vehicle that steers the rear wheels as well as the front wheels, which includes a hydraulic power steering mechanism that is attached to the rear wheel steering mechanism and assists in steering the rear wheels, and the power steering system. a hydraulic release means that releases hydraulic pressure in the mechanism to enable the rear wheels to be steered regardless of the operating state of the power steering mechanism; and a hydraulic release means that is linked to the rear wheel steering mechanism and when the hydraulic pressure release means is activated; A neutral position return means for returning the rear wheels to the neutral position, a steering ratio detection means for detecting that the steering ratio is in a small steering ratio region below a predetermined value, and a control system for controlling rear wheel steering. failure detection means for detecting a failure of the control system; and a failure detection means for receiving outputs from both of the detection means and operating the hydraulic pressure release means only when the control system is malfunctioning and in a small steering ratio region. A four-wheel steering system for a vehicle, comprising: a backup control means for placing rear wheels in a neutral position; and a four-wheel steering system for a vehicle.