JPH0231980A - Device for steering rear wheel of vehicle - Google Patents

Abstract

PURPOSE:To prevent the generation of excessive yaw rate by making rear wheels non-following condition in the initial stage of turning and making front and rear wheels the same phases at least when the absolute value of the yaw rate becomes above a defined value, at the time of carrying out a delay control or a phase inversion control. CONSTITUTION:A rear wheel steering device has a rear wheel steering means 22, a control means 24 which drivingly controls the rear wheel steering means 22 so as to steer rear wheels 6L, 6R, and a yaw rate detecting means 98 for detecting the yaw rate phi' of a vehicle. After starting the steering of front wheels in the initial stage of turning, first, the control means 24 carries out a delay control for making rear wheels a non-following condition not in the same phase as front wheels and, at least when the absolute value of the yaw rate phi' detected by the yaw rate detecting means 98 becomes above a defined value, the delay control is stopped to steer the rear wheels to be the same phase as the front wheels.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a rear wheel steering device for a four-wheel steering vehicle that steers the rear wheels in at least the same phase (same direction) as the front wheels in response to the steering of the front wheels.

(Prior art) Some of the above-mentioned rear wheel steering devices include those that steer the rear wheels only in the same phase as the front wheels, and those that steer the rear wheels only in the same phase as the front wheels, and those that steer the rear wheels in the opposite phase and the same phase as the front wheels. There is something to steer in phase.

Such in-phase steering is normally proportional control in which the rear wheels are steered in the same phase at the same time as the front wheels start steering.In such in-phase proportional control, it is possible to improve the running stability of the vehicle, but on the other hand, the yaw There is a problem in that (rotation around the vertical axis of the vehicle) is less likely to occur and the ability to turn the head is reduced.

Therefore, in order to deal with this problem of decreased turning ability,
Delay control that provides a non-following state in which the rear wheels are not made to follow the front wheels at the beginning of a turn, that is, the rear wheels are not steered in the same phase direction as the front wheels, and after the non-following state ends, the rear wheels are made to follow the front wheels and are steered in the same phase. Phase inversion control is being considered.

The above delay control is, for example, disclosed in Japanese Patent Application Laid-Open No. 58-184477.
As stated in the publication, the rear wheels are not steered (rear wheel steering angle is zero) for a predetermined period of time after the front wheels start steering, and after that predetermined period of time the rear wheels are made to follow the front wheels. The purpose is to generate the necessary yaw rate by creating a non-following state in which only the front wheels are steered at the beginning of a turn.

The above-mentioned phase reversal control puts the rear wheels in a non-following state in which the rear wheels are steered in an opposite phase to the front wheels for a predetermined period of time from the start of steering of the front wheels;
After a predetermined period of time has elapsed, the rear wheels follow the front wheels and are steered in the same phase.By creating a non-following state in which the rear wheels are steered in the opposite phase to the front wheels at the beginning of a turn, the required yaw rate can be adjusted. It is intended to generate

(Problem to be Solved by the Invention) Incidentally, the magnitude of the yaw rate generated by the delay control or phase inversion control as described above is the state quantity of the non-following state in those controls, that is, the predetermined time (delay time) in the delay control. τ, a predetermined time (inversion time) τ in phase inversion control, or inverse phase steering jl (inversion f
f1) Varies depending on α, etc. Therefore, when performing the above control, the yaw rate (
In order to obtain the target yaw rate), set the above non-tracking state in advance! ! It is conceivable to set the quantity appropriately and perform the above control according to the set state quantity.

However, even if the delay control and the like are performed in accordance with the state quantities set so as to obtain the target yaw rate as described above, the yaw rate as desired is not necessarily obtained. This is because the magnitude of the yaw rate generated by the above control changes depending on various parameters such as front wheel steering angular speed, vehicle speed, vehicle acceleration, road resistance, etc., and also the slope of the road surface, the strength of the crosswind, the number of passengers (weight), etc.
This is because it also changes depending on factors such as.

Therefore, depending on these parameters, the target yaw rate may occur before the above-mentioned predetermined time τ has elapsed, and in such a case, the target yaw rate has already been obtained and the rear wheels should not be moved any further. There is no need to set the vehicle in the following state, and if the rear wheels are kept in the non-following state any longer, an excessively excessive yaw rate will occur, which may lead to a spin or the like.

This problem occurs not only when the state quantity of the non-following state is fixed in advance, but also when the state quantity is controlled based on various parameters that affect the magnitude of the generated yaw rate. This can also occur if the This is because there are a large number of such parameters, and it is extremely difficult to accurately detect and understand all of them.

In view of the above circumstances, an object of the present invention is to perform control to generate a yaw rate with the rear wheels in a non-following state at the beginning of a turn, and when a yaw rate exceeding a predetermined value occurs, the rear wheels are thereafter steered to the same phase as the front wheels. An object of the present invention is to provide a rear wheel steering device for a vehicle that prevents a yaw rate exceeding a predetermined value from occurring.

(Means for Solving the Problems) In order to achieve the above object, the vehicle rear wheel steering device according to the present invention provides a four-wheel steering vehicle that steers the rear wheels at least in the same phase as the front wheels in response to the steering of the front wheels. The rear wheel steering device comprises: a yaw rate detection means for detecting a yaw rate of the vehicle; and control means for causing the rear wheels to follow the front wheels and steering them to the same phase when the absolute value of the yaw rate detected by the yaw rate detection means exceeds a predetermined value. It is characterized by

In short, the rear wheel steering device according to the present invention basically performs delay control or phase reversal control that puts the rear wheels in a non-following state at the beginning of a turn in the same phase steering region, and at least performs delay control when the yaw rate exceeds a predetermined value. The system also cancels phase reversal control and steers the rear wheels to the same phase as the front wheels.

The rear wheel steering device according to the present invention may be any device as long as it steers the rear wheels at least in the same phase as the front wheels, but the device can also be a device that steers the rear wheels only in the same phase as the front wheels, and a device that steers the rear wheels in the same phase and opposite phase as the front wheels. It is also applicable to

Further, the rear wheel steering device according to the present invention may be such that at least when the yaw rate reaches a predetermined value, delay control or phase reversal control is stopped and the rear wheels are steered to the same phase as the front wheels. A predetermined time period τ for the non-following state is determined in advance, and when the yaw rate reaches a predetermined value or more before the elapse of the predetermined time period τ, the delay control, etc. is stopped, the rear wheels are steered in the same phase, and the yaw rate is set to the predetermined value. Even if the yaw rate does not reach the predetermined value, the rear wheels may be steered in the same phase after the predetermined time τ has elapsed, or such predetermined time τ may not be provided and delay control etc. may be performed until the yaw rate exceeds the predetermined value. The same phase steering of the rear wheels may be performed continuously, and only when the value exceeds a predetermined value.

Note that the predetermined value of the yaw rate when stopping the delay control etc. may be a fixed value, but may be a variable value that can be changed depending on parameters such as vehicle speed.

In addition, the above predetermined value is the yaw rate (
It may be a target yaw rate), or it may be an upper limit yaw rate which is undesirable because if the yaw rate becomes larger during a turn, spin or the like will occur.

(Function) The rear wheel steering system configured as described above detects the actually occurring yaw rate, and when the yaw rate exceeds a predetermined value, it prohibits delay control, etc., and moves the rear wheels in the same phase. Therefore, under any circumstances, it is possible to prevent an excessive yaw rate exceeding a predetermined value from occurring due to the delay control, etc. under any circumstances, and it is possible to eliminate the fear of spin due to the occurrence of such an excessive yaw rate.

Furthermore, if the predetermined value is the target yaw rate, it is possible to not only prevent excessive yaw rates that may cause spins, but also to prevent unnecessary yaw rates that exceed the target yaw rate when a yaw rate that exceeds the target yaw rate occurs. This makes it possible to prevent this occurrence and achieve optimal turning performance using the target yaw rate.

Furthermore, in the case where the above-mentioned predetermined time τ, etc. is not provided, and the delay control etc. is continued until the yaw rate reaches a predetermined value or more, and when the yaw rate reaches the predetermined value or more, the rear wheels are steered to the same phase, the predetermined value is set as the target. If the yaw rate is set, the troublesome setting of a predetermined time τ, etc. is not necessary, and the target yaw rate can always be achieved. Therefore, it is possible to extremely easily and always perform optimal delay control, etc.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an outline of an embodiment of a rear wheel steering device for a vehicle according to the present invention. As shown in the figure, this embodiment includes a rear wheel steering means 22 for steering the rear wheels 6L and 6R, a control means 24 for driving and controlling the rear wheel steering means 22 to steer the rear wheels 6L and 6R, and a yaw rate control means for controlling the rear wheels 6L and 6R. When steering the rear wheels in the same phase as the front wheels in response to front wheel steering, the control means 24 first controls the rear wheels in the same phase as the front wheels at the beginning of a turn, that is, after starting front wheel steering. When the absolute value 1φl of the yaw rate φ detected by the yaw rate detection means 98 exceeds a predetermined value φ1, the delay control or phase inversion control is performed to put the vehicle in a non-tracking state in which no steering is performed. The system is configured so that the rear wheels are steered in the same phase as the front wheels.

FIG. 2 is a schematic diagram showing an example of a four-wheel steering system equipped with the embodiment shown in FIG. 1.

The four-wheel steering system shown in Fig. 2 has left and right front wheels 2L and 2R.
The vehicle includes a front wheel steering device 4 for steering the left and right rear wheels 6L and a rear wheel steering device 8 for steering the left and right rear wheels 6L and 6R.

The front wheel steering device 4 includes a front wheel steering shaft 14 that extends in the vehicle width direction and has both ends connected to a pair of left and right front wheels 2L and 2R via a pair of left and right tie rods IOL and IOR and knuckle arms 12L and 12R. and a steering shaft 20 having a pinion 16 at one end that meshes with rack teeth (not shown) formed on the steering shaft 14 and a steering wheel 18 at the other end. By operating the steering wheel 18, the front wheel steering shaft 14 is displaced in the vehicle width direction to steer the front wheels 2L and 2R.

The rear wheel steering device 8 includes a rear wheel steering means 22 for steering the rear wheels 6L and 6R, and a control means 2 for controlling the rear wheel steering means 22.
4, and various information for controlling the rear wheel steering means such as the vehicle speed detection means 26 and the front wheel steering angle detection means 28 are transmitted to the control means 24.
and a yaw rate detection means 98 that detects the yaw rate φ of the vehicle body.

The rear wheel steering means 22 includes a rear wheel steering shaft 30 and a servo motor 32 which is an actuator.

The rear wheel steering shaft 30 extends in the vehicle width direction, and has both ends connected to a pair of left and right rear wheels 6L, 6 via a pair of left and right tie rods 34L, 34R and knuckle arms 36L, 36R.
R, and the rear wheels 6L and 6R are steered by stroke displacement of the rear wheel steering shaft 30 in the vehicle width direction. Further, this rear wheel steering shaft 30 is provided with a centering spring means 38 which is a neutral position return means for urging the shaft 30 to return to the neutral position.

Stroke displacement of the rear wheel steering shaft 30 in the axial direction is performed by the servo motor 32. That is, the servo motor 32 is composed of a step motor, and transmits rotation to the pawl screw means 46 via a driving force transmission system consisting of a brake means 40, a clutch means 42, and a reduction gear 44. The rear wheel steering shaft 80 is driven from the neutral position against the biasing force of the centering spring means 38, that is, it is configured to perform a stroke displacement.

The brake means 40 locks the driving force transmission system between the servo motor 32 and the rear wheel steering shaft 30 to maintain the rear wheel steering shaft 30 in a predetermined displacement state. That is,
During steady steering (when the target rear wheel steering angle does not change), it is necessary to maintain the rear wheel steering shaft 30 at a predetermined displacement state.
This is done by the brake means 40 rather than the servo lock by the servo motor 321, thereby saving power consumption. The brake means 40 in this embodiment is constituted by an electromagnetic brake that locks the output shaft of a servo motor.

The clutch means 42 disconnects the driving force transmission system between the servo motor 32 and the rear wheel steering shaft 30 when a predetermined abnormality occurs, thereby freeing the rear wheel steering shaft 30, thereby moving the steering shaft 30 toward the centering spring. The means 38 returns it to the neutral position to bring it into the 2WS state, thereby providing a so-called fail-safe.

The clutch means 42 in this embodiment is a normal oven (disconnection when no current is applied) type electromagnetic clutch 4 arranged in series.
2A and a normally closed (connected when not energized) type electromagnetic clutch 42B.

The reason why the clutch means 42 is constituted by two clutches, the normal oven type electromagnetic clutch 42A and the normally closed type electromagnetic clutch 42B arranged in series, is to improve disconnection reliability and save power consumption. This is to aim for.

In other words, by installing two clutches in series, even if one clutch cannot be disconnected due to seizure, etc., the drive power transmission system can be disconnected by the other clutch, which greatly improves disconnection reliability. It will be done. Also, when installing two in series, for example, if both are normal oven type,
During normal times (when no abnormality occurs), power must be applied to both, which doubles the power consumption. On the other hand, if both of them are of normally closed type, the problem of power consumption will be eliminated, but disconnection will become impossible if, for example, the clutch power supply fails. Therefore, by making one of them a normally closed type, it is possible to save power consumption, and by making the other one a normal oven type, it is possible to improve disconnection reliability in the event of a power supply failure.

The above-mentioned pole screw means 4G includes a pole nut 48,
A pole screw 5o carved in the steering shaft 30 and both 48.
The pole nut 48 is fixed to a gear 54 that meshes with the reduction gear 44 and rotates integrally with the gear 54, and cannot be displaced in the axial direction of the steering shaft 30. When the pole nut 48 is rotated by the servo motor 32, the steering shaft 30 is stroked in the axial direction accordingly.

The centering spring means 38 includes a pair of stoppers 58.58 provided on the steering shaft 30 at a predetermined interval, and is disposed within the two stoppers 58.58 while being loosely fitted on the steering shaft 30. A pair of spring receivers 60 and 62 whose movement in the expansion direction is regulated by 56 and 58, and both spring receivers 6
Centering spring 6 arranged in a compressed state between 0.62
4, and both spring receivers 60 and 62 are connected to both stoppers 56.
．． 58, the stopper 56.5
11, it is provided with a casing-side stopper portion 88.88 that comes into contact with both spring receivers 80.62 in order to restrict the movement of both spring receivers 80.82 in the expansion direction, and the compressive load of the centering spring 64 ( The steering shaft 30 is always biased toward the neutral position by a preset load (preset load).

The rear wheel steering by the servo motor 32 is controlled by the control means 24.
controlled by The basic control of the rear wheel steering by the control means 24 is so-called vehicle speed sensitive control, in which the vehicle speed and the front wheel steering angle are used as control parameters, and the rear wheels are steered in accordance with the front wheel steering, and the steering ratio (rear wheel steering angle) at that time is rudder angle/front wheel rudder angle)
is changed according to the vehicle speed. An example of changing the steering ratio according to the vehicle speed is as shown in FIG. 3. When the control characteristics shown in the figure are applied, the rear wheel steering angle relative to the front wheel steering angle changes in the same phase direction as the vehicle speed increases, for example, changes from opposite phase to the same phase at a vehicle speed of 401 m/h. As a result, this situation will be described in the fourth
As shown in the figure.

In order to perform such rear wheel steering control, the control means 24
Signals from the vehicle speed detection means 26, the front wheel steering angle detection means 28, and the rotary encoder 72 for detecting the rotational position of the servo motor 32 are input to the control means 24.
Then, a target rear wheel steering angle is calculated based on the front wheel steering angle and the vehicle speed, and a control signal corresponding to the required rear wheel steering angle is output to the servo motor 32.

The rotary encoder 72 constantly monitors whether or not the servo motor 32 is operating properly, that is, under feedback control, the rear wheels 6L and 6R are operated.
The vehicle is now being steered.

The control means 24 also controls the operation of the brake means 40 and the clutch means 42 in addition to the servo motor 32. As described above, the brake means 40 is controlled by locking the output shaft of the servo motor during steady steering so as to control the rear wheel steering shaft 3.
0 is maintained at a predetermined displacement state, and as described above, the clutch means 42 is controlled to be in a disconnected state when a predetermined abnormality occurs, and the rear wheel steering shaft 30 is returned to the neutral position by the centering spring means 38 for fail-safe purposes. It is done as much as possible.

The control means 24 includes ON/OF signals from a neutral clutch switch 76, an inhibitor switch 78, a brake switch 80, and an engine switch 82.
It is configured such that the F signal and a signal from the alternator terminal 84 indicating the presence or absence of power generation are input. 86 is a warning lamp that is turned on when an abnormality occurs.

As described above, the rear wheel steering device operates to rotate the rear wheels at a predetermined vehicle speed relative to the front wheels, for example, in the opposite phase when the vehicle speed is less than 40 hours.
When the vehicle speed is greater than &/h, the steering is performed in the same phase. Furthermore, in the same phase steering region where the vehicle speed is greater than or equal to a predetermined vehicle speed, the control means 24 controls the steering for a predetermined time from the initial stage of the turn, that is, from the start of front wheel steering. is configured to put the rear wheels in a non-following state in which the rear wheels are not steered in the same phase as the front wheels, and after a predetermined period of time has passed, perform delay control or phase reversal control in which the rear wheels follow the front wheels and are steered to the same phase.

Furthermore, in performing the delay control or phase reversal control, a yaw rate detection means 98 for detecting the yaw rate φ of the vehicle body is provided, and the absolute value of the yaw rate φ detected by the yaw rate detection means 98 is 1φ1 (the yaw rate φ is right (left)). The rotation is (+), and the left (right) rotation is (
- ) becomes equal to or greater than a preset value φ1, the delay control or phase reversal control is stopped at that point even before the above-mentioned predetermined time has elapsed, that is, the non-following state of the rear wheels is stopped. , so that the rear wheels follow the front wheels and are steered in the same phase.

In addition, in the embodiment shown in FIG. 2, change control that changes the state amount of a non-following state in delay control or phase inversion control based on a predetermined parameter, or delay control or phase inversion control in the case of a predetermined state Prohibition control that prohibits control is also performed.

In the above change control, the magnitude of the yaw rate generated or required during a turn is determined by various parameters, such as front wheel steering angle speed θF1 vehicle speed V, vehicle acceleration! , road surface resistance μ, etc., and therefore, the state quantity of the non-following state is appropriately changed based on these parameters in order to generate the optimum yaw rate in each situation. In order to perform this change control, the apparatus shown in FIG. 2 is provided with a predetermined parameter detection means 92, which detects the vehicle speed detection means 26, the road resistance detection means 90, and the front wheel steering angular velocity detection means. 94, and an acceleration detection means 96.

Figure 5 shows the steering angle relationship between the front wheels and rear wheels in the case of delay control, and Figure 6 shows the steering angle relationship between the front wheels and rear wheels in the case of phase reversal control. It shows the rear wheel steering angle in case of proportional control.

In the delay control, the predetermined time (delay time) τ is changed as the state quantity of the non-following state,
In the phase reversal control described above, the state quantity in the non-following state is the predetermined time (reversal time) τ or the reverse phase steering amount (
(inversion amount) α is changed.

For example, the delay time τ is controlled to be changed by each of the parameters described above based on the following equation.

r-r□X (1+CJ +cv+ CG + Cm
) However, 0≦τ≦τ1.1 In the above equation, r□ is the basic delay time that is set appropriately, Ci is the correction coefficient determined by the magnitude of front steering angular velocity + p, and CV is the value of vehicle speed V. CG is a correction coefficient determined by the magnitude of acceleration, C1 is a correction coefficient determined by the magnitude of road resistance μ, and τ and □ are upper limits set as appropriate.

In the above delay control, if τ is long, the generated yaw rate is large and the turning performance is high, and when τ is short, the generated yaw rate is small and the turning performance is low, but on the other hand, the running stability is high.

When the front wheel steering angular velocity υP is large, the driver's intention to turn is large, and therefore, high verbal ability is required, and when υF is small, running stability is more important than turning ability. Therefore, the coefficient Ci is set to increase as θF increases.

When the vehicle speed V is high, it is desirable to improve the high-speed straight running stability and not to increase the turning performance too much from a safety perspective.On the other hand, in the medium speed range, it is desirable to increase the turning performance to create a sharp feeling.

Therefore, the coefficient Cv is set to become smaller as V becomes larger. In addition, V in the above clothing is 4
Although Cv is not shown when V is less than 0/h, this is because in this embodiment, in-phase steering control is performed only when V is equal to or greater than 40/h.

The above acceleration! When is large, it is better to improve safety than to increase turning ability from a safety standpoint, and! When the coefficient 00 is small, especially when the vehicle is decelerating at (-), it is desirable to increase the turning performance.Therefore, the coefficient 00 is set to become smaller as the coefficient 00 becomes larger.

When the road surface μ is small, it is preferable not to increase the turning ability too much from a safety standpoint, and when μ is large, there is no such restriction, so it is desirable to increase the turning ability. Therefore, C1 is set to increase as μ increases, and to prohibit delay control when μ is 0.2 or less.

The above-mentioned prohibition control is implemented under the circumstances that it is not always desirable to generate a large yaw rate by performing delay control etc. when the front wheels are steered. In this case, delay control and phase inversion control are prohibited.

The predetermined state may include, for example, a second or subsequent steering state in which the front wheels are continuously switched and steered. When right (left) steering and left (right) steering of the front wheels are performed consecutively, that is, within a predetermined short period of time, if delay control, etc. is performed continuously for the second and subsequent steerings, the vehicle body will There is a tendency to diverge, and convergence deteriorates. Therefore, by prohibiting delay control, etc. in the second and subsequent steering operations, the convergence of the vehicle body can be improved, for example, when the steering wheel is turned too far and the steering wheel is immediately turned to the opposite side to correct the vehicle body posture. It can be made into a good one.

Further, as the above-mentioned predetermined state, for example, the absolute value 1θ of the front wheel steering angle θ (the right or left steering angle is (+) and the opposite side steering angle is (-)), 1 is a predetermined small steering angle. A small steering angle state smaller than θ1 (for example, steering wheel steering angle Go”) or the 1θP
1 is the predetermined large steering angle θ2 (for example, the steering wheel angle 200
@) A larger rudder angle state can be mentioned. As mentioned above, the same-phase steering region is a high-speed driving region, and when driving at high speed, the small front wheel steering angle has a greater meaning of correcting the course rather than turning, so in that case, the rear wheels are also immediately steered in the same phase. This is because driving stability must be ensured.
Furthermore, it is not desirable from a safety point of view to perform delay control or the like when driving at high speeds when the steering angle is large to improve turning performance. This is because it is desirable to enable stable lane changes through proportional control.

Furthermore, the predetermined state may include a case where the road surface resistance μ is smaller than a predetermined value. This is because it is undesirable from a safety standpoint to perform delay control or the like to generate large yaw when road resistance is low.

Furthermore, the predetermined state may include a case where the vehicle speed V is less than or equal to a predetermined value. However, the case where the vehicle speed is less than the predetermined value is, for example, 40! This is an anti-phase steering region below R/h, and the delay control etc. mentioned above is originally control in the same-phase steering region, so naturally delay control etc. are not performed in the anti-phase steering region. It should be noted that the anti-phase steering region is a region where sufficient turning performance is originally obtained, and if delay control is performed in this region, the eloquence will be reduced.

In the embodiment shown in FIG. 2, a predetermined state detection means 29 for detecting the above-described predetermined state is provided.
The prescribed condition 1! The detection means includes a front wheel steering angle sensor 28, which is also used for calculating the target rear wheel steering angle, a vehicle speed sensor 26, and a road resistance detection means 9o.

FIG. 7 is a flowchart showing an example of delay control in the above embodiment.

In this example, first, the vehicle speed V is manually inputted to the control means 24 at S1, then the front wheel steering angle θ is inputted to the control means 24 at S2, and the control means, particularly its control section 24b, inputs the front wheel steering angle θ from the above V and θP at S3. The target rear wheel steering angle θ is determined, and S4
Whether or not θ and T do not change in , that is, θ,
It is determined whether the differential value υ of T, T, is 0 or not. Assuming that the vehicle has just started to steer the front wheels to make a turn, θ and ↑ are also changing as the front wheel steering angle changes, so the process proceeds to the next step 85. In S5, it is determined whether or not the delay control prohibition flag FD has been reset. If it has been reset, the process proceeds to S6 where the vehicle speed V≧v1 (vl is the vehicle speed at which the reverse phase steering changes to the same phase steering in FIG. 3). For example, 40KIn/h), it is determined whether V≧
v1, that is, in the same phase steering region, the process advances to the next step 87, where θ1≦θP≦θ2 (θ1.θ2
is a predetermined steering angle that is appropriately set, and it is determined whether or not vl+θ2). And the above S5. S6. If NO in any of S7, delay control is not performed, and the process proceeds to S8, where proportional control is performed.

Above S5. S6. If YES in all of S7, the correction coefficients Ca, CV, c*IcII for determining the delay time τ are determined in S9, and the delay time τ is calculated in SIO based on the above formula (%). However, as a general rule, do not steer the rear wheels until one hour has passed, and after one hour has passed, proceed from S1 to S12, set the delay control prohibition flag FD in Si2, proceed to 88, and start there. Steering of the rear wheels begins.

Specifically, for example, the actuator drive signal in the case of the proportional control is delayed by one hour and output from the control section 24b. However, before one hour has elapsed, the vehicle's yaw rate φ is input in 513, and in S14 it is determined whether the absolute value 1φ1 of the yaw rate φ is smaller than a predetermined yaw rate φl, and φ1≧φ1. In this case, even if one hour has not yet elapsed, the process proceeds to S12 to set the delay control prohibition flag FD, and then proceeds to S8 to start steering the rear wheels.

After setting the delay control aM stop flag FD in S12 and starting rear wheel steering in 88, it is determined that θr is 7-0 in S4, and until it is determined that the predetermined time has elapsed in S15, the The delay control prohibition flag FD is kept set and continuously switched to prohibit delay control in the second and subsequent steering operations, and θ71
Delay control is performed only after the -0 state has passed for a predetermined period of time.
The prohibition flag FD is reset to permit the next delay control.

Note that the predetermined yaw rate φ in the above flowchart
1 is set to the above-mentioned upper limit yaw rate. Of course, the aforementioned target yaw rate may be used as this predetermined yaw rate φ1.

The yaw rate detecting means 98 is a tiG lateral G detecting means for detecting the lateral G of the vehicle body which is equivalent to the yaw rate, and when the absolute value of FAG detected by the lateral G detecting means exceeds a predetermined value tank 01, delay control is performed. etc., and the rear wheels may be steered in the same phase as the front wheels.

The predetermined value may be fixed or variable depending on a predetermined parameter. As an example of a variable predetermined value, a specific example of a predetermined value like 01 that varies depending on the vehicle speed V is the absolute value 1φ of the yaw rate.
In in-phase steering of the rear wheels after 1 (has become equal to or greater than a predetermined value φ1), for example, yaw rate feedback control is used, that is, when the absolute value Iφ1 of the yaw rate becomes greater than or equal to the predetermined value φ1, the yaw rate is lowered, that is, in the same phase as the front wheels. When the rear wheels are steered and the yaw rate absolute value 1φ1 decreases to a predetermined value φ1, the rear wheels may be steered at that point.

Alternatively, the predetermined time τ is not determined as in the above embodiment, and the rear wheels are kept in a non-following state until 1φ1 becomes 41 or more, and the rear wheels are steered in phase only when 1φ1 becomes 41 or more. good.

(Effects of the Invention) As explained above, the rear wheel steering device according to the present invention includes a yaw rate detection means, and when performing delay control or phase reversal control, the rear wheels are placed in a non-following state at the beginning of a turn and at least detected. If the absolute value of the yaw rate exceeds a predetermined value, the rear wheels are steered in the same phase as the front wheels, so under any circumstances, an excessive yaw rate exceeding the predetermined value will occur due to the delay control, etc. It is possible to prevent the occurrence of excessive yaw rate, and eliminate the fear of spin, etc. due to excessive yaw rate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an overview of an embodiment of the present invention, FIG. 2 is a schematic diagram showing an example of a four-wheel steering device equipped with the embodiment shown in FIG. 1, and FIGS. 3 and 4 are FIG. 1 is a diagram showing an example of the basic rear wheel steering control characteristics of the embodiment shown in FIG. 1. FIG. 5 is a diagram showing an example of the delay control performed by the embodiment shown in FIG. FIG. 7 is a flowchart showing an example of a procedure for delay control performed by the embodiment shown in FIG. 1. FIG. 2L, 2R...Front wheel 6L, 6R...Rear wheel 24
... Control means 92 ... Yaw rate detection means Fig.

Claims (1)

[Scope of Claims] A rear wheel steering device for a four-wheel steering vehicle that steers the rear wheels to at least the same phase as the front wheels in response to steering of the front wheels, comprising: yaw rate detection means for detecting a yaw rate of the vehicle; When the rear wheels are steered in the same phase as the front wheels in response to the steering of the front wheels, the rear wheels are set in a non-following state in which the rear wheels are not steered in the same phase as the front wheels in the initial stage of steering of the front wheels, and the yaw rate detected by the yaw rate detection means is set to a predetermined value. A rear wheel steering device for a vehicle, comprising: control means for steering the rear wheels to follow the front wheels and to be in the same phase when the value exceeds the value.