JP2009166524A - Steering control device of vehicle equipped with four-wheel steering mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid difficulty of acquiring and estimating a track of a vehicle and an increase in a possibility that the vehicle comes into contact with an ambient obstacle caused by a difference in tracks between when the vehicle retreats and advances in the vehicle steered by 4 wheels in advance and 2 wheels in retreat. <P>SOLUTION: This four-wheel steering control device of the vehicle includes a traveling direction detection part for detecting the advancing direction of the vehicle, and a storage part for storing that the vehicle retreats; when the retreat of the vehicle is detected, controls a rear-wheel steering device to set the steering angle of the rear wheels to zero and, when the retreat of the vehicle is stored by the storage means, controls the rear-wheel steering device to retain the steering angle of the rear wheels zero till predetermined conditions are satisfied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a steering control device for a vehicle such as an automobile equipped with a four-wheel steering mechanism (4WS) that steers not only front wheels but also rear wheels, and more specifically, operation of the rear wheel steering device, The present invention relates to a device that performs control according to the driving situation of a vehicle.

  In vehicles such as automobiles, 4WS or active 4WS (A4WS) configured to steer both front wheels and rear wheels by the driver's steering for the purpose of improving the maneuverability or maneuvering stability of the vehicle is provided. May be installed. In such 4WS or A4WS, generally, during high speed running, the rear wheels are steered in the same direction (the same phase direction) as the front wheels, and the rear wheels (steering only the front wheels 2). A large lateral force can be generated (compared to the wheel steering mechanism (2WS)), and the deviation between the turning direction of the vehicle and the longitudinal direction of the vehicle body can be made smaller when turning, or when the lane is changed, etc. (In other words, it is possible to distribute the lateral force required for turning or changing lanes to the rear wheels. Improving steering stability). On the other hand, when driving at low speed, with 4WS or A4WS, the rear wheels are steered in the opposite direction (reverse phase direction) to the front wheels, and the turning radius is reduced by generating a yaw moment from the rear of the vehicle body in the turning direction of the vehicle. As a result, there is an advantage that a small turn becomes effective at a narrow turn (an improvement in maneuverability).

  As for the 4WS or A4WS as described above, one of the problems is that the rear part of the vehicle body is out of turning compared to a 2WS vehicle, particularly when the rear wheel rudder angle is controlled in the opposite phase to the front wheel rudder angle. It has been pointed out that the possibility of contact with other vehicles and obstacles around the vehicle can be increased by swinging in the direction. Therefore, in a vehicle equipped with 4WS or A4WS, in order to avoid contact with other vehicles and obstacles in the vicinity of the vehicle, for example, until a predetermined time elapses after the vehicle starts moving, Steering control device (Patent Document 1) configured to steer only the front wheels by prohibiting the rudder (forcibly setting the rear wheel rudder angle to 0), is detected by providing an obstacle sensor around the vehicle body. A device that prohibits the steering of the rear wheels according to the distance to the obstacle (Patent Document 2) or a device that controls the size and direction of the rear wheel steering angle (Patent Documents 3 and 4) has been proposed.

As for 4WS or A4WS, in the control, depending on the driving / running state of the vehicle, the direction and size of the rear wheel rudder angle is automatically and appropriately linked to the front wheel rudder angle. Control is also a problem. In the 4WS or A4WS control, the phase and magnitude of the rear wheel steering angle with respect to the front wheel steering angle are generally controlled based on parameters such as the vehicle speed and the yaw rate. However, for example, it is necessary to consider that the relationship between the direction of the yaw rate and the direction of the driver's steering wheel angle is reversed between when the vehicle moves forward and when the vehicle moves backward. obtain. Therefore, for example, Patent Document 5 proposes an apparatus configured to prohibit steering of the rear wheels and to steer by two-wheel steering of only the front wheels when the vehicle is reverse. In fact, because many of the vehicle drivers are accustomed to driving and manipulating 2WS vehicles, when the rear wheels are steered by 4WS or A4WS when the vehicle is moved backward, the movement of the vehicle body becomes 2WS. The driver often feels that it is difficult for the driver to handle the vehicle (difficult to steer) or that the driver cannot adjust the vehicle's orientation as intended by the driver (driver skill) Also depends on). Therefore, in an actual vehicle such as an automobile, in order to avoid difficulty in handling when the vehicle body moves backward, the vehicle is operated in a state of 4WS in which the rear wheel is steered in conjunction with the front wheel when moving forward, In reverse, the steering control mode is often automatically switched to steer the vehicle in a 2WS state where only the front wheels are steered.
JP 59-81273 A JP 61-181778 A JP-A-63-312270 Japanese Patent Laid-Open No. 2-128966 JP-A-2-212275

  As described above, a 4WS or A4WS steering control device is often configured to be operated in a 4WS state when moving forward and in a 2WS state when moving backward. Therefore, for example, when the vehicle is placed in the rearward direction, the vehicle is moved backward at 2WS, and when the vehicle is removed from the garage, the vehicle is moved forward at 4WS. In such a case, that is, when the vehicle moves backward after moving backward, the manner of steering is different before and after the stop, and therefore the vehicle track is different even if the steering wheel angle of the driver is the same. It becomes. If the driver's understanding of the difference in the vehicle track is insufficient, there is a high possibility of contact with surrounding obstacles such as a garage wall. Of course, if the vehicle moves forward after reversing in the state of 4WS, the vehicle will not touch the obstacle even when moving forward if the vehicle is operated on a track that does not touch the obstacle when reversing. I will be able to move forward. In other words, in the case of a vehicle that is steered at 4WS when moving forward and 2WS when moving backward, the driver knows the track of the vehicle because the track when the vehicle moves forward is different from the track when the vehicle moves backward just before It becomes difficult to predict, and it can be said that there is a high possibility that the vehicle will come into contact with surrounding obstacles. More specifically, such a situation occurs when the vehicle is put in and out of the garage or when the vehicle is turned over when passing through a narrow curved road.

  Avoiding contact with obstacles around the vehicle as described above, as described in Patent Document 2 above, prohibits the rear wheels from being steered using a sensor that detects the distance between the vehicle and the obstacle. It is also achieved by controlling. However, in that case, it is essential to equip or adjust the obstacle sensor that can detect the distance to the obstacle with sufficient accuracy. In addition, when the operation mode of the rear wheel steering control is determined depending only on the detected value of the obstacle sensor as in the method of the above-mentioned literature, the obstacle is always applied regardless of the background of the driving / maneuvering of the vehicle. An object sensor is operated, and it must be configured to monitor the distance to the obstacle.

  Thus, one object of the present invention is to grasp the trajectory of a vehicle driven by 4WS when traveling forward and by 2WS when traveling backward, because the trajectory when the vehicle moves backward and forward is different. By making it difficult to predict and thereby avoiding the possibility that the vehicle will come into contact with surrounding obstacles, especially when the driver's recognition or familiarity is insufficient. is there.

  According to the present invention, in short, in a vehicle that is steered at 4WS at the time of forward movement and at 2WS at the time of backward movement, once the vehicle is moved backward, the next time the vehicle moves forward, A 4WS or A4WS steering control device is provided that maintains the 2WS state (until a predetermined condition is satisfied), thereby making it easier for the driver to grasp the trajectory of the vehicle after moving backward. The

  A four-wheel steering control device for a vehicle having a front wheel steering device and a rear wheel steering device according to the present invention detects a rear wheel steering control unit for controlling a steering angle of a rear wheel and whether the vehicle is moving forward or backward. And a storage unit for storing that the vehicle is moving backward, and when the rear wheel steering control unit detects that the vehicle is moving backward by the traveling direction detection means, The rear wheel steering device is controlled so that the magnitude of the rudder angle is smaller than a predetermined value, and when the fact that the vehicle is moving backward is stored by the storage means, the vehicle is moving forward by the traveling direction detection means. When detected, the rear wheel steering device is controlled so that the state of the rear wheel steering angle being smaller than a predetermined value is maintained until a predetermined condition is satisfied. Note that the control for making the steering angle of the rear wheel smaller than a predetermined value may be a state where the vehicle is substantially steered at 2WS, and the rear wheel steering angle is set to 0 by prohibiting the rear wheel steering. It may be.

  The four-wheel steering control device of the present invention and the front-wheel steering device and the rear-wheel steering device mounted on the vehicle may be basically any known device. Therefore, in normal steering control, when the vehicle moves forward, the steering control device refers to, for example, the vehicle speed and / or yaw rate according to the steering angle of the steering wheel of the front wheel and the rear wheel. Steering angle target values are determined, and the front wheel steering device and the rear wheel steering device are operated in accordance with these target values. In particular, in typical control of the rear wheel steering angle, first, a target value of the yaw rate or the slip angle of the vehicle body is determined based on the steering wheel angle of the driver and the vehicle speed, and the rear wheel steering angle control unit The target value of the steering angle of the rear wheel is determined so as to realize the target value of the yaw rate or the slip angle of the vehicle body, but is not limited thereto. On the other hand, at the time of reverse of the vehicle, as already mentioned, the rear wheel steering is prohibited so that the driver can easily handle the vehicle body, that is, the rear wheel steering angle control unit sets the rear wheel steering angle. By controlling the operation of the rear wheel steering device held at 0, the vehicle is steered in a 2WS state.

  However, as described above, when the vehicle is moved forward after the vehicle is once moved backward, if the vehicle is going straight ahead when the rear wheel steering is permitted, that is, the state of 4WS is restored, the vehicle When the vehicle is turned, even if the steering angle of the driver's steering wheel is the same as that at the time of reverse, the vehicle's track is different from that at the time of reverse because the rear wheel rudder angle is different from that at the time of reverse. Of course, there is no problem if the driver fully understands that and the steering is executed. However, in the case of an inexperienced driver, the vehicle trajectory moves backward on the same trajectory as when reversing. In that case, there is a higher possibility that the vehicle will come into contact with obstacles around the vehicle (in fact, as already mentioned, 4WS is more than 2WS , The rear part of the car body swings outwards.) In particular, it is assumed that the situation in which the vehicle is moved forward after the vehicle has once moved backward occurs when the vehicle passes through a garage or when it turns over a narrow curved road. In such a case, there is an obstacle around the vehicle. A thing is likely to exist.

  Therefore, in the present invention, as understood from the above configuration, a storage unit is provided for storing that the vehicle is moving backward, and the vehicle is stored when the storage means stores that the vehicle is moving backward. When it is detected that the vehicle is moving forward, the prohibition of the rear wheel rudder angle control is not canceled immediately, but the size of the rear wheel rudder angle is maintained to be smaller than a predetermined value or 0, and a predetermined condition is satisfied. The vehicle is operated at 2WS. According to such a configuration, the vehicle remains 2WS unless a predetermined condition is satisfied after the vehicle has been moved backward. In other words, it is expected that the driver can easily predict the trajectory of the vehicle and reduce the possibility of accidental contact with an obstacle.

  The above-mentioned predetermined condition, that is, the state in which the restoration of the 4WS state is determined from the state in which the 2WS maintained when the vehicle moves forward after the backward movement is determined, for example, is one in which the vehicle travels straight ahead. It may be a state determined to be. When the vehicle is traveling forward and straight, it can be said that the track of the vehicle is easily predicted by the driver, and there is a possibility that there are obstacles such as walls that touch the surroundings. It can be said that it is low. In addition, if the rear wheel steering is restored at any time during the turning or turning of the vehicle, the behavior of the vehicle may change, and the driver may feel uncomfortable. If steering is possible, there is no need to worry about such a sense of incongruity with changes in vehicle behavior. Accordingly, when the vehicle is in a straight traveling state, the rear wheel steering may be made executable so that the 4WS effect can be advantageously exhibited when the vehicle subsequently turns or turns. In order to achieve such an aspect, in the apparatus of the present invention, when the absolute value of the steering angle of the front wheels or the steering angle of the driver's steering wheel is below a predetermined value, or when the vehicle is A straight traveling determination unit that determines that the vehicle is traveling straight when traveling a predetermined distance may be provided.

  Another aspect of the predetermined condition may be that there is no obstacle that may come into contact with the surroundings of the vehicle. Even if an operation for switching the traveling direction of the vehicle from backward to forward is performed, if there are no obstacles around the vehicle, it is unlikely that the situation is going in and out of a garage or passing through a narrow curved road (or It is also expected that this is the case after leaving a narrow alley or garage.) Therefore, when such an obstacle does not exist in the surrounding area or when it has reached a state where it does not exist, it is rather desirable to immediately obtain the advantage that the turning radius of 4WS is small, so that 4WS is restored. It may be like this. In order to achieve such an aspect, in the apparatus of the present invention, an obstacle determination means for determining the presence or absence of an obstacle in a predetermined range around the vehicle is provided, and the obstacle determination means is in a predetermined range. The predetermined condition may be satisfied when it is determined that there is no obstacle. The predetermined range in this configuration may be arbitrarily set experimentally or theoretically. Of course, as the obstacle determination means, the distance between the vehicle body and the obstacle may be detected, but it simply detects the presence or absence of an obstacle within a predetermined range. There may be. In addition, when turning the vehicle at 4WS, as described above, the rearward of the vehicle body projects more outward than when turning the vehicle at 2WS. It may be a lateral region of the outer vehicle. The size or range of the lateral region may be arbitrarily set experimentally or theoretically.

  According to the above-described steering control device according to the present invention, the rear wheel steering angle control at the time of forward movement is limited by detecting that the vehicle has moved backward after moving backward. In the first place, it is often the case that the operation that the vehicle moves backward and then moves forward is turning the vehicle into and out of the garage and turning over when passing through a narrow curved road. When the vehicle is in such a situation, the vehicle is likely to come into contact with obstacles such as surrounding walls. Therefore, it is better for the driver to easily understand the track of the vehicle at that time. However, it is not easy for the vehicle itself to recognize that the garage is currently being taken in and out, or that it is a turnover when passing through a narrow bend (information from a sensor or video camera). Or it is possible in principle by using GPS information, but at the present time, it will be difficult to achieve easily.) In the present invention, the vehicle traveling direction is switched from reverse to forward, that is, by referring to the history of the vehicle traveling direction, the vehicle can be put in and out of the garage, and can be turned over when passing through a narrow curved road. It can be said that the current situation is simply estimated, thereby making it easier for the driver to handle the vehicle body by limiting the control of rear wheel steering.

  Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention.

Configuration of Device FIG. 1 (A) a car that preferred embodiments of the 4-wheel steering control apparatus of the present invention is incorporated is shown schematically. In the figure, the vehicle 10 having the left and right front wheels 12FL and 12FR and the left and right rear wheels 12RL and 12RR is operated in a normal manner according to the depression of an accelerator pedal (not shown) by the driver. In the example shown in the figure, a drive system 20 that generates braking / driving force is mounted on only the rear wheels because it is a rear wheel drive vehicle. In the normal manner, the drive system 20 receives the drive torque or rotational force from the engine and / or the electric motor 22 via the torque converter 24, the transmission 26, a differential gear device (not shown), etc. It is configured to be transmitted to 12RL and 12RR. The transmission 26 may typically be an automatic transmission of a known type, and each of P (parking), N (neutral), R (reverse), and D (drive) depending on the position of the shift lever 26a. When the shift lever 26a is in the D range and the R range, the rotation of the engine is transmitted to the drive wheels 12RL and RR so as to move the vehicle forward and backward, respectively. The transmission 26 may be a manual transmission. In addition, a braking system device (not shown) that generates a braking force on each wheel in the same manner as a normal vehicle is provided.

  Furthermore, the illustrated vehicle 10 is a 4WS vehicle in which not only the front wheels but also the rear wheels are steered. The front wheels 12FL and FR and the rear wheels 12RL and RR are respectively driven by the front wheel steering device 30 and the rear wheel steering device 40. Steered. In the front wheel steering device 30, the rotation of the steering wheel (handle) 32 actuated by the driver is transmitted to the booster device 34 through a VGRS (Variable Gear Ratio Steering) device 32a. By driving the tie rods 36L, R while the force device 34 boosts the rotational force, the steering angle δf of the front wheels is changed. The VGRS device 32a is a device that realizes so-called “active steering”. Under the control of the electronic control device 50 described later, the front wheel steering angle δf is based on information such as the steering wheel steering angle δd of the driver and the vehicle speed. The auxiliary steering device can change the steering angle of the front wheels by correcting the steering angle δd of the driver so as to coincide with the determined target steering angle or independently of it. In the rear wheel steering device 40, the drive motor 44 responds to a control command from the electronic control device 50 and is determined based on information such as the steering wheel steering angle δd of the driver and the vehicle speed. The tie rods 54L and R are driven so as to coincide with each other, thereby turning the rear wheels 12RL and RR. Although not shown, the front wheel VGRS device 32a, the front wheel steering device 30, and the rear wheel steering device are each provided with a steering angle sensor, a steering wheel steering angle δd, an actual steering angle δf of the front wheel, and a rear wheel. The detected value of the actual steering angle δr is given to the electronic control unit 50. [4WS as described above may be “active 4WS (A4WS)”, but is not limited thereto. ]

  The control of the steering angles of the front wheels and rear wheels of the vehicle shown in the figure and the operation control of other parts of the vehicle are executed by the electronic control device 50 as already mentioned, and the steering control device of the present invention is controlled by the electronic control device 50. Is realized. The electronic control unit 50 may include a microcomputer having a CPU, a ROM, a RAM, and an input / output port device, which are connected to each other by a bidirectional common bus, and a driving circuit. In the figure, the electronic control unit 50 includes a wheel speed sensor 14i (i = FL) provided on each wheel, in addition to the steering wheel steering angle δd, the actual steering angle δf of the front wheels, and the actual steering angle δr of the rear wheels. , FR, RL, RR (the same applies hereinafter), a wheel speed Vwi, a shift lever position signal (not shown) provided on the shift lever 26a, a direction indicator (winker) operated by the driver W) The position information of the direction indicator from 32b, the detected value such as the yaw rate γ and the lateral acceleration Gy from the sensor 62 are input. In addition to the signals listed above, various parameters necessary for various controls to be executed in the vehicle of the present embodiment, for example, various detection signals such as front and rear G sensor values, brake pressure, etc. May be entered.

  Also, particularly for the purpose of implementing some embodiments of the steering control of the present invention, any number of obstacle sensors 60fl, cl, rl, fr, cr, rr are preferably mounted around the vehicle. These detection values may be input to the electronic control unit 50. Each of these obstacle sensors 60 detects whether or not an object exists in a predetermined range on the outer periphery of the vehicle (see FIG. 3B). Each sensor may be any known type of sensor capable of transmitting a signal indicating the presence of an object within the monitoring range to the electronic control unit 50, such as an infrared sensor, a video camera, and a radar sensor. Etc. The distance from the outer periphery of the vehicle to the object may be detected, but the presence / absence of the object in each predetermined range may be detected (the latter is generally cheaper).

Configuration of Steering Control Device FIG. 1B shows the configuration of a four-wheel steering control device realized by the electronic control device 50 in the form of a control block. It should be understood that the configuration and operation of the illustrated four-wheel steering control device are realized by processing operations of the CPU and the like in the electronic control device 50 during operation of the vehicle.

  Referring to the figure, the four-wheel steering control device may be similar to any known type of four-wheel steering control device in its basic configuration. Generally speaking, the four-wheel steering control device includes a vehicle body model unit 50a and a 4WS / 2WS selection unit 50b. The steering wheel steering angle δd and the vehicle speed Vx of the driver are input to the vehicle body model unit 50a (an actual value of the yaw rate may be arbitrarily input from the yaw rate (γ) sensor 62). Here, the vehicle speed Vx may be determined in any known manner from the wheel speed value Vwi of each wheel from the wheel speed sensor (50c: if a vehicle speed sensor is provided, the detected value is used). Yes.) Then, using these input values, a target yaw rate (γ) and / or a target vehicle body slip angle (β) is determined based on a turning / turning motion model of an arbitrary vehicle body, and further, such a target yaw rate is realized. The target values of the front wheel steering angles δf and δr are determined. The target values of the front wheel steering angles δf and δr thus determined are given as control commands to the driver 34 of the front wheel steering device and the driver 44 of the rear wheel steering device, and the front and rear wheels are steered (each wheel The actual rudder angle value may be fed back to the control device, and the actual rudder angle may be controlled to match the respective target values.

  In a typical 4WS control mode, the direction and magnitude of the rear wheel rudder angle are determined depending on the vehicle speed and the traveling direction of the vehicle. As mentioned in the section “Background Art”, for example, when the vehicle moves forward, the rear wheels are steered in a phase opposite to the steering angle of the steering wheel until the vehicle speed reaches a certain predetermined speed from 0. (The front wheels are basically always in phase with the steering angle of the steering wheel.) As a result, the turning radius of the vehicle is made smaller (than in the case of 2WS), and the vehicle is able to make a small turn. When the vehicle speed exceeds a predetermined speed, the rear wheels are steered in the same phase as the steering wheel steering angle, more lateral force required for turning and turning is distributed to the rear wheels, and the vehicle body slip angle is also increased. It becomes possible to approach the turning direction of the vehicle (the moving direction of the center of gravity of the vehicle) (than in the case of 2WS). On the other hand, when the vehicle moves backward, as described above, the steering of the rear wheels is prohibited or restricted for reasons such as ease of handling the vehicle body for the driver. In order to execute such a mode, information indicating which range the driver has selected is input from the shift lever position sensor to the 4WS / 2WS selection unit 50b, and when the shift lever is in the R range, 4WS / 2WS selection is performed. The unit 50b transmits to the vehicle body model unit 50a that 2WS should be selected. When the 2WS selection information is received, the vehicle body model unit calculates the target value of the front wheel steering angle in a state where the rear wheel steering angle is fixed to 0 (or the size of the rear wheel steering angle is limited). The operation of the front wheel and rear wheel steering devices is controlled based on the target value. Thus, as described above, in the conventional vehicle steering control, simply speaking, the vehicle is steered at 4WS when moving forward and at 2WS when moving backward.

  However, as described in the “Disclosure of the Invention” section, when the vehicle is moved backward once and then moved forward, as described above, if the steering angle control mode of the rear wheels is different between backward and forward, the vehicle Because the tracks are different, it may be difficult for the driver, particularly for an inexperienced driver, to grasp or predict the vehicle track (see FIG. 4 and its description). Further, when considering when the maneuvering that the vehicle is moved forward after being retracted, such a maneuvering mode is generally in a situation where the vehicle is put into a garage, out of a garage, or turned on a narrow curved road. In practice, however, there are often garage walls, other vehicles and other obstacles in the surrounding area of the vehicle. Therefore, it can be said that the situation where the vehicle is moved backward after being moved backward is a situation where the track of the vehicle should be easily grasped or predicted. In addition, in the case of 4WS, compared to the case of 2WS, the rear of the vehicle will shake more greatly due to the turning and turning outward of the vehicle, and if there are obstacles around the vehicle, such obstacles The possibility of touching increases (see FIG. 4B).

  Therefore, in the steering control device of the present invention, when the vehicle is moved backward once and then moved forward, the state of 2WS is maintained until the predetermined condition is satisfied, and the rear wheel steering is performed. The mode of switching between 4WS and 2WS is modified so that the behavior or trajectory of the vehicle immediately after the travel direction of the vehicle changes from backward to forward is easily recognized by the driver. In order to execute such correction, as shown in FIG. 1B, the 4WS / 2WS selector 50b includes a steering wheel steering angle δd, a vehicle speed Vx, an obstacle sensor in addition to the shift lever position information. At least one of the information on the presence / absence of the obstacle, the position information of the direction indicator, or a combination thereof is input and used to determine whether or not the predetermined condition is satisfied. Hereinafter, several preferable aspects of the configuration and operation of the novel 4WS / 2WS selector 50b of the present invention will be described.

Configuration and Operation of 4WS / 2WS Selection Unit FIG. 2 shows a control process of the 4WS / 2WS selection unit 50b in the form of a flowchart. Such control processing may be executed repeatedly at all times during operation of the vehicle.

  Referring to the figure, in 4WS / 2WS selection unit 50b, first, information from the shift lever position sensor is monitored to determine whether or not the reverse range is selected (step 100: traveling direction). Detection unit). If the vehicle is traveling normally forward, 4WS is selected as it is, and the information is transmitted to the vehicle body model unit (step 120). When 4WS is selected, the flag Ws is set to F (step 130). However, when the shift lever is in the reverse range, that is, when the vehicle is instructed to reverse, the flag Ws is set to R (step 140. Accordingly, the flag Ws functions as a “storage unit”). . Then, 2WS is selected and the information is transmitted to the vehicle body model unit (step 150).

  Thus, after the vehicle is moved backward (steps 140 and 150 are always executed while the vehicle is moving backward), whether or not the flag Ws is R when the shift lever is set to other than the reverse range. Is determined (step 110), and if Ws = R, that is, it is stored that the vehicle has moved backward, a permission condition (predetermined condition) for switching to 4WS, which will be described in detail later, is satisfied. It is determined whether or not there is (step 160). When the permission condition is not satisfied, 2WS is maintained as it is, and the steering control is switched to 4WS only when the permission condition is satisfied. According to such a configuration, switching from 2WS to 4WS is not performed unless the permission condition is satisfied. For example, when the driver performs an operation that frequently changes the shift lever. It should be understood that the 2WS state is maintained, frequent switching of the steering control state is avoided, and control stability is also improved.

The permission condition for switching from 2WS to 4WS may be, for example, one of the following exemplary states.
(A1) A state in which the absolute value of the steering angle δd of the steering wheel is equal to or smaller than a predetermined minute value δdo, that is,
| Δd | <δdo (1)
(A2) When traveling for a predetermined distance or more in the state of the expression (1).
(B) When the obstacle sensor does not detect or stops the obstacle (c) When the obstacle sensor outside the turn does not detect or stops the obstacle

  In the above description, the determination processing of (a1) and (a2) using the expression (1) determines whether or not the vehicle is traveling straight ahead (straight ahead determination means). Whether or not the state of the expression (1) in (a1) has passed for a predetermined time may be measured after the vehicle speed value Vx becomes equal to or higher than the predetermined value (after the vehicle starts moving forward) (measured in a stopped state). Not to do). Further, whether or not the vehicle has advanced the predetermined distance (a2) may be calculated by vehicle speed Vx × time. The predetermined time or the predetermined distance may be set to an appropriate value experimentally. If the expression (1) is not satisfied after the expression (1) is satisfied and before the predetermined time or distance is reached, the switching is not performed, and the measurement is started when the expression (1) is satisfied again. The

  The determination processes (b) and (c) described above determine the presence or absence of an obstacle in a predetermined range around the vehicle (obstacle determination means). The determination in (b) may be made by referring to signals from all obstacle sensors and determining the presence or absence of a signal indicating the presence of an obstacle. In the determination of (c), it may be determined by the direction of the steering angle of the steering wheel or the position of the direction indicator which of the corners is turned outward. In this case, when the steering wheel steering angle or the direction indicator indicates the right direction (left direction), it is determined that the left side (right side) of the vehicle is turning outward, and the left side (right side) obstacle sensor is detected as an obstacle. Whether or not is detected is determined.

  FIG. 3 shows the track of the vehicle and the switching timing when the above conditions (a1) to (c) are set as the permission conditions in step 160 of FIG.

  First, FIG. 3A shows a case where the above conditions (a1) and / or (a2) are used as permission conditions. Referring to the figure, when the vehicle moves backward on a curved road as indicated by a dotted arrow, the vehicle is steered in a 2WS state. Then, when the vehicle moves forward again, when turning in the backward direction, the vehicle moves forward in the state of 2WS, and after turning, the steering wheel steering angle becomes a state satisfying the formula (1), and then a predetermined time. When the time elapses or after a predetermined distance has been reached, the 4WS state will be restored. When traveling in any of these directions, the vehicle behavior corresponding to the steering angle of the steering wheel is the same as when the vehicle is traveling backwards (the turning radius does not suddenly become smaller than when traveling backwards). This makes it easier for the user to grasp or predict the trajectory. In addition, when the vehicle moves backward after moving backward, the vehicle will not be swung out to the area that did not pass when the vehicle was moved backward. (For example, if there is an obstacle on one side as shown in the figure, the driver should steer away from the obstacle when moving forward. If it is switched, the traveling direction of the vehicle may turn excessively.) Furthermore, according to this aspect, since the switching to 4WS is performed when the steering angle is small, the switching behavior becomes unstable, and the driver feels uneasy when the turning radius suddenly changes. Avoided.

  FIG. 3B shows a case where the above condition (b) is set as a permission condition. In the figure, for example, the case where the position is adjusted to park the own vehicle between two other vehicles in a parking lot or the like is illustrated, and when the vehicle first moves backward, it is switched to 2WS. Thereafter, when the position is adjusted, the track or turning radius of the vehicle with respect to the steering angle of the steering wheel is maintained at 2WS unless the other vehicle deviates from the monitoring area of the obstacle sensor. Therefore, it is easy to handle and predict the vehicle and the track of the vehicle body. And when taking the vehicle out of the parking lot, 4WS will be revived after the other vehicle is completely separated, so it is expected that the possibility of contact with the other vehicle will be reduced (whether the handle is turned off) Regardless of this, it is advantageous in that the 2WS state is maintained so that the driver can easily grasp the track until the surroundings are completely cleared.)

  FIGS. 3C1 and 3C2 illustrate a case where the above condition (c) is set as a permission condition, and illustrates a case where the own vehicle is put into and out of a parking lot such as a garage. As shown in the figure, when the vehicle moves backward by 2WS while turning, the vehicle is often put in the garage in a state of being biased outward from the turn. In that case, when the vehicle moves forward in the same direction as the reverse, if it is set to 4WS, the rear of the vehicle swings more outward than the reverse when the steering angle is the same as the reverse (how much it swings). Depends on the method of determining the target yaw rate with respect to the steering angle and the target vehicle body slip angle.), The vehicle body may contact the wall. Therefore, when the vehicle moves forward in the same direction as when moving backward, the state of 2WS is maintained until the obstacle (wall) outside the turn is eliminated, thereby avoiding a vehicle trajectory that is difficult for the driver to anticipate. On the other hand, if the wall is outside the sensor monitoring area, as shown in the figure, such as when turning forward in the direction opposite to the reverse direction, the possibility of contact is low even with 4WS, so switching of 4WS is executed. The

  Of the above conditions (a1) to (c), one of them may be used as a permission condition, and some of a plurality of conditions are set as permission conditions, and any one of them is satisfied. It may be assumed that the permission condition is satisfied when the condition is satisfied or when all are satisfied. It should be understood that when only (a1) and (a2) are adopted as permission conditions, it is not necessary to equip an obstacle sensor.

  Thus, in the above-described embodiment of the present invention, the fact that the vehicle has moved backward is stored, and the switching timing from 2WS to 4WS is corrected using the stored information. In other words, in the present invention, it can be said that the mode of steering control is controlled by the traveling history of the vehicle. In the above-described configuration, 2WS is maintained when the vehicle moves forward, immediately after the vehicle moves backward and then moves forward. For example, 4WS is maintained when the vehicle passes through a narrow curved path only by moving forward. It should be understood that this may be the case. In the present invention, the important thing is that once the vehicle is switched to 2WS to move backward, the vehicle track is grasped and predicted by the driver so as not to immediately switch to 4WS when moving forward again. It is to make it easy.

  While the present invention has been described in detail with respect to one embodiment thereof, it will be apparent to those skilled in the art that various modifications can be made within the scope of the present invention.

  For example, the control process of FIG. 2 may be executed in response to the shift lever being in the R position. The obstacle sensor may be provided only at the rear of the vehicle body. In the embodiment, when 2WS is selected, the rear wheel rudder angle is controlled to be substantially maintained at 0, but the rear wheel rudder angle is completely zero. Instead of being fixed to, fluctuations may be allowed within a predetermined minute range (so as not to make it difficult for the driver to grasp and predict the trajectory of the vehicle after the vehicle has moved backward).

FIG. 1A is a schematic diagram of a vehicle on which a preferred embodiment of the four-wheel steering control device of the present invention is mounted. FIG. 1B is a diagram of the present invention configured in an electronic control device 50. It is a control block diagram of a preferred embodiment of a four-wheel steering control device. A signal to be input to the 4WS / 2WS selection unit 50b may be changed according to a condition adopted as a permission condition for switching from 2WS to 4WS. FIG. 2 shows the control processing in the 4WS / 2WS selection unit 50b of FIG. 1B in the form of a flowchart. FIG. 3 is a diagram for explaining a state or timing at which switching from 2WS to 4WS is performed when the vehicle moves backward (dotted arrow) and moves forward again (solid arrow). FIG. 3 (A) shows a vehicle that is set when the permission condition for switching from 2WS to 4WS is such that the steering wheel steering angle magnitude (absolute value) is less than or equal to a predetermined value for a predetermined time or longer or a predetermined travel distance. Orbit (solid arrow) is shown, and switching to 4WS is performed in the vicinity of the position labeled “4WS”. FIG. 3 (B) shows the vehicle permission condition for switching from 2WS to 4WS when the obstacle sensors on the outer periphery of the vehicle no longer detect obstacles in their respective monitoring areas (shaded areas). The state is shown, and switching from 2WS to 4WS is executed when an obstacle (such as another vehicle) completely leaves the monitoring area. FIGS. 3C1 and 3C2 show the vehicle trajectory set when the permission condition for switching from 2WS to 4WS is that there are no obstacles outside the turning and turning of the vehicle. In (C1), since the garage wall is present in the monitoring area of the obstacle sensor outside the turn, the vehicle moves forward in the state of 2WS. In (C2), there is an obstacle in the monitoring area of the obstacle sensor outside the turn. Since it does not exist, switching to 4WS is performed. FIG. 4 is a diagram schematically showing a trajectory when the vehicle is once moved backward in a 2WS state and then advanced in a 2WS (A) or 4WS (B) state. In (A), at the time of forward movement, if the steering wheel has the same steering angle, the vehicle's trajectory will follow the backward movement, so that the vehicle (even when steering with a different steering angle) is used for the driver. It is easy to grasp and predict the trajectory. Further, since the rear part of the vehicle moves in the turning direction (the direction of arrows A and a in the figure), the possibility of contact is low even if there is an obstacle outside the turning. On the other hand, in (B), at the time of forward movement, even when the steering wheel steering angle is the same, the track of the vehicle is different from the track at the time of backward movement, so it is difficult for the driver to grasp and predict the vehicle trajectory. Since the rear of the vehicle moves outward (in the direction of arrows B and b in the figure), the possibility of coming into contact with obstacles outside the turn increases.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Vehicle 12FL-RR ... Wheel 14FL-RR ... Wheel speed sensor 20 ... Drive system device 26a ... Shift lever 30 ... Front wheel steering device 32 ... Steering wheel 32a ... VGRS device 32b ... Direction indicator (blinker)
34 ... Booster (steering drive)
DESCRIPTION OF SYMBOLS 40 ... Rear-wheel steering apparatus 44 ... Driver for rear-wheel steering 50 ... Electronic control unit 60fl-rr ... Obstacle sensor 62 ... Yaw rate and / or lateral acceleration sensor

Claims (5)

  A four-wheel steering control device for a vehicle having a front wheel steering device and a rear wheel steering device, the rear wheel steering control unit for controlling the steering angle of the rear wheel, and detecting whether the vehicle is moving forward or backward The rear wheel steering control unit detects that the vehicle is moving backward by the driving direction detecting means. Sometimes the rear wheel steering device is controlled so that the steering angle of the rear wheel is smaller than a predetermined value, and the travel direction detecting means is stored when the storage means stores that the vehicle is moving backward. When the vehicle detects that the vehicle is moving forward, the rear wheel steering device is controlled so that the rudder angle of the rear wheel is kept smaller than a predetermined value until a predetermined condition is satisfied. A device characterized by.   The apparatus according to claim 1, further comprising a straight traveling determination unit that determines that the vehicle is traveling straight when a state where the absolute value of the steering angle of the driver's steering wheel is less than a predetermined value continues for a predetermined time. The predetermined condition is that the straight traveling determination means determines that the vehicle is in a straight traveling state.   3. The straight traveling determination according to claim 1, wherein when the vehicle travels a predetermined distance when the absolute value of the steering angle of the driver's steering wheel is below a predetermined value, the vehicle is traveling straight. And the predetermined condition is that the straight traveling determining means determines that the vehicle is in a straight traveling state.   4. The apparatus according to claim 1, further comprising obstacle determining means for determining presence or absence of an obstacle in a predetermined range around the vehicle, wherein the predetermined condition is determined by the obstacle determining means. A device characterized in that it has been determined that there is no obstacle within the range.   The apparatus according to claim 4, wherein the predetermined range is a lateral region of the vehicle outside the turning direction of the vehicle.

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