JP4135158B2 - Vehicle front and rear wheel steering angle control device - Google Patents

Description

  The present invention relates to a front and rear wheel steering angle control device for a vehicle.

  Conventionally, a rear-wheel steering angle control device for a vehicle as described in Patent Document 1 is known. In the first prior art, the vehicle rear end portion is near the main rear wheel steering angle calculated by multiplying the front wheel steering angle operated by the driver's steering by a predetermined ratio so as to realize a predetermined turning radius. The rear wheel rudder angle is limited so that the fixed point B falls within the locus of the fixed point A near the front end of the vehicle.

  However, in the first conventional technique, the main rear wheel rudder angle and the limit value of the rear wheel rudder angle are switched according to the magnitude relationship, and thus there are the following problems.

  FIG. 13 shows the result of simulating the first prior art. However, when the rear wheel rudder angle is switched, the side slip angle and yaw rate of the vehicle change, which causes a problem that the driver feels uncomfortable. It was.

  Further, the locus of the fixed point A in the vicinity of the front end of the vehicle needs to be calculated with ground coordinates. For this reason, it is necessary to calculate the center of gravity of the vehicle and the yaw angle of the vehicle, and the calculation is complicated. There was also a point.

  In order to solve such a problem, the applicant of the present application, in the application described in Patent Document 2 (hereinafter referred to as the second prior art), can easily calculate the target rotation center position and perform predetermined rotation while turning the vehicle. A vehicle front and rear wheel steering angle control device that can limit the amount of overhang of the rear end of the vehicle while realizing a radius is proposed.

  The second prior art aims to realize a turning radius corresponding to the steering angle operated by the driver while suppressing the outward protrusion when the vehicle turns. To achieve this aim, while the turning center is fixed in the vehicle fixed coordinate system, the turning center radius matches the turning radius of the vehicle, and the turning center elevation angle matches the attitude angle of the vehicle. , Is used.

That is, when the vehicle starts to move, so that the overhang of the vehicle is eliminated (= the attitude angle of the rear end of the vehicle is 0 or less), the turning center is on the extension of the rear end of the vehicle (point S1 in FIG. 14), After the collision with the obstacle due to the overhang is avoided, the turning center is set to the side of the vehicle center (point F1 in FIG. 14) so that the turning radius of the vehicle becomes small, and the behavior of the vehicle continues in the meantime. As the vehicle advances, the turning center is gradually moved from point S1 to point F1 in FIG.
Japanese Patent Laid-Open No. 2-74473 Japanese Patent Application 2000-82465

  However, in the second prior art, since the influence of the movement of the turning center on the turning radius of the vehicle is not taken into consideration, while the turning center is moved, it is associated with the turning angle operated by the driver. There is a problem that a desired turning radius cannot be realized.

  FIG. 15 shows the simulation conditions for showing the example, and FIG. 16 shows the simulation results. Here, although the reference point on the vehicle is the center of the vehicle, the turning center radius is kept constant between point B and point C where the turning center is moved forward of the vehicle. The turning radius of the vehicle has become larger than before.

  As described above, in the second conventional technique, it is impossible to change the attitude angle of the vehicle while making the turning radius of the vehicle coincide with a desired value.

  In order to solve the above problems, the invention according to claim 1 is a vehicle front and rear wheel steering angle control device including a device for independently controlling a front wheel turning angle and a rear wheel turning angle. A target turning radius calculating means for calculating a target turning radius Re of the reference point P on the vehicle, a target posture angle calculating means for calculating a target posture angle β of the reference point P, and the target turning radius Re. And calculating the target turning angle of the front and rear wheels based on the target posture angle β and turning the target steering angle relative to the front and rear wheel target turning angle when the target posture angle is constant while the target posture angle β is increased. While the target turning angle is corrected so that the center point Q approaches the vehicle and the target posture angle β is reduced, the turning center point Q with respect to the front and rear wheel target turning angles when the target posture angle is constant. The target turning angle is corrected by calculating the target turning angle in the direction away from the vehicle A steering angle calculating means, further comprising a a gist.

  According to a second aspect of the present invention, there is provided a vehicle front and rear wheel steering angle control device including a device for independently controlling a front wheel turning angle and a rear wheel turning angle in order to solve the above-described problem. Based on the target turning radius Re of the reference point P on the vehicle calculated based on the amount and the target posture angle β of the reference point P, the target turning angle of the front and rear wheels is calculated and the target posture angle is calculated. While the target posture angle β is constant, the target turning angle is corrected so that the turning center point Q approaches the vehicle with respect to the target turning angle when the target posture angle β is constant. And a target turning angle calculating means for correcting the target turning angle in a direction in which the turning center point Q moves away from the vehicle with respect to the target turning angle when the target posture angle β is constant. The gist.

  In order to solve the above-described problems, the invention according to claim 3 is the vehicle front and rear wheel steering angle control device according to claim 1 or 2, wherein the target turning angle calculation means calculates the turning center radius R, Approximately 1 / R = 1 / Re + δβ / δz according to the amount of change δβ / δz of the target posture angle with respect to the target turning radius Re and the movement distance δz of the vehicle reference point P, and the turning center elevation angle θ is approximately β. The gist is to calculate the target turning angle so that the point Q is the turning center point.

Invention of claim 4, wherein, in order to solve the above problems, in the front and rear wheel steering angle control apparatus for a vehicle according to claim 1 Symbol placement, the target posture angle calculating means, the target attitude angles with respect to the moving distance δz of the reference point P The gist is to calculate the target posture angle so that the change amount δβ / δz does not change suddenly.

  According to a fifth aspect of the present invention, in order to solve the above-described problem, in the vehicle front and rear wheel steering angle control device according to any one of the first to fourth aspects, a certain point on the vehicle moves a certain distance. The target turning angle calculation means executes the calculation in synchronization with the pulse of the vehicle speed sensor.

  According to a sixth aspect of the present invention, there is provided a vehicle front and rear wheel steering angle control device according to any one of the first to fifth aspects, wherein vehicle speed detecting means for detecting a moving speed of the vehicle is provided. And the target turning angle calculation means is in a state where the vehicle can be regarded as almost stopped, the turning center radius R matches Re regardless of the direction and rate of change of the target attitude angle, The gist is to calculate the target turning angle from the point Q at which the turning center elevation angle θ is β.

  According to a seventh aspect of the present invention, in order to solve the above-mentioned problem, in the front and rear wheel steering angle control device for a vehicle according to any one of the first to sixth aspects, the target turning angle calculation means is the reference The gist is to calculate the target turning angle so as to limit the upper limit value of the change amount δθ / δz of the turning center elevation angle θ with respect to the moving distance δz of the point P according to the target posture angle and the target turning radius Re. .

  Next, definitions of terms used in this specification will be clarified with reference to FIG. This definition shall apply to the claims, the problem-solving means, and the embodiments.

◆ Vehicle reference point P
Coordinate origin fixed on the vehicle. The reference point can be taken at any position on the vehicle, but usually the bisector of the line segment connecting the bisector of the front axle and the bisector of the rear axle for easy calculation As the reference point. The center of gravity of the vehicle may be selected as the reference point.

◆ Vehicle fixed coordinates As shown in FIG. 12, the coordinates are fixed to the vehicle and the origin, x and y axes are determined. In the following, a reference point (described later) on the vehicle is taken as the origin, the x-axis is taken forward of the vehicle, and the y-axis is taken laterally as shown in FIG. Here, regarding the y-axis, the vehicle turning direction is assumed to be positive (in FIG. 12, since the vehicle is turning right, the right side is positive). Take the left side positive while turning left.

◆ Attitude angle It is defined as an angle β formed by the front of the vehicle in the traveling direction (the x axis in FIG. 12) with respect to the traveling direction of a reference point (described later) on the vehicle, and the direction around the vehicle turning is defined as positive. In FIG. 12, since it is turning right, clockwise (clockwise) is taken positively. When turning left, turn counterclockwise (counterclockwise).

◆ Steering angle In FIG. 12, the angle formed by the x-axis and each wheel (the turning angle of the front right wheel is indicated by δfr).

◆ Steering center A point on the vehicle fixed coordinate that becomes the turning center when turning with the front and rear wheels turning angle constant.

◆ Steering center radius Distance R between the reference point (described later) on the vehicle and the turning center.

◆ Steering Center Elevation Angle An angle formed by a line connecting a reference point on the vehicle (described later) and a turning center and a line extending from the reference point on the vehicle (described later) in the vehicle lateral direction (parallel to the y-axis). Take a positive angle of rotation in the direction of travel of the vehicle (counterclockwise is positive when turning right, clockwise is positive when turning left).

  According to the first aspect of the present invention, in the vehicle front and rear wheel steering angle control device including a device for independently controlling the front and rear wheel steering angles, the target steering angle calculation means increases the target posture angle β. While the target posture angle is constant, the target turning angle is corrected so that the turning center point Q approaches the vehicle with respect to the front and rear wheel target turning angles when the target posture angle is constant, and the target posture angle β is reduced. In addition, with respect to the front and rear wheel target turning angles when the target posture angle is constant, the target turning angle is corrected and calculated in a direction in which the turning center point Q moves away from the vehicle.

  According to the study by the present inventors, when the turning center is moved forward in the vehicle traveling direction (direction in which the turning center elevation angle is increased), the turning radius of the vehicle becomes larger than the turning center radius and conversely, It is known that the turning radius of the vehicle is smaller than the turning center radius when the rudder center is moved to the rear of the vehicle (in the direction of decreasing the turning center elevation angle). By applying the present invention in which correction is performed in consideration of this characteristic in advance, the actual turning direction of the vehicle can be realized so as to approach a desired turning radius even while the target posture angle is changed.

  Further, since the front and rear wheel turning angles of the vehicle are corrected according to the change in the target posture angle, it is possible to obtain an effect that the turning radius Re and the posture angle β of the vehicle can be realized independently.

  From the viewpoint of the driver, the vehicle can be rotated with a small turning radius while preventing overhanging at the time of starting, so that, for example, a U-turn can be made even on a narrow road.

  According to the second aspect of the present invention, in the vehicle front and rear wheel turning angle control device including a device for independently controlling the turning angle of the front wheels and the turning angle of the rear wheels, calculation is performed based on the steering operation amount. While calculating the target turning angle of the front and rear wheels based on the target turning radius Re of the reference point P on the vehicle and the target posture angle β of the reference point P, while increasing the target posture angle, While the target turning angle is corrected so that the turning center point Q approaches the vehicle with respect to the target turning angle when the target posture angle β is constant, the target posture angle β Since the target turning angle is corrected in the direction in which the turning center point Q moves away from the vehicle with respect to the target turning angle when is constant, the same effect as in the first aspect can be obtained.

According to the invention described in claim 3, in the target turning angle calculation means, the turning center radius R is set in accordance with the change amount δβ / δz of the target attitude angle with respect to the target turning radius Re and the movement distance δz of the vehicle reference point. In general, the following equation (1)
1 / R = 1 / Re + δβ / δz (1)
In addition, the target turning angle is calculated so that the turning center is a point Q where the turning center elevation angle is approximately β. According to the study by the present inventors, the relationship among the turning radius Re of the vehicle reference point P, the turning center radius R, the movement distance δz of the vehicle reference point, and the vehicle attitude angle change δβ therebetween is quantitative. It is known that it is represented by the following equation (1). It has also been found that the attitude angle of the vehicle reference point substantially matches the turning center elevation angle regardless of the movement of the turning center.

  Therefore, according to the present invention, these findings can be quantitatively considered in advance, so that the turning radius of the vehicle can be accurately approached to the desired turning radius even while the target posture angle is changed. At the same time, since the front and rear wheel turning angles of the vehicle are corrected according to the change in the target posture angle, it is possible to obtain an effect that the turning radius Re and the posture angle β of the vehicle can be realized independently and accurately.

  From the viewpoint of the driver, the vehicle can be rotated with a small turning radius while preventing overhanging at the time of starting, so that, for example, a U-turn can be made even on a narrow road.

  According to the fourth aspect of the invention, the target posture angle calculating means calculates the target posture angle β so that the target posture angle change amount δβ / δz with respect to the vehicle reference point moving distance δz does not change suddenly. Since the front and rear wheel steering servo systems are inertial position control, it is impossible to immediately realize the desired stepwise target position. Will be realized. Therefore, when the target positions are generated discontinuously, the vehicle turning center is not realized at a desired position in a transient state until the target value is followed. However, according to the present invention, when 1 / Re is given as a continuous value in equation (1), δβ / δz takes a value so that it does not change suddenly, so 1 / R is also calculated as a value that does not change suddenly. . Therefore, the target position is also calculated with a value that does not change suddenly, and the above-mentioned problems can be avoided.

  According to the fifth aspect of the present invention, the target turning angle calculation is executed in synchronization with the pulse of the vehicle speed sensor. Since the vehicle speed pulse is output for each moving distance of the vehicle, it becomes easy to calculate the target turning angle based on the target posture angle change amount δβ with respect to the moving amount δz of the predetermined vehicle reference point. In other words, when calculating in time synchronization, it is necessary to calculate the target turning angle after calculating the moving distance for a predetermined time. However, when this method is used with the reference point P as the vehicle speed sensor position, the moving distance is Since it is known in advance, the calculation for that amount becomes unnecessary. Furthermore, in the method of calculating the moving distance in time synchronization and obtaining the vehicle speed from the number of pulses generated within the time, the measurement accuracy of the moving distance deteriorates depending on the situation where the number of pulses is small. It is possible to perform computations that make full use of the resolution of the vehicle speed sensor without having to deal with the above.

  According to the sixth aspect of the present invention, when the target turning angle calculation means is in a state where the vehicle can be regarded as almost stopped, the turning center radius is not affected by the direction and rate of change of the target posture angle. Calculation is performed from a point Q where R is substantially equal to Re and the turning center elevation angle θ is substantially β. As a result, the movement of the vehicle (turning radius and attitude angle) can be changed discontinuously while the driver stops the vehicle.

  According to the seventh aspect of the present invention, in the target turning angle calculation means, the upper limit value of the change amount δθ / δz of the turning center elevation angle θ with respect to the movement distance δz of the reference point P is set as the target posture angle and the target turning radius. The target turning angle is calculated so as to be limited according to Re. The possible range of the turning center radius R is limited by the turning ability of the front and rear wheels (FIG. 11). Therefore, when calculating the turning center radius R according to the equation (1), an unrealizable R is calculated depending on the size of the turning radius Re, δβ / δz, and as a result, turning according to the steering amount of the driver. There is a disadvantage that the deformation cannot be realized. The present invention takes this point into consideration, and the size of δθ / δz is constrained so that a steerable center radius R in a feasible range is derived. I was able to do that.

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

  FIG. 1 is a system configuration diagram showing the configuration of Embodiment 1 of a vehicle front and rear wheel steering angle control device according to the present invention. In FIG. 1, 1 is a front wheel, 2 is a rear wheel, 3 is a steering wheel operated by a driver, and 4 is a steering angle sensor for detecting a steering angle of the steering wheel. Some devices detect the amount of rotation. 5 and 6 are front wheel left and right wheel steering actuators, and 7 and 8 are rear wheel left and right wheel steering actuators. Each has a DC motor, and the turning angle of the front, rear, left and right wheels can be adjusted by converting the turning motion of the motor to the left and right motion of the steering rack via the worm gear and adjusting the amount of movement. Here, the motor is not limited to a DC motor, and may be an induction motor, a switched reluctance motor, or a linear motor that can directly adjust the amount of movement of the steering rack.

  20, 21, 22, and 23 are drive circuits that drive each wheel steering DC motor, and are configured by H bridges. Current feedback of the DC motor is performed so as to realize a motor current commanded from an ECU (12) described later. Reference numerals 31, 32, 33, and 34 denote potentiometric rack stroke sensors that detect the amount of movement of the steering rack of the front, rear, left, and right wheels, respectively. Reference numerals 14, 15, 16, and 17 denote vehicle speed sensors that detect the rotational speed of each wheel of the vehicle 11. There is a Hall IC type that outputs a pulse when reaching the position of a tooth from a groove according to the rotation of a gear attached to the rotation shaft of each wheel.

  Reference numeral 12 is a control circuit (ECU) centered on a microcomputer, which performs signal input / output with the outside and various calculations. The CPU executes computations, and the ROM stores a control program and various data described later. The RAM temporarily stores information during program execution. The I / O interface performs input of information from an external sensor or the like and a signal for driving an external actuator. It also has a timer that measures the time between pulses of the vehicle speed sensor.

  FIG. 2 is a block diagram illustrating a configuration of the front and rear wheel steering angle control device according to the first embodiment. The front and rear wheel steering angle control device includes a target turning radius calculator 1401 that calculates a target turning radius based on a steering angle that is a steering operation amount, a target attitude angle calculator 1402 that calculates a target attitude angle of a vehicle reference point, A target turning angle calculation unit 1403 that calculates the target turning angle of the front and rear wheels based on the target turning radius and the target attitude angle, and a turning angle adjustment unit that adjusts the actual turning angle so as to match the target turning angle. 1404.

  The constituent elements of these front and rear wheel steering angle control devices are all realized in the ECU (12) in the order of 1401, 1402, 1403, and 1404. Since the reference point P on the vehicle can be described in the same manner for any place on the vehicle, an application example will be described below with the reference point P as the center of the vehicle (the midpoint of a line connecting the front and rear tread centers).

  In 1401, the target turning radius Re corresponding to the rotation angle detection value ST of the steering wheel is calculated. As shown in FIG. 4, the target turning radius Re is stored in advance in the ROM in the form of a table for the rotation angle of the steering wheel, and is calculated by referring to the table. At this time, since the turning radius in the straight traveling state of the vehicle corresponds to infinity, it is convenient to input the table value as an inverse value of the target turning radius as shown in FIG. This calculation is performed every 10 ms, and the target turning radius Re is output every 10 ms.

  In 1402, a target posture angle β corresponding to the surrounding situation of the vehicle is calculated. In this example, when the reference point on the vehicle is the vehicle center, as shown in FIG. 5, the turning center is set at the vehicle rear end extension upper point S1 according to the moving distance z of the reference point P from the vehicle stop state. It is generated so as to move from FIG. 14 to point F1 to 0.

  Here, when the invention of claim 4 is applied, the target posture angle β may be generated so as to change with respect to the movement of the vehicle as shown in FIG. In obtaining the moving distance z of the reference point P, the moving distance of each wheel is calculated in advance. The movement distance of each wheel is obtained by calculating the movement speed of each wheel by dividing the vehicle movement distance per pulse by the time between pulses of the vehicle speed sensor, and integrating it with time.

  Alternatively, the value obtained by multiplying the number of pulses generated by the vehicle speed sensor by the wheel movement distance per pulse may be integrated. At present, a total of four vehicle speed sensors are provided for each wheel, but since the reference point P is the center of those wheels, the average value of the movement distance calculated from the output of each of the four vehicle speed sensors is used as the reference point P. The movement distance z is simply calculated.

  In addition to this, the calculation of the target turning radius Re and the target attitude angle β can automatically enter the parking lot while detecting surrounding obstacle conditions as in the automatic parking system. The target turning radius and the target posture angle may be calculated as described above.

In 1403, a target turning center (point Q) for realizing the target turning radius Re and the target attitude angle β is obtained, and then the target turning angle (front left wheel δfl ^* ) of each wheel that realizes the target turning center ^. , front right wheel δfr ^*, left rear wheel δrl ^*, rear right wheel δrr ^*) to calculate the.

  FIG. 3 is a schematic flowchart for explaining the operation of the front and rear wheel steering angle control device according to the first embodiment. First, the steering angle is detected (step 1501), and then the vehicle speed is detected (step 1502). Then, the target turning radius of the vehicle is calculated based on the steering angle (step 1503), the target attitude angle is calculated (step 1504), and finally the target turning angle is calculated (step 1505).

  Hereinafter, an example of calculating the turning center radius R and the turning center elevation angle θ for specifying the target turning center (point Q) will be described with reference to Flowchart 1 (FIG. 7) and Flowchart 2 (FIG. 8). Flowchart 1 performs calculations in synchronization with the pulse rise of the wheel speed sensor on the right front wheel when turning left, and in synchronization with the pulse rise of the wheel speed sensor on the left front wheel when turning right and almost straight. Perform the operation. In the flowchart 2, calculation is performed every 10 ms.

In the flowchart 1, the turning center in a state where the vehicle is moving is calculated. In step 1901, the distance dz that the vehicle has traveled during 1 JOB is calculated from the reference point travel distance z in the current JOB and the reference point travel distance zold in the preceding JOB. Dz = z−zold (2)
It calculates | requires by Formula (2).

  Here, if the reference point P is set as the wheel speed sensor position of the right front wheel when turning left, and the reference point P is set as the wheel speed sensor position of the left front wheel when turning right and almost straight, the dz value is calculated in advance. Since it corresponds to the distance determined according to the pulse generation interval, it is not necessary to calculate the expression (2).

In Step 1902, the target attitude angle β calculated by the target attitude angle calculation means and the turning center elevation angle θold calculated in Step 1906 before 1 JOB are used to obtain the elevation angle dθ of the target turning center from 1 JOB before dθ = β−. θold (3)
It calculates | requires by Formula (3).

  In step 1903, the minimum turning center radius Rmin that can be realized at that time is calculated from the turning center elevation angle θold at the time of the first job. Rmin is the distance between the point V and the point P in FIG. 11 and can be calculated by experimentally measuring the Rmin value in advance as table data for θ, storing it in the ROM, and drawing the table. it can.

  In Step 1904, the maximum value of the turning center elevation angle change dθ that can realize the target turning radius Re is calculated by the following equation in consideration of the minimum value Rmin of the turning center radius.

dθmax = (1 / Rmin−1 / Re) * dz (4)
In step 1905, the change dθ of the turning center elevation angle is constrained by the value.

  In step 1906, the final target attitude angle β is calculated, and the turning center elevation angle θ is calculated from the change dθ value of the turning center elevation angle.

Finally, in step 1907, the turning center radius R is changed to R = 1 / (dθ / dz + 1 / Re) (5)
To complete the routine.

  Here, claim 3 is realized in steps 1906 and 1907, claim 5 is applied by synchronizing this flowchart 1 with generation of a vehicle speed pulse, and claim 7 is a step. 1903, 1904, 1905.

  As an example of applying claim 1, step 1907 is as follows. When the target posture angle change amount with respect to the movement distance δz of the reference point P is a positive value, the turning center radius R is associated as a value smaller than the target turning radius Re, and the target posture angle corresponding to the movement distance δz of the reference point P When the amount of change is a negative value, data in which the turning center radius R is associated with a value larger than the target turning radius Re is stored in the ROM, and R is derived by tabulating the data.

  In the flowchart 2 (FIG. 8), the turning center when the vehicle is almost stopped or when the turning direction is changed is calculated. In step 2001, it is determined whether or not a vehicle speed pulse is generated for a predetermined time (T1). Here, T1 is a pulse generation interval at a vehicle speed of 1 km / h. Further, in step 2001, when it is detected from the steering operation amount by the driver that the turning center required for the vehicle has changed from right to left or vice versa, the routine proceeds to step 2002. If none of the above applies, this routine is terminated.

  In step 2002, the turning center elevation angle is immediately set to the target attitude angle β, and in step 2003, the turning center radius R is immediately set to the target turning radius Re, and this routine is finished.

  According to the flowchart 2, claim 6 of the present invention is realized.

Then the target turning angle of each wheel from a target wheel-turning center (point Q) (front left wheel .DELTA.Fl ^*, right front wheel .DELTA.fr ^*, left rear wheel δrl ^*, rear right wheel .DELTA.RR ^*) for explaining an example of calculating the. Experiments on the relationship between each wheel turning angle and the turning center when the turning angle (front left wheel δfl, front right wheel δfr, rear left wheel δrl, rear right wheel δrr) of each wheel is changed within an adjustable range. Sought after. At this time, the turning center is uniquely determined with respect to the turning angle of the four wheels. Conversely, when the turning center is determined, the combination of the four wheel turning angles is not uniquely determined, and there is a degree of freedom of the combination.

  Therefore, in those degrees of freedom, as shown in FIG. 9, in the combination when the turning angle of each wheel is determined so that the line connecting each wheel and the turning center is orthogonal to the direction of each wheel. Associate each wheel turning angle with the turning center.

  However, when the turning center is sufficiently away from the vehicle (when the vehicle travels substantially straight), a combination that realizes toe-in that sufficiently keeps the vehicle straight running stability is selected and associated. By associating in this way, the running resistance when the vehicle is run at a low speed can be reduced, and the energy required for running can be suppressed. In addition, since the slip angle of the tire of each wheel is reduced, an effect of suppressing tire slip noise can be obtained.

As described above, the data in which the turning angles (front left wheel δfl, front right wheel δfr, rear left wheel δrl, rear right wheel δrr) of each wheel are associated with the turning center in a possible range in the ROM. storage, and the data target steering angle of each wheel to the target wheel-turning center point Q by look-up (the front left wheel .DELTA.Fl ^*, right front wheel .DELTA.fr ^*, left rear wheel Derutarl ^*, rear right wheel .DELTA.RR ^*) operations To do.

  Here, since the turning center changes depending not only on the wheel turning angle but also on the speed of the vehicle, the influence is experimentally obtained in advance and given as the ROM data, and the vehicle speed is also referred to. Then it is better.

In step 1404, the steering angle of each wheel (left front wheel .DELTA.Fl, front right wheel .DELTA.fr, left rear wheel Derutarl, rear right wheel .DELTA.RR) the target turning angle ^{δfl *, δfr *, δrl *} , to match the .DELTA.RR ^* The current command value commanded to the 20, 21, 22, and 23 DC motor drive circuits is calculated. Here, the relationship between the detected value of each stroke sensor and each wheel turning angle is experimentally obtained, and the relationship data is stored in advance in a ROM and is tabulated, so that the turning angle of each wheel is determined as a stroke. Each detected turning angle value is calculated from the detected values of the sensors 31, 32, 33, and 34.

  The current command value is feedback-calculated so that the detected turning angle value of each wheel matches the target turning angle. There are PID control, sliding mode control, model reference control, and the like as feedback calculation methods, but since all of them are generally well known, detailed description thereof is omitted here.

  FIG. 6 shows the result of simulating the control system in such an embodiment and simulating under the conditions of FIG. Even between the points B and C, it is possible to gradually change the posture angle while keeping the turning radius of the vehicle constant.

  In the above description, the case of a vehicle having a mechanism that can independently adjust the turning angles of the four wheels has been described. Applicable.

  FIG. 10 shows a configuration of a second embodiment in which the present invention is applied to a vehicle including a mechanism in which the left and right turning angles cannot be adjusted independently for both the front and rear wheels.

  In FIG. 10, 45 and 46 are actuators that simultaneously adjust the left and right turning angles, and have a DC motor and can move the rack stroke to the left and right via a worm gear. When the present invention is applied to such a mechanism, the target turning angle calculating means and the turning angle adjusting means in the first embodiment may be changed as follows.

Regarding the target turning angle calculation, after calculating the target turning center in the same manner as described above, the stroke amount before and after realizing the turning center may be calculated (at this time, the target value is the turning angle). Rather, there is virtually no inconvenience that the stroke amount corresponds to the turning angle). Experimentally, the front and rear wheel stroke amounts with respect to the turning center are measured in advance, the data is stored in the ROM, and the data is tabulated to target the front and rear wheel target stroke amounts (front wheel STf ^* , rear wheel STr ^* ). Is calculated. As described above, the influence of the vehicle speed is also stored as ROM data, and it is even better to refer to the vehicle speed.

With this configuration, the turning angle adjustment means performs feedback control on each wheel so that the detected values of the front and rear stroke sensors coincide with the target stroke amounts of the front and rear wheels (front wheel STf ^* , rear wheel STr ^* ). To do. As feedback control methods, there are PID control, sliding mode control, model reference control, and the like.

  Similarly, it can be similarly applied to a mechanism in which only the front wheels or the rear wheels cannot independently adjust the left and right turning angles, and the front wheels are uniquely determined mechanically according to the steering operation amount of the driver, and only the rear wheels are The same applies to a mechanism that can be adjusted independently of the steering operation amount. Even in such a case, the target turning angle calculation means and the turning angle adjustment means may be similarly configured according to the above-described modification according to the mechanism.

  Further, the target posture angle may be stored in a memory as pre-mapped data and used.

  As described above, the case where the vehicle is moving forward has been described. However, when the vehicle is moving backward, it can be similarly realized by taking the backward direction as the positive direction of the x-axis. For example, in a vehicle equipped with an automatic transmission and capable of selecting a forward / reverse command by a driver, it is determined that the vehicle is moving forward while the forward command is issued. Then, it may be determined that the vehicle is moving backward while the reverse command is issued.

1 is a system configuration diagram illustrating a configuration of a vehicle to which a front and rear wheel steering angle control device according to a first embodiment is applied. It is a block diagram which shows the structure of the front-and-rear wheel steering angle control apparatus of Example 1. FIG. 3 is a schematic flowchart illustrating the operation of the first embodiment. It is a figure which shows the example of a production | generation of a target turning radius. It is a figure which shows the example of a production | generation of a target attitude angle. It is a figure which shows the simulation result of Example 1. FIG. It is the flowchart 1 which calculates the target turning center of Example 1. FIG. It is the flowchart 2 which calculates the target turning center of Example 1. FIG. It is a figure explaining the steering angle calculation method of each wheel. FIG. 6 is a diagram illustrating Example 2. It is a figure explaining the range which a turning center can take. It is a figure explaining the definition of the term used by this invention. It is a graph which shows the change of the rudder angle by the simulation of the front-and-rear wheel steering control in a 1st prior art, a vehicle skid angle, and a yaw rate. It is a figure which shows the control system of the 2nd prior art. It is a figure which shows the example of conditions of the simulation for demonstrating the problem of a 2nd prior art. It is a figure which shows the example of a simulation result for demonstrating the problem of 2nd prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Front wheel 2 Rear wheel 3 Steering wheel 4 Steering angle sensor 5 Front wheel steering actuator 6 Rear wheel steering actuator 7 Steering angle sensor 8 Steering angle sensor 9 Vehicle speed sensor 10 Yaw rate sensor 12 Front and rear wheel steering angle control device 13 Drive circuit

Claims (7)

In the vehicle front and rear wheel steering angle control device including a device for independently controlling the steering angle of the front wheel and the steering angle of the rear wheel,
Target turning radius calculating means for calculating a target turning radius Re of the reference point P on the vehicle based on the steering operation amount;
Target posture angle calculation means for calculating a target posture angle β of the reference point P;
While calculating the target turning angle of the front and rear wheels based on the target turning radius Re and the target posture angle β, while increasing the target posture angle β, the front and rear wheel target turning angles when the target posture angle is constant are set. On the other hand, while correcting the target turning angle so that the turning center point Q approaches the vehicle and reducing the target posture angle β, the front and rear wheel target turning angles when the target posture angle is constant, Target turning angle calculation means for correcting and calculating the target turning angle in a direction in which the turning center point Q moves away from the vehicle;
A vehicle front and rear wheel steering angle control device characterized by comprising: In the vehicle front and rear wheel steering angle control device including a device for independently controlling the steering angle of the front wheel and the steering angle of the rear wheel,
While calculating the target turning angle of the front and rear wheels based on the target turning radius Re of the reference point P on the vehicle calculated based on the steering operation amount and the target attitude angle β of the reference point P,
While increasing the target posture angle, the target turning angle is corrected so that the turning center point Q approaches the vehicle with respect to the target turning angle when the target posture angle β is constant,
While the target posture angle is reduced, the target turning angle calculation for correcting the target turning angle so that the turning center point Q moves away from the vehicle with respect to the target turning angle when the target posture angle β is constant. Means,
A vehicle front and rear wheel steering angle control device characterized by comprising:   The target turning angle calculation means sets the turning center radius R to approximately 1 / R = 1 / Re + δβ according to the amount of change δβ / δz of the target attitude angle with respect to the target turning radius Re and the movement distance δz of the vehicle reference point P. 3. The vehicle according to claim 1, wherein the target turning angle is calculated so that a point Q having a turning center elevation angle θ of approximately β is set as a turning center point. Front and rear wheel steering angle control device. The target posture angle calculating means, the front and rear of the vehicle according to claim 1 Symbol mounting, characterized in that the target posture angle variation .delta..beta / .delta.z for travel .delta.z of the reference point P to calculate the target attitude angle so as not to suddenly changed Wheel steering angle control device.   The vehicle has at least one vehicle speed sensor that outputs a pulse every time a certain point on the vehicle moves by a certain distance, and the target turning angle calculation means executes calculation in synchronization with the pulse of the vehicle speed sensor. The front and rear wheel steering angle control device for a vehicle according to any one of claims 1 to 4. Vehicle speed detecting means for detecting the moving speed of the vehicle,
When the target turning angle calculation means can assume that the vehicle is almost stopped, the turning center radius R coincides with Re regardless of the direction and rate of change of the target posture angle, and the turning is performed. The vehicle front and rear wheel steering angle control device according to any one of claims 1 to 5, wherein a target turning angle is calculated from a point Q at which the central elevation angle θ is β.   The target turning angle calculation means is configured to limit the upper limit value of the change amount δθ / δz of the turning center elevation angle θ with respect to the movement distance δz of the reference point P according to the target posture angle and the target turning radius Re. The vehicle front and rear wheel steering angle control device according to any one of claims 1 to 6, wherein a steering angle is calculated.

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