JP3972711B2 - Rear wheel steering device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rear wheel steering device that can improve not only the front wheels but also the rear wheels according to the motion state of the vehicle to improve the running stability of the vehicle. The present invention is applied to a rear-wheel steering device that performs rear-wheel overhang suppression control that prevents an operation to protrude outside the front traveling locus.
[0002]
[Prior art]
Conventionally, there has been known a rear wheel steering control device capable of improving the running stability and turning ability of a vehicle by controlling the steering angle of a rear wheel in response to steering of a front wheel by a driver's steering operation. Yes. In such a rear wheel steering device, there is a problem of how to set an optimal target rear wheel steering angle in accordance with the front wheel steering angle and the situation of the vehicle. For example, in the publication “Automotive Steering System and Maneuverability” (publishing place: Sankai-do Co., Ltd., author: Kayaba Kogyo Co., Ltd., first printing issue date: September 10, 1996), page 7.5, “7.5 According to the column “.3 Side slip zeroing 4WS control” (hereinafter referred to as “Publication 1”), pay attention to the vehicle body slip angle (deviation angle between the vehicle traveling direction and the vehicle longitudinal direction). In order to make the slip angle zero, the rear wheel steering angle is controlled in the opposite phase in proportion to the front wheel rudder angle below the predetermined vehicle speed to ensure the turning ability, while the rear wheel angle is proportional to the front wheel rudder angle above the predetermined vehicle speed. It is described that ideal vehicle characteristics with excellent maneuverability can be obtained by controlling the wheel steering angle in phase (hereinafter, this control is referred to as “steering angle proportional control”, see FIG. 12).
[0003]
In the steering angle proportional control described in the publication 1, in the case of a low speed range where the vehicle starts from a stop, the rear wheel is steered in a reverse phase with respect to the front wheel, thereby improving the turning ability. is there. However, in this case, if the steering angle of the rear wheels is large, the rear end of the vehicle (especially the shoulder of the rearmost end of the vehicle) will protrude outside the traveling locus of the front end of the vehicle, and the driver will be careless. When the steering is completed, the vehicle easily comes into contact with an obstacle on the side of the vehicle.
[0004]
Therefore, in order to solve the problem of overhang of the rear end of the vehicle and to ensure a small turning ability, the publication “105 4WS car” in the publication “The Society of Automotive Engineers of Japan Academic Lecture Preprint 882 Showa 63-10” There is a method for controlling the rear wheel steering angle so that the rear end of the vehicle follows the front end locus of the vehicle, as described in “One Control Method for Controlling Overhang” (hereinafter referred to as “Publication 2”). Proposed. Specifically, the traveling locus of the front end of the vehicle is stored for each predetermined sampling distance, and the traveling direction of the front end of the vehicle at the nearest sample point that is closest to the rear end of the vehicle at that point in time is stored. And the rear wheel rudder angle value are controlled so that the traveling direction of the rear end of the vehicle coincides.
[0005]
In addition, in the Japanese Patent Application No. 2001-242842, the applicant of the present application uses the front point g as the front end point and the rear side of the vehicle among the two points where the line segment having the two points at both ends is parallel to the vehicle front-rear direction. The target point is set so that the rear end point f is set to the rear end point f, an averaged trajectory obtained by smoothly averaging the traveling trajectory of the front end point g is calculated, and the rear end point f does not protrude from the inner region of the averaged trajectory. An invention for calculating a target rear wheel steering angle so as to limit the angle is performed.
[0006]
[Problems to be solved by the invention]
In the rear wheel steering control device that performs the rear end protrusion suppression control that suppresses the rear end protrusion as described above, the steering angle of the rear wheel does not necessarily correspond to the steering operation of the driver. For example, immediately after starting the vehicle, if the steering angle of the rear wheel is zero and an attempt is made to make a large turn, the rear wheel will first be steered largely in reverse phase with the front wheel by normal rear wheel steering angle control. To do. Here, in order to suppress the protrusion of the rear end, the rear wheel may be in phase with the front wheel. However, when the front wheels and the rear wheels are in phase, the vehicle feels to move in parallel, contrary to the driver's intention to turn, and the driver feels a great sense of discomfort.
[0007]
In order to cope with this, it is conceivable to prohibit a state in which the front wheels and the rear wheels are in phase in the rear end overhang suppression control. In this case, since the front wheels and the rear wheels are not in phase, it is possible to prevent the driver from feeling uncomfortable due to the parallel movement. Since the rear end protrusion is the same as that of a two-wheel steering vehicle, there is no particular problem. However, if the vehicle travels for a while in this state, the rear end overhang suppression control will turn the rear wheel at a large angle in an attempt to control the rear wheel in the opposite phase to the front wheel. If the rudder angle amount of the rear wheels at this time is large, the driver has a great sense of incongruity in the sudden rear wheel rudder angle control.
[0008]
Therefore, in the present invention, the first problem is to eliminate the driver's uncomfortable feeling caused by the vehicle moving in parallel when the vehicle is running at a low speed.
[0009]
In the present invention, a second problem is to eliminate the driver's uncomfortable feeling due to abrupt steering of the rear wheels by the rear end overhang suppression control.
[0011]
[Means for solving the problems]
  In order to solve the second problem, in the present invention, a claim is provided.1In the rear wheel steering device that steers the rear wheel in accordance with the steering angle of the front wheel, the rear end overhang suppression control means for suppressing the rear end overhang of the vehicleWhen,When the rear end overhang suppression control means steers the rear wheel so as to suppress the rear end overhang,Rear wheel steering speed limiting means for limiting the rear wheel steering speed to a range in which the yaw rate fluctuation speed difference is within an allowable range around the target angular speed of the rear wheel steering angle;Prepared. According to this, the amount of change per unit time of the target rear wheel steering angle when the rear end overhang suppression control means steers the rear wheel so as to suppress the rear end overhang.The value of the target rear wheel steering angle is changed so that the yaw rate fluctuation speed difference does not exceed the allowable range around the target angular speed of the rear wheel steering angle.The rear wheel steering angle is changed slowly by the rear end overhang suppression control.
[0012]
    In order to solve the first and second problems, the present invention claims2In the rear wheel steering device that steers the rear wheel in accordance with the steering angle of the front wheel, the rear end overhang suppression control means for suppressing the rear end overhang of the vehicleWhen,In-phase steering angle limiting means for limiting the steering angle so that the front and rear wheels are not steered in the same phase when the rear end overhang suppression control means steers the rear wheel so as to suppress the rear end overhang; When the end overhang suppression control means steers the rear wheel to suppress the rear end overhang,Rear wheel steering speed limiting means for setting the rear wheel steering speed to a range in which the yaw rate fluctuation speed difference is within an allowable range around the target angular speed of the rear wheel steering angleEquipped with. According to this, when the rear wheels are controlled so that the rear end overhang suppression control means suppresses the rear end overhang, the front wheels and the rear wheels are not steered in the same phase. Further, in the state where the rear end overhang suppression control means is not working, the in-phase of the front wheel and the rear wheel is allowed. In addition, when the rear end overhang suppression control means steers the rear wheel so as to suppress the rear end overhang, the amount of change per unit time of the target rear wheel steering angle isThe difference in yaw rate fluctuation that is allowed around the target angular velocity of the rear wheel rudder angleSince the value of the target rear wheel steering angle is changed so as not to exceed, the rear wheel steering angle is changed slowly by the rear end overhang suppression control.
[0013]
The specific range may be a predetermined value given in advance, or may be adjusted according to the running state.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a conceptual diagram of a vehicle including a rear wheel steering control device according to the present invention. In the vehicle 1, wheel speed sensors 9 that detect the rotational speeds of the wheels of the front wheels are disposed on the front wheels 3. The wheel speed sensor 9 emits a pulse every time the front wheel 3 rotates by a predetermined angle. Since the traveling distance can be obtained by counting the number of pulses, the wheel speed sensor 9 has a function as a traveling distance sensor. Yes. An actuator 15 for steering the rear wheel 5 is disposed at the rear of the vehicle. The actuator 15 is provided with a rear wheel steering angle sensor 13 for detecting the actual steering angle amount of the rear wheel 5. A steering wheel 7 that steers the front wheels 3 is provided with a front wheel steering angle sensor 11 that detects an actual steering angle amount of the front wheels 3. In the vehicle, a shift position sensor 23 for detecting the shift position of the transmission of the vehicle, a yaw rate sensor 17 for detecting the yaw rate generated in the vehicle 1, a controller 21 for controlling the actuator 15, and a vehicle engine are activated. An ignition switch 19 is attached. The outputs of the front wheel steering angle sensor 11, the rear wheel steering angle sensor 13, the wheel speed sensor 9, the shift position sensor 23, the yaw rate sensor 17, and the ignition switch 19 are input to the controller 21. The controller 21 calculates the target rear wheel steering angle according to the detection values of these various sensors, and gives a command to the actuator 15 so that the actual rear wheel steering angle amount becomes the target rear wheel steering angle.
[0018]
Next, the outline of the control will be described with reference to FIG. 10 which is a model diagram of the vehicle. Here, each angle is expressed as an angle in which the counterclockwise direction in the drawing is positive. In FIG. 10, a point g indicates a front end point of the vehicle, and a point f indicates a rear end point of the vehicle.
[0019]
Points a, b, c, and d are sampling points on the traveling locus 30 of the front end point g. The front end point g travels in the order of the points d, c, b, and a, and the point a is the latest sampling. A point indicates the current position of the front end point g. The wheel speed sensor 9 emits a pulse every time the rotation angle of the front wheel 3 reaches a predetermined angle, and the latest sampling point is updated every time the wheel speed sensor 9 transmits a pulse. Therefore, the sampling distance Dx, which is the distance between these sampling points, corresponds to the travel distance of the vehicle when the front wheel 3 rotates by a predetermined angle.
[0020]
A curve 32 represents an averaged trajectory obtained by smoothly averaging the actual travel trajectory 30 of the front end point g using an arc. The averaging trajectory 32 is updated as the sampling points are updated, as will be described later. The point e is a predetermined distance = k · Dx (k is a natural number obtained by rounding off the value of the total vehicle length Le / Dx from the latest sampling point a toward the rear end point f on the average trajectory 32, and k · Dx is , And the vicinity of the rear end point f on the averaged trajectory 32. The total length of the vehicle, that is, a distance approximately equal to the distance between the front end point g and the rear end point f). θfear represents the traveling direction angle of the front end point g on the averaged locus at the neighboring point e. In FIG. 10, since the vehicle is turning to the left in the traveling direction, the inner region of the averaged trajectory 32 of the front end point g is the left region in the traveling direction with respect to the averaged trajectory 32 (left side in FIG. 10). ).
[0021]
θet is a deviation angle between the line segment connecting the latest sampling point a and the rear end point f and the line segment connecting the latest sampling point a and the rear end point vicinity point e on the averaged trajectory. The deviation angle θet is calculated as a positive value in the state shown in FIG. 10, and the positional relationship between the rear end point f and the rear end point neighboring point e on the averaged trajectory is reversed with respect to the latest sampling point a. When it is in the state, it is calculated as a negative value.
[0022]
If it is intended to prevent the rear end point from protruding, the rear wheel rudder angle may be adjusted so that the rear end point f passes through the inner region of the averaging trajectory 32. In the present embodiment, the rear wheel steering angle is adjusted so that the rear end point f is an inner region of the averaged trajectory 32 and approaches the averaged trajectory 32, that is, to reduce the deviation angle θet.
[0023]
FIG. 11 is a schematic diagram showing how the averaging trajectory 32 is updated each time the latest sampling point changes. A case where the front end point g of the vehicle travels a distance Dx from the previous sampling point a1 at time t1 and moves to a new sampling point a0 at time t0 is shown. In the previous sampling point, the vicinity point of the rear end point f is e1, the averaging trajectory is 32 (t1), the length is k · Dx, and the center angle is k · θato. When the sampling point is updated to a new sampling point a0, the averaging trajectory is updated from 32 (t1) to 32 (t0), and the vicinity point of the rear end point is updated from e1 to e0.
[0024]
At this time, in this embodiment, the vicinity point e0 of the rear end point is placed on the previous average trajectory 32 (t1), and the average trajectory 32 (t0) is set to the sampling point a0 and the rear end point vicinity point e0. An arc having both ends and a length of k · Dx is set as an arc at the latest sampling point a0. The length k · Dx corresponds to the central angle k · θat of the averaging locus 32 (t0). In this way, the vicinity point of the rear end point is always set to be the inner region of the traveling locus of the front end point. By setting the averaging trajectory 32 as described above and adjusting the steering angle of the rear wheels so that the rear end point f passes through the inner region of the average trajectory 32, the rear end point can be prevented from protruding.
[0025]
Next, details of the control of the controller 21 will be described with reference to FIGS.
[0026]
FIG. 2 shows a main routine executed by the controller 21. When the ignition switch 19 is turned on, the main routine starts and the routine proceeds to step 101.
[0027]
In step 101, various variables are initialized. As shown in FIG. 3, the specific contents of the initialization process in step 101 are set to 0 rad for both θfeao and θato, and the current time is set to t0. Further, a time obtained by subtracting an initial vehicle speed pulse input interval time Td0 which is a predetermined value from the current time t0 is set as t1. Further, the actual rear wheel steering angle δm detected from the rear wheel steering angle sensor 13 is substituted into variables δrlimits1, δrlimit, and δrlimitst0, respectively. The variables δrlimits1 and δrlimitst0 are variables representing the smoothed limit value (rad) of the target rear wheel steering angle, δrlimits1 is the previous value in the calculation cycle, and δrlimitst0 is the value at time t0. δrlimit is a variable representing the limit value of the rear wheel steering angle. In the initialization process, the current actual rear wheel steering angle Δm is given to Δrlimits1, Δrlimits, and Δrlimitst0.
[0028]
When the initialization process is executed, the process proceeds to step 102. The processing from step 102 to step 110 is then repeatedly looped. On the other hand, if an output pulse from the wheel speed sensor 9 is input while the loop process is being executed, a vehicle speed sensor pulse input process as shown in FIG. 4 is executed as needed as an interrupt process. In the vehicle speed sensor pulse input process, a sampling point update process is performed.
[0029]
In the vehicle speed sensor pulse input process, the limit value δrlimits for which the target rear wheel steering angle is smoothed at the interrupt time t0 is substituted for δrlimitst0, δrlimit is substituted for δrlimit1, time t0 is assigned to time t1, and the current time is assigned to time t0. substitute. The time of the latest sampling point is t0, and the time of the previous sampling point is t1. Δrlimits is a value calculated by a rear wheel limit steering angle smoothing calculation process or the like, which will be described later. By substituting this value into Δrlimitst0, the limit value subjected to the smoothing process of the target rear wheel steering angle at the latest sampling point is held as Δrlimitst0. In addition, δrlimit is an actual rear wheel steering angle δm in the initial value, but thereafter is a calculated value of a limit value of the rear wheel steering angle calculated by a rear wheel limit steering angle calculation process described later. By substituting this value into δrlimit1, the value is held as the rear wheel steering angle limit value δrlimit1 at the previous sampling point. That is, at the latest sampling point, the interrupt time is t0, the target smoothed steering wheel limit value is δrlimitst0, and at the previous sampling point, the interrupt time is t1, and the rear wheel steering angle limit value. Is δrlimit1. In this way, the sampling point is updated each time this interrupt is executed.
[0030]
In step 102, it is determined whether or not the control cycle Ts has elapsed. If the control cycle Ts has not elapsed, the next processing is suspended until it has elapsed. The control cycle Ts is set to a value larger than the time required for the main routine to make a round. When the control cycle Ts has elapsed, the process proceeds to the next step 103. In step 103, signals from various sensors such as the wheel speed sensor 9 and the front wheel steering angle sensor 11 are taken in and the current situation of the vehicle is grasped.
[0031]
In step 104, normal rear wheel steering angle calculation is performed based on the information from the various sensors input in step 103. The normal rear wheel rudder angle calculation is a calculation in which the controller 21 calculates the normal target rear wheel rudder angle δrt0 based on a control rule that is fundamental in calculating the optimum target rear wheel rudder angle. In this embodiment, steering angle proportional control is adopted as a basic control law. The steering angle proportional control is a method in which a value proportional to the actual front wheel steering angle δf is set as the target rear wheel steering angle. Furthermore, here, the target rear wheel steering angle is changed according to the vehicle speed. Specifically, as shown in FIG. 5, the rear wheel / front wheel steering angle ratio map shown in FIG. 12 is a rear wheel / front wheel steering angle ratio ratio_map (v) corresponding to the vehicle speed v obtained from the output of the wheel speed sensor 9. The normal target rear wheel steering angle δrt0 is obtained by multiplying it by the actual front wheel steering angle δf. The rear wheel / front wheel steering angle ratio ratio_map (v) is set to a negative value below a predetermined vehicle speed and to a positive value above a predetermined vehicle speed. Therefore, the normal target rear wheel steering angle δrt0 is calculated in phase opposite to the actual front wheel steering angle δf below the predetermined vehicle speed, and the normal target rear wheel steering angle δrt0 is calculated in phase with the actual front wheel steering angle δf above the predetermined vehicle speed. It has become so.
[0032]
In step 105, it is determined whether or not the vehicle speed sensor pulse input process, which is the interrupt process described above, has been performed. If the vehicle speed sensor pulse input process has been performed, the process proceeds to the rear wheel limit steering angle calculation in step 106. If the vehicle speed sensor pulse input process has not been performed, the process proceeds to step 107 without performing step 106. That is, the rear wheel limit steering angle calculation process is performed only when the latest sampling point is updated.
[0033]
In step 106, a rear wheel limit steering angle calculation is performed. In this rear wheel limit steering angle calculation routine, a target rear wheel steering angle limit value δrlimit is calculated. The details are shown in FIG. In the rear wheel limit steering angle calculation routine, the previous values θfeao and θato of the traveling direction angle θfea of the front end point on the averaged trajectory and the trajectory angle θat of the front end point on the averaged trajectory are determined in step 208 described later. Saved.
[0034]
First, at step 201, the traveling direction angle θfe of the front end point is set to the absolute angle θb of the vehicle body, the actual front wheel steering angle δf, the rear wheel steering angle δr, the axle length Lf from the center of gravity to the front wheels, and the axle length Lr from the center of gravity to the rear wheels. Using the wheel base L (= Lf + Lr), the length Lfe from the center of gravity to the front end, the yaw rate γ, and the vehicle speed v, the following calculation is performed.
[0035]
(Equation 1)
θfe = θb + Lr / L · δf + Lf / L · δr + Lfe · γ / v
Next, in step 202, the trajectory angle θat of the front end point on the averaged trajectory is changed to the travel direction angle θfe of the front end point, the previous value θfeao of the front end point of the front end point on the averaged trajectory, and the front end on the averaged trajectory. Using the previous value θato of the locus angle of the point, it is calculated by the following formula.
[0036]
(Equation 2)
θat ＝ f^-1(sin (θfe−θfeao + (k−1) · θato) + (1-cos ((k−1) · θato)) / θato)
Where f (θ) = (1−cos (k · θ)) / θ)
From this equation, the trajectory angle θat, which is the average value of the center angles k · θat of the average trajectory as shown in FIG. 11, is obtained.
[0037]
Next, in step 203, the travel direction angle θfea of the front end point on the averaged trajectory at the updated latest sampling point a0 is set to the previous value θfeao of the travel direction angle of the front end point on the averaged trajectory, on the averaged trajectory. Using the trajectory angle θat of the front end point and its previous value θato, the following formula is used.
[0038]
(Equation 3)
θfea ＝ θfeao + k ・ θat− (k−1) ・ θato
Since the trajectory angle θat and the traveling direction angle θfea of the front end point on the averaged trajectory can be obtained by the above formulas 2 and 3, the averaged trajectory at the latest sampling point can be specified.
[0039]
Next, in step 204, the deviation angle θet, which is the angle formed by the rear end point f, the front end point g, and the vicinity point e of the rear end point on the averaged trajectory, is converted into the travel direction angle θfea of the front end point on the averaged trajectory, the average Using the trajectory angle θat of the front end point on the conversion trajectory and the absolute angle θb of the vehicle body, the following equation is used.
[0040]
(Equation 4)
θet = θfea + k · θat / 2−θb
Next, in step 205, the traveling direction angle θfear of the front end point on the averaged trajectory and in the vicinity of the rear end point e is set to the central angle k · θat from the traveling direction angle θfea of the front end point on the averaged trajectory. Subtract and calculate as follows.
[0041]
(Equation 5)
θfear ＝ θfea−k ・ θat
Next, in step 206, the limit value θrelimit of the traveling direction angle θre of the rear end point f is calculated as follows by subtracting C1 · θat from the traveling direction angle θfear of the front end point. Here, C1 is a gain for limiting a predetermined steering angle, and is a value given in advance.
[0042]
(Equation 6)
θrelimit = θfear−C1 ・ θat
The target rear wheel steering angle may be obtained so that the traveling direction angle θre of the rear end point f coincides with the limit value θrelimit.
[0043]
Next, in step 207, using the θrelimit calculated in step 206, the target rear wheel steering angle limit value δrlimit, which is the final calculation target of this routine, is calculated as follows. The calculation formula here calculates the steering angle value of the rear wheels for making the traveling direction angle θre of the rear end point f coincide with the limit value θrelimit.
[0044]
(Equation 7)
δrlimit = L / (Lf + Lre) · (θrelimit−θb) − (Lr−Lre) / (Lf + Lre) · δf
That is, when the rear wheel rudder angle is controlled so that the target rear wheel rudder angle coincides with the target rear wheel rudder angle limit value δrlimit, the rear end point f passes through the inner region of the averaging trajectory, and the rear end point overhangs. Can be suppressed.
[0045]
Finally, in step 208, as preparation for calculation in the next sampling, the traveling direction angle θfea of the front end point on the averaged trajectory and the trajectory angle θat of the front end point on the averaged trajectory are respectively set as the previous values θfeao and θato. Substitute.
[0046]
Here, the physical meaning of the target rear wheel steering angle limit value δrlimit calculated in step 207 will be described. If, in step 206, there is no -C1 · θet term and θrelimit = θfear, the limit value δrlimit of the target rear wheel steering angle in step 207 is the average of the traveling direction angle θre of the rear end point f at the neighboring point e0. It is calculated as a rear wheel steering angle value that matches the traveling direction angle θfear of the front end point on the control locus. Thus, even if the limit value δrlimit is calculated by omitting the term of −C1 · θet, the rear end point f does not protrude from the inner region of the averaged trajectory 32 (t0). However, as shown in FIG. 4, when there is a deviation angle θet, the limit value of the rear wheel steering angle can be relaxed by an angle that takes this deviation angle θet into account, and the rear wheel steering angle can be increased. The rear end point f can be prevented from protruding from the inner region of the arc 32 (t0), which is the averaging trajectory. As described above, this calculation routine assumes only the case where the rear wheel rudder angle is calculated in the opposite phase to the front wheel rudder angle. That is, it is desirable to improve the turning ability by increasing the absolute value of the rear wheel steering angle limit value. Accordingly, in step 206, by adding the term -C1 · θet, the limit value θrelimit of the rear end point traveling direction angle is relaxed and obtained, and the relaxed rear end point traveling direction angle limit value θrelimit is set at the rear end point f. By calculating the target rear wheel steering angle limit value δrlimit so that the rear end point traveling direction angles θre coincide with each other, the target rear wheel steering angle limit value δrlimit is relaxed as much as possible.
[0047]
When C is increased, control is performed so that the rear end point f quickly gets on the averaged trajectory. In this case, the rear end point f temporarily appears outside the averaged trajectory due to control hunting or the like. There is a fear. Therefore, the value of C is preferably adjusted and set according to the characteristics of the vehicle.
[0048]
When step 208 is executed, the rear wheel limit steering angle calculation routine ends, and the process returns to the main routine shown in FIG. Next, a rear wheel limit steering angle smoothing calculation routine in step 107 is executed.
[0049]
In step 107, a rear wheel limit rudder angle smoothing calculation is performed. The target rear wheel steering angle limit value δrlimit is calculated by the rear wheel limiting steering angle calculation (step 207 in FIG. 6). This calculation is performed as shown in steps 105 and 106 in FIG. It is executed only when the input is updated, that is, when the sampling point is updated. Therefore, the limit value Δrlimit of the target rear wheel steering angle is a numerical value for each sampling point and becomes discrete. If this value is adopted as the target rudder angle as it is, the target rudder angle is suddenly changed after the sampling point. Since the sampling interval becomes longer during low-speed traveling, if the target rudder angle is discrete, the steering of the rear wheels also becomes discrete and the feeling becomes worse. Therefore, the target rear wheel steering angle limit value δrlimits, which is a continuous value complementing the discrete target rear wheel steering angle limit value δrlimit, is calculated, and this value is used as the rear wheel steering angle target value. I am doing so.
[0050]
When the rear wheel limit steering angle calculation routine is completed, a rear wheel limit steering angle smoothing calculation routine in step 107 is executed. Details of this routine are shown in FIG.
[0051]
In FIG. 8, as shown in step 401, the limit value δrlimits subjected to the smoothing process of the target rear wheel steering angle has a specific gradient (2δrlimit−δrlimit1−δrlimitst0) to the limit value δrlimits1 subjected to the smoothing process one control cycle before. By adding the increment calculated by multiplying / (t0−t1) by the control cycle Ts, the following equation is obtained.
[0052]
(Equation 8)
δrlimits = δrlimits1 + Ts · (2δrlimit−δrlimit1−δrlimitst0) / (t0−t1)
This particular slope is expressed as a fraction, the denominator is (t0−t1), ie, the sampling interval between time t0 of the latest sampling point and time t1 of the previous sampling point, and the numerator is (2δrlimit −δrlimit1−δrlimitst0) = (δrlimit−δrlimit1) + (δrlimit−δrlimitst0). That is, the difference between the target rear wheel steering angle limit value δrlimit at the latest sampling point and the target rear wheel steering angle limit value δrlimit1 at the previous sampling point is the difference between the target rear wheel steering angle limit value δrlimit at the latest sampling point. And a limit value Δrlimitst0 obtained by smoothing the target rear wheel rudder angle at the latest sampling point. Therefore, at the next sampling, the limit value Δrlimits subjected to the smoothing process of the target rear wheel steering angle is adjusted so as to approach the limit value Δrlimit of the target rear wheel steering angle.
[0053]
FIG. 13 is a diagram schematically showing the process of this interpolation calculation. Point i is the target rear wheel steering angle limit value δrlimit1 at the previous sampling point (at t1), j is the target rear wheel steering angle limit value δrlimit at the latest sampling point (at t0), and k is the latest sampling The limit value Δrlimitst0 subjected to the smoothing process at the point (at time t0) is shown. When the limit value δrlimits smoothed at the next sampling point approaches the limit value of the target rear wheel steering angle, the smoothing process was performed when the current sampling point (at t0) further advanced by (t0−t1). The limit value Δrlimits only needs to be at the point m obtained by extending the line segment ij. Therefore, the limit value δrlimits subjected to the smoothing process of the current target rear wheel steering angle may be determined so that the slope (2δrlimit−δrlimit1-δrlimitst0) / (t0−t1) of the line segment k-m becomes a gradient.
[0054]
When step 401 is executed, the process proceeds to step 402 next. In step 402, as a preparation for executing step 401 in the next control cycle, the current smoothed limit value δrlimits is substituted into the smoothed limit value δrlimits1 one control cycle before.
[0055]
When step 402 is executed, the rear wheel limit steering angle smoothing calculation routine ends. Then, returning to the main routine of FIG. 2, the rear wheel steering angular speed limit calculation of step 108 is executed.
[0056]
In step 108, a rear wheel steering angular speed limit calculation is performed. Here, the amount of change in the smoothed limit value Δrlimits obtained in the above step is viewed, and a process of correcting the limit value Δrlimits according to the magnitude of the amount of change is performed. Note that the smoothing-processed limit value δrlimits before one control period is stored as δrlimits_old in step 608 described later.
[0057]
As shown in FIG. 8, the details of this process are as follows. First, at step 601, the maximum allowable amount Drl_max of the differential value of the limit value and the minimum allowable amount Drl_min of the differential value of the limit value are determined according to the vehicle speed v. / The front wheel rudder angle ratio ratio_map (v), the differential value dδsw / dt of the steering angle δsw, the maximum allowable yaw rate fluctuation speed difference Gtmax, and the yaw rate gain Grdr (0) for the rear wheels are obtained by the following equation.
[0058]
(Equation 9)
Drl_max = ratio_map (v) · dδsw / dt + Gtmax / Grdr (0)
(Equation 10)
Drl_min = ratio_map (v) · dδsw / dt−Gtmax / Grdr (0)
Here, the target angular velocity of the rear wheel steering angle is obtained by multiplying the differential value dδsw / dt of the steering angle δsw by the rear wheel / front wheel steering angle ratio ratio_map (v), and Gtmax / Grdr (0 ), That is, a range in which the yaw rate fluctuation speed difference falls within the allowable range is set as the allowable range.
[0059]
Next, in step 602, it is checked whether or not the time differential value dδrlimits / dt of the limit value δrlimits subjected to the smoothing process exceeds the maximum allowable amount Drl_max of the limit value differential value. In step 603, it is checked whether the time differential value dδrlimits / dt of the smoothed limit value δrlimits has reached the minimum allowable amount Drl_min of the limit value differential value. When the time differential value dδrlimits / dt of the limit value δrlimits subjected to the smoothing process exceeds the maximum allowable amount Drl_max of the differential value of the limit value, in step 605, the limit value δrlimits is differentiated to the limit value δrlimits subjected to the smoothing process. Multiply the maximum allowable value Drl_max by the control period Ts and substitute the previous value δrlimits_old. If the time differential value dδrlimits / dt of the limit value δrlimits subjected to the smoothing process exceeds the minimum allowable amount Drl_min of the differential value of the limit value, in step 604, the limit value δrlimits is differentiated to the limit value δrlimits subjected to the smoothing process. Multiply the minimum allowable value Drl_min by the control period Ts and substitute the previous value δrlimits_old.
[0060]
(Equation 11)
δrlimits ＝ δrlimits_old ＋ Ts ・ Drl_max
(Equation 12)
δrlimits ＝ δrlimits_old ＋ Ts ・ Drl_min
Next, in step 606, it is determined whether or not the sign of the steering angle δsw matches the sign of the limit value δrlimits subjected to the smoothing process of the rear wheel steering angle. If they match, in step 607, 0 (zero) is substituted for the smoothed limit value δrlimits. In other words, if the limit value δrlimits smoothed so that the steering of the front wheels and the steering of the rear wheels are in phase, the smoothed limit value δrlimits is set to zero so that the rear wheels are steered in phase. Is prevented.
[0061]
Finally, in step 608, the current smoothing limit value δrlimits is substituted into δrlimits_old for the next calculation, and this subroutine is terminated, and the process returns to the main routine of FIG.
[0062]
In the rear wheel steering angular speed limit calculation, the steering speed of the rear wheel when the rear end overhang suppression control is performed is limited. Further, the steering angle of the rear wheels is limited so that the front wheels and the rear wheels are not steered in phase when the rear end overhang suppression control is performed.
[0063]
The rear wheel steering speed limitation will be described with reference to FIG. FIG. 14 shows the characteristics of the steering angular velocity dδdw / dt and the rear wheel steering angular velocity dδrlimits / dt when steering is performed. The center dotted line is dδrso / dt = ratio_map (v) · dδsw / dt, and the rear wheel steering angle obtained by multiplying the differential value dδsw / dt of the steering angle δsw by the rear wheel / front wheel steering angle ratio ratio_map (v). Indicates the target angular velocity. Since the rear wheel / front wheel steering angle ratio ratio_map (v) has a negative value at a low vehicle speed as shown in FIG. 12, the inclination of the dotted line is negative. Two parallel solid lines indicate a boundary line dδrlimits / dt = ratio_map (v) · dδsw / dt ± Gtmax / Grdr (0). When the steering angular velocity dδdw / dt and the rear wheel steering angular velocity dδrlimits / dt are out of parallel boundaries, the steering speed of the rear wheels is limited. For example, when the steering wheel angular velocity is zero while the driver holds the steering wheel, the rear wheel steering angular velocity is limited to a range of ± dt−Gtmax / Grdr (0). Then, the limit range of the rear wheel steering angular speed is increased and decreased in inverse proportion to the steering angular speed.
[0064]
When the rear wheel steering angular speed restriction calculation is completed, the target rear wheel steering angle restriction calculation in step 109 is executed. Here, the target rear wheel steering angle δrt, which is the final calculation target of the controller 21, is calculated. The details are shown in FIG. In step 501, it is determined whether the actual front wheel steering angle δf is positive or zero. If the actual front wheel steering angle δf is positive or zero, the process proceeds to step 502, and if the actual front wheel steering angle δf is negative, the process proceeds to step 503. In Step 502, the normal target rear wheel steering angle δrt0 calculated in Step 104 and the target rear wheel steering angle calculated in Step 107 that are smoothed by the limit value δrlimits are large in consideration of the sign. This value is used as the target rear wheel steering angle δrt. On the other hand, in step 503, the smaller one of the normal target rear wheel steering angle δrt0 and the smoothed limit value δrlimits in consideration of the sign is used as the target rear wheel steering angle δrt.
[0065]
During traveling at a low vehicle speed, the rear wheel steering angle is calculated in reverse phase to the front wheels as shown in FIG. Here, when the front wheel is turned in the positive direction, the rear wheel is turned in the negative direction, and δrlimits and δrt0 have negative or zero values. Here, when the absolute value of δrt0 is smaller than the absolute value of δrlimits, δrlimits <δrt0 <0, and the larger normal target rear wheel steering angle δrt0 is used as it is as the target rear wheel steering angle δrt. When the absolute value of δrt0 is larger than the absolute value of δrlimits, δrt0 <δrlimits <0, and the limit value δrlimits subjected to a larger smoothing process is used as the target rear wheel steering angle δrt. When the front wheel is turned in the negative direction, the rear wheel is turned in the positive direction, and δrlimits and δrt0 are positive values. Here, when the absolute value of δrt0 is larger than the absolute value of δrlimits, 0 <δrt0 <δrlimits, and the smaller normal target rear wheel steering angle δrt0 is used as it is as the target rear wheel steering angle δrt. When the absolute value of δrt0 is smaller than the absolute value of δrlimits, 0 <δrlimits <δrt0, and the smaller smoothed limit value δrlimits is used as the target rear wheel steering angle δrt. When traveling at high speed, the rear wheels are in phase with the front wheels. In this case, in step 607, if δrlimits is in phase with the steer angle, δrlimits = 0 is set, and the absolute value of δrlimits <absolute value of δrt0 is always established, so that the normal target rear wheel steering angle δrt0 remains as it is. Used as the angle δrt.
[0066]
Finally, in step 110, the actuator 15 is controlled so that the steering angle of the rear wheels becomes equal to the target rear wheel steering angle δrt. In this control, the actual steering angle of the rear wheel 5 is detected by the rear wheel steering angle sensor 13, and servo control is preferably performed using PID control or the like so that the steering angle becomes equal to the target rear wheel steering angle δrt. Thereby, the rear wheel 5 is controlled to an appropriate steering angle, and the rear end of the vehicle is prevented from protruding at a low vehicle speed.
[0067]
According to the embodiment of the rear wheel steering apparatus according to the present invention described above, the following effects are obtained. That is, the controller 21 limits the target rear wheel steering angle δrt so that the rear end point f of the vehicle does not protrude from the inner region of the averaged trajectory 32 or the like obtained by smoothly averaging the travel trajectory of the front end point g. Even if the rear wheel 5 is steered in reverse phase with respect to the front wheel 3 while the vehicle 1 is traveling in the low speed region, the rear end point f does not protrude from the outer region with respect to the averaged trajectory 32 of the front end point g. The target rear wheel steering angle δrt is limited, and the problem of overhang of the vehicle rear end point f can be solved.
[0068]
Further, since the target rear wheel steering angle δrt is limited based on an averaged trajectory 32 or the like obtained by smoothly averaging the travel trajectory 30 of the front end point g, even when the travel trajectory 30 of the front end point is disturbed, The influence of the disturbance is less likely to be reflected in the calculation result of the target rear wheel steering angle δrt. Therefore, according to the present invention, it is possible to further improve the turning performance of the vehicle.
[0069]
Further, when calculating the target rear wheel steering angle limit value δrlimits, the calculation is performed in consideration of the deviation angle θet, which is a relaxation amount related to the deviation between the rear end point f on the average trajectory and the rear end point f. ing. Therefore, when the deviation occurs, the absolute value of the target rear wheel steering angle limit value δrlimits can be calculated so as to be set larger. Therefore, when the rear wheel 5 is steered in reverse phase with respect to the front wheel 3, it is possible to improve the turning ability while reliably solving the problem of the rear end point f of the vehicle 1 protruding.
[0070]
In addition, when updating the arc 32 which is an averaged trajectory, it can be performed based only on the information of the arc 32 calculated last time and the information of the latest sampling point when the latest sampling point is updated. Accordingly, in calculating the arc 32 that is the averaged trajectory, the controller 21 only needs to store information on the latest sampling point a, and does not need to store information on a plurality of past sampling points. . Further, since the traveling locus 30 is approximated by the arc 32, the geometric characteristics peculiar to the arc can be used, and the averaged locus can be calculated easily compared to a complicated method such as polynomial approximation. it can. Therefore, the work space and memory capacity required for the controller 21 can be saved, and the calculation speed is improved.
[0071]
In addition, when interpolating the limit value δrlimit of the target rear wheel rudder angle to the smoothed limit value δrlimits that is a continuous value, not only the limit value δrlimit1 calculated at the past sampling point input time t1, but also the latest sampling The current smoothed limit value δrlimits from the latest sampling point input time t0 to the next sampling point input time is calculated after taking into account the smoothed limit value δrlimits at the point input time t0. The current smoothed limit value δrlimits is a highly reliable value that also takes into account the trend of increase and decrease of the past limit value and the deviation between the past limit value δrlimit and the smoothed limit value δrlimits. It becomes.
[0072]
Furthermore, the front end point g and the rear end point f are set at the foremost end and the rearmost end of the vehicle 1, respectively. Therefore, the rear end of the vehicle that is most likely to contact an obstacle on the side of the vehicle due to the rear end of the vehicle does not protrude outward from the averaged trajectory 32 related to the front end of the vehicle. It is possible to more reliably prevent contact with the obstacle on the side of the vehicle due to the overhang of the end.
[0073]
In addition, depending on the shape of the vehicle, when it is known that there is an appendage with a shape projecting forward or laterally from the front end point g and an appendage with a shape projecting rearward or laterally from the rear end point f. The calculation may be performed by replacing the front end point g and the rear end point f with the position of the end of the accessory.
[0074]
As described above, the rear wheel steering device of this embodiment is a device for steering the rear wheels in accordance with the steering angle of the front wheels, and the rear wheel limiting steering angle calculation routine 106 for calculating the limiting steering angle of the rear wheels. The rear wheel limit steering angle smoothing calculation routine 107 for smoothing the calculated value, the target rear wheel steering angle limit calculation routine 109 for restricting the normal target rear wheel steering angle of the rear wheel to the limit value, and the actual rear wheel steering. A rear-end overhang suppression control unit including a rear-wheel steering actuator driving step 110 is provided.
[0075]
Further, the steps 601 to 601 limit the rear wheel steering speed dδrlimits / dt, which is a differential value of the limit value of the rear end overhang suppression control means, to a specific range ratio_map (v) · dδsw / dt ± Gtmax / Grdr (0). A rear-wheel steering speed limiting means configured from 604 is provided. Therefore, the limit value δrlimits subjected to the smoothing process is further limited so that the change speed, which is a differential value thereof, does not deviate from the specific range ratio_map (v) · dδsw / dt ± Gtmax / Grdr (0). The rear wheel does not change greatly in response to the operation.
[0076]
FIG. 15 shows a steering angle of 545 ° (left) (front wheel) when a 2WS vehicle (rear wheel steering angle is zero), steering angle proportional control, rear end overhang suppression control, and control according to the embodiment of the present invention is adopted. The simulation results of the vehicle when assuming a U-turn at a left steering angle of 38.93 ° and a constant vehicle speed of 5 km / h are shown. It is assumed that the actual rear wheel steering angle δm at the start when the control according to the embodiment of the present invention is adopted is zero. This is because if the driver steers the steering when the engine is stopped, the rear wheels may be steered along the travel locus before the stop, which may move in any direction.
[0077]
As is apparent from the results of FIG. 15, the target rear wheel steering angle δrt0 changes abruptly at the portion c, whereas when the control according to the embodiment of the present invention is employed, the target as shown by d The change in the rear wheel steering angle δrt0 is gentle.
[0078]
Further, when the limit value of the rear end overhang suppression control means is in phase with the steering angle δs, the rear end overhang suppression control means is In the case where the rear wheels are steered so as to suppress overhanging, there is provided in-phase steering angle limiting means constituted by steps 606 to 607 for limiting the steering angle so that the front wheels and the rear wheels are not steered in phase. Thereby, the parallel movement of the vehicle by the rear end protrusion suppression control does not occur.
[0079]
In the above embodiment, the rear end overhang suppression control is performed by another method, for example, a method of examining the overhang without averaging the travel locus, or an averaged locus proposed in the second embodiment of 001-242842. It is possible to substitute a method such as dividing the number into two or more.
[0080]
【The invention's effect】
According to the first and third aspects of the invention, it is possible to eliminate the driver's uncomfortable feeling due to the vehicle moving in parallel when the vehicle is running at a low speed.
[0081]
According to the second and third aspects of the invention, it is possible to eliminate the driver's uncomfortable feeling due to abrupt steering of the rear wheels by the rear end overhang suppression control.
[0082]
According to the invention of claim 4, since the yaw rate fluctuation due to the steering of the rear wheels is within the allowable speed difference, the driver's uncomfortable feeling can be solved.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a four-wheel steering vehicle including a rear wheel steering device according to the present invention.
FIG. 2 is a flowchart of a main routine executed by a controller.
FIG. 3 is a flowchart showing initialization processing in the embodiment of the present invention.
FIG. 4 is a flowchart showing interrupt processing in the embodiment of the present invention.
FIG. 5 is a flowchart showing normal rear wheel steering angle calculation processing in the embodiment of the present invention.
FIG. 6 is a flowchart showing rear wheel limit steering angle calculation processing in the embodiment of the present invention.
FIG. 7 is a flowchart showing rear wheel limit steering angle smoothing calculation processing in the embodiment of the present invention.
FIG. 8 is a flowchart showing rear wheel steering angular speed limit calculation processing in the embodiment of the present invention.
FIG. 9 is a flowchart showing a target rear wheel steering angle limit calculation in the embodiment of the present invention.
FIG. 10 is a model diagram showing the motion of the vehicle in the embodiment of the present invention.
FIG. 11 is a schematic diagram showing how the averaging trajectory is updated each time the latest sampling point changes.
FIG. 12 is a diagram showing a rear wheel / front wheel steering angle ratio map in steering angle proportional control.
FIG. 13 is a diagram schematically illustrating an interpolation calculation process in the embodiment of the present invention.
FIG. 14 is a graph showing characteristics of a steering angular velocity dδdw / dt and a rear wheel steering angular velocity dδrlimits / dt in the embodiment of the present invention.
FIG. 15 is a graph showing changes in a vehicle speed v, a target rear wheel steering angle δrt, and a steering angle when a vehicle motion simulation is performed.
[Explanation of symbols]
1 vehicle
3 Front wheels
5 Rear wheels
7 Steering
9 Wheel speed sensor
11 Front wheel steering angle sensor
13 Rear wheel steering angle sensor
17 Yaw rate sensor
19 Ignition switch
21 Controller
23 Shift position sensor
30 Actual travel trajectory
30 Traveling track
32 curves
32 Averaging trajectory
a, a0, a1, b, c, d sampling points
C1 Gain for limiting the rudder angle
Drl_max Maximum allowable differential value of the limit value
Drl_min Minimum permissible limit value derivative
Dx sampling distance
dδdw / dt Steer angular velocity
dδrlimits / dt Rear wheel steering angular speed
e, e0, e1 Neighbor points of the rear end point on the averaging trajectory
g Front end point
Grdr (0) Yaw rate gain for rear wheel
Gtmax Maximum allowable yaw rate fluctuation speed difference
k ・ θat, k ・ θato Center angle of averaged trajectory
L Wheelbase
Le / Dx Total length of vehicle
Lf Axle length from center of gravity to front wheel
Lfe Length from the center of gravity to the front edge
Lr Axle length from center of gravity to rear wheel
ratio_map (v) Rear wheel / front wheel rudder angle ratio
t0 Time of latest sampling point
t1 Time of previous sampling point
Td0 initial vehicle speed pulse input interval time
Ts control cycle
v Vehicle speed
γ Yaw rate
δf Front wheel rudder angle
δm Real rear wheel rudder angle
δr Rear wheel rudder angle
δrlimit Limit value of the target rear wheel steering angle at the latest sampling point
δrlimit1 Target rear wheel steering angle limit value at the previous sampling point
δrlimits Smoothed limits
δrlimits1 Limit value that is smoothed before one control cycle
δrlimitst0 Smoothed limit value at the latest sampling point
δrt, δrt0 Normal target rear wheel rudder angle
δsw steering angle
θat, θato Trajectory angle of front end point on average trajectory
θb Absolute angle of vehicle body
θet Deviation angle
θfe Advancing direction angle of front end point
θfea, θfeao Advancing direction angle of front end point on averaging trajectory
θfear Advancing direction angle of the front end point on the averaging trajectory and near the rear end point e
θre Traveling direction angle of rear end point
θrelimit Limit value of the direction angle of the trailing end
Step 106 Rear wheel limit rudder angle calculation
Step 107: Rear wheel limit rudder angle smoothing calculation routine
Step 108: Rear wheel rudder angular speed limit calculation
Step 109 Target rear wheel rudder angle limit calculation

Claims (2)

In the rear wheel steering device that steers the rear wheel according to the steering angle of the front wheel,
Rear end overhang suppression control means for suppressing overhang of the rear end of the vehicle ;
When the rear end overhang suppression control means steers the rear wheel so as to suppress the rear end overhang,
A rear wheel steering apparatus comprising rear wheel steering speed limiting means for limiting a rear wheel steering speed to a range in which a yaw rate fluctuation speed difference is within an allowable range centering on a target angular speed of a rear wheel steering angle . In the rear wheel steering device that steers the rear wheel according to the steering angle of the front wheel,
Rear end overhang suppression control means for suppressing overhang of the rear end of the vehicle ;
In- phase steering angle limiting means for limiting the steering angle so that the front wheels and the rear wheels are not steered in the same phase when the rear end overhang suppression control means steers the rear wheels so as to suppress the rear end overhang ;
When the rear end overhang suppression control means steers the rear wheel so as to suppress the rear end overhang, the rear wheel steering speed is within the allowable range of the yaw rate fluctuation speed centered on the target angular speed of the rear wheel steering angle. A rear-wheel steering device comprising a rear-wheel steering speed limiting means within a range that falls within the range .

Images