Steering control device

Abstract

To provide a steering control device that allows a vehicle to operate stably when turning at a high vehicle speed in an independently steered vehicle with three or more wheels.SOLUTION: A final steering command value generation unit 55 of a steering control device 50 generates a final steering command value St** on the basis of a steering angle signal θst output by a steering mechanism 95 of a steer-by-wire system or a steering command value St* output by a steering command device 96 of automatic driving. A steering angle command value calculation unit 56 calculates steering angle command values θ1*-θ4* for respective wheels 91-94. A plurality of steering actuator control units 601-604 control a drive current energizing the steering actuators so that the steering angles output by the steering actuators 71-74 follow the steering angle command values θ1*-θ4*. The steering angle command value calculation unit 56 calculates the steering angle command value θ1*-θ4* for the respective wheels 91-94 on the basis of the final steering command value St** and a vehicle speed V, so that the higher the vehicle speed V is, the more the steering is suppressed with respect to the final steering command value St**.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a steering control device. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in a steer-by-wire system, a steering device that determines a target steering angle for each of a plurality of independent steering mechanisms is known.

[0003] For example, the host ECU of the steering device disclosed in Patent Document 1 includes a steering angle determination unit that calculates target steering angles for the left and right steering mechanisms based on the steering angle detected by a steering angle sensor. The relationship between the steering angle and the target steering angle is shown in a map. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2019 / 188951 Summary of the Invention [Problem to be solved by the invention]

[0005] If the steering angle command value corresponding to the steering angle by the driver's steering or the steering command value of automatic driving remains the same regardless of vehicle speed, vehicle behavior may change significantly in response to a small steering command when turning at high vehicle speed, which could cause discomfort to the driver and passengers. Patent Document 1 states that the characteristics of the target steering angle relative to the steering angle may change depending on the vehicle speed. However, the prior art in Patent Document 1 only targets vehicles with left and right steerable wheels, i.e., two wheels, that can be steered independently, and does not take into account the behavior of vehicles with three or more independently steerable wheels, including four-wheel independently steerable vehicles.

[0006] The present invention was created in consideration of the above points, and its purpose is to provide a steering control device that allows a vehicle with three or more independently steering wheels to operate stably when turning at high vehicle speeds. [Means for solving the problem]

[0007] The steering control device of the present invention controls the steering of each wheel in a vehicle (100) equipped with a plurality of steering actuators (71-74) that independently steer three or more wheels (91-94) that are not mechanically constrained from one another, and a steering mechanism (95) of a steer-by-wire system or a steering command device (96) for automatic driving that is provided mechanically separated from the steering actuators.

[0008] This steering control device includes a final steering command value generating unit (55), Turning center setting section (56) and a plurality of steering actuator control units (601-604).

[0009] The final steering command value generator generates the steering angle signal (θst) output by the steering mechanism or the steering command value (St * ) based on the final steering command value (St ** ) The turning center setting unit sets the vehicle turning center (C) based on the final steering command value and the vehicle speed (V), and further The steering angle command value for each wheel (θ1 * -θ4 * ) is calculated by the steering angle command value calculation unit. function as The plurality of steering actuator control units are provided corresponding to the plurality of steering actuators, and control the drive currents supplied to the steering actuators so that the steering angles output by the steering actuators follow the steering angle command values.

[0010] The turning center setting unit sets the vehicle turning center while manipulating a turning center setting distance (Dc), which is the distance from the vehicle front-rear axis (Y0) to the vehicle turning center. The turning center setting unit determines the turning center setting distance using a three-dimensional map that defines the relationship between the final steering command value and the turning center setting distance for a plurality of vehicle speeds. In the three-dimensional map, the turning center setting distance in a medium vehicle speed range where the vehicle speed is within a predetermined range and corresponding to the maximum steering angle (θst_max) is set to the same value as the minimum value (DC_min) of the turning center setting distance in a low vehicle speed range that is slower than the vehicle speed in the medium vehicle speed range. The steering angle command value calculation unit calculates a steering angle command value for each wheel based on the final steering command value and the vehicle speed so that the higher the vehicle speed, the more the steering is suppressed relative to the final steering command value. 。

[0011] As a result, the steering control device of the present invention can operate the vehicle stably when turning at high vehicle speeds. By suppressing sudden steering when turning at high vehicle speeds, it is possible to prevent the driver and passengers from feeling uncomfortable. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of an independently steering vehicle to which a steering control device according to an embodiment is applied; [Figure 2] 1A and 1B are diagrams illustrating a turning operation according to Ackermann geometry. [Figure 3] FIG. 10 is a diagram showing a first example of setting the vehicle turning center according to the vehicle speed. [Figure 4] FIG. 4 is a diagram showing the relationship between the steering angle, the vehicle speed, and the turning center setting distance. [Figure 5] FIG. 10 is a diagram showing a second example of setting the vehicle turning center according to the vehicle speed. [Figure 6] FIG. 10 is a diagram showing a third example of setting the vehicle turning center according to the vehicle speed. [Figure 7] 10 is a flowchart of a steering angle command value calculation process. [Figure 8] 1A and 1B are diagrams illustrating a turning operation according to parallel geometry. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of a steering control device according to the present invention will be described with reference to the drawings. The steering control device of this embodiment controls the steering of each wheel of a vehicle (four-wheel independently steering vehicle) in which four wheels that are not mechanically constrained from one another can be steered independently.

[0014] (One embodiment) The configuration of an independently steering vehicle 100 to which steering control device 50 of one embodiment is applied will be described with reference to Figure 1. Four wheels 91-94 of vehicle 100 are not mechanically constrained to one another and can be steered independently. The left front wheel 91 is labeled "FL", the right front wheel 92 "FR", the left rear wheel 93 "RL", and the right rear wheel 94 "RR". For example, each wheel 91-94 is a drive wheel equipped with an in-wheel motor, and can be steered independently as well as driven independently.

[0015] Four steering actuators ("Steering Act" in the figure) 71-74 steer the wheels 91-94, respectively. For example, in this embodiment, steering actuators 71-74 are configured with dual-system three-phase brushless motors having two redundant winding sets. Four steering actuator control units ("Steering Act control unit" in the figure) 601-604 are provided corresponding to the four steering actuators 71-74. The steering actuators 71-74 and steering actuator control units 601-604 operate by receiving power supply voltage from an on-board battery (not shown).

[0016] In this embodiment, vehicle 100 is equipped with both a steering mechanism 95 of a steer-by-wire system that is provided mechanically separated from steering actuators 71-74, and an automatic driving steering command device 96. Note that in other embodiments, vehicle 100 may be equipped with only one of steering mechanism 95 or steering command device 96.

[0017] A steering wheel 95 is typically used as the steering mechanism of a steer-by-wire system, but other steering mechanisms such as a joystick may also be used. A steering angle signal θst is output when the driver manually operates the steering wheel 95. The steering command device 96 is realized by, for example, an ADAS (Advanced Driver Assistance System), and outputs a steering command value St according to the route to the destination and road conditions. * Output.

[0018] The steering control device 50 comprises a final steering command value generating section 55, a turning center setting section 56, and a plurality of steering actuator control sections 601-604.

[0019] The final steering command value generating unit 55 receives the steering angle signal θst output from the steering wheel 95 and the steering command value St output from the steering command device 96. * Based on the final steering command value St ** Here, the steering command value St * and final steering command value St **is assumed to be an angle dimension value equivalent to the steering angle. However, for example, a torque dimension value may be used as the angle correlation amount. * and final steering command value St ** is defined to be 0 when the vehicle 100 is traveling straight, and to take a positive or negative value depending on the steering direction relative to the neutral position. For example, it is expressed as a positive value when turning left, and a negative value when turning right.

[0020] Final steering command value St ** is a quantity that is mediated by taking into consideration the priority of manual driving and automated driving. In a situation where the driver is primarily driving manually and the automated driving system provides auxiliary steering assistance, the contribution ratio of the steering angle signal θst is set high. During driving assistance such as lane keep assist, the steering command value St * When a steering torque whose absolute value is equal to or greater than a predetermined value is input due to the driver's intention during driving assistance, the steering angle signal θst is switched to have priority.

[0021] The turning center setting unit 56 receives the final steering command value St from the final steering command value generating unit 55. ** is input to the turning center setting unit 56, and the vehicle speed V is input from the vehicle speed sensor 97 of the vehicle 100. The turning center setting unit 56 receives the final steering command value St ** and the vehicle speed V. The details will be described later. Also, the turning center setting unit 56 calculates the turning angle command value θ1 of each wheel 91-94 from the turning center C of the vehicle. * -θ4 * That is, the turning center setting unit 56 calculates the final steering command value St ** and the vehicle speed V, the steering angle command value θ1 of each wheel 91-94 via the vehicle turning center C is calculated. * -θ4 * By calculating the above, the control unit 100 functions as a "steered angle command value calculation unit."

[0022] The steering actuator control units 601-604 are configured to control the steering angle output from the steering actuators 71-74 in accordance with the steering angle command value θ1 * -θ4 *The driving currents Ia1-Ia4 supplied to the steering actuators 71-74 are controlled so as to follow the steering angle. The steering angle is defined, for example, with the neutral position as the reference, so that the left side is positive and the right side is negative. In the following description, the term "maximum steering angle" means the steering angle at which the absolute value is maximum, regardless of sign.

[0023] A set of a steering actuator and a steering actuator control section corresponding to each of wheels 91-94 is referred to as a unit. Steering actuator 71 and steering actuator control section 601 form FL unit 81 corresponding to left front wheel 91. Steering actuator 72 and steering actuator control section 602 form FR unit 82 corresponding to right front wheel 92. Steering actuator 73 and steering actuator control section 603 form RL unit 83 corresponding to left rear wheel 93. Steering actuator 74 and steering actuator control section 604 form RR unit 84 corresponding to right rear wheel 94.

[0024] Each unit may be configured as an electromechanically integrated steering module in which the steering actuator and the steering actuator control unit are integrated. In this case, the steering module may be further configured as one unit with the wheels. Alternatively, each unit may have a separate steering actuator and steering actuator control unit electrically connected by wiring.

[0025] In this embodiment, the turning center setting unit 56 sets the vehicle turning center C so that each of the wheels 91-94 turns in accordance with the Ackermann geometry. Referring to FIG. 2, the vehicle turning center C and the steering angle command value θ1 based on the Ackermann theory are * -θ4 * The relationship between these two will be explained below. According to the Ackermann theory, the steering direction of each wheel 91-94 is perpendicular to the straight lines N1-N4 that connect the vehicle turning center C and the center of each wheel 91-94. In other words, each wheel 91-94 is steered in the tangent direction of a circle centered on the vehicle turning center C. The steering angle ratio of the steering angle of the wheel on the outside of the turning to the steering angle of the wheel on the inside of the turning is a value that is smaller than 1.

[0026] The turning center setting unit 56 of this embodiment calculates the steering angle command value θ1 of each wheel 91-94 from the vehicle turning center C based on the Ackermann theory. * -θ4 * Here, the axis that passes through the center of the front wheels 91, 92 and is perpendicular to the vehicle longitudinal axis Y0 is defined as the front wheel axis X12, and the axis that passes through the center of the rear wheels 93, 94 and is perpendicular to the vehicle longitudinal axis Y0 is defined as the rear wheel axis X34. The distance between the front wheel axis X12 and the rear wheel axis X34 is the wheelbase L.

[0027] Additionally, the axis that passes through the center of gravity G and is perpendicular to the vehicle longitudinal axis Y0 is represented as the center of gravity axis X0. Assuming that the weight distribution in the longitudinal direction of the vehicle is uniform, the center of gravity axis X0 is located midway between the front wheel axis X12 and the rear wheel axis X34. When the vehicle turning center C is set on the center of gravity axis X0, the left front wheel 91 and the left rear wheel 93, and the right front wheel 92 and the right rear wheel 94 each turn on the same arc, so the difference between the inside and outside wheels becomes zero, and running resistance during turning is reduced.

[0028] Additionally, the axis passing through the centers of the front and rear wheels on the same side in the left-right direction of the vehicle is defined as the front and rear wheel axis. The axis passing through the centers of the left front wheel 91 and the left rear wheel 93 is represented as the left front and rear wheel axis Y13, and the axis passing through the centers of the right front wheel 92 and the right rear wheel 94 is represented as the right front and rear wheel axis Y24. The distance between the left front and rear wheel axis Y13 and the right front and rear wheel axis Y24 is the tread width D. The left front and rear wheel axis Y13 and the right front and rear wheel axis Y24 are symmetrical with respect to the vehicle's front-rear axis Y0, and the distance between the left front and rear wheel axis Y13 and the vehicle's front-rear axis Y0, and the distance between the right front and rear wheel axis Y24 and the vehicle's front-rear axis Y0 are both expressed as (D / 2).

[0029] Next, with reference to Figs. 3 to 6, a specific example will be described in which the turning center setting unit 56 sets the vehicle turning center C in accordance with the vehicle speed V. As the vehicle speed V increases, the turning center setting unit 56 sets the final steering command value St ** The vehicle turning center C is set to suppress steering for each wheel 91-94, and the steering angle command value θ1 * -θ4 * Each figure shows an example of turning left, i.e., the steering angle has a positive sign. Turning right is basically the same except that the steering angle has a negative sign.

[0030] In setting example 1 shown in Fig. 3, one set axis Xs perpendicular to the vehicle longitudinal axis Y0 is defined. Fig. 3 shows an example in which the set axis Xs is set on the rear wheel side of the center of gravity axis X0, but the set axis Xs may be set on the center of gravity axis X0 or on the front wheel side of the center of gravity axis X0. The position of the set axis Xs is determined from the viewpoint of, for example, whether reducing discomfort for the driver or passenger in the front passenger seat or for passengers in the rear seats is given higher priority.

[0031] Here, the distance from the vehicle front-rear axis Y0 to the vehicle turning center C is defined as the "turning center set distance Dc." When the left front wheel 91 is steered +90 degrees and the left rear wheel 93 is steered -90 degrees, the vehicle turning center C is set on the left front-rear wheel axis Y13. The turning center set distance Dc at this time is (D / 2), which becomes the minimum value Dc_min. If the maximum turning angle is less than ±90 degrees, the minimum value Dc_min of the turning center set distance becomes greater than (D / 2).

[0032] When the vehicle 100 is traveling straight and the steering angle of each wheel 91-94 is 0 degrees, the turning center setting distance Dc is theoretically infinite. When starting to turn from a straight traveling state, the turning center setting distance Dc corresponding to the steering angle with the minimum resolution is recognized as the realistic maximum value Dc_max of the turning center setting distance. The turning center setting unit 56 sets the vehicle turning center C on the setting axis Xc while manipulating the turning center setting distance Dc within the range from the minimum value Dc_min to the maximum value Dc_max so that the higher the vehicle speed V, the larger the turning center setting distance Dc is set.

[0033] Solid lines indicate the positions of the wheels 91-94 at low vehicle speeds and the straight lines connecting the vehicle turning center C and the centers of the wheels 91-94. Dashed lines indicate the positions of the wheels 91-94 at high vehicle speeds and the straight lines connecting the vehicle turning center C and the centers of the wheels 91-94. The higher the vehicle speed V, the farther the vehicle turning center C is from the vehicle longitudinal axis Y0, and the larger the turning radius Rg from the vehicle turning center C to the center of gravity G. Therefore, steering during turning is suppressed.

[0034] Figure 4 shows the final steering command value St for various vehicle speeds V. **and the turning center setting distance Dc. The turning center setting unit 56 determines the turning center setting distance Dc using this 3D map. Here, the "map" is not limited to a large number of data groups stored in a readable manner, but also includes a calculation formula. In other words, outputting the calculation result of a calculation formula based on input variables can also be interpreted as a form of calculation using a map.

[0035] The horizontal axis of the map in Fig. 4 is the final steering command value St ** However, assuming that a steering angle signal θst is mainly input from the steering wheel 95, the horizontal axis of the map will be explained as the steering angle θst for convenience. The vertical axis of the map is the set turning center distance Dc, which indicates a range from a minimum value Dc_min to a maximum value Dc_max. As a plurality of vehicle speeds V, characteristic lines for a low vehicle speed (e.g., 0 km / h), a medium vehicle speed (e.g., 60 km / h), and a high vehicle speed (100 km / h) are indicated by a solid line, a dashed line, and a dashed double-dot line, respectively.

[0036] The "steering angle with minimum resolution" is expressed as the "minimum steering angle θst_min." The turning center setting distance Dc at low vehicle speeds changes from a maximum value Dc_max corresponding to the minimum steering angle θst_min to a minimum value Dc_min corresponding to the maximum steering angle θst_max. When the steering angle θst starts to increase from the minimum steering angle θst_min in the low vehicle speed range, the characteristic in which the turning center setting distance Dc suddenly decreases from the maximum value Dc_max is expressed as "a steep downward slope." As the vehicle speed V increases, the downward slope becomes gentler. In other words, there is a tendency for understeer, with steering being suppressed in response to steering.

[0037] For example, in the medium vehicle speed range of 60 km / h, the downward slope is gentler than in the low vehicle speed range, but the turning center setting distance Dc corresponding to the maximum steering angle θst_max is set to the same value as the minimum value Dc_min in the low vehicle speed range. Therefore, in the vehicle speed range of 60 km / h or less, when the driver steers to the maximum, the maximum steering angle is realized.

[0038] In contrast, in a high vehicle speed range, for example, 100 km / h, the set turning center distance Dc corresponding to the maximum steering angle θst_max is set to a reference value Dc_ref that is greater than the minimum value Dc_min. In a conventional vehicle in which the left and right wheels are mechanically coupled, the wheels rotate as the steering wheel is turned, so the theoretical set turning center distance should be the same as the minimum value Dc_min. However, in a high vehicle speed range, tires slip, so the realistic set turning center distance becomes greater than the minimum value Dc_min. The reference value Dc_ref in this embodiment is a value that is approximately the same as the realistic set turning center distance of a conventional vehicle. Therefore, in this embodiment, even in a high vehicle speed range, a "steering response to steering" that is at least equivalent to that of a conventional vehicle is ensured.

[0039] In this way, the turning center setting unit 56 of this embodiment sets the vehicle turning center C in accordance with the vehicle speed V, and calculates the steering angle command value θ1 of each wheel 91-94 from the vehicle turning center C. * -θ4 * Therefore, it is not necessary to create a steering angle command value map for each wheel. Therefore, the four wheels 91-94 can be controlled simply.

[0040] In particular, in Example 1 of setting the vehicle turning center C, the turning center setting distance Dc is manipulated on one setting axis Xs according to the vehicle speed V, thereby achieving a steering feeling similar to that of a conventional vehicle in which the left and right wheels are mechanically coupled.

[0041] Next, in setting examples 2 and 3 shown in Fig. 5 and Fig. 6, a plurality of set axes Xl, Xm, and Xh perpendicular to the vehicle longitudinal axis Y0 are defined. The turning center setting unit 56 sets the vehicle turning center C on one of the set axes while manipulating a turning center set distance Dc, which is the distance from the vehicle longitudinal axis Y0 to the vehicle turning center C. The turning center setting unit 56 changes the set axis for setting the vehicle turning center C in accordance with the vehicle speed V. Furthermore, the turning center setting unit 56 calculates the final steering command value St for the plurality of vehicle speeds V for the set set axes. ** The turning center setting distance Dc is determined based on a three-dimensional map that defines the relationship between the turning center setting distance Dc and the turning center setting distance Dc.

[0042] In setting examples 2 and 3 shown in Figures 5 and 6, three setting axes Xl, Xm, and Xh are defined for low, medium, and high vehicle speeds. In Figures 5 and 6, the setting axis Xl for low vehicle speed is on the center of gravity axis X0, the setting axis Xm for medium vehicle speed is located closer to the rear wheels than the setting axis Xl for low vehicle speed, and the setting axis Xh for high vehicle speed is located even closer to the rear wheels than the setting axis Xm for medium vehicle speed. The positions are not limited to these, and only the setting axis Xl for low vehicle speed may be located closer to the front wheels than the center of gravity axis X0, or all of the setting axes Xl, Xm, and Xh may be located closer to the front wheels than the center of gravity axis X0. Other notes regarding the illustrations in Figures 5 and 6 are the same as those in Figure 3. In setting examples 2 and 3, the same three-dimensional map as in Figure 4 is basically used for each setting axis.

[0043] In the setting example 2 shown in Fig. 5, the set axis of the vehicle turning center C is changed according to the vehicle speed V, but the same steering angle (strictly speaking, the final steering command value St ** ) is set constant. As the vehicle speed V increases, the vehicle turning center C moves parallel to the vehicle longitudinal axis Y0 from the side of the center of gravity axis X0 toward the rear wheel side. The higher the vehicle speed V, the larger the turning radius Rg from the vehicle turning center C to the center of gravity G, so steering is suppressed. In this case, when the left and right front wheels 91, 92 are viewed individually, the steering angle at high vehicle speeds is larger than the steering angle at low vehicle speeds, but steering is suppressed for the vehicle as a whole.

[0044] In the setting example 3 shown in Fig. 6, the set axis of the vehicle turning center C is changed according to the vehicle speed V, and the same steering angle (strictly speaking, the final steering command value St ** ) changes. In Figure 6, the dashed lines for each wheel 91-94 at high vehicle speeds are omitted. As the vehicle speed V increases, the vehicle turning center C moves obliquely with respect to the vehicle longitudinal axis Y0, from the side of the center of gravity axis X0 toward the rear wheels. At this time, as shown by the solid arrow, the vehicle turning center C may move outward, i.e., away from the vehicle longitudinal axis Y0. Also, as shown by the dashed arrow, the vehicle turning center C may move inward, i.e., closer to the vehicle longitudinal axis Y0, as long as the turning radius Rg is within a range where it increases.

[0045] In setting examples 2 and 3 of the vehicle turning center C, in addition to the effect of setting example 1, by changing the setting axis according to the vehicle speed V, it is possible to set the vehicle turning center C to the understeer side where the vehicle behavior becomes stable as the vehicle speed V increases.

[0046] Next, the steering angle command value calculation process according to this embodiment will be described with reference to the flowchart in Figure 7. In the explanation of the flowchart, the symbol "S" means a step. In S1, the final steering command value generation unit 55 calculates the steering angle signal θst output by the steering wheel 95 or the steering command value St generated by the steering command device 96. * Based on the final steering command value St ** Generate.

[0047] In S2, the absolute value of the final steering command value |St ** If YES in S2, the process proceeds to S3. In S3, the turning center setting unit 56 determines whether the final steering command value St ** and the vehicle speed V. Then, in step S4, the turning center setting unit 56 calculates the turning angle command value θ1 of each wheel 91-94 from the turning center C of the vehicle. * -θ4 * Calculate.

[0048] S2 is NO, that is, the absolute value of the final steering command value |St ** If | is smaller than the steering lower limit threshold StLth, in S5, the turning center setting unit 56 adjusts the steering angle command value θ1 of each wheel 91-94 so as to maintain the straight traveling state of the vehicle 100. * -θ4 * In other words, the absolute value of the final steering command value |St ** The region where | is smaller than the steering lower limit threshold StLth is treated as a steering dead zone. Therefore, stability during high-speed driving is ensured.

[0049] As described above, the steering control device 50 of this embodiment can operate the vehicle stably when turning at high vehicle speeds. By suppressing sudden steering when turning at high vehicle speeds, it is possible to prevent the driver and passengers from feeling uncomfortable.

[0050] The prior art disclosed in Patent Document 1 (International Publication No. 2019 / 188951) is only intended for vehicles in which two steerable wheels, left and right, are steered independently, and does not take into consideration the behavior of four-wheel independently steerable vehicles. In contrast, in this embodiment, the vehicle turning center C of the four-wheel independently steerable vehicle 100 is appropriately set, and the steering angle command value θ1 of each wheel 91-94 is * -θ4 * can be calculated.

[0051] (Other embodiments) (a) In the above embodiment, the vehicle turning center C is set by the turning center setting unit 56 so that each of the wheels 91-94 turns in accordance with the Ackermann geometry. In other embodiments, for example, as shown in Fig. 8, the vehicle turning center C may be set so that the left and right front wheels 91, 92 and the left and right rear wheels 93, 94 each turn in accordance with a parallel geometry. Alternatively, the vehicle turning center C may be set so that a turning operation intermediate between the Ackermann geometry and the parallel geometry is achieved.

[0052] In the turning operation according to the parallel geometry, the steering angle command value θ2 of the right front wheel 92 * is the steering angle command value θ1 of the left front wheel 91 * and the steering angle command value θ4 of the right rear wheel 94 is set equal to * is the steering angle command value θ3 of the left rear wheel 93 * In other words, the steering angle ratio of the wheel on the outside of the turn to the wheel on the inside of the turn is set to 1.

[0053] (b) The turning center setting unit 56 is not limited to a configuration in which it functions as a "turning angle command value calculation unit." Regardless of the vehicle turning center C, the turning angle command value calculation unit 56 may set the turning angle command value θ1 of each wheel 91-94. * -θ4 * In this case, the steering angle command value calculation unit 56 may calculate the final steering command value St ** Based on the three-dimensional map of the vehicle speed V and the steering angle command value, the steering angle command value θ1 of each wheel 91-94 is calculated. * -θ4 *The higher the vehicle speed V, the higher the final steering command value St ** The steering angle command value calculation unit 56 calculates the steering angle command value θ1 of each wheel 91-94 so as to suppress steering. * -θ4 * By calculating the above, sudden steering is suppressed when turning at high vehicle speeds, thereby preventing the driver and passengers from feeling uncomfortable.

[0054] (c) In the system configuration of Fig. 1, a plurality of steering actuator control sections 601-604 form units together with corresponding steering actuators 71-74. This configuration is not limiting, and a plurality of steering actuator control sections 601-604 may be centrally arranged to control drive currents Ia1-Ia4 supplied to corresponding steering actuators 71-74.

[0055] (d) The steering control device of the present invention is not limited to four-wheel vehicles, but can also be applied to three-wheel vehicles, or six-wheel or eight-wheel independently steering vehicles having three or more rows of left and right wheel pairs in the longitudinal direction of the vehicle. In summary, the steering control device of the present invention is applied to "vehicles in which three or more wheels that are not mechanically constrained from each other can be steered independently."

[0056] (e) The vehicle 100 may be provided with only a steering mechanism 95 for manual driving by a driver, or may be provided with only a steering command device 96 for automatic driving, as a steering input configuration. In this case, the final steering command value generating unit 55 generates the steering command value St * Without arbitrating between the two, either input is used as the final steering command value St ** The same applies to the case where the function of either the steering mechanism 95 or the steering command device 96 is temporarily disabled in the vehicle 100 equipped with both the steering mechanism 95 and the steering command device 96.

[0057] (f) Each of the wheels 91-94 may be steerable independently and may not be driven independently. For example, the front wheels 91 and 92 may be drive wheels and the rear wheels 93 and 94 may be driven wheels.

[0058] The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention.

[0059] The control device and methods described herein may be implemented by a special-purpose computer configured with a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the control device and methods described herein may be implemented by a special-purpose computer configured with a processor comprising one or more dedicated hardware logic circuits. Alternatively, the control device and methods described herein may be implemented by one or more special-purpose computers configured with a processor and memory programmed to perform one or more functions in combination with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible storage medium as instructions executed by a computer. [Explanation of symbols]

[0060] 50 Steering control device, 55 Final steering command value generation unit, 56 Turning center setting unit (steering angle command value calculation unit), 601-604···Steering actuator control unit, 71-74···Steering actuator, 91-94...wheels, 95 Handle (steering mechanism), 96 Steering command device, 100···(independent steering) vehicle.

Claims

1. A steering control device for controlling the steering of each wheel in a vehicle (100) equipped with a plurality of steering actuators (71-74) that independently steer three or more wheels (91-94) that are not mechanically constrained from one another, and a steering mechanism (95) of a steer-by-wire system or a steering command device (96) for automatic driving that is provided mechanically separated from the steering actuators, comprising: The steering angle signal (θst) output by the steering mechanism or the steering command value (St ＊ ) based on the final steering command value (St ＊＊ a final steering command value generating unit (55) for generating a final steering command value; The vehicle turning center (C) is set based on the final steering command value and the vehicle speed (V), and the steering angle command value (θ1 ＊ -θ4 ＊ a turning center setting unit (56) that functions as a turning angle command value calculation unit that calculates the turning angle command value; a plurality of steering actuator control units (601-604) provided corresponding to the plurality of steering actuators, and controlling drive currents supplied to the steering actuators so that the steering angles output by the steering actuators follow the steering angle command values; Equipped with The turning center setting unit is The vehicle turning center is set while manipulating a turning center setting distance (Dc) which is the distance from the vehicle front-rear axis (Y0) to the vehicle turning center, determining the turning center set distance based on a three-dimensional map that defines the relationship between the final steering command value and the turning center set distance for a plurality of vehicle speeds; In the three-dimensional map, the turning center set distance in a medium vehicle speed range where the vehicle speed is within a predetermined range and which corresponds to a maximum steering angle (θst_max) is set to the same value as a minimum value (DC_min) of the turning center set distance in a low vehicle speed range which is a range lower than the vehicle speed in the medium vehicle speed range, The steering angle command value calculation unit calculates the steering angle command value for each wheel based on the final steering command value and a vehicle speed so that the higher the vehicle speed, the more the steering is suppressed with respect to the final steering command value.

2. The turning center setting unit is 2. The steering control device according to claim 1, wherein the steering angle command value of each wheel is calculated so that the steering direction of each wheel is perpendicular to a straight line connecting the vehicle turning center and the center of each wheel, and functions as the steering angle command value calculation unit.

3. One setting axis (Xs) perpendicular to the vehicle longitudinal axis is defined, 3. The steering control device according to claim 2, wherein the turning center setting unit sets the vehicle turning center on the setting axis.

4. A plurality of setting axes (Xl, Xm, Xh) perpendicular to the vehicle longitudinal axis are defined, the turning center setting unit sets the vehicle turning center on any one of the setting axes, 3. A steering control device according to claim 2, wherein the set axis for setting the vehicle turning center is changed in accordance with vehicle speed, and the turning center set distance is determined for the set set axis using the three-dimensional map.

5. the steering angle signal, the steering command value, and the final steering command value are defined to be 0 when the vehicle is traveling straight, and to take positive or negative values ​​depending on the steering direction with respect to a neutral position, The steering angle command value calculation unit 5. The steering control device according to claim 1, wherein when the absolute value of the final steering command value is smaller than a steering lower limit threshold (StLth), the steering angle command value of each wheel is calculated so as to maintain a straight traveling state of the vehicle.

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