Steering control device

Abstract

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 ([theta] st) 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) for automatic driving. A steering angle command value calculation unit (56) calculates a steering angle command value ([theta] 1 *-[theta] 4 *) for each of the wheels (91-94). The plurality of steering actuator control units (601-604) control the drive current supplied to the steering actuators such that the steering angle output by the steering actuators (71-74) follows the steering angle command value ([theta] 1 *-[theta] 4 *). On the basis of the final steering command value (St * *) and the vehicle speed (V), a steering angle command value calculation unit (56) calculates a steering angle command value ([theta] 1 *-[theta] 4 *) for each of the wheels (91-94) such that steering is suppressed with respect to the final steering command value (St * *) as the vehicle speed (V) increases.

Description

[0001] Cross-references of related applications

[0002] This application is based on Japanese Patent Application No. 2022-103551 filed on June 28, 2022, and the contents thereof are incorporated herein by reference. Technical Field

[0003] The invention relates to a steering control device. Background Art

[0004] Conventionally, in a steer-by-wire system, a steering device is known that determines target steering angles for a plurality of independent steering mechanisms. For example, the upper ECU of the steering device disclosed in Patent Document 1 includes a steering angle determination unit that calculates target steering angles of left and right steering mechanisms based on a steering angle detected by a steering angle sensor. The relationship between the steering angle and the target steering angle is shown in a mapping diagram.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2019 / 188951

[0008] If the steering angle generated by the driver's steering and the steering angle command value corresponding to the steering command value of the automatic driving are the same regardless of the vehicle speed limit, the vehicle behavior changes significantly for a small steering command when turning at a high speed, which may cause discomfort to the driver and passengers. Patent document 1 records that the characteristics of the target steering angle for the steering angle can also change according to the speed of the vehicle. However, the prior art of patent document 1 only takes the left and right steering wheels, that is, two-wheel independent steering vehicles as the object, and does not consider the behavior of three or more independent steering vehicles headed by four-wheel independent steering vehicles. Summary of the invention

[0009] An object of the present invention is to provide a steering control device for a vehicle having three or more independent steering wheels, which enables the vehicle to operate stably when turning at a high speed.

[0010] The steering control device of the present invention controls the steering of each wheel in a vehicle, and the vehicle has multiple steering actuators that independently steer more than three wheels that are not mechanically constrained to each other, and a steering mechanism of a wire-controlled steer system or a steering command device for automatic driving that is mechanically separated from the steering actuator.

[0011] The steering control device includes a final steering command value generating unit, a steering angle command value calculating unit, and a plurality of steering actuator control units.

[0012] The final steering command value generating unit generates the final steering command value based on the steering angle signal output by the steering mechanism or the steering command value output by the steering command device. The steering angle command value calculating unit calculates the steering angle command value of each wheel. The plurality of steering actuator control units are provided corresponding to the plurality of steering actuators, and control the driving current supplied to the steering actuators so that the steering angle output by the steering actuators follows the steering angle command value.

[0013] The steering angle command value calculation unit calculates the steering angle command value of 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 with respect to the final steering command value. For example, in a steering control device having a turning center setting unit that sets a turning center of the vehicle, the turning center setting unit may function as the steering angle command value calculation unit.

[0014] The steering control device of the present invention can make the vehicle operate stably when turning at high speed. By suppressing abrupt steering when turning at high speed, it is possible to avoid causing discomfort to the driver and passengers. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above-mentioned object and other objects, features and advantages of the present invention will become more apparent through the following detailed description with reference to the accompanying drawings. The accompanying drawings are as follows:

[0016] Figure 1 This is a schematic structural diagram of an independent steering vehicle to which a steering control device according to one embodiment is applied.

[0017] Figure 2 is a diagram illustrating a turning maneuver following Ackermann geometry.

[0018] Figure 3 1 is a diagram showing a first example of setting the vehicle turning center according to the vehicle speed.

[0019] Figure 4 This is a diagram showing the relationship between the steering angle, vehicle speed, and the turning center setting distance.

[0020] Figure 5 1 is a diagram showing a second example of setting the vehicle turning center according to the vehicle speed.

[0021] Figure 6 1 is a diagram showing a third example of setting the vehicle turning center according to the vehicle speed.

[0022] Figure 7 4 is a flowchart of the steering angle command value calculation process.

[0023] Figure 8 is a diagram illustrating a turning maneuver that follows parallel geometry. DETAILED DESCRIPTION

[0024] An embodiment of a steering control device will be described with reference to the drawings. The steering control device of this embodiment controls the steering of each wheel in a vehicle in which four wheels are independently steerable without mechanical constraints to each other (four-wheel independent steering vehicle).

[0025] (One embodiment)

[0026] Reference Figure 1 , the structure of an independent steering vehicle 100 to which a steering control device 50 according to an embodiment is applied is described. The four wheels 91-94 of the vehicle 100 are not mechanically constrained to each other and can be steered independently. The left front wheel 91 is denoted as "FL", the right front wheel 92 is denoted as "FR", the left rear wheel 93 is denoted as "RL", and the right rear wheel 94 is denoted as "RR". For example, each wheel 91-94 is a drive wheel having an in-wheel motor, and can be steered and driven independently.

[0027] Four steering actuators ("steering Act" in the figure) 71-74 steer each wheel 91-94. For example, the steering actuators 71-74 of this embodiment are composed of a dual-system three-phase brushless motor having two sets of windings for redundancy. Four steering actuator control units ("steering Act control units" in the figure) 601-604 are provided corresponding to the four steering actuators 71-74. The steering actuators 71-74 and the steering actuator control units 601-604 are operated by being supplied with power voltage from a vehicle-mounted battery (not shown).

[0028] In this embodiment, the vehicle 100 includes both the steering mechanism 95 of the steer-by-wire system and the steering command device 96 of the automatic driving system, which are mechanically separated from the steering actuators 71 to 74. In other embodiments, the vehicle 100 may include only one of the steering mechanism 95 and the steering command device 96.

[0029] As a steering mechanism of the steer-by-wire system, a steering wheel 95 is typically used, but other steering mechanisms such as a joystick may also be used. The driver manually operates the steering wheel 95 to output a steering angle signal θst. The steering command device 96 is implemented, for example, by an ADAS (Advanced Driver Assistance System) and outputs a steering command value St according to the route to the destination and the road conditions. * .

[0030] The steering control device 50 includes a final steering command value generating unit 55 , a turning center setting unit 56 , and a plurality of steering actuator control units 601 - 604 .

[0031] The final steering command value generating unit 55 generates a steering command value St based on the steering angle signal θst outputted from the steering wheel 95 and the steering command value St outputted from the steering command device 96. * , generating the final steering command value St** Here, basically, the steering command value St * and the final steering command value St ** It is assumed that the value of the angle dimension is based on the steering angle. However, as the angle-related quantity, for example, the value of the torque dimension may also be used. In addition, the steering angle signal θst and the steering command value St * And the final steering command value St ** It is defined to be 0 when the vehicle 100 is traveling straight, and to take positive or negative values ​​depending on the steering direction relative to the neutral position. For example, it is represented by a positive value when turning left, and by a negative value when turning right.

[0032] Final steering command value St ** The contribution ratio of the steering angle signal θst is set high in the case where the driver mainly drives manually and the automatic driving system assists the steering. In the case of driving assistance such as lane keeping assistance, the steering command value St * When a steering torque having an absolute value greater than or equal to a predetermined value is inputted by the driver's will during driving assistance, the steering angle signal θst is switched to be prioritized.

[0033] The turning center setting unit 56 receives the final steering command value St from the final steering command value generating unit 55. ** The vehicle speed V is input from the vehicle speed sensor 97 of the vehicle 100. The turning center setting unit 56 is based on the final steering command value St ** The turning center C of the vehicle is set based on the vehicle speed V. The details will be described later. In addition, the turning center setting unit 56 calculates the steering angle command value θ1 of each wheel 91-94 based on the vehicle turning center C. * -θ4 * That is, the turning center setting unit 56 sets the final steering command value St ** The steering angle command value θ1 of each wheel 91-94 is calculated by the vehicle speed V and the vehicle turning center C. * -θ4 * , thereby functioning as a "steering angle command value calculation unit".

[0034] The steering actuator control units 601-604 control the driving currents Ia1-Ia4 supplied to the steering actuators 71-74 so that the steering angles outputted from the steering actuators 71-74 follow the steering angle command values ​​θ1. * -θ4 * The steering angle is defined as, for example, positive for the left side and negative for the right side, based on the neutral position. In the following description, the "maximum steering angle" is defined as the steering angle with the largest absolute value regardless of the sign.

[0035] The groups of steering actuators and steering actuator control units corresponding to the wheels 91-94 are represented as units. The steering actuator 71 and the steering actuator control unit 601 constitute the FL unit 81 corresponding to the left front wheel 91. The steering actuator 72 and the steering actuator control unit 602 constitute the FR unit 82 corresponding to the right front wheel 92. The steering actuator 73 and the steering actuator control unit 603 constitute the RL unit 83 corresponding to the left rear wheel 93. The steering actuator 74 and the steering actuator control unit 604 constitute the RR unit 84 corresponding to the right rear wheel 94.

[0036] Each unit may also be configured as a mechatronic steering assembly in which a steering actuator and a steering actuator control unit are integrated. In this case, the steering assembly may also be integrated with the wheel. Alternatively, each unit may also be configured by electrically connecting a separate steering actuator and a steering actuator control unit through wiring.

[0037] In the present embodiment, the turning center setting unit 56 sets the vehicle turning center C so that each wheel 91 to 94 performs a turning motion in accordance with Ackerman geometry. Figure 2 , based on the Ackerman theory, the vehicle turning center C and the steering angle command value θ1 * -θ4 * In the Ackerman theory, the steering direction of each wheel 91-94 is orthogonal to the straight line N1-N4 connecting the vehicle turning center C and the center of each wheel 91-94. That is, each wheel 91-94 turns in the direction of the tangent of the circle centered on the vehicle turning center C. The steering angle ratio of the steering angle of the wheel on the outer side of the turn to the steering angle of the wheel on the inner side of the turn becomes a value less than 1.

[0038] The turning center setting unit 56 of the present embodiment calculates the steering angle command value θ1 of each wheel 91 to 94 based on the vehicle turning center C based on the Ackerman theory. * -θ4 * Here, the axis passing through the center of the front wheels 91, 92 and perpendicular to the vehicle front-rear axis Y0 is defined as the front wheel axis X12, and the axis passing through the center of the rear wheels 93, 94 and perpendicular to the vehicle front-rear 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.

[0039] In addition, the axis passing through the center of gravity G and orthogonal to the front-rear axis Y0 of the vehicle is represented as the center of gravity axis X0. When the weight distribution in the front-rear direction of the vehicle is assumed to be uniform, the center of gravity axis X0 is the position exactly in the middle of the front wheel axis X12 and the rear wheel axis X34. When the turning center C of the vehicle is set on the center of gravity axis X0, the left front wheel 91 and the left rear wheel 93, the right front wheel 92 and the right rear wheel 94 turn on the same arc, so the inner wheel difference and the outer wheel difference are zero, and the driving resistance when turning is small.

[0040] In addition, the axis passing through the center of the front wheel and the rear wheel on the same side of the left-right direction of the vehicle is defined as the front-rear wheel axle. The axis passing through the center of the left front wheel 91 and the left rear wheel 93 is represented as the left front-rear wheel axle Y13, and the axis passing through the center of the right front wheel 92 and the right rear wheel 94 is represented as the right front-rear wheel axle Y24. The distance between the left front-rear wheel axle Y13 and the right front-rear wheel axle Y24 is the tread width D. The left front-rear wheel axle Y13 and the right front-rear wheel axle Y24 are symmetrical with respect to the vehicle front-rear axis Y, and the distance between the left front-rear wheel axle Y13 and the vehicle front-rear axis Y0 and the distance between the right front-rear wheel axle Y24 and the vehicle front-rear axis Y0 are both represented by (D / 2).

[0041] Next, refer to Figure 3 to Figure 6 The turning center setting unit 56 sets the vehicle turning center C according to the vehicle speed V. The turning center setting unit 56 sets the vehicle turning center C according to the vehicle speed V. ** The vehicle turning center C is set in a manner to suppress steering, and the steering angle command value θ1 of each wheel 91-94 is calculated. * -θ4 * In each figure, an example of a left turn, that is, an example in which the sign of the steering angle is positive, is shown. In a right turn, the situation is basically the same except that the sign of the steering angle is negative.

[0042] exist Figure 3 In the setting example 1 shown, a setting axis Xs is defined which is orthogonal to the vehicle front-rear axis Y0. Figure 3 , an example is shown in which the setting axis Xs is set closer to the rear wheel side than the center of gravity axis X0, but the setting axis Xs may be set on the center of gravity axis X0 or closer to the front wheel side than the center of gravity axis X0. The position of the setting axis Xs is determined, for example, from the perspective of which of the driver or passenger in the front passenger seat and the passenger in the rear seat should be given priority in reducing discomfort.

[0043] Here, the distance from the vehicle front and rear axle Y0 to the vehicle turning center C is defined as the "turning center setting distance Dc". When the left front wheel 91 is turned at +90 degrees and the left rear wheel 93 is turned at -90 degrees, the vehicle turning center C is set on the left front and rear wheel axle Y13. At this time, the turning center setting distance Dc is (D / 2), which is the minimum value Dc_min. When the maximum steering angle is less than ±90 degrees, the minimum value Dc_min of the turning center setting distance is greater than (D / 2).

[0044] When the steering angle of each wheel 91-94 is 0 degrees in the straight-moving state of the vehicle 100, the turning center setting distance Dc is theoretically infinite. When turning starts from the straight-moving state, the turning center setting distance Dc corresponding to the steering angle of the minimum resolution is recognized as the maximum value Dc_max of the turning center setting distance in reality. The turning center setting unit 56 operates the turning center setting distance Dc in a 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, and sets the vehicle turning center C on the setting axis Xc.

[0045] The solid lines represent the wheels 91-94 at low speeds and the straight lines connecting the vehicle turning center C and the centers of the wheels 91-94. The dashed lines represent the wheels 91-94 at high speeds and the straight lines connecting the vehicle turning center C and the centers of the wheels 91-94. As the vehicle speed V increases, the vehicle turning center C moves further away from the vehicle front and rear axles Y0, and the turning radius Rg from the vehicle turning center C to the center of gravity G increases. Therefore, steering during turning is suppressed.

[0046] Figure 4 represents the final steering command value St specified for a plurality of vehicle speeds V. ** The three-dimensional map of the relationship between the input variable and the turning center setting distance Dc. The turning center setting unit 56 determines the turning center setting distance Dc based on the three-dimensional map. Here, the "map" is not limited to storing a large number of data groups in a readable manner, but may also include a calculation formula. That is, outputting a calculation result based on a calculation formula of an input variable is also interpreted as a method of calculation using a map.

[0047] Figure 4 The horizontal axis of the mapping diagram is the final steering command value St ** , but it is mainly assumed that the steering angle signal θst is input from the steering wheel 95. For convenience, the horizontal axis of the mapping diagram is the steering angle θst. The vertical axis of the mapping diagram is the turning center setting distance Dc, which represents the range from the minimum value Dc_min to the maximum value Dc_max. As multiple vehicle speeds V, the characteristic lines of low vehicle speed (e.g., 0 km / h), medium vehicle speed (e.g., 60 km / h), and high vehicle speed (100 km / h) are respectively represented by solid lines, single-dot chain lines, and double-dot chain lines.

[0048] The "steering angle of minimum resolution" is expressed as "minimum steering angle θst_min". The turning center setting distance Dc at low vehicle speed changes from the maximum value Dc_max corresponding to the minimum steering angle θst_min to the minimum value Dc_min corresponding to the maximum steering angle θst_max. When the steering angle θst increases from the minimum steering angle θst_min in the low vehicle speed area, the characteristic that the turning center setting distance Dc decreases sharply from the maximum value Dc_max is manifested as a "steep descending slope". As the vehicle speed V increases, the descending slope becomes gentler. That is, there is a tendency to understeer relative to the steering suppression steering.

[0049] For example, in the medium speed range of 60 km / h, the descending slope is gentler than that in the low 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 speed range. Therefore, for example, in the speed range below 60 km / h, when the driver performs the maximum steering, the maximum steering angle is achieved.

[0050] In contrast, in a high vehicle speed region of, for example, 100 km / h, the turning center setting distance Dc corresponding to the maximum steering angle θst_max is set to a reference value Dc_ref that is larger than the minimum value Dc_min. Here, in a conventional vehicle in which the left and right wheels are mechanically coupled, the wheels turn by the amount by which the steering wheel is steered, and therefore, the theoretical turning center setting distance should be the same as the minimum value Dc_min. However, in a high vehicle speed region, the tires slip, and therefore the actual turning center setting distance is larger than the minimum value Dc_min. The reference value Dc_ref of the present embodiment is a value of the same degree as the actual turning center setting distance of a conventional vehicle. Therefore, in the present embodiment, at least the same degree of "steering to steering" response as that of a conventional vehicle is ensured even in a high vehicle speed region.

[0051] The turning center setting unit 56 of the present embodiment sets the vehicle turning center C according to the vehicle speed V, and calculates the steering angle command value θ1 of each wheel 91 to 94 according to the vehicle turning center C. * -θ4 * Therefore, it is not necessary to prepare a steering angle command value map for each wheel. Therefore, the four wheels 91-94 can be easily controlled.

[0052] In particular, in setting example 1 of the vehicle turning center C, the turning center setting distance Dc is operated on one setting axis Xs according to the vehicle speed V, thereby achieving the same steering feeling as that of a conventional vehicle in which the left and right wheels are mechanically coupled.

[0053] Then, in Figure 5 , Figure 6In the setting examples 2 and 3 shown, a plurality of setting axes Xl, Xm, and Xh orthogonal to the front and rear axles Y0 of the vehicle are defined. The turning center setting unit 56 operates the turning center setting distance Dc which is the distance from the front and rear axles Y0 of the vehicle to the turning center C of the vehicle, and sets the turning center C of the vehicle on any one of the setting axes. The turning center setting unit 56 changes the setting axis for setting the turning center C of the vehicle according to the vehicle speed V. In addition, for the set setting axis, the turning center setting unit 56 determines the turning center setting distance Dc according to a three-dimensional mapping map which defines the final steering command value St for a plurality of vehicle speeds V. ** Relationship with the set distance Dc from the turning center.

[0054] exist Figure 5 , Figure 6 In the setting examples 2 and 3 shown in the figure, three setting axes Xl, Xm, and Xh are defined for low vehicle speed, medium vehicle speed, and high vehicle speed. Figure 5 , Figure 6 In the figure, the setting axis X1 for low speed is on the center of gravity axis X0, the setting axis Xm for medium speed is on the rear wheel side of the setting axis X1 for low speed, and the setting axis Xh for high speed is on the rear wheel side of the setting axis Xm for medium speed. It is not limited to this position, and only the setting axis X1 for low speed may be set on the front wheel side of the center of gravity axis X0, or all the setting axes X1, Xm, and Xh may be set on the front wheel side of the center of gravity axis X0. Other Figure 5 , Figure 6 The relevant annotations of the diagram are Figure 3 In setting examples 2 and 3, the same setting is also basically used for each setting axis. Figure 4 Same 3D mapping.

[0055] exist Figure 5 In the setting example 2 shown in the figure, the setting axis of the vehicle turning center C is changed according to the vehicle speed V, but at the same steering angle (strictly referring to the final steering command value St ** ) is set to be constant. As the vehicle speed V increases, the vehicle turning center C moves from the center of gravity axis X0 side toward the rear wheel side, parallel to the vehicle front and rear axis Y0. When the vehicle speed V is higher, the turning radius Rg from the vehicle turning center C to the center of gravity G is larger, so the steering is suppressed. In addition, in this case, if the left and right front wheels 91 and 92 are observed separately, the steering angle at high speed is larger than the steering angle at low speed, but the steering is suppressed as a whole vehicle.

[0056] exist Figure 6 In the setting example 3 shown in the figure, the setting 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 ** ) corresponding to the turning center setting distance Dc. Figure 6 The dashed line illustration of each wheel 91-94 at high vehicle speed is omitted. As the vehicle speed V increases, the vehicle turning center C moves obliquely relative to the vehicle front and rear axle Y0 from the center of gravity axis X0 side toward the rear wheel side. At this time, as shown by the solid arrow, the vehicle turning center C may also move outward, that is, in a direction away from the vehicle front and rear axle Y0. In addition, as shown by the dashed arrow, as long as it is within the range of increasing turning radius Rg, the vehicle turning center C may also move inward, that is, in a direction close to the vehicle front and rear axle Y0.

[0057] 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, the vehicle turning center C can be set to the understeering side where the vehicle behavior is stable as the vehicle speed V increases.

[0058] Next, refer to Figure 7 The flowchart of FIG. 1 is used to explain the steering angle command value calculation process according to the present embodiment. In the flowchart, the symbol "S" means a step. In S1, the final steering command value generating unit 55 generates a steering command value St based on the steering angle signal θst output by the steering wheel 95 or the steering command value St generated by the steering command device 96. * , generating the final steering command value St ** .

[0059] In S2, the absolute value of the final steering command value |St ** |Whether it is greater than the steering lower limit threshold value StLth. If yes in S2, the process proceeds to S3. In S3, the turning center setting unit 56 sets the final steering command value StLth based on the final steering command value StLth. ** The vehicle turning center C is set based on the vehicle turning center C and the vehicle speed V. Then, in S4, the turning center setting unit 56 calculates the steering angle command value θ1 of each wheel 91-94 based on the vehicle turning center C. * -θ4 * .

[0060] In S2, if it is No, the absolute value of the final steering command value |St ** | When the steering angle is less than the lower limit threshold value StLth, in S5, the turning center setting unit 56 calculates the steering angle command value θ1 of each wheel 91-94 * -θ4 * To maintain the straight-moving state of the vehicle 100. That is, the absolute value of the final steering command value |St ** The area less than the steering lower limit threshold StLth is treated as the insensitive zone of steering. Therefore, the stability at high speed is ensured.

[0061] As described above, the steering control device 50 of this embodiment can stably operate the vehicle when turning at a high speed. By suppressing sudden steering when turning at a high speed, it is possible to prevent the driver and passengers from feeling uncomfortable.

[0062] In addition, the prior art disclosed in Patent Document 1 (International Publication No. 2019 / 188951) only takes the vehicle with two steering wheels of the left and right wheels as the object, and does not consider the behavior of the four-wheel independent steering vehicle. In contrast, in this embodiment, the vehicle turning center C of the four-wheel independent steering vehicle 100 can be appropriately set, and the steering angle command value θ1 of each wheel 91-94 can be calculated. * -θ4 * .

[0063] (Other Embodiments)

[0064] (a) In the above embodiment, the vehicle turning center C is set by the turning center setting unit 56 so that each wheel 91-94 performs a turning action in accordance with Ackerman geometry. In other embodiments, for example, Figure 8 As shown, the vehicle turning center C is set so that the left and right front wheels 91, 92 and the left and right rear wheels 93, 94 perform turning actions following parallel geometry. Alternatively, the vehicle turning center C may be set so that a turning action intermediate between Ackermann geometry and parallel geometry is achieved.

[0065] In the turning maneuver following the parallel geometry, the steering angle command value θ2 of the right front wheel 92 is * is set equal to the steering angle command value θ1 of the left front wheel 91 * , the steering angle command value θ4 of the right rear wheel 94 * is set equal to the steering angle command value θ3 of the left rear wheel 93 * That is, the steering angle ratio of the steering angle of the wheel on the outer side of the turn to the steering angle of the wheel on the inner side of the turn is 1.

[0066] (b) The turning center setting unit 56 is not limited to functioning as a "steering angle command value calculation unit". The steering angle command value calculation unit 56 may calculate the steering angle command value θ1 of each wheel 91-94 regardless of the vehicle turning center C. * -θ4 * In this case, the steering angle command value calculation unit 56 can calculate the final steering command value St generated for each wheel. ** The steering angle command value θ1 of each wheel 91-94 is calculated individually by using the three-dimensional map of the vehicle speed V and the steering angle command value. * -θ4 * The steering angle command value calculation unit 56 calculates the final steering command value St as the vehicle speed V increases.** The steering angle command value θ1 of each wheel 91-94 is calculated in a manner that suppresses steering * -θ4 * , thereby suppressing sudden steering when turning at high speed. This can avoid causing discomfort to the driver and passengers.

[0067] (c) Figure 1 In the system structure, the plurality of steering actuator control units 601-604 and the corresponding steering actuators 71-74 constitute a unit. The present invention is not limited to this structure, and the plurality of steering actuator control units 601-604 may be centrally arranged to control the driving currents Ia1-Ia4 supplied to the corresponding steering actuators 71-74.

[0068] (d) The steering control device of the present invention is not limited to four-wheeled vehicles, but can also be applied to three-wheeled vehicles or six-wheel or eight-wheeled independent steering vehicles having three or more rows of left and right wheel pairs in the front-rear direction of the vehicle. In short, the steering control device of the present invention is applied to "a vehicle having three or more wheels that are not mechanically constrained to each other and can be steered independently".

[0069] (e) As the steering input structure, the vehicle 100 may include only the steering mechanism 95 for manual driving by the driver, or only the steering command device 96 for automatic driving. In this case, the final steering command value generating unit 55 does not mediate between the steering angle signal θst and the steering command value St * Instead, the input of either party is directly used as the final steering command value St ** The same applies when the function of either the steering mechanism 95 or the steering command device 96 is temporarily disabled in the vehicle 100 including both the steering mechanism 95 and the steering command device 96.

[0070] (f) The wheels 91 to 94 may be independently steerable and may not be independently driven. For example, the front wheels 91 and 92 may be driving wheels, and the rear wheels 93 and 94 may be driven wheels.

[0071] The present invention is not limited to the above-described embodiments, and can be implemented in various forms without departing from the gist of the invention.

[0072] The control device and method thereof recorded in the present invention can be implemented by a special-purpose computer, which is provided by constituting a processor and a memory programmed to execute one or more functions embodied by a computer program. Alternatively, the control device and method thereof recorded in the present invention can also be implemented by a special-purpose computer, which is provided by constituting a processor composed of one or more special-purpose hardware logic circuits. Alternatively, the control device and method thereof recorded in the present invention can also be implemented by one or more special-purpose computers, which are composed of a combination of a processor and a memory programmed to execute one or more functions and a processor composed of one or more hardware logic circuits. In addition, the computer program can be stored as an instruction executed by a computer in a computer-readable non-transient physical storage medium.

[0073] The present invention has been described based on the embodiments. However, the present invention is not limited to the embodiments and structures. The present invention also includes various modifications and variations within the equivalent range. In addition, various combinations and modes, even other combinations and modes including only one element, more than one or less than one element, also fall within the scope and thought range of the present invention.

Claims

1. A steering control device for controlling the steering of each wheel in a vehicle (100), the vehicle comprising a plurality of steering actuators (71-74) for independently steering three or more wheels (91-94) that are not mechanically constrained from each other, and a steering mechanism (95) of a steer-by-wire system or a steering command device (96) for automatic driving that is mechanically separated from the steering actuators, characterized in that: have: A final steering command value generating unit (55) is configured to generate a final steering command value based on the steering angle signal (θst) output by the steering mechanism or the steering command value (St * ), generate the final steering command value (St ** ); A steering angle command value calculation unit (56) is configured to calculate a steering angle command value (θ1 * -θ4 * ); as well as a plurality of steering actuator control units (601-604), which are provided corresponding to the plurality of steering actuators and control the driving current supplied to the steering actuators so that the steering angle output by the steering actuators follows the steering angle command value; 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 (V) so that the steering is more suppressed with respect to the final steering command value as the vehicle speed increases.

2. The steering control device according to claim 1, characterized in that: A turning center setting unit (56) is provided, which sets the vehicle turning center (C) based on the final steering command value and the vehicle speed, The turning center setting unit calculates the steering angle command value of each wheel so that the steering direction of each wheel is orthogonal 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. The steering control device according to claim 2, characterized in that: A set axis (Xs) is defined that is orthogonal to the front and rear axes (Y0) of the vehicle. The turning center setting unit operates a turning center setting distance (Dc) which is the distance from the front and rear axles of the vehicle to the turning center of the vehicle and sets the turning center of the vehicle on the setting axis. The turning center setting unit determines the turning center setting distance based on a three-dimensional map that defines a relationship between the final steering command value and the turning center setting distance for a plurality of vehicle speeds.

4. The steering control device according to claim 2, characterized in that: A plurality of setting axes (Xl, Xm, Xh) orthogonal to the front and rear axes (Y0) of the vehicle are defined. The turning center setting unit operates a turning center setting distance (Dc) and sets the turning center of the vehicle on any one of the setting axes, wherein the turning center setting distance is the distance from the front and rear axles of the vehicle to the turning center of the vehicle. The turning center setting unit sets the setting axis of the vehicle turning center according to the vehicle speed change, and for the set setting axis, determines the turning center setting distance according to a three-dimensional mapping diagram, which stipulates the relationship between the final steering command value and the turning center setting distance for multiple vehicle speeds.

5. The steering control device according to any one of claims 1 to 4, characterized in that: The steering angle signal, the steering command value, and the final steering command value are defined as 0 when the vehicle is moving straight, and as positive or negative values ​​according to the steering direction relative to the neutral position. The steering angle command value calculation unit calculates the steering angle command value for each wheel so as to maintain a straight traveling state of the vehicle when the absolute value of the final steering command value is smaller than a steering lower limit threshold value (StLth).

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