steering device

Abstract

To provide a steering device which can achieve a desired vehicle operation mode, in an independent steering wheel having three or more wheels.SOLUTION: A steering device 801 controls steering angles of each wheel 91 to 94, in a vehicle 100 where three or more wheels 91 to 94 that are not mutually mechanically restricted are independently steerable. A vehicle operation determination part 65 determines a vehicle operation mode including an advance / turning mode, a non-advance / turning mode and a lateral movement mode on the basis of a vehicle state. A turning center coordinate determination part 66 determines a coordinate of a turning center C of a vehicle 100 on the basis of the vehicle operation mode determined by the vehicle operation determination part 65. Steering angle calculation parts 671 to 674 calculate steering angle command values of the respective wheels 91 to 94, on the basis of the coordinate of the turning center C determined by a turning center coordinate determination part 67. Steering actuators 71 to 74 are provided corresponding to the respective wheels 91 to 94, and steer the respective wheels 91 to 94 according to the steering angle command values calculated by the steering angle calculation parts 671 to 674.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] 2. Description of the Related Art Conventionally, steering devices are known that attempt to realize a turning operation suited to the vehicle state.

[0003] For example, the vehicle steering system disclosed in Patent Document 1 changes the steering ratio between the inner wheel and the outer wheel based on vehicle speed so that the left and right front wheels are steered according to Ackermann geometry at low speeds and according to parallel geometry at high speeds. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-169248 Summary of the Invention [Problem to be solved by the invention]

[0005] In the vehicle steering system of Patent Document 1, the left and right rear wheels do not steer, and the area in which the vehicle's turning center can be set is limited to the rear wheel axle passing through the center of the left and right rear wheels. In contrast to this conventional technology, in a four-wheel independently steering vehicle, in which the left and right rear wheels can be steered independently in addition to the left and right front wheels, the area in which the turning center can be set is expanded to a wider range. By setting the turning center within this expanded area and steering each wheel, turning operations suitable for driving in urban areas, which were not possible with conventional non-independently steering vehicles, are possible. A steering theory unique to such independently steering vehicles has not been known until now.

[0006] The present invention has been made in view of the above points, and its object is to provide a steering device that can realize a desired vehicle operation mode in an independently steering vehicle having three or more wheels. [Means for solving the problem]

[0007] The steering device of the present invention controls the steering angle of each wheel in a vehicle (100) in which three or more wheels (91-94) that are not mechanically constrained to one another, including one or more front wheels and one or more rear wheels, can be steered independently. The steering device includes a vehicle operation determination unit (65), a turning center coordinate determination unit (66), one or more steering angle calculation units (67, 671-674), and a plurality of steering actuators (71-74).

[0008] The vehicle operation determination unit determines a vehicle operation mode based on the vehicle state, including a forward turning mode in which the vehicle turns while moving forward, a non-forward turning mode in which the vehicle turns without moving forward, and a lateral movement mode in which the vehicle moves laterally relative to the front and rear axes. The vehicle state includes, for example, vehicle speed and actual steering angles of each wheel. The turning center coordinate determination unit determines the coordinates of the turning center (C) of the vehicle based on the vehicle operation mode determined by the vehicle operation determination unit. The steering angle calculation unit calculates a steering angle command value for each wheel based on the coordinates of the turning center determined by the turning center coordinate determination unit. The steering actuators are provided corresponding to each wheel and steer each wheel in accordance with the steering angle command value calculated by the steering angle calculation unit.

[0009] An axis that passes through the center of the front wheels and is perpendicular to the vehicle's front-rear axis (Y0) is defined as the front wheel axis (X12), and an axis that passes through the center of the rear wheels and is perpendicular to the vehicle's front-rear axis is defined as the rear wheel axis (X34). When the vehicle operation determination unit commands a forward turning mode, the turning center coordinate determination unit determines the coordinates of one turning center on the inside of the turning and outside the vehicle between the front wheel axis and the rear wheel axis. When the vehicle operation determination unit commands a non-forward turning mode, the turning center coordinate determination unit determines the coordinates of one turning center inside the vehicle.

[0010] When the vehicle operation determination unit commands a lateral movement mode from forward travel, the turning center coordinate determination unit determines the coordinates of two turning centers rearward of the rear wheel axle and spaced apart in the left-right direction of the vehicle.When the vehicle operation determination unit commands a lateral movement mode from reverse travel, the turning center coordinate determination unit determines the coordinates of two turning centers forward of the front wheel axle and spaced apart in the left-right direction of the vehicle.

[0011] In the present invention, by setting the coordinates of the turning center in vehicle operation modes such as forward turning mode, non-forward turning mode, and lateral movement mode to an expanded range that is wider than the conventional settable range, it is possible to achieve vehicle operation with a high degree of freedom that is particularly suitable for driving in urban areas. Preferably, the steering angle calculation unit calculates the steering angle of each wheel so that the steering direction of each wheel is perpendicular to a line connecting the turning center and the center of each wheel. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a block diagram of a steering device according to a first embodiment. [Figure 2] 3A and 3B are diagrams showing specific examples of the steering module; [Figure 3] 1A and 1B are diagrams illustrating a turning operation according to parallel geometry. [Figure 4] FIG. 1 is a diagram showing a turning operation according to Ackermann geometry. [Figure 5]Schematic diagram showing link mechanisms corresponding to (a) parallel geometry and (b) Ackermann geometry. [Figure 6] 10A and 10B are diagrams showing vehicle operation in forward turning mode (small U-turn); [Figure 7] 10A and 10B are diagrams showing vehicle operation in a forward turning mode (narrow road crank traveling); [Figure 8] FIG. 10 is a diagram showing a turning center setting region in a forward turning mode. [Figure 9] 10A and 10B are diagrams showing vehicle operation (spin turn) in a non-progressive turning mode. [Figure 10] FIG. 10 is a diagram showing a turning center setting region in a non-progressive turning mode (spin turning). [Figure 11] 10A and 10B are diagrams showing vehicle operation (pivot turning) in a non-forward turning mode. [Figure 12] FIG. 10 is a diagram showing a turning center setting region in a non-forward turning mode (point turning). [Figure 13] 10A and 10B are diagrams showing vehicle operation in a lateral movement mode from forward movement; [Figure 14] FIG. 10 is a diagram showing a turning center setting region in a lateral movement mode (when moving diagonally) from forward movement. [Figure 15] FIG. 10 is a diagram showing a turning center setting region in a lateral movement mode from forward movement (when moving directly lateral). [Figure 16] 10A and 10B are diagrams showing the vehicle operation in a lateral movement mode from reverse; [Figure 17] FIG. 10 is a diagram showing a turning center setting region in a lateral movement mode (when moving diagonally) from reverse. [Figure 18] FIG. 10 is a diagram showing a turning center setting region in a lateral movement mode from reverse (when moving directly lateral). [Figure 19] 10A and 10B are diagrams illustrating vehicle operation in a lateral movement mode from a stop. [Figure 20] A diagram summarizing the turning center setting area (extension area) for each vehicle operation mode. [Figure 21] 10 is a flowchart of a vehicle operation mode switching determination process. [Figure 22] FIG. 4 is a diagram illustrating a calculation formula for a steering angle using coordinates with the center of gravity as the origin. [Figure 23] FIG. 4 is a diagram for explaining determination of turning center coordinates when turning left; [Figure 24] FIG. 4 is a diagram for explaining determination of turning center coordinates when turning right. [Figure 25] FIG. 10 is a diagram illustrating a first embodiment of determining the coordinates of the turning center in the forward turning mode. [Figure 26] FIG. 10 is a diagram illustrating a second embodiment of determining the turning center coordinates in the forward turning mode. [Figure 27] FIG. 10 is a diagram illustrating a third embodiment of determining the turning center coordinates in the forward turning mode. [Figure 28] FIG. 10 is a diagram illustrating a fourth embodiment of determining the turning center coordinates in the forward turning mode. [Figure 29] FIG. 10 is a diagram illustrating a first embodiment of determining turning center coordinates in a non-progressing turning mode. [Figure 30] A reference diagram showing the turning center coordinates in non-forward turning mode (ultra-spin turning). [Figure 31] FIG. 10 is a diagram of a second embodiment for determining turning center coordinates in a non-progressing turning mode. [Figure 32] FIG. 10 is a diagram illustrating a third embodiment of determining the turning center coordinates in the non-progressing turning mode. [Figure 33] FIG. 10 is a diagram illustrating a first embodiment of determining the coordinates of the turning center in the lateral movement mode. [Figure 34] FIG. 10 is a diagram illustrating a second embodiment of determining the coordinates of the turning center in the lateral movement mode. [Figure 35] FIG. 10 is a diagram illustrating a third embodiment of determining the coordinates of the turning center in the lateral movement mode. [Figure 36] FIG. 6 is a block diagram of a steering device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Several embodiments of the steering device according to the present invention will be described with reference to the drawings. In several embodiments, substantially the same configurations are assigned the same reference numerals and descriptions thereof will be omitted. The first and second embodiments will be collectively referred to as "the present embodiment." The steering device of the present embodiment controls the steering angle of each wheel in a vehicle in which four wheels that are not mechanically constrained from one another can be steered independently.

[0014] (First embodiment) The configuration of steering device 801 of the first embodiment will be described with reference to Figures 1 and 2. In independently steering vehicle 100 shown in Figure 1, four wheels 91-94 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."

[0015] Steering modules 81-84, in which steering angle calculation units 671-674 and steering actuators 71-74 are integrated, are provided corresponding to each of the wheels 91-94. The steering actuators 71-74 are typically constituted by motors. The numbers "1" to "4" at the end of the reference numerals of each element indicate the corresponding wheels 91-94. For example, steering module 81, in which steering angle calculation unit 671 and steering actuator 71 are integrated, corresponds to left front wheel 91.

[0016] The steering device 801 includes a vehicle operation command device 601 and four steering modules 81-84 corresponding to each of the wheels 91-94. The vehicle operation command device 601 is equipped with a vehicle operation determination unit 65 and a turning center coordinate determination unit 66. The vehicle operation determination unit 65 determines a vehicle operation mode (described later) based on vehicle state information including the vehicle speed and the actual steering angle of each of the wheels 91-94. Although not shown, the vehicle speed is detected by, for example, a vehicle speed sensor. The actual steering angle of each of the wheels 91-94 is estimated by, for example, converting the rotation angle detection value of a steering actuator. 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.

[0017] Turning center coordinate determiner 66 determines the coordinates of the turning center of the vehicle based on the vehicle operation mode determined by vehicle operation determiner 65. Steering angle calculators 671-674 calculate steering angle command values ​​for the corresponding wheels 91-94 based on the coordinates of the turning center determined by turning center coordinate determiner 66. Steering actuators 71-74 steer each of the wheels 91-94 in accordance with the steering angle command values ​​calculated by steering angle calculators 671-674.

[0018] Figure 2 shows a specific example of the form of steering modules 81-84. In the first embodiment, an "electronic integrated" configuration is adopted in which steering angle calculation units 671-674 corresponding to each wheel 91-94 and steering actuators 71-74 are provided integrally. Steering actuators 71-74 operate in accordance with the steering angle command values ​​calculated by steering angle calculation units 671-674 for each wheel. By providing steering angle calculation units 671-674 in a dispersed manner, the risk of the steering angle calculation function for all wheels 91-94 failing all at once is avoided.

[0019] In contrast to the independently steering vehicle 100 in which the wheels 91-94 are not mechanically constrained to one another, a conventional vehicle is a "non-independently steering vehicle" in which the left and right front wheels and the left and right rear wheels are connected by rack bars. Before explaining the steering theory according to this embodiment, turning operations according to parallel geometry and Ackermann geometry will be explained as steering theories for conventional vehicles with rack bars with reference to FIGS. The following explanation mainly focuses on a left turning operation as an example.

[0020] As shown in Figures 3 and 4, in a non-independently steered vehicle 109, the left and right front wheels 91, 92 are connected by a rack bar 95, and the left and right rear wheels 93, 94 are connected by a rack bar 96. The mechanism connecting the left and right front wheels 91, 92 is shown in Figures 5(a) and 5(b). The left and right front wheels 91, 92 can be steered within a predetermined range by a link mechanism of a tie rod 97 and a knuckle 98. On the other hand, the left and right rear wheels 93, 94 do not steer, so the turning center C is set on the rear wheel axis X34.

[0021] As shown in FIG. 5(a), in a parallel geometry link mechanism, the positional relationship between the tie rod 97 and the knuckle 98 is fixed. As shown in FIG. 3, in a turning operation according to parallel geometry, the left front wheel 91 and the right front wheel 92 are steered in parallel. That is, the turning angle θ1 of the left front wheel 91 and the turning angle θ2 of the right front wheel 92 are equal. The center of gravity G of the vehicle moves in an arc with a turning radius R relative to the turning center C. The left front wheel 91 and the right front wheel 92 turn while the tires skid. In addition, an inner wheel difference Δi between the left front wheel 91 and the left front wheel 93 and an outer wheel difference Δo between the right front wheel 91 and the right rear wheel 93 occur.

[0022] As shown in Fig. 5(b), in the link mechanism of Ackermann geometry, the positional relationship between the tie rod 97 and the knuckle 98 is set to be flexible. As shown in Fig. 4, in a turning operation according to the Ackermann geometry, the steering direction of the left front wheel 91 is perpendicular to a line N1 connecting the turning center C and the center of the left front wheel 91, and the steering direction of the right front wheel 92 is perpendicular to a line N2 connecting the turning center C and the center of the right front wheel 92.

[0023] When viewed from directly above, the straight lines that pass through the center of the width of the left and right front wheels 91, 92 and that run along the steering direction are referred to as "wheel width center lines S1, S2." In a turning operation according to Ackermann geometry, the wheel width center lines S1, S2 of the left and right front wheels 91, 92 are tangents to a turning circle centered at the turning center C. In other words, the straight lines N1, N2 that connect the turning center C and the center of each front wheel 91, 92 are normals to the wheel width center lines S1, S2.

[0024] The front wheel 91 on the inside of the turn describes an arc with a turning radius ri, and the front wheel 92 on the outside of the turn describes an arc with a turning radius ro, turning without skidding. The steering angle θ1 of the front wheel 91 on the inside of the turn is greater than the steering angle θ2 of the front wheel 92 on the outside of the turn. Furthermore, the steering angles θ1 and θ2 become smaller as the turning center C moves away from the vehicle, and the steering angles θ1 and θ2 become larger as the turning center C moves closer to the vehicle. When the turning center Ce is set at the limit position closest to the vehicle, the steering angles θ1 and θ2 are maximum. In this way, the area on the rear wheel axle X34 outside the limit position becomes the turning center setting area.

[0025] With parallel geometry, tire force can be used effectively at high speeds, making stable cornering possible. However, tire sideslip occurs significantly at low to medium speeds, making smooth cornering difficult. On the other hand, with Ackermann geometry, tire force cannot be used effectively at high speeds, making stable cornering difficult. However, tire sideslip is minimal at low to medium speeds, making smooth cornering possible. Therefore, Ackermann geometry is effective for driving in urban areas at low to medium speeds.

[0026] However, assuming that rear wheels 93, 94 are not steered, the turning center setting region is limited to a region outside the limit position on rear wheel axis X34. Also, an inner wheel difference Δi and an outer wheel difference Δo occur. As a result, the benefits of Ackermann geometry may not be fully utilized for the desired vehicle operation. Therefore, in this embodiment, an object is to establish a steering theory that extends the Ackermann theory in order to preferably realize a desired vehicle operation mode with independently steering vehicle 100.

[0027] The vehicle operation determination unit 65 of this embodiment determines the following three vehicle operation modes based on the vehicle state: [1] a "forward turning mode" in which the vehicle turns while moving forward, [2] a "non-forward turning mode" in which the vehicle turns without moving forward, and [3] a "lateral movement mode" in which the vehicle moves laterally relative to the front-rear axis.

[0028] Next, each vehicle operation mode and its turning center setting region will be described with reference to Figures 6 to 19. In Figure 8 and other figures, 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. Furthermore, 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 vehicle's longitudinal direction is uniform, the center of gravity axis X0 is located midway between the front wheel axis X12 and the rear wheel axis X34.

[0029] 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 referred to 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 referred to 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). The vehicle's center of gravity G is located on the vehicle's front-rear axis Y0.

[0030] The area between the front wheel axis X12 and the rear wheel axis X34 in the longitudinal direction of the vehicle, and between the left front and rear wheel axis Y13 and the right front and rear wheel axis Y24 in the transverse direction of the vehicle, is referred to as the "interior of the vehicle." Areas other than the interior of the vehicle are referred to as the "exterior of the vehicle." According to this definition, the front of the engine compartment and the rear of the trunk are technically inside the vehicle body, but are also outside the vehicle. However, in reality, the boundary area can be considered flexibly, and the "exterior of the vehicle" and the "exterior of the vehicle body" can be interpreted as synonymous.

[0031] [1] Progressive turning mode Please refer to Figures 6 to 8. As examples of vehicle operation in the forward turning mode, Figure 6 shows a tight U-turn, and Figure 7 shows narrow road cranking. In the case of a tight U-turn, the vehicle 100 turns continuously in the same direction (for example, to the left) while moving forward. In the case of narrow road cranking, the vehicle 100 transitions, for example, from a left turn to a right turn while moving forward.

[0032] Figure 8 shows the turning center setting region in forward turning mode. When the vehicle operation determination unit 65 commands the forward turning mode, the turning center coordinate determination unit 66 determines the coordinates of one turning center C on the inside of the turn and outside the vehicle between the front wheel axle X12 and the rear wheel axle 34. Once the turning center C is determined, the turning radius R of the vehicle center of gravity G is determined. The turning radius R in the forward turning mode is equal to or greater than half the tread width D. In other words, the relationship "R≧(D / 2)" holds.

[0033] Furthermore, the steering angle calculation units 671-674 calculate the steering angle of each of the wheels 91-94 based on the Ackermann theory so that the steering direction of each of the wheels 91-94 is perpendicular to the straight lines N1-N4 connecting the turning center C and the center of each of the wheels 91-94. A specific equation for calculating the steering angle will be described later with reference to FIG.

[0034] The turning center of the turning operation according to the Ackermann geometry in the non-independently steered vehicle 109 shown in FIG. 4 is defined as the "conventional turning center Co." As described above, the conventional turning center Co is set on the rear wheel axle X34. The operation of moving the turning center C from the conventional turning center Co to the turning center setting region hatched with dashed lines represents an "extension of the Ackermann theory." Therefore, the turning center setting region of this embodiment is also referred to as the "extended region."

[0035] As shown in Figure 8, the extended area for left turning is defined on the left side of the vehicle. On the other hand, the extended area for right turning is defined on the right side of the vehicle. In the first half of the narrow crank driving, the turning center C is set in the extended area on the left side of the vehicle, which corresponds to the inside of the turn. In the second half of the narrow crank driving, the turning center C is set in the extended area on the right side of the vehicle, which corresponds to the inside of the turn.

[0036] In the example shown in Fig. 8, the turning center C is set on the center of gravity axis X0 in the extended region. In this case, 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 inner wheel difference Δi and the outer wheel difference Δo are zero. On the other hand, if the turning center C is set other than on the center of gravity axis X0, the inner wheel difference Δi and the outer wheel difference Δo can be set to any value.

[0037] [2] Non-progressive turning mode See Figures 9 to 12. As examples of vehicle operation in the non-advancing turning mode, Figure 9 shows a super-spin turn, and Figure 11 shows a pivot turn. In the case of a super-spin turn, the vehicle 100 turns on the spot from a stopped state. For example, when there is a dead end ahead, it is possible to turn 180 degrees by performing a super-spin turn and return without having to drive in reverse. In the case of a pivot turn, the vehicle 100 turns from a stopped state by using one wheel as a fulcrum to drive the other wheels. For example, when there is an obstacle directly ahead, it is possible to turn diagonally by performing a pivot turn and move forward.

[0038] 10 and 12 show the turning center setting region (extended region) in non-advancing turning mode. When vehicle operation determination unit 65 commands non-advancing turning mode, turning center coordinate determination unit 66 determines the coordinates of one turning center C inside the vehicle. The turning radius R in non-advancing turning mode is less than 1 / 2 the tread width D. In other words, the relationship "R<(D / 2)" holds. As in the advancing turning mode, steering angle calculation units 671-674 calculate the steering angle of each wheel 91-94 based on Ackermann's theory so that the steering direction of each wheel 91-94 is perpendicular to the straight lines N1-N4 connecting the turning center C and the center of each wheel 91-94.

[0039] As shown in Fig. 10, in the case of a pivot turn, the turning center C coincides with the vehicle center of gravity G, and the turning radius R is "R = 0." The four wheels 91-94 turn on the same circle.

[0040] As shown in FIG. 12, in the case of a pivot turn, the turning center C coincides with the center of one of the wheels. For example, if the left rear wheel 93 is set as the turning center C, the steering direction of the left front wheel 91 is perpendicular to the line N1 on the left front / rear wheel axis Y13, so it faces straight sideways. In other words, the steering angle is 90°. The steering direction of the right rear wheel 94 is perpendicular to the line N4 on the rear wheel axis X34, so it faces straight ahead. In other words, the steering angle is 0°.

[0041] [3A] Sideways movement mode from forward movement Please refer to Figs. 13 to 15. Fig. 13 shows an example of vehicle operation in the lateral movement mode from forward movement. Assume a situation in which the host vehicle 100 is parallel parking in the space between other vehicles 201 and 202 parked on the left side of the road. The host vehicle 100, which has come forward, faces straight in the direction of travel, Move diagonally and then <ii>Move sideways to reach the target position.

[0042] 14 and 15 show the turning center setting region (extended region) in lateral movement mode from forward movement. In lateral movement mode, the turning center C cannot be set so that a straight line perpendicular to the wheel width center lines S1-S4 of the four wheels 91-94 intersects at a single point. In other words, the lateral movement mode is a vehicle operation that goes beyond the conventional concept of turning of a non-independently steered vehicle 109, and requires further theoretical extension to the steering theory that assumes a single turning center Co.

[0043] Therefore, when the vehicle operation determination unit 65 commands a lateral movement mode from forward travel, the turning center coordinate determination unit 66 determines the coordinates of two turning centers C1, C2 that are located rearward of the rear wheel axis X34 and spaced apart in the left-right direction of the vehicle 100. The first turning center C1 is the turning center for the front and rear wheels 91, 93 on the inside of the turn. The second turning center C2 is the turning center for the front and rear wheels 92, 94 on the outside of the turn. Since there is no point in simply comparing this with a conventional turning center Co, dashed arrows pointing to the conventional turning center Co and the turning center C of this embodiment are omitted in Figures 14 and 15.

[0044] As shown in Figure 14, when the vehicle 100 moves diagonally from forward, the first and second turning centers C1 and C2 are set at the rear left of the vehicle 100. As the vehicle 100 moves diagonally forward to the left, the first and second turning centers C1 and C2 approach directly behind the vehicle 100. In addition, the steering angles of the wheels 91-94 gradually approach 90°. The vehicle 100 gradually approaches the target position while moving diagonally.

[0045] As shown in Figure 15, when the steering angle of each wheel 91-94 reaches 90°, the vehicle 100 transitions to lateral movement. The turning center coordinate determination unit 66 determines the coordinate of a first turning center C1 on the front and rear wheel axis Y13 on the inside of the turning, and determines the coordinate of a second turning center C2 on the front and rear wheel axis Y24 on the outside of the turning. The wheel width center lines S1, S3 of the left front wheel 91 and the left rear wheel 93 are perpendicular to the straight lines N1, N3 on the left front and rear wheel axis Y13. The wheel width center lines S2, S4 of the right front wheel 92 and the right rear wheel 94 are perpendicular to the straight lines N2, N4 on the right front and rear wheel axis Y24. The vehicle 100 moves lateral and reaches the target position.

[0046] [3B] Lateral movement mode from reverse Please refer to Figs. 16 to 18. Figs. 16 to 18 are the reversed versions of Figs. 13 to 15, which relate to the lateral movement mode from forward travel, and therefore basically follow the explanation above. Fig. 16 shows an example of vehicle operation in the lateral movement mode from reverse travel. The host vehicle 100, which has been reversing, remains facing straight in the direction of travel, Move diagonally and then <ii>Move sideways to reach the target position.

[0047] 17 and 18 show the turning center setting region (extended region) in the lateral movement mode from reverse. When the vehicle operation determination unit 65 commands the lateral movement mode from reverse, the turning center coordinate determination unit 66 determines the coordinates of two turning centers C1 and C2 that are spaced apart in the left and right directions of the vehicle 100 and are forward of the front wheel axis X12. The first turning center C1 is the turning center for the front and rear wheels 91 and 93 on the inside of the turn. The second turning center C2 is the turning center for the front and rear wheels 92 and 94 on the outside of the turn.

[0048] 17, when the vehicle 100 moves diagonally from reverse, the first and second turning centers C1 and C2 are set to the left front of the vehicle 100. As the vehicle 100 moves diagonally rearward to the left, the first and second turning centers C1 and C2 approach directly in front of the vehicle 100. In addition, the steering angles of the wheels 91-94 gradually approach -90°.

[0049] 18, when the steering angle of each wheel 91-94 reaches -90°, the vehicle shifts to lateral movement. The turning center coordinate determination unit 66 determines the coordinate of a first turning center C1 on the front and rear wheel axis Y13 on the inside of the turning, and determines the coordinate of a second turning center C2 on the front and rear wheel axis Y24 on the outside of the turning.

[0050] [3C] Sideways movement mode from a stop Figure 19 shows an example of vehicle movement in the sideways movement mode from a stop. In the same parallel parking situation as [3A] and [3B], the vehicle moves forward or backward to a position directly beside the parking space, stops once, and then moves sideways with the steering angle of all wheels 91-94 set to ±90°. This vehicle movement is similar to that of [3A] and [3B]. There is no diagonal movement stage, <ii>15 and 18, the turning center coordinate determination unit 66 determines the coordinate of the first turning center C1 on the front and rear wheel axis Y13 on the inside of the turning, and determines the coordinate of the second turning center C2 on the front and rear wheel axis Y24 on the outside of the turning.

[0051] Figure 20 is a diagram summarizing the turning center setting range (extension range) in each vehicle operation mode. As described above with reference to Figure 4, the conventional turning center Co can be set only outside the limit position on the rear wheel axis X34. This limits the range of vehicle operation in which the benefits of Ackermann geometry can be utilized.

[0052] In contrast, in this embodiment, the area outside the vehicle on the inside of the turn between the front wheel axle X12 and the rear wheel axle X34 is the extended area [1] in the forward turning mode. The area inside the vehicle is the extended area [2] in the non-forward turning mode. Furthermore, the area behind the rear wheel axle X34 is the extended area [3A-3C] in the forward or lateral movement from a stop mode, and the area ahead of the front wheel axle X12 is the extended area [3B-3C] in the reverse or lateral movement from a stop mode. This increases the degree of freedom in setting the turning center C according to the desired vehicle operation.

[0053] 21, a description will be given of the vehicle operation mode switching process performed by the vehicle operation determination unit 65. The vehicle operation determination unit 65 determines whether the vehicle operation mode can be appropriately switched between the forward turning mode, the non-forward turning mode, and the lateral movement mode according to the current vehicle state, and if switching is possible, turns on a switching permission flag. When the vehicle operation mode is switched, the turning center coordinate determination unit 66 determines the coordinates of the turning center in the new extended region.

[0054] On the other hand, if the vehicle operation determination unit 65 determines that the vehicle operation mode cannot be switched appropriately, the switching permission flag is not turned on and the current vehicle operation mode is maintained. The turning center coordinate determination unit 66 can freely move the coordinates of the turning center within the current extended area. In the following explanation of the flowchart, the symbol "S" means a step.

[0055] In S1, the vehicle operation determination unit 65 acquires the current vehicle speed and the actual steering angles of the wheels 91-94. The vehicle operation determination unit 65 also calculates, as an evaluation value, for example, the average value or the value with the maximum absolute value among the actual steering angles of the four wheels.

[0056] In S2, it is determined whether the vehicle speed is lower than a vehicle speed threshold (for example, several km / hr). If the vehicle is traveling at an extremely low speed or stopped, the answer is YES in S2, and the process proceeds to S3. In S3, it is determined whether the vehicle speed is 0, i.e., whether the vehicle is stopped. If the vehicle is stopped, the answer is YES in S3, and the process proceeds to S5. If the vehicle is traveling at a low speed (several km / hr or more) to a medium to high speed, the answer is NO in S2.

[0057] When the vehicle is not stopped but moving, S3 judges NO, and S4 judges whether the absolute value of the actual steering angle is smaller than the steering angle threshold. For example, when starting a turn from straight driving, S4 judges YES, and the process moves to S6. When returning from a turn to straight driving, if the wheels have not returned to a straight position, S4 judges NO.

[0058] In S5, the vehicle operation determination unit 65 turns on a switching permission flag for the [1] forward turning mode, [2] non-forward turning mode, or [3C] lateral movement mode from stop, which enables the turning center coordinate determination unit 66 to determine the coordinates of the turning center C in the extended areas [1], [2], and [3C].

[0059] In S6, the vehicle operation determination unit 65 turns on a switching permission flag for the [1] forward turning mode, the [3A] lateral movement mode from forward, or the [3B] lateral movement mode from reverse, thereby enabling the turning center coordinate determination unit 66 to determine the coordinates of the turning center C in the extended areas [1], [3A], and [3B].

[0060] If the answer is NO in S2 or S4, the switching permission flag is not turned on and the routine returns to before S1 and is repeated. In other words, the current vehicle operation mode is maintained until the vehicle stops or moves at an extremely low speed and in a substantially straight line.

[0061] Next, with reference to Figure 22, we will explain how the turning center coordinate determiner 66 determines the coordinates of the turning center C. There are several ways of thinking about where to set the origin of the coordinates. For example, the turning center C could be set as the origin, but because the coordinates of each wheel 91-94 viewed from the turning center C change from moment to moment, it would be necessary to constantly correct the steering angle, which would require a huge amount of calculation.

[0062] Therefore, preferably, the turning center coordinate determination unit 66 determines the coordinate of the turning center C using the center of gravity G of the vehicle 100 as the origin. The coordinates of each wheel 91-94 as viewed from the center of gravity G are defined using the tread width and wheelbase. By setting the coordinate of the turning center C as a variable, the steering angle of each wheel 91-94 can be described by a simple calculation formula. This can also be used in all expansion areas.

[0063] As shown in Figure 22, an xy coordinate system is defined with the vehicle center of gravity G as the origin (0,0), the center of gravity axis X0 as the x axis, and the vehicle longitudinal axis Y0 as the y axis. On the x axis, the right side of the center of gravity G is positive and the left side is negative, and on the y axis, the front side of the center of gravity G is positive and the rear side is negative. The coordinates of the turning center C are expressed as (X,Y). When turning left, "X<0", and when turning right, "X>0".

[0064] The tread width of the front wheels 91, 92 is represented as Df, and the tread width of the rear wheels 93, 94 is represented as Dr. Furthermore, within the wheelbase L, the distance from the center of gravity axis X0 to the front wheel axle X12 is defined as the front wheel axle distance Lf, and the distance from the center of gravity axis X0 to the rear wheel axle X34 is defined as the rear wheel axle distance Lr. The values ​​of Df, Dr, Lf, and Lr are stored as vehicle characteristics.

[0065] The steering angle calculation units 671-674 calculate the tangent values ​​of the steering angles δFL, δFR, δRL, and δRR of each wheel 91-94 using equations (0.1)-(0.4) so ​​that the steering direction of each wheel 91-94 is perpendicular to the straight lines N1-N4 connecting the turning center C and the center of each wheel 91-94. The steering angles are expressed as positive in the counterclockwise direction from the neutral position and negative in the clockwise direction from the neutral position. The subscripts "FL, FR, RL, RR" in Figure 22 will be written in normal letters in the specification.

[0066] tanδFL=(Y-Lf) / {X+(Df / 2)}···(0.1) tanδFR=(Y-Lf) / {X-(Df / 2)}···(0.2) tanδRL=(Y+Lr) / {X+(Dr / 2)}···(0.3) tanδRR=(Y+Lr) / {X-(Dr / 2)}···(0.4)

[0067] [Determining the turning center coordinates based on the steering angles of the inside front and rear wheels] In the basic configuration of vehicle operation command device 601 of the first embodiment described above, steering angle calculation units 671-674 calculate command values ​​for steering angles δFL, δFR, δRL, δRR of each wheel 91-94 based on the coordinate of turning center C determined by turning center coordinate determination unit 66. When all wheels 91-94 can be steered within a range of ±90°, the coordinate of turning center C can be determined without any restrictions.

[0068] However, various types of steering modules are used for independently steering vehicles depending on the vehicle's use, and depending on the structure of the steering module, the maximum steering angle may be less than 90°. In the following description, "maximum steering angle" refers to the steering angle with the largest absolute value, regardless of sign. For example, "maximum steering angle of 90°" means that steering is possible within a range from a steering angle of -90° to the right to a steering angle of 90° to the left.

[0069] For example, a steering module with an integrated structure in which the steering motor is attached to the inside of the wheel is a "small steering module" with a maximum steering angle of about 45°. A rack bar type steering module is a "medium steering module" with a maximum steering angle of about 70°. As shown in Fig. 2, an arm type steering module in which the rotation of a steering motor installed above the wheel is transmitted to the wheel via an arm is a "large steering module" with a maximum steering angle of 90° or more.

[0070] When the basic configuration of vehicle operation command device 601 is applied to a vehicle with a small steering module or a medium steering module, even if the coordinate of turning center C is determined based on the vehicle operation mode and then the steering angle command value for each wheel is calculated, there may be cases where that steering angle is mechanically impossible to achieve. Alternatively, even if the steering angle is within a range below the mechanical maximum steering angle, it is conceivable that the maximum steering angle will be temporarily limited due to an abnormality in the steering actuator at that time, a current limit, or the like. And, particularly when turning according to the Ackermann geometry, the bottleneck that determines the limit of vehicle operation is the maximum steering angle of the wheel on the inside of the turn.

[0071] One possible control configuration is to redetermine the coordinate of turning centre C if the calculated steering angle command value is not achievable. However, if the steering angles achievable by the inside wheel are determined in advance, it is more efficient for turning centre coordinate determiner 66 to determine the coordinate of turning centre C based on the steering angle of the inside wheel. After turning centre coordinate determiner 66 determines the coordinate of turning centre C, steering angle calculation units 671-674 calculate the steering angle command value for the outside wheel, as in the basic configuration.

[0072] 23 and 24, a control configuration for determining the coordinate of the turning center C according to a preferred embodiment will be described. Fig. 23 is a diagram for explaining calculation of the coordinate of the turning center C when turning left, and Fig. 24 is a diagram for explaining calculation of the coordinate of the turning center C when turning right. This control configuration is applied to a four-wheeled vehicle 100 including two front wheels 91, 92 and two rear wheels 93, 94, and is premised on the four-wheeled vehicle 100 performing a turning operation in accordance with Ackermann geometry.

[0073] Of the front wheels 91, 92 and rear wheels, the wheels closest to the turning center C are defined as the "inner front wheel" and "inner rear wheel." As shown by the bold frame in Figure 23, when turning left, the left front wheel 91 and left rear wheel 93 are the inner front and rear wheels. As shown by the bold frame in Figure 24, when turning right, the right front wheel 92 and right rear wheel 94 are the inner front and rear wheels. The steering angle of the inner front wheel is represented as δFI, and the steering angle of the inner rear wheel is represented as δRI. The subscripts "FI, RI" in Figures 23 and 24 will be written in normal letters in the specification.

[0074] It is assumed that the steering angle δFI of the inside front wheel and the steering angle δRI of the inside rear wheel have been determined before the coordinate of the turning center C is determined by turning center coordinate determination unit 66. In this case, turning center coordinate determination unit 66 determines the coordinate of the turning center C of the vehicle based on the steering angle δFI of the inside front wheel, the steering angle δRI of the inside rear wheel, the front wheel axle distance Lf, the rear wheel axle distance Lr, the front wheel tread width Df, and the rear wheel tread width Dr.

[0075] Turning center coordinate determination unit 66 uses the same x and y coordinates as in Figure 22 and defines positive and negative steering angles in the same way as in Figure 22. It is also assumed that the steering angle δFI of the inside front wheel and the steering angle δRI of the inside rear wheel satisfy the relationship "δFI ≠ δRI, -90° < δFI < 90°, -90° < δRI < 90°." This assumption is necessary to prevent the denominators from becoming 0 and the tangent values ​​from diverging to infinity in the following equations (1) to (4).

[0076] Examples for each vehicle operation mode will be described later, but the following formulas are commonly applied to calculating the coordinates of the turning center C in the forward turning mode and the non-forward turning mode, as well as the coordinates of the first turning center C1 for the inside front wheel and the inside rear wheel in the lateral movement mode.

[0077] The coordinates (XL, YL) of the turning center C or the first turning center C1 when turning left are calculated using the following equations (1) and (2). The subscript "L" of XL and YL in Figure 23 will be written in normal letters in the specification.

[0078]

number

[0079] The coordinates (XR, YR) of the turning center C or the first turning center C1 when turning right are calculated using the following equations (3) and (4). The subscript "R" of XR and YR in Figure 24 will be written in normal letters in the specification.

[0080]

number

[0081] Equation (1) can be obtained by eliminating Y from equations (0.1) and (0.3) in Figure 22. Equation (2) can be obtained by substituting equation (1) into equation (0.1) and rearranging. Equation (3) can be obtained by eliminating Y from equations (0.2) and (0.4) in Figure 22. Equation (3) can be obtained by substituting equation (0.2) and rearranging. Equation (4) can be obtained.

[0082] Here, the above formulas (1)-(4) are formulas obtained based on the x-y coordinate system with the center of gravity G as the origin and the definitions of positive and negative steering angles used in Figures 22 to 24. The present invention is not limited to these formulas, and the coordinates of the turning center C or the first turning center C1 may be calculated based on other coordinate systems and other definitions of positive and negative steering angles, using formulas with the steering angles δFI, δRI of the front and rear wheels on the inside of the turn, front wheel axle distance Lf, rear wheel axle distance Lr, front wheel tread width Df, and rear wheel tread width Dr as parameters.

[0083] 25 to 35 (excluding FIG. 30), examples are shown in which the coordinates of the turning center C are determined based on the steering angles δFI and δRI of the front and rear wheels on the inside of the turn in each vehicle operation mode. These examples are for the case of a left turn, and the coordinates (XL, YL) of the turning center C are calculated using equations (1) and (2). When turning left, "XL<0".

[0084] To simplify the calculations, the front wheel tread width Df and rear wheel tread width Dr of the vehicle 100 are assumed to be equal, and the tread width D of the front and rear wheel axles (= Df = Dr) is assumed to be 1 except in Figure 32. Also, the front wheel axle distance Lf and the rear wheel axle distance Lr are assumed to be 0.5. In other words, the wheelbase L (= Lf + Lr) is assumed to be 1, and the centers of the four wheels 91-94 are assumed to be located at the vertices of a square with the center of gravity G as the center. "1" and "0.5" are values ​​that indicate a unit length in the length (meter) dimension. For example, "1" corresponds to a length of 1.5 m or 2 m.

[0085] The steering modules 81-84 equipped in the vehicle 100 are assumed to be of three types: [a] small steering module (equivalent to a maximum steering angle of 45°), [b] medium steering module (equivalent to a maximum steering angle of 70°), and [c] large steering module (equivalent to a maximum steering angle of 90° or more). However, for the large steering module, in the following embodiments, the maximum steering angle will be treated as being less than 90°. For example, "less than 90°" may correspond to 89.5° or less, or 89.9° or less, depending on the realistic minimum resolution. In this embodiment, "less than 90°" is treated as "89° or less" in increments of 1°.

[0086] [1] Progressive turning mode See Figures 25 to 28. Examples 1 to 3 shown in Figures 25 to 27 assume a small steering module. In Example 1 shown in Figure 25, the steering angle δFI of inside front wheel 91 is set to 45° and the steering angle δRI of inside rear wheel 93 is set to -45°, and the coordinates of turning center C are calculated as XL = -1.0 and YL = 0. When the front and rear wheels are in opposite phase, that is, when the steering angle δFI of inside front wheel 91 and the steering angle δRI of inside rear wheel 93 have opposite signs but equal absolute values ​​(-δFI = δRI), the coordinate of turning center C is set on the center of gravity axis X0.

[0087] In Example 2 shown in Figure 26, the steering angle δFI of inside front wheel 91 is set to 45°, the steering angle δRI of inside rear wheel 93 is set to 0°, and the coordinates of turning center C are calculated to be XL = -1.5, YL = -0.5. In other words, when only front wheel 91 is steered while rear wheel 93 is kept pointed straight, the coordinates of turning center C are set on rear wheel axis X34. This example is not limited to four-wheel independently steering vehicles, but can also be applied to vehicles in which only left and right front wheels 91, 92 are independently steered.

[0088] In Embodiment 3 shown in FIG. 27, the steering angle δFI of the inner front wheel 91 during turning is determined to be 0°, and the steering angle δRI of the inner rear wheel 93 during turning is determined to be -45°. The coordinates of the turning center C are calculated as XL = -1.5 and YL = 0.5. That is, when only the rear wheel 93 is steered while keeping the front wheel 91 straight, the coordinates of the turning center C are set on the front wheel axis X12. This embodiment is applicable not only to a four-wheel independent steering vehicle but also to a vehicle in which only the left and right rear wheels 93 and 94 are independently steered.

[0089] FIG. 28 shows Embodiment 4 with reverse phase of the front and rear wheels assuming a medium steering module. When the steering angle δFI of the inner front wheel 91 during turning is determined to be 70° and the steering angle δRI of the inner rear wheel 93 during turning is determined to be -70°, the coordinates of the turning center C are calculated as XL ≈ -0.68 and YL = 0. Hereinafter, the decimal places of the calculated values are represented by two significant figures. Further, in the case of reverse phase of the front and rear wheels with a large steering module, as the front wheel steering angle δFI approaches 90° and the rear wheel steering angle δRI approaches -90°, the coordinates of the turning center C asymptote to a point on the center of gravity axis X0 where "XL = -0.5", that is, on the left front and rear wheel axis Y13.

[0090] [2] Non-Advancing Turning Mode Refer to FIGS. 29 to 32. As described above, in the non-advancing turning mode, among each of the front wheels 91 and 92 and each of the rear wheels 93 and 94, the wheels on the side closer to the turning center C are defined as the inner front wheel and the inner rear wheel during turning. When "XL < 0" and the coordinates of the turning center C are on the left side of the vehicle longitudinal axis Y0, a left-handed ground turning is possible. In other words, when the calculated XL is 0 or a positive value, with the steering angles δFI and δRI of the inner front and rear wheels in that vehicle specification being that value, it is determined that the non-advancing turning mode cannot be realized.

[0091] Embodiment 1 shown in FIG. 29 assumes a medium steering module. The steering angle δFI of the inner front wheel 91 during turning is determined to be -70°, and the steering angle δRI of the inner rear wheel 93 during turning is determined to be 70°. The coordinates of the turning center C are calculated as XL ≈ -0.32 and YL = 0. In the case of reverse phase of the front and rear wheels (δFI = -δRI), the coordinates of the turning center C are set between the left front and rear wheel axis Y13 and the vehicle longitudinal axis Y0 (-0.5 < XL < 0) on the center of gravity axis X0.

[0092] 30 is a reference diagram showing a pivot turn in which the turning center C coincides with the center of gravity G in a small steering module in which the steering angle δFI of the inside front wheel 91 is -45° and the steering angle δRI of the inside rear wheel 93 is 45°. When the turning center C coincides with the center of gravity G, the distance from the turning center C to the left front and rear wheels 91, 93 and the distance from the turning center C to the right front and rear wheels 92, 94 are equal, creating a special situation in which both left and right turns are possible. In this case, the "inside front and rear wheels" are not defined, so the turning center coordinate determiner 66 does not apply equations (1) to (4) and determines the coordinates of the turning center C as a special case.

[0093] In contrast, Example 2 shown in Figure 31 assumes the use of a modified steering module in which the maximum steering angle of inside front wheel 91 is expanded to 50° compared to the small steering module. When the steering angle δFI of inside front wheel 91 is -50° and the steering angle δRI of inside rear wheel 93 is 45°, the coordinate of turning center C is slightly shifted toward left rear wheel 93 from center of gravity G. Therefore, left front and rear wheels 91, 93 are defined as the "inside front and rear wheels," and using equations (1) and (2), the coordinates of turning center C are calculated to be XL ≒ -0.044 and YL ≒ -0.044. In this case, a pivot turn that is close to a super pivot turn is achieved.

[0094] Also, in Example 3 shown in Figure 32, tread width D (= Df = Dr) is set to 1.5 in this example only. In this long-tread vehicle in which tread width D is longer than wheelbase L, when steering angle δFI of inside front wheel 91 is -45° and steering angle δRI of inside rear wheel 93 is 45°, the coordinates of turning center C are shifted to the left of center of gravity G. Therefore, left front and rear wheels 91, 93 are defined as "inside front and rear wheels," and using equations (1) and (2), the coordinates of turning center C are calculated as XL = -0.25 and YL = 0. In this case too, a pivot turn that is close to a super pivot turn is achieved.

[0095] [3] Horizontal movement mode See Figures 33 to 35. We will exclude lateral movement (Figure 15) in which the steering angle of each wheel 91-94 is 90°, and focus on diagonal movement from forward travel (Figures 14 and 17). There is a 1° difference between the steering angle δFI of the inside front wheel 91 of the turn and the steering angle δRI of the inside rear wheel axle 93 during diagonal movement. For diagonal movement to the left from forward travel, the conditions are "δFI > 1, δRI = δFI - 1 > 0." Note that for diagonal movement to the left from reverse travel, the conditions are "δFI = δRI + 1 < 0, δRI < -1."

[0096] In lateral movement mode, there are two turning centers C1 and C2 separated laterally. In the case of a left turn, the coordinates of the first turning center C1 for the left front and rear wheels 91 and 93 on the inside of the turn are calculated using equations (1) and (2). Fractions of the calculated values ​​are expressed to two significant digits. The second turning center C2 for the right front and rear wheels 92 and 94 on the outside of the turn is calculated by offsetting the first turning center C1 to the right by the tread width D. In the case of a right turn, the coordinates of the first turning center C1 for the right front and rear wheels 92 and 94 on the inside of the turn are calculated using equations (3) and (4), and the second turning center C2 for the left front and rear wheels 91 and 93 on the outside of the turn is calculated by offsetting the first turning center C1 to the left by the tread width D.

[0097] Example 1 shown in Figure 33 assumes a small steering module. The steering angle δFI of inside front wheel 91 is set to 45°, and the steering angle δRI of inside rear wheel 93 is set to 44°, and the coordinates of turning center C are calculated to be XL ≈ -30 and YL ≈ -29. In other words, turning center C is set considerably far away from vehicle 100. The larger the difference between steering angle δFI of inside front wheel 91 and steering angle δRI of inside rear wheel 93, the closer turning center C gets to vehicle 100.

[0098] Example 2 shown in Figure 34 is based on the assumption of a center steering module. The steering angle δFI of inside front wheel 91 is set to 70°, and the steering angle δRI of inside rear wheel 93 is set to 69°, and the coordinates of turning center C are calculated to be XL ≒ -7.5 and YL ≒ -19.

[0099] Example 3 shown in Figure 35 assumes a large steering module. The steering angle δFI of inside front wheel 91 is set to 89°, and the steering angle δRI of inside rear wheel 93 is set to 88°, and the coordinates of turning center C are calculated to be XL ≈ -0.54 and YL ≈ -1.5. Note that as steering angle δFI of inside front wheel 91 approaches 90° infinitesimally, XL gradually approaches -0.5.

[0100] As described above, it has been verified that the coordinate of the turning center C in the forward turning mode, the coordinate of the turning center C in the non-forward turning mode, and the coordinate of the first turning center C1 in the lateral movement mode are all calculated using equations (1) and (2) when turning left. Similarly, when turning right, the coordinate of the turning center C or the first turning center C1 is calculated using equations (3) and (4). This makes it possible to calculate the coordinate of the turning center C or the first turning center C1 depending on the maximum steering angle of the front and rear wheels on the inside of the turn, and also makes it possible to determine in advance whether a requested vehicle operation mode can be executed.

[0101] (Second embodiment) The configuration of steering device 802 of the second embodiment will be described with reference to Figure 36. The second embodiment employs a "mechatronically separated" configuration in which one steering angle calculation section 67 is arranged inside vehicle operation command device 602. Steering angle calculation section 67 collectively calculates steering angle command values ​​for all wheels 91-94 based on the coordinates of the turning centre determined by turning centre coordinate determination section 66, and communicates these to each of the steering actuators 71-74. Steering actuators 71-74 for each of the wheels operate in accordance with the steering angle command values ​​calculated by steering angle calculation section 67.

[0102] The configuration of the second embodiment also provides the same effects as those of the first embodiment. Furthermore, one steering angle calculation unit 67 can efficiently calculate the steering angle of each wheel.

[0103] (Other embodiments) (a) The steering device of the present invention is not limited to four-wheel vehicles, but can also be applied to three-wheel vehicles consisting of one front wheel and two rear wheels, or two front wheels and one rear wheel. The front and rear wheel axes that determine the setting range of the turning center in the forward turning mode are similarly defined using the rotation axis of one wheel. However, in the lateral movement mode of a three-wheel vehicle, unlike a four-wheel vehicle, three turning centers corresponding to each wheel are set.

[0104] The steering device of the present invention can also be applied to 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 device of the present invention is applied to "vehicles in which three or more wheels, including one or more front wheels and one or more rear wheels, that are not mechanically constrained to one another and can be steered independently."

[0105] (b) The electromechanical integrated configuration according to the first embodiment and the electromechanical separate configuration according to the second embodiment may coexist. For example, the left and right front wheels 91, 92 may have an electromechanical integrated configuration, and the left and right rear wheels 93, 94 may have an electromechanical separate configuration. Alternatively, an integrated steering angle calculation unit and a separate steering angle calculation unit may be provided redundantly for one steering actuator.

[0106] (c) In addition to the vehicle speed and the actual steering angle of each wheel, the vehicle operation determination unit 65 may acquire information on other vehicles and obstacles in the vicinity, road surface inclination and friction coefficient, wind direction and speed, and other information as vehicle conditions, and may determine vehicle operation based on this information. For example, when steering on an inclined road surface or a road surface with a small road surface friction coefficient, the vehicle operation may be determined to cause the wheels to skid, taking into account the braking effect, without adopting Ackermann geometry.

[0107] 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.

[0108] The invention of "a steering device according to claim 1, wherein the vehicle state input to the vehicle operation determination unit includes the vehicle speed and the actual steering angle of each wheel" may be specified by citing any one of claims 1 to the immediately preceding claim if the description requirements are permitted.

[0109] The invention of "a steering device as described in claim 1, wherein the turning center coordinate determination unit determines the coordinate of the turning center using the center of gravity (G) of the vehicle as the origin" may be specified to cite any one of claims 1 to the immediately preceding claim if the description requirements are permitted.

[0110] The invention of "the steering device according to claim 1, wherein the steering angle calculation unit (671-674) corresponding to each wheel and the steering actuator are integrally provided, and the steering actuator operates in accordance with the steering angle command value calculated by the steering angle calculation unit for each wheel," and the invention of "the steering device according to claim 1, comprising one steering angle calculation unit (67) that calculates steering angle command values ​​for all wheels, and the steering actuator for each wheel operates in accordance with the steering angle command value calculated by the steering angle calculation unit," may be specified so that each of them cites any one of claim 1 to the claim immediately preceding it, while maintaining their independence from each other, if the recitation requirements are permitted.

[0111] Each control unit (vehicle operation determination unit, turning center coordinate determination unit, steering angle calculation unit) and its method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor and memory programmed to execute one or more functions embodied in a computer program. Alternatively, each control unit and its method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, each control unit and its method described in the present disclosure may be realized by one or more special-purpose computers configured by combining a processor and memory programmed to execute one or more functions 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 recording medium as instructions executed by a computer. [Explanation of symbols]

[0112] 65... Vehicle operation decision unit, 66....Turning center coordinate determination unit, 67, 671-674···Steering angle calculation section, 71-74···Steering actuator, 801, 802... Steering device, 91-94...wheels, 100···(independent steering) vehicle, C (C1, C2) - Center of rotation, G - Center of gravity.< / ii> < / ii> < / ii>

Claims

1. A steering device for controlling the steering angle of each wheel in a vehicle (100) in which three or more wheels (91-94) that are not mechanically constrained to one another, including one or more front wheels and one or more rear wheels, can be steered independently, comprising: A forward turning mode in which the vehicle turns while moving forward; Non-progressive turning mode, in which the vehicle turns without moving forward; Lateral movement mode in which the vehicle moves laterally relative to the longitudinal axis; a vehicle operation determination unit (65) that determines a vehicle operation mode including the above based on a vehicle state; a turning center coordinate determination unit (66) that determines the coordinates of a turning center (C) of the vehicle based on the vehicle operation mode determined by the vehicle operation determination unit; one or more steering angle calculation units (67, 671-674) that calculate steering angle command values ​​for each wheel based on the coordinates of the turning center determined by the turning center coordinate determination unit; a plurality of steering actuators (71-74) provided corresponding to the respective wheels, for steering the respective wheels in accordance with the steering angle command value calculated by the steering angle calculation unit; Equipped with If the axis that passes through the center of the front wheels 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 and is perpendicular to the vehicle longitudinal axis (Y0) is defined as the rear wheel axis (X34), then: When the vehicle operation determination unit commands the forward turning mode, The turning center coordinate determination unit determines the coordinates of one turning center within the entire range on the inside of the turning and outside the vehicle between the front wheel shaft and the rear wheel shaft.

2. A steering device for controlling the steering angle of each wheel in a vehicle (100) in which three or more wheels (91-94) that are not mechanically constrained to one another, including one or more front wheels and one or more rear wheels, can be steered independently, comprising: A forward turning mode in which the vehicle turns while moving forward; Non-progressive turning mode, in which the vehicle turns without moving forward; Lateral movement mode in which the vehicle moves laterally relative to the longitudinal axis; a vehicle operation determination unit (65) that determines a vehicle operation mode including the above based on a vehicle state; a turning center coordinate determination unit (66) that determines the coordinates of a turning center (C) of the vehicle based on the vehicle operation mode determined by the vehicle operation determination unit; one or more steering angle calculation units (67, 671-674) that calculate steering angle command values ​​for each wheel based on the coordinates of the turning center determined by the turning center coordinate determination unit; a plurality of steering actuators (71-74) provided corresponding to the respective wheels, for steering the respective wheels in accordance with the steering angle command value calculated by the steering angle calculation unit; Equipped with When the vehicle operation determination unit commands the non-progressive turning mode, The turning center coordinate determination unit is a steering device that determines the coordinates of one turning center within the entire range inside the vehicle.

3. A steering device for controlling the steering angle of each wheel in a vehicle (100) in which three or more wheels (91-94) that are not mechanically constrained to one another, including one or more front wheels and one or more rear wheels, can be steered independently, comprising: A forward turning mode in which the vehicle turns while moving forward; Non-progressive turning mode, in which the vehicle turns without moving forward; Lateral movement mode in which the vehicle moves laterally relative to the longitudinal axis; a vehicle operation determination unit (65) that determines a vehicle operation mode including the above based on a vehicle state; a turning center coordinate determination unit (66) that determines the coordinates of a turning center (C) of the vehicle based on the vehicle operation mode determined by the vehicle operation determination unit; one or more steering angle calculation units (67, 671-674) that calculate steering angle command values ​​for each wheel based on the coordinates of the turning center determined by the turning center coordinate determination unit; a plurality of steering actuators (71-74) provided corresponding to the respective wheels, for steering the respective wheels in accordance with the steering angle command value calculated by the steering angle calculation unit; Equipped with If the axis that passes through the center of the rear wheel and is perpendicular to the vehicle longitudinal axis (Y0) is defined as the rear wheel axis (X34), then: When the vehicle operation determination unit commands the lateral movement mode from forward movement, The turning center coordinate determination unit is a steering device that determines the coordinates of two turning centers that are located rearward of the rear wheel axle and separated in the left and right direction of the vehicle.

4. A steering device for controlling the steering angle of each wheel in a vehicle (100) in which three or more wheels (91-94) that are not mechanically constrained to one another, including one or more front wheels and one or more rear wheels, can be steered independently, comprising: A forward turning mode in which the vehicle turns while moving forward; Non-progressive turning mode, in which the vehicle turns without moving forward; Lateral movement mode in which the vehicle moves laterally relative to the longitudinal axis; a vehicle operation determination unit (65) that determines a vehicle operation mode including the above based on a vehicle state; a turning center coordinate determination unit (66) that determines the coordinates of a turning center (C) of the vehicle based on the vehicle operation mode determined by the vehicle operation determination unit; one or more steering angle calculation units (67, 671-674) that calculate steering angle command values ​​for each wheel based on the coordinates of the turning center determined by the turning center coordinate determination unit; a plurality of steering actuators (71-74) provided corresponding to the respective wheels, for steering the respective wheels in accordance with the steering angle command value calculated by the steering angle calculation unit; Equipped with If the axis that passes through the center of the front wheels and is perpendicular to the vehicle longitudinal axis (Y0) is defined as the front wheel axis (X12), When the vehicle operation determination unit commands the lateral movement mode from reverse, The turning center coordinate determination unit is a steering device that determines the coordinates of two turning centers that are located forward of the front wheel axles and separated in the left and right directions of the vehicle.

5. Applied to a four-wheel vehicle including two front wheels and two rear wheels, 5. The steering device according to claim 3 or 4, wherein the turning center coordinate determination unit determines the coordinate of a first turning center (C1) for the front and rear wheels on the inside of the turning and the coordinate of a second turning center (C2) for the front and rear wheels on the outside of the turning as the coordinates of the two turning centers.

6. If the axis passing through the center 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, When moving horizontally in the horizontal movement mode, The turning center coordinate determination unit 6. A steering device according to claim 5, wherein the coordinates of the first turning center are determined on the front and rear wheel axles on the inside of the turning, and the coordinates of the second turning center are determined on the front and rear wheel axles on the outside of the turning.

7. 5. The steering device according to claim 1, wherein the steering angle calculation unit calculates the steering angle command value of each wheel so that the steering direction of each wheel is perpendicular to a straight line connecting the turning center and the center of each wheel.

8. 5. The steering device according to claim 1, wherein the turning center coordinate determining unit determines the coordinates of the turning center using the center of gravity (G) of the vehicle as an origin.

9. A steering device for controlling the steering angle of each wheel in a four-wheel vehicle (100) in which four wheels (91-94) including two front wheels and two rear wheels that are not mechanically constrained to one another can be steered independently, comprising: A forward turning mode in which the vehicle turns while moving forward; Non-progressive turning mode, in which the vehicle turns without moving forward; Lateral movement mode in which the vehicle moves laterally relative to the longitudinal axis; a vehicle operation determination unit (65) that determines a vehicle operation mode including the above based on a vehicle state; a turning center coordinate determination unit (66) that determines the coordinates of a turning center (C) of the vehicle based on the vehicle operation mode determined by the vehicle operation determination unit; one or more steering angle calculation units (67, 671-674) that calculate a steering angle command value for each wheel based on the coordinates of the turning center determined by the turning center coordinate determination unit so that the steering direction of each wheel is perpendicular to a line connecting the turning center and the center of each wheel; a plurality of steering actuators (71-74) provided corresponding to the respective wheels, for steering the respective wheels in accordance with the steering angle command value calculated by the steering angle calculation unit; Equipped with Including the non-progressive turning mode, the wheels that are closer to the turning center among the front wheels and the rear wheels are defined as the inside front wheels and the inside rear wheels, The axis that passes through the center of gravity (G) of the vehicle and is perpendicular to the vehicle longitudinal axis (Y0) is defined as the center of gravity axis (X0), the axis that passes through the center of the front wheels and is perpendicular to the vehicle longitudinal axis is defined as the front wheel axis (X12), and the axis that passes through the center of the rear wheels and is perpendicular to the vehicle longitudinal axis is defined as the rear wheel axis (X34). If the distance from the center of gravity axis to the front wheel axle is defined as a front wheel axle distance (Lf), and the distance from the center of gravity axis to the rear wheel axle is defined as a rear wheel axle distance (Lr), then: When the steering angle of the front inside wheel (δFI) and the steering angle of the rear inside wheel (δRI) are determined before the coordinates of the turning center are determined by the turning center coordinate determination unit, The turning center coordinate determination unit The coordinate system is used, with the center of gravity of the vehicle as the origin, the center of gravity axis as the x-axis, and the front-rear axis of the vehicle as the y-axis, with the right side of the center of gravity being positive and the left side being negative on the x-axis, and the front side of the center of gravity being positive and the rear side being negative on the y-axis. Regarding the steering angles of the front wheel on the inside of the turning wheel and the rear wheel on the inside of the turning wheel, a counterclockwise direction from a neutral position is defined as positive, and a clockwise direction from the neutral position is defined as negative, When the steering angle of the front wheel on the inside of the turn is represented as δFI, the steering angle of the rear wheel on the inside of the turn is represented as δRI, the front wheel axle distance is represented as Lf, the rear wheel axle distance is represented as Lr, the front wheel tread width is represented as Df, and the rear wheel tread width is represented as Dr, δFI≠δRI, −90°<δFI<90°, −90°<δRI<90°, Regarding the coordinates of the turning center (C) in the forward turning mode and the non-forward turning mode, and the coordinates of a first turning center (C1) relative to the turning inside front wheel and the turning inside rear wheel in the lateral movement mode, The coordinates (XL, YL) of the turning center or the first turning center during a left turn are calculated using the following equations (1) and (2): A steering device that calculates the coordinates (XR, YR) of the turning center or the first turning center when turning right using the following equations (3) and (4). [Equation 1] [Equation 2]

10. 10. The steering device according to claim 1, wherein the vehicle state input to the vehicle operation determination unit includes a vehicle speed and an actual steering angle of each wheel.

11. 10. A steering device according to any one of claims 1 to 4 and 9, wherein the steering angle calculation unit (671-674) corresponding to each wheel and the steering actuator are integrally provided, and the steering actuator operates in accordance with the steering angle command value calculated by the steering angle calculation unit for each wheel.

12. a single steering angle calculation unit (67) that calculates steering angle command values ​​for all wheels; 10. The steering device according to claim 1, wherein the steering actuators for the respective wheels are operated in accordance with the steering angle command value calculated by the steering angle calculation section.

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