Steering gear

Abstract

To avoid influence on vehicle operation, caused by a communication time difference between steering command signals, in an independent turning vehicle with three or more wheels.SOLUTION: In a turning device 801 of an independent turning vehicle 100, a target-turning-angle calculation unit 67 calculates a target turning angle of each of wheels 91 to 94, based on coordinates of a determined turning center, and transmits turning command signals ST1 to ST4 for turning the respective wheels to the target turning angle. Turning execution units 751 to 754 output drive signals DR1 to DR4 for executing turning of the respective wheels, based on the received turning command signals ST1 to ST4. Turning actuators 771 to 774 turn the wheels in accordance with the drive signals DR1 to DR4 output from the turning execution units 751 to 754. A timing correction unit 68 corrects a timing relating to the transmission of the turning command signals ST1 to ST4 in accordance with a communication time from the target-turning-angle calculation unit 67 to each of the turning execution units 751 to 754 so that the turning actuators 771 to 774 simultaneously start turning operations.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Conventionally, steering systems that allow the left and right wheels to be steered independently are known.

[0003] For example, the vehicle steering system disclosed in Patent Document 1 determines the steering angle ratio between the inner and outer turning wheels for the left and right front wheels according to Ackermann geometry or parallel geometry. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-169248 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In contrast to the steering system described in Patent Document 1, in which only the left and right front wheels can be independently steered, a three-wheeled or four-wheeled independently steered vehicle in which both the front and rear wheels can be independently steered enables a wider variety of vehicle operation patterns. In the steering device of such an independently steered vehicle, when a target steering angle calculation unit calculates the steering angle of each wheel based on the desired vehicle operation, a steering command signal is communicated, for example, via CAN communication, and the steering actuator corresponding to each wheel is driven.

[0006] Here, the communication time from the target steering angle calculation unit to the steering execution unit that drives each steering actuator may vary due to physical factors such as cable length. As a result, differences in communication time may cause a delay in the timing at which each steering actuator starts its steering operation, which could affect vehicle operation.

[0007] This invention was created in view of the above-mentioned points, and its purpose is to provide a steering device for a vehicle with three or more wheels that has independent steering, which avoids the influence of differences in the communication time of steering command signals on vehicle operation. [Means for solving the problem]

[0008] 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), including one or more front wheels and one or more rear wheels, are not mechanically constrained to each other and can be steered independently. The steering device comprises a vehicle operation determination unit (65), a turning center coordinate determination unit (66), a target steering angle calculation unit (67), a plurality of steering execution units (751-754), a plurality of steering actuators (771-774), and one or more timing correction units (68, 761-764).

[0009] The vehicle motion determination unit determines the steering mode according to the desired vehicle motion. The turning center coordinate determination unit determines the coordinates of the vehicle's turning center based on the determined steering mode. The turning center coordinate determination unit determines the coordinates of the vehicle's turning center based on the determined steering mode. The target steering angle calculation unit calculates the target steering angle for each wheel based on the determined turning center coordinates and transmits steering command signals (ST1-ST4) to steer each wheel to the target steering angle.

[0010] The steering execution unit outputs drive signals (DR1-DR4) that execute the steering of each wheel based on the received steering command signal. The steering actuators steer each wheel according to the drive signals output by the steering execution unit.

[0011] The timing correction unit corrects the timing of the transmission of steering command signals or the output of drive signals according to the communication time (TC1-TC4) from the target steering angle calculation unit to each steering execution unit, so that each steering actuator starts steering operation simultaneously.

[0012] As a result, the steering device of the present invention can avoid the influence on vehicle operation caused by differences in the communication time of steering command signals.

Brief Description of the Drawings

[0013] [Figure 1] Block diagram of the steering device according to the first embodiment. [Figure 2] Diagram showing a specific form example of the steering module. [Figure 3] Diagram for explaining the calculation formula of the steering angle based on the turning center coordinates. [Figure 4] Timing chart of timing correction by the steering device according to the first embodiment. [Figure 5] Main flowchart of timing correction according to this embodiment. [Figure 6] Sub - flowchart for two - wheel / four - wheel steering mode determination. [Figure 7] Diagram showing vehicle motion examples (a), (b) in two - wheel steering mode during forward turning. [Figure 8] Diagram showing vehicle motion example in four - wheel steering mode during forward turning. [Figure 9] Diagram showing vehicle motion examples (a), (b) in four - wheel steering mode during spot turning. [Figure 10] Diagram showing vehicle motion example in two - wheel steering mode during spot turning. [Figure 11] Block diagram of the steering device according to the second embodiment. [Figure 12] Timing chart of timing correction by the steering device according to the second embodiment. [Figure 13] Block diagram of the steering device according to the third embodiment. [Figure 14] Block diagram of the steering device according to the fourth embodiment. [Figure 15] Diagram of a three - wheel independent steering vehicle to which the steering device of other embodiments is applied.

Modes for Carrying Out the Invention

[0014] Multiple embodiments of the steering device according to the present invention will be described with reference to the drawings. In multiple embodiments, substantially identical components are denoted by the same reference numerals and their description is omitted. The first to fourth embodiments are collectively referred to as "this embodiment." The steering device of this embodiment controls the steering angle of each wheel in a vehicle in which four wheels that are not mechanically constrained to each other can be steered independently.

[0015] (First Embodiment) Referring to Figures 1 to 4, the steering device 801 of the first embodiment will be described. As shown in Figure 1, in the independently steered vehicle 100 to which the steering device 801 is applied, the four wheels 91-94 are not mechanically constrained to each other and can be steered independently. The left front wheel 91 is labeled "FL", the right front wheel 92 is labeled "FR", the left rear wheel 93 is labeled "RL", and the right rear wheel 94 is labeled "RR".

[0016] Each wheel 91-94 is corresponding to a steering module 81-84, in which a steering ECU 701-704 and a steering actuator (indicated as "Steering Act" in the figure) 771-774 are integrated. The steering actuators 771-774 are typically motors. The digits "1"-"4" at the end of the symbols of each element represent the corresponding wheels 91-94. For example, the steering module 81, in which the steering ECU 701 and steering actuator 771 are integrated, corresponds to the left front wheel 91. As an exception, the symbols of the steering devices in each embodiment are numbered by adding the embodiment number as the third digit following "80".

[0017] The steering device 801 includes a vehicle operation ECU 60 and four steering modules 81-84 corresponding to each wheel 91-94. In both the first and second embodiments, the vehicle operation ECU 60 includes a vehicle operation determination unit 65, a turning center coordinate determination unit 66, and a target steering angle calculation unit 67. For example, in a steer-by-wire system vehicle where the driver operates the steering wheel, a reaction force device is provided that applies reaction force torque to the steering wheel. In that case, the vehicle operation ECU 60 may also serve as the ECU for the reaction force device.

[0018] The vehicle motion determination unit 65 determines a steering mode corresponding to the desired vehicle motion based on information such as vehicle speed and actual steering angle. The turning center coordinate determination unit 66 determines the coordinates of the vehicle's turning center based on the steering mode determined by the vehicle motion determination unit 65.

[0019] The target steering angle calculation unit 67 calculates the target steering angle for each wheel 91-94 based on the coordinates of the turning center determined by the turning center coordinate determination unit 66. Furthermore, the target steering angle calculation unit 67 transmits steering command signals ST1-ST4 to the steering execution units 751-754 of each steering ECU 701-704, for example via CAN communication, to steer each wheel 91-94 to the target steering angle.

[0020] Each steering ECU 701-704 includes a steering execution unit 751-754. Based on the received steering command signals ST1-ST4, the steering execution unit 751-754 outputs drive signals DR1-DR4 to the steering actuator 771-774 to execute the steering of each wheel 91-94. The steering actuator 771-774 steers each wheel 91-94 according to the drive signals DR1-DR4 output by the steering execution unit 751-754.

[0021] Here, the communication time via CAN communication from the target steering angle calculation unit 67 to each steering execution unit 751-754 is represented as TC1-TC4. The communication time TC1-TC4 may vary due to physical factors such as cable length. As a result, depending on the difference in the communication time TC1-TC4, there may be a delay in the timing at which each steering actuator 771-774 starts its steering operation, which may affect the vehicle's operation.

[0022] Let us now move away from the first embodiment and refer to the entire embodiment encompassing the first to fourth embodiments. To address the above issues, the steering device of this embodiment includes one or more timing correction units to avoid the influence on vehicle operation due to differences in the communication time of steering command signals. The timing correction unit corrects a certain timing according to the communication time TC1-TC4 from the target steering angle calculation unit 67 to each steering execution unit 751-754 so that each steering actuator 771-774 starts steering operation simultaneously.

[0023] The configuration of the timing correction unit in each embodiment can be divided into two types. In the first and third embodiments, one timing correction unit corrects the timing related to the transmission of steering command signals ST1-ST4. In the second and fourth embodiments, multiple timing correction units corresponding to each steering actuator 771-774 correct the timing related to the output of drive signals DR1-DR4.

[0024] Returning to the description of the steering device 801 of the first embodiment, the vehicle operation ECU 60 further includes a timing correction unit 68. The timing correction unit 68 calculates the target steering angle 6 according to the communication times TC1-TC4. 7 This corrects the timing at which steering command signals ST1-ST4 are transmitted to each steering execution unit 751-754. Details of the timing correction according to the first embodiment will be described later with reference to Figure 4.

[0025] Incidentally, Figure 1 only shows the one-way steering command signals ST1-ST4 from the vehicle operation ECU 60 to each steering ECU 701-704, but in addition, reverse communication may also occur from each steering ECU 701-704 to the vehicle operation ECU 60. For example, information on the actual steering angle estimated by converting the rotation angle detection values ​​of the steering actuators 771-774 is transmitted to the vehicle operation ECU 60 via CAN communication and used for monitoring steering operations and determining the steering mode by the vehicle operation determination unit 65. However, the difference in communication time in reverse communication is not considered, and illustrations and explanations regarding reverse communication are omitted.

[0026] Figure 2 shows a specific example of the steering modules 81-84, illustrating a "mechatronic integrated" configuration in which the steering ECUs 701-704 and steering actuators 771-774 corresponding to each wheel 91-94 are provided as a single unit. Although only one of the four steering modules 81-84 is shown in Figure 2, for convenience, the reference numerals are four consecutive numbers. In other embodiments, the steering ECUs 701-704 and steering actuators 771-774 may be configured as separate units.

[0027] Next, referring to Figure 3, the determination of the coordinates of the pivot center C by the pivot center coordinate determination unit 66 will be explained. In this example, the pivot center coordinate determination unit 66 determines the coordinates of the pivot center C with the center of gravity G of the vehicle 100 as the origin.

[0028] The axis passing through the centers of the front wheels 91 and 92 and perpendicular to the vehicle's longitudinal axis Y0 is defined as the front axle X12, and the axis passing through the centers of the rear wheels 93 and 94 and perpendicular to the vehicle's longitudinal axis Y0 is defined as the rear axle X34. The distance between the front axle X12 and the rear axle X34 is the wheelbase L. The axis passing through the center of gravity G and perpendicular to the vehicle's longitudinal axis Y0 is represented as the center of gravity axis X0. Assuming that the weight distribution in the longitudinal direction of the vehicle is uniform, the center of gravity axis X0 is located midway between the front axle X12 and the rear axle X34.

[0029] The tread width of the front wheels 91 and 92 is denoted as Df, and the tread width of the rear wheels 93 and 94 is denoted as Dr. In Figure 3, it is assumed that the front wheel tread width Df and the rear wheel tread width Dr are equal (Df=Dr), and 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 axle. The axis passing through the centers of the left front wheel 91 and the left rear wheel 93 is denoted as the left front and rear axle Y13, and the axis passing through the centers of the right front wheel 92 and the right rear wheel 94 is denoted as the right front and rear axle Y24. Furthermore, the distance from the center of gravity axis X0 to the front axle X12 of the wheelbase L is defined as the front axle distance Lf, and the distance from the center of gravity axis X0 to the rear axle X34 is defined as the rear axle distance Lr (L=Lf+Lr). The values ​​of Df, Dr, Lf, and Lr are stored as vehicle characteristics.

[0030] The coordinates of each wheel 91-94 as viewed from the center of gravity G are defined using the tread width Df, Dr and wheelbase L. Specifically, the vehicle's center of gravity G is set as the origin (0,0), the center of gravity axis X0 is the x-axis, and the vehicle's longitudinal axis Y0 is the y-axis, defining an xy coordinate system. For the x-axis, the right side of the center of gravity G is positive and the left side is negative, and for 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 represented as (X,Y). In the case of a left turn, "X<0", and in the case of a right turn, "X>0".

[0031] the goalThe steering angle calculation unit 67 calculates the tangent values of the steering angles δ1-δ4 of the respective wheels 91-94 according to formulas (1)-(4) such that the steering directions of the respective wheels 91-94 are orthogonal to the straight lines N1-N4 connecting the turning center C and the centers of the respective wheels 91-94. The steering angles δ1-δ4 are represented with the counterclockwise direction from the neutral position being positive and the clockwise direction from the neutral position being negative. In the case of front-wheel steering, the front-wheel steering angle during a left turn from straight-ahead travel is positive, and the front-wheel steering angle during a right turn from straight-ahead travel is negative.

[0032] tanδ1=(Y-Lf) / {X+(Df / 2)} ···(1) tanδ2=(Y-Lf) / {X-(Df / 2)} ···(2) tanδ3=(Y+Lr) / {X+(Dr / 2)} ···(3) tanδ4=(Y+Lr) / {X-(Dr / 2)} ···(4)

[0033] Referring to the time chart of FIG. 4, the timing correction by the steering device 801 of the first embodiment will be described. Regarding the communication times of the steering command signals ST1-ST4, it is assumed that the communication time TC1 to the steering execution unit 751 corresponding to the left front wheel 91 is the shortest. Also, it is assumed that the communication times TC2, TC3, TC4 to the steering execution units 752, 753, 754 corresponding to the right front wheel 92, left rear wheel 93, and right rear wheel 94 become longer in this order. That is, "TC1 < TC2 < TC3 < TC4". The longest communication time TC4 is also represented as "TCmax".

[0034] As a steering mode, assume a scenario of turning left in the front-rear wheel reverse-phase steering mode shown in FIG. 8 starting from the initial straight-ahead state. Regarding the target steering angles δ * 1-δ * 4 of the respective wheels 91-94, δ * 1 and δ * 2 are positive, and δ * 3 and δ * 4 are negative. The absolute values of δ * 1 and δ * 3 are equal, and the absolute values of δ * 2 and δ * 4 are equal. Also, δ * 1 and δ *The absolute value of 3 is the δ on the outside of the turn. * 2 and δ * It will be greater than the absolute value of 4.

[0035] The timing correction unit 68 calculates the waiting time WT1-WT4 from the target steering angle calculation timing tcalc to transmission, delaying the transmission timing for steering command signals with shorter communication times. Here, the "waiting time WT1-WT4 and communication time TC1-TC4 for each steering command signal ST1-ST4" is generalized and expressed as "waiting time WTn and communication time TCn (n=1,2,3,4) for each steering command signal STn".

[0036] For each steering command signal STn, the waiting time WTn is set such that the sum of the waiting time WTn and the communication time TCn (WTn + TCn) is a constant value. If the constant value is set to the maximum communication time TCmax (=TC4), then WT4 is set to 0. The waiting time WTn is set based on the communication time TCn measured, for example, during the manufacture or maintenance of the vehicle 100, and is stored in the timing correction unit 68 of the vehicle operation ECU 60.

[0037] In the diagram, steering ECUs 701-704 are denoted as "Steering ECU_1" - "Steering ECU_4". If timing correction is not performed, as shown by the dashed line, steering command signals ST1-ST4 are simultaneously transmitted from the vehicle operation ECU 60 to each steering ECU 701-704 at the target steering angle calculation timing tcalc. As a result, the reception timing at each steering ECU 701-704 differs depending on the communication time T1-T4, causing a discrepancy in the timing at which each steering actuator 771-774 starts its steering operation. This may affect vehicle operation.

[0038] In contrast, in the first embodiment, the timing correction unit 68 corrects the transmission timing of each steering command signal ST1-ST4 so that it is delayed by a waiting time WT1-WT4 from the target steering angle calculation timing tcalc. In other words, as shown by the solid line, steering command signal ST3 is transmitted at transmission timing ts3, steering command signal ST2 at transmission timing ts2, and steering command signal ST1 at transmission timing ts1 in sequence. When WT4=0, the transmission timing ts4 of steering command signal ST4 becomes simultaneous with the target steering angle calculation timing tcalc.

[0039] As a result, the steering execution units 751-754 of each steering ECU 701-704 simultaneously receive the steering command signals ST1-ST4 at a common reception timing tr_com. Then, each steering execution unit 751-754 simultaneously outputs drive signals DR1-DR4 to the corresponding steering actuators 771-774. This causes each steering actuator 771-774 to simultaneously begin steering. The steering angles δ1-δ4 of each wheel 91-94 are the target steering angle δ as shown by the dashed line. * 1-δ * It changes towards 4.

[0040] In the first embodiment, the target steering angle calculation Part 6 7 The timing at which steering command signals ST1-ST4 are transmitted to the steering execution units 751-754 of each steering ECU 701-704 is corrected by the timing correction unit 68 according to the difference in communication times TC1-TC4. Therefore, the influence of the difference in communication times TC1-TC4 of the steering command signals ST1-ST4 on the steering operation can be avoided.

[0041] Next, the timing correction according to this embodiment will be explained with reference to the main flowchart in Figure 5 and the subflowchart in Figure 6. In the following flowchart explanation, the symbol "S" means step. The reference numeral for the "timing correction unit" described in S5 is "68" in the first and third embodiments, and "761-764" in the second and fourth embodiments. The configuration of the timing correction units 761-764 in the second and fourth embodiments will be described later. In the explanation of S5, the timing correction units 68 and 761-764 of both configurations will be described together.

[0042] In S1, the vehicle operation determination unit 65 determines a steering mode corresponding to the desired vehicle operation. In S2, the turning center coordinate determination unit 66 determines the vehicle's turning center coordinate C based on the determined steering mode. In S3, the target steering angle calculation unit 67 calculates the target steering angle δ of each wheel based on the determined turning center coordinate C. * 1-δ * Calculate 4.

[0043] In S5, the timing correction unit 68 or timing correction units 761-764 correct the timing related to the transmission of steering command signals ST1-ST4 or the output of drive signals DR1-DR4 according to the difference in communication times TC1-TC4. In S6, each steering actuator 771-774 simultaneously starts steering operation.

[0044] Here, S4 may be executed between S3 and S5, as shown by the dashed line. In S4, it is determined whether the steering mode determined by the vehicle operation determination unit 65 is a four-wheel steering mode or a two-wheel steering mode. Assuming that the independently steering vehicle 100 to which this embodiment is applied is a four-wheel vehicle, the four-wheel steering mode means a steering mode in which all wheels 91-94 are steered.

[0045] The term "two-wheel steering mode" refers to a steering mode in which "some of the wheels, including a pair of left and right wheels," that is, two wheels such as the left front wheel 91 and the right front wheel 92, or the left rear wheel 93 and the right rear wheel 94, are steered. Steering modes in which two wheels opposite each other (for example, the left front wheel 91 and the left rear wheel 93) or two wheels diagonally opposite each other (for example, the left front wheel 91 and the right rear wheel 94) are steered are not considered.

[0046] Figure 6 shows the details of the 4-wheel / 2-wheel steering mode determination (S4). In S41, it is determined whether the vehicle is in 4-wheel steering mode. If the result in S41 is NO, then in S42, it is determined whether the vehicle is in 2-wheel steering mode. If the result in S42 is NO, it means that all wheels 91-94 are not steered and the vehicle is in straight-line mode, and the process ends there.

[0047] If the answer in S41 is YES, then in S43, it is determined that the "timing correction by the timing correction unit 68, 761-764" in S5 will be performed on all four wheels, i.e., all wheels 91-94.

[0048] If the answer in S42 is YES, then in S44, it is determined that the "timing correction by timing correction units 68, 761-764" in S5 will be executed only for the wheels that are being steered. In other words, wheels that are not being steered, with a target steering angle of 0°, are excluded from the timing correction. This reduces the computational load on the ECU. Note that in a processing configuration that does not include S4, timing correction for the zero signal is performed computationally even for wheels with a target steering angle of 0°, where no actual steering action occurs.

[0049] Referring to Figures 7(a) to 10, specific examples of the two-wheel steering mode and four-wheel steering mode in a four-wheel independently steering vehicle will be explained. In Figures 7(a) to 10, the steering angles of each wheel 91-94 are illustrated according to the Ackermann theory. In each figure, the arc arrows attached to the wheels indicate the steering direction. Except for Figure 9(a), the thick arc arrows originating from the center of gravity G indicate the direction of movement of the center of gravity G. In Figure 9(a), the thick arc arrow centered on the center of gravity G indicates the turning direction of the vehicle 100.

[0050] Here, in Figure 3, the region between the front axle X12 and the rear axle X34 in the vehicle's longitudinal direction, and between the left front / rear axle Y13 and the right front / rear axle Y24 in the vehicle's lateral direction, is referred to as the "vehicle interior." The region outside the vehicle interior is referred to as the "vehicle exterior."

[0051] Figures 7(a), 7(b), and 8 show examples of steering modes during a forward turn in which the vehicle 100 turns while moving forward. For example, in the case of a left turn, the turning center coordinate C is set to the left outside of the vehicle, within the range from the front axle X12 to the rear axle X34, including each axle on the front axle X12 and the rear axle X34 in the longitudinal direction of the vehicle. During a forward turn, all wheels 91-94 rotate in the direction of travel, regardless of whether steering is performed or not.

[0052] In the front-wheel steering mode shown in Figure 7(a), the pivot center coordinate C is set on the rear axle X34 outside the vehicle. In this case, the left and right rear wheels 93 and 94 are not steered, and the left and right front wheels 91 and 92 are steered. In the rear-wheel steering mode shown in Figure 7(b), the pivot center coordinate C is set on the front axle X12 outside the vehicle. In this case, the left and right front wheels 91 and 92 are not steered, and the left and right rear wheels 93 and 94 are steered.

[0053] In the front and rear wheel counter-phase steering mode shown in Figure 8, the pivot center coordinate C is set outside the vehicle, excluding the areas on each axle between the front axle X12 and the rear axle X34. In this case, all four wheels, 91-94, are steered. In particular, in the example shown in Figure 8, the pivot center coordinate C is set on the center of gravity axis X0. When the front axle distance Lf and the rear axle distance Lr are equal, the steering angles of the front wheels 91 and 92 and the steering angles of the rear wheels 93 and 94 are in opposite phases with positive and negative symmetry.

[0054] Figures 9(a), 9(b), and 10 show examples of steering modes during pivot turns, including super-pivot turns. In a pivot turn, a pivot center coordinate C is set inside the vehicle, and in particular, in a super-pivot turn, the pivot center coordinate C is set at the center of gravity G. The dashed outline of the vehicle shows the position of vehicle 100 when the vehicle's longitudinal axis Y0 is rotated by 60°.

[0055] In the super-ground-rotation mode shown in Fig. 9(a), all the wheels 91-94 are steered in the tangential direction of concentric circles centered on the center of gravity G. In the ground-rotation mode shown in Fig. 9(b), the turning center coordinate C is set at the intersection of the left front and rear wheel axis Y13 and the center of gravity axis X0. In this case, the left front wheel 91 is steered at 90°, and the left rear wheel 93 is steered at -90°. Also, the right front wheel 92 and the right rear wheel 94 are steered in the tangential direction of a circle centered on the turning center coordinate C. The ground-rotation modes in Figs. 9(a) and 9(b) are both four-wheel steering modes.

[0056] In the ground-rotation mode shown in Fig. 10, the turning center coordinate C is set at the intersection of the front wheel axis X12 and the vehicle longitudinal axis Y0. In this case, the left front wheel 91 and the left rear wheel 93 are not steered, and the two wheels, the right front wheel 92 and the right rear wheel 94, are steered in the tangential direction of a circle centered on the turning center coordinate C.

[0057] (Second Embodiment) Referring to Figs. 11 and 12, the steering device 802 of the second embodiment will be described. As shown in Fig. 11, the steering device 802 is different from the steering device 801 of the first embodiment in that timing correction units 761-764 are provided in each of the steering ECUs 701-704. The timing correction units 761-764 correct the timing at which the steering execution units 751-754 output drive signals DR1-DR4 to the corresponding steering actuators 771-774 according to the difference in the communication times TC1-TC4.

[0058] Referring to the time chart of Fig. 12, the timing correction by the steering device 802 of the second embodiment will be described. The assumptions regarding the steering mode and the order of the communication times TC1-TC4 (TC1 < TC2 < TC3 < TC4), and the notes regarding the figure format follow Fig. 4. The difference from Fig. 4 is that the "waiting times WT1-WT4" in Fig. 12 are the adjustment times from when each of the steering execution units 751-754 receives the steering command signals ST1-ST4 until they output the drive signals DR1-DR4. In the first embodiment, the waiting times WT1-WT4 are set before the transmission of the steering command signals ST1-ST4, whereas in the second embodiment, the waiting times WT1-WT4 are set after the transmission of the steering command signals ST1-ST4.

[0059] Similar to the first embodiment, the "communication times TC1-TC4 and the waiting times WT1-WT4 for the output of each drive signal DR1-DR4" are generalized and expressed as "communication time TCn and the waiting time WTn for the output of each drive signal DRn (n=1,2,3,4)". For each drive signal DRn, the waiting time WTn is set such that the sum of the communication time TCn and the waiting time WTn (TCn+WTn) is a constant value. If the constant value is the longest communication time TCmax (=TC4), then WT4 is set to 0. The waiting time WTn is set based on the communication time TCn measured during the manufacture or maintenance of the vehicle 100, for example, and is stored in the timing correction units 761-764 of each steering ECU 701-704.

[0060] The target steering angle calculation unit 67 of the vehicle operation ECU 60 calculates the target steering angle δ * 1-δ * When 4 is calculated, steering command signals ST1-ST4 are simultaneously transmitted to the common transmission timing ts_com. The steering execution units 751-754 of each steering ECU 701-704 sequentially receive the steering command signals ST1-ST4 from the common transmission timing ts_com at reception timings tr1-tr4, after communication time TC1-TC4.

[0061] If timing correction is not performed, as shown by the dashed line, the steering execution units 751-754 will sequentially output drive signals DR1-DR4 at different timings, causing a timing discrepancy in when each steering actuator 771-774 starts its steering operation. This may affect vehicle operation.

[0062] In contrast, in the second embodiment, the timing correction unit 761-764 corrects the output timing of each drive signal DR1-DR4 by delaying it by a waiting time WT1-WT4 from the reception timing tr1-tr4 of the steering command signal ST1-ST4. In other words, as shown by the solid line, each drive signal DR1-DR4 is output simultaneously to the common drive timing tdr_com. As a result, each steering actuator 771-774 starts steering simultaneously. The steering angles δ1-δ4 of each wheel 91-94 are the target steering angle δ as shown by the dashed line. *1-δ * It changes towards 4.

[0063] In the second embodiment, the timing at which the steering execution unit 751-754 outputs drive signals DR1-DR4 to the corresponding steering actuators 771-774 is corrected by the timing correction unit 761-764 according to the difference in communication times TC1-TC4. Therefore, the influence of the difference in communication times TC1-TC4 on the steering operation of the steering command signals ST1-ST4 can be avoided.

[0064] (Third embodiment) Referring to Figure 13, the steering device 803 of the third embodiment will be described. The steering device 803 comprises four steering ECUs 701-704, each including a steering execution unit 751-754 corresponding to one of the wheels 91-94. One of the four steering ECUs is the main steering ECU, and the other three steering ECUs are sub-steering ECUs.

[0065] In the example shown in Figure 13, the steering ECU corresponding to the left front wheel 91 is the main steering ECU 701. The sub-steering ECUs 702, 703, and 704 are provided to communicate with the main steering ECU 701. This example is not limited to this one; the steering ECU corresponding to any wheel may be the main steering ECU. Also, similar to the communication relationship between the vehicle operation ECU 60 and the steering ECUs 701-704 in the first embodiment, the illustrations and explanations regarding the reverse communication from the sub-steering ECUs 702-704 to the main steering ECU 701 are omitted.

[0066] The main steering ECU 701 includes a vehicle operation determination unit 65, a turning center coordinate determination unit 66, and a target steering angle calculation unit 67. The target steering angle calculation unit 67 internally transmits a steering command signal ST1 to the steering execution unit 751 of the steering ECU 701 itself, and externally transmits steering command signals ST2, ST3, and ST4 to the steering execution units 752, 753, and 754 of each sub-steering ECU 702, 703, and 704. Here, "internal transmission" and "external transmission" are used to distinguish between them. External transmission has substantially the same meaning as "transmission" from the vehicle operation ECU 60 in the first and second embodiments.

[0067] Furthermore, in the steering device 803 of the third embodiment, a timing correction unit 68 is provided in the main steering ECU 701. The timing correction unit 68 adjusts the target steering angle according to the difference in communication times TC1-TC4. calculation The timing of internal transmission of steering command signal ST1 by unit 67, and the timing of external transmission of steering command signals ST2, ST3, and ST4 are corrected.

[0068] The timing correction time chart according to the third embodiment is equivalent to the one in Figure 4 of the first embodiment, but with the "vehicle operation ECU" and one "steering ECU" replaced by a "main steering ECU," and the other "steering ECUs" replaced by "sub-steering ECUs." The internal transmission communication time TC1 can be considered to be close to 0. In the third embodiment, even in an independently steering vehicle 100 that does not have a vehicle operation ECU 60 (for example, an independently steering vehicle with fully autonomous driving and no reaction force device), the steering function can be completed with only the four steering ECUs 701-704.

[0069] (Fourth Embodiment) Referring to Figure 14, the steering device 804 of the fourth embodiment will be described. The steering device 804 differs from the steering device 803 of the third embodiment in that, similar to the second embodiment, each steering ECU 701-704 is provided with a timing correction unit 761-764. The timing correction unit 761-764 corrects the timing at which the steering execution unit 751-754 outputs drive signals DR1-DR4 to the corresponding steering actuator 771-774 according to the difference in communication times TC1-TC4.

[0070] The timing correction time chart according to the fourth embodiment is equivalent to that of Figure 12 of the second embodiment, but with each ECU replaced by a "main steering ECU" and a "sub steering ECU," similar to the third embodiment. Similar to the third embodiment, the fourth embodiment is applicable to an independently steering vehicle 100 that does not have a vehicle operation ECU 60.

[0071] (Other embodiments) (a) The steering device of the present invention is not limited to four-wheel independent steering vehicles, but is also applicable to three-wheel independent steering vehicles consisting of one front wheel and two rear wheels, or two front wheels and one rear wheel. Figure 15 shows a three-wheel independent steering vehicle 100 consisting of two front wheels 91 and 92 and one rear wheel 95. In this configuration, the "steering mode in which all wheels are steered" is the three-wheel steering mode. Also, the two-wheel steering mode using the left and right front wheels 91 and 92 corresponds to the "steering mode in which some of the wheels, including a pair of left and right wheels, are steered."

[0072] (b) The steering device of the present invention is also applicable to 6-wheeled or 8-wheeled independently steerable vehicles having three or more pairs of left and right wheels in the longitudinal direction of the vehicle. For example, a steering mode using two pairs (four wheels) of the front and middle rows of a 6-wheeled vehicle corresponds to a "steering mode in which some of the wheels, including a pair of left and right wheels, are steered." In summary, the steering device of the present invention is applicable to "vehicles in which three or more wheels, including one or more front wheels and one or more rear wheels, are independently steerable and are not mechanically constrained by each other."

[0073] (c) In the examples in Figures 4 and 12, the minimum waiting time WT4 corresponding to the steering command signal ST4 with the longest communication time TC4 (TCmax) is set to 0, but the minimum waiting time WT4 may be set to a value greater than 0. The waiting times WT1-WT4 are not fixed to initial values ​​set during manufacturing or maintenance, but may be updated through learning during use, etc.

[0074] The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit.

[0075] The disclosures regarding "a steering device in which, when a steering mode is determined in which some of all wheels, including a pair of left and right wheels, are steered, the timing correction unit performs timing correction only on the wheels that are steered" and "a steering device in which, when a steering mode is determined in which all wheels are steered, the timing correction unit performs timing correction on all wheels" may be combined with the respective disclosures regarding a steering device that specify which ECU the timing correction unit is located in.

[0076] Each control unit (vehicle motion determination unit, turning center coordinate determination unit, target steering angle calculation unit, timing correction unit, etc.) and its method described in this disclosure may be implemented by a dedicated computer provided by configuring a processor and memory programmed to execute one or more functions embodied by a computer program. Alternatively, each control unit and its method described in this disclosure may be implemented by a dedicated computer provided by configuring a processor by one or more dedicated hardware logic circuits. Alternatively, each control unit and its method described in this disclosure may be implemented by one or more dedicated computers configured by a combination of a processor and memory programmed to execute one or more functions and a processor configured by one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by the computer on a computer-readable non-transitional tangible recording medium. [Explanation of Symbols]

[0077] 65...Vehicle motion determination unit, 66...Swing center coordinate determination unit, 67. Target steering angle calculation unit, 68, 761-764... Timing correction section, 751-754... Steering Execution Unit, 771-774... Steering actuator, 801-804... Steering gear, 91-94...wheels, 100... (Independent steering) vehicles, ST1-ST4... Steering command signals, DR1-DR4... Drive signals, TC1-TC4...Communication time.

Claims

1. In a vehicle (100) having three or more wheels (91-94) that are not mechanically constrained to each other and can be steered independently, including one or more front wheels and one or more rear wheels, a steering device for controlling the steering angle of each wheel, A vehicle operation determination unit (65) that determines the steering mode according to the desired vehicle operation, A turning center coordinate determination unit (66) that determines the coordinates of the vehicle's turning center based on the determined steering mode, A target steering angle calculation unit (67) calculates the target steering angle of each wheel based on the determined coordinates of the turning center and transmits steering command signals (ST1-ST4) to steer each wheel to the target steering angle, Multiple steering execution units (751-754) that output drive signals (DR1-DR4) to execute steering based on the received steering command signal, A plurality of steering actuators (771-774) that steer each wheel according to the drive signal output by the steering execution unit, One or more timing correction units (68, 761-764) correct the timing of transmitting the steering command signal or outputting the drive signal according to the communication time (TC1-TC4) from the target steering angle calculation unit to each steering execution unit, so that each steering actuator starts steering operation simultaneously. A steering device equipped with a steering mechanism.

2. The vehicle operation ECU (60) includes the vehicle operation determination unit, the turning center coordinate determination unit, and the target steering angle calculation unit, Multiple steering ECUs (701-704) including the steering execution unit, The steering device according to claim 1, comprising:

3. The system comprises a plurality of steering ECUs (701-704) including the steering execution unit, One of the multiple steering ECUs is a main steering ECU that includes the vehicle motion determination unit, the turning center coordinate determination unit, and the target steering angle calculation unit. The steering device according to claim 1, wherein the plurality of steering ECUs other than the main steering ECU are sub-steering ECUs provided to communicate with the main steering ECU.

4. The timing correction unit (68) is provided in the vehicle operation ECU, The steering device according to claim 2, wherein the target steering angle calculation unit corrects the timing at which it transmits the steering command signal to the steering execution unit of each steering ECU.

5. The timing correction unit (68) is provided in the main steering ECU, The steering device according to claim 3, wherein the target steering angle calculation unit corrects the timing at which it internally transmits the steering command signal to the steering execution unit of the main steering ECU itself, and the timing at which it externally transmits the steering command signal to the steering execution unit of each of the sub-steering ECUs.

6. The timing correction unit (761-764) is provided in each of the steering ECUs, The steering device according to claim 2 or 3, wherein the steering execution unit corrects the timing of outputting the drive signal to the corresponding steering actuator.

7. The steering device according to any one of claims 1 to 3, wherein when a steering mode is determined in which some of all wheels, including a pair of left and right wheels, are steered, the timing correction by the timing correction unit is performed only on the wheels that are steered.

8. When a steering mode in which all wheels are steered is determined, the timing correction by the timing correction unit is performed on all wheels, as described in any one of claims 1 to 3.

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