Steering control device

Abstract

To provide a wheel-turn control device that ensures an appropriate vehicle control capability when the drive of any one of wheel-turn actuators is restricted in an independent wheel-turn vehicle with equal to or greater than three wheels.SOLUTION: A wheel-turn control device 501 controls, in a vehicle 100 that has equal to or greater than three wheels 91 to 94 which are independently turnable and which are not mechanically constraint from each other, the turn of each wheel. Wheel-turn actuator control units 601 to 604 are provided so as to correspond to multiple wheel-turn actuators 71 to 74 that turn the corresponding wheel, and controls a drive current in such a way that the turn angles output by the wheel-turn actuators 71 to 74 become a desired value. A set of the wheel-turn actuator corresponding to each wheel and the corresponding wheel-turn actuator control unit is represented as a unit. The plurality of wheel-turn actuators 601 to 604 communicate, with each other, drive restrict information that is information relating to the drive restriction of each of the wheel-turn actuators 71 to 74, and restricts the drive of the wheel-turn actuator of the own unit on the basis of the drive restrict information of the own unit and that of the other units.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Conventionally, in a steer-by-wire system, a technique for switching the target steering angle of another steering wheel when any one of the steering wheels fails is known.

[0003] For example, in the vehicle steering device disclosed in Patent Document 1, when one of the left and right steering wheels fails, the target steering angle setting means calculates a turning limit steering angle according to the vehicle speed and the steering direction. When the absolute value of the steering angle of the normal steering wheel is larger than the absolute value of the calculated turning limit steering angle, the target steering angle setting means sets the turning limit steering angle as the target steering angle for the normal steering wheel.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, the case where "the steering wheel fails" means a case where the steering angle control for the steering wheel cannot be normally performed, such as when the steering actuator cannot generate a steering torque. However, not only in the case of an abnormality where the steering angle control function is completely lost, but also when the drive current is limited, for example, due to overheat protection when an excessive load is applied to any one of the steering actuators. When the steering angle is limited in some of the steering wheels, the vehicle may not move along the target trajectory, and the vehicle controllability may deteriorate.

[0006] Patent Document 1 does not mention anything about such measures during drive restriction. Further, Patent Document 1 targets a vehicle in which only the left and right front wheels independently steer, and does not consider three or more independently steerable vehicles including four-wheel independently steerable vehicles.

[0007] The present invention was created in view of the above points, and its object is to provide a steering control device that appropriately ensures vehicle controllability when driving of any of the steering actuators is restricted in a three or more independently steerable vehicle.

Means for Solving the Problems

[0008] The steering control device of the present invention controls the steering of each wheel in a vehicle (100) in which three or more wheels (91 - 94) that are not mechanically constrained to each other can independently steer. This steering control device includes a plurality of steering actuator control units (601 - 604).

[0009] The steering actuator control unit is provided corresponding to a plurality of steering actuators (71 - 74) that steer each wheel, and controls the drive current supplied to the steering actuator so that the steering angle output by the steering actuator becomes a desired value. A set of the steering actuator corresponding to each wheel and the steering actuator control unit is represented as a unit.

[0010] The plurality of steering actuator control units communicate with each other the drive restriction information, which is information regarding the drive restriction of the steering actuator, and restrict the drive of the steering actuator of its own unit based on the drive restriction information of its own unit and other units. For example, the drive restriction information is the current limit value of the drive current of each unit, the steering angle limit value, or the turning center setting range.

[0011] In the present invention, based on the drive restriction information of each unit, the plurality of steering actuator control units cooperate to restrict the drive of the steering actuator. Therefore, when the drive of any of the steering actuators is restricted, vehicle controllability can be appropriately ensured.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0013] A plurality of embodiments of the steering control device according to the present invention will be described with reference to the drawings. Substantially the same configurations in the plurality of embodiments are denoted by the same reference numerals and the description thereof is omitted. The "present embodiment" includes the first and second embodiments. The steering control device of the present embodiment controls the steering of each wheel in a vehicle in which four wheels that are not mechanically constrained from each other can be independently steered.

[0014] (First Embodiment) Referring to FIGS. 1 to 3, the configuration of the steering control device 501 according to the first embodiment will be described. In the independent steering vehicle 100 shown in FIG. 1, the four wheels 91-94 are not mechanically constrained to each other and can be steered independently. The left front wheel 91 is denoted as "FL", the right front wheel 92 as "FR", the left rear wheel 93 as "RL", and the right rear wheel 94 as "RR". For example, each of the wheels 91-94 is a drive wheel equipped with an in-wheel motor, and can be independently steered and independently driven.

[0015] The four steering actuators (denoted as "Steering Act" in the figure) 71-74 steer the respective wheels 91-94. For example, the steering actuators 71-74 of the present embodiment are composed of two-system three-phase brushless motors having two sets of winding sets redundantly. Corresponding to the four steering actuators 71-74, four steering actuator control units (denoted as "Steering Act Control Unit" in the figure) 601-604 are provided. The steering actuators 71-74 and the steering actuator control units 601-604 are operated by a power supply voltage supplied from an in-vehicle battery (not shown).

[0016] The steering actuator control units 601-604 control the drive current supplied to the steering actuators 71-74 so that the steering angles output by the steering actuators 71-74 become desired values. The steering angle is defined such that, for example, the left side is positive and the right side is negative with respect to the neutral position. The steering control device 501 includes these four steering actuator control units 601-604.

[0017] A set of a steering actuator and a steering actuator control unit corresponding to each wheel 91-94 is represented as a unit. The steering actuator 71 and the steering actuator control unit 601 constitute the FL unit 81 corresponding to the left front wheel 91. The steering actuator 72 and the steering actuator control unit 602 constitute the FR unit 82 corresponding to the right front wheel 92. The steering actuator 73 and the steering actuator control unit 603 constitute the RL unit 83 corresponding to the left rear wheel 93. The steering actuator 74 and the steering actuator control unit 604 constitute the RR unit 84 corresponding to the right rear wheel 94.

[0018] Each unit may be configured as an electromechanical integrated steering module in which a steering actuator and a steering actuator control unit are integrated. In this case, the steering module may be further integrated with the wheels. Alternatively, each unit may have a separate steering actuator and a steering actuator control unit electrically connected by wiring.

[0019] When the drive is not restricted, each of the steering actuators 71-74 can steer the corresponding wheels 91-94 independently in any direction. That is, it is possible to generate a steering angle in the range of ±90 deg with respect to the neutral position. However, if a wheel gets stuck in a rut or collides with an obstacle during turning, an excessive load may be applied to any of the steering actuators. Then, in some units, the drive current may be restricted by a thermal protection function that suppresses heat generation of elements and wiring components due to overcurrent. Also, when the power supply voltage drops, the drive current is restricted when driving one system of a steering actuator composed of a two-system motor.

[0020] Information regarding such drive restrictions of the steering actuators 71-74 is referred to as "drive restriction information". In FIG. 1, the double-headed dashed arrows represent communication of drive restriction information between the plurality of steering actuator control units 601-604. The plurality of steering actuator control units 601-604 communicate the drive restriction information with each other and restrict the drive of the steering actuators 71-74 of their own unit based on the drive restriction information of their own unit and other units.

[0021] FIG. 2 shows a block diagram of the steering control device 501. The steering actuator control units 601-604 of each unit include a steering angle calculation unit 671-674 and a drive current supply unit 681-684. The steering angle calculation units 671-674 receive a vehicle operation command indicating a desired vehicle operation from the outside and calculate a steering angle command value for each of the wheels 91-94 based on the vehicle operation command.

[0022] For example, when a left-turn vehicle operation command is received, the steering angle calculation units 671 of the FL unit 81 and 672 of the FR unit 82 calculate a positive steering angle. When a right-turn vehicle operation command is received, the steering angle calculation units 671 of the FL unit 81 and 672 of the FR unit 82 calculate a negative steering angle.

[0023] In the case of a turning operation in which the front wheels are steered according to parallel geometry, the steering angles of the left and right front wheels 91 and 92 are set to be equal. That is, the steering angle ratio of the outer wheel to the inner wheel in the turn is 1. The "steering angle ratio" in the following text is used in this sense. In the case of a turning operation in which the front wheels are steered according to Ackermann geometry, the absolute value of the steering angle of the inner wheel in the turn is set to be larger than the absolute value of the steering angle of the outer wheel. That is, the steering angle ratio in the turning operation of the Ackermann theory is a value smaller than 1. The Ackermann theory will be described later with reference to FIG. 7 in the second embodiment. In a turning operation intermediate between parallel geometry and Ackermann geometry, the steering angle ratio is larger than the Ackermann steering angle ratio and smaller than 1.

[0024] The drive current supply units 681-684 calculate and supply a drive current for energizing the steering actuators 71-74 according to the steering angle command values calculated by the steering angle calculation units 671-674. For example, an inverter that converts the DC power of a battery into three-phase AC power is included in the drive current supply unit. In addition, the drive current supply units 681-684 have a function of limiting the drive current calculated by themselves based on overheat protection information, power supply voltage drop information, single-system drive information, and the like.

[0025] The current limit values of the drive currents in the drive current supply units 681-684 of each unit are denoted as Ia1_lim - Ia4_lim. The current limit value may be defined by any of dq-axis current, phase current, effective value, etc. Also, the steering angle limit values corresponding to the current limit values Ia1_lim - Ia4_lim are denoted as θ1_lim - θ4_lim. The steering angle limit value is represented as a positive value as a limit value for the absolute value of the steering angle, regardless of the positive or negative of the steering angle, that is, whether it is a left turn or a right turn.

[0026] As shown in FIG. 3, the current limit value and the steering angle limit value have a positive correlation. The current limit value corresponding to the steering angle limit value with a margin added to 90 deg becomes the substantial limit upper value Ia_UL. When not restricted, for example, the current limit value may be set to a value larger than the limit upper value Ia_UL. Alternatively, the presence or absence of current limit may be discriminated by a flag.

[0027] The steering angle calculation units 671-674 of each unit calculate the steering angle command value so that the absolute value of the steering angle command value corresponding to the turning direction is equal to or less than the steering angle limit values θ1_lim-θ4_lim. For example, when the steering angle limit value is 15 deg, the steering angle calculation units 671-674 calculate the steering angle command value in the range of 0 to +15 deg for left turn and -15 to 0 deg for right turn.

[0028] Similar to FIG. 1, in FIG. 2, the double-headed dashed arrows indicate the communication of drive limit information. In the first embodiment, as drive limit information, the current limit values Ia1_lim-Ia4_lim of the drive current of each unit, or the steering angle limit values θ1_lim-θ4_lim of each unit are communicated with each other. Both the current limit value and the steering angle limit value may be communicated with each other.

[0029] When the drive limit information is the current limit values Ia1_lim-Ia4_lim of the drive current of each unit, the steering actuator control units 601-604 of each unit limit the drive current of its own unit to be equal to or less than the minimum value of the current limit values of all units.

[0030] When the drive limit information is the steering angle limit values θ1_lim-θ4_lim of each unit, the steering actuator control units 601-604 of each unit limit the absolute value of the steering angle command value of its own unit to be equal to or less than the minimum value of the steering angle limit values of all units, for example. When the absolute values of the steering angle command values of the left and right units are both set equal to the minimum value of the steering angle limit value, a turning operation according to the parallel geometry is realized.

[0031] Alternatively, a correction calculation of the steering angle may be defined for each unit, and a corrected steering angle limit value obtained by performing the correction calculation may be calculated with respect to the minimum value of the steering angle limit values of all the units. The steering actuator control units 601-604 of each unit limit the absolute value of the steering angle command value of its own unit to be equal to or less than the "corrected steering angle limit value obtained by performing the correction calculation with respect to the minimum value of the steering angle limit values of all the units".

[0032] For example, it is assumed that a correction steering angle ratio (<1) according to the vehicle speed or the like is defined between the left and right units on the inside and outside of the turn, and an operation of multiplying or dividing by the correction steering angle ratio is performed. When the steering angle limit value of the unit on the inside of the turn is the minimum value, in the unit on the outside of the turn, the absolute value of the steering angle command value is limited to be equal to or less than the corrected steering angle limit value smaller than the minimum value of the steering angle limit value. When the steering angle limit value of the unit on the outside of the turn is the minimum value, in the unit on the inside of the turn, the absolute value of the steering angle command value is limited to be equal to or less than the corrected steering angle limit value larger than the minimum value of the steering angle limit value.

[0033] As a result, the degree of freedom in realizing a turning operation according to the Ackermann geometry or a turning operation intermediate between the parallel geometry and the Ackermann geometry is improved. Not limited to the operation of multiplying or dividing by the correction steering angle ratio between the left and right units, a correction calculation such as adding or subtracting an offset angle may be performed.

[0034] Subsequently, referring to FIG. 4, an example of a steering limit operation by communication of drive limit information between units in the first embodiment will be described. In this operation example, the drive current is limited to the current limit value Ia2_lim in the FR unit corresponding to the right front wheel 92. The absolute value of the steering angle command value of the FR unit is limited to the steering angle limit value θ2_lim. To simplify the explanation, it is assumed that the rear wheels 93 and 94 do not steer from the neutral position, and only the front wheels 91 and 92 steer to turn left.

[0035] Before the drive limit, based on the desired vehicle motion to be realized, a steering angle command value θ1 * is calculated for the left front wheel 91, and a steering angle command value θ2 * is calculated for the right front wheel 92. The right front wheel 92 is at the command value θ2* The virtual state of the steered wheels in a straight-ahead position is indicated by a dashed line. However, based on the steering angle limit value θ2_lim of the FR unit, the state indicated by the solid line becomes the limit steering angle of the right front wheel 92. If the vehicle turns in this state, that is, when only the right front wheel 92 is subject to steering limit while the left front wheel 91 is not, the vehicle 100 will enter an uncontrollable state.

[0036] Therefore, in order to avoid entering an uncontrollable state, the current limit value Ia2_lim or the steering angle limit value θ2_lim is communicated as drive limit information from the steering actuator control unit of the FR unit to the steering actuator control units of the other FL, RL, and RR units. The steering actuator control unit of the FL unit restricts the drive current of its own unit to be equal to or less than the current limit value Ia2_lim. Alternatively, the steering actuator control unit of the FL unit restricts the absolute value of the steering angle command value of its own unit to be equal to or less than θ2_lim, or to be equal to or less than the corrected steering angle limit value (θ2_lim / ρ) obtained by performing a correction operation using, for example, the correction steering angle ratio ρ. The steering angle command value of the FL unit after the drive restriction is denoted as θ1. ** and so on.

[0037] As a result, the steering angle of the left front wheel 91 is restricted to be equal to or less than the steering angle of the right front wheel 92. Since the steering angle command values of the RL unit and the RR unit corresponding to the left and right rear wheels 93 and 94 are originally 0 deg, they are not affected by the drive limit information. Thus, in this embodiment, when the drive current of the steering actuator is restricted in some units, each unit cooperatively changes the steering angle command value within the restricted range. Therefore, vehicle controllability is ensured, and the vehicle 100 can achieve a stable turning operation.

[0038] Here, if the characteristics of the current limit value and the steering angle limit value in each unit are the same, there is no substantial difference regardless of which is communicated as drive limit information. However, when there are differences in the characteristics of the current limit value and the steering angle limit value for each unit, communicating the steering angle limit value as drive limit information can more directly and evenly limit the steering angles of each unit.

[0039] Incidentally, the characteristics of the actual steering angle with respect to the drive current vary depending on road surface conditions such as the road surface friction coefficient and unevenness, and the characteristics of the steering angle limit value with respect to the current limit value also change. Next, with reference to FIGS. 5(a) and 5(b), the calculation of the steering angle limit value reflecting the road surface conditions will be described.

[0040] Each steering actuator control unit 601-604 stores a drive current-actual steering angle map shown in FIG. 5(a) and a current limit value-steering angle limit value map shown in FIG. 5(b). Here, the "map" is not limited to one in which a large number of data groups are stored so as to be readable, but includes a calculation formula. That is, it is also interpreted that calculating the calculation result of the calculation formula based on the input variable is also a form of calculation using the map.

[0041] The drive current-actual steering angle map defines the actual steering angle of the wheels 91-94 with respect to the drive current of the steering actuators 71-74 for each of one or more load regions divided according to the magnitude of the load. Relatively, [1] a low load region, [2] a medium load region, and [3] a high load region are divided. In the low load region, a relatively small drive current generates a large actual steering angle, whereas in the high load region, a larger drive current is required to generate the same steering angle.

[0042] The current limit value-steering angle limit value map defines the relationship between the current limit value of the drive current of the steering actuators 71-74 and the steering angle limit value for each load region. When the current limit value is the same value, the steering angle limit value in the low load region is larger than the steering angle limit value in the high load region.

[0043] Each steering actuator control unit 601-604 may calculate the actual steering angle based on, for example, the rotation angle detection value of the steering actuators 71-74, or may acquire the actual steering angle from a steering angle sensor provided on the wheels 91-94. The steering actuator control units 601-604 determine the load region using the drive current-actual steering angle map based on the drive current supplied to the steering actuators 71-74 and the detected actual steering angle.

[0044] Then, the steering actuator control units 601-604 calculate a steering angle limit value corresponding to the current limit value in the determined load region using a current limit value-steering angle limit value map. Thereby, the steering angle limit values of the respective wheels 91-94 can be appropriately set according to the road surface conditions.

[0045] (Second Embodiment) Referring to FIGS. 6 to 9, the second embodiment will be described. As shown in FIG. 6, in the steering control device 502 of the second embodiment with respect to the first embodiment, after setting the turning center based on the vehicle operation command, the steering angle command values of the respective units are calculated. In the configuration example shown in FIG. 6, turning center setting units 661-664 are provided inside the steering actuator control units 601-604 of the respective units. The steering angle calculation units 671-674 calculate the steering angle command values based on the turning center set by the turning center setting units 661-664. Further, the steering angle limit values θ1_lim-θ4_lim are notified from the steering angle calculation units 671-674 to the turning center setting units 661-664.

[0046] Referring to FIG. 7, the calculation of the steering angle command values θ1 * -θ4 * based on the Ackermann theory will be described. In the Ackermann theory, 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. That is, the respective wheels 91-94 are steered in the tangential direction of a circle centered on the turning center C.

[0047] Here, an axis passing through the centers of the front wheels 91, 92 and orthogonal to the vehicle longitudinal axis Y0 is defined as the front wheel axis X12, and an axis passing through the centers of the rear wheels 93, 94 and orthogonal 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. Also, an axis passing through the center of gravity G and orthogonal to the vehicle longitudinal axis Y0 is represented as the center of gravity axis X0. Assuming that the weight distribution in the vehicle longitudinal direction is uniform, the center of gravity axis X0 is located in the middle of the front wheel axis X12 and the rear wheel axis X34. When the turning center C is set on the center of gravity axis X0, the left front wheel 91 and the left rear wheel 93, and the right front wheel 92 and the right rear wheel 94 each turn on the same arc, so the inner wheel difference and the outer wheel difference become zero, and the running resistance during turning is reduced.

[0048] Referring to FIG. 8(a), the setting of the turning center C by the turning center setting units 661-664 will be described. According to the steering angle limit values θ1_lim - θ4_lim of each unit, the allowable steering angle range for each wheel 91-94 is determined. The range obtained by rotating the steering angle range 90° toward the turning center C is the turning center setting range A1 - A4 of each unit.

[0049] FIG. 8(a) shows a left turn assuming that the steering angle limit value θ2_lim of the right front wheel 92 is smaller than the steering angle limit values of the other wheels 91, 93, and 94. Note that the turning center setting range A2R for the right turn of the right front wheel 92 is symmetric with A2 about the left and right. Also, the hatching ranges of the turning center setting ranges A3 and A4 of the rear wheels 93 and 94 are omitted halfway.

[0050] The turning center setting ranges A1 - A4 are communicated with each other between units as drive limit information. Also, the range where the turning center setting ranges A1 - A4 of each unit overlap (the cross-hatched range in the figure) is defined as the turning center common setting range Acom. The turning center setting units 661-664 of each unit set the turning center C in the turning center common setting range Acom. The steering angle calculation units 671-674 calculate the steering angle command values θ1 * -θ4 * based on the turning center C.

[0051] In the second embodiment, the turning center setting ranges A1 - A4 set according to the steering angle limit values θ1_lim - θ4_lim of each unit are used as drive limit information, and the plurality of steering actuator control units 601-604 cooperate to limit the driving of the steering actuators 71-74. Therefore, while suppressing the running resistance during turning according to the steering angle ratio of the Ackermann theory, the vehicle controllability can be appropriately ensured. Also, since the turning center setting units 661-664 are provided dispersedly for each unit, the risk that the turning center setting function is lost all at once for all units can be avoided.

[0052] Next, referring to FIG. 8(b), the change of the turning center when the pre-limit turning center C0 set based on the desired vehicle motion deviates from the common turning center setting range Acom will be described. In this case, the turning center setting units 661-664 set the position where the distance from the pre-limit turning center C0 is minimized in the common turning center setting range Acom as the post-limit turning center C#. Thereby, while minimizing the deviation from the desired vehicle turning motion, the vehicle controllability can be appropriately ensured.

[0053] Referring to FIG. 9, an example of a steering limit operation by communication of drive limit information between units in the second embodiment will be described. For the operation example in the first embodiment shown in FIG. 4, in the operation example of FIG. 9, when the drive is limited in the FR unit, a situation where the four wheels 91-94 independently steer and turn left according to the Ackermann geometry is assumed. Note that, in order to make the difference before and after the drive limit easier to see, an example is shown in which the post-limit turning center C# is changed to a position relatively far from the pre-limit turning center C0, regardless of the method of FIG. 8(b).

[0054] Before the drive limit, using the turning center C0 set based on the desired vehicle motion, the steering angle command values θ1 * -θ4 * of each wheel 91-94 are calculated. The virtual state in which the right front wheel 92 steers according to the command value θ2 * is shown by a broken line. However, based on the steering angle limit value θ2_lim of the FR unit, the state shown by the solid line becomes the limit steering angle of the right front wheel 92. If, in this state, that is, when only the right front wheel 92 is steered limited while the other wheels 91, 93, 94 are not steered limited, the vehicle 100 will be in an uncontrollable non-control state.

[0055] Therefore, in order to avoid entering a non-control state, the turning center setting range determined according to the steering angle limit value θ2_lim is communicated as drive limit information from the steering actuator control unit of the FR unit to the steering actuator control units of the other FL, RL, and RR units. Each steering actuator control unit of the FL, RL, and RR units communicates with each other and sets the post-limitation turning center C# within the common turning center setting range for all units. Then, each steering actuator control unit of the FL, RL, and RR units calculates the steering angle command values θ1 ** , θ3 ** , θ4 ** of its own unit after drive limitation.

[0056] As a result, according to the steering angle limit value θ2_lim of the FR unit, the steering angle command values of all units are reset according to the Ackermann geometry using the post-limitation turning center C#. Therefore, even when the drive current of the steering actuator is limited in some units, vehicle controllability is ensured, and the vehicle 100 can achieve a stable turning operation.

[0057] (Modification of the Second Embodiment) As shown in FIG. 10, in the steering control device 502C of the modification of the second embodiment, one turning center setting unit 66 is provided in common for the steering actuator control units 601-604 of each unit. That is, the turning center setting unit 66 is provided outside the steering actuator control units 601-604 of each unit.

[0058] The turning center setting unit 66 sets the turning center C based on the desired vehicle operation and commands the steering angle calculation units 671-674 of each unit. Further, the turning center setting unit 66 determines the common turning center setting range based on the steering angle limit values θ1_lim-θ4_lim notified from the steering angle calculation units 671-674 of each unit. With this configuration, the same operational effects as those of the second embodiment can be obtained. Also, by aggregating the turning center setting function into one turning center setting unit 66, efficient calculation becomes possible.

[0059] (Other Embodiments) (a) The steering control device of the present invention is applicable not only to four-wheel vehicles but also to three-wheel vehicles or independent steering vehicles with six or eight wheels having three or more pairs of left and right wheels in the front-rear direction of the vehicle. Generally speaking, the steering control device of the present invention is applied to "vehicles in which three or more wheels that are not mechanically constrained from each other can be independently steered".

[0060] (b) The steering actuators 71-74 are not limited to two systems of three-phase brushless motors, and may be composed of one system of polyphase motors, DC motors, or linear actuators, etc.

[0061] (c) Each of the wheels 91-94 only needs to be independently steerable and does not need to be independently driven. For example, the front wheels 91 and 92 may be drive wheels, and the rear wheels 93 and 94 may be driven wheels.

[0062] As described above, the present invention is not limited to such embodiments, and can be implemented in various forms without departing from the gist thereof.

[0063] The control unit and its method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied by a computer program. Alternatively, the control unit and its method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Or, the control unit and its method described in the present disclosure may be realized by one or more dedicated computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured by one or more hardware logic circuits. Also, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executable by a computer.

Explanation of Reference Numerals

[0064] 501, 502, 502C ··· Steering control devices, 601 - 604 ··· Steering actuator control units, 71 - 74 ··· Steering actuators, 91 - 94 ··· Wheels, 100 ··· (Independently steerable) vehicle.

Claims

1. A steering control device for controlling the steering of each wheel in a vehicle (100) having three or more wheels (91 - 94) that are not mechanically constrained to each other and are independently steerable, comprising a plurality of steering actuator controllers (601 - 604) provided corresponding to a plurality of steering actuators (71 - 74) for steering each wheel, and controlling drive current supplied to the steering actuators so that the steering angle output by the steering actuators becomes a desired value, wherein when a set of the steering actuator corresponding to each wheel and the steering actuator controller is represented as a unit, the plurality of steering actuator controllers communicate drive limit information, which is information regarding drive limitations of the steering actuators, with each other, and limit the drive of the steering actuators of its own unit based on the drive limit information of its own unit and other units.

2. The drive limit information is a current limit value of the drive current of each unit, and the steering actuator controller of each unit limits the drive current of its own unit to be equal to or less than the minimum value of the current limit values of all units. The steering control device according to claim 1.

3. The drive limit information is a steering angle limit value of each unit, and the steering actuator controller of each unit limits the absolute value of the steering angle command value of its own unit to be equal to or less than the minimum value of the steering angle limit values of all units, or to be equal to or less than a corrected steering angle limit value obtained by performing a correction operation defined for each unit with respect to the minimum value. The steering control device according to claim 1.

4. The steering actuator controller of each unit calculates a steering angle command value for each wheel so that the steering direction of each wheel is orthogonal to a straight line connecting the center of the turning center set based on the desired vehicle motion and the center of each wheel, the drive limit information is a turning center setting range corresponding to a steering angle range allowed for each wheel according to the steering angle limit value of each unit, and the steering actuator controller of each unit sets the turning center within a common turning center setting range where the turning center setting ranges of all units overlap, and calculates the steering angle command value of its own unit. The steering control device according to claim 1.

5. The steering control device according to claim 4, wherein when the pre-turn center set based on the desired vehicle motion is outside the common turning center setting range, a position where the distance from the pre-turn center in the common turning center setting range is minimized is set as the post-turn center.

6. The steering actuator control unit stores a drive current-actual steering angle map that defines the relationship between the drive current of the steering actuator and the actual steering angle of the wheel for each of one or more load regions classified according to the magnitude of the load, and a current limit value-steering angle limit value map that defines the relationship between the current limit value and the steering angle limit value of the drive current of the steering actuator for each of the load regions. Based on the drive current supplied to the steering actuator and the detected actual steering angle, the load region is determined using the drive current-actual steering angle map. The steering control device according to any one of claims 3 to 5, wherein a steering angle limit value corresponding to the current limit value in the determined load region is calculated by the current limit value-steering angle limit value map.

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