Steering control device

Abstract

To provide a steering control device for suppressing bias of loads of steering actuators in an independent steering vehicle.SOLUTION: A steering control device 601 controls the steering of each wheel by driving a plurality of steering actuators 71-74 provided corresponding to each wheel 91-94 in an independent steering vehicle 100. The vehicle operation determination unit 65 determines a target vehicle operation. The turning center coordinate determination unit 67 determines the turning center coordinates. The target steering angle determining unit 681-684 determines the target steering angles δ1* to δ4* of the respective wheels based on the determined turning center coordinates. The temperature detection unit 55 detects the temperature of the highest temperature actuator, which is the turning actuator having the highest temperature among the plurality of turning actuators 71 to 74, as the determination temperature Tj. The execution determination unit 59 determines whether or not to execute "deviation suppression control" for adjusting the steering operation of each wheel so as to suppress the deviation of the load of each steering actuator 71 to 74 in accordance with the determination temperature Tj.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] 2. Description of the Related Art Conventionally, there are known techniques for enabling a vehicle to operate even when some of the wheels of the vehicle malfunction.

[0003] For example, Patent Document 1 discloses a driving force control device that causes multiple driving sources (electric motors) corresponding to each wheel to generate driving force independently from each other. When an abnormality detection unit detects an abnormality in any of the driving sources, a driving force control unit identifies a high-load driving source from the multiple driving sources excluding the driving source in which the abnormality was detected, which is expected to be under high load when traveling along the road section to the destination. The driving force control unit controls the multiple driving sources so that the driving force of the high-load driving source when traveling along that road section is smaller than the driving force estimated for the high-load driving source. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2023-178847 Summary of the Invention [Problem to be solved by the invention]

[0005] In the prior art of Patent Document 1, even if an abnormality occurs in one of the drive sources, the drive force is distributed so that the vehicle reaches its destination without placing an overload on the other drive sources. The same concept can be applied to steering actuators that steer each wheel to a target steering angle when an independently steering vehicle turns, instead of drive actuators that rotate each wheel at a target rotation speed when the vehicle is traveling.

[0006] Generally, actuators such as motors are provided with a protection function that limits the current when a predetermined temperature is reached to protect the elements from heat generation due to high load. In this case, drive sources other than the drive source detected as abnormal in the conventional technology of Patent Document 1 may be subject to current limiting due to heat generation, making it impossible to generate the desired drive force, which could prevent the vehicle from reaching its destination.

[0007] In an independently steering vehicle in which each wheel can be steered independently, it is expected that the load state of each steering actuator will become uneven depending on the driving condition and steering pattern. "Depending on the driving condition" refers to driving factors such as frequent left turns or frequent driving on slopes. "Depending on the steering pattern" refers to differences in the magnitude of the steering angle of each wheel depending on the position of the turning center coordinate. If some steering actuators with a high load heat up and current limitation is triggered, situations may arise in which it becomes impossible to steer the vehicle while stationary or perform emergency avoidance. Therefore, it is necessary to suppress the uneven load on each steering actuator so as to avoid current limitation.

[0008] The present invention has been made in view of the above points, and an object of the present invention is to provide a steering control device that suppresses uneven loads on the steering actuators in an independently steering vehicle. [Means for solving the problem]

[0009] The steering control device of the present invention controls the steering of each wheel of a vehicle (100) in which three or more wheels (91-94) that are not mechanically constrained from one another can be steered independently by driving a plurality of steering actuators (71-74) provided corresponding to each wheel. The steering control device includes a vehicle operation determination unit (65), a turning center coordinate determination unit (67), a target steering angle calculation unit (681-684, 68), a temperature detection unit (55), and an execution determination unit (59).

[0010] The vehicle operation determination unit determines a target vehicle operation based on the vehicle state. The turning center coordinate determination unit determines turning center coordinates based on the target vehicle operation. The target steering angle determination unit determines a target steering angle (δ1* -δ4 * ) is determined.

[0011] The temperature detection unit detects the temperature of the hottest actuator, which is the steering actuator with the highest temperature among the plurality of steering actuators, as a judgment temperature (Tj). The execution judgment unit judges whether or not it is necessary to execute "bias suppression control," which adjusts the steering operation of each wheel so as to suppress bias in the loads on each steering actuator, in accordance with the judgment temperature.

[0012] As a result, the steering control device of the present invention can suppress uneven loads on the steering actuators in an independently steering vehicle. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram showing an independently steering vehicle equipped with a steering control device according to a first embodiment; [Figure 2] FIG. 4 is a diagram showing the relationship between the temperature of the steering actuator and the current limit value. [Figure 3] FIG. 4 is a diagram illustrating terms related to setting the coordinates of the turning center. [Figure 4] Diagram of steering patterns A, B, and C. [Figure 5] Diagram of steering pattern D. [Figure 6] Diagram of steering patterns E, F, and G. [Figure 7] FIG. 10 is a diagram showing the output simulation of each steering actuator when turning left in seven different steering patterns, and the ranking in order of lowest output. [Figure 8] FIG. 4 is a diagram showing the running state of the vehicle when it is determined whether to perform bias suppression control. [Figure 9] 4 is a main flowchart for determining whether to perform bias suppression control. [Figure 10] Sub-flowchart of S2 in Figure 9. [Figure 11] FIG. 10 is a diagram of an independently steering vehicle equipped with a steering control device according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of a steering control device according to the present invention will be described with reference to the drawings. This steering control device controls the steering of each wheel of a vehicle in which three or more wheels that are not mechanically restricted from one another can be steered independently by driving a plurality of steering actuators provided corresponding to each wheel. In the first and second embodiments described below, the basic functions of the steering control device are the same, but the form of the system configuration in which it is mounted on the vehicle is different. The first and second embodiments will be collectively referred to as "the present embodiment." In this embodiment, a steering control device will be described that is mounted on a four-wheel independently steerable vehicle including left and right front wheels and left and right rear wheels, as a typical vehicle.

[0015] (First embodiment) Figure 1 shows the configuration of an independently steering vehicle 100 equipped with a steering control device 601 of the first embodiment. The four wheels 91-94 of the independently steering vehicle 100 are not mechanically constrained to one another and can be steered independently. The left front wheel 91 is labeled "FL", the right front wheel 92 "FR", the left rear wheel 93 "RL", and the right rear wheel 94 "RR".

[0016] For each wheel 91-94, there is provided a steering module 81-84 that integrates a target steering angle determination unit 681-684 and a steering actuator ("Steering Act" in the drawing) 71-74. Typically, the steering actuator 71-74 is made up of a motor and an inverter that supplies drive power to the motor. The digits "1" to "4" at the end of the reference numeral of each element indicate the corresponding wheel 91-94.

[0017] The steering control device 601 of the first embodiment is configured to include a vehicle operation command section that commands the operation of the entire vehicle, and target steering angle determination sections 681-684 for each of the steering modules 81-84. In a vehicle with a steer-by-wire system in which the driver operates the steering wheel, the vehicle operation command section may also function as a control section for a reaction force device that applies a reaction torque to the steering wheel.

[0018] The vehicle operation command unit includes a vehicle operation determination unit 65, a turning center coordinate determination unit 67, a temperature detection unit 55, an execution determination unit 59, and a turning center coordinate restriction unit 66. The vehicle operation determination unit 65 determines a target vehicle operation based on vehicle conditions such as the vehicle speed and the actual steering angle. The turning center coordinate determination unit 67 determines turning center coordinates based on the target vehicle operation and notifies target steering angle determination units 681-684 of the steering modules 81-84.

[0019] Temperature detection unit 55 acquires the temperature of each steering actuator 71-74 from a temperature sensor or the like provided corresponding to each steering actuator 71-74. In steering actuators 71-74, power switching elements are used in the inverters that convert DC power from the battery into AC power and supply it to the motor windings. When the load on steering actuators 71-74 is high and the amount of current flowing increases, the power switching elements in particular generate heat, so the temperature of the circuit board on which the power switching elements are mounted is detected, for example.

[0020] The steering actuator with the highest temperature among steering actuators 71-74 is referred to as the "hottest actuator." The hottest actuator may change from time to time depending on the driving conditions, steering pattern, or ambient temperature. Temperature detection unit 55 detects the temperature of the hottest actuator as the "determination temperature Tj" (see Figures 2, 9, etc.). Determination temperature Tj means the "temperature used to determine whether to perform bias suppression control."

[0021] The "bias suppression control" is a control unique to this embodiment that adjusts the steering operation of each wheel 91-94 so as to suppress bias in the load on each steering actuator 71-74, and its technical significance will be described later with reference to FIG. 2. Execution determination unit 59 determines whether or not to execute bias suppression control in accordance with determination temperature Tj. Turning center coordinate limiting unit 66 limits the setting range of the turning center coordinate in the bias suppression control. Turning center coordinate determination unit 67 determines the turning center coordinate within the setting range limited by turning center coordinate limiting unit 66.

[0022] The target steering angle determination units 681-684 determine the target steering angles δ1 of the wheels 91-94 based on the determined turning center coordinates. * -δ4 * The steering angle is defined such that the neutral position is 0 and the left side is positive and the right side is negative. The steering actuators 71-74 determine the target steering angle δ1 determined by the target steering angle determination units 681-684. * -δ4 * The corresponding wheels 91-94 are steered in accordance with the

[0023] In independently steering vehicle 100, it is expected that the load state of each steering actuator 71-74 will become uneven depending on driving conditions such as frequent left turns or frequent driving on slopes, or depending on steering patterns with different turning center coordinate positions. Here, to avoid the risk of malfunction due to heat generation in the power switching elements, a current limiting function is provided in the drive circuits of steering actuators 71-74.

[0024] Referring to Figure 2, the relationship between the temperature of the steering actuator and the current limit value will be explained. As shown in the upper diagram, when the steering actuator temperature is at or below a limit temperature Tlim (for example, 70°C), the current limit value is set to the maximum current, so that commanded steering operations can be performed without restriction. However, when the steering actuator temperature exceeds 70°C, the current limit value decreases as the temperature increases. Since the steering torque and steering speed are limited, it may not be possible to achieve the desired steering operation. If some of the steering actuators 71-74 that are under a heavy load overheat and a current limit is imposed, this could have an impact such as making it impossible to steer the vehicle at a fixed position or perform emergency avoidance.

[0025] As shown in the table at the bottom, for example, suppose the steering actuator temperatures corresponding to FL (front left wheel 91), FR (front right wheel 92), RL (rear left wheel 93), and RR (rear right wheel 94) are 60°C, 40°C, 30°C, and 35°C, respectively. In this case, steering actuator 71 for FL is the hottest actuator, and 60°C, the temperature of steering actuator 71, is detected as judgment temperature Tj. At this stage, the temperature of steering actuator 71 has not reached limit temperature Tlim, but if it is operated under a higher load than this, there is a risk that current limitation will occur.

[0026] Therefore, the aim of this embodiment is to suppress the imbalance in the load on each of steering actuators 71-74 by using FR, RL and RR steering actuators 72, 73 and 74 other than steering actuator 71 as main steering actuators during the next turning operation. This control is called "imbalance suppression control", and execution determination unit 59 determines whether or not to execute imbalance suppression control according to determination temperature Tj. Furthermore, as a specific method of imbalance suppression control, turning center coordinate limiting unit 66 limits the setting range of the turning center coordinate when the vehicle next performs a turning operation.

[0027] 3, the terms used to set the coordinates of the turning center P will be described. In the independently steering vehicle 100, the four wheels 91-94 are individually steered around the turning center P by the operation of the corresponding steering modules 81-84 according to, for example, the Ackermann theory.

[0028] In this embodiment, an X coordinate is set in the longitudinal direction of the vehicle, and a Y coordinate is set in the transverse direction of the vehicle. For the symbols of each axis, the first letter of the axis that defines the position of the Y coordinate is designated as Y. An axis that passes through the vehicle center O and extends in the longitudinal direction of the vehicle is defined as the "vehicle longitudinal axis Y0." The vehicle longitudinal axis Y0 is a set of points that have the same Y coordinate as the vehicle center O. Furthermore, the first letter of the axis that defines the position of the X coordinate is designated as X. An axis that passes through the vehicle center O and is perpendicular to the vehicle longitudinal axis Y0 is defined as the "front-rear central axis X0." The front-rear central axis X0 is a set of points that have the same X coordinate as the vehicle center O. When the center of gravity coincides with the center O as shown in FIG. 3, the front-rear central axis X0 is also the center of gravity axis X0.

[0029] The axis that passes through the centers 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 centers 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. The distance from the longitudinal center axis X0 to the front wheel axis X12 is defined as the front wheel axis distance Lf, and the distance from the longitudinal center axis X0 to the rear wheel axis X34 is defined as the rear wheel axis distance Lr. 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. The values ​​of Lf, Lr, Df, and Dr are stored as vehicle specifications. Note that the tread widths Df and Dr will not be mentioned in the following explanation.

[0030] The seven steering patterns will be explained with reference to Figures 4 to 6. Seven steering patterns A to G are defined depending on whether the X coordinate of the turning center P in the vehicle's longitudinal direction is located on one of the three axes, the front wheel axis X12, the longitudinal center axis X0, and the rear wheel axis X34, or whether it is located in front of or behind each axis.

[0031] According to Ackermann's theory, each of the wheels 91-94 is steered in the tangent direction of a circle centered on a common turning center P. The steering patterns A to G have different X coordinates of the turning center P, and the front / rear wheel steering ratio is determined according to each steering pattern. In the steering patterns A to G in each diagram, the distance Rop from the vehicle center O to the turning center P (turning radius of the vehicle center O) is constant.

[0032] As shown in Figure 4, in steering pattern A, the coordinate of turning center P is located forward of front wheel axis X12. In steering pattern B, the coordinate of turning center P is located on front wheel axis X12, and only rear wheels 93, 94 are steered while front wheels 91, 92 face in a straight ahead direction (steering angle 0). In other words, steering pattern B is a "rear wheel steering" pattern. In steering pattern C, the coordinate of turning center P is located between front wheel axis X12 and longitudinal center axis X0.

[0033] As shown in Fig. 5, in steering pattern D, the coordinates of turning center P are located on the longitudinal central axis X0. When front wheel axle distance Lf and rear wheel axle distance Lr are equal (Lf = Lr), the steering angles of front wheels 91, 92 and rear wheels 93, 94 are symmetrical in the front-rear direction with respect to longitudinal central axis X0. In other words, steering pattern D is a pattern in which front and rear wheels are steered in opposite phases.

[0034] As shown in Figure 6, in steering pattern E, the coordinate of turning center P is located between the longitudinal center axis X0 and the rear wheel axis X34. In steering pattern F, the coordinate of turning center P is located on the rear wheel axis X34, and only the front wheels 91, 92 are steered while the rear wheels 93, 94 are facing in a straight ahead direction (steering angle 0). Steering pattern F is a "front wheel steering" pattern similar to that of a conventional, general left-right wheel articulated vehicle. In steering pattern G, the coordinate of turning center P is located behind the rear wheel axis X34.

[0035] Referring to Figure 7, we will explain the output simulation of each steering actuator when turning left using seven different steering patterns, and the ranking in order of lowest output. This output simulation is for turning left, and when turning right, FL and FR, and RL and RR are swapped. It is assumed that the center of gravity of the vehicle is located near the center. If the center of gravity of the vehicle is shifted from the center to the front / rear or left / right, the output ranking depending on the steering pattern may be swapped.

[0036] The top of Figure 7 shows a comparison of the integrated output values ​​of steering actuators 71-74 in a stacked bar graph. Each bar graph shows the stacked output values ​​of steering actuators 71-74 for FL, FR, RL, and RR. The vertical axis shows values ​​that correlate with output [W], but as the purpose is a relative evaluation, reference to absolute numerical values ​​will be omitted. The lower the output, the lower the load, and the less heat generated by the steering operation, so temperature rise is suppressed. The total output of all wheels is relatively small for steering patterns B, C, D, and E, and is the smallest for steering pattern D.

[0037] The table at the bottom of Figure 7 shows the steering pattern ranking from 1st to 7th place for each wheel in order of lowest output (load). For each wheel FL, FR, RL, and RR, the steering pattern ranked first in order of lowest output is marked with a circle. In addition, the steering patterns ranked first to fourth in order of lowest output are surrounded by a two-dot chain line frame. Regarding the first and second limits of the setting range of the turning center coordinate described in S6 and S7 of Figure 9, in this example, the two-dot chain line frame corresponds to the first range, which is the range of the first limit, and the circle corresponds to the second range, which is the range of the second limit. The second range is a part of the first range.

[0038] When the determination temperature Tj is relatively high and the load on the hottest actuator needs to be reduced, the turning center coordinate limiting unit 66 limits the selectable steering patterns from the seven steering patterns A to G to some steering patterns in which the load on the hottest actuator is relatively low. When the determination temperature Tj is higher than a first threshold (e.g., 50°C), the first limitation limits the selectable steering patterns to four patterns ranked first to fourth in order of low output. When the determination temperature Tj is further higher than a second threshold (>first threshold, e.g., 60°C), the second limitation limits the selectable steering pattern to just one pattern, ranked first in order of low output.

[0039] For FL (left front wheel steering actuator 71), the first in the ranking in order of lowest output is steering pattern A, and the second, third and fourth in order are steering patterns B, C and D, respectively. For FR (right front wheel steering actuator 72), the first in the ranking in order of lowest output is steering pattern B, and the second, third and fourth in order are steering patterns C, A and D, respectively. For RL and RR (left and right rear wheel steering actuators 73, 74), the first in the ranking in order of lowest output is steering pattern D, and the second, third and fourth in order are steering patterns E, F and C, respectively.

[0040] For example, if the hottest actuator is FL (steering actuator 71), the steering patterns selectable in the first limit are steering patterns A to D, and the steering pattern selectable in the second limit is steering pattern A. If the hottest actuator is RL (steering actuator 73), the steering patterns selectable in the first limit are steering patterns C to F, and the steering pattern selectable in the second limit is steering pattern C.

[0041] Next, with reference to Figures 8 to 10, an example of the execution determination of the bias suppression control will be described. In the explanation of the flowchart, the symbol "S" means a step. In Figure 8, the vehicle 100 has completed a turning operation at the first curve Rc1 and is currently traveling on a straight road Rs, and it is predicted that the vehicle will next perform a turning operation at the second curve Rc2. In the S-shaped curve, the turning direction at the second curve Rc2 is opposite to the turning direction at the first curve Rc1. S1 to S7 in Figure 9 (main flowchart) are repeatedly performed while the vehicle 100 is traveling from the start point Rss to the end point Rse of the straight road Rs. S8 and S9 are performed at the end point Rse of the straight road Rs. Figure 10 is a sub-flowchart of S2, showing an example of a method for detecting the determination temperature Tj.

[0042] In S1, it is determined whether the vehicle is traveling straight. A "straight traveling state" is defined as "a traveling state in which there is no turning center coordinate and the center of gravity of the vehicle moves linearly in the direction of travel," and is typically assumed to be a traveling state in which the vehicle is traveling straight ahead. For example, when the yaw rate is equal to or less than a threshold close to 0, it is determined that the vehicle is traveling substantially straight. The shortest distance of the straight path Rs may be a distance (e.g., several tens of centimeters) at which a straight traveling state can be recognized. If YES in S1, proceed to S2. If NO in S1 while the vehicle is turning, the determination of bias suppression control is not initiated. In other words, the turning center coordinate determination unit 67 does not change the turning center coordinate while the vehicle is turning, so as not to affect the turning operation being performed.

[0043] In S2, temperature detection unit 55 detects the temperature of the warmest actuator as a judgment temperature Tj. Specifically, in S21 of FIG. 10, temperature detection unit 55 detects the temperature of each of steering actuators 71-74 using a temperature sensor. The temperature of each of steering actuators 71-74 may reflect heat generated by the steering operation on first curve Rc1. It may also be due to heat transfer from a heat source within vehicle 100, the outside air temperature, or the road surface temperature. In S22, the steering actuator with the highest detected temperature is selected as the "warmest actuator." In S23, the temperature of the warmest actuator is stored as a judgment temperature Tj.

[0044] 10, the detected temperatures of the four steering actuators 71-74 are compared to select the hottest actuator. Alternatively, if it is known that a particular steering actuator has the highest temperature, for example because it is close to a heat source, that particular actuator may be considered the "hottest actuator." In this case, in S2, temperature detection unit 55 detects the temperature of the particular hottest actuator as determination temperature Tj, regardless of the detected temperatures of the other steering actuators.

[0045] In this embodiment, a first threshold value (for example, 50°C) and a second threshold value (for example, 60°C) higher than the first threshold value are set for the determination temperature Tj. In steps S3 to S7, the setting range of the turning center coordinate for "the next time the vehicle performs a turning operation" is limited in two stages by two temperature threshold values ​​based on the determination temperature Tj. While the determination in S8 is NO and steps S1 to S7 are repeated, the limit on the setting range of the turning center coordinate is updated.

[0046] In S3, it is determined whether the judgment temperature Tj is higher than the first threshold value. If the judgment temperature Tj is equal to or lower than the first threshold value and the answer to S3 is NO, the execution judgment unit 59 determines in S5 that execution of bias suppression control is unnecessary. In this case, the turning center coordinate limiting unit 66 does not limit the turning center coordinate. If the answer to S3 is YES, the execution judgment unit 59 determines that execution of bias suppression control is necessary, and the turning center coordinate limiting unit 66 limits the turning center coordinate.

[0047] If the answer is YES in S3, then in S4 it is determined whether the judgment temperature Tj is higher than the second threshold. If the judgment temperature Tj is higher than the first threshold but equal to or lower than the second threshold, then the answer is NO in S4, and in S6 the turning center coordinate limiting unit 66 implements a "first limit" that limits the turning center coordinates to a first range.

[0048] When the determination temperature Tj is higher than the second threshold, YES is determined in S4, and in S7 the turning center coordinate limiting unit 66 implements a "second limit" that limits the turning center coordinate to a second range. The second range is a portion of the first range, i.e., a range narrower than the first range. In the example of FIG. 7, the range of turning center coordinates according to the steering patterns ranked first to fourth in order of low output corresponds to the first range, and the range of turning center coordinates according to the steering pattern ranked first in order of low output corresponds to the second range.

[0049] Next, in S8, it is determined whether a turning operation command has been received from vehicle operation determination unit 65. If there is no turning operation command and S8 is NO, S1 to S7 are repeated. In other words, since the temperature of each steering actuator 71-74 changes while the straight-ahead state continues, the determination of whether or not bias suppression control needs to be performed, and if so, the restriction of the setting range of the turning center coordinate, are repeated based on the latest updated determination temperature Tj. Here, the repetition cycle of the update process may be set to the order of several seconds to several tens of seconds, or several minutes, corresponding to the time it takes for the temperature to change.

[0050] When a turning operation command is received from vehicle operation determination unit 65, a YES determination is made in S8. At this time, in S9, turning center coordinate determination unit 67 determines turning center coordinates within the setting range limited by turning center coordinate limit unit 66. Then, target steering angle determination unit 68 sets target steering angle δ1 to each of steering actuators 71-74. * -δ4 * is instructed, and the turning operation is executed.

[0051] As described above, steering control device 601 of this embodiment can suppress uneven loads on steering actuators 71-74 in independently steering vehicle 100. Therefore, even if uneven loads occur on steering actuators 71-74 depending on the running state or steering pattern, it is possible to prevent the load from concentrating on some of the steering actuators and current limitation from being applied. This appropriately avoids situations where stationary steering or emergency avoidance becomes impossible.

[0052] Furthermore, in the first embodiment, target steering angle determination sections 681-684 are provided separately corresponding to steering actuators 71-74, so the risk of the steering angle control function for all wheels 91-94 failing all at once is avoided.

[0053] (Second embodiment) Figure 11 shows the configuration of an independently steering vehicle 100 equipped with a steering control device 602 of the second embodiment. Components that are substantially the same as those in Figure 1 are given the same reference numerals and explanations thereof will be omitted. The steering control device 602 of the second embodiment is provided with a target steering angle determination unit 68 inside a vehicle operation command unit that commands the operation of the entire vehicle. The target steering angle determination unit 68 determines the target steering angles δ1 of all wheels 91-94 based on the turning center coordinates determined by the turning center coordinate determination unit 67. * -δ4 * The target steering angle δ1 notified from the target steering angle determination unit 68 is calculated collectively and notified to each of the steering actuators 71-74. * -δ4 * The steering actuators 71-74 operate in accordance with the above.

[0054] In the configuration of the second embodiment, similarly to the first embodiment, it is possible to suppress uneven loads on the steering actuators 71-74 in the independently steering vehicle 100. Furthermore, the target steering angle δ1 of each wheel is determined by one target steering angle determination unit 68. * -δ4 * can be calculated efficiently.

[0055] (Other embodiments) (a) The steering control device of the present invention is not limited to a four-wheel independently steering vehicle, but may be applied to a vehicle with three or more independently steering wheels.

[0056] (b) The "straight traveling state" in S1 of Figure 9 is defined as "a traveling state in which there is no turning center coordinate and the center of gravity of the vehicle moves linearly in the traveling direction." This "straight traveling state" may include a traveling state in which the vehicle moves straight ahead, as well as a traveling state in which all wheels move diagonally while maintaining the same steering angle.

[0057] (c) The restriction on selectable steering patterns among the seven steering patterns A to G is not limited to "four types in the first limit and one type in the second limit," but may be set so that the second range is part of the first range, for example, "three types in the first limit and two types in the second limit." Also, the restriction is not limited to two stages, and the setting range of the turning center coordinate may be limited in one stage, or in multiple stages of three or more stages.

[0058] (d) The method for limiting the range of the turning center coordinate in the bias suppression control is not limited to the method using the seven types of steering patterns shown in Figures 4 to 6. For example, the turning center coordinate limiting unit 66 may directly calculate the limit range of the turning center coordinate in X and Y coordinates.

[0059] (e) As described above, it is preferable that the turning center coordinate determination unit 67 does not change the turning center coordinate during a turning operation in principle. However, there is a risk that the temperature of the hottest actuator will rise to the limit temperature Tlim (see FIG. 2) while the vehicle continues to travel around curves without any straight-ahead sections. Therefore, for example, when the elapsed time since the end of the previous straight-ahead state during a turning operation exceeds a predetermined time, the turning center coordinate determination unit 67 may exceptionally change the turning center coordinate depending on the turning radius and the current temperature of the hottest actuator.

[0060] 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.

[0061] "If a traveling state in which there is no turning center coordinate and the center of gravity of the vehicle moves linearly in the traveling direction is defined as a straight-ahead state, the turning center coordinate limiting unit updates the limit of the setting range of the turning center coordinate when the vehicle next performs a turning operation based on the judgment temperature when the vehicle is in the straight-ahead state, and the turning center coordinate determining unit does not change the turning center coordinate during the turning operation of the vehicle, and when a turning operation command is received from the vehicle operation determining unit in the straight-ahead state, determines the turning center coordinate within the setting range limited by the turning center coordinate limiting unit." and "a steering control device that is applied to a four-wheel vehicle including left and right front wheels and left and right rear wheels, and and a steering control device that defines seven types of steering patterns depending on whether the turning center coordinate in the vehicle longitudinal direction is located on one of three axes: a front wheel axis (X12) which is an axis perpendicular to axis (X0), a longitudinal center axis (X0) which passes through the center of the vehicle and is perpendicular to the vehicle longitudinal axis; and a rear wheel axis (X34) which is an axis which passes through the center of the rear wheels and is perpendicular to the vehicle longitudinal axis, or whether it is located in front of or behind each axis, and the turning center coordinate limiting unit limits the selectable steering patterns from the seven types of steering patterns to some steering patterns in which the load on the highest temperature actuator is relatively low.

[0062] Each control unit (vehicle operation determination unit, turning center coordinate limiting unit, turning center coordinate determination unit, target steering angle determination unit, temperature detection unit, execution determination 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 (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 (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 as instructions executed by a computer on a computer-readable non-transitory tangible recording medium. [Explanation of symbols]

[0063] 601, 602... Steering control device, 55 Temperature detection unit, 59... Execution determination unit, 65... Vehicle operation decision unit, 66...Turning center coordinate limiting section, 67....Turning center coordinate determination unit, 681-684, 68···Target steering angle determination unit; 71-74···Steering actuator, 91-94...wheels, 100···(independent steering) vehicle.

Claims

1. A steering control device for a vehicle (100) in which three or more wheels (91-94) that are not mechanically constrained from one another can be steered independently, the steering control device controlling the steering of each wheel by driving a plurality of steering actuators (71-74) provided corresponding to each wheel, a vehicle operation determination unit (65) that determines a target vehicle operation based on a vehicle state; a turning center coordinate determination unit (67) that determines turning center coordinates based on the target vehicle movement; Based on the determined turning center coordinates, the target steering angle (δ1 ＊ -δ4 ＊ a target steering angle determination unit (681-684, 68) for determining the target steering angle; a temperature detection unit (55) that detects the temperature of a hottest actuator, which is the steering actuator with the highest temperature among the plurality of steering actuators, as a judgment temperature (Tj); an execution determination unit (59) that determines whether or not it is necessary to execute bias suppression control that adjusts the steering operation of each wheel so as to suppress bias in the load on each of the steering actuators according to the determination temperature; A steering control device comprising:

2. 2. A steering control device according to claim 1, further comprising a turning center coordinate limiting section (66) that limits a setting range of the turning center coordinate in the bias suppression control.

3. If we define a straight-ahead state as a state in which there is no turning center coordinate and the vehicle center of gravity moves linearly in the direction of travel, then: the turning center coordinate limiting unit, when the vehicle is traveling straight, updates a limit on a setting range of a turning center coordinate for the next time the vehicle performs a turning operation, based on the determination temperature; The turning center coordinate determination unit The turning center coordinates are not changed during the turning operation of the vehicle, 3. A steering control device according to claim 2, wherein when a turning operation command is received from said vehicle operation determination unit while the vehicle is traveling straight, said turning center coordinate limiting unit determines the turning center coordinate within a set range limited by said turning center coordinate limiting unit.

4. Applies to four-wheel vehicles including left and right front wheels and left and right rear wheels, Seven types of steering patterns can be defined based on whether the turning center coordinate in the vehicle's longitudinal direction is located on one of the three axes: the front wheel axis (X12), which is an axis that passes through the center of the front wheels and is perpendicular to the vehicle's longitudinal axis (Y0); the longitudinal center axis (X0), which is an axis that passes through the center of the vehicle and is perpendicular to the vehicle's longitudinal axis; and the rear wheel axis (X34), which is an axis that passes through the center of the rear wheels and is perpendicular to the vehicle's longitudinal axis.

3. The steering control device according to claim 2, wherein the turning center coordinate limiting section limits selectable steering patterns from the seven types of steering patterns to some steering patterns in which the load on the highest temperature actuator is relatively low.

5. Two or more temperature thresholds are set for the determination temperature, including a first threshold and a second threshold higher than the first threshold, The turning center coordinate limiting unit When the determination temperature is higher than a first threshold value, the setting range of the turning center coordinate is limited to a first range; 5. The steering control device according to claim 2, wherein when the determination temperature is higher than a second threshold value, the setting range of the turning center coordinate is limited to a second range that is a part of the first range.

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