Vehicle control system

Abstract

The present invention provides a vehicle control device that improves the energy efficiency of a vehicle in which two or more tires are capable of independent driving. [Solution] The driving instruction unit 51 of the vehicle control device 50 instructs the target direction of movement of the vehicle. The driving force calculation unit 53 calculates the driving force instruction value for each drive motor 851-854 and instructs the motor control device. The target tire angle calculation unit 54 calculates the target tire angle for each tire 91-94 and instructs the steering mechanism. The efficiency characteristic storage unit 55 stores the efficiency of the drive motors according to the driving force and rotational speed of the drive motors. When there are multiple driving patterns in which one or more driveable tires are driven with one or more driving force instruction values ​​of the corresponding drive motors to drive the vehicle with respect to the target driving force of the entire vehicle, the driving force calculation unit 53 selects a combination of driveable tires to drive and the corresponding driving force instruction value of the drive motor so as to minimize the total power consumption calculated from the driving force, rotational speed and efficiency of each drive motor.

Description

Technical Field

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

Background Art

[0002] Conventionally, in a vehicle in which a plurality of wheels can be independently driven from each other, a device for controlling the driving force of the vehicle is known.

[0003] For example, Patent Document 1 discloses a device for controlling the driving force of a plurality of motor generators each connected to left and right wheels in a vehicle with independently driven wheels. This driving force control device drives only the left wheel during a right turn and only the right wheel during a left turn. By concentrating the output on one driving wheel, a region with good motor efficiency in the rotational speed-torque characteristics is used.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the driving force control of Patent Document 1, the turning radius and wheel speed are not considered. When the turning radius and wheel speed are considered, simply determining the driving wheel of one wheel only by the turning direction is not always an efficient method. Depending on the selection of the driving wheel, there is a problem that the efficiency deteriorates and the electricity cost decreases.

[0006] The present invention has been created in view of the above points, and its object is to provide a vehicle control device that improves the electricity cost in a vehicle in which two or more tires can be independently driven from each other.

Means for Solving the Problems

[0007] A vehicle (100, 103, 104) equipped with the vehicle control device according to the present invention comprises three or more tires (91-94) including two or more driveable tires that can be driven independently of each other, a plurality of drive motors (851-854), a plurality of motor control devices (801-804), a plurality of wheel speed sensors (691-694), and a steering mechanism (70).

[0008] The drive motors are capable of driving each driveable tire. The motor control device controls the operation of each drive motor. The wheel speed sensor detects the wheel speed of each tire, which is correlated with the rotational speed of each drive motor. The steering mechanism is capable of steering one or more of the aforementioned tires.

[0009] The vehicle control device includes a driving instruction unit (51), a tire position storage unit (52), a driving force calculation unit (53), a target tire angle calculation unit (54), and an efficiency characteristic storage unit (55).

[0010] The driving instruction unit instructs the target direction of movement of the vehicle and, based on that target direction of movement, instructs the target driving force and target turning center of the vehicle. The tire position memory unit stores the positions of the driveable tires. The driving force calculation unit distributes the target driving force of the entire vehicle instructed by the driving instruction unit to calculate the driving force instruction value for each drive motor and instructs each motor control device accordingly.

[0011] The target tire angle calculation unit calculates the target tire angle for each steerable tire based on the target turning center instructed by the driving instruction unit, and instructs the steering mechanism accordingly. The efficiency characteristic storage unit stores the efficiency of the drive motor according to the driving force and rotational speed of the drive motor.

[0012] Assume there are multiple driving patterns in which, with respect to the overall target driving force of the vehicle, one or more driveable tires are driven by one or more driving force indication values ​​of their respective drive motors to propel the vehicle. In this case, the driving force calculation unit selects a combination of driveable tires to be driven and the corresponding driving force indication value of the drive motor such that the sum of the power consumption calculated from the driving force, rotational speed, and efficiency of each drive motor is minimized.

[0013] In the present invention, in a vehicle in which two or more tires can be independently driven, the electricity cost can be improved.

Brief Description of the Drawings

[0014] [Figure 1] The figure which shows the example of the four-wheel independent steering vehicle equipped with the vehicle control apparatus of one Embodiment. [Figure 2] The figure which shows the example of the front two-wheel independent steering vehicle equipped with the vehicle control apparatus of one Embodiment. [Figure 3] The figure which shows the example of the front two-wheel linked steering vehicle equipped with the vehicle control apparatus of one Embodiment. [Figure 4] The block diagram of the vehicle control apparatus of one Embodiment. [Figure 5] The figure explaining the distribution of the target driving force of the whole vehicle. [Figure 6] The map which shows the relationship between the driving force and the rotational speed of the drive motor and the efficiency. [Figure 7] The figure explaining the calculation formula of the motor power consumption. [Figure 8] The figure comparing the electricity cost at the time of turning between four-wheel equal drive and one-wheel drive. [Figure 9] The figure explaining the relationship between the rotational speed of each wheel, the vehicle speed, and the turning radius. [Figure 10] The map which selects the combination of the drive tire and the driving force of the drive motor at which the total power consumption becomes minimum. [Figure 11] The figure explaining the selection of the drive tire according to the target movement direction by the first Example. [Figure 12] The figure explaining the selection of the drive tire at the time of skid turning or minimum turning by the second Example. [Figure 13] The figure explaining the suppression of the vectoring by the third Example. [Figure 14] The figure explaining the feedback control of the yaw rate by the fourth Example. [Figure 15] The figure explaining the correction of the calculated value of the power consumption by the fifth Example. [Figure 16] The figure explaining the selection of the drive tire according to the total tire load by the sixth Example. [Figure 17] Main flowchart of the processing by the vehicle control device according to an embodiment. [Figure 18] Sub flowchart of the B1 - B2 section in FIG. 17. [Figure 19] Diagram showing an example of other vehicles on which the vehicle control device is mounted.

Mode for Carrying Out the Invention

[0015] An embodiment of the vehicle control device will be described based on the drawings. The vehicle control device of this embodiment is mounted on, for example, a battery - powered electric vehicle (BEV) with all - wheel drive (AWD) in which all tires can be independently driven. This vehicle control device aims to reduce the total power consumption of the drive motors and improve the electricity cost of the electric vehicle by selecting the tires to be driven based on the positional relationship between the turning center and the tires during turning.

[0016] (Configuration example of a vehicle equipped with a vehicle control device) Referring to FIGS. 1 to 3, a configuration example of a vehicle 100 equipped with the vehicle control device 50 of this embodiment will be described. Hereinafter, "tires that can be independently driven" are referred to as "drivable tires". In this specification, "tire" and "wheel" are used as synonymous terms. The vehicle 100 shown in FIGS. 1 to 3 is an all - wheel drive electric vehicle including four "drivable tires 91 - 94". That is, all tires are drivable tires and there are no tires that cannot be independently driven. Configuration examples of vehicles including tires other than drivable tires will be described as other embodiments.

[0017] The drivable tires are, for example, tires independently driven by in - wheel motors and can actually be "controlled and driven" independently of each other. That is, in addition to driving during acceleration, braking during deceleration is also possible. However, since the vehicle control device 50 of this embodiment is characterized by control during driving, "braking" will not be mentioned and descriptions will be made using terms such as "drive motor" and "driving force".

[0018] While fuel efficiency [km / L or L / km] is used for engine-powered vehicles, electric vehicles use electric energy consumption [kWh / km] as an indicator showing the relationship between driving distance and energy consumption. The smaller the electric energy consumption figure, the longer the distance that can be traveled with less electricity. Here, the power consumed by the drive motor has a large impact on electric energy consumption. In this embodiment, in an electric vehicle equipped with multiple drive motors, electric energy consumption is improved by control based on motor efficiency and control based on motor power consumption.

[0019] Each vehicle 100 shown in Figures 1 to 3 is a four-wheel independent drive vehicle including four driveable tires 91-94, but the configuration of the steering mechanism 70 differs. In addition to the designation "100", sub-designations "100A, 100B, 100C" are also indicated to distinguish them by the configuration of the steering mechanism 70. The sub-designations "100A, 100B, 100C" are used only in the explanation of Figures 1 to 3.

[0020] First, the configuration of the four-wheeled vehicle 100 other than the steering mechanism 70 will be explained in Figures 1 to 3. 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". The symbols for each element below, and the digits "1" to "4" at the end of the symbols for driving force, rotational speed, power consumption, etc., correspond to the driveable tires 91-94 of FL, FR, RL, and RR, respectively. In this embodiment, all tires are driveable tires, so "driveable" is omitted as appropriate and they are written as "tires 91-94".

[0021] Vehicle 100 is equipped with four sets of drive motors 851-854 corresponding to each tire 91-94, motor control devices 801-804, and wheel speed sensors 691-694. The drive motors are, for example, in-wheel motors. The motor control devices 801-804 are integrated with the corresponding drive motors 851-854.

[0022] The drive motors 851-854 can drive each tire 91-94 by outputting a driving force τ1-τ4. The motor control devices 801-804 control the operation of each drive motor 851-854. The wheel speed sensors 691-694 detect the wheel speeds ω1-ω4 of each tire 91-94, which are correlated with the rotational speed of each drive motor 851-854.

[0023] The vehicle control device 50 controls vehicle operation according to the driver's driving operations and command signals from the automated driving system. The vehicle control device 50 detects the rotational speed (wheel speed) ω1-ω4 of the drive motors 851-854 from the wheel speed sensors 691-694. In addition, depending on the embodiment described later, it acquires information from the turning information detection device 67 and the power consumption sensor 68.

[0024] Based on the acquired information, the vehicle control device 50 sets the driving force instruction value τ for each drive motor 851-854. * 1-τ * The system calculates 4 and instructs each motor control device 801-804. The vehicle control device 50 also calculates the target tire angle for each steerable tire and instructs the steering mechanism 70. The target tire angle is expressed with the neutral position parallel to the vehicle's longitudinal axis being 0, and for example, the counterclockwise direction is positive and the clockwise direction from the neutral position is negative.

[0025] Next, the configuration of each steering mechanism 70 in Figures 1 to 3 will be described. The vehicle 100 is equipped with a steering mechanism 70 capable of steering one or more tires. The vehicle 100A shown in Figure 1 is a four-wheel independent steering vehicle in which the four tires 91-94 can be steered independently. The steering mechanism 70 includes steering actuators ("Steering Act" in the figure) 71-74 corresponding to each tire 91-94. The vehicle control device 50 calculates the target tire angles δ1-δ4 for each tire 91-94 and instructs the steering actuators 71-74.

[0026] The vehicle 100B shown in Figure 2 is a front-two-wheel independently steered vehicle in which the left front wheel 91 and the right front wheel 92 can be steered independently, while the rear wheels 93 and 94 are connected by a shaft 96 and do not steer. The steering mechanism 70 includes steering actuators 71 and 72 corresponding to the left front wheel 91 and the right front wheel 92. The vehicle control device 50 calculates the target tire angles δ1 and δ2 for the left front wheel 91 and the right front wheel 92 and instructs the steering actuators 71 and 72. A rear-two-wheel independently steered vehicle with the front and rear wheels swapped with vehicle 100B can also be envisioned in a similar manner.

[0027] The vehicle 100C shown in Figure 3 is a front-wheel-connected steering vehicle in which the left front wheel 91 and the right front wheel 92 are connected by tie rods 95 and steer at the same tire angle. The rear wheels 93 and 94 are connected by shafts 96 and do not steer. The steering mechanism 70 includes one steering actuator 75 that drives the tie rods 95 left and right. The vehicle control device 50 calculates target tire angles δ1 and δ2 for the left front wheel 91 and the right front wheel 92, which are equal to each other, and instructs the steering actuator 75. A rear-wheel-connected steering vehicle in which the front and rear wheels are swapped with that of vehicle 100C can be similarly envisioned.

[0028] The degree of steering freedom is highest in the four-wheel independent steering vehicle 100A, followed by the front two-wheel independent steering vehicle 100B, and then the front two-wheel linked steering vehicle 100C. When turning, in the four-wheel independent steering vehicle 100A, the turning center can be freely set according to the required vehicle behavior. In vehicles 100B and 100C, the turning center is set on the straight line connecting the rear wheels 93 and 94.

[0029] Specifically, the turning center is calculated using the Ackermann theory, assuming that the tires and vehicle do not skid. In manual driving, the turning center is determined by the steering angle of the driver and the tire positions (tread width, wheelbase). In autonomous driving, the system internally stores information on tread width and wheelbase, and the turning radius is determined according to the target turning instruction processed within the autonomous driving system. In the Ackermann theory, independently steerable tires are steered in a direction perpendicular to the straight line connecting the position of each tire and the turning center.

[0030] The vehicle control device 50 of this embodiment can be installed in any of the vehicles 100A, 100B, and 100C, which have different configurations of the steering mechanism 70. Some of the controls in the embodiments described later are specific to the four-wheel independent steering vehicle 100A, but the other basic controls are applicable to all vehicles 100A, 100B, and 100C.

[0031] Next, with reference to Figure 4, the configuration of the vehicle control device 50 will be described. Only one of the four sets of blocks for the tires 91-94, drive motors 851-854, motor control devices 801-804, and wheel speed sensors 691-694 will be shown. The vehicle control device 50 includes a driving instruction unit 51, a tire position memory unit 52, a driving force calculation unit 53, a target tire angle calculation unit 54, and an efficiency characteristic memory unit 55.

[0032] The driving instruction unit 51 is a concept that encompasses, for example, steering, accelerator, and automatic driving systems. The driving instruction unit 51 instructs the target direction of movement of the vehicle and, based on that target direction of movement, instructs the target driving force and target turning center of the vehicle. Specifically, the driving instruction unit 51 includes a target direction of movement instruction unit 511 that instructs the target direction of movement, a straight-line motion conversion unit 513 that converts the target direction of movement into straight-line motion, and a turning motion conversion unit 514 that converts the target direction of movement into turning motion. The straight-line motion conversion unit 513 instructs the driving force calculation unit 53 to provide the target driving force and target turning center. The turning motion conversion unit 514 instructs the target tire angle calculation unit 54 to provide the target turning center. In particular, in the case of automatic driving, the turning motion conversion unit 514 may further instruct the target tire angle calculation unit 54 to provide the target yaw rate.

[0033] The tire position memory unit 52 stores the positions of the tires 91-94. For example, the center position in the width direction on the rotation axis is defined as the tire position. The position information of the tires 91-94 is acquired by the driving force calculation unit 53 and the target tire angle calculation unit 54. The driving force calculation unit 53 acquires the wheel speed, i.e., the rotational speed ω1-ω4 of each drive motor 851-854, from the wheel speed sensors 691-694, and the efficiency η from the efficiency characteristic memory unit 55.

[0034] Based on the acquired information, the drive force calculation unit 53 distributes the target drive force for the entire vehicle, as instructed by the driving instruction unit 51, to improve energy efficiency, and sets the drive force instruction value τ for each drive motor 851-854. * 1-τ * Calculate 4 and instruct each motor control device 801-804. Specific methods for improving energy efficiency and each embodiment will be described later with reference to Figures 5 to 18.

[0035] The target tire angle calculation unit 54 calculates the target tire angle for each steerable tire based on the target turning center and target yaw rate instructed by the driving instruction unit 51, and instructs the steering mechanism 70 accordingly. The efficiency characteristic storage unit 55 stores the efficiency η of the drive motors 851-854 according to the driving force τ1-τ4 and rotational speed ω1-ω4 (see Figure 6).

[0036] In the fourth embodiment described later, the vehicle control device 50 acquires the actual yaw rate γsns or the actual turning radius detected by the turning information detection device 67 and performs feedback control with respect to the target yaw rate or target turning radius. In the fifth embodiment, the vehicle control device 50 acquires the actual power consumption Wsns of the drive motors 851-854 detected by the power consumption sensor 68 and corrects the calculated power consumption value.

[0037] Referring to Figures 5 and 6, we will explain the concept of distributing the total driving force of an all-wheel-drive (AWD) vehicle to the four driveable tires. Here, regarding the use of the term "distribution" of driving force, if the vehicle as a whole outputs a driving force of, for example, 160 [Nm] to one wheel, we consider that 160 [Nm] is distributed to that wheel and 0 [Nm] to the remaining three wheels. Therefore, even when only one driveable tire is engaged, the expression "distributing driving force" is used in common, just as in the cases of two-wheel to four-wheel drive.

[0038] In Figure 5, while vehicle 100 is traveling in a straight line, each tire 91-94 does not slip, and each drive motor 851-854 rotates at the same speed of 200 [rpm]. If the target driving force for the entire vehicle is 160 [Nm], in the drive pattern Q shown in the upper section, 40 [Nm] of driving force is distributed to each of the four wheels 91-94. In the drive pattern D shown in the lower section, 80 [Nm] of driving force is distributed to each of the two rear wheels 93 and 94. In other words, the driving force distributed to the left and right front wheels 91 and 92 is 0 [Nm]. The total driving force is the same 160 [Nm] in both the four-wheel drive pattern Q and the two-wheel drive pattern D, and the vehicle's behavior will not change unless there is an effect of pitching or slipping.

[0039] However, as shown in the efficiency map in Figure 6, motor efficiency η changes depending on the driving force and rotational speed. Generally, efficiency η is better in the high driving force and high rotational speed range than in the low driving force and low rotational speed range. At a rotational speed of 200 [rpm], efficiency η is 60-90% in the driving force range of approximately 20-200 [Nm]. More specifically, efficiency η is 66% at a driving force of 40 [Nm] and 71% at a driving force of 80 [Nm]. Therefore, the two-wheel drive pattern D is more efficient than the four-wheel drive pattern Q. Furthermore, the efficiency η of the one-wheel drive pattern M at a driving force of 160 [Nm] is about the same as the efficiency η of the two-wheel drive pattern D at a driving force of 80 [Nm].

[0040] Referring to Figure 7, the formulas for calculating the power consumption of the drive motors 851-854 corresponding to each tire 91-94 are explained below. Assuming the driving force of the drive motor is τk [Nm] and the rotational speed is ωk [rpm], the power consumption Wk [W (=Nm / s)] of each drive motor is calculated by formula (1). The "k" at the end of the symbol represents one of "1, 2, 3, or 4" corresponding to each tire 91-94. The wheel speed of each tire 91-94 correlates with the rotational speed ω1-ω4 of the drive motor 851-854. Furthermore, the total power consumption Wsum is calculated by formula (2).

[0041] Wk=2π×τk×ωk / 60η (1) Wsum = W1 + W2 + W3 + W4 ... (2)

[0042] As shown in equation (1), the power consumption Wk of each drive motor is proportional to the product of the driving force τk and the rotational speed (wheel speed) ωk. In other words, even if the driving force τk is the same, a smaller rotational speed (wheel speed) ωk results in lower power consumption.

[0043] Figure 7 shows a steady-state circular turn with a turning radius Lg to the right. The turning center C is set on the straight line connecting the rear wheels 93 and 94, and the left and right front wheels 91 and 92 are steered to the right with target tire angles δ1 and δ2, respectively. In this situation, we consider the wheel speed ωk of each tire 91-94 in relation to the turning center C. The closer the tire is to the turning center C, the smaller the wheel speed ωk, and the further away the tire is from the turning center C, the larger the wheel speed ωk. Therefore, the wheel speed ω4 of the right rear wheel 94 is the smallest, and the wheel speed ω1 of the left front wheel 91 is the largest. Thus, from the viewpoint of minimizing the total power consumption Wsum, it is desirable to drive with only the right rear wheel 94.

[0044] Figure 8 shows the results of a CAE-based comparison of energy consumption when the vehicle is driven with equal force on all four wheels during a steady-state circular turn, and when it is driven by a selected single wheel. Under all four conditions—vehicle speed 5 [km / h] - turning radius 15 [m], vehicle speed 40 [km / h] - turning radius 50 [m], vehicle speed 50 [km / h] - turning radius 180 [m], and vehicle speed 120 [km / h] - turning radius 3000 [m]—improvement in energy consumption was confirmed with single-wheel drive compared to equal force on all four wheels.

[0045] Thus, in this embodiment, the driveable tire is selected to minimize power consumption by taking into account the positional relationship between the turning center C and the tire position, as well as the motor efficiency η and other factors. In the following description, the driveable tire will be referred to as the drive tire. In the control of each embodiment, the key point is how to select the drive tire from among the tires 91-94.

[0046] Referring to Figures 9 and 10, a method for selecting a combination of drive tires and driving force input values ​​to minimize total power consumption will be explained. Power consumption W is calculated from the driving force τ1-τ4, rotational speed ω1-ω4, and efficiency η of each drive motor 851-854 using the above formula (1). Referring to Figure 9, the relationship between the distance Lk [m] from the turning center C to the position of each tire 91-94, the rotational speed (wheel speed) ωk [rpm] of each tire, and the peripheral speed Vk [m / s] will be explained. The turning radius Lg [m] of the vehicle corresponds to the distance from the turning center C to the vehicle's center of gravity G, and the vehicle speed V [m / s] corresponds to the speed at which the vehicle's center of gravity G moves.

[0047] The coordinates of the vehicle's center of gravity G are set as the origin (0,0), and the coordinates of the turning center C are set as (xc,yc). The distance Lk is calculated from the coordinates of the turning center C (xc,yc) and the coordinates of the position of each tire stored in the tire position memory unit 52 (xk,yk) using equation (3.1). The peripheral speed Vk of each tire 91-94 is calculated by multiplying the vehicle speed V by the ratio of the distance from the turning center C using equation (3.2). The rotational speed (wheel speed) ωk of each tire 91-94 is calculated by dividing the peripheral speed Vk by the tire radius Rtire [m] using equation (3.3).

[0048] Lk = √{(xc - xk)} 2 +(yc-yk) 2} ···(3.1) Vk = (Lk / Lg) × V ... (3.2) ωk=60Vk / (2πRtire) ···(3.3)

[0049] Figure 10 shows multiple drive patterns in which, with respect to the target driving force of the entire vehicle, one or more driveable tires are driven by one or more driving force values ​​of their respective drive motors to propel the vehicle. For example, when the target driving force of the entire vehicle is 50 [Nm], in combination No. 1, only the right rear wheel 94 is responsible for the driving force of 50 [Nm], and the total power consumption is Wsum_1. In combination No. 2, the right rear wheel 94 is responsible for 49 [Nm] of driving force and the left rear wheel 93 is responsible for 1 [Nm] of driving force, and the total power consumption is Wsum_2.

[0050] Of the n possible combinations from No. 1 to No. n, the one with the smallest total power consumption is, hypothetically, combination No. 3. In combination No. 3, the right rear wheel 94 contributes 48 [Nm] of driving force and the left rear wheel 93 contributes 2 [Nm], resulting in a total power consumption of Wsum_3. Therefore, the driving force calculation unit 53 selects combination No. 3 and drives the vehicle. This method is a common method for calculating all combinations, taking into account cases such as acceleration during cornering.

[0051] In contrast, during constant-speed turns where acceleration does not occur during the turn, it is sufficient to output a driving force equivalent to a relatively small rolling resistance, thus simplifying the selection process for "the combination of drive tire and driving force instruction value that minimizes total power consumption." As shown in Figure 5, efficiency tends to be better the greater the driving force per wheel, so it is generally best to output the driving force from the driveable tire closest to the turning center C (the right rear wheel 94 in the example of Figure 9).

[0052] However, various embodiments of the method for selecting the driveable tires can be envisioned depending on the configuration of the vehicle's steering mechanism 70, the target direction of movement, the position of the turning center C, etc. Next, the first to sixth embodiments will be described in order with reference to Figures 11 to 16. Each embodiment can be implemented in combination with one another. The configuration of the vehicle 100 and the vehicle control device 50 will be shown in Figures 1 to 4 as appropriate. Regardless of the configuration of the steering mechanism 70, the vehicle will be denoted as "100".

[0053] (First embodiment) Referring to Figure 11, a first embodiment of control by the vehicle control device 50 will be described. The upper part of Figure 11 shows an example of a front-wheel steering vehicle, and the lower part shows an example of a four-wheel independent steering vehicle. In the figure, the block arrow pointing to the right front of the vehicle indicates the target direction of movement, which is defined as either a right turn or a left turn. "R-turn" attached to the tire means that the turning direction (vectoring) of the vehicle 100 due to the driving force of the drive motor corresponding to that tire is a right turn. "L-turn" means that the turning direction (vectoring) of the vehicle 100 due to the driving force of the drive motor corresponding to that tire is a left turn.

[0054] When the target direction of movement is a right turn (R-turn), the left and right front wheels 91 and 92 are steered to the target tire angle to the right, while the left and right rear wheels 93 and 94 remain straight without being steered. The turning direction due to the driving force of the drive motors for the left and right front wheels 91 and 92 and the left rear wheel 93 is a right turn, the same as the target direction of movement. On the other hand, the turning direction due to the driving force of the drive motor for the right rear wheel 94 is a left turn, the opposite of the target direction of movement, which increases the load on the vehicle 100 during turning. Therefore, the driving force calculation unit 53 either excludes the right rear wheel 94 from the drive tires or lowers its priority in the distribution of driving force.

[0055] In other words, the driving force calculation unit 53 selects a drive tire from among the tires whose turning direction due to the driving force of the corresponding drive motor 851-854 is the same as the target direction of movement, with each tire 91-94 steered to the target tire angle. This makes it possible to appropriately select a drive tire while taking into account the vectoring effect due to the driving force applied to the driveable tire.

[0056] In a four-wheel independently steered vehicle, each tire 91-94 is steered according to the Ackermann theory. When the target direction of movement is a right turn, the turning direction due to the driving force of the drive motor corresponding to the right rear wheel 94 will also be a right turn, so no tire is excluded from the selection of drive tires. Therefore, the drive tires are selected so as to minimize the total power consumption, taking into account the tire angles of each tire 91-94. For example, depending on the position of the turning center C in the longitudinal direction of the vehicle, either the right front wheel 92 or the right rear wheel 94 may be selected as the drive tire. Alternatively, both the right front wheel 92 and the right rear wheel 94 may be selected as drive tires.

[0057] (Second example) Referring to Figure 12, a second embodiment of control by the vehicle control device 50 will be described. In the second embodiment, a situation is assumed in which one driveable tire is close to the target turning center C. Here, the driveable tire closest to the target turning center C (for example, the right rear wheel 94) is defined as the "nearest driveable tire NT". The distance between the target turning center C and the position of the nearest driveable tire NT is expressed as the nearest distance d_c-nt.

[0058] The upper panel of Figure 12 shows the case where the target turning center C coincides with the position of the nearest driveable tire NT, the nearest-neighbor distance d_c-nt is substantially 0, and the vehicle performs a pivot turn. The lower panel shows the case where the nearest-neighbor distance d_c-nt is less than or equal to the proximity threshold d_c-nt_th, and the vehicle performs a minimal turn.

[0059] In these cases, even if the driving force of the drive motor is applied to the nearest driveable tire NT, the vehicle may not turn, or the tire may slip, potentially increasing the driving load or causing a deviation in the turning radius. Therefore, when the nearest distance d_c-nt is less than or equal to the proximity threshold d_c-nt_th, the driving force calculation unit 53 selects a driveable tire from among the driveable tires other than the nearest driveable tire NT. This allows for the appropriate selection of a driveable tire during pivot turns and extremely tight turns.

[0060] (Third embodiment) Referring to Figure 13, a third embodiment of control by the vehicle control device 50 will be described. Assume that the target direction of movement is a right turn, and that the right rear wheel 94 is selected as the drive tire to minimize the total power consumption. The left rear wheel 93 and the right rear wheel 94 correspond to a "pair of driveable tires". A large driving force τ4 is applied to the right rear wheel 94, while the driving force τ3 applied to the left rear wheel 93 is zero, or an extremely small value compared to the driving force τ4 applied to the right rear wheel 94.

[0061] In this case, left-turn vectoring occurs due to the difference in driving force ΔτR-L (=|τ4―τ3|) between the left and right rear wheels 93 and 94. As shown in the upper section, if the difference in driving force ΔτR-L applied to the left and right rear wheels 93 and 94 exceeds the allowable value ΔτR-L_lim, the vehicle behavior may become unstable due to the effects of excessive vectoring.

[0062] Therefore, as shown in the lower section, the drive force calculation unit 53 suppresses vectoring by calculating a drive force instruction value such that the difference in drive force ΔτR-L applied to the left and right rear wheels 93 and 94 is less than or equal to the allowable value ΔτR-L_lim. This prevents the vehicle behavior from becoming unstable and the driving load from increasing. Note that the allowable value ΔτR-L_lim is not limited to a fixed value and may be changed according to the vehicle speed, turning radius, etc.

[0063] (Fourth embodiment) Referring to Figure 14, a fourth embodiment of control by the vehicle control device 50 will be described. In particular, in the field of autonomous driving, the actual yaw rate (hereinafter referred to as "actual yaw rate") or the actual turning radius (hereinafter referred to as "actual turning radius") during turning is an important vehicle behavior value. Vectoring occurs when the driving force is concentrated on some of the driveable tires, which affects the yaw rate and turning radius. In the fourth embodiment, the vehicle control device 50 performs feedback control to bring the actual yaw rate or actual turning radius acquired from the turning information detection device 67 closer to the target yaw rate or target turning radius.

[0064] Figure 14 shows an example of correcting the target tire angle using yaw rate feedback control. As shown in the upper panel, when the actual yaw rate γsns is smaller than the target yaw rate γtar, the target tire angle calculation unit 54 corrects the target tire angle δ2 of the right front wheel 92, for example, in the direction of advancing it. As shown in the lower panel, when the actual yaw rate γsns is larger than the target yaw rate γtar, the target tire angle calculation unit 54 corrects the target tire angle δ2 of the right front wheel 92, for example, in the direction of returning it to its original position.

[0065] Here, the relationship between the yaw rate γ [rad / s], the vehicle speed V [m / s], and the turning radius Lg [m] of the vehicle's center of gravity (see Figure 9) is "γ = V / Lg". The actual turning radius calculated from the actual yaw rate γsns may be fed back to the target turning radius. In addition, the driving force calculation unit 53 may correct the driving force instruction value of the drive motor instead of, or in addition to, the correction of the target tire angle by the target tire angle calculation unit 54. This makes it possible to control the vehicle in accordance with its actual turning behavior.

[0066] (Fifth example) Referring to Figure 15, a fifth embodiment of control by the vehicle control device 50 will be described. The vehicle 100 is equipped with a power consumption sensor 68 that detects the actual power consumption Wsns of the drive motors 851-854. There may be a discrepancy between the power consumption calculated from the driving force τ1-τ4, rotational speed ω1-ω4, and efficiency η of each drive motor 851-854 using equation (1) and the actual power consumption.

[0067] For example, even if the specifications of each tire 91-94 are the same, differences in air pressure and deterioration can result in differences in rolling resistance against the actual road surface. Assuming no slippage occurs, high rolling resistance necessitates generating a greater driving force than the required driving force. In the example in Figure 15, the left and right front wheels 91 and 92 are low-friction (Lo-μ) tires with relatively low rolling resistance, while the left and right rear wheels 93 and 94 are high-friction (Hi-μ) ​​tires with relatively high rolling resistance.

[0068] Therefore, the drive force calculation unit 53 changes the drive tire selected from the driveable tires, The calculated power consumption value is compared with the actual detected value. However, assuming that the drive tires are changed, the target tire angle calculation unit 54 adjusts the target tire angle, or the drive force calculation unit 53 adjusts the drive force instruction value of the drive motors 851-854, so that the vehicle behavior such as vehicle speed and turning radius does not change. Specifically, adjusting "so that the vehicle behavior does not change" is achieved by adjusting "so that the change in vehicle behavior falls within a predetermined range."

[0069] The driving force calculation unit 53 corrects the calculated power consumption value to approximate the actual power consumption Wsns detected by the power consumption sensor 68. For example, the power consumption value calculated by equation (1) is multiplied by a correction coefficient corresponding to the rolling resistance of the driveable tires. The driving force calculation unit 53 receives feedback from the power consumption sensor 68 and calculates and stores the correction coefficients for each drive motor 851-854. Furthermore, by repeatedly changing the drive tires in sequence and selecting the drive tire with the smaller actual power consumption Wsns before and after the change, the drive tire that minimizes the actual power consumption Wsns is searched for. This makes it possible to improve energy efficiency while reflecting the difference in rolling resistance of each driveable tire.

[0070] (Sixth embodiment) Referring to Figure 16, a sixth embodiment of control by the vehicle control device 50 will be described. For example, if the same turning route is repeated every day, load may accumulate on specific tires, potentially leading to uneven wear. In the sixth embodiment, the driving tire is selected based on the cumulative value of the tire load, which is proportional to the product of the driving force and the rotational speed, thereby equalizing the tire load. Here, the cumulative value of the tire load is defined as the "total load".

[0071] As shown in Figure 16, in a right turn of the four-wheel independently steered vehicle 100, the turning center C is set on the centerline between the right front wheel 92 and the right rear wheel 94 in the longitudinal direction of the vehicle, and the distance L2 from the turning center C to the right front wheel 92 is equal to the distance L4 to the right rear wheel 94. For the purpose of calculating power consumption, either the right front wheel 92 or the right rear wheel 94 may be selected as the drive tire. Thus, we assume a case where there are two or more driveable tires that can be selected as drive tires.

[0072] In this case, comparing the total load of each tire, the total load ΣLd4 of the right rear wheel 94 is smaller than the total load ΣLd2 of the right front wheel 92. Therefore, the driving force calculation unit 53 selects the right rear wheel 94, which has the smallest total load, as the driving tire for single-wheel drive. Alternatively, when driving with two wheels, the driving force calculation unit 53 preferentially distributes the driving force to the right rear wheel 94 rather than the right front wheel 92. This equalizes the total load of each driving tire, extending their lifespan.

[0073] The flowcharts in Figures 17 and 18 show the processing performed by the vehicle control device 50. The sub-flowchart in Figure 18 is linked to the main flowchart in Figure 17 via linking marks B1 and B2. In the flowchart explanation, the symbol "S" means step. S2 corresponds to the first embodiment, and S3 and S4 correspond to the second embodiment. The part (ΔτR-L≦ΔτR-L_lim) written in parentheses in S5 corresponds to the third embodiment. Also, S6, S7, and S8 correspond to the fifth embodiment, and S10 corresponds to the fourth embodiment. The sixth embodiment is omitted from the flowchart. The steps corresponding to each embodiment may be selectively performed in part, and do not necessarily have to be performed in whole.

[0074] In S1, the driving instruction unit 51 instructs the target driving force and target turning center of the vehicle based on the target direction of movement. After S1, the process branches into the steps following S2 concerning the driving force of the drive motors 851-854 and the steps following B1 concerning the target tire angle of the steering mechanism 70. If the first and second embodiments are omitted regarding the driving force, the process proceeds to S5.

[0075] In the first embodiment, in S2, the drive force calculation unit 53 selects a drive tire from among the driveable tires such that, with each tire 91-94 steered to the target tire angle, the turning direction of the vehicle due to the driving force of the corresponding drive motor is the same as the target movement direction.

[0076] In the second embodiment, in S3, it is determined whether the closest proximity distance d_c-nt between the target turning center C and the nearest driveable tire NT is greater than the proximity threshold d_c-nt_th. If YES, the process proceeds to S5. If the closest proximity distance d_c-nt is less than or equal to the proximity threshold d_c-nt_th, in S4 the driving force calculation unit 53 selects a driveable tire from among the driveable tires other than the nearest driveable tire NT.

[0077] In S5, the drive force calculation unit 53 selects a combination of drive tires and the corresponding drive force instruction value for the drive motor such that the sum of power consumption Wsum, calculated from the drive force, rotational speed, and efficiency of each drive motor 851-854, is minimized. In this third embodiment, the drive force calculation unit 53 instructs the drive force instruction value such that the difference in drive force ΔτR-L between the left and right drive motors is less than or equal to the allowable value ΔτR-L_lim.

[0078] In the fifth embodiment, in S6, the target tire angle or driving force instruction value is adjusted so as not to change the vehicle behavior, and the driving tire is changed. In S7, it is determined whether the actual power consumption Wsns detected by the power consumption sensor 68 differs from the calculated power consumption value Wcalc. Specifically, it is determined whether the difference between the detected power consumption value Wsns and the calculated value Wcalc is greater than or equal to a predetermined value. If the answer in S7 is YES, in S8 the driving force calculation unit 53 corrects the calculated value Wcalc to bring it closer to the detected power consumption value Wsns.

[0079] Meanwhile, regarding the tire angles of the steering mechanism 70, in S9 following S1, the target tire angle calculation unit 54 calculates the target tire angles δ1-δ4 for each tire and instructs the steering mechanism 70.

[0080] In the fourth embodiment, in S10, the actual yaw rate γsns obtained from the turning information detection device 67 is feedback controlled to the target yaw rate γtar, and the target tire angle or the driving force instruction value of the drive motor is corrected.

[0081] (Other embodiments) (a) The vehicle on which the vehicle control device 50 is installed is not limited to a four-wheeled vehicle, but can be any vehicle with three or more tires. Furthermore, it is sufficient that two or more of the three or more tires are driveable tires that can be driven independently of each other. For example, as shown in the upper part of Figure 19, it may be a three-wheeled vehicle 103 having one front wheel 91s made of a non-driveable tire and two rear wheels 93, 94 made of driveable tires. Non-driveable tires are excluded from the selection of "driveable tires that can be driven". The vehicle control device 50 performs control of the above embodiment targeting only two or more driveable tires.

[0082] Furthermore, it is sufficient for at least one tire to be steerable. For example, in a three-wheeled vehicle 103, only the front wheel 91s may be steerable.

[0083] (b) As shown in the lower part of Figure 19, the front wheels 91 and 92 of the four-wheeled vehicle 104 may be driven by a common power source 86, and only the rear wheels 93 and 94 may be driven independently of each other. In this configuration as well, the drive force calculation unit 53 selects one or both of the rear wheels 93 and 94 as drive tires so as to minimize the total power consumption of each drive motor.

[0084] (c) As described above, the "drive motors 851-854" such as in-wheel motors actually function as "braking drive motors," and the drive force calculation unit 53 may function as a "braking drive force calculation unit" and instruct each motor control device 801-804 to provide a "braking drive force instruction value." In addition to controlling the drive force in this embodiment, the vehicle control device 50 can also control the braking force within a range that does not contradict each other.

[0085] The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit.

[0086] (Disclosure of technical ideas) This specification discloses several technical concepts, as listed in the following paragraphs. Some paragraphs are written in a multiple dependent form, where subsequent paragraphs optionally refer to preceding paragraphs. Furthermore, some paragraphs are written in a multiple dependent form, referring to other multiple dependent forms. These paragraphs written in multiple dependent forms define several technical concepts.

[0087] (Technical thought 1) Three or more tires (91-94) including two or more driveable tires that can be driven independently of each other, Multiple drive motors (851-854) capable of driving each of the aforementioned driveable tires, A plurality of motor control devices (801-804) that control the operation of each of the aforementioned drive motors, A plurality of wheel speed sensors (691-694) that detect the wheel speed of each tire which is correlated with the rotational speed of each of the drive motors, A steering mechanism (70) capable of steering one or more of the aforementioned tires, It is installed in vehicles equipped with (100, 103, 104), A driving instruction unit (51) that indicates the target direction of movement of the vehicle and, based on the said target direction of movement, indicates the target driving force and target turning center of the vehicle, A tire position storage unit (52) that stores the position of each of the aforementioned driveable tires, A driving force calculation unit (53) distributes the target driving force for the entire vehicle instructed by the driving instruction unit to calculate the driving force instruction value for each of the drive motors and instructs each of the motor control devices, A target tire angle calculation unit (54) calculates the target tire angle of each steerable tire based on the target turning center instructed by the aforementioned driving instruction unit and instructs the steering mechanism accordingly. It has an efficiency characteristic storage unit (55) that stores the efficiency of the drive motor according to the driving force and rotational speed of the drive motor, When there are multiple driving patterns in which one or more of the driveable tires are driven by one or more drive force instruction values ​​of the corresponding drive motors with respect to a target driving force for the entire vehicle, the driving force calculation unit selects a combination of the driveable tires to be driven and the corresponding drive force instruction value of the drive motor such that the sum of the power consumption calculated from the driving force, rotational speed, and efficiency of each drive motor is minimized. (Technical thought 2) The vehicle control device according to Technical Concept 1, wherein the driving force calculation unit selects a driveable tire to be driven from among the driveable tires whose turning direction due to the driving force of the corresponding drive motor is the same as the target movement direction, when each driveable tire is steered to a target tire angle. (Technical Thought 3) If the distance between the target turning center and the position of the nearest driveable tire, which is the driveable tire closest to the target turning center, is less than or equal to the proximity threshold, The vehicle control device according to technical concept 1 or 2, wherein the driving force calculation unit selects the driveable tire to be driven from among the driveable tires other than the nearest driveable tire. (Technical Thought 4) The vehicle control device according to any one of the technical concepts 1 to 3, wherein the driving force calculation unit calculates the driving force instruction value of the corresponding drive motor so that the difference in driving force applied to the left and right pair of driveable tires is less than or equal to an allowable value. (Technical Thought 5) A vehicle control device according to any one of the technical concepts 1 to 4, wherein the target tire angle calculation unit corrects the target tire angle or the driving force calculation unit corrects the driving force instruction value of the drive motor by feedback control that brings the actual yaw rate acquired from the turning information detection device (67) closer to the target yaw rate, or brings the acquired actual turning radius closer to the target turning radius. (Technical Thought 6) It is mounted on a vehicle equipped with a power consumption sensor (68) that detects the actual power consumption of the drive motor, The target tire angle calculation unit adjusts the target tire angle, or the driving force calculation unit adjusts the driving force instruction value of the drive motor, while changing the driveable tire being driven, so that the change in vehicle behavior falls within a predetermined range. The vehicle control device according to any one of the technical concepts 1 to 5, wherein the driving force calculation unit corrects the calculated value of power consumption so that it approaches the actual power consumption detected by the power consumption sensor. (Technical Thought 7) If we define the total load as the cumulative value of the tire load, which is proportional to the product of the driving force and the rotational speed for each of the aforementioned driveable tires, A vehicle control device according to any one of the technical concepts 1 to 6, wherein when there are two or more driveable tires that can be selected as the driveable tires to be driven, the driving force calculation unit selects the driveable tire with the smallest total load as the driveable tire to be driven, or preferentially distributes the driving force to the driveable tire with the smallest total load.

[0088] Each control unit (driving instruction unit, tire position memory unit, driving force calculation unit, target tire angle calculation unit, efficiency characteristic memory unit) 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]

[0089] 50...Vehicle control device, 51... Driving instruction unit, 52... Tire position memory unit, 53...Driving force calculation unit, 54...Target tire angle calculation unit, 55. Efficiency characteristic storage means section, 691-694...Wheel speed sensor, 70... Steering mechanism, 801-804...Motor drive unit, 851-854... Drive motor, 91-94 (driveable) tires, Vehicles numbered 100 (100A, 100B, 100C), 103, 104, etc.

Claims

1. Three or more tires (91-94) including two or more driveable tires that can be driven independently of each other, A plurality of drive motors (851-854) capable of driving each of the aforementioned driveable tires, A plurality of motor control devices (801-804) that control the operation of each of the drive motors, A plurality of wheel speed sensors (691-694) that detect the wheel speed of each tire which is correlated with the rotational speed of each of the drive motors, A steering mechanism (70) capable of steering one or more of the aforementioned tires, It is mounted on vehicles (100, 103, 104) equipped with the following: A driving instruction unit (51) that indicates the target direction of movement of the vehicle and, based on the said target direction of movement, indicates the target driving force and target turning center of the vehicle, A tire position storage unit (52) that stores the position of each of the aforementioned driveable tires, A driving force calculation unit (53) distributes the target driving force for the entire vehicle instructed by the driving instruction unit to calculate the driving force instruction value for each of the drive motors and instructs each of the motor control devices, A target tire angle calculation unit (54) calculates the target tire angle of each steerable tire based on the target turning center instructed by the aforementioned driving instruction unit and instructs the steering mechanism accordingly. It has an efficiency characteristic storage unit (55) that stores the efficiency of the drive motor according to the driving force and rotational speed of the drive motor, When there are multiple driving patterns in which one or more of the driveable tires are driven by one or more drive force instruction values ​​of the corresponding drive motors with respect to a target driving force for the entire vehicle, the driving force calculation unit selects a combination of the driveable tires to be driven and the corresponding drive force instruction value of the drive motor such that the sum of the power consumption calculated from the driving force, rotational speed, and efficiency of each drive motor is minimized.

2. The vehicle control device according to claim 1, wherein the driving force calculation unit selects a driveable tire to be driven from among the driveable tires whose turning direction due to the driving force of the corresponding drive motor is the same as the target movement direction, with each driveable tire steered to a target tire angle.

3. If the distance between the target turning center and the position of the nearest driveable tire, which is the driveable tire closest to the target turning center, is less than or equal to the proximity threshold, The vehicle control device according to claim 1, wherein the driving force calculation unit selects a driveable tire to be driven from among the driveable tires other than the nearest driveable tire.

4. The vehicle control device according to claim 1, wherein the driving force calculation unit calculates the corresponding driving force instruction value of the drive motor so that the difference in driving force applied to the left and right pair of driveable tires is less than or equal to an allowable value.

5. The vehicle control device according to claim 1, wherein the target tire angle calculation unit corrects the target tire angle or the driving force calculation unit corrects the driving force instruction value of the drive motor by feedback control that brings the actual yaw rate acquired from the turning information detection device (67) closer to the target yaw rate, or brings the acquired actual turning radius closer to the target turning radius.

6. It is mounted on a vehicle equipped with a power consumption sensor (68) that detects the actual power consumption of the drive motor, The target tire angle calculation unit adjusts the target tire angle, or the driving force calculation unit adjusts the driving force instruction value of the drive motor, while changing the driveable tire being driven, so that the change in vehicle behavior falls within a predetermined range. The vehicle control device according to claim 1, wherein the driving force calculation unit corrects the calculated power consumption value so that it approaches the actual power consumption detected by the power consumption sensor.

7. If we define the total load as the cumulative value of the tire load, which is proportional to the product of the driving force and the rotational speed for each of the aforementioned driveable tires, The vehicle control device according to claim 1, wherein, when there are two or more driveable tires that can be selected as the driveable tires to be driven, the driving force calculation unit selects the driveable tire with the smallest total load as the driveable tire to be driven, or preferentially distributes the driving force to the driveable tire with the smallest total load.

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