Braking / driving force control device

Abstract

In a vehicle in which all tires (91-94) can be steered and each tire (91–94) can be independently braked and driven, a braking / driving force control device controls braking / driving forces (F1-F4) outputted by braking / driving actuators (81-84). A steering state determination unit (26) determines whether the tires (91-94) are in the same phase state. A braking / driving force instruction unit (28) calculates braking / driving force instruction values (F*1-F*4) and instructs the braking / driving actuators (81-84). When it is determined by the steering state determination unit (26) that the tires (91-94) are in the same phase state, and either it is assessed that yaw motion of the vehicle is occurring on the basis of information acquired from a yaw motion detection device (30) or it is predicted that yaw motion of the vehicle will occur, the braking / driving force instruction unit (28) corrects the braking / driving force instruction values (F*1-F*4) instructed to at least one of the braking / driving actuators.

Description

Braking / driving force control device CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on Japanese Application No. 2023-096235, filed on June 12, 2023, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a braking / driving force control device.

[0003] Conventionally, there are known technologies for suppressing the yaw motion of a vehicle other than when turning. For example, a vehicle control device disclosed in Patent Document 1 controls the rear wheel steering angle of a four-wheel steering vehicle in accordance with the steering angle of the front wheels, and when the front and rear wheels are steered in the same phase, the rear wheels are controlled to assume a rear wheel target steering angle determined in accordance with the steering angle of the front wheels.

[0004] JP 2010-285036 A

[0005] The technology of Patent Document 1 modifies the steering angle of the wheels to suppress the yaw rate, which increases running resistance. Patent Document 1 also makes no mention of controlling the braking / driving force of each wheel of a vehicle. Note that, from a technical perspective, the term "vehicle" in this specification includes all mobile objects capable of running on the ground using wheels, regardless of legal classifications regarding running on public roads. For example, green slow mobility and AGVs (automated guided vehicles) are also included in the term "vehicle."

[0006] An object of the present disclosure is to provide a braking / driving force control device that suppresses unintended yaw motion during in-phase steering.

[0007] A vehicle to which the braking / driving force control device of the present disclosure is applied has three or more wheels that can all be steered, and each wheel can be independently braked and driven by the braking / driving forces output by the braking / driving actuators corresponding to the wheels. The vehicle is also equipped with a yaw motion detection device that detects yaw motion. The braking / driving force control device controls the braking / driving forces output by the braking / driving actuators.

[0008] The braking / driving force control device includes a target tire angle calculation control unit, a steering state determination unit, and a braking / driving force instruction unit. The target tire angle calculation control unit calculates a target tire angle for each tire based on the movement direction instruction value and instructs the steering actuator.

[0009] The steering state determination unit determines whether the tires are in phase with each other based on the target tire angles of each tire specified by the target tire angle calculation control unit or the detected tire angles of each tire obtained from the tire angle sensors. The braking / driving force command unit calculates braking / driving force command values ​​that are command values ​​for the braking / driving forces to be output by the braking / driving actuators and commands the braking / driving actuators.

[0010] When the steering state determination unit determines that the tires are in the same phase as each other and determines that yaw motion of the vehicle is occurring based on information obtained from the yaw motion detection device, or predicts that yaw motion of the vehicle will occur, the braking / driving force instruction unit corrects the braking / driving force instruction value to be instructed to at least one braking / driving actuator.

[0011] The braking / driving force control device of the present disclosure can suppress unintended yaw motion during in-phase steering by adjusting the balance of braking / driving forces of each tire in a vehicle in which each tire can be braked and driven independently.

[0012] The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is a block diagram of a four-wheel independently steering vehicle equipped with a braking / driving force control device according to this embodiment, Fig. 2 is a block diagram of a four-wheel steering vehicle equipped with a braking / driving force control device according to this embodiment, Fig. 3 is a diagram illustrating a four-wheel independently steering vehicle and diagonal movement due to in-phase steering in the four-wheel steering vehicle (absolute value of tire angle less than 90 degrees), Fig. 4 is a diagram illustrating lateral movement and tight turns of the four-wheel independently steering vehicle, Fig. 5 is a block diagram of the braking / driving force control device according to the first embodiment, Fig. 6 is a diagram illustrating the four-wheel geometric centers of a four-wheel vehicle, Fig. 7 is a diagram illustrating the balance of yaw moment when the center of gravity is aligned with the four-wheel geometric centers during diagonal movement, and Fig. 8 is a diagram illustrating the occurrence of yaw motion and yaw moment when the center of gravity is displaced from the four-wheel geometric centers during diagonal movement. FIG. 11 is a flowchart showing braking / driving force distribution for suppressing yaw movement, FIG. 9 is a flowchart showing braking force control processing according to the first embodiment, FIG. 10 is a block diagram of a braking / driving force control device of the second embodiment, FIG. 11 is a flowchart showing braking force control processing according to the second embodiment, FIG. 12 is a block diagram of a braking / driving force control device of the third embodiment, FIG. 13 is a diagram showing braking / driving force distribution when all tires are not in a slip state during diagonal movement, FIG. 14 is a diagram showing the occurrence of yaw movement when slip suppression processing is performed during diagonal movement, and braking / driving force distribution for suppressing yaw movement, FIG. 15 is a flowchart showing braking force control processing according to the third embodiment, and FIG. 16 is a block diagram of a braking / driving force control device of the fourth embodiment.

[0013] Several embodiments of the braking / driving force control device will be described with reference to the drawings. Substantially identical components in the several embodiments are assigned the same reference numerals, and description thereof will be omitted. The following first to fourth embodiments will be collectively referred to as "the present embodiment." The braking / driving force control device of the present embodiment is mounted on a vehicle in which all three or more wheels can be steered, typically a four-wheel independently steered vehicle, or a four-wheel steered vehicle in which the front left and right wheels and the rear left and right wheels are connected. Furthermore, all three or more tires can be independently braked and driven by braking / driving forces output by braking / driving actuators corresponding to each tire. The braking / driving force control device controls the braking / driving forces output by the braking / driving actuators.

[0014] The configurations of a four-wheel independently steering vehicle 100 and a four-wheel steering vehicle 105 equipped with the braking / driving force control device 20 of this embodiment will be described with reference to Figures 1 and 2. The four-wheel independently steering vehicle 100 shown in Figure 1 and the four-wheel steering vehicle 105 shown in Figure 2 each have four tires 91-94. 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 suffixes "1" to "4" in each symbol correspond to the FL, FR, RL, and RR tires 91-94, respectively.

[0015] The vehicles 100, 105 are equipped with braking / driving actuators 81-84 corresponding to each of the tires 91-94. In the drawings, "actuator" is denoted as "Act." For example, the braking / driving actuators 81-84 are configured as a set of an electric brake as a braking actuator and an in-wheel motor as a driving actuator. Each of the tires 91-94 can be independently braked / driven by the braking / driving forces F1-F4 output by the braking / driving actuators 81-84. When driven by the driving actuators, the driving force of each tire 91-94 is transmitted to the road surface, generating positive acceleration, and the vehicles 100, 105 accelerate. When braking by the braking actuators, the braking force of each tire 91-94 is transmitted to the road surface, generating negative acceleration, and the vehicles 100, 105 decelerate.

[0016] A movement direction instruction value is input to the braking / driving force control device 20 from the movement direction instruction device 15. The movement direction instruction value includes operation signals from the driver for the steering wheel, accelerator, brake, etc., as well as signals from the automatic driving control device, and includes information on not only the movement direction but also the movement speed. Based on the movement direction instruction value, the braking / driving force control device 20 calculates a braking / driving force instruction value F , which is an instruction value for the braking / driving force to be output by the braking / driving actuators 81-84. * 1-F * 4 and instructs the braking / driving actuators 81-84.

[0017] In all of the first to fourth embodiments, the vehicles 100, 105 are equipped with a yaw motion detection device 30. The yaw motion detection device 30 detects yaw motion of the vehicles 100, 105, such as yaw rate, yaw angular acceleration, and yaw angle. In all embodiments except the second, the vehicles 100, 105 are equipped with a center-of-gravity position detection device 40. The center-of-gravity position detection device 40 calculates the center-of-gravity position of the vehicles 100, 105 from the difference in moment in the fore-and-aft direction (pitch direction) of the vehicle, based on, for example, wheel load information of each tire 91-94. In the third embodiment, the vehicles 100, 105 are further equipped with a slip ratio detection device 50, indicated by a dashed line frame. The slip ratio detection device 50 detects the slip ratio of each tire 91-94 using, for example, wheel speed information from wheel speed sensors.

[0018] The braking / driving force control device 20 determines the braking / driving force command value F according to the situation based on the information acquired from the detection devices 30, 40, 50 of the vehicles 100, 105. * 1-F * 4 is corrected based on the information that the braking / driving force control device 20 acquires from the respective detection devices 30, 40, 50 and the braking / driving force command value F * 1-F * The correction of 4 will be described in detail later.

[0019] In the four-wheel independently steering vehicle 100 shown in Figure 1, all of the tires 91-94 can be steered independently. The vehicle 100 is equipped with steering actuators 71-74 corresponding to the tires 91-94, and tire angle sensors 671-674 that detect the actual tire angles (hereinafter referred to as "actual tire angles"). The tire angle is expressed as 0 at a neutral position parallel to the vehicle's longitudinal axis, with a counterclockwise direction being positive and a clockwise direction from the neutral position being negative.

[0020] For example, steering actuators 71-74 are configured integrally with a motor section such as a three-phase brushless motor including a stator and rotor wound with windings, and a motor drive device that controls the drive current passed through the windings. Tires 91-94 can be steered independently by the steering torques Tst1-Tst4 output by steering actuators 71-74.

[0021] Tire angle sensors 671-674 may be configured with encoders or the like that directly detect actual tire angles. Alternatively, if there is a correlation between the drive current of steering actuators 71-74 and the tire angles, the drive current of steering actuators 71-74 detected by a current sensor may be converted into detected tire angles δs1-δs4 based on the current-torque characteristics or torque transmission coefficient. In this case, the current sensors are considered to function as tire angle sensors 671-674.

[0022] The braking / driving force control device 20 determines the target tire angle δ of each tire 91-94 based on the movement direction instruction value input from the movement direction instruction device 15. * 1-δ * Braking / driving force control device 20 also acquires detected tire angles δs1-δs4 of tires 91-94 detected by tire angle sensors 671-674.

[0023] In a four-wheel steering vehicle 105 shown in Figure 2, left and right front wheels 91, 92 and left and right rear wheels 93, 94 are mechanically connected by rack shafts 95, 96, respectively. Each tire 91-94 is connected to both ends of the rack shafts 95, 96 via a link mechanism such as a tie rod. This type of vehicle corresponds to a so-called "4WS" vehicle. For each rack shaft 95, 96, steering actuators 75, 76 and tire angle sensors 675, 676 are provided, which convert the stroke of the rack shafts 95, 96 to detect the tire angle.

[0024] The target tire angle for the front row is δ * The steering torque output from steering actuator 75 in response to steering torque signal δs12 is transmitted to rack shaft 95, which drives rack shaft 95 left and right, thereby steering front left and right wheels 91, 92 in conjunction with each other. Tire angle sensor 675 detects detected tire angle δs12 of front left and right wheels 91, 92, and notifies braking / driving force control device 20 of the detected tire angle δs12.

[0025] In the rear row, the target tire angle is δ * The steering torque output by steering actuator 76 in response to steering angle δs34 is transmitted to rack shaft 96, which drives rack shaft 96 left and right, thereby steering rear row left and right wheels 93, 94 in conjunction with each other. Tire angle sensor 676 detects detected tire angle δs34 of rear row left and right wheels 93, 94, and notifies braking / driving force control device 20.

[0026] In addition to the vehicles 100 and 105 shown in Figures 1 and 2, the braking / driving force control device 20 may also be installed in a partially independently steering vehicle in which the left front wheel 91 and the right front wheel 92 can be steered independently and the rear left and right wheels 93 and 94 are mechanically connected, or conversely, in a partially independently steering vehicle in which the left rear wheel 93 and the right rear wheel 94 can be steered independently and the front left and right wheels 91 and 92 are mechanically connected.

[0027] 3 and 4, a description will be given of driving that is unique to four-wheel independently steering vehicle 100 and four-wheel steering vehicle 105. In the vehicle diagrams below, the symbol Cg indicates the center of gravity. Conventionally, in a typical vehicle, a pair of left and right tires are mechanically connected via a link, and only the front left and right wheels are steered by steering the steering wheel. In the future, developments are expected to include steer-by-wire systems in which the steering wheel and the link between the left and right wheels are mechanically separated, four-wheel steering vehicle 105 in which the rear left and right wheels can be steered in addition to the front left and right wheels, and further four-wheel independently steering vehicle 100 in which all wheels can be steered independently.

[0028] As shown in FIG. 3 , four-wheel independently steering vehicle 100 and four-wheel steering vehicle 105 are able to move diagonally by steering all of the wheels in the same phase. The angle of the vehicle's traveling direction relative to the front-to-rear axis during diagonal movement is referred to as the diagonal movement angle θ. For example, when changing lanes while traveling straight, steering all four wheels in the same phase to move diagonally makes it possible to change lanes with zero yaw rate while suppressing travel loss due to tire drag. Steering all four wheels in the same phase is achieved by performing feedback control so that the actual tire angles δ1-δ4 of each tire 91-94 are equal, based on the current detected tire angles δs1-δs4 of each tire 91-94.

[0029] Except for those equipped with special link mechanisms, in a typical four-wheel steering vehicle 105, the absolute value of the maximum tire angle is less than 90 degrees, and the absolute value of the diagonal movement angle θ is also less than 90 degrees. In contrast, as shown in the upper part of Figure 4, the four-wheel independently steering vehicle 100 can achieve a maximum tire angle of 90 degrees or more in absolute value, allowing lateral movement by in-phase steering of ±90 degrees. Furthermore, as shown in the lower part of Figure 4, the four-wheel independently steering vehicle 100 can make tight turns by significantly changing the tire angles of the wheels on the inside and outside of the turn about the turning center Ct.

[0030] Below, the first to fourth embodiments will be described in order, focusing mainly on the oblique movement achieved by in-phase steering where the absolute value of the tire angle is less than 90 degrees. The reference numerals for the braking / driving force control devices of each embodiment are designated by the third digit following "20", which indicates the embodiment. In the following description, the vehicle reference numerals "100, 105" will be omitted, and only the reference numeral "100" will be used for the four-wheel independently steering vehicle as a representative. Furthermore, in the description of the steering actuators, the reference numerals for the steering actuators 71-74 etc. in the four-wheel independently steering vehicle 100 and the target tire angle δ * 1-δ * 4, etc. This description is "the steering actuators 75, 76 in the four-wheel steering vehicle 105, the target tire angle δ * 12. δ * 34, etc." may be read as such.

[0031] First Embodiment A first embodiment will be described with reference to Figures 5 and 6. As shown in Figure 5, a braking / driving force control device 201 of the first embodiment has a target tire angle calculation control unit 25, a turning state determination unit 26, and a braking / driving force instruction unit 28.

[0032] The target tire angle calculation control unit 25 calculates the target tire angle δ of each tire 91-94 based on the movement direction instruction value input from the movement direction instruction device 15. * 1-δ * For example, when a lane change is instructed at a diagonal movement angle θ while the vehicle is traveling straight ahead, the target tire angle calculation control unit 25 calculates the diagonal movement angle θ and issues a command to the steering actuators 71-74. * 1-δ * It is designated as 4.

[0033] The steering state determination unit 26 determines whether the tires 91-94 are in phase with each other based on the detected tire angles δs1-δs4 of each tire obtained from the tire angle sensors 671-674, and notifies the braking / driving force instruction unit 28. For example, when the range from the minimum value to the maximum value of the detected tire angles δs1-δs4 is equal to or less than the determination threshold, the tires 91-94 are determined to be in phase with each other. By making a determination based on the detected tire angles δs1-δs4, it is possible to perform control that reflects the actual vehicle behavior.

[0034] The braking / driving force instruction unit 28 calculates a braking / driving force instruction value F , which is an instruction value for the braking / driving force to be output by the braking / driving actuators 81-84, based on the movement direction instruction value. * 1-F * 4 and instructs the braking / driving actuators 81-84.

[0035] Braking / driving force instruction unit 28 receives a notification of the in-phase determination from steering state determination unit 26. Braking / driving force instruction unit 28 also acquires yaw motion parameters such as yaw rate, yaw angular acceleration, and yaw angle from yaw motion detection device 30. Based on the information acquired from yaw motion detection device 30, braking / driving force instruction unit 28 determines whether yaw motion of vehicle 100 is occurring.

[0036] When the steering state determination unit 26 determines that the tires 91-94 are in the same phase with each other and determines that yaw motion of the vehicle 100 is occurring based on information acquired from the yaw motion detection device 30, the braking / driving force instruction unit 28 outputs a braking / driving force instruction value F * 1-F * Correct 4.

[0037] 6 to 8, the mechanism by which yaw motion occurs during diagonal movement and the braking / driving force command value F * 1-F * The significance of correcting 4 will now be explained. First, refer to Figure 6. The front-to-rear axis of the vehicle is the X axis (front is positive), the left-to-right axis is the Y axis (right is positive), the wheelbase is denoted as Lx, and the tread width is denoted as Ly. The wheelbase Lx corresponds to the distance between the front wheel axis yf connecting the centers of the front left and right wheels 91, 92 and the rear wheel axis yr connecting the centers of the rear left and right wheels 93, 94.

[0038] The point that is the center of the wheelbase Lx in the vehicle longitudinal direction and the center of the tread width Ly in the vehicle lateral direction is defined as the four-wheel geometric center Cm. The distance from the four-wheel geometric center Cm to the center of each tire in the vehicle longitudinal direction is expressed as (Lx / 2), and the distance in the vehicle lateral direction is expressed as (Ly / 2). The diagonal movement angle θ is defined as positive, for example, in the counterclockwise direction, with the X axis being 0.

[0039] 7 shows a state in which the center of gravity Cg coincides with the four-wheel geometric center Cm during diagonal movement. A straight line passing through the center of gravity Cg and extending in the direction of the diagonal movement angle θ is represented as the traveling direction center of gravity line p. The lengths of perpendicular lines drawn from the centers of the tires 91-94 to the traveling direction center of gravity line p are defined as the acting distances L1-L4. For example, in diagonal movement to the right (θ<0), if the intersection of the front wheel axis yf and the traveling direction center of gravity line p is P, the center of the left front wheel 91 is Q, and the length of the line PQ is Lo1, then acting distance L1 can be calculated using equation (1.1).

[0040] L1=Lo1・cosθ={(Ly / 2)−(Lx / 2)tanθ}cosθ...(1.1)

[0041] Similarly, the action distance L2 is calculated by the formula (1.2).

[0042] L2={(Ly / 2)+(Lx / 2)tanθ}cosθ...(1.2)

[0043] The acting distance L1 is equal to the acting distance L4, and the acting distance L2 is equal to the acting distance L3 (L1 = L4, L2 = L3). The same magnitude of braking / driving force F is distributed to each wheel 91-94, and the yaw moments on the left and right sides of the traveling center of gravity line p are balanced, as shown in equation (1.3).

[0044] (L1+L3)F=(L2+L4)F...(1.3)

[0045] In this way, if the center of gravity Cg of the vehicle 100 coincides with the four-wheel geometric center Cm, the braking / driving force F is distributed equally to each tire 91-94 during diagonal movement, and when acceleration or deceleration occurs in the vehicle 100, the yaw moment is balanced and no yaw motion occurs in the vehicle 100. Therefore, diagonal movement with a yaw rate of zero is possible.

[0046] However, when the loading status of occupants, luggage, etc. changes, the center of gravity Cg of the vehicle 100 may shift from the four-wheel geometric center Cm, as shown in FIG. 8. In the example shown at the top of FIG. 8, the position of the center of gravity Cg is shifted forward from the four-wheel geometric center Cm. Hereinafter, "center of gravity position shift" refers to the shift of the center of gravity Cg from the four-wheel geometric center Cm. The amount of shift in the center of gravity position is represented as "ΔGx," and the acting distance in a state where the center of gravity position shifts is represented as Lg1-Lg4. Because the traveling direction center of gravity line p shifts forward, the acting distance Lg1 is not equal to the acting distance Lg4, and the acting distance Lg2 is not equal to the acting distance Lg3. In this example, "Lg1<Lg4, Lg2>Lg3."

[0047] As a result, in a situation where the same magnitude of braking / driving force F is distributed to each wheel 91-94, the balance of the yaw moment is lost during acceleration / deceleration, as shown in equation (1.4), and a yaw rate γ is generated. In this example, the yaw moment due to the braking / driving force F of the right front wheel 92 and the right rear wheel 94 exceeds the yaw moment due to the braking / driving force F of the left front wheel 91 and the left rear wheel 93, so a yaw rate γ is generated that turns the vehicle 100 left, destabilizing the vehicle behavior.

[0048] (Lg1+Lg3)F<(Lg2+Lg4)F...(1.4)

[0049] Therefore, the braking / driving force command unit 28 of the braking / driving force control device 201 calculates the initially calculated braking / driving force command value F based on the deviation amount ΔGx of the center of gravity position obtained from the center of gravity position detection device 40. * 1-F * When the command value F4 is issued, it is predicted that yaw motion will occur in the vehicle 100. The braking / driving force command unit 28 then sets the braking / driving force command value F4 to the braking / driving actuators 81-84 so as to suppress the yaw rate that occurs due to the shift in the center of gravity position. * 1-F * For this correction, braking / driving force instructor 28 uses the deviation amount ΔGx of the center of gravity position, and also estimates the oblique movement angle θ from the detected tire angles δs1-δs4 acquired by steering state determiner 26.

[0050] The center-of-gravity position detection device 40 acquires the wheel loads Fz1-Fz4 of each tire 91-94, for example, from a load sensor, and calculates the amount of deviation ΔGx of the center-of-gravity position using equation (2). The part "Fz1 + Fz2 - Fz3 - Fz4" in the numerator of equation (2) represents the difference in wheel load between the front wheels 91, 92 and the rear wheels 93, 94, i.e., the difference in moment in the pitch direction. When the moment in the pitch direction is balanced, "ΔGx = 0," and there is no deviation in the center-of-gravity position. Furthermore, when "Fz1, Fz2 >> Fz3, Fz4," "ΔGx ≒ (Lx / 2)" holds, and the center of gravity Cg is asymptotically approaching the front wheel axle yf. "x" and "z" in the equation are subscripts.

[0051] "

[0052] Braking / driving force indicator 28 calculates acting distances Lg1-Lg4 for each tire 91-94 using the center of gravity position deviation ΔGx and the oblique movement angle θ according to equations (3.1) to (3.4), where "x" and "y" are subscripts.

[0053]

[0054] Next, braking / driving force instruction unit 28 calculates braking / driving forces Fg1-Fg4 for each tire 91-94 so that equation (4) holds. As shown in the bottom of Figure 8, when equation (4) holds, the yaw moment is balanced during acceleration / deceleration, and the generation of yaw rate is suppressed.

[0055] Lg1・Fg1+Lg3・Fg3=Lg2・Fg2+Lg4・Fg4...(4)

[0056] For example, when the longitudinal forces Fg1-Fg4 determined by equations (5.1) and (5.2) are substituted into both sides of equation (4), the following equation is established: where L is calculated by equation (5.3).

[0057]

[0058] L=Lg1+Lg2+Lg3+Lg4...(5.3)

[0059] The braking / driving forces Fg1-Fg4 calculated in this way are used as the corrected braking / driving force command values ​​F * 1-F* 4 is instructed from braking / driving force instructing unit 28 to each of braking / driving actuators 81-84. * 1 = Fg1, F * 2 = Fg2, F * 3 = Fg3, F * The braking / driving force command value Fg4 is set to Fg4. * 1-F * Therefore, the yaw rate caused by the deviation of the center of gravity position is suppressed before the yaw movement actually occurs.

[0060] The flowchart in Figure 9 shows the braking / driving force control process according to the first embodiment. In the following description of the flowchart, the symbol "S" denotes a step. Common step numbers are used for steps that are common to the second embodiment shown in Figure 11. Steps that correspond to but differ partially between the first and second embodiments are distinguished by adding the symbol "A / B" to the end of the step number. This process is repeatedly performed while the vehicle 100 is traveling, from when it starts traveling until it stops.

[0061] In S1A, the braking / driving force instruction unit 28 calculates the braking / driving force instruction values ​​F * 1-F * 4. In S2, the steering state determination unit 26 acquires the detected tire angles δs1-δs4 of the tires 91-94 from the tire angle sensors 671-674. In S3, it is determined whether the tires 91-94 are in phase with each other based on the detected tire angles δs1-δs4. If the answer is NO in S3, such as when turning, the process proceeds to before S10A. If the answer is YES in S3, the process proceeds to S4.

[0062] In S4, braking / driving force instruction unit 28 acquires the center of gravity position of vehicle 100 from center-of-gravity position detection device 40. In S5, it is determined whether the absolute value of center-of-gravity position deviation amount ΔGx is equal to or greater than a determination threshold. If NO in S5, the process proceeds to before S10A. If YES in S5, braking / driving force instruction unit 28 acquires pre-correction braking / driving force instruction value F * 1-F * If 4 is specified as is, it is predicted that yaw motion of the vehicle 100 will occur, and the process proceeds to S9A.

[0063] In S9A, braking / driving force instruction unit 28 calculates braking / driving force instruction values ​​F for each tire 91-94 using the center of gravity position deviation amount ΔGx acquired from center of gravity position detection device 40 in equations (3.1) to (3.4). * 1-F * In S10A, braking / driving force instruction unit 28 corrects braking / driving force instruction value F * 1-F * 4 is instructed to the braking / driving actuators 81-84. When the process proceeds from S9A, the corrected braking / driving force instruction value F * 1-F * If the result of step S3 or step S5 is NO, the braking / driving force command value F4 before correction is set. * 1-F * 4 is indicated.

[0064] When the braking / driving force instruction unit 28 of the first embodiment predicts that yaw motion of the vehicle 100 will occur based on the center-of-gravity position deviation amount ΔGx acquired from the center-of-gravity position detection device 40, the braking / driving force instruction value F * 1-F * 4 is corrected to cancel the yaw moment of the vehicle 100 caused by the displacement of the center of gravity. * 1-F * By correcting 4, unintended yaw movement can be suppressed during diagonal movement (in-phase steering).

[0065] Second Embodiment A second embodiment will be described with reference to Figures 10 and 11. A vehicle 100 equipped with a braking / driving force control device 202 according to the second embodiment does not need to include a center-of-gravity state detection device 40. Alternatively, even if the vehicle 100 includes a center-of-gravity position detection device 40, the braking / driving force control device 202 does not need to acquire center-of-gravity position information from the center-of-gravity position detection device 40 in cases where, for example, there is little change in the load status of occupants or luggage and the center-of-gravity position remains substantially constant.

[0066] 10, center of gravity position information is not input to braking / driving force control device 202. Instead, braking / driving force control device 202 stores an estimated value of the center of gravity position as a default value. * 1-F *When correcting ΔGx, braking / driving force indicator 28 uses an estimated value of center of gravity position deviation ΔGx stored internally.

[0067] 11, the braking / driving force control process according to the second embodiment will be described, particularly the differences from FIG. 9. In S1B, braking / driving force instruction unit 28 calculates braking / driving force instruction values ​​F * 1-F * 4 is calculated and issued to the braking / driving actuators 81-84. In other words, it differs from S1A in FIG. 9 in that it is calculated and then issued. S2 and S3 are the same as in FIG. 9. However, if NO in S3, the braking / driving force command value F * 1-F * Since 4 has already been designated, the routine ends after passing S10B. If YES in S3, the routine proceeds to S7.

[0068] In S7, the braking / driving force instruction unit 28 acquires yaw motion parameters such as yaw rate, yaw angular acceleration, and yaw angle from the yaw motion detection device 30. Here, the larger the absolute value of the yaw motion parameter, the more the vehicle 100 is yaw moving. In S8, it is determined whether the absolute value of the yaw motion parameter is equal to or greater than a determination threshold. If the answer is NO in S8, such as when the vehicle is traveling straight ahead, the routine ends. If the answer is YES in S8, it is determined that "yaw motion of the vehicle 100 is occurring," and the process proceeds to S9B.

[0069] In S9B, braking / driving force instruction unit 28 calculates braking / driving force instruction values ​​F for each tire 91-94 using the internally estimated center of gravity position deviation amount ΔGx in equations (3.1) to (3.4). * 1-F * In S10B, braking / driving force instruction unit 28 corrects the corrected braking / driving force instruction value F * 1-F * 4 is instructed to the braking / driving actuators 81-84.

[0070] Although the second embodiment differs from the first embodiment in that the yaw rate is suppressed after yaw motion actually occurs, unintended yaw motion can be suppressed during oblique movement (in-phase steering) as in the first embodiment. Furthermore, the second embodiment can be installed on a vehicle 100 that does not have a center-of-gravity state detection device 40, and therefore has a wider range of application than the first embodiment.

[0071] Third Embodiment A third embodiment will be described with reference to FIGS. 12 to 15. When the friction characteristics of each tire are similar, the braking / driving force that causes the tire's slip limit depends on the tire's wheel load. When the center of gravity Cg is offset from the four-wheel geometric center Cm, the wheel loads of each wheel are different, and therefore the slip limit is also different. Furthermore, correcting the braking / driving force of each tire using the first embodiment may result in a phenomenon in which only a specific tire slips.

[0072] As shown in Figure 12, the braking / driving force control device 203 of the third embodiment is mounted on a vehicle equipped with a slip ratio detection device 50 that detects the slip ratio of each tire. The slip ratio is the difference between the vehicle body speed and the wheel speed divided by the vehicle body speed. The slip ratio is 0% when the tires are rolling on the road surface without any slip, and 100% when the tires are completely locked. The slip ratio detection device 50 calculates the slip ratio of each tire using wheel speed information from wheel speed sensors on each wheel, for example.

[0073] The braking / driving force control device 203 of the third embodiment further includes a slip state determination unit 27 in addition to the configuration of the braking / driving force control device 201 of the first embodiment. The slip state determination unit 27 determines whether or not each tire is in a slip state based on the slip ratio obtained from the slip ratio detection device 50. That is, for each tire, the slip state determination unit 27 determines that the tire is not in a slip state when the slip ratio is less than a threshold value, and determines that the tire is in a slip state when the slip ratio is equal to or greater than the threshold value. The slip state determination unit 27 notifies the braking / driving force instruction unit 28 of the determination result.

[0074] One or more tires that are determined to be in a slipping state are defined as "slip tires," and one or more tires other than the slipping tires are defined as "non-slip tires." Since at least one non-slip tire is required, a four-wheel vehicle has three or fewer slipping tires. Generally speaking, an N-wheel vehicle has (N-1) or fewer slipping tires.

[0075] When slip state determination unit 27 determines that one or more tires are in a slip state, i.e., when it determines that one or more slipping tires exist, braking / driving force instruction unit 28 executes a "slip suppression process" to maintain or reduce the braking / driving force of the slipping tire. Acceleration due to an increase in driving force is prohibited during driving, and deceleration due to an increase in braking force is prohibited during braking. The target values ​​at which braking / driving force instruction unit 28 maintains or reduces the braking / driving force may be stored in a map or the like using parameters such as the diagonal movement angle θ and the vehicle speed, for example.

[0076] Braking / driving force instruction unit 28 corrects the braking / driving force instruction values ​​of the non-slip tires so as to cancel out the yaw moment of vehicle 100 that occurs due to the slip suppression process.

[0077] Figure 13 shows the braking force distribution when none of the tires 91-94 are slipping during diagonal movement. Similar to the lower diagram in Figure 8, this shows a state in which the center of gravity Cg is offset from the geometric center Cm of the four wheels. As shown in the same equation (4) as above, the yaw moments on both sides of the traveling center of gravity line p are balanced, so no yaw moment is generated in the vehicle 100.

[0078] Lg1・Fg1+Lg3・Fg3=Lg2・Fg2+Lg4・Fg4...(4)

[0079] FIG. 14 shows the braking force distribution when the left rear wheel 93 is in a slipping state. The "s" in the braking force symbol Fgs refers to slip. As shown in the upper diagram, slip suppression processing reduces the braking / driving force of the slipping tire 93 from Fg3 (FIG. 13) to Fgs3. If the braking / driving forces of the non-slip tires 91, 92, and 94 are the same as those in FIG. 13, the yaw moments on both sides of the traveling center of gravity line p will become unbalanced, as shown in equation (6.1). Furthermore, a yaw moment will be generated in the vehicle 100 due to the discrepancy between the driving force command value and the actual braking / driving force of the slipping tire 93.

[0080] Lg1・Fg1+Lg3・Fgs3<Lg2・Fg2+Lg4・Fg4 ... (6.1)

[0081] Therefore, as shown in the lower diagram, in order to suppress the yaw moment, braking / driving force instruction unit 28 sets braking / driving force instruction values ​​F for non-slip tires 91, 92, 94 so that equation (6.2) holds. * 1. F * 2. F * 4 are corrected to the values ​​of Fgs1, Fgs2, and Fgs4, respectively.

[0082] Lg1・Fgs1+Lg3・Fgs3 = Lg2・Fgs2+Lg4・Fgs4 ... (6.2)

[0083] The braking force control process according to the third embodiment is shown in the flowchart of Figure 15. In S21, the slip state determination unit 27 obtains the slip ratio from the slip ratio detection device 50 and determines whether each tire is in a slip state. In S22, it is determined whether one or more tires are in a slip state. If the result in S22 is NO, the routine ends.

[0084] If the answer is YES in S22, slip suppression processing is executed in S23. That is, braking / driving force instruction unit 28 maintains or reduces the braking / driving force of the slipping tire. In S24, braking / driving force instruction unit 28 adjusts the braking / driving force instruction value F of the non-slip tire so as to cancel out the yaw moment of vehicle 100 that occurs due to the slip suppression processing. * 1-F * Correct 4.

[0085] In this way, in the third embodiment, slippage is suppressed by maintaining or reducing the braking / driving force of the slipping tire. Furthermore, the yaw moment of the vehicle 100 generated by the slip suppression process is calculated by the braking / driving force command value F * 1-F * Therefore, even if a specific tire is in a slip state, unintended yaw motion can be suppressed during oblique movement (in-phase steering).

[0086] (Fourth embodiment) A braking / driving force control device 204 of a fourth embodiment will be described with reference to Fig. 16. The third embodiment differs from the first embodiment only in the tire angle information used by the steering state determination unit 26 to determine the in-phase state, and the other configurations are the same. In the fourth embodiment, feedback control of the tire angle is performed appropriately, and the target tire angle δ * 1-δ * Assume that 4 corresponds to the actual tire angle.

[0087] The steering state determination unit 26 determines the target tire angle δ of each tire instructed by the target tire angle calculation control unit 25 instead of the detected tire angles δs1-δs4 of each tire. * 1-δ * 4, it is determined whether the tires are in phase with each other. This allows for quick determination without being affected by communication delays from the tire angle sensors 671-674. Note that the first and fourth embodiments may be combined, and the steering state determination unit 26 may determine whether the detected tire angles δs1-δs4 and the target tire angle δ * 1-δ * 4, two types of determinations regarding the in-phase state may be made, and then the results of the determinations may be reconciled.

[0088] "The slip state determination unit 27 is provided, and the braking / driving force instruction unit 28 determines the braking / driving force instruction value F of the non-slip tire so as to cancel the yaw moment of the vehicle generated by the slip suppression process. * 1-F * 4” and “the braking / driving force control device of the fourth embodiment in which the steering state determination unit 26 determines whether the tires are in the same phase with each other based on the detected tire angles δs1-δs4.”

[0089] (Other Embodiments) (a) In the first embodiment, the braking / driving force indicator 28 always acquires the center-of-gravity position detected by the center-of-gravity position detection device 40, but does not acquire it in the second embodiment. In other embodiments, it is assumed that the vehicle 100 is equipped with the center-of-gravity position detection device 40, and the first embodiment and the second embodiment may be switched depending on the situation. For example, depending on the loading status of occupants or luggage, if there is a large change in the loading status, the braking / driving force indicator 28 may acquire the center-of-gravity position detected by the center-of-gravity position detection device 40, but if there is a large change in the loading status, the braking / driving force indicator 28 may not acquire the center-of-gravity position, but may use an estimated value stored internally.

[0090] (b) In the third embodiment, the slip state determination unit 27 determines whether each tire is in a slip state or not. In other embodiments, the slip rate may be evaluated in more stages, for example, determining the state in three or more stages, such as "heavy slip state, light slip state, no slip state." The slip suppression process may then be divided into two steps, for example, reducing the driving / braking force in a heavy slip state and maintaining the driving / braking force in a light slip state.

[0091] 1 and 2, braking / driving force control device 20 is shown as a higher-level control device for steering actuators 71-74 and braking / driving actuators 81-84. This configuration is not limiting, and braking / driving force control device 20 and the drive devices for each of steering actuators 71-74 or braking / driving actuators 81-84 may function as a single unit. For example, the drive devices for the four steering actuators 71-74 may communicate information with each other to cooperate and realize the functions of braking / driving force control device 20.

[0092] (d) The independently steered vehicle or steered vehicle on which the braking / driving force control device 20 is installed is not limited to a four-wheeled vehicle, but may be any vehicle with three or more wheels, all of which can be steered, including three-wheeled vehicles, six-wheeled vehicles, etc. For example, in a three-wheeled vehicle with one front wheel and left and right rear wheels, or left and right front wheels and one rear wheel, when the tire angles of all three wheels are in phase, the vehicle is determined to be in phase. Furthermore, when the center of gravity is displaced from the geometric center of the three wheels during diagonal movement, yaw motion occurs, just like in a four-wheeled vehicle.

[0093] (e) "Vehicle" includes not only vehicles that travel on public roads in accordance with the steering operation of a driver or the steering signals of an automatic driving device, but also green slow mobility vehicles and AGVs (automated guided vehicles) that travel at low speeds in specific areas.

[0094] As described above, the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms without departing from the spirit of the present disclosure.

[0095] Each control unit (target tire angle calculation control unit, turning state determination unit, braking / driving force instruction unit) and its method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor and memory programmed to execute one or more functions embodied in a computer program. Alternatively, each control unit and its method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, each control unit and its method described in the present disclosure may be realized by one or more special-purpose computers configured by combining a processor and memory programmed to execute one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer.

[0096] The present disclosure has been described based on the embodiments. However, the present disclosure is not limited to the embodiments and structures. The present disclosure also encompasses various modifications and variations within the scope of equivalents. Furthermore, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

Claims

1. A vehicle (100, 105) in which all tires (91-94) of three or more wheels are steerable and can be independently braked and driven by braking / driving forces (F1-F4) outputted by braking / driving actuators (81-84) corresponding to each tire, and which is equipped with a yaw motion detection device (30) for detecting yaw motion, comprising: a braking / driving force control device for controlling the braking / driving forces outputted by the braking / driving actuators, the braking / driving force control device controlling a target tire angle (δ) of each tire based on a moving direction indication value; * 1-δ * 4. δ * 12. δ * a target tire angle calculation control unit (25) that calculates a target tire angle (δs1-δs34) for each tire and instructs the steering actuators (71-76); a steering state determination unit (26) that determines whether the tires are in the same phase as each other based on the target tire angle of each tire instructed by the target tire angle calculation control unit or the detected tire angles (δs1-δs4, δs12, δs34) of each tire acquired from the tire angle sensors (671-676); and * 1-F * and a driving / braking force instruction unit (28) that calculates the driving / braking force command value (4) and instructs the driving / braking actuator, wherein when the steering state determination unit determines that the tires are in the same phase with each other and it has been determined that a yaw motion of the vehicle is occurring or has predicted that a yaw motion of the vehicle will occur based on information obtained from the yaw motion detection device, the driving / braking force instruction unit corrects the driving / braking force command value to be instructed to at least one of the driving / braking actuators.

2. A driving / braking force correction device as described in claim 1, which is mounted on a vehicle equipped with a center-of-gravity position detection device (40) that detects the center of gravity of the vehicle, and the driving / braking force command control unit corrects the driving / braking force command value based on the center of gravity of the vehicle obtained from the center-of-gravity position detection device.

3. A braking / driving force control device as described in claim 1 or 2, which is mounted on a vehicle equipped with a slip ratio detection device (50) that detects the slip ratio of each tire, and further has a slip state determination unit (27) that determines whether each tire is in a slip state or not based on the slip ratio obtained from the slip ratio detection device, and when the slip state determination unit determines that one or more tires are in a slip state, defines the one or more tires determined to be in a slip state as slip tires, and defines the one or more tires other than the slip tires as non-slip tires, and the braking / driving force instruction unit executes a slip suppression process to maintain or reduce the braking / driving force of the slip tire, and corrects the braking / driving force instruction value of the non-slip tire so as to cancel out the yaw moment of the vehicle generated by the slip suppression process.

4. The driving / braking force control device according to claim 1 or 2, wherein the steering state determination unit determines whether or not the tires are in phase with each other based on the detected tire angles.

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