Braking and driving force control device

Abstract

To provide a braking and driving power control device capable of appropriately controlling braking and driving power while reflecting the condition of a tire.SOLUTION: A braking and driving power control device includes: a front wheel forward and rearward power generation unit 10; a rear wheel forward and rearward power generation unit 20; a tire slip angle output unit that outputs a tire slip angle of front and rear wheels; a tire lateral force output unit that outputs a tire lateral force of the front and rear wheels; a slip rate output unit that outputs a slip rate of the front and rear wheels on the basis of the tire slip angle and the tire lateral force; a tire lateral force change rate output unit that outputs a change rate of the tire lateral force with respect to the slip rate; a target yaw moment setting unit that sets a target value of an addition yaw moment; and a braking and driving power distribution control unit 130 that controls an output sharing ratio of the front wheel forward and rearward power generation unit and the rear wheel forward and rearward power generation unit on the basis of the target value of the addition yaw moment and the change rate of the tire lateral force with respect to the slip rate of the front and rear wheels.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The present invention relates to a drive and braking force control device provided in a vehicle capable of individually controlling the drive and braking forces of front and rear wheels.

Background Art

[0002] As a technique related to the drive force control of a four-wheel drive electric vehicle having independent drive motors for front and rear wheels, for example, in Patent Document 1, in a vehicle behavior control device having a front-wheel drive motor, a rear-wheel drive motor, and a braking device that applies a braking force independently to each wheel, when the tire force of each wheel when each drive motor is controlled based on a target drive torque set to control the vehicle behavior is below the friction circle limit value, each motor is controlled based on the target drive torque, and when the tire force of each wheel when each motor is controlled based on the target drive torque is greater than the friction circle limit value, it is described that the braking device is controlled based on the target braking torque.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a well-known concept regarding the relationship between the drive and braking force (longitudinal force) and lateral force of a tire, there is something called a friction circle. The friction circle is a circle connecting points where the resultant force of the drive and braking force and the lateral force (cornering force) generated by the tire becomes maximum. In the technique described in Patent Document 1, based on such a concept of the friction circle, for example, control is performed to reduce the lateral force by increasing the drive force distribution of the rear axle. However, in reality, even if the drive force distribution is changed to add a yaw moment to the vehicle, there is a delay in the change in the slip angle of the vehicle body and tires due to the vehicle's yaw inertia. Therefore, the resultant force of the braking force and lateral force that can be generated at the moment the front-to-rear drive force distribution is changed will be smaller than the so-called friction circle limit, and the lateral force will change even before the braking force reaches the friction circle limit described in Patent Document 1. In the technology described in Patent Document 1, the control system is constructed on the premise that the resultant force of the braking and driving forces and the lateral force can be used to the limit of the friction circle under any circumstances. Therefore, depending on the control system, excessive slip may occur in the tires, requiring additional control that is not originally necessary, such as applying braking force by friction brakes. This raises concerns that problems such as energy loss in the vehicle, noise and vibration associated with the operation of friction brakes, and discomfort (unnatural deceleration) may arise. In view of the above-mentioned problems, the object of the present invention is to provide a braking force control device that can perform appropriate braking force control that reflects the condition of the tires. [Means for solving the problem]

[0005] To solve the above-mentioned problems, a braking and driving force control device according to one aspect of the present invention includes: a front wheel longitudinal force generating unit that generates longitudinal force of the front wheels; a rear wheel longitudinal force generating unit that generates longitudinal force of the rear wheels; a tire slip angle output unit that outputs the tire slip angles of the front wheels and the rear wheels according to the turning state of the vehicle; and a tire lateral force output unit that outputs the tire lateral force of the front wheels and the rear wheels according to the turning state of the vehicle. Using the slip ratio formula determined by the nonlinear approximation formula for the tire lateral force and the characteristic formula based on the numerical calculation model of the tire, The tire slip angles of the front wheel and the rear wheel and , the cornering power when the tire slip angle is zero, the coefficient of friction of the road surface in contact with the front and rear wheels, the ground contact load of the front and rear wheels, the parameter values ​​in the numerical calculation model of the tire, and Tire lateral force and, A slip ratio output unit that outputs the slip ratios of the front and rear wheels based on the slip ratios of the front and rear wheels, a tire lateral force change rate output unit that outputs the rate of change of the tire lateral force with respect to the slip ratios of the front and rear wheels, and a target yaw moment setting unit that sets a target value for the additional yaw moment applied to the vehicle. Based on the rate of change of tire lateral force with respect to the slip ratio of the front and rear wheels, target slip ratios for the front and rear wheels are set to obtain the target value of the additional yaw moment, and the actual slip ratios of the front and rear wheels are set to match the target slip ratios. The system is characterized by comprising a braking and driving force distribution control unit that controls the output distribution ratio of the front wheel longitudinal force generating unit and the rear wheel longitudinal force generating unit. According to this, by determining the rate of change of the tire's lateral force with respect to the slip ratio based on the current tire's lateral force and slip angle, and controlling the output distribution ratio of the front and rear wheel longitudinal force generating units based on this rate of change of the tire's lateral force with respect to the slip ratio, it is possible to perform appropriate braking and driving force distribution control that reflects the current tire's slip angle and lateral force in a real vehicle where yaw inertia exists in the vehicle body and the slip angle of the vehicle body and tires does not change immediately. This prevents situations where excessive braking and driving force distribution control exceeds the limit of tire-generated force, necessitating intervention by friction brakes, thereby reducing vehicle energy loss and preventing noise and discomfort caused by the operation of friction brakes.

[0006] In the present invention, the front wheel longitudinal force generating unit and the rear wheel longitudinal force generating unit are electric motors, and system The drive force distribution control unit controls the output distribution ratio. Before The system can be configured to control the rotational speed of the output shafts of the front wheel longitudinal force generating unit and the rear wheel longitudinal force generating unit so that the actual slip ratio of the front wheel and the rear wheel becomes the target slip ratio. According to this method, the slip ratio of the front and rear wheels can be appropriately controlled by controlling the rotational speed of the electric motor, and the desired additional yaw moment can be generated with relatively simple control and with high precision.

[0007] In the present invention, the braking force distribution control unit can be configured to control the sum of the longitudinal forces of the front wheels and the longitudinal forces of the rear wheels to match a predetermined required longitudinal force, at least in the region where the absolute value of either the longitudinal force of the front wheels or the longitudinal force of the rear wheels becomes 0. According to this, by controlling the distribution of braking and driving forces between the front and rear wheels, the total driving force or total braking force of the vehicle does not change, thus ensuring the vehicle's drivability (ease of driving).

[0008] In the present invention, the braking and driving force distribution control unit can be configured to prohibit the reversal of the sign of the longitudinal force of the front wheels or the longitudinal force of the rear wheels by changing the output distribution ratio of the front longitudinal force generating unit and the rear longitudinal force generating unit. According to this, for example, reducing the driving force (or braking force) of either the front or rear wheel in order to increase the lateral force of the tire can result in the sign of the front and rear forces reversing, generating braking force (or driving force) and thus preventing the lateral force of the tire from actually decreasing.

[0009] In the present invention, the tire lateral force change rate output unit can be configured to have a map that reads out the rate of change of tire lateral force with respect to the slip ratio of the front wheels and the rear wheels according to the turning state of the vehicle. According to this, when calculating the rate of change of tire lateral force with respect to slip ratio in real time, for example by a processor mounted on the vehicle, the computational load can be reduced and the responsiveness of the control can be improved. [Effects of the Invention]

[0010] As described above, the present invention provides a braking force control device that can perform appropriate braking force control that reflects the condition of the tires. [Brief explanation of the drawing]

[0011] [Figure 1] This figure schematically shows the configuration of the drive system of a vehicle having a first embodiment of the braking and driving force control device to which the present invention is applied. [Figure 2] This diagram shows an equivalent two-wheeled vehicle model for a four-wheeled vehicle. [Figure 3] This figure shows the correlation between vehicle slip angle gain and vehicle speed. [Figure 4] This is a schematic diagram illustrating the forces acting on a vehicle during turning and acceleration / deceleration. [Figure 5] This figure shows an example of a front-to-rear torque distribution diagram for a vehicle. [Figure 6] This figure shows an example of the correlation between tire lateral force and slip ratio. [Figure 7] This diagram illustrates the concept of driving stiffness in tires. [Figure 8] This figure shows the correlation between slip ratio and tire driving force at different slip angles. [Figure 9] This figure shows the correlation between tire slip angle and driving stiffness. [Figure 10] This figure shows the correlation between the absolute value of the actual lateral acceleration and the pseudo-lateral acceleration that saturates the reference lateral acceleration. [Figure 11] This is a flowchart showing the process when performing drive force control to generate an additional yaw moment in the vehicle in the first embodiment of the braking and driving force control device. [Figure 12] This figure shows an example of the yaw moment to be added by drive force control and the braking and driving forces of the front and rear wheels in the braking and driving force control device of the first embodiment. [Figure 13] This figure plots the braking and driving forces and lateral forces generated by the tires for each slip angle. [Figure 14] This figure shows an example of a map of the rate of change of tire lateral force with respect to slip ratio in a second embodiment of a braking and driving force control device to which the present invention is applied. [Figure 15] This figure shows an example of the yaw moment to be added and the braking and driving force of the front and rear wheels by the driving force control of the third embodiment of the braking and driving force control device to which the present invention is applied. [Modes for carrying out the invention]

[0012] <First Embodiment> The following describes a first embodiment of a braking and driving force control device to which the present invention is applied. The braking and driving force control device of the first embodiment is installed in a vehicle (for example, a passenger car) that has independent braking and driving motors (motor generators) for the front wheel drive and rear wheel drive.

[0013] Figure 1 is a schematic diagram showing the configuration of the drive system of a vehicle having a braking force control device according to the first embodiment. Vehicle 1 is a four-wheeled vehicle having a pair of front wheels (FW) and rear wheels (RW). Vehicle 1 is equipped with a front motor 10, a rear motor 20, a battery 30, a front inverter 110, a rear inverter 120, a drive control unit 130, and the like.

[0014] The front motor 10 is a rotating electric machine that generates the driving force for the front wheels FW. For example, a permanent magnet synchronous motor (PM motor) can be used as the front motor 10. The front motor 10 receives power from the battery 30 to generate driving force for the front wheels FW, and also functions as a motor generator that regenerates power using the torque transmitted from the front wheels FW to charge the battery 30. The front motor 10 is the front wheel front-rear force generating unit of the present invention.

[0015] The output of the front motor 10 is transmitted to the front wheels FW via the front differential 11 and the front drive shaft 12. The front differential 11 is a differential mechanism that transmits the output of the front motor 10 to the left and right front drive shafts 12, and absorbs the difference in rotation between the left and right front wheels FW, for example, when turning. The front drive shaft 12 is a rotating shaft that transmits power from the front differential 11 to the left and right front wheels FW. The front drive shaft 12 is equipped with universal joints, such as constant velocity joints, to follow the steering of the front wheels FW and the stroke of the front suspension.

[0016] The rear motor 20 is a rotating electric machine that generates the driving force for the rear wheels RW. For example, a permanent magnet synchronous motor can be used as the rear motor 20. The rear motor 20 receives power from the battery 30 to generate driving force for the rear wheels RW, and also functions as a motor generator that regenerates power using the torque transmitted from the rear wheels RW to charge the battery 30. The rear motor 20 is the rear wheel front-to-rear force generating unit of the present invention.

[0017] The output of the rear motor 20 is transmitted to the rear wheels RW via the rear differential 21 and rear drive shaft 22. The rear differential 21 is a differential mechanism that transmits the output of the rear motor 20 to the left and right rear drive shafts 22, and absorbs the difference in rotation between the left and right rear wheels RW, for example, when turning. The rear drive shaft 22 is a rotating shaft that transmits power from the rear differential 21 to the left and right rear wheels RW. The rear drive shaft 22 is equipped with universal joints, such as constant velocity joints, to follow the stroke of the rear suspension.

[0018] Battery 30 is a secondary battery that stores electricity primarily used for driving the vehicle 1. For example, a lithium-ion battery can be used as the battery 30.

[0019] The front inverter 110 converts the DC current supplied from the battery 30 into AC current in response to a command from the drive control unit 130, and supplies it to the front motor 10 as power for driving. Furthermore, the front inverter 110 also functions as a regenerative inverter that converts the AC current supplied from the front motor 10 into DC current to charge the battery 30 during regenerative power generation by the front motor 10.

[0020] The rear inverter 120 converts the DC current supplied from the battery 30 into AC current in response to a command from the drive control unit 130, and supplies it to the rear motor 20 as drive power. Furthermore, the rear inverter 120 also functions as a regenerative inverter that converts the AC current supplied from the rear motor 20 into DC current to charge the battery 30 during regenerative power generation by the rear motor 20. The front inverter 110 and rear inverter 120 have the function of controlling the output torque and output shaft rotation speed of the front motor 10 and rear motor 20 according to the target driving force (target slip ratio) of the front wheels FW and rear wheels RW commanded by the drive control unit 130.

[0021] The drive control unit 130 controls the output of the front motor 10 and rear motor 20 by issuing commands to the front inverter 110 and rear inverter 120 in accordance with the driver-requested torque, which is set based on, for example, the driver's accelerator operation. Furthermore, the drive control unit 130 sets the braking force sharing ratio between the regenerative braking system and the hydraulic brakes, for example, in response to the driver's brake operation. At this time, the drive control unit 130, in response to a braking request by regenerative braking, issues commands to the front inverter 110 and the rear inverter 120, causing the front motor 10 and the rear motor 20 to perform regenerative power generation and generate braking force.

[0022] The drive control unit 130 can be configured as a microcomputer having, for example, an information processing unit such as a CPU, a storage unit such as RAM or ROM, an input / output interface, and a bus connecting these.

[0023] The drive control unit 130 is connected to vehicle speed sensors 131 and 132, steering angle sensor 133, acceleration sensor 134, yaw rate sensor 135, and the like. The vehicle speed sensors 131 and 132 are provided on the hub portion that rotatably supports the front wheel FW and rear wheel RW. Vehicle speed sensors 131 and 132 are provided on the left and right front wheels (FW) and rear wheels (RW), respectively. Vehicle speed sensors 131 and 132 output vehicle speed signals corresponding to the rotational speed of each wheel. The drive control unit 130 calculates the wheel speed of each wheel according to the vehicle speed signal.

[0024] The steering angle sensor 133 detects the angle position (steering wheel angle θ) of the steering wheel used by the occupant (driver) to steer.H This is a sensor that detects ). The drive control unit 130 controls the steering angle θ detected by the steering angle sensor 133. H Furthermore, the steering angle of the front wheels (FW) can be calculated based on the gear ratio (constant) n of the steering gearbox, which is not shown in the diagram. The acceleration sensor 134 is a sensor that detects acceleration acting on the vehicle body in the longitudinal direction and the lateral direction (vehicle width direction). The yaw rate sensor 135 is a sensor that detects the yaw rate, which is the rotational speed of the vehicle body around its vertical axis.

[0025] The drive control unit 130 has a function to set the output distribution of each motor (front-to-rear distribution of driving force between the front wheels FW and the rear wheels RW) when the front motor 10 and rear motor 20 are driven. Furthermore, the drive control unit 130 has a function to set the distribution of power generated by each motor (front-to-rear braking force distribution between the front wheels FW and rear wheels RW) when the front motor 10 and rear motor 20 are regenerating power. Furthermore, the drive control unit 130 has a function to control the distribution of driving force and braking force according to the yaw moment to be applied to the vehicle 1, for example, when the vehicle is turning. The drive control unit 130 has the functions of a tire slip angle output unit, a tire lateral force output unit, a slip ratio output unit, a tire lateral force change rate output unit, a target yaw moment setting unit, and a braking and driving force distribution control unit according to the present invention. The following explains this point in more detail. In the following explanation, we will mainly use the driving state as an example, but the front-to-rear distribution control of braking force during braking using regenerative braking can also be performed in the same way.

[0026] Figure 2 shows an equivalent two-wheeled vehicle model of a four-wheeled vehicle. The vehicle slip angle β can be estimated using the following equation 1.

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[0027] From the vehicle body slip angle β obtained by Equation 1, the slip angles α of the tires of the front wheels FW and the rear wheels RW can be converted by the following Equations 2 and 3. f , α r It can be converted to.

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[0028] Figure 3 is a diagram showing the correlation between the vehicle speed and the vehicle speed of the vehicle body slip angle gain. In Figure 3, the horizontal axis represents the vehicle speed V [km / h], and the vertical axis represents the vehicle body slip angle gain β / δ (vehicle body slip angle β per steering angle δ). As shown in Figure 3, it can be seen that the vehicle body slip angle gain β / δ decreases as the vehicle speed increases.

[0029] Figure 4 is a schematic diagram showing the acting forces during vehicle turning and acceleration / deceleration. When the vehicle is going straight, the ground contact load including the front and rear load transfer caused by acceleration and deceleration can be expressed by the following Equations 4 and 5. F zf = F zf0 -ΔF zx (Equation 4) F zr =F zr0 +ΔF zx (Formula 5) F zf Front wheel ground contact load F zr : Rear wheel ground contact load F zf0 : Front wheel ground contact load when stationary F zr0 : Ground contact load of the rear wheels when stationary ΔF zx : Load transfer amount due to acceleration

[0030] ΔF of longitudinal load transfer due to acceleration of vehicle 1 zx This can be expressed by the following equation 6.

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[0031] The lateral load transfer due to lateral acceleration during turning can be expressed by the following equations 7 and 8. F zfi =F zf0 -ΔF zx -ΔF zy ·K zy (Formula 7) F zri =F zr0 +ΔF zx -ΔF zy (1-K zy ) (Equation 8) F zfi : Ground contact load of the front wheel on the inner wheel side during slewing F zri : Ground contact load of the rear wheel on the inner wheel side during slewing F zf0 : Front wheel ground contact load when stationary F zr0 : Ground contact load of the rear wheels when stationary ΔF zy : Amount of lateral load transfer due to turning K zy : Front axis load distribution ratio for lateral load transfer

[0032] ΔF - Lateral load shift due to turning zy This can be expressed by the following equation 9.

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[0033] Figure 5 shows an example of a front-to-rear torque distribution diagram for a vehicle. In Figure 5, the horizontal axis shows the value obtained by dividing the driving force of the front wheels by the ground contact load of the front wheels, and the vertical axis shows the value obtained by dividing the driving force of the rear wheels by the ground contact load of the rear wheels. Front-to-rear distribution of ground load F zf :F zr (If you prioritize the inner wheel of the slewing wheel, then F zfi :F zri This is used as the basis for the driver's required driving force when the additional yaw moment is zero. In Figure 5, the front-to-rear torque distribution during straight-line driving is shown by a solid line, and the front-to-rear torque distribution during cornering is shown by a dashed line.

[0034] To prevent irregular slippage of the front wheels (FW) and rear wheels (RW) due to road surface disturbances (uneven road surface) or fluctuations in the coefficient of friction μ (uneven road surface), the driving force distribution to the front axle is set to be larger to prevent slippage of the rear wheels (RW). For example, in the example shown by the dashed line in Figure 5, an uneven road surface with a ground load fluctuation of ±7.5% is assumed. Furthermore, in the example shown by the dashed line in Figure 5, a non-uniform road surface with a road surface μ variation of ±0.075 is assumed. Furthermore, in situations such as sports driving on a race track, if the driver selects a driving mode that tends towards oversteer, the torque distribution to the rear axle can be set to be larger than during normal driving.

[0035] Next, we will explain a method for estimating the slip ratio κ individually for the front and rear axles from the tire slip angle α and lateral force Fy. Tire lateral force Non The characteristic equations, which combine the linear approximation formula and the Magic Formula, a numerical calculation model of the tire, are shown in Equations 10 and 11.

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[0036] The slip ratio κ can be expressed by the following equation 12.

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[0037] The rate of change of tire lateral force (for the front and rear axles individually) for a 1% change in slip ratio can be expressed by the following equation 15.

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[0038] Figure 6 shows an example of the correlation between tire lateral force and slip ratio. In Figure 6, the horizontal axis represents the slip ratio, and the vertical axis represents the lateral force of the tire. As shown in Figure 6, the tire lateral force Fy increases with increasing slip angle and decreases with increasing slip ratio.

[0039] Figure 7 illustrates the concept of driving stiffness in tires. In Figure 7, the horizontal axis represents the slip ratio, and the vertical axis represents the braking and driving force of the tire. As shown in Figure 7, in the region where the slip ratio is relatively small, the braking force changes linearly with respect to the slip ratio. In this region, the rate of change of braking and driving force with respect to the slip ratio (the slope of the diagram) is the driving stiffness in the case of driving, and the braking stiffness in the case of braking. Generally, driving stiffness and braking stiffness often coincide.

[0040] Figure 8 shows the correlation between slip ratio and tire driving force at different slip angles. In Figure 8, the horizontal axis represents the slip ratio, and the vertical axis represents the tire driving force. Figure 8 shows diagrams for slip angles of 0, 1, 2, 5, 10, and 20 degrees. Figure 9 shows the correlation between tire slip angle and driving stiffness. In Figure 9, the horizontal axis represents the slip angle, and the vertical axis represents the driving stiffness. As shown in Figures 8 and 9, driving stiffness tends to decrease with increasing slip angle.

[0041] The driving stiffness Kx of a tire can be expressed by the following equation 16.

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[0042] The slip ratio and driving force of the front and rear wheels that allow vehicle 1 to maintain total driving force (Fxf + Fxr) while adding a target yaw moment Mz can be expressed by the following equations 18 to 23.

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[0043] However, if the modified driving force exceeds Fx=0 (the state where the tire lateral force is maximized) due to the aforementioned change in driving force, the control that should increase the tire lateral force will actually decrease it. Therefore, the modified driving force is limited so that it does not exceed Fx=0.

[0044] Next, we will explain how to set the target yaw moment (additional yaw moment) to be added by braking and driving force control when vehicle 1 is turning. The additional yaw moment is, for example, the steering angle θ detected by the steering angle sensor 133. H The following equations 24 and 25 can be used to calculate the yaw rate γ detected by the yaw rate sensor 135 and the lateral acceleration detected by the acceleration sensor 134.

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[0045] Here, the lateral acceleration deviation is set as shown in equation 26 below.

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[0046] The reference lateral acceleration is the excessive turning radius during large steering turns on low-friction surfaces. head To prevent moment generation, set it as shown in Equation 27 below.

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[0047] Handle angle θ H Linear calculation of unsigned reference lateral acceleration

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[0048] The pseudo-lateral acceleration that saturates the reference lateral acceleration can be expressed as shown in Equation 29 below.

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[0049] The unsigned reference lateral acceleration saturated by the pseudo-lateral acceleration that saturates the reference lateral acceleration can be expressed as shown in equation 30 below.

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[0050] The lateral acceleration / handle angle gain Gy can be expressed as shown in equation 33 below.

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[0051] Figure 11 is a flowchart showing the process when performing drive force control to generate an additional yaw moment in the vehicle in the first embodiment of the braking and driving force control device. The following explains each step in order.

[0052] <Step S01: Obtain each parameter> The drive control unit 130 acquires the parameters necessary for subsequent processing based on the outputs of each sensor, etc. Then, proceed to step S02.

[0053] <Step S02: Additional Yaw Moment Calculation> The drive control unit 130 calculates the additional yaw moment to be added by braking force control using equations 24 and 25 described above. Then, proceed to step S03.

[0054] <Step S03: Calculation of slip angle for each tire> The drive control unit 130 calculates the tire slip angles of the front wheels FW and rear wheels RW using equations 2 and 3 described above. Then proceed to step S04.

[0055] <Step S04: Calculation of ground contact load for each wheel> The drive control unit 130 calculates the ground contact load of the left and right front wheels FW and the left and right rear wheels RW using the above-described equations 4 to 9. Then, proceed to step S05.

[0056] <Step S05: Basic front / rear force distribution setting> The drive control unit 130 sets the basic front-to-rear drive force distribution (front-to-rear drive force distribution when the additional moment is 0) using, for example, a drive force distribution diagram as shown in Figure 5, or a map generated based on such a drive force distribution diagram. Then, proceed to step S06.

[0057] <Step S06: Estimation of lateral force on each tire> The drive control unit 130 calculates (estimates) the tire lateral force Fy of the front wheel FW and rear wheel RW using the above-described equations 13 and 14. Then proceed to step S07.

[0058] <Step S07: Calculation of slip ratio for each wheel> The drive control unit 130 calculates the slip ratio κ of the front wheel FW and rear wheel RW tires using the equation 12 described above. Then proceed to step S08.

[0059] <Step S08: Calculation of tire lateral force change rate for each wheel slip ratio> The drive control unit 130 uses the above-described equation 15 to calculate the rate of change of tire lateral force for each unit of slip ratio change (for example, 1%) for the front and rear wheels individually. Then, proceed to step S09.

[0060] <Step S09: Calculation of the front-to-rear ratio of driving stiffness> The drive control unit 130 uses the above-described equation 17 to calculate the front-to-rear wheel ratio of driving stiffness during driving and braking stiffness during regenerative braking. Then proceed to step S10.

[0061] <Step S10: Calculation of target slip ratio for front and rear wheels> The drive control unit 130 uses equations 18 to 23 described above to calculate the target slip ratio of the front wheel FW and rear wheel RW tires (which can be converted to a target driving force using the driving stiffness Kx) that will yield the additional yaw moment calculated in step S02. Then proceed to step S11.

[0062] <Step S11: Determine if the braking / driving force crosses zero> In step S10, the drive control unit 130 determines whether the braking force of either the front wheel FW or the rear wheel RW crosses zero (transitions from the drive side to the braking side, or from the braking side to the drive side) when changing the braking force to obtain the slip ratio of the front wheel FW and the rear wheel RW calculated. If the braking / driving force crosses zero, proceed to step S12; otherwise, proceed to step S13.

[0063] <Step S12: Target driving force limit> The drive control unit 130 limits the braking force of the wheel on the side of the front wheel FW and rear wheel RW whose braking force crosses zero to zero. After limiting the target braking force, proceed to step S13.

[0064] <Step S13: Front and rear motor drive control> The drive control unit 130 issues commands to the front inverter 110 and the rear inverter 120, and during driving, drives the front motor 10 and the rear motor 20 while controlling the output shaft rotation speed of the front motor 10 and the rear motor 20 so that the slip ratio of the front wheels FW and the rear wheels RW becomes the target slip ratio set in step S10. Furthermore, during braking, the output shaft rotation speed of the front motor 10 and rear motor 20 is controlled so that the slip ratio of the front wheel FW and rear wheel RW becomes the target slip ratio set in step S10, while the front motor 10 and rear motor 20 are made to perform regenerative power generation. After that, the series of processes will be terminated.

[0065] Figure 12 shows an example of the yaw moment to be added by drive force control and the braking and driving forces of the front and rear wheels. Figure 12(a) shows the driving force of the front and rear wheels during driving, and Figure 12(b) shows the braking force of the front and rear wheels during braking using regenerative braking. In Figure 12, the horizontal axis represents the yaw moment Mz, indicating that the effect of reducing understeer is greater on the right side. As shown in Figure 12, by reducing the braking and driving force of the front wheels (FW) to increase the lateral force that can be generated, and by increasing the braking and driving force of the rear wheels (RW) to decrease the lateral force that can be generated, a difference in lateral force between the front and rear wheels can be created, thereby generating a yaw moment that reduces understeer. On the other hand, by increasing the braking and driving force of the front wheels (FW) to reduce the lateral force that can be generated, and by decreasing the braking and driving force of the rear wheels (RW) to increase the lateral force that can be generated, an opposite lateral force difference between the front and rear wheels can be created, thereby generating a yaw moment that suppresses oversteer. In principle, both braking and driving forces are designed so that the total driving force and total braking force of the vehicle do not change due to changes in the driving force distribution. As a result, the braking and driving force of one of the front or rear wheels is reduced in proportion to the increase in the braking and driving force of the other wheel. However, as mentioned above, if the braking or driving force of either the front or rear wheel becomes zero, the control system does not reverse the sign of the braking or driving force (from driving to braking, or from braking to driving), but rather maintains the front-to-rear tire force at zero.

[0066] Figure 13 is a plot of the braking and driving forces and lateral forces generated by the tires for each slip angle. In Figure 13, the horizontal axis represents braking and driving force (tire longitudinal force), and the vertical axis represents tire lateral force. As shown in Figure 13, the plot of braking force and lateral force (tire force characteristic diagram) changes according to the tire slip angle. The concept commonly known as the friction circle is formed by connecting the outermost edges of such diagrams with different slip angles. However, in reality, due to the yaw inertia of the vehicle body, there is a time response delay between the current slip angle and the slip angle at which the tire generates the maximum force at the friction circle limit. If these points are ignored and control is performed based on the assumption of the friction circle limit, for example, the braking and driving force of the tires may become excessive, causing excessive slip. If slip occurs on the driving side, for example, it becomes necessary to intervene with braking control using friction brakes to suppress the slip. In this case, energy loss and noise generated by the operation of friction brakes can become problems.

[0067] In contrast, in the first embodiment, the slip angle α of the front wheel FW and rear wheel RW is f ,α r After calculating the current slip angle α, f ,α r In order to set the target braking force according to the characteristics of the tire, the current tire slip angle α f ,α r By effectively utilizing the changes in tire force that occur in this manner, a desired yaw moment can be applied to the vehicle 1, thereby improving handling stability and cornering performance. For example, in Figure 13, when the slip angle of the rear wheel RW is 5 degrees and the driving force and lateral force of the front wheel FW and rear wheel RW are at position P0 (driving force 2500 N), by setting the driving force and lateral force of the front wheel FW to position P1 (driving force 0) and transitioning the driving force and lateral force of the rear wheel RW to position P2 (the point where it touches the tire force characteristic curve at a slip angle of 5 degrees, driving force 5000 N), the front-to-rear wheel lateral force difference shown in Figure 13 can be generated without changing the total driving force of the vehicle 1, and a desired additional yaw moment can be applied to the vehicle 1 without intervention such as braking control by friction brakes.

[0068] According to the first embodiment described above, the following effects can be obtained. (1) Current lateral force Fy and slip angle α of the front wheel FW and rear wheel RW. f ,α r Based on this, the rate of change of the tire lateral force Fy with respect to the slip ratio κ is determined, and the tire lateral force Fy with respect to this slip ratio κ is determined. Power By controlling the output (driving force or braking force) distribution ratio of the front motor 10 and rear motor 20 based on the rate of change, it is possible to perform appropriate braking and driving force distribution control that reflects the current tire slip angle and lateral force in a real vehicle where yaw inertia exists in the vehicle body and the slip angle of the vehicle body and tires does not change immediately. 。 This prevents situations where excessive braking and driving force distribution control exceeds the limit of tire generation force, necessitating intervention by friction brakes, thereby reducing energy loss in the vehicle and preventing noise and discomfort caused by the operation of friction brakes. (2) In controlling the output distribution ratio, target slip ratios for the front wheels FW and rear wheels RW are set, and the output shaft rotation speeds of the front motor 10 and rear motor 20 are controlled so that the actual slip ratios of the front wheels FW and rear wheels RW become the target slip ratios. By controlling the rotation speed of the electric motors, the slip ratio κ of the front wheels FW and rear wheels RW can be appropriately controlled, and the desired additional yaw moment can be generated with relatively simple control and with high accuracy. (3) In the region where the absolute value of either the longitudinal force of the front wheels FW or the longitudinal force of the rear wheels RW becomes 0, the braking and driving force distribution is controlled so that the sum of the longitudinal forces of the front wheels and the rear wheels matches a predetermined required longitudinal force. By controlling the braking and driving force distribution between the front and rear wheels, the total driving force or total braking force of the vehicle 1 does not change, and the drivability (ease of driving) of the vehicle 1 can be ensured. (4) By prohibiting the reversal of the sign of the longitudinal force of the front wheel FW or the longitudinal force of the rear wheel RW due to a change in the output distribution ratio of the front motor 10 and the rear motor 20, it is possible to prevent the reversal of the sign of the longitudinal force and the generation of braking force (or driving force) Fx of either the front or rear wheel, which would result in a decrease in the lateral force of the tire Fy, for example, when the driving force (or braking force) Fx of either the front or rear wheel is reduced in order to increase the lateral force of the tire Fy.

[0069] <Second Embodiment> Next, a second embodiment of a braking and driving force control device to which the present invention is applied will be described. In the embodiments described below, the same reference numerals are used for parts that are the same as in previous embodiments, and their descriptions are omitted. The differences will be explained in detail. In the second embodiment, instead of sequentially calculating the rate of change of tire lateral force with respect to the slip ratio of each wheel using mathematical calculations with respect to the slip ratio as in the first embodiment, a map value of slip angle and slip ratio predetermined for each lateral acceleration of the vehicle is used.

[0070] Figure 14 shows an example of a map of the rate of change of tire lateral force with respect to slip ratio. As shown in Figure 14, the map is configured as a three-dimensional map that takes the tire slip angle and slip ratio as input and outputs (reads out) the rate of change of the tire lateral force with respect to the slip ratio. Multiple such maps can be created to correspond to changes in lateral acceleration. Furthermore, for lateral acceleration for which no map is set, it can be obtained by performing interpolation, such as linear interpolation, on the rate of change of tire lateral force with respect to slip ratio read from multiple maps. According to the second embodiment described above, in addition to the same effects as those of the first embodiment described above, the computational load on the drive control unit 130 can be reduced and the responsiveness of the control can be improved.

[0071] <Third Embodiment> Next, a third embodiment of a braking and driving force control device to which the present invention is applied will be described. In the third embodiment, the setting of the braking force is changed from that of the first embodiment as follows. Figure 15 shows an example of the yaw moment to be added by the driving force control of the third embodiment and the braking and driving forces of the front and rear wheels. In the third embodiment, when setting the target braking and driving forces for the front wheels FW and rear wheels RW, if the braking and driving force of one of the front wheels FW or rear wheels RW crosses zero, the rate of change of the amount of change in the driving force ΔFx with respect to the additional yaw moment Mz of the other wheel is increased. According to the third embodiment described above, in addition to the effects similar to those of the first embodiment described above, even if the change in the braking force of one of the front wheels FW or rear wheels RW is constrained by the fact that the braking force crosses zero, the amount of yaw moment actually generated in the vehicle body can be secured by increasing the amount of change in the braking force of the other wheel.

[0072] (modified version) The present invention is not limited to the embodiments described above, and various modifications and changes are possible, all of which fall within the technical scope of the present invention. (1) The configuration of the vehicle, the vehicle's drive system, and the braking force control device can be modified as appropriate, without being limited to the embodiments described above. For example, a function that is implemented by a single unit in one embodiment may be implemented by distributing the responsibility among multiple components. Conversely, a function that is implemented by multiple components may be implemented by consolidating it into a single unit. (2) The vehicle and tire models and specific forms of the mathematical formulas used in the embodiments are examples only, and the present invention is not limited thereto and can be modified as appropriate. (3) In this embodiment, the left and right front wheels are driven and controlled by a single front motor, and the left and right rear wheels are driven and controlled by a single rear motor. However, the present invention is not limited to this, and can be applied to vehicles that have independent motor generators (typically in-wheel motors) for each wheel, for example. (4) In the embodiment, the braking force control device controls the front-to-rear distribution of both the driving force and braking force of the vehicle, but the present invention is not limited to this, and the device may be configured to control the front-to-rear distribution of only one of the driving force or braking force. (5) In the embodiment, the vehicle is a battery electric vehicle as an example, but the present invention is not limited to this and can be applied to other types of electric vehicles such as fuel cell vehicles and engine-electric series hybrid vehicles. [Explanation of Symbols]

[0073] 1 vehicle FW front wheel RW rear wheel 10 Front motor 11 Front differential 12 Front drive shafts 20 Rear motors 21 Rear differential 22 Rear drive shaft 30 batteries 110 Front Inverter 120 Rear Inverter 130 Drive control unit 131,132 Vehicle speed sensor 133 Rudder angle sensor 134 Acceleration sensor 135 Yaw Rate Sensor

Claims

1. A front wheel longitudinal force generating unit that generates longitudinal force on the front wheels, A rear wheel longitudinal force generating unit that generates longitudinal force on the rear wheel, A tire slip angle output unit outputs the tire slip angles of the front and rear wheels according to the turning state of the vehicle, A tire lateral force output unit that outputs tire lateral forces for the front and rear wheels according to the turning state of the vehicle, A slip ratio output unit outputs the slip ratio of the front and rear wheels based on the tire slip angles of the front and rear wheels, the cornering power when the tire slip angle is zero, the friction coefficient of the road surface in contact with the front and rear wheels, the contact load of the front and rear wheels, the parameter values ​​in the numerical calculation model of the tire, and the tire lateral force, using a slip ratio formula determined by the nonlinear approximation formula for the tire lateral force and a characteristic formula based on a numerical calculation model of the tire. A tire lateral force change rate output unit outputs the rate of change of tire lateral force with respect to the slip ratio of the front wheel and the rear wheel, A target yaw moment setting unit sets a target value for the additional yaw moment applied to the vehicle, Based on the rate of change of tire lateral force with respect to the slip ratio of the front and rear wheels, a target slip ratio of the front and rear wheels is set to obtain the target value of the additional yaw moment, and a braking and driving force distribution control unit controls the output distribution ratio of the front and rear force generating unit and the rear and rear force generating unit so that the actual slip ratio of the front and rear wheels becomes the target slip ratio. A braking and driving force control device characterized by comprising:

2. The front wheel longitudinal force generating unit and the rear wheel longitudinal force generating unit are electric motors, The braking and driving force distribution control unit controls the output shaft rotation speed of the front wheel longitudinal force generating unit and the rear wheel longitudinal force generating unit so that the actual slip ratio of the front wheel and the rear wheel becomes the target slip ratio in controlling the output distribution ratio. A braking and driving force control device according to claim 1, characterized by the above.

3. The braking force distribution control unit controls the sum of the longitudinal forces of the front wheels and the longitudinal forces of the rear wheels to match a predetermined required longitudinal force, at least in the region where the absolute value of either the longitudinal force of the front wheels or the longitudinal force of the rear wheels becomes zero. A braking and driving force control device according to claim 1 or claim 2, characterized by the above.

4. The braking force distribution control unit prohibits the reversal of the sign of the longitudinal force of the front wheels or the longitudinal force of the rear wheels by changing the output distribution ratio of the front longitudinal force generating unit and the rear longitudinal force generating unit. The braking and driving force control device according to claim 3, characterized by the above.

5. The tire lateral force change rate output unit has a map that reads out the rate of change of tire lateral force with respect to the slip ratio of the front and rear wheels according to the turning state of the vehicle. A braking and driving force control device according to claim 1 or claim 2, characterized by the above.

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