Vehicular braking / driving force control method and control device

Abstract

The present invention controls braking / driving forces of front wheels and / or rear wheels of a vehicle by determining whether the vehicle is in a grip region of a tire cornering force being proportional to a driver's input or in a non-grip region of the tire cornering force not being proportional to the driver's input, and if the vehicle is in the grip region, calculating a target slip angle of the vehicle to control the braking / driving forces of front wheels and / or rear wheels such that a slip angle of the vehicle approaches the target slip angle, or if the vehicle is in the non-grip region, calculating a target yaw rate of the vehicle to control the braking / driving forces of front wheels and / or rear wheels such that a yaw rate of the vehicle approaches the target yaw rate.

Description

Vehicle braking / driving force control method and device

[0001] The present invention relates to a method and a device for controlling braking / driving force for a vehicle.

[0002] The following Patent Document 1 describes that the direction of the yaw rate generated in the vehicle is compared with the direction of the slip angle of the vehicle (car body), and if the two are in the same direction, the driving force of the front wheels is increased, and if the two are in opposite directions, the driving force of the rear wheels is increased.

[0003] JP 2007-302115 A

[0004] In the above-mentioned Patent Document 1, the direction of the yaw rate and the direction of the slip angle are compared to determine whether the vehicle is in an oversteer or understeer state when turning. This type of turning state occurs primarily in a non-grip region where the tire cornering force is not proportional to the driver's input. In contrast, in a grip region where the tire cornering force is proportional to the driver's input, the driver may need to make corrective steering, and this problem still needs improvement. The present invention aims to provide a method and a control device for controlling braking / driving force for a vehicle that can reduce corrective steering in a grip region and improve handling stability during cornering in a non-grip region.

[0005] One aspect of the present invention is to determine whether the tire cornering force is in a grip region, where it is proportional to the driver's input, or in a non-grip region, where it is not proportional; in the grip region, a target slip angle for the vehicle is calculated, and the braking / driving force of the front wheels and / or rear wheels is controlled so that the slip angle generated in the vehicle approaches the target slip angle; and in the non-grip region, a target yaw rate for the vehicle is calculated, and the braking / driving force of the front wheels and / or rear wheels is controlled so that the yaw rate generated in the vehicle approaches the target yaw rate.

[0006] According to one aspect of the present invention, corrective steering is reduced in grip areas by appropriately setting the target slip angle of the vehicle, and the yaw rate of the vehicle approaches the target yaw rate in non-grip areas, thereby improving handling stability during cornering. The objects and advantages of the present invention are realized and achieved by using the elements and combinations thereof set forth in the claims. It should be understood that both the foregoing general description and the following detailed description are merely exemplary and explanatory and do not limit the invention as defined by the claims.

[0007] 9 is a plan view showing a schematic configuration of an example of a vehicle braking / driving system according to an embodiment; FIG. 10 is a block diagram of an example functional configuration of a controller; FIG. 11 is a flowchart showing an example of calculation processing carried out in a front and rear motor torque correction value calculation unit; FIG. 12 is a flowchart of a subprogram carried out in the calculation processing of FIG. 3; FIG. 13 is a flowchart of a subprogram carried out in the calculation processing of FIG. 3; FIG. 14 is an explanatory diagram of a target slip angle; FIG. 15 is a flowchart of a subprogram carried out in the calculation processing of FIG. 3; FIG. 16 is an explanatory diagram of a target yaw rate; FIG. 17 is a flowchart showing another example of calculation processing carried out in a front and rear motor torque correction value calculation unit; FIG. 18 is an explanatory diagram of the action of the calculation processing of FIG. 3 and FIG. 19;

[0008] The braking / driving system of the embodiment shown in FIG. 1 includes a front motor 2F that drives the front wheels 1FL, 1FR (front axle 10F) and a rear motor 2R that drives the rear wheels 1RL, 1RR (rear axle 10R). Both the front motor 2F and the rear motor 2R are three-phase AC electric motors. Therefore, the vehicle of this embodiment is an electric four-wheel drive vehicle in which the front wheels 1FL, 1FR and the rear wheels 1RL, 1RR are driven by separate electric motors. The vehicle is equipped with a drive battery 4 that supplies power to the front motor 2F and the rear motor 2R. The battery 4 is a DC storage battery that generates high-voltage, high-current power. A front inverter 3F and a rear inverter 3R are provided to convert the DC power from the battery 4 into three-phase AC power and apply it to the front motor 2F and the rear motor 2R, respectively. The front inverter 3F and the rear inverter 3R also have the function of regenerating the front motor 2F and the rear motor 2R to charge the battery 4. When the front motor 2F and the rear motor 2R are in regenerative operation, braking force (braking torque) is applied to the front wheels 1FL, 1FR and the rear wheels 2RL, 2RR. The front inverter 3F and the rear inverter 3R can adjust the operating conditions of the front motor 2F and the rear motor 2R, such as the driving torque and braking torque, by adjusting the power applied to or regenerated from the front motor 2F and the rear motor 2R. The driving torque and braking torque of the front motor 2F and the rear motor 2R by the front inverter 3F and the rear inverter 3R can be controlled in response to command signals from a controller. In other words, the front motor 2F and the rear motor 2R can adjust the driving force or braking force of the front wheels 1FL, 1FR and the rear wheels 1RL, 1RR, respectively, in accordance with their operating conditions. The driving force and braking force are collectively referred to as the braking / driving force.

[0009] The vehicle is provided with an accelerator position sensor 5 for detecting the depression amount of the accelerator pedal and a brake pedal force sensor 6 for detecting the depression amount (push force) of the brake pedal. The vehicle is also provided with a steering angle sensor 7 for detecting the operation amount (including the operation direction) of the steering wheel. The vehicle is also provided with a yaw rate sensor 8 for detecting the yaw rate generated in the vehicle and a wheel speed sensor 16 for detecting the rotational speed (wheel speed) of the front wheels 1FL and 1FR and the rear wheels 1RL and 1RR. The vehicle is also provided with a driving characteristics selection switch 9 for selecting a driving condition of the vehicle, such as driving characteristics during cornering. The driving characteristics selection switch 9 can select, for example, a sport mode that provides sharp cornering characteristics on winding roads, an eco mode that reduces power consumption of the battery 4, or a snow mode that provides stable driving characteristics on slippery roads such as snowy roads. For example, in the sport mode, the responsiveness of the driving torque and braking torque of the front motor 2F and the rear motor 2R is enhanced, and regenerative operation is emphasized. In the eco mode, the responsiveness of the drive torque of the front motor 2F and the rear motor 2R is suppressed and regenerative operation is emphasized.In the snow mode, the drive torque and braking torque of the front motor 2F and the rear motor 2R are suppressed and regenerative operation is slightly emphasized.

[0010] The controller 11 is an electronic control unit (ECU) that controls the operating state of the front motor 2F and the rear motor 2R, particularly the braking / driving force (braking / driving torque) applied to the front wheels 1FL, 1FR and the rear wheels 1RL, 1RR. Therefore, the controller 11 includes a computer system with advanced processing capabilities. Like well-known computer systems, this computer system includes a processor 12 with advanced processing capabilities and a storage device 13 that stores information such as programs and sensor signals. The processor 12 is configured, for example, by a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage device 13 is configured by a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device 13 may also include a register, a cache memory, and a memory used as a main storage device. The arithmetic processing executed by the controller 11 is realized, for example, by the processor 12 executing a computer program stored in the storage device 13 of the controller 11. Alternatively, the arithmetic processing executed by the controller 11 may be executed by a functional logic circuit set in a general-purpose semiconductor integrated circuit. For example, the controller 11 may include a programmable logic device such as a field programmable gate array. In this embodiment, the following logic is executed by the controller 11, but, for example, the controller 11 may control only the operating states of the front motor 2F and the rear motor 2R, and the following logic may be executed by individual controllers.

[0011] 2 shows the logic of the calculation process executed by the controller 11 to calculate command values ​​for the front motor torque and rear motor torque required for the front motor 2F and rear motor 2R and output command signals. In this calculation process, a target front and rear motor torque calculation unit 14 calculates a target front motor torque and a target rear motor torque, while a front and rear motor torque correction value calculation unit 15 calculates a front motor torque correction value and a rear motor torque correction value. A value obtained by adding the front motor torque correction value to the target front motor torque is output as a front motor torque command value, and a value obtained by adding the rear motor torque correction value to the target rear motor torque is output as a rear motor torque command value. These front motor torque correction value and rear motor torque correction value are set depending on whether the frictional force between the vehicle (tires) and the road surface is in a grip region or a non-grip region. The word "grip" means to "hold firmly" in the English word "grip," and in light of the above, it means that the tires are firmly gripping the road surface. Therefore, in a non-grip region, the tires (vehicle) are prone to skidding. Generally, in the grip region, the cornering force of a tire is considered to be proportional to the vehicle's slip angle (region where the slip angle is small), and the proportionality coefficient is called cornering power. The vehicle's slip angle depends on the front wheel turning angle (steering angle), the vehicle's running speed, and the vehicle's acceleration / deceleration state, so the cornering force of a tire in the grip region is proportional to the driver's (operational) input. Conversely, in the non-grip region, the cornering force of a tire is not proportional to the driver's input.

[0012] As can be inferred from the above description, the target front motor torque and the target rear motor torque are reference values ​​that take into account a front motor torque correction value and a rear motor torque correction value that correspond to whether the friction between the tires and the road surface is in a grip region or a non-grip region. In this embodiment, the driver-requested braking / driving force requested by the driver is calculated based on the accelerator pedal depression amount detected by the accelerator position sensor 5 and the brake pedal depression amount (push force) detected by the brake depression force sensor 6. Filtering processing may be applied as appropriate during this calculation. The driving force of the driver-requested braking / driving force corresponds to the driving torque obtained by powering the front motor 2F and the rear motor 2R. Similarly, the braking force of the driver-requested braking / driving force corresponds to the braking torque obtained by regeneratively operating the front motor 2F and the rear motor 2R. When the driver-requested braking / driving force is calculated and set, for example, at a predetermined sampling period, the increase / decrease from the previous setting is adjusted depending on the driving mode selected by the driving characteristics selection switch 9. The driver-requested braking / driving force calculated and set in this manner is distributed to the front axle 10F and the rear axle 10R, for example, using a preset front / rear wheel braking / driving force distribution ratio, and a target front motor torque of the front motor 2F that achieves the front axle braking / driving force and a target rear motor torque of the rear motor 2R that achieves the rear axle braking / driving force are calculated and set. The front / rear wheel braking / driving force distribution ratio can be, for example, 50:50 so that the driver-requested braking / driving force is equally divided between the front axle 10F and the rear axle 10R. As in another control mode described below, the driver-requested braking / driving force can be allocated only to the rear wheels (or front wheels) when the steering wheel is not being steered, and the driver-requested braking / driving force can be distributed to both the front and rear wheels when the steering wheel is being steered. If the sum of the braking torques obtained by regeneratively operating each motor is less than the driver-requested braking force, the shortage may be compensated for by a hydraulic brake device or an electric brake device according to individual calculation processing (not shown).

[0013] Next, an example of the calculation process executed in the controller 11 as the front and rear motor torque correction value calculation unit 15 will be described with reference to the flowchart of FIG. 3 . This calculation process is executed, for example, at a predetermined sampling period. First, in step S1, necessary data is read and calculated according to the individual calculation processes described below. Next, proceeding to step S2, it is determined whether the friction force between the vehicle (tires) and the road surface is in the grip region. If it is in the grip region, proceed to step S3. If it is not, i.e., if it is in the non-grip region, proceed to step S4. In this example, the grip region is determined based on whether the difference obtained by subtracting the absolute value of the yaw rate (actual yaw rate) detected by the yaw rate sensor 8 from the absolute value of the reference yaw rate described below is equal to or less than a threshold value (e.g., 3 deg / sec). If it is equal to or less than the threshold value, it is determined to be in the grip region. If it is not equal to or less than the threshold value, it is determined to be in the non-grip region. At this time, if the snow mode is selected by the driving characteristics selection switch, the threshold value may be reduced, thereby enabling the non-grip region to be determined at an earlier timing. Note that the positive and negative values ​​of the yaw rate (actual yaw rate, target yaw rate) will be described later. In step S3, motor torque (front and rear motor torque) correction values ​​in the grip region are calculated according to individual calculation processes described later, and then the program returns. In step S4, motor torque (front and rear motor torque) correction values ​​in the non-grip region are calculated according to individual calculation processes described later, and then the program returns.

[0014] Next, the subprogram executed in step S1 of the calculation process in Fig. 3 will be described with reference to the flowchart in Fig. 4. In this calculation process, first, in step S11, the steering angle θ of the steering wheel detected by the steering angle sensor 7 and the wheel speeds Vw of the front wheels 1FL and 1FR and the rear wheels 1RL and 1RR detected by the wheel speed sensors 16 are read. Next, the process proceeds to step S12, where the vehicle traveling speed V is calculated using the wheel speeds Vw read in step S11. The traveling speed V may be calculated, for example, from the average value of the wheel speeds Vw of all the wheels, or from the average value of the remaining wheel speeds Vw excluding wheel speeds Vw that deviate from the other wheel speeds Vw, i.e., wheel speeds Vw with a large slip ratio. Other calculation methods are also applicable. Next, the process proceeds to step S13, where the reference yaw rate γ is calculated according to the following equation 1: Ｒ Calculates and returns. Ｆ is the front wheel steering angle, which is generally proportional to the steering angle θ. Also, m is the vehicle mass, I is the yaw radius of inertia, L is the wheelbase, L Ｆ is the distance from the center of gravity of the vehicle to the front axle 10F, L Ｒ is the distance from the center of gravity of the vehicle to the rear axle 10R, K Ｆ is the equivalent cornering power of the front wheels 1FL and 1FR, K Ｒ is the equivalent cornering power of the rear wheels 1RL and 1RR. Ｒ The positive and negative signs of are given according to the direction of the yaw rate γ, and this is the front wheel steering angle δ Ｆ When the actual yaw rate γ detected by the yaw rate sensor 8 is given a positive or negative sign depending on the direction of the yaw rate generated in the vehicle, the reference yaw rate γ is set to match the sign of the actual yaw rate γ. Ｒ The sign of the front wheel steering angle δ Ｆ Just match the signs.

[0015]

[0016] Next, the subprogram executed in step S3 of the calculation process in Fig. 3 will be described with reference to the flowchart in Fig. 5. In this calculation process, first, in step S31, the target slip angle β ＴThis target slip angle β Ｔ For example, when the vehicle is making a steady circular turn in the grip area as shown by the broken line in FIG. 6, the driver is gazing ahead of the vehicle, and the distance to the gaze position is defined as the forward gaze distance L Ｇ This forward gaze distance L Ｇ is expressed as the product of the vehicle's running speed V and the forward gaze time t, and the forward gaze time t is the time during which the driver can correct the vehicle's running direction (destination position), and is generally 1 to 3 seconds. If the radius of the steady circle during turning is R, since it is the grip area, R = V / γ, and the deviation ε from the turning trajectory to the forward gaze position is ε = (R ２ +L Ｇ ２ ) １／２ The angle at which this forward gaze position is returned to the turning trajectory (= steady circle) is the target slip angle β Ｔ Then, β Ｔ is small enough, so L Ｇ ・sinβ Ｔ ε, which is further expressed by the following two equations. Ｔ The sign of the front wheel steering angle δ Ｆ Match the sign of

[0017] Next, the process proceeds to step S32, and the current slip angle β is calculated according to the following three equations: Ｃ As mentioned above, the front wheel steering angle δ Ｆ If a positive or negative sign is given to the current slip angle β Ｃ Next, the process proceeds to step S33, where the target slip angle β Ｔ From the current slip angle β Ｃ Next, the process proceeds to step S34, where the target slip angle β Ｔ Current slip angle β Ｃ If the target slip angle β is outward, the process proceeds to step S35. If the target slip angle β is not outward, i.e., if the target slip angle β is inward, the process proceeds to step S37. Ｔ Current slip angle β Ｃis outward, the target slip angle β Ｔ The absolute value of the current slip angle β Ｃ In step S35, the target slip angle β is calculated by subtracting the absolute value of Ｔ Current slip angle β Ｃ is outward, the amount of decrease in front wheel braking / driving force and the amount of increase in rear wheel braking / driving force corresponding to the slip angle difference Δβ are calculated. The amount of decrease in front wheel braking / driving force and the amount of increase in rear wheel braking / driving force may be set in accordance with the so-called friction circle theory. Next, the process proceeds to step S36, where the amount of correction for the front wheel motor torque (decrease) in the grip area corresponding to the amount of decrease in front wheel braking / driving force and the amount of correction for the rear wheel motor torque (increase) in the grip area corresponding to the amount of increase in rear wheel braking / driving force are calculated, and then the process returns. In step S37, the target slip angle β is calculated. Ｔ Current slip angle β Ｃ is inward, the amount of increase in front wheel braking / driving force and the amount of decrease in rear wheel braking / driving force corresponding to the slip angle difference Δβ are calculated. These amounts of increase in front wheel braking / driving force and decrease in rear wheel braking / driving force are also set in accordance with the friction circle theory. Next, the process proceeds to step S38, where the amount of correction for increasing the front wheel motor torque (grip area) corresponding to the amount of increase in front wheel braking / driving force and the amount of correction for decreasing the rear wheel motor torque (grip area) corresponding to the amount of decrease in rear wheel braking / driving force are calculated, and then the process returns.

[0018]

[0019] Next, the subprogram executed in step S4 of the calculation process in Fig. 3 will be described with reference to the flowchart in Fig. 7. In this calculation process, first, in step S41, the reference yaw rate γ Ｒ is determined to be greater than the absolute value of the actual yaw rate γ, and the reference yaw rate γ Ｒ If the absolute value of the reference yaw rate γ is greater than the absolute value of the actual yaw rate γ, the vehicle is considered to be in an understeer state and the process proceeds to step S42, otherwise the vehicle is considered to be in an oversteer state and the process proceeds to step S46. ＲIn the case where the positive and negative signs are assigned to the actual yaw rate γ and the actual yaw rate γ, if the signs of both are the same, it may be determined that the vehicle is in an understeer state, and if the signs are different, it may be determined that the vehicle is in an oversteer state. In step S42, the understeer-corresponding target yaw rate γ is calculated according to the following four equations: ＵＳＴ Next, the process proceeds to step S43, and the understeer corresponding target yaw rate γ is calculated. ＵＳＴ The actual yaw rate γ is subtracted from the understeer yaw rate difference Δγ ＵＳ Next, the process proceeds to step S44, where the understeer yaw rate difference Δγ is calculated. ＵＳ The front wheel braking / driving force reduction amount and rear wheel braking / driving force increase amount are calculated according to the following equations. The front wheel braking / driving force reduction amount and rear wheel braking / driving force increase amount are set according to the friction circle theory. Next, the process proceeds to step S45, where an understeer-related non-grip region front wheel motor torque (decrease) correction amount is calculated according to the front wheel braking / driving force reduction amount, and an understeer-related non-grip region rear wheel motor torque (increase) correction amount is calculated according to the rear wheel braking / driving force increase amount, before returning. Meanwhile, in step S46, the oversteer-related target yaw rate γ is calculated according to the following four equations: ＯＳＴ Next, the process proceeds to step S47, where the oversteer countermeasure target yaw rate γ is calculated. ＯＳＴ Subtract the actual yaw rate γ from the oversteer yaw rate difference Δγ ＯＳ Next, the process proceeds to step S48, where the oversteer yaw rate difference Δγ is calculated. ＯＳ The system then calculates an increase in front wheel braking / driving force and a decrease in rear wheel braking / driving force corresponding to the increase in front wheel braking / driving force and the decrease in rear wheel braking / driving force, respectively. These increase in front wheel braking / driving force and decrease in rear wheel braking / driving force are also set in accordance with the friction circle theory. Next, the system proceeds to step S49, where an oversteer-related non-grip region front wheel motor torque (increase) correction amount corresponding to the increase in front wheel braking / driving force and an oversteer-related non-grip region rear wheel motor torque (decrease) correction amount corresponding to the decrease in rear wheel braking / driving force are calculated, and then the system returns.

[0020] Equation 4 is the reference yaw rate γ ＲCompared to equation 1, which calculates the reference yaw rate γ given by equation 1, a coefficient c for adjusting the gain and coefficients a and b for adjusting the response are added. Ｒ When the gain adjustment coefficient c is increased, the target yaw rate γ Ｔ On the other hand, in this example, the response adjustment coefficients a and b are set large at the same time. If the only thing needed to speed up the response was to increase the numerator coefficient a, then the target yaw rate γ Ｔ will overshoot, and at the same time, convergence will deteriorate. In order to suppress this, by also increasing the coefficient b in the denominator, overshooting will be suppressed as shown in Figure 8, and convergence will also improve. In terms of the vehicle turning state, there is a demand to suppress oversteer states more quickly than understeer states, so the coefficients a to c are set to be larger in oversteer states than in understeer states. At this time, the turning state differs depending on the acceleration / deceleration state of the vehicle. In other words, when the vehicle is accelerating, the rear wheel load is large and the front wheel load is small, so the understeer tendency increases and the oversteer tendency decreases. Therefore, during acceleration, the understeer-compatible target yaw rate γ ＵＳＴ is set large, and the target yaw rate γ ＯＳＴ Conversely, during deceleration, the rear wheel load is small and the front wheel load is large, so the understeer tendency is small and the oversteer tendency is large. Therefore, during deceleration, the understeer countermeasure target yaw rate γ ＵＳＴ is set small, and the target yaw rate γ ＯＳＴ In this case, the degree of non-grip (the degree of lack of grip) increases in proportion to, for example, the magnitude of the difference between the target yaw rate (absolute value) and the actual yaw rate (absolute value) (the absolute value of the yaw rate difference Δγ), so the understeer-compatible target yaw rate γ ＵＳＴ and oversteer target yaw rate γ ＯＳＴ The amount of change in the target yaw rate γ ＴThe gain and response in the target yaw rate γ may be adjusted by adjusting the gain adjustment coefficient c in accordance with the acceleration / deceleration state and the degree of non-grip. Ｔ Set.

[0021] According to the calculation process of FIG. 3, it is determined whether the friction force between the vehicle (tires) and the road surface is in the grip region or the non-grip region. If it is in the non-grip region, the vehicle running speed V and the front wheel steering angle δ are calculated. Ｆ Target yaw rate γ according to (∝ steering angle θ) Ｔ The front motor torque and rear motor torque, i.e., the front wheel braking / driving force and the rear wheel braking / driving force are controlled so that the target yaw rate γ is achieved. In the non-grip region, the vehicle tends to turn in an understeer or oversteer state, so these turning states are corrected or converged to approach a neutral steering state. Ｔ is the reference yaw rate in the grip area γ Ｒ Since the gain is set to be larger or the response is set to be faster than the target yaw rate γ ＯＳＴ is the target yaw rate when understeer is in progress γ ＵＳＴ Since the gain is set larger or the response is set faster than the target yaw rate γ Ｔ By adjusting the slip angle θ in accordance with the acceleration / deceleration state of the vehicle, the vehicle's understeer or oversteer state can be more accurately converged to a neutral steer state. On the other hand, in the grip region, the slip angle that makes the vehicle position at the forward gaze position coincide with the position on the turning trajectory is set as the target slip angle, and the front motor torque and rear motor torque, i.e., the front wheel braking / driving force and the rear wheel braking / driving force, are controlled to achieve this target slip angle. In the grip region, the vehicle moves in accordance with the travel speed V and the steering angle θ (∝ front wheel steering angle δ). Ｆ), but as will be explained later, due to the characteristics of a typical vehicle, the actual slip angle β that actually occurs in the vehicle changes depending on the traveling speed. Due to this change in the actual slip angle β, the driver performs corrective steering to correct the vehicle trajectory. In this embodiment, however, the current slip angle β Ｃ is the target slip angle β Ｔ Since the front wheel braking / driving force and the rear wheel braking / driving force are controlled so as to coincide with the above, corrective steering is unnecessary or almost unnecessary.

[0022] Next, a different control mode of the vehicle braking / driving force control device of this embodiment will be described using the flowchart of FIG. 9. This flowchart of FIG. 9 replaces the flowchart of FIG. 3 and is executed, for example, similarly at a predetermined sampling period. This calculation process includes steps equivalent to those of the calculation process of FIG. 3, and to avoid duplication of explanation, the same reference numerals are used to denote these steps. Note that the step numbers are therefore not in order. In this control mode, as described above, the target front motor torque and the target rear motor torque are calculated and set so that the driver-requested braking / driving force is allocated only to the rear wheels (or front wheels) when the steering wheel is not being steered, and the driver-requested braking / driving force is distributed to the front and rear wheels when the steering wheel is being steered. In this case, the front / rear braking / driving force distribution is arbitrary.

[0023] In the calculation process of FIG. 9, first, in step S0, it is determined whether the steering angle θ is not 0. If the steering angle θ is not 0, the process proceeds to step S1. If not, i.e., if the steering angle θ is 0, the process proceeds to step S7. For this determination, a dead zone for non-steering may be provided near the neutral state of the steering wheel. In step S1, as in the calculation process of FIG. 3, the subprogram of FIG. 4 is executed to read and calculate necessary data. Next, the process proceeds to step S3, as in the calculation process of FIG. 3, the subprogram of FIG. 5 is executed to calculate a grip area motor torque correction value. Next, the process proceeds to step S2', where it is determined whether the friction force between the vehicle (tires) and the road surface is in the non-grip area. If it is in the non-grip area, the process proceeds to step S4. If it is not, i.e., if it is in the grip area, the process proceeds to step S6. In this example, the non-grip area is determined based on, for example, the vehicle traveling speed V and the steering angle θ (∝ front wheel steering angle δ). Ｆ ) and determines whether the running speed V and the steering angle θ are both equal to or greater than the threshold value. If the running speed V and the steering angle θ are both equal to or greater than the threshold value, it is determined that the vehicle is in a non-grip region. ＦThe lateral acceleration generated in the vehicle, calculated by (∝ steering angle θ), has a saturation point corresponding to the frictional force between the vehicle (tires) and the road surface. For example, a calculated lateral acceleration of 0.6 G or greater is considered to be in the non-grip region. Therefore, thresholds corresponding to this saturation point of the lateral acceleration are set for the traveling speed V and the steering angle θ, and the vehicle is determined to be in the non-grip region when both the traveling speed V and the steering angle θ are equal to or greater than the thresholds. Note that when the snow mode is selected with the driving characteristics selection switch, the thresholds set for the traveling speed V and the steering angle θ are set to values ​​corresponding to a lateral acceleration of 0.4 G, for example, to enable the vehicle to be determined to be in the non-grip region at an earlier timing. In step S4, similar to the calculation process of FIG. 3, the subprogram of FIG. 7 is executed to calculate a non-grip region motor torque correction value, and then the process proceeds to step S5. Meanwhile, in step S6, both the front motor torque correction value and the rear motor torque correction value in the non-grip region are set to 0, and then the process proceeds to step S5. In step S5, the grip region motor torque correction value and the non-grip region motor torque correction value are added together to calculate a total motor torque correction value, and then the process returns. On the other hand, in step S7, the (total) front motor torque correction value and rear motor torque correction value are both set to 0, and then the process returns.

[0024] According to the calculation process of FIG. 9, even in the non-grip region, the target slip angle β Ｔ and set the target slip angle β Ｔ The current slip angle β ＣIn a grip region (or more accurately, a non-grip region) where the front and rear motor torque correction values ​​coincide with each other, a front motor torque correction value and a rear motor torque correction value are calculated, and a total motor torque correction value is calculated and set by adding these slip angle-dependent motor torque correction value and yaw rate-dependent motor torque correction value, and the target motor torque is corrected by this total motor torque correction value. Both Figures 10 and 11 show simulation results of the rear motor torque command value obtained by the calculation process of Figure 2, corrected by the rear motor torque correction value set by the calculation process of Figure 3 and the calculation process of Figure 7. In both figures, the upper half shows the rear motor torque command value (switching control) using the rear motor torque correction value calculated and set by the calculation process of Figure 3, and the lower half shows the rear motor torque command value (slip angle difference-taking control) using the (total) rear motor torque correction value calculated and set in Figure 7. The dashed lines in both figures indicate the target yaw rate γ Ｔ and the yaw rate difference Δγ between the actual yaw rate γ. In this simulation, it is assumed that the frictional force between the vehicle (tires) and the road surface changes over time from the grip region to the non-grip region, then to the grip region, then to the non-grip region, and then to the grip region, with the vehicle switching its turning direction in the intermediate grip region, and the vehicle entering an oversteer state in both non-grip regions. In all cases, the solid line indicates the rear motor torque command value, and in switching control, the dashed line indicates the yaw rate-corresponding rear motor torque command value, and the dashed two-dot line indicates the slip angle-corresponding rear motor torque command value.

[0025] This simulation shows the change in the rear motor torque command value when the friction force between the vehicle (tires) and the road surface transitions from the grip region to the non-grip region, or from the non-grip region to the grip region. That is, the target slip angle β Ｔ and the target yaw rate γ Ｔ Since the rear motor torque command value does not affect the rear motor torque switching control performed by the calculation process in Fig. 3, a step change occurs in the rear motor torque command value during this transition. On the other hand, no step change occurs in the rear motor torque command value due to the slip angle difference consideration control performed by the calculation process in Fig. 7. In this embodiment, the reference yaw rate γ ＴSince the actual yaw rate γ is determined based on whether it is equal to the yaw rate difference Δγ, the yaw rate difference Δγ becomes (almost) 0 when the vehicle transitions between the non-grip region and the grip region, and therefore the yaw rate corresponding rear motor torque correction value also becomes (almost) 0, so only the slip angle corresponding rear motor torque correction value remains at each transition. Therefore, no step-like changes occur in the rear motor torque command value due to slip angle difference consideration control. When electronic control intervenes while the vehicle is running, the driver is more sensitive to step-like control inputs, so braking / driving force control based on slip angle difference consideration control is less likely to cause discomfort.

[0026] The above describes a vehicle braking / driving force control method and control device according to an embodiment. However, the present invention is not limited to the configurations described in the above embodiment, and various modifications are possible within the scope of the present invention. For example, in the above embodiment, in the grip region, a target slip angle is set to a slip angle that aligns the vehicle position at the forward-looking position with a position on the turning trajectory, and the front motor torque and rear motor torque are corrected to achieve this target slip angle. Alternatively, the target slip angle may be set inward when the vehicle speed is in the low-speed region and outward when the vehicle speed is in the high-speed region. That is, in a typical vehicle, the slip angle actually generated by the vehicle is outward in the low-speed region and inward in the high-speed region, and this actual slip angle represents a deviation from the turning trajectory of the vehicle at the forward-looking position. Therefore, by setting the target slip angle inward in the low-speed region and outward in the high-speed region, the vehicle position at the forward-looking position can be returned to the turning trajectory. In this case, for example, the lower the vehicle speed, the larger the inward target slip angle, and the higher the speed, the larger the outward target slip angle, thereby enabling more accurate correction of positional deviation. Also, if the actual slip angle of the vehicle is known in advance, setting the target slip angle so that the slip angle becomes smaller (in absolute value) can provide the same effect.

[0027] Furthermore, in the above embodiment, a vehicle capable of controlling the braking / driving force of both the front and rear wheels has been described, but the braking / driving force control method and device of the present invention can be similarly applied to vehicles in which the braking / driving force of only the front wheels or only the rear wheels can be controlled. Furthermore, the present invention can be similarly applied to vehicles in which the braking / driving force of only the front wheels or only the rear wheels can be controlled. Because the principles of braking / driving force control remain the same, the details of the control can be determined by, for example, leaving the description related to the controllable wheels and ignoring the description related to the rear wheels, or ignoring the description related to the front wheels. Furthermore, in the above embodiment, the braking / driving force of the front and rear wheels is controlled by front wheel motor torque and rear wheel motor torque (including powering operation and regenerative operation). However, the braking / driving force control method and device of the present invention can also be applied to vehicles in which the driving force of the engine is transmitted to the front wheels and / or rear wheels, and the braking forces of the front and rear wheels are adjusted by a brake device using fluid pressure (hydraulic pressure) or a motor. Of these, the driving force corresponds to the torque of each motor during power running, and the braking force corresponds to the torque of each motor during regenerative operation, so the driving force can be controlled by the engine, and the braking force can be controlled by the brake device.

[0028] In this way, the vehicle braking / driving force control device of this embodiment determines whether the tire cornering force is in a grip region where it is proportional to the driver's input, or in a non-grip region where it is not proportional. In the grip region, the target slip angle β of the vehicle is Ｔ and calculate the current slip angle β Ｃ The target slip angle β Ｔ On the other hand, in the non-grip region, the braking / driving force of the front wheels 1FL, 1FR and / or the rear wheels 1RL, 1RR is controlled so as to approach the target yaw rate γ Ｔ is calculated, and the actual yaw rate γ occurring in the vehicle is set to the target yaw rate γ Ｔ The braking / driving force of the front wheels 1FL, 1FR and / or the rear wheels 1RL, 1RR is controlled so that the slip angle β of the vehicle approaches the target slip angle β in the grip region. Ｔ , the corrective steering is reduced, and in the non-grip region, the yaw rate γ of the vehicle approaches the target yaw rate γ Ｔ Therefore, the steering stability during cornering can be improved.

[0029] In addition, even in the non-grip region, the target slip angle β Ｔ and calculate the current slip angle β Ｃ The target slip angle β Ｔ Then, the braking / driving force of the front wheels 1FL, 1FR and / or the rear wheels 1RL, 1RR is calculated to bring the actual yaw rate γ generated in the vehicle closer to the target yaw rate γ Ｔ The braking / driving forces of the front wheels 1FL, 1FR and / or rear wheels 1RL, 1RR are controlled taking into account the braking / driving forces of the front wheels 1FL, 1FR and / or rear wheels 1RL, 1RR that are approaching the target slip angle β in the grip region. This makes it difficult for a step change to occur in the braking / driving forces of the front wheels 1FL, 1FR and / or rear wheels 1RL, 1RR when transitioning between the grip region and the non-grip region, thereby eliminating any sense of discomfort felt by the driver. Ｔ is set to an angle that makes the forward gaze position calculated from the forward gaze time and the vehicle's traveling speed V coincide with the position on the turning trajectory obtained from the yaw rate γ occurring in the vehicle and the traveling speed V. This makes it possible to eliminate in advance the driver's corrective steering in response to changes in the slip angle that actually occur in the vehicle. In addition, the target yaw rate γ in the non-grip region Ｔ is the reference yaw rate in the grip area γ Ｒ By increasing the gain for the front wheel steering angle and / or making the response faster than the target yaw rate γ, undesirable vehicle steering characteristics can be quickly corrected or converged. Ｔ If the directions are the same, the target yaw rate γ Ｔ If the gain is different, the target yaw rate γ Ｔ By making the response of γ faster, it becomes possible to converge an oversteer state more quickly than an understeer state. Also, in the non-grip region, the target yaw rate γ ＴBy adjusting the steering force, it becomes possible to more accurately correct the steering characteristics of the vehicle to a neutral steering state. Also, by controlling the braking / driving force of the front and rear wheels when there is a steering input from the driver of the vehicle, and controlling the braking / driving force of only the front wheels or the rear wheels when there is no steering input, it is possible to obtain effects such as reducing power consumption and fuel consumption during straight-ahead driving that do not require corrective steering or improvement of vehicle behavior.

[0030] 1FL, 1FR...front wheels, 1RL, 1RR...rear wheels, 2F...front (front wheel) motor, 2R...rear (rear wheel) motor, 5...accelerator opening sensor, 6...brake pedal force sensor, 7...steering angle sensor, 8...yaw rate sensor, 9...driving characteristic selection switch, 11...controller, 16...wheel speed sensor

Claims

A vehicle braking / driving force control method for controlling braking / driving force of front wheels and / or rear wheels of a vehicle, comprising: Determine whether the tire cornering force is in a grip area, where it is proportional to the driver's input, or in a non-grip area, where it is not proportional; In the grip region, a target slip angle of the vehicle is calculated, and a braking / driving force of the front wheels and / or the rear wheels is controlled so that a slip angle generated in the vehicle approaches the target slip angle; A method for controlling braking / driving force for a vehicle, comprising: calculating a target yaw rate for the vehicle in the non-grip region; and controlling the braking / driving force of the front wheels and / or rear wheels so as to bring the yaw rate generated in the vehicle closer to the target yaw rate.

2. The method for controlling braking / driving force for a vehicle according to claim 1, further comprising the steps of: calculating a target slip angle of the vehicle in the non-grip region; calculating braking / driving forces of the front wheels and / or rear wheels that bring the slip angle generated in the vehicle closer to the target slip angle; and controlling the braking / driving forces of the front wheels and / or rear wheels by taking this into account in the braking / driving forces of the front wheels and / or rear wheels that bring the yaw rate generated in the vehicle closer to the target yaw rate.

2. The method for controlling braking and driving forces for a vehicle according to claim 1, characterized in that the target slip angle in the grip area is an angle that causes a forward gaze position calculated from a forward gaze time and the vehicle's traveling speed to coincide with a position on a turning trajectory obtained from a yaw rate generated in the vehicle and the traveling speed.

2. The method for controlling braking and driving forces for a vehicle according to claim 1, wherein the target yaw rate in the non-grip region has a larger gain with respect to the front wheel steering angle and / or has a faster response than the reference yaw rate in the grip region.

2. The method for controlling braking and driving forces for a vehicle according to claim 1, further comprising: determining whether a direction of a yaw rate occurring in the vehicle in the non-grip region is the same as a direction of the target yaw rate; and, if the directions are the same, increasing a gain of the target yaw rate; and, if they are different, increasing the responsiveness of the target yaw rate.

2. The method for controlling braking / driving force for a vehicle according to claim 1, wherein the target yaw rate is adjusted in accordance with an acceleration / deceleration state of the vehicle in the non-grip region.

2. The method for controlling braking / driving force for a vehicle according to claim 1, further comprising the steps of: controlling the braking / driving force of the front wheels and the rear wheels when there is a steering input from a driver of the vehicle; and controlling the braking / driving force of only one of the front wheels or the rear wheels when there is no steering input. 　 A vehicle driving force control device that controls braking and driving forces of front and rear wheels of a vehicle, a front wheel motor capable of adjusting the braking / driving force of the front wheels according to an operating state; a rear wheel motor capable of adjusting the braking / driving force of the rear wheels according to an operating state; a controller that determines whether the cornering force of a tire is in a grip region, where it is proportional to a driver's input, or a non-grip region, where it is not proportional, calculates a target slip angle for the vehicle in the grip region, and controls the operating state of the front wheel motor and / or the rear wheel motor so as to bring the slip angle generated in the vehicle closer to the target slip angle, and calculates a target yaw rate for the vehicle in the non-grip region, and controls the operating state of the front wheel motor and / or the rear wheel motor so as to bring the yaw rate generated in the vehicle closer to the target yaw rate.

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