Vehicular braking / driving force control method and control device

Abstract

The present invention is such that, when the braking / driving force of a front wheel and / or a rear wheel of a vehicle is to be controlled, a determination is made regarding whether the cornering force of a tire is in a non-grip region that is not proportional to an operation input of a driver, and in the non-grip region, control to bring the yaw rate, generated in the vehicle, so as to approach to a target yaw rate is executed by an individual yaw rate control device, a target vehicle body slip angle of the vehicle is calculated, and the braking / driving force of the front wheel and / or the rear wheel is controlled so that the vehicle body slip angle, generated in the vehicle, approaches the target vehicle body slip angle.

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] Japanese Patent Application Laid-Open No. 2004-144994 discloses that the direction of the yaw rate generated in a vehicle is compared with the direction of the vehicle body slip angle, and if the two are in the same direction (oversteer), the driving force of the front wheels is increased, and if the two are in opposite directions (understeer), the driving force of the rear wheels is increased. It is also common to detect the yaw rate and lateral acceleration acting on the vehicle and allocate driving force to the front and rear wheels in consideration of the vehicle's turning state (oversteer, understeer) determined from the magnitude of the estimated vehicle body slip angle, thereby improving handling stability during cornering.

[0003] JP 2007-302115 A

[0004] When a vehicle is turning, the driver predicts the vehicle's movement several seconds into the future as a forward gaze position and steers (corrects) the steering so that this forward gaze position coincides with the target turning trajectory. Meanwhile, the vehicle's turning state tends to oversteer or understeer mainly in a non-grip region where the tire cornering force is not proportional to the driver's operational input. In such a non-grip region, if the vehicle's turning state, i.e., the yaw rate generated in the vehicle, is controlled by the braking / driving forces of the front and rear wheels, the driver may need to perform corrective steering so that the forward gaze position coincides with the target turning trajectory. The present invention aims to provide a vehicle braking / driving force control method and control device that can simultaneously improve handling stability during cornering in a non-grip region and reduce the need for corrective steering.

[0005] One aspect of the present invention is a vehicle equipped with a yaw rate control device capable of controlling yaw rate, which determines whether the tire cornering force is in a non-grip region that is not proportional to the driver's operational input, and, if in the non-grip region, causes the yaw rate control device to implement control to bring the yaw rate generated in the vehicle closer to a target yaw rate, calculates a target vehicle body slip angle for the vehicle, and controls the braking / driving force of the front wheels and / or rear wheels so as to bring the vehicle body slip angle closer to the target vehicle body slip angle.

[0006] According to one aspect of the present invention, the yaw rate of the vehicle in the non-grip region approaches the target yaw rate, thereby improving handling stability during cornering, and at the same time, corrective steering can be reduced by appropriately setting the target body slip angle of the vehicle in the non-grip region. The objects and advantages of the present invention are realized and achieved by using the elements and combinations thereof recited 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] 5 is a plan view showing a schematic configuration of an example of a vehicle braking / driving system according to an embodiment; FIG. 6 is a block diagram of an example of the functional configuration of a controller; FIG. 7 is a flowchart showing an example of calculation processing carried out in a front and rear motor torque correction value calculation unit; FIG. 8 is a flowchart of a subprogram carried out in the calculation processing of FIG. 3; FIG. 9 is a flowchart of a subprogram carried out in the calculation processing of FIG. 3; FIG. 10 is an explanatory diagram of a target vehicle body slip angle set in the calculation processing of FIG. 5; FIG. 11 is a flowchart of a subprogram carried out in the calculation processing of FIG. 10; FIG. 11 is an explanatory diagram of a target vehicle body slip angle set in the calculation processing of FIG. 10;

[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 applied power or regenerated power to 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 the controller 11. 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, depending on their operating conditions. The driving force and braking force are collectively referred to as the braking / driving force. The front wheels 1FL, 1FR and the rear wheels 2RL, 2RR are also provided with hydraulic brake devices 17 that can individually brake each wheel, as in existing vehicles. This hydraulic brake device 17 applies braking force to each wheel by hydraulic pressure, but instead of this hydraulic brake device, an electric brake device that applies braking force to each wheel by an electric motor can also be used.

[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, for example, 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.

[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. Note that 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] The vehicle is also provided with a brake controller 18 that can individually control the braking force of each wheel applied by hydraulic brake devices 17 provided on front wheels 1FL, 1FR and rear wheels 2RL, 2RR, and a hydraulic unit 19 that adjusts the hydraulic pressure applied to the hydraulic brake devices 17 of each wheel in response to a control signal from the brake controller 18. The hydraulic unit 19 is composed of a hydraulic pressure adjustment circuit that can not only maintain or reduce the hydraulic pressure of the hydraulic brake devices 17 of each wheel, but also increase the pressure. The brake controller 18 not only performs anti-skid control that maintains or reduces the hydraulic pressure of the hydraulic brake devices 17 of wheels whose wheel speed is too slow relative to the vehicle speed (body speed) during hydraulic braking, but also performs control (electronically controlled brake force distribution) that increases the hydraulic pressure of the hydraulic brake devices 17 of wheels whose wheel speed is too high relative to the vehicle speed (body speed) during vehicle acceleration, for example. The brake controller 18 can also perform yaw rate control, for example, to match the yaw rate generated in the vehicle with a target yaw rate corresponding to the vehicle's traveling speed and steering angle (front wheel steering angle). For example, the target yaw rate can be a reference yaw rate (described later) corresponding to the front wheel steering angle (steering angle) as is, or the reference yaw rate adjusted by a proportional gain. For example, when the vehicle is turning in an oversteer state, i.e., when the yaw rate generated in the vehicle is greater than the target yaw rate, well-known hydraulic control can be applied. For example, when the vehicle is turning in an oversteer state, i.e., when the yaw rate generated in the vehicle is greater than the target yaw rate, hydraulic pressure is applied only to the hydraulic brake device 17 of the front outer wheel. When the vehicle is turning in an understeer state, hydraulic pressure is applied to the hydraulic brake device 17 of the left and right rear wheels and the front outer wheel. When an electric brake device is used, hydraulic pressure can be read as braking force.

[0012] 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 of 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 state of friction between the vehicle (tires) and the road surface is in the grip region or the non-grip region. The word "grip" is a reference to the English word "grip" and means "to hold firmly," and in light of the above, it means that the tires are firmly gripping the road surface. Generally, in the grip region, the cornering force of a tire is considered to be proportional to the vehicle's body slip angle (region where the body slip angle is small), and the proportionality coefficient is called cornering power. The vehicle's body slip angle depends on the front wheel steering angle (steering angle), the vehicle's running speed, and the vehicle's acceleration and 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 operational input. Note that "body slip angle" refers to the angle between the direction of the vehicle body and the direction of the vehicle's velocity vector.

[0013] 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 the front motor torque correction value and the rear motor torque correction value. 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 performed 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. A target front motor torque for the front motor 2F that achieves the front axle braking / driving force and a target rear motor torque for 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. In this embodiment, 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 the latter case, the front / rear braking / driving force distribution is arbitrary. If the sum of the braking torques obtained by regeneratively operating each motor is less than the driver-requested braking force, the hydraulic brake device 17 (or an electric brake device) may compensate for the shortfall according to individual calculation processing (not shown).

[0014] 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 S0, it is determined whether the steering angle θ is not zero. If the steering angle θ is not zero, the process proceeds to step S1. If not, i.e., if the steering angle θ is zero, the process proceeds to step S6. For this determination, a dead zone for non-steering may be provided near the neutral state of the steering wheel. In step S1, necessary data is read and calculated according to individual calculation processes described below. Next, in step S2, it is determined whether the frictional force between the vehicle (tires) and the road surface is in the grip region. If it is in the grip region, the process proceeds to step S3. If it is not, i.e., if it is in the non-grip region, the process proceeds to step S4. In this example, the grip area 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 a reference yaw rate (described later) is equal to or greater than a threshold value (e.g., 3 deg / sec). If the difference is equal to or greater than the threshold value, the vehicle is determined to be in a non-grip area; otherwise, the vehicle is determined to be in a grip area. If the snow mode is selected using the driving characteristics selection switch, the threshold value may be reduced, thereby enabling the vehicle to be determined to be in a non-grip area at an earlier timing. The positive and negative yaw rates (actual yaw rate, target yaw rate) will be explained later. In step S3, motor torque (front and rear motor torque) correction values ​​for the grip area are calculated according to individual calculation processes (described later), and the process returns. In step S4, a control command is output to the brake controller 18 to match the yaw rate (actual yaw rate) generated in the vehicle with the target yaw rate, and the process then proceeds to step S5. In step S5, motor torque (front and rear motor torque) correction values ​​for the non-grip area are calculated according to individual calculation processes (described later), and the process returns. In step S6, both the front motor torque correction value and the rear motor torque correction value are set to 0, and then the process returns. The grip area is determined based on, for example, the vehicle running 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. Ｆ The lateral acceleration generated by 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 driving speed V and steering angle θ, and the vehicle is determined to be in the non-grip region when both the driving speed V and 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 driving speed V and steering angle θ are set to values ​​corresponding to a lateral acceleration of 0.4 G, for example, so that the vehicle is determined to be in the non-grip region at an earlier timing.

[0015] 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 (small) 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 Ｒis 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.

[0016]

[0017] Next, the subprogram executed in step S3 of the calculation process in Fig. 3 will be explained using the flowchart in Fig. 5. In this calculation process, first, in step S31, the target vehicle body slip angle β in the grip region is calculated. Ｔ This target vehicle 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 traveling 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 traveling direction (destination position), and is generally 1 to 3 seconds. If the radius of the steady circle during turning is R, it is the grip area, so R = V / γ Ｒ (In this case, the same applies to 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 (also called the steady circle or target turning trajectory) is the target vehicle 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

[0018] Next, the process proceeds to step S32, and the current vehicle body slip angle β in the grip region 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 vehicle slip angle β Ｃ Next, the process proceeds to step S33, where the target vehicle body slip angle β Ｔ Current vehicle slip angle β Ｃ Next, the process proceeds to step S34, where the target vehicle slip angle β Ｔ The current vehicle slip angle β Ｃ If it is outward, the process proceeds to step S35, and if it is not outward, i.e., if it is inward, the process proceeds to step S37. Ｔ The current vehicle slip angle β Ｃ is outward, the target vehicle slip angle β Ｔ The absolute value of the current vehicle slip angle β Ｃ In step S35, the target vehicle body slip angle β is calculated by subtracting the absolute value of Ｔ The current vehicle 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 are calculated according to the vehicle body slip angle difference Δβ. 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 according 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 according to the amount of increase in rear wheel braking / driving force are calculated, and then the process returns. In step S37, the target vehicle body slip angle β is calculated. Ｔ The current vehicle slip angle β Ｃis inward, the front wheel braking / driving force increase amount and rear wheel braking / driving force decrease amount corresponding to the vehicle body slip angle difference Δβ are calculated. These front wheel braking / driving force increase amount and rear wheel braking / driving force decrease amount are also set in accordance with the friction circle theory. Next, the process proceeds to step S38, where the grip area front wheel motor torque (increase) correction amount corresponding to the front wheel braking / driving force increase amount and the grip area rear wheel motor torque (decrease) correction amount corresponding to the rear wheel braking / driving force decrease amount are calculated, and then the process returns.

[0019]

[0020] Next, the subprogram executed in step S5 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 S51, the target vehicle body slip angle β' in the non-grip region is calculated. Ｔ This target vehicle body slip angle β' is calculated. Ｔ is calculated and set as follows. For example, FIG. 8 shows the forward gaze distance L when the vehicle is turning in an understeer state in the non-grip region. Ｇ The dashed arc in the figure is the target turning trajectory, and the turning radius R of this target turning trajectory is R=V / γ Ｒ In this case, the actual turning radius R' of the vehicle is expressed as R'=V / γ using the actual yaw rate γ. Ｇ is the forward gaze distance L in the grip area Ｇ The angle at which the vehicle's traveling direction is changed to match the target gaze position corresponding to the turning trajectory that is deviated from the target turning trajectory in this understeer state with a position on the target turning trajectory is defined as the target vehicle body slip angle β'. Ｔ On the other hand, FIG. 9 shows the forward gaze distance L when the vehicle is turning in an oversteer state in the non-grip region. Ｇ The actual turning radius R' of the vehicle in this case is also expressed as R' = V / γ using the actual yaw rate γ. The angle of change in the vehicle's traveling direction that causes the target gaze position based on the turning trajectory that is deviated from the target turning trajectory in this oversteer state to coincide with a position on the target turning trajectory is defined as the target vehicle body slip angle β'. ＴIn these cases, the deviation ε' from the target turning trajectory to the forward gaze position is expressed as ε'=(R' ２ +L Ｇ ２ ) １／２ -R. The deviation ε' is ε'≒L Ｇ sinβ' Ｔ Therefore, the deviation amount ε' is corrected to return the turning trajectory of the vehicle to the target turning trajectory, and the target vehicle slip angle β' is obtained. Ｔ is expressed by the following four equations.

[0021] Next, the process proceeds to step S52, and the current vehicle body slip angle β' in the non-grip region is calculated according to the following equation (5). Ｃ The current vehicle slip angle β' in the non-grip region is calculated. Ｃ is the current vehicle slip angle β in the grip area Ｃ The actual yaw rate γ and the reference yaw rate γ (in the grip area) Ｒ Next, the process proceeds to step S53, where the target vehicle body slip angle β' in the non-grip region is calculated. Ｔ to the current vehicle slip angle β' in the non-grip region Ｃ Next, the process proceeds to step S54, where the target vehicle slip angle β' is calculated. Ｔ Current vehicle slip angle β' Ｃ If it is outward, the process proceeds to step S55, and if it is not, that is, if it is inward, the process proceeds to step S57. Ｔ Current vehicle slip angle β' Ｃ is outward, the target vehicle slip angle β' Ｔ The absolute value of the current vehicle slip angle β' Ｃ In step S55, the target vehicle body slip angle β' is calculated by subtracting the absolute value of Ｔ Current vehicle slip angle β' Ｃis 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 vehicle body slip angle difference Δβ' are calculated. Next, the process proceeds to step S56, where the amount of correction for (decrease in) non-grip region front wheel motor torque corresponding to the amount of decrease in front wheel braking / driving force and the amount of correction for (increase in) non-grip region rear wheel motor torque corresponding to the amount of increase in rear wheel braking / driving force are calculated, and then the process returns. In step S57, the target vehicle body slip angle β' is calculated. Ｔ Current vehicle 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 vehicle body slip angle difference Δβ' are calculated. Next, the process proceeds to step S58, where the amount of correction for (increasing) non-grip region front wheel motor torque corresponding to the amount of increase in front wheel braking / driving force and the amount of correction for (decreasing) non-grip region rear wheel motor torque corresponding to the amount of decrease in rear wheel braking / driving force are calculated, and then the process returns. Note that the amount of change in braking / driving force follows the friction circle theory, as described above.

[0022] According to the calculation process of FIG. 3, it is determined whether the friction force between the vehicle (tire) and the road surface is in the grip region or the non-grip region. If it is in the grip region, the vehicle slip angle that matches the vehicle position at the forward gaze position with the position on the target turning trajectory is set as the target vehicle slip angle β Ｔ and the target vehicle slip angle β Ｔ In the grip region, the vehicle operates in a state where the vehicle speed V and the steering angle θ (∝ front wheel steering angle δ) are in a range of 0.05 to 1.05. Ｆ ), but as will be explained later, due to the characteristics of a typical vehicle, the actual vehicle body slip angle β that actually occurs in the vehicle changes depending on the traveling speed. Due to this change in the actual vehicle body slip angle β, the driver performs corrective steering to correct the vehicle trajectory. In this embodiment, however, the current vehicle body slip angle β Ｃ is the target vehicle slip angle β Ｔ On the other hand, when the vehicle is in the non-grip region, for example, the vehicle running speed V and the front wheel steering angle δ are controlled so that the front wheel braking / driving force and the rear wheel braking / driving force are controlled to match each other. ＦTarget yaw rate γ according to (∝ steering angle θ) Ｔ Therefore, the turning state of the vehicle in the non-grip region, such as understeer or oversteer, is corrected toward a neutral steer state. At the same time, the vehicle body slip angle that matches the vehicle position at the forward gaze position with the position on the target turning trajectory in the non-grip region is set to the target vehicle body slip angle β' in the non-grip region. Ｔ and the target vehicle body slip angle β' 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 as to achieve the above. The vehicle turning behavior is corrected toward a neutral steering state by yaw rate control by the brake controller 18, but before that, the actual turning trajectory of the vehicle may deviate from the target turning trajectory. Taking such a case into consideration, a forward gaze position is calculated according to the turning trajectory of the vehicle that deviates from the target turning trajectory, and the vehicle slip angle that matches this forward gaze position to a position on the target turning trajectory is set to the target vehicle slip angle β' in the non-grip region. Ｔ Therefore, the target vehicle body slip angle β' is set to Ｔ By controlling the front wheel braking / driving force and the rear wheel braking / driving force to achieve the above, corrective steering, including that for returning the turning trajectory of the vehicle to the target turning trajectory, becomes unnecessary or almost unnecessary.

[0023] Next, the target vehicle body slip angle β' in the non-grip region Ｔ The following formula 4' is used to calculate the current vehicle slip angle β in the grip region. Ｃ is multiplied by a proportional gain d to obtain the target vehicle body slip angle β' in the non-grip region. Ｔ This proportional gain d is, for example, as shown in FIG. Ｔ When the yaw rate difference Δγ is a positive value, the target yaw rate γ can be set using the yaw rate difference Δγ obtained by subtracting the actual yaw rate γ from the target yaw rate γ. Ｔ Since the actual yaw rate γ is insufficient relative to the target vehicle slip angle β', the proportional gain d is set to a value smaller than 1. ＴThe current vehicle slip angle β of the grip area Ｃ On the other hand, when the yaw rate difference Δγ is a negative value, the target yaw rate γ Ｔ Since the actual yaw rate γ is in an excessive oversteer state, the proportional gain d is set to a value greater than 1 to set the target vehicle slip angle β' Ｔ The current vehicle slip angle β of the grip area Ｃ In this example, the proportional gain d is set to increase linearly with an increase in the yaw rate difference Δγ. Modifications of the proportional gain d include providing a dead zone where the proportional gain d=1 when the yaw rate difference Δγ is near 0, or setting the proportional gain d so that it is saturated in a region where the absolute value of the yaw rate difference Δγ is large.

[0024] It is also possible to reflect other vehicle running conditions in the proportional gain d. For example, the component of the proportional gain corresponding to the yaw rate difference Δγ can be set as gain component a, and the gain component corresponding to the vehicle running speed V as gain component b, so that d = a x b. This gain component b corresponding to the running speed V can be set, for example, as shown in FIG. 11. In a typical vehicle, the vehicle body slip angle that actually occurs in the vehicle is outward in the low speed range and inward in the high speed range, and this actual vehicle body slip angle is, for example, the deviation from the target turning trajectory of the forward gaze position in the grip range. Therefore, the target vehicle body slip angle β' in the low speed range Ｔ By setting the target vehicle body slip angle β' inward in the low-grip region and outward in the high-speed region, it is possible to return the vehicle position at the forward gaze position to the target turning trajectory. In this case, for example, the lower the traveling speed, the larger the inward amount of the target vehicle body slip angle, and the higher the traveling speed, the larger the outward amount, so that the position deviation can be corrected more accurately. This is called the target vehicle body slip angle β' in the non-grip region. Ｔ 11, the gain component b is set to decrease linearly with an increase in the running speed V, so that the target vehicle body slip angle β' ＴIn an actual vehicle, the gain component b for the running speed V can be set to a fixed value less than 1, for example 0.8, so that the target vehicle body slip angle β' can be adjusted with respect to the change in the running speed V. Ｔ When the tendency of the vehicle body slip angle actually occurring in the vehicle as a function of running speed is considered in terms of the vehicle body slip angle gain divided by the steering angle, multiplying this vehicle body slip angle gain by d=0.8 will cause the vehicle body to turn inward relative to the actual vehicle body slip angle at low speeds and outward at high speeds, i.e., the target vehicle body slip angle β' similar to the above will be obtained. Ｔ can be set.

[0025] Furthermore, the longitudinal acceleration G of the vehicle Ｘ The component of the proportional gain corresponding to the vehicle slip angle β' is defined as the gain component c, and d can be set to d = a x c or d = a x b x c. In other words, when the vehicle is accelerating, the rear wheel load is large and the front wheel load is small, so the vehicle tends to turn outward. Conversely, when the vehicle is decelerating, the rear wheel load is small and the front wheel load is large, so the vehicle tends to turn inward. Therefore, when accelerating, the target vehicle body slip angle β' is set to Ｔ Inward, during deceleration, the target vehicle slip angle β' Ｔ By directing the wheel load from the front to the rear, the vehicle's turning trajectory can be made closer to the target turning trajectory. Ｘ As the absolute value of G increases, the longitudinal acceleration G Ｘ By setting the gain component c to increase linearly with the increase in the target vehicle body slip angle β', the target vehicle body slip angle β' increases as the acceleration increases. Ｔ The larger the deceleration, the larger the target vehicle slip angle β' Ｔ can be set outward, thereby correcting the change in the direction of the vehicle due to acceleration or deceleration.

[0026] The above describes a method and a control device for controlling braking / driving force for a vehicle 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, the braking / driving force of the front and rear wheels is controlled by the front wheel motor torque and the rear wheel motor torque (including powering operation and regenerative operation). However, the braking / driving force control method and control device of the present invention can also be applied to a vehicle in which the driving force of an engine is transmitted to the front wheels and / or the rear wheels and the braking force of the front and rear wheels is adjusted by a brake device using fluid pressure (hydraulic pressure) or a motor. Of these, the driving force corresponds to the motor torque during powering operation, and the braking force corresponds to the motor torque during regenerative operation. Therefore, the driving force can be controlled by the engine, and the braking force can be controlled by the brake device. However, in this case, a yaw rate control device, as described below, other than the brake controller 18 may be required.

[0027] In the above embodiment, the brake controller 18 capable of individually controlling the braking force of each wheel is used as a yaw rate control device for controlling the yaw rate generated in the vehicle. However, various yaw rate control devices can be used instead of the brake controller 18. Examples of such yaw rate control devices include a front wheel steering angle control device that controls the steering angle of the front wheels, and a rear wheel steering angle control device that can control the steering angle of the rear wheels and controls the steering angle of the rear wheels. In these yaw rate control devices, the control mode for matching the yaw rate generated in the vehicle to a target yaw rate can be any control mode that has been previously known or proposed. Furthermore, the braking / driving force control method and control device of the present invention can be similarly applied to those that control the braking / driving force of only the front wheels or only the rear wheels. 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. Since the principles of the braking / driving force control mode remain the same, the details of the control can be, for example, left as is for the controllable wheels and ignoring the description of the rear wheels, or ignoring the description of the front wheels.

[0028] In this way, the vehicle braking / driving force control device of this embodiment determines whether the tire cornering force is in a non-grip region that is not proportional to the driver's operational input. In the non-grip region, the actual yaw rate γ generated in the vehicle is compared with the target yaw rate γ Ｔ and outputs a control command to the brake controller 18 so as to bring the target vehicle body slip angle β' of the vehicle closer to Ｔ and calculate the current vehicle slip angle β' Ｃ Target vehicle slip angle β' Ｔ The braking / driving forces (motor torque) of the front wheels 1FL, 1FR and / or the rear wheels 1RL, 1RR are controlled so that the actual yaw rate γ of the vehicle in the non-grip region approaches the target yaw rate γ Ｔ Therefore, the steering stability during cornering is improved, and the target vehicle slip angle β' in the non-grip region is Ｔ Corrective steering can be reduced by appropriately setting

[0029] The angle at which the forward gaze position calculated from the forward gaze time, the vehicle speed, and V coincides with the position on the target turning trajectory of the vehicle is defined as the target vehicle body slip angle β'. Ｔ By doing so, it is possible to correct the forward gaze position deviation in the non-grip region and reliably bring the actual turning trajectory of the vehicle closer to the target turning trajectory. Ｆ Reference yaw rate γ according to (∝ steering angle) Ｒ By setting the target turning trajectory based on the actual yaw rate γ and the running speed V, it becomes possible to drive a turning trajectory equivalent to the turning trajectory in the grip area even in the non-grip area. Also, by setting the forward gaze position according to the turning trajectory of the vehicle obtained from the actual yaw rate γ generated in the vehicle and the running speed V, it becomes possible to reduce the amount of corrective steering to the target turning trajectory as much as possible even if the turning trajectory of the vehicle deviates from the target turning trajectory. Also, when the vehicle is in an understeer state, the current vehicle body slip angle β in the grip area Ｃ than the target vehicle slip angle β' ＴWhen the front wheel steering angle δ is set to the inside of the turn, and when the front wheel steering angle δ is set to the outside of the turn, the actual turning trajectory of the vehicle can be reliably brought closer to the target turning trajectory. Ｆ Reference yaw rate γ according to (∝ steering angle) Ｒ and the actual yaw rate γ occurring in the vehicle is determined to be equal to or greater than a predetermined threshold value, thereby making it possible to reliably determine the non-grip region. Also, by controlling the braking / driving forces of the front and rear wheels when there is a steering input from the driver of the vehicle, and controlling the braking / driving forces 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, 17...hydraulic brake device, 18...brake controller, 19...hydraulic unit

Claims

A vehicle braking / driving force control method for controlling braking / driving force of front wheels and / or rear wheels of a vehicle equipped with a yaw rate control device capable of controlling yaw rate, comprising: Determine whether the tire cornering force is in a non-grip region that is not proportional to the driver's operation input; A method for controlling braking / driving force for a vehicle, comprising the steps of: in the non-grip region, causing the yaw rate control device to control the yaw rate generated in the vehicle to approach a target yaw rate; calculating a target vehicle body slip angle for the vehicle; and controlling the braking / driving force of the front wheels and / or rear wheels so as to bring the vehicle body slip angle generated in the vehicle closer to the target vehicle body slip angle.

2. The method for controlling braking and driving forces for a vehicle according to claim 1, wherein the target vehicle body slip angle is a change angle of the vehicle's traveling direction that causes a forward gaze position calculated from a forward gaze time and a traveling speed of the vehicle to coincide with a position on a target turning trajectory of the vehicle.

3. The method for controlling braking and driving forces for a vehicle according to claim 2, wherein the target turning trajectory is obtained from a reference yaw rate of the vehicle corresponding to a steering angle or a turning angle and the traveling speed.

3. The method for controlling braking and driving forces for a vehicle according to claim 2, wherein the forward gaze position is set based on a turning trajectory of the vehicle 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, when the vehicle is in an understeer state, the target vehicle body slip angle is set to be more inwardly in a turning motion than a vehicle body slip angle of the vehicle corresponding to a steering angle or a turning angle.

2. The method for controlling braking and driving forces for a vehicle according to claim 1, wherein, when the vehicle is in an oversteer state, the target vehicle body slip angle is set to be more outwardly turned than a vehicle body slip angle of the vehicle corresponding to a steering angle or a turning angle.

2. The method for controlling braking and driving forces for a vehicle according to claim 1, characterized in that the non-grip area is determined to be in the non-grip area when a difference between a reference yaw rate of the vehicle corresponding to a steering angle or a turning angle and a yaw rate occurring in the vehicle is equal to or greater than a predetermined threshold value.

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 equipped with a yaw rate control device capable of controlling a yaw rate, 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 a cornering force of a tire is in a non-grip region that is not proportional to a driver's operational input, and, in the non-grip region, causes the yaw rate control device to implement control to bring the yaw rate generated in the vehicle closer to a target yaw rate, calculates a target vehicle body slip angle of the vehicle, and controls the operating state of the front wheel motor and / or the rear wheel motor so as to bring the vehicle body slip angle closer to the target vehicle body slip angle.

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