Vehicle turning behavior control system

Abstract

To provide a turning behavior control device of a vehicle which can efficiently decrease, when detecting a strong degree of understeering, the understeering at an early stage.SOLUTION: A travel control unit 6 outputs, when deflection between a standard yaw rate at the time of turning of an own vehicle M and the yaw rate detected by a yaw rate detection part exceeds a deflection reference value set in advance so that occurrence of a strong degree of understeering is determined in an early stage, a signal to a liquid pressure supplying part so as to apply brake force to right and left front wheels in addition to a turning inner rear wheel.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a vehicle turning behavior control device configured to efficiently reduce a large degree of understeer occurring in a vehicle at an initial stage.

Background Art

[0002] In traveling trajectory control as automatic steering control (also referred to as "lane keeping control"), when the deviation between the target traveling trajectory of a vehicle and the actual traveling trajectory of the vehicle becomes large, the steering wheel is steered and feedback control is performed so that the actual traveling trajectory converges to the target traveling trajectory. For example, when the turning radius of the actual traveling trajectory of the vehicle becomes larger than the turning radius set as the target traveling trajectory and the difference becomes large, the degree of understeer acting on the vehicle becomes strong. Therefore, the steering control device tries to correct the turning radius to the side of the turning radius set as the target traveling trajectory by steering the steering wheel in the increasing direction.

[0003] However, for example, when the front wheels are steering wheels and drive wheels, the ground contact load of the inner front wheel during turning decreases due to the lateral load transfer acting on the vehicle during turning. Therefore, even if the inner front wheel during turning is steered in the increasing direction, the lateral force of the inner front wheel during turning does not sufficiently increase, and the necessary yaw moment cannot be applied to the vehicle. As a result, it becomes difficult to converge the actual traveling trajectory of the vehicle to the target traveling trajectory.

[0004] As a countermeasure, for example, in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2020-50024), when the deviation between the reference yaw rate (target yaw rate) of the vehicle and the actual yaw rate during turning exceeds a preset deviation reference value and the time change rate of the deviation exceeds a start reference value, a braking force is applied to the drive wheel on the inner side of the turn to generate a load transfer from the drive wheel on the outer side of the turn to the drive wheel on the inner side of the turn, thereby increasing the ground contact load of the drive wheel on the inner side of the turn.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-50024 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Incidentally, in the initial stages when a strong degree of understeer is detected, applying a transient load transfer to the inner front wheel, which is the drive wheel, can efficiently reduce the degree of understeer.

[0007] However, the technology disclosed in Patent Document 1 merely applies a constant braking force to the inner drive wheel when a strong degree of understeer is detected, thereby generating a static load transfer from the outer drive wheel to the inner drive wheel. As a result, it is difficult to efficiently reduce the degree of understeer in the initial stages. Consequently, there is a delay in the control to reduce the degree of understeer, causing discomfort to passengers, including the driver.

[0008] The present invention aims to provide a vehicle turning behavior control device that can efficiently reduce the degree of strong understeer at an early stage when it is detected, thereby reducing discomfort to passengers, including the driver. [Means for solving the problem]

[0009] The present invention provides a vehicle turning behavior control device comprising: a yaw rate detection unit for detecting the yaw rate acting on the vehicle; front and rear suspensions having anti-dive and anti-lift geometries; a brake system for independently applying braking force to the left and right front wheels and left and right rear wheels; a hydraulic pressure supply unit for supplying brake fluid pressure to the brake system; and a driving control unit for controlling the brake fluid pressure supplied from the hydraulic pressure supply unit, wherein the left and right front wheels of the vehicle are both steering and driving wheels, the driving control unit includes: a deviation value calculation unit for calculating the deviation between a reference yaw rate for determining the degree of understeer during turning of the vehicle and the yaw rate detected by the yaw rate detection unit; and when the deviation calculated by the deviation value calculation unit is determined to exceed a preset deviation reference value, 、 In addition to the inner rear wheel during turning, braking force is applied to the left and right front wheels. scheduled time grant Perform turning behavior control It includes a braking force control unit. [Effects of the Invention]

[0010] According to the present invention, when it is determined that a strong degree of understeer has occurred, exceeding a preset deviation threshold, the hydraulic supply unit applies braking force to the inner rear wheel and the left and right front wheels during a turn. Therefore, even when a strong degree of understeer is detected, it can be efficiently reduced in the initial stages, thereby reducing discomfort for the driver and other passengers. [Brief explanation of the drawing]

[0011] [Figure 1] Schematic diagram of the driver assistance system installed in the vehicle. [Figure 2] Flowchart showing the turning behavior control routine [Figure 3A] An explanatory diagram showing the load transfer when braking the inner front wheel of a vehicle during a turn. [Figure 3B] Side view showing the load transfer immediately after applying braking force to the inner front wheel of the vehicle during a turn. [Figure 3C]Front view showing load transfer immediately after starting to apply braking force to the inner front wheel during vehicle turning [Figure 4A] Explanatory drawing showing load transfer when braking the inner rear wheel during vehicle turning [Figure 4B] Side view showing load transfer immediately after starting to apply braking force to the inner rear wheel during vehicle turning [Figure 4C] Front view showing load transfer immediately after starting to apply braking force to the inner rear wheel during vehicle turning [Figure 5A] Explanatory drawing showing load transfer when braking the outer front wheel during vehicle turning [Figure 5B] Side view showing load transfer immediately after starting to apply braking force to the outer front wheel during vehicle turning [Figure 5C] Front view showing load transfer immediately after starting to apply braking force to the outer front wheel during vehicle turning [Figure 6A] Explanatory drawing showing load transfer when braking the outer rear wheel during vehicle turning [Figure 6B] Side view showing load transfer immediately after starting to apply braking force to the outer rear wheel during vehicle turning [Figure 6C] Front view showing load transfer immediately after starting to apply braking force to the outer rear wheel during vehicle turning [Figure 7] Explanatory drawing showing load transfer when braking the inner front and rear wheels and the outer front wheel during vehicle turning [Figure 8] Time chart showing the braking force applied to the inner front and rear wheels and the outer front wheel immediately after detecting a strong degree of understeer [Figure 9] Time chart showing the braking force applied to the inner front and rear wheels and the outer front wheel in cooperation with the torque of the drive source immediately after detecting a strong degree of understeer [Figure 10] Time chart showing the change in the ground contact load of each wheel immediately after detecting a strong degree of understeer

Mode for Carrying Out the Invention

[0012] Hereinafter, an embodiment of the present invention will be described based on the drawings. The host vehicle M shown in FIG. 1 is a front-wheel drive vehicle in which the front wheels Fl and Fr function as steering wheels and drive wheels. The output shaft 1a of the drive source (engine or electric motor) 1 of the host vehicle M is connected in series to the drive shafts 3l and 3r of the front wheels Fl and Fr via a front differential 2. As shown in FIGS. 3B, 4B, 5B, and 6B, the left and right front wheels Fl and Fr are respectively supported by the left and right front wheel suspensions Fsus, and the left and right rear wheels Rl and Rr are respectively supported by the left and right rear wheel suspensions Rsus.

[0013] Furthermore, a hydraulic brake mechanism 4 is provided for each of the left and right front wheels Fl and Fr and the left and right rear wheels Rl and Rr. Each of these hydraulic brake mechanisms 4 is a well-known friction brake device such as a disc brake or a drum brake. The piston of the wheel cylinder is actuated by the brake hydraulic pressure supplied from a hydraulic control unit (HCU) 5 serving as a hydraulic supply unit to apply a hydraulic braking (friction braking) force. The HCU 5 includes a hydraulic generating device composed of a pressure boosting pump, an accumulator, etc., a pressure control valve that adjusts the hydraulic pressure during brake differential and supplies it to the wheel cylinder of each hydraulic brake mechanism 4, and actuators and valves such as an on-off control valve that opens and closes the hydraulic circuit for supplying brake hydraulic pressure to each hydraulic brake mechanism 4.

[0014] The HCU 5 is operated by a control signal from a driving control unit 6 serving as a driving control unit. The driving control unit 6 is composed of a microcontroller including a CPU, a RAM, a ROM, a rewritable non-volatile memory (flash memory or EEPROM), and peripheral devices. The ROM stores programs and fixed data necessary for the CPU to execute each process. The RAM is provided as a work area for the CPU, and various data in the CPU are temporarily stored. The CPU is also called a MPU (Microprocessor) or a processor. Instead of the CPU, a GPU (Graphics Processing Unit) or a GSP (Graph Streaming Processor) may be used. Alternatively, the CPU, GPU, and GSP may be selectively combined and used.

[0015] Furthermore, in addition to normal driving control, the driving control unit 6 is equipped with a turning behavior control function that restores the ground contact load of the inner front wheel during a turn, increases the lateral force of the inner front wheel during a turn, and reduces the degree of understeer. Sensors that detect the driving state of the vehicle M are connected to the input side of this driving control unit 6, including a steering angle sensor 21 that detects the steering angles of the left and right front wheels Fl and Fr, a vehicle speed sensor 22 that detects the vehicle speed (own vehicle speed) of the vehicle M, a yaw rate sensor 23 that acts as a yaw rate detection unit to detect the actual yaw rate acting on the vehicle body, and a torque sensor 24 that detects the shaft torque acting on the output shaft 1a of the drive source 1.

[0016] The turning behavior control by the driving control unit 6 reduces the degree of understeer by selectively applying braking force to each wheel Fl, Fr, Rl, and Rr according to the driving state of the vehicle M when the degree of understeer that occurs when the vehicle M is driving on a curved road is strong.

[0017] In this case, in the vehicle M, the front suspension Fsus and rear suspension Rsus have anti-dive and anti-lift geometries, respectively, in order to reduce the change in the pitch attitude of the vehicle M during braking and deceleration. That is, the instantaneous center of the left and right front wheels Fl and Fr, which are suspended from the vehicle body by the left and right front suspension Fsus, is set to be located above the contact point of each left and right front wheel Fl and Fr and behind the vehicle body. Therefore, each front suspension Fsus has an anti-dive geometry. On the other hand, the instantaneous center of the left and right rear front wheels Rl and Rr, which are suspended from the vehicle body by the left and right rear suspension Rsus, is set to be located above the contact point of each left and right rear wheel Rl and Rr and behind the vehicle body. in front of body It is set to be positioned to the side. Therefore, each rear wheel suspension Rsus is anti lift It has the following geometry. Therefore, when braking and driving forces are applied to the wheels, an upward force is exerted from the wheels on the vehicle body.

[0018] For example, applying braking force to the outer front wheel during a turn generates an upward force on the outer side of the front of the vehicle M, suppressing body roll and further increasing the ground contact load on the inner front wheel. Conversely, applying braking force to the outer rear wheel during a turn generates a downward force on the outer side of the rear of the vehicle, preventing a sufficient increase in the ground contact load on the diagonally opposite inner front wheel.

[0019] Specifically, the turning behavior control by this driving control unit 6 is performed according to the turning behavior control routine shown in Figure 2.

[0020] This routine is executed at predetermined calculation cycles after the driving control unit 6 is started. First, in step S1, it reads sensor outputs such as the steering angle detected by the steering angle sensor 21, the vehicle speed detected by the vehicle speed sensor 22, and the actual yaw rate detected by the yaw rate sensor 23.

[0021] Next, the process proceeds to step S2, where a reference yaw rate acting on the vehicle M is calculated based on the steering angle and vehicle speed, and the yaw rate deviation ΔYr is obtained from the difference between the reference yaw rate and the actual yaw rate detected by the yaw rate sensor 23. Note that the processing in this step corresponds to the deviation value calculation unit of the present invention.

[0022] Next, the process proceeds to step S3, where it is checked whether the vehicle M is in a non-braking state and turning. Whether it is braking or not is determined by whether or not a braking signal is output from the driving control unit 6 to the HCU 5. Whether or not it is turning is determined based on the output value of the yaw rate sensor 23.

[0023] If the system determines that vehicle M is not braking and is turning, proceed to step S4. If the system determines that the vehicle is braking or not turning, exit the routine.

[0024] Step S4 involves comparing the yaw rate deviation ΔYr with a pre-set deviation reference value Yrc. This deviation reference value Yrc is a reference value used to determine whether the degree of understeer occurring in the vehicle M is strong or not, and is set in advance based on experiments and other factors.

[0025] If ΔYr > Yrc, it is determined that the degree of understeer is strong, and the process proceeds to step S5. If ΔYr ≤ Yrc, it is determined that no strong degree of understeer has occurred, and the process exits the routine.

[0026] Step S5 involves determining the target yaw moment Myt required for the vehicle M to maintain driving stability based on the yaw rate deviation ΔYr, using map reference, etc. Next, step S6 involves determining the target deceleration Gxt required to reduce the current yaw moment to the target yaw moment Myt.

[0027] Next, the process proceeds to step S7, where, based on the target yaw moment Myt and target deceleration Gxt, it is determined which of the wheels Fl, Fr, Rl, and Rr should be subjected to braking force, and the target braking force Fbti for the wheels Fl, Fr, Rl, and Rr to be subjected to braking force is determined. Then, the process proceeds to step S8, where the driving control unit 6 controls the HCU5 so that the wheels Fl, Fr, Rl, and Rr to be subjected to braking force achieve their corresponding target braking force Fbti, and then exits the routine. Note that the processing in steps S4 to S8 corresponds to the braking force control unit of the present invention.

[0028] Next, we will explain the behavior when braking force is selectively applied to each wheel, Fl, Fr, Rl, and Rr. <Load transfer due to braking force being applied to the inner front wheel during a turn> As shown in Figure 3A, during a turn (left turn in the figure), the wheels Fl, Fr, Rl, and Rr of the vehicle M are in an unbraked state, the longitudinal forces Flf and Frf acting on the left and right front wheels Fl and Fr are the same, and the longitudinal forces Rlf and Rrf acting on the left and right rear wheels Rl and Rr are the same. In this state, a constant braking force is continuously applied to the inner front wheel (Fl) during the turn, as indicated by the solid arrow.

[0029] As a result, the longitudinal forces Rlf and Rrf acting on the left and right rear wheels Rl and Rr are the same, so the difference between them (Rlf-Rrf) remains 0. However, the longitudinal forces on the left and right front wheels Fl and Fr are negative because a braking force is applied to the inner front wheel (Fl) during a turn. Therefore, the difference between the longitudinal forces (Flf, Frf) between the inner front wheel (Fl) and the outer front wheel (Fr) during a turn (Flf-Frf) is a negative value. Furthermore, the longitudinal forces Flf, Frf, Rlf, and Rrf acting on each wheel Fl, Fr, Rl, and Rr are positive on the driving force side and negative on the braking force side.

[0030] As a result, as shown by the dashed arrows in Figure 3A, a load transfer occurs from the outer front wheel (Fr) to the inner front wheel (Fl), decreasing the ground contact load on the outer front wheel (Fr) and increasing the ground contact load on the inner front wheel (Fl). On the other hand, between the left and right rear wheels Rl and Rr, as shown by the dashed arrows, a load transfer occurs from the inner rear wheel (Rl) to the outer rear wheel (Rr), decreasing the ground contact load on the inner rear wheel (Rl) and increasing the ground contact load on the outer rear wheel (Rr).

[0031] This describes the case of static load transfer where a constant braking force is continuously applied to the inner front wheel (Fl) during a turn. Transient load transfer immediately after applying braking force to the inner front wheel (Fl) during a turn (approximately 0.5 seconds) exhibits different behavior. Specifically, immediately after applying braking force to the inner front wheel (Fl), as shown in Figures 3B and 3C, an upward anti-dive force is first generated in the front suspension Fsus of the inner front wheel (Fl), attempting to increase the roll angle of the vehicle body. As a result, the load transfer from the outer front wheel (Fr) to the inner front wheel (Fl) during a turn temporarily decreases. Conversely, the load transfer from the inner rear wheel (Rl) to the outer rear wheel (Rr) during a turn increases further. <Load transfer due to braking force being applied to the inner rear wheel during a turn> Furthermore, as shown by the solid arrows in Figure 4A, if a constant braking force is continuously applied to the inner rear wheel (Rl) while the vehicle M is turning, the amount of load transfer between the left and right front wheels Fl and Fr decreases, resulting in a load transfer from the outer front wheel (Fr) to the inner front wheel (Fl), as shown by the dashed arrows. Consequently, the ground contact load of the outer front wheel (Fr) decreases, and the ground contact load of the inner front wheel (Fl) increases. On the other hand, the amount of load transfer between the left and right rear wheels Rl and Rr increases, resulting in a load transfer from the inner rear wheel (Rl) to the outer rear wheel (Rr), as shown by the dashed arrows. This reduces the ground contact load of the inner rear wheel (Rl) and increases the ground contact load of the outer rear wheel (Rr).

[0032] In this case, the transient load transfer immediately after applying braking force to the inner rear wheel (Rl) exhibits different behavior. Specifically, immediately after applying braking force to the inner rear wheel (Rl), as shown in Figures 4B and 4C, a downward anti-lift force is generated in the rear suspension Rsus of the inner rear wheel (Rl), attempting to reduce the roll angle of the vehicle body. As a result, the load shifts to the front axle, the load transfer from the outer front wheel (Fr) to the inner front wheel (Fl) temporarily increases, and the ground contact load of the inner front wheel (Fl) increases. On the other hand, the load transfer from the inner rear wheel (Rl) to the outer rear wheel (Rr) decreases. <Load transfer due to braking force being applied to the outer front wheel during a turn> Furthermore, as shown by the solid arrows in Figure 5A, if a constant braking force is continuously applied to the outer front wheel (Fr) during a turn, the longitudinal forces Rlf and Rrf of the left and right rear wheels Rl and Rr are the same, but the difference between the longitudinal forces Flf and Frf of the left and right front wheels Fl and Fr (Flf-Frf) becomes a positive value. Consequently, the amount of load transfer between the left and right front wheels Fl and Fr increases, and a load transfer occurs from the inner front wheel (Fl) to the outer front wheel (Fr) during a turn, as shown by the dashed arrows. As a result, the ground contact load of the inner front wheel (Fl) decreases, and the ground contact load of the outer front wheel (Fr) increases. On the other hand, the amount of load transfer between the left and right rear wheels Rl and Rr decreases, so a load transfer occurs from the outer rear wheel (Rr) to the inner rear wheel (Rl) during a turn, as shown by the dashed arrows, and the ground contact load of the outer rear wheel (Rr) decreases, while the ground contact load of the inner rear wheel (Rl) increases.

[0033] In this case as well, the transient load transfer immediately after applying braking force to the outer front wheel (Fr) during a turn (approximately 0.5 seconds) exhibits different behavior. Specifically, immediately after applying braking force to the outer front wheel (Fr), as shown in Figures 5B and 5C, an upward anti-dive force is generated in the front suspension Fsus of the outer front wheel (Fr), attempting to reduce the roll angle of the vehicle body. As a result, the load transfer from the inner front wheel (Fl) to the outer front wheel (Fr) during a turn temporarily decreases, while the load transfer from the outer rear wheel (Rr) to the inner rear wheel (Rl) during a turn increases further. <Load transfer due to braking force being applied to the outer rear wheel during a turn> Furthermore, as shown by the solid arrow in Figure 6A, if a constant braking force is continuously applied to the outer rear wheel (Rr) of the vehicle M during a turn, the difference between the longitudinal force (Rrf) of the outer rear wheel (Rr) and the longitudinal force (Rrl) of the inner rear wheel (Rl) (Rrf-Rrl) becomes a positive value. Therefore, the amount of load transfer between the left and right front wheels Fl and Fr increases, and as shown by the dashed arrow, a load transfer occurs from the inner front wheel (Fl) to the outer front wheel (Fr), the ground contact load of the inner front wheel (Fl) decreases, and the ground contact load of the outer front wheel (Fr) increases. On the other hand, the amount of load transfer between the left and right rear wheels Rl and Rr decreases, so as shown by the dashed arrows, load transfer occurs from the outer rear wheel (Rr) to the inner rear wheel (Rl), the ground contact load on the outer rear wheel (Rr) decreases, and the ground contact load on the inner rear wheel (Rl) increases.

[0034] In this case as well, during the transient load transfer immediately after applying braking force to the outer rear wheel (Rr) during a turn, a downward anti-lift force is generated in the rear suspension Rsus of the outer rear wheel (Rr), as shown in Figures 6B and 6C, attempting to increase the roll angle of the vehicle body. Therefore, the load transfer from the inner front wheel (Fl) to the outer front wheel (Fr) during a turn temporarily increases, while the load transfer from the outer rear wheel (Rr) to the inner rear wheel (Rl) during a turn decreases.

[0035] Although the diagram uses a left turn as an example, load transfer between the inner and outer wheels during a turn occurs regardless of the turning direction of the vehicle M. Therefore, for a right turn, the left and right wheels should be reversed. <Reduction of understeer degree through the application of braking force> As explained above, when the turning behavior of the vehicle M is in a state of strong understeer, braking force is applied to the inner front and rear wheels (Fl, Rl) during the turn. This increases the ground contact load on the inner front wheel (Fl), and it can be seen that this lateral force generates a yaw moment in the turning direction for the vehicle M.

[0036] Incidentally, in situations with a high degree of understeer, the lateral force on the inner front wheel (Fl) during a turn is particularly insufficient compared to the required lateral force. Therefore, it is necessary to maximize the load transfer to the inner front wheel (Fl) during a turn due to the deceleration of the vehicle M generated by applying braking force.

[0037] Here, considering the transient changes immediately after applying braking force to any of the wheels Fl, Fr, Rl, and Rr, the load transfer to the inner front wheel (Fl) during a turn is summarized in Table 1.

[0038] [Table 1]

[0039] As is clear from Table 1, applying braking force to the inner rear wheel (Rl) during a turn can increase the ground contact load on the inner front wheel (Fl) during a turn.

[0040] Conversely, braking the outer rear wheel (Rr) during a turn reduces the ground contact load on the inner front wheel (Fr) the most. Therefore, when the degree of understeer is strong, as shown by the solid arrows in Figure 7, during cornering, in the initial state when the degree of understeer becomes strong, braking force is applied to both the inner rear wheel (Rl) and the inner and outer wheels (Fl, Fr) of the front axle. This applies an appropriate deceleration to the vehicle M and generates a moving load that maximizes the ground contact load on the inner front wheel (Fl). Furthermore, the lateral force on the inner front wheel (Fl) can be increased, efficiently reducing the degree of understeer.

[0041] Furthermore, if braking force is applied to the outer rear wheel (Rr) during a turn in order to decelerate the vehicle M, the effect of increasing the ground contact load on the inner front wheel (Fl) during a turn can be maintained by setting the braking force of the outer rear wheel (Rr) to a smaller value than that of the inner rear wheel (Rl).

[0042] Furthermore, in the case of four-wheel drive vehicles, where the front wheels Fl and Fr are the drive wheels, the braking force applied to the inner and outer wheels (Fl and Fr) of the front axle cancels out the driving force of the left and right front wheels, thereby minimizing the load on the front wheels due to braking and driving forces and maximizing the lateral force of the inner and outer wheels (Fl and Fr) of the front axle. The driving force generated in these left and right front wheels Fl and Fr can be calculated based on the shaft torque acting on the output shaft 1a of the drive source 1, which is detected by the torque sensor 24.

[0043] In other words, the driving force is, Driving force = Shaft torque × Final reduction ratio × Transmission efficiency / Tire's radius of motion This can be determined from the following. Here, if the final reduction ratio, transmission efficiency, and tire's movable radius are fixed values, the driving force is determined by the shaft torque variable, and therefore the torque sensor 24 functions as the driving force detection unit of the present invention.

[0044] Furthermore, by keeping the braking force applied to the inner and outer front axle wheels (Fl, Fr) below the maximum value considering the friction of the steering system, the change in steering force due to the difference in braking and driving forces between the inner and outer front axle wheels (Fl, Fr) can also be minimized.

[0045] Incidentally, the maximum value Δmax of the braking force difference applied to the inner and outer front axle rings (Fl, Fr) is: Δmax = Tfric·Gstr / |Lscr| Here, Tfric is the friction torque of the steering system, Gstr is the steering gear ratio, and Lscr is the scrub radius.

[0046] Table 1 above considers the transient load transfer immediately after applying braking force to any of the wheels Fl, Fr, Rl, and Rr. In this case, as shown in Figure 8, if the braking force applied to the outer front wheel (Fr) is reduced and the braking force applied to the inner front wheel (Fl) is increased after a predetermined time (t1) has elapsed since the start of braking force control (elapsed time t0), the yaw moment in the turning direction generated in the vehicle M can be gradually increased. This can also reduce the total drive torque.

[0047] Furthermore, as shown in Figure 9, when applying deceleration to the vehicle M by using the total drive torque (torque reduction of the drive source 1) control of the driving control unit 6, the braking force applied to the drive wheels (front wheels Fl and Fr in this embodiment) is reduced in coordination with the control of the drive source 1. Therefore, the driving control unit 6 is equipped with the function of a torque control unit according to the present invention.

[0048] As explained using Figures 3B and 3C, in the transient load transfer immediately after applying braking force to the inner front wheel (Fl) during a turn, an upward anti-dive force is generated in the front suspension Fsus of the outer front wheel (Fr), attempting to increase the roll angle of the vehicle body. As a result, the load transfer from the inner front wheel (Fl) to the outer front wheel (Fr) during a turn temporarily decreases.

[0049] To suppress the reduction in load transfer from the inner front wheel (Fl) to the outer front wheel (Fr) during a turn, braking force is applied to the outer wheel (Fr), as explained in Figure 5A, during the transient phase immediately after applying braking force to the inner front and rear wheels (Fl, Rl), as explained individually in Figures 3A and 4A. In other words, as shown in Figure 7, braking force is applied to the inner front and rear wheels (Fl, Rl) during a turn to generate the necessary yaw moment corresponding to the vehicle's understeer state, and braking force is also applied to the outer front wheel (Fr) during a turn to provide the vehicle with appropriate deceleration.

[0050] Furthermore, as explained using Figures 5B and 5C, by applying braking force to the outer front wheel (Fr) during a turn, the roll angle of the vehicle is reduced. As a result, the load transfer from the inner front wheel (Fl) to the outer front wheel (Fr) is temporarily reduced. Consequently, as shown in Figure 10 during the elapsed time t0-t1, the inner front wheel (Fl) rises instantaneously, and the ground contact load on the inner front wheel (Fl) is temporarily increased to its maximum. As a result, understeer and widening of the vehicle's trajectory can be effectively corrected.

[0051] The characteristics shown in Figure 10 represent the characteristics when braking force is applied to the inner front and rear wheels (Fl, Rl) and the outer front wheel (Fr) during a turn. However, in actual turning behavior control, this is only performed for a very short time t0~t1 (0.5 [sec] in this embodiment) after the braking force is applied, and after the elapsed time t1 has passed, the system returns to normal turning behavior control.

[0053] Thus, according to this embodiment, by applying braking force to the left and right wheels of the front axle in addition to the inner rear wheel during a turn, when a strong degree of understeer is detected, the vehicle M is given the necessary yaw moment in the turning direction, and the ground contact load of the inner front wheel during a turn is increased to the maximum extent, thereby effectively correcting the understeer acting on the vehicle M and the widening of the driving trajectory. As a result, the degree of strong understeer can be efficiently reduced in the early stages, thereby reducing discomfort for passengers, including the driver.

[0054] Furthermore, by making the braking force on the left and right front axle wheels approximately the same as the driving force, the cornering force of the front axle wheels can be maximized, and fluctuations in steering force can be minimized.

[0055] Furthermore, the present invention is not limited to the embodiments described above, and can also be applied to hybrid vehicles in which the drive source selectively drives both an engine and an electric motor, or both. [Explanation of Symbols]

[0056] 1... Power source, 1a... Output shaft, 2…Front differential, 3l, 3r... drive shaft, 4… Hydraulic brake mechanism, 6…Travel control unit, 21... Steering angle sensor, 22... Vehicle speed sensor, 23... Yaw rate sensor, 24... Torque sensor, Fbti…Target braking force, Flf, Frf, Rlf, Rrf…back and forth force, Fl,Fr...Front wheel, Fsus...front wheel suspension, Gxt…Target deceleration, M... Own vehicle, Myt... Target yaw moment, Rl,Rr…Left and right rear wheels, Rsus... rear wheel suspension, Yrc... Standard deviation, Δmax...maximum value, ΔYr…Yaw rate deviation

Claims

1. A yaw rate detection unit that detects the yaw rate acting on the vehicle, Front and rear wheel suspensions having anti-dive and anti-lift geometry, A braking system that applies braking force independently to the left and right front wheels and the left and right rear wheels, A hydraulic pressure supply unit that supplies brake fluid pressure to the aforementioned brake device, A travel control unit that controls the brake fluid pressure supplied from the hydraulic supply unit. A vehicle turning behavior control device comprising the left and right front wheels of the vehicle being both steering wheels and drive wheels, The aforementioned driving control unit, A deviation value calculation unit calculates the deviation between a reference yaw rate used to determine the degree of understeer of the vehicle during turning and the yaw rate detected by the yaw rate detection unit. If the deviation calculated by the deviation calculation unit determines that it exceeds a preset deviation reference value, the braking force control unit performs turning behavior control by applying braking force to the left and right front wheels in addition to the inner rear wheel for a predetermined time. A vehicle turning behavior control device characterized by comprising the following:

2. The vehicle further includes a driving force detection unit that detects the driving force acting on the vehicle, The braking force control unit, in the cornering behavior control, applies the braking force to the left and right front wheels to cancel out the driving force detected by the driving force detection unit. The vehicle turning behavior control device according to claim 1.

3. The aforementioned drive control unit further includes a torque control unit that controls the drive torque of the drive source, The torque control unit is If the deviation calculated by the deviation calculation unit determines that it exceeds a predetermined deviation standard value, Torque reduction control is performed to gradually reduce the drive torque of the drive source. The aforementioned braking force control unit, After performing the aforementioned turning behavior control, In coordination with the torque reduction control, the braking force applied to the left and right front wheels is reduced. The braking force is applied only to the rear wheel on the inside of the turn. A vehicle turning behavior control device according to claim 1 or 2.

4. After performing the turning behavior control, the braking force control unit performs control to apply braking force only to the inner front and rear wheels during the turn. A vehicle turning behavior control device according to claim 1 or 2.

5. The aforementioned drive control unit further includes a torque control unit that controls the drive torque of the drive source, The torque control unit, in coordination with the braking force control unit's control of applying braking force only to the inner front and rear wheels during a turn, gradually reduces the drive torque of the drive source. The vehicle turning behavior control device according to feature 4.

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