Vehicle behavior control device

Abstract

To achieve a stable vehicular behavior even if an own vehicle speed decreases and a grip force of a tire recovers after an under-steering tendency and / or over-steering tendency is shown.SOLUTION: A vehicular behavior controller includes executing: determining (S23) a recovery vehicle speed Sr of recovering gripping of a tire when an own vehicle while curve road traveling is determined to be under an under-steering tendency; setting estimated yaw rates y1, y2 on the basis of an own vehicle speed S and a steering angle θst when the own vehicle speed S decreases up to the recovery vehicle speed Sr (S24); setting a target yaw rate y0 when gripping recovers on the basis of a curve curvature and the recovery vehicle speed Sr; and steering control of converging a yaw rate yaw of working on an own vehicle M to a target yaw rate y0 on the basis of a difference between the estimated yaw rates y1, y2 and the target yaw rate y0 (S27-S32).SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a vehicle behavior control device that stabilizes vehicle behavior when tire grip is restored after the host vehicle exhibits a tendency toward understeer or oversteer. [Background technology]

[0002] Conventionally, there is known a vehicle dynamics control (VDC) or electronic stability control (ESC) system that controls the vehicle's behavior in a safe direction when the vehicle becomes unstable due to slippage or other reasons while traveling on a curved road, etc. When this vehicle dynamics control system detects that the vehicle is experiencing a tendency toward understeer or oversteer (hereinafter collectively referred to as "yaw behavior") while traveling on a curved road, it applies an appropriate deceleration to the drive wheels to suppress the unstable behavior.

[0003] For example, if an anti-skid system detects that a vehicle is understeering, it applies braking force to the rear wheel on the inside of a turn in a four-wheel drive vehicle, causing the vehicle to oversteer.Also, if an anti-skid system detects that a vehicle is oversteering, it applies braking force to the front wheel on the outside of a turn in a four-wheel drive vehicle, causing the vehicle to understeer.

[0004] This type of yaw behavior also occurs when driving on curved roads with a low friction coefficient (low μ roads), but even if the above-mentioned anti-skid device is activated, it is difficult to sufficiently suppress the yaw behavior because the tire grip force is low.

[0005] When driving on a curved road with low μ, and the driver turns the steering wheel to make the vehicle follow the trace line, if the vector sum of the longitudinal and lateral forces generated in the front tire (the steered wheel) reaches the limit of the friction circle, the yaw rate will saturate, making it difficult to make the vehicle follow the trace line, and the vehicle will tend to understeer or oversteer.

[0006] When the driver recognizes that the vehicle is tending to understeer, he or she will turn the steering wheel further to try to return the vehicle to the original trace line, as shown in Figure 7A. Also, when the driver is traveling on a curved road with low μ coefficient, when the driver recognizes that the vehicle is tending to oversteer, he or she will turn the steering wheel back to try to return the vehicle to the original trace line.

[0007] However, in understeer, as shown in Figure 7A, even if the driver turns the steering wheel back and increases the steering angle θst, steering becomes impossible because the yaw rate yaw [deg / s] is saturated. Also, in oversteer, as shown in Figure 7B, even if the driver turns the steering wheel back and increases the steering angle θst to countersteer, steering becomes impossible because the yaw rate yaw [deg / s] is saturated.

[0008] Generally, when a driver recognizes that the vehicle is understeering or oversteering, they release the accelerator pedal, which reduces torque due to the running resistance caused by coasting. Even if the driver keeps their foot on the accelerator pedal, the traction control system (TCS) operates and torque reduction control is carried out.

[0009] When the speed decreases while the yaw rate remains saturated, the grip of the tires on the drive wheels recovers at a certain speed. If the steering wheels are turned more or less along the trace line at that time, the recovery of tire grip will cause the vehicle behavior to become unstable.

[0010] For example, Patent Document 1 (JP 2015-143483 A) discloses a technology in which, when a driver attempts to turn the steering wheel further on a low μ road, the assist motor of an electric power steering device generates a steering reaction force that counteracts the driver's steering force, making it difficult to turn the steering wheel further. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-143483 Summary of the Invention [Problem to be solved by the invention]

[0012] However, with the technology disclosed in Patent Document 1, when the vehicle is prone to understeer and the driver tries to turn the steering wheel further to return the vehicle to the original trace line, the technology simply makes it difficult for the driver to turn the steering wheel further against his will, and the vehicle's tendency to understeer continues, causing the driver to feel uncomfortable and uneasy.

[0013] To provide a vehicle behavior control device capable of obtaining stable vehicle behavior even when the grip force of tires is recovered when the driver turns a steering wheel further or turns it back without making the driver feel uncomfortable or uneasy. [Means for solving the problem]

[0014] a steering angle detection unit that detects the steering angle of a steering wheel; a yaw rate detection unit that detects a yaw rate acting on the host vehicle; a deceleration detection unit that detects deceleration from a change in the host vehicle speed; a target yaw rate setting unit that sets a target yaw rate based on the host vehicle speed and the curve curvature; a vehicle behavior determination unit that determines whether the host vehicle is exhibiting a yaw behavior with a tendency toward understeer or oversteer from the difference between the yaw rate and the target yaw rate; and a vehicle behavior control unit that controls the behavior of the host vehicle when it is determined that the host vehicle is exhibiting the yaw behavior. In the vehicle behavior control device having a unit, the vehicle behavior control unit comprises: a grip recovery speed estimation unit that estimates a tire grip recovery vehicle speed based on the deceleration; an estimated yaw rate setting unit that sets an estimated yaw rate that will act on the host vehicle based on the host vehicle speed and the steering angle when the host vehicle speed drops to the tire grip recovery vehicle speed; a recovery target yaw rate setting unit that sets a target yaw rate at the time of grip recovery based on the curve curvature and the tire grip recovery vehicle speed; and a steering control unit that performs steering control to converge the yaw rate of the host vehicle to the grip recovery target yaw rate based on the difference between the estimated yaw rate and the target yaw rate at the time of grip recovery. [Effects of the Invention]

[0015] According to the present invention, when a vehicle exhibits yaw behavior while traveling on a curved road, the tire grip recovery speed is estimated based on the deceleration, and when the vehicle speed drops to the tire grip recovery speed, an estimated yaw rate acting on the vehicle is set based on this vehicle speed and the steering angle, a target yaw rate at the time of grip recovery is set based on the curve curvature and the tire grip recovery speed, and steering control is performed to converge the yaw rate of the vehicle to the target yaw rate at the time of grip recovery based on the difference between this estimated yaw rate and the target yaw rate at the time of grip recovery. Therefore, stable vehicle behavior can be obtained even if the tire grip force is recovered when the driver turns the steering wheel further or back, without causing the driver to feel uncomfortable or uneasy. [Brief explanation of the drawings]

[0016] [Figure 1] Schematic diagram of the vehicle's behavior control device [Figure 2] Flowchart showing a vehicle behavior recovery processing routine [Figure 3] Flowchart showing an understeer control processing routine [Figure 4] Flowchart showing oversteer control processing routine [Figure 5] Illustration of a vehicle traveling on a curve with a tendency to understeer [Figure 6] Illustration of a vehicle traveling on a curve with a tendency to oversteer [Figure 7A] A characteristic diagram showing the relationship between yaw rate and steering angle when the steering wheel is turned further with an understeer tendency [Figure 7B] A characteristic diagram showing the relationship between yaw rate and steering angle when turning the steering wheel back with an oversteer tendency DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of the present invention will be described below with reference to the drawings. In Fig. 1, a vehicle (host vehicle) M is a four-wheel drive vehicle, with left and right front wheels FL, FR and left and right rear wheels RL, RR as drive wheels, and the left and right front wheels FL, FR as steered wheels. Note that the steering direction and yaw rate of the front wheels FL, FR have different signs depending on the left and right direction, so for convenience, they will be expressed as absolute values ​​below.

[0018] The steering device 1 employs a steering-by-wire system in which the steering shaft 2a and the pinion shaft 2b are not mechanically connected. A handle 3 operated by the driver is provided at the base end of the steering shaft 2a. A reaction motor 4 is provided at the tip end of the steering shaft 2a.

[0019] This reaction motor 4 generates a pseudo steering reaction force in response to the steering operation by the driver. Also, a steering motor 5 is fixed to the base end of the pinion shaft 2b, which is independent from the steering shaft 2a. This steering motor 5 basically steers the pinion shaft 2b in synchronization with the rotation of the steering shaft 2a. Incidentally, the reaction motor 4 and steering motor 5 are fixed to the body frame.

[0020] Furthermore, the tip of the pinion shaft 2b is connected to a steering mechanism 6, such as a rack and pinion mechanism. The left and right front wheels FL, FR are connected to this steering mechanism 6 via a tie rod 7 and a front knuckle 8.

[0021] The reaction force motor 4 and the steering motor 5 described above are controlled by a driving support control unit (DSS (Driving Support System)_ECU) 11 for steering when the driver operates the steering wheel. Connected to the input side of this DSS_ECU 11 are various parameters required for behavior control by automatic steering, such as a first steering angle sensor 9a provided on the steering shaft 2a for detecting the rotation angle of the steering wheel 3 (steering wheel angle), a second steering angle sensor 9b serving as a steering angle detection unit for detecting the rotation angle of the pinion shaft 2b (steering angle), a yaw rate sensor 12 serving as a yaw rate detection unit for detecting the yaw rate acting on the host vehicle M, and a vehicle speed sensor 13 serving as a host vehicle speed detection unit for detecting the vehicle speed of the host vehicle M (host vehicle speed).

[0022] A forward recognition device 21 is provided in the front of the cabin of the host vehicle M. This forward recognition device 21 processes images of the driving environment information ahead of the host vehicle captured by an on-board camera 22 configured as a stereo camera consisting of a main camera 22a and a sub-camera 22b. For example, in lane keeping control during autonomous driving, the device recognizes the dividing lines that separate the left and right sides of the driving lane, and determines the center between the dividing lines (the center of the lane).

[0023] Furthermore, this forward recognition device 21 may be an ultrasonic sensor, millimeter wave radar, LiDAR (Light Detection and Ranging), etc. instead of a stereo camera, as long as it can recognize at least the left and right lane lines, or may be configured as a combination of these with a monocular camera.

[0024] The forward recognition device 21 and the DSS_ECU 11 are connected to each other for bidirectional communication via an in-vehicle communication line 23 such as a CAN (Controller Area Network). The forward recognition device 21 and the DSS_ECU 11 are each configured with a microcontroller including a CPU, RAM, ROM, a rewritable non-volatile memory (flash memory or EEPROM), and peripheral devices. The ROM stores programs and fixed data required for the CPU to execute various processes. The RAM serves as a work area for the CPU, and temporarily stores various data for the CPU. The CPU is also called an MPU (Microprocessor) or a processor. A GPU (Graphics Processing Unit) or a GSP (Graph Streaming Processor) may be used instead of the CPU. Alternatively, a CPU, a GPU, and a GSP may be selectively combined.

[0025] During manual driving by the driver operating the steering wheel, the DSS_ECU 11 calculates a reaction torque equivalent to the steering reaction force that the driver normally experiences based on the steering angle detected by the first steering angle sensor 9a, the steering angle angular velocity obtained by differentiating it with respect to time, and the vehicle speed detected by the vehicle speed sensor 13, and outputs a corresponding drive signal to the reaction motor 4 to apply the steering reaction force to the steering shaft 2a.

[0026] In addition, in steering control during manual driving, the DSS_ECU 11 first obtains a target steering angle corresponding to the steering wheel angle detected by the first steering angle sensor 9a, and outputs a drive signal corresponding to this target steering angle to the steering motor 5 to rotate the pinion shaft 2b and operate the steering mechanism 6 to steer the left and right front wheels FL, FR, which are steered wheels, in a predetermined direction. In addition, the DSS_ECU 11 reads the steering angle detected by the second steering angle sensor 9b and performs feedback control so that this steering angle converges to the target steering angle.

[0027] On the other hand, when lane keeping control is functioning, the DSS_ECU 11 sets a target trace line as a driving line in the center of the left and right lane markings recognized by the forward recognition device 21, and sets a target steering angle for driving the center of the host vehicle M in the vehicle width direction along the target trace line. Then, the DSS_ECU 11 outputs a drive signal corresponding to the target steering angle to the steering motor 5 to steer the left and right front wheels FL, FR in a predetermined direction. At this time, the DSS_ECU 11 performs feedback control so that the steering angle detected by the second steering angle sensor 9b converges to the target steering angle.

[0028] Incidentally, when the host vehicle M is traveling on a curved road and the host vehicle M exhibits a tendency to understeer as shown in Figure 5, the driver will steer the steering wheel 3 toward the inside of the turn (clockwise in the figure) to make the host vehicle M travel along the target trace line, even if the vehicle is in automatic driving or lane keeping control.

[0029] Similarly, when the vehicle M is traveling on a curved road and begins to oversteer as shown in Figure 6, the driver will steer (countersteer) the steering wheel 3 toward the outside of the turn (counterclockwise in the figure) to correct the vehicle M's position and make it travel along the target trace line.

[0030] However, when turning around a curved road at high speed, or when turning at medium to low speeds on a road with a low μ surface, the grip force of the tires of the left and right front wheels FL and FR, which are the steered wheels, is low and sufficient steering is not possible. In this situation, the driver tries to correct the attitude of the vehicle M by turning the steering wheel 3 further if there is a tendency for understeer, or turning the steering wheel 3 back more if there is a tendency for oversteer.

[0031] At this time, the driver releases the accelerator pedal, so the vehicle M gradually decelerates. Even if the driver depresses the accelerator pedal, the TCS operates and torque reduction control is executed. When tire grip recovers below a certain decelerating vehicle speed, the steering angles of the left and right front wheels FL, FR are turned significantly further or further back relative to the target tracing line, so that vehicle behavior suddenly becomes unstable when tire grip recovers.

[0032] The DSS_ECU 11 estimates the vehicle speed at which tire grip will be restored due to deceleration from an understeer or oversteer tendency (yaw behavior), and when the vehicle speed drops to that speed, it executes automatic steering to restore the vehicle behavior to a stable state.

[0033] The process of recovering the vehicle behavior from understeer or oversteer caused by automatic steering, which is executed by the DSS_ECU 11, is specifically executed according to a vehicle behavior recovery process routine shown in FIG.

[0034] This routine is executed at predetermined calculation intervals after the system is started up, and first, in step S1, information on the road ahead is acquired from information on the driving environment ahead of the host vehicle M, which has been captured by the on-board camera 22 of the forward recognition device 21 and subjected to predetermined image processing. This information on the road ahead includes marking lines that separate the left and right sides of the lane in which the host vehicle M is traveling.

[0035] Next, the process proceeds to step S2, where a target trace line is set in the center of the left and right lane markings included in the forward travel road information. Since the target trace line includes the curve curvature, step S2 functions as a curve curvature setting unit of the present invention.

[0036] Then, the process proceeds to step S3, where it is determined whether the lane on which the vehicle M is currently traveling is a curved road. Whether the lane on which the vehicle M is currently traveling is a curved road or not is determined, for example, by comparing the curvature (1 / R [m]) of the target trace line with a preset curved road judgment curvature, and if the curvature of the target trace line is equal to or greater than the curved road judgment curvature, it is determined to be a curved road. Alternatively, if the vehicle M is equipped with a navigation system, it may obtain information about the road on which the vehicle M is currently traveling from road map information to determine whether the road is a curved road or not.

[0037] If it is determined that the vehicle is traveling on a curved road, the process proceeds to step S4. If it is determined that the vehicle is traveling on a straight road, the process exits the routine. In step S4, the absolute value |θst(n)| of the current steering angle θst(n) detected by the second steering angle sensor 9b is compared with the absolute value |θst(n-1)| of the steering angle θst(n-1) detected in the previous calculation to determine whether the steering angle θst has been turned further.

[0038] If it is determined that the steering angle has been turned further (|θst(n)|>|θst(n-1)|), it is determined that the vehicle M is proceeding from the entrance of the curved road in the direction of a constant curvature, and the process proceeds to step S5. On the other hand, if it is determined that the steering angle θst is constant or has been turned back (|θst(n)|≦|θst(n-1)|), it is determined that the vehicle M is proceeding from the curved road in the direction of an exit of a constant curvature, and the process exits the routine.

[0039] In step S5, the absolute value |yaw(n)| of the current yaw rate yaw(n) [deg / s] detected by the yaw rate sensor 12 is compared with the absolute value |yaw(n-1)| of the yaw rate yaw(n-1) detected in the previous calculation. If |yaw(n)| > |yaw(n-1)|, it is determined that the tires of the left and right front wheels FL, FR are gripping the road surface, and the routine is terminated. On the other hand, if |yaw(n)| ≦ |yaw(n-1)|, it is determined that the tires of the left and right front wheels FL, FR are slipping and the yaw rate yaw is saturated, and the routine proceeds to step S6.

[0040] In step S6, the lane-to-lane yaw angle θyaw [deg] is calculated. The lane-to-lane yaw angle θyaw is the angle between the tangent to the target trace line, which is the driving line of the host vehicle, and the traveling direction of the center of the vehicle M in the vehicle width direction. That is, when the host vehicle M shown in FIG. 5 is in an understeer tendency, or when the host vehicle M shown in FIG. 6 is in an oversteer tendency, the intersection point between the tangent to the target trace line at the current position of the host vehicle M and the traveling direction of the center of the vehicle M in the vehicle width direction is obtained. In addition, a perpendicular line is drawn from a predetermined gaze point ahead in the traveling direction to the tangent line, and the lane-to-lane yaw angle θyaw is calculated based on the distance Lx from the intersection point to the gaze point and the distance Ly of the perpendicular line. θyaw = tan -1 (Ly / Lx) Calculated from.

[0041] Next, the process proceeds to step S7, where it is determined whether the absolute value |θyaw| of the lane-to-lane yaw angle θyaw is within a preset allowable yaw angle θy0. If |θyaw|≦θya0, it is determined that yaw behavior has not yet occurred, and the process exits the routine. On the other hand, if |θyaw|>θya0, it is determined that yaw behavior is occurring or has occurred, and the process proceeds to step S8.

[0042] In step S8, yaw motion suppression control is executed. This yaw motion suppression control performs the same control as a well-known skid prevention device (VDC). That is, first, it examines whether the oncoming lane yaw angle θyaw is outside or inside the target trace line. And when the oncoming lane yaw angle θyaw is outside the target trace line, it is determined that the host vehicle M has an understeer tendency, and braking force is applied to the rear wheel on the inside of the turn to make the host vehicle M have an oversteer tendency. On the other hand, when the oncoming lane yaw angle θyaw is inside the target trace line, it is determined that the host vehicle M has an oversteer tendency, and braking force is applied to the front wheel on the outside of the turn to make the host vehicle M have an understeer tendency.

[0043] After that, it proceeds to step S9, and in steps S9 and S10, it examines whether the yaw motion has been suppressed. That is, in step S9, first, based on the curvature of the target trace line and the host vehicle speed detected by the vehicle speed sensor 13, map data, etc. are referred to and the target yaw rate ya0 is set.

[0044] Next, the difference between the absolute value |yaw| of the yaw rate detected by the yaw rate sensor 12 and the absolute value |ya0| of the target yaw rate ya0 is obtained (|yaw| - |ya0|), and this difference is compared with a preset understeer determination value ya1. And when (|yaw| - |ya0|) < ya1, it is determined that the understeer tendency has not been suppressed, and it proceeds to step S11, where understeer control processing is executed and the routine is exited, and normal steering-by-wire steering control is performed.

[0045] Also, when |yaw| - |ya0| ≥ ya1, it branches to step S10, and the above-mentioned difference (|yaw| - |ya0|) is compared with a preset oversteer determination value ya2. And when (|yaw| - |ya0|) > ya2, it is determined that the oversteer tendency has not been suppressed, and it proceeds to step S12, where oversteer control processing is executed and the routine is exited, and normal steering-by-wire steering control is performed.

[0046] On the other hand, if ya1≦(|yaw|-|ya0|)≦ya2, it is determined that the yaw behavior is suppressed, and the routine is terminated. Therefore, steps S9 and S10 have the function of a vehicle behavior determination unit that determines whether the host vehicle M is exhibiting a yaw behavior with a tendency toward understeer or oversteer.

[0047] The understeer control processing in step S11 is executed in accordance with an understeer control processing subroutine shown in Fig. 3. The processing in step S11 and the processing in step S12, which will be described later, correspond to the vehicle behavior control unit of the present invention.

[0048] In this subroutine, first, in step S21, the vehicle speed S [m / s] detected by the vehicle speed sensor 13 is read, and in step S22, the vehicle speed S is time-differentiated to obtain the deceleration (negative acceleration) α [m / s 2 ] is calculated. This deceleration α is the torque reduction due to running resistance during coasting or the torque reduction due to control by the traction control system (TCS). Therefore, this deceleration α includes a factor of the coefficient of friction (road surface μ) between the tire and the road surface. Note that the processing in step S22 and step S42 described later corresponds to the deceleration detection unit of the present invention.

[0049] Next, the process proceeds to step S23, where the tire grip recovery vehicle speed Sr is estimated based on the deceleration α by referring to table data or using a calculation formula. As described above, the deceleration α includes a factor of road surface μ, so the vehicle speed Sr at which tire grip will recover can be estimated to some extent from the deceleration α. ​​In other words, the deceleration α and the tire grip recovery vehicle speed Sr are proportional, and if the road surface μ is low (high), the deceleration α becomes small (large), so a low (high) tire grip recovery vehicle speed Sr is estimated. This step S23 and the processing in step S43, which will be described later, correspond to the grip recovery vehicle speed estimation unit of the present invention.

[0050] Thereafter, the process proceeds to step S24, where it is determined whether or not the host vehicle speed S has reached the tire grip recovery vehicle speed Sr. If the host vehicle speed S has not yet reached the tire grip recovery vehicle speed Sr, the process waits until the host vehicle speed S reaches the tire grip recovery vehicle speed Sr.

[0051] Thereafter, when the host vehicle speed S reaches the tire grip recovery vehicle speed Sr, it is estimated that the tire grip has recovered, and the process proceeds to step S25. In step S25, first, a target yaw rate y0 when tire grip has recovered is set by referring to map data or the like, based on the curvature of the target trace line at the current position of the host vehicle M and the tire grip recovery vehicle speed Sr. In addition, an estimated yaw rate y1 when tire grip has recovered is set based on the tire grip recovery vehicle speed Sr and the steering angle θst detected by the second steering angle sensor 9b.

[0052] In understeer, the left and right front wheels FL, FR are turned slightly more in the direction of the target trace line (see FIG. 5), so this estimated yaw rate y1 is set to a value that turns the host vehicle M in the direction of the target trace line. Therefore, this step S25 and step S45 described later have the function of the estimated yaw rate setting unit and the function of the recovery target yaw rate setting unit of the present invention.

[0053] Next, in steps S25 and S26, it is checked whether the difference (|y1|-|y0|) between the absolute value |y1| of the estimated yaw rate y1 and the absolute value |y0| of the target yaw rate y0 is within the allowable value ±yα.

[0054] First, in step S25, it is determined whether the difference (|y1|-|y0|) is lower than the allowable lower limit value -yα. Then, in step S26, it is determined whether the difference (|y1|-|y0|) exceeds the allowable upper limit value yα. If it is determined that (|y1|-|y0|)<-yα, it is determined that there will be a further understeer tendency when the tire grip force recovers, and the process proceeds to step S27.

[0055] If (|y1|-|y0|)≧-yα, the process branches to step S26 to check whether the difference (|y1|-|y0|) exceeds the allowable upper limit yα. If (|y1|-|y0|)<-yα, it is determined that the vehicle will tend to oversteer when tire grip is restored, and the process proceeds to step S28.

[0056] Also, if -yα≦(|y1|-|y0|)≦y0, it is determined that the host vehicle M will travel along the target trace line when the tire grip force is recovered, and the routine is exited.

[0057] Meanwhile, when the process proceeds from step S25 to step S27, the steering increase speed |ω| corresponding to the difference (|y1|-|y0|) is calculated based on the difference (|y1|-|y0|) by referencing table data or using a calculation formula. The larger (smaller) the difference (|y1|-|y0|) is, the faster (slower) the steering increase speed |ω| is set. The larger the difference (|y1|-|y0|), the faster the steering increase speed |ω| is set, allowing unstable behavior to be suppressed earlier.

[0058] Next, the process proceeds to step S29, where the steering motor 5 is driven at an additional steering speed |ω| to increase the steering of the left and right front wheels FL, FR. After that, the process proceeds to step S30, where it is determined whether the yaw rate yaw detected by the yaw rate sensor 12 has reached the target yaw rate y0. The processes of steps S29 and S30 are repeated until the yaw rate yaw reaches the target yaw rate y0. When the yaw rate yaw reaches the target yaw rate y0 (yaw≧y0), the process stops increasing the steering of the left and right front wheels FL, FR and exits the routine.

[0059] On the other hand, when the process proceeds from step S26 to step S28, the steering return speed -|ω| corresponding to the difference (|y1|-|y0|) is calculated based on the difference (|y1|-|y0|) by referencing table data or using a calculation formula. The larger (smaller) the difference (|y1|-|y0|) is, the faster (slower) the return speed -|ω| is set to be, as the difference (|y1|-|y0|) is. The larger the difference (|y1|-|y0|), the faster the return speed -|ω| is set, allowing unstable behavior to be suppressed earlier.

[0060] Next, the process proceeds to step S31, where the steering motor 5 is driven at a steering return speed -|ω| to return the left and right front wheels FL, FR. After that, the process proceeds to step S32, where it is determined whether the yaw rate yaw detected by the yaw rate sensor 12 has reached the target yaw rate y0. The processes of steps S31 and S32 are repeated until the yaw rate yaw reaches the target yaw rate y0, and when the yaw rate yaw reaches the target yaw rate y0 (yaw≧y0), the return of the left and right front wheels FL, FR is stopped and the routine is terminated. The processes of steps S27 to S32 and the processes of steps S47 to S52, which will be described later, correspond to the steering control unit of the present invention.

[0061] The steering motor 5 operates regardless of the driver's will, and a reaction force corresponding to the driver's steering operation is applied to the steering wheel 3 by the reaction motor 4. Therefore, the driver does not feel uncomfortable even when the steering motor 5 is driven.

[0062] The oversteer control process in step S12 in FIG. 2 is executed in accordance with an oversteer control process subroutine shown in FIG.

[0063] In this subroutine, steps S41 to S44 are the same as steps S21 to S24 of the understeer control processing subroutine described above.

[0064] Then, in step S45, the target yaw rate y0 is set by referencing map data or the like based on the curvature of the target trace line at the current position of the vehicle M and the tire grip recovery vehicle speed Sr. Also, an estimated yaw rate y2 when tire grip force is recovered is set based on the tire grip recovery vehicle speed Sr and the steering angle θst detected by the second steering angle sensor 9b. In oversteer, the left and right front wheels FL, FR are steered somewhat counter-steered toward the target trace line (see FIG. 6), so this estimated yaw rate y2 is set to a value that turns the vehicle M toward the target trace line.

[0065] Next, in steps S45 and S46, it is checked whether the difference (|y2|-|y0|) between the absolute value |y2| of the estimated yaw rate y2 and the absolute value |y0| of the target yaw rate y0 is within the allowable value ±yα.

[0066] First, in step S45, it is determined whether the difference (|y2|-|y0|) is lower than the allowable lower limit value -yα. Then, in step S46, it is determined whether the difference (|y2|-|y0|) exceeds the allowable upper limit value yα. If it is determined that (|y2|-|y0|)<-yα, it is determined that there will be a further tendency for oversteer when the tire grip force recovers, and the process proceeds to step S47.

[0067] If (|y2|-|y0|)≧-yα, the process branches to step S46 to check whether the difference (|y2|-|y0|) exceeds the allowable upper limit yα. If (|y21|-|y0|)<-yα, it is determined that the vehicle will tend to oversteer when tire grip is restored, and the process proceeds to step S48.

[0068] Also, if -yα≦(|y2|-|y0|)≦yα, it is determined that the host vehicle M will travel along the target trace line when the tire grip force is recovered, and the routine is exited.

[0069] Meanwhile, when the process proceeds from step S45 to step S47, the steering increase speed |ω| corresponding to the difference (|y2|-|y0|) is calculated based on the difference (|y2|-|y0|) by referencing table data or using a calculation formula. The larger (smaller) the difference (|y2|-|y0|) is, the faster (slower) the steering increase speed |ω| is set. The larger the difference (|y2|-|y0|), the faster the steering increase speed |ω| is set, allowing unstable behavior to be suppressed earlier.

[0070] Next, the process proceeds to step S49, where the steering motor 5 is driven at an increasing steering speed |ω| to increase the steering of the left and right front wheels FL, FR.

[0071] Thereafter, the process proceeds to step S50, where, similarly to step S30 of the understeer control processing subroutine described above, it is checked whether the yaw rate yaw detected by the yaw rate sensor 12 has reached the target yaw rate y0, and the processes of steps S49 and S50 are repeated until the yaw rate yaw reaches the target yaw rate y0. Then, when the yaw rate yaw has reached the target yaw rate y0 (yaw≧y0), the steering of the left and right front wheels FL, FR is stopped, and the routine is exited.

[0072] On the other hand, when the process proceeds from step S46 to step S48, the steering return speed -|ω| corresponding to the difference (|y2|-|y0|) is calculated based on the difference (|y2|-|y0|) by referencing table data or using a calculation formula. The larger (smaller) the difference (|y2|-|y0|) is, the faster (slower) the return speed -|ω| is set to be, as the difference (|y2|-|y0|) is. The larger the difference (|y2|-|y0|), the faster the return speed -|ω| is set, allowing unstable behavior to be suppressed earlier.

[0073] Next, the process proceeds to step S51, where the steering motor 5 is driven at a steering return speed -|ω| to return the left and right front wheels FL, FR. Thereafter, the process proceeds to step S52, where, similar to step S32 of the understeer control processing subroutine described above, it is checked whether the yaw rate yaw detected by the yaw rate sensor 12 has reached the target yaw rate y0. The processes of steps S51 and S52 are repeated until the yaw rate yaw reaches the target yaw rate y0. When the yaw rate yaw reaches the target yaw rate y0 (yaw≧y0), the process of returning the left and right front wheels FL, FR is stopped and the routine is terminated. Note that in this case as well, the steering motor 5 operates regardless of the driver's intention, and therefore the driver does not feel uncomfortable even when the steering motor 5 is driven.

[0074] As described above, in this embodiment, when the host vehicle M is traveling on a curved road and has a tendency to understeer or oversteer, the DSS_ECU 11 calculates the vehicle speed (tire grip recovery vehicle speed) Sr at which the tire grip force will be restored based on the deceleration α of the host vehicle M. Then, when the host vehicle speed S reaches the tire grip recovery vehicle speed Sr, the DSS_ECU 11 sets the target yaw rate y0 based on the curvature of the current target trace line and the tire grip recovery vehicle speed Sr.

[0075] Furthermore, the estimated yaw rates y1 and y2 when the tire grip force is recovered are calculated based on the tire grip recovery vehicle speed Sr and the steering angle θst detected by the second steering angle sensor 9b.Then, the left and right front wheels FL and FR are turned further or turned back so that the estimated yaw rates y1 and y2 fall within a predetermined tolerance ±α with respect to the target yaw rate y0.

[0076] As a result, when the grip force of the tires is restored, the behavior of the host vehicle M can be restored in the determined state. Furthermore, since a steering-by-wire system is employed in which the reaction force acting on the steering wheel 3 held by the driver is driven by the reaction motor 4 and the left and right front wheels FL, FR are driven by the steering motor 5, the driver's steering operation is not hindered, and stable vehicle behavior can be obtained even if the grip force of the tires is restored when the driver turns the steering wheel further or back, thereby preventing the driver from feeling uncomfortable or uneasy.

[0077] The present invention is not limited to the above-described embodiment, and the present invention can be applied to, for example, whether the vehicle M is a front-wheel drive vehicle or a rear-wheel drive vehicle. Also, a steering-by-wire system may be adopted by connecting and disconnecting the steering shaft 2a and the pinion shaft 2b with a multi-plate clutch. In this case, a reaction force is applied to the steering wheel 3 by adjusting the frictional force of the multi-plate clutch. [Explanation of symbols]

[0078] 1...Steering device, 2a...Steering shaft, 2b...Pinion shaft, 3...Handle, 4...Reaction motor, 5...Steering motor, 6...Steering mechanism, 7...tie rod, 8...Front knuckle, 11...Driver assistance control unit (DSS_ECU), 12...Yaw rate sensor, 13... Vehicle speed sensor, 21...Forward recognition device, 22...In-car camera, 22a...Main camera, 22b...Sub camera, 23...In-vehicle communication line, FL, FR…Left and right front wheels, Lx,Ly…distance, M...own vehicle, RL, RR...Left and right rear wheels, S...Vehicle speed, Sr... Tire grip recovery speed, y0: target yaw rate, y0...tolerance value, y1,y2...Estimated yaw rate, ya0: target yaw rate, ya1...understeer judgment value, ya2...oversteer judgment value, yaw...yaw rate, ±yα...tolerance value, α...Deceleration, θy0: Allowable yaw angle θyaw: yaw angle relative to the lane θst: Steering angle

Claims

1. a host vehicle speed detection unit that detects a host vehicle speed; a curve curvature setting unit that sets a curve curvature based on a driving line on which the host vehicle is traveling; a steering angle detection unit that detects the steering angle of the steering wheels; a yaw rate detection unit that detects a yaw rate acting on the host vehicle; a deceleration detection unit that detects deceleration from a change in the host vehicle speed; a target yaw rate setting unit that sets a target yaw rate based on the host vehicle speed and the curve curvature; a vehicle behavior determination unit that determines whether the host vehicle is exhibiting a yaw behavior that tends to understeer or oversteer based on a difference between the yaw rate and the target yaw rate; a vehicle behavior control unit that controls the behavior of the host vehicle when it is determined that the host vehicle is in the yaw behavior; In a vehicle behavior control device comprising: The vehicle behavior control unit a grip recovery vehicle speed estimation unit that estimates a tire grip recovery vehicle speed based on the deceleration; an estimated yaw rate setting unit that sets an estimated yaw rate acting on the host vehicle based on the host vehicle speed and the steering angle when the host vehicle speed decreases to the tire grip recovery vehicle speed; a recovery target yaw rate setting unit that sets a target yaw rate at the time of grip recovery based on the curve curvature and the tire grip recovery vehicle speed; a steering control unit that performs steering control to converge the yaw rate of the host vehicle to the target yaw rate at the time of grip recovery based on the difference between the estimated yaw rate and the target yaw rate at the time of grip recovery; A vehicle behavior control device comprising:

2. The steering control unit sets a steering speed that causes the yaw rate of the host vehicle to converge to the target yaw rate when grip is recovered, based on a difference between the estimated yaw rate and the target yaw rate when grip is recovered.

2. The vehicle behavior control device according to claim 1.

3. The steering control unit increases the steering angle when the estimated yaw rate is smaller than the target yaw rate at the time of grip recovery.

3. The vehicle behavior control device according to claim 1 or 2.

4. The steering control unit turns back the steering angle when the estimated yaw rate is greater than the target yaw rate at the time of grip recovery.

4. The vehicle behavior control device according to claim 1, wherein the vehicle behavior control device is a vehicle control device.

5. The steering control unit controls the steering with a steering motor that is independent of the steering wheel side.

5. The vehicle behavior control device according to claim 1, wherein the vehicle behavior control device is a vehicle control device.

Images