JP2010069984A - Drive assistance device - Google Patents

Abstract

A driving support device for appropriately setting a control sharing ratio between steering force control and braking / driving force control is provided.
A driving support device that steers a host vehicle based on environmental information in front of the host vehicle includes an environment recognition unit that recognizes an environment in front of the host vehicle, and a target steering amount of the host vehicle using the environment recognition unit. Target steering amount calculating means 140 for calculating the tire force, tire force calculating means 170 for calculating the tire force generated by the steered wheel tire, limit tire force estimating means 167 for estimating the limit tire force of the steered wheel tire, and the steering mechanism. Steering force control means 200 for controlling the applied steering force, braking / driving force control means 190 for controlling the braking / driving force difference between the left and right wheels, and steering force control means by allocating the target steering amount at a predetermined control sharing ratio. Difference between the target steering force and the braking / driving force control means, and the control sharing ratio of the braking / driving force control means to the steering force control means according to the approach of the tire force to the limit tire force. A configuration and a control distribution ratio setting means 180 for pressurizing.
[Selection] Figure 1

Description

  The present invention relates to a driving support device that steers a vehicle such as an automobile, and more particularly, to a device that appropriately sets a control sharing ratio of steering force application control to a steering mechanism and yaw moment control based on a braking / driving force difference between left and right wheels.

As driving assistance devices that steer a vehicle based on environmental information ahead of the host vehicle, a lane departure prevention device, a lane maintenance assistance device, and the like are known.
The lane departure prevention device steers the vehicle in a direction to return the vehicle to the lane center side when the tendency of the vehicle to deviate from the traveling lane is determined.
The lane keeping assist device sets a target travel position in the travel lane, and steers the host vehicle so as to travel along the target travel position.
Such steering of the vehicle is performed, for example, by applying a steering force to the steering mechanism by an actuator to steer the front wheels, or by generating a yaw moment by giving a braking / driving force difference between the left and right wheels.

For example, in Patent Document 1, when it is determined that the host vehicle may deviate from the driving lane, the control amounts of the steering control and the braking force control are calculated to calculate the steering torque and the braking force of each wheel. In the lane departure prevention device that controls the above, the degree of curvature of the curve, the degree of lane departure, the road surface gradient, and the road surface μ increase the share of steering torque control when there are few corrections, and braking force control when there are many corrections. It is described that the uncomfortable feeling to the driver is reduced by increasing the sharing.
JP 2005-178743 A

Using braking / driving force control that generates a braking / driving force difference between the left and right wheels, for example, when the road surface μ is low or during high-speed cornering, the steering wheel tire grip force approaches the tire force limit, and the steering angle Even when there is not enough room to steer the vehicle by the application, the yaw moment can be generated. However, generally, when a yaw moment is generated by braking / driving force control, acceleration / deceleration of the vehicle speed occurs, which may give the driver a feeling of strangeness.
In the case of the technique described in Patent Document 1 described above, since the control share changes for each traveling scene and environmental state, the movement of the vehicle due to the control is not stable, and the vehicle limit is sufficient. In some cases, the braking force control may be performed, which may cause the driver to feel uncomfortable.
An object of the present invention is to provide a driving support device that appropriately sets a control sharing ratio between steering force control and braking / driving force control.

The present invention solves the above-described problems by the following means.
According to a first aspect of the present invention, in a driving support device that steers the host vehicle based on environment information in front of the host vehicle, environment recognition means for recognizing the environment in front of the host vehicle, and the environment recognition unit using the environment recognition unit. Target steering amount calculating means for calculating the target steering amount, tire force calculating means for calculating the tire force generated by the steered wheel tire, limit tire force estimating means for estimating the limit tire force of the steered wheel tire, and steering mechanism Steering force control means for controlling the steering force applied to the vehicle, braking / driving force control means for controlling the braking / driving force difference between the left and right wheels, and the steering force control by allocating the target steering amount at a predetermined control sharing ratio. And setting the target braking / driving force difference of the braking / driving force control means, and the steering force control means of the braking / driving force control means according to the approach of the tire force to the limit tire force Against A driving support device, characterized in that it comprises a control distribution ratio setting means for increasing the control sharing ratio.

  According to a second aspect of the present invention, the control / sharing ratio setting means generates the braking / driving force difference by the braking / driving force control means only when the tire force exceeds a threshold value set to be smaller than the limit tire force. The driving support device according to claim 1, wherein:

  According to the present invention, the control share ratio of the braking / driving force control means with respect to the steering force control means is increased in accordance with the approach of the tire force to the limit tire force. Therefore, it is possible to prevent the driver from feeling uncomfortable due to acceleration / deceleration caused by steering the vehicle with steering force control and intervention of braking / driving force control. In addition, when the tire force is insufficient, the vehicle can be steered reliably by increasing the control sharing ratio of the braking / driving force control.

  The present invention aims to provide a driving support device that appropriately sets a control sharing ratio between steering force control and braking / driving force control, according to the approach of tire force to the friction circle limit of a steered wheel tire. It was solved by increasing the control sharing ratio of force control.

Embodiments of a driving support apparatus to which the present invention is applied will be described below.
The driving assistance device of the embodiment is provided in a four-wheeled vehicle such as a passenger car that steers the two front wheels. In the present embodiment, the vehicle is, for example, a four-wheel drive vehicle that includes a center differential that distributes torque back and forth with a predetermined base torque distribution and has a differential limiting clutch.
FIG. 1 is a diagram illustrating a system configuration of a vehicle including a driving support apparatus according to an embodiment. This driving assistance device steers the vehicle by applying a steering torque (steering force) to the steering mechanism 10 and generating a yaw moment by causing a difference in braking force between the left and right wheels. .
The steering mechanism 10 performs steering by rotating the housing H that supports the front wheel FW about a predetermined steering axis (king pin).

The steering mechanism 10 includes a steering wheel 11, a steering shaft 12, a steering gear box 13, a tie rod 14, and the like.
The steering wheel 11 is an annular operation member through which a driver inputs a steering operation.
The steering shaft 12 is a rotating shaft that transmits the rotation of the steering wheel 11 to the steering gear box 13.
The steering gear box 13 includes a rack and pinion mechanism that converts the rotational movement of the steering shaft 12 into a straight movement in the vehicle width direction.
The tie rod 14 is a shaft-like member having one end connected to the rack of the steering gear box 13 and the other end connected to the knuckle arm of the housing H. The tie rod 14 rotates the housing H by pushing and pulling the knuckle arm of the housing H to perform steering.

  The vehicle also includes an electric power steering (EPS) control unit 20, a steering control unit 30, an engine control unit 40, a transmission control unit 50, a vehicle integration unit 60, and the like.

The EPS control unit 20 comprehensively controls an electric power steering device that generates a steering assist force in accordance with a driver's steering operation. The EPS control unit 20 is connected to an electric actuator 21, a torque sensor 22, and the like.
The electric actuator 21 is, for example, an electric motor that is provided in the middle of the steering shaft 12 and applies a steering torque (steering force) to the steering mechanism 10 via a speed reduction mechanism.
The torque sensor 22 is inserted into the steering shaft 12 between the electric actuator 21 and the steering wheel 11 and detects torque acting on the steering shaft 12. Normally, the torque detected by the torque sensor 22 is substantially equal to the steering torque input to the steering wheel 11 by the driver.

The steering control unit 30 performs vehicle steering control and ABS control for individually controlling the braking force of each wheel brake. In vehicle stability control, when understeer or oversteer occurs, the braking force on the turning inner wheel side and the outer wheel side is made different to generate a yaw moment in the restoring direction. ABS control (anti-lock brake control) is for reducing and recovering the braking force of a wheel when the tendency of the wheel to lock is detected.
The steering control unit 30 is connected to a hydraulic control unit (HCU) 31, a vehicle speed sensor 32, a yaw rate sensor 33, a lateral acceleration (lateral G) sensor 34, a steering angle sensor 35, and the like.

The HCU 31 is a device that individually controls the brake fluid hydraulic pressure applied to the hydraulic service brake of each wheel. The HCU 31 includes a motor pump that pressurizes the brake fluid, a solenoid valve that adjusts the pressure applied to the caliper cylinder of each wheel, and the like.
The vehicle speed sensor 32 is provided in a housing that holds the hub bearing of each wheel, and outputs a vehicle speed pulse signal corresponding to the wheel speed. The vehicle speed pulse signal is subjected to predetermined processing, whereby the traveling speed of the vehicle can be obtained.
The yaw rate sensor 33 and the lateral G sensor 34 include a MEMS sensor that detects a rotational speed around the vertical axis of the vehicle body and a lateral acceleration, respectively.
The steering angle sensor 35 includes an encoder that detects the angular position of the steering shaft 12 (substantially equal to the angular position of the steering wheel 11).

The engine control unit 40 controls the engine, which is a driving power source for the vehicle, and its auxiliary equipment.
The engine control unit 40 is connected to an electronically controlled throttle control device (ETC) 41, a throttle opening sensor 42, an engine (E / G) rotation speed sensor 43, and the like.
The ETC 41 controls a throttle actuator that drives a throttle valve that adjusts the output of an engine (not shown). The ETC 41 drives a throttle actuator in accordance with a target throttle opening set by the engine control unit 40 based on an operation amount of an accelerator pedal (not shown).
The throttle opening sensor 42 detects the current opening θth of the throttle valve and transmits it to the engine control unit 40.
The engine rotational speed sensor 43 detects the rotational speed (engine rotational speed) Ne of the crankshaft that is the output shaft of the engine, and transmits it to the engine control unit 40.

The transmission control unit 50 controls the automatic transmission that changes the output of the engine and transmits it to the differential gear of the drive shaft. The transmission control unit 50 provides the tire force margin calculating means 160 of the steering assist control unit 100 with information necessary for calculating the transmission output torque such as the gear ratio at the current gear stage and the turbine speed Nt of the torque converter. .
The vehicle integration unit 60 controls the electrical components of the vehicle other than those related to each unit.

Further, the driving support device of the embodiment includes a steering support control unit 100 described below. The steering assistance control unit 100 steers the vehicle by applying a steering torque to the steering mechanism 10 and applying a left-right wheel braking force difference by the HCU 31, and performs steering control of the vehicle such as vehicle deviation prevention control. It is.
The steering assist control unit 100 is connected to the EPS control unit 20, the steering control unit 30, the engine control unit 40, the transmission control unit 50, and the vehicle integration unit 60 described above via an in-vehicle LAN such as a CAN communication system. Various information and signals can be acquired.

  The steering assist control unit 100 includes an environment recognition unit 110, a target travel position setting unit 120, a host vehicle traveling path estimation unit 130, a target steering amount setting unit 140, a road surface μ estimation unit 150, and a tire force margin calculation unit 160. , Control share ratio setting means 180, left and right wheel braking force difference control means 190, steering force control means 200, and the like. Each of these means may be configured as independent hardware, or a part or all of them may be configured as common hardware.

The environment recognition unit 110 recognizes the shape of the traveling lane of the host vehicle based on image information obtained by capturing the front of the host vehicle.
The environment recognition unit 110 is connected to a stereo camera 111, an image processing unit 112, and the like.
The stereo camera 111 includes, for example, a pair of main cameras and sub-cameras provided near the room mirror base at the upper end of the front window of the vehicle. Each of the main camera and the sub camera has a CCD camera. The main camera and the sub camera are installed apart from each other in the vehicle width direction. The main camera and the sub camera capture a reference image and a comparative image, respectively, and output image data related to these images to the image processing unit 112.
The image processing unit 112 performs A / D conversion on the image data of the reference image and the comparison image output from the stereo camera 111, performs predetermined image processing, and outputs the result to the environment recognition unit 110. This image processing includes, for example, correction of an attachment position error of each camera, noise removal, gradation optimization, and the like. The digitized image has, for example, a plurality of pixels arranged in a matrix in the vertical direction and the horizontal direction. Each of these pixels has a luminance value corresponding to the brightness of the subject.

  The environment recognition unit 110 detects the parallax of a pixel group that is a block composed of an arbitrary pixel or a plurality of pixels on the reference image based on the data of the reference image and the comparison image. This parallax is the amount of deviation between the position on the reference image and the position on the comparison image of a certain pixel or pixel group. Using this parallax, the distance from the vehicle to the subject corresponding to the pixel can be calculated based on the principle of triangulation.

Moreover, the environment recognition means 110 recognizes the shape of the white line etc. which are arrange | positioned at the lane both ends ahead of the own vehicle. In this specification, claims, etc., a white line means a continuous line or a broken line drawn at the end in the width direction of the lane, and the actual color is other than white (for example, amber) Includes lines.
The environment recognition unit 110 detects a pixel group of a white line portion based on pixel luminance data from reference image data. The orientation of the pixel group of the white line portion with respect to the host vehicle is detected based on the pixel position on the image data. Specifically, a region in which the pixel position in the vertical direction corresponds to the road surface is scanned in the horizontal direction, and a portion where the luminance value changes suddenly is recognized as a white line outline. Then, the position of the white line is detected by calculating the distance of the pixel group in the white line portion.
The environment recognition means 110 can continuously detect the position of the white line to set a plurality of lane candidate points in the traveling direction of the vehicle, ignore the lane candidate points that cannot be matched, and set the lane candidate points. The area that does not exist is subjected to a predetermined complement process to recognize the lane shape ahead of the host vehicle.

  The target travel position setting unit 120 sets the target travel position Xc at the center in the width direction of the travel lane of the host vehicle set by the environment recognition unit 110.

The own vehicle traveling path estimating means 130 is based on information from the environment recognizing means 110, the running state of the vehicle detected by the vehicle speed sensor 32, the yaw rate sensor 33, the rudder angle sensor 35, etc., and known vehicle specifications. The vehicle traveling path is estimated.
The own vehicle traveling path is estimated by, for example, calculating the lateral position Xe of the own vehicle OV at the gaze distance Z in front of the vehicle.
This will be described below using a coordinate system having an X-axis extending in the vehicle width direction and a Z-axis extending forward of the vehicle body with the center of gravity of the host vehicle OV as the origin.
The estimated lateral position Xe of the host vehicle's center of gravity at the gaze distance Z is obtained by the following equation 1 using the handle angle α.

In addition, the vehicle traveling path estimation unit 130 may estimate the lateral position using the yaw rate detected by the yaw rate sensor 33 as shown in the following equation 2, instead of estimating the lateral position using the steering wheel angle. it can.

Xe = Z ² γ / 2V (Formula 2)
Xe: Estimated lateral position of the center of gravity of the vehicle at the gaze distance Z [m]
Z: Gaze distance [m]
γ: vehicle yaw rate [rad / sec]

The target steering amount setting unit 140 sets a target steering amount (for example, a target yaw rate) of the host vehicle using the environment recognition unit 110, the target travel position setting unit 120, the host vehicle traveling path estimation unit 130, and the like. is there. For example, the target steering amount setting unit 140 reduces this deviation according to the deviation of the lateral position Xe of the host vehicle estimated by the host vehicle traveling path estimation unit 130 with respect to the target traveling position Xc set by the target traveling position setting unit 120. Set the target steering amount in the direction to go.
This target steering amount setting means 140 functions as a target steering amount calculation means according to the present invention.

  The road surface μ estimation means 150 estimates the friction coefficient μ of the road surface on which the host vehicle is currently traveling. Here, the method for estimating the road surface μ is not particularly limited. For example, the road surface μ can be estimated based on the vehicle state quantities such as the vehicle speed, the steering angle, the lateral acceleration, the yaw rate, and the vehicle model.

The tire force margin calculating means 160 calculates the friction circle limit and the tire force of each tire of the vehicle, and further calculates the approach degree of the tire force (tire margin) with respect to the friction circle limit.
The tire force margin calculation means 160 includes an engine torque calculation unit 161, a transmission output torque calculation unit 162, a total driving force calculation unit 163, a front and rear ground load calculation unit 164, a left wheel load ratio calculation unit 165, and each wheel ground load calculation unit 166. Each wheel friction circle limit value calculation unit 167, each wheel longitudinal force calculation unit 168, each wheel lateral force calculation unit 169, each wheel tire resultant force calculation unit 170, each wheel tire force margin calculation unit 171 and the like. ing.

  The engine torque calculation unit 161 uses the throttle opening degree θth detected by the throttle opening degree sensor 42 and the engine speed Ne detected by the engine speed sensor 43 to map a map set based on known engine characteristics. The engine torque Teg currently generated is obtained by referring to the table.

The transmission output torque calculation unit 162 calculates the output torque of the transmission using the engine speed Ne, the transmission gear ratio i, the turbine speed Nt of the torque converter, the engine torque Teg, and the like.
The output torque Tt of the transmission can be obtained by the following equation 3.

Tt = Teg · t · i (Formula 3)

Teg: Engine output torque t: Torque converter torque ratio i: Transmission gear ratio

Here, the torque ratio t of the torque converter can be obtained by referring to a map of the rotational speed ratio Nt / Ne between the turbine speed Nt and the engine speed Ne and the torque ratio t of the torque converter.

The total driving force calculation unit 163 calculates the total driving force Fx transmitted from each tire to the road surface. The total driving force Fx is obtained by the following equation 4.

Fx = Tt · η · if / Rt (Formula 4)

Tt: Transmission output torque η: Drive system transmission efficiency if: Final reduction ratio Rt: Tire radius

The front / rear ground load calculation unit 164 calculates the front wheel ground load Fzf and the rear wheel ground load Fzr using the total driving force calculation unit 163 and the like.
The front wheel ground load Fzf and the rear wheel ground load Fzr are obtained by the following formulas 5 and 6, respectively.

Fzf = Wf − ((m · (d ² x / dt ² ) · h) / L (Expression 5)
Fzr = W−Fzf (Formula 6)

Wf: front wheel static load m: vehicle mass d ² x / dt ² : longitudinal acceleration (= Fx / m)
h: Height of vehicle center of gravity L: Wheel base W: Vehicle weight (= m · G (G is gravitational acceleration))

The left wheel load ratio calculation unit 165 calculates a left wheel load ratio WR_l that is a ratio of the load applied to the left tire in the axial weight of the front and rear wheels. The left wheel load ratio WR_l is obtained by the following Expression 7.

WR — 1 = 0.5 − ((d ² y / dt ² ) / G) · (h / Ltred) (Expression 7)
WR — l: Left wheel load ratio d ² y / dt ² : Lateral acceleration G: Gravity acceleration h: Height of vehicle center of gravity Ltred: Average tread value of front and rear wheels

Each wheel ground load calculating unit 166 uses the front and rear ground load calculating unit 164 and the left wheel load ratio calculating unit 165 to calculate the left front wheel ground load Fzf_l, the right front wheel ground load Fzf_r, and the left rear wheel according to the following equations 8 to 11. The ground load Fzr_l and the right rear wheel ground load Fzr_r are calculated.

Fzf_l = Fzf · WR_l (Expression 8)
Fzf_r = Fzf · (1-WR_l) (Equation 9)
Fzr_l = Fzr · WR_l (Expression 10)
Fzr_r = Fzr. (1-WR_l) (Formula 11)

Each wheel friction circle limit value calculation unit 167 calculates the friction circle limit value of each tire using each wheel ground contact load calculation unit 166 and the road surface μ estimation means 150.
FIG. 3 is a diagram showing the relationship between the tire friction circle limit and the tire force. The horizontal axis represents the front-rear tire force, and the vertical axis represents the lateral tire force.
The friction circle is a circle determined by the friction coefficient μ of the road surface and the ground contact load Fz of the tire. The friction circle limit value, which is the radius of the friction circle, is a value obtained by multiplying the ground contact load Fz of the tire by the friction coefficient μ. It is known that the resultant force of the lateral force and the longitudinal force generated on the tire contact surface does not exceed the friction circle (does not go outside the friction circle). That is, the following expression 12 is established.

Fy ² + Fx ² ≦ (μ · Fz) ² (Expression 12)
Fy: lateral force Fx: longitudinal force μ: friction coefficient Fz: tire ground contact load

Each wheel friction circle limit value calculation unit 167 functions as a limit tire force estimation unit according to the present invention.

Each wheel longitudinal force calculation unit 168 calculates the longitudinal force generated by each tire. Each wheel longitudinal force calculation unit 168 includes a transmission output torque Tt output from the transmission output torque calculation unit 162, a tightening torque T _LSD of the differential limiting clutch in the center differential output from the transmission control unit 50, and a total driving force calculation unit 163. Based on the total driving force Fx output and the ground contact loads Fzf_l, Fzf_r, Fzr_l, Fzr_r, etc., output by each wheel ground load calculation unit 166, the left front wheel front / rear force Fxf_l, the right front wheel front / rear force Fxf_r, the left rear A wheel longitudinal force Fxr_l and a right rear wheel longitudinal force Fxr_r are calculated.

Hereinafter, an example of a calculation procedure of the left front wheel longitudinal force Fxf_l, the right front wheel longitudinal force Fxf_r, the left rear wheel longitudinal force Fxr_l, and the right rear wheel longitudinal force Fxr_r will be described.
First, the front wheel load distribution ratio WR_f is obtained by the following equation (13).

WR_f = Fzf / W (Formula 13)
WR_f: front wheel load distribution ratio Fzf: front wheel ground contact load W: vehicle weight

Next, the minimum front wheel front-rear torque Tfmin and the maximum front wheel front-rear torque Tfmax are obtained by the following expressions 14 and 15.

Tfmin = Tt · Rf_cd−T _LSD (≧ 0) (Equation 14)
Tfmax = Tt · Rf_cd + T _LSD (≧ 0) (Equation 15)

Rf_cd: Center differential base torque distribution T _LSD : Engagement torque of differential limiting clutch

Next, the minimum front wheel longitudinal force Fxfmin and the maximum front wheel longitudinal force Fxfmax are obtained by the following equations 16 and 17.

Fxfmin = Tfmin · η · if / Rt (Expression 16)
Fxfmax = Tfmax · η · if / Rt (Expression 17)

η: Transmission efficiency of drive system if: Final reduction ratio Rt: Tire radius

Then, the state is determined as follows.
(1) When WR_f ≦ Fxfmin / Fx, it is assumed that the differential limiting torque is increased on the rear wheel side, and the determination value I = 1.
(2) When WR_f ≧ Fxfmax / Fx, it is assumed that the differential limiting torque is increased on the front wheel side, and the determination value I = 3.
(3) In cases other than the above, it is determined as normal time, and the determination value I = 2.

Then, the front wheel longitudinal force Fxf is obtained by the following Expression 18 to Expression 20 according to the determination value I described above.
(1) When I = 1 Fxf = Tfmin · η · if / Rt (Equation 18)
(2) When I = 2 Fxf = Fx · WR_f (Equation 19)
(3) When I = 3 Fxf = Tfmax · η · if / Rt (Equation 20)
Further, the rear wheel longitudinal force Fxr is obtained by the following equation (21).

Fxr = Fx−Fxf (Formula 21)

The left front wheel front / rear force Fxf_l, the right front wheel front / rear force Fxf_r, the left rear wheel front / rear force Fxr_l, and the right rear wheel front / rear force Fxr_r are obtained by the following equations 22 and 23.

Fxf_l = Fxf_r = Fxf / 2 (Expression 22)
Fxr_l = Fxr_r = Fxr / 2 (Expression 23)

Each wheel lateral force calculation unit 169 calculates the lateral force generated by each tire based on lateral acceleration, vehicle speed, steering angle, yaw rate, and the like.
Each wheel lateral force calculation unit 169 outputs lateral acceleration (d ² y / dt ² ) output from the lateral acceleration sensor 34, wheel speeds ωfl, ωfr, ωrl, ωrr output from the vehicle speed sensor 32, and a yaw rate sensor 33. The yaw rate γ and the left wheel load ratio WR_l output from the left wheel load ratio calculation unit 165 are input.

The front wheel lateral force Fyf and the rear wheel lateral force Fyr are obtained by the following equations 24 and 25.

Fyf = (Iz · (dγ / dt) + m · (d ² y / dt ² ) · Lr) / L (Equation 24)
Fyr = (− Iz · (dγ / dt) + m · (d ² y / dt ² ) · Lf) / L (Equation 25)

Iz: Yaw moment of inertia of vehicle Lf: Distance between front axis and center of gravity Lr: Distance between rear axis and center of gravity m: Mass of vehicle

Further, the left front wheel lateral force Fyf_l, the right front wheel lateral force Fyf_r, the left rear wheel lateral force Fyr_l, and the right rear wheel lateral force Fyr_r are obtained by the following equations 26 to 29.

Fyf_l = Fyf · WR_l (Expression 26)
Fyf_r = Fyf. (1-WR_l) (Expression 27)
Fyr_l = Fyr · WR_l (Equation 28)
Fyr_r = Fyr. (1-WR_l) (Expression 29)

Each wheel tire resultant force calculator 170 calculates the resultant force of the longitudinal force calculated by each wheel longitudinal force calculator 168 and the lateral force calculated by each wheel lateral force calculator 169.
The left front wheel tire resultant force F_fl, the right front wheel tire resultant force F_fr, the left rear wheel tire resultant force F_rl, and the right rear wheel tire resultant force F_rr are obtained by the following Expressions 30 to 33.

F_fl = (Fxf_l ² + Fyf_l ² ) ^1/2 (Expression 30)
F_fr = (Fxf_r ² + Fyf_r ² ) ^1/2 (Expression 31)
F_rl = (Fxr_l ² + Fyr_l ² ) ^1/2 (Expression 32)
F_rr = (Fxr_r ² + Fyr_r ² ) ^1/2 (Expression 33)

Each wheel tire force margin calculating unit 171 is a difference between the friction circle limit value of each tire calculated by each wheel friction circle limit value calculating unit 167 and the tire resultant force of each tire calculated by each wheel tire resultant force calculating unit 170. Is calculated as a margin of each tire. That is, the tire force margin indicates a tire force that can be further generated without the tire exceeding the friction circle.
Of the margin of each tire, information on the left and right front wheels, which are steered wheels, is provided to the control sharing ratio setting means 180.

The control share ratio setting means 180 is based on the difference between the frictional circle limit value of each of the left and right front wheels and the tire resultant force, which is output from each wheel tire force allowance calculating unit 171 of the tire force allowance calculating means 160. A control sharing ratio R _DYC : R _STR (R _DYC + R _STR = 1) between the power difference control unit 190 and the steering force control unit 200 is set. The setting of the control sharing ratio will be described in detail later.

The left and right wheel braking force difference control means 190 controls the HCU 31 via the operation control unit 30 to generate a brake braking force difference between the left and right wheels, thereby generating a yaw moment in the vehicle. The target yaw moment generated here is set based on the target steering amount set by the target steering amount setting means 140 and the control sharing ratio set by the control sharing ratio setting means 180.
The target yaw moment is obtained by the following equation 34.

The steering force control means 200 controls the electric actuator 21 via the EPS control unit 20 and steers the vehicle by applying a steering torque to the steering mechanism 10. The target steering torque applied here is set based on the target steering amount set by the target steering amount setting unit 140 and the control sharing ratio set by the control sharing ratio setting unit 180.
The target steering torque is obtained by the following equation 35.

Hereinafter, the control sharing ratio setting between the left and right wheel braking force difference control means 190 and the steering force control means 200 in the driving assistance apparatus of the present embodiment will be described.
FIG. 4 is a flowchart showing the operation of the driving support apparatus when the control sharing ratio is set. Hereinafter, the steps will be described step by step.

<Step S01: Tire Force Calculation>
Each wheel tire resultant force calculating section 170 of the tire force margin calculating means 160 calculates the tire resultant force of the left and right front wheels that are the steered wheels.
Thereafter, the process proceeds to step S02.

<Step S02: Calculate Friction Circle Limit of Tire Force>
Each wheel friction circle limit value calculation unit 167 of the tire force margin calculation means 160 calculates the friction circle limit value of the left and right front wheels that are the steering wheels.
Thereafter, the process proceeds to step S03.

<Step S03: Determination of whether tire force exceeds threshold>
Each wheel tire force allowance calculating unit 171 of the tire force allowance calculating means 160 uses a threshold obtained by multiplying the friction circle limit value of the left and right front wheels by a predetermined safety factor a (0 <a <1) as the tire resultant force. It is determined whether it is over.
If the tire resultant force of the left and right front wheels does not exceed the threshold value as in the case of the tire resultant force F1 shown in FIG. 3, it is assumed that the tire steering force is sufficient and the target steering amount can be obtained only by the steering force control. move on. On the other hand, if the tire resultant force of at least one of the left and right front wheels exceeds the threshold value as shown in the tire resultant force F2 shown in FIG. 3, the tire force is not sufficient and an attempt is made to obtain the target steering amount only by the steering force control. In such a case, the process proceeds to step S05 assuming that there is a high possibility that the tire grip limit will be exceeded.

<Step S04: Only steering torque control is executed>
Control sharing ratio setting unit 180 sets a control distribution ratio _{R STR} of the steering force control unit 200 to 1 (100%), the control sharing ratio of the left and right wheel braking force difference control unit 190 is set to 0%. Thereby, the steering force control means 200 uses the above-described equation 35 to control the electric actuator 21 so that the target steering amount can be obtained only by applying the steering force to the steering mechanism 10 (giving the steering angle). Set the torque.
Thereafter, the process ends (returns).

<Step S05: Execution of braking force control and steering torque control>
The control sharing ratio setting unit 180 sets the control sharing ratio between the left and right wheel braking force difference control unit 190 and the steering force control unit 200 to a predetermined ratio (R _DYC > 0) set in advance.
The left and right wheel braking force difference control means 190 and the steering force control means 200 use Equation 34 and Equation 35 so that the steering amount obtained by dividing the target steering amount by the control sharing ratio R _DYC : R _STR described above can be obtained. The yaw moment due to the braking force difference between the left and right wheel brakes and the steering torque applied to the steering mechanism 10 are respectively controlled.
Thereafter, the process ends (returns).

According to the embodiment described above, in the state where the resultant tire force of either the left or right front wheel exceeds the threshold value obtained by multiplying the frictional circle limit value by a predetermined safety factor, it is assumed that the tire force has no margin, and the steering mechanism By applying the steering torque to the wheel and steering the vehicle by generating a yaw moment due to the difference in braking force between the left and right wheels, it is possible to prevent the tire force from exceeding the friction circle limit value and to make the vehicle unstable, Good steering control can be performed even when the tire force is not sufficient, such as when traveling on a low μ road or during high-speed cornering.
Also, in the state where the tire resultant force of the left and right front wheels does not exceed the threshold value, it is assumed that the tire force is sufficient, and the driver is driven by the braking force difference control by steering the vehicle only by applying the steering torque to the steering mechanism. Does not cause any discomfort.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
(1) In the above-described embodiment, the control sharing ratio is changed according to the approach to the currently occurring tire force (friction circle limit value), but the present invention is not limited to this, and steering control is performed. A tire force that is estimated to be generated when it is performed may be estimated, and the control sharing ratio may be changed according to the approach of the estimated value to the limit tire force.
(2) The method of calculating the friction circle limit value and the tire force is not limited to the method of the above-described embodiment, and can be changed as appropriate.
(3) In the above-described embodiment, when the difference between the friction circle limit value and the tire force changes at a predetermined threshold, the control sharing ratio of the steering control and the braking force control is changed stepwise. The control sharing ratio may be continuously changed according to the change in the difference.
(4) In the above-described embodiment, the yaw moment is generated by the difference between the left and right braking forces. However, the present invention is not limited to this, and the left and right driving is performed using a left and right torque distribution device that distributes the driving force unevenly. The present invention can also be applied to setting a control sharing ratio between driving force control that generates a yaw moment by giving a driving force difference to wheels and steering control that applies steering force to a steering mechanism. Further, in the case of an electric vehicle or an engine-electric hybrid vehicle, the braking / driving force difference may be generated by an output difference or a regenerative braking force difference between driving motors provided on the left and right wheels, respectively.
(5) In the embodiment, the environment recognizing means detects the lane shape using a stereo camera. However, the present invention is not limited to this. For example, the map data prepared for the navigation device or the like and the vehicle position The lane shape may be detected based on the positioning information.
(6) The configuration of the actuator that applies the steering torque to the steering mechanism is not limited to the column assist type as in the embodiment. For example, the pinion assist type that drives the pinion shaft connected to the steering shaft, the steering shaft A double pinion type that drives a pinion that is independent of the connected pinion, a rack direct-acting type that drives the steering rack itself in a straight direction, or the like may be used.

It is a figure which shows the system configuration | structure of the vehicle provided with the Example of the driving assistance device to which this invention is applied. It is a figure which shows the structure of the tire force margin calculation means in the driving assistance device of FIG. It is a schematic diagram which shows the relationship between the friction-circle limit of a tire, and a tire force. It is a flowchart which shows the setting operation | movement of the control sharing ratio in the driving assistance device of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Steering mechanism 11 Steering wheel 12 Steering shaft 13 Steering gear box 14 Tie rod FW Front wheel H Housing 20 Electric power steering (EPS) control unit 21 Electric actuator 22 Torque sensor 30 Stabilization control unit 31 Hydraulic control unit (HCU)
32 Vehicle speed sensor 33 Yaw rate sensor 34 Lateral acceleration (lateral G) sensor 35 Rudder angle sensor 40 Engine control unit 41 Electronically controlled throttle control device (ETC)
42 Throttle opening sensor 43 Engine speed sensor 50 Transmission control unit 60 Vehicle integrated unit 100 Steering support control unit 110 Environment recognition unit 111 Stereo camera 112 Image processing unit 120 Target travel position setting unit 130 Own vehicle travel path estimation unit 140 Target Steering amount setting means 150 Road surface μ estimating means 160 Tire force margin calculating means 161 Engine torque calculating section 162 Transmission output torque calculating section 163 Total driving force calculating section 164 Front and rear ground load calculating section 165 Left wheel load ratio calculating section 166 Each wheel ground load Calculation unit 167 Each wheel friction circle limit value calculation unit 168 Each wheel longitudinal force calculation unit 169 Each wheel lateral force calculation unit 170 Each wheel tire resultant force calculation unit 171 Each wheel tire force margin calculation unit 180 Control sharing ratio setting means 190 Left and right wheels Braking force difference Control means 200 steering force control means

Claims (2)

In a driving assistance device that steers the vehicle based on environmental information ahead of the vehicle,
Environment recognition means for recognizing the environment ahead of the vehicle;
Target steering amount calculation means for calculating a target steering amount of the host vehicle using the environment recognition means;
Tire force calculating means for calculating tire force generated by the steered wheel tire;
Limit tire force estimating means for estimating a limit tire force of the steered wheel tire;
Steering force control means for controlling the steering force applied to the steering mechanism;
Braking / driving force control means for controlling the braking / driving force difference between the left and right wheels;
By allocating the target steering amount at a predetermined control sharing ratio, a target steering force of the steering force control means and a target braking / driving force difference of the braking / driving force control means are set, and the tire force is changed to the limit tire force. And a control sharing ratio setting means for increasing a control sharing ratio of the braking / driving force control means to the steering force control means in response to the approach of the driving support device. The control / sharing ratio setting means causes the braking / driving force difference to be generated by the braking / driving force control means only when the tire force exceeds a threshold set to be smaller than the limit tire force. Item 2. The driving support device according to Item 1.

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