JP5068638B2 - Vehicle rear wheel toe angle control device and rear wheel toe angle control method - Google Patents

Description

  The present invention relates to a vehicle rear wheel toe angle control device and a rear wheel toe angle control method, and more particularly to a rear wheel toe angle control device capable of individually controlling the toe angles of left and right rear wheels in a four-wheeled vehicle such as an automobile. The present invention relates to a rear wheel toe angle control method.

  In a four-wheeled vehicle such as an automobile, a hub carrier (knuckle) that supports the left and right rear wheels is connected to the vehicle body including an electric or hydraulic linear actuator on the way, and the rear wheel A rear-wheel steering device that changes the toe angle separately on the left and right is known (see, for example, Patent Document 1).

In vehicles equipped with this type of rear wheel toe angle control device, it is known that the rear wheels are toe-in or toe-out depending on the acceleration / deceleration state of the vehicle. For example, whether the vehicle is in a braking state or not. When the vehicle is in a braking state, there is one that controls the rear wheels to steer in the toe-in direction to improve running stability (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 9-30438 JP-A-5-58320

  The conventional rear wheel toe angle control device determines the toe angle exclusively in accordance with the driving state of the vehicle regardless of the driving environment such as the acceleration / deceleration state of the vehicle.

  On the other hand, the road surface gets wet due to rain and the coefficient of friction of the tire against the road surface decreases, the vehicle runs with an emergency spare tire whose tire width is narrower than the normal tire, or the tire grip performance deteriorates due to tire wear In such a case, the vehicle behavior is different from the normal time, and the steering operation feeling is different.

  The problem to be solved by the present invention is to obtain a stable feeling of steering operation regardless of changes in the driving environment such as rain or use of emergency spare tires, and to further improve the driving stability.

  A vehicle rear wheel toe angle control device according to the present invention is a rear wheel toe angle control device capable of individually controlling the toe angles of the left and right rear wheels of a vehicle, the parameter having a correlation with the tire grip force of the vehicle. A grip force correlation parameter detecting means for detecting the tire force and the grip force correlation parameter detected by the grip force correlation parameter detecting means when the tire grip force of the vehicle is judged to be lower than that when it is not And a toe-in tendency increasing means for controlling the toe angle of the left and right rear wheels in the toe-in direction.

  In the vehicle rear wheel toe angle control device according to the present invention, preferably, the grip force correlation parameter detecting means is an in-vehicle raindrop sensor, and when a raindrop is detected by the raindrop sensor, the tire grip force of the vehicle is detected. Judge that has declined.

  The vehicle rear wheel toe angle control device according to the present invention preferably has a yaw rate sensor for detecting the yaw rate of the vehicle and a toe angle sensor for detecting a toe angle of the rear wheel, and is detected by the toe angle sensor. The ratio value of the yaw rate detected by the yaw rate sensor with respect to the toe angle is used as the grip force correlation parameter, and the toe-in tendency increasing means determines that the tire grip force of the vehicle has decreased when the ratio value decreases. To do.

  A vehicle rear wheel toe angle control method according to the present invention is a rear wheel toe angle control method for individually controlling the toe angles of the left and right rear wheels of a vehicle, the parameter having a correlation with the tire grip force of the vehicle. When it is detected and it is determined that the tire grip force of the vehicle has decreased due to the change in the grip force correlation parameter, the toe angle of the left and right rear wheels is controlled in the toe-in direction compared to the case where this is not the case.

  According to the rear wheel toe angle control device and method of the present invention, when it is determined that the tire grip force of the vehicle has decreased due to a change in a parameter (grip force correlation parameter) having a correlation with the tire grip force of the vehicle. Compared to the other cases, the toe angle of the left and right rear wheels is controlled in the toe-in direction. When the tire is used, the left and right rear wheels are steered in the toe-in direction to compensate for a decrease in tire grip force. As a result, a stable steering operation feeling can be obtained regardless of changes in the driving environment such as rain or use of emergency spare tires, and further improvement in driving stability can be achieved.

  Embodiments of a vehicle rear wheel toe angle control device and a rear wheel toe angle control method according to the present invention will be described below with reference to FIGS.

  First, a four-wheeled vehicle to which a rear wheel toe angle control device and a rear wheel toe angle control method according to the present invention are applied will be described with reference to FIG.

  The four-wheel vehicle 1 of the present embodiment includes left and right front wheels 4L and 4R and left and right rear wheels 6L and 6R. The front wheels 4L and 4R are fitted with tires 3L and 3R, respectively, suspended by the vehicle body 2 by left and right front suspensions 7L and 7R, and attached to the vehicle body 2 by knuckles 7aL and 7aR so as to be turnable. The rear wheels 6L and 6R are fitted with tires 5L and 5R, respectively, suspended by the vehicle body 2 by left and right rear suspensions 8L and 8R, and attached to the vehicle body 2 by knuckles 8aL and 8aR so as to be turnable.

  Disc brakes 16L, 16R, 17L, and 17R are provided on the front wheels 4L and 4R and the rear wheels 6L and 6R, respectively.

  The four-wheel vehicle 1 includes a front wheel steering device 10 that directly steers the left and right front wheels 4L and 4R by steering the steering wheel 11. The front wheel steering device 10 includes a pinion 13 that is integrally connected to a steering wheel 11 via a steering shaft 12 and a tooth portion that meshes with the pinion 13 so as to be reciprocally movable in the vehicle width direction. A rack and pinion mechanism having a rack shaft 14 is also provided. Both ends of the rack shaft 14 are connected to the left and right knuckles 7aL and 7aR via tie rods 15. The left and right front wheels 4L, 4R are steered (turned) when the rack shaft 14 is moved in the vehicle width direction by the rotation operation of the steering wheel 11.

  The steering shaft 12 is provided with a steering angle sensor 26 that detects the steering angle of the steering wheel 11 corresponding to the actual steering angle of the front wheels 4L, 4R. Thereafter, the steering angle sensor 26 outputs a sensor signal indicating the actual front wheel steering angle.

  The four-wheeled vehicle 1 is a rear wheel steering device (rear wheel toe angle varying device) 20 having one end connected to the vehicle body 2 and the other end connected to the knuckle 8aL of the left rear wheel 6L. And a right linear actuator 21R having one end connected to the vehicle body 2 and the other end connected to the knuckle 8aR of the right rear wheel 6R. The left and right linear actuators 21L and 21R are electrically operated or hydraulic, and expand and contract by a linear operation to individually change the toe angles of the left and right rear wheels 6L and 6R. In the rear wheel steering device 20 configured as described above, the toe angles of the left and right rear wheels 6L and 6R can be set from toe-in to neutral (normal) to toe-out by the left and right linear actuators 21L and 21R.

  The left and right linear actuators 21L and 21R are controlled by a rear wheel toe angle control device (ECU) 40. The rear wheel toe angle control device 40 is of an electronic control type including a microcomputer, and includes an input interface 41 for inputting sensor signals, a rear wheel toe angle control target value calculation unit 42, and a grip force correlation parameter detection unit. 43, a toe-in tendency increase correction calculation unit 44, a drive signal generation unit 45, and an output interface 46 that outputs an actuator drive signal.

  The rear wheel toe angle control target value calculation unit 42 receives the sensor signal indicating the vehicle speed from the vehicle speed sensor 24 that detects the vehicle speed of the four-wheeled vehicle 1, and the vehicle body 2 from the front / rear acceleration / deceleration sensor 25 that detects the vehicle longitudinal acceleration / deceleration. A sensor signal indicating the front / rear acceleration / deceleration is sent from the accelerator opening sensor 27 for detecting the accelerator opening (accelerator pedal depression amount), and a sensor signal indicating the accelerator opening is sent from the brake pedal depression amount sensor 28 for detecting the brake pedal depression amount. Sensor signals indicating the amount of depression of the brake pedal are input, and the left and right rear wheel toe angle control target values (control target rear steering angles) are calculated according to a preset control law using these sensor signals.

  The basic rear wheel toe angle control law in the present embodiment detects the longitudinal acceleration / deceleration of the vehicle body 2 based on the sensor signals of the longitudinal acceleration / deceleration sensor 25, the accelerator opening sensor 27, and the brake pedal depression amount sensor 28. , Neutral (normal) to slightly toe-in setting at constant speed, toe-out setting to improve steering response when the vehicle body 2 is accelerated in the longitudinal direction, and toe-out setting to improve stability when the vehicle body 2 is decelerated in the longitudinal direction Do. As a result, the toe-out tendency increases as the acceleration increases, and the toe-in tendency increases as the deceleration increases.

  The grip force correlation parameter detection unit 43 indicates a sensor signal indicating the presence or absence of raindrops (rainfall) from the in-vehicle raindrop sensor 30 that detects the presence or absence of raindrops (rainfall), and indicates the yaw rate from the yaw rate sensor 29 that detects the yaw rate of the vehicle 2. As sensor signals, sensor signals indicating the actual stroke amounts of the linear actuators 21L and 21R are respectively input from the stroke sensors 23L and 23R that detect the actual stroke amounts of the linear actuators 21L and 21R. Based on these sensor signals, tire grip force and A parameter having a correlation is detected. Since the actual stroke amounts of the linear actuators 21L and 21R detected by the stroke sensors 23L and 23R correlate with the rear wheel toe angle, the stroke sensors 23L and 23R can be rephrased as a toe angle sensor.

  The tire grip force is a force with which the tires 3L, 3R, 5L, and 5R grab the road surface, and a larger tire grip force does not cause a drift phenomenon and has good steering stability. When the road surface is wet due to rain (wet), the tire grip force is reduced by reducing the friction coefficient as compared with the case where the road surface is not wet (dry). In addition to this, in the case of traveling with an emergency spare tire (T tire) used for emergency treatment at the time of puncture, the tire width of the emergency spare tire is narrower than the tire width of the normal tire, and the contact area of the tire is reduced. Tire grip is reduced. Further, even when the tread is worn away due to wear of the tire, the tire grip force is reduced by reducing the friction coefficient.

  The grip force correlation parameter detection unit 43 detects raindrops as one of the grip force correlation parameters based on the sensor signal of the raindrop sensor 30. If a raindrop is detected, the grip force correlation parameter detection unit 43 determines that the tire grip force has decreased due to rain or the like. . The raindrop sensor 30 can be used for an auto wiper.

  The grip force correlation parameter detection unit 43 uses the ratio value of the yaw rate detected by the yaw rate sensor 29 to the actual stroke amount (toe angle) of the linear actuators 21L and 21R detected by the stroke sensors 23L and 23R as another grip force. Calculated as a correlation parameter. When the tire grip force decreases, the ratio value of the yaw rate to the actual stroke amount decreases. Therefore, the reduction of the tire grip force is judged based on the ratio value, and the use of emergency spare tires, tire wear, etc. are indirectly detected. be able to.

  Thus, in the present embodiment, as the grip force correlation parameter, the presence / absence of raindrops detected by the raindrop sensor 30 and the actual stroke amounts (toe angles) of the linear actuators 21L and 21R detected by the stroke sensors 23L and 23R. The ratio value of the yaw rate detected by the yaw rate sensor 29 is used.

  The toe-in tendency increase correction calculation unit 44 receives information on the grip force correlation parameter from the grip force correlation parameter detection unit 43 and grips the toe angle control target value of the left and right rear wheels fetched from the rear wheel toe angle control target value calculation unit 42. Correction in the toe-in direction according to the force correlation parameter. This correction in the toe-in direction is a toe-in tendency increase correction, an addition correction for adding a toe-in tendency increase value (including zero) determined according to the grip force correlation parameter to the rear wheel toe angle control target value, and grip force There is multiplication correction for multiplying a rear wheel toe angle control target value by a toe-in tendency increase coefficient (including 1) determined according to the correlation parameter. The toe-in tendency increase correction may be the same for the left and right rear wheels 6L and 6R.

  As a specific example of the toe-in tendency increase correction, when the raindrop sensor 30 does not detect a raindrop, it is assumed that there is no decrease in grip force on the dry road surface. Then, the rear wheel toe angle control target value from the rear wheel toe angle control target value calculation unit 42 is passed to the drive signal generation unit 45 as it is. That is, the toe-in tendency increase correction is not performed.

  On the other hand, when the raindrop sensor 30 detects raindrops, it is assumed that the grip force is low on the wet road surface, and the toe-in tendency increase value is greater than zero in the addition correction, and the toe-in tendency increase coefficient is greater than 1 in the multiplication correction. The rear wheel toe angle control target value calculation unit 42 applies toe-in tendency increase correction to the rear wheel toe angle control target value, and the rear wheel toe angle control target value corrected to increase toe-in tendency is supplied to the drive signal generation unit 45. hand over.

  When the ratio value of the yaw rate detected by the yaw rate sensor 29 to the actual stroke amount (toe angle) of the linear actuators 21L and 21R detected by the stroke sensors 23L and 23R is equal to or greater than a predetermined value, the normal tire is used. Assuming that there is no decrease in grip force, the toe-in tendency increase value is zero for addition correction, and the toe-in tendency increase coefficient is 1 for multiplication correction, and the rear wheel toe angle control target value from the rear wheel toe angle control target value calculation unit 42 is The value is passed to the drive signal generator 45 as it is. That is, the toe-in tendency increase correction is not performed.

  Further, when the ratio value of the yaw rate detected by the yaw rate sensor 29 to the actual stroke amount (toe angle) of the linear actuators 21L and 21R detected by the stroke sensors 23L and 23R is less than a predetermined value, an emergency spare tire As a result, the toe-in tendency increase coefficient is set to a value larger than 1 in the multiplication correction, and the toe-in tendency increase coefficient is set to 1 in accordance with the amount of decrease in the ratio value. The rear wheel toe angle control target value calculation unit 42 applies a toe-in tendency increase correction to the rear wheel toe angle control target value calculation unit 42, and the rear wheel toe angle control target value corrected to increase toe-in tendency is used as a drive signal generation unit. Pass to 45.

  The drive signal generation unit 45 converts the rear wheel toe angle control target value from the toe-in tendency increase correction calculation unit 44 into a control target stroke amount of the linear actuators 21L and 21R, and a stroke sensor provided in the linear actuators 21L and 21R. Sensor signals indicating the actual stroke amounts of the linear actuators 21L and 21R are input from 23L and 23R, and the control deviation between the control target stroke amount and the actual stroke amount and the control deviation between the control target stroke amount and the actual stroke amount SR are each zero. The control target signal is output from the output interface 46 to each of the linear actuators 21L and 21R. Thus, feedback control is performed so that the toe angles of the left and right rear wheels 6L and 6R become the target rear wheel toe angle.

  Next, a processing routine for rear wheel toe angle control according to the present embodiment will be described with reference to a flowchart shown in FIG. The processing routine is repeatedly executed at predetermined intervals by time interruption.

  First, it is determined whether or not the vehicle is traveling at a constant speed (step 1). If the vehicle is traveling at a constant speed, the rear wheel toe angle control target value (target toe angle) is set to a predetermined constant speed traveling appropriate value (step 13). This constant speed running appropriate value may be, for example, a neutral (normal) or slightly toe-in rear wheel toe angle.

  On the other hand, if it is determined that the traveling speed of the vehicle is changing, it is determined whether the vehicle is accelerating (accelerating and decelerating) or decelerating (step 2).

  If it is determined that the vehicle is accelerating (Yes at Step 2), it is then determined whether or not the current vehicle speed has reached a predetermined vehicle speed Va that is permitted to execute acceleration toe angle variable control ( Step 3). When it is determined that the vehicle speed does not reach the predetermined vehicle speed Va, the rear wheel toe angle control target value is set to a predetermined default value (step 7). The default value, for example, the rear wheel toe angle may be neutral (normal) or slightly toe-in.

  On the other hand, if it is determined that the vehicle speed Va has been reached, the target toe angle is calculated based on the accelerator opening detected by the accelerator opening sensor 28, that is, the operation amount of the accelerator pedal (step 4). ). The target toe angle at the time of acceleration is such that the rear wheel toe angle is toe-out.

  Next, a target toe angle is calculated based on the acceleration actually acting on the vehicle 2 based on the longitudinal acceleration / deceleration detected by the longitudinal acceleration / deceleration sensor 25 (step 5). Here, the target toe angle value based on the operation amount of the accelerator pedal is reevaluated. In other words, even if the accelerator pedal operation amount is the same, the acceleration of the vehicle varies depending on the running resistance.Therefore, if the accelerator pedal operation amount is large but the corresponding acceleration does not occur, the target toe angle is set. Modify toe-out reduction. Then, the corrected target toe angle is set as a rear wheel toe angle control target value (step 6).

  If it is determined that the vehicle is decelerating (No at Step 2), it is next determined whether or not the current vehicle speed has reached a predetermined vehicle speed Vb that is permitted to execute the toe angle variable control during deceleration ( Step 8). If it is determined that the vehicle speed does not reach the predetermined vehicle speed Vb, the rear wheel toe angle control target value is set to a predetermined default value (step 12). This default value may be, for example, a neutral (normal) or slightly toe-in rear wheel toe angle.

  On the other hand, if it is determined that the vehicle speed has reached the predetermined vehicle speed Vb, the target toe angle is calculated based on the brake pedal depression amount detected by the brake pedal depression amount sensor 28 (step 9). The target toe angle during deceleration is such that the rear wheel toe angle is toe-in.

  Next, based on the longitudinal acceleration / deceleration detected by the longitudinal acceleration / deceleration sensor 25, the target toe angle is calculated based on the deceleration actually acting on the vehicle 2 (step 10). Here, the target toe angle value based on the operation amount of the brake pedal is reevaluated. In other words, even if the brake pedal operation amount is the same, the vehicle's deceleration varies depending on the running resistance, so if the brake pedal operation amount is large but the corresponding deceleration does not occur, the target torque Correct the corner to reduce the toe-in. The corrected target toe angle is set as a rear wheel toe angle control target value (step 11).

  The processing in steps 1 to 13 is performed by the rear wheel toe angle control target value calculation unit 42. When the rear wheel toe angle control target value is determined in any one of steps 6, 7, 11, 12, and 13, next, grip force correlation parameter detection is performed (step 14). The grip force correlation parameter detection is performed by the grip force correlation parameter detection unit 43. In this embodiment, the presence or absence of raindrops by the raindrop sensor 30, the actual stroke amounts of the linear actuators 21L and 21R detected by the stroke sensors 23L and 23R. This is a ratio value of the yaw rate detected by the yaw rate sensor 29 with respect to (toe angle).

  Next, the toe-in tendency increasing correction calculation unit 44 determines whether or not the grip force correlation parameter has decreased from a steady value (step 15). If the grip force correlation parameter has not decreased, the rear wheel toe angle control target value is not corrected for toe-in tendency increase, and an actuator drive command is sent to the linear actuators 21L and 21R based on the rear wheel toe angle control target value. The output process is performed (step 17).

On the other hand, when the grip force correlation parameter is decreased, the rear wheel toe angle control target value is corrected to increase the toe-in tendency (step 16), and the rear wheel toe angle control target value corrected to increase the toe-in tendency is set. Based on the above-described feed control, a process of outputting an actuator drive command to the linear actuators 21L and 21R is performed (step 17).
The

  Due to the above control, the left and right rear wheels are steered in the toe-in direction when the tire grip force is lower than that in fine weather, or when the tire grip force is an emergency spare tire when using normal tires. Is compensated. As a result, a stable steering operation feeling can be obtained regardless of changes in the driving environment such as rain or use of emergency spare tires, and further improvement in driving stability can be achieved.

  Next, another embodiment of the vehicle rear wheel toe angle control device according to the present invention will be described with reference to FIG.

  In the present embodiment, a model reference type rear wheel steering angle control device 50 is provided as an ECU that performs rear wheel toe angle control. The rear wheel steering angle control device 50 includes front (front wheel) steering transmission characteristic calculation units 51A and 51B, rear (rear wheel) steering transmission characteristic calculation units 52A and 52B, reference yaw rate transmission characteristic calculation units 53A and 53B, and a grip. A force correlation parameter detection unit 54 and a control target rear steering angle calculation unit 55 are included. The grip force correlation parameter detection unit 54 is equivalent to the grip force correlation parameter detection unit 43 of the above-described embodiment.

  First, an outline of a control rule for rear wheel steering according to the present embodiment will be described. When the front wheel steering angle (actual steering angle) detected by the steering angle sensor 26 is δf and the rear wheel steering angle (actual steering angle) is δr, the vehicle (four-wheeled vehicle) with respect to the front wheel steering angle δf and the rear wheel steering angle δr. The yaw rate characteristic γ of 1 is expressed by the following equation (1).

γ = (Gf · δf) − (Gr · δr) (1)
However, Gf is a front steering transmission characteristic, and Gr is a rear steering transmission characteristic.

Assuming that the yaw rate characteristic to be realized with respect to the front wheel steering angle δf, that is, the reference yaw rate transmission characteristic, is set to Gideal, if the rear wheel steering angle δr is set such that γideal = (Gideal · δf) and γideal = γ, the reference yaw rate transmission is performed. The characteristic Gideal can be realized. In consideration of this, the rear wheel steering angle control device 50 performs the following arithmetic processing to calculate the control target rear steering angle δr ^* that realizes the reference yaw rate transmission characteristic Gideal.

  For the three models of the front steering transmission characteristic Gf, the rear steering transmission characteristic Gr, and the standard yaw rate transmission characteristic Gideal, the dry traveling mode A (when the grip force correlation parameter is not lowered) and the wet traveling mode B ( The grip force correlation parameter is switched according to the grip force correlation parameter detected by the grip force correlation parameter detection unit 54. The wet travel mode B is a toe-in tendency increasing correction mode, and as compared with the dry travel mode A, the toe angle of the left and right rear wheels is generally set in the toe-in direction (toe-in tendency increasing).

  Hereinafter, the front steering transmission characteristic calculation unit 51A, the rear steering transmission characteristic calculation unit 52A, and the standard yaw rate transmission characteristic calculation unit 53A are calculation units suitable for the dry travel mode A, and the front steering transmission characteristic calculation unit 51B, the rear steering transmission The characteristic calculation unit 52B and the standard yaw rate transfer characteristic calculation unit 53B are calculation units adapted to the wet running mode B.

  The front steering transfer characteristic calculation units 51A and 51B receive a sensor signal indicating the actual front wheel steering angle δr from the steering angle sensor 26 and a sensor signal indicating the vehicle speed V from the vehicle speed sensor 24, respectively. Then, the front steering transmission characteristic Gf is calculated by the following equation (2).

Gf = K (af · s + 1) / (b ₁ · s ² + b ₂ · s + 1) (2)

  The rear steering transfer characteristic calculation units 52A and 52B receive a sensor signal indicating the actual front wheel steering angle δr from the steering angle sensor 26 and a sensor signal indicating the vehicle speed V from the vehicle speed sensor 24, respectively, and receive primary and secondary transfer functions. As a result, the rear steering transmission characteristic Gr is calculated by the following equation (3).

Gr = K (ar · s + 1) / (b ₁ · s ² + b ₂ · s + 1) (3)

  The reference yaw rate transfer characteristic calculation units 53A and 53B receive the sensor signal indicating the actual front wheel steering angle δr from the steering angle sensor 26 and the sensor signal indicating the vehicle speed V from the vehicle speed sensor 24, respectively, and the reference yaw rate according to the following equation (4). The transfer characteristic Gideal is calculated.

Ideal = (V / L) {1 / (1 + A · V ² ) (c ₁ · s + 1) / (d ₂ · s ² +
d ₁ · s + 1)} (4)
Each parameter of the equations (2) to (4) is calculated by the following equations (5) to (10).
K = (V / L) {1 / (1 + A · V ² )} (5)
A = − (m / L ² ) {(Lf · Kf−Lr · Kr) / (Kf · Kr)} (6)
af = (V / L) (m · Lf / Kr) (7)
ar = (V / L) (m · Lr / Kf) (8)
b ₁ = K (m · V · I) / (Kf · Kr · L) (9)
b ₂ = K {m (Lf · Kf ² + Lr · Kr ² ) + I (Kf + Kr)} / (Kf · Kr · L) (10)

Where m: vehicle mass L: wheel base Lf: center of gravity-front wheel axle distance Lr: center of gravity-rear wheel axle distance Kf: front wheel cornering power Kr: rear wheel cornering power V: vehicle speed s: Laplace operator A: star Bility factor I: vehicle yaw inertial rotating mass c ₁ , d ₁ , d ₂ : arbitrarily set coefficients

The coefficients c ₁ , d ₁ , d ₂ are set to different values in the dry travel mode A and the wet travel mode B. Thereby, in the wet travel mode B, as compared with the dry travel mode A, the toe angles of the left and right rear wheels are generally set in the toe-in direction (toe-in tendency increase).

The control target rear steering angle calculation unit 55 receives a signal indicating the front steering transmission characteristic Gf from the front steering transmission characteristic calculation unit 51A or 51B31, and a signal indicating the rear steering transmission characteristic Gr from the rear steering transmission characteristic calculation unit 52A or 52B. A signal indicating the reference yaw rate transfer characteristic Gideal is input from the reference yaw rate transfer characteristic calculation unit 53A or 53B, and a sensor signal indicating the actual front wheel steering angle δr is input from the steering angle sensor 26. A target rear steering angle δr ^* is calculated.

δr ^* = Gr ⁻¹ (Gf−Gideal) δf (11)

  When the grip force correlation parameter detected by the grip force correlation parameter detection unit 54 is equal to or greater than a predetermined value, the front steering transmission characteristic calculation unit 51A, the rear steering transmission characteristic calculation unit 52A, and the reference yaw rate transmission characteristic calculation unit 53A are selected. Thus, the toe angle and the steering angle in the dry travel mode A are set.

  On the other hand, when the grip force correlation parameter detected by the grip force correlation parameter detection unit 54 is less than a predetermined value, the front steering transmission characteristic calculation unit 51A, the rear steering transmission characteristic calculation unit 52A, the standard yaw rate transmission characteristic calculation. Instead of the unit 53A, the front steering transmission characteristic calculation unit 51B, the rear steering transmission characteristic calculation unit 52B, and the standard yaw rate transmission characteristic calculation unit 53B are selected, and the toe angle and the steering angle in the wet travel mode B are set.

  Thereby, also in the present embodiment, when the rain grip where the tire grip force is reduced as compared with the time of fine weather or when the tire grip force is an emergency spare tire when using a normal tire, the left and right rear wheels are steered in the toe-in direction, A decrease in tire grip force is compensated. As a result, a stable steering operation feeling can be obtained regardless of changes in the driving environment such as rain or use of emergency spare tires, and further improvement in driving stability can be achieved.

1 is an overall configuration diagram illustrating one embodiment of a four-wheeled vehicle to which a rear wheel toe angle control device and a rear wheel toe control method according to the present invention are applied. 1 is a block diagram showing one embodiment of a rear wheel toe angle control device of a vehicle according to the present invention. 4 is a flowchart showing a processing routine for rear wheel toe angle control by the vehicle rear wheel toe angle control device according to the present invention. It is a block diagram which shows other embodiment of the rear-wheel toe angle control apparatus of the vehicle by this invention.

Explanation of symbols

4L, 4R Front wheel 6L, 6R Rear wheel 21L, 21R Linear actuator 23L, 23R Stroke sensor 24 Vehicle speed sensor 25 Front / rear acceleration / deceleration sensor 26 Steering angle sensor 27 Accelerator opening sensor 28 Brake pedal depression sensor 29 Yaw rate sensor 30 Raindrop sensor 40 Rear Wheel toe angle control device 42 Rear wheel toe angle control target value calculation unit 43 Grip force correlation parameter detection unit 44 Toe-in tendency increase correction calculation unit 45 Drive signal generation unit 51A, 51B Front steering transmission characteristic calculation unit 52A, 52B Rear steering transmission characteristic Calculation unit 53A, 53B Reference yaw rate transfer characteristic calculation unit 54 Grip force correlation parameter detection unit 55 Control target rear steering angle calculation unit

Claims (2)

A rear wheel toe angle control device capable of individually controlling the toe angles of left and right rear wheels of a vehicle,
A yaw rate sensor for detecting the yaw rate of the vehicle ;
A toe angle sensor for detecting a toe angle of the rear wheel;
Grip force correlation parameter detection means for detecting a ratio value of the yaw rate detected by the yaw rate sensor with respect to the toe angle detected by the toe angle sensor as a parameter having a correlation with the tire grip force of the vehicle;
When the ratio value detected by the grip force correlation parameter detecting means is reduced, it is determined that the tire grip force of the vehicle is reduced, and the toe angle of the left and right rear wheels is compared with the case where the ratio is not so. Toe-in tendency increasing means to control
A rear wheel toe angle control device having a vehicle. A rear wheel toe angle control method for individually controlling the toe angles of the left and right rear wheels of a vehicle,
When the ratio value of the yaw rate detected by the yaw rate sensor with respect to the toe angle of the rear wheel detected by the toe angle sensor is detected as a parameter having a correlation with the tire grip force of the vehicle, and the ratio value decreases Is a vehicle rear wheel toe angle control method that determines that the tire grip force of the vehicle has decreased and controls the toe angle of the left and right rear wheels in the toe-in direction compared to when the tire grip force is not.

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