JP4813154B2 - Vehicle road friction coefficient estimation device - Google Patents

Description

  The present invention relates to a road surface friction coefficient estimating device for a vehicle that accurately estimates a road surface friction coefficient even in straight traveling.

  In recent years, various control technologies such as traction control, braking force control, or torque distribution control have been proposed and put into practical use in vehicles. Many of these techniques use a road surface friction coefficient for calculation or correction of necessary control parameters, and it is necessary to accurately estimate the road surface friction coefficient in order to reliably execute the control.

As a technique for estimating such a road surface friction coefficient, paying attention to the fact that the magnitude of the self-aligning torque with respect to the slip angle of the tire changes according to the road surface friction coefficient, for example, in Japanese Patent Laid-Open No. 11-287749, a steering wheel An apparatus for estimating a road surface friction coefficient from an angle and a steering torque is disclosed. Japanese Patent Application Laid-Open No. 6-258196 discloses a technique that enables a road surface friction coefficient during normal running by performing a frequency analysis of wheel vibrations.
Japanese Patent Laid-Open No. 11-287749 JP-A-6-258196

  However, in the technology of the road surface friction coefficient estimation device disclosed in Patent Document 1 described above, since the road surface friction coefficient is estimated from the steering wheel angle and the steering torque, the road surface friction coefficient cannot be estimated when the vehicle is traveling straight. There is a problem. In addition, in the technique of the road surface friction coefficient estimating device disclosed in Patent Document 2 described above, in order to perform frequency analysis, it is necessary to continuously acquire wheel vibration data for a certain period of time. There is a problem that a delay occurs, and this road surface friction coefficient estimated value cannot be controlled with good response.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a vehicle road friction coefficient estimation device capable of quickly and accurately estimating a road friction coefficient even in a straight traveling state. .

The present invention provides a toe angle varying means for varying the toe angle of the left and right wheels, a detecting means for detecting either the lateral force acting on the left and right wheels or the self-aligning torque, and determining whether or not the vehicle is in a straight traveling state. A straight-running determination means, a front-wheel slip angle calculating means for estimating a front-wheel slip angle, and a signal for changing the toe angle of the left and right front wheels by a preset amount with respect to the toe-angle changing means when the vehicle is in a straight-running state. When the road friction coefficient is estimated based on either the toe angle of the left and right front wheels, the lateral force detected by the detecting means, or the self-aligning torque, while the vehicle is determined not to be in a straight traveling state It is characterized in that a road surface friction coefficient estimation means for estimating a road surface friction coefficient based on either the lateral force and the self-aligning torque detected by the front wheel slip angle and the detection means

  According to the vehicle road surface friction coefficient estimating apparatus according to the present invention, it is possible to quickly and accurately estimate the road surface friction coefficient even in a straight traveling state.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 to 11 show an embodiment of the present invention, FIG. 1 is a schematic configuration diagram of a vehicle equipped with a road surface friction coefficient estimating device, FIG. 2 is a functional block diagram of the road surface friction coefficient estimating device, and FIG. 4 is a functional block diagram showing the configuration of the vehicle slip angle calculation unit, FIG. 5 is an explanatory diagram showing a two-wheel model of lateral movement of the vehicle, and FIG. FIG. 7 is an explanatory diagram showing the characteristics of the front wheel slip angle (toe angle) and the lateral force with respect to the road surface friction coefficient, FIG. 8 is an explanatory diagram of the characteristics of the specified time set based on the vehicle speed, and FIG. Is a flowchart of the road surface friction coefficient estimation, FIG. 10 is a flowchart of the first road surface μ estimation process, and FIG. 11 is a flowchart of the second road surface μ estimation process.

  In FIG. 1, reference numeral 1 denotes a vehicle, and the driving force of the vehicle 1 by the engine 2 is transmitted to the center differential device 4 via an automatic transmission 3 (including a torque converter and the like) 3 behind the engine 2. .

  The driving force transmitted to the center differential device 4 is input to the rear wheel final reduction device 8 via the rear drive shaft 5, the propeller shaft 6, and the drive pinion shaft portion 7, while the front wheel end is transmitted via the front drive shaft 9. Input to the reduction gear 10.

  The driving force input to the rear wheel final reduction gear 8 is transmitted to the left rear wheel 12rl through the rear wheel left drive shaft 11rl, and is transmitted to the right rear wheel 12rr through the rear wheel right drive shaft 11rr. The driving force input to the front wheel final reduction gear 10 is transmitted to the left front wheel 12fl through the front wheel left drive shaft 11fl, and is transmitted to the right front wheel 12fr through the front wheel right drive shaft 11fr.

  Reference numeral 15 denotes a steering device. As the steering device 15 in this embodiment, a four-wheel steering mechanism that can independently control the steering angles (wheel angles) of the individual wheels 12fl, 12fr, 12rl, and 12rr is adopted. Has been. This four-wheel steering mechanism is, for example, a steer-by-wire mechanism in which the wheels 12fl, 12fr, 12rl, 12rr and the handle 16 are mechanically separated. The relationship with the steering angle can be set arbitrarily.

  That is, the handle 16 rotated by the driver is fixed to one end of the steering input shaft 17, and the other end of the steering input shaft 17 is connected to the power transmission mechanism 18. The output shaft of the motor 19 is connected. Thus, the power generated in the motor 19 is transmitted to the handle 16 as a steering reaction force via the power transmission mechanism 18 and the steering input shaft 17.

  The individual wheels 12fl, 12fr, 12rl, 12rr are provided with steering actuators 20fl, 20fr, 20rl, 20rr as wheel adjustment devices in units of wheels.

  Thus, the steering angles of the left and right front wheels 12fl and 12fr are independently adjusted by the pair of steering actuators 20fl and 20fr provided on the front wheel side.

  Further, the steering angles of the left and right rear wheels 12rl and 12rr are independently adjusted by a pair of steering actuators 20rl and 20rr provided on the rear wheel side.

  Drive rods 21fl, 21fr, 21rl, and 21rr are inserted into the respective steering actuators 20fl, 20fr, 20rl, and 20rr, and a motor rotor (inside each steering actuator 20fl, 20fr, 20rl, and 20rr) The drive rods 21fl, 21fr, 21rl, 21rr can be expanded and contracted in the vehicle width direction, that is, in the left-right direction, according to the rotation of the motor (not shown).

  The ends of the drive rods 21fl, 21fr, 21rl, 21rr are connected to tie rods 22fl, 22fr, 22rl, 22rr connected to the wheels 12fl, 12fr, 12rl, 12rr, and the drive rods 21fl, 21fr, 21rl, 21rr, When the tie rods 22fl, 22fr, 22rl, 22rr move in conjunction with 21rr, the wheels 12fl, 12fr, 12rl, 12rr are steered.

  The left front wheel 12fl and the right rear wheel 12rr are steered in the right direction by extending the drive rods 12fl and 12rr, and steered in the left direction by contracting the drive rods 12fl and 12rr. On the other hand, the steering direction for the right front wheel 12fl and the left rear wheel 12rl is opposite to that of the left front wheel 12fl and the right rear wheel 12rr described above.

  Each steering actuator 20fl, 20fr, 20rl, 20rr is controlled by a steering control device 23. The steering control device 23 is attached to the steering input shaft 17 with the vehicle speed V detected by the vehicle speed sensor 31, and the steering wheel angle θH from the steering wheel angle sensor 32 that detects the rotation angle from the neutral position of the steering wheel 16 as the steering wheel angle θH. The steering angle sensors 33fl, which are attached to the steering actuators 20fl, 20fr, 20rl and 20rr, respectively, detect the steering angles of the wheels 12fl, 12fr, 12rl and 12rr by detecting the rotation angles of the rotors of the respective motors. The steering angle from 33fr, 33rl, and 33rr is input.

  Then, the steering control device 23 controls the steering reaction force applied to the handle 16 by controlling the motor 19 according to the handle angle θH. At the same time, the steering control device 23 controls the steering angles of the wheels 12fl, 12fr, 12rl, and 12rr by controlling the steering actuators 20fl, 20fr, 20rl, and 20rr, respectively. For example, the steering control device 23 normally sets the steering angles of the left and right front wheels 12fl and 12fr to be in phase with each other based on the steering wheel angle θH, and the steering angles of the left and right rear wheels 12rl and 12rr are also in phase with each other. Set. In the present embodiment, the normal phase is that the steering angle corresponds to the traveling direction as a reference, and the reverse phase is that the wheel angle corresponds to the opposite direction based on the traveling direction. The correspondence does not need to be exactly the same. Further, leftward steering is defined as a positive value.

  Further, when a toe-in or toe-out signal is input to the steering control device 23 from a road surface friction coefficient estimating device 50 described later, the steering actuators 20fl and 20fr are actuated to apply to the left and right front wheels 12fl and 12fr. A toe-in state or a toe-out state is realized by varying the steering angle at a preset value (for example, 2 to 3 °). Thus, the steering device 15 has a function as toe angle varying means.

  On the other hand, the vehicle 1 is provided with a front environment recognition device 34 for detecting obstacles ahead and detecting changes in the road surface condition ahead. , And input to the road surface friction coefficient estimating device 50.

  For example, the front environment recognition device 34 detects a front obstacle and a change in road surface condition based on image data captured by a pair of cameras 35L and 35R.

  The set of cameras 35L and 35R is composed of a set of (left and right) CCD cameras using a solid-state imaging device such as a charge coupled device (CCD) as a stereo optical system. These left and right CCD cameras are each mounted at a predetermined interval in front of the ceiling in the passenger compartment, and take images of objects outside the vehicle (pedestrians, preceding cars, parked vehicles, obstacles, etc., solid objects, etc.) from different viewpoints. And output to the forward environment recognition device 34.

  The recognition processing of the image data from the pair of cameras 35L and 35R in the front environment recognition device 34 is performed as follows, for example. First, a process of obtaining distance information (distance data) from the corresponding position shift amount by the triangulation principle is performed on a stereo image pair in front of the host vehicle 1 captured by a pair of cameras 35L and 35R. Based on the well-known grouping process and compared with pre-stored frames (windows) such as 3D road shape data, side wall data, and solid object data, white line data, guardrails that exist along the road Side wall data such as curbs, and three-dimensional object data such as vehicles and pedestrians are extracted. Then, among the three-dimensional objects, for example, an area with a width of 1.1 m on the left and right sides is defined as the own vehicle traveling area around the own vehicle traveling path determined by the guard rail, the white line, etc. Extract as a forward obstacle.

  Further, the detection of the road surface condition ahead is performed by performing histogram processing on the luminance value of the monitoring area set in the captured image and classifying the luminance distribution into any of a plurality of preset luminance distribution patterns. For example, as disclosed in Japanese Patent Application Laid-Open No. 2005-84959, a pattern in which luminance values are concentrated within a predetermined narrow luminance range according to a luminance distribution pattern is a single-sided snow road, a clean dry road without white lines, a wet road It is.

  A luminance distribution pattern in which luminance values are distributed in a predetermined luminance range or more and a luminance distribution peak exists on the black side and the white side is a snow melting road and a dry road surface having a sharp shadow.

  Furthermore, the luminance distribution pattern in which the luminance values are distributed in a luminance range equal to or higher than a predetermined value and most of the luminance values are relatively biased to the white side is a one-sided snow road and a wet road surface.

  A luminance distribution pattern in which luminance values are distributed over a predetermined luminance range and most of luminance values are relatively biased toward the black side is a dry road surface with white lines.

  Furthermore, the luminance distribution pattern in which the luminance values are uniformly distributed in a predetermined luminance range or more is a snow melting road, a wet road surface, and a dirty dry road surface.

  Then, by combining and classifying these cases, it is determined whether the front road surface is a snow road, a wet road surface, or a dry road surface. If the road surface state is different from the previously detected road surface state, the road surface state changes. It is judged that there is.

  As described above, the change in the front obstacle and the road surface condition detected by the front environment recognition device 34 is input to the road surface friction coefficient estimation device 50.

In addition to the vehicle speed sensor 31, the steering wheel angle sensor 32, the steering angle sensors 33fl, 33fr, 33rl, 33rr, the front environment recognition device 34, the vehicle 1 includes force detection sensors 36fl, 36fr for the front wheels 12fl, 12fr, sideways. An acceleration sensor 37, a yaw rate sensor 38, and a brake switch 39 are provided. Among these, a vehicle speed sensor 31, a steering wheel angle sensor 32, a front environment recognition device 34, front wheel 12fl, 12fr force detection sensors 36fl, 36fr, lateral acceleration. The sensor 37, the yaw rate sensor 38, and the brake switch 39 are connected to the road surface friction coefficient estimating device 50, and the vehicle speed V, the steering wheel angle θH, the front obstacle, the change in the road surface condition, the lateral force Fyfl acting on the front wheels 12fl and 12fr, Fyfr, lateral acceleration ^{d 2} y / dt 2, a yaw rate (yaw angular velocity) dψ / dt, ON signal of the brake road surface friction Is input to the estimating unit 50.

  Here, the force detection sensors 36fl and 36fr are sensors disclosed in, for example, Japanese Patent Laid-Open No. 9-2240, and the lateral (y-direction) forces Fyfl and Fyfr acting on the front wheels 12fl and 12fr are applied to the respective axles. The detection is based on the amount of displacement generated in the housing.

  That is, in the present embodiment, the forward environment recognition device 34 is provided as an obstacle detection means and a road surface condition detection means, the force detection sensors 36fl and 36fr are provided as detection means, and the brake switch 39 is provided as a braking operation detection means. It has been.

  The road surface friction coefficient estimating device 50 performs a first road surface μ estimation process to be described later when the vehicle is traveling and turning based on the above-described input signals. A road surface μ estimation process is performed, and the estimated road surface friction coefficient μ is output to a predetermined control device (for example, a four-wheel drive control device or a braking force control device) not shown.

  Therefore, as shown in FIG. 2, the road surface friction coefficient estimating device 50 is mainly composed of a road surface μ estimation processing selection unit 51, a first road surface μ estimation processing unit 52, and a second road surface μ estimation processing unit 53. Yes.

The road surface μ estimation process selection unit 51 receives the vehicle speed V from the vehicle speed sensor 31 and the lateral acceleration d ² y / dt ² from the lateral acceleration sensor 37. When the vehicle is traveling (V ≠ 0) and the lateral acceleration d ² y / dt ² is equal to or greater than a preset value (d ² y / dt ² ) c 1, it is determined that the vehicle is turning, and the first A signal is output to the first road surface μ estimation processing unit 52 to perform the road surface μ estimation processing. When the vehicle is traveling (V ≠ 0) and the lateral acceleration d ² y / dt ² is less than a preset value (d ² y / dt ² ) c 1, it is determined that the vehicle is in a straight traveling state, and the second A signal is output to the second road surface μ estimation processing unit 53 to perform the road surface μ estimation processing. In addition, the determination of the straight travel may be performed by a yaw rate (yaw angular velocity) dψ / dt or the like in addition to the lateral acceleration d ² y / dt ² . As described above, the road surface μ estimation process selection unit 51 is provided as a straight traveling determination unit.

  As shown in FIG. 3, the first road surface μ estimation processing unit 52 mainly includes a vehicle body slip angle calculating unit 52a, a front wheel slip angle calculating unit 52b, and a road surface friction coefficient setting unit 52c.

  The vehicle slip angle calculation unit 52a receives the vehicle speed V from the vehicle speed sensor 31 and the handle angle θH from the handle angle sensor 32, and detects the detected handle angle based on a vehicle motion model based on a preset motion equation of the vehicle. The vehicle slip angle corresponding to θH and vehicle speed V is calculated and output to the front wheel slip angle calculator 52b.

Using the vehicle motion model of FIG. 5, a motion equation of the lateral motion of the vehicle is established. Equation of motion relating to the translational motion of the vehicle transverse direction, the cornering force (one wheel) to Cf of the front and rear wheels, Cr, the body mass M, when the lateral acceleration and ^{d 2} y / dt 2,
2 · Cf + 2 · Cr = M · (d ² y / dt ² ) (1)
It becomes.

On the other hand, the equation of motion related to the rotational motion around the center of gravity is expressed by the following (2) where the distance from the center of gravity to the front and rear wheel axes is Lf, Lr, the yaw moment of inertia of the vehicle body is Iz, and the yaw angular acceleration is d ² ψ / dt ^2. It is shown by the formula.
2 · Cf · Lf−2 · Cr · Lr = Iz · (d ² ψ / dt ² ) (2)

Further, if the vehicle slip angle is β and the vehicle slip angular velocity dβ / dt, the lateral acceleration d ² y / dt ² is
(D ² y / dt ² ) = V · ((dβ / dt) + (dψ / dt)) (3)
It is represented by
Therefore, the above equation (1) becomes the following equation (4).
2 · Cf + 2 · Cr = M · V · ((dβ / dt) + (dψ / dt)) (4)

The cornering force responds close to the first-order lag with respect to the side slip angle of the tire, but this response lag is ignored, and the suspension corner characteristics are linearized using an equivalent cornering power incorporating the tire characteristics. .
Cf = Kf · αf (5)
Cr = Kr · αr (6)
Here, Kf and Kr are equivalent cornering powers of the front and rear wheels, and αf and αr are slip angles of the front and rear wheels.

In consideration of the influence of rolls and suspensions in the equivalent cornering powers Kf, Kr, the front and rear wheel slip angles αf, αr are set to the front and rear wheel steering angles δf, δr, using the equivalent cornering powers Kf, Kr. The steering gear ratio can be simplified as follows, where n is n.
αf = δf− (β + Lf · (dψ / dt) / V)
= (ΘH / n) − (β + Lf · (dψ / dt) / V) (7)
αr = δr− (β−Lr · (dψ / dt) / V) (8)

ａ11＝−２・（Ｋｆ＋Ｋｒ）／（Ｍ・Ｖ）
ａ12＝−１．０−２・（Ｌｆ・Ｋｆ−Ｌｒ・Ｋｒ）／（Ｍ・Ｖ^２）
ａ21＝−２・（Ｌｆ・Ｋｆ−Ｌｒ・Ｋｒ）／Ｉｚ
ａ22＝−２・（Ｌｆ^２・Ｋｆ＋Ｌｒ^２・Ｋｒ）／（Ｉｚ・Ｖ）
ｂ11＝２・Ｋｆ／（Ｍ・Ｖ・ｎ）
ｂ12＝２・Ｋｒ／（Ｍ・Ｖ）
ｂ21＝２・Ｌｆ・Ｋｆ／Ｉｚ
ｂ22＝−２・Ｌｒ・Ｋｒ／Ｉｚ Summarizing the above equations of motion, the following equation of state is obtained.
(Dx (t) / dt) = A · x (t) + B · u (t) (9)
x (t) = [β (dψ / dt)] ^T
u (t) = [θH δr] ^T

a11 = −2 · (Kf + Kr) / (M · V)
a12 = −1.0−2 · (Lf · Kf−Lr · Kr) / (M · V ² )
a21 = -2. (Lf.Kf-Lr.Kr) / Iz
a22 = −2 · (Lf ² · Kf + Lr ² · Kr) / (Iz · V)
b11 = 2 · Kf / (M · V · n)
b12 = 2 · Kr / (MV)
b21 = 2 · Lf · Kf / Iz
b22 = −2 · Lr · Kr / Iz

であり、上記（１２）式は以下となる。
（ｄｘ'(t)／ｄｔ）＝Ａ・ｘ'(t)＋Ｂ・ｕ(t) −Ｋ・（ｘ' −ｘ）
…（１４）

Here, the configuration of the observer for estimating the vehicle slip angle will be described with reference to FIG.
When the output that can be measured (detected by the sensor) is shown below,
y (t) = C · x (t) (10)
The structure of the observer is as follows.
(Dx ′ (t) / dt) = (AK · C) · x ′ (t) + K · y (t) + B · u (t)
... (11)
Here, “′” in x ′ (t) indicates an estimated value.
Or
(Dx '(t) / dt) = A.x' (t) + B.u (t) -K.C. (x'-x)
(12)
When the above equation (12) is applied to a vehicle motion model,

The above equation (12) is as follows.
(Dx ′ (t) / dt) = A · x ′ (t) + B · u (t) −K · (x′−x)
... (14)

  Here, if K is set so that the matrix (AK · C) is a stable matrix, that is, the real part of the eigenvalue of (AK · C) is negative (complex left half surface), x ′ (t) → x (t) is guaranteed.

Since u (t) = [θH δr] ^T and x (t) = [β (dψ / dt)] ^T , the observer 61 that changes only the front wheel steering angle δf has a handle as shown in FIG. With respect to the input of the angle θH, the yaw rate and the vehicle body slip angle β are estimated.

  That is, the estimated yaw rate and the estimated vehicle slip angle β are the deviations between the actual yaw rate (the yaw rate from the yaw rate sensor 5) and the actual vehicle slip angle β ′ obtained by the calculation from the actual vehicle slip angle calculation unit 62 ( (Yaw rate deviation, vehicle slip angle deviation) is calculated, the yaw rate deviation is integrated with K1, and the vehicle slip angle deviation is integrated with K2, and each of these values is estimated as the product of the steering wheel angle θH and B, By subtracting the sum of the product of the estimated vehicle slip angle β and A and integrating the result, the yaw rate and the estimated vehicle slip angle β are accurately estimated and calculated. By using the vehicle motion model in this way, it is possible to effectively remove high-frequency sensor noise and the like that cannot be achieved with an actual vehicle.

Further, the actual vehicle slip angle calculation unit 62 calculates the actual vehicle slip angle β ′ necessary for feedback of the observer 61 by the following equation (15) instead of the sensor signal itself.
β ′ = ∫ ((d ² y / dt ² ) / V− (dψ / dt)) dt (15)

  The front wheel slip angle calculation unit 52b is configured to output the vehicle speed V from the vehicle speed sensor 31, the handle angle θH from the handle angle sensor 32, the yaw rate dψ / dt from the yaw rate sensor 38, and the estimated vehicle slip angle from the vehicle slip angle calculation unit 52a. β is input, and the slip angle αf of the steered wheel, that is, the front wheel is calculated according to the above-described equation (7), and the front wheel slip angle αf is output to the road surface friction coefficient setting unit 52c.

  The road surface friction coefficient setting unit 52c calculates the selection signal from the road surface μ estimation processing selection unit 51, the vehicle speed V from the vehicle speed sensor 31, the lateral forces Fyfl and Fyfr acting on the front wheels 12fl and 12fr from the force detection sensors 36fl and 36fr, and the front wheel slip angle calculation. When the front wheel slip angle αf estimated by the observer is input from the unit 52b and the selection signal from the road surface μ estimation processing selection unit 51 is input, the road surface friction coefficient μ is set and output based on the above-described signals. .

  The setting of the road surface friction coefficient μ in the road surface friction coefficient setting unit 52c is basically based on the front wheel slip angle αf and lateral force obtained in advance through experiments and calculations, for example, the front wheel slip angle (shown in FIG. Toe angle) and a map of the characteristics of the lateral force against the road friction coefficient. Here, the lateral force is an average value of the lateral force Fyfl of the left front wheel 12fl and the lateral force Fyfr of the right front wheel 12fr or the larger value.

  That is, the map of the characteristics of the front wheel slip angle (toe angle) and the lateral force with respect to the road surface friction coefficient shows a characteristic in which the lateral force increases as the road becomes higher at a high μ road for each front wheel slip angle αf. It is a map expressed in

  Further, when the vehicle speed V is very low (when it is lower than the preset threshold value Vc), the road surface friction coefficient setting unit 52c is greatly affected by the steering stationary torque, and the estimation accuracy is expected to deteriorate. Therefore, the setting of the road surface friction coefficient μ is prohibited.

  On the other hand, returning to FIG. 2, the second road surface μ estimation processing unit 53 receives a selection signal from the road surface μ estimation processing selection unit 51, a vehicle speed V from the vehicle speed sensor 31, a front obstacle from the front environment recognition device 34, and changes in road surface conditions. Lateral forces Fyfl and Fyfr acting on the front wheels 12fl and 12fr are input from the force detection sensors 36fl and 36fr, and a brake ON signal is input from the brake switch 39. When a selection signal is input from the road surface μ estimation processing selection unit 51, the road surface friction coefficient μ is set and output based on the above-described signals as follows.

  When a forward obstacle is detected by the forward environment recognition device 34, a signal is output to the steering control device 23 so that the front wheels 12fl and 12fr have a preset toe-out angle (for example, 2 to 3 °), and the steering actuator 20fl, 20fr is operated and the left and right front wheels 12fl, 12fr are toe-out. Then, by measuring the lateral force of the front wheels 12fl and 12fr, the front wheel slip angle (toe angle) and the map of the characteristics of the lateral force with respect to the road surface friction coefficient shown in FIG. Set and output.

  When a change in road surface condition is detected by the forward environment recognition device 34, a signal is output to the steering control device 23 so that the front wheels 12fl and 12fr have a preset toe-in (for example, 2 to 3 °) angle. Then, the left and right front wheels 12fl and 12fr are toe-in by operating the steering actuators 20fl and 20fr. Then, by measuring the lateral force of the front wheels 12fl and 12fr, the front wheel slip angle (toe angle) and the map of the characteristics of the lateral force with respect to the road surface friction coefficient shown in FIG. Set and output.

  Further, when a brake ON signal is input, a signal is output to the steering control device 23 so that the front wheels 12fl and 12fr have a preset toe-out angle (for example, 2 to 3 °), and the steering actuators 20fl and 20fr are output. And the left and right front wheels 12fl and 12fr are toe-out. Then, by measuring the lateral force of the front wheels 12fl and 12fr, the front wheel slip angle (toe angle) and the map of the characteristics of the lateral force with respect to the road surface friction coefficient shown in FIG. Set and output.

  If none of the above cases applies, a predetermined time Tc is set according to the vehicle speed V with reference to a preset map or the like, and the steering control device 23 is set for each predetermined time Tc. On the other hand, the front wheels 12fl and 12fr are output with a predetermined toe-in angle (for example, 2 to 3 °), and the steering actuators 20fl and 20fr are operated so that the left and right front wheels 12fl and 12fr are toe-in. Then, by measuring the lateral force of the front wheels 12fl and 12fr, the front wheel slip angle (toe angle) and the map of the characteristics of the lateral force with respect to the road surface friction coefficient shown in FIG. Set and output.

  For example, as shown in FIG. 8, the specified time Tc is set shorter as the vehicle speed V becomes higher. This is because the moving distance per unit time increases as the vehicle speed V increases. Further, the specified time Tc may be a certain fixed time (for example, 5 seconds).

  As described above, the second road surface μ estimation processing unit 53 is provided as a road surface friction coefficient estimation unit.

Next, the flow of the road surface friction coefficient estimation process in the road surface friction coefficient estimation device 50 will be described with reference to the flowchart of FIG. This program is executed every predetermined time. First, in step (hereinafter abbreviated as “S”) 101, the vehicle speed V and the lateral acceleration d ² y / dt ² are read.

  Next, the process proceeds to S102, where it is determined whether the vehicle speed V is 0, that is, whether or not the vehicle is stopped. If the vehicle is stopped (when V = 0), the program exits as it is and the vehicle is traveling (V ≠ 0). In case), the process proceeds to S103.

In S103, as compared with the lateral acceleration ^{d 2} y / dt 2 value previously set the ^{(d 2 y / dt 2)} c1, (d 2 y / dt 2) c1 or more when ^(d 2 y / If dt ² ≧ (d ² y / dt ² ) c 1), the vehicle is determined to be turning, and the process proceeds to S104 to execute the first road surface μ estimation process and exit the program.

Conversely, if it is less than (d ² y / dt ² ) c 1 (in the case of d ² y / dt ² <(d ² y / dt ² ) c ¹ ), it is determined that the vehicle is traveling straight ahead and the process proceeds to S105. Then, the second road surface μ estimation process is executed to exit the program.

The flow of the first road surface μ estimation process executed in S104 will be described with reference to the flowchart of FIG. First, in S201, the vehicle speed V, the steering wheel angle θH, the yaw rate dψ / dt, and the lateral acceleration d ² y / dt ² are read, and the process proceeds to S202 to determine whether or not the vehicle speed V is greater than or equal to a preset threshold value Vc. .

  If the vehicle speed V is less than the threshold value Vc in S202 (when V <Vc), the estimation accuracy is expected to deteriorate, and the routine exits without setting the road surface friction coefficient μ. On the other hand, when the vehicle speed V is equal to or higher than the threshold value Vc (when V ≧ Vc), the process proceeds to S203.

  In S203, the vehicle slip angle calculation unit 52a estimates the vehicle slip angle β with an observer, and further proceeds to S204. In the front wheel slip angle calculation unit 52b, the vehicle slip angle β is estimated based on the vehicle slip angle β estimated in S203. The front wheel slip angle αf is calculated by the equation (7).

  Thereafter, the process proceeds to S205, in which it is determined whether or not the front wheel slip angle αf calculated in S204 is equal to or greater than a preset threshold value θc. If the front wheel slip angle αf is equal to or greater than the threshold value θc (when αf ≧ θc), the process proceeds to S206. When the front wheel slip angle αf is less than the threshold value θc (when αf <θc), it is determined that the error in the front wheel slip angle αf is large, and the routine exits without setting the road surface friction coefficient μ.

  When the process proceeds from S205 to S206, the lateral forces Fyfl and Fyfr acting on the front wheels 12fl and 12fr are read.

  In S207, the road surface friction coefficient setting unit 52c determines the road friction of the front wheel slip angle and the lateral force based on the front wheel slip angle αf and the lateral force (average value of Fyfl and Fyfr or larger value). The road friction coefficient μ is set with reference to the characteristic map for the coefficient, and is output to exit the routine.

  Next, the flow of the second road surface μ estimation process executed in S105 described above will be described with reference to the flowchart of FIG. First, in step S <b> 301, a front obstacle is extracted by the front environment recognition device 34.

  Next, the process proceeds to S302, where it is determined whether or not there is a front obstacle. If there is a front obstacle, the process proceeds to S303, and the front wheels 12fl and 12fr are set to the steering control device 23 in advance. A signal with an angle of 2 to 3 ° is output. With this signal, the steering control device 23 operates the steering actuators 20fl and 20fr to make the left and right front wheels 12fl and 12fr toe out.

  Thereafter, the process proceeds to S304 to detect the lateral forces Fyfl and Fyfr of the front wheels 12fl and 12fr, and the process proceeds to S305 to refer to the map of the characteristics of the front wheel slip angle (toe angle) and the lateral force with respect to the road surface friction coefficient shown in FIG. Then, the road surface friction coefficient μ is set and output to exit the routine.

  In other words, when there are obstacles ahead, toe out makes it possible to improve the steering response for obstacle avoidance as well as improve the assist control performance of obstacle avoidance by estimating the road surface μ. Estimation can be performed.

  If it is determined in step S302 that there is no forward obstacle, the process proceeds to step S306, and changes in road surface conditions recognized by the forward environment recognition device 34 are read.

  Then, the process proceeds to S307, where it is determined whether or not there is a change in the road surface condition. If it is determined that there is a change in the road surface condition, the process proceeds to S308 and the front wheels 12fl and 12fr are set in advance for the steering control device 23. A signal having an angle of toe-in (for example, 2 to 3 °) is output. With this signal, the steering control device 23 operates the steering actuators 20fl and 20fr to make the left and right front wheels 12fl and 12fr toe-in.

  Thereafter, the process proceeds to S309 to detect the lateral forces Fyfl and Fyfr of the front wheels 12fl and 12fr, and the process proceeds to S310 to refer to the characteristic map of the front wheel slip angle (toe angle) and the lateral force with respect to the road surface friction coefficient shown in FIG. Then, the road surface friction coefficient μ is set and output to exit the routine.

  That is, when there is a change in the road surface condition, it is possible to estimate the road surface μ while improving the straight running stability by using toe-in.

  If it is determined in S307 that there is no change in the road surface condition, the process proceeds to S311 to determine whether the brake switch is ON and a braking operation is being performed.

  If the result of this determination is that the brake switch is ON, the process proceeds to S312 and a signal is output to the steering control device 23 with the front wheels 12fl and 12fr having a preset toe-out (for example, 2 to 3 °) angle. With this signal, the steering control device 23 operates the steering actuators 20fl and 20fr to make the left and right front wheels 12fl and 12fr toe out.

  Thereafter, the process proceeds to S313 to detect the lateral forces Fyfl and Fyfr of the front wheels 12fl and 12fr, and the process proceeds to S314 to refer to the map of the characteristics of the front wheel slip angle (toe angle) and the lateral force with respect to the road surface friction coefficient shown in FIG. Then, the road surface friction coefficient μ is set and output to exit the routine.

  In other words, when there is a braking operation, the toe-out makes it possible not only to estimate the road surface μ and improve the braking efficiency, but also to estimate the road surface μ while improving the stability during braking. Yes.

  If it is determined in S311 above that the brake switch is OFF, the process proceeds to S315 and, for example, a specified time Tc based on the vehicle speed is set with reference to a map shown in FIG.

  Then, the process proceeds to S316, where it is determined whether or not the specified time Tc has elapsed since the previous estimation. If the specified time Tc has not elapsed, the routine is directly exited. If the specified time Tc has elapsed, the process proceeds to S317, and a signal for setting the front wheels 12fl and 12fr to a predetermined toe-in angle (for example, 2 to 3 °) is output to the steering control device 23. With this signal, the steering control device 23 operates the steering actuators 20fl and 20fr to make the left and right front wheels 12fl and 12fr toe-in.

  Thereafter, the process proceeds to S318 to detect the lateral forces Fyfl and Fyfr of the front wheels 12fl and 12fr, and the process proceeds to S319 to refer to the map of characteristics of the front wheel slip angle (toe angle) and the lateral force with respect to the road surface friction coefficient shown in FIG. Then, the road surface friction coefficient μ is set and output to exit the routine.

  In other words, during normal straight running, it is possible to perform road surface μ estimation while improving straight-line stability without making the driver feel uncomfortable by executing toe-in and executing road surface μ estimation at each specified time Tc. Yes.

  As described above, according to the embodiment of the present invention, it is possible to estimate the road friction coefficient quickly and accurately even in a straight traveling state.

  In this embodiment, the independent steering mechanism using the steer-by-wire mechanism is described as an example. However, it goes without saying that the present invention can also be applied to an alignment variable mechanism in which the toe angle can be varied.

  In this embodiment, the lateral force acting on the front wheel is detected, and the road surface μ is estimated from the characteristics of the lateral force and the front wheel slip angle (toe angle). The acting self-aligning torque may be detected, and the road surface μ may be estimated from the characteristics of the self-aligning torque and the front wheel slip angle (toe angle).

Schematic configuration diagram of a vehicle equipped with a road surface friction coefficient estimation device Functional block diagram of road friction coefficient estimation device Functional block diagram of the first road surface μ estimation processing unit Functional block diagram showing the configuration of the body slip angle calculation unit Explanatory drawing showing a two-wheel model of lateral movement of a vehicle Explanatory drawing showing the structure of a general observer Explanatory diagram of characteristics of front wheel slip angle (toe angle) and lateral force against road friction coefficient Explanatory diagram of characteristics of specified time set based on vehicle speed Flowchart of road friction coefficient estimation First road surface μ estimation process flowchart Flowchart of second road surface μ estimation process

Explanation of symbols

1 Vehicle 12fl, 12fr, 12rl, 12rr Wheel 15 Steering device (toe angle variable means)
23 Steering control device 34 Front environment recognition device (obstacle detection means, road surface condition detection means)
36fl, 36fr Force detection sensor (detection means)
39 Brake switch (braking operation detection means)
50 Road Surface Friction Coefficient Estimator 51 Road Surface μ Estimation Process Selection Unit (Straight Advancing Determination Unit)
52 first road surface μ estimation processing unit 53 second road surface μ estimation processing unit (road surface friction coefficient estimating means)

Claims (6)

Toe angle varying means for varying the toe angle of the left and right wheels;
Detecting means for detecting either the lateral force acting on the left and right wheels or the self-aligning torque;
Straight-ahead determining means for determining whether or not the vehicle is in a straight-ahead state;
Front wheel slip angle calculating means for estimating the front wheel slip angle;
When the vehicle is traveling straight, a signal for changing the toe angle of the left and right front wheels by a preset amount is output to the toe angle varying means, and the toe angle of the left and right front wheels and the lateral force detected by the detecting means While estimating the road friction coefficient based on either the self-aligning torque or
Road friction coefficient estimating means for estimating a road surface friction coefficient based on either the front wheel slip angle, the lateral force detected by the detecting means or the self-aligning torque when it is determined that the vehicle is not in a straight traveling state. When,
An apparatus for estimating a road surface friction coefficient of a vehicle.   The road surface friction coefficient estimating means outputs a signal for setting the left and right wheels to a preset toe-in angle to the toe angle varying means when the vehicle is traveling straight, and detecting the toe-in angle and the detecting means by the detecting means. 2. The road surface friction coefficient estimating device for a vehicle according to claim 1, wherein the road surface friction coefficient is estimated for each preset time based on either the lateral force or the self-aligning torque. Toe angle varying means for varying the toe angle of the left and right wheels;
Detecting means for detecting either the lateral force acting on the left and right wheels or the self-aligning torque;
An obstacle detecting means for detecting an obstacle ahead,
Straight-ahead determining means for determining whether or not the vehicle is in a straight-ahead state;
When detecting a front obstacle, and outputs a signal vehicles is to the toe angle changing means toe-out angle set in advance the left and right wheels relative to the time of running straight, at an angle and the detection means of the toe Road surface friction coefficient estimating means for estimating a road surface friction coefficient based on either the detected lateral force or self-aligning torque ;
Vehicles of the road surface friction coefficient estimating device you comprising the. Toe angle varying means for varying the toe angle of the left and right wheels;
Detecting means for detecting either the lateral force acting on the left and right wheels or the self-aligning torque;
And road surface conditions detection means for detecting a change in front of the road conditions,
Straight-ahead determining means for determining whether or not the vehicle is in a straight-ahead state;
When detecting a change in the front of the road surface condition, and outputs a signal vehicles is to the toe angle varying means preset angle of toe of the left and right wheels relative to the time of straight traveling state, the toe angle and the Road friction coefficient estimating means for estimating the road friction coefficient based on either the lateral force detected by the detecting means or the self-aligning torque ;
Vehicles of the road surface friction coefficient estimating device you comprising the. Toe angle varying means for varying the toe angle of the left and right wheels;
Detecting means for detecting either the lateral force acting on the left and right wheels or the self-aligning torque;
Braking operation detecting means for detecting the execution of the braking operation,
Straight-ahead determining means for determining whether or not the vehicle is in a straight-ahead state;
When detecting the execution of the braking operation, and outputs a signal to the angle of toe-out set in advance the left and right wheels relative to the toe angle changing means when vehicles are running straight, the toe-out angle and the detection means Road surface friction coefficient estimating means for estimating a road surface friction coefficient based on either the lateral force or the self-aligning torque detected in step ;
Vehicles of the road surface friction coefficient estimating device you comprising the. Front wheel slip angle calculating means for estimating the front wheel slip angle;
  When it is determined that the vehicle is not in a straight traveling state, the road surface friction coefficient estimating means determines the road surface friction coefficient based on either the front wheel slip angle, the lateral force detected by the detection means, or the self-aligning torque. The road surface friction coefficient estimating device for a vehicle according to any one of claims 3 to 5, wherein:

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