JP2017001625A - Vehicular steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vehicular steering device by which it becomes possible to obtain appropriate assist torque corresponding to environmental change and secular change by correcting the assist torque by a new method.SOLUTION: A correction gain calculation part 52 intermittently calculates an average rate (an average value μof inclination μ) of variation of a normalized yaw rate Yr/V to variation of a steering angle θ. Then, the correction gain calculation part 52 calculates a correction gain G on the basis of the calculated average value of the inclination. A gain multiplication part 53 corrects a lane keep assist current value by multiplying a lane keep assist current value Irocalculated by a lane keep assist current value calculation part 51 by the correction gain G set by the correction gain calculation part 52.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a vehicle steering apparatus.

A vehicle steering device has been developed that causes a lane keeping assist torque to be generated by a steering motor so that the vehicle travels along a target route. In such a vehicle steering apparatus, the lane keep assist torque may not necessarily be an appropriate value due to environmental changes such as changes in road surface conditions and changes over time such as tire deterioration.
Patent Document 1 discloses a vehicle steering apparatus that can adjust a lane keep assist torque so as to obtain an appropriate lane keep assist torque according to an environmental change or a change over time. In the vehicle steering apparatus described in Patent Document 1, the model yaw rate is calculated from the vehicle speed and the steering angle. A vehicle state index is calculated based on the model yaw rate and the actual yaw rate. A gain for adjusting the lane keep assist torque is calculated based on the vehicle state index.

JP-A-11-78951 JP 2013-212839 A Japanese Patent No. 4292562 JP-A-11-34774

  An object of the present invention is to provide a vehicle steering apparatus that can obtain an appropriate assist torque corresponding to an environmental change or a change over time by correcting the assist torque by a novel method.

The invention according to claim 1 is an electric motor (18) for applying a steering driving force to the steering mechanism (4) of the vehicle, a steering angle detecting means (25) for detecting a steering angle, and the vehicle. A yaw rate detecting means (26) for detecting the yaw rate, a vehicle speed detecting means (23) for detecting the vehicle speed, an assist current value calculating means (51) for calculating an assist current value corresponding to a target value of the assist torque, and the steering The assist current value calculation is based on the steering angle (θ) detected by the angle detection means, the yaw rate (Yr) detected by the yaw rate detection means, and the vehicle speed (V) detected by the vehicle speed detection means. The target current value is calculated using the correction means (52, 53) for correcting the assist current value calculated by the means and the assist current value corrected by the correction means. Standard current value calculating means (44), and control means (45, 46) for driving and controlling the electric motor based on the target current value calculated by the target current value calculating means, and the correcting means, Estimating means for intermittently estimating an average ratio (μ _(n) ) of the change amount of the normalized yaw rate to the change amount of the steering angle, with a value obtained by dividing the yaw rate by the vehicle speed as a normalized yaw rate (Yr / V); And a means for correcting the assist current value calculated by the assist current value calculating means using the average ratio estimated by the estimating means. In addition, although the alphanumeric character in parentheses represents a corresponding component in an embodiment described later, of course, the scope of the present invention is not limited to the embodiment. The same applies hereinafter.

In the present invention, the average ratio (μ _(n) ) of the change amount of the normalized yaw rate (Yr / V) with respect to the change amount of the steering angle (θ) is estimated intermittently, and the assist current is estimated using the estimated average ratio. The value is corrected. That is, in the present invention, the assist torque is corrected by a novel method. The average ratio of the change amount of the normalized yaw rate to the change amount of the steering angle changes according to the environmental change and the change with time. Therefore, according to the present invention, an appropriate assist torque corresponding to an environmental change or a change with time can be obtained.

According to a second aspect of the present invention, the assist current value calculating means is configured to calculate a lane keep assist current value corresponding to a target value of lane keep assist torque for causing the vehicle to travel along the target travel line. The vehicle steering device according to claim 1.
The invention according to claim 3 further includes information acquisition means (42) for acquiring a lateral deviation of the vehicle from the target travel line and a lateral deviation change rate that is a change rate per unit time of the lateral deviation, The assist current value calculating means is configured to calculate a lane keep assist current value corresponding to a target value of lane keep assist torque for making the lateral deviation and the lateral deviation change rate close to zero. It is a steering device for vehicles given in.

  The invention according to claim 4 further includes steering assist current value setting means (41) for setting a steering assist current value corresponding to a target value of the steering assist torque, wherein the target current value calculation means is a steering assist current value setting. 4. The target current value is calculated using the steering assist current value set by the means and the lane keep assist current value corrected by the correcting means. This is a vehicle steering apparatus.

FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus to which a vehicle steering apparatus according to an embodiment of the present invention is applied. FIG. 2 is a block diagram showing an electrical configuration of the ECU. FIG. 3 is a graph showing a setting example of the steering assist current value Is ^* with respect to the detected steering torque T. FIG. 4 is a schematic diagram for explaining the operation of the information acquisition unit. FIG. 5 is a block diagram showing an electrical configuration of the lane keep assist current value calculation unit. 6A is a graph showing an example of a first lane keep assist current value Ir1 ^* relationship with respect to the lateral deviation w, FIG. 6B, another example of the first lane keep assist current value Ir1 ^* relationship to the lateral deviation w FIG. 6C is a graph showing still another example of the relationship between the first lane keep assist current value Ir1 ^* and the lateral deviation w. FIG. 7A is a graph showing an example of the relationship of the second lane keep assist current value Ir2 ^* with respect to the lateral deviation change rate dw / dt, and FIG. 7B shows the second lane keep assist current value with respect to the lateral deviation change rate dw / dt. It is a graph which shows the other example of the relationship of Ir2 ^* . FIG. 8 is a graph showing a setting example of the vehicle speed gain Gv with respect to the vehicle speed V. FIG. 9 is a schematic diagram for explaining the operation of the correction gain calculation unit. FIG. 10 is a flowchart for explaining the operation of the correction gain calculation unit.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing a schematic configuration of an electric power steering apparatus to which a vehicle steering apparatus according to an embodiment of the present invention is applied.
An electric power steering device (EPS) 1 includes a steering wheel 2 as a steering member for steering a vehicle, and a steering mechanism that steers the steered wheels 3 in conjunction with the rotation of the steering wheel 2. 4 and a steering assist mechanism 5 for assisting the driver's steering. The steering wheel 2 and the steering mechanism 4 are mechanically coupled via a steering shaft 6 and an intermediate shaft 7.

The steering shaft 6 includes an input shaft 8 connected to the steering wheel 2 and an output shaft 9 connected to the intermediate shaft 7. The input shaft 8 and the output shaft 9 are connected via a torsion bar 10 so as to be relatively rotatable.
Around the input shaft 8, a steering angle sensor 25 for detecting a steering angle θ that is a rotation angle of the input shaft 8 is arranged. In this embodiment, the rudder angle sensor 25 detects the amount of rotation (rotation angle) of the input shaft 8 in both forward and reverse directions from the neutral position of the input shaft 8, and the amount of rotation from the neutral position to the right is detected. For example, it outputs as a positive value, and outputs the amount of rotation from the neutral position to the left as, for example, a negative value.

  A torque sensor 11 is disposed around the torsion bar 10. The torque sensor 11 detects the steering torque T applied to the steering wheel 2 based on the relative rotational displacement amount of the input shaft 8 and the output shaft 9. In this embodiment, the steering torque T detected by the torque sensor 11 is detected, for example, as a torque for steering in the right direction as a positive value and a torque for steering in the left direction as a negative value. It is assumed that the magnitude of the steering torque increases as the absolute value thereof is detected.

  The steered mechanism 4 includes a rack and pinion mechanism including a pinion shaft 13 and a rack shaft 14 as a steered shaft. The steered wheel 3 is connected to each end of the rack shaft 14 via a tie rod 15 and a knuckle arm (not shown). The pinion shaft 13 is connected to the intermediate shaft 7. The pinion shaft 13 rotates in conjunction with the steering of the steering wheel 2. A pinion 16 is connected to the tip of the pinion shaft 13 (the lower end in FIG. 1).

  The rack shaft 14 extends linearly along the left-right direction of the vehicle. A rack 17 that meshes with the pinion 16 is formed at an intermediate portion in the axial direction of the rack shaft 14. By the pinion 16 and the rack 17, the rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. The steered wheels 3 can be steered by moving the rack shaft 14 in the axial direction.

When the steering wheel 2 is steered (rotated), this rotation is transmitted to the pinion shaft 13 via the steering shaft 6 and the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into an axial movement of the rack shaft 14 by the pinion 16 and the rack 17. Thereby, the steered wheel 3 is steered.
The steering assist mechanism 5 includes a steering assist electric motor 18 for generating a steering assist force (steering assist torque) and a deceleration mechanism 19 for transmitting the output torque of the electric motor 18 to the steering mechanism 4. . The speed reduction mechanism 19 includes a worm gear mechanism that includes a worm shaft 20 and a worm wheel 21 that meshes with the worm shaft 20. The speed reduction mechanism 19 is accommodated in a gear housing 22 as a transmission mechanism housing.

The worm shaft 20 is rotationally driven by the electric motor 18. The worm wheel 21 is coupled to the steering shaft 6 so as to be rotatable in the same direction. The worm wheel 21 is rotationally driven by the worm shaft 20.
When the worm shaft 20 is rotationally driven by the electric motor 18, the worm wheel 21 is rotationally driven and the steering shaft 6 rotates. The rotation of the steering shaft 6 is transmitted to the pinion shaft 13 via the intermediate shaft 7. The rotation of the pinion shaft 13 is converted into the axial movement of the rack shaft 14. Thereby, the steered wheel 3 is steered. That is, the wheel 3 is steered by rotating the worm shaft 20 by the electric motor 18. That is, the electric motor 18 is a motor for generating a driving force for turning for turning the steered wheels 3.

The vehicle is equipped with a vehicle speed sensor 23 for detecting the vehicle speed V, a yaw rate sensor 26 for detecting the yaw rate Yr of the vehicle, and a CCD (Charge Coupled Device) camera 24 for photographing a road ahead in the direction of travel of the vehicle. Yes.
The steering angle θ detected by the steering angle sensor 25, the steering torque T detected by the torque sensor 11, the vehicle speed V detected by the vehicle speed sensor 23, the yaw rate Yr detected by the yaw rate sensor 26, and the CCD camera 24 are output. The image signal is input to an ECU (Electronic Control Unit) 12. The ECU 12 controls the electric motor 18 based on these input signals.

FIG. 2 is a block diagram showing an electrical configuration of the ECU 12.
The ECU 12 includes a microcomputer 31 for controlling the electric motor 18, a drive circuit (inverter circuit) 32 that is controlled by the microcomputer 31 and supplies electric power to the electric motor 18, and a motor current (actual current) that flows through the electric motor 18. A current detection circuit 33 for detecting the value (I).

  The microcomputer 31 includes a CPU and a memory (ROM, RAM, non-volatile memory, etc.), and functions as a plurality of function processing units by executing a predetermined program. The plurality of function processing units include a steering assist current value setting unit 41, an information acquisition unit 42, a lane keep assist current value setting unit 43, a target current value calculation unit 44, a current deviation calculation unit 45, and a PI. A control unit 46 and a PWM control unit 47 are included.

The steering assist current value setting unit 41 sets a steering assist current value Is ^* that is a motor current value corresponding to the target value of the steering assist torque. The steering assist current value setting unit 41 sets the steering assist current value Is ^* based on the steering torque T detected by the torque sensor 11 and the vehicle speed V detected by the vehicle speed sensor 23. A setting example of the steering assist current value Is ^* with respect to the detected steering torque T is shown in FIG. For the detected steering torque T, for example, the torque for steering in the right direction is a positive value, and the torque for steering in the left direction is a negative value. The steering assist current value Is ^* is a positive value when a steering assist force for rightward steering is to be generated from the electric motor 18, and a steering assist force for leftward steering is generated from the electric motor 18. When power is to be negative.

The steering assist current value Is ^* is positive for a positive value of the detected steering torque T, and is negative for a negative value of the detected steering torque T. When the detected steering torque T is a small value (torque dead zone) in the range of -T1 to T1 (for example, T1 = 0.4 N · m), the steering assist current value Is ^* is set to zero. When the detected steering torque T is outside the range of -T1 to T1, the steering assist current value Is ^* is set so that the absolute value of the steering assist current value Is ^* increases as the absolute value of the detected steering torque T increases. Has been. The steering assist current value Is ^* is set such that the absolute value thereof decreases as the vehicle speed V detected by the vehicle speed sensor 23 increases. As a result, a large steering assist force can be generated during low-speed traveling, and the steering assist force can be reduced during high-speed traveling.

  As shown in FIG. 4, the information acquisition unit 42 recognizes a pair of lane boundary lines (white lines) Ll and Lr indicating a lane in which the vehicle 100 is traveling based on an image captured by the CCD camera 24. The travel lane of the vehicle 100 is recognized. Then, the information acquisition unit 42 sets the target travel line Ls of the vehicle 100 in the travel lane of the vehicle 100. In this embodiment, the target travel line Ls is set at the center of the width of the travel lane. The information acquisition unit 42 also acquires the lateral deviation w of the vehicle 100 from the target travel line Ls and the lateral deviation change rate dw / dt, which is the rate of change per unit time of the lateral deviation w.

  The lateral deviation w of the vehicle 100 represents the distance from the reference position C of the vehicle 100 to the target travel line Ls in plan view. The reference position C of the vehicle 100 may be the position of the center of gravity of the vehicle 100, or may be the arrangement position of the CCD camera 24 in the vehicle 100. In this embodiment, when the reference position C of the vehicle 100 is on the right side of the target travel line Ls in the traveling direction, the sign of the lateral deviation w is positive, and when the vehicle is on the left side of the target travel line Ls. The lateral deviation w is set so that the sign of the lateral deviation w is negative.

  The lateral deviation change rate dw / dt is a deviation (w (t) −w (t−) between the lateral deviation w (t) acquired this time and the lateral deviation w (t−Δt) acquired before a predetermined unit time Δt. Δt)). The lateral deviation change rate dw / dt is the deviation (w (t + Δt) −w (t)) between the lateral deviation w (t + Δt) predicted after a predetermined unit time Δt and the lateral deviation w (t) acquired this time. ). The predicted value w (t + Δt) of the lateral deviation may be obtained in consideration of the vehicle speed, the yaw angle, and the like.

  Further, the lateral deviation change rate dw / dt includes a lateral deviation w (t + Δtx) predicted at a time point t1 after a predetermined time Δtx and a lateral deviation w (a predicted time t2 after a predetermined unit time Δt from the time point t1). It may be a deviation (w (t + Δtx + Δt) −w (t + Δtx)) from t + Δtx + Δt). The predicted values w (t + Δtx) and w (t + Δtx + Δt) of the lateral deviation may be obtained in consideration of the vehicle speed, the yaw angle, and the like. A method for calculating or predicting the lateral deviation w of the vehicle by imaging a road ahead in the traveling direction of the vehicle is well known as described in Patent Documents 2, 3, 4 and the like, and thus the description thereof is omitted.

Returning to FIG. 2, the lane keep assist current value setting unit 43 moves the vehicle 100 along the target travel line Ls based on the vehicle speed V, the lateral deviation w, the lateral deviation change rate dw / dt, the steering angle θ, and the yaw rate Yr. A lane keep assist current value Ir ^* for running is set. Details of the lane keep assist current value setting unit 43 will be described later.
The target current value calculation unit 44 adds the lane keep assist current value Ir ^* set by the lane keep assist current value setting unit 43 to the steering assist current value Is ^* set by the steering assist current value setting unit 41. Thus, the target current value I ^* is calculated. The current deviation calculation unit 45 calculates a deviation (current deviation ΔI = I ^* −I) between the target current value I ^* obtained by the target current value calculation unit 44 and the actual current value I detected by the current detection circuit 33. To do.

The PI control unit 46 generates a drive command value for guiding the current I flowing through the electric motor 18 to the target current value I ^* by performing a PI calculation on the current deviation ΔI calculated by the current deviation calculation unit 45. The PWM control unit 47 generates a PWM control signal having a duty ratio corresponding to the drive command value and supplies the PWM control signal to the drive circuit 32. As a result, electric power corresponding to the drive command value is supplied to the electric motor 18.

The current deviation calculation unit 45 and the PI control unit 46 constitute a current feedback control unit. By the function of this current feedback control means, the motor current I flowing through the electric motor 18 is controlled so as to approach the target current value I ^* .
Hereinafter, the lane keep assist current value setting unit 43 will be described in detail. As shown in FIG. 2, the lane keep assist current value setting unit 43 includes a lane keep assist current value calculation unit 51, a correction gain calculation unit 52, and a gain multiplication unit 53.

The lane keep assist current value calculation unit 51 is configured to bring the lateral deviation w and the lateral deviation change rate dw / dt close to zero based on the lateral deviation w and the lateral deviation change rate dw / dt acquired by the information acquisition unit 42. A lane keep assist current value Iro ^* corresponding to the lane keep assist torque is calculated.
FIG. 5 is a block diagram showing an electrical configuration of the lane keep assist current value calculation unit 51. The lane keep assist current value calculation unit 51 includes a first current value calculation unit 61, a second current value calculation unit 62, an addition unit 63, a vehicle speed gain setting unit 64, and a multiplication unit 65.

The first current value calculation unit 61 calculates a first lane keep assist current value Ir1 ^* based on the lateral deviation w. The second current value calculation unit 62 calculates the second lane keep assist current value Ir2 ^* based on the lateral deviation change rate dw / dt. The adder 63 adds the first lane keep assist current value Ir1 ^* calculated by the first current value calculator 61 and the second lane keep assist current value Ir2 ^* calculated by the second current value calculator 62. Thus, the third lane keep assist current value Ir3 ^* (= Ir1 ^* + Ir2 ^* ) is calculated. The vehicle speed gain setting unit 64 sets a vehicle speed gain Gv corresponding to the vehicle speed V. The multiplying unit 65 multiplies the third lane keep assist current value Ir3 ^* (= Ir1 ^* + Ir2 ^* ) calculated by the adding unit 63 by the vehicle speed gain Gv set by the vehicle speed gain setting unit 64, thereby maintaining the lane keep. The assist current value Iro ^* (= Gv · (Ir1 ^* + Ir2 ^* )) is calculated. The lane keep assist current value Iro ^* is given to the gain multiplier 53.

Hereinafter, each of the 1st electric current value calculating part 61, the 2nd electric current value calculating part 62, and the vehicle speed gain setting part 64 is demonstrated more concretely.
The first current value calculation unit 61 calculates the first lane keep assist current value Ir1 ^* based on a map or a calculation formula indicating the relationship of the first lane keep assist current value Ir1 ^* to a preset lateral deviation w. . The second current value calculator 62 calculates the second lane keep assist current value Ir2 based on a map or a calculation formula indicating the relationship of the second lane keep assist current value Ir2 ^* to a preset lateral deviation change rate dw / dt. ^* Is calculated.

When a1 and a2 are constants of the same sign, b1 is an order composed of two or more natural numbers, and b2 is an order composed of a natural number smaller than b1, the first current value calculation unit 61 and the second current value calculation unit 62 are It is preferable to calculate the first lane keep assist current value Ir1 ^* and the second lane keep assist current value Ir2 ^* as follows.
That is, the first current value calculation unit 61, if b1 is set to ^odd, Ir1 * = is represented by a function of a1 · ^{w b1,} based on the relationship between w and Ir1 ^*, first lane It is preferable to calculate the keep assist current value Ir1 ^* . On the other hand, if b1 is set to an even number, in the range of w ≧ ^0, Ir1 * = expressed in function of a1 · ^{w b1,} in the range of w ^<0, Ir1 * = function -a1 · ^{w b1} It is preferable to calculate the first lane keep assist current value Ir1 ^* based on the relationship between w and Ir1 ^* .

Further, when b2 is set to an odd number, the second current value calculation unit 62 has a relationship between dw / dt and Ir2 ^* represented by a function of Ir2 ^* = a2 · (dw / dt) ^b2. Therefore, it is preferable to calculate the second lane keep assist current value Ir2 ^* . On the other hand, when b2 is set to an even number, it is expressed by a function of Ir2 ^* = a2 · (dw / dt) ^b2 in the range of dw / dt ≧ 0, and Ir2 ^{* in} the range of dw / dt <0 ^. = −a2 · (dw / dt) It is preferable to calculate the second lane keep assist current value Ir2 ^* based on the relationship between dw / dt and Ir2 ^* expressed by the function of ^b2 .

As described above, in this embodiment, the steering assist current value Is ^* is a positive value when a steering assist force for rightward steering is to be generated from the electric motor 18, and the leftward steering of the electric motor 18 is determined. When the steering assist force is to be generated, a negative value is set. When the reference position of the vehicle is on the right side of the target travel line Ls in the traveling direction, the sign of the lateral deviation w is positive, and when it is on the left side of the target travel line Ls, the lateral deviation w The lateral deviation w is set so that the sign of is negative. When the sign is set in this way, the constants a1 and a2 are set to negative values.

Even when the sign of the steering assist current value Is ^* is set opposite to that in the above embodiment and the sign of the lateral deviation w is set opposite to that in the above embodiment, the constants a1 and a2 are negative values. Set to
On the other hand, when the sign of the steering assist current value Is ^* is set in the same manner as in the embodiment and the sign of the lateral deviation w is set opposite to that in the embodiment, or the sign of the steering assist current value Is ^* is When the reverse of the embodiment is set and the sign of the lateral deviation w is set similarly to the embodiment, the constants a1 and a2 are set to positive values.

The reason why it is preferable that the first current value calculation unit 61 and the second current value calculation unit 62 calculate the first lane keep assist current value Ir1 ^* and the second lane keep assist current value Ir2 ^* as described above. ,explain.
In general, when a is a constant, in the function represented by f (x) = ax ^b (b is a natural number), the absolute value of f (x) increases as the absolute value of x increases. . When the value of b is 2 or more, the average rate of change increases as the absolute value of x increases. The average rate of change means (change amount of f (x)) / (change amount of x).

If the value of b1 is 2 or more, the absolute value of the first lane keep assist current value Ir1 ^* increases as the absolute value of the lateral deviation w increases, and the average rate of change increases as the absolute value of the lateral deviation w increases. (Increase rate of absolute value of first lane keep assist current value Ir1 ^* ) increases. For this reason, the vehicle can be quickly guided to the target travel line side (in this embodiment, the width center side of the travel lane).

Further, in the function represented by f (x) = ax ^b , the larger b is, the smaller the average change rate in the range where the absolute value of x is less than 1, and the average change in the range where the absolute value of x is 1 or more. The rate increases.
When a1 is equal to a2 and b1 is greater than b2, the average change rate of the first lane keep assist current value Ir1 ^* in the range where the absolute value of the lateral deviation w is less than 1 is the lateral deviation change rate. First lane keep assist in the range where the absolute value of the lateral deviation w is larger than 1 and smaller than the average change rate of the second lane keep assist current value Ir2 ^* in the range where the absolute value of dw / dt is less than 1. The average change rate of the current value Ir1 ^* is larger than the average change rate of the second lane keep assist current value Ir2 ^{* when} the absolute value of the lateral deviation change rate dw / dt is larger than 1.

Accordingly, when the reference position of the vehicle is in a region away from the target travel line, the sign of the second lane keep assist current value Ir2 ^* is opposite to the sign of the first lane keep assist current value Ir1 ^*. Even so, the first lane keep assist current value Ir1 ^* works to bring the lateral deviation w closer to zero, while the second lane keep assist current value Ir2 ^* tries to bring the lateral deviation change rate dw / dt closer to zero. It is considered that the vehicle is likely to become stronger than the function to perform, so that the vehicle can be guided to the target travel line side (in this embodiment, the width center side of the travel lane).

Further, regardless of the value of the lateral deviation w, the second lane keep assist current value Ir2 ^* corresponding to the magnitude of the lateral deviation change rate dw / dt is obtained, so that the reference position of the vehicle is in the region near the target travel line. Even in some cases, the vehicle can be guided such that the center line in the width direction of the vehicle is parallel to the target travel line.
In this embodiment, the first current value calculation unit 61 is based on a map storing the relationship of the first lane keep assist current value Ir1 ^* with respect to the lateral deviation w shown in FIG. 6A or an arithmetic expression representing the relationship. The first lane keep assist current value Ir1 ^* is calculated. In the example of FIG. 6A, the first lane keeping assist current value Ir1 ^* is the a1 as negative constant ^is represented by a cubic function of Ir1 * = a1 · ^{w 3.} That is, this function corresponds to the case where a1 is negative and b1 is 3.

For example, the first current value calculation unit 61 is based on a map storing the relationship of the first lane keep assist current value Ir1 ^* to the lateral deviation w shown in FIG. 6B or an arithmetic expression representing the relationship. One lane keep assist current value Ir1 ^* may be calculated. The curve shown in FIG. 6B moves the curve in the region where Ir1 ^* is zero or more in FIG. 6A by −A (A> 0) in the horizontal axis direction, and the curve in the region where Ir1 ^* is less than zero in FIG. 6A. Is moved by + A in the horizontal axis direction. In the curve of FIG. 6B, a dead zone is set in which the first lane keep assist current value Ir1 ^* becomes zero in the range from the first lane keep assist current value Ir1 ^* to -A (A> 0) to A.

For example, the first current value calculation unit 61 is based on a map storing the relationship of the first lane keep assist current value Ir1 ^* to the lateral deviation w shown in FIG. 6C or an arithmetic expression representing the relationship. One lane keep assist current value Ir1 ^* may be calculated. In the example of FIG. 6C, the first lane keep assist current value Ir1 ^*, when the a1 and negative constant in a range of w ≧ ^0, represented by Ir1 * = a1 · ^{w 2} of the quadratic function, w <0 in the range ^of, represented by Ir1 * = -a1 · ^{w 2} of a quadratic function. This function corresponds to the case where the a1 is negative and the b1 is 2.

In this embodiment, the second current value calculation unit 62 stores a map storing the relationship of the second lane keep assist current value Ir2 ^{* to} the lateral deviation change rate dw / dt shown in FIG. 7A or represents the relationship. Based on the calculation formula, the second lane keep assist current value Ir2 ^* is calculated. In the example of FIG. 7A, the second lane keep assist current value Ir2 ^* is represented by a linear function of Ir2 ^* = a2 · dw / dt, where a2 is a negative constant. That is, this function corresponds to the case where a2 is negative and b2 is 1. A dead zone in which the second lane keep assist current value Ir2 ^* is zero may be provided when the absolute value of the lateral deviation change rate dw / dt is near zero.

For example, the second current value calculation unit 62 stores a map storing the relationship of the second lane keep assist current value Ir2 ^* with respect to the lateral deviation change rate dw / dt shown in FIG. 7B or a calculation expression representing the relationship. Based on this, the second lane keep assist current value Ir2 ^* may be calculated. In the example of FIG. 7B, the second lane keep assist current value Ir2 ^* is a quadratic function of Ir2 ^* = a2 · (dw / dt) ^{2 in} the range of dw / dt ≧ 0, where a2 is a negative constant. In the range of dw / dt <0, it is expressed by a quadratic function of Ir2 ^* = − a2 · (dw / dt) ² . This function corresponds to the case where the a2 is negative and the b2 is 2.

  Returning to FIG. 5, the vehicle speed gain setting unit 64 sets the vehicle speed gain Gv based on the vehicle speed V detected by the vehicle speed sensor 23. An example of setting the vehicle speed gain Gv with respect to the vehicle speed V is shown in FIG. In the example of FIG. 8, the vehicle speed gain Gv is fixed to 0 when the vehicle speed V is in the vicinity of zero, and is fixed to 1 when the vehicle speed V exceeds a predetermined value. The vehicle speed gain Gv is set according to a characteristic that increases from 0 to 1 according to the vehicle speed V when the vehicle speed V is a value within the intermediate range.

The lane keep assist current value Iro ^* calculated by the lane keep assist current value calculation unit 51 is given to the gain multiplication unit 53 (see FIG. 2).
Returning to FIG. 2, the correction gain calculation unit 52 calculates the lane keep assist current value calculated by the lane keep assist current value calculation unit 51 in accordance with an environmental change such as a change in road surface condition or a change over time such as tire deterioration. A correction gain G for correcting Iro ^* is calculated. Specifically, the correction gain calculation unit 52 calculates a correction gain G for correcting the lane keep assist current value Iro ^* based on the vehicle speed V, the steering angle θ, and the yaw rate Yr. Details of the operation of the correction gain calculation unit 52 will be described later.

The gain multiplication unit 53 multiplies the lane keep assist current value Iro ^* calculated by the lane keep assist current value calculation unit 51 by the correction gain G set by the correction gain calculation unit 52 to thereby obtain the lane keep assist. The current value Iro ^* is corrected. The corrected lane keep assist current value G · Iro ^* is provided to the target current value calculation unit 44 as the final lane keep assist current value Ir ^* . The correction gain calculation unit 52 and the gain multiplication unit 53 constitute correction means for correcting the lane keep assist current value Iro ^* .

  Hereinafter, the correction gain calculation unit 52 will be described in detail. Assuming that the steering angle θ is constant, the absolute value of the yaw rate Yr is almost directly proportional to the vehicle speed V except when the vehicle speed is low and when the absolute value of the steering angle is large. Therefore, assuming that the absolute value of the yaw rate Yr is almost directly proportional to the vehicle speed V, the yaw rate Yr is normalized by the vehicle speed V by dividing the yaw rate Yr by the vehicle speed V. The yaw rate value (Yr / V) normalized in this way is referred to as “normalized yaw rate”. When the condition including the road surface condition and the vehicle condition is a certain condition, as shown in FIG. 9, the relationship between the steering angle θ and the normalized yaw rate Yr / V is Yr / V = μ · It is considered that the function is close to a linear function represented by θ. μ is the slope of the linear function and is the ratio of the change amount of the normalized yaw rate Yr / V to the change amount of the steering angle θ. This slope μ changes according to the condition including the road surface condition and the vehicle state.

Therefore, the correction gain calculation unit 52 intermittently calculates (estimates) the average value of the slope μ (the average ratio of the change amount of the normalized yaw rate Yr / V to the change amount of the steering angle θ). Then, the correction gain calculation unit 52 calculates the correction gain G based on the average value of the calculated (estimated) slope μ. Therefore, the lane keep assist current value Iro ^* is corrected based on the estimated average value of the slope μ. As described above, the slope μ is a value that changes according to the condition including the road surface condition and the vehicle state. Accordingly, by correcting the lane keep assist current value Iro ^* based on the average value of the slope μ calculated (estimated) intermittently, an appropriate lane keep assist according to the condition including the road surface condition and the vehicle state The current value Ir ^* is obtained.

FIG. 10 is a flowchart for explaining an operation example of the correction gain calculation unit 52. The process of FIG. 10 is repeatedly executed at every predetermined calculation cycle.
The correction gain calculation unit 52 acquires the vehicle speed V, the steering angle θ, and the yaw rate Yr (step S1). Then, the correction gain calculation unit 52 determines whether or not the vehicle speed V is equal to or higher than a predetermined threshold E (E> 0) (step S2). When the vehicle speed V is less than the threshold value E (step S2: NO), it is highly possible that the assumption that the absolute value of the yaw rate Yr is almost directly proportional to the vehicle speed V is not satisfied when the steering angle is constant. The correction gain calculation unit 52 ends the process in the current calculation cycle.

  When it is determined in step S2 that the vehicle speed V is equal to or higher than the threshold E (step S2: YES), the correction gain calculation unit 52 has the absolute value | θ | of the steering angle θ equal to or lower than the predetermined threshold F. It is determined whether or not there is (step S3). When the absolute value | θ | of the steering angle θ is larger than the threshold F (step S3: NO), it is assumed that the absolute value of the yaw rate Yr is almost directly proportional to the vehicle speed V when the steering angle is constant. Since there is a high possibility that the correction is not performed, the correction gain calculation unit 52 ends the processing in the current calculation cycle.

  When it is determined in step S3 that the absolute value | θ | of the steering angle θ is equal to or smaller than the predetermined threshold F (step S3: YES), the correction gain calculation unit 52 inks the count value i by 1. (+1) (step S4). The initial value of the count value i is 0. Then, the correction gain calculator 52 determines whether or not the count value i is larger than a predetermined value m (m is a predetermined natural number) (step S5).

When the count value i is a value equal to or less than m (step S5: NO), the correction gain calculation unit 52 calculates the integrated value Sx _i ² of the square value of the steering angle θ, the steering angle θ, and the normalized yaw rate Yr / An integrated value calculation process for calculating the integrated value Sxy _i of the product θ · Yr / V with V is performed (step S6).
The integrated value calculation process will be specifically described. When the steering angle theta obtained in step S1 and x _i, the correction gain calculation unit 52, based on the following equation (1), calculates the integrated value Sx ² of the square value of the steering angle theta.

Sx ² _i = Sx ² _(i−1) + x _i ² (1)
Sx ² _(i−1) represents an integrated value of the square value of the steering angle θ calculated when the count value i is a value smaller by 1 than the current count value i.
When the value obtained by dividing the yaw rate Yr acquired in step S1 by the vehicle speed V acquired in step S1 (normalized yaw rate) is y _i , the correction gain calculation unit 52 is based on the following equation (2). Then, the integrated value Sxy _i of the product θ · Yr / V of the steering angle θ and the normalized yaw rate Yr / V is calculated.

Sxy _i = Sxy _(i−1) + x _i · y _i (2)
Sxy _(i−1) represents an integrated value of the product θ · Yr / V calculated when the count value i is a value smaller by 1 than the current count value i. When Sx ² _i and Sxy _i are calculated in this way, the correction gain calculation unit 52 ends the processing in the current calculation cycle.
When it is determined in step S4 that the count value i is larger than the predetermined value m (step S5: YES), the correction gain calculation unit 52 calculates a gain for calculating the correction gain G. Arithmetic processing is performed (step S7).

The gain calculation process will be specifically described. First, the correction gain calculator 52 calculates the average value μ _ML of the likelihood of the slope μ based on the following equation (3).
μ _ML = Sxy _i / Sx ² _i (3)
Sxy _i is an integrated value of the product θ · Yr / V of the steering angle θ and the normalized yaw rate Yr / V, which is calculated most recently in step S6. Sxy _i is an integrated value of the product θ · Yr / V for m times from i = 1 to i = m. Sx ² _i is an integrated value of the square value of the steering angle θ calculated at the latest in step S6. Sx ² _i is an integrated value of square values of m steering angles θ from i = 1 to i = m.

Further, the correction gain calculator 52 calculates the variance σ ² _ML of the likelihood of the slope μ based on the following equation (4).
σ ² _ML = σ ² / Sx ² _i (4)
σ ² is the variance of the population with the slope μ, which is obtained in advance and stored in a non-volatile memory (not shown).

Next, the correction gain calculation unit 52 calculates the average value μ _(n) of the slope μ based on the following equation (5), and the average value σ ² _{(n) of the} variance based on the following equation (6 _). Is calculated.

In the equation (5), μ _(n−1) represents the average value of the gradient μ previously calculated in step S7. In equations (5) and (6), σ ² _(n−1) represents the average value of the variances calculated last time in step S7.
Next, the correction gain calculation unit 52 calculates the correction gain G based on the following equation (7).

G = μ _(n) / μo (7)
In Expression (7), μo is a reference value of the slope μ and is set in advance.
Thus, when the correction gain G is calculated, the correction gain calculator 52 sets the count value i, the integrated value Sx ² and Sxy to zero (step S8). Then, the correction gain calculation unit 52 ends the process in the current calculation cycle.

As mentioned above, although embodiment of this invention was described, this invention can also be implemented with another form.
For example, in the above-described embodiment, the lane keep assist current value Iro ^* calculated by the lane keep assist current value calculation unit 51 is corrected using the correction gain G calculated by the correction gain calculation unit 52. However, in addition to or instead of this, the steering assist current value Is ^* set by the steering assist current value setting unit 41 may be corrected by the correction gain G calculated by the correction gain calculation unit 52. Good.

Further, for example, a limiter for limiting the absolute value of the third lane keep assist current value Ir3 ^* (= Ir1 ^* + Ir2 ^* ) to a predetermined range is provided between the adder 63 (see FIG. 5) and the multiplier 65. May be.
In the above-described embodiment, the multiplication unit 65 (see FIG. 5) is provided, but the multiplication unit 65 may be omitted. When the multiplication unit 65 is omitted, the vehicle speed gain setting unit 64 is not necessary.

In the above-described embodiment, the steering assist current value setting unit 41 sets the steering assist current value Is ^* using the steering torque T (specifically, based on the steering torque T and the vehicle speed V). However, the steering assist current value Is ^* may be set using the steering angle.
In the above-described embodiment, the example in which the present invention is applied to the electric power steering apparatus has been described. However, the present invention can be applied to a steer-by-wire (SBW) system and other vehicle steering apparatuses.

The present invention can also be applied in an automatic driving mode in which the steering wheel 2 is not steered.
In addition, various design changes can be made within the scope of matters described in the claims.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 18 ... Electric motor, 11 ... Torque sensor, 23 ... Vehicle speed sensor, 42 ... Information acquisition part, 43 ... Lane keep assist electric current value setting part, 44 ... Target electric current value calculating part, 45 ... Current deviation Calculation unit, 46 ... PI control unit, 51 ... Lane keep assist current value calculation unit, 52 ... Correction gain calculation unit, 53 ... Gain multiplication unit, 61 ... First current value calculation unit, 62 ... Second current value calculation unit , 63 ... addition unit, 64 ... vehicle speed gain setting unit, 65 ... multiplication unit

Claims (4)

An electric motor for applying a steering driving force to the steering mechanism of the vehicle;
Steering angle detection means for detecting the steering angle;
Yaw rate detection means for detecting the yaw rate of the vehicle;
Vehicle speed detection means for detecting the vehicle speed;
Assist current value calculating means for calculating an assist current value corresponding to a target value of the assist torque;
Assist current calculated by the assist current value calculating means based on the steering angle detected by the steering angle detecting means, the yaw rate detected by the yaw rate detecting means, and the vehicle speed detected by the vehicle speed detecting means. Correction means for correcting the value;
Target current value calculating means for calculating a target current value using the assist current value corrected by the correcting means;
Control means for driving and controlling the electric motor based on the target current value calculated by the target current value calculating means,
The correction means includes
Estimating means for intermittently estimating the average ratio of the change amount of the normalized yaw rate to the change amount of the steering angle, using a value obtained by dividing the yaw rate by the vehicle speed as a normalized yaw rate;
A vehicle steering apparatus comprising: means for correcting the assist current value calculated by the assist current value calculating means using the average ratio estimated by the estimating means.   2. The assist current value calculating means is configured to calculate a lane keep assist current value corresponding to a target value of lane keep assist torque for causing the vehicle to travel along a target travel line. Vehicle steering system. It further includes information acquisition means for acquiring a lateral deviation of the vehicle from the target travel line and a lateral deviation change rate that is a change rate per unit time of the lateral deviation,
The assist current value calculation means is configured to calculate a lane keep assist current value corresponding to a target value of lane keep assist torque for making the lateral deviation and the lateral deviation change rate close to zero. The vehicle steering device according to claim 1. A steering assist current value setting means for setting a steering assist current value corresponding to the target value of the steering assist torque;
The target current value calculating means calculates the target current value using the steering assist current value set by the steering assist current value setting means and the lane keep assist current value corrected by the correcting means. The vehicle steering device according to claim 2, wherein the vehicle steering device is configured as follows.

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