WO2024062514A1

WO2024062514A1 - Steering control method and steering control device

Info

Publication number: WO2024062514A1
Application number: PCT/JP2022/034905
Authority: WO
Inventors: 一弘五十嵐; 範規久保川; 友明種田
Original assignee: 日産自動車株式会社
Priority date: 2022-09-20
Filing date: 2022-09-20
Publication date: 2024-03-28

Abstract

This steering control method comprising: calculating a target steering angle of a steering wheel (S1); driving a steering motor on the basis of a difference between the target steering angle and an actual steering angle of the steering wheel (S2); estimating first estimated current axial force which is steering rack axial force, by multiplying a steering current, which is the current that drives the steering motor, by a first coefficient (S3); estimating second estimated current axial force which is steering rack axial force, by multiplying the steering current by a second coefficient larger than the first coefficient (S4); calculating an estimated steering rack axial force on the basis of the first estimated current axial force, when the steering state of the steering wheel is a largely-turned steering state (S6); calculating an estimated steering rack axial force on the basis of the second estimated current axial force when the steering state is a turn-back steering state (S7); calculating a target reaction force current on the basis of the estimated steering rack axial force (S8); and driving a reaction force motor that applies a steering reaction force to the steering wheel on the basis of the estimated target reaction force current (S9).

Description

Steering control method and steering control device

The present invention relates to a steering control method and a steering control device.

The steering control device described in Patent Document 1 below drives a reaction motor based on a control amount of the steering reaction force, which is based on the steering angle, and a control amount calculated by multiplying the current of the steering motor by a set gain, thereby reflecting the influence of an external force acting on the steered wheels in the steering reaction force.

Japanese Patent Application Publication No. 2000-108914

However, the relationship between the magnitude of the current of the steering motor and the strength of the steering rack axial force changes depending on whether the steering state of the steering device is an additional steering state or a reverse steering state. Therefore, if the gain used when estimating the steering rack axial force from the current of the steering motor is fixed, an inappropriate steering reaction force may be generated, which may give the driver a sense of discomfort.
An object of the present invention is to improve the accuracy of estimating the steering rack axial force from the current of the steering motor.

In the steering control method of one aspect of the present invention, a target steering angle, which is a target value of the steering angle of the steered wheels, is calculated based on the steering angle of a steering wheel that is mechanically separated from the steered wheels. Drives a steering motor that steers the steering wheels based on the difference between the steering angle and the actual steering angle of the steering wheels, and multiplies the steering current, which is the current that drives the steering motor, by a first coefficient. By this, the first current estimated axial force, which is the steering rack axial force, is estimated, and by multiplying the steering current by a second coefficient, which is larger than the first coefficient, the second current estimated axial force, which is the steering rack axial force, is estimated. , when the steering state of the steering wheel is an additional steering state, the estimated steering rack axial force is calculated based on the first current estimated axial force, and when the steering state is a reverse steering state, the second current is calculated. The target reaction force current is the target value of the current that drives the reaction force motor that calculates the estimated steering rack axial force based on the estimated axial force and applies a steering reaction force to the steering wheel based on the estimated estimated steering rack axial force. is calculated, and the reaction force motor is driven based on the estimated target reaction force current.

According to the present invention, it is possible to improve the accuracy of estimating the steering rack axial force from the current of the steering motor.
The objects and advantages of the invention will be realized and attained by means of the elements and combinations recited in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.

FIG. 1 is a schematic configuration diagram of an example of a steering control device according to an embodiment. FIG. 2 is a block diagram of an example of a functional configuration of a controller. FIG. 3 is a block diagram of an example of a functional configuration of a target steering reaction force calculation section. FIG. 2 is a block diagram of an example of a functional configuration of an FB axial force calculation section. It is a characteristic diagram which shows the relationship between the current axial force calculated by multiplying the steering current by a fixed torque constant, and the actual steering rack axial force. FIG. 3 is a characteristic diagram showing the relationship between positive efficiency current axial force and actual steering rack axial force. FIG. 3 is a characteristic diagram showing the relationship between reverse efficiency current axial force and actual steering rack axial force. FIG. 3 is an explanatory diagram of an example of a mixing ratio of axial force according to a steering angular velocity. FIG. 4 is a characteristic diagram showing the relationship between a feedback axial force and an actual steering rack axial force. It is a flow chart of an example of a steering control method of an embodiment.

(composition)
FIG. 1 is a schematic configuration diagram of an example of a steering control device according to an embodiment. In the following description, the vehicle in which the steering control device of the embodiment is mounted will be referred to as the "host vehicle." The steering control device of the embodiment is a steer-by-wire type steering control device that can mechanically separate the steering wheel 1a and the front wheels 2, which are steered wheels.
The steering control device of the embodiment includes a steering angle sensor 3, a turning angle sensor 4, a vehicle speed sensor 5, an acceleration sensor 6, a steering control section 8, a reaction force control section 9, and a controller 11.

The steering angle sensor 3 detects the steering angle δ of the steering wheel 1a. The steering angle sensor 3 outputs information on the detected steering angle δ to the controller 11. The steering angle sensor 4 detects the steering angle θ of the front wheels (steering wheels) 2. The steering angle sensor 4 outputs information on the detected steering angle θ to the controller 11. Vehicle speed sensor 5 detects vehicle speed V of the host vehicle. The vehicle speed sensor 5 outputs information on the detected vehicle speed V to the controller 11. Acceleration sensor 6 detects lateral acceleration Gy acting on the host vehicle. The acceleration sensor outputs information on the detected lateral acceleration Gy to the controller 11.

The steering control section 8 includes a steering motor 8A, a steering current detection section 8B, and a steering motor drive section 8C.
The steering motor 8A is connected to the pinion shaft 10d via a reduction gear. The steering motor 8A is driven by the steering motor drive section 8C, and moves the steering rack 10a left and right via the pinion shaft 10d and pinion gear 10e. Thereby, the steering motor 8A steers the front wheels 2. The steering motor 8A may be driven, for example, by controlling a steering current Itm that is a current flowing through the steering motor 8A.

The steering current detection section 8B detects the steering current Itm. The steering current detection section 8B outputs a signal indicating the steering current Itm to the steering motor drive section 8C and the controller 11.
The steering motor drive section 8C controls the steering motor 8A based on the target steering current Itt calculated by the controller 11 so that the steering current Itm detected by the steering current detection section 8B matches the target steering current Itt. The steering current Itm is controlled. Thereby, the steering motor drive section 8C drives the steering motor 8A. The target steering current Itt is a target value of the current flowing through the steering motor 8A.

The reaction force control section 9 includes a reaction force motor 9A, a reaction force current detection section 9B, and a reaction force motor drive section 9C.
The reaction motor 9A is connected to the steering shaft 1b via a reduction gear. The reaction motor 9A is driven by the reaction motor drive section 9C, and applies rotational torque to the steering wheel 1a via the steering shaft 1b. Thereby, the reaction force motor 9A generates a steering reaction force. The reaction motor 9A may be driven, for example, by controlling the reaction current Ism flowing through the reaction motor 9A.
The reaction current detection section 9B detects the reaction current Ism. Then, the reaction current detection section 9B outputs a detection signal indicating the reaction current Ism to the reaction force motor drive section 9C and the controller 11.
The reaction motor drive section 9C controls the reaction motor 9A based on the target reaction current Ist calculated by the controller 11 so that the reaction current Ism detected by the reaction current detection section 9B matches the target reaction current Ist. The reaction force current Ism is controlled. Thereby, the reaction force motor drive section 9C drives the reaction force motor 9A. The target reaction force current Ist is a target value of the current flowing through the reaction force motor 9A.

The backup clutch 12 is provided between the steering shaft 1b and the pinion shaft 10b. The pinion shaft 10b is connected to the steering rack 10a via a pinion gear 10c, and when the backup clutch 12 is engaged, the steering shaft 1b and the pinion shaft 10b are connected, thereby connecting the steering wheel 1a and the front wheel 2. are mechanically connected. When the backup clutch 12 is released, the steering shaft 1b and pinion shaft 10b are disconnected, thereby mechanically separating the steering wheel 1a and the front wheels 2. In the following description, it is assumed that the backup clutch 12 is in a released state and that the steering wheel 1a and the front wheels 2 are mechanically separated.

The controller 11 is an electronic control unit that controls the driving of the steering motor 8A by the steering control section 8 and the driving of the reaction force motor 9A by the reaction force control section 9. The controller 11 may include a processor 20 and peripheral components such as a storage device 21. The processor 20 may be, for example, a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The storage device 21 may include any one of a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device 21 may include memory such as a register, a cache memory, a ROM (Read Only Memory) used as a main storage device, and a RAM (Random Access Memory). The functions of the controller 11 described below are realized, for example, by the processor 20 executing a computer program stored in the storage device 21.

FIG. 2 shows an example of the functional configuration of the controller 11. The controller 11 includes a target steering angle calculation section 11A, a target steering reaction force calculation section 11B, a target steering current calculation section 11C, a subtractor 11D, and a differentiator 11E.
The target turning angle calculation unit 11A calculates a target turning angle θt, which is a target value of the turning angle θ, based on the steering angle δ detected by the steering angle sensor 3 and the vehicle speed V detected by the vehicle speed sensor 5. The target turning angle θt may be calculated, for example, by multiplying the steering angle δ by the variable gear ratio of the steering angle δ and the turning angle θ.
The subtractor 11D calculates a deviation Δθ by subtracting the turning angle θ detected by the turning angle sensor 4 from the target turning angle θt. The target steering current calculation unit 11C calculates the target steering current Itt based on the deviation Δθ. The target steering current calculation section 11C outputs the target steering current Itt to the steering motor drive section 8C.
The differentiator 11E calculates the target turning angular velocity ωt by differentiating the target turning angle θt. The target turning angular speed ωt is an example of the “steering speed” described in the claims.

Target steering reaction force calculation unit 11B calculates a target reaction force current Ist based on the steering angle δ detected by steering angle sensor 3, the vehicle speed V detected by vehicle speed sensor 5, the lateral acceleration Gy detected by acceleration sensor 6, the steering current Itm detected by steering current detection unit 8B, and the target steering angular velocity ωt. Target steering reaction force calculation unit 11B outputs the calculated target reaction force current Ist to reaction force motor drive unit 9C.
Refer to Fig. 3. The target steering reaction force calculation unit 11B includes a feedforward axial force calculation unit 30, a feedback axial force calculation unit 31, a mixture ratio setting unit 32, a subtractor 33,

multipliers

34 and 35, an adder 36, a conversion unit 37, and a target reaction force current calculation unit 38. In the following description and drawings, the feedforward axial force may be expressed as "FF axial force" and the feedback axial force as "FB axial force".

The FF axial force calculation unit 30 calculates the FF axial force Fff, which is a steering rack axial force that provides a steering reaction force according to the steering angle δ, based on the steering angle δ or the target steering angle θt (i.e., the steering command value) and the vehicle speed V. The steering rack axial force is the rack axial force applied to the steering rack 10a. For example, the FF axial force calculation unit 30 may calculate the FF axial force Fff based on the target steering angle θt calculated based on the steering angle δ and the vehicle speed V, and the pinion stiffness, pinion viscosity, rack inertia, and rack viscosity of the pinion and rack of the steering mechanism. For example, the FF axial force Fff may be an axial force applied to the steering rack that includes at least a proportional component according to the target steering angle θt and a damping component according to the steering angular speed. The FF axial force calculation unit 30 outputs the calculated FF axial force Fff to the multiplier 34.

The FB axial force calculation unit 31 calculates the FB axial force Ffb based on the lateral acceleration Gy, the steering current Itm, the target turning angular velocity ωt, and the vehicle speed V. The FB axial force Ffb is a steering rack axial force that applies force from the road surface as a steering reaction force to the steering wheel 1a and returns it to the driver. The configuration and function of the FB axial force calculation unit 31 will be described later.
The mixing ratio setting unit 32 sets a mixing ratio Gf: (1-Gf) for calculating a mixed axial force by mixing the FF axial force Fff and the FB axial force Ffb. For example, the mixing ratio setting section 32 may set the mixing ratio Gf: (1-Gf) according to the axial force difference between the FF axial force Fff and the FB axial force Ffb.
The subtracter 33,

multipliers

34 and 35, and adder 36 mix the FF axial force Fff and the FB axial force Ffb at a mixing ratio Gf: (1-Gf) to obtain the result given by the following equation (1). Calculate the mixed axial force.
Mixed axial force = Fff×Gf+Ffb×(1-Gf)… (1)

The converter 37 calculates the target steering reaction force based on the mixed axial force calculated by the subtracter 33, the

multipliers

34 and 35, and the adder 36. The target steering reaction force is a target value of the steering reaction force. For example, the conversion unit 37 may convert the mixed axial force into a target steering reaction force using an axial force-steering reaction force conversion map that defines a target steering reaction force corresponding to the vehicle speed V and the axial force.
The target reaction force current calculation section 38 calculates the target reaction force current Ist based on the target steering reaction force calculated by the conversion section 37 according to the following equation (2). The target reaction force current calculation section 38 outputs the calculation result to the reaction force motor drive section 9C.
Target reaction force current Ist = target steering reaction force x gain... (2)

FIG. 4 is a block diagram of an example of the functional configuration of the FB axial force calculation unit 31. The FB axial force calculation unit 31 includes a first current axial force conversion unit 40, a first correction unit 41, a second current axial force conversion unit 42, a second correction unit 43, and a lateral G-axis force conversion unit 44. , a first mixed axial force calculation section 45, a second mixed axial force calculation section 46, and an axial force switching section 47.
The first current axial force conversion unit 40 converts the steering current Itm into a positive efficiency current axial force Fcf0=Itm×Nf by multiplying the steering current Itm by a positive efficiency torque constant Nf. When the steering state of the steering wheel 1a is an increased turning state, the FB axial force Ffb is estimated based on the positive efficiency current axial force Fcf0. The positive efficiency torque constant Nf and the positive efficiency current axial force Fcf0 are examples of a "first coefficient" and a "first estimated current axial force", respectively, described in the claims.

The first correction unit 41 corrects the positive efficiency current axial force Fcf0 by removing the friction component accompanying the steering of the steering wheels 2 from the positive efficiency current axial force Fcf0, and corrects the positive efficiency current axial force Fcf0. Output. For example, when the sign of the positive efficiency current axial force Fcf0 before correction is positive, a predetermined friction component (constant) is subtracted from the positive efficiency current axial force Fcf0, and the sign of the positive efficiency current axial force Fcf0 is negative. In this case, the corrected positive efficiency current axial force Fcf is calculated by adding the friction component to the positive efficiency current axial force Fcf0. The corrected positive efficiency current axial force Fcf is an example of the "second axial force component based on the first estimated current axial force" described in the claims.
The positive efficiency torque constant Nf and the friction component are set so that the positive efficiency current axial force Fcf and the steering rack axial force actually applied to the steering rack 10a generally match in the increased steering state.

FIG. 5 is a characteristic diagram showing the relationship between the current axial force calculated by multiplying the steering current by a constant torque constant and the actual steering rack axial force. In the additional steering state, the self-aligning torque acts in the opposite direction to the rotation direction of the steering motor 8A, and in the return steering state, the self-aligning torque acts in the same direction as the rotation direction of the steering motor 8A. Therefore, the ratio (inclination) of the current axial force to the actual steering rack axial force is smaller in the reverse steering state than in the additional steering state.
Furthermore, the friction component always acts in the opposite direction to the rotational direction of the steering motor 8A as the steering wheel 2 is turned (that is, when the steering motor 8A is rotating). For this reason, there is a difference between the timing when the actual steering rack axial force becomes "0" and the timing when the current axial force becomes "0" when the absolute value of the steering angle decreases and passes the neutral position. arise. As a result, the relationship between the current axial force and the actual steering rack axial force has a hysteresis characteristic as shown in FIG. The deviation between the axial force and the axial force increases. Further, in the characteristic diagram of FIG. 5, the intersection with the vertical axis is shifted from "0".

FIG. 6 is a characteristic diagram showing the relationship between the positive efficiency current axial force Fcf and the actual steering rack axial force. The positive efficiency torque is adjusted so that the slope of the positive efficiency current axial force Fcf0 with respect to the actual steering rack axial force (that is, the ratio (positive efficiency current axial force Fcf0/actual steering rack axial force)) is "1" in the increased steering state. By removing the friction component in the first correction unit 41 while setting the constant Nf, it is possible to make the positive efficiency current axial force Fcf substantially coincide with the actual steering rack axial force in the increased steering state.

See FIG. 4. The second current axial force conversion unit 42 converts the steering current Itm into a reverse efficiency current axial force Fcr0=Itm×Nr by multiplying the steering current Itm by a reverse efficiency torque constant Nr. When the steering state of the steering wheel 1a is the reversed state, the FB axial force Ffb is estimated based on the reverse efficiency current axial force Fcr0. The reverse efficiency torque constant Nr and the reverse efficiency current axial force Fcr0 are examples of a "second coefficient" and a "second estimated current axial force", respectively, described in the claims.
As described above, in the reverse steering state, the self-aligning torque acts in the same direction as the rotational direction of the steering motor 8A, so the steering current Itm is smaller than in the additional steering state. Therefore, if the reverse efficiency torque constant Nr used to estimate the FB axial force Ffb in the reverse steering state is made the same as the positive efficiency torque constant Nf used to estimate the FB axial force Ffb in the additional steering state, Efficiency current axial force Fcr0 becomes too small. Therefore, the reverse efficiency torque constant Nr is set to a larger value than the positive efficiency torque constant Nf.

The second correction unit 43 corrects the reverse efficiency current axial force Fcr0 by removing the friction component accompanying the steering of the steering wheel 2 from the reverse efficiency current axial force Fcr0, and corrects the reverse efficiency current axial force Fcr0 after correction. Output Fcr. For example, when the sign of the reverse efficiency current axial force Fcr0 before correction is positive, a predetermined friction component (constant) is added to the reverse efficiency current axial force Fcr0, and the sign of the reverse efficiency current axial force Fcr0 is negative. In this case, the corrected reverse efficiency current axial force Fcr is calculated by subtracting the friction component from the reverse efficiency current axial force Fcr0. The corrected reverse efficiency current axial force Fcr is an example of the "second axial force component based on the second current estimated axial force" described in the claims.
The reverse efficiency torque constant Nr and the friction component are set so that the reverse efficiency current axial force Fcr and the steering rack axial force actually applied to the steering rack 10a generally match in the reverse steering state.

FIG. 7 is a characteristic diagram showing the relationship between the reverse efficiency current axial force Fcr and the actual steering rack axial force. The reverse efficiency torque is adjusted so that the slope of the reverse efficiency current axial force Fcr0 with respect to the actual steering rack axial force (i.e., the ratio (reverse efficiency current axial force Fcr0/actual steering rack axial force)) is "1" in the reverse steering state. By removing the friction component in the second correction unit 43 while setting the constant Nr, it is possible to make the reverse efficiency current axial force Fcr substantially coincide with the actual steering rack axial force in the reverse steering state.

See FIG. 4. The lateral G-axis force converter 44 calculates the lateral G-axis force Ft, which is the steering rack axial force according to the lateral acceleration acting on the vehicle. For example, the lateral G-axis force conversion unit 44 may calculate the lateral G-axis force Ft by multiplying the lateral acceleration Gy by a gain that is a coefficient according to the vehicle speed V.
The first mixed axial force calculation section 45 predetermines the positive efficiency current axial force Fcf0 before correction calculated by the first current axial force conversion section 40 and the lateral G axial force Ft calculated by the lateral G axial force conversion section 44. The first mixed axial force Fm1 is calculated by mixing at a ratio of . The first mixed axial force Fm1 is an example of a "first axial force component" described in the claims.

The second mixed axial force calculation unit 46 calculates the second mixed axial force Fm2 by mixing the reverse efficiency current axial force Fcr and the first mixed axial force Fm1.
Please refer to the range of "return steering state" in FIG. The second mixed axial force calculation unit 46 outputs the first mixed axial force Fm1 as the second mixed axial force Fm2 when the target turning angular velocity ωt is greater than or equal to "0" and less than the first steered angular velocity ω1. When the target turning angular speed ωt is equal to or higher than the second turning angular speed ω2, which is larger than the first turning angular speed ω1, the reverse efficiency current axial force Fcr is output as the second mixed axial force Fm2. When the target turning angular speed ωt is greater than or equal to the first turning angular speed ω1 and less than the second turning angular speed ω2, the first mixed axial force Fm1 and the reverse efficiency current axial force Fcr are mixed according to the target turning angular speed ωt. The second mixed axial force Fm2 is calculated by mixing at the ratio. The second mixed axial force calculation unit 46 increases the mixing ratio of the reverse efficiency current axial force Fcr as the target turning angular velocity ωt increases.

Refer to Figure 4. The axial force switching unit 47 determines whether the steering state of the steering wheel 1a is an additional steering state or a reverse steering state. For example, the axial force switching unit 47 determines that the steering current is in the additional steering state when the sign of the steering current Itm and the sign of the target turning angular velocity ωt are the same, and If the sign of ωt is different from that of ωt, it may be determined that the vehicle is in the reverse steering state. Instead of the steering current Itm, it may be determined that the additional steering state is present when the sign of the positive efficiency current axial force Fcf0 and the sign of the target turning angular velocity ωt are the same.

The axial force switching unit 47 switches the axial force output as the FB axial force Ftb between the positive efficiency current axial force Fcf and the second mixed axial force Fm2 based on the steering state and the target turning angular velocity ωt.
For example, in the case of the return steering state, the axial force switching unit 47 outputs the second mixed axial force Fm2 as the FB axial force Ftb. Therefore, as shown in FIG. 8, when the steering state is the return steering state and the target turning angular velocity ωt is equal to or higher than the second turning angular velocity ω2, the reverse efficiency current axial force Fcr is output as the FB axial force Ftb. do. In addition, when the steering state is a reverse steering state and the target turning angular velocity ωt is greater than or equal to the first turning angular velocity ω1 and less than the second turning angular velocity ω2, the first mixed axial force Fm1 and the reverse efficiency current axial force Fcr The axial force obtained by mixing these at a mixing ratio according to the target turning angular velocity ωt is output as the FB axial force Ftb. Further, when the steering state is the return steering state and the target turning angular velocity ωt is greater than or equal to “0” and less than the first turning angular velocity ω1, the first mixed axial force Fm1 is output as the FB axial force Ftb.

On the other hand, when the steering state is an additional steering state and the target turning angular velocity ωt is equal to or higher than the third turning angular velocity ω3, the axial force switching unit 47 changes the positive efficiency current axial force Fcf to the FB axial force Ftb. Output. When the steering state is an additional steering state and the target turning angular velocity ωt is greater than or equal to “0” and less than the third turning angular velocity ω3, the second mixed axial force Fm2 and the positive efficiency current axial force Fcf are set to the target turning angular velocity ωt. The axial force mixed at a mixing ratio according to the angular velocity ωt is output as the FB axial force Ftb. The axial force switching unit 47 increases the mixing ratio of the positive efficiency current axial force Fcf as the target turning angular velocity ωt increases.

The value of the third turning angular velocity ω3 may be set to the same value as the first turning angular velocity ω1, for example. As described above, when the target turning angular velocity ωt is greater than or equal to "0" and less than the first turning angular velocity ω1, the second mixed axial force calculation unit 46 outputs the first mixed axial force Fm1 as the second mixed axial force Fm2. .
Therefore, when the steering state is the additional steering state and the target turning angular velocity ωt is greater than or equal to "0" and less than the third turning angular velocity ω3, the axial force switching unit 47 selects the first mixed axial force Fm1 and the positive efficiency current. An axial force obtained by mixing the axial force Fcf at a mixing ratio according to the target turning angular velocity ωt is output as the FB axial force Ftb.

Note that the value of the third turning angular velocity ω3 may be set to a value different from the first turning angular velocity ω1, for example. In this case, for example, the FB axial force calculation unit 31 includes a third mixed axial force calculation unit (not shown) that calculates a third mixed axial force that is a mixture of the first mixed axial force Fm1 and the positive efficiency current axial force Fcf. May be added.
The third mixed axial force calculation unit outputs the positive efficiency current axial force Fcf as the third mixed axial force when the target turning angular velocity ωt is equal to or higher than the third turning angular velocity ω3. When the target turning angular speed ωt is greater than or equal to “0” and less than the third turning angular speed ω3, the first mixed axial force Fm1 and the positive efficiency current axial force Fcf are mixed at a mixing ratio according to the target turning angular speed ωt. The resulting axial force is output as a third mixed axial force. The third mixed axial force calculation unit increases the mixing ratio of the positive efficiency current axial force Fcf as the target turning angular velocity ωt increases.
The axial force switching unit 47 outputs the third mixed axial force as the FB axial force Ftb in the additional steering state, and outputs the second mixed axial force as the FB axial force Ftb in the reverse steering state.

By generating the FB axial force Ffb as described above, the mixing ratio of the axial forces included in the FB axial force Ffb becomes as shown in FIG. 8.
When the steering state of the steering wheel 1a is the additional steering state and the target turning angular velocity ωt is equal to or higher than the third turning angular velocity ω3, the positive efficiency current axial force Fcf is output as the FB axial force Ffb.
Further, when the steering state of the steering wheel 1a is the return steering state and the target turning angular velocity ωt is equal to or higher than the second turning angular velocity ω2, the reverse efficiency current axial force Fcr is output as the FB axial force Ffb.

On the other hand, when the steering state is an additional steering state and the target turning angular velocity ωt is greater than or equal to "0" and less than the third turning angular velocity ω3, the first mixed axial force Fm1 and the positive efficiency current axial force Fcf are set as the targets. The axial force mixed at a mixing ratio according to the steering angular velocity ωt is output as the FB axial force Ftb. When the steering state is the return steering state and the target turning angular velocity ωt is greater than or equal to “0” and less than the first turning angular velocity ω1, the first mixed axial force Fm1 is output as the FB axial force Ffb.
As a result, it is possible to reduce the estimation error of the FB axial force Ffb in a state where the steering speed is low (for example, in a state where the steering is held). That is, if the estimated steering rack axial force is always calculated based on the positive efficiency current axial force Fcf when the steering speed is low in order to prevent chatter of the current axial force when the steering speed is low, the calculation result will be too small. Sometimes. By mixing the lateral G-axis force Ft according to the lateral acceleration, errors can be reduced and estimation accuracy can be improved.

Furthermore, when the steering state is a reverse steering state and the target turning angular velocity ωt is greater than or equal to the first turning angular velocity ω1 and less than the second turning angular velocity ω2, the first mixed axial force Fm1 and the reverse efficiency current axial force Fcr The axial force obtained by mixing these at a mixing ratio according to the target turning angular velocity ωt is output as the FB axial force Ftb.
This prevents the estimation result of the FB axial force Ffb from changing suddenly when the steering state switches between the additional steering state and the reverse steering state, until the target turning angular velocity ωt reaches the second turning angular velocity ω2. The FB axial force Ffb can be changed gently.

FIG. 9 is a characteristic diagram showing the relationship between the FB axial force Ffb and the actual steering rack axial force. The difference between the estimation result of the FB axial force Ffb in the additional steering state and the estimation result of the FB axial force Ffb in the reverse steering state is reduced, and the friction component is removed, so that the FB axial force Ffb and It can be seen that the actual steering rack axial force matches well.
In particular, the discrepancy between the estimated result of the FB axial force Ffb in the increased steering state and the estimated result of the FB axial force Ffb in the reverse steered state in the region where the steering rack axial force is large is reduced, and the bulge in the hysteresis characteristic is reduced. can.
In addition, by limiting the target steering angular velocity ωt that includes the lateral G-axis force Ft in the FB axial force Ffb to a low steering angular velocity range, the lateral G-axis force Ft with respect to the positive efficiency current axial force Fcf and the reverse efficiency current axial force Fcr It is possible to suppress a decrease in the estimation accuracy of the FB axial force Ffb due to the phase delay.

(motion)
FIG. 10 is a flowchart of an example of the steering control method according to the embodiment.
In step S1, the target turning angle calculation unit 11A calculates a target turning angle θt, which is a target value of the turning angle θ.
In step S2, the steering motor drive unit 8C drives the steering motor 8A based on the difference between the target steering angle θt and the actual steering angle of the steered wheels 2.
In step S3, the first current axial force conversion section 40 and the first correction section 41 calculate the positive efficiency current axial force Fcf.

In step S4, the second current axial force conversion section 42 and the second correction section 43 calculate the reverse efficiency current axial force Fcr.
In step S5, the axial force switching unit 47 determines whether the steering state of the steering wheel 1a is an additional steering state or a reverse steering state. If the steering state is the additional steering state, the process advances to step S6. If the steering state is the steering state, the process advances to step S7.
In step S6, the second mixed axial force calculation unit 46 and the axial force switching unit 47 calculate the positive efficiency current axial force Fcf as the FB axial force Ftb. However, if the target turning angular speed ωt is greater than or equal to "0" and less than the third turning angular speed ω3, the first mixed axial force Fm1 and the positive efficiency current axial force Fcf are mixed at a mixing ratio according to the target turning angular speed ωt. The mixed axial force is calculated as FB axial force Ftb. Thereafter, the process proceeds to step S8.

In step S7, the second mixed axial force calculation unit 46 and the axial force switching unit 47 calculate the reverse efficiency current axial force Fcr as the FB axial force Ftb. However, if the target turning angular velocity ωt is greater than or equal to "0" and less than the first turning angular velocity ω1, the first mixed axial force Fm1 is calculated as the FB axial force Ffb. When the target turning angular speed ωt is greater than or equal to the first turning angular speed ω1 and less than the second turning angular speed ω2, the first mixed axial force Fm1 and the reverse efficiency current axial force Fcr are mixed according to the target turning angular speed ωt. The axial force mixed in the ratio is calculated as the FB axial force Ftb. Thereafter, the process proceeds to step S8.

In step S8, the conversion unit 37 of the target steering reaction force calculation unit 11B (FIG. 3) calculates the target steering reaction force based on the mixed axial force obtained by mixing the FF axial force Fff and the FB axial force Ffb. The target reaction force current calculation unit 38 calculates the target reaction force current Ist based on the target steering reaction force.
In step S9, the reaction motor drive unit 9C drives the reaction motor 9A based on the target reaction current Ist.
The process then ends.

(Modified example)
(1) The FB axial force calculation unit 31 of the above embodiment calculates the first An axial force obtained by mixing the mixed axial force Fm1 and the positive efficiency current axial force Fcf at a mixing ratio according to the target turning angular velocity ωt is output as the FB axial force Ftb. Instead, if the steering state is an additional steering state and the target turning angular velocity ωt is greater than or equal to "0" and less than the third turning angular velocity ω3, the first mixed axial force Fm1 is output as the FB axial force Ftb. You may.

(2) The FB axial force calculation unit 31 of the above embodiment calculates that when the steering state is the return steering state and the target turning angular velocity ωt is greater than or equal to the first turning angular velocity ω1 and less than the second turning angular velocity ω2, , the first mixed axial force Fm1 and the reverse efficiency current axial force Fcr are mixed at a mixing ratio according to the target turning angular velocity ωt, and an axial force is output as the FB axial force Ftb. Alternatively, if the steering state is the return steering state and the target turning angular velocity ωt is greater than or equal to the first turning angular velocity ω1 and less than the second turning angular velocity ω2, the reverse efficiency current axial force Fcr is set to the FB axial force. It may also be output as Ftb.

(Effects of embodiment)
(1) In the steering control method, a target steering angle, which is a target value of the steering angle of the steered wheels, is calculated based on the steering angle of a steering wheel that is mechanically separated from the steered wheels. Steering is performed by driving a steering motor that steers the steering wheel based on the difference between the actual steering angle of the steering wheel and multiplying the steering current, which is the current that drives the steering motor, by a first coefficient. The first current estimated axial force, which is the rack axial force, is estimated, and the steering current is multiplied by a second coefficient, which is larger than the first coefficient, to estimate the second current estimated axial force, which is the steering rack axial force. When the steering state is an additional steering state, the estimated steering rack axial force is calculated based on the first current estimated axial force, and when the steering state is a reverse steering state, the second current estimated axial force is calculated. The estimated steering rack axial force is calculated based on the estimated steering rack axial force, and the target reaction force current, which is the target value of the current that drives the reaction force motor that applies a steering reaction force to the steering wheel, is calculated based on the estimated steering rack axial force. , the reaction force motor is driven based on the estimated target reaction force current.
As a result, the current axial force can be estimated by multiplying the current axial force by a coefficient tailored to each specific state when the steering state is an additional steering state or a reverse steering state, so the estimation accuracy of the steering rack axial force is accurate in both steering states. can be improved.

(2) When the steering state is in a return state and the steering speed is less than a predetermined steering speed, the estimated steering rack axial force may be calculated based on the axial force obtained by adding the steering rack axial force corresponding to the lateral acceleration acting on the vehicle and the first current estimated axial force.
For example, when the steering state is an add-on steering state and the steering speed is less than a predetermined steering speed, the estimated steering rack axial force may be calculated based on an axial force obtained by mixing the steering rack axial force corresponding to the lateral acceleration acting on the vehicle and a first axial force component obtained by adding the first current estimated axial force and a second axial force component based on the first current estimated axial force, and the mixing ratio of the second axial force component may be made higher when the steering speed is high than when the steering speed is low.
If the estimated steering rack axial force is always calculated based on the first current estimated axial force in order to prevent chattering of the current axial force when the steering speed is low (e.g., when the steering wheel is held), the calculation result may be too small. By mixing the steering rack axial force according to the lateral acceleration, the error can be reduced and the estimation accuracy can be improved.

(3) If the steering state is a reverse steering state and the steering speed is greater than or equal to the predetermined first steering speed and less than the predetermined second steering speed, the steering is performed according to the lateral acceleration acting on the vehicle. The steering rack axial force is estimated based on the axial force that is a mixture of the first axial force component obtained by adding the rack axial force to the first current estimated axial force, and the second axial force component based on the second current estimated axial force. When the steering speed is high, the mixing ratio of the second axial force component may be set higher than when the steering speed is low.
As a result, in order to prevent the estimated steering rack axial force from changing suddenly when the steering state switches between the additional steering state and the reverse steering state, the estimated steering rack is gradually adjusted until the steering speed reaches the second steering speed. Axial force can be switched.

All examples and conditional terms herein are provided for educational purposes and to assist the reader in understanding the invention and the concepts presented by the inventor for the advancement of the technology. The foregoing examples and conditions are specifically described and should be construed without limitation to the construction of the examples herein with respect to demonstrating the advantages and disadvantages of the present invention. It is something. Although embodiments of the invention have been described in detail, it should be understood that various changes, substitutions, and modifications can be made thereto without departing from the spirit and scope of the invention.

1a... Steering wheel, 1b... Steering shaft, 2... Front wheel, 3... Steering angle sensor, 4... Steering angle sensor, 5... Vehicle speed sensor, 6... Acceleration sensor, 8... Steering control unit, 8A... Steering motor, 8B... Steering current detection section, 8C... Steering motor drive section, 9... Reaction force control section, 9A... Reaction force motor, 9B... Reaction force current detection section, 9C... Reaction force motor drive section, 10a... Steering rack, 10b, 10d... Pinion shaft, 10c, 10e... Pinion gear, 11... Controller, 12... Backup clutch, 20... Processor, 21... Storage device

Claims

A target steering angle, which is a target value of the steering angle of the steering wheel, is calculated based on the steering angle of the steering wheel, which is mechanically separated from the steering wheel.
driving a steering motor that steers the steered wheels based on a difference between the target steered angle and the actual steered angle of the steered wheels;
Estimating a first current estimated axial force, which is a steering rack axial force, by multiplying a steering current, which is a current that drives the steering motor, by a first coefficient;
estimating a second current estimated axial force that is a steering rack axial force by multiplying the steering current by a second coefficient larger than the first coefficient;
When the steering state of the steering wheel is an additional steering state, the estimated steering rack axial force is calculated based on the first current estimated axial force, and when the steering state is a reverse steering state, the estimated steering rack axial force is calculated. Calculating the estimated steering rack axial force based on the second current estimated axial force,
Calculating a target reaction force current that is a target value of a current that drives a reaction force motor that applies a steering reaction force to the steering wheel based on the estimated steering rack axial force;
driving the reaction motor based on the estimated target reaction current;
A steering control method characterized by:
When the steering state is a reverse steering state and the steering speed is less than a predetermined steering speed, the steering rack axial force corresponding to the lateral acceleration acting on the vehicle and the first current estimated axial force are added. The steering control method according to claim 1, wherein the estimated steering rack axial force is calculated based on the obtained axial force.
When the steering state is an additional steering state and the steering speed is less than a predetermined steering speed, the steering rack axial force corresponding to the lateral acceleration acting on the vehicle and the first current estimated axial force are added to the steering rack axial force and the first current estimated axial force. Calculating the estimated steering rack axial force based on an axial force that is a mixture of a first axial force component based on the first current estimated axial force and a second axial force component based on the first current estimated axial force,
When the steering speed is high, the mixing ratio of the second axial force component is made higher than when it is low.
The steering control method according to claim 1, characterized in that:
When the steering state is a reverse steering state and the steering speed is greater than or equal to a predetermined first steering speed and less than a predetermined second steering speed, the steering rack axis is adjusted according to the lateral acceleration acting on the vehicle. The estimated steering rack shaft is adjusted based on an axial force that is a mixture of a first axial force component obtained by adding a force to the first current estimated axial force and a second axial force component based on the second current estimated axial force. Calculate the force,
When the steering speed is high, the mixing ratio of the second axial force component is made higher than when it is low.
The steering control method according to claim 1, characterized in that:
a steering angle sensor that detects the steering angle of a steering wheel that is mechanically separated from the steered wheels;
a steering motor that steers the steering wheel;
a reaction force motor that applies a steering reaction force to the steering wheel;
A target steering angle, which is a target value of the steering angle of the steering wheel, is calculated based on the steering angle, and the steering angle is calculated based on the difference between the target steering angle and the actual steering angle of the steering wheel. A first current estimated axial force, which is a steering rack axial force, is estimated by driving a steering motor, and a first current estimated axial force, which is a steering rack axial force, is estimated by multiplying a steering current, which is a current that drives the steering motor, by a first coefficient. A second current estimated axial force, which is the steering rack axial force, is estimated by multiplying by a second coefficient larger than the first coefficient, and when the steering state of the steering wheel is an additional steering state, the first current estimation is performed. An estimated steering rack axial force is calculated based on the axial force, and when the steering state is a reverse steering state, the estimated steering rack axial force is calculated and estimated based on the second current estimated axial force. A target reaction force current, which is a target value of a current for driving a reaction force motor that applies a steering reaction force to the steering wheel, is calculated based on the estimated steering rack axial force, and the target reaction force current is calculated based on the estimated target reaction force current. a controller that drives a reaction force motor;
A steering control device characterized by: