CN119998187A - Steering control method and steering control device - Google Patents

Abstract

In a steering control method of the present invention, a front wheel slip angle is estimated, a steering reaction force based on a feedforward axial force is applied when a road surface on which a vehicle is running is a low-mu road surface and an axial force difference between one of a standard axial force and a feedforward axial force and a feedback axial force is smaller than a first predetermined value (S6), a steering reaction force based on a feedback axial force is applied when the road surface is a low-mu road surface and the axial force difference is equal to or larger than the first predetermined value (S9), a steering reaction force based on a feedforward axial force is applied when the road surface is not a low-mu road surface and the front wheel slip angle is smaller than a third predetermined value (S12), and a steering reaction force based on a feedback axial force is applied when the road surface is not a low-mu road surface and the front wheel slip angle is equal to or larger than the third predetermined value (S13).

Description

Steering control method and steering control device

Technical Field

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

Background

The steering control device described in patent document 1 drives the reaction motor based on a control amount of a steering reaction force based on a steering angle and a control amount calculated by multiplying a current of the steering motor by a set gain, thereby reflecting an influence of an external force acting on the steering wheel on the steering reaction force.

Prior art literature

Patent literature

Patent document 1 Japanese patent laid-open No. 2000-108914

Problems to be solved by the invention

In the related art, a reaction motor is driven based on a control amount of a steering reaction force based on a steering angle and a control amount calculated by multiplying a current of the steering motor by a set gain. Therefore, in the related art, for example, when the vehicle behavior becomes large, the control amount of the steering reaction force based on the steering angle may become inappropriate. The purpose of the present invention is to provide a steering control device of a steer-by-wire system in which a steering wheel and a steering wheel are separated from each other, and which is capable of applying a more appropriate steering reaction force.

Disclosure of Invention

In the steering control method according to the aspect of the present invention, when the road surface is a low μ road surface and the axial force difference between the feedback axial force and one of the normal axial force or the feedforward axial force, which is the steering rack axial force corresponding to the actual steering angle of the steering wheel, is smaller than the first predetermined value, the steering reaction force based on the feedforward axial force is applied without using the feedback axial force, when the road surface is a low μ road surface and the axial force difference is equal to or larger than the first predetermined value, the steering reaction force based on the feedback axial force is applied, when the road surface is not a low μ road surface and the front wheel slip angle is smaller than the third predetermined value, the steering reaction force based on the feedforward axial force is applied without using the feedback axial force, and when the road surface is not a low μ road surface and the front wheel slip angle is equal to or larger than the third predetermined value.

Effects of the invention

According to the present invention, in the steering control device of the steer-by-wire system in which the steering wheel and the steering wheel are separated from each other, a more appropriate steering reaction force can be applied.

Drawings

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 a functional configuration example of the controller.

Fig. 3 is a block diagram showing a functional configuration example of the target steering reaction force calculation unit.

Fig. 4 is an explanatory diagram of the axial force switching control for each running scene.

Fig. 5 is a flowchart showing an example of the steering control method according to the embodiment.

Fig. 6 is a block diagram showing a functional configuration example of the axial force mixing section.

Fig. 7 (a) to (c) are explanatory diagrams showing examples of setting of the mixing ratio.

Fig. 8 is a block diagram showing a functional configuration example of the axial force difference-dependent mixing ratio calculation section.

Fig. 9 (a) and 9 (b) are explanatory diagrams of an example of setting the correction gain.

Fig. 10 (a) and 10 (b) are explanatory diagrams of setting examples of the switching range limit value.

Fig. 11 is an explanatory diagram of an example of setting the inclination correction value.

Fig. 12 is an explanatory diagram of a setting example of the axial force difference depending on the mixing ratio.

Fig. 13 is a block diagram showing a functional configuration example of the front wheel slip angle-dependent mixture ratio calculation unit.

Fig. 14 is an explanatory diagram of an example of setting of the front wheel slip angle-dependent mixing ratio.

Detailed Description

(First embodiment)

(Constitution)

Fig. 1 is a schematic configuration diagram of an example of a steering control device according to an embodiment. The steering control device according to the embodiment is a steer-by-wire steering control device capable of mechanically separating a steering wheel 1a and a front wheel 2 as a steered wheel. The steering angle sensor 3 detects a steering angle δ of the steering wheel 1 a. The steering angle sensor 4 detects an actual steering angle θ of the front wheel (steering wheel) 2. The vehicle speed sensor 5 detects the vehicle speed V of the host vehicle. The acceleration sensor 6 detects a lateral acceleration Gy acting on the host vehicle. The yaw rate sensor 7 detects an actual yaw rate (yaw rate) γa of the own vehicle. The steering control unit 8 includes a steering motor 8A, a steering current detection unit 8B, and a steering motor drive unit 8C. The steering motor 8A is coupled to the pinion shaft 10d via a speed reducer. The steering motor 8A is driven by a steering motor driving unit 8C, and moves the steering rack 10a laterally via the pinion shaft 10d and the pinion gear 10 e. Thereby, the steering motor 8A steers the front wheels 2. The steering current detection unit 8B detects a steering current Itm flowing through the steering motor 8A. The steering current detection unit 8B outputs a signal indicating the steering current Itm to the steering motor drive unit 8C and the controller 11. The steering motor driving unit 8C controls the steering current Itm of 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 detecting unit 8B coincides with the target steering current Itt. Thereby, the steering motor driving unit 8C drives the steering motor 8A.

The reaction force control unit 9 includes a reaction force motor 9A, a reaction force current detection unit 9B, and a reaction force motor drive unit 9C. The reaction motor 9A is coupled to the steering shaft 1b via a speed reducer. The reaction motor 9A is driven by a reaction motor driving unit 9C, and applies a rotational torque to the steering wheel 1a via the steering shaft 1 b. Thereby, the reaction force motor 9A generates a steering reaction force. The reaction current detection unit 9B detects a reaction current Ism flowing through the reaction motor 9A. Then, the reaction force current detection unit 9B outputs a detection signal indicating the reaction force current Ism to the reaction force motor drive unit 9C and the controller 11. The reaction motor driving unit 9C controls the reaction current Ism of 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 detecting unit 9B coincides with the target reaction current Ist. Thereby, the reaction motor driving unit 9C drives the reaction motor 9A.

The backup clutch 12 is provided between the steering shaft 1b and the pinion shaft 10 b. The pinion shaft 10b is coupled to the steering rack 10a via a pinion 10c, and when the backup clutch 12 is in the coupled state, the steering wheel 1a is mechanically connected to the front wheels 2. When the backup clutch 12 is in the released state, the steering wheel 1a is mechanically disconnected from the front wheel 2.

The controller 11 controls driving of the steering motor 8A by the steering control unit 8 and driving of the reaction motor 9A by the reaction control unit 9. The controller 11 may include peripheral components such as a processor 13 and a storage device 14. The functions of the controller 11 are implemented, for example, by the processor 13 executing a computer program stored in the storage device 14. Fig. 2 shows an example of the functional configuration of the controller 11. The target steering angle calculation unit 11A calculates a target steering angle θt, which is a target value of the actual steering angle θ, based on the steering angle δ and the vehicle speed V. For example, the target steering angle θt may be calculated by multiplying the steering angle δ by the variable gear ratio. The subtractor 11D calculates a deviation value Δθ obtained by subtracting the actual rudder angle θ from the target rudder angle θt. The target steering current calculation unit 11C calculates the target steering current Itt based on the deviation value Δθ. The target steering current operation unit 11C outputs the target steering current Itt to the steering motor driving unit 8C.

The target steering reaction force calculation unit 11B calculates a target reaction force current Ist based on the steering angle δ, the vehicle speed V, the actual steering angle θ, the actual yaw rate γa, the lateral acceleration Gy, and the steering current Itm. The target steering reaction force calculation unit 11B outputs the calculated target reaction force current Ist to the reaction force motor drive unit 9C. Fig. 3 is a block diagram showing a functional configuration example of the target steering reaction force calculation unit. In the following description and drawings, the feedforward axial force may be referred to as "FF axial force", and the feedback axial force may be referred to as "FB axial force". The FF axial force calculation unit 20 calculates the FF axial force Fff, which is the steering rack axial force that gives the steering reaction force corresponding to the steering angle δ, based on the steering angle δ and the vehicle speed V. The steering rack axial force refers to a rack axial force applied to the steering rack 10 a. For example, FF axial force Fff may be calculated based on target steering angle θt calculated from steering angle δ and vehicle speed V, pinion rigidity of pinion and rack of steering mechanism, pinion viscosity, rack inertia, rack viscosity. For example, FF axial force Fff may be an axial force applied to the steering rack that includes at least a proportional component corresponding to the target steering angle θt and a damping component corresponding to the steering angular velocity.

The FB axial force calculating unit 21 calculates the FB axial force FB based on the steering current Itm, the vehicle speed V, the lateral acceleration Gy, and the actual yaw rate γa. The FB axial force Ffb is a steering rack axial force that applies a force transmitted from the road surface to the front wheel 2 as a steering reaction force to the steering wheel 1a and transmits the force to the driver's sense of touch. The FB axial force calculating unit 21 calculates a steering rack axial force reflecting the influence of the tire lateral force acting on the steered wheel 2 based on the steering current Itm. The steering rack axial force calculated based on the steering current is expressed as "current axial force".

The FB axial force calculating unit 21 calculates a steering rack axial force reflecting the influence of the tire lateral force acting on the steered wheel 2 based on the lateral acceleration Gy. The steering rack axial force calculated based on the lateral acceleration Gy is expressed as "lateral G axial force". The FB axial force calculating unit 21 calculates a steering rack axial force reflecting the influence of the tire lateral force acting on the steered wheels 2 based on the actual yaw rate γa. The steering rack axial force calculated based on the actual yaw rate γa is expressed as "yaw rate axial force". The FB axial force calculating unit 21 calculates the FB axial force Ffb by mixing the current axial force, the lateral G axial force, and the yaw rate axial force.

The axial force mixing unit 23 estimates the front wheel slip angle, which is the slip angle of the front wheels 2, and determines whether or not the road surface on which the host vehicle is traveling is a low μ road surface having a friction coefficient equal to or smaller than a threshold value. The axial force mixing unit 23 includes a road surface μ estimating unit 23a that determines whether or not the road surface on which the vehicle is traveling is a low μ road surface. In the case where the road surface is a low μ road surface, even if FF axial force Fff is large, FB axial force Ffb becomes small. The road surface μ estimating unit 23a determines that the road surface is a low- μ road surface when the FF axial force Fff is equal to or greater than the upper limit Fff and the FB axial force Ffb is less than the lower limit Ffb 1. When FF axial force Fff is equal to or lower than lower limit Fff1 or FB axial force Ffb is equal to or higher than upper limit Ffb2, it is determined that the road surface is not a low μ road surface.

The axial force mixing portion 23 calculates the estimated rack axial force Frk based on the FF axial force Fff without using the FB axial force FF when the road surface is a low μ road surface and the axial force difference Δfs between the FF axial force Fff and the FB axial force FF is smaller than the first prescribed value. In addition, as the axial force difference Δfs, a difference between the standard axial force Frm and the FB axial force Ffb may also be used. This is because the standard axial force Frm is a steering rack axial force calculated according to the vehicle model from the actual steering angle θ, and the difference from the FF axial force Fff is very small in the steady state. When the road surface is a low μ road surface and the axial force difference Δfs is equal to or greater than a first predetermined value, the axial force mixing unit 23 determines that the vehicle is in an understeer state (hereinafter referred to as "US state") and calculates an estimated rack axial force Frk based on the FB axial force Ffb. When the road surface is not a low-mu road surface and the front wheel slip angle is less than a third predetermined value, the estimated rack axial force Frk is calculated based on the FF axial force Fff without using the FB axial force FB, and when the road surface is not a low-mu road surface and the front wheel slip angle is not less than the third predetermined value, it is determined that the host vehicle is in the US state, and the estimated rack axial force Frk is calculated based on the FB axial force Ffb.

The conversion unit 24 converts the estimated rack axial force Frk calculated by the axial force mixing unit 23 into a target steering reaction force. The conversion unit 24 may convert the estimated rack axial force into the target steering reaction force using a conversion map in which target steering reaction forces corresponding to the respective values of the estimated rack axial force are stored. The target reaction force current calculation unit 25 calculates a target reaction force current based on the target steering reaction force output from the conversion unit 24. The target reaction current calculation unit 25 outputs the target reaction current to the reaction motor drive unit 9C.

As described above, the controller 11 changes the determination of whether the host vehicle is in the US state according to whether the road surface is a low μ road surface. The reason is described with reference to fig. 4.

Fig. 4 is an explanatory diagram of the axial force switching control for each running scene. When the tire of the vehicle is in the ground-gripping state, a steering reaction force is applied based on the FF axial force Fff. This is because, in the ground-gripping state, the FF axial force is used to apply steering reaction force that is not affected by the disturbance. On the other hand, in an oversteer state (hereinafter referred to as "OS state") or in the US state, a steering reaction force is applied based on the FB axial force Ffb. This is because the use of FB axial force Ffb can transmit road surface information as a steering reaction force.

Further, if the road surface is not a low μ road surface, it is determined whether or not the US state is present based on the front tire slip angle. By making a determination based on the front wheel slip angle as the information of the tire end, the timing delay of detection of the US state can be reduced. On the other hand, on a low μ road surface, the influence of the decrease in road surface μ is less likely to occur in the front wheel slip angle. Thus, on a low mu road surface. The US state is judged based on an axial force difference value that directly reflects the US state caused by the road surface μ drop. Further, whether the host vehicle is in the OS state is determined based on the yaw rate difference or the vehicle body slip angular velocity difference.

(Action)

Fig. 5 is a flowchart showing an example of the steering control method according to the embodiment. In step S1, the controller 11 calculates FF axial force Fff and FB axial force Ffb. In step S2, the controller 11 estimates a front wheel slip angle. In step S3, the controller 11 estimates whether the road surface is a low μ road surface. In the case where the road surface is a low mu road surface (step S4: yes), the process proceeds to step S5. In the case where the road surface is not a low mu road surface (step S4: NO), the process proceeds to step S10. In step S5, the controller 11 determines whether the axial force difference value is smaller than a first prescribed value. If the axial force difference is smaller than the first predetermined value (yes in step S5), the process proceeds to step S6. If the axial force difference is not smaller than the first predetermined value (no in step S5), the process proceeds to step S7. In step S6, the controller 11 applies a steering reaction force corresponding to the FF axial force Fff, and in step S7, applies a steering reaction force corresponding to the FB axial force Ffb. The process then ends.

In step S8, the controller 11 determines whether the front wheel slip angle is smaller than a third prescribed value. When the front wheel slip angle is smaller than the third predetermined value (yes in step S8), the process proceeds to step S9. If the front wheel slip angle is not smaller than the third predetermined value (step S8: NO), the process proceeds to step S10. In step S9, the controller 11 applies a steering reaction force corresponding to the FF axial force Fff, and in step S10, applies a steering reaction force corresponding to the FB axial force Ffb. The process then ends.

(Modification)

The axial force mixing portion 23 may set a larger first predetermined value when the inclination angle of the road surface is larger than that of the road surface. This can reduce the influence of the estimation error of the FB axial force Ffb due to the inclination. For example, the axial force mixing portion 23 calculates a lateral acceleration, that is, a lateral G offset amount Gyo, added to the lateral acceleration Gy output by the acceleration sensor 6 due to the influence of the inclination angle or gradient of the road surface. For example, the axial force mixing portion 23 may calculate the lateral G offset amount gyo=v×γa-Gy based on the vehicle speed V, the actual yaw rate γa, and the lateral acceleration Gy. The axial force mixing unit 23 calculates a tilt correction value Cb, which is a correction value of a first predetermined value and a second predetermined value corresponding to the tilt correction value Cb. Refer to fig. 11. The inclination correction value Cb increases from "0" to a value Cb2 as the lateral G offset amount Gyo becomes larger. For example, in a range in which the lateral G offset amount Gyo is smaller than the value Gy1, the inclination correction value Cb is "0", the inclination correction value Cb increases from "0" to the value Cb1 as the lateral G offset amount Gyo increases from the value Gy1 to the value Gy2, and the inclination correction value Cb increases from the value Cb1 to the value Cb2 as the lateral G offset amount Gyo increases from the value Gy2 to the value Gy 3. The axial force mixing unit 23 adds the inclination correction value Cb to correct the first predetermined value and the second predetermined value. Thus, when the inclination angle of the road surface is large, the first predetermined value becomes larger.

(Second embodiment)

In the second embodiment, when the steering speed ω of the steering wheel 1a is equal to or greater than the predetermined speed, a steering reaction force based on the FB axial force is applied. Refer to fig. 3. The differentiator 22 differentiates the steering angle δ to calculate the steering angular velocity ω of the steering wheel 1 a. The axial force mixing unit 23 determines whether the steering angular velocity ω is equal to or greater than a predetermined velocity. When the steering angular velocity ω is equal to or greater than a predetermined velocity, an estimated rack axial force Frk is calculated based on the FB axial force Ffb, regardless of whether the road surface is a low μ road surface, whether the axial force difference Δfs is equal to or greater than a second predetermined value, and whether the front wheel slip angle is equal to or greater than a fourth predetermined value. For example, the axial force mixing portion 23 may calculate the estimated rack axial force Frk by calculating the steering angular velocity dependent mixture ratio R1 corresponding to the steering angular velocity ω and mixing the FF axial force Fff and the FB axial force Ffb at the steering angular velocity dependent mixture ratio R1. The steering angular velocity-dependent mixing ratio R1 is set to a ratio that decreases the FF axial force Fff when the steering angular velocity ω is high. Refer to fig. 7 (a). The steering angular velocity changes from "1" to "0" as the steering angular velocity becomes higher depending on the mixing ratio R1 and the steering angular velocity ω. For example, in a range where the steering angular velocity ω is lower than the lower limit value ω1, the steering angular velocity is "1" depending on the mixing ratio R1. In the range where the steering angular velocity ω is higher than the upper limit value ω2, the steering angular velocity is "0" depending on the mixing ratio R1. In the range from the lower limit value ω1 to the upper limit value ω2, as the steering angular velocity ω becomes higher, the steering angular velocity decreases from "1" to "0" depending on the mixing ratio R1. The lower limit value ω1 and the upper limit value ω2 may be variable in accordance with the vehicle speed V. The axial force mixing portion 23 can calculate the estimated rack axial force frk=r1× Fff + (1-R1) ×ffb by mixing the FF axial force Fff and the FB axial force Ffb depending on the mixing ratio R1 at the steering angular velocity.

(Third embodiment)

In the third embodiment, in addition to the control of the first and second embodiments, when the host vehicle is in the OS state, a steering reaction force based on the FB axial force is applied. For example, when the host vehicle is in the OS state, the yaw rate difference Δγ between the standard yaw rate γm, which is the standard value of the yaw rate calculated according to the vehicle model, and the actual yaw rate γa increases. Therefore, when the yaw rate difference Δγ is large, a steering reaction force based on the FB axial force is applied. In addition, for example, when the host vehicle is in the OS state, the vehicle body slip angular velocity difference Δα, which is the difference between the standard vehicle body slip angular velocity αm, which is the standard value of the vehicle body slip angular velocity calculated in accordance with the vehicle model, and the actual vehicle body slip angular velocity αa of the actual host vehicle, becomes larger. Therefore, when the vehicle body slip angular velocity difference Δα is large, a steering reaction force based on the FB axial force is applied.

Fig. 6 is a block diagram showing a functional configuration example of the axial force mixing portion 23 of the third embodiment. The axial force mixing unit 23 calculates a steering angular velocity dependent mixing ratio R1 corresponding to the steering angular velocity ω, and calculates a first mixing axial force Fmf by mixing the FF axial force Fff and the FB axial force FB at the steering angular velocity dependent mixing ratio R1. The axial force mixing unit 23 calculates a yaw rate difference-dependent mixture ratio R2 corresponding to the yaw rate difference Δγ, a vehicle body slip angular velocity difference-dependent mixture ratio R3 corresponding to the vehicle body slip angular velocity difference Δα, an axial force difference-dependent mixture ratio R4 corresponding to the axial force difference Δfs, and a front wheel slip angle-dependent mixture ratio R5 corresponding to the front wheel slip angle. The axial force mixing section 23 selects any one of these mixing ratios R2 to R5 as the final mixing ratio Rf according to the driving scene. The axial force mixing portion 23 calculates the estimated rack axial force Frk by mixing the first mixing axial force Fmf and the FB axial force Ffb at the final mixing ratio Rf.

The axial force mixing section 23 includes a steering angular velocity dependent mixture ratio calculating section 30, mixers 31 and 32, a model calculating section 33, a yaw rate difference dependent mixture ratio calculating section 34, a vehicle body slip angular velocity difference dependent mixture ratio calculating section 35, an axial force difference dependent mixture ratio calculating section 36, a front wheel slip angle dependent mixture ratio calculating section 37, and a selector 38. As described above with reference to fig. 7 (a), the steering angular velocity dependent mixture ratio calculating unit 30 calculates the steering angular velocity dependent mixture ratio R1 based on at least the steering angular velocity ω. The mixer 31 calculates the first mixed axial force Fmf =r1× Fff + (1-R1) ×fb by mixing the FF axial force Fff and the FB axial force FB depending on the mixing ratio R1 at the steering angular velocity. The mixer 32 calculates the second mixing axial force fmm=r1× Frm + (1-R1) ×fb by mixing the standard axial force Frm and the FB axial force FB depending on the mixing ratio R1 at the steering angular velocity.

The model calculation unit 33 calculates a standard yaw rate γm and a standard vehicle body slip angular velocity αm based on the actual steering angle θ and the vehicle speed V according to a predetermined linear two-degree-of-freedom model. An example of the linear two-degree-of-freedom model is shown in the following formula.

[ Number 1]

V _x is the speed of the host vehicle in the front-rear direction, V _y is the lateral speed, θ _f is the steering angle of the front wheels, θ _r is the steering angle of the rear wheels, M is the mass of the host vehicle, I _z is the moment of inertia, L _f is the length from the center of gravity to the front wheels, L _r is the length from the center of gravity to the rear wheels, K _f is the angular stiffness (tire deflection stiffness) of the front wheels, and K _r is the angular stiffness of the rear wheels. The model calculation unit 33 calculates a first estimated front wheel slip angle βfm1, which is a front wheel slip angle calculated based on the actual yaw rate γa, and a second estimated front wheel slip angle βf2, which is a front wheel slip angle calculated based on the standard yaw rate γm. For example, the model calculation unit 33 may calculate the first estimated front wheel slip angle βfm1 and the second estimated front wheel slip angle βfm2 according to the following equations.

βfm1=θ/N-(V_y+L_f×γa)/V_x

βfm2=θ/N-(V_y+L_f×γm)/V_x

Wherein N is the total speed ratio. Further, the model calculation unit 33 calculates the standard axial force Frm based on the actual steering angle θ. For example, the model calculation unit 33 may multiply the first estimated front wheel slip angle βf1 or the second estimated front wheel slip angle βf2 by the front wheel angular rigidity K _f to estimate the tire lateral force of the front wheel 2, and may convert the estimated tire lateral force into the standard axial force Frm.

The yaw rate difference-dependent mixture ratio calculation unit 34 calculates a yaw rate difference-dependent mixture ratio R2 for calculating the estimated rack axial force Frk based on the FB axial force Ffb when the host vehicle is in the OS state. The yaw rate difference dependent mixture ratio R2 may be calculated based on at least the standard yaw rate γm and the actual yaw rate γa. The yaw rate difference value is set to a ratio (a ratio of decreasing FF axial force Fff) at which the first hybrid axial force Fmf is decreased in the case where the yaw rate difference Δγ between the standard yaw rate γm and the actual yaw rate γa is large, depending on the mixture ratio R2. Refer to fig. 7 (b). The yaw rate difference value is changed from "1" to "0" depending on the mixture ratio R2 as the yaw rate difference Δγ becomes larger. For example, in a range where the yaw rate difference Δγ is smaller than the lower limit value Δγ1, the yaw rate difference value depends on the mixture ratio R2 as "1". In the range where the yaw rate difference Δγ is larger than the upper limit value Δγ2, the yaw rate difference depends on the mixture ratio R2 being "0". In the range from the lower limit value Δγ1 to the upper limit value Δγ2, the yaw rate difference value decreases from "1" to "0" depending on the mixture ratio R2 as the yaw rate difference value Δγ becomes larger. The lower limit value Δγ1 and the upper limit value Δγ2 may be variable according to the vehicle speed V.

Refer to fig. 6. The vehicle body slip angular velocity difference-dependent mixture ratio calculating section 35 calculates a vehicle body slip angular velocity difference-dependent mixture ratio R3 for calculating the estimated rack axial force Frk based on the FB axial force Ffb when the host vehicle is in the OS state. The vehicle body slip angular velocity difference-dependent mixture ratio calculating section 35 calculates an actual vehicle body slip angular velocity αa=γa-Gy/V based on the vehicle speed V, the actual yaw rate γa, and the lateral acceleration Gy, calculates a vehicle body slip angular velocity difference Δα between the standard vehicle body slip angular velocity αm and the actual vehicle body slip angular velocity αa, and calculates a vehicle body slip angular velocity difference-dependent mixture ratio R3 based on the vehicle body slip angular velocity difference Δα. The vehicle body slip angular velocity difference dependent mixture ratio R3 is set to decrease the ratio of the first mixture axial force Fmf in the case where the vehicle body slip angular velocity difference Δα is large.

Refer to fig. 7 (c). The vehicle body slip angular velocity difference value is changed from "1" to "0" as the vehicle body slip angular velocity difference value Δα becomes larger depending on the mixture ratio R3. For example, in a range where the vehicle body slip angular velocity difference Δα is smaller than the lower limit value Δα1, the vehicle body slip angular velocity difference is "1" depending on the mixture ratio R3. In the range where the vehicle body slip angular velocity difference Δα is greater than the upper limit value Δα2, the vehicle body slip angular velocity difference is "0" depending on the mixture ratio R3. In the range from the lower limit value Δα1 to the upper limit value Δα2, the vehicle body slip angular velocity difference decreases from "1" to "0" depending on the mixture ratio R3 as the vehicle body slip angular velocity difference Δα becomes larger. The lower limit value Δα1 and the upper limit value Δα2 may be variable according to the vehicle speed V. Refer to fig. 6. The vehicle body slip angular velocity difference-dependent mixture ratio calculating section 35 calculates the above-described lateral G offset amount Gyo.

The axial force difference-dependent mixture ratio calculating section 36 calculates an axial force difference-dependent mixture ratio R4. Refer to fig. 8. The axial force difference-dependent mixture ratio calculation unit 36 includes a subtractor 40, a low-pass filter 41, correction gain calculation units 42 and 43, multipliers 44 and 45, a lower limit value calculation unit 46, an upper limit value calculation unit 47, an inclination correction value calculation unit 48, adders 49 and 50, and a mixture ratio calculation unit 51. Subtractor 40 calculates an axial force difference Δfs between second hybrid axial force Fmm and FB axial force Ffb. Instead of the second mixing axial force Fmm, an axial force difference between FF axial force Fff and FB axial force Ffb may also be calculated as an axial force difference Δfs. The axial force difference Δfs from which the high frequency component is removed by the low pass filter 41 is input to the multiplier 44.

The correction gain calculation units 42 and 43 calculate a first correction gain G1 and a second correction gain G2 corresponding to whether the road surface is a low μ road surface. Thus, the axial force difference-dependent mixture ratio R4 corresponding to the axial force difference Δfs is calculated in the case where the road surface is a low- μ road surface, and the axial force difference-dependent mixture ratio R4 is fixed to "1" in the case where the road surface is not a low- μ road surface. In the case where the road surface is a low μ road surface, even if FF axial force Fff is large, FB axial force Ffb becomes small. Then, when FF axial force Fff is equal to or greater than upper limit Fff2 and FB axial force FB is smaller than lower limit Ffb1, correction gain calculation units 42 and 43 determine that the road surface is a low μ road surface, and set first correction gain G1 and second correction gain G2 to "1". Referring to fig. 9 (a). The first correction gain G1 changes from "1" to "0" as the FB axial force Ffb becomes larger. For example, in a range where FB axial force Ffb is smaller than lower limit value Ffb1, first correction gain G1 is "1", and in a range where FB axial force FB is larger than upper limit value Ffb2, first correction gain G1 is "0". In the range from the lower limit value Ffb1 to the upper limit value Ffb2, the first correction gain G1 decreases from "1" to "0" as the FB axial force Ffb increases.

In contrast, when FF axial force Fff is equal to or lower than lower limit Fff1 or FB axial force FB is equal to or higher than upper limit Ffb2, it is determined that the road surface is not a low μ road surface, and first correction gain G1 and second correction gain G2 are set to "0". Refer to fig. 9 (b). The second correction gain G2 changes from "0" to "1" as the normal axial force Frm becomes larger. For example, in a range where the standard axial force Frm is smaller than the lower limit value Fff1, the second correction gain G2 is "0", and in a range where it is larger than the upper limit value Fff2, the second correction gain G2 is "1". In the range of the lower limit value Fff to the upper limit value Fff2, the second correction gain G2 increases from "0" to "1" as the standard axial force Frm increases. Multiplier 44 and 45 calculate corrected axial direction force difference Δfsc=g 1 XG2 XΔFs. The mixture ratio calculating section 51 calculates an axial force difference dependent mixture ratio R4 based on the axial force difference Δfsc. Thus, in the case where the road surface is a low μ road surface, the axial force difference Δfs is directly input to the mixture ratio calculating section 51. Therefore, the mixture ratio calculating section 51 calculates the axial force difference dependent mixture ratio R4 corresponding to the axial force difference Δfs. On the other hand, in the case where the road surface is not a low μ road surface, the axial force difference Δfsc=0 is input to the mixture ratio calculating section 51, and as described later, the axial force difference is fixed to "1" depending on the mixture ratio R4.

The lower limit value calculation unit 46 calculates a switching range lower limit value LL1, which is a lower limit value of a switching range in which the axial force difference value is switched between "1" and "0" according to the axial force difference value Δfsc, and the mixing ratio R4 is switched. The upper limit value calculation unit 47 calculates a switching range upper limit value LU1 as an upper limit value of the switching range. For example, the lower limit value calculation unit 46 and the upper limit value calculation unit 47 may calculate the switching range lower limit value LL1 and the switching range upper limit value LU1 from the vehicle speed V. Referring to fig. 10 (a). The switching range lower limit value LL1 may be a constant value L1 at any vehicle speed V, or may be variable according to the vehicle speed. Refer to fig. 10 (b). The switching range upper limit LU1 may be a constant value L2 at any vehicle speed V, or may be variable according to the vehicle speed.

Refer to fig. 8. The inclination correction value calculation unit 48 calculates the inclination correction value Cb described with reference to fig. 11. Adders 49 and 50 add the inclination correction value Cb to the switching range lower limit value LL1 and the switching range upper limit value LU1, respectively, to thereby calculate a corrected switching range lower limit value ll2=ll1+cb and a corrected switching range upper limit value LU 2=lu 1+cb. As described above, the larger the inclination angle or gradient of the road surface, the larger the value of the lateral G offset amount Gyo. Therefore, the larger the inclination angle or gradient of the road surface is, the larger the switching range lower limit value LL2 and the switching range upper limit value LU2 are set.

The mixture ratio calculating section 51 calculates an axial force difference dependent mixture ratio R4 based on the axial force difference Δfsc. The axial force difference value is set depending on the mixing ratio R4 to decrease the ratio of the first mixing axial force Fmf in the case where the axial force difference Δfsc is large.

Refer to fig. 12. The axial force difference value is changed from "1" to "0" as the axial force difference value Δfsc becomes larger depending on the mixing ratio R4. For example, in a range in which the axial force difference Δfsc is smaller than the switching range lower limit value LL2, the axial force difference is "1" depending on the mixing ratio R4. Therefore, in the case where the road surface is not a low μ road surface, since Δfsc=0 is input, the axial force difference value is fixed to "1" depending on the mixing ratio R4. In a range in which the axial force difference Δfsc is larger than the switching range upper limit value LU2, the axial force difference is "0" depending on the mixing ratio R4. In the range from the switching range lower limit value LL2 to the switching range upper limit value LU2, as the axial force difference Δfsc becomes larger, the axial force difference decreases from "1" to "0" depending on the mixing ratio R4. The switching range lower limit value LL2 and the switching range upper limit value LU2 are examples of "first predetermined value" and "second predetermined value" described in the scope of the claims, respectively.

Refer to fig. 13. The front-wheel slip angle-dependent mixture ratio calculating portion 37 calculates a front-wheel slip angle-dependent mixture ratio R5. The front wheel slip angle-dependent mixture ratio calculating unit 37 includes a road surface condition estimating unit 60, mixture ratio calculating units 61 and 62, a DRY (DRY) switching range lower limit calculating unit 63, a WET (WET) switching range lower limit calculating unit 64, mixers 65 and 68, a DRY switching range upper limit calculating unit 66, a WET switching range upper limit calculating unit 67, and a selector 69. The road surface state estimating unit 60 determines the dry state (or wet state) of the road surface from the axial force difference Δfs, and calculates the mixing ratio R6 corresponding to the dry state (or wet state) of the road surface. The mixing ratio R6 changes from "1" to "0" as the axial force difference Δfs becomes larger. Therefore, the mixing ratio R6 is "1" in the case where the road surface is dry, and decreases to "0" with wetting of the road surface. The road surface state estimating unit 60 may correct the axial force difference Δfs by the correction gain corresponding to the FB axial force FB and the standard axial force Frm, and calculate the mixing ratio R6 from the corrected axial force difference, similarly to the correction gain calculating units 42 and 43 and the multipliers 44 and 45 in fig. 8. In addition, as in the lower limit value calculation unit 46, the upper limit value calculation unit 47, the inclination correction value calculation unit 48, and the adders 49 and 50, the lower limit value and the upper limit value of the switching range for converting the mixing ratio R6 in the ranges of "1" and "0" may be set according to the vehicle speed V.

The mixture ratio calculation portion 61 calculates the first front wheel slip angle-dependent mixture ratio R5a based on the first estimated front wheel slip angle βfm1. The first front wheel slip angle-dependent mixing ratio R5a is set such that the ratio of the first mixing axial force Fmf is reduced when the first estimated front wheel slip angle βf1 is large. Refer to fig. 14. The first front wheel slip angle-dependent mixture ratio R5a changes from "1" to "0" as the first estimated front wheel slip angle βfm1 becomes larger. For example, in a range where the first estimated front wheel slip angle βf1 is smaller than the switching range lower limit value LL5, the first front wheel slip angle-dependent mixture ratio R5a is "1". In the range where the first estimated front wheel slip angle βfm1 is larger than the switching range upper limit value LU5, the first front wheel slip angle-dependent mixture ratio R5a is "0". In the range from the switching range lower limit value LL5 to the switching range upper limit value LU5, the first front wheel slip angle depending on the mixture ratio R5a decreases from "1" to "0" as the first estimated front wheel slip angle βfm1 increases. The switching range lower limit value LL5 and the switching range upper limit value LU5 are examples of "third predetermined value" and "fourth predetermined value" described in the scope of the claims, respectively.

The mixture ratio calculation portion 62 calculates the second front wheel slip angle-dependent mixture ratio R5b based on the second estimated front wheel slip angle βfm2. The second front wheel slip angle-dependent mixture ratio R5b is calculated in the same manner as the first front wheel slip angle-dependent mixture ratio R5a, except that the second estimated front wheel slip angle βfm2 is used instead of the first estimated front wheel slip angle βfm1.

The dry switching range lower limit value calculation unit 63, the wet switching range lower limit value calculation unit 64, and the mixer 65 calculate the switching range lower limit value LL5. For example, the dry switching range lower limit value calculation unit 63 and the wet switching range lower limit value calculation unit 64 calculate the switching range lower limit value LL3 for the dry state and the switching range lower limit value LL4 for the wet state, respectively. The lower limit values LL3 and LL4 of the switching range may be constant at any vehicle speed V or may be variable according to the vehicle speed. The mixer 65 calculates the switching range lower limit value LL5 by mixing the switching range lower limit values LL3 and LL4 at the mixing ratio R6. The dry switching range upper limit value calculation unit 66, the wet switching range upper limit value calculation unit 67, and the mixer 68 calculate the switching range upper limit value LU5. For example, the dry switching range upper limit value calculation unit 66 and the wet switching range upper limit value calculation unit 67 calculate the switching range upper limit value LU3 for the dry state and the switching range upper limit value LU4 for the wet state, respectively. The switching range upper limit values LU3 and LU4 may be constant at any vehicle speed V, or may be variable according to the vehicle speed. The mixer 68 mixes the switching range upper limit values LU3 and LU4 at the mixing ratio R6, thereby calculating the switching range upper limit value LU5. The selector 69 selects the smaller one of the first front-wheel-slip-angle-dependent mixture ratio R5a and the second front-wheel-slip-angle-dependent mixture ratio R5b as the front-wheel-slip-angle-dependent mixture ratio R5 and outputs it.

Refer to fig. 6. The selector 38 selects any one of these mixing ratios R2 to R5 as the final mixing ratio Rf according to the driving scene. For example, when the yaw rate difference-dependent mixture ratio R2 is smaller than "1", it may be determined that the host vehicle is in the OS state and the yaw rate difference-dependent mixture ratio R2 may be selected. In addition, when the vehicle body slip angular velocity difference-dependent mixture ratio R3 is smaller than "1", it may be determined that the host vehicle is in the OS state and the vehicle body slip angular velocity difference-dependent mixture ratio R3 may be selected. In addition, when the axial force difference-dependent mixture ratio R4 is smaller than "1", it may be determined that the host vehicle is in the US state and the road surface is a low μ road surface, and the axial force difference-dependent mixture ratio R4 may be selected. In addition, when the front wheel slip angle dependent mixture ratio R5 is smaller than "1", it may be determined that the host vehicle is in the US state and the road surface is a low μ road surface, and the front wheel slip angle dependent mixture ratio R5 may be selected.

The selector 38 may select the smallest one of the mixing ratios R2 to R5 as the final mixing ratio Rf. The selector 38 may calculate a mixture axial force obtained by mixing the first mixture axial force Fmf and the FB axial force Ffb at the final mixture ratio Rf as the estimated rack axial force Frk. This can alleviate abrupt changes in steering reaction force caused by abrupt switching of the estimated rack axial force Frk between the FF axial force Fff and the FB axial force Ffb.

(Effects of the embodiment)

(1) In the steering control method, a steering reaction force based on the FF axial force is applied when the road surface is a low- μ road surface and the axial force difference is smaller than a first predetermined value, and a steering reaction force based on the FB axial force is applied when the road surface is a low- μ road surface and the axial force difference is equal to or larger than a second predetermined value which is equal to or larger than the first predetermined value. In this way, when the road surface is a low μ road surface, the FF axial force and the FB axial force can be switched according to the axial force difference in which μ drop can be detected, and therefore when the road surface is in the US state, the steering reaction force by the FB axial force can be quickly switched, and the drop in road surface μ can be appropriately transmitted to the driver.

When the road surface is not a low-mu road surface and the front wheel slip angle is smaller than a third predetermined value, a steering reaction force based on the FF axial force is applied, and when the road surface is not a low-mu road surface and the front wheel slip angle is equal to or larger than a fourth predetermined value which is equal to or larger than the third predetermined value, a steering reaction force based on the FB axial force is applied. Thus, when the road surface is not a low μ road surface, the steering reaction force by the FB axial force can be quickly switched to the US state, and the road surface state can be appropriately transmitted to the driver.

(2) When the steering speed is equal to or higher than a predetermined speed, a steering reaction force based on the FB axial force can be applied regardless of whether the road surface is a low μ road surface or not and whether the front wheel slip angle is equal to or higher than a fourth predetermined value. In this way, in the emergency avoidance scene, the steering reaction force can be switched based on the FB axial force that can appropriately transmit the road surface state to the driver.

(3) When the difference between the standard yaw rate and the actual yaw rate is greater than the predetermined value, a steering reaction force based on the FB axial force can be applied regardless of whether the road surface is a low μ road surface or not and whether the front wheel slip angle is a fourth predetermined value or more.

Further, when the difference between the standard vehicle body slip angular velocity and the actual vehicle body slip angular velocity is greater than a predetermined value, a steering reaction force based on the FB axial force can be applied regardless of whether the road surface is a low μ road surface or not and whether the front wheel slip angle is a fourth predetermined value or more. This makes it possible to switch to a steering reaction force based on the FB axial force that can appropriately transmit the vehicle behavior to the driver in the case of the OS state.

(4) The road surface may be determined to be a low- μ road surface when FF axial force Fff is equal to or greater than a fifth predetermined value and FB axial force is less than a sixth predetermined value. Thus, it is possible to determine whether the road surface is a low mu road surface with a simple structure.

(5) When the inclination angle of the road surface is larger than the small inclination angle, a larger first predetermined value is set. This can reduce the influence of the estimation error of the FB axial force Ffb due to the inclination.

Symbol description

1A steering wheel, 1B steering shaft, 2 front wheel, 3 steering angle sensor, 4 steering angle sensor, 5 vehicle speed sensor, 6 acceleration sensor, 7 yaw rate sensor, 8 steering control unit, 8A steering motor, 8B steering current detection unit, 9 counter force control unit, 9A counter force motor, 9B counter force current detection unit, 10a steering rack, 10B, 10d pinion shaft, 10c, 10e pinion, 12 standby clutch.

Claims (8)

1. A steering control method for a vehicle in which a steering wheel and a steering wheel are separated from each other, wherein a feed-forward axial force, which is a steering rack axial force that imparts a steering reaction force transmitted to the steering rack, and a feedback axial force, which is a steering rack axial force transmitted from a road surface on which the vehicle is traveling to the steering rack via the steering wheel, are calculated, and a steering reaction force is applied to the steering wheel based on at least one of the feed-forward axial force and the feedback axial force when the steering rack connected to the steering wheel is driven by a steering motor according to steering of the steering wheel,

Estimating a front wheel slip angle which is a slip angle of the steering wheel,

Determining whether the road surface is a low mu road surface having a coefficient of friction below a threshold value,

When the road surface is a low-mu road surface and the axial force difference between one of the normal axial force and the feedforward axial force, which is the steering rack axial force corresponding to the actual steering angle of the steering wheel, and the feedback axial force is smaller than a first predetermined value, a steering reaction force based on the feedforward axial force without using the feedback axial force is applied,

When the road surface is a low-mu road surface and the axial force difference is equal to or greater than the first predetermined value, a steering reaction force based on the feedback axial force is applied,

When the road surface is not a low mu road surface and the front wheel slip angle is smaller than a third prescribed value, a steering reaction force based on the feedforward axial force without using the feedback axial force is applied,

When the road surface is not a low μ road surface and the front wheel slip angle is equal to or greater than the third predetermined value, a steering reaction force based on the feedback axial force is applied.

2. The steering control method according to claim 1, characterized in that,

When the road surface is a low- μ road surface and the axial force difference is a second predetermined value that is equal to or greater than the first predetermined value and less than the first predetermined value, a steering reaction force based on a mixed axial force that mixes the feedforward axial force and the feedback axial force is applied,

When the road surface is not a low- μ road surface, and the front wheel slip angle is equal to or greater than the third predetermined value and is smaller than a fourth predetermined value equal to or greater than the third predetermined value, a steering reaction force is applied based on a mixed axial force that mixes the feedforward axial force and the feedback axial force.

3. The steering control method according to claim 2, characterized in that,

When the steering speed is equal to or higher than a predetermined speed, a steering reaction force based on the feedback axial force is applied regardless of whether the road surface is a low- μ road surface, whether the axial force difference is equal to or higher than the second predetermined value, and whether the front wheel slip angle is equal to or higher than the fourth predetermined value.

4. The steering control method according to claim 2, characterized in that,

The actual yaw rate generated at the vehicle and the vehicle speed of the vehicle are detected by sensors,

A standard yaw rate which is a standard value of the yaw rate generated in the vehicle is calculated based on the steering angle of the steering wheel, the vehicle speed of the vehicle and a vehicle model,

When the difference between the standard yaw rate and the actual yaw rate is greater than a predetermined value, a steering reaction force based on the feedback axial force is applied regardless of whether the road surface is a low μ road surface, whether the axial force difference is equal to or greater than the second predetermined value, and whether the front wheel slip angle is equal to or greater than the fourth predetermined value.

5. The steering control method according to claim 2, characterized in that,

The actual yaw rate generated at the vehicle, the lateral acceleration and the vehicle speed of the vehicle are detected by means of sensors,

A standard vehicle body slip angular velocity, which is a standard value of a vehicle body slip angular velocity generated in the vehicle, is calculated based on a steering angle of the steering wheel, a vehicle speed of the vehicle, and a vehicle model,

An actual vehicle body slip angular velocity is calculated based on the actual yaw rate, the lateral acceleration and the vehicle speed,

When the difference between the standard vehicle body slip angular velocity and the actual vehicle body slip angular velocity is greater than a predetermined value, a steering reaction force based on the feedback axial force is applied regardless of whether the road surface is a low μ road surface, whether the axial force difference is equal to or greater than the second predetermined value, and whether the front wheel slip angle is equal to or greater than the fourth predetermined value.

6. The steering control method according to claim 1, characterized in that,

When the feedforward axial force is equal to or greater than a fifth predetermined value and the feedback axial force is less than a sixth predetermined value, the road surface is determined to be a low- μ road surface.

7. The steering control method according to claim 1, characterized in that,

When the inclination angle of the road surface is large, the first predetermined value is set to be larger than when the inclination angle of the road surface is small.

8. A steering control device is provided with:

a steering angle sensor that detects a steering angle of a steering wheel in a vehicle in which the steering wheel is separated from a steering wheel turbine;

A reaction motor that applies a steering reaction force to the steering wheel;

A controller that calculates a feed-forward axial force that is a steering rack axial force that is a steering reaction force applied to the steering rack when the steering rack connected to the steering wheel is driven by a steering motor in accordance with steering of the steering wheel, and a feedback axial force that is a steering rack axial force transmitted to the steering rack from a road surface on which the vehicle is running via the steering wheel, and causes the reaction motor to generate a steering reaction force applied to the steering wheel based on at least one of the feed-forward axial force and the feedback axial force,

The controller is characterized by performing the following processing:

And estimating a front wheel slip angle, which is a slip angle of the steering wheel, determining whether the road surface is a low μ road surface having a coefficient of friction equal to or less than a threshold value, and when the road surface is a low μ road surface and an axial force difference between a steering rack axial force corresponding to an actual steering angle of the steering wheel, that is, a standard axial force or a feed-forward axial force, and the feed-forward axial force is smaller than a first predetermined value, causing the reaction motor to generate a steering reaction force based on the feed-forward axial force without using the feed-forward axial force, when the road surface is a low μ road surface and the axial force difference is equal to or greater than the first predetermined value, causing the reaction motor to generate a steering reaction force based on the feed-back axial force, when the road surface is not a low μ road surface and the feed-forward axial force is smaller than a third predetermined value, causing the reaction force to be generated based on the feed-forward axial force when the road surface is not a low μ road surface and the feed-forward axial force is equal to or greater than the third predetermined value.