Motor vehicle steering system

• US 8,660,749 B2
• Filed: 05/04/2007
• Issued: 02/25/2014
• Est. Priority Date: 05/09/2006
• Status: Active Grant

• Current Assignee: Jtekt Corporation (Toyota Motor Corporation)
• Original Assignee: Jtekt Corporation (Toyota Motor Corporation)
• Inventors: Hayama, Ryouhei, Nakano, Shiro, Kada, Tomoyasu
• Primary Examiner(s): Nguyen, John Q
• Assistant Examiner(s): KIM, KYUNG J
• Application Number:
  US11/797,657
• Publication Number:
  US 20070265752A1
• Time in Patent Office: 2,489 Days
• Field of Search: 701/41, 180/204, 180/6.2, 180/6.6, 180/402, 180/446
• US Class Current: 701/41
• CPC Class Codes: B62D 6/003 in order to control vehicle yaw movement, i.e. around a vertical axis B62D6/007 takes precedence
• CPC Class Codes: B62D 6/007 adjustable by the driver, e.g. sport mode
• CPC Class Codes: B62D 6/008 Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications

Abstract

A motor vehicle steering system steers vehicle wheels in response to the operation of an operation member for steering a vehicle. The system includes a rutted road judging unit which judges whether the vehicle is driving on a rutted road or not, and a steering enhancement control unit which enhances steering of vehicle wheels in response to operation of the operation member when the rutted road judging unit judges that the vehicle is driving on a rutted road than when the rutted road judging unit judges that the vehicle is not driving on a rutted road.

Claims

1. A motor vehicle steering system which steers vehicle wheels in response to an operation of an operation member for steering a vehicle, comprising:

a rutted road judging unit judging whether or not the vehicle is driving on a rutted road based on

an operation amount of the operation member,

a difference in heights between a first height based on a distance between a tire and a vehicle body on a left side, and a second height based on a distance between a tire and the vehicle body on a right side of the vehicle, and

a lateral acceleration of the vehicle; and

a steering enhancement control unit that switches a used transfer function from a first transfer function to a second transfer function and vice versa according to a result of judgment by the rutted road judging unit such that steering of vehicle wheels in response to operation of the operation member is enhanced, by applying the second transfer function, when the rutted road judging unit judges that the vehicle is driving on a rutted road as compared to when the first transfer function is applied based on the rutted road judging unit'"'"'s judgment that the vehicle is not driving on a rutted road, wherein

the steering enhancement control unit includes a steering ratio control unit that switches the used transfer function from the first transfer function to the second transfer function so as to increase a ratio of a target steering angle of the vehicle wheels to the operation amount of the operation member when traveling on a rutted road as compared to when the first transfer function is applied, and

the first transfer function does not include a time differential component of the operation amount of the operation member while the second transfer function includes a time differential component of the operation amount of the operation member,

wherein the steering enhancement control unit obtains as the target steering angle a first steering angle δ

₁* based on the operation amount δ

h of the operation member according to the first transfer function, that is δ

₁*=K_v K₀ δ

h, when the rutted road judging unit judges that the vehicle is not driving on a rutted road, while obtaining as the target steering angle a second steering angle δ

₂* based on the operation amount δ

h of the operation member according to the second transfer function, that is δ

₂*=K_v K₁ K₂ K₃ δ

h, when the rutted road judging unit judges that the vehicle is driving on a rutted road, and

wherein K_v is a coefficient that is a function of a vehicle speed, K₀ and K₁ are coefficients that are functions of the operation amount δ

h, K₂ is a coefficient that is a function of a time-based first-order differential value δ

h′

of the operation amount δ

h, and K₃ is a coefficient that is a function of a time-based second-order differential value of the operation amount δ

h.

2. The motor vehicle steering system according to claim 1, wherein the rutted road judging unit judges that the vehicle is driving on a rutted road if the operation amount of the operation member is less than a first predetermined value, the difference in heights exceeds a second predetermined value, and the lateral acceleration of the vehicle is less than a third predetermined value.

3. The motor vehicle steering system according to claim 1, further comprising vehicle height sensors that detect angles of suspension arms of the vehicle to determine the difference in heights.

4. The motor vehicle steering system according to claim 1, wherein the steering ratio control unit switches the used transfer function to said second transfer function to obtain the target steering angle based on the operation amount of the operation member.

5. The motor vehicle steering system according to claim 1, wherein the coefficient K_v is set to be smaller as the vehicle speed becomes larger.

6. The motor vehicle steering system according to claim 1, wherein the coefficients K₀ and K₁ are set to be equal to each other.

7. The motor vehicle steering system according to claim 1, wherein the coefficients K₀ and K₁ are set such that the coefficient K₁ is larger than the coefficient K₀ with regard to an arbitrary operation amount δ

h.

8. The motor vehicle steering system according to claim 1, wherein the coefficients K₀ and K₁ are set such that the coefficients K₀ and K₁ are zero when the operation amount δ

h equals to zero.

9. The motor vehicle steering system according to claim 1, wherein the coefficients K₀ and K₁ are set such that the coefficients K₀ and K₁ are larger as an absolute value of the operation amount |δ

h| becomes larger.

10. The motor vehicle steering system according to claim 9, wherein the coefficients K₀ and K₁ are set such that an increasing rate of the coefficients K₀ and K₁ with respect to the absolute value of the operation amount |δ

h| is small when the operation angle amount value |δ

h| is within a range near a steering midpoint, while the increasing rate is large when the absolute value of the operation amount |δ

h| is within a range near a steering end point.

11. The motor vehicle steering system according to claim 1, wherein the coefficient K₂ is not less than zero, and set to be zero when the time-based first-order differential value δ

h′

is zero.

12. The motor vehicle steering system according to claim 11, wherein the coefficient K₂ is set to be larger as an absolute value of the time-based first-order differential value δ

h′

becomes larger.

13. The motor vehicle steering system according to claim 1, wherein the coefficient K₃ is not less than zero, and set to be zero when the time-based second-order differential value δ

h″

is zero.

14. The motor vehicle steering system according to claim 13, wherein the coefficient K₃ is set to be larger as an absolute value of the time-based second-order differential value δ

h″

becomes larger.

15. The motor vehicle steering system according to claim 1, further comprising a target electric current computing section that computes a target electric current value that is used to supply electric current to a steering actuator within the steering system.

16. The motor vehicle steering system according to claim 1, further comprising a target reaction force torque computing section that determines a target reaction force torque used to drive a reaction force actuator within the steering system.