STEERING SYSTEM DETECTING VEHICLE MOTION STATES

• US 20170232998A1
• Filed: 02/16/2017
• Published: 08/17/2017
• Est. Priority Date: 02/16/2016
• Status: Active Grant

• Current Assignee: Steering Solutions IP Holding Corporation (Nexteer Automotive Group Ltd.)
• Original Assignee: Steering Solutions IP Holding Corporation (Nexteer Automotive Group Ltd.)
• Inventors: Ramanujam, Rangarajan, Sanford, Scott T., Varunjikar, Tejas M., Yang, Tao
• Granted Patent: US 10,099,720 B2
• Time in Patent Office: Days
• CPC Class Codes: B60Y 2300/0223 related to over-steering
• CPC Class Codes: B60Y 2300/0227 related to under-steering
• CPC Class Codes: B62D 15/025 Active steering aids, e.g. helping the driver by actively influencing the steering system after environment evaluation B62D1/28 takes precedence
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input
• CPC Class Codes: B62D 6/00 Arrangements for automatically controlling steering depending on driving conditions sensed and responded to, e.g. control circuits means for initiating a change in direction B62D1/00; steering valves B62D5/06; combined with means for inclining the vehicle body or wheels on bends B62D9/00
• 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 6/008 Control of feed-back to the steering input member, e.g. simulating road feel in steer-by-wire applications
• CPC Class Codes: B62D 6/02 responsive only to vehicle speed
• CPC Class Codes: B62D 6/10 characterised by means for sensing or determining torque

Abstract

Technical features are described for a steering system to compute a state flag value that is indicative of a vehicle motion state, such as an understeer or an oversteer condition. The steering system further generates a reference torque signal based on the state flag value, and generates a motor-assist torque signal based on the reference torque signal. The state flag value indicates the vehicle motion state in both a dynamic-state or a steady-state. Further, the steering system generates the reference torque signal based on the state flag value by blending a first rack force generated based on a vehicle-speed signal and motor angle, and a second rack force generated based on a motor torque and an input torque provided to a handwheel of the steering system.

Claims

1. A steering system comprising:

a control module configured to;

compute a state flag value that is indicative of a vehicle motion state;

generate a reference torque signal based on the state flag value; and

generate a motor-assist torque signal based on the reference torque signal.

2. The steering system of claim 1, wherein the state flag is computed based on a vehicle-speed signal, a yaw-rate signal, and an angle signal indicative of a position of a motor of the steering system.

3. The steering system of claim 1, wherein the vehicle motion state detected is a dynamic state.

4. The steering system of claim 1, wherein the vehicle motion state detected is a steady state.

5. The steering system of claim 1, wherein the reference torque signal is generated based on the state flag value by blending a first rack force generated based on a vehicle-speed signal and motor angle, and a second rack force generated based on a motor torque and an input torque provided to a handwheel of the steering system.

6. The steering system of claim 1, further comprising a yaw observer module configured to compute a first yaw-rate and a yaw-acceleration based on a road-wheel angle signal, a vehicle-speed signal, and a measured yaw-rate signal, wherein the first yaw-rate and the yaw-acceleration are used to compute the state flag.

7. The steering system of claim 6, further comprising a reference yaw module configured to compute a reference yaw-rate and a reference yaw-acceleration based on the road-wheel angle signal, and the vehicle-speed signal, wherein the reference yaw-rate and the reference yaw-acceleration are used to compute the state flag.

8. The steering system of claim 7, further comprising an error calculation module configured to compute a yaw-rate error and a yaw-acceleration error by computing differences between the first yaw-rate and the reference yaw-rate, and between the yaw-acceleration and the reference yaw-acceleration, respectively, wherein the first yaw-rate and the yaw-acceleration are used to compute the state flag.

9. The steering system of claim 1, further comprising a condition threshold calculation module configured to compute a plurality of thresholds corresponding to each condition from a plurality of oversteer and understeer conditions.

10. The steering system of claim 9, wherein the thresholds are computed based on a vehicle-speed signal.

11. The steering system of claim 9, wherein the thresholds are computed based on a surface-friction signal.

12. A method for computing an assist torque by a steering system, the method comprising:

detecting, by the steering system, a non-neutral vehicle motion state;

in response, determining a blending-factor based on a type of the vehicle motion state;

generating a rack force signal by blending a first rack force from a vehicle model and a second rack force from a steering system observer model based on the blending-factor; and

generating the assist torque based on the rack force signal.

13. The method of claim 12, wherein the vehicle motion state is a dynamic-state condition.

14. The method of claim 12, wherein the vehicle motion state is a steady-state condition.

15. The method of claim 12, wherein detecting the vehicle motion state comprises:

computing a yaw-rate error and a yaw-acceleration error; and

comparing the yaw-rate error and the yaw-acceleration error with a plurality of thresholds corresponding respectively to a plurality of types of the vehicle motion state.

16. The method of claim 15, wherein the plurality of types of the vehicle motion state comprise a dynamic-state understeer condition, a dynamic-state oversteer condition, a steady-state understeer condition, and a steady-state oversteer condition.

17. The method of claim 15, wherein computing the yaw-rate error and the yaw-acceleration error further comprises:

generating a yaw-rate and a yaw-acceleration based on a road-wheel angle signal, a vehicle-speed signal, and a measured-yaw signal;

generating a reference yaw-rate and a reference yaw-acceleration based on the road-wheel angle signal and the vehicle-speed signal; and

computing differences between the yaw-rate and the reference yaw-rate, and the yaw-acceleration and the reference yaw-acceleration as the yaw-rate error and the yaw-acceleration error respectively.

18. The method of claim 15, further comprising computing the plurality of thresholds based on a vehicle-speed signal.

19. The method of claim 15, further comprising computing the plurality of thresholds based on a surface-friction signal.

20. The method of claim 12, wherein the vehicle motion state is detected based on a vehicle-speed signal, a yaw-rate signal, and a motor-angle signal indicative of a position of a motor of the steering system.