PAYLOAD ESTIMATION USING ELECTRIC POWER STEERING SIGNALS

• US 20170101127A1
• Filed: 10/07/2016
• Published: 04/13/2017
• Est. Priority Date: 10/09/2015
• 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: Varunjikar, Tejas M., Champagne, Anthony J.
• Granted Patent: US 10,569,801 B2
• Time in Patent Office: Days
• CPC Class Codes: B62D 5/0463 calculating assisting torque from the motor based on driver input
• 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 payload estimation system and a method for estimating payload estimation using electric power steering (EPS) signals are provided. In certain embodiments, the aspects of the invention may include: receiving, by a payload detection module, multiple EPS signals to generate an additional axle load factor, determining, by a blend factor table, a load blend factor according to the additional axle load factor, generating, by a first multiplier, a blended nominal base assist signal by combining the load blend factor and a handwheel torque signal processed by a nominal base assist module, generating, by a second multiplier, a blended highload base assist signal by combining the load blend factor and the handwheel torque signal processed by a highload base assist module, and combining, by a merge module, the blended nominal base assist and the blended highload base assist to generate a motor torque command for the EPS system.

Claims

1. A payload estimation system of an electric power steering (EPS) system comprising:

a payload detection module configured to detect payload according to a plurality of EPS signals and generate an axle load factor;

a blend factor table configured to determine a load blend factor according to the axle load factor;

a nominal base assist module configured to generate a nominal base assist based on a handwheel torque signal;

a highload base assist module configured to generate a highload base assist based on the handwheel torque; and

a signal combiner configured to combine a blended nominal base assist and a blended highload base assist to generate a motor torque command.

2. The payload estimation system of claim 1, wherein the payload detection module is configured to receive

a motor position signal received from a power steering motor position sensor, a motor velocity signal received from a power steering motor velocity sensor, the handwheel torque signal received from a handwheel torque sensor, a vehicle speed signal received from one or more vehicle speed sensors, and

a previous motor torque command signal associated with a unit time delayed motor torque command signal.

3. The payload estimation system of claim 1, wherein the blended nominal base assist includes the nominal base assist multiplied by an offset load blend factor, wherein the offset load blend factor comprises 1 minus the load blend factor, and the blended highload base assist comprises the highload base assist multiplied by the load blend factor.

4. The payload estimation system of claim 1, wherein the motor torque command is combined with at least one of a high frequency assist signal, and a damping signal.

5. The payload estimation system of claim 2, wherein the payload detection module comprises:

a condition detection module configured to generate a flag, wherein when one or more conditions are desirable to compare an estimated rack torque with a reference rack torque, the flag is TRUE;

a rack torque estimation module configured to generate the estimated rack torque;

a reference model module configured to generate the reference rack torque according to a stiffness factor and an offset factor; and

a load factor calculation module configured to generate the additional axle load factor based on a difference between the estimated rack torque and the reference rack torque, and the flag.

7. The payload estimation system of claim 7, wherein the payload detection module includes an amplifier configured to convert the motor position signal to a handwheel position.

6. The payload estimation system of claim 7, wherein the reference rack torque is calculated according to following formula:

Reference rack torque=K*HWPOS+B,

wherein K is the stiffness factor obtained by a first lookup table based on the vehicle speed, HWPOS is the handwheel position, and B is the offset factor obtained by a second lookup table based on the vehicle speed.

8. The payload estimation system of claim 7, wherein the rack torque estimation module comprises:

a first amplifier configured to increase the previous motor torque command by a factor of GAIN1, wherein the GAIN1 comprises an assist mechanical ratio;

a second amplifier configured to further increase the previous motor torque command by a factor of GAIN2, wherein the GAIN2 comprises a motor efficiency;

a third amplifier configured to increase the handwheel torque by a factor of GAIN3, wherein the GAIN3 comprises a handwheel efficiency; and

a lowpass filter module configured to filter the amplified previous motor torque command combined with the amplified handwheel torque to generate the estimated rack torque.

11. A method of estimating a payload for maintaining a substantially consistent steering feel produced at least in-part by an electric power steering (EPS) system, the method comprising:

receiving, by a payload detection module of a payload estimation system, a plurality of EPS signals to generate an additional axle load factor;

determining, by a blend factor table of the payload estimation system, a load blend factor according to the additional axle load factor;

generating, by a first multiplier, a blended nominal base assist signal by combining the load blend factor and a handwheel torque signal processed by a nominal base assist module;

generating, by a second multiplier, a blended highload base assist signal by combining the load blend factor and the handwheel torque signal processed by a highload base assist module; and

combining, by a merge module, the blended nominal base assist and the blended highload base assist to generate a motor torque command.

9. The payload estimation system of claim 10, wherein the load factor calculation module comprises:

a divider module configured to calculate an initial load factor, wherein the initial load factor is a difference between the estimated rack torque and the reference rack torque divided by a normalizing factor, wherein the normalizing factor is calculated by passing an absolute value of the reference rack torque through a first saturation module;

a switch module configured to update the initial load factor only when the flag is TRUE; and

a plurality of conditioning modules configured to minimize noise of the additional axle load factor and generate the additional axle load factor.

10. The payload estimation system of claim 11, wherein the plurality of conditioning modules comprises:

a deadzone module configured to condition the filtered initial load factor;

a rate limiter module configured to limit the filtered initial load factor to a first predetermined range;

a second lowpass filter module configured to minimize the noise; and

a third saturation module to limit the additional axle load factor to a second predetermined range.

12. The method of claim 11, wherein the plurality of EPS signals comprises:

a motor position signal received from a power steering motor position sensor;

a motor velocity signal received from a power steering motor velocity sensor;

the handwheel torque signal received from a handwheel torque sensor;

a vehicle speed signal received from one or more vehicle speed sensors; and

a previous motor torque command signal associated with a unit time delayed motor torque command signal.

13. The method of claim 12, wherein the blended nominal base assist comprises the nominal base assist multiplied by an offset load blend factor, wherein the offset load blend factor comprises 1 minus the load blend factor, and the blended highload base assist comprises the highload base assist multiplied by the load blend factor.

14. The method of claim 11, further comprising:

combining the motor torque command with at least one additional EPS signal, wherein the at least one additional EPS signal includes at least one of a high frequency assist signal and a damping signal.

15. The method of claim 11, further comprising:

generating, by a condition detection module of the payload detection module, a flag according to the plurality of EPS signals, wherein when one or more conditions are desirable to compare an estimated rack torque with a reference rack torque, the flag is TRUE;

generating, by a rack torque estimation module, the estimated rack torque;

generating, by a reference model module, the reference rack torque according to a stiffness factor and an offset factor; and

calculating, by a load factor calculation module the additional axle load factor based on a difference between the estimated rack torque and the reference rack torque, and the flag.

16. The method of claim 15, wherein generating the reference rack torque comprises:

generating the stiffness factor K according to a first lookup table based on the vehicle speed;

generating the offset factor B according to a second lookup table based on the vehicle speed; and

generating the reference rack torque by multiplying the stiffness factor K with the handwheel position HWPOS and adding the offset factor B.

17. The method of claim 15, further comprising:

converting, by an amplifier of the payload detection module, the motor position signal to a handwheel position.

18. The method of claim 15, further comprising:

multiplying, by a first amplifier of the rack torque estimation module, the previous motor torque command by a factor of GAIN1, wherein the GAIN1 comprises an assist mechanical ratio;

multiplying, by a second amplifier of the rack torque estimation module, the previous motor torque command by a factor of GAIN2, wherein the GAIN2 comprises a motor efficiency;

multiplying, by a third amplifier of the rack torque estimation module, the handwheel torque by a factor of GAIN3, wherein the GAIN3 comprises a handwheel efficiency; and

filtering, by a lowpass filter module of the rack torque estimation module, the amplified previous motor torque command combined with the amplified handwheel torque to generate the estimated rack torque.

19. The method of claim 11, further comprising:

calculating, by a divider module, an initial load factor, wherein the initial load factor is a difference between the estimated rack torque and the reference rack torque divided by a normalizing factor, wherein the normalizing factor is calculated by passing an absolute value of the reference rack torque through a first saturation module;

updating, by a switch module, the initial load factor only when the flag is TRUE; and

minimizing, by a plurality of conditioning modules, noise of the additional axle load factor to generate the additional axle load factor.

20. The method of claim 19, further comprising:

conditioning, by a deadzone module of the load factor calculation module, a filtered initial load factor;

limiting, by a rate limiter module, the filtered initial load factor to a first predetermined range;

filtering, by a second lowpass filter module, to minimize noise in the additional axle load factor; and

producing, by a third saturation module, the additional axle load factor by limiting the additional axle load factor to a second predetermined range.