# US 10,768,075 B2 · Rack disturbance test for determining the frequency response of an electric power steering system

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- Number: US 10,768,075 B2
- Document ID: US10768075B2
- Status: Granted
- Kind: B2
- Application number: 16/008,677
- Filed: 2018-06-14
- Published: 2019-12-19
- Granted: 2020-09-08
- Earliest claimed: 2018-06-14
- Assignees: GM Global Technology Operations LLC
- Applicants: GM Global Technology Operations LLC
- Inventors: Bo Yu; Ian Y. Hwa
- Web page: https://patentgrep.com/patent/US10768075B2

## CPC

- G01M 17/06: Steering behaviour; Rolling behaviour
- B62D 5/0457: {characterised by control features of the drive means as such}
- B62D 5/0481: {monitoring the steering system, e.g. failures}
- B62D 15/021: {Determination of steering angle}
- G01L 5/221: {to steering wheels, e.g. for power assisted steering}
- G01M 7/00: Vibration-testing of structures; Shock-testing of structures (G01M9/00 takes precedence)
- G01M 13/028: Acoustic or vibration analysis
- G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- B62D: MOTOR VEHICLES; TRAILERS (steering, or guiding on a desired track, of agricultural machines or implements A01B69/00; wheels, castors, axles, increasing wheel adhesion B60B; vehicle tyres, tyre inflation or tyre changing B60C; connections between vehicles of a train or the like B60D; vehicles for use on rail and road, amphibious or convertible vehicles B60F; suspension arrangements B60G; heating, cooling, ventilating or other air treating devices B60H; windows, windscreens, non-fixed roofs, doors or similar devices, protective coverings for vehicles not in use B60J; propulsion plant arrangements, auxiliary drives, transmissions, controls, instrumentation or dashboards B60K; electric equipment or propulsion of electrically-propelled vehicles B60L; power supply for electrically-propelled vehicles B60M; passenger accommodation not otherwise provided for B60N; adaptations for load transportation or to carry special loads or objects B60P; arrangement of signalling or lighting devices, the mounting or supporting thereof or circuits therefor, for vehicles in general B60Q; vehicles, vehicle fittings or vehicle parts not otherwise provided for B60R; servicing, cleaning, repairing, supporting, lifting, or manoeuvring, not otherwise provided for, B60S; brake arrangements, brake control systems or parts thereof B60T; air-cushion vehicles B60V; motor-cycles, accessories therefor B62J, B62K; testing of vehicles G01M)
- G01L: MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE (weighing G01G)

## Abstract

A system and method for determining a frequency response of a power steering system is disclosed including a steering assist motor configured to generate an assist torque about an axis of a steering shaft when activated. The method includes monitoring, by a controller, a torque transducer that measures a steering output torque of the steering shaft experienced during a first frequency sweep and a second frequency sweep. The method also includes determining, by the controller, a transfer function based on the steering output torque monitored during the first frequency sweep and the second frequency sweep, where the transfer function indicates the response by the power steering system.

## Claims

### Claim 1

A method of determining a frequency response of a power steering system including a steering assist motor configured to generate an assist torque about an axis of a steering shaft when activated, the method comprising:
transmitting, by a controller, a commanded steering angle to a rotary actuator connected to the steering shaft;
in response to receiving the commanded steering angle, actuating the rotary actuator to the commanded steering angle, wherein the rotary actuator maintains position by exerting a steering wheel torque and the steering shaft is connected to the rotary actuator by a compliant torsion bar and inertial wheel;
transmitting, by the controller, a rack disturbance force control signal to at least one actuator, wherein the at least one actuator is coupled to a rack and configured to apply a rack disturbance force on the rack in a substantially linear direction;
in response to receiving the rack disturbance force control signal, generating a first frequency sweep and a second frequency sweep by the at least one actuator, wherein the steering assist motor is deactivated during the first frequency sweep and activated during the second frequency sweep;
monitoring, by the controller, a torque transducer that measures a steering output torque of the steering shaft experienced during the first frequency sweep and the second frequency sweep; and
determining, by the controller, a transfer function based on the steering output torque monitored during the first frequency sweep and the second frequency sweep, wherein the transfer function indicates the frequency response by the power steering system.

### Claim 2 (depends on 1)

The method of claim 1, further comprising determining the transfer function by:
calculating, by the controller, a mechanical transfer function based on the steering output torque measured during the first frequency sweep.

### Claim 3 (depends on 2)

The method of claim 2, further comprising determining the mechanical transfer function based on:
RDF
⁢
⁢
2
⁢
SWT
na
⁡
(
s
)
=
MTF
1
⁡
(
s
)
=
SWT
na
⁡
(
s
)
RDF
na
⁡
(
s
)
wherein RDF2STna(s) is an estimated transfer function from the rack disturbance force to the steering wheel torque without assistance from the steering assist motor, SWTna is the steering wheel torque without assistance from the steering assist motor, and RDFna is the rack disturbance force without assistance from the steering assist motor.

### Claim 4 (depends on 3)

The method of claim 3, further comprising determining an estimated transfer function from the rack disturbance force to the steering wheel with assistance from the steering assist motor by:
RDF
⁢
⁢
2
⁢
SWT
wa
⁡
(
s
)
=
SWT
wa
⁡
(
s
)
RDF
wa
⁡
(
s
)
wherein RDF2SWTwa(s) represents an estimated transfer function from the rack disturbance force to the steering wheel with assistance from the assist motor, SWTwa is the steering wheel torque with the steering assist motor activated, and RDFwa is a rack disturbance force with the steering assist motor activated.

### Claim 5 (depends on 4)

The method of claim 4, further comprising determining the transfer function by:
L
1
⁡
(
s
)
=
RDF
⁢
⁢
2
⁢
SWT
na
⁡
(
s
)
RDF
⁢
⁢
2
⁢
SWT
wa
⁡
(
s
)
-
1

### Claim 6 (depends on 1)

The method of claim 1, wherein algorithms for determining a steering torque assist control signal are stored in a memory of a steering controller, and wherein the controller is unable to access the algorithms stored in the memory of the steering controller.

### Claim 7 (depends on 1)

The method of claim 1, further comprising:
determining, by the controller, a gain margin of the power steering system, wherein the gain margin is an additional amount of gain required for a magnitude of the power steering system to be 0 decibels when a phase of the power steering system is −180 degrees.

### Claim 8 (depends on 7)

The method of claim 7, further comprising:
determining, by the controller, a phase margin of the power steering system by calculating an amount of phase lag required for the power steering system to be −180 degrees when the magnitude of the power steering system is 0 decibels.

### Claim 9 (depends on 8)

The method of claim 8, further comprising:
determining, by the controller, a Nyquist plot including the gain margin and phase margin; and
calculating a stability margin based on the Nyquist plot.

### Claim 10 (depends on 1)

The method of claim 1, wherein the rack disturbance force control signal is a variable waveform that is either a sinusoidal wave, a white noise signal, or a multi-sine signal.

### Claim 11

A method of determining a frequency response by a power steering system for either a steer-by-wire or an autonomous vehicle, wherein the power steering system includes a steering assist motor configured to generate an assist torque about an axis of a steering shaft when activated, the method comprising:
transmitting, by a controller, a commanded steering angle to a rotary actuator connected to the steering shaft;
in response to receiving the commanded steering angle, actuating the rotary actuator into the commanded steering angle, wherein the rotary actuator maintains position by exerting a steering wheel torque and the steering shaft is connected to the rotary actuator by a compliant torsion bar and inertial wheel;
transmitting, by the controller, a rack disturbance force control signal to at least one actuator, wherein the at least one actuator is coupled to a rack and is configured to apply a rack disturbance force on the rack in a substantially linear direction;
in response to receiving the rack disturbance force control signal, generating a first frequency sweep by the at least one actuator, wherein the steering assist motor is deactivated during the first frequency sweep;
generating a second frequency sweep by the at least one actuator, wherein the steering assist motor is activated and the commanded steering angle is set to zero during the second frequency sweep;
generating a steering angle frequency sweep based on the commanded steering angle, wherein the steering assist motor is activated and the at least one actuator is disconnected during the steering angle frequency sweep;
monitoring, by the controller, a rotary encoder coupled to the steering shaft, wherein the rotary encoder measures a steering angle experienced during the first frequency sweep, the second frequency sweep, and the steering angle frequency sweep;
determining, by the controller, a transfer function based on the steering angle monitored during the first frequency sweep and the second frequency sweep, wherein the transfer function indicates the frequency response of the power steering system; and
determining, by the controller, effects of a feedforward algorithm upon the power steering system based on the steering angle monitored during the steering angle frequency sweep.

### Claim 12 (depends on 11)

The method of claim 11, further comprising:
deactivating the at least one actuator and the steering assist motor;
monitoring, by the controller, the rotary encoder that measures the steering angle; and
determining, by the controller, effects of a feedforward algorithm upon the power steering system based on the steering angle.

### Claim 13 (depends on 11)

The method of claim 11, comprising determining the transfer function by:
calculating, by the controller, a mechanical transfer function based on the steering angle measured during the first frequency sweep.

### Claim 14 (depends on 13)

The method of claim 13, comprising determining the mechanical transfer function by:
RDF
⁢
⁢
2
⁢
SWA
na
⁡
(
s
)
=
MTF
1
⁡
(
s
)
=
SWA
na
⁡
(
s
)
RDF
na
⁡
(
s
)
wherein RDF2SWAna(s) is an estimated transfer function from the rack disturbance force to the steering angle without assistance from the steering assist motor, SWAna is the steering angle without assistance from the steering assist motor, and RDFna is the rack disturbance force without assistance from the steering assist motor.

### Claim 15 (depends on 14)

The method of claim 14, comprising determining an estimated transfer function from the rack disturbance force to the steering angle with assistance from the steering assist motor by:
RDF
⁢
⁢
2
⁢
SWA
wa
⁡
(
s
)
=
SWA
wa
⁢
⁡
(
s
)
RDF
wa
⁡
(
s
)
wherein RDF2SWAwa(s) represents the estimated transfer function from the rack disturbance force to the steering angle with the steering assist motor activated, SWTwa is the steering angle with the steering assist motor activated, and RDFwa is a rack disturbance force with the steering assist motor activated.

### Claim 16 (depends on 15)

The method of claim 15, comprising determining an estimated transfer function from a steering wheel command to the steering angle by:
Cmd
⁢
⁢
2
⁢
SWA
FF
⁡
(
s
)
=
SWA
ff
⁡
(
s
)
550
ff
⁢
(
s
)
wherein Cmd2SWAFF(s) is the estimated transfer function from the steering wheel command to the steering angle, SWAff is the steering angle with the steering assist motor activated and the at least one actuator disengaged, and 550ff is the commanded steering angle with the steering assist motor activated and the at least one actuator disengaged.

### Claim 17 (depends on 11)

The method of claim 11, wherein algorithms for determining a steering torque assist control signal are stored in a memory of a steering controller, and wherein the controller is unable to access the algorithms stored in the memory of the steering controller.

### Claim 18 (depends on 11)

The method of claim 11, further comprising:
determining, by the controller, a gain margin of the power steering system, wherein the gain margin is an additional amount of gain required for a magnitude of the power steering system to be 0 decibels when a phase of the power steering system is −180 degrees; and
determining, by the controller, a phase margin of the power steering system by calculating an amount of phase lag required for the power steering system to be −180 degrees when the magnitude of the power steering system is 0 decibels.

### Claim 19 (depends on 11)

The method of claim 11, wherein the rotary actuator is disengaged during the first frequency sweep.

### Claim 20

A power steering system, comprising:
a rack defining a first end portion and a second end portion;
a first actuator disposed on the first end portion of the rack and a second actuator disposed on the second end portion of the rack;
a steering shaft rotatable about a steering axis;
a pinion gear connecting the rack to the steering shaft;
a steering assist motor configured to generate an assist torque about the steering axis of the steering shaft;
a torque transducer configured to measure a steering output torque of the steering shaft;
a rotary actuator;
a compliant torsion bar and inertial wheel configured to connect the rotary actuator to the steering shaft; and
a controller in communication with the first actuator, the second actuator, and the rotary actuator, the controller configured to:
transmit a commanded steering angle to the rotary actuator, wherein the rotary actuator into the commanded steering angle and maintains position by exerting a steering wheel torque;
transmit a rack disturbance force control signal to the first actuator and the second actuator;
instruct the first actuator and the second actuator to generate a first frequency sweep and a second frequency sweep, wherein the steering assist motor is deactivated during the first frequency sweep and activated during the second frequency sweep;
monitor the torque transducer for the steering output torque of the steering shaft experienced during the first frequency sweep and the second frequency sweep; and
determine a transfer function based on the steering output torque monitored during the first frequency sweep and the second frequency sweep, wherein the transfer function indicates a frequency response of the power steering system.