# US 10,118,636 B2 · Electric power steering apparatus

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- Number: US 10,118,636 B2
- Document ID: US10118636B2
- Status: Granted
- Kind: B2
- Application number: 15/520,162
- Filed: 2015-12-24
- Published: 2017-11-16
- Granted: 2018-11-06
- Earliest claimed: 2014-12-25
- Assignees: Nsk Ltd.
- Applicants: Nsk Ltd.
- Inventors: Toru Sakaguchi; Shoya Maruyama
- Web page: https://patentgrep.com/patent/US10118636B2

## CPC

- B62D 5/0463: {calculating assisting torque from the motor based on driver input}
- B62D 5/0469: {End-of-stroke control}
- 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)
- B62D 1/166: {Means changing the transfer ratio between steering wheel and steering gear}
- G05B 13/04: involving the use of models or simulators
- 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)
- G05B: CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS (systems for controlling or regulating non-electric variables G05D; systems for regulating electric or magnetic variables G05F; control devices or systems insofar as characterised by mechanical features only G05G)

## Abstract

A high-performance electric power steering apparatus that includes a control system based on a physical model, includes a model following control that an output (a distance to a rack end) of a controlled object follows-up to a reference model, eliminates or reduces the occurrences of a noisy sound and a shock force at an end hitting without giving any uncomfortable steering feeling to a driver, and reduces the end hitting. The electric power steering apparatus calculates a current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on the current command value, including: a configuration of a model following control including a viscoelastic model as a reference model within a predetermined angle at front of a rack end so as to suppress a rack end hitting.

## Claims

### Claim 1

An electric power steering apparatus that calculates a first current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on said first current command value, comprising:
a first converting section to convert said first current command value to a first rack axial force;
a rack position converting section to convert a rotational angle of said motor to a judgment rack position;
a rack end approach judging section to judge that a steering approaches to a rack end based on said judgment rack position and to output a rack displacement and a switching signal;
a viscoelastic model following control section to generate a second rack axial force including a viscoelastic model as a reference model based on said first rack axial force, said rack displacement and said switching signal; and
a second converting section to convert said second rack axial force to a second current command value;
wherein said viscoelastic model following control section comprising:
a feed-forward control section to feed-forward control based on said first rack axial force and to output a third rack axial force;
a feed-back control section to feed-back control based on said rack displacement and said first rack axial force and to output a fourth rack axial force;
a first switching section to switch-ON/OFF an output of said third rack axial force by said switching signal;
a second switching section to switch-ON/OFF an output of said fourth rack axial force by said switching signal; and
an adding section to output said second rack axial force by adding outputs of said first and second switching sections;
wherein said assist-control is performed by adding said second current command value to said first current command value so as to suppress a rack end hitting.

### Claim 2 (depends on 1)

The electric power steering apparatus according to claim 1, wherein parameters of said feed-back control section and said feed-forward control section are changed based on said rack displacement.

### Claim 3 (depends on 1)

The electric power steering apparatus according to claim 1, wherein said first rack axial force, said second rack axial force, said third rack axial force and said fourth rack axial force are respectively equivalent to a first column shaft torque, a second column shaft torque, a third column shaft torque and a fourth column shaft torque.

### Claim 4

An electric power steering apparatus that calculates a first current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on said first current command value, comprising:
a first converting section to convert said first current command value to a first rack axial force;
a rack position converting section to convert a rotational angle of said motor to a judgment rack position;
a rack end approach judging section to judge that a steering approaches to a rack end based on said judgment rack position and to output a rack displacement and a switching signal;
a viscoelastic model following control section to generate a second rack axial force including a viscoelastic model as a reference model based on said first rack axial force, said rack displacement and said switching signal; and
a second converting section to convert said second rack axial force to a second current command value;
wherein said viscoelastic model following control section comprising:
a feed-forward control section to feed-forward control based on said rack displacement and to output a third rack axial force;
a feed-back control section to feed-back control based on said rack displacement and said first rack axial force and to output a fourth rack axial force;
a first switching section to switch-ON/OFF an output of said third rack axial force by said switching signal;
a second switching section to switch-ON/OFF an output of said fourth rack axial force by said switching signal; and
an adding section to output said second rack axial force by adding outputs of said first and second switching sections;
wherein said assist-control is performed by adding said second current command value to said first current command value so as to suppress a rack end hitting.

### Claim 5 (depends on 4)

The electric power steering apparatus according to claim 4, wherein parameters of said feed-back control section and said feed-forward control section are changed based on said rack displacement.

### Claim 6 (depends on 4)

The electric power steering apparatus according to claim 4, wherein said first rack axial force, said second rack axial force, said third rack axial force and said fourth rack axial force are respectively equivalent to a first column shaft torque, a second column shaft torque, a third column shaft torque and a fourth column shaft torque.

### Claim 7

An electric power steering apparatus that calculates a first current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on said first current command value, comprising:
a first converting section to convert said first current command value to a first rack axial force;
a rack position converting section to convert a rotational angle of said motor to a judgment rack position;
a rack end approach judging section to judge that a steering approaches to a rack end based on said judgment rack position and to output a rack displacement and a switching signal;
a viscoelastic model following control section to generate a second rack axial force including a viscoelastic model as a reference model based on said first rack axial force, said rack displacement and said switching signal; and
a second converting section to convert said second rack axial force to a second current command value;
wherein said viscoelastic model following control section comprising:
a feed-back control section to feed-back control based on said rack displacement and said first rack axial force and to output a second rack axial force, and
a switching section to switch-ON/OFF an output of said second rack axial force by said switching signal,
wherein control parameters of said feed-back control section are changed based on said rack displacement or a target rack displacement,
wherein said assist-control is performed by adding said second current command value to said first current command value so as to suppress a rack end hitting.

### Claim 8 (depends on 7)

The electric power steering apparatus according to claim 7, wherein said control parameter is changed so that said control parameter is small where said rack displacement or said target rack displacement is small, and a larger said rack displacement or said target rack displacement, a larger said control parameter.

### Claim 9 (depends on 7)

The electric power steering apparatus according to claim 7, wherein parameters of said reference model are changed based on said rack displacement.

### Claim 10 (depends on 7)

The electric power steering apparatus according to claim 7, wherein said first rack axial force and said second rack axial force are respectively equivalent to a first column shaft torque and a second column shaft torque.

### Claim 11 (depends on 8)

The electric power steering apparatus according to claim 8, wherein parameters of said reference model are changed based on said rack displacement.

### Claim 12

An electric power steering apparatus that calculates a current command value based on at least a steering torque and performs an assist-control of a steering system by driving a motor based on said current command value, comprising:
a configuration of a model following control comprising a feed-back control section including a viscoelastic model as a reference model within a predetermined angle (x0)at front of a rack end;
wherein said feed-back control section comprises a feed-back element to calculate a target rack displacement based on an input-side rack axial force (f), and a control element section to output an output-side rack axial force (ff) based on a positional deviation between said target rack displacement and a rack displacement (x);
wherein said electric power steering apparatus further comprising:
a correcting section to change parameters of at least one-side of said feed-back control section and said control element section and set corrected parameters;
an axial force calculating section to calculate a rack axial force (f4) based on said steering torque and said current command value;
a limiter to limit a maximum value of said rack axial force (f4) with a limiting value and to output said input-side rack axial force (f); and
a steering state judging section to judge a steering state;
wherein said parameters of said feed-forward control section are changed or switched in accordance with said rack displacement (x) and a judgment result of said steering state judging section.

### Claim 13 (depends on 12)

The electric power steering apparatus according to claim 12, wherein said model following control further including a feed-forward control section, and parameters of said feed-forward control section are changed or switched according to said rack displacement (x) and a judgment result of said steering state judging section.

### Claim 14 (depends on 12)

The electric power steering apparatus according to claim 12, wherein said steering state judging section judges a steer-forward/steer-back based on said rack displacement (x) and a rack displacement velocity.

### Claim 15 (depends on 13)

The electric power steering apparatus according to claim 13, wherein said steering state judging section judges a steer-forward/steer-back based on said rack displacement (x) and a rack displacement velocity.

### Claim 16 (depends on 12)

The electric power steering apparatus according to claim 12, wherein said steering state judging section judges a steer-forward/steer-back based on a column axial angle and a column axial angle velocity.

### Claim 17 (depends on 13)

The electric power steering apparatus according to claim 13, wherein said steering state judging section judges a steer-forward/steer-back based on a column axial angle and a column axial angle velocity.

### Claim 18 (depends on 14)

The electric power steering apparatus according to claim 14, wherein said change or switching of said parameters are gradually performed according to a judgment result of said steer-forward/steer-back.

### Claim 19 (depends on 18)

The electric power steering apparatus according to claim 18, wherein a state amount of a state of said turning/returning is calculated as a state amount gain 0 to 1, and a final parameter is calculated by weighting said state amount gain for said parameter of said steer-forward/ steer-back.

### Claim 20 (depends on 19)

The electric power steering apparatus according to claim 19, wherein said state amount gain is a, and said final parameter is calculated by said steer-forward parameter×α+said steer-back parameter×(1−α).