# US 2001/0022249 A1 · Electric power steering control system

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- Number: US 2001/0022249 A1
- Document ID: US20010022249A1
- Status: Published application
- Kind: A1
- Application number: 09/802,874
- Filed: 2001-03-12
- Published: 2001-09-20
- Earliest claimed: 2000-03-15
- Assignees: Koyo Seiko Co., Ltd.
- Inventors: Kazuyuki Yoshida
- Web page: https://patentgrep.com/patent/US20010022249A1

## CPC

- B62D 5/0463: {calculating assisting torque from the motor based on driver input}
- 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)

## Abstract

A control system for an electric power steering system which generates a steering assist force by an electric motor driven on the basis of a steering torque applied to an operation member. The control system includes: a target current determining circuit for generating a target current value according to the steering torque; a compensation value determining circuit for generating a compensation current value according to a time-based differential value of the steering torque; a waveform transforming circuit for performing a waveform transformation to convert the compensation current value into a modified compensation value which sinusoidally changes with time; a circuit for generating a control command value by superimposing the modified compensation value obtained through the waveform transformation on the target current value; and a motor driving circuit for driving the electric motor on the basis of the control command value.

## Claims

### Claim 1

A control system for an electric power steering system adapted to generate a steering assist force by an electric motor driven on the basis of a steering torque applied to an operation member, the control system comprising:
a target current determining circuit for generating a target current value according to the steering torque;
a compensation value determining circuit for generating a compensation current value according to a time-based differential value of the steering torque;
a waveform transforming circuit for performing a waveform transformation to convert the compensation current value generated by the compensation value determining circuit into a modified compensation value which sinusoidally changes with time;
a circuit for generating a control command value by superimposing the modified compensation value generated by the waveform transforming circuit on the target current value determined by the target current determining circuit; and
a motor driving circuit for driving the electric motor on the basis of the control command value.

### Claim 2 (depends on 1)

A control system as set forth in claim 1, wherein the compensation value determining circuit generates the compensation current value in a digital data form on the basis of the time-based differential value of the steering torque in a digital data form.

### Claim 3 (depends on 1)

A control system as set forth in claim 1, wherein the waveform transforming circuit performs the waveform transformation so that a pulse indicative of the compensation current value for a minimum value of the time-based differential value of the steering torque is converted into a digital signal having a stepwise sinusoidal waveform expressed by at least three discrete values.

### Claim 4

An electric power steering system comprising:
an electric motor for generating a steering assist force; and
a control system for driving the electric motor on the basis of a steering torque applied to an operation member,
the control system comprising:
a target current determining circuit for generating a target current value according to the steering torque;
a compensation value determining circuit for generating a compensation current value according to a time-based differential value of the steering torque;
a waveform transforming circuit for performing a waveform transformation to convert the compensation current value generated by the compensation value determining circuit into a modified compensation value which sinusoidally change with time;
a circuit for generating a control command value by superimposing the modified compensation value generated by the waveform transforming circuit on the target current value determined by the target current determining circuit; and
a motor driving circuit for driving the electric motor on the basis of the control command value.

### Claim 5 (depends on 4)

An electric power steering system as set forth in claim 4, wherein the compensation value determining circuit generates the compensation current value in a digital data form on the basis of the time-based differential value of the steering torque in a digital data form.

### Claim 6 (depends on 4)

An electric power steering system as set forth in claim 4, wherein the waveform transforming circuit performs the waveform transformation so that a pulse indicative of the compensation current value for a minimum value of the time-based differential value of the steering torque is converted into a digital signal having a stepwise sinusoidal waveform expressed by at least three discrete value.