# US 2009/0266641 A1 · Electric power steering system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2009/0266641 A1 - Document ID: US20090266641A1 - Status: Published application - Kind: A1 - Application number: 12/406,375 - Filed: 2009-03-18 - Published: 2009-10-29 - Earliest claimed: 2008-04-23 - Assignees: Honda Motor Co., Ltd. - Inventors: Shigeki Ehara; Hiroyuki Tokunaga - Web page: https://patentgrep.com/patent/US20090266641A1 ## CPC - B62D 5/0466: {for returning the steering wheel to neutral position} - 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 In an electric power steering system for a vehicle that controls a force that urges a steering wheel toward a neutral position thereof, a control unit (21) for the system is configured such that an electric motor (9) for providing an assisting force produces a relatively large returning force when a rotational direction of a steering wheel (2) agrees with a direction of the steering torque applied to the road wheel (7), and a relatively small returning force when a rotational direction of the steering wheel disagrees from a direction of the steering torque applied to the road wheel. Thereby, the effort required for a vehicle operator to steer the vehicle is reduced and the steering feel can be thereby and otherwise improved while providing a favorable returning force that urges a steering wheel toward a neutral position. ## Claims ### Claim 1 An electric power steering system, comprising: a steering mechanism for converting a rotational movement of a steering wheel to a steering movement of a road wheel; a steering torque sensor for detecting a steering torque applied to the road wheel; an electric motor for providing an assisting force for causing the steering movement of the road wheel; and a control unit for providing a control variable for the electric motor; the control unit including a target control base value determining unit for determining a target control base value for the electric motor at least according to a steering torque applied to the steering wheel, a correction value determining unit that modifies the target control base value so as to determine a retuning force that urges the steering wheel toward a neutral position, and forwards the modified target control base value to a drive unit for the electric motor, wherein the correction value determining unit modifies the target control base value so as to cause the electric motor to produce a relatively large returning force when a rotational direction of the steering wheel agrees with a direction of the steering torque applied to the road wheel, and a relatively small returning force when a rotational direction of the steering wheel disagrees from a direction of the steering torque applied to the road wheel. ### Claim 2 (depends on 1) The electric power steering system according to claim 1, wherein the system further comprises a steering angle sensor for detecting a steering angle of the steering wheel, and the correction value determining unit is configured such that the returning force produced by the electric motor is substantially proportional to the steering angle of the steering wheel when the steering angle is smaller than a prescribed value, and is substantially constant when the steering angle is greater than the prescribed value. ### Claim 3 (depends on 1) The electric power steering system according to claim 1, wherein the correction value determining unit is configured such that the returning force produced by the electric motor is reduced with an increase in a steering angle velocity of the steering wheel when a rotational direction of the steering wheel agrees with a direction of the steering torque applied to the road wheel at least in a range of the steering angle velocity. ### Claim 4 (depends on 3) The electric power steering system according to claim 3, wherein the correction value determining unit is configured such that the returning force produced by the electric motor is reduced with an increase in a steering angle velocity of the steering wheel when a rotational direction of the steering wheel agrees with a direction of the steering torque applied to the road wheel and only when the steering angle velocity is greater than a prescribed value.