# US 8,751,108 B2 · Steering device for vehicle > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,751,108 B2 - Document ID: US8751108B2 - Status: Granted - Kind: B2 - Application number: 12/990,850 - Filed: 2009-04-03 - Published: 2011-03-03 - Granted: 2014-06-10 - Earliest claimed: 2008-05-14 - Assignees: Toyota Jidosha Kabushiki Kaisha - Applicants: Masaharu Yamashita - Inventors: Masaharu Yamashita - Web page: https://patentgrep.com/patent/US8751108B2 ## CPC - B62D 5/0463: {calculating assisting torque from the motor based on driver input} - B62D 5/0484: {for reaction to failures, e.g. limp home} - 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 If the main electric power source has failed, an assist control portion shifts the characteristic of an assist map in which the steering torque and the target current are connected in a relation by one step of shift in a direction of increase of the steering torque each time a steering operation that satisfies a steering operation criterion condition is performed. This allows a driver to feel a decline in the steering assist force each time of performing steering operation and therefore become aware of the abnormality. Besides, an upper-limit current of the assist map may be reduced each time the steering operation that satisfies the steering operation criterion condition is performed. Besides, an upper-limit electric power of an electric motor may be reduced each time the steering operation that satisfies the steering operation criterion condition is performed. ## Claims ### Claim 1 A vehicle steering device comprising: a steering mechanism that steers a wheel of a vehicle upon steering operation of a steering handle; an electric motor that is supplied with source power from an electric power source device and that generates assist force that assists in the steering operation of the steering handle; a steering torque detection unit that detects steering torque that a driver of the vehicle inputs to the steering handle; a control value computation unit that stores an assist characteristic that sets a motor control value that corresponds to the steering torque, and computes the motor control value based on the assist characteristic; a motor control unit that controls driving of the electric motor so that if the motor control value is larger, a larger assist force is generated, based on the motor control value computed by the control value computation unit; an electric power source abnormality detection unit that detects abnormality of source power supply capability of the electric power source device; an abnormality-time steering operation determination unit that determines whether or not a steering operation that satisfies a pre-set steering operation criterion condition has been started if the abnormality of the source power supply capability of the electric power source device has been detected by the electric power source abnormality detection unit; and a control value reduction unit that reduces the motor control value that corresponds to the steering torque by one step, if the abnormality-time steering operation determination unit determines that the steering operation that satisfies the steering operation criterion condition has been started, wherein the abnormality-time steering operation determination unit determines that the steering operation that satisfies the steering operation criterion condition has been started, if the steering torque detected by the steering torque detection unit is greater than a pre-set reference value. ### Claim 2 (depends on 1) The vehicle steering device according to claim 1, wherein the abnormality-time steering operation determination unit repeatedly determines whether or not the steering operation that satisfies the steering operation criterion condition has been started, and the control value reduction unit reduces the motor control value that corresponds to the steering torque each time the abnormality-time steering operation determination unit determines that the steering operation that satisfies the steering operation criterion condition has been started. ### Claim 3 (depends on 1) The vehicle steering device according to claim 1, wherein: the motor control value is a target current value of the electric motor; the assist characteristic sets a relation between the steering torque and the target current value such that the target current value has a characteristic of increasing with an increase in the steering torque; and the control value reduction unit reduces the motor control value that corresponds to the steering torque by shifting value of the steering torque relative to the target current value in the assist characteristic to a side of increase. ### Claim 4 (depends on 3) The vehicle steering device according to claim 3, wherein the control value computation unit stores a plurality of steps of assist characteristics that are gradually shifted from one another in value of the steering torque to the side of increase; and the control value reduction unit shifts the value of the steering torque relative to the target current value in the assist characteristic by one step to the side of increase each time the abnormality-time steering operation determination unit determines that the steering operation that satisfies the steering operation criterion condition has been started. ### Claim 5 (depends on 4) The vehicle steering device according to claim 4, wherein an amount of shift by which the value of the steering torque relative to the target current value in the assist characteristic is shifted by one step to the side of increase is a pre-set amount, and is a value that allows the driver to feel a decrease in the assist force. ### Claim 6 (depends on 3) The vehicle steering device according to claim 3, further comprising a steering operation end determination unit that determines whether or not one performance of steering operation has ended, wherein if the abnormality-time steering operation determination unit determines that the steering operation that satisfies the steering operation criterion condition has been started, the control value reduction unit gradually increases the value of the steering torque relative to the target current value in the assist characteristic during a time from determination that the steering operation has been started until determination that the steering operation has ended. ### Claim 7 (depends on 1) The vehicle steering device according to claim 1, wherein: the motor control value is a target current value of the electric motor; the assist characteristic sets a relation between the steering torque and the target current value such that the target current value increases with an increase in the steering torque, and such that the target current value is restricted to be less than or equal to an upper-limit current value; and the control value reduction unit reduces the motor control value that corresponds to the steering torque by reducing the upper-limit current value. ### Claim 8 (depends on 7) The vehicle steering device according to claim 7, wherein: the control value computation unit stores a plurality of steps of descending values of assist characteristics that are lowered from one another in the upper-limit current value; and the control value reduction unit reduces the upper-limit current value by one step each time the abnormality-time steering operation determination unit determines that the steering operation that satisfies the steering operation criterion condition has been started. ### Claim 9 (depends on 8) The vehicle steering device according to claim 8, further comprising a steering operation end determination unit that determines whether or not one performance of steering operation has ended, wherein if the abnormality-time steering operation determination unit determines that the steering operation that satisfies the steering operation criterion condition has been started, the control value reduction unit gradually decreases the upper-limit current value during a time from determination that the steering operation has been started until determination that the steering operation has ended. ### Claim 10 (depends on 1) The vehicle steering device according to claim 1, wherein the control value reduction unit reduces the motor control value that corresponds to the steering torque by reducing an upper-limit electric power value that sets an upper limit of electric power consumption of the electric motor. ### Claim 11 (depends on 10) The vehicle steering device according to claim 10, wherein: the control value computation unit stores a plurality of steps of descending values of assist characteristics that are gradually lowered from one another in the upper-limit electric power value of the electric power consumption of the electric motor; and the control value reduction unit reduces the upper-limit electric power value by one step each time the abnormality-time steering operation determination unit determines that the steering operation that satisfies the steering operation criterion condition has been started. ### Claim 12 (depends on 10) The vehicle steering device according to claim 10, further comprising a steering operation end determination unit that determines whether or not one performance of steering operation has ended, wherein if the abnormality-time steering operation determination unit determines that the steering operation that satisfies the steering operation criterion condition has been started, the control value reduction unit gradually decreases the upper-limit electric power value during a time from determination that the steering operation has been started until determination that the steering operation has ended. ### Claim 13 (depends on 1) The vehicle steering device according to claim 1, further comprising: a steering speed detection unit that detects steering speed; and a reduction amount restriction unit that decreases a reduction amount by which the control value reduction unit reduces the motor control value if the steering speed detected by the steering speed detection unit is greater than a pre-set reference steering speed. ### Claim 14 (depends on 1) The vehicle steering device according to claim 1, further comprising a reduction amount restriction unit that decreases a reduction amount by which the control value reduction unit reduces the motor control value if the steering torque detected by the steering torque detection unit is greater than a pre-set reduction amount restriction criterion torque. ### Claim 15 (depends on 1) The vehicle steering device according to claim 1, wherein: the electric power source device has a main electric power source that supplies source power to a plurality of electrical loads in the vehicle that include the electric motor, and a subsidiary electric power source which is connected in parallel between the main electric power source and the electric motor, and which stores electric power that the main electric power source outputs, and which assists in supply of source power to the electric motor by using the electric power stored; and the electric power source abnormality detection unit detects a state in which source power is unable to be supplied from the main electric power source to the electric motor. ### Claim 16 (depends on 15) The vehicle steering device according to claim 15, wherein if the electric power source abnormality detection unit determines that the state in which the source power is unable to be supplied from the main electric power source is detected, supply of the source power to the electric motor is switched from the main electric power source to the subsidiary electric power source. ### Claim 17 A control method for a vehicle steering device that includes: a steering mechanism that steers a wheel of a vehicle upon steering operation of a steering handle; an electric motor that is supplied with source power from an electric power source device and that generates assist force that assists in the steering operation of the steering handle; a steering torque detection unit that detects steering torque that a driver of the vehicle inputs to the steering handle; a control value computation unit that stores an assist characteristic that sets a motor control value that corresponds to the steering torque, and that computes the motor control value based on the assist characteristic; and a motor control unit that controls driving of the electric motor so that if the motor control value is larger, a larger assist force is generated, based on the motor control value computed by the control value computation unit, the control method comprising: detecting abnormality of source power supply capability of the electric power source device; determining whether or not a steering operation that satisfies a pre-set steering operation criterion condition has been started if the abnormality of the source power supply capability of the electric power source device has been detected; and reducing, with the motor control unit, the motor control value that corresponds to the steering torque by one step, if it is determined that the steering operation that satisfies the steering operation criterion condition has been started, wherein it is determined that the steering operation that satisfies the steering operation criterion condition has been started, if the steering torque detected by the steering torque detection unit is greater than a pre-set reference value. ### Claim 18 (depends on 17) The control method according to claim 17, wherein: it is repeatedly determined whether or not the steering operation that satisfies the steering operation criterion condition has been started; and the motor control value that corresponds to the steering torque is reduced each time it is determined that the steering operation that satisfies the steering operation criterion condition is started. ### Claim 19 (depends on 18) The control method according to claim 18, wherein degree of reduction of the motor control value by the control value reduction unit increases with an increase in number of times of it being determined that the steering operation that satisfies the steering operation criterion condition has been started.