The disclosure of Japanese Patent Application No. HEI 11-307930 filed on Oct. 29, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a vehicular electric power steering device which assists steering operation of a steering handle through rotation of an electric motor and methods for controlling the same.
2. Description of the Related Art
Japanese Utility Model No. 2524450 discloses a vehicular electric power steering device which is equipped with a torque sensor device for detecting a steering torque, which controls rotation of an electric motor in accordance with a steering torque detected by the torque sensor device, and which assists steering operation of a steering handle through the rotation of the electric motor. In this electric power steering device, the torque sensor device has two sensors, i.e., a main sensor and a sub-sensor. The torque sensor device utilizes an output from the main sensor as a detected steering torque to control the electric motor. When there is a large difference between outputs from the main sensor and the sub-sensor, it is determined that there is an abnormality in the torque sensor device. Then, control of the electric motor is stopped.
However, in the aforementioned electric power steering device, if a power-supply voltage supplied from a battery to the torque sensor device through rotation of the electric motor or the like has dropped, both the torque sensor device and its marginal circuit are affected by the drop in the power-supply voltage. This is problematic in that judgment of the occurrence of an abnormality is made unnecessarily and in that the occurrence of an abnormality in the torque sensor device is misjudged. Further, if it is detected that there is a large difference in outputs from the main sensor and the sub-sensor, the occurrence of an abnormality in the torque sensor device is judged immediately. Thus, even in the case where the difference has become large temporarily due to noise or emergency, the occurrence of the abnormality is judged. In this manner, the occurrence of an abnormality may sometimes be misjudged.
The invention has been made to solve the aforementioned problems by providing an electric power steering device and methods for controlling same capable of suitably detecting an abnormality in a torque sensor device.
A vehicular electric power steering device in accordance with a first exemplary embodiment of the invention has a power circuit which is supplied with a voltage from a battery and which supplies a constant voltage to a torque sensor to activate the torque sensor, an abnormality detector which detects an abnormality in the power circuit, and an abnormality detection forbidder which forbids the abnormality detector from detecting an abnormality in the power circuit if the voltage supplied to the power circuit is equal to or smaller than a predetermined voltage.
In the electric power steering device in accordance with the first exemplary embodiment of the invention, if the voltage supplied from the battery to the power circuit has dropped, the abnormality detection forbidder forbids the abnormality detector from detecting an abnormality in the power circuit. Thus, even in the case where the voltage supplied from the battery to the power circuit has dropped to the extent of hampering suitable operation of the power circuit, there is no possibility of an abnormality in the power circuit being detected erroneously. Also, unnecessary detection of an abnormality in the power circuit is abolished, whereby it becomes possible to suitably detect the occurrence of an abnormality in the power circuit.
A vehicular power steering device in accordance with another exemplary embodiment of the invention has an abnormality detector which detects an abnormality in a torque sensor and an abnormality detection forbidder which forbids the abnormality detector from detecting an abnormality in the torque sensor.
In the vehicular electric power steering device in accordance with this exemplary embodiment of the invention, if the voltage supplied to the torque sensor has dropped, the abnormality detection forbidder forbids the abnormality detector from detecting an abnormality in the torque sensor. Thus, even in the case where the voltage supplied to the torque sensor has dropped to the extent of hampering suitable operation of the torque sensor, there is no possibility of an abnormality in the torque sensor being detected erroneously. Also, unnecessary detection of an abnormality in the torque sensor is abolished, whereby it becomes possible to suitably detect the occurrence of an abnormality in the torque sensor. Further, a vehicular power steering device in accordance with still another exemplary embodiment of the invention has an abnormality judger which detects an abnormality in a detection signal from the torque sensor and which judges that the torque sensor is abnormal if detection of the abnormality in the detection signal continues for a predetermined period or more, and a steering torque holder which holds a steering torque represented by a detection signal during normal operation of the torque sensor at least until judgment of an abnormality made by the abnormality judger if an abnormality in a detection signal from the torque sensor has been detected, and which controls the motor controller so as to control rotation of the electric motor in accordance with the held steering torque instead of the steering torque represented by the detection signal.
In the aforementioned exemplary embodiment of the invention, the abnormality judger detects an abnormality in a detection signal from the torque sensor and judges that the torque sensor is abnormal if detection of the abnormality continues for a predetermined period or more. Hence, if the abnormality in the torque sensor has been caused due to noise or emergency, the abnormality judger does not conclude the occurrence of an abnormality in the torque sensor. Further, while the abnormality judger judges the occurrence of an abnormality for a predetermined period, the detected steering torque during normal operation of the torque sensor is utilized to control the electric motor due to operation of the steering torque holder. Thus, control of the electric motor can be performed in parallel with judgment of the occurrence of an abnormality in the torque sensor. Therefore, control of the electric motor is not unnecessarily hampered, and the occurrence of an abnormality in the torque sensor is judged suitably.
Further, a vehicular power steering device in accordance with still another exemplary embodiment of the invention has a power circuit which is supplied with a voltage from a battery and which supplies a constant voltage to a torque sensor to activate the torque sensor, an abnormality judger which detects an abnormality in a detection signal from the torque sensor and which judges that the torque sensor is abnormal if detection of the abnormality in the detection signal continues for a predetermined period or more, and a steering torque holder which holds a steering torque represented by a detection signal during normal operation of the torque sensor at least until judgment of an abnormality made by the abnormality judger if an abnormality in a detection signal from the torque sensor has been detected and which controls the motor controller so as to control rotation of the electric motor in accordance with the held steering torque instead of the steering torque represented by the detection signal.
In the aforementioned exemplary embodiment of the invention, the abnormality judger detects an abnormality in a voltage supplied from the power circuit to the torque sensor, and judges that the power circuit is abnormal if detection of the abnormality continues for a predetermined period or more. Hence, if the abnormality in the power circuit has been caused due to noise or emergency, the abnormality judger does not conclude the occurrence of an abnormality in the power circuit. Further, while the abnormality judger judges the occurrence of an abnormality for a predetermined period, the detected steering torque during normal operation of the torque sensor is utilized to control the electric motor due to operation of the steering torque holder. Thus, control of the electric motor can be performed in parallel with judgment of the occurrence of an abnormality in the torque sensor. Therefore, control of the electric motor is not unnecessarily hampered, and the occurrence of an abnormality in the power circuit is judged suitably.
The aspects of the invention is not limited to a vehicular electric power steering device as described above. A further aspect of the invention is, for example, and a method for controlling the vehicular electric power steering device.