Indicating instrument for a vehicle

An indicating instrument for a vehicle comprising:

• a dial plate having a display portion displaying an analog value between a maximum value and a minimum value in an arc shape;
• a pointer disposed to move over said display portion between a zero position corresponding to said minimum value and a maximum position corresponding to said maximum value;
• a step motor including a stator and a magnet rotor;
• a stopper unit for stopping said pointer when said pointer reaches said zero position;
• drive means for supplying said stator of said step motor with a drive alternating signal to move said pointer in response to said analog value;
• zero-return means for supplying said stator with a zero-return alternating signal to move said pointer toward said zero-position;
• storing means for storing a phase angle of said zero-return signal as a zero-return angle correction value if an induced voltage, which is induced in said stator when said zero-return alternating signal is interrupted after said zero-return alternating signal becomes a zero level at least twice, becomes lower than a threshold value that indicates that said pointer is stopped;
• adjusting means for adjusting said zero-return alternating signal to zero phase by said zero-return angle correction value when said zero-return alternating signal is supplied to said stator;
• synchronizing means for synchronizing said zero-return alternating signal and rotation of said magnet rotor when said zero-return alternating signal is supplied to said stator after said phase of said zero-return alternating signal is adjusted;
• first examining means for examining whether phase angle of said zero-return alternating signal reaches a zero-level electric angle that corresponds to a zero level of said zero-return alternating signal at least twice or not after said alternating signal is supplied to said stator;
• and
• second examining means for examining whether said induced voltage is equal to or lower than a threshold voltage that indicates that said pointer is stopped;
• wherein
• said drive means supplies said drive alternating signal at the phase thereof immediately when said second examining means judges that said induced voltage is equal to or lower than said threshold voltage.

A system for setting zero-return correction angle of a step motor including a stator, a magnet rotor for rotating in response to an alternating signal supplied to said stator and a stopper unit for stopping said magnet rotor when said magnet rotor reaches a zero position, said system comprising:

• adjusting means (110) for adjusting said alternating signal to zero phase when said alternating signal is supplied to said stator;
• first examining means for examining whether phase angle of said alternating signal reaches a zero-level electric angle that corresponds to a zero level of said alternating signal at least twice or not after said alternating signal is supplied to said stator;
• second examining means for examining whether said induced voltage is equal to or lower than a threshold voltage that indicates that said magnet rotor is stopped;
• and
• setting means for setting said zero-level electric angle at which said induced voltage is equal to or lower than said threshold voltage as a zero-return-angle correction-value.

A system for setting zero-return correction angle of a pointer of an indicating instrument for a vehicle including a step motor having a stator and a magnet rotor for moving said pointer when an alternating signal is supplied to said stator, and a stopper unit for stopping said pointer when said pointer reaches said zero position and a drive unit for driving said step motor, wherein said system comprises:

• first means for adjusting said alternating signal to zero phase when said alternating signal is supplied to said stator;
• second means for examining whether phase angle of said alternating signal reaches a zero-level electric angle that corresponds to a zero level of said alternating signal at least twice or not after said alternating signal is supplied to said stator;
• third means for cutting supply of said alternating signal to said stator to provide an induced voltage in said stator induced by said magnet rotor when said second means judges that the phase angle of said alternating signal reaches said zero-level electric angle;
• fourth means for examining whether said induced voltage is equal to or lower than a threshold voltage that indicates that said pointer is stopped by said stopper unit;
• and
• fifth means for setting said zero-level electric angle at which said induced voltage is equal to or lower than said threshold voltage as a zero-return-angle correction-value.