Rotation angle detector for detecting a rotational position of a steering wheel of a vehicle

A rotation angle detector comprises:

• (1) a disc having a plurality of through holes arranged with a predetermined pitch along a perimeteric direction thereof, and a cutout portion provided in a predetermined position along the perimeteric direction;
• (2) a first and a second sensor elements, each comprising a light-emitting element and a light-receiving element, and disposed within a predetermined angle in a manner to correspond with said through holes in said disc;
• (3) a third sensor element comprising a light-emitting element and a light-receiving element, and disposed in a manner to correspond with said cutout portion in said disc;
• and
• (4) a control means comprising a signal processing unit for generating an output of detection signal corresponding to an angle and a direction of rotation of said disc using signals provided by said first, second and third sensor elements, and a memory unit for storing, as a positional information, the output provided by said signal processing unit when a main switch is turned on, and wherein said control means includes:
• (a) a first means for introducing a dark current mode for maintaining said sensor elements operative with a lower supply current than a current consumed under a normal operating condition, even when said main switch is in an OFF position;
• (b) a second means for introducing a memory backup mode for maintaining a storing condition of the positional information supplied from said signal processing unit by providing a current supply to said memory unit, even when said main switch is in the OFF position;
• (c) a third means for canceling the memory backup mode and the dark current mode so as to turn said sensor elements and said control means into normal operating conditions thereof, when said sensor elements operated under the dark current mode of said first means detect a motion of said disc;
• and
• (d) a fourth means for activating said first and second means into operation so as to resume the memory backup mode and the dark current mode, when said sensor elements no longer detect motion of said disc while in a condition after said third means has canceled the memory backup mode and the dark current mode.