Relative-rotational-position detection apparatus

A relative-rotational-position detection apparatus for detecting a relative rotational position between a first shaft and a second shaft rotatable relative to each other, which comprises:

• an outer cylindrical section rotatable with said first shaft, said outer cylindrical section being formed of a magnetic-shielding substance or antimagnetic substance and having patterns of open windows of first to fourth channels;
• an inner cylindrical section inserted in said outer cylindrical section and rotatable with said second shaft, said inner cylindrical section being formed of a magnetic substance and having patterns of nonmagnetic windows of said first to fourth channels;
• and
• first to fourth coils provided in corresponding relation to said first to fourth channels and excitable by a predetermined A.C. signal, and
• wherein, for each of said channels, the pattern of the open window in said outer cylindrical section and the pattern of the nonmagnetic window in said inner cylindrical section are arranged to overlap with each other,
• an arrangement of the open windows and nonmagnetic windows in said channels is set such that:
• degree of overlap between the pattern of the open window and the pattern of the nonmagnetic window in each of said channels varies in accordance with a variation in a relative rotational position, within a predetermined range, between said first shaft and said second shaft;
• a variation in the degree of overlap in said second channel presents a differential characteristic relative to a variation in the degree of overlap in said first channel;
• a variation in the degree of overlap in said fourth channel presents a differential characteristic relative to a variation in the degree of overlap in said third channel;
• and variations in said third and fourth channels present a predetermined difference from variations in said first and second channels, and
• said first to fourth coils corresponding to said first to fourth channels present impedance corresponding to the degree of overlap between the open windows and the nonmagnetic windows of the corresponding channels.