Magnetic sensor, method for designing the same, and assembly thereof

A method for designing a magnetic sensor, the magnetic sensor comprising:

• first to fourth magnets that are rotatable around a central axis of rotation and that have a fixed positional relationship with each other;
• and
• a magnetic field detecting element that passes through the central axis of rotation, wherein:
• in an XY coordinate system that is perpendicular to the central axis of rotation and that passes through the origin, the first to fourth magnets are located in first to fourth quadrants, respectively, the first to fourth magnets include first to fourth element-facing surfaces, respectively, that face the magnetic field detecting element, the first to fourth element-facing surfaces have elongated shapes having first to fourth long axes, respectively, the first element-facing surface and the second element-facing surface have the same polarity, and the third element-facing surface and the fourth element-facing surface have a polarity different from that of the first and second element-facing surfaces, the method comprising:
• defining straight lines that are parallel to the first to fourth long axes, that have the origin as their ends, and that pass through the first to fourth quadrants as first to fourth imaginary lines,
• defining the angles that the first to fourth imaginary lines make counterclockwise with respect to the boundary line between the first and fourth quadrants as θ1 to θ4,
• determining a relationship between angle measurement error that is a difference between a calculated rotation angle of a rotating body to which the first to fourth magnets are fixed and an actual rotation angle of the rotating body and, θ1 to θ4 at a plurality of positions of the magnetic field detecting element in a direction parallel to the central axis of rotation;
• and
• determining θ1 to θ4 based on the position of the magnetic field detecting element in the direction parallel to the central axis of rotation so that the angle measurement error becomes zero.

A magnetic sensor, comprising:

• first to fourth magnets that are rotatable around a central axis of rotation and that have a fixed positional relationship with each other;
• and
• a magnetic field detecting element, wherein:
• in an XY coordinate system that is perpendicular to the central axis of rotation and that passes through the origin, the first to fourth magnets are located in first to fourth quadrants, respectively, the first to fourth magnets include first to fourth element-facing surfaces, respectively, that face the magnetic field detection element, the first to fourth element-facing surfaces have elongated shapes having first to fourth long axes, respectively, the first element-facing surface and the second element-facing surface have the same polarity, and the third element-facing surface and the fourth element-facing surface have a polarity different from that of the first and second element-facing surfaces;
• when straight lines that are parallel to the first to fourth long axes, that have the origin as their ends, and that pass through the first to fourth quadrants are defined as first to fourth imaginary lines and the angles that the first to fourth imaginary lines make counterclockwise with respect to the boundary line between the first and fourth quadrants are θ1 to θ4, θ1 is greater than or equal to 0 degrees and less than or equal to 90 degrees, θ2 is greater than or equal to 90 degrees and less than or equal to 180 degrees, θ3 is greater than or equal to 180 degrees and less than or equal to 270 degrees, and θ4 is greater than or equal to 270 degrees and less than or equal to 360 degrees;
• and
• the first to fourth element-facing surfaces are rectangular having long sides and short sides, and a ratio of the length of the long sides to the length of the short sides is 1.2 or more and 2.5 or less.