Rotation detector
View Patent ↗A rod-shaped magnet is mounted on a rotating unit. The rod-shaped magnet has end surfaces which are oriented in a rotating direction and are magnetized to different magnetic poles. An angle detecting unit including magnetoresistive elements is disposed so as to be offset in a radial direction of a revolution path of the magnet from the revolution path and is configured to detect a change in angle of rotation of the rotating unit by detecting a leakage magnetic field in the vicinity of a side surface of the magnet. Two position detecting units each include magnetoresistive elements and are configured to detect a change in orientation of a magnetic field in the direction of a tangent to the revolution path when facing the rod-shaped magnet and produce a switch output.
1. A rotation detector comprising:
a rotating unit;
a magnet disposed on the rotating unit;
an angle detecting unit configured to detect a change in angle of rotation of the rotating unit by detecting a leakage magnetic field from the magnet; and
at least one position detecting unit configured to operate when the magnet reaches a predetermined position,
wherein the magnet has two end surfaces that are away from a rotation axis of the rotating unit and are oriented in a rotating direction and are magnetized to different magnetic poles, and has a flat surface parallel to a rotation plane including a rotation path of the rotating unit,
wherein the angle detecting unit is disposed away from a revolution path of the magnet in a radial direction of the revolution path, the angle detecting unit includes a magnetoresistive element including a free magnetic layer, a direction in which magnetization of the free magnetic layer changes is set so as to be parallel to the rotation plane, and the magnetoresistive element is operable to detect a change in angle of rotation of the rotating unit, and
wherein the at least one position detecting unit is disposed away from the flat surface of the magnet in a direction parallel to the rotation axis of the rotating unit and includes a magnetoresistive element and a switch circuit, the magnetoresistive element has a resistance that depends on a change in intensity of a magnetic field component parallel to a direction of a tangent to the revolution path, the magnetic field component is included in a leakage magnetic field in the vicinity of the flat surface of the magnet, and the switch circuit is configured to produce a switch output based on a change in the resistance.
2. The rotation detector according to claim 1 ,
wherein the at least one position detecting unit comprises a plurality of position detecting units, and
wherein the magnetoresistive elements included in the position detecting units are arranged so as to be offset in the radial direction from a center line that divides a width of the magnet into two halves in the radial direction.
3. The rotation detector according to claim 1 , wherein the magnet is a rod-shaped rectangular magnet that has side surfaces along long sides and end surfaces along short sides and has a uniform thickness, the end surfaces are magnetized to different magnetic poles, and a longitudinal direction of the magnet is oriented in the direction of the tangent to the revolution path.
4. The rotation detector according to claim 1 , wherein the at least one position detecting unit comprises two position detecting units and the position detecting units simultaneously produce switch outputs when the rotating unit rotates by a predetermined angle.
5. The rotation detector according to claim 4 , wherein the angle detecting unit detects an amount of pressing a brake pedal of a motor vehicle, one of the switch outputs of the two position detecting units is used to perform control for turning on a brake light, and the other one of the switch outputs is used to perform control for releasing cruise control.