Patent ID: 8829896

Claim:
A stroke amount detecting device for detecting a stroke of a detection object which moves rectilinearly, the device comprising: a magnetism detecting unit that includes a magnetism sensing surface and is displaced on a rectilinear axis in accordance with the rectilinear movement of the detection object; and a first magnetic field generating unit and a second magnetic field generating unit that are disposed on one side of the rectilinear axis, wherein: the magnetism detecting unit is displaced relative to the first magnetic field generating unit and the second magnetic field generating unit; the first magnetic field generating unit and the second magnetic field generating unit are arranged to be spaced away from each other and opposed to each other in a direction of the stroke; a magnetic pole of the first magnetic field generating unit and a magnetic pole of the second magnetic field generating unit, which are opposed to each other, are magnetized so as to have different polarities; the first magnetic field generating unit and the second magnetic field generating unit are arranged such that a distance between a gap end of the first magnetic field generating unit and a gap end of the second magnetic field generating unit, which are located on a farther side of the rectilinear axis and are magnetized so as to have different polarities, is smaller than a distance between an open end of the first magnetic field generating unit and an open end of the second magnetic field generating unit, which are located on a closer side of the rectilinear axis; and the magnetism detecting unit is configured to detect an amount of the stroke of the detection object based on a magnetic flux generated between the open end of the first magnetic field generating unit and the open end of the second magnetic field generating unit.