Solenoid

A solenoid, comprising:

• a coil portion having a coil that generates a magnetic field when energized;
• a yoke including a side surface portion along an axial direction and a bottom portion formed along a direction intersecting the axial direction, and being configured to accommodate the coil portion;
• a cylindrical core portion that is disposed inside the coil portion in a radial direction perpendicular to the axial direction;
• a columnar plunger that slides inside the core portion in the radial direction in the axial direction;
• a magnetic attraction core arranged in the axial direction to face a distal end portion of the plunger and configured to attract magnetically the plunger by a magnetic force generated by the coil;
• a first magnetic flux transfer portion configured to transfer a magnetic flux between the yoke and the core portion on a radial outside of a core end portion, which is an axial end of the core portion and faces the bottom portion;
• a second magnetic flux transfer portion configured to transfer the magnetic flux between the magnetic attraction core and the side surface portion on a radial outside of the magnetic flux that is disposed radially outside a magnetic attraction core end, which is an end in the axial direction of the magnetic attraction core and is opposite to a side facing the distal end portion;
• and
• a magnetic flux passage suppressing portion configured to suppress a passage of magnetic flux between the core portion and the magnetic attraction core;
• wherein
• a gap in the radial direction that communicates a radial outside of the first magnetic flux transfer portion with an outside of the solenoid is formed between an inner surface of the side surface portion and an outer surface of the coil portion, and
• a protrusion is formed on at least one of the inner surface and the outer surface and protrudes in the radial direction to reduce a size of at least a part of the gap.