Patent ID: 8143984
Filing Date: 2012-03-27
Classification: F16K,H01F

Abstract:
1. A linear solenoid comprising: a cylindrical solenoid housing made of magnetic material; a cylindrical electromagnetic coil supported in the solenoid housing for generating magnetic force when electric power is supplied thereto; a plunger made of magnetic material and movably inserted into an inside of the coil so that the plunger is movable in its axial direction, the plunger being biased by a biasing means in a backward direction thereof; a first magnetic pulling portion made of magnetic material and formed at a forward end of the solenoid housing for magnetically pulling a forward end of the plunger in a forward direction when the magnetic force is generated at the coil; and a magnetic path portion formed at a rear end of the solenoid housing and surrounding an outer periphery of a rear end portion of the plunger so that magnetic flux passes in a radial direction of the plunger from the rear end portion to the magnetic path portion, wherein a plunger side-gap portion is formed at the rear end portion of the plunger so that the magnetic flux passes in the radial direction of the plunger from the plunger side-gap portion to the magnetic path portion, and a second magnetic pulling portion is formed at the magnetic path portion for magnetically pulling the plunger side-gap portion in the forward direction when the magnetic force is generated at the coil, wherein the magnetic path portion comprises: a constant overlapping area which overlaps with the plunger side-gap portion in the radial direction, when the plunger is in its rear-most position; and a temporal overlapping area which overlaps with the plunger side-gap portion in the radial direction, when the plunger is moved in the forward direction, wherein the temporal overlapping area is increased as the plunger is further moved in the forward direction, wherein a first radial gap is formed in the radial direction between the magnetic path portion of the constant overlapping area and the plunger side-gap portion, wherein a second radial gap is formed in the radial direction between the magnetic path portion of the temporal overlapping area and the plunger side-gap portion, and wherein the first radial gap is made larger than the second radial gap.