Patent ID: 7688169
Filing Date: 2010-03-30
Classification: H01F,H02K

Abstract:
1. A long-proportional-stroke force motor comprising: a magnetic circuit formed of: a guide made of a magnetic material, a sleeve made of a magnetic material, and a spacer made of a non-magnetic material and disposed between the guide and the sleeve, the guide, the spacer and the sleeve forming an inner cylindrical surface defining an inner cylindrical opening; and an armature made of a magnetic material and disposed movably in the inner cylindrical opening; wherein the guide has an end portion adjacent to the spacer, and the end portion of the guide has a sectional profile including, at a side opposite the armature, points located on a curve, which curve satisfies both of the following expressions: where X is a coordinate on an axis of the guide; where a positive direction on the X-axis is a direction in which the armature is attracted through the application of exciting current; and where Y is a coordinate on the guide along a direction orthogonal to the X-axis; wherein the sectional profile of the guide has a shape including a plurality of stepped portions formed such that the points on the curve of the sectional profile are located on respective concave corners of the stepped portions; wherein the armature has an armature end portion with a conical surface facing the inner cylindrical surface, the conical surface defining, in cooperation with the inner cylindrical surfaces, a radial gap between the inner cylindrical surface and the armature, which gap increases toward the guide; and wherein the armature end portion has a recess including three or more stepped portions.