Variable reluctance resolver
View Patent ↗A variable reluctance resolver has a rotor which includes a noncircular core and which is rotatably supported inside a stator with a gap therebetween. The shape of the rotor is such that the gap permeance, which is based on the gap, varies according to a sine function of the rotational angle. Each of the salient poles of the rotor has an outer periphery comprising an arc of radius r centered on a point which is offset from the center of the rotor by a prescribed offset distance. The outer periphery of each salient pole does not extend to the inner periphery of the stator.
1. A variable reluctance resolver wherein angular position is determined by detection of permeance between a rotor pole and a stator pole, the resolver comprising:
a rotor and a stator wherein the rotor includes a noncircular core of magnetic material which is rotatably supported inside the stator with a magnetic gap therebetween,
said noncircular core including a central circular portion having a circular inner periphery, and a plurality of salient poles protruding from the central circular portion,
wherein each salient pole of the rotor has a center which is offset by a prescribed offset distance in the radial direction from the center of the rotor, and the outer peripheral shape of each salient pole comprises an arc of a circle of radius r which is centered on the center of the salient pole and which does not extend to the inner peripheral surface of the stator,
wherein a shape of said rotor is such that a permeance of the magnetic gap varies according to a sine function for the rotational angle and said offset distance.
2. A variable reluctance resolver as claimed in claim 1 wherein the shape of the rotor is defined in accordance with the rotational angle, which is expressed by the mechanical angle φ or the electrical angle θ corrected by the shaft angle multiplier, and the offset distance A such that the outer radius Rr of the rotor has a value given by the following equation:
Rr=A cos φ+√{square root over ( r 2 −A 2 sin 2 φ)}= A cos(θ/ N )+√{square root over ( r 2 −A 2 sin 2 (θ/ N ))}
wherein r is the radius of each salient pole, A is the offset distance, φ is the mechanical angle (φ=electrical angle θ/shaft angle multiplier N), θ is the electrical angle, and N is the shaft angle multiplier.
3. A variable reluctance resolver as claimed in claim 2 wherein the rotor includes at least four abutting salient poles protruding from and evenly spaced around the periphery of the central circular portion.
4. A variable reluctance resolver as claimed in claim 1 wherein the shape of the rotor is defined in accordance with the rotational angle, which is expressed by the mechanical angle φ or the electrical angle θ corrected by the shaft angle multiplier, such that the gap δ between the stator and the rotor has a value given by the following equation:
δ =R s −A cos φ+√{square root over ( r 2 −A 2 sin 2 φ)}= R s −A cos(θ/ N )+√{square root over ( r 2 −A 2 sin 2 (θ/ N ))}
wherein δ is the gap, R s is the inner radius of the stator, A is the offset distance, φ is the mechanical angle (φ=electrical angle θ/shaft angle multiplier N), θ is the electrical angle, N is the shaft angle multiplier, and r is the radius of each salient pole.
5. A variable reluctance resolver as claimed in claim 3 wherein the rotor includes at least four abutting salient poles protruding from and evenly spaced around the periphery of the central circular portion.