Resolver, motor and power steering apparatus
A resolver of a variable reluctance type includes a resolver stator portion of a substantially annular shape centered about a central axis, and a resolver rotor portion which is attached to a shaft of a motor rotor portion arranged inwardly of the resolver stator portion. The resolver is operable to increase accuracy for detecting a rotational angle when a size of gap g between a rotor core and a resolver stator portion at a predetermined point at an outer circumferential edge of the rotor core is set by using a maximum value for the gap g (g max ), a minimum value for the gap g (g min ), angle θ defined by a predetermined point and a reference point, axial double angle n, and the coefficient.
1. A variable reluctance resolver, comprising:
a resolver stator portion having a substantially annular shape centered about a central axis and including an excitation coil and an output coil; and
a rotor portion having a rotor core arranged concentrically with respect to the central axis, rotatably supported with respect to the resolver stator portion, and arranged radially inward of the resolver stator portion via a gap g therebetween, wherein
a size of the gap g is calculated by a following equation:
g
=
1
1
2
(
1
g
min
+
1
g
max
)
+
1
2
(
1
g
min
-
1
g
max
)
·
cos
(
n
θ
)
+
K
(
1
-
cos
(
2
n
θ
)
in which g max is a minimum value for the gap g, g min is a maximum value for the gap g, angle θ is defined between a point of reference and a predetermined point set at an outer circumferential end of the core, n is an axial double angle which is a positive integer, and K is a coefficient.
2. The resolver according to claim 1 , wherein the coefficient K is greater than about −0.024 and smaller than 0.000.
3. The resolver according to claim 1 , wherein the resolver stator portion includes a stator core having a laminated member including a plurality of thin magnetic steel plates, and the rotor core includes a laminated member having a plurality of thin magnetic steel plates.
4. The resolver according to claim 3 , wherein the stator core and the rotor core are defined by the same thin magnetic steel plates.
5. The resolver according to claim 1 , wherein the resolver stator portion includes an excitation coil and a plurality of output coils.
6. The resolver according to claim 1 , wherein the resolver stator portion includes 16 magnetic poles, and an axial double angle is 4.
7. The resolver according to claim 1 , wherein an outer circumferential surface of the rotor portion is solely comprised of a curved surface.
8. An electrically powered motor comprising:
the resolver according to claim 1 ;
a motor stator portion having an armature;
a motor rotor portion having a field magnet generating between the armature a torque centered about the central axis, and having attached thereon a portion of a rotor portion of the resolver; and
a bearing mechanism rotatably supporting the motor rotor portion centered about the central axis with respect to the motor stator portion.
9. An electrically powered power steering apparatus used for assisting in steering a steering wheel, the power steering apparatus comprising:
the motor according to claim 8 ;
a torque sensor detecting a rotary force applied to the steering wheel; and
a control unit controlling the steering apparatus based on an output from the torque sensor the motor.