1. A variable valve operating device for mechanically changing the operating characteristic of a valve relative to the rotation of a camshaft, the variable valve operating device comprising:
a drive cam installed over the camshaft;
a control shaft that is positioned in parallel with the camshaft and capable of changing a rotation position continuously or stepwise;
control means for controlling the control shaft so that it is fixed at a rotation position corresponding to a desired valve lift amount;
a swing member that is installed over the control shaft and allowed to swing around the control shaft;
a swing cam surface that is formed on the swing member, comes into contact with a valve support member, which supports the valve, and presses the valve in a lifting direction;
a slide surface that is formed on the swing member so as to face the drive cam;
an intermediate roller that is positioned between the drive cam and the swing member and comes into contact with both the slide surface and a cam surface of the drive cam;
a control member that is fastened to the control shaft and has a swing fulcrum at a position eccentric to the center of the control shaft; and
a coupling member that supports the intermediate roller in such a manner as to permit free rotation and couples the intermediate roller to the swing fulcrum in such a manner as to permit free swinging;
wherein, the swing fulcrum is positioned closer to a position opposite to the intermediate roller with respect to the control shaft when the control shaft is fixed at a rotation position giving a large lift to the valve than when the control shaft is fixed at a rotation position giving a small lift to the valve.
2. The variable valve operating device according to claim 1, wherein, when the control shaft is positioned at a predetermined rotation position, the swing fulcrum, the control shaft, and the intermediate roller are substantially aligned.
3. The variable valve operating device according to claim 2, wherein the predetermined rotation position is a rotation position for giving the maximum lift to the valve.
4. The variable valve operating device according to claim 2, wherein the predetermined rotation position is a rotation position used for a longest duration of time.
5. A variable valve operating device for mechanically changing the operating characteristic of a valve relative to the rotation of a camshaft, the variable valve operating device comprising:
a drive cam installed over the camshaft;
a control shaft that is positioned in parallel with the camshaft and capable of changing a rotation position continuously or stepwise;
a swing member that is installed over the control shaft and allowed to swing around the control shaft;
a swing cam surface that is formed on the swing member, comes into contact with a valve support member, which supports the valve, and presses the valve in a lifting direction;
a slide surface that is formed on the swing member so as to face the drive cam;
an intermediate roller that is positioned between the drive cam and the swing member and comes into contact with both the slide surface and a cam surface of the drive cam;
a control member that is fastened to the control shaft and has a swing fulcrum at a position eccentric to the center of the control shaft; and
a coupling member that supports the intermediate roller in such a manner as to permit free rotation and couples the intermediate roller to the swing fulcrum in such a manner as to permit free swinging;
wherein, when the control shaft is positioned at a rotation position used for a longest duration of time, the swing fulcrum is positioned opposite to the intermediate roller with respect to the control shaft.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An electric motor comprising a stator and a rotor rotatably mounted confronting the stator, wherein the stator comprises:
a housing having a polygonal cross section comprising a plurality of side portions and a plurality of curved corner portions, each corner portion connecting two adjacent side portions;
a permanent magnet fixed to an inner surface of the housing; and
an air gap formed between the rotor and the permanent magnet,
wherein the permanent magnet is a ring magnet and the thickness of the ring magnet at portions corresponding to said corner portions of the housing is larger than the thickness of the ring magnet at portions corresponding to said side portions of the housing.
2. The electric motor of claim 1, wherein each of said corner portions curve around a center which is offset from the rotational center of the rotor.
3. The electric motor of claim 1, wherein the thickness of said air gap at portions corresponding to said corner portions of the housing is larger than the thickness of said air gap at portions corresponding to said side portions of the housing.
4. The electric motor of claim 3, wherein the thickness of said air gap is largest at portions corresponding to the thickest portions of the ring magnet, and is smallest at portions corresponding to the thinnest portions of the ring magnet.
5. The electric motor of claim 1, wherein gaps are formed between the ring magnet and said corner portions of the housing.
6. The electric motor of claim 1, wherein gaps are formed between the ring magnet and said side portions of the housing.
7. The electric motor of claim 1, wherein the radius of curvature of the inner surface of said corner portions is larger than the radius of curvature of the outer surface of the ring magnet at portions corresponding to said corner portions.
8. The electric motor of claim 1, wherein the ratio of the radius of curvature of the inner surface of said corner portions to the radius of curature of the inner surface of the ring magnet is between 1.1 and 1.8.
9. The electric motor of claim 1, wherein the housing has an even thickness.
10. The electric motor of claim 1, wherein the thickness of the housing at said corner portions is larger than the thickness of the housing at said side portions.
11. The electric motor of claim 1, wherein the housing has a tetragonal cross section.