Patent Application
20080060901
Embodiments of the present invention will be described in detail hereinunder with reference to the accompanying drawings. There are three types of thin electromagnetic clutches according to the present invention.
The electromagnetic coil 2 is accommodated within a coil bobbin (not shown) of a U-shaped section, has a square or rectangular longitudinal section and is formed in an annular shape when seen in the rotational axis direction. The electromagnetic coil 2 is fixed to the stator yoke 3 by caulking performed at several positions of an open end outside 3i of the cylindrical portion of the stator yoke 3.
The stator yoke 3 is formed of a magnetic metal material and a radial section thereof cut from the axis (coincident with the rotational axis 12 of the shaft 6) of the cylindrical portion of the stator yoke is formed in L shape so as to accommodate the electromagnetic coil 2, as shown in
As shown in
A draw-out hole 3f for a lead wire of the electromagnetic coil 2 is formed in the annular base plate portion 3b. Further, several tapped holes 3d for fixing the entire clutch to an object device to which the clutch is to be mounted, as well as a positioning cylindrical surface 3h, are formed in the annular base plate portion 3b. The stator yoke 3 with L-shaped section is free of any complicated morphological portion and is easy to manufacture.
The rotor 5 is formed of a magnetic metal material and is made up of a truncated inverse circular cone portion 5b having a central circular through hole 5a for the shaft, an annular plate portion 5c disposed annularly around the truncated inverse circular cone portion 5b as a central portion, and an outer cylindrical portion 5d contiguous perpendicularly to the outer periphery of the annular plate portion 5c. A projecting retaining portion 5f for retaining a driving force transfer part such as the worm wheel 10 is formed on an outer periphery surface of the outer cylindrical portion 5d. The truncated inverse circular cone portion 5b is sideways formed with a slant surface 5bc, the slant surface 5bc being formed in opposition to the slant surface 3ac as the inner surface of the cylindrical portion 3a so that the diameter thereof decreases rectilinearly in the same direction as the converging direction of the slant surface 3ac whose diameter decreases rectilinearly from the armature 8 side toward the small-diameter bearing mounting portion 3c.
It can be said that the truncated inverse circular cone portion of the rotor and the cylindrical portion with the slant inner surface of the stator yoke correspond respectively to bisected portions obtained by making an oblique cut, as shown in the figure, in a thick-walled pipe as viewed from a longitudinal section thereof. The surfaces formed by the cut-in portion cause the outer cylindrical portion 5d and the annular base plate portion 3b to be disposed so that the inner periphery surface of the open end of the outer cylindrical portion 5d and the outer periphery surface of the annular base plate portion 3b confront each other. Since the outside diameter of the annular base plate portion 3b is several times larger than the average diameter of the conical surface of the cylindrical portion, the opposed areas become larger and the magnetic flux density does not become high. The thickness of the truncated inverse circular cone portion 5b is made large in comparison with the thickness (as seen in the radial direction) of the outer cylindrical portion 5d of the rotor 5. Like the truncated inverse circular cone portion 5b, the thickness of the cylindrical portion 3a with the slant inner surface of the stator yoke 3 which is combined with the truncated inverse circular cone portion 5b to form a magnetic path is also large. Consequently, in connection with a section cut along a plane perpendicular to the rotational axis 12, by setting the radial lengths of the portions concerned in such a manner that the sum of the cross-section areas of the truncated inverse circular cone portion 5b and the cylindrical portion 3a with the slant inner surface equals the cross-section area of the outer cylindrical portion 5d, it is possible to diminish the difference in magnetic flux density, diminish the extension of magnetic flux to unnecessary portions and make the magnetic flux act effectively. An example thereof will now be explained with reference to
In
S3a+S5b=S5d
For example, if the thickness of 5d is given and the thickness of the combined portion of 5b and 3a is to be determined, the inside diameter concerned is determined from the size of the shaft and that of the bearing, assuming that the gap between 5b and 3a is small, the outside diameter can be determined from the inside diameter and the thickness of 5d using the above equation, because the cross-section areas which satisfy the above equation are determined by these dimensions, then 5b and 3a are brought into oblique opposition to each other within the thickness.
The open side of rotor 5 is disposed opposite to the armature so as to accommodate the cylindrical portion 3a with the slant inner surface of the stator yoke 3 and also accommodate the electromagnetic coil 2 adjacent to the cylindrical portion 3a. Magnetic shielding portions 5g are formed by blanking in the annular plate portion 5c of the rotor 5 at positions corresponding to both inner and outer periphery sides of magnetic shielding portions 8a of the armature 8.
The small-diameter bearing 11 retained by the shaft 6 is disposed in abutment against a lower end of the truncated inverse circular cone portion 5b. The outer periphery surface of the outer cylindrical portion 5d is formed as a flat surface free of any concave and convex. The worm wheel 10 having for example a flat inner periphery surface and an outer periphery surface formed with worm teeth is fitted on the outer periphery surface of the outer cylindrical portion 5d. An inserting/positioning groove 10a corresponding to the retaining portion 5f is formed in the inner periphery surface of the worm wheel 10. When press-fitting the worm wheel 10 onto the outer periphery surface of the rotor 5, the fitting operation is performed while inserting the retaining portion 5f into the insertion/positioning groove 10a to prevent the worm wheel from dislodging. Driving force provided from a motor (not shown) is transmitted to the rotor 5 through the worm wheel 10 and the shaft 6 rotates together with the rotor 5.
The armature 8 is formed of a magnetic material such as iron, and is disposed in opposition to the frictional surface of the rotor 5, between which a distance is spaced. Formed in the shape like a ring, the armature 8 is made of a flat plate, and has a magnetic shielding slit at an intermediate position thereof formed by blanking. Its frictional surface for contact with the rotor 5 is treated with nitriding to improve the wearability. With several arms of a pulley (not shown) disposed at an upper position and adapted to be loosely fitted in the slit, the armature 8 is kept incapable of performing a relative angular displacement and capable of performing an axial relative displacement with respect to the pulley. Upon energization of the electromagnetic coil 2, the armature 8 is attracted to the rotor 5 and the driving force acting at this instant is transferred to the armature 8. Separating from the rotor 5 and reverting to the original position of the armature 8 are performed by the action of a spring connected to the pulley. Mounted on the shaft 6, the pulley can perform a relative angular displacement and cannot perform an axial relative displacement with respect to the shaft 6.
The shaft 6 is supported through the large-diameter bearing 9 by a housing indicated with dotted lines at a position above the armature 8. Since the shaft 6 is supported at both ends of the electromagnetic mechanism, there is little vibration of the shaft.
Since the electromagnetic coil 2 is disposed in contact with both the cylindrical portion 3a with the slant inner surface and the annular base plate portion 3b of the stator yoke 3 having an L-shaped longitudinal section, the magnetic flux generated in the electromagnetic coil 2 can be allowed to pass effectively through the cylindrical portion 3a and the annular base plate portion 3b of the stator yoke 3 positioned closest to the electromagnetic coil 2. In the case of the cylindrical portion 3a with the slant inner surface, magnetic resistance becomes low because the magnetic flux density distribution is uniform. Moreover, since the longitudinal section of the stator yoke 3 is L-shaped, the magnetic flux generated by the electromagnetic coil 2 of a quadrangular section (including square and rectangle) can be effectively utilized.
The truncated inverse circular cone portion 5b of the rotor 5 and the cylindrical portion 3a with the slant inner surface of the stator yoke 3 confront each other through the respective slant surfaces. Facing surface areas of the rotor 5 and that of the stator yoke 3 become larger by an amount corresponding to the aforesaid truncated cone surfaces in comparison with the conventional cylindrical surfaces (by the difference between the length of a vertical line at an angle of 90° from a horizontal plane and that of an edge line running along a truncated cone surface laid down at a predetermined angle) and an axial surface 3g of the open end of the cylindrical portion of the stator yoke 3 becomes smaller. Consequently, most of the magnetic flux transfer between the truncated inverse circular cone portion of the rotor 5 and the cylindrical portion of the stator yoke 3 is performed at the facing surfaces of the two truncated cones and the magnetic flux passing the axial opposed surface 3g of the open end of the cylindrical portion of the stator yoke 3 is diminished. Thus, the axial attractive force decreases and it is possible to make the clutch diameter small and reduce the size of the bearing 11 which bears the axial attractive force of the clutch.
The thickness of the truncated inverse circular cone portion 5b is made larger than the thickness (as seen in the radial direction) of the outer cylindrical portion 5d of the rotor 5. The thickness of the cylindrical portion 3a with the slant inner surface of the stator yoke 3 which is combined with the truncated inverse circular cone portion 5b to form a magnetic path is also made large like the truncated inverse circular cone portion 5b. As a result, in connection with a section cut along a plane perpendicular to the shaft 6, the sum of the cross-section areas of the truncated inverse circular cone portion 5b of the rotor 5 and the cylindrical portion 3a with the slant inner surface of the stator yoke 3 is made equal to the cross-section area of the outer cylindrical portion and hence it is possible to diminish the difference in magnetic flux density, diminish the extension of magnetic flux to unnecessary portions and make the magnetic flux act effectively.
When the electromagnetic coil 2 is not energized, input torque from the outer periphery side of the rotor 5 causes only the rotor 5 and the shaft 6 to rotate. When the electromagnetic coil 2 is energized, the armature 8 is attracted to the rotor 5 and causes the pulley (not shown) disposed in an upper position to rotate together with the rotor 5, providing an output.
(1) By making the opposition surfaces of the inner cylindrical portion of the rotor 5 and the inner cylindrical portion of the stator yoke 3 in the form of circular cone surfaces, in comparison with the conventional cylindrical surfaces, the facing surface area becomes larger and the area of the axial opposed surface 3g of the open end of the cylindrical portion of the stator yoke 3 becomes smaller. As to the influence on magnetic characteristics of the clutch, most of the magnetic flux transfer between the truncated inverse circular cone portion 5b of the rotor 5 and the cylindrical portion 3a with the slant inner surface of the stator yoke 3 is performed at the facing surfaces of the two truncated cone, the magnetic flux passing the axial opposed surface 3g of the open end of the cylindrical portion 3a with the slant inner surface of the stator yoke 3 is diminished and the axial attractive force decreases. As a result, it is possible to make the clutch diameter small, reduce the thickness of the clutch and reduce the size of the bearing which bears the axial attractive force.
(2) By changing the way of assembly between the rotor 5 and the inner cylindrical portion of the stator yoke 3 from the conventional cylindrical body telescopic type into the truncated cone telescopic type, in connection with a section cut along a plane perpendicular to the shaft 6 and in various positions from the open end to the base part, the cross-section area of either of inner cylindrical bodies increases (decreases) continuously in accordance with increase (decrease) of the amount of magnetic flux flowing therein. As to the influence on magnetic characteristics of the clutch, the magnetic flux density distribution in either of inner cylindrical bodies becomes uniform, magnetic resistance becomes lower and the efficiency of the magnetic circuit becomes higher. As a result, it is possible to reduce the clutch size.
(3) The stator yoke 3 having an L-shaped longitudinal section not only acts as part of the magnetic circuit but also plays a part in fixing and positioning the entire clutch, fixing the electromagnetic coil, and supporting the shaft 6 through a bearing. Besides, the stator yoke 3 does not have any complicated morphological portion and is easy to manufacture. The rotor 5 not only acts as part of the magnetic circuit but also plays a part in receiving the input torque. The inner cylindrical portion having an truncated inverse circular cone section of the rotor 5 is of high efficiency and is of high resistant to deformation caused by an imbalance input torque. As a result, the structure of the clutch is simple, the number of parts is small, and the clutch is easy to manufacture and highly reliable.
In the electromagnetic clutch of type 2, indicated with numeral 1A, a rotor 5A is supported on a shaft 6 through two small-diameter bearings 14 and the shaft 6 is supported by a stator yoke 3 through a large-diameter bearing 15. An armature 8 is mounted on the shaft 6 through a hub 7 in such a manner that they are relatively displaceable in axial direction but no relative angular displacement can be performed.
The rotor 5A is made up of a truncated inverse circular cone portion 5Ab having a central circular through hole 5Aa for both the shaft 6 and the small-diameter bearings 14, an annular plate portion 5c disposed annularly around the truncated inverse circular cone portion 5Ab as the central portion, and an outer cylindrical portion 5d contiguous perpendicularly to the outer periphery of the annular plate portion 5c. A projecting retaining portion 5Af for retaining a driving force transfer part such as a worm wheel 10 is formed on an outer periphery surface of the outer cylindrical portion 5d. The two small-diameter bearings 14 are disposed on an inner wall of the central circular through hole 5Aa of the truncated inverse circular cone portion 5Ab and they are locked to the shaft 6.
The rotor 5A and the stator yoke 3 are positioned by the bearings 14 and 15 in such a manner that the surface of the truncated inverse circular cone portion 5Ab and a surface of the cylindrical portion 3a with the slant inner surface are spaced with a predetermined distance from each other. The bearing 15 provided in the stator yoke 3 is large in diameter and therefore, with only the large-diameter bearing 15, it is possible to support the shaft 6 with the rotor 5A mounted thereon. Thus, unlike the clutch of type 1, it is possible to eliminate the need of disposing another bearing at a position spaced from the large-diameter bearing.
For simplifying the shape, the bottom of an annular base plate portion 3b of the stator yoke 3 is made flat. Moreover, for further increasing the opposition area with respect to the outer cylindrical portion 5d of the rotor 5A to further diminish the axial attractive force with the rotor 5A, a projection 3j is formed on top of the outer periphery surface of the annular base plate portion 3b. Thus, the shape of the stator yoke 3 becomes simple, so that it can be formed for example by a single forging except a bearing mounting portion 3c and tapped holes 3d, consequently, to reduce the manufacturing cost is possible.
When the electromagnetic coil 2 is not energized, input torque from the outer periphery side of the rotor 5 causes the rotor 5 alone to rotate. When the electromagnetic coil 2 is energized, the armature 8 is attracted to the rotor 5 and drives the shaft 6 to rotate together with the rotor 5 through the hub 7, providing an output. Separating from the rotor 5 and reverting to the original position of the armature 8 are performed by spring action of the hub.
As to the structure of the annular base plate portion, in the electromagnetic clutch of type 2 wherein the rotor and the shaft are rotatable with respect to each other, there may be adopted such a configuration as that described above in connection with the electromagnetic clutch of type 1 wherein the thickness of the annular base plate portion 3b becomes smaller toward the radial outer end, or conversely, in the electromagnetic clutch of type 1 wherein the rotor and the shaft always rotate in one piece with each other, there may be adopted such a configuration as described above in connection with type 2 wherein the bottom of the annular base plate portion 3b is made flat.
According to the second embodiment there are obtained the following effects in addition to the effects obtained in the first embodiment. Since the two small-diameter bearings 14 are disposed between the rotor 5A and the shaft 6, no bearing is disposed outside the armature 8 like type 1, so that the manufacturing cost of the stator yoke 3 is reduced. In the second embodiment, moreover, since only the rotor 5A can be rotated through the bearing 14 without restraining the shaft 6, the shaft 6 is not rotated at all times like type 1. On the other hand, since three bearings are mounted to a clutch body, the thickness and the diameter of the clutch body somewhat increases as compared with the first embodiment.
The first and second embodiments can be adopted selectively according to a demand in the place where the present invention is applied.
A cylindrical portion 3a with a stepped surface 3as as an inner surface whose diameter decreases (the radial thickness of the cylindrical portion 3a increases) stepwise from an armature 8 side toward a bearing mounting portion 3c.
An truncated inverse circular cone portion 5b is sideways provided with a stepped surface 5bs whose diameter decreases stepwise from the armature 8 side toward the bearing mounting portion 3c, the stepped surface 5bs being provided in opposition to the stepped surface 3as as the inner surface of the cylindrical portion 3a the diameter of which stepped surface 3as decreases stepwise in the same direction as the decreasing direction of the above diameter.
As shown in the first and third embodiments, the “slant inner surface” includes both a slant surface whose diameter decreases rectilinearly and a stepped surface whose diameter decreases stepwise.
A magnetic path formed by the cylindrical portion 3a with the stepped inner surface and the truncated inverse circular cone portion 5b in
Consequently, like the slant surface of a rectilinearly decreasing diameter in the first embodiment, the stepped surface of a stepwise decreasing diameter in the third embodiment includes no concentrated place of magnetic flux, permitting magnetic flux to pass through both stepped surfaces along a radial magnetic path.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006/244864 | Sep 2006 | JP | national |
