Rotary shafts – gudgeons – housings – and flexible couplings for ro – Overload release coupling
Reexamination Certificate
2000-01-27
2001-11-06
Browne, Lynne H. (Department: 3629)
Rotary shafts, gudgeons, housings, and flexible couplings for ro
Overload release coupling
C464S161000, C464S036000, C192S056620
Reexamination Certificate
active
06312339
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a safety coupling comprising two coupling disks pressed against each other by a spring device, in particular for employment in screwing tools used for tightening a screw at a predetermined torque.
In DE 296 18 871 U a safety coupling in described which comprises two coupling disks accommodated in a housing. The coupling disks are provided with engaging profiles and are pressed against each other by a spring device. When the screwing resistance of a screw to be tightened is larger that the adjusted trip moment of the safety coupling, the profiles disengage so that the first coupling disk rotates. In this way the torque to be applied can be limited. However, the contiguous profiles of the two coupling disks cause friction which affect the trip moment in an unforeseeable way. On the one hand it must be taken into consideration that the static friction is larger than the sliding friction caused by displacement of the profiles, and further that the sliding friction may vary depending on the material and lubricant properties.
Further, safety couplings are known which comprise rolling bodies in the form of balls or rollers between the two coupling disks. However, balls are suitable only for low trip moments because of their point contact with the adjacent coupling disk since they do not withstand larger pressure forces or cause bulging-in of the coupling disk concerned. The rollers pose the problem that the rollers are aligned radially with the coupling disks and that the support along the inner radius does not conform to that on the outer radius. If the troughs of the coupling track have parallel boundary edges corresponding to the form of the cylindrical rollers, the boundary edges of the troughs do not extend radially to the respective coupling disk so that the roller leaves one end of the trough earlier than the other end. Consequently, the carrying capacity of the rollers can be utilized only up to a certain extent, and when a high load is applied the coupling track may be damaged and thus the torque residence time and accuracy adversely affected.
SUMMARY OF THE INVENTION
It is the object of the invention to create a safety coupling comprising elongate carrier bodies, where the trip moment can be adhered to with high accuracy due to uniform load distribution.
The coupling track of the safety coupling according to the invention is generally radially aligned with the coupling disk concerned. For cylindrical carrier bodies this means that the troughs of the coupling track do no have any parallel edges or margins or other boundaries. All contour lines extend radially so that no parallel contour lines exist. According to the invention the coupling track of the coupling disk is a path described by a carrier body radially aligned with the coupling disk having the same form and size as the carrier bodies, whereby the carrier body performs a periodical axial movement relative to the second coupling disk during a uniform rotation of the second coupling disk. This defines a possible production process of the coupling track. A coupling track suitable for cylindrical or partially cylindrical carrier bodies can be produced by means of a rotating cylindrical milling cutter axially aligned with the coupling disk, whose peripheral area processes the coupling track. The rotating milling cutter is moved axially to the coupling disk, e.g., by a sinusoidal reciprocating movement, while the coupling disk is uniformly rotated about its axis. The milling cutter then produces the desired contour of the coupling track. On said track the carrier bodies will later roll or slide, which have the same diameter as the milling cutter. When the carrier bodies leave the troughs, they rest against the coupling track along an exact radial line, i.e., they are in line contact. Thus, the carrier body provides support and is supported, respectively, over its overall length and a uniform load distribution is achieved. The fact that the contact line is exclusively radially aligned with the coupling disk results in a defined rolling or sliding movement, as well as a defined tripping of the safety coupling when the carrier bodies have reached the apex areas of the coupling track.
With regard to a coupling track for cylindrical carrier bodies it must be noted that the areas of the coupling track cooperating with the carrier bodies do not come too close to the axis of the coupling disk since this would prevent the line contact from being maintained until the apex of the coupling track has been reached. Therefore, the inner (smaller) radius of the coupling track must be so large that the track has the same height at its inner radius as at its outer radius.
The safety coupling according to the invention is particularly suitable for heavy loads. This means that it is of relatively small size and light weight for a given load or a given trip moment.
Preferably the contour of the coupling track is approximately sinusoidal on the outer radius. Thus, a good rolling behavior is achieved. The apexes of the sine shape may however also be flattened.
The carrier bodies with cylindrical surface may either be rollers which are rotatable relatively to the two coupling disks and thus roll on the coupling track, or cylindrical bodies which are integrally moulded to one of the coupling disks. The surface of the carrier bodies must be of cylindrical configuration only in the area cooperating with the coupling track. Alternatively, it is also possible to use conical carrier bodies or other carrier bodies whose surface is produced by rotation of a straight line.
It is also possible to provide each of the two coupling disks with a coupling track of varying height. In this case the coupling bodies are rollers guided in a roller cage. The advantage of such a configuration is that the fully cylindrical carrier bodies may roll on the coupling tracks of both coupling disks without any sliding friction occurring. This results in a small degree of wear and a high accuracy of the trip moment.
If the carrier bodies are configured as cylindrical rollers, two (or more) cylindrical rollers may be provided instead of a single cylindrical roller with the two (or more) cylindrical rollers being axially aligned with each other. This improves compensation for the speed difference between the inner and outer portions of the coupling track since the external cylindrical rollers may have a larger peripheral speed than the internal cylindrical rollers.
The invention further relates to a safety coupling for which the trip moment is adjustable by relative movement of two housing parts. The safety coupling according to DE 296 18 815 U comprises a housing capsule and a housing cover screwed onto the former. By turning the housing cover relatively to the housing capsule the tension of the spring device can be changed thus allowing the trip moment to be adjusted.
The invention is designed to ensure exact adherence to the adjusted trip moment of a safety coupling.
For this purpose the invention provides a releasable locking device which retains the housing cover in its adjusted screwed-on position.
The invention proceeds from the idea that tripping of the safety coupling produces impacts which may lead to unintentional twisting of the housing cover relative on the housing capsule. The fact that the housing cover must be capable of being manually turned for adjusting the desired trip moment offers another possibility of unintensional twisting. This requires the housing cover to be capable of being smoothly turned, which has the effect that unintentional twisting may occur. The locking device according to the invention helps to reliably maintain an adjusted position.
According to a preferred embodiment of the invention the locking device comprises a catch element shiftable along the housing cover, which engages with the internal toothing of the housing capsule. The internal toothing extending over a certain length of the housing capsule allows the catch element to engage in different axial positions of the housing capsule
Browne Lynne H.
Diller Ramik & Wight
Kuerten Martina
Thompson Kenn
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