Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
2001-03-07
2003-05-13
Rodriguez, Pam (Department: 3683)
Machine element or mechanism
Gearing
Directly cooperating gears
C074S424820
Reexamination Certificate
active
06561053
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a rolling-body screw drive having a threaded spindle and a threaded nut enclosing the threaded spindle, a helically running threaded channel provided between an outer circumferential surface of the threaded spindle and an inner circumferential surface of the threaded nut, the threaded channel forming, together with a return channel which connects the two end regions of the threaded channel, an endless circulatory channel in which an endless series of rolling bodies is accommodated, and in which each of the two end regions of the threaded channel is assigned a deflecting element, which is retained on the threaded nut and has a deflecting channel, for transferring the rolling bodies between the threaded channel and the return channel and between the return channel and the threaded channel.
Such a rolling-body screw drive is known, for example, from DE 29 14 756 C2. It can easily be recognized that the task of producing those deflecting elements of the rolling-body screw drive which have a closed deflecting channel involves a relatively high cost outlay since the injection mold, for forming the deflecting channel, has to have at least two core elements inserted into the mold cavity from different sides. It is necessary for these core elements, once the deflecting element has cured, to be removed from the deflecting element and, in order to produce the next deflecting element, to be reintroduced into the mold and repositioned there. Furthermore, the deflecting elements of the known rolling-body screw drive, in particular in the case of heavy-load embodiments with large rolling-body diameters, were occasionally found to be insufficiently robust. This resulted in practice, in particular in the embodiments with an open deflecting channel, in undesired deformations of the deflecting elements on account of vastly differing wall thicknesses.
Deflecting elements as have been described above are also known from DE 24 37 4,7 C2. Reference is made in that regard to a brochure from A. Mannesmann, Remscheid entitled “AM-Werknorm 26” (AM Works Standard 26), which discloses the production of a deflecting element with a deflecting channel that is not fully closed in the circumferential direction. The deflecting channel is formed by means of an end mill which has cutting edges provided in spherical form on the tip.
SUMMARY OF THE INVENTION
In contrast to the foregoing, the object of the present invention is to provide a rolling-body screw drive of the type mentioned in the introduction with deflecting elements which are easier to produce.
This object is achieved according to the invention by a rolling-body screw drive of the aforementioned type in which at least one of the deflecting elements is made up of at least two deflecting-element parts which together form the deflecting channel. In the preferred production of the deflecting-element parts as plastic parts using injection molding, there is thus no need for any cores to be inserted into the mold in order to form the deflecting channel. It is thus possible for a completely cured deflecting-element part to be demolded simply by virtue of the mold halves being opened and for the mold to be prepared for the production of the next deflecting-element part simply by virtue of being reclosed. Cutting-type follow-up machining of the deflecting-element parts is not necessary. In particular, when a boundary surface of each of the deflecting-element parts, which boundary surface helps to bound the deflecting channel, extends from an inlet end of the deflecting channel to an outlet end of the deflecting channel, a deflecting element with a deflecting channel which is closed over its entire circumference can easily be produced.
The deflecting element may have, for example, a main deflecting-element part and at least one secondary, deflecting-element part. The main deflecting-element part, in addition to bounding the deflecting channel, may also perform other functions, for example, serving for fastening the deflecting element on the threaded nut. The deflecting-element parts may be clamped to one another, for example, or connected to one another by means of at least one pin which is arranged on one of the deflecting-element parts and engages in a corresponding recess in the respectively other deflecting-element part. If a plurality of such pin/recess pairs are provided, not all of the pins have to be arranged on one and the same deflecting-element part. At least one pin/recess pair may be designed such that the pin is introduced into the recess under pressure, with the result that a press fit is produced. Within the context of the present application, this type of connection may also be regarded as “clamping” of the deflecting-element parts. In principle, however, it is also conceivable for the deflecting-element parts to be adhesively bonded to one another.
A particularly reliable manner of fitting the deflecting element on the threaded nut to secure these two parts together by a screw-threaded fastener. It is possible here for a through-passage hole to be provided in the deflecting element for the through-passage of a screw-bolt fastener. Preferably, the through-passage hole is located only in the main deflecting-element part. In that case, as a result of the fastening, the at least one secondary deflecting-element part may be retained on the threaded nut by the main deflecting-element part.
In a particular aspect of the deflecting elements of the rolling-body screw drive according to the invention, the penultimate thread turn of the threaded surface bounding the threaded channel on the part of the threaded nut is formed, at least in part, by the outer surface of the deflecting element. In this way, the deflecting element can take up a relatively large amount of space in the threaded nut without adversely affecting the functioning of the latter. This means that the deflecting element may be of robust design, even when rolling bodies of large diameter are used.
If the course of that running-path flank of the penultimate thread turn which “cuts into ” the deflecting element is selected such that said running-path flank is specifically relieved of loading as the rolling bodies move past, it is possible for wear to which the deflecting element is subjected by said rolling-body movement to be minimized, if not completely prevented. Such specific influencing of the course of running-path flanks is also referred to in specialist circles as “shifting”.
In a further aspect of the invention, the deflecting element may also have a cutout or recess into which there is inserted a retaining element which is formed from a harder or softer material than the deflecting element. The retaining element is dimensioned in the direction of the depth of the cutout such that the retaining element accommodated in the cutout projects from the cutout to a greater extent than corresponds to the play or clearance provided between the deflecting element and the recess in the threaded nut which accommodates the deflecting element. It is possible, for example, for the retaining element to project from the cutout by between approximately 0.05 mm and approximately 0.4 mm, and preferably approximately 0.2 mm. In a particularly simple embodiment, the retaining element may be a ball. This ball may be produced from a material which may be either softer or harder than the material of the deflecting element. The ball may thus be produced, for example, from NBR (Nitrile-Butadiene Rubber) or from hardened steel. Use of a softer material, for example NBR, has the advantage that, when the deflecting element is forced into its accommodating recess, rather than the deflecting element being deformed, which could adversely affect the deflecting channel, it is the retaining ball that is deformed.
If the cutout is provided in a sub-surface of the outer surface of the deflecting element which is arranged essentially opposite that sub-surface of the outer surface of the deflecting element into which that end section of the deflecting channel wh
Rexroth Satr GmbH
Rodriguez Pam
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