Patent Publication Number: US-2013239722-A1

Title: Swivel drive

Description:
The invention is directed to a so-called swivel drive, that is a device for the rotary drive of a part of a machine or a facility, for example a crane, an elevating working platform, a tracking photovoltaic assembly or a heliostat or the like equipment for tracking mirrors within the context of a solar thermal power station, etc., on a foundation or on a chassis, for example of a heavy duty vehicle, or to another part of a machine or a facility, comprising a worm gear mechanism having a housing, which has a connecting surface for connecting to a part of a machine or a facility, to a chassis or to a foundation, with a worm, which is rotatable manually or by means of a drive motor, and with a worm wheel which is rotatably mounted in the housing, in that there is provided at least one rolling contact bearing on each of both sides of the toothing of the worm wheel provided to engage with the worm, and which comprises a connecting surface for connecting to a part of a machine or a facility, to a chassis or to a foundation. 
     On the one hand, the housing of a generic swivel device serves for the bearing of the worm wheel and of the worm by means of rolling contact bearings; on the other hand, it shall enclose the toothing area of the worm wheel and of the worm as entirely as possible and thereby shall prevent the intrusion of dirt and other particles, for example. For this reason, known housings for example comprise a base part with a footprint in the shape of a “D”, whereby the worm runs parallel to the secant of the “D”. A cross-section through the lateral surface of such base part has a “D”-like shape, too; thereupon, after installation of the worm and worm wheel, a lid is fitted and is screwed to the base part. Although a recess is provided at both the base part and the lid, by what the worm wheel is accessible for mounting to a part of a machine or a facility, such recesses however are not big enough for inspection of the toothing of the worm wheel. At an inspection of the worm wheel&#39;s toothing, therefor the lid has to be disassembled first, what—due to the mutual interpenetration—is impossible, as long as the worm wheel is linked to the connected part of a machine or facility. 
     From the disadvantages of the described state of the art, the problem initiating the present invention results, to improve a generic for the rotary drive of a first part of a machine or a facility relative to a further part of a machine or a facility, foundation, chassis or the like such that—for example for the purpose of an inspection of the worm wheel&#39;s toothing—a disassembling of the housing can be performed with as less effort as possible. 
     The solution of this problem is accomplished in that at least that area of the housing which is concentric to the swivel axis of the swivel drive, is formed in one piece, wherein the smallest internal diameter of the housing is larger than the largest external diameter of the worm wheel. 
     This measure aims to entirely avoid a lid, such that a disassembling of the housing does not require a previous removal of a lid. Instead, both parts—the housing on the one hand and the worm wheel on the other hand—can be pulled apart in an axial direction relative to a swivel axis of the swivel drive according to the invention, possibly after previous removal of parts of the (contact roller) bearing. 
     It has proven favourable that the worm wheel comprises a central recess. By such a recess, the mass of a device according to the invention can be reduced, and thereby its weight, too. 
     When the central recess traverses the worm wheel entirely, in a built-in state, cables or other conduits can be fed there through from a foundation, chassis or the like to a swiveling part of a facility. 
     The worm wheel may be fabricated as a cast part, whereby at least one lateral projection for receiving of a worm (each) may be integrated, that means be formed jointly. Such complex shapes may be produced as a cast part with less material input and effort. 
     Within the scope of the invention, the inner surface of the central recess in the worm wheel follows a conical course. Such a shape facilitates the demoulding of a cast blank. 
     Preferably, the raceways of the worm wheel for the rolling elements are fabricated out of the same base body as its toothing. Thereby, the manufacturing process can be simplified further. 
     The toothing of the worm wheel may be adapted to the cross-section of the worm. This is especially the case at a so-called globoid worm wheel, whose toothed reference surface corresponds to a globoid, that is to say to a surface which is generated by rotation of an arc of a circle around an axis, which lies within the same plane than the generating arc of a circle itself. 
     The invention further provides that the minimum cross-sectional area of the worm wheel in the meshing region is smaller than its connecting surface. Such an arrangement appears especially in the case of a globoid toothing, if this is machined deepend into the cicumferential end face of the worm wheel, and has the advantage that there is only a minimum space required in case of a maximally firm connection to a part of a machine or a facility. 
     On the other hand, the connecting surface(s) of the worm wheel and/or of the housing should be plane, because plane surfaces may be produced with highest precision, thereby providing a particularly intimate contact with a high frictional coefficient. 
     The connecting surfaces of the worm wheel and of the housing should lie in planes parallel to each other, so that both can be penetrated rectangularly by the rotational axis of the bearing in a likewise manner. 
     For producing a stable joint to a part of a machine or of a facility or foundation or chassis to be connected, the invention provides annularly distributed fixing elements in the connecting surface of the worm wheel and/or of the housing. The fixing elements at one, both or all connecting surfaces can be formed as through-bores or as tapped blind holes. If thereby the bottom of such a blind hole is situated at the height of a row of roller elements, in most cases an optimum compromise is found between a minimum design height of the swivel drive according to the invention and a maximum mechanical stability thereof. 
     Furthermore, the invention is characterized by two angular rolling contact bearings, especially two angular contact ball bearings, which are arranged in the style of a double angular rolling contact bearing, preferably in the style of a double angular contact ball bearing. Preferably, these two rolling contact bearings are braced against each other, so that no relative movement occurs between worm wheel and housing even in case of a varying axial load. 
     The raceways of the rolling contact bearings should be hardened, especially surface-hardened. Therefor inductive hardening is recommended, but also flame hardening, etc. Thereby, the invention prefers progressive hardening or slip-free hardening. Even a nitriding is possible as well as a combination of such treatments. 
     According to the invention, the roller elements or balls respectively are held at equidistant positions by a cage or by several cage segments. Thereby, the cage or the cage segments may comprise a two-dimensional, comb-like structure, whereby the free ends of the comb&#39;s teeth of both rolling contact bearings are directed vis-à-vis. Such a cage can be inserted subsequently via a bearing gap and can be removed in the same way, without having to disassemble the bearing or the swivel drive according to the invention. So that such a cage or such a cage segment cannot loosen inadvertently, its comb&#39;s teeth may comprise indentations, which encompass a roller element to beyond its equator and have to be snapped onto the roller elements indeed, to be held there in a tight fit afterwards. 
     A further constructional rule according to the invention provides that, in assembled state, the minimum width W min  of the clear gap between the outer surface of the worm wheel and the inner surface of the housing is equal to or greater than half the value of the diameter D of a roller element: W min ≧D/2. Thereby, it is achieved that—before the insertion of the roller elements—the worm wheel can be displaced eccentrically relative to the housing, namely at least for an amount of D/2. Thereby, at the circumferential area a gap opens up to a maximum value W max ≧D, and at this site, the roller elements can then be inserted subsequently into the raceways there, without requiring an insertion opening for their own. 
     For lubricating the rolling contact bearings as well as the toothing within the hollow space of the gap in a durable manner, the gap between the housing and the worm wheel should be sealed at both end faces of the rolling contact bearing. 
     Thereby, at least one such sealing can be designed as a shaft seal ring, especially as a radial shaft seal ring. This has the advantage that it can subsequently be installed and disassembled if needed, without much effort. 
     For enhancement of the sealing effect, at least one sealing can comprise a sealing lip, which is pressed tightly against the regarding sealing thrust surface by means of a circumferential tension wire. Such a tension wire can improve the pressing effect of the sealing lip considerably, so that a liquid lubricant like oil may be used in some cases. 
     It has proved successfully to manufacture the housing as a cast part, so that for example a lateral projection at the housing for receiving the worm can be manufactured in one single working step. 
     For an easier demoulding of such a cast part, one can grant the outer lateral surface of the housing part surrounding the worm wheel a conical shape, possibly with attached stiffening ribs and/or with a circumferential flange in the area of the connecting surface. 
     Within the scope of the invention, within a lateral housing projection, a worm is pivoted by means of rolling contact bearings, for example by means of roller bearings and/or by means of ball bearings. 
     The invention offers the possibility to adjust or minimize the tooth flank clearance between worm wheel and worm. Therewith, an early attrition shall be counteracted, which otherwise would be caused by repeated clashing of the tooth or, respectively, thread areas meshing with each other. 
     Such a minimizing of the tooth flank clearance can be achieved by the geometry of the worm and/or of the worm thread varying in their longitudinal directions. For example, the worm could have a slightly conical or cone-like basic shape, so that the thread meshing area of the worm extends more or less deep into the tooth gaps of the worm wheel, depending upon the displacement of the worm in its longitudinal direction. 
     In tracking this thought further, the invention reaches an arrangement, whereby the distance between the flanks of the worm thread varies along the longitudinal direction of the worm, especially according to a duplex worm thread. Owing to slightly different thread leads, the tooth width or, respectively, the width of the thread&#39;s elevation of the worm varies along the longitudinal direction thereof. Such an arrangement has improved properties compared to the previously described conical shape of the worm, because the distance between the meshing parts of the gear does not vary and therefore no clamping has to be feared. 
     Finally, it corresponds to the teaching of the invention, that the position of the worm is variable in its longitudinal direction. This may happen in that the position of the worm is adjusted only at an open end face of the worm projection at the housing, while at the opposite end of the worm, there is provided only a pure radial bearing, without an axially effective force component. In contrast, at the driven end of the worm, where it leaves the housing, a combined radial and axial bearing is provided, for example in the form of a single-row or multiple-row angular rolling contact bearing, preferably in the shape of a double angular rolling contact bearing, especially in the shape of a double angular contact ball bearing. Between the mounting assembly thereof and the housing itself, there can be placed one or more washers or spacer rings, for varying the position of the worm in its longitudinal direction. This can be done first-time upon the manufacturing by the working personnel initially determining the optimum position of the worm for a clearance-free gear combination by way of trial, and then choosing and mounting the appropriate spacer ring. Later, this procedure can be repeated after each maintenance or inspection interval. 
    
    
     
       Further features, details, advantages and effects on the basis of the invention will become apparent from the following description of a preferred embodiment of the invention as well as from the drawing. Thereby: 
         FIG. 1  shows a plan view of a swivel drive according to the invention; 
         FIG. 2  shows a lateral view of  FIG. 1 ; 
         FIG. 3  shows a cross-sectional view traverse through the swivel drive along the line III-Ill of  FIG. 2 ; 
         FIG. 4  shows a cross-sectional view through  FIG. 1  along the line IV-IV; 
         FIG. 5  shows the detail V of  FIG. 4  in an enlarged view; as well as 
         FIG. 6  shows the detail VI of  FIG. 4  in an illustration corresponding to that of  FIG. 5 . 
     
    
    
     The device  1  according to the invention for rotational driving a part of a machine or a facility relative to a foundation or chassis or another part of a facility shows a particularly simple construction, namely a housing  2 , wherein a worm  3  and a worm wheel  4  are pivoted in rotatable manner. 
     The plan view of the housing  2  according to  FIG. 1  shows its two main segments, namely a first annular housing segment  6  concentrical to the swivel axis  5  of the rotational drive device  1 , accommodating the worm wheel  4 , as well as a second straight extending housing segment  7  for the accommodation of the worm  3 . 
     The cross-sectional view in  FIG. 4  indicates the structure of the annular housing segment  6 : This has a sleeve-like geometry, substantially without a base or closure plate at its underside and without a lid on the upper side. As aberration from a pure cylindrical geometry, some stiffening ribs  9  parallel to the swivel axis are recognizable at the outer lateral surface  8 , radially slightly broadening from the upper bearing&#39;s end face  10  to the lower bearing&#39;s end face  11  in cross-section and ending at the lower bearing&#39;s end face  11  in an encircling, flange-like extension  12 . Thanks to these stiffening ribs, the thickness of the actual annular lateral surface  6  of the housing can be minimized. 
     Like visible in  FIG. 2 , the end face of the annular housing segment  6 , preferably that with the encircling, flange-like extension  12 , serves as plane connecting surface  13 , to which a part of a facility or of a machine, a foundation, chassis or the like may be connected. Several bores, especially tapped blind holes  14 , incorporated into this connecting surface  13  in an annularly distributed manner in parallel to the swivel axis  5  of the rotational drive device  1  serve to connect such part of a facility, etc. For receiving of these blind holes  14 , the dimension parallel to the swivel axis  5  of the encircling, flange-like extension  12  is bigger than the depth of the blind holes  14 , for example one and a half times as big or bigger. 
     The worm wheel  4  comprises a central recess  15  concentric to the swivel axis  5 , and therefore also has a sleeve-like geometry without substantial radial elevations or indentations in its inner or outer lateral surface  16 ,  17 . The inner lateral surface  16  is slightly conical, what facilitates the manufacture of the worm wheel as a cast part and thereby especially its demoulding ability. Thereby, in the mounted condition, the tapered region of the central recess  15  preferably faces the flange-like extension  12  of the annular housing segment  6  in an axial direction—that means at the opposite end face of the bearing—and shows a plane end face, which serves as connecting surface  18  for a part of a facility, etc. This connecting surface  18  comprises several bores annularly distributed around the swivel axis  5 , especially tapped blind holes  19  in parallel to the swivel axis  5 . Preferably, the depth of the blind holes  19  within the worm wheel  4  approximately corresponds with the depth of the blind holes  14  within the annular housing segment  6 . 
     The worm wheel  4  has nearly the same axial extension as the housing  2 , but it is slightly displaced relative to that in axial direction, so that always the regarding connecting surface  13 ,  18  protrudes slightly over the end face of the respectively other element—worm wheel  4  or connecting surface  13 ,  18  respectively—so that in case of a connection with a plane connecting surface of a part of a facility, etc., a scraping of the relatively rotatable part  4 ,  2  is impossible. 
     Between the inner side  20  of the annular housing segment  6  on the one hand and the outer laterals surface  17  of the worm wheel  4 , there exists a gap  21 , so that these parts can rotate relative to each other. 
     Two rolling contact bearings  22 ,  23  are arranged within the gap  21  for a rotatable bearing of the worm wheel  4  within the annular housing segment  6 , one of which is located near the upper end face  10  of the bearing, while the other is situated in the region of the lower end face  11 . 
     In  FIG. 5 ,  6 , the rolling contact bearings  22 ,  23  are illustrated in a highlighted manner to show the inner structure in a better way. As both rolling contact bearings  22 ,  23  have a substantially identical structure, they can be described in the following in common: 
     In both cases, ball bearings are concerned, that is to say rolling contact bearings  22 ,  23  with spherical rolling elements  24  having a diameter D. Both rolling contact bearing  22 ,  23  are angular rolling contact bearings or, respectively, angular contact ball bearings with an absolute value of the support angle |α| of 20° or more, for example of approximately 45°. The supporting angles α of both angular contact ball bearings are opposite to each other, that means positive on the one hand, and negative on the other hand, preferably ±α, so that one bearing  22  may absorb axial pressing forces, the other bearing  23  can absorb axial tension forces. Furthermore, both angular contact ball bearings  22 ,  23  are pre-stressed against each other, so that failing of a clearance in axial direction, there is no relative movement between worm wheel  4  and housing  2  in case of loads varying between axial tension and axial pressing. 
     A specialty of the bearings  22 ,  23  is that the raceways  25 ,  26  are directly machined, especially cut, into the (casted) base body of the regarding element—housing  2  or worm wheel  4 . Furthermore, the raceways  25 ,  26  are preferably surface hardened to be able to sustain significant loads like frequent overrunning by the spherical rolling elements  24  for a term as long as possible without recognizable signs of wear. 
     The width W of the gap  21  may vary in axial direction, like apparent from  FIG. 4 . However, the minimum gap width W min  along the entire gap  21  is at least similar or greater than half the diameter D of a rolling element  24 : 
         W   min   ≧D/ 2. 
     Thereby, it is ensured that the worm wheel  3  within the housing  2  can be displaced for at least d/2, as long as the rolling elements  24  are not yet positioned within the gap  21 . By such a displacement, the gap  21  opens at one side: W≧D/2+D/2=D, while closing at the region situated diametrically opposite: W=D/2−D/2=0. Now, the rolling elements  24  may be inserted into the region of the raceways  25 ,  26  at the maximally opened site of the gap  21 . After this has taken place, the rolling elements  24  are distributed along the circumferential direction, until finally they reside at equidistant positions, whereby the worm wheel  4  returns to a position concentric to the annular housing segment  6 . At these equidistant positions, the rolling elements  24  are finally held by a cage  27  or by several cage segments per rolling contact bearing  22 ,  23 . Preferably, the cage  27  has a comb-like structure with a rearward bridge or back  28  and with webs  29  protruding from that nearly parallel to each other within a common plane in the style of a comb&#39;s teeth. 
     However, due to the above described insertion procedure, the number Z of the rolling elements  24  per bearing  22 ,  23  is substantially smaller than the theoretical maximum value Z=U/D, with the pitch circle perimeter U, namely Z≦0.8*U/D, especially Z≦0.6*U/D. At Z=1/2*U/D, both adjacent rolling elements have a distance a in the magnitude of their diameter D: a=D. For this reason, webs  29  of the cage  27  have a relatively large extension in a longitudinal direction of the cage back  28 . Therebetween, one can find indentations for receiving rolling elements  24 , which follow a circular curve, preferably along a center angle of more than 180°, related to the center of the regarding rolling element  24 . At such geometry, the webs  24  must be able to deform within a plane during the plugging onto the pre-positioned rolling elements  24 . To facilitate this, it is further provided that, between two adjacent recesses, each for receiving a rolling element, the webs  29  of the cage  27  have at least one slit each, which gives an increased measure of flexibility to the cage  27 . 
     Both bearings  22 ,  23  may be lubricated with grease as well as with oil, whereby the lubricant can contain metallic or non-metallic solid lubricants to avoid wear and jamming. The gap  21  is sealed in the area of both end faces  10 ,  11  of the bearing device beyond both rolling contact bearings  22 ,  23 , to retain the lubricant within the gap  21  and at the same time protect it against contamination by intruding dirt and other particles. 
     These seals  30  may have the same structures, too, what, however, is not compulsory. 
     The illustrated seals  30  are each fixed to the housing  2 , especially within a chamfer-like extension of the inner side  20  of the housing facing the gap  21 . For this purpose, they possess a core  32  embedded in an elastic sealing material  31 , in the form of a metal profile, especially of L-shaped cross-section, whereby the legs of this L-profile  32  running nearly orthogonally to each other stabilize themselves mutually and simultaneously press the rearward area of the elastic sealing material  31  against the inner side  20  of the housing. 
     Furthermore, one or, respectively, each sealing  30  is equipped with one or more sealing lips  33 ,  34 , which are sliding along the outer lateral surface  17  of the worm wheel  4 . The main sealing lip  33  facing the gap  21  is located at a cross-sectionally nearly V-shaped extension  35  of the elastic sealing material  31  in the area of the radially inner end of that leg of the L-shaped core  32  running transverse to the direction of the gap, especially at that flank of the core leg facing the gap. The tip of the extension  35  of V-shaped cross-section forms the main sealing lip  33  and points radially inwardly to the swivel axis  5 . At that flank situated further outwardly, the V-shaped extension  35  forms a chamfer, wherein a tension wire  36  is seated, additionally pretensioning the sealing lip  33  inwardly, in the direction to the worm wheel  4 . 
     A second, outer sealing lip  34  first of all serves as a dust seal and shall keep intruding particles away from the main sealing lip  33 . 
     In the area of the outer lateral surface  17  of the worm wheel  4  between the both rolling contact bearings  22 ,  23 , there are provided an external teeth system  37  with an encircling row of teeth  38  meshing with the thread  39  of the worm  3 . Thereby, the area of the toothing  37  may be designed similar to a globoid wheel, that is a toothed wheel whose geared reference surface is a globoid, namely a rotational body whose lateral surface is generated by an arc of a circle rotating around an axis within the plane of the circle. This has the advantage that a greater part of a tooth  38  gets in contact with the worm  3 ; due to the enlarged contact area, bigger forces or, respectively, torques can be transferred. However, in some cases, a spur gear could be used with straight teeth, if the forces or, respectively, torques transferrable by that are sufficient. 
     Preferably, the worm  3  meshing therewith is formed as a cylindrical worm. However, it is also possible to use an hourglass worm, whose threaded reference surface is a globoid. 
     Furthermore, the worm  3  may be provided with a simplex toothing, whereby both flanks of the thread pitch, that are the flanks forward and rearward with regard to the longitudinal direction of the worm  3 , have the same modules or, respectively, the same pitches, so that the cross-sectional geometry of the thread does not vary along its extension. 
     Such geometry is simple to manufacture; however, thereby often exists no possibility to compensate or adjust the clearance between tooth flanks. In contrast, the invention provides that the tooth flank clearance of the worm gear, that is the clearance between worm  3  and worm wheel  4 , may be adjusted and/or readjusted. This may be achieved in the most elegant way by using a worm  3  with a so-called duplex toothing. This structure is characterized in that both flanks of the thread pitch, that are the flanks forward and rearward with regard to the longitudinal direction of the worm  3 , have slightly different modules or, respectively, pitches, so that the cross-sectional geometry of the thread varies continuously along its extension. 
     Therefore, by a displacement of the worm  3  along its longitudinal axis, areas of the thread elevation with different width can be brought into meshing contact with the worm wheel  4 , whereby the tooth flank clearance can be adjusted precisely. 
     Thereby, preferably, the area with narrower cross-section of the thread elevation is situated at the free end  40  of the worm  3 , that is the non-driven end of the worm  3 . In this way it is possible to insert the worm  3  into the cylindrical housing segment  7  thus far until the tooth flank clearance entirely vanishes, but just no increased friction or even jamming occurs. In this position, the worm  3  can then be pivoted. 
     The worm bearing illustrated in  FIG. 3  serves for this purpose: 
     The forward or, respectively, free end  40  of the worm  3  is cylindrically shaped and is made longer than the rolling contact bearing  41  there, for example a needle bearing. Thereby, the worm  3  can be displaced in its longitudinal direction relative to this rolling contact bearing  41 . 
     The rearward or, respectively, driven end  42  of the worm  3  comprises a gradation  43  between a proximal, thickened area  44  and a distal, tapered area  45  adjacent thereto. A for instance two-rowed rolling contact bearing  46 , for example a double angular contact ball bearing, is slipped over this area  45 . Within an encircling, groove- or notch-shaped recess  47  in the tapered shaft area  45 , a lock ring  48  is inserted in alignment with that end face of the rolling contact bearing  46  near the driven side, so that the rolling contact bearing  46  is fixed onto the worm shaft  3  in an axially non-relocatable manner. 
     The outer ring(s) of the single-row or multiple-row rolling contact bearing  46  is/are incorporated within a sleeve  49  and are fixed therein in a similar, axially non-relocatable manner. For example, for this purpose, the sleeve  49  comprises at its inner end a collar  50  protruding inwardly, while an encircling recess  51  is provided at the inner side  52  of the sleeve  49  in alignment with that end face of this rolling contact bearing  46  near the driven side for insertion of a second lock ring  53 , whereby the rolling contact bearing  46  is fixed to the sleeve  49  in an axially non-relocatable manner. 
     This sleeve  49  in turn is fixed to the open end face  54  of the elongated housing segment  7 , for example screwed thereto. For this purpose, a radial outwardly projecting collar  56  may be provided at the peripheral or, respectively, outer end  55  of the sleeve  49 . Therein, fixing bores parallel to the longitudinal axis of the worm shaft  3  are annularly distributed. These are each aligned with tapped blind holes  58  in the end face  54  of the elongated housing segment  7  and serve for passing fixing screws  59  through. By inserting spacer rings  60  of different thickness between the collar  56  of the sleeve  49  and the end face  54  of the elongated housing part  7 , the axial position of the sleeve  49  can be varied and thereby the position of the worm shaft  3 , too. 
     The above described usage of a duplex worm  3 , where both flanks of the thread comprise slightly different modules or, respectively, pitches, results in both tooth flanks having different pitch angles, so that the thickness of or, respectively, the recess between elevations of the thread varies continuously along the toothed area of the worm. On the other hand, the thickness of and the recess between the teeth at the circumference of the worm wheel  4  remain constant. At the worm wheel  4 , different modules of the worm  3  lead to different pitch circle diameters and therewith to different flank shapes at the forward and rearward flanks. 
     In this manner, the tooth flank clearance can be adjusted to any convenient value and may be sensitively and infinitely variably readjusted at any time, without significantly altering the meshing relationship of the toothing  37 . A similar effect is achieved by a worm  3 , whose reference surface is cut slightly conical. 
     Owing to the axially adjustable bearing of the worm shaft, the rotary clearance of the worm can be readjusted even then, when the swivel drive  1  is immovably installed within a facility. The readjustment is effected through a displaceable sleeve  49 , which is fixed via a spacer ring; depending on the height of the spacer ring or, respectively, the set-up discs, the position of the worm  3  can be varied. 
     Furthermore, for control purposes, the worm  3  may be removed from the housing  2  along its longitudinal axis and/or may be replaced. 
     Typically, the housing  2  and/or the worm wheel  4  consist of a hardenable cast material, for example GGG-50. 
     The invention may be improved further in a manifold manner: 
     For example, a single-row or multiple-row ball or roller bearing can be provided for pivoting the worm wheel  4 , preferably as double-row four point bearing or as angular ball bearing; even at an embodiment as roller bearing, the insertion of roller elements is possible through the gap  21 . 
     At a multiple-row raceway system, the toothing of the worm wheel  37  does not have to be situated between the bearing raceways  22 ,  23 , but could also be situated at one side thereof. 
     In case of heavy loads to transfer, the raceway system may be filled via fill bores in the housing  2  or in the worm wheel  4 , so that a great number of roller elements is realizable. The fill bore is then closed by a plug and secured by pin or the like. In this way, roller elements may be inserted, which have a higher static and dynamic load capacity. The roller elements are then kept at narrow distances via a suitable cage or by intermediate pieces. 
     For increasing the load capacity, the surfaces of the bearing raceways  25 ,  26  are submitted to a heat treatment like inductive hardening or case hardening. 
     Furthermore, the raceways  25 ,  26  may be formed at preferably hardened annular segments, which are laid into a regarding groove or recess. The adjustment of the clearance or, respectively, of a pre-tension within the raceway system is effected by means of the selection of roller elements with a regarding diameter, whereby at multiple-row systems, roller elements of different size may be used for different rows of roller elements. 
     The worm wheel  4  carries a worm wheel toothing  37  at its circumference, which may be slightly greater in diameter as the outer diameter of the remaining areas of the worm wheel  4 . However, even an elevated region of the toothing always has to be equal to or smaller than the inner diameter of the housing  2 . 
     For control purposes, a lid srewable to the housing  2  opposite to the motor connection face  54  may be provided. There, a measuring device could be installed for data-acquisition above the rotation of the worm  3 . Furthermore, for determining of the position, it would be possible to use the teeth of the worm wheel  4  sweeping past the housing  2  or to use other marks attached thereto. This can be done for example in an inductive manner by means of a bore in the housing  2 , wherein an inductive proximity switch could be arranged. In such cases, one or more additional marks or special marked teeth could serve for determination of a zero point reference position. 
     Reference Numerals 
       1  device 
       2  housing 
       3  worm 
       4  worm wheel 
       5  swivel axis 
       6  housing area 
       7  housing area 
       8  lateral surface 
       9  stiffening rib 
       10  bearing&#39;s end face 
       11  bearing&#39;s end face 
       12  flange-like extension 
       13  connecting surface 
       14  blind hole 
       15  recess 
       15  lateral surface 
       16  lateral surface 
       17  connecting surface 
       18  blind hole 
       19  inner surface 
       20  gap 
       21  rolling contact bearing 
       22  rolling contact bearing 
       23  roller element 
       25  raceway 
       26  raceway 
       27  cage 
       28  back 
       29  web 
       30  sealing 
       31  sealing material 
       32  core 
       33  sealing lip 
       34  sealing lip 
       35  projection 
       36  tension wire 
       37  external toothing 
       38  tooth 
       39  thread 
       40  free end 
       41  rolling contact bearing 
       42  driven end 
       43  increment 
       44  thickened area 
       45  tapered area 
       46  rolling contact bearing 
       47  recess 
       48  lock ring 
       49  sleeve 
       50  collar 
       51  recess 
       52  inner surface 
       53  lock ring 
       54  end face 
       55  end 
       56  collar 
       57  fixing bore 
       58  blind hole 
       59  fixing screw 
       60  spacer ring