Abstract:
An apparatus for forming internal gear teeth at large workpieces at a gear shaper or gear shaping machine comprising a machine bed at which there are arranged a workpiece table for chucking a workpiece and an upright or stand. The workpiece table and the stand are rotatable, relative to one another, about the workpiece axis and radially feedable relative thereto. The stand has guide means along which there can be moved to-and-fro a plunger by means of a plunger drive. An auxiliary stand is rotatably and radially displaceable about the workpiece axis upon a bearing rim which is coaxially attached at the workpiece. The auxiliary stand has a guide arrangement along which there can be moved to-and-fro, in the tooth lengthwise direction of the internal teeth, an auxiliary plunger driven by the plunger by means of a bridge arrangement.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a new and improved construction of apparatus for forming internal teeth at large workpieces at a gear shaping machine or gear shaper. 
     In its more specific aspects, the inventive apparatus for providing internal gear teeth at large workpieces at a gear shaping machine, comprises a machine bed upon which there are arranged a workpiece table for chucking or clamping a workpiece and an upright or stand. The workpiece table and stand are rotatable, relative to one another, about the workpiece axis and can be advanced or fed radially with respect thereto. The stand has guide means along which there can be moved to-and-fro a plunger by means of a plunger drive. 
     There are already known to the art gear shaping machines which, according to indexing techniques or part-rolling techniques, not only can fabricate external gear teeth, but also internal gear teeth, such as for instance spline teeth for shaft-hub connections as well as coupling or clutch teeth, with great accuracy and surface quality. To fabricate internal teeth the plunger, which carries the gear cutting tool, must have a cantilever, in other words, must protrude a certain distance away from the stand which is greater than one-half of the external diameter of the workpiece. In the case of workpieces of large diameter this causes difficulties, since if the plunger is extensively cantilevered, the machining forces exerted by the gear cutting tool, produce considerable bending moments at the plunger. Therefore, it is necessary to either tolerate appreciable deformations of the plunger, and thus, attendant impairment of the accuracy and surface quality of the internal teeth, or else the plunger must be structured to be particularly sturdy, and thus heavy, increasing the cost of the entire gear shaping machine and its operating speed is lowered. Hence, such machine then no longer operates economically when fabricating external gear teeth, and it is for this reason that it was necessary to produce the external teeth and the internal teeth of gears of large diameter at different machines. The necessity of rechucking or clamping the workpiece, when working at different machines, again is associated with the drawback that, not only are there present time losses, but especially there cannot be prevented loss in accuracy of the arrangement, especially axial alignment, between the internal teeth and the external teeth. 
     SUMMARY OF THE INVENTION 
     Therefore, with the foregoing in mind it is a primary object of the present invention to provide a new and improved construction of apparatus for forming internal teeth at large workpieces at a gear shaper which is not associated with the aforementioned drawbacks and limitations of the prior art proposals. 
     Another and more specific object of the present invention aims at providing an apparatus for forming internal teeth at large workpieces, where it is possible, at heretofore known and existing gear shaping machines having a non-cantilevered plunger or only a modestly cantilevered plunger, and therefore suitable only for producing external teeth, to also fabricate central bores or hubs of large size gears with spline and/or clutch teeth. 
     Now in order to implement these and still further objects of the invention, which will become more readily apparent as the description proceeds, the apparatus of the present development is manifested by the features that an auxiliary stand is arranged rotatably and radially displaceable about the workpiece axis upon a bearing rim secured coaxially at the workpiece. This auxiliary stand has a guide arrangement or guide means along which there can be moved to-and-fro, in the teeth lengthwise direction of the internal teeth of the workpiece, an auxiliary plunger equipped with a gear cutter tool. This auxiliary plunger is driven by means of the aforementioned plunger through the intermediary of a bridge arrangement or bridge means. 
     With the inventive apparatus, which can be easily installed at existing gear shaping machines, the plunger drive moves, through the agency of the plunger and the bridge arrangement or bridge means, the auxiliary plunger to-and-fro. This to-and-fro movement is generally a vertical up-and-down movement, since gear shaping machines for larger workpieces generally are constructed such that the workpiece is chucked or clamped with its axis extending vertically at the machine table, and since internal teeth such as spline or clutch teeth formed at larger size workpieces, usually are straight or linear teeth. However, the inventive apparatus also can be structured such that there can be produced therewith helical internal teeth. To this end, it is only necessary that the guide means at the auxiliary stand can be adjusted at an inclination with respect to the lengthwise axis of the workpiece, as such is known for guide means at stands for gear shaping machines and other gear processing machines. 
     All of the movements of the inventive apparatus, needed for fabricating a tooth system, can be derived from drives which are provided anyway at the gear shaping machine. This is particularly valid, first of all, as concerns the displacement movements or strokes of the auxiliary plunger, which, as described, are generated by the plunger drive of the gear shaping machine. Moreover, the inventive bridge arrangement ensures that the auxiliary stand, and together therewith, the auxiliary plunger, participate in the radial feed or advance movements as well as also in the indexing movements and possible generating movements of the stand in relation to the workpiece table. The inventive apparatus therefore need not be equipped with its own drive. Consequently, it is simple and non-bulky in construction, and with appropriately low expenditure in work can be installed, on the one hand, at a gear shaping machine, and, on the other hand, at the workpiece which has been chucked or clamped at the machine table. 
     It is advantageous if the bridge arrangement or bridge means possesses a displacement or sliding drive, controlled by the plunger movements, in order to change the spacing of the auxiliary stand from the stand or upright. This displacement drive renders it possible to raise the gear cutting tool arranged at the auxiliary plunger, following each work stroke for the duration of the return stroke from the workpiece. Consequently, the tool can be protected and there can be produced internal teeth of highest surface quality. The displacement or sliding drive can not only be controlled by the plunger movements, but furthermore, its drive force can be obtained by a reversing gearing or transmission of known construction, for instance a spline gearing. According to preferred embodiments of the invention, the displacement drive however has its own power source, for instance an electrical, pneumatic or hydraulic power source. 
     Although, for the reasons described herein, it is advantageous to be able to periodically alter the spacing between the auxiliary stand and the stand, nonetheless the inventive bridge means also can be constructed such that it rigidly connects the auxiliary stand with the stand of the gear shaping machine. This is possible, for instance, when the inner diameter of the internal gearing, which is to be fabricated with the inventive apparatus, is sufficiently large in order to render possible a pivotal arrangement of the gear cutting tool at the auxiliary plunger, corresponding to the usual arrangement of the tool at the plunger of a gear shaping machine where the tool is pivoted away from the workpiece during each return stroke. 
     The inventive bridge means or arrangement can be structured such that it directly connects the auxiliary plunger with the plunger of the gear shaping machine. In this case, although the bridge means is loaded with bending moments by the machining or cutting forces, nonetheless bending of the bridge means does not have any appreciable effect upon the machining accuracy, since the auxiliary plunger, with adequate sturdy structuring of the auxiliary stand and the components carrying such, is sufficiently accurately guided. 
     According to preferred embodiments of the invention there are, however, avoided appreciable bending loads being applied to the bridge means and also the remaining components of the inventive apparatus in that, there is operatively associated with the bridge means a shaft which, on the one hand, is mounted at the stand, on the other hand, at the auxiliary stand. The shaft supports two pinions, of which the one meshes with a gear rack arranged at the plunger and the other with a gear rack arranged at the auxiliary plunger. It is possible, with relatively little expenditure, to design the shaft to be sufficiently strong in order to withstand the rotational moments or torques acting thereat without any appreciable torsion. Furthermore, even any significant torsion of the shaft does not have any effect upon the auxiliary plunger and its guiding at the auxiliary stand. 
     If the bridge means is provided with a displacement or sliding drive, then the shaft is telescopically extendable. Hence, the displacement drive either can be arranged at a rod which is essentially parallel to the shaft and interconnecting the stand with the auxiliary stand or at the shaft itself. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and objects other than those set forth above, will become apparent when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings wherein: 
     FIG. 1 is a perspective view of a known gear shaping machine and a workpiece and equipped with an apparatus constructed according to the invention; 
     FIG. 2 is a perspective view of part of the apparatus of FIG. 1, looking in the direction of the arrow II thereof; 
     FIG. 3 is a sectional view of the arrangement of FIG. 1 showing modified details of the apparatus; and 
     FIG. 4 is a vertical sectional view of the arrangement of FIG. 1, taken substantially along the line IV--IV thereof, showing further modified details of the apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Describing now the drawings, the exemplary embodiment of gear shaping machine or gear shaper, particularly as shown in FIG. 1, will be seen to comprise a machine bed 10 upon which there is rotatably mounted a workpiece table 12 about an essentially vertical axis A. Furthermore, upon the machine bed 10 there is displaceably guided a bed carriage or slide 14, in the direction of the double-headed arrow B, tangentially with respect to the workpiece table 12. Secured at the workpiece table 12 is a workpiece 16 having a lengthwise axis. This workpiece 16 is shown provided with external teeth 16&#39; and should be provided with internal teeth 16&#34;. Displaceably guided upon the bed carriage 14 is a stand or upright 18, movable in the direction of the arrows C and C&#39; radially with respect to the workpiece table 12. At the stand or upright 18 there is attached a plunger guide or plunger guide means 20 which is rotatably adjustable about a radial rotational axis in relation to the workpiece table 12. The plunger guide or guide means 20, in the illustrated embodiment, has been shown vertically adjusted. At the plunger guide 20 there is attached an electric motor 22 or other suitable drive. A spindle 24 is rotatably mounted at the plunger guide 20, spindle 24 being in threaded meshing engagement with a plunger 26 displaceable at the plunger guide 20. Also constituting part of the gear shaping machine is a not particularly visible drive arranged below the workpiece table 12, by means of which this workpiece table 12 can be rotated, in increments or steps of adjustable length, in the direction of the arrows E or in the opposite direction, these adjustable increments or steps being accommodatable to the pitch of each of the teeth 16&#39; and 16&#34; of the workpiece 16. 
     What has been described above essentially corresponds to the standard construction of a gear shaping machine or gear shaper as is known in the art. 
     Now installed upon the workpiece 16 is an apparatus for fabricating internal teeth 16&#34;. As concerns this apparatus the same comprises a bearing rim or collar 28, or equivalent structure, which is secured exactly coaxially with respect to the workpiece 16 and the workpiece table 12 upon such workpiece. For attachment purposes there are used, by way of example, in the illustrated embodiment, threaded bolts 30 or the like, extending through the bearing rim 28 and being threaded into support or contact plates 32. These support plates 32 are, for instance, welded or otherwise suitably affixed at the workpiece 16 and machined in such a manner that, their upper faces or surfaces come to lie in a common plane extending exactly perpendicular to the workpiece axis A. At the bearing rim 28 there is rotatably mounted, by means of extremely precise axial and radial bearings 34, a rotatable plate 36 about the workpiece axis A. Upon the rotatable plate 36 there are secured two guide rails 38 arranged perpendicular to and in spaced relationship from the workpiece axis A. These guide rails or rail members 38 guide an auxiliary stand carriage or slide 40 upon which there is secured an auxiliary stand 42. 
     Now there is guided in the guide or guide means 42&#39; of the auxiliary stand 42 so as to be vertically displaceable an auxiliary plunger 44, at the lower end of which there is attached a gear cutting or shaping tool 46 in the form of a single hobbing tooth. Formed or attached at the auxiliary plunger 44 is a gear rack 48. Meshing with this gear rack 48 is a pinion 50 which is attached at a shaft 52. This shaft 52 is mounted in the auxiliary stand or upright 42 at the neighborhood of the pinion 50. In FIG. 4 there has been shown a radial bearing 54 and an axial bearing 54&#39;. 
     The shaft 52, according to the showing of FIG. 1, possesses a multi-edge, typically a square portion 56, which is telescopically displaceable in a tubular-shaped shaft section 58 of corresponding internal shape or profile. The shaft section or piece 58 is mounted at a traverse or crossbar 60 which is displaceably guided at the plunger guide or guide means 20 and bridges the plunger 26, so that it does not hinder it during its up-and-down movements. By means of a clamping screw 62 or other suitable or equivalent device, the traverse or crossbar 60 is fixedly mounted at the plunger guide or guide means 20 at an elevational position which depends upon the thickness of the workpiece 16. At the shaft section or piece 58 there is attached a pinion 64 which meshes with a gear rack 66 secured at the plunger 26. The up-and-down motions, imparted to the plunger 26 by the electric motor 22 through the intermediary of the spindle 24, are thus transmitted by means of the gear rack 66, the pinion 64, the shaft 52, the pinion 50 and the gear rack 48 to the auxiliary plunger 44, so that such auxiliary plunger 44 is moved always in the same direction and, since the pinion 64 and the pinion 50, in the illustrated embodiment, are identical, also move up-and-down through the same distance or amount as the plunger 26. 
     According to the showing of FIGS. 1 and 2, a larger gear 68 meshes with the pinion 50. This larger gear 68 is connected by means of a shaft 70, mounted at the auxiliary stand 42, with a cam disk 72. At the circumference of the cam disk 72 there are attached two cams or dogs 74 and 74&#39; which control a valve 76 arranged at the auxiliary stand carriage or slide 40. The valve 76, in turn, controls lines or conduits 78 and 78&#39; which flow communicate a hydraulic pump 80 with a displacement or sliding drive 82 constructed as a double-acting piston-and-cylinder unit 82&#39;, 82&#34;. 
     With the exemplary embodiment according to the showing of FIGS. 1 and 2 the cylinder 82&#39; of the displacement drive or drive means 82 is secured at the auxiliary stand carriage or slide 40 and the related piston 82&#34; is attached at a rod 84. The rod 84 extends essentially parallel to the shaft 52 and is secured at the traverse 60 at the piston rod end remote from the displacement drive 82. 
     Instead of providing this arrangement, a modification is shown in FIG. 3 wherein the cylinder 82&#39; of the displacement drive 82 is attached at the traverse or crossbar 60, whereas the end of the rod 84, remote from the displacement drive 82, is secured at the auxiliary stand carriage 40. In this case there is provided, instead of the mechanically actuatable valve or valve means 76, preferably an electromagnetically actuatable valve or valve means 86. This valve 86 is directly secured at the traverse 60 and can be actuated by the switches 88 and 88&#39;. These switches 88 and 88&#39; are arranged at the plunger guide 20 and are actuated by the cams or dogs 90 and 90&#39;, or equivalent structure, adjustably fixed at the gear rack 66. 
     According to a further modification, as shown in FIG. 4, the displacement drive 82, likewise in the form of a piston-and-cylinder unit 82&#39;, 82&#34;, is arranged at the shaft 52 and there is dispensed with the use of the rod 84. According to the showing of FIG. 4, it will be seen that at the shaft 52 there is attached an externally toothed-coupling or clutch element 92 which, at the same time, is constructed to form the piston 82&#34; of the displacement drive 82. The hollow shaft section or piece 58 mounted in the traverse 60 forms at the same time the internally toothed-coupling or clutch element and is structured so as to constitute the double-acting cylinder 82&#39; and is connected with the valve 86. 
     The apparatus for machining internal teeth, for the illustrated and described embodiments, operates in the following manner: during each downward stroke of the plunger 26 the auxiliary plunger 44 likewise carries out a downwardly directed work stroke, so that the gear cutting or shaping tool 46 machines the internal teeth 16&#34;. As soon as the gear cutting tool 46 has moved downwardly, out of the internal teeth 16&#34;, then the cam or dog 74 of the arrangement of FIGS. 1 and 2 controllably switch the valve 76, or for the modified embodiments of FIGS. 3 and 4, the cam or dog 90 switch the valve 86, and thus, the displacement drive 82 is pressurized in a manner such that it displaces the auxiliary stand 42 in a direction away from the stand 18, through a distance which has been indicated in FIG. 1 by the thin arrows F. At the end of the upward stroke of the plunger 26 and the auxiliary plunger 44 the cams or dogs 74&#39; (FIGS. 1 and 2) and 90&#39; (FIGS. 3 and 4), respectively, again switch the valves 76 and 86, respectively, so that the displacement drive 82 is pressurized in the opposite direction and the auxiliary stand 42 is shifted back into its work position in the direction of the arrow F&#39;. During the upward stroke the auxiliary stand 42 can be displaced in the direction of one of the arrows C of FIG. 1, so that the gear cutting or shaping tool 46 carries out an advancing or feed movement. This feed movement is accomplished in that, the stand 18 is shifted by means of its standard feed drive, of which there has been shown in FIG. 1 the threaded spindle 94 thereof, likewise through the directional distance C, and thereby, by means of the rod 84, entrains the auxiliary stand carriage 40 together with the auxiliary stand 42. Thereafter, there is accomplished the next work stroke of the auxiliary plunger 44. After there has been finished hobbed, in this manner, following a certain number of work strokes, a tooth gap of the internal teeth 16&#34; and there is necessary an indexing movement of the workpiece 16, then the stand 18, and together therewith the auxiliary stand 42, are moved back through a distance indicated by the arrows C&#39; in FIG. 1, so that the workpiece 16 can freely rotate below the apparatus for forming the internal teeth. 
     While there are shown and described present preferred embodiments of the invention, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims. ACCORDINGLY,