Abstract:
An assembly comprises a spindle and a moving nut disposed on the spindle. The spindle and the moving nut are made of plastics. At least one of the two components spindle and moving nut being resilient such that the moving nut is prevented from getting stuck on the spindle. There is further proposed an actuator including such assembly.

Description:
TECHNICAL FIELD 
   This invention relates to an assembly comprising a spindle and a moving nut disposed on the spindle. 
   BACKGROUND OF THE INVENTION 
   Such assemblies are used for converting rotational movements into translational movements. When such an assembly is designed for small loads, for instance in a motor vehicle for actuating ventilation nozzles or air outflow grids, the two components spindle and moving nut are preferably made of plastics. With regard to a small mounting effort it would be desirable to form the two components as injection-molded parts, one of which is inseparably connected with the other. 
   In principle, it is possible to directly apply one part onto another by injection-molding such that the two injection-molded parts are movable relative to each other. There can be used for instance a method of injection molding articles which consist of at least two parts, as it is known from DE 33 40 122 C2. In this method, a first injection-molded part is fabricated in a first mold, the same is then removed from the first mold and placed into a second mold. The first injection-molded part will cool in the process and solidify to such an extent that subsequently in the second mold the second injection-molded part can be injected into the first injection-molded part. The two injection-molded parts can thus movably, but inseparably be connected with each other. 
   Since the first injection-molded part already has solidified in part, before the second injection-molded part is formed, the first injection-molded part already has experienced part of its inevitable shrinkage, before the material for the second injection-molded part is injected. This can lead to the second injection-molded part getting jammed on the first injection-molded part, when the second injection-molded part now shrinks for its part. When the second injection-molded part is the moving nut, it will get shrunk onto the spindle upon solidification, so that the two components are very tight or are even blocked relative to each other. 
   Therefore, it is the object of the invention to provide an assembly comprising a spindle and a moving nut as described above, in which the movability between spindle and moving nut is not impaired, even if one of the components is applied on the other one by injection-molding or is injected into the other one. 
   BRIEF SUMMARY OF THE INVENTION 
   According to the invention, an assembly comprises a spindle and a moving nut disposed on the spindle. The spindle and the moving nut are made of plastics. At least one of the two components spindle and moving nut being resilient such that the moving nut is prevented from getting stuck on the spindle. By means of the resilient design of spindle or moving nut it is achieved that even with a reduction of the radial dimensions of the moving nut at least either the spindle or the moving nut will give way elastically such that the movability of the moving nut with respect to the spindle is not disturbed. 
   In a preferred embodiment of the invention, an actuator is equipped with an assembly comprising a spindle and a moving nut disposed on the spindle. Such actuator can be used in particular for adjusting a ventilation flap of a ventilation system of a motor vehicle or an adjustable headlamp. 
   Further advantageous aspects of the invention can be taken from the sub-claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a perspective view of a spindle in accordance with a first embodiment of the invention, 
       FIG. 2  shows a perspective view of the assembly comprising spindle and moving nut in accordance with the first embodiment of the invention, 
       FIG. 3   a  shows a side view of the first embodiment of the assembly in accordance with the invention, 
       FIG. 3   b  shows a second side view of the first embodiment of the assembly in accordance with the invention, 
       FIG. 3   c  shows a third side view of the first embodiment of the assembly in accordance with the invention, 
       FIG. 3   d  shows a sectional view of the first embodiment of the assembly in accordance with the invention along line IIID—IIID in  FIG. 3   c,    
       FIG. 4  shows another side view of the first embodiment of the assembly in accordance with the invention, 
       FIG. 5  shows a sectional view of the first embodiment of the assembly in accordance with the invention along line V—V in  FIG. 4 , and 
       FIG. 6  shows a perspective view of the moving nut in accordance with a second embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a spindle  10  which is made of plastics and comprises a spindle head  12  and a spindle shank  14 . The spindle shank  14  is hollow, as a cylindrical through hole  16  with a longitudinal axis  18  extends in its interior. Furthermore, the spindle shank is provided with a continuous spindle slot  15 , which extends from the outer surface of the spindle shank to the through hole. 
   At its axial end opposite the spindle head  12 , the spindle shank  14  has a first stop  20 , and in an approximately middle portion of the spindle shank a second stop  22 . Both stops are integrally formed with the spindle. 
     FIGS. 2 to 5  illustrate an assembly  24  comprising the spindle  10  and a moving nut  26 . The moving nut  26 , which substantially has the shape of a hollow cylinder, is made of plastics and is disposed on the spindle shank  14  between the first stop  20  and the second stop  22 . The external thread provided on the spindle shank  14  is represented only schematically. There is not represented the internal thread of the moving nut  26 , which corresponds with the external thread of the spindle shank. 
   By rotating the spindle  10 , the moving nut  26  can be moved between the first stop  20  and the second stop  22 . The first stop serves to limit the travel of the moving nut beyond the end of the spindle shank  14 , the second stop serves to limit the travel of the moving nut towards the spindle head  12 . This is particularly advantageous, as on the one hand the moving nut  26  cannot get lost, but on the other hand the travel of the moving nut on the spindle shank is limited to a defined region. 
   In the following, there will be explained a method of producing the first embodiment of the assembly comprising a spindle and a moving nut. 
   The spindle  10  is produced as injection-molded part, an integral core being used for generating the through hole  16  and the spindle slot  15 . The core slightly protrudes beyond the outer surface of the spindle shank, so that it can easily be removed later on. This protruding “back” is not provided with a thread. 
   Upon injection molding the spindle, the same is inserted into a second tool, without the core having been removed, and the moving nut  26  is applied by injection-molding. In this step, the core left in the spindle shank is used for stabilization; it prevents the spindle shank from deforming under the molding pressure. 
   Upon injection-molding the moving nut  26 , the core can be withdrawn from the spindle  10  in longitudinal direction. This is easily possible, as the back of the core protruding beyond the outer surface of the spindle shank is non-threaded. The depression in the internal thread of the moving nut, which is formed by the protruding back, does not disturb. 
   The shrinkage which occurs during the solidification of the moving nut  26  along with the corresponding reduction of the inside diameter of the thread of the moving nut is compensated in that the spindle shank gives way elastically, i.e. the width of the spindle slot  15  is reduced. As a result, the moving nut can be moved on the spindle shank  14  with little friction. 
   The amount of friction between the moving nut and the spindle can be adjusted by the ratio between the inside diameter of the through hole  16  and the outside diameter of the spindle shank  14 , i.e. by selecting the wall thickness of the spindle shank. The smaller the wall thickness, the smaller the spring force of the spindle shank acting against a deformation, and the friction also is correspondingly small. 
   The elasticity of the spindle shank can be adjusted such that a kind of sliding clutch is achieved between the moving nut and the spindle shank. When the moving nut strikes against one of the stops, but the spindle is moved on, the spindle slot is narrowed to such an extent that the moving nut slips through on the thread of the spindle shank and snaps into the next thread. 
     FIG. 6  shows the moving nut  26  of the second embodiment, which substantially has the shape of a hollow cylinder and comprises an inner wall  30  and an outer wall  32 . The moving nut includes a nut slot  28  which extends across the entire length of the moving nut from the inner wall  30  to the outer wall  32 . 
   The second embodiment of the assembly comprising spindle and moving nut is produced as follows: First of all, the spindle is produced as a solid injection-molded part. There is used an injection molding tool provided with an oblong projection in the vicinity of the thread, the dimensions of this projection approximately corresponding to the nut slot, so that a non-threaded groove is formed at one point of the spindle shank. In a second step, the moving nut is applied onto the spindle by injection-molding. Provided on the injection molding tool is a web which is used for producing the nut slot and extends into the non-threaded groove of the spindle. 
   In principle, it is also possible to form the spindle without the non-threaded groove and provide the web at the second injection molding tool with a counterpart of the thread of the spindle, so that the web can exactly engage in the external thread of the spindle shank. However, this involves a great manufacturing effort. 
   The moving nut undergoes shrinkage, but can resiliently expand over the spindle shank  14  of the spindle  10  because of the nut slot  28  extending across the entire length of the moving nut. Here as well, a smooth movement of the moving nut  26  on the spindle shank  14  is ensured. There can also be produced the above-described effect of a sliding clutch.