Patent Publication Number: US-6655937-B2

Title: Plastic vane for a vane-cell vacuum pump

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 35 USC 371 application of PCT/DE 01/03598 filed on Sep. 19, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is based on a plastic vane for a vane cell vacuum pump in which the vane has a body portion and a terminal part of different materials. 
     2. Description of the Prior Art 
     From German Utility Model DE-GM 75 03 397, a cell compressor is known that is equipped with plastic laminations or vanes. While the part of the laminations associated with the rotor of the cell compressor comprises a low-grade material, the terminal part of the laminations, which is associated with a jacket wall of the compressor housing, should conversely comprise a highly wear-resistant material. The parts of the laminations are produced separately from one another and joined together by methods such as adhesive bonding, riveting and welding. The two lamination parts can also be pressed together already during the production process. A multi-part lamination structure has the disadvantage that the individual tolerances of the lamination parts add up. This is especially harmful if laminations with parts of highly wear-resistant material disposed on both ends are produced in this way. Laminations or vanes produced in this way reach through the rotor and are meant to engage the housing sealingly on both ends, as is known for instance from U.S. Pat. No. 3,877,851. 
     SUMMARY OF THE INVENTION 
     The vane of the invention is advantageous in the sense that on the one hand, there is no need to mount separately produced individual parts, and on the other, the injection-molding tool determines the final shape of the vane replicably, with relatively close tolerances. 
     In one embodiment a structure of the vane is defined in which the body of the vane is first created by injection molding, transfer molding, or compression molding, and then, in the same injection-molding tool or a different one, the terminal part of the vane is completed. 
     A further feature of the invention is advantageous in the sense that on the one hand the dimensional accuracy of the vane is improved by a reduced influence of material shrinkage at the terminal part, and on the other, if the material of the terminal part is expensive, the costs of the vane can be kept low. 
     A joining of the parts can be accomplished in a simple way in the course of producing the vane, especially if with the materials used for the body and the terminal part of the vane, material engagement is not attainable. 
     With the heat treatment of the body of the vane an increase in the strength of the vane is attained by means of the maximum attainable, three-dimensional degree of cross-linking of the molecular structures and a constancy in the vane geometry by a reduction of tension in the microstructure of the material, as well as an avoidance of aftershrinkage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and advantages of the invention will become apparent from the description contained herein below, with reference to the drawings, in which: 
     FIG. 1 shows a three-dimensional view of a vane cell vacuum pump with a single vane; 
     FIG. 2, as a three-dimensional view, shows the body of the vane; and, 
     FIG. 3, also as a three-dimensional view, shows the vane completed with two terminal parts. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A vane cell vacuum pump  10  shown in FIG. 1 has a pump housing  11 , shown without a cap, with an interior  12  in which a drivable rotor  13  is disposed eccentrically. The rotor  13  is provided with a transversely extending slot  14  for longitudinal guidance of a vane  15  made of plastic. The vane  15  both slidingly and sealingly engages an inner wall  16  on the jacket, an end wall  17 , and the cap, not shown, of the pump housing  11 . The pump housing  11  also has a suction neck  18  with an inlet opening  19 , discharging on the jacket side into the interior  12 , and an outlet opening  20  on the face end. The suction neck  18  communicates with a negative-pressure brake booster, not shown, of a vehicle brake system. The function of the vane cell vacuum pump  10  is known and therefore requires no further explanation here. 
     The vane  15 , embodied in the form of a lamination, is of plastic. Its body  21 , shown in FIG. 2 of the drawing, is made from a duroplastic. It is produced by injection molding, transfer molding or compression molding from a glass-fiber-reinforced molding composition of phenol and Novolak, or a material of comparable properties. This material is distinguished by high mechanical and dynamic load-bearing capacity and oil resistance. Its material properties are largely constant in the temperature range from −40° C. to +150° C. The subsidence of the material is very slight over the service life of the vacuum pump  10 . The material properties of the duroplastic named can be improved by tempering the body  21  for several hours. 
     The vane  15  has formed-on terminal parts  22  and  23 , which comprise a high-temperature-resistant thermoplastic such as polyaryletherketone (PEEK), or a material of comparable properties. This plastic, optionally modified with a specially assembled combination of fillers, has a wear resistance and a low coefficient of friction. The terminal parts  22  and  23  are united with the body  21  of the vane  15  by an injection-molding operation. To that end, the body  21 , which is provided with graduatedly recessed end portions  28 ,  29  opposite its long sides  24 ,  25  and its narrow sides  26 ,  27  (see FIG.  2 ), is received in a tool mold and supplemented with the aforementioned thermoplastic to make the shape shown in FIG.  3 . The two terminal parts  22  and  23  of the vane  15  in the process form semicylindrical shells of slight layer thickness, which as a lubricant coating envelop the end portions  28  and  29  of the body  21  and are flush with at least the short sides  26  and  27  of the body  21 . 
     Since the plastics used for the body  21  and the terminal parts  22 ,  23  of the vane  15  cannot enter into a material or molecular engagement, or can enter only into an inadequate material engagement, provisions for attaining a positive engagement between the aforementioned parts and the body of the vane  15  are provided in the above-described embodiment of the vane  15 . To that end, the end portions  28  and  29  of the body  21  have three longitudinally extending, rectilinear grooves  30  of semicircular to three-quarter-circular cross section, which in the injection-molding operation are filled up with the material of the terminal parts  22  and  23 . In this way, detachment or separation of the terminal parts  22 ,  23  from the body  21  of the vane  15  is prevented. 
     In a modification of the above-described production process of the vane  15 , the tempering of the body  21  can also be done, without damage to the terminal parts  22 ,  23 , after the latter have been united with the body. 
     The production process can also be employed in vane cell vacuum pumps in which vanes having only a single terminal lubricant coating are used. 
     The foregoing relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.