Abstract:
A vacuum pump has a rotor mounted on a rotor shaft and provided with pump active components cooperating with opposite stationary pump active components, fastening element for securing the rotor on the rotor shaft, and a safety element provided in addition to the fastening element for preventing rotation of the rotor and the rotor shaft relative to each other.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vacuum pump. 
     2. Description of the Prior Art 
     State of the Art (DE 20 2005 019 644 U1) discloses a vacuum pump, e.g., a turbomolecular pump having a rotor with rotatable pump active components and mounted on a rotor shaft. The rotatable pump active components cooperate with stationary pump active components, so-called stator. 
     The above-mentioned state of the art discloses securing of a bell-shaped rotor to an end side of a rotor shaft with a screw. To this end, the rotor shaft is provided with a recess in which the rotor journal engages. 
     The drawback of the embodiment disclosed in the state of the art consists in that the rotor can rotate relative to the rotor shaft because the connection of the rotor with the rotor shaft is essentially based on a frictional connection. Because of this, a relative rotation can occur in case of overload. The overload leads to loosening of the connection so that the security of the screw connection is not insured. 
     Loosening of the rotor during operation leads to a total damage of the pump. Prior art (WO 2012/077411 A1) discloses means for preventing rotation of the rotor. According to this state of the art, there is provided a formlocking connection at which the rotor is secured to the end side of the rotor shaft with several screws. This prevents rotation of the rotor relative to the rotor shaft and, thus, disengagement of the rotor from the rotor shaft. However, the drawback of this state-of-the-art embodiment consists in that the mounting of the rotor is rather expensive and a number of high-cost components, screws, is necessary which make the pump more costly. 
     The object of the invention is to provide a vacuum pump in which the above-discussed drawbacks of the prior art solutions are absent. 
     SUMMARY OF THE INVENTION 
     This and other objects of the invention which will become apparent hereinafter are achieved by providing a vacuum pump having at least one gas inlet opening, at least one gas outlet opening, at least one rotor shaft, a rotor mounted on the at least one rotor shaft and having rotatable therewith pump active components arranged opposite stationary pump active components, at least one fastening element extending in an axial direction and provided in or on the rotor shaft for securing the rotor on the rotor shaft, and at least one safety element provided in addition to the at least one element for preventing rotation of the at least one rotor and the at least one rotor shaft relative to each other. 
     The relative rotation-preventing safety element can be easily designed and formed, thus, providing a cost-effective solution of preventing rotation of the rotor relative to the rotor shaft and, thereby, loosening of at least one axially extending fastening element provided in or on the rotor shaft. 
     According to a particularly advantageous embodiment of the present invention, the safety element is provided on the centering journal of the rotor. The centering journal is easily accessible for the centrally arranged fastening element during mounting of the rotor, so that the arrangement of the safety element in the centering journal makes sense. 
     Basically, there also exists a possibility to provide the centering journal on the rotor shaft so that it would engage in a bore formed in the rotor. 
     When the centering journal is provided on the rotor, it engages in a corresponding opening of the rotor shaft. 
     There also exists a possibility that no journal is provided on the rotor and the rotor shaft. In this case, centering can be effected with one or several eccentric shaped elements such as register pins or combined shaped and fastening elements such as close-tolerance screws. 
     According to a particularly advantageous embodiment of the present invention, the safety element is formed as at least one pin engaging through or in the rotor shaft and through or in the rotor. 
     Such a pin can be very cost-effectively formed. In addition, the pin need not meet high requirements to the fitting precision, because the rotation of the rotor relative to the rotor shaft is prevented even if the pin retains the rotor shaft and the rotor with a clearance in some positions. 
     There exists a possibility to arrange the pin radially or axially. Basically, there exists also a possibility to arrange the pin radially inclined. 
     According to a further advantageous embodiment of the present invention, the pin is arranged in a groove or a bore formed in the centering journal of the rotor. The pin engages with one of its ends in the groove or the bore of the rotor and with another end in the groove or the bore of the rotor shaft. 
     According to a further advantageous embodiment of the present invention, the safety element is formed as a friction ring. The friction ring has, as a result of selection of an appropriate material and/or a corresponding surface coating, a higher friction coefficient in comparison with rotor and stator components, higher than the friction coefficient which is directly achieved between respective surfaces of the rotor and the rotor shaft. The friction ring is arranged between the rotor and the rotor shaft, preferably between the end surface of the rotor shaft and the surface of the centering journal of the rotor facing the end surface of the rotor shaft. This embodiment insures that the relative rotation between the rotor and the rotor shaft is prevented, without the need to structurally change the rotor or the rotor shaft. 
     According to a still another advantageous embodiment of the present invention, for increasing the friction coefficient, a coating layer is provided on one or both of connection or bearing surfaces of the rotor and the rotor shaft. With this embodiment, it is possible to prevent a relative rotation between the rotor and the rotor shaft, without using a friction ring. 
     Basically, there exists a possibility to use both the friction ring and providing a coating on one or both connection or bearing surfaces of the rotor and the rotor shaft. 
     A yet another advantageous embodiment of the present invention provides a projection in one of the cooperating contact surfaces of the rotor and the rotor shaft and that forms a plastic deformation in an opposite of the contact surfaces of the rotor and the rotor shaft, with the plastic deformation defining a counter-projection. 
     Such a projection can be formed, e.g., as a so-called punch mark. This punch mark can be formed, e.g., of a rotor material. When the rotor is pressed against the rotor shaft, upon tightening of the fastening element, e.g., a screw, the punch mark plastically deforms the adjacent surface. When the punch mark is provided in the rotor, it plastically deforms the rotor shaft. It is also possible to provide a punch mark in the rotor shaft. Then, the punch mark plastically deforms the rotor. Formation one or several punch marks is advantageous when the rotor and the rotor shaft are formed of different materials. In this case, the punch mark is formed in a material having a greater strength, i.e., a high yield stress Re. In this case, the punch mark is pressed in a softer material. 
     According to a still further advantageous embodiment of the invention, a radially extending projection is provided in the rotor or the rotor shaft, and a recess for formlockingly receiving the projection is provided in another of the rotor and the rotor shaft. 
     There is also exists, e.g., a possibility to provide a radial circular elevation having different heights on the end surface of the rotor shaft. A corresponding counter-recess is then provided on the rotor in which the elevation is received. This likewise prevents relative rotation between the rotor and the rotor shaft. 
     According to a further embodiment, a projection extending in the radial direction is provided in the rotor shaft or the rotor, and in another of the rotor and the rotor shaft, a recess for formlockingly receiving the projection is provided. In this embodiment, it is contemplated, e.g., to provide a projecting nose on the centering journal of the rotor and which is received in a groove in the rotor shaft. The groove defines a stop for the nose, so that the relative rotation of the rotor and the rotor shaft is prevented. 
     The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments of a rotor/rotor shaft connection, when read with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings show: 
         FIG. 1  a longitudinal cross-sectional view of a rotor of a turbomolecular pump and of the drive region of the turbomolecular pump according to the state of the art; 
         FIG. 2 a    a longitudinal cross-sectional view of a rotor/rotor shaft connection with a pin; 
         FIG. 2 b    a perspective view of the rotor and the shaft shown in  FIG. 2 a    in a non-connected condition; 
         FIG. 3 a    a longitudinal cross-sectional view of a rotor/rotor shaft connection according to another embodiment of the present invention; 
         FIG. 3 b    a perspective view of the rotor and the shaft shown in  FIG. 3 a    in a non-connected condition; 
         FIG. 4 a    a longitudinal cross-sectional view of a rotor/rotor shaft connection with a radially inclined pin; 
         FIG. 4 b    a perspective view of the rotor and the shaft shown in  FIG. 4 a    in a non-connected condition; 
         FIG. 5 a    a longitudinal cross-sectional view of a rotor/rotor shaft connection according to a further embodiment of the present invention; 
         FIG. 5 b    a perspective view of the rotor and the shaft shown in  FIG. 5 a    in a non-connected condition; 
         FIG. 6 a    a longitudinal cross-sectional view of a rotor/rotor shaft connection with a radial pin; 
         FIG. 6 b    a perspective view of the rotor and the shaft shown in  FIG. 6 a    in a non-connected condition; 
         FIG. 7 a    a longitudinal cross-sectional view of a rotor/rotor shaft connection with a friction ring; 
         FIG. 7 b    a perspective view of the rotor and the shaft shown in  FIG. 7 a    in a non-connected condition; 
         FIG. 8 a    a longitudinal cross-sectional view of a rotor/rotor shaft connection with a punch mark; 
         FIG. 8 b    a perspective view of the rotor and the shaft shown in  FIG. 8 a    in a non-connected condition; 
         FIG. 9 a    a longitudinal cross-sectional view of a rotor/rotor shaft connection with an axial geometrical safety element; 
         FIG. 9 b    a perspective view of the rotor and the shaft shown in  FIG. 9 a    in a non-connected condition; 
         FIG. 10 a    a longitudinal cross-sectional view of a rotor/rotor shaft connection with a radial geometrical safety element; and 
         FIG. 10 b    a perspective view of the rotor and the shaft shown in  FIG. 10 a    in a non-connected condition; 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a cross-sectional view of a turbomolecular pump according to the state of the art. In the pump, a shaft  232 , which is located in the pump housing  260 , is surrounded by a safety bearing  295 , a radial bearing coil  291 , a radial sensor  293 , and a motor coil  261 . The motor coil  261  cooperates with a motor magnet  262  secured on the shaft  232  with a sleeve  263 , so that upon energizing the motor coil  261 , the shaft  232  rotates with a greater speed. The radial sensor  292  cooperates with a shaft-side radial sensor target  294 . 
     The turbomolecular pump stationary structure is formed of a Holweck stator  228  located adjacent to fore-vacuum and in which helix-shape channels extend that cooperate with a sleeve  227  arranged on the rotor, with the Holweck stator  228  and the sleeve  227  forming a Holweck stage  226 . 
     Further stationary structures are formed by stator discs  212 ,  216 ,  220  and  224  which are provided with blade rings and which are axially spaced from each other by spacer rings  213 ,  217 ,  221 , and  225 . In the axial intermediate spaces between the stator disc  212 ,  216 ,  220  and  224 , pump structures which are formed as rotor blades  211 ,  215 ,  219  and  223  extend. Stationary and rotor-side pump structures cooperate in pairs. The rotor blade  211  and the stator disc  212  form together a first pump stage  210  adjacent to the chamber and operating in high vacuum. Correspondingly, the stator disc  216  and the rotor blade  215  form the following second stage  214 , the stator disc  220  and the rotor blade  219  from the third stage, and, finally, the stator disc  224  and the rotor blade  223  form the fourth stage  222  that provides for transmission of pressure to the Holweck stage  228 . The blades are located in spaced from each other, planes  250 ,  251 ,  252 , and  253 , with the plane  254  forming the connection region of the rotor sleeve. 
     The rotor-side pump structures in form of rotor blades  219  and  223  are provided on the first rotor part  201  and form therewith a one-piece body. The rotor Holweck sleeve is connected with the first rotor part  201 . The first rotor part  201  has a recess  230  in its center. The recess forms a hollow space extending radially and axially from the center, and receives, at least partially, the safety bearing  295 . 
     The first rotor part  201  is connected to the end side  258  of the rotor shaft  232  by a fastening element, e.g., a screw  280 . The shaft  232  has a recess in which a journal  289  of the first rotor part  201  engages. This simplifies the radial positioning. The first rotor part  201  has, in the embodiment shown in the drawing, a retaining section  201   a  that extends axially from the first rotor part  201  in the high-vacuum direction, i.e., in the direction remote from the rotor shaft  232 . A retaining ring  208  is arranged on the retaining section  201   a . The rotor blade  211  is connected with the retaining ring  208 . A further retaining ring  209  and the rotor blade  215  are likewise connected with each other. The retaining rings with rotor blades are conveniently formed. 
     Balancing boreholes  270 , in which balancing weights  271  can be inserted, are provided in the end side retaining section  201   a . In the rotor blades  219  and  223 , also balancing bores  272  can be provided in which balancing weights  273  can be arranged 
     In order to prevent rotation of the first rotor part  201  relative to the shaft  232 , a pin  281  is used as a rotation preventing or safety element and has one of its ends secured in the first rotor part  201  and the other of its ends secured in the shaft  232 . Because the pin  281  is radially spaced from the centrally located screw  280 , it prevents rotation of the first part  201  relative to the shaft  232 . 
       FIG. 2  shows the rotor shaft  232  on which the rotor part  201  is secured with the screw  280 . The pin  281  prevents rotation of the rotor part  201  relative to the rotor shaft  232 . 
     According to  FIG. 2 b   , an axial bore  300  is formed in the central journal  289 . In the shaft  232 , likewise, a bore  301  is formed. The pin  281 , not shown in  FIG. 2 b   , engages with its opposite ends in the bores  300  and  301 . 
       FIGS. 3 a  and 3 b    show the rotor shaft  232  in which again the bore  301  is formed. The centering journal  289  of the rotor part  201  has, instead of a bore, a groove  302 . The pin  281  has one of its ends arranged in the bore  301  of the rotor shaft  232 , and has the other of its ends arranged in the groove  302  of the centering journal  289 . 
     The advantage of the embodiment with the groove  302  in comparison with the embodiment with a bore consists in that the groove  302  permits to build a statically determined fit system, without maintaining precise tolerances. The radial centering of the rotor part  201  and the rotor shaft  232  is effected with the centering journal  289 . Two further bores with a pin, which must be aligned, would negatively influence this solution because of available tolerances and plays. 
     The groove  302  insures that the pin  281  alone provides for the rotatory degree of freedom, while both radial degrees of freedom, which are insured by the centering journal  289 , are not influenced. 
     According to  FIGS. 4 a  and 4 b   , the pin  281  is arranged in the groove  303  of the centering journal  289  of the rotor part  201  with a radial inclination and extends into a radial bore  304  of the shaft  232 . 
     In this embodiment, the pin  281  is secured by a centrifugal force. 
     According to  FIGS. 5 a  and 5 b   , the pin  281  is arranged in the bore  305  of the rotor part  201  so that it is radially spaced from the region of the centering journal  289 . A corresponding counter-bore  306  is provided in the shaft  232 . The bore  305  is provided in the rotor part  201  in contact with the bearing surface of the shaft  232 . 
       FIGS. 6 a  and 6 b    show a further embodiment. The pin  281  extends radially into the rotor centering journal  289 , being arranged in the bore  307  of the centering journal  289 . The other end of the pin  281  engages in a groove  308  in the shaft  232 . 
     Another embodiment is shown in  FIGS. 7 a  and 7 b   . In this embodiment, a friction ring  309  is provided between the centering journal  289  and the end side  258  of the shaft  232 . The screw  280  presses the rotor part  201  to the shaft  232 . The friction ring  309  prevents rotation of the rotor part  201  relative to the shaft  232 . 
     According to the embodiment shown in  FIGS. 8 a  and 8 b   , a punch mark  311  is provided on the contact surface  310  of the shaft  232 . The punch mark lies on the contact surface  312  of the rotor part  201 . The shaft  232  is formed of a stronger material than the rotor part  201 . When the rotor part  201  is connected with the shaft  232  by the screw  280 , the punch mark  311  plastically deforms the contact surface  312  of the rotor part  201 . The interlocking of the punch mark  311  with the deformed contact surface provides a form-locking connection that prevents the rotation of the rotor part  201  relative to the shaft  232 . It is possible to provide several punch marks. 
     According to  FIGS. 9 a  and 9 b   , the shaft  232 , has, as its end, a deformed geometrical safety element  313  projecting in the axial direction, with its counter-part  314  being provided in the rotor part  201 . The projecting in the axial direction, deformed geometrical safety element  313  has two elevations  315   a ,  316   b  engaging in corresponding indentations  316   a ,  316   b . The formlocking connection of elements  313  and  314  prevents relative rotation between the rotor part  201  and the rotor shaft  232 . 
     A still further embodiment of the present invention is shown in  FIGS. 10 a  and 10 b   . In this embodiment, the centering journal  289  has an extending in the radial direction, deformed projection  317  arranged in a groove  318  of the rotor shaft  232 . 
     In the groove  318  of the rotor shaft  232 , there is provided a stop (not shown), whereby rotation of the rotor part  201  relative to the shaft  232  is prevented. 
     It is possible to combine the embodiments shown in  FIGS. 1 through 10  with each other. 
     Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and is not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.