Abstract:
A vacuum pump, in particular for brake booster systems in motor vehicles, with a drivable rotor via which a blade in a housing can be set in rotation is proposed. The vacuum pump is distinguished by the fact that the rotor consists of plastic and is formed as one piece.

Description:
RELATED APPLICATIONS 
     The present Application is a divisional application of U.S. patent application Ser. No. 10/211,509, filed Aug. 2, 2002, which is a divisional application of U.S. patent application Ser. No. 09/787,651, which is the National Phase of PCT/EP99/07111, filed Sep. 24, 1999, claiming priority to German Patent App. No. 29823809.8, filed Sep. 30, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     STATE OF THE ART 
     The invention relates to a vacuum pump, in particular for brake booster systems in motor vehicles, according to the preamble of claim  1 . 
     Vacuum pumps of the type addressed here are known. They have a rotor consisting of metal, usually sintered metal, which can be set in rotation by a drive shaft. The rotor disposed in a housing is in engagement with a blade which slides along a contour ring. The rotor consists of several individual parts which are removably connected to one another. It has been shown that the rotor has great inertia due to its weight, whereby the power consumption of the vacuum pump is undesirably high. The rotor furthermore has a massive and expensive structure. 
     It is thus the objective of the invention to provide a vacuum pump of the type stated initially which does not have these disadvantages. 
     SUMMARY OF THE INVENTION 
     For the realization of this objective a vacuum pump is proposed which has the features stated in claim  1 . It is distinguished by the fact that the rotor consists of plastic and is formed as one piece. The rotor can be produced in a simple and cost-effective manner, for example in the injection-molding process, and has, in comparison to the prior-art rotors, a lighter weight. Due to the unipartite form of the rotor, a compact structure is possible so that the space needed for the vacuum pump can be reduced. The power consumption of the vacuum pump is relatively low due to the low inertia of the rotor. 
     An exemplary embodiment of the vacuum pump is preferred in which the rotor has at least one cavity open at the edge. In case of the preferred production of the rotor in the injection-molding process the cavity or cavities can be produced in a simple manner by the laying into the injection mold of correspondingly formed cores. By the introduction of cavities in the rotor, thin walls can be realized, for example outwards up to a slot in which the blade can be displaced. Furthermore, the weight of the rotor, which is already lighter because it consists of plastic, can be reduced. 
     An exemplary embodiment of the vacuum pump is also preferred which is distinguished by the fact that the curve of wall thickness of the rotor is continuous or essentially continuous. That is, the transition between two wall areas having a different thickness is uniform and has no clear discontinuities in wall thickness. 
     An exemplary embodiment of the vacuum pump is also preferred in which the rotor has at least two cavities disposed next to one another, said cavities being separated from one another by a rib. The rigidity of form of the rotor is increased further by the ribbing. The rib formed between two cavities is preferably thinner than the other wall of the rotor. Thereby points of incidence in the transitional area of the rib and a wall of the rotor are avoided. In the case of a preferred exemplary embodiment the thickness of the rib or ribs lies in the range of 1.0 mm to 2.0 mm while the wall thicknesses of the rotor in comparison thereto then preferably lie in the range 1.5 mm to 3.0 mm. 
     A form of embodiment of the vacuum pump is also particularly preferred which is distinguished by the fact that the rotor has at least one closed wall running transversely or essentially transversely to the central longitudinal axis of the rotor. Thereby it can be insured that in the case of a rotor having a cavity no air can reach from the drive side through the rotor into the vacuum pump. Therefore no additional seals are necessary. 
     In the case of a preferred exemplary embodiment of the vacuum pump it is provided that the rotor has an elastic drive element working together with a drive shaft. Through the drive element, which is in engagement with the rotor directly or via a coupling, the torque spikes or oscillations transmitted from the drive shaft coupled to, for example, the internal combustion engine of a motor vehicle, as, for example, occur in the case of direct-injection motors, are damped so that a break of the motor is avoided with high reliability. 
     In the case of an advantageous form of embodiment the drive element consisting, for example of metal, preferably spring metal, is formed as a torsion rod which is twisted under the torque conducted. Thus, for example in the case of an exemplary embodiment in which the rotor is driven by the internal combustion engine of the motor vehicle, any torque spikes, such as occur, for example during the cold start of the vacuum pump and/or in connection with direct injection motors, can be smoothed and clearly reduced. 
     Finally, an exemplary embodiment of the vacuum pump is also preferred which is distinguished by the fact that the drive element projects into a slot in the drive shaft and is displaceably guided in it. Thereby a shift of the axis between the vacuum pump and the drive shaft can be compensated in an advantageous manner without a coupling being needed for that purpose. A compensation of a shift of the axis perpendicularly to the slot can be compensated in the case of a fixed connection of the drive element to the rotor by the bending of the drive element in its elastic range. If the drive element is loosely connected to the rotor so that it can execute a relative motion with respect to the rotor, then a shift of the axis perpendicularly to the slot can be compensated by a tilting of the drive element. 
     According to an extension of the invention it is provided that the rotor can be driven with the aid of the internal combustion engine of a motor vehicle. In the case of another exemplary embodiment of the vacuum pump the rotor can also be driven by a motor, in particular an electric motor, when the vacuum pump is used in a motor vehicle, for example in connection with a brake booster system of the motor vehicle. The motor can, for example, also be operated hydraulically or pneumatically. In the case of an additional variation of embodiment the rotor is optionally drivable by the internal combustion engine or the motor. 
     Additional advantageous forms of embodiment follow from the subordinate claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail in the following with the aid of the drawings. 
     Shown are: 
     FIG. 1 three images of a first exemplary embodiment of a rotor mounted on one side of a vacuum pump; 
     FIGS. 2 to  7  each a lateral view and a frontal view of additional exemplary embodiments of the rotor; 
     FIGS. 8A and 8B each a plan view of the frontal side turned away from the drive of additional exemplary embodiments of the rotor; 
     FIG. 9 a lateral view of an additional exemplary embodiment of the rotor; 
     FIGS. 10A to  10 C each a plan view of the drive-side frontal side of several exemplary embodiments of a rotor driven via a coupling; 
     FIG. 11 a lateral view of a rotor with a drive tongue which is provided with a cap; 
     FIG. 12 a greatly enlarged extract of the rotor according to FIG. 11 in the area of the drive tongue; 
     FIGS. 13 and 14 each a longitudinal section and a plan view of the drive-side frontal view of two exemplary embodiments of a rotor having a drive element; 
     FIG. 15 a plan view of an exemplary embodiment of the drive element; 
     FIG. 16 a plan view of the drive element represented in FIG. 15 in the mounted state; 
     FIG. 17 a greatly enlarged extract of an end area of a fourth exemplary embodiment of the drive element; 
     FIG. 18 an extract of a rotor in the area of the base of a recess for the drive element; 
     FIG. 19 a plan view of the recess represented in FIG. 18; 
     FIG. 20 an extract of an additional exemplary embodiment of a drive element in its end area; 
     FIG. 21 a plan view of the drive-side frontal view of an additional exemplary embodiment of the rotor; 
     FIG. 22 a plan view of the end area of an additional exemplary embodiment of the drive element; 
     FIG. 23 three images of an additional exemplary embodiment of the rotor according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     It is common to each of the exemplary embodiments of the rotor for a vacuum pump described in the following that it is formed as one piece and consists of plastic. The rotor can be produced in an advantageous manner in the injection-molding process and has only a light weight. 
     FIG. 1 shows three images of a first exemplary embodiment of the rotor  1  of a vacuum pump not represented, said rotor being provided with a slot  3  passing through. The slot  3  serves to accommodate a blade not represented which can be displaced within the slot  3  in the direction of the diameter. In the case of this exemplary embodiment the slot  3  is introduced into a frontal face  6  from the frontal side  5  turned away from the drive of the rotor  1 , and therefore is formed open at the edge. A drive shaft which can be energized with a torque usually serves as drive. The outer face of the rotor  1  is formed cylindrically. 
     A first longitudinal section  7  of the rotor formed as the double surface  9  to which a torque transmitted from the drive shaft not represented is applied. Adjacent to the first longitudinal section  7  is a second longitudinal section  11  which has a greater outer diameter than the first adjacent to the first longitudinal section  7 . The second longitudinal section  11  serves as the support  13  of the rotor  1  mounted fluidly here. A sliding support is preferably provided as the type of support. Adjacent to the support  13  is a third longitudinal section  15  of greater diameter which, seen in the radial direction, is penetrated by the slot  3  for the blade. 
     FIG. 2 shows a lateral view and a frontal view of the drive-side frontal side  17  of an additional exemplary embodiment of the rotor  1  which has two supports. A sliding support is also preferred for the support of the rotor on both sides. The second longitudinal section  11  of the rotor  1  forms the first support  13  and a fourth longitudinal section  19  adjacent to the third longitudinal section  15  forms the second support  21 . Both supports  13  and  21  have diameters which are only negligibly, preferably 1 mm to 5 mm, smaller than the diameter of the rotor in the area of the slot  3  for the blade which is introduced in the third longitudinal section  15 . The outer diameters of the supports  13  and  21  are different here and can also be identical in the case of another exemplary embodiment. 
     The support of the rotor  1  on both sides has, with respect to support on one side only, functional advantages as well as advantages in production. The functional advantages consist of the fact that the rotor is not anchored in the support or supports as it has been until now in the case of a rotor supported on one side. Furthermore, a compact structure of the rotor can be realized because both supports can be made to be very short. Furthermore, a rotor supported on both sides has a high stability of form. Due to the high stability of form of the rotor narrow tolerances can be adhered to in the production of the rotor. 
     FIG. 3 shows two images of an additional exemplary embodiment of the rotor  3  which is distinguished from the rotor described with the aid of FIG. 2 merely by the fact that cavities are provided in the rotor for the reduction of its weight. On the rotor  1 &#39;s frontal side  17  facing the drive two cavities  23  are introduced both into the frontal face  24  of the support  13  and on the frontal side  5  turned away from the drive into the frontal face  6 , said cavities having a cross-section in the form of a circular arc, as can be seen from the right image of FIG.  3 . In the left image of FIG. 3 it can be seen that the cavities  23  extend into the central area of the rotor or the third longitudinal section  15 . The wall area remaining between the cavities disposed opposite one another has only a slight thickness. Furthermore, walls are formed by the cavities, for example the outer wall of the rotor in the area of the supports  13  and  21  which have only a slight thickness. Also the walls between the slot  3  for the blade and the cavities are relatively thin. The form of the cavities can vary and can be circular or oval. It is important that thin walls are provided by the introduction of the cavities so that the weight of the rotor can be reduced. The transition between two walls which have a different thickness is preferably continuous. 
     FIG. 4 shows a lateral view and a plan view of the drive-side frontal side  17  of an additional exemplary embodiment of the rotor in which cavities  23  are introduced exclusively on the frontal side  5  turned away from the drive. A circular indentation  25  is introduced into the frontal face  6 , said indentation extending in its central area up to directly at the slot  3 . In the base of the indentation  25  cavities in the form of a circular arc are introduced which extend up to into the second longitudinal section  11 , therefore through the entire rotor up to the first support  13 . It is common to all the exemplary embodiments that cavities are introduced in them, if only from a frontal side, which preferably will be the frontal side  5  of the rotor turned away from the drive side. 
     In the case of the exemplary embodiment of the rotor  1  represented in FIG. 5 the support  13  disposed on the drive side has a diameter which is clearly smaller than the diameter of the rotor  1  in the area of the slot  3 , therefore in the third longitudinal section  15 . It has been shown that a smaller centering diameter of the vacuum pump can be realized by the small outer diameter of the support  13 . Here the second support  21  turned away from the drive side is negligibly smaller in diameter in the area of the blade  3  than the rotor  1 . Here the cavities  23  and the indentation  25  are also introduced into the rotor  1  from the frontal side  5 . 
     FIG. 6 shows two images of an additional exemplary embodiment of the rotor in which the diameter of the second support  21  and that of the third longitudinal section  15 , in which the slot  3  for the blade is introduced, are identical. The advantage therein is that by the indentation  25  introduced into the frontal face  6  on the frontal side  5  and the cavities  23  adjacent thereto an extremely thin and technologically optimal wall thickness in the outer area of the rotor is possible. This lies in the case of a rotor consisting of plastic preferably in a range from 1.5 mm to 3.0 mm. Obviously, it is also possible that both supports  13  and  21  have the same diameter as the rotor  1  in the area of the blade slot. It is also conceivable that only the first support  13  disposed on the drive side has the same diameter as the rotor in the area of the third longitudinal section  15  having the slot  3 , while the second support  21  has a smaller diameter. 
     In the case of the exemplary embodiment of the rotor  1  represented in FIG. 7 the second support  21 , which is provided on the frontal side  5  of the rotor  1  turned away from the drive, has a diameter which is significantly smaller than the diameter of the rotor  1  in the area of its third longitudinal section  15 . In order to provide thin walls two cavities  23  are introduced into each of the frontal faces  24  of the second longitudinal section  11  and the frontal face  26  of the third longitudinal section  15 , said cavities having a cross-section in the form of a circular arc, as can be seen from the right image of FIG.  7 . Due to this structure thin walls can be realized in the area between the rotor&#39;s outer diameter in the area of the third longitudinal section  15  and in the area of the second support  21 . 
     FIG. 8A shows a frontal view of the frontal side  5  turned away from the drive of an exemplary embodiment of the rotor  1 , from which several cavities are introduced. The rotor  1  is formed symmetrically to a transverse axis  27  which runs perpendicularly to the central longitudinal axis  29  of the rotor  1 . Thus merely the cavities above the transverse axis  27  are described in the following. The cavities, three in all,  23 A,  23 B, and  23 C are disposed at a small distance from one another. The cavity  23 B is separated from each of the cavities  23 A and  23 C by a rib  31  which is formed by a wall of the rotor  1  formed as one-piece. The ribs  31  increase the rigidity of form of the rotor  1  and are preferably thinner than the other walls of the rotor in order to avoid points of incidence, therefore tapering or constrictions in the wall areas, in which the ribs merge into the remaining wall areas of the rotor  1 . Due to the arrangement and the structure of the cavities  23 A to  23 C they have in common the form of a circular arc, where due to the V-shaped arrangement of the ribs  31  the central cavity  23 B has a cross-section in the form of a circular arc. Due to the form of the cavities thin walls are also realized here, in particular in the outlying areas of the rotor. 
     The exemplary embodiment of the rotor  1  represented in FIG. 8B is distinguished from that described with the aid of FIG. 8A merely by the fact that here the ribs  31  are disposed at a distance from and parallel to one another. It becomes clear that the arrangement of the ribs can be varied and is determined preferably as a function of the required rigidity characteristics. 
     FIG. 9 shows a lateral view of an additional exemplary embodiment of the rotor  1  from whose frontal sides  17  and  5  cavities  23  or an indentation  25  and cavities  23  adjacent thereto are introduced in the supports  13  and  21 . The cavities  23  extend up to into the central area of the rotor. The rotor  1  has a roofed, closed wall ( 33 ) running essentially transversely to its central longitudinal axis ( 29 ), the curve of said wall being represented with a dotted line. The wall  23  extends, seen transversely to the longitudinal extension of the rotor, over the entire cross-section of the rotor and contains here the first, support  13  facing the drive shaft. Thereby it is ensured that despite the cavities  23  no air can reach into the vacuum pump from the drive side through the rotor  1 . 
     It is common to all the exemplary embodiments of the rotor  1  that the rotor can be set in rotation by the drive shaft either directly or via a coupling. Which of the two drive capabilities comes into use depends, i.e., on the magnitude of the drive moment, the uniformity of rotation of the drive shaft, and any possible shift of axis between the rotor and the drive shaft. In the following two exemplary embodiments of a coupling are described with the aid of FIGS. 10A and 10B, which each show a plan view of the frontal side  17  facing the drive shaft. 
     The coupling  35  represented in FIG. 10A is formed by a disk  37  into whose central area a long rectangular hole  39  is introduced which penetrates the disk  37 . The long hole  39 , into which the drive shaft engages with a correspondingly formed section, makes possible a compensation of a shift of the axis between the vacuum pump and the drive shaft. The disk is preferably formed in such a manner that is can be produced by stamping. The one disk  37  having a circular cross-section has two recesses introduced in the circumference on opposite sides, whereby a bearing surface  41  for each is formed which, as is represented in FIG. 10A, is preferably plane. To transmit a torque from a drive shaft to the rotor  1  each bearing face  41  can be pressed on an opposing surface  43  provided on the rotor  1 . From FIG. 10A it can be seen that the form of the recess is chosen so that despite a small diameter d of the disk  37  the bearing surfaces between the rotor  1  and the coupling are large. Due to the large bearing surfaces the pressure of the surface in these areas is small so that hardening of the coupling, in case it consists of steel or sintered iron, can be omitted in given cases. In the case of a preferred exemplary embodiment it is provided that the ratio of the thickness b and the diameter d of the disk  37  lies in a range of 0.1≦b/d≦0.3. 
     The opposing surfaces  43  are each located on a drive segment  45 A or  45 B connected as one piece to the rotor which projects over the frontal face  24  of the first support  13  in the manner of a dome. The distance between the drive segments  45 A and  45 B as well as their form is chosen so that the coupling is disposed with play between the drive segments and they can be pivoted about their central longitudinal axis over a small angular range. The rotor  1  has in its drive area a very stable form. This became possible in particular since here a very large support length l of the drive segments  45 A and  45 B in the direction of force is realized. Thus a ratio of the length l of the support length l and the diameter D of the rotor  1  is preferably realized which lies in a range of 0.35≦l/D≦0.65. 
     In the exemplary embodiment of the rotor represented in FIG. 10B the drive segments  45 A and  45 B are connected to one another by a closed ring  47  whereby the rigidity of form of the rotor  1  can be increased. Furthermore, the ring  47  can also be used as a support, in particular a sliding support, for the rotor. This form of embodiment of the rotor has very compact structure in the axial direction. 
     In the case of the variation of embodiment of the coupling  35  represented in FIG. 10B a double surface  49  is provided in its central area instead of a long hole, said double surface engaging in a correspondingly formed slot in the drive shaft. Via the double surface  49  the torque is transmitted from the drive shaft to the coupling. 
     FIG. 10C shows a plan view of the frontal side  17  of the rotor  1  described with the aid of FIG. 10A in an additional form of embodiment of a coupling  35  which is formed by a disk  37 ′. The same parts are provided with the same reference numbers so that reference should be made to their description in FIG.  10 A. In the circumference of the disk  37 ′ two identical recesses are introduced whereby for each a plane bearing surface  41  and a lateral wall  46  running perpendicular or essentially perpendicular to the bearing surface  41  is formed. As can be seen from FIG. 10C when the bearing surfaces  41  of the disk  37 ′ lie on the opposing surfaces  43  of the rotor the lateral walls  46  are disposed parallel to a partial wall  48  of the drive segment  45 A or  45 B disposed at a distance, while in the case of the exemplary embodiment represented in FIG. 10A in this position of the coupling the lateral walls  46  are inclined with respect to the partial walls  48  of the drive segments or make an acute angle with them. The transitions  50  between the lateral walls  46  and the circumferential surface of the disk  37 ′ are rounded in the case of this exemplary embodiment and have no sharp edges. If oscillations in the torque should occur in the operation of the vacuum pump, as can arise, for example, in the case of direct-injection motors, which leads a striking of the disk  37 ′ in the area of its transitions  50  to the drive segments  45 A and  45 B, damage of the partial walls  80  of the drive segments consisting of plastic is avoided. 
     FIG. 11 shows, described with the aid of the preceding figures, an exemplary embodiment of the rotor  1  which has a first longitudinal section  7  formed as a double surface  9 . The tongue-like double surface  9  is provided with a vat-like cap preferably consisting of sheet metal, said cap being able to be pressed or clipped onto the double surface. It is also possible that the cap is already laid in on injection of the rotor into the injection mold and thus is connected irremovably to it during its production. The cap  51  protects the double surface  9 , whose strength is sufficient for the transmission of the required torque, against wear which is caused by a relative motion between the double surface and a coupling, or in the case of direct driving of the rotor, i.e., without a coupling, between the double surface and the drive shaft. 
     FIG. 12 shows a greatly enlarged extract of the cap  51  mounted on the first longitudinal section  7  which has at least one pressure point  53  whereby on the inner side of the cap  51  a forward arch is formed which engages form-lockingly in an indentation  55  introduced in the double surface of the rotor [sic]  7 . Thereby the cap  51 , which is elastic and/or consists of an elastic material, can be clipped onto the double surface  5  in a simple manner. 
     FIG. 13 shows a longitudinal section and a plan view of the drive-side frontal side  17  of an additional exemplary embodiment of a rotor  1  which is formed as one piece and consists of plastic. Here the rotor  1  includes an elastic drive element  57  working together with the drive shaft not represented, said drive element consisting, for example, of sheet metal, preferably spring metal. The legs  59  and  59 ′ of the U-shaped drive element  57  are each introduced into a recess  61  in the rotor  1 . The end areas of the two legs are molded in the rotor  1  whereby the drive element  57  is connected irremovably to the rotor  1 . The recesses  61  extend from the frontal face  24  of the first support  13  up to beyond the central area of the rotor, whereby the size of the recesses is chosen so large that the legs  59  and  59 ′ can move with respect to the rotor in the area of the recesses. The section  63  of the unipartite drive element  57  connecting the legs  59  and  59 ′ projects over the frontal face  24 . The arrangement of the recesses  61  is chosen so that the legs  59  and  59 ′ enclose a large area of the slot  3  in which the blade of the vacuum pump is guided. Due to this structure the drive moment here is conducted directly into the areas of the rotor on which the blade of the vacuum pump mounted displaceably in the slot  3  is supported. 
     In the mounted state of the vacuum pump the drive element  57  engages with its section  63  in a slot in the drive shaft. In the case of a rotation of the drive shaft the drive moment is conducted into the rotor via the drive element  57  where the elastic drive element  57  smooths spikes in the torque which may arise. 
     In the case of the exemplary embodiment represented in FIG. 14 the legs  59  and  59 ′ each have in their end areas two pressure points  67  whereby a convex arch is formed on one side of the drive element and a concave arch is formed on the other side. The pressure points in the legs  59  and  59 ′ are introduced on different sides of the drive element so that the convex arches of the legs are also located on different sides of the drive element. The convex arches in the ends of the legs serve for the purpose of clamping the two legs  59  and  59 ′ in the recess  61  so that the drive element  57  is held securely on or in the rotor. The force of compression required to bring the legs into the recesses is relatively slight. So that the section  63  of the drive element  57  engaging in a slot of the drive shaft can also be disposed free of play in this slot, the section  63  has on each side of the drive element two pressure points  67  in whose area the drive element has a concave or convex arch. Through the pressure points  67  introduced on both sides a back and forth striking of the legs in the recesses and the section  63  in the slot of the drive shaft during an oscillating motion of the drive element  57 , for example as a consequence of oscillations in the torque, is prevented since the drive element  57  lies in this area with both sides in the recesses or the slot. 
     FIG. 15 shows a lateral view of an additional exemplary embodiment of an extended drive element  57  which has at each of its ends, on opposite sides, two pressure points  67  whereby concavely and convexly curved areas are formed. With the aid of the elastic drive element  57  a shift a of the axis between the vacuum pump and the drive shaft can be compensated, as can be seen from FIG. 16, without a coupling being necessary for that purpose. As is represented in FIG. 16 the drive element  57  projects for this purpose into a slot  69  of a drive shaft  71 . The other end of the drive element  57  projects into a slot or into a recess in the rotor  1 . Due to this structure a shift of the axis can be compensated in the longitudinal extension of the slot  69  by the drive element  57  being displaced in the slot  69 . A shift of the axis perpendicularly to the longitudinal extension of the slot  69  is achieved in the case of a drive element fixedly connected to the rotor by the fact that it is bent in its elastic range. If the drive element is guided with play in the slot or the recess of the rotor, then it tilts on transmission of the torque to a wall of the slot. In FIG. 16 the beating areas of the drive element  57  on the walls of the slot are indicated in the drive shaft and in the rotor with dots. 
     Alternatively to the exemplary embodiment of the drive element  57  represented in FIG. 15 it can also have, instead of the pressure points  67  in its end area as represented in FIG. 17, ball-like surface sections  73  which are formed on both sides of the drive element  57  by a coating of material or are connected to the drive element  57  as one piece. Thereby it is insured that the drive moment is not transmitted via the edges of the thin drive element  57  but rather via surfaces. 
     FIG. 18 shows an extract of a rotor  1  in the area of a recess  61  for the legs  59  and  59 ′ of the U-shaped drive element in whose base an accommodation  75  for the clamp fastening of the end areas of the legs is provided. As can be seen from FIG. 19, which shows a plan view of the recesses  61  in the rotor, an accommodation  75  is provided for each leg of the drive element  57  which are formed by a stud  77  which has a slot into which a leg of the drive element is pressed. 
     FIG. 20 shows a drive element  57  plugged with play into a recess  61  in the rotor  1 , said drive element being able to compensate a shift of axis by tilting. The drive element  57  is formed on both sides as a ball in its bearing surface, that is, the drive element has at its end areas on both sides a convex arch. It is particularly advantageous in the case of the exemplary embodiment represented in FIG. 20 that through tilting of the drive element in case of a shift of axis no additional supporting force arises but rather that only the torque is conducted into the rotor. The ball-like end areas of the drive element  57  prevent the torque from being transmitted via the edges but rather via ball-like surfaces. 
     The recesses  61  in the rotor  1  accommodating the drive element  57  are preferably structured so that the drive element  57  deforming under pressure comes to bear on a stop before the range of plastic deformation is reached. For this purpose several stop surfaces  77  are provided in the case of the exemplary embodiment represented in FIG. 21 which are disposed on both sides of the drive element  57 . 
     FIG. 22 shows an end area of an exemplary embodiment of the drive element  57  which is doubly angled off here whereby in an advantageous manner it can be adapted to slots of different size in the drive shaft and the rotor. 
     FIG. 23 shows three images of an additional exemplary embodiment of the rotor  1  which has a drive element  57  described with the aid of the preceding figures and several cavities  23  introduced from both frontal sides  5  and  17  which serve to reduce the weight of the rotor. As can be seen from the images of FIG. 23 the walls of the rotor  1  have thicknesses appropriate to plastic. Here the legs  59  and  59 ′ of the drive element  57  are so long that they encircle the slot  3  for the blade completely and reach up to the second support  21 . The end of the legs are completely encircled by the rotor material and thus are irremovably connected to the rotor. Due to this structure the drive moment is conducted directly into the end of the rotor turned away from the drive so that the remaining areas of the rotor  1  are at least essentially free of stress. 
     In summary it remains to be said that by making the rotor from plastic the costs for the vacuum pump can clearly be reduced. The plastic rotor has with respect to rotors consisting of metal only a light weight which is further reduced by at least one cavity. The cavities can be formed in the case of a rotor produced in the injection-molding process by laying cores into the injection mold or after the production of the rotor by subsequent machining. The form, structure, and the number of cavities can vary and is, for example, determined by the drive moment which can be applied to the rotor. Furthermore, each cavity-possessing form of embodiment of the rotor can be provided with reinforcing ribs  31  as are described with the aid of FIGS. 8A and 8B. 
     Since the vacuum pump can also be disposed in areas in which high temperatures prevail, for example in the rotor space of a motor vehicle, the rotor is made of plastic in the case of a preferred exemplary embodiment whose durability can be insured preferably at least to 80° C. Obviously those plastics can also be used which do not lose, at least essentially, their strength characteristics at least up to 140° C. and above. 
     Independently of the structural development of the rotor it can be driven either directly by the drive shaft or via a coupling. The forms of embodiment of the rotor in which no coupling is provided or required are preferred since by omitting the coupling the costs for the vacuum pump can be reduced. In the case of a direct drive of the rotor the form of embodiment is preferred which has a drive element described with the aid of the figures which weakens and smooths spikes and oscillations in torque. Thereby a compactly structured rotor with only slight wall thicknesses can be realized even when the drive moment is high. 
     From the figures it can be seen that merely those forms of embodiment of the rotor which are driven neither via a coupling nor an above-described elastic drive element have a first longitudinal section  7  which is preferably formed as a double surface.