Abstract:
The invention relates to a compact eccentric screw pump including a sliding articulation. The long-lasting operation of the pump is ensured by a plurality of functions. According to the invention, both the reaction pressure resulting from the transport pressure and the concomitant phenomena emerging from the eccentrically rotating rotor and acting on the articulation and the drive are approximately equalized.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application is a continuation of pending International patent application PCT/DE2005/002303 filed on Dec. 14, 2005 which designates the United States and claims priority from German patent application 10 2004 060 222.0 filed on Dec. 15, 2004, the content of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to an eccentric screw pump with a stator with screw-shaped cavity and a screw-shaped rotor eccentrically arranged in said cavity, whose rotor head is connected with a joint, wherein a seal is seated between the rotor and the joint which follows the eccentric rotor movement.  
       BACKGROUND OF THE INVENTION  
       [0003]     An eccentric screw pump is known from DE OS 20 57 860. With this pump a guide disc is seated on the drive shaft. On both of its radial faces this disc is guided on fixed surfaces.  
         [0004]     An abutment ring having a sealing ring is seated in the direction to the drive. This sealing ring abuts the disc and is subjected to pressure by a spring.  
         [0005]     The object of the invention is to shorten the length of an eccentric screw pump, avoid impairment of the articulation and the bearings in compact pumps and to reduce the drive power without impairing the delivery rate of said pump.  
       SUMMARY OF THE INVENTION  
       [0006]     This object is solved with the characteristics of claims  1 .  
         [0007]     Advantageous further developments according to the invention are evident from the characteristics of the sub-claims.  
         [0008]     An exemplary embodiment of the invention more preferably relates to a compact pump. Compact pump because a very short design is achieved with this pump through the use of a so-called sliding joint. The length of the pump housing in this case only amounts to a small part of the total pump length if the otherwise usual lengths when using cardan shafts or electric flexural member connections are compared.  
         [0009]     The invention is based on that the optimum design of the invention is embodied in that the stator region and the joint region are spatially separated from each other through a seal, wherein the rotor head or a rotor extension has at least a diameter reduction in the region between the support ring, which is part of the slide ring seal and the rotor. Through this one or several diameter reductions, deflections created by the rotor are already reduced in the region of the rotor before the seal, as a result of which a more even contact of the slide ring/s on the sealing disc is made possible.  
         [0010]     Depending on the products and delivery rates for which the pump is designed and which materials are employed the diameter and the diameter reductions can be selected differently. Thus the diameter reductions can have a value of 30% to 80% of the value of the diameter of the rotor. As a function of the rotor diameter the diameter reduction can also amount to 30% to 60% more preferably 50%.  
         [0011]     With special (wear-resistant) materials it can be advantageous if not only one diameter reduction but several with different reduction values are provided. Here, the axial distances of the diameter reductions range between the two to tenfold value of the respective diameter reduction. Thus, if the diameter is reduced to 10 mm the next reduction can be arranged at a distance of 20 mm to 100 mm from the first. In special cases the ratio amounts to two to six times the value of the respective diameter reduction.  
         [0012]     To improve the operation of the slide ring seal and its sealing through the bellows the region of the rotor head or the rotor extension on which the bellows or the spring is fastened, can assume a greater value compared with the rotor diameter. The corresponding rotor head or the rotor extension part in this case has 1.2 to 2× the value of the rotor diameter.  
         [0013]     In special application cases of the pump according to the invention a double-sided slide ring seal will be employed to prevent entry of product in the bearing region and entry of lubricant in the pump space.  
         [0014]     With the eccentric screw pump according to the invention the seal is arranged between the pump inlet housing and the pump lantern in which the joint is seated. Under certain preconditions it is advantageous if the width of the constrictions or diameter reductions in the region of the rotor is at least 20% greater than in the region of the sealing disc.  
         [0015]     According to a development of the invention a slide ring each is arranged on both sides of a sealing disc. The sealing disc has at least a radial bore which is connected to the sealing fluid space.  
         [0016]     According to the invention, the rotor extension extends over both regions on the other side of the sealing disc. In this case the diameter of the rotor extension has different sizes in both regions.  
         [0017]     The largest diameter of the rotor extension in both regions corresponds to 1.2 to 3 times the smallest diameter of the rotor extension. On both of its sides the sealing disc is provided with sliding surfaces.  
         [0018]     The slide rings arranged on these sliding surfaces are connected with springs which are supported on the clamping pieces.  
         [0019]     According to the invention, bellows are arranged between the springs and the pump shaft which seal off the sealing fluid space.  
         [0020]     The bellows are further developed in that one side of the bellows is connected with a clamping piece each fastened to the rotor head or rotor head extension.  
         [0021]     The sealing disc is arranged between the pump inlet housing and the pump lantern in which a sliding joint is situated.  
         [0022]     The sliding joint is fastened to the end of the rotor extension.  
         [0023]     In a version of the invention the sliding joint is connected with the drive shaft and consists of two linear units which are arranged  900  offset to each other, wherein each linear unit consists of a profile rail and a carriage each. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]      FIG. 1  longitudinal section of an eccentric screw pump.  
         [0025]      FIG. 2  part view of an eccentric screw pump.  
         [0026]      FIG. 3  part view of an eccentric screw pump.  
         [0027]      FIG. 4  part view of an eccentric screw pump.  
         [0028]      FIG. 5  part view of an eccentric screw pump.  
         [0029]      FIG. 6  part view of an eccentric screw pump. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]      FIG. 1  shows an eccentric screw pump  10  having a rotor/stator region  12 , a pump housing  14  and a drive  16 . At the left end of the eccentric screw pump shown a flange  18  is seated which is clamped to the pump housing  14  via tension rods  20  and thus also firmly connects the stator  22  arranged in-between with the pump housing. The eccentric screw pump stands on the two feet  24  which are connected to the flange and the housing. The cross section of the rotor head  26  or the extension of the rotor  28  is reinforced in the region of the inlet  30 . In this region a slide ring seal  32  with a slide ring  34  is seated on the rotor, which slide ring is in contact with the left of the two support discs  36 ,  36 ′. A seal, in this case a slide ring seal  32  or the slide ring  34  follows the eccentric rotational movement of the rotor  28 . To offset an angular displacement and a possible axial play of the rotor  28  the slide ring  34  is provided with an elastic bellows  38 .  
         [0031]     Between the two support discs  36 ,  36 ′ a centre disc  40  moves in radial direction corresponding to the eccentricity with which the rotor head  26  rotates. To this end, the centre disc  40  sits on a self-aligning roller bearing  42  and thus does not rotate itself but can merely move in axial direction via the spring washers which joins the centre disc, the bearing and the rotor with one another. Although axial rotor displacement is possible, this is prevented by a device  46 . This device consists of several components of which the centre disc  40  assumes an essential role. The width of the centre disc  40  and the width of the pressure medium space  48  are not the same. The width of the pressure medium space  48  is determined by the length of the spacer tube  50  and is deliberately selected so large that between the right support disc  36 ′ and the front end of the centre disc a gap develops in which hydraulic pressure becomes active. The pressure that operates in the pressure medium space and thus between centre disc  40  and support disc  36 ′ depends on the pressure value that is present in the interior of the flange  18  on the pressure side. The value of this pressure is dependent on the back pressure created by the delivery pressure. A diaphragm in the flange  18  picks up this value and transfers it to a fluid in the pipeline  52  which is connected with the fluid in the pressure medium space  48 . Thus, identical pressure conditions exist in the region of the flange  18  at the front end of the free end of the rotor and in the region of the centre disc, i.e. at the joint end of the rotor.  
         [0032]     The equalization of the pressure conditions or an increase of the pressure between the centre disc  40  and the support disc  36 ′ unloads the sliding joint  44  so that it is operated free of pressure. The hydraulic connection between the flange  18  on the pressure side and the pressure medium space  48  is a pipeline  52  which is connected with the pump housing  14  in the region of the support disc  36 . The hydraulic connection between the interior of the pipeline  52  and the pressure medium space exists both via a radial and also an axial bore in the support disc  36 .  
         [0033]     The bearing and the joint region are connected with each other via a bore in the support disc  36 ′. The end of the rotor head  26  directly connected with the sliding joint  44  extends through this bore. The second part of the sliding joint is fastened to the drive shaft  54  via a feather key in a rotationally fixed but axially displaceable manner via the sleeve  56 . Just as the distance between the support disc  36 ,  36 ′ is predetermined by the spacer tube  50 , the distance between the support disc  36  and the housing flange  58  is predetermined by a spacer tube  60 .  
         [0034]      FIG. 2  shows an exemplary embodiment of the invention in which the rotor is driven in clockwise direction. Here, the back pressure acting on the rotor, which could lead to increased loading of the sliding joint  44 , does not develop at the free end of the rotor  28  but in the pump housing in the region of the slide ring seal or the pump outlet. Consequently hydraulic pressure equalization occurs between the part region of the pump housing and the pressure medium space ( 48 ). To this end, only a short U-shaped pipeline  52 ′ is required. This short hydraulic connection, like the connection leading to the free pump end as well, can be established directly in the pump housing wall or the stator via a longitudinal bore to the pressure medium space. The pressure of the product acting on a diaphragm  64  is transmitted via the fluid in the pipeline to the fluid located in the pressure medium space  48 . In contrast with anti-clockwise operation, a narrow gap is formed in this exemplary embodiment between the front end of the centre disc  40  and the support disc  36  so that the rotor is loaded with pressure in the direction towards the sliding joint. The gap length and thus the size of the front end of the centre disc which creates the back pressure here depends on the radial distance of the seals to the longitudinal axis of the rotor  28 . The shorter the distance to the axis of the rotor the greater the effective pressure surface. To prevent that a pressure medium gap is also formed on the other side of the centre disc, the seal itself is selected larger in this case and is arranged with a greater distance from the rotor axis near the outer circumference of the centre disc. In total the surface on which the pressure medium acts on the centre disc must be equal or greater than the total of the surfaces on which the delivery back pressure acts on the rotor.  
         [0035]     The construction of the device  46  is explained with the embodiment shown in  FIG. 3 . Here the centre disc  40  is in the lowermost position. Even the arrangement of the differently dimensioned seals  66 ,  68  alone shows the side of the centre disc on which a gap is formed through the pressure medium. Here, the gap develops between the support disc  36  and the centre disc  40 . The size of the ultimately acting pressure surface  70  is determined by the distance of the seal  66  to the longitudinal axis  76  of the rotor  28  or rotor head  26 . The pressure medium in the pipeline  52 ′ thus exerts pressure on the pressure surface  70 ,  72  via the bore  74  and the pressure medium space  48  and thus equalizes the pressure differential that develops during the pumping process which would otherwise result in an axial displacement or loading of the pump parts connected with the rotor. The pressure surfaces  70 ,  72  of the centre disc  40  and/or the complementary surfaces of the support discs  36 ,  36 ′ themselves are made of wear-resistant material or coated with such.  
         [0036]     The exemplary embodiment according to  FIG. 4  shows a contact pump with a joint, in this special design a sliding joint  92 . Although the sliding joint  92  over a very short distance is able to convert the eccentric rotational movement caused by the rotor into a concentric one, damping of the oscillating rotational movement through a diameter reduction  90  is already brought about in the region of the slide ring seal  88 . This first diameter reduction  90  provides the rotor extension with a higher elasticity characteristic and thus transmits a lesser angular load to the joint  92 . The sealing to be introduced via the radial bore  78  of the sealing disc  82  fills the region of the slide ring seal just as the space  98  in which the sliding joint  92  is arranged. The rotor extension, consisting of the rotor head  26  and the shoulder  96 , extends through the central bore  94  located in the slide ring. The shoulder  96  at its right end is connected with a part of the sliding joint  92  from which the drive force is transmitted to the rotor  28 . In the region of the central bore  94  the rotor head  26  follows the diameter reduction which presents itself as constriction or as a notch. A clamping piece  100 , on which both the spring  102  and also a bellows  104  are held is seated on the rotor head. The bellows  104 , which radially is arranged closer to the pump longitudinal axis than the spring  102  jointly seals the sealing space  80  towards the pump inlet housing  84  with the slide ring  34 .  
         [0037]      FIG. 5  shows an eccentric screw pump which largely corresponds to the exemplary embodiment of  FIG. 4 . The essential difference between this exemplary embodiment  FIG. 5  consists in that the rotor  28  is directly followed by a second diameter reduction  108 . Both diameter reductions  90 ,  108  can have the same width b and the same diameter d. The distance A of the diameter reductions  90 ,  108  in this case corresponds to 3.2× the value of the diameter reduction or the cross section of the corresponding rotor head and rotor extension sections. Depending on which material was selected or is required, the width b of the second diameter reduction  108  can be greater than the width of the diameter reduction  90 . The diameter d of the diameter reductions  90 ,  108  can be just as different. To avoid unnecessary wear the diameter reductions are made in the form of round notches. To improve the sealing function the bellows  104  and the spring  102  are fastened between the diameter reductions on a part of the rotor head  26  whose diameter D corresponds to 0.5 to 2× the rotor diameter.  
         [0038]     If a liquid operating medium other than the sealing is to be employed in the so-called pump lantern in which the sliding joint  92  with its two linear units is arranged, a double-sided slide ring seal will be employed in this case.  
         [0039]     In  FIG. 6 a  seal  110  is shown where on both sides of the sealing disc  82 , slide rings  34 ,  34 ′ are in contact with the sliding surfaces  114 ,  114 ′. The slide ring  34 ′ contacts the right sealing surface of the sealing disc  82  under the pressure of the spring  102 ′. The diameter jump between the rotor head  26  and the shoulder  96  with regard to the fixing and bearing adaptation of the slide ring  34 ′ is offset through the clamping piece  112  which is strengthened in diameter. Both clamping pieces are clamped to the rotor by means of screws. The sliding joint has two linear units offset by 90° consisting of profile rails and associated carriages.