LOBE PUMP

Abstract

The invention relates to a lobe pump with a. a housing (10), having an inlet (11) and an outlet (12) for the medium to be pumped, b. at least one lobe (20), which is mounted in the housing (10) so as to be drivable and rotatable and which has at least two conveying vanes (22) provided with a contour, which lobe conveys the medium to be delivered from the inlet (11) to the outlet (12), c. and one sealing element (30) per lobe (20), which is mounted on a sealing body (42) and runs over the contour of the lobe (20) during rotation of the lobe (20) and performs an outward travel movement from a minimum diameter of the lobe (20) to a maximum diameter of the lobe (20) and an inward travel movement from the maximum diameter of the lobe (20) to the minimum diameter of the lobe (20) on different sides of the conveying vanes (22), wherein d. the distance which the sealing element (30) covers on the inward travel side (221) of the conveying vane (22) during the inward travel movement is smaller than the distance on the outward travel side (222) during the outward travel movement.

Claims

1. A lobe pump, comprising: a housing having an inlet and an outlet for a medium to be pumped, at least one lobe mounted in the housing so as to be drivable and rotatable and which has at least two conveying vanes wherein each of said at least two conveying vanes is provided with a contour, wherein said at least one lobe conveys the medium to be delivered from the inlet to the outlet, at least one sealing element per lobe mounted on a sealing body, wherein the at least one sealing element runs over a contour of the at least one lobe during rotation of the at least one lobe and performs an outward travel movement from a minimum diameter of the at least one lobe to a maximum diameter of the at least one lobe and an inward travel movement from the maximum diameter of the at least one lobe to the minimum diameter of the at least one lobe on different sides of each the at least two conveying vanes, wherein a distance which the at least one sealing element covers on an inward travel side of each the conveying vane during the inward travel movement is smaller than a distance on an outward travel side which the at least one sealing element covers during the outward travel movement.

2. The lobe pump as claimed in claim 1, wherein a contour on the outward travel side has a curvature without inflection point and a contour on the inward travel side has at least one inflection point.

3. The lobe pump as claimed in claim 1 wherein a minimum lobe radius on the inward travel side is reached by the at least one sealing element at an angle of rotation ranging from 20° to 90° from the maximum lobe radius.

4. The lobe pump as claimed in claim 1 wherein a maximum lobe radius is reached by the at least one sealing element, once it has left a minimum lobe radius on the outward travel side, at an angle of rotation ranging from 90° to 160°.

5. The lobe pump as claimed in claim 1 wherein a cross-sectional area of each conveying vane is smaller on the inward travel side than on the outward travel side.

6. The lobe pump according to claim 1 wherein the at least one lobe has two conveying vanes, wherein the contours of the two conveying vanes are point-symmetrical to an axis of rotation.

7. The lobe pump as claimed in claim 1 wherein the at least one sealing body is mounted swivelably within the housing on a locking vane or the at least one sealing body is embodied as a displaceable, spring-loaded slide.

8. The lobe pump as claimed in claim 7, wherein a distance between a bearing point of the locking vane and a point of contact of the at least one sealing element with the conveying vane ranges from is 1.5 times to 2 times as large as a lobe radius.

9. The lobe pump as claimed in claim 7, wherein the locking vane is mounted in the housing on the outlet side and has a swivel arm with a rounded or oval cross-section.

10. The lobe pump as claimed in claim 1 wherein the at least one sealing element has a planar contact surface and at least one adjacent rounded contact portion.

11. The lobe pump as claimed in claim 10, wherein the at least one rounded contact portion extends over a circular arc with a central angle of greater than or equal to 90° and is adjoined by a scraping surface.

12. The lobe pump as claimed in claim 10 wherein an angle (α) between a straight line through a bearing point of a swivel arm and a point of contact of the at least one sealing element and a planar contact surface, is at the maximum lobe radius from 5° to 25°.

13. The lobe pump as claimed in claim 1 wherein at a point of contact of the at least one lobe and the at least one sealing element, an angle (β) between a perpendicular to a lobe surface and a tangent to a direction of movement of the at least one sealing element ranges from 0° to 70° on the inward travel movement and from 0° to 45° on the outward travel movement.

14. The lobe pump as claimed in claim 1 wherein a line of action of the at least one sealing element as a profile of a distance between a point of contact of the at least one sealing element and a bearing point thereof, is different on an outward travel side from the line of action of the at least one sealing element on an inward travel side.

15. The lobe pump as claimed in claim 14, wherein the line of action of the at least one sealing element on the outward travel side has a smaller radius than on the inward travel side.

16. The lobe pump of claim 12 wherein the angle α ranges from 10 to 20 degrees.

17. The lobe pump of claim 12 wherein the angle α ranges from 12 to 18 degrees.

Description

[0022] Exemplary embodiments of the invention are explained in greater detail below with reference to the attached figures, in which:

[0023] FIG. 1—is a sectional representation of a pump in overall view;

[0024] FIG. 2—is a representation of a detail of a lobe with sealing element but without housing;

[0025] FIG. 3—is a sectional representation through a lobe contour;

[0026] FIG. 4—shows a lobe contour according to FIG. 3 with labeled regions;

[0027] FIG. 5—is a partial representation of a sealing element;

[0028] FIG. 6—is an exemplary representation of the sequence of the points of contact over a half-rotation of a lobe with two conveying vanes and clarification of the lines of action; and

[0029] FIG. 7—is a schematic diagram of the interaction of sealing element and lobe.

[0030] FIG. 1 is a schematic sectional representation of a lobe pump 1 with a housing 10, which has an inlet 11 at the top and an outlet 12 oriented substantially perpendicularly to the inlet 11 and arranged, in FIG. 1, on the right-hand side. A lobe 20 is mounted inside the housing 10 so as to be rotatable about an axis of rotation 21. By means of the lobe 20, which has two conveying vanes 22 on mutually opposing sides, the in particular viscous medium, in particular magma in sugar production, is conveyed from the inlet 11 to the outlet 12. The direction of rotation of the lobe 20 is in this case anticlockwise, as indicated by the arrow. The lobe 20 with the two conveying vanes 22 runs in part over a cylindrical housing wall and, together with a sealing element 30, which runs over the outer contour of the lobe 20 during rotation thereof, and a sealing body 42 of a locking vane 40, forms the separator between the inlet side and the outlet side.

[0031] The sealing element 30 is mounted or formed on the sealing body 42 of the locking vane 40, which is in turn mounted in a bearing mounting 41 by means of a swivel arm 43. The locking vane 40 is mounted within the housing 10 on the outlet side so as to be swivelable about a swivel axis and moves as a function of the position of the lobe 20 towards the axis of rotation 21 of the lobe or away from the axis of rotation 21 towards a maximum lobe radius.

[0032] In sectional representation the sealing element 30 lies against a point of contact 24, in three-dimensional configuration along a line of contact 24 against the contour of the lobe 20. In the depicted position according to FIG. 1, the sealing element 30 lies against the maximum lobe radius and is thus swiveled maximally clockwise about the bearing point 41 or the swivel axis through the bearing point 41. When the lobe 20 is rotated anticlockwise to convey the medium to be pumped, the sealing element slides on the surface of the lobe 20 towards the swivel axis 21 and thus travels from a maximum lobe radius towards a minimum lobe radius along an inward travel side 221. Once a minimum lobe radius is reached, the sealing element 30 slides along the contour of the lobe and is urged back outwards in the clockwise direction towards the position depicted in FIG. 1, optionally against a spring force which urges the sealing element 30 together with the sealing body 42 of the locking vane 40 towards the lobe 20. The sealing element 30 thus performs an outward movement or outward travel movement when the sealing element 30 slides along the outward travel side 222.

[0033] The swivel arm 43 may be loaded with a corresponding spring force in the region of the bearing point 41 or swivel axis through the bearing point 41, which spring force brings about pretensioning against movement in the clockwise direction. The sealing body 42 and in particular the sealing surface of the locking vane 40 extends over the entire depth of the housing, such that the lobe 20, together with the sealing element 30 and the sealing body 42, always brings about effective separation between the inlet side and the outlet side.

[0034] FIG. 2 shows a detail representation of lobe and sealing means according to FIG. 1 in a mirror-inverted representation. The direction of rotation of the lobe 20 is indicated by the arrow. In addition to the axis of rotation 21, the lobe 20 has two conveying vanes 22, which are formed point-symmetrically relative to the center point, which is defined by the point of rotation 21 or by the axis of rotation 21. The sealing element 30 has slid along the inward travel side 21 on the outer contour of the first conveying vane 22, wherein, due to the contour of the lobe 20 and the contour of the sealing element 30, there was always linear contact between the sealing element 30 and the lobe 20. The point of contact 24 in FIG. 2 or line of contact 24 advances along the surface of the sealing element 30 as the lobe 20 rotates. The radius RF of the distance of the contact point 24 from the bearing point 41 or the line of contact 24 from the axis of rotation of the swivel arm 43 through the bearing point 41 thus varies during movement of the lobe 20. To minimize friction losses, the orientation of the surface of the sealing element 30 to the contour of the lobe 20 is selected such that, on the outward travel side 222, the angle β between the perpendicular S to the lobe surface and the tangent T to the direction of movement of the sealing element 30 lies between 0° and at most 45° and such that, on inward travel, the angle β between the perpendicular S and the tangent T amounts in particular constructions to between 0° and 70° and otherwise to between 0° and at most 50°.

[0035] FIG. 2 likewise indicates the oval or elliptical cross-section 430 of the swivel arm 43. As a result of the flow-optimized, droplet-shaped or oval embodiment of the swivel arm 43, it is possible, in the case of high rigidity relative to the forces and torques applied by the pumping process, to provide a minimum flow resistance against the mass flow rate of the pumped medium in the outlet region. Since the swivel arm 43 and the overall sealing arrangement is arranged on the outlet side, the differential pressure between the outlet side and the inlet side may be used to increase the contact force between the sealing element 30 and the contour of the lobe 20.

[0036] The distance between the line of contact 24 and the swivel axis 41 of the swivel arm 43 varies depending on the angle of rotation and position of the sealing element 30 on the contour of the lobe 20. The maximum line of action radius R.sub.Wmax is achieved if the rounded contact portion 32 rests with its remotest point against the lobe surface, while the minimum line of action radius R.sub.Wmin is achieved if the end remote from the rounded contact portion 32 comes into contact with the lobe surface.

[0037] FIG. 3 is a schematic sectional representation of a lobe 20, which is mounted so as to be rotatable about the swivel axis 21. The lobe 20 has an inward travel side 221 and an outward travel side 222. The two-vaned lobe 20 has a contour which is point-symmetrical relative to the center point 21, which forms the point of rotation. The maximum lobe radius R.sub.Pmax results from the maximum distance from the axis of rotation 21 to the external contour of the lobe 20. To the right and left of the connecting line between the two maximum lobe radii R.sub.Pmax, it is apparent that the contour of the conveying vane 22 on the outward travel side 222 is further from the connecting line than the contour of the conveying vane 22 on the inward travel side 221. There is thus more material in the region associated with the outward travel side 222. After reaching the maximum lobe radius R.sub.Pmax the sealing element 30 travels, on further rotation of the lobe 20, very rapidly towards a minimum lobe radius, whereas an outward travel movement on the outward travel side 222 takes place significantly more slowly.

[0038] FIG. 4 shows the geometric relationships and the contour of the lobe 20 in greater detail. The represented contour of the lobe 20 is point-symmetrical relative to the center point 21 of the minimum lobe radius R.sub.Pmin. From the maximum lobe radius R.sub.Pmax, the contour falls away steeply on the inward travel side 221 towards the minimum lobe radius R.sub.Pmin. On the inward travel side, the contour curve has an inflection point in the curvature, roughly at the level of half the maximum lobe radius. The contour then runs on to the minimum lobe radius R.sub.Pmin, follows this and then develops into the outward travel side 222, on which the contour experiences curvature without inflection point to the maximum lobe radius R.sub.Pmax.

[0039] If the contour of the lobe is observed over the angle of rotation, the inward travel side 221 extends in this exemplary embodiment over an angle of rotation of around 40°, if the represented position is the starting position. Over an angular range of around 20° the contour follows the minimum lobe radius R.sub.Pmin, in order then to form the outward travel side 222 for an angle of rotation range of around 120°.

[0040] Due to the non-mirror-symmetrical embodiment of the lobe contour relative to the connecting line of the two maximum lobe radii R.sub.Pmax, different inward travel speeds and outward travel speeds are achieved at a constant rotational speed of the lobe 20. Due to the gentle gradient of the contour on the outward travel side, the sealing element 30 and thus also the sealing body 42 are urged outwards significantly more slowly than they can travel inwards. In addition to the improvements with regard to energy consumption, the embodiment of the lobe 20 with a steeper gradient on the inward travel side 221 compared with the gradient behavior on the outward travel side 220 leads to an enlarged pump chamber volume, since the material and volume of the lobe 20 are reduced on the inward travel side. The comparatively larger amount of material on the outward travel side ensures sufficient stability of the lobe 20. Thus, an enlargement of the pump volume may be achieved per revolution of the lobe 20 with constant stability and improved pump behavior.

[0041] FIG. 5 shows an individual representation of a sealing element 30 which can be arranged interchangeably on the sealing body 42. The sealing element 30 has a planar contact surface 31 and an adjacent rounded, distal contact portion 32, which is oriented away from the bearing point 41. The sealing element 30 likewise has a proximal rounded contact portion 33 oriented towards the bearing point 41, which may likewise come into contact with the contour of the lobe 20. As is apparent in FIGS. 1 and 2, the rounded contact portion 32 slides substantially over the contour of the lobe 20 during the inward travel movement, while, once the minimum lobe radius has been reached, the line of contact 24 or the point of contact 24 between the sealing element 30 and the lobe 20 runs over the planar contact surface 31 and advances towards the end 33 of the sealing element 30 of rounded configuration opposite the rounded contact portion 32. The line of contact 24 or the point of contact 24 thus advances along the sealing element 30 over the angle of rotation of the lobe. It has proven particularly advantageous for the small radius 33 to extend over an angle greater than 90°, before the adjoining surface 34 is reached. In this way, the surface 34 acts as a scraper for scraping the medium to be delivered off the lobe.

[0042] FIG. 6 shows the sequence of points of contact over a half-revolution of a lobe with two conveying vanes and thus clarifies the line of action between the extreme values R.sub.Wmax and R.sub.Wmin. The line of action for outward travel on the outward travel side 222 provides first of all that the swivel arm 43 is moved outwards away from the axis of rotation 21 towards the maximum lobe radius. This is shown by the ascending right-hand portion of the diagram in FIG. 6. Once the maximum lobe radius is reached, the line of action advances to the left-hand region of the diagram, this being made clear by the arrow at the upper portion of the diagram extending obliquely leftward. Then the point of contact or the line of contact advances downwards over an enlarged line of action radius on the inward travel side 221, i.e. towards the axis of rotation 21. Once the minimum lobe radius is reached, the line of contact or the point of contact advances back to a smaller radius, which is shown by the lower right-hand half-region of the diagram.

[0043] FIG. 7 is a basic representation of how the point of contact 24 or the line of contact 24 between the sealing element 30 and the contour of the lobe 20 advances between a maximum line of action radius R.sub.Wmax and a minimum line of action radius R.sub.Wmin. To ensure that there is no double contact between sealing element 30 and lobe 20, the sealing strip is inclined at an angle α of between 5° and 25°, in particular between 12° and 18° between the straight line through the point of rotation of the swivel arm 43 and the point of contact of the sealing element 30 and the planar contact surface 31 in the maximum lobe radius position.

[0044] With a lobe pump as described above, it is possible to move the sealing element over the smallest possible path from a maximum lobe radius to a minimum lobe radius, without the sealing element coming away from the lobe surface. The inward arching of the conveying vane on the inward travel side makes it possible to bring about on the one hand different lines of action on inward travel and outward travel of the sealing element and on the other hand a maximum inward travel speed of the sealing element and a reduced outward travel speed of the sealing element. Furthermore, the particular shaping reduces friction between the sealing element and the piston, in particular during the outward travel movement as a result of limitation of the angle between the perpendicular to the lobe and the tangent to the direction of movement of the sealing element.

[0045] A quasi-linear movement of the sealing element is achieved due to the comparatively large radius in the event of swivelable mounting of the sealing body on a swivel arm, this being 1.5 to two times as large as the radius of the lobe.

LIST OF REFERENCE NUMERALS

[0046] 1—Lobe pump [0047] 10—Housing [0048] 11—Inlet [0049] 12—Outlet [0050] 20—Lobe [0051] 21—Axis of rotation of lobe [0052] 22—Conveying vane [0053] 221—Inward travel side [0054] 222—Outward travel side [0055] 24—Point of contact/line of contact [0056] 30—Sealing element [0057] 31—Contact surface [0058] 32—Contact portion [0059] 33—Contact portion [0060] 34—Scraping surface [0061] 35—Sealing strip [0062] 36—Top [0063] 37—Thread [0064] 38—Bottom [0065] 39—Step [0066] 40—Sealing body [0067] 41—Bearing point [0068] 42—Locking vane [0069] 43—Swivel arm [0070] 44—Cavity [0071] 45—Hole [0072] 430—Swivel arm cross-section [0073] B.sub.D—Width of sealing element [0074] R.sub.Pmin—Minimum lobe radius [0075] R.sub.Pmax—Maximum lobe radius [0076] R.sub.Wmin—Minimum line of action radius [0077] R.sub.Wmax—Maximum line of action [0078] S—Perpendicular to the lobe surface [0079] T—Tangent to the direction of movement of the sealing element [0080] α—Angle between contact surface and connecting line bearing point of contact [0081] β—Angle between S and T