PUMP, WOBBLE PLATE PUMP AND CUTTER ARRANGEMENT IN PUMPS Technical field of the invention

The present invention relates to pumps for pumping liquids, and more specifically to pumps that are suitable for pumping liquid containing solid matter and having means arranged therein for cutting the solid matter contained in the liquid. The invention also relates to a cutter arrangement comprising a cutter and a cutting plate, the two cooperating in a pump to provide the cutting function. The invention further relates to a wobble plate pump wherein the cutter arrangement is implemented.

Background of the invention and prior art

The patent literature contains numerous examples of pumps which comprise cutter arrangements, often referred to as chopping pumps. Known chopping pumps notoriously comprise cutting edges formed on a cutter wheel that co-rotates with a pump wheel, in coaxial relation with the pump wheel and a pump wheel's drive shaft. This solution is often employed in connection with submersible radial or centrifugal pumps, comprising an impeller pump wheel which is driven by the drive shaft for rotation in a cavity having an axial inlet and a radial outlet, e.g. A cutter wheel in a cutter arrangement may be formed as an impeller rotating within an inlet opening, or alternatively formed as a propeller rotating on the upstream side of the inlet opening. The cutter wheel typically has one or several cutting edges, running in the first case in an axial direction on the periphery of the cutter wheel, and in the second case running generally in a radial direction of the cutter wheel and on a side thereof facing the inlet opening. In both cases, the cutter wheel cooperates with stationary edges that may be formed integrally in the inlet opening, or on a separate ring insert which is mounted in the opening, e.g. Cutting edges that define an opening formed through a separate cutting plate which is detachably mounted to a pump house are also previously known in connection with propeller cutter wheels mounted on the upstream side of the cutter plate.

One problem encountered with propeller cutter wheels rotating about a stationary cutter wheel centre is the tendency of fibrous material, such as cloth and shreds, to get entangled about the wheel structure, thereby obstructing the liquid flow.

Another type of pump employed in the transport of liquid is the swash plate or wobble plate pump. US 5, 125,809, US 5,454,699, DE 1 090 966 disclose typical examples on this type of pump. Briefly, the wobble plate is a non-rotating pumping member which is driven in nutation via an eccentric journal to a rotating drive shaft. The distal and proximal sides of the wobbling plate provide positive displacement surfaces that propel the liquid through a part-spherical cavity housing the wobble plate. Inlet and outlet are usually axially aligned and tangential to the circular cavity, however separated through a partition that projects radially into the wobble plate, preventing the same from rotation.

The wobble plate pump provides advantageous features, such as a continuous flow also at increasing lifting height. Also, by avoiding cavitation, a wobble plate pump largely maintains its capacity for liquid transport albeit the existence of gas volumes included in the liquid. However, in practise the wobble plate pump has insofar found less implementation as a submersible pump for drainage, sewage water and similar applications. A plausible cause for this is that solids and fibrous matter in the liquid may obstruct the nutation and cause undesired loads upon drive and bearing structures.

The wobble plate pump is not readily fitted with prior art cutter arrangements including rotating cutters in coaxial rotation with a drive shaft. One specific problem in such a combination is the unavoidable sealing of a drive shaft that is extended through the pump house structures to an upstream cutter wheel, resulting in corresponding increase in production costs.

Summary of the invention

The present invention generally aims at providing a pump and cutter arrangement that is adapted for transport of liquids containing solid matter such as cloth, shreds of cloth and other fibrous matter.

An object of the present invention is thus to provide a pump having a cutter arrangement that is less prone to get entangled by shreds and fibrous material contained in an in-homogenous liquid.

Another object of the present invention is to provide a cutter and a cutter plate in a cutter arrangement that is adapted to operate in a wobble plate pump.

Still another object of the present invention is to provide a wobble plate pump having improved capacity for pumping in-homogenous liquid through the incorporation of a cutter arrangement.

One or several of these objects are met in a pump and cutter arrangement as defined in appended claims.

In a first aspect of the present invention, a pump comprises a house having a cavity therein, an inlet leading to the cavity and an outlet leading from the cavity, and in the cavity a pumping member which is operated by a drive shaft for pumping a liquid through the cavity, the drive shaft driven for rotation about a drive shaft axis. A cutter arrangement is comprised in the pump, and arranged upstream of the cavity inlet, the cutter arrangement comprising a cutter having a centre, a centre axis and a periphery, wherein at least one cutting edge is arranged adjacent the cutter periphery, said cutter arrangement further comprising a cutter plate having at least one inlet opening communicating with the cavity inlet and having at least one cutting edge arranged adjacent to the inlet opening, the cutter extending the centre axis through the cutter plate to be operatively connected to the drive shaft. In said cutter arrangement and pump, the cutter is journalled to the drive shaft with the cutter's centre axis at non-coaxial orientation relative to the drive shaft axis, the drive shaft upon rotation moving the cutter eccentrically with respect to the inlet opening, wherein in said eccentric movement the cutting edge formed adjacent to the periphery of the cutter intersects the cutting edge formed adjacent to the inlet opening.

In a preferred embodiment, the cutter is journalled to the drive shaft axis with the centre axis of the cutter forming an acute angle relative to the drive shaft axis. Such embodiment advantageously includes, that the cutter is journalled to the end of the drive shaft via an eccentric bushing that is comprised in a part-spherical member, which in turn is journalled for nutation in a part-spherical cavity in the house. The cutter is then typically mounted centrally onto a distal end of the part-spherical

member. In order to compensate for wear, the cutter is preferably mounted so as to be adjustable along its centre axis.

On a side thereof facing the cutter plate in the cutter and cutter plate arrangement in the pump, the cutter can have a generally concave sectional profile adjacent the cutter periphery, whereas the cutter plate, on a side thereof facing the cutter, has an outer convex region adjacent the inlet opening through the cutter plate. Preferably, the convex region is part of a sphere.

Further in accordance with the first aspect of the invention, a cutter for a cutter arrangement in a pump substantially as explained above has a periphery and a cutting edge, wherein preferably the cutting edge is continuous adjacent the periphery of the cutter, the cutting edge defining a generally concave profile in a section through a centre axis of the cutter, the profile containing a region adjoining the cutting edge at a sloping angle relative to the centre axis.

In one embodiment, the cutter's cutting edge is arranged on the periphery of the cutter, and circular in a planar view. In other embodiments, the cutter's cutting edge is arranged on the periphery of the cutter, however wave-shaped or cog- shaped, in a planar view.

Still further in accordance with the first aspect of the invention, a cutter plate for a cutter arrangement in a pump substantially as explained above has at least one opening for liquid flow and at least one cutting edge adjacent the opening, wherein the opening and the at least one cutting edge are formed in an outer convex region of the cutter plate. The convex region preferably is part of a sphere.

In one embodiment, the cutter plate's cutting edge is arranged on the periphery of the opening, and circular in a planar view. In other embodiments, the cutter plate's cutting edge may be arranged on the periphery of the opening, however wave- shaped or cog-shaped, in a planar view.

In a cog-shaped configuration of the cutter plate's cutting edge, a radius of the convex or part-spherical region is continued substantially through the teeth of the cog-shaped cutting edge.

In yet another embodiment, the cutter plate comprises several cutting edges formed on the peripheries of several discrete inlet openings which are arranged on a circle radially outside a central hole through the cutter plate, symmetrically to the drive shaft axis of a pump wherein the cutter plate is installed.

According to a second aspect of the present invention, a wobble plate pump comprises a house having a part-spherical cavity therein, an inlet leading to the cavity and an outlet leading from the cavity, and in the cavity a wobble plate which is operated by a drive shaft for pumping a liquid through the cavity, and drive means for driving the drive shaft in rotation about a drive shaft axis, wherein a cutter arrangement is arranged on the wobble plate pump upstream of the cavity. The cutter arrangement comprises a cutter having a centre, a centre axis and a periphery, wherein at least one cutting edge is arranged adjacent the cutter periphery, and the cutter arrangement further comprising a cutter plate having at least one inlet opening communicating with the cavity inlet and having at least one cutting edge arranged adjacent to the inlet opening, the cutter extending the centre axis through the cutter plate so as to be operatively connected to the drive shaft. In said cutter arrangement and wobble plate pump, the cutter is journalled to the drive shaft with the cutter's centre axis at non-coaxial orientation relative to the drive shaft axis, the drive shaft upon rotation moving the cutter eccentrically with respect to the inlet opening, wherein in said eccentric movement the cutting edge formed adjacent to the periphery of the cutter intersects the cutting edge formed adjacent to the inlet opening.

In a preferred embodiment, the cutter is connected to a distal end of a hub in the wobble plate, the hub in turn journalled to the drive shaft via an eccentric bushing comprised in the hub, whereby the centre axis of the cutter is oriented at an acute angle relative to the drive shaft axis. Said acute angle may be within a range of 2- 10°, preferably in the range of 2-6°, and most preferred 4° relative to the drive shaft axis. It is likewise preferred, that the cutter is mounted to the wobble plate hub adjustable along its centre axis, in order to compensate for wear.

The wobble plate hub and cutter may be journalled to a tapered end of the drive shaft, via a bushing receiving the tapered shaft's end in an eccentric bore through

the bushing, such as under frictional engagement, e.g. The eccentric bushing advantageously attaches a bearing arrangement non-rotationally to the drive shaft. The bearing arrangement may be realized in form of an angle contact ball bearing, e.g.

The bearing arrangement may be seated in a separable wobble plate hub comprising a proximal hub part connectable to a distal hub part. In this embodiment, a ring-shaped wobble plate is clamped between the hub parts to project radially from a part-spherical periphery of the wobble plate hub. The wobble plate then advantageously consists of two wobble plate halves. The two wobble plate halves can be formed to provide, in clamped position in the hub, an attachment for a ring-shaped seal member that slightly projects in radial direction from the periphery of the wobble plate.

Further features and advantages will come forward from the following detailed description of the invention and preferred embodiments thereof.

Brief description of the drawings

The invention is more closely described below, reference being made to accompanying drawings wherein embodiments of the invention are illustrated as examples. In the drawings,

Figs. la- Id schematically illustrate cutter arrangements in pumps, comprising a cutter which is arranged adjacent to an inlet opening for liquid and wherein the cutter is driven for rotation in non-coaxial relation with the opening;

Fig. 2 is a sectional view schematically illustrating a cutter which is connected to a drive shaft of a pump at acute angles via an eccentric journal, and which is driven in nutation about a drive shaft axis and in non-coaxial relation with an inlet opening for liquid;

Fig. 3 is a corresponding sectional view illustrating a nutating cutter which is journalled to a drive shaft via the hub of a wobble plate in a wobble plate pump;

Fig. 4a shows in a perspective view an eccentric bushing comprised in the hub;

Fig. 4b shows the eccentric bushing in a sectional view through its centre axis;

Fig. 4c is an end view of the eccentric bushing;

Fig. 5 shows in a perspective view a cutter plate comprised in the cutter arrangement;

Fig. 6 shows in perspective view, and on a larger scale, a cutter comprised in the cutter arrangement, and

Fig. 7 illustrates schematically in radial and axial views the movement of a cutter that is brought in nutation.

Detailed description of the invention and preferred embodiments

In the following description, "upper" and "lower" refer to the relative position of elements in drawings as these are oriented for legibility. The expressions "upstream" and "downstream" refer to the relative position of elements related to a flow direction of liquid. Further as used herein, the expressions "distal" and "proximal" explain the position of elements in longitudinal direction through a pump, as viewed from an upper end towards a lower end as illustrated in the drawings. The expressions "nutation, nutating" originates from the Late Latin word nutatio, referring to periodical sway or oscillation in an axis that rotates in a cone- shaped path.

A first aspect of the present invention is illustrated schematically in figs. Ia to Id. Omitted from the schematic representation in figs. Ia- Id are the typical pump components comprising a house having a cavity therein, an inlet leading to the cavity and an outlet leading from the cavity, and in the cavity a pumping member which is operated by a drive shaft in rotation for pumping a liquid through the cavity.

In all drawings, a generally disc-shaped and substantially circular cutter member 1 is non-coaxially connected or journalled to a drive shaft 2. The cutter 1 is arranged adjacent to an opening 3 which is symmetrically arranged relative to the drive shaft,

the cutter driven by the drive shaft for rotation in non-coaxial relation with the opening. The diameters of the cutter 1 and the opening 3 are interrelated such that the cutter, in its movement, opens and successively closes a window 4 which is continuously displaced circumferentially inside the periphery 5 of the opening. The window 4, which has the shape of a crescent in planar view as illustrated in fig. Id, thus moves in a circular path concentrically about the drive shaft axis A. The rotating window 4 creates in a liquid flow a vortex formation F which ensures liquid flow by advantageously avoiding blockage from solid matter contained in the flow.

Thus, fig. Ia shows in solid line the cutter 1 which is connected eccentrically to the end of drive shaft 2, a cutter centre c and a cutter centre axis C being offset from the drive shaft axis A and rotating concentrically about the same. The diametrically opposite position of the cutter is shown with a dash-dot line.

Correspondingly, fig. Ib shows in solid line the cutter 1 which is connected eccentrically to the end of drive shaft 2, achieved through a linkage or deviation 6 to the drive shaft, the cutter centre c and cutter centre axis C being offset from the drive shaft axis A and rotating concentrically about the same. Again, the diametrically opposite position of the cutter is shown with a dash-dot line.

Fig. Ic shows the cutter 1 which is connected eccentrically to the end of drive shaft 2, the cutter centre axis C forming an acute angle α to the drive shaft axis A and rotating concentrically about the same, through a cone-shaped path.

As is readily appreciated from the above and from figs. Ia- Id, the cutter centre axis C runs perpendicularly to the general extension of the cutter 1 , and from its geometrical centre c. In either case, the geometrical centre c and centre axis C are non-coaxial with the drive shaft axis A, providing the cutter an eccentric journal with respect to the drive shaft axis A. In any position of its eccentric movement, the cutter will only partly overlap the inlet opening at a position opposite the window 4.

A realization of the novel cutter arrangement will now be explained with reference to fig. 2. The cutter arrangement of fig. 2 is arranged upstream of a pumping member (which is not shown in the drawing and which may comprise any suitable type of pumping member) which is operable for liquid transport through the driven rotation

of a drive shaft 2. A cutter 1 is journalled to the end of drive shaft 2 via a wobble bearing 7. The wobble bearing 7 has an eccentric 8 which is comprised in a hub of a part-spherical member 9. The part-spherical member 9 is accommodated in a part-spherical cavity 10 which is formed in a house 1 1. A passage 12 is opened through the house for liquid flow to the pumping member that is arranged downstream of the wobble bearing 7. The passage 12 mouths through a house wall

13, via an inlet opening 14 through the wall. The said wall may advantageously be included in a cutter plate 15 which is separately mountable to the house. Arranged upstream of the opening 14, the cutter 1 is non-rotationally connected to a lower or distal end 16 of the part-spherical member 9, and at a centre of that distal end of member 9. The centre axis C of the cutter 1 thus extends through the inlet opening

14, perpendicularly towards the distal end of the part-spherical member 9. On rotation of the drive shaft 2, the part-spherical member 9 and the cutter 1 are imparted a nutating movement resulting from the eccentric journal to the drive shaft 2, via the eccentric 8. In nutation, the centre c of the cutter 1 moves in a circular path concentrically about the drive shaft axis A, as the centre axis C follows a conical path about the drive shaft axis, and at an acute angle α thereto. In other words, the cutter 1 wobbles non-rotationally and non-coaxially but in a circular path about the drive shaft axis A, and about the centre of inlet opening 14 which is coincident with the drive shaft axis.

The cutter arrangement of fig. 2 can be implemented in different types of pumps, such as whirl wheel pumps, centrifugal pumps, half-axial pumps or axial pumps, e.g. In each case, the cutter arrangement will provide an effective cutting function and improved operation, as will be explained further on in the disclosure.

In accordance with a second aspect of the present invention, a cutter arrangement substantially as explained above is implemented in a wobble plate pump. A preferred embodiment of the wobble plate pump having a cutter arrangement will now be described with reference to figs. 3-6 of the drawings.

In a house structure 1 1 of a wobble plate pump, a part-spherical hub 17 is journalled to a drive shaft 2 via an eccentric bushing 8 which is comprised in the hub 17. In the illustrated embodiment, the bushing 8 is non-rotationally connected to the end of drive shaft 2 through a frictional engagement. To this purpose, see

also figs. 4a-4c, the bushing has a tapering bore receiving a tapered drive shaft end. The drive shaft end has a threaded bore in which a bolt 18 is received and effective for securing the bushing 8 to the drive shaft 2. The longitudinal centre of the bore through bushing 8 is inclined at an acute angle α relative to the longitudinal axis of the bushing, resulting in the eccentric journal of the hub 17 and a cutter 1 to the drive shaft 2. In the illustrated embodiment, said angle α is 4°. In other embodiments other angles may be applicable, such as angles α within the range of 2-6°, or even within the range of 2- 10° if required by other structural parameters and operation conditions.

Also comprised in the wobble plate hub is a bearing arrangement 19. The inner race of bearing 19 is non-rotationally secured to the bushing 8, thus in operation co- rotating with the bushing 8 and the drive shaft 2. More precisely, the eccentric bushing 8 is formed in its one end with a radial flange 20 supporting the corresponding end of an inner ball race 21 of the bearing 19. The opposite end of inner ball race 21 is arrested by a washer 22 which is axially secured on the drive shaft by means of a locking ring 23. The flange 20 and washer 22 are both machined to have a non-uniform thickness, and in assembly oriented such that their opposing faces run mutually in parallel and perpendicularly to the longitudinal axes of the eccentric bushing 8. Because of the axial length of bearing 19 being larger than that of the bushing 8, an axial clearance is created between the washer 22 and the adjacent end of the bushing. In result of the bushing 8 being slotted axially from its tapered bore to its outer surface, as illustrated in figs. 4a-4c, the eccentric bushing 8 operates like a clamping sleeve when pressed by the bolt 18 axially and under a slight radial expansion onto the tapered end of drive shaft 2. Correspondingly, the inner ball race 21 is axially arrested between the bushing's flange and the washer, while simultaneously being frictionally connected to the drive shaft in result of the wedging action exerted by the bushing 8.

An outer ball race 24 of bearing 19 is received and secured in the hub 17. More precisely, the outer ball race is accommodated in a cylinder seat which is formed in an upper or proximal part of a separable hub 17, composed of the proximal part 17' and a lower or distal part 17". Bolts 25 hold the hub parts together in a state of assembly. A radial shoulder 26 defines the cylinder seat axially in the proximal direction, the shoulder supporting the proximal end of outer ball race 24 of bearing

arrangement 19. Since, in the illustrated embodiment, the bearing arrangement 19 is an angle contact ball bearing , both axial and radial forces are handled in the bearing arrangement 19. A support ring 27 is interposed between the outer ball race 24 and the shoulder 26. A first end of a tubular seal element 28 made of flexible material is clamped between the support ring 27 and the shoulder 26. The opposite second end of seal 28 is secured in the house 1 1. The seal 28 provides about the drive shaft 2 a bellows-like, liquid-tight enclosure of the hub and bearing arrangement.

From the spherical outer periphery of the hub 17, a ring-shaped wobble plate 29 projects radially into an annular cavity 30 which in turn projects radially into the structure of house 1 1 from the spherical inner periphery of a cavity 31 , said cavity 31 housing the part-spherical hub 17. The ring-shaped plate 29 is comprised of two identical plate halves, each carrying a circular flange 32 rising from its inner periphery. Upon assembly of the hub 17 and wobble plate 29, the flanges 32 are insertable into corresponding circular grooves formed in the meeting sides of the proximal and distal parts of the hub. In their mutually facing sides, the plate halves are shaped to provide in combination a seat for a ring-shaped seal element 33. Seated in the ring-shaped plate 29, the seal element 33 slightly projects outside the wobble plate's periphery, providing this way a sealed separation of an upper pump chamber 30' from a lower pump chamber 30" in the annular cavity 30. Also illustrated in fig. 3 are resilient coatings attached to the opposite proximal and distal annular sides of the pump chambers 30' and 30", outwardly diverging in radial direction.

Similar to known wobble plate pumps the drive shaft 2 will upon rotation impart to the ring-shaped wobble plate 29 a nutation movement in the annular cavity 30, in result of the eccentric journal of the hub 17 to the drive shaft. Liquid that enters into the cavity 30 via an inlet 34 is this way circulated about the hub, in the upper and lower pump chambers 30' and 30" respectively, to be discharged via an outlet 35. Inlet 34 and outlet 35 are separated through a partition wall 36 that projects radially into a slot formed in the ring-shaped plate 29, the partition wall preventing the wobble plate 29 and hub 17 from rotation in the cavities 30 and 31.

In accordance with the present invention the inlet 34 to the pump chambers 30' and 30" is in flow communication with an inlet opening which is located upstream, and which is symmetrically disposed with respect to the drive shaft axis A. The flow communication is realized through a passage 36 that is formed in the house 1 1. Especially, the upstream inlet has at least one central opening 14, the centre of which is co-axial with the drive shaft axis A. The inlet opening 14 is formed through a separate cutter plate 15 that is detachably mountable to the house 1 1.

Further in accordance with the present invention, a cutter 1 is disposed on the upstream side of the inlet opening 14 through the cutter plate 15. The cutter 1 comprises a periphery 37 defining a generally disc shaped body 38. In that side of the cutter which faces the cutter plate in a state of assembly, and in a sectional view through its centre axis C, the cutter 1 has a generally concave profile radially inside of its periphery. The concave profile includes a sloping region 37' adjoining the periphery at an angle which is inclined to the centre axis C. The sloping region 37' may be planar as part of a conical surface, or arcuate as part of a spherical surface. The concave profile essentially provides an acute angle β at the point of a cutting edge running adjacent to or at the periphery, as is better illustrated in fig. 6. In the opposite side, the cutter 1 may advantageously be shaped to have a convex and substantially smooth, cup-shaped profile. In a planar view, the cutter 1 preferably has a circular or substantially circular configuration.

From that side of the cutter 1 which faces the cutter plate, a socket 39 rises concentrically about the centre axis C. The socket 39 reaches through the inlet opening 14 to mate with a cylinder stud 40 projecting centrally from the distal end of that distal hub part 17". A locking bolt 41 is engaged in a central bore in the stud 40, and by means of an adjusting nut 42 engaging the cutter 1 and the bolt, the locking bolt 41 is operable for mounting the cutter to the wobble plate hub 17 while being axially adjustable along its centre axis C.

From the aforesaid it will be understood that the cutter 1 , in operation of the pump, is brought in nutation together with the wobble plate and the wobble plate hub about a common wobble point WP located at the intersection between the drive shaft axis A and the cutter's centre axis C. During its nutation, the cutter 1

performs a cutting action in cooperation with the cutter plate 15, as will be explained hereinafter.

In the following, reference is made specifically to figs. 5 and 6. On its upstream side, facing the cutter 1 in a state of assembly, the cutter plate 15 is formed with a generally convex region 43 containing the inlet opening 14. The convex region is preferably spherical, or more precisely comprising a part of a sphere concentrically about the inlet opening 14. The cutter 1 has a diameter which is adapted to a diameter of the inlet opening 14. The diameter of the cutter may be similar to or slightly less than the largest diameter of inlet opening 14. In result of the eccentric journal of the cutter 1 , a major portion of the cutter's periphery 37 will always overlap the convex or spherical region 43 of the cutter plate, while rest of the cutter periphery and the periphery of the inlet opening define in cooperation a window 4 having the general shape of a crescent, that is continuously displaced circumferentially about the inlet opening in the nutating movement of the cutter 1.

Interacting cutting edges are formed on the cutter 1 and on the cutter plate 15, respectively, at locations that are brought in mutual contact during nutation of the cutter. More precisely, at least one cutting edge 44 is formed near the periphery of the cutter 1. Likewise, at least one cutting edge 45 is formed near the periphery of inlet opening 14. A cutting edge 44 is preferably formed to run continuously about the cutter's periphery, as illustrated in fig. 5. Correspondingly, a cutting edge 45 is advantageously formed to run continuously about the periphery of the inlet opening 14.

Preferably, as illustrated in figs. 3, 5 and 6, a cutting edge 46 runs cog-shaped about the periphery of the inlet opening 14, whereas the cutter 1 has a circular cutting edge 44 running continuous about the cutter's periphery. This embodiment provides the additional advantage, that the cutter 1 is always circumferentially opposed in any position of its nutating movement, i.e. in part opposed from the convex cutter plate region 43 surrounding the inlet opening, and in part opposed from the teeth 47 on the cog-shaped periphery of the inlet opening 14.

Fig. 7 illustrates the eccentric movement of a cutter 1 which is brought in nutation. The lower portion of the drawing is an axial view or end view, from which

construction lines are extended to a radial or sectional view in the upper portion of the drawing. A cutter 1 , having a peripheral cutting edge 44, is shown in four positions of nutation indicated through reference numerals 44 ( 1); 44(2), 44(3) and 44(4), respectively. The geometrical centre of cutter 1 is correspondingly indicated from c( l) to c(4). Arrows E indicate the eccentric movement of the cutter centre c as the cutter 1 moves about the drive shaft axis A, creating a shear between cutting edges 44 on the cutter and 45 on the periphery of the inlet opening 14, respectively. The displacement of the cutter's cutting edge 44 as the cutter centre moves from c(3) to c(4), e.g., is indicated by reference numeral 44(3 to 4). In nutation, a rotating crescent-shaped window 4 is opened for liquid flow, as indicated by the hatched area on the right hand side of the drawing. From the upper portion of the drawing it is apparent, that in nutation, the cutter centre c rotates in a radial plane R perpendicular to the drive shaft axis A, while in an axial plane, the cutter's centre axis C oscillates through the sector of 2α.

Advantages and feasible modifications to disclosed embodiments

Alternatively, a cog-shaped cutting edge may be formed on the periphery of the cutter 1 , whereas the cutting plate has a circular and continuous cutting edge on the periphery of the inlet opening. This embodiment provides substantially the same advantage as the previous one. In both embodiments, the radius of the convex or spherical region 43 of the cutter plate should preferably be continued all through the radial extension of teeth formed on the opening periphery, or transferred, respectively, to cutting edge teeth that are formed on the cutter periphery, if appropriate.

Yet another embodiment foresees that the inlet opening has a continuous cutting edge formed on a wave-shaped periphery, whereas the cutter 1 has a circular cutting edge, or vice versa.

It is further not necessary, however preferred, that the cutting edge of cutter 1 coincides with the periphery thereof. It is also not necessary that the cutter has an arcuately concave region on the side facing the cutter plate. Instead, a cutting edge may be shaped as a cylindrical or conical knife projecting towards the cutter plate from a substantially planar face of the cutter, and if appropriate also at a distance

radially inside the cutter's periphery. As used herein, concave shall thus be understood to encompass both arcuate and angled concave profiles.

It is likewise not necessary that the cutting edge of the cutter 1 is continuous. Instead, multiple cutting edges may be formed on that side of the cutter which faces the cutter plate in a state of assembly. In such case, e.g., the cutter's cutting edges may be arranged like spokes on a wheel, having a radial component of direction, though successively swept into an arc whose major or sole component of direction is circumferential near the cutter's periphery. Alternatively, two or more cutting edges may be arranged in concentric relation within the cutter periphery. The benefit of such modification is an improved grinding effect in the concave region 43 of the cutter plate, when this region is overlapped by the cutter in nutation. Similarly, cutting edges on the cutter plate 15 may extend into the concave region 43 for a grinding effect in cooperation with the at least one cutting edge formed on the cutter 1.

Still another embodiment foresees that multiple discrete inlet ports are arranged on a circle and in overlapping relation with the cutter's periphery. Such inlet ports may have the shape of segments of a circle, or may be circular in shape, e.g., and formed with cutting edges on their peripheries. Similar to the singular inlet opening 14 of the previous embodiments, a central through-hole is in this case arranged for allowing the passage of socket 39 and centre axis C of the cutter 1 through the cutter plate for connection to the wobble plate hub 17. It is however not necessary, in order to benefit from the disclosed solution, that the singular inlet opening 14 or the multiple inlet ports are disposed in perfect symmetry with the drive shaft axis, even if such configuration typically would be preferred.

Instead of an eccentric bushing 8 formed as a cone-clamping sleeve, however preferred, other eccentric journals to tapered and non-tapered drive shafts will of course be possible and within reach of the skilled person. Likewise, instead of the angle contact ball bearing illustrated in fig. 3, however preferred, other bearing arrangements are envisaged including roller bearings or slide bearings, e.g.

Through the novel cutter arrangement, the advantageous features of wobble plate pumps can be exploited for implementation in situations where the wobble plate

pump has heretofore mostly been excluded. Such implementation comprises for example drainage of flooded areas, municipal and industrial waste water, sewage water, etc. The novel cutter arrangement including the nutating cutter also provides, when implemented in any type of pump, an improved capacity through the reduced tendency for shreds and other fibrous matter to get entangled about the cutter. Through an eccentric journal of the cutter is provided a non-static inlet opening for liquid, which continuously moves in circle to escape clogging from solid matter contained in the liquid.