Pump

Abstract

A pump includes a pump housing (10, 11, 20) that has a circular-cylindrical piston chamber (14), a rotatable and axially movable circular-cylindrical pump piston (40) in said chamber, means (30, 43) for rotationally driving the piston in the chamber, and means (11, 41; 13, 42; 67, 68) for imparting to the piston guided axially reciprocating movement in the piston chamber through the medium of piston rotation, wherein the pump includes lines and valve means for permitting one-way suction and one-way propulsion of pump fluid respectively into and out of the pump chambers between the ends of the piston chamber and the respective adjacent end of the piston. The means for imparting axial reciprocating movement to the piston are adapted to cause the piston to move axially at a constant speed at a constant rotational speed of the piston, at least during the expulsion of pump fluid.

Description

[0001] The present invention relates to a pump of the kind defined in the preamble of Claim 1.

[0002] SE-B-393441 discloses a rotationally driven circular-cylindrical piston, which is received in a corresponding piston chamber in a pump housing. The two end surfaces of the pump housing are mutually symmetrical in relation to a plane normal to the housing axis. The two end surfaces of the piston are generally parallel with one another. The periphery of each end surface is shown to lie in one plane. The end surfaces of the pump housing and the end surfaces of the piston extend obliquely to the piston axis and to tie chamber axis. The length of the piston is such that the peripheral edges of respective end surfaces of the piston run concomitantly in contact with the respective periphery of the two end surfaces of the chamber as the piston rotates, whereby the piston is guided to move alternately forwards and backwards as a result of the co-action between the end surfaces of the piston and the chamber. The pump housing includes two diametrically opposed regions and has midway of its length pipe connectors for the supply and discharge of fluid. The pump piston includes midway of its length two diametrically opposed sides that include recesses which communicate with the inlet and the outlet respectively. A first channel extends between one recess in the piston to one end surface thereof. A second channel extends from the other recess of the piston to its other end surface.

[0003] It is suggested in SE-393441 that the end surfaces are slightly concave, such that the concave sides of respective pairs of adjacent end surfaces of the housing and the piston will face one another.

[0004] However, the flow rate generated by the known pump is highly pulsating and is not positive throughout. Moreover, the pump has serious dead volumes in the end positions of the piston.

[0005] Accordingly, one object of the invention is to provide a pump of the kind indicated above that has a smoother flow rate and a smaller dead volume at the end positions of the piston than known pumps of this kind.

[0006] This object is achieved either fully or partially by means of the present invention.

[0007] The inventive pump is defined in the accompanying independent Claim 1.

[0008] Further embodiments of the invention will be apparent from the accompanying dependent Claims.

[0009] According to the present invention, there is provided a mechanical transfer curve which functions to convert rotary movement of the piston to a constant axial piston speed, during at least its fluid delivery phases, and ensures that the output flow rate of the pump will be constant at a constant speed of piston rotation.

[0010] The inventive concept encompasses several different embodiments.

[0011] In a first embodiment, the end surfaces of the piston are obliquely cut, so that the end surfaces of the piston will co-act with the edge of respective end surfaces of the pump chambers. By special design of the peripheral edge of the piston-ends and the ends of the pump chamber respectively, the axial speed of the piston will be constant for a constant rotational speed of the piston. Both peripheral edges of the piston-ends lie continuously in contact with the end surfaces of the pump chambers as the pump is at work.

[0012] In a second embodiment of the invention, the piston includes a peripherally extending guide groove, and the wall of the pump chamber is provided with a guide pin which engages the guide groove. The end surfaces of the piston and the end surfaces of the chamber are planar and perpendicular to the piston axis. By appropriate design of the guide groove, the piston will move axially at a constant speed for a constant rotational speed. In this latter variant, the end surfaces of the piston and the pump chambers may be designed solely with the aim of being complementary in the end positions of the piston. The end surfaces of the piston and the pump chambers may then, e.g., be planar and perpendicular to the axis of the piston and of the pump chamber.

[0013] The pump may have in both of these variants an internal valve arrangement of the kind disclosed in SE-B-393441, for example. Alternatively, the pump chambers may have separate lines for the infeed and outfeed of the fluid concerned. These lines may include check valves for maintaining one-way flow of the fluid through respective lines. The two outlet lines may take fluid from one source and the two outlet lines may be combined to form a common outlet channel which delivers fluid at an essentially uniform rate of flow when the piston is rotated at a constant speed relative to the pump chamber.

[0014] Naturally, the groove may alternatively be arranged in the wall of the pump chamber in the second variant, and the guide pin fitted on the piston. However, it is preferred at present to provide the groove in the piston.

[0015] In a third variant, the piston may be divided into two axially separated parts which are movable relative to one another axially. These parts are rotated about their respective axes at a constant speed. One of the piston parts may be driven from a motor. The other piston part may be driven by the first part through the medium of a coupling, such as a splines coupling, which while providing a rotation-guided coupling between the piston parts enables said parts to move axially relative to one another. Extending through the cylinder wall is an outfeed port which, during axial displacement of the piston part, is in contact with a fluid delivery groove on the barrel surface of said piston part during the delivery phase of the pump. The groove has an arcuate extension of slightly more than 180°. This provides compensation for the size of the delivery port, so as to ensure that fluid will be delivered throughout a rotational angle of 180° with respect to said piston part, wherewith the piston part has a constant axial speed. The speed of the piston Dart concerned is of less interest during the suction phase. Moreover, suction takes place throughout an angle that is smaller than 180°. A complete suction phase can be ensured whilst the pump rotates over an angle smaller than 180°, by modifying the guide groove.

[0016] Such modification of the guide groove will establish relative axial movement of the piston parts, which is made possible by the splines coupling or some corresponding coupling.

[0017] Thus, in the third variant the extension of the guide groove 67 will enable the piston part to move at a constant speed between its end positions over a rotational angle of precisely 180°, whereafter the piston is moved at a different speed through an angle smaller than 180° between the terminal positions of the piston part during a suction phase. The two piston parts are mutually phase-shifted through 180°.

[0018] The invention will now be described by way of example with reference to the accompanying drawings.

[0019] FIG. 1 is a schematic axially sectioned view of a pump according to the invention.

[0020] FIG. 2 is a sectioned view taken on the line II-II in FIG. 1.

[0021] FIG. 3 is a sectioned view taken on the line III-III in FIG. 1.

[0022] FIG. 4 is an end view of one end surface of the pump piston.

[0023] FIG. 5 is a side view of the end surface shown in FIG. 4.

[0024] FIG. 6 is a schematic axially sectioned view of another embodiment of a pump according to the invention.

[0025] FIG. 7 illustrates schematically a guide groove for the piston of the FIG. 6 embodiment.

[0026] FIG. 8 illustrates schematically a further embodiment of an inventive pump arrangement.

[0027] The pump according to FIGS. 1-5 is based fundamentally on the construction according to SE-B-393441, the contents of which shall be considered as being incorporated in the present document.

[0028] The piston includes a piston chamber defined by a wall 10 which has a circular-cylindrical inner surface, and two end walls 11, 13. The pump housing defines a chamber 14 for a piston 40 that has a circular-cylindrical outer wall, which borders closely on the barrel wall of the housing. The piston 40 can be moved axially and rotated in the chamber 14. The piston 40 has generally parallel end surfaces 41, 42, which define an angle with the plane normal to the axis of the piston 40. The end surfaces 11, 13 are mutually mirror-symmetrical in relation to a plane normal to the axis of a housing.

[0029] The end wall 13 of the housing is formed by a cover member 20, which is detachably connected to the housing wall 10, for instance by a bayonet joint 21. The cover member 20 includes a central axially extending bore 22 for accommodating a corresponding drive shaft 30. That part of the bore 22 which connects with the chamber 14 includes a co-axially extending and circular-cylindrical enlarged part 23 which receives a widened sealing-portion 31 of the shaft 30 and a blade-like shaft portion 32 extending outwardly therefrom and a pair of projections 48 from the piston, as shown more clearly in FIG. 3.

[0030] The barrel surface of the piston 40 includes two diametrically opposed recesses 44, 45. A pump chamber 51, 52 is formed in the pump housing, at respective ends of the piston. A channel or passageway 46 extends from the recess 45 to the pump chamber 51. A channel or passageway 47 extends from the recess 44 to the pump chamber 52. Extending from the end surface 42 of the piston is a central, blind recess 43 for receiving the shaft part 32.

[0031] As will be seen from FIG. 3, the shaft part 32 and the projections 48 are formed so that they will together essentially fill the cross-sectional area of the bore 23. It will also be seen that the ends of the projections 48 are terminated in a plane normal to the piston 40, so that the bore 23 will be generally filled completely by the illustrated components. The end wall 11 of the pump and the end 41 of the piston have essentially complementary surfaces. This also applies to the surfaces 13, 42.

[0032] As will be seen from FIG. 2, the wall 10 has two diametrically opposed connection lines or ports 15, 16 for the infeed and outfeed of fluid respectively. It will also be seen from FIG. 2 that the disc-shaped part 49 of the piston bordering on the recesses 44, 45 have a valve function with respect to the ports or lines 15, 16.

[0033] In a preferred embodiment of the invention, the end surfaces 11, 41; 42, 13 are generally complementary. Moreover, the end surfaces have co-acting peripheries which guide axial movement of the piston and cause the piston to travel at a substantially constant speed at a constant rotational speed. One advantage in this respect is that the pump delivers an even fluid rate of flow.

[0034] It will be seen that during one half of a revolution, respective chambers 51, 52 will function as a suction chamber and an expulsion chamber respectively, and will switch functions during the second half of a revolution.

[0035] FIG. 4 is an end view of the piston-end 41 whose surface S can be considered to be defined by points Pn.

[0036] FIGS. 4 and 5 illustrate an orthogonal co-ordinate system where the Z-axis coincides with the housing axis and the piston axis. The surface S is tangential to the X-Y plane.

[0037] Each point Pn is defined by its angular distance &agr; from X in the XY-plane and its radial distance &agr; from the Z-axis and its height Z above the XY-plane. FIG. 4 shows the channel 46. The surface S is symmetrical in relation to the X-Z plane.

[0038] Each point Pn (X, Y, Z) is defined by the relationship

[0039] Xn=a cos &agr;

[0040] Yn=a sin &agr;

[0041] Zn=a &agr; h/r &pgr;

[0042] where the variable &agr; has the limits 0<a≦r and the variable &agr; has the limits −&pgr;<&agr;≦&pgr;, wherein

[0043] r=the radius of the piston

[0044] h=the length of piston stroke

[0045] &pgr;=constant.

[0046] Each of the housing surfaces 11, 13 and the piston surfaces 41, 42 have this form in the preferred embodiment.

[0047] The surface S is conveniently rounded in its plane of symmetry. The small degree of rounding required in order for acceleration of the piston to be finite in the turning positions of the piston may be adapted between strength requirements on the one hand and the acceptance of fluctuations in respect of the resultant fluctuations in the rate of fluid flow on the other hand. The pump can be used to pump liquid or gas and has universal use. It is also suitable for pumping sensitive fluids.

[0048] The pump components can be injection-moulded with tolerances that avoid the need for separate seals, such as O-rings and the like.

[0049] FIG. 6 illustrates an embodiment in which the barrel surface of the pump piston 40 includes a guide groove 67. In this embodiment, the chamber wall carries a pin 68 which engages the groove 67. The groove 67 is designed to cause the piston 40 to travel axially at a constant speed between its end positions when the rotational speed of said piston 40 is constant.

[0050] It will be seen that in an octagonal three-dimensional co-ordinate system xyz, the groove 67 will follow the barrel surface of the piston 40 and also follow the function z=(&agr;)−h/&pgr;

[0051] FIG. 7 shows the angle &agr; for an arbitrary point p on the curve 67. The length of stroke of the piston, i.e. the distance with the Z-axis between the lowest and highest points of the groove 67 corresponds to the length of stroke h of the piston. The ends of the piston are complementary with the end surfaces of the pump chamber. The dead volume is substantially 0 at the end positions of the piston. In the case of the FIG. 6 embodiment, the end surfaces of the piston 40 are shown to be planar and perpendicular to the piston axis. The end surfaces of the pump chamber are also shown to be planar and perpendicular to the axis of the pump housing.

[0052] The guide curve provides an axial cycle of piston movement with each revolution of the piston, which is beneficial with respect to a vertical arrangement of the kind shown in FIG. 1, although it will be understood that the curve can be modified so as to provide two or more piston movement cycles with each revolution when so permitted by the chosen valve arrangement.

[0053] In the embodiments shown in FIGS. 1-7, the valve function is formed by connection of the inlet and outlet ports or lines 15, 16 with axially extending piston recesses 44, 45 which widen circumferentially, where each widening is slightly smaller than one-half turn around the piston circumference, wherewith the fluid suction and fluid delivery phases are of equal length. There is a risk of irregularities in the rate of flow of the fluid at the end positions of the piston, because the ports 15, 16 that connect with the recesses 44, 45 have a peripheral extension.

[0054] In a further development of the embodiment with a guide pin mounted on the cylinder wall and engaging in a guide groove in the peripheral surface of the piston (or vice versa), the piston is divided axially into two parts 40, 40′ which are coupled via a spline-coupling 81, 82, i.e. a rotationally rigid joint which couples together the piston parts 40, 40′ while enabling said parts to move axially in relation to one another. The piston part 40′ is rotationally driven via a spline-connection 32, 33 from an axially driven shaft 30 which rotates at a constant speed.

[0055] Each piston part 40 has a circumferentially extending guide groove 67 in which a pin 68 engages. The groove 67 has the form shown in FIG. 7 and extends through, or contains, an angle somewhat greater than 180°. The pump also includes an outfeed port or line 16, 16′ which co-acts with a peripheral groove 145, 145′ which widens over a peripheral angle that is slightly greater than 180°. As a result of this widening of the port 16, 16′, fluid can be pumped out during rotation of respective piston parts 40, 40′ through an angle of exactly 180°, wherewith said fluid is transported from respective chambers 51, 52 via a channel 146, 146′ and via the groove 145, 145′ to the port 16, 16′ and through check valves 19 arranged therein. Between the fluid delivery phases, the pin 68, 68′ moves around the groove 67, 67′ through an angle smaller than 180°, wherein the piston 40, 40′ has corresponding suction grooves 144, 144′ which are then held in alignment with the suction ports 15, 15′. The suction grooves 144, 144′ are in contact with respective pump chambers 51, 52 via channels 147, 147′ in the piston 40, 40′. The suction lines connecting with the ports 15, 15′ may also include check valves 19, as shown in FIG. 8.

[0056] Because the groove 67 has a steeper rise in the part that corresponds to the suction groove 144, it is ensured that the piston will be displaced between the end positions despite the groove 144 extending through an angle of less than 180°, wherewith the speeds of the piston parts 40, 40′, however, will be different during the suction phase and the delivery phase respectively. These different speeds result in relative axial movements between the piston parts 40, 40′, permitted by the coupling 81, 82. The length of the pump housing is suitably chosen to ensure that the volumes of the chambers 51, 52 will be generally equal to 0 in the end positions of the piston.

[0057] The two piston parts are conveniently phase-shifted through 180° with respect to their fluid delivery phases, so that their common outflow will be constant.

Claims

1. A pump comprising a pump housing (10, 11, 20), that includes a circular-cylindrical piston chamber (14), a circular-cylindrical pump piston (40) which is rotatable and axially displaceable in the chamber, means (30, 43) for rotationally driving the piston in the chamber, and means (11, 41; 13, 42; 67, 68) for imparting to the piston guided axial reciprocating movement in the piston chamber through the medium of piston rotation, wherein the pump includes lines and valve means for enabling pump fluid to be sucked into and pumped out of the pump chambers in one single direction between the ends of the piston chamber and a respective closely adjacent end of the piston, characterised in that the means for imparting axial reciprocating movement to the piston are adapted to cause the piston to travel axially at a constant speed at a constant piston rotating speed, at least during delivery of pump fluid.

2. A pump according to claim 1, characterised in that the mutually adjacent end surfaces (11, 41; 13, 42) of the piston and the piston chamber respectively, said adjacent end surfaces defining pump chambers (51, 52) with the cylindrical inner wall (10) of the piston chamber, are generally complementary so as to minimise the dead volume of said pump chambers (51, 52).

3. A pump according to claim 2, characterised in that each of the end surfaces is defined by points Pn Q(n, Yn, Zn) in a three-dimensional orthogonal co-ordinate system X, Y, Z, wherein Z lies in the chamber axis and the piston axis, and wherein the end surface is tangential to the XY-plane of the system

Xn=a cos &agr;

Yn=a sin &agr;

Zn=a &agr; h/r &pgr;

where the variable &agr; denotes the radial distance of the point from the Z-axis, and the variable &agr; denotes the angular distance of the point from the XZ-plane about Z

0<a≦r

−&pgr;<&agr;≦&pgr;,

wherein

r=the radius of the piston

h=the length of piston stroke

&pgr;=constant.

4. A pump according to claim 1 or 2, characterised in that the barrel wall of the piston (40) or of the chamber (14) includes a guide groove (67); in that the barrel wall of the chamber or of the piston (40) carries a guide pin (68) that engages in the groove (87); and in that the groove (67) is designed to cause the piston to move axially at a constant speed between its end positions at a constant rotational speed of the piston.

5. A pump according to any one of claims 1-4, characterised in that a drive shaft (30) co-axial with the piston extends along a channel (22, 23) through a housing wall (20) and has a non-round dogging part (32) which engages in a dogging opening (43) in the adjacent end of the piston (40); in that the channel (22, 23) has adjacent the piston a widened part which receives a longitudinal section of the non-round dogging part on the one hand and filling bodies (48) disposed on the piston on the other hand, wherein the dogging part (32) and the filling bodies (48) fill the cross-sectional area of the widened part (23).

6. A pump according to any one of claims 2-5, characterised in that the shaft (30) has a widened part (31) which fills an axially outer part of the widened portion (23) of the channel; in that the filling bodies (48) are terminated in a plane normal to the axis of the piston (40) and fill the remaining part of the widened portion of the channel together with the dogging part (32) when the adjacent pump chamber (52) has a minimised volume.

7. A pump according to any one of claims 4-6, characterised in that the piston (40) has rotationally symmetrical ends.

8. A pump according to claim 7, characterised in that the ends of the piston and of the pump chambers are generally planar and perpendicular to the axis of the piston.

9. A pump according to any one of claims 1-8, characterised by an inlet port or line (15) and an outlet port or line (16) which connect through the pump chamber wall (10) in two diametrically opposed regions of the piston chamber (14) in a longitudinal centre region thereof, two diametrically opposed recesses or cavities (44, 45) in the longitudinal centre region of the piston, a first channel (46) in the piston between its latter recess (45) and its one end surface (41), a second channel (47) in the piston between its second recess (44) and its second end surface (42).

10. A pump according to any one of claims 1, 2, 4-8, characterised in that the piston is divided into two axially separated parts (40, 40′); in that each of said piston parts has an own device (67, 68; 67′, 68′) for translating rotational speed to axial movement speed; in that each piston part has a first groove (144, 144′) which is in contact with a fluid inlet port (15, 15′) and has a peripheral widening of less than 180°; in that each piston part has a second groove (145) which is in contact with an outlet port (16, 16′) and which has a peripheral widening of more than 180°, so that fluid will be delivered through a rotational angle of 180°; in that the guide groove (67) is adapted to cause the piston to move at a constant axial speed during the pump delivery phase at a constant speed of piston rotation; and in that the piston parts (40, 40′) are adapted to be rotationally driven at a constant and similar speed of rotation and are adapted for axial movement in relation to each other.