SCROLL PUMP CRANK SLEEVE

Abstract

The invention provides a crank sleeve for a scroll pump. The crank sleeve has a longitudinal axis and is configured to provide a radially extending crank offset for imparting an orbital path on an orbital scroll of the scroll pump. The crank sleeve further comprises an integrally formed counterbalance for reducing pump vibration extending radially in a direction substantially opposite to the crank offset.

Claims

1. A crank sleeve for a scroll pump, said crank sleeve having a longitudinal axis and being configured to provide a radially extending crank offset for imparting an orbital path on an orbital scroll of the scroll pump, said crank sleeve further comprising an integrally formed counterbalance for reducing pump vibration extending radially in a direction substantially opposite to the crank offset.

2. The crank sleeve according to claim 1, the crank sleeve comprising a first portion which is eccentric and, in use, provides the crank offset.

3. The crank sleeve according to claim 2, the crank sleeve comprising a second portion, longitudinally offset from the first portion, which comprises the counter balance.

4. The crank sleeve according to claim 2, the crank sleeve further comprising a conduit for receiving a drive shaft of the scroll pump.

5. The crank sleeve according to claim 4, the conduit having a length in longitudinal direction that is longer than the first portion.

6. The crank sleeve according to claim 4, wherein the ratio of the length of the conduit defined by the first portion of the crank sleeve to the full length of the conduit is from about 1:1.3 to about 1:3, preferably from about 1:1.5 to about 1:2.5.

7. The crank sleeve according to claim 1, wherein the crank sleeve has an external surface coupled to a bearing unit, preferably the inner race of a rolling element bearing.

8. The crank sleeve according to claim 1 wherein the crank sleeve is machined from a single piece of material.

9. A scroll pump comprising a crank sleeve according to claim 1.

10. The scroll pump according to claim 9 wherein the crank sleeve is coupled to an orbiting scroll bearing and biases the orbiting scroll bearing in a fixed scroll direction.

11. The scroll pump according to claim 10 wherein the crank is received on a drive shaft of the scroll pump, said drive shaft comprising a non-permanent fixation for attaching the crank sleeve to the drive shaft, said non-permanent fixation providing said bias to the orbiting scroll bearing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the following disclosure, which is given by way of example only, reference will be made to the drawings, in which:

[0020] FIG. 1 is a schematic representation of a prior art scroll pump crank sleeve and counterbalance; and

[0021] FIG. 2 is a schematic representation of a crank sleeve according to the invention.

DETAILED DESCRIPTION

[0022] The present invention provides a crank sleeve for a scroll pump, preferably a vacuum scroll pump.

[0023] Referring to FIG. 2, the illustrated crank sleeve (4) is an eccentric member with a centre of rotation parallel to, but radially offset from, the axis of rotation (X) of the drive shaft (5). The eccentricity of the crank sleeve (4) provides a crank offset which, in use, imparts an orbital path on the orbital scroll of the scroll pump (not shown). The crank offset extends in a first radial direction substantially perpendicular to the axis of rotation of the drive shaft (5) and/or the crank sleeve (4).

[0024] The illustrated crank sleeve (4) further comprises an integrally formed counterbalance (6) for reducing pump vibration. The counterbalance (6) extends radially in a direction substantially opposite to the crank offset. The counterbalance (6) typically extends further radially than the crank offset. The mass and geometry of the counterbalance (6) will be determined by the mass and geometry of the orbiting scroll and the extent of the crank offset.

[0025] Advantageously, the illustrated crank sleeve (4) removes the need for a key and provides intrinsic alignment of the orbiting mass and the counterbalance, reducing the number of parts and easing manufacture.

[0026] The illustrated crank sleeve (4) comprises a first portion (7) defined by an outer surface (8) which engages the inner race (9) of the bearing unit (10). A second portion (11) is defined by the distally extending remainder of the crank sleeve (4), including the counterbalance (6). The first portion (7) is eccentric and provides the crank offset. The first (7) and second (11) portions are integrally formed. The illustrated crank sleeve (4) is made (e.g. machined) from a single piece of material, in this instance mild steel. Typically, the crank sleeve (4) is formed by machining.

[0027] As illustrated, the crank sleeve (4) comprises a conduit (13) for receiving the drive shaft (5) of the scroll pump. The conduit comprises an inner surface (12) which, in use, engages an outer surface of the drive shaft (5). Typically, the inner surface (12) of the conduit is configured to circumferentially engage with the outer surface of the drive shaft (5) along substantially the entire length (L) of the conduit (13).

[0028] An axial thrust is provided to the crank sleeve (4) by an orbiting scroll biaser (14). The scroll biaser (14) is located at a distal end of the drive shaft (5). The thrust provided by the biaser (14) may be varied to ensure an adequate seal is obtained without damaging the scroll components.

[0029] The illustrated orbiting scroll biaser (14) comprises an abutment surface (15) which engages the crank sleeve (4). The abutment surface (15) of the orbiting scroll biaser (14) extends in a plane transverse to the axis of rotation of the drive shaft (5) and engages with an abutment surface (16) provided on the crank sleeve (4). The abutment surface (16) of the crank sleeve is substantially parallel to the abutment surface (15) of the orbiting scroll biaser (14). The illustrated crank sleeve abutment surface (16) is located in the second portion (11) of the crank sleeve (4). The axial thrust provided by the orbiting scroll biaser (14) is arranged to securely push the orbiting scroll into contact with the fixed scroll.

[0030] The crank sleeve (4) transmits the axial thrust to the orbiting scroll via the bearing unit (10). In this regard, the crank sleeve (4) comprises a second abutment surface (17) extending transverse to its axis of rotation, which, in use, engages a bearing unit (10). The second abutment surface (17) is typically located in the second portion (11) of the crank sleeve (4).

[0031] The force exerted by the orbiting scroll biaser (14) should be sufficient to overcome the pressure loads generated in use of the scroll pump that will tend to force the fixed and orbiting scroll apart. The force provided by the orbiting scroll biaser (14) should be sufficient to balance this pressure loading and cause sufficient engagement between the base and opposed tip faces of the scrolls to provide a reliable seal.

[0032] The crank sleeve (4) is configured to reversibly couple to the drive shaft (5) and bearing unit (10), for instance using an interference fit. In the illustrated example, the bearing unit (10) is a ball bearing.

[0033] It will be appreciated that various modifications may be made to the embodiments shown without departing from the spirit and scope of the invention as defined by the accompanying claims as interpreted under patent law.

[0034] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0035] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.