Scroll pump and method of assembling same

#The present invention related to a scroll pump and to a method of assembling a scroll pump.

#A prior art scroll pump 100 is shown in FIG. 3, and comprises a housing 102, a drive shaft 103 having a concentric shaft portion 104 and an eccentric shaft portion 106. The shaft is supported at its concentric portion by bearing means 108, which is fixed relative to housing 102, and is driven by a motor 110 which is mounted in the housing. A second bearing means 112 supports an orbiting scroll 114 on the eccentric shaft portion 106 so that during use rotation of said shaft imparts an orbiting motion to said orbiting scroll 114 which co-operates with a second, fixed, scroll 116 for pumping fluid along a fluid flow path 117 between an inlet and outlet of the pump. The radial clearances between the orbiting and fixed scrolls are accurately controlled so that lubricant is generally not required for scaling. The axial clearances between the scrolls are sealed with tip seals 118. The arrangement means that a scroll pump may be used when it is desired to maintain a dry environment for the pumping media along the fluid flow path. A bellows arrangement 120 isolates the first bearing means and the second bearing means from the fluid flow path, thereby restricting contamination of the pumping media, since the bearing means are generally lubricated. O-ring seals 121 and 122 are disposed between the bellows arrangement and orbiting scroll 114 and housing 102, respectively, to resist the passage of contaminants. The bellows arrangement is sufficiently flexible to allow orbiting motion of the orbiting scroll 114, second bearing means 112 and eccentric shaft portion 106. A counter-weight 123 is provided for balancing the weight of the orbiting components of the pump. The counter-weight is adapted to be fitted about the concentric shaft portion 104 of the drive shaft 103 radially between a flexible portion of the bellows arrangement 120 and the drive shaft 103.

#During assemble, shaft 103, bearing means 108 and motor 110 are mounted relative to the housing 102. Counter-weight 123 is fitted onto the drive shaft 103 and fastened with a radially extending fastener of pin 125. Second bearing means 112 is then fixed to a hub 124 of orbiting scroll 114 with fasteners 126 (only one is shown). A flange 128 of the bellows arrangement is then fixed to the orbiting scroll with fasteners 129 (only one is shown). The orbiting scroll 114, second bearing means 112 and bellows arrangement 120 are then inserted together into the housing in the direction shown by arrow A. This assembly step involves passing the flexible portion of the bellows arrangement over the counter-weight, which is relatively awkward to achieve. When is position, flange 130 of bellows arrangement 120 is fastened to the housing by fasteners 132 (only one is shown). The fastening of fastener 132 is a difficult procedure since access to the fastener is through the relatively small gap G between the orbiting scroll 114 and the housing 102. It will be appreciated that insertion of a tool through gap G whilst also maintaining line of sight of fastener 132 is cumbersome and intricate. Once the tool is inserted through gap G there remains the difficulty of passing the bellows arrangement the latter of which has been expanded radially outwardly by the counter-weight 123.

#In order that the present invention may be well understood, an embodiment thereof, which is given by way of example only, will now be described with reference to the Figures, in which:

#FIG. 1 is a cross-section of a scroll pump;

#FIG. 2 is an enlarged view of part of the scroll pump shown in FIG. 1; and

#Referring to FIG. 1, a scroll pump 10 is shown which comprises a housing 12, a drive shaft 14 having a concentric shaft portion 16 and an eccentric shaft portion 18. The shaft is supported at its concentric portion by first bearing means 20 and is driven by a motor 22, both the first bearing means and the motor being mounted in said housing 12. As shown, the first bearing means comprises two rolling bearings that are spaced apart. A second bearing means 24 supports an orbiting scroll 26 on said eccentric shaft portion 18 so that during use rotation of said shaft 14 imparts an orbiting motion to said orbiting scroll 26 which co-operates with a second, fixed. scroll 28 for pumping fluid along a fluid flow path 30 between an inlet and outlet of the pump 10. The second bearing means 24 comprises two rolling bearings as shown. The radial clearances between the orbiting and fixed scrolls are accurately controlled so that lubricant is generally not required for sealing. The axial clearances between the scrolls are sealed with tip seals 32. The arrangement allows a scroll pump to be used when it is desired to maintain a dry environment for the pumping media along the fluid flow path 30. A bellows arrangement 34 isolates the first bearing means 20 and the second bearing means 24 from the fluid flow path 30, which restricts contamination of the pumping media since the bearing means are generally lubricated. O-ring seals 36 and 38 are disposed between the bellows arrangement and orbiting scroll 26 and housing 12, respectively, to resist the passage of contaminants. The bellows arrangement 34 further serves to provide relative rotational location of the orbiting scroll 26 with respect to the second scroll 28. By virtue of the torsional stiffness of the bellows arrangement, the bellows arrangement limits undesirable travel in to circular translation of the orbiting scroll 26 and thus maintains the correct angular position between the second scroll 28 and the orbiting scroll 26. The bellows arrangement may be formed from any suitable material, such as metallic or plastics material, having a sufficient torsional stiffness so as to maintain the correct angular position between the scrolls, whilst having sufficiently flexible to allow orbiting motion of the orbiting scroll 26, second bearing means 24 and eccentric shaft portion 18.

#A counter-weight 40 for the orbiting scroll 26 is fixed to the drive shaft 14 so as to be adjacent to the orbiting scroll and generally axially aligned with the second bearing means 24. The relatively small distance between the counter-weight 40 and the orbiting scroll 26 allows the counter-weight to be reduced in mass as compared with the prior art, since the distance from the dynamic counterbalance mounted on the motor rotor 22 is increased. Therefore, the total weight of the pump 10 is reduced.

#During assembly, shaft 14, first bearing means 20 and motor 22 are mounted relative to the housing 12. Motor 22 may however be mounted at any suitable stage in the assembly process. As shown, the first bearing means 20 is fixed to housing 12. O-ring 38 is positioned in an accommodating annular recess formed in the housing and then a flange, or flange portion, 48 of the bellows arrangement 34 is fixed relative to housing 12 by fasteners 50. Flange 48 is located in position with dowels 52 before fastening. The orbiting scroll 26 is not fixed to the bellows arrangement 34 when the latter is attached relative to the housing, and therefore it is easier to fasten the first flange 48 of the bellows arrangement 34 to housing 12. The bellows arrangement 34 is itself relatively flexible and the free end (ie. the end thereof to the right in the drawing) can be moved to one side to allow easy access for fastening fastener 50 with a tool.