A prior art scroll compressor, or pump, 10 is shown in FIG. 7. The pump 10 comprises a pump housing 12 and a drive shaft 14 having an eccentric shaft portion 16. The shaft 14 is driven by a motor 18 and the eccentric shaft portion is connected to an orbiting scroll 20 so that during use rotation of the shaft imparts an orbiting motion to the orbiting scroll relative to a fixed scroll 22 for pumping fluid along a fluid flow path between a pump inlet 24 and pump outlet 26 of the compressor.

The fixed scroll 22 comprises a scroll wall 28 which extends perpendicularly to a generally circular base plate 30 and has an axial end face, or surface, 29. The orbiting scroll 20 comprises a scroll wall 34 which extends perpendicularly to a generally circular base plate 37 and has an axial end face, or surface, 35. The orbiting scroll wall 34 cooperates, or meshes, with the fixed scroll wall 28 during orbiting movement of the orbiting scroll. Relative orbital movement of the scrolls causes a volume of gas to be trapped between the scrolls and pumped from the inlet to the outlet.

A scroll pump may be a dry pump and not lubricated. In this case, in order to prevent back leakage, the space between the axial ends 29, 35 of a scroll wall of one scroll and the base plate 30, 37 of the other scroll is sealed by sealing arrangement, which generally comprise tip seals. The tip seals close the gap between scrolls caused by manufacturing and operating tolerances, and reduce the leakage to an acceptable level. However, tip seals suffer from the generation of tip seal dust and require a period of bedding in before achieving operational requirements. Further, in a normal scroll pump, tip seals require replacement at regular intervals after they become worn. An enlarged cross-section through a portion of the fixed scroll 22 showing the tip seal 36 in more detail is shown in Figure 6. The tip seal 36 has an aspect ratio of axial length to radial width which is 1 : 1. That is, the radial width of the tip seal is equal to the axial length of the tip seal so that as shown in cross-section in Figure 6 the tip seal has a square cross-section. Accordingly, the tip seal is relatively stiff in a radial direction.

The tip seal is located in a channel 38 at the axial end of the fixed scroll wall. There is a small axial gap between an axial end of the tip seal 36 and the base of the channel 38 so that in use fluid occupying the gap forces the tip seal axially towards the base plate 37 of the orbiting scroll. Accordingly, the tip seal is supported on a cushion of fluid which serves to urge the seal towards an opposing seal surface. Additionally, and although not shown in Figure 6, there is a radial clearance between the tip seal and the inner radial facing surfaces of the channel. During relative orbiting motion of the scrolls, the seal is urged against one inner radial surface for part of its motion and against the other inner radial surface for another part of its motion. As the seal moves between these positions, leakage is increased because there is a leakage path formed from one side of the seal to the other side of the seal. The tip seal 36 which is relatively stiff in the radial direction changes position in the channel relatively slowly thereby increasing leakage.

The present invention seeks at least to mitigate one or more of the problems associated with the prior art.

The present invention provides a scroll compressor comprising:

an orbiting scroll having an orbiting scroll wall extending axially from an orbiting scroll plate towards a fixed scroll;

a fixed scroll having an fixed scroll wall extending axially from a fixed scroll plate towards the orbiting scroll; and an axially extending drive shaft having an eccentric shaft portion so that rotation of the eccentric shaft portion imparts an orbiting motion to the orbiting scroll relative to the fixed scroll;

wherein an axial end portion of the orbiting scroll wall has a first seal for sealing between the orbiting scroll wall and the fixed scroll plate, and an axial end portion of the fixed scroll wall has a second seal for sealing between the fixed scroll wall and the orbiting scroll plate; and

wherein the first seal or the second seal has an aspect ratio of axial length to radial width which is 1 : 1.25 or greater.

Other preferred and/or optional aspects of the invention are defined in the accompanying claims.

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 accompanying drawings, in which:

Figure 1 shows a section through part of a fixed scroll of a scroll compressor;

Figures 2 and 3 show enlarged views of a tip seal as shown in Figure 1 in first and second locations in a channel;

Figures 4 and 5 show a plan view of part of a prior art scroll wall and seal and a plan view of part of a scroll wall and seal according to an embodiment;

Figure 6 is a section through part of a fixed scroll of a prior art scroll compressor; and

Figure 7 shows a schematic diagram of a prior art scroll compressor.

A section through part of a fixed scroll 50 is shown in Figure 1. The fixed scroll 50 forms part of a scroll compressor embodying the invention which is similar in construction and operation to the prior art scroll compressor shown in Figure 7, except for those aspects shown in Figures 1 to 5 and described below. For the sake of brevity therefore, the structure and operation of the whole scroll compressor will not be described again in detail.

The fixed scroll 50 shown in Figure 1 comprises a fixed scroll plate 52 and a fixed scroll wall 54 extending generally perpendicularly therefrom typically in the form of an involute. Alternatively, in scroll pumps which are multi-start, the scroll wall may form an involute over only a portion of its length, usually its radially inner portion. The axial end of the fixed scroll wall comprises a channel 56 in which a tip seal 58 is located for sealing against an orbiting scroll 60 shown in Figures 2 and 3.

The description herein refers to the tip seal of the fixed scroll. It will be appreciated however that additionally or alternatively a similar tip seal arrangement may be provided for the orbiting scroll.

When the tip seal is installed, the tip seal 58 has an aspect ratio of axial length to radial width which is greater than 1 : 1.25. That is, where the ratio is x (axial length) :y (radial width), and x equals 1, y is 1.25 or greater. As shown in Figures 1 to 3, the axial length is similar to the length shown in Figure 4, however tip seal 58 is thinner in the radial direction and therefore lighter and more flexible. In the embodiment shown the ratio is 1 : 1.5 and depending on pumping requirements, the tip seal has an axial extent and radial width in the range from about 1.8mm and 1.2mm to 4mm and 2.6mm respectively. It will be seen therefore that the aspect ratio may be more than 1 :2.

The arrangement shown offers a number of advantages over the prior art. When manufacturing the tip seal 58 from the materials used currently, the wear rate & tip-seal life (pressure-velocity regime) remains generally unchanged. Additionally, tip seal 58 shows shorter bedding-in or stabilisation times. The tip seal 58 is thinner, and therefore more flexible, in the radial direction; in addition, its sectional area is smaller, making it also more flexible in the axial direction. Therefore it demonstrates better capability of presenting its full axial end face 62 against the orbiting scroll. Accordingly, most if not all of the axial face becomes bedded in quickly during initial use.

As the axial end face 62 occupies relatively less area than the axial end face of the prior art tip seal, less dust is generated due to abrasion against the orbiting scroll during use. As dust generated during use must be periodically removed, less dust generation decreases the cost of ownership. Further, in the prior art where the tip seal is relatively stiff in the radial direction, only a portion or corner of the axial end face may be presented to the orbiting scroll. It will be appreciated that whilst in the embodiment the axial end face is smaller than the axial end face in the prior art, a more flexible seal is better able to present its entire end face to the orbiting scroll whereas in the prior art only a corner of the scroll end face may be presented to the orbiting scroll.

Figures 4 and 5 show respectively a plan view of a portion of a tip seal in a groove of a scroll wall for a prior art arrangement and an arrangement in accordance with an embodiment of the invention. In both Figures, although the scroll wall is spiral, for the sake of explanation the scroll wall has been shown as linear.

In both Figures 4 and 5, during orbiting motion of a scroll wall 29, 35, crescent shaped pockets of fluid are trapped between the scroll walls 20, 22 and compressed as they are forced along flow paths towards the outlet of the pumping arrangement. As the trapped pockets of fluid pass along the paths, a tip seal 36, 58 experiences a changing direction of pressure difference across it. In this regard, the pressure difference across the seal tends to drive the seal radially inwards during a first part of orbiting motion and then radially outwards in a second part of orbiting motion, in a cyclic manner that repeats with every revolution of the shaft. A portion of a tip seal therefore is driven against a radially inner side of the groove when it is at an upstream portion of a trapped pocket and against a radially outer side of the groove when it is at a downstream portion of a trapped pocket. The reverse would be true of the tip seal of the opposing scroll.

In more detail, when considering the full length of the tip seals 36, 58 at any given time during use of the pump, first portions 68, 70 of the tip seals are located at the radially inner side 72 of the groove 74 and second portions 76, 78 of the tip seals are located at the radially outer side 80 of the groove. In between first and second portions, intermediate portions 82, 84 of the tip seals 36, 58 bridge the gap between the radially inner side 72 and the radially outer side 80 of the groove. Fluid can leak across the tip seals at the intermediate portions, since there is a leakage path which extends between the tip seals and the radially inner side 72 of the groove, underneath the tip seals and between the tip seals and the radially outer side 80 of the groove. That is, at the intermediate portions 82, 84 the tip seal does not block the seepage path by pressing against one of the sides of the groove. The prior art tip seal 36 has a larger radial width to axial depth and is therefore relatively stiff in the radial direction. Consequently, the length of the intermediate portions 82 are longer meaning that more leakage occurs. The tip seal 58 has a smaller radial width to axial depth and is therefore relatively flexible in the radial direction.

Consequently, the length of the intermediate portions 84 are shorter meaning that less leakage occurs.

A further advantage of the present embodiment is that the space occupied by the tip seal is smaller in the radial direction and therefore scroll wall thickness is reduced. Accordingly, as shown in Figure 1 , six wraps are shown whereas in Figure 6 only five wraps are shown. Therefore, for a pump of any given size, the present embodiment allows increased pumping capability because more wraps equates to a longer pumping path between inlet and exhaust, which increases compression. Alternatively the embodiment allows similar pumping capability in a smaller pump. In this latter regard, a pump which occupies less volume than the prior art is generally less expensive to manufacture as it requires less material and occupies a smaller foot-print when in use.

Figures 2 and 3 show the radial clearance R between a portion of tip seal 58 and the radial sides 72, 80 of the channel or groove 74. The clearance has been exaggerated in the Figures for the purposes of explanation. The tip-seal is pressure-loaded against the counter- face 62 of the orbiting scroll 60 by the gas that occupies the space G underneath the seal. The seal is urged against the sides of the channel by a combination of pressure differential in the radial direction and friction against the counter- face as the orbiting scroll orbits.

As described above, at different points along the length of a single tip-seal 58, the seal is located in the position shown in either Figure 2 or 3, or is in the process of moving between the two shown positions. That is, the first portions 70 of the tip seal 58 are located at the radially inner side 72 of the channel in Figure 2 and the second portions 78 of the tip seal are located at the radially outer side 80 of the channel in Figure 3. When the tip seal is between the two shown positions a seepage path is formed across the tip seal causing leakage. The seepage path extends along one radial face of the tip seal, across gap G and along an opposing radial face of the tip seal. As tip seal 58 is more flexible in the radial direction than in the prior art, it moves between the two shown positions more quickly and therefore less leakage occurs. As indicated above, one or both of the tip seals may have increased aspect ratio of more than 1 : 1.25. Preferably, the aspect ratio is approximately the same along the full length of the each tip seals, however one or both of the tips seals may have different aspect ratios along their lengths.

Whilst a scroll compressor is typically operated for pumping fluid, instead it can operated as a generator for generating electrical energy when pressurised fluid is used to rotate the orbiting scroll relative to the fixed scroll. The present invention is intended to cover use of the scroll compressor for pumping and energy generation.