Shown in Figure 1 is a diagrammatic illustration of a conventional rotary vane compressor comprising a cylindrical rotor (1) driven by an electric motor (not shown) and mounted eccentrically within the cylindrical bore of a stator (2).

Formed in the rotor (1) is a plurality of radially extending grooves or slots (9) each of which accommodates a freely slideable blade or vane (5). During rotation R of the rotor by the electric motor each vane (5) is thrown outwards by centrifugal force so that its outer edge sweeps the internal cylindrical surface of the stator (2). The free space between adjacent vanes is thus divided formed into closed cells (7, 8). Air or other gas taken in at inlet (1) through port (3) is thus compressed as the free space in each cell diminishes as the rotor turns and the compressed air is output at (O) via outlet port (4). The compressor further comprises oil injection means via inlet (6) to provide lubrication and sealing between the outer edges of the vanes and the inner surface of the stator.

Accordingly in operation of a rotary vane compressor the vanes or blades 5 are required to be freely slidable within the slots 9 in the rotor. However in practice lubrication oil is liable to build up under the blade in the region of the radially inner end or bottom of the slot. This excess of incompressible lubrication oil can unduly resist movement of the blade radially inwardly into the slot. This can have a detrimental effect on the performance of the compressor and on the wearing of the blade top and the interior cylindrical surface.

For the relief of such excess lubricating oil it is known to provide radially outwardly extending grooves in the surface of the blades, said grooves extending from the radially inner bottom of the blade to the radially outer top of the blade.

The short length of the grooves, extending perpendicular to the outer edge of each blade, assists in ensuring that they present only minimum resistance to flow of oil.

However, as the known grooves extend radially outwardly i. e. at right angles to the axis of rotation of the rotor, then over time the movement of the - blade in the rotor slot can produce a wear pattern characterised by a radially extending ridge or ridges in the rotor slot sidewall adjacent to the groove in the blade. Such radially extending ridges may impair the long term performance of the compressor and present problems when replacing worn or broken blades with new blades.

It is an object of the present invention to eliminate or at least mitigate the formation of wear related ridges in the rotor slots of an eccentric rotor sliding vane compressor.

According to one aspect of the present invention a rotary sliding vane compressor comprises a rotatable cylindrical rotor provided with a plurality of radially extending rotor slots each defined by a radially inner most slot bottom and two parallel rotor slot watts extending outwardly therefrom, and accommodated within each rotor slot a blade having a radially inner bottom end and a radially outer top end and being freely slidable in a direction perpendicular to the axis of rotation of the rotator, wherein at least one blade has a groove extending longitudinally continuously from the blade bottom end to the blade top end such that no longitudinal portion of the groove extends in a direction perpendicular to the axis of rotation of the rotor.

The at least one blade may have a plurality of such grooves and they may be disposed on the same side of the blade or on opposite sides of the blade.

Preferably the groove or grooves extend in a longitudinally continuous straight line and preferably such straight grooves are in the range 45° to 75° to the axis of rotation of the rotor. An angle of 60° is considered particularly suitable.

Most preferably four straight grooves are provided on one side face of the blade, a first pair of adjacent grooves being inclined at an angle of plus 30° to the direction perpendicular to the axis of rotation of the rotor and a second pair of adjacent grooves being disposed at an angle of minus 30° to the direction perpendicular to the axis of rotation of the rotor such that the ends of the first and second pairs of grooves are closest together at the radially outward top edge of the blade.

Also most preferably all of the blades of the rotary sliding vane compressor are provided with such grooves.

The blades of the present invention are suitable for use in a rotary sliding vane compressor of the type comprising a cylindrical rotor provided with a plurality of radially extending slots each defined by a radially inner most slot bottom and two parallel groove walls extending outwardly therefrom wherein at least one of the slot walls is joined to the slot bottom by a radius portion. The compressor additionally or alternatively may be of the type in which a or each slot comprises a pair of planar confronting surfaces one of which extends further radially inwards than the other.

Further aspects of the present invention will become apparent from the following description given, by way of example only, of an embodiment of the invention in conjunction with the following diagrams in which :- Figure 2 shows a schematic diagram of a cross section of a rotor of a compressor in accordance with the present invention, the cross section being taken perpendicularly to the rotational axis of the rotor ; and Figure 3 shows in more detail the radially inner end of one of the slots in the rotor in Figure 2 ; and Figure 4 a diagrammatic cross section of a vane or blade of a compressor of the present invention; and Figure 5 show further detail of the radially inward end of the blade of Figure 4; and Figures 6a-6g show further details of the vane or blade of the present invention.

The rotor 21 of the compressor of the present invention shown in Figure 2 has six equal sized and equi-spaced apart slots 22 extending radially outwards from a slot bottom 25 to the cylindrical outer peripheral surface 27 of the rotor.

Each of the slots 22 is defined by two parallel slot walls 23, 24, slot wall 23 being the leading slot wall when the rotor turns around rotational axis C in the direction R as indicated. Accordingly the opposing slot wall 24 is the trailing slot wall. 1'6 the centre of the rotor 21 is a longitudinally extending circular hole 26 enabling the rotor 21 to be mounted on the extended shaft of an electric motor (not shown).

As shown in Figure 3 the junction of the trailing slot wall 24 with the groove bottom 25 is radiused to the extent that the concavely curved portion 29 extends beyond the centre line of the slot, i. e. beyond 50 percent of the width W of the slot. In accordance with the preferred aspect of the invention the radius of curvature RADG of the curved portion is between 50 percent and 90 percent of the width W of the slot. In this particular embodiment the value of rad is 76 percent of the width W.

As also shown in Figure 3 the portion 28 at the junction of the leading slot wall 23 with the slot base 25 is chamfered. In this particular embodiment the portion 28 is chamfered at an angle of 45° but it may be of radiused with a radius of curvature preferably between 0.5 and 1. 0 mm.

The curved portion 29 in a preferred configuration has a radius of curvature RADG equal to the slot width W minus the radius of curvature of the portion 28 if portion 28 is curved, not chamfered with the centres of curvature positioned such that the curved portions 28,29 are tangential with their respective slot walls 24,23.

In this particular embodiment the radial length L of the slot is substantially three times as great as the distance D between the slot bottom 25 and the central hole 26. In accordance with the preferred aspects of the present invention the radius of curvature RADG of the curved portion 29 is between 20 and 30 percent of the distance D between the slot bottom 25 and the central hole 26.

Shown in Figure 4 is a cross section of a rectangular slab-like blade or vane 30 of the present invention for use in conjunction with the rotor 21. In operation of the compressor the blade 30 is positioned within slot 22 such that the blade side 31 is the leading side whereas the opposite side 32 is the trailing side. Further details of the radially inner end of the blade 30 are shown in Figure 5 where it can be seen that the portion 34 at the junction of the trailing blade side 32 and the blade bottom 33 is convexly curved in a matching form to the concavety formed portion 29 adjacent slot bottom. Similarly the junction portion 35 between the leading blade side 31 and the blade bottom 33 is chamfered to conform with the chamfered portion 28 of the groove. in a preferred embodiment of the present invention the configuration of the radially inner end of the blade is substantially identical to the radially inner end of the slot with the radius of curvature RADB of the curved portion 34 being the same as the radius RADG of the groove portion 29.

Shown in Figures 6a to 6f are further details of a compressor blade 60 in accordance with the present invention. Shown in Figures 6a and 6c are schematic views of the rectangular slab-like planar sides of the blade and Figures 6b shows a cross-sectional view of the blade 30 taken along the section A-A'in Figure 6a.

Figures 6d shows a view of the blade 30 taken in the direction B indicated in Figure 6a and Figures 6e and 6f are two isometric schematic views of the blade.

As shown one slab-like rectangular surface of the blade is provided with four shallow grooves 61, 62, 63, and 64 which extend continuously in a straight line from end face 65 which is the radially inner face to the opposite end face 66 which is the radially outer end face.

In this embodiment the grooves are arranged chevron-like in two pairs the grooves in each pair being parallel to each other. In this embodiment the grooves 61 and 62 in the first pair are inclined at an angle of plus 1° to the radial direction whilst the grooves of 63, 64 of the second pair of grooves are disposed at an angle of minus 1° to the radial direction. The groove ends of each of the four grooves are thus closer together at the edge 65 of the blade which is the radially inner edge. The value of 1° in this embodiment is 30°.

In accordance with the invention the number and dimensions of the grooves formed in the compressor blade may vary according to the machine size and oil relief requirement. However it is preferred that the groove depth GD is not more than 40% of the blade thickness BT and at the groove width GW is between 2 and 4 mm. In this embodiment the groove depth GD is 1.0 mm and the groove width GW is 3.0 mm.

The cross sectional shape of the groove 61 to 64 is in this embodiment a U shape groove having a flat bottom. However, other cross sectional shapes are possible.

In this particular embodiment the groove width GW. the groove inclination 1°, and the groove spacing GS are chosen such that there is in the longitudinal direction of the blade no overlapping of the end of one groove and the opposite end of the adjacent groove, that is to say there is a positive distance d maintained between the end of one groove and the opposite end of the adjacent groove.

Whilst the present embodiment shows four grooves arranged in two pairs of parallel grooves inclined in respect of each other at the same angle other combinations of numbers and grooves and inclinations and combinations of inclinations are possible within the scope of the invention.

As will be apparent from the blade shown in Figures 6a to 6f the grooves 61 to 64 have no longitudinal portion which extends in the radial direction of a rotor, that is to say they have no longitudinal portion which extends in a direction perpendicular to the rotational axis of the rotor.

Whilst the present invention is illustrated by straight grooves other longitudinal configurations such as curved or S shaped grooves are possible within the scope of the invention provided that in accordance with the invention no longitudinal portion of the groove extends in a direction perpendicular to the rotational axis of the rotor.