ROTARY PISTON AND CYLINDER DEVICES

Abstract

A rotary piston and cylinder device (1) comprising a rotor (2), a stator and a shutter disc (3), the rotor comprising a piston (5) which extends from the rotor into the cylinder space, the rotor and the stator together defining the cylinder space, the shutter disc passing through the cylinder space and forming a partition therein, and the disc comprising a slot (32a) which allows passage of the piston therethrough, and a surface of the rotor and a surface of the stator opposing each other forming a close-running surface pair, and at least one of the surfaces comprising an abradable coating (10) which is provided with a plurality of recess formations, and the recess formations are discontinuous from each other.

Claims

1. A rotary piston and cylinder device comprising a rotor, a stator and a shutter disc, the rotor comprising a piston which extends from the rotor into the cylinder space, the rotor and the stator together defining the cylinder space, the shutter disc passing through the cylinder space and forming a partition therein, and the disc comprising a slot which allows passage of the piston therethrough, and a surface of the rotor and a surface of the stator opposing each other forming a close-running surface pair, and at least one of the surfaces comprising an abradable coating which is provided with a plurality of recess formations, and the recess formations are discontinuous from each other.

2. A device as claimed in claim 1 in which the recess formations are discrete and spaced apart from each other.

3. A device of claim 1 in which the abradable coating is provided on the stator.

4. A device of claim 1 in which the abradable coating is provided on the rotor.

5. A device as claimed in claim 1 in which each recess has an angular circumferential extent on a respective surface of a maximum of 10.

6. A device as claimed in claim 1 in which the recesses form a regular, repeating pattern.

7. A device as claimed in claim 1 in which the recess formations are arranged in a staggered arrangement, in relation to a net direction of relative travel between the close-running surfaces.

8. A device as claimed in claim 1 in which a surface portion of either of the shutter disc or the piston, which serves to provide a close-running region is substantially devoid of recess formations.

9. A device as claimed in claim 1 in which the recess formations comprise a base and a surrounding wall.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Various embodiments of the invention will now be described, by way of example only, with reference to the drawings in which:

[0030] FIG. 1 is a perspective view of a rotary piston and cylinder device,

[0031] FIG. 2 is a exploded view of a rotor and a stator of a rotary piston and cylinder device,

[0032] FIG. 3 is a rearward view of a rotor and a stator of a rotary piston and cylinder device,

[0033] FIG. 4 shows examples of recessed abradable coatings,

[0034] FIG. 5 is a cross-sectional view of an abradable surface provided with differently shaped recesses,

[0035] FIG. 6 is a plan view of a staggered pattern of recesses provided in an abradable coating,

[0036] FIG. 7 shows a perspective view of a rotor illustrating bi-directional fluid flow across a close-running area,

[0037] FIG. 8 is an exploded forward perspective view of a variant embodiment of a rotary piston and cylinder device, and

[0038] FIG. 9 is a rearward perspective view of the device in FIG. 8.

DETAILED DESCRIPTION

[0039] Reference is made to FIG. 1 which shows a rotary piston and cylinder device 1 which comprises a rotor 2, a stator (not shown), and a shutter disc 3. The stator comprises a formation which is maintained relative to the rotor, and a surface of the stator facing the surface 2a of the rotor, together define a cylinder space. Integral with the rotor and extending from the inner surface there is provided a blade 5. A slot 3a provided in the shutter disc 3 is sized and shaped to allow passage of the blade therethrough. Rotation of the shutter disc 3 is geared to the rotor by way of a transmission assembly to ensure that the timing of the rotor remains in synchrony with the shutter disc.

[0040] The areas of close-running faces present in a rotary piston and cylinder device highlighted (by shading) in FIGS. 2 and 3 experience fluid flow in more than one direction, as demonstrated in FIG. 7. The highlighted regions are opposed surfaces of the rotor and the stator, and not surfaces of either of the blade or the disc, which form a close-running surface pair. This is due to the fluid leakage to/from the cylinder and the leakage past/into/out of the discrete features of the device (blade, port apertures, shutter disc). FIG. 7 shows the two possible routes (referred to as leak paths from now on) that leaking fluid can take when escaping from the high-pressure cylinder. This means that the solutions described above will result in increased fluid flow through some of the leak paths, resulting in decreased volumetric efficiency and hence poor performance of the device.

[0041] The solution disclosed herein is to apply a texture, or what may be described as a surface relief, on the surface of the abradable coating. The texture can be characterised as a pattern of non-continuous indentations or dimples on the surface of the coating. Each of the indentations does not span the axial length of the face, and do not extend circumferentially for greater than 10. Since the indentations no longer span the length or circumference of the close-running area, they offer no clear method for removing abraded coating particles, but surprisingly in testing this solution has shown to have the same benefit of reducing gouging as the continuous grooves described above. Also, since these patterned indentations are non-continuous (ie they are discrete and spaced from each other), they do not change the minimum clearance of any of the paths for fluid flow through leak paths in/out of the cylinders, and hence do not significantly adversely affect leaks in any direction across the close-running area.

[0042] The texturing can be of a range of shapes and not limited to circular, polygonal, zigzagged, staggered or aligned, or grooved in a range of angles with respect to the relative motion. The cross-sectional profile of the texture can also vary. The texture can also be achieved in a number of ways and not limited to laser etching, water jet cutting, machining, moulding, screening during abradable application, or media blasting. FIG. 4 shows a range of differently shaped recesses formed in an abradable coating, shown generally by reference numeral 10. Each recess (formation) comprises a base portion and a surrounding wall (which dictates the depth of the recess), thereby forming a discrete recess formation. An alternative to a square cross section recess is a rounded recess, such as could be created with a ball-nose shaped tool. Further, FIG. 5 shows a surface 10 which is provided with a plurality of differently shaped recesses, illustrating that the recesses do not need to be of the same shape.

[0043] FIG. 6 shows a staggered pattern of recesses 20 provided in an abradable coating, and is intended to illustrate the advantage of a staggered arrangement of recesses. The solid arrow indicates the (relative) direction of movement between the close-running pair. The direction of travel between the close-running pair is interrupted by recesses, such that a substantial area of coating in the net direction of travel is interrupted by recess formations.

[0044] FIGS. 8 and 9 show a variant embodiment of a device in which a rotor 102 is encased in a stator 109 (comprising front and rear parts). The stator is provided with a slot 110 arranged to receive a shutter disc (not illustrated) therein, and similarly in relation to the embodiment above, the shutter disc comprises a slot to allow periodic passage of the piston blade 105. The cylinder space is defined by concave surface 102a of the rotor and the inner surface 109a of the stator. The shaded regions of the rotor and the stator are provided with an abradable coating. These surfaces are opposed surfaces of the rotor and the stator which form the close-running regions. It will be appreciated that only one of the stator surface and the rotor surface may be provided with the recessed abradable coating. The same proposed solution applies to this and other potential embodiments where there are two close-running surfaces, and which are largely continuous over ninety degrees of circumference.