Compressors

Abstract: An engine-exhaust gas driven turbo compressor has a controllable diaphragm valve (13, 15) in a flow path (20, 24) between a compressor delivery port (6) and an atmospheric inlet port (4), this valve being controllable to regulate gas flow via the compressor wheel member (2) to avoid compressor surging when the demand is low and a compressed torroidal wire mesh element (23) is accomodated in an annular region (22) of the compressor housing between the valve (13, 15) and the inlet port to suppress noise resultant upon operation of the valve.

Description: This invention relates to rotary compressors and relates more especially but not exclusively to turbo charger compressors. In the Specification of United States Patent No. 4,517,803 a turbo charger compressor is described for delivering air under pressure to the induction system of an engine. The compressor has a housing which accommodates a controllable diaphragm valve permitting selective recirculation of air via a recirculation duct from a compressor delivery to the compressor inlet to avoid surging the compressor during engine transients when the throttle is closed. Whilst such a valve arrangement is inexpensive and functionally satisfactory it can introduce undesirable noise in transition between open and closed conditions and the object of the present invention is to improve such a compressor by reducing the discernible noise produced by the controllable valve. According to the present invention there is provided a compressor having a compressor member rotatable in a compressor housing to induce air at an intake port for delivery at elevated pressure at a delivery port said housing including a control valve via which a recirculation path is able to connect said delivery port to said intake port for regulating flow through the compressor member characterised in that said recirculation path is directed through an open cell or mesh element the density of which is such as to attenuate noise produced by the action of said valve. Said element may preferably comprise an annular element of woven or knitted metallic stainless steel mesh, rolled and pressed into predetermined dimensions element. Preferably the valve comprises a spring-loaded diaphragm having an annular surface engageable with an annular seat defining a bounding periphery of said recirculation path said path including an annular region which receives said element said element being of correspondingly torroidal configuration to match said annular region. In order that the invention may be more clearly understood and readily carried into effect the same will now be further described by way of example with reference to the single figure of the accompanying drawings which illustrates in part-sectional view part of a turbo charger compressor employing an element as proposed in accordance with the invention. Referring to the drawing, the turbo charger compressor includes an end housing portion 1 within which an engineexhaust turbine-driven centrifugal compressor wheel member 2 of known form is mounted for rotation on a shaft 3 to draw air from an atmospheric inlet port 4 into a scroll-configured compressor passage 5. The scroll-configured passage 5 terminates in a delivery opening 6 leading to the fuel induction or carburation system of the engine. Adjacent the delivery opening 6, the housing portion 1 has a planar surface 7 which receives a recirculation valve housing 8 accommodating a diaphragm valve and a valve control port 9. The diaphragm valve comprises a moulded generally cup-shaped diaphragm 10 formed of a suitable synthetic rubber with a nylon fabric reinforcement. The diaphragm 10 has a peripheral bead 11 which upon assembly is trapped between the rim 12 of an annular member 13 and an internal shoulder 14 of the housing 8. The central portion 13 of the diaphragm defines an annular valve element 15 and is moulded to provide a snap-fit over a central portion of a mouvable cup-shaped member 16. The member 16 is spring loaded by a captive spring 17 to urge the valve element 15 against the inner surface of member 13. The housing 8 is provided with a gasket 18 and member 13 is provided with an o-ring seal 19, which seals against the outer end of an internal annular portion 25 defining a flow passage 20. The annular portion 25 and the outer wall 26 of the housing define between them an annular region 22 connecting with the interior of member 13 via openings 21. The recirculation valve thereby provides a path for air from delivery port 6 via the passage 20 the diaphragm valve when unseated, side openings 21 of member 13 and an annular chamber 22 and then via a passage 24 to the inlet port 4. The mentioned annular region 22 houses a push fitted torroidal open-cell element 23 via which all air flow between passages 20, 21 is constrained to flow. In operation, the compressor member 2 causes air to be drawn from intake port 4 via the scroll-configured passage 5 to the delivery port 6. If the flow rate is low, the compressor tends to "surge" which means the flow can become unstable with flow reversals alternating with flow into the compressor. Such a condition can occur if a throttle downstream of the compressor is closed suddenly as, for instance, occurs during a gear change on a turbocharged gasoline engine. In such a case, a depression exists downstream of the throttle with a high pressure in the compressor delivery port 6. This depression is communicated to port 9 and the diaphragm is lifted by the pressure differential acting on the annular valve 15 and overcoming the pre-load provided by spring 17. Some of the air is thereby recirculated to the intake port 4 via passages 20, 21, 23 and 24 and the annular open-cell element 23. This action allows the compressor to deliver a high enough flow rate to avoid "surge" if the flow passages 20, 21, 23 and 24 are adequately dimensioned and if the element 23 is not too restrictive. The push fitted torroidal open-cell element 23 is preferably formed of a tubular knitted sock-like stainless steel fabric element rolled about itself to form the torroidal open cell form half of the volume of which is free air. Preferably, the element is so folded that any wire ends are internally contained. The torroidal open-cell element 23 is preferably formed of a mesh of 18/8 stainless steel wire, typically of 0.25mm gauge. The wire is woven to produce a tubular stocking-like form as illustrated at 30 in Fig. 2a. Thereafter a length, predetermined to produce the desired density and torroidal dimensions is cut and flattened to form a band as at 31 in Fig. 2b. The ends 32 and 33 of this band are folded over to eventually contain all raw wire ends and the band 31 is rolled into a coil 34 as illustrated in Fig. 2c. This coil is such as to be loosely acceptable in a mould 35 as in Fig. 2d wherein it is pressed by an annular platten to take up the precise desired external dimensions of the final element 36 of Fig. 2e. Being formed of a stocking-like element with the raw ends turned inwards no external single thickness or raw wire ends are exposed present on the final-compressed torroid. The element 23 may alternatively comprise knitted or woven synthetic fibres. Open cell plastic foam may also be employed or an air-laid open-cell fibrous felt-like batt may be formed to the desired shape. The principle desirable attributes for the form of the element 23 are that it shall withstand the known high operating temperatures attained by a turbo charger compressor, that it shall have sufficiently close open-cell or mesh structure to achieve the desired noise attenuation and that it shall not be liable to shed strands or particles into the engine induction system throughout entire useful life of the compressor. Typically, the element has 50% free volume, that is half its volume comprises the wire or other material and the other half comprises free air.

Claims: A compressor having a compressor member (2) rotatable in a compressor housing (1) to induce air at an intake port (4) for delivery at elevated pressure at a delivery port (6) said housing including a control valve (13, 15) via which a recirculation path (24) is able to connect said delivery port (6) to said intake port (4) for regulating flow through the compressor member (2) characterised in that said recirculation path (24) is directed through an open cell or mesh element (23) the density of which is such as to attenuate noise produced by the action of said valve (13, 15). A compressor as claimed in claim 1, characterised in that said compressor housing has an internal annular portion (25) defining a recirculation flow passage between said delivery port and said control valve (13, 15) and said annular portion (25) also defining an inner wall of an annular region (22) in the path (24) between said valve (13, 15) and said intake port (4), said open cell element (23) being a torroidal element fitting in said region (22). A compressor as claimed in claim 2, characterised in that said valve comprises a valve housing (8) and a cupshaped diaphragm (10) the periphery (11) of which is clamped via an inner member (13) between the valve housing (8) and the compressor housing (11). A compressor as claimed in claim 3, characterised in that said inner member (13) defines a valve seat against which the diaphragm (10) is engageable and said inner member (13) being sealingly engaged with an outer end of said annular portion (25). A compressor as claimed in claim 1, 2, 3 or 4 characterised in that said element (23) is formed of a coiled length (31) of woven mesh to provide a generally annular shape. A compressor as claimed in claim 1, 2, 3 or 4, characterised in that said element is formed of a predetermined length of tubular woven mesh which is flattened to produce a ribbon of which the raw ends are then folded inwards before the ribbon is coiled to form a generally annular shape. A compressor as claimed in claim 5 or 6 when dependent of claim 2 characterised in that said annular shape is compressed into a torroid of predetermined dimensions to fit said annular region.

Inventors: FLAXINGTON DAVID, GRAINGER JOHN KEITH, FLAXINGTON, DAVID, GRAINGER, JOHN KEITH
Applicants: ALLIEDSIGNAL LTD, ALLIEDSIGNAL LIMITED
Application year: 1991
Main classification: F04D29
IPC codes: F02B1, F02B33, F04D17, F04D27, F04D29, F02B37, F02B39