GB2243194A - Cylinder head gasket of a reciprocating compressor - Google Patents

Abstract

The present invention relates to reciprocating compressors, for example, as used in refrigerators. A head gasket 10 is compressed between a cylinder block which has an apertured end carrying suction and discharge valves (3a, 3b) and a cylinder cover 5 which has corresponding suction and discharge chambers. The gasket is made of compressible material and has apertures for suction and discharge. The discharge aperture is smaller than the width of the discharge chamber. Accordingly, a portion of the gasket provides a shoulder which projects into the discharge chamber and is of a greater thickness than the regions of the gasket which are compressed. Such a shoulder prevents sliding and breaking of the cylinder cover upon high pressure discharge. <IMAGE>

Description

1 1 Cylinder Head GasRet of a Reciprocating Compressor The present.

reciprocating machines invention relates, in a general way, to compressors for small refrigerating and, more particularey, to a new constructive solution applied to the. cylinder cover gasket of an hermetic compressor with a reciprocating piston.

In compressors with a reciprocating piston, the cylinder head normally carries a valve plate defining therein the suction and discharge valves, a cylinder head which is normally cast ou molded, a cylinder gasket located between the valve plate and the cylinder block, and a cylinder cover gasket, disposed between the cylinder cover and the valve plate, such joints being provided to avoid leakage from the discharge chamber to the suction chamber, coming from the discharge side of the compressor and cylinder to the interior o+ the housing encapsulating the assembly.

The cylinder cover and the valve plate generally have a rectangular shape and are attached together to the cylinder block by means of bolts, usually +our, which are provided near the corners of the cover and valve plate.

Due to a malfunction in the operation of the the pressure inside the discharge chamber compressor, formed within the cylinder cover may suffer a sudden and accentuated increase. These pressure peaks in the discharge chamber may happen due to dif+erent reasons as, for example, liquid compression (condensed cooling fluid) in the cylinder or any restriction (obstruction) in the discharge +low o+ the compressor after the discharge chamber, in the acoustic filters 2 or in the discharge tube. These malfunctions are not very rare to occur and the compressor, specially the hermetic ones, should be designed in order to hold such pressure peaks.

In certain situations, this pressure peak within the discharge chamber can be sufficient to cause the sliding and even the breaking of the cylinder cover gasket. In both situations, the gasket will be irremediably damaged.

io Up to now, the solutions used to minimize the risks of displacement or rupture in the cover gasket can be summarized as follows:

One of the prior art solutions refers to applying an overtorque in the bolts for fixing the cover-valve plate assembly to the cylinder block. This solution is not reliable because it can easily lead to a warping in the cylinder cover, or produce undesirable deformations in the fixing elements, i.e., bolts and threads in the cylinder.

In another known solution, there is the provision of increasing -the surface roughness of the cylinder cover edges on which the edge portion of the cylinder cover gasket is laid.

Although increasing the strength of the gasket to the pressure peaks within the discharge chamber, this solution requires the execution of an expensive operation and difficult maintenance in the casting or molding mold, requiring constant restoring due to wear caused in the production process. This surface roughness increase may also be produced by aftermachining, though representing an increase in the manufacturing cost.

In another prior art solution described in the German patent document No DE 3534289 Al, rims or ribs are provided on the side edges of the cylinder cover, so as to operate as retention stops to the cylinder 1 cover gasket. This solution is not reliable because it only prevents the gasket from sliding at its outer contour, not avoiding internal sliding, at the surface of the cylinder cover gasket resting against the wall which separates the suction and discharge chambers, or externally, at the clearance existing between the rib and the valve plate end.

An advantage of one embodiment of the present invention is to provide a head gasket, more specifically a cylinder cover gasket, for reciprocating compressors, such gasket having a construction which is simple and easy to control, without any cost increase in relation to the known solutions, and also being very reliable.

The head gasket, according to the present invention, is applied to a reciprocating hermetic compressor comprising: a cylinder block having one open end and lodging a piston with a reciprocating movement; a valve plate with one of its faces being attached to the open end of the cylinder block and carrying suction and discharge valves; a cylinder gasket disposed between said cylinder block and valve plate; a cylinder cover internally defining a suction chamber and a discharge chamber and having an open rear face defined by an edge surrounding said suction and discharge chambers and being attached against the other face of the valve plate; and a cylinder cover gasket bgtween said cover and the valve plate.

According to the invention, a portion of the cylinder cover gasket extends to the interior of the cylinder cover, from the surrounding rear edge, at least in the portion of the latter surrounding the discharge chamber and presenting a larger extension, said gasket portion having, within the chamber, a larger thickness than the thickness of the gasket portion being compressed between said surrounding edge and 4 the valve plate.

The gasket usually has a uniform thickness before being assembled. In this case, it is only the tightening of the fixing means of the cover and valve plate to the cylinder block that causes a thickness differentiation between a compressed gasket portion and a non-compressed gasket portion that projects to the interior of the surrounded chamber.

Nevertheless, it should be understood that the gasket io portion, which extends to the interior of the surrounded chamber and which is not going to be compressed when mounting the assembly to the cylinder block, will have a slightly larger thickness than that of the remaining width of the gasket, this thickness differential being increased upon normal compression of the gasket when the assembly is mounted.

The invention allows the formation of a usually continuous shoulder in the own body of the gasket, along the edge thereof facing the interior of the chamber to be surrounded by said gasket portion, said shoulder operating as a stop together with the inner face of the cover surrounding edge, preventing the gasket from sliding outwardly from said cover, or breaking.

The width of said gasket portion is made larger than the width of the surrounding edge of the cylinder cover, in order to have part of its width occupying the entire width of the cover surrounding edge and being compressed thereby, and also a part of the remaining non compressed width being projected to the interior of the surrounded chamber.

The invention will hereihafter be described with 35 reference to the attached drawings, in which:

Figure 1 shows a longitudinal section view of the i 7 head assembly of a reciprocating hermetic compressor; Figure 2 shows a plan view of the cover rear face, taken according to line II-II of figure i:

Figure 3 illustrates a plan view of the cylinder cover gasket; Figure 4 illustrates, schematically, in partial section and enlarged scale, the relative positioning between a cover gasket portion and the surrounding edge of the discharge chamber of the cylinder cover, before the compression assembly of the gasket; and Figure 5 illustrates a similar view to that of figure 4, but showing the assembly after the compression assembly of the gasket.

As illustrated in figure i, the invention is used in a reciprocating compressor comprising a cylinder block I arranged within a housing (not shown) in the case of hermetic compressors and -having a cylindric cavity with a reciprocating piston 2 moving therewithin.

The cylinder block i has one end of its cavity, normally the front end, opened to receive a valve plate 3 having one of its two opposite faces seated against the end front face of the cylinder block i and sealed against the same with the help of a cylinder joint 4.

The valve plate 3 is axially perforated in order to lodge a suction valve 3a and a discharge valve 3b which are arranged in fluid communication with the interior of the inner cavity or compression chamber of the cylinder block 1.

Against the front face of the valve plate 3, opposite to the cylinder block i, it is seated a cylinder 5, made of cast iron or molded aluminum and internally define cover being shaped so as to chamber 5a in a suction fluid communication with the suction -6valve 3a, and a discharge chamber 5b in fluid communication with the discharge valve 3b, these chambers being opened towards the rear face of the cover which is seated against the valve plate.

The cylinder cover 5 has its rear face, to be seated against the valve plate 3, defined only by a flat edge 5c (see Figure 2) with a reduced width in relation to the peripheral dimensions of the cover and circumscribing the suction chamber 5a and discharge chamber 5b. This known constructive arrangement makes the valve plate 3 define the flat rear wall of the suction chamber 5a and discharge chamber 5b.

In order to assure the tightness of the suction and discharge chambers Sa and 5b, there is provided a head gasket 10 between the rear surrounding edge 5c of the cylinder cover 5 and the adjacent front face of the valve plate 3.

The attachment of the cylinder cover 5 and valve plate 3 to the cylinder block 1 is done by means of bolts (not shown) passing through corresponding axial holes 5d and 13 provided in cover 5 and head gasket 10, respectively, and being threaded in apertures provided in cylinder block 1, after passing through corresponding axial holes (not shown) provided in plate 3 and cylinder gasket 4.

The head gasket 10 has a thickness sufficient to assure, after its compression and deformation caused by tightening said screws for fixing the cylinder cover, an adequate tightness in the suction chamber 5a and discharge chamber 5b. This head gasket 10 can be made of any proper material as, for example, hydraulic cardboard with amianthus or asbestos or cotton fibers joined with rubber and is provided with an opening 14, corresponding to the discharge chamber 5b and a hole 15 corresponding to the suction valve opening of the valve plate 3.

The head gasket 10 made of hydraulic cardboard with rubber has a thickness that is normally between the range of 0.3 to 0.5mm.

As illustrated in Figures 3, 4 and 5, a solution embodying the present invention comprises the provision of a cylinder gasket 10 having a dimensioning, in terms of contour and width, such as to permit the formation of a gasket portion 11 projecting to the interior of the cylinder cover 5, from the rear surrounding edge Sc, at least at the portions thereof which circumscribe the discharge chamber 5b and have less tightening force of the gasket against the cylinder cover or valve plate.

In the illustrated embodiment, the entire head gasket 10 has the same original thickness "E", before it is compressed between the cylinder cover 5 and the valve plate 3. In this configuration, all the portions of the head gasket 10 circumscribing the discharge chamber 5b( see Figure 3) have a width that is larger than the necessary width to cover the corresponding portion of the surrounding rear edge, so as to form the mentioned inwardly projecting portion 11 along the entire joint periphery between the discharge chamber 5b and valve plate 3.

It should be understood that the increase in the width of the head gasket could only be made in the portions of the surrounding rear edge 5c that would be more likely to undergo ruptures.

In the embodiment illustrated in the drawings, before tightening the fixing screws of the cylinder cover 5, the head joint 10 presents the same thickness "E" along the entire length, including that portion 11 that projects towards the interior of the discharge chamber 5b (see Figure 4).

By tightening the fixing screws, the portion of the head joint 11 between the surrounding rear edge 5c and valve plate is compressed, thus having a thickness "e" lower than the original thickness "E", which is kept in the inwardly projecting portion 11 of the head gasket (see Figure 5).

With the thickness differential above mentioned, the inwardly projecting portion 11 of the head gasket defines a shoulder 12 close to the inner edge of the adjacent portion of the surrounding rear edge 5c, avoiding the sliding of the head gasket 10 away from the fixing surface between the valve plate 3 and the cylinder cover 5.

In order to form a shoulder 12, adequate to the secure retention of the gasket under peak pressure conditons, it is advisable to provide an inwardly projecting portion 11 with a width in-the order of 1.2 times the edge width of the cylinder cover.

1 - Cylinder CLA I M5 head gasket of a reciprocating compressor, comprising a cylinder block (i) having a cylindric cavity lodging a reciprocating piston (2) and with one end being opened to an end face of the block; a valve plate (3) with a front face and a rear face being attached against said end face of the cylinder block (1) and carrying a suction valve (3a) and a discharge valve (3b); a cylinder gasket between io said rear face of the valve plate and said end face of the cylinder block; a cylinder cover (5) defining internally a suction chamber (5a) and a discharge chamber (5b) which are opened to an end face of the cylinder cover defined by an edge (5c) surrounding 13 said suction chamber (5a) and discharge chamber (5b) and being. attached against the front face of the valve plate (3); and a head gasket (10) disposed so as to be compressed between the cylinder cover (5) and the valve plate (3), characterized in that a portion (ii) of the head gasket (10) is projected to the inner part of the cylinder cover (5) from the surrounding edge (5c), at least in the portions thereof which surround the discharge chamber (5b) and are more susceptible to sliding or breaking, -said gasket portion (11) having, inside the chamber, a thickness (E) which is larger than the thickness (e) of the gasket portion being compressed between said surrounding edge (5c) and valve plate (3).

2 - Cylinder head gasket, according to claim 1, 30 characterized in that it has the same thickness (E) along the entire extension before being compressed between the valve plate (3) and the surrounding edge (5c) of the cylinder cover (5).

i i -93. A reciprocating compressor comprising a block (1) having a cylindrical cavity which houses a reciprocating piston (2), the block having an end portion comprising a suction valve (3a) and discharge valve (3b), the compressor further comprising an end cover (5) defining internally a suction chamber (5a) and a discharge chamber (5b) which are open to the corresponding suction and discharge valves, and a gasket (10) which is disposed compressed between the cover (5) and the end portion of the block, a portion (11) of the gasket (10) overlapping an edge of the discharge chamber of the cover (5) so as to extend at least partially into the discharge chamber (5b), the portion (11) of the gasket (10) having a larger thickness (E) where uncompressed than the thickness (e) of the gasket where compressed.

Published 1991 at The Patent Office. Concept House. Cardiff Road.-Nev, port. Gwent NP9 1RH. Further copies may be obtained frorn Sales Branch. Unit 6. Nine Mile Point. Cwrnfelinfach. Cross Keys. Newport. NPI 7H.Z. Printed by Multiplex techniques lid. St Marv Cray. Kent-