FIELD The present disclosure relates to hermetic compressors and in particular to the suction arrangement of a hermetic compressor.

BACKGROUND Hermetic compressors typically comprise a suction arrangement which allows refrigerant gas returning from a refrigeration cycle to be drawn into the hermetic shell of the hermetic compressor and drawn through a suction muffler into a compression chamber within a cylinder block of the hermetic compressor. Examples of suction arrangements in hermetic compressors are described in US Patent 8,992,186 and Japanese Patent Application Publication 2008-267365.

SUMMARY OF THE INVENTION According to a first aspect of the present disclosure, a hermetic compressor is provided. The hermetic compressor comprises: a hermetic shell having a hermetically sealed interior; a suction tube passing through the hermetic shell and having a suction tube outlet within the hermetically sealed interior; a cylinder block arranged within the hermetic shell and defining a compression chamber; a cylinder head forming a closed end of the compression chamber; a suction muffler having a suction muffler inlet opening within the hermetically sealed interior; and a discharge tube passing through the hermetic shell and in communication with the closed end of the compression chamber, the hermetic compressor being configured to draw a refrigerant into the compression chamber from suction tube outlet through the suction muffler, and to compress the refrigerant in the compression chamber such that compressed refrigerant passes through the closed end of the compression chamber and into the discharge tube, wherein the suction tube outlet is arranged to direct refrigerant flowing from the suction tube towards a surface of the cylinder head such that refrigerant flows over the surface of the cylinder head before entering the suction muffler inlet. Since the return gas refrigerant travelling from the suction tube outlet to the suction muffler inlet is applied to the cylinder head, the temperature of the compressed discharge gas refrigerant can be reduced, thus improving both reliability and robustness of the hermetic compressor.

In an embodiment, the suction muffler inlet is laterally offset from the suction tube outlet. By laterally offsetting the suction muffler inlet from the suction tube outlet, the refrigerant is forced to flow over the surface of the cylinder head.

In an embodiment, the suction muffler inlet is arranged adjacent to a first side of the cylinder head and the suction tube outlet is arranged to be closer to a second side of the cylinder head which opposes the first side than to the first side of the cylinder head. In an embodiment, the suction muffler is vertically offset from the suction tube outlet, by vertically offsetting the suction muffler inlet from the suction tube outlet, the refrigerant is forced to flow over the surface of the cylinder head.

In embodiment, the suction muffler inlet is arranged in a position which is vertically higher than the position of the suction tube outlet. This provides for suppressing the amount of liquid refrigerant that enters the suction muffler inlet.

In an embodiment, the suction tube outlet and suction muffler inlet are arranged such that refrigerant in a gaseous form flows from the suction tube outlet Into the suction muffler inlet and refrigerant in a liquid state flows from the suction tube outlet into the hermetically sealed interior of the hermetic shell.

In an embodiment, the suction muffler inlet faces vertically upwards. This also provides for suppressing the amount of liquid refrigerant that enters the suction muffler inlet,

In an embodiment, the refrigerant is a mixed refrigerant. The refrigerant may comprise at least one of R404A, and R448A.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, embodiments of the present invention will be described as non-limiting examples with reference to the accompanying drawings in which:

FIG.1 shows a perspective view of a hermetic compressor according to an embodiment of the present invention;

FIG.2 shows a top down view of a hermetic compressor according to an embodiment of the present invention;

FIG.3 shows a side view of hermetic compressor according to an embodiment of the present invention; and

FIG.4 shows a suction muffler of a hermetic compressor according to an embodiment of the present invention.

DETAILED DESCRIPTION

FIG.1 shows a perspective view of a hermetic compressor according to an embodiment of the present invention. The hermetic compressor 100 is housed within a hermetic shell which is formed from a lower shell portion 101 and an upper shell portion 102. The hermetic shell forms a hermetically sealed interior in which an electromotive part 110 and a compression part 120 of the hermetic compressor 100 are located.

The electromotive part 110 comprises a stator and a rotor. The stator and the rotor are arranged coaxially and the rotor is arranged within the stator. The electromotive part 110 electrically is coupled to an electrical connection 111 located on the lower shell portion 102. The electromotive part 110 is supported above the base of the hermetic shell by springs 103.

The compression part 120 is arranged above the electromotive part 110. The compression part 120 comprises a cylinder block 121. The cylinder block 121 has a cylindrical cavity that forms a compression chamber. A piston is movable within the cylindrical cavity. The piston is coupled to a connecting rod. The connecting rod is coupled to a crankshaft. The crankshaft comprises a main shaft portion and an eccentric shaft portion. The main shaft portion is attached to the rotor of the electromotive part 110.

An end of the compression chamber is closed by a cylinder head 122. The cylinder head 122 is held to the cylinder block by bolts. The cylinder head 122 forms a closed end of the compression chamber. A suction muffler 130 is located adjacent to the cylinder head. The suction muffler 130 has a suction muffler inlet which opens to the hermetically sealed interior of the hermetic shell. The suction muffler 130 has a suction muffler outlet which is coupled to the compression chamber.

A suction tube 140 passes through the hermetic shell and has a suction tube outlet 141 located inside the hermetically sealed interior. A discharge tube 150 is coupled to the closed end of the compression chamber and passes through the hermetic shell.

In operation, electrical power is supplied to the electromotive part 110 though the electrical connection 111. This causes the rotor to rotate relative to the stator. The rotation of the rotor causes the crankshaft to rotate. The rotation of the crankshaft is converted into reciprocating motion by the eccentric shaft portion and the connecting rod. This reciprocating motion causes the piston to reciprocate in the cavity of the cylinder block 121. As the piston moves away from the cylinder head 122, refrigerant is drawn into the compression chamber through the suction muffler 130, and refrigerant is drawn into the suction muffler inlet 131 from the suction tube 140. As the refrigerant passes from the suction tube outlet 141 to the suction muffler inlet 131, it passes through the hermetically sealed interior of the hermetic shell.

A suction valve is provided between the suction muffler 130 and the compression chamber, and a discharge valve is provided between the compression chamber and the closed end of the compression chamber which is coupled to the discharge tube. The suction valve is open and the discharge valve is closed as the piston moves away from the cylinder head 122. As the piston moves towards the cylinder head 122, the suction valve closes and the refrigerant in the compression chamber is compressed. The increase in pressure as the piston moves towards the cylinder head 122 causes the discharge valve to open. When the discharge valve is open, the compressed refrigerant passes through the cylinder head 122 and into the discharge tube 150.

As shown in FIG.1 , the suction tube outlet 141 is arranged to overlap with the cylinder head 122. This means that the refrigerant exiting the suction tube outlet 141 is directed towards the cylinder head 122. The suction muffler inlet 131 is located at an opposite side of the cylinder head 122 from the location of the suction tube outlet 141. This means that the refrigerant exiting the suction tube outlet 141 and flowing into the suction muffler inlet 131 flows over a surface of the cylinder head 122. This has an effect of reducing the temperature of the compressed refrigerant which enters the discharge tube 150. As the refrigerant is compressed in the compression chamber, the temperature of the refrigerant increases. Therefore, the compressed refrigerant entering the discharge tube 150 from the from the closed end of the compression chamber has a higher temperature than the refrigerant entering the hermetically sealed interior formed by the hermetic shell. The compressed refrigerant passes inside the cylinder head 122. By causing the lower temperature refrigerant in the hermetically sealed interior to flow over a surface of the cylinder head 122, the cylinder head 122 and therefore the compressed refrigerant within the cylinder head 122 are cooled. This reduction of the temperature of the compressed refrigerant makes the operation of the refrigeration cycle incorporating the hermetically sealed compressor 100 more efficient.

FIG.2 shows a top down view of a hermetic compressor according to an embodiment of the present invention.

As shown in FIG.2, the suction tube outlet 141 is formed where the suction tube 140 meets the hermetic shell of the hermetic compressor 100. The location of the suction tube outlet 141 overlaps with the cylinder head 122 and is close to one of the sides of the cylinder head 122. The suction muffler 130 is located adjacent to the cylinder head 122 and on the opposite side of the cylinder head 122 from the location of the suction tube outlet 141. This means that refrigerant flowing from the suction tube outlet 141 to the suction muffler inlet 131 flows over the surface of the cylinder head 122. FIG.3 shows a side view of hermetic compressor according to an embodiment of the present invention. As shown in FIG.3, the suction tube outlet 141 of the suction tube 140 is arranged on the upper shell portion 102 of the hermetic shell. The suction tube outlet 141 is positioned to overlap with the cylinder head 122. Position of the suction tube outlet 141 is close to one side of the cylinder head 122. The suction muffler 130 is arranged adjacent to and below the cylinder head 122. The suction muffler inlet 131 is positioned adjacent to the side of the cylinder head 122 which is opposite to the side of the cylinder head 122 close to the suction tube outlet 141. Thus, the suction tube outlet 141 is laterally offset from the suction muffler inlet 131.

As shown in FIG.3, the suction tube outlet 141 is vertically offset from the suction muffler inlet 131. The vertical position of the suction tube outlet 141 is offset from the suction muffler inlet 131. This has the effect of increasing the distance over the surface of the cylinder head 122 that the refrigerant travels when flowing from the suction tube outlet 141 to the suction muffler inlet 131. This increases the cooling effect on the compressed refrigerant which flows to the discharge tube 150.

Further, as shown in FIG.3, the suction muffler inlet 131 is vertically above the suction tube outlet 141.

In addition to the cooling effect on the cylinder head 122 and therefore the compressed refrigerant, the offsetting of the positions of the suction muffler inlet 131 and the suction tube outlet 141 and in particular the positioning of the suction muffler inlet 131 above the suction tube outlet 141 has an additional effect of suppressing the intake of liquid refrigerant. Refrigerant, in both liquid and gaseous state, exits from the suction tube outlet 141 flows pass the cylinder block. Due to the offset position of the suction muffler inlet 131, and the suction tube outlet 141, most of the liquid refrigerant will remain in the hermetically sealed interior of the hermetic shell, leaving mainly the gaseous refrigerant to be admitted into the suction muffler inlet 131.

FIG.4 shows a suction muffler of a hermetic compressor according to an embodiment of the present invention. As shown in FIG.4, the suction muffler 130 has a suction muffler inlet 131 which faces upwards and is arranged in a position above the suction muffler body 132. A suction muffler outlet 133 extends from the suction muffler body 132 and couples to the interior of the compression chamber of the cylinder block 121.

As mentioned above, the configuration of the suction muffler 130 shown in FIG.4 provides for reducing the intake of liquid refrigerant into the suction muffler 130 and therefore suppresses the presence of liquid refrigerant in the compression chamber. This effect is achieved because the gas intake into the suction muffler inlet 131 is faces upwards, reducing the amount of liquid that enters the suction muffler 130. Further, the suction muffler inlet 131 is positioned at vertically high position, this means that the distance from oil and liquid refrigerant that collects in the bottom of the hermetic shell is maximized.

Compressors having the suction arrangement described above may be used in commercial refrigeration applications. R404A and R448A and other mixed refrigerants are used in these applications. An embodiment uses R404A, but since there is a global shift towards the usage of low global warming potential (GWP) refrigerants, R448A is considered since it has lower GWP.

R448A is a non-azeotropic refrigerant blend that possess temperature glide which results from the different refrigerant blends that boils across a range of temperatures at any given pressure. Temperature glide varies depending on each mixed refrigerant composition. Due to the characteristics of these refrigerants, there is an increase in the discharge gas temperature during operation, which eventually affects the efficiency and the reliability of the compressor. Due to this increase in discharge gas temperatures, the suction configuration described above which acts to reduce the discharge gas temperature is particularly advantageous.

Whilst the foregoing description has described exemplary embodiments, it will be understood by those skilled in the art that many variations of the embodiments can be made within the scope and spirit of the present invention.