Reciprocating compressor with intake pre-chamber

Abstract

A reciprocating compressor with a single head in which the intake chamber and discharge chamber are defined, including an intake pre-chamber in which the flow of cool, low-pressure gas is homogenized and forms a stream tube that delivers it directly into the cylinder, without mixing with the liminal layer of gas adjacent to the walls of the intake chamber.

Description

[0001] DESCRIPTION

[0002] Title

[0003] RECIPROCATING COMPRESSOR WITH INTAKE PRE-CHAMBER

[0004] Technical field

[0005]

[0001] The present invention belongs to the technical field of reciprocating piston compressors used in the refrigeration and heat pump industry as well as more generally in the fields of commerce, industry, transportation, process cooling, etc...

[0006]

[0002] More specifically, the present invention relates to a reciprocating compressor of the type preferably used with closed-type refrigeration circuits, of the type that draws in a refrigerant fluid in gas phase and compresses it into a refrigerant circuit in which the gas expands and then re-enters the compressor at a lower pressure.

[0007]

[0003] The present invention is specially applied in the field of both transcritical and subcritical carbon dioxide compressors.

[0008] Present status of the art

[0009]

[0004] In general, inside reciprocating compressors, a low-pressure portion is identified, i.e., the suction pressure of the gas inside the machine, and a high-pressure portion, i.e., the discharge pressure of the refrigerant fluid, which has been compressed by the pistons inside the cylinders.

[0010]

[0005] The pistons are connected to connecting rods that are in turn driven by a crankshaft; these crank mechanisms require lubrication, and the latter is provided by feeding lubricating oil into special circuits that deliver it to various locations within the compressor.

[0011]

[0006] It should be noted that in the present patent text the expression "refrigerant circuit" or "refrigeration circuit" means collectively the set of piping and equipment in which a refrigerant fluid discharged from the compressor is circulated. Hereafter this term will refer to both refrigeration circuits as such and heat pump circuits.

[0012]

[0007] The configuration of reciprocating compressors generally includes a crankcase inside of which are housed the cylinders, the crankshaft with connecting rods and pistons, as well as the lubrication system; very often the electric motor that drives the compressor is also housed inside the crankcase.

[0008] Generally, in this type of compressors, the upper part of the cylinders is closed by a valve carrier plate to which are attached the reed valves that open and close the inlet and exhaust ports of the cylinders. Above the valve plate is the compressor head, which includes the intake and discharge chambers.

[0013]

[0009] In small commercial-type compressors, the two chambers are defined within the same head and are subdivided by a bulkhead; this architecture has established itself for several reasons: one reason is that making a single head with two chambers is less expensive than it would be to make two heads each with only one chamber; another reason is related to the fact that in this way the number of seals, which are always a source of potential refrigerant gas leakage, is reduced; finally, it must also be kept in mind that in small compressors it would not always be possible to find the necessary space for all the screws that would be needed to attach two heads to the crankcase instead of only one.

[0014]

[0010] Normally, compressors of this type are configured so that the cold gas flow is routed through the crankcase by lapping and / or passing through the electric motor to cool it and to separate from the refrigerant the lubricating oil, which falls back into the lower portion of the crankcase, then the flow of cold gas crosses the valve carrier plate from down to up and reaches the intake chamber, where it makes a turn to descend into the cylinder during the intake phase, passing through the reed valve, moving by virtue of the pressure difference caused by the descent of the piston to the bottom dead center.

[0015] [Oil] The discharge chamber is the portion of the compressor at the highest temperature because the gas has been heated by the compression action exerted by the pistons; in machines that compress carbon dioxide, this phenomenon is particularly pronounced because the compressed gas can reach particularly high temperatures, even in the range of 150 °C. As a result, a significant portion of the thermal energy is transferred to the walls of the discharge chamber, between which is the partition wall with the suction chamber, and by conduction the heat raises the temperature of the entire head, including the intake chamber; the latter inevitably gives up some of the heat to the low-pressure gas flowing through it, with the unfortunate consequence of expanding the gas and reducing the amount of mass that is drawn into the cylinder, thus reducing the efficiency of the compressor

[0016]

[0012] Shown in US2180493A is a compressor in which the intake of gas is from the side of the crank mechanism, through a duct that then delivers the gas into the crankcase of the compressor, in this compressor the expanded gas is introduced into a pre-chamber that has only the function of separating the lubricating oil, which is dragged by the cold gas, causing it to drain to the lower portion of the crankcase, while the actual gas is directed upward to the intake chamber.

[0017] Objects and summary of the invention

[0018]

[0013] In the field of reciprocating compressors with the intake chamber and discharge chamber defined in a single head, and particularly in the field of reciprocating compressors working with carbon dioxide as the refrigerant fluid, there is a need to reduce as much as possible the heating of the cold fluid as it passes through the compressor, before it is heated in a cylinder by compression.

[0019]

[0014] At the same time, there is a need not to increase the manufacturing costs, weight and overall dimensions of the compressor.

[0020]

[0015] It is therefore the objective of the present invention to provide a reciprocating compressor in which the temperature differential of cold gas that occurs between the inlet to the compressor and the inlet to the cylinder is less than the temperature rise that occurs in known-art compressors with equal other characteristics such as displacement, number of cylinders, crankshaft rotational speed, compression ratio, etc...

[0021]

[0016] A further objective of the present invention is to provide a more efficient and less expensive device than compressors built according to the known art.

[0022]

[0017] These and other objectives, which will become clear to the skilled person from reading this text, are achieved by means of a device comprising at least one intake pre-chamber defined inside the crankcase, below the valve plate, at the intake chamber defined inside the head. The configuration of the intake pre-chamber, intake chamber and passage sections defined in the valve plate being such as to create within the intake chamber a streamtube of the cool low-pressure gas so that the latter does not mix with the hot layer of low-pressure gas that is adjacent to the walls of the intake chamber. Within the crankcase are defined two portions pneumatically separated by a wall, the first of which houses the motor and the second of which houses the crank mechanism driven by the motor via a shaft that runs through the wall; the cock through which the low-pressure gas is introduced into the compressor is located in correspondence with the first portion of the crankcase, so that the flow of gas entering the compressor passes through the portion that accommodates the electric motor and cools it and then reaches the intake pre-chamber without passing through the second portion of the crankcase, the one that accommodates the crank mechanism.

[0023]

[0018] In contrast to the configuration described in US2180493A, in the compressor which is the subject of the present invention, the separation of the oil from the cold suction gas takes place mainly in the first portion of the crankcase, which houses the motor, so that the excess oil collects at the bottom in said first portion of the crankcase and is then transferred from there to the second portion, to lubricate the crank mechanism, however, a residual part of the lubricating oil that is mixed with the refrigerant fluid inevitably tends to reach and remain in the intake pre-chamber, and for this reason the lower portion of the latter is conformed so as to convey the oil to the communication passages with the crankcase below, facilitating its draining; this conformation is advantageous, but not indispensable, since in the present invention the suction prechamber performs the main function of distributing the flow of cold suction gas below the head by keeping that gas stationary in its interior to prevent that gas from mixing with the layer of low-pressure gas that has been heated by the head walls and that is located in the proper suction chamber, above the valve plate; holes are defined in the latter to guide the flow directly into the inner zone of the pre-chamber to avoid the mixing with the heated gas layers that stay adjacent to the head walls.

[0024]

[0019] According to an embodiment that facilitates the formation of the streamtube, the holes and ducts traversed by the low-pressure gas may develop according to inclined axes, even only partially; for the same reason, their ends may have chamfers.

[0020] The same inventive concept is applicable both to reciprocating compressors with motor outside the crankcase, also known as open compressors, and to reciprocating compressors with motor integrated inside the crankcase, known as semi-hermetic or hermetic compressors.

[0025] Brief description of the drawings

[0026]

[0021]

[0027] Fig. 1 shows a view of the compressor from the motor side.

[0028] Fig. 2 shows a view of the compressor from the nameplate side.

[0029] Fig. 3 shows a first longitudinal section (A-A) of the compressor.

[0030] Fig. 4 shows a first cross section (B-B) of the compressor.

[0031] Fig. 5 shows a second cross-section (C-C) of the compressor, with an enlarged view of the pre-chamber and intake chamber, with a schematic of the stream (F) of fresh gas.

[0032] Fig. 6 shows a second longitudinal section (D-D) of the compressor, with an enlarged view of the pre-chamber and intake chamber.

[0033] Fig. 7 shows a view of the valve plate (7) of a two-cylinder compressor; in the example shown, chamfers are defined at the extremities of the holes (14) to facilitate the formation of the stream tube (F).

[0034] Fig. 8 shows a section (E-E) of the valve plate from Fig. 7.

[0035] Detailed description of an embodiment of the invention

[0036]

[0022] In the embodiment shown in the attached figures, the device that is the subject of the present invention comprises a crankcase (1) within which two portions are defined separated by a wall (17), a first portion in which an electric motor (2) is housed and a second portion that accommodates the crank mechanism placed in rotation by the motor (2) by means of a crankshaft (3), which passes through the wall (17), to which are rotationally connected connecting rods (4) each of which makes a piston (5) slide inside the respective cylinder (6). It should be noted that the term crankshaft is used to refer to any typical embodiment of a crank mechanism that receives rotary motion from the shaft of a motor and transforms it into the reciprocating motion of pistons sliding inside cylinders, for example, an eccentric shaft. The wall (17) pneumatically separates the first portion of the crankcase from the second portion, it is traversed by the shaft that transmits motion from the motor to the crank mechanism, and a bottom drainage channel is defined in it that transfers into the second portion the excess oil that gradually collects at the bottom of the first portion.

[0037]

[0023] The upper part of the cylinders is closed by a valve plate (7) above which is the head (10) in which the discharge chamber (12), which accommodates the high-pressure hot fluid, and the intake chamber (11), which accommodates the low-pressure cold fluid, are defined.

[0038]

[0024] In correspondence with the latter, at least one admission port (8) is defined in the valve plate, which opens and closes by means of a reed valve (9), movable toward the inside of the cylinder.

[0025] In the crankcase, in correspondence with the intake chamber, there is defined an intake prechamber (13) that communicates with the intake chamber (11) through one or more holes (14) defined in the valve plate (7). Filling of the intake pre-chamber by the low-pressure gas occurs through one or more ducts (15) that connect the lower portion of the pre-chamber with the inside of the first portion of the crankcase (1). The inlet of the low-pressure fluid inside the compressor is through a cock (16) located in correspondence with the first portion of the crankcase (1), so that the cold fluid to reach the intake pre-chamber (11) laps the motor (2) and cools it. In this way, the low-pressure fluid does not come into contact with the crank mechanism, which is located in the second portion of the crankcase (1).

[0039]

[0026] The reciprocal positioning of the ducts (15) with respect to that of the holes (14) is very important to achieve the effect of homogenizing the cold fluid inside the intake pre-chamber (13).

[0040]

[0027] The holes (14) are defined in the valve plate (7) in such a position as to direct the flow of suctioned gas directly to the admission port (8) through which the gas is fed into the cylinder (6).

[0041]

[0028] The effect of the described conformation is to create within the intake chamber (11) a stream tube (F) of the cold low-pressure gas, leaving, in contact with the walls of the intake chamber, a liminal layer of gas under quasi-static conditions, which heats up due to contact with the walls of the intake chamber (11), the latter in turn being inevitably heated due to contiguity with the discharge chamber (12). Thus inside the intake chamber (11) there is a great reduction in gas mixing and consequent homogenization between the incoming cool flow and the gas already present in the intake chamber, which, on the other hand, has been heated due to contact with the walls of the latter.

[0042]

[0029] In order to achieve the effect described above, it is important that the diameter of the holes (14) defined in the valve plate be proportionate to the height of the intake chamber; moreover, it should be noted that the holes (14) can be conformed in various ways, and only for convenience of exposition in the present text we refer to them as if they were holes with a circular cross-section.

[0043]

[0030] In the case of circular holes, good results are obtained if the distance between the extrados of the valve plate (7) and the intrados of the intake chamber (11) is between one and two times the diameter of the holes (14), preferably one and a half times.

[0044]

[0031] It is preferable that an inlet hole (14) is defined in the valve plate (7) for each admission port (8) in the cylinder.

[0045]

[0032] It is also advantageous for the volume of the intake pre-chamber (13) to be at least equal to the total volume of the fed cylinders, and for the cross-section of the ducts (15) to be large enough to minimize pressure losses.

[0046]

[0033] A particularly efficient solution is that, in order to facilitate the formation of the stream tube, the holes (14) on the valve plate (7) can be inclined or that chamfers of varying cathetus and angle are defined at their ends; the latter are made by drilling in a straight line and then making a chamfer with a countersink whose axis is inclined with respect to the axis of the hole.

[0047]

[0034] Again, in order to facilitate stream tube formation, chamfers with variable cathetus and / or angle can also be formed on the admission ports (8) of the cylinder on the intake chamber side.

[0048]

[0035] To prevent oil accumulation in the intake pre-chamber (13), it is important that the wall that delimits the lower portion of the intake pre-chamber is inclined toward the ducts (15) and that the ducts are also conformed in such a way as to facilitate the outflow of oil to the crankcase itself; this configuration proves useful especially in conjunction with a series of starts and stops of the compressor.

Claims

CLAIMS1. Reciprocating piston compressor, comprising a crankcase (1) within which is defined a first portion accommodating a motor (2) which transmits motion to a crank mechanism which is located in a second portion defined within said crankcase (1) and is pneumatically separated from said first portion by means of a wall (17), said crank mechanism comprising a crankshaft (3), which passes through said wall (17) and is set in rotation by said motor (2), to drive by means of connecting rods (4) one or more pistons (5) which slide within respective cylinders (6) above which is a valve plate (7) in which, for each cylinder, is defined at least one admission port (8), closed by an intake valve (9), and at least one exhaust port, also closed by its own exhaust valve; above said valve plate (7) being located a head (10) in which are defined a discharge chamber (12) and an intake chamber (11), contiguous to each other and placed respectively in correspondence with said exhaust valve and said intake valve (9), characterized by comprising a cock (16), located in correspondence with said first portion of said crankcase (1), through which a low-pressure fluid enters said first portion of said crankcase (1) which, by means of one or more ducts (15), is in communication with an intake prechamber (13), which is located below said valve plate (7) and communicates with said intake chamber (11) by means of one or more holes (14) defined in said valve plate (7).

2. Compressor according to the preceding claim characterized in that, the lower portion of said pre-chamber (13) is inclined toward the inlet of said one or more ducts (15) to facilitate drainage of oil into the crankcase.

3. Compressor as according to one of the preceding claims characterized in that, the volume of said intake pre-chamber (13) is at least equal to the total volume of cylinders fed by it.

4. Compressor according to one of the preceding claims characterized in that in correspondence with the outlet in said pre-chamber (13) the axis of each of said one or more ducts (15) is respectively aligned with the central portion of said one or more holes (14) defined in said valve plate (7).

5. Compressor according to one of the preceding claims characterized in that said one or more holes (14) are substantially circular and in that the distance between the extrados of said valve plate (7) and the intrados of said intake chamber (11) is between one and two times the diameter of said one or more holes (14).

6. Compressor according to the preceding claim characterized in that said distance between the extrados of said valve plate (7) and the intrados of said intake chamber (11) is between one and one- half times the diameter of said one or more holes (14).

7. Compressor according to one of the preceding claims characterized in that the proportions of said intake chamber (11), said intake pre-chamber (13), said ducts (15) and all the passages defined in said valve plate (7) are such as to define within said intake chamber (11) a stream tube (F) within which cool gas flows without mixing with the gas that is in proximity to the walls of said intakechamber (11).

8. Compressor according to the preceding claim characterized in that said one or more holes (14) defined in said valve plate (7) are arranged along an axis at least partially inclined so as to facilitate the formation of said stream tube (F) within said intake chamber (11).

9. Compressor according to the preceding claims 6 or 7 characterized in that chamfers are defined at the ends of said one or more holes (14) defined in said valve plate (7).

10. Compressor according to one of the preceding claims from 6 to 8 characterized in that said at least one admission port (8) defined in said valve plate (7) is arranged along an at least partially inclined axis so as to facilitate the formation of said stream tube (F).

11. Compressor according to one of the preceding claims characterized in that chamfers are defined at the ends of said at least one admission port (8) defined in said valve plate (7).

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