Reciprocating compressor with suction pre-chamber

Abstract

A reciprocating compressor having a single head in which a suction chamber and a discharge chamber are defined includes a suction pre-chamber in which a flow of cold low pressure gas is homogenized and forms a flow tube that delivers the flow of cold low pressure gas directly into a cylinder, the gas is not mixed with a gas boundary layer adjacent to the wall of the suction chamber.

Description

Technical Field

[0001] This invention belongs to the technical field of reciprocating piston compressors used in the refrigeration and heat pump industries, and more generally in commercial, industrial, transportation, and process cooling fields.

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

[0003] This invention is particularly applicable to the field of transcritical and subcritical carbon dioxide compressors. Background Technology

[0004] Typically, inside a reciprocating compressor, there are markings for a low-pressure section and a high-pressure section. The low-pressure section is the suction pressure of the gas inside the machine, while the high-pressure section is the discharge pressure of the refrigerant fluid that has been compressed by the piston inside the cylinder.

[0005] The piston is connected to a connecting rod, which is driven by the crankshaft; these crank mechanisms require lubrication, which is achieved by supplying lubricating oil to a dedicated circuit that delivers the lubricating oil to various locations within the compressor.

[0006] It should be noted that in this patent text, the terms "refrigerant circuit" or "refrigeration circuit" refer to the collection of pipes and devices in which refrigerant fluid discharged from the compressor circulates. In the following text, the term refers both to the refrigeration circuit itself and to the heat pump circuit.

[0007] The configuration of a reciprocating compressor typically includes a crankcase, inside which are housed the cylinder, the crankshaft with connecting rods and pistons, and the lubrication system; the electric motor that drives the compressor is often also housed in the crankcase.

[0008] Typically, in this type of compressor, the upper portion of the cylinder is enclosed by a valve support plate, to which a reed valve is attached. This reed valve opens and closes the cylinder's inlet and outlet ports. Above the valve plate is the compressor head, which includes an intake chamber and an outlet chamber.

[0009] In small commercial compressors, the two chambers are confined within the same head and separated by a partition. This architecture was established for several reasons: one reason is that it is less expensive to manufacture a single head with two chambers than to manufacture two heads, each with only one chamber; another reason involves the fact that this reduces the number of seals, which are always potential sources of refrigerant gas leakage; and finally, it must be considered that in small compressors, the necessary space cannot always be found for all the screws required to attach both heads—instead of just one head—to the crankcase.

[0010] Typically, this type of compressor is configured such that: the cold gas flow follows a path through the crankcase, passes through and / or through the electric motor to cool the electric motor, and separates the lubricating oil from the refrigerant, while the lubricating oil falls back to the lower part of the crankcase. Then, the cold gas flow passes from bottom to top through the valve support plate and reaches the intake chamber, where it turns in the intake chamber during the intake phase and passes through the reed valve down into the cylinder, moving by means of the pressure difference generated by the piston moving down to bottom dead center.

[0011] The discharge chamber is the hottest part of the compressor because the gas has already been heated by the compression action applied by the piston; this is especially pronounced in machines that compress carbon dioxide, where the compressed gas can reach exceptionally high temperatures, even in the range of 150°C. Therefore, a significant portion of the heat is transferred to the walls of the discharge chamber, which are separated from the suction chamber by a partition wall, and heat is conducted to raise the temperature of the entire head—including the suction chamber; the suction chamber inevitably releases some heat to the low-pressure gas flowing through it, the undesirable consequence of which is gas expansion and a reduction in the mass drawn into the cylinder, thus decreasing the compressor's efficiency.

[0012] US2180493A discloses a compressor in which gas is drawn in from the side of a crank mechanism, passed through a pipe, and then delivered to the crankcase of the compressor. In the compressor, the expanded gas is introduced into a pre-chamber, which has only the function of separating lubricating oil. The lubricating oil is driven by the cold gas, causing the lubricating oil to be discharged into the lower part of the crankcase, while the actual gas is guided upward to the intake chamber. Summary of the Invention

[0013] In the field of reciprocating compressors with an intake chamber and an exhaust chamber confined in a single head, and particularly in the field of reciprocating compressors using carbon dioxide as the refrigerant fluid, it is necessary to minimize the heating of the cold fluid as it passes through the compressor and before it is heated by compression within the cylinder.

[0014] At the same time, it is necessary to avoid increasing the manufacturing cost, weight, and overall size of the compressor.

[0015] Therefore, the object of the present invention is to provide a reciprocating compressor in which the temperature difference of the cold gas occurring between the compressor inlet and the cylinder inlet is less than the temperature rise occurring in a prior art compressor having the same other characteristics such as displacement, number of cylinders, crankshaft rotation speed, compression ratio, etc.

[0016] Another object of the present invention is to provide a device that is more efficient and less expensive than compressors manufactured according to the prior art.

[0017] These and other objectives, which will be readily apparent to those skilled in the art upon reading this document, are achieved by means of a device comprising at least one intake pre-chamber defined within a crankcase, below a valve plate, corresponding to an intake chamber defined within a head. The configuration of the intake pre-chamber, the intake chamber, and the passage portion defined in the valve plate creates a flow path for cold, low-pressure gas within the intake chamber, thereby preventing the cold, low-pressure gas from mixing with a layer of hot, low-pressure gas adjacent to the walls of the intake chamber. The crankcase defines two pneumatically separated sections by walls; a first section houses a motor, and a second section houses a crank mechanism driven by the motor via a shaft passing through the wall; a stopcock, through which low-pressure gas is directed into the compressor, is positioned corresponding to the first section of the crankcase such that the gas flow into the compressor passes through and cools the electric motor within the section housing the electric motor, and then reaches the intake pre-chamber without passing through the second section of the crankcase, i.e., the section housing the crank mechanism.

[0018] Unlike the configuration described in US2180493A, in the compressor of the subject matter of this invention, the separation of oil from the cold suction gas mainly occurs in the first part of the crankcase, i.e., the part that houses the motor, so that excess oil accumulates at the bottom of the first part of the crankcase and is then transferred from there to the second part to lubricate the crankshaft mechanism. However, the remaining portion of lubricating oil mixed with the refrigerant fluid inevitably tends to reach and remain in the suction pre-cavity. Therefore, the lower part of the suction pre-cavity is shaped to deliver oil to a channel communicating with the crankcase below, thereby facilitating oil discharge. This structure is advantageous but not essential because, in this invention, the suction pre-cavity functions to distribute the flow of cold suction gas below the head. By keeping the gas stationary inside the suction pre-cavity, the cold suction gas is prevented from mixing with the low-pressure gas layer in the appropriate suction cavity, which has been heated by the head wall and is located above the valve plate. The valve plate is defined with orifices to guide the flow directly into the internal region of the pre-cavity to avoid mixing with the heated gas layer adjacent to the head wall.

[0019] According to the implementation method that facilitates the formation of flow channels, the holes and pipes through which the low-pressure gas passes can extend along an inclined axis, or even only partially along an inclined axis; for the same reason, the ends of the holes and pipes can have chamfers.

[0020] The same inventive concept applies to reciprocating compressors with the motor outside the crankcase, also known as open compressors, as well as reciprocating compressors with the motor integrated inside the crankcase, also known as semi-hermetic or hermetic compressors. Attached Figure Description

[0021] Figure 1 This shows a view of the compressor as seen from the side of the motor.

[0022] Figure 2 The image shows a view of the compressor as seen from the nameplate side.

[0023] Figure 3 A first longitudinal section view (AA) of the compressor is shown.

[0024] Figure 4 A first cross-sectional view (BB) of the compressor is shown.

[0025] Figure 5 A second cross-sectional view (CC) of the compressor is shown, along with an enlarged view of the pre-chamber and the intake chamber, and a schematic diagram of the fresh gas flow (F).

[0026] Figure 6 A second longitudinal section (DD) view of the compressor is shown, with an enlarged view of the pre-chamber and the suction chamber.

[0027] Figure 7 A view of the valve plate (7) of a twin-cylinder compressor is shown; in the example shown, a chamfer is defined at the end of the orifice (14) to facilitate the formation of the flow tube (F).

[0028] Figure 8 It shows Figure 7 A cross-sectional view (EE) of the valve plate in the diagram. Detailed Implementation

[0029] In the embodiment shown in the accompanying drawings, the device of the subject of the invention includes a crankcase (1) that is divided into two parts by a wall (17). A first part houses an electric motor, and a second part houses a crank mechanism that is rotated by the motor (2) via a crankshaft (3) passing through the wall (17). Connecting rods (4) are rotatably connected to the crankshaft, each connecting rod causing a piston (5) to slide within a corresponding cylinder (6). It should be noted that the term crankshaft is used to refer to any typical embodiment of the crank mechanism that receives rotational motion from the motor shaft and converts it into reciprocating motion of the piston sliding within a cylinder, such as an eccentric shaft. The wall (17) pneumatically separates the first and second parts of the crankcase, through which the shaft transmitting motion from the motor to the crank mechanism passes, and defines a bottom discharge channel that transfers excess oil that gradually accumulates at the bottom of the first part to the second part. The upper part of the cylinder is closed by a valve plate (7), and above the valve plate is a head (10), which defines a discharge chamber (12) for receiving high-pressure hot fluid and a suction chamber (11) for receiving low-pressure cold fluid.

[0030] Corresponding to the intake chamber, at least one inlet port (8) is defined in the valve plate, which is opened and closed by means of a reed valve (9) movable toward the interior of the cylinder.

[0031] In the crankcase, corresponding to the intake chamber, an intake pre-chamber (13) is defined, which communicates with the intake chamber (11) through one or more holes (14) defined in the valve plate (7). The filling of the intake pre-chamber by low-pressure gas occurs through one or more pipes (15) that connect the lower portion of the pre-chamber to the interior of the first part of the crankcase (1). The inlet for the low-pressure fluid in the compressor is through a stopcock (16) positioned to correspond to the first part of the crankcase (1), such that the cold fluid reaching the intake pre-chamber (11) passes through the motor (2) and cools the motor. In this way, the low-pressure fluid does not come into contact with the crank mechanism located in the second part of the crankcase (1).

[0032] The mutual positioning of the pipe (15) relative to the hole (14) is very important for achieving the homogenization effect of cold fluid in the suction pre-cavity (13).

[0033] The orifice (14) is confined in the valve plate (7) in such a position that the drawn gas is directly guided to the inlet port (8) through which the gas is supplied to the cylinder (6).

[0034] The effect of this structure is that it creates a flow channel (F) of cold, low-pressure gas within the intake chamber (11), while the boundary layer of gas in quasi-static conditions contacts the wall of the intake chamber. This boundary layer is heated due to its contact with the wall of the intake chamber (11), and the wall of the intake chamber is inevitably heated due to its proximity to the exhaust chamber (12). Therefore, within the intake chamber (11), the mixing of the incoming cold flow with the gas already present in the intake chamber but heated due to contact with the wall of the intake chamber, as well as the subsequent homogenization, is significantly reduced.

[0035] To achieve the above effect, it is crucial that the diameter of the hole (14) confined in the valve plate is proportional to the height of the suction chamber; in addition, it should be noted that the hole (14) can be formed in a variety of ways, and for the sake of illustration, we will consider the hole as having a circular cross-section.

[0036] In the case of a circular hole, if the distance between the outer edge of the valve plate (7) and the inner edge of the suction chamber (11) is between 1 and 2 times the diameter of the hole (14), preferably, if the distance between the outer edge of the valve plate and the inner edge of the suction chamber is 1.5 times the diameter of the hole, a good effect can be obtained.

[0037] Preferably, the valve plate (7) defines an inlet hole (14) for each inlet port (8) in the cylinder.

[0038] It is also advantageous that the volume of the intake pre-chamber (13) is at least equal to the total volume of the supply cylinder, and the cross-section of the pipe (15) is large enough to minimize pressure loss.

[0039] One particularly effective solution is that, in order to facilitate the formation of flow tubes, the holes (14) on the valve plate (7) can be inclined, or have chamfers with different right-angled sides and angles defined at their ends; the latter is achieved by drilling along a straight line and then making the chamfers by countersinking the hole with its axis inclined relative to the axis of the hole.

[0040] Similarly, to facilitate the formation of the flow tube, a chamfer with variable right angle sides and / or angles can also be formed on the inlet port (8) of the cylinder located on the suction chamber side.

[0041] To prevent oil from accumulating in the intake pre-chamber (13), it is important that the wall defining the lower portion of the intake pre-chamber is inclined toward the pipe (15), and that the pipe is also configured to facilitate oil return to the crankcase itself; this configuration is particularly useful in the case of a series of frequent starts and stops of the compressor.

Claims

1. A reciprocating piston compressor comprising a crankcase (1) having a first portion defined within the crankcase (1) for receiving a motor (2) that transmits motion to a crank mechanism located in a second portion defined within the crankcase (1) and pneumatically separated from the first portion by means of a wall (17), the crank mechanism comprising a crankshaft (3) passing through the wall (17) and configured to rotate by the motor (2) thereby driving one or more by means of a connecting rod (4). A piston (5) slides within a corresponding cylinder (6), above which is a valve plate (7) defining at least one inlet port (8) and at least one outlet port for each cylinder, the inlet port being closed by an intake valve (9) and the outlet port also being closed by its own outlet valve; a head (10) is positioned above the valve plate (7), defining an outlet chamber (12) and an intake chamber (11), the outlet chamber and the intake chamber being adjacent to each other and respectively arranged to correspond to the outlet valve and the intake valve (9), characterized in that, The reciprocating piston compressor includes a cock (16) positioned to correspond to the first portion of the crankcase (1), through which low-pressure fluid enters the first portion of the crankcase (1), which is connected to a pre-intake chamber (13) via one or more pipes (15), the pre-intake chamber being positioned below the valve plate (7) and connected to the intake chamber (11) via one or more holes (14) defined in the valve plate (7).

2. The compressor according to the preceding claim, characterized in that, The lower portion of the pre-cavity (13) is inclined toward the inlet of the one or more pipes (15) to facilitate the discharge of oil into the crankcase.

3. The compressor according to any one of the preceding claims, characterized in that, The volume of the intake pre-chamber (13) is at least equal to the total volume of the cylinder supplied by the intake pre-chamber.

4. The compressor according to any one of the preceding claims, characterized in that, Corresponding to the outlet in the pre-cavity (13), the axis of each of the one or more pipes (15) is aligned with the central portion of the one or more holes (14) defined in the valve plate (7).

5. The compressor according to any one of the preceding claims, characterized in that, The one or more holes (14) are generally circular, and the distance between the outer edge of the valve plate (7) and the inner edge of the suction chamber (11) is between 1 and 2 times the diameter of the one or more holes (14).

6. The compressor according to the preceding claim, characterized in that, The distance between the outer edge of the valve plate (7) and the inner edge of the suction chamber (11) is between 1 and 1.5 times the diameter of the one or more holes (14).

7. The compressor according to any one of the preceding claims, characterized in that, The proportions of the suction chamber (11), the pre-suction chamber (13), the conduit (15), and all the channels defined in the valve plate (7) are such that: a flow tube (F) is defined in the suction chamber (11) in which cold gas flows without mixing with the gas adjacent to the wall of the suction chamber (11).

8. The compressor according to the preceding claim, characterized in that, The one or more holes (14) defined in the valve plate (7) are arranged along an at least partially inclined axis to facilitate the formation of the flow tube (F) within the suction chamber (11).

9. The compressor according to claim 6 or 7, characterized in that, A chamfer is defined at the end of one or more holes (14) defined in the valve plate (7).

10. The compressor according to any one of claims 6 to 8, characterized in that, The at least one inlet port (8) defined in the valve plate (7) is arranged along an axis that is at least partially inclined to facilitate the formation of the flow tube (F).

11. The compressor according to any one of the preceding claims, characterized in that, A chamfer is defined at the end of the at least one inlet port (8) defined in the valve plate (7).

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