EP0195486A2

EP0195486A2 - Hermetic motor-compressor unit for a refrigeration circuit

Info

Publication number: EP0195486A2
Application number: EP86200422A
Authority: EP
Inventors: Riccardo Bianchi; Vittorio Bianchi
Original assignee: Philips Gloeilampenfabrieken NV; Whirlpool International BV
Current assignee: Whirlpool International BV
Priority date: 1985-03-21
Filing date: 1986-03-18
Publication date: 1986-09-24
Also published as: ES293027Y; IT1184167B; EP0195486A3; IT8519995A0; CN86102710A; IT8519995A1; JPS61223276A; ES293027U; CN1006489B

Abstract

In a motor-compressor unit for a refrigerant circuit the suction or inlet plenum chamber (A) is made as a separate part (27) of a plastics material in order to reduce heat transfer from the cylinder head (17) to the suction chamber (A). Preferably, the suction chamber (27) is integrally formed with the inlet muffler (40). A further reduction of heat transfer to the refrigerant gas is obtained by an elastic connection (52) between the inlet conduit (60) and the inlet muffler (40).

Description

The invention relates to a hermetic motor-compressor unit for a refrigeration circuit, said motor-compressor unit being mounted in a sealed outer casing and comprising an electric motor and a reciprocating compressor driven by said motor, said compressor having a metal cylinder head including a compression chamber, and having an inlet conduit rigidly connected to the outlet casing, an inlet muffler and a suction chamber.
United States Patent Specification No. 4,370,104 discloses such a hermetic motor-compressor unit In this Specification the-refrigeration gas in the circuit is returned to the compressor through an inlet conduit into an open mouth of an inlet muffler and from there into a suction or inlet plenum chamber in the metal cylinder head of the compressor. Subsequently, the gas is drawn into a compressor cylinder via a suction valve so as to be compressed. The compressed gas, which has attained a high temperature, discharges viaan outlet valve into a compression or outlet plenum chamber also disposed in the metal cylinder head and adjacent to the suction chamber. From the compression chamber, the compressed gas passes through an outlet muffler and outlet conduit to leave the sealed casing. The cylinder head comprises both the suction and compression chamber and these chambers are separated by a metal wall. A disadvantage of this construction is, that the gas inside the suction chamber is heated by the walls of the chamber, which are at a high temperature due to the hot gas in the adjacent compression chamber, the outlet conduit and the valve plate between cylinder head and cylinder. This results in a lower refrigeration capacity and a lower efficiency because of the reduction in the gas specific gravity and thus a reduction in the mass of refrigeration gas drawn into the compressor cylinder during each stroke of the piston.
The main object of the present invention is to provide improvements which reduce the heating of the refrigerant gas entering the cylinder.
According to the invention there is provided a hermetic motor-compressor of the type defined in the opening paragraph, characterized in that the suction chamber is constructed as a separate part of a synthetic material having a low heat transfer coefficient and which is compatible with the refrigerant gas and the lubricating oil. The heat transfer to the gas in the suction chamber is now considerably reduced.
In a preferred embodiment of the invention, said part is formed by an appendix of the inlet muffler and is formed integrally with at least with a part of said muffler. In this respect it is to be noted that mufflers of a plastics material are known.
According to a further embodiment of the invention the metal cylinder head comprises a slot into which said appendix can be inserted and which faces inlet ports of a valve plate. Elastically deformable means, such as flat or wire springs, ensure a stable connection between the cylinder head and the appendix.
Further, it is known to reduce heating of the inflowing refrigerant gas by means of a so-called direct suction system, which is attained by a direct connection between the inlet conduit and the inlet muffler. As the muffler, which is connected directly to the compressor, vibrates with respect to the outer casing and thus with respect to the inlet conduit, a special construction between the inlet conduit and the muffler is necessary. (n the cited U.S. Patent 4,370,104 the muffler is provided with a flared mouth and the open end of the inlet conduit ends near the opening of the mouth. In this way there is no mechanical connection between the inlet conduit and the muffler, which reduces vibrations (and noise). However, due to the open connection between the inlet conduit and the flared mouth, a part of the refrigerant gas may enter into the space inside the casing and may be heated before it is drawn into the muffler. To obviate this it has also been proposed to connect the inlet conduit to the muffler by means of special antivibration joints, but this metal construction leads again to an undesired temperature rise of the refrigerant gas.
Therefore a further object of the present invention is to provide improvements which further reduce the heating of the inflowing refrigerant gas without causing an increase in the transmission of vibrations from the motor-compressor unit to the outer casing.
According to an embodiment of the invention the lower end of the inlet muffler is closed by an elastic cap having a central hole in which the end of the inlet conduit is inserted.
In another embodiment the connection between the inlet conduit and the inlet muffler is formed by an elastic bellows.
In still another embodiment the open lower end of the inlet muffler dips into the lubricant and the inlet conduit opens into the inlet muffler above the level of the lubricant
The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a perspective view (showing the side facing the cylinder) of a conventional cylinder head of a hermetic motor-compressor unit for a refrigeration circuit;
Figure 2 is a sectional view of a hermetic motor-compressor unit according to the invention;
Figure 3 is an end view of the motor-compressor unit taken on the line III-III of Figure 2;
Figure 4 is a perspective view of a spring used for connecting the muffler and the suction chamber to the compressor cylinder head;
Figure 5 is an enlarged-scale cross-sectional view taken on the line V-V in Figure 3;
Figure 6 is a perspective view of another embodiment of the invention;
Figure 7 is a partial perspective view in the direction of the arrow VII of Figure 6 after connection of the muffler to the cylinder head;
Figures 8, 9 and 10 cross-sectional views of three different examples of the connection between the inlet conduit and the muffler.

Figure 1 shows a conventional cylinder head 1 of a hermetic motor-compressor unit The head in question is necessarily made of a metal because it has to resist the pressure of the refrigerant gas leaving the cylinder. The head comprises a suction or inlet plenum chamber 2 surrounded on three sides by a compression or outlet plenum chamber 3. The suction chamber 2 receives the refrigerant gas returning from the working cycle by way of an inlet muffler (not shown). The head is connected to the compressor cylinder via a perforated plate and the appropriate inlet and outlet valves.
The plate contains the ports which connect the chamber 2 to the inlet muffler and the cylinder, and the chamber 3 to the outlet muffler and the cylinder.
In addition to being situated in the same cylinder head 1, the two chambers are disposed adjacent each other and are separated laterally by an internal wall 6. Due to the high temperature of the refrigerant gas flowing through the compression chamber3 the refrigerant gas, which enters the suction chamber 2 at a substantially lower temperature, becomes unduly heated with the consequences stated above.
In order to preclude this, the invention provides the embodiments shown in Figures 2 to 10, and described hereinafter. One of these embodiments is shown in Figures 2 to 5. In these figures, the reference numeral 10 indicates the sealed casing in which the motor-compressor unit comprises a conventional electric motor 12 and a reciprocating compressor 13. The motor comprises a stator 14, a rotor 15 and a crankshaft 16 connected directly to the rotor. The compressor 13 comprises a metal cylinder head 17 and a perforated valve plate 18, which in known manner is provided with the suction valve 19 and the outlet valve 19b. The assembly formed by the cylinder head 17, the valve plate 18 and the valves 19, 19b is secured to the end of the cylinder 20 in which slides the piston 21, which is connected to the eccentric part of the crankshaft 16 by a connecting rod 22.
The metal cylinder head 17 comprises only the compression chamber 23, and a slot or recess24 and not the suction chamber 2 as in the conventional cylinder head 1 shown in Figure 1. The slot 24 has two straight parallel sides and a rounded end. Each of said straight sides is provided with an undercut 25 which commences with a widened portion forming a lead-in (at 26) towards the inlet end of the slot.
This slot which as shown in Figure 2 is bounded towards the cylinder 20 by the valve plate 18, receives at least part of a hollow plastics part 27 inserted into it through the inlet side thereof. In its terminal part, inside the slot 24, the part 27 is laterally open at 28 towards the cylinder 20 at locations in register with some of the ports 30 in the valve plate 18 and the inlet valve formed by a flap 19. The part 27 is pressed against the valve plate 18 and held in position by a flat spring 31, which is shown in detail in Figure 4. This spring comprises a central elongated portion 32 with arcuate ends33. In the centre of this portion there is a rectangular aperture 34 by means of which the spring is mounted on a corresponding protrusion 38 provided on the part 27. In its middle portion the spring 31 comprises two identical side lugs 35 with slits 36 which enable the ends of said lugs to be bent out of the plane of the central portion 32, as shown in Figure 4.
The dimensions of the spring 31 are such that its lugs 35 engage in the undercuts 25 in the cylinder head 17 when the part 27 is inserted into the slot 24. During the insertion of the part these lugs bend and press against the cylinder head to prevent the part 27 from being disengaged from the slot 24 as a result of vibrations and also cause the arcuate ends 33 of the spring 31 to press against the part 27, thereby urging this part firmly against the perforated valve plate 18. The hollow part 27 forms an appendix or extension of a box-shaped inlet muffler 40, with which it communicates. The hollow part 27 is formed integrally with the silencer or with a part thereof if the muffler comprises more than one part, for example two parts, one of box shape and the other in the form of a cover. '
The muffler may comprise a plurality of interconnected internal chambers (see Figure 2) separated by perforated baffles 50.
In the present example, at its lower end the muffler comprises a downwardly open cylindrical extension 51 onto which a cap 52 of an elasctically deformable material is fitted, the grooved periphery 53 of the cap engaging over the edge of the extension 51. The cap comprises a central hole 54. The end of a refrigerant inlet conduit 60 having a diameter greater than of the hole 54 is inserted into this hole with consequent conical deformation of the central part of the cap (see Figure 2). The conduit 60 passes through the casing 10, to which it is welded. In this manner, the vibrations of the motor-compressor unit are not transmitted to the sealed casing in which the motor-compressor unit is disposed. The refrigerant gas enters the muffler 40 through the conduit 60, flows into the hollow appendix 27 and then through the ports 28, 30 and the inlet valve 19 into the cylinder 20 where it is compressed. The compressed refrigerant gas flows into the compression chamber 23 through ports in the valve plate 18 and the outlet valve 19b. From the chamber 23 the compressed gas flows via outlet mufflers and outlet conduits back to the condenser of the refrigeration circuit (not shown).
The part 27 and the inlet muffler are made of a plastics material having a low thermal conductivity and resistant to the working conditions. They may, for example, be injection- moulded from a reinforced thermoplastics material.
This embodiment substantially reduces the transfer of 'heat from the compression chamber 23 to the suction chamber represented by the cavity A in the part 27. In this respect it is to be noted that this cavity is not bounded by metal parts of good thermal conductivity via which the heat of the compressed refrigerant gas can easily heat the refrigerant gas returning from the working cycle.
Figures 6 and 7 show a modification. In these figures, parts equal or corresponding to those of Figures 2 to 5 bear the same reference numerals but with a suffixed letter X. In this modification, the hollow plastics part 27X comprising the suction chamber again constitutes an extension of the inlet muffler 40X. Part 27X is inserted into the slot 24X of the metal cylinder head 17X. One side of part 27X projects somewhat from the slot 24X as shown in Figure 7. A wire spring 70 of open U configuration, whose fixed ends are to the cylinder head 17X by means of screws 71, presses against this projecting side.
Figures 8, 9 and 10 show three different methods of feeding the refrigerant gas returning from its working cycle back to the inlet muffler. In these figures, parts equal or corresponding to those already described in Figures 2 to 5 bear the same reference numerals to which the letters Y, Z and W respectively are suffixed.
In Figure 8, the refrigerant gas inlet conduit 60Y terminates at a hole in the sealed casing 10Y, to which it is welded. A grooved end 81 of an elastic bellows 80 engages the periphery of a hole 82 provided in a side wall of the mutter 40Y comprising the appendix 27Y which defines the suction chamber. The other end of the bellows 80 presses against the inside of the casing 10Y at a location where it surrounds the mouth of the inlet conduit 60Y. In this manner, vibrations of the motor-compressor unit are not transmitted to the refrigeration circuit through the conduit 60Y, and a continuous gas flow between the conduit 60Y and muffler 40Y is ensured.
Figure 9 shows a different elastic bellows 8OZ comprising steps of frusto-conical shape.
Figure ₁0 shows an inlet conduit 60W which passes through the sealed casing 10W to which it is welded. Inside the casing the end portion of the inlet conduit is bent upwards at its inner end. The outlet opening of the bent portion of the conduit extends above the maximum level H which the lubricant L attains in the casing 10W.
The open lower end of the muffler dips to a certain depth into the lubricant L The bent position of the conduit 60W extends into the muffler. For pressure compensation purposes a hole 90 may be provided in the muffler wall above the lubricant level H.

Claims

₁. A hermetic motor-compressor unit for a refrigeration circuit, said motor-compressed unit being mounted in a sealed outer casing and comprising an electric motor and a reciprocating compressor driven by said motor, said compressor having a metal cylinder head including a compression chamber, and having an inlet conduit rigidly connected to the outlet casing, an inlet muffler and a suction chamber, characterized in that the suction chamber is constructed as a separate part of a synthetic material having a low heat transfer coefficient and which is compatible with the refrigerant gas and the lubricating oil.

2. A motor-compressor unit as claimed in claim 1, characterized in that said part is formed by an appendix of the inlet muffler and is formed integrally with at least a part of said muffler.

3. A motor-compressor unit as claimed in claim 2, characterized in that the metal cylinder head comprises a slot into which said appendix can be inserted and which faces inlet ports of a valve plate.

4. A motor compressor unit as claimed in Claim 3, characterized in that the slot comprises undercuts and a flat spring is arranged between the undercuts and the appendix so as to urge this said appendix into position against the cylinder.

5. A motor-compressor unit as claimed in Claim 3, characterized in that the appendix which is inserted into the slot projects from the terminal face of the metal cylinder head and a spring mounted on a cylinder head pressing against the projecting part of the appendix.

6. A motor-compressor unit as claimed in any of the preceding claims, characterized in that the lower end of the muffler is closed by an elastic cap having a central hole in which the end of the inlet conduit is inserted.

7. A motor-compressor unit as claimed in any of claims 1 to 5, characterized in that the inlet muffler is connected to the inlet conduit by means of an elastic bellows.

8. A motor-compressor unit as claimed in any of claims 1 to 5, characterized in that the open lower end of the inlet muffler dips into a lubricant and the inlet conduit opens into the inlet muffler above the level of the lubricant.