Motor-compressor unit with its cylinder head formed in parts of different materials

Abstract

 A motor-compressor unit (1), in particular for a refrigerator, comprises a cylinder head (10) fixed onto a cylinder body (5), between said cylinder head (10) and body (5) there being interposed a plate (11) with which usual valves (14, 15) are associated, acting on an intake port (12) and a delivery port (13).
According to the invention, the cylinder head (10) is formed of at least two mutually coupled hollow portions (21, 22), at least one of said portions (22) being constructed of a material of low thermal conductivity. The two portions (21, 22) of the cylinder head (10) are physically separated from each other. One of them (22) comprises at least one cavity acting as the intake cavity, the other portion having at least One cavity acting as the discharge cavity.

Description

[0001] This invention relates to a motor-compressor unit, in particular for a refrigerator, comprising a cylinder body within which a piston moves to compress a gas, a cylinder head fixed to one end of said cylinder body, and a plate (valve plate) which is interposed between said cylinder head and body and with which usual valves are associated acting on the intake port and delivery port.

[0002] Cavities are provided in the cylinder head. One of these, the intake cavity, is positioned to correspond with the intake valve to collect the gas to be compressed within the cylinder body (or simply cylinder). A further cavity (discharge cavity) is positioned to correspond with the delivery valve, to receive the compressed gas which is to be discharged from the cylinder head. As is well known, the cylinder head is constructed of metal (cast iron, pressed plate, aluminium), to reliably resist the mechanical stresses generated within it during gas compression and the thermal stresses deriving from the gas after its compression. However, such a construction is detrimental to the thermodynamic efficiency of the compressor.

[0003] In this respect, being completely of metal, the high temperature of the compressed gas present in the discharge cavity is transferred by conduction through the material of the head to reach the part which defines its intake cavity.

[0004] Consequently, in this latter there is a state of high temperature which heats the intake gas, so reducing the efficiency of the compression process.

[0005] Various methods have been devised to prevent heating of the intake gas.

[0006] However, these methods have not adequately solved the problem. In addition, the known methods do not provide high reliability during the operation of the motor-compressor unit.

[0007] Finally, the cylinder heads of known motor-compressor units generate intense noise, as they act as resonance boxes for the gas passing through them.

[0008] An object of the invention is therefore to provide a motor-compressor unit in which the heating of the cylinder head intake cavity is reduced, so preventing excessive heating of the intake gas.

[0009] A further object is to provide a motor-compressor unit having a thermodynamic efficiency greater than motor-compressor units of the state of the art.

[0010] A further object is to provide a motor-compressor unit of the stated type which is of simple construction, low cost and reliable operation.

[0011] These and further objects which will be apparent to the expert of the art are attained by a motor-compressor unit of the aforesaid type, characterised in that the cylinder head is formed of at least two mutually coupled hollow portions defining respectively at least one intake cavity and one discharge cavity, at least one of said portions being constructed of a material of low thermal conductivity.

[0012] The present invention will be more apparent from the accompanying drawing, which is provided by way of non-limiting example and in which:

Figure 1 is a partial view, shown in section on the line I-I of Figure 3, of a motor-compressor unit constructed in accordance with the invention;

Figure 2 is an exploded view from above of part of the motor-compressor unit of Figure 1;

Figure 3 is an assembled view from above of the part shown in Figure 2; and

Figure 4 is a section on the line IV-IV of Figure 2.

[0013] With reference to said figures the compressor is indicated overall by 1 and comprises a casing 2 comprising two half-casings 3 and 4 joined together in known manner.

[0014] The casing 2 contains a cylinder body 5 (or simply cylinder) within which a usual piston 6 moves, operated by a connecting rod 7 associated with a usual shaft (not shown) driven in known manner. The cylinder 5 is connected in the usual manner to a stator 8, the assembly thus formed being supported by usual springs 9 (only one of which is shown) secured in known manner to the half-casing 4.

[0015] A cylinder head 10 is associated with one end of the cylinder 5. Between the cylinder and head 10 there is a plate 11 in which ports 12 and 13 are provided for the intake and discharge of the gas to be compressed respectively, and on which movable valves 14 and 15 (not shown in Figure 4) are positioned. The plate 11 therefore acts as a valve plate and is separated from the head 10 and cylinder 11 by seal members or gaskets 16 and 17.

[0016] The body 18 of the cylinder head 10 is provided with holes 19 for receiving usual elements (screws) 19A for fixing the head 10 to the cylinder 5.

[0017] A usual gas intake duct 20 is also connected to the head 10. According to the invention the head 10 comprises at least two hollow portions 21 and 22 to be coupled together, a first portion 21 being constructed of metal and the second portion 22 being constructed of plastics material or in any event a material of low thermal conductivity.

[0018] The two portions 21 and 22 are physically separated from each other by a space 23 and comprise cavities 21A and 22A acting as the discharge and intake cavity respectively.

[0019] Specifically, the first portion 21 comprises a flat part 25 containing the holes 19 for the elements or screws 19A for its fixing to the cylinder 5. From the part 25 there extends a raised part 26 (in which the discharge cavity 21A is formed) comprising a recess 28 to receive a projecting part or projection 29 of the second portion 22, which has a sunken part 31 from which there extends a raised part 32 provided with the projection 29. In this latter there is provided the intake cavity 22A, which is connected to other cavities 22B and 22C. The projection 29 is prolonged so that the intake cavity is positioned over the port 12 in the valve plate 11.

[0020] On the edge 28A of the recess 28 there are projections 33 facing the interior of said recess, and undercuts 34. The projections are intended to cooperate with indentations 35 in the projection 29, whereas the undercuts 34 are intended to cooperate with shoulders 36 provided on the sides of said projection.

[0021] In addition, on the end of this latter there is a depression 38 from which there extends a foot 39 intended to cooperate with a hollow seat 40 provided in the portion 21.

[0022] This latter also comprises further lateral hollow seats 41 and 42 intended to cooperate with feet 44 provided on the sunken part 31 (overlying this latter). The cooperation between the feet 39 and 44 and the seats 40, 41 and 42 maintains the two portions 21 and 22 coupled to each other on tightening the screws 19A, and maintains the plastics portion 22 clamped against the gasket 16 and against the valve plate 5.

[0023] In this respect, after suitably engaging the portions 21 and 22 with each other (by inserting the foot 39 and feet 44 in the seats 40, 41 and 42) the assembly is placed on the valve plate 11 on which the gasket 16 is present.

[0024] Then by inserting the screws (or other fixing members) through the holes 19 and tightening them, the portion 21 is clamped against this gasket.

[0025] Via the seats 40, 41 and 42, the portion 21 presses against the foot 32 and feet 44. In this manner the clamping force of the screws against said portion 21 is also transferred to the portion 22, which is pressed against the gasket 16. By this means the portion 22 is secured to the body of the cylinder 5.

[0026] It should be noted that the feet 39 and 44 can deform under the action (pressing towards the plate 11) of the portion 21, ie under the clamping force of the screws in the holes 19.

[0027] The feet 39 and 44 deform elastically by an amount which can be previously evaluated and be chosen by the designer.

[0028] In this respect, the relationship between deformation and elastic reaction of the material and the relationship between the elastic reaction and temperature of the material as a function of time enables the designer to determine the dimensions of the feet, the system for fixing the portion 22 onto the plate 11 and hence the dimensions of this portion and of its feet in a very reliable manner.

[0029] With such a construction it is not the clamping force of the screws but the elastic reaction of the component plastics material of the portion 22 and said feet which ensures a sufficient force to keep the portion 22 retained (clamped) against the gasket 16 and plate 11.

[0030] The construction of the cylinder head 10 is apparent from the aforegoing description.

[0031] During the use of the compressor, as the portion 22 is constructed of a material of low thermal conductivity (ie a poor heat conductor) and as it is physically separated from the metal portion 21 (by the space 23), there is no heat passage between said portions 21 and 22.

[0032] Heat passage is further impeded by the presence of the usual refrigerant gas within the casing 2 of the motor-compressor unit and thus within the space 23.

[0033] High temperature is therefore not reached within the intake cavity 22A of the cylinder head 10 of the motor-compressor unit 1. This prevents heating of the intake gas and improves the thermodynamic compression efficiency.

[0034] In addition, the portion 22 acts as a silencer as it does not function as a resonance box for the sounds generated by the fluid passing through it. This may allow the silencer present in known motor-compressor units to be dispensed with, thus reducing construction time, and contributes to noise reduction.

[0035] In any event, to further increase noise reduction a plastics muffler (indicated by 50 in Figure 4) can be provided, associated with the portion 22.

[0036] The motor-compressor unit is of simpler construction than known units, is of lower cost than these and is very reliable in use. In addition, with the plastics portion 22 there are no mechanical strength problems associated with the cylinder head, as the gas present in the portion 22 is of low temperature and pressure such as not to generate within the head any stresses harmful to its mechanical integrity.

[0037] A particular embodiment of the invention has been described. However, modifications can be made such as joining the two portions 21 and 22 together by mechanical fixing using screws or adhesion (such as gluing).

[0038] This and equivalent embodiments are however to be considered as falling within the scope of the present document.

Claims

1. A motor-compressor unit, in particular for a refrigerator, comprising a cylinder body within which a piston moves to compress a gas, a cylinder head fixed to one end of said cylinder body, and a plate which is interposed between said cylinder head and body and with which usual valves are associated acting on the intake port (12) and delivery port (13), characterised in that the cylinder head (10) is formed of at least two mutually coupled hollow portions (21, 22) defining respectively at least one intake cavity (22A) and one discharge cavity (21A), at least one of said portions (22) being constructed of a material of low thermal conductivity.

2. A motor-compressor unit as claimed in claim 1, characterised in that the portions (21, 22) of the cylinder head (10) are physically separated from each other, at least in part.

3. A motor-compressor unit as claimed in claim 1, characterised in that a first portion (21) is constructed of metal and comprises a flat part (25) in which holes (19) are provided to allow the cylinder head (10) to be fixed to the cylinder body (5), from said flat part (25) there extending a raised portion (26) defining the discharge cavity (21A) and comprising a recess (28) to receive a projection (29) from a corresponding part (32) of the second portion (22) defining the intake cavity (22A), said second portion (22) being constructed of material of low thermal conductivity.

4. A motor-compressor unit as claimed in claim 3, characterised in that the second portion (22) is of plastics material.

5. A motor-compressor unit as claimed in claim 3, characterised in that on the edge (28A) of the recess (28) of the first portion (21) there are provided projecting elements (33) and undercuts (34) arranged to cooperate with indentations (35) and shoulders (36) of the second portion (22).

6. A motor-compressor unit as claimed in claim 3, characterised in that the second portion (22) carries deformable projecting elements (39, 44) arranged to cooperate, by pressing, with seats (40, 44) provided in the first portion (21).

7. A motor-compressor unit as claimed in claims 2 and 3, characterised in that between the portions (21, 22) of the cylinder head (10) there is provided a space (23), said space being advantageously between the projection (29) on the second portion (22) and the respective recess (28) in said first portion.

8. A motor-compressor unit as claimed in claims 1 and 3, characterised in that the two portions (21, 22) of the cylinder head (10) are mechanically fixed together.

Drawing