LINEAR COMPRESSOR DESCRIPTION OF THE INVENTION
The present invention relates to a linear compressor, in particular designed for use in home-type or industrial-type refrigeration equipment. In the course of recent years, due to a need that is increasingly felt by manufacturers of refrigeration equipment to be able to rely on the availability of compressors characterized by an increasing level of efficiency, it has been produced a gradual change in the type of compressors used, ie the manufacturers have gradually moved from conventional reciprocating compressors driven by a rotary electric motor to reciprocating compressors of the linear class, that is, driven by a linear electric motor consisting of generally of a stator in relation to which it is slidably distributed, with a linear reciprocating movement, generated by a magnetic field, a moving element on which the piston of the compressor is mounted. Although clearly advantageous from the standpoint of performance, efficiency and reliability, linear compressors generally present certain problems with respect to the ability to actually obtain such favorable characteristics thereof, and these problems can make these compressors of a design and rather complex construction. First of all, unlike conventional compressors, linear compressors do not have any mechanically determined upper and lower dead centers, that is, in a positive way, so here the need arises for a special system that is provided to control the position of the piston inside the cylinder, in order to prevent the same pistons from hitting the head of the cylinder damaging it. This control must operate with great precision in order to ensure that the upper dead center of the piston is at a very small distance from the cylinder head, generally in the order of 0.1 mm, so as to minimize the so-called volume of free space. Any greater distance, even of a few tenths of a millimeter, could generate a drastic fall in the operating characteristics so that the need arises to supply very expensive and sophisticated electronic controls simply for this purpose. In addition, these linear compressors require that a return force proportionate to the displacement of the movable member be available in order to ensure a correct travel stroke of the piston, and the simplest method available to secure this force is to supply a connected mechanical spring. duly both to the stationary base of the compressor and to the mobile element, so that, in this way, a mechanical system capable of working in a manner to a resonant harmonic oscillator forced on the line frequency is obtained; however, linear compressors equipped with such a system generally experience a marked deterioration in their general operating characteristics when deviating from this resonance condition. Furthermore, it is known that the value of the cooling capacity, ie the cooling effect that can be obtained with linear compressors of the currently known kind, can not vary to a significant degree, that is, by a factor of approximately 2 without this implying a considerable loss of performance; Such variation in cooling capacity may be required, for example, when considering the needs related to the particular application or even for the purpose of saving energy by adapting the compressor's power consumption to the actual cooling capacity required by the refrigerator in a given operating period thereof. In fact, since this has already been indicated in the foregoing, a variation in the piston stroke leads to a loss of performance due to the limitations that result from the dead center position - in relation to the cylinder head and the position of the average oscillation point of the piston, even this last one 'is practically unmodifiable without a reduction in the efficiency of the motor and therefore in the performance of the compressor that results from this. Also, a variation in the oscillation frequency of the piston is not a feasible option given that it can not be carried out without generating a loss in the performance of the compressor due to the limitation that requires that the resonance condition of the system be maintained without alterations. Therefore, a main objective of the present invention is to correct all the drawbacks mentioned before the solutions of the prior art by providing a linear compressor in which the performance and efficiency characteristics are not related to, that is, they are not conditioned in any way and are not substantially altered in any way by the construction, design and operation requirements and variations thereof. A main purpose of the present invention within the stated objective before it is to provide a linear compressor in which the possibility of obtaining wide variations in the output of cooling power thereof is generated without these variations determining a deterioration in the characteristics of general performance of the same compressor. Another main purpose of the present invention is to provide a linear compressor in which the positioning of the upper dead center of the piston in relation to the cylinder head can allow greater tolerances without this impairing the overall performance characteristics of the compressor and thus allowing that the systems used to control the position of the piston are simplified and therefore become less expensive. A further main purpose of the present invention is to ensure the possibility that the compressor cooling power expenditure can be modulated by varying the stroke of the piston or the amplitude of oscillation thereof in relation to the midpoint and the volume of free space or dead and at the same time maintain efficiency values of. energy without alterations, at a high level. - Another additional main purpose of the present invention is to provide a linear compressor which is significantly simplified in construction and which at the same time ensures unchanged or possibly improved efficiency together with increased flexibility - in its operation, compared to linear compressors of the prior art. Last but not least, the purpose of the present invention is to provide a linear compressor with low and competitive costs and which is capable of being manufactured with the use of currently available machinery and technology. According to the present invention, the objectives and advantages indicated in the foregoing together with additional ones will become apparent from the
'description that is provided in the following and that reach in a linear compressor that incorporates the features and characteristics as described in appended claim 1. The additional features and advantages of the linear compressor according to the present invention can be more easily understood from the description that is provided in the following of a particular embodiment, although not the only one, which is illustrated by way of example not limiting with reference to the accompanying drawings, which: Figure 1 is a longitudinal sectional view of a linear compressor according to the present invention; - figure 2 is a detailed view of the sectional view of figure 1; Figure 3 is a diagrammatic view of a schematic representation of the operation cycle of a linear compressor according to the present invention; Figure 4 is a view, along a section plane at 90 ° with respect to Figure 1, of a linear compressor according to the present invention. With reference to the figures mentioned and included in the above, the linear compressor, which is generally indicated with the number 1, comprises a body
2 stator that. is constituted substantially by a yoke
3 outside around which a bobbin (not shown) and an inner yoke 4 are rolled towards the external yoke 3 and separated from the latter in a manner defining a space 5 of air. The linear compressor further comprises a movable element 6 comprising a base plate 7 from which a pair of arms (not shown) extend in a manner known in the art, these arms are provided with a magnet and are housed within the space 5 air The linear compressor also comprises an arrow 8, in the end portion thereof there is firmly attached a piston 9 wherein the base plate 7 is firmly attached to a tray 10 which in turn is connected to a spring 11 of resonance.
As is well known in the art, the energization of the compressor with an alternating current supply results in the generation of a magnetic flux which causes the mobile element 6 to perform a reciprocating (reciprocating) movement relative to the body 2. stator; via the arrow 8, this movement is then transmitted to the piston 9. The arrow 8 is slidably placed inside a cylindrical guide body 12 that ends with a flange 13 which is advantageously obtained integrally with the guide body and against this abuts the lining 14 of a cylinder 15, within which the piston 9 is slidably located. The rim 13 is provided with at least one suction orifice 16 controlled by a suction valve means 17 such as a reed valve, in communication with the suction conduit comprising a conduit 18 connected to a reservoir 19 in which the gas that is admitted is collected, which then flows into the conduit 18 to finally undergo compression. In an advantageous manner,. the suction duct is coupled between the flange 13 and the stator body 2 so that the admission of the gas in the cylinder 15 is carried out from the side in which the temperature of the wall is at a lower value. This helps to reduce the degree to which the gas heats up during the suction phase, thereby reinforcing the efficiency of the compressor. The cylinder 15 is closed by a head 20; the stroke of the piston 9 inside the cylinder 15 is therefore limited, on the one hand, by the flange 13 and, on the opposite side, by the head 20. The latter is provided with at least one exhaust or supply orifice 25 which is provided with an outlet or supply valve means 30, for example a reed valve for controlling the supply orifice 25. Within the cylinder 15, the piston 9 defines a first chamber 21, or a low pressure chamber as will be better explained later, and a second chamber 22, or high pressure chamber, as will also be better explained later, both chambers in which they are variable volumes depending on the position of the piston 9 in the cylinder 15; The two chambers 21 and 22 are placed in communication with each other via at least one through opening 23 which is provided in the piston 9 and which is controlled by the communication valve means 24, such as a reed valve. Thanks to the configuration obtained in this way, the piston 9 is able to alternately compress the gas in any direction inside the cylinder 15 and thus generates two compression stages in which the escape or supply phase in the first chamber 21 of low pressure occurs at the same time as the suction phase in the second high pressure chamber 22 through the communication opening 23 and the communication valve means 24 that is provided in the piston 9. In other words, the compression cycle is divided into two stages in opposition of phase one with respect to the other, with a phase shift of 180 °. The way in which the linear compressor described in the above works is the following, with particular reference to Figure 2 and the diagram of the compression cycle illustrated in Figure 3, in which, corresponding to the abscissa axis, represents the position of the piston 9 in the cylinder 15 and in correspondence with the axis of the ordinates represents the value of the gas pressure; starting from the lower dead center Xi, in which the piston 9 is placed adjacent the rim 13, as the piston 9 moves away from the rim 13 'during its stroke, the gas contained in the volume of free space of the first chamber 21 ( curve AB of the diagram in figure 3) undergoes an expansion from the pressure Pi to the pressure P2 corresponding to the suction pressure (point B); this pressure P2 causes the suction valve means 17 to open and, as a result, the gas to be admitted from the reservoir -
19 of the suction duct inside the first low pressure or precompression chamber 21 through the conduit 18 and the suction orifice 16 (suction phase, line B-C); at the end of the suction phase, the piston 9 is in the upper dead center X2 which is located at a minimum distance from the head 20, whereby the maximum volume for the first low pressure chamber 21 is defined. At the same time this suction phase ABC is carried out in the first low pressure chamber 21 and, starting from the position of the piston 9 corresponding to the lower dead center Xx, the gas emerging in the second chamber 22 of high pressure pressure is first compressed from the pressure Px to the point at which the supply or supply pressure P3 (curve AE) is reached, whose value is such that it causes the outlet or supply valve means 30 to open and therefore the exhaust is carried out, that is to say, the supply of the gas through the supply orifice 25 in the head 20 (supply phase, line EF). At the end of this exhaust or supply phase (point F), the piston 9 is in a position corresponding to its upper dead center X2, at a minimum distance from the head 20 where the supply orifice 25 is located. From this position, the displacement movement of the piston 9 begins to reverse so that the expansion of the gas in the volume of the free space in the second chamber 22 of high pressure (curve FD) and at the same time the compression of the gas is determined. of suction contained in the first low pressure chamber 21 (CD curve) up to the point at which the pressure Pi is reached establishing a balance between the first chamber 21 and the second chamber 22 (point D). This pressure value causes the communication valve means 24 provided on the piston 9 to open thereby enabling the precompressed gas to flow from the first chamber 21 to the second chamber 22 via the through hole 23 in the piston 9 ( DA line) until it finally reaches the lower dead center Xi in its travel stroke. In this way, the linear compressor according to the present invention performs a cycle that corresponds to two stages of compression in phase opposition with respect to each other, as indicated in figure 3 by the area between points A, B , C and D with respect to the low pressure stage that is carried out in the first chamber 21, and the area comprised between points A, E, F and D with respect to the high pressure stage which it is carried out in the second chamber 22. In figures 1 and 4 there is further illustrated a lubrication and cooling system which advantageously can be used in a linear compressor according to the present invention: with the help of the pump 31, the The lubricant is collected in the tank 32 and caused to flow through a first channel 33 and one or more first holes 34 that are circumferentially provided in the cylindrical guide body 12 so as to lubricate the arrow 8. From this place, the lubricate The fluid then flows through a second channel 35 to a second orifice 36 which is provided in the flange 13 and a third channel 37 in the coating 14 of the cylinder 15 within a hollow space, i.e. the jacket 38 that is provides in the liner 14 for cooling the cylinder wall 15 in order to maintain it at a lower temperature for the purpose of promoting thermal efficiency and reinforcing the overall energy efficiency of the compressor. In order to lubricate the piston 9 and reduce friction during displacement thereof, a certain amount of lubricant is drawn through the outer surface of the portion of the arrow 8 entering the first low pressure chamber 21. From the description provided in the foregoing it can therefore be easily appreciated that the linear compressor according to the present invention is actually capable of achieving all of the objectives and advantages indicated in the foregoing: in fact, with the linear compressor according to the present invention the possibility is generated that high cooling performances are obtained even in the presence of oscillation limits of the piston 9 -which corresponds to the upper and lower dead centers- that can be located at a considerable distance from the portions of the head of the respective cylinder, ie the head 20 and the flange .13. Therefore, there is no need to ensure minimum free spaces of the order of magnitude of 0.1 mm in any case as required, on the contrary, in the single-stage compressors of the prior art, and in this way the use of less sophisticated and precise systems and therefore less expensive to control the position of the piston 9. In addition, the fractionation in the manner described in the above of the two-stage compression phase allows much larger volumetric efficiencies to be obtained in comparison with single-stage compressors for the same amount of free space volume. In addition, the cooling capacity output of the compressor can be modulated up to a factor of 2 by varying the displacement stroke of the piston 9 relative to the midpoint between the upper dead center and the lower dead center or by varying the volume of the free space and at the same time maintain the energy efficiency at a high level without alterations and exclude any appreciable deterioration in the total functioning of the compressor. In this way, the performance and efficiency characteristics of the compressor according to the present invention are not related, that is, they are not subject and in any way they are not substantially affected by the construction, design and operation requirements and variations thereof. . An additional advantage of the linear compressor according to the present invention derives from the fact that its modality in this way ensures a maximum degree of simplicity in its construction and, at the same time, high performance capabilities without the need to duplicate constituent part any of the compressor, such as piston, cylinder head or valves. Of course, it will be appreciated that the present invention can be subjected to numerous modifications and variants and that it can be used in conjunction with numerous different applications without departing from the scope of the present invention. It should also be noted that the materials used to implement the present invention as well as the shapes and size of the individual constituent parts in each case can be selected so as to be adapted more adequately to a particular need or to comply with any requirement related to the application without this implying a deviation from the scope of the present invention.