Linear Compressor With a Gas Spring

Abstract

A refrigeration appliance, in particular at least one of a refrigerator, freezer and an air conditioning unit, includes a cooling chamber; a linear compressor having a piston housing; a compressor piston disposed within the piston housing and configured for reciprocatory motion along an axis within the piston housing; and buffer means for storing kinetic energy associated with the motion of the compressor piston, wherein the buffer means is configured to store the kinetic energy of the compressor piston in an interim manner by compression of a gaseous fluid during reciprocatory motion of the compressor piston.

Description

The present invention relates to a refrigeration appliance, in particular a refrigerator and/or freezer or an air conditioning unit, comprising a cooling chamber and a linear compressor, the linear compressor having a piston housing and a compressor piston that can move forward and backward along an axis therein as well as a buffer means for the kinetic energy of the compressor piston moving forward and backward, a linear compressor for a refrigeration appliance and a method for compressing a gas and a method for cooling goods.

With a linear compressor the compressor piston that can move forward and backward along an axis between a first and second reversal point must be supported or guided in a direction perpendicular to said axis. The kinetic energy of the compressor piston moving forward and backward must also be buffered at the reversal points, in other words at the points where the direction of movement of the compressor piston is reversed, in order to allow the direction of movement of the compressor piston to be reversed with as little loss as possible. By reversing the direction of movement, the compressor piston performs an oscillating, essentially translatory, forward and backward movement in a compressor housing. A compression process is executed with the aid of the forward and backward movement.

It is known that the movement energy of the compressor piston can be buffered using one or more helical springs. The compressor piston must also be supported in a direction perpendicular to the direction of movement. Systems with an open structure, for example a serially arranged motor-pump arrangement, use a set of springs with one or more very thin diaphragm springs or sets of diaphragm springs and one or more helical springs or sets of helical springs to buffer the movement energy and to support the sides of the compressor piston in a direction perpendicular to the direction of movement. To ensure adequate stability, such springs or spring sets are made of metal. The diaphragm springs are designed to be so thin and soft that the springs can absorb the forces of the overall system produced perpendicular to the oscillation direction in the sum of their perpendicular rigidities with adequate reliability. To achieve appropriate longitudinal rigidity spring arrangements are known, in which diaphragm springs are backed up by one or more helical springs or sets of helical springs. Such spring arrangements are however relatively complex in structure and are therefore time-consuming to produce and assemble. If the spring force of the springs decreases over time or the spring forces of the individual springs become unbalanced, friction can result between the compressor piston and the piston housing, having an adverse effect on the efficiency of the linear compressor or the refrigeration unit and leading to increased energy consumption.

The object of the present invention is to specify a refrigeration appliance or a linear compressor for a refrigeration appliance, in which a forward and backward movement of the compressor piston used is realized both reliably and with energy savings in a simple manner during compression. The object is also to specify a method for compressing a gas and a method for cooling goods, with which a compression and/or cooling process can be carried out with a high level of reliability in a particularly energy-saving manner.

According to the invention this object is achieved by the refrigeration appliance and by the linear compressor for the refrigeration appliance and by the method for compressing a gas and by the method for cooling goods, as set out in the independent claims. Further advantageous embodiments and developments, each of which can be applied individually or combined in any manner with one another, are the subject matter of the respectively dependent claims.

The inventive refrigeration appliance, in a particular a refrigerator and/or freezer or an air conditioning unit, preferably an air conditioning unit for motor vehicles, comprises a cooling chamber and a linear compressor, the linear compressor having a piston housing and a compressor piston that can move forward and backward along an axis therein as well as a buffer means for the kinetic energy of the compressor piston moving forward and backward, it being possible for the buffer means to store the kinetic energy of the compressor piston in an interim manner by compression of a gaseous fluid during the forward and backward movement.

The linear compressor is used to compress a second fluid, in particular a refrigerant, in order to be able to produce refrigeration with a downstream evaporation stage. The second fluid is compressed by a movement of the compressor piston in the piston housing. The second fluid can also be the gaseous fluid used for buffering.

Movement of the compressor piston essentially takes place along an axis. The compressor piston hereby oscillates between two reversal points, at which it briefly comes to rest, in order to change its direction of movement. At the reversal points a forward movement changes to a backward movement.

The buffer means is used to buffer the kinetic energy present in the movement of the compressor piston in the form of potential energy. An overall energy present in the movement of the compressor piston, which is made up of the kinetic energy of the compressor piston and the potential energy stored in the buffer means, remains essentially constant. The buffer means in particular absorbs the movement energy of the compressor piston shortly before a reversal point and transfers it essentially totally back to the compressor piston after the movement direction has been reversed. The aim of this is to convert the mechanical energy brought by a drive unit almost totally into work at the fluid to be compressed; in particular the drive unit should not take on any slowing function for the compressor piston.

The gas to be compressed is located in particular in a sealed volume, on which a piston acts in a reducing manner. The pressure in the fluid increases during compression. In particular during compression a pressure is reached, which is greater, preferably 1 bar to 10 bar greater, in particular preferably 2 bar to 7 bar greater, than a pressure that can be generated on a pressure side of the linear compressor.

The buffer means can be used for example to prevent the compressor piston striking a stop or a valve plate of the linear compressor in an uncontrolled manner, thereby reducing wear and saving energy for the operation of the refrigeration appliance.

In contrast to known solutions, which provided a metal spring as the buffer means, according to the invention the kinetic energy of the compressor piston is stored by compressing a gaseous fluid. The buffer means can be in the form of a gas pressure spring.

The buffer means absorbs preferably at least 90%, in particular at least 95%, preferably at least 99%, of the kinetic energy present in the movement of the compressor piston before a reversal point. The buffer means then transfers at least 88%, in particular at least 97%, of this energy back to the compressor piston, with the result that the compressor piston, which has slowed down out of the forward movement and come to rest at the reversal point, is again accelerated during its backward movement.

The gaseous fluid can be identical to or different from a second fluid compressed by the linear compressor. The gaseous fluid can for example be a refrigerant compressed by the linear compressor. Essentially however any gas can be used for buffering. Air could be used for example in a compressed air spring.

The means advantageously comprises a compression chamber formed by the piston housing and the compressor piston and in particular being able to be sealed during and/or due to the forward and backward movement of the compressor piston. The compression chamber can be sealed by the compressor piston itself but it can also be sealed with the aid of valves.

The compression chamber can be formed by a dead space in the piston housing. The dead space is bounded by walls of the compressor housing and a top face of the compressor piston. In this embodiment no valves are required to bring about interim compression of the gaseous fluid in the dead space, as the compressor piston compresses the gaseous fluid in the dead space.

In an alternative embodiment the compression chamber has valves, which are activated in phase, in other words opened or closed, during the forward and backward movement of the compressor piston.

The means advantageously has a valve, which closes before the movement direction of the compressor piston is reversed and opens again after the movement direction of the compressor piston has been reversed. This means that the valve opens and closes at least once per cycle.

In particular the valve closes during a forward movement and opens during a backward movement immediately following the forward movement.

In one particular embodiment the valve closes during a forward movement within a segment of 50% of the piston travel of the forward and backward movement before a reversal point of the compressor piston, in particular within a segment of 20% of the piston travel before a reversal point of the compressor piston, in particular within 10% of the piston travel before the reversal point of the compressor piston. The compressor piston is slowed down within the segment until it stops at a reversal point.

In a further specific embodiment of the invention the valve opens during a backward movement within a segment of 50% of the piston travel of the forward and backward movement after a reversal point of the compressor piston, in particular within a segment of 20% of the piston travel after a reversal point of the compressor piston, in particular within 10% of the piston travel after the reversal point of the compressor piston. The compressor piston is accelerated back to its original speed within this segment, the buffer means transferring the energy stored in it back to the compressor piston.

Similarly during a forward or backward movement a top surface of the compressor piston can extend into the dead space by a segment of at least 5% of the piston travel of the forward and backward movement, in particular by a segment of at least 10% of the piston travel, preferably by a segment of at least 30% of the piston travel, in order to compress the gaseous fluid enclosed by the inner chamber and the compressor piston.

The compressor piston is advantageously guided in the piston housing with the aid of a housing wall with openings and a gaseous fluid flowing through the openings, in particular a refrigerant. Such guide systems can operate without oil. This guide system allows the compressor piston to be supported in a radial direction, in other words in a direction perpendicular to the axis. The fluid flowing through the openings causes a gas cushion to be produced in front of the housing wall, by means of which the compressor piston is supported in a contactless manner in the piston housing.

A buffer means is advantageously provided at both reversal points of the compressor piston, it being advantageously possible for the buffer means to store the kinetic energy of the compressor piston in an interim manner by compression of a gaseous fluid during the forward and backward movement.

Combined forms can also be used, in which the kinetic energy is stored at the one reversal point by compression of the gaseous fluid, while at the other reversal point the kinetic energy is buffered with the aid of a spring or a set of springs, in particular with the aid of a metal spring or a set of metal springs.

The buffer means can also be an elastic element, in particular a spring, preferably a diaphragm spring or a set of diaphragm springs, made of a composite material. A composite material is a structural material made up of two or more different materials, e.g. fibers, plastic, metal, ceramics. At least one component, for example fibers, is inlaid in the base structure, known as a matrix. The intention here is to combine the different advantages of the individual materials in the final material and to eliminate their disadvantages. Carbon fiber reinforced plastics (CFK), glass fiber reinforced plastics (GfK), TiGr composite, in other words a compound of titanium, graphite and epoxy resin, as well as certain polyaramides, in particular polyphenylene terephthalamide (known under the trade name Kevlar) and others can be used as the composite material.

Compression of the gaseous fluid allows the kinetic energy of the compressor piston to be buffered reliably for the movement direction reversal, thereby allowing reliable and energy-saving operation of the refrigeration appliance.

The inventive linear compressor is particularly suitable and intended for the inventive refrigeration appliance and has a piston housing and a compressor piston that can move forward and backward along an axis therein as well as a buffer means for the kinetic energy of the compressor piston moving forward and backward, it being possible for the buffer means to store the kinetic energy of the compressor piston in an interim manner by compression of a gaseous fluid during the forward and backward movement.

The means can comprise a compression chamber, in particular a dead space, formed by the piston housing and a top surface of the compressor piston, which can in particular be sealed by the forward and backward movement. The means preferably has a valve, which closes before the movement direction of the compressor piston is reversed and opens again after the movement direction of the compressor piston has been reversed.

The valve can close during a forward movement within a segment of 50% of the piston travel of the forward and backward movement before a reversal point of the compressor piston, in particular within a segment of 20% of the piston travel before a reversal point of the compressor piston, in particular within 10% of the piston travel before the reversal point of the compressor piston.

The valve can also open during a backward movement within a segment of 50% of the piston travel of the forward and backward movement after a reversal point of the compressor piston, in particular within a segment of 20% of the piston travel after a reversal point of the compressor piston, in particular within 10% of the piston travel after the reversal point of the compressor piston.

A top face of the compressor piston can also by a segment of at least 5%, in particular by at least 10%, preferably by at least

Similarly during a forward or backward movement a top surface of the compressor piston can extend into a dead space by a segment of at least 5% of the piston travel of the forward and backward movement, in particular by a segment of at least 10% of the piston travel, preferably by a segment of at least 30% of the piston travel, in order to compress the gaseous fluid enclosed by the inner chamber and the compressor piston.

The compressor piston can be guided in the piston housing with the aid of a housing wall with openings and a gaseous fluid flowing through the openings, in particular a refrigerant.

In particular the linear compressor has a buffer means at both reversal points of the compressor piston.

All the features of the linear compressor described in relation to the refrigeration appliance can thus be applied to the inventive linear compressor and advantageously utilized. This provides a linear compressor, which is particularly robust and reliable and operates in an energy-saving manner.

The inventive method for compressing a gas with the aid of a refrigeration appliance comprising a linear compressor, the linear compressor having a piston housing and a compressor piston that can move forward and backward along an axis therein provides for a majority of the kinetic energy of the compressor piston moving forward and backward, in particular up to more than 90%, preferably up to more than 95%, in particular preferably essentially in its totality, to be buffered with the aid of a gas cushion, to bring about a reversal of the movement direction of the compressor piston moving forward and backward.

A gaseous fluid is advantageously compressed by the movement of the compressor piston, with the result that the compressor piston is slowed down and comes to rest. The energy stored in the compression is then used again to accelerate the compressor piston in the counter direction, in other words in the backward direction, to the sum of the original speed so that the energy stored in the form of a potential energy is converted back to kinetic energy. The movement direction can be reversed essentially without the aid of a drive unit, i.e. in a drive-free manner.

The gas cushion can be produced by compressing the gaseous fluid. The gaseous fluid is in particular a refrigerant for a refrigeration appliance. The gas cushion can however also be formed by compressing another gas, in particular air.

The gas cushion is advantageously formed by a gaseous fluid compressed by means of the compressor piston itself. To this end the gas cushion is formed in that an inner chamber is enclosed and sealed by the piston housing and the compressor piston shortly before the movement direction of the compressor piston is reversed. After the movement direction has been reversed, the inner chamber is opened again. The opening and closing of this inner chamber takes place in phase with the forward and backward movement of the compressor piston.

However the gas cushion can also be produced using a separate gas pressure spring.

For example the inner chamber can be sealed by the compressor piston itself, if the inner chamber is embodied as dead space, and the compressor piston compresses the enclosed gaseous fluid during its movement into the inner chamber. Compression causes the compressor piston to slow down out of the forward movement and accelerate into a backward movement.

The inner chamber is advantageously sealed within a time interval of a quarter of the period length of the forward and backward movement, in particular an eighth of the period length of the forward and backward movement, before the time of the movement direction reversal. Sealing the inner chamber within this time interval causes the compressor piston to be slowed down in this time interval.

The inner chamber is advantageously opened within a time interval of a quarter of the period length of the forward and backward movement, in particular an eighth of the period length of the forward and backward movement, after the time of the movement direction reversal. Within this time interval the compressor piston is accelerated back to its original speed that it had before the inner chamber was sealed.

The inventive method for cooling goods uses the inventive refrigeration appliance and/or the inventive linear compressor. Such use allows a particularly reliable, energy-saving and fast cooling of goods.

Further advantageous details and specific embodiments are described in more detail with reference to the drawing below, which is not intended to restrict the invention but simply to illustrate it by way of examples and in which:

FIG. 1 shows a schematic sectional view of an inventive linear compressor;

FIG. 2 shows a schematic sectional view of an inventive refrigeration appliance; and

FIG. 3 shows a schematic sectional view of a further inventive linear compressor.

FIG. 1 shows a sectional view of an inventive linear compressor 1 with a piston housing 1, in which a compressor piston 4 moves forward and backward along an axis 3 between a first reversal point 8 of the compressor piston 4 and a second reversal point 9 of the compressor piston 4. The kinetic energy of the compressor piston 4 is stored in an interim manner with the aid of a buffer means 6, in order to bring about a reversal of the movement direction of the compressor piston 4 with little energy loss. The linear compressor 1 has a suction connection 14 with a first valve 10 and a pressure connection 15 with a second valve 11. The linear compressor 1 is used to compress a gaseous fluid 5. While the pressure supplied at the pressure connection 15 is around 8 to 9 bar, the pressure in the compression chamber 7 is somewhat higher during compression for buffering and is around 10 bar. The first valve 10 and second valve 11 are hereby activated with the aid of a valve plate 16 in phase with the forward and backward movement of the compressor piston 4, so that a gas compression cushion 12 is formed in an inner chamber 13 in front of the compressor piston 4, in which the gaseous fluid 5 is compressed. Compressing the gaseous fluid 5 in the inner chamber 13 slows down the movement of the compressor piston 4, its kinetic energy being converted essentially totally to the potential energy inherent in the gas compression cushion 12. The compressor piston 4 is supported with the aid of a housing wall 23 with openings 22, in that some of the fluid 5 flows through the openings 22, thereby forming a gas pressure bearing, which guides the compressor piston 4 in a contactless manner in front of the housing wall 23. The fluid 5 required for this is supplied continuously via a feeder 17 and forms a gas bearing cushion 18 between the compressor piston 4 and the housing wall 23. The compressor piston 4 is driven with the aid of a drive unit 25 by way of a piston rod 19. The housing wall 23 embodied as a sleeve is sealed with the aid of an O-ring 21. A spring 26 is used to assist the storage of the kinetic energy by the buffer means 6, said spring 26 being carbon fiber reinforced and therefore able to absorb lateral forces of the piston rod 19, i.e. forces directed in a direction perpendicular to the axis 3.

The compressor piston 4 moves between the reversal points 8 and 9 with a piston travel H. The compressor piston 4 is slowed down over a segment S by closing the valves 10, 11 and forming a gas compression cushion 12 and then accelerated again after reversal of the movement direction. The housing wall 23 together with the compressor piston 4 forms a compression chamber 7, when the valves 10, 11 are closed, in which compression chamber 7 the gaseous fluid 5 can be compressed.

FIG. 2 shows a sectional view of the inventive refrigeration appliance 20 with the linear compressor 1 and a cooling chamber 27, in which goods 24, in particular food, can be cooled swiftly, reliably and in an energy-saving manner.

FIG. 3 shows a sectional view of a further embodiment of the inventive linear compressor 1, the inner chamber 13 being embodied as dead space 28. Whenever the compressor piston enters this dead space 28, the gaseous fluid 7 is compressed to form a gas cushion 12. The compressor piston 4 itself seals the dead space 28. It is advantageous here that it is impossible for the compressor piston 4 to strike the valve plate 16, even if the valves 10, 11 temporarily fail to close correctly, as the dead space 28 does not require any further valves closing in phase. The valves 10, 11 can only be used to open and/or close the suction connection 14 and/or the pressure connection 15 at a thermodynamically favorable time.

The invention relates to a refrigeration appliance 20, in particular a refrigerator and/or freezer or an air conditioning unit, comprising a cooling chamber 27 and a linear compressor 1, the linear compressor 1 having a piston housing 2 and a compressor piston 4 that can move forward and backward along an axis 3 therein as well as a buffer means 6 for the kinetic energy of the compressor piston 4 moving forward and backward, it being possible for the buffer means 6 to store the kinetic energy of the compressor piston 4 in an interim manner by compression of a gaseous fluid during the forward and backward movement; a linear compressor with such a buffer means 6 and a method for compressing a gaseous fluid 5 with the aid of said refrigeration appliance 20 and a method for cooling goods. The invention is characterized in that simple and efficient buffering of the kinetic energy of the moving parts in the linear compressor 1 is possible with the aid of gas compression, allowing reliable and energy-saving operation during compression and/or during cooling.

LIST OF REFERENCE CHARACTERS

• 1 Linear compressor
• 2 Piston housing
• 3 Axis
• 4 Compressor piston
• 5 Fluid
• 6 Buffer means for the kinetic energy of the compressor piston 4 moving forward and backward
• 7 Compression chamber
• 8 First reversal point of compressor piston 4
• 9 Second reversal point of compressor piston 4
• 10 First valve
• 11 Second valve
• 12 Gas compression cushion
• 13 Inner chamber
• 14 Suction connection
• 15 Pressure connection
• 16 Valve plate
• 17 Feeder
• 18 Gas bearing cushion
• 19 Piston rod
• 20 Refrigeration appliance
• 21 O-ring
• 22 Openings
• 23 Housing wall
• 24 Goods
• 25 Drive unit
• 26 Spring
• 27 Cooling chamber
• 28 Dead space
• Top surface
• H Piston travel
• S Segment within piston travel H

Claims

1-14. (canceled)

15. A refrigeration appliance, in particular at least one of a refrigerator, freezer and an air conditioning unit, comprising a cooling chamber; a linear compressor having a piston housing; a compressor piston disposed within the piston housing and configured for reciprocatory motion along an axis within the piston housing; and buffer means for storing kinetic energy associated with the motion of the compressor piston, wherein the buffer means is configured to store the kinetic energy of the compressor piston in an interim manner by compression of a gaseous fluid during reciprocatory motion of the compressor piston.

16. The refrigeration appliance according to claim 15 wherein the buffer means includes a compression chamber formed by the piston housing and the compressor piston configured for being sealed during compressor piston movement.

17. The refrigeration appliance according to claim 15 wherein the buffer means includes a valve configured for closing before the compressor piston reverses direction and opening after the compressor piston reverses direction.

18. The refrigeration appliance according to claim 17 wherein the valve closes during a forward compressor piston movement within a segment of 50% of the piston travel of the reciprocatory movement before a reversal point of the compressor piston, in particular within a segment of 20% of the piston travel before a reversal point of the compressor piston, in particular within 10% of the piston travel before the reversal point of the compressor piston.

19. The refrigeration appliance according to claim 17 wherein the valve is configured for opening during a backward movement within a segment of 50% of the piston travel of the forward and backward movement after a compressor piston reversal point, in particular within a segment of 20% of the piston travel after a compressor piston reversal point, in particular within 10% of the piston travel after a compressor piston reversal point.

20. The refrigeration appliance according to claim 15 and further comprising a plurality of openings formed in the housing wall, wherein the compressor piston is guided in the piston housing with the aid of the housing wall and a gaseous fluid, in particular a refrigerant, flowing through the openings.

21. The refrigeration appliance according to claim 15 wherein buffer means for storing kinetic energy associated with the motion of the compressor piston is provided at each respective reversal point of the compressor piston.

22. A linear compressor particularly suitable and intended for a refrigeration appliance comprising a piston housing; a compressor piston disposed within the piston housing and configured for reciprocatory motion along an axis within the piston housing; and buffer means for storing kinetic energy associated with the motion of the compressor piston, wherein the buffer means is configured to store the kinetic energy of the compressor piston in an interim manner by compression of a gaseous fluid during reciprocatory motion of the compressor piston.

23. A method for compressing a gaseous fluid with the aid of a refrigeration appliance comprising the steps of: providing a linear compressor, the linear compressor having a piston housing and a compressor piston configured for recriprocatory movement along an axis therein; providing buffer means for storing kinetic energy associated with the motion of the compressor piston, the buffer means including a gas cushion;buffering a majority of the kinetic energy of the compressor piston moving in a recriprocating manner, in particular up to more than about 90%, using the gas cushion, to cause a reversal of the movement direction of the compressor piston moving in a recriprocating manner.

24. The method according to claim 23 and further comprising the step of forming the gas cushion using a gaseous fluid sealed using the compressor piston.

25. The method according to claim 24 wherein the step of forming the gas cushion includes using an inner chamber formed by the piston housing and sealing the compressor piston prior to reversal of the piston movement direction, the inner chamber being opened again after the movement direction of the compressor piston has been reversed.

26. The method according to claim 25 wherein the step of forming the gas cushion includes sealing the inner chamber within a time interval of about ¼ of the period length of the compressor piston reciprocatory movement, in particular about ⅛ of the period length of the compressor piston reciprocatory movement, before the time of the movement direction reversal.

27. The method according to claim 25 wherein the step of forming the gas cushion includes the step of opening the inner chamber within a time interval of about ¼ of the period length of the compressor piston reciprocatory movement, in particular about ⅛ of the period length of the compressor piston reciprocatory movement, after the time of the movement direction reversal.

28. A method for cooling goods including the steps of providing a refrigeration appliance including a linear compressor, the linear compressor having a piston housing and a compressor piston configured for recriprocatory movement along an axis therein; providing buffer means for storing kinetic energy associated with the motion of the compressor piston, the buffer means including a gas cushion; buffering a majority of the kinetic energy of the compressor piston moving in a recriprocating manner, in particular up to more than about 90%, using the gas cushion, to cause a reversal of the movement direction of the compressor piston moving in a recriprocating manner; storing goods for cooling in the refrigeration appliance; and operating the refrigeration appliance.