Bistable compressor driven by shape memory alloy and used for refrigerator

Abstract

Device for actuating a compressor, the device comprising: a rocker (5) movable between a first stable state and a second stable state, the rocker being arranged such that upon movement of the rocker, a piston (6) in a variable volume compressor chamber (7) is driven; one or more shape memory alloy (SMA) elements (9, 10) coupled to the rocker, drivable to change between a first shape and a second shape; at least one temperature control region, at least one of the shape memory alloy (SMA) elements being disposed within the at least one temperature control region, where a temperature within the temperature control region is controlled to change a temperature of the SMA included therein.

Description

[0001] The invention relates to a compressor for a refrigerator.

[0002] The present invention relates to a compressor for use on the suction or discharge side of a refrigeration system. The compressor may also be used in air conditioning, to actuate a jackhammer, or to force air into an inflatable object.

[0003] In a refrigeration system, a compressor is generally provided, which is arranged to compress air or other gas. The air is generally heated in such a way that heat can then be removed from the compressed gas. The compressed gas is then allowed to expand, further cooling, thereby providing the desired refrigeration.

[0004] The most widely used compressors are based on reciprocating piston motion driven by an electric motor or a linear solenoid motor. Unfortunately, such drives have a large mass, heat up quickly and operate relatively noisily. Compressors that work with shape memory alloys (SMA) have small dimensions, but they require a lot of energy to overcome the gas force and the force of the biasing spring.

[0005] US 5,622,482 discloses a pump utilizing an SMA wire and a bias spring. The bias spring stretches the SMA wire and pushes the piston of the pump. Electricity heats the SMA wire, which pulls the piston and compresses the bias spring. Cutting off the power causes the SMA wire to cool and the piston to return to its initial position under the action of the bias spring. The pump has a simple structure, which is light and easy to repair and maintain, but the SMA force must overcome the force of the spring and the gas pressure throughout the stroke of the piston, which results in higher energy consumption.

[0006] US 6,132,187 discloses a liquid / gas pump utilizing a stainless steel strip of uniform width, which is enclosed within a flexible and liquid / gas impermeable plastic tube. Thus, two elongated channels are formed above and below the metal strip. A linear series of bistable positions and slightly overlapping shallow domes are formed in the metal strip. The pump is actuated by reciprocating motion. Although the liquid / gas is pumped without relative motion between the structural elements, the bistable behavior of the strip does not reduce energy consumption due to the lack of recovery.

[0007] GB2558618A (of the present inventor) discloses valve actuation of two SMA wires, in which opposite forces are applied to a bistable mechanism having a restoring spring interacting with a valve spring. The forces of the restoring spring and the valve spring are in opposite directions and have similar characteristics, which, combined with the bistability, allow the SMA wires to apply a small driving force. Furthermore, these SMA forces drive the mechanism only in half of the valve closing stroke and valve opening stroke, and the rest is driven by the spring. In this way, energy consumption is reduced. The bistable actuator is small in size and operates quietly.

[0008] It is desirable to provide a compressor that is efficient and requires as little energy input as possible to produce the desired refrigeration.

[0009] According to a first aspect of the present invention, a compressor is provided, comprising: a housing having a fluid inlet and a fluid outlet, through which a compressible fluid can be provided, and the fluid outlet enables the fluid to pass through the housing; a compressor cylinder, which is coupled to the housing and has a movable member, which is arranged to be driven to reciprocate during a compression cycle, and the cylinder is arranged to receive fluid from the housing; a rocker, which is capable of moving between a first stable state and a second stable state, and is arranged so that when the rocker moves, the movable member is driven in the compressor cylinder; and one or more shape memory alloy (SMA) elements, which are coupled to the rocker and can be driven to change between a first shape and a second shape, thereby driving the rocker.

[0010] In one embodiment, the housing defines a hermetically sealed space such that the only passage for fluid to enter or leave the housing is via the fluid inlet and outlet.

[0011] A compressor is provided, comprising a rocker driven in use by one or more SMA elements. A space for accommodating a fluid is formed in a compressor housing, the space enabling temperature control of the SMA elements in the compressor. In an embodiment, the housing defines a hermetically sealed space, such that the fluid can only enter or leave via a fluid inlet or a fluid outlet, i.e., the housing is hermetically sealed except for the fluid inlet and the fluid outlet.

[0012] In normal use, the fluid flow through the compressor (from inlet to outlet) will be used to provide temperature control of the space within the housing, and therefore control the ambient temperature of the one or more SMA wires. The preferred hermetic seal of the housing ensures that the temperature can be accurately controlled due to the absence of external fluid temperature disturbances (such as the atmosphere).

[0013] Preferably, the housing is formed from a thermally insulating material.

[0014] In one embodiment, the cylinder has a valve that opens and closes timed so that when the piston moves in one direction, air is compressed and then driven out of the piston, and when the piston moves in the other direction, air is drawn into the piston.

[0015] In one embodiment, the housing includes a cover to define a hermetically sealed space.

[0016] In one embodiment, the rocker is a three-part rocker arranged to pivot in a reciprocating motion.

[0017] In one embodiment, the compressor further includes a first spring connected to the rocker arm to provide a balancing force to the SMA element.

[0018] In one embodiment, the compressor further includes a second spring connected to the rocker to provide a balancing force to the SMA element.

[0019] In an embodiment, the fluid inlet is arranged to receive cold gas into the hermetically sealed space.

[0020] In an embodiment, the fluid inlet is arranged to receive gas within a temperature range of -2.8 to 3.7 degrees Celsius.

[0021] In one embodiment, the first spring is a compression spring arranged to pivot at a first end at a fixed position inside the housing and at a second end to the rocker.

[0022] In one embodiment, the first spring is a piston spring arranged to bias the piston to a bottom dead center position, and the second spring is a return spring to provide a return force to the rocker during a compression cycle.

[0023] In an embodiment, the compressor includes one or more adjustable retainers for adjustably connecting the SMA element to the housing.

[0024] There is also provided a refrigeration system comprising a compressor according to the first aspect of the invention, the refrigeration system further comprising: a condenser for receiving vapor from the compressor, and an evaporator for receiving liquid and providing cooled vapor as input to the compressor for compression.

[0025] According to a third aspect of the present invention, a method for compressing fluid is provided, the method comprising: providing a shell, a compressor cylinder, a rocker and one or more shape memory alloy (SMA) elements, the shell preferably defining an airtight sealed space, the compressor cylinder being coupled to the shell and having a movable member, the movable member being arranged to be driven to reciprocate during a compression cycle, the rocker being capable of moving between a first stable state and a second stable state, the rocker being arranged so that when the rocker moves, the movable member is driven in the compressor cylinder, the one or more SMA elements being coupled to the rocker and being capable of being driven to change between a first shape and a second shape, thereby driving the rocker; providing a cooling fluid to the airtight sealed space; and providing the fluid from the (preferably airtight sealed) space to the cylinder for compression.

[0026] According to another aspect of the present invention, there is provided a device for actuating a compressor, the device comprising: a rocker arm capable of moving between a first stable state and a second stable state, arranged so that when the rocker arm moves, a piston in a variable volume compressor chamber is driven; one or more shape memory alloy (SMA) elements coupled to the rocker arm and capable of being driven to change between a first shape and a second shape; and at least one temperature control zone, at least one of the shape memory alloy (SMA) elements being arranged within the at least one temperature control zone, wherein the temperature within the temperature control zone is controlled to change the temperature of the SMA contained therein.

[0027] In one embodiment, the device comprises at least two SMA elements, each SMA element being disposed in a temperature controlled region.

[0028] In one embodiment, the device comprises a fluid flow conduit arranged to direct, in use, fluid flow into and out of a compressor to which the device is connectable.

[0029] In an embodiment, the device comprises at least one cold fluid flow conduit and at least one hot fluid flow conduit, wherein the or each temperature controlled zone is a zone thermally coupled to the cold fluid flow conduit and the hot fluid flow conduit, or to each cold fluid flow conduit and each hot fluid flow conduit.

[0030] In one embodiment, the piston is arranged to move in a reciprocating manner in a cylinder coupled to the housing of the device.

[0031] In one embodiment, the cylinder has a valve that opens and closes timed so that when the piston moves in one direction, air is compressed and then driven out of the piston, and when the piston moves in the other direction, air is drawn into the piston.

[0032] According to another aspect of the present invention, a refrigeration system is provided, which includes an apparatus according to the first aspect of the present invention, and the refrigeration system also includes a condenser for receiving vapor from a compressor and an evaporator for receiving liquid and providing vapor as input to the compressor for compression.

[0033] The actuator overcomes the above problems of pumps and compressors by using the principle of SMA actuation, which is achieved by a bistable linkage with a return spring that acts opposite to the piston spring in order to reduce the total potential energy and achieve minimum power consumption. The bistable linkage remains stable in two positions corresponding to the bottom dead center (BDC) and the top dead center (TDC) of the compressor piston. These two positions are switched by an electrically heated SMA wire. The SMA wire is operated in cold gas generated by the compressor system. The operation of the wire in a cold environment reduces the cooling time of the wire from the SMA, and this increases the operating frequency of the pump.

[0034] According to another aspect of the present invention, a compressor is provided, comprising: a housing having a fluid inlet and a fluid outlet, a compressible fluid being provided through the fluid inlet so that the fluid can pass through the housing; a compressor chamber coupled to the housing and having a movable member, the movable member being arranged to be driven to reciprocate during a compression cycle, the compressor chamber being arranged to receive fluid from the housing; a rocker arm being movable between a first stable state and a second stable state, the rocker arm being arranged so that when the rocker arm moves, the movable member is driven in the compressor chamber; and one or more shape memory alloy (SMA) elements, the one or more shape memory alloy elements being coupled to the rocker arm and being driven to change between a first shape and a second shape, thereby driving the rocker arm.

[0035] Preferably, the cylinder is a cylinder. Preferably, the cylinder is a cylinder of circular cross-section. In an alternative example, the cross-section is elliptical.

[0036] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which:

[0037] Figure 1 It is a schematic diagram of the refrigeration cycle;

[0038] Figure 2 is a schematic cross-sectional view of a compressor for a refrigeration cycle in a bottom dead center (BDC) position of a piston;

[0039] Figure 3 is another schematic diagram of a compressor for a refrigeration cycle at a top dead center (TDC) position of a piston;

[0040] Figure 4 is a variation of a schematic cross-sectional view of a compressor for a refrigeration cycle in a bottom dead center (BDC) position of a piston;

[0041] Figure 5 is another schematic diagram of a compressor for a refrigeration cycle at a top dead center (TDC) position of a piston;

[0042] Figure 6 shows a graph of the piston spring force F and the piston gas force C versus the displacement s of the piston during compression-discharge;

[0043] Figure 7 Graphs showing the piston spring force F and the piston gas force E versus the piston displacement s during expansion-intake;

[0044] Figure 8 shows a graph of the sum of the piston compression gas force C plus the piston spring force F and the restoring force Q versus the piston displacement s;

[0045] Fig. 9 shows a graph of the sum of the piston suction gas force E plus the piston spring force F and the restoring force Q versus the piston displacement s;

[0046] Fig.10 A graph showing the shape memory alloy force required during compression-discharge versus piston displacement s; and

[0047] Fig.11 shows a graph of shape memory alloy force required during expansion-inhalation versus piston displacement s; and

[0048] Fig.12 is with Figure 2 and Figure 3 A compressor is a schematic cross-sectional view of a similar compressor.

[0049] The system is also arranged so that the shape memory alloy wire operates in a cold room or cold area through which the cold gas of the compressor passes. The cold room or cold area accelerates the cooling of the shape memory alloy wire, thereby creating the prerequisite for increasing the switching frequency.

[0050] See also Figure 1 , a schematic diagram of a known arrangement for a refrigeration cycle is shown. The refrigeration cycle shown is a schematic diagram, and is itself a known arrangement. As will be explained below, the compressor provided within the refrigeration cycle is new and provides clear and unique technical advantages.

[0051] refer to Figure 1In a refrigeration system of the type shown in FIG. 1 , a compressor 100 is provided having an input 28 arranged to receive a gas for compression. An output 31 is provided through which the compressed gas is coupled to a condenser 106. Upon condensation, the cooled fluid is output as a liquid via a conduit 108 into a receiver 109. From the receiver 109, the liquid is pumped into an evaporator 110, where the fluid is once again evaporated and provided as a vapor at 28 as input to the compressor 100. The receiver 109 is shown as including both the liquid and the vapor, which will be provided to the evaporator for evaporation and as input to the compressor 100.

[0052] Such systems are well known, but as will be explained below, the present invention provides a method for Figure 1 A modified version of compressor 100 for use within a refrigeration system of FIG. 1 is shown. It will be appreciated that the evaporator and condenser are shown schematically and will typically include serpentine or other tortuous passages and other components within them to enable them to perform the function of condensing or evaporating a fluid. A metering device / expansion valve 111 is provided upstream of the evaporator 110 and provides the fluid for evaporation to the evaporator 110. It will be further appreciated that no temperature or pressure gauges such as would typically be provided or, in fact, for ensuring that the fluid is flowing through the evaporator 110 are shown. Figure 1 Typically, a pump will be provided to pump the liquid from the receiver 109 to the evaporator 110.

[0053] Figure 1 The temperature and pressure of the liquid and / or vapor in the system can be varied or set at a desired level. Typically, the vapor pressure at the compressor inlet is between 1.1 and 1.5 bar. Typically, the pressure of the compressed vapor leaving the compressor will be between 8 and 15 bar.

[0054] The present system provides a compressor designed to draw gas from or discharge gas into a system such as a refrigeration system, air conditioning, actuate a jackhammer or force air into an inflatable object. As will be explained below, in a non-limiting embodiment, it is based on two springs ( Figure 2 As will be explained in detail below, two shape memory alloy (SMA) wires ( Figure 2 9' and 10') are used in Figure 2 The system shown is triggered between two stable configurations. The combination of bistable and energy recovery reduces the energy consumption of the compressor and accelerates (speeds up) SMA actuation. Thus, the compressor can be used in applications such as Figure 1 In the refrigeration system shown, the overall efficiency of the refrigeration system is improved.

[0055] Referring now to the drawings, examples of compressors will be described. An exemplary bistable compressor is provided, which is driven by a shape memory alloy SMA and a spring and, in a general sense, comprises two mechanisms acting in parallel to actuate a piston: a first restoring mechanism and a second driving mechanism, respectively.

[0056] refer to Figure 2 and Figure 3 , the compressor comprises a housing member 1 having a rigidly coupled compressor chamber 7, in this example in the form of a cylinder 7, in which a piston 6 is arranged to reciprocate. As described herein, the compressor chamber 7 may be a cylinder of circular cross-section or any other suitable shape or configuration, as long as it is capable of accommodating a member such as the piston 6 to be driven by the operation of the compressor. For example, it may be an elliptical, square, rectangular, diamond or any other shaped cross-section. The piston will be shaped accordingly.

[0057] The housing member 1 has a cover 30. As will be explained below, valves 26 and 27 are provided at the bottom end of the cylinder 7 and are controlled or controllable so that the compressor can compress and expand the gas and further control the gas by means of, for example, Figure 1 The system shown performs the discharge and intake of gas or air. This activity is achieved by actuation and control of the SMA wire, which will be explained below. An inlet pipe 28 is provided, which enables gas to enter the airtight sealing area defined by the housing member 1 and the cover 30. The housing member 1 and the cover 30 together provide a housing for the compressor. In one example, the housing member and the cover can be formed integrally, or they can be formed as separate connectable components. The housing member 1 and / or the cover 30 are preferably formed of an insulating material, such as a thermoplastic or a composite material, so as to provide insulation for the space within the housing, and the SMA element is arranged in the space.

[0058] Furthermore, the compressor chamber 7 is preferably formed integrally with the housing 1 or even as a part of the housing 1 , although it may be formed of a separate component and fixedly coupled to the housing 1 .

[0059] Another connecting pipe 29 is arranged to couple the cold gas received from the cover 30 and the defined space within the housing member 1 through the valve 26 into the compression cylinder 6 to start the compression cycle.

[0060] like Figure 1 As shown, an outlet pipe 31 is provided at one end of the cylinder 6 to enable the compressed high temperature fluid to flow out of the cylinder through the (correspondingly controlled) valve 27 and allow the compressed fluid to enter the rest of the refrigeration system. An opening is formed in the side wall of the housing member 1 through which the arm 5 passes. As will be explained below, the size of the opening is designed to enable the arm 5 to move up and down without restriction.

[0061] The restoring spring mechanism comprises a rocker arm 5, a third rocker arm 12, a coupler 13 having an engagement tip in the form of a sharp tip 15 that engages (e.g. meshes) with a recess 16 provided in a lever 14. The restoring spring mechanism further comprises a connecting rod 11, a restoring spring 18 and a piston 6 (arranged to be slidably movable in a cylinder provided as part of the compressor housing).

[0062] The second actuation mechanism comprises a compression-exhaust SMA wire 9 and an expansion-intake SMA wire 10. A second rocker arm 8 is provided, and the system further comprises a first rocker arm 5. An opening adjustable retainer 19 and a closing adjustable retainer 20 are provided with the connecting rod 11 and the piston 6.

[0063] The piston spring 17 is arranged to be coupled to the connecting rod 11 and is arranged in the normal position to ensure that the piston 6 remains in the BDC position. At the connection point of the rocker arm 5, the second rocker arm 8 and the third rocker arm 12, there is a pivot joint 24 between the housing member 1 and the rigidly connected rocker arms 5, 8 and 12. At the free end of the second rocker arm 8, the compression exhaust SMA wire 9 is attached. The expansion-intake SMA wire 9 is rigidly connected at the other end to the closing adjustable retainer 19 that can only move vertically. One end of the expansion-intake SMA wire 10 is attached to the rocker arm 5 at point 48, and the other end of the expansion-intake SMA wire 10 is rigidly connected to the opening adjustable retainer 20, which can only move vertically. In the BDC position, the rotation of the second rocker arm 8 is limited by the adjustable stop 22. In the TDC position, the rocker arm 5 is supported by the adjustable stop 23.

[0064] The restoring spring mechanism comprises a rocker arm 5, a third rocker arm 12, a coupler 13 having an engagement tip in the form of a sharp tip 15 that engages (e.g. meshes) with a recess 16 provided in a lever 14. The restoring spring mechanism further comprises a connecting rod 11, a restoring spring 18 and a piston 6 (arranged to be slidably movable within a cylinder 7 provided as part of the compressor housing 1). As mentioned above, preferably, the cylinder 7 has a circular cross section, but any suitable cross section may be provided with a piston of a corresponding shape.

[0065] The second actuation mechanism comprises a compression-exhaust SMA wire 9 and an expansion-intake SMA wire 10. A second rocker arm 8 is provided and the system also comprises a first rocker arm 5.

[0066] At the free end of the third rocker arm 12, a coupler 13 in the form of a longitudinal member is connected via a pivot joint 3. The other end of the coupler is shaped as an engagement area and preferably a sharp tip 15, which is arranged to interact or engage with a recess or notch 16 formed in the lever 14. The lever 14 is connected to the housing 1 via a pivot joint 32. A return spring 18 is provided attached to the free end of the lever 14. The other end of the return spring is connected to the adjustable screw 21 by a thread.

[0067] The adjustable screw 21 is connected to the housing member 1 by a pivot joint 41. The connecting rod 11 is attached at the free end of the arm 5 by a pivot joint 4. The connecting rod 11 and the piston 6 are connected by a pivot joint 2. The piston spring 17 is mounted to the arm 5 and the connecting rod 11 at the pivot joint 4. The other end of the piston spring is fixed to the housing member 1 at point 25. A cover 30 is provided for the housing.

[0068] As will be explained below, reference Figure 2 In a non-limiting and preferred embodiment, the compressor device comprises a rocker consisting of three arms, including a first arm 5 and a second arm 8 and a third arm 12. In this example, the second arm 8 and the third arm 12 are part of a single continuous member, wherein the first arm 5 protrudes vertically from the single continuous member. The three-arm rocker is coupled to SMA elements 9 and 10. The three-arm rocker moves under the action of the SMA elements 9 and 10. A piston 6 is provided, which is coupled to one end of the arm 5 of the three-arm rocker by a connecting rod 11 at the piston connection 2. Therefore, when the three-arm rocker swings about the pivot point 24, it drives the piston 6 to reciprocate in the cylinder 7. Valves 26 and 27 are provided at one end of the cylinder 7 away from the rocker arm 5 and are controlled so that when the piston moves in the cylinder 7, a gas such as air can be compressed and driven from the cylinder or sucked into the cylinder for further operation.

[0069] The first rocker arm 5 and the second rocker arm 8 are connected to the SMA elements 9 and 10 at points 46 and 48. The SMA elements 9 and 10 are themselves connected to the housing 1 at connectors 19 and 20, respectively.

[0070] With reference to the rocker, at the distal end, a first rocker arm 5 is coupled to a connecting rod 11 by a pivot joint 4, which itself is attached to a piston 6 by a second joint (e.g. a pivot joint) 2. The piston 6 is arranged and configured to be slidably movable within a cylinder 7. At the pivot joint or piston connection 4 between the connecting rod 11 and the arm 5 of the rocker, a piston spring 17 is mounted, which is coupled to a fixed position 25 relative to the housing member 1.

[0071] The rocking of the three-arm rocker (comprising the rocker arms 5, 8 and 12) is caused by the action of two SMA elements or two SMA wires, one SMA element or SMA wire 10 being attached to the first rocker arm 5 and the other SMA element or SMA wire 9 being attached to the second rocker arm 8. The third arm 12 of the rocker is connected to a coupler 13. The coupler 13 has a tip 15, preferably sharp, which engages in a notch 16 of a lever 14. The lever 14 itself is connected to the housing 1 by a pivot joint 32.

[0072] A restoring spring 18 is connected to the free end of the lever 14. The other end of the restoring spring 18 is connected to the housing 1 through a connector such as a screw. Preferably, the screw is an adjustable screw 21.

[0073] The dimensions of the three-arm rocker 5, 8 and 12, the coupler 13 and the lever 14 are selected so that around the central angular position of the stroke of the three-arm rocker, the piston force and the piston spring force are balanced with the restoring spring force. Therefore, in this intermediate state, i.e. the central angular position, the three-arm rocker 5, 8 and 12 is in an unstable equilibrium position.

[0074] To understand the movement of the rocker and piston 6 during the operating cycle, first consider the situation before the unstable position. Figure 2 As shown, at the beginning of the stroke or cycle, the piston 6 is in its bottom dead center (BDC) position. Gas has been sucked into the cylinder by the control of valves 26 and 27, so that it is ready to start compression with valves 26 and 27 now closed. This BDC characterizes the beginning of compression or the end of suction of the compressor cycle and corresponds to the first stable equilibrium position of the compressor. In this position, the force from the return spring 18 (i.e., the return spring force) is less than the sum of the piston force and the force of the piston spring 17.

[0075] Due to the balance of forces between springs 17 and 18 and SMA elements 9 and 10, the piston moves from its BDC position ( Figure 2 ) is driven to its TDC position ( Figure 3 ). At the end of compression coinciding with the start of intake, the piston is now in its top dead center (TDC) position.

[0076] Then, the restoring force is greater than the sum of the piston force and the compression spring force, and the three-arm rocker is in its second closed stable equilibrium position, i.e., Figure 3 As shown, the end where the pivot joint 4 is located is in a lower position corresponding to the TDC position of the piston 6. Therefore, in simple terms, it can be seen that the rocker moving about the pivot joint 24 can effectively rock so that the end 4 coupled to the piston 6 moves up and down cyclically, thereby driving the movement of the piston in the cylinder accordingly.

[0077] The piston achieves two end on / off stable positions.The general operation of this mechanism will be understood by reference to, for example, GB2558618A by the same inventor as the present invention (and referenced above).

[0078] Before being sucked into the cylinder 7, the compressor system (see above) Figure 1 Description) The returned cooling gas passes through the airtight sealed space between the housing 1 and the cover 30, in which the SMA wire is positioned, and increases the operating speed of the SMA wire and thus improves the operating frequency of the compressor.

[0079] Since the energy is reduced due to the recovery, a very weak force is required to switch the compressor on / off. This force is applied by two SMA wires.

[0080] When the piston starts from its BDC, the first SMA wire rotates the rocker from the open position to the unstable position, and thereafter the return spring continues the discharge of the compressor. When the piston is TDC, the second SMA wire rotates the rocker from the stable TDC position to the unstable position, and thereafter the compression spring continues to drive the piston to its BDC. Due to the change in direction and shape of the piston force, the unstable position of the piston is not consistent in the two directions of movement from BDC to TDC and vice versa from TDC to BDC. After the movement from TDC to BDC and from BDC to TDC ends, the non-driving SMA wire is extended to avoid shock and imbalance.

[0081] Since the driving force of the SMA wire is very weak, its shortened actuation stroke significantly reduces the overall energy consumption of the compressor.

[0082] A bistable compressor is provided, which is driven by a shape memory alloy (SMA) wire and a spring and has a restoring action. The optimal distribution of the potential energy of the spring and the gas pressure achieved by the bistable restoring mechanism and the cooling of the SMA wire reduce energy consumption and increase the operating frequency under the guaranteed minimum size and noise of the compressor.

[0083] A compressor is a pneumatic device having a wide range of applications in refrigeration systems, air conditioning, and devices for compression or expansion of air.

[0084] As will be explained in detail below, the compressor consists of a housing to which a cylinder is fixedly mounted or integrally formed. A piston is arranged to reciprocate within the cylinder and is coupled to an output connecting rod of a bistable mechanism so as to slide the piston in the cylinder.

[0085] The piston 6 is coupled to the connecting rod 11 through a pivot joint 2. Through an auxiliary pivot joint 4, the connecting rod 11 is attached to the first arm 5 of the rocker, which itself is connected to the housing through a pivot joint 24. At the same first arm of the rocker, an SMA wire 10 is attached for moving the piston from top dead center (TDC) to bottom dead center (BDC). At the end of the second arm 8 of the rocker, which is co-linear with the first arm but located on the opposite side of the pivot joint 24 between the rocker and the housing, an SMA wire 9 is provided for moving the piston from BDC to TDC.

[0086] The ends of the opening and closing SMA wires are connected to the housing by means of retainers 19 and 20 with adjustable positions. The rocker also comprises a third arm 12, the axis of which passes through a fixed pivot joint 24 and is perpendicular to the line of the first two arms 5 and 8 or the longitudinal axis of the first two arms 5 and 8. At the end of this third rocker arm 12, by means of another pivot joint 3, a coupler 13 with a sharp tip 15 is attached. The sharp tip 15 of the coupler 13 engages with a notch 16 formed in a lever 14, which itself is connected to the housing by means of a pivot joint 32.

[0087] At the free end of the lever, a restoring spring 18 is attached. In this example, the second end of the restoring spring 18 is attached to the housing by an adjustable screw 21. The screw 21 can also be used to adjust the spring length and its stiffness.

[0088] The rotation or pivoting of the rocker about the pivot point 24 is limited by two stops 20 and 22 preferably fixedly mounted to the housing. The stops 23 and 22 preferably have a variable height for adjusting the stroke of the piston. The two SMA wires 9 and 10 are always in two different drive or idle states.

[0089] When the SMA wire is in the actuated state, it is stretched with the help of an electric current and its temperature is raised. The heating then causes the SMA wire to shorten and, at a certain temperature, trigger the bistable mechanism by relaxing and entering an idle mode.

[0090] Figure 4 and Figure 5 shows the dependency on the reference above Figure 2 and Figure 3 Another embodiment of the principle similar to the principle described above. However, in Figure 4 and Figure 5 In the example of FIG. 1 , the lever 14 with the notch 16 and the coupler 13 with the sharp tip are removed. Figure 2 and Figure 3The example of the tension type return spring 18 is replaced by a compression type return spring 50, which is suspended to the base 1 by a guide cylinder 53 through a hinge or a rotatable pivot joint 52. The other end of the compression type return spring 50 is attached to the arm 12 by a second guide cylinder 51 through a rotatable joint such as a hinge 3.

[0091] therefore, Figure 4 and Figure 5 The embodiments or examples provide Figure 2 and Figure 3 Simpler construction. Reduced component count while still providing Figure 2 and Figure 3 In this example, first refer to Figure 4 , the assembly with the piston 6 in its BDC position can be seen. The compression spring 50 is in a compressed state (its length is shorter than Figure 5 The actuators of the system are also SMA elements 9 and 10, which can be controlled by a desired current or control input to cause the state to switch. Springs 17 and 50 provide a force combined with the force of the SMA elements, so that the system can be operated in the same manner as Figure 2 and Figure 3 The way is quite the way to operate.

[0092] In general, and applicable to all embodiments, it will be appreciated that in an idle state, the SMA wires are unstressed and gradually cool due to their presence and placement within a cooling chamber formed by the housing 1 and cover 30. When the bistable mechanism switches, such as upon application of an electric current or other such control signal, the SMA elements 9 and 10 extend and are therefore in an actuated state.

[0093] In the idle state, the SMA wire has a changed geometry. Cold gas sucked from outside the refrigeration system cools the SMA wire, which creates the prerequisite for increasing the switching frequency.

[0094] The mechanical advantage of the compressor described herein is essentially based on the parallel action of two mechanisms for actuating the piston, a first reaction mechanism and a second actuation mechanism, respectively. The thermal advantage results from positioning the SMA in the cool gas temperature in the compressor to reduce energy consumption and extend the frequency bandwidth.

[0095] As will be explained in detail below, the restoring mechanism is preferably composed of a restoring spring, a lever, a coupler, a connecting rod and a piston. Through this kinematic chain, the restoring spring generates a reaction F that acts opposite to the sum of the piston spring force Q and the compression-exhaust gas force C, or the sum of the spring force Q and the expansion-intake gas force E.

[0096] When the piston is at BDC, the restoring force is less than the piston force. The rocker is supported to the opening stop and the four-bar linkage is in its first stable open position.

[0097] The dimensions of the link are chosen to ensure an unstable position near the middle of the rocker's travel, where the restoring and piston forces are equal but opposite in direction.

[0098] When the piston is in the TDC position, the restoring force is greater than the piston force, which ensures a second stable position. In this position, the rocker is constrained by the closed stop 23.

[0099] The effect of the system is that the activation of the restoring mechanism produces a reciprocating movement of the piston 6 .

[0100] The second actuation mechanism includes a compression-exhaust SMA wire and an expansion-intake SMA wire, first and second rocker arms, a connecting rod 13 , and a piston 6 .

[0101] When actuated, the SMA wire overcomes only the difference between the restoring force and the piston force and actuates the piston only halfway through its stroke. The second half of the piston stroke is performed by the positive difference between the two forces Q and F.

[0102] A significant advantage of the compressor is that the travel of the SMA wire and the force to be overcome are significantly reduced through the recovery of the piston spring energy achieved, the piston spring energy being transferred to the return spring during the expansion-intake valve and vice versa from the return spring to the piston spring during the compression-discharge stroke of the piston.

[0103] As will be explained further below, preferably an actuator is provided which itself includes an electronic control system for optimal pulse width modulation (PWM) of the SMA wire.

[0104] In operation, cold gas, such as Freon or air, is sucked in by the inlet valve 26 and passes through the pipes 28 and 29, thereby supplying the sealed space defined by the housing, which in the embodiment is itself defined by the housing member 1 and the cover 30. This provides a low temperature environment for the SMA wire. Typically, the temperature in the closed space may be between -2.8 and 3.7 degrees Celsius. This low temperature shortens the cooling time of the idle wire and increases the triggering frequency of the bistable mechanism. The refrigeration system is supplied with gas under pressure and high temperature by means of the pipe 31, which is compressed due to the compression cycle (i.e., due to the movement of the piston 6 from BDC to TDC).

[0105] The restoring spring 18, the lever 14, the notch 16, the tip 15, the coupler 13, the third rocker arm 12, the rocker arm 5, the connecting rod 11 and the cylinder 6 form a restoring mechanism which generates a force Q called a restoring force at the piston 6. The direction of this restoring force Q is opposite to the forces acting on the piston. During the compression-discharge period (CDP), these forces acting on the piston are the sum of the piston spring (17) force F and the compression-discharge force C (see Figure 6 ), or during the expansion-suction period (ESP) is the sum of the piston spring (17) force F and the expansion-suction E (see Figure 7 ). It can be seen that the piston spring force F increases linearly with the displacement of the piston from BDC.

[0106] When the piston 6 is at BDC, the restoring force Q is less than the sum of the piston gas force C and the spring piston force F, and during the compression-release period, near any midpoint of the stroke, the equation Q=F+C is satisfied. Therefore, an unstable equilibrium position occurs near the middle of the compression-discharge stroke. When the rocker arm 5 rotates to contact the stopper 23, the piston 6 is at TDC, and the restoring force Q of the restoring spring 18 is greater than the sum of the resultant forces F+C. The piston 6 is in its second stable position ( Figure 3 ).

[0107] A useful result is that in the proposed device, the closing SMA wire 9 and the opening SMA wire 10 are only loaded with the difference between the force Q and the reaction force F+C or F+E. The loading of the SMA is only during the first half of the stroke of the piston 6. During the second half of the stroke piston 6, the difference between the forces is in the direction of movement of the piston 6, and the return spring 18 is the driver.

[0108] In this way, the energy recovery of the spring 18 is achieved (see Figures 6 to 8 ).

[0109] When the piston 6 moves from TDC to BDC, the SMA wire 10 rotates the rocker arm 5 only in the first part of the stroke of the piston 6. Near the middle of the stroke, the sum of the piston spring force F plus the piston gas force E is equal to the restoring force Q. Therefore, the piston 6 is in an unstable equilibrium state again during the expansion-intake period. The force of the opening SMA wire 10 must only act on the rocker arm 5 to this position. After the closing unstable equilibrium position, the difference between the restoring force Q and the sum of the piston spring force F plus the piston gas force E becomes positive, and this difference acts in the direction of movement. In this case, after the expansion-intake instability point, the piston spring 17 is the driver ( Fig. 9 ).

[0110] In this way, the energy recovery of the piston spring 17 is achieved (see Fig. 9 and 11 ). The hatched (shaded) area (see Fig.10 and Fig.11 ) is the SMA wire in the expansion and suction stage ( Fig.10 ) and compression discharge stage ( Fig.11 )The necessary potential energy that must be overcome.

[0111] Therefore, the proposed object is to provide a bistable compressor driven by a shape memory alloy with minimum power consumption.

[0112] Fig.12 is with Figure 2 and Figure 3 A compressor is similar to a schematic cross-sectional view of a compressor. Identical components are marked with the same reference numerals and their functions correspond. Fig.12 In the example, Figure 2 and Figure 3 Compared to the example of the embodiment of the present invention, the lever 14 having the notch 16 and the coupler 13 pivotally coupled to the arm 12 at point 3 is replaced by a cam 60 of generally elliptical cross-section and a roller 62 rotatably coupled to the lever 14 at point 64. In operation, when the rocker is rotated with reference to the above Figure 2 and Figure 3 When the cam 60 is swung about the pivot joint 24 in the manner described, the cam 60 engages the roller 62 to achieve a rotational movement as compared to the conventional method. Figure 2 and Figure 3 's example (even though the example itself works well) to achieve a smoother engagement.

[0113] The cam 60 is fixedly connected to the arm 12, ie, it does not rotate or move at all relative to the end of the arm 12. However, when the arm 12 pivots about the joint 24, the roller 62 pivots about its axis defined by the joint 64.

[0114] Embodiments of the invention have been described with particular reference to the examples shown. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the invention.

Claims

1. A compressor, comprising: a housing having a fluid inlet and a fluid outlet through which a compressible fluid can be provided to or removed from the housing; a compressor cylinder coupled to the housing and having a movable member arranged to be driven into reciprocating motion during a compression cycle, the cylinder being arranged to receive fluid from the housing; a rocker movable between a first stable state and a second stable state, the rocker being arranged such that upon movement of the rocker the movable member is driven in the compressor cylinder; One or more shape memory alloy (SMA) elements are coupled to the rocker, the one or more shape memory alloy (SMA) elements being actuatable to change between a first shape and a second shape to drive the rocker.

2. The compressor according to claim 1, wherein: The housing defines a hermetically sealed space, and has the fluid inlet and the fluid outlet.

3. The compressor according to claim 1 or 2, wherein: The cylinder has a valve that opens and closes timed so that air is compressed and then driven away from the piston as the piston moves in one direction, and air is drawn into the piston as the piston moves in the other direction.

4. The compressor according to any one of claims 1 to 3, wherein: The housing includes a cover to define the hermetically sealed space.

5. The compressor according to any one of claims 1 to 4, wherein: The rocker is a three-part rocker arranged to pivot in a reciprocating motion.

6. A compressor according to any one of claims 1 to 5, comprising a lever arranged to engage the rocker, the lever having one end pivotally mounted to the housing.

7. The compressor of any one of claims 1 to 6, further comprising a first spring connected to the rocker to provide a balancing force to the SMA element. 8 . The compressor of claim 7 , further comprising a second spring connected to the rocker to provide a balancing force to the SMA element.

9. The compressor according to any one of claims 1 to 8, wherein: The fluid inlet is arranged to receive cold air into the hermetically sealed space.

10. The compressor according to claim 9, wherein: The fluid inlet is arranged to receive gas at a temperature in the range of -2.8 degrees Celsius to 3.7 degrees Celsius.

11. The compressor according to claim 7, wherein: The first spring is a compression spring arranged to pivot at a first end at a fixed position on the inner side of the housing and at a second end with respect to the rocker.

12. The compressor according to claim 8, wherein: The first spring is a piston spring arranged to bias the piston to a bottom dead center position, and the second spring is a return spring to provide a return force to the rocker during the compression cycle.

13. The compressor of any one of claims 1 to 12, comprising one or more adjustable retainers for adjustably connecting the SMA element to the housing.

14. The compressor according to claim 1, wherein: The rocker is further arranged to be in a third state between the first state and the second state, the third state being unstable, and wherein two or more SMA elements are coupled to the rocker, wherein the two or more SMA elements are electrothermally actuatable to change the position of the rocker between a first stable state and a third unstable state or between a second stable state and a third unstable state, thereby actuating the rocker; a return spring that drives the rocker from the third unstable state to the second stable state; A piston spring drives the rocker from the third unstable state to the first stable state.

15. A compressor according to any one of claims 7 to 14, when dependent on claim 6, wherein The rocker includes a coupler for engaging the lever.

16. The compressor according to claim 16, wherein: The coupler is an arm pivotally coupled to the rocker.

17. The compressor according to claim 16, wherein: The coupler is a cam fixedly coupled to the rocker, the cam being arranged to engage with the lever.

18. The compressor according to claim 17, wherein: The cam is arranged to engage with a pivotally mounted roller on the lever.

19. A refrigeration system, comprising the device according to any one of claims 1 to 18, the refrigeration system further comprising: A condenser for receiving vapor from the compressor, and an evaporator for receiving liquid and providing cooling vapor as input to the compressor for compression.

20. A method of compressing a fluid, the method comprising: providing a housing, a compressor cylinder, a rocker, and one or more shape memory alloy (SMA) elements, the compressor cylinder being coupled to the housing and having a movable member, the movable member being arranged to be driven to reciprocate during a compression cycle, the rocker being movable between a first stable state and a second stable state, the rocker being arranged such that when the rocker moves, the movable member is driven in the compressor cylinder, the one or more shape memory alloy (SMA) elements being coupled to the rocker, the one or more shape memory alloy (SMA) elements being drivable to change between a first shape and a second shape, thereby driving the rocker; providing a cooling fluid to the housing; Fluid is provided from the housing to the cylinder for compression.

21. The method according to claim 15, wherein: The housing is hermetically sealed such that fluid can only enter or leave the housing through a defined inlet and outlet, respectively.

22. A method of compressing a fluid, the method comprising: Providing a compressor according to any one of claims 1 to 19; as well as The compressor is operated to compress a fluid.

23. A compressor, comprising: a housing having a fluid inlet through which a compressible fluid can be provided and a fluid outlet to allow fluid to pass through the housing; a compressor chamber having a movable member arranged to be driven into reciprocating motion during a compression cycle, the compressor chamber arranged to receive fluid from the housing; a rocker movable between a first stable state and a second stable state, the rocker being arranged such that upon movement of the rocker, the movable member is driven in the compressor chamber; as well as One or more shape memory alloy (SMA) elements are coupled to the rocker, the one or more shape memory alloy (SMA) elements being actuatable to change between a first shape and a second shape to drive the rocker.

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