Patent Publication Number: US-11384746-B2

Title: Centrally located linear actuators for driving displacers in a thermodynamic apparatus

Description:
FIELD OF INVENTION 
     The present disclosure relates to placement of a linear actuation system for displacers within a heat pump. 
     BACKGROUND 
     Vuilleumier heat pumps have been known since the early 20 th  century. Such heat pumps, as disclosed in U.S. Pat. No. 1,275,507, have two displacers that separate the internal volume into hot, warm, and cold chambers. The displacers are crank driven with a 90 degree offset. In a more recent development, the displacers in the heat pump are driven by a mechatronic system, as described in commonly-assigned U.S. Pat. No. 9,677,794. In  FIG. 1 , based on a figure from the &#39;794 reference, a heat pump  100  has a hot displacer  102  that reciprocates within a hot displacer cylinder  107  and a cold displacer  104  that reciprocates within a cold displacer cylinder  106 . The hot and cold displacer cylinder  107  and  106  are share a centerline  108 . Displacers  102  and  104  are controlled by mechatronic actuators, the linear actuator portion of the mechatronic actuators being disposed in the lower half of the heat pump  100 . A hot displacer actuator  110  and a cold displacer actuator  120  are coupled to the hot and cold displacers  102  and  104 , respectively. Each of actuators  110  and  120  have a ferromagnetic bucket,  116  and  126 , respectively. Ferromagnetic buckets  116  and  126  act as armatures. Armature  116  has a plate portion that extends outwardly from a cylindrical portion through which a spring  124  passes and to which a spring  114  is coupled. Spring  114  is associated with hot displacer  102 ; and spring  124  is associated with cold displacer  104 . Armature  126  has a plate portion and a cylindrical portion to which springs  114  and  124  are coupled. Springs  114  and  124  are, in this example, springs that go between compression and tension as the displacer to which it is coupled moves between ends of travel. 
     Actuator  110  has coils  112  and  118  on either side of armature  116 . When coil  112  is activated, armature  116  is attracted toward coil  112 . When coil  112  is deactivated spring  114  causes armature  116  (and displacer  102 ) to move downward. If coil  118  is then activated, it attracts armature  116  toward coil  118 . By deactivating coil  118 , spring  114  causes armature  116  to move toward coil  112 . By acting on armature  116  coupled to displacer  102 , displacer  102  is caused to reciprocate between two ends of travel within cylinder  106 . Similarly, displacer  104  is caused to reciprocate between its two ends of travel by judicious actuation of coils  122  and  128  that are disposed on either side of armature  126 . Springs  114  and  126  are provided to exert force on displacers  102  and  104 , respectively, to effect movement of the displacer between ends of travel. Particularly when the displacer is at the middle portion of travel, the coils acting on the armature associated with the displacer are much less effective than when the displacer is nearer ends of travel. The current draw for the armature to the coils at the middle of the stroke is high, thereby increasing the size of the coils, increasing the electrical energy losses, and possible overheating of the coils. The springs provide much of the force to move the displacers and the coils are used to control the last part of the travel and to cause the displacer to dwell at the end of travel for a desired duration. 
     In heat pump  100 , displacers  102  and  104  separate the volume within cylinders  106  and  107  into four volumes: a hot volume  140 , a hot-warm volume  142 , a cold-warm volume  144 , and a cold volume  146 . A bridge  150  separates hot-warm volume  142  from cold-warm volume  144 . 
     In addition to spring  114  that acts on hot displacer  102  and spring  114  that acts on cold displacer  104 , it has been found to be advantageous to provide a gas spring that acts between displacers  102  and  104 . A portion of the gas spring is volume  138  that is disposed with cold displacer  104 . In addition, the gas spring can include volume within hot displacer  102  and cold displacer  104 . Bridge  150  has a plunger  151  that causes volume  138  to be almost zero when cold displacer  104  is at its upper end of travel. Cold displacer  104  is shown at a middle position in  FIG. 1 , in which volume  138  is at an intermediate volume. By selecting the cross-sectional areas of plunger  151  and the shafts and selecting the total volume of the gas spring, the pressure in the gas spring can assist movement of displacers  102  and  104 . 
     In heat pump  100 , displacers  102  and  104  separate the volume within cylinders  106  and  107  into four volumes: a hot volume  140 , a hot-warm volume  142 , a cold-warm volume  144 , and a cold volume  146 . A bridge  150  separates hot-warm volume  142  from cold-warm volume  144 . 
     Hot displacer  102  is coupled to shaft  130  that is coupled to shaft  134  via a coupler  132 . Shaft  134  couples to armature  126 . Movement of armature  126  moves hot displacer  102 . Cold displacer  104  is coupled to armature  116  via hollow shaft  136 . 
     Some less than desirable features are inherent in the actuation system represented in  FIG. 1 . By having shaft  134  move within hollow shaft  136 , i.e., concentric shafts, leads to undesirable friction. Because shaft  134  is very long, it must be of a certain diameter and strength to prevent buckling. The critical buckling load is proportional to the inverse of the square of the length. Thus, the longer the length of the shaft, the greater the challenge to avoid buckling. In addition to buckling concerns, preserving concentricity and avoiding cocking of hot displacer  102  within cylinder  106  are complicated by longer shafts. Another concern is the number of gas seals to largely prevent gas flows between shafts  134  and  136  and at bridge  150 , etc. Such seals lead to additional friction. 
     SUMMARY 
     To overcome at least one problem in the prior art, the linear actuator is disposed between the displacers. A thermodynamic apparatus is disclosed that has a hot displacer disposed in a hot displacer cylinder and a cold displacer disposed in a cold displacer cylinder. A central axis of the cold displacer cylinder collinear with a central axis of the hot displacer cylinder. A linear actuator section is disposed between the hot and cold displacer cylinders. the linear actuator section comprising a hot displacer linear actuator and a cold displacer linear actuator. 
     The hot displacer linear actuator includes: a first coil disposed within the linear actuator section at a first axial location within the linear actuator section, a second coil disposed within the linear actuator section at a second axial location within the linear actuator section, and a hot displacer armature disposed between the first coil and the second coil. 
     A hot displacer actuator of the thermodynamic apparatus includes: the hot displacer linear actuator, a shaft coupled between the armature of the hot displacer linear actuator and the hot displacer, and at least one spring disposed between the displacer and the linear actuator. 
     The cold displacer linear actuator has a third coil disposed within the linear actuator section at a third axial location within the linear actuator section, a fourth coil disposed within the linear actuator section at a fourth axial location within the linear actuator section, and a cold displacer armature disposed between the third coil and the fourth coil. The thermodynamic apparatus includes a cold displacer shaft coupled between the cold displacer armature and the cold displacer, a hot displacer shaft coupled between the hot displacer armature and the hot displacer. 
     In some embodiments, the spring is a tension-compression spring that is coupled to the displacer at a first end and coupled to a stationary element of the thermodynamic apparatus at a second end. The linear actuator section has a first end plate and a second end plate; and the stationary member is the first end plate. In other embodiments, the at least one spring is a pair of compression springs disposed in the heat pump with a first of the compression springs biased to exert an upward force on the hot displacer and a second of the springs biased to exert a downward force on the hot displacer. 
     A cold displacer actuator to move the cold displacer includes: a cold displacer shaft coupled between the cold displacer linear actuator and the cold displacer, a first coil disposed within the linear actuator section at a first axial location within the linear actuator section, a second coil disposed within the linear actuator section at a second axial location within the linear actuator section, a cold displacer armature coupled to the cold displacer shaft, the cold displacer armature disposed between the first coil and the second coil, a spring having a first end coupled to the cold displacer and a second end coupled to a stationary member of the thermodynamic apparatus. 
     The linear actuator section has a first end plate proximate the cold displacer cylinder and a second end plate proximate the hot displacer cylinder. The thermodynamic apparatus also has: a hot displacer shaft coupled to the hot displacer linear actuator, a cold displacer shaft coupled to the cold displacer linear actuator, a first orifice defined in the first end plate with a first a seal disposed in the first orifice, and a second orifice defined in the second end plate with a second seal disposed in the second orifice. The hot displacer shaft passes through the first seal and the cold displacer shaft passes through the second seal. 
     A passage through the cold shaft fluidly couples a volume within the cold displacer with a volume within the linear actuator section. 
     The hot displacer shaft has a diameter smaller than a diameter of the cold displacer shaft. 
     The thermodynamic apparatus includes: a power electronics module electrically coupled to the first, second, third, and fourth coils and an electronic control unit coupled to the power electronics module. 
     The thermodynamic apparatus includes: a gas spring disposed between the hot and cold displacer, the gas spring being partially comprised of gas-filled volume within the linear actuator section and volume within the cold displacer. 
     Also disclosed is a heat pump with a hot displacer disposed in a hot displacer cylinder, a cold displacer disposed in a cold displacer cylinder, a first linear actuator coupled to a shaft of the hot displacer, and a second linear actuator coupled to a shaft of the cold displacer. The first linear actuator is adjacent to the second linear actuator. The shaft of the cold displacer extends outwardly from the first linear actuator in a first direction. The shaft of the hot displacer extends outwardly from the second linear actuator in a second direction. The first direction is opposed to the second direction. 
     The hot displacer is disposed proximate a first end of the heat pump. The cold displacer is disposed proximate a second end of the heat pump. The first and second linear actuators are disposed in a linear actuator section. The linear actuator section is disposed between the hot and cold displacers. 
     Each of the first and second linear actuators has: first and second coils displaced along a central axis of the hot displacer cylinder from each other and disposed within the linear actuator section and an armature. The armature has one of a permanent magnet and a ferromagnetic material. 
     The armature of the first linear actuator is coupled to the shaft of the hot displacer and the armature of the second linear actuator is coupled to the shaft of the cold displacer. 
     The heat pump also includes: a power electronics module electrically coupled to the first and second coils of each of the first and second linear actuators, a first position sensor proximate one of: the hot displacer; the shaft associated with the hot displacer, and the armature associated with the hot displacer, and a second position sensor proximate one of: the cold displacer; the shaft associated with the cold displacer, and the armature associated with the cold displacer. The heat pump further includes an electronics control unit electronically coupled to the first and second position sensors and to the power electronics module. 
     The heat pump includes a gas spring coupled between the hot displacer and the cold displacer. A portion of the volume comprising the gas spring is disposed within the linear actuator section. 
     The shaft coupled to the hot displacer has a smaller diameter than the shaft coupled to the cold displacer. When the displacers move, the shafts reciprocate within orifices defined in end plates of the linear actuator section. 
     Also disclosed is heat pump having hot displacer disposed in a hot displacer cylinder, a cold displacer disposed in a cold displacer cylinder, with a central axis of the cold displacer cylinder collinear with a central axis of the hot displacer cylinder. The heat pump has a hot displacer actuator coupled to the hot displacer, the hot displacer actuator including a hot displacer linear actuator and a hot displacer spring. The heat pump also has a cold displacer actuator coupled to the cold displacer, the cold displacer actuator having a cold displacer linear actuator and a cold displacer spring. The hot displacer and cold displacer linear actuators are disposed in a linear actuator section. The linear actuator section is located between the hot and cold displacer cylinders. 
     The linear actuator section is delimited by a cylinder, a first end plate and a second end plate. The first and second end plates each have an orifice defined therein The heat pump also includes: a first seal disposed in the orifice of the first end plate, a second seal disposed in the orifice of the second end plate, a hot displacer shaft coupled between the hot displacer and the hot displacer linear actuator, the hot displacer shaft passing through the first seal, and a cold displacer shaft coupled between the cold displacer and the cold displacer linear actuator, the cold displacer shaft passing through the second seal. 
     Advantages of disclosed embodiments include at least:
         less bending of the shaft;   elimination of friction of the shafts reciprocating one inside the other;   easier assembly;   ability to remove the hot end from the cold end for repair purpose without complete disassembly of both ends;   reduced conduction between the hot end and the cold end   improvement of alignment of the shafts and the displacers;   reduction in the number of seals (reduced part count; better overall sealing; easier assembly; fewer failure opportunities; and lower friction); and   use of the mechatronics volume as a gas spring.       

    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic of a linear actuation system for a gas-fired heat pump with the linear actuators at one end of the heat pump; 
         FIG. 2  is a schematic of a linear actuation system for a heat pump with the linear actuators disposed between two actuators within the heat pump; 
         FIG. 3  is an illustration of one embodiment of a seal in an orifice in an end plate of a linear actuator section and the shaft which goes through the orifice; 
         FIGS. 4 and 5  are illustrations of a displacer that is driven by two compression springs biased against each other, shown at an upper position of the displacer and a lower position of the displacer, respectively; and 
         FIG. 6  is an illustration of the power and control electronics coupled to the hot and cold displacer actuators. 
     
    
    
     DETAILED DESCRIPTION 
     As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations whether or not explicitly described or illustrated. 
     In  FIG. 2 , a heat pump  10  has a hot displacer section  16  which includes a hot displacer  12  that reciprocates within a hot displacer cylinder  22 . Heat pump  10  also has a cold displacer section  18  which includes a cold displacer  14  that reciprocates within a cold displacer cylinder  24 . Not illustrated in  FIG. 1  for the sake of clarity is a burner section or other energy input section that sits above the hot displacer section. 
     Hot displacer  12  is actuated by a linear actuator which includes coils  50  and  52  that are within a back iron  56 . Hot displacer  12  is coupled via a shaft  38  to an armature, which includes a permanent magnet  54 , pole pieces  55  that sandwich magnet  54 , and a disk  51 . In some alternatives, element  54  is a ferromagnetic material, one which is attracted when subjected to a magnetic field, yet largely unmagnetized when there is no such electric field. When coil  50  is energized, the armature moves upward thereby moving hot displacer  12  upwards; when coil  52  is energized, hot displacer  12  moves downwards. That actual movement is more complicated than described when element  54  is a permanent magnet because the magnet  54  is attracted when the current flow is in one direction in the coil (either  50  or  52 ) and is repelled when the current flow is in the opposite direction. If the energy to move hot displacer  12  between its ends of travel were supplied solely from energizing coils, the electrical energy draw would require too much electrical energy thereby seriously impairing the overall efficiency of heat pump  10 . To provide much of the force to move hot displacer  12 , springs  34  and  36  are disposed between hot displacer  12  and linear actuator section  8 , i.e., the section of the chamber with coils and the magnets or any stationary element within heat pump  10 . In the embodiment in  FIG. 1 , the springs are in tension when hot displacer  12  is at its upper position (farthest away from linear actuator section  8 ) and in compression when hot displacer  12  is at its lower position. Consequently, springs  34  and  36  bias hot displacer  12  toward a position near the middle of travel and provide much of the force for hot displacer  12  to move from end to end. Current to coils  50  and  52  are activated to draw hot displacer  12  to complete the stroke and to control the rate of approach of hot displacer  12  when approaching the end of travel. 
     A similar mechatronics system is provided for cold displacer  14  with coils  250  and  252  that are energized to act upon an armature that includes a permanent magnet  254  in a back iron  256 . The armature (including permanent magnet  244 , pole pieces  255 , and disk  251 ) is coupled to cold displacer  14  via a shaft  48 . A spring  48  is disposed between cold displacer  14  and a stationary element of heat pump  10 , linear actuator section  8  of heat pump  10  in the present embodiment. 
     The upper linear actuator in  FIG. 2  is delimited by end plates  57  and  58 , which also serve as back irons. The lower linear actuator is delimited by end plates  257  and  258 , which also serve as back irons. End plate  57  and end plate  258  delimit linear actuator section  8  from the rest of heat pump  10 . In operation, shaft  38 , along with displacer  12  and the armature coupled to shaft  38 , reciprocates. An orifice is provided in end plate  57  to accommodate shaft  38 ; and, shaft  48  reciprocates through an orifice defined in end plate  258 . 
     One embodiment of a sealing system for a reciprocating shaft through an orifice is shown in  FIG. 3 . An end plate  360  has an orifice defined therein with a shaft  350  passing through the orifice. A circumferential groove around the orifice is provided to house a split ring seal  362  that has an O-ring  364  outside. In one embodiment, spring ring seal  362  is made of a metallic material and O-ring  364  is made of an elastomeric material. O-ring, pushes split ring seal  362  together so that seal  362  largely prevents flow of gases between shaft  350  and seal  362 . O-ring  364  also prevents gases from short circuiting behind seals  362  and  364 . 
     A hot chamber  60  is defined by an upper dome  20 , hot displacer cylinder  22 , and a top of hot displacer  12 . In  FIG. 2 , hot displacer  12  is in its lowest position, in which there is almost no volume in a hot-warm chamber. The hot-warm chamber is defined by linear actuator section  8 , a bottom of hot displacer  12  and hot displacer cylinder  22 . A cold chamber  66  is defined by a lower dome  24 , cold displacer cylinder  26 , and a lower end of cold displacer  14 . Cold displacer  14  is shown in its most upward position. Thus, a cold-warm chamber is not visible in  FIG. 2 . The cold-warm chamber is defined by linear actuator section  8 , a top of cold displacer  14 , and cold displacer cylinder  24 . 
     In addition to the springs  34 ,  36 , and  44 , a gas spring is provided between displacers  12  and  14 . Volume within the gas spring includes volumes  70  and  72  within linear actuator section  8  and an interior volume  270  within cold displacer  14 . Linear actuator section  8  has gas-filled volumes  70  and  72  that move depending on where on the position of the armatures. The total volume contained within the gas spring depends on the position of hot displacer  12 , at least, due to shaft  38  displacing gases when reciprocating within volume  70 . 
     As part of the volume of the gas spring is contained within linear actuator section  8 , a seal between shaft  38  reciprocating within an orifice in end plate  57  and between shaft  48  reciprocating through an end plate  258  is used to isolate the volume within the linear actuator section. One embodiment of a seal system is shown in  FIG. 3 . An end plate  360  has an orifice through which a shaft  350  extends. The seal system in  FIG. 3  has a groove in end plate  360 , proximate the orifice that accommodates shaft  350 . O-ring  364  and a split ring  362  are disposed in the groove. 
     An alternative to the spring configuration shown in  FIG. 2  is shown in  FIGS. 4 and 5 . In  FIG. 4 , a displacer  300  is coupled to a shaft  302  and a crosshead  304 . Crosshead  304  is disposed between two stationary elements  320  and  322 . Elements  320  and  322  can be held together with walls  324 . Alternatively, the assembly shown in  FIG. 4  is installed in a heat pump with accommodations to support stationary elements  320  and  322 . Compression springs  330  and  332  are disposed between crosshead  304  and stationary element  320  and between cross head  304  and stationary element  322 , respectively. In  FIG. 4 , displacer is at an upper position in which spring  330  is compressed. Spring  330  is pushing down on cross head  304  in such a configuration. In  FIG. 5 , spring  330  is less compressed, and thus pressing less on crosshead  304  compared to the configuration illustrated in  FIG. 4 . Spring  332 , is compressed in the configuration in  FIG. 5  and exerts an upward force on crosshead  304 . Such pairs of compression springs could be used in place of a spring system that is in compression at one end of the displacer&#39;s travel and in tension at the other end of the displacer&#39;s travel. 
     Current is supplied to the coils to cause them to exert a force on the armature. In the interest of clarity, the electronic and electrical hardware to do that is not illustrated in  FIG. 2 . It is instead shown in  FIG. 6  in a simplified form. In  FIG. 6 , an illustration of a thermodynamic apparatus  260  (or heat pump) has a hot displacer  262  and a cold displacer  264 . A linear actuator section  268  is located between displacers  260  and  262 . Coils  290 ,  292 ,  294 , and  296  are housed in  268 . Hot displacer  262  couples to an armature  282  via a shaft; cold displacer  264  couples to an armature  284  via a shaft. A power electronics module  270  is electrically coupled to coils  290 ,  292 ,  294 , and  296 . Power electronics module provides the current to coils  290 ,  292 ,  294  and  296 . An electronic control unit  280  electronically coupled to power electronics module  270  provides control signals to the power electronics module  270  to control the pulses of current to the coils. ECU  280  determines the desired current to send to the coils based on at least: demanded heating or cooling output from the heat pump, a signal from a position sensor  272  associated with hot displacer  262 , a signal from a position sensor  274  associated with cold displacer  264 , and other sensors  282 , which may include sensors for determining ambient conditions such as temperature and humidity and temperature and pressure sensors within the heat pump. 
     Various embodiments of the present disclosure present advantages over prior art configurations of such a heat pump. One issue determined with the configuration shown in  FIG. 1  is that there is conduction between the hot displacer cylinder and the cold displacer cylinder. Such conduction reduces system efficiency. The  FIG. 2  configuration in which the linear actuator section separates the hot end from the cold end reduces the conduction losses. 
     An advantage present by the present configuration is that the hot end and cold end of the heat pump are coupled via a flange. If a fault in the hot end or the cold end is found, the functioning end can be disconnected from the end of the heat pump with a fault and the functioning end can otherwise remain assembled. 
     While the best mode has been described in detail with respect to particular embodiments, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. While various embodiments may have been described as providing advantages or being preferred over other embodiments with respect to one or more desired characteristics, as one skilled in the art is aware, one or more characteristics may be compromised to achieve desired system attributes, which depend on the specific application and implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described herein that are characterized as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.