Linear Actuation System Having Side Stators

Abstract

A linear actuator is disclosed that is a double-ended solenoid with springs to provide much of the force for movement. The linear actuator can be used in a thermodynamic apparatus, such as a Vuilleumier heat pump in which two linear actuators are provided to drive two displacers. The linear actuator also has a cylindrical back iron section having first and second recesses with coils disposed in the recesses. The linear actuator assists in moving the armature from one end to the other and holds the armature at the end of travel. However, much of the force for moving the armature is provided by a spring exerting a force on the shaft with respect to the back iron section. In one embodiment, the spring is a compression-tension spring. Alternatively, two compression springs acting in opposition are provided.

Claims

1. A linear actuator, comprising: a substantially cylindrical back iron section having a central axis, the back iron section having at least first and second recesses defined therein, with the first recess displaced from the second recess in a direction parallel to the central axis; a first side coil disposed in the first recess; a second side coil disposed in the second recess; an armature disposed within the back iron, the armature being free to move along the central axis between a first end of travel and a second end of travel; and a spring system coupled to the armature, wherein: the spring system exerts a force on the armature with respect to the cylindrical back iron section; the force is in a direction parallel to the central axis; and the first and second side coils are located radially outside of the path of travel of armature when moving from the first end of travel to the second end of travel.

2. The linear actuator of claim 1, further comprising: a shaft coupled to the armature, wherein: the coupling between the spring system and the armature is one of direct and indirect; and the coupling between the spring system and the cylindrical back iron section is one of direct and indirect.

3. The linear actuator of claim 1 wherein: the armature is comprised of a radially-symmetric permanent magnet and two ferromagnetic, radially-symmetric pole pieces; and the two pole pieces abut the permanent magnet and are mutually separated.

4. The linear actuator of claim 1, further comprising: a shaft coupled to the armature, wherein the armature comprises: first and second substantially-annular pole pieces coupled to the shaft; and an annular permanent magnet with a first face of the permanent magnet abutting a face of the first pole piece and a second face of the permanent magnet abutting a face of the second pole piece, the first pole piece being separated from the second pole piece.

5. The linear actuator of claim 4 wherein the shaft is magnetically insulated from: the first pole piece, the second pole piece, and the permanent magnet by one of: the shaft being made of a substantially non-magnetic material; and a magnetically insulating element interposed between the shaft and at least one of: the first pole piece, the second pole piece, and the permanent magnet.

6. The linear actuator of claim 1, further comprising: a first substantially disk-shaped back iron section abutting the cylindrical back iron section proximate a first end of the cylindrical back iron section; and a second substantially disk-shaped back iron section abutting the cylindrical back iron section proximate a second end of the cylindrical back iron section wherein the first and second disk-shaped back iron sections and the cylindrical back-iron section form a back iron.

7. The linear actuator of claim 1 wherein the spring system comprises one of the following: a single compression-tension spring: a plurality of nested springs with first ends of the springs mounted in a first common element and second end of the springs mounted in a second common element; and a pair of compression springs that are mutually biased against each other.

8. The linear actuator of claim 1, further comprising: a power electronics module electrically coupled to first and second side coils; and an electronic control unit (ECU) electronically coupled to the power electronics module wherein: the ECU determines a desired trajectory of the armature; computes a current to provide to the first and second side coils; and commands the power electronic module to deliver such current to the first and second side coils.

9. The linear actuator of claim 84, further comprising: a user input electronically coupled to the ECU; and a position sensor electronically coupled to the ECU wherein the ECU computes the desired trajectory of the armature based at least on user input and a signal from the position sensor.

10. (canceled)

11. An apparatus, comprising: a cylinder having a central axis; a reciprocating component disposed in the cylinder; a shaft coupled to the reciprocating component; and a linear actuation system, comprising: an armature coupled to the shaft, the armature having a first end of travel and a second end of travel, a path of travel from the first end to the second end being parallel to the central axis of the cylinder; a substantially cylindrical back iron section having first and second recesses defined therein; a first coil disposed in the first recess; a second coil disposed in the second recess; and a spring coupled to the shaft, wherein: the spring exerts a force on the shaft with respect to the cylindrical back iron section; and the force being in a direction parallel to the central axis.

12. The apparatus of claim 11, further comprising: a first disk-shaped back iron section delimiting the armature travel at the first end of travel; and a second disk-shaped back iron section delimiting the armature travel at the second end of travel wherein: the first disk-shaped back iron section abuts the cylindrical back iron at a first end of the cylindrical back iron; and the second disk-shaped back iron section abuts the cylindrical back iron at a second end of the cylindrical back iron.

13. The apparatus of claim 11 wherein the substantially cylindrical back iron section is comprised of a plurality of contiguous sections.

14. The apparatus of claim 11 wherein the spring is a first compression spring, the apparatus further comprising: a second compression spring exerting a force on the shaft with respect to the cylindrical back iron section, the force of the second compression spring acting in a direction opposite to the direction of the force of the first compression spring.

15. The apparatus of claim 11 wherein: the spring is a compression-tension spring; the force exerted on the shaft is in a first direction parallel to the central axis when the armature is at the first end of travel; the force exerted on the shaft is in a second direction parallel to the central axis when the armature is at the second end of travel; and the first direction is opposite the second direction.

16. The apparatus of claim 11 wherein: the armature comprises: first and second substantially-annular pole pieces coupled to the shaft; and an annular permanent magnet with a first face of the permanent magnet abutting a face of the first pole piece and a second face of the permanent magnet abutting a face of the second pole piece, wherein: the first pole piece is separated from the second pole piece; and the first pole piece, the second pole piece, and the permanent magnet are magnetically isolated from the shaft.

17. The apparatus of claim 11, further comprising: a position sensor coupled to the apparatus that senses position of the reciprocating component; an electronic control unit (ECU) electronically coupled to the position sensor; and the for a power electronics module electronically coupled to the ECU and electrically coupled to the first and second coils wherein the ECU commands the power electronics module to provide current to the coils based at least on a signal from the position sensor.

18. A thermodynamic apparatus, comprising: a first cylinder having a central axis; a second cylinder have a central axis; a first displacer disposed in the first cylinder; a second displacer disposed in the second cylinder; a first shaft coupled to the first displacer; a second shaft coupled to the second displacer; a first linear actuation system, comprising: a first substantially-cylindrical back iron section defining first and second recesses with the first recess displaced from the second recess along a direction parallel to the central axis of the first cylinder; first and second coils disposed in the first and second recesses; a first armature located within the first back iron section and coupled to the first shaft; and a first spring coupled between the first back iron section and the first armature, the first spring exerting a relative force between the first back iron section and the first armature in a direction substantially parallel to the central axis of the first cylinder; and a second linear actuation system, comprising: a second substantially-cylindrical back iron section defining third and fourth recesses with the third recess displaced from the fourth recess along a direction parallel to the central axis of the second cylinder; third and fourth coils disposed in the third and fourth recesses; a second armature located within the second back iron section and coupled to the second shaft; and a second spring coupled between the second back iron section and the second armature, the second spring exerting a relative force between the second back iron section and the second armature in a direction substantially parallel to the central axis of the second cylinder.

19. The thermodynamic apparatus of claim 18, further comprising: a first disk-shaped back iron section delimiting the first armature travel at a first end of travel within the first cylindrical back iron; a second disk-shaped back iron section delimiting the first armature travel at a second end of travel within the first cylindrical back iron; a third disk-shaped back iron section delimiting the second armature travel at a first end of travel within the second cylindrical back iron; a second disk-shaped back iron section delimiting the first armature travel at a second end of travel within the second cylindrical back iron wherein: the first disk-shaped back iron section abuts the first cylindrical back iron at a first end of the first cylindrical back iron; the second disk-shaped back iron section abuts the first cylindrical back iron at a second end of the first cylindrical back iron; the third disk-shaped back iron section abuts the second cylindrical back iron at a first end of the second cylindrical back iron; and the fourth disk-shaped back iron section abuts the second cylindrical back iron at a second end of the second cylindrical back iron.

20. The thermodynamic apparatus of claim 18, further comprising: a first position sensor coupled to the thermodynamic apparatus that senses the position of the first displacer; a second position sensor coupled to the thermodynamic apparatus that senses the position of the second displacer; an electronic control unit (ECU) electronically coupled to the first position sensor and the second position sensor; and a power electronics module electronically coupled to the ECU and electrically coupled to the first, second, third, and fourth coils.

21. The thermodynamic apparatus of claim 17, wherein each of the first and second armature comprises: first and second pole pieces coupled to the shaft; and an annular permanent magnet with a first face of the permanent magnet abutting a face of the first pole piece and a second face of the permanent magnet abutting a face of the second pole piece, wherein: the first pole piece is separated from the second pole piece; and the first pole piece, the second pole piece, and the permanent magnet are magnetically isolated from the shaft.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0033] FIG. 1 is a schematic of an actuation system for a displacer of a gas-fired heat pump according to the prior art;

[0034] FIG. 2 is a schematic of a linear actuation system of the type in FIG. 1 with one linearly moving component, i.e., a single displacer;

[0035] FIG. 3 is a graph of the force of a coil on attracting an armature as a function of gap between the two;

[0036] FIG. 4 is an illustration of a linear actuation system for a single linearly moving component according to the present disclosure;

[0037] FIG. 5 is a graph of force applied to an armature having a permanent magnet as a function of current provided to a side stator; and

[0038] FIG. 6 shows a linear actuator with end coils;

[0039] FIG. 7 shows a linear actuator with side coils; and

[0040] FIG. 8 is an illustration of one type of spring system.

DETAILED DESCRIPTION

[0041] 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.

[0042] A linear actuator system 48 system is shown FIG. 4 in cross section. A displacer 52, or other member, reciprocates within a cylinder 50 that has a centerline 51. Displacer 52 is coupled to a shaft 54 that has an armature that extends outwardly from post 54. The armature is made up of a permanent magnet 96, pole pieces 94 that sandwich permanent magnet 96, and insulators 92. Armature is magnetically isolated from shaft 54 by insulator 92. Alternatively, shaft 54 is a non-ferromagnetic material and such insulators are not provided. A shaft 55 extends from the armature (elements 92, 94, and 96) in an opposite direction than shaft 54. Bridges 70 and 74 extend across cylinder 50 and define a volume in which back iron sections 44, 46, and 56 are disposed. A coil 60 disposed in a first recess in back iron section 56 is a first side stator; and coil a 62 in a second recess in back iron section 56 is a second side stator. Back iron section 56, in an alternative embodiment, is made up of two back iron sections. Contiguous back iron sections 44, 46, and 56 together form a back iron. Many alternatives are contemplated that include more or fewer sections to form the back iron.

[0043] Coils 60 and 62 are located near the end of travel of the armature so that they are able to hold the armature 56 for a dwell period. This obviates face stators 24 and 26 such as shown in FIG. 2. Coils 60 and 62, which form side stators, are also able to affect movement of armature 56 during mid-travel better than coils 20 and 22 of FIG. 2 because coils 60 and 62 are closer to the armature during mid-travel than coils 20 and 22 of FIG. 2.

[0044] If movement of the displacer system (displacer 52, shaft 54, the armature (elements 92, 94, and 96) shaft 55, and plate 76, which is coupled to shaft 55) were driven solely by activating coils 60 and 62, the electrical draw can be very high. Much of the force to move the displacer system is provided by a spring 78 which is affixed to bridge 74, which is in turn affixed to cylinder 50, and affixed to plate 76 which moves within cylinder 50. When the armature is at the top of travel, i.e., proximate coil 60, spring 78 is in compression. When the armature is at the bottom of travel, i.e., proximate back iron section 46, spring 78 is in tension. Consequently, when armature 90 is at the top of travel, spring 78 pushes on plate 76 to cause displacer 52 to move downward when coil 60 is deactivated. And, when the armature is at the bottom of travel, spring 78 pulls upward on plate 76 to cause displacer 52 to move upward when coil 62 is deactivated. Spring 78 provides much of the force to move the displacer system between ends of travel. The force provided by spring 78 cannot be controlled. Side coils 60 and 62 provide additional force during travel, such force being controllable to ensure completing the travel and approaching the end of travel slowly enough to avoid impact.

[0045] The armature in FIG. 4 includes an insulator 92 that magnetically isolates shafts 54 and 55 from the armature. Armature 90 includes a permanent magnet 96 sandwiched between pole pieces 94, which are ferromagnetic blocks. Pole pieces 94 are flux carriers that move proximate a wall of back iron section 56 with a small air gap between an outer end of pole pieces 94 and an inner surface of back iron section 56.

[0046] In FIG. 4, an electronic control unit (ECU) 80 is electronically coupled to a position sensor 82 and other sensors 84 that may include pressure and temperature sensors, as examples. Furthermore, ECU 80 may be provided user input 85, such as a desired output from system 48. ECU 80 provides a signal or signals to a power electronics module 86 that is electrically coupled to coils 60 and 62. Module 86 is provided to control the current flow to coils 60 and 62 to obtain the desired travel of displacer 52. ECU 80 signals to power electronics module 86 are based on one or more of user input, a signal from position sensor 82, and signals from other sensors 84.

[0047] Armature 90 has a permanent magnet 96. When current in one direction is provided to a coil, it attracts armature 90. However, when current in the opposite direction is provided to the coil, it repels armature 90. During travel of armature 90 between ends of travel, a signal from position sensor 82 can be used to determine whether the armature is predicted to reach the end of travel or not and at what impact speed. Current can be provided to coils 60 or 62 in either direction to provide attractive or repulsive force acting on armature 90. A graph of force that can be provided as a function of distance between the armature and the stator is shown in FIG. 5. When there is no current, due to the armature having a permanent magnet, the attractive force is shown as dashed line 500. Current applied to the coil in a first direct yields curve 502. Current of the same magnitude in the opposite direction causes a repulsive force, curve 504. Providing a repulsive force allows for the following control options: braking, so as to prevent a hard impact when the armature is approaching the end of travel; braking for electrical energy recovery (which might be useful for some operating conditions of a heat pump); and for pushing off the armature from an end of travel.

[0048] Obtaining reliable operation of the linear actuation system such as shown in FIG. 1 was a concern as well as the high electrical energy demand. Such electrical energy demand impairs the overall efficiency of the heat pump. The parasitic losses to the electrical energy demand of the face coil design (FIG. 2) may be inherent. The present disclosure of a side coil design (FIG. 4) is to diminish such parasitic losses.

[0049] A less complicated illustration of the salient features of the coils and armature portion of a linear actuator is shown in FIGS. 6 and 7 showing face coils 202 in back iron 200 and side coils 212 in back iron 210, respectively. Coils 202 act on ferromagnetic armature 206 in FIG. 6. Armature 218 in FIG. 7 is made up of pole pieces 214 and a permanent magnet 216. Alternatively, the configuration of FIG. 7 could have an armature such as that shown in FIG. 6, although would have less capability. A permanent magnet, which provides the possibility for attractive and repulsive forces. Repulsion, achieved by reversing the current in the coil, provides another degree of freedom in control, thereby permitting smooth landing, another issue yet unresolved in the design with face stators. Additionally, at some operating conditions, electrical energy may be extracted during part of the cycle to provide energy for other parts of the cycle. Because coils 212 of FIG. 7 are located nearer armature 218 along the travel path (as compared to coils 202 in relation to armature 016, coils 212 provide mid-travel assist and better control as well as more than sufficient holding current at the ends of travel.

[0050] Because the side stators are located nearer the armature along the travel path (as shown in FIG. 6), they provide mid-travel assist and control as well as more than sufficient holding current at the ends of travel. Significantly, the Gen 3.0 armature includes a permanent magnet, which provides the possibility for attractive and repulsive forces. Repulsion, achieved by reversing the current in the coil, provides another degree of freedom in control, thereby permitting smooth landing, another issue yet unresolved in the design with face stators. Additionally, at some operating conditions, electrical energy may be extracted during part of the cycle to provide energy for other parts of the cycle. A conservative estimate indicates parasitic losses for linear actuation drops 60%. Such a decrease in parasitic losses has a substantial positive impact on overall efficiency of the system.

[0051] There are several options for the spring system. A single, machined spring such as spring 78 in FIG. 4 is one option. Alternatively, the spring system shown in FIG. 1 is another option. A first spring system acts upon ferromagnetic bucket 116. The first spring system includes first and second compression springs 170 and 172 that are biased against each other. The second spring system includes third and fourth compression springs 180 and 182 that are biased against each other and act upon ferromagnetic bucket 126. Another compression-tension option is a spring system shown in FIG. 8. A first spring 240 has a first hook with an end that couples to a first common element 248. A second spring 250 has an opposite sense as first spring 240. Second spring has a hook 252 that couples to first common element 248. At the other ends of springs 240 and 250 are hook ends 244 and 254, respective, both of which couple to a second common element 246. Common elements 246 and 248 prevent relative rotation of hooks ends 242 and 252 and of hook ends 244 and 254, respectively. Common element 248 has an orifice 256 through which a shaft or other element may pass. Springs 240 and 250 and common elements 248 and 246 substantially share a common central axis 260.

[0052] 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.