Attachment of cylinders in the housing of free-piston stirling machines

Abstract

An improvement to a free-piston Stirling machine having a cylinder mounted within a housing. The cylinder has a flange for mounting the cylinder within the housing to a transition plate with a central opening for receiving the cylinder. An elastic rim bounds and surrounds the opening and extends in an axial direction from the plate to a crest of the rim. The crest of the rim is in contact against a first axially facing side of the cylinder flange. The interior side of the rim is outwardly spaced from the exterior side of the cylinder. A compliant clamp is attached to the transition plate and is positioned on the opposite, axially facing side of the cylinder flange. The compliant clamp has an elastic spring extending against the cylinder flange which applies a force urging the cylinder flange in an axial direction against the crest of the elastic rim.

Claims

1. An improved free-piston Stirling machine 1 having a cylinder mounted within a housing, the cylinder having an outwardly extending cylinder flange for mounting the cylinder within the housing, the housing including a plate having an opening with a central axis for mounting the cylinder within the opening, wherein the improvement comprises: (a) an elastic rim bounding and surrounding the opening and extending from the plate to a crest of the rim, the crest being in engagement against a first axially facing side of the cylinder flange, the interior side of the rim being outwardly spaced from the exterior side of the cylinder wherein a circular groove extends coaxially around the opening and into the plate in an axial direction to form the elastic rim between the groove and the interior side of the rim; and (b) a compliant clamp attached to the plate and positioned on the opposite, axially facing side of the cylinder flange, the compliant clamp having an elastic spring extending against the cylinder flange and applying a force urging the cylinder flange in an axial direction against the crest of the elastic rim.

2. An improved free-piston Stirling machine 1 in accordance with claim 1 wherein the clamp comprises: (a) a ring surrounding the cylinder, fastened to an axially facing end surface of the plate and spaced from the opposite, axially facing side of the cylinder flange; and (b) at least one spring extending and in compression between the ring and the opposite, axially facing side of the cylinder flange.

3. An improved free-piston Stirling machine in accordance with claim 2 wherein the rim is cylindrical and coaxial with the central axis of reciprocation.

4. An improved free-piston Stirling machine in accordance with claim 3 wherein the spring is a wave spring.

5. An improved free-piston Stirling machine in accordance with claim 1 wherein the clamp comprises: (a) a ring surrounding the cylinder, fastened to an axially facing end surface of the plate and spaced from the opposite, axially facing side of the cylinder flange; and (b) at least one spring extending and in compression between the ring and the opposite, axially facing side of the cylinder flange.

6. An improved free-piston Stirling machine in accordance 1 with claim wherein the rim is cylindrical and coaxial with the central axis of reciprocation.

7. An improved free-piston Stirling machine in accordance with claim 6 wherein the spring is a wave spring.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 is a symbolic view in axial section of a prior art Stirling machine having components that are used with the invention.

(2) FIG. 2 is a view in section of the cylinder shown in FIG. 1.

(3) FIG. 3 is a view in section of a segment of the Stirling engine in FIG. 1 but modified in accordance with the invention and taken along the line 3-3 of FIG. 4.

(4) FIG. 4 is an end view of a portion of a transition plate of a Stirling machine showing some of the structural features of the invention.

(5) FIG. 5 is a view similar to FIG. 3 but illustrating an alternative embodiment of the invention.

(6) In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific term so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

DETAILED DESCRIPTION OF THE INVENTION

(7) The preferred embodiment of the invention is illustrated in FIGS. 3 and 4 and is a modification of a free-piston Stirling machine like that illustrated in FIG. 1. FIGS. 3 and 4 illustrate a modified and enlarged version of the portion of FIG. 1 that is in the rectangle 26 in FIG. 1. FIG. 3 shows an assembled embodiment of the invention but FIG. 4 shows only the central portion of the transition plate 16 after being modified according to the invention. The cylinder 12 and other components of the preferred embodiment of the invention are removed from FIG. 4 in order to expose the transition plate 16. The plate 16 has an opening 28, like the 16 plate in FIG. 1, with a central axis 22 (FIG. 1 only) for mounting the cylinder 12 within the opening 28. As in FIGS. 1 and 2, the cylinder 12 has an outwardly extending cylinder flange 14 for mounting the cylinder 12 within the housing. However, FIG. 3 also shows the heat rejection port 29 through the cylinder 12 that is well known in Stirling machines and is not related to the invention. Similarly, the cylinder of FIG. 3 is thinner on the displacer side (to the left) of the heat rejection port 29 but this too is not related to the invention.

(8) However, in this preferred embodiment the plate 16 is formed with the structural features of the invention in order to accomplish the purpose and object of the invention. An elastic rim 30 that is formed in the plate 16 bounds (forms an inner boundary of) and surrounds the opening 28 and extends, preferably in an axial direction, from the plate 16 to a crest 32 of the rim 30. Preferably and typically the rim 30 is cylindrical and coaxial with the central axis 22 of reciprocation. The crest 32 contacts in engagement against a first axially facing side 34 of the cylinder flange 14. The interior side 36 of the rim 30 is outwardly spaced from the exterior side 38 of the cylinder 12 to provide a space 40 between the rim 30 and the cylinder 12. This space 40 allows some movement of the plate 16 with respect to the cylinder 12 in the event of distortion of the plate 16 in the radial direction 2 or radial rotation direction 3.

(9) A compliant clamp 42 is attached to the transition plate 16 by machine screws 44 that are fastened in threaded holes 46. The compliant clamp 42 is positioned on the opposite, axially facing side 48 of the cylinder flange 14. The compliant clamp 42 comprises an annular ring 50 surrounding the cylinder 12 and fastened against the axially facing end surface 54 of the plate 16. The ring 50 is spaced from the opposite, axially facing side 48 of the cylinder flange 16 so that an elastic spring 52 can extend from the annular ring 50 to the cylinder flange 14. The spring 52 is in compression so it applies a force urging the cylinder flange 14 in an axial direction against the crest 32 of the elastic rim 30. The preferred spring 52 is a wave spring but various other kinds of springs can be used to form a compliant clamp to push the cylinder flange firmly against the crest 32 of the elastic rim 30.

(10) Although the elastic rim 30 can be formed or constructed in a variety of ways, it is preferably and most conveniently formed as an integral part of the plate 16. A circular groove 56 is machined into the plate 16 in an axial direction to extend coaxially around the opening 28 in order to form the elastic rim 30 between the groove 56 and the interior side 36 of the rim 30.

(11) It is not necessary that the elastic rim 30 be formed as an integral part of the plate 16. Instead, the rim 30 can be formed as a separate part. For example, FIG. 5 shows, in phantom lines, a separation line 58 that defines a rim component 60 that is separate from a transition plate 16A. The rim component 60 is clamped by the annular clamping ring 50 against the transition plate 16A. As another alternative, the elastic rim 30 and the compliant clamp 42 can be discontinuous arcuate segments instead of the preferred continuous annular structures. As yet another alternative, the rim can be formed with circularly arranged, spaced apart elastic fingers that may, for example, appear in a cross section through the fingers like the rim in the figures but be like castling.

(12) The invention operates to accomplish the purposes of the invention because it maintains the axial position of the cylinder in the housing but will not distort the cylinder from radial translation or radial rotation of the housing or any other component part that contacts the cylinder or its flange. In other words it is rigid in the axial direction 1, but elastic (compliant) in the radial direction 2 and elastic in the radial rotation direction 3.

(13) The invention provides rigidity in the axial direction because the cylinder flange 14 is held against the crest 32 of the elastic rim 30. Axial force against the rim 30 that is applied by the cylinder flange 14 is applied in a direction that is longitudinal along the rim. That force is strongly resisted by the rim 30 because the rim will not bend but rather can only compress because an axial force applies no bending force against the rim 30.

(14) However, forces applied in the radial direction 2 and in the radial rotation direction 3 are in a direction urging the bending of the rim 30. So the rim 30 can bend in response rather than applying a force against the cylinder 12 or its flange 14. The rim 30 is elastic in those directions because the circular groove 56 is positioned sufficiently close to the interior side 36 of the rim 30 to make the rim 30 sufficiently thin that it provides elasticity in a bending direction. Because of the temperatures and pressures encountered by Stirling machines, their internal mechanical parts are constructed of a metal. Metals have a characteristic known as elasticity. Elasticity means that the metal, when subjected to a force, will deform and when the force is removed will return to its original shape. The stress applied to a metal is directly proportional to its strain, which are related to each other by the proportionality constant for the metal known as its modulus of elasticity (Young's modulus). This property of elasticity remains unless the strain causes the metal's elastic limit to be exceeded. Therefore, the elastic rim 30 can bend like a cantilevered spring and the spring constant for that spring is a function of both the elasticity of the metal and the thickness of the elastic rim 30. Consequently, the designer who is implementing the invention can position the circular groove 56 a distance from the interior side 36 of the elastic rim that gives a rim thickness that in turn provides a desired spring constant. The desired spring constant will permit the elastic rim to bend without exceeding the elastic limit when the transition plate 16 is distorted by temperature or pressure and to return if and when that distortion ceases to exist. The preferred rim thickness and its resulting spring constant will be different for different Stirling machines because different Stirling machines will subject the elastic rim to different forces. Ultimately, the rim thickness can be determined by experimentation, testing and trial and error methods. In addition to the compliance characteristic of the elastic rim 30, the space 40 between the rim 30 and the cylinder 12 also allows some movement of the cylinder 12 in the radial direction 2 and in the radial rotation direction 3.

(15) In summary, the invention minimizes distortion to the cylinder when the machine is pressurized or heated. It has a local mounting seat at the crest 32 which is rigid in the axial location but has flexibility in the lateral on-axis direction as well as being locally compliant to on-axis rotation. It applies an axial force to seat the flange of an engine cylinder against the rim.

REFERENCE NUMBER KEY

(16) 10 housing 12 cylinder 14 cylinder flange 16 housing transition plate 18 machine screws attaching cylinder flange 14 20 piston 21 displacer 22 central axis 23 backspace 24 cylinder wall distortion contour 26 rectangle (FIG. 1) 28 opening in transition plate 29 heat rejection port 30 elastic rim 32 crest of rim 30 34 first axially facing side of cylinder flange 14 36 interior side of rim 38 exterior side of cylinder 12 40 space between rim 30 and cylinder 12 42 compliant clamp 44 machine screws attaching clamp 42 46 threaded holes for screws 44 48 opposite axially facing side of cylinder flange 14 50 annular clamping ring 52 spring 54 end surface of plate 16 56 circular groove 58 separation line separating two parts 60 separate rim component of the invention

(17) This detailed description in connection with the drawings is intended principally as a description of the presently preferred embodiments of the invention, and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the designs, functions, means, and methods of implementing the invention in connection with the illustrated embodiments. It is to be understood, however, that the same or equivalent functions and features may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention and that various modifications may be adopted without departing from the invention or scope of the following claims.