Hot Gas Engine Heater Head

This invention relates to a hot gas engine heater head adapted to guide and heat an oscillating flow of gaseous working medium between a cylinder top and a space containing a regenerator surrounding said cylinder top.

In the past, the heater heads of hot gas engines have included a number of tubes, each being connected at one end to a first manifold providing entrance to the cylinder top, and connected at the other end to a second manifold providing entrance to the regenerator canister. The said manifolds may have been arcuately shaped and--in case of multi cylinder engines--they may have been juxtaposed to form concentric circles horizontally arranged in a combustion chamber symmetrically designed around a vertical axis. A heater head of this type has been described and shown in the UK Patent Specification No. 2,040,003A, said specification corresponding to U.S. Pat. No. 4,261,173.

In the known heater heads the manifolds have been designed as integral parts of the cylinder tops or of the upper parts of the regenerator canisters. The manufacture of heater heads involves the problems of joining the heater tubes to the manifolds, the problem of manufacturing the manifolds, and the problems of dealing with materials capable of withstanding thermal stresses in cylinders, regenerator canisters, manifolds and heater tubes.

Accordingly, the objects of the present invention are to provide a hot gas engine heater head having a configuration which simplifies the manufacturing of manifolds and the joining of heater tubes to the manifold, and which the present invention makes it possible to use separate materials in the components exposed to thermal stresses with a minimum of problems in connection with the necessary joints.

These objects are attained by the invention in that the connection between the first manifold and the cylinder top is a single duct surrounded by an annular duct which connects said second manifold with said regenerator connecting space.

The invention along with its many attendant objects and advantages, will become better understood upon reading the following detailed description of the preferred embodiment in conjunction with the following drawings, wherein:

FIG. 1 shows schematically a vertical section through a hot gas engine provided with a heater head of conventional design;

FIG. 2 is a section along the line II--II in FIG. 1;

FIG. 3 is a vertical section through a part of a heater head according to the invention, the section following the line III--III in FIG. 4;

FIG. 4 is a section along the line IV--IV in FIG. 3;

FIG. 5 is a vertical section through a second embodiment of a heater head according to the invention;

FIG. 6 is a section along the line VI--VI in FIG. 5; and

FIG. 7 is a section along the line VII--VII in FIG. 5.

Referring first to FIGS. 1 and 2, a known type of double acting hot gas engine is shown including a main body portion having bored therein four cylinders 1-4 in square formation. The four cylinders 1-4 are each surrounded by one of four annular regenerators units 5-8. The tops of the cylinders 1-4 are provided with individual arcuately shaped cylinder manifolds 9 which form a circle in their relative positions shown in FIG. 2. The tops of the regenerator units are provided with individual regenerator manifolds 10 which form a circle of greater diameter than the circle formed by the cylinder manifolds 9.

The pairs of cylinder manifolds 9 and regenerator manifolds 10 thus formed are interconnected by tubes 11 which extend between the cylinder and regenerator manifolds.

Each cylinder 1-4 has a piston 12 and attached piston rod 13 mounted for reciprocating therein. The piston rod 13 is secured to a connecting rod 14 which is journaled to a crank on one of a pair of parallel crankshafts 15 and 16 of a conventional drive mechanism. Each piston 12 separates its cylinder into a high temperature, variable volume chamber 17 and a low temperature, variable volume chamber 18. The tubes 11 which are partly provided with fins 19 extend into a combustion chamber 20 for absorbing heat. The engine also includes a preheater 21 for preheating combustion air by exchanging heat with exhaust gases.

As shown in FIG. 2 the cylinder manifold 9, the regenerator manifold 10 and the connecting tubes 11 for each of the cylinders 1-4 and its respective regenerator housing form separate units. The heater head in FIG. 2 is composed of four identical separate units.

For reasons of manufacture it may be advantageous to design each unit as an assembly of separate elements, viz. a cylinder, a regenerator housing, manifolds and tubes, and then join these elements together in a suitable way. It may even be advantageous to reduce costs by using different materials in the different elements. However, due to the complexity and great number of the joints it is difficult to avoid leakages of the working gas used in the engine.

FIGS. 3 and 4 show an embodiment of the invention on a larger scale than that of the corresponding parts shown in FIGS. 1 and 2.

As shown in FIG. 3 a cylinder 30 made of, e.g. a ceramic material such as silicon nitride is connected to a manifold housing 31 made of a precision cast, heat resistent stainless steel or a ceramic material. The manifold housing 31 has a central downwardly directed duct 32 communicating with the upper variable volume chamber 17 in the cylinder 30 above the piston 12. The cylinder 30 is surrounded by a regenerator housing 33, which also could be made of a ceramic. The manifold housing 31 is brazed to the regenerator housing 33 and provides a duct 34 having annular cross section surrounding the central duct 32 to the cylinder. The manifold housing 31 is made as a single unit, but acts as a manifold 35 to the cylinder 30 as well as a manifold 36 to the regenerator housing 33. Tubes 11 are connected to the manifold housing 31 by brazing and correspond to the tubes 11 of the heater head shown in FIGS. 1 and 2.

It will be understood that the only joints exposed to maximum gas pressure are joints 37 between the regenerator housing 33 and the housing 31 and joints 39 between the tubes 11 and the housing 31. The joints 39 are small and thus not exposed to substantial forces. The joint 37 is comparatively short and may easily be inspected after manufacture. The joint 38 between the cylinder 30 and the housing 31 is only exposed to the differences in the working gas pressure and any leakage here will not cause a loss of gas. Thus the joint 38 need not be brazed.

FIGS. 5, 6 and 7 show another embodiment of a heater head unit according to the invention. The primed reference numerals used correspond to the unprimed numerals used for corresponding elements shown in FIGS. 3 and 4. The embodiment of FIGS. 5, 6 and 7 could be used in case it is desired to arrange the heater tubes 11 at larger diameters. In order to obtain short ducts and small dead volumes the manifold 36' to the regenerator housing 33' has been located at a lower level than the manifold 35' to the cylinder 30'.