WO2016146159A1

WO2016146159A1 - Steam engine

Info

Publication number: WO2016146159A1
Application number: PCT/EP2015/055417
Authority: WO
Inventors: Robert Duschl
Original assignee: Aross 3d GmbH
Current assignee: Aross 3d GmbH
Priority date: 2015-03-16
Filing date: 2015-03-16
Publication date: 2016-09-22
Anticipated expiration: 2017-09-16
Also published as: EP3271557A1; EP3271557B1

Abstract

Steam engine comprising: a cylinder (10), a steam chamber (44) to be supplied with live steam, the steam, chamber (44) having an opening (43) for introducing live steam into the cylinder (10) and a valve seat (59), a valve member (52) urged against the valve seat (59) by an elastic element (60) in a closing position closing the opening (43), a piston (30) slidable within the cylinder (10) between a bottom dead center and a top dead center, wherein the piston (30) has a projection (34) at its top end (33) facing the opening (43), the projection (34) lifting the valve member (52) against a spring force of the elastic element (60) from the valve seat (59), when the piston (30) is in the area of the top dead center for releasing the opening (43), wherein the valve member has a shaft (53), extending through the steam chamber (44), and a valve disc (55) disposed, at a first end (54) of the shaft (53), wherein the elastic element (60) is disposed outside the steam chamber (44) at a second end (57) of the shaft (53) opposite to the first end (54).

Description

Steam engine

The invention relates to a steam engine, i.e. a heat engine that performs mechanical work using steam as its working fluid. More particular, the invention relates to a piston steam engine preferably for use in power generation.

Piston steam, engines are known already since the

18^th century. One specific type as disclosed in US 4,050,357 A, WO 2010/099941 Al, JP 57-212311 A or JP 57-135209 A comprises a cylinder and a steam chamber to be supplied with live steam, wherein the steam chamber has an opening for introducing live steam into the cylinder and a valve seat.

In addition, a valve member is disclosed, which is urged against the valve seat by an elastic element in a closing position closing the opening. In addition, all these

documents disclose a piston slidable between a bottom dead center and top dead center having a projection at its top end facing the opening and being configured to lift the valve member against the spring force of the elastic element from the valve seat, when the piston approaches the top dead center for releasing the opening and introducing steam into the cylinder. The elastic element in these documents is formed by a spring which is either directly disposed inside the steam chamber or supported by a casing, in turn being disposed within the steam chamber.

Such steam engines are operated at relatively high pressures between 40 bar - 150 bar and high temperatures between 300°C and 600 °C to achieve a desired efficiency (it should be clear that the invention is not limited to such pressure and temperature ranges) . However, the relaxation behavior of the spring is heavily influenced when directly or indirectly disposing the spring in the hot steam chamber. Moreover WO 2010/099941 Al and US 4, 050, 357 A both use a plate or disc like valve member without any particular guidance of the valve member. The disc-like or plate-like valve members, therefore, tend to break easily, thus not providing for a sufficient lifetime of the steam engine. In addition the little guidance of the valve members bears the risk of an undefined opening behavior of the valve.

JP 57-212311 A and JP 57-135209 A suggest a valve member, which is translationally guided within a supporting housing disposed in the steam chamber. Thus, also here and as

described earlier, the relaxation behavior of the spring is greatly influenced. In addition, disposing the valve member within a supporting housing requires steam channels within the supporting housing. This complicates the structure and bears the risk of relatively short maintenance intervals because of the high pressure of the steam acting on the elements .

In addition, this relatively complicated structure is not sufficiently rigid to allow a long lifetime of the steam engine, when considering the large impact of the projection of the piston contacting the valve member for opening the valve. In particular, the forces of the valve train are in an example in a range between 4000 N and 5000 N, which results in excessive wear and, thus, a reduced lifetime.

Further steam engines are known, which use a valve member having a shaft and a valve disc such as DE 10-2012 001 630 Al or US 3,638,533 A. However, all these documents require a relatively complicated operating mechanism for lifting the valve and are, hence, complicated to assemble and maintain. In addition, these devices are relatively expensive, because of the complicated structure.

In view of the aforesaid, it is the object of the invention to provide a steam engine that has a relatively long

maintenance interval, is easy to assemble, simple, inexpensive and provides for a defined opening behavior of the valve.

This object is solved by a steam engine as defined in

claim 1, Preferred embodiments of the invention are defined in the dependent claims .

The basic idea is the use of a shaft valve that is a valve having a shaft and a valve disc at one end of the shaft, as the valve member to be opened by a projection of the piston when the piston approaches the top dead center. Such a shaft valve enables to position the elastic element e.g. spring such as a steel spring, outside the steam chamber and, hence, in a less hot portion of the steam engine without the need of a complicated construction . Thereby, the relaxation behavior of the spring is not influenced by the hot steam and a well- defined opening behavior of the valve may be achieved . In addition , a shaft valve is very reliable valve member in regard of stability under load and provides for a good guidance possibility .

In one embodiment , a steam engine is suggested comprising a cylinder and a steam chamber to be supplied with live steam. The steam chamber has an opening for introducing live steam into the cylinder and a valve seat . The opening is preferably centered relative to the cylinder . Thereby, it may be

prevented that live steam, introduced into the cylinder, excessively contacts the walls of the cylinder . Furthermore, in the present application "the opening" is always considered as the main opening for introducing live steam into the cylinder. Even if further openings and valves (sub-openings and sub-valves ) as described later are provided, these usually have a smaller isentropic flow cross section as compared to the main opening and the main valve . The valve seat is preferably defined by a portion or edge surrounding the opening. Further, the steam engine comprises a valve member . The valve member is that member of a valve which is movable and in a particular case slidable to open and close the valve or the opening to which the valve is associated. The valve member is urged against the valve seat in a closing position, i.e. the portion or edge surrounding the opening, by an elastic element and the pressure of the steam inside the steam chamber. The elastic element may be a spring, particularly a steel spring. The elastic element may as well be formed by a plurality of coaxially arranged springs. The closing position defines the closed position of the valve, in which the opening of the steam chamber is closed and hence, is sealed so that no steam from the steam chamber may be introduced into the cylinder. In this context, the spring is particularly needed for initiating closing of the valve and a reproducible valve movement, particularly preventing valve fluttering .

Further, the steam engine comprises a piston, slidable within the cylinder between a bottom dead center and a top dead, center. The piston has a projection at its top end facing the opening, wherein the projection is used for lifting the valve member against a spring force of the elastic element from the valve seat , when the piston is in the area of the top dead center that is, approaches the dead center . As such, the valve member is pushed and lifted towards the steam chamber by the movement of the piston for releasing the opening and allowing steam from the steam chamber to be introduced to the cylinder via the opening . According to this embodiment , the valve member has a shaft, which extends through the steam chamber and a valve disc disposed at the first end of the shaft. As described earlier, because the valve is lifted into the steam chamber , the steam within the steam chamber acts on the upper surface of the valve disc and the valve is in the closed position and thereby assists the elastic element in urging the valve member onto the valve seat in the closing position . In addition, the use of the shaft enables to position the elastic element outside the steam chamber ( in an axial direction of the shaft) at the second end of the shaft opposite to the first end at which the valve disc is

disposed. In other words, the second end of the shaft is disposed outside the steam chamber a preferably a certain distance of more than 20mm away from the steam chamber.

Thereby, the relaxation behavior of the spring is not

influenced by the hot steam within the steam chamber and a defined opening behavior of the valve may be achieved .

According to an embodiment, the steam engine is additionally provided with a valve guide. The valve guide is used for translationally guiding the shaft of the valve member. The valve guide is preferably arranged outside the steam chamber and may border the steam chamber at one side extending towards the second end. Thereby, a defined opening behavior may be achieved at the same time increasing the stability of the movement of the valve member. As a result, the life cycle of the valve may be increased and the maintenance interval be prolonged. The valve guide may be made of graphite antimony which in combination with a chromed shaft provides for a translationai guide with a very low amount of play and makes the use of a lubricant unnecessary. In particular, the presence of water contained in the wet steam is sufficient to provide for an excellent lubrication. However, any other lubricant-free guide or any other guide that uses water as lubricant is conceivable. Yet, the above mentioned material combination has been proven most reliable and suitable for the steam engine described herein and having a relatively small valve lift.

In order to even further improve the opening behavior of the valve, the ratio of the guiding length, that is the length at which the shaft of the valve member is guided in the valve guide and the maximum valve lift of the valve member when being lifted by the projection of the piston is at least 70, preferably at least 80, more preferably at least 90 and most preferred at least 100. Thereby a relatively long guidance of the shaft may be achieved and the tilting of the valve member in the guidance can be avoided leading to a very well-defined opening behavior of the valve member.

In this context, it is also preferable that at least 50%·, preferably 60%, more preferably at least 75% and most

preferred at least 80% of the length of the shaft are guided by the valve guide. In one particular embodiment, a concave fillet is formed between the valve disc and the valve shaft. The valve guide is preferably provided so that the valve guide extends up to the end of the concave fillet opposite to the valve disc, when the valve member is in the opening position that is lifted from the valve seat,

The valve lift depends on the stroke of the piston and, hence, the output of the engine. As such, the valve lift relative to the isentropic flow cross-section is less than 0,25, preferably less than 0,2 and more preferably less than 0,17. In one particular example, the valve lift can be below 3.5 mm and preferably within a range of 0.50 mm and 3.0 mm, preferably 0.50 mm and 2.0 mm. In another example the valve lift corresponds to less than 3%, preferably less than 2% and more preferably less than 1% of the stroke of the piston. Certainly, the valve lift is larger than 0.1%, preferably larger than 0.3% and more preferably more than 0.4%. By reducing the valve lit in this manner, the injection period is reduced whereas the expansion period is increased. Thereby a more efficient engine may be provided. In addition, a smaller valve lift leads to less wear and, therefore, less maintenance .

The above steam engine has been described as a one cylinder engine. However, a plurality of said cylinders may be implemented .

According to another embodiment, which may as well be implemented without the piston being used for opening the valve member by means of its projection and the shaft valve, is a steam engine which may have the previously described features and additionally has a cylinder head unit having a first housing body provided with the steam chamber and the opening and having an open end with an inner surface, and a second housing body having an outer surface, wherein the inner surface and. conical outer surface are engaged. In one embodiment, a recess is formed in the inner and outer

surfaces so as to define a hollow space when the inner and outer surfaces are engaged, whereby the material of the cylinder head having a relatively high thermal conductivity is reduced and less heat is conducted from the steam chamber toward the top of the cylinder head away from, the cylinder. For this purpose, it is preferred that the recesses are formed above the steam chamber. Additionally or

alternatively, the inner surface and the outer surface are each conical and sealingly engaged. An engine in which these aspects are independently implemented may be a steam engine comprising a cylinder, a steam chamber to be supplied with live steam and having an opening for introducing live steam into the cylinder and a valve seat as well as a valve member urged against a valve seat by an elastic element in. a closing position closing the opening and having the first and second housing body as previously described, Particularly, the steam chamber is mainly defined by the first housing body but has an open end at one side, which has a conical inner surface. By fixing the second housing body to the first housing body, the conical outer surface of the second housing body and the conical inner surface of the first housing body engage so as to form a very secure sealing. Thereby it can surely be prevented that high temperature and high pressure steam from the steam chamber escapes at the top of the cylinder head unit thus providing for a very safe engine .

For ease of assembly , it is preferred that the conical inner surface is disposed at the side of the first housing opposite to the opening for introducing live steam into the cylinder. This is one feature that enables assembly of the entire engine in only one direction.

Another feature assisting this, assembly is that the center axis of the cone of the conical inner surface, and hence the conical outer surface is aligned with the center axis of the opening and/or the center axis of the cylinder. In principle, it is preferred, that the entire engine has a substantial symmetrical configuration, which is advantageous from the viewpoint of load distribution, ease of manufacture and assembly.

Further assisting the easy assembly is that the valve guide is provided within the second housing body . That is, the valve member , the valve guide and second housing body may be pre-assembled and by fixing the first and second housing bodies , also the valve member is assembled .

Preferably, the first and second housing bodies are fixed together by screws . If the screws extend substantially parallel to the center axis of the cylinder, the assembly may be performed in one direction as previously explained ,

"Substantially" in this regard means, that there may of course be a certain deviation from the parallel orientation of the screws up to ±40° as long as the screw heads are accessible from one direction, e.g. the top .

Furthermore, it is preferred to have a top cover and screw the top cover to the crankcase by screws . If the screws again extend substantially parallel to the center axis of the cylinder the assembly may again be achieved in only one direction and from one side, e.g. the top . Further, by the use of the top cover screwed to crankcase , the cylinder head unit may be clamped between the top of the cylinder and the top cover and hence be fixed without the need of further attachment means and sealing . In addition, a metal sealing ring may be used between the top of the cylinder and the bottom of the cylinder head unit which makes the steam engine less complicated and less expensive with an easy assembly.

Furthermore, the top cover also enables very easy assembly and pre-tensioning of the valve member in that the elastic element particularly the spring is inserted after the

cylinder unit has been mounted on the cylinder at the second end of the shaft of the valve and is automatically pre- tensioned by attaching the top plate and screwing the top plate to the crankcase . In addition, the top cover is

preferably configured to have a relatively high heat capacity and thereby extracts heat from the elastic element (the spring) thereby assisting the maintenance of a constant relaxation behavior of the elastic element. Additionally, cooling ribs or fins may be provided at the top cover and being directed toward the environment, i.e. away from the spring. Thereby, heat may be conducted away from the spring assisting the aforesaid effect. Furthermore, a relatively high pre-tension may be achieved, which again provides for a well-defined and controlled opening behavior of the valve preventing valve fluttering. The pre-tensioning may be adjusted by means of the top cover and - if necessary - the use of washers between the spring and the top cover and/or the spring and the cylinder head. By these measures, not only the spring, but also the screws are disposed relatively far away from the relatively high temperature steam chamber, preferably, the distance between the screws and/or elastic element is more than 100 mm, preferably more 120 mm.

Moreover, this may provide for the advantage that relatively inexpensive springs such as spring steel springs may be used as they do not need to be heat resistant . These kinds of springs are relatively insensitive and have a long lifetime as compared to specific other springs , which is important considering the high valve train forces .

Furthermore, in order to balance a certain small play between the valve guide and the valve member, it is preferred, that the valve seat or the edge of the valve disc is spherical (curved) and the edge of the valve disc or the valve seat is chamfered. In particular, the combination of a spherical surface at one element and a chamfer, that is flat surface at the other element, it may be achieved, that the two elements find their optimum position automatically and balance some manufacturing tolerances or play in between the elements . In this context, "optimum position" does not necessarily always mean the same position. Rather, this pair

(spherical/chamfered) ensures that the two elements will always find a line of contact ensuring leak tightness.

Another important issue is that the valve member particularly the valve disc and the valve seat have a matching hardness, i.e. a similar hardness, so as to prevent biting of one element into the other , thereby, avoiding damaging of the sealing surfaces.

Furthermore, it is preferred that the engine is a uniflow engine that is that the steam flows from the steam chamber through the opening into the cylinder at a top of the cylinder and is exhausted from the cylinder at a bottom of the cylinder . Thereby it is achieved, that the live steam is not cooled by exhaust steam exhausted from the cylinder whereby the efficiency of the entire engine is improved . For this purpose, the cylinder has exhaust openings released during movement of the piston to the bottom dead center for exhausting the steam from the cylinder . These exhaust openings are formed near the bottom of the cylinder or in other words closer to the bottom than to the top .

According to another embodiment , the surface of the

projection facing the opening is convex and the portion of the valve disc facing the projection is flat . Thereby , an optimum pressure point of the projection against the valve member for lifting the valve member may be achieved. At the same time, the convex surface of the projection serves as a baffle plate for preventing that the steam impinges on the top face of the piston . This is of particular importance, if the piston is made from a light metal such as aluminum (see later) which tends to be more sensible with respect to the hot live steam. In addition, the baffle plate serves for a better distribution of the steam into the cylinder for having a steam distribution at the top of the cylinder which is as uniform as possible.

Further, according to one embodiment, the piston is made from a light metal such as aluminum or aluminum alloy, which provides for high damping and good running characteristics of the piston. On the other hand, the surface of the projection which contacts the valve disc for opening the valve member and to which the high temperature steam is applied is made from a different material, preferably a material with higher rigidity such as stainless steel . Yet, the present invention may also be implemented with a piston made from ductile iron or steel.

For example, the projection may be made as a different element and be connected to the piston by means of a form fit, a force fit and/or an adhesive bond.

A further embodiment implements the provision of an

additional opening ( sub-opening) in the steam chamber, preferably with a smaller area (e.g. diameter or isentropic flow cross section) closed by an additional valve member (sub-valve) . Moreover, the piston comprises an additional proj ection facing the additional opening . When the piston approaches the top dead center, the additional projection lifts the additional valve member releasing the additional opening before the proj ection lifts the valve member

releasing the opening . As the area of the additional opening closed by the additional valve member is smaller than that of the opening closed by the valve member, the force required for lifting the additional valve member is a smaller and, thus , the impact forces on the valve member can be reduced as compared to the case in which only the valve member and the opening are provided. In one embodiment more than one

additional opening and additional valve member may be

provided, in which instance it is preferred to dispose the additional opening and additional valve member symmetrically, particularly diametrically opposite to each other.

Further features and advantages of the invention, which may be implemented alone or in combination with any of the other features described beforehand are disclosed in the following description of a preferred embodiment. This description refers to the accompanying drawings in which:

Fig. 1 shows a schematic cross section of a steam engine according to one embodiment of the invention with the valve member in the closing position and the piston in the bottom dead center; and

Fig, 2 shows the same cross section as Fig. 1 with the valve member in the opening position and the piston at the top dead center .

The steam engine shown in Fig. 1 has a cylinder 10. The cylinder 10 has a top end 11 and a bottom end 12. At bottom end 12, the cylinder 10 is connected to a crankcase 20. A plurality of exhaust openings 13 are circumferentially provided in the cylinder wall 14 of the cylinder . The exhaust openings 13 communicate a cylinder chamber 15 with a ring chamber 16 for exhausting used steam from the cylinder chamber 15 to the ring chamber 16. The exhaust openings 13 are disposed near a bottom dead center of a piston 30 .

The piston 30 is translationally moveable along the center axis CA of the cylinder 10 between a bottom dead center (Fig . 1 ) and a top dead center (Fig . 2). The piston 30 is connected to a non-shown crank shaft accommodated in the crankcase 20 via a non-shown piston connection rod or piston con rod . The piston 30 has a sealing ring 31 at its bottom end 32 and plural sealing rings 31 at its top end 33.

Further, a projection 34 is provided at its top end 33, The projection 34 has a convex, preferably spherical surface 35, which is preferably made from a different material than a main body 36 of the piston 30. The material is preferably more rigid than the material of the main body 36. It is also preferred that the material has a relatively low thermal conductivity in order to prevent heat from being transferred to the main body 36 of the piston. As regards rigidity and thermal conductivity it is preferred to use stainless steel. The main body 36 is preferably made from a light metal, preferably aluminum or aluminum, alloy to provide good running characteristics of piston 30 within the cylinder 10, The material of the projection 34 and particularly its surface 35 is selected for the purpose of opening the later described valve member 52 and for distributing live steam introduced into the cylinder chamber 15 acting as a baffle plate.

The engine further comprises a cylinder head unit 40. The cylinder head unit 40 has a first housing body 41 and a second housing body 42. Further provided is an opening 43 with a preferably circular shape . The center axis of the opening 43 is aligned with center axis CA of the cylinder 10. Further , the opening 43 is provided in the first housing body 41. Further, the cylinder head unit 40 has a steam chamber 44 to be supplied with live steam through one or more openings , which are not shown in the drawings . The steam chamber 44 is mainly defined in the first housing body 41 but with one open side opposite to the opening 43. In particular, the first housing body 41 has a first end 45 facing the cylinder 10 and particularly the cylinder chamber 15. The opening 43 is provided at this first end 45. Opposite to this first end 45, the first housing body has a second end 46 facing away from the cylinder chamber 15 or to put it differently opposite the opening 43 at the first end 45. This second end 46 is

provided with a conical inner surface 47 and is open.

The second housing body 42 has a conical outer surface 48. The conical inner surface 47 and the conical outer surface 48 are sealingly engaged with each other. In this context, it is preferred, that the cone angle of the surfaces 47 and 48 are different to a small extent (e.g. equal to or less than 4°, more preferred equal to or less than 2° ) . Alternatively or additionally, one of the surfaces 47, 48 may be provided with a higher surface roughness than the other surface so as to provide for a certain biting of one of the surface into the other , thus , creating kind of a labyrinth sealing . Thus by engaging the surfaces , a secure sealing is achieved which may be as strong that if the screws 62 described later are removed, the first and second housing body 41 and 42 still maintain fixed to each other . The cones of the surfaces 47 and 48 are preferably centered with the center axis relative to the center axis CA of the cylinder and the opening 43.

Moreover , an annular recess 71 and 72 is formed in each of the surfaces 47 and 48 so as to form an annular hollow space 70. Thereby, the material of the cylinder head unit is reduced at the position of the hollow space 70 forming an interruption in the thermal conductivity . As a result , less heat is conducted from the steam chamber 44 to the top, where the spring 60 and the screws 62 and 63 are located.

The second housing body 42 additionally comprises a bottomed hole 49. A valve guide 50 is press fit into the bottomed hole 49 of the second housing body 42. The valve guide 50 is preferably made from graphite antimony (Guides having such a material are for example available from SGL CARBON SE ,

Wiesbaden, Germany) , A through hole 51 is provided at the bottom of the bottomed hole in the second housing body 42 , A valve member 52 having a shaft 53 translationally guided within the valve guide 50 passes through the through hole 51. The shaft 53 has a first end 54 facing the opening 43 and being connected to a valve disc 55 via a concave fillet 56. A second end 57 of shaft 53 extends beyond the cylinder head unit 40 extending (protruding) from the through hole 51.

The valve disc 55 has an outer edge 58, which is configured spherical and rests on a valve seat 59 at the edge

surrounding the opening 43. This edge 59 of the opening 43 is chamfered. A spring 60 as an elastic element is provided at the second end 57 of the shaft 53 and is positioned outside the steam chamber 44 ,

The first and second housing bodies 41 and 42 are screwed together by means of screws 62 which extend parallel to the center axis CA of the cylinder 10. A top cover 61 is screwed by means of screws 63 to the crankcase 20. The screws 63 also extend parallel to the center axis CA.

The top cover 61 additionally has a recess 64 for

accommodating the spring 60. The spring 60 is thereby

supported by the top cover 61 at one end 65 and a plate 66 connected to the shaft 53 of the valve member 52 at the other end 67. Thereby, the valve member 52 is pre-tensioned or urged towards the valve seat 59, whereby the valve disc

(particularly its edge 55 ) is pressed against the valve seat 59 thereby sealingly closing the steam chamber 44 or its opening 43, respectively in the closing position of the valve member 52.

The shaft 52 has a length SL of 150 mm, defined between its two ends 54 and 57. The length of the valve guide 50 referred to as GL is 120 mm. Thus , the shaft 53 is guided along 80% of its length . In addition, the valve lift is 1 mm in the present embodiment so that the ratio of the shaft length to the valve lift in the present embodiment is 150. The valve lift is particular defined as the movement of the valve member between the position in Fig. 1 and the position in Fig. 2.

Next, the assembly process of the engine shown in Figs, 1 and 2 is described.

First, the cylinder 10 is placed with a shoulder 70 at an opening of the crankcase 20 with the piston being inserted into the cylinder 10.

Further, the cylinder unit 40 is pre-assembled the valve guide 50 inserted into the bottomed hole 49 and then the shaft 53 inserted into the opening of the valve guide 50. Subsequently, the first and second housing bodies 41 and 42 are connected by inserting the outer conical surface 48 into the inner conical surface 47 and fixing the bodies by

tightening the screws 62. The preassembled cylinder head unit 40 is placed with its shoulder 71 at the top end 11 of the cylinder 10.

In a next step, the spring 60 is placed on the plate 66 and the top cover 61 is positioned . Subsequently, the screws 63 are tightened to fix the top cover 61 to the crankcase 20 whereby the cylinder 10 and the cylinder head unit 40 are clamped and the spring 60 is pre- tensioned .

It becomes apparent from the above description, that the assembly is fairly easy and may be performed from one

direction, namely the top . All the screws may be tightened from the top and all the elements may be inserted from the top . This is not only advantageous from the perspective of the manufacturing process , i.e. the assembly during the first manufacture , but also from maintenance point of view . Finally, the function of the engine is described in the following .

In Fig. 1, the piston 30 is disposed in the bottom dead center. In this stage, live steam is stored in the steam chamber 44 and its high pressure assisted by the spring 60 urges the valve disc 55 or particularly its spherical edge 58 against the valve seat 58 thereby closing the opening 43,

When the piston 30 translationally moves along center axis CA towards its top dead center as shown in Fig. 2, the convex surface 35 of the projection 34 contacts the flat lower surface 73 of the valve disc 55 thereby pushing the valve member 52 towards the top into the steam chamber and

releasing (lifting) the valve disc or particularly its edge from the valve seat 59 thereby releasing the opening 43.

Thus, live steam from the steam chamber 44 is introduced into the cylinder chamber 15 forcing the piston 30 again towards its bottom dead center.

Upon movement of the piston 30 towards the bottom dead center by means of the live steam, the projection 34 particularly its surface 35 comes again out of contact with the valve member 52 which is thereby closed by means of the spring 60 again closing the opening 43. Once the piston 30 reaches its bottom, dead center, the exhaust openings 13 are released and the steam is exhausted to the ring chamber 16, This process is continued during operation of the engine .

Claims

Claims :

1. Steam engine comprising:

a cylinder (10)

a steam chamber (44) to be supplied with live steam, the steam chamber (44) having an opening (43) for introducing live steam into the cylinder (10) and a valve seat (59) ,

a valve member (52) urged against the valve seat (59) by an elastic element (60) in a closing position closing the opening (43 ) ,

a piston (30) slidable within the cylinder (10) between a bottom dead center and a top dead center, wherein the piston (30) has a projection (34) at its top end (33) facing the opening (43), the projection (34) lifting the valve member (52) against a spring force of the elastic element (60) from the valve seat (59), when the piston (30) is in the area of the top dead center for releasing the opening (43) , characterized in that

the valve member has a shaft (53), extending through the steam chamber (44), and a valve disc (55) disposed at a first end (54) of the shaft (53), wherein the elastic element (60) is disposed outside the steam chamber (44) at a second end (57) of the shaft (53) opposite to the first end (54),

2. Steam engine according to claim 1, further comprising a valve guide (50) translationally guiding the shaft (53) of the valve member (52) »

3. Steam engine according to claim 2 , wherein the ratio of the guiding length (GL) , corresponding to the length at which the shaft (53) of the valve member (52) is guided in the valve guide (50), and the maximum valve lift when being lifted by the projection (34) is at least 70, preferably at least 80, more preferably at least 90 and most preferred at least 100,

4. Steam engine according to claim 1 or 3 , wherein at least 50%, preferably at least 60%, more preferably at least 75% and most preferred at least 80% of the length of the shaft (53) are guided by the valve guide (50) .

5. Steam engine according to any one of the preceding claims, further comprising a cylinder head unit (40) having a first housing body (41) provided with the steam chamber (44) and the opening (43) and having an open end with a conical inner surface (47}, and

a second housing body (42) having a conical outer surface (48) , wherein the conical inner surface and the conical outer surface are sealingly engaged.

6. Steam engine according to claim 5, wherein the conical inner surface (47) is disposed at a side of the first housing (41) opposite to the opening (43),

7. Steam engine according to claim 6, wherein the center axis (CA) of the cone of the conical inner surface (47) is aligned with the center line (CA) of the opening (43) and/or the center axis (CA) of the cylinder (10),

8. Steam engine according to one of claims 6 to 7 and one of claims 2 to 4, wherein the valve guide (50) is provided in the second housing body (42) .

9. Steam engine according to any one of claims 5 to 8, wherein the first (41) and second (42) housing bodies are screwed together by screws (62) » the screws (62) extending substantially parallel to the center axis (CA) of the cylinder ( 10 ) .

10. Steam engine according to any one of claims 5 to 9 , further comprising a top cover (61) screwed to a crankcase (20) by screws (63), the screws (63) preferably extending substantially parallel to the center axis (CA) of the cylinder (10) , whereby the cylinder head unit (40) is fixed to the cylinder (10) .

11. Steam engine according to claim 10, wherein the elastic element (60) is directly or indirectly pre-tensioned between the second housing body (42) and the top cover (61) ,

12. Steam engine according to any one of claims 5 to 11, wherein the inner (47) and outer (48) surfaces are each provided with a recess (71, 72) forming a hollow space (70), the recesses being positioned so as to face each other with the inner and outer surfaces being engaged.

13. Steam engine according to any one of the preceding claims, wherein the valve seat (59) or the edge of the valve member (523 is spherical and the edge of the valve member (52) or the valve seat (59) is chamfered.

14. Steam engine according to any one of the preceding claims, wherein the cylinder has exhaust openings (13) released during movement of the piston (30) to the bottom dead center for exhausting the steam from the cylinder (10).

15. Steam engine according to any one of the preceding claims , wherein a surface (35) of the proj ection ( 34 ) facing the opening (43) is convex and the portion of the valve member (52) facing the projection (34) is flat.

16. Steam engine according to any one of the preceding claims, wherein the piston (30) is made from a light alloy, preferably aluminum or an aluminum alloy and at least the surface (35) of the projection (34) is made of a different material than the piston and having a higher rigidity.

17. Steam engine according to any one of the preceding claims, further comprising at least one further valve member urged against a further valve seat by a further elastic element in a closing position closing a further opening, the piston (30) having a further projection, at its top end facing the further opening, the further projection lifting the further valve member against a spring force of the further elastic element from the further valve seat, when the piston is in the area of the top dead center for releasing the further opening in advance of the projection (34) lifting the valve member (52) against the spring force of the elastic element (60) from, the valve seat (59) .