Piston type internal combustion engine of annular section

Abstract

 In order to increase the volumetric efficiency of piston-type internal-combustion engines, a cylinder/piston torque of annular preferably circular, cross section, is provided for. In one four-stroke form, the value arrangement comprises several values (10, 11) arranged in a circle around one central value (14) concentric with the engine cylinder (2).
The two-stroke versions comprise crank-case scavenging with different slot arrangement in the inner resp. outer cylinder wall (103, 2).

Description

[0001] The invention refers to piston type internal-combustion engines, both two and four-stroke-cycle ones, with controlled ignition or of diesel type.

[0002] It is known that the limited rating increases of the traditional engines of the above mentioned type especially depend on the fact that the volumetric efficiency - for a certain inlet valve port - decreases substantially as soon as the rounds per minute reach a speed, at which the speed of theinput gases exceeds the approximate value of 0,5 mach. For high speeds it is therefore necessary to increase the inlet openings, i.e. in order to considerably increase the rating of a piston-irternal-combustion engine it is necessary to increase both the speed and the inlet port. Such increase, however, should not exceed particular limits, because the comparatively short strokes of the pistons in high-speed engines make it difficult to achieve the exact compression ratios, while the control mechanism of the valves show a critical speed and the inertial forces increase exceedingly opposing the speed increase.

[0003] In order to obviate the above mentioned difficuties, with the USA 4 256 068 patent, cylinders with corresponding pistons have been proposed which in cross section show an oval or similar shape. In this way the volumetric efficiency can be considerably increased, but on the other hand there are practical difficulties in carrying this out and both considerable sealing problems and high costs arise.

[0004] The invention has the object to increase the rating of the above mentioned internal-combustion engines, augmenting their volumetric efficiency, without creating problems or difficulties for the construction, the sealing and the costs, i.e. eliminating the disadvantages of the well known cylinder/piston torques with oval-shaped cross section as described in the USA 4 256 068 patent.

[0005] This object is attained by the invention providing a cylinder/piston torque with an annular or preferably a circular-shaped cross section.

[0006] The cylinder/piston torque of annular cross section according to the invention allows to sensibly increase the volumetric efficiency compared with the traditional circular bore cylinder/piston torques and permits to reach and even to exceed the volumetric efficiency of the cylinders of oval-shaped cross section according to the USA 4 256 068 patent. In comparison with the latter, the cylinder/piston torque of annular circular-shaped cross section according to the invention is far more simple to build and allows machinings and maintenances with conventional mechanical tools, due to the fact that it comprises only circular shapes. The solution according to the invention can therefore be carried out with comparatively low costs if compared to the attained performances and offers the possibility to reduce the number of cylinders, the performance being equal.

[0007] These and other characteristics of the invention and the resulting advantages will be pointed out by the following description of some feasible forms which are illustrated as a non-restrictive example in the enclosed drawings, in which:

Fig. 1 is a partial axial section through a cylinder of annular cross section according to the invention, for four-stroke-cycle engines.

Fig. 2 is a section of the above mentioned according to the broken line II-II of Fig. 1.

Fig. 3 illustrates a feasible variant of the cylinder according to Fig. 1 in partial axial section.

[0008] Eg. 4 illustrates another feasible example of a cylinder of annular cross section according to the invention in partial axial section, both usable for two and four-stroke-cycle engines.

[0009] Figures 5 and 6 illustrate in plan and in elevation, with parts in section, a possible control meccanism of the cylinder valves of annular cross section according to Fig. 3.

[0010] Fig. 7 illustrates in partial axial section a feasible variant of a cylinder of annular cross section according to the invention, for two-stroke-cycle engines.

[0011] Fig. 8 illustrates the piston of the feasible example according to Fig. 7, with the right half in elevation and the left half in axial section.

[0012] Fig. 9 illustrates in partial axial section a further feasible form of a cylinder of annular cross section for two-stroke-cycle engines, with a normal feed version in the left half of the figure and a supercharged one in the right half of the figure.

[0013] Fig. 10 illustrates the piston of the feasible form according to Fig. 9. The left half of the Fig. 10, in particular, is a top view of the piston shown in the left half of Fig. 9, whereas the right half of Fig. 10 illustrates the piston of the right half of Fig. 9, in sectional view according to the line X-X.

[0014] Fig. 11 illustrates in partial axial section another feasible form of the cylinder of annular cross section according to the invention, for two-stroke-cycle engines. The left half of this figure illustrates the normal feed version, whereas the right half shows the supercharged one.

[0015] Fig. 12 illustrates in partial axial section a further feasible form of a cylinder of annular cross section according to the invention, for two-stroke-cycle engines.

[0016] In this case too, the left half of the figure illustrates the normal feed version, while the right half of the figure shows the supercharged one.

[0017] The Figures 13 to 16 illustrate some characteristic diagrams of the cylinders of annular cross section according to the invention for comparison with other cylinder types.

[0018] Refering to Figures 1 and 2, pertinent to a four-stroke-cycle engine, the invention provides for a cylinder comprising an internal circular cylinder liner or wall 1 and an external circular cylinder liner or wall 2, which are coaxial and interspaced and delimit a cylinder space 12 of circular annular cross section. In this annular space 12 there is a seal-tight guided piston 3 of circular annular shape which is articulated in order to be somehow fitted to the connecting rod (not illustrated). In a preferred version, the piston has an annular head 3 forming a single unit with a tubolar or cup-shaped extension 4 which forms the piston skirt and is connected to the rod.

[0019] The seal between the piston 3 and the cylinder is obtained by means of piston rings 5 which are mounted on the outer surface of the piston head and cooperate with the external cylinder wall 2, and by means of piston rings 6 which are fixed to the internal cylinder wall 1 and cooperate with the internal cylinder surface of the head 3 and the skirt 4 of the annular piston, working in an opposite way compared to the piston ring 5. On the other hand, also the internal piston ring 6 might be mounted on the annular piston 3 and can cooperate with the internal cylinder wall 1. The 7 indicates the cylinder head, in which the inlet 8 and outlet manifolds 9 with the respective inlet 10 and outlet valves 11 are provided for. As shown in Fig. 2, one or preferably more inlet valves 10 and one or preferably more outlet valves 11 can be provided for. In the shown example, the valves 10 and 11 are placed and distributed on the annular ring corresponding to the annular cross section of the cylinder space 12 and can be controled by a camshaft provided for at the head, for example as described later refering to figures 5 and 6. However, other arrangements of the inlet and outlet valves are possible, while both the cylinder head 7 and the valves 10, 11 and their control mechanism might be carried out in any way, obvious to the competent engineers.

[0020] In the example illustrated in figures 1 and 2, the internal cylinder wall 1, which makes up the cylinder core of annular cross section, forms a single unit with the cylinder head 7 and comprises a cavity 13, which might be used for the cooling water circulation.

[0021] Obviously, also the external cylinder wall 2 can be adequately cooled, by air or water, for example in a conventional manner (not illustrated).

[0022] Fig. 3 illustrates a feasible variant of the cylinder of annular cross section for four-stroke-cycle engines according to the invention. This version is substantially in conformity with the one according to figures 1 and 2, the parts being indicated with the same reference numbers. In the variant according to fig. 3, in addition to the valves 10, 11, placed along the annular cross section of the cylinder, or in place of at least one of these valves, a central inlet or outlet valve 14 is forseen which preferably is seal-tight guided in the cylinder cavity 13 of the internal wall 1 forming the annular cylinder core and controls the inlet of a manifold 15 (inlet or outlet) in the cylinder head 7, which communicates with the annular cylinder space 12 through one or more lateral openings 16 of the internal cylinder wall 1. When the valve 14 is closed, it opens both the manifold inlet 15 and the lateral inlets 16 of the wall 1 thus permitting the communication between the above mentioned manifold 15 and the annular cylinder space 12.

[0023] Figures 5 and 6 illustrate an example of the control mechanism of the valves in the version according to Fig. 3. At the cylinder head a camshaft 17 is provided that controls, through the cams 18, the stems 111 of the outlet valves placed in correspondence to the annular cylinder space 12.

[0024] The inlet valve stems 111 arranged in correspondence to the annular cylinder space 12 too, are connected by a frame 19 on which the cams 20 of the camshaft 17 operate. The stem 114 of the control valve 14, placed in the area of the annular cylindercore, is controled by a further cam 21 of the shaft 17. An analogues mechanism, except for the cam 21 for the central valve, can be utilized also for the control of valves 10 and 11 in the version according to figures 1 and 2.

[0025] Fig. 4 shows a variant of the control valve according to Fig. 3. In the version according to Fig. 4, the manifold inlet 23, provided in the cylinder head 7 and communicating with the annular cylinder space 12 through lateral inlets 16 in the internal cylinder wall 1, is closed and opened by means of a central valve 22 forming a single unit with a body 222 axially sliding in the cavity 13 of the annular cylinder core.

[0026] This valve 22 is controled by its stem 122 on the opposite side of the cylinder head 7 and might have, at its end toward the cylinder head 7 a profiled deflecting head 322 which conveys the gases between the annular cylinder space 12 and the manifold inlet 23 through the side inlets 16, in the open position of the same valve 22 shown in Fig. 4.

[0027] In the open position of the valve 22 the valve closes the manifoldIDlet 23 and thus interrupts the communication between the manifold 23 and the annular cylinder space 12.

[0028] The feasible example of the cylinder of annular cross section according to Fig. 4, with central valve, might be used both for four and two-stroke-cycle engines, with the suitable modifications, obvious to the competent engineers.

[0029] Instead of only one central valve 14 or 22, in the area of the central core of the annular cylinder, there might also be two or more valves, suitably arranged and controled, which might be inlet and/or outlet valves. Obviously, if the cylinders of annular cross section according to the invention, are part of engines with controled ignition (carburetion), they will be designed with a suitably placed spark plug, even if it is not always shown in the figures of the enclosed drawings.

[0030] Figures 7 and 8 show a cylinder of annular cross section according to the invention, for two-stroke-cycle engines.

[0031] In this case too, the cylinder space 12 shows in cross sectional view a circular annular shape and consists of the gap between an internal cylinder wall 1 and an external cylinder wall 2. The internal wall 1 forms the central core of the annular cylinder and is fixed to the cylinder head 7, whereas it shows a cavity 13 in which the cooling water may circulate.

[0032] In the external cylinder wall 2, also furnished with cavities 24 for the cooling water circulation, transfer manifolds 25 are provided, each of them having a top transfer inlet 125 and a bottom transfer inlet 225. In this same external cylinder wall 2 there is also the exhaust manifold 26 with the respective entry 126. In the cylinder space 12 of annular cross section, the piston 3 is provided, which acts as seal, by means of its external 5 and internal piston rings and which shows in cross-sectional view a corresponding annular shape. The suitably profiled annular piston head forms a single unit, on the opposite side of the cylinder head 7, with a coaxial tubular cylinder extension 4 which forms the piston skirt. This piston skirt 4 communicates with the crank case/pump (not illustrated) of the engine and is furnished with transfer openings 104. The tubular extension 4 which forms the piston skirt comprises also the seat 204 for the articulated joint pin of the connecting rod (not illustrated).

[0033] The actual section of the piston 3, 4 shown in the left half Fig. 8 is made according to a plan VIII-VIII perpendicular to the plan of the elevation as shown in the right half of the same Fig. 8. The seal is assured by means of piston rings 5 externally mounted on the head of the annular piston 3 and cooperating with the external cylinder wall 2, as well as by means of piston rings 6 internally mounted on the head of the annular piston 3 and cooperating with the internal cylinder wall 1. The internal wall 1, forming the central core of the annular cylinder, has its ends opposite to the head 7 and beyond the bottom of that end, a tubular cylindrical extension which leads inward into the piston 3 and communicates through it and its tubular skirt with the crank-case/pump of the engine, showing lateral transfer openings 201. Reference number 26 indicates the seat for the spark plug (not illustrated).

[0034] In the lower position of the piston 3 as shown in the Fig. 7, the piston opens the mouth-piece 126 of the exhaust manifold 26 and the transfer openings 201 placed in the tubular extension 101 of the cylinder core formed by the internal wall 1.

[0035] Also the top inlets 125 of the transfer manifolds 25 are opened, the bottom inlets 225 thus coinciding with the transfer openings 104 of the skirt 4 of the piston 3. The annular cylinder space 12 hence communicates on one side with the exhaust manifold 26 through the respective inlet 126 and on the other side with the crank-case/pump through the annular piston 3 and both through the central transfer openings 201 in the cylinder core and the piston head 3, and through the transfer manifold 25 in the external cylinder wall 2 and the lateral transfer openings 104 of the skirt 4 of the piston 3. With its stroke towards the cylinder head 7, the annular piston 3 overtakes and closes both the transfer inlets 125 and the transfer openings 201, as well as the inlet 126 of the exhaust manifold.

[0036] The two versions of the cylinder of annular cross section for two-stroke-cycle engines, as shown in the figures 9 and 10, substantially correspond to the example shown in the figures 7 and 8, equal or equivalent parts being indicated with the same references. Unlike the version according to figures 7 and 8, however, in both versions as shown in figures 9 and 10, as a sole or additional exhaust manifold the central core of the cylinder of annular cross section is used. To this aim, according to the left half of the figures 9 and 10, the cavity j3 of the internal cylinder wall 1, forming a single unit with the cylinder head 7, constitutes the exhaust manifold and is furnished with lateral transfer openings 301 on the upper side of its closing bottom, i.e. on the side of the mentioned bottom leading towards the cylinder head 7.

[0037] In the version according to the right half of figures 9 and 10, instead, the cylinder core of annular cross section is not made up of a fix internal cylinder wall, i.e.forming a single unit with the cylinder head 7, but is constituted of a corresponding cylindrical extension 103 of the piston 3. This extension 103 of the piston slides in a corresponding coaxial hole 107, provided for in the cylinder head 7. The seal between the head 7 and the extension 103 of the piston 3 is assured by means of piston rings 106 provided in the wall of the hole 107 or on the extension 103 of the piston 3. The coaxial cylindrical extension 103 of the piston 3 is tubular-shaped and its cavity 13 communicates on the upper side with the exhaust, whereas in the lower part it is closed by means of a bottom 303 thus separating it from the internal space of the piston 3 and its tubular skirt 4 and hence from the crankcase/pump.

[0038] Above the bottom 303, i.e. on the side of it leading towards the exhaust in the tubular cylindrical coaxial extension 103_.of the piston 3, lateral transfer openings 203 are provided. In correspondence to the combustion chamber 12 of the cylinder the seat 26 for the spark plug is provided for.

[0039] In the lower position of the piston 3 as shown in the left half of Fig. 9, the transfer inlets 125, 225 of the transfer manifold 25 placed in the external cylinder wall 2 are uncovered. Also the transfer openings 203 of the coaxial cylindrical extension 103 of the piston 3 are uncovered. Consequently, the annular space 12 of the cylinder communicates both with the crankcase/pump, through the transfer manifolds 25 of the external wall 2 and the transfer openings 104 of the skirt 4 of the piston 3, and with the exhaust through the transfer openings 203 and the cavity 13 of the central cylindrical extension 103 of the same piston 3. During its stroke upwards, the piston 3 overtakes and covers the upper transfer inlets 125 of the transfer manifolds 25 and closes also the transfer openings 203 of its coaxial cylindrical extension 103, as soon as the latter penetrates into the corresponding hole 107 of the head 7. The working annular surface of the piston 3 is cone-shaped in order to favour the unidirectional gas flow.

[0040] Obviously, in both versions as shown in figures 9 and 10, in addition to the central exhaust formed by the coaxial tubular extension 103 of the piston 3, it is possible to provide also at least one lateral exhaust similar to that of the exhaust manifold 26 in the external cylinder wall 2, as shown in Fig. 7.

[0041] The illustrated example in two versions as shown in Fig. 11 essentially corresponds to the version shown in the right half of figures 9 and 10, i.e. the cylinder core of annular cross section is made up of a coaxial cylindrical extension 103 of the annular piston 3. The piston therefore acquires - analogously to the version of the right half of fig. 9 - a shape resembling an upside-down mush-room, the stem of which, made up of the above mentioned coaxial extension 103 of the piston 3, is seal-tight guided into the hole 107 provided for in the cylinder head 7. Unlike the version according to the right half of fig. 10, however, the example as shown in fig. 11 has an exhaust manifold 26 in the external lateral cylinder wall 2 and the coaxial cylindrical extension 103 of the piston 3, carried out tubular-shaped, communicates with the crank-case/pump through the annular piston 3 and through its tubular skirt 4. Moreover, the above mentioned extension 103 of the piston 3 is furnished with lateral transfer openings 203 which are uncovered, together with the exhaust opening 126 and the transfer openings 125, as soon as the piston 3 is in the lower position as shown in Fig. 11.

[0042] In the version shown in the left half of Fig. 11, the coaxial tubular extension 103 of the piston 3 is open and can communicate, at its end opposite to the crankcase-pump, with any fixed volume or with a feeding line (induction), for example with a carburettor. This feed, connected to the tubular extension 103 of the piston 3 can be provided additionally to the feed connected to the crankcase-pump or designed instead of the latter. In the version shown in the right half of Fig. 11, instead, the coaxial tubular extension 103 of the piston 3 is closed by means of a bottom 303, placed above the transfer openings 203, i.e. on their side opposite to the piston 3. In this case, as well as in all versions according to figures 7 to 10, the feed is carried out in a conventional manner by means of the crankcase-pump.

[0043] The version according to Fig. 12 too, essentially corresponds to the examples shown in Fig. 11. The coaxial tubular extension 103 of the annular piston 3, resembling an upside-down mushroom, seal-tight guided into the hole 107 of the head 7 and making up the cylinder core of annular cross section, does not have the transfer openings and therefore the feed through the crankcase-pump is carried out only through the transfer manifolds 25 placed in the external lateral cylinder walls 2. In this external wall 2 there is at least one lateral exhaust manifold 26. In the version according to the left half of Fig. 12, the coaxial tubular extension 103 of the annular piston 3 is open and communicates on the lower part with the crank-case/pump and on the upper side with a fixed volume. In the version according to the right half of Fig. 12, instead, the coaxial tubular extension 103 of the piston 3 is closed by a bottom 303.

[0044] Figures 13 to 16 show some characteristic diagrams in order to point out the efficiency of engines with cylinders of annular cross section according to the invention and to compare it to the performance of the engines known sofar.

[0045] Fig. 13 refers to a two-stroke-cycle engine (2T)and shows a diagram of the power factor A dipendent on the volume

=

, where "d" is the inside diameter and "D" the outside diameter of the annular cross section of the cylinder according to the invention.

[0046] The power factor A has been determined on the base of the expression A =

, where L = peripherical length of the expansion of the transfer openings, and D = diameter of the equivalent cylinder, i.e. D = (D² - d ) and assuming that the hight of the transfer openings is hold constant.

[0047] Considering that for

= 0 one obtains the value of the power factor A for the traditional cylinder of circular bore of a two-stroke-cycle engine, Fig. 13 clearly shows the increase of the power factor A as the value ₁ increases.

[0048] m Fig. 14 refers to a four-stroke-cycle engine (4T) and shows the diagrams of the power factor A dependent on the number "n" of the inlet valves, if the valves move parallely to the cylinder axis. The power factor A has been determined on the base of the expression A =

, where n = number of inlet valves, D_v = diameter of inlet valves and De = diameter of the equivalent above mentioned cylinder. The diagram of the traditional circular bore cylinder is indicated with a line and two points, whereas a chain indicates the diagram relative to a cylinder of oval cross section according to the USA 4 256 068 patent.

[0049] A short dashes line indicates the diagram of a normal cylinder of annular cross section according to the invention, as shown in figures 1 and 2, while a continuous line indicates the diagram of a cylinder of cross section according to the invention, with a central valve, as shown for example in Fig. 3.

[0050] Fig. 14 clearly shows that the power factor A of a normal cylinder of annular cross section according to the invention is practically equivalent to the power factor of a cylinder of oval cross section, but the annular cylinder according to the invention, compared to the oval one, has the advantage of being far more simple to built. The power factor A relative to an annular cylinder according to the invention, with a central valve, is remarkably higher than the one of the oval cylinder. Fig. 15 again shows a two-stroke-cycle engine (2T) and illustrates the diagrams of the specific horsepower B, i.e. of the power factor A divided by the equivalent diameter D_e (B = A ) as a function of the unitary displacement indicated with the equivalent diameter D and for different values of m = D , the ratio bore/stroke being equal. The diagram for m = ∞ corresponds to that for a traditional cylinder of circular bore. Fig. 15 clearly shows that, for instance, for a 55 mm diameter for a traditional cylinder there is an equivalent diameter larger than 85 mm for an annular cylinder according to the invention, where m = 2, it is therefore possible to achieve specific horsepowers, for unitary displacements higher than 500 cc of an annular cylinder, equal to those of 125 cc.

[0051] Fig. 16 refers to a four-stroke-cycle engine (4T) and shows the diagrams for the specific horsepower B, i.e. for the power factor A divided by the equivalent diameter D (B = DA ) as a function of the equivalent e _e diameter D itself and for different numbers "n" of e the inlet valves, the ratio bore/stroke being equal. A short dashes line and two points indicate the diagram for a traditional cylinder of circular bore. All the other diagrams refer to a cylinder of annular cross section according to the invention. Fig. 16 clearly shows that with the cylinder of annular cross section according to the invention it is possible to obtain substantially higher specific horsepowers than with the traditional cylinders, which is also due to the facility of placing a relatively large number of inlet valves both on the perimeter of the annular cylinder and in correspondence to the cylinder core.

[0052] Obviously the invention is not restricted to the feasible versions described and illustrated herein, but can be varied and modified, especially from the point of view of the construction, as well as applied to any piston-type internal-combustion engine, always within the above described principles in subject matter of the following claims.

Claims

1. Internal-combustion piston type engine, two or four-stroke-cycle, controlled ignition or diesel, characterized in that it contains at least one cylinder (1, 2) and the respective piston (3) which in cross section show an annular or preferably a circular shape.

2. Engine as described in claim 1, characterized in that the combustion chamber is made up of the space (12) interposed between an external circular cylinder wall (2) and a central core which is delimited by a central circular cylinder wall (1,103), coaxial to the external one (2) and having a smaller diameter than the latter, while the piston is made up of an annular head (3) seal-tight guided between the two coaxial cylinder walls (2 and 1, 103) and forming a single unit with a tubular skirt (4), to which the connecting rod is hinged.

3. Four-stroke-cycle engine as described in claims 1 and 2, characterized in that the admission openings and/or exhaust ports (10,11) are-placed along the perimeter of the cylinder of annular cross section (12).

4. Two or four-stroke-cycle engine as described in claim 1 and 2 or 3, characterized in that it is provided for at least one inlet and/or exhaust valve (14) in correspondence of the central core (1) of the cylinder of annular cross section.

5. Two or four-stroke-cycle engine as described in claims 1 to 4, characterized in that the cylinder central core, made up of the internal cylinder wall (1), is a component of the cylinder head (7) and shows cavities (13) through which the cooling water circulates.

6. Two-stroke-cycle engine as described in claims 1, 2 or 5, characterized in that in the external circular cylinder wall (2) there are transfer manifolds (25) in which the outlets (125) are communicating with the cylinder (12) and are closed and opened by the annular piston (3), and with outlets (225) on the opposite side cooperating with the transfer openings (104) provided for in the tubular skirt (4) of the piston and communicating with the crankcase-pump by means of the same skirt.

7. Two-stroke-cycle engine as described in claim 6, characterized in that the cylinder central core, made up of the internal cylinder wall (1), shows communicating cavities (13) on one side with the crankcase-pump and, on the other side, with the combustion chamber (12).

8. Two-stroke-cycle engine as described in clam 6, characterized in that in the central cylinder wall (1) which forms the cylinder core of annular cross section, transfer openings (16,201,301,203) are provided for.

9. Two-stroke-cycle engine as described in claim 8, characterized in that the transfer openings (16, 201,203), provided for in the central cylinder wall (1, 103) and making up the cylinder core, communicate with the crankcase-pump through the annular head and the tubular skirt (4) of the piston (3).

10. Two-stroke-cycle engine as described in claim 8, characterized in that the transfer openings (16, 201,301,203), provided for in the central cylinder wall (1,103) and making up the cylinder core, communicate with an exhaust (13) which might be the only exhaust of the cylinder or with an additional one in combination with one or more lateral exhausts (26) provided for in the external cylinder wall (2) of the cylinder.

11. Two-stroke-cycle engine as described in claim 8, characterized in that the transfer openings (16,203), provided for in the central cylinder wall (1,103) and making up the cylinder core, communicate with a carburettor.

12. Two-stroke-cycle engine described in one of the claims from 8 to 11, characterized in that the central cylinder wall (1) making up the cylinder core forms a single unit with the cylinder head (7) and its transfer openings (201,301) are covered and uncovered by the annular piston (3) during its stroke.

13. Two or four-stroke-cycle engine as described in any of the previous claims, characterized in that the central cylinder wall (103) making up the core of the annular cylinder forms a single unit with the annular piston (3) and is sealtight guided in a correspondent bore (107) of the cylinder head (7).

14. Two-stroke-cycle engine as described in any of the previous claims, characterized in that the active annular surface of the piston head

(3) is profiled and is, in particular, substantially carried out cone-shaped.

Drawing