Two-stroke engine, especially large margine engine

Abstract

 The present invention relates to a two-stroke engine, especially high power marine diesel engine, with uniflow scavenging, having at least one cylinder (1) mounted in an engine case (7), comprising a cylinder head (2) and liner (4) and provided with an exhaust valve (3), preferably situated in the head (2), a piston (5) situated in said cylinder, optionally provided with a compression ring or rings (13), connected with a crankshaft in a crankcase (9) and having the possibility to move in the cylinder (1) in a reciprocating motion, characterised in that outside the cylinder liner (4), between the engine case (7) and the cylinder liner (4), the scavenge air space (8) is located, the cylinder liner (4) has at least one scavenge air port (15), leading from the scavenge air space (8) to the inside of the cylinder liner (4), provided with closing means (14), enabling opening and closing of the port (15), wherein the bottom port of the cylinder liner (4) is tightly separated from the scavenge air space (8).

Description

Technical Field

[0001] The invention relates to a two-stroke engine with uniflow scavenging, especially high power marine diesel engine, supercharged, with at least one cylinder in which a piston having the possibility to move in a reciprocating motion is situated. The conversion of reciprocating motion to rotary motion is realised through crank mechanism consisting of a crankshaft connected by a connecting rod with a crosshead provided with a piston rod connected with the piston.

Prior Art

[0002] In engines of this type, due to supercharging, the scavenge air space is separated from the crankcase space, which obstructs the lubrication of the cylinder liner.

[0003] A solution to this problem is known to be the use of lubricators situated in the upper part of the cylinder liner, dispensing oil between piston rings each time the piston is in the upper position. The oil is then being distributed over the liner when the piston is moving downwards. In order to ensure proper lubrication of the liner's entire surface, the oil has to be dispensed in excess, however due to character of the solution the reuse of that excess is impossible. It leads to a significant cylinder oil consumption.

[0004] Another known solution is presented in the international patent application no. WO 2011 022030, in which supplying the scavenge air into the valve in the piston through a series of telescopic tubes situated under the piston in the crankcase is proposed. Thereby, the scavenge air was separated from the crankcase space in a way enabling the oil mist to reach under the piston, thereby enabling the realisation of cylinder liner lubrication and the regression of oil excess scraped off by compression rings into the crankcase. This solution is defective in that, in the case of large marine engines having piston stroke up to 2.5 metres, it remarkably increases the weight of the piston, and therefore the loads of the crankshaft and piston assembly. Due to the length and geometry of pipelines supplying the scavenge air into the cylinder chamber, the scavenging of the cylinder is also obstructed.

[0005] The object of the invention is to provide a construction characterised in a lowered cylinder oil consumption and free from the above-mentioned defects. This object has been achieved thanks to the separation of a part of space inside the cylinder liner located under the piston and the scavenge air space, which allows depositing oil on the surface of the liner by means of oil mist, by spraying or in another way, and then reusing the oil excess after scraping it off the sides of the liner through the downward movement of the piston.

Disclosure of the Invention

[0006] According to the invention, a two-stroke engine, especially high power marine diesel engine, with uniflow scavenging, having at least one cylinder mounted in the engine case, comprising a cylinder head and liner and provided with an exhaust valve, preferably situated in the head, a piston situated in said cylinder, optionally provided with a compression ring or rings, connected with a crankshaft in a crankcase and having the possibility to move in the cylinder in a reciprocating motion, is characterised in that outside the cylinder liner, between the engine case and the cylinder liner, the scavenge air space is located, the cylinder liner has at least one scavenge air port, leading from the scavenge air space to the inside of the cylinder liner, provided with closing means, enabling opening and closing of the port, wherein the bottom port of the cylinder liner is tightly separated from the scavenge air space. The closing means close the scavenge air ports when the charge exchange in the cylinder is not being realised.

[0007] Preferably, the cylinder liner has two or more scavenge air ports, leading from the scavenge air space into the inside of the cylinder liner, preferably arranged symmetrically about the perimeter of the cylinder liner, wherein each port is provided with the closing means enabling opening and closing of ports.

[0008] Preferably, the scavenge air space is created by the proper shaping of the engine case as a cavity between the engine case and the cylinder liner.

[0009] Preferably, the closing means are constituted by a ring mounted on the outer surface of the cylinder liner in a way enabling to move it along this surface, said ring preferably sealed with a seal with the surface of the cylinder liner.

[0010] In that case, preferably, the ring is situated in a flange mounted on an outlet of the engine case, wherein an empty space is located between the flange and the ring, said empty space connected via hydraulic hose with a source of compressed air and preferably sealed with seals above and below the hydraulic hose inlet.

[0011] Preferably, the ring is supported by at least one hydraulic actuator, preferably it is supported from the bottom by at least one hydraulic actuator.

[0012] Preferably, the scavenge air space is tightly separated from the crankcase space.

[0013] Preferably, between the engine case and the cylinder liner, below scavenge air ports, an oil space is located, the oil space being connected with a part of the cylinder inner space located under the piston, wherein the oil space is tightly isolated from the crankcase space and, preferably, also tightly isolated also from the scavenge air space.

[0014] If said closing means are constituted by a ring slidably mounted on the outer surface of the cylinder liner, the length of scavenge air ports measured on the outer surface of the cylinder liner along the vertical axis of the cylinder is preferably greater than the height of the ring, whereas the position of the ring in relation to the cylinder liner is selected so that the air purge from the space through the port into the oil space is possible in a certain range of the ring's motion along the cylinder liner.

[0015] Then, preferably, the scavenge air ports are connected with grooves in the outer surface of the cylinder liner, due to which the length of the scavenge air ports measured on the outer surface of the cylinder liner along the vertical axis of the cylinder is greater than the length of the scavenge air ports measured on the inner surface of the cylinder liner along the vertical axis of the cylinder.

[0016] In the case of large engines, the piston is preferably connected with the crankshaft in the crankcase through a piston rod.

Description of the Drawings

[0017] The invention will be now presented in more detail in the preferred embodiment, with reference to the enclosed drawings, in which:

Fig. 1

presents schematically the substantial elements of a two-stroke engine according to the invention, where 1 - cylinder, 2 - head, 3 - exhaust valve, 4 - cylinder liner, 5 - piston, 6 - piston rod, 7 - engine case, 8 - scavenge air space, 9 - crankcase space, 10 - oil space, 11 - seal, 12 - outflow, 13 - compression rings, whereas "A" symbol - indicates the portion of the engine comprising substantial elements of the invention at a moment when the scavenge ports remain closed;

fig.2

illustrates in more detail the portion of the engine marked in fig. 1 with "A" symbol, comprising primary elements of the invention at a moment when the scavenge ports remain closed, where 14 - ring, 15 - scavenge air ports, 16, 18, 19 and 25 - seal, 17 - flange, 20 - inlet tube, 21 - hydraulic actuator, 22 - tube from the hydraulic actuator, 23 - outlet, 24 - groove, 25 - seal,

fig. 3

shows the moment of transition between the full closure and the full opening of the scavenge ports, whereas

fig. 4

presents the arrangement of elements during charge exchange in the cylinder.

Detailed Description of the Invention

[0018] Preferred embodiment of the invention is described below in detail. This embodiment serves only as an illustration and does not limit the scope of the present invention.

[0019] Fig. 1 represents one of typically several cylinders of a two-stroke diesel engine with uniflow scavenging. A cylinder 1 consisting of a head 2, wherein an exhaust valve 3 is mounted and a cylinder liner 4, wherein a piston 5 is moving. The piston 5 is provided with compression rings 13, and is connected by a piston rod 6 with a crosshead (not shown) which crosshead is connected, from its side, with a connecting rod (not shown) transferring the loads on a crankshaft (not shown). The cylinder 1 is mounted in an engine case 7 in such a way that it creates a scavenge air space 8 isolated from a crankcase space 9, and an oil space 10, preferably isolated from the scavenge air space 8 as shown in fig. 2, as well as, via a seal 11 cooperating with the piston rod 6, isolated from the crankcase space 9, which allows to preferably separate more contaminated oil lubricating the cylinder liner 4 from the oil in the crankcase space 9 and to output of the excess of cylinder oil scraped off by the compression rings 13 through an outflow 12 into a purification system.

[0020] Fig. 2 presents the portion of a technical embodiment of the invention marked in fig. 1 with "A" symbol, comprising primary elements of the invention in the position realising the separation of the scavenge air space 8 from the oil space 10. A ring 14 closing the scavenge air ports 15 is mounted on the outer surface of the cylinder liner 4 in a way enabling to move it along this surface and sealed with it with a seal 16. On the other side, the ring 14 cooperates with the a 17 and is sealed with said surface using seals 18 and 19 in such a way that after supplying the air under pressure through a tube 20, the vapour creates an air spring. The ring 14 is being held in the upper position by several hydraulic actuators 21 to which the oil is supplied under pressure via tubes 22. The flange 17 is mounted on a cylindrical outlet 23, which outlet is an element of the engine case 7.

[0021] Fig. 3 illustrates the arrangement of detail "A" elements during opening of the scavenge air ports 15. The valve, controlled by the timing system, supplying the oil under pressure into the tubes 22, is being closed while the draining valve of the hydraulic oil is simultaneously being opened, allowing its outflow via the tubes 22 from the hydraulic actuators 21. Compressed air between the flange 17 and the ring 14 induces the downwards movement of the ring 14, opening the scavenge air ports 15 remaining covered from the inner side of the cylinder liner by the piston in the given moment. The groove 24 in the outer surface of the cylinder liner 4 has been intentionally shaped in such a way that, in a certain range of the ring's 14 motion, it enables to purge the scavenge air port 15 surface with the air from the scavenge air space 8 into the oil space 10 and therefore removing from that surface the oil excess accumulated when the piston 5 remains above the scavenge air ports 15, which preferably prevents the passage of that oil excess above the piston 5.

[0022] Fig. 4 presents the portion marked in fig. 1 with "A" symbol when the charge exchange is realised in the cylinder 1. Both the piston 5 and the ring 14 are in the bottom position, uncovering the entire space of scavenge air ports 15 and enabling, therefore, the passage of air from the scavenge air space 8 above the piston 5, into the inside of the cylinder liner 4, and the realisation of charge exchange. The scavenge air space 8 is separated from the oil space 10 by the piston 5, sealed with the cylinder liner 4 inner surface using compression rings 13, and by a portion of the cylinder liner 4, sealed with the ring 14 with the seal 25 and the flange 17 mounted on the cylindrical outlet 23 and sealed with the ring 14 with seals 18 and 19.

Claims

1. A two-stroke engine, especially high power marine diesel engine, with uniflow scavenging, having at least one cylinder (1) mounted in an engine case (7), comprising a cylinder head (2) and liner (4) and provided with an exhaust valve (3), preferably situated in the head (2), a piston (5) situated in said cylinder, optionally provided with a compression ring or rings (13), connected with a crankshaft in a crankcase (9) and having the possibility to move in the cylinder (1) in a reciprocating motion, characterised in that outside the cylinder liner (4), between the engine case (7) and the cylinder liner (4), a scavenge air space (8) is located, the cylinder liner (4) has at least one scavenge air port (15), leading from the scavenge air space (8) into the inside of the cylinder liner (4), provided with closing means (14), enabling opening and closing of the port (15), wherein the bottom port of the cylinder liner (4) is tightly separated from the scavenge air space (8).

2. The engine according to claim 1, characterised in that the cylinder liner (4) has one or more scavenge air ports (15), leading from the scavenge air space (8) to the inside of the cylinder liner (4), preferably arranged symmetrically about the perimeter of the cylinder liner (4), wherein each port (15) is provided with the closing means (14) enabling opening and closing of ports (15).

3. The engine according to claim 1 or 2, characterised in that the scavenge air space (8) is created by the proper shaping of the engine case (7) as a cavity between the engine case (7) and the cylinder liner (4).

4. The engine according to any one of the preceding claims characterised in that the closing means (14) are constituted by a ring (14) mounted on the outer surface of the cylinder liner (4) in a way enabling to move it along this surface, said ring (14) preferably sealed with a seal (16) with the surface of the cylinder liner (4).

5. The engine according to claim 4, characterised in that the ring (14) is situated in a flange (17) mounted on an outlet (23) of the engine case (7), wherein an empty space is located between the flange (17) and the ring (14), said empty space connected via a hydraulic hose (20) with a source of compressed air and preferably sealed with seals (18, 19) above and below the hydraulic house (20) inlet.

6. The engine according to claim 4 or 5, characterised in that the ring (14) is supported by at least one hydraulic actuator (21), preferably the ring (14) is supported from the bottom by at least one hydraulic actuator (21).

7. The engine according to any one of the preceding claims, characterised in that the scavenge air space (8) is tightly separated from the crankcase space (9).

8. The engine according to any one of the preceding claims, characterised in that between the engine case (7) and the cylinder liner (4), below scavenge air ports (15), an oil space (10) is located, the oil space (10) being connected with a part of the cylinder (1) inner space located under the piston (5), wherein the oil space (10) is tightly isolated from the crankcase space (9) and preferably also tightly isolated from the scavenge air space (8).

9. The engine according to any one of the preceding claims from 4 to 8, characterised in that the length of scavenge air ports (15) measured on the outer surface of the cylinder liner (4) along the vertical axis of the cylinder is preferably greater than the height of the ring (14), whereas the position of the ring (14) in relation to the cylinder liner (4) is selected so that an air purge from the space (8) through the port (15) into the oil space (10) is possible in a certain range of the ring's (14) motion along the cylinder liner (4).

10. The engine according to claim 9, characterised in that the scavenge air ports (15) are connected with grooves (24) in the outer surface of the cylinder liner (4), due to which the length of scavenge air ports (15) measured on the outer surface of the cylinder liner (4) along the vertical axis of the cylinder is greater than the length of scavenge air ports (15) measured on the inner surface of the cylinder liner (4) along the vertical axis of the cylinder.

11. The engine according to any one of the preceding claims, characterised in that the piston (5) is connected with the crankshaft in the crankcase (9) through a piston rod (6).

Drawing