The present invention relates to a piston engine according to the preamble of claim 1 . The invention also concerns a cylinder liner for a piston engine in ac- cordance with the preamble of the other independent claim.

Background of the invention

Because of the high temperature in the combustion chambers of piston engines, the cylinder liners need to be provided with cooling arrangements. Ex- cept for very small engines, the cooling arrangements involve the use of cooling liquid that is circulated in cooling channels around the cylinder liners. In many engine constructions, the cooling channels are located at least partly inside the engine block. This makes the construction of the engine block more complicated and expensive. In some cases, the cooling channels are located partly in the cylinder heads. Also the cylinder heads are expensive components, and if the cylinder heads need to be provided with cooling channels for cooling the cylinder liners, the costs of the cylinder heads are increased even more. Another problem with many existing cylinder liner cooling arrangements is that in case of the failure of the cylinder head gasket, the combustion gases from the cylinder can mix with the cooling water.

Summary of the invention

An object of the present invention is to provide an improved piston engine, in which the above mentioned problems are reduced or avoided. The characteriz- ing features of the piston engine according to the present invention are given in the characterizing part of claim 1 . Another object of the invention is to provide an improved cylinder liner for a piston engine.

An engine according to the invention comprises an engine block, at least one cylinder liner that is arranged partly inside the engine block, a cylinder head for closing the upper end of the cylinder liner, and a cooling jacket that is arranged around the cylinder liner and delimits together with the cylinder liner a cooling channel. Each cylinder of the engine is provided with only one cooling channel for cooling the cylinder liner, and the whole cooling channel is arranged above the engine block. A cylinder liner according to the invention comprises a first support surface that can be arranged against an upper surface of an engine block for carrying forces in the axial direction of the cylinder liner, a second support surface that is located below the first support surface in the axial direction of the cylinder liner for supporting the cylinder liner in the radial direction, and a third support sur- face that is arranged below the second support surface in the axial direction of the cylinder liner for supporting the cylinder liner in the radial direction. The cylinder liner is provided with a single cooling recess encircling the outer circumference of the cylinder liner, and the cooling recess is located above the first support surface in the axial direction of the cylinder liner. Since each of the cylinders of the engine is provided with only one cooling channel, the cooling channel can be located exclusively around the upper end of the cylinder liner outside the engine block and the cylinder liner. The complexity of the engine block and the cylinder liner can thus be reduced. Also, the risk of mixing of the combustion gases and the cooling water in case of a cyl- inder head gasket failure can be eliminated. The risk of cooling liquid leakages inside the engine block is also eliminated. The invention enables increased modularization, which makes the assembling and servicing of the engine easier. An engine according to the invention has lower production and operating costs and better reliability. The cooling channel can be located so that it is around the uppermost piston ring when the piston is at top dead center. Effective cooling of this point is critical for ensuring reliable functioning of the piston rings.

According to an embodiment of the invention, the outer circumference of the cylinder liner is provided with an annular recess below the cooling channel for reducing thermal stresses. When a single cooling channel is used, thermal stresses in the cylinder liner increase. With the recess below the cooling channel, the thermal stresses can be reduced.

According to an embodiment of the invention, the recess is located at least partly below the first support surface. The recess can be merged with the first support surface. The recess can also be located above the second support surface and merged with it.

According to an embodiment of the invention, the cross-section of the recess comprises a first portion that is a sector of a circle. The radius of the circle is preferably 30-60 % of the thickness of the wall of the cylinder liner. According to another embodiment of the invention, the recess comprises a second portion, where the wall of the recess is at an angle a relative to the longitudinal center line of the cylinder liner. The angle is preferably 15-50 degrees, more preferably 25-35 degrees. According to another embodiment of the invention, the recess comprises a third portion that is a sector of a circle and has a smaller radius than the first portion of the recess. According to another embodiment, the third portion of the recess is arranged between the first support surface and the first portion of the recess.

Brief description of the drawings

Embodiments of the invention are described below in more detail with reference to the accompanying drawings, in which

Fig. 1 shows a cross-sectional view of one cylinder of a piston engine according to an embodiment of the invention, Fig. 2 shows a cross-sectional view of the cylinder liner of figure 1 ,

Fig. 3 shows a detail of figure 2,

Fig. 4 shows a cross-sectional view of the upper part of the cylinder together with a cooling jacket,

Fig. 5 shows a cooling jacket of the engine, and Fig. 6 shows a cross-sectional view of the cooling jacket of figure 5. Description of embodiments of the invention

In figure 1 is shown one cylinder 1 of a piston engine according to an embodiment of the invention. The engine is a large internal combustion engine, such as a main or an auxiliary engine of a ship or an engine that is used at a power plant for producing electricity. The engine can comprise any reasonable number of cylinders 1 , which can be arranged, for instance, in line or in a V- configuration. Each cylinder 1 is provided with a cylinder liner 2 (best seen in Fig. 2), which is arranged partly inside an engine block 3. The upper end of the cylinder liner 2 is above the engine block 3. The term 'upper' means here the cylinder head end of the cylinder 1 . Each cylinder 1 of the engine is provided with an own cylinder head 4, which is provided with gas exchange valves and ducts. The gas exchange ducts 5, 6 and the gas exchange valves (not shown) can be of conventional design and are therefore not described in more detail here. There is a reciprocating piston 9 inside the cylinder 1 . The piston 9 is provided with a plurality of piston rings 9a. Also the piston 9 can be of conventional design.

For cooling the cylinder liner 2, the engine is provided with a cooling jacket 10. The cooling jacket 10 is arranged around the upper end of the cylinder liner 2. The cooling jacket 10 is completely above the engine block 3 and below the cylinder head 4. Together with an annular cooling recess 1 1 on the outer circumference of the cylinder liner 2, the cooling jacket 10 defines a cooling channel 12 between the cylinder liner 2 and the cooling jacket 10. The cooling channel 12 extends in the axial direction of the cylinder liner 2 over the area where the piston rings 9a are located when the piston 9 is at top dead center. This is the most critical point in regard to the cooling of the cylinder liner 2. The cross-section of the cooling recess 1 1 comprises a flat middle portion 1 1 a and edge portions 1 1 b, 1 1 c. The depth of the upper edge portion 1 1 b decreases towards the upper end of the recess 1 1 and the depth of the lower edge portion 1 1 c decreases towards the lower end of the recess 1 1 . The cooling recess 1 1 is thus substantially U-shaped. The shape of the cooling channel 12 enables effective cooling of the cylinder liner 2 but keeps the thermal stresses in the cylinder liner 2 low. Seals 13, 14 are provided at the upper and the lower ends of the cooling jacket 10 between the cylinder liner 2 and the cooling jacket 10 for preventing leakages from the cooling channel 12. Since the cooling channel 12 is completely above the engine block 3 and below the cylinder head 4, expensive cooling channels in the engine block 3 are not needed. The risk of cooling liquid leakages inside the engine block 3 is also eliminated and pressure testing of the engine block 3 is not needed.

The cylinder liner 2 is provided with three support surfaces 15, 16, 17 for supporting the cylinder liner 2 against the engine block 3. A first support surface 15 is arranged in the upper part of the cylinder liner 2 and it supports the cylinder liner 2 against the engine block 3 in the axial direction, i.e. in the direction of the longitudinal axis 18 of the cylinder liner 2. The first support surface 15 is an elbow that can be arranged against the upper surface of the engine block 3. A second support surface 16 is arranged in the upper part of the cylinder liner 2 below the first support surface 15. The second support surface 16 supports the cylinder liner 2 against the engine block 3 in the radial direction of the cylinder liner 2. The second support surface 16 is a portion of the cylinder liner 2 having a greater outer diameter than the basic outer diameter of the cylinder liner 2. A third support surface 17 is located in the lower part of the cylinder liner 2. Also the third support surface 17 carries radial forces.

Because the engine is provided with a single cooling channel 12 around the upper end of the cylinder liner 2, the thermal stresses of the cylinder liner 2 are larger than in conventional designs, where there are several cooling channels around the cylinder liner. To reduce the thermal stresses, the cylinder liner 2 is provided with an annular recess 19 that is arranged below the cooling recess 1 1 of the cylinder liner 2. Figure 3 shows an enlarged view of the recess 19. In the embodiment of the figures, the recess 19 is located above the second support surface 16. The recess 1 1 is also partly below the first support surface 15. The recess 19 encircles the whole cylinder liner 2. The recess 19 is formed of a first portion 19a, a second portion 19b, and a third portion 19c. When seeing the cross-section of the recess 19, the first portion 19a of the recess 19 is a sector of a circle. The radius of the first portion 19a of the recess is preferably 30-60 % of the thickness of the wall of the cylinder liner 2, more preferably 35-50 % of the thickness of the wall of the cylinder liner 2. In the embodiment of the figures, the radius is approximately 40 % of the thickness of the wall of the cylinder liner 2. The thickness of the wall refers to the thickness outside of the support surfaces 15, 16, 17 or other reinforced areas of the cylinder liner 2. It is thus the thickness of the main part of the cylinder liner 2 between the second support surface 16 and the third support surface 17. The width of the sector that forms the first portion 19a is preferably in the range of 90 to 130 degrees. In the embodiment of the figures, the sector is approximately 1 10 de- grees. The center 25 of the radius of the first, circular portion 19a of the recess 19 is located in the axial direction of the cylinder liner 2 at such a distance from the first support surface 15, which is less than the radius of the first portion 19a. Therefore, part of the first portion 19a of the recess 19 is located above the first support surface 15. In the radial direction of the cylinder liner 2, the center 25 of the radius is located inwards from the second support surface 16. The second portion 19b of the recess 19 is a straight cut that is merged with the first portion 19a of the recess 19. The second portion 19b is also merged with the second support surface 16 of the cylinder liner 2. The second portion 19b of the recess is at an angle a relative to the longitudinal axis 18 of the cylinder liner 2. Angle a is preferably 15 to 50 degrees, more preferably 25-35 degrees. In the embodiment of the figures, the angle is approximately 30 degrees. Also the third portion 19c of the recess 19 is a sector of a circle. The radius of the third portion 19c is smaller than the radius of the first portion 19a. The radius of the third portion 19c is preferably 5-15 % of the thickness of the wall of the cylinder liner 2. The width of the sector that forms the third portion 19c is preferably in the range of 30 to 60 degrees. The third portion 19c of the recess 19 is merged with the first support surface 15 of the cylinder liner 2 and with the first portion 19a of the recess 19. In the axial direction of the cylinder liner 2, the third portion 19c is above the first support surface 15. In the radial direction of the cylinder liner 2, the center 26 of the radius of the third portion 19c of the recess 19 is located outwards from the center 25 of the radius of the first portion 19a and inwards from the first support surface 15.

The construction of the cooling jacket 10 is best seen in figures 5 and 6. The cooling jacket 10 can be manufactured, for instance, by casting. The cooling jacket 10 is provided with a plurality of brackets 20, which can be used for attaching the cooling jacket 10 to the engine block 3. Since the cooling jacket 10 is fastened directly to the engine block 3, the cylinder liner 2 can be removed without removing the cooling jacket 10. This makes servicing of the cylinder liner 2 easier. The cooling jacket 10 is provided with an inlet 21 for introducing the cooling liquid into the cooling channel 12 and for draining the cooling channel 12 when needed. An outlet 22 is provided for discharging the cooling liquid from the cooling channel 12. From the outlet 22 the cooling liquid can be introduced into the cooling channels of the cylinder head 4. Also an inlet pipe 23 for the cooling liquid is integrated into the cooling jacket 10. In figure 4, the cooling jacket 10 can be seen in connection with the cylinder liner 2 and the cylinder head 4. Figure 4 also shows a gasket 24 between the cylinder liner 2 and the cylinder head 4. As it can be seen, the construction of the engine prevents mixing of the combustion gases and the cooling liquid even in case some of the seals 13, 14, 24 is leaking.

It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims.