The present invention relates to a cylinder liner in accordance with the preamble of claim 1 . The invention also concerns an anti-polishing ring for a cylinder liner as defined in the preamble of the other independent claim.

Background of the invention

Large internal combustion engines, such as ship and power plant engines, are often provided with means for monitoring cylinder pressures. Cylinder pressure can be measured either directly using a pressure sensor that is exposed to the pressure inside a cylinder, or indirectly using strain gages, force sensors or similar devices monitoring deformation or displacement of a component of the engine. If direct pressure measuring is used, the pressure sensors are typically arranged in the cylinder heads of the engine. A disadvantage of direct pres- sure monitoring is that the lifetime of the pressure sensors is limited due to the high temperatures and the vibrations occurring in the cylinder heads.

Summary of the invention

An object of the present invention is to provide an improved cylinder liner for forming a cylinder of a piston engine, which comprises a piston that is configured to move in the cylinder in a reciprocating manner between bottom dead center and top dead center, the piston comprising at least one piston ring. The characterizing features of the cylinder liner according to the invention are given in the characterizing part of claim 1 . Another object of the invention is to pro- vide an improved anti-polishing ring for a cylinder liner. The characterizing features of the anti-polishing ring are given in the characterizing part of the other independent claim.

The wall of the cylinder liner according to the invention comprises a through hole, which is configured to allow transmission of pressure from the cylinder to a pressure sensor and arranged in the wall of the cylinder liner at such a height that when the cylinder liner is mounted in an engine for forming a cylinder and a piston inside the cylinder is at top dead center, the hole opens inside the cylinder at a location that is above all the piston rings of the piston.

With the cylinder liner according to the invention, cylinder pressure can be measured directly via the wall of the cylinder liner. Temperature and vibration levels in the cylinder liner are lower than in a cylinder head. The lifetime of pressure sensors is thus increased.

According to an embodiment of the invention, the hole is configured to receive a pressure sensor. The diameter of the hole can increase in steps towards the outer surface of the cylinder liner.

According to an embodiment of the invention, the upper end of the cylinder liner comprises a recess for receiving an anti-polishing ring.

According to an embodiment of the invention, the hole of the cylinder liner opens to the area of the recess. This allows a pressure sensor to be arranged behind an anti-polishing ring, which protects the pressure sensor from heat.

In an anti-polishing ring according to the invention, the outer surface of the anti-polishing ring comprises a groove, which extends in the axial direction from the upper end of the anti-polishing ring towards the lower end and is configured to allow transmission of pressure from the cylinder to the through hole of the cylinder liner.

A piston engine according to the invention comprises at least one cylinder and a piston that is configured to move in the cylinder in a reciprocating manner between bottom dead center and top dead center, the piston comprising at least one piston ring. The cylinder is formed by a cylinder liner defined above. According to an embodiment of the invention, the engine comprises a cylinder liner having at the upper end a recess for accommodating an anti-polishing ring and an anti-polishing ring defined above. 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 schematically a cylinder pressure monitoring arrangement of a piston engine,

Fig. 2 shows a cylinder liner of a piston engine according to an embodiment of the invention, and

Fig. 3 shows a cylinder liner of a piston engine according to another embodiment of the invention.

Description of embodiments of the invention

In figure 1 is shown schematically an internal combustion engine 1 with a cylinder pressure monitoring arrangement. The engine 1 is a large piston 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 cylinder bore of the engine 1 is at least 150 mm. In figure 1 , four cylinders 2 are shown. However, the engine 1 can comprise any reasonable number of cylinders 2, which can be arranged in line or in a V-configuration. For monitoring pressures in the cylinders 2, each cylinder of the engine 1 is provided with a pressure sensor 3. The pressure sensors 3 are arranged to measure the cylinder pressures directly. Each pressure sensor 3 is thus exposed to the cylinder pressure in the respective cylinder 2. Each pressure sensor 3 is connected to a control unit 4.

Figure 2 shows a simplified cross-sectional view of a cylinder liner 5 according to an embodiment of the invention. The cylinder liner 5 is arranged at least partly inside an engine block and forms one of the cylinders 2 of the engine 1 . A piston 6 is arranged inside the cylinder 2. The piston 6 is connected via a connecting rod 8 to a crankshaft (not shown). The piston 6 is configured to move in a reciprocating manner between bottom dead center and top dead center. A cylinder head 7 closes the upper end of the cylinder 2. The expres- sion "upper end" refers here to the end that is farther from the crankshaft, i.e. the top dead center end of the cylinder 2. The cylinder 2 does not need to be arranged in a vertical position. In figure 2, the piston 6 is shown at top dead center. The piston 6 is provided with piston rings 10. In the example of figure 2, the piston 6 comprises three piston rings 10. However, the number of piston rings 10 could also be different. The main functions of the piston rings 10 are sealing of the combustion chamber for preventing escaping of combustion gases, heat transfer from the piston 6 to the cylinder liner 5 and regulation of the oil film on the inner surface of the cylinder liner 5. The outer diameter of the piston 6 above the piston rings 10 is smaller than the inner diameter of the cylinder liner 5. In a gap 14 between the piston 6 and the cylinder liner 5 above the piston rings 10, the pressure is thus substantially the same as above the piston 6.

For monitoring pressure inside the cylinder 2, the wall of the cylinder liner 5 is provided with a through hole 9. The hole 9 is arranged at such a height that when the cylinder liner 5 is arranged in the engine 1 for forming the cylinder 2 and the piston 6 is at top dead center, the hole 9 opens onto the inner surface of the cylinder liner 5 at a location, which is above all the piston rings 10 of the piston 6. The cylinder pressure is thus transmitted to the hole 9 regardless of the position of the piston 6. The diameter of the hole 9 increases in steps towards the outer surface of the cylinder liner 5. The innermost end of the hole has thus a smaller diameter than the outermost end of the hole 9. The outer- most end of the hole 9 can be configured to receive a pressure sensor 3. The innermost end of the hole 9 can function as a conduit transmitting pressure from the cylinder 2 to the pressure sensor 3. The hole 9 can be provided with a thread for attaching the pressure sensor 3 to the cylinder liner 5. By arranging the pressure sensor 3 in the cylinder liner 5, the pressure sensor 3 is not sub- jected to as high temperatures and vibration levels as a pressure sensor that is arranged in a cylinder head 7.

Figure 3 shows another embodiment of the invention. The cylinder liner 5 of figure 2 differs from the cylinder liner 5 of figure 2 in that it is provided with a recess 13 for receiving an anti-polishing ring 1 1 . The recess 13 is located at the upper end of the cylinder liner 13. The anti-polishing ring 1 1 is a sleeve-like element, which is used for removing carbon deposits from a piston 6. The inner diameter of the anti-polishing ring 1 1 is smaller than the inner diameter of the cylinder liner 5, but larger than the outer diameter of the piston 6 in the area above the piston rings 10. The lower end of the anti-polishing ring 1 1 is at such a height that when the piston 6 is at top dead center, the lower end of the anti- polishing ring 1 1 is above all the piston rings 10 of the piston 6, but the upper end of the piston 6 is above the lower end of the anti-polishing ring 1 1 . The anti-polishing ring 1 1 can thus scrape carbon deposits from a piston crown above the piston rings 10.

The hole 9 of the cylinder liner 5 is arranged at the area of the recess 13. The hole 9 is thus behind the anti-polishing ring 1 1 . For allowing transmission of pressure from the cylinder 2 to the hole 9 of the cylinder liner 5, the anti- polishing ring 1 1 is provided with a groove 12. The groove 12 is arranged on the outer surface of the anti-polishing ring 1 1 . The groove 12 extends from the upper end of the anti-polishing ring 1 1 to such a location that fluid communica- tion is established between the cylinder 2 and the hole 9 of the cylinder liner 5. In the embodiment of figure 3, the groove 12 is vertical. The anti-polishing ring 1 1 is not in contact with the cylinder head 7, but a small gap 15 is formed between the cylinder head 7 and the anti-polishing ring 1 1 . Cylinder pressure can thus be transmitted through the gap to the groove 12. By locating the hole 9 of the cylinder liner 5 behind the anti-polishing ring 1 1 , pressure can be transmitted to a pressure sensor 3 but the pressure sensor 3 is protected from the most extreme heat. The anti-polishing ring 1 1 can be provided with a locking pin and the cylinder liner 5 or the cylinder head 7 with a cooperating recess for keeping the groove 12 of the anti-polishing ring 1 1 aligned with the hole 9 of the cylinder liner 5.

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.