Technical field of the invention

The present invention relates to a cooling arrangement for a reciprocating piston of an internal combustion engine according to the preamble of claim 1. The invention also concerns a cylinder liner for a piston engine in accordance with the preamble of the other independent claim.

Background of the invention

Piston cooling in large medium speed engines is typically arranged through drillings in the crankshaft, connecting rods and gudgeon pins. In high speed engines, piston cooling is often implemented by utilizing oil jets. Jet cooling is advantageous also in medium speed engines, since it omits the need for oil drillings in the crank gear components and allows thus higher loading and lower manufacturing costs. In a typical jet cooling arrangement, the cooling arrangement is provided with a separate oil system for piston cooling. Oil injection nozzles for spraying the cooling oil are arranged inside the engine block. Through the injection nozzles, the oil is sprayed onto the bottom side of each piston. The piston skirt is provided with a space for receiving the oil. Drillings from the oil receiving space lead into a piston crown cooling gallery. A drawback of the present piston cooling arrangements is that the spraying distance is relatively long, which has an adverse effect on the functioning of the cooling system. The cooling arrangements may also be challenging to implement, since the space inside the engine block and especially below the cylinders is limited because of the moving connecting rods and counterweights.

Summary of the invention

An object of the present invention is to provide an improved cooling arrangement for a reciprocating piston of an internal combustion engine. The piston is arranged inside a cylinder liner of the engine and comprises a piston crown and a piston skirt. The characterizing features of the piston cooling arrangement according to the present invention are given in the characterizing part of claim 1. Another object of the invention is to pro- vide an improved cylinder liner for a piston engine. The characterizing features of the cylinder liner are given in the characterizing part of the other independent claim.

The cooling arrangement according to the invention comprises a cooling oil gallery that is arranged at least partly inside the piston crown, a cooling medium injector for injecting cooling oil into a space between the piston and the cylinder liner below the piston crown, an opening that is arranged on the bottom surface of the cooling oil gallery for introducing the cooling oil from the space below the piston crown into the cooling oil gallery, and a cooling medium duct for supplying the cooling oil to the cooling medium injector. The cooling medium injector is arranged inside the cylinder at such a height that the tip of the cooling medium injector is above the center axis of the gudgeon pin of the piston when the piston is at bottom dead center.

Since the cooling medium injector is arranged close to the bottom surface of the cooling oil gallery, the spraying distance is short and the cooling effect of the cooling oil is improved.

According to an embodiment of the invention, the tip of the injector is above the whole gudgeon pin when the piston is at bottom dead center.

According to another embodiment of the invention, the piston is a box-type piston, where the piston skirt is open in the direction of the gudgeon pin. According to another embodiment of the invention, the cooling medium injector is arranged to protrude into the cylinder in the direction of the gudgeon pin. With a box-type piston, the cooling medium injector can be fastened directly to the cylinder liner and located close to the bottom surface of the cooling oil gallery.

According to an embodiment of the invention, part of the cooling medium duct is arranged inside the wall of the cylinder liner in parallel with the longitudinal axis of the cylinder liner. According to another embodiment of the invention, the lower end surface of the cylinder liner is provided with an opening for introducing the cooling oil into the cooling medium duct inside the wall of the cylinder liner. According to another embodiment of the invention, the arrangement comprises a drilling in the engine block for in- traducing the cooling oil into the cooling medium duct inside the wall of the cylinder liner. If the cooling medium duct is arranged inside the wall of the cylinder liner, the need for separate pipes can be eliminated. By arranging the drilling in the lower radial support of the cylinder liner, the cooling oil can be used also as dampening medium for reducing wear and fretting of the contact surfaces between the engine block and the cylinder liner.

According to an embodiment of the invention, the cylinder liner is provided with an opening on its outer surface, which opening is arranged against a supporting surface of the engine block for introducing cooling oil into the cooling medium duct. According to another embodiment of the invention, the supporting surface of the engine block is arranged to support the lower end of the cylinder liner in the radial direction.

According to still another embodiment of the invention, the arrangement comprises a volume between the engine block and the cylinder liner, from which volume the cooling oil is introduced to the cooling medium injector. The cooling oil can thus also be used as dampening and cooling medium for the cylinder liner. Effective cooling of the cylinder liner can thus be achieved and because of the dampening effect, wear and fretting between the engine block and cylinder liner surfaces is also reduced.

The cylinder liner according to the invention comprises a cooling medium duct that is arranged inside the wall of the cylinder liner and an opening that is arranged on the inner surface of the cylinder liner and in fluid communication with the cooling medium duct for supplying cooling oil to a cooling medium injector and further to a piston of the engine. The outer surface of the cylinder liner is provided with an opening for introducing cooling oil into the cooling medium duct, the opening being arrangeable against a surface that is arranged in an engine block for supporting the lower end of the cylinder liner in the radial direction. With the cylinder liner according to the invention, cooling oil can be introduced through the lower end of the cylinder liner to a cooling medium injector, which can be located close to the piston crown. According to an embodiment of the invention, the opening on the inner surface of the cylinder liner is at such a height that the tip of the cooling medium injector can be arranged above the center axis of the gudgeon pin of the piston when the piston is at bottom dead center.

According to an embodiment of the invention, at least part of the cooling medium duct inside the wall of the cylinder liner is parallel with the longitudinal axis of the cylinder liner.

Brief description of the drawings

Fig. 1 shows a piston cooling arrangement according to an embodiment of the invention.

Fig. 2 shows a cross-sectional view of Fig. 1 taken along line A-A.

Fig. 3 shows a piston cooling arrangement according to another embodiment of the in- vention.

Fig. 4 shows a piston cooling arrangement according to still another embodiment of the invention.

Detailed description of the invention

Embodiments of the invention are now described in more detail with reference to the accompanying drawings.

In figure 1 is shown a cooling arrangement for a reciprocating piston 2 of an internal combustion engine according to an embodiment of the invention. In figure 1, the piston 2 is at bottom dead center. The engine where the piston cooling arrangement is used is a large medium or high speed internal combustion engine. The engine can be used, for instance, as a main or an auxiliary engine of a ship, or at a power plant for producing electricity. The engine can be provided with any reasonable number of cylinders, which can be arranged for example in line or in a V-configuration. Each cylinder of the engine is provided with a cylinder liner 1. The cylinder liner 1 is arranged in an engine block 12. The upper end of the cylinder liner 1 is provided with a collar 18, which rests against the upper surface of the engine block 12. The engine block 12 comprises a pro- trusion 19, which extends towards the longitudinal axis of the cylinder liner 1 and supports the upper end of the cylinder liner 1 in the radial direction. A second protrusion 13 forms a lower radial support for supporting the lower end of the cylinder liner 1 in the radial direction. The piston 2 is arranged inside the cylinder. The piston comprises a piston crown 2a and a piston skirt 2b. The piston 2 is connected to a connecting rod 3 with a gudgeon pin 4. The piston 2 is a so-called box-type piston, where the piston skirt 2b is open in the direction of the gudgeon pin 4. An empty space 10 is thus formed below the piston crown 2a between the cylinder liner 1 and the piston 2 at both ends of the gudgeon pin 4.

For cooling the piston 2, the engine is provided with a cooling arrangement. The cooling arrangement is used for introducing cooling oil onto the bottom surface of the piston 2 and further into a cooling oil gallery 7 that is arranged at the upper end of the piston 2 and at least partly inside the piston crown 2a. The cooling arrangement comprises a cooling medium injector 5 that is arranged inside the cylinder. A cooling oil pump (not shown) is connected with a cooling medium duct 6 to the cooling medium injector 5 for supplying the cooling oil to the cooling medium injector 5. The cooling medium injector 5 is located at such a height inside the cylinder that when the piston 2 is at bottom dead center, the tip 5a of the cooling medium injector 5 is above the center axis of the gudgeon pin 4. In the embodiment of figure 1, the tip 5a of the cooling medium injector 5 is above the whole gudgeon pin 4. Since the cooling medium injector 5 is located close to the bottom surface of the cooling oil gallery 7, short spraying distance and effective cooling is enabled. The cooling oil is injected into the space 10 between the cylinder liner 1 and the piston 2 below the piston crown 2a. The cooling medium injector 5 is arranged to inject the cooling oil towards the upper part of the piston 2. From the space 10 below the piston crown 2a, the cooling oil can flow into the cooling oil gallery 7 through an opening 8 that is arranged in the bottom of the cooling oil gallery 7.

In the embodiment of the figure 1, the cooling medium duct 6 is arranged partly inside the wall of the cylinder liner 1. With this arrangement, the need for separate pipes can be reduced. The cooling medium injector 5 is arranged to protrude from the wall of the cylinder liner 1 into the cylinder in the direction of the gudgeon pin 4. However, it is also possible that the cooling medium injector 5 protrudes into the cylinder in a differ- ent angle. The cooling medium injector 5 can also be offset from the center line of the gudgeon pin 4. The cooling medium injector 5 is L-shaped, and the open end of the cooling medium injector 5 points towards the cylinder head. The cooling oil spray is thus directed at the bottom surface of the cooling oil gallery 7. The lower end of the cylinder liner 1 is provided with an opening 9 for introducing the cooling oil into the cooling medium duct 6 inside the wall of the cylinder liner 1. The opening 9 is on an end surface of the cylinder liner 1.

In figures 1 and 2 there is shown also a second cooling medium injector 5' . A second cooling medium duct 6' is arranged partly inside the wall of the cylinder liner 1 for connecting the second cooling medium injector 5' to the cooling oil pump. The cooling oil is introduced into the second cooling medium duct 6' inside the wall of cylinder liner 1 through a drilling 11 in the lower radial support 13 of the cylinder liner 1. The cylinder liner 1 is provided with an opening 17, which is arranged on the outer surface of the cylinder liner 1. The opening 17 is arranged against the surface of the engine block, which surface supports the lower end of the cylinder liner 1 in the radial direction. The opening 17 is aligned with the drilling 11 of the engine block 12. A seal 21 is arranged between the cylinder liner 1 and the engine block 12 around the opening 17. Through the opening 17, the cooling oil can be introduced into the cooling medium duct 6' inside the wall of the cylinder liner 1. By arranging the drilling 11 in the protrusion 13, which supports the cylinder liner 1, the cooling oil can be used also as a dampening medium for reducing wear and fretting of the contact surfaces between the engine block 12 and the cylinder liner 1. The inner surface of the cylinder liner 1 is provided with an opening 20, which is in fluid communication with the cooling medium duct 6, 6' . Through the opening 20, the cooling oil can be supplied to the cooling medium injector 5' . The opening 20 is located at such a height that the tip 5a' of the cooling medium injector 5' can be arranged above the center axis 4a of the gudgeon pin 4 when the piston 2 is at bottom dead center. Although two different cooling arrangements are shown in figure 1, each cylinder of the engine is preferably provided with identical arrangements at both ends of the gudgeon pin 4.

In the embodiment of figure 3, the cooling medium duct 6 for introducing the cooling oil to the cooling medium injector 5 is arranged partly inside the engine block 12. The cooling oil is introduced in the cooling medium duct 6 into a volume 14 between the engine block 12 and the cylinder liner 1. The cylinder liner 1 is provided with a drilling 16 for introducing the cooling oil from the volume 14 between the engine block 12 and the cylinder liner 1 into the cooling medium injector 5. By arranging the cooling oil supply via the volume 14 between the engine block 12 and the cylinder liner 1, the cooling oil can be used also as a dampening medium for reducing wear and fretting of the contact surfaces between the engine block 12 and the cylinder liner 1. The arrangement also enables effective cooling of the cylinder liner 1. The embodiment of figure 4 is similar to the embodiment of figure 3. The difference is that the cooling oil is intro- duced into the volume 14 between the engine block 12 and the cylinder liner 1 through the upper end of the volume 14. A separate pipe 15 is used for introducing the cooling oil into the cooling medium duct 6 of the engine block 12.

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. For instance, features of the different embodiments can be combined.