Technical field of the invention

The present invention relates to a piston engine, as defined in claim 1 .

Background of the invention

In large piston engines, such as in engines used as main or auxiliary engines in ships or in engines used at powerplants for producing electricity, each cylinder of the engine is provided with an own cylinder head. The cylinder head closes the upper end of the cylinder and delimits a main combustion chamber. In four-stroke engines, the cylinder head serves for several purposes. For instance, the cylinder head is provided with an inlet channel for introducing intake air into the combustion chamber and with an exhaust channel for discharging exhaust gas from the combustion chamber.

The exhaust gas discharged from the cylinders of an engine has a high temperature. Hot surfaces of the exhaust system can cause safety risks, and therefore the hot parts of the exhaust system need to be protected, for example by different heat insulation solutions. Different heat insulation solutions are often bulky and may limit the possibilities to position various components of the engine.

Summary of the invention

An object of the invention is to provide an improved piston engine comprising a plurality of cylinders arranged in at least one row of cylinders. The characterizing features of the piston engine according to the invention are presented in claim 1 .

The piston engine according to the invention comprises a plurality of cylinders arranged in at least one row of cylinders, each cylinder being provided with a cylinder head comprising an exhaust channel for discharging exhaust gas from the cylinder and a cooling liquid cavity, through which cooling liquid cavity cooling liquid can be circulated, the engine comprising at least one exhaust manifold having a longitudinal portion extending in the longitudinal direction of the row of cylinders and branches connecting the longitudinal portion to the exhaust channels of the cylinder heads, wherein the engine comprises at least one cooling liquid module that is attached to a cylinder head of the engine and arranged to receive cooling liquid from the cooling liquid cavity of the cylinder head, the cooling liquid module comprising at least a lower portion that is arranged to protrude from the cylinder head below the respective branch of the exhaust manifold to a direction that is perpendicular to the longitudinal direction of the row of cylinders, and wherein a projection of the lower portion of the cooling liquid module on a horizontal plane extends from the cylinder head to at least the same distance in a direction that is perpendicular to the longitudinal direction of the row of cylinders as a projection of the branch of the exhaust manifold on said plane.

The lower portion of the cooling liquid cavity forms a heat shield below the branch of the exhaust manifold, thus reducing heat radiation from the branch of the exhaust manifold downwards. This reduces heating of the engine components below the exhaust manifold and minimizes the risk of fire. Also the heat insulation of the exhaust manifold is simplified.

According to an embodiment of the invention, the engine is a V-engine comprising a first row of cylinders, a second row of cylinders and at least one exhaust manifold that is arranged in the lateral direction of the engine between the first row of cylinders and the second row of cylinders. The cooling liquid module provides particular benefits in V-engines, where the insulation between the cylinder banks below the exhaust manifold is difficult to implement. However, the invention also provides benefits in in-line engines.

According to an embodiment of the invention, the exhaust channels of the cylinder heads of each row of cylinders are arranged to open towards the other row of cylinders and the engine comprises at least one cooling liquid module attached to a cylinder head of the first row of cylinders and at least one cooling liquid module attached to a cylinder head of the second row of cylinders. When the exhaust gas from both cylinder banks is conducted in exhaust manifolds arranged between the cylinder banks, the heat insulation of the exhaust manifolds is challenging. The cooling liquid modules provided for both banks of the engine provide an effective heat shield between the cylinder banks.

According to an embodiment of the invention, the cooling liquid modules of the first row of cylinders and the second row of cylinders are identical with each other. This simplifies the assembly and maintenance of the engine and reduces the number of different parts needed for engines with different cylinder configurations.

According to an embodiment of the invention, the lower portions of the cooling liquid modules of the first row of cylinders and the second row of cylinders are dimensioned such that the gap between the lower portion of the cooling liquid module of the first row of cylinders and the lower portion of the respective cooling liquid module of the second row of cylinders is at most 20 mm. According to an embodiment of the invention, the gap is at most 10 mm, preferably at most 5 mm. A small gap between the cooling liquid modules ensures an effective heat shielding effect.

According to an embodiment of the invention, the gap is at least 2 mm. Although it is beneficial to keep the gap small, it is also advantageous to arrange the cooling liquid modules at a distance from each other to allow heat expansion.

According to an embodiment of the invention, the engine comprises a heat insulation cover extending above the exhaust manifold from the cooling liquid module of the first row of cylinders to the cooling liquid module of the second row of cylinders. The heat insulation cover complements the protection provided by the cooling liquid modules.

According to an embodiment of the invention, the engine comprises a first exhaust manifold for the first row of cylinders and a second exhaust manifold for the second row of cylinders.

According to an embodiment of the invention, the lower portion of the cooling liquid module protrudes from the cylinder head to such a direction that the distance between the respective branch of the exhaust manifold and the lower portion of the cooling liquid module increases towards those ends of said module and said branch that are located farther from said row of cylinders. The space in the cylinder head is limited, and the cooling liquid module needs to be attached close to the branch of the exhaust manifold. The increasing distance between the branch and the cooling liquid module ensures that unnecessary cooling of the exhaust gas is avoided.

According to an embodiment of the invention, the lower portion of the cooling liquid module comprises at least one cooling liquid inlet that is arranged to receive cooling liquid from the cooling liquid cavity of the cylinder head. Direct cooling liquid supply from the cylinder head ensures effective circulation of the cooling liquid in the cooling liquid module.

According to an embodiment of the invention, the cooling liquid module further comprises a first side portion extending from the lower portion upwards on a first side of the branch of the exhaust manifold and a second side portion extending from the lower portion upwards on a second side of the branch of the exhaust manifold. The side portions allow conducting the cooling liquid to the upper side of the exhaust manifold.

According to an embodiment of the invention, the lower portion extends in the lateral direction of the row of cylinders farther from the cylinder head than the side portions. This allows providing an effective heat shield below the branch of the exhaust manifold, while minimizing cooling of the exhaust gas.

According to an embodiment of the invention, the cooling liquid module comprises an upper portion connecting the first side portion to the second side portion above the branch of the exhaust manifold. The upper portion allows collecting the cooling liquid from the side portions.

According to an embodiment of the invention, the lower portion extends in the lateral direction of the row of cylinders farther from the cylinder head than the upper portion. As with the side portions, this allows providing an effective heat shield, while minimizing cooling of the exhaust gas.

According to an embodiment of the invention, the upper portion of the cooling liquid module comprises at least one cooling liquid inlet arranged to receive cooling liquid from the cylinder head. This allows optimizing the cooling liquid flow in the cylinder head.

According to an embodiment of the invention, the upper portion of the cooling liquid module comprises at least two cooling liquid inlets arranged to receive cooling liquid from the cylinder head. The two cooling liquid inlets allow arranging a greater cooling liquid flow in the upper parts of the cylinder head.

According to an embodiment of the invention, each cylinder of the engine is provided with an own cooling liquid module. By providing each cylinder of the engine with an own cooling liquid module, the same components can be used in engines with different number of cylinders. Also, the serviceability of the engine is improved.

According to an embodiment of the invention, each cooling liquid module is arranged in fluid communication with at least one adjacent cooling liquid module. The cooling liquid modules can thus form part of a return line for cooling liquid.

According to an embodiment of the invention, each branch of the exhaust manifold is attached to the respective cylinder head by means of a mounting flange, and the cooling liquid module is configured such that a projection of the cooling liquid module on a plane of the mounting flange is located outside of said mounting flange. The mounting flange can thus be accessed even when the cooling liquid module is mounted, thus allowing mounting and dismounting of the exhaust manifold.

According to an embodiment of the invention, the lower portion of the cooling liquid module has an end surface that is located away from the respective cylinder head, and the mutual angle between the end surface and the axial direction of the respective cylinder is 15 to 40 degrees, the upper edge of the end surface being located farther from the cylinder than the lower edge. The inclination of the end surface allows the same module to be used in in-line engines and for both banks of a V-engine. Because of the inclination, in a V-engine the end surfaces of opposite cooling liquid modules can be arranged close to each other.

According to an embodiment of the invention, the engine is a V-engine, and said angle is substantially equal to the inclination angle of the cylinders from the vertical direction. When the angle equals the inclination angle of the cylinders, the gap between the end surfaces has a constant width.

According to an embodiment of the invention, the cylinder head comprises an integral extension formed on an exhaust side of the cylinder head, the extension comprising a first push rod passage and a second push rod passage, each of the first push rod passage and the second push rod passage being configured to allow through passage of a push rod that is configured to operate intake and/or exhaust valves of the cylinder, and the exhaust channel is arranged to pass through the extension between the first push rod passage and the second push rod passage, and the cooling liquid module is attached to the extension of the cylinder head. The extension reduces heat radiation from the exhaust channel downwards, and thus provides a synergistic effect with the cooling liquid module.

According to an embodiment of the invention, the exhaust manifold comprises a plurality of exhaust manifold modules, each module comprising a section of the longitudinal portion of the exhaust manifold and one branch of the exhaust manifold. Together with the cooling liquid modules, the exhaust manifold modules help to reduce the number of different components needed for engines with different number of cylinders.

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 part of an engine according to an embodiment of the invention,

Fig. 2 shows a cross-sectional view of a part of an engine according to an embodiment of the invention,

Fig. 3 shows another cross-sectional view of a part of an engine according to an embodiment of the invention,

Fig. 4 shows a cross-sectional view of a V-engine according to an embodiment of the invention,

Fig. 5 shows another cross-sectional view of an engine according to an embodiment of the invention,

Fig. 6 shows a further cross-sectional view of an engine according to an embodiment of the invention,

Fig. 7 shows a further cross-sectional view of an engine according to an embodiment of the invention,

Fig. 8 shows a perspective view of a cylinder head that can form part of an engine according to an embodiment of the invention, Fig. 9 shows the cylinder head of figure 8 seen from the direction of an extension of the cylinder head,

Fig. 10 shows a cross-sectional view of an extension of the cylinder head of figure 8, and

Fig. 11 shows a cross-sectional view of a lower part of the cylinder head of figure 8.

Detailed description of embodiments of the invention

Figures 1 -11 show different partial views of piston engines according to different embodiments of the invention and the components of the engines.

The engine according to the invention is a large piston engine. The expression “large piston engine” refers here to an engine having a cylinder diameter of at least 150 mm. The engine can be, for instance, an engine that is used as a main or an auxiliary engine in a ship or an engine that is used at a power plant for driving a generator for producing electricity. The engine is a multi-cylinder four-stroke engine. The number of cylinders in the engine can be, for instance, 5 to 20. The cylinders can be arranged in-line or in a V-configuration. Figure 4 shows an example of a V-engine. Figure 2 shows an example of an in-line engine. Most of the various components shown in the figures can be used both in V-engines and in-line engines.

An in-line engine comprises a single row 41 of cylinders 2. In an in-line engine, the cylinders 2 of the engine are preferably arranged in an upright position. The longitudinal axis of each cylinder 2 is thus parallel to the vertical direction.

A V-engine comprises two rows of cylinders, i.e. two banks of cylinder. The cylinders 2 are arranged in a first row 41 of cylinders and a second row 42 of cylinders. The cylinders 2 of each row 41 , 42 of cylinders 2 are inclined relative to the vertical direction such that at the upper ends of the cylinders 2 the distance between the two rows 41 , 42 of cylinders is greater than at the lower ends of the cylinders 2. In the embodiment of figure 4, the inclination angle is approximately 20 degrees. The angle between the axial direction of the cylinders 2 of the first row 41 of cylinders and the axial direction of the cylinders 2 of the second row 42 of cylinders is thus approximately 40 degrees. The inclination angle between the vertical direction and the axial direction of the cylinders 2 could be, for instance, 15-40 degrees. The longitudinal direction of the second row 42 of cylinders is parallel to the longitudinal direction of the first row 41 of cylinders.

The engine comprises an engine block 56 and cylinder liners 19 arranged in the engine block 56. The cylinders 2 are formed by the cylinder liners 19. The upper end of each cylinder liner 19 extends above the upper surface of the engine block 56. Each cylinder 2 of the engine is provided with a cylinder head 1 that can be arranged against the upper end of the cylinder liner 19 and attached to the engine block 56.

The engine according to the invention can be configured to be operable using at least a first, gaseous fuel. The expression “gaseous fuel” refers here to a fuel that is gaseous in atmospheric pressure and at a temperature of 20 °C. The first fuel can be, for instance, natural gas or biogas. The term “biogas” refers here to a gas that mainly consists of methane and which is obtained from renewable sources. The biogas can be produced for example from organic waste. Natural gas could be stored either as a liquefied gas (LNG) or compressed gas (CNG). Biogas could be stored in a similar manner. Instead of methane-based fuels, the first fuel could be, for instance, hydrogen or ammonia or a mixture of two or more types of gaseous fuel.

The engine can be further configured to be operable using a second fuel. The second fuel can be either gaseous fuel or liquid fuel. If the first fuel is natural gas or biogas, the second fuel could be, for instance, hydrogen. Alternatively, the second fuel could be liquid fuel, such as light fuel oil or heavy fuel oil. The engine can also be operable using a third fuel or even further fuels.

The engine can thus be a gas engine, a dual-fuel engine or a multi-fuel engine. However, the engine could also be operable solely using one or more liquid fuels.

The engine can be configured to be operable using mixtures of different fuels. For instance, the engine could be operable using a mixture of hydrogen and some other gaseous fuel and/or a mixture of ammonia and some other gaseous fuel.

When the engine is operated using a gaseous fuel, it can utilize a liquid fuel, such as light fuel oil as a pilot fuel facilitating ignition of the gaseous fuel. However, that is not necessary, but the gaseous fuel could be self-igniting or spark plugs or other ignition means could be used for igniting the gaseous fuel.

Each cylinder 2 of the engine is provided with an own cylinder head 1. The cylinder head 1 is configured to close the upper end of the cylinder 2. The cylinder head 1 is preferably a one-piece part. The cylinder heads 1 of the engine are preferably identical with each other. In the embodiments of the figures, the cylinder heads 1 of the V-engine are identical with the cylinder heads 1 of the in-line engine.

In particular figures 5-11 show details of a cylinder head 1 that can be used in an engine according to the invention. However, the cylinder heads 1 of an engine according to the invention could also differ from the cylinder head 1 described below.

The cylinder head 1 has a bottom surface 1A configured to delimit an upper end of a main combustion chamber 31 of a cylinder 2, and a top surface 1 B facing an opposite direction than the bottom surface 1A. As discussed above, the cylinders 2 of the engine do not need to be in an upright position, but the cylinders 2 can be inclined from the vertical direction. For instance in a V-en- gine, the upper ends of the cylinders 2 can be located farther outwards from the longitudinal center line of the engine than the lower ends. The term “bottom surface” thus refers to that side of the cylinder head 1 that is facing the main combustion chamber 31 , but the bottom surface 1A does not need to be a horizontal surface facing downwards.

The cylinder head 1 is a crossflow cylinder head. The term “crossflow cylinder head” means that the intake and exhaust valves are located on opposite sides of the cylinder head 1 .

The cylinder head 1 has an intake side 11 and an exhaust side 12. When the cylinder head 1 is divided into two halves by an imaginary plane 32, which is in a mounted state of the cylinder head 1 parallel to the axial direction of the cylinder 2, the intake side 11 is that side of the cylinder head 1 on which the intake valves 8 of the cylinder 2 are located, and the exhaust side 12 is that side of the cylinder head 1 on which the exhaust valves 9 of the cylinder 2 are located. The imaginary plane 32 does not need to be in the middle of the cylinder head 1 . In the embodiment of the figures, the imaginary plane 32 dividing the cylinder head 1 into the intake side 11 and the exhaust side 12 is located such that in the mounted state of the cylinder head 1 , the imaginary plane 32 crosses with the longitudinal center axis of the cylinder 2. In a mounted state of the cylinder head 1 , the intake side 11 of the cylinder head 1 is on a first side of the longitudinal center line of a row of cylinders. The exhaust side 12 of the cylinder head 1 is on a second side of said longitudinal center line of said row of cylinders. In an in-line engine, the intake sides 11 of all the cylinder heads 1 of the engine are on the same side of the longitudinal center line of the row of cylinders. In a V-engine the cylinder heads 1 can be mounted such that the exhaust sides 12 of the cylinder heads 1 of a first bank face the exhaust sides 12 of the cylinder heads 1 of a second bank. The intake sides 11 of the cylinder heads 1 can thus point laterally outwards from the longitudinal center line of the engine.

It is not necessary that the imaginary plane 32 crosses with the longitudinal center axis of the cylinder 2, but the imaginary plane 32 could be offset from the longitudinal center axis of the cylinder 2.

The cylinder head 1 comprises attachment holes 34 for attaching the cylinder head 1 to the engine block 56. In the embodiment of the figures, the cylinder head 1 comprises four attachment holes 34. Each attachment hole 34 is configured to receive a stud bolt for attaching the cylinder head 1 to the engine block 56. In a mounted state of the cylinder head 1 , the radial distances of the attachment holes 34 from the longitudinal center axis of the cylinder 2 are equal to each other.

The cylinder head 1 comprises an inlet channel 3 arranged on the intake side 11 of the cylinder head 1. The inlet channel 3 is configured for introducing intake air into the main combustion chamber 31 of the cylinder 2. In the embodiment of the figures, the inlet channel 3 is further configured to allow introducing gaseous main fuel into the inlet channel 3 and further into the main combustion chamber 31. The cylinder head 1 further comprises an exhaust channel 4 arranged on the exhaust side 12 of the cylinder head 1 . The exhaust channel 4 is configured for discharging exhaust gas from the main combustion chamber 31 .

The cylinder head 1 comprises a first intake valve hole 5A and a second intake valve hole 5B arranged on the intake side 11 of the cylinder head 1. Each intake valve hole 5A, 5B extends from the bottom surface 1A of the cylinder head 1 to the top surface 1 B and is configured to receive an intake valve 8. The cylinder head 1 can thus be provided with two intake valves 8.

The cylinder head 1 comprises a first exhaust valve hole 6A and a second exhaust valve hole 6B arranged on the exhaust side 12 of the cylinder head 1 . Each exhaust valve hole 6A, 6B extends from the bottom surface 1 A to the top surface 1 B and is configured to receive an exhaust valve 9. The cylinder head 1 can thus be provided with two exhaust valves 9.

In the embodiment of the figures, the cylinder head 1 further comprises a central hole 29 arranged between the intake and exhaust valve holes 5A, 5B, 6A, 6B and extending from the bottom surface 1 A of the cylinder head 1 to the top surface 1 B. In the embodiment of the figures, the central hole 29 is configured to receive a fuel injector 30. The fuel injector 30 is configured to inject liquid pilot fuel into the main combustion chamber 31 . However, the central hole 29 could also be configured to receive a prechamber assembly.

The cylinder head 1 further comprises an integral extension 13 that is formed on the exhaust side 12. In the embodiment of the figures, the cylinder head 1 extends on the exhaust side 12 farther form the area that is configured to cover the cylinder 2 in a mounted state of the cylinder head 1 than on the intake side 11.

The extension 13 comprises a first push rod passage 14A and a second push rod passage 14B. Each of the push rod passages 14A, 14B is configured to allow through passage of a push rod 15. In a mounted state of the cylinder head 1 , the push rod passages 14A, 14B are located farther from the longitudinal center axis of the cylinder 2 than the attachment holes 34.

One of the push rods 15 is configured to operate the intake valves 8 of the cylinder 2 and one of the push rods 15 is configured to operate the exhaust valves 9 of the cylinder 2. The push rods 15 are lifted by means of the cams of a camshaft 47. If the cylinder head 1 is used in a V-engine, cams for the cylinders 2 of both banks of the engine can be arranged in the same camshaft. In the embodiment of figure 4, the engine comprises a single camshaft that is configured to operate all the intake valves 8 and exhaust valves 9 of the engine. The push-rods are spring-biased against the cams. The push-rod passages 14A, 14B collect lubricating oil from the valve actuating mechanism above the cylinder head 1 and conduct it past the exhaust channel 4.

The exhaust channel 4 is arranged to pass in the extension 13 between the first push rod passage 14A and the second push rod passage 14B. The exhaust channel 4 opens to the side of the cylinder head 1 in the extension 13. The extension 13 is configured to allow an exhaust manifold 43, 44 to be attached to the extension 13 and in fluid communication with the exhaust channel 4. The push rod passages 14A, 14B are thus arranged on the sides of the exhaust channel 4, forming heat shields on the sides of the exhaust channel 4. This reduces heat radiation and conduction from the exhaust channel 4 to the outside of the cylinder head 1 . The extension 13 is provided with threaded holes 35 for allowing the exhaust manifold 43, 44 to be attached to the extension 13 by means of screws 36.

The exhaust channel 4 comprises a first branch 4A from the first exhaust valve hole 6A and a second branch 4B from the second exhaust valve hole 6B. The first branch 4 and the second branch 4B merge into a common portion 4C that passes through the extension 13 of the cylinder head 1 . The exhaust channel 4 is merged into the common portion 4C before the push rod passages 14A, 14B.

The cylinder head 1 comprises a cooling liquid cavity 16. The cooling liquid cavity 16 is configured to receive and discharge cooling liquid to allow circulation of cooling liquid in the cylinder head 1 . In the embodiment of the figures, the cooling liquid is received from a cooling liquid duct 20 of the cylinder liner 19 and discharged from the extension 13 of the cylinder head 1 . In the embodiment of the figures, the cooling liquid cavity 16 is arranged partly in the extension 13.

The cooling liquid cavity 16 comprises a lower portion 16A and upper portion 16B. The lower portion 16A is arranged below the exhaust channel 4, i.e. on the bottom surface side of the exhaust channel 4. The upper portion 16B is arranged above the exhaust channel 4, i.e. on the top surface side of the exhaust channel 4. In the embodiment of the figures, the upper portion 16B connects to the lower portion 16A on the sides of the exhaust channel 4. The cylinder head 1 comprises a cooling liquid duct 17 for introducing cooling liquid into the cooling liquid cavity 16. In the embodiment of the figures, the cooling liquid duct 17 comprises a first branch 17A for introducing cooling liquid into the lower portion 16A of the cooling liquid cavity 16 and a second branch 17B for introducing cooling liquid into the upper portion 16B of the cooling liquid cavity 16. The cooling liquid duct 17 has an inlet end 18 opening onto the bottom surface 1A of the cylinder head 1 . The inlet end 18 of the cooling liquid duct 17 is arranged to open in an area that is configured to be aligned in a mounted state of the cylinder head 1 with an upper end of the cylinder liner 19 for receiving cooling liquid from the cooling liquid channel 20 of the cylinder liner 19.

The second branch 17B of the cooling liquid duct 17 comprises a portion extending in the direction of the central hole 29 of the cylinder head 1 . Said portion is arranged between the central hole 29 and the exhaust channel 4 such that said portion is located closer to the central hole 29 than the exhaust channel 4. That helps avoiding excessive cooling of the exhaust gas.

The cylinder head 1 comprises at least one cooling liquid outlet 21 , 22A, 22B that is arranged in the extension 13 of the cylinder head 1 for discharging cooling liquid from the cooling liquid cavity 16. In the embodiment of the figures, the cylinder head 1 comprises three cooling liquid outlets 21 , 22A, 22B. A first cooling liquid outlet 21 is arranged below the exhaust channel 4. The first cooling liquid outlet 21 is configured to discharge cooling liquid from the lower portion 16A of the cooling liquid cavity 16. The cylinder head 1 further comprises a second cooling liquid outlet 22A and a third cooling liquid outlet 22B. The second and third cooling liquid outlets 22A, 22B are configured to discharge cooling liquid from the upper portion 16B of the cooling liquid cavity 16.

The extension 13 of the cylinder head 1 is configured for attachment of a cooling liquid module 23 that is configured to receive cooling liquid from the cooling liquid cavity 16. The cylinder head 1 comprises threaded attachment holes for allowing the cooling liquid module to be attached to the cylinder head 1 by means of screws 57. The cooling liquid module 23 is arranged to receive cooling liquid via the cooling liquid outlets 21 , 22A, 22B of the cylinder head 1 . The cooling liquid module 23 forms a heat shield below the exhaust manifold 43. The construction and function of the cooling liquid module 23 will be explained in more detail further below. The exhaust channel 4 in the extension 13 of the cylinder head 1 is configured to receive an inner sleeve 24. In the embodiment of the figures, the exhaust channel 4 in the extension 13 comprises an outer support portion 25 configured to support an outer end of the inner sleeve 24 and an inner support portion 26 configured to support an inner end of the inner sleeve 24. The exhaust channel 4 further comprises an intermediate portion 27 having a larger diameter than the inner support portion 26 such that a free space 28 is formed between the exhaust channel 4 and the inner sleeve 24 in a mounted state of the inner sleeve 24. In the embodiment of the figures, the outer diameter of the inner sleeve 24 is constant. The inner diameter of the inner support portion 26 is substantially the same as the inner diameter of the outer support portion 25. However, the inner diameter of the outer support portion 25 could be greater than the inner diameter of the inner support portion 26. In that case, the diameter of the inner sleeve 24 could increase towards the outer end, or an intermediate piece could be arranged between the inner sleeve 24 and the outer support portion 25. The exhaust gas flows in the inner sleeve 24. The inner sleeve and the free space 28 around the inner sleeve 24 reduces heat radiation and conduction from the exhaust channel 4.

The engine comprises at least one exhaust manifold 43, 44, into which the exhaust gas from the cylinders 2 of the engine is conducted. The in-line engine shown in the figures comprises a single exhaust manifold 43. The exhaust channels 4 of all cylinder heads 1 of the engine are thus connected to the same exhaust manifold 43.

In the embodiment of figure 4, the V-engine comprises a first exhaust manifold 43 for the first row 41 of cylinders and a second exhaust manifold 44 for the second row 42 of cylinders. The cylinders 2 of the first row 41 are thus connected to the first exhaust manifold 43 and the cylinders 2 of the second row 42 are connected to the second exhaust manifold 44. The exhaust manifolds 43, 44 are arranged in the lateral direction of the engine between the two rows 41 , 42 of cylinders. In the vertical direction, the exhaust manifolds 43, 44 are arranged above the engine block 56.

Each exhaust manifold 43, 44 comprises a longitudinal portion 45. The axial direction of the longitudinal portion 45 is parallel to the longitudinal direction of the row 41 , 42 of cylinders. Each exhaust manifold 43, 44 further comprises a plurality of branches 46 connecting the longitudinal portion 45 to the exhaust channels 4 of the cylinder heads 1 . The number of branches 46 in the exhaust manifold 43, 44 equals the number of cylinders 2 to which the exhaust manifold

43, 44 is connected.

In the embodiments of the figures, each exhaust manifold 43, 44 comprises a plurality of exhaust manifold modules, each module comprising a section of the longitudinal portion 45 of the exhaust manifold 43, 44 and exactly one branch 46 of the exhaust manifold 43, 44. In the embodiment of the figures, the section of the longitudinal portion 45 of each exhaust manifold module is attached to the adjacent exhaust module by means of an intermediate piece 55. The intermediate piece 55 can be flexible to reduce vibrations.

In the embodiments of the figures, each branch 46 is attached to the respective cylinder head 1 by means of a mounting flange 53. The mounting flange 53 is attached to the cylinder head 1 by means of screws 58.

The cooling liquid module 23 is arranged to receive cooling liquid from the cooling liquid cavity 16 of the cylinder head 1. The cooling liquid module 23 comprises a lower portion 23A that is arranged to protrude from the cylinder head 1 below the respective branch 46 of the exhaust manifold 43, 44 to a direction that is perpendicular to the longitudinal direction of the row 41 , 42 of cylinders. The lower portion 23A of the cooling liquid module 23 thus protrudes from the cylinder head 1 laterally outwards, i.e. to a direction away from the cylinder head 1 . A projection of the lower portion 23A of the cooling liquid module 23 on a horizontal plane extends from the cylinder head 1 to at least the same distance in a direction that is perpendicular to the longitudinal direction of the row 41 , 42 of cylinders as a projection of the branch 46 of the exhaust manifold 43, 44 on the same plane. The outermost point of the lower portion 23A of the cooling liquid module 23 is thus located in the lateral direction of the engine at least as far from the respective cylinder 2 of the engine as the furthest point of the joint between the branch 46 and the longitudinal portion 45 of the exhaust manifold 43, 44. Alternatively, or in addition, the projection of the lower portion 23A of the cooling liquid module 23 on the horizontal plane can extend from the cylinder head 1 to at least the same distance as the longitudinal center axis of the longitudinal portion 45 of the exhaust manifold 43,

44. For example figure 2 shows an embodiment, where the outermost point of the lower portion 23A of the cooling liquid module 23 is substantially aligned with the longitudinal center axis of the longitudinal portion 45 of the exhaust manifold 43. In a V-engine, said projection of the lower portion 23A of the cooling liquid module 23 can extend from the cylinder head 1 farther than the respective exhaust manifold 43, 44, as shown in figure 4.

In a V-engine, preferably both rows 41 , 42 of cylinders are provided with the cooling liquid modules 23. The cooling liquid modules 23 can be identical with each other.

In the embodiments of the figures, each cylinder 2 of the engine is provided with an own cooling liquid module 23. A lower portion 23A of a cooling liquid module 23 is thus provided below each branch 46 of the exhaust manifolds 43, 44. The lower portions 23A of the cooling liquid modules 23 of each row 41 , 42 of cylinders form a substantially continuous heat shield below the respective exhaust manifold 43, 44. Instead of providing each cylinder 2 of the engine with an own cooling liquid module 23, the engine could be provided with a cooling liquid module 23 comprising a lower portion 23A extending in the longitudinal direction of an exhaust manifold 43, 44 below at least two branches 46 of the exhaust manifold 43, 44. Alternatively, or in addition, the cooling liquid module 23 could comprise two or more separate lower portions 23A.

According to an embodiment of the invention, in a V-engine the lower portions 23A of the cooling liquid modules 23 of the first row 41 of cylinders and the second row 42 of cylinders are dimensioned such that the gap 48 between the lower portion 23A of a cooling liquid module 23 of the first row 41 of cylinders and the lower portion 23A of a respective cooling liquid module 23 of the second row 42 of cylinders is at most 20 mm. According to an embodiment of the invention, the gap 48 is at most 10 mm, preferably at most 5 mm. However, the gap 48 is preferably at least 2 mm. As shown in figure 4, the cooling liquid modules 23 arranged opposite to each other form a nearly continuous heat shield in the lateral direction of the engine. The small gap 48 between the opposite cooling liquid modules 23 does not allow significant heat radiation past the lower portions 23A of the cooling liquid modules 23, but allows heat expansion of the components.

In the embodiments of the figures, the cooling liquid module 23 further comprises a first side portion 23B extending from the lower portion 23A upwards on a first side of the branch 46 of the exhaust manifold 43, 44 and a second side portion 23 extending from the lower portion 23A upwards on a second side of the branch 46 of the exhaust manifold 43, 44. The side portions 23B, 23C are configured to allow cooling liquid flow from the lower portion of the cooling liquid module 23.

The lower portion 23A extends in the lateral direction of the row 41 , 42 of cylinders farther from the cylinder head 1 than the side portions 23B, 23C. The cooling liquid flowing through the side portions 23B, 23D of the cooling liquid module 23 does thus not significantly cool down the exhaust gas flowing in the branch 46 of the exhaust manifold 43, 44.

In the embodiments of the figures, the cooling liquid module 23 further comprises an upper portion 23 connecting the first side portion 23B to the second side portion 23C above the branch 46 of the exhaust manifold 43, 44. The cooling liquid module 23 thus forms a collar around the branch 46 of the exhaust manifold. The upper portion 23D of the cooling liquid module 23 collects cooling liquid from the side portions 23B, 23C. The lower portion 23A extends in the lateral direction of the row 41 , 42 of cylinders farther from the cylinder head 1 than the upper portion 23D. The cooling liquid flowing through the upper portion 23D of the cooling liquid module 23 does thus not significantly cool down the exhaust gas flowing in the exhaust manifold 43, 44.

The upper portion 23D of each cooling liquid module 23 is arranged in fluid communication with the upper portions 23D of the adjacent cooling liquid modules 23 of the same row 41 , 42 of cylinders.

In the embodiments of the figures, the lower portion 23A of the cooling liquid module 23 protrudes from the cylinder head 1 to such a direction that the distance between the respective branch 46 of the exhaust manifold 43, 44 and the lower portion 23A of the cooling liquid module 23 increases towards those ends of said module 23 and said branch 46 that are located farther from the respective row 41 , 42 of cylinders. In case of the in-line engine of the figures, the lower portion 23A of the cooling liquid module 23 is substantially horizontal. The branch 46 of the exhaust manifold 43 extends from the cylinder head 1 diagonally upwards. In case of the V-engine of figure 4, both the lower portion 23A of the cooling liquid module 23 and the branch 46 of the exhaust manifold 43, 44 extend from the cylinder head 1 diagonally upwards, but the branch 46 of the exhaust manifold 43, 44 extends at a greater angle. The space in the cylinder head 1 is limited, and the cooling liquid module 23 thus needs to be arranged close to the branch 46 of the exhaust manifold 43, 44 in the cylinder head 1 . The increasing distance between the lower portion 23A of the cooling liquid module 23 and the branch 46 of the exhaust manifold 43, 44 helps keeping the cooling effect of the cooling liquid module 23 on the exhaust gas minimized, thus maintaining high exhaust gas temperature.

In the embodiments of the figures, the cooling liquid module 23 is configured such that a projection of the cooling liquid module 23 on a plane of the mounting flange 53 is located outside of said mounting flange 53. The screws 58 attaching the mounting flange 53 to the cylinder head 1 can thus be accessed even when the cooling liquid module 23 is attached to the cylinder head 1 .

In the embodiments of the figures, the lower portion 23A of the cooling liquid module 23 comprises a cooling liquid inlet 50 that is arranged to receive cooling liquid from the cooling liquid cavity 16 of the cylinder head 1. The lower portion 23A of the cooling liquid module 23 is connected to the lower portion 16A of the cooling liquid cavity 16 of the cylinder head 1 . The upper portion 23D of the cooling liquid module 23 comprises two cooling liquid inlets 51 arranged to receive cooling liquid from the cylinder head 1. The upper portion 23D of the cooling liquid module 23 is connected to the upper portion 16B of the cooling liquid cavity 16 of the cylinder head 1 .

In the embodiments of the figures, each cylinder 2 of the engine is provided with an own cooling liquid module 23. This reduces the number of different components needed for engines with different cylinder configurations. However, a single cooling liquid module 23 could also serve two or more cylinders 2 of the engine.

The lower portion 23A of the cooling liquid module 23 has an end surface 54 that is located away from the respective cylinder head 1. The mutual angle between the end surface 54 and the axial direction of the respective cylinder 1 is preferably 15 to 40 degrees, the upper edge of the end surface 54 being located farther from the cylinder 2 than the lower edge. This allows the same cooling liquid modules 23 to be used both in V-engines and in-line engines. The angle is preferably substantially equal to the inclination angle of the cylinders 2 of the V-engine from the vertical direction. In an in-line engine, the end surface 54 can be used as an attachment point for a heat insulation cover 49 surrounding the exhaust manifold 43, as shown in figure 2. In the embodiment of figure 4, the engine comprises a heat insulation cover 49 that extends above the exhaust manifolds 43, 44 from the cooling liquid modules 23 of the first row 41 of cylinders to the cooling liquid modules 23 of the second row 42 of cylinders. An in-line engine could be provided with a similar heat insulation cover. Figure 2 shows a heat insulation cover 49 of an in-line engine. The heat insulation cover 49 extends from the end surface 54 of the lower portion 23A of the cooling liquid module 23 around the longitudinal portion 45 of the exhaust manifold 43 to the upper side of the branch 46 of the exhaust manifold 43. Because of the cooling liquid module 23, no heat insula- tion cover is needed directly below the branch 46 of the exhaust manifold 43.

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.