SE541831C2 - A Cylinder Head for an Internal Combustion Engine - Google Patents

Description

A Cylinder Head for an Internal Combustion Engine Field of the invention The present invention relates to a cylinder head for a liquid-cooled internal combustion engine, an internal combustion engine comprising such a cylinder head and to a vehicle comprising such an internal combustion engine. It also relates to a method for cooling such a cylinder head.

Background of the invention In an internal combustion engine an air-fuel mixture combusts in a combustion chamber under high pressure. In a compression ignited engine, such as a diesel engine, the combustion chamber is delimited by a fire deck in the cylinder head, the cylinder walls and the piston head. The diesel fuel is ignited when the air-fuel mixture is compressed by the piston. The air added to the combustion is cool and the exhausts are very warm. For the air and fuel to enter and the exhaust to exit the combustion chamber, the cylinder head is provided with intake ports and exhaust ports to each cylinder, each provided with a valve closing against the fire deck. A fuel injector is typically placed centred between the ports in the fire deck. The intake and exhaust ports are positioned in close proximity to each other. As a consequence, the cylinder head is exposed to, in addition to the large pressure loads due to the combustion, large temperature gradients.

To avoid malfunction and ruptures of the valves and the cylinder head, effective cooling of the cylinder head is needed. Most modern internal combustion engines are liquid-cooled, where a coolant is circulating through the cylinder head. Particularly in the case of high-power diesel combustion engines with high heat generation and high combustion pressures, insufficient heat removal from the cylinder head may lead to leaks, cracks and warping phenomena in the cylinder head, and especially the fire deck.

A cooling system for an internal combustion engine is presented in WO 2015/094086 A1 by the same applicant as the present application, which is hereby incorporated by reference. According to WO 2015/094086 A1, the coolant enters the cylinder head in a lower cooling chamber. The lower cooling chamber is positioned close to a fire deck of the combustion chamber. After passing through the lower cooling chamber, the coolant are led in parallell to an upper cooling chamber in the cylinder head and an cooling passage in the upper part of a cylinder liner.

In order to maximize the coolant flow through a cylinder head and thereby achieve enough cooling of the fire deck, especially in the area between the valves, also known as the valve bridge area, the lower cooling chamber is made large as possible. In a state-of-the-art cylinder head for a liquid-cooled engine, the walls of the cylinder head surrounding the lower cooling chamber are therefore very thin.

In order to increase the efficiency of internal combustion engines while fulfilling present and future emission legislation, there is a desire to increase both the pressure and the temperature in the combustion chamber during combustion.

However, as indicated above, there is a conflict between increasing the strength of the cylinder and increasing the coolant flow through of the cooling chamber in the cylinder head.

Summary of the invention It would be advantageous to achieve a cylinder head overcoming, or at least alleviating, the above mentioned drawbacks. In particular, it would be desirable to enable a cylinder head which enables both efficient cooling and high strengh, thereby allowing both very high combustion pressure and very high combustion temperature in the engine. It would also be desirable to enable a cylinder head where the thermal and mechanical loads are reduced.

To better address one or more of these concerns, a cylinder head and a method for cooling a cylinder head having the features defined in the independent claim are provided. Preferable embodiments are defined in the dependent claims.

Hence, according to an aspect, a cylinder head for at least one cylinder of a liquid-cooled internal combustion engine, comprising at least two intake ports, at least two exhaust ports, a fire deck and a first cooling chamber is provided. The first cooling chamber comprises an inlet passage and an outlet passage. The inlet passage is arranged to connect the first cooling chamber to the cool side of the engine’s cooling system. The first cooling chamber comprises two outer passages and at least one inner passage. The outer passages bypasses the intake and exhaust ports on the outside and the at least one inner passage passes between the intake ports and between the exhaust ports. The outer and inner passages connects to the inlet passage at an inlet junction and connects to the outlet passage at an outlet junction. The at least one inner passage is at least partially flow wise separated from the outer passages between the inlet junction and the outlet junction.

Separating the coolant flow through the first cooling chamber into at least partially flow wise separated passages, facilitates an improved coolant flow and heat transfer from the cylinder head to the coolant. With improved heat transfer, the cylinder head can withstand higher combustion temperatures. Futher the coolant flow may be reduced without impairing the cooling of the cylinder head. Thereby, the thickness of the walls of the first cooling chamber in the cylinder head can be increased, thereby further increasing the strengh of the cylinder head, without imparing the cooling of the cylinder head.

The at least partially flow wise separation of the at least one inner passage and the outer passages is created by wall means arranged between each exhaust port and the adjacent intake port.

By such wall means, the flow in the passages may be directed in a favourable direction from the inlet junction to the outlet junction, thereby increasing the cooling of the cylinder head. Further, the region between an exhaust port and an intake is particulary exposed to stresses, as the thermal gradients are large here. This is because the intake air entering the combustion chamber through the intake valve typically has a temperature close to the ambient temperature, typicially below 70°C, while the exhaust gases leaving the combustion chamber through the exhaust valve is 200 - 700 °C, for the most common operating conditions 350 - 400 °C. As this region is relatively centered above the combustion chamber, forces on the fire deck is high here, as it is far from the walls. Therefore, arranging wall means here improves the strengh of the cylinder head in a very positive way.

According to embodiments, the wall means completely separates the at least one inner passage from the outer passages between the inlet and outlet junctions. By limiting the open portion of the cross section area, an improved flow wise separation of the main passages can be achieved as the influence of the boundary conditions of the flow through the cooling chamber for the flow wise separation of the flow between the channels can be reduced.

Thereby, a cylinder head that need less adaption to other components of the engine and the cooling system may be achieved.

According to embodiments, the cylinder head comprise two exhaust ports and two intake ports. For an engine where each cylinder has as two inlet valves and exhaust valves, arranging wall means between each exhaust valve through hole and the closest intake valve through hole, the flow through the different main passages is essentially parallel through the cooling chamber, facilitating a stable and efficient cooling of the cylinder head. By arranging wall means in this way, the cooling chamber has supporting walls essentially equidistantly arranged across the width of the cooling chamber, thereby facilitating a cylinder head that can sustain high combustion pressures.

According to embodiments, the cylinder head comprises a through hole for a device, such as a fuel injector or a spark plug, arranged between the intake and exhaust ports. The inner passage of the first cooling chamber is divided into a first inner sub-passage and a second inner sub-passage at a third junction on the inlet junction side of the through hole, and the inner two subpassages are joined at a forth junction on the outlet junction side of the through hole.

According to embodiments, the diameter of the first cooling chamber is 100 -200 mm, preferably 120-180 mm, most preferably 140 - 160 mm, and the hight (in the axial direction, coolinear with the axial direction of the cylinder bore of the cylinder arrangement) of the first cooling chamber is 5 - 50 mm, preferably 10 - 30 mm and most preferably 15-25 mm. For cooling chambers with these dimensions, very good cooling may be achieved.

According to an aspect, a method for cooling a cylinder head for at least one cylinder of a liquid-cooled internal combustion engine, comprising at least two intake ports, at least two exhaust ports, a fire deck and a first cooling chamber is provided. The first cooling chamber comprises an inlet passage and an outlet passage. The inlet passage is arranged to connect the first cooling chamber to the cool side of the engine’s cooling system. The coolant being circulated through the first cooling chamber entering through the inlet passage and exiting through the outlet passage. The coolant is led through the first cooling chamber in two outer passages and at least one inner passage. The inner and outer passages each connects to the inlet passage at an inlet junction and connects to the outlet passage at an outlet junction. The coolant flow through the at least one inner passage are at least partially flow wise separated from the coolant flow through the outer passages between the inlet junction and outlet junction.

By this method, an improved cooling of a cylinder head may be achieved.

Further features of, and advantages with, the present invention will become apparent when reading the appended claims and the following detailed description. It will be appreciated that the various embodiments described for the cylinder head are all combinable with the method as defined in accordance with that aspect of the present invention.

Brief description of the drawings Various aspects of the invention, including particular features and advantages, will be readily understood from the example embodiments in the following detailed description and the accompanying drawings, in which: Fig. 1 shows a schematic side view of a vehicle, comprising internal combustion engine with a cylinder head according to an embodiment, Fig. 2a shows a cutaway view of a cylinder arrangement including a cylinder head, Fig. 4b shows a schematic side view of the cooling system of a cylinder head and an internal combustion engine according to an embodiment, Fig. 3a shows a schematic view along the section A - A in Fig. 2b of a known cylinder head, Fig. 3b shows a schematic view along the section A - A in Fig. 2b of a cylinder head according to an embodiment, Fig. 4a shows coolant flow velocities in the plane in Fig. 3a.

Fig. 4b shows coolant flow velocities in the cooling chamber in Fig. 3b.

Fig. 6 shows a method according to an embodiment.

All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the embodiments, wherein other parts may be omitted. Like reference numerals refer to like elements throughout the description.

Detailed description of embodiments Fig- 1 shows a schematic side view of a vehicle 1, which vehicle comprises an internal combustion engine 2. The internal combustion engine 2 is connected to a cooling system 8. The internal combustion engine 2 and the cooling system 8, per se, are well known in the art and are therefore not further described.

Fig. 2a shows a section of a cylinder arrangement 3 of an internal combustion engine 2.

The at least one cylinder arrangement comprises a piston 4, a cylinder bore 5, an inlet port arrangement 6, an exhaust port arrangement 7 and a not shown fuel injection arrangement. The piston 4 is arranged to reciprocate in the cylinder bore 5. The piston 4 typically connected to a crankshaft of the internal combustion engine via a piston rod 8. A combustion chamber 9 is formed above the piston 4 inside the cylinder arrangement. The combustion chamber 9 is delimited by a fire deck 10 which is construed by the bottom of a cylinder head 11 and the seats of the intake valves 6a and the exhaust valves 7a.

As may be most easily seen in Figs 3a and 3b, the cylinder head 3 has two intake ports 31a, 31b through which the two inlet valves 6a extend and two exhaust ports 32a, 32b through which the two exhaust valves 7a extend. The cylinder arrangement 3 may have other number of valves, e.g. one intake and one exhaust valve; two intake and one exhaust valve or three intake and two exhaust valves. When closed the valves seats are abutted against the bottom wall of the cylinder head 11, together defining the fire deck 10, as seen in Fig. 2. Centred between the intake and exhaust ports is a through hole 33 for a fuel injector that injects fuel into the combustion chamber. In Otto engines, a spark plug is usually fitted in this local and the fuel injector is usually arranged outside the valves.

The temperatures of the combustion flame in the combustion chamber of an Diesel engine may be above 1000°C and the temperatures of the combustion gases (exhaust gases) leaving the combustion chamber through the exhaust port can be up to around 500°C. To keep the engine from beeing destroyed by the high temperatures, modern internal combustion engines are provided with a liquid cooling system.

Fig. 2b shows a schematic geometry of the cooling system in an internal combustion engine fitted with a cylinder head according to the invention. The cooling system comprises a first cooling chamber 14 in the cylinder head 11. The first cooling chamber 14 is arranged adjacent to the fire deck 10 and the wall Wf between the first cooling chamber 14 and the fire deck 10 is typically quite thin. For a diesel engine with a swept cylinder volume of 1 - 3 dm<3>, e.g. 2 dm<3>, which is common for engines in heavy goods vehicles, this wall may be around 10 mm thick. The height of the first cooling chamber for an engine of this size may be around 20 mm. This thickness of the fire deck wall wt need to resist the combustion pressure in combustion chamber 9 that can reach 250 bar in a state of the art engine, and even higher pressures are discussed for future engines. For smaller engines and for Otto engines where the combustion pressure may be considerably lower, this wall may be even thinner.

The first cooling chamber 14 has at least one inlet connected to the cool side of a cooling system 8. The first cooling chamber has at least one outlet connected to a second cooling chamber 16 arranged above the first cooling chamber (i.e. the opposite side from the combustion chamber 9 - vertically in the Figs.). The first cooling chamber 14 also has at least one outlet to coolant channels 19 in the cylinder jacket 19. The cylinder jacket 19 has at least one outlet to the cooling system 8.

The second cooling chamber 16 has a larger vertical extension (i.e. in the axial direction of cylinder bore) the than the first cooling chamber 14. The second cooling chamber has an outlet to the cooling system 8.

The second cooling chamber 16 is larger than the first chamber 14. The vertical extension is about twice as large, thereby is the flow velocity of the coolant much lower than in the first cooling chamber 14. Also, as the second cooling chamber is positioned further away from the firedeck 10 and a large quantity of the heat in the cylinder head than the first cooling chamber, the tensional and thermal stresses on the cylinder head is much lower here. As a consequence, the design of the second cooling chamber 16 is not as critical as the design of the first cooling chamber 14.

The coolant flow through the cylinder arrangement is schematicly shown by the arrows in Fig. 2b. The cool coolant from the engine’s cooling system 8 enters the first cooling chamber 14 where it absorbs heat from the cylinder head 3. The coolant then enters either the second cooling chamber 16 or the cylinder jacket 19 where it absorbs more heat. From there, the now significally warmer coolant is led back to the warm side of the engine’s coolant system 8. It should be noted that the coolant flow can be directed through the cylinder arrangement 3 in the opposite direction.

Fig. 3a schematically shows the section A-A of Fig. 2 in a known cylinder head and Fig. 3b shows the section A-A of Fig. 2 in a cylinder head 11 according to an embodiment. According to the embodiment in Fig. 3b, the outer passages 21, 22 and the inner passage 23 are flow wise separated by wall means 25a, 25b. These wall means can be solid and completely block any flow between the main passages 21, 22, 23. In other embodiments, the wall can be open to a limited degree, eg. 5 - 30%. By opening the wall to a limited extent, the pressure in the passages may be leveled, without introducing a crossflow between the main passages 21, 22, 23. The walls 25a, 25b may also increase the strengh of the cylinder head, allowing for higher combustion pressures in the combustion chamber.

The flow wise separation of the main passages may for some embodiments also be achieved so called virtual walls, i.e, by creating structures in the flow so there is no or very little flow between the main passages. This can e.g. be achieved by designing the inside of the walls of the first cooling chamber so that a stable recirculation zone is created where the walls 25a, 25b are located in other embodiments, thereby preventing cross flow between the main passages.

In Fig. 4a the coolant flow in a cooling chamber in the section A-A of Fig. 2 in a known cylinder head is illustrated. The coolant flow enters the cooling chamber at the inlet 41 and exits at through the outlet 42. As may be seen in the flow lines shown in Fig. 5a, there is a substantial crossflow in the passages 24a, 24b between the intake port and the closest exhaust port. Due to the crossflows, there is also significant stagnation/recirculation, mainly in the central passage 44 between the intake port upstream of the fuel injector through hole 33 and in the passages 24a, 24b between each intake port 31a, 31b and closest exhaust port 32a, 32b. These recirculation zones restricts the active width of the passages, thereby limiting the maximal coolant flow through the cooling chamber 14. As the recirculation zones, where the flow velocity is much lower than in the free stream, are located against the chamber walls, they also reduce the convectional heat transfer from the wall to the coolant.

In Fig. 4b, the coolant flow in the first cooling chamber according to an aspect is shown. The boundary conditions in Figs. 4a and 4b are the same. In this aspect, the outer and inner passages are completely separated between the inlet junction 41a and the outlet junction 42a, i.e. there is a wall 25a blocking the passage 24a between the intake port 31a and the closest exhaust port 32a and a corresponding wall 25b blocking the passage 24b between the intake port 31b and the closest exhaust port 32b. As may be readily seen from Fig 5b, the removed cross flow has also led to the recirculation zones being dimished. Thereby the flow velocity, especially in the central inner passage 23 between the ports, is noticably increased as well as the thermal transmittance from the cylinder head 3 to the coolant.

By the flow wise separation of the outer and passages 21, 22 and the inner passage 23, the limitation in effective flow area and thermal transmittance by disadvantageously placed recirculations may be reduced or even eliminated. Thereby an increased cooling of the cylinder head may be achieved, allowing for higher combustion temperatures in the cylinder chamber 9. Alternatively or in combination, the same cooling effect may be achieved with smaller cooling chambers than in known cylinder heads. As the flow area may be reduced, the thickness of the walls of the cylinder head, especially around the intake ports 31a, 31b and the exhaust ports 32a, 32b, 33 may be increased.

Thereby the strengh of the cylinder head may be improved further.

In Fig 5, a method for circulating the coolant through the first cooling chamber according to an embodiment is shown. In a first step S1, the coolant enters through the inlet passage 11. In a second step S2, the coolant is led through the first cooling chamber in the two outer passages 21,22 and the inner passage 23, which passages each connects to the inlet passage 11 at the inlet junction 11a and the outlet passage 12 at the outlet junction 12a. The coolant flow through the outer and inner passages 21, 22, 23 are at least partially flow wise separated between the inlet junction 11a and the outlet junctions 12a. In a third step S3, the coolant exits the first cooling chamber through at the outlet passage 12.

The person skilled in the art realizes that the present invention by no means is limited to the embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the coolant can be led through the cylinder arrangement in the opposite direction; the inlet and outlet of the first cooling chamber 14 may be switched.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the descriptions, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims (4)

1. A cylinder head (11) for at least one cylinder of a liquid-cooled internal combustion engine (2), comprising at least two intake ports (31a, 31b), at least two exhaust ports (32a, 32b), a fire deck (10) and a first cooling chamber (14); which first cooling chamber (14) comprises an inlet passage (41) and an outlet passage (42), and wherein the inlet passage (41) is arranged to connect the first cooling chamber to the cool side of the internal combustion engine’s (2) cooling system (8), characterized in that the first cooling chamber (14) comprises two outer passages (21, 22), and at least one inner passage (23), which outer passages (21,22) bypasses the intake and exhaust ports on the outside and the at least one inner passage (23) passes between the intake ports (31a, 31b) and between the exhaust ports (32a, 32b), which outer and inner passages (21, 22, 23) connects to the inlet passage (41) at an inlet junction (41a) and connects to the outlet passage (42) at an outlet junction (42a), and wherein the at least one inner passage (23) is at least partially flow wise separated from the outer passages (21, 22) between the inlet junction (41a) and the outlet junction (42a), wherein the at least partially flow wise separation of the at least one inner passage (23) and the outer passages (21, 22) is created by wall means (25a, 25b) arranged between each exhaust port (32a, 32b) and the adjacent intake port (31a, 31b).

2. The cylinder head (11) according to claim 1, wherein the wall means (25a, 25b) completely separates the at least one inner passage (23) from the outer passages (21, 22) between the inlet and outlet junctions (41 a, 42a).

3. The cylinder head (11) according to anyone of the previous claims, wherein the cylinder head comprises two exhaust ports (32a, 32b) and two intake ports (31a, 31b). 4. The cylinder head (11) according to claim 3, wherein the cylinder head comprises a through hole (33) for a device, such as a fuel injector or a spark plug, arranged between the intake and exhaust ports (31a, 31b, 32a, 32b), and wherein the inner passage (23) of the first cooling chamber (14) is divided into a first inner sub-passage and a second inner subpassage at a third junction (44a) on the inlet junction (41 a) side of the through hole (33), and the inner two sub-passages are joined at a forth junction (44b) on the outlet junction (42a) side of the through hole (33). 5. The cylinder head (11) according to any of the previous claims, wherein the inlet passage (41) of the first cooling chamber (14) is arranged at the intake port side of the cylinder head (11) and the outlet passage (42) is arranged at the exhaust port side of the cylinder head (11). 6. The cylinder head (11) according to any of claims 1 - 4, wherein the inlet passage (41) of the first cooling chamber (14) is arranged at the exhaust port side of the cylinder head (11) and the outlet passage (42) is arranged at the intake port side of the cylinder head (11). 7. The cylinder head (11) according to any of the previous claims, wherein the cylinder head (11) comprises a second cooling chamber (16) arranged on the opposite side of the first cooling chamber (14) from the fire deck (10), which second cooling chamber (16) comprises an inlet passage (52) and an outlet passage (53), wherein the outlet passage (42) of the first cooling chamber (14) is flow connected to the inlet passage (52) of the second cooling chamber, and the outlet passage (53) of the second cooling chamber (16) is arranged to connect to the warm side of the engine’s cooling system (8). 8. The cylinder head (11) according to any of the previous claims, wherein the first cooling chamber’s outlet passage (42) is arranged to be flow connected to a connection passage (17) connected to cooling passages (19a) in the cylinder jacket (19). 9. The cylinder head (11) according to any of the previous claims, wherein the outer diameter of the first cooling chamber (14) is 100 - 200 mm, preferably 120-180 mm, most preferably 140 - 160 mm. 10. An internal combustion engine (2), characterized in that the internal combustion engine (2) comprises a cylinder head (11) according to any of the claims 1 - 9. 11. The internal combustion engine (2) according to claim 10, wherein the internal combustion engine is a compression ignited engine, such as a diesel engine. 12. A vehicle (1), preferably a heavy vehicle such as a truck or a bus, characterized in that it comprises an internal combustion engine according to claim 10 or 11. 13. A method for cooling a cylinder head (11) for at least one cylinder of a liquid-cooled internal combustion engine (2), comprising at least two intake ports (31a, 31b), at least two exhaust ports (32a, 32b), a fire deck (10) and a first cooling chamber (14); which first cooling chamber (14) comprises an inlet passage (41) and an outlet passage (42); wherein the inlet passage (41) is arranged to connect the first cooling chamber to the cool side of the engine’s cooling system (3), wherein coolant being circulated through the first cooling chamber (14) entering through the inlet passage (41) and exiting through the outlet passage (42), characterized in that the coolant is led through the first cooling chamber in two outer passages (21, 22) and at least one inner passage (23), which inner and outer passages (21, 22) each connects to the inlet passage (41) at an inlet junction (41 a) and connects to the outlet passage (42) at an outlet junction (42a), wherein the coolant flow through the at least one inner passage (23) is flow wise separated from the coolant flow through the outer passages (21, 22) between the inlet junction (41a) and outlet junction (42a).

4. The method according to claim 13, wherein the coolant flow through the first cooling chamber (4) is in the range of 0.01 - 5 kg/s, preferably 0.01 -3 kg/s, most preferably 0.1 - 1.5 kg/s.