SE1650836A1 - A Cylinder Head for an Internal Combustion Engine - Google Patents

Abstract

A cylinder head (11) for a liquid-cooled internal combustion engine (2). The cylinder head comprises a first cooling chamber (14) arranged adjacent to a fire deck (10). The first cooling chamber comprises two first outer passages (21, 22) and at least one inner passage (23). These passages each connects to one inlet passage (41) at an inlet junction (41a) and to one outlet passage (42) at an outlet junction (42a), wherein the passages are at least partially flow wise separated between the inlet and outlet junctions. This facilitates an improved coolant flow and heat transfer from the cylinder head to the coolant.

Description

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

Background of the invention ln an internal combustion engine an air-fuel mixture combusts in acombustion chamber under high pressure. ln a compression ignited engine,such as a diesel engine, the combustion chamber is delimited by a fire deckin the cylinder head, the cylinder walls and the piston head. The diesel fuel isignited when the air-fuel mixture is compressed by the piston. The air addedto the combustion is cool and the exhausts are very Warm. For the air and fuelto enter and the exhaust to exit the combustion chamber, the cylinder head isprovided with intake ports and exhaust ports to each cylinder, each providedwith a valve closing against the fire deck. A fuel injector is typically placedcentred between the ports in the fire deck. The intake and exhaust ports arepositioned in close proximity to each other. As a consequence, the cylinderhead is exposed to, in addition to the large pressure loads due to thecombustion, large temperature gradients.

To avoid malfunction and ruptures of the valves and the cylinder head,effective cooling of the cylinder head is needed. l\/lost modern internalcombustion engines are Iiquid-cooled, where a coolant is circulating throughthe cylinder head. Particularly in the case of high-power diesel combustionengines with high heat generation and high combustion pressures, insufficientheat removal from the cylinder head may lead to leaks, cracks and warpingphenomena 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, whichis hereby incorporated by reference. According to WO 2015/094086 A1, thecoo|ant 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 coo|ant are led inparallell to an upper cooling chamber in the cylinder head and an cooling passage in the upper part of a cylinder liner. ln order to maximize the coo|ant flow through a cylinder head and therebyachieve enough cooling of the fire deck, especially in the area between thevalves, also known as the valve bridge area, the lower cooling chamber ismade large as possible. ln a state-of-the-art cylinder head for a liquid-cooledengine, the walls of the cylinder head surrounding the lower cooling chamberare therefore very thin. ln order to increase the efficiency of internal combustion engines whilefulfilling present and future emission legislation, there is a desire to increaseboth the pressure and the temperature in the combustion chamber duringcombustion.

However, as indicated above, there is a conflict between increasing thestrength of the cylinder and increasing the coo|ant flow through of the coolingchamber in the cylinder head.

Summary of the invention lt would be advantageous to achieve a cylinder head overcoming, or at leastalleviating, the above mentioned drawbacks. ln particular, it would bedesirable to enable a cylinder head which enables both efficient cooling andhigh strengh, thereby allowing both very high combustion pressure and veryhigh combustion temperature in the engine. lt 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 amethod 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 aliquid-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 coolside of the engine”s cooling system. The first cooling chamber comprises twoouter passages and at least one inner passage. The outer passagesbypasses the intake and exhaust ports on the outside and the at least oneinner passage passes between the intake ports and between the exhaustports. The outer and inner passages connects to the inlet passage at an inletjunction and connects to the outlet passage at an outlet junction. The at leastone inner passage is at least partially flow wise separated from the outerpassages between the inlet junction and the outlet junction.

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

According to embodiments, the at least partially flow wise separation of the atleast one inner passage and the outer passages is created by wall meansarranged between each exhaust port and the adjacent intake port.

By such wall means, the flow in the passages may be directed in a favourabledirection from the inlet junction to the outlet junction, thereby increasing thecooling of the cylinder head. Further, the region between an exhaust port andan intake is particulary exposed to stresses, as the thermal gradients arelarge here. This is because the intake air entering the combustion chamber through the intake valve typically has a temperature close to the ambienttemperature, typicially below 70 °C, while the exhaust gases leaving thecombustion chamber through the exhaust valve is 200 - 700 °C, for the mostcommon operating conditions 350 - 400 °C. As this region is relativelycentered 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 thestrengh of the cylinder head in a very positive way.

According to embodiments, the wall means completely separates the at leastone inner passage from the outer passages between the inlet and outletjunctions. By limiting the open portion of the cross section area, an improvedflow wise separation of the main passages can be achieved as the influenceof the boundary conditions of the flow through the cooling chamber for theflow wise separation of the flow between the channels can be reduced.Thereby, a cylinder head that need less adaption to other components of theengine and the cooling system may be achieved.

According to embodiments, the cylinder head comprise two exhaust portsand two intake ports. For an engine where each cylinder has as two inletvalves and exhaust valves, arranging wall means between each exhaustvalve through hole and the closest intake valve through hole, the flow throughthe different main passages is essentially parallel through the coolingchamber, facilitating a stable and efficient cooling of the cylinder head. Byarranging wall means in this way, the cooling chamber has supporting wallsessentially 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 adevice, such as a fuel injector or a spark plug, arranged between the intakeand exhaust ports. The inner passage of the first cooling chamber is dividedinto a first inner sub-passage and a second inner sub-passage at a thirdjunction on the inlet junction side of the through hole, and the inner two sub-passages 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 thehight (in the axial direction, coolinear with the axial direction of the cylinderbore 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 chamberswith these dimensions, very good cooling may be achieved.

According to an aspect, a method for cooling a cylinder head for at least onecylinder of a liquid-cooled internal combustion engine, comprising at least twointake ports, at least two exhaust ports, a fire deck and a first coolingchamber is provided. The first cooling chamber comprises an inlet passageand an outlet passage. The inlet passage is arranged to connect the firstcooling chamber to the cool side of the engine”s cooling system. The coolantbeing circulated through the first cooling chamber entering through the inletpassage and exiting through the outlet passage. The coolant is led throughthe first cooling chamber in two outer passages and at least one innerpassage. The inner and outer passages each connects to the inlet passage atan inlet junction and connects to the outlet passage at an outlet junction. Thecoolant flow through the at least one inner passage are at least partially flowwise 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 becomeapparent when reading the appended claims and the following detaileddescription. lt will be appreciated that the various embodiments described forthe cylinder head are all combinable with the method as defined inaccordance with that aspect of the present invention.

Brief description of the drawinqs Various aspects of the invention, including particular features andadvantages, will be readily understood from the example embodiments in thefollowing detailed description and the accompanying drawings, in which: Fig. 1 shows a schematic side view of a vehicle, comprising internalcombustion engine with a cylinder head according to an embodiment, Fig. 2a shows a cutaway view of a cylinder arrangement including a cylinderhead, 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 cylinderhead 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 onlyshow parts which are necessary in order to elucidate the embodiments,wherein other parts may be omitted. Like reference numerals refer to likeelements throughout the description.

Detailed description of embodiments Fig. 1 shows a schematic side view of a vehicle 1, which vehicle comprisesan internal combustion engine 2. The internal combustion engine 2 isconnected to a cooling system 8. The internal combustion engine 2 and thecooling system 8, per se, are well known in the art and are therefore notfurther described.

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

The at least one cylinder arrangement comprises a piston 4, a cylinder bore5, an inlet port arrangement 6, an exhaust port arrangement 7 and a notshown fuel injection arrangement. The piston 4 is arranged to reciprocate inthe 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 isformed above the piston 4 inside the cylinder arrangement. The combustionchamber 9 is delimited by a fire deck 10 which is construed by the bottom of acylinder head 11 and the seats of the intake valves 6a and the exhaust valves7a.

As may be most easily seen in Figs 3a and 3b, the cylinder head 3 has twointake ports 31 a, 31 b through which the two inlet valves 6a extend and twoexhaust ports 32a, 32b through which the two exhaust valves 7a extend. Thecylinder arrangement 3 may have other number of valves, e.g. one intake andone exhaust valve; two intake and one exhaust valve or three intake and twoexhaust valves. When closed the valves seats are abutted against the bottomwall 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 afuel injector that injects fuel into the combustion chamber. ln Otto engines, aspark 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 anDiesel engine may be above 1000 °C and the temperatures of the combustiongases (exhaust gases) leaving the combustion chamber through the exhaustport can be up to around 500 °C. To keep the engine from beeing destroyedby 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 internalcombustion engine fitted with a cylinder head according to the invention. Thecooling 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 thewall wf between the first cooling chamber 14 and the fire deck 10 is typicallyquite thin. For a diesel engine with a swept cylinder volume of 1 - 3 dm3, e.g.2 dm3, which is common for engines in heavy goods vehicles, this wall maybe around 10 mm thick. The height of the first cooling chamber for an engineof this size may be around 20 mm. This thickness of the fire deck wall wf 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 discussedfor future engines. For smaller engines and for Otto engines where thecombustion 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 sideof a cooling system 8. The first cooling chamber has at least one outletconnected to a second cooling chamber 16 arranged above the first coolingchamber (i.e. the opposite side from the combustion chamber 9 - vertically inthe Figs.). The first cooling chamber 14 also has at least one outlet to coolantchannels 19 in the cylinder jacket 19. The cylinder jacket 19 has at least oneoutlet to the cooling system 8.

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

The second cooling chamber 16 is larger than the first chamber 14. Thevertical extension is about twice as large, thereby is the flow velocity of thecoolant much lower than in the first cooling chamber 14. Also, as the secondcooling chamber is positioned further away from the firedeck 10 and a largequantity of the heat in the cylinder head than the first cooling chamber, thetensional and thermal stresses on the cylinder head is much lower here. As aconsequence, the design of the second cooling chamber 16 is not as criticalas the design of the first cooling chamber 14.

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

Fig. 3a schematically shows the section A-A of Fig. 2 in a known cylinderhead and Fig. 3b shows the section A-A of Fig. 2 in a cylinder head 11according to an embodiment. According to the embodiment in Fig. 3b, theouter passages 21, 22 and the inner passage 23 are flow wise separated bywall means 25a, 25b. These wall means can be solid and completely blockany flow between the main passages 21, 22, 23. ln other embodiments, thewall can be open to a limited degree, eg. 5 - 30%. By opening the wall to alimited extent, the pressure in the passages may be leveled, withoutintroducing a crossflow between the main passages 21, 22, 23. The walls25a, 25b may also increase the strengh of the cylinder head, allowing forhigher combustion pressures in the combustion chamber.

The flow wise separation of the main passages may for some embodimentsalso be achieved so called virtual walls, i.e, by creating structures in the flowso there is no or very little flow between the main passages. This can e.g. beachieved by designing the inside of the walls of the first cooling chamber sothat a stable recirculation zone is created where the walls 25a, 25b arelocated in other embodiments, thereby preventing cross flow between the main passages. ln Fig. 4a the coolant flow in a cooling chamber in the section A-A of Fig. 2 ina known cylinder head is illustrated. The coolant flow enters the coolingchamber at the inlet 41 and exits at through the outlet 42. As may be seen inthe flow lines shown in Fig. 5a, there is a substantial crossflow in thepassages 24a, 24b between the intake port and the closest exhaust port. Dueto the crossflows, there is also significant stagnation/recirculation, mainly inthe central passage 44 between the intake port upstream of the fuel injectorthrough hole 33 and in the passages 24a, 24b between each intake port 31 a,31 b and closest exhaust port 32a, 32b. These recirculation zones restricts theactive width of the passages, thereby limiting the maximal coolant flowthrough the cooling chamber 14. As the recirculation zones, where the flowvelocity is much lower than in the free stream, are located against thechamber walls, they also reduce the convectional heat transfer from the wall to the coolant. ln Fig. 4b, the coolant flow in the first cooling Chamber according to an aspectis shown. The boundary conditions in Figs. 4a and 4b are the same. ln thisaspect, the outer and inner passages are completely separated between thein|et junction 41 a and the outlet junction 42a, i.e. there is a wall 25a blockingthe passage 24a between the intake port 31 a and the c|osest exhaust port32a and a corresponding wall 25b blocking the passage 24b between theintake port 31 b and the c|osest exhaust port 32b. As may be readily seenfrom Fig 5b, the removed cross flow has also led to the recirculation zonesbeing dimished. Thereby the flow velocity, especially in the central innerpassage 23 between the ports, is noticably increased as well as the thermaltransmittance from the cylinder head 3 to the coolant.

By the flow wise separation of the outer and passages 21, 22 and the innerpassage 23, the limitation in effective flow area and thermal transmittance bydisadvantageously placed recirculations may be reduced or even eliminated.Thereby an increased cooling of the cylinder head may be achieved, allowingfor higher combustion temperatures in the cylinder chamber 9. Alternatively orin combination, the same cooling effect may be achieved with smaller coolingchambers than in known cylinder heads. As the flow area may be reduced,the thickness of the walls of the cylinder head, especially around the intakeports 31 a, 31 b and the exhaust ports 32a, 32b, 33 may be increased.Thereby the strengh of the cylinder head may be improved further. ln Fig 5, a method for circulating the coolant through the first cooling chamberaccording to an embodiment is shown. ln a first step S1, the coolant entersthrough the in|et passage 11. ln a second step S2, the coolant is led throughthe first cooling chamber in the two outer passages 21,22 and the innerpassage 23, which passages each connects to the in|et passage 11 at thein|et junction 11a and the outlet passage 12 at the outlet junction 12a. Thecoolant flow through the outer and inner passages 21, 22, 23 are at leastpartially flow wise separated between the in|et junction 11a and the outletjunctions 12a. ln a third step S3, the coolant exits the first cooling chamberthrough at the outlet passage 12. 11 The person skilled in the art realizes that the present invention by no meansis limited to the embodiments described above. On the contrary, manymodifications and variations are possible within the scope of the appendedclaims. For example, the coolant can be led through the cylinder arrangementin the opposite direction; the inlet and outlet of the first cooling chamber 14may be switched.

Additionally, variations to the disclosed embodiments can be understood andeffected by the skilled person in practicing the claimed invention, from a studyof the drawings, the descriptions, and the appended claims. ln the claims, theword "comprising" does not exclude other elements or steps, and theindefinite article "a" or "an" does not exclude a plurality. The mere fact thatcertain measures are recited in mutually different dependent claims does notindicate that a combination of these measures cannot be used to advantage.

Claims (15)

12 Claims 1 _

1. A cylinder head (11) for at least one cylinder of a Iiquid-cooled internalcombustion engine (2), comprising at least two intake ports (31a, 31b), atleast two exhaust ports (32a, 32b), a fire deck (10) and a first coolingChamber (14); which first cooling Chamber (14) comprises an inletpassage (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 theinternal combustion engine”s (2) cooling system (8), characterized in that the first cooling chamber (14) comprises two outerpassages (21, 22), and at least one inner passage (23), which outerpassages (21 ,22) bypasses the intake and exhaust ports on the outsideand the at least one inner passage (23) passes between the intake ports(31 a, 31 b) and between the exhaust ports (32a, 32b), which outer andinner passages (21, 22, 23) connects to the inlet passage (41) at an inletjunction (41 a) and connects to the outlet passage (42) at an outlet junction(42a), and wherein the at least one inner passage (23) is at least partiallyflow wise separated from the outer passages (21, 22) between the inletjunction (41a) and the outlet junction (42a).

2. The cylinder head (11) according to claim 1, wherein the at least partiallyflow wise separation of the at least one inner passage (23) and the outerpassages (21, 22, 23) is created by wall means (25a, 25b) arrangedbetween each exhaust port (32a, 32b) and the adjacent intake port (31 a,31 b).

3. The cylinder head (11) according to claim 3, wherein the wall means (25a,25b) completely separates the at least one inner passage (23) from theouter passages (21, 22, 23) between the inlet and outlet junctions (41a,42a). 13

4. The cylinder head (11) according to anyone of the previous claim 1, wherein the cylinder head comprises two exhaust ports (32a, 32b) and twointake ports (31 a, 31 b).

5. _ The cylinder head (11) according to claim 4, wherein the cylinder head comprises a through hole (33) for a device, such as a fuel injector or aspark plug, arranged between the intake and exhaust ports (31 a, 31 b,32a, 32b), and wherein the inner passage (23) of the first cooling chamber(14) is divided into a first inner sub-passage (43a) and a second inner sub-passage (43b) at a third junction (44a) on the inletjunction (41a) side ofthe through hole (33), and the inner two sub-passages (43a, 43b) arejoined at a forth junction (44b) on the outlet junction (42a) side of thethrough hole (33).

6. _ 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 theintake port side of the cylinder head (11) and the outlet passage (42) isarranged at the exhaust port side of the cylinder head (11).

7. _ The cylinder head (11) according to any of claims 1 - 5, wherein the inlet passage (41) of the first cooling chamber (14) is arranged at the exhaustport side of the cylinder head (11) and the outlet passage (42) is arranged at the intake port side of the cylinder head (11).

8. _ The cylinder head (11) according to any of the previous claims, wherein the cylinder head (11) comprises a second cooling chamber (16) arrangedon 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 firstcooling chamber (14) is flow connected to the inlet passage (52) of thesecond cooling chamber, and the outlet passage (53) of the secondcooling chamber (16) is arranged to connect to the warm side of the engine”s cooling system (8). 14

9. The cylinder head (11) according to any of the previous claims, whereinthe first cooling chamber”s outlet passage (42) is arranged to be flowconnected to a connection passage (17) connected to cooling passages(19a) in the cylinder jacket (19).

10.The cylinder head (11) according to any of the previous claims, whereinthe outer diameter of the first cooling chamber (14) is 100 - 200 mm,preferably 120-180 mm, most preferably 140 - 160 mm.

11.An internal combustion engine (2), characterized in that the internalcombustion engine (2) comprises a cylinder head (11) according to any ofthe claims 1 - 10.

12.The internal combustion engine (2) according to claim 11, wherein theinternal combustion engine is a compression ignited engine, such as a diesel engine.

13.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 11 or 12.

14.A method for cooling a cylinder head (11) for at least one cylinder of aliquid-cooled internal combustion engine (2), comprising at least twointake ports (31 a, 31 b), 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 theinlet passage (41) is arranged to connect the first cooling chamber to thecool side of the engine”s cooling system (3), wherein coolant beingcirculated through the first cooling chamber (14) entering through the inletpassage (41) and exiting through the outlet passage (42), characterizedin that the coolant is led through the first cooling chamber in two outerpassages (21, 22) and at least one inner passage (23), which inner and outer passages (21, 22, 23) each connects to the inlet passage (41) at an inlet junction (41 a) and connects to the outlet passage (42) at an outletjunction (42a), wherein the coolant flow through the at least one innerpassage (23) is at least partially flow wise separated from the coolant flow through the outer passages (21, 22) between the inlet junction (41a) andoutletjunction (42a).

15.The method according to claim 14, wherein the coolant flow through thefirst 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.