AU2013391199B2

AU2013391199B2 - Water cooling system for a cylinder head of an engine

Info

Publication number: AU2013391199B2
Application number: AU2013391199A
Authority: AU
Inventors: Xiaoxuan Guo; Zhisheng Hu; Suhua JIN; Ming Lu; Duode QIAN; Lei Yang; Jiulin ZHENG
Original assignee: Anhui Jianghuai Automobile Group Corp
Current assignee: Anhui Jianghuai Automobile Group Corp
Priority date: 2013-05-27
Filing date: 2013-09-06
Publication date: 2016-03-17
Anticipated expiration: 2033-09-06
Also published as: AU2013391199A1; CN103291487A; CL2015003450A1; WO2014190633A1; RU2625894C1; BR112015029750A2; CN103291487B

Abstract

A cooling water system for a cylinder head of an engine. A cooling water cavity is formed in a cylinder head. The cooling water cavity of the cylinder head is divided into an upper-layer water cavity and a lower-layer water cavity by a middle partition plate. Cooling water enters the lower-layer water cavity through a water inlet hole. A communicating hole is disposed between the upper-layer water cavity and the lower-layer water cavity. Lower-layer cooling water enters the upper-layer water cavity through the communicating hole. In the cooling water system for a cylinder head of an engine, the bottom of the cylinder head can be cooled by cooling liquid in the cylinder head to the greatest extent. A water filling hole of the cylinder head is disposed below an air outlet channel, and a communicating hole between the two layers of water jackets is disposed beside an air inlet channel, so that the cooling liquid enters the cylinder head from a lower side of the air outlet channel, and in the cylinder head, the cooling liquid flows through a region between the air outlet channel and the cylinder head, a region between the air outlet channels and a region between the air outlet channel the air inlet channel, and then enters the upper-layer water jacket of the cylinder head from an air inlet side, thereby fully cooling a high-temperature region around the air outlet channel.

Description

WATER COOLING SYSTEM FOR A CYLINDER HEAD OF AN ENGINE TECHNICAL FIELD [0001] The present invention relates to the field of automobile engines, particularly to the field of cylinder head of an engine, and in particular to a water cooling system for cylinder head of an engine. BACKGROUND [0002] Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field. [0003] The current design of cylinder heads for engines typically include an air inlet channel, an air outlet channel, bolt bosses, an injector mounting hole and other parts are arranged in the cylinder head. A hollow cavity is defined by outer surfaces of the air inlet channel, the air outlet channel, the bolt bosses, the injector mounting hole and an inner surface of the cylinder head. Cooling water flows in the hollow cavity so as to cool the cylinder head and corresponding parts. A water inlet hole of the cylinder head is distributed at a bottom surface of the cylinder head facing a periphery of a cylinder block. According to actual needs, regions which need strengthened cooling most include the bottom surface of the cylinder head, a bridge zone near the injector mounting hole and a region near the air outlet channel. [0004] In many existing cylinder heads, there are two kinds of cavities in which cooling water flows, one being a single layer water cavity structure, and the other being a double-layer water cavity structure. In the single layer water cavity 1 structure, the cooling water, after entering into the cylinder head through the water inlet hole, flows directly on a top portion of the cylinder head, and then a void region is likely produced at the bottom of the cylinder head where little or no cooling occurs. This is problematic as the bottom surface of the cylinder head is the region which needs cooling most, thus, there is limited room to improve the cooling effect provided by the cooling water system of the single layer water cavity structure for the cylinder head. [0005] The double-layer water cavity structure has been widely used. Particularly with the increase of environmental problems involving internal combustion engines, requirements for engine exhaust emissions are becoming stricter and stricter. In order to meet the strict requirements for emissions, reinforcement requirements of the engines are higher and higher. While the cylinder head is a thin wall casting component, the stiffness and strength thereof is relatively weak. Further, due to the requirements of process of the cylinder head, a mold is divided into two layers by taking air channels as a center for manufacturing. When casting, sand cores of two-layer water cavities are adhered together, thereby, inevitable casting fins are formed between the two layers of water cavities, and the rejection rate is increased. [0006] In the cylinder head of two-layer water cavity structure, cooling water is usually supplied by a cooling water channel. Cooling water from the water inlet hole simultaneously enters into both the upper-layer water cavity and the lower-layer water cavity through the cooling water channel in order to improve the cooling effect of the cylinder head. But in this structure, one channel for introducing cooling water 2 into the upper-layer water cavity is added, which increases the volume of the cylinder head, or reduces the volume of the water cavity in the cylinder head, and has little impact on actual cooling effect. [0007] Chinese patent application number CN200810235221.1 discloses a high-strength cylinder head with a two-layer water flow channel, of which the technical solution includes: a cylinder head is composed of an upper bottom board and a lower bottom board; the cylinder head is provided with an oil injector mounting hole; a plurality of gas passages are arranged in the cylinder head surrounding the oil injector mounting hole; the lower bottom board of the cylinder head is provided with a water inlet hole; an upper top board is provided with a water outlet hole; a cooling water cavity is arranged in the cylinder head; a medium partition board is arranged in the cylinder head and divides the cooling water cavity into an upper water cavity and a lower water cavity; an upper connecting water cavity and a lower connecting water cavity are arranged between the oil injector mounting hole and the gas passage; a reinforcing partition board is arranged between the upper connecting water cavity and the lower connecting water cavity; and the reinforcing partition board is provided with an communicating hole connecting the upper connecting water cavity and the lower connecting water cavity into a whole. The water inlet hole is connected to the lower water cavity. The water outlet hole is connected to the upper water cavity. Although the technical solution improves cooling effects, it still has some deficiencies, which mainly includes interrupt of the communicating hole connecting the upper connecting water cavity and the lower connecting water cavity on the flowing path of the cooling 3 water and a certain endless loop existed in parts of the cylinder head away from the water outlet hole, resulting in poor cooling effects. [0008] For the cooling of the cylinder head, there are competing design considerations between the bottom portion and the top portion, and an air inlet side and an air outlet side further have different cooling requirements. This is because although the bottom portion of the cylinder head contacts gas of high temperature, exhausted gas flowing in the air outlet channel can further heat the air outlet side, thus, reducing heat load of the air outlet side is also a key to improve the reliability of the cylinder head. SUMMARY [0009] It is an object of the present invention, at least in the preferred embodiments, to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative. [0010] According to the invention there is provided a water cooling system for a cylinder head of an engine, comprising an integrally formed cylinder head for an engine having at least four cylinders, wherein the cylinder head is provided with an injector mounting hole, two air inlet channels and two air outlet channels distributed at a periphery of the injector mounting hole, and a cooling water cavity defined by an inner surface of the cylinder head, an outer surface of the air inlet channels, an outer surface of the air outlet channels and an outer surface of the injector mounting hole, and wherein: 4 the cooling cavity of the cylinder head is divided into an upper-layer water cavity and a lower-layer water cavity by a partition plate; a water outlet hole is defined in one end of the upper-layer water cavity; water inlet holes for the lower-layer water cavity are evenly distributed in a bottom surface of the cylinder head facing a cylinder block ; cooling water enters into the lower-layer water cavity through the water inlet holes; a communicating hole is disposed between the upper-layer water cavity and the lower-layer water cavity; and the cooling water in the lower-layer water cavity enters into the upper-layer water cavity through the communicating hole; the upper-layer water cavity is comprised of an upper water cavity between an inner wall of the cylinder head and the outer surface of the air inlet channels, an upper surface of the air outlet channels, an upper bridge zone between the outer surface of the injector mounting hole and the outer surface of the air inlet channels, the upper surface of the air outlet channels, and an upper connection water cavity which communicates with the upper water cavity and the upper bridge zone; the lower-layer water cavity is comprised of a lower water cavity between the inner wall of each cylinder head and the outer surface of the air inlet channels, the upper surface of the air outlet channels, a lower bridge zone between the outer surface of the injector mounting hole and the outer surface of the air inlet channels, the upper surface of the air outlet channels, and a lower connection water cavity which communicates with the lower water cavity and the lower bridge zone; and 5 the communicating hole communicates with the upper water cavity and the lower water cavity; wherein a second cylinder head and a third cylinder head further comprise inclined communicating holes which connect the lower connection water cavity of a first cylinder head near the second cylinder head with the upper water cavity of the second cylinder head, and which connect the lower connection water cavity of the second cylinder head near the third cylinder head with the upper water cavity of the third cylinder head, respectively. [0011] Preferably, the communicating hole is defined in an outer side of the air inlet channels in a direction away from the injector mounting hole. [0012] Preferably, an auxiliary water filling hole is defined beside the air outlet channels. [0013] Preferably, in two sides of each air inlet channel or each air outlet channel, there are two upper connection water cavities and lower connection water cavities. [0014] Preferably, the lower-layer water cavity comprises at least four cooling water flow paths which respectively are: a first cooling water flow path along which cooling water from the water inlet holes enters into the lower water cavity, is then guided by the lower connection water cavity to enter into the lower bridge zone near the injector mounting hole, and then to enter into a lower-layer water cavity flow paths of a adjacent cylinder head through the lower connection water cavity near the adjacent cylinder head; 6 a second cooling water flow path along which cooling water enters into the lower water cavity and flows along the inner wall of the cylinder head and the bottom surface of the cylinder head, then flows towards the communicating hole and enters into the upper water cavity; a third cooling water flow path along which cooling water from the water inlet holes enters into the lower water cavity, and then flows towards the lower-layer water cavity flow paths of the adjacent cylinder head; and a fourth cooling water flow path along which cooling water from the water inlet holes enters into the lower water cavity, then is guided by the lower connection water cavity and enters into the lower bridge zone near the injector mounting hole, and then enters into the upper water cavity through the lower connection water cavity near the adjacent cylinder head and through the inclined communicating hole. [0015] Preferably, the upper-layer water cavity comprises at least two cooling water flow paths which respectively are: a fifth cooling water flow path along which cooling water enters into the upper water cavity through the communicating hole, enters into the upper bridge zone through the upper connection water cavity, then flows towards a upper-layer water cavity flow paths of a adjacent cylinder head for collection at the water outlet hole; and a sixth cooling water flow path along which cooling water enters into the upper water cavity through the communicating hole, flows past the inner wall of the cylinder head and the outer surface of the air inlet channels or the outer surface of the 7 air outlet channels, and then flows towards a upper-layer water cavity flow paths of the adjacent cylinder head for collection at the water outlet hole. Preferably, the water inlet holes comprise a main water inlet hole and an auxiliary water inlet hole; and wherein: both the main water inlet hole and the auxiliary water inlet hole are provided below the air outlet channels; area of the auxiliary water inlet hole is gradually increased from the cylinder head distant from the water outlet hole towards the cylinder head near the water outlet hole. [0016] Preferred embodiments of the present invention provide a water cavity of a cylinder head of an engine, which can change flow path of cooling liquid, so as to improve cooling of the cylinder head and increase service life of the cylinder head. [0017] Another object of the preferred embodiments of the present invention is to provide a cylinder head of an engine having the above water cavity. [0018] At least some of the preferred embodiments of the present invention are achieved through the following technical solutions. [0019] A cooling water system for a cylinder head of an engine, includes integrated formed cylinder head of an engine having at least four cylinders; wherein the cylinder head is provided with an injector mounting hole, two air inlet channels and two air outlet channels distributed at a periphery of the injector mounting hole, and a cooling water cavity defined by an inner surface of the cylinder head, an outer surface of the air inlet channels, an outer surface of the air outlet channels and an outer surface of the injector mounting hole; wherein the cooling water cavity of the cylinder head is divided into an upper-layer water cavity and a lower-layer water 8 cavity by a partition plate; a water outlet hole is defined in one end of the upper-layer water cavity, water inlet holes for the lower-layer water cavity are evenly distributed in a bottom surface of the cylinder head facing a cylinder block; cooling water enters into the lower-layer water cavity through the water inlet hole; a communicating hole is disposed between the upper-layer water cavity and the lower-layer water cavity, and the cooling water in the lower-layer water cavity enters into the upper-layer water cavity through the communicating hole; the upper-layer water cavity is composed of an upper water cavity between an inner wall of the cylinder head and the outer surface of the air inlet channels as well as an upper surface of the air outlet channels, an upper bridge zone between the outer surface of the injector mounting hole and the outer surface of the air inlet channels as well as the upper surface of the air outlet channels, and an upper connection water cavity which communicates with the upper water cavity and the upper bridge zone; the lower-layer water cavity is composed of a lower water cavity between the inner wall of the cylinder head and the outer surface of the air inlet channels as well as the upper surface of the air outlet channels, a lower bridge zone between the outer surface of the injector mounting hole and the outer surface of the air inlet channels as well as the upper surface of the air outlet channels, and a lower connection water cavity which communicates with the lower water cavity and the lower bridge zone; the communicating hole communicates with the upper water cavity and the lower water cavity. 9 [0020] A second cylinder head and a third cylinder head further include inclined communicating holes, which connects the lower connection water cavity of a first cylinder head near the second cylinder head with the upper water cavity of the second cylinder head, and connects the lower connection water cavity of the second cylinder head near the third cylinder head with the upper water cavity of the third cylinder head, respectively. [0021] The communicating hole is defined in an outer side of the air inlet channels in a direction away from the injector mounting hole. [0022] An auxiliary water filling hole is defined beside the air outlet channels. [0023] In two sides of each air inlet channel or each air outlet channel, there are two upper connection water cavities and two lower connection water cavities. [0024] The lower-layer water cavity includes at least four cooling water flow paths which respectively are: a first cooling water flow path in which cooling water from the water inlet hole enters into the lower water cavity, then is guided by the lower connection water cavity and enters into the lower bridge zone near the injector mounting hole, and then enters into a lower-layer water cavity flow paths of a adjacent cylinder head through the lower connection water cavity near the adjacent cylinder head; a second cooling water flow path in which cooling water entering into the lower water cavity flows along the inner wall of the cylinder head and the bottom surface of the cylinder head, then flows towards the communicating hole and enters into the upper water cavity; 10 a third cooling water flow path in which cooling water from the water inlet hole enters into the lower water cavity, and then flows towards the lower-layer water cavity flow paths of the adjacent cylinder head; a fourth cooling water flow path in which cooling water from the water inlet hole enters into the lower water cavity, then is guided by the lower connection water cavity and enters into the lower bridge zone near the injector mounting hole, and then enters into the upper water cavity through the lower connection water cavity near the adjacent cylinder head and through the inclined communicating hole. [0025] The upper-layer water cavity includes at least two cooling water flow paths which respectively are: a fifth cooling water flow path in which cooling water enters into the upper water cavity through the communicating hole, enters into the upper bridge zone through the upper connection water cavity, then flows towards an upper-layer water cavity flow paths of the adjacent cylinder head and is collected towards the water outlet hole; a sixth cooling water flow path in which cooling water enters into the upper water cavity through the communicating hole, flows past the inner wall of the cylinder head and the outer surface of the air inlet channels or the outer surface of the air outlet channels, and then flows towards the upper-layer water cavity flow paths of the adjacent cylinder head and is collected towards the water outlet hole. [0026] The water inlet hole includes a main water inlet hole and an auxiliary water inlet hole; both the main water inlet hole and the auxiliary water inlet hole are 11 provided below the air outlet channels; areas of the auxiliary water outlet holes are gradually increased from the cylinder head distant from the water outlet hole towards the cylinder head near the water outlet hole. [0027] Comparing with the prior art, beneficial effects of the present invention are as follows. [0028] For the cooling of the cylinder head, in addition to contradiction between the bottom portion and the top portion, the air inlet side and the air outlet side further have different cooling requirements. This is because although the bottom portion of the cylinder head contacts gas of high temperature, exhausted gas flowing in the air outlet channels can further heat the air outlet side, thus, reducing heat load of the air outlet side is also a key to improve the reliability of the cylinder head. The present invention provides a cylinder head of a double-layer water cavity, which can make cooling liquid in the cylinder head cool the bottom of the cylinder head to the greatest extend. Meanwhile, the water filling hole of the cylinder head is disposed below the air outlet channels, the communicating hole between two layers of water cavities are designed to be at the air inlet channels side, in this way, the cooling liquid enters into the cylinder head from a position below the air outlet channels; in the cylinder head, the cooling liquid flows past a region between the air outlet channels and the cylinder head, a region between the air outlet channels and a region between the air outlet channels and the air inlet channels, and then enters into the upper-layer water cavity of the cylinder head from the air inlet side. Meanwhile, some of the 12 cooling liquid flows into the adjacent cylinder head. By such a design, a high temperature region around the air outlet channels can be sufficiently cooled. [0029] Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of "including, but not limited to". BRIEF DESCRIPTION OF THE DRAWINGS [0030] Embodiments of the invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a schematic cross-sectional view of a cylinder head according to the present invention; Fig. 2 is a sectional view of a communicating hole according to the present invention; Fig. 3 is a top view of an upper-layer water cavity of the cylinder head according to the present invention; and Fig. 4 is a top view of a lower-layer water cavity of the cylinder head according to the present invention. DETAILED DESCRIPTION [0031] The technical solutions of the preferred embodiments of the present invention will be described in detail hereinafter in conjunction with the detailed embodiments shown in the drawings. It should be appreciated that, the following embodiments are merely exemplary and merely used to illustrate and explain the 13 technical solutions of the present invention, but shall not be used to limit the technical solutions of the present invention. [0032] Figs. 1-4 show a cooling water system for cylinder head of an engine, which merely refer to cylinder head including first to fourth cylinder head of a four-cylinder engine. An injector mounting hole 3 is defined in a central position of each cylinder head. Two air inlet channels and two air outlet channels 4 are distributed in a diamond shape at a periphery of the injector mounting hole 3. The cylinder head has an internal hollow structure, and an outer surface of the air inlet channels, an outer surface of the air outlet channels and an outer surface of the injector mounting hole define a cooling water cavity of the cylinder head. The cooling water cavity of the cylinder head is divided into an upper-layer water cavity 1 and a lower-layer water cavity 2 by a partition plate. A water outlet hole is defined in one end of the upper-layer water cavity at a side of the fourth cylinder head. Water inlet holes for the lower-layer water cavity are evenly distributed in a bottom surface of the cylinder head facing a cylinder block. Cooling water flows through an outer water channel of the cylinder block and enters into the lower-layer water cavity through the water inlet holes. A communicating hole is disposed between the upper-layer water cavity and the lower-layer water cavity. The lower-layer cooling water enters into the upper-layer water cavity through the communicating hole. The communicating hole is defined in an outer side of the air inlet channels in a direction away from the injector mounting hole. Here, the outer side of the air inlet channels means that the communicating hole 14 is defined in an outer side of an arc of a circumscribed circle of the diamond shape defined by the air inlet channels and the air outlet channels. [0033] The upper-layer water cavity is composed of an upper water cavity between an inner wall of the cylinder head and the outer surface of the air inlet channels as well as an upper surface of the air outlet channels, an upper bridge zone between the outer surface of the injector mounting hole and the outer surface of the air inlet channels as well as the upper surface of the air outlet channels, and an upper connection water cavity which communicates with the upper water cavity and the upper bridge zone. [0034] The lower-layer water cavity is composed of a lower water cavity between the inner wall of the cylinder head and the outer surface of the air inlet channels as well as the upper surface of the air outlet channels, a lower bridge zone between the outer surface of the injector mounting hole and the outer surface of the air inlet channels as well as the upper surface of the air outlet channels, and a lower connection water cavity which communicates with the lower water cavity and the lower bridge zone. The communicating hole connects the upper water cavity with the lower water cavity. [0035] The second cylinder head and the third cylinder head further include inclined communicating holes, which connects the lower connection water cavity of the first cylinder head near the second cylinder head with the upper water cavity of the second cylinder head, and connects the lower connection water cavity of the 15 second cylinder head near the third cylinder head with the upper water cavity of the third cylinder head, respectively. [0036] An auxiliary communicating hole is defined beside the air outlet channel. The auxiliary communicating hole is defined beside the air outlet channel of the fourth cylinder head. [0037] Two upper connection water cavities and two lower connection water cavities are provided in two sides of each air inlet channel or each air outlet channel, i.e., one upper connection water cavity and one lower connection water cavity are provided between every two air outlet channels, and between one air inlet channel and one air outlet channel. [0038] A flowing direction of cooling water in the upper connection water cavity and the lower connection water cavity defined by the air outlet channel and the air inlet channel at a side of the first cylinder head near the second cylinder head is from the first cylinder head to the second cylinder head. A flowing direction of cooling water in the upper connection water cavity and the lower connection water cavity defined by the air outlet channel and the air inlet channel at a side of the second cylinder head near the third cylinder head is from the second cylinder head to the third cylinder head. A flowing direction of cooling water in the upper connection water cavity and the lower connection water cavity defined by the air outlet channel and the air inlet channel at a side of the third cylinder head near the fourth cylinder head is from the third cylinder head to the fourth cylinder head. A flowing direction of cooling water in the upper connection water cavity and the lower connection water 16 cavity defined by the air inlet channel and the air outlet channel at a side of the fourth cylinder head near the water outlet hole is from the fourth cylinder head to the water outlet hole. In addition, cooling water flow paths in the cylinder head further include: at least four cooling water flow paths in the lower-layer water cavity which respectively are: a first cooling water flow path in which cooling water from the water inlet hole enters into the lower water cavity, then is guided by the lower connection water cavity and enters into the lower bridge zone near the injector mounting hole, and then enters into lower-layer water cavity flow paths of the adjacent cylinder head through the lower connection water cavity near the adjacent cylinder head; a second cooling water flow path in which cooling water entering into the lower water cavity flows along the inner wall of the cylinder head and the bottom surface of the cylinder head, then flows towards the communicating hole and enters into the upper water cavity; a third cooling water flow path in which cooling water from the water inlet hole enters into the lower water cavity, and then flows towards the lower-layer water cavity flow paths of the adjacent cylinder head; a fourth cooling water flow path in which cooling water from the water inlet hole enters into the lower water cavity, is guided by the lower connection water cavity and enters into the lower bridge zone near the injector mounting hole, and then enters into the upper water cavity through the lower connection water cavity near the adjacent cylinder head and through the inclined communicating hole. 17 [0039] There are at least two cooling water flow paths in the upper-layer water cavity, which respectively are: a fifth cooling water flow path in which cooling water enters into the upper water cavity through the communicating hole, enters into the upper bridge zone through the upper connection water cavity, then flows towards upper-layer water cavity flow paths of the adjacent cylinder head and is collected towards the water outlet hole; a sixth cooling water flow path in which cooling water enters into the upper water cavity through the communicating hole, flows past the inner wall of the cylinder head and the outer surface of the air inlet channel or the outer surface of the air outlet channel, and then flows towards the upper-layer water cavity flow paths of the adjacent cylinder head and is collected towards the water outlet hole. [0040] The water inlet hole includes a main water inlet hole and an auxiliary water inlet hole. Both the main water inlet hole and the auxiliary water inlet hole are provided below the air outlet channel. Along a direction from the first cylinder head towards the fourth cylinder head, areas of the auxiliary water oulet holes are gradually increased. The purpose for such a design is to gradually reduce flow speed and pressure of the cooling water by increasing the areas of the water inlet holes near the water outlet hole, thereby facilitating distant cooling water to be collected towards the water outlet hole without being blocked. [0041] First embodiment 18 [0042] In the following examples, only water cavities in the cylinder head and flowing directions of the cooling water and other technical solutions are illustrated, and structures of various parts of the cylinder head will not be described in details. In this embodiment, a communication hole through which cooling water enters into the upper-layer water cavity is defined in an outer side of an air inlet side 7 of each cylinder head. In other embodiment, the communicating hole may also be defined in an air outlet side 6, which is not the best choice of the present invention. [0043] Water flows in the cylinder head of the present invention are controlled through a double-layer control strategy. The water cavity of the cylinder head is composed of the upper-layer water cavity and the low-layer water cavity. The partition plate is provided between the upper-layer water cavity and the low-layer water cavity. Cooling water in the upper-layer water cavity and the low-layer water cavity flows separately and is not interfered with each other. The low-layer water cavity is controlled to be within a limited space so that water speed is easily guaranteed to strengthen the cooling of a bottom plate of the cylinder head. This helps to control water flow in the cylinder head, reduce heat load of the cylinder head and increase service life of the cylinder head. Meanwhile, the partition plate can increase the rigidity of the cylinder head, and improves mechanical load strength of the cylinder head. A main water filling hole is at the air outlet side of the cylinder head and the communicating hole 5 of two layers of water cavities are in the air inlet side so that all cooling water entering into the cylinder head flows past a region surrounding the air outlet channels, and the water flow first flows past a region 19 between air outlet channels and a region between the air outlet channels and the cylinder head. Such a design first ensures cooling of regions having the maximum heat load of the cylinder head. Second, a region between the air inlet channels and the air outlet channels is also a region which needs strengthened cooling, thus, after flowing past the region between the air outlet channels, the water flow is organized to flow past a region between the air outlet channels and the air inlet channels and a region between the air inlet channels at two sides thereof, respectively. The upper-layer water cavity 1 and the lower-layer water cavity 2 are communicated at the air inlet side, i.e., the communicating hole 5 between the upper-layer water cavity and the lower-layer water cavity. Then, all the water flows flow towards the main communicating hole 5 and then enters into the upper-layer water cavity of the cylinder head. The water flows flow towards the main communicating hole 5 of water cavities of adjacent cylinder, respectively. The water flow entering into the cylinder head from the auxiliary water filling hole below the air outlet channels flows past a region connected between the two cylinders, and then flows towards the closest main communicating hole 5 to enter into the upper-layer water cavity 2 of the cylinder head. There is a trend that the auxiliary water filling holes are gradually increased from the first cylinder to the fourth cylinder. [0044] Second embodiment [0045] Water flows in the cylinder head of the present invention are controlled through a double-layer control strategy. The water cavity of the cylinder head is composed of the upper-layer water cavity 1 and the low-layer water cavity 2. The 20 partition plate is provided between the upper-layer water cavity 1 and the low-layer water cavity 2. Cooling water in the upper-layer water cavity 1 and the low-layer water cavity 2 flows separately and is not interfered with each other. The low-layer water cavity 2 is controlled to be within a limited space so that water speed is easily guaranteed to strengthen the cooling of the bottom plate of the cylinder head. This helps to control water flow in the cylinder head, reduce heat load of the cylinder head and increase service life of the cylinder head. Meanwhile, the partition plate can increase the rigidity of the cylinder head, and improves mechanical load strength of the cylinder head. The main water inlet hole is at the air outlet side of the cylinder head and the communicating holes 5 of two layers of water cavities are in the air inlet side so that all cooling water entering into the cylinder head flows past a region surrounding the air outlet channels. In addition, an auxiliary communicating hole is added in the air outlet side. [0046] The second cylinder head and the third cylinder head further include inclined communicating holes, which connects the lower connection water cavity of the first cylinder head near the second cylinder head with the upper water cavity of the second cylinder chamber, and connects the lower connection water cavity of the second cylinder head near the third cylinder head with the upper water cavity of the third cylinder chamber, respectively. The water flow first flows past the region between the air outlet channels and the region between the air outlet channels and the cylinder head. Such a design first ensures cooling of regions having the maximum heat load of the cylinder head. Second, the region between the air inlet channels and 21 the air outlet channels is a region which needs strengthened cooling, thus, after flowing past the region between the air outlet channels, the water flow is organized to flow past the region between the air outlet channels and the air inlet channels and the region between the air inlet channels at two sides thereof, respectively. The upper-layer water cavity 1 and the lower-layer water cavity 2 are communicated at the air inlet side, i.e., the communicating hole between the upper-layer water cavity and the lower-layer water cavity. Then, all the water flows flow towards the main communicating hole 5 and then enters into the upper-layer water cavity of the cylinder head. The water flows flow towards the main communicating hole 5 of water cavities of adjacent cylinder, respectively. The water flow entering into the cylinder head from the auxiliary water filling hole below the air outlet channels flows past the region connected between the two cylinders, and then flows towards the closest main communicating hole 5 to enter into the upper-layer water cavity 2 of the cylinder head. There is a trend that the auxiliary water filling holes are gradually increased from the first cylinder to the fourth cylinder. [0047] In this embodiment, the second cylinder head and the third cylinder head further include inclined communicating holes, which connect the lower connection water cavity of the first cylinder head near the second cylinder head with the upper water cavity of the second cylinder chamber, and connect the lower connection water cavity of the second cylinder head near the third cylinder head with the upper water cavity of the third cylinder chamber, respectively. By such a design, the cylinder head will have a cooling water flow path in which cooling water from the 22 water inlet hole enters into the lower water cavity, then is guided by the lower connection water cavity and enters into the lower bridge zone near the injector mounting hole, and then enters into the upper water cavity through the lower connection water cavity near the adjacent cylinder head and the inclined communicating hole. [0048] Although some embodiments of the present invention have been shown and described, it should be appreciated that, a person skilled in the art shall make further changes, modifications substitutions and improvements without departing from the principle of the present invention. The scope of the present invention is defined by appended claims and their equivalents. 23

Claims

1. A water cooling system for a cylinder head of an engine, comprising an integrally formed cylinder head for an engine having at least four cylinders, wherein the cylinder head is provided with an injector mounting hole, two air inlet channels and two air outlet channels distributed at a periphery of the injector mounting hole, and a cooling water cavity defined by an inner surface of the cylinder head, an outer surface of the air inlet channels, an outer surface of the air outlet channels and an outer surface of the injector mounting hole, and wherein: the cooling cavity of the cylinder head is divided into an upper-layer water cavity and a lower-layer water cavity by a partition plate; a water outlet hole is defined in one end of the upper-layer water cavity; water inlet holes for the lower-layer water cavity are evenly distributed in a bottom surface of the cylinder head facing a cylinder block; cooling water enters into the lower-layer water cavity through the water inlet holes; a communicating hole is disposed between the upper-layer water cavity and the lower-layer water cavity; and the cooling water in the lower-layer water cavity enters into the upper-layer water cavity through the communicating hole; the upper-layer water cavity is comprised of an upper water cavity between an inner wall of the cylinder head and the outer surface of the air inlet channels, an upper surface of the air outlet channels, an upper bridge zone between the outer surface of the injector mounting hole and the outer surface of the air inlet channels, the upper 24 surface of the air outlet channels, and an upper connection water cavity which communicates with the upper water cavity and the upper bridge zone; the lower-layer water cavity is comprised of a lower water cavity between the inner wall of each cylinder head and the outer surface of the air inlet channels, the upper surface of the air outlet channels, a lower bridge zone between the outer surface of the injector mounting hole and the outer surface of the air inlet channels, the upper surface of the air outlet channels, and a lower connection water cavity which communicates with the lower water cavity and the lower bridge zone; and the communicating hole communicates with the upper water cavity and the lower water cavity; wherein a second cylinder head and a third cylinder head further comprise inclined communicating holes which connect the lower connection water cavity of a first cylinder head near the second cylinder head with the upper water cavity of the second cylinder head, and which connect the lower connection water cavity of the second cylinder head near the third cylinder head with the upper water cavity of the third cylinder head, respectively.

2. The cooling water system according to claim 1, wherein the communicating hole is defined in an outer side of the air inlet channels in a direction away from the injector mounting hole.

3. The cooling water system according to any one of the preceding claims, wherein an auxiliary water filling hole is defined beside the air outlet channels. 25

4. The cooling water system according to any one of the preceding claims, wherein in two sides of each air inlet channel or each air outlet channel, there are two upper connection water cavities and lower connection water cavities.

5. The cooling water system according to any one of the preceding claims, wherein the lower-layer water cavity comprises at least four cooling water flow paths which respectively are: a first cooling water flow path along which cooling water from the water inlet holes enters into the lower water cavity, is then guided by the lower connection water cavity to enter into the lower bridge zone near the injector mounting hole, and then to enter into a lower-layer water cavity flow paths of a adjacent cylinder head through the lower connection water cavity near the adjacent cylinder head; a second cooling water flow path along which cooling water enters into the lower water cavity and flows along the inner wall of the cylinder head and the bottom surface of the cylinder head, then flows towards the communicating hole and enters into the upper water cavity; a third cooling water flow path along which cooling water from the water inlet holes enters into the lower water cavity, and then flows towards the lower-layer water cavity flow paths of the adjacent cylinder head; and a fourth cooling water flow path along which cooling water from the water inlet holes enters into the lower water cavity, then is guided by the lower connection water cavity and enters into the lower bridge zone near the injector mounting hole, 26 and then enters into the upper water cavity through the lower connection water cavity near the adjacent cylinder head and through the inclined communicating hole.

6. The cooling water system according to any one of claims 1 to 5, wherein the upper-layer water cavity comprises at least two cooling water flow paths which respectively are: a fifth cooling water flow path along which cooling water enters into the upper water cavity through the communicating hole, enters into the upper bridge zone through the upper connection water cavity, then flows towards a upper-layer water cavity flow paths of a adjacent cylinder head for collection at the water outlet hole; and a sixth cooling water flow path along which cooling water enters into the upper water cavity through the communicating hole, flows past the inner wall of the cylinder head and the outer surface of the air inlet channels or the outer surface of the air outlet channels, and then flows towards a upper-layer water cavity flow paths of the adjacent cylinder head for collection at the water outlet hole.

7. The cooling water system according to any one of the preceding claims, wherein the water inlet holes comprise a main water inlet hole and an auxiliary water inlet hole; and wherein: both the main water inlet hole and the auxiliary water inlet hole are provided below the air outlet channels; area of the auxiliary water inlet hole is gradually increased from the cylinder head distant from the water outlet hole towards the cylinder head near the water outlet hole. 27