Cylinder head having EGR gas cooling structure, and method for manufacturing same

It has been difficult to manufacturing a cylinder head having an EGR gas cooling structure which has high cooling performance and can be easily configured. A cylinder head having an EGR gas cooling structure is configured in such a manner that a gas passage which guides to the air intake port side a part of the exhaust gas discharged from the exhaust port is disposed within the cylinder head water jacket to cool the exhaust gas flowing through the gas passage. The gas passage comprises a cooling section which makes contact with the coolant within the cylinder head water jacket, and also comprises a hollow pipe which has high-strength sections located at side portions of the cooling section and having higher strength than the cooling section. The high-strength sections of the gas passage are molded within and surrounded by the cylinder head.

This is a 371 national phase application of PCT/JP2010/058280 filed 17 May 2010, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a cylinder head with an EGR gas cooling structure which has a cooling passage for the EGR gas disposed in a water jacket and to a method for manufacturing the cylinder head.

BACKGROUND ART

Conventionally, an internal-combustion engine such as a gasoline engine includes an exhaust gas recirculation (EGR) device to reduce nitrogen oxides (NOx) generated in combustion processes and to improve fuel economy.

High combustion temperature in the combustion chamber causes oxidation of nitrogen in the air, thereby producing nitrogen oxides as toxic chemicals. The EGR device recirculates a part of the exhaust gas (EGR gas) as non-active gas (with low amount of oxygen) from the exhaust side to the intake side and mixes the exhaust gas with an intake air. Thus, the combustion temperature in the combustion chamber is lowered, and therefore the amount of nitrogen oxides is reduced.

As such EGR device, JP H6-76644 U discloses a technique that the gas passage guiding the EGR gas from the exhaust side to the intake side is disposed in the water jacket of the cylinder head in order to cool it effectively. In JP H6-76644 U, the gas passage may be formed by pipes (e.g., made of stainless) which are molded within the cylinder head.

SUMMARY OF INVENTION

Technical Problem

In the case that the EGR gas passage is arranged in the water jacket, inserting the thin hollow pipe into the cylinder head is preferable from the viewpoint of cooling performance for the EGR gas and productivity thereof. For instance, when the thin hollow pipe is molded within the cylinder head, the gas passage may be crashed under molding pressure (i.e., weight of molten metal and pressure due to contraction of the molten metal) acted on the outer surface of the pipe.

As mentioned above, it is difficult to manufacture the cylinder head having the EGR gas cooling structure with high cooling performance and being easily configurable.

The present invention provides a cylinder head having an EGR gas cooling structure and a method for manufacturing the same with high cooling performance and being easily configurable.

Technical Solutions

The present invention related to the cylinder head with the EGR gas cooling structure and the method for manufacturing the same includes following technical features.

The first embodiment of the invention is a cylinder head formed with an exhaust port, an intake port and a water jacket, which includes an EGR cooling structure including a gas passage guiding a part of exhaust gas from the exhaust port to the intake port, disposed in the water jacket for cooling the exhaust gas passing through the gas passage. The gas passage is configured by a pipe including: a cooling section being contact with a coolant in the water jacket; and high-strength sections disposed at both ends of the cooling section, having higher strength than the cooling section, and the high-strength sections are molded within the cylinder head.

The cooling section is free from the molding pressure and the deformation caused by the molding pressure rarely occurs on the cooling section, so that the cooling section can be configured as the flat pipe or thinner pipe than the high-strength section in order to achieve a high-cooling performance.

In the embodiment that the gas passage is arranged in the water jacket, EGR gas coolers disposed outside of the cylinder head are not necessary, thereby facilitating the structure of cooling the EGR gas. Moreover, the gas pipes for the EGR gas coolers are not necessary, whereby cooling the EGR gas is provided with saving space and with low cost.

Preferably, the cooling section is configured by a flat pipe.

The inner dimension along the short-side direction of the cooling section is small, thereby increasing the rate of the turbulent flow region in the EGR gas flow through the cooling section and increasing the surface area with respect to the section area in the cooling section. As the result, the heat exchanger effectiveness of the EGR gas is enhanced and the cooling performance is improved.

More preferably, the cooling section is configured by a pipe separated from the high-strength sections, and each of the high-strength sections includes a tubular side wall and a bottom closing one end of the side wall, the bottom having a slot into which the cooling section is inserted, and the ends of the cooling section are inserted into the slot, whereby the cooling section and the high-strength sections are connected.

Therefore, the gas passage can be easily configured and the productivity of manufacturing the cooling structure can be improved.

In the preferable embodiment, the tubular side wall has a circular section.

When the pressure accompanied by contraction of molten metal works on the outside of the high-strength section, the circular tubular side wall evenly receives the pressure, thereby prevented from deformation.

As the result, the high-strength sections are kept in contact with the cylinder head, so that the sealing performance of the water jacket can be secured.

Advantageously, the cooling section has a side face along the short-side direction, the cooling section is disposed such that the flow direction of the exhaust gas passing therethrough crosses the flow direction of the coolant passing through the water jacket and that the side face faces the flow direction of the coolant.

Such arrangement of the gas passage does not prevent the flow of the coolant in the water jacket and makes the coolant contact the outer surfaces of the cooling sections effectively, thereby improving the cooling performance for the EGR gas.

In the advantageous embodiment, the gas passage includes multiple cooling sections, which are aligned along the short-side direction.

The surface areas of cooling sections being contacted with the coolant in the water jacket can be enlarged with saving space, and the cooling performance can be enhanced.

More advantageously, the side wall has a groove or a projection formed along the circumferential direction thereof.

The part of the cylinder head that is inserted into the high-strength section is engaged with the groove or projection, thereby preventing the high-strength section from falling off the cylinder head and securing the sealing property between the cylinder head and the high-strength section.

Alternatively, the side wall has a slope in the inside thereof at the downstream side of the EGR gas flow, the inner diameter of the slope expanding from the upstream side to downstream side of the EGR gas flow.

As the result, condensed water generated in the cooling section is removed from the side wall and the gas passage is prevented from damage or degradation such as corrosion caused by the condensed water.

The second embodiment of the invention is a method for manufacturing a cylinder head formed with an exhaust port, an intake port and a water jacket, comprising: an EGR cooling structure including a gas passage guiding a part of exhaust gas from the exhaust port to the intake port, disposed in the water jacket for cooling the exhaust gas passing through the gas passage. The method includes configuring the gas passage by a pipe that includes: a cooling section being contact with a coolant in the water jacket; and high-strength sections disposed at both ends of the cooling section, having higher strength than the cooling section, and followed by inserting the high-strength sections into the cylinder head, whereby arranging the cooling section within the water jacket.

The cooling section is free from the molding pressure and the deformation caused by the molding pressure rarely occurs on the cooling section, so that the cooling section can be configured as the flat pipe or thinner pipe than the high-strength section in order to achieve a high-cooling performance.

In the embodiment that the gas passage is arranged in the water jacket, EGR gas coolers disposed outside of the cylinder head are not necessary, thereby facilitating the structure of cooling the EGR gas. Moreover, the gas pipes for the EGR gas coolers are not necessary, whereby cooling the EGR gas is provided with saving space and with low cost.

Preferably, the cooling section is configured by a flat pipe.

The inner dimension along the short-side direction of the cooling section is small, thereby increasing the rate of the turbulent flow region in the EGR gas flow through the cooling section and increasing the surface area with respect to the section area in the cooling section. As the result, the heat exchanger effectiveness of the EGR gas is enhanced and the cooling performance is improved.

In the preferable embodiment, he cooling section is configured by a pipe separated from the high-strength section, and each of the high-strength section includes a tubular side wall and a bottom closing one end of the side wall, the bottom having a slot into which the cooling section is inserted. The method further includes: connecting the ends of the cooling section inserted into the slot to the high-strength sections; forming a core surrounding the cooling section; holding the high-strength sections by a mold; and pouring molten metal into the mold for molding.

Such structure makes the production of the gas passage easier than the structure where the cooling sections and the high-strength sections are integratedly formed, so that the productivity of the cylinder head having the EGR gas cooling structure is improved.

The connecting step, the core forming step, the holding step and the molding step are performed in order, and in such case, the connection of the cooling sections with the high-strength sections is performed more easily than the case that they are connected after fitting the high-strength sections to the holder of the mold. Thus, the cylinder head with the EGR gas cooling structure can be produced with high productivity.

In the preferable embodiment, the tubular side wall has a circular section, and the high-strength section is molded within the cylinder head while holding the side wall by the mold.

As the result, the high-strength sections are kept in contact with the cylinder head, so that the sealing property of the water jacket can be secured.

Advantageously, the cooling section has a side face along the short-side direction, the cooling section is disposed such that the flow direction of the exhaust gas passing therethrough crosses the flow direction of the coolant passing through the water jacket and that the side face faces the flow direction of the coolant.

Such arrangement of the gas passage does not prevent the flow of the coolant in the water jacket and makes the coolant contact the outer surfaces of the cooling sections, thereby improving the cooling performance for the EGR gas.

In the advantageous embodiment, the gas passage includes multiple cooling sections, which are aligned along the short-side direction.

The surface areas of cooling sections being contacted with the coolant in the water jacket can be enlarged with saving space, and the cooling performance can be enhanced.

Advantageous Effects of Invention

Advantageous effects of the invention are described below.

According to the invention, the cooling section can be configured as the flat pipe or thinner pipe than the high-strength section in order to achieve a high-cooling performance. Furthermore, the EGR gas cooling structure can be easily configured, whereby cooling the EGR gas is provided with saving space and with low cost.

REFERENCE SIGNS LIST

DESCRIPTION OF EMBODIMENTS

Referring to attached drawings, the embodiment according to the present invention is described below.

FIGS. 1 to 5depict a cylinder head11in accordance with the invention having a cooling structure for EGR gas. The cylinder head11is, for example, installed in an engine having multiple cylinders (in the embodiment, four cylinders) and has two intake ports12and two exhaust ports13corresponding to each of the cylinders.

The cylinder head11is formed with a water jacket15to cool the exhaust ports13and the like.

The water jacket15is formed from the front end (one end of the cylinder arrangement; left side inFIG. 1) of the cylinder head11to the rear end (the other end of the cylinder arrangement; right side inFIG. 1) thereof.

The water jacket15is filled with coolant and connected with a pump and a radiator (both not shown). Actuating the pump makes the coolant flow through the water jacket15, thereby cooling the inside of the cylinder head11.

In this embodiment, the coolant is flown into the water jacket15through the front side to the rear side of the cylinder head11, and discharged via a coolant outlet15athat is arranged at the rear end of the cylinder head11.

The engine provided with the cylinder head11includes an EGR device for recirculating a part of the exhaust gas exhausted from the exhaust ports13(EGR gas) and mixing the EGR gas with an intake air.

The EGR device includes a gas passage for guiding the EGR gas to the intake ports12. The gas passage includes an EGR gas cooling pipe31disposed in the cylinder head11, through which the EGR gas is cooled by the coolant in the water jacket15, a first connection pipe22(seeFIG. 3) that is disposed between one end of the cooling pipe31(upper end inFIG. 3) and the exhaust pipe, guiding the EGR gas to the cooling pipe31, and a second connection pipe23that is disposed between the other end of the cooling pipe31(lower end inFIG. 3) and the intake manifold communicated with the intake ports12, guiding the EGR gas cooled in the cooling pipe31to the intake ports12.

At the middle portion of the second connection pipe23, there is an EGR valve to control the amount of the EGR gas recirculated to the intake ports12.

In the EGR device, if the EGR valve is open when driving the engine, the EGR gas flows in the first connection pipe22and is guided into the cooling pipe31. The EGR gas guided into the cooling pipe31is cooled in the cooling pipe31by the coolant in the water jacket15. Therefore, the cooled EGR gas is recirculated to the intake manifold via the second connection pipe23.

In the engine, the EGR device works in the above-described way, so that the EGR gas as non-active (low-oxygen) gas is mixed with the intake air in the intake manifold. As the result, the combustion temperature in the combustion chamber of the cylinder head is lowered, which reduces the nitrogen oxides.

The EGR gas cooling pipe31arranged in the water jacket15is described below.

The cooling pipe31is disposed between the coolant outlet15aand the intake and exhaust ports12,13, which are arranged at the most downstream side of the coolant flow in the water jacket15.

As depicted inFIGS. 3 to 5, the cooling pipe31includes a cooling section32being contacted with the coolant in the water jacket15through which the EGR gas passes and two high-strength sections33that are arranged at both ends of the cooling section32and are molded within the cylinder head11. The high-strength sections33are located at the both ends of the cooling section32.

The cooling section32is configured in a thin hollow pipe having flat shape. In the EGR gas cooling pipe31, the multiple cooling sections32are aligned in the short-side direction of the cooling section32, spaced away from each other.

The cooling section32has a rectangular or oval shape having a short side along the alignment direction of them and a long side along the direction perpendicular to the alignment direction. The cooling section32has wide faces32aand the multiple cooling sections are aligned to face the wide faces with each other.

The cooling section32is configured in the thin hollow pipe and the inner dimension along the short-side direction of the cooling section32is small, thereby increasing the rate of the turbulent flow region in the EGR gas flow through the cooling section32and increasing the surface area with respect to the section area in the cooling section32. As the result, the heat exchanger effectiveness of the EGR gas is enhanced and the cooling performance is improved. Moreover, the cooling section32is constructed by the thin and hollow pipe, so that the cooling performance for the EGR gas can be improved.

In the cooling pipe31, the multiple cooling sections32of flat hollow pipe are arranged in the short-side direction, and therefore the surface areas of cooling sections32being contacted with the coolant in the water jacket15can be enlarged with saving space. Thus, the cooling performance can be enhanced.

The cooling pipe31is arranged such that the flow direction of EGR gas in the cooling sections32crosses that of the coolant in the water jacket15. In this embodiment, the flow direction of the EGR gas passing through the cooling sections32is perpendicular to the flow direction of the coolant passing through the water jacket15.

In the cooling pipe31, each of the side faces32balong the short-side direction of the cooling pipes32faces the flow direction of the coolant passing through the water jacket15. That is, the cooling sections32are arranged such that the wide faces32aare parallel to the flow direction of the coolant in the water jacket15.

Such arrangement of the EGR gas cooling pipe31does not prevent the flow of the coolant in the water jacket15and makes the coolant contact the outer surfaces of the cooling sections32, thereby improving the cooling performance for the EGR gas.

As shown inFIGS. 6 and 7, each of the high-strength sections33has a side wall33aformed in a circular tubular shape and a bottom33bclosing one end (in the axial direction) of the side wall33a. The bottom33bis formed with multiple slots33chaving shapes corresponding to the end of the cooling section32, into which the end of the cooling section32can be inserted.

As shown inFIG. 8, the cooling sections32are inserted into the slots33cof the bottom33b, whereby each of the cooling sections32is connected to the high-strength section33.

The bottom33band the cooling sections32are blazed and fixed to each other, in which the cooling sections32are inserted into the slots33c.

In the high-strength section33, the side wall33aand the bottom33bmay be formed integratedly or fixed by blazing to each other.

The high-strength section33has higher strength than the cooling section32. In particular, the high-strength section33has higher resistance against the contracting force acted on the outer surface than the cooling section32. The higher strength can be provided by forming the side wall33aof the high-strength section33in tubular shape with circular section, and in this respect, the cooling section32is formed in the flat shape.

Alternatively, the high-strength section33can be made of a material being thicker than that of the cooling section32. The high-strength section33may be formed with a reinforcing portion such as a rib to provide the high strength.

The cooling section32and the high-strength section33may be made of aluminum or stainless steel.

As described above, the high-strength section33has the cylindrical tube shape with high strength and the cooling sections32are formed in the thin hollow pipes of flat shape having lower strength than the high-strength section33. The cooling sections32and the high-strength section33have different characteristics from each other, and they are separated from each other. However, the EGR gas cooling pipe31is constructed in such a way that the cooling sections32are inserted into the slots33cof the high-strength section33. Therefore, the EGR gas cooling pipe31can be easily configured and the productivity of manufacturing the cooling structure can be improved.

The cylinder head11has two pipe supports11afor supporting the high-strength sections33that are formed at the side walls parallel to the flow direction of the coolant passing through the water jacket15.

The EGR gas cooling pipe31is attached to the cylinder head11via the pipe supports11aholding the high-strength sections33. In this embodiment, the high-strength sections33of the cooling pipe31are molded within the cylinder head11to be supported by the pipe supports11a.

The cooling pipe31is fixed to the cylinder head11by inserting the high-strength sections33into the cylinder head11. Thus, the cooling pipe31can be fixed without bolts, thereby reducing the number of parts constructing the cooling structure and manufacturing the cylinder head having the cooling structure with low cost.

When the high-strength sections33is molded within the cylinder head11, the molding pressure (that is the weight of the molten metal and the pressure accompanied by contraction of the molten metal) acts on the high-strength sections33, however the high-strength sections33have tubular side walls33ato be reinforced against the pressure from the outside, so that the high-strength sections do not deform caused by the molding pressure.

In detail, when the pressure accompanied by the contraction of the molten metal works on the outside of the high-strength section33, the circular tubular side wall33aevenly receives the pressure, thereby prevented from deforming.

As the result, the high-strength sections33are kept in contact with the cylinder head11, so that the sealing property of the water jacket15can be secured.

The cooling section32is disposed in the water jacket15where the pressure of molding the cylinder head11does not work, and therefore the cooling section can be configured with lower strength than the high-strength sections33.

In the EGR gas cooling pipe31, the high-strength sections33are molded within the cylinder head11to be held by the cylinder head11, and the cooling section32for cooling the EGR gas is free from the molding pressure. So, the deformation caused by the molding pressure rarely occurs on the cooling section, and the cooling section32can be configured as the flat pipe or thinner pipe than the high-strength section33in order to achieve a high-cooling performance.

The flow of inserting the EGR gas cooling pipe31into the cylinder head11(molding the cooling pipe31within the cylinder head11) is described below.

As shown inFIG. 9, before molding the cooling pipe31, the ends of the cooling section32are inserted into the slots33cformed in each of the bottom33bof the high-strength section33, and the cooling section32and the high-strength sections33are connected (Connecting step S01). The high-strength sections33are connected to the ends of the cooling section32, thereby configuring the EGR gas cooling pipe31.

After the connecting step, the cooling section32is surrounded by core sand to form the core (Core forming step S02).

The inner side of the high-strength section33(near the cooling section32) may be surrounded by the core. It should be noted that the outer side of the high-strength section33is the portion inserted into the cylinder head11and held by a mold1, so that the core is formed not to surround that portion.

The high-strength sections33are held with the mold for molding the cylinder head11(Holding step S03). The mold holds the high-strength sections33, and the core formed in the core forming step is installed in the mold.

As shown inFIG. 10, the mold1is formed with ring holders1aprojecting inwardly. The outside of the high-strength section33is fitted into the inside of the holder1a, and the mold1holds the high-strength section33.

After the installation of the core in the mold, the molten metal is poured into the mold1, thereby the cylinder head11is molded (Molding step S04). Thus, the high-strength sections33of the EGR as cooling pipe31are molded within the cylinder head11.

When holding the high-strength section33by the holder1aof the mold1, there is a clearance by the predetermined distance d between the outer end of the high-strength section33and the inside1bsurrounded by the holder1a. When holding the high-strength section33by the holder1aof the mold1, there is a sealing member between the holder1aand the high-strength section33so that the molten metal poured into the mold1is not flown in the clearance of the predetermined distance d.

Due to such structures, the outer end of the high-strength section33is molded within the cylinder head11with spaced by the distance d from the outside of the cylinder head11(seeFIG. 3).

The high-strength sections33arranged at both ends of the EGR gas cooling pipe31do not touch the connection pipes22and23connected to the cylinder head11, and the high-strength sections33are free from load, thereby enhancing the sealing property between the cylinder head11and the high-strength sections33.

The connecting step S01, the core forming step S02, the holding step S03and the molding step S04are performed in order, and the high-strength sections33of the EGR gas cooling pipe31are molded within the cylinder head11.

The high-strength sections33are inserted in the cylinder head11and the EGR gas cooling pipe31is disposed in the water jacket15, and therefore the cylinder head11is manufactured, in which the EGR gas cooling structure passes through the water jacket15.

In the embodiment that the EGR gas cooling pipe31is arranged within the water jacket15, EGR gas coolers disposed outside of the cylinder head11are not necessary, thereby facilitating the structure of cooling the EGR gas. Moreover, the gas pipes for the EGR gas coolers are not necessary, whereby cooling the EGR gas is provided with saving space and with low cost.

In the EGR gas cooling pipe31disposed in the water jacket15of the cylinder head11, the cooling sections32and the high-strength sections33are configured as individual members. Such structure makes the production of the EGR gas cooling pipe31easier than the structure where the cooling sections32and the high-strength sections33are integratedly formed, so that the productivity of the cylinder head11having the EGR gas cooling structure is improved.

When inserting the high-strength sections33into the cylinder head11, the cooling sections32and the high-strength sections33are connected before the high-strength sections33are fitted to the holder1aof the mold1, and the mold1holds the EGR gas cooling pipe31. The connection of the cooling sections32with the high-strength sections33is performed more easily than the case that they are connected after fitting the high-strength sections33to the holder1aof the mold1. Thus, the cylinder head11with the EGR gas cooling structure can be produced with high productivity.

As descried before, the cooling sections32are configured by the flat pipes so that the cooling performance for the EGR gas passing through the cooling sections32is enhanced. The flatter the cooling sections are, the higher cooling performance is obtained.

FIG. 11shows a relationship between the length of the short side (height) h in the section of the flat cooling section32and the temperature of the EGR gas at the outlet of the cooling section32, that is, temperature of the EGR gas after cooling.

FIG. 11indicates that as the height h becomes smaller, the temperature at the outlet becomes lower, namely that as the flatness of the cooling32becomes larger, the cooling performance becomes higher. The reason is that if the height h is small (i.e., if the cooling section32become thinner), the flow speed and heat conductivity of the EGR gas passing through the cooling section32is high.

In the embodiment ofFIG. 12, the side wall33aof the high-strength section33has a groove33dthat is formed along the circumferential direction at the outside corresponding to the portion surrounded by the cylinder head11(at the portion supported by the supports11a).

The side wall33ahas the groove33dformed in the outside thereof, with which the part of the cylinder head11that is inserted into the high-strength section is engaged, thereby preventing the high-strength section33from falling off the cylinder head11and securing the sealing property between the cylinder head11and the high-strength section33.

The side wall33amay have a projection substituted for the groove, which achieves the same effects.

In the embodiment ofFIG. 13, the side wall33aof the high-strength section33has a slope33ethat is formed in the inside thereof at the outlet side of the EGR gas cooling pipe31(at the downstream side of the EGR gas flow), and the inner diameter of the slope is expanded from the upstream side to downstream side of the flow direction of the EGR gas.

If the EGR gas is cooled in the cooling section32, there occurs condensed water in the cooling section32, which flows to the side wall33aof the outlet side due to the EGR gas flow. The condensed water is guided by the slope33eformed in the inside of the side wall33a, whereby the condensed water is discharged to outside from the side wall33a.

As the result, the condensed water is removed from the side wall33aand the EGR gas cooling pipe31is prevented from degradation or damage such as corrosion caused by the condensed water.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a cylinder head of an engine that includes an EGR device, in which the cylinder head has a cooling structure for the EGR gas.