Cylinder head of an internal combustion engine

Abstract

To early raise a temperature of lubrication oil by heat of an EGR gas when an engine is cold.SOLUTION: In an inside of a cylinder head 1, a water jacket 15 and an EGR passage 21 are formed by a core in a form of extending in a planar shape, respectively. At a top of the cylinder head 1, there is a valve gear chamber portion 11 with an open top, through which lubrication oil always flows. The EGR passage 21 is formed between the lower water jacket 15 and the upper valve gear chamber portion 11, and the three vertically overlap. A heat exchange area between the bottom of the valve gear chamber portion 11 through which the lubrication oil flows and the EGR passage 21 is large, and the direct heat exchange between the lubrication oil and cooling water is suppressed by interposition of the EGR passage 21, so that the temperature of the lubrication oil rises early after start up of cooling.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a cylinder head for a water-cooled internal combustion engine. [Background technology]

[0002] When the lubricating oil temperature is low, such as when the internal combustion engine is cold, friction in each part of the internal combustion engine increases, which is detrimental in terms of fuel consumption rate.

[0003] Patent Document 1 discloses a cylinder head in which an EGR passage through which EGR gas flows and an oil passage through which lubricating oil flows are formed by drilling or casting inside the cylinder head. The EGR passage is formed above the water jacket along the width direction of the cylinder head (a direction perpendicular to the cylinder row direction), and an oil passage is formed further above the EGR passage, adjacent to each other. Patent Document 1 also describes that the EGR gas is cooled by both the coolant and the lubricating oil, and that the lubricating oil is warmed by the EGR gas when the engine is cold. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-045498 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the configuration of Patent Document 1, the EGR passage and the oil passage are simply formed adjacent to each other as narrow pipes formed by drilling or casting, and the actual heat exchange area between them is small, so the effect of heating the lubricating oil by the EGR gas, for example, when the engine is cold, is limited.

[0006] In addition, lubricating oil always flows above the cylinder head to lubricate the valve train. However, in areas other than where the EGR passage is provided, the lubricating oil flowing to lubricate the valve train exchanges heat with the cooling water in the water jacket, so the temperature of the lubricating oil rises more slowly during warm-up. [Means for solving the problem]

[0007] This invention is a combustion chamber in which a water jacket is formed inside to surround the combustion chamber, and a valve train chamber for accommodating a valve train is provided at the top. An EGR passage, which is a part of the EGR path from the exhaust system to the intake system of the internal combustion engine, is formed inside for heat exchange of the EGR gas. A cylinder head for an internal combustion engine, Between the bottom of the valve chamber through which lubricating oil flows and the water jacket, the above The EGR passage is expanded in a flat shape. In the shape It has been completed. [Effects of the Invention]

[0008] According to this invention, a large heat exchange area is obtained between the valve chamber through which the lubricating oil flows and the EGR passage through which the EGR gas flows, and the presence of the EGR passage suppresses direct heat exchange between the water jacket through which the cooling water flows and the valve chamber through which the lubricating oil flows, thereby enabling the lubricating oil temperature to rise quickly after, for example, a cold start. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view of a cylinder head according to an embodiment of the present invention; [Figure 2] Cross-sectional view taken along line AA in Figure 1. [Figure 3] FIG. 3 is a cross-sectional view taken along line BB in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view showing the water jacket taken along line CC in FIG. 3 . [Figure 5] FIG. 4 is a cross-sectional view showing the water jacket taken along line DD in FIG. 3. [Figure 6] FIG. 4 is a cross-sectional view showing an EGR passage taken along line EE in FIG. 3 . DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an entire cylinder head 1 according to the embodiment, and FIGS. 2 to 6 are cross-sectional views of the cylinder head 1 taken along different cross sections. As shown in FIG. 1, the cylinder head 1 according to the embodiment is a cylinder head for an in-line three-cylinder spark-ignition internal combustion engine (a so-called gasoline engine) to which the present invention is applied, and each part is integrally cast using an appropriate metal material such as an aluminum alloy. The cylinder head 1 has an overall, approximately rectangular parallelepiped shape that is elongated along the direction in which the cylinders are aligned. As is well known, the cylinder head 1 forms the main body of the internal combustion engine in combination with a cylinder block (not shown) having cylinder bores. The cylinder head 1 is disposed on the cylinder block and fixed to the cylinder block by a plurality of cylinder head bolts (not shown) that pass through cylinder head bolt holes 9 (see FIG. 3).

[0011] The combustion chamber 2 (see Figure 2) of each cylinder is formed in a recessed shape on the underside (so-called lower deck) of the cylinder head 1, and an intake port 3 extending from one side of the cylinder head and an exhaust port 4 extending from the other side are each connected to the ceiling surface of the combustion chamber 2. In Figure 1, the intake port 3 is hidden and not shown. Parts of the intake port 3 and exhaust port 4 are visible in the cross section of Figure 3.

[0012] In the present invention, unless otherwise specified, the terms "upper and lower" do not refer to the direction of a vertical line according to gravity, but rather to the direction along the cylinder center axis, which is the reference for the internal combustion engine. In the illustrated inline three-cylinder engine, even if there is a slight tilt angle, the cylinder center axis is mounted on the vehicle in a position along the vertical line, so the "up-down direction" is roughly synonymous with the vertical direction. In slant-type internal combustion engines and V-type internal combustion engines that are mounted on the vehicle at a large tilt angle, the "up-down direction" along the cylinder center axis is relatively significantly different from the vertical direction.

[0013] The combustion chamber 2 in the illustrated cylinder head 1 has a so-called four-valve configuration (e.g., a pent roof type) equipped with a pair of intake valves and a pair of exhaust valves. A spark plug is located in the center of the combustion chamber 2, surrounded by these four valves. As shown in FIG. 1 , plug holes 6, each with a cylindrical portion 6a into which a spark plug is inserted, are formed on the top surface of the cylinder head 1 at a position corresponding to the center of each cylinder. Four tappet holes 7, into which a pair of cylindrical tappets for the intake valves and the exhaust valves are slidably fitted, are provided around each plug hole 6 for each cylinder. In addition, bearing portions 8, each with a semicircular bearing surface, are formed at multiple locations to rotatably support the intake camshaft and the exhaust camshaft (not shown). Cam brackets (not shown), each with a similar semicircular bearing surface, are attached to these bearing portions 8.

[0014] Here, the upper part of the cylinder head 1 is configured as a deep-dish-shaped valve train chamber 11 that constitutes a valve train chamber for accommodating a valve train mechanism including a camshaft and tappets. That is, the upper part of the cylinder head 1 has a wall 12 that rises so as to surround the entire periphery of the cylinder head 1, and a cylinder head cover mounting flange 12a is formed along one plane at the upper edge of this wall 12. That is, the valve train chamber 11 surrounded by the wall 12 is formed in a deep-dish shape with an open top, and the spark plug hole 6, tappet hole 7, bearing 8, etc. are formed on the inner periphery of the wall 12. A cylinder head cover made of hard synthetic resin or the like (not shown) is attached to the cylinder head cover mounting flange 12a, so that a substantially sealed valve train chamber is formed between them.

[0015] As described above, the valve train chamber houses a valve train mechanism including a camshaft and tappets. To lubricate the valve train mechanism, pressurized lubricating oil from an oil pump is supplied to each part of the valve train mechanism via an oil passage (not shown in detail). The lubricating oil used in the valve train chamber flows through the bottom of the deep-dish-shaped valve train chamber 11 and is ultimately collected in the crankcase below the cylinder block (not shown) through an oil drop hole 13 (see FIG. 3) provided on one side of the cylinder head 1 (the side that is relatively low when mounted on the vehicle; in this embodiment, the intake side). Therefore, the bottom of the valve train chamber 11 can also be considered a kind of oil passage through which lubricating oil constantly flows.

[0016] Next, the internal structure of the cylinder head 1 will be described with reference to Figures 2 to 6. As shown in Figures 2 and 3, a water jacket 15 through which cooling water flows is formed in the lower part of the cylinder head 1 so as to surround the combustion chamber 2. The water jacket 15 is formed using a core when the cylinder head 1 is cast, and as shown in Figures 4 and 5, it is formed continuously around the three cylinders (in other words, the combustion chambers 2), and is formed so that cooling water flows around the spark plug holes 6, between the opposing intake and exhaust valves, etc. Around the combustion chamber 2, the water jacket 15 communicates with a water jacket on the cylinder block side (not shown) via a plurality of oval water holes 16 (see Figure 5).

[0017] Here, Fig. 5 is a cross section taken at a position relatively close to the underside of the cylinder head 1, as indicated by line DD in Fig. 3, and Fig. 4 is a cross section taken at a position higher than that of Fig. 5, as indicated by line CC in Fig. 3. For example, since the height of the combustion chamber 2 at the center of the cylinder is higher than that at the periphery of the cylinder, the water jacket 15 is located relatively higher to avoid interference with the combustion chamber 2. In other words, the water jacket 15 shown in the cross sections of Figs. 4 and 5 constitutes a single continuous flow path. In other words, the water jacket 15 extends in a planar shape along a substantially single plane at a relatively low height position near the underside of the cylinder head 1. In one embodiment, the coolant flows through the water jacket 15 in a manner generally aligned along the cylinder row direction.

[0018] As shown in FIGS. 2 and 3 , an EGR passage 21 through which EGR gas flows is formed above the water jacket 15. Like the water jacket 15, the EGR passage 21 is formed using a core during casting of the cylinder head 1. As shown in FIG. 6 , the EGR passage 21 is continuously formed in the cylinder row direction so as to surround the spark plug holes 6 of the three cylinders. The EGR passage 21 includes a first row-wise passage 21A extending along the cylinder row direction on one side of the cylinder head 1, a second row-wise passage 21B extending along the cylinder row direction on the other side of the cylinder head 1, and multiple lateral passages 21C extending perpendicular to the cylinder row direction between the cylinders to connect the first row-wise passage 21A and the second row-wise passage 21B. The EGR passage 21 thus spreads widely within the cylinder head 1. Therefore, the EGR gas flows widely in the cylinder row direction and in a direction perpendicular to the cylinder row direction. In other words, the EGR passage 21 has a shape that spreads out along a substantially single plane at an intermediate height position of the cylinder head 1. In one embodiment, high-temperature EGR gas flows through the EGR passage 21 in a manner that generally follows the cylinder row direction. For example, the EGR gas flows in the same direction as the flow of cooling water in the water jacket 15. In another example, the EGR gas may flow in the opposite direction to the flow of cooling water in the water jacket 15.

[0019] When casting the cylinder head 1, a skeleton-shaped core for forming the water jacket 15 and a skeleton-shaped core for forming the EGR passage 21 are arranged vertically stacked in a mold that forms the cylinder head 1. The cores do not intersect vertically, and the core for the EGR passage 21 is arranged relatively higher than the core for the water jacket 15. Therefore, the space formed by the core as the water jacket 15 and the space formed by the core as the EGR passage 21 are provided independently and vertically stacked inside the cylinder head 1.

[0020] 2 and 3, the EGR passage 21 is positioned below the bottom of the valve train chamber 11, through which lubricating oil always flows at the top of the cylinder head 1, and when viewed from above in a plan view, the EGR passage 21 is also formed in a wide, planar shape below the valve train chamber 11, which extends over almost the entire surface of the cylinder head 1. Therefore, the part of the bottom of the valve train chamber 11 that can be considered an oil passage, the EGR passage 21, and the water jacket 15 are all vertically stacked over a wide area.

[0021] For example, as shown in FIGS. 2 and 3, at each inter-cylinder position, the lower water jacket 15, the intermediate EGR passage 21, and the upper valve chamber 11 are vertically overlapped.

[0022] According to the cylinder head 1 of the above embodiment, the cylinder head 1 functions as a kind of EGR gas cooler, and the EGR gas flowing through the EGR passage 21 is cooled by the cooling water flowing through the water jacket 15 and by the lubricating oil flowing at the bottom of the valve train chamber 11. When the internal combustion engine is cold, the high-temperature EGR gas flowing through the EGR passage 21 warms the lubricating oil flowing at the bottom of the valve train chamber 11, and the temperature of the lubricating oil involved in friction in various parts rises quickly.

[0023] In particular, with the above configuration, a large heat exchange area is obtained between the bottom of the valve chamber 11, through which the lubricating oil flows, and the EGR passage 21, through which the EGR gas flows, and direct heat exchange between the water jacket 15, through which the cooling water flows, and the bottom of the valve chamber 11, through which the lubricating oil flows, is suppressed by the presence of the EGR passage 21. Therefore, during cold engine operation, the lubricating oil flowing at the bottom of the valve chamber 11 is heated by the EGR gas, but is less likely to be cooled by the cooling water, and the lubricating oil temperature can be increased quickly after cold engine start.

[0024] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, the number of cylinders, the layout of the intake ports or exhaust ports, etc. may be different from those in the above embodiment, and the present invention can also be applied to V-type internal combustion engines, etc. [Explanation of symbols]

[0025] 1...Cylinder head 2...Combustion chamber 6...Plug hole 11...Valve chamber 13...Oil drip hole 15...Water jacket 21...EGR passage 21 21A, 21B...cylinder row direction passage section 21C…lateral passage section

Claims

1. A cylinder head for an internal combustion engine, the cylinder head having a water jacket formed inside the cylinder head to surround a combustion chamber, a valve operating chamber provided at an upper portion for accommodating a valve operating mechanism, and an EGR passage formed inside the cylinder head to serve as a part of an EGR path extending from an exhaust system to an intake system of the internal combustion engine for heat exchange of EGR gas, The cylinder head of an internal combustion engine, wherein the EGR passage is formed in a planar shape between the bottom of the valve chamber, through which lubricating oil flows, and the water jacket.

2. 2. The cylinder head for an internal combustion engine according to claim 1, wherein the lower water jacket, the intermediate EGR passage, and the upper valve chamber are vertically overlapped at each inter-cylinder position.

3. 3. The cylinder head for an internal combustion engine according to claim 1, wherein the space formed as the water jacket and the space formed as the EGR passage are provided independently of each other and overlap one another vertically within the cylinder head.

4. 2. The cylinder head for an internal combustion engine according to claim 1, wherein the EGR passage comprises: a first row-wise passage portion extending in the cylinder row direction on one side of the cylinder head; a second row-wise passage portion extending in the cylinder row direction on the other side of the cylinder head; and at least one lateral passage portion extending in a direction perpendicular to the cylinder row direction between cylinders to connect the first row-wise passage portion and the second row-wise passage portion.

5. 5. The cylinder head for an internal combustion engine according to claim 1, wherein the EGR passage is formed continuously in the direction of alignment of the cylinders so as to surround the spark plug holes of the respective cylinders.

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