JP5192975B2 - Engine cylinder head with internal EGR mechanism - Google Patents

Description

  The present invention relates to an engine cylinder head having an internal EGR mechanism, and more particularly to an improvement in a valve seat provided in the cylinder head.

As a valve seat provided in a cylinder head of a conventional engine, for example, those described in Patent Document 1 and Patent Document 2 are known.
Japanese Utility Model Publication No. 3-25804 JP-A-9-14047

FIG. 1 of Patent Document 1 will be described with reference to FIG. In addition, the code | symbol was reassigned.
FIG. 12 is a first sectional view showing a conventional valve seat. A valve seat ring 100 has a lower end 101 facing a combustion chamber of the cylinder head and an upper end 102 facing an exhaust port of the cylinder head.

  The inner surface of the valve seat ring 100 is tapered so as to be reduced in diameter from the lower end 101, and is disposed so as to be adjacent to the valve seat surface 103 on which the seat contact surface of the exhaust valve abuts. And a tapered surface 104 having a smaller taper angle than the valve seat surface 103 and a cylindrical surface 105 formed so as to be adjacent to the tapered surface 104.

FIG. 1 of Patent Document 2 will be described with reference to FIG. In addition, the code | symbol was reassigned.
FIG. 13 is a second cross-sectional view showing a conventional valve seat. The valve seat 110 has an opening edge 111 that opens to the combustion chamber side on the inner surface thereof, and a contact formed on the downstream side of the exhaust gas from the opening edge 111. A contact surface 112.

  The contact surface 112 is a portion where the valve of the exhaust valve is in surface contact with the outer peripheral surface of the truncated cone shape, and from the downstream edge 113 of the contact surface 112 to the partial inner peripheral surface 114 side of the exhaust port. The extending portion 115 is partly smoothly connected to the inner peripheral surface 114.

  In the valve seats as described in Patent Document 1 and Patent Document 2, the opening area between the umbrella portion of the exhaust valve and the valve seat gradually increases as the exhaust valve lifts and widens. In an internal EGR mechanism that lifts in the stroke and recirculates a part of the exhaust gas into the combustion chamber, an increase in the lift amount of the exhaust valve increases the exhaust gas recirculation amount, that is, the EGR amount.

  If the lift amount of the exhaust valve is always constant, it is possible to obtain a desired EGR amount by setting the lift amount to a predetermined value. However, the exhaust valve may vary depending on variations in valve clearance adjustment or changes in valve clearance over time. If the lift amount changes, the desired EGR amount cannot be obtained.

  Therefore, in order to eliminate such lift valve lift amount change, for example, a method of zeroing the valve clearance by hydraulic LHA (hydraulic lash adjuster) can be considered. For engines that are expensive and do not have a hydraulic circuit, expensive mechanical lash adjusters must be used.

  An object of the present invention is to provide a cylinder head of an engine equipped with an internal EGR mechanism that can obtain a desired EGR amount while suppressing cost.

The invention according to claim 1 is the cylinder head 50 of the engine 10 including the internal EGR mechanism 70 that lifts the exhaust valve 44 by a predetermined amount during the intake stroke of the engine 10 and circulates a part of the exhaust gas to the combustion chamber 37. The cylinder head 50 is provided with a valve seat 72 that closes the exhaust port 42 when the umbrella portion 44b of the exhaust valve 44 is seated. The valve seat 72 is attached to the male taper portion 44d formed in the umbrella portion 44b. A female taper portion 72e that increases in diameter as it approaches the combustion chamber 37 so as to be in close contact, a hole portion 72g that extends from the female taper portion 72e toward the combustion chamber 37 so that the inner diameter Din is constant, and combustion in this hole portion A chamfered portion formed at an end portion on the chamber side, and the female taper portion includes a first female taper portion connected to the inlet of the exhaust port on the combustion chamber side, and the first female taper. The diameter of the valve seat surface gradually increases from the end of the valve to the combustion chamber side and can be in close contact with the male taper portion of the exhaust valve, and the diameter of the valve seat surface gradually increases from the end of the valve seat surface to the combustion chamber side. The second female taper portion reaching the hole portion is characterized in that the length L of the hole portion 72g is set to be the same as the lift amount of the exhaust valve 44 when the exhaust gas recirculates.

  When the exhaust valve lifts and the space between the exhaust valve and the valve seat opens, the exhaust valve lift amount in the range of the length of the hole is the opening area between the exhaust valve and the hole in the valve seat. Regardless of the lift amount of the valve, it remains constant, and even if the lift amount of the exhaust valve changes with respect to the specified value, the opening area does not change.

In the invention according to claim 1, the cylinder head is provided with a valve seat that closes the exhaust port when the umbrella portion of the exhaust valve is seated, and the valve seat is in close contact with the male tapered portion formed in the umbrella portion. Are formed at the end of the hole on the combustion chamber side of the hole, the hole extending toward the combustion chamber so that the inner diameter is constant from the female taper. A female taper portion, a first female taper portion continuous with an inlet of an exhaust port on the combustion chamber side, and an exhaust valve that gradually expands from the end of the first female taper portion to the combustion chamber side. A female taper-shaped valve seat surface that can be in close contact with the male taper portion, and a second female taper portion that gradually increases in diameter from the end of the valve seat surface toward the combustion chamber and reaches the hole, The length of the hole Since setting is made so as to become the same as the lift amount at the time of scan reflux, when performing EGR by lifting the exhaust valve during the intake stroke, in order to avoid the influence of aging of adjustment variation and valve clearance of the valve clearance In addition, no complicated mechanism or frequent maintenance is required, and the opening area between the exhaust valve and the valve seat hole is constant regardless of the lift amount of the exhaust valve. In addition, a desired EGR amount can be obtained.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
FIG. 1 is a front view (partially sectional view) showing a general-purpose engine having an exhaust gas recirculation structure according to the present invention. The general-purpose engine 10 includes a crankcase 11 and a cylinder block attached to the upper part of the crankcase 11. 12, a piston 13 movably inserted into a cylinder hole 12 a opened in the cylinder block 12, a connecting rod 16 connected to the piston 13 via a piston pin 14, and a connecting rod 16 In addition, the crankshaft 17 rotatably supported by the mating portions of the crankcase 11 and the cylinder block 12, a cylinder head body 18 formed integrally with the upper portion of the cylinder block 12, and an upper portion of the cylinder head body 18 Head cover 19 that closes the opening, and cylinder head book 18, a timing drive member 22 delivered to each of the crankshaft 17 and the valve mechanism 21 to drive the valve mechanism 21, and fluctuations in load from the start of the engine On the other hand, a governor (not shown) for adjusting the engine speed so that the engine speed becomes a working speed, that is, a constant rated engine speed, by automatically adjusting the opening of a throttle valve (not shown). It consists of.

  The valve mechanism 21 includes a camshaft 25 rotatably attached to the center of the cylinder head body 18, an intake side rocker shaft 31 and an exhaust side rocker shaft 32 provided on the cylinder head body 18, and the intake side thereof. An intake-side rocker arm 33 and an exhaust-side rocker arm 34 that are swingably attached to the rocker shaft 31 and the exhaust-side rocker shaft 32 and driven by cams (not shown) provided on the camshaft 25, and these intake-side rocker arms. 33 and the exhaust side rocker arm 34 are composed of an intake valve 43 and an exhaust valve 44 with shaft end portions applied to the respective end portions via adjustment screws 36 and 36.

The intake valve 43 and the exhaust valve 44 are components for opening and closing the openings on the combustion chamber 37 side of the intake port 41 and the exhaust port 42 communicating with the combustion chamber 37 formed above the piston 13, respectively.
The cylinder head main body 18 and the valve operating mechanism 21 constitute a cylinder head 50.

  The timing drive member 22 includes a drive pulley 51 attached to the crankshaft 17, a driven pulley 52 attached to the camshaft 25, and a toothed belt stretched over each of the drive pulley 51 and the driven pulley 52. 53 and a belt tensioner (not shown) for applying tension to the toothed belt 53.

An intake device 61 that communicates with the intake port 41 and a silencer 62 as an exhaust device that communicates with the exhaust port 42 are attached to the cylinder head body 18.
The intake device 61 includes an air cleaner 64 and a carburetor 65 connected to the air cleaner 64 and attached to the cylinder head body 18 so as to communicate with the intake port 41.

  The carburetor 65 is provided with a choke valve (not shown) in order to improve the startability of the general-purpose engine 10, and a choke lever 66 that opens and closes the choke valve at the front of the general-purpose engine 10, and the choke lever 66 and the carburetor 65. And a link 67 for connecting the two. Reference numeral 68 denotes a fuel tank that supplies fuel to the carburetor 65.

  The governor has a generally known structure. For example, the governor has the same structure as that of the governor G described in FIG. 1 of JP-A-8-177441, or a structure close to this.

2 (a) and 2 (b) are explanatory views showing an internal EGR mechanism according to the present invention.
(A) shows a state where one end portions 33 a and 34 a of the intake side rocker arm 33 and the exhaust side rocker arm 34 are in contact with a reference circle 75 a of a cam 75 formed on the camshaft 25. In this state, the intake valve 43 (see FIG. 1) and the exhaust valve 44 (see FIG. 1) are closed. Reference numeral 77 denotes a lock nut for locking the adjustment screw 36.

  In (b), the camshaft 25 rotates from the state (a), one end 33a of the intake side rocker arm 33 hits the regular cam crest 75b formed on the cam 75, and the intake side rocker arm 33 moves from the state (a) to the arrow. As shown to A, the state swung centering on the intake side rocker shaft 31 is shown. As a result, the adjustment screw 36 at the other end of the intake side rocker arm 33 presses the shaft end of the intake valve 43 (see FIG. 1), and the intake valve 43 opens.

  (B) shows one end 34a of the exhaust side rocker arm 34 hitting an exhaust recirculation cam crest 75c formed on the cam 75, and the exhaust side rocker arm 34 is in the state shown in FIG. A state of slight swing about 32 is shown. As a result, in the intake stroke in which the intake valve 43 is opened, the adjustment screw 36 at the other end of the exhaust side rocker arm 34 presses the shaft end of the exhaust valve 44 (see FIG. 1), and the exhaust valve 44 is slightly opened. Is recirculated into the combustion chamber 37 (see FIG. 1).

3 is a cross-sectional view taken along line 3-3 of FIG. 1, and shows the positional relationship between the exhaust gas recirculation cam 75c and the exhaust side rocker arm 34. FIG.
The camshaft 25 is rotatably supported by a support shaft 78 attached to the cylinder head body 18, and an exhaust gas recirculation cam 75c is formed on the side of the cam 75 far from the combustion chamber 37. One end 34a of the exhaust side rocker arm 34 is disposed radially outward. Accordingly, the exhaust rocker arm 34 can be driven by the exhaust gas recirculation cam 75c.

Further, since the one end 34a of the exhaust side rocker arm 34 extends to the outside in the radial direction of the portion of the cam 75 where the exhaust gas recirculation cam 75c is not present, the exhaust side rocker arm 34 also in the regular cam crest 75b (see FIG. 2B). Is driven in the exhaust stroke, and the exhaust gas is discharged from the combustion chamber 37.
The exhaust recirculation cam 75 c, the exhaust side rocker arm 34, and the exhaust valve 44 constitute an internal EGR mechanism 70.

The exhaust valve 44 includes a rod-shaped shaft portion 44a and an umbrella portion 44b provided at one end portion of the shaft portion 44a.
The cylinder head body 18 is a member in which an exhaust side valve seat 72 is attached to an inlet of the exhaust port 42 on the combustion chamber 37 side.

4 (a) and 4 (b) are explanatory views for explaining a valve seat according to the present invention.
(A) is sectional drawing which shows the shape of the exhaust valve 44 and the valve seat 72, The umbrella part 44b of the exhaust valve 44 has the diameter-expanded part 44c gradually expanded from the axial part 44a side, and this diameter-expanded part 44c. A valve face 44d that further expands from the end and closes the exhaust port 42 in close contact with the valve seat 72, an umbrella peripheral portion 44e formed to have the same outer diameter as the maximum outer diameter of the valve face 44d, and the umbrella It comprises an end bulging portion 44f bulging from the peripheral portion 44e toward the combustion chamber 37.

  The valve seat 72 is a ring-shaped component that is press-fitted into an annular step portion 18 a formed in the opening of the exhaust port 42 of the cylinder head body 18, and a valve seat body 72 a to which the umbrella portion 44 b of the exhaust valve 44 is applied. The cylindrical portion 72b is formed integrally with the valve seat main body 72a so as to protrude from the valve seat main body 72a to the combustion chamber 37 side. In addition, the code | symbol Dout is the diameter of the umbrella part 44b (namely, diameter of the umbrella part peripheral part 44e), C is the clearance gap (one side clearance) between the umbrella part peripheral part 44e of the umbrella part 44b, and the cylindrical part 72b of the valve seat 72. ).

  FIG. 4B is a cross-sectional view of the main part of the valve seat 72 attached to the cylinder head body 18, and the inner surface 72 c of the valve seat 72 is formed on the side close to the bottom surface 18 b of the annular step portion 18 a of the cylinder head body 18. The first female taper portion 72d and the diameter of the first female taper portion 72d are gradually increased from the end of the first female taper portion 72d toward the combustion chamber 37, and in close contact with the valve face 44d (see (a)) of the exhaust valve 44 (see (a)). A possible female tapered valve seat surface 72e, a second female tapered portion 72f that gradually expands from the end of the valve seat surface 72e toward the combustion chamber 37, and an end of the second female tapered portion 72f The straight hole portion 72g extending to the combustion chamber 37 side with a constant inner diameter Din and a chamfered portion 72h formed at the end portion of the straight hole portion 72g on the combustion chamber 37 side. Tapered portion 72d, the valve seat surface 72e and the second female tapered portion 72f is formed in the valve seat body 72a, the straight bore portion 72g and the chamfered portion 72h is formed in the cylindrical portion 72b. Note that the symbol L is the length of the straight hole portion 72g, which is equal to or close to the lift amount of the exhaust valve when EGR is performed, that is, the EGR lift amount.

5 is a cross-sectional view taken along line 5-5 of FIG. 1, and shows the positional relationship between the exhaust gas recirculation cam 75c and the intake side rocker arm 33. FIG.
That is, one end portion 33a of the intake side rocker arm 33 is not disposed on the radially outer side of the exhaust gas recirculation cam 75c, and the combustion chamber of the cam 75 is a portion where the exhaust gas recirculation cam 75c is not formed. It is arranged on the radially outer side closer to 37. Accordingly, the intake-side rocker arm 33 is not driven by the exhaust gas recirculation cam 75c.

  FIG. 6 is a cross-sectional view showing a main part of the carburetor according to the present invention. A main air passage 81a is opened in a carburetor body 81 constituting a part of the carburetor 65, and other parts are provided at the central portion of the main air passage 81a. A venturi portion 81b having a smaller inner diameter is formed, a choke valve 82 capable of adjusting the opening degree is provided on the upstream side of the air flow with respect to the venturi portion 81b, and on the downstream side of the air flow with respect to the venturi portion 81b. In addition, a throttle valve 83 whose opening degree is automatically adjusted by a governor is provided.

  An operation member such as a throttle lever for manually adjusting the throttle valve 83 is not provided in the general-purpose engine 10 (see FIG. 1). Therefore, the operator cannot adjust the opening degree of the throttle valve 83.

  Here, reference numeral 84 denotes a main nozzle that discharges fuel into the main air passage 81a, 86 denotes a choke valve shaft that is rotatably attached to the carburetor body 81 to support the choke valve 82, and 87 supports the throttle valve 83. Therefore, a throttle valve shaft is rotatably attached to the carburetor body 81.

Next, the operation of the valve seat 72 described above will be described. First, a comparative example for the valve seat 72 will be described.
FIGS. 7A and 7B are cross-sectional views showing the shape and operation of a comparative example of a valve seat.
In (a), the valve seat 121 has a first female taper portion 121d on the inner surface 121c, and the diameter of the valve seat 44d of the exhaust valve 44 gradually increases from the end of the first female taper portion 121d toward the combustion chamber 37. And a female taper shaped valve seat surface 121e that can be in close contact with the inner surface, and a second female taper portion 121f that gradually increases in diameter from the end of the valve seat surface 121e toward the combustion chamber 37. 44 shows a closed state.

  In (b), the exhaust valve 44 is lifted from the state of (a) as indicated by the white arrow, the valve face 44d of the exhaust valve 44 is separated from the valve seat surface 121e of the valve seat 121, and the exhaust valve 44 is It shows the open state.

  During the opening of the exhaust valve 44, the gap CB between the valve face 44d and the valve seat surface 121e gradually increases, that is, the opening area between the exhaust valve 44 and the valve seat 121 gradually increases.

FIGS. 8A and 8B are operation diagrams showing the operation of the valve seat according to the present invention.
(A) shows a state in which the valve face 44d of the exhaust valve 44 is in close contact with the valve seat surface 72e of the valve seat 72 and the exhaust valve 44 is closed. At this time, the gap between the umbrella peripheral portion 44e of the exhaust valve 44 and the straight hole portion 72g of the valve seat 72 is C.

  (B), the exhaust valve 44 is lifted by a predetermined amount for EGR as indicated by the white arrow from the state of (a), and the valve face 44d of the exhaust valve 44 is lifted by the valve seat surface of the valve seat 72. The exhaust valve 44 is opened away from 72e. At this time, the clearance between the umbrella peripheral portion 44e of the exhaust valve 44 and the straight hole inner surface 72g of the valve seat 72 is C.

Thus, by providing the straight hole 72g in the cylindrical portion 72b of the valve seat 72, the valve face 44d of the exhaust valve 44 and the valve seat surface 72e of the valve seat 121 are within the lift amount range for EGR. The gap between them gradually increases, but the gap between the umbrella peripheral edge 44e and the straight hole 72g is always constant C, and as a result, the opening area between the exhaust valve 44 and the valve seat 72 is constant. .
Therefore, the EGR amount can be made constant, and even if the valve lift amount changes with respect to the specified value, the change in the EGR amount can be made smaller.

The imaginary line in the figure indicates the position of the exhaust valve 44 in the exhaust stroke that has further lifted beyond the lift amount for EGR. At this position, the exhaust gas in the combustion chamber is discharged.
When the lift amount of the exhaust valve 44 exceeds the lift amount for EGR, the umbrella peripheral portion 44e of the exhaust valve 44 is disengaged from the straight hole portion 72g of the valve seat 72. Therefore, as the lift amount of the exhaust valve 44 increases, The opening area between the exhaust valve 44 and the valve seat 72 is gradually increased, and the amount of exhaust gas discharged is increased.

  FIG. 9 is a graph for explaining the lift amounts of the intake valve and the exhaust valve according to the present invention, wherein the vertical axis indicates the valve lift amounts of the intake valve and the exhaust valve, and the horizontal axis indicates the crank angle (unit: degrees). The solid line in the graph indicates the exhaust valve, and the alternate long and short dash line indicates the intake valve.

The exhaust valve starts to open in the second half of the expansion stroke of the general-purpose engine and closes in the first half of the intake stroke.
The intake valve begins to open in the second half of the exhaust stroke of the general-purpose engine and closes in the first half of the compression stroke.
At some time within the crank angle range when the intake valve is open, i.e., during the intake stroke, the exhaust valve is reopened and closed for EGR. The valve lift amount of the exhaust valve at this time is smaller than the valve lift amount during the exhaust stroke.

  As described above, when the exhaust valve is opened during the intake stroke, the exhaust gas once flowing out from the combustion chamber to the exhaust port and the silencer is recirculated into the combustion chamber. Thereby, the excessive raise of the combustion temperature in a combustion chamber is suppressed, and NOx in exhaust gas can be reduced.

  FIG. 10 is a graph showing the relationship between the valve opening area and the valve lift amount in the cylinder head according to the present invention. The vertical axis represents the opening area (valve opening area) between the exhaust valve and the valve seat, and the horizontal axis represents the exhaust. Indicates the valve lift amount of the valve. The solid line in the figure indicates the valve seat 72 (see FIG. 4) of the example (this embodiment), and the broken line indicates the valve seat 121 of the comparative example (see FIGS. 7A and 7B).

  In the comparative example, the valve opening area increases in proportion to the valve lift amount as the valve lift amount increases. However, in the embodiment, the valve opening area is exhausted up to the EGR lift amount for EGR. Just increasing slightly immediately after the valve starts to open, it has remained almost constant thereafter. In the embodiment, when the EGR lift amount is exceeded, the valve opening area increases almost in proportion to the valve lift amount as the valve lift amount increases.

  FIG. 11 is a graph showing the relationship between the EGR rate and the valve lift amount in the cylinder head according to the present invention, and the vertical axis shows the EGR rate (the ratio of the exhaust gas flow rate (EGR amount) recirculated to the total gas flow rate). The horizontal axis represents the valve lift amount of the exhaust valve. The solid line in the figure indicates the valve seat 72 (see FIG. 4) of the example (this embodiment), and the broken line indicates the valve seat 121 of the comparative example (see FIGS. 7A and 7B).

  In the comparative example, the EGR rate tends to increase with an increase in the valve lift amount in the range of the valve lift amount within the EGR lift amount. However, in the example, the increase in the EGR rate with the increase in the valve lift amount is Smaller than the comparative example.

  Also in the embodiment, the EGR rate slightly increases as the valve lift amount increases, not only because the opening area between the exhaust valve and the valve seat increases when the valve lift amount increases, This is because the flow rate of the exhaust gas passing through the opening changes and the amount of EGR increases.

  As shown in FIGS. 1, 3, and 4 (b) above, the internal EGR mechanism that lifts the exhaust valve 44 by a predetermined amount in the intake stroke of the general-purpose engine 10 and circulates a part of the exhaust gas to the combustion chamber 37. The cylinder head 50 of the general-purpose engine 10 including the valve seat 72 that closes the exhaust port 42 when the umbrella portion 44b of the exhaust valve 44 is seated is provided on the cylinder head 50. The valve seat surface 72e as a female taper portion that increases in diameter as it approaches the combustion chamber 37 so as to be in close contact with the valve face 44d as a male taper portion formed in the umbrella portion 44b, and an inner diameter Din from the valve seat surface 72e. A straight hole 72g as a hole extending toward the combustion chamber 37 so as to be constant, and the length of the straight hole 72g However, when the EGR is performed by lifting the exhaust valve 44 during the intake stroke, the valve clearance of the exhaust valve 44 is set to be the same as or close to the lift amount when the exhaust valve 44 is exhausted gas recirculation. To avoid the effects of variations in adjustment and changes in valve clearance over time, no complicated mechanism or frequent maintenance is required, and the opening area between the exhaust valve 44 and the straight hole 72g of the valve seat 72 is small. Since it becomes constant regardless of the lift amount of the exhaust valve 44, a desired EGR amount can be obtained while suppressing the cost.

  The cylinder head provided with the internal EGR mechanism of the present invention is suitable for a general-purpose engine.

1 is a front view showing a general-purpose engine having an exhaust gas recirculation structure according to the present invention. It is explanatory drawing which shows the internal EGR mechanism which concerns on this invention. FIG. 3 is a sectional view taken along line 3-3 in FIG. 1. It is explanatory drawing explaining the valve seat which concerns on this invention. FIG. 5 is a sectional view taken along line 5-5 of FIG. It is sectional drawing which shows the principal part of the carburetor which concerns on this invention. It is sectional drawing which shows the shape and effect | action of the comparative example of a valve seat. It is an operation view showing an operation of a valve seat in the present invention. It is a graph explaining the lift amount of the intake valve and exhaust valve which concern on this invention. It is a graph which shows the relationship between the valve opening area in the cylinder head which concerns on this invention, and valve lift amount. It is a graph which shows the relationship between the EGR rate and valve lift amount in the cylinder head which concerns on this invention. It is a 1st sectional view showing the conventional valve seat. It is a 2nd sectional view showing the conventional valve seat.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Engine (general purpose engine), 37 ... Combustion chamber, 42 ... Exhaust port, 44 ... Exhaust valve, 44b ... Umbrella part, 44d ... Male taper part (valve face), 50 ... Cylinder head, 70 ... Internal EGR mechanism, 72 ... valve seat, 72e ... female taper part (valve seat surface), 72g ... hole part (straight hole part), L ... length of hole part (length of straight hole part).

Claims (1)

A cylinder head of the engine having an internal EGR mechanism that lifts an exhaust valve by a predetermined amount in an intake stroke of the engine and circulates a part of the exhaust gas to the combustion chamber;
The cylinder head is provided with a valve seat that closes the exhaust port by seating the umbrella portion of the exhaust valve,
The valve seat has a female taper portion that increases in diameter as it approaches the combustion chamber so as to be in close contact with the male taper portion formed in the umbrella portion, and an inner diameter that is constant from the female taper portion to the combustion chamber. A hole extending toward the end, and a chamfered portion formed at an end of the hole on the combustion chamber side,
The female taper portion has a first female taper portion continuous with an inlet of the exhaust port on the combustion chamber side, and gradually expands from the end of the first female taper portion to the combustion chamber side, and the exhaust valve A female taper-shaped valve seat surface that can be in close contact with the male taper portion, and a second female taper portion that gradually expands from the end of the valve seat surface to the combustion chamber side and reaches the hole,
An engine cylinder head having an internal EGR mechanism, wherein the length of the hole is set to be equal to a lift amount when the exhaust valve recirculates exhaust gas.

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