Valve bridge and valve bridge manufacturing method

Abstract

To provide a valve bridge which is further improved to enable an oil to be collected sufficiently from a vent hole to supply air and the oil to a guide hole part properly and prevent scuffing of a fixed shaft by comprehensive reviewing including reviewing of a structure, a shape, and a forming method of the vent hole.SOLUTION: A valve bridge has a bridge body 5 which slidably fits on a fixed shaft 14 and transmits motion of a rocker arm 8 to a plurality of valves 1, 1. A guide hole part 16 in which the fixed shaft 14 is fitted is formed at the bridge body 5. A vent hole 17 which allows an upper end of the guide hole part 16 and the outside of the bridge 5 to communicate is provided. The vent hole 17 is set as an externally expanding hole in which a cross sectional area becomes larger in a direction away from the guide hole part 16.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an improved valve bridge used in the valve train of various engines such as diesel engines for agricultural machinery, and to an improvement in a manufacturing method thereof. [Background technology]

[0002] In industrial engines, in order to achieve highly efficient intake and exhaust operations, it is common for each cylinder to have two or more intake valves or exhaust valves (such as a three-valve or four-valve type).For example, in an OHV (overhead valve) engine, if two intake and / or exhaust valves are arranged per cylinder, a valve bridge is used to connect the two valves so that the rocker arm can push and drive both valves simultaneously (see Patent Document 1).

[0003] By installing a valve bridge, in which multiple valve output parts protrude in opposite directions from the bridge body, it becomes possible to move multiple valves simultaneously with one rocker arm. In this case, in order to guide and prevent the valve bridge from shifting position as it reciprocates (moves up and down), the valve bridge is typically fitted slidably onto a fixed shaft supported by the cylinder head, and is configured so that the valve bridge can smoothly slide back and forth while being guided by the fixed shaft.

[0004] In a configuration in which a fixed shaft is fitted onto the guide hole of the bridge body, an input member that receives the pushing force of the rocker arm is usually provided at the upper end of the guide hole, so the upper end of the guide hole is blocked by the input member, making it a nearly sealed hole. Therefore, since the volume of a nearly sealed guide hole that is blocked on one side by the fixed shaft and on the other side by the input member changes when the valve bridge moves up and down, a vent hole (air hole) that communicates with the outside is provided by machining such as drilling to allow breathing.

[0005] In Patent Document 1 (see Figures 1 and 3), one large-diameter ventilation hole (oil hole and breathing hole: 10a) is formed, and in Patent Document 2, a pair of small-diameter ventilation holes (communication holes: 5d) that penetrate a guide hole (guide hole: 5a) are formed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-3687 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-204914 Summary of the Invention [Problem to be solved by the invention]

[0007] The vent holes in the bridge body not only allow air to flow in and out, enabling volumetric changes, but also function to draw oil into the guide hole. Therefore, in terms of lubrication between the fixed shaft and the guide hole through oil suction, a larger diameter (wider area) of the vent hole is preferable. However, as exemplified in Patent Document 1, a larger diameter vent hole (10a) increases the dimensional ratio to the relatively small diameter of the guide hole, making it more likely for scuffing to occur between the opening edge of the vent hole and the fixed shaft. Furthermore, due to layout constraints, vent holes have the problem of easily changing the workpiece's position and causing breakage of the machining blade, making it difficult to drill a large diameter vent hole horizontally during machining.

[0008] Therefore, it is preferable to provide small-diameter ventilation holes in the bridge body, as this allows for easy machining and prevents scuffing, but this is inconvenient as it tends to result in a shortage of oil supply. Also, as disclosed in Patent Document 2, it is possible to provide two small-diameter ventilation holes (5d) concentrically, but in this case, the amount of machining required to penetrate the bridge body increases, which has the disadvantage of increasing the amount of work and time, resulting in increased costs.

[0009] As described above, the vent holes formed in the bridge body were not satisfactory, regardless of their diameter, whether large or small, and so there was still room for improvement in order to create a valve bridge with vent holes that could provide a sufficient oil supply while simplifying the processing.

[0010] The object of the present invention is to provide an improved valve bridge that, through extensive research and a comprehensive review of the structure and shape of the vent holes, as well as their manufacturing method, ensures sufficient oil supply to the guide holes without scuffing the fixed shaft, and also enables cost reductions through streamlining of production. [Means for solving the problem]

[0011] The present invention provides a valve bridge having a bridge body slidably fitted onto a fixed shaft and transmitting the movement of a rocker arm to a plurality of valves, a guide hole portion into which the fixed shaft is fitted is formed in the bridge body, and a vent hole is provided to connect an upper end of the guide hole portion to the outside of the bridge body; The ventilation hole is characterized in that it is set as a hole that flares outward and has a cross-sectional area that increases with increasing distance from the guide hole portion.

[0012] In this case, it is advantageous if the opening of the vent hole on the external communication side is formed to have an elliptical or oval shape that is long in the circumferential direction of the guide hole portion.

[0013] The second aspect of the present invention is a method for manufacturing a valve bridge having a bridge body with a guide hole into which a fixed shaft is slidably fitted, and a pair of bridge arms having valve output portions that abut against the shaft ends of the valves and protruding in opposite directions from the bridge body, a first molding die and a second molding die are prepared, each having a parting surface passing through the pair of bridge arm portions and the bridge body, and a protrusion portion is formed in one of the first and second molding dies to create a recess at the upper end of the bridge body having a depth that reaches the guide hole; The guide holes are formed in the bridge body by machining after molding using the first and second molding dies.

[0014] Regarding the present invention, for characteristic configurations and means other than those described above, please refer to claims 3 to 5. Regarding the second invention, for methods (production methods) other than those described above, please refer to claims 7 and 8. [Effects of the Invention]

[0015] In the valve train, when the valve bridge moves in the direction pushing the valve, the volume of the guide hole (surplus space s: see Figure 2) expands, and negative pressure causes outside air to be sucked into the guide hole from the air vent. According to the present invention, the air vent is an outward-flaring hole whose cross-sectional area increases with increasing distance from the guide hole, so the speed at which air and oil are sucked into the air vent from outside is accelerated within the air vent.

[0016] Therefore, the opening area on the outside of the vent hole can be made large enough to allow sufficient oil collection, and even if the opening area on the guide hole side of the vent hole is made small so as not to cause the scuffing described above, sufficient oil can be supplied to the guide hole section due to acceleration within the vent hole.

[0017] As a result, by comprehensively reviewing the structure and shape of the vent hole, as well as the method of making it, it is possible to provide an improved valve bridge that allows sufficient oil to be collected from the vent hole so that air and oil can be appropriately supplied to the guide hole portion that slides against the fixed shaft, while also preventing scuffing of the fixed shaft due to the presence of the vent hole.

[0018] The second invention is a method for producing a valve bridge by molding a two-part structure, in which a protrusion that creates a recess in the bridge body deep enough to reach the guide hole is formed in one of the molding dies, and after molding using the first and second molding dies, the guide hole is formed in the bridge body by machining.

[0019] Since the position of the innermost end (maximum depth) of the recess is set to a depth that reaches (or will reach) the planned formation range of the guide hole, when the guide hole is formed by machining, the innermost end portion of the recess is also cut by that machining, and an inner opening is created. Therefore, the guide hole formation process, which is performed after molding, penetrates the innermost side of the recess, making it possible to form the vent hole, so that the "dedicated machining process for forming the vent hole" that was previously required can be omitted.

[0020] As a result, by comprehensively reviewing the structure and shape of the vent holes, as well as the method of making them, it is possible to provide an improved valve bridge manufacturing method that eliminates the need for a dedicated manufacturing process for making vent holes in the bridge body, thereby enabling cost reductions through streamlining of production. [Brief explanation of the drawings]

[0021] [Figure 1] The valve train of an industrial diesel engine is shown. (A) is a longitudinal cross-sectional view of the main part seen from the rear, and (B) is a cross-sectional view of the valve bridge. [Figure 2] Enlarged cross section of the valve bridge, cut front to back at the bridge body [Figure 3] Showing the valve bridge, (A) is a rear view, (B) is a right side view [Figure 4] The valve bridge of Figure 3 is shown in (A) plan view and (B) front view. [Figure 5] The valve bridge of Figure 3 is shown. (A) is a cross-sectional view of the ZZ line in Figure 3(A), and (B) is a manufacturing diagram showing the guide hole formation process after die-cutting. DETAILED DESCRIPTION OF THE INVENTION

[0022] An embodiment of a valve bridge and a manufacturing method for the valve bridge according to the present invention will be described below with reference to the drawings, using a valve train for a vertical multi-cylinder diesel engine. While an overall view of the engine is omitted, the side with the engine cooling fan in the cylinder alignment direction will be described as the front, the opposite side as the rear, the side with the exhaust manifold as the left, and the side with the intake manifold as the right.

[0023] 1(A), a cylinder head 21 is attached to the top of a cylinder block (not shown), and a head cover (not shown) is attached on top of the cylinder head 21. An intake port 23, an exhaust port 22, and a push rod insertion hole 24 are provided inside the cylinder head 21. A pair of exhaust valve ports 25, 25 are provided in the exhaust port 22, and a pair of exhaust valves 1, 1 are arranged to open and close the pair of exhaust valve ports 25, 25.

[0024] A rocker arm bracket 26 is attached to the top of the cylinder head 21, and a rocker arm 8 is attached to the rocker arm bracket 26 so as to be able to swing via a pivot (rocker arm shaft) 27 having an axis 27p. A push rod 28 is inserted through the push rod insertion hole 24. The rocker arm bracket 26 and the rocker arm 8 are housed in a head cover (not shown).

[0025] 1(A) and 1(B), a pair of exhaust valves 1, 1 are linked in sequence from a valve cam (not shown) through a tappet (not shown), a pushrod 28, a rocker arm 8, and a valve bridge 4. Although not shown, the intake port 23 also has two intake and exhaust valve openings, and the pair of intake valves are linked from a valve cam through a tappet, a pushrod, a rocker arm, and a valve bridge.

[0026] 1(A), engine oil (not shown) from an oil pan (not shown) is supplied to oil outflow hole 30 at the top of rocker arm 8 of exhaust valve 1,1 by the pumping force of an oil pump (not shown) via an oil gallery (not shown) and pivot 27. Although not shown, engine oil from the oil pan is also supplied to oil outflow hole 30 at the top of rocker arm 8 of intake valve in a similar manner.

[0027] The valve train A for the exhaust valve 1 is outlined below (the valve train for the intake valve has the same configuration as that for the exhaust valve 1, so the case of the exhaust valve 1 will be explained as a representative example). 1(A) and 1(B), the valve train A is made up of a pair of valves (exhaust valves) 1, 1, a valve bridge 4 that can push down each of the valves 1, 1, and a rocker arm 8 that can push down the valve bridge 4 by acting on its bridge body 5. The rocker arm 8 swings about an axis 27p of a pivot 27, so that the pair of valves 1, 1 can be simultaneously pushed down and driven via the valve bridge 4.

[0028] 1(A), (B) and 2, each valve 1 is supported by a cylinder head 21 so as to be slidable while being biased in the valve closing direction by a valve spring 2. The rocker arm 8 includes a central boss portion 9 into which a pivot 27 is fitted so as to be relatively rotatable, an arm input portion 10 that receives the upward thrust of a push rod 28 from below, and an arm output portion 11 that pushes down the valve bridge 4. Reference numeral 31 denotes an injector, which is arranged between the exhaust-side valve bridge 4 and the intake-side valve bridge (not shown) (in front of the exhaust-side valve bridge 4).

[0029] As shown in Figures 1 to 3, the valve bridge 4 is configured as a generally T-shaped component (see Figure 3(A)), comprising a bridge main body 5 with a guide hole into which a fixed shaft 14 is slidably fitted, and a pair of first and second bridge arm portions 6, 7 that protrude in opposite directions from the bridge main body 5 and have a pair of first and second valve output portions 12, 13 that abut against the shaft end portion 3 of the valve 1.

[0030] As shown in Fig. 1, a circular, upward-opening receiving seat 5A (see Figs. 4(A) and 5(A)) is formed on the top of bridge body 5, which is the longitudinal center of valve bridge 4. A disk-shaped bridge input portion 15 made of metal is fitted into the seat 5A. The top surface 15a of bridge input portion 15 is configured so that the bottom surface (not shown) of arm output portion 11 on the tip side of rocker arm 8 can abut against it. As shown in Figs. 3(B) and 4(B), each valve output portion 12, 13 has a pair of opposing hanging pieces 12a, 13a formed in a cantilever shape so that the shaft end portion 3 of valve 1 can be sandwiched between them.

[0031] Therefore, as the rocker arm 8 swings and the arm output portion 11 moves downward, the valve bridge 4 is pushed downward and the valve output portions 12, 13 push the corresponding shaft end portions 3, 3 downward, causing the pair of valves 1, 1 to move downward against the biasing force of the valve springs 2, 2 and open. Then, as the rocker arm 8 swings and the arm output portion 11 moves upward, the pair of valves 1, 1 and the valve bridge 4 are raised by the biasing force of the valve springs 2, 2 and the pair of valves 1, 1 are closed.

[0032] As shown in Fig. 4, a guide hole portion (guide hole) 16 having an axis P and extending in the longitudinal direction (up-down direction) of the bridge body 5 is formed through the cylindrical (boss-shaped) bridge body 5. The first bridge arm portion 6 and the second bridge arm portion 7 protrude sideways from the upper end of the bridge body 5. As shown in Figs. 1 and 2, a fixed shaft 14 having an axis 14p has its lower end fitted and fixed to the cylinder head 21, and protrudes with an axis P facing in the same direction as the axes Q, Q of the valves 1, 1.

[0033] As shown in Figures 2 and 3, an air vent 17 is provided at the upper end of the bridge body 5, connecting the upper end of the guide hole 16 with the outside of the bridge body 5. A thick-walled portion 5B that protrudes slightly rearward is formed at the upper end of the rear side of the bridge body 5, and the air vent 17, which has a hole axis 17P in a side view, is formed in the thick-walled portion 5B with an outer opening 17b facing rearward and sideways. Note that the axis P of the guide hole 16 and the axis 14p of the fixed shaft 14 are theoretically concentric (coaxial) in the assembled state (see Figure 1). The thick-walled portion 5B is provided on the side (rear side) of the valve bridge 4 opposite to the side (front side) where the injector 31 is arranged.

[0034] 3(A), 4(A), and 5, the vent hole 17 has an inner opening 17a facing forward and sideways, whose interior side (innermost side) communicates with the guide hole portion 16. In other words, the outer opening 17b, which is the opening on the outside-communicating side of the vent hole 17, is provided in a portion of the bridge main body 5 where the first and second bridge arm portions 6, 7 are not formed (thick-walled portion 5B). This configuration, which will be described in detail later, has the advantage that when the valve bridge 4 is manufactured by molding a two-split structure, the hole axis 17P is aligned with the direction in which a pair of molds move toward and away from each other, allowing the vent hole 17 to be molded integrally by molding.

[0035] The inner opening 17a is circular (or an ellipse close to a circle), and the outer opening 17b is formed to have an ellipse (or oval) that is long in the circumferential direction (left-right direction) of the guide hole portion 16, and the cross-sectional shape of the ventilation hole 17 is elliptical or oval except for the inner opening 17a. In addition, the ventilation hole 17 is set as an outwardly flaring hole whose cross-sectional area increases with increasing distance from the guide hole portion 16 (from the inner opening 17a to the outer opening 17b).

[0036] The elliptical or oblong outer opening 17b is elongated in the circumferential direction of the bridge body 5 (the circumferential direction of the cylindrical bridge body 5 having the axis P) or in the lateral direction (left-right direction) of the thick-walled portion 5B (see FIG. 3(A)). Furthermore, the "outwardly expanding" shape of the air vent 17 can be said to mean that the air vent 17 is funnel-shaped or nozzle-shaped when viewed from the side of the outer opening 17b in the direction of the hole axis 17P.

[0037] Next, a method for manufacturing the valve bridge 4 will be described, focusing on the bridge body 5. As shown in Figures 2 and 5, the ventilation hole 17 is configured so that a recess 17H formed in the bridge main body 5 by molding opens into the guide hole portion 16 (inner opening 17a) by processing to form the guide hole portion 16.

[0038] That is, as shown in Figure 5(B), first and second molding dies K1, K2 are prepared, on which a parting surface w is formed that passes through a pair of bridge arm portions 6, 7 and the bridge main body 5 (see Figure 4(A)), and a protrusion 18 that creates a recess 17H at the upper end of the bridge main body 5 with a depth that reaches the guide hole portion 16 is formed in either of the first or second molding dies K1, K2 (e.g., the first molding die K1), and after molding using the first and second molding dies K1, K2, the guide hole portion 16 is formed in the bridge main body 5 by machining.

[0039] For example, as shown in FIG. 5(B), the valve bridge 4 is a forged product, and a molding process is performed to form the valve bridge 4 having the bridge body 5, which is integrally formed with a recess (depression) 17H due to the protrusion 18, by molding using a first molding die K1 and a second molding die K2, which are forging dies.

[0040] Then, a guide hole forming process is performed in which the bridge main body 5 having the recess 17H is drilled (an example of machining) using a drill bit 19 to form the guide hole portion 16. Next, a seat surface forming process is performed in which the receiving seat 5A is formed on the upper surface (notation omitted) of the bridge main body 5 by milling using an end mill 20 (other machining processes may also be used). Note that the order of the guide hole forming process and the seat surface forming process may be reversed.

[0041] The position of the innermost end (maximum depth) 29 of the recess 17H is set to a depth that reaches (or will reach) the planned formation range of the guide hole portion 16, so when the guide hole portion 16 is formed by machining, the inner opening 17a is also automatically formed, as shown in Fig. 5(A), thereby completing the vent hole 17. Therefore, the guide hole forming step performed after molding forms the vent hole 17, penetrating the innermost side of the recess 17H, so that the "dedicated machining step for forming the vent hole" that was conventionally required can be omitted.

[0042] [About the effects] As described above, the valve bridge 4 is characterized in that the guide hole portion 16 into which the fixed shaft 14 is fitted is formed in the bridge body 5, and the air vent 17 is provided to connect the upper end of the guide hole portion 16 to the outside of the bridge body 5, and the air vent 17 is set as an outward-flaring hole whose cross-sectional area increases with increasing distance from the guide hole portion 16.

[0043] In other words, the following solutions are proposed: (1) to (3). (1) The shape of the forged recess (depression) 17H is utilized to process the inner diameter of the guide hole portion 16 to penetrate it and form the ventilation hole 17. (2) By concentrating the vent holes 17 at one location (thick-walled location 5B) on the opposite side from the injector 31 while maintaining the opening area, the opening area of ​​the vent holes 17 is substantially increased. (3) The ventilation hole 17 portion is squeezed over the guide hole portion 16, taking advantage of the gradient of the forging die.

[0044] Specifically, two-part molds K1 and K2, which are relatively inexpensive for forging or casting, are used, and a protrusion 18 extending in the mold-splitting direction (a direction perpendicular to the mold-splitting plane w: see FIG. 4(A) for the mold-splitting plane w) is provided on one of the molds K1, so that the recess 17H is simultaneously formed when the valve bridge 4 is molded. Therefore, as mentioned above, there is an advantage in that the guide hole forming process for creating the guide hole 16 is subsequently performed, so that the vent hole 17 is also formed at the same time. Furthermore, to make the vent hole 17 flared outward, the protrusion 18 is made flared at the base, which can be easily achieved by increasing the draft angle required for molding, and a large draft angle is also advantageous in terms of the mold-release structure.

[0045] In addition, the following actions and effects (4) to (6) can be obtained. (4) Since the basic shape of the ventilation hole 17 (recess 17H) is also created by molding, there is an advantage that it is possible to eliminate the processing step that was previously required to "create the ventilation hole by special machining from the side." (5) The area of ​​the outer opening 17b of the vent hole 17 is larger (than that of the conventional product), so that the efficiency of collecting splashed oil at the outer opening 17b is improved.

[0046] (6) When the valve bridge 4 moves downward (opening of the valve 1), the volume of the surplus space s (see FIG. 2) in the guide hole portion 16 other than the fixed shaft 14 expands, and negative pressure causes external air to be drawn into the surplus space s through the vent hole 17. The vent hole 17 has a throttle shape that flares outward, with the area of ​​the outer opening 17b clearly larger than the area of ​​the inner opening 17a, and this accelerates the suction speed of the air and oil collected in the vent hole 17 from the outer opening 17b. Therefore, even though the inner opening 17a has a relatively small area that does not create scuffs on the fixed shaft 14 due to the presence of the vent hole 17, an impactor effect can be achieved that allows sufficient ventilation (breathing) and oil suction.

[0047] As a result, it is possible to provide an improved valve bridge 4 that eliminates conventional problems by eliminating the need for dedicated machining to create the vent holes 17, thereby reducing costs, and by naturally forming the vent holes 17 in an outwardly expanding shape, thereby eliminating scuffing of the fixed shaft and allowing sufficient breathing and oil supply.

[0048] If the area of ​​the outer opening 17b is at least twice the area of ​​the inner opening 17a, the above-mentioned functions and effects can be enhanced, which is advantageous. Furthermore, when the valve bridge 4 is installed in an actual vehicle (valve train A), the thick-walled portion 5B, i.e., the outer opening 17b, is located on the opposite side of the bridge body 5 from the injector (the side opposite to the side where the injector 31 is located: the rear side), so there is almost nothing to obstruct the suction action of the outer opening 17b, which has the advantage of allowing breathing and oil collection through the vent hole 17 to be carried out efficiently.

[0049] [Another Example] The guide hole portion 16 into which the fixed shaft 14 is fitted is formed as a "hole" that penetrates the bridge main body 5, as shown in Figure 5(B). Also, although not shown, in the case where the bridge input portion 15 is configured by attaching the top wall of the bridge main body itself or a separate member, it is possible to make it a "hole" that does not penetrate the upper side. Therefore, the guide hole portion 16 is defined as an expression that includes both a guide hole and a guide hole.

[0050] The shape of the outer opening 17b as viewed from the hole axis 17P direction may be a circle or a rounded rectangle having a larger diameter than the diameter of the inner opening 17a, other than a horizontally long ellipse or an oval. [Explanation of symbols]

[0051] 1 valve 3 shaft end 5 Bridge body 6 First bridge arm 7 Second bridge arm 8 Rocker Arm 12 First valve output section 13 Second valve output section 14 Fixed axis 16 Guide hole section (guide hole) 17 Ventilation holes 17H dent 17b External communication side opening 18 Protrusion K1 1st mold K2 2nd mold w Mold cutting surface

Claims

1. A valve bridge having a bridge body slidably fitted onto a fixed shaft and transmitting the movement of a rocker arm to a plurality of valves, a guide hole portion into which the fixed shaft is fitted is formed in the bridge body, and a vent hole is provided to connect an upper end of the guide hole portion to the outside of the bridge body; The valve bridge has a flared hole whose cross-sectional area increases with increasing distance from the guide hole portion.

2. 2. The valve bridge according to claim 1, wherein the opening of the vent hole on the external communication side is formed to have an elliptical or oval shape that is long in the circumferential direction of the guide hole portion.

3. The valve bridge according to claim 2 , wherein the vent hole extends in a direction perpendicular to the guide hole portion.

4. The valve bridge according to any one of claims 1 to 3, wherein the air vent is configured such that a recess formed in the bridge body by molding opens into the guide hole portion by processing to form the guide hole portion.

5. a plurality of bridge arm portions each having a valve output portion that abuts against a shaft end of the valve, the bridge arm portions being protruding from the bridge body; The valve bridge according to claim 4 , wherein the opening of the vent hole on the external communication side is provided in a location on the bridge body where the bridge arm portion is not formed.

6. A method for manufacturing a valve bridge having a bridge body with a guide hole into which a fixed shaft is slidably fitted, and a pair of bridge arms having valve output portions that abut against shaft ends of a valve and protruding in opposite directions from the bridge body, comprising: a first molding die and a second molding die are prepared, each having a parting surface passing through the pair of bridge arm portions and the bridge body, and a protrusion portion is formed in one of the first and second molding dies to create a recess at the upper end of the bridge body having a depth reaching the guide hole; a valve bridge manufacturing method, wherein the guide holes are formed in the bridge body by machining after molding using the first and second molding dies;

7. 7. The method for manufacturing a valve bridge according to claim 6, wherein the protrusion is tapered so that the cross-sectional area of ​​the recess decreases as the depth of the recess increases.

8. 8. A method for manufacturing a valve bridge according to claim 7, wherein the tapered shape of the protrusion is set so that the area of ​​the opening on the external communication side of the recess is twice the area of ​​the opening formed on the guide hole side of the recess as a result of the formation of the guide hole.

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