The present disclosure relates to a cylinder head into which a pivot member, such as a lash adjuster for pivotably supporting a rocker arm is incorporated.
Conventionally, for example, JP2018-059439A discloses a lash adjuster (HLA: Hydraulic Lash Adjuster) of a hydraulic operation type which automatically and hydraulically carries out a zero-point adjustment of a valve clearance as a pivot member (mechanism) for pivotably supporting a rocker arm (swing arm).
The HLA is disposed in a side wall part of a cam chamber formed in an upper surface of a cylinder head. This is to supply oil pressure for operating the HLA through the inside of the side wall part. In detail, in the side wall part (side surface) of the cam chamber, a part protruding inwardly in the cam chamber while being coupled to an inner bottom part (inner bottom surface) is formed, and the HLA is attached to (incorporated into) a hole formed in the protruding part. An oil-pressure supply passage is formed inside the side wall part, and this oil-pressure supply passage communicates with the hole. Therefore, the oil pressure for operation is supplied to the HLA attached to the hole.
In engines, a fastening position of a cylinder head and a cylinder block with bolts and nuts may be set inside the cam chamber. That is, bolt holes are formed in the inner bottom surface of the cam chamber, bolts are inserted into the bolt holes from the cam chamber side, and the bolts are inserted into and threadedly engaged with nut members embedded in the cylinder block.
With such a structure, if the fastening force of the bolts and nuts are too large, the inner bottom surface of the cam chamber may be deformed, and according to this deformation, stress occurs in a boundary part between the inner bottom surface and the protruding part (i.e., the side wall part) of the cam chamber, thereby causing a crack at the boundary part in a worst case scenario. In particular, since in high compression type engines (diesel engine, etc.) the cylinder head and the cylinder block are fastened with a large fastening force in order to prevent leaks of combustion gas, the above-described inconvenience may occur.
In order to avoid such an inconvenience, for example, it is possible to increase the thickness of the wall part which forms the cam chamber and to increase the strength of the cylinder head. However, this will be accompanied by a decrease in fuel efficiency and a cost increase due to the weight increase in the cylinder head, and thereby, this is not ideal.
The present disclosure is made in view of the above situations, and one purpose thereof is to provide a technology which is capable of easing stress generated by fastening a cylinder head and a cylinder block, without increasing the weight of the cylinder head.
In order to solve the problem described above, according to one aspect of the present disclosure, a cylinder head, where a pivot member configured to pivotably support a rocker arm is fastened with a bolt, is provided. The cylinder head includes a bottom wall part forming an inner bottom surface of a cam chamber that is a space where the rocker arm is disposed, and a side wall part forming an internal surface continuously rising from the inner bottom surface. A bolt hole into which the bolt is inserted is formed in the inner bottom surface. The side wall part has a protrusion protruding inward in the cam chamber from the internal surface at a position separated from the inner bottom surface, and having a support hole configured to support the pivot member.
According to this configuration, since the part at which the pivot member is supported (i.e., the protrusion) is separated from the inner bottom surface of the cam chamber, a position of stress generated by the fastening of the bolt is separated from the bolt fastening position by a separation amount of the protrusion compared to a conventional cylinder head. The magnitude of the stress in this case becomes larger as the distance from the fastening position to the generated position of the stress is shorter. Therefore, according to this configuration, it is possible to reduce (ease) the stress, compared to the conventional cylinder head, without increasing the thickness of the wall part which forms the cam chamber, and accordingly, without increasing the weight of the cylinder head.
A part of the internal surface, facing a space between the protrusion and the inner bottom surface, may be recessed in a direction along the inner bottom surface heading away from the bolt hole.
According to this configuration, the generated position of the stress is further separated from the bolt fastening position. Therefore, the stress can be further eased.
In this case, the recessed part of the internal surface may have a curved shape or a rectangular shape in cross-section.
According to this configuration, the generated position of the stress can be separated from the fastening position of the bolt with a simple configuration.
Note that the pivot member which pivotably supports the rocker arm may be a lash adjuster of a hydraulic operation type configured to automatically and hydraulically carry out a zero-point adjustment of a valve clearance. In the case where the lash adjuster is applied, oil pressure for operating the lash adjuster needs to be supplied through the inside of the side wall part of the cylinder head, and therefore, the lash adjuster also needs to be incorporated in (supported by) the side wall part.
Thus, the configuration of the cylinder head described above is useful especially for the cylinder head in which the lash adjuster of hydraulic operation type is incorporated as the pivot member.
Moreover, the cam chamber may have a rectangular shape in a plan view, the bolt hole may be formed substantially at the center of the inner bottom surface, and the pivot member may be disposed at a corner part of the cam chamber in the plan view.
As described above, according to the configuration in which the bolt is fastened at the center of the cam chamber (the inner bottom surface) of the rectangular shape in a plan view, and the pivot member is disposed at the corner part of the cam chamber, as a result of the depression of the inner bottom surface centering on the bolt (the bolt hole), the deformation of the inner bottom surface influences also the corner part of the cam chamber. Therefore, the configuration described above is useful also in the case where the bolt hole is formed at the center of the cam chamber, and the pivot member is disposed at the corner part of the cam chamber.
Hereinafter, one embodiment of the present disclosure is described in detail with reference to the accompanying drawings.
[1. Engine Structure]
The engine 1 includes a head cover 3, a cylinder head 4, a cylinder block 5, a crank case (not illustrated), and an oil pan (not illustrated) which are coupled in series in the vertical direction. A plurality of cylinder bores 7 are formed in the cylinder block 5, and a piston 8 is slidably accommodated inside each cylinder bore 7. A combustion chamber 11 is formed by the piston 8, the cylinder bore 7, and the cylinder head 4, for every cylinder. The piston 8 of each cylinder is coupled to a crankshaft (not illustrated) rotatably supported by the crank case through a connecting rod (not illustrated).
The cylinder head 4 is provided with two exhaust ports 12 which open to each combustion chamber 11 and two exhaust valves 14 which open and close the respective exhaust ports 12.
The exhaust valve 14 is biased by a return spring 16 in a direction to close the exhaust port 12 (upward in
Note that the hydraulic lash adjuster 24 (hereinafter, referred to as “HLA 24”) is one example of a pivot member (mechanism) which pivotably supports the rocker arm 20, and is to automatically carry out a zero-point adjustment of a clearance between the rocker arm 20 and the exhaust valve 14 (valve clearance) by hydraulically pushing up the rocker arm 20.
Although illustration is omitted, on the right side of the cylinder head 4 in
[2. Structure of Cylinder Head 4]
The cylinder head 4 has a head body 30 where the exhaust port 12, the intake port (not illustrated), etc. are formed (an example of a “bottom wall part” of the present disclosure). In an upper part of the head body 30, a central wall part 32 extending in the front-and-rear direction so as to pass through the center of each cylinder bore 7 in the plan view, an exhaust-side wall part 34 extending in the front-and-rear direction at a position separated from the central wall part 32 to the exhaust side, an intake-side wall part 36 extending in the front-and-rear direction at a position separated from the central wall part 32 to the intake side, a plurality of partition wall parts 38 each extending in the width direction at a plurality of positions in the front-and-rear direction of the head body 30, covering the wall parts 34 and 36 are provided so as to stand. Therefore, a plurality of cam chambers 40, which are the spaces where the rocker arm 20, etc. are disposed, are formed in the upper part of the cylinder head 4 in a grid shape. In detail, a plurality of exhaust-side cam chambers 40A of substantially square shapes in the plan view lined up in the front-and-rear direction, and a plurality of intake-side cam chambers 40B (the same number as the exhaust-side cam chambers 40A) of substantially square shapes in the plan view lined up in the front-and-rear direction, are formed in two rows.
As illustrated in
Although illustration is omitted, the intake-side cam shaft is disposed above each intake-side cam chamber 40B so as to extend in the front-and-rear direction. Similar to the exhaust-side cam shaft 18, the intake-side cam shaft is rotatably held by the cam shaft cap 37 and the partition wall part 38.
A bolt hole 44 and a valve hole 46 are formed in an inner bottom surface 42a of the exhaust-side cam chamber 40A. The bolt hole 44 is a hole into which a head bolt B for fastening the cylinder head 4 with the cylinder block 5 is inserted, and the valve hole 46 is a hole into which the exhaust valve 14 is inserted.
The bolt hole 44 is formed substantially in the central part of the inner bottom surface 42a. As illustrated in
Note that as illustrated in
The valve holes 46 are formed at respective corner parts of the exhaust-side cam chamber 40A, in detail, at respective corner parts closer to the central wall part 32. The exhaust valve 14 is inserted in each valve hole 46 through a cylindrical valve guide 15 (see
Note that the center of each cylinder (cylinder bore 7) of the engine 1 is set at a position where the central wall part 32 and the partition wall part 38 intersect in the plan view of the cylinder head 4. Therefore, the two exhaust valves 14 which open and close the two exhaust ports 12 of the same cylinder are inserted in the valve holes 46 of the exhaust-side cam chamber 40A which are adjacent to each other in the front-and-rear direction on both sides of the partition wall part 38. That is, the exhaust valves 14 of the cylinders which are adjacent to each other are inserted into the front and rear, two valve holes 46 which are formed in the same exhaust-side cam chamber 40A.
As illustrated in
Support holes 50 for the HLA 24 are formed at both ends of the protrusion 48 in the front-and-rear direction, i.e., in corner parts of the exhaust-side cam chamber 40A, in detail, in corner parts closer to the exhaust-side wall part 34. These support holes 50 penetrate in the thickness direction of the protrusion 48 (in the height direction of the exhaust-side wall part 34), and the HLA 24 is fitted into these support holes 50. Roughly, as illustrated in
Note that a seat surface part 50a for the HLA 24 of a circular recess is formed at a position of the inner bottom surface 42a of the exhaust-side cam chamber 40A, which corresponds to each support hole 50, and a lower-end part of the HLA 24 (body 24a) is received by this seat surface part 50a.
As illustrated in
The recessed part (referred to as a “recess 421”) of the side surface 42b has a curved shape in the cross-section, and in this example, as illustrated in
Here, although the structure of the exhaust-side cam chamber 40A of the cylinder head 4 is mainly described, the structure of the intake-side cam chamber 40B is fundamentally common to the structure of the exhaust-side cam chamber 40A because it is simply symmetrical with the exhaust-side cam chamber 40A with respect to the central wall part 32, as illustrated in
That is, a bolt hole 44 and a seat surface part 44a for the head bolt, two valve holes 46 for the intake valves, and two seat surface parts 50a for the HLA 24 are formed in the inner bottom surface 42a of the intake-side cam chamber 40B. Moreover, in a side surface 42c (another example of the “internal surface” of the present disclosure) of the intake-side cam chamber 40B formed by the intake-side wall part 36 (another example of the “side wall part” of the present disclosure), the protrusion 48, which protrudes from the side surface 42c toward the inward of the cam chamber at a position separated upwardly from the inner bottom surface 42a and extends in the front-and-rear direction, is formed, and support holes 50 for the HLA 24 are formed at both ends of the protrusion 48 in the front and rear directions. The HLA 24 is supported by the protrusion 48 while being fitted into the support hole 50, and oil pressure for operation is supplied to the HLA 24 through the oil passage 49 formed inside the protrusion 48.
Moreover, a part of the side surface 42c of the intake-side cam chamber 40B, which faces a space between the protrusion 48 and the inner bottom surface 42a, is recessed outwardly (downwardly and outwardly in
[3. Operation and Effects]
As described above, in the engine 1, the cylinder head 4 is fastened to the cylinder block 5 with the head bolts B, and the HLA 24 for pivotably supporting the rocker arm 20 is incorporated into the cylinder head 4.
The cylinder head 4 includes the head body 30 which forms the inner bottom surfaces 42a of the exhaust-side cam chambers 40A (intake-side cam chambers 40B), and the exhaust-side wall part 34 (intake-side wall part 36) which forms the side surfaces 42b (side surfaces 42c) which rise continuously from the inner bottom surfaces 42a. The bolt hole 44 into which the head bolt B is inserted is formed in the inner bottom surface 42a. Moreover, the exhaust-side wall part 34 (intake-side wall part 36) of the cylinder head 4 has the protrusion 48 which protrudes toward the inside of the cam chamber 40A (40B) from the side surface 42b (side surface 42c) at the position separated from the inner bottom surface 42a along the side surface 42b (side surface 42c), and the support hole 50 which can support the HLA 24 is formed in the protrusion 48.
According to such a structure of the cylinder head 4, since the part of the exhaust-side wall part 34 (intake-side wall part 36) at which the HLA 24 is supported (i.e., the protrusion 48) is separated from the inner bottom surface 42a of the exhaust-side cam chamber 40A (intake-side cam chamber 40B), the generated position of the stress resulting from the deformation of the inner bottom surface 42a caused by fastening of the head bolt B separates from the fastening position of the head bolt B (the bolt hole 44 and the seat surface part 44a) by the separated amount of the protrusion 48. Therefore, according to the cylinder head 4, the stress is eased, compared with the cylinder head of the conventional structure, thereby reducing the generation of a crack, etc., in the cylinder head 4.
This is described in detail using the drawings.
The cylinder head 4 illustrated in
On the other hand, the cylinder head 4′ of the comparative example illustrated in
In either of the cylinder head 4 or 4′, when the head bolt B is fastened to the cylinder block 5, the seat surface part 44a is depressed toward the cylinder block 5 by the fastening, which causes a deformation of the perimeter of the seat surface part 44a. Such a depression of the seat surface part 44a becomes larger as the fastening force of the head bolt B relatively increases.
Here, in the cylinder head 4′ of the comparative example in which the protrusion 48 is coupled to the inner bottom surface 42a, since the protrusion 48 is restrained by the exhaust-side wall part 34, the protrusion 48 cannot follow the displacement of the inner bottom surface 42a as illustrated in
On the other hand, in the cylinder head 4 of this embodiment, the protrusion 48 is not coupled to the inner bottom surface 42a. In addition, the recess 421 of the semicircular shape (arc shape) in the cross-section, which is recessed so as to be separated from the bolt hole 44 (head bolt B), is formed in the part of the side surface 42b of the exhaust-side wall part 34, which faces the space between the protrusion 48 and the inner bottom surface 42a. With such a structure, as illustrated in
Here, the magnitude of the stress caused at the boundary part P2 becomes larger as the depressed amount H relatively increases and becomes larger as the distance L is relatively shortened. Therefore, if the fastening torque of the head bolt B is the same, the stress caused at the boundary part P2 becomes smaller (eased) in the cylinder head 4 of this embodiment in which the distance L from the depression starting point P1 to the boundary part P2 becomes longer, compared with the cylinder head 4′ of the comparative example. Therefore, according to the cylinder head 4 of this embodiment, it can be said that the generation of a crack, etc. resulting from the fastening of the head bolts B can be reduced, compared with the cylinder head of the conventional structure.
[4. Modifications, etc.]
As described above, although the cylinder head 4 according to the embodiment of the present disclosure is described, the cylinder head 4 described above is an illustration of a desirable embodiment of the cylinder head according to the present disclosure, and its specific structure may suitably be changed without departing from the spirit of the present disclosure. For example, the cylinder head 4 may be structured as follows.
(1) In the cylinder head 4 of this embodiment, the recess 421 of the semicircular shape (arc shape) in the cross-section is formed in the part of the side surface 42b of the exhaust-side wall part 34 which forms the exhaust-side cam chamber 40A, which faces the space between the inner bottom surface 42a and the protrusion 48. However, the cross-sectional shape of the recess 421 is not limited to the arc shape and may be any curved cross-sectional shapes other than the arc shape.
(2) Moreover, the recess 421 may have any shapes other than the curved cross-sectional shape, in detail, may have a rectangular or triangular cross-sectional shape (a cross-sectional shape with a corner part). For example,
(3) Although in the cylinder head 4 of this embodiment the recess 421 is formed in the side surface 42b of the exhaust-side wall part 34 which forms the exhaust-side cam chamber 40A, the recess 421 may be eliminated as illustrated in
(4) In this embodiment, the HLA 24 is applied as the pivot member which pivotably supports the rocker arm 20. However, the present disclosure can be applied also to cylinder heads in which the pivot member other than the HLA 24 is incorporated, and therefore, operation and effects equivalent to the cylinder head 4 of this embodiment can be expected from this application.
It should be understood that the embodiments herein are illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof, are therefore intended to be embraced by the claims.
Number | Date | Country | Kind |
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JP2019-099540 | May 2019 | JP | national |
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