JP2020125698A - Cylinder block - Google Patents

Abstract

To provide a cylinder block which can decrease striking sound.SOLUTION: A cylinder block has a cylinder bore formed so that a piston is reciprocatingly moved therethrough. A bore wall of the cylinder bore in a thrust side extends straight along a reciprocating direction of the piston in a cross-sectional view. Between a bottom dead center and a top dead center of a top end of the piston, the diameter of the cylinder bore is gradually reduced upward.SELECTED DRAWING: Figure 1

Description

The present invention relates to a cylinder block.

In order to prevent the friction between the bore wall of the cylinder bore and the piston from becoming excessive, a technique of enlarging the diameter of the cylinder bore between the bottom dead center and the top dead center has been proposed (Patent Document 1, etc.).

JP, 2017-198174, A

However, when the diameter of the cylinder bore is increased in this way, when the piston collides with the bore wall in the portion where the diameter changes, a tapping sound is generated and noise is increased. Then, it aims at providing the cylinder block which can reduce a tapping sound.

The above-mentioned object is a cylinder block in which a cylinder bore in which a piston reciprocates is formed, and a bore wall of the thrust-side cylinder bore extends straight in a cross-sectional view along the reciprocating direction of the piston, and This can be achieved by a cylinder block characterized in that between the bottom dead center and the top dead center of the upper end of the piston, the diameter of the cylinder bore becomes smaller as it goes upward.

A cylinder block capable of reducing tapping sound can be provided.

FIG. 1 is a sectional view illustrating a cylinder block according to the first embodiment. FIG. 2 is a schematic perspective view of the cylinder bore according to the first embodiment. 3A to 3G are cross-sectional views sequentially showing the operation of the internal combustion engine including the cylinder block according to the first embodiment. FIG. 4 is a schematic perspective view for explaining an example of dimensions of the cylinder bore according to the first embodiment. FIG. 5 is an enlarged cross-sectional view showing a preferable inclination of the first inclined surface according to the first embodiment. FIG. 6 is a schematic cross-sectional view of a cylinder block according to the first comparative example. FIG. 7 is a schematic cross-sectional view of a cylinder block according to the second comparative example. 8A to 8G are schematic cross-sectional views of the cylinder block according to the second comparative example. FIG. 9 is a schematic perspective view of a cylinder bore according to the second embodiment. FIG. 10 is a schematic perspective view of a cylinder bore according to the third embodiment. FIG. 11 is a schematic perspective view of a cylinder bore according to the fourth embodiment.

(First embodiment)
Hereinafter, the cylinder block 10 according to the present embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a cylinder block 10 according to the first embodiment.

The cylinder block 10 is a block that houses a piston 12 of an in-line 4-cylinder internal combustion engine, for example, and is formed by molding an aluminum alloy. The piston 12 is connected to the connecting rod 11, and its upper end 12a reciprocates in the cylinder block 10 between the top dead center P1 and the bottom dead center P2.

Further, the cylinder block 10 is formed with a cylinder bore 13 for accommodating the piston 12. The cylinder bore 13 has a substantially cylindrical shape extending along the reciprocating direction L of the piston 12, and has a first bore wall 13a and a second bore wall 13b with which the piston 12 slides. Of these, the first bore wall 13a is a wall on the thrust side and extends straight along the reciprocating direction L in a sectional view.

On the other hand, the second bore wall 13b is a wall on the anti-thrust side and has a first inclined surface 13c and a second inclined surface 13d. The first inclined surface 13c is an inclined surface starting from a point P3 between the top dead center P1 and the bottom dead center P2, and the diameter D of the cylinder bore 13 between the top dead center P1 and the bottom dead center P2. Is provided so as to decrease toward the upper side.

The second inclined surface 13d is an inclined surface having a point P4 below the point P3 as a starting point, and is provided so that the diameter D of the cylinder bore 13 becomes smaller as it goes downward from the point P4.

FIG. 2 is a schematic perspective view of the cylinder bore 13.
In the present embodiment, the diameter D of the cylinder bore 13 is changed according to the height of the cylinder block 10, but a step due to the change of the diameter D is not formed in the first bore wall 13a on the thrust side. On the other hand, the diameter D is changed in the second bore wall 13b on the anti-thrust side to form the above-mentioned first inclined surface 13c and second inclined surface 13d.

Further, as the diameter D changes, the central axis C of the cylinder bore 13 does not become a straight line, and a step following the second bore wall 13b on the anti-thrust side is added to the central axis C.

Next, the operation of the internal combustion engine equipped with this cylinder block 10 will be described. 3A to 3G are cross-sectional views sequentially showing the operation of the internal combustion engine including the cylinder block 10. In these figures, the reaction force N of the connecting rod 11 and the in-cylinder pressure P are also shown.

As shown in FIG. 3A, the upper end 12a of the piston 12 is initially at the bottom dead center P2, and the compression stroke starts from this state. When the piston 12 rises from this state, as shown in FIG. 3B, the piston 12 is moved toward the second bore wall 13b on the anti-thrust side by the resultant force of the in-cylinder pressure P and the reaction force N, and the thrust The space d between the first bore wall 13a on the side and the upper end 12a of the piston 12 starts to open. Thereby, the sliding friction between the first bore wall 13a and the piston 12 can be reduced, and the fuel consumption of the internal combustion engine can be improved.

When the piston 12 further rises, the distance d becomes maximum as shown in FIG. 3C, and the upper end 12b of the piston 12 starts to move along the first inclined surface 13c. As a result, as shown in FIG. 3(d), the upper end 12a of the piston 12 approaches the first bore wall 13a on the thrust side, and the distance d between the two becomes narrower again.

As described above, in the compression stroke, the piston 12 rises while following the ups and downs of the second bore wall 13b on the anti-thrust side. The resultant force between the in-cylinder pressure P pressing against 13b and the reaction force N is also weak. Therefore, the sliding friction between the piston 12 and the second bore wall 13b in the compression stroke is also weak, and the sliding friction is unlikely to deteriorate fuel efficiency.

Immediately before the combustion stroke, as shown in FIG. 3(e), the distance d between the upper end 12a of the piston 12 and the first bore wall 13a becomes extremely small, and the two are in close proximity to each other.

When the upper end 12a reaches the top dead center P1 in this state, the combustion stroke is performed as shown in FIG. 3(f). In the combustion stroke, the piston 12 is pressed against the thrust-side first bore wall 13a by the resultant force of the reaction force N and the in-cylinder pressure P. At this time, as described above, since the upper end 12a and the first bore wall 13a are close to each other in advance, it is possible to reduce the relative speed between the upper end 12a and the first bore wall 13a when the upper end 12a collides with the first bore wall 13a. It is possible to reduce the tapping sound that occurs between.

Then, as shown in FIG. 3G, the piston 12 descends while slidingly contacting the first bore wall 13a on the thrust side, and the expansion stroke is performed.

At this time, in this embodiment, since the first bore wall 13a on the thrust side is straight along the reciprocating direction of the piston 12 as described above, the descending piston 12 is struck against the first bore wall 13a. There is no. Therefore, the tapping sound generated between the first bore wall 13a and the piston 12 can be reduced, and the energy released as the tapping sound can be used for the movement of the piston 12 to improve the fuel consumption. ..

Moreover, since the sliding resistance between the first bore wall 13a and the piston 12 is reduced, the fuel consumption of the internal combustion engine is further improved.
Next, an example of the dimensions of the cylinder bore 13 will be described.

FIG. 4 is a schematic perspective view for explaining an example of dimensions of the cylinder bore 13.

In this example, the diameters D1 and D3 of the lower portion 13e and the upper portion 13f of the cylinder bore 13 are set to be approximately the same. Further, the height H1 of the lower portion 13e and the height difference Z1 between the lower end and the upper end of the second inclined surface 13d are set to the same value. Similarly, the height H2 of the upper portion 13f and the height difference Z2 between the lower end and the upper end of the first inclined surface 13c are set to the same value.

The numerical value of each dimension is not particularly limited. As a result of examination by the inventor of the present application, it has been found that the difference between the diameter D2 and the diameter D3 (D2-D3) of about 30 μm to 50 μm has an effect of reducing the hitting sound. This corresponds to making the diameter D3 larger by about 0.05% to 0.07% than the diameter D2.

Further, the inclination of the first inclined surface 13c is not particularly limited.
FIG. 5 is an enlarged cross-sectional view showing a suitable inclination of the first inclined surface 13c.

As a result of a study by the inventor of the present application, the striking sound is reduced by setting the angle θ formed by the second bore wall 13b and the first inclined surface 13c in the upper portion 13f to about 0.01° to 0.14°. There was found.
Next, each comparative example of the first embodiment will be described.

(First Comparative Example)
FIG. 6 is a schematic cross-sectional view of a cylinder block according to the first comparative example.

The first comparative example is an example in which a third inclined surface 13x and a fourth inclined surface 13y are formed on the first bore wall 13a. The third inclined surface 13x is located at the same height as the first inclined surface 13c, and the fourth inclined surface 13y is located at the same height as the second inclined surface 13d.

As a result, the diameter of the cylinder bore 13 is increased between the inclined surfaces 13x and 13y, and it is considered that the friction between the piston 12 and the cylinder bore 13 can be prevented from becoming excessive. However, when the expansion stroke is performed in the first comparative example, when the piston 12 descends and comes into contact with the fourth inclined surface 13y, the sliding resistance between the two increases.
On the other hand, in this embodiment, since the first bore wall 13a on the thrust side is straight as described above, it is possible to reduce the sliding resistance between the first bore wall 13a and the piston 12.

(Second Comparative Example)
FIG. 7 is a schematic cross-sectional view of a cylinder block according to the second comparative example.

The second comparative example is an example in which both the first bore wall 13a and the second bore wall 13b are straight in cross section.

FIGS. 8A to 8G are cross-sectional views sequentially showing the operation of the internal combustion engine including the cylinder block according to the second comparative example.

First, as shown in FIGS. 8A to 8E, the piston 12 moves upward to start the compression stroke. In the compression stroke, the piston 12 rises while being pressed against the second bore wall 13b by the resultant force of the reaction force N of the connecting rod 11 and the in-cylinder pressure P. Therefore, at the end of the compression stroke (FIG. 8(e)), the upper end 12a of the piston 12 and the first bore wall 13a are greatly separated from each other, and the distance d between them is larger than that in the present embodiment (FIG. 3(e)). Also grows.

Then, as shown in FIG. 8F, when the in-cylinder pressure P rapidly rises in the combustion stroke, the upper end 12a of the piston 12 collides with the first bore wall 13a in response to the in-cylinder pressure P. In particular, when the distance d is thus wide, the speed at which the piston 12 acquires before the collision increases and the tapping sound at the time of the collision increases.

On the other hand, in the present embodiment, as shown in FIG. 3E, the upper end 12a comes close to the first bore wall 13a due to the copying operation of the piston 12 and the first inclined surface 13c at the end of the compression stroke. As a result, the speed at which the piston 12 obtains before the collision with the first bore wall 13a in the combustion stroke becomes small, and the tapping sound at the time of collision can be reduced.

(Second embodiment)
FIG. 9 is a schematic perspective view of the cylinder bore 13 according to the second embodiment.

Note that, in FIG. 9, the same elements as those described in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and description thereof will be omitted below.

As shown in FIG. 9, in the present embodiment, the diameter D2 of the cylinder bore 13 is not changed in the portion below the first inclined surface 13c, and the second bore wall 13b on the anti-thrust side of the portion is formed in a straight shape. To As a result, the sliding resistance between the second bore wall 13b and the piston 12 in the straight portion can be reduced, and the fuel consumption can be improved.

(Third Embodiment)
FIG. 10 is a schematic perspective view of the cylinder bore 13 according to the third embodiment.

In FIG. 10, the same elements as those described in the first and second embodiments are designated by the same reference numerals as those in these embodiments, and the description thereof will be omitted below.

As shown in FIG. 10, in the present embodiment, the diameter of the upper portion 13f of the cylinder bore 13 is increased upward. As a result, the diameter D4 at the upper end of the upper portion 13f becomes larger than the diameter D3 at the lower end of the upper portion 13f.

Regarding the cylinder bore 13 in the portion below the first inclined surface 13c, the diameter D2 is not changed as in the second embodiment, and the second bore wall 13b on the anti-thrust side in that portion is viewed in cross section. Make straight. As a result, similar to the second embodiment, it is possible to reduce the sliding resistance between the straight bore portion of the second bore wall 13b and the piston 12.

(Fourth Embodiment)
FIG. 11 is a schematic perspective view of the cylinder bore 13 according to the fourth embodiment.

In FIG. 11, the same elements as those described in the first to third embodiments are designated by the same reference numerals as those in these embodiments, and the description thereof will be omitted below.

As shown in FIG. 11, in the present embodiment, the diameter of the cylinder bore 13 is continuously reduced from the bottom to the top, and the diameter D6 at the upper end of the cylinder bore 13 is made smaller than the diameter D5 at the lower end. As a result, the space between the piston 12 and the cylinder bore 13 is opened near the lower end of the cylinder bore 13, so that the sliding resistance between them can be reduced.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. It can be changed.

10 cylinder block 11 connecting rod 12 piston 13 cylinder bore 13a first bore wall 13b second bore wall 13c first inclined surface 13d second inclined surface 13e lower portion 13f upper portion
P1 top dead center
P2 bottom dead center

Claims (1)

A cylinder block having a cylinder bore in which a piston reciprocates,
A bore wall of the cylinder bore on the thrust side extends straight in a cross-sectional view along the reciprocating direction of the piston, and between the bottom dead center and the top dead center of the upper end of the piston, the diameter of the cylinder bore is A cylinder block characterized by becoming smaller as it goes upward.

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