JP2002115570A - Internal combustion engine with variable compression ratio mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively improve the durability and the lubricity in a sliding part between a cylinder 12 and the outer circumference of a piston 14. SOLUTION: This variable compression ratio mechanism changes the attitudes of a lower ling 21 and an upper ling 22 by turning a control shaft 23 via an eccentric cam 24 and a control link 25 so as to variably control the compression ratio. The bottom end of the upper link offsets from the upper end in a thrust direction(first direction) in the cylinder orthogonal direction in a view in the crankshaft direction in the piston lowest descent state, and the bottom end position Lb-at of the cylinder 12at toward the counter-thrust direction is disposed in a position lower than the bottom end position Lp-at of the piston outer circumference 14at opposed thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine having a variable compression ratio mechanism of a multi-link type, and more particularly to improvement of durability, lubricity and reduction of friction in a sliding contact portion between a cylinder and a piston outer peripheral portion. About

[0002] In this specification, the upward direction of the piston along the cylinder axis direction is defined as "up", and the downward direction of the piston along the cylinder axis direction is defined as "down". Also,
In the cylinder orthogonal direction as viewed in the cylinder axis direction, the upstream side in the rotation direction of the crankshaft with respect to the cylinder center line is defined as the thrust direction, and the downstream side in the crank rotation direction is defined as the anti-thrust direction.

[0003]

2. Description of the Related Art Conventionally, various internal combustion engines having a variable compression ratio mechanism have been proposed (for example, an article published in 1997: MTZ Motortechnische Zei).
tschrift 58, no. Eleventh 706-71
See page 1.)

[0004]

In addition, the present applicant has filed a Japanese Patent Application No. 2000-230232 (hereinafter, referred to as "Japanese Patent Application No. 2000-230232").
(Referred to as a prior application)) proposes a variable compression ratio mechanism that is compact and has excellent engine mountability. The variable compression ratio mechanism according to the prior application includes an upper link 2 having an upper end connected to a piston pin 1a of a piston 1, as shown in FIG.
One end of the lower link 4 connected to the lower end of the upper link 2 and the crankpin 3a of the crankshaft 3, the control shaft 5 extending substantially parallel to the crankshaft 3, and the eccentric cam 5a of the control shaft 5 swings. And a control link 6 that is movably connected and has the other end connected to the lower link 4. By changing the rotation position of the control shaft 5 according to the engine operation state, the eccentric cam 5
The swing fulcrum of the control link 6 changes via a, and the attitude of the upper link 2 and the lower link 4 changes accordingly, whereby the engine compression ratio is variably controlled.

In such a variable compression ratio mechanism, the bottom dead center is caused by the fact that the axis 3c of the crankshaft 3 is disposed on the axis (center line) 7c of the cylinder 7 in order to achieve compactness. In the lowermost state of the piston (the state shown in FIG. 7), the center line 2a connecting the upper end and the lower end of the upper link 2 is generally located at the cylinder center line 7c.
It is greatly inclined with respect to. That is, the lower end of the upper link 2 is offset from the upper end in one direction (the thrust direction in the example of FIG. 7) along the direction perpendicular to the cylinder.

Here, in such a state where the piston is at its lowest position, a large downward inertial force Fi acts on the piston 1, and in order to obtain a load Fb that pushes the piston 1 upward against the inertial force Fi, an upper link is formed. 2 to piston 1
A load Fa along the link center line 2a acts. Therefore, the thrust load Ft is applied to the piston 1 in the anti-thrust direction.
Acts, and a peculiar phenomenon occurs in which the outer peripheral portion of the piston 1 closest to the thrust direction is strongly pressed against the wall surface (cylinder liner) of the cylinder 7 opposed thereto. As a result, the outer peripheral portion of the piston 1 and the cylinder 7 come into strongest sliding contact with each other in the portion closest to the thrust direction, and durability and lubricity of this portion are particularly required.

More specifically, if the lower end portion 1b of the piston 1 closest to the thrust direction protrudes downward from the lower end of the cylinder 7 as shown in FIG. The sliding area between the piston 1 and the cylinder 7 becomes narrower in a portion closer to the anti-thrust direction, which is disadvantageous in terms of durability and lubricity. In addition, a galling phenomenon between the outer peripheral portion of the piston 1 and the lower end of the cylinder 7 is caused. This may lead to scuffing or the like, which is very undesirable.

The present invention has been made in view of such a problem, and in an internal combustion engine having a variable compression ratio mechanism, the durability and lubricity of a sliding contact portion between a piston outer peripheral portion and a cylinder are effectively improved. One purpose is to improve.

Another object of the present invention is to effectively reduce the friction of the outer peripheral portion of the piston and the cylinder in sliding contact with the cylinder without impairing durability and lubrication performance.

[0010]

According to the present invention, there is provided an internal combustion engine comprising: an upper link having an upper end connected to a piston which can be moved up and down in a cylinder; a lower end of the upper link and a crankshaft crank. A lower link connected to the pin, a control shaft extending substantially parallel to the crankshaft, an eccentric cam provided eccentrically to the control shaft, one end of which is swingably connected to the eccentric cam; And a control link connected to the lower link.

With such a configuration, by rotating the control shaft around the axis, the position of the swing fulcrum of the control link changes via the eccentric cam, and the postures of the lower link and the upper link change. Variably controls the engine compression ratio.

In the internal combustion engine provided with such a variable compression ratio mechanism, the lower end of the upper link is often in the first direction in the direction perpendicular to the cylinder as compared to the upper end when viewed from the crankshaft in the lowest state of the piston. Will be offset. In other words, it is very difficult to configure the line connecting the lower end and the upper end of the upper link to be parallel to the cylinder center line in the state where the piston is at the lowest position.
Even if possible, the size of the mechanism is inevitable.

As described above, a large thrust load acts on the piston in the second direction opposite to the first direction due to the inclination of the upper link.
Therefore, since the outer peripheral portion of the piston closest to the second direction is locally strongly pressed against the wall surface of the cylinder opposed thereto, sufficient durability and lubricity are required for this portion.

Therefore, according to the first aspect of the present invention, the lower end position of the cylinder closest to the second direction most opposite to the first direction is opposed to the first direction when viewed in the crankshaft direction when the piston is at the lowest position. It is arranged below the lower end position of the outer periphery of the piston.

Therefore, the outer peripheral portion of the piston in the second direction, where a large thrust load is applied in the state of the lowermost position of the piston, does not protrude below the lower end position of the cylinder. Since it is in the form of sliding contact with the cylinder wall surface over the entire length, it is advantageous in terms of durability and lubricity, and there is no possibility of galling between the outer peripheral portion of the piston and the lower end of the cylinder as described above. The occurrence of scuffing or the like due to this is suppressed, and sufficient durability and lubricity can be ensured.

More preferably, in the piston lowermost state, the lowermost position of the outer peripheral portion of the piston closest to the first direction is lower than the lowermost position of the cylinder opposed thereto. Are located in

Thus, the sliding area between the outer peripheral portion of the piston and the cylinder near the first direction where the thrust load hardly acts when the piston is at the lowest position is reduced, that is, unnecessary sliding area is effectively suppressed. Therefore, the friction of the sliding portion can be effectively reduced without impairing durability and lubricity.

By the way, the direction in which lubricating oil leaking from around the crankshaft (excess oil from bearings) or lubricating oil scraped up by the counterweight of the crankshaft or the like is scattered along the turning direction of the crankshaft. Therefore, the lubricating oil is easily supplied to the cylinder wall near the anti-thrust direction in the cylinder.

Therefore, by setting the first direction to the thrust direction and setting the second direction to the anti-thrust direction as in the invention according to claim 3, the second direction in which lubricity is required, that is, the anti-thrust direction is set. Sufficient lubricating oil can be efficiently supplied to the cylinder wall near the thrust direction, and the lubricating performance is further improved.

Further, as in the second aspect of the present invention,
If the lower end position of the cylinder in the lowermost position of the piston is located below the lower end position of the piston on the anti-thrust side, and is located above the lower end position of the piston on the thrust side, in most cases the most anti-thrust direction The lower end position of the closer cylinder is arranged below the lower end position of the cylinder closest to the thrust direction. In this case, the scattered lubricating oil is more easily supplied to the cylinder wall closer to the anti-thrust direction.

The invention according to claim 4 is characterized in that, in the outer peripheral portion of the piston, the portion closest to the second direction has a longer dimension in the cylinder axial direction than the portion closest to the first direction. I have.

In this case, as described above, the sliding contact area between the outer peripheral portion of the piston and the cylinder closer to the second direction, which comes into strong sliding contact with the piston at the lowest position, is increased, and the durability and lubricity are further improved. On the other hand, in the portion near the first direction, an unnecessary sliding area between the outer peripheral portion of the piston and the cylinder can be reduced,
The friction can be further reduced, and the weight of the piston can be reduced. That is, the outer peripheral portion of the piston has an optimal shape according to the request.

The invention according to claim 5 is characterized in that, in the outer peripheral portion of the piston, a portion closer to the second direction has higher rigidity than a portion closer to the first direction.

In this case, as described above, the rigidity of the outer peripheral portion of the piston in the second direction, which comes into strong sliding contact with the piston at the lowest position, is increased, and the durability of this portion is further improved.

According to a sixth aspect of the present invention, a water jacket is provided around the cylinder, and a lower end position of the water jacket closest to the second direction is higher than an upper end position of the piston when the piston is at the lowest position. Are also arranged above.

In this case, when the piston is at the lowest position, the wall temperature of the cylinder closest to the second direction where a large thrust load acts tends to increase, and the lubricating oil adhering to the cylinder wall surface increases with this wall temperature increase. Since the temperature also increases, and as a result, the viscosity of the lubricating oil decreases, friction at this portion can be effectively reduced.

According to a seventh aspect of the present invention, a water jacket is provided around the cylinder, and a lower end position of the water jacket closest to the first direction is higher than an upper end position of the piston when the piston is at the lowest position. Are also arranged above.

In this case, the wall temperature of the cylinder closest to the first direction where the thrust load hardly acts in the state where the piston is at the lowest position is apt to rise, and as the wall temperature rises, it adheres to the cylinder wall in this portion. The lubricating oil temperature also rises,
As a result, the viscosity of the lubricating oil is reduced, so that drag friction at a portion where this thrust load hardly occurs can be reduced.

[0029]

As described above, according to the present invention, the durability at the sliding contact portion between the outermost portion of the piston and the cylinder closest to the second direction where a strong thrust load is applied in the lowest state of the piston, Lubricity can be effectively improved.

In particular, according to the second aspect of the present invention, friction in the sliding contact portion between the outermost portion of the piston and the cylinder closest to the first direction where the thrust load hardly acts when the piston is at the lowest position is effectively reduced. can do.

That is, the improvement of durability and lubricity at the sliding contact portion between the outer peripheral portion of the piston and the cylinder and the reduction of friction can be achieved at a high level.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 to 3 show a first embodiment of an internal combustion engine provided with a variable compression ratio mechanism according to the present invention. In the cylinder block 11, a cylindrical cylinder 12 is formed for each cylinder, and a water jacket 13 is formed around each cylinder 12. A piston 14 is provided in each cylinder 12 so as to be able to move up and down. A piston pin 15 of each piston 14 and a crankshaft 16
Is mechanically linked to the crank pin 17 via a multiple link variable compression ratio mechanism. In addition, 18 is a counterweight.

The above variable compression ratio mechanism comprises a crank pin 1
7, a lower link 21 rotatably fitted on the outer link 7, an upper link 22 cooperating with the lower link 21 and the piston pin 15, a control shaft 23 extending in the cylinder row direction in parallel with the crankshaft 16, and a control shaft An eccentric cam 24 provided eccentrically to 23 and a control link 25 for linking the eccentric cam 24 and the lower link 21 are roughly constituted.

The lower link 21 has a half structure that can be assembled to the crank pin 17 later. The upper end of the rod-shaped upper link 22 is connected to the piston pin 15 so as to be relatively rotatable, and the lower end is connected to the lower link 21 via the connecting pin 26 so as to be relatively rotatable.

The control link 25 has a half structure that can be assembled to the eccentric cam 24 later. One end of the control link 25 is rotatably connected to the eccentric cam 24, and the other end is connected to the lower link 21. It is connected via a pin 27 so as to be relatively rotatable.

The control shaft 23 has a main bearing cap 28 for rotatably supporting the crankshaft 16.
And the sub bearing cap 29 so as to be rotatable. An actuator (not shown) is provided at one end of the control shaft 23, and the actuator rotates the control shaft 23 within a predetermined control range in accordance with an engine operating state and holds the control shaft 23 at a predetermined rotation position. .

With such a configuration, when the control shaft 23 is rotated in accordance with the operating state of the engine, the swing fulcrum of the control link 25 fitted on the eccentric cam 24 changes. As a result, the postures of the lower link 21 and the upper link 22 change, the stroke of the piston 14 changes, and the compression ratio of the combustion chamber defined above the piston 14 is variably controlled.

Next, a description will be given of the characteristic configuration, operation and effect of this embodiment. In this variable compression ratio mechanism, the cylinder axis (center line)
The shaft center 16c of the crankshaft 16 is arranged on 12c, and the control shaft 23 is arranged obliquely below the crankshaft 16 on the anti-thrust side (the right side in FIGS. 1 to 3). Due to these factors, the lower end of the upper link 22 is more offset than the upper end in the thrust direction (first direction) in the direction perpendicular to the cylinder (the left-right direction in FIG. 1) during most of the piston up-and-down stroke. .

In particular, when the piston 14 is at the lowest position where the piston 14 is located at the bottom dead center, the center line 22a connecting the upper end and the lower end of the upper link 22 is greatly inclined with respect to the cylinder axis 12c, as shown in FIG. The lower end of the upper link 22 is more greatly offset in the thrust direction than the upper end when viewed in the cylinder axis direction when the piston is at the lowest position.
Therefore, the outer peripheral portion 1 of the piston closest to the anti-thrust direction
A large thrust load acts on the cylinder 12at which is opposed to and slidably contacts the 4at, and the sliding contact portion is particularly required to have durability and lubricity.

Therefore, in the present embodiment, in such a state that the piston is in the lowest position, the cylinder 12 closest to the anti-thrust direction is moved.
The lower end position Lb-at of at is disposed slightly lower than the lower end position Lp-at of the piston outer peripheral portion 14at opposed thereto. In the lowermost state of the piston, the lower end position Lpt of the piston outer peripheral portion 14t closest to the thrust direction is disposed below the lower end position Lb-t of the cylinder 12t opposed thereto.

In other words, the piston 14 has a thrust
The cylinder 12 is formed in a liner shape that is asymmetric in the thrust-anti-thrust direction while being formed in a substantially symmetric shape in the anti-thrust direction. More specifically, as shown in FIG.
In the portion 31 on the thrust side than c, a substantially uniform height Lb-t
On the other hand, the portion 32 on the anti-thrust side of the cylinder axis 12c is inclined downward in the anti-thrust direction so as to have a predetermined height Lb-at at a portion closest to the thrust. .

As described above, in this embodiment, when the piston is at the lowest position, the lower end position Lb-at of the cylinder 12at, which is closest to the thrust direction where a large thrust load acts, is:
The lower end position Lp of the piston outer peripheral portion 14at opposed thereto.
−at, the outer peripheral portion 14at of the piston extends over the entire length of the cylinder 12 in the vertical direction.
At and sliding contact with at, the sliding contact area of this portion is sufficiently ensured, which is advantageous in terms of durability and lubricity, and may cause a galling phenomenon between the piston outer peripheral portion 14at and the lower end of the cylinder 12at. In addition, scuffing caused by such galling can be suppressed, and sufficient durability and lubricity can be obtained.

On the other hand, the piston outer peripheral portion 14t closest to the thrust direction where no thrust load is applied and the cylinder 12t
At the lower end position L of the outer peripheral portion 14t of the piston.
Since pt protrudes below the lower end position Lb-t of the cylinder 12t, an unnecessary sliding contact area is reduced.
That is, friction can be effectively reduced without impairing durability and lubricity.

Further, as shown in FIG. 3, lubricating oil leaking from around the crankshaft 16 (excess oil from bearings, etc.)
Also, the direction in which the lubricating oil scraped up by the counterweight 18 scatters is along the turning direction ω of the crankshaft, as shown by the arrow 33. Lubricating oil is easily supplied to the cylinder wall surface 12at near the thrust direction.

In this embodiment, since the lower end of the upper link 22 is set to be offset more in the thrust direction than the upper end at least in the state of the lowermost end of the piston, a large thrust load is applied to a portion closer to the anti-thrust direction. It is a form that acts on In addition, the cylinder lower end position Lb-at, which is closest to the thrust direction, protrudes sufficiently (ΔLb) below the thrust side cylinder lower end position Lpt. Therefore, the scattered lubricating oil is efficiently supplied to the cylinder 12at on the opposite thrust side. For this reason, the lubrication performance between the piston outer peripheral portion 14at and the cylinder 12at near the anti-thrust direction where a large thrust load acts is further improved.

FIG. 4, FIG. 5 and FIG.
And a fourth embodiment. Note that the same components are denoted by the same reference numerals, and redundant description will be omitted as appropriate.

In the second embodiment shown in FIG. 4, the shape of the piston 34 is changed from that of the first embodiment. That is,
The vertical dimension (skirt length) of the piston outer peripheral portion 34at closest to the thrust direction is set longer than the vertical dimension of the piston outer peripheral portion 34t closest to the thrust direction. More specifically, the piston 3 on the opposite thrust side
Only the lower end of 4 is partially projected downward.

The other structure is substantially the same as that of the first embodiment. That is, in the lowermost state of the piston, the lower end position of the cylinder 12at closest to the thrust direction is disposed below the lower end position of the piston outer peripheral portion 34at opposed thereto, while the piston outer peripheral portion closest to the thrust direction is located. The lower end position of 34t is disposed lower than the lower end position of cylinder 12t opposed thereto.

In such a second embodiment, the first embodiment
In addition to obtaining the same effects as the embodiment, the sliding area required for forming the lubricating oil film is further secured because the vertical dimension of the piston outer peripheral portion 34at on the anti-thrust side is relatively long. And the durability on the anti-thrust side,
Lubricity is further improved. Further, since the skirt length of the outer peripheral portion 34t on the thrust side is relatively short, unnecessary sliding area is suppressed, friction is further reduced, and the weight of the piston can be reduced.

In order to obtain substantially the same effect as in the second embodiment, the rigidity of the outer peripheral portion of the piston closest to the thrust direction may be higher than the rigidity of the outer peripheral portion of the piston closest to the thrust direction. In this case, in particular, in the outer peripheral portion of the piston on the side opposite to the thrust, it becomes easier to secure the strength durability corresponding to the maximum thrust load.

In the third embodiment shown in FIG. 5, the shape of the water jacket 35 is changed from that of the second embodiment. That is, in the water jacket 35 provided around the cylinder 12, the lower end position Hw-at of the portion closest to the thrust direction in the lowermost state of the piston is located above the upper end position Hp of the piston 34. . The lower end position Hw-t of the water jacket 35 closest to the thrust direction is disposed below the upper end position Hp of the piston 34.

With such a structure, in the state where the maximum thrust load is applied, the water jacket 35 does not exist at a position opposed to the outer peripheral portion 34at of the piston which is closest to the thrust direction where the maximum thrust load is applied. Since the wall temperature easily rises, this cylinder 12a
Since the temperature of the lubricating oil attached to t also increases, and as a result, the viscosity of the lubricating oil decreases, it is possible to effectively reduce the friction at the position where the maximum thrust load occurs.

In the fourth embodiment shown in FIG. 6, the shape of the water jacket 36 is changed from that of the second embodiment. That is, in the water jacket 36 provided around the cylinder 12, the lower end position Hw-t ′ of the portion closest to the thrust direction in the lowermost state of the piston is located higher than the upper end position Hp of the piston 34. .
The lower end position Hw-at ′ of the water jacket 36 closest to the anti-thrust direction is located below the upper end position Hp of the piston 34 in this embodiment,
Like the third embodiment, it may be arranged above.

With such a configuration, in the lowest state of the piston, the water jacket 36 does not exist at a position opposed to the piston outer peripheral portion 34t closest to the thrust direction where the thrust load hardly acts, and the wall of the cylinder 12t in this portion is not provided. Since the temperature easily rises, this cylinder 12t
The temperature of the lubricating oil adhering to the oil also increases, and the viscosity of the lubricating oil decreases. As a result, drag friction at a portion where the thrust load hardly acts can be reduced more reliably.

As described above, the present invention has been described with reference to the specific embodiments. However, the present invention is not limited to the above embodiments. For example, the present invention can be applied to an internal combustion engine in which the lower end of the upper link is offset from the upper end on the side opposite to the thrust in the lowermost state of the piston. In this case, however, a large thrust load acts in the thrust direction in the lowest state of the piston in the thrust direction contrary to the first embodiment, so that the effect of improving the lubrication performance as described with reference to FIG. 3 is obtained. I can't.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an internal combustion engine provided with a variable compression ratio mechanism according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the cylinder block of the first embodiment alone;

FIG. 3 is an operation explanatory view of the first embodiment.

FIG. 4 is a sectional view showing an internal combustion engine provided with a variable compression ratio mechanism according to a second embodiment of the present invention.

FIG. 5 is a sectional view showing an internal combustion engine provided with a variable compression ratio mechanism according to a third embodiment of the present invention.

FIG. 6 is a sectional view showing an internal combustion engine equipped with a variable compression ratio mechanism according to a fourth embodiment of the present invention.

FIG. 7 is a sectional view showing an internal combustion engine provided with a variable compression ratio mechanism according to the prior art.

[Explanation of symbols]

 12 ... Cylinder 14,34 ... Piston 13,35,36 ... Water jacket 16 ... Crankshaft 17 ... Crank pin 21 ... Lower link 22 ... Upper link 23 ... Control shaft 24 ... Eccentric cam 25 ... Control link

Claims (7)

[Claims] 1. An upper link having an upper end connected to a piston arranged to be able to move up and down in a cylinder, a lower link connected to a lower end of the upper link and a crankpin of a crankshaft, and the crankshaft. A control shaft extending substantially in parallel with the control shaft, an eccentric cam provided eccentrically to the control shaft, a control link having one end swingably connected to the eccentric cam and the other end connected to the lower link, In the internal combustion engine provided with the variable compression ratio mechanism having the above, the lower end of the upper link is offset from the upper end in the first direction in the direction perpendicular to the cylinder, as viewed in the crankshaft direction when the piston is at the lowest position. The lower end position of the cylinder closest to the second direction opposite to the first direction is closer to the lower end position of the outer peripheral portion of the piston than the first direction. Internal combustion engine having a variable compression ratio mechanism, characterized in that arranged underneath. 2. In the lowermost state of the piston, a lower end position of the outer peripheral portion of the piston closest to the first direction is disposed lower than a lower end position of a cylinder opposed thereto. Item 6. An internal combustion engine comprising the variable compression ratio mechanism according to item 1. 3. The first direction is set in the thrust direction, and the second direction is set in the anti-thrust direction. The lower end position of the cylinder closest to the thrust direction is smaller than the lower end position of the cylinder closest to the thrust direction. The internal combustion engine provided with the variable compression ratio mechanism according to claim 1 or 2, wherein the internal combustion engine is disposed below. 4. A part of the outer peripheral portion of the piston that is closest to the second direction has a dimension in the cylinder axial direction longer than a portion that is closest to the first direction. An internal combustion engine comprising the variable compression ratio mechanism according to any one of the above. 5. The piston according to claim 1, wherein a portion closer to the second direction in the outer peripheral portion of the piston has higher rigidity than a portion closer to the first direction. An internal combustion engine comprising the variable compression ratio mechanism according to any one of claims 1 to 3. 6. A water jacket is provided around the cylinder, and a lower end position of the water jacket closest to the second direction is located higher than an upper end position of the piston in the lowermost state of the piston. An internal combustion engine provided with the variable compression ratio mechanism according to any one of claims 1 to 5. 7. A water jacket is provided around the cylinder, and a lower end position of the water jacket closest to the first direction is disposed higher than an upper end position of the piston in the lowermost state of the piston. An internal combustion engine provided with the variable compression ratio mechanism according to any one of claims 1 to 6.