JP2590145B2 - Piston for internal combustion engine - Google Patents

Description

The present invention relates to a piston for an internal combustion engine, and more particularly to a piston for an internal combustion engine.
The present invention relates to a piston for an internal combustion engine for mounting a total of two rings, one pressure ring and one oil ring.

[Conventional technology]

A piston used for an internal combustion engine such as a gasoline engine or a diesel engine usually has a total of three rings, two pressure rings located on the combustion chamber side and one oil ring located on the crankcase side. I have. As is well known, the piston ring maintains the airtightness between the piston and the cylinder wall and minimizes the leakage (blow-by) of the combustion gas in the combustion chamber (mainly by the pressure ring) and the function of the cylinder wall. It must have a function (mainly by an oil ring) that scrapes off the lubricating oil from the crankcase appropriately and keeps the lubricating oil consumption properly.

Here, the ring is formed with an abutment for attachment to the piston ring groove.
Combustion gases and lubricating oil inevitably leak. In order to suppress this phenomenon as much as possible, at least three rings were required.

In recent years, with the demand for high-power and high-speed engines, there has been a demand for lighter and smaller pistons. Therefore, it is necessary to shorten the axial length of the piston itself. Here, a plurality of annular ring grooves are formed on the piston to mount a ring, and a portion (land portion) between the ring grooves also has a predetermined axial length in consideration of mechanical strength around the ring grooves. Must. Therefore, the number of lands having a predetermined length also increases, and the overall length of the piston inevitably increases. Therefore, in order to reduce the size and weight of the piston itself, it is essential to reduce the number of rings.

[Problems to be solved by the invention]

However, reducing the number of rings lowers various functions such as prevention of leakage of the combustion gas, which should be originally performed by the rings, toward the crankcase and prevention of oil consumption due to lubricating oil rising toward the combustion chamber.

In particular, at the time of high vacuum boost with the throttle closed, that is, when the engine brake is applied,
Since the intake manifold and the inside of the cylinder have a high negative pressure, lubricating oil tends to be sucked out toward the combustion chamber. The negative pressure in the cylinder causes the lubricating oil on the crankcase side to be sucked upward (toward the combustion chamber) through the gap between the piston ring groove and the ring side surface.

Therefore, if the number of rings is reduced, it becomes difficult to prevent the lubricating oil suction phenomenon during the high vacuum boost.

Japanese Patent Publication No. Sho 62-36147 discloses a piston equipped with only two rings which shortens the overall length of the piston and suppresses consumption of lubricating oil. The configuration is shown in FIG. In FIG. 4, the piston 101 has a piston ring groove 10.
2, 103 are formed, a top land 104 is formed above the piston ring groove 102 (toward the combustion chamber), and a second land portion 105 is formed between the piston ring grooves 102 and 103. A pressure ring 106 is mounted on the upper ring groove 102, and an oil ring 110 constituted by a pair of side rails 107 and 108 and a spacer 109 is mounted on the lower (groove) ring groove 103. The lower part of the piston ring groove 103 constitutes a piston skirt portion 111.

In the second land portion 105, a concave portion 112 depressed inward in the piston radial direction is formed adjacent to the piston groove 103. By forming the concave portion 112, the capacity of the annular gap defined by the outer peripheral surface of the second land 105 and the inner peripheral surface of the cylinder opposed thereto is increased. Therefore, when the lubricating oil that has passed through the gap between the oil ring 110 and the piston groove 103 from the crankcase side at the time of high boost reaches this gap, the oil is allowed, and it is possible to reduce the hydraulic pressure. This will reduce the inflow of lubricating oil into the combustion chamber.

However, by forming the concave portion, the passage formed by the oil ring upper rail and the piston becomes large, and at the time of high boost, the lubricating oil is lost together with the gas from the inside of the crankcase toward the combustion chamber. An object of the present invention is to provide a piston for an internal combustion engine that overcomes the above-mentioned drawbacks of the conventional piston for an internal combustion engine and that can maintain sufficient airtightness and adjust lubricating oil even when only two rings are mounted. Aim.

[Means for solving the problem]

To achieve the above object, the present invention provides a top land on the engine combustion chamber side, a first annular ring groove for mounting a pressure ring adjacent to the top land, and a second annular ring for mounting an oil ring. An internal combustion engine having a ring groove and a second land defined between the first and second annular ring grooves and having one pressure ring and one oil ring mounted thereon and reciprocating in a cylinder; In the piston for
(1) The gap distance between the edge of the second land adjacent to the oil ring and the cylinder inner peripheral surface is equal to or shorter than the gap distance between the other portion of the second land and the cylinder inner peripheral surface. (2) The gap distance between the edge of the top land adjacent to the pressure ring and the inner circumferential surface of the cylinder is shorter than the gap distance between the other portion of the top land and the inner circumferential surface of the cylinder. It is.

[Action]

In the load region operation, the gap distance between the cylinder of the second land portion closest to the oil ring and the cylinder is minimized, so that the gas unavoidably leaking from the pressure ring is formed by the land and the cylinder of the second land. The pressure in the space is increased, the oil ring is lowered, and the lubricating oil that has stayed in the vicinity of the oil ring is blown off to the crankcase side through the gap between the oil ring upper surface and the ring groove. This prevents the lubricating oil from flowing toward the combustion chamber.

In the case of engine braking operation, the gap distance of the second land portion closest to the oil ring to the cylinder is minimized, so that leakage of lubricating oil in the direction of the pressure ring is prevented.

Further, since the gap distance of the top land portion closest to the pressure ring to the cylinder is minimized, it is possible to prevent the oil that has reached the second land from being lifted upward (combustion chamber). In addition, in the mode operation in which the load region operation and the engine brake operation are mixed, in addition to the above-described effects, the pressure of the combustion gas enters the gap and increases, and the lower surface of the pressure ring comes into surface contact with the ring groove without fail. The gas passage due to the gap between the pressure ring and the ring groove can be blocked. In addition, since the lubricating oil can be prevented from flowing into the combustion chamber even at this minimum gap distance, the function of preventing the leakage of the lubricating oil is enhanced in combination with the minimum gap distance of the second land.

〔Example〕

Hereinafter, embodiments of the present invention will be described. In FIG. 1, an annular piston ring first groove 2 and a second groove 3 are formed on the outer periphery of a piston 1 reciprocating in a cylinder 13, and a pressure ring 6 and an oil ring 10 are respectively formed in the grooves 2 and 3. Be attached. A top land 4 facing the combustion chamber is formed above the first ring groove 2, and a second land 5 is formed between the ring grooves 2 and 3. A piston skirt 11 facing the crankcase is formed below the second groove. A passage 14 is formed in the piston 1 to allow the second groove 3 to communicate with the crankcase.

The general structure described above is the same as that of the conventional piston for an internal combustion engine shown in FIG. 4, but in the present invention, the shapes of the top land 4 and the second land 5 are particularly formed as follows. That is, in the present invention, the radial gap distance C between the lower edge portion 4a of the top land and the cylinder inner peripheral surface facing the lower edge portion 4a.
₂ and the diameter D ₀ of the cylinder inner circumference are formed so that C ₂ <0.003D ₀ , and a radial gap between the lower edge portion 5a of the second land 5 and the cylinder inner peripheral surface opposed thereto is formed. the relationship between the distance C ₄ and the cylinder inner peripheral diameter D ₀ is formed so as to C ₄ <0.0045D _0. Gap distance with respect to the cylinder inner peripheral surface of the top land 4, C ₂ portion becomes a minimum value, also the gap distance with respect to the cylinder inner peripheral surface of the second land 5, C ₄ moiety is the minimum value.

Further, in the present invention, the annular gap volume defined by the lower surface of the pressure ring 6, the upper surface of the oil ring 10, the inner peripheral surface of the cylinder 13, and the outer peripheral surface of the second land 5 is set to a predetermined volume. This gap volume is determined not only by the gap distance between the second land and the inner peripheral surface of the cylinder, but also by the cylinder inner diameter and the second land 5.
Although it depends on the length in the axial direction, when a cylinder having an inner diameter of 100 mm or less is targeted, the void volume is set to 300 mm ² or less, preferably 260 mm ² or less. The axial length h of the second land portion is set within the range of h <0.05 D _0.

With respect to radial gap distance C ₁ between the top land on the edge 4b and the cylinder inner peripheral surface is not particularly limited. However, since the top land upper edge 4b faces the heat of the combustion chamber, the thermal expansion is taken into account, and the tapered land 4, the stepped land, and the barrel land that satisfy C ₁ > C ₂ are obtained. It is preferable to use

With respect to radial gap distance C ₃ between the upper edge portion 5b and the cylinder inner peripheral surface of the second lands, and C ₃ ≧ C _4. Further, it is necessary to capacitive suitably selected from C ₄ and h is designed so as not to exceed 300 mm ^2.

The reason for setting the annular void volume to 300 mm ² or less is to set the leak gas pressure in the annular void volume to 1 to ² kg / cm ² . The upper side rail 7 constituting the oil ring 10 has a constant pressure receiving area, and the above-mentioned pressure acts on the pressure receiving surface to effectively bias the oil ring 10 toward the crankcase. As a result, a flow path A of the lubricating oil can be provided between the upper surface of the oil ring and the ring groove 3. The lubricating oil is positively guided by the blow-by gas through the passage A and the passage 14 to the crankcase.

FIG. 2 is a graph showing the relationship between the annular void volume and the lubricating oil consumption. Engine operating conditions include:
A cylinder with an inner diameter of 100 mm or less was used for high-speed, high-load operation. As is clear from the figure, the annular void volume is 300 mm ²
Beyond, the consumption of lubricating oil increased sharply. When the annular void volume was 260 mm ² or less, the consumption decreased.

FIG. 3 is a graph showing the relationship between the radial gap distances C ₂ and C ₄ between the lower edges of the first and second lands and the inner circumference of the cylinder, and the amount of lubricating oil consumed.

The operating condition of the engine was an engine brake operation, and a state in which suction of lubricating oil toward the combustion chamber was promoted.

As is apparent from this figure, the radial gap distance C ₂ top land lower edge portion exceeds 0.003D _0, consumption rapidly lubricant is increased. The radial gap distance C ₄ of the second land under edge, exceeds 0.0045D _0, consumption rapidly lubricant is increased.

In the present invention, the cross-sectional shape of the second land 5 is C ₃ ≧ C ₄
Anything that satisfies is sufficient.

Further, when the capacity of the annular gap is extremely reduced, in other words, when the outer diameter of the second land is set to an extent close to the inner diameter of the cylinder, the outer circumferential surface of the second land 5 and the inner circumferential surface of the cylinder are set. In order to avoid thermal expansion of the land 5 due to direct sliding contact of the second land, a solid lubricant such as a tetrafluoroethylene resin film, a polyimide resin, a polyamide resin, an epoxy resin, a phenol resin, or the like may be applied to the outer periphery of the second land. It is even more desirable to add a lubricant such as molybdenum disulfide or carbon to the resin.

Further, the oil ring 10 mounted on the second ring groove is constituted by a pair of side rails 7, 8 and the spacer 9,
It is particularly effective for the spacer to have a configuration that exhibits a waveform in the radial direction of the ring. The spacer 9 is elastically deformed,
This is because, even when the spacer is mounted in the ring groove 3, since the entire spacer does not undulate in the axial direction, effective oil scraping action and close contact between the ring groove 3 and the side rails 7, 8 can be achieved.

〔The invention's effect〕

As described above, according to the piston for an internal combustion engine of the present invention, the leakage of the lubricating oil in the engine brake region in the direction of the combustion chamber can be effectively prevented by the minimum gap immediately after passing through each ring, and in the load region operation. The pressure of the leaked combustion gas from the combustion chamber is effectively generated in the annular gap, and the leaked lubricating oil can be caused to flow by the blow-by gas in the crankcase direction. In other words, when the same amount of leaked gas as in the past flows into the annular space around the second land, the volume of the annular space of the present invention is extremely small, so that the inflow gas pressure becomes high, It is possible to effectively blow off the leaked lubricating oil toward the crankcase. Therefore, the piston for an internal combustion engine according to the present invention provides a particularly effective leakage prevention function against leakage of lubricating oil in the direction of the pressure ring in all operation states during the mode operation when the load region is in a high vacuum boost.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a piston for an internal combustion engine of the present invention, FIG. 2 is a graph showing a relationship between an annular gap volume around a second land and a lubricating oil consumption, and FIG. FIG. 4 is a graph showing the relationship between the gap distance between the peripheral portion of the cylinder and the inner peripheral surface of the cylinder and the amount of lubricating oil consumed. FIG. 1 ... piston, 2 ... first annular ring groove, 3 ... second
Annular ring groove, 4 top land, 5 second land, 6 pressure ring, 10 oil ring.

Claims (5)

(57) [Claims] 1. A first land for mounting a pressure ring adjacent to the top land on an engine combustion chamber side.
It has an annular ring groove, a second annular ring groove for mounting an oil ring, and a second land defined between the first and second annular ring grooves. One pressure ring and one (1) The gap distance between the edge of the second land adjacent to the oil ring and the inner circumferential surface of the cylinder is determined by the following formula: (2) The gap distance between the edge of the top land adjacent to the pressure ring and the cylinder inner peripheral surface is equal to or shorter than the gap distance between the other portion and the cylinder inner peripheral surface. A piston for an internal combustion engine, which is shorter than a gap distance between a portion and an inner peripheral surface of a cylinder. 2. When the inner diameter of the cylinder is D ₀ , and the distance between the edge of the second land and the cylinder is C ₄ , C ₄ <0.0045.
D ₀ and the axial length h of the second land is h <0.
05D ₀ is satisfied, and the annular gap volume defined by the pressure ring, the oil ring, the cylinder inner peripheral surface, and the second land outer peripheral surface is 300 mm ³ or less when the cylinder inner diameter is 100 mm or less. 2. The piston for an internal combustion engine according to claim 1, wherein: 3. When the gap distance between the edge of the top land and the cylinder is C ₂ , and the cylinder inner diameter is D <sub>0.
2. The</sub> piston for an internal combustion engine according to claim 1, wherein C ₂ <0.003D ₀ . Wherein when the gap distance between the the edge of the pressure ring near the second lands cylinder was C _3, Claims second term, wherein it is a C ₄ ≦ C ₃ Pistons for internal combustion engines. 5. When the gap distance between the combustion chamber side edge of the top land cylinder and C _1, C ₂ <combustion of Claims paragraph 3, wherein it is a C ₁ Engine piston.