JP2001214805A - Piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston capable of suppressing oil consumption and blow-by gas, and reducing coagulation which a pressure ring holds by itself and a sudden rise of blow-by gas amount caused by fluttering under light load high rotation. SOLUTION: A straight abutment is used for a top ring 22, and an annular groove 34 having a wedge cross section which is diametrically increased in the size thereof near the top ring groove and downwardly decreased in a size is formed in a second land 31 under a top land groove. The straight abutment positively releases combustion gas in a high pressure side to a low pressure side, so that oil stored in the second land 31 is descended to return to an oil pan. Consequently, a piston capable of reducing both of oil consumption and blow-by gas can be obtained. Coagulation or a sudden rise of the blow-by gas can be prevented by using the straight abutment for the top ring 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for an internal combustion engine, and more particularly to a piston having an improved land under a top ring groove.

[0002]

2. Description of the Related Art A piston of an internal combustion engine is provided with two pressure rings, a top ring and a second ring, on its outer peripheral surface, and an oil ring is mounted below the pressure ring. It is airtight and prevents oil from leaking into the combustion chamber. 2. Description of the Related Art Recently, pistons having a two-ring configuration including one pressure ring and one oil ring have been increasing in order to reduce the size of an engine or reduce friction loss.

Generally, in a piston having a two-ring configuration, it is difficult to suppress the rise of oil into the combustion chamber (oil consumption) and the blow-by of combustion gas (blow-by gas). Further, in order to further reduce the friction, it is necessary to reduce the tension of each ring, and it becomes more severe to reduce the oil consumption. Even in such a two-ring piston, a piston for a reciprocating internal combustion engine in which the sealing performance of the top ring 1 is improved as shown in FIG. 7 as a piston capable of reducing oil consumption and blow-by gas. Is known (actually fair 1-22
No. 916). This piston for a reciprocating internal combustion engine uses a so-called double wrap abutment structure for the top ring 1. As shown in FIG. 8, the double wrap abutment structure includes an outer peripheral surface 2 at one end of the abutment and a corner near the side facing the combustion chamber side, the side surface 3 and the outer peripheral surface 2 and the abutment corner. It has a concave portion 4 which is open, and has a structure having a convex portion 5 which is accommodated and seated in the concave portion 4 at the other end of the mouth.

As shown in FIG. 7, the combustion gas from the combustion chamber on the high pressure side passes through a gap 7 between the upper wall surface 6a of the ring groove and the upper side surface 1a of the top ring 1, and a space behind the top ring 1. Flows into the gap 8, but the lower surface 1 b of the top ring 1 facing the low pressure side is in close contact with the lower wall surface 9 of the ring groove, and the top ring 1 originally has tension outward. As a result, the combustion gas on the high pressure side is suppressed from flowing into the low pressure side.

A high-top ring piston as shown in FIG. 9 is known as a piston for preventing oil from rising into the combustion chamber (utility model registration No. 257974).
No. 0). This high top ring piston is devised by modifying the shape of the second land 12 of the piston 11, forming a substantially wedge-shaped annular groove having a cross-section that increases in size in the radial direction near the top ring groove 13 and decreases in size as going downward. Has formed. Oil flowing upward along the piston 11 accumulates in the annular groove. That is, the oil goes to the groove bottom along the linear slope 14 of the annular groove,
Therefore, a hand going to the groove bottom wall 15 in the radial direction is blocked, and it is difficult to move upward. On the other hand, when the combustion gas leaking from the top ring 16 blows from above, the second land 1 is caused by the flow of the combustion gas along the linearly inclined wall.
The oil stored in 2 falls down and returns to the oil pan.

[0006]

However, in a conventional piston for a reciprocating internal combustion engine, the top ring 1
Since the double wrap joint is used, the sealing performance can be improved, but the thickness of the pressure ring cannot be reduced due to the problem of the strength of the joint, particularly the convex portion 5, and the top ring 1 itself Can not reduce the weight of
During light-load operation, fluttering occurs on the high-speed rotation side, that is, flapping of the top ring 1 occurs. As a result, there is a problem that blow-by gas increases. In addition, there was a problem that the top ring 1 adhered to the piston due to the weight. Further, there is a problem that forming a joint of a double wrap on the top ring 1 is difficult to process.

Therefore, the present invention can suppress the oil consumption and the blow-by gas, and can also reduce the adhesion of the pressure ring itself and the sudden increase in the blow-by gas amount due to the fluttering at the time of light load and high rotation. It is intended to provide a piston.

[0008]

Hereinafter, the present invention will be described. In order to solve the above-mentioned problems, the present inventors have conducted intensive studies. As a result, conventionally, in order to reduce oil consumption and blow-by gas, a double wrap abutment was used for the top ring to emphasize the sealing performance. However, to reduce oil consumption, the top ring abutment was rather used. It was found that it was better to open the oil tank and actively release the combustion gas from the combustion chamber on the high pressure side to the low pressure side, and return the oil accumulated on the land to the oil pan with the combustion gas. Specifically, the present invention uses a straight abutment for the top ring,
The above-mentioned piston is characterized in that an annular groove having a substantially wedge-shaped cross section is formed in the land under the top land groove, and the dimension is increased in the radial direction near the top ring groove and the size is reduced as going downward. Solved the problem. Here, the straight abutment refers to an abutment where both abutments of the pressure ring are cut in a direction orthogonal to the circumferential direction of the ring,
Both abutment end faces have a planar shape. The land is
In the case of a ring having two parts, a gap (second land) between the piston and the cylinder between the top ring and the oil ring. In the case of a ring having three parts, a piston between the top ring and the second ring, It refers to a gap (second land) sandwiched between the cylinder and / or a gap (third land) sandwiched between the cylinder and the piston between the second ring and the oil ring.

According to the present invention, it is possible to secure a volume for storing oil in the land. Straight joints
As the high-pressure side combustion gas is actively released to the low-pressure side, the oil stored in the land descends downward by the flow of the combustion gas along the straight wedge and along the wedge-shaped inclined wall, and the oil pan Return. In addition, by giving the land a volume, the behavior of the top ring can be improved. As a result, it is possible to obtain a piston that can reduce both oil consumption and blow-by gas. further,
By using a straight abutment for the top ring, the thickness of the top ring can be reduced, and accordingly the weight of the top ring itself can be reduced. A sudden increase in blow-by gas due to fluttering at the time can also be prevented.

According to the present invention, an annular groove is formed in the land below the top ring groove so that the diameter of the piston becomes larger as approaching the oil ring, so that the piston has a stepped shape. The above-mentioned problem has been solved by a piston characterized in that.

In order to reduce oil consumption, it is also an important factor to increase the volume of land that can store oil as much as possible. According to the present invention, an annular groove is formed on the land so that the diameter increases as the piston approaches the oil ring so that the piston has a step-like shape. Therefore, the same shape effect as that of the wedge-shaped annular groove can be obtained, and the wedge can be obtained. The volume for storing oil can be increased more than the annular groove.

Further, the present invention is characterized in that the pressure ring is constituted by only one top ring.

When the present invention is applied to a so-called two-piece ring composed of one pressure ring and one oil ring, three of low friction, reduced oil consumption, and reduced blow-by gas can be made parallel. .

[0014]

FIG. 1 shows a piston 29 according to a first embodiment of the present invention. The piston 29 includes a top ring 22 as one pressure ring located near the top land 21 and one oil ring 23 located below the top ring 22.

FIG. 2 is a perspective view showing a straight joint of the top ring 22. As shown in FIG. As shown in this figure, a part of the top ring 22 is cut to form a straight abutment. The straight abutment refers to a state in which both abutment ends 24 of the top ring 22 are cut in a direction orthogonal to the circumferential direction of the top ring 22. That is, both the abutment end faces 25, 25 have a planar shape without unevenness unlike the double wrap abutment.
In the case of a double wrap apex top ring, it is difficult to manufacture the top ring because irregularities must be formed.
2 can be kept cut, so that its manufacture becomes extremely easy.

FIG. 3 shows that the top ring 22 is
Shows a straight abutment attached to. A slight gap 25 is provided between the two end portions 24, 24 in consideration of the thermal expansion of the top ring 22. As shown in FIGS. 1 and 3, the combustion gas from the combustion chamber on the high pressure side
5 and flows into the low pressure side. Further, the combustion gas flows into the space behind the top ring through the gap 27 between the ring groove upper wall surface 26 and the upper surface of the top ring 22, and the lower surface 22b of the top ring 22 facing the low pressure side. It is brought into close contact with the lower wall surface 28 of the ring groove. Therefore, the combustion gas flows from the space behind the top ring 22 to the top ring 2.
2 is prevented from flowing into the low pressure side through the lower surface 22b.

As shown in FIG. 1, a piston 29 between the top ring 22 and the oil ring 23 and a gap 31 (hereinafter referred to as a second land 31) sandwiched between cylinders 30 have radial dimensions near the top ring groove. An annular groove 34 having a substantially wedge-shaped cross section is formed, the size of which decreases as the size increases and decreases downward. The annular groove 34 has a straight portion 32 that fits on the outer peripheral surface of the piston above the second ring groove. The upper surface of the annular groove 34 is a flat surface inward in the radial direction.

As described above, by forming the wedge-shaped annular groove 34, it is possible to secure a volume for storing the oil in the second land 31. Then, the oil flowing along the piston 29 in the axial direction of the piston 29 goes to the groove bottom along the linear inclination of the annular groove 34, where
The hand reaching the groove bottom wall 33 in the radial direction is obstructed and it is difficult to move upward, and accumulates in the second land 31. Second Land 3
The oil stored in 1 passes through the straight abutment and descends downward due to the flow of combustion gas along the wedge-shaped inclined wall, and returns to the oil pan. In addition, by giving the second land 31 a volume, pressure fluctuation can be reduced and the behavior of the top ring 22 can be improved. As a result, it is possible to obtain the piston 29 that can achieve both reduction in oil consumption and reduction in blow-by gas.
Furthermore, by using a straight abutment for the top ring 22, the thickness of the top ring 22 can be reduced,
Accordingly, the weight of the top ring 22 itself can be reduced, and adhesion between the top ring 22 and the piston 29,
It is also possible to prevent a sudden increase in blow-by gas due to fluttering during light load high rotation.

FIG. 4 shows experimental data comparing the blow-by amount between the piston of the present invention and the conventional piston. The piston has a wedge-shaped annular groove in the second land using a straight abutment on the top ring and a wedge-shaped annular groove in the second land. Three types were prepared: a formed one (wedge shape + double wrap abutment) and a normal one (STD piston + straight abutment) using a straight abutment for the top ring and not forming an annular groove in the second land. Further, each piston performs two types of operations, a light load operation (NLD) and a maximum load (WOT). As shown in this figure, in the case of the wedge shape + double lap abutment, 55
On the high-speed rotation side exceeding 00 rpm, the blow-by gas amount sharply increases. This seems to be due to fluttering of the top ring, that is, flapping of the top ring. On the other hand, in the case of the piston wedge shape + straight joint according to the present invention, the blow-by gas amount can be reduced to a substantially constant value irrespective of the rotation speed, similarly to the case of the STD piston + straight joint.

FIG. 5 shows experimental data comparing oil consumption between the piston of the present invention and the conventional piston. The above-described three types of pistons are used as pistons. As shown in this figure, the light load operation (NL) in which the oil consumption in the case of the STD piston + straight joint is 7,500 revolutions
D) at 74.8 g / h, 7500 rpm full load (F
ULL) is 42.5 g / h, and the wedge shape + double wrap abutment is 14.5 g with 7500 rpm NLD
/ H, FULL of 7,500 revolutions is 7.7 g / h, whereas the wedge shape + double wrap abutment is 750
9.8 g / h with 0 rotation NLD, 7500 rotation FUL
L is 13.3 g / h. For oil consumption,
The wedge shape + straight joint and the wedge shape + double wrap joint have good and bad, but the combination of wedge shape + straight joint is the best as a whole.

FIG. 6 shows a piston 41 according to a second embodiment of the present invention. This piston 41 is the second land 4
The second embodiment differs from the piston 29 of the first embodiment in that an annular groove 43 is formed so that 2 has a stepped shape. The top ring 44 has a straight abutment similarly to the piston 29 of the first embodiment. The diameter of the annular groove 43 increases as it approaches the oil ring 45. Two or more steps, in this embodiment, two steps, are formed in the piston 41 by the annular groove 43. The cross-sectional shape of the outer peripheral surfaces 46a, 46b, 46c of the piston 41 forming the steps is straight and substantially parallel to the center line of the piston 41. On the other hand, the side surfaces 47a, 47b of the piston 41 forming the stairs
Has a straight line and is substantially perpendicular to the center line of the piston 41. Then, the side surfaces 47a, 47b and the outer peripheral surfaces 46a,
The diameters of 46b and 46c increase as the piston 41 moves downward. That is, the outer peripheral surface has the smallest diameter at a portion 46c in the figure, has the next largest diameter at 46b, and has a larger diameter at 46a. The diameter of 46a is equal to or smaller than the diameter of the portion 48 directly below the top ring groove. In addition, in the directly below the top ring groove 48,
The outer diameter of the piston 41 is the largest, and the cross section of the outer peripheral surface is parallel to the center line of the piston 41. The corners at which the outer peripheral surfaces 46a, 46b, 46c intersect with the side surfaces 47a, 47b may be chamfered as necessary or may be formed in an arc shape.

Here, the case where the step-shaped annular groove 43 is formed and the case where the wedge-shaped annular groove 34 is formed will be compared. As described above, the wedge-shaped annular groove 34 has a larger size in the radial direction near the top ring groove, and has a smaller size as it goes downward. The inclination of the step-shaped annular groove 43 substantially matches the inclination of the wedge-shaped annular groove 34. The point P where the outer peripheral surface 46b and the side surface 47b forming the stairs intersect is located substantially on the wedge-shaped annular groove 43. Annular groove 4
When making 3 stepwise, compared to when making it wedge-shaped,
The space of the second land 42 can be increased only by the portion S in the drawing, and the second land 42 can have a volume. Thus, the capacity for storing the oil in the limited second land 42 can be increased. In addition, substantially in the same manner as the wedge-shaped annular groove 34, a flow of combustion gas that can lower the oil stored in the second land 42 can be generated, so that the oil stored in the second land 42 Can be returned to bread.

The present invention is effective even if the abutment between the top rings 22 and 44 is narrowed to reduce blow-by gas. It is possible to further reduce oil consumption and blow-by gas. Further, in each of the above embodiments, the description has been given of the piston having the two-ring structure. However, the present invention is not limited to the two-ring structure, and the three-ring structure includes two pressure rings and one oil ring. It can also be applied to configurations. Also when applied to the three-ring configuration, the same operation and effect as the piston of the two-ring configuration can be obtained.

[0024]

As described above, according to the present invention,
Since a straight abutment was used for the top ring and the land below the top land groove was formed with a substantially wedge-shaped annular groove that increased in the radial direction near the top ring groove and decreased in size as it went down, The volume for storing the oil in the land can be secured. Since the straight joint actively releases the high-pressure side combustion gas to the low-pressure side, the oil stored in the land descends by the flow of combustion gas along the straight wedge and along the wedge-shaped inclined wall. , Return to the oil pan. In addition, the behavior of the top ring can be improved by giving the land a volume. As a result, it is possible to obtain a piston that can reduce both oil consumption and blow-by gas. further,
By using a straight abutment for the top ring, the thickness of the top ring can be reduced. In the double lap joint of the prior art, which is the most serious problem in the two-ring configuration, it is impossible to further reduce the width due to the decrease in the breaking strength of the section, but by using a straight joint as in the present invention. Further thinning is possible. Accordingly, the weight of the top ring itself can be reduced, and adhesion of the top ring to the piston and a sudden increase in blow-by gas due to fluttering during high-speed light load rotation can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a piston according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a straight abutment of a top ring.

FIG. 3 is a partial front view showing attachment of the top ring to a piston.

FIG. 4 is a graph showing a blow-by gas amount.

FIG. 5 is a graph showing oil consumption.

FIG. 6 is a sectional view showing a piston according to a second embodiment of the present invention.

FIG. 7 is a sectional view showing a piston according to a fourth embodiment of the present invention.

FIG. 8 is a perspective view showing a double wrap abutment of a top ring.

FIG. 9 is a sectional view showing another conventional piston.

[Explanation of symbols]

 22, 44 Top ring 23, 45 Oil ring 29, 41 Piston 31, 42 Second land (land) 34 Wedge-shaped annular groove 43 Step-shaped annular groove 24, 24 Mating end (straight abutment) 25, 25 Mating end ( Straight joint)

Claims (3)

[Claims] 1. Use a straight abutment for the top ring,
A piston having a substantially wedge-shaped annular groove formed in a land under a top land groove in a radial direction near the top ring groove and having a smaller size as it goes down. 2. A straight joint for the top ring,
A piston characterized in that an annular groove is formed in a land under the top ring groove so that the diameter increases as approaching the oil ring so that the land has a stepped shape. 3. The piston according to claim 1, wherein the pressure ring comprises only one top ring.