Piston for internal combustion engine

Abstract

To provide a piston for an internal combustion engine that reduces unburned loss and improve exhaust emission by reducing an unburned region between an outer peripheral wall surface of a piston and a wall surface of a cylinder while ensuring strength of the piston.SOLUTION: In a piston for an internal combustion engine, a compression ring 30 that slides against a cylinder wall surface 11 of the internal combustion engine is provided on a piston body 21, and an auxiliary ring 40 that slides against the cylinder wall surface 11 is provided on the piston body 21 closer to a piston crown surface 22 than the compression ring 30, where a radial cross-sectional shape of the auxiliary ring 40 has a radial dimension a that is smaller than a cylinder axial dimension h, and the radial dimension a is smaller than the radial dimension of the compression ring 30.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a piston for an internal combustion engine.

Background Art

[0002] Conventionally, as a piston for an internal combustion engine, as described in Patent Document 1, a compression ring that slidably contacts the cylinder wall surface of the internal combustion engine is provided on the piston body, and an auxiliary ring that slidably contacts the cylinder wall surface is provided on the piston body closer to the piston crown surface than the compression ring.

[0003] This conventional piston for an internal combustion engine attempts to improve the deterioration of unburned and exhaust emissions in the annular gap (clevis region) formed between the outer peripheral wall surface of the piston and the cylinder wall surface above the compression ring.

[0004] That is, in the above-described clevis region, generally, since the cylinder wall surface is cooled, the temperature is low, and the combustion of the air-fuel mixture sent into the combustion chamber in the cylinder is difficult to occur, unburned gas is generated for this reason, and unburned increases. In addition, since unburned HC also increases, exhaust emissions also deteriorate. On the other hand, the above-described conventional piston for an internal combustion engine suppresses the intrusion of the air-fuel mixture from the combustion chamber into the clevis region by the auxiliary ring, and stably reduces the unburned region between the outer peripheral wall surface of the piston and the cylinder wall surface. As a result, the generation of unburned gas is reduced to improve unburned, and the generation of unburned HC is reduced to improve exhaust emissions.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the conventional piston for an internal combustion engine described above has the problems shown in FIG. 2. In FIG. 2, 1 is a cylinder, 2 is a piston body, 2A is a ring groove, 3 is an auxiliary ring incorporated in the ring groove 2A, and C indicates a clevis region.

[0007] That is, as shown in FIG. 2, the radial cross-sectional shape of the auxiliary ring 3 (the cross-sectional shape along the radial direction of the auxiliary ring 3) has its radial dimension (the dimension along the radial direction of the auxiliary ring 3) a larger than its cylinder axial dimension (the dimension along the cylinder axial direction of the auxiliary ring 3) h.

[0008] On the other hand, in a piston for an internal combustion engine, generally, in order to ensure the strength of the piston 2, it is necessary to ensure a certain wall thickness for each part of the piston 2. At the same time, the crown surface shape of the piston 2 has a complex concave and convex shape for combustion transfer in the combustion chamber and for preventing interference with the intake valve and the exhaust valve, and has a concave portion 2R such as a valve recess.

[0009] When providing the ring groove 2A for the above-described auxiliary ring 3 in such a piston 2, if the ring groove 2A with a deeper groove depth for the auxiliary ring 3 having a large radial length a is provided on the side closer to the piston crown surface 2K, the minimum wall thickness tmin (FIG. 2(A)) formed between the ring groove 2A and the piston crown surface 2K becomes too small and insufficient, making it difficult to ensure the strength of the piston 2. Conversely, if an appropriate wall thickness ta (FIG. 2(B)) is ensured between the ring groove 2A and the concave portion 2R, the ring groove 2A moves far from the piston crown surface 2K, and it becomes impossible to reduce the unburned region due to the existence of the clevis region C.

[0010] An object of the present invention is, in a piston for an internal combustion engine, to reduce unburned loss and improve exhaust emissions by reducing the unburned region between the outer peripheral wall surface of the piston and the cylinder wall surface while ensuring the strength of the piston.

Means for Solving the Problems

[0011] The invention according to claim 1 provides a compression ring that slidably contacts the cylinder wall surface of an internal combustion engine on a piston body, and an auxiliary ring that slidably contacts the cylinder wall surface is provided on the piston body closer to the piston crown surface than the compression ring. In the piston for an internal combustion engine, the radial cross-sectional shape of the auxiliary ring is such that its radial dimension a is smaller than its cylinder axial dimension h, and its radial dimension a is smaller than the radial dimension of the compression ring.

Effects of the Invention

[0012] (i) In the piston for an internal combustion engine, the radial cross-sectional shape of the auxiliary ring is such that its radial dimension a is smaller than its cylinder axial dimension h, and its radial dimension a is smaller than the radial dimension of the compression ring. Therefore, the ring groove for the auxiliary ring with a small radial dimension a is provided on the side closer to the piston crown surface of the outer peripheral wall surface of the piston with a shallow groove depth in the piston radial direction. Therefore, the wall thickness for forming a recess such as a valve recess for the auxiliary ring in the piston can be ensured to be larger than the required value, and the strength of the piston can be ensured.

[0013] (ii) According to (i) above, an auxiliary ring can be provided in the annular space (clevis region) formed between the outer peripheral wall surface of the piston and the cylinder wall surface on the side closer to the piston crown surface above the compression ring. This means that the clevis region can be filled with the auxiliary ring, and while ensuring the strength of the piston, the unburned region between the outer peripheral wall surface of the piston and the cylinder wall surface can be reduced. Thereby, the generation of unburned gas can be reduced to improve unburning, and the generation of unburned HC can be reduced to improve exhaust emissions.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Best Mode for Carrying Out the Invention

[0015] FIG. 1 shows a main part of an internal combustion engine according to the present embodiment, where 10 is a cylinder, 20 is a piston, and 30 is a compression ring.

[0016] Here, the cylinder 10 has a generally circular cylinder wall surface 11 extending vertically, and a cylinder head (not shown) is provided at the upper part of the cylinder 10. The cylinder 10 forms a combustion chamber 10A surrounded by the cylinder wall surface 11, the lower surface of the cylinder head, and the crown surface 22 of the piston body 21 in the piston 20. The piston 20 slides up and down inside the cylinder 10 to expand and contract the combustion chamber 10A. The shape of the crown surface 22 of the piston 20 has a complex concave and convex shape for promoting combustion in the combustion chamber 10A and preventing interference with the intake valve and exhaust valve, and is provided with a concave portion 22R such as a valve recess. The lower surface of the cylinder head is provided with an intake valve for allowing the combustion mixture to be inhaled into the combustion chamber 10A and an exhaust valve for allowing the burned exhaust gas to be discharged from the combustion chamber 10A.

[0017] In addition, in this specification, along the central axes of the cylinder 10 and the piston 20, the direction facing the piston crown surface 22 is defined as upward, and the opposite direction is defined as downward.

[0018] The piston 20 is provided with a plurality of piston rings that are in sliding contact with the cylinder wall surface 11 fitted on the cylindrical outer peripheral wall surface 23 of the piston body 21. In the present embodiment, an annular compression ring 30 (top ring) is inserted into a compression ring groove 24 formed on the outer peripheral wall surface 23 of the piston body 21, and the compression ring 30 inserted into the compression ring groove 24 is in contact with the cylinder wall surface 11 via an oil film in a state having a certain tension that maintains the airtightness of the combustion chamber 10A. On the outer peripheral wall surface 23 of the piston body 21, an oil ring groove (not shown) is formed below the compression ring groove 24, and an annular oil ring is inserted into this oil ring, and the oil ring inserted into the oil ring scrapes off the excess oil on the cylinder wall surface 11 and forms an appropriate oil film. The compression ring 30 and the oil ring each have a joint in a part in the circumferential direction and are in contact with the cylinder wall surface 11 via an oil film in a state having a certain tension. Note that a plurality of compression rings 30 may be provided, and in this case, the one closer to the piston crown surface 22 is called the top ring.

[0019] The piston 20 of the present embodiment further has an annular auxiliary ring 40 that is in sliding contact with the cylinder wall surface 11 provided on the side closer to the piston crown surface 22 than the compression ring 30 on the outer peripheral wall surface 23 of the piston body 21. That is, the piston 20 is provided with an auxiliary ring groove 25 above the compression ring groove 24 provided on the outer peripheral wall surface 23 of the piston body 21, and the auxiliary ring 40 is inserted into this auxiliary ring groove 25. The auxiliary ring groove 25 may be connected to the compression ring groove 24 as shown in FIG. 1, or may have a shape that is independent of each other.

[0020] The auxiliary ring 40 has a joint in a part in the circumferential direction and is in contact with the cylinder wall surface 11 via an oil film in a state having a certain tension (extremely low tension) that is weaker than the tension of the compression ring 30.

[0021] Here, in order to ensure the strength of the piston 20 in the piston body 21, the auxiliary ring 40 has the following dimensions so that the necessary wall thickness can be ensured on the piston crown surface 22 provided with the recess 22R.

[0022] (1) The radial cross-sectional shape of the auxiliary ring 40 (the shape of the cross-section including the central axis of the auxiliary ring 40) has its radial dimension a smaller than its cylinder axial dimension h (a < h).

[0023] (2) The radial dimension a of the auxiliary ring 40 is made smaller than the radial dimension b of the cross-section of the compression ring 30 (a < b).

[0024] Therefore, according to the present embodiment, the following operational effects are achieved. (i) In the piston 20 for an internal combustion engine, the radial cross-sectional shape of the auxiliary ring 40 is such that its radial dimension a is smaller than its cylinder axial dimension h and its radial dimension a is smaller than the radial dimension b of the compression ring 30. Therefore, the auxiliary ring groove 25 for the auxiliary ring 40 with a small radial dimension a is provided on the side closer to the piston crown surface 22 of the piston outer peripheral wall surface 23 with a shallow groove depth in the radial direction of the piston 20. Therefore, the thickness formed by the auxiliary ring groove 25 for the auxiliary ring 40 in the piston 20 and the recess 22R such as a valve recess can be ensured to be large enough to a required value (appropriate thickness ta), and the strength of the piston 20 can be ensured.

[0025] (ii) According to (i) above, the auxiliary ring 40 can be provided in the annular space (clevis region C) formed between the piston outer peripheral wall surface 23 and the cylinder wall surface 11 on the side closer to the piston crown surface 22 above the compression ring 30. This means that the clevis region C can be filled with the auxiliary ring 40, and while ensuring the strength of the piston 20, the unburned region between the piston outer peripheral wall surface 23 and the cylinder wall surface 11 can be reduced. Thereby, the generation of unburned gas can be reduced to improve unburning, and the generation of unburned HC can be reduced to improve exhaust emissions.

[0026] In addition, in the present embodiment, since the tension of the auxiliary ring 40 is set weaker than the tension of the compression ring 30, the following operational effects are also achieved.

[0027] (iii) Even if the auxiliary ring 40 is provided, the mechanical loss caused by the sliding contact of the auxiliary ring 40 with the cylinder wall surface 11 can be reduced.

[0028] In addition, the combustion pressure extends beyond the auxiliary ring 40 and around the compression ring 30, which becomes the back pressure that presses the compression ring 30 against the cylinder wall surface 11, improving the airtightness of the compression ring 30 and reducing the amount of unburned HC discharged from that part.

[0029] Also, since the auxiliary ring 40 slides on the cylinder wall surface 11 with a weak force, seizure does not occur even when exposed to the combustion flame.

[0030] As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration of the present invention is not limited to this embodiment, and design changes and the like within the scope not departing from the gist of the present invention are also included in the present invention.

Industrial Applicability

[0031] According to the present invention, in a piston for an internal combustion engine, by reducing the unburned region between the outer peripheral wall surface of the piston and the cylinder wall surface while ensuring the strength of the piston, unburned loss can be reduced and exhaust emissions can be improved.

Explanation of Reference Numerals

[0032] 10 Cylinder 11 Cylinder Wall Surface 20 Piston 21 Piston Body 22 Piston Crown Surface 23 Piston Outer Peripheral Wall Surface 24 Compression Ring Groove 25 Auxiliary Ring Groove 30 Compression Ring 40 Auxiliary Ring

Claims

[Claim 1] A compression ring that is in sliding contact with a cylinder wall surface of an internal combustion engine is provided on a piston body, In a piston for an internal combustion engine, an auxiliary ring that is in sliding contact with a cylinder wall surface is provided on a side of the piston body closer to a piston crown surface than the compression ring, a piston for an internal combustion engine, the piston having a radial cross-sectional shape such that the radial dimension a of the auxiliary ring is smaller than the dimension h of the auxiliary ring in the cylinder axial direction, and the radial dimension a of the auxiliary ring is smaller than the radial dimension of the compression ring.

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