JPH0989106A - Piston structure of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the piston slap due to a skirt part and friction between the skirt part and cylinder by restraining the large inclination of the piston near the upper dead center in compression. SOLUTION: The axis 20 of a piston pin hole 19a or the like of a pair of pin boss parts 19 or the like formed on the inner peripheral surface of a piston 10 is offset to the thrust side relative to the center line X in the diametral direction of a skirt part 16, while thick ribs 22, 23 are provided along the axial direction of the piston on the respective inner surface of the thrust side skirt position and anti-thrust side skirt position. Also, slits 21, 21 are formed along the peripheral direction of the skirt part 16 on the bottom wall of a third ring groove 15 located on the upper end side of the ribs 22, 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in piston structure of an internal combustion engine for automobiles.

[0002]

As is well known, for example, in a piston of an internal combustion engine for an automobile, a thrust force (side force) and a moment around a piston pin act due to an inertial force and a combustion pressure during an expansion stroke. The skirt portion on the thrust side and the anti-thrust side is pressed against the inner surface of the cylinder by tilting to the swinging state.

That is, as shown in FIG. 6, for example, in the vicinity of the top dead center of the expansion stroke, the piston 1 generates a moment in the clockwise direction around the piston pin 3 via the connecting rod 2 due to the combustion pressure. Therefore, the piston 1 tilts from the substantially vertical posture at the time of rising, and the skirt portion 6b on the anti-thrust side is tilted.
The upper end portion or the outer peripheral edge of the crown portion 4 contacts the anti-thrust side inner surface 5a of the cylinder 5, while the lower end portion of the thrust side skirt portion 6a contacts the thrust side inner surface 5b of the cylinder 5. At this time, the skirt portion 6a on the thrust side receives the largest thrust force in one cycle, so that a large slap sound is easily generated between the skirt portion 6a on the thrust side and the cylinder inner surface 5b.

Therefore, as in the invention disclosed in Japanese Utility Model Laid-Open No. 64-21239, the thickness of the piston skirt is made thinner on the thrust side than on the anti-thrust side, and the thrust side skirt is made thinner. By lowering the rigidity of the portion, when the thrust side skirt portion comes into contact with the thrust side inner surface of the cylinder, the thrust side skirt portion is easily deformed to reduce the surface pressure by increasing the contact area. There is. As a result, the piston slap can be reduced, and the wear of the skirt can be reduced.

[0005]

However, in the conventional example described in the above publication, the thickness of the thrust side skirt portion of the piston is simply reduced to reduce the rigidity. Therefore, under operating conditions where the thrust load is small enough to cause piston wrap, its suppression effect is exhibited, but in order to ensure good drivability at full load in the maximum output speed range and in cold / cold conditions. When the ignition timing is advanced, an excessive thrust load is generated, so due to the low rigidity of the thrust side skirt portion,
The thrust side skirt is largely deformed, and the angle of inclination of the piston is increased. As a result, the pressure contact force between the thrust side skirt and the cylinder inner surface increases and friction increases, causing seizure between the cylinder inner surfaces, and the ring side on the anti-thrust side strongly hits the cylinder inner surface, resulting in a large hammering noise. There is a fear that will occur.

[0006]

The present invention has been devised in view of the above problems of the prior art. The invention of claim 1 has a cylindrical skirt portion at the lower portion of the crown portion and the skirt portion. In the piston structure of an internal combustion engine having a pair of pin boss portions that support both ends of the piston pin through the piston pin holes on the inner surface of the portion, the axis lines of the piston pin holes are with respect to the diametrical center line of the skirt portion. Along with the offset arrangement on the thrust side, a thick rib is provided on at least the thrust-side inner surface of the skirt along the thrust axis in the vertical direction of the piston, and the skirt is formed on the bottom wall of the oil ring groove located on the upper end side of the rib. It is characterized in that a slit is formed along the circumferential direction.

The invention of claim 2 is characterized in that the thickness of the skirt portion from both side edges of the rib of the skirt portion to each pin boss portion is set to be equal along the axial direction of the piston.

According to a third aspect of the present invention, the skirt portion is formed such that the circumferential wall thickness from the both side edges of the rib to each pin boss portion is gradually increased.

The invention of claim 4 is characterized in that the thickness of the skirt portion from both side edges of the rib of the skirt portion to each pin boss portion is formed so as to be changed along the piston axial direction.

According to a fifth aspect of the present invention, the thickness of the skirt portion from both side edges of the rib of the skirt portion to each pin boss portion is formed such that the thickness gradually increases from the upper side to the lower side of the skirt portion. Is characterized by.

[0011]

According to the invention of claim 1, a moment around the piston pin acts due to the compression pressure and combustion pressure of the air-fuel mixture in the vicinity of the compression top dead center of the piston, and the crown portion of the piston is on the anti-thrust side and the skirt. Although the lower part of the part tries to tilt toward the thrust side, the thrust side skirt part that hits the inner surface of the cylinder has a thick rib and is independent of the oil ring groove by the slit. A large tilting of the piston is suppressed by the inward bending and a spring reaction force such as a leaf spring in the circumferential direction. That is, when tilting power acts on the piston and the lower end of the thrust side skirt portion contacts the inner surface of the cylinder, the thrust side skirt portion becomes a supporting point for thrust load and bends slightly inward. At the same time, a spring reaction force is generated in the circumferential direction portion of the skirt portion that wraps around the rib from the rib toward the piston boss side, and the thrust side skirt portion tries to be deformed and returned outward. For this reason, the load supporting point moves upward from the lower end of the skirt and tries to move to the vicinity of the center of the piston pin while receiving the thrust load at the thrust side skirt portion having high rigidity. Therefore, the spring reaction force of the circumferential portion of the skirt portion and the movement of the load supporting point suppress a large inclination of the piston, and the piston can be maintained in a substantially vertical state.

Further, according to the invention of claims 4 to 5, the thickness of the circumferential portion from the rib to the piston boss is changed along the axial direction of the piston, so that the thrust load fulcrum at the portion of high rigidity described above. Can be changed to any position in the vertical direction. Therefore, the behavior of the piston can be stabilized according to the specific operating conditions.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1 to 3 show a first embodiment of a piston structure according to the present invention.

In this piston 10, a piston body, which is in sliding contact with the inner peripheral surface of the cylinder (not shown), is integrally formed of an aluminum alloy material in a cylindrical shape with a lid, and a substantially disc-shaped crown portion 1 formed on the upper portion.
1, and the first, second, and third piston ring grooves 13, 14, and 15 are formed from the top on the outer periphery of the ring land portion 12 provided at the lower portion of the crown portion 11. Further, a thin-walled tubular skirt portion 16 is integrally formed at a lower portion of the ring land portion 12, and a small end portion of a connecting rod (not shown) is provided at a position facing the inner circumferential surface of the skirt portion 16 in a substantially diametrical direction. Pin boss portions 18 and 19 for supporting both ends of the piston pin 17 connected to the are formed to project inward.

The pin boss portions 18 and 19 are set at positions where the axial centers 20 of the piston pin holes 18a and 19a formed inside are slightly offset to the thrust side with respect to the axial center line X of the piston body. There is.

Further, slits 21 and 2 are formed in the bottom wall of the third piston ring groove (oil ring groove) 15 at the lowermost stage.
1 is formed, and the slits 21 and 21 are formed along the circumferential direction up to the vicinity of both side portions of both pin boss portions 18 and 19.

Further, the skirt portion 16 is integrally formed with thick ribs 22 and 23 at opposed inner surface positions orthogonal to the axis 20 of the piston pin holes 18a and 19a. The ribs 22 and 23 are a side force received by the skirt portion 16 from the inner surface of the cylinder when the piston 10 shifts from the compression top dead center to the expansion process, that is, the thrust side and the ring land portion 12. The vicinity is formed on both the anti-thrust side received from the inner surface of the cylinder. The ribs 22 and 23 each have a long plate shape and have a width W in the circumferential direction around the diameter line Y orthogonal to the axis 20 set to the same predetermined length, and the skirt portion. The upper end portion 2 is extended along the vertical direction of 16
2a and 23a are located directly below the slits 21 and 21.

Further, the skirt portion 16 extending from both side edges of the ribs 22 and 23 to both side edges of the pin boss portions 18 and 19, respectively.
The circumferential portions 24, 24, 25, 25 of the two ribs 22,
The thickness from 23 to both side edges of both pin boss portions 18 and 19 is gradually increased, and as shown in FIG. 3, the thickness in the vertical direction is uniform.

The operation of this embodiment will be described below.
During operation of the engine, a moment around the piston pin 17 acts due to the compression pressure and combustion pressure of the air-fuel mixture near the compression top dead center of the piston 10, so that the piston 20 tilts and transforms around the piston pin 17 and the piston 10 moves. The crown portion 11 tends to tilt toward the anti-thrust side of the cylinder inner surface, and the lower end portion of the skirt portion 16 tends to tilt toward the thrust side. However, the axis 20
Are offset to the thrust side, and the thrust side skirt portion 16a has a thick rib 22 and the skirt portion 16a is formed by the slit 21 into the third ring groove 1a.
5, the skirt portion 16a, which contacts the thrust side of the inner surface of the cylinder, has a characteristic like a leaf spring and suppresses a large tilt of the piston 20.

That is, the thrust side skirt portion 16a is
Since the rigidity is high, when the lower end portion 16c comes into pressure contact with the inner surface of the cylinder, the piston 1 passes through the slit 21.
At the same time, the spring reaction force is generated in the circumferential direction portions 24, 24 having low rigidity. Therefore, the thrust-side skirt portion 16a tries to move to the vicinity of the centers of the piston pin holes 18a and 19a while receiving the thrust load and the load supporting point moves upward from the lower end portion 16c of the skirt portion 16a. Therefore, the circumferential portion 24,
24 spring reaction force and the piston pin hole 18 at the load supporting point
The large inclination of the piston 10 is suppressed by the movement to the vicinity of the centers a and 19a, and it becomes possible to maintain the substantially vertical posture in the cylinder. In addition, even if it is once inclined, it can easily return to the vertical posture side smoothly.

As a result, the occurrence of piston slap under operating conditions with a small thrust load can be sufficiently prevented, and even when an excessive thrust load is generated at the time of full load in the maximum output rotation range, etc. , Piston 10
The large tilt of the skirt is suppressed and the thrust side skirt part 1
The sliding area between 6a and the inner surface of the cylinder is reduced, and thus the friction is significantly reduced. As a result, the fuel efficiency of the engine is improved and the response can be improved. Further, it is possible to prevent a large impact hitting sound between the ring land portion 12 and the inner surface of the cylinder, thereby improving the sound vibration performance.

Since the anti-thrust side skirt portion 16b of the skirt portion 16 and the circumferential direction portions 25, 25 have the same structure as the thrust side, an excessive inclination of the piston 10 even when the piston 10 is tilted in the reverse direction. Suppressed. Therefore, the occurrence of piston slap or the like is prevented.

4 and 5 show the second and third embodiments of the present invention. In each of these embodiments, the circumferential portions 24, 24, 2 are shown.
In the second embodiment shown in FIG. 4, the circumferential portions 24, 24, 25, 2 are formed by changing the wall thicknesses of the 5, 5 and 25 in the vertical direction.
The thin-walled portions 26, 26 are formed in the upper portion of 5, that is, immediately below the third piston ring groove 15, and the thin-walled portions 26, 26 are gradually thickened as they go downward.

In the third embodiment shown in FIG. 5, the skirt portion 1
A thin portion 27 was formed at a substantially central position in the up-down direction of the circumferential portions 24, 24 of 6, and the thickness gradually increased from the thin portion 27 in the up-down direction.

Therefore, according to the second and third embodiments, the piston 10 near the compression top dead center as described above is used.
It becomes possible to control the load supporting point of the thrust side skirt portion 16a at the time of tilting, and as a result, the substantially vertical posture of the piston 10 can be stabilized in accordance with a specific operating condition. Therefore, the behavior of the piston 10 can be stabilized under characteristics peculiar to the engine, for example, under large operating conditions of piston slap and operating conditions with large friction and low fuel efficiency, and piston slap and friction under predetermined operating conditions can be improved. It becomes possible to do.

The present invention is not limited to the structure of the above embodiment, and for example, the thickness and width of the ribs 22 and 23 and the change in the wall thickness of the circumferential portions 24, 24, 25 and 25 in the axial direction can be controlled. It can be arbitrarily set according to the specifications of the engine.

[0027]

As is apparent from the above description, according to the present invention, it is possible to sufficiently suppress the large tilt of the piston when the tilt of the piston is converted near the compression top dead center. For this reason, it is possible to prevent the occurrence of piston slap under operating conditions where the thrust load is small, and, even when an excessive thrust load occurs, for example, at full load in the maximum output rotation range, the thrust side skirt part and the cylinder inner surface Sliding area is reduced, which can reduce friction. As a result, the fuel efficiency of the engine and the response can be improved. Further, it is possible to prevent a large impact hitting sound between the ring land portion and the inner surface of the cylinder, thereby improving the sound vibration performance.

According to the third aspect of the present invention, the spring reaction force characteristic from each rib to the pin boss portion can be effectively exhibited, so that the inclination of all pistons can be further suppressed.

Further, according to the inventions of claims 4 and 5, the load supporting point of the thrust load received by the skirt portion can be controlled, so that the behavior of the piston can be stabilized in accordance with a specific operating condition. It will be possible.

[Brief description of drawings]

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

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

FIG. 4 is a sectional view taken along line BB of FIG. 1 showing a second embodiment of the present invention.

5 is a sectional view taken along line BB of FIG. 1 showing a third embodiment of the present invention.

FIG. 6 is a cross-sectional view showing the behavior of a piston of the present invention and a conventional piston in a cylinder.

[Explanation of symbols]

 10 ... Piston 11 ... Crown 12 ... Ring land 15 ... 3rd piston ring groove (oil ring groove) 16 ... Skirt 16a ... Thrust side skirt 17 ... Piston pin 18, 19 ... Pin boss 20 ... Shaft 21 ... Slit 22 ... Rib 24, 25 ... Circumferential portion

Claims (5)

[Claims] 1. A piston structure for an internal combustion engine, which has a cylindrical skirt portion at a lower portion of a crown portion, and a pair of pin boss portions for supporting both end portions of a piston pin through piston pin holes on an inner surface of the skirt portion. In the above, the axial lines of the piston pin holes are offset to the thrust side with respect to the diametrical center line of the skirt portion, and at least the thrust-side inner surface of the skirt portion has a thick wall along the thrust axial line in the vertical direction of the piston. With ribs
A piston structure for an internal combustion engine, characterized in that a slit along the circumferential direction of the skirt is formed in the bottom wall of the oil ring groove located on the upper end side of the rib. 2. The piston structure for an internal combustion engine according to claim 1, wherein the thickness of the skirt portion from both side edges of the rib of the skirt portion to each pin boss portion is set to be equal along the piston axial direction. 3. The piston structure for an internal combustion engine according to claim 2, wherein the skirt portion is formed so that the circumferential wall thickness from the rib both side edges to each pin boss portion becomes gradually thicker. 4. The internal combustion engine according to claim 1, wherein the thickness of the skirt portion from both side edges of the rib of the skirt portion to each pin boss portion is formed to vary along the piston axial direction. Piston structure. 5. The wall thickness of the skirt portion from the both side edges of the rib of the skirt portion to each pin boss portion is formed so as to become gradually thicker from the upper side to the lower portion of the skirt portion. Item 4. A piston structure for an internal combustion engine according to item 4.