JPH04244675A - Piston for internal combustion engine - Google Patents

Abstract

PURPOSE:To make it lighter in weight and compact in size in addition to the promotion of high rigidity, in a piston for an internal combustion engine. CONSTITUTION:A skirt part 10 is composed of a skirt upside part 5 extending along a cylinder from a ring groove part 3, a skirt downside part 6 extending along the cylinder at relatively small circumferential width from the skirt upside part 6, and the skirt upside part 5 is installed in the side range of a piston pin, while such a reinforcing rib part 11 as protuberating in a rib form from a head part back 2b and connecting the skirt upside part 5 and a pin boss part 4, is formed there. In addition, a beam part jutting out to the radial inside of a piston over both these skirt upside and downside parts is formed as well.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvements in pistons for internal combustion engines.

0002

[Prior art and its problems] In automobile engines, etc., there is a strong demand for lighter and smaller pistons in order to improve fuel efficiency, but on the other hand, there is a demand for higher strength as the load increases in order to achieve higher output. It is being

[0003] Conventional pistons include a skirt section that extends cylindrically from the head section that defines the combustion chamber along the cylinder, and this skirt section has a notch formed in the direction of the end of the piston pin where side pressure is not applied. , the mass is reduced and the sliding contact area with the cylinder is reduced (for example, Japanese Patent Laid-Open No. 61-8
1558, see).

However, in such conventional devices, since the skirt portion is formed into a cylindrical shape over a wide area, the skirt portion is pressed against the cylinder by the combustion pressure or inertia force applied to the piston, such as on the thrust side or on the opposite side. On the thrust side, the surface pressure on the cylinder may become excessive in the lateral region of the pin where this load is greatest.
Alternatively, the area of sliding contact with the cylinder is unnecessarily increased in other areas.

[0005] Furthermore, as a countermeasure to this problem, if the region of the cylindrical skirt portion to which no lateral pressure is applied is largely cut out, the stiffness distribution of the skirt portion becomes uneven, causing scuffing and the like.

The present invention aims to solve these conventional problems.

[0007]

[Means for Solving the Problems] A first invention includes a head portion defining a combustion chamber, a skirt portion extending from the head portion along a cylinder via a ring groove portion, and a pin boss portion into which a piston pin is inserted. and a pair of skirt upper sides extending along the cylinder from the ring groove, and a skirt lower side extending along the cylinder from the skirt upper side with a relatively small circumferential width. A skirt part is formed, and the skirt upper part is provided in a lateral region of the piston pin including the piston pin axial center surface perpendicular to the piston center axis, and a rib-like protrusion is formed from the back surface of the head part, and the skirt upper part and the A reinforcing rib portion was formed to connect the pin boss portion. In a second aspect of the invention, a beam portion is formed extending inward in the radial direction of the piston across the skirt upper side and the skirt lower side.

[0008]

[Operation] On the thrust side or anti-thrust side where the skirt is pressed against the cylinder due to the combustion pressure or inertia applied to the piston, in the side region of the piston pin where this load is greatest, the upper side of the skirt extends over a wide area in the circumferential direction. Since the skirt is widened, the contact pressure of the upper side of the skirt against the cylinder is effectively dispersed, and wear of the piston and cylinder is suppressed.

The load in which the upper side of the skirt is pressed against the cylinder due to the combustion gas pressure or inertial force that the piston receives is supported by the reinforcing rib section that connects the upper side of the skirt and the pin boss section in a rib shape, and this load causes the skirt section to press against the piston. Reduces the amount of deflection that causes the radially inward bending of the
Sufficient rigidity can be ensured.

[0010] Since the lower side of the skirt extends in the axial direction on the thrust side or the anti-thrust side, a sufficient contact length is ensured in the axial direction of the cylinder, the attitude of the piston relative to the cylinder is controlled, and slap noise can be reduced. .

[0011] In this way, by forming the skirt portion from the upper side of each skirt to the lower side of the skirt extending along the cylinder with a relatively small circumferential width, the weight of the piston is reduced, and the skirt Friction loss of the piston can be reduced by reducing unnecessary contact area at the piston.

[0012] Furthermore, since the beam portion extending inward in the radial direction of the piston is formed across the upper side of the skirt and the lower side of the skirt, the lower side of the skirt comes into sliding contact with the cylinder, thereby suppressing the inclination of the piston. In some cases, sufficient rigidity can be ensured against the bending stress applied to the lower side of the skirt.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings. As shown in FIGS. 1, 2, and 3, the disk-shaped head portion 2 of the piston 1 defines a combustion chamber on its top surface 2a, and has a ring groove portion 3 on its outer periphery.

A pressure ring and an oil ring are interposed between each ring groove 3 and the cylinder to prevent high-pressure combustion gas from leaking from the combustion chamber to the crankcase and to adjust the lubricating oil film on the cylinder wall. It has become.

In the figure, S1 is a piston axis surface that is orthogonal to the piston pin's central axis O4 and includes the piston central axis O1;
4 is a piston pin axial center surface that is orthogonal to the piston center axis O1 and includes the center axis O4 of the piston pin.

The skirt portion 10 extends symmetrically in a T-shape with respect to the piston axial center surface S1, and has a pair of skirt upper side portions 5 extending along the cylinder from the land portion 3a of the ring groove portion 3, and a pair of skirt upper side portions 5 extending relatively from each skirt upper side portion 5. and a pair of skirt lower sides 6 extending along the cylinder with a small circumferential width.

Each skirt upper side portion 5 is provided in a lateral region of the piston pin including the piston pin axial center surface S4, and the area located above the pin axial center surface S4 is larger than the area located below it by a predetermined ratio. formed to become larger. This ratio is set so as to equalize the distribution of contact surface pressure on the cylinder in response to the fact that the load applied to the area above the piston pin is greater than the load applied to the area below the piston pin.

Each skirt upper side 5 has a predetermined width X1 in the piston axial direction, and the area of each skirt upper side 5 corresponds to the maximum load on the thrust side or anti-thrust side that the piston 1 receives. It is set to suppress the contact surface pressure to below the allowable value.

Two pairs of reinforcing rib portions 11 are integrally formed, which protrude in a rib shape from the back surface 2b of the head portion 2 and connect each skirt upper side portion 5 and each pin boss portion 4.

Each reinforcing rib portion 11 has one end connected to the outer periphery of the front and rear pin boss portions 4 substantially orthogonally, and the other end connected to the peripheral end of the back surface 5a of each skirt upper side portion 5. The upper end is coupled to the back surface 2b of the head portion 2 substantially orthogonally. The cross-sectional thickness of the reinforcing rib portion 11 gradually becomes thinner from each pin boss portion 4 to each skirt upper side portion 5, and is curved in the tangential direction of the arc cross section of each skirt upper side portion 5.

As shown in FIGS. 4 and 5, the cross sections of the skirt upper side 5 and the skirt lower side 6 are formed in an elliptical shape with a focal point on the piston axis plane S1 perpendicular to the piston pin. This ellipse has longer diameters in the thrust and anti-thrust directions, and during engine operation, the ellipse approaches a perfect circle due to thermal expansion, increasing the area in contact with the cylinder.

As shown in FIGS. 6 and 7, the longitudinal cross-sectional shape from the skirt upper side 5 to the skirt lower side 6 is basically formed by changing the long axis of the former ellipse along the piston axis direction. It is formed into a barrel shape that is squeezed by. As a result, a gap with a wedge-shaped cross section is created between the edges of the skirt upper side 5 and the skirt lower side 6 and the cylinder, and lubricating oil is sent between the surface of the skirt and the cylinder through this wedge-shaped gap, thereby providing lubrication. This prevents the oil film from running out and maintains good lubricity.

Although the dimensions of each part shown in FIGS. 4 to 7 are exaggerated to be larger than the actual size for convenience, they are actually quite small, on the order of several tens of μm.

The distance X2 of each skirt lower side portion 6 in the piston axial direction is set so as to sufficiently suppress the inclination of the piston 1 with respect to the cylinder.

As shown in FIGS. 8, 9, and 10, the cross section from the skirt upper side 5 to the skirt lower side 6 consists of two arcuate beams 1 lined up with a predetermined gap 14 in between.
2, 13, and a central beam portion 15 that connects the center portions of each arcuate beam portion 12, 13 and projects inward in the piston radial direction.
It is formed into an I-shaped cross section. Thereby, when the skirt lower side 6 slides on the cylinder and the inclination of the piston 1 is suppressed, sufficient rigidity can be ensured against the bending stress that the skirt lower side 6 that forms the lower side of the T-shape receives.

Arc-shaped beam portions 12 and 13 of the skirt lower side portion 6
If the thickness across the skirt is constant as Y1, then the cross-sectional thickness of the skirt upper side 5 is from Y2 to the axial length X5 from the lower end and the same circumferential angular range as the skirt lower side 6. A tapered portion 16 is formed that gradually increases to Y1. The gap 14 also has an axial length X in the tapered portion 16.
6, and the total length from the lower end of the skirt lower side portion 6 is X3. Thereby, when the inclination of the piston 1 with respect to the cylinder is suppressed, sufficient bending rigidity can be ensured even at the root (base end) portion of the skirt lower side portion 6 where stress is concentrated.

In this manner, since the skirt portion 10 is composed of the skirt upper side portion 5 and the skirt lower side portion 6 extending from the skirt upper side portion 5 with a relatively small circumferential width, the combustion gas pressure and inertia force are applied to the cylinder. A large notch 9 is formed in the direction of the end of the piston pin where almost no pressure is applied, reducing the mass of the piston 1 and unnecessary contact area of the skirt portion 10 with the cylinder. Friction loss can be reduced.

By providing the skirt upper side portions 5 in the side areas of the piston pin, the contact surface pressure of each skirt upper side portion 5 pressed against the cylinder by the combustion gas pressure or inertia force applied to the piston 1 is effectively dispersed. Piston and cylinder wear is suppressed.

The load that each skirt upper side 5 is pressed against the cylinder due to the combustion gas pressure or inertia force applied to the piston 1 is supported by each reinforcing rib portion 11 that connects each skirt upper side 5 and each pin boss portion 4 in a rib shape. Thus, the rigidity of the skirt upper side portion 5 is sufficiently ensured. On the other hand, in a structure in which the reinforcing rib part 11 is not provided and the skirt upper side part 5 is connected to the ring groove part 3 only through its upper end,
Due to the load that is pressed against the cylinder, the skirt upper side portion 5 is deflected by a large amount such that its circumferential end portion collapses inward in the radial direction of the piston 1, leaving a highly rigid circumferential center portion, resulting in the risk of scuffing. There is.

In addition, the reinforcing rib portion 11 of the head portion 2 is raised in a rib shape from the back surface 2b and is connected to the head portion 2 together with the pin boss portion 4, so that the head portion 2 has sufficient resistance to the combustion pressure applied to the top surface 2a. Strength can be ensured.

Next, other embodiments shown in FIGS. 11 and 12 will be described.

The skirt portion 20 includes a pair of skirt upper side portions 25 extending along the cylinder from the head portion 2 via the ring groove portion 3, and a pair of skirt upper side portions 25 extending from each skirt upper side portion 25 along the cylinder with a relatively small circumferential width. It is constituted by two pairs of extending skirt lower side portions 26.

Each skirt upper side 25 has a predetermined width X1 in the piston axial direction, and the area of each skirt upper side 25 is determined in accordance with the maximum load on the thrust side or anti-thrust side that the piston 1 receives. It is set to suppress the contact surface pressure to below the allowable value.

The load that each skirt upper side 25 is pressed against the cylinder due to the combustion pressure or inertia force applied to the piston 1 is supported by the reinforcing rib portion 21 that connects each skirt upper side 25 and each pin boss portion 4 in a rib shape. Sufficient rigidity of the skirt upper side portion 25 is ensured.

The distance X2 of each skirt lower side portion 26 in the piston axial direction is set so as to sufficiently suppress the inclination of the piston 1 with respect to the cylinder. The cross section from the skirt upper side 25 to the skirt lower side 26 is formed into an I-shaped cross section as in the previous embodiment, and can ensure sufficient rigidity against the bending load that the skirt lower side 26 receives. The total contact area of the two pairs of skirt lower sides 26 is set to be equal to the total contact area of the pair of skirt lower sides 6 in the embodiment.

In this case, the four skirt lower sides 26 extend along the cylinder, thereby suppressing the horizontal inclination of the piston 1 and effectively suppressing the longitudinal inclination. Alternatively, wear of the piston pin can be suppressed, and the piston 1 can be prevented from slamming against the cylinder wall surface and generating noise.

Next, other embodiments shown in FIGS. 13, 14, and 15 will be described.

The skirt portion 30 extends symmetrically into a T-shape with respect to the piston axial center surface S1, and has a pair of skirt upper sides 35 extending along the cylinder from the ring groove, and a relatively small circumferential portion extending from each skirt upper side 35. and a pair of skirt lower sides 36 extending along the cylinder in width.

From the skirt upper side 35 to the skirt lower side 3
6 shows the arcuate beam portion 37 and the arcuate beam portion 3.
6 and a central beam portion 38 projecting radially inward from the center portion of the cross section. Thereby, when the skirt lower side part 36 slides on the cylinder and the inclination of the piston 1 is suppressed, sufficient rigidity can be ensured against the bending load that the skirt lower side part 36 receives.

The thickness of the arcuate beam portion 37 of the skirt lower side portion 36 is constant as Y1, and the skirt upper side portion 35 has a central beam portion that protrudes inward in the radial direction of the piston within an axial length X5 range from the lower end thereof. 38 is integrally formed, and this central beam portion 38
A tapered portion 38a whose radial cross-sectional thickness gradually increases from Y1 to Y2 is formed at the base of the skirt lower side portion 36 where stress is concentrated when the inclination of the piston 1 with respect to the cylinder is suppressed. ) has sufficient bending rigidity.

Next, other embodiments shown in FIGS. 16, 17, and 18 will be described.

The skirt portion 40 extends symmetrically in a T-shape with respect to the piston axial center surface S1, and has a pair of skirt upper sides 45 extending along the cylinder from the ring groove 3 and a relatively small circumferential direction from each skirt upper side 45. and a pair of skirt lower sides 46 extending along the cylinder with a width of .

From the skirt upper side 45 to the skirt lower side 4
6 shows the arcuate beam portion 47 and the arcuate beam portion 4.
It is formed in a U-shaped cross section and has peripheral end beam portions 48 that protrude inward in the piston radial direction from both ends of the piston. Thereby, when the skirt lower side part 46 slides on the cylinder and the inclination of the piston 1 is suppressed, sufficient rigidity can be ensured against the bending load that the skirt lower side part 46 receives.

From the skirt upper side 45 to the skirt lower side 4
The thickness across the arcuate beam portion 47 of No. 6 is constant as Y1, and the skirt upper side portion 45 has a radial cross-sectional thickness of Y1 to Y2 in the axial direction length X5 from the lower end, and the peripheral end beam portion 48 has a radial cross-sectional thickness of Y1 to Y2.
A tapered portion 48a is formed to gradually increase the height of the piston 1, and when the inclination of the piston 1 with respect to the cylinder is suppressed, sufficient bending rigidity is ensured at the root (base end) portion of the skirt lower side portion 46 where stress is concentrated. There is.

As described above, the cross-sectional shape of the skirt lower side extending along the cylinder with a relatively small circumferential width from the skirt upper side has sufficient rigidity in response to the maximum input to the skirt lower side due to the engine load. and determine the strength to be ensured.

[0046]

As explained above, the present invention provides a piston for an internal combustion engine with a skirt extending along the cylinder from the ring groove, and a skirt extending along the cylinder with a relatively small circumferential width from the skirt upper side. The skirt part is formed by the extending lower part of the skirt, and the upper part of the skirt is provided in the side area of the piston pin, and a reinforcing rib part is formed in a rib-like shape that rises from the head part and connects the upper part of the skirt and the pin boss part. The skirt portion has sufficient rigidity to effectively disperse the contact pressure against the cylinder, thereby making it possible to reduce the weight and size of the piston while ensuring operability and durability of the piston. In addition, by forming the beam portion extending inward in the radial direction of the piston across the skirt upper side and the skirt lower side, when the skirt lower side comes into sliding contact with the cylinder and the inclination of the piston is suppressed, Sufficient rigidity can be ensured against the bending stress applied to the lower side of the skirt, and the piston can be further reduced in weight and size.

[Brief explanation of the drawing]

FIG. 1 is a front view of a piston showing an embodiment of the present invention.

FIG. 2 is a side view of the piston.

FIG. 3 is a plan view of the piston seen from below.

4 is a contour view taken along line DD in FIG. 2; FIG.

FIG. 5 is a contour view taken along line BB in FIG. 2;

6 is a contour view taken along line AA in FIG. 2; FIG.

7 is a contour view taken along line CC in FIG. 2; FIG.

8 is a longitudinal cross-sectional view taken along line AA in FIG. 2; FIG.

9 is a side view similarly seen from the direction of arrow X in FIG. 1. FIG.

FIG. 10 is a cross-sectional view taken along line BB in FIG. 2;

FIG. 11 is a side view of a piston showing another embodiment.

FIG. 12 is a plan view of the piston seen from below.

FIG. 13 is a side view of a skirt portion showing still another embodiment.

14 is a longitudinal cross-sectional view taken along line AA in FIG. 13; FIG.

FIG. 15 is a cross-sectional view taken along line BB in FIG. 13;

FIG. 16 is a side view of a skirt portion showing still another embodiment.

17 is a longitudinal cross-sectional view taken along line AA in FIG. 16; FIG.

18 is a cross-sectional view taken along line BB in FIG. 16. FIG.

[Explanation of symbols]

1 Piston 2 Head part 3 Ring groove 4 Pin boss part 5 Upper part of skirt 6 Lower part of skirt 10 Skirt part 11 Reinforcement rib part 15 Beam part

Claims (2)

[Claims] 1. A piston for an internal combustion engine, each comprising: a head portion defining a combustion chamber; a skirt portion extending from the head portion along the cylinder through a ring groove; and a pin boss portion into which a piston pin is inserted. The skirt portion is constituted by a pair of skirt upper side portions extending from the ring groove portion along the cylinder, and a skirt lower side portion extending from the skirt upper side portion along the cylinder with a relatively small circumferential width, and the skirt upper side portion is A reinforcing rib portion is provided in a side region of the piston pin including the piston pin axis surface perpendicular to the piston central axis, and is raised in a rib shape from the back surface of the head portion to connect the skirt upper side portion and the pin boss portion. A piston for an internal combustion engine that is characterized by: 2. The piston for an internal combustion engine according to claim 1, further comprising a beam portion projecting inward in the radial direction of the piston across the upper side of the skirt and the lower side of the skirt.