JPH08312452A - Internal combustion engine pistons - Google Patents

Abstract

(57) [Summary] [Purpose] To increase the rigidity of the piston. [Structure] The piston 1 is provided with a recess 3 on its top surface 2. The center of the circular cross section of the recess 3 is the axis L- of the piston 1.
It is located on L. The piston 1 is provided with a pair of pin bosses 4a and 4b for accommodating piston pins. These pin bosses 4a, 4b are arranged on the circumferential surface of the piston 1 so as to be separated from each other in the common axis MM direction. The substantially cylindrical pin bosses 4a, 4b are connected to the inner peripheral surface of the skirt portion 6 of the piston 1 by corresponding connecting portions 5a, 5b on the outer peripheral surface. The connection portion is such that the gap WC between the connection portions 5a and 5b in the axial direction MM of the pin boss is smaller than the width of the recess 3 in the axial direction MM of the pin boss, that is, the diameter WD of the outer peripheral edge 3a of the recess 3. 5
a and 5b are formed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a piston for an internal combustion engine.

[0002]

2. Description of the Related Art As shown in FIGS. 7 and 8, a piston 1'of an internal combustion engine having a recess 3 ', which is a main combustion chamber, on a top surface 2'of a pair of piston pins for receiving piston pins. The pin bosses 4a ', 4b' are provided separately from each other in the direction of the axis M'-M 'of the pin boss.
A piston 1'is known in which the outer peripheral surface of 4b 'and the inner peripheral surface of the skirt portion 6'of the piston 1'are connected by connecting portions 5a', 5b '(see Japanese Utility Model Laid-Open No. 57-10440). . In this piston 1 ', the pin boss axis M'-
A gap WC 'between the connecting portions 5a' and 5b 'in the M'direction
Is longer than the width WD 'of the recess 3'with respect to the direction of the axis M'-M'. The pin bosses 5a 'and 5b' are arranged such that the axis line M'-M 'of the pin boss is located on the axis line L'-L' of the piston 1 '.

[0003]

By the way, when the explosion stroke of the engine is performed, both mechanical stress due to combustion pressure and thermal stress due to combustion heat act on the top surface 2'of the piston 1 ', As a result, the opening of the recess 3'is expanded by these stresses. In this case, the pressure acting on the piston 1'is supported by the piston pin located in the central portion of the piston 1 ', so that the recess 3'is provided with the pin boss axis M'-M'.
It will be spread out in a direction perpendicular to. That is, stress acts on the lip portion 1a 'around the recess 3', and therefore the lip portion 1a 'of the lip portion 1a' located above the pin bosses 4a ', 4b' in the drawing.
A tensile stress in the circumferential direction acts on b'as indicated by the arrow in FIG. As a result, there is a problem that cracks are likely to occur in the lip portion 1b '.

In this case, since the connecting portions 5a 'and 5b' extend from the respective pin bosses 4a 'and 4b' to the skirt portion 6'in a direction perpendicular to the axis M'-M 'of the pin boss, these connecting portions are formed. The rigidity of the piston 1'in this direction can be increased somewhat by 5a ', 5b'.
However, as in this example, the connections 5a ', 5
If the gap WC 'between b'is made longer than the width WD' of the recess 3 ', that is, in FIG. 8, the inner peripheral edge of each connecting portion 5a', 5b 'is located outside the outer peripheral edge of the recess 3'. The rigidity of the piston 1'in the direction perpendicular to the axis M'-M 'of the pin boss cannot be sufficiently increased by these connecting portions 5a', 5b ', and therefore the lip portion 1b' may be cracked. Not reduced.

[0005]

In order to solve the above problems, according to the present invention, in a piston of an internal combustion engine having a recess on the top surface, a pair of pin bosses for receiving piston pins are arranged in the axial direction of the pin boss. The pin bosses are provided so as to be separated from each other, and the outer peripheral surface of each pin boss and the inner peripheral surface of the skirt portion of the piston are connected by a connecting portion, and a gap between these connecting portions in the axial direction of the pin boss is a recess in the axial direction. Each connecting portion is formed so as to be shorter than the width of.

[0006]

The rigidity of the piston in the direction perpendicular to the axis of the pin boss is increased by the connecting portion.

[0007]

The present invention can be applied to a piston for a cylinder direct injection spark ignition type internal combustion engine, for example. However, the invention can also be applied to pistons for diesel engines. 1 and 2, a piston 1 having a circular cross section has a recess 3 on its top surface 2. In the plane perpendicular to the axis L-L of the piston 1, this recess 3 has a circular cross section, and the center of the circular cross section is arranged on the axis L-L of the piston 1. In this embodiment, as shown in FIG. 1, the concave portion 3 near the top surface 2 is formed.
Is formed so as to project toward the center of the concave portion 3, and the cross-sectional area of the concave portion 3 is largest near the bottom surface of the concave portion 3. The contour of the recess 3 at the position where the cross-sectional area of the recess 3 is the largest is called the outer peripheral edge of the recess 3.
The outer peripheral edge 3a is indicated by a broken line in FIG. In the following, the piston 1 forming an annular shape around the recess 3
The top portion 1a of the above will be referred to as a lip portion. Although the combustion chamber is defined by the top surface 2 of the piston 1 and the inner wall surface (not shown) of the cylinder head, the recess 3 constitutes the main combustion chamber.

As shown in FIG. 2 in particular, the piston 1 has a pair of pin bosses 4a and 4b for accommodating piston pins (not shown). These pin bosses 4a and 4b are arranged on the peripheral surface of the piston 1 so as to be separated from each other in the common axis MM direction, and thus are arranged to face each other. The piston 1 is connected to a connecting rod (not shown) by a piston pin. Further, the substantially cylindrical pin bosses 4a, 4b are connected to the inner peripheral surface of the skirt portion 6 of the piston 1 on the outer peripheral surface by corresponding connecting portions 5a, 5b. In this embodiment, the pin bosses 4a and 4b, the connecting portions 5a and 5b, and the skirt portion 6 of the piston 1 are used.
Are integrally formed by casting. In this embodiment, the axis MM of the pin boss is the axis LL of the piston 1.
The pith bosses 4a and 4b are arranged so as to be located above. Further, in this embodiment, the pin bosses 4a and 4b are arranged symmetrically with respect to a vertical plane NN passing through the piston axis L-L and perpendicular to the pin boss axis MM.
The connection parts 5a and 5b are also arranged symmetrically with respect to the vertical plane NN.

As shown in FIG. 2, the pin boss axis M is shown.
The gap between the connection portions 5a and 5b in the −M direction is represented by WC, and when the width of the recess 3 in the MM direction of the pin boss, that is, the diameter of the outer peripheral edge 3a of the recess 3 is represented by WD, WC is greater than WD. Connection part 5a, so that
5b is formed. That is, in FIG. 2, the inner peripheral edge of each of the connecting portions 5 a and 5 b is located inside the outer peripheral edge 3 a of the recess 3 with respect to the axis MM direction of the pin boss.

By the way, when the explosion stroke of the engine is performed, as described above with reference to FIGS. 7 and 8, the top surface 2 of the piston 1 has a mechanical stress due to combustion pressure and a thermal stress due to combustion heat. Both act and as a result of these stresses,
The lip portion 1 located above the pin boss 4a in FIG.
A tensile stress acts on b. However, in the present embodiment, the connecting portion 5 extending in the axis MM direction of the pin boss.
a, 5b are provided, and these connection parts 5a,
Since 5b is formed such that WC <WD, the rigidity of the piston 1 in the direction perpendicular to the axis MM of the pin boss is higher than that in the case of FIGS. 7 and 8 due to the connecting portions 5a and 5b. Has been elevated. As a result, the tensile stress acting on the lip portion 1b can be made smaller than that in the case of the example shown in FIGS. 7 and 8, so that the lip portion 1b can be prevented from being cracked. Thus, the durability of the piston 1 can be improved.

Further, according to this embodiment, since the rigidity of the piston 1 is increased, the deformation of the piston 1 can be reduced. As a result, the friction between the piston 1 and the inner wall surface of the cylinder bore can be reduced, and the gap between the piston 1 and the inner wall surface of the cylinder bore can be set small, so that blow-by gas can be reduced. In order to increase the rigidity of the piston 1, for example, a reinforcing member is used for each pin boss 5a, 5
It can also be achieved by mounting between b and the inner peripheral surface of the skirt portion 6. On the other hand, in this embodiment, the rigidity of the piston 1 is increased without providing a reinforcing member, and therefore the number of parts is not increased.

FIG. 3 and FIG. 4 show another embodiment. In this embodiment, components similar to those in the embodiment of FIGS. 1 and 2 are designated by the same reference numerals. Referring to FIGS. 3 and 4, in this example as well, the connection portions 5a and 5b have WC <WD.
It is formed so that. However, the wall thickness of each connecting portion 5a, 5b in the direction of the axis MM of the pin boss is made thinner than that of the example shown in FIGS. However,
Even if the wall thickness of each connection portion 5a, 5b in the direction of the axis MM of the pin boss is reduced, the connection portions 5a, 5 are set so that WC <WD.
If b is formed, the rigidity of the piston 1 in the direction of the axis MM of the pin boss can be increased, and therefore, in the present embodiment as well, it is possible to prevent the lip portion 1b from cracking.

By thus reducing the wall thickness of each of the connecting portions 5a and 5b, the weight of the piston 1 can be reduced. Therefore, in this embodiment, the weight of the piston 1 can be reduced while ensuring the rigidity of the piston 1. It will be possible. Other configurations and operations of the piston 1 are similar to those of the embodiment described with reference to FIGS.

FIG. 5 and FIG. 6 show another embodiment. Also in this embodiment, the same components as those of the embodiment of FIGS. 1 and 2 are indicated by the same numbers. With reference to FIGS. 5 and 6, the recess 3 is formed such that the center C of the outer peripheral edge 3 a of the recess 3 having a circular shape is eccentric from the axis L-L of the piston 1. That is, the center C of the outer peripheral edge 3a is located on the line of intersection between the longitudinal section K-K eccentric from the axis MM of the pin boss and the longitudinal section J-J eccentric from the vertical plane NN.

Also in this embodiment, the connecting portions 5a and 5b are formed so that WC <WD, but in this example, the connecting portions 5a and 5b are not formed symmetrically with respect to the vertical plane N--N. That is, the inner peripheral end of the connecting portion 5a and the inner peripheral end of the connecting portion 5b are arranged symmetrically with respect to the vertical cross section JJ. In a piston having a recess on the top surface, the rigidity of the top around the recess is usually low. Therefore, as in this embodiment, the center C of the outer peripheral edge 3a of the recess 3 is the axis L- of the piston 1.
When eccentric from L, the rigidity of the piston 1 in the direction perpendicular to the axis MM of the pin boss is improved by arranging the inner peripheral ends of the connecting portions 5a and 5b symmetrically with respect to the longitudinal section J-J. It can be improved well. Therefore, it is possible to prevent the lip portion 1b from being cracked. Other configurations and operations of the piston 1 are similar to those of the embodiment described with reference to FIGS.

In the above-described embodiments, the pin bosses 5a and 5b are arranged so that the axis MM of the pin boss is located on the axis LL of the piston 1. However, the axis MM of the pin boss is the axis LL of the piston 1.
The pin bosses 5a and 5b may be formed so as to be eccentric from each other. Further, in the embodiments described so far, the recess 3 is formed so that the opening cross section of the recess 3 is circular. However, the opening cross section of the recess 3 may not be circular.

[0017]

Since the rigidity of the piston can be increased, cracking of the piston can be prevented, and therefore the durability of the piston can be increased.

[Brief description of drawings]

FIG. 1 is a partial vertical sectional view of a piston.

2 is a cross-sectional view of the piston taken along the line II-II in FIG.

FIG. 3 is a partial vertical sectional view of a piston according to another embodiment.

4 is a sectional view of the piston taken along line IV-IV in FIG.

FIG. 5 is a partial vertical sectional view of a piston according to another embodiment.

6 is a cross-sectional view of the piston taken along line VI-VI in FIG.

FIG. 7 is a partial vertical cross-sectional view of a piston showing an unfavorable example.

8 is a cross-sectional view of the piston taken along the line VIII-VIII in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piston 1a ... Lip part 2 ... Top surface 3 ... Recessed part 4a, 4b ... Pin boss 5a, 5b ... Connection part 6 ... Skirt part L ... Piston axis M ... Pin boss axis

Claims (1)

[Claims] 1. A piston of an internal combustion engine having a recess on its top surface, wherein a pair of pin bosses for receiving piston pins are provided apart from each other in the axial direction of the pin boss,
The outer peripheral surface of each pin boss and the inner peripheral surface of the skirt portion of the piston are connected by a connecting portion, and the gap between these connecting portions in the axial direction of the pin boss is shorter than the width of the concave portion in the axial direction. A piston that has a connection.