TECHNICAL FIELD

The present disclosure relates to a cylinder liner that is mounted on a cylinder block of an internal combustion engine and slidably accommodates a piston along the axial direction, and to a sealing structure for the cylinder liner.

BACKGROUND

In a water-cooled engine (internal combustion engine), a cooling water passage may be formed between an inner peripheral surface of a bore of a cylinder block and an outer peripheral surface of a cylinder liner (see Patent Document 1). The cylinder liner has a seal groove formed in an annular shape along the circumferential direction. By inserting an O-ring in the seal groove, the cooling water passage is sealed to prevent the leakage of cooling water.

The cylinder liner accommodates a piston slidably along the axial direction. The piston is connected to one longitudinal end of a connecting rod via a piston pin. The other longitudinal end of the connecting rod is connected to a crankshaft. During operation of the internal combustion engine, the piston performs a reciprocating motion along the axial direction. The reciprocating motion of the piston is converted to a rotational motion of the crankshaft by the piston pin and the connecting rod.

Due to the reciprocating motion of the piston and the rotational motion of the crankshaft, the cylinder liner is subjected to a thrust force from the piston toward the outside in the radial direction. The thrust force acts in a direction (thrust direction) perpendicular to the axis of the cylinder liner and the axis of the piston pin.

CITATION LIST

Patent Literature

Patent Document 1: JPH7-166954A

SUMMARY

Problems to be Solved

The cylinder liner moves in the thrust direction for a short time due to the thrust force generated by the piston. As the cylinder liner moves in the thrust direction for a short time, the volume in the thrust direction of a portion of the cooling water passage in the vicinity of the cooling-water-passage-side seal groove decreases, and cooling water is pushed from the vicinity portion in a direction away from the seal groove. If the flow velocity of cooling water pushed from the vicinity portion is too high, a negative pressure area may be generated in the cooling water passage, and cavitation may occur. If cavitation occurs frequently in the cooling water passage, the O-ring may wear out, and cooling water may leak from the cooling water passage.

To prevent cavitation from occurring and progressing in the cooling water passage, chemicals may be added to cooling water to form a film, but this may worsen the operating cost of the internal combustion engine because of the need to add the chemicals and to manage the adding process.

Patent Document 1 merely discloses the use of plating on the cylinder liner to prevent damage to the cylinder liner due to cavitation, but does not disclose any means to prevent the occurrence of cavitation.

In view of the above, an object of at least one embodiment of the present invention is to provide a cylinder liner that can suppress the occurrence of cavitation.

Solution to the Problems

(1) A cylinder liner according to at least one embodiment of the present invention is a cylinder liner mounted on a cylinder block of an internal combustion engine and slidably accommodating a piston along an axial direction. The cylinder liner comprises: a small diameter portion configured to form a cooling water passage between the small diameter portion and an inner peripheral surface of the cylinder block; a large diameter portion disposed adjacent to the small diameter portion in the axial direction and formed to have a larger diameter than the small diameter portion; and at least one seal groove formed on an outer peripheral surface of the large diameter portion in an annular shape along a circumferential direction. The large diameter portion includes a one-side wall portion formed between the cooling water passage and a cooling-water-passage-side seal groove which is a seal groove disposed closest to the cooling water passage in the axial direction, and an other-side wall portion disposed farther from the cooling water passage than the cooling-water-passage-side seal groove is in the axial direction. The one-side wall portion is configured to have, in at least part in a circumferential direction including a thrust direction of the piston, a larger distance to the inner peripheral surface of the cylinder block than a distance from the other-side wall portion to the inner peripheral surface of the cylinder block.

According to the above configuration (1), the one-side wall portion of the cylinder liner is configured to have, in at least part in the circumferential direction including the thrust direction of the piston, a larger distance to the inner peripheral surface of the cylinder block than the distance from the other-side wall portion to the inner peripheral surface of the cylinder block. In other words, a portion of the cooling water passage in the vicinity of the cooling-water-passage-side seal groove has a large volume in at least part in the circumferential direction including the thrust direction of the piston. Since the cylinder liner has a large volume in the vicinity portion to increase the volume of cooling water in the vicinity portion, the pressure applied to cooling water in the vicinity portion can be dispersed when the cylinder liner moves in the thrust direction for a short time. As a result, it is possible to suppress the increase in flow velocity of cooling water pushed from the vicinity portion. By suppressing the increase in flow velocity of cooling water pushed from the vicinity portion, the cylinder liner can suppress the occurrence of negative pressure area in the cooling water passage, and thus suppress the occurrence of cavitation.

(2) In some embodiments, in the cylinder liner described in the above (1), the one-side wall portion is configured to have, over the entire circumference in the circumferential direction, a larger distance to the inner peripheral surface of the cylinder block than a distance from the other-side wall portion to the inner peripheral surface of the cylinder block.

According to the above configuration (2), the one-side wall portion of the cylinder liner is configured to have, over the entire circumference in the circumferential direction, a larger distance to the inner peripheral surface of the cylinder block than the distance from the other-side wall portion to the inner peripheral surface of the cylinder block. Since the cylinder liner has a large volume in the vicinity portion to increase the volume of cooling water in the vicinity portion over the entire circumference in the circumferential direction, the pressure applied to cooling water in the vicinity portion can be dispersed even when the cylinder liner moves in the anti-thrust direction (direction opposite to the thrust direction) for a short time. As a result, it is possible to suppress the increase in flow velocity of cooling water pushed from the vicinity portion. By suppressing the increase in flow velocity of cooling water pushed from the vicinity portion over the entire circumference in the circumferential direction, the cylinder liner can suppress the occurrence of negative pressure area in the cooling water passage, and thus suppress the occurrence of cavitation over the entire circumference in the circumferential direction including the anti-thrust direction.

(3) In some embodiments, in the cylinder liner described in the above (1) or (2), the one-side wall portion has a cooling water passage side surface that faces the cooling water passage. The cooling water passage side surface is formed such that, in at least part in the circumferential direction including the thrust direction of the piston, a distance to the inner peripheral surface of the cylinder block gradually increases with an increase in distance from the seal groove.

According to the above configuration (3), the one-side wall portion of the cylinder liner has the cooling water passage side surface formed such that, in at least part in the circumferential direction including the thrust direction of the piston, a distance to the inner peripheral surface of the cylinder block gradually increases with an increase in distance from the seal groove. In other words, a portion of the cooling water passage contiguous with the portion in the vicinity of the cooling-water-passage-side seal groove has a gradual volume change in at least part in the circumferential direction including the thrust direction of the piston. Since the cylinder liner has a gradual volume change in the portion contiguous with the vicinity portion, cooling water in the vicinity portion can easily flow to the portion contiguous with the vicinity portion when the cylinder liner moves in the thrust direction for a short time. As a result, it is possible to suppress the increase in flow velocity of cooling water pushed from the vicinity portion. By suppressing the increase in flow velocity of cooling water pushed from the vicinity portion, the cylinder liner can suppress the occurrence of negative pressure area in the cooling water passage, and thus suppress the occurrence of cavitation.

(4) In some embodiments, in the cylinder liner described in the above (3), the cooling water passage side surface is formed such that, over the entire circumference in the circumferential direction, a distance to the inner peripheral surface of the cylinder block gradually increases with an increase in distance from the seal groove.

According to the above configuration (4), the one-side wall portion of the cylinder liner has the cooling water passage side surface formed such that, over the entire circumference in the circumferential direction, a distance to the inner peripheral surface of the cylinder block gradually increases with an increase in distance from the seal groove. Since the cylinder liner has a gradual volume change in the portion contiguous with the vicinity portion over the entire circumference in the circumferential direction, cooling water in the vicinity portion can easily flow to the portion contiguous with the vicinity portion even when the cylinder liner moves in the anti-thrust direction (direction opposite to thrust direction) for a short time. As a result, it is possible to suppress the increase in flow velocity of cooling water pushed from the vicinity portion. By suppressing the increase in flow velocity of cooling water pushed from the vicinity portion over the entire circumference in the circumferential direction, the cylinder liner can suppress the occurrence of negative pressure area in the cooling water passage, and thus suppress the occurrence of cavitation over the entire circumference in the circumferential direction including the anti-thrust direction.

(5) In some embodiments, the cylinder liner described in any one of the above (1) to (4) further comprises a seal member mounted on the cooling-water-passage-side seal groove. The seal member includes an O-ring, and a back-up ring disposed closer to the cooling water passage than the O-ring is. The back-up ring is configured to have, in at least part in the circumferential direction including the thrust direction of the piston, a smaller distance to the inner peripheral surface of the cylinder block than a distance from the one-side wall portion to the inner peripheral surface of the cylinder block.

If a distance between the inner peripheral surface of the cylinder block and the one-side wall portion is large, when the cylinder liner is mounted on the cylinder block, the O-ring can easily come out of the cooling-water-passage-side seal groove, which may reduce the workability of the mounting process.

According to the above configuration (5), the back-up ring is disposed closer to the cooling water passage than the O-ring is, and is configured to have, in at least part in the circumferential direction including the thrust direction of the piston, a smaller distance to the inner peripheral surface of the cylinder block than a distance from the one-side wall portion to the inner peripheral surface of the cylinder block. Thus, when the cylinder liner is mounted on the cylinder block, it is possible to prevent the O-ring from coming out of the cooling-water-passage-side seal groove. Thus, the back-up ring can improve the workability of mounting the cylinder liner on the cylinder block.

(6) A cylinder liner according to at least one embodiment of the present invention is a cylinder liner mounted on a cylinder block of an internal combustion engine and slidably accommodating a piston along an axial direction. The cylinder liner comprises: a small diameter portion configured to form a cooling water passage between the small diameter portion and an inner peripheral surface of the cylinder block; a large diameter portion disposed adjacent to the small diameter portion in the axial direction and formed to have a larger diameter than the small diameter portion; and at least one seal groove formed on an outer peripheral surface of the large diameter portion in an annular shape along a circumferential direction. The large diameter portion includes a one-side wall portion formed between the cooling water passage and a cooling-water-passage-side seal groove which is a seal groove disposed closest to the cooling water passage in the axial direction. The one-side wall portion has a cooling water passage side surface that faces the cooling water passage, and the cooling water passage side surface is formed such that, in at least part in a circumferential direction including a thrust direction of the piston, a distance to the inner peripheral surface of the cylinder block gradually increases with an increase in distance from the seal groove.

According to the above configuration (6), the one-side wall portion of the cylinder liner has the cooling water passage side surface formed such that, in at least part in the circumferential direction including the thrust direction of the piston, a distance to the inner peripheral surface of the cylinder block gradually increases with an increase in distance from the seal groove. In other words, a portion of the cooling water passage contiguous with the portion in the vicinity of the cooling-water-passage-side seal groove has a gradual volume change in at least part in the circumferential direction including the thrust direction of the piston. Since the cylinder liner has a gradual volume change in the portion contiguous with the vicinity portion, cooling water in the vicinity portion can easily flow to the portion contiguous with the vicinity portion when the cylinder liner moves in the thrust direction for a short time. As a result, it is possible to suppress the increase in flow velocity of cooling water pushed from the vicinity portion. By suppressing the increase in flow velocity of cooling water pushed from the vicinity portion, the cylinder liner can suppress the occurrence of negative pressure area in the cooling water passage, and thus suppress the occurrence of cavitation.

(7) In some embodiments, in the cylinder liner described in the above (6), the cooling water passage side surface is formed such that, over the entire circumference in the circumferential direction, a distance to the inner peripheral surface of the cylinder block gradually increases with an increase in distance from the seal groove.

According to the above configuration (7), the one-side wall portion of the cylinder liner has the cooling water passage side surface formed such that, over the entire circumference in the circumferential direction, a distance to the inner peripheral surface of the cylinder block gradually increases with an increase in distance from the seal groove. Since the cylinder liner has a gradual volume change in the portion contiguous with the vicinity portion over the entire circumference in the circumferential direction, cooling water in the vicinity portion can easily flow to the portion contiguous with the vicinity portion even when the cylinder liner moves in the anti-thrust direction (direction opposite to thrust direction) for a short time. As a result, it is possible to suppress the increase in flow velocity of cooling water pushed from the vicinity portion. By suppressing the increase in flow velocity of cooling water pushed from the vicinity portion over the entire circumference in the circumferential direction, the cylinder liner can suppress the occurrence of negative pressure area in the cooling water passage, and thus suppress the occurrence of cavitation over the entire circumference in the circumferential direction including the anti-thrust direction.

(8) A sealing structure for a cylinder liner according to at least one embodiment of the present invention is a sealing structure for a cylinder liner mounted on a cylinder block of an internal combustion engine. The sealing structure comprises: the cylinder block; the cylinder liner described in any one of the above (1) to (7); and a seal member mounted on the cooling-water-passage-side seal groove.

According to the above configuration (8), since the sealing structure for a cylinder liner includes the cylinder block, the cylinder liner, and the seal member, when a thrust force of the piston acts on the cylinder liner, the cylinder liner can suppress the increase in flow velocity of cooling water pushed from the vicinity portion, and thus suppress the occurrence of cavitation.

Advantageous Effects

At least one embodiment of the present invention provides a cylinder liner that can suppress the occurrence of cavitation.

