This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2019-233460, filed on Dec. 24, 2019, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a piston.
A piston reciprocates in a bore of an internal combustion engine. The piston and the bore are lubricated to reduce friction. There is a technique in which a wavy groove provided in a circumferential direction on a surface of a piston skirt suppresses oil from leaking in the circumferential direction (for example, Japanese Unexamined Patent Application Publication No. 2008-231972).
However, oil might leak upward from the piston due to the reciprocating motion of the piston. The leaked oil might enter a combustion chamber and burn together with fuel or the like. This might increase oil consumption and degrade exhaust emission.
An object of the present disclosure is to provide a piston capable of suppressing oil leakage. It is therefore an object of the present disclosure to provide a piston including: a piston head; and a piston skirt connected to the piston head, wherein the piston skirt includes wall portions protruding outward from a surface of the piston skirt, the wall portions adjacent to each other in a circumferential direction of the piston skirt are inclined in directions opposite to each other with respect to a direction of movement of the piston in a bore for the piston, and define a tapered portion, and the tapered portions are spaced away from each other in the circumferential direction of the piston skirt.
Hereinafter, a description will be given of a piston according to the present embodiment with reference to the drawings. First, a description will be given of an internal combustion engine to which a piston is assembled.
The cylinder head 11 is mounted on the cylinder block 12. The oil pan 30 is disposed below the cylinder block 12. The crankshaft 16 is housed in the cylinder block 12. An ignition plug 18 and a fuel injection valve 29 are provided in the cylinder head 11.
One end of the connecting rod 15 is connected to the piston 14 by a pin 17, and the other end is connected to the crankshaft 16. The piston 14 is slidably housed in a bore 19 of the cylinder block 12. A combustion chamber 13 is defined in the bore 19 by the piston 14. A direction in which the pin 17 is inserted is defined as a Y-axis direction. A direction of movement of the piston 14 is defined as a Z-axis direction. A direction perpendicular to the Y-axis direction and the Z-axis direction is defined as an X-axis direction. One side in the Z-axis direction may be described as an upper side, and the other side in the Z-axis direction may be described as a lower side.
An intake passage 20 and an exhaust passage 21 are connected to the cylinder head 11. The intake passage 20 is provided with an air cleaner 22 and a throttle valve 24 in order from the upstream side, and may further be provided with an air flow meter and the like. A catalyst 25 is provided in the exhaust passage 21.
Intake air flowing through the intake passage 20 is purified by the air cleaner 22, and is introduced into the combustion chamber 13 when an intake valve 26 opens. The fuel injection valve 29 injects fuel into the combustion chamber 13. The ignition plug 18 ignites an air-fuel mixture. When an exhaust valve 27 opens, exhaust gas generated by combustion is discharged to the exhaust passage 21. The catalyst 25 is, for example, a three-way catalyst and purifies the exhaust gas.
Combustion in the combustion chamber 13 causes the piston 14 to move downward, and then power is transmitted from the piston 14 to the crankshaft 16 through the connecting rod 15. Rotation of the crankshaft 16 and combustion in the combustion chamber 13 cause the piston 14 to reciprocate upward and downward in the bore 19.
Oil maintains lubrication between the piston 14 and an inner wall of the bore 19. Oil is stored in the oil pan 30 and is pumped from the oil pan 30 by an oil pump 32. An oil supply unit 34 is, for example, an oil jet or the like, and injects oil supplied from the oil pump 32 into the combustion chamber 13.
As illustrated in
The piston skirt 46 is connected below the piston head 48 and is located at both sides with respect to the X axis. When the piston 14 is disposed in the bore 19, the grooves 40 to 42 are located at the combustion chamber 13 side in the piston, and the piston skirt 46 is located on the side opposite to the combustion chamber 13. The hole 47 illustrated in
When the piston 14 reciprocates in the bore 19 in the vertical direction, the piston rings 43 to 45 push oil upward and remove oil downward. A part of oil is dropped into the oil pan 30 illustrated in
If oil leaks from gaps between the piston rings 43 to 45 and the inner wall portions of the grooves 40 to 42 of the piston 14 toward the combustion chamber 13 when the piston 14 moves from the upper side to the lower side, the oil burns together with intake air and the like in the combustion chamber 13. This makes it difficult to reuse oil to increase oil consumption. Also, the burning of oil might increase pollutants in the exhaust gas.
In the present embodiment, in order to reduce oil consumption and improve exhaust emission, the piston skirt 46 is provided with wall portions 50 as illustrated in
The wall portions 50a and 50b adjacent to each other define the tapered portion 52. An upper end portion of the wall portion 50a and an upper end portion of the wall portion 50b are connected to each other, and define an upper end portion 54 of the tapered portion 52. A lower end portion of the wall portion 50a and a lower end portion of the wall portion 50b are separated from each other, and define a lower end portion 55 of the tapered portion 52. The upper end portion 54 of the tapered portion 52 is located at the upper end portion of the piston skirt 46. The lower end portion 55 of the tapered portion 52 is located at the lower end portion of the piston skirt 46. The tapered portion 52 has a V shape that tapers upward and widens downward. A gap 56 is defined between the two lower end portions 55 of the tapered portion 52.
The tapered portions 52 are arranged in the circumferential direction of the piston skirt 46. The tapered portions 52 adjacent to each other are separated from each other, extend upward away from each other, and extend downward close to each other. A gap 57 is defined between the upper end portions 54 of the adjacent tapered portions 52. A gap 58 is defined between the lower end portions 55 of the adjacent tapered portions 52.
A distance L1 between the upper end portions 54 of the adjacent tapered portions 52 is greater than the width W1 of the wall portion 50 in the Y-axis direction. The distance L1 is greater than a distance L2 between the lower end portions 55 of the adjacent tapered portions 52. The distance L1 is greater than a distance L4 of the gap 56 in the tapered portion 52. The distance L1 is, for example, 5 to 10 times the width W1. The distance L2 between the lower end portions 55 of the adjacent tapered portions 52 is smaller than the distance L1. The distance L2 is smaller than the distance L4. The distance L2 is, for example, half or less, one third or less, quarter or less of the distance L1. A decrease in the distance L2 suppresses oil leakage toward the combustion chamber 13 as described later. A length L3 of the tapered portion 52 in the Z-axis direction is, for example, equal to the length of the piston skirt 46.
The distance L1 is, for example, 500 μm. The distance L2 between the lower end portions 55 is, for example, 200 μm. The length L3 of the piston skirt 46 is, for example, 25 mm. The length of the piston head 48 is, for example, 20 mm. The width W1 of the wall portion 50 is, for example, not less than 50 μm and not more than 100 μm. A diameter of the piston 14 is, for example, 80 mm.
Next, the flow of oil when the piston 14 moves will be described. When the piston 14 moves from the upper side to the lower side in the bore 19, oil does not tend to flow from the lower side to the upper side. When the piston 14 moves from the lower side to the upper side in the bore 19, oil tends to flow from the upper side to the lower side.
Details will be described. The wall portion 50a and the wall portion 50b are connected to each other at the upper end portion 54 of the tapered portion 52. The upper end portions 54 of the adjacent tapered portions 52 are separated from each other with the gap 57 therebetween. The distance L1 between the upper end portions 54 is greater than the distance L2 between the lower end portions 55. Therefore, when the piston 14 moves upward from the lower side, oil tends to flow from the upper side to the lower side through the gap 57 between the tapered portions 52. A part of oil flows downward from the gap 58 to the oil pan 30 and is reused.
On the other hand, the distance L2 between the lower end portions 55 of the adjacent tapered portions 52 is smaller than the distance L1 between the upper end portions 54. For this reason, when the piston 14 moves downward from the upper side, oil does not tend to flow into the narrow gap 58, which suppresses oil from flowing upward. Oil flowing through the gap 56 is blocked by the wall portion 50. Thus, oil does not tend to flow upward from the lower side, which suppresses oil leakage toward the combustion chamber 13.
According to the present embodiment, the piston skirt 46 is provided with the wall portions 50a and 50b. The wall portion 50a and the wall portion 50b are inclined in directions opposite to each other, are connected to each other at the combustion chamber 13 side of the piston 14, and are separated from each other at a side opposite to the combustion chamber 13, thereby defining the tapered portion 52. The tapered portions 52 are separated from each other. The gap 58 between the lower end portions 55 of the adjacent tapered portions 52 is smaller than the gap 57 between the upper end portions 54 thereof. Thus, when the piston 14 moves from the upper side to the lower side, oil does not tend to flow upward from the gap 58. This suppresses oil leakage above the piston skirt 46. Oil does not tend to enter the combustion chamber 13. It is thus possible to reduce oil consumption and suppress deterioration of exhaust emission.
The wall portions 50a and 50b may be separated from each other at the upper end portion 54 of the tapered portion 52, and a small gap smaller than the gap 58 may be generated between the wall portions 50a and 50b. However, when the gap at the upper end portion 54 increases, the tapered portion 52 comes to have a vertically symmetrical shape. In this case, a degree to which oil flows from the upper side to the lower side might be comparable to a degree to which oil flows from the lower side to the upper side, so that it might difficult to suppress oil leakage. Therefore, as illustrated in
If the gap 58 between the lower end portions 55 is wide, oil tends to flow upward from the gap 58. In order to make it difficult for oil to flow, the tapered portions 52 are made close to each other so as to narrow the gap 58. The distance L2 between the lower end portions 55 (the width of the gap 58) may be smaller than each of the distance L1 between the upper end portions 54 and the distance L4 of the gap 56. The distance L2 may be, for example, not more than half of the distance L1, not more than one third thereof, not more than quarter thereof. The narrowing of the gap 58 effectively suppresses oil leakage toward the combustion chamber 13.
The inclination angle θ of the wall portion 50a with respect to the Z-axis direction is, for example, 15 degrees, and may be 10 degrees to 30 degrees. The inclination angle of the wall portion 50b is −0, and the magnitude of the inclination angle thereof is equal to the magnitude of the inclination angle of the wall portion 50a. The inclination angle θ approaches the inclination angle (i) of the groove 36 on the inner wall of the bore 19 with respect to the X-axis direction, so that the tapered portion 52 tends to catch oil.
The number of the tapered portions 52 is two or more, and may be, for example, five or more. Particularly, as illustrated in
However, as illustrated in
As illustrated in
As illustrated in
The height H1 of the wall portion 50 is adjusted by controlling the conditions of the cutting process. The height H1 may be equal to or greater than a thickness of the oil film formed between the surface 46a of the piston skirt 46 and the inner wall of the bore 19. For example, if the thickness of the oil film is several tens μm, the height H1 may be set to 100 μm to 200 μm. The wall portion 50 blocks oil flow.
In the example of
Although some embodiments of the present disclosure have been described in detail, the present disclosure is not limited to the specific embodiments but may be varied or changed within the scope of the present disclosure as claimed.
Number | Date | Country | Kind |
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2019-233460 | Dec 2019 | JP | national |