PISTON AND PISTON RING ASSEMBLY

Abstract: A piston ring assembly consists of an upper ring and a lower ring. Said upper ring and lower ring have a common axis, an outer toward common annular surface, and inner toward common annular surface and mutual contact surfaces. Said two contact surfaces keep to contact with each other in a contact section which has radially an outer end and an inner end. Said tow contact surfaces stretch radially oppositely from said outer end to form a first wedge space, the vertex of which being in the outer end and, with said outer toward common annular surface. The vertex angle is about 1030□. The distance between said outer end and said outer toward common annular surface is greater than the distance between said inner end and said inner toward common annular surface. The present invention also includes a piston wherein said piston ring assembly is being used.

Description: Technical Field The present invention relates to a piston and a piston ring. Related Art There is a conventional piston comprising a couple of seal rings including an upper ring and a lower ring, such as disclosed in document US-A-2938758. The piston reciprocates up and down in a cylinder having a cylindrical wall, on which the rings slide while being lubricated by oil. As the lower ring slides down, it scrapes or wipes from the wall some of the oil that accumulates under the outer lower edge of the lower ring and builds up a high pressure. In the meanwhile, an annular gap is generated between the lower annular side surface of the lower ring and the upper annular wall of a ring groove formed in the piston for receiving the upper and lower rings. A combustion chamber is usually provided between the top of the piston and the cylinder. The accumulated oil is squeezed under the high pressure into the combustion chamber through the annular gap and a back gap provided between the inner cylindrical surface of the rings and the bottom of the groove. Thus, the oil is burnt out in the chamber, which pollutes the atmosphere in addition to a waste of oil. Summary of the Invention Therefore, it is an object of the invention to provide a pair of sealing rings having a better performance for sealing combustion gas and oil. It is another object of the invention to provide a pair of sealing rings for releasing a built-up pressure in scraped oil. According to the present invention, there is provided a pair of sealing rings comprising an upper sealing ring and a lower sealing ring; wherein the rings have a common axis, a common outer cylindrical surface, a common inner cylindrical surface, and a pair of facing surfaces; wherein the facing surfaces contact one another along a radially extending part of the sealing rings to form an engaging length having a radially outer end and a radially inner end; wherein the facing surfaces and the common outer cylindrical surface define between them a wedge-shaped gap with a radially inwardly directed leading edge at the outer end of said engaging length; and wherein the outer end of said engaging length is spaced further from the common outer cylindrical surface than from the common inner cylindrical surface; characterised in that the radially inwardly directed leading edge defines an angle in a range of from 10 seconds to 1 degree and 30 seconds. Brief Description of the Drawings Figure 1 shows an axial section of a piston provided in a ring groove with a pair of seal rings according to the present invention; Figure 2 shows a top view of an arrangement of the sealing rings of Figure 1; Figure 3 shows an embodiment according to the present invention; Figure 4 shows a preferred arrangement of sealing rings; and Figure 5 shows a partially broken away section of Figure 3 illustrating an operation of the embodiment. Detailed Description of the Embodiments Figures 1 and 2, which are not according to the present invention, show a piston 8 including a first ring groove for receiving a couple of gas-sealing upper and lower rings 1 and 2 and a second ring groove for receiving an oil-scraper ring 10. In plan view, the upper sealing ring 1 has a rectangular cutout, while the lower sealing ring 2 has a radially stepped cutout, and they are so arranged side by side that their cutouts are disposed diametrically opposite to each other (as shown in Figure 2). The piston reciprocates up and down in a cylinder, which defines a combustion chamber above the top of the piston. Specifically, the lower sealing ring 2 has an outer lower edge, which scrapes or wipes oil from a cylindrical wall of the cylinder as the piston moves down. The scraped oil flows into the cavity 7 as shown, while a lateral gap 9 is generated between the underside of the lower sealing ring 2 and the lower wall of the groove. As the cavity is recessed adjacent the lower wall surface of the first ring groove or the lateral gap, or it has a narrower section at the apex of the recess, the pressure is so distributed in the cavity that the notch 5 of the lower ring 2 contains a higher pressure than the notch 6 formed in the piston 8. As the scraped oil flows through the narrowed section of the cavity under the differential pressure from the notch 5 to the notch 6, the lateral gap 9 is subjected to a reduced pressure that sucks from the lateral gap 9 the oil accumulated therein so as to prevent the oil from running into the combustion chamber. On the other hand, the cavity is designed to have a sufficient volume for freely accumulating any oil which may be scraped, so that there is not a high pressure built up in the cavity 7. Thus, the scraped oil will not be forced into the combustion chamber through the gaps bypassing the rings in the groove. As a result, the present invention is provided with a decreased waste of oil and a reduced pollution. In a prior art technical solution, a piston is provided with a pair of conventional seal rings. Because of a limited interface for heat exchange, the rings are subject to a high temperature and a poor lubrication so that they would be worn out frequently. It will be appreciated the present invention is provided with a reduced friction between the cylinder wall and the sealing rings and a reduced consumption of oil and gasoline, and hence a substantially more efficient dynamic performance. As the present invention provides an efficient heat dissipation or transfer from the piston and the sealing rings, and a better lubrication between the rings and the cylinder wall, the present rings have a life twice as long as that of a conventional one. A preferred embodiment of the present invention will be described in detailed as follows. As shown in Figure 3, a piston is provided with a pair of gas-sealing rings and an oil-scraper ring. The gas-sealing rings are received in a first groove formed in the piston, with their cutouts arranged diametrically opposite to each other and staggered away from a gudgeon pin of the piston. As shown in Figure 4, this embodiment is provided with a pair of gas-sealing rings comprising an upper ring 1 and a lower ring 2, both of which constitute a rectangular radial section when assembled onto a piston. A wedge-shaped gap is formed between the rings radially inward from their outer cylindrical surfaces, with an angle in a range of from 10 seconds to 1 degree and 30 seconds. It is preferable that such an angle is in a range of from 30 seconds to 1 degree and 30 seconds, or more preferably from 10 seconds to 1 degree. On the other hand, it is still preferable that another wedge-shaped gap is formed between the rings radially outward from their inner cylindrical surfaces, with an angle in a range of from 2 degrees to 7 degrees and 30 seconds, more preferably from 2 to 6 degrees. Thus, there are two wedge-shaped gaps 22 and 23 in a radial section of the sealing rings, with their acute apexes being pointed radially to each other. The radially outer gap has a greater radial length than the inner one. It is preferable that the former is at least 10 times as long radially as the latter. Furthermore, in order to allow the upper and lower sealing rings to pivot somewhat against each other, there is a pivot provided between the acute apexes. Obviously, the pivot is radially nearer to the inner cylindrical surface of the pair of sealing rings than the outer one. Another embodiment of the present invention comprises an upper ring 1 constituting a polygonal radial section and a lower ring 2 assuming a rectangular radial section. There is another annular gap 9' provided between the upper side surface of the upper ring and the upper wall of the groove, and a back gap 9" formed between the rings and the radial bottom of the groove. In an engine according to the present invention, the present piston and seal rings operate in the following manner: In an induction stroke, as the piston returns from a top dead centre point of a working cycle at the conclusion of an exhaust stroke, the piston moves towards a bottom dead centre point thereof, while the upper ring 1 squeezes out the deposited carbon from the gap 9'. At the same time, the upper side surface of the upper sealing ring and the lower side surface of the lower sealing ring, being engaged with the upper and lower walls of the groove, form sealing means for blocking any substantial oil flow into the back gap 9" from the lateral gap 9. In the present stroke, the sealing rings and the ring groove automatically form a sealing means for blocking any leakage of combustion gas from the combustion chamber and oil into the chamber. In a compression stroke, the piston moves from the bottom dead centre point to the top dead centre point, after the induction stoke is completed, while the lower ring 2 squeezes oil outward radially to the cylinder wall from the lateral gap 9. The lower side surface of the lower sealing ring 2 and the lower wall of the groove are urged against each other to form a sealing means, while the radially inner upper edge of the upper ring 1 is urged against the upper wall of the groove to form another sealing means, with those sealing means cutting off any substantial leakage of air compressed in the chamber. In a power stroke, after the compression stroke is finished, the piston moves down from the top dead centre point to the bottom dead centre point. As a mixture of air and gasoline is ignited in the combustion chamber, there is a sharply increased pressure in the chamber, which applies onto the top of the piston and the upper side surface of the upper sealing ring. This certainly results in a high pressure in the back gap 9", which urges the upper sealing ring against the cylinder wall to prevent the ring from floating or vibrating, avoiding any substantial leakage of combustion gas. In an exhaust stroke, after the power stroke is ended, as the piston moves up from the bottom dead centre point to the top dead centre point, the sealing rings operate in the same manner as in the compression stroke. It is obvious from the above illustration of those strokes that as there is a clearance provided respectively between the groove walls and the seal rings, the upper and lower rings 1 and 2 is movable with respect to the piston or the groove to form sealing means for presenting any substantial leakage of oil into the chamber and gas therefrom. Furthermore, the present rings will have a long life and an excellent performance.

Claims: A pair of sealing rings comprising an upper sealing ring (1) and a lower sealing ring (2); wherein the rings have a common axis, a common outer cylindrical surface, a common inner cylindrical surface, and a pair of facing surfaces; wherein the facing surfaces contact one another along a radially extending part of the sealing rings (1, 2) to form an engaging length having a radially outer end and a radially inner end; wherein the facing surfaces and the common outer cylindrical surface define between them a wedge-shaped gap (22) with a radially inwardly directed leading edge at the outer end of said engaging length; and wherein the outer end of said engaging length is spaced further from the common outer cylindrical surface than from the common inner cylindrical surface; characterised in that the radially inwardly directed leading edge defines an angle in a range of from 10 seconds to 1 degree and 30 seconds. A pair of sealing rings according to claim 1, wherein the facing surfaces define a second wedge-shaped gap (23) with a radially outwardly directed leading edge at the inner end of said engaging length, wherein the radially outwardly directed leading edge defines a second angle in a range of from 2 degrees to 7 degrees 30 seconds. A pair of sealing rings according to claim 1 or 2, wherein the first mentioned angle is in the range of from 10 seconds to 1 degree. A pair of sealing rings according to any one of claims 1 to 3, wherein the second angle is in a range of from 2 to 6 degrees. A pair of sealing rings according to any one of claims 1 to 4, wherein the first mentioned wedge-shaped gap has a radial length at least 10 times as great as that of the second wedge-shaped gap.

Inventors: WANG BAODONG, ZHU ZHIHONG, WANG, BAODONG, ZHU, ZHIHONG
Applicants: WANG BAODONG, ZHU ZHIHONG, WANG, BAODONG, ZHU, ZHIHONG
Application year: 2000
Main classification: F02F5
IPC codes: F02F5, F02F3, F16J9, F16J1