649results about "Pistons" patented technology

The present invention relates to the technical field of forging, and particularly to an automated piston forging feeding robot. The automated piston forging feeding robot comprises a sliding mechanism, a supporting mechanism, a base, a telescopic mechanism, a pushing mechanism, and a gripping mechanism, wherein the sliding mechanism is fixedly mounted on a walking beam, the supporting mechanism is fixedly mounted at a lower end of the sliding mechanism, the base is movably mounted on the ground, the telescopic mechanism is fixedly mounted in the supporting mechanism, the pushing mechanism is fixedly mounted on the ground, and the gripping mechanism is fixedly mounted at a front end of the walking beam. The present invention solves the problems of the high maintenance costs and high energy consumption associated with existing hydraulic feeding methods, achieves the ejection of billets during device movement, and provides appropriate cooling to prevent sticking. When billet jumping occurs, the hydraulic feeding methods fail to grip a workpiece, which causes the workpiece to remain in a deviated state and results in a failure to correct the position of the workpiece for delivery to a forging area for further processing. The present invention suppresses billet jumping and corrects the position of the workpiece.

An internal combustion engine has a uniblock that defines a blind cylinder bore that terminates within the uniblock. A piston is inserted into the cylinder bore from a bottom end of the cylinder bore. Parallel first and second vertical planes extend along first and second lateral sides of the cylinder bore. A cylinder zone being defined between the first and second vertical planes. A crosshead is coupled to the piston. A first crankshaft has a first crankshaft axis that extends parallel to the first vertical plane and that is positioned outside of the cylinder zone. A second crankshaft has a second crankshaft axis that extends parallel to the second vertical plane and that is positioned outside of the cylinder zone. The first crankshaft is coupled to the crosshead with a first connecting rod and the second crankshaft is coupled to the crosshead with a second connecting rod.

The invention discloses a high-performance heterogeneously-welded special-shaped combustion chamber piston and a preparation method thereof, a special-basin-shaped combustion chamber and an oil duct structure are directly formed through a rolling process, and heterogeneously-connected between a head part and a skirt part of the piston is realized in combination with a nitrogen protection friction welding technology. The piston head is made of low-silicon high-chromium ferrite-based alloy, the skirt is made of quenched and tempered steel, non-quenched and tempered steel or nodular cast iron, and the welding face is designed to be in a wave shape so as to enhance the bonding strength. The preparation process comprises vacuum smelting, multi-pass rolling, precise welding and surface treatment, the combustion efficiency, the lightweight level and the reliability of the piston are remarkably improved, and the piston is suitable for high-load working conditions such as diesel engines and natural gas engines.

The invention relates to the technical field of engine casting molds, in particular to a cylinder sleeve limiting system of a high-pressure casting aluminum alloy slope type box, which comprises a mold, a core pulling device fixed on the mold and a limiting assembly connected in the mold in a sliding manner, and the core pulling device is used for driving the limiting assembly to axially move in a mold cavity; the limiting assembly comprises a sliding base connected to the mold in a sliding mode, a sliding block fixed to the sliding base and an insert fixed to the sliding block, and two symmetrically-arranged expansion blocks are connected to the insert in the diameter direction in a sliding mode. A cavity is formed in the center of the insert, an expansion pin is slidably connected into the cavity, and the expansion pin controls the end heads of the two expansion blocks to synchronously eject out or retract towards the peripheral face of the insert through axial movement. A channel is formed in the center of the expansion pin, an air inlet is formed in the sliding seat, one end of the channel is communicated with the cavity in the center of the insert, and the other end of the channel is communicated with the air inlet of the sliding seat. According to the scheme, the cylinder sleeve positioning precision of the engine box can be improved, and the casting process quality is guaranteed.

The invention provides a casting method of a copper-steel double-metal cylinder body, and belongs to the technical field of pump body part machining, the casting method comprises the following steps: pre-treating a steel substrate and a copper alloy, and then heating and preserving heat together; cooling is conducted, cooling is conducted in four stages, the blowing direction of the first stage cooling, the blowing direction of the third stage cooling and the blowing direction of the fourth stage cooling are all from bottom to top, the blowing direction of the second stage cooling is from top to bottom, and solidification of the molten copper is completed after the third stage cooling; and after cooling is completed, tempering treatment is conducted, and the copper-steel double-alloy cylinder body is obtained. In the cylinder body casting process, the heated cylinder body is subjected to multi-stage cooling, the gas blowing directions of different cooling stages are controlled, rapid solidification of molten copper can be achieved, the situation that the molten copper fluctuates is avoided, the solidification defect is effectively controlled, and a compact copper layer is obtained; and through the final-stage cooling and tempering process control, the matrix structure of the steel matrix is regulated and controlled, tempered sorbite is formed, and the mechanical property of the cylinder body is improved.

The invention relates to the technical field of engines, in particular to a piston combustion chamber for a diesel and natural gas engine and the engine, and the piston combustion chamber for the diesel and natural gas engine comprises an omega-shaped pit. The straight opening type omega-shaped pit structure is adopted, compared with a traditional ignition type combustion chamber, the ineffective conical volume in the center of the combustion chamber is removed, the top dead center injection diffusion combustion mode is better met, the air utilization rate is higher, the compression ratio is higher, and higher heat efficiency can be better achieved; compared with a traditional necking omega-shaped diesel engine combustion chamber, a plurality of necking structures are removed, the first annular concave face and the second annular concave face are designed, the characteristic of natural gas injection is better met, the front end space of flames is fully released, the air utilization rate is increased, the heat transfer loss is reduced, and the combustion efficiency and the heat efficiency are improved; due to the design of the large-curvature concave surface, the problems of heat load concentration and particle friction caused by a sharp structure can be avoided, and the problems of out-of-control combustion, knocking and engine damage are reduced.

The utility model discloses an inner cooling oil chamber, oil cooling piston and engine, including: inner cooling oil chamber body, including oil chamber body lower part and oil chamber body upper part, oil chamber body upper part at least includes first vortex area and second vortex area, first vortex area is closer to piston center than second vortex area, and the first vortex area is closer to piston center than second vortex area. The second vortex region is closer to the piston ring groove than the first vortex region. Engine oil is sprayed into the oil inlet channel through an engine oil pump and enters the inner cooling oil cavity body through the oil inlet channel. Along with rapid and high-frequency up-and-down movement of the piston, engine oil continuously collides with the upper wall face and the lower wall face of the inner cooling oil cavity body under the action of inertia force, part of the engine oil impacts the first vortex area to form a first vortex, and part of the engine oil impacts the second vortex area to form a second vortex. The contact area of engine oil and the inner cooling oil cavity body is increased, the flowing speed of the engine oil in the vortex area is higher, a better cooling effect is generated, the temperature of a piston can be more effectively reduced, and the phenomenon that the engine oil in the inner cooling oil cavity is coked is reduced.

A piston head includes a piston head lower portion and a piston head upper portion coupled to the piston head lower portion. The piston head upper portion includes an end wall, an outer wall, and an inner wall. The end wall includes, an outer portion and an inner portion, angled with respect to the outer portion. The outer wall extends axially away from the end wall in a first direction. The inner wall extends axially away from the end wall in the first direction and is separated from the outer wall such that an outer chamber is defined between the outer wall and the inner wall and an inner chamber is defined within the inner wall. The inner wall defines one or more openings fluidly connecting the inner chamber to the outer chamber. An axis of each of the one or more openings is substantially parallel to the inner portion.

The internal combustion engine piston comprises a piston body, an inner cooling oil cavity is formed in the piston body, a groove is formed in the top of the inner cooling oil cavity and extends upwards from the top of the inner cooling oil cavity, the groove is filled with a heat conduction block, and the heat conduction block is used for conducting heat of the part, located above the inner cooling oil cavity, of the piston body to the inner cooling oil cavity. The heat conductivity of the heat conduction block is higher than that of the piston body, so that more heat is transferred to the inner cooling oil cavity from the top of the piston in unit time, the heat transfer speed of the heat of the part, located above the inner cooling oil cavity, of the piston body to the inner cooling oil cavity is increased, the heat taking efficiency of engine oil is improved, and the piston cooling capacity of the inner cooling oil cavity is improved. The problems of abnormal temperature of the piston, carbon deposition, clamping stagnation of movement of the ring group and the like are avoided, and heat dissipation of the piston in the movement process is met.

The invention relates to the technical field of internal combustion engine pistons, in particular to an eccentric inner-cooling oil cavity piston, an eccentric combustion chamber is arranged at the top, the center line of the eccentric combustion chamber and the center line of the piston are offset by the distance L1, an inner-cooling oil cavity comprises an outer ring cavity and an inner ring cavity which are communicated with each other, and the center line of the outer ring cavity and the center line of the piston are collinear; the center line of the inner ring cavity and the center line of the eccentric combustion chamber are collinear. The weight of the piston can be effectively reduced, and the overall performance is improved. Meanwhile, the surface temperature of a piston combustion chamber part can be reduced, carbon deposition layers and oxide layers on the part are reduced, and the reliability and the service life of the piston are improved.

The invention provides a pure ammonia engine system and a control method thereof. The pure ammonia engine system comprises a cylinder block; the air cylinder cover covers the air cylinder body, and a combustion chamber is formed between the air cylinder cover and the air cylinder body; the glow plug comprises a heating body which extends into the combustion chamber from the center of the cylinder cover; the controller is configured to regulate and control the temperature of the hot surface of the heating body based on the operation condition of the pure ammonia engine system; the liquid ammonia ejector is inserted into the combustion chamber from the cylinder cover and is positioned on one side of the glow plug; the spark plug is inserted into the combustion chamber from the cylinder cover and is positioned on the other side, radially opposite to the liquid ammonia ejector, of the glow plug; a plurality of spraying hole sets are formed in the side, facing the heating body, of the end, extending into the combustion chamber, of the liquid ammonia ejector, so that part of liquid ammonia mist sprayed out of the liquid ammonia ejector is filled around the heating body to be ignited by a sparking plug.

The invention relates to powder, a method and a coating for cold spraying of combustion chamber parts of internal combustion engines, in particular to the technical field of internal combustion engines, and the powder comprises the following components in percentage by mass: 5-15% of stainless steel powder, 10-30% of ceramic powder and 55-85% of metal elementary substance powder; the D80 particle size of the stainless steel powder is larger than the D80 particle size of the ceramic powder and smaller than the D80 particle size of the metal elementary substance powder. According to the powder provided by the invention, through the design of the powder for cold spraying, an obtained coating has good corrosion resistance, and meanwhile, the bonding strength of the coating obtained through cold spraying and a combustion chamber part of a cast iron internal combustion engine can be effectively ensured, so that the obtained coating has good use performance.

The utility model belongs to the technical field of diesel engines, and relates to a hydrogen fuel single-cylinder engine which comprises a piston and a piston pit located at the end of the piston, and the piston pit is of a shallow-basin-shaped structure. The system further comprises a hydrogen inlet system and an electric control system, the hydrogen inlet system comprises a hydrogen sprayer, a hydrogen cylinder, a gas delivery pipe and a pressure increasing valve, the electric control system comprises a control unit, an electronic accelerator and a crankshaft position sensor, the hydrogen cylinder is communicated with the hydrogen sprayer through the gas delivery pipe, the hydrogen sprayer is communicated with the combustion chamber, and the pressure increasing valve is arranged on the gas delivery pipe. And the control unit is electrically connected with the hydrogen sprayer, the electronic throttle and the crankshaft position sensor respectively. The structure of the piston pit is improved, the electronic control gas injection system and the fuel oil injection system are adopted to replace a traditional pure fuel oil injection system, timing and quantification of hydrogen gas injection can be guaranteed, good economical efficiency is achieved, and the hydrogen gas replacement rate can reach about 90%; pollutant emission is greatly reduced, and low oil consumption is kept.

The invention provides a piston crown, a piston and a diesel engine, the piston crown comprises a piston outer surface layer, a piston inner surface layer and a filling layer, the piston outer surface layer and the piston inner surface layer define a containing space, and the containing space is filled with the filling layer; the filling layer comprises a plurality of crystal lattice structures, at least one liquid inlet and at least one liquid outlet which are communicated with the containing space are formed in the inner surface layer of the piston, and first cooling flow channels are formed among the liquid inlets, gaps among the crystal lattice structures in the filling layer and the liquid outlets; the first cooling flow channel is configured in the mode that cooling lubricating oil can flow into the containing space through the liquid inlet and flow to the liquid outlet through gaps between the lattice structures to flow out.

The utility model relates to the technical field of engine pistons, in particular to an engine piston which comprises a piston body, the piston body comprises a top, a head and a skirt, the top, a cylinder cover and a cylinder wall jointly form a combustion chamber, and a first piston groove, a second piston groove and a third piston groove are formed in the periphery of the head. The skirt part is provided with a connecting hole for connecting a piston bolt; piston ring check blocks are arranged in the first piston groove, the second piston groove and the third piston groove and arranged in a staggered mode. A first gas ring, a second gas ring and a combined ring are respectively clamped on the first piston groove, the second piston groove and the third piston groove; the combined ring comprises a detachable ring body, an upper scraping piece, a lower scraping piece and a lining spring, wherein the upper scraping piece and the lower scraping piece are arranged on the upper side and the lower side of the ring body respectively, and the lining spring is arranged in the ring body and used for providing axial elastic force. The problem that a piston ring in a traditional engine piston is troublesome to mount and dismount is solved.

The present application provides an engine piston connecting rod positioning and installation structure, belonging to the technical field of piston connecting rod positioning. The engine piston connecting rod positioning and installation structure includes a piston body, a connecting component and a positioning component. The big-end collar is arranged at the bottom of the connecting rod body. The small-end collar is movably sleeved on the piston pin. The positioning component includes a crankpin, a crank body and a positioning collar. A pin hole through which the crankpin can pass is formed in the crank body. There are two crank bodies symmetrically arranged with respect to the connecting rod body. The big-end collar is movably sleeved outside the middle end of the crankpin. The crankpin sequentially passes through the two pin holes. Two symmetric threaded portions are arranged on the surface of the crankpin. The positioning collar is arranged on both sides of each crank body. The positioning collar is threadedly sleeved on the corresponding threaded portion. The engine piston connecting rod positioning and installation structure facilitates the adjustment of the distance between the big-end collar and the crank body.

To provide an internal combustion engine that easily promotes mixing of spray and air.SOLUTION: An internal combustion engine comprises: a cylinder head; and a cavity formed in a top surface of a piston, and forming a combustion chamber between itself and the cylinder head. The cavity comprises: a first surface arranged in a top surface center part of the piston; a second surface arranged around the first surface, and arranged closer to the side of the cylinder head than the first surface; a groove part provided in the second surface, and recessed toward the side of the first surface; and a wall provided in the groove part on the side of the first surface, and separating a first space formed on the first surface, and a second space formed in the groove part. The wall includes a first slit connecting the first space and the second space.SELECTED DRAWING: Figure 3

A piston alignment tool for a cylinder liner and a piston, comprising: a body; an inner guide surface extending along an inner diameter of the body, the inner guide surface being configured to guide the piston with respect to an inner diameter of the cylinder liner; and an axially extending projection engagement tab extending from the body, the axially extending projection engagement tab being configured to cooperate with an outer periphery of the cylinder liner.

The utility model discloses a gasoline engine cylinder body piston wear-resisting structure which comprises a cylinder body, the cylinder body is provided with a piston rod, the surface of the cylinder body is fixedly connected with two installation frames, the two installation frames are distributed oppositely in the left-right direction, and the upper end and the lower end of the right surface of the installation frame located on the right side are fixedly connected with telescopic rods. A universal joint is fixedly connected between the right end of the telescopic rod and the right end of the piston rod, a protective sleeve is fixedly connected to the penetrating position of the piston rod on the right surface of the machine cylinder body, two grooves are formed in the inner wall of the protective sleeve, the two grooves are oppositely distributed left and right, the protective sleeve is divided into a sealing area and an impurity collecting area through the two grooves, and the sealing area is located in the machine cylinder body. A sponge gasket is arranged on the surface of the piston rod, and the left end and the right end of the sponge gasket make contact with the protective sleeve and the universal joint. Through the device, the stability of the cylinder piston is improved, and the influence of impurities and collision on the piston is reduced.

A piston (22) for an internal combustion engine (12) includes a piston skirt (64) and a piston crown (70) attached to the piston skirt and including a combustion face (72). The combustion face forms a piston rim (74) and a combustion bowl (78). A bowl rim (82) defines an intersection of the combustion bowl and the piston rim, and a reentry surface (84) defining a reentry angle extends between the bowl rim and the bowl outer wall. A ratio of a bowl depth dimension coincident with the piston central axis to a compressed height dimension coincident with the piston central axis is from about 0.30 to about 0.35.

The internal combustion engine piston capable of reducing abrasion comprises a piston body and a piston head, the piston body and the piston head are fixed, a piston ring groove is formed in the outer wall of the circumference of the piston head, a sealing ring is fixedly connected in the piston ring groove, a plurality of reinforcing rings are fixed in the piston head, the piston body comprises a high-temperature-resistant filling layer, and the high-temperature-resistant filling layer is arranged in the piston ring groove. A high-temperature-resistant filling layer is fixedly connected to the outer side of the plug body, a wear-resistant layer is fixedly connected to the outer side of the high-temperature-resistant filling layer, the high-temperature-resistant filling layer is made of aluminum alloy or nickel alloy, the wear-resistant layer is a dlc coating or a high-silicon aluminum alloy coating, and an assembly hole is formed in the bottom of the plug body. According to the wear-resistant piston, the high-temperature-resistant filling layer and the wear-resistant layer are matched for use, so that the piston body is more wear-resistant and high-temperature-resistant, the service life of the piston is prolonged, meanwhile, the piston and an external device can be connected more tightly through the sealing ring, and the piston head can be firmer and more durable through the reinforcing ring.

The invention relates to a combustion system, an engine and a vehicle. The combustion system comprises an air inlet channel, an exhaust channel, an air inlet valve, an exhaust valve, a cylinder cover, a cylinder sleeve and a piston, a cylinder cover combustion chamber is arranged in the combustion system, and at least one of the inner surface of the cylinder cover combustion chamber, the surface, facing the interior of the combustion system, of the air inlet valve, the surface, facing the interior of the combustion system, of the exhaust valve and the top surface of the piston is provided with a thermal barrier coating.

The utility model discloses a steel piston which is characterized in that an inclined oil hole platform is arranged at the bottom of an inner cavity of an inner cavity surface of a steel piston main body and protrudes out of the surface of the inner cavity surface, and an inclined oil hole communicated with a lubricating oil channel is formed in the inclined oil hole platform; cooling lubricating oil stored in the cooling oil cavity enters the contact faces of the connecting rod, the piston pin and the piston pin hole sequentially through the lubricating oil channel, the inclined oil hole and the oil hole in the connecting rod small end, the protruding inclined oil hole platform structure is easier to forge and form compared with a small pit structure, the blank manufacturing difficulty is lowered, and the machining efficiency is improved. The protruding inclined oil hole platform structure can better guide cooling lubricating oil in the cooling oil cavity to flow into the connecting rod and the piston pin, lubrication is provided for contact between the piston pin hole and the connecting rod and the piston pin, and the occlusion risk is effectively reduced. The lightweight design and the machining quality are both considered, and meanwhile the failure risk of the piston in an engine is reduced.

The dual-fuel engine piston capable of reducing methane emission comprises a piston body, a concave pit is formed in the top face of the piston body to serve as a combustion chamber, the top face of the piston body is connected with the side face of the piston body through a flow guide face, and the combustion chamber is communicated with the flow guide face through a plurality of vortex grooves. A set included angle is formed between the vortex groove and the tangent line of the outer circumference of the combustion chamber; according to the utility model, the flow guide surface is arranged between the piston top surface and the piston side surface, so that natural gas in the backlash can be guided into the combustion chamber for combustion, and methane emission is further reduced. A vortex groove is formed in the top face of the piston, natural gas in a side gap passes through a flow guide face to a motion chamber in a combustion chamber and inevitably passes through the vortex groove, airflow is guided by the vortex groove to form a certain vortex in a cylinder, later-stage combustion is accelerated, combustion is more sufficient, and methane emission is further reduced.

The utility model provides a piston, and relates to the technical field of pistons. The piston can comprise a body and a coating, and the body is provided with a peripheral face close to a cylinder sleeve. At least one groove is formed in the outer circumferential face of the body. The coating forms a latticed structure, and at least part of the coating is arranged in the groove and protrudes out of the peripheral face of the piston. The coating is of the latticed structure and protrudes out of the peripheral face, airflow is blocked and guided by grids and can form turbulent flow when passing through the area of the latticed structure, and complex and disordered airflow forms resistance relative to stable airflow, so that the blow-by amount is reduced. Besides, in the movement process of the piston, a part of engine oil can be stored in the latticed structure, and the upward movement of the engine oil can be reduced, so that the engine oil consumption is reduced. The coating is at least partially arranged in the groove, so that the binding force between the coating and the body can be increased, and the coating is prevented from falling off from the body in the piston movement process.

The present application relates to the field of diesel engine piston forging, in particular to a diesel engine piston material, a diesel engine piston and a preparation method and a forging die thereof. The diesel engine piston material provided by the present application comprises the following components: Si: 14.1-18.3 wt%; Ni: 1.6-3.2 wt%; Fe: 0.8-1.6 wt%; Mg: 0.3-0.6 wt%; Cr: 0.01-0.05 wt%; Zn: 0.06-0.3 wt%; Ti: 0.02-0.2 wt%; Zr: 0.07-0.2 wt%; V: 0.1-0.18 wt%; Al: balance. The piston material is applied to piston preparation, the layered temperature of the forging part is maintained during the forging process, the deformation and forming performance of the piston material is improved, the linear expansion coefficient is reduced, the volume stability is improved, the thermal deformation amount is reduced, and the service life of the piston is improved.

An engine system (S) includes an internal combustion engine (1) and a control unit (100). The internal combustion engine includes: a main chamber (5) defined by a piston (2), a cylinder (3), and a cylinder head (4); a spark plug (10) mounted on the cylinder head; a secondary chamber tube (11) surrounding the spark plug and protruding downward from the cylinder head; a secondary chamber hole (17) formed in the piston and capable of receiving the secondary chamber tube; and an injector (9) for injecting fuel supplied into the main chamber. The control unit ignites the spark plug when the secondary chamber tube is inserted into the secondary chamber hole, and injects fuel from the injector before the spark plug is ignited and before the secondary chamber tube is inserted into the secondary chamber hole.

The utility model relates to a multi-sparking plug ignition system, combustion chamber and gas engine, multi-sparking plug ignition system includes precombustion chamber and second sparking plug, precombustion chamber is provided in dome structure center, precombustion chamber is provided with first sparking plug, precombustion chamber is provided with a plurality of jet orifice at interval along the circumference, second sparking plug is provided with second sparking plug. At least one spray hole points to a high-frequency detonation area near an exhaust throat of an exhaust passage in the combustion chamber, the second spark plug and the pre-combustion chamber are arranged between the air inlet passage and the exhaust passage in a spaced mode, and the second spark plug is close to the edge of the dome structure. The high-speed jet jetted by the pre-combustion chamber in the multi-spark-plug ignition system enables flame to reach the edge of the combustion chamber as soon as possible, and the second spark plug can accelerate combustion in the nearby space, so that the multi-spark-plug ignition system can effectively improve the flame propagation speed, shorten the time for the flame to propagate to the edge of the combustion chamber and improve the combustion efficiency. Flame can reach the edge of a combustion chamber of an engine as soon as possible, and the aim of reducing the knocking tendency is achieved.

A ferrous piston for gasoline powered engines having dimensions which achieve reduced mass and improved performance is provided. The piston crown has a thickness of less than 4mm and includes valve pockets with an axial clearance between the valve pockets and an uppermost ring groove of less than 1.5mm. The pin bosses have an axial thickness of less than 3.7% of a bore diameter, which is the largest outer diameter of the piston, measured between a pin bore and the crown at 1mm from an inner face forming the pin bore. Each pin boss has a radial thickness of less than 3% of the bore diameter measured between the pin bore and a lower end of the pin boss. An undercrown surface presents a projected area of less than 45% of a total piston bore area, wherein the total piston bore area is πBD2 / 4, BD being the bore diameter.

The utility model is suitable for the field of pistons, and particularly relates to a novel piston which comprises a piston body, the piston body comprises a head portion and a skirt portion, the head portion is divided into a piston top face, a combustion chamber groove and an oil ring, and a round through hole is formed in the middle of the skirt portion. The piston top face, the combustion chamber groove and the skirt portion are provided with a plurality of circular pits, and an arch-shaped protrusion is arranged in the combustion chamber groove. A plurality of grooves are formed in the top surface of the piston and the combustion chamber groove, so that a lot of irregular turbulent flows and extrusion flows are formed when the piston sucks air, the effect of fully mixing fuel oil and air when an engine works is achieved, the fuel oil is burnt more fully, emission of harmful substances is effectively reduced, the pits are additionally formed in the skirt part, and the service life of the engine is prolonged. The pressure difference between the combustion chamber groove and the crankcase is reduced, upward movement of lubricating oil during exhaust of an engine is reduced, and consumption of the engine oil is reduced.