Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J1/00—Pistons; Trunk pistons; Plungers
  • F16J1/02—Bearing surfaces
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
  • F02F1/00—Cylinders; Cylinder heads 
  • F02F1/02—Cylinders; Cylinder heads  having cooling means
  • F02F1/10—Cylinders; Cylinder heads  having cooling means for liquid cooling
  • F02F1/16—Cylinder liners of wet type
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
  • F02F1/00—Cylinders; Cylinder heads 
  • F02F1/18—Other cylinders
  • F02F1/22—Other cylinders characterised by having ports in cylinder wall for scavenging or charging
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J10/00—Engine or like cylinders; Features of hollow, e.g. cylindrical, bodies in general
  • F16J10/02—Cylinders designed to receive moving pistons or plungers
  • F16J10/04—Running faces; Liners
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B75/00—Other engines
  • F02B75/02—Engines characterised by their cycles, e.g. six-stroke
  • F02B2075/022—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle
  • F02B2075/025—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle two

Definitions

• the present invention relates to a cylinder liner for an internal combustion engine, particularly a two- stroke crosshead engine, having a piston which is movable in the liner in its longitudinal direction between a bottom dead centre, at which scavenging air ports in the wall of the cylinder liner are exposed above the top surface of the piston, and a top dead centre, at which the piston is in its top position in the cylinder liner, the piston being provided with several piston rings, the outer surfaces of which slide along the inner surface of the liner, the cylinder liner being provided with several recesses in its inner surface, said recesses forming gas flow connections between the spaces above and below a piston ring being positioned opposite the recesses.
• a cylinder liner of this type is known from JP-A 62-26346, which, with a view to reduction of the pressure drop across the top piston ring and achievement of uniform pressure drops across all piston rings, prescribes that the inner surface of the cylinder liner should be provided with recesses.
• the recesses are of a considerable depth and have an extent in the longi ⁇ tudinal direction of the liner which is only slightly larger than the height of a piston ring.
• These recesses act as small chambers, which are filled with compressed air during the compression stroke of the piston, which air is passed into the annular space below the piston ring after its passage and thus increases the pressure below the piston ring so that the pressure drop across the piston ring is smaller during the continued upward piston movement. It is mentioned as an advantage of this known cylinder liner that the filling of the spaces between the piston rings with clean compressed air counteracts dirtying of annular grooves and of the inner liner surface.
• the object of the present invention is to improve the operating conditions for and the life of the piston rings and the liner in a manner which only has a small negative effect on engine efficiency.
• the cylinder liner according to the invention is characterized in that at least some of the recesses are opposite to the top piston ring when the piston is at its top dead centre, and that, seen in the longitudinal direction of the liner, the individual recesses have an extent of at least twice the height of the top piston ring.
• the position of the recesses in the inner liner surface with a location opposite to the top piston ring when the piston is at its top dead centre means that the strong pressure increase caused by initiation of the combustion in the combustion chamber above the piston results in a leakage flow of combustion gas through the recesses and down below the upper piston ring or rings so that the pressure difference across it or them is reduced at the very time of the engine cycle when the pressure difference is largest. This provides an effective reduction of the ring and liner wear.
• the piston rings slide on a section of the liner where there are no recesses and thus no flow of leakage gas.
• the cylinder liner according to the invention thus provides the advantage that the pressure in the combustion chamber which is important to the engine efficiency only leaks down below the piston rings at the piston positions near the top dead centre where there are recesses in the liner inner surface opposite to the rings.
• Another advantage obtained is that the heat supply to the material around the recesses is smaller, because the combustion gas only flows through the recesses during a relatively small part of the engine cycle.
• the forming of recesses with lengths substantially longer than the height of the top piston ring causes the combustion gas to flow past the piston ring/rings over a longer period of time, and as the volume of the spaces between the piston rings is not influenced by the design of the recesses, a desired reduction of the pressure differences across the piston rings can be achieved by a smaller volume flow of leakage gas per time unit.
• the leakage area of the recesses can be made advantageously small, which further limits the local heat influence on the liner material around the recesses and reduces the stress concentrations occurring in this material .
• the top piston ring By locating the recesses acting as leakage grooves in the inner liner surface, at least the top piston ring can be formed without such leakage grooves, thus obviating a diminution in strength of the piston rings and simplifying the manufacture of the rings.
• the liner material can withstand higher temperatures than the piston rings, and contrary to the piston rings, the material of the upper section of the liner is normally cooled by cooling bores removing the heat supplied to the material.
• the location of the recesses in the upper section of the inner liner surface furthermore provides the advantage that the recesses are in a liner area where the nominal stress level is compressive stresses owing to heat stresses produced by the high temperature level at the start of the combustion. This substantially reduces the risk of formation of fatigue cracks in the material around the recesses. It is a further advantage of the invention that the cylinder liner is usually worn at a substantially slower rate than the piston rings, and thus the recesses will maintain a leakage area of a desired size for a longer time than when leakage grooves are provided in the outer surface of the piston rings .
• the liner is provided with at least three groups of recesses, of which the recesses of the first group are opposite to the top piston ring, the recesses in the second group are opposite to the second piston ring from the top and are displaced in the circumferential direction of the liner in relation to the recesses of the other groups, and the recesses of the third group are opposite to the third piston ring from the top when the piston is at its top dead centre, and the recesses in the second group extend over a liner length section in which the recesses of the first and the third groups are located at least partial ⁇ ly.
• the three groups of recesses enable controlled leakage of combustion gas past not only the top piston ring, but also the two subjacent piston rings, and thus control of the pressure differences across these three piston rings.
• the recesses of the second group ensure continuous leakage of combustion gas down below the top piston ring while it is moved down past the area with the recesses at the downward movement of the piston.
• the circumferential displacement of the recesses of the second group in relation to the other recesses forces the leakage gas flowing past a piston ring to flow in the circumferential direction before the flowing continues, if possible, down below the subjacent piston ring.
• This extension of the flow path cools the leakage gas and produces an advantageous pressure loss in the gas by the flow from one to the other group of recesses .
• the division of recesses into groups also provides the advantage that the leakage volumes are reduced stepwise when the lower surfaces of the piston rings pass down past the lower ends of the recesses in the various groups at the movement of the piston away from the top dead centre.
• the recesses of the third group are located in continuation of the recesses of the first group with a mutual separation in the longitudinal direction of the recesses larger than the height of the second piston ring from the top.
• the second piston ring from the top is opposite to the separation between the recesses of the first and third groups and interrupts the direct flow connection from the combustion chamber down below the third piston ring from the top.
• having the recesses in two groups located in continuation of each other provides manufacturing advantages.
• At at least one longitudinal position of the liner there may suitably be at least four, preferably at least eight recesses distributed over the periphery of the liner, these recesses, seen in the circumferential direction, belonging alternately to the second group and either the first or the third group. Distribution of the total leakage area on more recesses reduces the cross- sectional area of the individual recess and distributes the heat influence from the leakage gas to several positions so that the local heating becomes lower. Insertion of a recess belonging to the second group between the recesses belonging to either the first or the third group depending on the relevant longitudinal position in the liner, produces the above advantageously long flow path for the gas flows through all recesses.
• the liner may be formed so that none of the recesses extends below the bottom piston ring when the piston is at its top dead centre.
• the ring pack on the piston provides full downward cutoff of the combustion chamber, and the leakage gas only flows down below the three uppermost piston rings during the relatively short period when they are opposite to the recesses.
• the recesses only form gas flow connections past one or more of the three uppermost piston rings, while the piston is located between the top dead centre at 0 crank degrees and piston positions which range between 15 and 20 degrees crank angle before or after the top dead centre for the top piston ring, between 10 and 15 degrees crank angle for the second piston ring from the top and between 5 and 8 degrees crank angle for the third piston ring from the top.
• the full movement of the piston from the top dead centre to the bottom dead centre occurs from 0 to 180 degrees crank angle, and it appears from the above degree intervals that the recesses may advantageously be located in the very top section of the inner surface of the cylinder liner.
• the leakage area A formed by the recesses for gas flow past the top piston ring is in the
• the pressure difference across the piston ring becomes unsuitably large, which results in high flow velocities for the leakage gas with consequent increased thermal loads in the material around the recesses as well as relatively heavy wear on the ring and the liner. If the leakage area becomes larger than D 2/2000 mm2 , the pressure difference across the piston ring becomes so small that the piston ring can only with difficulty seal tightly against the inner surface of the cylinder liner with the result that an important part of the combustion pressure above the piston risks escaping past the piston ring.
• an upper section of the cylinder liner may be provided with cooling bores, the longitudinal axes of which extend obliquely in relation to the longitudinal axis of the liner.
• the longitudinal axis of each recess preferably extends substantially in parallel with the longitudinal axis of the adjacent cooling bore. This recess course promotes removal of the heat supplied by the leakage gas so that the temperature level in the material around the recesses is kept suitably low and as far as possible at the same level along the entire length of the recesses.
• Said EP patent publication describes how the cooling intensity of the individual cooling bore can be con ⁇ trolled by mounting or dismounting of a screen cutting off the coolant from a section of the cooling bore closest to the inner surface of the liner. If the recesses extend immediately opposite to a cooling bore, the screen in the cooling bore may be removed in the section opposite to the recess so that the cooling here is stronger than in the areas without a nearby recess .
• the liner according to the invention can be further developed so that the cylinder liner has several cooling bores evenly distributed over the periphery of the liner, that each recess extends at substantially the same distance from the two most nearby cooling bores of the evenly distrib- uted cooling bores, and that opposite to the recesses supplementary cooling bores are provided in the areas between the evenly distributed cooling bores.
• the supplementary cooling bores may remove the amount of heat supplied to the material around the recesses.
• the supplementary cooling bores opposite to the recesses belonging to the first group preferably extend higher up in the wall of the liner than the evenly distributed cooling bores.
• Fig. 1 is a partial longitudinal section showing an outline of a cylinder liner according to the inven ⁇ tion
• Fig. 2 is a longitudinal sectional view in a larger scale of an upper section of the cylinder liner mounted in the engine
• Fig. 3 is a developed view of a segment of the upper section of the cylinder liner with recesses in its inner surface, a part of a piston at the top dead centre being inserted in the left-hand side of the figure, and a longitudinal section with a projecting cooling bore being inserted in the right-hand side of the figure
• Fig. 4 shows enlarged segments of the liner areas around the recesses of Fig. 3,
• Fig. 5 is a cross-sectional view through the cylinder liner according to the invention, and Fig. 6 in a larger scale shows a segment indicated by the circle S in Fig. 5 of the wall part around a recess.
• Fig. 1 shows a cylinder liner generally designated 1 for a large two-stroke crosshead engine to be used as a stationary engine for operation of a power generator or as a propulsion engine of a ship.
• the cylinder liner may be manufactured in different sizes with cylinder bores typically ranging from 250 mm to 1000 mm, and corresponding typical lengths ranging from 1000 mm to 4500 mm.
• the liner is normally manufactured in cast iron, and it may be integral or divided into two or more parts assembled end to end. In case of the divided liner it is also possible to manufacture the upper part in steel.
• Crosshead engines of said type are developed towards very high effective compression ratios, such as 1:16 to 1:20, which entail heavy loads on the piston rings.
• the liner half to the right of the longitudinal axis 2 is shown in a longitudinal section.
• the liner can be mounted in the engine, only partially shown, by an annular downward surface 3 being positioned on the top plate 4 in the framebox or cylinder block of the engine, whereupon a piston 5 is mounted in the cylinder liner, and a cylinder cover 6 is arranged on top of the liner on its annular, upward surface 7 and clamped onto the top plate by means of cover studs, not shown.
• the lower section of the cylinder liner has an annular row of scavenging air ports 8.
• the piston is movable in the longitudinal direction of the liner between a top dead centre where the piston upper surface 9 is located in a bore in the cylinder cover 6 (see Fig. 2) at a position marked A in Fig. 1, and a bottom dead centre where the piston upper surface 9 is immediately below the lower end of the scavenging air ports at a position marked B.
• the piston is connected with the crankshaft of the engine in a well-known manner. For each time the crankshaft carries out a rotation of 360°, the piston is moved from the bottom dead centre to the top dead centre and back again. Thus there is an unambiguous connection between the angular position of the crank ⁇ shaft and the position of the piston in the cylinder liner. If the angular position corresponding to the top dead centre of the piston is designated 0 degrees crank angle, the downward piston movement to the bottom dead centre occurs in the course of the subsequent 180 degrees crank angle.
• the inner liner surface is provided with a wave-shaped lubricating oil track 11 supplied with lubricating oil through supply holes 12 for lubrication of the running surface of the inner surface 13 of the liner.
• the cylinder liner 1 In the upper section located between surfaces 3 and 7, the cylinder liner 1 is formed with a larger external diameter, and at the top of this section a number of longitudinal cooling bores 14 are bored into the liner wall from an external recess 15 so that the longitudinal axes of the straight cooling bores have an oblique or skew course in relation to the longitudinal axis 2 of the liner.
• a pipe or guide plate In each cooling bore, a pipe or guide plate is inserted for guiding the in-flowing coolant from the recess 15 to the upper dead end of the bore, from where the coolant flows downwards and out into a chamber 16, from where the coolant is passed up into the cylinder cover via pipes 17. It should be noted that the cooling bores of Fig.
• Fig. 2 shows the piston 5 at the top dead centre.
• the piston is provided with four piston rings, of which the top piston ring 19 is preferably of a gastight type, viz., the cut of the ring shown at 20 in Fig. 5 is formed so that gas is substantially prevented from flowing through the ring cut.
• This may be effected, for example by designing the ring with mutually overlapping ring ends, by one end of the ring having a flat project ⁇ ing tongue projecting into a corresponding recess in the other end of the ring.
• the tongue and the recess have a smaller radial width than the piston ring so that on the inner surface of the ring, a wall portion covers the recess and prevents gas from flowing through.
• the second piston ring 21 from the top, the third piston ring 22 from the top and the bottom piston ring 23 are usual rings the cut of which is formed as a gap extending obliquely in the circumferential direction from the upper to the lower ring surface.
• the gap in the third piston ring from the top extends obliquely in the opposite direction of the gaps in the second piston ring from the top and the bottom piston ring.
• the ring may be of the same type as the subjacent piston rings 21-23.
• the outer ring surfaces sliding along the inner liner surface 13 are smooth and can be formed without leakage grooves .
• piston rings means piston compression-rings.
• the piston rings are opposite to an upper section of the inner liner surface, which section is designated 24 in Fig. 1.
• Fig. 3 shows this section in a larger scale.
• the inner liner surface is provided with a first group of recesses 25 opposite to and extending past the top piston ring 19, and with a second group of recesses 26 opposite to and extending past the second piston ring 21 from the top, and with a third group of recesses 27 opposite to and extending past the third piston ring 22 from the top when the piston is at its top dead centre as shown.
• the longi- tudinal positions in the liner corresponding to the middle of the piston rings at the top dead centre are marked by lines designated 19', 21', 22' and 23' in Fig. 4.
• the longitudinal axes of the recesses have an oblique or skew course in relation to the longitudinal axis 2 of the liner similarly to the cooling bores 14 with the result that the recesses extend substantially in parallel with the adjacent cooling bores. It is also seen that none of the recesses extends below the bottom piston ring 23.
• the recesses 27 in the third group extend in parallel with and in continuation of the recesses 25 of the first group, but with a mutual separation 28, which may advantageously be larger than the height of the second piston ring 21 from the top, but need not be so.
• the recesses 26 of the second group are longer than the other recesses to provide a continuous gas leakage past the top piston ring 19 until the latter has moved down to the lower end of the recesses 27.
• the segment in the right-hand side of Fig. 4 shows an example of the possibility that at least one of the recesses 27 extends further down in the liner than the other recesses of the third group so that the flow of leakage gas through the recesses 27 is interrupted and opened stepwise.
• hot combustion gas flows from the combustion chamber above the piston down through the recesses 25 to the annular space between the piston rings 19 and 21 located between the outer piston surface and the liner inner surface 13.
• the gas can flow in the circumferential direction to the recesses 26 and onwards down into the annular space between the piston rings 21 and 22, from where the gas can again flow in the circumferential direction and via the recesses 27 reach down to the annular space between piston rings 22 and 23.
• the gas can flow through the ring cuts in piston rings 21-23 and possibly also through the ring cut of the top piston ring 19, if it is not of a gastight type.
• the leakage volumes will be reduced as the piston rings pass the lower ends of the recesses 27.
• the cooling bores 14 are evenly distributed along the periphery of the liner, and each of the recesses 25-
• supplementary cooling bore 14' has been bored for removing the heat supplied from the flow of leakage gas through the recesses 26.
• a supplementary cooling bore 14' ' has been bored to remove the heat supplied from the flow of leakage gas through recesses 25 and 27.
• the cooling bores 14'' extend higher up in the liner wall than the cooling bores 14. It is possible to place recesses 25-27 immediately opposite to the evenly distributed cooling bores 14 to avoid manufacturing the supplementary cooling bores.
• the cross-sectional view shown in Fig. 5 extends in the piston immediately above the top piston ring 19 and in the liner at a slightly lower level so that the upper ends of the cooling bores are seen in the cross- section.
• the piston itself is omitted from the figure.
• the first group has four recesses 25 evenly distributed along the periphery of the liner and, right between these, four recesses 26 of the second group. Below the recesses 25 there are four recesses 27 of the third group. It is obvious that each group may have fewer, for example two, or more, such as six, eight, ten or twelve recesses.
• the number is adapted to the desired cross-sectional area of the individual recess and to the desired maximum leakage area for gas flow past the top piston ring. If the top piston ring is not of a gastight type, the cross- sectional area of the gap at the ring cut positioned outside of the piston must be included in the desired maximum leakage area with the result that the inner liner surface can be formed with fewer recesses.
• cylinder liner 1 shown in Fig. 5 has an internal diameter of 600 mm, it may be suitable in case of four recesses in each group to give each recess a cross-
• the liner with the recesses according to the invention can also be manufactured on the basis of a cylinder liner already put to use.
• recesses 25-27 can be machined into the inner liner surface opposite to and longitudinally to the already existing cooling bores.
• the recesses can extend in parallel with the longitudinal axis 2 of the liner.
• the liner may also be formed with only one or with more than three groups of recesses.
• One or more of the recesses may be at a lower level than the bottom piston ring when the piston is at its top dead centre, but no advantages are gained by having the recesses further down in the liner than the oil distribution track 11.
• the cylinder liner according to the invention can also be used for other types of engines than those described above, for example for a four-stroke medium- speed engine with no cooling bores inside the liner wall .

Landscapes

• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• Pistons, Piston Rings, And Cylinders (AREA)
• Cylinder Crankcases Of Internal Combustion Engines (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8094786

Family Applications (1)

Country Status (9)

Cited By (8)

Families Citing this family (5)

Citations (3)

• 1996
  • 1996-05-07 DK DK199600547A patent/DK173116B1/da not_active IP Right Cessation
• 1997
  • 1997-04-28 WO PCT/DK1997/000191 patent/WO1997042406A1/en not_active Application Discontinuation
  • 1997-04-28 CN CN97194448A patent/CN1081739C/zh not_active Expired - Fee Related
  • 1997-04-28 KR KR1019980708746A patent/KR20000010686A/ko not_active Application Discontinuation
  • 1997-04-28 GB GB9823276A patent/GB2326446B/en not_active Expired - Fee Related
  • 1997-04-28 AU AU27632/97A patent/AU2763297A/en not_active Abandoned
  • 1997-04-28 TW TW086105550A patent/TW384356B/zh not_active IP Right Cessation
  • 1997-04-28 JP JP9539439A patent/JP2000509460A/ja not_active Ceased
  • 1997-05-06 HR HR970228A patent/HRP970228A2/hr not_active Application Discontinuation

Patent Citations (3)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events