Internal combustion engine

Abstract

An internal combustion engine (10) comprising a cylinder head (11), a piston (20) and an engine block (12). The piston (20) is slideably mounted in a cylinder bore (16) in the engine block (12) or a cylinder liner (14) therein for reciprocating between a top dead centre (TDC) at a top of the cylinder bore (16) and a bottom dead centre at a bottom of the cylinder bore (16). The cylinder bore (16) comprises a cylinder wall (15) and at least one pocket (40) is recessed into the cylinder wall (15) for controlling the flow of oil during reciprocation of the piston (20).

Description

[0001]Description INTERNAL COMBUSTION ENGINE Technical Field This disclosure relates to an internal combustion engine, and more specifically to an internal combustion engine having at least one pocket in the cylinder wall for the control of oil. Background Internal combustion engine design continues to evolve to increase fuel economy and reduce emissions, such as with increased power density, hybridisation and changes in combustion strategies. The evolving engine operation and technologies change boundary conditions between the engine components and the oil. This can lead to changes to the traditional operating conditions the lubricating oil is exposed to, such as low soot contamination, longer oil drain intervals and exposure to higher temperatures and pressures for sustained periods within the combustion area. Therefore, matching the engine technology to the oil formulation performance capability is pivotal to ensure that no additional / increased risk of current failure modes occur. Many of the technologies implemented on internal combustion engines to control emissions are, in particular, leading to higher temperatures or prolonged time at high temperature at or near the top piston ring turn around (TRTA) location of the bore or liner. These may include the use of alternative fuels and conventional fuels with downsizing or down speeding, for example. The hotter TRTA means that oil, particularly on the cylinder wall, can cause uncontrolled combustion, in addition to increasing oil consumption. There is also an increased risk of volatisation of key lubricant additives due to the hotter TRTA. These individually can result in unwanted emissions and / or increased engine wear. US20120132069A1 discloses a cylinder bore for minimizing the friction loss including a plurality of oil pockets formed on stroke sections that contact a piston on an interior circumference of the cylinder bore. The oil pockets are formed by a laser honing method and have different shapes over the stroke sections or different shapes over the stroke sections according to stroke speeds. Moreover, the oil pockets have a structure such that more oils can be supplied to an upper stroke section or to a lower stroke section than to a centre stroke section of the cylinder bore. Furthermore, the oil pockets are formed symmetrically with respect to a centre stroke section of the cylinder bore. An object of the present disclosure is to improve the operation of an internal combustion engine with higher top ring turnaround temperatures. A further object is to prevent uncontrolled combustion due to oil in or near the combustion chamber. A further object is to control the consumption of oil and its effect on emissions. A further object is to control the consumption of certain additives to the oil, particularly resulting from the volatisation and / or combustion of such additives. A further object is to ensure that the oil can control and reduce the wear between the piston ring and bore or liner. A further object is to improve the use of oil as a seal to control blowby flow rate. The present disclosure therefore provides an internal combustion engine and method in accordance with the claims. This disclosure relates to controlling the way in which oil is distributed across and along a bore / liner, in some embodiments this can be considered oil flow axially or circumferentially, or a combination thereof, along the bore / liner. This may include oil splash, the oil film distribution due to the piston ring motion, the oil present on the liner / bore honing. Throughout this document the dynamic behaviour of the mass distribution of oil along the bore / liner is considered to be oil flow. Thus, the present disclosure relates to controlling the oil flow, or the way in which the oil is distributed across and along the bore / liner in or near the TRTA location, particularly to overcome the aforementioned technical problems related to novel engine technologies. By controlling oil flow along the bore / liner through optimised surface texturing of the bore / liner using a pattern of oil reservoir pockets, oil flow close to or into a combustion chamber can be controlled and / or prevented. This inhibits oil induced abnormal combustion (improving operation, particularly of internal combustion engines using alternative fuels and the like) reduces oil consumption and reduces additive consumption (thereby reducing wear). An additional benefit may be improving the time for a full oil film to form, thereby allowing the use of low viscosity oils to reduce friction losses. Furthermore, the risk of oil failure modes associated with high power density architectures can be reduced. In certain embodiments the oil film between the bore / liner and piston rings seal the combustion chamber. In certain cases, if that seal is disrupted, blowby gases can flow past the ring, which can both lead to increased emissions as well as disrupt piston ring dynamics. This seal can be made more robust through the use of the surface texture pockets outlined below. Using the surface texture pockets the seal can be optimised for controlling emissions without increasing frictional losses. Using pockets near the ring reversal points, the speed at which an oil film develops can be increased, ensuring the seal between the piston ring and the liner is further enhanced, leading to further control of piston ring dynamics. This can be further improved through optimising the piston ring end gap and surface texture together, to minimise blowby gases. The present disclosure provides an internal combustion engine. The internal combustion engine comprising a cylinder head, a piston and an engine block. The engine block has a cylinder bore therein and in which the piston is slideably mounted for reciprocating between a top dead centre (TDC) at a top of the cylinder bore and a bottom dead centre at a bottom of the cylinder bore. The cylinder bore comprising a cylinder wall. At least one pocket is recessed into the cylinder wall for controlling the flow of oil during reciprocation of the piston. The present disclosure further provides a cylinder liner for an internal combustion engine. The cylinder liner comprises a cylinder bore therein and the internal combustion engine comprises a cylinder head, a piston and an engine block for locating the cylinder liner therein. The piston is slideably mounted in the cylinder bore for reciprocating between a top dead centre (TDC) at a top of the cylinder bore and a bottom dead centre at a bottom of the cylinder bore. The cylinder bore comprises a cylinder wall into which at least one pocket is recessed for controlling the flow of oil during reciprocation of the piston. The present disclosure further provides an engine block for an internal combustion engine. The engine block comprises a cylinder bore therein and the internal combustion engine comprises a cylinder head and a piston. The piston is slideably mounted in the cylinder bore for reciprocating between a top dead centre (TDC) at a top of the cylinder bore and a bottom dead centre at a bottom of the cylinder bore. The cylinder bore comprises a cylinder wall into which at least one pocket is recessed for controlling the flow of oil during reciprocation of the piston. Brief Description of the Drawings By way of example only, embodiments of the present disclosure are now described with reference to, and as shown in, the accompanying drawings, in which: FIGURE 1 is a cross-sectional view of a portion of the internal combustion engine of the present disclosure, in particular showing a top portion of a cylinder thereof, in which the piston is at a top dead centre position; FIGURES 2 to 4 are schematic two-dimensional views of different embodiments of the layout of pockets on the cylinder wall of the engine of Figure 1; FIGURES 5 to 7 are schematic cross-sectional views of different embodiments of pockets extending into the depth of the cylinder wall of the engine of Figure 1 and / or the pockets of Figures 2 to 4; FIGURE 8 is a schematic cross-sectional view of the engine of Figure 1 illustrating the area and location of pockets of the piston and cylinder wall around a top piston ring when the piston is at top dead centre, in which the pockets may comprise the features of any of Figures 2 to 7; FIGURE 9 is a schematic plan view illustrating (exaggerated) distortion of the cylinder wall and bore of the engine of Figure 1 when in use; and FIGURE 10 is a schematic cross-sectional view of the engine of Figure 1 illustrating the area and location of pockets of the piston and cylinder wall around a top piston ring when the piston is at bottom dead centre, in which the pockets may comprise the features of any of Figures 2 to 7. Detailed The ensuing description provides preferred exemplary embodiment(s) only, and is not intended to limit the scope, applicability, or configuration of the invention. Rather, the ensuing description of the preferred exemplary embodiment(s) will provide those skilled in the art with an enabling description for implementing a preferred exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements, including combinations of features from different embodiments, without departing from the scope of the invention. Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that embodiments may be practised without these specific details. For example, well- known processes, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments. It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and / or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. This flexibility is required in practise to allow the implementation of the technique in different iterations to allow the technology to be targeted at the intended use, varying for engine architectures, application usage patterns, or alternative fuels. Figure 1 illustrates a partial cross section of a portion of an internal combustion engine 10, such as a diesel engine. The internal combustion engine 10 may provide power to various types of applications and / or machines. For example, the internal combustion engine 10 may power a generator or a vehicle such as an off-highway machine, a railway locomotive, an earth-moving machine, such as a wheel loader, excavator, dump truck, backhoe, motor grader, material handler. The internal combustion engine 10 includes a cylinder head 11 attached to an engine block 12. The engine block 12 has a cylinder bore 16 therein to form a cylinder or cylinder assembly. The cylinder bore 16 may be formed by a cylinder liner 14 as illustrated. The engine block 12 may include a chamber that forms a liner bore 13, which is lined with the cylinder liner 14. The cylinder liner 14 includes an interior surface or cylinder wall 15 that defines the cylinder bore 16. Alternatively, if the engine 10 does not comprise a cylinder liner 14, the cylinder bore 16 may be formed directly in the engine block 12. For example, in Figure 1 the cylinder liner 14 is not present and the cylinder bore 16 is the same as the liner bore 13, with the cylinder wall 15 being formed by the engine block 12 itself. The cylinder bore 16 is configured to house a piston 20 slideably mounted therein that, during operation of the engine 10, reciprocally moves within the cylinder bore 16. The piston 20 reciprocates, in use, between a top dead centre (TDC) position at a top of the cylinder bore 16 (as illustrated in Figure 1) and a bottom dead centre (BDC) position at a bottom of the cylinder bore 16. The volume defined between the cylinder bore 16, the cylinder head 11, and the piston 20 forms a combustion chamber 21. In the combustion chamber 21, a mixture of air and fuel is burned providing the power to drive the piston 20 away from the cylinder head 11. The cylinder head 11 includes at least one valve 22 that allows for one or more functions selected from intake of air into the combustion chamber 21, intake of fuel into the combustion chamber 21, and expulsion of exhaust gases from the combustion chamber 21. Suitable types of internal combustion engines include spark ignition engines or compression ignition engines (e.g., a diesel fuel engine or a natural gas fuelled engine). In addition there can be dual fuelled engines such as those using both liquid and gas fuel types. The internal combustion engine 10 may include any number of cylinders. Each of the cylinders of the internal combustion engine 10 may individually have a single cylinder head 11. Alternatively, two or more cylinders may be associated with the cylinder head 11. The engine 10 further comprises at least one piston ring 30, 31, including a top ring 30, mounted to the piston 20. The at least one piston ring 30, 31 may comprise at least one further ring 31. A single further ring 31 is illustrated, although further rings 31 may be distributed along the piston. The at least one piston ring 30, 31 extends around the circumference of the piston 20 and may be located closer to the top or crown of the piston 20 than the opposing end of the piston 20. The at least one piston ring 30, 31 is in contact with the cylinder wall 15 for sliding there along, assisted by oil lubrication. The piston 20 may not generally contact the cylinder wall 15 when in use, since the at least one piston ring 30, 31 separates them from one another. The top ring 30 may be a compression ring for sealing the combustion chamber such that gases cannot substantially escape the combustion chamber around the top ring 30 or piston 20 during the power stroke. The at least one further ring 31 may be a compression ring for sealing cylinder gas, a scraper ring for managing the oil film on the cylinder wall 15 and / or an oil control ring for lubricating the cylinder walls and allowing heat to dissipate. The at least one piston ring 30, 31 may comprise any suitable material and ring geometry, such as by being keystone, trapezoidal, barrel-faced, rectangular (as illustrated), inside bevel and / or taper-faced in shape. The oil may be supplied to the piston and cylinder bore 16 through any known means, such as by rifled bores in connecting rods or piston crown and / or piston colling jets. A top land 32 may separate the top of the piston 20 from the top ring 30 and a second land 33 extends below the top ring 30. The second land 33 may in particular extend to the further ring 31. Third and onwards lands 34 may separate further ring(s) 31 from the bottom of the piston. The top ring 30 is located in a top groove 35 around the outer circumference of the piston 20 and the top land 32 may extend between the top of the piston 20 and the top edge of the top groove 35. The at least one further ring 31 is located in at least one further groove 36, which may be separated from the adjacent grooves 35, 36 by the second, third or further lands 33, 34. As the piston 20 reciprocates within the cylinder bore 16, the at least one piston ring 30, 31 contacts the cylinder wall 15. The at least one piston ring 30, 31 typically deforms during such contact and has a different shape depending upon the direction and speed of travel of the piston 20. For example, each piston ring 30, 31 will be pushed towards the bottom of each groove 35, 36 during upward travel and pushed towards the top of each groove 35, 36 during downward travel. Hence the ring contact area 38 will vary in shape at in different stages of the engine cycle. A ring contact area 38 is the area of contact between the piston ring 30, 31 and cylinder wall 15. The ring contact area 38 under such deformation can be determined or estimated through modelling and calculation, such as by using the RINGPAK software offered by Realis Simulation Ltd in the United Kingdom. The present disclosure is generally directed to controlling the flow of oil to, above and / or around the top ring 30, particularly in response to higher TRTA temperatures. The cylinder wall 15, whether formed by the cylinder liner 14 or directly by the engine block 12, comprises at least one pocket 40 for controlling the flow of oil during reciprocation of the piston 20. The at least one pocket 40 is a recess, or concave bowl, in the cylinder wall 15 and may be formed in the cylinder liner 14 or in the engine block 12. The at least one pocket 40 may be formed by laser etching or other manufacturing technique, for example. The at least one pocket 40 may be configured to control the flow of oil so that it is distributed to where it is needed for lubrication and so that uncontrolled combustion of the oil is prevented or minimised. The at least one pocket 40 may act as a reservoir of oil and may be configured for oil to enter and / or be retained therein as the piston 20 passes the at least one pocket 40. In particular, the at least one pocket 40 may be configured so as to control, reduce and / or prevent the flow of oil up the cylinder wall 15 above the location of top ring 30 when the piston 20 is at TDC (i.e. the top ring turnaround location, TRTA). As a result, the amount of oil available for uncontrolled combustion in the combustion chamber 21 is minimised. Alternatively, the at least one pocket 40 may be configured so as to control, reduce and / or prevent the flow of gas from the combustion chamber down the cylinder liner / bore, thereby controlling blowby flow rates. The pocket 40 may be configured to control the gas flow rate from the combustion chamber down the cylinder / bore in effort to control the piston ring interland pressures, and thereby control the piston ring dynamics. Finally the one pocket 40 may be configured such that the bore / liner lobing, or bore / liner distortion, is such to enable increased conformity in geometry between the piston ring and liner / bore. The at least one pocket 40 may be fabricated in accordance with the design of the at least one piston ring 30, 31 and may in particular provide lubrication to the top piston ring 30 to decrease frictional losses in the engine 10. For example, the piston ring may be designed to have a specific contact area between the piston ring and bore / liner. The pocket 40 may then be designed to ensure a geometry and / or surface area of less than, or more than, the contact area between the piston ring and bore / liner interface. The exact relationship between the piston ring design and bore / liner interface may be different dependent on the location of the pocket on the stroke to control the oil flow to that where needed for lubrication purposes, but not so high as to allow the oil to affect combustion. Figure 2 to 4 illustrate exemplary embodiments of two-dimensional views of patterns of the at least one pocket 40 extending along the height H of the cylinder wall 15 (i.e. the dimension along the direction of reciprocation of the piston 200) and along the width W of the cylinder wall 15 (i.e. the dimension around the surface of the cylinder wall 15 perpendicular to the height). The at least one pocket 40 extends into the depth D of the cylinder wall 15. Each pocket 40 extends along a pocket width PW, a pocket height PH and a pocket depth PD. The at least one pocket 40 may comprise a plurality of pockets 40 arranged in an array 45, which may comprise at least one row of adjacent pockets 40 extending around the circumference of the cylinder wall 15. The arrays 45 of Figures 2 and 3 comprise one row whilst the array of Figure 4 comprises two rows. The pockets 40 may have the same spacing therebetween around the or each row of the array 45, or the spacing may vary, as discussed further in respect of Figure 9 below. The spacing may also be regular (i.e. the same spacing or spacing that varies in a regular manner) or irregular (i.e. with no substantial pattern to a variation in spacing). The spacing between the pockets 40 needs to be suitable to avoid disrupting the oil film whilst controlling the amount of oil directed above the top ring 30 at TDC. The distance around the width W of the cylinder wall 15 between adjacent pockets 40 may be of a similar magnitude, or larger, than the pocket sizes (such as pocket heights PH) themselves. If the array 45 comprises a plurality of rows, the distance along the height H of the cylinder wall 15 between adjacent rows may be of a similar magnitude, or larger, than the pocket sizes (such as pocket heights PH) themselves.. The array 45 may extend across an array height AH. The array height AH is the height of a single pocket 40 if the array 45 comprises one row. If the array 45 comprises a plurality of rows extending along the height H of the cylinder wall 15, the array height AH is the height between the top of the pockets 40 in the top row and the bottom of the pockets 40 in the bottom row. The pocket depth PD may be in the range of from about 1 micron to about 100 microns. The pocket height PH and / or pocket width PW may in the range of from about 1 micron to about 1 mm or about 2 mm. The pockets 40 may each have the same shape in the array 45. Alternatively, the pockets 40 may have different shapes around the array 45, particularly if certain areas around the circumference of the cylinder wall 15 have different oil control requirements (for example due to bore distortion, as discussed further below in respect of Figure 9). As illustrated in Figure 2, the or each pocket 40 may have a greater pocket height PH than pocket width PW and may comprise a substantially vertical line or dash. As illustrated in Figure 4, the or each pocket 40 may have a greater pocket width PW than pocket height PH and may comprise a substantially horizontal line or dash. As illustrated in Figure 3, the or each pocket 40 may comprise at least a portion extending at an acute angle to the height H and / or width W of the cylinder wall 15. The or each pocket 40 may have a chevron shape as illustrated, the chevron shape diverging downwardly from the top of the cylinder wall 15. A chevron shape, diverging from its top, may be beneficial for squeezing oil out through each leg of the chevron, in an effort to minimise or control oil flow to the top of the bore / liner. Figures 5 to 7 illustrate exemplary embodiments of the shape of the pocket depth PD of the or each at least one pocket 40 taken across a cross section of the depth D and height H of the cylinder wall 15. The change in depths illustrated is exaggerated for the purposes of illustration. The pocket depth PD may be substantially the same or vary along the pocket height PH. As in Figure 5, the pocket depth PD may be V-shaped, such as symmetrically V-shaped, along the pocket height PH and the pocket depth PD may decrease away from, on either side of, the deepest location of the at least one pocket 40. The V shape angle may be used to control the oil flow towards the top of the bore / liner. As in Figure 6, the pocket depth PD may be U-shaped and the at least one pocket 40 may have a continuous pocket depth PD along the pocket height PH. As in Figure 7, the at least one pocket 40 may have a pocket depth PD that is asymmetrically V-shaped. In particular, the deepest location of the at least one pocket 40 may be offset from the centre along the pocket height PH and the deepest location of the at least one pocket 40 may be closer to the top than bottom of the at least one pocket 40. Such an arrangement means that, as the at least one piston ring 30, 31 passes the at least one pocket 40 and presses oil therein, oil is directed downwardly out of the at least one pocket 40, rather than upwardly. Figure 8 schematically illustrates the piston 20 at TDC with the top ring 30 in contact with the cylinder wall 15 over a top ring contact area 38 and illustrates different embodiments of locations 50, 51, 52 of the at least one pocket 40 along the height H of the cylinder wall 15, relative to the top ring 30. At the different locations 50, 51, 52, the at least one pocket 40 may comprise any of the shapes, sizes, arrays and / or arrangements as discussed above. The at least one pocket 40 may be located on the cylinder wall 15 such that the pocket height PH at least partially overlaps the top ring contact area 38 or top ring 30 when the piston 20 is at TDC. The overlap along the pocket height PH between the at least one pocket 40 and top ring contact area 38 may be at least 25%, at least 50% or at least 75% of the height H of the top ring contact area 38. The pocket may also or instead be just below this location, allowing 0% overlap but used to throttle or control the flow to this location. In the case of an array of pockets 40, the total combined area of the cylinder wall 15 covered by the pockets 40 (i.e. the total area of indentations, excluding spaces between pockets 40) on the cylinder wall 15 may be at least 0.5%, at least 1%, at least 5% or at least 10% of the top ring contact area 38. The at least one pocket 40 may be located or extend across positions 50, 51 and / or 52 as in Figure 8 and / or positions 70, 71 as in Figure 10. In an embodiment, illustrated by location 51, the at least one pocket 40 is located such that, when the piston 20 is at TDC, the pocket height PH of the at least one pocket 40 partially overlaps the top ring contact area 38 and the at least one pocket 40 is located below or is separated from an upper edge 55 of the top ring contact area 38. The at least one pocket 40 may also extend along the pocket height PH outside of the top ring contact area 38 and below the top ring 30 and top ring contact area 38 at TDC as illustrated. The pocket height PH may be the same or greater than the height of the top ring contact area 38 (the area may be that when the top ring 30 passes the at least one pocket 40). As a result, when the piston 20 moves downwardly from TDC, the area of contact of the top ring 30 with the cylinder wall 15 above the at least one pocket 40 squeezes the oil down away from above the top ring 30. Some oil will extend above the at least one pocket 40 to provide lubrication, but separating the oil reservoir in the at least one pocket 40 from the top of the top ring 15 means that oil can never reach above or substantially above the top ring 30 at TDC. At location 51, the at least one pocket 40 may be configured so as to avoid oil starvation. In particular, if the top ring 30 stops over the at least one pocket 40, oil may be forced out of the at least one pocket 30 whilst it is stationary. Thus oil may not be present in the at least one pocket 40 when the top ring 30 moves downwardly, resulting in oil starvation. Therefore, the dimensions of the at least one pocket 40, such as the pocket width PW and / or pocket depth PD, may be configured to avoid such oil starvation. For example, the pocket depth PD may be higher, such as by being greater than at least one pocket 40 not overlapping the top ring contact area 38 at TDC, such that more oil is retained therein and is not pushed out when the top ring 30 is stationary. When at location 51, the at least one pocket 40 may have a chevron shape as in Figure 3. Since the legs of the chevron extend below the top ring contact area 38 at TDC, as the piston 20 moves downwards oil is efficiently moved downwards and away from the combustion chamber, having two legs to be directed along rather than one as in the vertical line embodiment. When at location 51, the at least one pocket 40 may have a pocket depth PD that is asymmetrically V-shaped, as in Figure 7. As discussed above, the oil will be more inclined to flow downwards, in a more controlled fashion, which such a pocket depth PD, which assists with the oil flow required at location 51. However, whilst such a location 52 of the at least one pocket 40 may prevent oil rising above the top ring 30 at TDC, it may not provide sufficient lubrication to the at least one piston ring 30, 31. When locating the at least one pocket 40 below the top ring 30 at TDC, the at least one pocket may be configured to control the oil flow up the cylinder wall 15 such that it does not extend substantially above the top ring 30 or top ring contact area 38 at TDC. Hence the at least one pocket 40 is configured to have a volume suitable to throttle the flow of oil up the cylinder wall 15. The volume may be configured so that enough, but not too much, oil is drawn up the cylinder wall 15 as the top ring 30 passes the at least one pocket 40 and the oil does not substantially extend above top ring 30 or top ring contact area 38 at TDC . The distance between the at least one pocket 40 and top ring 30 at TDC (i.e. the distance between the top edge of the at least one pocket and a lower edge 56 of the top ring contact area 38) may be configured to control the flow of oil based upon the time for ring reversal (i.e. the time taken for the top ring 30 to travel past the at least one pocket 40, reach TDC and return to the at least one pocket 40). In particular, the at least one pocket 40 may be located and have dimensions such that the oil flow or film is maintained on the cylinder wall 15 for a greater time period than the time for ring reversal. The at least one pocket 40 may thus be located in the range of from about 0.1 mm to about 100 mm below the top ring contact area 38 (such as below the lower edge 56 of the top ring contact area 38) when the top ring 30 is at TDC. As a result, at least one pocket 40 may be located and / or comprise a second or further row below the top ring 30 and outside of the top ring contact area 38 at TDC, such as at location 52. At location 52 the at least one pocket 40 may have a different shape to location 51 in order to promote distribution of oil therearound, such as comprising the vertical or horizontal lines. At location 52, the pocket depth PD may be V-shaped as in Figure 5. Alternatively, illustrated by location 50, the at least one pocket 40 may be located such that, when the piston 20 is at TDC, the pocket height PH of the at least one pocket 40 substantially overlaps the entire top ring contact area 38. Thus the at least one pocket 40 extends along the full height of the top ring 30 when the piston 20 is at TDC. In such an arrangement the pocket depth PD may be discrete or continuous as in Figure 6. The location, density, size, shape and / or spacing of pockets 40 around the circumference or width W of the cylinder bore 16 and cylinder wall 15 may also vary and / or be configured to account for distortion of the cylinder bore 16 in use. In particular, the density and / or size of pockets 40 in the or each row may vary around the circumference of the cylinder wall 15. The density and / or size of pockets 40 may be increased (such as with lower spacing between pockets 40) in areas of the circumference with relatively higher oil flow (such as where the piston 20 is further from the cylinder wall 15). The density and / or size of pockets 40 may be decreased (such as with higher spacing between pockets 40) in areas of the circumference with relatively lower oil flow (such as where the piston 20 is closer to the cylinder wall 15). This could also vary dependent on the location along the bore / liner. Along the bore / liner the pocket density and dimensions could vary to account for bore distortion and oil film thickness simultaneously. For example, in regions of the stroke of full flooded film, the density of pockets may vary circumferentially to account for bore distortion such as by being increased for thicker films, and decreased for thinner films circumferentially, but in regions of the stroke of mixed friction the density of the pockets may be increased for thicker films, and decreased for thinner films. Or vice versa, the density of the pockets may be decreased for thicker films and increased for thinner film regions around the circumference of the bore, varying longitudinally too. The shape and location of the pockets 40 may also be varied according to the locations of higher and lower oil flow. The pockets 40 may be located so as to at least partially overlap the top ring 30 at TDC (i.e. locations 50 or 51) in areas of the circumference with relatively higher oil flow. The pockets 40 may be located so as to not overlap the top ring 30 at TDC (i.e. location 52) in areas of the circumference with relatively lower oil flow. By way of example, Figure 9, which is a plan view of the top of the cylinder bore 16 and engine block 12, schematically illustrates the known distortion of the cylinder bore 16 due to high temperatures and pressures when in use, such as due to the location of bolts 60 around the cylinder bore 16. In particular, the distortion can result in “pinch points” 62, which may be driven by the bolt locations 60, where the cylinder wall 15 and piston 20 are closer than at expanded points 61. In prior systems the flow of oil is uneven due to its movement being inhibited by the pinch points 62 and promoted by the expanded points 61. Pockets may also be implemented to force this lobing or distortion in a different manner under fired conditions, again with the intention of controlling the oil flow. Therefore, the pockets 40 may be spaced around the circumference of the cylinder wall 15 so as to promote or increase the flow of oil at the pinch points 62 and inhibit or decrease the flow of oil at the expanded points 61. An increased density and / or size of pockets 40, or shapes of pockets with improved oil flow, may therefore be provided at the pinch points 62 as compared to the density and / or size of pockets 40 at the expanded points 61. The pockets 40 may be positioned at locations 50 or 51 at the expanded points 61 since improved oil control is required. The pockets may be positioned at location 52 (i.e. below the top ring 30 at TDC) at the pinch points 62 because less oil control is required, given that the pinch points 62 themselves inhibit oil flow. The at least one pocket 40 may additionally or alternatively be located substantially below the top ring 30 at TDC, such as towards or adjacent the location of the top ring 30 at BDC. The control of oil away from the TRTA may impact the amount of oil at the TRTA, such that the flow of oil above or to the top ring contact area 38 at TDC can be controlled. For example, at least one pocket 40 may be located at or adjacent to the location of the top ring 30 at BDC, or may be located between the locations of the top ring 30 at TDC and BDC. In particular, at least one pocket 40 may be located anywhere along the cylinder wall 15 where metal-to-metal contact between the piston 20 and cylinder wall 15 could arise during reciprocation of the piston 20. Hence at least one pocket 40 may be located in the region of 0-25%, 0-50% or 0-75% of the height H from the location of the top ring 30 at BDC towards the location of the top ring 30 at TDC. Figure 10 illustrates the top ring 30 when the piston 20 is at BDC. In particular, at least one pocket 40 may be located adjacent to the top ring contact area 38, such as by being at location 71, and may not overlap the top ring contact area 38 or top ring 30 at BDC. As a result, oil will not be pushed out of the at least one pocket 40 because the top ring 30 will not stop on the at least one pocket 40 during turnaround of the piston 20 at BDC, maintaining sufficient oil in that location for lubrication. In a similar manner to location 52 at TDC, the distance between the at least one pocket 40 and top ring 30 at BDC (i.e. the distance between the bottom edge of the at least one pocket and the top edge 55 of the top ring contact area 38) may be configured to control the flow of oil based upon the time for ring reversal (i.e. the time taken for the top ring 30 to travel past the at least one pocket 40, reach BDC and return to the at least one pocket 40). In particular, the at least one pocket 40 may be located and have dimensions such that the oil flow or film is maintained on the cylinder wall 15 for a greater time period than the time for ring reversal. The at least one pocket 40 may thus be located in the range of from about 0.1 mm to about 100 mm above the top ring contact area 38 (such as above the upper edge 55 of the top ring contact area 38) when the top ring 30 is at BDC. In addition, the pocket height PH of at least one pocket 40 adjacent the top ring 30 at BDC may be less than the height of the top ring 30 or top ring contact area 38. Therefore, when the top ring 30 passes the at least one pocket 40, oil is not forced out of the at least one pocket 40, maintaining sufficient oil in that location for lubrication. Alternatively, at least one pocket 40 may at least partially overlap the top ring 30 and top ring contact area 38 when the piston 20 is at BDC, as illustrated by location 71. This may prevent oil from being lost below the top ring 30 at TDC and, as the piston 20 moves upwards, oil may be pushed out of the at least one pocket 40 in the upward direction. In a similar manner to location 51 at TDC, the size and geometry of the at least one pocket may be arranged such that the flow of the oil is forced upwards, and at such a rate that the motion of the top ring 30 as it starts the upwards stroke always has oil between the bore / liner and top ring 30. Thus the dimensions of the pocket may force the oil in an upward manner, but at a rate that, when the top ring 30 moves, there is still sufficient lubrication to not cause wear, meaning the pocket geometry is a function of the top ring 30 speed near and around the bottom turn around location. At location 71, the at least one pocket 40 may be configured so as to avoid oil starvation. In particular, if the top ring 30 stops over the at least one pocket 40, oil may be forced out of the at least one pocket 30 whilst it is stationary. Thus oil may not be present in the at least one pocket 40 when the top ring 30 moves upwardly, resulting in oil starvation. Therefore, the dimensions of the at least one pocket 40, such as the pocket width PW and / or pocket depth PD, may be configured to avoid such oil starvation. For example, the pocket depth PD may be higher, such as by being greater than at least one pocket 40 not overlapping the top ring contact area 38 at BDC, such that more oil is retained therein and is not pushed out when the top ring 30 is stationary. Such oil control, by at least one pocket 40 at locations 70, 71 and located along the cylinder wall 15 between the TDC and BDC top ring 30 locations, may provide suitable lubrication around the bottom or middle of the cylinder wall 15, but also control of oil in this location may result in the control of oil around the top ring 30 at TDC.

Claims

Claims 1. An internal combustion engine comprising: a cylinder head; a piston; an engine block having a cylinder bore therein and in which the piston is slideably mounted for reciprocating between a top dead centre (TDC) at a top of the cylinder bore and a bottom dead centre at a bottom of the cylinder bore, the cylinder bore comprising a cylinder wall, wherein at least one pocket is recessed into the cylinder wall for controlling the flow of oil during reciprocation of the piston; and at least one piston ring, including a top ring, mounted to the piston, wherein the at least one pocket is configured to control the flow of oil to, across and / or above the top ring when the piston is at or adjacent TDC for prevent uncontrolled combustion of the oil in the combustion chamber.

2. The internal combustion engine of claim 1 wherein: the internal combustion engine comprises a cylinder liner and the engine block comprises a liner bore in which the cylinder liner is mounted, the cylinder liner forming the cylinder bore such that the at least one pocket is formed in the cylinder liner; or the cylinder bore is formed directly in the engine block such that the at least one pocket is formed in the engine block.

3. The internal combustion engine of any preceding claim wherein the at least one pocket is for controlling the flow of oil upwards towards the top of the cylinder bore and / or for controlling the flow of gas downwards.

4. The internal combustion engine of any preceding claim wherein a volume between the cylinder bore, cylinder head and piston forms a combustion chamber, optionally wherein the at least one pocket is for controlling the flow of oil into the combustion chamber for preventing uncontrolled combustion of the oil therein.

5. The internal combustion engine of any one of the preceding claims wherein at least one pocket is located on the cylinder wall and at least partially overlaps the top ring when the piston is at TDC.

6. The internal combustion engine of claim 5 wherein at least one pocket entirely overlaps the top ring when the piston is at TDC and / or at least one pocket extends along the cylinder wall below the top ring when the piston is at TDC.

7. The internal combustion engine of claim 5 or claim 6 wherein at least one pocket partially overlaps the top ring when the piston is at TDC such that the at least one pocket is located below and is separated from an upper edge of a top ring contact area between the top ring and cylinder wall.

8. The internal combustion engine of any preceding claim wherein at least one pocket does not overlap the top ring when the piston is at TDC, optionally wherein the at least one pocket is located from approximately 0.1 mm to approximately 100 mm from the top ring when the piston is at TDC.

9. The internal combustion engine of any preceding claim wherein the at least one pocket comprises a plurality of pockets arranged in an array comprising at least one row of adjacent pockets extending around a circumference of cylinder wall.

10. The internal combustion engine of claim 9 wherein the spacing between each pocket is the same along the or each row and / or wherein the spacing between each pocket varies along the or each row.

11. The internal combustion engine of claim 9 or claim 10 wherein the location, density, size, shape and / or spacing of pockets around the circumference of the cylinder wall varies and / or the pockets are configured to account for distortion of the cylinder bore in use.

12. The internal combustion engine of any of claims 9 to 11 wherein: the density and / or size of pockets is relatively higher in areas of the circumference of the cylinder wall with relatively higher oil flow; the density and / or size of pockets is relatively lower in areas of the circumference of the cylinder wall with relatively lower oil flow; the pockets are located to at least partially overlap the top ring at TDC in areas of the circumference with relatively higher oil flow; and / or the pockets are located to not overlap the top ring at TDC in areas of the circumference with relatively lower oil flow.

13. The internal combustion engine of any preceding claim wherein: the at least one pocket has a shape, along a pocket width and pocket height, of a chevron, horizontal line or vertical line; and / or the at least one pocket has a pocket depth that is the same or varies along a pocket height, such as by being symmetrically or asymmetrically V- shaped or U-shaped.

14. A cylinder liner for an internal combustion engine, the cylinder liner comprising a cylinder bore therein and the internal combustion engine comprising: a cylinder head; a piston; an engine block for locating the cylinder liner therein such that the piston is slideably mounted in the cylinder bore for reciprocating between a top dead centre (TDC) at a top of the cylinder bore and a bottom dead centre at a bottom of the cylinder bore, wherein the cylinder bore comprises a cylinder wall into which at least one pocket is recessed for controlling the flow of oil during reciprocation of the piston; andat least one piston ring, including a top ring, mounted to the piston, wherein the at least one pocket is configured to control the flow of oil to, across and / or above the top ring when the piston is at or adjacent TDC for prevent uncontrolled combustion of the oil in the combustion chamber.

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