Abstract: A piston for internal combustion engines has a skirt coating, consisting of a wear resistant inner layer consisting of a polymer matrix having ceramic particles, aramide fibers and/or carbon fibers dispersed therein and an outer layer consisting of a polymer matrix having solid lubricants dispersed therein and an outer layer consisting of a polymer matrix having solid lubricants dispersed therein.

Abstract: A piston for an internal combustion engine includes a piston crown (2) and a cylindrical side wall (4), an annular piston ring groove (8) being formed in the side wall (4) which accommodates an annular spring (14). The spring (14) includes an annular radially extending portion (16) and first (20) and second (22) projections. The radially extending portion (16) divides the annular groove into two chambers in the axial direction of the piston. The upper chamber closest to the piston crown accommodates an annular compression ring (10). The lower chamber furthest from the piston crown accommodates an annular oil scraper ring (12). The first projection (20) is arranged to contact the upper surface closest to the piston crown of the annular groove (8). The second projection (22) is arranged to contact the inner surface of the oil scraper ring (12) to urge it outwardly.

Abstract: A compression ring assembly for a piston of an internal combustion engine includes a first compression ring and a second compression ring, with the second compression ring overlaid adjacent to and in abutting engagement with the first compression ring. When both the first compression ring and the second compression ring are uncompressed and in a free state, the second compression ring includes an outer second ring diameter that is greater than an outer first ring diameter of the first compression ring. Additionally, the first compression ring includes a first radial width that is greater than a second radial width of the second compression ring. A first gap of the first compression ring is positioned relative to a second gap of the second compression ring in a non-overlapping orientation.

Abstract: produced according to the method having a piston crown with annular grooves, a combustion-chamber bowl, and piston shaft having a pin bore for receiving a pin, wherein both a combustion-chamber rim and a combustion-chamber bowl base are melted and thereafter solidified.

Abstract: A piston apparatus for an engine includes a piston pin that is inserted in a smaller end portion of a connecting rod and having a cross-section changing portion where a cross section changes at a portion of the piston pin, and a fixing member that engages the connecting rod and a piston through the cross-section changing portion so as to restrain longitudinal movement of the piston pin with respect to the connecting rod.

Abstract: A piston for an internal combustion engine has an upper part and a lower part. The upper part has a collar with a ring rib and the lower part has a wall and a contact part radially within the wall. When the upper part is connected with the lower part by friction welding, the face surfaces of the ring rib, the collar, the wall, and the contact part form friction-welding surfaces and form a cooling channel and a cooling cavity between them. To supply the cooling channel and the cooling cavity with cooling oil, radial bores are introduced into the ring rib, which bores connect the cooling channel with the cooling cavity. In this way, it is guaranteed that a sufficient residual amount of oil collects in the cooling channel and in the cooling cavity, which amount is constantly renewed, and leads to good cooling of the piston crown.

Abstract: An engine assembly includes an engine structure including an engine block defining a cylinder bore and a cylinder head, a piston located in the cylinder bore, and a camshaft assembly. The piston, cylinder head, and cylinder bore cooperate to define a combustion chamber including first and second longitudinal end surfaces defined by the cylinder head and the piston. A first protrusion may extend longitudinally from one of the first and second longitudinal end surfaces and radially inward from a circumference of the combustion chamber to a location between a first intake port and a first exhaust port in communication with the combustion chamber. The camshaft assembly may include a first intake lobe that opens a first intake valve and a second intake lobe that opens a second intake valve. The first intake lobe may be rotationally offset from the second intake lobe in a rotational direction of the camshaft assembly.

Abstract: A method for the production of a multi-part piston for an internal combustion engine involves producing an upper piston part having a piston crown as well as an inner and an outer support element, and producing a lower piston part having a skirt and having pin boss supports and pin bosses connected with the pin boss supports, and an inner and an outer support element. A separate cooling oil collector having at least one cooling oil opening is inserted into the upper piston part or the lower piston part. The upper piston part and the lower piston part are connected in such a manner that the inner and outer support elements of the upper and lower piston parts, delimit an outer circumferential cooling channel and a cavity that is open toward the pin bosses and provided with the cooling oil collector.

Abstract: A piston for an internal combustion engine including a piston body (20). The piston body (20) defines a first cooling chamber (46) that is sealed closed and contains a first cooling medium (48) other than air. During operation of the piston, the first cooling medium (48) extracts heat from the surrounding regions of the piston body (20) to cool the piston body (20). The piston body (20) also defines a second cooling chamber (50) adjacent to the first cooling chamber (46). A cooling oil (51) is projected into the second cooling chamber (50) and against the portion of the piston body (20) separating the first and second cooling chambers (46, 50) to extract heat from the first cooling medium (48). The cooling oil (51) is redirected within the second cooling chamber (50) to extract additional heat from the first cooling medium (48) or directly from the piston body (20).

Abstract: A method for preparing ceramic powders in the presence of a carbon powder including a step which consists in homogenizing a mixture of particles capable of resulting in a ceramic by heat treatment. Said method can be carried out in the presence of an accelerated solvent and provides, at reduced energy consumption, carbon-coated ceramic powders and then ceramics.

Abstract: A wrist pin and method of reducing wear between members thereof, a piston, a connecting rod, and methods of construction thereof are provided. The wrist pin has a first portion extending between opposite ends configured for receipt in piston pin bores and a second portion extending between opposite ends configured for receipt in the pin bores. The second portion is configured for relative movement with the first portion. The piston includes a piston body having axially aligned pin bores, wherein at least one of the pin bores has a feature to prevent relative rotation of a wrist pin member. The connecting rod includes a connecting rod body having small end bore. The small end bore has a contour to allow relative rotation of a first wrist pin member therein and a feature to prevent relative rotation of a second wrist pin member therein.

Abstract: A piston includes a piston head, two skirt walls disposed opposite one another and at least one pin bearing disposed between the skirt walls and supported on the piston head. Each skirt wall extends over a partial region of the periphery of the piston or piston head. The two skirt walls are connected by at least one self-supporting support wall disposed at a distance from the piston head. A cylinder and piston assembly and a piston ring for a cylinder, are also provided.

Abstract: A piston for a compression ignition internal combustion engine includes a piston body having a combustion face defining a combustion bowl, and the combustion face including a compound bowl surface and a compound rim surface. The combustion face is profiled to balance a combustion efficiency property of the piston with emissions properties of the piston. A ratio of a diameter of the combustion bowl to a diameter of the cylinder bowl bore is from 0.68 to 0.74. Other dimensional and proportional features of the piston support low smoke and NOx production during operation.

Abstract: A piston for an internal combustion engine is provided. The piston includes a piston body of steel and including a crown portion, a pair of skirt portions and a pair of pin boss panels. The crown portion has an upper combustion surface, a lower surface having an undercrown surface area and an outer annular ring belt with at least one ring groove. The pin boss panels depend from the crown portion and extend in spaced relationship with one another between the skirt portions. Each pin boss panel includes a pin boss having a pin bore, and the pin bores are aligned with one another for receiving a wrist pin. Each pin boss panel also has at least one recess located vertically between the associated one of the pin bores and the crown portion to increase the undercrown surface area for improved cooling of the crown portion.

Abstract: A method for the production of a piston (1) made of steel, for an internal combustion engine, in which the upper piston part (3) is produced using the forging method, and the lower piston part (4) is produced using the forging or casting method, and they are subsequently welded to one another. To simplify the production method and make it cheaper, the upper piston part is forged using the method of semi-hot forming, to finish it to such an extent that further processing of the combustion bowl and of the upper cooling channel regions can be eliminated.

Abstract: The invention relates to a steel piston for internal combustion engines, comprising at least one piston upper part (12) provided with a combustion cavity (11) and an annular wall (5), and a piston lower part (13) provided with a connecting rod bearing (8). The steel piston is cast as a single component from a reduced-density steel alloy or a special steel alloy in the same material by means of a low-pressure casting method.

Abstract: A modified piston for a reciprocating engine, the piston having a piston face that comprises a plurality of radially-oriented grooves. Each groove comprises a distal end proximate a periphery of the piston face and a proximal end proximate a center of the piston face. The width of the distal end of each groove is greater than the width of the proximal end of the groove. The depth of the distal end of each groove is greater than the depth of the proximal end of the groove. The proximal end of each groove terminates in a point.

Abstract: A piston for an engine is disclosed. The piston may include a piston crown, and a piston bowl recessed within the piston crown. The piston bowl includes a center portion, a cone portion, and an annular toroidal portion. The geometry of the piston bowl is designed to correspond with a fuel injection nozzle having a specific spray angle. An exemplary piston bowl may include a toroidal major diameter between about 4.645 and 4.895 inches and a toroidal minor radius between about 1.165 and 1.235 inches. The cone portion includes an angle between about 26 to 34 degrees. The compression ratio of the piston is about 17.95 to 1.

Abstract: A combustion chamber for an opposed-piston engine is defined between a pair of pistons disposed for opposing reciprocal movement in a cylinder. The combustion chamber is formed between crowns of the pistons and has a radius that decreases from the longitudinal axis of the cylinder. Each crown includes a periphery, a bowl within the periphery defining a concave surface with a first portion curving inwardly toward the interior of the piston and a second portion curving outwardly from the interior, and a convex surface within the periphery curving outwardly and meeting the second portion of the concave surface to form a ridge. Each ridge has a height that decreases with the distance from a longitudinal axis.

Abstract: A cooling duct piston (1) for combustion engines. The cooling duct piston has a piston basic body (2) that is connected to a lining part (3), which is facing an assigned combustion chamber. Here, the lining part (3) completely forms the piston surface (4) of the cooling duct piston (1) that faces the combustion chamber. An encircling depression (5) is provided in the surface of the piston basic body (2) facing the combustion chamber. The lining part (3) provides a permanent connection at least with the surface of the piston basic body (2) facing the combustion chamber, and thus bridges the encircling depression (5), such that the encircling depression (5), with the lining part (3) that bridges it, forms a cooling duct (6).

Abstract: In an internal combustion engine having at least one cylinder, in which a combustion chamber is delimited between a piston and a cylinder head, a fuel injector, is arranged in the cylinder head and has an injection nozzle with a plurality of injection bores. A piston depression is arranged in the piston, and a compression projection, with a projection cone angle, is positioned opposite the injection nozzle in the piston depression. The injection bores are formed such that, during a fuel injection in a range from 20° CA before top dead center to 35° CA after top dead center, the fuel jets emerging from the injection bores with a fuel cone angle impinge on the piston depression and are guided by a piston depression surface. The injection bores and the compression projection are formed such that a generated ratio of fuel cone angle to projection cone angle is in a range between 0.95 and 1.

Abstract: A piston, piston ring and method of construction thereof is provided. The piston ring is L-shaped, having a first portion configured to extend upwardly from a ring groove of a piston along a top land of the piston and a second portion configured for receipt in the ring groove. The first and second portions of the ring have an enclosed hollow cooling chamber with a cooling medium disposed therein such that the cooling medium is free to flow internally to the piston ring groove and upwardly from the piston ring groove along the top land.

Abstract: A piston for an internal combustion engine is provided. The piston includes a body having a cylindrical outer surface with a ring belt region including an annular uppermost ring groove and a lower ring groove extending into the outer surface. A top land extends from the uppermost ring groove to an upper combustion surface. The body has a pair of pin bosses with pin bores aligned with one another along a pin bore axis. A first piston ring is disposed in the uppermost ring groove and a second piston ring is disposed in the lower ring groove. The body has an annular sealed cooling gallery with a cooling medium contained therein. The sealed cooling gallery is configured in substantial radial alignment between the first and second piston rings to provide optimal cooling to the ring belt region, top land and upper combustion surface.

Abstract: A piston for an internal combustion engine has a body including an upper combustion wall having an upper combustion surface; cylindrical outer wall with a ring belt region adjacent the upper combustion surface, and a closed annular cooling gallery located in radial alignment with the ring belt region. A cooling medium is contained in the cooling gallery. The cooling gallery has an inner surface including a radially outermost portion extending along the ring belt region. The outermost portion converges from the upper combustion wall toward a longitudinal central axis. During reciprocating motion of the piston, the cooling medium flows and remains in contact with the cooling gallery walls, thereby maximizing the capacity for heat to be transferred from the upper combustion wall to the contained cooling medium and from the cooling medium to the piston body, ring belt region and ultimately to the engine cooling system.

Abstract: A piston for an internal combustion engine has a crown, a skirt extending from the crown, a pair of pin bosses, and a plurality of struts connecting the pin bosses to inner sides of the crown and skirt. An internal combustion engine having the piston is also disclosed.

Abstract: An engine piston has a connecting rod connected rigidly to the piston. At least one cavity is formed in the piston head, the cavity communicating in the region thereof close to the piston longitudinal axis with an oil supply line running through the connecting rod. The cavity is formed by a number of channels which run, preferably radially, in the piston head and are connected to one another in the circumferential region of the piston via an annular space or an annular line, and wherein a return line leading to the connecting rod is connected to the annular space or the annular line. The cavity or the channels forming the cavity and/or the return line are inclined at an angle of 1° to 4°, preferably 1° to 3°, to a plane perpendicular to the piston longitudinal axis.

Abstract: A piston and method of construction are provided. The piston includes a piston body having an upper combustion surface configured for direct exposure to combustion gases within a cylinder bore with an undercrown surface located beneath the upper combustion surface. The piston body also includes a ring belt region configured for receipt of at least one piston ring adjacent the upper combustion surface with a cooling gallery configured radially inwardly and in substantial radial alignment with the ring belt region. The piston further includes a non-stick material contained in or bonded to at least one of the undercrown surface and at least a portion of the cooling gallery, wherein the non-stick material inhibits the build-up of carbon deposits thereon.

Abstract: A process for near-net-shape manufacturing of a formed metallic work piece with armoring, with the armoring having different properties than the basic work piece material, including the steps of providing an armoring blank; providing a basic work piece blank; arranging the armoring blank on the basic work piece blank; welding together a surface section of the work piece blank and the armoring blank, thereby creating a blank with an armored surface section; and forming the resulting blank with an armored surface section, thus producing a near-net-shape work piece contour by means of a process which is selected from the group comprising: forging, upsetting, electro upsetting, and extrusion, at a temperature in one of a cold, half-warm and warm temperature range, thereby producing a near-net-shaped formed armored work piece.

Abstract: A piston and an engine are provided that includes various precise configuration parameters, including dimensions, shape and/or relative positioning of the combustion chamber features, resulting in a combustion process that yields improved mixing of fuel and intake air and increased uniformity of load on the engine pistons. The piston provides a piston bowl with a concave curvilinear portion that may be semi-spherical and extends inwardly to a depth; an angled surface extends inwardly from the crown surface to intersect the concave curvilinear portion at an edge at a depth; and a curved surface that extends inwardly from the crown surface to intersect the concave curvilinear portion at a tangent at a depth. The angled surface may be part of a frusto-conical surface that may extend from both sides of the angled surface to an area proximate the curved surface.

Abstract: A piston engine may include a heat pipe capable of transferring heat away from a portion of the piston engine such as a combustion section. The heat pipe may be included as part of a piston assembly, a cylinder, or both. The heat pipe may be filled with a suitable heat pipe fluid that may undergo a phase change such as, for example, water, ethanol, ammonia, sodium, other fluids or combinations thereof. Boiling and condensing of the fluid within the heat pipe may utilize the latent heat of the fluid during heat transfer. Multiple heat pipes may be used in some instances.

Abstract: A multi-part piston for an internal combustion engine has a piston upper part and a piston lower part. The piston upper part comprises a piston head, a continuous fire land and a continuous ring part. The piston upper part and the piston lower part are connected together by securing means and form a continuous cooling channel. According to the invention, the connecting means connecting the piston upper part and the piston lower part are embodied as cooling elements that are arranged in the cooling channel and that are made of heating-conducting material.

Abstract: A piston for an internal combustion engine and method of construction thereof is provided. The piston includes a piston body having an upper combustion surface with a combustion bowl depending from the upper combustion surface. The piston body has a ring belt region configured for receipt of at least one piston ring adjacent the upper combustion surface. A cooling gallery is configured in radial alignment with the ring belt region. An annular combustion bowl rim region extends between the upper combustion surface and the combustion bowl, and a bonded seam extends from the combustion bowl rim region radially outwardly to the cooling gallery. The bonded seam has material properties exhibiting an enhanced ability to withstand the extreme temperature, pressure, stress and highly corrosive and erosive effects of the combustion gases relative to the surrounding material of the piston body.

Abstract: A method for the production of a piston for an internal combustion engine, composed of at least two components, each of which has at least one corresponding joining surface, has the following steps: a) pre-working the at least two components, at least in the region of the joining surfaces; b) coating at least a part of the surface of at least one component with a covering medium containing at least one phyllosilicate; c) assembling the at least two components; d) connecting the at least two components along their corresponding joining surfaces, by means of beam welding, to produce a piston blank; e) removing the covering medium and any excess weld material adhering to it; and f) machining the piston blank to produce a finished piston.

Abstract: A multi-part piston for an internal combustion engine has an upper piston part with a piston crown, and a lower piston part, each of the piston parts having an inner and an outer support element that delimit an outer circumferential cooling channel and an inner cooling chamber. The cooling chamber bottom has an opening. A holding element is disposed in the inner cooling chamber and extends from the underside of the piston crown vertically toward the opening. The holding element carries a closure element that closes the opening and has at least one cooling oil opening.

Abstract: A piston and method of construction are provided. The piston includes a piston body having an upper combustion surface configured for direct exposure to combustion gases within a cylinder bore with an undercrown surface located beneath the upper combustion surface. The piston body also includes a ring belt region configured for receipt of at least one piston ring adjacent the upper combustion surface with a cooling gallery configured radially inwardly and in substantial radial alignment with the ring belt region. The piston further includes a non-stick coating material bonded to at least one of the undercrown surface and at least a portion of the cooling gallery, wherein the non-stick coating material inhibits the build-up of carbon deposits thereon.

Abstract: A method for producing a cooling channel system for an internal combustion engine, which has a cooling channel in the piston crown. The piston crown is adjoined by a lower piston part having a piston boss, pin bores and piston skirts. Firstly, a piston blank having a peripheral collar projecting radially in the region of the piston crown is produced, wherein the collar, forming a subsequent ring zone wall is then reshaped and, in a transition area between the piston crown and the lower piston part, a contact area for the collar is formed, and the collar is reshaped in such a way until the outer radially peripheral edge comes very close to or completely into contact with the contact area in order to form a closed cooling channel. Following the reshaping, the end region of the ring zone wall forms a defined gap (X) with respect to the upper edge of the piston skirt.

Abstract: A piston for a diesel internal combustion engine including a crown portion at least partially formed of steel and having a combustion surface with a combustion bowl formed therein is provided. The combustion bowl presents a combustion bowl rim area, and a coating including at least one of a noble metal and a refractory metal is applied to substantially only the combustion bowl rim area. The coating is preferably applied in the areas of the combustion bowl rim area that are in line with the sprays of diesel fuel when the piston is in a top dead center position during operation of the engine.

Abstract: A system for moving fluids includes a pump device having a housing and at least one piston movable in the housing to displace fluids thereby causing flow. An actuator device is connected to the at least one piston for moving the piston within the housing to displace fluids as the actuator device is moved. The actuator device includes a plurality of side portions connected to one another to form a vacuum therein and movable relative to one another as the actuator device moves reciprocally between first and second positions with one of the side portions being connected to at least one piston thereby moving the at least one piston within the housing.

Abstract: A piston construction with an end surface is equipped with a pattern of insulating cavities embedded in an upper end of the piston, between the end surface and interior portions of the piston that are cooled by circulating liquid coolant.

Abstract: The present invention relates to a piston (10, 110, 210, 310) for an internal combustion engine, having a piston base body (11, 111, 211, 311) and a piston head element (12, 112, 212, 312), wherein the piston base body (11, 111, 211, 311) has a piston skirt (16) that is provided with pin bosses (18) having pin bores (17), wherein the piston head element (12, 112, 212, 312) forms at least one part of a piston head (25, 125, 225, 325), and wherein a circumferential cooling channel (26, 126, 226, 326) is provided in the piston head (25, 125, 225, 325). According to the invention, it is provided that at least one heat conduction element (27, 127, 227, 327) is disposed in the cooling channel (26, 126, 226, 326).

Abstract: In a method for producing a piston for an internal combustion engine, at least the region of the upper annular groove is at least partially recessed, an adhesion promoter layer containing aluminum is then applied, a wear-resistant layer is thermally sprayed onto said adhesion promoter layer and at least the upper annular groove is at least partially formed in said layers. The invention also relates to a piston for an internal combustion engine that comprises a base material, an adhesion promoter layer that contains aluminum and is applied to at least some regions of said material and a wear-resistant layer that is thermally sprayed onto said adhesion promoter layer. At least the upper annular groove is at lest partially formed in said layers.

Abstract: A plurality of convex portions are radially fanned and spaced apart from each other by a constant angle in a planar view on a tapered surface of a land portion formed on a bottom surface of a cavity formed in a top portion of a piston. Each convex portion is positioned such that the extending direction of the convex portion aligns with an axis X of a corresponding fuel spray. Thereby, each fuel spray moves forward through a space (convex portion space) between the corresponding convex portion and an inner wall of a cylinder head portion along the extending direction of the corresponding convex portion. When a fuel injection is performed during the latter half of a compression stroke, a pressure in a convex portion space is increased, compared with a pressure in a space of the other portion by the decrease of a ratio of the volume of the convex portion space relative to the volume of the space of the other portion by the proceeding of the compression by the piston.

Abstract: A piston cooling apparatus of an engine may include a combustion chamber formed between a piston disposed in a cylinder block and a cylinder head disposed on the cylinder block, wherein a surface area-enlarging portion is formed inside the piston on bottom surface of a crown of the piston.

Abstract: A piston for an internal combustion engine has a piston crown, a circumferential top land, and a circumferential ring belt having ring grooves, as well as having a piston skirt that has two skirt walls disposed on the major thrust side and the minor thrust side of the piston, and two box walls, set back with regard to the ring belt, that connect the skirt walls. The box walls have pin bosses with pin bores. The skirt wall disposed on the major thrust side is shorter, in a circumference direction of the piston, than the skirt wall disposed on the minor thrust side.

Abstract: A piston of an internal combustion engine has a piston crown with annular grooves and a shaft part disposed on the piston crown. The shaft part has bearing shaft wall sections which are connected to one another via inclined connecting walls which are retracted with respect to the outer diameter of the piston. Piston-pin bosses for accommodating a piston pin are disposed in connecting walls. The connecting walls are retracted at such an angle that, in progressing from the lower edge over an intermediate region which lies further back than the lower edge, into an end region which lies further back than the intermediate region the connecting walls to over flush into a hub supporting region below the piston crown.

Abstract: A piston 1 is employed in an engine 50 where a tumble flow is generated within a combustion chamber 53. The piston 1 includes: a top ring channel 3; and a portion 10 of an outer circumferential portion of a top surface, the portion 10 positioned opposite to an adjacent cylinder of the engine 50, the portion 10 having a raised shape so as not to expose a position P, of a bore wall surface, facing the top ring channel 3 face in the top dead center during at least a period from a time when the piston 1 is positioned at a compression top dead center to a time when a quantity of heat transfer in the combustion chamber 53 is the highest.

Abstract: A piston for an internal combustion engine has a piston crown, a circumferential ring belt, a circumferential cooling channel in the region of the ring belt, pin boss supports connected below the piston crown, and pin bosses connected with the pin boss supports, as well as a piston skirt. A cavity closed all around is provided below the piston crown and a coolant in the form of a metal or metal alloy having a low melting point is accommodated in the cavity.

Abstract: A piston is positioned for reciprocal movement in a combustion engine cylinder. Half way between flame plume impingement areas are arranged a first type of protrusions protruding into the combustion chamber and having a smooth form adapted for preserving kinetic energy in a flame plume. Each of the first type of protrusions has a shape of a longitudinal ridge that extends only in the outer bowl area. The first type of protrusions have a left side flank and a right side flank of the ridge when seen from the injector. The left side flank is formed differently compared to the right side flank in order to redirect the movement of a flame plume progressing towards the left side flank in a plane perpendicular to the reciprocal movement, differently compared to corresponding flame plume progressing, towards the right side flank.

Abstract: A piston and a reciprocating expansion engine with a piston having a piston head, a piston neck, and a piston shaft are described. The piston head has at least one groove which runs in a circumferential direction suitable for receiving a piston ring, and the piston shaft has a pin boss and, at its outer circumference, a guide surface which is suitable for guiding the piston along a cylinder inner wall. An outer diameter of the piston neck is smaller than an outer diameter of the piston head and/or of the piston shaft, and the length of the piston neck approximately corresponds to the travel of the piston in the installed state.

Abstract: A piston for a four valve direct injection diesel engine defines a combustion chamber comprising a recess (10) in the piston crown, which is rotationally symmetrical about the axis of the piston in axial cross-section and is defined by a base and a side wall. A generally conical projection (5) is upstanding from the base. The recess (10) includes a lower toroidal portion (8) and an upper portion (10), whose diameter progressively increases towards the piston crown. The upper and lower portions of the recess are separated by an annular, arcuate lip (12) extending into the recess.