Piston and Internal Combustion Engine System

Abstract

The present disclosure relates to a piston (3) for an internal combustion engine (ICE), the piston having an axial upper end (16) that extends in an axial direction (A) and a radial direction (R) and comprises a piston bowl (6) intended to form part of a combustion chamber, the piston bowl having an axial floor part (11) with a floor surface (11a), and a peripheral part (20) that extends in the axial direction (A) between the floor surface and an upper face (5) of the axial upper end, the piston bowl further having an axial depth (H) defined by an axial distance between the floor surface and the upper face, the piston bowl further comprising a plurality of spaced-apart protrusions (40) circumferentially dispersed around the peripheral part (20), each of the spaced-apart protrusions having opposing radial sides (41, 42), and further having a flat surface (43, 43a) or a concave surface (43, 43b) extending between the opposing radial sides. The present disclosure also relates to an internal combustion engine system.

Description

Technical Field

[0001] The present disclosure relates to a piston for an internal combustion engine. The present disclosure further relates to an internal combustion engine system for a vehicle, where the internal combustion engine includes the piston. The present disclosure is applicable to vehicles, particularly large vehicles such as trucks. However, although the present disclosure is mainly described in relation to trucks, the internal combustion engine system is also applicable to other types of vehicles propelled by an internal combustion engine. In particular, the present disclosure is applicable not only to large vehicles such as trucks, buses, and construction machinery, but also to automobiles and other lightweight vehicles. Further, although the internal combustion engine is usually a diesel internal combustion engine, other fuels such as hydrogen and natural gas can also be used in combination with the piston. The present disclosure is also applicable to other machines such as generators and construction machinery. The present disclosure can further be applied to ships and the like.

Background Art

[0002] In the field of internal combustion engine devices, many efforts have been made to achieve satisfactory and efficient combustion from the viewpoints of residual products, particularly soot particles and NOx emissions. However, carbon monoxide emissions and hydrocarbon emissions from diesel fuel can also be considered as a matter of course.

[0003] For example, a combustion process in which diesel fuel is directly injected into a cylinder and ignited by an increase in temperature and pressure in the cylinder is generally called a compression ignition combustion process. Another type of ignition process for some gaseous fuels is a spark ignition combustion process. When the fuel is ignited in the cylinder, the combustion gas present in the cylinder turbulently mixes with the fuel during combustion, and a diffusion flame with controlled mixing is formed. When the fuel / gas mixture burns in the cylinder, heat is generated, and as a result, the gas in the cylinder expands. The expansion of the gas causes the piston to move in the cylinder. Depending on several parameters such as the type of fuel, the injection pressure of the fuel, the amount of exhaust gas recirculated to the cylinder, the injection time of the fuel, and the turbulence in the cylinder, different engine efficiency and emission values can be obtained.

[0004] It has been proposed to utilize the shape of the piston bowl surface facing the combustion chamber in order to control, and in particular reduce, emissions from the combustion process of a combustion engine. The piston bowl surface is part of the piston crown of a reciprocating piston within a cylinder. For this purpose, the surface of the piston bowl can be designed to influence various parameters within the combustion chamber, such as flame propagation, mixing energy, distribution of kinetic energy, and / or vortices.

[0005] It has also been observed that the shape of the piston bowl can potentially affect the combustion and / or mixing of fuel within the cylinder of other types of internal combustion engines, such as gas fuel engines like hydrogen internal combustion engines.

[0006] International Patent Publication No. WO 2017 / 108103 discloses an example of a piston crown for a piston, the piston crown comprising a piston bowl surface having a plurality of protrusions arranged at circumferential intervals at the periphery.

[0007] Despite the activity in this field, it is desirable to further improve such types of pistons for internal combustion engine (ICE) systems of large vehicles. SUMMARY OF THE INVENTION

[0008] The object of the present disclosure is to provide an improved piston design for a reciprocating piston intended to operate in an internal combustion engine system. This object is at least partially achieved by the piston according to claim 1. This object is also at least partially achieved by the piston according to claim 18. This object is also at least partially achieved by the other independent claims. The dependent claims relate to advantageous embodiments.

[0009] According to a first aspect of the present disclosure, a piston for an internal combustion engine (ICE) is provided. The piston extends in an axial direction and a radial direction. The piston has an axial upper end with a piston bowl intended to form part of a combustion chamber. The piston bowl has an axial floor portion with a floor surface, and a peripheral portion extending axially between the floor surface and an upper surface of the axial upper end. The piston bowl further has an axial depth defined by an axial distance between the floor surface and the upper surface. Further, the piston bowl comprises a plurality of spaced-apart protrusions arranged circumferentially dispersed around the peripheral portion. Each of the spaced-apart protrusions extends mostly radially towards a central axis and further extends mostly axially from the floor surface towards the upper surface, and each of the spaced-apart protrusions has opposing radial side portions. Further, each of the spaced-apart protrusions comprises a flat or concave surface extending between the opposing radial side portions. The flat or concave surface has a first circumferential extension at an intersection between the flat or concave surface and the floor surface, and further has a second circumferential extension at an axial distance from the floor surface, the axial distance being one quarter of the axial depth of the piston bowl. In addition, a ratio of the second circumferential extension to the first circumferential extension is 0.4 or less.

[0010] Accordingly, the first circumferential extension is larger than the second circumferential extension.

[0011] Thereby, the proposed piston has an improved design of the protrusions in the lower region of the piston bowl and generally intersects the dome portion of the piston bowl.

[0012] The present disclosure is based at least in part on the insight that it is a challenge to simultaneously achieve fuel consumption and emissions reduction without sacrificing piston durability. As an example, some dimensions of the protrusions are advantageous for proper combustion performance, while other dimensions can directly affect piston durability. That is, using protrusions in the piston bowl of a piston for a diesel ICE system typically also results in stress concentrations on or within the piston. In this context, it has been observed that the lower region of the protrusion, i.e., the region near the floor of the piston bowl, is one of the regions where the impact on combustion performance is relatively low, but the impact on durability is relatively high among many regions.

[0013] Accordingly, the proposed piston aims to improve the protrusions of the piston bowl of the piston to provide sufficiently reliable durability with respect to fatigue life without impairing any function of the protrusions related to the combustion of fuel in the combustion chamber of the cylinder.

[0014] By providing protrusions, the piston design contributes to improving the combustion process of fuels such as diesel fuel and / or improving the air-fuel mixing of other types of fuels such as hydrogen gas fuel. The protrusions can also provide a sharp change in the side profile of the protrusion to achieve a clearly defined flow release location.

[0015] Furthermore, by combining with the condition that the protrusion has a flat or concave surface extending between opposite radial sides and the ratio of the second circumferential extension to the first circumferential extension is 0.4 or less, the proposed piston provides a design with less influence of the protrusion with respect to the required fatigue life and required durability. Therefore, the piston can better withstand the severe fatigue conditions that occur during normal use of the piston in large vehicles.

[0016] More specifically, due to the configuration of the above-mentioned protrusions, the part of the protrusion that has little influence on combustion performance minimizes the compressive stress, i.e., the radial compressive stress, in the protrusion at the lower part on the dome (center of the piston) side with respect to the temperature load, and is designed to separate the position of the maximum compressive stress due to the temperature load from the position of the maximum tensile stress due to the pressure load. The piston bowl with protrusions having the maximum stress regions separated from each other contributes to an increase in the fatigue life of the protrusions and the piston.

[0017] The proposed protrusions are generally provided to enhance the interaction of the fuel flame with the surface forming the piston bowl and the adjacent flame. However, although the proposed pistons can be incorporated into many different types of ICE systems, the proposed pistons may be particularly suitable for ICE systems in which fuel is supplied by high-pressure injection of fuels including liquid diesel or pressure injection of gaseous fuels such as hydrogen fuel, where the fuel injection period occurs near top dead center (TDC). In a hydrogen ICE system, the proposed piston design with the above-mentioned protrusion segments can improve the mixing of hydrogen gas and compressed air before the ignition event.

[0018] The protrusions can be provided in several different geometric forms and shapes and can be arranged at various positions along the side. As an example, the ratio of the sum of the first circumferential extensions of all the spaced protrusions along the peripheral edge to the circumferential extension of the peripheral edge may be at least 30%, preferably at least 45%, and most preferably at least 60%. Such an arrangement of the protrusions with respect to the circumferential extension further improves the characteristics of the piston design in terms of required durability and the like.

[0019] The first radial side of the opposing radial sides may intersect a flat surface or a concave surface along an intersecting edge. Similarly, the second radial side of the opposing radial sides may intersect a flat surface or a concave surface along another opposing intersecting edge.

[0020] The intersecting edge, in combination with the first circumferential extension and the second circumferential extension, can define an extension of a flat surface or a concave surface.

[0021] Each of the intersecting edges may slope linearly from the first circumferential extension to the second circumferential extension, or may slope non-linearly such as curvilinearly. Usually, the intersecting edge may slope towards a central region located on the second circumferential extension. As an example, the intersecting edge may slope curvilinearly from the first circumferential extension to the second circumferential extension when viewed in the circumferential and radial directions.

[0022] The intersecting edge, in combination with the first circumferential extension and the second circumferential extension, can define a surface similar to a trapezoid or a triangle. Such a shape can further improve the characteristics of the protrusion in terms of required durability.

[0023] The concave surface extending substantially in the circumferential direction contributes to the improvement of the configuration of the protrusion. The concave surface of the protrusion may generally be the surface of the protrusion arranged to face the axial center of the piston bowl. Usually, although not strictly essential, the radius of curvature of the concave surface can always be essentially perpendicular to the axial center of the piston bowl.

[0024] The extension of the flat surface or the concave surface from the first circumferential extension to the second circumferential extension may further include a concave axial extension region.

[0025] One of the advantages of the axial concave surface is that the portion of the protrusion intersecting the floor surface smoothens the transition between the protrusion and the floor portion.

[0026] The extension of the flat surface from the first circumferential extension to the second circumferential extension may be defined by a flat surface profile. That is, in the axial direction, the flat surface from the first circumferential extension to the second circumferential extension may be defined by a flat surface profile.

[0027] The radially side portions may each typically be curved convex side portions. Each of the opposing radially side portions can comprise a plurality of regions of different convex curved profiles.

[0028] The radially side portions may generally extend in the radial direction. Thus, the radially side portions are side portions that extend in the radial direction. The radially side portions can typically extend from the peripheral edge. The radially side portions can typically extend from the peripheral edge towards the central axis. The radially side portions can typically also extend substantially in the axial direction.

[0029] The spaced-apart protrusions may be uniformly circumferentially dispersed along the peripheral edge.

[0030] The spaced-apart protrusions may be non-uniformly circumferentially dispersed along the peripheral edge.

[0031] Each of the spaced-apart protrusions may extend axially from the floor surface to the upper end surface of the piston upper end. In another example, each of the spaced-apart protrusions may extend axially from the floor surface to the second circumferential extension. As described above, the second circumferential extension is axially disposed at an axial distance from the floor surface. The axial distance is one-fourth of the depth of the piston bowl. In other examples, each of the spaced-apart protrusions may extend axially from the floor surface to a predetermined intermediate axial distance that is greater than one-fourth of the depth of the piston bowl but less than the depth of the piston bowl. In other words, each of the spaced-apart protrusions may extend axially towards an axial distance that is in a range greater than one-fourth of the depth of the piston bowl but less than the depth of the piston bowl.

[0032] Furthermore, or alternatively, the flat or concave surface may extend axially from the intersection between the flat or concave surface and the floor surface towards the upper end surface of the piston upper end.

[0033] In some examples, the flat or concave surface may extend axially from the intersection between the flat or concave surface and the floor surface to the upper end surface of the upper end of the piston. In another example, the flat or concave surface may extend axially from the floor surface to the second circumferential extension. As an example, the flat or concave surface extends axially from the intersection between the flat or concave surface and the floor surface to the second circumferential extension.

[0034] As described above, the second circumferential extension is axially disposed at an axial distance from the floor surface. The axial distance is one-fourth of the depth of the piston bowl. In other examples, the flat or concave surface may extend axially from the floor surface to a predetermined intermediate axial distance that is greater than one-fourth of the depth of the piston bowl but less than the depth of the piston bowl. In other words, the flat or concave surface may extend axially towards an axial distance that is greater than one-fourth of the depth of the piston bowl but less than the depth of the piston bowl.

[0035] Each of the spaced projections may extend radially at least partially beyond the floor portion.

[0036] The first circumferential extension may generally be the maximum circumferential extension of the extension of the flat or concave surface measured along the circumferential direction. Thus, the first circumferential extension is the maximum circumferential extension of the flat or concave surface. Thus, the first circumferential extension may generally be referred to as the first maximum circumferential extension. One of the advantages of having a projection with a maximum circumferential extension at the bottom (near the floor surface of the piston bowl design) is that it can reduce the radial tensile stress compared to previously known designs of piston bowl projections. In other words, the wider the circumferential extension of the flat or concave surface at the intersection with the floor surface, the more generally it can contribute to reducing the level of radial tensile stress.

[0037] Each of the projections may extend axially mostly from the floor surface to the upper end surface of the piston.

[0038] The flat or concave surface may generally extend circumferentially between laterally extending side portions that face each other.

[0039] According to a second aspect of the present disclosure, a piston for an internal combustion engine (ICE) is provided, the piston having an axial upper end with a piston bowl that extends axially and radially and is intended to form part of a combustion chamber. The piston bowl has an axial floor with a floor surface, and a peripheral portion that extends axially between the floor surface and an upper surface of the axial upper end. The piston bowl further has an axial depth defined by an axial distance between the floor surface and the upper surface. The piston bowl further comprises a plurality of spaced-apart protrusions distributed circumferentially around the peripheral portion, each of the spaced-apart protrusions extending mostly radially towards a central axis and further extending mostly axially from the floor surface towards the upper surface. Each of the spaced-apart protrusions has opposing radially extending side portions and further has a flat or concave surface extending between the opposing radially extending side portions. The flat or concave surface has a first circumferential extension at an intersection between the flat or concave surface and the floor surface. Further, a ratio of a sum of the first circumferential extensions of all the spaced-apart protrusions along the peripheral portion to a circumferential extension of the peripheral portion is at least 30%, preferably at least 45%, and most preferably at least 60%.

[0040] The effects and features of this second aspect of the present disclosure are substantially the same as those described above with respect to the first aspect of the present disclosure. The embodiments referred to with respect to the first aspect of the present disclosure are largely compatible with the second aspect of the present disclosure.

[0041] According to a third aspect of the present disclosure, an internal combustion engine system is provided that includes an internal combustion engine for burning fuel and has a combustion chamber at least partially delimited by a cylinder and a reciprocating piston according to any one of the first and second aspects. The reciprocating piston is movable within the cylinder between a bottom dead center BDC and a top dead center TDC, and an upper end of the piston is arranged to form part of the combustion chamber.

[0042] The effects and features of this third aspect of the present disclosure are substantially the same as those described above with respect to the first and second aspects of the present disclosure. The embodiments referred to with respect to the third aspect of the present disclosure are largely compatible with the first and second aspects of the present disclosure.

[0043] The present disclosure can be used in any type of ICE system including the proposed piston, but is particularly useful in diesel internal combustion engine systems. Thus, according to at least one embodiment, the ICE system is a diesel ICE system. However, the proposed piston can also be used in a hydrogen ICE system. Thus, according to at least one embodiment, the ICE system is a hydrogen ICE system.

[0044] According to a fourth aspect of the present disclosure, a vehicle is provided that includes a piston according to any one of the first and second aspects and / or an internal combustion engine combustion system according to the third aspect. Thus, the vehicle includes a piston according to the first aspect of the present disclosure. Further, or alternatively, the vehicle includes a piston according to the second aspect of the present disclosure. Further, or alternatively, the vehicle includes an internal combustion engine system according to the third aspect of the present disclosure.

[0045] The effects and features of this fourth aspect of the present disclosure are substantially the same as those described above with respect to the first, second, and third aspects of the present disclosure. The embodiments referred to with respect to the fourth aspect of the present disclosure are largely compatible with the second and third aspects of the present disclosure.

[0046] Further advantages and advantageous features of the present disclosure are disclosed in the following description and the dependent claims. It will also be readily understood that embodiments other than those described below can be created by combining different features without departing from the scope of the present disclosure.

[0047] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "includes" and / or "including", when used herein, specify the presence of the stated feature, integer, step, operation, element, and / or component, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0048] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms used herein should be construed to have a meaning that is consistent with their meaning in the context of this specification and the relevant art and should not be construed in an idealized or overly formal sense unless expressly so defined herein.

[0049] The foregoing, as well as additional objects, features, and advantages of the present disclosure, will be better understood through the following non-limiting detailed description of the exemplary embodiments of the present disclosure.

Brief Description of the Drawings

[0050]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 3C

Figure 3D

Figure 3E

Figure 4A

Figure 4B

Figure 4C

Figure 5A

Figure 5B

Figure 5C

Figure 6

[0051] The present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the present disclosure are shown. However, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete. Throughout the description, like reference numerals refer to like elements.

[0052] Referring specifically to FIG. 1, a vehicle 1 in the form of a truck is provided. The vehicle 1 includes an internal combustion engine (ICE) system 100 for supplying power to and driving the vehicle 1. The ICE system 100 of FIG. 1 also includes an ICE 10. The ICE 10 is intended for the combustion of diesel fuel. However, in other examples, the ICE 10 may be provided in the form of a hydrogen internal combustion engine, i.e., an ICE intended for the combustion of hydrogen gas fuel. Specifically, the ICE system 100 is a piston ICE system. Here, the truck is the vehicle 1 having a single propulsion system with tractive force provided by the ICE system 100. However, the truck may equally well be a hybrid electric vehicle. As an example, a hybrid electric vehicle includes an auxiliary electric propulsion system having at least one high-voltage battery and at least one electromechanical machine, and further includes the ICE system 100.

[0053] As shown in FIG. 1, the ICE system 100 further includes a control unit 90, also referred to herein as a controller. Here, the controller 90 is an integral part of the main electronic control unit for controlling the vehicle and various components of the vehicle. The controller 90 is arranged to communicate with components of the ICE system 100, particularly the ICE 10. As an example, the controller 90 is configured to control a controllable fuel injector to inject at least one gas fuel jet towards the piston during a fuel injection period. The controller 90 may be a separate component of the vehicle 1 and communicate with the main electronic control unit for controlling the vehicle and various components of the vehicle.

[0054] Referring now to FIG. 2, as described above in connection with FIG. 1, one exemplary embodiment of an ICE system 100 for incorporation into a vehicle 1 is shown. In particular, FIG. 2 is a perspective cross-sectional view of the components of an ICE according to an exemplary embodiment of the present disclosure. As shown in FIG. 2, the ICE 10 includes at least one cylinder 2. Further, the ICE 10 has at least one combustion chamber 7 that is at least partially delimited by the cylinder 2. Further, the ICE 10 includes a piston 3 as disclosed herein, for example, in FIGS. 2 and 3A-3E. Other examples of pistons 3 suitable for incorporation into the ICE 10 and ICE system 100 of FIG. 2 will be described in connection with FIGS. 4A-4C, FIGS. 5A-5C, and FIG. 6. The piston 3 is arranged and configured to reciprocate within the cylinder 2. The piston 3 is arranged to reciprocate within the cylinder 2, and the ICE 10 is operative to combust a fuel (e.g., diesel fuel), whereby the movement of the piston 3 reciprocating within the cylinder 2 is transmitted to the rotational movement of the crankshaft 4 as shown in FIG. 2. Accordingly, the ICE system 100 includes a crankshaft 4.

[0055] Note that FIG. 2 shows only a single cylinder 2 having a combustion chamber 7 and a reciprocating piston 3 disposed therein, but the ICE 10 typically includes a plurality of cylinders 2 operative to combust a fuel (e.g., diesel fuel), whereby the movement of the pistons 3 reciprocating within the cylinders 2 is transmitted to the rotational movement of the crankshaft 4. The crankshaft 4 is further coupled to a transmission (not shown) for supplying torque to a drive element. In the case of a large vehicle such as a truck, the drive element is a wheel, but the ICE system 10 can also be used in other equipment such as construction machinery, marine applications, and generators.

[0056] Generally, each cylinder 2 is provided with a corresponding piston 3 connected to the crankshaft 4 of the ICE10. As shown in FIG. 2, the piston 3 is disposed within the cylinder 2 so as to reciprocate along the central axis Ac. Since the piston 3 is mechanically connected to the crankshaft 4 of the ICE10, the piston 3 is movable within the cylinder 2 between the top dead center position and the bottom dead center position. Therefore, the piston 3 reciprocates within the cylinder 2 and is connected to the crankshaft 4 such that the piston 3 moves in the reverse direction at the top dead center position and the bottom dead center position within the cylinder 2. As indicated by the arrows in FIG. 2, the position of the upper dead center is shown as the top dead center (TDC), and the position of the lower dead center is shown as the bottom dead center (BDC).

[0057] As shown, for example, in FIG. 2 and further in other figures such as FIGS. 3A - 3E, the piston 3 extends in the axial direction A and the radial direction R. The diameter of the piston 3 is smaller than the inner diameter of the cylinder CD, as shown in FIG. 2. Further, the piston 3 has a circumferential extension along the circumferential direction C. The piston 3 also has a longitudinal central axis Ac, which will generally be referred to hereinafter as the axial central axis. The axial central axis Ac of the piston 3, although not strictly necessary, is usually arranged coaxially with the axial central axis of the gas injector 13, as shown in FIG. 2. However, in some examples, the axial central axis of the fuel gas injector 13 may be slightly offset from the axial central axis Ac of the piston 3.

[0058] As used herein, the terms "radial" or "radially" refer to a relative direction that is substantially perpendicular to the axial centerline of a particular component. Further, the terms "longitudinal", "longitudinally", "axially" or "axial" refer to a relative direction that is substantially parallel and / or coaxial with the axial centerline of a particular component. Also, the terms "longitudinal", "longitudinally", "axially" or "axial" refer to a direction that at least extends between the axial ends of a particular component, and typically refers to the direction of the longest extension of the device and / or component along the device or component. The terms "perpendicular" and "perpendicularly" typically correspond to the axial direction. The axial direction is generally the same as the direction in which the piston moves within the cylinder. Further, the terms "circumference", "circumferential", or "circumferentially" refer to the circumference or circumferential direction with respect to a central axis that extends in the direction of the axis, typically the longest extension of the device and / or component.

[0059] As used herein, the terms "upstream" and "downstream" refer to the relative directions with respect to the flow of fluid within a fluid path. For example, "upstream" refers to the direction in which the fluid flows in, and "downstream" refers to the direction in which the fluid flows out. Thus, in this context, the terms upstream and downstream are generally defined with respect to the flow of fuel from the fuel tank to the combustion chamber 7 of cylinder 2, as shown in FIG. 2.

[0060] Similarly, terms such as "upper", "above", "uppermost", and "floor", "lower", "bottom", "below", etc. generally refer to the relative positions of components or components with respect to the axial direction A.

[0061] Each of the cylinders 2 at least partially defines a combustion chamber 7. Each of the cylinders 2 comprises a cavity 2a that defines an internal volume. One end of the cylinder cavity is closed by a cylinder head 14. Further, each of the cylinders 2 has an inner circumferential side wall 29. Similarly, the cylinder head 14 has an inner surface 21. These components, together with the portion of the piston 3 facing the combustion chamber, generally define the combustion chamber 7. The cylinder head can be provided in several different shapes, and thus it should be noted that it does not necessarily have to be in the so-called pent-roof shape as shown in FIG. 2. As an example, the cylinder head 14 can have a basically flat bottom inner surface 21. Other examples of the cylinder head are also possible. In addition, the inner wall of the cylinder may be provided by a so-called cylinder liner as is generally known in the art.

[0062] As shown in FIG. 2 and further, for example, in FIGS. 3A - 3E, the reciprocating piston 3 has a piston upper end, which is shown here as the axial upper end 16 of the piston 3. The piston axial upper end is here the so-called piston crown. The piston axial upper end 16 comprises a piston bowl 6. Thus, the piston bowl 6 is arranged at the upper axial end of the piston 3 as shown in FIG. 2. The piston bowl 6 is arranged and intended to form part of the combustion chamber 7. Thus, the piston bowl 6 is here the portion of the piston 3 facing the combustion chamber. FIG. 2 shows one example of a piston 3 having a piston bowl 6 at its piston axial upper end 16, and the surface 6a of the piston bowl 6 is arranged to define the combustion chamber 7 together with the cavity 2a of the cylinder 2. Thus, as shown in FIG. 2, the piston bowl surface 6a forms the combustion chamber 7 together with the inner surface 21 of the cylinder head 14 and the circumferential side wall 29 of the cylinder 2.

[0063] Similar to the piston 3, the piston bowl 6 extends in the axial direction A, in the radial direction R, and has a circumferential extension in the circumferential direction C. In this example, the longitudinal central axis Ac of the piston 3, i.e., the axial central axis, is coaxial with the axial central axis of the piston bowl 6 as shown in FIG. 2.

[0064] Each cylinder 2 may further include at least one, usually a plurality of, inlet channels having at least one intake valve 70 for controlling the flow of intake air into the combustion chamber 7 at its vertical upper end, and at least one, usually a plurality of, exhaust channels having at least one exhaust valve 60 for controlling the discharge of exhaust gas generated from the fuel combustion process taking place within the cylinder 2.

[0065] In particular, one or more introduction ports equipped with corresponding intake valves 70 are arranged in the cylinder head 14. Thus, as shown in FIG. 2, the ICE system 100 further includes an intake manifold 72 that forms one or more intake guides arranged to direct air to the cylinders 2. Similarly, one or more exhaust ports equipped with corresponding exhaust valves 60 are arranged in the cylinder head 14. Thus, as shown in FIG. 2, the ICE system 100 further includes an exhaust guide 62 arranged to direct the gas from the cylinders 2.

[0066] The configuration of the cylinders can be, for example, linear, V-shaped, or other suitable types. The ICE system 100 may also include additional engine components and system components.

[0067] Furthermore, at least one fuel injector 13 is arranged in the cylinder head 14, and fuel is injected into the cylinder 2 as a fuel spray 51 via this fuel injector 13. The fuel here is diesel fuel. In other examples, the fuel is hydrogen fuel. Thus, the fuel injector 13 is vertically arranged at the center of the roof of the combustion chamber 7.

[0068] In the case of a diesel ICE system, the fuel is preferably injected at a pressure in the range of 600 to 3000 bar. Generally, in the case of an engine system using EGR, it may be preferable to be about 1000 to 2500 bar, and in the case of not using EGR, it may be preferable to be about 800 to 1400 bar. In the case of a hydrogen ICE system, the hydrogen gas fuel is injected into the combustion chamber 7 at a low injection pressure of 15 to 60 bar and is injected toward the piston bowl 6. However, in the case of other gas ICE systems, the controllable fuel injector is controllable to inject the gas fuel into the combustion chamber at an injection pressure of up to about 500 bar.

[0069] The ignited fuel spray may form a plume, for example, inside the combustion chamber 7.

[0070] The injector 13 may be any suitable type of injector capable of injecting fuel. Generally, the fuel injector 13 is disposed axially above the piston 3 within the cylinder 2. The fuel injector 13 is usually disposed at the center of the cylinder head 14, and thus, the geometric central axis A of the fuel injector 13 coincides with the geometric central axis of the cylinder 2, and the geometric central axis of the cylinder 2 is also the axis of the reciprocating motion of the piston 3, which is indicated herein by the reference numeral Ac. Therefore, the geometric central axis of the cylinder 2 and the central axis of the piston 3 may be collectively indicated by the reference numeral Ac.

[0071] The ICE 10 advantageously includes a plurality of cylinders 2, each cylinder 2 is provided with a piston 3, and each piston 3 is connected to a common crankshaft 4, for example, and is a 4-stroke ICE. An ICE operable according to the conventional 4-stroke process performs an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke.

[0072] The fuel injector 13 can directly inject fuel into the combustion chamber 7 and towards the piston 3. The fuel injector 13 is provided with at least one, preferably a plurality of, injection orifices 46 that allow pressurized fuel to flow into the combustion chamber 7. Thereby, the injected fuel provides kinetic energy within the combustion chamber 7 and causes a complete mixing of the fuel and the air contained therein. To promote the combustion of the fuel and air within the combustion chamber 7, the piston 3 further includes a piston bowl 6 according to any one of the examples shown in FIGS. 3A - 3E, FIGS. 4A - 4C, FIGS. 5A - 5C, and FIG. 6. The design of the piston 3 and its piston bowl will be further described in more detail below.

[0073] The fuel injector 13 is configured to be controlled by a controller 90 (FIG. 1). Thus, the fuel injector is a controllable fuel injector 13. The fuel injector 13 can be controlled by several different types of actuators including, but not limited to, pneumatic actuation control, electronic actuation control, electromechanical actuation control, hydraulic actuation control, and combinations thereof.

[0074] The fuel injector 13 is connected to and in fluid communication with a fuel tank (not shown). The number of fuel gas injectors 13 may be equal to the number of cylinders 2 of the ICE 10. Each of the fuel gas injectors 13 is arranged to be in fluid communication with the fuel tank.

[0075] In the case of a hydrogen ICE system, the ICE 10 may be provided with an ignition source such as a spark plug (not shown).

[0076] Here, once again, the design of the piston 3 of the ICE system 100 will be described. FIGS. 3A - 3E show one exemplary embodiment of a piston and a piston crown for the ICE 10 and the ICE system 100 as described above in connection with FIGS. 1 and 2. In particular, FIG. 3A is a perspective top view of the axial upper end 16 of the piston having a piston bowl 6 according to one exemplary embodiment, FIG. 3B is a top view of the piston upper end of FIG. 3A, and FIG. 3C is a perspective cross - sectional view of the axial upper end 16 of the piston of FIG. 3A according to one exemplary embodiment. FIG. 3D is a cross - sectional view of the piston 3 and its upper end 16 along the axial A and radial R directions. FIG. 3E is a perspective axial cross - sectional view of the piston 3 taken along a predetermined axial distance (height) of the piston bowl and along the radial R and circumferential C directions.

[0077] In the illustrated embodiment, the axial upper end 16 of the piston forms an integral part of the piston 3. However, it is also conceivable to provide the axial upper end 16 of the piston as a separate unit and attach it to one or more piston base parts to form the complete piston 3. The axial upper end 16 of the piston generally corresponds to the so - called piston crown. The axial upper end 16 of the piston usually has an axial upper end face 5, i.e., an upper face, which faces the combustion chamber 7 of the cylinder 2 when the piston is disposed within the cylinder. Here, the axial upper end face 5 is the uppermost part of the piston 3. For ease of reference, the axial upper end face may be denoted as the upper end face 5.

[0078] FIGS. 3A - 3E show the axial upper end 16 of the piston in more detail. For example, as shown in FIG. 3C, the piston bowl surface 6a faces the combustion chamber 7 when disposed within the ICE 10 as illustrated in FIG. 2. The piston bowl surface 6a comprises a peripheral portion 20 and a floor portion 11 connected to and surrounded by the peripheral portion 20. In other words, the piston bowl 6 comprises a peripheral portion 20 and an axial floor portion 11 connected to and surrounded by the peripheral portion 20. The axial floor portion 11 comprises a floor surface 11a.

[0079] The piston bowl 6 can be provided in several different ways. As shown in FIGS. 3A-3E, the floor portion 11 is at least partially defined by the piston bowl surface 6a. The floor portion 11 typically has a floor surface 11a that is part of the piston bowl surface 6a. As shown in FIG. 2, in combination with FIGS. 3A-3E, the piston bowl 6 is here defined by a peripheral portion 20, a central apex 18, and an intermediate portion 19. Thus, as can be seen from FIGS. 3A-3E, the floor portion 11 may be substantially dome-shaped with the central apex 18 coinciding with the central axis Ac of the piston 3. The floor portion 11 may form part of the intermediate portion 19 and extend circumferentially from the dome shape to form a dome side surface that forms a dome angle therebetween. Thus, the floor portion 11 can generally have a dome-shaped configuration that is at least partially defined by the central apex 18. Here, the floor portion 11 extends from the peripheral portion 20 to the central axis Ac at the center of the central apex 18. The floor portion 11 may be aligned with the peripheral portion 20, as shown, for example, in FIGS. 3A and 3E.

[0080] Generally, although not strictly essential, the intermediate portion 19 extends between the peripheral portion 20 and the central apex 18, thereby forming the piston bowl surface 6a. As an example, here at least the intermediate portion 19 and the central apex 18 together define the floor surface 11a. In other examples, a part of the peripheral portion 20, the intermediate portion 19, and the central apex 18 together define the floor surface 11a and thus together define the piston bowl surface 6a.

[0081] Here too, the peripheral portion 20 extends in the axial direction A. The peripheral portion 20 extends in the axial direction A between the floor surface 11a and the upper end surface 5 of the axial upper end 16. The peripheral portion 20 is here the radially outermost portion of the piston bowl 6, while the central apex 18 is the radially innermost portion of the piston bowl 6. The peripheral portion 20, the intermediate portion 19, and the central apex 18 together form a cavity that opens outward, as shown, for example, in FIG. 3A. In other piston bowl designs where the upper end surface may be an integral part of the piston bowl, the upper end surface 5 may be the radially outermost portion of the piston bowl 6.

[0082] The piston bowl 6 has an axial depth H, as shown, for example, in FIGS. 3C, 3D, and 3E. The axial depth H of the piston bowl 6 is shown in FIG. 3D and is defined by the axial distance between the floor surface 11a and the upper end surface 5, as also shown, for example, in FIGS. 3C and 3E. Generally, the axial depth H defines the maximum axial distance between the floor surface 11a and the upper end surface 5. Thus, the axial depth H is defined as the distance between the lowermost surface portion of the floor of the piston bowl 6 and the upper end surface 5, as shown in FIG. 3D.

[0083] In addition, the piston bowl 6 includes a plurality of spaced-apart protrusions 40, as shown in FIGS. 3A-3E. Here, the protrusions 40 are disposed on the peripheral portion 20. The spaced-apart protrusions 40 are circumferentially dispersed around the central axis Ac. In particular, the protrusions 40 are circumferentially dispersed and spaced apart from each other in the circumferential direction C around the peripheral portion 20. Thus, the plurality of spaced-apart protrusions 40 are circumferentially dispersed and arranged around the peripheral portion 20.

[0084] In FIGS. 3A-3E, the peripheral portion 20 includes a plurality of spaced-apart protrusions 40. The spaced-apart protrusions 40 are circumferentially dispersed around the peripheral portion 20 and around the central axis Ac. In this way, the plurality of spaced-apart protrusions 40 are circumferentially dispersed and arranged around the peripheral portion 20.

[0085] From the term "protrusion", it can be seen that the protrusion portion must have a certain axial extension in the axial direction A, a certain radial extension in the radial direction R, and a certain circumferential extension along the circumferential direction C.

[0086] Thus, each of the spaced-apart protrusions 40 extends mostly in the axial direction A from the floor surface 11a toward the upper end surface 5. In FIGS. 3A-3E, each of the spaced-apart protrusions 40 extends in the axial direction A from the floor surface 11a to the upper end surface 5 of the piston upper end 16. Thus, each of the spaced-apart protrusions 40 extends continuously in the axial direction A from the floor surface 11a to the piston upper end surface 15. As will be further described below, other extensions are also conceivable.

[0087] Furthermore, as shown in, for example, FIG. 3A, each of the spaced-apart protrusions 40 mostly extends in the radial direction R toward the central axis Ac. Each protrusion 40 extends from an adjacent side surface of the peripheral portion 20 toward the central axis Ac of the piston 3 and forms a vertex toward the central axis Ac. Accordingly, each of the protrusions 40 faces the central axis Ac of the piston 3. The protrusions 40 are arranged on the peripheral portion 20.

[0088] Each of the spaced-apart protrusions includes, for example, opposing radial side portions 41, 42 as shown in FIG. 3A. Each of the radial side portions 41, 42 extends in the radial direction R from the peripheral portion 20. One of the radial side portions is the first radial side portion 41, and the other of the radial side portions is the second radial side portion 42. The first radial side portion 41 and the second radial side portion 42 each extend in the radial direction. Accordingly, in the present specification, the radial side portion may also be referred to as a side portion extending in the radial direction or a radial side portion extending in the radial direction. The first radial side portion 41 and the second radial side portion 42 are arranged to face each other in the circumferential direction C as shown in, for example, FIGS. 3A and 3C.

[0089] As shown in FIGS. 3A to 3E, the radially extending side portions 41, 42 are curved convex side portions. In other examples, the radially extending side portions 41, 42 may be curved concave side portions. In still other examples, the radially extending side portions 41, 42 may be flat side portions.

[0090] Furthermore, in FIGS. 3A - 3E, each of the opposing radial side portions 41, 42 comprises a plurality of regions of different convex - curved profiles. In FIG. 3C, an example of a protrusion 40 is shown, which includes a first radially - extending side portion 41 having first and second convex - curved profiles 41a, 41b of different curved convex profiles, and a second radially - extending side portion 42 having first and second convex - curved profiles 42a, 42b of different curved convex profiles. In other examples, the first radially - extending side portion 41 has a uniform curved convex profile, and the second radially - extending side portion 42 has a uniform curved convex profile.

[0091] Each of the spaced - apart protrusions 40 extends at least partially beyond the floor portion 11 in the radial direction R here. Further, each of the spaced - apart protrusions 40 extends in the radial direction R so as to align with the floor surface 11a of the floor portion 11.

[0092] In the embodiment shown in FIGS. 3A - 3E, the piston bowl 6 comprises a total of six protrusions 40 evenly distributed around the piston bowl 40. However, the number of protrusions 40 may be other numbers, such as eight protrusions.

[0093] The protrusions 40 may be distributed at 45 - degree intervals around the central axis Ac. Other intervals are also conceivable.

[0094] In FIG. 3A, the spaced - apart protrusions 40 are evenly circumferentially distributed around the peripheral portion 20. In other design variations, although not shown, the spaced - apart protrusions 40 may be unevenly circumferentially distributed on the peripheral portion 20.

[0095] As shown in FIGS. 3A - 3E, each of the spaced - apart protrusions 40 further includes a surface 43 that extends between opposing radially - extending sides 41, 42. In FIGS. 3A - 3E, the surface 43 extends in the circumferential direction C between opposing radially - extending sides 41b, 42b. Further, in FIGS. 3A - 3E, the surface 43 is a concave surface 43b. FIG. 3E is a cross - sectional view of the concave surface 43b, showing the concave profile of the concave surface 43b in more detail. The radius of the concave profile of the concave surface 43b is selected in consideration of the use of the piston 3. As an example, the radius of the concave profile of the concave surface 43b follows the radius of curvature of the peripheral portion 20. That is, the concave radius of curvature of the concave surface 43b coincides with the concave radius of curvature of the peripheral portion 20. In such an example, the radius of curvature of the concave surface is essentially perpendicular to the axis center of the piston bowl 6. However, it should be easily understood that the radius of the concave profile of the concave surface 43b may have a concave curvature different from the concave curvature of the peripheral portion 20. As an example, FIG. 3C shows a design where the concave radius of curvature of the concave surface 43b is different from the concave radius of curvature of the peripheral portion 20. When defining and designing the recess of the concave surface 43b, the recess of the concave surface is usually determined based on a Cartesian coordinate system (not a cylindrical coordinate system), as is also generally known in the art. In other words, in the case of the concave surface 43b, the radius of curvature is the radius of the circle that best fits the normal cross - section or a combination thereof. The radius of curvature of the concave surface 43b may be constant along the circumferential direction C or may vary slightly along the circumferential direction C.

[0096] In other examples, the surface may be a flat surface. FIG. 6 shows an example of the surface 43 in the shape of a flat surface 43a in more detail.

[0097] For ease of reference, the following description of the surface 43 is made with reference to the concave surface 43b, as shown in FIGS. 3A - 3E, for example. However, this description is equally applicable to a surface in the shape of a flat surface 43a, as shown in FIG. 6.

[0098] The concave surface 43b extends mostly in the circumferential direction C. As described above, the concave surface 43b extends here between the radially extending radial side portions 41, 42 that face each other. More specifically, the concave surface 43b extends in the circumferential direction C between the radially extending radial side portions 41, 42 that face each other. In FIGS. 3a - 3E, of the opposing radial side portions, the first radial side portion 41 intersects the concave surface 43b along the intersection edge 45. Similarly, the second radial side portion 42 of the opposing radial side portions intersects the concave surface 43b along another opposing intersection edge 46.

[0099] Therefore, the concave surface 43b is arranged to form a bridging surface between the opposing radial side portions 41, 42.

[0100] The concave surface 43b is also arranged to face the central axis Ac of the piston 3.

[0101] In other words, by providing the flat surface 43a or the concave surface 43b between the opposing radial side portions 41, 42, the surfaces 43, 43a, 43b between the opposing radial side portions become non - convex surfaces. As used herein, the term "non - convex" means that the surface 43 does not protrude towards the central axis Ac of the piston 3. Rather, the surfaces 43, 43a, 43b are, as can be seen from FIG. 3E, straight or concave towards the circumferential surface on the outer side in the radial direction of the piston 3.

[0102] In some examples, as can be seen from FIG. 3E, the radial cross - sectional profile passing through the protrusion 40 is similar to, for example, a truncated triangle, with the truncated side forming the flat surface 43a or the concave surface 43b.

[0103] The piston bowl 6 is usually obtained by forging. As an example, the surfaces 43, 43a, 43b of the piston bowl 6 are forged.

[0104] Further, the concave surface 43b extends substantially over the axial direction A. As also shown in FIGS. 3A and 3E for example, the concave surface 43b extends basically in the axial direction A from the intersection 44 between the concave surface 43b and the floor surface 11a to the upper end surface 5 of the piston upper end 16. The intersection 44 defines the distinction between the concave surface 43b and the floor surface 11a. Thus, the intersection 44 also defines the distinction between the protrusion 40 and the floor surface 11a. The intersection 44 extends in the circumferential direction C. Also, the intersection 44 may generally be an imaginary line indicating the circumferential extension at the maximum circumferential extension of the concave surface 43b, and is indicated by reference numeral a in FIG. 3C.

[0105] In FIGS. 3A to 3E, the concave surface 43b has at least an extension between a first circumferential extension a at the intersection 44 and a second circumferential extension b at an axial distance h from the intersection 44. In this example, the first circumferential extension a is larger than the second circumferential extension b. The first circumferential extension a is larger than the second circumferential extension b in the circumferential direction C.

[0106] Generally, the first circumferential extension a is the maximum circumferential extension in the circumferential direction C of the concave surface 43b. That is, the first circumferential extension a defines the maximum circumferential extension in the circumferential direction C of the concave surface 43b. Thus, in the following description, the first circumferential extension generally refers to the first maximum circumferential extension a.

[0107] In particular, as shown in FIGS. 3A to 3E, the concave surface 43b has the first maximum circumferential extension a at the intersection 44 between the concave surface 43b and the floor surface 11. In addition, as shown in FIGS. 3A to 3E, the concave surface 43b has a second circumferential extension b at a position of an axial distance h from the floor surface 11a. The axial distance h is one-fourth of the piston bowl depth H. The axial distance h and the depth H refer to the distance in the axial direction A. In addition, the axial distance h and the depth H refer to the distance in the axial direction A measured in the direction from the floor surface 11a toward the upper end surface 5.

[0108] As shown by combining FIGS. 3A and 3E, for example, the intersecting edges 45, 46, in combination with the first maximum circumferential extension a and the second circumferential extension b, define an extension of the concave surface 43b.

[0109] Furthermore, the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.4 or less. Thereby, the protrusion 40 is designed such that the durability and fatigue characteristics of the protrusion are improved during the normal operation of the piston 3. The protrusion 40 is an improved design that can withstand a higher fatigue level compared to other designs of piston bowl protrusions. The ratio of the second circumferential extension b to the first maximum circumferential extension is also referred to herein as the relative circumferential width ratio.

[0110] In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.4.

[0111] In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.

[0112] In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.26. As an example, the second circumferential extension b is 2.4 mm and the first maximum circumferential extension a is 9.3 mm. In this example, the depth H is 18.6 mm.

[0113] In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.25. As an example, the second circumferential extension b is 4.2 mm and the first maximum circumferential extension a is 16.8 mm. In this example, the depth H is 19.4 mm.

[0114] In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.17. As an example, the second circumferential extension b is 2.9 mm and the first maximum circumferential extension a is 17.5 mm. In this example, the depth H is 18.5 mm.

[0115] In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is from 0.4 to 0. In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.4 or less, but greater than 0. Thus, in one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is from 0.4 to 0.05. In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is from 0.4 to 0.1. In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is from 0.3 to 0.15. In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is from 0.26 to 0.17. In one example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is from 0.25 to 0.17.

[0116] The combination of the above-described ratio of the relative circumferential widths and the configuration in which the surface 43 has the shape of the flat surface 43a or the concave surface 43b improves the design of the lower region of the protrusion, and thus the protrusion at the lower part of the piston bowl 6. More specifically, the protrusion 40 having the flat surface 43a or the concave surface 43b extending between the opposing radial side portions 41, 42 and the condition that the ratio of the second circumferential extension b to the first circumferential extension a is 0.4 or less results in a design of the piston 3 that is less affected in terms of required durability. Such a design can better withstand even the severe fatigue conditions that occur during normal use of the piston 3 in large vehicles.

[0117] The configuration of the above-described protrusion is based in part on the observation that when the piston is operating in a "hot state", i.e., when the piston 3 is subjected to a high-temperature load, a high compressive stress is generated in the protrusion. If the magnitude of the compressive stress exceeds a critical level, stress relaxation may occur in the material of the protrusion at a specific temperature. Stress relaxation may occur, for example, as a result of being subjected to a high level of stress for a long time below the yield strength of the material. Thereafter, when the ICE is turned off, i.e., when the vehicle is parked with the ICE not operating or when the ICE is in an idling state, the piston 3 is cooled to a "cold state", and as a result, the stress changes from compressive stress to tensile stress. Thereafter, when the piston 3 is subjected to a cylinder pressure load, fatigue cracks may occur and propagate in more common protrusions due to the cycle of the maximum tensile stress due to the cylinder pressure and the maximum tensile stress due to stress relaxation.

[0118] With the above configuration of the flat surface and the concave surface, it is possible to avoid or at least reduce the important material regions of the protrusion from being subjected to high tensile stress.

[0119] In addition, by combining the ratio of the relative circumferential width and configuring the surface 43 into the shape of the flat surface 43a or the concave surface 43b, it is ensured that the portion of the protrusion 40 that has little influence on the combustion performance is designed such that the compressive stress in the protrusion in the lower axial region is minimized with respect to the temperature load generated during combustion. In addition, the flat surface 43a or the concave surface 43b disposed between the radial side portions 41, 42 contributes to separating the position of the maximum compressive stress due to the temperature load and the position of the maximum tensile stress due to the pressure load. The piston bowl 6 provided with the protrusion 40 in which the maximum stress regions are separated from each other also contributes to an increase in the durability and fatigue life of the protrusion 40 and thus the durability of the piston 3.

[0120] As shown in FIG. 3E, the convex surface 43b itself provides a bowl-shaped design for the lower part of the protrusion 40.

[0121] It should be noted that the concave surface 43b may extend further in the axial direction A than the second circumferential extension b. As shown in FIGS. 3A to 3E, the concave surface 43b extends in the axial direction A from the floor surface 11a and extends substantially to the upper end surface 5. As an example, the concave surface 43b extends in the axial direction A from the floor surface 11a and extends completely to the upper end surface 5. However, in other examples, the concave surface 43b extends in the axial direction A from the floor surface 11a to a predetermined intermediate axial distance between one-fourth of the depth of the piston bowl 6 and the depth H of the piston bowl 6. Therefore, the concave surface 43b extends generally in the axial direction A from the floor surface 11a toward the upper end surface 5. As an example, the concave surface 43b extends generally in the axial direction A from the floor surface 11a toward the upper end surface 5, and the extension in the axial direction A is greater than one-fourth of the depth of the piston bowl 6 but less than the depth H of the piston bowl 6.

[0122] Therefore, as shown in FIG. 3D for example, the extension of the concave surface 43b from the first circumferential extension a to the second circumferential extension b further includes a concave axial extension region. Here too, the concave axial extension region extends from the floor surface 11a toward the upper end surface 5. The protrusion 40 here also has an additional upper convex axially extending surface as shown in FIG. 3D. The lower concave axially extending region and the upper convex axially extending surface form an "S" shape as shown in FIG. 3D.

[0123] In other examples, the concave surface 43b simply extends in the axial direction A from the floor surface 11a to the second circumferential extension b. As described above, the second circumferential extension b is axially disposed at a position axially distant h from the floor surface 11a. The axial distance h is one-fourth of the depth of the piston bowl 6.

[0124] As described above, although not shown in the figures, in an example where the ratio of the second circumferential extension b to the first maximum circumferential extension a is zero (0), the concave surface 43b simply extends in the axial direction A from the floor surface 11a to the second circumferential extension b. In this way, a concave surface 43b similar to a triangle extending in the axial direction A and the circumferential direction C is provided.

[0125] Therefore, the extension of the concave surface 43b is defined by the combination of the axially inclined intersecting edges 45 and 46, the first circumferential extension a at the intersection 44, and the second circumferential extension b at an axial distance h from the intersection 44. Such an extension of the concave surface 43b resembles a trapezoid, i.e., a triangular base shape that has a maximum circumferential width at the intersection 44 and a minimum width at the other axial side, i.e., the second circumferential extension b. For example, in FIG. 3C, the concave surface 43b that forms a trapezoidal surface in the axial direction A and the circumferential direction C can be essentially designed as a duck's foot. It should be understood that the term "triangular base shape" includes triangles with rounded corners, and even triangles with truncated vertices that form isosceles trapezoids. Triangles with non-linear circumferential edges are also conceivable.

[0126] As shown in FIGS. 3A - 3E, the intersecting edges 45, 46 are inclined non-linearly (curvilinearly) from the first maximum circumferential extension a to the second circumferential extension b. However, the intersecting edges 45, 46 may also be inclined linearly in the same manner from the first maximum circumferential extension a to the second circumferential extension b. The intersecting edges 45, 46 are inclined towards the central region (circumferential direction) located on the second circumferential extension b, as shown in FIGS. 3A - 3E. The intersecting edges 45, 46, in combination with the first circumferential extension a and the second circumferential extension b, define the overall extension of the concave surfaces 43, 43a, 43b.

[0127] Similar to the concave surface 43b, the spaced-apart protrusions 40 can extend in several different ways in the axial direction A. As described above and as shown in FIGS. 3A - 3E, each of the spaced-apart protrusions 40 extends in the axial direction A between the floor surface 11a of the floor portion 11 and the upper end surface 5 of the piston upper end 16. In particular, each of the spaced-apart protrusions 40 extends in the axial direction A between the floor surface 11a of the floor portion 11 and the upper end surface 5 of the piston upper end 16. It should be noted that the intersecting edges 45, 46 in FIGS. 3A - 3B may generally extend in the axial direction A between the floor surface 11a of the floor portion 11 and the upper end surface 5.

[0128] In another example, each of the spaced-apart protrusions 40 may simply extend axially A from the floor surface 11a to the second circumferential extension b. As described above, the second circumferential extension b is axially disposed at a position axially distant h from the floor surface 11a. The axial distance h is one quarter of the depth H of the piston bowl 6. In other examples, each of the spaced-apart protrusions 40 may extend axially A from the floor surface 11a to a predetermined intermediate axial distance greater than one quarter of the depth of the piston bowl 6 but less than the depth of the piston bowl 6. In other words, each of the spaced-apart protrusions 40 may extend axially A from the floor surface 11a towards the upper end surface 5 to an axial A distance greater than one quarter of the depth of the piston bowl 6 but less than the depth H of the piston bowl 6. In this example, the concave surface 43b extends axially A in generally the same manner, i.e., from the floor surface 11a towards the upper end surface 5 to a distance greater than one quarter of the depth of the piston bowl 6 but less than the depth H of the piston bowl.

[0129] Optionally, the ratio of the sum of the first circumferential extensions a1, a2, an of all the spaced-apart protrusions 40 along the peripheral edge 20 to the circumferential extension E of the peripheral edge 20 is at least 30%, preferably at least 45%, and most preferably at least 60%. This ratio is also referred to as the circumferential extension ratio. The circumferential extension ratio is a ratio defined as a percentage. Although the percentage is a dimensionless number, the basic unit of the extension is in terms of length.

[0130] In one example, the circumferential extension ratio between the sum of the first circumferential extensions a1, a2, an of all the spaced-apart protrusions 40 along the peripheral edge 20 and the circumferential extension E of the peripheral edge 20 is 0.36. As an example, the first maximum circumferential extension a is 9.3 mm and the circumferential extension E is 26.1 mm. In this example, the second circumferential extension b may be, for example, 2.4 mm.

[0131] In one example, the circumferential extension ratio between the sum of the first circumferential extensions a1, a2, an of all the spaced-apart protrusions 40 along the peripheral portion 20 and the circumferential extension E of the peripheral portion 20 is 0.65. As an example, the first maximum circumferential extension a is 16.8 mm and the circumferential extension E is 26.0 mm. In this example, the second circumferential extension b may be, for example, 4.2 mm.

[0132] In one example, the circumferential extension ratio between the sum of the first circumferential extensions a1, a2, an of all the spaced-apart protrusions 40 along the peripheral portion 20 and the circumferential extension E of the peripheral portion 20 is 0.64. As an example, the first maximum circumferential extension a is 17.5 mm and the circumferential extension E is 27.4 mm. In this example, the second circumferential extension b may be, for example, 2.9 mm.

[0133] In some examples, each of the spaced-apart protrusions 40 extends radially R from the peripheral portion 20 at least to the intermediate portion 19. Further, the peripheral portion 20 extends axially A between the floor portion 11 and the piston upper end 16, usually between the floor surface 11a of the floor portion 11 and the upper end surface 5 of the piston upper end 16.

[0134] Figures 4A - 4C show another design of the piston bowl 6, where the concave surface 43b has a smaller first maximum circumferential extension a compared to the first maximum circumferential extension a of the concave surface 43b in Figures 3A - 3E, while the second circumferential extension b of the concave surface 43b in Figures 4A - 4C is the same as the second circumferential extension b of the concave surface 43b in Figures 3A - 3E. The piston design in Figures 4A - 4C is another example of the concave surface 43b, and the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.4 or less.

[0135] Furthermore, in FIGS. 4A to 4C, the concave surface 43b extends in the axial direction A from the floor surface 11a to an axial distance h corresponding to the axial position of the second circumferential extension b. Here, the protrusion 40 includes an additional surface area 47. The additional surface area 47 extends axially from the axial distance h corresponding to the axial position of the second circumferential extension b to the upper end surface 5. The additional surface area 47 has, here, a profile different from that of the surface 43, for example, a convex surface. Thus, the additional surface area 47 has, here, a profile different from that of the concave surface 43a. The additional surface area 47 may have a curved surface profile similar to the curved profiles of the radial side portions 41, 42. Similarly, the additional surface area 47 may have a surface profile different from the curved profiles of the radial side portions 41, 42. As shown in FIGS. 4A to 4C, the additional surface area 47 extends in the circumferential direction C and generally extends between the radial side portions 41, 42. The additional surface area 47 also mates with the upper end surface 5 as shown in FIGS. 4A to 4C. Here, the additional surface area 47 mates with the upper end surface 5 in a convexly curved shape when viewed in the radial direction R.

[0136] Therefore, as can be easily understood from the above, the concave surface 43b extends in the axial direction A at least from the first maximum circumferential extension a to the axial distance h (H / 4) corresponding to the axial position of the second circumferential extension b. Depending on the design of the protrusion 40, the concave surface 43b extends either to the axial distance h (H / 4), i.e., ends at the second circumferential extension b, or to a predetermined intermediate axial distance between one-fourth of the depth H of the piston bowl 6 and the depth H of the piston bowl 6. When the concave surface 43b ends at the axial distance h (H / 4), i.e., at the second circumferential extension b, the remaining part of the protrusion 40 above the concave surface 43b is generally formed by the additional surface area 47 and the radial side portions 41, 42. Similarly, when the concave surface 43b ends at a predetermined intermediate axial distance between one-fourth of the depth H of the piston bowl 6 and the depth H of the piston bowl 6, the remaining part of the protrusion 40 above the concave surface 43b is generally formed by the additional surface area 47 together with the radial side portions 41, 42. However, as shown in FIGS. 3A - 3E, in other examples, there is no additional surface area 47. That is, the surface 43 of the shape of the concave surface 43b extends basically up to the upper end surface 5. Depending on the overall design of the protrusion 40, as can be seen from FIG. 3C for example, there may be a generally smooth curved transition surface between the concave surface 43b and the upper end surface 5.

[0137] FIGS. 5A - 5C show another design of the piston bowl 6, and each of the spaced protrusions 40 extends to an axial distance shorter than the upper end surface 5 measured from the floor surface 11a. Further, in this example, the concave surface 43b has the same first maximum circumferential extension a as the first maximum circumferential extension a of the concave surface 43b in FIGS. 4A - 4E, while the second circumferential extension b of the concave surface 43b in FIGS. 5A - 5C is the same as the second circumferential extension b of the concave surface 43b in FIGS. 3A - 3E and FIGS. 4A - 4C. The piston design in FIGS. 5A - 5C is another example of the concave surface 43b, and the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.4 or less. Therefore, the fatigue of the protrusion can be increased by a number of different concave surfaces 43b.

[0138] Similar to the design shown in FIGS. 4a - 4C, the concave surfaces 43b in FIGS. 5A - 5C simply extend axially A from the floor surface 11a by an axial distance h corresponding to the axial position of the second circumferential extension b. Thus, the protrusion 40 also has an additional surface area 47 here. The additional surface area 47 extends axially from the axial distance h corresponding to the axial position of the second circumferential extension b to the upper end surface 5. The additional surface area 47 is also a convex profile here. However, in other examples, the concave surfaces 43b in FIGS. 5A - 5C may extend similarly up to the upper end surface 5 as in FIGS. 3A - 3C.

[0139] It should be noted that the other conditions, examples, and features described in relation to FIGS. 1, 2, and 3A - 3E can be combined with the conditions, examples, and features of FIGS. 4A - 4C and FIGS. 5A - 5C unless otherwise defined.

[0140] FIG. 6 shows an example of a protrusion 40 having a flat surface 43a instead of a concave surface. Also in this example, the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.4 or less. Thus, if the ratio of the second circumferential extension b to the first maximum circumferential extension a is 0.4 or less, fatigue of the protrusion can be increased by either the concave surface 43b or the flat surface 43a. In FIG. 6, the axial extension of the flat surface 43a from the first circumferential extension a to the second circumferential extension b is also defined by the concave surface. However, in other examples, the axial extension of the flat surface 43a from the first circumferential extension a to the second circumferential extension b is also defined by a flat surface.

[0141] It should be noted that the other conditions, examples, and features described in relation to FIGS. 1, 2, FIGS. 3A - 3E, FIGS. 4A - 4C, and FIGS. 5A - 5C may be incorporated into and combined with the piston bowl 6 in FIG. 6 unless otherwise defined in another way.

[0142] Briefly, a piston 3 extending in an axial direction A and a radial direction R is provided. The piston 3 comprises an axial upper end 16 having a piston bowl 6 intended to form part of a combustion chamber 7. The piston bowl 6 comprises an axial floor 11 having a floor surface 11a and a peripheral portion 20 extending in the axial direction A between the floor surface 11a and an upper surface 5 of the axial upper end 16. The piston bowl 6 defines an axial depth H defined by an axial distance between the floor surface 11a and the upper surface 5. Further, the piston bowl 6 comprises a plurality of spaced-apart projections 40 arranged circumferentially distributed around the peripheral portion 20. Each of the spaced-apart projections 40 extends mostly in the radial direction R towards a central axis Ac and further extends mostly in the axial direction A from the floor surface 11a towards the upper surface 5. Each of the spaced-apart projections 40 has opposing radial side portions 41, 42 and further comprises flat surfaces 43, 43a or concave surfaces 43, 43b extending between the opposing radial side portions 41, 42. The flat surface 43a or the concave surface 43b comprises a first circumferential extension a at an intersection 44 between the flat or concave surface and the floor surface 11a and further comprises a second circumferential extension b at an axial distance h from the floor surface 11a. The axial distance h is one quarter of the depth H of the piston bowl. Additionally, the second circumferential extension b and the first circumferential extension a define a ratio of 0.4 or less.

[0143] Advantages related to the improvement of fatigue can also be provided only by the circumferential extension ratio, i.e., the ratio of the sum of the first circumferential extensions a1, a2, an of all the spaced-apart projections 40 along the peripheral portion 20 to the circumferential extension E of the peripheral portion 20 is at least 30%, preferably at least 45%, most preferably at least 60%.

[0144] Accordingly, a piston 3 extending in the axial direction A and the radial direction R is also provided. The piston 3 comprises an axial upper end 16 having a piston bowl 6 intended to form part of the combustion chamber 7. The piston bowl 6 comprises an axial floor portion 11 having a floor surface 11a and a peripheral portion 20 extending in the axial direction A between the floor surface 11a and the upper end surface 5 of the axial upper end 16. The piston bowl 6 defines an axial depth H defined by the axial distance between the floor surface 11a and the upper end surface 5. Further, the piston bowl 6 comprises a plurality of spaced-apart protrusions 40 arranged circumferentially dispersed around the peripheral portion 20. Each of the spaced-apart protrusions 40 extends mostly in the radial direction R towards the central axis Ac and further extends mostly in the axial direction A from the floor surface 11a towards the upper end surface 5. Each of the spaced-apart protrusions 40 has opposing radial side portions 41, 42 and further comprises flat surfaces 43, 43a or concave surfaces 43, 43b extending between the opposing radial side portions 41, 42. The flat surface 43a or the concave surface 43b comprises a first circumferential extension a at the intersection between the flat or concave surface and the floor surface 11a. Further, the ratio of the sum of the first circumferential extensions a1 - an of all the spaced-apart protrusions 40 along the peripheral portion 20 to the circumferential extension E of the peripheral portion 20 is at least 30%, preferably at least 45%, most preferably at least 60%.

[0145] The present disclosure also relates to an ICE system 100 comprising a diesel internal combustion engine as described herein. The ICE system 100 comprises an internal combustion engine 10 for burning fuel and has a combustion chamber 7 at least partially delimited by a cylinder 2 and a reciprocating piston 3 according to any one of the above examples of FIGS. 3A - 3E, FIGS. 4A - 4C, FIGS. 5A - 5C, and FIG. 6. The reciprocating piston is movable within the cylinder between a bottom dead center BDC and a top dead center TDC, and the upper end of the piston is arranged to form part of the combustion chamber.

[0146] The present disclosure also relates to a vehicle 1 comprising an ICE system 100 and a piston 3 according to any one of the above embodiments of FIGS. 3A - 3E, FIGS. 4A - 4C, FIGS. 5A - 5C, and FIG. 6.

[0147] Although the present disclosure has been described with reference to specific exemplary embodiments, many different changes, modifications, etc. will become apparent to those skilled in the art. Accordingly, it is understood that the present disclosure is not limited to the embodiments described above and shown in the drawings, but rather that those skilled in the art will recognize that many changes and modifications are possible within the scope of the appended claims.

Claims

1. A piston (3) for an internal combustion engine (ICE) (10), said piston having an axial upper end (16) extending in an axial direction (A) and a radial direction (R) and comprising a piston bowl (6) intended to form part of a combustion chamber. Said piston bowl has an axial floor (11) having a floor surface (11a) and a peripheral portion (20) extending in said axial direction (A) between said floor surface and an upper end surface (5) of said axial upper end. Said piston bowl further has an axial depth (H) defined by an axial distance between said floor surface and said upper end surface. Said piston bowl further comprises a plurality of spaced-apart protrusions (40) arranged circumferentially dispersed around said peripheral portion (20). Each of said spaced-apart protrusions extends mostly in said radial direction towards a central axis (Ac) and further extends mostly in said axial direction from said floor surface towards said upper end surface. Each of said spaced-apart protrusions has opposing radial side portions (41, 42) and further has a flat or concave surface extending between said opposing radial side portions, said flat surface (43, 43a) or concave surface (43, 43b) having a first circumferential extension (a) at an intersection (44) between said flat or concave surface and the floor surface and further having a second circumferential extension (b) at an axial distance (h) from said floor surface, said axial distance (h) being one quarter of said axial depth (H) of said piston bowl. The ratio of said second circumferential extension (b) to said first circumferential extension (a) is 0.4 or less. Said piston for an internal combustion engine.

2. The ratio of the sum of said first circumferential extensions (a1, a2, an) of all the spaced-apart protrusions along said peripheral portion (20) to the circumferential extension (E) of said peripheral portion (20) is at least 30%, preferably at least 45%, most preferably at least 60%. The piston according to Claim 1.

3. The first radial side portion (41) of said opposing radial side portions intersects said flat or concave surface along an intersection edge (45), and the second radial side portion (42) of said opposing radial side portions intersects said flat or concave surface along another opposing intersection edge (46). The piston according to Claim 1 or Claim 2.

4. The piston according to claim 3, wherein the intersecting edge, in combination with the first circumferential extension and the second circumferential extension, defines the extension of the flat surface or the concave surface.

5. The piston according to claim 3 or 4, wherein each of the intersecting edges is inclined linearly or non-linearly, for example, curvilinearly, from the first circumferential extension to the second circumferential extension.

6. The piston according to any one of claims 3 to 5, wherein the intersecting edge, in combination with the first circumferential extension and the second circumferential extension, defines a surface similar to a trapezoid or a triangle.

7. The piston according to any one of claims 1 to 6, wherein the extension of the flat surface or the concave surface from the first circumferential extension to the second circumferential extension further comprises a concave axial extension region.

8. The piston according to any one of claims 1 to 7, wherein the extension of the flat surface from the first circumferential extension to the second circumferential extension is defined by a flat surface profile.

9. The piston according to any one of claims 1 to 8, wherein each of the opposing radial side portions comprises a plurality of regions with different convex curved profiles.

10. The piston according to any one of claims 1 to 9, wherein the spaced-apart protrusions are uniformly circumferentially dispersed along the peripheral edge.

11. The piston according to any one of claims 1 to 9, wherein the spaced-apart protrusions are non-uniformly circumferentially dispersed along the peripheral edge.

12. The piston according to any one of claims 1 to 11, wherein each of the spaced-apart protrusions extends axially from the floor surface to the upper end surface of the piston upper end.

13. The piston according to any one of claims 1 to 12, wherein the flat surface or the concave surface extends axially from the intersection between the flat surface or the concave surface and the floor surface to the upper end surface of the piston upper end.

14. The piston according to claim 13, wherein the flat surface or the concave surface extends axially from the intersection between the flat surface or the concave surface and the floor surface to the upper end surface of the piston upper end.

15. The piston according to claim 13, wherein the flat surface or the concave surface extends axially from the intersection between the flat surface or the concave surface and the floor surface to the second circumferential extension.

16. The piston according to any one of claims 1 to 15, wherein each of the spaced projections extends at least partially beyond the floor portion in the radial direction.

17. The piston according to any one of claims 1 to 16, wherein the first circumferential extension is the maximum circumferential extension of the flat surface or the concave surface.

18. A piston (3) for an internal combustion engine (ICE) (10), the piston extending in an axial direction (A) and a radial direction (R), and having an axial upper end (16) provided with a piston bowl (6) intended to form part of a combustion chamber. The piston bowl has an axial floor portion (11) having a floor surface (11a), and a peripheral portion (20) extending in the axial direction (A) between the floor surface and an upper end surface (5) of the axial upper end. The piston bowl further has an axial depth (H) defined by an axial distance between the floor surface and the upper end surface. The piston bowl further comprises a plurality of spaced projections (40) circumferentially distributed around the peripheral portion (20). Each of the spaced projections extends mostly in the radial direction toward a central axis (Ac), and further extends mostly in the axial direction from the floor surface toward the upper end surface. Each of the spaced projections has opposing radial side portions (41, 42), and further has a flat surface (43a) or a concave surface (43, 43b) extending between the opposing radial side portions. The flat surface (43, 43a) or the concave surface (43, 43b) has a first circumferential extension (a) at an intersection (44) between the flat surface or the concave surface and the floor surface. The ratio of the sum of the first circumferential extensions (a1, a2, an) of all the spaced projections along the peripheral portion (20) to the circumferential extension (E) of the peripheral portion (20) is at least 30%, preferably at least 45%, and most preferably at least 60%. A piston for an internal combustion engine.

19. An internal combustion engine (ICE) system (100) comprising an internal combustion engine (10) for burning fuel, and having a combustion chamber (7) at least partially delimited by a cylinder (2) and a reciprocating piston (3) according to any one of claims 1 to 18. The reciprocating piston is movable within the cylinder between a bottom dead center (BDC) and a top dead center (TDC), and the upper end of the piston is arranged to form part of the combustion chamber.

20. A vehicle (1) comprising a piston according to any one of claims 1 to 18 and / or an internal combustion engine combustion system according to claim 19.

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