WO2023072429A1

WO2023072429A1 - Piston for an internal combustion chamber provided with a piston bowl

Info

Publication number: WO2023072429A1
Application number: PCT/EP2022/025482
Authority: WO
Inventors: Olaf Berger
Original assignee: Caterpillar Energy Solutions Gmbh
Priority date: 2021-10-29
Filing date: 2022-10-24
Publication date: 2023-05-04
Also published as: GB2612358B; WO2023072429A8; GB202115621D0; GB2612358A

Abstract

The present invention refers to a piston (14) for an internal combustion engine, having a piston crown (22) provided with a piston bowl (40) which includes a circumferential edge portion (42) connecting a circumferential side wall portion (44) of the piston bowl (40) to a front surface (34) of the piston crown (22), wherein a first radial diameter (dl) at the edge portion (42) is smaller than a second radial diameter (d2) at the side wall portion (44), and wherein the edge portion (42) is provided with at least one recessed section (48).

Description

PISTON FOR AN INTERNAL COMBUSTION CHAMBER PROVIDED WITH A PISTON BOWL

Technical Field

The present invention refers to a piston for an internal combustion engine having a piston crown which is provided with a piston bowl. Further, the present invention refers to a piston removal tool for removing such a piston from an engine.

Technological Background

In general, for improving thermal efficiency of internal combustion engines, a common technique is to adapt the geometry of a piston’s end face delimiting a combustion chamber so as to improve blending of a fuel-air mixture when being directed into the combustion chamber. In this way, homogeneity of the fuel-air mixture present in the combustion chamber prior to being ignited may be increased, thereby reducing unburned hydrocarbons, preventing the engine from being locally subjected to unintended high thermal loads and avoiding undesirable operational phenomena, such as engine knock. For doing so, the use of a piston is known, for example from US 8,833,327 B2, which is provided with a piston bowl at an end face of its piston crown.

The change of the design and geometry of the piston, however, typically affects the thermal load of the piston during operation of the engine. Specifically, the provision of a piston bowl may have the effect that the temperature in that region of the piston increases during operation of the engine, thereby reducing the fatigue strength of the piston. Thus, the level of freedom when designing such piston bowls is typically limited by the thermal characteristic of the piston. In order to prevent the piston from being locally subjected to excessive loads, a smooth geometry of the piston bowl is typically preferred.

Accordingly, when designing a piston with a piston bowl there exists a trade-off between generating a geometry that effectively improves blending characteristics of the piston and at the same time ensures that the piston is not subjected to excessive thermal loads during operation.

Summary of the Invention

Starting from the prior art, it is an objective to provide an improved piston for an internal combustion engine having a structural configuration, which in particular, on the one hand, increases thermal efficiency of the internal combustion engine and at the same time effectively prevents the piston from being subjected to excessive thermal loads and/or, on the other hand, allows for easily removing the piston from an engine. Further, it is an objective to provide a piston removal tool for removing such a piston from an engine.

These objectives are solved by the subject matter of the independent claims. Preferred embodiments are set forth in the present specification, the Figures as well as the dependent claims.

Accordingly, a piston for an internal combustion engine is provided. The piston comprises a piston crown which is provided with a piston bowl. The piston bowl includes a circumferential edge portion connecting a circumferential side wall portion of the piston bowl to a front surface of the piston crown. A first radial diameter at the edge portion is smaller than a second radial diameter at the side wall portion. Further, the piston bowl is designed such that its edge portion is provided with at least one recessed section.

Furthermore, a piston removal tool is provided for removing such a piston, comprising a structural interface configured for form -fittingly connecting the piston removal tool to the piston bowl of the piston. The structural interface comprises a base section and a distal engagement section which are arranged adjacent to one another along a further longitudinal axis of the piston removal tool, wherein the base section has a maximum radial diameter that is smaller than the first radial diameter at the edge portion of the piston bowl, and wherein the engagement section is provided with at least one protruding element and has a maximum radial diameter at the protruding element that is greater than the first radial diameter at the edge portion of the piston bowl.

Since the piston removal tool is intended and configured to remove the above-described piston, technical features described herein in the context of the piston may also refer and be applied to the piston removal tool, and vice versa.

Brief Description of the Drawings

The present disclosure will be more readily appreciated by reference to the following detailed description when being considered in connection with the accompanying drawings in which:

Fig. 1 shows a schematic representation of an internal combustion engine;

Fig. 2 schematically shows a perspective view of a longitudinal section of a piston used in the engine depicted in Fig. 1;

Figs. 3 and 4 schematically show a front view of a longitudinal section of the piston depicted in Fig. 2 before and after being subjected to a method for manufacturing a recessed section of the piston;

Fig. 5 schematically shows a side view of a longitudinal section of the piston depicted in Fig. 1 and of a piston removal tool in a non-engaged state;

Fig. 6 schematically shows a side view of a longitudinal section of the piston and the piston removal tool depicted in Fig. 5 in an engaged state;

Fig. 7 schematically shows a cross section of the piston and the piston removal tool along the section plane A-A indicated in Fig. 6; and

Fig. 8 schematically shows a cross section of the piston and the piston removal tool depicted in Fig. 7 in a form-fittingly engaged state. Detailed Description of Preferred Embodiments

In the following, the invention will be explained in more detail with reference to the accompanying Figures. In the Figures, like elements are denoted by identical reference numerals and repeated description thereof may be omitted in order to avoid redundancies.

Fig. 1 schematically shows an internal combustion engine 10 in the form of a reciprocating engine, also referred to as ‘engine’ herein, which can be installed in a vehicle, such as a vessel or a construction vehicle, as a main or auxiliary engine. The engine 10 comprises a plurality of cylinders 12 and may be, e.g., a diesel engine. In the shown configuration, the engine 10 is exemplarily provided in the form of a V-engine comprising, e.g., four, eight, twelve or eighteen cylinders 12 arranged in a V-configuration, thereby forming two parallel cylinder lines. The present invention, however, is not limited to this specific engine configuration and alternatively may be applied to any suitable configuration of an internal combustion engine, such as an in-line configuration.

Each cylinder 12 accommodates one piston 14 which, together with an inner surface of the cylinder 12, delimits a combustion chamber 16 within the cylinder 12. Specifically, the combustion chamber 16 extends from a head portion of the piston 14, i.e. an end face thereof, to a cylinder head which sits on the cylinder 12 on top of an engine block. As such, the cylinder head closes a top end of the cylinder 12, thereby delimiting the combustion chamber 16 from above.

Each piston 14 is connected to a crankshaft 18 of the engine 10 via a connecting rod 20. Further, the pistons 14 are configured for reciprocating and axial movement within their associated cylinder 12 along a longitudinal axis L of the piston 14 and the cylinder 12. In the context of the present disclosure, the term ‘longitudinal axis’ refers to an axis which coincides with a middle axis of the cylinder 12 and the piston 14, in particular which coincides with a symmetry axis of a circumferential inner surface of the cylinder’s side wall and with a symmetry axis of a circumferential outer surface of the piston 14.

The engine 10 further comprises a control device (not shown) which controls actuation of an intake system (not shown) for selectively supplying a fuel-air mixture into the combustion chamber 16, an ignition system (not shown) for selectively igniting the fuel-air mixture received in the combustion chamber 18, and an expelling system (not shown) for selectively expelling combustion gases from the combustion chamber 16.

By such a configuration, i.e. upon igniting the fuel-air mixture in the combustion chamber 16, high-temperature and high-pressure gases are produced in the combustion chamber 16 which apply forces to and thus axially move the piston 14 along its longitudinal axis L, thereby rotating the crankshaft 18. In this way, chemical energy is transformed into mechanical energy.

The basic structure and mode of operation of the engine 10 and its components are well known to a person skilled in the art and are thus not further specified. Rather, characteristics of the piston 14 employed in the engine 10 which are interlinked with the present invention are addressed in the following.

Fig. 2 shows a longitudinal section of a piston 14 in a perspective view which is used in the engine 10 depicted in Fig. 1. For the sake of better visualization, the piston 14 is depicted isolated from other parts of the engine 10. In the following, structural characteristics of a piston 14 employed in the engine 10 are described based on the piston configuration depicted in Fig. 2 which may apply correspondingly to any one of the different pistons 14 of the engine 10.

As set forth above, the piston 14 is intended to be employed in an internal combustion engine, in particular the reciprocating engine 10. Accordingly, the piston 14 is configured to be received in the cylinder 12 of the engine 10.

The basic structure of the piston 14 is constituted by a piston crown 22, also referred to as ‘piston head’, and a piston skirt 24. The piston 14 may have a multi-part design, for example a two-part design, in which the piston crown 22 and a piston skirt 24 constitute distinct parts of the piston 14 which may be mounted, in particular releasably mounted, to one another. Alternatively, the piston 14 may be provided with an integral design, also referred to as monobloc construction or monobloc piston, in which the piston 14 is cast of a single piece.

The piston skirt 24 provides a structural connection between the piston crown 22 and the connecting rod 20. Specifically, the piston skirt 24 comprises two recessed pin boss portions 26 which are arranged on opposed sides of the piston skirt 24. In other words, the pin boss portions 26 are arranged opposed to each other with respect to the longitudinal axis L of the piston 14. In the pin boss portions 26, a wrist pin 28 is received for pivotably coupling the piston 14 to the connecting rod 20.

The piston crown 22 has an end face 30 which is configured to delimit the combustion chamber 16 in a state in which the piston 14 is mounted in a cylinder 12 of the engine 10. Further, the piston crown 22 is configured to guide the piston 14 within the cylinder 12. For doing so, the piston crown 22, at a circumferential outer surface thereof, is provided with a cylindrical ring belt 32 which is arranged spaced apart from a front surface 34 of the piston crown 22 delimiting the combustion chamber 16 of the cylinder 12. The ring belt 32 is formed at its circumferential outer surface with a plurality of piston ring grooves 36, each of which is designed for accommodating a piston ring (not shown), also referred to as oil control rings. By such a configuration, the piston crown 22 is configured to seal the combustion chamber 18 from a crank case of the engine 10 and, at the same time, to maintain a proper quantity of oil between the piston 14 and the cylinder wall during operation of the engine 10.

The piston head 22 is further equipped with an internal cooling galley 38 in which a cooling medium, in particular cooling oil, is circulated to cool the piston 14, i.e. its piston crown 22, during operation of the engine 10. By such a configuration, thermal energy is transferred from the piston crown 22 to the cooling oil upon flowing through the cooling galley 38, thereby decreasing the thermal load of the piston 14 during operation of the engine 10. As can be gathered from Fig. 2, the cooling galley 38 extends circumferentially around the longitudinal axis L of the piston 14 in the area of the cylindrical ring belt 32 such that the top end of the cooling galley 38, i.e. its end facing the front surface 34 of the piston 14, is aligned or substantially aligned with the upper piston ring groove 36. The basic structural and function configuration of such an internal cooling galley 38 is well known to the skilled person and is thus not further specified.

In the context of the piston described herein, the terms ‘top’, ‘upper’, etc., refer to portions and parts which are arranged in the vicinity of or are oriented toward the end face 30 of the piston 14.

Further, the piston crown 22 is provided with a piston bowl 40. The piston bowl 40 is arranged at the end face 30 of the piston crown 22 and thus delimits the combustion chamber 16. As can be gathered from Fig. 2, the piston bowl 40 comprises a circumferential edge portion 42 and a circumferential side wall portion 44. The edge portion 42 is provided at a top end of the piston bowl 40. In other words, the edge portion 42 is arranged adjacent to the front surface 34. As such, an outside surface of the edge portion 42 merges into the front surface 34 of the piston 14. Accordingly, the edge portion 42 connects the side wall portion 44 of the piston bowl 40 to the front surface 34 of the piston crown 22. As can be gathered from Fig. 2, the edge portion 42 extends circumferentially around the longitudinal axis L. Further, the side wall portion 44 extends circumferentially around the longitudinal axis L of the piston. Alternatively, the edge portion and/or the side wall portion may extend circumferentially around another axis which particularly is parallel to but displaced relative to the longitudinal axis.

In the shown configuration, the piston bowl 40 extends along a first radial diameter dl at the edge portion 42 and along a second radial diameter d2 at the side wall portion 44. In the context of the present disclosure, the term ‘radial diameter’ refers to a diameter which is perpendicular to the longitudinal axis L of the piston 14 and thus perpendicular to a moving direction of the piston 14 when being employed in the engine 10. Accordingly, the first radial diameter dl is a diameter extending between opposing sections of the edge portion 42 along a radial direction, i.e. along a direction perpendicular to the longitudinal axis L. The second radial diameter d2 is a diameter extending between opposing sections of the side wall portion 44. More specifically, the first radial diameter dl may be a minimal radial diameter at the edge portion 42. In other words, the first radial diameter dl may refer to a distance between closest opposing sections of the edge portion 42 along the radial direction. Further, the second radial diameter d2 may be a maximum radial diameter at the side wall portion 44. That is, the second radial diameter d2 refers to a diameter between opposing sections of the side wall portion 44 which are most distanced in a radial direction.

In the proposed configuration, the first radial diameter dl at the edge portion 42 is smaller than the second radial diameter d2 at the side wall portion 44 of the piston bowl 40. In other words, the edge portion 42 is designed such that it extends in a direction perpendicular to and toward the longitudinal axis L beyond the side wall portion 44. Thus, the side wall portion 44 forms an undercut of the piston bowl 40. By such a configuration, the proposed piston bowl 44 has a geometry which may favorably affect blending characteristics of the piston 14. That is, in a state in which the piston 14 is installed in the engine 10, the geometry of the piston bowl 40 may particularly contribute to an improved blending of a fuel-air mixture upon being direct into the combustion chamber 16. Specifically, by being provided with the undercut, the proposed piston bowl 40 may deflect the fuel-air mixture injected into the combustion chamber 16 such that intended turbulences occur which increase homogeneity of the fuel-air mixture present in the combustion chamber prior to being ignited. In this way, thermal efficiency of the engine 10 may be increased, particularly since increased homogeneity of the fuel-air mixture may reduce unburned hydrocarbons, prevent the engine from being locally subjected to unintended high thermal loads and avoid undesirable operational phenomena, such as engine knock.

To that end, the side wall portion 44 is concavely shaped. In other words, the side wall portion constitutes a concave portion. That is, an outer surface of the side wall portion 44 curves inward and thus has a concave shape. Further, a bottom portion 46 of the piston bowl 44 is convexly shaped as can be gather from Fig. 2. That is, an outer surface of the bottom portion 46 curves outward, thereby having a spheroidal shape. Further, the edge portion 42 partly is convexly shaped. That is, an outer surface of the edge portion 42 curves outward and thus has a convex shape. By this configuration, the outer surfaces of the piston bowl 40 may be provided with smooth and seamless transitions across its different portions and also may smoothly merge into the front surface 34 of the piston crown 22. This may contribute to the above-described favorable blending characteristics of the piston 14.

Further, as can be gathered from Fig. 2, the edge portion 42 comprises different sections, i.e. first sections 48 and second sections 50, which are arranged one after the other along a circumferential direction around the longitudinal axis L. The first section constitutes a recessed section 48, which may also be referred to as ‘chamfer section’. The second section may be referred to as a blend section 50, in particular due to its geometry which may contribute to the above described improved blending characteristics of the piston 14.

In the shown configuration, the piston 14 is mirror symmetric in relation to two symmetry planes along which the longitudinal section of the piston 14 depicted in Fig. 2 is cut open. Specifically, the symmetry planes vertically divide the piston 14 along the longitudinal axis L. Accordingly, in the shown configuration of the piston 14, the edge portion 42 is provided with two recessed sections 48 and two blend sections 50 which are arranged alternatingly in a circumferential direction, i.e. in the circumferential direction around the longitudinal axis L. Alternatively, the edge portion may have more or less than two recessed sections and, accordingly, more or less than two blend sections.

In general, the recessed section 48, as indicated by its name, is cut back or retracted compared to the blend section 50. That is, in a direction perpendicular to and pointing toward the longitudinal axis L, the blend section 50 extends beyond the recessed section 48.

As indicated in Fig. 2, the first radial diameter dl preferably refers to a diameter at the blend section 50 of the edge portion 42, wherein a further first radial diameter dl’ refers to a diameter, in particular a minimal diameter, at the recessed section 48 of the edge portion 42, i.e. between opposing recessed section 48. The further first radial diameter dl’ at the recessed section 48, i.e. between opposing recessed sections 48, is smaller than the second radial diameter d2 at the side wall portion 44 but greater than the first radial diameter dl at the blend section 50 of the edge portion 42. Alternatively, the further first radial diameter dl’ at the recessed section 48 may be equal or substantially equal to the second radial diameter d2 at the side wall portion 44 and greater than the first radial diameter dl at the blend section 50 of the edge portion 42.

Further, the recessed section 48 and the blend section 50 are designed such that a maximum first distance si between the cooling galley 38 and an outer surface of the recessed section 48 is smaller than a maximum second s2 distance between the cooling galley 38 and an outer surface of the blend section 50. In this context, the term ‘first distance si’ refers to a maximum distance between a middle section of the outer surface of the recessed section 48 and the cooling galley 38 in a vertical plane in which the longitudinal axis L lies, in particular in the symmetry plane. Accordingly, the term ‘second distance s2’ refers to a maximum distance between a middle section of the outer surface of the blend section 50 and the cooling galley 38 in another vertical plane in which the longitudinal axis L lies, in particular in the other symmetry plane. Further, the recessed section 48 has an edge radius, in particular a minimum edge radius, that is smaller than an edge radius, in particular a minimum edge radius, of the blend section 50. Specifically, in the shown configuration, the blend section 50 is convexly shaped. In other words, an outer surface of the blend section 50 has a convex shape, i.e. is curved outward. By this configuration, particularly favorable blending characteristics of the piston bowl 40 may be achieved.

In the context of the present disclosure, the term ‘recessed section’ generally refers to a section of the edge portion which extends or protrudes less compared to an adjacent section of the edge portion. In the shown configuration, the recessed section 48 forms a chamfered edge portion. In other words, an outer surface of the recessed section 48 has a shape that is less curved compared to the outer surface of the blend section 50. Preferably, the other surface of the recessed section 48 has a shape that is bent in only one direction, in particular the circumferential direction around the longitudinal axis L. In other words, the other surface of the recessed section 48 preferably is bent in a plane perpendicular to the longitudinal axis L and is not bent, i.e. flat, in a plane in which the longitudinal axis L lies. As such, the outer surface of the recessed section 48 has a shape that corresponds to a section of an outer surface of a cone.

Specifically, the recessed section 48 is designed such that it comprises a chamfered edge 51 which is inclined relative to the longitudinal axis L. In other words, the chamfered edge 51 is inclined relative to the longitudinal axis L at the angle a as indicated in Fig. 4. More specifically, the chamfered edge 51 forms the angle a to the longitudinal axis L in the range of 20° to 60°, in particular in the range of 30° to 40°, for example of about 35°.

By being provided with the recessed sections 48, the shown structural configuration of the piston crown 22 may effectively prevent the piston 14 from being subjected to excessive thermal loads. This may be due to the following effects. On the one hand, the recessed sections 48 of the edge portion 42 may have the effect that the heat input from the combustion chamber 16 into the piston crown 22 is reduced during operation of the engine 10. This is because, by providing the recessed sections 48, the effective surface area of the piston bowl 40 is reduced. In other words, the surface area of the piston 14 delimiting the combustion chamber 16 is reduced by providing the recessed sections 48, i.e. compared to a configuration of the piston in which an edge portion is not provided with the recessed sections. Since the heat flow transferred from the combustion chamber 16 into the piston crown 22 depends on the size of the surface area delimiting the combustion chamber 16, the heat input into the piston 14 during operation of the engine 10 is effectively reduced by the recessed sections 48 as they decrease the surface area of the piston 14 delimiting the combustion chamber 16.

On the other hand, also heat transfer between the piston crown 22 and the cooling medium circulating through the cooling galley 38 may be increased by the recessed sections 48. This may be due to the fact that, by providing the recessed section 48, the distance between the edge portion 42 and the cooling galley is locally, i.e. at the recessed sections 48, reduced, thereby increasing the heat transfer coefficient of the piston’s geometry allowing a higher heat flow toward the cooling medium circulating through the cooling galley 38, i.e. compared to a configuration of the piston in which an edge portion is not provided with the recessed section.

As a result, by providing the edge portion 42 which extends beyond the side wall portion 44 and which includes at least one recessed section 48, the suggested piston 14 allows for solving the trade-off between increasing thermal efficiency of the internal combustion engine, i.e. by the piston bowl having the protruding edge region, and effectively preventing the piston 14 from being subjected to excessive thermal loads, i.e. induced by the recessed section 48 as described above. In other words, by the suggested configuration of the piston, the efficiency advantages provided by the edge portion 42, i.e. the blend sections 50, may be provided on a big part of the edge portion while excessive thermal loads on at least critical parts of the edge portion may locally be avoided. Preferably, the recessed sections 48 may be provided in zones of the piston 14 which otherwise, i.e. when not being provided with the recessed section, would be subjected to particularly high thermal loads.

The recessed sections 48 of the edge portion 42 may be manufactured by a subtractive manufacturing process. With reference to Fig. 3 and 4, a subtractive manufacturing process for manufacturing the recessed section 48 is specified. Specifically, the recessed sections 48 are manufacture by using a cone-shaped tool 52 which is rotated about its middle axis M when machining the piston 14. Specifically, the middle axis M of the cone-shaped tool 52 during processing of the piston 14 is parallel but spaced apart from the longitudinal axis L, as can be gathered from Fig. 4.

In the following, individual steps of the method for manufacturing the recessed section 48 are described. At first, the piston 14’ in the form of a semi-finished product is provided. Hereinafter, reference signs provided with an apostrophe at their end indicate that the associated elements refer to the semifinished piston 14’. As can be gathered from Fig. 3, the semi-finished piston 14’ comprises an edge portion 42’ which is formed by as circumferential blend section 50’. Then, the cone-shaped tool 52 is provided and positioned in a starting position as depicted in Fig. 3 in which it is placed spaced apart from the piston 14’ such that the middle axis M of the cone-shaped tool 52 is parallel but spaced apart from the longitudinal axis L, e.g. about 8.5 mm. Then, the cone-shaped tool 52 is rotated about and translationally guided along its middle axis M toward an end position which is depicted in Fig. 4. By doing so, i.e. when the rotated cone- shaped tool 52 gets into contact with the edge portion 42’, material of the edge portion 42’ is removed, thereby forming one recessed section 48. For manufacturing more than one recessed section 48, the above described method steps are performed in several cycles during each of which one recessed section 48 is manufactured. By doing so, the recessed sections 48 are manufactured subsequently, wherein the starting position of the cone-shaped tool 52 relative to the piston 14 is changed for each cycle.

In a further development, the piston 14 may be configured and designed to be installed in the engine 10 in a position relative to a fuel injection mechanism of the engine 10 such that fuel or the fuel-air mixture is directed into the combustion chamber 16 toward at least one recessed section 48. For doing so, the fuel injection mechanism may open into the combustion chamber 16 through the cylinder head in the vicinity of or above the recessed section 48. In other words, the fuel injection mechanism may open into the combustion chamber 16 so as to face and/or be arranged opposed to the recessed section 48. In this way, particularly favorable blending characteristics of the piston bowl 40 may be achieved.

Figs. 5 to 8 show a piston removal tool 54 intended and configured to get into structural engagement with the piston 14 and, when being structurally engaged with the piston 14, to remove the piston 14 from the engine.

For establishing the structural engagement, the piston removal tool 54 is provided with a structural interface 56 which extends along a further longitudinal axis LL of the piston removal tool 54. The structural interface 56 is configured for form-fittingly connecting the piston removal tool 54 to the piston bowl 40 of the piston 14. Specifically, the structural interface 56 is configured for form-fittingly connect the piston removal tool 54 to the piston bowl 40 along the longitudinal axis L of the piston 14 and along the further longitudinal axis LL of the piston removal tool 54. In an engaged state of the piston removal tool 54 in which its structural interface 56 is engaged with the piston bowl 40, the further longitudinal axis LL is parallel or substantially parallel to the longitudinal axis L, in particular coincides or substantially coincides with the longitudinal axis L. In the context of the present disclosure, the term ‘from-fittingly connected along an axis’ refers to an engagement between two components which cannot be released upon moving these two components relative to one another along the axis, in particular in any direction along the axis.

The structural interface 56 comprises a base section 58 and a distal engagement section 60 which are arranged adjacent to one another along the further longitudinal axis LL. The base section 58 has a radial diameter d3, also referred to as ‘third radial diameter’ herein, that is smaller than the first radial diameter dl at the edge portion 42 of the piston bowl 40, in particular in the area of the blend section 50. Further, the third radial diameter d3 is smaller than the further first radial diameter dl’ at the edge portion 42 of the piston bowl 40, in particular at the recessed section 48. With this configuration, the base section 58 is enabled to be placed and introduced into the piston bowl 40 of the piston 14, as can be gathered from Fig. 7. The third radial diameter d3 is a maximum radial diameter of the base section 58 and extends or is perpendicular or substantially perpendicular to the further longitudinal axis LL of the piston removal tool 54. A cross section of the base section 58, i.e. in a plane perpendicular to the further longitudinal axis LL, is circular or substantially circular, but is not limited to such a shape.

The engagement section 60 is provided with at least one protruding element 62, in particular in the shown configuration with two opposed protruding elements 62. At the protruding element 62, the engagement section 60 has a radial diameter d4, also referred to as ‘fourth radial diameter’ herein, that is greater than the first radial diameter dl and smaller than the further first radial diameter dl’ and the second radial diameter d2 of the piston bowl 40. In a radial direction of the piston removal tool 54, i.e. extending radially from the further longitudinal axis LL, the protruding element 62 protrudes beyond the base section 58. Further, the engagement section 60 is designed such that sections which are arranged adjacent to the protruding element 62 in a circumferential direction and/or which connect different protruding elements 62 in the circumferential direction of the piston removal tool 54 have a radial diameter which are smaller than the first radial diameter dl at the edge portion 42 of the piston bowl 40, in particular in the area of the blend section 50.

Further, as depicted in Fig. 7, the protruding element 62 has a circumferential width, i.e. extending perpendicular to the radial direction and the further longitudinal axis LL, in particular a maximum circumferential width wl that is smaller than a circumferential width w2 of a recessed section 48, in particular an associated recessed section 48 of the piston bowl 40. With this configuration, it may be ensured that, by positioning the protruding element 62 to be arranged in alignment with the recessed section along the further longitudinal axis LL, the structural interface 56 can be placed into the piston bowl 40 upon being translationally moved along the further longitudinal axis LL of the piston removal tool 54 relative to the piston.

In other words, the engagement section 60 has a cross sectional profile which is designed complementary to a cross sectional profile of the edge portion 42 of the piston bowl 40 to allow that the engagement section 60 can be introduced into the piston bowl 40 upon translational displacement along the further longitudinal axis LL. With this configuration, the engagement section 60 enables that the protruding element 62 of the piston removal tool 54 can be positioned in the piston bowl 40 beneath the edge portion 42, in particular the blend section 50, thereby establishing a form-fitting connection between the structural interface 56 and the piston bowl 40 along the longitudinal axis L and the further longitudinal axis LL. This may be achieved by, at first, placing the engagement section 62 into the piston 40, as depicted in Figs. 6 and 7, and thereafter pivoting it around its further longitudinal axis LL to be arranged into a form-fitting state, as depicted in Fig. 8.

In the configuration depicted in Figs. 5 to 8, the protruding element 62 is integrally formed with the engagement section 60, but alternatively may also be provided in the form of a separate part which may be firmly fixed to the engagement section 60.

The structural interface 56 may be made of a metal material, such as aluminum. Alternatively, the structural interface 56 may be made of a synthetic or plastic material. Optionally, at its tip end, the structural interface 56 may be provided with a stopper element 64, preferably made of a plastic or rubber material. By this configuration, damages of the piston bowl 40 upon inserting the structural interface 56 thereinto may be prevented.

The piston removal tool 54 is preferably manually actuated by an operator and may comprise a handle on which structural interface 56 is mounted.

In the following, under reference to Fig. 6 to 9, a method of removing a piston 14 from an engine 10 is described. Specifically, the method refers to removal of the above-described piston 14 by utilizing the abovedescribed piston removal tool 54.

In a first step of the method, a cylinder head of the engine 10 is removed so as to uncover and expose the cylinders 12 and the piston crown 22 of the pistons 14 received therein. Then, the piston removal tool 54 is placed above a piston crown 22 of a piston 14 to be removed such that the structural interface 56 of the piston removal tool 54 faces the piston bowl 40. Specifically, in this state, the further longitudinal axis LL of the piston removal tool 54 coincides with the longitudinal axis L of the piston 14 or a longitudinal axis of the piston bowl 40. Then, the piston removal tool 54 is pivoted around its further longitudinal axis LL to align the protruding elements 62 with the recessed section 48 when viewed along the further longitudinal axis LL. Such an alignment of the protruding elements 62 and the recessed sections 48 is depicted in Fig. 5 and 7.

In a next step, the structural interface 56 is placed into the piston bowl by pushing, i.e. translationally displacing, the piston removal tool 54 along the further longitudinal axis LL towards the piston 14. This state is referred to as the ‘introduced state’ in the following and is shown in Fig. 6 and 7. Thereafter, the piston removal tool 54 is pivoted around its further longitudinal axis LL to position the protruding element 62 beneath the edge portion 42, in particular the blend section 50, thereby establishing a form-fitting connection between the structural interface 56 and the piston bowl 40 along the longitudinal axis L and the further longitudinal axis LL. This state is referred to as ‘form-fittingly engaged state’ and is shown in Fig. 8. In other words, in this form-fittingly engaged state, the protruding elements 62 are aligned with the associated blend sections 50 when viewed along the further longitudinal axis LL.

Thereafter, in this form-fittingly engaged state of the structural interface 56 and the piston bowl 40, the piston removal tool 54 is pulled up together with the piston 14 engaged thereto, thereby removing the piston 14 from the cylinder 12.

Optionally, for ensuring that the protruding elements 62 are properly aligned relative to the blend sections 50 for establishing the form-fitting connection, the structural interface 56 may be provided with a turn limiter. Such a turn limiter may be configured to limit relative rotational movement between the structural interface and the piston bowl 40 around the further longitudinal axis LL when the structural interface is placed within the piston bowl 40. Specifically, the turn limiter may be designed such that, when the structural interface 56 is pivoted around its further longitudinal axis LL from its introduced state to its form- fittingly engaged state, the turn limiter gets into contact with a blend section 50 of the piston bowl 40, thereby preventing further pivoting movement of the structural interface 56.

According to an alternative configuration of the piston removal tool, compared to the configuration depicted in Fig. 6 to 9, the at least one protruding element may be configured and mounted to the structural interface such that it is movable relative to the engagement section between a retracted position and an extracted position. For doing so, the piston removal tool may comprise an adjustment unit configured to move the at least one protruding element relative to the engagement section between the retracted position and the extracted position. Specifically, the adjustment unit may be mechanically actuated and may move the protruding element in response to a user actuation. In an extracted state of the tool in which the protruding element is placed in the extracted position, the engagement section may have a maximum radial diameter at the protruding element that is greater than the first radial diameter dl . In a retracted state of the tool in which the protruding element is placed in the retracted position, the engagement section may have a maximum radial diameter at the protruding element that is smaller than the first radial diameter dl.

It will be obvious for a person skilled in the art that these embodiments and items only depict examples of a plurality of possibilities. Hence, the embodiments shown here should not be understood to form a limitation of these features and configurations. Any possible combination and configuration of the described features can be chosen according to the scope of the invention.

This is in particular the case with respect to the following optional features which may be combined with some or all embodiments, items and/or features mentioned before in any technically feasible combination.

A piston for an internal combustion engine may be provided. The piston may have a piston crown provided with a piston bowl which includes a circumferential edge portion connecting a circumferential side wall portion of the piston bowl to a front surface of the piston crown, wherein a first radial diameter at the edge portion is smaller than a second radial diameter at the side wall portion, and wherein the edge portion is provided with at least one recessed section.

By being provided with the at least one recessed section, the proposed piston is provided with a structural configuration of the piston crown which may effectively prevent the piston from being subjected to excessive thermal loads. This may be due to the following effects. The piston may be intended to be used in any suitable internal combustion engine, in particular any suitable reciprocating engine. For example, the piston may be used in a diesel engine, but is not limited to this application. Rather, the piston may also be used in a gas engine or dual fuel engine.

The first radial diameter and the second radial diameter may be or may extend perpendicular to a longitudinal axis of the piston. Specifically, the first radial diameter may be a diameter between opposing sections of the edge portion. Alternatively or additionally, the second radial diameter may be a diameter between opposing sections of the side wall portion.

More specifically, the first radial diameter may be a minimal radial diameter at the edge portion. Alternatively or additionally, the second radial diameter may be a maximum radial diameter at the side wall portion of the piston bowl.

The piston bowl may be designed such that, in a direction perpendicular to and towards the longitudinal axis, the edge portion may extend beyond the side wall portion. As such, the side wall portion may constitute an undercut of the piston bowl. Alternatively or additionally, the side wall portion may be concavely shaped.

The edge portion of the piston bowl may further comprise at least one blend section. The blend section may be arranged adjacent to the recessed section in a circumferential direction of the edge portion, which in particular may be perpendicular to the longitudinal axis. The blend section may be convexly shaped. Further, the recessed section may have a minimum edge radius that is smaller than a minimum edge radius of the blend portion.

In a further development, the edge portion may comprise at least two recessed sections and at least two blend sections which may be arranged altematingly along the circumferential direction. Alternatively, the edge portion may comprise only one recessed section and only one blend section. Further, the first radial diameter may be a radial diameter at the blend section. The first radial diameter may be smaller than a further first radial diameter at the recessed section, in particular between opposing recessed sections or between a recessed section and an opposing blend section.

Alternatively or additionally, the recessed section may comprise a chamfered edge. In a further development, the chamfered edge may be inclined relative to the longitudinal axis of the piston at an angle in the range of 20° to 60°, particular in the range of 30° to 40°.

The recessed section may be manufactured by a subtractive manufacturing process. In the context of the present disclosure, the term ‘subtractive manufacturing process’ may refer to any manufacturing process in which material is removed from a part. For example, the subtractive manufacturing process may be a machining process and/or a milling process and/or a drilling process, and so forth.

Furthermore, an internal combustion engine may be provided which is equipped with a piston as described above. The internal combustion engine may comprise a fuel injection mechanism and may be configured and designed such that the fuel injection mechanism is configured to direct fuel or a fuel-air mixture toward one of the at least one recessed section.

Furthermore, a piston removal tool for removing the abovedescribed piston may be provided. The piston removal tool may comprise a structural interface configured for form-fittingly connecting the piston removal tool to the piston bowl of the piston. The structural interface may comprise a base section and a distal engagement section which are arranged adjacent to one another along a further longitudinal axis of the piston removal tool. The base section may have a maximum radial diameter that is smaller than the first radial diameter at the edge portion of the piston bowl, wherein the engagement section may be provided with at least one protruding element and may have a maximum radial diameter at the protruding element that is greater than the first radial diameter at the edge portion of the piston bowl.

By allowing for form-fittingly being connected to the piston, the proposed piston removal tool may effectively prevent pistons to be removed from damages compared to known tools which are configured to force-fittingly engage with pistons to be removed.

Further, the protruding element may have a maximum first circumferential width that is smaller than a circumferential width of the recessed section of the piston bowl. Alternatively or additionally, the piston removal tool may further comprise an adjustment unit configured to move the protruding element relative to engagement section between a retracted position and an extracted position, wherein in an extracted state in which the protruding element is placed in the extracted position, the engagement section may have a maximum radial diameter at the protruding element that is greater than the first radial diameter and, in an retracted state in which the protruding element is placed in the retracted position, the engagement has a maximal radial diameter at the protruding element which is smaller than the first radial diameter.

Industrial Applicability

With reference to the Figures and their accompanying description, a piston for an internal combustion engine and a piston removal tool for removing such a piston are suggested. The suggested piston may replace conventional pistons and may serve as a replacement or retrofit part.

Claims

-23- Claims

1. Piston (14) for an internal combustion engine (10), having a piston crown (22) provided with a piston bowl (40) which includes a circumferential edge portion (42) connecting a circumferential side wall portion (44) of the piston bowl (40) to a front surface (34) of the piston crown (22), wherein a first radial diameter (dl) at the edge portion (42) is smaller than a second radial diameter (d2) at the side wall portion (44), and wherein the edge portion (42) is provided with at least one recessed section (48).

2. Piston according to claim 1, wherein the first radial diameter (dl) and the second radial diameter (d2) are perpendicular to a longitudinal axis (L) of the piston (14).

3. Piston according to claim 1 or 2, wherein the first radial diameter (dl) is a diameter between opposing sections of the edge portion (42) and the second radial diameter (d2) is a diameter between opposing sections of the side wall portion (44).

4. Piston according to any one of claims 1 to 3, wherein the first radial diameter (dl) is a minimal radial diameter at the edge portion (42) and the second radial diameter (d2) is a maximum radial diameter at the side wall portion (44) of the piston bowl (40).

5. Piston according to any one of claims 1 to 4, wherein the piston bowl (40) is designed such that, in a direction perpendicular to and toward the longitudinal axis (L), the edge portion (42) extends beyond the side wall portion (44).

6. Piston according to any one of claims 1 to 5, wherein the side wall portion (44) constitutes an undercut and in particular is concavely shaped.

7. Piston according to any one of claims 1 to 6, wherein the edge portion (42) further comprises at least one blend section (50) which is arranged adjacent to the recessed section (48) in a circumferential direction of the edge portion (42).

8. Piston according to claim 7, wherein the blend section is convexly shaped, and wherein the recessed section (48) has a minimum edge radius that is smaller than a minimum edge radius of the blend portion (50).

9. Piston according to claim 7 or 8, wherein the edge portion (22) comprises at least two recessed sections (48) and at least two blend sections (50) which are arranged alternatingly along the circumferential direction.

10. Piston according to any one of claims 7 to 9, wherein the first radial diameter (dl) is a radial diameter at the blend section (50) which is smaller than a further first radial diameter (dl’) at the recessed section (48).

11. Piston according to any one of claims 1 to 10, wherein the recessed section (48) comprises chamfered edge (51) which is inclined relative to the longitudinal axis (L) at an angle in the range of 30° to 40°.

12. Piston according to any one of claims 1 to 11, wherein the recessed section (48) is manufactured by a subtractive manufacturing process.

13. Piston removal tool (54) for removing a piston according to any one of claims 1 to 12, comprising a structural interface (56) configured for form-fittingly connecting the piston removal tool (54) to the piston bowl (40) of the piston (14), the structural interface (56) comprising a base section (58) and a distal engagement section (60) which are arranged adjacent to one another along a further longitudinal axis (LL) of the piston removal tool (54), wherein the base section (58) has a maximum radial diameter (d3) that is smaller than the first radial diameter (dl) at the edge portion (42) of the piston bowl (40), and wherein the engagement section (60) is provided with at least one protruding element (62) and has a maximum radial diameter (d4) at the protruding element (62) that is greater than the first radial diameter (dl) at the edge portion (42) of the piston bowl (40).

14. Piston removal tool according to claim 13, wherein the protruding element (62) has a first circumferential width (wl) that is smaller than a circumferential width (w2) of the recessed section (48) of the piston bowl (40).

15. Piston removal tool according to claim 13 or 14, further comprising an adjustment unit configured to move the protruding element relative to engagement section between a retracted position and an extracted position, wherein in an extracted state in which the protruding element is placed in the extracted position, the engagement section may have a maximum radial diameter at the protruding element that is greater than the first radial diameter (dl) and, in an retracted state in which the protruding element is placed in the retracted position, the engagement has a maximal radial diameter at the protruding element which is smaller than the first radial diameter (dl).