阅读说明：本技术 引擎活塞、引擎、手持式工具和制造引擎活塞的方法 (Engine piston, engine, hand-held tool and method for manufacturing engine piston ) 是由 亨里克·阿萨尔松 约翰·伦尼 于 2020-03-02 设计创作，主要内容包括：公开了一种二冲程引擎活塞(1),其包括：活塞顶部(3)、罩表面(5)、罩表面(5)中的分层扫气通道(7)、以及设置在活塞顶部(3)和分层扫气通道(7)之间的重量减轻空间(9)。所述重量减轻空间(9)在罩表面(5)处具有最大第一轴向范围(a1)并且在罩表面(5)的径向内侧处具有第二轴向范围(a2),并且其中,所述第二轴向范围(a2)大于最大第一轴向范围(a1)。本公开还涉及一种引擎(30)、一种手持式工具(40)和一种制造引擎活塞(1)的方法。(A two-stroke engine piston (1) is disclosed, comprising: a piston crown (3), a mantle surface (5), stratified scavenging ducts (7) in the mantle surface (5), and a weight-saving space (9) arranged between the piston crown (3) and the stratified scavenging ducts (7). The weight-saving space (9) has a maximum first axial extent (a1) at the mantle surface (5) and a second axial extent (a2) at a radially inner side of the mantle surface (5), and wherein the second axial extent (a2) is larger than the maximum first axial extent (a 1). The disclosure also relates to an engine (30), a hand tool (40) and a method of manufacturing an engine piston (1).)

1. A two-stroke engine piston (1) comprising:

the top part (3) of the piston,

a cover surface (5),

stratified scavenging ducts (7) in the mantle surface (5), and

a weight-saving space (9) provided between the piston crown (3) and the stratified scavenging passage (7),

wherein the weight-saving space (9) has a maximum first axial extent (a1) at the mantle surface (5) in a direction parallel to the centre axis (ax) of the piston (1) and a second axial extent (a2) at the radially inner side of the mantle surface (5) in a direction parallel to the centre axis (ax) of the piston (1), and wherein the second axial extent (a2) is larger than the maximum first axial extent (a 1).

2. The piston (1) according to claim 1, wherein the second axial extent (a2) is at least 10% greater, or at least 40% greater, than the maximum first axial extent (a 1).

3. The piston (1) according to claim 2, wherein the second axial extent (a2) is at least 80% greater, or at least 100% greater, than the maximum first axial extent (a 1).

4. The piston (1) according to any one of the preceding claims, wherein the weight-saving space (9) comprises a first uppermost delimiting surface (10 ') at the mantle surface (5) and a second upper delimiting surface (10 ") at a radially inner side of the mantle surface (5), and wherein the second upper delimiting surface (10") is arranged closer to the piston crown (3) than the first uppermost delimiting surface (10').

5. A piston (1) according to any of the preceding claims, wherein the piston (1) comprises a first piston ring groove (11) in the mantle surface (5), and wherein the weight-saving space (9) extends radially inside the first piston ring groove (11).

6. A piston (1) according to claim 5, wherein the piston (1) comprises a second piston ring groove (13) in the mantle surface (5), and wherein the weight-saving space (9) extends radially inside the second piston ring groove (13).

7. The piston (1) according to any of the preceding claims, wherein the weight-saving space (9) comprises a first lowest delimiting surface (15 ') at the mantle surface (5) and a second lower delimiting surface (15 ", 15"') at a radially inner side of the mantle surface (5), and wherein the second lower delimiting surface (15 ", 15" ') is arranged further away from the piston crown (3) than the first lowest delimiting surface (15').

8. The piston (1) according to claim 7, wherein the weight-saving space (9) extends radially inside the stratified scavenging channel (7).

9. The piston (1) according to any of the preceding claims, wherein the radial extent (r1) of the weight-saving space (9) is at least 15%, or at least 35%, of the radius (r) of the piston (1).

10. The piston (1) according to any of the preceding claims, wherein the weight-saving space (9) has a maximum first tangential extent (T1) at the mantle surface (5) and a second tangential extent (T2) radially inside the mantle surface (5), and wherein the second tangential extent (T2) is larger than the maximum first tangential extent (T1).

11. The piston (1) according to claim 10, wherein the second tangential extent (T2) is at least 5% greater, or at least 10% greater, than the maximum first tangential extent (T1).

12. A piston (1) according to any of the preceding claims, wherein the weight-saving space (9) is configured to be isolated from any gas transmission channels during operation of an engine (30) comprising the piston (1) so as to avoid interconnection.

13. The piston (1) according to any one of the preceding claims, wherein the piston (1) comprises:

a second stratified scavenging channel (7') in the mantle surface (5); and

a second weight-reducing space (9 ') arranged between the piston crown (3) and the second stratified scavenging duct (7').

14. The piston (1) according to claim 13, wherein the weight-saving space (9) is provided on a first side (s1) of a plane (p1) extending along the centre axis (ax) of the piston (1), and wherein the second weight-saving space (9') is provided on a second side (s2) of the plane (p 1).

15. A piston (1) according to claim 13 or 14, wherein the second weight-reducing space (9') has substantially the same but mirrored shape as the weight-reducing space (9).

16. A two-stroke engine (30) comprising a piston (1) according to any of the preceding claims.

17. A hand-held tool (40) comprising a two-stroke engine (30) according to claim 16.

18. A method (100) of manufacturing a two-stroke engine piston (1), comprising the steps of:

a step (110) of providing a mould (50) with a cavity (52) arranged such that a piston (1) cast in the cavity (52) accommodates a piston crown (3), a mantle surface (5), and a stratified scavenging channel (7) in the mantle surface (5), and

a step (120) of arranging a core (54) in the cavity (52) such that an outer surface (54') of the core (54) defines an inner surface (8) of a weight-saving space (9) of the piston (1) and such that the weight-saving space (9) is arranged between the piston crown (3) and the stratified scavenging channel (7) and accommodates a maximum first axial extent (a1) at the mantle surface (5) in a direction parallel to a centre axis (ax) of the piston (1) and a second axial extent (a2) at a radially inner side of the mantle surface (5) in a direction parallel to the centre axis (ax) of the piston (1), wherein the second axial extent (a2) is larger than the maximum first axial extent (a 1).

19. The method (100) of claim 18, wherein the step (120) of providing the core (54) comprises:

a step (122) of providing the core (54) of a different material than the mould (50).

20. The method (100) according to any one of claims 18 or 19, wherein the step (120) of providing the core (54) comprises:

a step (124) of arranging the core (54) such that the core (54) becomes a lost core (54).

21. The method (100) according to any one of claims 18 to 20, wherein the step (120) of providing the core (54) comprises:

a step (126) of providing a core (54) of porous material.

22. The method (100) of claim 21, wherein the step (126) of providing a core (54) of porous material comprises:

a step (128) of setting a core (54) of sand and/or salt.

23. The method (100) according to any one of claims 18 to 22, wherein the step (120) of providing the core (54) includes:

a step (130) of disposing the core (54) using an additive manufacturing method (100).

24. A method (200) of manufacturing an engine piston (1), comprising the steps of:

a step (150) of providing a mould (50) having a cavity (52) arranged such that a piston (1) cast in the cavity (52) accommodates a piston crown (3) and a mantle surface (5), and

a step (160) of disposing a core (54) in the cavity (52) such that an outer surface (54') of the core (54) defines an inner surface (8) of a weight-saving space (9) of the piston (1) and such that the weight-saving space (9) is accommodated at the mantle surface (5) along a maximum first axial extent (a1) in a direction parallel to a central axis (ax) of the piston (1) and at a radially inner side of the mantle surface (5) along a second axial extent (a2) in a direction parallel to the central axis (ax) of the piston (1), wherein the second axial extent (a2) is greater than the maximum first axial extent (a 1).

Technical Field

The present invention relates to a two-stroke engine piston including a weight-saving space. The invention also relates to a two-stroke engine comprising a piston, a hand-held tool comprising a two-stroke engine, and a method of manufacturing a piston of an engine.

Background

A two-stroke engine is an internal combustion engine that completes a power cycle through two strokes of a piston during only one revolution of a crankshaft. The highest position of the piston in the cylinder is generally referred to as the top dead center and the lowest position of the piston in the cylinder is generally referred to as the bottom dead center. The number of moving parts of a two-stroke engine is greatly reduced compared to a four-stroke engine and can therefore be made more compact and lighter. Two-stroke gasoline engines are therefore used in applications where mechanical simplicity, light weight, and high power to weight ratio are of primary concern. A typical application is a hand held tool, e.g. a chain saw.

Most small two-stroke engines are crankcase scavenged engines, meaning that they utilize the area under the piston as an oil charge pump, building up pressure in the crankcase during the power stroke of the piston. Some of these engines are equipped with a fuel supply, e.g. a carburettor, for supplying an air/fuel mixture to the crankcase. The increased pressure and temperature in the cylinder obtained by the combustion of the fuel is partly converted into mechanical work provided to the engine crankshaft in the power stroke of the two-stroke engine. At the same time, the pressure in the crankcase increases as the piston moves towards bottom dead center. An exhaust port provided in the cylinder wall opens to allow exhaust gas to flow out of the cylinder when the piston reaches a first position relative to the cylinder in movement toward bottom dead center. The piston continues to move towards bottom dead center and the inlet provided in the cylinder wall opens when it reaches a second position located below the first position. The intake port is fluidly connected to the crankcase via a transfer conduit. The overpressure in the crankcase forces the air/fuel mixture in the crankcase to flow into the cylinder via the intake port.

Therefore, as described above, in this type of engine, the exhaust port and the intake port in the cylinder are simultaneously opened during the scavenging phase of the engine, i.e., when the piston is in the bottom dead center region. Thus, during the scavenging phase, some air/fuel mixture may flow through the cylinder from the intake port to the exhaust port. Thus, a problem associated with small two-stroke engines is the emission of unburned hydrocarbons (i.e., unburned fuel). One way to solve this problem is to provide the engine with a stratified scavenging arrangement.

In such an engine, the piston may be provided with stratified scavenging passages that are provided to superimpose the delivery conduit and the air passage in the cylinder wall when the piston is in the top dead center region. When the piston is in this position, clean air (i.e., air without added fuel) may flow from the air passage into the delivery conduit. As a result, when the piston reaches the second position, as described above, in which the inlet port is open, clean air will first enter the cylinder, and then the air/fuel mixture will reach the cylinder further down the transfer duct. In this way, less fuel will flow out through the exhaust port during the scavenging phase, and thus unburned hydrocarbon emissions can be significantly reduced.

However, a disadvantage of stratified scavenging passages in the piston is that the weight of the piston is increased, because passage walls in the piston are required. The weight of the engine piston is an important aspect and the increase in piston weight results in several disadvantages. For example, a piston with a higher weight may increase the vibration caused by the piston motion. Thus, the engine including the piston will vibrate more and may require a higher weight counterweight on the crankshaft and a larger and higher weight bearing. Thus, such an engine may add weight to the hand held tool and may cause it to vibrate more during use. As mentioned above, a number of advantages can be obtained by reducing the weight of the engine piston. However, many challenges also exist when attempting to reduce the weight of the piston, in part because the piston requires some structural strength and rigidity to withstand the high temperatures, forces, and pressures experienced during engine operation. Furthermore, the reduction in weight of the piston can be problematic due to the required structure and geometry of the piston.

Disclosure of Invention

It is an object of the present invention to overcome or at least alleviate at least some of the above problems and disadvantages.

According to a first aspect of the invention, this object is achieved by a two-stroke engine piston comprising a piston crown, a mantle surface, stratified scavenging galleries in the mantle surface, and a weight-saving space arranged between the piston crown and the stratified scavenging galleries. The weight-reduction space has a maximum first axial extent at the mantle surface and a second axial extent radially inside the mantle surface, wherein the second axial extent is larger than the maximum first axial extent.

Since the second axial extent is greater than the maximum first axial extent, conditions are provided for a structurally strong and rigid piston, while at the same time providing for a significant reduction in the weight of the piston. This is because the relatively small first axial extent of the weight-reducing space at the mantle surface does not significantly impair the structural strength and rigidity of the piston, whereas the relatively large second axial extent of the weight-reducing space radially inside the mantle surface can significantly reduce the weight of the piston. The relatively small first axial extent of the weight-saving space at the mantle surface does not significantly impair the structural strength and rigidity of the piston, since the mantle surface of the piston is more important for the structural strength and rigidity of the piston than the material of the radially inner part of the mantle surface.

In addition, the mantle surface of the piston has many engine related functions, such as providing a seal as the piston moves along the cylinder, conducting heat, and stabilizing the piston relative to the engine cylinder. Thus, since the second axial extent is greater than the maximum first axial extent, conditions are provided for a significant reduction in the weight of the piston, while the engine-related functions of the mantle surface are not significantly impaired.

Furthermore, since conditions are provided for a significant weight reduction of the piston, conditions are also provided for an internal combustion engine with a significant weight reduction and vibration reduction during operation.

Furthermore, since the piston comprises stratified scavenging passages, conditions are provided for low emissions of hydrocarbons when the piston is used in a two-stroke engine. Furthermore, due to the weight saving space, a low weight piston can be provided, although the piston comprises stratified scavenging passages which increase the weight of the piston.

Accordingly, a piston is provided that overcomes or at least alleviates at least some of the above problems and disadvantages. As a result, the above object is achieved.

Optionally, the second axial extent is at least 10% greater than the maximum first axial extent, or at least 40% greater. Thus, conditions are provided for a structurally strong and rigid piston, while at the same time providing for a significant reduction in the weight of the piston.

Optionally, the second axial extent is at least 80% greater than the maximum first axial extent, or at least 100% greater. Thus, conditions are provided for a structurally strong and rigid piston, while at the same time providing for a significant reduction in the weight of the piston.

Optionally, the weight-reducing space comprises a first uppermost delimiting surface at the mantle surface and a second upper delimiting surface radially inside the mantle surface, and wherein the second upper delimiting surface is arranged closer to the piston crown than the first uppermost delimiting surface. Thus, conditions are provided for a structurally strong and rigid piston, while at the same time providing for a significant reduction in the weight of the piston. This is because the relatively large axial distance between the first uppermost delimiting surface at the mantle surface and the piston top ensures a structurally strong and rigid piston, while the relatively small axial distance between the second uppermost delimiting surface and the piston top provides for a significant reduction of the piston weight.

Optionally, the piston comprises a first piston ring groove in the mantle surface, and wherein the weight saving space extends radially inside the first piston ring groove. Thus, provision is made for further weight reduction of the piston without significant loss of structural strength and rigidity. This is because the radial material in the piston ring groove has little effect on the structural strength and stiffness of the piston. Furthermore, a significant reduction of the weight of the piston is provided without significant impairment of the engine-related functions of the mantle surface.

Optionally, the piston comprises a second piston ring groove in the mantle surface, and wherein the weight saving space extends radially inside the second piston ring groove. Thus, provision is made for further weight reduction of the piston without the functions associated with the engine and the structural strength and rigidity of the piston being significantly impaired. Furthermore, since the piston according to these embodiments comprises two piston ring grooves, the piston is provided with conditions for obtaining an improved sealing between the piston and the cylinder wall.

Optionally, the weight-reduction space comprises a first lowest delimiting surface at the mantle surface and a second lower delimiting surface at a radially inner side of the mantle surface, and wherein the second lower delimiting surface is arranged further away from the piston crown than the first lowest delimiting surface. Thus, conditions are provided for a structurally strong and rigid piston, while at the same time providing for a significant reduction in the weight of the piston. This is because the relatively large axial distance between the second lower delimiting surface and the piston top provides for a significant reduction of the weight of the piston, whereas the relatively small axial distance between the first lowest delimiting surface at the housing and the piston top ensures a structurally strong and rigid piston.

Alternatively, the weight-saving space extends radially inside the stratified scavenging passage. Thus, although the piston includes stratified scavenging passages that increase the weight of the piston, conditions are provided for further weight reduction of the piston.

Optionally, for a generally cylindrical piston, the radial extent of the weight-reduction space is at least 15%, or at least 35%, of the piston radius. Thus, a significant weight reduction of the piston can be ensured.

Optionally, the weight-reduction space has a maximum first tangential extent at the shroud surface and a second tangential extent radially inward of the shroud surface, and wherein the second tangential extent is greater than the maximum first tangential extent. Thus, conditions are provided for a structurally strong and rigid piston, while providing for further reduction in the weight of the piston. This is because the material of the piston cage surface is more important for the structural strength and rigidity of the piston than the material of the radially inner part of the cage surface. Furthermore, a significant reduction of the weight of the piston is provided without significant impairment of the engine-related functions of the mantle surface.

Optionally, the second tangential range is at least 5% greater, or at least 10% greater, than the largest first tangential range. Thus, a significant weight reduction of the piston can be ensured, while the functions associated with the engine and the structural strength and rigidity of the piston are not significantly impaired.

Optionally, the weight-reduction space is configured to be isolated from any gas transfer passage interconnections during operation of the engine including the piston. Thus, a piston is provided wherein the sole purpose of the weight saving space is to reduce the weight of the piston. Thus, a piston is provided in which the weight-saving space will not participate in the connection between any gas transfer channels. Still alternatively, the weight-saving space may be configured to be isolated from any gas transfer passages during operation of the engine including the piston.

Optionally, the piston includes a second stratified scavenging gallery in the cover surface and a second weight-reducing space disposed between the crown of the piston and the second stratified scavenging gallery. Thus, a condition is provided for a piston having a low weight, although the piston includes two stratified scavenging passages, each of which adds to the weight of the piston.

According to any of the embodiments of the weight-saving space defined above, the second weight-saving space may have a maximum first axial extent at the mantle surface and a second axial extent at a radially inner side of the mantle surface, wherein the second axial extent is larger than the maximum first axial extent.

Optionally, the weight-saving space is provided on a first side of a plane extending along the central axis of the piston, and wherein the second weight-saving space is provided on a second side of the plane. Thus, conditions are provided for a structurally strong and rigid piston, while providing for further weight reduction of the piston.

Optionally, the second weight-mitigation space has substantially the same, but mirrored, shape as the weight-mitigation space. Thus, conditions are provided for a structurally strong and rigid piston, while providing for further weight reduction of the piston.

According to a second aspect of the present invention, the object is achieved by a two-stroke engine comprising a piston according to some embodiments of the present disclosure.

Thus, conditions are provided for a low weight two-stroke engine that generates a small amount of vibration and hydrocarbons during use. This is because the engine includes pistons which have a condition of significantly reducing its weight, and because the pistons include stratified scavenging passages.

Accordingly, a two-stroke engine is provided which overcomes or at least alleviates at least some of the above problems and disadvantages. As a result, the above object is achieved.

According to a third aspect of the present invention, the object is achieved by a hand-held tool comprising a two-stroke engine according to some embodiments of the present disclosure.

Thus, conditions are provided for a hand-held tool having low weight while producing little vibration and hydrocarbons during use. This is because the engine includes pistons which have a condition of significantly reducing its weight, and because the pistons include stratified scavenging passages.

Accordingly, a hand held tool is provided that overcomes or at least alleviates at least some of the above problems and disadvantages. As a result, the above object is achieved.

According to a fourth aspect of the invention, this object is achieved by a method of manufacturing a two-stroke engine piston, comprising the steps of:

providing a mold having a cavity arranged such that a piston cast in the cavity accommodates the piston crown, the mantle surface, and the layered scavenging passages in the mantle surface, and

the core is disposed in the cavity such that an outer surface of the core defines an inner surface of a weight-reduction space of the piston, and such that the weight-reduction space is disposed between the piston crown and the stratified scavenging gallery and accommodates a maximum first axial extent at the shroud surface and a second axial extent radially inward of the shroud surface, wherein the second axial extent is greater than the maximum first axial extent.

Since the method comprises the step of providing the core such that the second axial extent becomes greater than the maximum first axial extent, the method provides for obtaining a significant reduction in the weight of the piston without significant loss of structural strength and stiffness of the piston. This is because the relatively small first axial extent of the weight-reducing space at the mantle surface does not significantly impair the structural strength and rigidity of the piston, whereas the relatively large second axial extent of the weight-reducing space radially inside the mantle surface may provide a significant weight reduction of the piston. The relatively small first axial extent of the weight-saving space at the mantle surface does not significantly impair the structural strength and rigidity of the piston, since the mantle surface of the piston is more important for the structural strength and rigidity of the piston than the material radially inside the mantle surface.

In addition, the mantle surface of the piston has many engine related functions, such as providing a seal as the piston moves along the cylinder, conducting heat, and stabilizing the piston relative to the engine cylinder. Thus, since the method comprises the step of arranging the core such that the second axial extent becomes greater than the maximum first axial extent, the method provides the condition of obtaining a significant reduction in the weight of the piston, without significant impairment of the engine-related functions of the mantle surface.

Furthermore, since the method comprises the step of providing the mould with a cavity arranged such that the piston cast in the cavity receives the stratified scavenging channel, conditions are provided for low emissions of hydrocarbons when the piston is used in a two-stroke engine. Further, a method is provided that is capable of providing a low weight piston despite the piston including stratified scavenging passages.

Accordingly, a method is provided that overcomes or at least mitigates at least some of the above-mentioned problems and disadvantages. As a result, the above object is achieved.

Optionally, the step of providing a core comprises the steps of:

a core of a different material than the mold is provided.

Thus, provision is made for an easily removable core of material to be provided after the piston is cast in the mould. Furthermore, the provision of a core of material is provided, allowing the core to have a more complex geometry, and thus the weight saving space.

Optionally, the step of providing a core comprises the steps of:

the core is arranged to be lost.

Thus, although the piston includes stratified scavenging passages, and although the second axial extent of the weight-reduced space is greater than the maximum first axial extent, the resulting core is easily removed after the piston is cast in the mold.

Optionally, the step of providing a core comprises the steps of:

a core of porous material is provided.

Thus, although the piston comprises stratified scavenging passages and although the second axial extent of the weight-saving space is larger than the maximum first axial extent, conditions are provided for removing the core in a simple manner after casting the piston in the mould.

Optionally, the step of providing a core of porous material comprises the steps of

A core of sand and/or salt is provided.

Thus, although the piston comprises stratified scavenging passages and although the second axial extent of the weight-saving space is larger than the maximum first axial extent, conditions are provided for removing the core in a simple manner after casting the piston in the mould.

Optionally, the step of providing a core comprises the steps of:

the core is provided using an additive manufacturing method.

Thus, conditions are provided for obtaining a core with a more complex geometry, and therefore also for obtaining a weight-saving space with a more complex geometry. As a further consequence thereof, conditions are provided for obtaining a further structurally strong and rigid piston and for obtaining a further weight reduction of the piston.

According to a fifth aspect of the invention, the object is achieved by a method of manufacturing an engine piston, comprising the steps of:

providing a mold having a cavity configured such that a piston cast in the cavity receives the piston crown and the mantle surface, and

the core is disposed in the cavity such that an outer surface of the core defines an inner surface of a weight-reduction space of the piston, and such that the weight-reduction space receives a maximum first axial extent at the cage surface and a second axial extent radially inward of the cage surface, wherein the second axial extent is greater than the maximum first axial extent.

According to these embodiments, the piston manufactured by the method may be another type of engine piston than a two-stroke engine piston, for example, a four-stroke piston. Such a piston may, for example, be configured for use in a compression ignition engine (e.g., a diesel engine) or an otto engine having a spark ignition device, wherein the otto engine may be configured to operate on gas, gasoline, alcohol, similar volatile fuels, or a combination thereof. However, it is to be understood that the method according to the fifth aspect may be combined with each embodiment defined above with reference to the method according to the fourth aspect.

Since the method includes the step of providing a core such that the second axial extent becomes greater than the maximum first axial extent, the method provides for a significant reduction in the weight of the piston without significant loss in the structural strength and stiffness of the piston. This is because the relatively small first axial extent of the weight-reducing space at the mantle surface does not significantly impair the structural strength and rigidity of the piston, whereas the relatively large second axial extent of the weight-reducing space radially inside the mantle surface may provide a significant weight reduction of the piston. The relatively small first axial extent of the weight-saving space at the mantle surface does not significantly impair the structural strength and rigidity of the piston, since the mantle surface of the piston is more important for the structural strength and rigidity of the piston than the material radially inside the mantle surface.

In addition, the mantle surface of the piston has many engine related functions, such as providing a seal as the piston moves along the cylinder, conducting heat, and stabilizing the piston relative to the engine cylinder. Thus, since the method comprises the step of arranging the core such that the second axial extent becomes greater than the maximum first axial extent, the method provides the condition of obtaining a significant reduction in the weight of the piston, without the function of the hood surface associated with the engine being significantly impaired.

Accordingly, a method is provided that overcomes or at least mitigates at least some of the above-mentioned problems and disadvantages. As a result, the above object is achieved.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description.

Drawings

The various aspects of the invention, including the specific features and advantages thereof, will be best understood from the following detailed description and the accompanying drawings, in which:

FIG. 1 illustrates a perspective view of a two-stroke engine piston, according to some embodiments;

FIG. 2 shows a first cross-section of the piston shown in FIG. 1;

FIG. 3 shows a second cross-section of the piston shown in FIGS. 1 and 2;

FIG. 4 illustrates a hand-held tool according to some embodiments;

FIG. 5 illustrates a mold according to some embodiments;

FIG. 6 illustrates a core according to some embodiments;

FIG. 7 illustrates a method of manufacturing a two-stroke engine piston, according to some embodiments; and

FIG. 8 illustrates a method of manufacturing an engine piston, according to some further embodiments.

Detailed Description

Aspects of the present invention will now be described more fully. Like numbers refer to like elements throughout. Well-known functions or constructions may not be described in detail for brevity and/or clarity.

Fig. 1 shows a perspective view of a two-stroke engine piston 1 according to some embodiments. For the sake of brevity and clarity, the two-stroke engine piston 1 is referred to herein in some places as "piston 1". The piston 1 comprises a piston top 3. When the piston 1 is arranged in an engine cylinder, the piston crown 3 is arranged to face the cylinder head of the engine cylinder of a two-stroke engine. The piston crown 3 is arranged to define a combustion chamber together with the cylinder wall of the engine cylinder. The piston crown 3 is thus arranged to be in contact with the hot combustion gases during the power stroke of the engine comprising the piston 1. Furthermore, the piston 1 comprises a cylindrical mantle surface 5. The mantle surface 5 has an outer diameter slightly smaller than the inner diameter of the engine cylinder, and the mantle surface 5 is arranged to face the cylinder wall of the engine cylinder when the piston 1 is arranged in the engine cylinder. The mantle surface 5 of the piston 1 is sometimes referred to as the piston skirt.

The piston 1 comprises a first piston ring groove 11 and a second piston ring groove 13 in the mantle surface 5. Each of the first and second piston ring grooves 11, 13 is arranged to receive a piston ring for providing a seal between the mantle surface 5 of the piston 1 and the cylinder wall of the engine cylinder. Furthermore, the piston 1 comprises a bore 12, which bore 12 is configured to receive a piston pin for connecting the piston 1 to a connecting rod of an engine.

The piston 1 also comprises stratified scavenging passages 7 in the mantle surface 5. The stratified scavenging channel 7 is arranged to overlap the transfer ducts and the air passages in the cylinder wall of the engine when the piston 1 is in a certain position in relation to the engine cylinder. When the piston 1 is in this position, clean air (i.e. air without added fuel) can flow from the air channel via the stratified scavenging channel 7 into the transfer ducts. As a result, the emission of unburned hydrocarbons produced by the engine may be significantly reduced.

As shown in fig. 1, the piston 1 further comprises a weight-saving space 9 provided between the piston crown 3 and the stratified scavenging conduit 7. According to the embodiment shown, the weight-saving space 9 is configured to be isolated from any gas transfer channels during operation of the engine comprising the piston 1 and is not assigned any gas transfer tasks during operation of the engine. The weight-saving space 9 extends through the mantle surface 5 of the piston 1 and has an opening 14 in the mantle surface 5. According to the shown embodiment, the opening 14 of the weight-saving space 9 is the only opening of the weight-saving space 9. In fig. 1, a portion of the bounding surface of the weight-saving space 9 radially inside the mantle surface 5, which is not visible through the opening 14, is shown in dashed lines. The weight-saving space 9 has a maximum first axial extent a1 at the mantle surface 5. The term "maximum first axial extent a 1" is intended here to encompass the maximum extent a1 of the weight-reduction space 9, which maximum extent a1 is measured between the two bounding surfaces of the weight-reduction space 9 (i.e. at the opening 14) at the mantle surface 5 in a direction parallel to the centre axis ax of the piston 1. The central axis ax of the piston 1 coincides with the direction of movement of the piston 1 during operation in the engine. Furthermore, the central axis ax of the piston 1 also coincides with the central axis ax of the cylindrical mantle surface 5.

Further, according to the present disclosure, the weight-reduction space 9 has a second axial extent a2 radially inward of the hood surface 5. As shown in fig. 1, the second axial extent a2 is greater than the maximum first axial extent a 1. The term "second axial extent a 2" is intended here to include the extent a2 of the weight-saving space 9, which extent a2 is measured between the two bounding surfaces of the weight-saving space 9 radially inside the mantle surface 5 in a direction parallel to the centre axis ax of the piston 1. According to some embodiments of the present disclosure, the second axial extent a2 is measured radially inward of the first axial extent a 1. That is, according to such an embodiment, the first axial extent a1 and the second axial extent a2 are measured in the same plane, wherein the plane extends along the central axis ax of the piston 1.

As further explained herein, since the second axial extent a2 is greater than the maximum first axial extent a1, conditions are provided for a structurally strong and rigid piston 1, while providing for a significant reduction in the weight of the piston 1. Furthermore, the mantle surface 5 of the piston 1 has many engine-related functions, such as providing sealing, conducting heat as the piston moves along the cylinder, and stabilizing the piston 1 relative to the cylinder of the engine. Thus, since the second axial extent a2 is greater than the maximum first axial extent a1, provision is made for a significant reduction in the weight of the piston 1, without the engine-related function of the mantle surface 5 being significantly impaired.

According to the illustrated embodiment, the second axial extent a2 is approximately 128% greater than the maximum first axial extent a 1. According to further embodiments, the second axial extent a2 may be at least 10% greater than the maximum first axial extent a1, or at least 40% greater. Further, according to some embodiments, the second axial extent a2 may be at least 80% greater than the maximum first axial extent a1, or at least 100% greater.

Fig. 2 shows a first cross section of the piston 1 shown in fig. 1. The first cross section of fig. 2 is formed at a position offset from the central axis in a plane parallel to the central axis of the piston 1. As shown in fig. 2, the weight-saving space 9 includes a first uppermost delimiting surface 10' at the mantle surface 5. The term "first uppermost delimiting surface 10" is here intended to comprise a delimiting surface 10 'of the weight-saving space 9 at the mantle surface 5 (i.e. at the opening 14), which delimiting surface 10' is closest to the piston crown 3, measured in a direction parallel to the centre axis ax of the piston 1. Furthermore, the weight-saving space 9 comprises a second upper delimiting surface 10 "located at the radially inner side of the mantle surface 5. As shown in fig. 2, the second upper delimiting surface 10 "is arranged closer to the piston crown 3 than the first uppermost delimiting surface 10'. In this way, conditions are provided for a structurally strong and rigid piston 1, while at the same time conditions are provided for a significant reduction in the weight of the piston 1.

The second upper delimiting surface 10 "may be the uppermost delimiting surface 10" of the weight-reduction space 9 radially inside the mantle surface 5, as is the case according to the illustrated embodiment, i.e. the delimiting surface 10 "of the weight-reduction space 9 radially inside the mantle surface 5 is closest to the piston crown 3, measured in a direction parallel to the centre axis ax of the piston 1. In case the piston 1 comprises a flat piston crown 3, both the surface normal of the first uppermost delimiting surface 10' and the surface normal of the second upper delimiting surface 10 "point in the opposite direction to the surface normal of the piston crown. Further, when the piston 1 is mounted in the engine and moves in the direction toward the bottom dead center, the surface normal of the first uppermost delimiting surface 10' and the surface normal of the second uppermost delimiting surface 10 ″ both point in a direction coinciding with the moving direction of the piston 1. It should be apparent, however, that the teachings herein are also applicable to pistons having non-flat piston crowns.

In fig. 1 and 2, a first piston ring groove 11 and a second piston ring groove 13 are shown. As best shown in fig. 2, the weight-saving space 9 extends radially inside the first piston ring groove 11 and radially inside the second piston ring groove 13. Furthermore, the weight-saving space 9 comprises a first lowermost delimiting surface 15' at the mantle surface 5 and a second lower delimiting surface 15 "at the radially inner side of the mantle surface 5. As shown in fig. 2, the second lower delimiting surface 15 "is further away from the piston crown 3 than the first lowest delimiting surface 15'. In this way, conditions are provided for a structurally strong and rigid piston 1, while at the same time conditions are provided for a significant reduction in the weight of the piston 1.

The term "first lowest delimiting surface 15 '" is here intended to comprise a delimiting surface 15 ' of the weight-saving space 9 at the mantle surface 5 (i.e. at the opening 14), which delimiting surface 15 ' is the farthest distance from the piston crown 3, measured in a direction parallel to the centre axis ax of the piston 1. The second lower delimiting surface 15 "may be the lowermost delimiting surface 15" of the weight-reduction space 9 radially inside the mantle surface 5, as is the case according to the shown embodiment, i.e. the delimiting surface 15 "of the weight-reduction space 9 radially inside the mantle surface 5 is the farthest away from the piston crown 3, measured in a direction parallel to the centre axis of the piston 1. In case the piston 1 comprises a flat piston crown 3, the surface normal of the first lowest delimiting surface 15' and the surface normal of the second lower delimiting surface 15 "both point in the direction of the surface normal of the piston crown. Further, when the piston 1 is mounted in the engine and moves in the direction toward the top dead center, the surface normal of the first lowest delimiting surface 15' and the surface normal of the second lower delimiting surface 15 ″ both point in a direction coinciding with the moving direction of the piston 1.

According to some embodiments of the present disclosure, the weight-saving space 9 may extend radially inside the stratified scavenging passage 7. The lower delimiting surface 15 "'of such a weight-saving space 9 is indicated in fig. 2 by a dashed line 15"'.

According to the shown embodiment the radial extent r1 of the weight-saving space 9 is about 57% of the radius of the piston 1. According to further embodiments, the radial extent r1 of the weight-saving space 9 may be at least 15%, or at least 35% of the radius of the piston 1. The radial extent r1 of the weight-saving space 9 can be measured in the radial direction of the piston 1, i.e. in a direction perpendicular to the centre axis of the piston 1, from the mantle surface 5 to the radially inner delimiting surface of the weight-saving space 9.

Fig. 3 shows a second cross section of the piston 1 shown in fig. 1 and 2. The second cross section of fig. 3 is formed in a plane perpendicular to the central axis ax of the piston 1. As shown in fig. 3, the weight-saving space 9 has a maximum first tangential extent T1 at the hood surface 5 and a second tangential extent T2 radially inside the hood surface 5, and wherein the second tangential extent T2 is greater than the maximum first tangential extent T1. Thus, conditions are provided for the piston 1 to be structurally strong and rigid, while conditions are provided for further reducing the weight of the piston 1. This is because the material at the mantle surface 5 of the piston 1 is more important for the structural strength and rigidity of the piston 1 than the material radially inside the mantle surface 5.

The tangential lengths T1, T2 referred to herein are the distances between the two bounding surfaces of the weight-saving space 9 measured along the measuring lines L1, L2 in a plane perpendicular to the central axis ax of the piston 1, which measuring lines have central normals c1, c2 intersecting the central axis ax. According to the illustrated embodiment, the second tangential range T2 is approximately 18% greater than the maximum first tangential range T1. According to further embodiments, the second tangential range T2 may be at least 5% greater than the maximum first tangential range T1, or at least 10% greater.

As shown in fig. 1, according to the shown embodiment the piston 1 comprises a second stratified scavenging channel 7' in the mantle surface 5. The second stratified scavenging channel 7' is also arranged to overlap the transfer ducts and the air passages in the cylinder wall of the engine when the piston 1 is in a certain position in relation to the engine cylinder. That is, when the piston 1 is in this position, clean air (i.e., air to which fuel is not added) can also flow from the air passage into the delivery pipe via the second stratified scavenging passage 7'. Further, as shown in fig. 1, 2 and 3, the piston 1 includes a second weight-reducing space 9 'provided between the piston crown 3 and the second stratified scavenging passage 7'. As shown in fig. 3, the weight-saving space 9 is provided on a first side s1 of a plane p1 extending along the central axis ax of the piston 1, and a second weight-saving space 9' is provided on a second side s2 of the plane p1, wherein the second side s2 is opposite to the first side s 1. The second weight saving space 9' has substantially the same but mirrored shape as the weight saving space 9 and will not be explained in detail here.

Furthermore, as shown in fig. 1 and 3, the piston 1 comprises a third weight mitigation space 9 "and a fourth weight mitigation space 9"'. According to the shown embodiment, the third weight mitigation space 9 "and the fourth weight mitigation space 9 '" are both arranged between the piston crown 3 and the stratified scavenging ducts 7, 7' of the piston 1. The third weight mitigation space 9 "and the fourth weight mitigation space 9'" may each comprise similar or corresponding features as the weight mitigation space 9 explained herein.

The piston 1 may be formed of an aluminum alloy. Furthermore, as further explained herein, the piston 1 may be manufactured using a cast manufacturing method. The piston 1 according to the embodiment shown in fig. 1-3 is a two-stroke engine piston 1 for a small crankcase scavenged two-stroke engine.

Fig. 4 illustrates a handheld tool 40 according to some embodiments. According to the illustrated embodiment, the hand held tool 40 is a chainsaw. According to further embodiments, the hand held tool 40 may be another type of portable tool, such as a hedge trimmer, a leaf blower, a multi-function tool, or the like. The hand tool 40 includes a two-stroke engine 30. The two-stroke engine 30 comprises a piston 1 according to the embodiment shown in fig. 1-3.

Fig. 5 illustrates a mold 50 according to some embodiments. According to the embodiment shown, the mould 50 has a cavity 52, the cavity 52 being arranged such that the piston cast in the cavity 52 receives a stratified scavenging channel in the piston top, the mantle surface and the mantle surface. According to the embodiment shown, the mold 50 comprises two mold halves 53, 53'. The two mold halves 53, 53' can be separated from each other along a separation plane extending along the central axis of the cavity 52.

Fig. 6 illustrates a core 54, according to some embodiments. As further explained herein, according to the illustrated embodiment, the core 54 is configured to be disposed in the cavity 52 of the mold 50.

Fig. 7 illustrates a method 100 of manufacturing a two-stroke engine piston 1 according to some embodiments. The piston 1 may be a piston 1 according to the embodiment shown in fig. 1 to 3. In addition, reference is now made to the mold 50 shown in FIG. 5 and the core 54 shown in FIG. 6. Accordingly, reference is now made to fig. 1 to 3 and 5 to 7 simultaneously. The method 100 of manufacturing a two-stroke engine piston 1 comprises the steps of:

providing 110 a mould 50 with a cavity 52, the cavity 52 being arranged such that the piston 1 cast in the cavity 52 accommodates the piston crown 3, the mantle surface 5 and the stratified scavenging passages 7 in the mantle surface 5, and

the core 54 is arranged 120 in the cavity 52 such that the outer surface 54' of the core 54 defines the inner surface 8 of the weight-saving space 9 of the piston 1 and such that the weight-saving space 9 is arranged between the piston crown 3 and the stratified scavenging ducts 7 and accommodates a maximum first axial extent a1 at the mantle surface 5 and a second axial extent a2 at the radially inner side of the mantle surface 5, wherein the second axial extent a2 is larger than the maximum first axial extent a 1.

The inner surface 8 of the weight-saving space 9 is shown in fig. 1. The step of disposing 120 the core 54 in the cavity 52 may be performed after the step of providing 110 the mold 50. According to such embodiments, the core 54 may be attached to a bounding surface of the cavity 52. Alternatively, the steps of providing 110 the mold 50 and disposing 120 the core 54 in the cavity 52 may be performed simultaneously. According to such embodiments, the core 54 may be integrated with the mold 50.

As shown in fig. 7, the step 120 of disposing the core 54 may include the steps of:

step 122: a core 54 of a different material than the mold 50 is provided.

By way of example, the mold 50 may be provided from a metallic material, such as a steel material, and the core 54 may be provided from a porous material, such as sand and/or salt.

As shown in fig. 7, the step 120 of disposing the core 54 includes the steps of:

step 124: the core 54 is arranged such that the core 54 becomes a lost core 54, i.e. a disposable core 54 intended for one-time use.

In this way, although the piston 1 includes the stratified scavenging passage 7, and although the second axial extent a2 of the weight-saving space 9 is larger than the maximum first axial extent a1, the core 54 can be easily removed after the piston 1 is cast in the mold 50.

As shown in fig. 7, the step 120 of disposing the core 54 includes the steps of:

step 126: a core 54 of porous material is provided.

In this way, although the piston 1 includes the stratified scavenging passage 7, and although the second axial extent a2 of the weight-saving space 9 is larger than the maximum first axial extent a1, the core 54 can be easily removed after the piston 1 is cast in the mold 50.

As shown in FIG. 7, the step 126 of providing the cellular material core 54 includes the following steps

Step 128: a core 54 of sand and/or salt is provided.

In this way, although the piston 1 includes the stratified scavenging passage 7, and although the second axial extent a2 of the weight-saving space 9 is larger than the maximum first axial extent a1, the core 54 can be easily removed after the piston 1 is cast in the mold 50.

As shown in fig. 7, the step of providing 120 the core 54 includes the steps of:

step 130: the core 54 is provided using an additive manufacturing method.

According to these embodiments, the core 54 and the mold 50 may be provided using an additive manufacturing method.

The step 130 of providing the core 54 using an additive manufacturing method may comprise the steps of:

the layers of material are deposited successively such that the deposited layers of material together form the core 54.

Optionally, the method 100 may comprise:

the layers of material are deposited successively such that the deposited layers of material together form mold 50 and core 54.

Additive manufacturing is sometimes referred to as 3D printing. The additive manufacturing method referred to herein may be an additive manufacturing method belonging to the following categories: photopolymerization, stereolithography, material jetting, adhesive jetting, powder bed melting, material extrusion, directed energy deposition, selective laser melting/sintering \ or sheet lamination.

The method 100 described herein may further include the steps of:

step 132: the piston 1 is cast in the cavity 52 of the mould 50.

The piston 1 may be cast, for example, using an aluminum alloy. Further, the piston 1 may be cast using die casting or gravity casting, as examples.

According to some embodiments, the method 100 described herein may further comprise the steps of:

after step 132 of casting the piston 1, one or more of the piston crown 3, the mantle surface 5 and the stratified scavenging conduit 7 are machined.

The machining step may for example comprise one or more of grinding, turning and milling.

Fig. 8 shows a method 200 of manufacturing an engine piston 1 according to some further embodiments. The method 200 comprises the following steps:

step 150: providing a mould 50 having a cavity 52, the cavity 52 being arranged such that the piston 1 cast in the cavity 52 accommodates the piston crown 3 and the mantle surface 5, and

step 160: the core 54 is arranged in the cavity 52 such that an outer surface 54' of the core 54 defines the inner surface 8 of the weight-saving space 9 of the piston 1 and such that the weight-saving space 9 receives a maximum first axial extent a1 at the mantle surface 5 and a second axial extent a2 at a radially inner side of the mantle surface 5, wherein the second axial extent a2 is larger than the maximum first axial extent a 1.

According to these embodiments, the piston may be another type of engine piston than the two-stroke engine piston 1, for example a four-stroke piston. Such a piston may, for example, be configured for use in a compression ignition engine (e.g., a diesel engine) or an otto engine having a spark ignition device, wherein the otto engine may be configured to operate on gas, gasoline, alcohol, similar volatile fuels, or a combination thereof.

Further, as shown in fig. 8, the method 200 may include any of the steps 122, 124, 126, 128, 130, 132 described herein with reference to fig. 7. Further, the piston manufactured by the method 200 may include one or more features, functions, and advantages, such as the piston 1 explained with reference to fig. 1-3.

It should be understood that the foregoing is illustrative of various exemplary embodiments and that the invention is limited only by the claims which follow. Those skilled in the art will recognize that the exemplary embodiments can be modified and different features of the exemplary embodiments can be combined to create embodiments other than those described herein without departing from the scope of the present invention, which is defined by the appended claims.

As used herein, the terms "comprising" or "having" are open-ended and include one or more stated features, elements, steps, components, or functions, but do not preclude the presence or addition of one or more other features, elements, steps, components, functions, or groups thereof.

In embodiments where the piston 1 comprises two or more weight-saving spaces 9, 9 ', 9 ", 9'", the "weight-saving space 9" mentioned herein may also be referred to as "first weight-saving space 9". Thus, throughout the present disclosure, the expression "weight-saving space 9" may be replaced by the expression "first weight-saving space 9".