Abstract
A piston for a two-stroke engine operating with advanced scavenging has a piston base and a piston skirt. The piston has a piston pocket which has a smallest distance (e) from a top side of the piston base. The piston has a section plane perpendicularly to the longitudinal center axis of the piston, the distance of which section plane from the top side of the piston base is greater than the smallest distance (e). A middle plane of the piston intersects the piston skirt at a location. In the circumferential direction between the pocket and this location, a thickened area is arranged in the section plane, the greatest wall thickness of which area is at least 1.1 times the wall thickness at the location. The piston has an edge at a recess at which the piston skirt has a reduced height. A chamfer is arranged on the radially outer side of the piston.
Claims
1. A piston for a two-stroke engine operating with advanced scavenging, the piston comprising: a piston base having a top side; a piston skirt defining a first center axis; said first center axis forming a longitudinal center axis of the piston; the piston having two piston pin eyelets defining a second center axis; said second center axis defining a transverse axis; the piston defining a middle plane containing said longitudinal center axis of the piston; said middle plane being perpendicular to said transverse axis; the piston having at least one piston pocket arranged completely on a first side of said middle plane; said piston pocket and said top side of said piston base mutually defining a smallest distance (e) therebetween; the piston having a section plane perpendicular to said longitudinal center axis; said section plane and said top side of said piston base mutually defining a distance (m) therebetween; said distance (m) being greater than said smallest distance (e); said piston skirt having a location at which said middle plane intersects said piston skirt in said section plane; said piston skirt having a wall thickness (b) at said location; the piston defining a circumferential direction; a thickened region arranged in said section plane between said pocket and said location in said circumferential direction; said thickened region having a wall thickness (a); and, said wall thickness (a) being at least 1.1 times said wall thickness (b) at said location.
2. The piston of claim 1, wherein: said at least one piston pocket includes a first piston pocket and a second piston pocket; said thickened region is a first thickened region; said first piston pocket and said second piston pocket are arranged on opposite sides of said middle plane; said first thickened region extends from said first piston pocket to said location; and, the piston has a second thickened region extending from said second piston pocket to said location.
3. The piston of claim 2, wherein said piston skirt has an edge facing away from said piston base.
4. The piston of claim 3, wherein: said edge defines a recess between said first piston pocket and said second piston pocket; said piston skirt having a reduced height (i) at said recess; and, said first thickened region and said second thickened region conjointly at least partially overlap said recess.
5. The piston of claim 4, wherein said edge has a chamfer at said recess at a radially outwardly lying side of the piston.
6. The piston of claim 4, wherein: said recess has a transition region in which said recess transitions into an adjacent region of said piston skirt; said adjacent region is adjacent to said recess in said circumferential direction; and, the piston has a height which increases by at least 5% in said transition region.
7. The piston of claim 3, wherein each of said first thickened region and said second thickened region extends up to said edge.
8. The piston of claim 1, wherein said piston skirt has an inner contour which runs straight in said thickened region in said section plane.
9. The piston of claim 1, wherein said thickened region extends over at least 50% of a height of the piston measured parallel to said longitudinal center axis.
10. The piston of claim 1 further comprising: at least one rib connecting said piston skirt and said piston base; and, at least one of said at least one ribs adjoins said thickened region radially within said thickened region.
11. The piston of claim 1, wherein the piston is made of a light metal.
12. The piston of claim 1, wherein the piston is made of magnesium.
13. A two-stroke engine comprising: a cylinder having a cylinder bore; a combustion chamber formed in said cylinder bore; a piston having a piston base and a piston skirt; said combustion chamber being delimited by said piston; a crankcase defining a crankcase interior; a crankshaft rotatably mounted in said crankcase; said piston being configured to drive said crankshaft; a transfer channel having a transfer window and being configured to connect said crankcase interior to said combustion chamber in at least one position of said piston; an air channel configured to supply scavenging air; said air channel opening at said cylinder bore via an air inlet; said piston including a piston base having a top side and a piston skirt defining a first center axis; said first center axis forming a longitudinal center axis of said piston; said piston having two piston pin eyelets defining a second center axis; said second center axis defining a transverse axis; said piston defining a middle plane containing said longitudinal center axis of said piston; said middle plane being perpendicular to said transverse axis; said piston having at least one piston pocket arranged entirely on a first side of said middle plane; said at least one piston pocket being configured to be at least partially overlapping with said air inlet and said transfer window in at least one position of said piston; said piston pocket and said top side of said piston base mutually defining a smallest distance (e) therebetween; said piston having a section plane perpendicular to said longitudinal center axis; said section plane and said top side of said piston base mutually defining a distance (m) therebetween; said distance (m) being greater than said smallest distance (e); said piston skirt having a location at which said middle plane intersects said piston skirt in said section plane; said piston skirt having a wall thickness (b) at said location; said piston defining a circumferential direction; a thickened region arranged in said section plane between said pocket and said location in said circumferential direction; said thickened region having a wall thickness (a); and, said wall thickness (a) being at least 1.1 times said wall thickness (b) at said location.
14. A piston for a two-stroke engine operating with advanced scavenging, the piston comprising: a piston base having a top side; a piston skirt defining a first center axis; said first center axis forming a longitudinal center axis of the piston; the piston having two piston pin eyelets defining a second center axis; said second center axis defining a transverse axis; the piston defining a middle plane containing said longitudinal center axis of the piston; said middle plane being perpendicular to said transverse axis; the piston having two piston pockets arranged on opposite sides of said middle plane; said piston skirt having an edge facing away from said piston base; the piston defining a circumferential direction; said edge defining a recess between said two piston pockets; said piston skirt having a reduced height (I) at said recess; and, said edge having a chamfer at said recess at a radially outer side of the piston.
15. A two-stroke engine comprising: a piston having a piston base and a piston skirt; a cylinder having a cylinder bore; a combustion chamber formed in said cylinder bore and delimited by said piston; a crankcase; a crankshaft rotatably mounted in said crankcase; a connecting rod having a connecting rod eye; said piston being configured to drive said crankshaft via said connecting rod; said connecting rod being mounted on said crankshaft via said connecting rod eye; said piston base having a top side; said piston skirt defining a first center axis; said first center axis forming a longitudinal center axis of said piston; said piston having two piston pin eyelets defining a second center axis; said second center axis defining a transverse axis; said piston defining a transverse plane containing said transverse axis and said longitudinal center axis; said piston defining a middle plane containing said longitudinal center axis of said piston; said middle plane being perpendicular to said transverse axis; said piston having two piston pockets arranged on opposite sides of said middle plane; said piston skirt having an edge facing away from said piston base; said piston defining a circumferential direction; said edge defining a recess between said two piston pockets; said piston skirt having a reduced height (I) at said recess; said edge having a chamfer at said recess at a radially outer side of said piston; said transverse plane of said piston defining a first side and a second side lying opposite to said first side; said connecting rod eye being configured to be disposed on said first side during an upward stroke of said piston; and, said chamfer being arranged on said second side of said transverse plane during an upward stroke of said piston.
16. A piston for a two-stroke engine operating with advanced scavenging, the piston comprising: a piston base having a top side; a piston skirt defining a first center axis; said first center axis forming a longitudinal center axis of the piston; the piston having two piston pin eyelets defining a second center axis; said second center axis defining a transverse axis of the piston; the piston defining a middle plane containing said longitudinal center axis of the piston; said middle plane being perpendicular to said transverse axis; the piston having at least one piston pocket arranged completely on a first side of said middle plane; the piston having a piston pin receptacle defining a receptacle longitudinal center axis; the piston defining a transverse plane containing said receptacle longitudinal center axis and said longitudinal center axis of the piston; said piston including at least one first rib having a first thickness (o) at said piston skirt; said piston including at least one second rib having a second thickness (n); and, said first thickness (o) being greater than said second thickness (n).
17. The piston of claim 16, wherein said thickness (o) is 1.1 to 1.8 times greater than said thickness (n).
18. The piston of claim 16, wherein said at least one first rib and said at least one second rib have different heights.
19. The piston of claim 16, wherein: said piston skirt has a top side; said at least one second rib has a second rib tip arranged at a side of said at least one second rib facing away from said top side of said piston skirt; said second rib tip is at a distance (f) to said top side; said at least one first rib has a first rib tip facing away from said top side of said piston skirt; said first rib tip is at a distance (g) to said top side; and, said distance (g) is 1.1 to 1.5 times as great as said distance (f).
20. The piston of claim 19, wherein: the piston has a height (h); and, said distance (g) is 50% to 80% of said height (h).
21. The piston of claim 19 wherein: the piston has a height (h); and, said distance (f) is 30% to 70% of said height (h).
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention will now be described with reference to the drawings wherein:
(2) FIG. 1 shows a schematic sectional illustration of a two-stroke engine;
(3) FIG. 2 shows a perspective illustration of the piston of the two-stroke engine from FIG. 1;
(4) FIG. 3 shows an enlarged cutout of an area of the edge of the piston from FIG. 2;
(5) FIG. 4 shows a side view of the piston from FIG. 2;
(6) FIG. 5 shows a section along the line V-V from FIG. 4;
(7) FIG. 6 shows a perspective view of the piston from the side facing the crankcase;
(8) FIG. 7 shows a perspective sectional illustration of the piston through the middle plane;
(9) FIG. 8 shows a section along the line VIII-VIII in FIG. 4;
(10) FIG. 9 shows a section along the line IX-IX in FIG. 8; and,
(11) FIG. 10 shows a section along the line X-X in FIG. 8.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
(12) FIG. 1 schematically shows an embodiment of a two-stroke engine 1. The two-stroke engine 1 is configured as a single cylinder engine and has a cylinder 2 in which a combustion chamber 3 is formed. The combustion chamber 3 is delimited by a piston 5 which is mounted so as to move to and fro in a cylinder bore 15 of the cylinder 2. FIG. 1 shows the piston 5 at the bottom dead center. The piston 5 drives a crankshaft 7 via a connecting rod 6. The crankshaft 7 is mounted in a crankcase interior 16 of a crankcase 4 so as to be rotatable about a rotational axis 8. The two-stroke engine 1 can be, for example, the drive motor in a handheld work apparatus, such as a power saw, an angle grinder, a blower device or the like. The crankshaft 7 advantageously serves for driving a tool of the work apparatus. The piston 5 advantageously has two piston pockets 14, one of which is shown in FIG. 1. The piston pockets 14 are arranged on the piston 5 symmetrically with respect to the section plane shown in FIG. 1.
(13) The two-stroke engine 1 has an air channel 9 which is connected to an air filter 22. Fuel-free or low-fuel advanced scavenging air is sucked up by the air filter 22 via the air channel 9. An air flap 21 for controlling the quantity of advanced scavenging air supplied via the air channel 9 is arranged in the air channel 9. The air channel 9 opens with an air inlet 11 at the cylinder bore 15. A mixture channel 10 is provided for supplying a fuel/air mixture. The mixture channel 10 is connected to the air filter 22 via a carburetor 18. In the embodiment, a throttle flap 19 and a choke flap 20 are mounted pivotably in the carburetor 18. The throttle flap 19 and the choke flap 20 serve to set the quantity of combustion air and fuel that is fed in via the mixture channel 10. Instead of by means of a conventional carburetor 18, the fuel can also be supplied in a different way, for example via an injection valve or a carburetor with a solenoid valve. The mixture channel 10 opens with a mixture inlet 12 at the cylinder bore 15. The air inlet 11 and the mixture inlet 12 are controlled by the piston 5.
(14) The two-stroke engine 1 has transfer channels 13 which open with transfer windows 17 into the combustion chamber 3. The transfer windows 17 are also controlled by the piston 5. In the area of the bottom dead center of the piston 5, the transfer channels 13 (not illustrated specifically in FIG. 1) connect the crankcase interior 16 to the combustion chamber 3. During operation, a fuel/air mixture is sucked up through the mixture inlet 12 into the crankcase interior 16 during the upward stroke of the piston 5. The upward stroke of the piston here denotes the movement of the piston 5 out of the position (shown in FIG. 1) of the piston 5 in the bottom dead center in the direction of the combustion chamber 3, that is, in the direction of the arrow 70 in FIG. 1. In the area of the top dead center of the piston 5, the piston pockets 14 each connect an air inlet 11 to transfer windows 17. As a result, advanced scavenging air is drawn out of the air channel 9 into the transfer channels 13. During the upward stroke of the piston 5, mixture which is already present in the combustion chamber 3 is compressed at the same time and is ignited in the area of the top dead center of the piston 5 by a spark plug (not illustrated).
(15) The combustion pressure accelerates the piston 5 back in the direction of the crankcase 4. An outlet 23 which is controlled by the piston 5 leads out of the combustion chamber 3. As soon as the outlet 23 is opened by the piston 5, the exhaust gases flow out of the combustion chamber 3 through the outlet 23. After a further downward stroke, the piston 5 opens the transfer windows 17 to the combustion chamber 3. The advanced scavenging air which is advanced in the transfer channels 13 flows into the combustion chamber 3 and flushes exhaust gases out of the combustion chamber 3 through the outlet 23. A fresh fuel/air mixture which has been pre-compressed in the crankcase interior 16 flows in from the crankcase interior 16. During the following engine cycle, the mixture in the combustion chamber 3 is compressed during the upward stroke of the piston 5, while fresh mixture is at the same time sucked up into the crankcase interior 16 and advanced scavenging air is drawn into the transfer channels 13.
(16) As FIG. 2 shows, the piston pockets 14 have an upper control edge 29 which is advantageously arranged in the area of the top dead center of the piston 5 in such a manner that the transfer windows 17 are arranged completely in congruence with the piston pocket 14. The upper control edge 29 is that control edge of the piston pocket 14 which lies closest to the combustion chamber 3. The piston pocket 14 also has a lower control edge 30 which lies facing the crankcase 4. The lower control edge 30 is that control edge of the piston pocket 14 which lies furthest away from the combustion chamber 3, and delimits the piston pocket 14 in the direction of the crankcase 4. At the top dead center of the piston 5, the lower control edge 30 is advantageously arranged in such a way that the air inlet 11 lies completely in congruence with the piston pocket 14. The piston 5 has an edge 31 on its side facing the crankcase 4. The edge 31 is that delimitation of the piston 5 which faces the crankcase 4. A web 32 which is formed by a section of a piston 26 is formed in each case between the piston pockets 14 and the edge 31. The edge 31 forms a bottom side of the piston 5.
(17) The piston 5 has a piston base 25 which delimits the combustion chamber 3 and which, in the embodiment, runs approximately perpendicularly to a longitudinal center axis 50 of the piston 5. In addition, the piston 5 has a piston skirt 26 which adjoins the piston base and which advantageously follows the profile of the cylinder bore 15. The outer side of the piston skirt 26 advantageously runs approximately cylindrically. The outer side of the piston skirt 26 here can have a cross section which is exactly cylindrical or which deviates slightly from the cylindrical form, for example is slightly oval or elliptical. The longitudinal center axis 50 of the piston 5 is the center axis of the piston skirt 26.
(18) As FIG. 2 shows, two piston ring grooves 24 which serve for receiving piston rings (not shown) are provided on the piston skirt 26 adjacent to the piston base 25. A bore 41 which serves for receiving a securing pin for a piston ring is shown in one of the piston ring grooves 24. A corresponding bore is also provided for the further piston ring groove 24 on that side of the piston 5 which is not shown in FIG. 2. As FIG. 2 also shows, a deepening 27 is provided on the piston skirt 26 between each piston pocket 14 and the lower piston ring groove 24. The deepening 27 serves for reducing the weight of the piston 5. The deepening 27 is configured here in such a manner that, during a piston stroke, it lies in congruence with just one or with both transfer windows 17, but not with the air inlet 11. As a result, a connection cannot be produced between the air inlet 11 and the transfer windows 17 via the deepening 27.
(19) The connecting rod 6 (FIG. 1) is connected to the piston 5 via a piston pin (not shown) which is held in piston pin receptacles 53 of the piston 5. As FIG. 2 shows, the piston pin receptacles 53 lie completely within the piston pockets 14 in the embodiment. The piston pin receptacles 53 are advantageously located in the space between the control edges 29 and 30 of the piston pockets 14. The piston pocket 14 is in each case delimited by a rear wall 58 toward the crankcase interior 16. As FIG. 2 also shows, connecting ribs 38 which connect the rear wall 58 of the piston pockets 14 to the piston skirt 26 are provided in the interior of the piston skirt 26. The piston 5 has inlet-near delimiting edges 36 on the piston pockets 14, on those sides of the piston pockets 14 which face the recess 33 in the circumferential direction. The inlet-near delimiting edges 36 run approximately parallel to the longitudinal center axis 50. In addition, the piston pockets 14 have outlet-near delimiting edges 69. The outlet-near delimiting edges 69 also run approximately parallel to the longitudinal center axis 50. Each piston pocket 14 is delimited by the control edges 29 and 30 in the direction of the longitudinal center axis 50 and by the delimiting edges 36 and 69 in the circumferential direction.
(20) On the side facing the mixture inlet 12, the piston skirt 26 has a recess 33 on the side which faces the crankcase 4 and lies away from the combustion chamber 3. The height of the piston skirt 26 is reduced at the recess 33. The recess 33 is formed as a bulge of the edge 31 in the direction of the piston base 25. The position of the edge 31 at the recess 33 defines the control time at which the mixture inlet 12 (FIG. 1) is opened and closed. At the edge 31, a chamfer 37 is provided in the area of the recess 33 at the transition of the edge 31 to the outer side of the piston skirt 26.
(21) FIG. 3 shows the configuration of the chamfer 37 in detail. The recess 33 has a roof 35 on which the edge 31 runs approximately parallel to the piston base 25 (FIG. 2). This is also shown in FIG. 4. A transition region 34 is in each case adjacent to the roof 35 of the recess 33 on both sides in the circumferential direction. At the transition region 34, the edge 31 runs at an inclination with respect to the longitudinal center axis 50 of the piston 5. The inclined profile of the transition regions 34 is also shown in FIG. 4. The transition regions 34 connect the roof 35 to those areas of the edge 31 which lie outside the recess 33.
(22) As FIG. 4 shows, the piston 5 has a diameter d. The diameter d is advantageously the largest diameter of the piston 5 and, in the embodiment, is measured on a top side 39 of the piston base 25. The top side 39 of the piston base 25 here is that side of the piston base 25 which delimits the combustion chamber 3 in an engine, for example in the two-stroke engine 1. The top side 39 is that side of the piston base 25 which faces away from the piston pin receptacles 53 (FIG. 2). The piston 5 has a height h which is measured parallel to the longitudinal center axis 50 of the piston 5. The height h is the greatest height of the piston 5. The diameter d of the piston 5 is advantageously 70% to 140%, in particular 80% to 130%, preferably 90% to 120% of the height h. The diameter d is particularly preferably greater than the height h.
(23) The piston pin receptacles 53 (FIG. 2) have a center axis which forms a transverse axis 49 of the piston 5. The transverse axis 49 is also shown in FIG. 2. In the side view shown in FIG. 4, the transverse axis 49 runs perpendicularly to the longitudinal center axis 50. The piston 5 has a middle plane 51 which contains the longitudinal center axis 50 of the piston 5 and runs perpendicularly to the transverse axis 49. In the side view shown in FIG. 4, the longitudinal center axis 50 and the middle plane 51 coincide. The piston 5 has a section plane 52 running perpendicularly to the longitudinal center axis 50. A section plane 52 which coincides with the transverse axis 49 is shown by way of example in the side view shown in FIG. 4. The section plane 52 has a distance m from the top side 39 of the piston base 25. The upper control edge 29 of the piston pocket 14 has a smallest distance e from the top side 39. In the embodiment, the control edge 29 runs in a plane which runs perpendicularly to the longitudinal center axis 50. If the upper control edge 29 does not run at a uniform distance from the top side 39, the distance e is measured at that location of the control edge 29 which has the smallest distance from the top side 39. The distance m of the section plane 52 is advantageously greater than the smallest distance e of the control edge 29 from the top side 39. Accordingly, the section plane 52 lies in an engine on that side of the upper control edge 29 which faces the crankcase 4 (FIG. 1). In the embodiment, the section plane 52 intersects the two piston pockets 14.
(24) The piston 5 has a reduced height i at the recess 33. The reduced height i is the distance, if measured parallel to the longitudinal center axis 50, of the edge 31 on the roof 35 of the recess 33 from the top side 39 of the piston 5. The reduced height i at the recess 33 is advantageously 70% to 98%, in particular 80% to 95% of the height h of the piston 5. In the embodiment, the height i is greater than the distance m of the section plane 52 from the top side 39. However, it can also be provided that the distance m is greater than the reduced height I, that is, the section plane 52 runs through the recess 33. In the transition region 34, the height of the piston 5 is increased by at least 5%, in particular at least 10%. Accordingly, the height h of the piston 5 is at least 105%, in particular at least 110% of the reduced height i at the recess 33.
(25) The piston 5 has an inlet end 47 on which the recess 33 is arranged. As FIG. 1 shows, the piston 5 also has an outlet end 48 which controls the outlet 23. The inlet end 47 and the outlet end 48 are separated by a transverse plane 65 (shown in FIG. 1) of the piston 5, the transverse plane containing the longitudinal center axis 50 and the transverse axis 49 (FIG. 2). As FIG. 1 shows, during operation the crankshaft 8 rotates in a rotational direction 64. The crankshaft 7 is connected to the connecting rod 6 at a connecting rod eye 61. The rotational direction 64 is directed in such a manner that, during the downward stroke of the piston 5, the connecting rod eye 61 is arranged on the outlet end of the transverse plane 65, the outlet end facing the outlet 23, and during the upward stroke of the piston 5, is arranged on the inlet end of the transverse plane 65, the inlet end facing the mixture inlet 12 and the air inlet 11. The outlet end of the transverse plane 65 here is that side of the transverse plane 65 on which the outlet end 48 of the piston 5 is located, and the inlet end of the transverse plane 65 is that side of the transverse plane 65 on which the inlet end 47 of the piston 5 is located. During the downward stroke of the piston 5, the connecting rod eye 61 and the recess 33 (FIG. 2) are located on opposite sides of the transverse plane 65. The formation of the chamfer 37 on the inlet end 47 of the piston 5 prevents the edge 31 of the piston 5 from scraping off oil, which has accumulated in the cylinder bore 15, in the region of the recess 33.
(26) As FIG. 4 shows, the web 32 has a height k. The height k can be approximately 1 mm to approximately 5 mm, in particular approximately 1 mm to approximately 3 mm. The height of the web 32 does not have to be constant here, but rather can change along the circumference of the piston 5. The web 32 serves for sealing between the volume enclosed by the piston pocket 26 and cylinder bore 15 and the crankcase interior 16.
(27) As FIG. 5 shows, the piston pin receptacles 53 are formed on piston pin eyelets 28 which project into the space surrounded by the piston skirt 26. FIG. 5 shows a section along the section plane 52. As FIG. 5 shows, the middle plane 51 intersects the piston skirt 26 on the inlet end 47 at a location 44. The location 44 has the form of a line oriented radially with respect to the longitudinal center axis 50 of the piston 5 since it constitutes the section of the section plane 52 with the middle plane 51. The location 44 is also shown in FIG. 4. At the location 44, the piston skirt 26 has a wall thickness b. As FIG. 5 also shows, a thickened area 40 is arranged in each case on both sides of the location 44 between the location 44 and the delimiting edge 36 of the piston pockets 14 in the circumferential direction. In the thickened area 40, the piston skirt 26 has a greatest wall thickness a which is at least 1.1 times the wall thickness b at the location 44. The wall thickness a is preferably at least 1.15 times, in particular at least 1.2 times the wall thickness b. The wall thickness a in the thickened area 40 is not constant over the entire thickened area 40 but rather initially increases, as viewed in the circumferential direction, from the area arranged adjacent to the location 44, and then decreases again.
(28) As FIG. 5 also shows, the thickened area 40 extends over a circumferential angle about the longitudinal center axis 50, the circumferential angle advantageously being of 5 to 45, in particular of 10 to 35, preferably of 15 to 25. The circumferential angle is measured here between a first reference line 71 and a second reference line 72. In the section plane 52, the first reference line 71 connects the longitudinal center axis 50 to that location of the piston skirt 26 at which the wall thickness of the piston skirt 26 increases in relation to the wall thickness b at the location 44. In the section plane 52, the second reference line 72 connects the longitudinal center axis 50 to the inlet-near delimiting edge 36 of the piston pocket 14. At the inlet-near delimiting edge 36, the piston skirt 26 has, in the section plane 52, a wall thickness c which is lower than the greatest wall thickness a of the thickened area 40. The wall thickness c at the delimiting edge 36 is greater than the wall thickness b at the location 44. The wall thickness c at the delimiting edge 36 is advantageously 1.05 times, in particular at least 1.1 times the wall thickness b at the location 44.
(29) As FIG. 5 shows, the piston pockets 14 are arranged and formed mirror-symmetrically to each other with respect to the middle plane 51. As FIG. 5 also shows, the thickened areas 40 are arranged and formed mirror-symmetrically to each other with respect to the middle plane 51. The piston pockets 14 and the thickened areas 40 are advantageously arranged and formed mirror-symmetrically to one another with respect to the middle plane 51. At the thickened areas 40, the piston skirt 26 has an inner contour 46 which runs rectilinearly. However, it can also be provided that the inner contour 46 runs in a curved manner. The thickened area 40 is in each case formed by a thickening 45 on the inner side of the piston skirt 26.
(30) The thickened areas 40 advantageously extend over at least 50% of the height h of the piston 5 (FIG. 2). As FIG. 6 shows, the thickened areas 40 in the embodiment extend as far as the edge 31, wherein the inner contour of the piston 5 merges with a chamfer or a rounding into the edge 31. In the embodiment, the thickened areas 40 connect the piston base 25 to the edge 31 of the piston 5. The inner contour 46 of the thickened areas 40 can run parallel to the longitudinal center axis 50 or can be configured to be slightly inclined with respect to the longitudinal center axis 50, thus resulting in a slight pull-out bevel. The pull-out bevel permits the piston 5 to be demolded during production in a casting process. The pull-out bevel is advantageously 0.5 to 3.
(31) A section plane 52 (FIG. 4) which contains the transverse axis 49 is shown in the embodiment. The thickened area 40 is advantageously provided in a corresponding manner in a section plane which runs perpendicularly to the longitudinal center axis 50 at the control edge 29 and/or in a section plane which runs perpendicularly to the longitudinal center axis 50 at a lower edge 66 (shown in FIG. 7) of the piston pin receptacles 53. The lower edge 66 of the piston pin receptacles 53 is in this case that edge of the piston pin receptacles 53 which lies away from the top side 39 (FIG. 4) of the piston base 25. The thickened area 40 preferably runs at least from a section plane containing the control edge 29 and running perpendicularly to the longitudinal center axis 50 as far as the edge 31 at the recess 33.
(32) As FIG. 6 shows, ribs 42 and 43 are provided on the inner side of the piston skirt 26. The ribs 42 and 43 connect the piston skirt 26 to the piston base 25. In the embodiment, a rib 43 is arranged on the inlet end 47 and a rib 43 is arranged on the outlet end 48. The ribs 43 advantageously run mirror-symmetrically to each other with respect to the transverse plane 65 (FIG. 5). The ribs 43 are intersected by the middle plane 51 and are formed mirror-symmetrically to the middle plane 51. On both sides of the ribs 43, ribs 42 are provided in each case on the inlet end 47 and on the outlet end 48. The ribs 42 and 43 are in each case formed individually and are connected to each other exclusively via the piston skirt 26 and the piston base 25, but not directly. As FIG. 5 shows, the ribs 42 and 43 end above the section plane 52 and do not project into the section plane 52.
(33) As FIG. 6 shows, the chamfer 37 on the inlet end 47 extends over a circumferential angle along the longitudinal center axis 50, the circumferential angle being less than 180, in particular less than 150, preferably less than 120, in particular less than 90. In the embodiment, an angle of less than 60 is provided. As FIG. 7 shows, a chamfer 59 at the edge 31 of the piston skirt 26 is also arranged on the outlet end 48. As shown schematically in FIG. 6, the chamfer 59 extends over a circumferential angle which is likewise less than 180, in particular less than 150, preferably less than 120, advantageously less than 100. The circumferential angle is advantageously greater than the circumferential angle . In the embodiment, a circumferential angle of approximately 80 to 100 is provided. The angles and are advantageously selected in such a manner that the chamfers 37 and 59 predominantly run in the area arranged in the circumferential direction between the piston pockets 14. During operation in a two-stroke engine 1 (FIG. 1), the piston 5 is placed against the inlet end 47 or against the outlet end 48 at the cylinder bore 15 because of the forces exerted via the connecting rod 6. In the process, the piston 5 tilts slightly about the transverse axis 49. The chamfers 37 and 59 advantageously extend in the circumferential regions of the piston 5, which circumferential regions are placed against the cylinder bore 15 of the two-stroke engine 1 during operation.
(34) As FIGS. 6 and 7 show, connecting ribs 38 run in each case between a piston pin eyelet 28 and the piston skirt 26. The connecting ribs 38 extend approximately parallel to the middle plane 51.
(35) As FIG. 7 shows, the ribs 42 and 43 each have at least one front end 67 projecting into the interior of the piston 5. The front ends 67 advantageously run along the ribs 42 and 43 in a curved manner, namely curved concavely. A stop surface 54 formed on the piston base 26 is also shown in FIG. 6 and FIG. 7. During the production of the piston 5, the stop surface 54 serves as a stop for fixing the piston 5 during the external machining of the piston skirt 26.
(36) FIG. 8 shows a section through the deepenings 27. The deepenings 27 extend, as FIG. 8 shows, into the piston pin eyelets 28, and therefore no accumulation of material is formed in the piston pin eyelets 28 between the piston pin receptacle 53 and the piston base 25 (FIG. 7). The deepenings 27 serve to reduce the weight of the piston 5.
(37) FIG. 8 shows the configuration of the ribs 42 and 43 in detail. As FIG. 8 shows, mutually opposite ribs 42 and 43 which are formed mirror-symmetrically with respect to the transverse plane 65 are each at a distance from one another. The stop surface 54 lies between the ribs 42 and 43 on the inlet end 47 and the ribs 42 and the rib 43 on the outlet end 48 (FIG. 7). Opposite ribs 42 have a distance p from each other. The distance p is advantageously more than 10% of the diameter d of the piston 5 (FIG. 4). The mutually opposite ribs 43 have a distance r from each other, the distance advantageously being smaller than the distance p. In the section plane shown in FIG. 8, the ribs 42 on the piston skirt 26 have a thickness n. The thickness n is the thickness of the ribs 42. The ribs 43 have a thickness o which is greater than the thickness n. The thickness o is the thickness of the ribs 43. The thickness o is advantageously 1.1 times to 1.8 times the thickness n. As FIG. 8 also shows, the ribs 42 and 43 lie at a small distance from each other and at a distance from the piston pin eyelets 28. As FIG. 8 shows, the connecting ribs 42 are arranged on the thickened areas 40 and additionally reinforce the piston skirt 26 at the thickened areas 40.
(38) The ribs 42 and 43 which are arranged on the inlet end 47 are shown in FIG. 9. As FIG. 9 shows, the ribs 42 each have a tip 62 which is arranged on those sides of the ribs 42 which face away from the top side 39. The tip 62 has a distance f from the top side 39. The distance f is advantageously 30% to 70% of the height h of the piston 5. The rib 43 has a tip 63 which lies facing away from the top side 39 and which has a distance g from the top side 39. The distance g is significantly greater than the distance f and is advantageously 1.1 times to 1.5 times the distance f. The distance g is advantageously 50% to 80% of the height h of the piston 5.
(39) FIG. 9 also shows the connecting rib 38. A deepening 56 is formed between the connecting rib 38 and the piston skirt 26. The connecting rib 38 runs in an extension of the rear wall 58 on the piston pocket 14. The deepening 56 is delimited by the connecting rib 38 and the web 32 and also by the rear wall 58 of the piston pocket 14 and the piston pin eyelet 28.
(40) FIG. 10 shows the outlet end 48 of the piston 5. Ribs 42 and 43 are arranged on the outlet end 48, the ribs being formed mirror-symmetrically with respect to the transverse plane 65 to the ribs 42 and 43 on the inlet end 47. The rib 43 has a tip 63 which lies at a distance g from the top side 39 of the piston 5. The ribs 42 arranged on both sides with respect to the rib 43 each have a tip 62 which is arranged at a distance f from the top side 39 of the piston 5.
(41) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.
