EP3284938B1 - Piston for a two-stroke engine working with direct injection and two-stroke engine - Google Patents

Piston for a two-stroke engine working with direct injection and two-stroke engine Download PDF

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Publication number
EP3284938B1
EP3284938B1 EP16001824.8A EP16001824A EP3284938B1 EP 3284938 B1 EP3284938 B1 EP 3284938B1 EP 16001824 A EP16001824 A EP 16001824A EP 3284938 B1 EP3284938 B1 EP 3284938B1
Authority
EP
European Patent Office
Prior art keywords
piston
connecting rib
pocket
stroke engine
skirt
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Active
Application number
EP16001824.8A
Other languages
German (de)
French (fr)
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EP3284938A1 (en
Inventor
Birger Loew
Jonas Lank
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Andreas Stihl AG and Co KG
Original Assignee
Andreas Stihl AG and Co KG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Andreas Stihl AG and Co KG filed Critical Andreas Stihl AG and Co KG
Priority to EP16001824.8A priority Critical patent/EP3284938B1/en
Priority to CN201710712798.6A priority patent/CN107762656B/en
Priority to US15/682,343 priority patent/US10344707B2/en
Publication of EP3284938A1 publication Critical patent/EP3284938A1/en
Application granted granted Critical
Publication of EP3284938B1 publication Critical patent/EP3284938B1/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/24—Pistons  having means for guiding gases in cylinders, e.g. for guiding scavenging charge in two-stroke engines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/0084—Pistons  the pistons being constructed from specific materials
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B75/00—Other engines
    • F02B75/02—Engines characterised by their cycles, e.g. six-stroke
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 
    • F02F3/0076—Pistons  the inside of the pistons being provided with ribs or fins
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B75/00—Other engines
    • F02B75/02—Engines characterised by their cycles, e.g. six-stroke
    • F02B2075/022—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle
    • F02B2075/025—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle two

Definitions

  • the invention relates to a piston for a two-stroke engine of the type specified in the preamble of claim 1 and a two-stroke engine that works with a flushing reservoir.
  • a piston for a two-stroke engine working with a scavenging reservoir which has piston pockets which serve to connect an air inlet opening at the cylinder bore with overflow windows of overflow ducts. Air from the air inlet is stored in the overflow ducts via the piston pockets. A plurality of depressions is provided on the piston skirt of the piston.
  • the JP S55 170 440 U and the DE 195 38 407 A1 show pistons for two-stroke engines.
  • the invention is based on the object of creating a piston for a two-stroke engine which works with a flushing device and which has a high level of stability. Another object of the invention is to provide a two-stroke engine with a piston.
  • the piston has piston pin bosses in which piston pin receptacles are formed. It is provided that at least one piston pin boss is connected to the piston skirt via at least one connecting rib.
  • the connecting rib runs on the side of the piston pocket facing away from the piston head.
  • the connecting rib leads to an improved support of the piston pin eye. Forces from the piston pin boss can be better transferred to the piston skirt via the connecting rib. This results in greater stability.
  • the introduction of force from the piston pin boss into the piston skirt is improved.
  • the connecting rib causes a stiffening and an increase in strength of the piston. Heat is also dissipated from the piston pin boss into the piston skirt via the connecting rib. As a result, improved cooling of the area of the piston pin boss, which is particularly thermally stressed, is achieved.
  • a recess is formed between the connecting rib and the piston skirt.
  • the recess avoids accumulations of material in this area, so that the piston can be manufactured more easily, in particular in a casting process. Casting errors can be avoided by the recess.
  • a weight reduction is achieved.
  • the depth of the recess is advantageously at least 3%, in particular at least 5% of the height of the piston.
  • the recess achieves good cooling of the connecting rib on both sides by the mixture flowing in the crankcase interior or by combustion air flowing in the crankcase interior.
  • the depth of the recess is advantageously less than 20% of the height of the piston. This leaves sufficient space for the piston pocket without increasing the overall height of the piston.
  • a sufficiently large piston pocket ensures that a sufficient amount of scavenging air is stored in the transfer ducts so that low exhaust gas values can be achieved for a two-stroke engine operating with the piston.
  • the connecting rib advantageously runs approximately parallel to the center plane of the piston.
  • the distance between the connecting rib and the central plane, measured perpendicular to the central plane, is advantageously at least 20% of the diameter of the piston.
  • the piston pin bosses have facing faces.
  • the connecting rib advantageously has a distance from the end face of the assigned piston pin eye, measured parallel to the transverse axis, which has at least 5%, in particular at least 10% of the diameter of the piston.
  • the connecting rib is accordingly, in the state installed in the two-stroke engine, offset radially outward relative to the end face of the piston pin boss facing a connecting rod of the two-stroke engine, based on a cylinder longitudinal axis.
  • the piston pin boss assigned to a connecting rib is the piston pin boss that connects this connecting rib to the piston skirt.
  • the piston pocket advantageously has a rear wall.
  • the rear wall of the piston pocket is the wall that separates the piston pocket from the interior of the piston enclosed by the piston skirt.
  • the connecting rib is advantageously arranged as an extension of the rear wall of the piston pocket. By arranging the connecting rib as an extension of the rear wall of the piston pocket, the connecting rib causes the rear wall of the piston pocket to be stiffened.
  • the connecting rib preferably adjoins the rear wall of the piston pocket.
  • the recess is advantageously delimited by the piston pin boss, the piston skirt, the connecting rib and the rear wall of the piston pocket.
  • the piston skirt advantageously has an edge facing away from the piston crown.
  • the connecting rib has an end face facing away from the piston head.
  • the end face of the connecting rib advantageously does not protrude as far as the bottom of the piston, but is offset in the direction of the piston head with respect to the edge of the piston, which forms the bottom of the piston.
  • the offset between the end face of the connecting rib and the edge in the direction of the longitudinal center axis of the piston is advantageously less than 5% of the height of the piston at each point on the end face. It can also be provided that the end face of the connecting rib extends up to the level of the edge. However, an offset of at least 0.5 mm between the end face is advantageous given the connecting rib and the edge in the direction of the longitudinal center axis of the piston.
  • a web of the piston skirt advantageously runs between the edge and the piston pocket.
  • the web In the circumferential area of the piston in which the recess is arranged, the web has a height which is at least 1.5 times the smallest height of the web. In the area of the recess, the web is accordingly made higher than in other areas of the piston pocket. As a result, good guidance of the piston in the area of the recess is achieved, and at the same time sufficient installation space is available for the recess.
  • the piston advantageously rests against the cylinder bore with at least one section of the web over at least a partial section of the piston stroke.
  • the piston pin receptacle is preferably arranged at least partially, in particular completely, in the piston pocket.
  • a low overall height of the piston and thus a low overall height of the cylinder of a two-stroke engine can be achieved.
  • the piston pin seat is at a comparatively large distance from the piston crown. The heat input into the piston pin and thus into the piston pin bearing with which the connecting rod is mounted on the piston pin can be reduced during operation by a comparatively large distance between the piston pin seat and the piston crown.
  • the piston preferably has two piston pockets on opposite sides of the center plane, a connecting rib being arranged on each of the two piston pin bosses.
  • the piston pockets and the connecting ribs are preferably arranged symmetrically to the center plane.
  • an asymmetrical design can also be advantageous.
  • the piston is advantageously made of light metal, in particular aluminum or magnesium. This results in a lower weight of the piston.
  • a two-stroke engine with a piston made of light metal, in particular made of magnesium can have an engine with a larger displacement and thus with greater power than, for example, a two-stroke engine with a piston that is not made of light metal, in particular not made of magnesium.
  • the connecting rib has advantages with regard to the stability of the piston, since light metal, in particular magnesium, itself has a lower strength.
  • the connecting rib is advantageously arranged on an outlet side of the piston between the piston pin boss and the piston skirt.
  • at least one connecting rib is alternatively or additionally provided on an inlet side of the piston, which connects the piston pin boss to the piston skirt.
  • a connecting rib on the inlet side is advantageously arranged and designed with mirror symmetry to a connecting rib on the outlet side with respect to a transverse plane of the piston.
  • a two-stroke engine with a piston advantageously has a cylinder in the cylinder bore of which a combustion chamber is formed.
  • the combustion chamber is limited by the piston.
  • the piston drives a crankshaft rotatably mounted in a crankcase.
  • the two-stroke engine has at least one overflow duct which, in at least one position of the piston, connects a crankcase interior of the crankcase with the combustion chamber.
  • the two-stroke engine has an air duct for the supply of scavenging air, which opens with an air inlet on the cylinder bore. In at least one position of the piston, the piston pocket is at least partially in overlap with the air inlet and an overflow window of an overflow channel.
  • flushing air can be supplied via the piston pocket from the air duct via the air inlet into the overflow window of the overflow duct and thus stored upstream in the overflow duct.
  • the purge air can be fuel-free or low-fuel combustion air. This results in low emissions.
  • Fig. 1 shows schematically an embodiment of a two-stroke engine 1.
  • the two-stroke engine 1 is designed as a single-cylinder engine and has a cylinder 2 in which a combustion chamber 3 is formed.
  • the cylinder 2 has a cylinder longitudinal axis 48.
  • the combustion chamber 3 is delimited by a piston 5, which is mounted to and fro in a cylinder bore 15 of the cylinder 2 in the direction of the cylinder longitudinal axis 48, in the direction of which the piston 5 moves during operation.
  • the piston 5 is shown in its bottom dead center.
  • the piston 5 drives a crankshaft 7 via a connecting rod 6.
  • the crankshaft 7 is mounted rotatably about an axis of rotation 8 in a crankcase interior 16 of a crankcase 4.
  • the crankshaft 7 rotates in one direction of rotation 69 during operation.
  • the two-stroke engine 1 can be, for example, the drive motor in a hand-held tool such as a power saw, a power cutter, a blower or the like.
  • the crankshaft 7 is advantageously used to drive a tool of the implement.
  • the piston 5 has two piston pockets 14, of which in Fig. 1 one is shown.
  • the piston pockets 14 are symmetrical to the cutting plane in FIG Fig. 1 arranged on the piston 5.
  • the two-stroke engine 1 has an air duct 9 which is connected to an air filter 22. Fuel-free or low-fuel scavenging air is supplied via the air duct 9. In the air inlet 9, an air flap 21 is arranged to control the amount of flushing original air supplied via the air duct 9.
  • the air duct 9 opens with an air inlet 11 at the cylinder bore 15.
  • a mixture duct 10 is provided for supplying the fuel / air mixture.
  • the mixture duct 10 is connected to the air filter 22 via a carburetor 18.
  • a throttle valve 19 and a choke valve 20 are pivotably mounted in the carburetor 18. The throttle valve 19 and the choke valve 20 are used to adjust the amount of combustion air and fuel supplied via the mixture duct 10.
  • the fuel can also be supplied in another way, for example via an injection valve or a carburetor with an electromagnetic 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.
  • the two-stroke engine 1 has transfer ducts 13 which open into the combustion chamber 3 with transfer windows 17.
  • the overflow windows 17 are also controlled by the piston 5.
  • the overflow ducts 13, not shown connect the crankcase interior 16 to the combustion chamber 3.
  • the upward stroke of the piston 5 denotes the movement of the piston 5 from the position shown in FIG Fig. 1
  • the piston pockets 14 each connect an air inlet 11 with overflow windows 17. As a result, flushing air is sucked from the air channel 9 into the overflow channels 13.
  • the mixture already present in the combustion chamber 3 is simultaneously compressed and ignited in the area of the top dead center of the piston 5 by a spark plug (not shown).
  • the design of the piston pockets 14 has a decisive influence on the amount of flushing air stored upstream in the overflow channels 13.
  • the piston pockets 14 have an upper control edge 29 which is advantageously arranged in the region of the top dead center of the piston 5 such that the overflow windows 17 are arranged completely in overlap with the piston pocket 14.
  • the upper control edge 29 is the control edge of the piston pocket 14 closest to the combustion chamber 3.
  • the piston pocket 14 also has a lower control edge 30 which faces the crankcase 4.
  • the lower control edge 30 is the control edge of the piston pocket 14 furthest away from the combustion chamber 3 and delimits the piston pocket 14 in the direction of the crankcase 4.
  • the lower control edge 30 is advantageously arranged so that the air inlet 11 is completely in Coverage with the piston pocket 14 is.
  • the piston pockets 14 also have delimiting edges 53 close to the inlet and delimiting edges 54 close to the outlet.
  • the delimiting edges 53 and 54 run approximately parallel to the cylinder longitudinal axis 48 ( Fig. 1 ).
  • Each piston pocket 14 is thus limited in the direction of the cylinder longitudinal axis 48 by the control edges 29 and 30 and in the circumferential direction by the delimiting edges 53 and 54.
  • the piston 5 has an edge 31 on its side facing the crankcase 4, which forms the boundary of the piston 5 facing the crankcase 4. Between the piston pockets 14 and the edge 31, a web 32 is formed in each case, which is formed by a section of a piston skirt 26.
  • the piston 5 has a piston head 25 which runs approximately perpendicular to the cylinder longitudinal axis 48 and delimits the combustion chamber 3.
  • the piston 5 has the piston skirt 26, which advantageously follows the course of the cylinder bore 15.
  • the outside of the piston skirt 26 is advantageously approximately cylindrical.
  • the outside of the piston skirt 26 can be exactly cylindrical or deviating from the circular shape Own cross-section.
  • the piston skirt can in particular have an elliptical, oval or cloverleaf shape.
  • a cloverleaf-shaped cross-section is a cross-section in which the diameter is reduced in two directions at an angle to one another. The deviation of the cross section from the circular shape is advantageously very small.
  • Adjacent to the piston head 25, two piston ring grooves 24 are provided on the piston skirt 26, which are used to receive piston rings.
  • a bore 34 is shown which serves to receive a locking pin for a piston ring.
  • a corresponding, in Fig. 2 The bore, which is not visible, is also provided in the other piston ring groove 24.
  • a recess 27 on the piston skirt 26 is provided between each piston pocket 14 and the piston ring grooves 24.
  • the recess 27 serves to reduce the weight of the piston 5.
  • the recess 27 is designed in such a way that it overlaps only one or both overflow windows 17 during a piston stroke, but not the air inlet 11.
  • the piston skirt 26 On the side facing the mixture inlet 12, the piston skirt 26 has a recess 33 on the side facing the crankcase 4 and remote from the combustion chamber 3.
  • the height of the piston skirt 26 is reduced at the recess 33.
  • the recess 33 is designed as a bulge of the edge 31 in the direction of the piston head 25.
  • the position of the edge 31 on the recess 33 defines the control time at which the mixture inlet 12 is opened and closed.
  • a bevel 37 is provided at the transition from the edge 31 to the outside of the piston skirt 26.
  • the connecting rod 6 ( Fig. 1 ) is connected to the piston 5 via a piston pin, not shown.
  • the piston pin is held in piston pin receptacles 35 on piston 5.
  • the piston pin receptacles 35 are arranged completely in the piston pockets 14.
  • the piston pin receptacles 35 are advantageously located in the space between the control edges 29 and 30 of the piston pockets 14.
  • the piston pocket 14 is delimited by a rear wall 58 towards the crankcase interior.
  • the piston 5 has a diameter a.
  • the diameter a is advantageously the largest diameter of the piston 5 and is measured on an upper side 40 of the piston head 25 in the exemplary embodiment.
  • the top 40 of the piston head 25 is the side of the piston head 25 that delimits the combustion chamber 3.
  • the piston 5 has a height h which is measured parallel to a longitudinal center axis 50 of the piston 5.
  • the height h is the greatest height of the piston 5.
  • the longitudinal center axis 50 of the piston 5 is the center axis of the piston skirt 26.
  • the longitudinal center axis 50 of the piston 5 coincides approximately with the cylinder longitudinal axis 48 when the piston 5 is arranged in the cylinder 2.
  • the piston pin sockets 35 ( Fig.
  • the piston 2 have a central axis which forms a transverse axis 49 of the piston 5.
  • the transverse axis 49 runs perpendicular to the longitudinal center axis 50.
  • the piston 5 has a center plane 51 which contains the longitudinal center axis 50 of the piston 5 and which runs perpendicular to the transverse axis 49.
  • the longitudinal center axis 50 and the center plane 51 coincide.
  • the piston 5 has a reduced height i.
  • the reduced height i is the distance, measured parallel to the longitudinal center axis 50, of the edge 31 on the recess 33 to the top 40 of the piston 5.
  • the reduced height i on the recess 33 is advantageously 70% to 98%, in particular 80% to 95% of the height h of the piston 5.
  • the diameter a is advantageously 70% to 140% of the height h, in particular 80% to 130%, preferably 90% to 120% of the height h.
  • the diameter a is particularly preferably greater than the height h.
  • the piston 5 has an inlet side 46 on which the recess 33 is arranged.
  • Fig. 3 shows a side view of the inlet side 46.
  • the web 32 between the piston pocket 14 and the edge 31 has a minimum height k on the inlet side 46.
  • the minimum height k is measured on the circumferential area of the piston pocket 14 facing the recess 33.
  • the minimum 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, but can vary along the circumference of piston 5 change.
  • the web 32 serves to seal between the volume enclosed by the piston pocket 26 and cylinder bore 15 and the crankcase interior 16.
  • Fig. 4 shows the interior of the piston 5.
  • the piston pin receptacles 35 are formed on piston pin bosses 28, which in the exemplary embodiment extend to the piston crown 25.
  • the piston pin bosses 28 have mutually facing front sides 57.
  • the front sides 57 run approximately parallel to the center plane 51.
  • the front sides 57 of the two piston pin bosses run approximately mirror-symmetrically with respect to the center plane 51.
  • small extension bevels are advantageously provided so that the piston 5 can be removed from the mold during manufacture in a casting process.
  • the extension bevels on the surfaces running approximately parallel to the center plane 51 can be, for example, from 0.5 ° to 3 °.
  • the end faces 57 of the piston pin bosses 28 are the areas of the piston pin bosses 28 which are closest to the center plane 51.
  • the piston pin receptacles 35 end at the end faces 57.
  • the end faces 57 each have a distance z from the central plane 51, which is perpendicular to the central plane 51 and parallel to the transverse axis 49 ( Fig. 3 ) is measured.
  • the distance z is advantageously at least 5%, in particular at least 10% of the diameter a of the piston 5 ( Fig. 3 ).
  • the piston pin bosses 28 are advantageously arranged symmetrically to the center plane 51, so that the same distance z results for both end faces 57.
  • the end faces 57 On the side facing away from the combustion chamber 3, the end faces 57 have an indentation 36 which extends as far as the piston pin receptacle 35 and at which the distance from the center plane 51 is increased.
  • the indentation 36 is used to lubricate a piston pin bearing with which the piston pin on the connecting rod 6 ( Fig. 1 ) is stored.
  • the end faces 57 of the piston pin bosses 28 each have a distance e from the connecting ribs 55, which is perpendicular to the center plane 51 and parallel to transverse axis 49 ( Fig. 3 ) is measured.
  • the distance e is advantageously at least 5%, in particular at least 10% of the diameter a of the piston 5 ( Fig. 3 ).
  • the piston pin bosses 28 and the connecting ribs 55 are advantageously arranged symmetrically to the central plane 51, so that the same distance e between an end face 57 and the connecting rib 55 arranged on the same side of the central plane 51 results on both sides of the central plane 51.
  • the piston 5 has the inlet side 46, which is shown in FIG Fig. 4 is arranged at the top and on which the recess 33 is provided on the piston skirt 26, as well as an outlet side 47.
  • the piston 5 is divided by a transverse plane 52 into the inlet side 46 and the outlet side 47, which are divided into Fig. 5 is shown schematically.
  • the transverse plane 52 is spanned by the longitudinal center axis 50 of the piston 5 and the transverse axis 49.
  • the piston pin bosses 28 are connected to the piston skirt 26 via connecting ribs 55.
  • the connecting ribs 55 extend on the side of the piston pin bosses 28 that faces away from the recess 33.
  • the connecting ribs 55 are arranged on the side of the cylinder 2 facing away from the mixture inlet 12 and facing the outlet 23 ( Fig. 1 ).
  • the connecting ribs 55 are arranged on the outlet side 47 of the piston 5.
  • a bevel 39 is also formed on the side of the edge 31 of the piston skirt 26 facing the outlet 23.
  • a recess 56 is formed between the connecting ribs 55 and the piston skirt 26.
  • Each recess 56 extends on the side of the connecting rib 55 facing away from the central plane 51 between the connecting rib 55 and the piston skirt 26.
  • the distance between the recess 56 and the central plane 51 is greater than the distance between the connecting rib 55 delimiting the recess 56 and the central plane 51.
  • the connecting ribs 55 have a distance d from the central plane 51. The distance d can vary in different areas of the connecting rib 55, for example when the width of the connecting rib 55 is not constant.
  • a greater width of the connecting rib 55 is preferably provided in the connection area to the piston pin boss 28 and in the connection area to the piston skirt 26.
  • the distance d is advantageously measured in a central region of the connecting rib 55.
  • the distance d is advantageously at least 20%, in particular at least 25% of the diameter a of the piston 5.
  • the distance d is particularly preferably at least 20%, in particular at least 25% of the diameter a of the piston 5 at each point of the connecting rib 55 Fig. 4 shows, both connecting ribs 55 advantageously run mirror-symmetrically to one another in relation to the central plane 51.
  • the connecting ribs 55 preferably run parallel to the center plane 51.
  • ribs 42 and 43 run between the piston crown 25 and piston skirt 26 both on the inlet side 46 and on the outlet side 47.
  • the ribs 42, 43 connect the piston skirt 26 and piston crown 25 and lie over their entire length directly on the piston skirt 26 or on the piston crown 25 at.
  • a central rib 43 is provided both on the inlet side 46 and on the outlet side 47, which rib runs along the central plane 51 and is intersected centrally by the central plane 51.
  • Lateral ribs 42 are provided on both sides of the central rib 43.
  • exactly one lateral rib 42 is arranged on each side of the central rib 43.
  • a stop surface 38 is formed in the area between the piston pin bosses 28 on the piston head 25. The stop surface 38 is used for the defined positioning of the piston 5 when the piston skirt 26 is machined.
  • the ribs 42 and 43 each connect the piston skirt 26 to the piston crown 25.
  • the ribs 42 and 43 on the inlet side 46 are advantageously arranged symmetrically to the ribs 42 and 43 on the outlet side 47 with respect to the transverse plane 52.
  • the end faces 41 of the ribs 42 and 43 protruding into the interior of the piston 5 are advantageously arcuate, namely concave.
  • the ribs 42 and 43 are not directly connected to one another.
  • the ribs 42 and 43 are also at a distance from the piston pin bosses 28. Between the ribs 42 and 43 and the piston pin bosses 28 therefore have no direct connection.
  • the ribs 42 and 43 are formed separately from the piston pin bosses 28.
  • the connecting rib 55 is not directly connected to the ribs 42 and 43 either. How Fig. 5 shows, the connecting ribs 55 are in extension of the rear wall 58 of the piston pocket 14. How Fig. 5 also shows, the piston pin bosses 28 each have two side surfaces 60 which run approximately parallel to the transverse plane 52 of the piston 5 with a slight extension slope. The piston 5 can be clamped on the side surfaces 60 for machining the piston skirt 26.
  • the connecting ribs 55 have an end face 59 of the connecting rib 55 facing away from the upper side 40 of the piston 5.
  • the end faces 59 are also shown in FIG Fig. 4 shown.
  • the end face 59 of the connecting rib 55 faces the crankcase 4 in the installed state.
  • the recess 56 has a maximum depth c, which is measured parallel to the longitudinal center axis 50 as far as the end face 59 of the connecting rib 55.
  • the maximum depth c is advantageously at least 3%, in particular at least 5% of the height h of the piston 5.
  • the maximum depth c is advantageously less than 20%, in particular less than 10% of the height h of the piston 5.
  • the Depth of recess 56 at each point of recess 56 is at least 3%, in particular at least 5% of the height h of piston 5.
  • the depth of recess 56 at each point of recess 56 is less than 20%, in particular less than 10 % of the height h of the piston 5.
  • the end face 59 has an offset b measured parallel to the longitudinal center axis 50 with respect to the edge 31.
  • the offset b is advantageously less than 5%, in particular less than 3% of the height h of the piston 5.
  • the offset b can also be zero.
  • An offset b of more than 1% of the height h of the piston 5 is particularly advantageous.
  • the end face 59 is advantageously arranged closer to the upper side 40 of the piston 5 than the edge 31 in the region of the recess 56.
  • the maximum depth c is advantageously significantly greater than the offset b.
  • the maximum depth c is advantageously at least twice the offset b.
  • the web 32 has a height m measured parallel to the longitudinal center axis 50, which larger than the in Fig. 3 The smallest height k of the web 32 is shown.
  • the height m is advantageously at least 1.5 times the height k.
  • the recess 56 has a bottom 61, which is the region of the recess 56 which is at the smallest distance from the top 40 of the piston 5.
  • the base 61 of the recess 56 has a distance f from the base 40 of the piston 5, measured parallel to the longitudinal center axis 50, which is advantageously more than 50%, in particular more than 60% of the height h of the piston 5.
  • the distance f is advantageously less than 90% of the height h of the piston 5.
  • the rear wall 58 of the piston pocket 14 has a wall thickness y between the piston pocket 14 and the interior of the piston 5 located between the rear walls 58 of the piston pockets 14.
  • the rear wall 58 has a reduced wall thickness x.
  • the reduced wall thickness x is advantageously at most 80%, in particular at most 60% of the wall thickness y.
  • the wall thickness x must not be less than a minimum for sufficient stability of the rear wall 58. This minimum dimension, which depends on the material and the geometry of the piston 5, determines the maximum possible depth c of the recess 56.
  • the middle rib 43 has an end 45 facing away from the top 40 of the piston 5.
  • the end 45 is at a distance g from the top 40.
  • the distance g is advantageously about 30% to about 60% of the height h of the piston 5.
  • the distance g is advantageously smaller than the distance f from the bottom 61 of the recess 56 to the top 40 of the piston 5.
  • the distance g is advantageously less than 90 %, in particular less than 80% of the distance f.
  • the connecting ribs 55 arranged on the opposite sides of the central plane 51 have a spacing n from one another, which is measured perpendicular to the central plane 51.
  • the distance n is advantageously at least 40%, in particular at least 50% of the diameter a of the piston 5.
  • the end faces 57 of the piston pin bosses 28 are at a distance s from one another.
  • the distance s is advantageously at least 10%, in particular at least 20% of the diameter a of the piston 5.
  • the distance s is significantly smaller than the distance n of the connecting ribs 55.
  • the distance s is advantageously less than 70% of the distance n are offset radially outward with respect to the end faces 57.
  • the piston pin bosses 28 have a width w measured from the end faces 57 to the piston skirt 26 and perpendicular to the central plane 51, which is advantageously at least 15%, in particular at least 20% of the diameter a of the piston.
  • the end 45 of the central rib 43 in the side view shown has a distance u to the transverse axis 49, measured parallel to the longitudinal center axis 50.
  • the end 45 is further away from the upper side 40 than the transverse axis 49.
  • the end 45 is arranged closer to the upper side 40 than the transverse axis 49.
  • the distance u is advantageously less than 10% of the height h of the piston 5.
  • the lateral ribs 42 have an end 44 facing away from the upper side 40, which has a distance o from the upper side 40 measured parallel to the longitudinal center axis 50.
  • the distance o is smaller than the distance g between the end 45 of the central rib 43 and the top 40 of the piston 5 ( Fig. 6 ).
  • the end 44 has a distance v from the transverse axis 49, which is significantly greater than the distance u from the end 45 to the transverse axis 49.
  • the distance v is advantageously 5% to 20% of the height h of the piston 5.
  • the upper control edge 29 of the piston pockets 14 has a distance t from the upper side 40 which is advantageously 30% to 60% of the height h of the piston 5.
  • the end 44 is approximately level with the control edge 29.
  • the recess 56 has a width r measured parallel to the transverse axis 49, which is advantageously less than 10% of the diameter a of the piston 5.
  • the bottom 61 has a parallel to the edge 31 in the region delimiting the recess 56 Longitudinal central axis 50 measured distance p.
  • the distance p is greater than the height m of the web 32 in this area.
  • the height m of the web 32 is advantageously 70% to 95% of the distance p.
  • the width r of the recess 56 can approximately correspond to the maximum depth c of the recess 56.
  • the width r is preferably 60% to 120% of the maximum depth c of the recess 56 ( Fig. 6 ).
  • Fig. 8 shows a schematic illustration of an exemplary embodiment for a piston 5.
  • the same reference symbols denote elements that correspond to one another in all figures.
  • the in Fig. 8 The piston 5 shown has two connecting ribs 55 on the inlet side 46, each of which runs between a piston pin boss 28 and the piston skirt 26 and which delimit a recess 56.
  • the connecting ribs 55 and the depressions 56 are designed as described for the previous embodiment.
  • Connecting ribs 55 ′ are provided on outlet side 47, each connecting a piston pin boss 28 to piston skirt 26.
  • the connecting ribs 55 ′ are designed corresponding to the connecting ribs 55.
  • Between the connecting ribs 55 'and the piston skirt 26, a recess 56' is arranged in each case on the side facing away from the central plane 51.
  • the depressions 56 ′ are designed corresponding to the depressions 56.
  • the connecting ribs 55 and the connecting ribs 55 ' are advantageously arranged and designed mirror-symmetrically with respect to the transverse plane 52.
  • the depressions 56 ′ can also be configured mirror-symmetrically to the depressions 56.
  • the depressions 56 ′ differ in depth and / or shape from the depressions 56. This can result in particular from a shape of the piston pockets 14 which is asymmetrical to the transverse plane 52.
  • the connecting ribs 55 'and the recesses 56' can as in FIG Fig. 8 shown in addition to the connecting ribs 55 and the recesses 56 may be provided.
  • connecting ribs 55 'and depressions 56' are arranged only on the outlet side 47 of the piston 5 and that no connecting ribs 55 and depressions 56 are arranged on the inlet side 46.
  • the piston 5, 5 ' consists of light metal, in particular magnesium.
  • a design made of aluminum can also be advantageous.

Description

Die Erfindung betrifft einen Kolben für einen mit Spülvorlage arbeitenden Zweitaktmotor der im Oberbegriff des Anspruchs 1 angegebenen Gattung sowie einen Zweitaktmotor.The invention relates to a piston for a two-stroke engine of the type specified in the preamble of claim 1 and a two-stroke engine that works with a flushing reservoir.

Aus der DE 10 2010 008 260 A1 ist ein Kolben für einen mit Spülvorlage arbeitenden Zweitaktmotor bekannt, der Kolbentaschen besitzt, die zur Verbindung eines an der Zylinderbohrung mündenden Lufteinlasses mit Überströmfenstem von Überströmkanälen dienen. Über die Kolbentaschen wird Luft aus dem Lufteinlass in den Überströmkanälen vorgelagert. Am Kolbenhemd des Kolbens ist eine Vielzahl von Vertiefungen vorgesehen.From the DE 10 2010 008 260 A1 a piston for a two-stroke engine working with a scavenging reservoir is known which has piston pockets which serve to connect an air inlet opening at the cylinder bore with overflow windows of overflow ducts. Air from the air inlet is stored in the overflow ducts via the piston pockets. A plurality of depressions is provided on the piston skirt of the piston.

Die JP S55 170 440 U und die DE 195 38 407 A1 zeigen Kolben für Zweitaktmotoren.The JP S55 170 440 U and the DE 195 38 407 A1 show pistons for two-stroke engines.

Der Erfindung liegt die Aufgabe zugrunde, einen Kolben für einen mit Spülvorlage arbeitenden Zweitaktmotor zu schaffen, der eine hohe Stabilität besitzt. Eine weitere Aufgabe der Erfindung besteht darin, einen Zweitaktmotor mit einem Kolben anzugeben.The invention is based on the object of creating a piston for a two-stroke engine which works with a flushing device and which has a high level of stability. Another object of the invention is to provide a two-stroke engine with a piston.

Diese Aufgabe wird bezüglich des Kolbens durch einen Kolben mit den Merkmalen des Anspruchs 1 gelöst. Bezüglich des Zweitaktmotors wird die Aufgabe durch einen Zweitaktmotor mit den Merkmalen des Anspruchs 14 gelöst.This object is achieved with respect to the piston by a piston with the features of claim 1. With regard to the two-stroke engine, the object is achieved by a two-stroke engine with the features of claim 14.

Der Kolben besitzt Kolbenbolzenaugen, in denen Kolbenbolzenaufnahmen ausgebildet sind. Es ist vorgesehen, dass mindestens ein Kolbenbolzenauge über mindestens eine Verbindungsrippe mit dem Kolbenhemd verbunden ist. Die Verbindungsrippe verläuft dabei an der dem Kolbenboden abgewandten Seite der Kolbentasche. Die Verbindungsrippe führt zu einer verbesserten Abstützung des Kolbenbolzenauges. Kräfte aus dem Kolbenbolzenauge können über die Verbindungsrippe besser auf das Kolbenhemd übertragen werden. Dadurch wird eine höhere Stabilität erreicht. Die Krafteinleitung aus dem Kolbenbolzenauge in das Kolbenhemd wird verbessert. Die Verbindungsrippe bewirkt eine Versteifung und Festigkeitserhöhung des Kolbens. Über die Verbindungsrippe wird auch Wärme aus dem Kolbenbolzenauge ins Kolbenhemd abgeleitet. Dadurch wird eine verbesserte Kühlung des thermisch besonders hoch belasteten Bereichs der Kolbenbolzenaugen erreicht.The piston has piston pin bosses in which piston pin receptacles are formed. It is provided that at least one piston pin boss is connected to the piston skirt via at least one connecting rib. The connecting rib runs on the side of the piston pocket facing away from the piston head. The connecting rib leads to an improved support of the piston pin eye. Forces from the piston pin boss can be better transferred to the piston skirt via the connecting rib. This results in greater stability. The introduction of force from the piston pin boss into the piston skirt is improved. The connecting rib causes a stiffening and an increase in strength of the piston. Heat is also dissipated from the piston pin boss into the piston skirt via the connecting rib. As a result, improved cooling of the area of the piston pin boss, which is particularly thermally stressed, is achieved.

Zwischen der Verbindungsrippe und dem Kolbenhemd ist eine Vertiefung ausgebildet. Die Vertiefung vermeidet Materialansammlungen in diesem Bereich, so dass eine bessere Herstellbarkeit des Kolbens, insbesondere in einem Gussverfahren, gegeben ist. Durch die Vertiefung können Gussfehler vermieden werden. Es wird eine Gewichtsreduzierung erreicht. Die Tiefe der Vertiefung beträgt vorteilhaft mindestens 3%, insbesondere mindestens 5% der Höhe des Kolbens. Über die Vertiefung wird eine gute beidseitige Kühlung der Verbindungsrippe durch im Kurbelgehäuseinnenraum strömendes Gemisch bzw. durch im Kurbelgehäuseinnenraum strömende Verbrennungsluft erreicht. Die Tiefe der Vertiefung beträgt vorteilhaft weniger als 20% der Höhe des Kolbens. Dadurch bleibt ausreichend Bauraum für die Kolbentasche, ohne dass sich die Bauhöhe des Kolbens vergrößert. Eine ausreichend große Kolbentasche stellt sicher, dass eine ausreichende Menge an Spülvorlagenluft in den Überströmkanälen vorgelagert wird, so dass sich geringe Abgaswerte eines mit dem Kolben arbeitenden Zweitaktmotors erreichen lassen. Vorteilhaft verläuft die Verbindungsrippe etwa parallel zur Mittelebene des Kolbens. Der senkrecht zur Mittelebene gemessene Abstand der Verbindungsrippe zur Mittelebene beträgt vorteilhaft mindestens 20% des Durchmessers des Kolbens.A recess is formed between the connecting rib and the piston skirt. The recess avoids accumulations of material in this area, so that the piston can be manufactured more easily, in particular in a casting process. Casting errors can be avoided by the recess. A weight reduction is achieved. The depth of the recess is advantageously at least 3%, in particular at least 5% of the height of the piston. The recess achieves good cooling of the connecting rib on both sides by the mixture flowing in the crankcase interior or by combustion air flowing in the crankcase interior. The depth of the recess is advantageously less than 20% of the height of the piston. This leaves sufficient space for the piston pocket without increasing the overall height of the piston. A sufficiently large piston pocket ensures that a sufficient amount of scavenging air is stored in the transfer ducts so that low exhaust gas values can be achieved for a two-stroke engine operating with the piston. The connecting rib advantageously runs approximately parallel to the center plane of the piston. The distance between the connecting rib and the central plane, measured perpendicular to the central plane, is advantageously at least 20% of the diameter of the piston.

Die Kolbenbolzenaugen besitzen einander zugewandte Stirnseiten. Die Verbindungsrippe besitzt zur Stirnseite des zugeordneten Kolbenbolzenauges vorteilhaft einen parallel zur Querachse gemessenen Abstand, der mindestens 5%, insbesondere mindestens 10% des Durchmessers des Kolbens besitzt. Die Verbindungsrippe ist demnach in dem im Zweitaktmotor eingebauten Zustand gegenüber der einem Pleuel des Zweitaktmotors zugewandten Stirnseite des Kolbenbolzenauges bezogen auf eine Zylinderlängsachse radial nach außen versetzt. Das einer Verbindungsrippe zugeordnete Kolbenbolzenauge ist dabei das Kolbenbolzenauge, das diese Verbindungsrippe mit dem Kolbenhemd verbindet.The piston pin bosses have facing faces. The connecting rib advantageously has a distance from the end face of the assigned piston pin eye, measured parallel to the transverse axis, which has at least 5%, in particular at least 10% of the diameter of the piston. The connecting rib is accordingly, in the state installed in the two-stroke engine, offset radially outward relative to the end face of the piston pin boss facing a connecting rod of the two-stroke engine, based on a cylinder longitudinal axis. The piston pin boss assigned to a connecting rib is the piston pin boss that connects this connecting rib to the piston skirt.

Vorteilhaft besitzt die Kolbentasche eine Rückwand. Die Rückwand der Kolbentasche ist die Wand, die die Kolbentasche von dem vom Kolbenhemd umschlossenen Innenraum des Kolbens trennt. Die Verbindungsrippe ist vorteilhaft in Verlängerung der Rückwand der Kolbentasche angeordnet. Durch die Anordnung der Verbindungsrippe in Verlängerung der Rückwand der Kolbentasche bewirkt die Verbindungsrippe eine Versteifung der Rückwand der Kolbentasche. Die Verbindungsrippe schließt bevorzugt an die Rückwand der Kolbentasche an. Die Vertiefung wird vorteilhaft vom Kolbenbolzenauge, vom Kolbenhemd, von der Verbindungsrippe und von der Rückwand der Kolbentasche begrenzt.The piston pocket advantageously has a rear wall. The rear wall of the piston pocket is the wall that separates the piston pocket from the interior of the piston enclosed by the piston skirt. The connecting rib is advantageously arranged as an extension of the rear wall of the piston pocket. By arranging the connecting rib as an extension of the rear wall of the piston pocket, the connecting rib causes the rear wall of the piston pocket to be stiffened. The connecting rib preferably adjoins the rear wall of the piston pocket. The recess is advantageously delimited by the piston pin boss, the piston skirt, the connecting rib and the rear wall of the piston pocket.

Das Kolbenhemd besitzt vorteilhaft einen dem Kolbenboden abgewandten Rand. Die Verbindungsrippe besitzt eine dem Kolbenboden abgewandte Stirnseite. Die Stirnseite der Verbindungsrippe ragt vorteilhaft nicht bis an die Unterseite des Kolbens, sondern ist gegenüber dem Rand des Kolbens, der die Unterseite des Kolbens bildet, in Richtung auf den Kolbenboden versetzt. Der Versatz zwischen der Stirnseite der Verbindungsrippe und dem Rand beträgt in Richtung der Längsmittelachse des Kolbens an jeder Stelle der Stirnseite vorteilhaft weniger als 5% der Höhe des Kolbens. Es kann auch vorgesehen sein, dass die Stirnseite der Verbindungsrippe bis auf die Höhe des Rands ragt. Vorteilhaft ist jedoch ein Versatz von mindestens 0,5 mm zwischen der Stirnseite der Verbindungsrippe und dem Rand in Richtung der Längsmittelachse des Kolbens gegeben.The piston skirt advantageously has an edge facing away from the piston crown. The connecting rib has an end face facing away from the piston head. The end face of the connecting rib advantageously does not protrude as far as the bottom of the piston, but is offset in the direction of the piston head with respect to the edge of the piston, which forms the bottom of the piston. The offset between the end face of the connecting rib and the edge in the direction of the longitudinal center axis of the piston is advantageously less than 5% of the height of the piston at each point on the end face. It can also be provided that the end face of the connecting rib extends up to the level of the edge. However, an offset of at least 0.5 mm between the end face is advantageous given the connecting rib and the edge in the direction of the longitudinal center axis of the piston.

Zwischen dem Rand und der Kolbentasche verläuft vorteilhaft ein Steg des Kolbenhemds. Der Steg besitzt in dem Umfangsbereich des Kolbens, in dem die Vertiefung angeordnet ist, eine Höhe, die mindestens das 1,5fache der kleinsten Höhe des Stegs beträgt. Im Bereich der Vertiefung ist der Steg demnach höher ausgebildet als in anderen Bereichen der Kolbentasche. Dadurch wird eine gute Führung des Kolbens im Bereich der Vertiefung erreicht, und gleichzeitig steht ausreichend Bauraum für die Vertiefung zur Verfügung. Vorteilhaft liegt der Kolben im Betrieb über mindestens einen Teilabschnitt des Kolbenhubs mit mindestens einem Abschnitt des Stegs an der Zylinderbohrung an.A web of the piston skirt advantageously runs between the edge and the piston pocket. In the circumferential area of the piston in which the recess is arranged, the web has a height which is at least 1.5 times the smallest height of the web. In the area of the recess, the web is accordingly made higher than in other areas of the piston pocket. As a result, good guidance of the piston in the area of the recess is achieved, and at the same time sufficient installation space is available for the recess. During operation, the piston advantageously rests against the cylinder bore with at least one section of the web over at least a partial section of the piston stroke.

Bevorzugt ist die Kolbenbolzenaufnahme mindestens teilweise, insbesondere vollständig in der Kolbentasche angeordnet. Dadurch kann eine geringe Bauhöhe des Kolbens und damit eine geringe Bauhöhe des Zylinders eines Zweitaktmotors erreicht werden. Gleichzeitig besitzt die Kolbenbolzenaufnahme einen vergleichsweise großen Abstand zum Kolbenboden. Durch einen vergleichsweise großen Abstand zwischen Kolbenbolzenaufnahme und Kolbenboden kann der Wärmeeintrag in den Kolbenbolzen und damit in das Kolbenbolzenlager, mit dem das Pleuel am Kolbenbolzen gelagert ist, im Betrieb verringert werden.The piston pin receptacle is preferably arranged at least partially, in particular completely, in the piston pocket. As a result, a low overall height of the piston and thus a low overall height of the cylinder of a two-stroke engine can be achieved. At the same time, the piston pin seat is at a comparatively large distance from the piston crown. The heat input into the piston pin and thus into the piston pin bearing with which the connecting rod is mounted on the piston pin can be reduced during operation by a comparatively large distance between the piston pin seat and the piston crown.

Der Kolben besitzt bevorzugt zwei Kolbentaschen auf gegenüberliegenden Seiten der Mittelebene, wobei an beiden Kolbenbolzenaugen jeweils eine Verbindungsrippe angeordnet ist. Bevorzugt sind die Kolbentaschen und die Verbindungsrippen symmetrisch zur Mittelebene angeordnet. Auch eine unsymmetrische Ausbildung kann jedoch vorteilhaft sein.The piston preferably has two piston pockets on opposite sides of the center plane, a connecting rib being arranged on each of the two piston pin bosses. The piston pockets and the connecting ribs are preferably arranged symmetrically to the center plane. However, an asymmetrical design can also be advantageous.

Der Kolben besteht vorteilhaft aus Leichtmetall, insbesondere aus Aluminium oder Magnesium. Dadurch ergibt sich ein geringeres Gewicht des Kolbens. Bei gleichem Gesamtgewicht kann ein Zweitaktmotor mit einem Kolben aus Leichtmetall, insbesondere aus Magnesium, einen Motor mit größerem Hubraum und damit mit größerer Leistung aufweisen als beispielsweise ein Zweitaktmotor mit einem Kolben, der nicht aus Leichtmetall, insbesondere nicht aus Magnesium besteht. Insbesondere bei einem Kolben aus Leichtmetall bringt die Verbindungsrippe Vorteile bezüglich der Stabilität des Kolbens, da Leichtmetall, insbesondere Magnesium, selbst eine geringere Festigkeit aufweist.The piston is advantageously made of light metal, in particular aluminum or magnesium. This results in a lower weight of the piston. With the same A two-stroke engine with a piston made of light metal, in particular made of magnesium, can have an engine with a larger displacement and thus with greater power than, for example, a two-stroke engine with a piston that is not made of light metal, in particular not made of magnesium. In the case of a piston made of light metal in particular, the connecting rib has advantages with regard to the stability of the piston, since light metal, in particular magnesium, itself has a lower strength.

Die Verbindungsrippe ist vorteilhaft auf einer Auslassseite des Kolbens zwischen dem Kolbenbolzenauge und dem Kolbenhemd angeordnet. In vorteilhafter Gestaltung ist alternativ oder zusätzlich auf einer Einlassseite des Kolbens mindestens eine Verbindungsrippe vorgesehen, die das Kolbenbolzenauge mit dem Kolbenhemd verbindet. Dabei ist vorteilhaft eine Verbindungsrippe auf der Einlassseite bezüglich einer Querebene des Kolbens spiegelsymmetrisch zu einer Verbindungsrippe auf der Auslassseite angeordnet und ausgebildet.The connecting rib is advantageously arranged on an outlet side of the piston between the piston pin boss and the piston skirt. In an advantageous embodiment, at least one connecting rib is alternatively or additionally provided on an inlet side of the piston, which connects the piston pin boss to the piston skirt. In this case, a connecting rib on the inlet side is advantageously arranged and designed with mirror symmetry to a connecting rib on the outlet side with respect to a transverse plane of the piston.

Ein Zweitaktmotor mit einem erfindungsgemäßen Kolben besitzt vorteilhaft einen Zylinder, in dessen Zylinderbohrung ein Brennraum ausgebildet ist. Der Brennraum ist von dem Kolben begrenzt. Der Kolben treibt eine in einem Kurbelgehäuse drehbar gelagerte Kurbelwelle an. Der Zweitaktmotor besitzt mindestens einen Überströmkanal, der in mindestens einer Stellung des Kolbens einen Kurbelgehäuseinnenraum des Kurbelgehäuses mit dem Brennraum verbindet. Der Zweitaktmotor besitzt einen Luftkanal zur Zufuhr von Spülvorlagenluft, der mit einem Lufteinlass an der Zylinderbohrung mündet. Die Kolbentasche liegt in mindestens einer Stellung des Kolbens mindestens teilweise in Überdeckung mit dem Lufteinlass und einem Überströmfenster eines Überströmkanals.A two-stroke engine with a piston according to the invention advantageously has a cylinder in the cylinder bore of which a combustion chamber is formed. The combustion chamber is limited by the piston. The piston drives a crankshaft rotatably mounted in a crankcase. The two-stroke engine has at least one overflow duct which, in at least one position of the piston, connects a crankcase interior of the crankcase with the combustion chamber. The two-stroke engine has an air duct for the supply of scavenging air, which opens with an air inlet on the cylinder bore. In at least one position of the piston, the piston pocket is at least partially in overlap with the air inlet and an overflow window of an overflow channel.

Über die Kolbentasche kann dadurch Spülvorlagenluft aus dem Luftkanal über den Lufteinlass in das Überströmfenster des Überströmkanals zugeführt und so im Überströmkanal vorgelagert werden. Die Spülvorlagenluft kann dabei kraftstofffreie oder kraftstoffarme Verbrennungsluft sein. Dadurch werden geringe Abgaswerte erreicht.In this way, flushing air can be supplied via the piston pocket from the air duct via the air inlet into the overflow window of the overflow duct and thus stored upstream in the overflow duct. The purge air can be fuel-free or low-fuel combustion air. This results in low emissions.

Die Merkmale der Ausführungsbeispiele können in beliebiger Weise miteinander kombiniert werden, um vorteilhafte Weiterbildungen zu bilden.The features of the exemplary embodiments can be combined with one another in any desired manner in order to form advantageous developments.

Ein Ausführungsbeispiel der Erfindung wird im Folgenden anhand der Zeichnung erläutert. Es zeigen:

Fig. 1
eine schematische Schnittdarstellung eines Zweitaktmotors,
Fig. 2
den Kolben des Zweitaktmotors aus Fig. 1 in perspektivischer Darstellung,
Fig. 3
eine Seitenansicht des Kolbens,
Fig. 4
eine perspektivische Darstellung des Kolbens von der dem Kurbelgehäuse zugewandten Seite,
Fig. 5
eine perspektivische Darstellung eines Schnitts durch den Kolben entlang der Mittelebene,
Fig. 6
einen Schnitt durch den Kolben senkrecht zur Mittelebene und parallel zur Längsmittelachse durch die Verbindungsrippe mit Blickrichtung auf die Einlassseite des Kolbens,
Fig. 7
einen Schnitt entlang der in Fig. 6 gezeigten Schnittebene mit Blickrichtung auf die Auslassseite des Kolbens,
Fig. 8
eine schematische Ansicht eines Ausführungsbeispiels eines Kolbens von der dem Kurbelgehäuse zugewandten Seite.
An embodiment of the invention is explained below with reference to the drawing. Show it:
Fig. 1
a schematic sectional view of a two-stroke engine,
Fig. 2
the piston of the two-stroke engine Fig. 1 in perspective view,
Fig. 3
a side view of the piston,
Fig. 4
a perspective view of the piston from the side facing the crankcase,
Fig. 5
a perspective view of a section through the piston along the center plane,
Fig. 6
a section through the piston perpendicular to the center plane and parallel to the longitudinal center axis through the connecting rib looking towards the inlet side of the piston,
Fig. 7
a section along the in Fig. 6 Section plane shown with a view of the outlet side of the piston,
Fig. 8
a schematic view of an embodiment of a piston from the side facing the crankcase.

Fig. 1 zeigt schematisch ein Ausführungsbeispiel für einen Zweitaktmotor 1. Der Zweitaktmotor 1 ist als Einzylindermotor ausgebildet und besitzt einen Zylinder 2, in dem ein Brennraum 3 ausgebildet ist. Der Zylinder 2 besitzt eine Zylinderlängsachse 48. Der Brennraum 3 ist von einem Kolben 5 begrenzt, der in einer Zylinderbohrung 15 des Zylinders 2 in Richtung der Zylinderlängsachse 48 hin- und hergehend gelagert ist, in deren Richtung sich der Kolben 5 im Betrieb bewegt. In Fig. 1 ist der Kolben 5 in seinem unteren Totpunkt gezeigt. Der Kolben 5 treibt über ein Pleuel 6 eine Kurbelwelle 7 an. Die Kurbelwelle 7 ist in einem Kurbelgehäuseinnenraum 16 eines Kurbelgehäuses 4 um eine Drehachse 8 drehbar gelagert. Die Kurbelwelle 7 dreht sich im Betrieb in einer Drehrichtung 69. Der Zweitaktmotor 1 kann beispielsweise der Antriebsmotor in einem handgeführten Arbeitsgerät wie einer Motorsäge, einem Trennschleifer, einem Blasgerät oder dergleichen sein. Die Kurbelwelle 7 dient vorteilhaft zum Antrieb eines Werkzeugs des Arbeitsgeräts. Der Kolben 5 besitzt zwei Kolbentaschen 14, von denen in Fig. 1 eine gezeigt ist. Die Kolbentaschen 14 sind symmetrisch zu der Schnittebene in Fig. 1 am Kolben 5 angeordnet. Fig. 1 shows schematically an embodiment of a two-stroke engine 1. The two-stroke engine 1 is designed as a single-cylinder engine and has a cylinder 2 in which a combustion chamber 3 is formed. The cylinder 2 has a cylinder longitudinal axis 48. The combustion chamber 3 is delimited by a piston 5, which is mounted to and fro in a cylinder bore 15 of the cylinder 2 in the direction of the cylinder longitudinal axis 48, in the direction of which the piston 5 moves during operation. In Fig. 1 the piston 5 is shown in its bottom dead center. The piston 5 drives a crankshaft 7 via a connecting rod 6. The crankshaft 7 is mounted rotatably about an axis of rotation 8 in a crankcase interior 16 of a crankcase 4. The crankshaft 7 rotates in one direction of rotation 69 during operation. The two-stroke engine 1 can be, for example, the drive motor in a hand-held tool such as a power saw, a power cutter, a blower or the like. The crankshaft 7 is advantageously used to drive a tool of the implement. The piston 5 has two piston pockets 14, of which in Fig. 1 one is shown. The piston pockets 14 are symmetrical to the cutting plane in FIG Fig. 1 arranged on the piston 5.

Der Zweitaktmotor 1 besitzt einen Luftkanal 9, der mit einem Luftfilter 22 verbunden ist. Über den Luftkanal 9 wird kraftstofffreie oder kraftstoffarme Spülvorlagenluft zugeführt. Im Lufteinlass 9 ist eine Luftklappe 21 zur Steuerung der über den Luftkanal 9 zugeführten Menge an Spülvorlagenluft angeordnet. Der Luftkanal 9 mündet mit einem Lufteinlass 11 an der Zylinderbohrung 15. Zur Zufuhr von Kraftstoff/Luft-Gemisch ist ein Gemischkanal 10 vorgesehen. Der Gemischkanal 10 ist über einen Vergaser 18 mit dem Luftfilter 22 verbunden. Im Vergaser 18 sind im Ausführungsbeispiel eine Drosselklappe 19 sowie eine Chokeklappe 20 schwenkbar gelagert. Die Drosselklappe 19 und die Chokeklappe 20 dienen zur Einstellung der über den Gemischkanal 10 zugeführten Menge an Verbrennungsluft und Kraftstoff. Anstatt mittels eines konventionellen Vergasers 18 kann die Kraftstoffzufuhr auch auf andere Weise, beispielsweise über ein Einspritzventil oder einen Vergaser mit einem elektromagnetischen Ventil, erfolgen. Der Gemischkanal 10 mündet mit einem Gemischeinlass 12 an der Zylinderbohrung 15. Der Lufteinlass 11 und der Gemischeinlass 12 sind vom Kolben 5 gesteuert.The two-stroke engine 1 has an air duct 9 which is connected to an air filter 22. Fuel-free or low-fuel scavenging air is supplied via the air duct 9. In the air inlet 9, an air flap 21 is arranged to control the amount of flushing original air supplied via the air duct 9. The air duct 9 opens with an air inlet 11 at the cylinder bore 15. A mixture duct 10 is provided for supplying the fuel / air mixture. The mixture duct 10 is connected to the air filter 22 via a carburetor 18. In the exemplary embodiment, a throttle valve 19 and a choke valve 20 are pivotably mounted in the carburetor 18. The throttle valve 19 and the choke valve 20 are used to adjust the amount of combustion air and fuel supplied via the mixture duct 10. Instead of using a conventional carburetor 18, the fuel can also be supplied in another way, for example via an injection valve or a carburetor with an electromagnetic 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.

Der Zweitaktmotor 1 besitzt Überströmkanäle 13, die mit Überströmfenstern 17 in den Brennraum 3 münden. Auch die Überströmfenster 17 sind vom Kolben 5 gesteuert. Im Bereich des unteren Totpunkts des Kolbens 5 verbinden die nicht näher dargestellten Überströmkanäle 13 den Kurbelgehäuseinnenraum 16 mit dem Brennraum 3. Im Betrieb wird beim Aufwärtshub des Kolbens 5 durch den Gemischeinlass 12 Kraftstoff/Luft-Gemisch in den Kurbelgehäuseinnenraum 16 angesaugt. Der Aufwärtshub des Kolbens 5 bezeichnet dabei die Bewegung des Kolbens 5 aus der in Fig. 1 gezeigten Stellung des Kolbens 5 im unteren Totpunkt in Richtung auf den Brennraum 3, also in Fig. 1 in Richtung des Pfeils 70. Im Bereich des oberen Totpunkts des Kolbens 5 verbinden die Kolbentaschen 14 jeweils einen Lufteinlass 11 mit Überströmfenstern 17. Dadurch wird Spülvorlagenluft aus dem Luftkanal 9 in die Überströmkanäle 13 angesaugt. Beim Aufwärtshub des Kolbens 5 wird gleichzeitig bereits im Brennraum 3 vorhandenes Gemisch komprimiert und im Bereich des oberen Totpunkts des Kolbens 5 von einer nicht dargestellten Zündkerze gezündet.The two-stroke engine 1 has transfer ducts 13 which open into the combustion chamber 3 with transfer windows 17. The overflow windows 17 are also controlled by the piston 5. In the area of the bottom dead center of the piston 5, the overflow ducts 13, not shown, connect the crankcase interior 16 to the combustion chamber 3. During operation, during the upward stroke of the piston 5, a fuel / air mixture is sucked into the crankcase interior 16 through the mixture inlet 12. The upward stroke of the piston 5 denotes the movement of the piston 5 from the position shown in FIG Fig. 1 The position of the piston 5 shown at bottom dead center in the direction of the combustion chamber 3, that is to say in FIG Fig. 1 in the direction of arrow 70. In the area of the top dead center of the piston 5, the piston pockets 14 each connect an air inlet 11 with overflow windows 17. As a result, flushing air is sucked from the air channel 9 into the overflow channels 13. During the upward stroke of the piston 5, the mixture already present in the combustion chamber 3 is simultaneously compressed and ignited in the area of the top dead center of the piston 5 by a spark plug (not shown).

Der Verbrennungsdruck beschleunigt den Kolben 5 zurück in Richtung auf das Kurbelgehäuse 4. Aus dem Brennraum 3 führt ein Auslass 23, der ebenfalls vom Kolben 5 gesteuert ist. Sobald der Auslass 23 vom Kolben 5 geöffnet wird, strömen die Abgase aus dem Brennraum 3 durch den Auslass 23 aus. Nach weiterem Abwärtshub öffnet der Kolben 5 die Überströmfenster 17 zum Brennraum 3. Die in den Überströmkanälen 13 vorgelagerte Verbrennungsluft strömt dann in den Brennraum 3 ein. Die vorgelagerte Luft spült Abgase aus dem Brennraum 3 durch den Auslass 23 aus. Aus dem Kurbelgehäuseinnenraum 16 strömt frisches Kraftstoff/Luft-Gemisch, das im Kurbelgehäuseinnenraum 16 vorkomprimiert wurde, nach. Beim folgenden Motorzyklus wird das Gemisch im Brennraum 3 beim Aufwärtshub des Kolbens 5 komprimiert, während gleichzeitig frisches Gemisch in den Kurbelgehäuseinnenraum 16 und Spülvorlagenluft in die Überströmkanäle 13 angesaugt wird.The combustion pressure accelerates the piston 5 back in the direction of the crankcase 4. An outlet 23, which is also 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 overflow window 17 to the combustion chamber 3. The combustion air upstream in the overflow ducts 13 then flows into the combustion chamber 3. The upstream air flushes exhaust gases from the combustion chamber 3 through the outlet 23. Fresh fuel / air mixture, which was precompressed 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 at the same time fresh mixture is sucked into the crankcase interior 16 and scavenging air into the overflow channels 13.

Die Gestaltung der Kolbentaschen 14 hat entscheidenden Einfluss auf die Menge an in den Überströmkanälen 13 vorgelagerter Spülvorlagenluft. Wie Fig. 2 zeigt, besitzen die Kolbentaschen 14 eine obere Steuerkante 29, die im Bereich des oberen Totpunkts des Kolbens 5 vorteilhaft so angeordnet ist, dass die Überströmfenster 17 vollständig in Überdeckung mit der Kolbentasche 14 angeordnet sind. Die obere Steuerkante 29 ist die dem Brennraum 3 am nächsten liegende Steuerkante der Kolbentasche 14. Die Kolbentasche 14 besitzt außerdem eine untere Steuerkante 30, die dem Kurbelgehäuse 4 zugewandt ist. Die untere Steuerkante 30 ist die am weitesten vom Brennraum 3 entfernt liegende Steuerkante der Kolbentasche 14 und begrenzt die Kolbentasche 14 in Richtung auf das Kurbelgehäuse 4. Im oberen Totpunkt des Kolbens 5 ist die untere Steuerkante 30 vorteilhaft so angeordnet, dass der Lufteinlass 11 vollständig in Überdeckung mit der Kolbentasche 14 liegt. Die Kolbentaschen 14 besitzen außerdem einlassnahe Begrenzungskanten 53 sowie auslassnahe Begrenzungskanten 54. Die Begrenzungskanten 53 und 54 verlaufen im Ausführungsbeispiel etwa parallel zur Zylinderlängsachse 48 (Fig. 1). Jede Kolbentasche 14 ist damit in Richtung der Zylinderlängsachse 48 von den Steuerkanten 29 und 30 und in Umfangsrichtung von den Begrenzungskanten 53 und 54 begrenzt. Der Kolben 5 besitzt einen Rand 31 an seiner dem Kurbelgehäuse 4 zugewandten Seite, der die dem Kurbelgehäuse 4 zugewandte Begrenzung des Kolbens 5 bildet. Zwischen den Kolbentaschen 14 und dem Rand 31 ist jeweils ein Steg 32 ausgebildet, der durch einen Abschnitt eines Kolbenhemds 26 gebildet ist.The design of the piston pockets 14 has a decisive influence on the amount of flushing air stored upstream in the overflow channels 13. How Fig. 2 shows, the piston pockets 14 have an upper control edge 29 which is advantageously arranged in the region of the top dead center of the piston 5 such that the overflow windows 17 are arranged completely in overlap with the piston pocket 14. The upper control edge 29 is the control edge of the piston pocket 14 closest to the combustion chamber 3. The piston pocket 14 also has a lower control edge 30 which faces the crankcase 4. The lower control edge 30 is the control edge of the piston pocket 14 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 so that the air inlet 11 is completely in Coverage with the piston pocket 14 is. The piston pockets 14 also have delimiting edges 53 close to the inlet and delimiting edges 54 close to the outlet. In the exemplary embodiment, the delimiting edges 53 and 54 run approximately parallel to the cylinder longitudinal axis 48 ( Fig. 1 ). Each piston pocket 14 is thus limited in the direction of the cylinder longitudinal axis 48 by the control edges 29 and 30 and in the circumferential direction by the delimiting edges 53 and 54. The piston 5 has an edge 31 on its side facing the crankcase 4, which forms the boundary of the piston 5 facing the crankcase 4. Between the piston pockets 14 and the edge 31, a web 32 is formed in each case, which is formed by a section of a piston skirt 26.

Der Kolben 5 besitzt einen Kolbenboden 25, der etwa senkrecht zur Zylinderlängsachse 48 verläuft und den Brennraum 3 begrenzt. Der Kolben 5 besitzt das Kolbenhemd 26, das vorteilhaft dem Verlauf der Zylinderbohrung 15 folgt. Die Außenseite des Kolbenhemds 26 verläuft vorteilhaft etwa zylindrisch. Die Außenseite des Kolbenhemds 26 kann dabei einen exakt zylindrischen oder einen von der Kreisform abweichenden Querschnitt besitzen. Das Kolbenhemd kann insbesondere eine elliptische, ovale oder kleeblattförmige Gestalt aufweisen. Ein kleeblattförmiger Querschnitt ist dabei ein Querschnitt, bei dem der Durchmesser in zwei schräg zueinander stehenden Richtungen verringert ist. Die Abweichung des Querschnitts von der Kreisform ist dabei vorteilhaft sehr gering. Benachbart zum Kolbenboden 25 sind am Kolbenhemd 26 zwei Kolbenringnuten 24 vorgesehen, die zur Aufnahme von Kolbenringen dienen. In einer der Kolbenringnuten 24 ist eine Bohrung 34 gezeigt, die zur Aufnahme eines Sicherungsstifts für einen Kolbenring dient. Eine entsprechende, in Fig. 2 nicht sichtbare Bohrung ist auch in der anderen Kolbenringnut 24 vorgesehen. Wie Fig. 2 auch zeigt, ist zwischen jeder Kolbentasche 14 und den Kolbenringnuten 24 eine Vertiefung 27 am Kolbenhemd 26 vorgesehen. Die Vertiefung 27 dient zur Gewichtsreduzierung des Kolbens 5. Die Vertiefung 27 ist dabei so ausgebildet, dass sie während eines Kolbenhubs nur mit einem oder beiden Überströmfenstern 17, jedoch nicht mit dem Lufteinlass 11 in Überdeckung liegt. An der dem Gemischeinlass 12 zugewandten Seite besitzt das Kolbenhemd 26 an der dem Kurbelgehäuse 4 zugewandten, dem Brennraum 3 entfernt liegenden Seite eine Ausnehmung 33. An der Ausnehmung 33 ist die Höhe des Kolbenhemds 26 verringert. Die Ausnehmung 33 ist als Ausbuchtung des Rands 31 in Richtung auf den Kolbenboden 25 ausgebildet. Die Lage des Rands 31 an der Ausnehmung 33 legt die Steuerzeit, bei der der Gemischeinlass 12 geöffnet und geschlossen wird, fest. Am Rand 31 ist im Bereich der Ausnehmung 33 eine Fase 37 am Übergang des Rands 31 zur Außenseite des Kolbenhemds 26 vorgesehen.The piston 5 has a piston head 25 which runs approximately perpendicular to the cylinder longitudinal axis 48 and delimits the combustion chamber 3. The piston 5 has the piston skirt 26, which advantageously follows the course of the cylinder bore 15. The outside of the piston skirt 26 is advantageously approximately cylindrical. The outside of the piston skirt 26 can be exactly cylindrical or deviating from the circular shape Own cross-section. The piston skirt can in particular have an elliptical, oval or cloverleaf shape. A cloverleaf-shaped cross-section is a cross-section in which the diameter is reduced in two directions at an angle to one another. The deviation of the cross section from the circular shape is advantageously very small. Adjacent to the piston head 25, two piston ring grooves 24 are provided on the piston skirt 26, which are used to receive piston rings. In one of the piston ring grooves 24, a bore 34 is shown which serves to receive a locking pin for a piston ring. A corresponding, in Fig. 2 The bore, which is not visible, is also provided in the other piston ring groove 24. How Fig. 2 also shows, a recess 27 on the piston skirt 26 is provided between each piston pocket 14 and the piston ring grooves 24. The recess 27 serves to reduce the weight of the piston 5. The recess 27 is designed in such a way that it overlaps only one or both overflow windows 17 during a piston stroke, but not the air inlet 11. On the side facing the mixture inlet 12, the piston skirt 26 has a recess 33 on the side facing the crankcase 4 and remote from the combustion chamber 3. The height of the piston skirt 26 is reduced at the recess 33. The recess 33 is designed as a bulge of the edge 31 in the direction of the piston head 25. The position of the edge 31 on the recess 33 defines the control time at which the mixture inlet 12 is opened and closed. On the edge 31, in the region of the recess 33, a bevel 37 is provided at the transition from the edge 31 to the outside of the piston skirt 26.

Das Pleuel 6 (Fig. 1) ist mit dem Kolben 5 über einen nicht gezeigten Kolbenbolzen verbunden. Der Kolbenbolzen ist am Kolben 5 in Kolbenbolzenaufnahmen 35 gehalten. Die Kolbenbolzenaufnahmen 35 sind im Ausführungsbeispiel vollständig in den Kolbentaschen 14 angeordnet. Die Kolbenbolzenaufnahmen 35 befinden sich vorteilhaft im Raum zwischen den Steuerkanten 29 und 30 der Kolbentaschen 14. Zum Kurbelgehäuseinnenraum hin wird die Kolbentasche 14 von einer Rückwand 58 begrenzt.The connecting rod 6 ( Fig. 1 ) is connected to the piston 5 via a piston pin, not shown. The piston pin is held in piston pin receptacles 35 on piston 5. In the exemplary embodiment, the piston pin receptacles 35 are arranged completely in the piston pockets 14. The piston pin receptacles 35 are advantageously located in the space between the control edges 29 and 30 of the piston pockets 14. The piston pocket 14 is delimited by a rear wall 58 towards the crankcase interior.

Wie Fig. 3 zeigt, besitzt der Kolben 5 einen Durchmesser a. Der Durchmesser a ist vorteilhaft der größte Durchmesser des Kolbens 5 und im Ausführungsbeispiel an einer Oberseite 40 des Kolbenbodens 25 gemessen. Die Oberseite 40 des Kolbenbodens 25 ist dabei die Seite des Kolbenbodens 25, die den Brennraum 3 begrenzt. Der Kolben 5 besitzt eine Höhe h, die parallel zu einer Längsmittelachse 50 des Kolbens 5 gemessen ist. Die Höhe h ist die größte Höhe des Kolbens 5. Die Längsmittelachse 50 des Kolbens 5 ist die Mittelachse des Kolbenhemds 26. Die Längsmittelachse 50 des Kolbens 5 fällt bei der Anordnung des Kolbens 5 im Zylinder 2 näherungsweise mit der Zylinderlängsachse 48 zusammen. Die Kolbenbolzenaufnahmen 35 (Fig. 2) besitzen eine Mittelachse, die eine Querachse 49 des Kolbens 5 bildet. Die Querachse 49 verläuft in der gezeigten Seitenansicht senkrecht zur Längsmittelachse 50. Der Kolben 5 besitzt eine Mittelebene 51, die die Längsmittelachse 50 des Kolbens 5 enthält und die senkrecht zur Querachse 49 verläuft. In der in Fig. 3 gezeigten Seitenansicht fallen die Längsmittelachse 50 und die Mittelebene 51 zusammen.How Fig. 3 shows, the piston 5 has a diameter a. The diameter a is advantageously the largest diameter of the piston 5 and is measured on an upper side 40 of the piston head 25 in the exemplary embodiment. The top 40 of the piston head 25 is the side of the piston head 25 that delimits the combustion chamber 3. The piston 5 has a height h which is measured parallel to a longitudinal center axis 50 of the piston 5. The height h is the greatest height of the piston 5. The longitudinal center axis 50 of the piston 5 is the center axis of the piston skirt 26. The longitudinal center axis 50 of the piston 5 coincides approximately with the cylinder longitudinal axis 48 when the piston 5 is arranged in the cylinder 2. The piston pin sockets 35 ( Fig. 2 ) have a central axis which forms a transverse axis 49 of the piston 5. In the side view shown, the transverse axis 49 runs perpendicular to the longitudinal center axis 50. The piston 5 has a center plane 51 which contains the longitudinal center axis 50 of the piston 5 and which runs perpendicular to the transverse axis 49. In the in Fig. 3 The side view shown, the longitudinal center axis 50 and the center plane 51 coincide.

An der Ausnehmung 33 besitzt der Kolben 5 eine verringerte Höhe i. Die verringerte Höhe i ist der parallel zur Längsmittelachse 50 gemessene Abstand des Rands 31 an der Ausnehmung 33 zur Oberseite 40 des Kolbens 5. Die verringerte Höhe i an der Ausnehmung 33 beträgt vorteilhaft 70% bis 98%, insbesondere 80% bis 95% der Höhe h des Kolbens 5. Der Durchmesser a beträgt vorteilhaft 70% bis 140% der Höhe h, insbesondere 80% bis 130%, bevorzugt 90% bis 120% der Höhe h. Besonders bevorzugt ist der Durchmesser a größer als die Höhe h.At the recess 33, the piston 5 has a reduced height i. The reduced height i is the distance, measured parallel to the longitudinal center axis 50, of the edge 31 on the recess 33 to the top 40 of the piston 5. The reduced height i on the recess 33 is advantageously 70% to 98%, in particular 80% to 95% of the height h of the piston 5. The diameter a is advantageously 70% to 140% of the height h, in particular 80% to 130%, preferably 90% to 120% of the height h. The diameter a is particularly preferably greater than the height h.

Der Kolben 5 besitzt eine Einlassseite 46, an der die Ausnehmung 33 angeordnet ist. Fig. 3 zeigt eine Seitenansicht auf die Einlassseite 46. Der Steg 32 zwischen der Kolbentasche 14 und dem Rand 31 besitzt an der Einlassseite 46 eine minimale Höhe k. Die minimale Höhe k ist im Ausführungsbeispiel an dem der Ausnehmung 33 zugewandten Umfangsbereich der Kolbentasche 14 gemessen. Die minimale Höhe k kann etwa 1 mm bis etwa 5 mm, insbesondere etwa 1 mm bis etwa 3 mm betragen. Die Höhe des Stegs 32 muss dabei nicht konstant sein, sondern kann sich entlang des Umfangs des Kolbens 5 ändern. Der Steg 32 dient zur Abdichtung zwischen dem von Kolbentasche 26 und Zylinderbohrung 15 eingeschlossenen Volumen und dem Kurbelgehäuseinnenraum 16.The piston 5 has an inlet side 46 on which the recess 33 is arranged. Fig. 3 shows a side view of the inlet side 46. The web 32 between the piston pocket 14 and the edge 31 has a minimum height k on the inlet side 46. In the exemplary embodiment, the minimum height k is measured on the circumferential area of the piston pocket 14 facing the recess 33. The minimum 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, but can vary along the circumference of piston 5 change. The web 32 serves to seal between the volume enclosed by the piston pocket 26 and cylinder bore 15 and the crankcase interior 16.

Fig. 4 zeigt das Innere des Kolbens 5. Die Kolbenbolzenaufnahmen 35 sind an Kolbenbolzenaugen 28 ausgebildet, die sich im Ausführungsbeispiel bis zum Kolbenboden 25 erstrecken. Die Kolbenbolzenaugen 28 besitzen einander zugewandte Stirnseiten 57. Die Stirnseiten 57 verlaufen im Ausführungsbeispiel näherungsweise parallel zur Mittelebene 51. In vorteilhafter Gestaltung verlaufen die Stirnseiten 57 der beiden Kolbenbolzenaugen 28 bezogen auf die Mittelebene 51 näherungsweise spiegelsymmetrisch zueinander. An allen Flächen des Kolbens 5, die näherungsweise parallel zur Längsmittelachse 50 des Kolbens 5 verlaufen, sind vorteilhaft geringe Auszugschrägen vorgesehen, damit der Kolben 5 bei der Herstellung in einem Gussverfahren entformt werden kann. Die Auszugsschrägen an den näherungsweise parallel zur Mittelebene 51 verlaufenden Flächen können beispielsweise von 0,5° bis 3° betragen. Die Stirnseiten 57 der Kolbenbolzenaugen 28 sind die Bereiche der Kolbenbolzenaugen 28, die den geringsten Abstand zur Mittelebene 51 besitzen. An den Stirnseiten 57 enden die Kolbenbolzenaufnahmen 35. Im Ausführungsbeispiel besitzen die Stirnseiten 57 jeweils einen Abstand z zur Mittelebene 51, der senkrecht zur Mittelebene 51 und parallel zur Querachse 49 (Fig. 3) gemessen ist. Der Abstand z beträgt vorteilhaft mindestens 5%, insbesondere mindestens 10% des Durchmessers a des Kolbens 5 (Fig. 3). Die Kolbenbolzenaugen 28 sind vorteilhaft symmetrisch zur Mittelebene 51 angeordnet, so dass sich für beide Stirnseiten 57 der gleiche Abstand z ergibt. An der dem Brennraum 3 abgewandten Seite besitzen die Stirnseiten 57 eine Einbuchtung 36, die sich bis zur Kolbenbolzenaufnahme 35 erstreckt und an der der Abstand zur Mittelebene 51 vergrößert ist. Die Einbuchtung 36 dient zur Schmierung eines Kolbenbolzenlagers, mit dem der Kolbenbolzen an dem Pleuel 6 (Fig. 1) gelagert ist. Fig. 4 shows the interior of the piston 5. The piston pin receptacles 35 are formed on piston pin bosses 28, which in the exemplary embodiment extend to the piston crown 25. The piston pin bosses 28 have mutually facing front sides 57. In the exemplary embodiment, the front sides 57 run approximately parallel to the center plane 51. In an advantageous embodiment, the front sides 57 of the two piston pin bosses run approximately mirror-symmetrically with respect to the center plane 51. On all surfaces of the piston 5, which run approximately parallel to the longitudinal center axis 50 of the piston 5, small extension bevels are advantageously provided so that the piston 5 can be removed from the mold during manufacture in a casting process. The extension bevels on the surfaces running approximately parallel to the center plane 51 can be, for example, from 0.5 ° to 3 °. The end faces 57 of the piston pin bosses 28 are the areas of the piston pin bosses 28 which are closest to the center plane 51. The piston pin receptacles 35 end at the end faces 57. In the exemplary embodiment, the end faces 57 each have a distance z from the central plane 51, which is perpendicular to the central plane 51 and parallel to the transverse axis 49 ( Fig. 3 ) is measured. The distance z is advantageously at least 5%, in particular at least 10% of the diameter a of the piston 5 ( Fig. 3 ). The piston pin bosses 28 are advantageously arranged symmetrically to the center plane 51, so that the same distance z results for both end faces 57. On the side facing away from the combustion chamber 3, the end faces 57 have an indentation 36 which extends as far as the piston pin receptacle 35 and at which the distance from the center plane 51 is increased. The indentation 36 is used to lubricate a piston pin bearing with which the piston pin on the connecting rod 6 ( Fig. 1 ) is stored.

Im Ausführungsbeispiel besitzen die Stirnseiten 57 der Kolbenbolzenaugen 28 jeweils einen Abstand e zu den Verbindungsrippen 55, der senkrecht zur Mittelebene 51 und parallel zur Querachse 49 (Fig. 3) gemessen ist. Der Abstand e beträgt vorteilhaft mindestens 5%, insbesondere mindestens 10% des Durchmessers a des Kolbens 5 (Fig. 3). Die Kolbenbolzenaugen 28 und die Verbindungsrippen 55 sind vorteilhaft symmetrisch zur Mittelebene 51 angeordnet, so dass sich auf beiden Seiten der Mittelebene 51 der gleiche Abstand e zwischen einer Stirnseite 57 und der auf der gleichen Seite der Mittelebene 51 angeordneten Verbindungsrippe 55 ergibt.In the exemplary embodiment, the end faces 57 of the piston pin bosses 28 each have a distance e from the connecting ribs 55, which is perpendicular to the center plane 51 and parallel to transverse axis 49 ( Fig. 3 ) is measured. The distance e is advantageously at least 5%, in particular at least 10% of the diameter a of the piston 5 ( Fig. 3 ). The piston pin bosses 28 and the connecting ribs 55 are advantageously arranged symmetrically to the central plane 51, so that the same distance e between an end face 57 and the connecting rib 55 arranged on the same side of the central plane 51 results on both sides of the central plane 51.

Der Kolben 5 besitzt die Einlassseite 46, die in der Darstellung in Fig. 4 oben angeordnet ist und an der die Ausnehmung 33 am Kolbenhemd 26 vorgesehen ist, sowie eine Auslassseite 47. Der Kolben 5 wird von einer Querebene 52 in die Einlassseite 46 und die Auslassseite 47 geteilt, die in Fig. 5 schematisch dargestellt ist. Die Querebene 52 wird von der Längsmittelachse 50 des Kolbens 5 sowie der Querachse 49 aufgespannt.The piston 5 has the inlet side 46, which is shown in FIG Fig. 4 is arranged at the top and on which the recess 33 is provided on the piston skirt 26, as well as an outlet side 47. The piston 5 is divided by a transverse plane 52 into the inlet side 46 and the outlet side 47, which are divided into Fig. 5 is shown schematically. The transverse plane 52 is spanned by the longitudinal center axis 50 of the piston 5 and the transverse axis 49.

Wie Fig. 4 zeigt, sind die Kolbenbolzenaugen 28 über Verbindungsrippen 55 mit dem Kolbenhemd 26 verbunden. Die Verbindungsrippen 55 erstrecken sich dabei an der Seite der Kolbenbolzenaugen 28, die der Ausnehmung 33 abgewandt liegt. Im Einbauzustand sind die Verbindungsrippen 55 an der dem Gemischeinlass 12 abgewandten, dem Auslass 23 zugewandten Seite des Zylinders 2 angeordnet (Fig. 1). Die Verbindungsrippen 55 sind auf der Auslassseite 47 des Kolbens 5 angeordnet. Wie Fig. 4 auch zeigt, ist auch an der dem Auslass 23 zugewandten Seite des Rands 31 des Kolbenhemds 26 eine Fase 39 ausgebildet.How Fig. 4 shows, the piston pin bosses 28 are connected to the piston skirt 26 via connecting ribs 55. The connecting ribs 55 extend on the side of the piston pin bosses 28 that faces away from the recess 33. In the installed state, the connecting ribs 55 are arranged on the side of the cylinder 2 facing away from the mixture inlet 12 and facing the outlet 23 ( Fig. 1 ). The connecting ribs 55 are arranged on the outlet side 47 of the piston 5. How Fig. 4 also shows, a bevel 39 is also formed on the side of the edge 31 of the piston skirt 26 facing the outlet 23.

Zwischen den Verbindungsrippen 55 und dem Kolbenhemd 26 ist jeweils eine Vertiefung 56 ausgebildet. Jede Vertiefung 56 erstreckt sich an der der Mittelebene 51 abgewandten Seite der Verbindungsrippe 55 zwischen der Verbindungsrippe 55 und dem Kolbenhemd 26. Der Abstand der Vertiefung 56 zur Mittelebene 51 ist größer als der Abstand der die Vertiefung 56 begrenzenden Verbindungsrippe 55 zur Mittelebene 51. Die Verbindungsrippen 55 besitzen zur Mittelebene 51 einen Abstand d. Der Abstand d kann dabei in unterschiedlichen Bereichen der Verbindungsrippe 55 variieren, beispielsweise wenn die Breite der Verbindungsrippe 55 nicht konstant ist. Bevorzugt ist im Anbindungsbereich an das Kolbenbolzenauge 28 und im Anbindungsbereich an das Kolbenhemd 26 eine größere Breite der Verbindungsrippe 55 vorgesehen. Der Abstand d ist vorteilhaft in einem mittleren Bereich der Verbindungsrippe 55 gemessen. Der Abstand d beträgt vorteilhaft mindestens 20%, insbesondere mindestens 25% des Durchmessers a des Kolbens 5. Besonders bevorzugt beträgt der Abstand d an jeder Stelle der Verbindungsrippe 55 mindestens 20%, insbesondere mindestens 25% des Durchmessers a des Kolbens 5. Wie Fig. 4 zeigt, verlaufen beide Verbindungsrippen 55 bezogen auf die Mittelebene 51 vorteilhaft spiegelsymmetrisch zueinander. Die Verbindungsrippen 55 verlaufen bevorzugt parallel zur Mittelebene 51.A recess 56 is formed between the connecting ribs 55 and the piston skirt 26. Each recess 56 extends on the side of the connecting rib 55 facing away from the central plane 51 between the connecting rib 55 and the piston skirt 26. The distance between the recess 56 and the central plane 51 is greater than the distance between the connecting rib 55 delimiting the recess 56 and the central plane 51. The connecting ribs 55 have a distance d from the central plane 51. The distance d can vary in different areas of the connecting rib 55, for example when the width of the connecting rib 55 is not constant. A greater width of the connecting rib 55 is preferably provided in the connection area to the piston pin boss 28 and in the connection area to the piston skirt 26. The distance d is advantageously measured in a central region of the connecting rib 55. The distance d is advantageously at least 20%, in particular at least 25% of the diameter a of the piston 5. The distance d is particularly preferably at least 20%, in particular at least 25% of the diameter a of the piston 5 at each point of the connecting rib 55 Fig. 4 shows, both connecting ribs 55 advantageously run mirror-symmetrically to one another in relation to the central plane 51. The connecting ribs 55 preferably run parallel to the center plane 51.

Wie Fig. 4 zeigt, verlaufen zwischen Kolbenboden 25 und Kolbenhemd 26 sowohl an der Einlassseite 46 als auch an der Auslassseite 47 Rippen 42 und 43. Die Rippen 42, 43 verbinden Kolbenhemd 26 und Kolbenboden 25 und liegen über ihre gesamte Länge unmittelbar am Kolbenhemd 26 bzw. am Kolbenboden 25 an. Sowohl an der Einlassseite 46 als auch an der Auslassseite 47 ist jeweils eine mittlere Rippe 43 vorgesehen, die entlang der Mittelebene 51 verläuft und mittig von der Mittelebene 51 geschnitten wird. Beidseitig der mittleren Rippe 43 sind seitliche Rippen 42 vorgesehen. Dabei ist an jeder Seite der mittleren Rippe 43 genau eine seitliche Rippe 42 angeordnet. Wie Fig. 4 auch zeigt, ist im Bereich zwischen den Kolbenbolzenaugen 28 am Kolbenboden 25 eine Anschlagfläche 38 ausgebildet. Die Anschlagfläche 38 dient zur definierten Positionierung des Kolbens 5 bei der Bearbeitung des Kolbenhemds 26.How Fig. 4 shows, ribs 42 and 43 run between the piston crown 25 and piston skirt 26 both on the inlet side 46 and on the outlet side 47. The ribs 42, 43 connect the piston skirt 26 and piston crown 25 and lie over their entire length directly on the piston skirt 26 or on the piston crown 25 at. A central rib 43 is provided both on the inlet side 46 and on the outlet side 47, which rib runs along the central plane 51 and is intersected centrally by the central plane 51. Lateral ribs 42 are provided on both sides of the central rib 43. Here, exactly one lateral rib 42 is arranged on each side of the central rib 43. How Fig. 4 also shows, a stop surface 38 is formed in the area between the piston pin bosses 28 on the piston head 25. The stop surface 38 is used for the defined positioning of the piston 5 when the piston skirt 26 is machined.

Wie die Schnittdarstellung in Fig. 5 zeigt, verbinden die Rippen 42 und 43 jeweils das Kolbenhemd 26 mit dem Kolbenboden 25. Die Rippen 42 und 43 an der Einlassseite 46 sind vorteilhaft bezogen auf die Querebene 52 symmetrisch zu den Rippen 42 und 43 an der Auslassseite 47 angeordnet. Die ins Innere des Kolbens 5 ragenden Stirnseiten 41 der Rippen 42 und 43 verlaufen vorteilhaft bogenförmig, nämlich konkav. Die Rippen 42 und 43 sind nicht unmittelbar miteinander verbunden. Die Rippen 42 und 43 besitzen auch zu den Kolbenbolzenaugen 28 einen Abstand. Zwischen den Rippen 42 und 43 und den Kolbenbolzenaugen 28 besteht demnach keine direkte Verbindung. Die Rippen 42 und 43 sind getrennt von den Kolbenbolzenaugen 28 ausgebildet. Auch die Verbindungsrippe 55 ist nicht unmittelbar mit den Rippen 42 und 43 verbunden. Wie Fig. 5 zeigt, liegen die Verbindungsrippen 55 in Verlängerung der Rückwand 58 der Kolbentasche 14. Wie Fig. 5 auch zeigt, besitzen die Kolbenbolzenaugen 28 jeweils zwei Seitenflächen 60, die mit geringer Auszugsschräge näherungsweise parallel zur Querebene 52 des Kolbens 5 verlaufen. An den Seitenflächen 60 kann der Kolben 5 zur Bearbeitung des Kolbenhemds 26 aufgespannt werden.Like the sectional view in Fig. 5 shows, the ribs 42 and 43 each connect the piston skirt 26 to the piston crown 25. The ribs 42 and 43 on the inlet side 46 are advantageously arranged symmetrically to the ribs 42 and 43 on the outlet side 47 with respect to the transverse plane 52. The end faces 41 of the ribs 42 and 43 protruding into the interior of the piston 5 are advantageously arcuate, namely concave. The ribs 42 and 43 are not directly connected to one another. The ribs 42 and 43 are also at a distance from the piston pin bosses 28. Between the ribs 42 and 43 and the piston pin bosses 28 therefore have no direct connection. The ribs 42 and 43 are formed separately from the piston pin bosses 28. The connecting rib 55 is not directly connected to the ribs 42 and 43 either. How Fig. 5 shows, the connecting ribs 55 are in extension of the rear wall 58 of the piston pocket 14. How Fig. 5 also shows, the piston pin bosses 28 each have two side surfaces 60 which run approximately parallel to the transverse plane 52 of the piston 5 with a slight extension slope. The piston 5 can be clamped on the side surfaces 60 for machining the piston skirt 26.

Wie Fig. 6 zeigt, besitzen die Verbindungsrippen 55 eine der Oberseite 40 des Kolbens 5 abgewandte Stirnseite 59 der Verbindungsrippe 55. Die Stirnseiten 59 sind auch in Fig. 4 gezeigt. Die Stirnseite 59 der Verbindungsrippe 55 ist dem Kurbelgehäuse 4 im Einbauzustand zugewandt. Die Vertiefung 56 besitzt eine maximale Tiefe c, die parallel zur Längsmittelachse 50 bis zu der Stirnseite 59 der Verbindungsrippe 55 gemessen ist. Die maximale Tiefe c beträgt vorteilhaft mindestens 3%, insbesondere mindestens 5% der Höhe h des Kolbens 5. Die maximale Tiefe c beträgt vorteilhaft weniger als 20%, insbesondere weniger als 10% der Höhe h des Kolbens 5. In besonders vorteilhafter Gestaltung beträgt die Tiefe der Vertiefung 56 an jeder Stelle der Vertiefung 56 mindestens 3%, insbesondere mindestens 5% der Höhe h des Kolbens 5. In besonders vorteilhafter Gestaltung beträgt die Tiefe der Vertiefung 56 an jeder Stelle der Vertiefung 56 weniger als 20%, insbesondere weniger als 10% der Höhe h des Kolbens 5. Die Stirnseite 59 besitzt gegenüber dem Rand 31 einen parallel zur Längsmittelachse 50 gemessenen Versatz b. Der Versatz b beträgt vorteilhaft weniger als 5%, insbesondere weniger als 3% der Höhe h des Kolbens 5. Der Versatz b kann auch null betragen. Besonders vorteilhaft ist ein Versatz b von mehr als 1% der Höhe h des Kolbens 5 vorgesehen. Die Stirnseite 59 ist vorteilhaft näher an der Oberseite 40 des Kolbens 5 angeordnet als der Rand 31 im Bereich der Vertiefung 56. Die maximale Tiefe c ist vorteilhaft deutlich größer als der Versatz b. Vorteilhaft beträgt die maximale Tiefe c mindestens das Doppelte des Versatzes b. Der Steg 32 besitzt in dem die Vertiefung 56 begrenzenden Bereich eine parallel zur Längsmittelachse 50 gemessene Höhe m, die größer als die in Fig. 3 gezeigte kleinste Höhe k des Stegs 32 ist. Die Höhe m beträgt vorteilhaft mindestens das 1,5fache der Höhe k.How Fig. 6 shows, the connecting ribs 55 have an end face 59 of the connecting rib 55 facing away from the upper side 40 of the piston 5. The end faces 59 are also shown in FIG Fig. 4 shown. The end face 59 of the connecting rib 55 faces the crankcase 4 in the installed state. The recess 56 has a maximum depth c, which is measured parallel to the longitudinal center axis 50 as far as the end face 59 of the connecting rib 55. The maximum depth c is advantageously at least 3%, in particular at least 5% of the height h of the piston 5. The maximum depth c is advantageously less than 20%, in particular less than 10% of the height h of the piston 5. In a particularly advantageous embodiment, the Depth of recess 56 at each point of recess 56 is at least 3%, in particular at least 5% of the height h of piston 5. In a particularly advantageous design, the depth of recess 56 at each point of recess 56 is less than 20%, in particular less than 10 % of the height h of the piston 5. The end face 59 has an offset b measured parallel to the longitudinal center axis 50 with respect to the edge 31. The offset b is advantageously less than 5%, in particular less than 3% of the height h of the piston 5. The offset b can also be zero. An offset b of more than 1% of the height h of the piston 5 is particularly advantageous. The end face 59 is advantageously arranged closer to the upper side 40 of the piston 5 than the edge 31 in the region of the recess 56. The maximum depth c is advantageously significantly greater than the offset b. The maximum depth c is advantageously at least twice the offset b. In the region delimiting the recess 56, the web 32 has a height m measured parallel to the longitudinal center axis 50, which larger than the in Fig. 3 The smallest height k of the web 32 is shown. The height m is advantageously at least 1.5 times the height k.

Die Vertiefung 56 besitzt einen Boden 61, der der Bereich der Vertiefung 56 ist, der den geringsten Abstand zur Oberseite 40 des Kolbens 5 besitzt. Der Boden 61 der Vertiefung 56 besitzt zum Boden 40 des Kolbens 5 einen parallel zur Längsmittelachse 50 gemessenen Abstand f, der vorteilhaft mehr als 50%, insbesondere mehr als 60% der Höhe h des Kolbens 5 beträgt. Der Abstand f beträgt vorteilhaft weniger als 90% der Höhe h des Kolbens 5.The recess 56 has a bottom 61, which is the region of the recess 56 which is at the smallest distance from the top 40 of the piston 5. The base 61 of the recess 56 has a distance f from the base 40 of the piston 5, measured parallel to the longitudinal center axis 50, which is advantageously more than 50%, in particular more than 60% of the height h of the piston 5. The distance f is advantageously less than 90% of the height h of the piston 5.

Die Rückwand 58 der Kolbentasche 14 besitzt eine Wandstärke y zwischen der Kolbentasche 14 und dem zwischen den Rückwänden 58 der Kolbentaschen 14 liegenden Innenraum des Kolbens 5. In dem Bereich zwischen der Vertiefung 56 und der Kolbentasche 14 besitzt die Rückwand 58 eine verringerte Wandstärke x. Die verringerte Wandstärke x beträgt vorteilhaft höchstens 80%, insbesondere höchstens 60% der Wandstärke y. Die Wandstärke x darf für eine ausreichende Stabilität der Rückwand 58 ein Mindestmaß nicht unterschreiten. Dieses Mindestmaß, das vom Material und der Geometrie des Kolbens 5 abhängt, bestimmt die maximal mögliche Tiefe c der Vertiefung 56.The rear wall 58 of the piston pocket 14 has a wall thickness y between the piston pocket 14 and the interior of the piston 5 located between the rear walls 58 of the piston pockets 14. In the area between the recess 56 and the piston pocket 14, the rear wall 58 has a reduced wall thickness x. The reduced wall thickness x is advantageously at most 80%, in particular at most 60% of the wall thickness y. The wall thickness x must not be less than a minimum for sufficient stability of the rear wall 58. This minimum dimension, which depends on the material and the geometry of the piston 5, determines the maximum possible depth c of the recess 56.

Wie Fig. 6 auch zeigt, besitzt die mittlere Rippe 43 ein der Oberseite 40 des Kolbens 5 abgewandtes Ende 45. Das Ende 45 besitzt zur Oberseite 40 einen Abstand g. Der Abstand g beträgt vorteilhaft etwa 30% bis etwa 60% der Höhe h des Kolbens 5. Der Abstand g ist vorteilhaft kleiner als der Abstand f des Bodens 61 der Vertiefung 56 zur Oberseite 40 des Kolbens 5. Der Abstand g beträgt vorteilhaft weniger als 90%, insbesondere weniger als 80% des Abstands f.How Fig. 6 also shows, the middle rib 43 has an end 45 facing away from the top 40 of the piston 5. The end 45 is at a distance g from the top 40. The distance g is advantageously about 30% to about 60% of the height h of the piston 5. The distance g is advantageously smaller than the distance f from the bottom 61 of the recess 56 to the top 40 of the piston 5. The distance g is advantageously less than 90 %, in particular less than 80% of the distance f.

Die auf den gegenüberliegenden Seiten der Mittelebene 51 angeordneten Verbindungsrippen 55 besitzen zueinander einen Abstand n, der senkrecht zur Mittelebene 51 gemessen ist. Der Abstand n beträgt vorteilhaft mindestens 40%, insbesondere mindestens 50% des Durchmessers a des Kolbens 5. Die Stirnseiten 57 der Kolbenbolzenaugen 28 besitzen zueinander einen Abstand s. Der Abstand s beträgt vorteilhaft mindestens 10%, insbesondere mindestens 20% des Durchmessers a des Kolbens 5. Der Abstand s ist deutlich kleiner als der Abstand n der Verbindungsrippen 55. Der Abstand s beträgt vorteilhaft weniger als 70% des Abstands n. Die Verbindungsrippen 55 sind gegenüber den Stirnseiten 57 radial nach außen versetzt. Die Kolbenbolzenaugen 28 besitzen eine von den Stirnseiten 57 zum Kolbenhemd 26 und senkrecht zur Mittelebene 51 gemessene Breite w, die vorteilhaft mindestens 15%, insbesondere mindestens 20% des Durchmessers a des Kolbens beträgt.The connecting ribs 55 arranged on the opposite sides of the central plane 51 have a spacing n from one another, which is measured perpendicular to the central plane 51. The distance n is advantageously at least 40%, in particular at least 50% of the diameter a of the piston 5. The end faces 57 of the piston pin bosses 28 are at a distance s from one another. The distance s is advantageously at least 10%, in particular at least 20% of the diameter a of the piston 5. The distance s is significantly smaller than the distance n of the connecting ribs 55. The distance s is advantageously less than 70% of the distance n are offset radially outward with respect to the end faces 57. The piston pin bosses 28 have a width w measured from the end faces 57 to the piston skirt 26 and perpendicular to the central plane 51, which is advantageously at least 15%, in particular at least 20% of the diameter a of the piston.

Wie Fig. 7 zeigt, besitzt das Ende 45 der mittleren Rippe 43 in der gezeigten Seitenansicht einen parallel zur Längsmittelachse 50 gemessenen Abstand u zur Querachse 49. Im Ausführungsbeispiel ist das Ende 45 weiter von der Oberseite 40 entfernt als die Querachse 49. Es kann jedoch auch vorgesehen sein, dass das Ende 45 näher an der Oberseite 40 angeordnet ist als die Querachse 49. Der Abstand u beträgt vorteilhaft weniger als 10% der Höhe h des Kolbens 5.How Fig. 7 shows, the end 45 of the central rib 43 in the side view shown has a distance u to the transverse axis 49, measured parallel to the longitudinal center axis 50. In the exemplary embodiment, the end 45 is further away from the upper side 40 than the transverse axis 49. However, it can also be provided that the end 45 is arranged closer to the upper side 40 than the transverse axis 49. The distance u is advantageously less than 10% of the height h of the piston 5.

Die seitlichen Rippen 42 besitzen ein der Oberseite 40 abgewandtes Ende 44, das zur Oberseite 40 einen parallel zur Längsmittelachse 50 gemessenen Abstand o besitzt. Der Abstand o ist kleiner als der Abstand g zwischen dem Ende 45 der mittleren Rippe 43 und der Oberseite 40 des Kolbens 5 (Fig. 6). Das Ende 44 besitzt in der gezeigten Seitenansicht zur Querachse 49 einen Abstand v, der deutlich größer als der Abstand u des Endes 45 zur Querachse 49 ist. Der Abstand v beträgt vorteilhaft 5% bis 20% der Höhe h des Kolbens 5. Wie Fig. 7 auch zeigt, besitzt die obere Steuerkante 29 der Kolbentaschen 14 zur Oberseite 40 einen Abstand t, der vorteilhaft 30% bis 60% der Höhe h des Kolbens 5 beträgt. Das Ende 44 liegt etwa auf der Höhe der Steuerkante 29.The lateral ribs 42 have an end 44 facing away from the upper side 40, which has a distance o from the upper side 40 measured parallel to the longitudinal center axis 50. The distance o is smaller than the distance g between the end 45 of the central rib 43 and the top 40 of the piston 5 ( Fig. 6 ). In the side view shown, the end 44 has a distance v from the transverse axis 49, which is significantly greater than the distance u from the end 45 to the transverse axis 49. The distance v is advantageously 5% to 20% of the height h of the piston 5. How Fig. 7 also shows, the upper control edge 29 of the piston pockets 14 has a distance t from the upper side 40 which is advantageously 30% to 60% of the height h of the piston 5. The end 44 is approximately level with the control edge 29.

Die Vertiefung 56 besitzt eine parallel zur Querachse 49 gemessene Breite r, die vorteilhaft weniger als 10% des Durchmessers a des Kolbens 5 beträgt. Der Boden 61 besitzt zum Rand 31 in dem die Vertiefung 56 begrenzenden Bereich einen parallel zur Längsmittelachse 50 gemessenen Abstand p. Der Abstand p ist im Ausführungsbeispiel größer als die Höhe m des Stegs 32 in diesem Bereich. Die Höhe m des Stegs 32 beträgt vorteilhaft 70% bis 95% des Abstands p. Die Breite r der Vertiefung 56 kann näherungsweise der maximalen Tiefe c der Vertiefung 56 entsprechen. Bevorzugt beträgt die Breite r 60% bis 120% der maximalen Tiefe c der Vertiefung 56 (Fig. 6).The recess 56 has a width r measured parallel to the transverse axis 49, which is advantageously less than 10% of the diameter a of the piston 5. The bottom 61 has a parallel to the edge 31 in the region delimiting the recess 56 Longitudinal central axis 50 measured distance p. In the exemplary embodiment, the distance p is greater than the height m of the web 32 in this area. The height m of the web 32 is advantageously 70% to 95% of the distance p. The width r of the recess 56 can approximately correspond to the maximum depth c of the recess 56. The width r is preferably 60% to 120% of the maximum depth c of the recess 56 ( Fig. 6 ).

Fig. 8 zeigt in schematischer Darstellung ein Ausführungsbeispiel für einen Kolben 5. Gleiche Bezugszeichen bezeichnen dabei in allen Figuren einander entsprechende Elemente. Der in Fig. 8 gezeigte Kolben 5 besitzt auf der Einlassseite 46 zwei Verbindungsrippen 55, die jeweils zwischen einem Kolbenbolzenauge 28 und dem Kolbenhemd 26 verlaufen und die eine Vertiefung 56 begrenzen. Die Verbindungsrippen 55 und die Vertiefungen 56 sind wie zum vorangegangenen Ausführungsbeispiel beschrieben ausgebildet. Auf der Auslassseite 47 sind Verbindungsrippen 55' vorgesehen, die jeweils ein Kolbenbolzenauge 28 mit dem Kolbenhemd 26 verbinden. Die Verbindungsrippen 55' sind entsprechend zu den Verbindungsrippen 55 ausgebildet. Zwischen den Verbindungsrippen 55' und dem Kolbenhemd 26 ist jeweils auf der der Mittelebene 51 abgewandten Seite eine Vertiefung 56' angeordnet. Die Vertiefungen 56' sind entsprechend zu den Vertiefungen 56 ausgebildet. Die Verbindungsrippen 55 und die Verbindungsrippen 55' sind vorteilhaft bezüglich der Querebene 52 spiegelsymmetrisch angeordnet und ausgebildet. Auch die Vertiefungen 56' können spiegelsymmetrisch zu den Vertiefungen 56 ausgebildet sein. Es kann jedoch auch vorgesehen sein, dass die Vertiefungen 56' in Tiefe und/oder Form von den Vertiefungen 56 abweichen. Dies kann sich insbesondere durch eine zu der Querebene 52 unsymmetrische Form der Kolbentaschen 14 ergeben. Die Verbindungsrippen 55' und die Vertiefungen 56' können wie in Fig. 8 gezeigt zusätzlich zu den Verbindungsrippen 55 und den Vertiefungen 56 vorgesehen sein. Es kann jedoch auch vorgesehen sein, dass nur auf der Auslassseite 47 des Kolbens 5 Verbindungsrippen 55' und Vertiefungen 56' angeordnet sind und auf der Einlassseite 46 keine Verbindungsrippen 55 und Vertiefungen 56 angeordnet sind. Fig. 8 shows a schematic illustration of an exemplary embodiment for a piston 5. The same reference symbols denote elements that correspond to one another in all figures. The in Fig. 8 The piston 5 shown has two connecting ribs 55 on the inlet side 46, each of which runs between a piston pin boss 28 and the piston skirt 26 and which delimit a recess 56. The connecting ribs 55 and the depressions 56 are designed as described for the previous embodiment. Connecting ribs 55 ′ are provided on outlet side 47, each connecting a piston pin boss 28 to piston skirt 26. The connecting ribs 55 ′ are designed corresponding to the connecting ribs 55. Between the connecting ribs 55 'and the piston skirt 26, a recess 56' is arranged in each case on the side facing away from the central plane 51. The depressions 56 ′ are designed corresponding to the depressions 56. The connecting ribs 55 and the connecting ribs 55 'are advantageously arranged and designed mirror-symmetrically with respect to the transverse plane 52. The depressions 56 ′ can also be configured mirror-symmetrically to the depressions 56. However, it can also be provided that the depressions 56 ′ differ in depth and / or shape from the depressions 56. This can result in particular from a shape of the piston pockets 14 which is asymmetrical to the transverse plane 52. The connecting ribs 55 'and the recesses 56' can as in FIG Fig. 8 shown in addition to the connecting ribs 55 and the recesses 56 may be provided. However, it can also be provided that connecting ribs 55 'and depressions 56' are arranged only on the outlet side 47 of the piston 5 and that no connecting ribs 55 and depressions 56 are arranged on the inlet side 46.

Der Kolben 5, 5' besteht aus Leichtmetall, insbesondere aus Magnesium. Auch eine Ausbildung aus Aluminium kann vorteilhaft sein. Durch die Vertiefungen 56, 56' wird eine Materialanhäufung zwischen der Verbindungsrippe 55, 55' und dem Kolbenhemd 26 vermieden, so dass der Kolben 5 gut in einem Gussverfahren aus Leichtmetall, insbesondere aus Magnesium, hergestellt werden kann.The piston 5, 5 'consists of light metal, in particular magnesium. A design made of aluminum can also be advantageous. The depressions 56, 56 'prevent an accumulation of material between the connecting rib 55, 55' and the piston skirt 26, so that the piston 5 can easily be produced in a casting process from light metal, in particular from magnesium.

Claims (13)

  1. Piston for a two-stroke engine working with forward scavenging, wherein the piston (5) has a piston crown (25) and a piston skirt (26), wherein the central axis of the piston skirt (26) forms a longitudinal central axis (50) of the piston (5), wherein the piston (5) has two piston bosses (28), in which piston pin receptacles (35) are formed, wherein the central axis of the piston pin receptacles forms a transverse axis (49) of the piston (5), wherein the piston (5) has a central plane (51), which contains the longitudinal central axis (50) of the piston (5) and extends perpendicularly to the transverse axis (49) of the piston (5), wherein the piston (5) has at least one piston pocket (14), wherein at least one piston boss (28) is joined to the piston skirt (26) by way of at least one connecting rib (55, 55'), wherein the connecting rib (55, 55') extends on the side of the piston pocket (14) which is averted from the piston crown (25),
    characterised in that a recess (56, 56') is formed between the connecting rib (55, 55') and the piston skirt (26).
  2. Piston according to claim 1,
    characterised in that the depth (c) of the recess (56, 56') is at least 3% of the height (h) of the piston (5).
  3. Piston according to claim 1 or 2,
    characterised in that the connecting rib (55, 55') extends parallel to the central plane (51).
  4. Piston according to any of claims 1 to 3,
    characterised in that the distance of the connecting rib (55, 55') from the central plane (51) as measured perpendicularly to the central plane (51) is at least 20% of the diameter (a) of the piston (5).
  5. Piston according to any of claims 1 to 4,
    characterised in that the piston bosses (28) have end faces (57) facing each other and the connecting rib (55, 55') has from the end face (57) of the associated piston boss (28) a distance (e) of at least 5% of the diameter (a) of the piston (5) as measured parallel to the transverse axis (49).
  6. Piston according to any of claims 1 to 5,
    characterised in that the piston pocket (14) has a rear wall (58) and the connecting rib (55, 55') is arranged in extension of the rear wall (58) of the piston pocket (14).
  7. Piston according to any of claims 1 to 6,
    characterised in that the piston skirt (26) has an edge (31) averted from the piston crown (25).
  8. Piston according to claim 7,
    characterised in that the connecting rib (55, 55') has an end face (59) averted from the piston crown (25) and in that the offset (b) between the end face (59) of the connecting rib (55, 55') and the edge (31) in the direction of the longitudinal central axis (50) of the piston (5) at any point of the end face (59) is less than 5% of the height (h) of the piston (5).
  9. Piston according to claim 7 or 8,
    characterised in that a web (32) of the piston skirt (26) extending between the edge (31) and the piston pocket (14), the web (32) having in the circumferential region of the piston (5), where the recess (56, 56') is located, a height (m) which is at least 1.5 times the minimum height (k) of the web (32).
  10. Piston according to any of claims 1 to 9,
    characterised in that the piston pin receptacle (35) is a least partially located in the piston pocket (25).
  11. Piston according to any of claims 1 to 10,
    characterised in that the piston (5) has two piston pockets (14) on opposite sides of the central plane (51) and a connecting rib (55, 55') is located at each of the two piston bosses (28).
  12. Piston according to any of claims 1 to 11,
    characterised in that the piston (5) consists of light metal.
  13. Two-stroke engine with a piston according to any of claims 1 to 12, wherein the two-stroke engine (1) has a cylinder (2), in the cylinder bore (15) of which a combustion chamber (3) bounded by the piston (5) is formed, wherein the piston (5) drives a crankshaft (7) rotatably mounted in a crankcase (4), wherein the two-stroke engine (1) has at least one transfer port (13), which in at least one position of the piston (5) connects a crankcase interior (16) of the crankcase (4) to the combustion chamber (3), and wherein the two-stroke engine (1) has an air duct (9) for feeding in forward scavenging air, which air duct (9) terminates at the cylinder bore (15) with an air inlet (11), wherein the piston pocket (14) in at least one position of the piston (5) at least partially overlaps the air inlet (11) and a transfer window (17) of the transfer port (13).
EP16001824.8A 2016-08-19 2016-08-19 Piston for a two-stroke engine working with direct injection and two-stroke engine Active EP3284938B1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP16001824.8A EP3284938B1 (en) 2016-08-19 2016-08-19 Piston for a two-stroke engine working with direct injection and two-stroke engine
CN201710712798.6A CN107762656B (en) 2016-08-19 2017-08-18 Piston for a two-stroke motor operating with a purging pre-stored quantity, and two-stroke motor
US15/682,343 US10344707B2 (en) 2016-08-19 2017-08-21 Piston for a two-stroke engine operating with advanced scavenging and a two-stroke engine

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP16001824.8A EP3284938B1 (en) 2016-08-19 2016-08-19 Piston for a two-stroke engine working with direct injection and two-stroke engine

Publications (2)

Publication Number Publication Date
EP3284938A1 EP3284938A1 (en) 2018-02-21
EP3284938B1 true EP3284938B1 (en) 2020-10-07

Family

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EP16001824.8A Active EP3284938B1 (en) 2016-08-19 2016-08-19 Piston for a two-stroke engine working with direct injection and two-stroke engine

Country Status (3)

Country Link
US (1) US10344707B2 (en)
EP (1) EP3284938B1 (en)
CN (1) CN107762656B (en)

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CN115190941A (en) * 2020-03-02 2022-10-14 Tvs电机股份有限公司 Reciprocating assembly for internal combustion engine
CN114017192A (en) * 2021-11-08 2022-02-08 博罗县标洁精工五金有限公司 Motor vehicle piston with strong tensile strength at normal temperature

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Also Published As

Publication number Publication date
CN107762656B (en) 2021-06-29
CN107762656A (en) 2018-03-06
US10344707B2 (en) 2019-07-09
EP3284938A1 (en) 2018-02-21
US20180051649A1 (en) 2018-02-22

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