Piston for a two-stroke engine working with advanced scavenging and a two-stroke engine

Patent metadata

Field	Value
Publication number	US-10240558-B2
Application number	US-201715682357-A
Country	US
Kind code	B2
Filing date	Aug 21, 2017
Priority date	Aug 19, 2016
Publication date	Mar 26, 2019
Grant date	Mar 26, 2019

Abstract

A piston for a two-stroke engine operating with advanced scavenging has a piston base and a piston skirt. The piston has a piston pocket which has a smallest distance (e) from a top side of the piston base. The piston has a section plane perpendicularly to the longitudinal center axis of the piston, the distance of which section plane from the top side of the piston base is greater than the smallest distance (e). A middle plane of the piston intersects the piston skirt at a location. In the circumferential direction between the pocket and this location, a thickened area is arranged in the section plane, the greatest wall thickness of which area is at least 1.1 times the wall thickness at the location. The piston has an edge at a recess at which the piston skirt has a reduced height. A chamfer is arranged on the radially outer side of the piston.

First claim

What is claimed is:

1. A piston for a two-stroke engine operating with advanced scavenging, the piston comprising:
a piston base having a top side;
a piston skirt defining a first center axis;
said first center axis forming a longitudinal center axis of the piston;
the piston having two piston pin eyelets defining a second center axis;
said second center axis defining a transverse axis;
the piston defining a middle plane containing said longitudinal center axis of the piston;
said middle plane being perpendicular to said transverse axis;
the piston having at least one piston pocket arranged completely on a first side of said middle plane;
said piston pocket and said top side of said piston base mutually defining a smallest distance (e) therebetween;
the piston having a section plane perpendicular to said longitudinal center axis;
said section plane and said top side of said piston base mutually defining a distance (m) therebetween;
said distance (m) being greater than said smallest distance (e);
said piston skirt having a location at which said middle plane intersects said piston skirt in said section plane;
said piston skirt having a wall thickness (b) at said location;
the piston defining a circumferential direction;
a thickened region arranged in said section plane between said pocket and said location in said circumferential direction;
said thickened region having a wall thickness (a); and,
said wall thickness (a) being at least 1.1 times said wall thickness (b) at said location.

2. The piston of claim 1 , wherein:
said at least one piston pocket includes a first piston pocket and a second piston pocket;
said thickened region is a first thickened region;
said first piston pocket and said second piston pocket are arranged on opposite sides of said middle plane;
said first thickened region extends from said first piston pocket to said location; and,
the piston has a second thickened region extending from said second piston pocket to said location.

3. The piston of claim 2 , wherein said piston skirt has an edge facing away from said piston base.

4. The piston of claim 3 , wherein:
said edge defines a recess between said first piston pocket and said second piston pocket;
said piston skirt having a reduced height (i) at said recess; and,
said first thickened region and said second thickened region conjointly at least partially overlap said recess.

5. The piston of claim 4 , wherein said edge has a chamfer at said recess at a radially outwardly lying side of the piston.

6. The piston of claim 4 , wherein:
said recess has a transition region in which said recess transitions into an adjacent region of said piston skirt;
said adjacent region is adjacent to said recess in said circumferential direction; and,
the piston has a height which increases by at least 5% in said transition region.

7. The piston of claim 3 , wherein each of said first thickened region and said second thickened region extends up to said edge.

8. The piston of claim 1 , wherein said piston skirt has an inner contour which runs straight in said thickened region in said section plane.

9. The piston of claim 1 , wherein said thickened region extends over at least 50% of a height of the piston measured parallel to said longitudinal center axis.

10. The piston of claim 1 further comprising:
at least one rib connecting said piston skirt and said piston base; and,
at least one of said at least one ribs adjoins said thickened region radially within said thickened region.

11. The piston of claim 1 , wherein the piston is made of a light metal.

12. The piston of claim 1 , wherein the piston is made of magnesium.

13. A two-stroke engine comprising:
a cylinder having a cylinder bore;
a combustion chamber formed in said cylinder bore;
a piston having a piston base and a piston skirt;
said combustion chamber being delimited by said piston;
a crankcase defining a crankcase interior;
a crankshaft rotatably mounted in said crankcase;
said piston being configured to drive said crankshaft;
a transfer channel having a transfer window and being configured to connect said crankcase interior to said combustion chamber in at least one position of said piston;
an air channel configured to supply scavenging air;
said air channel opening at said cylinder bore via an air inlet;
said piston including a piston base having a top side and a piston skirt defining a first center axis;
said first center axis forming a longitudinal center axis of said piston;
said piston having two piston pin eyelets defining a second center axis;
said second center axis defining a transverse axis;
said piston defining a middle plane containing said longitudinal center axis of said piston;
said middle plane being perpendicular to said transverse axis;
said piston having at least one piston pocket arranged entirely on a first side of said middle plane;
said at least one piston pocket being configured to be at least partially overlapping with said air inlet and said transfer window in at least one position of said piston;
said piston pocket and said top side of said piston base mutually defining a smallest distance (e) therebetween;
said piston having a section plane perpendicular to said longitudinal center axis;
said section plane and said top side of said piston base mutually defining a distance (m) therebetween;
said distance (m) being greater than said smallest distance (e);
said piston skirt having a location at which said middle plane intersects said piston skirt in said section plane;
said piston skirt having a wall thickness (b) at said location;
said piston defining a circumferential direction;
a thickened region arranged in said section plane between said pocket and said location in said circumferential direction;
said thickened region having a wall thickness (a); and,
said wall thickness (a) being at least 1.1 times said wall thickness (b) at said location.

14. A piston for a two-stroke engine operating with advanced scavenging, the piston comprising:
a piston base having a top side;
a piston skirt defining a first center axis;
said first center axis forming a longitudinal center axis of the piston;
the piston having two piston pin eyelets defining a second center axis;
said second center axis defining a transverse axis;
the piston defining a middle plane containing said longitudinal center axis of the piston;
said middle plane being perpendicular to said transverse axis;
the piston having two piston pockets arranged on opposite sides of said middle plane;
said piston skirt having an edge facing away from said piston base;
the piston defining a circumferential direction;
said edge defining a recess between said two piston pockets;
said piston skirt having a reduced height (I) at said recess; and,
said edge having a chamfer at said recess at a radially outer side of the piston.

15. A two-stroke engine comprising:
a piston having a piston base and a piston skirt;
a cylinder having a cylinder bore;
a combustion chamber formed in said cylinder bore and delimited by said piston;
a crankcase;
a crankshaft rotatably mounted in said crankcase;
a connecting rod having a connecting rod eye;
said piston being configured to drive said crankshaft via said connecting rod;
said connecting rod being mounted on said crankshaft via said connecting rod eye;
said piston base having a top side;
said piston skirt defining a first center axis;
said first center axis forming a longitudinal center axis of said piston;
said piston having two piston pin eyelets defining a second

Assignees

• Stihl Ag & Co Kg Andreas

Inventors

• Loew Birger
• Lank Jonas

Classifications

• F02F3/24 Primary

  having means for guiding gases in cylinders, e.g. for guiding scavenging charge in two-stroke engines · CPC title

• F02F3/00 Primary

  Pistons · CPC title

• F02B2075/025

  two · CPC title

• F02F3/0076

  the inside of the pistons being provided with ribs or fins · CPC title