GB2276221A - Piston for a two-stroke engine - Google Patents

Piston for a two-stroke engine Download PDF

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Publication number
GB2276221A
GB2276221A GB9305673A GB9305673A GB2276221A GB 2276221 A GB2276221 A GB 2276221A GB 9305673 A GB9305673 A GB 9305673A GB 9305673 A GB9305673 A GB 9305673A GB 2276221 A GB2276221 A GB 2276221A
Authority
GB
United Kingdom
Prior art keywords
piston
crown
skirt
port
stroke engine
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.)
Granted
Application number
GB9305673A
Other versions
GB2276221B (en
GB9305673D0 (en
Inventor
Roger Harvey Slee
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.)
Federal Mogul Technology Ltd
Original Assignee
T&N Technology Ltd
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 T&N Technology Ltd filed Critical T&N Technology Ltd
Priority to GB9305673A priority Critical patent/GB2276221B/en
Publication of GB9305673D0 publication Critical patent/GB9305673D0/en
Publication of GB2276221A publication Critical patent/GB2276221A/en
Application granted granted Critical
Publication of GB2276221B publication Critical patent/GB2276221B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

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 
    • F02F3/16—Pistons  having cooling means
    • F02F3/20—Pistons  having cooling means the means being a fluid flowing through or along piston
    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
    • F05C—INDEXING SCHEME RELATING TO MATERIALS, MATERIAL PROPERTIES OR MATERIAL CHARACTERISTICS FOR MACHINES, ENGINES OR PUMPS OTHER THAN NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES
    • F05C2201/00—Metals
    • F05C2201/04—Heavy metals
    • F05C2201/0433—Iron group; Ferrous alloys, e.g. steel
    • F05C2201/0448—Steel

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Pistons, Piston Rings, And Cylinders (AREA)

Abstract

A piston (10) for a two-stroke engine has a hollow cylindrical skirt (26). The skirt (26) defines a port (34) adjacent to a crown (12) of the piston. Gases can enter the skirt (26) through an open end thereof remote from the crown (12) and leave through the port (34). A flow deflector (36) is mounted within the skirt (26) and constrains the gas to impinge on an edge area of the underside of said crown (12) to cool said area. <IMAGE>

Description

PISTON FOR A TWO-STROKE ENGINE This invention is concerned with a piston for a twostroke engine.
In an orthodox two-stroke engine, a piston, which comprises a crown and a skirt depending from the crown, reciprocates in a cylinder bore which has ports formed in its wall. These ports comprises a number of scavenge ports through which fuel charge enters the bore and an exhaust port through which exhaust gases leave the bore. The underside of the piston is used as a compressor to drive fuel charge gases from the crankcase through the scavenge ports into the bore above the piston.
The piston of an orthodox two-stroke engine experiences an asymmetric cooling effect during its cycle.
Relatively cool gases entering the bore through the scavenge ports cool those parts of the piston which are adjacent to these ports, whereas hot exhaust gases travelling towards the exhaust port heat the part of the piston which is adjacent to that port. This asymmetric cooling effect causes parts of the piston to run hotter than other parts so that thermal expansion causes the piston to alter its shape as it warms up during operation.
This shape alteration has to be compensated for during manufacture of the piston if seizure of the piston is to be avoided.
It is known to arrange for fuel charge to enter the open bottom end of the skirt of a piston, and to pass out of the piston through ports defined by the skirt and located high up on the piston i.e. adjacent to the crown.
These ports communicate with ports in the bore wall which communicate with the bore above the piston. Thus, a flow of relatively cool charge gases passes upwardly within the skirt and has a cooling effect thereon. However, while such an arrangement produces a slight reduction in the temperature of the centre of the crown of the piston and provides cooling for the bearing of the small end of the connecting rod, it also tends to further cool areas of the piston which are already subject to scavenge cooling and thereby increases the asymmetry of the cooling effect.
It is an object of the present invention to provide a piston for a two-stroke engine which has reduced asymmetric cooling.
The invention provides a piston for a two-stroke engine comprising a crown, and a skirt depending from said crown, the skirt being hollow and open at an end thereof remote from the crown, the skirt also defining at least one port adjacent to the crown arranged so that gases entering the skirt through the open end thereof can pass out through said port, wherein at least one flow deflector is mounted within said skirt and is arranged to constrain gas flowing between said open end and said port to impinge on an edge area of the underside of said crown.
The flow deflector of the invention enables the relatively cool charge gases to be directed against the edge area of the crown which is subjected to the most heating or least cooling from other causes. This area is most likely to be an area which, in the operation of the piston, is adjacent to an exhaust port.
Preferably, the flow deflector constrains the gas to flow parallel to the crown from said edge area of the crown to said port. This arrangement enhances cooling of the crown generally.
Preferably, the flow deflector is mounted on bosses of the skirt which support a gudgeon pin which connects the piston to a connecting rod. The flow deflector can, for example, be staked to said bosses. If necessary, the flow deflector can be given an arch-shape so that it clears the gudgeon pin and the small end of the connecting rod.
There now follows a detailed description, to be read with reference to the accompanying drawing, of a piston which is illustrative of the invention.
The drawing is a vertical cross-section taken through the illustrative piston.
The illustrative piston 10 is for a two-stroke engine and comprises a crown 12 which is generally in the form of a domed disc. The crown 12 receives the impact of the combustion of fuel charge in a bore 14 in which the piston 10 reciprocates. The crown 12 defines ring grooves 16 around its periphery which contain the usual piston rings (not shown).
The bore 14 defines an entry port 18 through which fuel charge enters the bore 14. The bore 14 also has other entry ports, one of which is indicated by 20, an exhaust port 22, and a by-pass port 24 which extends between an entrance and an exit higher up the bore 14. The by-pass port 24 is diametrically-opposed to the exhaust port 22 with its exit level with the port 24 and its entrance lower down the bore 14.
The piston 10 also comprises a skirt 26 depending from, and integral with, the crown 12. The skirt 26 is generally in the form of a hollow cylinder which is open at the bottom end thereof remote from the crown 12. The skirt 26 comprises two diametrically-opposed bosses 28 (only one visible in the drawing) which project inwardly and provide support bores 30 for a gudgeon pin (not shown) by which the piston 10 is connected to a connecting rod (not shown).
The skirt 26 is cut away (as shown at 32) at the bottom end thereof below the bosses 28 to facilitate flow into the scavenge port 18.
The skirt 26 also defines a port 34 which is adjacent to the crown 12. This port 34 is arranged to align with the entrance of the by-pass port 24 during part of the stroke of the piston 10 so that gases entering the skirt 26 through the open bottom end thereof can pass out through the port 34 into the port 24.
The piston 10 also comprises a flow deflector 36 mounted within the skirt 26. The deflector 36 is in the form of a steel plate secured to the bosses 28. The deflector 36 extends from a lower lip of the port 34 across the interior of the skirt 26 generally parallel to the crown 12. The deflector 36 arches over the gudgeon pin and the small end of the connecting rod. The deflector 36 extends to an edge thereof which, with the skirt 26, defines an opening 38 at an opposite side of the skirt 12 to the port 34.
In the operation of the piston 10, the deflector 36 constrains gas flowing between the open bottom end of the skirt 26 and the port 34 to flow through the opening 38 and to impinge on an edge area of the crown which is adjacent to the exhaust port 22. Thus, this edge area is cooled by said gas. The cooling is enhanced by turbulence created as the gas passes through the opening 38 and turns towards the port 34. After turning towards the port 34, the gas flows over the deflector 36 parallel to the crown 12 and has a cooling effect on the crown 12.

Claims (5)

  1. CLAINS
    1A piston for a two-stroke engine comprising a crown, and a skirt depending from said crown, the skirt being hollow and open at an end thereof remote from the crown, the skirt also defining at least one port adjacent to the crown arranged so that gases entering the skirt through the open end thereof can pass out through said port, wherein at least one flow deflector is mounted within said skirt and is arranged to constrain gas flowing between said open end and said port to impinge on an edge area of the underside of said crown.
  2. 2 A piston according to Claim 1, wherein the flow deflector constrains the gas to flow parallel to the crown from said edge area of the crown to said port.
  3. 3 A piston according to either one of Claims 1 and 2, wherein said flow deflector is mounted on bosses of the skirt which support a gudgeon pin which connects the piston to a connecting rod.
  4. 4 A piston according to any one of Claims 1 to 3, wherein said edge area of the crown is an area which, in the operation of the piston, is adjacent to an exhaust port.
  5. 5 A piston for a two-stroke engine substantially as hereinbefore described with reference to the accompanying drawing.
GB9305673A 1993-03-19 1993-03-19 Piston for a two-stroke engine Expired - Fee Related GB2276221B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9305673A GB2276221B (en) 1993-03-19 1993-03-19 Piston for a two-stroke engine

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9305673A GB2276221B (en) 1993-03-19 1993-03-19 Piston for a two-stroke engine

Publications (3)

Publication Number Publication Date
GB9305673D0 GB9305673D0 (en) 1993-05-05
GB2276221A true GB2276221A (en) 1994-09-21
GB2276221B GB2276221B (en) 1996-01-03

Family

ID=10732343

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9305673A Expired - Fee Related GB2276221B (en) 1993-03-19 1993-03-19 Piston for a two-stroke engine

Country Status (1)

Country Link
GB (1) GB2276221B (en)

Also Published As

Publication number Publication date
GB2276221B (en) 1996-01-03
GB9305673D0 (en) 1993-05-05

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Legal Events

Date Code Title Description
PCNP Patent ceased through non-payment of renewal fee

Effective date: 19990319