GB2361030A

GB2361030A - Two-stroke engine with stepped piston and cylinder

Info

Publication number: GB2361030A
Application number: GB0008194A
Authority: GB
Inventors: John Anthony Clarke
Original assignee: JOHN CLARKE ENGINEERING
Current assignee: JOHN CLARKE ENGINEERING
Priority date: 2000-04-05
Filing date: 2000-04-05
Publication date: 2001-10-10
Anticipated expiration: 2020-04-05
Also published as: GB0008194D0; GB2361030B

Abstract

The two-stroke engine, eg for use in light aircraft, comprises a piston arrangement 1 operating in a cylinder assembly 2 and cooperating with cylinder head 3 .The piston arrangement 1 is of stepped form having a first cylindrical portion 4 of greater diameter forming a scavenge piston and surrounding a first end region of a hollow second cylindrical portion 5 of lesser diameter and forming a sleeve valve. The cylindrical portion 4 may have reed valves (28, fig.7) and a carbon piston ring (27, fig.8). The second cylindrical portion 5 has a second end region 6 terminating in a piston skirt 7 and provided with bearing means 8 for receiving an end of a connecting rod cooperating with a crankshaft (not shown). A piston crown component 9 is provided inside the second cylindrical portion 5, the cylinder head 3 having a cylinder component 42 slidably received inside the first end region of the second cylindrical portion of the piston arrangement 1, the cylinder component 42 having a closed end 43. One of the piston crown component 9 and the closed end of the cylinder component 42 has a recess forming a combustion chamber 10 which cooperates with the stepped closed end 43 of the other of those components. The cylinder component 42 may have a sealing sleeve (51, fig.11).

Description

2361030 TWO-STROKE ENGINE The present invention relates to two-stroke

engines, particularly but not exclusively f or use in light aircraft.

According to a first aspect of the present invention there is provided a two-stroke engine comprising a piston arrangement operating in a cylinder assembly and cooperating with a cylinder head, the piston arrangement being of stepped form having a first cylindrical portion of a first diameter forming a scavenge piston and securedly surrounding a first end region of a hollow second cylindrical portion of a second diameter less than the first diameter, the first end region of the second cylindrical portion forming a sleeve valve, the second cylindrical portion having a second end region terminating in a piston skirt and provided with bearing means for receiving an end of a connecting rod cooperating between the piston assembly and a crankshaft, a piston crown component being provided inside the second cylindrical portion, the cylinder head having a cylinder component slidably received inside the first end region of the second cylindrical portion of the piston arrangement, the cylinder component having a closed end, one of the piston crown component and the closed end of the cylinder component having a recess formed therein forming a combustion chamber in cooperation with the -2other of the piston crown component and the closed end and the other of the piston crown component and the closed end being of stepped configuration adapted to be accommodated in the recess formed in the said one of the 5 piston crown component and the closed end.

The cylinder component may be hollow.

The first end region of the second cylindrical portion may be an upper end or a lower end of the second cylindrical portion.

The closed end of the cylinder component may be adapted to accommodate a spark plug and/or fuel injector.

is The closed end of the cylinder component may be in the form of a plug which may be hollow and which may be arranged to be liquid-cooled.

One or more piston rings may be provided on the cylinder component of the cylinder head, and preferably at a region at or near the closed end thereof.

The cylinder component may be surrounded by a sealing sleeve, which may be of split form, such as of diagonally split form.

The cylinder component of the cylinder head may have a flange provided at an end thereof remote from the closed end.

The cylinder head may comprise a heat-conducting light alloy.

The sleeve valve, formed by the first end region of the hollow second cylindrical portion of the piston arrangement, may be provided therethrough with a plurality, preferably more than two, of circumferentially arranged inlet ports at or near the first end thereof. Such inlet ports may be tangentially disposed to effect swirling of scavenge air passing therethrough.

is A plurality of exhaust ports, preferably more than two, may be provided, disposed circumferentially at or near a an end of the sleeve valve remote from the first end and preferably extending laterally through a circumferential wall of the sleeve valve and through the piston crown and into the combustion chamber.

The combustion chamber may be of cylindrical form in the piston crown, the closed end of the cylinder component of the cylinder head being of complementa.ry cylindrical form. Alternatively, the combustion chamber may be of cylindrical form in the closed end of the cylinder component of the cylinder head, the piston crown being of complementary cylindrical form.

The piston crown may be provided at a region thereof opposite the combustion chamber with a heat sink means, such as of metal alloy, which may be arranged to be cooled by means of oil jets. Such oil jets may also be arranged to provide lubrication for the bearing means, which may be a gudgeon pin bearing, receiving the end of 10 the connecting rod.

The scavenge piston formed by the first cylindrical portion of the piston arrangement may be provided with one or more piston rings, which may comprise carbon.

The scavenge piston may be formed separately from and secured to the f irst end of the sleeve valve f ormed by the first end region of the hollow second cylindrical portion of the piston arrangement. The scavenge piston may have a central cylindrical aperture arranged to encircle the first end of the sleeve valve, and may engage a flange which may be provided at the first end of the sleeve valve.

The scavenge piston may be secured to the first end of the sleeve valve by threaded fasteners which may cooperate with one or more grooves and/or rings and/or circlips associated with the scavenge piston and/or the sleeve valve.

A plurality of reed valves may be provided in the scavenge piston, preferably at a surface thereof facing the second cylindrical portion. Such reed valves may cooperate with associated reed valve stop plates and cut out portions in the scavenge piston. Alternatively, a single circular (annular) shaped reed valve may be provided, for example in the form of a plate.

The cylinder assembly may be of stepped form and may comprise a scavenge cylinder, cooperating with the scavenge piston, and a working cylinder, cooperating with the sleeve valve.

The scavenge cylinder may be secured coaxially in end-toend relationship with the working cylinder by means of a joining flange.

An exhaust manifold may be provided at least partly encircling the working cylinder and incorporating ports extending into the working cylinder and arranged for alignment with the exhaust ports disposed at or near the end of the sleeve valve remote from the first end of the second cylindrical portion.

Coolant jackets may be provided surrounding the scavenge cylinder and the working cylinder.

A flange member may be provided securing the cylinder assembly to a crankcase provided with the crankshaft.

The sleeve valve formed by the first end region of the hollow second cylindrical portion of the piston arrangement may be formed separately, and optionally of different material to, the second end region, the two regions being secured to each other such as by threaded fastener means or bayonet connection means.

The piston crown may be formed integrally with the second end region of the hollow second cylindrical portion of the piston arrangement, including the piston skirt.

2 The piston skirt is suitably dimensioned whereby it covers the ports in the working cylinder when the piston 0 assembly is at a top dead centre position.

The scavenge piston may have a displacement which is substantially twice that of the working cylinder.

According to a second aspect of the present invention there is provided a two-stroke engine incorporating one or more reed valves. Such one or more reed valves may be incorporated with a scavenge piston of the engine.

-7According to a third aspect of the present invention there is provided a two-stroke engine provided with spark-plug ignition means and fuel injection means and a stepped piston assembly incorporating a sleeve valve and a scavenge piston.

The two-stroke engine according to the second aspect of the present invention or according to the third aspect of the present invention may optionally include one or more features described above of the two-stroke engine according to the first aspect of the present invention.

For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 is a perspective view of a piston assembly of an embodiment of two-stroke engine according to the present invention; Figure 2 is a perspective view of a cylinder assembly for use with the piston assembly of Figure 1; Figure 3 is a perspective view of a cylinder head for use with the cylinder assembly and piston assembly of Figures 1 and 2; -8Figure 4 is a cross---sectional view of part of the piston assembly of Figure 1 showing a securing arrangement between the sleeve valve and piston crown; Figure 5 is a cross---sectional view of part of the piston assembly of Figure 1 showing an alternative securing arrangement between the sleeve valve and piston crown; Figure 6 is a perspective view of the scavenge piston of 10 the assembly of Figure 1; Figure 7 is a cross-section along line A - A of Figure 6; Figure 8 is an alternative cross-section along line A - A 15 of Figure 6; Figure 9 is a side view of the lower end of a cylinder component of the cylinder head of Figure 3; Figure 10 is a detail of an end plug at the lower end of the cylinder component of the cylinder head of Figure 3; Figure 11 is a side view of the cylinder head of Figure 3 having a split sleeve seal; Figure 12 is a detail showing interrelationship between the lower end of the cylinder head of Figure 3 and inlet ports in the sleeve valve of the piston assembly of Figure 1; and Figure 13 is a diagrammatic perspective view of a piston and cylinder head assembly of another embodiment of twostroke engine according to the present invention.

Referring to Figures 1, 2 and 3, a two-stroke engine, which is particularly suitable for use in light aircraft, comprises a piston arrangement 1 operating in a cylinder assembly 2 and cooperating with a cylinder head 3.

The piston arrangement is of stepped form, having a scavenge piston 4 of cylindrical form secured to and surrounding an upper end of a hollow cylindrical sleeve valve 5. The diameter of the scavenge piston 4 is greater than that of the sleeve valve 5.

Extending below the hollow cylindrical sleeve valve 5 is a cylindrical lower end region 6 terminating in a piston skirt 7 and provided with bearings in the form of bushes 8 for receiving a gudgeon pin (not shown) of well-known form and which enables a connecting rod (not shown) of suitable light alloy form to cooperate between the piston assembly 1 and a crankshaft (not shown) of the engine.

A piston crown 9 is provided, intermediate the sleeve valve 5 and the cylindrical lower end region 6. The -10piston crown 9 has an upwardly-facing cylindrical recess forming a combustion chamber 10.

A plurality of exhaust ports 11 are circumferentially disposed at the bottom end of the sleeve valve 5, extending through a circumferential wall of the sleeve valve 5 and through the piston crown 9 into the combustion chamber 10. More than two such ports 11 are preferably provided spaced apart around the edge of the combustion chamber 10.

As shown in Figure 4, the piston crown 9, with the combustion chamber 10, is suitably formed integrally with the cylindrical lower end region 6. The lower end of the sleeve valve 5 f its over the piston crown 9 and is secured thereto by means of countersunk bolts 12.

Alternatively, as shown diagrammatically in Figure 5, a bayonet form of connection 13 can be provided between the lower end of the sleeve valve 5 and the piston crown 9, a shallow cut out 14 being formed in the piston crown and a filler piece 15 being inserted as a locking member after assembling the components.

The underside 16 of the piston crown may be provided of a relatively thick metal alloy material, to serve as a heat sink, and may be arranged to be cooled by means of oil -11jets 17. Such oil jets may also serve to lubricate the bushes 8 f or the connecting rod.

The formation of the sleeve valve 5 and the piston crown 9, with the cylindrical lower end region 6, as separate components enables different materials, with optimised properties, to be selected for these components.

A plurality of inlet ports 18 are provided through the sleeve valve 5 at the top thereof. More than two such inlet ports 18 are preferably provided, spaced apart circumferentially around the sleeve valve 5. The inlet ports 18 are arranged in tangential manner to provide a swirl action to the scavenge air and force expended gases out of the cylinder 19 without undue mixing taking place.

As shown in Figure 6, the scavenge piston 4 has a central cylindrical aperture 20 which enables it to be fitted over the top end of the hollow cylindrical sleeve valve 5.

The scavenge piston 4 can be secured to the sleeve valve 5 as shown in Figure 7. A lip or flange 21 is provided on the top edge of the sleeve valve 5, such lip or f lange 21 having threaded holes arranged to receive bolts or screws 22 passing through the scavenge piston 4.

-12Alternatively, as shown in Figure 8, the scavenge piston 4 can be secured to the sleeve valve 5 by means of grub screws 23 which cooperate with a circlip form of steel ring 24 and grooves 25, 26 in the scavenge piston 4 and sleeve valve 5 respectively.

The scavenge piston 4 is provided with one or more piston rings 27, suitably comprising carbon.

A plurality of reed valves 28 are provided in the scavenge piston 4, particularly at a lower surface thereof. As particularly shown in Figure 7, such reed valves 28 cooperate with associated reed valve stop plates 29 and cut out portions 30 in the scavenge piston 4.

The piston assembly 1 of Figure 1 is assembled with the cylinder assembly 2 of Figure 2. The cylinder assembly 2 has a scavenge cylinder 31 secured coaxially in end-to- end relationship with a working cylinder 32 by means of joining flange 33. The scavenge cylinder 31 cooperates with the scavenge piston 4 and the working cylinder 32 cooperates with the sleeve valve 5 and the cylindrical lower end region 6.

An exhaust manifold 34, with a flange 35, encircles the working cylinder 32 and incorporates ports 36 extending into the working cylinder 32 and arranged for alignment -13with the exhaust ports 11 communicating with the combustion chamber 10.

Coolant jackets 37, 38 surround the scavenge cylinder 31 5 and the working cylinder 32.

A flange member 39 is arranged for securing the cylinder assembly 2 to a crankcase 40 of the engine.

The cylinder head 3 of Figure 3 is secured to the cylinder assembly 2 by means of a flange 41 and has a hollow cylinder component 42, which is closed at its lower end 43, and which slides in the interior 19 of the sleeve valve 5.

As shown in Figure 9, the closed lower end 43 of the cylinder component 42 of the cylinder head 3 is provided with one or more h igh-temperature with stand i ng piston rings 44 and an end plug 45 which is adapted to be accommodated in the cylindrical combustion chamber 10 in the piston crown 9 and shaped to provide an optimised 'IsquishIl and "swirl" effect in the combustion chamber 10.

The end plug 45 is shown in detail in Figure 10 and includes a bush 46 to accommodate a spark plug and a bush 47 to accommodate a fuel injector. Conduits 48 are provided to convey a space 49. A reduced liquid coolant to and from a coolant diameter portion 50 contributes to -14the optimisation of the 'IsquishIl and "swirl" effect in the combustion chamber 10.

The components of the end plug 45 are suitably welded together and such that all welded connections are in compression when under mechanical load.

As shown in Figure 11, a sealing sleeve 51 with a diagonal split 52 is provided around the cylinder component 42 of the cylinder head 3. This prevents scavenge air escaping from the lower high pressure side of the scavenge piston 4 into the upper low pressure inlet side.

As shown in Figure 12, the plug 45 at the lower end 43 of the cylinder component of the cylinder head 3 cooperates with the tangential inlet ports 18 in the sleeve valve 5 to provide a swirl space 53 for the scavenge air and to assist in the process of expelling expended cylinder gases.

The engine of the present invention is preferably constructed with a stroke to bore ratio of about 1.6 to 1, thus giving a long stroke. This dictates a slow running engine (maximum about 3000 rpm) which suits the application to light aircraft, cruising at 2400 rpm. A direct drive is possible, avoiding the weight and -15complexity of reduction gears. The use of fuel injection results in improved exhaust emissions.

Use of kerosene f uel results in reduced running costs, lower vapour pressure and higher flash point, thereby giving greater safety. However, it may be necessary to use methanol/water injection for maximum power at take off and climb.

The scavenge piston displacement is suitably arranged to be double that of the working cylinder, thus ensuring complete scavenging of spent gases from the cylinder.

Location of the reed valves 28 in the lower surf ace of the scavenge piston 4 results in assistance in opening and closing thereof by the acceleration and deceleration of the piston. Because the reed valves are mounted on the scavenge piston 4, rather than in a remote position, scavenge compression "dead" space is reduced and higher scavenge pressure is available.

The two-stroke engine shown in Figure 13 has the combustion chamber 10 formed as a recess in the cylinder head rather than in the piston crown. The piston crown 9 is correspondingly stepped to fit into the recess in the cylinder head. In this embodiment, supplementary radial inlet ports 18A are provided through the wall of the recessed portion of the combustion chamber.

-16The supplementary radial inlet ports 18A provide for additional cooling of the cylinder head. Moreover, the sleeve valve can be attached to the piston by way of a flat base of the sleeve valve by bolts in a manner that reduces the unwanted effect of differential expansion of dissimilar metals.

Claims

1. A two-stroke engine comprising a piston arrangement operating in a cylinder assembly and cooperating with a cylinder head, the piston arrangement being of stepped form having a first cylindrical portion of a first diameter forming a scavenge piston and securedly surrounding a first end region of a hollow second cylindrical portion of a second diameter less than the first diameter, the first end region of the second cylindrical portion forming a sleeve valve, the second cylindrical portion having a second end region terminating in a piston skirt and provided with bearing means for receiving an end of a connecting rod cooperating between the piston assembly and a crankshaft, a piston crown component being provided inside the second cylindrical portion, the cylinder head having a cylinder component slidably received inside the first end region of the second cylindrical portion of the piston arrangement, the cylinder component having a closed end, one of the piston crown component and the closed end of the cylinder component having a recess formed therein forming a combustion chamber in cooperation with the other of the piston crown component and the closed end and the other of the piston crown component and the closed end being of stepped configuration adapted to be accommodated in the recess formed in the said one of the piston crown component and the closed end.

-182. An engine as claimed in claim 1, wherein the cylinder component is hollow.

3. An engine as claimed in claim 1 or 2, wherein the first end region of the second cylindrical portion is an upper end or a lower end of the second cylindrical portion.

4. An engine as claimed in any preceding claim, wherein the closed end of the cylinder component is adapted to accommodate a spark plug and/or fuel injector.

5. An engine as claimed in any preceding claim, wherein the closed end of the cylinder component is in the form of a plug.

6. An engine as claimed in claim 5, wherein the plug is hollow.

7. An engine as claimed in claim 5 or 6, wherein the plug is arranged to be liquid-cooled.

8. An engine as claimed in any preceding claim, wherein one or more piston rings are provided on the cylinder component of the cylinder head.

-199. An engine as claimed in claim 8, wherein the piston rings are provided at a region at or near the closed end of the cylinder component.

10. An engine as claimed in any preceding claim, wherein the cylinder component is surrounded by a sealing sleeve.

11. An engine as claimed in claim 10, wherein the sealing sleeve is of split form.

12. An engine as claimed in claim 11 is of diagonally split form.

wherein the sleeve

13. An engine as claimed in any preceding claim, wherein the cylinder component of the cylinder head has a flange provided at an end thereof remote from the closed end.

14. An engine as claimed in any preceding claim, wherein the cylinder head comprises a heat-conducting light alloy.

15. An engine as claimed in any preceding claim, wherein the sleeve valve, formed by the first end region of the hollow second cylindrical portion of the piston arrangement, is provided therethrough with a plurality, preferably more than two, of circumferentially arranged inlet ports at or near the first end thereof.

-2016. An engine as claimed in claim 15, wherein the inlet ports are tangentially disposed to effect swirling of scavenge air passing therethrough.

17. An engine as claimed in any preceding claim, wherein a plurality of exhaust ports, preferably more than two, is provided, is disposed circumferentially at or near an end of the sleeve valve remote from the first end and preferably extending laterally through a circumferential wall of the sleeve valve and through the piston crown and into the combustion chamber.

18. An engine as claimed in any preceding claim, wherein the combustion chamber is of cylindrical form in the piston crown, the closed end of the cylinder component of the cylinder head being of complementary cylindrical f orm.

19. An engine as claimed in any one of claims 1 to 17, wherein the combustion chamber is of cylindrical form in the closed end of the cylinder component of the cylinder head, the piston crown being of complementary cylindrical form.

20. An engine as claimed in any preceding claim, wherein the piston crown is provided at a region thereof opposite the combustion chamber with a heat sink means, such as of -21metal alloy, which may be arranged to be cooled by means of oil jets.

21. An engine as claimed in claim 20, wherein the oil jets are also arranged to provide lubrication for the bearing means, which may be a gudgeon pin bearing, receiving the end of the connecting rod.

22. An engine as claimed in any preceding claim, wherein the scavenge piston formed by the first cylindrical portion of the piston arrangement is provided with one or more piston rings, which may comprise carbon.

23. An engine as claimed in any preceding claim, wherein the scavenge piston is formed separately from and secured to the first end of the sleeve valve formed by the first end region of the hollow second cylindrical portion of the piston arrangement.

24. An engine as claimed in claim 23, wherein the scavenge piston has a central cylindrical aperture arranged to encircle the first end of the sleeve valve, and may engage a flange which may be provided at the first end of the sleeve valve.

25. An engine as claimed in any preceding claim, wherein the scavenge piston is secured to the f irst end of the sleeve valve by threaded fasteners which may cooperate -22with one or more grooves and/or rings and/or circlips associated with the scavenge piston and/or the sleeve valve.

26. An engine as claimed in any preceding claim, wherein a plurality of reed valves is provided in the scavenge piston, preferably at a surface thereof facing the second cylindrical portion.

27. An engine as claimed in claim 26, wherein the reed valves cooperate with associated reed valve stop plates and cut out portions in the scavenge piston.

28. An engine as claimed in claim 26, wherein a single circular (annular) shaped reed valve is provided, for example in the form of a plate.

29. An engine as claimed in any preceding claim, wherein the cylinder assembly is of stepped form and may comprise a scavenge cylinder, cooperating with the scavenge piston, and a working cylinder, cooperating with the sleeve valve.

30. An engine as claimed in ant preceding claim, wherein the scavenge cylinder is secured coaxially in end-toend relationship with the working cylinder by means of a joining flange.

-2331. An engine as claimed in any preceding claim, wherein an exhaust manifold is provided at least partly encircling the working cylinder and incorporating ports extending into the working cylinder and arranged for alignment with the exhaust ports disposed at or near the end of the sleeve valve remote from the first end of the second cylindrical portion.

32. An engine as claimed in any preceding claim, wherein coolant jackets are provided surrounding the scavenge cylinder and the working cylinder.

33. An engine as claimed in any preceding claim, wherein a flange member is provided securing the cylinder assembly to a crankcase provided with the crankshaft.

34. An engine as claimed in any preceding claim, wherein the sleeve valve formed by the first end region of the hollow second cylindrical portion of the piston arrangement is formed separately, and optionally of different material to, the second end region, the two regions being secured to each other such as by threaded fastener means or bayonet connection means.

35. An engine as claimed in any preceding claim, wherein the piston crown is formed integrally with the second end region of the hollow second cylindrical portion of the piston arrangement, including the piston skirt.

-2436. An engine as claimed in any preceding claim, wherein the piston skirt is dimensioned whereby it covers the ports in the working cylinder when the piston assembly is at a top dead centre position.

37. An engine as claimed in any preceding claim, wherein the scavenge piston has a displacement which is substantially twice that of the working cylinder.

38. A two-stroke engine substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.