Split piston two-stroke four cycle internal combustion engine

Abstract

A two-stroke, four-cycle internal combustion engine is provided with a split piston which reciprocates within a cylinder having primary and secondary pre-combustion chambers. The lower portion of the piston is split by means of a partition which divides the cylinder into opposed air and combustible charge pumping chambers. One-way flow valves are provided to control the flow of air and a combustible charge into respective pumping chambers as the piston moves along its compression stroke. Movement of the piston along its power stroke compresses volumes of air and the charge within the pumping chambers, with these volumes then being directed through ports formed in a piston skirt and the cylinder wall into the pre-combustion chambers through one-way flow valves. Exhaust gases are scavenged through exhaust ports in the cylinder wall which are exposed as the piston completes its power stroke, with scavenging being assisted by injection of air directed from the pumping chamber through a one-way flow valve in a mid-portion of the cylinder wall. Certain of the one-way flow valves are threadably mounted for axial adjusting movement to vary valve lift and to facilitate valve replacement. The partition is formed integral with the piston and slidably projects through the end wall of the cylinder which forms the pumping chambers. Reciprocating movement of the piston and partition is converted into rotary motion through a cam follower mounted on the plate and moving in the cam track of a cylindrical cam.

Description

BACKGROUND OF THE INVENTION

This invention relates to two-stroke, four-cycle internal combustion engines.

Two-stroke, four-cycle internal combustion engines have heretofore been utilized in applications requiring simplicity, low cost and a relatively high horsepower-to-weight ratio, such as engines for motorcycles, outboard motors, small utility motors and the like. It is conventional in engines of this type to mix oil with the gasoline fuel, and part of the oil is burned during the power stroke to form harmful exhaust emissions. Moreover, such engines function by directing the air-fuel mixture through an intake port while spent gases exhaust through an opposite side of the cylinder, with the result that some of the mixture is carried out with the exhaust products. This loss, together with the relatively rich mixtures required for smooth operation and good response in such engines, results in a relatively high hydrocarbon and carbon monoxide content in the exhaust gases, as well as a relatively high fuel cost in relation to power output.

Conventional four-stroke, four-cycle combustion engines, on the other hand, develope practically twice the power of a two-stroke engine with equivalent bore and piston speeds, and also do not require a separate crankcase for each cylinder. The four-stroke engine is also more flexible, and is better adapted to the use of a carburetted mixture. However, such an engine provides only one power stroke for each cylinder in two revolutions of the crankshaft and, as with the two-stroke engine, does not develope complete expansion within the combustion chamber.

Recent Federal and State legislation has been enacted to require manufacturers of mobile equipment powered by gasoline fuel internal combustion engines to reduce harmful exhaust emissions by means of external emissions control devices, engine modifications or other methods. However, these objectives have heretofore not been fully realized.

OBJECTS AND SUMMARY OF THE INVENTION

It is a general object of the invention to provide an improved two-stroke internal combustion engine which will operate with reduced amounts of harmful exhaust emissions.

Another object is to provide an engine of the type described which will operate with more efficient fuel utilization.

Another object is to provide an engine of the type described which will achieve a relatively higher horsepower-to-weight ratio.

Another object is to provide an engine of the type described which can be employed in a wide range of power applications such as small utility engines, motorcycles, automobiles and multi-cylinder airplane engines.

The invention provides a two-stroke, four-cycle internal combustion engine having a piston mounted for reciprocating movement through power and compression strokes within a cylinder. One end of the piston is formed with a transversely extending partition or plate which separates an end of the cylinder into an air pumping chamber and an opposed combustible charge pumping chamber. The other end of the cylinder is formed with interconnected primary and secondary pre-combustion chambers, both of which communicate with the main combustion chamber in the cylinder. One-way flow control valves are provided to direct air and a combustible charge into respective air and charge pumping chambers as the piston moves through its compression stroke. Return of the piston on its power stroke compresses the volumes of air and combustible charge contained within the pumping chambers and these volumes are then directed to the pre-combustion chambers as ports in the piston skirt register with ports formed in the cylinder wall. An air injection valve is formed in the cylinder wall to direct air into the cylinder for scavenging products of combustion through exhaust ports, and to form a stratified charge in the combustion chamber, as the piston moves toward the end of its power stroke. One-way flow valves are provided to control flow into the pre-combustion chambers. The one-way flow valves include a valve element and plunger slidable within a valve body for movement to and from a valve seat. Reciprocating motion of the piston and its partition is converted to rotary motion by means of a cam follower mounted at the end of the partition in rolling contact with a cam track formed about the periphery of a cylindrical cam.

The foregoing and additional objects and features of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an axial sectional view of an internal combustion engine embodying the invention;

FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG. 1;

FIG. 3 is a cross-sectional view taken along the line 3--3 of FIG. 1;

FIG. 4 is a side elevational view of a flow control valve utilized in the engine of FIG. 1; and

FIG. 5 is an axial sectional view taken along the line 5--5 of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the drawings FIG. 1 illustrates generally at 10 a two-stroke, four-cycle internal combustion engine constructed in accordance with the invention. Engine 10 includes a pair of cylinders 11, 12 mounted together above a common casing 13. While a two-cylinder engine is shown, it is understood that the invention is adaptable for use as a single-cylinder engine, or as an engine utilizing more than two cylinders.

The construction and operation of the two cylinders is substantially identical and thus it will suffice to describe in detail that for cylinder 11. A cylinder block 14 is mounted above casing 13 and defines a circular cylinder wall 16. The cylinder wall may be cooled by suitable means such as by circulation of a liquid coolant in jacket 15, FIG. 3, which encloses the cylinder. The cylinder head is formed with a primary precombustion chamber 17 and a secondary pre-combustion chamber 18. The two pre-combustion chambers are in fluid communication by means of a by-pass port 19. The two chambers are also in communication with the main combustion chamber 21 of cylinder 11 by means of ports 22, 23. Suitable combustible charge ignition means such as the illustrated spark plug 24 is provided in pre-combustion chamber 17, and the spark plug is energized through a suitable electrical ignition system, not shown.

A piston 26 is mounted for reciprocating movement through power and compression strokes within cylinder wall 16. A flat piston plate or partition 27 is integrally formed below piston 26 and extends transversely across the cylinder to separate the lower portion of the cylinder into air pumping chamber 28 and an opposed combustible charge pumping chamber 29. The piston plate slidably projects through an opening 31 formed in cylinder end wall 32. Suitable sealing elements 33 are mounted on opposite sides of opening 31 to provide a fluid-tight seal between the piston plate and cylinder end wall.

Reciprocating motion of the piston is converted into rotary motion by means of a cam follower 34 rotatably carried at the lower end of the piston plate and mounted for rolling contact within a cam track 36 formed about the outer periphery of a cylindrical cam 37. The cylindrical cam is mounted on bearings 38, 39 within casing 13 for rotation about an axis extending parallel with and between the longitudinal axes of the cylinders 11, 12. A power shaft 41 is connected with the cam and extends upwardly between the two cylinders where it is supported on a bearing 42. The power shaft in turn is connected with a suitable drive train such as a clutch, transmission and road wheels or gear train, not shown. The cylindrical cam itself acts as a flywheel so that a separate flywheel is not required on the power shaft.

Cam track 36 is formed about the surface of the cam in a curve which has an amplitude equal to the stroke of the two pistons. Each of the cam followers for the two pistons are mounted in the same cam track. The cam followers comprise truncated cones, and the side walls of the cam track conform with the inclination of the cam followers. Adequate clearance is provided between the side walls of the track and the cam followers to permit rolling contact along the track.

Where three or more cylinders are provided in an engine of the type described, the diameter of the cam is enlarged with the cylinders equally spaced about the axis of the cam and with all of the cam followers engaging in the same cam track. In such a case the cam track can be configured to provide one or more power strokes of each cylinder per revolution of the cam. This permits a relatively larger horsepower-to-weight ratio for the engine. In addition, the curvature of the cam track can be designed to provide a variation in piston speed for different sectors of cam rotation. Thus, the cam track curve could provide for faster piston speed during the power stroke as compared to the piston speed during the induction stroke. Also, the cam track curve could provide for relatively faster piston speed during the first portion of the power stroke and slower speed through the end of that stroke to afford additional time for exhaust scavenging.

A combustible charge such as an air-fuel carburetted charge is induced into the cylinders from an intake manifold 45, FIG. 2, through inlet passages 43, 44. A one-way flow valve 46 directs flow from passage 43 into the lower portion of charge pumping chamber 29. A port 47 is formed in the mid-portion of cylinder wall 16 to direct a compressed volume of the charge from the pumping chamber through a passage 48 to a one-way flow valve 49 which in turn directs the charge into pre-combustion chamber 17. Piston 26 is formed with an integral downwardly extending annular piston skirt 51 fitted for sliding movement within the inner surface of the cylinder wall. A piston port 52 is formed in the upper portion of the piston skirt at a position such that the piston port moves into register with outlet port 47 as the piston approaches the end of its power stroke so that the compressed charge can be released into passage 48.

Atmospheric air is inducted into the cylinders of the engine through a one-way flow valve 53 which directs the air into charge pumping chamber 28. An outlet port 54 is formed at a midportion of cylinder wall 16 to direct the compressed volume of air from the pumping chamber into a passage 56 leading upwardly to a one-way flow valve 57 which directs the air into secondary precombustion chamber 18. A piston port 58 is formed in the upper portion of piston skirt 51 at a position such that it moves into register with outlet port 54 as the piston reaches the end of its power stroke to release the compressed air from the pumping chamber into passage 56.

A plurality of exhaust ports 59, 60 are formed through cylinder wall 16 at a position such that the exhaust ports are uncovered by the piston as it reaches the end of its power stroke. The exhaust ports are connected to a suitable exhaust manifold 61, as shown in FIG. 3. Exhaust scavenging is greatly enhanced in the invention by the injection of air through a one-way flow valve 62 at the completion of the power stroke. Valve 62 is mounted in the cylinder wall at a position above the piston head when the latter is at the end of its power stroke. Valve 62 communicates with passage 56 and opens responsive to a differential pressure as a result of reduction in combustion chamber pressure as the exhaust ports are uncovered.

The one-way flow valves 46, 53 controlling flow into the pumping chambers 28, 29 preferably comprise pressure responsive valves which include a valve element 63 and integral plunger or stem 64 mounted for axial sliding movement within a valve body 66. The valve element moves to and from a valve seat 67 responsive to differential pressure across the valve element due to variation in pressures within the pumping chamber. Thus, valve 53 is closed due to the increasing pressure in pumping chamber 28 as the piston moves downwardly along its power stroke. After the volume of air within the pumping chamber has been released through ports 58 and 54 upward movement of the piston along its compression stroke reduces pumping chamber pressure to a level at which the greater atmospheric pressure opens valve element 63 for inducting additional air. The operation of one-way valve 46 is similar to that described for valve 53.

Blow-by gases which enter the interior of casing 13 from the cylinders 11, 12 are removed by means of a passage 65 formed in cylinder block 14 and providing communication between the casing and flow valve 53. Induction of air through this valve draws blow-by gases from the passage 65 into air pumping chamber 28 for recycling in the engine.

The air injection valve 62 and one-way flow valve 49, 57 in the cylinder head preferably comprise pressure operated valves assembled in relatively small cartridges which afford simplified valve lift adjustment and which also can be readily inserted and removed for replacement purposes. FIGS. 4 and 5 illustrate details of a valve cartridge assembly for the typical valve 62, and it is understood that the construction and operation of the valves 49, 57 is similar thereto. The valve 62 comprises a valve body 68 formed with external threads adapted for engagement with internal threads formed in a bore through the walls of the passage 56 and cylinder wall 16. The end of the body 68 forms a valve seat 69 which communicates through passages 71 with a plurality of openings 72 which are formed in the body side walls. A valve element 73 comprising a circular valve head 74 and integral plunger 76 is mounted for axial sliding movement within a central bore in the body. A differential gas pressure across the valve head moves the same between the valve seat and a fixed stop 79 which is recessed in the cylinder wall. The position of the valve cartridge may be axially adjusted with respect to the fixed stop by turning the valve body within the threaded bore. This in turn varies the amount of valve lift, i.e. the clearance between the valve head and seat when the valve is in its fully open position. This permits selective variation of the flow rate of scavenging air which is injected through valve 62. Similar fixed stops 78, 79 are mounted within the pre-combustion chambers adjacent valves 49, 57 for selective variation of charge and air flow rates into these chambers by turning the respective valve bodies.

This use and operation of engine 10 will be explained assuming that a carburetor, not shown, is provided to supply an air-fuel charge through manifold 45 into the passages 43, 44 for the two cylinders. With power shaft 41 initially turned by a suitable starter motor, not shown, the pistons are reciprocated through action of the cylindrical cam 37 and cam followers. Movement of piston 26 upwardly along its compression stroke within cylinder 11 causes a pressure reduction within the two pumping chambers 28, 29. The resulting pressure differential across the flow valves 46, 53 causes these valves to open to induct atmospheric air and the combustible charge into respective air and charge pumping chambers. This phase continues until the piston reaches the top of its compression stroke, as illustrated for the right-hand cylinder 81 in FIG. 1. As piston 26 then moves downwardly along its power stroke the volumes of gas within the two pumping chambers are compressed so that the higher internal pressure closes flow valves 46, 53. Compression of the two volumes within the pumping chambers continues until the piston ports 52, 58 move into register with respective outlet ports 47, 54 as the piston reaches the end of its power stroke. The compressed combustible charge is then exhausted from pumping chamber 29 into passage 48 where it travels upwardly to act against and open the valve element of flow valve 49. The relatively rich charge mixture then flows into primary pre-combustion chamber 17. A portion of this flow is directed through by-pass port 19 and into secondary pre-combustion chamber 18.

The volume of air which is compressed within pumping chamber 28 is also exhausted into outlet port 54 and passage 56 from piston port 58. The pressure of this air acts against and opens the valve element of flow valve 62 to inject a portion of the flow into combustion chamber 21 for scavenging exhaust gases and form a stratified layer, while the remaining portion flows upwardly to act against and open the valve element of flow valve 57. This air flows into secondary pre-combustion chamber 18 where it mixes with the portion of the charge entering from port 19 to form a relatively lean fuel-air mixture.

As piston 26 then moves upwardly on its compression stroke a stratified charge is formed within cylinder 21 comprising the lower layer of fresh air introduced from injection valve 62 together with residual products of combustion which have not been exhausted, and an upper layer comprising the rich fuel-air mixture of chamber 17 and the relatively leaner mixture of chamber 18. Continued movement of the piston toward the top of this stroke compresses the gases within main combustion chamber 21 and the pre-combustion chambers. The ignition system, operating in timed relationship with rotation of power shaft 41, then energizes spark plug 24 to ignite the compressed charge within the primary pre-combustion chamber. The flame front propagates across this chamber and through by-pass port 19 to ignite the lean mixture within secondary chamber 18. The flames from the two pre-combustion chambers emerge through ports 22, 23 and continue burning with the rich source of oxygen supplied from the lower portion of the stratified charge. The rapidly burning and expanding gases within the main combustion chamber drive the piston downwardly through its power stroke, and this in turn drives power shaft 41 through rolling contact between cam follower 34 and cam 37.

As piston 26 nears the end of its power stroke the exhaust ports 59, 60 are uncovered for exhausting the products of combustion from the combustion chamber. Air injection valve 62 opens in the manner explained above, and the current of air which is injected from this valve both scavenges exhaust gases out through the exhaust ports and also acts as a shield between the exhaust ports and the combustible charge entering the chamber through ports 22, 23. At the same time the gases within the air and charge pumping chambers are released into the passages 48 and 56 for the next cycle of operation.

From the foregoing it is apparent that there has been provided herein a new and improved two-stroke, four-cycle internal combustion engine. The split piston arrangement provides a novel air and combustible charge pumping mechanism for injecting air for exhaust scavenging and to form a stratified charge within the combustion chamber. The two pre-combustion chambers provide for burning separate volumes of rich and lean mixtures which may be controlled by simple adjustment of the one-way flow valves. The cycle of operation closely approaches complete expansion of the burning charge. The rich fuel mixture burns relatively fast and at a high temperature, but the mixture is low in oxygen so that formation of NO.sub.x products is minimal. The lean mixture burns relatively slower and at a lower temperature, and when the flame fronts emerge from the pre-combustion chambers into the main combustion chamber the gases burn slower at a relatively high temperature because of the presence of residual products of combustion from the previous cycle. As the exhaust ports are exposed by movement of the pistons the products of combustion are subjected to a cooling flow of the injected air which oxidizes any remaining hyrocarbons and carbon monoxide into water and harmless carbon dioxide.

While the foregoing embodiments are at present considered to be preferred it is understood that numerous variations and modifications may be made therein by those skilled in the art and it is intended to cover in the appended claims all such variations and modifications as fall within the true spirit and scope of the invention.

Claims

I claim:

1. In a two-stroke, four cycle internal combustion engine, the combination of means forming at least one cylinder having opposed first and second end walls, a piston mounted for reciprocating movement through power and compression strokes within the cylinder, one end of the piston separating the cylinder and cooperating with said first end wall to define a combustion chamber, the other end of the piston having a partition extending transversely across the cylinder and cooperating with said second end wall to define an air pumping chamber and an opposed combustible charge pumping chamber, first means to direct volumes of air and a combustible charge into respective air and charge pumping chambers during movement of the piston along its intake compression stroke, said volumes being compressed in respective chambers during movement of the piston along its power stroke, second means to direct the volume of compressed air from the air pumping chamber into the combustion chamber, third means to direct the volume of compressed charge from the charge pumping chamber into the combustion chamber, fourth means to ignite the charge in the combustion chamber which is compressed by movement of the piston along its compression stroke, and exhaust means to exhaust the products of combustion from the combustion chamber.

2. An engine as in claim 1 which includes means forming a primary pre-combustion chamber communicating both with said third means and said first mentioned combustion chamber, means forming a secondary pre-combustion chamber communicated both with said second means, with said first mentioned combustion chamber and with said primary pre-combustion chamber.

3. An engine as in claim 1 in which said second means includes air injection valve means for injecting air which is compressed in the air pumping chamber into the combustion chamber for scavaging products of combustion through the exhaust means.

4. An engine as in claim 1 in which the third and second means include respective ports formed at a mid-portion of the cylinder, the piston includes a cylindrical skirt adapted to occlude said ports while the piston is moving through its compression stroke and is compressing the air and combustible charge within respective pumping chambers, and the skirt is formed with ports communicating with respective pumping chambers and positioned to move into register with said first mentioned ports when the piston substantially reaches the end of its power stroke.

5. An engine as in claim 1 in which the partition comprises a flat plate mounted for close-spaced sliding movement through the second end wall of the cylinder, and means forming a seal between said cylinder and the facing surfaces of the plate.

6. An engine as in claim 5 which includes means for converting reciprocating movement of said piston and plate into rotary motion comprising a cylindrical cam mounted for rotation about a longitudinal axis parallel with the longitudinal axis of the cylinder, means forming a curvilinear cam track about the periphery of said cylindrical cam, and cam follower means carried by said plate and mounted for movement in said cam track whereby reciprocating movement of said plate causes the cam follower to react against and rotate the cam about its longitudinal axis.

7. An engine as in claim 1 in which said first means includes valve means for controlling one-way flow into respective air and combustible charge pumping chambers comprising a valve body having a valve seat, and a valve element having an integral plunger slidably mounted in said body for moving the valve element to and from the seat responsive to a pressure differential on opposite sides of the valve element.

8. An engine as in claim 1 in which said second and third means includes valve means for controlling one-way flow into the combustion chamber comprising a fixed valve stop, a valve body threadably mounted for axial adjustable positioning with respect to the valve stop, the valve body including a valve seat, a valve element including a plunger slidably mounted in the valve body for guiding the valve element between the seat and valve stop responsive to a pressure differential on opposite sides of the valve element.

9. An engine as in claim 3 in which the air injection valve means includes valve means for controlling one-way flow into the combustion chamber comprising a fixed valve stop, a valve body threadably mounted for axial adjustable positioning with respect to the valve stop, the valve body including a valve seat, a valve element including a plunger slidably mounted in the valve body for guiding the valve element between the seat and valve stop responsive to a pressure differential on opposite sides of the valve element

10. An engine as in claim 1 which includes a drive member, formed as an extension of said partition, mounted for reciprocating movement with the piston and projecting in slidable sealing relationship with the second end wall of the cylinder, a casing mounted with said cylinder and enclosing the portion of the drive member which projects from the second end wall, and means to direct blow-by gases from within the casing to said first means for injection into said air pumping chamber.