US3756206A - Engine - Google Patents

Abstract

A 4-cycle, internal combustion engine comprising a crankcase and a pair of cylinders, each cylinder being open at one end into communication with the crankcase. Each cylinder is provided with an inlet port, and a crankshaft is disposed in the crankcase to be adjacent the open ends of the cylinders. A piston is reciprocably received in each cylinder to define therewithin a variable-volume combustion chamber, each piston being drivingly connected in a conventional manner to the crankshaft. A system is provided for admitting a gaseous mixture to the crankcase, and there is a passageway leading from the crankcase to each inlet port. valves are provided for respectively opening and closing the passageways, the valves being drivingly connected to and operated by the crankshaft. The valves are arranged and driven such that each passageway is opened only on alternate occasions when both pistons move toward the axis of the crankshaft. Thus, the pumping action of both pistons drives the gaseous mixture through the only open passageway into one of the two cylinders. The inlet port and an exhaust port is provided in the side wall of each cylinder at peripherally spaced apart points remote from the closed end of the cylinder. An auxiliary chamber in open communication with each exhaust port is provided, each said auxiliary chamber being provided with a port at a point remote from the point of communication of the chamber with the cylinder exhaust port. A butterfly valve is provided for dominating each auxiliary chamber port, the butterfly valve being drivingly connected to the crankshaft.

Description

United States Patent 91 Gommel 51 Sept. 4, 1973 ENGINE [76] Inventor: Dewey E. Gommel, P.O. Box 4627,

Greenville, Miss. 38701 [22] Filed: Jan. 17, 1972 [21] App]. No.: 218,373

[52] US. Cl. 123/75 CC, 123/59 A, 123/73 R [51] Int. Cl. F02b 75/02, F02d 39/02 [58] Field of Search 123/75 CC, 59 A, 123/57, 75, 59, 73

[56] References Cited UNITED STATES PATENTS 1,046,392 12/1912 Kessler 123/75 CC 1,255,150 2/1918 Franklin 123/77 CC 1,267,128 5/1918 Seguin 123/75 CC 1,925,851 9/1933 Spencer.... 123/75 CC 2,242,538 5/1941 Naccache..... 123/75 CC 3,200,799 8/1965 Hammick..... 123/59 A 3,499,425 3/1970 Gommel 123/73 R Primary Examiner-Laurence M. Goodridge Assistant Examiner-Cort R. Flint Attorney-William R. Coffey et a1.

[5 7] ABSTRACT A 4-cycle, internal combustion engine comprising a crankcase and a pair of cylinders, each cylinder being open at one end into communication with the crankcase. Each cylinder is provided with an inlet port, and a crankshaft is disposed in the crankcase to be adjacent the open ends of the cylinders. A piston is reciprocably received in each cylinder to define therewithin a variable-volume combustion chamber, each piston being drivingly connected in a conventional manner to the crankshaft. A system is provided for admitting a gaseous mixture to the crankcase, and there is a passageway leading from the crankcase to each inlet port. valves are provided for respectively opening and closing the passageways, the valves being drivingly connected to and operated by the crankshaft. The valves are arranged and driven such that each passageway is opened only on alternate occasions when both pistons move toward the axis of the crankshaft. Thus, the pumping action of both pistons drives the gaseous mixture through the only open passageway into one of the two cylinders. The inlet port and an exhaust port is provided in the side wall of each cylinder at peripherally spaced apart points remote from the closed end of the cylinder. An auxiliary chamber in open communication with each exhaust port is provided, each said auxiliary chamber being provided with a port at a point remote from the point of communication of the chamber with the cylinder exhaust port. A butterfly valve is provided for dominating each auxiliary chamber port, the butterfly valve being drivingly connected to the crankshaft.

1 Claim, 14 Drawing Figuresl 1 I I 3,756,206

Sept. 4, 1973 United States Patent 1m Gommel PATENIEDSEP 4am 3.756206SHEET 3 0F 4 a 4 I J I FIRING ORDER- l'3-2-4 Fig.6

Fig.7

2- CYLINDER 4- CYLINDER 6- CYLlNDER FIRING ORDER- l-3-5-2-4-6PATENTEUSEP 4 ma 3.756206 sumuom -YLIND Fig.9

2 3 Z-CYLINDER 4-CYLINDER FIRING ORDER l-2-3-4 Fig-l2 6- LJ NDER Fl G ORDER-l-2-3-4-5-6 5 6Y 8 1 155.13 Q-CYLINDER Fl RIN G ORDER-i-2-4-3-5-6 8-7 ENGINE The primary object of the present invention is to provide an improved internal combustion engine of the reciprocating piston type, embodying many of the desirable characteristics of 2-cycle engines and of 4-cycle engines while eliminating undesirable characteristics of both types. Particularly, an object of the present invention is to provide a 4-cycle, internal combustion engine comprising a crankcase and a pair of cylinders opening away from the crankcase and being in communication therewith. A piston is reciprocably disposed in each cylinder to define therewithin a variable-volume combustion chamber. The two cylinders, which may be opposed or side-by-side, are provided with inlet ports, and there is a gaseous mixture carrying passageway leading from the crankcase to each inlet port. Means for admitting a gaseous mixture to the crankcase is provided. Valve means for opening and closing the passageways are provided, the valve means being arranged and driven such that each passageway is opened only on alternate occasions when both pistons move toward the axis of the crankshaft in the crankcase so that the gaseous mixture in the crankcase is pumped through the open passageway into its associated cylinder. In this manner, since the firing cycle of the two cylinders alternate, a two-piston volume charge of gaseous mixture is driven into each cylinder before its piston begins its compression stroke.

In the illustrative embodiment, the gaseous mixture is admitted into the crankcase by means including reed valves which open when the pressure in the crankcase is below the pressure of the source of gaseous mixture and which close when the pressure in the crankcase exceeds that of the gaseous mixture. The reeds open, therefore, when the pistons move away from the axis of the crankshaft and close when the pistons move toward the axis of the crankshaft. The crankshaft and the pistons and the connecting rods are proportioned and designed such that, at any time, the positions of the pistons respectively in the cylinders are substantially identical. That is, it is the simultaneous movement of the pistons away from the crankshaft which draws a gaseous mixture into the crankcase and toward the crankshaft which pumps two-piston volumes of gaseous mixture through the open passageway into one of the cylinders.

One important advantage of the engine of the present invention is that the inlet valve to each cylinder, i.e., the valve which opens and closes the passageway leading from the crankcase to the inlet port of each cylinder, is out of the high heat and high pressure area of the cylinder. Additionally, an exhaust chamber with a butterfly valve dominating its exhaust port is attached to each cylinder to be out of the high heat and high pressure area of the cylinder. This chamber between the exhaust port in the side wall of each cylinder and the butterfly valve permits the gases to burn completely at low heat and low pressure, thereby very significantly to reduce the temperature of the exhaust. This factor will, of course, reduce the pollution content of the exhaust and particularly the nitrous oxide content of the exhaust. It will be appreciated that a simple butterfly valve may not be air tight, and this is an advantage of my structure. Butterfly valves are inexpensive as compared to conventional poppet exhaust valve assemblies.

The engine of the present invention includes two cylinders or any multiple of two cylinders. The cylinders may be either opposed or side-by-side.

I refer to my US. Pat. No. 3,499,425 issued Mar. 10, 1970 and also disclosing an engine combining many of the desirable characteristics of 2-eycle and 4-cycle engmes.

To the accomplishment of the above and related objects, my invention may be embodied in the forms illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that change may be made in the specific constructions illustrated and described, so long as the scope of the appended claims is not violated.

In the drawings:

FIG. 1 is a sectional view taken along two planes perpendicular to the axis of the crankshaft and showing the opposed cylinder version of the engine of the present invention, the two planes being respectively on the centers of the two cylinders;

FIG. 2 is a sectional view taken along a plane perpendicular to the axis of the crankshaft and showing the side-by-side version of the engine of the present invention;

FIG. 3 is a fragmentary sectional view showing the inlet valve means which controls the flow of gaseous mixture from the crankcase alternately'to each side-byside cylinder;

FIGS. 4a and 4b are sectional views of the rotary valve member of FIG. 3 taken along the respective indicated section lines;

FIG. 5 is a diagrammatical view showing the manner in which the rotary valves and butterfly valves are drivingly connected to the crankshaft of the opposed cylinder engine of FIG. 1;

FIGS. 6-9 are diagrammatical views of a 2-cylinder, 4-cylinder, 6-cylinder and 8-cylinder engine with the cylinders side-by-side and showing the firing order of the cylinders; and

FIGS. 10-13 are diagrammatical views showing 2- cylinder, 4-cylinder, 6-cylinder and 8-cylinder engines of the opposed type and showing the firing orders of the cylinders.

Referring more particularly to FIG. 1, it will be seen that I have illustrated an engine of the internal combustion, reciprocating-piston type, indicated generally by thereference numeral 10, and comprising acylinder block assembly 12 providing a generally cylindricallyshaped crankcase 14 withopposed cylinders 16, 18 extending radially outwardly from the crankcase. Acrankshaft 20 is disposed in the crankcase to extend axially therealong, and apiston 22, 24 is reciprocably received in eachcylinder 16, 18 conventionally to define therewithin a variable-volume combustion chamber. Eachpiston 22, 24 is drivingly connected to the crankshaft in a conventional manner by arod 26, 28. Eachpiston 22, 24 conventionally includes apiston head 30 and askirt 32 depending from the head and extending toward thecrankshaft 20 and atrunnion 34 extending diametrically across the skirt. Eachrod 26, 28 has oneend 36 journal mounted to thetrunnion 34 of its associated piston and itsother end 38 journal mounted on an eccentric bearingportion 40 of thecrankshaft 20.

importantly, it will be appreciated that eachpiston 22, 24 also includes shield means 46 closing the space bounded by itspiston head 30 andskirt 32, the shield means being formed to provide a cavity opening toward thecrankshaft 20 and proportioned to provide clearance for the oscillation of the said oneend 38 of the associatedpiston rod 26, 28. The purpose of this shield means 46 is to reduce the overall volume of the space within thecrankcase 14 and pistons. This feature will be discussed in more detail as this description progresses.

Each cylinder l6, 18 is conventionally provided with a threaded spark plug opening 52 in its closed end. It will be appreciated that the illustrative engine is an air-cooled engine; but it will be understood that the basic engine may be either water cooled or air cooled, depending upon the particular application requirements.

Theengine 10 is constructed such that a gaseous mixture is admitted to thecrankcase 14 and then distributed to thecylinders 16, 18. For this reason, the volume of the space within thecrankcase 14 is reduced by defining that space, where possible, by a wall such as indicated at 58 cylindrically formed about therotational axis 60 of thecrankshaft 20. Further, thecrankshaft 20 is formed to provideeccentric bearing portions 40 on which the ends 38 of therods 26, 28 are journal mounted and cylindrical counter balance portions concentric with the axis of thecrankshaft 20 and of a diameter just slightly smaller than the internal diameter of thecrankcase 14. The combined axial length of the concentric cylindrical portions of thecrankshaft 20 are generally equal to the axial length of thecrankcase 14 less the combined axial length of the bearingportions 40, thereby to reduce the volume of the gaseous mixture receiving space in thecrankcase 14. In other words, thecrankcase 14 is made generally cylindrical and the crankshaft is made concentrically cylindrical at all portions other than theeccentric bearing portions 40 and of a diameter such that it will occupy as much of the space of a crankcase as possible. This structural feature accompanied by the shield means 46 on eachpiston 22, 24 creates a very effective pump for driving the gaseous mixture admitted to thecrankcase 14 alternately into thecylinders 16, 18 when thepistons 22, 24 simultaneously move toward the axis of thecrankshaft 20. Thecrankshaft 20, connectingrods 26, 28 andcylinders 16, 18 are proportioned and designed such that, at any time, the positions of thepistons 22, 24, respectively, in the cylinders are substantially identical.

In this description and in the appended claims, the words gaseous mixture are intended to include air by itself or air mixed with the vapor of a fuel such as gasoline orveven a fuel vapor by itself. When fuel injection techniques are used, air by itself is admitted to thecrankcase 14. In non-fuel injection engines, a mixture of air and gasoline vapors is admitted to thecrankcase 14.

Means are provided for admitting a gaseous mixture to thecrankcase 14, the illustrative means including aninlet conduit 62, aplate 63 providing a pair ofports 64 leading from theconduit 62 to aspace 66 in thecrankcase 14, and a pair ofreed valves 65 for closing theports 64. Thereed valves 65 normally close theports 64. Thevalves 65, which may conventionally be 0.008 to 0.012 inches thick, are arranged such that when the pressure in thecrankcase 14 drops below the pressure of the gaseous mixture source, the valves open to admit the gaseous mixture into the crankcase and, when the pressure in the crankcase exceeds that of the gaseous mixture source, the valves close theports 64. Particularly, thevalves 65 open when thepistons 22, 24 move away from thecrankshaft 20 and close when the pistons move toward the crankshaft. Thepistons 22, 24 and thereed valves 65, therefore, act as a pump. Conventionally, curved stops 68 are provided for limiting the flexing of the reed valves.

Eachcyinder 16, 18 is provided at peripherally spaced points remote from its closed end, with an inlet port orports 70 and an exhaust port orports 72. The arrangement of theseports 70, 72 is such that they are opened and closed by movement of thepistons 22, 24 in thecylinders 16, 18. The advantages of such a port arrangement are discussed in my said prior US. Pat. No. 3,499,425.

Thecylinder block assembly 12 includes, with eachcylinder 16, 18, ahousing 74 including aport 76 therein providing anauxiliary chamber 78 in open communication with thecylinder exhaust port 72. It will be appreciated that theport 76 is at a point remote from the point of communication of theauxiliary chamber 78 with theexhaust port 72, and that theport 76 is dominated by abutterfly valve 80 carried on ashaft 82. Thebutterfly valve 80 may be rotatably or oscillably driven.

Thecylinder block assembly 12 includes means providing apassageway 90, 92 leading from thecrankcase 14 to eachinlet port 70. In theillustrative engine 10, adjacent eachinlet port 70 is a fuel injector fitting ornozzle 94, 96 which may be conventionally connected to a source of fuel vapor. in such a case, when air is pumped from thecrankcase 14 through thepassageway 90, 92, the fuel vapor is mixed with the air and admitted to thecylinder 16, 18 through theport 70.

Then, arotary valve 100, 102 extends across eachpassageway 90, 92 to open and close that passageway, each rotary valve being received in abore 104, 106 which is parallel with theaxis 60 of thecrankshaft 20. Eachrotary valve 100, 102 is provided with acutout 110, 112 on its periphery such that eachpassageway 90, 92 is opened during a portion of each revolution of each valve. Thevalves 100, 102 are both drivingly connected to thecrankshaft 20 and are arranged so that theirrespective passageways 90, 92 are opened only on alternate occasions when bothpistons 22, 24 move toward theaxis 60 of thecrankshaft 20. That is, each time thepistons 22, 24 move toward theaxis 60, the fuel mixture in thecrankcase 14 is pumped through the opened passageway or 92 into thecylinder 16 or 18 to be compressed. In preferred embodiments, eachpassageway 90, 92 remains open throughout the period when its associatedinlet port 70 is opened by thepiston 22, 24. The manner in which therotary valves 100, 102 may be driven to open eachpassageway 90, 92 only on alternate occasions when bothpistons 22, 24 are moving toward theaxis 60 will be discussed in conjunction with FIG. 5.

Turning now to FIGS. 2, 3, 4a and 4b, a discussion of my side-by-side version of the engine of the present invention will be discussed, like reference numerals indicating like parts. This engine 10' is arranged such that itscylinders 16, 18 are disposed side-by-side with their axes lying in a plane which is radial to theaxis 60 of thecrankshaft 20. The twocylinders 16, 18 open into the common crankcase 14' which is generally cylindrically formed for the reasons discussed above.

The twopassageways 90, 92 leading to theinlet ports 70 from the crankcase 14' are alternately opened and closed by means of a singlerotary valve member 130 which extends parallel to the axis of the crankshaft and across both passageways. Thisillustrative valve member 130 is provided with acutout 132 associated with thepassageway 90 and a diametricallyopposite cutout 134 associated with thepassageway 92. Thevalve member 130 is driven from the crankshaft and thecutouts 132, 134 are positioned such that eachpassageway 90, 92 is opened only on alternate occasions when the twopistons 22, 24 move toward theaxis 60 of thecrankshaft 20. Theeccentric bearing portions 40 associated with thepistons 22, 24 are identically disposed so that the two pistons move simultaneously together toward and away from the axis of thecrankshaft 20.

Turning now to FIG. 5, it will be seen that I have shown diagrammatically therotary valves 100, 102, thecrankshaft 20 and theshafts 82 on which thebutterfly valves 80 are carried. Illustratively, anidler gear 146 is used drivingly to connect agear 147 on thecrankshaft 20 to agear 148 on therotary valve 100. Thegear 148 is engaged with agear 150 on therotary valve 102. A cogwheel 152 is mounted on therotary valve 100, acogwheel 154 is mounted on theshaft 82 and acogbelt 156 drivingly connects theshaft 82 associated with thecylinder 16 to therotary valve 100. Similarly, aco'gwheel 158 is mounted on thevalve 102, acogwheel 160 is mounted on theother shaft 82 associated with thecylinder 18, and acogbelt 162 is trained about these cogwheels. It will be appreciated that this drive system is merely illustrative and that other forms of drive systems may be used.

In some embodiments of the present engine, thevalves 100, 102 may be rotated at' one-half the speed of thecrankshaft 20 while the twoshafts 82 are rotated at one-fourth the speed of the crankshaft.

With the above description in mind, the 4cycle operation of the engine of the present invention will be discussed. The firing sequence for thecylinder 16 with itspiston 22 is as follows:

On the power stroke thepiston 22 moves toward theaxis 60 and the exhaust goes out theexhaust port 72 and theport 76 which is opened by thebutterfly valve 80. The exhaust continues to go out theport 72 until thepiston 22 moves back up to closeport 72. Theinlet valve 100 is closed to block thepassage 90 during the power stroke of thepiston 22 so that the fuel mixture cannot be pumped from thecrankcase 14 into thecylinder 16 during the power stroke. Thepiston 22 then goes up again. Thepiston 22 then goes down again or toward theaxis 60. During this stroke, thevalve 100 is in a position such that thepassageway 90 is open and thebutterfly valve 80 is closing theport 76. The twopiston volumes of air resulting from movement of bothpistons 22, 24 toward theaxis 60 pumps the gaseous mixture through thepassageway 90 into thecylinder 16. Thepiston 22 then goes up or away from theaxis 60 on its compression stroke to compress the gaseous mixture for firing.

Recapitulating, the engine of the present invention is a 4-cycle engine with eachpiston 22, 24 having four strokes including stroke N o. 1 which is a power stroke at the bottom of which the exhaust leaves the cylinder through the exhaust port and the open butterfly valve; stroke No. 2 is the piston moving up again in the cylinder; stroke No. 3 is the piston moving downwardly again in the cylinder to pump (together with its associated piston) the gaseous mixture from thecrankcase 14 into the cylinder; and stroke No. 4 is a compression stroke.

Thecylinder 18 has the same firing sequence as thecylinder 16 except that thecylinder 18 is on opposite cycles. That is, when thepiston 22 is on its power stroke, thepiston 22 and thepiston 24 pump the gaseous mixture from the crankcase .14 through thepassageway 92 into thecylinder 18 for compression and firing. When thepiston 24 is on its power stroke, thepiston 24 and thepiston 22 pump the gaseous mixture from thecrankcase 14 through thepassageway 90 into thecylinder 16 for compression and firing. Thus, when onepiston 22, 24 is on its power stroke, the other piston is on its intake stroke, and when one piston is on its compression stroke, the other piston is on its stroke which is conventionally referred to as the exhaust stroke in the Otto cycle engine.

When the engine of the present invention is running at high speeds, e.g., over 4,000 rpm, the butterfly exhaust valves may be eliminated or held steadily open.

Modern automobile engines often include means for recycling the exhaust through the intake to reduce pollution. Some other modern automobile engines supply compressed air to the exhaust to burn the exhaust gases at low pressure to reduce pollution. The engine of the present invention obtains this feature of burning the exhaust gases at low pressure to reduce pollution. Particularly, the fresh gases pumped into thecylinders 16, 18 will mix with and burn the exhaust gases trapped in thechambers 78, and this burning will take place at low pressure. The effect of this is to reduce the pollution content of the exhaust and particularly the unburned hydrocarbon content of the exhaust.

The exhaust of the engine of the present invention is extremely cool. An engine constructed in accordance with the present invention can be operated and a person can place his hand in the output side of the butterfly exhaust valve and not be burned by the exhaust itself. This, of course, reduces the nitrous oxide content of the exhaust which is a pollution factor producing smog and eye irritation.

Butterfly valves of the engine of the present invention may rotate at one-fourth, three-fourths or 1% the speed of thecrankshaft 20. The butterfly valves may be oxcillated by a crank running at one-half the speed of thecrankshaft 20.

An important advantage of the engine of the present invention is that the fuel injection fittings ornozzles 94, 96, if they are used, may be out of the high heat and high pressure zones of thecylinders 16, 18.

The 4-cycle engine of the present invention has approximately the same weight as comparable 2-cycle engines, approximately the same manufacturing costs as comparable 2-cycle engines and approximately the same height as comparable 2-cycle or I. head engines.

Turning now to FIGS. 6-9, it will be seen that I have shown, by diagrammatical views, how a 2-cylinder, 4- cylinder, 6-cylinder or S-cylinder engine may be constructed using the side-by-side arrangement discussed in conjunction with FIG. 2 as well as a proposed firing order for such 4-cyclinder, 8-cylinder and 8 cylinder engines. Then, in FIGS. 10-13, I have provided diagrammatical views showing how a Z-cylinder, 4- cylinder, 6-cylinder or S-cylinder engine may be constructed using the opposed cylinder concept discussed in conjunction with FIG. 1 as well as a proposed firing order for the 4-cylinder, 6-cylinder and 8-cylinder engine.

lt will be appreciated that an extremely compact and relatively short engine may be provided by constructing the engines of FIGS. 10-13 as horizontally opposed engines.

Lubrication may be provided by making oil with the fuel mixture going into the crankcase or by positive pressure pumping of oil to the bearings and pistons.

What is claimed is:

l. A 4-cycle, internal combustion engine comprising a pair of cylinders, each cylinder being open at one end and provided, at peripherally spaced points remote from the other end of said cylinder, with an inlet port and an exhaust port in its side walls, a crankshaft arranged adjacent the open ends of said cylinders, a piston reciprocably received in each said cylinder and defining therewithin a variable-volume combustion chamber, means extending through the open end of each said cylinder and drivingly connecting the piston therein to said crankshaft, the last said means and said crankshaft being arranged so taht said pistons move simultaneously toward and away from the axis of said crankshaft, each said piston being movable in its associated cylinder past its said ports to close and open same during each revolution of said crankshaft, a crankcase for said crankshaft, means for admitting a gaseous mixture to said crankcase, means providing a passageway from said crankcase to the inlet port of each said cylinder, and valve means for opening and closing said passageways, said valve meeans being drivingly connected to and operated by said crankshaft, and said valve means being arranged alternately to open said passageways only on occasions when said pistons move toward the axis of said crankshaft, said crankcase being generally cylindrically shaped about the axis of said crankshaft, said crankshaft being formed to provide eccentric bearing portions on which said means for drivingly connecting said pistons to said crankshaft are journalled and, on opposite ends of said bearing portions, counter balance portions which are fully cylindrical and concentric with the axis of said crankshaft and of a diameter slightly smaller than the internal diameter of said crankcase, the combined axial length of said counter balance portions being generally equal to the axial length of said crankcase less the combined axial lengths of said bearing portions, thereby to reduce the volume of the gaseous mixture receiving space in the crankcase to increase the efficiency with which the piston movement pumps said gaseous mixture to said cylinders, said means for admitting a gaseous mixture to said crankcase including reed valve means arranged to open when the pressure in said crankcase drops below the pressure of the gaseous mixture source and to close when the pressure in said crankcase exceeds the pressure of said source, said first mentioned valve means including rotary valve means, said rotary valve means including one or more valve members extending parallel to the axis of said crankshaft and across each said passageway, each of said valve members being formed to close its associated passageway during a portion of each revolution and to open it during the rest of each revolution throughout the period when its associated inlet port is opened by its associated piston, means defining an auxiliary chamber in open communication with the exhaust port of each said cylinder, each said auxiliary chamber being provided with a port at a point remote from the point of communication of said auxiliary chamber with said exhaust port, butterfly valve means dominating said auxiliary chamber port, and means driven from said crankshaft for opening said butterfly valve means only on the occasions when its associated cylinder exhaust port is opened by the piston therein moving downwardly on its power stroke.

i i i t

Claims (1)

1. A 4-cycle, internal combustion engine comprising a pair of cylinders, each cylinder being open at one end and provided, at peripherally spaced points remote from the other end of said cylinder, with an inlet port and an exhaust port in its side walls, a crankshaft arranged adjacent the open ends of said cylinders, a piston reciprocably received in each said cylinder and defining therewithin a variable-volume combustion chamber, means extending through the open end of each said cylinder and drivingly connecting the piston therein to said crankshaft, the last said means and said crankshaft being arranged so taht said pistons move simultaneously toward and away from the axis of said crankshaft, each said piston being movable in its associated cylinder past its said ports to close and open same during each revolution of said crankshaft, a crankcase for said crankshaft, means for admitting a gaseous mixture to said crankcase, means providing a passageway from said crankcase to the inlet port of each said cylinder, and valve means for opening and closing said passageways, said valve meeans being drivingly connected to and operated by said crankshaft, and said valve means being arranged alternately to open said passageways only on occasions when said pistons move toward the axis of said crankshaft, said crankcase being generally cylindrically shaped about the axis of said crankshaft, said crankshaft being formed to provide eccentric bearing portions on which said means for drivingly connecting said pistons to said crankshaft are journalled and, on opposite ends of said bearing portions, counter balance portions which are fully cylindrical and concentric with the axis of said crankshaft and of a diameter slightly smaller than the internal diameter of said crankcase, the combined axial length of said counter balance portions being generally equal to the axial length of said crankcase less the combined axial lengths of said bearing portions, thereby to reduce the volume of the gaseous mixture receiving space in the crankcase to increase the efficiency with which the piston movement pumps said gaseous mixture to said cylinders, said means for admitting a gaseous mixture to said crankcase including reed valve means arranged to open when the pressure in said crankcase drops below the pressure of the gaseous mixture source and to close when the pressure in said crankcase exceeds the pressure of said source, said first mentioned valve means including rotary valve means, said rotary valve means including one or more valve members extending parallel to the axis of said crankshaft and across each said passageway, each of said valve members being formed to close its associated passageway during a portion of each revolution and to open it during the rest of each revolution throughout the period when its associated inlet port is opened by its associated piston, means defining an auxiliary chamber in open communication with the exhaust port of each said cylinder, each said auxiliary chamber being provided with a port at a point remote from the point of communication of said auxiliary chamber with said exhaust port, butterfly valve means dominating said auxiliary chamber port, and means driven from said crankshaft for opening said butterfly valve means only on the occasions when its associated cylinder exhaust port is opened by the piston therein moving downwardly on its power stroke.

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