US1936841A - Internal combustion engine - Google Patents

Description

Nov. 28, 1933. F. T. IRGENS INTERNAL COMBUSTION ENGINE 3 Sheets-Sheet 1 Filed March 17, 1950 61cm neg a Nov. 28, 1933.

Filed March 17, 1950 3 Sheets-Sheet 2 4 FIG. /6J A6- 0 za I 7 m z/ 52 0 45 jl 7 i /0 A5- Nov. 28, 1933. F IRGEN 1,936,841

INTERNAL COMBUSTION ENGINE Filed March 17, 1950 v a Sheets-*Shet s 5 v I I I 43 3mm /5' Z/ M M I Patented Nov. 28, 1933 UNITED STATES PATENT OFFICE Outboard Motors Corporation, Wis., a corporation of Michigan Milwaukee,

Application March 17, 1930. Serial No. 436,287

34 Claims. (Cl. 123-56) This invention relates to improvements in internal combustion engines and has particular reference to a novel and improved rotary valve mechanism which controls the flow of mixture to the crank case of a two-cycle engine, and also in efiect varies the volumetric capacity of the crank case at different points of the cycle.

It is the primary object of the invention to improve the volumetric efliciency of two-cycle engines while avoiding difficulties heretofore experienced in the way of imperfect mixtures which have resulted from previous attempts to increase crank case compression.

It has become standardv practice in two-cycle engine construction to limit the crank case capacity as much as possible by filling the crank case almost completely with the cranks and associated parts. By this means volumetric efficiency has been improved due to the increased crank case compression, but there has been .a corresponding decrease in the efficiency of combustion resulting from the high velocity at which the compressed gases have been transferred to the combustion chamber, which they must necessarily enter before the burning charge has been completely scavenged.

' In the practice of the present invention I not only use a rotary valve for the purpose of prolonging and more adequately controlling communication between the crank case and the carburetor, but I further accomplish a very important result in designing my rotary valve to provide an expansion chamber which is made to communicate with the crank case and transfer port prior to and during transfer of gases from the crank case to the commistion chamber. 'The additional capacity thus provided receives a portion of the highly compressed gases in the sub-piston space, and not only maintains such gases more immediately adjacent the point of delivery to the cylinder, but also reduces the sub-piston compression to an extent such that the flow of gases to the cylinder is slower and more uniform, thereby promoting better and cleaner scavenging with fewer eddy currents and a much better and more highly combustible mixture remaining in the combustion chamber. While I have referred to crank case compression, it will be observed that there is very little compression space in the crank case, and that actually compression occurs quite largely in the lower ends of the respective cylinders beneath the pistons operating therein. To avoid loss of pressure which would be occasioned by transferring gases between the respective cylinders, I prefer to provide each cylinder with its own separate carburetion and valve.

Another object of the invention relates to the provision of means whereby the rotary valve is permitted to operate at substantially uniform rates of rotation notwithstanding periodic or cyclic variations in rate of rotation of the crank shaft and associated parts.

In the drawings:

Figure 1 is a plan view of a two-cycle twocylinder opposed engine embodying this invention, one of the cylinders and associated valve mechanism being shown in axial section.

Figure 2 is a vertical axial section tothe engine shown in Fig. 1. 0

Figure 3 is a rear elevation thereof.

Figure 4 is a fragmentary detail similar to a portion of Fig. 1, showing the piston at the end of its compression stroke.

Figure 5 is a view taken in section in the plane indicated at 5-5 in Fig. 4.

Figure 6 is a view taken in section in the'plane indicated .at 66 in Fig. 4.

Figure '7. is a detail view taken in section in the plane indicated at 77 in Fig. 2.

Like parts are identified by the same reference characters throughout the several views.

The invention has been shown, byway of illustration, applied to a two-cycle, two-cylinder opposed engine of an outboard motor, but obviously it may be employed in connection with two-cycle engines having a different number of cylinders and organized for different purposes.

In this exemplification of the invention a sleeve or so-called shaft housing member 10 supports the crank case 11 upon which are mounted the respective cylinders 12. In the top and bottom of the crank case 11 are bearings for the crank shaft 15, at the upper end of which is the usual fly wheel 16. It will be noted that the crank disks 18, pins 19, connecting rods 20, and connecting rod bearings 21 are so designed as to leave a very small amount of gas' capacity in the crank case, the object being to-fill the crankcase as nearly as possible.

The cylinders 12 are provided in the usual way with exhaust ports at 22 communicating with manifolds 23 and mufller 24. Each cylinder has also an inlet or transfer port at 25 which at bottom dead center communicates with the cylinder above and below the piston 26 therein. The piston preferably comprises a hollow body open at 2'? for intermittent communication with the exhaust port 22, and having an inclined that the capacity of the space beneath the piston lower face at 28 for guiding gases to and from the compression space below the piston.

Controlling the admission of mixture to the inlet and transfer ports 25, is the rotary valve mechanism which comprises the particular subject matter of the present invention.

Each cylinder is provided with an integral forward extension at 30, of which the cylindrical bore communicates with the cylinder through ports 25. These bores are capped at their outer ends by closures 31, each of which comprises a carburetor having a flaring air inlet mouth at 3 a float chamber at 33, a jet at 34, and a throttle valve at 35.

The valves mounted in the bores of the respective cylinder extensions 30 comprise sleeves 38, each of which is ported at 3'? and 38, the latter port being placed in direct communication with the air inlet valve 32 by means of a pipe 39 which is cast integrally with sleeve 36, and is formed to provide an axially disposed inlet portion at if), and a radially disposed discharge portion at 41. The discharge portion ll. of pipe 39 is joined to the margin of the sleeve about the port 38 therein.

Each such sleeve is closely fitted to rotate within its respective bore, and each is provided with a shaft extension 43 upon which is mounted a' bevel gear 44. The two bevel gears 44 in the present construction receive motion from a bevel pinion 45, flexibly keyed to a jack shaft 46. The jack shaft in turn is driven by a spur gear 47 from a complementary spur gear 48 on the crank shaft. The hub of this latter-gear extends into the upper crank shaft bearing. as shown in Fig. 2. The jack shaft 46 may constitute a timer shaft provided with the interrupter mechanism shown at 49. I

The flexible connection of the driving pinion 45 to the jack shaft or timer shaft 46, is best shown in Fig. '7. Shaft 46 is provided with a slot at 50 in which the resiliently flexible spring key 51 is held by a cross pin 52. The free end of the resilient key 51 has arms 53 which project from the slot 50 into engagement with suitable --;-grooves in the pinion 45, as shown in Fig. 2. The

result is a construction which permits pinion 45 a limited degree of independent movement with respect to the shaft 46 upon which it is mounted.

It will be understood that the two cylinders in this type of 7 engine fire simultaneously, and the energy developed in the expansion stroke must be used in the subsequent compression stroke. As a result, there is an appreciable cyclic change 1 in speed of crank shaft and fly wheel, and in .order to avoid transmitting this varying rate of rotation through the pinion 45 and driven gears 44 to the rotary valves, I may, if I so desire, employ the resilient pinion mounting illustrated.

In practice, the movement of the piston to the position in which it appears in Fig. 4 not only compresses the'combustible charge in the outer end of thecylinder, but draws a fresh charge through the carburetor and the rotary valve'into the inner end of the cylinder next to the crank case. As above noted, the charge for each givencylinder is drawn directlyinto the base thereof. thus avoiding any necessity for the transfer of gases across the crank case,'in-which the space is purposely very limited.

It will be noted from an inspection of Fig. 4

is at a minimum during the stroke which sucks the'fresh charge therein. The rotation of the valve sleeve 36 has brought pipe 39'through a position of registry with the inlet of transfer port 25 through which the carbureted air or combustible mixture has been entering the compression space. The remainder of sleeve 36 is completely cut off from communication with this space. Practically the complete displacement of the piston, therefore, is effective to draw combustible mixture into the inner end of the cylinder' in accordance with the most approved twocycle practice.

During the expansion stroke of the piston toward the position in which it is shown in Fig. l, the valve sleeve 36 is caused to rotate to the position shown in Fig. 1 whereby its pipe member 39 is wholly'cut off from communication with cylinder port 25. The cylinder port 25 has now been placed in communication, through sleeve port 37, with the receiver in the interior of the valve sleeve 36 into which a large portion of the combustible mixture has been forced by the descending piston 26. Thus, instead of holding un der high compression the large quantity of gas drawn into the restricted sub-piston compression space, I have already caused such gas to start on its movement toward the cylinder, and I am holding it under reduced compression in a space of very' much larger capacity than could have been provided in the cylinder and transfer port alone.

Ash. result of this constructionthe transfer of mixture to the cylinder, and the consequent scavenging of the exhaust gases from the cylinder, takes place more smoothly than has been possible in any two-cycle engine having a like efficiency of mixture intake. The power of the engine is greatly increased by this means of controlled variation of the capacity of the sub-piston compression space and transfer port, whereby such space is at a minimum during the compression stroke, and is at a maximum during the expansion stroke and transfer. 1 5

As an example of the timing of the rotary valve mechanism disclosed, I shall refer to a particular engine embodying the invention in which the transfer port 25 communicates almost continuously with one or the other of ports3'7 and 120 38 of the valve. As soon as the piston 26 moves upwardly sufiiciently to cut off communication between the transfer port and the combustion chamber, port 38 moves into initial registry with transfer port 25 to admit carbureted air to the sub-piston compression space. Port 38 continues open until the piston has started downwardly on its expansion stroke to a position representing approximately 25 degrees of crank rotation past top dead center. At this point port 38 closes and port 3'? moves into registration with transfer port 25, thereby allowing the mixture compressed below the piston to pass into the receiver within the'valve sleeve 36 until the piston has completed its expansion stroke and moved upwardly to a point where the transfer of gas has ceased.

The organization disclosed will be found 'useful in many internal combustion engine constructions using a means of compressing mixture in advance of delivery to the combustion chamber. It will, however, be found particularly valuable in the type of two-cycle engine disclosed.

I claim:

1. An internal combustion engine comprising the combination with a cylinder and crank case 145 assembly providing a sub-piston compression space including an open transfer passage controlled by said piston, of a crank shaft in said case, a receiver chamber provided with a port adapted for communication with said space, and 150 means operated by said crank shaft for intermittently opening and closing communication between said chamber and space.

2. An internal combustion engine comprising the combination with a piston, a crank shaft, and a cylinder and crank case assembly providing a sub-piston compression space, of a chamber provided with a port for communication with said space, an air inlet conduit, and valve means driven by said crank shaft for timed control of alternating communication of said space with said chamber and conduit.

3. An internal combustion engine comprising the combination with a cylinder, a piston and an air compressor provided with a transfer port to the cylinder, of an air receiver and a single valve means controlling the admission and discharge of air-from said compressor and adapted to place said receiver in communication with said compressor during a portion of the period of discharge of air from the compressor, and to cut off said receiver from communication with said compressor during the period of admission of air to said compressor.

4. In an internal combustion engine, the combination with a piston and a cylinder therefor, providing a sub-piston compression space and a transfer port affording communication controlled by said piston between said space and the combustion chamber in said cylinder, and a rotary chamber operatively connected to be actuated from said piston and provided with a port registerable with said transfer port during the cycle of piston movement during a period such as to limit compression in said space.

5. In a two-cycle internal combustion engine, the combination with a piston, of a crank case, a cylinder providing a sub -piston compression space, valve means for admitting air thereto, a crank in said case connected with the piston,an auxiliary chamber provided with valve means controlling communication between said chamber and said space, and connections operatively arranged between said valve means and crank shaft for the operation of said last mentioned valve means to establish communication between said space and chamber during the piston movement contracting said space, and to cut off such communication when said air admitting valve means is operative.

6. A two-cycle internal combustion engine comprising the combination with a piston, of a cylinder and crank case assembly providing a sub-piston compression space and a transfer port whereby delivery of mixture from said space to the head of the cylinder may be effected at predetermined periods in the cycle of piston operation, a crank shaft in said crank case to which said piston is operatively connected, a storage chamber potentially communicating through said port with said space and the head of the cylinder and provided with valve means controlling such communication, and connections operatively arranged to actuate said valve means from said crank shaft in accordance with the cycle of piston movement, said chamber being cut off from communication with said space during thelatter portion of that piston stroke by which said space is enlarged.

7. A multi-cylinder two-cycle engine including the combination with a plurality of pistons, a crank case, a plurality of cylinders for the pistons providing transfer ports respectively affording communication between the heads of the cylinders and the crank case compression space beneath the pistons therein, and a crank shaft to which the several pistons are respectively connected for simultaneous-inward and outward movement, said crank shaft, including means for filling substantially all crank case capacity not required for the piston connections, of a plurality of chambers potentially communicating with respective cylinders and provided with valve means operatively connected for actuation by said crank shaft for controlling communication between said chambersjand the compression space beneath the pistons of different cylinders, whereby to vary the capacity of the respective spaces in the cycle of piston movement.

8. In an internal combustion engine, the combination with a piston, of a crank case and cylinder assembly for said piston providing a subpiston compression space and a transfer port from said space to the head of the cylinder, a mixture inlet, an expansion chamber, and a valve operatively connected for operation from said piston and provided with means controlling communication of said inlet and said chamber with said space, whereby said inlet and said chamber are alternately placed in communication with said space during each cycle of piston movement.

9. In an internal combustion engine, the combination with a piston, of a crank case and cylinder assembly for said piston providing a sub-piston compression space and a transfer port from said space to the head of the cylinder, a mixture inlet, an expansion chamber, and a valve operatively connected for operation from said piston and provided with means controlling communication of said inlet and said chamber with said space, whereby said inlet and said chamber are alternately placed in communicationwith said space during each cycle of piston movement, said chamber being excluded from communication with said space during the period of mixture admission responsive to outward piston movement, and said inlet being cut off from communication with said space during the period of mixture compression in and transfer from said space by inward piston movement.

10. Ina two-cycle engine, the combination with a crank case, a cylinder providing an unobstructed transfer port from the crank case to the cylinder and a piston reciprocable in the cylinder and controlling said port, of a mixture inlet, an expansion chamber, and means controlled in accordance with piston movement for placing said inlet and chamber alternately in communication with said port.

11. In a two-cycle engine, the combination with a cylinder providing a transfer port and a piston reciprocable in the cylinder, of a mixture inlet and an expansion chamber, and means controlled in accordance with piston movement for placing said inlet and chamber alternately in communication with said port, said means comprising a rotary valve, a crank shaft connected with the piston, and motion transmitting connections between said shaft and valve.

l2.Ir 1 a two-cycle engine, the combination with a cylinder providing a transfer port and. a piston reciprocable in the cylinder to compress mixture alternately in the head thereof and in the sub-piston space and to control the transfer, of a rotary valve providing a mixture inlet port and an expansion chamber alternately adapted to communicate with the transfer port in the rotation of the valve, and means for rotating the valve in accordance with piston movement and in timed relation to admit mixture to said space during piston induced depression therein, and to reduce compression of such mixture in said space during transfer to the head by receiving a portion thereof into said chamber.

13. In a two-cycle engine, the combination with a cylinder providing a transfer port and a piston reciprocable in said cylinder to compress mixture alternately at one end or the other thereof, of means actuated from the piston for admitting mixture to said transfer port during compression of mixture in the cylinder head, and means actuated from the piston during its expansion stroke for interrupting the admission of mixture and enlarging the capacity of the space accessible to the mixture previously admitted.

14. In a two-cycle internal combustion engine, the combination with a piston and a crank case and cylinder therefor providing a sub-piston compression space and a transfer port, of a'rotatable chamber provided with a port registerable with said transfer port during the contraction of said space by the expansion stroke of the piston, and means controlled in accordance with the rotation of said chamber for admitting gas to said space during the enlargement thereof by the compression stroke of the piston, said ports being out of registry.

15. A two-cycle engine comprising the combination with a piston and a cylinder and crank case assembly providing a sub-piston compression space and a port leading thereto, of a crank shaft in said crank case connected with said piston, and an expansion chamber provided with rotary valve means controlling communication between it and said port, said means being connected with said crank shaft for operation in accordance with piston movement to open communication to said chamber from said space during the contraction thereof by the expansion stroke of the piston.

16. A two-cycle engine comprising the combination with a piston and a cylinder and crank case assembly providing a sub-piston compression space and a port leading thereto, of a crank shaft in said crank case connected with said piston, and an expansion chamber provided with rotary valve means controlling communication between it and said port, said means being connected with said crank shaft for operation in accordance with piston movement to open communication to said chamber from said space during the contraction thereof by the expansion stroke of the piston, said rotary valve means including a gas inlet arranged to communicate with said port alternately with said chamber.

17. A two-cycle engine comprising the combination with a reciprocable piston provided with a connecting rod and crank, and a cylinder and crank case assembly for said piston, a crank having a sub-piston compression space and a transfer po t leading to the head of the cylinder, of a rotary valve structure including a peripherally ported receiving chamber operatively connected to said crank and timed to communicate through said port with the transfer port substantiallyduring the period of gas compression in said subpiston space and the period of transfer of gas from said space to the combustion chamber, and a conduit carried by said chamber and arranged to communicate with said transfer port'for the admission of gas to the sub-piston space for the approximate period during which gas may be drawn therein by piston movement.

18. Atwo-cycle engine comprising the com-- bination with a piston, connecting rod and crank, of a cylinder and crank case assembly providing a sub-piston compression space and a port opening thereto, a chamber rotatably mounted adjacent said port and provided with a complementary port adapted to communicate with said first mentioned port during a predetermined period of chamber rotation, motion transmitting connections between said chamber and crank shaft so timed with reference to the movement of said piston as to place said chamber in communication with said space during a portion of the period of compression of gas in said space, and a conduit leading through said chamber and communicating with said first mentioned port during a portion of the period for which said chamber is out of communication therewith, said conduit being adapted to admit air to said space during the said last mentioned period.

19. A two-cycle engine comprising the combination with a piston, connecting rod and crank, of a cylinder and crank case assembly providing a sub-piston compression space and a port opening thereto, a chamber rotatably mounted adja cent said port and provided with a complementary port adapted to communicate with said first mentioned port during a predetermined period of chamber rotation, motion transmitting connections between said chamber and crank shaft so timed with reference to the movement of said piston as to place said chamber in communication with said space during a portion of the period of compression of gas in said space, and a conduit leading through said chamber and communicating with said first mentioned port during a portion of the period for which said chamher is out of communication therewith, said conduit having an opening disposed approximately upon the axis of said chamber and a point of discharge approximately at the periphery thereof.

20. An internal combustion engine comprising the combination with a piston, connecting rod and crank shaft, and a cylinder and crank case assembly providing a sub-piston compression space, of a valve chamber associated with said cylinder and provided with a peripheral port communicating with said space and a substantially axial inlet, a valve rotatable in said chamber and including a conduit from said axial inlet to a peripheral point registerable with said port in rotation of said valve, and means for carbureting air adjacent said inlet.

21. In a .two-cycle engine, the combination with a crank case and opposed cylinders, a crank shaft in said case and pistons reciprocable in said cylinders and connected thereto, of valve chambers associated with the respective cylinders, rotary valves in said chambers having peripheral ports and axial inlets at opposite ends of the respective chambers, and separate means for carbureting air admitted to said inlets.

22. In a two-cycle engine, the combination with a crank case and opposed cylinders, a crank shaft in said case and pistons reciprocable in said cylinders and connected thereto, of valve chambers associated with the respective cylinders, rotary valves in said chambers having peripheral ports and axial inlets at opposite ends of the respective chambers, and separate means for carbureting air admitted to said inlets, the respective cylinders being provided with sub-piston compression spaces to which the carbureted air is admitted by the individual valves, and said crank shaft being formed to reduce the space for communication between the compression spaces of the respective cylinders.

23. In a two-cycle engine, the combination I with a crank case and opposed cylinders, a crank ports and axial inlets at opposite ends of the respective chambers, and separate means for carbureting air admitted to said inlets, the respective cylinders being provided with sub-piston compression spaces to which the carbureted air is admitted by the individual valves, and said crank shaft being formed to reduce the space for communication between the compression spaces of the respective cylinders, each such valve having an auxiliary airreceiver communicating with said spaces alternatively with the air admission ports.

24. In a two-cycle, two-cylinder engine comprising a crank case and opposed cylinders, a crank shaft in said case and pistons in said cylinders adapted for sub-piston compression, transfer passages around the pistons, valve chambers ported for communication with said passages, rotary valves in the respective chambers controlling air admission to the respective transfer passages, a common driving shaft to which said valves are geared and which is operatively connected to said crank shaft to receive motion therefrom, and means for carbureting air admitted through said valves to said passages.

25. In a two-cycle, two-cylinder engine comprising a crank case and opposed cylinders, a

crank shaft in said case and pistons in said cylinders adapted for sub-piston compression, transfer passages around the pistons, valve chambers ported for communication with said passages, rotary valves in the respective chambers controlling air admission to the respective transfer passages, a common driving shaft to which said valves are geared and which is operatively connected to said crank shaft to receive motion therefrom, and means for carbureting air admitted through said valves to said passages, each of said valve chambers comprising an auxiliary receiver, and each of said valves having an auxiliary port registerable with the transfer passage when the admission port is out of register therewith and adapted to admit transferred air to said receiver.

26. A two-cycle internal combustion engine comprising a crank case and opposed cylinders provided with transfer passages and associated valve chambers, carburetors at opposite ends of the respective chambers, and intergearedrotary valves in the chambers provided with inlets adjacent the carburetors, and peripheral outlets adapted for registry with the respective passages in the course of valve rotation.

27. A two-cycle internal combustion engine comprising a crank case and opposed cylinders provided with transfer passages and associated valve chambers, carburetors at opposite ends of the respective chambers, and intergeared rotary valves in the chambers provided with inlets ad-.

jacent the carburetors, and peripheral outlets adapted for registry with the respective passages in the course of valve rotation, and gas receivers housed within. the respective valves and ported for registry with the transfer passages when the said discharge ports are out of registry therewith.

28. A two-cycle internal combustion engine comprising a crank case and opposed cylinders provided with transfer passages and associated valve chambers, carburetors at opposite ends of the respective chambers, and intergeared rotary valves in the chambers provided with inlets adjacent the carburetors and peripheral outlets ad'ap'ced for registry with the respective passages in the course of valve rotation, a crank shaft in said case provided with pistons in said cylinders, and driving connections from said shaft to said valves including a flexible member sumciently yieldable to permit a substantially uniform valve speed irrespective of cyclic speed variation 'of said shaft.

29. An internalcombustion engine comprising the combination witha cylinder and crank case assembly providing a transfer port, of a crank shaft in said crank case including means for filling unused capacity therein, a piston reciprocable in the cylinder controlling communication between said transfer port, a connecting rod between said piston and crank shaft and the head portion of the cylinder, carbureting means connected with said cylinder at said transfer port, and a valve operatively connected with said crank shaft for the timed admission of carbureted air to said transfer port and the cylinder space beneath said piston, said valve being arranged to close during the expansion stroke of said piston whereby the carbureted gas below the piston will be compressed in the transfer port immediately adjacent the head portion of the cylinder for instantaneous delivery thereto when said port is uncovered by the piston.

30. Aninternal combustion engine comprising the combination with a cylinder and crank case assembly providing a transfer port, of a. crank shaft in said crank case including means for filling unused capacity therein, a piston reciprocable in the cylinder controlling communication between said transfer port, a connecting rod between said pis'ton and crank shaft and the head portion of-the cylinder, carbureting means connected with said cylinder at said transfer port, and a valve operatively connected with said crank shaft for the timed admission of carbureted air to said transfer port and the cylinder space beneath said piston, said valve being arranged to close during the expansion stroke of said piston whereby the carbureted gas below the piston will be compressed in the transfer. port immediately adjacent the head portion of the cylinder for instantaneous delivery thereto when said port is uncovered by the piston, together with a chamber connected with said rotary valve for communication with said transfer port alternatively with said valve, whereby the capacity'of said port is at a minimum when gases are being drawn therein on the compression stroke of the piston, and as a maximum upon communication of said chamber with said port during the compression stroke of the piston.

31. An internal combustion engine comprising the combination with a cylinder assembly providing a combustion chamber and a sub-piston compression space, a transfer port affording piston controlled communication between said space and chamber, and an exhaust port opening outwardly from said chamber, of a piston reciprocable in said cylinder arranged to control said ports and having an internal cavity opening laterally below the face of the piston and positioned to register with one of said ports when said port is closed by the piston.

32. An engine comprising the combination with a cylinder assembly providing a combustion chamber and a sub-piston compression space, transfer means affording piston controlled communication between said chamber and space, and an exhaust port opening outwardly from said chamber, of a piston reciprocable in said cylinder and arranged to control said means and port, said piston having a bottom closure web defining an interior cavity and having an opening through its side wall from said cavity arranged to register with said port when said port is covered by the piston.

33. In an engine, the combination with a cylinder assembly provided with a combustion chamber and sub-piston compression space and having transfer and exhaust ports, of a piston reciprocable in said cylinder for the control of said ports, said piston being closed ofi at its bottom to limit the capacity of said space whereby to cause gases compressed in said space to accumulate in said transfer port, and a part immediately adjacent said port operatively connected with said piston for movement in synchronism therewith and including a valve for the admission of fuel to said port, and a chamber arranged to communicate with said port when said valve is out of communication therewith, whereby to increase the capacity of said port when mixture is compressed therein and to reduce its capacity when mixture is being admitted thereto.

34. In an engine, the combination with a cylinder assembly provided with a combustion chamber and sub-piston compression space and having transfer and exhaust ports, of a piston reciprocable in said cylinder for the control of said ports, said piston having an internal cavity opening laterally for registry with said exhaust port and bounded by a lower closure wall inclined from the bottom of the piston on the exhaust port side thereof upwardly and across said piston to maintain communication between said transfer port and the sub-piston compression space.

FINN T. IRGENS.

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