US2259660A - Two cycle internal combustion engine - Google Patents

Description

Oct. 21, 1941. H. R. RICARDO TWO CYCLE INTERNAL COMBUSTION ENGINE Filed May 22, 1940 4 sheets-sheet 1 Atto/wey Oct. 2l, 1941. H. R. RICARDO 2,259,660

TWO CYCLE -:[NTERNL COMBUSTION ENGINE Filed May 22, 1940 4 sheets-sheet 2 I /nventor I Z.. i

Atorneg Oct. 21, 1941. H. R. RICARDO TWO CYCLE I-NTERNCAL COMBUSTION ENGINE Filed May 22, 1940 Fig. 3.

4 Sheets-Sheet 3 /nvenof Attorney MJ* M? Oct. 21, 1941. H, R. memno- TWO CYCLEl INTERNAL COMBSTION ENGINE Filed may 22, 1940 v 4 sheets-skelet 4 Pig.Y 6.

Patented Oct. 21, 1941 oFFtcE TWO CYCLE INTERNAL COMBUSTION ENGINE Harry Ralph Ricardo, London, England Application May 22, 1940, Serial No. 336,669 In Great. Britain April 10, 1940 (Cl. 12S-72) 3 Claims.

This invention relates to high speed two-stroke internal combustion engines operating with compression ignition having in the head of the cylinder a combustion chamber with a fuel injector therein and into which substantially the whole of the air charge is forced at the end of the compression stroke of the working piston, this air charge having been delivered into the cylinder through ports in the wall thereof by a pump of the displacement type. The object of the invention is to avoid undesirable accelerations in the valve-operating .mechanism while attaining a determined relation between the times of closing of the exhaust port and closing of the air inlet ports.

According to this invention there is an exhaust port in the inner wall of the combustion chamber in the head of the cylinder and this port is controlled by a poppet valve which is masked, that is to say the valve and its seat in the port are respectively formed and arranged so that after the valve is first lifted off its seat it must move a determined distance before the port is effectively opened for the outflow of the exhaust gases and similarly when returning to its seat the valve will move a determined distance after the port is closed. A pump comprising a cylinder and piston reciprocating therein delivers air through a transfer passage controlled by a valve to the ports in the cylinder wall and the masked exhaust valve is mechanically actuated in such timed relation to the movements of the working piston that the exhaust port will be closed before the air inlet ports are covered by the working piston on its instroke and before the air pump piston has completed its inward stroke. Consequently after closing of the exhaust port air will continue to be delivered by the pump into the working cylinder through the ports in the Wall of the Vlatter thus causing a rise in pressure in the cylinder. To effect this the pump piston is driven from the crankshaft` and reciprocates out of phase with the Working piston. With regard to the masking of the exhaust valve this is arranged so that the valve will move a distance which is between one-sixth and one-twelfth of the total lift of the valve before the port ls effectively opened and similarly after the port has been closed. The exhaust port with the masked valve therein is centrally positioned inthe combustion chamber whose contour is a gure of revolution about an axis coincident with the cylinder axis. This chamber is in open communication with the cylinder through a mouth whose diameter is less than the maximum diameter of the combustion chamber but is greater than the diameter of the exhaust valve. 4 With the above-mentioned construction it is possible to operate a high speed two-stroke internal combustion engine of the type indicated according to a method in which the outflow of exhaust gases through an exhaust port in the head of the cylinder ceases before the air inlet ports in the wall of the cylinder are closed thus 'increasing by the continued action of the pump which supplies the air the pressure of the air charge in the cylinder at an early stage in the compression stroke of the Working piston. In operating an engine according to this method and as a result of the exhaust port being controlled by a masked valve and by employing suitable timing, there is obtained an efiicient scavenging first by the rapid opening of the exhaust port due to the masking of the valve and secondly by the inflow of air when the scavenge air inlet ports are uncovered this air having been locked up under 'pressure in the scavenge air belt from which these ports lead.

As a result of the masking of the exhaust valve the longer period available for the operation of the total movement that must be imparted to this valve enables more gradual accelerations and decelerations to be provided in the valve-actuating mechanism than would be the case in a similar high speed engine if an unmasked valve were used. In a two-stroke engine of this type operating at high speed the period during which the valve is open is necessarily very short as compared with the valve movements in an engine operating on the four-stroke cycle and at a similar speed. Further, in such a two-stroke engine free egress of the exhaust gases is of vital importance for eciency so that an adequate valve lift must be provided.

Excessive accelerations and decelerations are difcult to achieve satisfactorily and place considerable stress on the valve gear being apt to cause valve bounce and other troubles. Hence the masking of the exhaust valve in the head of the cylinder is an important factor in operating the engine according to the method set out above, this( feature being necessarily'associated with the timing of thevalve and the movements of the working piston and pump piston respectively and in relation to each other.

mal to the crankshaft axis and through the axes' of the working and pump cylinders.

Figure 2 is a longitudinal section through the rotary valve which controls the air flow through the transfer passage between the pump cylinder and the Working cylinder. This section is taken on the line 2-2 in Figure 3 looking in the direction of the arrow.

Figure'3 is a sectional end elevation showing part of the mechanism by which the exhaust valve, the rotary valve and the fuel pump are operated from the crankshaft.

Figure 4 is a transverse section on the line 4-4 in Figure 1 showing the scavenge air belt and inlet ports in the wall of the cylinder.

Figure 5 is a sectional elevation on an enlarged scale of the combustion chamber'in the head of the cylinder and the "masked exhaust valve and port in that chamber, the valve being shown lifted oi its seat.

Figure 6 is a view similar to Figure 5 showing an alternative construction of the combustion chamber.

Referring more particularly to Figures 1, 2v

and 3 the cylinder A is conveniently provided with a liner B in which are formed the ports B1 through which scavenging air enters the cylinder when these ports are uncovered by the piston C. The head D of the cylinder may be detachable and in it is a combustion chamber E of the open type, that is to say, the chamber communicates with the end of the cylinder by Way of a mouth of substantial diameter. This combustion chamber E is centrally situated with respect to the axis of the cylinder A and the contour of this chamber is a figure of revolution about this axis. Centrally situated in the inner wall of this chamber is an exhaust port F in which is seated an exhaust valve G the detailed construction of this valve and its seat in the port F being more particularly described hereunder and illustrated on an enlarged scale in Figures 5 and 6. The exhaust port F opens into the exhaust manifold F1. The exhaust valve G is operated by the camshaft G1.

Scavenging air is delivered into the cylinder through the ports B1 from a pump comprising a cylinder` H in which is a piston H1 reciprocated by a link H2 which connects the piston to the big`end of the connecting rod C1. The axis of the pump cylinder H is arranged at right angles to the axis of the crankshaft J but conveniently the pump cylinder axis is in a horizontal plane which lies below the horizontal plane whichcontains the crankshaft axis. With this arrangement the pump piston H1 will be reciprocated out of phase with the working piston C. The air .from the pump cylinder H is delivered through a transfer passage K to a scavenging air belt K1 surrounding the portsB1. .[n the end of the transfer passage K adjacent to the pump cylinder H is a rotary valve L which controls not only the delivery of air from the pump into the transfer passage but also the inlet of air to the pump cylinder.

`The/'construction and arrangement of the rotary valve L is also shown in Figure 2. The valve L lies within a ported liner M and the valve is mounted on a shaft L1 on one end of which is a crank pin L2. The valve itself cooperates with ports M1, M2 in the liner M these ports communicating respectively with the .pump cylinder H and the transfer passage K. There is also a communication with the main air inlet N. In the valve itself the part L3, as seen in Figure 2, Vcontrols the delivery ofy air from the pump into the transfer passage K. Parts L4 control the suction through the inlet N to the pump.

Referring now to Figure 3, this shows the linkage by means of which the camshaft G1, the

shaft L1 of the valve L and certain other auxiliaries are driven from the crankshaft J. On the end of the crankshaft is an eccentric J1 which engages a bearing in a cross-shaped fourarmed link. One arm O of this link extends upwardly and engages a crank pin G11 on the end of the camshaft G1. The horizontally extending cam O1 of this link engages the crank pin L' on the end of the shaft L1 which carries the rotary valve L. The second and oppositely extending horizontal arm O2 of the link engages a crank pin P on a shaft which actuates the fuel pump P1 and conveniently also a dynamo. The

fourth downwardly directed arm 03 drives through a crank pin Q an oil pump situated in the engine sump.

'I'he crank pin I..2 on the end of the shaft L1 conveniently serves also to drive through a drag link a water-circulating pump R as seen in Figure 2. 1

The air inlet ports B1 in the wall of the cylinder liner B are preferably arranged tangentially in the manner shown in the cross-section in Figure 4.

Referring now to Figure 5 which shows on an enlarged scale` the detailed construction of the exhaust valve G and its seat in the port F, the valve seat l1'2 is arranged at the bottom of a cylindrical recess Fs of suitable depth. The valve itself has a cylindrical part G3 adapted toengage this recess l5'3 and having substantially the same depth. The conical part G1 of the valve which engages the seat Fz lies beyond this cylindrical part G3. This.arrangement is known as masking of the valve, the effect being that both during the initial opening movement and during the final closing movement of the valve, the flow of gas through` the port F is prevented.

With this arrangement the valve-operating mechanism can be constructed so as to cause lifting of the valve to commence before the exhaust gases are actually permitted to pass out through the-port, while similarly the port is in effect closed before the valve has actually come down on to its seat. There is therefore a longer period available for the operation of the valve with the result that the accelerations and' decelerations involved in the actuation of the valve by the cam can be more gradual than if the same actual effective period of opening of the valve were to be obtained with an unmasked valve. In order to determine the extent of masking" requisite, it may be said that taking engine speed and multiplying this by the valve lift, then the greater the product thus obtained so much deeper should be the masking, that is to say, the depth of the cylindrical recess F3 in the port.

In a high speed two-stroke engine of the kind to which the present invention relates the angular period during which the exhaust valve is open is very short as compared with the time during which the exhaust valve is open in an engine. operating on the four-stroke cycle at the same speed or even when such -an engine is runningat a slower speed. Further free egress of the exhaust gases is of vital importance for the efficiency of a two-stroke engine of the kind referred to so that an adequate valve lift is required. This masking of the valve enables an a-dequate valve lift to be provided and the valve to be opened and closed in the short interval necessary in a high speed engine while avoiding the disdavantages of excessive accelerations and decelerations which in practice it is not easy to achieve satisfactorily and which place considerable stress on the valve gear and are apt to lead to various troubles.

The employment of masked inlet valves for internal combustion engines has been proposed by the present inventor and also by others. In the .present invention, however, not only is this masking utilised on an exhaust valve, but in an engine, namely a two-stroke high speed internal combustion engine operating with compression ignition, a particular type which had not been evolved when the present inventor and others p proposed the use of masked inlet valves. It may be said therefore that the advantages accruing from the use of a masked exhaust valve are peculiar to such a valve when used in an engine of the particular type indicated.

in the present instance the masked exhaust Valve is combined with an engine having the features described above in which by means of the link member O, O1, O2, O3 the exhaust valve G and the rotary valve L are operated in timed relation to each other and to the working pistonA C and thepump piston H1, with the result that the exhaust port F will be closed before the air inlet'ports B1 are covered by the working piston C on its instroke and before the air pump piston H1 has completed its inward stroke. As air thus continues to be delivered into the cylinder after closing of the exhaust port the air pressure in the` cylinder is increased above that of the normal scavenging air pressure at the beginning of the compression stroke of the working piston.

It is to be noted further that owing to the timing of the rotary valve L air continues to bedelivered by the pump into the transfer passage K and air belt K1 after the ports B1 have been closed by the piston C. This results in air under some pressure being locked up in the transfer passage K and the air belt K1 so that when on the outstroke of the piston C the ports B1 are uncovered and at the same time the exhaust port F is rapidly opened owing to the masking of the exhaust valve, air under pressure will at once enter the cylinder and cause an efllcient commencement of the scavenging period which is continued by the delivery of air from the pump.

The combustion chamber E is conveniently formed as shown in Figure 5, ,being provided around its mouth which opens into the end of the cylinder with a lip constituted by an inserted ring E1 which is at least to some extent heatinsulated in that it is merely held in place by the screwed-in ring E2. A slight protrusion C1 on the face of the piston C enters the lipped mouth at the end oi' the compression stroke.

it will be seen from Figure 5 that the combustion chamber E which, as mentioned above, is a figure of revolution about the cylinder axis, has a maximum diameter greater than the diameter of its mouth measured inside the lip member El, The diameter or this mouth however is slightly greater than the diameter of the Valve G `This allows for the insertion of the valve. The fuel injector is arranged to deliver the fuel spray into the chamber E through its side wall.

The extent to which the valve should move after it has left its seat and before the effective lopening'of the port, and similarly the distance sixth to one-twelfth of the total lift of the valve.

Figure 6 shows an alternative construction of the combustion chamber. In this instance this chamber E3 is substantially cylindrical with the masked exhaust port F centrally situated 'in the inner Wall'. In this instance the combustion chamber E3 is in effect a recess of suitable dimensions formed in the water-cooled head of the cylinder. arranged substantially as shown in this figure.

What I claim as my invention and desire to secure by Letters Patent is:

1. In an internal combustion engine operating with compression ignition the combination of a cylinder, a combustion chamber in the head of the cylinder with a fuel injector therein into which chamber substantially the whole of the air charge is forced at the end of the compression stroke by the piston in the cylinder, an exhaust port centrally situated in the inner Wall of the said combustion chamber with a poppetvalve seated in this port the valve seat in this port being set in a cylindrical recess and the valve having a corresponding cylindrical part, an air pump comprising a cylinder and a piston reciprocated therein directly from the engine crankshaft, the pump cylinder being mounted on the crankshaft casing with the axis of that cylinder substantially at right angles to the axes of the working cylinder and of the crankshafhair inlet ports in the wall of the Working cylinder and controlled by the piston therein, a transfer passage between the pump cylinder and said air inlet ports with a valve in this passage adjacent to the pump cylinder, and mechanism operated by the engine crankshaft and actuating said exhaust valve and`n said valve in the transfer passage in timed relation with the working piston and the pump piston as set forth.

2. A method of operating a high speed twostroke internal combustion engine of the type indicated, according to which the operation of a masked valve in an exhaust port in the head of the cylinder is timed in relation to the movements of the working piston and of a displacement pump, which operates out of phase with the valve a rapid opening and closing of theexhaust portis obtained and the exhaust port is closed before the air inlet ports in the wall ofthe cylinder are covered on the instroke of the piston,

through which the valve must move after the port has in eect been closed and until the valve is seated, should be of the order of from onewhen by the action of the pump air continues to be supplied raising the pressure of the air charge in the cylinder at an early stage in the compression stroke of the working piston, and finally when on the outstroke of the piston the air inlet ports are uncovered air under a pressure above that of the atmosphere will at onceenter the cylinder as set forth.

3. The construction of internal combustion v- Y RALPH RICARDO.

The fuel injector S is conveniently

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