US2242871A - Valve arrangement for two-stroke cycle internal combustion engines - Google Patents

Description

May 20, 1941. L. RAAB ETAL 2,242,871

VALVE ARRANGEMENT FOR TWO-STROKE CYCLE INTERNAL COMBUSTION ENGINES Filed Jan. 21, 1959 s Sheets-Sheet 1 attornqgs May 20, 1941. 1 RAAB ET AL 2,242,871 VALVE ARRANGEMENT FOR TWO-STROKE CYCLE INTERNAL COMBUSTION ENGINES Filed Jan. 21, 1959 I a Sheets-Sheet 2 In ventors:

I affomgs May 20, 1941. L. RAAB ETAL 2,242,871

VALVE ARRANGEMENT FOR TWO-STROKE CYCLE INTERNAL COMBUSTION ENGINES Filed Jan. 21; 1939 3'Sheets-Sheet 5 Hg. 3 E 4 Inventors- Leo cold Raa and A/emer slrobel Qttomgys Patented May 20, 1941 VALVE ARRANGEMENT FOB TWO-STROKE CYCLE INTERNAL COMBUSTION ENGINES Leopold Raab, Chemnitz, and Werner Strobel, Siegmar-Schonau, Germany Application January 21, 1939, Serial No; 252,188 In Germany January 22, 1938 4 Claims. (01. 123-65) This invention relates to a. valve arrangement for two-stroke cycle internal combustion engines employing equally distributed flow scavenging.

It is known to provide two-stroke cycle internal combustion engines employing equally distributed flow scavenging, with a sleeve valve having an axially reciprocating as well as a circumferentially oscillating movement. In order to ensure that the timing of the port opening and closing was unsymmetrical with respect to the piston dead centres, the top piston edge in such known constructions was used to assist in the control of admission and exhaust periods, the oscillating movement of the sleeve valve only serving-to ensure easy movement of the sleeve. It has also previously been suggested to provide a cam face drive for a reciprocating sleeve valve, in order to obtain unsymmetrical timing. A cam drive, however, necessitates a complicated construction and increases the manufacturing costs, on the other hand a sleeve valve which merely rotates entails drawbacks in regard to rapid opening and closing of the ports in cases where a large total port area has to be provided such as by distributing the various ports over the whole circumference of the cylinder, as is necessary in high speed engines.

Furthermore, sleeve valve control is known in which a reciprocating sleeve valve controls the inlet and exhaust ports in the cylinder as well as the induction ports in the crank case. Here again. however, this sleeve valve requires the assistance of the piston edge to obtain unsymmetrical timing and the construction moreover, is attended by the drawback that the sleeve valve and the piston periodically make movements in opposite directions, which means increased piston speed and results in increased wear.

The object of the present invention is to avoid the above mentioned drawbacks, and to achieve any desired unsymmetrical timing of the port control with respect to the piston dead centres, by the use of an axially reciprocating and circumferentially oscillating sleeve valve in which the sleeve valve utilises its oscillating movement about its longitudinal axis independently of the piston to control both the inlet and exhaust and also the induction-ports, if any, and any other ports in the cylinder.

A further object of the invention is to use the oscillating movement of the sleeve valve to control the cylinder ports whereby movement of piston and sleeve valve in opposite directions is avoided.

A further object of the invention is to distribute the various ports over the whole cylinder circumference, and thus obtain a large total port area.

A still further object of the invention is to provide a sleeve valve arrangement whereby the sleeve valve controls not only the upper port of a transfer passage that is the inlet port into the cylinderbut also the lower port of the transfer passage which ends in the crank case, whereby the latter is opened earlier than the upper port of the transfer passage.

Another object of the invention is to make ues of the same port in the sleeve valve to control the induction port leading into the crank case and the lower port of the transfer passage to the crank case, the said port in the sleeve valve being caused to move over the induction port in the crank case on the upward stroke and over the lower transfer passage .port on the downward stroke.

The invention is illustrated 'by way of example as applied to a two-stroke cycle engine employing crank case compression which will now be described with reference to the accompanying drawings. In the drawings:

Fig. 1 is a longitudinal section of the cylinder and the crank case, of the engine;

Fig. 2 is a developed elevation of the sleeve valve;

Figs. 3 to 5 are diagrammatic representations of the sleeve valve ports in relation to the associated cylinder or crank case ports during the various working phases of the engine.

Referring first to Fig. l, a two-stroke cycle internal combustion engine employing crank case compression comprises a cylinder l, the upper end of which is provided with a ring of exhaust ports 2 distributed around the whole circumference of the cylinder. At a suitable distance below the exhaust ports 2, there is provided a ring of inlet ports 3 (this arrangement/of the inlet and exhaust ports brings about what has been termed equally distributed fiow scavenging).

Some distance below the inlet ports 3 there is provided another ring of ports 6 which serve for the induction of scavenging fluid or fuel mixture intothe crank case and in turn below these there is afourthringof ports 5 which are the lower orifices of the transfer passage 6 the upper end of which ends in the cylinder inlet ports 3. All the ports are preferably distributed around the whole cylinder circumference in like manner as thering of ports 2. The ports of each series end in a common conduit extending around the cylinder, namely, the exhaust ports 2 in the exhaust pipe I, and the induction ports 4 in the induction pipe 8..

Mounted within the cylinder in a manner known per se is a. sleeve valve 9, which is driven from the crank shaft I through a pinion II geared thereto in the ratio 1:1 and through a pivot I2 which is movably mounted in the pinion II. The sleeve valve 9 itself is provided in'its upper part with a ring of exhaust ports I3 controlling the cylinder exhaust ports 2 and some distance 'below these with a ring of inlet ports I4, controlling the cylinder inlet ports 3. Below the ports I4 is provided a single ring of ports I5, which control both the induction port 4 and the lower transfer passage ports 5. The sleeve valve makes in the cylinder not only an axially reciprocating movement but also simultaneously a circumferentially oscillating movement. Each point of the,sleeve valve therefore describes a movement relative to the cylinder wall in an elliptic path l6 as shown in dotted lines in Fig. 2. It is, therefore, possible, to control, for example, by means of the same sleeve valve ports 'I5, the induction ports 4, near the top dead centre of the sleeve valve, and the lower ports of the transfer passages near the bottom dead centre of the sleeve valve.

In orderto arrange thevalve timing according to the speed range that the engine is intended to have, the ports I4 for controlling the fresh fuel mixture inlet and the induction ports are arranged in mutually staggered relation circumferentially of the sleeve valve.

It is an advantage that all the ports in the cylinder and in the sleeve valve should be'circular whereby it is possible to make all the ports alike in the most simple manner, whereas to provide ports of non-circular shape would either necessitate a more expensive manufacturing process or it would be liable to entail inaccuracies which would have a detrimental effect on the timing.

Fig. 3 shows the movement of one of the exhaust valve ports I3, relative to the associated exhaust cylinder port 2. The sleeve valve is shown in its top dead centre in Fig. 3. In Fig. 4, which shows the relative position of one of the passage port 5 is still partly open when the port 3 has just been closed by the sleeve valve.

It will be seen, therefore, that the transfer passage is open against the crank case earlier than against the cylinder so that during the crank case compression stroke the pre-compression of the charge or scavenging fluid can take place in the transfer passage also. The lower transfer passage port 5 and/or the port I5 in the sleeve valve is or are preferably of larger diameter than the upper transfer passage port or cylinder inlet port 3. The actual admission of the new charge in the cylinder is however, efiected by the opening of the port 3, by means of the valve port I4.

In order to keep the overall height of the engine reasonably smallin spite of the control of transfer passage 6 through the ports 5.

all the ports by the sleeve valve, the engine piston is provided with short transfer passages II (Fig. 1) both for the induction of the new charge into the crank case through the ports 4 and for the entry of the charge from the crank case into the The transfer passages Il may however, be replaced with equal effect by equivalent ports in the piston skirt. The provision of transfer passages in the piston instead of ports, however, is attended by the advantage that the piston can be made with a more continuous skirt surface. The passages II or any piston ports which might be provided in their stead do not, however, take any part in the control of the charge, induction or transfer the ports 2, 3 and 5, principally takes place during valve inlet ports I4 in relation to the associated cylinder inlet port 3, the port I4 is also shown in the top dead centre of the sleeve valve. In addition Fig. 3-shows in thinner lines the position of the port I3, designated I3a, when the port I4 in the corresponding position a in Fig. 4 is just about to open the associated port 3 in the cylinder. By comparison Fig. 4 shows the valve port II in the position I Ib, when the exhaust port 2 has just been .closed, and the valve port .Fig. 5, corresponds to the positions I3a and Ila of the ports I3 and H in Figs. 3 and 4 respectively, and it will be seen that in position I5a the port 5 has already been partly opened when the upper port 3 of the transfer passage is-just about to be opened by the valve port I4 in its position a. A thirdposition'of the sleeve-valve is shown in Figs. 4 and 5 when the port I4 is in the position I40 and the port I5 in thecorresponding position I50, which shows that the lower' transfer the oscillating movement of the sleeve valve in the circumferential direction. This fact is of particular advantage in connection with the opening of the cylinder inlet ports 3. As the sleeve valve has a certain thickness a step is formed at the beginning of the opening of the port 3 which is of such a shape as to tend to deflect the charge entering the cylinder towards one side of the cylinder approximately in a horizontal plane. As the port I4 continues to pass over the port 3, the inflowing fuel mixture enters the cylinder in directions more and: more approaching. the radial direction until towards the end of the opening when theport 3 is already gases such as would be the case in engines employing a reverse or other principle of scavenging. What we claim and desire to secure by letters Patent is:

1. In avalve arrangement for a two-stroke cycle internal combustion engine employing equally distributed flow scavenging by crankcase comprwsion, a cylinder and piston, a sleeve valve disposed between said piston and said cylinder,

a plurality of superimposed rings of cooperative ports in both said sleeve and said cylinder, comprising exhaust, inlet and transfer ports respectively, and means for imparting a combined reciprocating and oscillating motion to said sleeve whereby the ports in said sleeve are caused to take an elliptical path relatively to the ports in said cylinder and be brought into operative relationship at timed intervals, the individual rings of ports in said cylinder and in said sleeve respectively being arranged in circumferentially staggered relationship one to each other.

2. In a valve arrangement for a two-stroke cycle internal combustion engine employing equally distributed flow scavenging by crankcase compression, a cylinder and piston, a sleeve valve disposed between said piston and said cylinder, three superimposed rings of ports in said sleeve comprising exhaust, inlet and transfer rings of ports respectively, four superimposed rings of ports in said cylinder, said rings of ports com-' prising exhaust, inlet and upper and lower transfer ports respectively, the diameter of the lower 'ring of induction ports in the cylinder being,

greater than the diameter of the inlet ports in said cylinder, transfer passages connecting the lower ring of transfer ports and the upper ring of transfer ports in said cylinder, and means for imparting an elliptical motion to said sleeve within said cylinder whereby the ports in said sleeve are caused to take an elliptical path relatively to the ports in said cylinder, and to be brought into co-operation relatively therewith at timed intervals, the lower ring of transfer ports and the ring of inlet ports in said cylinder alternately cooperating with the single ring of inlet ports in said sleeve during the reciprocating motion thereof. I

3. In -a valve arrangement for a two-stroke cycle internal combustion engine employing equally distributed flow scavenging by crankcase compression, a cylinder and piston, a sleeve valve disposed between said piston and said cylinder, three superimposed rings of ports in said sleeve comprising exhaust, inlet and transfer rings of ports, respectively, four superimposed rings of ports in said cylinder comprising exhaust, inlet and upper and lower transfer rings of ports respectively, transfer passages connecting the upper and the lower transfer ports in said cylinder, the diameter of the lower transfer ports in said cylinder and the diameter of the inlet ports in said sleeve each being greater than the diameter of the upper transfer ports in said cylinder, and means for imparting a combined axially reciproeating and circumferentially oscillating motion inlet ports.

to said sleeve whereby the ports in said sleeve are caused to take an elliptical path relatively to the ports in said cylinder and to be brought into cooperative relationship therewith at timed intervals, the ring of inlet ports and the lower ring of transfer ports in said cylinder being arranged in circumferentially staggered relationship one to the other whereby the co-operative relation between the lower transfer ports in said cylinder and the inlet ports in said sleeve is timed to occur earlier than the co-operative relation between the upper transfer ports in said cylinder and the transfer portsin said sleeve.

4. In a valve arrangement for a two-stroke cycle internal combustion engine employing equally distributed flow scavenging by crankcase compression, a cylinder and piston, a sleeve valve disposed between said piston and said cylinder and a plurality of superimposed rings of c0-op.- erative ports comprising exhaust, inlet and transfer ports respectively, means for imparting a combined reciprocating and oscillating motion to said sleeve whereby the ports in said sleeve are caused to take an elliptical path relatively to the ports in said cylinder, and produce a timed cooperative relationship, and transfer passage in said piston for placing the transfer and inlet ports in said cylinder ,into communication with the crank-chamber of said engine and for providing a passage from the crank-chamber to said LEOPOLD RAAB.

WERNER. STROBEL.

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