EP0776423B1

EP0776423B1 - Two-stroke engine with spark ignition

Info

Publication number: EP0776423B1
Application number: EP95928040A
Authority: EP
Inventors: Stanislaw Jarnuszkiewicz; Sobieslaw Zasada
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-08-16
Filing date: 1995-08-16
Publication date: 1998-11-04
Anticipated expiration: 2015-08-16
Also published as: WO1996005426A1; ATE173055T1; HUT76953A; PL174629B1; PL304731A1; DE69505831D1; CZ43197A3; EP0776423A1

Abstract

In a two-stroke engine with ports controlled by the piston and with the air charge or a lean fuel-air mixture precompressed in the crankcase (11), the cylinder space is fed with a jet of rich fuel-exhaust gas mixture from the feed chamber (13) by means of a feed canal (14). The feed chamber (13) is formed by the inner space of the rotary distributor (A) closed by a rotary control element (16) driven by a non-slip transmission (17) from the engine crankshaft (10). The feed canal (14) ends at the cylinder wall with an opening situated between the upper edge of the exhaust port (4) and the position of the edge of the head of the piston (5) at the moment of ignition. The control element (16) has two openings, an inlet one (18) and an outlet one (19), spaced at the angle ( alpha ) and coupled in such a position that, while rotating, the inlet opening (18) meets the opening of the feed canal (14) during the engine power stroke, and the outlet opening (19) - during the compression stroke.

Description

Field of the invention

The subject matter of this invention is the two-stroke multi-cylinder engine with spark ignition, in which the energy of exhaust gases produced during the engine operation is used to prepare the combustible charge.

Background of the invention

The main reason for the limited application of two-stroke engines, especially to mechanical vehicles, is toxicity of the exhaust gases they release. One of the design trends which improve operation of the two stroke engine consists in eliminating the outlet losses by supplying fuel to the cylinder space after the exhaust port has been closed, and controlling combustion by spacial qualitative differentiation of the fuel charge, which consists, among other things, in producing an enriched mixture in the spark plug zone. A method of producing such a laminar structure of the mixture is known, in which a gaseous charge containing fuel is introduced from a separate feed chamber to the air, or to a lean combustible mixture compressed by the piston in the cylinder space. The charge containing fuel consists of vaporized liquid fuel mixed with air or with exhaust gases; it is very rich in fuel, beyond the flammability limit. The fuel charge jet is introduced during the compression stroke through the feed canal leading from the feed chamber where the fuel charge is compressed to a pressure higher than that in the cylinder space at the moment of delivering the fuel charge. The feed canal is oriented towards the spark plug. Mutual mixing of the two charges results in the desired differentiation of the mixture, as regards its combustibility properties, in the engine cylinder space.

There are many engine designs in which the fuel charge is prepared in this manner. In the engine presented in the specification of the German patent No. DE 2 241 643 a piston compressor driven by a gear from the crankshaft plays the role of the feed chamber. The compressor cylinder space is connected, via a suction canal, with a device spraying fuel into the drawn-in air, and with the engine cylinder space via a feed canal in which a non-return valve is mounted. The feed canal, positioned in the compressor cylinder wall, is uncovered when it meets the orifice in the piston projection at the moment the compressed charge containing fuel should be introduced to the engine cylinder space.

In an other engine, described in the specification WO 91/02144, the fuel is delivered into the cylinder space in the stream of pressurized air flowing from the feed chamber. Two solutions are presented. In the first one the feed chamber is connected with the cylinder space via feed canal and with the crankcase via exhaust gas charging canal. In the second one the two mentioned canals are leading to the cylinder wall. In these engines the feed chamber constitutes a pressurized air accumulator. It is supplied by means of exhaust gas charging canal from the crankcase during the power stroke in the first example, and from the cylinder space during the pressure stroke in the second example. The fuel is introduced to the feed canal by means of opened nozzle of the spraying device.
In the second solution the feed canal is leading to the cylinder wall through the opening situated directly above the upper edge of the exhaust port and exhaust gas charging canal closely below the piston top at the moment of ignition.
The inner space of rotary element constitutes the feed chamber. The cylindrical control element is driven by non-slip transmission from the crankshaft. In the wall of the control element the opening is disposed which meets, during the pressure stroke, alternatively, the exhaust gas charging canal and the feed canal at the moments directly before the closing of the openings of these canals by the upper edge of the piston.
In multi-cylinder unit the common air feed chamber is provided and the fuel is introduced separately to each feed canal.

Among the designs which use the energy of pressure and temperature of the exhaust gas to prepare the fuel charge, is the engine presented in the German journal VDI Bericht, appendix No. 1066 entitled "Direkte Gemischeinblasung an 2-Takt-Ottomotoren", which describes the oral presentation by G.K.Fraidl, R.Knoll, and H.P. Hazeu at a conference held in Dresden on 3-4 June 1993. In the engine head, a feed chamber is made which is connected with the cylinder space by means of a feed canal with an electromagnetically operated cut-off valve. A spray nozzle is installed in the feed chamber. The operation of the nozzle and the cut-off valve are controlled by a processor performing a program based on a general principle: the valve is opened at the end of the compression stroke and is closed after the moment of ignition; fuel is injected during the power stroke. With the cut-off valve open, the direction of gas flow depends on the pressure difference between the two connected spaces. In the first period after the valve is opened, a rich fuel-exhaust gas mixture, prepared in the previous phase, leaves the feed chamber. The increase in pressure in the cylinder space, caused by the piston movement, results in the reversed flow direction even before the moment of ignition. The computer-controlled valve is closed after the mixture is ignited, and the pressure in the feed chamber is sufficient to prepare the mixture in the next cycle, the exact moment depending on the engine load. During the phases of power, charge exchange, and the first moments of compression, a computer-controlled amount of fuel is injected to the gases accumulated in the feed chamber under high pressure. The fuel vaporizes quickly in hot exhaust gases, thus producing a rich, chemically active fuel-exhaust gas mixture used in the next engine operation cycle. In a multi-cylinder engine, each cylinder has its own feed chamber equipped with a cut-off valve and a spray nozzle.

The engine presented in the patent specification DE 4 116 303 has the feed chamber connected with the cylinder working space via feed canal and exhaust gas charging canal, leading to the cylinder wall, with its outlet being located above the upper edge of the exhaust port and below the piston top edge at the moment of ignition. The inner space of the rotary distributor constitutes the feed chamber, with the cylindrical control element driven by a non-slip transmission from the crankshaft. The wall of the control element is provided with two openings, an inlet and outlet one, spaced along the axis of the element. The openings are disposed at such a central angle and coupled with the non-slip transmission in such a position, that while the element is rotating, the inlet opening meets the exhaust gas charging canal during the power stroke and the outlet opening meets the feed canal during the compression stroke. The matings are realized when the piston is below the openings of the canals in the cylinder wall. In the plane perpendicular to the axis of rotation of the control element and taking through the inlet opening, the fuel spraying device is mounted, with its nozzle directed to the center to the feed chamber.
During the power stroke some portion of the exhaust gases flows to the feed chamber. The rotation of the control element results in closing of the exhaust gas charging canal and connecting the feed chamber via the inlet opening with the fuel spraying device. In the cylinder space the changing of the charge and flowing of the air from the crankcase is realized simultaneously. After closing the exhaust gas charging canal and inlet canals the feed chamber is connected via feed canal with the cylinder space.
The above presented engine is the one-cylinder unit. The multi-cylinder realization is the assembly of one-cylinder engines coupled with the common crankshaft together, each with its own feed chamber and fuel spraying device.

Disclosure of the invention

The engine developed by this invention prepares the combustible charge using a method similar to that described above, in DE 4 116 303 specification, however with a different design, developped to multi-cylinder unit.
The cylinder space of each cylinder is connected with the feed chamber which is formed by the inner space of a rotary distributor, which space is closed by a rotary control element driven by a non-slip transmission from the engine crankshaft. The control element has two openings, an inlet and outlet one, spaced at such a central angle, and coupled with the transmission in such a position that, when the element is rotating, the inlet opening meets the feed canal outlet in the rotary distributor during the power stroke, and the outlet opening is met in the compression stroke. The two spaces become connected when the piston is below the feed canal opening in the cylinder wall. In the feed chamber the fuel spraying device is mounted.

In the first mode of carrying out the invention the cylinder spaces are connected with one common feed chamber by means of separate feed canals, the openings of which are spaced at symmetrical pitch of the rotary distributor central angle, corresponding to the number of cylinders and the sequence of ignition. In such an engine, there are particularly advantageous conditions for gas flow, which minimize the effect of inertia. The possibility of uncovering simultaneously the inlet opening which comes from the cylinder that performs the power stroke, and the outlet opening leading to the cylinder which performs the compression stroke, creates conditions that enhance the flow - the feed chamber acts as a pressure accumulator which simultaneously discharges the fuel-exhaust gas mixture produced in it and is fed with exhaust gases. Such an operation system diminishes the importance of cutting off the controlled spaces tightly. Pressure pulsation is considerably reduced which favourably reduces wave phenomena which disturb the flow of gas.

The rotary distributor can actually be of any design. The design that is particularly advantageous has the feed chamber formed by the inner space of the control element - designed as a rotary chamber supported by bearings in the distributor body. One end of the chamber is connected with a non-slip transmission by means of a coupling and a pressure spring. The other end of the chamber, which has an inlet and outlet openings, is pressed against the cover of the body in which the opening of the feed canal is placed to mate with the two openings mentioned above. In the cover, positioned in the distributor rotation axis, there is a fuel spraying device directed towards the axially positioned opening made in the bottom of the control element.

A further mode of carrying out the invention aims at ensuring an orderly flow in the feed chamber, increasing homogeneity of the mixture at high frequencies caused by high rotation speeds of the engine and/or the high number of cylinders controlled by one distributor. In such an engine the cylinder spaces of each cylinder are connected with one common feed chamber via two canals - feed canal and exhaust gas charging canal. The control element of the rotary distributor is made as a shaft with a machined concentric chamber at the front end, closed by the distributor body cover in which a fuel spraying device is installed. The feed and exhaust gas charging canals are connected separately with two control sections of the rotary distributor; the sections are spaced along the axis of the annular wall of the shaft. The exhaust gas charging canal section has an inlet opening, and the feed canal section has an outlet opening.
The exhaust gas charging canals and the feed canals are spaced on the circumference of the rotary distributor sections at a symmetrical pitch of the rotary distributor phase angle, corresponding to the number of cylinders and the sequence of ignition.

A further development of the invention consists in placing the outlet opening and feed canal section closer to the rotary distributor cover.

In the design presented here, irrespective of the number of cylinders, there is one direction of flow through the feed chamber, in countercurrent to the flow of the sprayed fuel; thus producing higher homogeneity of the mixture and a better flow dynamics.

Brief description of the drawings

The several examples of engine designs presented below will permit the essence of the invention to be understood thoroughly. The engines are shown schematically; the following figures show: Fig. 1 - cross section of the three-cylinder engine equipped with a rotary distributor having control openings positioned on the circumference of the control element which has the form of a hollow shaft, Fig. 2 - longitudinal section of the same engine, Figs. 3, 4, and 5 - cross sections through the engine shaft of Fig. 2; the cross sections are taken through the feed canal planes of individual cylinders, Fig. 6 - an axial cross section through another distributor with control openings located on the front surface, Fig. 7 - view of the front surface of the distributor of Fig. 6 designed to co-operate with a three cylinder engine, and driven by 1:1 transmission, Fig. 8 - a longitudinal section of a three-cylinder engine controlled by a two-sectional distributor, Figs. 9 and 10 - sections through the exhaust gas charging section and the feed canal section, respectively.

Modes of carrying out the invention

In the engine shown in Fig. 1, a working space 8 is enclosed by the walls of the cylinder 1, the head 6, and the bottom of the piston 5. The piston 5 is connected with the crankshaft 10 by means of a connecting rod 9. The crankshaft 10 is supported on bearings in the crankcase 11. On the reverse movement, the piston 5 uncovers the inlet 3 and exhaust 4 ports located in the wall of the cylinder 1. Air is sucked into the crank case 11 through a suction canal and a self-closing one-way plate valve 12. The basic design of the two-stroke engine with precompression of charge in the crankcase, as described above, is supplemented with a device for preparing the combustible load. The rotary distributor unit A is equipped with a sleeve-type control element 16 driven by 1:1 non-slip transmission 17 from the crankshaft 10. The inner space of the control element 16 constitutes the feed chamber 13 which is periodically connected with the cylinder space 8 through the inlet 18 and outlet 19 openings, and the feed canal 14. The nozzle of the fuel spraying unit 15, in this case - an injector with electromagnetic control, is built into the feed chamber 13. The feed canal 14 ends at the wall of the cylinder 1, with the opening situated slightly above the upper edge of the outlet port 4 and directed towards a hole in the head 6 where the spark plug 7 is installed. The operation of the feed chamber 13 is controlled on a geometric basis: the value of the central angle a between the inlet 18 and outlet 19 openings on the circumference of the control element 16 is slightly greater than the angle of rotation of the crankshaft 10 for the travel of the piston 5 between covering and uncovering of the feed canal 14. In the single-cylinder engine described here, the angle α equals 220°.

The description of the process occurring in the engine begins with the situation shown in Fig. 1 when the piston 5 is at the bottom dead centre during the charge exchange phase. Rotation of the crankshaft 10 and the upward movement of the piston 5 result in closing the inlet ports 3 and then the exhaust port 4 thus beginning the compression phase. Subsequently, as the feed chamber 13 is opened, a very strong pulse of a rich fuel-exhaust gas mixture flows into the cylinder space 8 through the feed canal 14 and the inlet opening 19. As the mixture stream moves towards the spark plug 7, it mixes with the air, which results in qualitative differentiation of the combustible mixture, the ultimate pattern of which is shaped by the piston 5. The opening of the feed canal 14 is closed by the piston head edge before the instance of ignition. During the power stroke, after the opening of the feed canal 14 is uncovered, the feed chamber 13 connected with the cylinder space 8 for the second time in the same cycle - this time through the inlet opening 18. Some portion of the exhaust gases flows into the feed chamber 13 which acts as a pressure accumulator and a generator of the fuel-exhaust gas mixture. The position of the opening of the feed canal 14 on the wall of the cylinder 1 controls the timing of connecting the feed chamber 13 with the cylinder space 8. In the process of preparing the combustible mixture, the connecting operation must meet two opposing conditions, the introduction of the mixture must sufficiently precede the moment of ignition and the pressure in the feed chamber 13 must reach a sufficient value.
The rotary distributor A shown in Fig. 2 has one common feed chamber 13 for three cylinders. The control element 16 has the form of a shaft with a machined concentric chamber at one end, closed by the cover 20 of the distributor body 21. In the cover 20, the fuel spraying device 15 is mounted. On the side surface of the control element 16, three sections can be distinguished, which correspond to individual cylinders. Each section has the input opening 18 and the output opening 19 in the shaft wall; the openings mate with the feed canals 14.1, 14.2, and 14.3 connecting the distributor with individual cylinders. The central angle α at which the inlet 18 and outlet 19 openings are spaced equals 240°. With three cylinders, the phase angle β representing the relative difference in the position of openings between the sections, must be 120°, in the direction opposite to the rotation of the crankshaft 10 and in accordance with the ignition sequence. With the geometry of control adopted here, which is thoroughly explained by cross sections taken along the sections of the control element, as shown in Figs. 3, 4, 5, and with the ignition sequence being 1-2-3, the feed chamber 13 is always simultaneously connected with cylinders on the power and compression strokes. Fig. 2 shows the first and the second cylinders in this situation, connected by means of the canals 14.1 and 14.2.

Fig. 6 shows an advantageous design of the rotary distributor A. The control element 16 takes in this design the form of a chamber supported by bearings in the distributor body 21; one end of the control element 16 is connected with the shaft of a non-slip transmission 17 by means of a dog clutch 23 movable along its axis. Unlike in the distributor used in the engine of Fig. 2, where the side surface acts as the control surface, in this design the inlet opening 18 and the outlet opening 19 are situated in a flat bottom of the control element 16, which is pressed against the cover 20 by means of a helical spring 24 incorporated in the clutch unit 23. The feed canals 14.1, 14.2, and 14.3 of the three cylinders are connected to the cover 20 in which a spray nozzle 15 is installed in the centre, along the axis of rotation. In such a design the control surface also seals the feed chamber 13.
Fig. 7 shows the position of the control openings in the distributor of Fig. 6 in a three-cylinder engine with a non-slip 1:1 transmission 17. It is an obvious solution to use a reduction transmission to drive the distributor with the transmission ratio expressed by a natural number, with a resulting division of the phase angle β.
A three-cylinder engine as shown in Fig. 8 embodies a somewhat modified, relative to those described above, principle of preparing the mixture. In addition to the feed canal 14.1, 14.2, or 14.3, each cylinder is equipped with an exhaust gas charging canal 22.1, 22.2, and 22.3, respectively, ending with an opening in the cylinder wall, positioned above the upper edge of the exhaust port 4. These canals run to the rotary distributor A separately to two control sections allocated to the functions of exhaust gas transfer and mixture feed, rather than to individual cylinders. The exhaust gas flows through the feed chamber in one direction. The section with the outlet opening 19 corresponding to the feed canals 14.1, 14.2, and 14.3, is situated closer to the distributor cover 20, which ensures the counter-current flow which intensifies evaporation and mixing of the sprayed fuel with the gas stream.

In traction engines exist varying operating conditions, especially as regards the rotation speed and load. Due to the flow inertia it is expedient to control in the rotary distributor A the angle at which the feed chamber 13 is connected with the cylinder space 8. With the double control system arranged in series, both in the distributor and on the cylinder wall, some improvement can be brought about by making the inlet 18 and outlet 19 openings oval rather than round. The rotation speed can be taken into account by using a coupling with controllable delay/advance angle 25 connected to the non-slip transmission
17. In the simplest design, such a coupling 25 can be controlled by a centrifugal governor. The full range of optimal control can be ensured with the assistance of a processor-based control unit 26 which, based on signals coming from numerous sensors which scrutinize the engine operation, external conditions, the throttle position, determines the required setting of the fuel feed, controllable clutch and other controllable engine units.

Claims

A two-stroke multi-cylinder internal combustion engine with spark ignition, with the air charge or a lean fuel-air mixture precompression in the crankcase (11), with ports controlled by the piston; with the space (8) of each cylinder connected via

a feed canal (14) ending at the cylinder wall (1) with an opening situated between the upper edge of the exhaust port (4) and the position of the piston's (5) top edge at the moment of ignition

with a feed chamber (13) which is formed by the inner space of a rotary distributor (A) closed by a rotary control element (16) driven by a non-slip transmission (17) from the engine crankshaft (10); wherein the rotary control element (16) has two openings per cylinder, an inlet one (18) and an outlet one (19), spaced at such a central angle (a) and coupled by the non-slip transmission (17) in such a position, that, while rotating, the inlet opening (18) meets the opening of the feed canal (14) in the rotary distributor (A) during the power stroke, the connection being open when the piston (5) is below the opening of the feed canal (14) on the wall of the cylinder (1),

and further, a fuel spray device (15) is built inside the feed chamber (13),

characterised in that the outlet opening (19) meets the feed canal (14) in the compression stroke, said feed chamber (13) is a common chamber for all the cylinders, the spaces (8) inside the cylinders (1) are connected with said common feed chamber (13) by means of the feed canal (14.1, 14.2, 14.3) of each cylinder, the openings of which are spaced in the rotary distributor (A) at the phase angle (β) corresponding to the division of the cycle by the number of cylinders (1), in the sequence of ignition.
The engine as claimed in the claim 1, characterised in that the common feed chamber (13) is formed by the inner space of the rotary control element (16) which is designed as a rotary container supported by bearings in the body (21) of the rotary distributor (A); one end of the control element being connected with the shaft of the non-slip transmission (17) by means of a coupling (23) and a helical pressure spring (24); the other end, which has the inlet opening (18) and the outlet opening (19), being pressed against the cover (20) of the regulator body (21), the cover having an opening of the feed canal (14) mating with the inlet (18) and outlet (19) openings, and equipped with a fuel spray nozzle (15) directed towards the axial opening in the bottom of the control element (16).
The engine as claimed in the claim 1, characterised in that the non-slip transmission (17) has a reducing ratio expressed by a natural number, and the control element (16) has pairs of inlet (18) and outlet (19) openings spaced according to the transmission ratio.
The engine as claimed in the claim 1, characterised in that the coupling (25) with controllable delay/advance angle is built into the non-slip transmission (17).
A two-stroke multi-cylinder internal combustion engine with spark ignition, with the air charge or a lean fuel-air mixture precompression in the crankcase (11), with ports controlled by the piston ; with the space (8) of each cylinder (1) connected via

a feed canal (14) and an exhaust gas charging canal (22), both ending at the cylinder wall with openings situated between the upper edge of the exhaust port (4) and the position of the top edge of the piston (5) at the moment of ignition

with a feed chamber (13) formed by the inner space of a rotary distributor (A), which is closed by a rotary control element (16) driven by a non-slip transmission (17) from the engine crankshaft (10), wherein the control element (16) has two openings, an inlet one (18) and an outlet one (19), spaced at such a central angle (α), and coupled with the transmission (17) in such a position that, when the element (16) is rotating, the inlet opening (18) meets the exhaust gas charging canal (22) outlet in the rotary distributor (A) during the power stroke, and the outlet opening (19) meets the outlet of the feed canal (14) in the compression stroke, and the mating is realized when the piston (5) is below the feed canal (14) opening in the cylinder wall, a

further, wherein a fuel spraying device (15) is built in the feed chamber (13),

characterized in that said chamber (13) is a common chamber for all the cylinders,
the spaces (8) of the cylinders (1) are connected to said common feed chamber (13) whose control element (16) takes the form of a shaft, i.e. with a concentric chamber at one end, closed by a cover (20) of the distributor body, fitted with the fuel spraying device (15), with the feed canal (14.1, 14.2, and 14.3) and the exhaust gas charging canal (22.1, 22.2, and 22.3) of each cylinder connected separately to two control sections of the rotary distributor (A), the sections being placed along the axis of the annular wall of the shaft, having an inlet opening (18) in the section connected to the exhaust gas charging canal (22) and the outlet opening (19) in the section connected to the feed canal (14), with the exhaust gas charging canals (22.1, 22.2, and 22.3) and the feed canals (14.1, 14.2, and 14.3) spaced on the circumference of the corresponding section at a phase angle (β), depending on the number of cylinders (1) and the sequence of ignition.
The engine as claimed in the claim 5, characterised in that the section corresponding to the outlet opening (19) and the feed canal (14), is situated closer to the cover (20) of the rotary distributor (A).