CN1145978A - Two-stroke internal combustion engine - Google Patents

Abstract

In a two-stroke internal combustion engine with a fuel injection cavity (20), the injection cavity (20) is combined in the combustion cylinder (11) and connected to the fuel injection device (22), and the injection cavity (20) passes through the discharge hole (202) In connection with the combustion chamber (13) in the cylinder (11), in order to improve the input of injecting fuel into the injection chamber (20) and spend less technical manufacturing surcharge, in the crankcase (10) or in the cylinder (11) A stroke piston-air compressor (25) is combined in the middle, and its compression chamber (24) forms communication with the inner cavity (15) of the crankcase (10) and passes through a pressure check valve (26) Connected to the injection chamber (20). When a predetermined compression pressure is reached, the pressure check valve (26) is opened so that the amount of fuel stored in the injection chamber (20) is blown out of the injection chamber (20).

Description

two-stroke internal combustion engine

The invention relates to a two-stroke internal combustion engine, especially suitable for use in hand-held drive units, which belongs to the technical field defined in the preceding part of claim 1 .

In a known two-stroke internal combustion engine of this type (EP 0514982A1) a guide sleeve is inserted into the injection chamber, which is closed to the combustion chamber by a spring-loaded shut-off valve with a shut-off cone. The guide sleeve accommodates the stroke piston, which is driven by an outwardly protruding auxiliary crankshaft via a connecting rod for stroke movement. The auxiliary crankshaft is driven via a toothed belt by a gear wheel arranged on the crankshaft for the cylinders. In addition to the injection openings for the fuel injection device, the injection chamber has an opening for the joint delivery of air and oil. The resulting mixture of fuel, air and oil in the injection chamber flows during the suction stroke of the piston through the overflow channel in the injection chamber into the chamber in the guide sleeve delimited by the shut-off valve and the end wall of the piston. During the delivery stroke of the stroke piston, this piston closes the above-mentioned overflow channel and compresses the stored mixture until the pressure is sufficient to open the shut-off valve. With the opening of the valve, the mixture is injected under pressure directly into the combustion chamber of the cylinder. The metering of the fuel quantity injected into the injection chamber is carried out by means of a solenoid valve.

In the same known two-stroke engine (DE3727266A, or DE4125593A1), the fuel metering is accomplished by a diaphragm piston pump, which is acted upon by the pressure in the crankcase. The amount of fuel dispensed by the pressure in the crankcase cavity is injected directly into the combustion chamber of the cylinder.

An aspect of the invention of the two-range internal combustion engine having the characterizing features of claim 1 has the advantage that the fuel distribution and the fuel supply are separated from each other and can be adjusted independently of each other. Thus, not only is a high-precision fuel metering obtained, but the introduction of fuel into the combustion chamber of the cylinder can be controlled from the very beginning to achieve a better mixture combustion. On the other hand, the structural expenditure for fuel injection is also very small due to the arrangement of a separate stroke piston compressor arranged inside the crankcase or inside the cylinder, because the stroke piston can be directly connected to the cylinder without a switching mechanism. On the crankshaft that drives the connecting rods of the combustion pistons. Therefore, a separate compressor lubrication mechanism such as a separate support structure can be omitted. This in turn avoids a shut-off valve subject to the hot gases in the combustion chamber.

Since the compression chamber of the compressor is filled with combustion air from the crankcase cavity and this air under pressure is used to complete the fuel injection, the start of the injection can be controlled according to the load. Since the pressure in the crankcase varies according to the load and is adjusted accordingly through the throttle valve connected to the air intake port, the pressure in the compression chamber necessary to open the pressure check valve will be reduced under full load. It is reached earlier and later at part load, which leads to a corresponding change in the injection start. Since the fuel is stored in the injection chamber before the start of the injection into the combustion chamber, the vaporization of the fuel in the injection chamber also begins before the above-mentioned injection into the combustion chamber, which can lead to an improved fuel injection during injection. Atomization.

Advantageous variants and modifications of the two-stroke internal combustion engine defined in claim 1 are made possible by the measures stated in the further claims.

According to a preferred embodiment of the invention, the stroke piston air compressor is realized by arranging the combustion piston as a stepped piston structure, the stepped piston having a rear piston part with a smaller diameter facing away from the combustion chamber, and the rear piston part is inserted into the Into a guide sleeve held in the cylinder and closed with the inner wall of the cylinder, the end face side of the guide sleeve and the annular shoulder formed on the piston step as the effective piston surface of the stroke piston to form a compression chamber. The necessary connecting lines to the injection chamber are arranged in the overflow channel and can be realized there via corresponding passage holes. This constructional measure minimizes the manufacturing effort for the compressor and requires only the configuration of the combustion piston as a stepped piston and an additional sleeve that is fastened in the cylinder.

When the control according to another embodiment of the present invention is provided with an annular leakage gap between the stroke piston and the sleeve, then in addition to the load-related injection start variation, a rotation-related injection start variation can be realized, This variation serves to improve fuel combustion, thus resulting in lower consumption and improved emission values. This speed-dependent injection start movement occurs when the leakage gap at low speeds allows a significantly larger leakage air volume than at high speeds, from which the air volume returns to the compression chamber during the delivery stroke of the stroke piston. Leaks into the interior of the crankcase, and at high speeds this leak is not always important. Therefore, at low rotational speeds, the pressure in the connecting line leading to the injection chamber necessary for opening the pressure check valve is reached later than at high rotational speeds, so that at low rotational speeds from the injection chamber Blowing out of fuel starts advantageously later.

In a preferred embodiment of the invention, the stroke piston air compressor can also be realized in that a stroke cylinder open to its interior is arranged radially on the crankcase, wherein the stroke piston is guided axially displaceably in it. The stroke piston is connected via a connecting rod to the crankshaft in the crankcase in such a way that at the bottom dead center of the gas piston it occupies approximately its top dead center. This compressor embodiment is slightly more expensive in manufacturing technology, but still brings the same advantages as the previously described solution.

A so-called "low-cost" embodiment, that is, a two-stroke internal combustion engine with low production costs, is that, in addition to realizing the stroke piston by placing the gas piston in a stepped structure, it is also used according to another embodiment of the present invention. The fuel metering fuel injection device has a diaphragm pump driven by the air pressure in the crankcase and has inlet and outlet valves in the form of a non-return valve. The injection device is connected on the outlet side to the injection chamber and the On the inlet side it is connected to a sub-delivery pump. These two-stroke internal combustion engines are powerful, noise-resistant and do not require batteries, since the electrical power supply components are generally omitted.

The invention is explained in more detail below with the aid of an exemplary embodiment depicted in the drawing.

1 and 2 are each a longitudinal section of a two-stroke internal combustion engine with different embodiments of fuel injection devices described in block diagrams,

Fig. 3 is a longitudinal sectional view of another embodiment of a two-stroke internal combustion engine,

In the longitudinal section of FIG. 1 a two-stroke internal combustion engine or two-stroke engine is schematically depicted, which is preferably used to drive hand-held drives, such as motorized chain saws, split grinders, free-cutting cutters and the like. However, it is also possible to drive mopeds, motor boats, lawn mowers and the like. In a known manner, it has at least one combustion cylinder 11 accommodated in a crankcase 10 , in which is accommodated an axially displaceable guided combustion piston 12 , whose upper end delimits a combustion chamber 13 accommodated in the combustion cylinder 11 . The combustion chamber 13 is connected via at least one transfer channel 14 to the interior 15 of the crankcase 10 . An intake hole 16 for combustion air is provided on the cylinder wall of the combustion cylinder 11, which is connected with an air intake passage controlled by a gas valve, and an exhaust hole 17 for exhaust gas is also provided, which is connected with the exhaust gas. connected to the gas system. During the movement stroke of the combustion piston 12, the intake port 16, the exhaust port 17, the overflow channel 14 and the opening 141 on the side of the combustion chamber are closed and opened by the combustion piston 12 in a determined sequence. The stroke movement of the combustion piston 12 is converted via a connecting rod 18 into a rotation of a crankshaft 19 accommodated in the crankcase 10 . In the combustion cylinder 11 , a fuel injection chamber 20 is arranged in the region of the transfer channel 14 , which has an injection opening 201 , an outlet opening 202 and a compressed air opening 203 . The discharge hole 202 is located inside the hole 141 on the combustion chamber side of the overflow channel 14, but it can also be realized by a through hole leading to the cylinder wall of the combustion chamber 13, which is arranged below the piston stroke plane, the stroke Outlet holes 17 are provided in the plane. A fuel injection device 22 is connected to the injection opening 201 via a throttle valve 21, which will be described in more detail below. The compressed air bore 203 is connected to a connecting channel 23 , which opens into a compression chamber 24 of a stroke piston air compressor 25 arranged in the combustion cylinder 11 . Arranged in the connecting channel 23 is a pressure check valve 26 which opens towards the injection chamber 20 when the compression pressure in the compression chamber 24 is greater than 2 bar, for example.

In the case of the embodiment of FIG. 1 , this stroke piston-air compressor 25 is realized by arranging the combustion piston 12 as a stepped piston structure and by arranging a guide sleeve 27 in the combustion cylinder 11 in which The smaller diameter piston part 121 is embedded and can be moved axially guided therein. At the same time, the compression chamber 24 is delimited on the end face side by the end face side of the sleeve 27 and the ring shoulder 122 formed between the stepped piston part of the piston 12, and on the inside by the outer wall of the small-diameter piston 121, and on the outside by the wall of the cylinder 11. limited by the cylinder wall. The cooperation of sleeve 27 and small-diameter piston part 121 is selected such that an annular leakage gap 28 remains between them. If the piston 12 moves upwards in the cylinder 11 , after the intake opening 16 has been opened by the piston 12 , air flows through this opening 16 into the interior 15 of the crankcase 10 . Next, air is charged into the compression chamber 24 of the compressor 25 . If the cylinder 12 moves downward again, the compression stroke of the compressor 25 starts with the closing of the intake opening 16 . The compressed air in the compression chamber 24 is fed into the injection chamber 20 through the open pressure check valve 26 at a pressure of, for example, greater than 2 bar. At the same time, part of the compressed air flows through the leak gap 28 into the interior 15 of the crankcase 10 . This slippage effect decreases with increasing rpm, so that the pressure in the compression chamber necessary to open the pressure check valve 26 is higher at higher rpm (based on the rotation of the crankshaft) than at lower The number of revolutions is reached in advance. With the air input from the compression chamber 24 of the compressor 25 into the injection chamber 20, the amount of fuel injected by the fuel injection device 22 in the injection chamber 20 is blown out from the injection chamber 20 through its discharge hole 202 and enters the cylinder. In the combustion chamber 13 at 11 o'clock. At the same time this blow-out starts to vary, as described above, depending on the number of revolutions and the load. Since the pressure in the crankcase 10 and thus the air pressure flowing into the compression chamber 24 also fluctuates via the load-dependent regulating throttle valve, which is located in the air intake duct arranged upstream of the intake opening 16 , In turn, the compression pressure in the compressor 25 will reach greater than 2 bar, for example earlier or later.

The fuel injection device 22 has a known double-membrane pump 30 which is driven by the pressure in the interior 15 of the crankcase 10 to deliver fuel from a fuel storage tank 31 . This double-membrane pump 30 has been described, for example, in DE 4223758A1. A working chamber 33 of the double-membrane pump 30 , which is bounded by a diaphragm 32 , is connected to the inner chamber 15 of the crankcase 10 via a conduit 34 . The diaphragm 33 actuates via a tappet 35 a pump diaphragm 36 which delimits a pump chamber 37 . The pump chamber 37 is connected via an inlet valve 38 to a fuel supply line 39 leading to a fuel storage tank 31 . The outlet of the pump chamber 37 is connected with the solenoid valve 40 on the one hand and the pressure limiter 41 on the other hand. The pressure maintained by the pressure limiter 41 in the line between the pump chamber 37 and the metering valve 40 is regulated at eg 3 bar. As soon as the solenoid valve 40 of the 2/2-channel solenoid valve configuration is closed, the fuel delivered by the double-membrane pump 30 from the fuel storage tank 31 flows back into the storage tank 31 via the pressure limiter 41 . If metering valve 40 is switched into its flow position, fuel flows through throttle valve 21 into fuel injection chamber 20 . The fuel quantity distributed to injection chamber 20 is then determined by the switching duration of metering valve 40 .

In order to fulfill the function of the metering valve 40 without electrical components, in the fuel injection system 22 depicted in FIG. 2 , the fuel is metered by means of a diaphragm gas piston pump 40 , which is pressurized by the crankcase 10 . The structure and mode of operation of such a diaphragm pump are described, for example, in DE 3727266 A1. A diaphragm 43 delimits a working chamber 44 which is connected via a line 45 to the interior 15 of the crankcase 10 . A pump piston 46 is fixed centrally on the diaphragm 43 , which is guided in a pump cylinder 47 and delimits a pump chamber 48 on the front side. The pump chamber 48 is connected via an inlet valve 49 to the outlet of a prefeed pump 50 . The pump 50 is likewise actuated by the pressure in the crankcase 10 and draws fuel from the fuel storage tank 31 via the fuel supply line 39 and returns it to the fuel storage tank 31 via the fuel return line 51 in circuit operation. During the suction stroke of the pump piston 46 , fuel flows into the pump chamber 48 via a feed valve 49 configured as a non-return valve. During the compression stroke of the pump piston 4668 , this fuel quantity is fed into the fuel injection chamber 20 via the discharge valve 52 , which is likewise designed as a non-return valve, and via the throttle valve 21 . The quantity of fuel supplied thereby is determined by the stroke of pump piston 46 .

The two-stroke internal combustion engine with crankcase 10 and at least one fuel cylinder 11 is equivalent to the two-stroke internal combustion engine described in FIG. 1 . Components marked with reference numbers are consistent with those in FIG. 2 . Therefore, the numbering in Fig. 2 has been omitted.

Another embodiment of a two-stroke internal combustion engine with a combined stroke piston air compressor 25 is shown in schematic longitudinal section in FIG. 3 . The two-stroke internal combustion engine has the same construction as in FIGS. 1 and 2 except for the compressor 25, and therefore the same components are given the same reference numerals.

Arranged radially on the crankcase 10 is a displacement cylinder 53 , which is open towards its interior 15 , and in which an axially displaceable displacement piston 54 is guided. The stroke piston 54 is connected to the crankshaft 19 via a connecting rod 55 in such a way that, at the bottom dead center of the combustion piston 12 , the stroke piston 54 approximately occupies its top dead center in the stroke cylinder 54 . The compression chamber 24 of the compressor 25 delimited by the stroke piston 54 in the stroke cylinder 53 is connected to the fuel injection chamber 20 in the cylinder 11 via a pressure line 56 leading here outside the crankcase 10 and the combustion cylinder 11. The pressure air holes 203 are connected. A pressure non-return valve 26 is again arranged in the pressure line 56 . Attached to the stroke piston 54 is a seal 57 which is configured in the manner of an air pump seal in such a way that it draws combustion air from the interior 15 of the crankcase 10 into the compression chamber 24 during the suction stroke of the stroke piston 54 During the compression stroke of the stroke piston 54, the stroke piston 54 forms a seal against the inner wall of the stroke cylinder 53 and thus the compression chamber 24 is closed. The compressor 25 functions in the same way as the compressor 25 of FIG. 1 . If the pressure in the compression chamber 24 rises above 2 bar, for example, the pressure check valve 26 opens and the fuel quantity fed into the injection chamber 20 by the fuel injection device is directly fed into the combustion chamber 13 via the blow-off hole 202 . Since the pressure in the inner cavity 15 of the crankcase 10 fluctuates according to the adjustment of the throttle valve placed in the air intake passage, which is connected to the intake hole 16), it is necessary to open the pressure check valve 26 When the pressure inside the compression chamber 24 is reached, the stroke piston 54 may undergo a shorter stroke movement, or a longer stroke movement. Therefore, the discharge of fuel from the injection chamber 20 is related to the crank angle, and sometimes occurs earlier or later. Since the throttle valve position is load-dependent, the start of fuel discharge from injection chamber 20 is also displaced in a load-dependent manner.

The two-stroke internal combustion engine shown schematically in FIG. 3 with a combined stroke piston compressor for fuel injection can not only be operated in coordination with the fuel injection system 22 described in FIG. 1 . It can also be operated in combination with the injection device 22 described in FIG. 2 . They are always connected to the fuel injection opening 201 of the fuel injection chamber 20 via the throttle valve 21 .

Claims (10)

1. A two-stroke internal combustion engine, especially suitable for hand-held drives, having at least one combustion cylinder (11) arranged on the crankcase (10), wherein an axially displaceable guide is guided on one end side to define a combustion chamber ( 13) of the combustion piston (12), and when the piston travels, it controls an intake hole (16) for introducing combustion air, a discharge hole (17) for exhaust gas and at least one crankcase ( 10) The overflow channel (14) that the inner cavity (15) is connected with the combustion chamber (13); it also has a set in the crankcase (10) and is connected to the combustion piston (12) through a connecting rod (18) The connected crankshaft (19) also has a fuel injection chamber (20) separated in the combustion cylinder (11), which is connected to the combustion chamber (13) through a discharge hole (202) and through an injection hole (201 ) is connected to the fuel injection device (22); and has a stroke piston (12; 54) driven by the crankshaft (19) for blowing out the fuel stored in the injection chamber (20) by the fuel injection device (22), which Characterized by: The stroke piston (12; 54) is a component of the stroke piston air compressor (25), which (25) is combined in the crankcase (10) or in the combustion cylinder (11), the compression chamber of the compressor (25) ( 24) is connected to the injection chamber (20) via a pressure check valve (26) and communicates with the interior chamber (15) of the crankcase (10) during the suction stroke of the stroke piston (12; 54). 2. The internal combustion engine according to claim 1, characterized in that: In order to realize the stroke piston compressor (25), the combustion piston (12) is arranged in a stepped structure and has a smaller diameter rear piston part (121) facing away from the combustion chamber (13), which is embedded in a cylinder held in the combustion cylinder ( In the guide sleeve (27) in 11) and the inner wall of the cylinder (11), one end face side of the guide sleeve (27) and a piston surface produced on the piston shoulder and play the effective role of the stroke piston Together the annular shoulders (122) close into a compression chamber (24). 3. The internal combustion engine as claimed in claim 2, characterized in that an annular leakage gap (28) is provided between the smaller-diameter piston part (121) and the guide sleeve (27). 4. The internal combustion engine according to claim 2 or 3, characterized in that: The pressure check valve (26) is arranged in the connecting pipe (23) arranged via the overflow channel (14) between the compression chamber (24) and the injection chamber (20). 5. The internal combustion engine according to claim 1, characterized in that: in order to realize the piston air compressor (25), the crankcase (10) is radially provided with a stroke cylinder (53) open to its inner chamber (15), The stroke piston (54) is guided axially displaceably; the stroke piston (54) is connected to the crankshaft (19) via a connecting rod (55) in such a way that at the bottom dead center of the piston (12) the stroke piston (54) occupies approximately its top dead center (position). 6. The internal combustion engine according to claim 5, characterized in that: The stroke piston (54) has a seal (57) that cooperates with the inner wall of the cylinder (53), and it allows the combustion air to flow from the inner cavity (15) of the crankcase (10) during the suction stroke of the piston (54). ) flows into the compression chamber (24), and when the stroke piston (54) compresses the stroke, it (54) forms a seal with respect to the inner wall of the cylinder (53). 7. The internal combustion engine according to any one of claims 1-6, characterized in that: the discharge hole (202) of the injection chamber (20) leads to the overflow passage (14) or is arranged on the cylinder wall of the cylinder (11) And be positioned at the bottom of waste gas discharge hole (17). 8. The internal combustion engine according to one of claims 1 to 7, characterized in that: the opening pressure of the pressure check valve (26) between the compression chamber (24) and the injection chamber (20) is adjusted at about 2 bar (bar) on. 9. The internal combustion engine according to one of claims 1 to 8, characterized in that: the fuel injection device (22) is connected to the injection chamber (20) through a throttle valve (21); one is connected to the injection chamber (20) by the crankcase (10) The double-membrane pump (30) driven by the air pressure in the fuel tank (31) delivers fuel from the fuel storage tank (31) and has a preferably 2/2-stroke-solenoid valve structure connected after the double-membrane pump (30) There is a spring return metering valve (40) and a pressure limiter (41) connected at the outlet of the double membrane pump (30). 10. The internal combustion engine according to any one of claims 1 to 8, characterized in that: the fuel injection device (22) is connected to the injection chamber (20) through a throttle valve (21); and has a crankcase ( 10) air pressure-driven diaphragm pump (42) with input and output valves (49, 52) configured as check valves and a prefeed pump (49) connected to the input valve (49) 50), which delivers fuel from the storage tank (31).

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