EP0236858A2 - Internal-combustion engine with a caburettor, particularly a diaphragm caburettor - Google Patents

Abstract

1. Internal combustion engine with a carburetor, more particularly a diaphragm-type carburetor, with a carburetion part, an induction part fitted before the carburetion part, a throttle valve part, a fuel inlet part fitted behind the throttle valve part, a main load and a part load jet chamber and a pressurized fuel supply pipe, characterized in that the mixture preparation area (20, 21, 60, 70, 7a, 8), in order to form a starting and control device, is provided with an additional bore (2) which communicates with the fuel supply pipe (10) via a feed pipe (4), the feed pipe being flow-controllable by means of a control device (3).

Description

The invention relates to an internal combustion engine with a carburetor, in particular with a diaphragm carburetor, with a gasification part, a suction part upstream of the gasification part, a throttle valve part, an inlet part downstream of the throttle valve part, a main and a part-load nozzle chamber and a pressurizable fuel supply line.

Such internal combustion engines have long been known in all areas of application and in particular for the use of motor chain saws. For the operation of an internal combustion engine, it is necessary to supply it with air and fuel in a certain air ratio for each operating point given by speed and load. The task of the carburetor is to allocate the correct amount of fuel to the intake air and to carry out the measurement of the amount of the mixture of air and fuel necessary for setting the operating point. This preparation and supply of the internal combustion engine with a corresponding fuel-air mixture can usually be carried out without problems during operation of the internal combustion engine.

Starting devices are required for the cold start or the dry start, that is to say the start after the carburetor has dried out with the internal combustion engine being strongly heated up beforehand. They ensure a very rich mixture, because to compensate for the poor evaporation under the above-mentioned conditions, the internal combustion engine is supplied with plenty of fuel until it starts. In addition, the starting devices enrich until normal operation is reached temperature of the internal combustion engine to the mixture to the extent necessary.

Starting devices are usually designed in the form of pre-throttle starters, in which the starter flap in front of the air funnel (Venturi) is closed and the throttle flap is opened a little at the same time. The intake manifold vacuum then also acts on the main nozzle system and it supplies the additional fuel required.

The use of such a starter flap system (choke) is particularly difficult when a diaphragm pump which is subjected to pressure impulses and which is acted upon by the pressure surges in the crankcase, for example of a two-stroke engine, is used as the fuel pump. By closing the starter flap, a pressure equilibrium is established between the fuel pump, the fuel flow area and the inlet area connected to the cylinder in such a way that the fuel flow does not start, or only to a very limited extent. In the case of internal combustion engines to be started by means of manually actuated starter devices, this leads to a considerable start-up effort, which reduces the ease of use of such an internal combustion engine.

In addition, the choke arranged in the intake part forms a considerable flow resistance during normal operation of the internal combustion engine, ie after the starting phase. This flow resistance leads to significant compromises in the carburettor design and the resulting disadvantages cannot be completely eliminated. For example, the additional one Do not remove turbulence in the incoming air through the starter flap.

It would therefore be advantageous to design the internal combustion engine and / or the carburetor so that a cold start or dry start can be carried out without a starter flap having to be provided.

In particular when using membrane carburettors, such as those often used for motor chainsaws, there are often problems with the control. Thus, at high carburetor temperatures, for example above 50 ° C, malfunctions in the fuel supply occur. These disturbances are usually caused by evaporating fuel, since the vaporous fuel presses on the fuel side onto the control membrane, whereby the control valve, which is usually designed as a needle valve, is closed. At summer temperatures in the range of 25 to 30 ° C, for example, the carburetor on a chain saw is heated to about 65 ° C in a period of about 10 minutes after a previous processing time in the subsequent saw break.

With such heating of the carburetor and thus the entire fuel delivery paths, such a strong fuel evaporation occurs that the engine can no longer be started. A forced cooling break of at least 20 minutes is the result, whereby the uses of the chainsaws, especially during summer use, are severely restricted, especially since it cannot be provided that such a chainsaw remains in use without a break. The given opportunity Keeping the engine of the chain saw at idle speed during breaks can no longer be accepted due to environmental considerations with regard to exhaust and noise pollution and energy waste.

A stronger spatial separation of the carburetor from the cylinder head of the internal combustion engine is associated with corresponding disadvantages due to the correspondingly longer flow paths.

It has therefore already been proposed to provide a stronger insulation between the carburetor and the cylinder of the internal combustion engine to solve this problem. However, this measure, which is effective per se, has the disadvantage that carburetor icing occurs at wintry temperatures where carburetor heating by the cylinder of the internal combustion engine is desired.

To solve the problems outlined above and in particular the problem of the cold starter, it has already been proposed to provide an additional manual fuel injection (primer). On the one hand, the constructional and space-related expenditure involved has proven to be a disadvantage, on the other hand, this possibility has also not previously led to the desired results, since it was also impossible to prevent vapor bubbles from forming. In addition, control is no longer possible with the primer after the internal combustion engine has started. An exact metering of fuel is also not feasible in this way, so that besides the already existing problems there is always the problem of the engine running down.

The invention therefore achieves the object of developing an internal combustion engine with a carburetor, in particular with a diaphragm carburetor, of the type mentioned at the outset in such a way that the internal combustion engine can be started without problems in all environmental conditions without additional manual fuel injection or a choke at the Carburettor must be provided, in particular the provision of an ignitable mixture should be ensured after a few start attempts even under extreme temperature conditions. In the case of internal combustion engines with a diaphragm carburettor in particular, the possible interference from the diaphragm control is also to be eliminated and an additional fuel supply is to be created.

This object is achieved in an internal combustion engine with a carburetor, in particular with a diaphragm carburetor, with a gasification part, an intake part upstream of the gasification part, a throttle valve part, an inlet part downstream of the throttle valve part, a main and a part-load nozzle chamber and a pressurizable fuel supply line in that the mixture preparation area to form a start and control device is provided with an additional hole which is connected to the fuel supply line via a supply line, the supply line being flow-controllable via a control device.

With this arrangement of an additional supply line in the manner described, a start and control device have been created, which effectively supplies fuel without additional devices being actuated, in particular in two-stroke internal combustion engines in all environmental and operating conditions, ie regardless of the outside temperatures and the operating temperatures of the internal combustion engine. The arrangement of the additional bore can be provided in the entire intake area and must be selected depending on the specific requirement profile of the internal combustion engine, because the only important thing is that additional fuel is brought into the intake area regardless of the main nozzle and part-load nozzle system.

With the design of the internal combustion engine according to the invention, for example, a cold start is possible even with a dry carburetor, without additional starting devices having to be provided. The necessary enrichment is carried out directly via the supply line in the part-load nozzle chamber, so that the fuel-air mixture is enriched to such an extent under normal negative pressure that a cold start is possible. There is an additional advantage over the known starting devices, particularly when using the internal combustion engine in motor chainsaws, that when using the known diaphragm carburettor the internal combustion engine often starts, but then becomes over-rich so quickly that it "drags down" and then subsequently without choke actuation must be started again. This disadvantage does not arise in the present system, since a regulated supply of fuel is possible. Since a starter device is omitted, a fuel supply from the fuel pump is already guaranteed when the starter is actuated for the first time, so that an ignitable mixture in dry or cold conditions is also very fast Carburetor is provided.

Another great advantage results from the fact that a starter flap in the form of a choke flap is no longer necessary and the flow conditions in the carburetor improve considerably as a result of the starter flap being eliminated. This also allows the diameter of the venturi nozzle formed in the gasification part to be reduced, which considerably improves the performance characteristics of the engine.

An effective starting option has also been created for the hot start with the internal combustion engine according to the invention, since the operating or starting malfunctions which occur at carburetor temperatures above 50 ° C., which are caused by evaporating fuel in the control area of the carburetor, by acting as a by-pass Supply line must be eliminated, since the bypass bypasses the needle valve which may be blocked by the pressurized control membrane. The supply line connects the pressurizable fuel supply line and thus the pressure area of the fuel pump directly to the part-load nozzle chamber. With this by-pass, the engine can be started reliably even at a carburetor temperature of 65 ° C with two to four attempts at half throttle setting of the throttle valve, while a cooling break of at least 20 minutes would be necessary at internal carburettor-powered chainsaws with previously known diaphragm carburettors at these carburetor temperatures at least fifty start attempts would have to be carried out to get a carburetor over the fresh air drawn in to achieve cooling, with a safe start of the engine is not feasible.

Since after hot starts the carburetor reached its operating temperature below 50 ° C after about 5 to 10 seconds of operation, which is then associated with a corresponding enrichment of the mixture and when the machine is cold started, it has reached the operating temperature after a corresponding period of time, starting from the starting temperature , the by-pass must be closed in this operating state. The supply line is therefore designed to be flow-controllable and lockable via a control device. By blocking the supply line, its influence on the carburetor function and thus on the operating behavior is excluded for the normal operating state. However, it can also be provided that the control of the main fuel mixture control, for example the diaphragm control, is blocked for certain operating states, for example fuel metering is now only carried out via the bypass.

According to a preferred embodiment it is provided that the bore in the mixture preparation area is arranged in the intake part, in front of the gasification part (Venturi), in front of or behind the throttle valve part, in the main or part-load nozzle chamber or in the crankcase.

According to this, the arrangement of the additional bore can take place exactly at the point where there is a need for an additional mixture enrichment in the fuel processing area. So it can be provided in internal combustion engines with crankcase purging, form the additional hole directly in the crankcase and inject it there.

According to a preferred embodiment, it is provided that a supply line connecting piece of the supply line is connected to the fuel supply line which can be pressurized with fuel pump, to the filter chamber or to the main nozzle supply line connected downstream of the filter chamber, with the arrangement of the bore in the crankcase providing in particular that the supply line connecting piece of the supply line is connected to a Pressure accumulator or a condenser chamber is connected, which is connected to the fuel supply line, to the filter chamber or to the main nozzle supply line connected downstream of the filter chamber. It can also be advantageously provided that the supply line connecting piece of the supply line is connected to a mechanical or electrical auxiliary fuel pump. In this way it has become possible to provide an additional mixture in internal combustion engines of different designs.

According to a further preferred embodiment it is provided that the flow diameter of the bore is chosen to be small compared to the flow diameter of a part-load nozzle of the part-load nozzle chamber. This configuration of the bore ensures that total flooding of the engine with fuel can be reliably prevented, even if pressure peaks occur in the fuel supply system due to the formation of vapor bubbles in the fuel.

According to a further embodiment it is provided that the control device is designed as a manually operated shut-off valve. With this structurally simple design, the actuation of the supply line can be carried out as a warm and cold start device, since the problems occurring during hot start attempts can be avoided by simply unlocking and releasing the supply line when the carburetor is warm. The shut-off valve is then locked again in a simple manner when the carburetor has reached its operating temperature, for example after about 10 seconds, which can be recognized by an enrichment of the mixture and the associated changes in the exhaust gas.

According to a preferred embodiment it is provided that the control device is designed as an electronically controlled shut-off valve. This means that both an automatic cold start and a warm start device for the internal combustion engine can be embodied in the diaphragm carburetor, without the need for further complex control and regulating parts. The sensor of the control switch is preferably arranged in the chamber or in the region downstream of the throttle valve in the air flow, so that the fuel / air mixture subjected to the gasifier temperature or directly the fuel itself serves as a control variable for the hot and cold starting device. It can be provided that the switch releases the supply line for the cold start in a certain low temperature range, then blocks the supply line in a further large operating temperature range and releases the supply line again when temperature peaks occur. Also a combination with a further operating and status variables visible control electronics is possible without any problems.

It can preferably also be provided that a sensor of the control switch is arranged on the throttle valve or the throttle valve actuation mechanism for detecting the throttle valve position. This can e.g. can be achieved that the additional fuel required for a hot or cold start is automatically injected during the starting process and the enrichment is maintained over the period until mixture enrichment occurs, when the throttle valve is at half-throttle and a certain temperature is detected by the electronics.

Overall, the novel design of the internal combustion engine has created a simplest device for the warm and cold start of internal combustion engines, in particular for motor chain saws. With this training there are not only manufacturing and cost advantages, since complex thermal insulation, an additional manual fuel injection (primer) or a choke flap with locking are no longer necessary, but there is also the advantage that in addition to a chain saw always desirable weight saving a constructive simplification of the membrane gasifier can be achieved, which significantly increases its operational safety and operational time.

In the drawing, an embodiment of the invention is explained in more detail, wherein only the mixture preparation part of the internal combustion engine is shown and, for this purpose, a diaphragm carburetor was chosen as an example.

The diaphragm carburetor 100 shown in section in the drawing consists of a housing 50 in which the gasification part 20 and the downstream throttle valve part 21 are arranged. The fuel entering via the fuel inflow 13 is pumped by the fuel pump 5 into the filter chamber 9 and from there it is led via the main nozzle supply line 11 to the needle valve 7, which is controlled by the control membrane 6. At the same time, the fuel is supplied to the part-load nozzle chamber 8 via corresponding supply lines.

In the part-load nozzle chamber 8, a nozzle bore 2 is formed, which is connected on the outside of the housing to a supply line 4 designed, for example, as a heat-insulated fuel hose. The supply line 4 is connected at its other end to the supply line connecting piece 1, which is arranged projecting into the main nozzle supply line 11 connected downstream of the filter chamber 9. In the course of the supply line 4, a regulating device 3 is arranged on the outside of the housing 50, which is designed as a check valve 30 regulated by a control switch 40. The sensor 41 of the control switch 40 is arranged inside the filter chamber 9.

In order to enable additional metering of the fuel supplied via the supply line 4 and possibly to avoid flooding the part-load nozzle chamber 8, the nozzle bore 2 has a small flow diameter compared to the nozzle (s) 80 of the part-load nozzle chamber 8 and, in a special embodiment, has one Diameter of 0.34 mm.

The control device 3 and the supply line 4 connected therewith do not necessarily have to be arranged in the manner indicated in the drawing, but it may also be advantageous if the control device 3, in particular if it is designed as a manually operated shut-off valve, does not have one in the drawing housing surface of a housing of a motor chain saw, not shown in the drawing, is arranged. For the function of the cold and warm start device, it is only essential that the supply line 4 is connected to the pressurized part of the fuel supply to the diaphragm carburettor, and on the other hand, additional fuel injection via the supply line 4 into the part-load nozzle area in the throttle valve part 21 of the diaphragm carburettor.

The bore 2, which can be designed as a nozzle bore as described above, can be located at any point on the carburetor, e.g. in the main nozzle chamber 7a or in front of the carburetor in the suction part 60 or behind the carburetor in the inlet part 70. It can also be provided that the bore 2 is arranged directly in the gasification part 20, so that parallel operation of the bore 2 with the main nozzle is possible. It can then even be provided via the control system that the by-pass system works as the main supply system and the control system with the carburetor membrane only acts as an ancillary system, but this is not shown in the drawing.

According to an embodiment, also not shown in the drawing, it can be provided that the Ver supply line connecting piece is connected directly to an additional fuel pump or is connected to the fuel pump 5 via a pressure accumulator or a condenser chamber. This has the result that the supply line 4 is actuated independently of the fuel via the impulse line 25, which is connected to the crankcase of the internal combustion engine, not shown in the drawing.

Claims (10)

1. Internal combustion engine with a carburetor, in particular with a diaphragm carburetor with a gasification part, a suction part upstream of the gasification part, a throttle valve part, a throttle valve part, an inlet part downstream of the throttle valve part, a main and a part-load nozzle chamber and a pressurizable fuel supply line, characterized in that the Mixture preparation area (20, 21, 60, 70, 7, 8) is provided with an additional bore (2) to form a start and control device, which is connected to the fuel supply line (10) via a supply line (4), the supply line (4) can be controlled by a flow control device (3). 2. Internal combustion engine according to claim 1, characterized in that the bore (2) in the mixture preparation area in the intake part (60), before the gasification part (Venturi) (20), before or after the throttle valve part (21), in the main (7a) or part-load nozzle chamber (8) or is arranged in the crankcase. 3. Internal combustion engine according to claim 1 or 2, characterized in that a supply line connection piece (1) of the supply line (4) with the fuel pump pressure pressurizable fuel supply line (10), with the filter chamber (9) or with the filter chamber (9) downstream main nozzle supply line (11) connected is. 4. Internal combustion engine according to claim 3, characterized in that the supply line connection piece (1) the supply line (4) is connected to a pressure accumulator or a condenser chamber which is connected to the fuel supply line (10), to the filter chamber (9) or to the main nozzle supply line (11) connected downstream of the filter chamber (9). 5. Internal combustion engine according to one of claims 1 to 4, characterized in that the supply line connection piece (1) of the supply line (4) is connected to a mechanical or electrical auxiliary fuel pump. 6. Internal combustion engine according to one of claims 1 to 5, characterized in that the flow diameter of the bore (2) compared to the flow diameter of a part-load nozzle (80) of the part-load nozzle chamber (8) is chosen small. 7. Internal combustion engine according to one of claims 1 to 6, characterized in that the control device (3) is designed as a manually operated check valve. 8. Internal combustion engine according to one of claims 1 to 7, characterized in that the control device (3) is designed as an electronically controlled shut-off valve (30). 9. Internal combustion engine according to claim 8, characterized in that a sensor (41) of the control switch (40) in the float chamber (9) or in the area upstream / downstream of the throttle valve (12) is arranged in the air flow. 10. Internal combustion engine according to claim 8 or 9, characterized in that a sensor (42) of the control switch (40) on the throttle valve (12) or the throttle valve actuating mechanism for detecting the throttle valve position is arranged.

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