EP0233612A2 - Carburetter for an internal-combustion engine - Google Patents

Abstract

A carburetor with an idling system is created, which uses the entire available pressure drop between approximately ambient pressure and the negative pressure in the intake pipe (3) to achieve the critical pressure ratio of a supersonic flow in a Laval nozzle (4l). For this purpose, a fuel-air emulsion formed with primary air is passed from a mixing channel (27) via an orifice (34) with a narrow cross-section to a tubular nozzle (32) in the area of the cross-sectional constriction (4l), at which the speed of sound is always at a critical and supercritical pressure ratio Secondary air flow introduced and there with maximum speed difference, supported by the following pressure surges, atomized. At least well into the partial load range, the idling system produces a homogeneous mixture with an almost molecular particle size of the fuel, which is distributed homogeneously in the intake pipe (3), so that it is fed evenly to all cylinders and burned completely with low-pollution combustion.

Description

The invention relates to a carburetor for internal combustion engines, according to the preamble of claim 1 and an idling installation part therefor according to the preamble of claim 20.

Such a carburetor is known from DE-AS 24 52 342. In this known carburetor, the idle duct arrangement is guided in the material of the carburetor housing, primary air being fed to the fuel in the vertically arranged fuel duct via a branch duct arranged at an acute angle to form an emulsion. At the lower end of the fuel channel, the emulsion first enters a storage space for transition bores, which open into the intake channel in the closed position in the contact area of the edge of the throttle valve. The fuel channel is in another on the side of the supply chamber opposite the inlet Feed chamber of the idling system, from which the fuel reaches a mixing chamber for the admixture of combustion air via a throttle bore which can be adjusted in cross section by means of an adjusting screw and throttle mandrel. On the side of the mixing chamber opposite the throttle bore, the fuel-air mixture enters a tube which extends far into the intake duct below the throttle valve and has a step-shaped throttle point on its side adjacent to the mixing chamber, which constricts the cross section to produce the speed of sound in the flow of the idle duct arrangement represents. The combustion air is fed to the mixing chamber from an intake opening in the wall of the intake duct above the throttle valve via a throttle, which in the mixing chamber leads to a negative pressure required for conveying the fuel out of the fuel duct.

The negative pressure generated in the mixing chamber must be quite substantial, since it must lead to an exit of the fuel from the adjacent throttle opening at a relatively high speed, which must be fed to the narrow inlet of the throttle point on the other side of the mixing chamber without the Mixing chamber is contaminated by coking condensate on its walls. This must be achieved, although considerable pressure losses occur in the area of the supply chamber for the transition bores and the supply chamber for the idling system with the throttle mandrel. Therefore, the vacuum of the combustion air in the mixing chamber must be quite substantial.

On the other hand, however, the pressure in the mixing chamber must still be almost twice the pressure in the intake pipe if the cross-sectional constriction is to achieve the speed of sound. So if you assume a pressure in the mixing chamber of 0.75 bar at which If the emulsion is just being adequately conveyed, a pressure in the intake pipe of at most about 0.4 bar is required in order to achieve the speed of sound at the cross-sectional constriction and thus the desired relatively fine atomization. The setting of such conditions may just be possible in idle mode under ideal conditions, but then already presupposes that the degree of closure of the throttle valve is high and not affected by manufacturing inaccuracies or other faults, and further that the nominal idle speed is actually reached; this can drop significantly when switching on power consumers such as an air conditioning system, a servo system or the like, which would already leave the required ideal conditions. In particular, these ideal conditions are already left at the transition to part-load operation in that the throttle valve is opened a little, which partially causes the negative pressure in the intake pipe to collapse, so that the critical pressure ratio required to achieve the speed of sound can no longer be achieved.

Thus, the desired fine atomization can no longer be achieved even in the lower part-load range, and the setting is extremely susceptible to failure even in the actual idling mode, so that the engine can die, for example, when the air conditioning system is switched on automatically. However, even under the ideal conditions that cannot be maintained in practice in the long run, an incomplete "gasification", i.e. reduction of the droplet diameter of the fuel down to almost the molecular range, is achieved, since the combustion air present at low pressure and low speed with the emulsion, the also enters the mixing chamber at a relatively slow speed, already together in the mixing chamber is brought so that there is no significant effect in terms of reducing the droplet diameter at the mixing point. The fuel-air mixture with relatively large droplet diameters thus reaches the range of the sound flow, if this is achieved at all, and the droplet diameter can only be reduced subsequently by the action of pressure waves. Even when the speed of sound is achieved in the cross-sectional constriction, subsequent crushing of the droplets in the mixture is thus achieved only to a limited extent, and such a reduction is almost completely eliminated without reaching the speed of sound.

In contrast, the invention has for its object to provide a carburetor of the type specified in the preamble of claim l, the idling system results in the best possible mixture preparation and homogeneous mixture supply to all cylinders with stable operation both in idle mode and under partial load.

This object is achieved by the characterizing features of claim 1.

The fact that the end of the fuel channel is designed as a tubular nozzle and is arranged in a concentric supply channel for the combustion air results in a concentric flow around the fuel channel and the outlet opening thereof with combustion air, which is rectified with the conveying direction of the fuel in the fuel channel. This also serves to cool the fuel and to avoid the formation of vapor bubbles in the fuel which cause inhomogeneities. Because the mouth of the tubular nozzle is arranged in the region of the cross-sectional constriction arranged in the combustion air duct, the fuel is added to the combustion air flowing at the speed of sound, and thus already in Torn into tiny droplets as the mixture mixes; In addition, pressure surges downstream of the admixing point lead to a further intensification of the mixing and homogenization of the mixture and to further comminution of larger droplets that are still present. This results in an almost real physical gasification of the fuel in the mixture, so that it is in an almost molecular particle size.

The speed of sound at the cross-sectional constriction is achieved with a high degree of certainty and in particular also in part-load operation, since the entire pressure drop between approximately ambient pressure and the pressure in the intake pipe can be used to achieve the critical pressure ratio. Even if the pressure in the intake pipe rises above 0.5 bar, the speed of sound at the cross-sectional constriction can still be achieved. Even with a possible transition from the Laval flow to a Venturi flow under certain operating conditions, there is still a very fine division and homogeneous mixing, since only the sonic pressure surges are eliminated, but the mixing is still carried out using the maximum achievable speed differences.

Since even with strong negative pressure in the intake pipe at the cross-sectional constriction, only the speed of sound is generated, but not the supersonic speed that occurs only after the cross-sectional constriction, a stable, constant mode of operation of delivering the fuel from the fuel channel results for all pressure ratios above the critical pressure ratio with automatically constant dosing. If the engine is decelerated and the vacuum is extremely high downstream of the closed throttle valve, there is no increase, regardless of the possibility of a fuel cut-off rer fuel share promoted, just as fluctuating idle speeds. Conversely, this stable mode of operation is maintained even in the part-load range, as long as the critical pressure ratio is not undershot due to an increase in pressure in the intake duct. If the critical pressure ratio falls below the limit and the change to Venturi flow, for example when accelerating in the upper part-load range, the atomization conditions change, but the best possible atomization is then still achieved, with a particularly homogeneous mixture preparation of the idling system in these operating states anyway not being of major importance more to come.

As a result of the homogeneous and fine-particle mixture preparation, there is a correspondingly complete combustion with reduced pollutant emissions. The maximum engine power corresponding to the fuel supply is thus achieved with minimized pollutant emissions.

From EP-PS 0 036 524 it is already known to work in the idling system with the speed of sound in the narrowest cross section of a Laval nozzle in order to always obtain the same suction conditions in different load ranges under these operating conditions. Here, however, an air-rich emulsion is generated upstream of the Laval nozzle and this emulsion is sucked through the Laval nozzle as such without any addition of combustion air. In the event that the speed of sound is not reached, this leads to an overflow of the fuel from the outlet opening and corresponding condensate formation. In the event that the speed of sound is reached, the mixing effect between the combustion air flowing at the speed of sound and the emulsion introduced into this flow is completely eliminated, so that an even worse mixture preparation is to be expected than in the prior art of the generic type.

Characterized in that the carburetor according to claim 2 in a manner known per se has a device for introducing primary air into the fuel to form an emulsion, is achieved in the context of the invention that a larger mass flow passes through the tubular nozzle to promote a certain amount of fuel than in promotion fuel alone. As a result, the use of extremely small nozzle openings, which is complex in terms of production technology, can be avoided and, at the same time, the risk of contamination in the region of the tubular nozzle is minimized.

If the fuel channel as a whole is designed as a tube lying in the air flow, there is, in addition to a correspondingly intensive cooling by the air flowing around, the possibility of sucking in the primary air to form the emulsion according to claim 4 in a simple manner through peripheral openings in the tube wall. The arrangement and design of the openings can easily be designed for the desired primary air quantity and primary air distribution. The primary air supplied to the fuel also serves to further cool the fuel from the inside. The relatively intensive cooling achieved in this way not only minimizes the risk of vapor bubbles forming, but also increases the thermal efficiency. Because the emulsion is only formed in the fuel tube thus serving as a mixing tube, segregation of the air and fuel components can be better avoided than when the primary air is introduced far upstream of the supply of the fuel or the emulsion into the combustion air.

The fact that the carburetor has an end-side cross-sectional constriction of the emulsion-containing fuel channel has a relatively small but not extremely small cross-sectional area view of the strong negative pressure present, a good command of the desired metering of the fuel without excess fuel.

The dimensioning of the cross-sectional constriction of the supply duct for combustion air according to claim 6 results in an addition of the combustion air to set a desired idling speed of the engine.

Since upstream of the fuel channel a throttling of the fuel supply per se is not desired in order not to generate unnecessary flow losses, it can also be advantageous for sucking in a defined desired amount of primary air in addition to the dimensioning of the openings in the wall of the tube, upstream of such Provide openings a pre-throttle to secure a corresponding negative pressure in the fuel channel. This pre-throttle is designed in a particularly simple and expedient manner as a cross-sectional constriction of the fuel channel, the cross-sectional area of which is matched to the desired pressure and delivery conditions. As a rule, the optimum cross-sectional area is found to be the same as that of the cross-sectional constriction of the tubular nozzle, but it must be taken into account that in the assumed preferred case of emulsion, the former is flowed through by fuel alone.

The opening in the fuel pipe is to meter in a certain amount of air to the fuel to form the emulsion under the pressure conditions that arise, and preferably has a cross-sectional area for this purpose. Instead of a single larger opening, a plurality of smaller openings are expediently provided, which are easier to adapt to the desired cross-sectional area in terms of production technology, and in particular an unintentional fuel outlet in unsteady phases then complicate if they are attached to the top of the fuel pipe.

The preferred dimensions of the individual cross-sectional constrictions or openings according to claims 5, 6, 8 and 9 result in optimal working conditions with a 2.8 liter engine. For engines with different cubic capacities, larger or smaller dimensions are considered optimal within the specified ranges, although the relation of the specified dimensions remains essentially the same.

In order to reliably avoid sucking in fuel from the float chamber in the event of service interruptions, in spite of the absence of air openings in the fuel line with regard to the introduction of primary air, in the area of the idle duct arrangement, a shut-off device is arranged in the fuel line according to claim 10, which isolates the fuel line during service interruptions closes automatically. If the shut-off device is placed as close as possible to the outlet area of the idle channel arrangement, the amount of fuel that inevitably drips from the fuel line when the operation is interrupted is also minimized.

According to claim 11, the air line and / or the fuel line of the idle channel arrangement are expediently designed as lines arranged freely next to the carburetor housing. Apart from the savings in construction and manufacturing costs, especially in the case of retrofitting, which results from a guide as channels in the carburettor housing, this results in a corresponding constructive freedom of movement for the upstream connection, which does not necessarily have to be done directly on the air filter , but also from the The cylinder head ventilation line can branch off, so that the oil mist contained therein can be sucked off in front of the air filter, possibly supplemented by air from the air filter, which is sucked in through the section of the cylinder head ventilation line leading to the air filter.

With regard to the fuel line, the design as a line arranged freely next to the carburetor housing results in the particular advantage of cooling the hot fuel drawn from the float housing in such a free line. This reduces hot start problems in particular.

In order to avoid that too much heat is transferred from the hot carburetor wall to the downstream end of the fuel line, which could lead to malfunctions due to strong vapor bubbles in the fuel line, it is provided according to claim l2 that the fuel line ends in a connecting piece that in a connection part made of poorly heat-conducting material, in particular plastic, is thereby prevented from directly transferring heat from hot metallic parts.

According to claim l3, the fuel line should end in the connecting piece with an axis lying transversely to the axis of the fuel channel, which at the same time results in a space-saving design that is regularly desired at this point. However, this arrangement further serves, in particular, to provide an annular catch chamber for small steam bubbles possibly striving back from the fuel pipe, the passage of which into the fuel line could coagulate too large steam bubbles to give rise to malfunctions. The connecting piece protrudes from above through the capture chamber and forms its inner wall. The entry opening of the Brenn is arranged laterally at a height that lies above the outlet opening of the connecting piece. Smaller steam bubbles striving back from the fuel pipe are thus caught in the trap chamber and prevented from passing into the lower outlet opening of the connecting piece of the fuel line, so that the continuous fuel delivery is not disturbed thereby. The vapor bubbles, which are in any case limited in size to the volume of the trap chamber, can be drawn back into the fuel channel in the course of further fuel delivery and can exit the fuel channel into the combustion air stream without malfunction together with the fuel or the emulsion.

According to claim l4, the arrangement is such that the fuel flow is guided from the float chamber to the entry into the inlet opening of the fuel pipe with the same flow cross section. This results in a uniform flow speed, and thus insensitivity to transient influences such as vibrations, different inclinations during ascent and descent, formation of dead zones or the like.

Both simplification of manufacture and in particular the possibility of retrofitting results from the fact that, according to claim 15, the outlet region of the idle duct arrangement which has the fuel duct is designed as a separate housing which penetrates the wall of the carburetor housing or of the intake duct with a nozzle pipe forming the combustion air duct, for example in the area of the carburetor base plate.

An adaptation to the respective operating conditions can be made according to claim l6 in a simple manner in that the exact position of the mouth of the fuel channel is kept adjustable relative to the cross-sectional narrowing of the combustion air duct. As a result, a fine adjustment can be made to each internal combustion engine if necessary, which is then normally maintained unchanged.

A particularly low-loss inflow and good acceleration into the supersonic area before detachment and flow change occur is achieved according to claim l7 in that the area of the cross-sectional constriction of the combustion air duct is designed in the manner of a converging-diverging Laval nozzle.

Due to the inclination of the axis of the outlet area of the idle channel arrangement according to claims l8 and l9 downwards and to the side in the direction of a more tangential inflow, a maximization of the negative pressure prevailing at the outlet mouth of the idle channel arrangement and optimization of the admixture is achieved in particular also in partial load operation. The introduction of the mixture from the idling system, which takes place at high speed but with a limited mass flow, has the tendency to describe a helical downward flow movement in the intake duct or in the intake pipe, which is an increasingly thorough mixing with the mixture flowing past the throttle valve with minimal flow losses favored. While the downward incline primarily contributes to minimizing the flow losses and in the part-load range to increasing the local negative pressure at the outlet mouth of the idling channel arrangement, the lateral inclination primarily serves to improve the mixing; Since the fuel is already in a practically "gasified" form at this point, centrifuging of fuel droplets with corresponding condensate formation is not to be feared times the flow, due to its downward direction, immediately enters the area of the considerably enlarged intake pipe.

In claim 20, an idle installation part according to the invention is specified, which can be produced as an individual and compact part independently of the carburetor and - also for subsequent installation - sold. This manufacturing and distribution possibility of such separate built-in parts is of particular importance in the context of the present invention, since it makes it possible to use the invention independently of the series products of the automobile or carburetor manufacturers and thus individual decisions of the end users in favor of a contribution to protecting the energy sources and to relieve the environment of pollutants.

Further details, features and advantages of the invention result from the following description of an embodiment with reference to the drawing.

• Fig. l in schematisch vereinfachter Darstellung einen Schnitt durch einen erfindungsgemäßen Vergaser,
• Fig. 2 einen Längsschnitt durch den Austrittsbereich der Leerlaufkanalanordnung des Vergasers gemäß Fig. l und
• Fig. 3 eine teilweise im Schnitt gehaltene Draufsicht auf die Anordnung gemäß Fig. 2.

It shows

• 1 is a schematic, simplified representation of a section through a carburetor according to the invention,
• 2 shows a longitudinal section through the outlet region of the idle channel arrangement of the carburetor according to FIGS
• FIG. 3 shows a top view, partly in section, of the arrangement according to FIG. 2.

The carburetor illustrated in FIG. 1 has in the usual way an air filter 1, a carburetor housing 2 and, penetrating this, an intake duct 3 which draws ambient air through the air filter 1. The Carburetor housing 2 has a base plate 4 for connection to an intake pipe 5 of an intake system 6, which supplies the cylinders of the internal combustion engine with fuel-air mixture in the usual way and on which the base plate 4 is fitted via a conventional seal 7.

A throttle valve 8 is arranged in the intake duct 3 and practically completely closes the intake duct 3 in the idle position.

The illustrated carburetor is designed as a register carburetor in the example and has an intake duct 9 of the second stage, the throttle valve 10 of which begins to open in the usual manner when higher speeds are reached. The carburetor housing 2 is formed in the usual way as a cast part and, in addition to the base plate 4, consists of two stacked housing parts ll and l2, the section in the illustration according to FIG. 1 in the area of the base plate 4 along the axes of the intake ducts 3 and 9, in Area of the housing parts ll and l2, on the other hand, is guided through a float chamber l4 in a plane in front of it.

Fuel is supplied to the float chamber l4 under the control of a float l3, from where the fuel is removed via a fuel line l5 in the form of a tube or hose freely arranged next to the carburetor housing 2. Oil mist accumulating in the crankcase and in the entire engine block is fed to the air filter l via a cylinder head ventilation line l6. In the example, the cylinder head ventilation line l6 does not lead directly to the air filter l, but rather into an air line l7 connected to the air filter l. The fuel line l5 and the air line l7 form part of an idle channel arrangement, designated overall by l8, with which the fuel and air form an idle system can be supplied, which opens downstream of the throttle valve 8 in the intake duct 3.

The other devices of the carburetor, such as an acceleration pump, etc., are conventional in nature and therefore do not require any further explanation here. It should be emphasized, however, that the throttle valve 8 in a carburetor according to the invention must be idling in a position in which it closes the intake duct 3 of the first stage practically completely, so that no noticeable air flow past the throttle valve 8 is possible, and also others channels that allow the supply of false air are missing or are closed. In the area of the edges of the throttle valve 8 in its idle position, transition openings 19 can be provided in the usual way, unless another transition system is used for the mixture supply in the transition area between idle and part load.

The exit region of the idling channel arrangement 18, designated 20, is illustrated in more detail in FIGS. 2 and 3. As can be seen from this, the fuel line l5 ends in a connecting piece 2l and the air line l7 in a connecting piece 22, which are mounted on a housing 23. The housing 23 consists essentially of a nozzle pipe 24 for forming a supply duct 25 for combustion air around a fuel pipe 26, which forms a fuel duct 27. Furthermore, the housing 23 is connected to a bearing section 28 essentially formed by the nozzle tube 24 for receiving in the carburetor wall 2 from a rear housing body 29 in the area of the connecting pieces 2l and 22 with end faces 30 adjacent to the bearing section 28 and a connecting part 3l made of poorly heat-conducting Material, in the example plastic, while all other elements are made of metal. The fuel pipe 26 has at its front end a pipe nozzle 32 with a cross-sectional constriction 33 with a cross-sectional area of 0.12 mm² in the example, which at the same time forms an orifice 34 for the exit of fuel or emulsion. In its rear area, the top of the fuel tube 26 is provided with, in the example, two round openings 35 which are axially spaced from one another and have a diameter of 0.5 mm or 0.6 mm, that is to say a total cross-sectional area of approximately 0.45 mm 2 , which allow the air flowing around the fuel pipe 26 to access the fuel channel 27, so that a fuel emulsion is formed there. Arranged upstream of the openings 35 is a pre-throttle 36 which, in the example, has the shape of a cross-sectional constriction 37 with a cross-sectional area of 0.12 mm 2.

The fuel channel 27 opens with an inlet opening 38 into a collecting chamber 39, through which the connecting piece 2l of the fuel line l5 protrudes, and which is made of plastic in the connecting part 3l. The outlet opening 2l labeled 40 is lower than the lower edge of the inlet opening 38 of the fuel channel 27 and thus also below the catch chamber 39, so that when fuel is supplied from the outlet opening 40 of the connection nozzle 20 via the catch chamber 39 into the inlet opening 38 of the fuel channel 27 creates a siphon-like effect.

The pipe nozzle 32 with the cross-sectional constriction 33 of the fuel tube 26 lies in the region of a cross-sectional constriction 4l upstream of the outlet opening of the idling duct arrangement l8 denoted by 42 into the intake duct 3. The cross-sectional constriction 4l is designed in the manner of a converging-diverging Laval nozzle, so that when the critical pressure is exceeded ratio between levels A and B in the cross-sectional constriction 4l flow at the speed of sound and in the subsequent slightly divergent part of the nozzle tube 24 there is supersonic flow until detachment and flow change take place. In the case of a supercritical pressure ratio, this is the case at the latest in level B, that is to say in the level of the outlet orifice 42. The cross-sectional constriction 4l in the example, which results in optimal working conditions for a 2.8l engine, has a free cross-sectional area of approximately 16 mm².

The fuel pipe 26 and the nozzle pipe 24 are concentric about an axis 43 which intersects the transverse axis 44 of the connecting piece 2l of the fuel line l5. The axis 45 of the connecting piece 22 of the air line l7 is transverse to the axis 43, but need not cut it.

As can be seen from FIG. 3, the connecting part 3l is rotatably mounted together with the fuel pipe 26 with a corresponding pivoting of the connecting piece 2l in the housing body 29, for which purpose the connecting piece 2l is guided in a slot 46 of the housing body 29. The axis 47 of the slot 46 is not perpendicular, but at an angle to the axis 43, so that the rotational movement of the connecting part 3l and the fuel pipe 26 while pivoting the connecting piece 2l also leads to an axial movement of the fuel pipe 26. As a result, the exact position of the mouth 34 of the tubular nozzle 32 relative to the cross-sectional constriction 4l can be finely adjusted according to the respective needs. In the example, the length of the slot 46 may allow a twist angle of the connecting part 3l of 30 ° and be inclined at an angle of l3 ° to the axis 43, so that there is an adjustment path of the order of one millimeter.

For assembly in the position illustrated in FIG. 1, the entire nozzle tube 24 can be inserted into a corresponding bore in the carburetor housing 2 up to the stop on the front end faces 30 of the housing body 29. As already indicated in FIG. 1, the axis 43 can be inclined by an angle α with respect to the horizontal, where α can be between approximately 0 ° and 30 ° and, in the example, due to the structural limitation due to the height of the base plate 4 at 10 ° may lie. Similarly, but not illustrated in the drawing, the axis 43 need not intersect the central axis of the intake duct 3, but instead the axis 43 can be tilted away from the radial in such a way that the mass flow exit from the outlet opening 42 is directed more tangentially into the interior of the intake pipe 3 is. Such a flare angle from the radial can be between 15 ° and 40 °, and in the example may be 20 °, measured at the intersection of the axis 43 in FIG. 1 with the extension of the lateral surface of the intake duct 3.

In idle operation, the throttle valve 8 is closed, so that the negative pressure which arises in the intake duct 3 downstream of the throttle valve 8, through the intake strokes of the cylinders, acts in full on the outlet mouth 42 and through it into the idle duct arrangement 18. As a result, air is first sucked through the air line l7, the oil mist present in the cylinder head ventilation line l6 also being sucked in, supplemented by air from the area of the air filter l. This air flow has only a slight pressure drop, so that there is approximately atmospheric pressure in plane A, while in the area of the intake duct 3 there is a pressure of, for example, only 0.4 bar at the outlet mouth 42. This is the critical pressure ratio between levels A and B. significantly exceeded, so that in the plane of the cross-sectional constriction 4l sound flow and then supersonic flow occurs.

Due to the strong pressure drop in the inlet area of the cross-sectional constriction 4l by converting static pressure into dynamic pressure of the air flow, a correspondingly strong suction effect on the fuel present there takes place via the mouth 34 of the tubular nozzle 32. This is therefore metered through the cross-sectional constriction 33 to the air flow. At the same time, however, primary air is drawn into the fuel pipe 26 upstream of the pipe nozzle 32 from the air flow present in the connecting piece 22 and forms a fuel-air emulsion with the fuel present in the fuel pipe. Therefore, the fuel at the mouth 34 in the form of such an emulsion enters the combustion air flow flowing in the supply duct 25, at a point where there is an extremely large speed difference due to the speed of sound of the combustion air flow. As a result, the fuel escaping at a much lower speed is shredded and atomized into very fine droplets, so that a fuel-air mixture of the desired lambda value is present in a very homogeneous distribution at least at the outlet orifice 42 downstream of the cross-sectional constriction 4l. At the latest at the outlet mouth 42 there is a further disintegrating action on larger droplets which may still be present due to the pressure surge there when the flow changes to subsonic. In the manner shown in FIG. 1, a mass flow from the outlet mouth 42 enters the intake pipe 3 with the direction pointing downward and to the side, which swirls at high speed through the intake pipe 3 and this very quickly homogeneously with finely divided fuel of approximately molecular weight Filled particle size.

This state remains unchanged as long as there is a critical or a supercritical pressure ratio between levels A and B, whereby even highly supercritical pressure conditions hardly change anything in the division conditions in the area of the cross-sectional constriction 4l, since there is always the speed of sound. In the event that the critical pressure ratio is undershot, for example at full load or in unsteady phases such as acceleration, the area of the nozzle tube 24 between levels A and B functions as a Venturi tube, but again the supply of fuel at the point of the maximum speed difference between the combustion air flow and the fuel take place and thus optimal atomization takes place even under these conditions, although this is of lesser importance in such load conditions. It is essential, however, that under steady-state conditions there is in any case a critical pressure ratio well into the partial load range, and so the idling mixture is supplied under constant stable conditions. This is also, in the illustrated manner, directly or via the air filter 1, the oil mist from the cylinder head ventilation line 16 is added, so that it is disposed of in an energy-saving and low-pollutant manner.

Since the fuel is supplied via the fuel line 15 without any particular pressure losses, it can be expedient to increase the negative pressure in the fuel channel 27 in the region of the openings 35 in order to ensure the desired entry of primary air. For this purpose, the pre-throttle 36 is used, the cross-sectional area of the cross-sectional constriction 37 there being adapted on the one hand to the pressure drop desired there and on the other hand to the total pressure loss as far as the mouth 34 in order to achieve a desired outflow velocity of the emulsion. The cross-sectional area of the cross-sectional veres is typically 37 depending on the displacement of the engine to be supplied between 0.03 mm² and 0.3 mm², with regard to the selected cross-sectional area of 0.12 mm² of the cross-section constriction 33 through which emulsion flows, in the example a cross-sectional area of 0.12 mm² for the cross-sectional constriction 37 through which fuel flows alone is selected. With the selected total cross-sectional area of the openings 35 of approx. 0.45 mm 2, optimal formation and conveyance of the emulsion through the tubular nozzle 23 results under the action of the combustion air flowing through the cross-sectional constriction 4l always at the speed of sound. A cross-sectional dimensioning of the cross-sectional constriction 4l with approx. L6 mm² results in a combustion air supply to the fuel conveyed in such an amount, which results in an easily ignitable mixture in such an amount that with an 2.8l engine at an idling speed of around 600 to 700 U / min leads.

The throttling cross-sectional constrictions 33 and 37 cannot prevent fuel from the float chamber 14 being replenished if the operation is interrupted by the lifting principle, since upstream of the connecting piece 2l no air access into the fuel line 15 is possible. The fuel line l5 is therefore provided with a shut-off element 49 which, for example, automatically closes the fuel line l5 below a pressure of 4 cm of gasoline column. Thus, at most the fuel standing downstream of the shut-off device 49 can drip, the volume of which can be minimized and which, due to the complete closure at the level of the shut-off device 49, moreover flows slowly and with difficulty at most; in this way, the amount of fuel dripping in the illustrated embodiment may be limited to the content of the fuel pipe 26 downstream of the openings 35.

The connecting part 3l made of poorly heat-conducting material prevents strong heat transfer between the hot peripheral wall of the housing body 29 and the connecting piece 2l and the fuel pipe 26, wherein it should be borne in mind that the connecting piece 2l is arranged in the slot 46 with lateral play. As a result, the cooling of the fuel pipe 26 by the surrounding combustion air flow in the supply duct 25 and also by the primary air introduced through the openings 35 also remain effective in the rear region of the fuel pipe 26, so that the latter remains relatively cool in the region of the inlet opening 38 as well.

The trapping chamber 39 prevents vapor bubbles, which are nevertheless formed in the fuel pipe 26, from being trapped in the trapping chamber 39, since steam bubbles trailing in the direction of the fuel line 15 are retained on the ceiling of the trapping chamber 39 until, for example, after slight growth and greater protrusion from above into the fuel stream, conveyed back into the fuel pipe 26 and from there are discharged together with the fuel or the emulsion from the mouth 34, which gives no cause for interference. The fact that the flow cross-sections of the fuel line l5, the connecting piece 2l, the annular catch chamber 39 and the transition between the outlet opening 40 and the catch chamber 39 are kept substantially the same, results in a non-sensitive, uniform flow of fuel between the float chamber l4 and the inlet opening 38 of the fuel tube 26, which also makes a not insignificant contribution to avoiding the formation of vapor bubbles even under the most unfavorable conditions, in particular at a relatively high flow velocity through a small cross section.

Due to the described embodiment, the result advantages explained in more detail at the beginning. It is particularly important that the relatively high pressure in the area of level A enables the critical pressure ratio to be maintained well into the partial load range, with the consequence of constant operating conditions of the idling system even in the partial load range. Since the idling system also supports the part-load system, which can make up a noticeable part of the total fuel-air mixture available in the cylinders, the optimal preparation of this part results in a significant reduction in consumption and pollutants even in the part-load range .

In order to achieve maximum negative pressure in the idle position, the throttle valve 8 can be completely closed in this position - possibly except for small gaps caused by manufacturing tolerances. This position of the throttle valve 8 in the idle position is also used as a basis for the specified dimensions of the openings of the idle system.

A certain problem can arise, however, if the transition opening l9, which is usually designed as an axially parallel longitudinal slot, is also completely closed in this position by the edge of the throttle valve 8 from the negative pressure below the throttle valve 8, since then, during the transition to the partial load range, an unsteady phase with the Desired value due to this load reduced fuel supply can occur, so an "acceleration hole" occurs because the promotion of the transition opening l9 starts from the previous zero delivery only with a delay.

To avoid such transient operating states, it can also be provided that the edge of the throttle valve 8 to the wall of the intake duct 3 in the idle position has a small gap with a maximum gap width of, for example, 0.2 to 0.3 mm, the throttle valve 8 in the idle position thus does not completely close off the flow in the intake duct 3, but only throttles it. A certain basic delivery of fuel or emulsion from the transition opening l9 and a corresponding air supply from the intake duct 3 then also take place in the idling position. With corresponding compensation of this additional fuel and air supply by correspondingly reduced fuel and air supply from the idling duct arrangement l8 thus the same operating conditions in the idle position as in the example mentioned above.

Claims (20)

1. Carburetor for internal combustion engines

- With at least one inlet duct open to the atmosphere at one end and at the other end connected to an intake pipe (5) of an intake system (6) of the internal combustion engine, in which a throttle valve (8) which at least largely closes the intake duct (3) in its idle position is arranged,

- With a throttle valve (8) bypassing the idle channel arrangement (l8), which has a device (tube nozzle 32) for supplying combustion air to form the desired fuel-air mixture, the fuel being produced by the vacuum at the outlet (34) of the fuel from a fuel channel (27) existing combustion air för derbar, and

with a cross-sectional constriction (4l) of the idle duct arrangement (l8) arranged upstream of the outlet mouth (42) of the idle duct arrangement (l8) in the intake duct (3) to produce a supersonic flow,
characterized,

- That at least the end of the fuel channel (27) is designed as a tubular nozzle (32) and is arranged in a concentric supply channel (25) for the combustion air, and

that the mouth (34) of the tubular nozzle (32) is arranged in the region of the cross-sectional constriction (4l). 2. Carburetor according to claim l, characterized in that a device (openings 35) is arranged upstream of the introduction of the fuel into the combustion air in a manner known per se for supplying primary air to the fuel to form an emulsion. 3. Carburetor according to claim l or 2, characterized in that the fuel channel (27) is designed as a fuel pipe (26) lying in the combustion air flow. 4. Carburetor according to claims 2 and 3, characterized in that the fuel pipe (26) has at least one peripheral opening (35) for the entry of the primary air. 5. Carburetor according to one of claims 2 to 4, characterized in that the tubular nozzle (32) has an end Cross-sectional constriction (33) to a cross-sectional area between 0.03 mm² and 0.3 mm², in particular of about 0.12 mm². 6. Carburetor according to one of claims l to 5, characterized in that the cross-sectional constriction (4l) of the feed channel (25) for combustion air has a free cross-sectional area between 4 mm² and 40 mm², in particular of about l6 mm². 7. Carburetor according to one of claims 4 to 6, characterized in that upstream of the opening (35) a pre-throttle (36) is provided for securing a negative pressure ensuring the primary air entry in the fuel channel (27). 8. Carburetor according to claim 7, characterized in that the pre-throttle (36) is designed as a cross-sectional constriction (37) of the fuel channel (27) to a cross-sectional area of 0.03 mm² to 0.3 mm², in particular about 0.12 mm². 9. Carburetor according to one of claims 4 to 8, characterized in that the cross-sectional area of the opening (35) or the sum of the cross-sectional areas of a plurality of openings (35) between 0.1 mm² and 1.0 mm², in particular at about 0 , 45 mm². l0. Carburetor according to one of Claims 4 to 9, characterized in that a shut-off device (48) which closes the fuel line (l5) when the carburettor is interrupted is arranged in the fuel line (l5) upstream of the fuel tube (26). 11. Carburetor according to one of claims l to l0, characterized characterized in that the air line (l7) and / or the fuel line (l5) of the idling channel arrangement (l8) are designed as lines freely arranged next to the carburetor housing (2). 12. Carburetor according to claim ll, characterized in that the fuel line (l5) ends in a connecting piece (2l) which is held in a connecting part (3l) made of poorly heat-conducting material, in particular plastic. 13. Carburetor according to claim l2, characterized in that the fuel line (l5) in the connecting piece (2l) with transverse to the axis (43) of the fuel channel (27) lying axis (44) ends that the outlet opening (40) of the connecting piece ( 2l) of the fuel line (l5) is arranged below the inlet opening (38) of the fuel channel (27), and that between the outlet opening (40) of the connecting piece (2l) and the inlet opening (38) of the fuel channel (27) there is an annular catch chamber (39 ) is arranged for steam bubbles. 14. Carburetor according to claim l3, characterized in that the cross sections of the fuel line (l5), the associated connection piece (2l), its outlet mouth (40), the trap chamber (39) and the transition between the outlet mouth (40) and the trap chamber ( 39) are at least approximately the same size. 15. Carburetor according to one of claims l to l4, characterized in that the fuel channel (27) having the end of the idle channel arrangement (l8) is designed as a separate housing (23) which with a supply channel (25) for combustion air forming nozzle tube ( 24) passes through the wall of the carburetor housing (2) or the intake duct (3). 16. Carburetor according to one of claims l to l5, characterized in that the exact position of the mouth (34) of the fuel channel (27) relative to the cross-sectional constriction (4l) of the supply channel (25) is kept adjustable for combustion air. 17. Carburetor according to one of claims l to l6, characterized in that the area of the cross-sectional constriction (4l) of the feed channel (25) for combustion air is designed in the manner of a converging-diverging Laval nozzle. 18. Carburetor according to one of claims l to l7, characterized in that the axis (43) of the outlet region (20) of the idle duct arrangement (l8) relative to the central axis of the intake duct (3) at an angle (α) of 0 ° to 30 ° , in particular is inclined downward from at least about 10 °. 19. Carburetor according to one of claims l to l8, characterized in that the axis (43) of the outlet region (housing 23) of the idle duct arrangement (l8) with respect to a radial to the central axis of the intake duct (3), measured at the intersection (48) of the axis (43) of the outlet region (20) of the idle duct arrangement (18) with the extension of the lateral surface of the intake duct (3), is inclined in the horizontal by an angle of 15 ° to 40 °, in particular at least about 20 °. 20. Idling installation part for a carburetor according to one of claims l to l9, characterized by a housing (23) which has a housing body (29) for mounting a connecting piece (2l) for fuel and a connecting piece (22) for combustion air and an inner, with the connecting piece (2l) for Has fuel flow-connected fuel pipe (26) and an outer nozzle pipe (24) which is flow-connected with the connection piece (22) for combustion air and concentrically around the fuel pipe (26) to form a bearing section (28) for storage in the carburetor housing (2) extends away from the housing body (29).

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