is supply system according to the invention, having the characterizing
features of Claim 1, is that the delivery of the second fuel pump can be influenced n a simple way. At the same time, the second fuel pump advantageously does not have to be adjustable. Furthermore, the dissipation in the fuel supply system according to the invention in substantially lower than in a fuel supply system in which the excess fuel conveyed by the second fuel pump, but not required by the fuel nozzle, in discharged via a pressure-regulating valve.
Advantageous developments and Improvements of the fuel supply system according to the main claim are possible as a result of the measures listed in the dependent claims.
Addition of air into the fuel conveyed to the fuel nozzle improves substantially the treatment and therefore the ignitability of the fuel in the combustion space of the internal combustion engine. The addition of air into the fuel connection between the first fuel pump and the second fuel pump can advantageously take place at little outlay. For adding the air, advantageously only a low-power air feed pump or no air feed pump is necessary.
Because of the particularly low pressure of the fuel in the fuel connection between the controllable flow R. 27498 cross-section and the second fuel pump, an addition of air into this part of the fuel connection in advantageously possible at particularly little additional energy outlay or without any additional energy outlay.
The feed of the air into the fuel connection in the region of the controllable flow cross-section also affords the advantage that the air can be added into the fuel without appreciable additional energy outlay or entirely without any additional energy outlay. In the region of the controllable flow cross-section, the pressure of the fuel is particularly low, thereby advantageously making the addition of the air particularly simple.
By means of the diffuser, a particularly homo- is geneous intermixing of the fuel with the fed air can advantageously be achieved.
The arrangement of the diffuser in the region of the entrance of the air feed into the fuel connection advantageously improves the effectiveness of the diffuser without any appreciable outlay.
The swirl device along the fuel connection between the first fuel pump and the second fuel pump substantially improves the intermixing of the fuel with the fed air in an advantageous way.
The arrangement of the swirl device in the region just in front of the entrance of the air feed substantially increases the effectiveness of the swirl device and advantageously leads to a particularly good intermixing of the fuel with the fed air.
The controllable flow cross-section can be provided with an actuating device which is designed in such a way that, when the actuating device is triggered, the flow cross-section is adjusted in the opening direction. However, the actuating device can also be designed in such a way that a triggering of the actuating device adjusts the flow cross-section In the closing direction. if the actuating device in designed in such a way that a triggering of the actuating device adjusts the flow cross-section in the opening direction, this means that, 4 - R. 27498 when the actuating device in not triggered, the controllable flow cross- section in adjusted in the closing direction, thus affording the advantage that, in the event of a fault, the controllable flow cross- section is not unintentionally opened completely.
The emergency throughtlow cross-section through the fuel connection between the first fuel pump and the second fuel pump affords the advantage that, if the actuating device adjusting the controllable flow crosssection fails, an emergency operation of the internal combustion engine remains possible.
If the actuating device is designed in such a way that, by triggering the actuating device, the controllable flow cross-section is adjusted in the closing is direction, this means that, when the actuating device in not triggered, the controllable flow cross-section is adjusted in the opening direction, thus affording the advantage that the conveyance of fuel to the uel nozzle is not prevented.
The control of the pressure in the reg.Lon in front of the fuel nozzle offers a particularly good possibility for the accurate control of the fuel conveyed into the combustion space of the internal combustion engine, and the control of the controllable flow cross- section in dependence on the pressure in front of the fuel nozzle offers a particularly simple and energysaving possibility for influencing the pressure in front of the fuel nozzle.
Drawing Selected particularly advantageous exemplary embodiments of the invention are represented in simplified form in the drawing and are explained in more detail in the following description. Figure 1 shows an overview of a selected particularly advantageously designed exemplary embodiment of the fuel supply system, and Figures 2 to 5 show by way of example various and differently designed details of the fuel supply system according to the invention.
Description of the exemplary embodiments R. 27498 The fuel supply system according to the invention for the metering of fuel for an internal combustion engine can be used in various types of internal combustion engines. The internal combustion engine is, for example, an Otto engine with external or internal mixture formation and spark ignition, and the engine can be provided with a piston moving to and fro (reciprocating-piston engine) or with a rotatably mounted piston (Wankel piston engine). The internal combustion engine can, for example, also be a hybrid engine. In this engine with charge stratification, the fuel/air mixture is enriched in the region of the spark plug to such an extent that reliable inflammation is guaranteed, but, on is average, combustion takes place with a very lean mixture.
The gas exchange in the combustion space of the internal combustion engine can, for example, take place according to the four-stroke method or accoraing to the two-stroke method. To control the gas exchange in the combustion space of the internal combustion engine, gasexchange valves (inlet valves and outlet valves) can be provided in a known way. The internal combustion engine can be designed in such a way that at least one fuel nozzle sprays the fuel directly into the combustion space of the internal combustion engine. The control of the power of the internal combustion engine is preferably carried out by controlling the quantity of fuel fed to the combustion space. Provision can, however, also be made for the fuel nozzle to pre-store the fuel at the inlet valve to the combustion space. In this version, the air fed to the combustion space for the combustion of the fuel is conventionally controlled by means of a throttle flap. The power output of the internal combustion engine can be controlled via the position of the throttle flap.
The internal combustion engine possesses, for example, one cylinder with one piston, or it can be provided with a plurality of cylinders and with a corre sponding number of pistons. One fuel nozzle is preferably provided for each cylinder.
R. 27498 To avoid the scope of the description becoming needlessly extensive, the following description of the exemplary embodiments in restricted to a reciprocating piston engine with four cylinders as an internal combus tion engine, the four fuel nozzles spraying the fuel directly into the combustion space of the internal combustion engine. The power of the internal combustion engine in controlled via the control of the injected fuel quantity. In the idling range and the range of (lower) part load, charge stratification takes place in the region of the spark plug. In the case of full load or upper part load, a homogeneous distribution between the fuel and air in the combustion space is sought after.
Figure 1 represents a selected particularly advantageous exemplary emb odiment of the fuel supply system.
Figure 1 shows a fuel tank 2, a auction conduit 4, a first fuel pump 6, an electric motor 8, a fuel connection 10, a throttle valve 12, an air feed 14, a second fuel pump 16, a fuel conduit 18 and four fuel nozzles 20, 201, 2011, 2C.
The fuel connection 10 is subdivided into a first connection piece 10g and into a second connection piece 10b. The fuel conduit 18 is subdivided into a conduit piece 18a, a distribution piece 18b and four nozzle connecting conduits 18c, 18cl, 18c11, 18c".
Figure 1 shows, furthermore, a control device 22, an energy supply unit 24, a pressure- regulating device 26, an air filter 28, a pressure sensor 30 and a pressure sensor 32.
The energy supply unit 24 delivers electrical energy to the electric motor 8 via an electrical lead Se.
The energy supply unit 24 is connected to the control device 22 via an electrical lead 24e. An electrical lead 8el connects the electric motor 8 to the control device 22. An electrical lead 26.e connects the pressure-regu lating device 26 to the control device 22. Control signals can be delivered to the throttle valve 12 by the control device 22 by way of an electrical lead 12e. The R. 27498 fuel nozzle 20 is connected to the control device 22 via an electrical lead 20e. The fuel nozzles 201, 2011, 20' are correspondingly connected to the control device 22 via electrical leads 20el, 20s", 20e". Electrical leads 30e and 32e connect the pressure sensors 30 and 32 to the control device 22. Via electrical leads 22e, 22e', 22e", the control device 22 is connected, for example, to various sensors (not shown) for sensing the working conditions of the internal combustion engine or to a desired-value transmitter (not shown) for the input of the power which a person requires from the internal combustion engine.
Via mechanical transmission means 16m, the second fuel pump 16 is coupled mechanically to an output shaft is (not shown) of the internal combustion engine. Since the second fuel pump 16 is mechanically coupled rigidly to the output shaft of the internal combustion engine, the second fuel pump works proportionally to th rotational speed of the output shaft of the internal combustion engine. The rotational speed of the output shaft varies greatly, depending on the instantaneous operating condi tions of the internal combustion engine.
The electric motor 8 drives the first fuel pump 6. The first fuel pump 6 conveys fuel out of the fuel tank 2 into the first connection piece 10a of the fuel connection 10.
The pressure-regulating device 26 comprises, for example, a hydraulically controlled pressure-limiting valve. By means of the pressure- limiting valve of the pressure-regulating device 26, the pressure in the first connection piece 10a can be maintained at a specific selectable level. If appropriate, the pressure- regulating device 26 can also be provided with an electrically controlled pressure- limiting valve and be designed in such a way that the control device 22 can, as required, control the pressure of the fuel in the first connection piece 10a according to the instantaneous operating conditions and to a program entered in the control device 22. However, the pressure -regulating device 26 can also - a - R. 27498 be designed in such a way that it comprises a pressure sensor, the pressure sensor sensing the pressure of the fuel in the first connection piece 10a and feeding corresponding signals to the control device 22 by way of the electrical lead 26e, the control device 22 in turn controlling the rotational speed of the electric motor 8 by way of the electrical lead Be', so that, depending on the instantaneous operating conditions and In dependence on a program entered in the control device 22, the desired pressure in established in the first connection piece loa.
A relatively low pressure is generated in the first connection piece 10a by means of the first fuel pump 6. The pressure in the first connection piece loa is selected to be relatively low so that the electric motor 8 for driving the first fuel pump 6 can be of relatively low-power design and requires little electrical energy.
The second fuel pump 16 conveys the fuel out of the second connection piece 10b of the fuel connection 10 into the conduit piece 18a of the fuel conduit 18. The second fuel pump 16 is preferably designed in such a way that a relatively high pressure prevails in the fuel conduit 18 under normal conditions. The direct mechanical drive of the second fuel pump 16 via the mechanical transmission means 16= with the aid of the internal combustion engine affords the advantage that a separate heavy-build drive motor Is not required for the second fuel pump 16.
The throttle valve 12 is located along the fuel connection 10 between the first fuel pump 6 and the second fuel pump 16. The fuel conveyed from the first fuel pump 6 to the second fuel pump 16 Is guided through the throttle valve 12.
The throttle valve 12 can be triggered by the control device 22 via the electrical lead 12e. The control device 22 can trigger the throttle valve 12 in such a way that the fuel between the first fuel pump 6 and the second fuel pump 16 in throttled to a greater or lesser extent, depending on the magnitude or nature of R. 27498 the trigger signals. The signals transmitted from the control device 22 to the throttle valve 12 are, for example, either digital or analog electrical signals.
In the exemplary embodiment represented in Figure 1, the throttle valve 12 additionally also possesses a connection, to which the air feed 14 in connected. Air is admixed with the fuel within the throttle valve 12. The control device 22, by way of the electrical lead 12e, can influence the quantity of air fed to the fuel. Along the air feed 14 there is the air filter 28. The air filter 28 filters the air admixed with the fuel. Instead of provid ing the separate air filter 28 for the air feed 14, the air feed 14 can also be connected directly to the engine air filter, via which the internal combustion engine is receives its auction air.
The fuel arrives without any appreciable pressure drop at the fuel nozzles 20, 201, 2011, 20" through the conduit piece 18a, the distribution piece 18b and the nozzle connecting conduits 18c, 18cl, 18c11, 18c". The conduit 18 and, in particular, the distribution piece 18b of the conduit 18 serve not only for guiding the fuel, but also as a buffer store.
The control device 22 can open and close the fuel nozzles 20, 201, 2011, 2C at any desired moment via the electrical leads 20e, 20el, 20ell, 20e", as a result of which the control device 22 can feed the fuel quantity desired in each case to the combustion spaces (not shown) of the internal combustion engine via the fuel nozzles 20, 201, 2011, 20".
The pressure sensor 30 is preferably connected to the distribution piece 18b and senses the pressure in the fuel conduit 18, and delivers a corresponding signal to the control device 22 by way of the electrical lead 30e.
In dependence on the pressure sensed by the pressure sensor 30, the control device 22 can, via the electrical lead 12e, influence the throttling of the fuel flowing through the fuel connection 10. The pressure in the fuel conduit 18 can be controlled by means of the throttle valve 12. A sharp throttling of the fuel by the throttle R. 27498 valve 12 reduces the delivery of the second fuel pump 16 and therefore the pressure in the fuel conduit 18 for an identical rotational speed of the internal combustion engine. Conversely, a reduction in the throttling results correspondingly in a rise of the pressure in the fuel conduit 18.
The first fuel pump 6, the electric motor 8, the fuel connection 10, the throttle valve 12, the second fuel pump 16 and the pressure- regulating device 26 can be combined in a common fuel supply block 34. It is also possible to combine only some of these components mentioned in the fuel supply block 34. In particular, the first fuel pump 6 can be arranged outside the fuel supply block 34. The first fuel pump 6 is preferably arranged is directly in the fuel tank 2. It is also possible for all the elements mentioned to be arranged separately. If the two fuel pumps 6, 16 are arranged separately, the fuel connection 10 is designed, for example, in th form of a f lexible hose, and if the two fuel pumps 6, 16 are combined in the common fuel supply block 34, the fuel connection 10 is, for example, a bore leading through the fuel supply block 34 and the throttle valve 12 is integrated as an insert into the fuel supply block 34 or is built on.
Since the pressure sensor 32 and the electrical leads Se', 26e, 32e are special design alternatives, these parts are represented by broken lines.
Figure 2 shows a detail of the fuel supply system according to the invention by way of example and on a different scale.
Identical or identically acting parts are provided with the same reference symbols in all the figures.
Insofar as nothing to the contrary is mentioned or represented in the drawing, what is mentioned and represented with reference to one of the figures also applies to the other exemplary embodiments. Insofar as the explanations do not yield anything else, the details of the various exemplary embodiments can be combined with one another.
11 - R. 27498 In the detail of the fuel supply system represented in Figure 2, the throttle valve 12 comprises a valve block 42, a valve body 44, an actuating device 46, a non-return valve 48, a diffuser 50, a swirl device 52 and a controllable flow cross-section 55.
Figure 2 shows a section through the valve block 42. For the sake of greater clarity, the valve block 42 in represented an though it consisted of a single undivided piece of material. However, the average person skilled in the art nevertheless knows how the valve block 42 has to be composed so that the parts to be arranged in it can be installed.
The actuating device 46 comprises, by way of example, an electromagnet 46a and a return spring 46b.
A control point 42a is provided on the valve block 42 and a control point 44a on the valve body 44.
The controllable flow cross-section 55 extends between the control point 42a on the valve block 2 and the control point 44a on the valve body 44.
The diffuser 50 consists, by way of example, essentially of an air-permeable annular material 58 which is inserted into an annular space 59 provided in the valve block 42. The air permeability is obtained, for example, by the use of porous material. The material 58 can, for example, be produced by the sintering of powder.
However, the diffuser 50 can also be formed by ducts or bores extending radially inwards from the annular recess 59.
By passing current through the electromagnet 46a of the actuating device 46, the valve body 44 in adjusted in such a way that the controllable flow cross-section 55 between the two control points 42a, 44a increases. if the supply of energy to the actuating device 46 is stopped, the return spring 46b adjusts the valve body 44 in the direction of the closing of the controllable flow cross section 55.
The swirl device 52 consists essentially, for example, of a bore 52a or of a plurality of bores 52a and of a conically extending baffle surface 52b.
R. 27498 The non-return valve 48 along the air feed 14 consists essentially of a valve plate 48a and of a valve spring 48b. A plurality of bores run through the valve plate 48a. The valve spring 48b and the valve plate 48a having the bores are arranged in the valve block 42 in such a way that the air flowing through the air feed 14 can flow in the direction of the fuel connection 10 guiding the fuel. On the other hand, the non-return valve 48 shuts off the opposite direction of flow through the air feed 14.
It was explained with reference to Figure 1 that the first fuel pump 6 conveys the fuel into the first connection piece 10a of the fuel connection 10. As shown in Figure 2, the fuel passes from the first connection is piece 10a through the bores 52a of the swirl device 52 to the controllable flow cross-section 55. After leaving the bores 52a, the fuel or part of the fuel flowing through strikes the baffle surface 52b of the swirl device 52. As a result of this multiple deflection of the fuel, the fuel flow acquires an intensive swirl. The fuel subsequently flows through the controllable flow crosssection 55. Depending on the position of the valve body 44 relative to the valve block 42, the fuel in the region of the controllable flow cross-section 55 in throttled to a greater or lesser extent. The fuel behind the flow cross-section 55 (as seen in the direction of flow) is therefore under a pressure which in lower than the pressure of the fuel in front of the controllable flow cross-section 55. By setting the controllable flow cross- section 55 to be appropriately small, that in to say by an appropriate throttling of the fuel in the region of the controllable flow cross- section 55, it in possible to ensure that the pressure behind the controllable flow cross-section 55 and therefore in the second connection piece 10b falls below the atmospheric pressure.
After leaving the controllable flow cross-section 55, the fuel passes into a valve space 60. The fuel can pass, virtually unthrottled, from the valve space 60 through a passage 42b or through a plurality of passages 2G R. 27498 42b into the second connection piece 10b of the fuel connection 10.
Air passes from the air filter 28 (Figure 1) through the air feed 14 into the annular space 59 via the non-return valve 48. The annular space 59 extends largely concentrically around the valve space 60 (Figure 2). As a result of the annular space 59, the air flows radially from all sides through the air-permeable.material 58 of the diffuser 50 into the valve space 60. The diffuser 50 is located directly at an entrance 14a of the air feed 14 into the fuel connection 10. The diffuser 50 ensures that, as far as possible, the air enters the fuel-containing valve space 60 uniformly from all sides and at very many widely distributed small points. The diffuser is 50 causes the air to come into contact with the fuel in a uniformly distributed manner. This ensures that as much air as possible is absorbed by the fuel and passes as a homogeneous mixture to the fuel nozzles 20, 201, 2011, 20"'.
The second connection piece 10b of the fuel connection 10 is connected to the auction side of the second fuel pump 16. The second fuel pump 16 sucks the fuel out of the second connection piece 10b. This leads to a pressure drop in the second connection piece 10b and therefore also to a pressure drop in the valve space 60. The fuel supply system can be designed in such a way that the pressure of the fuel in the valve space 60 drops so f ar that air is sucked out of the air f eed 14 into the valve space 60 without any pump. With a reduction in the controllable flow cross-section 55, the pressure in the valve space 60 falls. When the flow cross-section 55 is opened relatively wide, the pressure drop in the valve space 60 is slight. When there is a pronounced pressure drop in the valve space 60, a large amount of air flows 3S through the air feed 14 into the valve space 60, and, when there is a slight pressure drop in the valve space 60, relatively little air flows through the air feed 14 into the valve space 60. Thus, by means of the actuating device 46, it is possible for the control device 22, by R. 27498 a variation in the controllable flow cross-section 55, to control the quantity of air passing through the air feed 14 into the valve space 60. By =cans of the second fuel pump 16, the pressure in the valve space 60 can be 5 lowered so far that the air flows through the air feed 14 Into the valve space 60 without the aid of an air pump. It in also possible, however, to provide along the air feed 14 an air pump which ensures some relatively slight overpressure at the entrance 14a of the air feed 14 into the valve space 60. Because the quantity of air to be added by the air f eed 14 Is relatively small, at least because this quantity of air is substantially smaller than the air required altogether by the internal combustion engine, this air pump possibly to be provided can be made relatively small and make do with little drive energy.
The second fuel pump 16 conveys the fuel or the mixture of air and fuel into the fuel conduit 18 (Figure 1). In the nozzle connecting conduits 18c, 18c I, 18c11, 1Sc" of the fuel conduit 18, the fuel or the mixture is stored under relatively high pressure in front of the fuel nozzles 20. Depending on the quantity of fuel required by the internal combustion engine, the control device 22 opens the fuel nozzles 20, so that the fuel can pass Into the individual cylinders (not shown) of the internal combustion engine at exactly the right time and in exactly the correct quantity.
A specific pressure is to prevail in the fuel conduit 18, depending on the operating condition of the internal combustion engine. This pressure in sensed by the pressure sensor 30. If the pressure in the fuel conduit 18 in too high, the pressure sensor 30 communicates this to the control device 22, and the latter in turn adjusts the controllable flow cross-section 55 in the closing direction via the actuating device 46. The second fuel pump 16 can consequently convey less fuel into the fuel conduit 18, and, because fuel is rem ved more or less continuously from the fuel conduit 18 by the fuel nozzles 20, 201, 2011, 20", the pressure in the fuel R. 27498 conduit 18 falls as a result of the closing of the controllable flow cross-section 55. conversely, the pressure in the fuel conduit 18 can be raised by opening the controllable flow cross-section 55.
The possibility for controlling the pressure in the fuel conduit 18 by opening or closing the control lable flow cross-section 55 affords, for example, the possibility of dispensing with a pressure control valve in the fuel conduit 18, which pressure control valve would otherwise be required in order to return to the fuel tank 2 a part quantity of the fuel which is under high pressure in the fuel conduit 18. Since, in the case of thin pressure control valve which is not required in the fuel supply system according to the invention, the is pressure drop would be substantially greater than the pressure drop in the region of the throttle valve 12 provided according to the invention and having the 1 controllable cross-section 55, the dissipation is sub stantially lower than if the pressure control valve had to be provided. This loads to a considerable saving of the power to be branched off from the internal combustion engine and therefore to a considerably lower heating of the fuel. The heating of the fuel entails the risk of vapour bubbles.
Figure 3 shown a further view of the throttle valve 12 on a different scale. The viewing direction marked by the arrow III in Figure 2 is represented.
Figure 3 shows that the bores 52a of the swirl device 52 start from the side of the throttle valve 12 facing the first connection piece 10a. The bores 52a extend from this side in the direction of the baffle surface 52b, specifically in such a way that the fuel is simultaneously deflected to the side and also acquires a swirl in the circumferential direction. The fuel is deflected once again at the baffle surface 52b and then passes rotationally through the controllable flow cross section 55 into the region of the valve space 60 having the entrance 14a of the air feed 14.
Figure 4 shows a further possibility, selected by R. 27498 way of example, for the design of the throttle valve 12 of the fuel supply system according to the invention.
As shown In Figure 4, in this exemplary ezabodiment the entrance 14a of the air feed 14 into the fuel connection 10 is located directly in the region between the control point 42a of the valve block 42 and the control point 44a of the valve body 44. Between the two control points 42a and 44a, the controllable flow cross-section 55 has its narrowest cross-section, so that the velocity of the flow of fuel attains the highest value in this region. Since the flow velocity is highest in the region between the two control points 42a, 44a, the pressure of the fuelis lowest at this point, f or which reason the auction effect for sucking the air out is of the air feed 14 Is the most effective at this point.
Furthermore, the relatively low pressure and the high f low velocity between the two control points 42a, 44a result in a particularly intensive homogenous inter mixing of the air with the fuel. During the subsequent compression of the mixture in the second fuel pump 16, the air in then dissolved in the fuel.
The measure with the swirl device 52 and the measure with the diffuser 50 an well an the measure of providing the diffuser 50 directly in front of the entrance 14a of the air feed 14 and also the measure of arranging the entrance 14a of the air feed 14 directly in the region of the controllable flow cross-section 55 each lead in themselves to an improvement in the intermixing of the air with the fuel. The combination of two or more or all of these measures leads to a further improvement in the intermixing of the fuel with the air.
Figure 5 shows by way of example a further possibility for the design of the fuel supply system according to the invention.
In the exemplary embodiments shown in Figures 2 and 4, the actuating device 46 is designed in such a way that, with an increasing passage of current through the electromagnet 46a, the controllable flow crosssection 55 is opened increasingly. With a decreasing passage of 17 - R. 27498 current through the electromagnet 46a, the return spring 46b adjusts the valve body 44 in the direction of the closing of the controllable flow cross-section 55. This is reversed in the exemplary embodiment represented in Figure 5. There, when the actuating device 46 is not triggered, that is to say when no current passes through the electromagnet 46a, the controllable flow cross section 55 reaches its maximum possible size. The version represented in Figure 5 thus affords the advantage that, if the supply of current to the actuating device 46 fails, the full cross-section of the controllable flow cross-section 55 is available. Consequently, even in the event of a failure of the triggering of the actuating device 46, the internal combustion engine can continue to is be operated in an emergency mode, but with some restric tions as regards its controllability andlor its effi ciency.
In the exemplary embodiment representd in Figure 2, if the passage of current through the electromagnet 46a fails, the valve body 44 is adjusted in the closing direction of the controllable flow cross-section 55. The exemplary embodiment represented in Figure 2 can be designed in such a way that the possibility of adjusting the valve body 44 in the closing direction is limited so that the return spring 46b of the actuating device 46 can actuate the valve body 44 in the closing direction only so f ar that, even when there in a complete absence of current through the electromagnet 46a, a clearance remains between the control point 42a and the control point 44a, so that, even if the supply of current to the actuating device 46 fails, the controllable flow cross section 55 is not closed completely. The components of the throttle valve 12 are, for example, dimensioned in such a way that, even if the electromagnet 46a is com pletely currentless, an emergency throughflow cross section 66 guaranteeing minimum passage remains between the two control points 42a, 44a. Since this possibility may possibly entail some problems of tolerance, it is proposed, as shown in Figure 2, to provide a passage 62.
- 18 R. 27498 The passage 62, bypassing the controllable flow cross section 55, connects the region located upstream of the controllable flow cross-section 55 to the valve space 60.
The passage 62 forms the emergency throughtlow cross section 66 which, even if there is a fault in the trig gering of the actuating device 46, ensures a minimum passage of fuel through the fuel connection 10. The passage 62 can also be provided in the valve body 44. In the exemplary embodiment represented in Figure 4, an indentation 64 is provided along a generatrix of the conically shaped control point 44a of the valve body 44.
This indentation 64 ensures that, even if there is a failure in the passage of current through the electro magnet 46a or if there is a fault in the triggering of is the actuating device 46, at least the emergency through flow cross-section 66 formed by the indentation 64 remains. The indentation 64 can be provided at the control point 42a and/or at the control point 4a. Figure also shows the passage 62. In the exemplary embodiment represented in Figure 5, the passage 62 ensures that, even when the full current intensity passes through the electromagnet 46a, at least the emergency throughflow cross-section 66 is present. If there in to be the possibility that the connection between the first fuel pump 6 and the second fuel pump 16 can be closed com pletely, in all the exemplary embodiments the emergency throughflow cross-section 66 can, of course, be dispensed with.
There are internal combustion engines in which, when no power is required, for example during an overrun, the supply of fuel into the combustion spaces is inter rupted. For these internal combustion engines, it is beneficial to design the throttle valve 12 in such a way that the controllable flow cross-section 55 can be closed completely, and therefore to dispense with the emergency throughflow cross-section 66. It is possible to ensure, by a complete closing of the throttle valve 12, that, even when the fuel nozzles 20, 201, 2011, 20' remain closed during the overrun, the pressure in the fuel R. 27498 conduit 18 in front of the fuel nozzles 20, 201, 2011, 20" can be maintained at a specific level.
For the overall efficiency of the internal combustion engine, it is beneficial if a high pressure prevails in the fuel conduit 18 in the range of full load and of upper part load, that is to say when the fuel nozzles 20, 201, 2011, 2C are to meter a large quantity of fuel. This applies particularly when the fuel nozzles 20, 201, 2011, 20.. inject directly into the combustion spaces of the internal combustion engine. if a large quantity of fuel per unit time is injected under high pressure, then it in not necessary to add a large amount of air to the fuel in front of the fuel nozzles 20, 201, 2011, 2C. To bring about stable injection in the case of small injection quantities, it is necessary to lower the injection pressure because the switching times of the fuel nozzles 20, 201, 2011, 2C cannot arbitrarily be reduced. So that this does not lead to any Impairment of the fuel treatment during injection, it is expedient, in this case, to admix air with the fuel according to the predetermined pressure level. These requirements can be satisfied simply and skilfully by means of the fuel supply system described and represented by way of example. The control device 22 can be designed in such a way that the controllable flow cross-section 55 is opened wide in the full-load range of the internal combustion engine. This ensures that a high pressure prevails in the fuel conduit 18 in front of the fuel nozzles 20, 201, 2011, 20", and that no or relatively little air is admixed into the fuel connection 10 via the air feed 14. Further more, in the range of lower part load and of idling of the internal combustion engine, the control device 22 can almost close the controllable flow cross-section 55 or, if the emergency throughflow cross-section 66 is pro vided, completely close the controllable flow cross section 55. This ensures that a low pressure prevails in the fuel conduit 18 in the range of idling and of lower part load, and at the same time a relatively large amount of air is admixed via the air feed 14 into the fuel - 20 R. 27498 flowing through the fuel connnection 10.
The quantity of air fed to the fuel via the air feed 14 serves essentially for treating the fuel in the bent possible way, so that a very easily ignitable mixture can form in the combustion space. Of course, the larger air quantity necessary for combustion can continue to be fed into the combustion spaces of the internal combustion engine in a known way and, if appropriate, via a auction pipe controllable by means of a throttle flap.
The quantity of air f ed via the air f eed 14 is rather small in relation to the air quantity fed into the combustion spaces via the auction pipe.
-21CLAIMS 1. Fuel supply system for delivering fuel for an internal combustion engine, with a fuel tank, a first fuel pump, a second fuel pump and with at least one fuel nozzle, the first fuel pump conveying fuel out of the fuel tank to the second fuel pump via a fuel connection and the second fuel pump conveying the fuel to the at least one fuel nozzle, via which the fuel passes at least indirectly into a combustion space of the internal combustion engine, characterized in that a throttle valve having a controllable flow crosssection is inserted into the fuel connection between the first fuel pump and the second fuel pump.