EP1124055B1 - Fuel supply system for a combustion engine - Google Patents

Description

The invention relates to a fuel supply system for an internal combustion engine according to the preamble of claim 1. Such is, for example, from DE 196 12 412 A known.

In general, but especially in internal combustion engines installed in motor vehicles, there is the problem that in a so-called. Hot start the engine, a sufficient amount of liquid fuel must be provided, even if that in the previous shutdown and the subsequent shutdown of the engine in the environment (ie in particular in the area of the motor vehicle engine compartment) located fuel quantity has at least partially passed into the vapor state due to the high ambient temperature, so that form in the internal combustion engine near fuel supply steam bubbles. In order nevertheless to enable a safe hot start of the internal combustion engine, the fuel pressure can be increased under these circumstances at least briefly, as proposed and described in DE 44 43 836 A1.

In principle, the described hot start problem, which may also occur in hot operation with low fuel requirements of the internal combustion engine (ie, for example, in the stop-and-go operation of the motor vehicle driven by the internal combustion engine), by using a corresponding Solve more powerful fuel pump, but this is undesirable in terms of efficiency and efficiency aspects. In the case of a high fuel requirement of the internal combustion engine, for example, a so-called fuel pressure of 3.5 bar is sufficient for the internal combustion engine, while for the hot start and possibly also for the hot operation with regard to the described vapor bubble formation a "relevant" fuel pressure of, for example. 6 bar would be desirable.

In the knowledge that under these mentioned critical operating conditions, the amount of fuel required by the engine is usually relatively low, therefore, the pressure level of 6 bar can be generated in a relatively simple manner with a lower-performance fuel pump, if a commonly existing pressure regulator, which required the übtichenrveise Pressure level of 3.5 bar (eg.) Sets, is properly detuned. In the already mentioned DE 44 43 836 A1 this pressure regulator is arranged in a branching off from the delivery line of the fuel pump and opening into the fuel tank return line. Now, if this return line downstream of the pressure regulator shut off or at least throttled, this inevitably leads to a pressure build-up or to a pressure increase in the delivery line due to the lower in the tank funded fuel quantity, so that with this simple measure in these temporally clearly limited operating conditions Excessive fuel pressure of, for example, 6 bar can be provided.

The described hot start and / or hot operation problem arises, moreover, even in working with direct fuel injection internal combustion engines, in which at or near the internal combustion engine (and thus in possibly again very hot engine compartment of a motor vehicle), a high-pressure fuel pump is arranged for which represents the previously mentioned and upstream of the said pressure regulator arranged fuel pump quasi a prefeed pump. When so-called. For the internal combustion engine relevant Fuel pressure is then the pressure applied to the suction side of the high-pressure fuel pump fuel pressure. This pressure should be under the usual operating conditions of the internal combustion engine, for example, in the order of 3.5 bar, in the mentioned critical hot start and / or hot operating conditions, but again in the range of 6 bar, and at a cold start of the engine in the order from 5 bar.

A possible embodiment of a fuel supply system for such an application, to which the well-known from the already repeatedly mentioned DE 44 43 836 A1 principle for increasing the relevant for the internal combustion engine or applied to the suction side of a high pressure fuel pressure level is implemented in a significantly modified manner, is shown in the attached Figure 4 and is explained in the following:

The reference numeral 1 denotes the fuel tank of a motor vehicle in which a fuel pump 2 is arranged, which provides the fuel required by an internal combustion engine, not shown, via a delivery line 3 of a high-pressure fuel pump 4. The example. Mechanically driven by the internal combustion engine high-pressure pump 4 thereby promotes the fuel provided by the fuel pump 2 under very high pressure (eg. In the order of 130 bar) in a provided on the internal combustion engine injection rail 5, from which the individual Brennkraftmaschinen- Cylinders associated, only symbolically represented fuel injectors 6 are supplied.

In the injection bar 5, a pressure relief valve 7 acting as a safety valve is arranged, which in an error case recirculates excess amount of fuel via a discharge line 8 to the suction side of the high-pressure pump 4. From the high-pressure pump 4 also branches off with the interposition of a Abspenventiles 9 a leakage line 10, which in a in the Tank 1 leading return line 11 opens, and be discharged via the low fuel leakage rates of the high-pressure pump 4.

In the delivery line 3, a pressure regulator 12 is disposed upstream of the high-pressure pump 4, from which the aforementioned return line 11 branches off, so that the pressure regulator 12 provides only such an amount of fuel via the delivery line 3 of the high-pressure pump 4 that under normal operating conditions there, ie At the suction side of the so-called. For the internal combustion engine relevant pressure of, for example, 3.5 bar (measured as differential pressure relative to the environment) adjusts. The for the achievement of this relevant pressure excess, funded by the fuel pump 2 and therefore not required amount of fuel is returned by the pressure regulator 12 via the return line 11 into the tank 1.

The pressure regulator 12 is preceded by a fuel filter 13, but this is negligible. Further, a check valve (not shown) is provided between the fuel pump 2 and the filter 13, so that it is only necessary when stopping the engine, at the same time close the already mentioned shut-off valve 9, to ensure that even at a standstill of the internal combustion engine at least for a certain period of time upstream of the high-pressure pump 4, the so-called. For the internal combustion engine relevant fuel pressure is maintained (for example, 3.5 bar as a differential pressure) or remains.

As already explained, this pressure level of, for example, 3.5 bar in critical operating conditions, so for example when starting or hot operation of the engine may not be high enough to counteract a possible formation of vapor bubbles on the suction side of the high-pressure pump 4. If now in these operating conditions of the internal combustion engine, possibly a much smaller amount of fuel is needed than the fuel pump 2 is able to promote, so may in these operating conditions the pressure level prevailing downstream of the pressure regulator 12 in the delivery line 3 is at least briefly increased by the fact that the amount of fuel diverted from the pressure regulator 12 into the return line 11 is considerably reduced.

To implement this principle 44 43 836 A1 already proposed several times in the (local) return line to provide a shut-off valve and parallel thereto a throttled bypass, where there is the pressure regulator in the return line itself upstream of this check valve with bypass. However, this known prior art is unsatisfactory insofar as practically only two concrete different pressure levels are adjustable. In addition to the pressure level applicable to the running internal combustion engine, only one further pressure level relevant for a hot start of the internal combustion engine is thus adjustable.

In contrast, it is more favorable when the pressure regulator 12 is designed as a fully variable controllable electronic pressure control valve with integrated pressure sensor. Such a pressure control valve allows, as required, the setting of different pressure levels in the delivery line 3 in front of the suction side of the high-pressure pump 4, i. generally different values of the relevant for the internal combustion engine fuel pressure. By this pressure regulator 12 or this electronic pressure control valve (12) is arranged directly in the delivery line 3, the default delay is kept as low as possible.

Electronically, this pressure regulator 12 is connected via a clock module 14 with a also the entire electronic engine control übemehmenden electronic control unit 15, so that depending on the respective existing boundary conditions for each possible operating state selectively set the optimal fuel pressure in the delivery line 3 downstream of this pressure regulator 12 can be.

However, since such an electronic pressure control valve with integrated pressure sensor, in spite of its advantages, is expensive and therefore expensive, this is intended to demonstrate a simplified solution which can replace it without any significant loss of function (= object of the present invention).

The solution to this problem is for a fuel supply system according to the preamble of claim 1, characterized in that the prevailing in the return line upstream of the throttle fuel pressure is used instead of the hitherto conventional atmospheric pressure as the input control pressure for the pressure regulator. Advantageous developments for this purpose are content of the dependent claims 2 to 7.

These embodiments, the contents of claims 1 to 7 are explained in more detail below with reference to Figures 1-3 , in which three different embodiments of a fuel supply system according to the invention are shown in a schematic representation analogous to Figure 4 and wherein like components denoted by like reference numerals are.

In all of these exemplary embodiments according to FIGS. 1-3, the pressure regulator 12 is arranged in the delivery line 3 and a throttle 16 is provided in a return line 11 leading from the pressure regulator 12 to the tank 1. When pressure regulator 12 is a conventional mechanical pressure regulator, which sets by controlling a certain fluid or fuel quantity here in the return line 11 in the delivery line 3 downstream of this pressure regulator 12, a certain pressure level. Usually, this pressure level is defined relative to the atmospheric pressure, ie a conventional pressure regulator receives the so-called. Input control pressure, the atmospheric pressure, so that the adjusted fluid pressure downstream of the Pressure regulator is determined as a differential pressure to the atmospheric pressure.

In a fuel supply system according to the invention according to the embodiments of Figures 1-3, however, now prevailing in the return line 11 upstream of the throttle 16 fuel pressure instead of the hitherto conventional atmospheric pressure as input control pressure for the pressure regulator 12 can be used. Thus, as soon as the pressure regulator 12 diverts a subset of the amount of fuel introduced via the delivery line 3 into the return line 11, this results in overpressure, i.e. due to the throttle 16, which has a flow cross-section which is considerably narrower than the other line cross-sections. set a relative to the atmosphere significantly increased pressure. This increased pressure is made available to the pressure regulator 12 as an input control pressure via a branch line 17 branched off from the return line 11 upstream of the throttle 16, after which it is provided on its output side, i. in the delivery line 3 downstream of the pressure regulator 12 and upstream of the high-pressure pump 4 sets a correspondingly higher pressure level.

For example, the control pressure of the pressure regulator 12 is at 3.5 bar, ie when atmospheric pressure is applied to the pressure regulator 12 (as an input control pressure), it sets an overpressure of 3.5 bar in the delivery line 3. If, instead of the atmospheric pressure, an overpressure of, for example, 2.5 bar is applied to the pressure regulator 12 as the input control pressure, this regulates the excess fuel pressure in the delivery line 3 to approximately 6 bar. With this extremely simple measure, namely essentially only the branch line 17 in the arrangement of the pressure regulator 12 in the delivery line 3, the fuel pressure downstream of the pressure regulator 12 and upstream of the engine, more precisely here the fuel high-pressure pump 4, can be increased as desired ,

Advantageously, this pressure increase quasi automatically takes place precisely in those operating conditions or under those boundary conditions in which this pressure increase is required. As explained above, said pressure increase is only required when relatively small amounts of fuel are required by the internal combustion engine, since only then there is the risk of vapor bubble formation. And only in this case is diverted by the pressure regulator 12, a larger amount of fuel in the return line 11, so that there is a significant overpressure due to the throttle 16, which causes the pressure regulator 12 via said branch line 17 as an input control pressure, in the delivery line. 3 upstream of the high-pressure pump 4 or upstream of the internal combustion engine to set an increased fuel pressure. On the other hand, if there is a relatively high fuel flow rate through the pressure regulator 12, i. If the internal combustion engine requires a relatively large amount of fuel, there is no danger of vapor bubble formation on the one hand, so that no elevated pressure level is required upstream of the high-pressure pump 4. On the other hand, the pressure regulator 12 can then also set there no excessive pressure level, since at most small amounts of fuel are diverted into the return line 11, so that there barely affects the throttle 16 and thus there is no higher pressure, as compared to the atmospheric pressure significantly increased Input control pressure for the pressure regulator 12 could be used.

In the embodiment of Figure 1 in the return line 11 downstream of the throttle 16, a switchable pressure relief valve 18 is provided with a lying at least at the level of the upper desired pressure level of the fuel pressure relevant to the internal combustion engine limit, whereby the already mentioned leakage line 10 of the fuel high pressure pump. 4 upstream of this pressure relief valve 18 opens into the return line 11. This switchable pressure relief valve 18 ensures that at each startup and when the internal combustion engine upstream of the throttle 16, an increased pressure, whereupon - as already explained - via the pressure regulator 12 upstream of the high-pressure pump 4, the desired higher pressure of, for example, 6 bar is set.

It should be mentioned as a particular advantage that no particularly increased demands are placed on the fuel pump 2 in the two fuel supply systems described so far, even if the pressure level downstream of the pressure regulator 12 is temporarily raised to elevated values. In fact, the operating times in which this increased pressure level is needed to ensure the function of the fuel supply system, are so low that a conventional fuel pump 2, which normally only against the lower pressure level (of, for example, 3.5 bar) must demand, also the increased for the internal combustion engine or for the high-pressure pump 4 relevant pressure value (of, for example, 6 bar) can provide, especially since - as already mentioned - when demand for this increased pressure only relatively small amounts of fuel must be provided.

Moreover, it should be noted that instead of a simple fuel pump 2 with a fixed capacity in terms of an advantageous development, a demand-controlled (especially electric motor driven and therefore preferably electronically controlled) fuel pump 2 can be used, as this relatively accurate a desired pressure value in the system can be adjusted.

In the embodiment according to FIG. 2 , the first pressure regulator 12 in the delivery line 3 of the fuel pump 2 connected upstream of the fuel pressure in the return line 11 is preceded by a second pressure regulator 19 whose pressure control value is approximately twice as high as that of the first pressure regulator 12 Acting with atmospheric pressure as the control pressure is. This second pressure regulator 19 is with the atmospheric pressure acted as input control pressure. Provided here is a particular designed as a solenoid valve 3/2-way valve 20, by means of which either the first pressure regulator 12 or the second pressure regulator 19 with the return line 11 upstream of the throttle 16 is connectable.

The reference numeral 20, this 3/2-way valve is shown in that switching position, which is relevant when the internal combustion engine. As can be seen from a comparison of FIG. 2 with FIG. 1 already explained, this switching position essentially leads to the arrangement explained in FIG. 1, since the second pressure regulator 19 is not effective due to its blocked discharge line, ie not connected to the return line 11. The function according to the invention is not affected, namely that the pressure regulator 12 can be acted upon with an increased input control pressure (of the order of a maximum of 1.5 bar), in that the branch line 17 branches off from the return line 11 at a somewhat different location, because this branch continues upstream of the throttle 16. Due to the reduced input control pressure, the leakage line 10 of the high-pressure pump 4 can already open into the return line 11 upstream of the throttle 16.

The reference numeral 20 'in FIG. 2 shows the 312-way valve in that switching position which is relevant when the internal combustion engine is switched off and at its start. For these operating conditions, ie for a restart of the internal combustion engine is thus due to the then active second pressure regulator 19, which can regulate, for example, to a pressure level in the order of 6 bar, a completely safe engine start guaranteed.

In the embodiment according to FIG. 3 , the fuel high-pressure pump 4 is a second one in a purge line 21 opening into the return line 11 Pressure regulator 19 is provided, whose pressure control value is approximately twice as large as that of the first pressure regulator 12 when exposed to atmospheric pressure as the control pressure, wherein alternatively the first pressure regulator 12 or the second pressure regulator 19 is connectable to the return line 11. For the realization of this optional connection function -analog Figure 2- a 3/2-way valve 20 in the return line 11 (both downstream of the spill line of the first pressure regulator 12 and downstream of the second pressure regulator 19) is provided, said 3/2 -Wege valve not only can work electromagnetically, but, for example, with the aid of the thermo-bimetal effect can also be controlled thermally.

This exemplary embodiment is thus relatively similar to that according to FIG. 2 already explained, with quasi complementarily the already mentioned flushing line 21 being integrated or provided, with the aid of which the high-pressure pump 4 can be flushed with fuel conveyed from the fuel tank 1 for heat removal. Thus, while reference numeral 20 indicates the 3/2-way valve in its usual shift position, i. is shown with the internal combustion engine, is shown under the reference numeral 20 ', the switching position of this 3/2-way valve at the start of the internal combustion engine, in which case the high-pressure fuel pump 4 is additionally flushed through the purge line 21.

Incidentally, such a flushing line can also be provided in a suitable manner in the other exemplary embodiments, as a large number of details, in particular of a constructive nature, can certainly be designed quite differently from the exemplary embodiments shown, without departing from the content of the patent claims. Always with the relevant features a fuel supply system, which is characterized even with high ambient temperatures and thus at the risk of vapor bubbles in the fuel system with relatively simple means by highest reliability.

LIST OF REFERENCE NUMBERS

1

Fuel Tank

2

Fuel pump

3

delivery line

4

(Fuel) high pressure pump

5

Fuel rail

6

Fuel injection valve

7

Pressure relief valve (in 5)

8th

diversion line

9

shut-off valve

10

leakage line

11

Return line

12

(first) pressure regulator

13

Fuel filter

14

clock module

15

electronic control unit

16

throttle

17

branch line

18

Pressure relief valve

19

second pressure regulator

20

3/2-way valve

21

flushing line

Claims (7)

1. A fuel supply system for an internal combustion engine, comprising a fuel pump (2) delivering fuel from a tank (1) through a delivery pipe (3) to the engine, and a pressure regulator (12) which sets different fuel pressure levels as required and as appropriate for the engine, wherein the pressure regulator (12) is disposed in the delivery pipe (3) and a throttle valve (16) is provided in a return pipe (11) leading from the pressure regulator (12) to the tank (1), characterised in that the fuel pressure upstream of the throttle valve (16) in the return pipe (11) is used instead of atmospheric pressure as the input control pressure for the pressure regulator (12).
2. A fuel supply system according to claim 1, wherein the delivery pipe (3) downstream of the pressure regulator (12) terminates at the suction side of a high-pressure pump (4) provided for direct ignition of fuel, and at this place fuel is provided at the pressure appropriate for the engine, and a leakage pipe (10) leading away from the high-pressure pump (4) terminates in the return pipe (11).
3. A fuel supply system according to claim 1 or 2, characterised in that a switchable pressure limiting valve (18) downstream of the throttle valve (16) in the return line (11) is provided with a limiting value at least equal to the upper desired fuel pressure level appropriate for the engine.
4. A fuel supply system according to claim 3, characterised in that the leakage pipe (10) upstream of the pressure limiting valve (18) terminates in the return pipe (11).
5. A fuel supply installation according to any of claims 1 to 3, characterised in that a second pressure regulator (19) is provided in the delivery pipe (3) in front of the first pressure regulator (12) supplied with the fuel pressure in the return line (11) as the input control pressure, the second pressure regulator being set at a pressure approximately twice as great as the setting of the first pressure regulator (12) when supplied with atmospheric pressure as the control pressure.
6. A fuel supply system according to claim 5, characterised in that the first pressure regulator (12) or alternatively the second pressure regulator (19) is connectable to the return line (11) upstream of the throttle valve (16).
7. A fuel supply system according to claim 2 or 3, characterised in that a second pressure regulator (19) is provided in a scavenging duct (21) of the high-pressure pump (4) opening into the return pipe (11) and is set at a pressure approximately twice that of the first pressure regulator (12) when supplied with atmospheric pressure as the control pressure, wherein the first pressure regulator (12) or alternatively the second pressure regulator (19) is connectable to the return pipe (11).

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