EP1124054B1 - Fuel supply system for a combustion engine - Google Patents

Description

The invention relates to a fuel supply system for an internal combustion engine with a fuel pump from a tank via a feed line to the engine promoting fuel pump and a pressure regulator, which adjusts the fuel pressure relevant for the internal combustion engine optionally to different pressure levels. For technical reasons, reference is made, for example, to DE 44 43 836 A1.

In general, but especially in motor vehicles installed in internal combustion engines, there is the problem that in a so-called. Hot start the engine, a sufficient amount of liquid fuel must be provided, even if the previous shutdown and the subsequent shutdown of Internal combustion engine in whose 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 vapor bubbles in the internal combustion engine near fuel supply system. 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 the above-mentioned document.

In principle, the described hot start problem, which can 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 correspondingly powerful fuel pump - usually come for this electrically driven fuel pumps are used - solve, 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. Moreover, a cold start of an internal combustion engine can also represent a critical operating state since, despite possibly reduced electrical voltage for operating the fuel pump, a sufficiently high fuel pressure level must be provided.

If under these mentioned critical operating conditions, the fuel required by the engine fuel quantity is relatively low, 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, the usually required pressure level of 3.5 bar (eg) adjusts, 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. If now this return line downstream of the pressure regulator shut off or at least throttled, this inevitably leads to a pressure build-up or pressure increase in the delivery line due to the smaller amount of fuel pumped back into the tank, so that at least in these temporally clearly limited operating conditions an excessive fuel pressure of For example, 6 bar can be provided.

The described start and / or hot operation problem arises, moreover, even in working with direct fuel injection internal combustion engines, in which on the one hand started with the provided by said (electric) fuel pump fuel pressure, the internal combustion engine is on the other hand, 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 the previously mentioned and upstream of said pressure regulator arranged fuel pump is virtually a prefeed pump. When so-called. For the internal combustion engine relevant fuel pressure is then applied to the suction side of the high pressure fuel pump fuel pressure. Also, 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 start and / or hot operating conditions, but again in the range of 6 bar.

Here, however, the well-known from the already repeatedly mentioned DE 44 43 836 A1 principle for increasing the relevant for the internal combustion engine or on the suction side of a high-pressure fuel pump pressure levels is practically unworkable because the flow rate of the usual fuel pump is not sufficient for this ie a hitherto conventional fuel pump, which can provide fuel in sufficient quantity at a pressure level of, for example, 3.5 bar (measured with respect to atmospheric pressure), is not able to safely provide the required amount of fuel even at a pressure level of 6 bar.

The technically simplest solution for achieving a sufficiently high pressure levels while ensuring the required fuel flow rate could thus be a correspondingly powerful fuel pump in addition to a pressure regulator, which always adjusts the fuel pressure relevant to the internal combustion engine to an elevated pressure level of, for example, 6 bar. Such a fuel supply system is shown as at least internal prior art in the attached Figure 3 and is explained below:
The reference numeral 1, the fuel tank of a motor vehicle is referred to, in which an electric fuel pump 2 is arranged, which provides via a delivery line 3 of a high-pressure fuel pump 4, the fuel required by an internal combustion engine, not shown. The example. Mechanically driven by the internal combustion engine high-pressure pump 4 thereby promotes the fuel provided by the electric fuel pump 2 under very high pressure (eg. On the order of 130 bar) in a provided on the internal combustion engine injection rail 5, from which the individual internal combustion engines Cylinders associated, only symbolically shown fuel injectors 6 are supplied. From the high-pressure pump 4 further branches with the interposition of a check valve 9 from a leakage line 10, which opens into a leading into the tank 1 return line 11, and be discharged via the low fuel leakage quantities 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 branches off in the already mentioned return line 11 Absteuerleitung 22 so that the pressure regulator 12 provides only such a quantity of fuel via the delivery line 3 of the high-pressure pump 4, that Under normal operating conditions there, ie at the suction side, the so-called. For the internal combustion engine relevant pressure of, for example, 6 bar (measured as differential pressure relative to the environment) adjusts. The amount of fuel required for achieving this relevant pressure, which is conveyed by the fuel pump 2 and therefore not required, is returned by the pressure regulator 12 via the discharge line 22 and 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 at a shutdown of the internal combustion engine, at the same time to 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 upstream of the high-pressure pump 4, the so-called. For the internal combustion engine relevant fuel pressure (eg. 6 Bar as differential pressure) is maintained or remains.

The far known state of the art is unsatisfactory insofar as a correspondingly powerful fuel pump 2 must be used, which can provide the required amount of fuel under the relatively high pressure level of, for example, 6 bar in all operating points of the internal combustion engine. This usually electrically powered fuel pump not only undesirably requires much energy but also causes increased heating in the fuel system, i. It is basically a larger amount of fuel circulated, which heats up. Furthermore, more powerful fuel pumps cause higher noise and are more expensive, which also applies to an alternative training with a preferably electronically demand-controlled in terms of their capacity electric fuel pump.

A fuel supply system according to the preamble of claim 1 is known from the document DE 195 30 261 A1.

On the other hand, to show improvements is the object of the present invention.
To solve this problem it is proposed that the pressure regulator is arranged in the delivery line and that the fuel pump is formed from two pump units, which promote parallel or in series depending on the adjusted pressure level. Advantageous developments are content of the dependent claims.

According to the invention, the delivery characteristics of the fuel pump can be adapted to the respectively required or adjusted by the pressure regulator pressure level. This can be achieved simply and in a particularly advantageous manner by the fuel pump having at least two pump stages or even consists of two individual pumps - (both variants are to fall under the chosen term of a "pump unit") -, which can be switched in different ways fluidically to each other.

If the pump units are connected in series, fuel is already present at the suction side of the downstream pump unit at an elevated pressure level, namely that which is provided by the upstream pump unit. For example, each of the pump units is able to produce a delivery pressure of 3 bar, so that the fuel pressure on the pressure side of the unit is 3 bar above that on the suction side of the unit. If the pump units are then connected in series, then a pressure level of 6 bar (= 3 bar + 3 bar) can be generated (from a simplified perspective) starting from the suction side of the upstream pump unit on the pressure side of the downstream pump unit.

If, on the other hand, the pump units are connected in parallel, only their pressure level is set to 3 bar on their common pressure side connected by parallel connection or side-by-side arrangement, however, twice the fuel quantity can then advantageously be conveyed or provided (again simplified) as if the two pump sets are connected in series.
The particular advantage of a fuel system according to the invention lies in the fact that, with relatively little effort and efficiency and without the disadvantages of the prior art, it has to be accepted for different operating states of the internal combustion engine the required fuel quantity can be provided at a favorable pressure level , Will namely by the When a large quantity of fuel is demanded from the internal combustion engine, a lower fuel pressure level is perfectly adequate, whereas when a high pressure level is required, an at least slightly reduced fuel quantity is demanded.

These requirements can fully meet the proposed Kraftstäffversorgungsanlage. By means of the pressure level adjusting pressure regulator, the most favorable pressure level for the respective operating state can be set for the pressure relevant to the internal combustion engine. Since usually two different pressure levels, namely a higher (of eg 6 bar overpressure compared to the atmosphere) and a lower (of eg 3.5 bar overpressure) are sufficient, with regard to a particularly simple and yet safe construction of such a variable pressure regulator be arranged in the delivery line in series two pressure regulator with different pressure control values, which can be selectively activated by connecting their Absteuerleitung with an opening in the tank return line.

Depending on the pressure level desired in each case, the pump units of the fuel pump are then connected either in series, whereby simply a higher pressure can be provided at a lower flow rate, or the pump units are connected in parallel, which efficiently and simply offers a higher flow rate at lower delivery pressure can.

In this case, the two pump units of the inventive fuel pump by means of a switching valve or automatically by means provided in a suitably arranged line connection pressure relief valve in response to each set by the pressure regulator pressure value in series or parallel can be switched promotional, such as also apparent from the two explained below preferred embodiments of the invention. In the accompanying figures 1 and 2 fuel supply systems according to the invention are shown, and in the process of the already explained prior art representation of Figure 3, wherein the same reference numerals are used for the same elements.

In both exemplary embodiments according to FIGS. 1 and 2, the pressure regulator 12 arranged in the delivery line 3 is quasi composed of two pressure regulators 12a, 12b connected in series with different pressure control values, wherein a discharge line 22a or 22b branches off from each pressure regulator 12a, 12b. of which either a preferably designed as a solenoid valve 3/2-way valve 20 with the leading to the tank 1 return line 11 is connectable. In the case of the two pressure regulators 12a, 12b, these are conventional mechanical pressure regulators that set a specific pressure level by controlling a certain amount of fluid or fuel quantity in the return line 11 in the delivery line 3. Usually, this pressure level is defined against the atmospheric pressure, i. a conventional pressure regulator receives the so-called. Input control pressure, the atmospheric pressure, so that the adjusted fluid pressure in the delivery line 3 is determined as a differential pressure to the atmospheric pressure.

The pressure regulator 12a provided here directly downstream of the filter 13 sets, for example, a pressure level of 3.5 bar when its diversion line 22a is connected to the return line 11 via the 3/2-way valve 20. However, this connection is interrupted by switching the 3/2-way valve 20, so this first pressure regulator 12a is not active. At the same time then the connection between the Absteuerleitung 22 b of the second pressure regulator 12 b and the return line 11 is made, so that the latter pressure regulator 12b is activated or is, which sets in the delivery line 3 a relation to the pressure regulator 12a higher pressure level of, for example, 6 bar. The associated switching position of the 3/2-way valve is otherwise shown by the reference numeral 20 ', this position is selected in particular for the start of the engine and in hot operation thereof, while the switching position shown under the reference numeral 20 and the resulting lower pressure level 3.5 bar in normal operation of the internal combustion engine should be relevant.

It is now necessary to adapt the delivery characteristics of the electric fuel pump 2 to the respectively selected pressure level in the delivery line 3. In this case, the fuel pump 2 consists of two electrically driven pump units 2a, 2b, depending on the adjusted pressure level, the fuel from the tank 1 can promote either parallel or connected in series. Each pump unit 2a, 2b is associated with a suction line 23a, 23b, wherein in the latter a to the pump unit 2b opening check valve 27b is provided.

The pressure line 24b of the second pump unit 2b opens directly into the delivery line 3, while the pressure line 24a of the first pump unit 2a can branch or branch into two sub-branches 24a ', 24a ".

In the embodiment according to FIG. 1, the first sub-branch 24a 'of the pressure line 24a of the first pump unit 2a flows while passing a check valve 27a in the delivery line 3, while the second sub-branch 24a "in which a pressure-limiting valve 25 is arranged in the suction line 23b of the second pump unit 2b, the pressure limiting valve 25 is at the lower pressure control value of the pressure regulator 12th out, ie here approximately to the pressure of 3.5 bar of the pressure regulator 12a.

Thus, if the pressure regulator 12a is active and thus a pressure of 3.5 bar arises in the delivery line 3, the partial branch 24a "is blocked due to the pressure limiting valve 25, so that the first pump unit 2a injects the fuel via the partial branch 24a 'into the As a result, the first pump unit 2a is then connected in parallel to the second pump unit 2b in terms of flow technology.

If, on the other hand, the pressure regulator 12b is active and thus a pressure of 6 bar is set in the delivery line 3, then the pressure limiting valve 25 and thus the partial branch 24a "are opened, so that the first pumping unit 2a transfers the fuel virtually completely via the partial branch 24a" into a Area lower pressure, namely the suction side of the second pump unit 2b and thus in the suction line 23 b promotes. Accordingly, the first pump unit 2a is then fluidly connected in series with the second pump unit 2b, whereby the required increased pressure level of 6 bar can be generated in a simple and efficiency-optimal manner.

In the embodiment according to FIG. 2, the pressure line 24a of the first pump unit 2a opens into a preferably designed as a solenoid valve 3/2-way valve 26 or general switching valve 26, from which optionally the first sub-branch 24a ', which opens into the feed line 3, or the second in the suction line 23b of the second pump unit 2b opening partial branch 24a "can be activated.

Is by appropriate control of the above-mentioned 3/2-way valve 20, the pressure regulator 12a active and thus arises in the delivery line 3 a pressure of 3.5 bar, so at the same time the switching valve 26 and the latter 3/2-way valve 26 is switched such that the first pump unit 2 a promotes the fuel via the sub-branch 24 a 'in the delivery line 3. As a result, the first pump unit 2a is then connected in parallel to the second pump unit 2b in terms of flow.

If, however, by appropriate control of the above-mentioned 3/2-way valve 20, the pressure regulator 12b active and thus sets in the delivery line 3, a pressure of 6 bar, so the switching valve 26 is simultaneously switched such that the first pump unit 2a Accordingly, the first pump unit 2a is then fluidly connected in series with the second pump unit 2b, whereby the required increased pressure level of .1 in a simple and efficient manner The associated switching position of the switching valve 26 designed as a 3/2-way valve is otherwise indicated by the reference numeral 26 '.

Of course, a variety of details, in particular of a constructive nature may well be designed differently from the embodiments shown, without departing from the content of the claims. Thus, the individual electrically driven pump units 2a, 2b differ in terms of their capacity to exploit the potential for improvement even more, ie a pressure-stable fuel pumping station with relatively low flow and thus even better efficiency both at start and while the internal combustion engine achieve. In this case, said pressure regulator can also work electronically, ie, the desired fuel pressure can be adjusted electronically, but also a single mechanically operating pressure regulator can be provided, the demand depends on different einzuregelnde Pressure levels is adjustable. 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. The aim of the described switching of the electric fuel pump is to be able to realize the higher required for a start of the engine fuel pressure values without having to design the fuel pump so strong that they in the usual operating condition with running internal combustion engine with too high performance or Current consumption works, which can be avoided otherwise by an electronic power control of the fuel pump, however, in a more complex manner than with the present invention.

LIST OF REFERENCE NUMBERS

1

Fuel Tank

2

Fuel pump

2a, b

pump unit

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, a, b

pressure regulator

13

Fuel filter

20

3/2-way valve

20 '

other switching position of 20

22, a, b

diversion line

23a, b

suction

24a, b

pressure line

24a ', a "

Sub branch of 24a

25

Pressure relief valve

26

switching valve

27a, b

check valve

Claims (4)

1. A fuel supply system for an internal-combustion engine comprising a fuel pump (2) conveying the fuel from a tank (1) to the internal-combustion engine via a feed line (3) and a pressure regulator (12) which selectively sets the fuel pressure relevant to the internal-combustion engine to different pressure levels, wherein the pressure regulator (12) is arranged in the feed line (3), characterised in that the fuel pump (2) is formed from two pump units (2a, 2b) which feed, connected in parallel or in series, depending on the set pressure level.
2. A fuel supply system according to claim 1, characterised in that the two pump units (2a, 2b) are connected to feed in series or in parallel by means of a change-over valve (26) or automatically by means of a pressure limitation valve (25) provided in a suitably arranged line connection, depending on the pressure value set, in each case, by the pressure regulator (12).
3. A fuel supply system according to claim 1 or 2, wherein two pressure regulators (12a, 12b) with different pressure regulation values are arranged in series in the feed line (3) and can be activated selectively by connecting their diversion line (22a, 22b) to a return line (11) opening in the tank (1).
4. A fuel supply system according to any one of the preceding claims, characterised in that the feed line (3) opens downstream from the pressure regulator (12) on the intake side of a high-pressure pump (4) provided for direct fuel injection and provides fuel at this point at the pressure relevant to the internal combustion engine and in that a leakage line (10) leading away from the high-pressure pump (4) opens in the return line (11) branching off from the pressure regulator (12).

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