WO2000020754A1

WO2000020754A1 - Fuel injection system

Info

Publication number: WO2000020754A1
Application number: PCT/DE1999/002896
Authority: WO
Inventors: Bernhard Arnold; Franz Wirzberger; Thomas Hofmann
Original assignee: Siemens Aktiengesellschaft
Priority date: 1998-10-02
Filing date: 1999-09-13
Publication date: 2000-04-13
Also published as: EP1117929A1; DE59903782D1; EP1117929B1; DE19845556A1

Abstract

The invention relates to a fuel injection system (1) for an internal combustion engine and to a method for controlling an injection system. According to said method, the fuel that is not required by a common-rail (14) is returned via a return line (24) to a fuel line area between a fuel filter (8) and a fuel tank (2). The fuel is heated as a result of being returned in this way, which prevents the filter (8) from becoming plugged below the cold filter plugging point.

Description

description

Fuel injection system

The invention relates to a fuel injection system for an internal combustion engine according to the preamble of patent claim 1 and a method for controlling an injection system according to the preamble of patent claim 9.

For many years, diesel engines lagged behind gasoline engines equipped with catalytic converters in terms of technological development. By developing new injection systems, however, this technological lead in gasoline engines has recently been achieved. Direct injection systems have been found to be particularly efficient, in which the fuel drawn from a fuel tank and pressurized is fed to a common high-pressure line, the so-called common rail, and from there to the injectors. Such fuel injection systems are also referred to in the art as common rail systems.

The fuel is drawn in from a fuel tank via a pre-feed pump and brought up to the pressure required in the common rail of, for example, 1,400 bar via a downstream high-pressure pump. The pressure in the common rail is limited by a pressure control valve, via which the excess, pressurized fuel can be returned to the fuel tank. The high-pressure pump is designed as a variable displacement pump, different types, for example a suction-restricted pump, a pump driven by an electric motor at different speeds, one Pump with adjustable stroke ring or with adjustable swash plate can be used.

In modern common rail systems, the pressure control in the common rail is often carried out via a volume flow control valve (suction throttle valve) upstream of the variable displacement pump, while the pressure control valve which limits the pressure in the common rail is only used for rapid pressure reduction.

Such a construction is described in EP 0299337A2. The advantage of such solutions is that only the required amount of fuel is led to the high-pressure pump by appropriate adjustment of the volume flow control valve, so that the amount of fuel returned from the common rail to the fuel tank is minimal.

A problem with such injection systems is that, for example, in winter, when the outside temperature is low, the fuel filter can be clogged by paraffin deposits. To reduce this risk to a minimum, diesel fuels are divided into CFPP classes (cold filter plugging point) in accordance with the EN 116 standard. These CFPP classes each define lower temperature limits below which paraffin deposits in the diesel fuel can occur.

To avoid such paraffin deposits, electrically heated fuel filters are used in conventional common rail systems, but they are comparatively complex and can only be operated with a considerable amount of energy.

In contrast, the invention has for its object a fuel injection system and a method for To create control of an injection system in which the cold start behavior is improved at low temperatures.

This object is achieved with respect to the fuel injection system by the features of patent claim 1 and with respect to the method by the features of the independent claim 9.

The measure of having a return line opening in the line area between the fuel tank and the fuel filter branch off between the common rail and the high-pressure pump enables a partial fuel flow heated by the action of the high-pressure pump and possibly a suction throttle valve to be returned to the inlet of the filter, so that a The fuel filter is only clogged at significantly lower temperatures than in the prior art. This means that the partial return of a heated amount of fuel to the filter enables the engine to be started well below the CFPP of the fuel used.

In a preferred exemplary embodiment, the high-pressure pump is actuated during the cold start in such a way that it delivers a maximum delivery quantity, so that the fuel volume flow returned through the return line is correspondingly maximum. This means that in this variant the variable displacement pump is practically operated as a constant pump with maximum delivery capacity and heated fuel is essentially introduced directly into the filter. In an alternative variant, the returned fuel can also be fed into the swirl pot of the tank or into another line area between the fuel tank and filter. The variable pump is preferably controlled as a function of the fuel temperature measured in the area of the filter. The duration of this cold start control can then be determined either as a function of a predetermined time interval or according to the temperature profile in the filter area.

In a preferred embodiment, the pressure control valve for limiting the pressure in the common rail is arranged in the return line, so that the circuitry complexity is minimized.

The leakage of the common rail injectors can either be fed into the return line or directly into the fuel tank.

In a variant of the fuel injection system according to the invention, the return line can be assigned a valve device via which the return line can be connected either to the fuel tank or to the line area between the fuel tank and filter, so that the amount of fuel not required by the common rail is directly in when the engine is warm the fuel tank is returned.

Other advantageous developments of the invention are the subject of the further subclaims.

A preferred exemplary embodiment of the invention is explained in more detail below with reference to a schematic drawing.

The single figure shows a hydraulic circuit diagram of a common rail diesel injection system, which is also referred to as an accumulator injection system. The common rail system 1 according to the invention has a conventional type of diesel fuel tank 2. This is equipped with a baffle from which the diesel fuel is pumped out. The fuel tank 2 is connected to a fuel line 4, through which the diesel fuel can be pumped out of the fuel tank 2 by means of a pre-feed pump 6. A fuel filter 8, for example a sieve or paper filter, is provided between the fuel tank 2 and the prefeed pump 6, via which solids, for example dirt or paraffin precipitates, can be removed from the diesel fuel. The diesel fuel pressurized via the prefeed pump 6 is led to the suction side of a high-pressure pump 10, which in the exemplary embodiment shown is designed as a variable displacement pump. Modern common rail injection systems require maximum pressures of up to 2,000 bar, so that radial piston pumps are preferably used as high pressure pumps.

The fuel can also be drawn in via a fuel pump which is arranged directly on or in the fuel tank 2 and is, for example, electrically driven. With such a construction, the prefeed pump 6 can be omitted.

In the subject matter of the invention, the type of variable pump 10 is not important. For example, it can be designed as a suction-throttled pump (similar to the construction in EP 0299337A2) or by an electric motor with different speeds or as a piston pump with an adjustable stroke.

Between the pressure side of the pre-feed pump 6 and the

On the suction side of the high-pressure pump 10, a volume flow control valve 12 is provided in the fuel line 4. adjustable 2/2-way valve is executed. By correspondingly controlling the volume flow control valve 12, the amount of diesel fuel delivered by the prefeed pump 6 to the suction side of the high-pressure pump 10 is throttled as a function of the load on the engine, so that the optimum delivery amount is always delivered into the common rail 14 arranged downstream of the high-pressure pump 10. The volume flow control valve 12 can be brought into a blocking position, so that the fuel supply to the high-pressure pump 10 and thus to the common rail 14 is interrupted.

The volume flow control valve 12 and / or the variable displacement pump 10 are controlled via a control unit 16, via which injectors 18 of the common rail 14 can also be controlled for fuel injection into the combustion chamber. The control of the variable displacement pump 10 or of the volume flow control valve 12 takes place, inter alia, as a function of the fuel temperature, which is detected by a temperature sensor 20. This can be arranged, for example, in the area of the fuel filter 8, so that the diesel fuel temperature is measured when the filter 8 flows through it.

The aforementioned common rail 14 is connected to the pressure side of the high-pressure pump 10 via a pressure line 22. A return line 24 branches off from the pressure line 22 and opens into the fuel line 4 in the area of the inlet of the filter 8. A pressure control valve 26 is provided in the return line 24, via which the pressure in the common rail 14 can be limited to a maximum value (for example approximately 1,500 bar).

The amount of leakage in the injectors 18 and the excess amount of the common rail 14 is indicated by a dashed line. indicated connection line 28 fed into the return line 24 or into a tank line 30.

To cool the high-pressure pump 10, a cooling line 32 branches off from the fuel line 4 in the area between the prefeed pump 6 and the high-pressure pump 10 and leads to cooling connections of the high-pressure pump 10. This means that a subset of the diesel fuel supplied by the prefeed pump 6 is used to cool the high-pressure pump 10.

In the exemplary embodiment shown in the figure, the diesel fuel partial flow used for cooling is led via a cooling outlet line 34 into the tank line 30 and thus back to the fuel tank 2. In principle, this partial quantity could also be introduced into the return line 24, since the partial flow emerging from the high-pressure pump 10 and used for cooling has a higher temperature than the diesel fuel in the fuel tank 2, and thus contributes to suppressing the paraffin excretion.

When the engine is cold started, the volume flow control valve 12 is first brought into a flow position, which is selected via the control unit 16 as a function of the operating state of the engine. The diesel fuel is sucked out of the fuel tank 2 via the prefeed pump 6 and conveyed through the filter 8 to the suction side of the high-pressure pump 10. The fuel temperature in the area of the filter 8 is measured via the temperature sensor 20 and a corresponding signal is supplied to the control unit 16. Depending on the fuel temperature, the control unit 16 emits control signals to the volume flow control valve 12 and / or the adjustment device of the high-pressure pump 10. According to the invention, the high pressure pump 10 and / or the volume flow control valve til 12 set such that a maximum flow of diesel fuel to the common rail 10 is promoted. That is, by means of appropriate control, the relatively large-sized variable displacement pump (high-pressure pump 10) is operated as a constant pump with a maximum delivery rate, so that an excess amount is led to the common rail 14. By throttling the diesel fuel when it flows through the volume flow control valve 12 and by the additional heating within the high-pressure pump 10, the diesel fuel flowing to the common rail 14 has a substantially higher temperature than the fuel taken directly from the cold fuel tank 2. A portion of this heated diesel fuel is returned to the inlet of the filter 8, so that the temperature at the filter 8 rises to a range above the CFPP. A paraffin excretion is thus reliably prevented, so that a cold start is also possible below the CFPP.

After a predetermined warm-up temperature has been exceeded at the filter 8 or in another area of the fuel injection system, a signal is sent to the adjusting pump 10 and / or the volume flow control valve 12 via the control unit 16, so that the delivery quantity to the common rail is reduced and practically only that required diesel fuel volume flow must be compressed by the high pressure pump 10.

The changeover of the injection system from the cold-run control to the warm-up process can be time-dependent or temperature-dependent. In the former case, the prescribed cold run control is maintained during a predetermined time interval, this time interval being selected such that the warm-up phase is reached even under unfavorable operating conditions. In the latter case, the cold run Control as a function of the filter temperature, that is to say the "normal" control of the variable pump 10 takes place only after the filter temperature has exceeded an upper limit value.

Of course, the return line 24 does not necessarily have to open into the input area of the filter 8, but can be provided practically anywhere between the fuel tank 2 and the filter 8. For example, the return line 24 can open into the surge chamber of the fuel tank 2 mentioned at the beginning. It is essential that the returned diesel fuel partial flow only releases its thermal energy to a negligible extent to the other fuel in the fuel tank 2 or to other materials, so that a comparatively high filter temperature is ensured.

In a variant, a valve device could also be provided in the return line 24, via which the returning partial flow can optionally be returned to the input area of the filter 8 or directly into the fuel tank 2.

Disclosed is a fuel injection system for an internal combustion engine and a method for controlling an injection system in which fuel that is not required by a common rail is returned via a return line to a fuel line area between a fuel filter and a fuel tank. This return causes the fuel to be heated so that the filter can be prevented from clogging when the CFPP is undershot.

Claims

Expectations

1. Injection system for an internal combustion engine, with a pre-feed pump (6) and a high-pressure pump (10), via which fuel can be delivered from a fuel tank (2) to a common rail (14), with a fuel filter () upstream of the pre-delivery pump (6). 8) is provided, characterized by a return line (24) branching off between the high-pressure pump (10) and the common rail (14) and opening into a fuel line area between the fuel tank (2) and the fuel filter (8).

2. Fuel injection system according to claim 1, characterized in that a pressure relief valve (26) is provided in the return line (24).

3. Fuel injection system according to claim 1 or 2, characterized in that the return line (24) opens directly in front of the fuel filter (8) or in a swirl pot associated with the fuel tank (2).

4. Fuel injection system according to one of the preceding claims, characterized in that the high pressure pump (10) is a variable displacement pump, and that the delivery rate is adjustable as a function of the fuel temperature.

5. Fuel injection system according to claim 4, characterized by a temperature sensor (20) for detecting the fuel temperature.

6. Fuel injection system according to one of the preceding claims, characterized by a Connecting line (28), via the leakage of the injectors (18) or fuel not required in the common rail (14) can be fed into the return line (24).

7. Fuel injection system according to one of the preceding claims, characterized by a cooling line (32) via which fuel for cooling the high-pressure pump (10) can be branched, which optionally opens into the fuel tank (2) or in the region of the filter (8).

8. Fuel injection system according to one of the preceding claims, characterized by a valve device via which the return line (24) can be connected either to the fuel tank (2) or to the fuel line area between the fuel tank (2) and the filter (8).

9. Method for controlling an injection system, in which the fuel is conveyed from a fuel tank (2) to a common rail (14) via a prefeed pump (6) and a high-pressure pump (10), characterized by the steps:

- sensing the fuel temperature (T); - Increase the delivery rate of the high pressure pump when the temperature falls below a limit;

- Returning the partial flow not required in the common rail (14) into a fuel line area between the fuel tank (2) and the fuel filter (8).

10. The method according to claim 9, characterized in that the high pressure pump (10) is a variable displacement pump and is operated when the temperature falls below the limit as a constant pump with maximum delivery.

11. The method according to claim 9 or 10, characterized in that the increase in the delivery rate takes place during a predetermined time interval or is controlled depending on the fuel temperature.