WO2021239316A1

WO2021239316A1 - Method for operating a fuel injection system, control device

Info

Publication number: WO2021239316A1
Application number: PCT/EP2021/059626
Authority: WO
Inventors: Oliver Schulz; Jean-Roch Julien; Raphael Combe
Original assignee: Robert Bosch Gmbh
Priority date: 2020-05-28
Filing date: 2021-04-14
Publication date: 2021-12-02
Also published as: DE102020206693A1

Abstract

The invention relates to a method for operating a fuel injection system (1), in particular a common rail injection system, for supplying an internal combustion engine with fuel, in which fuel is brought to high pressure and fed with the aid of a high-pressure pump (2) to a high-pressure reservoir (3), and in which the pressure in the high-pressure reservoir (3) is controlled by means of a pressure regulating valve (4) arranged at the high-pressure reservoir (3). According to the invention and for the purpose of fuel detection, the pressure regulating valve (4) is initially closed and/or opened before starting the motor and a type of fuel or at least one fuel property, in particular the viscosity of the fuel, is derived from the opening and/or closing behavior. The invention also relates to a control device (7) for carrying out the method according to the invention or at least one method step.

Description

description

Title:

Method for operating a fuel injection system, control unit

The invention relates to a method for operating a fuel injection system which is used to supply an internal combustion engine with fuel. The fuel injection system can in particular be a common rail injection system. The invention also relates to a control device with the aid of which the method can be carried out.

State of the art

A fuel injection system usually comprises a high pressure pump for delivering the fuel to high pressure and a high pressure accumulator. At least one injection valve for metering and injecting the fuel into a combustion chamber of the internal combustion engine is connected to the high-pressure accumulator. The metering accuracy depends on the fuel temperature and the fuel quality, with the influence of the fuel quality increasing as the temperature falls. It is therefore an advantage to know not only the fuel temperature but also the fuel quality.

Methods for determining fuel properties or for fuel detection are already known from the prior art. As an example, reference is made to the laid-open specification DE 10 2007 045 574 A1, which writes a method for determining fuel properties in a common rail system. In the method, the time course of at least one variable is recorded, which characterizes the pressure in the high-pressure accumulator or rail. At least one property characterizing the fuel is then deduced from the time profile of the at least one variable. No additional sensors are required to carry out the method, since an already existing rail pressure sensor is used to determine the fuel properties will. The evaluation is based on the output signals of the rail pressure sensor.

Furthermore, methods are known in which the fuel quality is determined via a function of the injection valve that takes place before the engine is started. It has been shown, however, that the method does not work with every type of injection valve, in particular not with piezo injectors.

The present invention is based on the object of eliminating the disadvantages of the prior art and enabling a more precise determination of the fuel quality via a new functionality. The new functionality should be implemented with existing resources as far as possible, so that no additional components are required.

To achieve the object, the method with the features of claim 1 is proposed. Advantageous further developments of the invention can be found in the subordinate claims. In addition, a control device for executing the method or at least one method step is proposed.

Disclosure of the invention

A method is proposed for operating a fuel injection system, in particular a common rail injection system, which is used to supply an internal combustion engine with fuel. In the process, fuel is pumped to high pressure with the aid of a high pressure pump and fed to a high pressure accumulator. The pressure in the high pressure accumulator is regulated with the aid of a pressure control valve arranged on the high pressure accumulator. According to the invention, the pressure control valve is initially closed and / or opened for fuel detection before the engine starts and a type of fuel or at least one fuel property, in particular the viscosity of the fuel, is derived from the closing and / or opening behavior of the pressure control valve.

For fuel detection, the proposed method uses a pressure regulating valve that is already present and arranged on the high-pressure accumulator, so that it can be implemented in a comparatively simple manner. Before the engine starts, i.e. before the engine actually starts, the pressure control valve is activated closed or open, depending on whether the pressure control valve is a normally open or normally closed valve. The behavior of the pressure regulating valve when it is initially closed or opened allows conclusions to be drawn about the type of fuel and / or at least one fuel property, so that this information can be taken into account when metering fuel. The metering accuracy increases accordingly.

It goes without saying that the fuel present in the high-pressure accumulator influences the closing and opening behavior of the pressure control valve. The viscosity of the fuel is particularly important here. If a vehicle is refueled with a fuel that has a higher viscosity than the fuel previously added, this becomes noticeable in the closing and opening behavior of the pressure control valve in that the pressure control valve closes and opens less quickly. Because with the viscosity of the fuel, the friction between the fuel and a moving valve member of the Druckre gel valve in the fuel increases. The closing and opening times therefore provide information about the viscosity of the fuel and thus about the fuel itself.

Therefore, as an alternative or in addition to evaluating the behavior when the pressure regulating valve is initially closed or opened, the behavior when it is reopened after the initial closing or when it is re-closed after the initial opening can also be evaluated.

For the initial closing or opening of the pressure control valve, an electromagnet is preferably energized, the magnetic force of which - directly or indirectly via a magnet armature - acts on a valve member of the pressure control valve that can move back and forth. If the pressure regulating valve is designed as a normally open valve, the energization of the electromagnet leads to the closing of the pressure regulating valve. In the version as a normally closed valve, the energization of the electromagnet leads to the opening of the pressure control valve. In any case, the energization leads to a movement of the valve member. Due to inductive effects, this can be read from the current signal of the electromagnet. Because as soon as the valve member moves, the current drops and only rises again when the valve member has reached its end position. The current curve thus has a kink, so that the closing or opening duration of the pressure regulating valve can be determined via this. This in turn provides information about the viscosity of the fuel. When the energization of the electromagnet is ended, the fall time can be evaluated in a similar way, depending on how the valve member is connected to a return spring and an electrical circuit.

When closing the pressure control valve, the end position is given by the valve seat. When opening, a stroke stop preferably specifies the end position.

When energizing the electromagnet for the initial closing or initial opening of the pressure regulating valve, the current curve is preferably determined and compared with stored current curves characteristic of certain types of fuel. A specific type of fuel can therefore be deduced from a simple comparison. The comparison is preferably made with current profiles that are stored in a control unit. This can be the engine control unit, for example. As an alternative or in addition, the evaluation can be carried out with the aid of artificial intelligence and / or neural networks.

In a further development of the invention, it is proposed that the current fuel temperature be determined and taken into account in the fuel detection. This is particularly advantageous since the temperature influences the viscosity of the fuel. There is no need for additional sensors, as they are usually available anyway and temperature readings are therefore already available. Alternatively or in addition, the fuel temperature can also be modeled.

As already mentioned, the method according to the invention can be carried out with the aid of a pressure control valve which is designed as a normally open valve or as a normally closed valve.

If a normally open pressure control valve is used, the closing behavior is evaluated during the initial closing. For this purpose, the closing process is carried out with a specified current curve, the closing behavior is determined and compared with values stored in the control unit that are characteristic of certain types of fuel. Alternatively or in addition, reopening can be assessed after the initial closing. If a normally closed pressure control valve is used, the opening behavior is evaluated when it is initially opened. For this purpose, the opening process is carried out with a specified current curve, the opening behavior is determined and compared with values stored in the control unit that are characteristic of certain types of fuel. As an alternative or in addition, the reclosing can be assessed after the initial opening.

The method according to the invention is advantageously carried out after a refueling process and the information derived therefrom is stored at least until the next refueling process. A change in the fuel composition is recognized immediately and can be taken into account when metering fuel. The derived information, that is to say the type of fuel and / or the at least one fuel property, is preferably stored, preferably in a control device, for example in the engine control device.

To achieve the object mentioned at the beginning, a control device is therefore also proposed which is set up to execute the method according to the invention or at least one method step of the method according to the invention.

The invention is explained in more detail below with reference to the accompanying drawings. These show:

1 shows a fuel injection system for supplying an internal combustion engine with fuel, which can be operated according to a method according to the invention,

2 shows a schematic longitudinal section through a pressure control valve for a fuel in the spray system,

3 shows a diagram for the graphic representation of the dynamic behavior of direct current magnets during a switching cycle, and FIG

Fig. 4 is a diagram to graphically depict the relationship between valve closing time and fuel viscosity. Detailed description of the drawings

1 shows a fuel injection system 1 which is suitable for implementing the method according to the invention. The fuel injection system 1 comprises a tank 8 for storing fuel. With the help of an electric fuel pump 9, which in the present case is arranged in the tank 8, the fuel is supplied from the tank 8 via a low-pressure line 19 to a high-pressure pump 2. The fuel passes through a fuel filter 11 arranged in the low pressure line 10. The fuel compressed by the high pressure pump 2 is fed via a high pressure line 12 to a high pressure accumulator 3 to which several injection valves 13 are connected. With the aid of the injection valves 13, fuel is injected from the high-pressure accumulator 3 into a combustion chamber of an internal combustion engine (not shown). The injection pressure is predetermined by the pressure in the high pressure accumulator 3. To regulate the pressure, a pressure regulating valve 4 is arranged on one end of the high-pressure accumulator 3. The pressure regulating valve 4, the injection valves 13 and the high-pressure pump 3 are connected to a control unit 7 via control lines 14. Another STEU line 14 is connected to a pressure sensor 15 arranged on the high pressure accumulator 3.

To carry out the method according to the invention, the pressure regulating valve 4 provided on the high pressure accumulator 3 is required in particular. A suitable pressure regulating valve 4 is shown in FIG. 2 by way of example. The pressure control valve 4 presented in FIG. 2 has an electromagnet 5 with an annular magnet coil for acting on a lifting magnet armature 16, which in the present case is designed as a flat armature. However, this is not absolutely necessary, so that a pressure control valve 4 is also suitable, which has a magnet armature 16 operating according to the plunger armature principle. The lifting magnet armature 16 is connected to a bolt-shaped valve member 6, so that the magnet armature 16 and valve member 6 move together. With the help of the valve member 6, a valve ball 17 can be actuated, in particular pressed into a valve seat 18. Since the illustrated pressure control valve 4 is designed as a normally open valve, the electromagnet 5 must be energized to close the valve. With the energization of the electromagnet 5, a Mag netfeld builds up, the magnetic force F _{M of} the magnet armature 16 against the spring force FF of a spring 19 and against a hydraulic pressure force FR in the direction of the solenoid and thus in the direction of the valve seat 18.

The valve member 6 connected to the magnet armature 16 is carried along and thereby presses the valve ball 17 into the valve seat 18. The pressure control valve 4 closes.

Since the valve member 6 moves in the fuel, in addition to the aforementioned forces FM, FF and FR, other forces act on the valve member 6. These are frictional forces that vary in size depending on the viscosity of the fuel. The closing and opening behavior of the pressure regulating valve 4 also changes with the viscosity of the fuel. If this is not taken into account during the operation of the fuel injection system when metering fuel, this has a negative effect on the metering accuracy.

In order to counteract this, according to the method according to the invention, the pressure control valve 4 shown in FIG. 2 is initially closed before the engine is started and the type of fuel and / or at least one fuel property is derived from the closing behavior. With knowledge of the type of fuel and / or the at least one fuel property, the injection parameters can be adapted so that the metering accuracy increases.

The closing process or the energization of the electromagnet 5 is carried out with a voltage established for the switching cycle. This is shown as curve A in FIG. 3 by way of example. The resulting current curve in the electromagnet 5 is illustrated by curve B in FIG. After a first period of time, which corresponds to the tightening time ti, this shows a clear “kink”. Because after an ascent and a descent, the curve suddenly rises again. The “kink”, which can be traced back to inductive effects, corresponds to the point in time at which the valve member 6 reaches its end position and the valve ball 17 closes the valve seat 18. The "kink" thus enables the closing time to be determined. Since the start of the pull-in time ti is also known, the closing time can be determined via the pull-in time t1 and compared with values that are characteristic of various fuels and stored in the control unit 7. The stroke of the valve member 6 is given in FIG. 3 by the curve C again. The curve C shows that the valve member 6 only changes with a time Delay sets in motion. However, this is irrelevant if the comparison values are also based on the tightening time ti.

Instead of the pull-in time ti, a fall time Ϊ2 can also be evaluated. The course of curve B is opposite to that of the pull-in time ti. Here, too, when a stroke stop is reached by the valve member 6, a “kink” in the course of curve B is indicated, so that the reopening time can be determined in this way.

With the aid of the illustration in FIG. 4, it should be made clear that the closing or opening duration when the pressure regulating valve 4 opens again increases as the viscosity of the fuel increases. The measurements were carried out with three different fuels, the measured values showing that there are differences between the fuels. The present invention makes use of this.

In FIGS. 1 to 4, reference is made in each case to a pressure control valve 4 which is designed as a normally open valve. However, this is not absolutely necessary. This means that the pressure regulating valve 4 can also be designed as a normally closed valve. When carrying out the method according to the invention, the pressure regulating valve 4 is not initially closed before the engine is started, but rather opened initially.

Regardless of whether the pressure regulating valve 4 is designed as a normally open or normally closed valve, the magnetic force of the electric magnet 5 should not be supported by a spring 19. If a Fe of 19 is provided, the spring force FF should counteract the magnetic force FM of the Elekt romagneten 5, otherwise the implementation of the fiction, contemporary method is not possible.

Claims

Expectations

1. A method for operating a fuel injection system (1), in particular a common rail injection system, for supplying a combustion engine with fuel, in which fuel is conveyed to high pressure with the aid of a high pressure pump (2) and fed to a high pressure accumulator (3) and at which the pressure in the high-pressure accumulator (3) is regulated with the aid of a pressure regulating valve (4) arranged on the high-pressure accumulator (3), characterized in that the pressure regulating valve (4) is initially closed and / or opened before the engine starts and from the closing and / or opening behavior, a type of fuel or at least one fuel property, in particular the viscosity of the fuel, is derived.

2. The method according to claim 1, characterized in that for the initial closing and / or opening of the pressure regulating valve (4) an electromagnet (5) is energized, the magnetic force of which acts on a reciprocating valve member (6) of the pressure regulating valve (4).

3. The method according to claim 2, characterized in that the current curve when energizing the electric magnet (5) is determined and compared with stored, for certain types of fuel cha characteristic current curves, which are preferably stored in a control device (7).

4. The method according to any one of the preceding claims, characterized in that the evaluation is carried out with the aid of artificial intelligence and / or neural networks.

5. The method according to any one of the preceding claims, characterized in that the current fuel temperature is determined and taken into account in the fuel detection.

6. The method according to any one of the preceding claims, characterized in that a normally open pressure control valve (4) is used and the closing behavior during the initial closing and / or the opening behavior is evaluated during the subsequent reopening.

7. The method according to any one of claims 1 to 5, characterized in that a normally closed pressure control valve (4) is used and the opening behavior during initial opening and / or the closing behavior during subsequent reclosing is evaluated.

8. The method according to any one of the preceding claims, characterized in that the method is carried out after a refueling process and the information derived therefrom is stored at least until the following refueling process.

9. Control device (7) which is set up to carry out a method or at least one method step of a method according to one of the preceding claims.