EP1325222B1 - Method for diagnosing a valve in a fuel supply system of an internal combustion engine - Google Patents

Abstract

The invention relates to a method for diagnosing a valve in a fuel supply system of an internal combustion engine. A first pump pumps fuel out of a fuel reservoir into a first fuel line in a first pressure area. The fuel is pumped from said first pressure area into a pressure accumulator in the second pressure area by a second pump. The fuel pressure in the pressure accumulator is determined by means of a pressure sensor. The pressure in the second pressure area is regulated and/or controlled with a pressure regulation and/or pressure control means, the fuel flowing out of the second pressure area and into a second fuel line via said pressure regulation and/or pressure control means. The valve is used to increase pressure in the first pressure area.

Description

The invention relates to a method for diagnosing a valve in a fuel supply system of an internal combustion engine, wherein with a first pump fuel is conveyed from a fuel tank into a first fuel line in a first pressure range. The fuel is conveyed by means of a second pump from the first pressure range in a pressure accumulator in the second pressure range, wherein the fuel pressure is determined in the pressure accumulator by means of a pressure sensor. With a pressure control and / or pressure control means, the pressure in the second pressure range is controlled and / or controlled, wherein the fuel flows from the second pressure range via the pressure regulating and / or pressure control means in a second fuel line. The valve serves to increase the pressure in the first pressure range.
The invention also relates to a corresponding diagnostic system for diagnosing a valve in a fuel supply system of an internal combustion engine, a corresponding control device for an internal combustion engine, a corresponding computer program with program code means and a corresponding computer program product with program code means.

State of the art

From DE 195 39 885 A a generic fuel supply system for a direct injection high-pressure internal combustion engine with a first and a second fuel pump is known. There is provided a valve means for generating an increased boost pressure for the second fuel pump. This boost pressure increase is usually controlled temporarily during a startup phase of the internal combustion engine in order to compress possible vapor bubbles in the fuel system or to flush the fuel system before the actual start of the internal combustion engine.

It is also known to subject a generic valve in a fuel supply system to an electrical diagnosis, wherein various errors can be determined. These faults include a cable drop, a short to ground, and a short to battery voltage.

From EP 1 008 741 A2 a fuel injection system with a fuel pump and two pressure accumulators is known in which the one fuel pump delivers fuel into a first pressure accumulator and from there the fuel is fed via a valve to an injection valve. A malfunction of this valve is detected when the fuel pressure downstream of the valve is outside a reference pressure range.

Object of the invention

The invention has for its object to improve a method for diagnosing a valve in a fuel supply system of an internal combustion engine and a corresponding diagnostic system of the type mentioned. This object is achieved by the feature combination of the independent claims. Advantageous developments emerge from the subclaims.

Compared with the prior art, the methods according to the invention have the great advantage that a reliable diagnosis of the valve is possible without integrating additional hardware sensor technology into the internal combustion engine.

In particular, fault conditions (valves that clamp in the open, closed or any state) that can not be detected with a diagnosis according to the prior art can be detected.

Of particular importance is the realization of the method according to the invention in the form of a control device for an internal combustion engine, in particular of a motor vehicle. In this case, means for carrying out the steps of the method described above are provided.

Of particular importance are also the implementations in the form of a computer program with program code means and in the form of a computer program product with program code means. The computer program according to the invention has program code means for carrying out all steps of the method according to the invention when the program is executed on a computer, in particular a control unit for an internal combustion engine of a motor vehicle. In this case, the invention is thus realized by a program stored in the control unit, so that this control unit provided with the program represents in the same way the invention as the method to whose execution the program is suitable. The computer program product according to the invention has program code means which are stored on a computer-readable data carrier in order to carry out the method according to the invention when the program product is executed on a computer, in particular a control unit for an internal combustion engine of a motor vehicle. In this case, therefore, the invention is realized by a data carrier, so that the inventive method can be performed when the program product or the data carrier is integrated into a control device for an internal combustion engine, in particular a motor vehicle. As disk or as Computer program product can be used in particular an electrical storage medium, for example a read-only memory (ROM), an EPROM or a permanent electrical memory such as a CD-ROM or DVD.

embodiment

The invention will be explained below with reference to an embodiment.

1 a and 1 b show generic fuel supply systems of an internal combustion engine,
Figures 2a, 2b and 2c show measured values in the execution of a method according to the invention and
FIG. 3 shows an exemplary embodiment of a method according to the invention.

Figure 1.a shows a generic fuel supply system. Starting from a fuel tank or a tank 3, the fuel is conveyed from the tank 3 into a first fuel line 1 with an electric fuel pump EKP. In the electric fuel pump EKP is usually a Pressure relief valve DBV integrated. The conveyed by the electric fuel pump EKP in the first pressure range 1 fuel is transported by means of a high-pressure pump HDP from the first pressure range 1 in a pressure accumulator Fuel Rail. In the pressure accumulator fuel rail, a pressure sensor DS is arranged, which detects pressure values from the second pressure range or the pressure accumulator Fuel Rail and forwards this pressure data to a not shown in Figure 1.a engine control unit. On the basis of the measured values detected by the pressure sensor DS, the control unit will carry out the method according to the invention for the diagnosis of a valve in a fuel supply system of an internal combustion engine, which will be explained below in the context of FIGS. 2a, 2b, 2c and 3. In the second pressure range, or arranged directly on the pressure accumulator Fuel Rail, there is a pressure control and / or pressure control means DSV, by means of which the pressure in the second pressure range or in the pressure accumulator Fuel Rail is regulated and / or controllable. In this embodiment, the pressure regulating and / or pressure control means is designed as a pressure control valve DSV, which is controlled by the engine control unit. The fuel, which flows from the pressure accumulator Fuel Rail via the pressure regulating and / or pressure control means DSV or the pressure control valve DSV, enters a second fuel line 2, or back into the first pressure range. In the further course of the second fuel line 2, a pressure regulator DR is arranged before the fuel returns to the tank 3. Between the first fuel line 1 and the second fuel line 2, a shut-off valve ASV is arranged, which connects the fuel lines 1 and 2 in the open state, while the ASV interrupts the connection in a closed state. In the design of the fuel supply system, the pressure limiting valve, which is integrated into the electric fuel pump EKP, dimensioned so that the Pressure relief valve DBV has a higher pressure response than the integrated pressure in the fuel line 2 pressure regulator DR, the function of the shut-off valve ASV is as follows:

When the shut-off valve ASV is opened, the pressure regulator DR is the means which determines the pressure in the first pressure range. This pressure in the first pressure range simultaneously represents the admission pressure for the high-pressure pump HDP, which conveys the fuel from the first pressure range to the second pressure range.

If, however, the shut-off valve ASV is closed, the decisive means which is responsible for the pressure setting in the first pressure range, the pressure relief valve DBV, which is integrated into the electric fuel pump EKP.

When the engine is warm, which is considered below as the normal state of the internal combustion engine, the shut-off valve is opened and the pressure in the first pressure range is determined by the pressure regulator DR in the fuel line 2. The pressure relief valve DBV, which is integrated in the electric fuel pump EKP, is in this case without function. In certain exceptional situations, such as during a cold start or a hot start, a temporary increase in pressure in the first pressure range or an increase in pressure of the form of the high-pressure pump HDP is required. In this state of emergency, the shut-off valve ASV is closed and the pressure limiting valve DBV in the electric fuel pump EKP responds. In this way, a higher admission pressure for the high-pressure pump HDP is realized. Particularly in hot start and hot idle situations, this increased pre-pressure prevents or reduces the formation of vapor bubbles in the hot fuel system, in particular in the high-pressure pump HDP.

Due to the higher pressure, the fuel system can be "purged" faster and existing vapor bubbles can be better compressed.

1. 1. Das Absperrventil ASV klemmt in geöffnetem Zustand. In diesem Zustand ist keine Druckerhöhung im ersten Druckbereich mehr möglich, was zu einer Dampfblasenbildung beim Heißstart und Heißleerlauf im Kraftstoffversorgungssystem führen kann. Im schlimmsten Fall kann es durch die Dampfblasenbildung zu einer Verhinderung des Hochdruckaufbaus kommen, wodurch die benötigten Kraftstoffmengen nicht mehr zugemessen werden können, das Gemisch magert aus und die Abgase verschlechtern sich. Im schlimmsten Fall würde der Motor des Kraftfahrzeugs ausgehen.
2. 2. Das Absperrventil ASV klemmt im geschlossenen Zustand. Dieser Zustand hätte die Folge, dass das Kraftstoffversorgungssystem ständig mit hohem Vordruck betrieben wird. Dies führt insbesondere zu einem erhöhten Verschleiß der Elektrokraftstoffpumpe EKP, was wiederum die Lebensdauer der Elektrokraftstoffpumpe EKP deutlich verringert. Es kann unter Umständen vorkommen, dass die Elektrokraftstoffpumpe EKP bei permanent erhöhtem Druck die Volllastmenge nicht mehr fördern kann, wodurch der Vordruck einbrechen kann. Zudem führt der ständige Betrieb mit hohem Vordruck zu einer erhöhten Geräuschentwicklung und zu einem erhöhten Verschleiß der Dichtungen an der Hochdruckpumpe HDP.

A diagnosis of the shut-off valve ASV according to the method according to the invention, which is explained in the other figures, significantly increases the operational reliability of the fuel supply system. If the diagnosis is not carried out, for example, the following errors could not be detected:

1. 1. The shut-off valve ASV jams in the opened state. In this state, no pressure increase in the first pressure range is possible, which can lead to a vapor bubble formation during hot start and hot idle in the fuel supply system. In the worst case, it may come through the formation of steam bubbles to prevent the high pressure build-up, whereby the required fuel quantities can no longer be measured, the mixture is leaning out and the exhaust gases deteriorate. In the worst case, the engine of the motor vehicle would go out.
2. 2. The shut-off valve ASV jams in the closed state. This condition would have the consequence that the fuel supply system is constantly operated with high admission pressure. This leads in particular to increased wear of the electric fuel pump EKP, which in turn significantly reduces the life of the electric fuel pump EKP. Under certain circumstances, it may happen that the electric fuel pump EKP can no longer deliver the full load when the pressure is constantly increased, as a result of which the admission pressure can break. In addition, the constant operation with high pressure leads to increased noise and a increased wear of the seals on the high-pressure pump HDP.

These fault conditions can be detected reliably with the method according to the invention for the diagnosis of a valve, which is a prerequisite for the initiation of countermeasures.

Figure 1.b shows a very similar fuel supply system as Figure 1.a. Here, the same objects with the same reference numerals as in Figure 1.a are marked. In contrast to FIG. 1 a, the pressure regulator DR and the shut-off valve ASV are arranged differently in FIG. 1 b. In the connection between the first fuel line 1 and the second fuel line 4, the pressure regulator DR is integrated here in addition to the shut-off valve ASV. The function is analogous to Figure 1.a as follows:

When the shut-off valve ASV is opened, the pressure regulator DR is the means which determines the pressure in the first pressure range.

If, however, the shut-off valve ASV is closed, the decisive means which is responsible for the pressure setting in the first pressure range, the pressure relief valve DBV, which is integrated into the electric fuel pump EKP.

The sequence of the arrangement of pressure regulator DR and shut-off valve ASV is not essential to the invention.

Another alternative is shown in Figure 1.b by the dashed lines shown fuel line 5. In this case, in which instead of the fuel line 4, the fuel line 5 is used, the pressure regulator DR and the shut-off valve ASV in the connecting line between the first fuel line 1 and the tank 3 used. The function is as follows:

When the shut-off valve ASV is opened, the pressure regulator DR is the means which determines the pressure in the first pressure range.

If, however, the shut-off valve ASV is closed, the decisive means which is responsible for the pressure setting in the first pressure range, the pressure relief valve DBV, which is integrated into the electric fuel pump EKP. FIGS. 2 a, 2 b and 2 c show measured values during the evaluation or execution of the method according to the invention for the diagnosis of a shut-off valve ASV in a fuel supply system of an internal combustion engine.

Figure 2a shows the time course of the duty cycle tadsv of the Druchsteuerventils DSV according to Figure 1. The duty cycle can assume values between 0 and 1, where 1 means that the duty cycle of the pressure control valve DSV is 100% or that the pressure control valve DSV fully operated in the open state becomes what is the case in the representation of Figure 2a over the entire time course.

In Figure 2b, the time course of the fuel pressure in the pressure accumulator Fuel Rail is shown. The fuel pressure prist is detected according to FIG. 1 with the pressure sensor DS and transmitted to an engine control unit (not shown in FIG. 1).

Figure 2c shows the time course of the engine speed nmot.

The measured values shown in FIGS. 2a, 2b and 2c have been recorded during a pushing operation. The The method according to the invention is explained below with reference to the times t1 to t11 marked in the figures.

At the times t1, t2 and t3, the pressure in the pressure accumulator Fuel Rail is measured when the shut-off valve ASV is open. These pressure values are transmitted to the engine control unit, which forms an average value from the measured pressure values. At time t4, the shut-off valve ASV is actuated in order to bring the shut-off valve ASV into a closed state. The times t5, t6 and t7 correspond to a waiting time, which has to be waited as a result of the method, until the pressure in the fuel rail has increased due to the closed shut-off valve ASV. After the pressure has been increased, pressure values with the pressure sensor DS are again detected at the times t8, t9 and t10 and likewise transmitted to the engine control unit. The engine control unit now also forms an average value from these pressure values. It can now be checked by the engine control unit, whether the difference or the amount of the difference between those at the times t1, t2, t3 and at the times t8, t9, t10 measured pressure values exceeds an applicable threshold. Exceeds the difference or the amount of an applied threshold, it can be concluded that a proper function of the shut-off valve. At time t11, the shut-off valve ASV is opened and the diagnostic process is completed.

The basic principle of the diagnostic method is that the pressure in the fuel rail Fuel Rail practically has the pressure of the first pressure range due to the open pressure control valve DSV after a sufficiently long waiting time or a time of pressure reduction in the fuel rail.

FIG. 3 shows an exemplary embodiment of the method according to the invention for the diagnosis of a valve in a fuel supply system of an internal combustion engine. In a step 301, it is first checked whether the conditions for the start of the diagnostic system are fulfilled. Only if these conditions are met is the process continued; otherwise it will continue to check whether the conditions for the diagnosis exist. The internal combustion engine must be in a predetermined operating state for carrying out the method according to the invention for the diagnosis of the shut-off valve. This can be in addition to the state of Schubabschaltens example, the start of the engine, the idle, the flow of the electric fuel pump or the time during a Steuergerätenachlaufs after switching off the engine.

In addition to the conditions mentioned for the diagnosis enable, it is necessary that the engine temperature is greater than an applicable threshold value and that the engine speed is less than a certain threshold value. The latter, that is, the engine speed is less than a certain threshold, is required so that the back pressure on the pressure control valve DSV, which is speed-dependent, must be significantly lower than the fuel pressure with the shut-off valve closed ASV, so that a pressure stroke when switching the shut-off valve can be measured.

If these conditions are satisfied, the process proceeds to step 302 where the pressure control valve DSV is opened. Furthermore, a sufficiently long time is waited in step 302 until the pressure in the pressure accumulator Fuel Rail approximately approaches the pre-pressure by the open pressure control valve DSV Has. If this has happened, the shut-off valve ASV is opened in step 303. In step 304, one or more pressure values are detected in the pressure accumulator with the pressure sensor DS, which corresponds in practice to a pre-pressure measurement. In FIG. 3, the repeated or multiple measurements are indicated by a dashed line. When acquiring a plurality of measured values, averaging of the measured data is expediently carried out. The averaging has the advantage that measured values can also be compared if there are different numbers of measured values. After at least one measured value of the admission pressure with opened shut-off valve ASV has been detected in step 304, the method proceeds to step 305. In step 305, the shut-off valve is closed. In the subsequent step 306, a time loop is passed, which is dimensioned such that the admission pressure can increase due to the closed shut-off valve ASV. This time corresponds to the times t5, t6 and t7 according to FIG. 2b.

After passing the time loop in step 306, the method proceeds to step 307. In step 307, analogously to step 304, one or more pressure values in the pressure accumulator Fuel Rail are detected by means of the pressure sensor DS and transmitted to an engine control unit. In the engine control unit, averaging is also carried out here in the event that several measured values have been detected. Also in step 307 the detection of several measured values is indicated by the dashed line.

In the subsequent step 308, the difference between the recorded pre-pressure values after step 307 and step 304 is compared with an applicable threshold value. The applicable threshold is chosen according to the invention, that it is safely exceeded in the event of proper operation of the shut-off valve ASV.

Alternative embodiments, which are likewise within the scope of the method according to the invention, could be that initially measured values are recorded when the shut-off valve is closed and only then are measured values at an opened shut-off valve. In addition to checking whether an applicable threshold is exceeded by the difference or the amount of the difference between the measured forms, further evaluation criteria can be used. At this point, only the time change or the gradient of the pressure change in the fuel rail is mentioned as an example.

If it is determined in step 308 that the admission pressure difference is not smaller than an applicable threshold value, that the shut-off valve thus has a proper function, it is determined in step 309 that there is no error. After step 309, the diagnostic process is ended in step 310.

For example, after this step 310, the method may begin again in step 301; Also, a memory entry can be made in the control unit, that the shut-off valve ASV has a proper function.

If, on the other hand, it is determined in step 308 that the admission pressure difference is smaller than the applicable threshold value, an error of the shut-off valve ASV is concluded and an error entry in a memory of the control device is made in step 311. Such an error entry can be read in a maintenance of the motor vehicle in a workshop to be able to determine the existence of the error in retrospect.

In step 312, subsequent to step 311, measures are taken which visually or acoustically display the error for the driver of the motor vehicle and / or initiate measures in the engine control system which counteract the malfunction of the shut-off valve ASV. After step 312, also in this branch of the method, the method is ended and proceeds to step 310, with which the diagnostic method is ended.

In a development of the method according to the invention, it is possible, in addition to the comparison of the admission pressure difference with an applicable threshold value, to determine the absolute values of the measured forms. By this measure, it would be possible to determine by the diagnostic method not only that the shut-off valve ASV is disturbed in its function, but it could be determined whether the shut-off valve ASV jammed in the open or closed state or is defective. In this case, when the shut-off valve ASV is clamped in the closed state, there would tend to be higher pre-pressure values than when the shut-off valve is clamped in the open state.

The further embodiment of the fuel supply systems shown in FIGS. 1.a and 1.b hereby is not essential to the invention. For example, a throttle may be provided in the fuel system, which ensures a controlled pressure reduction in the system after stopping the motor vehicle, or after deactivation of the internal combustion engine and thus of the fuel supply system. Furthermore, filters may be inserted into the fuel lines at various points of the fuel supply system, for example behind the EKP.

Claims (12)

1. Method for diagnosing a valve (ASV) in a fuel supply system of an internal combustion engine, fuel being fed from a fuel reservoir (3) into a first pressure region by means of a first pump (EKP), the fuel being fed from the first pressure region into a second pressure region by means of a second pump (HDP), the fuel pressure in the second pressure region being determined by means of a pressure sensor (DS), the valve (ASV) serving to increase the pressure in the first pressure region, characterized in that before the diagnostic method begins the pressure closed-loop and/or pressure open-loop control means (DSV) in the second pressure region is placed in an opened state, in that at least the valve position (ASV) is changed, in that the fuel pressure in the second pressure region is sensed at least before and after the valve adjustment (ASV), and in that a faulty state of the valve (ASV) is determined from the acquired pressure data.
2. Method according to Claim 1, characterized in that the diagnostic method is carried out only in specific operating states and/or under specific operating conditions of the internal combustion engine.
3. Method according to Claim 2, characterized in that the specific operating states are at least the starting of the internal combustion engine and/or the idling of the internal combustion engine and/or the time of a primary flow of the first pump (EKP) and/or the state of overrun deactivation of the internal combustion engine and/or a control device run on after the internal combustion engine has been switched off.
4. Method according to Claim 2, characterized in that the specific operating conditions are at least a minimum engine temperature and/or a maximum engine speed and/or a maximum pressure in the second pressure region.
5. Method according to Claim 1, characterized in that after the pressure closed-loop and/or pressure open-loop control means (DSV) has been opened, the diagnosis is not carried out until the pressure in the second pressure region has approximately reached the pressure value of the first pressure region.
6. Method according to Claim 1, characterized in that a fault state of the valve (ASV) is determined if the difference between the pressure values measured before and after the valve adjustment (ASV) exceeds an applicable threshold value.
7. Method according to Claim 1, characterized in that in each case a multiplicity of pressure values which are each summed and/or averaged is measured before and after the valve adjustment (ASV).
8. Method according to Claim 1, in which the fuel from the second pressure region flows off into a second fuel line (2, 4) via the pressure closed-loop and/or pressure open-loop control means (DSV), the valve (ASV) connecting the first fuel line (1) and the second fuel line (2, 4) in an opened state and disconnecting the connection in a closed state.
9. Method according to Claim 1, in which the pressure in the second pressure region can be closed-loop and/or open-loop controlled using a pressure closed-loop and/or pressure open-loop control means (DSV), the fuel from the second pressure region flowing off into a second fuel line (5) via the pressure closed-loop and/or pressure open-loop control means (DSV), the valve (ASV) connecting the first fuel line (1) and the fuel reservoir (3) in an opened state and disconnecting the connection in a closed state.
10. Control device for an internal combustion engine, in particular of a motor vehicle, characterized in that means for carrying out the steps of the method according to at least one of Claims 1 to 10 are present.
11. Computer program with program code means for carrying out all the steps of any of Claims 1 to 10 if the program is run on a computer, in particular a control device for an internal combustion engine.
12. Computer program product with program code means which are stored on a computer-readable data carrier for carrying out the method according to any of Claims 1 to 10 if the program product is run on a computer, in particular a control device for an internal combustion engine.

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