EP1278949B1 - Method for operating a fuel supply system for an internal combustion engine, especially of an automobile - Google Patents

Abstract

The invention relates to a fuel supply system (1) for an internal combustion engine, especially of an automobile. In said fuel supply system (1), fuel can be pumped into a pressure accumulator (2) by a pump (6, 10). The pressure in said pressure accumulator (2) can be measured and can be controlled in such a way that an anticipated pressure (prbk) should result in the pressure accumulator (2). The pressure control valve (4) can be regulated to a predetermined value by means of a control device (16). Said control device (16) enables an anticipated pressure to be determined in the pressure accumulator (2) and enables the operativeness of the pressure control valve (4) to be determined based on the anticipated pressure and the measured pressure.

Description

State of the art

The invention relates to a method for operating a fuel supply system for an internal combustion engine, in particular of a motor vehicle in which fuel is pumped by a pump in a pressure accumulator, wherein the pressure in the pressure accumulator is measured, and wherein the pressure in the pressure accumulator by the control of a Pressure control valve is changeable. Such a method is known from US 5,727,515. Furthermore, the invention relates to a corresponding fuel supply system for an internal combustion engine and a control device for such a fuel supply system.

US-A-5 727 515 discloses a pressure control valve 40 which is associated with the accumulator 35 for control purposes, since it can adjust the pressure in the pressure accumulator 35; and this document discloses the detection of a failure of the pressure control valve (remaining in the closed or partially closed position, i.e. it is clogged) when the measured pressure deviates more than a threshold (delta1 / 2) from the (variable) expected pressure PI.

To an internal combustion engine, for example, a motor vehicle ever higher demands are made in terms of reducing fuel consumption and the exhaust gases generated at the same time desired increased performance. For this purpose, modern internal combustion engines are provided with a fuel supply system, in which the supply of fuel in the combustion chamber of the internal combustion engine electronically, in particular with a computer-aided control device, controlled and / or regulated. It is possible to use the fuel in one Inject air intake pipe of the internal combustion engine or directly into the combustion chamber of the internal combustion engine.

In particular, in the latter type, the so-called direct injection, it is necessary that the fuel is injected under pressure into the combustion chamber. For this purpose, an accumulator is provided, in which the fuel is pumped by means of a pump and placed under a high pressure. From there, the fuel is then injected via injection valves into the combustion chambers of the internal combustion engine.

Due, inter alia, to the high pressure, it is possible for components to damage the fuel supply system, e.g. due to aging change. Thus, it is possible that the pressure control valve, with which the pressure in the pressure accumulator can be controlled and / or regulated, gradually changes its functionality. It is also possible that the pressure control valve abruptly fails due to contamination. Such changes in the function of the pressure control valve can. Misfires or other faulty running of the internal combustion engine result.

Purpose and advantages of the invention

The object of the invention is to provide a method for operating a fuel supply system for an internal combustion engine, with which an error of the pressure control valve is detected quickly and safely.

This object is achieved in a method of the type mentioned by the features of claim 1.

There is a defined relationship between the control of the pressure control valve and the resulting pressure in the pressure accumulator. This relationship can be determined in advance for an intact pressure control valve. Thus, an expected pressure is known for each control, which would have to be set in an intact pressure control valve. This expected pressure and the actually measured pressure are used according to the invention to infer the operability of the pressure control valve.

With the invention, it is thus possible to detect a defect of the pressure control valve. The diagnostic method of the pressure control valve according to the invention can be carried out quickly and safely without much effort. The diagnostic method also has no negative influences on the running behavior of the internal combustion engine or on their pollutant emissions.

In the invention, the expected pressure is determined as a function of operating variables of the internal combustion engine, in particular as a function of the rotational speed of the internal combustion engine. This ensures that the dependence of the pressure in the pressure accumulator, e.g. is taken into account by the speed of the internal combustion engine. The higher the speed of the internal combustion engine, the higher the delivery of fuel and thus the pressure in the pressure accumulator. Such a consideration of the operating variables of the internal combustion engine thus substantially improves the diagnostic method according to the invention.

Furthermore, a pressure difference is determined from the expected pressure and the measured pressure, a pressure gradient is determined from the pressure difference, the pressure difference and / or the pressure gradient are compared with a threshold value, and the pressure control valve is detected as defective if the pressure difference and the pressure gradient exceeds the threshold.

It is particularly advantageous if the pressure control valve is opened in a linear manner or is closed, so that the pressure difference and / or the pressure gradient are approximately constant.

Further applications and advantages of the invention will become apparent from the following description of embodiments of the invention, which are illustrated in the figures of the drawing.

Embodiments of the invention

FIG. 1

shows a schematic representation of an embodiment of a fuel supply system according to the invention,

FIG. 2

shows a schematic block diagram of an embodiment of a method according to the invention for operating the fuel supply system of Figure 1, and

FIGS. 3a and 3b

show schematic diagrams with signals of the method of Figure 2 with intact and defective fuel supply system

In the figure 1, a fuel supply system 1 is shown, which is provided for use in an internal combustion engine of a motor vehicle. The fuel supply system 1 is a so-called common rail system which is used in particular in a direct injection internal combustion engine comes. Such common rail systems are known from gasoline, 1 as well as diesel internal combustion engines.

The fuel supply system 1 has a pressure accumulator 2, which is provided with a pressure sensor 3 and a pressure control valve 4. The accumulator 2 is connected via a pressure line 5 with a high-pressure pump 6. The high-pressure pump 6 is connected via a pressure line 8 to the pressure control valve 4. Via a pressure line 9 and a filter, the pressure control valve 4 and thus also the high pressure pump 6 is connected to a preferably electric fuel pump 10, which is adapted to suck fuel from a fuel tank 11.

The fuel supply system 1 has four injection valves 13, which are connected via pressure lines 14 to the pressure accumulator 2. The injection valves 13 are suitable for injecting fuel into corresponding combustion chambers of the internal combustion engine.

By means of a signal line 15, the pressure sensor 3 is connected to a control unit 16, to which further a plurality of other signal lines are connected as input lines. By means of a signal line 17, the fuel pump 10 and a signal line 18, the pressure control valve 4 is connected to the control unit 16. Furthermore, the injection valves 13 are connected by means of signal lines 19 to the control unit 16.

The fuel is pumped by the fuel pump 10 from the fuel tank 11 to the high-pressure pump 6. With the help of the high-pressure pump 6, a pressure is generated in the accumulator 2, which is measured by the pressure sensor 3 and can be adjusted by a corresponding actuation of the pressure control valve 4 to a desired value. about the injection valves 13, the fuel is then injected into the combustion chamber of the internal combustion engine.

Among other things, the pressure in the pressure accumulator 2 is essential for the dimensioning of the fuel quantity or fuel mass injected into the combustion chamber. The greater the pressure in the pressure accumulator 2, the more fuel is injected into the combustion chamber during the same injection time. This pressure in the pressure accumulator 2 can be adjusted and adjusted by the control unit 16.

For this purpose, the control unit 16 controls the pressure control valve 4 in its closed state, so that the high-pressure pump 6 and the fuel pump 10 generate an ever increasing pressure in the pressure accumulator 2. This increasing pressure can be measured by the pressure sensor 3.

The pressure control valve 4 is driven by a pulse width modulated signal. A duty cycle TV of 0% results in a completely closed pressure control valve 4, and at a duty cycle TV of 100%, the pressure control valve 4 is fully open.

There is a defined relationship between the pulse duty factor TV of the pressure control valve 4 and the pressure in the pressure accumulator 2. This relationship results from the opening cross-section of the pressure control valve 4, which adjusts itself at a certain duty cycle TV. The relationship can be determined in advance for a pressure control valve 4 working without errors and is stored in the form of a characteristic curve or a characteristic field in the control unit 16. To generate a desired pressure in the pressure accumulator 2, the pressure control valve 4 is driven on the basis of this relationship. Surrender between the desired pressure and the actual pressure measured by the pressure sensor 3 deviations, these deviations are corrected.

In addition to this regulation of the pressure in the pressure accumulator 2, the output of the control is monitored. If the value of the manipulated variable present at this controller output exceeds a predetermined threshold value, the fuel supply system 1 is identified as "possibly defective". This leads to starting a diagnostic procedure, which is described below.

After the diagnostic method has been started, the pressure control valve 4 is actuated with a pulse-width-modulated signal whose duty cycle TV has a first value. Thereafter, the duty ratio TV is changed from the first to a second value. The limited by the first and the second value range is selected such that the internal combustion engine does not have deteriorated driving behavior or even misfires of the internal combustion engine occur.

Due to the defined relationship between the duty cycle TV of the pressure control valve 4 and the pressure in the pressure accumulator 2, the change in the duty cycle TV has a change in the pressure in the accumulator 2 result.

An embodiment of the diagnostic method is shown in FIG. The signals resulting from this process are shown in FIGS. 3a and 3b. 3 a relates to an intact pressure control valve 4 and FIG. 3 b to a defective pressure control valve 4. The method illustrated in FIG. 2 is carried out by the control unit 16,

After the diagnostic process is started, in a block 20, the duty cycle TV is set, for example, to a first value TV1 of 35%. It is then measured in a block 21 of the currently measured by the pressure sensor 3 pressure prist in the pressure accumulator 2. This pressure prist is shown in Figures 3a and 3b.

By the control unit 16, a modeled pressure prbk is determined in a block 22, which takes into account the current operating variables of the internal combustion engine, such as their current speed, their engine temperature and the like. This pressure prbk is shown in FIGS. 3a and 3b.

In a subsequent block 23, the control unit 16 calculates a pressure difference dpr for which dpr = prbk-prist. Thereafter, a pressure gradient grddpr for the pressure difference dpr is calculated by the control unit 16 in a block 24. This pressure difference dpr and this pressure gradient grddpr are also shown in FIGS. 3a and 3b.

Now, in a block 25, the control unit 16 checks whether the amount of the pressure difference dpr exceeds a threshold value S1. If this is not the case, it is concluded that the pressure control valve 4 is not defective.

In a subsequent block 26, the duty cycle TV is then increased by one increment, for example by 1%. Thereafter, the controller 16 checks in a block 27 whether the duty ratio TV has reached a second value TV2 of, for example, 45%. If this is not the case, the diagnostic procedure is continued with the block 21 and the re-measurement of the pressure prist. If the second value TV2 of the duty cycle TV is reached, the diagnostic procedure is ended.

FIG. 3a is based on an intact pressure control valve 4. Thus, for example, for the value TV1 of the duty ratio TV, the pressure difference dpr between the measured pressure prist and the modeled pressure prbk is relatively small. In any case, the amount of Pressure difference dpr less than the threshold S1. This has the consequence that the diagnostic method of Figure 2, the blocks 21 to 27 passes through successively.

If the duty ratio TV is then incremented, nothing essential changes at the above pressure difference dpr. Furthermore, the amount of the pressure difference dpr remains smaller than the threshold value S1, and blocks 21 to 27 continue to pass through. This is repeated until the value TV2 of the duty ratio TV is reached.

In FIG. 3a, this results in a linearly increasing measured pressure prist and a linearly rising modeled pressure prbk. Due to the consideration of the current operating variables of the internal combustion engine, the slope of the modeled pressure prbk is approximately equal to the slope of the measured pressure prist. Thus, the pressure difference dpr remains relatively small. In any case, the pressure difference dpr in the intact pressure control valve 4 of Figure 3a always remains smaller than the threshold value S1.

Thus, it can be correctly concluded by the controller 16 by means of the method of Figure 2 in the figure 3a to an intact pressure control valve 4.

If, during one of the repetitions of the drip through the blocks 21 to 27, the amount of the pressure difference dpr exceeds the threshold value S1, this is determined by the control unit 16 in block 25. The method of FIG. 2 is then continued with a block 28, with which an observation period, Z, is started.

In a subsequent block 29, the control unit 16 checks whether the magnitude of the pressure gradient grddpr exceeds a threshold value S2. If this is the case, then closed by the controller 16 to an error of the pressure control valve 4 and the diagnostic method of Figure 2 is completed.

This case of the defective pressure control valve 4 is shown in FIG. 3b. There, the course of the measured pressure prist in the pressure accumulator 2 to a significant burglary, which is identified by the reference numeral 40. This break-in may result, for example, from jamming of the pressure control valve 4 due to contamination. The break-in 40 has the consequence that also the pressure difference dpr has a relatively large deflection, which is identified by the reference numeral 41. The same applies to the pressure gradient grddpr, which also has a relatively large deflection 42.

The amount of the pressure difference dpr is greater than the threshold value S1 in the region of the deflection 41. Thus, the block 28 of the method of Figure 2 is achieved. The magnitude of the pressure gradient in the region of the deflection 42 is also greater than the threshold value S2. This is recognized by the block 29 of Figure 2, that the pressure control valve 4 is defective.

If the magnitude of the pressure difference dpr is greater than the threshold value S1, but the magnitude of the pressure gradient grddpr is less than the threshold value S2, then in a block 30 the observation period Z is increased, e.g. incremented. In a subsequent block 31, the control unit 16 checks whether the observation time Z has reached a maximum value ZM.

If this is the case, then the method of FIG. 2 is continued with the block 26 and thus ultimately with the repetitions of the blocks 21 to 27. This case may occur when not with an intact pressure control valve 4 comprehensible reasons the amount of pressure difference dpr has exceeded the threshold S1 and thus at least the appearance of a defective pressure control valve 4 has been generated. By block 29 is then checked whether an error of the pressure control valve 4 actually exists. If this is not the case until the expiration of the maximum value ZM of the observation period Z, the return to the above-described test of the pressure control valve 4 with the aid of the block 25 is again returned.

If, in the block 31 of FIG. 2, the controller 16 determines that the maximum value ZM has not yet been reached, then in a block 32 the duty cycle is increased, e.g. incremented by 1%. Thereafter, it is checked in a block 33 whether the second value TV2 of the duty ratio TV has been reached. If this is the case, then the method of Figure 2 is completed. The blocks 32 and 33 correspond to the extent blocks 26 and 27th

If the second value TV2 of the duty ratio TV has not yet been reached, the current pressure prist in the pressure accumulator 2 is successively measured in block 34 with the aid of the pressure sensor 3, the modeled pressure prbk is determined as a function of the current operating variables of the internal combustion engine, and Pressure difference dpr and the pressure gradient grddpr calculated. The block 34 represents a summary of the blocks 21, 22, 23, 24 in this respect.

After block 34, the method of FIG. 2 is continued with block 29 and thus with the comparison of the amount of pressure gradient grddpr with threshold value S2. The blocks 29 to 34 are then repeated until either an error of the pressure control valve 4 is detected by the control unit 16, or the maximum value ZM of the observation period Z is reached or the second value TV2 of the duty cycle TV is achieved.

Overall, an error of the pressure control valve 4 is thus detected with the diagnostic method of Figure 2, if the amount of the pressure difference dpr and the amount of pressure gradient grddpr exceed respective thresholds S1, S2. If one of the threshold values S1, S2 is not exceeded, then the function of the pressure control valve 4 is closed by the control unit 16.

Claims (6)

1. Method for operating a fuel supply system (1) for an internal combustion engine, in particular of a motor vehicle, in which fuel is pumped by a pump (6, 10) into a pressurized reservoir (2), in which the pressure (prist) in the pressurized reservoir (2) is measured, and in which the pressure (prist) in the pressurized reservoir (2) can be altered by actuating a pressure control valve (4), characterized in that the pressure control valve (2) is actuated in such a manner that an expected pressure (prbk) in the pressurized reservoir (2) would have to result, in that the expected pressure (prbk) is determined as a function of operating variables of the internal combustion engine, in particular as a function of the engine speed of the internal combustion engine, in that a pressure difference (dpr) is determined from the expected pressure (prbk) and the measured pressure (prist), in that the pressure difference (dpr) is compared with a first threshold value (S1), in that the pressure control valve (4) is recognized as defective if the pressure difference (dpr) exceeds the first threshold value (S1), in that a pressure gradient (grddpr) is determined from the pressure difference (dpr), in that the pressure gradient (grddpr) is compared with a second threshold value (S2), and in that the pressure control valve (4) is recognized as defective if the pressure gradient (grddpr) exceeds the second threshold value (S2).
2. Method according to Claim 1, characterized in that the pressure control valve (4) is opened or closed in a linear way, and in that the pressure difference (dpr) and/or the pressure gradient (grddpr) are approximately constant.
3. Computer program, characterized in that it is programmed for use in a method according to one of the preceding claims.
4. Electrical storage medium for a control unit (16), characterized in that a computer program for use in a method according to either of Claims 1 and 2 is stored on it.
5. Control unit (16) for a fuel supply system (1), characterized in that it is designed for use in a method according to either of Claims 1 and 2.
6. Fuel supply system (1), in particular for a motor vehicle, having a control unit (16) which is designed for use in a method according to either of Claims 1 and 2.

Images