DE102008024545A1 - Method for determining cause of defect in low pressure area of fuel injection system of internal combustion engine of motor vehicle, involves determining actual cause of defect by monitoring reaction of injection system to load step - Google Patents

Abstract

The method involves determining a value for rail pressure and/or a time characteristic of the rail pressure, and comparing with a predetermined threshold. A high load step i.e. torque jump, or a high rotational speed is controlled during a control mode, when the value complies with the predetermined threshold. Another value for the rail pressure and/or another temporal characteristic of the rail pressure is detected, and the actual cause of the defect is determined in the low pressure area by monitoring the reaction of a fuel injection system (1) to the load step i.e. torque jump. An independent claim is also included for a device for determining cause of defect in a low pressure area of a fuel injection system of an internal combustion engine.

Description

The The invention relates to a method and a device for determining a cause of failure in a low pressure area of one with a Low pressure range and a high-pressure region formed fuel injection system an internal combustion engine according to the preamble of the independent claims 1 and 7. It is already known that modern internal combustion engines are formed with a common rail injection system, as Essential component has a high-pressure accumulator (common rail). From the common rail lines go to one or more fuel injectors from that assigned to the individual cylinders of the internal combustion engine are. Often piezoelectric injectors are used with which a controllable multiple injection with pre and main injections and sometimes very short injection times feasible is. These injection systems are very complex and work with great precision.

kick However, if there is an error then it is very hard to do the actual thing Determine cause of this error. For example is the starting behavior bad or the internal combustion engine brings not the full power. Recognize known on-board diagnostic systems only during dynamic operating conditions to a limited extent a component error, e.g. B. an electrical short circuit. Because in the fault diagnosis may the exam can only be done in the way that the driving behavior of the motor vehicle does not adversely affect becomes. In addition, the location of a fault cause by the Variety of on-board components and sensor information in significant Dimensions is difficult.

So far However, for the reasons mentioned above, only an error message is generated and saved. The real one The cause of an error that has occurred is not automatic but in many cases by trial and error Exchanging individual modules, for example by replacing the pre-feed pump, the high-pressure pump, the fuel filter or detected and corrected by searching for leaks in a workshop. This procedure can be very time consuming and therefore costly. This also leads to unwanted components being replaced which are not faulty, so-called NTF components (no trouble found components).

From the DE 10031066 C2 a common rail injection system for an internal combustion engine and a method for operating the injection system is known. The injection system essentially has an accumulator in which the pressure accumulator existing in the pressure accumulator is detected by means of a pressure sensor. With the aid of a controllable actuator, a predetermined rail pressure is set in the accumulator. The controllable actuator is actuated by a control unit to adjust the pressure in the pressure accumulator. In this case, component-specific parameters for the pressure calculation are determined from at least two value pairs of the control signal and the associated measured rail pressure. A fault diagnosis on this injection system is not provided.

Of the Invention is based on the object in a fuel injection system to determine the cause of an error that occurred at a Low-pressure component of the fuel injection system occurs. This object is achieved with the characterizing features of independent claims 1 and 7 solved.

at the method or the device according to the invention to determine a cause of failure in a low pressure region of a Fuel injection system of an internal combustion engine with the characterizing Characteristics of the independent claims 1 and 7 results the advantage that with a simple test routine a faulty Component can be identified very easily. This can be a Repair done much faster and cheaper Be replaced as before, because not unnecessarily many components must be to find the actual cause of the error. By the targeted search of the actual cause of the error, the Number of NTF components can be advantageously reduced. Especially during the warranty period, there are significant cost savings for the manufacturer. It is considered particularly advantageous the determination of the actual cause of the error on a component can be done with a simple test routine. For error detection, the invention suffices Evaluation of the rail pressure and / or its time course two different operating conditions of the internal combustion engine in common rail.

By those listed in the dependent claims Measures are advantageous developments and improvements of indicated in the independent claims 1 and 7 Given the method or the device. Especially advantageous is that from monitoring the pressure drop of the rail pressure after the occurrence of the load jump on the proper function the high-pressure pump can be closed. exceeds the pressure drop a predetermined limit, then it can be assumed that the priming pump is not working properly, because it does not supply enough fuel after the injection, to reach the given rail pressure.

In Another embodiment of the invention is provided that after the Occurrence of the load jump the time course of the reconstruction monitored the rail pressure within a predetermined period of time becomes. When rebuilding the rail pressure takes longer than the predetermined period of time, then the pressure build-up of the Rail pressure too slow. That means that the fuel filter at least partially blocked and thus not the fuel is sufficient to a faster pressure increase in the common rail to effect.

One Another aspect of the invention is that for the Setting the first mode an idle speed specified which is given for example at 700 rpm. At this low speed, the load torque is very low, so that under stationary conditions can be achieved under these conditions can. In this steady state operation, a first measurement the rail pressure or its time course performed and the measured values are preferably stored. The recorded values are compared with preset limits to determine that at low speed or low load the injection system still working properly and thus other errors in the injection system can be excluded.

Farther is provided that for the low load of the first mode a low consumption mode is set, for example can be generated by a single main injection.

For the second mode is a high speed with at least 2000 Rpm. At the high speed and a big one Load torque has to deliver a corresponding amount of fuel become. Due to the high load requirement can in the second mode the easiest way to determine which bug is on a component exists in the low pressure range, for example, whether the feed pump is defective, the fuel filter is clogged and / or a leak present in the pipe system.

In Another embodiment of the invention is provided that the device the diagnostic unit is formed with an algorithm that in shape a software program is implemented in the diagnostic unit. The Software program is preferably in a parent Testing or monitoring program implemented, so no separate costs for training one additional hardware device are required.

The Diagnostic unit is preferably in an existing engine control unit fixed within the vehicle. Alternatively, it is intended to install the diagnostic unit in an external diagnostic device, to use it as a workshop device. This results the advantage that the test routine for determining the cause of the error controlled when the vehicle is stationary can. This avoids the test routine having a corresponding Torque jump requires, not unintentionally during the Operation of the vehicle may occur.

One Embodiment of the invention is in the drawing and will become more apparent in the following description explained.

1 shows an embodiment of the invention with a common rail injection system to which a diagnostic device can be connected via a plug connection,

2 shows a schematic representation of a block diagram of a diagnostic device according to the invention,

3 shows a flowchart for determining a cause of failure,

4a - 4c show three diagrams for the analysis of the pressure drop and

5a - 5c show three diagrams to analyze the recovery of the rail pressure curve after a load jump.

This in 1 illustrated embodiment of the invention shows a schematic representation of a fuel injection system 1 to which via a diagnostic connector 40 a diagnostic unit 30 is electrically connected. The injection system 1 has a prefeed pump 3 on, by a drive shaft 2 is mechanically driven and fuel from a fuel tank 5 via a fuel filter 3a and two check valves 4.1 . 4.2 sucks. Parallel to the output and input of the pre-feed pump 3 is a form control valve 6 arranged when exceeding a predetermined fuel pressure at the output of the feed pump 3 a part of the pre-feed pump 1 subsidized fuel and to the input of the feed pump 3 returns, so that the fuel pressure at the exit of the feed pump 3 is kept substantially constant in normal operation.

The pre-feed pump 3 is also the output side via a fuel line 7 and a flow control valve 17 with an input of a high pressure pump 8th connected. On the output side is the high-pressure pump 8th with a pressure accumulator 9 connected, which is referred to in the text as Common Rail. At the common rail 9 For example, there are four injectors 10.1 - 10.4 connected, via which the fuel with high pressure into the individual cylinders (combustion chambers) of the combustion motors is injected. The injectors 10.1 - 10.4 are preferably formed with a piezoelectric actuator. The injectors 10.1 - 10.4 are further with a return line 11 connected via the excess fuel via a return line 13 in the tank 5 is returned. At the high pressure pump 8th On the output side is the further a high pressure control valve 12 arranged that when exceeding a predetermined maximum rail pressure, a part of the high-pressure pump 8th funded fuel flow also via the return line 13 and a check valve 14 in the tank 5 returns.

At the common rail 9 is also a pressure sensor 15 arranged, the pressure and / or its time course in the common rail 9 detected, converted into a voltage signal and an electronic control unit 16 and an evaluation unit 24 supplies. The control unit 16 calculated using the evaluation unit 24 as a function of the measured rail pressure, a manipulated variable S, which on an electrical line to the high pressure control valve 12 is fed and thus the stationary high pressure in the common rail 9 regulates. The arrows shown on the fuel lines indicate the respective flow direction of the fuel. In the 1 lines without arrows, however, are designed as electrical control and supply lines.

So far For the most part, the components of the high-pressure range were described.

The low pressure range of the injection system will be explained in more detail below. From the exit of the feed pump 3 or the fuel line 7 leads to a housing inlet of the high-pressure pump 8th a purge line 6a with its second end in the housing inlet of the high-pressure pump 8th is guided. The one in the flushing line 6a flowing fuel part is used to cool the housing of the high-pressure pump 8th , Subsequently, the fuel is returned via the return lines 18 . 13 in the tank 5 recycled. In the flushing line 6a are a throttle 19 and a check valve 20 arranged. Furthermore, a membrane filter is parallel to it 21 and in two more check valves 22 . 23 arranged in a row. The membrane filter 21 serves to bleed the fuel line 7 over the housing of the high-pressure pump 8th ,

The Operation of this fuel injection system is known per se and does not need to be explained in detail.

Essential to the invention is that on the electronic control unit 16 a data output is arranged, via which the current rail pressure and / or its time course in the common rail 9 is available as electrical parameter. According to the invention it is provided that a connector is arranged, which serves as a diagnostic connector 40 is trained. To the diagnostic connector 40 is via electrical lines 32 . 35 ( 2 ) a diagnostic unit 30 connected. The diagnostic unit 30 can be designed in conjunction with an existing control unit of the internal combustion engine or the motor vehicle. The diagnostic unit 30 is essentially designed as a software program. The program contains an algorithm with which the current pressure values, pressure differences and the time profile of the rail pressure can be recorded and evaluated, as explained in more detail below.

2 shows a block diagram of a diagnostic unit according to the invention 30 , with a faulty component in the low-pressure region of the fuel injection system 1 can be detected reliably. The diagnostic unit 30 essentially has an evaluation unit 31 on, which is formed with a corresponding algorithm, as later 3 will be explained in more detail. The evaluation unit 31 receives via lines 32 the current rail pressure and saves it in a memory 34 depending on the time and possibly other parameters, such as the speed, the load torque and other parameters. Furthermore, the evaluation unit 31 with a block 33 connected, in which the algorithm according to the invention, control programs for switching to a second operating mode, etc. are stored. The evaluation unit 31 is designed essentially as a software program and is able to evaluate the one hand, the received pressure values of the rail pressure and on the other hand via lines 35 to control the combustion engine in different operating modes.

According to the invention, it is provided that the diagnostic unit 30 is preferably implemented in an existing engine control unit in the form of a software routine.

Alternatively, it is provided that the diagnostic unit 30 is designed as an independent diagnostic device for workshop operation, via the diagnostic connector 40 ( 1 ) to the fuel injection system 1 can be coupled. With this arrangement, a targeted troubleshooting can be performed in a specialist workshop without the normal operation of the motor vehicle is impaired while driving.

Over the lines 35 the test intervention can be activated. The evaluation unit 31 is also with an error output 36 connected, which is designed as a display. The display serves as an input and output device for controlling the fault diagnosis. With the help of the output unit 36 can preferably be based on the principle of an interactive dialogue on simple Way the sequence of fault diagnosis during the test run are controlled and controlled. After expiration of the test routine then an indication of the suspected faulty component in the low pressure region of the fuel injection system 1 output.

The following is the flowchart of the 3 the operation of the test routine according to the invention for determining a cause of error in a low pressure region of a fuel injection system explained in more detail. For the start of the test routine is necessary that the vehicle can still be started or the internal combustion engine can be operated. It is assumed that the vehicle is tested in a workshop, wherein the internal combustion engine is operated in a defined first operating mode at low speed or at low torque. It is envisaged that a low-consumption mode is used in which instead of a multiple injection, for example, only one main injection is activated. The speed is set as the idling speed, for example, to 700 rpm.

Corresponding 3 starts the program in position 50 with the fault diagnosis and checks in position 51 whether the engine was started. If this is not the case then the program jumps to position 50 back. In the other case, when the engine is running, is in position 52 Checks whether the stationary case at low speed, preferably the idle speed is set. The program waits until this stationary case has occurred. In position 53 a first measurement of the rail pressure and / or its time course is performed and recorded. In this case, the speed is preferably retained.

The first measurement of the rail pressure and its time course is provided, to determine that the injection system is at low load and lower Speed is still working properly. If that does not happen should, it is also conceivable that a suspected error, for example a missing maximum power, bad acceleration values or a poor starting behavior not with the components of the low pressure range the fuel injection system is looking for, but possibly with another module.

In the further procedure of the fault diagnosis, it is assumed that the internal combustion engine operates without errors in idle mode, so that in the flowchart with position 54 can be continued. In position 54 Now a load step is activated, in which a high speed, for example> 2000 U / min is specified with a corresponding load jump. In position 55 a second measurement is carried out, in which in turn the current rail pressure and / or its time course are detected and stored. Furthermore, other parameters such as speeds, load requirements, temperatures, etc. can be stored. The load jumps are quickly repeated in order to have correspondingly many measured values available for statistical evaluation methods. In position 56 an analysis of the measured rail pressure values or the time course of the individual load jumps is analyzed. In particular, the pressure difference after occurrence of the load jump in the common rail 9 and the temporal increase in the pressure curve analyzed in more detail, as later to the 4a to 4c respectively. 5a to 5c will be explained in more detail.

In position 57 it is queried whether the rail pressure drop has adhered to a predetermined limit. If this is the case, the program jumps to position at j 59 and is finished. Otherwise, the program jumps to position at n 58 and analyzes an error in the low pressure region of the injection system. For example, the cause of the error may be an at least partially clogged fuel filter 3a , a mistake in the pre-feed pump 3 or a leak can be determined.

The determination of a detailed cause of failure in the low pressure range is described below on the basis of 4a to 4c respectively. 5a to 5c explained in more detail. In the 4a to 4c three diagrams are shown above the time axis t. 4a shows the set speed curve N _SP (set point, setpoint speed) during the test phase. First, a low speed, for example, an idle speed N ₀ = 700 U / min is set. At the times t _1, t ₂ and t ₃ is in each case a load jump, in which the rotational speed N rises to ₁ at short notice. It then falls back to the speed N ₀ when the load jump was withdrawn. The curve 4b shows a corresponding curve of the torque T _Q , wherein the time axis t has remained the same. Every time the load jumps, the torque increases from the value T _Q1 to the value T _Q2 . The torque T _Q2 is given only as a short pulse, so that the torque falls back to the original value T _Q1 analogous to the speed N _SP .

The curve of 4c shows the part of the error analysis that is relevant for the evaluation. The curve of 4c are analogous to the 4a and 4b the course of the rail pressure PFU _mes again. For example, at time t ₁ , when the torque on the first load step increases to T _Q2 , the rail pressure in the common rail drops very sharply with a certain time delay until it reaches the value PFU ₃ . After completion of the load step, the rail pressure is built up again, and then reaches to a predetermined recharge the rail pressure PFU. ₁ As 4c can be further removed, the pressure drop may fall to a maximum of the value PFU ₂ in a properly functioning injection system. If the pressure drop were smaller than the difference PFU ₁ minus PFU ₂ , then there would be no error in the low pressure region of the injection system. In this embodiment, the amount of the pressure difference PFU ₁ -PFU _{3 is} greater than the predetermined maximum pressure difference PFU _max . It is therefore assumed that the pre-supply pump of the low-pressure region can not feed enough fuel into the common rail when a large load step occurs. It is therefore assumed that in this case there is an error on the pre-supply pump.

The point A on the curve of 4c shows the intersection with the lower allowable pressure value PFU ₂ . By repeatedly checking the pressure curve, it is very easy to hide a statistical error by weighting the individual measured values.

The 5a to 5c show a second embodiment of the inventive evaluation of the error analysis in the low pressure region of the injection system. The 5a to 5c correspond in their course those of 4a to 4c , However, only a single load jump is shown here on an enlarged scale. In 5a Therefore, in turn, the predetermined target speed N _{SP is} plotted against the time axis t for a single load step. First, the idle speed N _{0 is} set. At time t ₁ skips the speed to the higher value N _1, for example> 2000 U / min, as well as to 4a was explained. After completion of the load jump, the speed falls back to the original speed N ₀ .

5b shows the corresponding course of the torque T _Q. Due to the load step, the torque jumps from the value T _Q0 to the value T _Q1 and then falls back to the original value T _Q0 after a short time.

The curve of 5c now shows the corresponding course of the rail pressure in the common rail. First, until the time t _1, the rail pressure is constant and has the value PFU ₁ . After occurrence of the sudden load change of the control pressure is lowered to the value of the common rail ₃ PFU be -because partially emptied. After the load jump has subsided, the rail pressure rises again due to the delivery of the fuel through the high-pressure pump until it has reached the original rail pressure PFU ₁ at time t ₃ . According to the illustrated example, however, a time interval t ₂ minus t _{1 is given} as the limit range for the resurgence of the rail pressure curve. Corresponding 5c reaches the rail pressure at time t _2, however, only the rail pressure PFU. ₂ However, this rail pressure PFU ₂ is lower than the required rail pressure PFU ₁ . This means that too little fuel is supplied to the high-pressure pump. The rail pressure in the common rail thus increases too slowly. This is interpreted as an error in that the fuel filter 3a is at least partially clogged and thus too little fuel can be promoted by the feed pump in the system. In this case, for example, a partially-clogged fuel filter would be recognized as the cause of the error.

In Another embodiment of the invention is provided that both the pressure difference as well as the increase of the rail pressure for the interpretation of a fault in the low pressure area of the fuel system be evaluated. Depending on the findings, therefore, more Causes of errors in the low-pressure area of the fuel system as the cause of the error be recognized.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10031066 C2 [0004]

Claims (11)

Method for determining an error cause in a low-pressure region of a fuel injection system formed with a low-pressure region and a high-pressure region ( 1 ) of an internal combustion engine, wherein the fuel pressure in the low-pressure region, preferably by means of a prefeed pump ( 3 ) and the high pressure in the high pressure area by means of a high pressure pump ( 8th ) and as a rail pressure on a high-pressure accumulator, a common rail ( 9 ) is detected, characterized in that - to determine the cause of the fault in the low pressure range, the internal combustion engine is initially operated stationary at low load and / or low speed in a first operating mode, - that a first value for the rail pressure and / or a first time course of Recorded rail pressure and compared with predetermined limits, - that then, if the predetermined limits were met, in a second mode, a high load jump or torque jump or a high speed is driven, - that there is a second value for the rail pressure and / or a second the time course of the rail pressure is detected and - that the actual cause of the fault is determined in Niederduckbereich by monitoring the response of the injection system to the load jump or torque jump. A method according to claim 1, characterized in that a fault on the prefeed pump ( 3 ) is assumed, if after the occurrence of the load jump, the pressure drop of the rail pressure exceeds a predetermined limit ( 4c ). A method according to claim 1, characterized in that an error of an at least partially clogged fuel filter is assumed if, after the occurrence of the load jump, the time profile of the rebuilding of the rail pressure exceeds a predetermined period of time ( 5c ). Method according to claim 1, characterized in that that for the setting of the first mode, an idle speed, For example, 700 rpm is specified. Method according to claim 1, characterized in that that for setting the first mode, a low-consumption mode, For example, a main injection is specified. Method according to one of the preceding claims, characterized in that for the second mode the speed is at least 2000 rpm. Device for determining an error cause in a low-pressure region of a fuel injection system formed with a low-pressure region and a high-pressure region ( 1 ) of an internal combustion engine, with a prefeed pump ( 3 ), with a high-pressure pump ( 8th ) and designed with a common rail high-pressure accumulator ( 9 ), to which a pressure sensor ( 15 ), for a method according to one of the preceding claims, characterized in that - the device has a diagnostic unit ( 30 ) having an algorithm, - that the algorithm is adapted to control the internal combustion engine in two modes with at least two predetermined load conditions or speeds and thereby at least detect the rail pressure and / or its time course and - that from the pressure drop after a load jump or a Speed jump and / or from the time course of the recovery of the rail pressure curve, the actual cause of the error in Niederduckbereich can be determined. Apparatus according to claim 7, characterized in that the algorithm in the form of a software program in the diagnostic unit ( 30 ) is realized. Apparatus according to claim 7 or 8, characterized that the software program is stored in a higher-level test or monitoring program is implemented. Device according to claim 7, characterized in that the diagnostic unit ( 30 ) is fixedly mounted in an engine control unit within a vehicle. Device according to one of claims 7 to 9, characterized in that the diagnostic unit ( 30 ) is designed in an external diagnostic device for use as a workshop device.