DE102013220814B3 - Diagnostic method and diagnostic device for detecting a defective fuel injector of an internal combustion engine - Google Patents

Abstract

A diagnostic method for detecting a defective fuel injector of an internal combustion engine, wherein the internal combustion engine is operable in a first operating state with an internal mixture formation of a fuel and is operable in a second operating state with an external mixture formation of a fuel and at least one fuel injector for generating the internal mixture formation in a combustion chamber comprising the internal combustion engine and having at least one fuel valve for generating the outer mixture formation outside the combustion chamber of the internal combustion engine, comprising the steps of: (a) analyzing (5) the running noise of the internal combustion engine in the first operating state and in the second operating state and thereby obtaining a first rough running value (LB) for the first operating state and a second rough running value (LG) for the second operating state, wherein the internal combustion engine in the first and in the second operation state is operated above a predetermined operating temperature; and (b) determining (6) a further analysis step for detecting a defect of the at least one fuel injector in dependence on the first and second rough running values.

Description

The invention relates to a diagnostic method and a diagnostic device for detecting a defective fuel injector of an internal combustion engine.

Basically, it is known that in internal combustion engines, the z. As are used in motor vehicles, fuel injectors are used in a fuel injection system for the fuel injection. Fuel injectors are complex components that z. B. can be designed as solenoid valve injectors or piezo injectors. Solenoid valve injectors are operated electromagnetically while the piezo injectors are operated piezoelectrically.

The task of the fuel injector is to meter the fuel and, by atomizing it, to achieve a mixing of combustion air with the fuel, thus ensuring optimum combustion in the combustion chamber of the internal combustion engine. Thus, fouling (eg, coking) that degrades atomization of the fuel or malfunction of a fuel injector typically results in deterioration of combustion of the air-fuel mixture in the combustion chamber of a cylinder of the internal combustion engine. This can, for example, lead to combustion misfires of the internal combustion engine, which is noticed, for example, in a rough running of the internal combustion engine.

Due to the complexity of the vehicles, fault detection, especially of the fuel injectors, is not an easy task. Typically, troubleshooting and diagnostics of combustion engine combustion faults are performed in workshops using testers with programs that allow guided troubleshooting. Due to the complexity of the injection system and internal combustion engine, however, it can lead to misdiagnosis, which can result in incorrect repairs to the vehicle.

Various methods for diagnosing errors of fuel injectors are known from the prior art.

From the publications DE 10 2010 043 150 A1 and 10 2007 038 537 A1 It is known to draw conclusions about their functionality due to resistance measurements on piezo injectors. However, these methods are complicated because they require a resistance measurement at the respective piezo injector. In addition, it is not readily possible to detect mechanical defects.

From the publication DE 10 2006 012 858 A1 For example, in a hybrid vehicle, it is known to detect combustion misfires of an internal combustion engine and to assist the detection of misfires by taking account of the rotational uniformity of an electric machine of the hybrid vehicle coupled to the internal combustion engine. This method is applicable only to hybrid vehicles.

A method for detecting ignition defects with the aid of exhaust gas values is known from the published patent application DE 38 35 285 A1 known.

From the publication 10 2005 049 069 A1 is a method for detecting errors in the mixture formation with the aid of the air ratio known.

A targeted troubleshooting to detect a fault of a fuel valve is disclosed in the publication DE 10 2008 041 406 A1 known. This method is suitable for bivalent designed internal combustion engines that are operable, for example. With gasoline and natural gas, and detects an error of the internal combustion engine depending on whether combustion misfires occur in gasoline mode or in natural gas operation. In addition, a failure of a fuel valve for gasoline or natural gas is detected by detecting misfiring in the gasoline or natural gas operation.

A device for operating an internal combustion engine with a diagnostic unit for determining a diagnosis characteristic value of a direct injection valve for the internal combustion engine is shown in the German Offenlegungsschrift DE 10 2012 204 332 A1 , The diagnostic characteristic value for an associated direct injection valve is determined as a function of a direct adaptation value for the respective cylinder.

The German patent application DE 102 15 906 A1 shows a method and apparatus for detecting a leak of a fuel valve in the fuel supply of an internal combustion engine. For this purpose, a shut-off valve is arranged in the fuel supply before the actual Gemischbildungs- or metering valves, which is open during normal operation of the engine and only closed when no injection or injection takes place. In addition, a sensor is arranged between the shut-off valve and the metering valves, with which a pressure drop is monitored during a Schubabschneidung the internal combustion engine. Based on the change in pressure can be concluded that the tightness of the downstream metering valves.

From the US 2013/02264437 A1 For example, an apparatus and a method for detecting an abnormal deviation of the air-fuel ratio between various cylinders of an internal combustion engine are known. From the abnormal deviation, it can be deduced that a fuel injector malfunctioned.

The European patent EP 0 754 845 B1 shows a method for detecting defective ignition or injection devices in internal combustion engines with multiple cylinders. The method is based on the detection of misfiring, which are detected by monitoring the smoothness of the engine.

Although various methods for detecting malfunctions in fuel injectors are known from the state of the art, there is still a need to improve these methods, since with the known methods a malfunction, in particular a mechanical malfunction, of a fuel injector is not recognized in certain situations.

Object of the present invention is to provide a diagnostic method and a diagnostic device for detecting a defective fuel injector of an internal combustion engine, which at least partially overcome the disadvantages mentioned above. This object is achieved by the diagnostic method according to the invention according to claim 1 and the diagnostic device according to claim 10.

Further advantageous embodiments of the invention will become apparent from the subclaims and the following description of preferred embodiments of the present invention.

An inventive diagnostic method relates to the detection of a defective fuel injector of an internal combustion engine. The internal combustion engine has a first operating state in which it is operable (exclusively) with internal mixture formation of a fuel, and a second operating state in which it is operable (exclusively) with external mixture formation of a fuel. The internal combustion engine has at least one fuel injector for generating the internal mixture formation in a combustion chamber of the internal combustion engine and at least one fuel valve for generating the external mixture formation outside the combustion chamber of the internal combustion engine.

In principle, it is known that in internal combustion engines an external mixture formation, for example in a suction pipe or a carburetor, takes place outside the actual combustion chamber. The outer mixture formation serves to produce a combustible gas or fuel mixture outside the combustion chamber. For this purpose, fuel valves are known to introduce the liquid or gaseous fuel according to the intake manifold and so to produce the combustible gas or mixture in the intake manifold. The internal mixture formation takes place in the combustion chamber. For this purpose, fuel injectors, as also described above, are known, which are arranged on the combustion chamber and inject the fuel into the combustion chamber and thus generate a combustible mixture there.

The internal combustion engine can be used, for example, to burn only liquid fuel, e.g. As gasoline or diesel, be designed. In such cases, the internal combustion engine is operated in the first operating state (exclusively) by means of the fuel injectors, each injecting the fuel into the combustion chamber for the internal mixture formation and in the second operating state, the internal combustion engine is operated by means of the fuel valves, which are provided for the external mixture formation in the first and in the second operating state, the same type of fuel is used.

In some embodiments, the internal combustion engine is designed for combustion of two different types of fuel, namely for combustion of a first (liquid) fuel, in particular gasoline, in the first operating state and in the second operating state for combustion of a second, gaseous fuel as the second fuel, in particular compressed natural gas. Such bivalent internal combustion engines are known in principle.

The internal combustion engine may be a gasoline engine with one, two, three, four or more cylinders, wherein a combustion chamber is arranged in each cylinder. It is for each combustion chamber, d. H. for each cylinder, at least one fuel injector for injecting the (first) fuel (eg gasoline) and at least one fuel valve for supplying a (second) fuel (for example compressed natural gas or also gasoline). As stated above, a fuel injector is a fuel valve that may be, for example, electromagnetically or piezoelectrically operable.

The basic structure of internal combustion engines for bivalent operation with two different fuels, such as gasoline and compressed natural gas, is basically known and need not be discussed further here. The same applies to the structure and operation of fuel valves, which are known in principle to those skilled in the art.

As mentioned above, fuel injectors are expensive and the replacement is expensive, so that an unnecessary exchange should be avoided if possible.

The diagnostic method comprises, as step (a), analyzing the rough running of the internal combustion engine in the first operating state (eg with the first fuel for internal mixture formation) and in the second operating state (eg with the second fuel for external mixture formation). As a result, (at least) a first rough-running value for the first operating state and (at least) a second rough-running value for the second operating state are obtained, wherein the internal combustion engine is operated above a predetermined operating temperature. The predetermined operating temperature corresponds to an operating temperature above which the internal combustion engine has a "warm" state. That is, the internal combustion engine is operated to be in a stable operating condition and, for example, to not further increase an oil temperature or other temperature characteristic of the operation of the internal combustion engine, but to remain almost stable above the predetermined operating temperature. The internal combustion engine can be operated at an idling speed or a rotational speed which is above the idling speed by a predetermined value.

The diagnostic method further comprises, as step (b), setting a further analysis step for detecting a defect of the at least one fuel injector as a function of the first and second rough running values.

The diagnostic method thus takes advantage of the fact that the rough running in the event of a defect of a fuel injector in the first operating state will be stronger or different than the rough running in the second operating state, if, for example, the fuel valve or fuel valves for supplying the second fuel are not defective in the first operating state (only) the fuel injectors are used for internal mixture formation, while in the second operating state only the fuel valves are used for external mixture formation, while in the second operating state consequently the fuel injectors are not used. In addition, the diagnostic method in step (a) makes use of the fact that many defects of fuel injectors are found particularly at the operating temperature of an internal combustion engine.

The diagnostic method is typically not performed by a controller that controls the internal combustion engine and typically has various diagnostic functions, but is performed "off-board," that is, outside of the controller and, for example, in a workshop. The diagnostic procedure may be performed in a diagnostic facility, as discussed below. In addition, the diagnostic method may also include work instructions to a mechanic or other service technician of a workshop.

Determining the uneven running is basically known and will be explained in the following only briefly. The uneven running can serve as a basic variable for detecting misfiring of the internal combustion engine or on individual cylinders of an internal combustion engine. However, the running disturbance analysis itself can also be designed as a diagnostic function in the engine control unit of the internal combustion engine. Furthermore, it is a diagnostic function prescribed by the European Union and is defined in on-board diagnosis II (OBD II) ISO 15031. A misfire is typically a missing or incomplete combustion. Causes of a misfire include, for example, the following issues: failure in ignition (no spark, too early, too late, too weak), fuel supply error (too much, too little, too late, inhomogeneously distributed), lack of air and too little compression on the cylinder.

The detection of combustion misfires by the analysis of the rough running is based in some embodiments on the effect of missing or bad combustion. A misfire typically causes a loss of power in a cylinder and correspondingly leads to a brief drop in engine torque (torque of the internal combustion engine). This results in a slowing down of the rotational movement of the crankshaft. The resulting short-term change in the rotational speed can be detected by a crankshaft sensor, which is mounted on a crankshaft of the internal combustion engine and detects the rotational angle of the crankshaft. With this signal of the crankshaft sensor different Laufunruhesignale can be calculated for different states and misfire types, which allow a decision as to whether a misfire exists or not by a comparison with associated thresholds. This is also known in principle and the running-noise analysis and the detection of the misfire for individual cylinders can be provided as a diagnostic function in the engine control or the engine control unit.

The diagnostic function that is used in the context of step (a), can be stimulated at standstill of the vehicle by z. B. a corresponding control command is sent to the engine control to determine the idling quality of the internal combustion engine.

The idling quality of the internal combustion engine is the idling behavior of an engine and can be greatly influenced by a bad combustion.

The step (a) of the diagnostic method can exploit the previously discussed uneven running principle in order to determine the idling quality of the internal combustion engine by integrating cylinder-selective positive rough running values of the internal combustion engine over a defined measuring time.

The integrals can be determined in a warm operating internal combustion engine in the first operating state and in the second operating state, wherein, as mentioned above, the warm operating state is reached when the operating temperature is above a predetermined operating temperature value. As will be explained later, these rough-running values and their integrals can also be determined in a warm-up phase of the internal combustion engine in the first or second operating state, wherein the warm-up phase is characterized in that the operating temperature is below the predetermined operating temperature value.

The starting of the diagnostic function of the engine control of the internal combustion engine in the different operating phases takes place in some embodiments by means of a diagnostic device, the z. B. is designed as a tester by stimulating various of the basic settings of the engine control. The storage of the diagnostic results can be done in a memory of the diagnostic device or directly even in the engine control.

The prerequisite for the end of the function in the warm-up phase in gasoline operation is that, as mentioned, the internal combustion engine is in a predetermined operating temperature range, in particular above a predetermined operating temperature. Exceeds the internal combustion engine within the execution of the diagnostic process this temperature range, for. B. by a predetermined maximum operating temperature is exceeded, in some embodiments, the diagnostic process can stop and the determined result for the rough running can be discarded. This can ensure that the test phase always has the same boundary conditions.

It can be checked before starting the integration of the Laufunruhesignale or values, whether the requested first or second operating state exists, otherwise it is requested accordingly. In addition, a delay time can be awaited afterwards to allow a settling of the Laufunruhesignals. In some embodiments, furthermore, a lambda control can be blocked, if present, and a mixture adaptation can be set to an initial value.

If the predetermined operating temperature of the internal combustion engine is reached, the execution of step (a) is started and the rough running values can in some embodiments be integrated respectively for the cylinders of the internal combustion engine. The measurement duration of the integration can be specified and depends on the specific design of the internal combustion engine.

The determined amounts of the integrals, which form the first and the second rough-running value for the first and second operating state, in some embodiments, in the engine control of the internal combustion engine or in the diagnostic device for further processing and read-out by a diagnostic device, for. A tester.

If, in accordance with step (a), the uneven running for the first operating state is analyzed, in some exemplary embodiments, in addition, the current lambda signal can be detected and stored by a lambda probe. The lambda signal can also be smoothed by a low pass filter.

After the completion of step (a), a first rough-running value and a second rough-running value are accordingly present, wherein the first rough-running value represents the rough running of a cylinder of the internal combustion engine during the first operating state for a predetermined measuring period and the second rough-running value represents the rough running of the cylinder during the second operating state represents the given measurement duration. In the case of a plurality of cylinders, two rough-running values are respectively determined for one cylinder, so that a first rough-running value for the first operating state is then available for each cylinder and a second rough-running value for the second operating state is present.

As mentioned above, in step (b), another analyzing step for detecting a defect of the least one fuel injector is determined depending on the first and second running noise values.

For this purpose, the first and second rough running values can be compared with a predetermined common threshold value or with a respective first and a second threshold value. The threshold may be specific to the internal combustion engine and may indicate a threshold above which the smooth running may be characteristic of a malfunction.

This makes it possible to define several scenarios as a function of the determined rough running values and to provide corresponding further troubleshooting strategies with suitable analysis means.

In some embodiments, up to five different scenarios may be specified. So z. B. in a first scenario, a lower, that is, below the threshold lying, first rough-running value, which characterizes the rough running in operation with the first fuel, and a high, that is above the threshold, second rough running, the uneven running in the Operation with the second fuel is an indication that the fuel injector for the first fuel is in order, but the fuel valve for the second fuel is defective.

In a second scenario, if the first and second rough-running values are high, that is, above the threshold, this may be due to another error, e.g. B. a faulty ignition coil, while the fuel injector is in order.

On the other hand, in a third scenario, if the first and second running disturbances are low (below the threshold), but an error is stored, for example, in a fault memory of the engine control of the internal combustion engine indicating that misfires have been detected (for example, in hot or cold operating condition). , so further analysis steps can be arranged to further investigate the fuel injectors and possibly to determine a defective fuel injector.

In a fourth scenario, if the first rough-running value is high and the second low, this indicates an error of a fuel injector and further analysis steps can follow in order to determine the defective fuel injector (s).

In a fifth scenario, for example, the first rough-running value may be undefined, that is, it varies, for example, and the second rough-running value may be low, so there may be a defect, possibly all fuel injectors, and further analysis steps selected accordingly.

Since the failure of a fuel injector can be excluded in the first two scenarios, the focus of the following description is also more on the scenarios three to five, in which a defective fuel injector may be present, which should be determined accordingly by further analysis.

In some embodiments, the further analysis step comprises determining a mixture deviation for the at least one fuel injector, that is, it is determined whether each fuel injector provides the predetermined mixture between, in particular, the first fuel and air. In some embodiments, the analysis of the mixture deviation is performed accordingly only for the first operating state in which the fuel injector (s) are used.

The diagnostic function that detects the mixture deviation may be stored in some embodiments in the engine control of the internal combustion engine, but it can also externally z. B. stored in a diagnostic device or the like.

In some embodiments, the analysis of the mixture deviation is performed at low-operating internal combustion engine, that is, the operating temperature is above the predetermined operating temperature.

In some embodiments, the analysis of the mixture deviation includes the following basic states, for example, performed by a state machine:

State 0: All required operating conditions are established and release conditions are checked for further analysis.

State 1: In this state, it is checked whether a cylinder has a noticeable running noise.

Condition 2: A fuel injector clamp test is performed by checking if it is still possible to control it

State 3: This state performs a pre-initialization of a mixture ramp.

Condition 4: In this state, a conspicuous cylinder is greased or emaciated depending on the rough running by means of a mixture ramp.

State 5: This state occurs when a diagnostic result has been determined or there are conditions that cause the function to terminate.

Condition 6: This condition is reached when specified operating parameters such as rail pressure or idle speed are not met. Accordingly, the analysis of the mixture deviation is interrupted and a restart is initialized.

Of course, these states are merely exemplary and the present invention is not limited to these states.

As a basic input signals for the analysis of the mixture deviation, a current lambda value (λ value) of the internal combustion engine and the respective Laufunruhesignal serve. These two signals can be smoothed by a low-pass filter for further processing. The lambda value describes the air ratio and is known to the person skilled in the art.

In state 1, it can first be checked whether the running noise signals of all cylinders are stable. If this stability criterion is fulfilled, an examination of the rough running values of all cylinders follows. If the criterion has not been met, the diagnostic is aborted. If the rough running value of the tested cylinder is below a predefined threshold value, the diagnosis with the result "i. O. "for this cylinder finished and the next cylinder is checked. If the rough-running value is above the threshold value, the test loop is interrupted and the fuel injector of the corresponding cylinder is further investigated. When the cylinder inspection is completed, the search continues until all cylinders have been tested. If the rough running values of all cylinders are below the threshold value, the diagnosis is ended.

With the exceeding of a predetermined Laufunruheschwellwertes of a cylinder, the state machine causes a change from state 1 to state 2. In state 2, the relevant fuel injector can be further examined for its operability, here is checked whether the fuel injector is stuck. For this purpose, for example, the fuel injector can be instructed to inject two different injection quantities and it is determined in each case the associated lambda value of the internal combustion engine. The ratio of the two lambda values may, for example, give a small value that is below a threshold value and accordingly indicates that the fuel injector is stuck.

Otherwise, it is possible to change to state 3 and to further investigate the fuel injector of a cylinder by means of a mixture ramp. A mixture ramp is a process in which the injection quantity of a cylinder is incrementally increased (enriched) or reduced (leaned out) by the associated fuel injector. As a result, the torque can be increased or decreased by a cylinder on the crankshaft and thus has an influence on the rough running of the engine (the internal combustion engine). The height of the lambda value can determine the type of mixture ramp. If, for example, the lambda value λ <1.0, first an attenuation ramp is generated, while at a lambda value λ> 1.0 an enrichment ramp is generated. After setting the type of mixture ramp this z. B. initialized by a factor of 1.0 and there is a transition to the state 4.

In state 4, the current rough running of the cylinder to be tested is continuously monitored. When the cylinder reacts to the mixture ramp, it falls below the adjustable and preset running disturbance threshold value after a certain time and the diagnosis result is "increased or reduced quantity". This is followed by the transition from state 4 to state 5. If the cylinder does not respond to the type of mixture ramp and the running noise deteriorates, the ramp direction can be switched.

In state 4, therefore, the rough running in connection with the mixture ramp is analyzed. If the mixture ramp and the rough running increase, it is assumed that, from exceeding the rough running value of a threshold value, the rough running is impaired, which leads to a change of the ramp direction. The ramp direction is also changed if a maximum value of the enrichment ramp or a minimum value of the weight loss ramp is reached. Before the ramp direction is changed, in some embodiments, the new mixture ramp must be initialized according to states 3 and 4. If, for example, after the change in the direction of the mixture ramp, it is determined that the rough-running value is below the threshold value, a diagnosis result for the relevant fuel injector is present and the transition to state 5 occurs. If no smooth-running improvement occurs despite the change in the ramp direction, the Diagnostics ended with the result "ignition defective".

In order for a stronger correlation between the mixture ramp result and rough running, a further plateau detection can be performed in state 4. A plateau in the Laufunruhe can arise, since despite further enrichment / emaciation the rough running does not change further. A plateau is recognized based on a given permissible difference between the current uneven running and a filtered uneven running. The input of the filtered ripple signal is the current ripple signal, which is smoothed by a low pass filter. If the amount of the difference over a defined delay time is less than the predetermined difference value, a plateau is detected and the mixture ramp is terminated. The delay time can be formed by a characteristic and can be dependent on the amount of the current rough running. In this case, the characteristic curve can be selected so that the delay time at high turbulence longer than at is lower, so it comes in a cylinder with high rough running at no premature end of the mixture ramp. Due to the plateau recognition of the above-mentioned Laufunruheschwellwert can be lowered, z. B. from 1.5 to 0.6, because it can be determined on the basis of the detection, if there is no reduction of rough running more.

The steps described above can be performed for each cylinder and thus also for each fuel injector of the internal combustion engine. From the mixture deviation can be detected which fuel injector is defective and must be replaced.

In some embodiments, the result of the mixture deviation can be output directly, so that, for example, a garage employee can decide based on the result whether a fuel injector is defective and needs to be replaced or not. In contrast, in other embodiments, the diagnostic method outputs whether and which fuel injector is to be replaced.

In some embodiments, it may be determined before step (a) whether a combustion misfire of the internal combustion engine has been detected in the first operating state. As stated above, engine control of the internal combustion engine may be configured to periodically check for combustion misfires. If this is the case, a corresponding error code is stored in the error memory in the engine control, which can be read later. Accordingly, it can also be determined whether a combustion misfire of the internal combustion engine has been detected above or below the predetermined operating temperature. This can be checked before the actual start of the diagnostic process, if there is possibly a fault with a fuel injector. In addition, in some embodiments, this information may also be used to select an analysis step.

In some embodiments, it is further checked before step (a) whether the internal combustion engine is "diagnosable". By this is meant that other causes for the detection of a misfire can be present, such as an error in the load detection, a defect of the lambda probe or a defect in the mechanics, in particular in the cylinder head gasket or the cylinder head itself, which can be checked, before the fuel injectors are analyzed.

In some embodiments, the rough running of the internal combustion engine is analyzed in the first operating state in a further analysis step, wherein the internal combustion engine is operated below the operating temperature. As a result, defects in a fuel injector can be detected, which can occur in the so-called warm-up phase. The warm-up phase is a phase in which the operating temperature of the internal combustion engine is not reached, but the internal combustion engine is started, for example, "cold" and the running noise of the internal combustion engine, as described above in connection with the step (a), analyzed and characterized is determined a rough running value (for each cylinder with fuel injector).

In some embodiments, this analysis is performed only if it is determined in step (b) that the first rough-running value and the second rough-running value are below a threshold, which also corresponds to the third scenario described above.

In some embodiments, a further step determines a mixture deviation for the at least one fuel injector in the first operating state, wherein the internal combustion engine can be operated above the predetermined operating temperature. This can be done, in particular, in the third and fourth scenarios explained above, in order, as explained above, to find cylinder-selectively a malfunction of a fuel injector.

Accordingly, in some embodiments, in a further step, a mixture deviation for the at least one fuel injector in the first operating state can be determined if it is determined in step (b) that the first rough-running value is above a threshold value and the second rough-running value is below a threshold value, in particular corresponds to the fourth scenario explained above.

The diagnostic method outlined above may also be implemented and executed as a computer program, and it may be stored as a computer program on a data carrier so that when executed on a computer, the computer causes the computer to at least partially perform the method steps described above.

Some embodiments relate to a diagnostic device for detecting a defective fuel injector of an internal combustion engine, as has been described above. The internal combustion engine is operable in a first and a second operating state, as stated above. In the first operating state, the internal combustion engine with an internal mixture formation of a fuel, as described above, operable and in the second operating state, it is operable with an external mixture formation of a fuel, as described above. The internal combustion engine has at least one fuel injector for generating the internal mixture formation in a combustion chamber of the internal combustion engine and at least one fuel valve for generating the external mixture formation outside the combustion chamber of the internal combustion engine, as described above. The diagnostic device also includes a microprocessor adapted to at least partially execute the method described above. The diagnostic device may further comprise a memory, in particular a volatile and a non-volatile memory, and an interface, with which the diagnostic device can be connected, for example, with the engine control of the internal combustion engine. In addition, the diagnostic device may include a display in which instructions are issued to a shop assistant and / or the measurements.

Some embodiments also relate to a motor vehicle having an internal combustion engine as described above and to a diagnostic device as described above.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

1 schematically illustrates an embodiment of a diagnostic method according to the present invention;

2 schematically a method step of the diagnostic method of 1 illustrated in detail; and

3 schematically illustrates an embodiment of a diagnostic device according to the present invention.

An embodiment of a diagnostic method 1 is in 1 illustrated. Hereinafter, it is assumed that the internal combustion engine is a gasoline engine operable with gasoline and compressed natural gas, without limiting the present invention thereto. That is, the first operating state corresponds to the gasoline operation without limiting the generality and the second operating state to the gas operation. In addition, it is assumed that the gasoline engine has four cylinders, wherein in each cylinder a fuel injector for injecting gasoline is arranged and a gas valve for introducing the natural gas. The gasoline engine burns gasoline in gasoline and gas in natural gas.

The diagnostic procedure described below 1 is designed as a so-called "offboard diagnosis", which does not run in an engine control unit of the gasoline engine, but externally on a diagnostic device 40 as related below 3 is explained.

Target of the diagnostic procedure 1 it is, as already stated above, to detect mechanically defective fuel injectors, which cause problems in the combustion of the gasoline engine and to indicate accordingly, when it is unlikely that a fuel injector is defective.

The procedure starts 2 Assuming that, for example, a user of the vehicle in which the gasoline engine is arranged, comes to the workshop, as, for example, a warning light indicates that there is a fault in the injection system or because he noticed a rough running in the gasoline engine of his vehicle. In this case, for example, there may be a fault memory entry in an engine control unit of the gasoline engine, which indicates that combustion misfires have been detected. However, this fault memory entry typically can not distinguish whether these misfires were caused by a fueling fault, an ignition fault, or a mechanical fault.

First, accordingly 3 checks whether there is a system error, that is, whether the onboard diagnosis, which runs in the engine control unit of the gasoline engine, has detected a combustion misfire in gasoline mode and has stored a corresponding error code in the error memory. The fault memory is read out, wherein in the present exemplary embodiment three fault codes for the combustion exposure are treated, namely an error code "FC = A" in which a combustion misfire is in the cold operating state, ie at an operating temperature of the engine of below 70 ° C .; an error code "FC = B" in which a combustion misfire is in hot operating condition, that is, at an engine operating temperature above 70 ° C and an error code "FC = C" where the onboard diagnostic has detected a mixture failure. The error codes may be cylinder-specific, as in the present embodiment, or not cylinder-specific.

It will be added next 4 the diagnostic capability of the engine tested. The diagnostic capability check is to find out if there is not a cause for the misfire that is not due to a malfunction of a fuel injector but is merely a consequence of another failure of another component. Such defects must first be eliminated and eliminated for the purposes described below Troubleshooting after faulty fuel injectors can be continued. 2 shows in detail the check of the diagnostic capability. It will be at 20 the error memory is read out to determine whether there are any other detected errors in addition to a detected misfire. at 21 the error codes are checked and depending on the detected error is at 22 a repair via a guided troubleshooting "GFS" performed, as also described below for the fuel injectors. at 23 the load detection is checked, and if at 24 it is recognized that an error exists when z. B. a load detection value is above a predetermined threshold, is at 25 recommended, the suction side after the repair indication z. B. via a guided troubleshooting depress. at 26 the lambda probe of the engine is checked, and at 27 Check for existing errors and at 28 it is recommended to replace the Lambda probe if the Lambda probe is defective. Finally, at 29 still checking the mechanics at the 30 In particular, a review of the compression of the cylinder and the tightness of the cylinder heads, wherein in the presence of an error in 31 the replacement of a cylinder head is recommended.

In the following it is assumed that the engine is capable of diagnosis and the diagnostic procedure 1 keep going. By ensuring the diagnostic capability of the engine, negative influences on the detection of a failure of a fuel injector can be avoided.

In some embodiments, a value for multiplicative mixture adaptation is still read from the engine control unit, since this may be an indicator for fuel injectors with a high shortage in long injection times and thus must be observed for the diagnostic method in some embodiments. For example, if this value is greater than a defined threshold, which may be greater than 1.0, in some embodiments, this may mean that the fuel injectors have a shortage in an upper load and speed range.

The next step will be at 5 started with the integration of the rough running in a warm engine with an engine temperature of 80 ° C and a locked lambda control. The lambda control can be disabled in some embodiments, as this would otherwise against one in step 5 would govern this fuel shortage. In addition, the mixture adaptation (see above) can be set to an initial value. The predetermined operating temperature is in this embodiment at 70 ° C, as already indicated above.

The analysis of the rough running is performed as described in detail above for step (a). The workshop can start to study the idling quality in the gas mode by integrating the rough running values for a given measuring interval and obtaining a rough running value "LG" for each cylinder (there are thus four rough running values "LG"). After completion of the examination, the results of the workshop will be made available. Subsequently, the rough running values of the cylinders are integrated in gasoline operation and four integral values "LB" are obtained, namely one for each cylinder. By completing the integration, the results are saved. Furthermore, in this measurement, the current lambda value of the engine is detected and also stored. As already stated, the values can be stored in the memory of the engine control unit and / or in the memory of the diagnostic facility.

• 1. Die Integration der Laufunruhe ergab einen bzw. mehrere hohe Werte „LG” im Gasbetrieb (LG > S, wobei S ein vorgegebener Schwellwert ist, wie es oben bereits erläutert wurde) und niedrige Laufunruhewerte „LB” im Benzinbetrieb (LB < S). Daraus resultiert, dass ein Fehler auf der Benzinseite ausgeschlossen werden kann und die Werkstatt die Fehlerursache auf der Gasseite lokalisieren muss. Dementsprechend kann bei 7 ein Hinweis ausgegeben werden, dass ein Gasinjektor defekt sein kann und bei 13 wird kein Tausch eines Kraftstoffinjektors empfohlen.
• 2. Sind die Beträge der Laufunruheintegrale im Gas- und Benzinbetrieb hoch (LB > S und LG > S), bedeutet dies, dass ein Fehler vorliegt, der beide Betriebsarten beeinflusst. Aufgrund dieser Tatsache wird bei 8 ein Hinweis ausgegeben, dass die Werkstatt die Zündung oder Motormechanik prüft und bei 14 wird kein Tausch eines Kraftstoffinjektors empfohlen.
• 3. Im Fehlerspeicher ist wenigstens ein Verbrennungsaussetzer bei einer Motortemperatur bis 70°C abgelegt („FC = A”), das heißt bei einer Temperatur unterhalb der vorgegebenen Betriebstemperatur von 70°C. Die ausgegebenen Integralwerte sind im Gas- und Benzinbetrieb niedrig, das heißt LB < S und LG < S. Hier sind weitere Prüfschritte von der Werkstatt erforderlich, die weiter unten beschrieben werden.
• 4. Verbrennungsaussetzer wurden bei einer Motortemperatur größer als 70°C im Fehlerspeicher hinterlegt („FC = B”). Der Betrag des Integrals im Benzinbetrieb ist hoch, das heißt LB > S, und im Gasbetrieb niedrig, das heißt LG < S. Weitere Prüfungen durch die Werkstatt sind hier notwendig, die weiter unten beschrieben werden.
• 5. Der Fehlerspeicher weißt auf einen Gemischfehler hin („FC = C”). Die Integrale im Gasbetrieb sind niedrig, das heißt LG < S und im Benzinbetrieb schwankend („LB <, > S), was bedeutet, dass die Ergebnisse LB einen hohen oder niedrigen Betrag aufweisen können. Des Weiteren ist der gemessene Lambdawert zum Beispiel im Benzinbetrieb größer als ein vorgegebener Schwellwert, der in einem mageren oder stark mageren Bereich liegen kann und entsprechend größer als 1,0 sein kann.

From these collected results, five more instructions can be generated for the workshop.

• 1. The integration of the rough running resulted in one or more high values "LG" in gas mode (LG> S, where S is a predetermined threshold, as explained above) and low rough running values "LB" in gasoline mode (LB <S) , As a result, an error on the gasoline side can be excluded and the workshop must locate the cause of failure on the gas side. Accordingly, at 7 be issued a note that a gas injector may be defective and at 13 it is not recommended to replace a fuel injector.
• 2. If the amounts of the running noise integral in gas and petrol mode are high (LB> S and LG> S), this means that there is an error affecting both operating modes. Because of this fact is added 8th issued a note that the workshop checks the ignition or engine mechanics and at 14 it is not recommended to replace a fuel injector.
• 3. At least one combustion misfire is stored in the fault memory at an engine temperature of up to 70 ° C ("FC = A"), ie at a temperature below the specified operating temperature of 70 ° C. The output integral values are low in gas and gasoline operation, ie LB <S and LG <S. Here further test steps are required by the workshop, which are described below.
• 4. Combustion misfires were stored in the fault memory at an engine temperature greater than 70 ° C ("FC = B"). The amount of integral in gasoline operation is high, that is, LB> S, and low in gas operation, that is, LG <S. Further testing by the workshop is required here, which will be described later.
• 5. The fault memory indicates a mixture error ("FC = C"). The integrals in the gas mode are low, that is, LG <S and fluctuating in gasoline mode ("LB <,> S), which means that the results LB may be high or low. Furthermore, the measured lambda value is, for example, in gasoline operation greater than a predetermined threshold, which may be in a lean or very lean range and may be correspondingly greater than 1.0.

It is clear from the instructions that only points 3 to 5 concern the fuel injectors, which is why only details of points 3 to 5 are discussed below.

In the case of point 3 (see also above "third scenario"), at step 9 the gas deviation in gasoline operation determined with warm engine. The determined mixture deviation is stored within the diagnostic procedure, as later in step 12 still an integration of the rough running in the warm-up phase is necessary to allow a targeted repair. Since the mixture deviation in a warm engine, that is at an engine temperature of z. B. 80 ° C is performed, must before performing analysis of the rough running in the step 12 the engine on z. B. Cool 50 ° C before the analysis of the rough running can be performed. For this purpose, a cooling time of the motor of about 6 hours in the present embodiment is necessary. After the engine has cooled to the appropriate temperature below the specified operating temperature of 70 ° C, z. B. below 50 ° C, can at 12 the analysis of the rough running in gasoline operation will be carried out and it will be started with the integration of the running noise signals in the warm-up phase. By combining the results from the determination of the mixture deviation in step 9 for the individual fuel injectors and the results from the analysis of the rough running and the obtained rough running integral values at step 12 is a targeted detection of defective fuel injectors possible and at 15 the workshop can be called the corresponding fuel injector, which is defective, or the workshop can determine this from the determined and issued values themselves.

Due to the high level of turbulence in combustion misfires, which are stored in the fault memory at an engine temperature of greater than 70 ° C ("FC = B"), is in the point 4 , the "fourth scenario" discussed above corresponds to the detection of defective fuel injectors only the mixture deviation, the step 10 is performed, needed. As a result, the targeted repair of individual fuel injectors can also take place here (as in step 16 specified).

Defective fuel injectors, which can not be detected by determining the mixture deviation, are indicated by the dot 5 covered, which corresponds to the above-described "fifth scenario". On the basis of the error code ("FC = C"), the above read-out mixture adaptation value and the measured lambda value of the engine in idle can be in the context of a diagnostic step 11 In this case, the workshop must all four fuel injectors, as in the step 17 indicated, change.

Through this troubleshooting strategy of the diagnostic method shown above 1 Due to the integrated diagnostic functions, it is possible to dispense with the transverse exchange of components, as is sometimes required in the prior art. Furthermore, the course of the repair can be documented and sent as part of a diagnostic protocol without the workshop having to make inputs to required measured variables. As a result, the subsequent monitoring can be tracked for the effectiveness of the diagnostic procedure. By combining several indicators and diagnostic results. the analysis of the rough running and the described determination of the mixture deviation (see steps 9 . 10 and 12 or see the explanations above to step (a) and the mixture deviation determination) can be made a clear statement which fuel injector is defective. Through this system-guided troubleshooting of the diagnostic procedure 1 Consequently, the workshop is able to carry out a targeted repair of a fuel injector.

The troubleshooting strategy of the diagnostic procedure explained here is based in part on the required fault memory entries and is thus error-code-oriented. In other embodiments, thresholds may be adjusted to a symptom-related behavior of the engine, and thus, in some embodiments, the error memory entries are not necessary.

3 illustrates an embodiment of a diagnostic device 40 , also called a tester. The diagnostic device 40 has a microprocessor 41 , an interface 42 and an ad 43 , There is also a memory 44 in which a program is stored that contains the microprocessor 41 caused to perform the method described above at least partially. In the store 44 It is also possible to store measured values such as the rough running values LB and LG, etc. The memory 44 can be configured as a volatile and / or non-volatile memory. the interface 42 serves the diagnostic device 40 to connect to an engine control unit to retrieve data such as error codes, and to call diagnostic functions and other functions, and the diagnostic method described above 1 perform. In particular, when analyzing the rough running and when determining the mixture deviation control commands to the engine control unit via the interface 42 be sent. The ad 43 The purpose of this is to output appropriate instructions and determined values, as described above in connection with the diagnostic procedure 1 have been described.

LIST OF REFERENCE NUMBERS

1

diagnostic procedures

2

begin

3

Check misfiring

4

Check diagnostic capability

5

Analyze rough running

6

Set next analysis step

7

Note gas injector

8th

Note Ignition coil

9

Determine mixture deviation

10

Determine mixture deviation

11

Further diagnosis

12

Analyze rough running

13, 14

No replacement

15, 16

Selective exchange

17

All swap

20

Read fault memory

21

Check error codes

22

Repair via GFS

23

load detection

24

Error present?

25

Press off suction side

26

lambda probe

27

Error present?

28

Exchange the probe

29

mechanics

30

Compression, tightness

31

Swap cylinder head

40

diagnostic device

41

microprocessor

42

interface

43

display

44

Storage

Claims (10)

A diagnostic method for detecting a defective fuel injector of an internal combustion engine, wherein the internal combustion engine is operable in a first operating state with an internal mixture formation of a fuel and is operable in a second operating state with an external mixture formation of a fuel and at least one fuel injector for generating the internal mixture formation in a combustion chamber Internal combustion engine and having at least one fuel valve for generating the outer mixture formation outside the combustion chamber of the internal combustion engine, characterized by the steps of: (a) analyzing ( 5 ) of the running noise of the internal combustion engine in the first operating state and in the second operating state and thereby obtaining a first rough running value (LB) for the first operating state and a second rough running value (LG) for the second operating state, wherein the internal combustion engine in the first and in the second operating state above a predetermined operating temperature is operated; and (b) determining ( 6 ) of a further analysis step for detecting a defect of the at least one fuel injector as a function of the first and second rough running values. The diagnostic method of claim 1, wherein the further analyzing step comprises determining ( 9 . 10 ) comprises a mixture deviation for the at least one fuel injector. The diagnostic method of claim 1, wherein liquid fuel is passed through the at least one fuel injector in the first operating state for the internal mixture formation and in the second operating state for the external mixture formation, a gaseous fuel is passed through the at least one fuel valve. Diagnostic method according to one of the preceding claims, wherein prior to step (a), 3 ), whether a combustion misfire of the internal combustion engine has been detected in the first operating state. A diagnostic method according to claim 4, wherein 3 ), whether a combustion misfire of the internal combustion engine has been detected above or below the predetermined operating temperature. Diagnostic method according to one of the preceding claims, in which in a further analysis step ( 12 ) the uneven running of the internal combustion engine is analyzed in the first operating state, wherein the internal combustion engine is operated below the operating temperature. The diagnostic method according to claim 6, wherein the analysis is performed only when it is determined in step (b) that the first rough-running value (LB) and the second rough-running value (LG) are below a threshold value (S). Diagnostic method according to one of claims 6 or 7, wherein in a further analysis step ( 9 . 10 ) a mixture deviation for the at least one fuel injector in the first operating state is determined. Diagnostic method according to one of the preceding claims, wherein in another Analysis step ( 10 ) a mixture deviation for the at least one fuel injector in the first operating state is determined if it is determined in step (b) that the first rough-running value (LB) is above a threshold value (S) and the second rough-running value (LG) is below a threshold value (S). lies. A diagnostic device for detecting a defective fuel injector of an internal combustion engine, wherein the internal combustion engine is operable in a first operating state with an internal mixture formation of a fuel and is operable in a second operating state with an external mixture formation of a fuel and at least one fuel injector for generating the internal mixture formation in a combustion chamber Internal combustion engine having at least one fuel valve for generating the outer mixture formation outside the combustion chamber of the internal combustion engine, wherein the diagnostic device ( 40 ) a microprocessor ( 41 ) arranged to carry out the method according to one of claims 1 to 9.

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