DE102011089317A1 - Method and device for operating an internal combustion engine - Google Patents

Abstract

The invention relates to a method for operating an internal combustion engine (100), in which at least one variable (PZa) characterizing the cylinder pressure in a cylinder (110a) of the internal combustion engine (100) is determined (200), characterized in that the variable characterizing the cylinder pressure with a predeterminable maximum value (PZmax) is compared (210), and that depending on the comparison (210) of the further operation of the internal combustion engine (100) is influenced (220, 230).

Description

State of the art

The invention relates to a method for operating an internal combustion engine, in which at least one variable characterizing the cylinder pressure in a cylinder of the internal combustion engine is determined.

The invention further relates to a device for operating an internal combustion engine according to the preamble of patent claim 8.

Disclosure of the invention

It is an object of the present invention to improve a method and a device of the type mentioned in that more precise information about an operating condition of the internal combustion engine can be obtained and unsafe operating conditions can be reliably avoided.

This object is achieved in the method of the aforementioned type according to the invention that the characterizing the cylinder pressure size is compared with a predetermined maximum value, and that is influenced depending on the comparison of the further operation of the internal combustion engine. As a result, the further operation of the internal combustion engine can advantageously be adapted to the cylinder pressure actually present in the cylinder, for example using a control method.

In a preferred embodiment, the variable characterizing the cylinder pressure in a cylinder of the internal combustion engine is a peak pressure, that is to say the maximum value of the time profile of the cylinder pressure during a compression or working phase of the cylinder.

The cylinder pressure or its time course can e.g. be detected by means of a cylinder pressure sensor metrologically.

In a further advantageous embodiment, it is provided that the predefinable maximum value depends on a current operating point of the internal combustion engine, wherein the current operating point is defined in particular by a rotational speed and / or an indicated mean pressure of the internal combustion engine. As a result, the comparison according to the invention between the characterizing variable and the predefinable maximum value can advantageously be carried out individually for different operating points of the internal combustion engine. The predefinable maximum value can be determined, for example, by means of a characteristic map as a function of the rotational speed and the indicated mean pressure.

• – Prüfen, ob eine Abgastemperatur der Brennkraftmaschine einen, vorzugsweise von einem Betriebspunkt der Brennkraftmaschine abhängigen, ersten Schwellwert überschreitet,
• – Prüfen, ob ein, insbesondere mittels eines Fahrpedalgebers signalisiertes, Fahrerwunschmoment einen zweiten Schwellwert überschreitet,
• – Prüfen, ob eine Temperatur in einem Ansaugtrakt der Brennkraftmaschine einen, vorzugsweise von einem Betriebspunkt der Brennkraftmaschine abhängigen, dritten Schwellwert überschreitet,
• – Prüfen, ob ein Druck in dem Ansaugtrakt der Brennkraftmaschine einen, vorzugsweise von einem Betriebspunkt der Brennkraftmaschine abhängigen, vierten Schwellwert überschreitet,
• – Erhöhen einer dem Zylinder zugeordneten einzuspritzenden Kraftstoffmenge, insbesondere dann, wenn festgestellt wird, dass die Abgastemperatur der Brennkraftmaschine den ersten Schwellwert nicht überschreitet und/oder die Temperatur in dem Ansaugtrakt der Brennkraftmaschine den dritten Schwellwert nicht überschreitet und/oder der Druck in dem Ansaugtrakt der Brennkraftmaschine den vierten Schwellwert nicht überschreitet.

In a further advantageous embodiment it is provided that, when the comparison between the characterizing quantity and the predeterminable maximum value has revealed that the characterizing quantity is smaller than the maximum value, at least one of the following steps is carried out:

• Checking whether an exhaust gas temperature of the internal combustion engine exceeds a first threshold, which is preferably dependent on an operating point of the internal combustion engine,
• Checking whether a driver's desired torque signaled, in particular by means of an accelerator pedal sensor, exceeds a second threshold value,
• Checking whether a temperature in an intake tract of the internal combustion engine exceeds a third threshold, preferably dependent on an operating point of the internal combustion engine,
• Checking whether a pressure in the intake tract of the internal combustion engine exceeds a fourth threshold, which is preferably dependent on an operating point of the internal combustion engine,
• Increasing an amount of fuel injected to the cylinder, in particular when it is determined that the exhaust temperature of the internal combustion engine does not exceed the first threshold and / or the temperature in the intake manifold of the internal combustion engine does not exceed the third threshold and / or the pressure in the intake manifold of the engine Internal combustion engine does not exceed the fourth threshold.

All of the above-mentioned steps of checking or increasing can generally be carried out advantageously independently of one another or in any desired order. However, in a further advantageous embodiment, the following steps are also particularly preferred: checking the exhaust gas temperature, checking the temperature in the intake tract of the internal combustion engine, checking the pressure in the intake tract of the internal combustion engine, and then increasing the amount of fuel allocated to the cylinder. In this embodiment, it is first determined by the various above-mentioned test steps, whether the internal combustion engine already operates in a boundary region with regard to the temperatures considered or the pressure under consideration, and if this is not the case, advantageously the fuel quantity to be injected assigned to the cylinder can be increased. As a result, taking into account the actual load state of the internal combustion engine, which is characterized by the checked temperatures or pressure values, a Increase the amount of fuel to be injected advantageously also be done beyond a level, as provided for example by a conventional method. For example, a map is provided in conventional methods, the various input variables of the internal combustion engine (speed, load, driver's desired torque, etc.) assigns a corresponding amount of fuel to be injected. Such a map always has a constant maximum injection quantity for at least one operating state of the internal combustion engine, which is permanently parameterized by means of the map and can not be changed in particular in the operation of the internal combustion engine.

In contrast, the present embodiment of the method according to the invention advantageously allows the consideration of the current temperatures in the intake tract and the exhaust tract or the pressure in the intake tract, and if certain conditions are met, can advantageously by the inventive step of increasing the amount of fuel to be injected, the amount of fuel on the Conventionally, for example, by means of a map defined maximum dimensions to be increased. That is, compared to conventional operating methods, the inventive method allows an "increase" of the fuel quantity to be injected and thus the generation of a particularly large torque by the internal combustion engine in such cases when the relevant temperatures and pressures are subject to certain limits, which are in particular less than corresponding allowable maximum values ,

• – Prüfen, ob eine Abgastemperatur der Brennkraftmaschine einen, vorzugsweise von einem Betriebspunkt der Brennkraftmaschine abhängigen, fünften Schwellwert überschreitet,
• – Prüfen, ob ein, insbesondere mittels eines Fahrpedalgebers signalisiertes, Fahrerwunschmoment einen sechsten Schwellwert überschreitet,
• – Verschieben eines Einspritzzeitpunkts und/oder eines Zündzeitpunkts auf einen späteren Zeitpunkt,
• – Ausführen einer Diagnosefunktion zur Überprüfung eines Ladedrucksensors und/oder mindestens eines Stellglieds einer Vorrichtung zum Aufladen der Brennkraftmaschine, insbesondere eines Turboladers,
• – Begrenzen eines maximal von der Brennkraftmaschine abzugebenden Drehmoments,
• – Verringern einer dem Zylinder zugeordneten einzuspritzenden Kraftstoffmenge, insbesondere dann, wenn festgestellt wird, dass die Abgastemperatur der Brennkraftmaschine den fünften Schwellwert überschreitet.

In a further advantageous embodiment it is provided that, when the comparison has revealed that the characterizing variable is greater than or equal to the maximum value, at least one of the following steps is carried out:

• Checking whether an exhaust gas temperature of the internal combustion engine exceeds a fifth threshold value, which is preferably dependent on an operating point of the internal combustion engine,
• Checking whether a driver's desired torque signaled, in particular by means of an accelerator pedal sensor, exceeds a sixth threshold value,
• Shifting an injection time point and / or an ignition point to a later point in time,
• Performing a diagnostic function for checking a boost pressure sensor and / or at least one actuator of a device for charging the internal combustion engine, in particular a turbocharger,
• Limiting a maximum torque to be output by the internal combustion engine,
• - Reduce an amount of fuel to be injected associated with the cylinder, in particular when it is determined that the exhaust gas temperature of the internal combustion engine exceeds the fifth threshold.

The steps of checking, shifting the injection timing, executing a diagnosis function, limiting and decreasing the amount of fuel mentioned above in the present embodiment may be generally performed in any order and independently of each other. Particularly advantageously, if the exhaust gas temperature exceeds the fifth threshold value after the test according to the invention, the fuel quantity allocated to the cylinder can be reduced in order to reduce the temperature again to a normal level. Furthermore, in such cases, when the driver's desired torque falls short of the predefinable sixth limit value, a diagnostic function can be carried out which, for example, serves to find possible causes for the exceeding of the predefinable maximum value for the characterizing variable or the peak pressure determined in the comparison according to the invention. In particular, in the present embodiment, a limitation of the maximum output by the internal combustion engine torque to ensure safe operation of the internal combustion engine. The limitation can be achieved, for example, by transmitting to the torque coordinator of the internal combustion engine a permissible maximum torque value to be used, which ensures that the internal combustion engine is operated in a safe operating range, since the torque limitation also limits and limits the peak pressure thus reducing the load on the internal combustion engine (= engine protection function).

In particular, unsafe operating conditions such as, for example, unintentional further acceleration of the internal combustion engine and the like can thereby also be avoided.

In a further advantageous embodiment, it is provided that for at least two cylinders of the internal combustion engine in each case a cylinder pressure in the cylinder characterizing size, in particular a peak pressure of the cylinder in question is determined, and that determines a measure of the deviation of the peak pressures of the respective cylinder from each other becomes. For example, for at least two, but preferably all, cylinders of the internal combustion engine, the respective peak pressure can be detected by measurement. Subsequently, differences between the peak pressure values of the different cylinders can be formed, and a maximum difference value between two cylinders of the internal combustion engine can be determined by evaluating all previously formed difference values. This maximum difference value, that is to say the deviation of the peak pressure of the two cylinders of the internal combustion engine which are extreme with regard to the peak pressure, is fed to a further evaluation in order to obtain even more precise information about a possible fault condition of the internal combustion engine.

• – Begrenzen eines maximal von der Brennkraftmaschine abzugebenden Drehmoments,
• – Ausführen einer weiteren Diagnosefunktion, die einen Fehlerspeichereintrag auslöst und/oder eine Signalisierung eines Wartungsbedarfs der Brennkraftmaschine.

In particular, it can be provided in a further advantageous embodiment that when the deviation of the peak pressures of the respective cylinder exceeds a predefinable maximum value, at least one of the following steps is carried out:

• Limiting a maximum torque to be output by the internal combustion engine,
• - Execute a further diagnostic function that triggers a fault memory entry and / or signaling a need for maintenance of the internal combustion engine.

As a further solution of the object of the present invention, an apparatus for operating an internal combustion engine according to claim 8 is provided. Further advantageous embodiments are the subject of the dependent claims.

Other features, 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. All described or illustrated features, alone or in any combination form the subject matter of the invention, regardless of their summary in the claims or their dependency and regardless of their formulation or representation in the description or in the drawing.

In the drawing shows:

1 a simplified flow chart of an embodiment of the method according to the invention,

2 schematically a simplified block diagram of an internal combustion engine with the device according to the invention, and

3 schematically a flowchart of another embodiment of the method according to the invention.

2 shows a simplified block diagram of an internal combustion engine 100 , the present four cylinders 110a . 110b . 110c . 110d having. The internal combustion engine 100 also has an intake tract 120 for supplying fresh air or an air / fuel mixture and an exhaust tract 140 ,

In the intake tract 120 is a pressure sensor 130 arranged, the pressure of the fresh gas in the intake 120 and to the control unit 160 for controlling the internal combustion engine 100 is provided, can forward. Analog is in the exhaust system 140 an exhaust gas temperature sensor 150 provided, which is the temperature of the exhaust gas in the exhaust tract 140 and to the control unit 160 can forward.

Alternatively or in addition to the exhaust gas temperature sensor 150 It is also possible to use a calculation model which determines the exhaust gas temperature as a function of operating variables of the internal combustion engine 100 determined, for example, as a function of an air volume and / or a pressure and / or a temperature in the intake tract of the internal combustion engine 100 ,

In the internal combustion engine 100 it may be, for example, a self-igniting or even a spark-ignited internal combustion engine. In particular, the internal combustion engine 100 also be associated with a device for charging the internal combustion engine, in particular a turbocharger (not shown), which is not absolutely necessary for the functioning of the invention described below.

1 shows a simplified flowchart of an embodiment of the method according to the invention. In a first step 200 will be at least one cylinder pressure in a cylinder 110a ( 2 ) of the internal combustion engine 100 characterizing size determined. For example, the variable characterizing the cylinder pressure in the cylinder of the internal combustion engine may be the peak pressure of the cylinder 110a act, so the maximum value of the time course of the cylinder pressure, as it is during a compression or duty cycle of the cylinder 110a the internal combustion engine 100 established.

The peak pressure or generally the cylinder pressure characterizing variable can, according to a preferred embodiment, by means of a cylinder pressure sensor 110a ' metrologically recorded and for further processing to the control unit 160 to get redirected. The other cylinders 110b . 110c . 110d the internal combustion engine 100 can also be associated with advantage own cylinder pressure sensors, which in 2 for the sake of clarity, however, are not shown.

According to the invention according to the method 1 in one step 210 the cylinder pressure characterizing size, in the present case the Peak pressure of the cylinder 110a , compared with a predefinable maximum value.

Subsequently, in step 220 the further operation of the internal combustion engine 100 depending on the comparison 210 affected. This advantageously ensures that the further operation of the internal combustion engine 100 an optionally occurring impermissibly high peak pressure or too low peak pressure of the cylinder in question 110a Takes into account. For example, diagnostic measures in the step can be particularly advantageous 220 initiated when in the comparison according to step 210 has been found that the peak pressure assumes impermissibly high values, that is above the predetermined maximum value. The inventive method can generally for a single or more, preferably for all, cylinder 110a . 110b . 110c . 110d ( 2 ) of the internal combustion engine 100 be carried out, for example, in each working cycle of the cylinder or periodically every n cycles, n> 1.

In a particularly preferred embodiment, the predefinable maximum value which depends on the comparison according to step 210 is based on a current operating point of the internal combustion engine 100 resulting in a particularly precise analysis of the behavior of the internal combustion engine 100 is possible. For example, thus for different operating points of the internal combustion engine 100 different maximum values for the characterizing size or the peak pressure can be specified.

The current operating point of the internal combustion engine 100 According to a further advantageous embodiment, in particular by a rotational speed and / or an indicated mean pressure of the internal combustion engine 100 be defined.

In a further very advantageous embodiment, it is provided that if the comparison according to step 210 ( 1 ) has shown that the characterizing size or the peak pressure is less than or equal to the predefinable maximum value, at least one of the steps described below is performed.

It can be advantageously checked whether an exhaust gas temperature of the internal combustion engine 100 For example, determined by the exhaust gas temperature sensor 150 , a first threshold, which is advantageous from an operating point of the internal combustion engine 100 depends, exceeds. If this is the case, for example, an injection timing or an ignition angle of the internal combustion engine 100 be adjusted, in particular be adjusted early.

Further advantageous diagnostic options are the embodiments of the invention given by the fact that it is checked whether a, in particular by means of an accelerator pedal signaled, driver request torque exceeds a second threshold, whether a temperature in the intake 120 the internal combustion engine 100 one, preferably from an operating point of the internal combustion engine 100 dependent, third threshold, or a check to see if a pressure in the intake 120 exceeds a fourth, preferably in turn operating point-dependent, fourth threshold.

The aforementioned test steps can advantageously be carried out independently or in any order and provide further information about the current operating state of the internal combustion engine.

A modification of the considered cylinders 110a amount of fuel to be injected may also be the subject of an embodiment of the method according to the invention. For example, the amount of fuel to be injected can be reduced if the peak pressure assumes unacceptably high values, for example by the comparison already described above 210 ( 1 ) is determined.

Similarly, an increase in the cylinder considered 110a be considered fuel quantity, for example, if the peak pressure according to comparison 210 ( 1 ) falls below the maximum value and further operating variables (temperature intake / exhaust gas, pressure intake tract) are within predeterminable ranges.

3 shows a flowchart of a further, particularly preferred, embodiment of the invention. In the first step 200 in turn will be the peak pressure of at least one cylinder 110a ( 2 ) of the internal combustion engine 100 determined. In the present embodiment, peak pressure values of all four cylinders advantageously become 110a . 110b . 110c . 110d the internal combustion engine 100 determined and executed the respective process sections individually for each cylinder or for all cylinders together. Overall, therefore, are after the step 200 of the method according to 3 the peak pressure values of all cylinders 110a , ..., 110d the internal combustion engine 100 in front.

The according to 3 on the step 200 following query 240 is optional and will therefore be explained later. In the present case, it is assumed that from the step 200 to which the peak pressure values of the cylinders of the internal combustion engine 100 present, directly in the step 210 is branched, which also represents a query. In the step 210 according to 3 is for at least one cylinder of the internal combustion engine 100 , but preferably for all cylinders, checks whether the respective peak pressure PZa is greater than the predefinable maximum value PZmax for the peak pressure. This query is exemplary here for the first cylinder 110a ( 2 ) of the internal combustion engine 100 through the in the block 210 ( 3 ) inequality PZa> PZmax symbolizes.

Depending on whether the peak pressure PZa of the considered cylinder 110a is greater than the predetermined maximum value PZmax or not, then in the process branches 220 . 230 branches, each one - largely different - influencing the further operation of the internal combustion engine 100 to the subject.

If, for example, for the considered cylinder 110a in the query step 210 has been determined that its peak pressure PZa is less than or equal to the predetermined maximum value PZmax, after the query step 210 in the process branch 220 branched.

In a first step 2210 of the branch 220 a check is made as to whether an exhaust gas temperature T3 of the internal combustion engine 100 is greater than a first threshold T3w, wherein the first threshold T3w preferably from an operating point of the internal combustion engine 100 depends, for example, in the same way as the operating point dependent selected maximum value PZmax.

Unless the review 2210 shows that the exhaust gas temperature T3 is greater than the first threshold T3w, is in the function block 2212 branches, which advantageously a shift of an injection timing or an ignition timing of the internal combustion engine 100 Provides early to counteract the high exhaust gas temperature T3. Thereafter, the process branches again into the step 200 and starts, for example, with a new cycle for the same cylinder or cylinder.

Unless the verification according to step 2210 however, the exhaust gas temperature T3 is less than or equal to the first threshold value T3w, the following is the subsequent polling step 2220 branched.

In the query step 2220 is advantageously checked whether a driver's desired torque PWG exceeds a second threshold PWG1. The driver's desired torque PWG can advantageously be determined, for example, by means of an accelerator pedal transmitter (not shown), which, like the sensors 130 . 150 ( 2 ) to the control unit 160 connected. Unless the review 2220 according to 3 For example, it results that the driver's desired torque PWG is smaller than the second threshold value, the method branches according to 3 turn to the starting step 200 for a new pass.

Otherwise, that means if the verification according to step 2220 shows that the current driver's desired torque PWG is greater than the second threshold PWG1, is in the other query steps 2230 . 2240 branched. The second threshold value PWG1 can advantageously be selected to be approximately 100% or at least approximately 90%. In this case, the step becomes 2220 So only in the subsequent queries 2230 . 2240 branches, if the current driver's desired torque PWG assumes relatively large values, namely over 90% or even in the range of about 100%, the driver of the internal combustion engine 100 For example, the motor vehicle containing a correspondingly high torque request.

In the query 2230 Finally, it is checked whether a temperature T22 in the intake tract 120 ( 2 ) of the internal combustion engine 100 one, preferably in turn from an operating point of the internal combustion engine 100 dependent, third threshold exceeds T22max. Further, in step 2240 Checks if there is a pressure p22 in the intake tract 120 the internal combustion engine 100 one, preferably from an operating point of the internal combustion engine 100 dependent, fourth threshold exceeds p22max. If neither the temperature in the intake T22 nor the pressure p22 in the intake 120 the respective threshold values T22max, p22max exceed, is in the following function block 2250 branched, in the advantageous one the cylinder considered 110a assigned fuel quantity to be injected is increased. This is possible in the present case, since the temperatures T3, T22 in the exhaust tract 140 and the intake tract 120 the internal combustion engine 100 below corresponding threshold values T3w, T22max, and since the pressure p22 in the intake tract 120 Furthermore, it is also below a corresponding threshold p22max, ie there are still reserves for higher operating temperatures or pressure values with respect to these operating variables of the internal combustion engine. Further, in step 2220 has been checked whether a relatively large driver request torque PWG> PWG1 has been requested. In this case, therefore, in the advantageous step 2250 the fuel quantity to be injected of the respective cylinder increases by a predeterminable amount to an increased torque of the internal combustion engine 100 to effect.

In this way, advantageously, the injection quantity of the internal combustion engine 100 can also be increased beyond the statically predetermined amount, for example, by a characteristic map, provided that the corresponding operating variables T3, T22, p22 of the internal combustion engine considered according to the invention do not already have their respective predeterminable ones Thresholds have exceeded. This means that if the temperature in the intake tract and in the exhaust tract and the pressure in the intake tract have not already exceeded the corresponding threshold values and the driver requests a particularly high torque, in step 2250 In the method according to the invention, the injection quantity may advantageously be further increased, in particular beyond the maximum dimension statically predetermined in a conventional system, so that the internal combustion engine 100 actually also gives the requested higher torque. After the step 2250 will turn to the beginning 200 branches of the process.

Unless in the query of the steps 2230 respectively 2240 it is determined that the temperature T22 in the intake tract 120 or the pressure p22 in the intake tract 120 exceeds the corresponding threshold value T22max or p22max, the above-described increase in the injection quantity is not performed, see step 2250 but rather, without increasing the injection quantity, it is in turn branched to the beginning of the process for a new run, cf. step 200 ,

The method steps of the method branch described above 220 can be particularly advantageous for a cylinder of the internal combustion engine 100 , for several, or for all cylinders of the internal combustion engine 100 be performed, either sequentially or simultaneously or temporally overlapping and eg synchronously with the respective duty cycle of the cylinder under consideration.

In the presence of sufficient reserves with regard to the current temperature or pressure values in the intake tract or in the exhaust gas tract can be using the method branch 220 In the present embodiment, an individual increase in the amount of fuel to be injected per cylinder is advantageously carried out, provided that in addition the peak pressure PZa is not already above the maximum permissible value PZmax for the peak pressure, compare the query according to step 210 ,

If, however, in the comparison according to step 2 has been determined for a cylinder considered that the peak pressure PZa is greater than or equal to the predetermined maximum value PZmax, is in the process branch 230 branches with the steps explained in more detail below.

In general, it should be noted that the predefinable maximum value PZmax, which in the comparison of the step 210 is used, preferably for all cylinders of the internal combustion engine 100 is equal to. Alternatively, however, it may be chosen differently for different cylinders of the internal combustion engine.

In a first step 2310 of the process branch 230 According to one embodiment, provision is made for the exhaust gas temperature T3 of the internal combustion engine to be checked for the exceeding of a preferably, in turn, operating point-dependent fifth threshold value. If this is the case, step immediately 2360 branches, in which the fuel quantity to be injected for the cylinder under consideration is reduced. After the step 2360 will turn into the starting step 200 branches of the process.

The fifth threshold for the comparison 2310 can be the same as in step 2210 selected first threshold value T3w or deviating from this. Unless the review in step 2310 has revealed that the exhaust gas temperature T3 is not already above the fifth threshold, is in the step 2320 branches, in which, analogous to the step 2220 , a driver request torque is checked for exceeding a sixth threshold. If the driver's desired torque exceeds the threshold, in step 2330 branches, in which an injection timing or an ignition timing of the internal combustion engine 100 is retarded. Then, that is after the step 2330 , in turn, is in the starting step 200 branched.

The sixth threshold for the comparison 2320 can be the same as in step 2220 used second threshold PWG1 or deviating from this.

Unless the verification according to step 2320 has shown that the driver's desired torque is less than the sixth threshold, is in the step 2340 branches, in which a diagnostic function is executed, which is used to check a boost pressure sensor 130 and / or - if present - at least one actuator of a device for charging the internal combustion engine 100 , in particular a turbocharger (not shown), is used.

Subsequently, it becomes advantageous in step 2350 a maximum of the internal combustion engine 110 to be delivered torque limited, which, for example, by appropriate signaling a maximum allowable torque to a torque coordinator (not shown) of the internal combustion engine 100 can be done. The torque coordinator may be in the form of a software function in a computer program of the control unit, for example 160 ( 2 ) of the internal combustion engine 100 be implemented. Likewise, the process according to the invention ( 1 ) or its various embodiments, eg according to 3 , also as a computer program of the control unit 160 be realized.

Optionally, preferably between the step 200 and the comparison 210 , another query 240 respectively. In this query 240 is for at least two cylinders of the internal combustion engine 100 , but preferably for all cylinders of the internal combustion engine 100 , A respectively the cylinder pressure in the cylinder characterizing size, in particular a peak pressure of the cylinder in question, determined, and formed a measure of the deviation of the peak pressures of the respective cylinder with each other. This can be done, for example, that the peak pressures of all cylinders are subtracted from each other, possibly with subsequent magnitude formation of the difference obtained, the two cylinders of the internal combustion engine 100 to identify whose peak pressure values have the largest difference. This difference will be in step 240 evaluated. Unless the largest difference in peak pressure readings in step 240 considered cylinder, so a deviation of the peak pressures of the respective cylinder from each other exceeds a predetermined maximum value, the method branches into the subsequent steps 2410 . 2420 , Provided that the deviation of the peak pressures of the cylinders concerned according to the check after step 240 does not exceed the predefinable maximum value is, as already described in the comparison step 210 branched.

In step 2410 is advantageously limited to a maximum torque to be output by the internal combustion engine, for example, in turn, using a torque coordinator, and in step 2420 For example, a further diagnostic function can be executed, for example a fault memory entry in a fault memory of the control unit 160 ( 2 ) causes and / or signaling a need for maintenance of the internal combustion engine 100 has the object, for example, acoustically and / or visually to a user of the internal combustion engine 100 ,

The optional further review 240 Advantageously, make sure that step 210 and the subsequent process branches 220 . 230 be executed only if the respective deviation of the peak pressures of the cylinder with each other does not exceed the predetermined maximum value. Otherwise, it becomes equal to the error or operational risk limiting steps 2410 . 2420 branched.

The method according to the invention enables a differentiated diagnosis on the basis of the cylinder pressure, in particular the peak pressure, of both a single and a plurality of, preferably all, cylinders of the internal combustion engine. In addition to the diagnosis, in the event of a fault (for example, too great deviations of the peak pressure of different cylinders from one another, absolutely high peak pressure, overtemperature), differentiated diagnostic or safety measures (warning signals, fault memory entry, torque limitation) can be carried out. If the method according to the invention shows that there are still operating reserves, in particular with regard to the sizes of peak pressure, temperature, the torque of at least one individual cylinder can advantageously also be further increased by increasing the quantity of fuel to be injected, as a result of which the operating behavior u.a. under full load is improved.

The method according to the invention can be applied to all internal combustion engines which make it possible to determine the cylinder pressure of at least one cylinder. Particularly advantageously, the determination of the cylinder pressure is performed metrologically by means of cylinder pressure sensors, but can alternatively or additionally also model-based as a function of other operating variables of the internal combustion engine (for example, temporal change in the speed of the internal combustion engine).

The method may also help to detect faults of other components in an air system and / or fuel system of the internal combustion engine, e.g. Failure of actuators of a turbocharger or injectors for fuel injection. The deviation of the signals of different cylinder pressure sensors can be detected.

Claims (8)

Method for operating an internal combustion engine ( 100 ), wherein at least one of the cylinder pressure in a cylinder ( 110a ) of the internal combustion engine ( 100 ) characterizing variable (PZa) ( 200 ), characterized in that the variable characterizing the cylinder pressure is compared with a predefinable maximum value (PZmax) ( 210 ) and that, depending on the comparison ( 210 ) the further operation of the internal combustion engine ( 100 ) ( 220 . 230 ) becomes. The method of claim 1, wherein the cylinder pressure in a cylinder of the internal combustion engine ( 100 ) characterizing size is a peak pressure. Method according to one of the preceding claims, wherein the predefinable maximum value (PZmax) from a current operating point of the internal combustion engine ( 100 ), wherein the current operating point in particular by a rotational speed and / or an indicated mean pressure of the internal combustion engine ( 100 ) is defined. Method according to one of the preceding claims, wherein if the comparison ( 210 ) has shown that the characterizing size is smaller than the maximum value, at least one of the following steps is performed: - Check ( 2210 ), whether an exhaust gas temperature (T3) of the internal combustion engine ( 100 ) one, preferably from an operating point of the internal combustion engine ( 100 ) dependent, first threshold (T3w) exceeds, - Check ( 2220 ), whether a driver desired torque (PWG), in particular signaled by means of an accelerator pedal signal, exceeds a second threshold value (PWG1), 2230 ), whether a temperature (T22) in an intake tract ( 120 ) of the internal combustion engine ( 100 ) exceeds a third threshold value (T22max), which is preferably dependent on an operating point of the internal combustion engine, 2240 ), whether a pressure (p22) in the intake tract ( 120 ) of the internal combustion engine ( 100 ) exceeds a fourth threshold value (p22max), which is preferably dependent on an operating point of the internal combustion engine, - increasing ( 2250 ) a cylinder ( 110a ) to be injected fuel quantity, in particular when it is determined that the exhaust gas temperature (T3) of the internal combustion engine ( 100 ) does not exceed the first threshold (T3w) and / or the temperature (T22) in the intake tract ( 120 ) of the internal combustion engine ( 100 ) does not exceed the third threshold (T22max) and / or the pressure (p22) in the intake tract ( 120 ) of the internal combustion engine ( 100 ) does not exceed the fourth threshold (p22max) and / or the driver command torque (PWG) exceeds the second threshold (PWG1). Method according to one of the preceding claims, wherein if the comparison ( 210 ) has shown that the characterizing quantity is greater than or equal to the maximum value, at least one of the following steps is carried out: - checking ( 2310 ), whether an exhaust gas temperature (T3) of the internal combustion engine ( 100 ) one, preferably from an operating point of the internal combustion engine ( 100 ) dependent, fifth threshold (T3w), - Check ( 2320 ), whether a driver's desired torque (PWG), in particular signaled by means of an accelerator pedal signal, exceeds a sixth threshold value (PWG2), - shifting ( 2330 ) of an injection point and / or an ignition point at a later point in time, 2340 ) a diagnostic function for checking a boost pressure sensor ( 130 ) and / or at least one actuator of a device for charging the internal combustion engine ( 100 ), in particular a turbocharger, - limiting ( 2350 ) a maximum of the internal combustion engine ( 100 ) Torque to be delivered, - Reduce ( 2360 ) a cylinder ( 110a ) to be injected fuel quantity, in particular when it is determined that the exhaust gas temperature (T3) of the internal combustion engine ( 100 ) exceeds the fifth threshold (T3w). Method according to one of the preceding claims, wherein for at least two cylinders ( 110a . 110b ) of the internal combustion engine ( 100 ) one each the cylinder pressure in the respective cylinder ( 110a . 110b ) characterizing size (PZa), in particular a peak pressure of the relevant cylinder ( 110a . 110b ), and wherein a measure of the deviation of the peak pressures of the respective cylinders ( 110a . 110b ) is determined. Method according to claim 6, wherein if the deviation ( 240 ) the peak pressures of the cylinders concerned ( 110a . 110b ) exceeds a predefinable maximum value, at least one of the following steps is performed: - Limit ( 2410 ) a maximum of the internal combustion engine ( 100 ) Torque to be output, - Execute ( 2420 ) of a further diagnostic function that triggers an error memory entry and / or a signaling of a maintenance requirement of the internal combustion engine ( 100 ). Contraption ( 160 ) for operating an internal combustion engine ( 100 ), wherein at least one of the cylinder pressure in a cylinder ( 110a ) of the internal combustion engine ( 100 ) characterizing variable (PZa) can be determined ( 200 ), characterized in that the device ( 160 ) is adapted to compare the variable characterizing the cylinder pressure with a predefinable maximum value (PZmax) ( 210 ) and depending on the comparison ( 210 ) the further operation of the internal combustion engine ( 100 ) to influence ( 220 . 230 ). Contraption ( 160 ) according to claim 8, wherein the device ( 160 ) is designed to carry out the method according to at least one of claims 1 to 7.

Images