Method for operating an internal combustion engine

Abstract

Method for operating an internal combustion engine, wherein: - a knock signal (1) from a knock sensor (2) is acquired, - a cylinder pressure signal (3) from a cylinder pressure sensor (4) is acquired, which cylinder pressure signal (3) is representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine, - an estimated cylinder pressure (6) is determined from a knock signal (1) on the basis of a model (5), - the cylinder pressure signal (3) is subjected to a plausibility check (7), and - if the cylinder pressure signal (3) is not plausible according to the plausibility check (7), the estimated cylinder pressure (6) is used for the operation of the internal combustion engine.

Description

[0001] The present invention relates to a method for operating an internal combustion engine, an internal combustion engine having the features of the preamble of claim 12 as well as a computer program product and a computer-readable storage medium.

[0002] In order to operate an internal combustion engine, it is known from the state of the art to extract parameters from the ongoing combustion process in order to obtain information about the current combustion process.

[0003] As such a parameter, the prevailing cylinder pressure of at least one combustion chamber of the internal combustion engine is usually used, whereby the pressure as well as the time of the prevailing pressure can provide a high degree of information about the combustion process and can be used to intervene in the combustion process in order to avoid deviations and / or to optimize the combustion process.

[0004] It is known to measure the cylinder pressure via cylinder pressure sensors which protrude into the combustion chamber of the internal combustion engine and are designed to provide a characteristic signal for the cylinder pressure prevailing in the combustion chamber.

[0005] Corresponding sensors available on the market exhibit a fairly wide range in terms of quality, robustness and the quality of the sensor signal. This quality range is based on the manufacturing effort and material requirements and is reflected in the prices.

[0006] A disadvantage of cylinder pressure sensors, however, is that they represent a certain weak point in the control chain of an internal combustion engine, since such cylinder pressure sensors—regardless of quality or price—develop damage after a certain number of operating hours, and their representative sensor signal deteriorates. With lower-quality (and usually cheaper) sensors, such deterioration usually occurs sooner.

[0007] This change in the sensor signal is due to the fact that cylinder pressure sensors are exposed to the combustion process of the internal combustion engine, which leads to enormous thermal as well as mechanical stress, which causes material fatigue and / or failure of the cylinder pressure sensor after a certain number of operating hours.

[0008] Furthermore, it is known from the prior art to use knock sensors in internal combustion engines. These sensors measure the structure-borne noise of the internal combustion engine and provide a corresponding, representative knock signal. These knock sensors or their knock signal are typically used to monitor the combustion process to determine whether misfires or knocking are occurring in the internal combustion engine.

[0009] However, it is also known from the prior art to determine the cylinder pressure via the knock signal, since the precision and accuracy of knock sensors have developed over the course of development to the point where individual operating parameters, such as ignition in the combustion chamber, can be deduced from the structure-borne sound and vibration of the internal combustion engine, and thus the cylinder pressure in the combustion chamber can also be calculated via the sensor signal of the knock sensor, which means that a cylinder pressure sensor can even be completely dispensed with in order to carry out control or regulation of the internal combustion engine.

[0010] However, it has been found to be disadvantageous that a corresponding determination of the cylinder pressure via the knock signal is not only individual for each module, but even individual for each internal combustion engine itself, which means that a certain adaptation of a model has to be carried out in order to arrive at a cylinder pressure via the knock signal.

[0011] However, it has also been found that the calculation of the cylinder pressure via the knock signal also changes with the operating condition (e.g. a fluctuation in fuel quality) and / or an aging of the internal combustion engine, which means that it is only possible to continuously provide a reliable statement about the cylinder pressure via the knock signal during the ongoing operation of the internal combustion engine with a very high adaptation effort and corresponding calibration work.

[0012] The object of the present invention is to provide a method for operating an internal combustion engine, as well as an internal combustion engine, in which the aforementioned problems of the prior art can be at least partially improved and / or a reliable and meaningful possibility is created to provide information about the prevailing cylinder pressure in an internal combustion engine during operation and / or to implement an economical as well as ecological variant for determining a cylinder pressure with the necessary accuracy.

[0013] This object is achieved according to the invention by a method for operating an internal combustion engine having the features of claim 1 and claim 11, an internal combustion engine - preferably a reciprocating piston engine - having the features of claim 12, a computer program product having the features of claim 13, and a computer-readable storage medium.

[0014] According to a first aspect of the invention, a method for operating an internal combustion engine - in particular a reciprocating piston engine - comprises the following steps: Detecting a knock signal from a knock sensor, detecting a cylinder pressure signal from a cylinder pressure sensor, which cylinder pressure signal is representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine, determining a cylinder pressure estimated on the basis of a model from the knock signal, subjecting the cylinder pressure signal to a plausibility check, and if the cylinder pressure signal is not plausible according to the plausibility check, using the estimated cylinder pressure for the operation of the internal combustion engine.

[0015] According to this aspect of the present invention, it is possible to use a cylinder pressure sensor which provides a more accurate, representative signal for the cylinder pressure prevailing in the combustion chamber, whereby even sensor models of less than high quality can be used, since in a sense a fail-safe is provided via the knock sensor and the knock signal.

[0016] The cylinder pressure signal of the cylinder pressure sensor is continuously checked for its plausibility by the plausibility check and, if the cylinder pressure signal of the cylinder pressure sensor is no longer plausible, the estimated cylinder pressure is used - as a kind of failure protection for the cylinder pressure - in order to ensure the continued operation of the internal combustion engine.

[0017] In this way, an internal combustion engine can continue to operate even if a cylinder pressure sensor fails, which significantly increases the economical operation of the internal combustion engine.

[0018] Furthermore, it is possible to supply the internal combustion engine with the most accurate cylinder pressure signals from the cylinder pressure sensor for as long as possible in order to enable optimal operation of the internal combustion engine, which can not only reduce emissions but also increase efficiency for the most environmentally friendly operation possible.

[0019] In a further aspect of the invention, it can be provided that the following steps are carried out in a method for operating an internal combustion engine - in particular a reciprocating piston engine: Detecting a knock signal from a knock sensor, detecting a cylinder pressure signal from a cylinder pressure sensor, which cylinder pressure signal is representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine, determining an estimated cylinder pressure based on a model from the knock signal, and adapting the model based on the cylinder pressure signal such that the estimated cylinder pressure approximates the cylinder pressure signal and / or the cylinder pressure prevailing in at least one combustion chamber.

[0020] In this way, in the course of a further aspect of the invention, the model which describes a relationship between the knock signal and the prevailing cylinder pressure in the combustion chamber can be continuously adapted during ongoing operation, so that aging or other changes in operating parameters have no effect on the accuracy of the estimated cylinder pressure with regard to the actual cylinder pressure prevailing in the combustion chamber.

[0021] In a particularly advantageous manner, it can be provided that the two aspects of the present invention are combined with one another, wherein during ongoing operation the model which describes the relationship between knock signal and estimated cylinder pressure is continuously adapted and if a cylinder pressure signal measured by the cylinder pressure sensor no longer appears plausible, the further operation of the internal combustion engine can be continued by taking the estimated cylinder pressure into account.

[0022] In other words, within the scope of the invention, the inherently counter-intuitive measure of using a cylinder pressure sensor and a knock sensor can also be used to take advantage of the fact that the knock signals can be calibrated for a very long time and in such a way that a high-quality cylinder pressure signal is available via the knock sensor even after a failure of the cylinder pressure sensor.

[0023] Internal combustion engines can be understood as thermal working machines in which thermal energy released through combustion is converted into mechanical work, such as in Otto engines, diesel engines, gas turbines, boilers or similar.

[0024] The invention has proven particularly advantageous for use in stationary internal combustion engines—preferably gas-powered reciprocating piston engines. Marine applications are also quite conceivable.

[0025] Internal combustion engines, especially stationary internal combustion engines, can be used to drive generators to generate electricity. Such units with a generator driven by an internal combustion engine are often referred to as gensets.

[0026] An internal combustion engine according to the invention or a method according to the invention can be used in existing systems of the prior art, as described, for example, in the introduction to the description, and can be installed subsequently.

[0027] Advantageous embodiments of the invention are defined in the dependent claims.

[0028] It can be provided that - preferably if the cylinder pressure signal is plausible according to the plausibility check - the model is adapted on the basis of the cylinder pressure signal such that the estimated cylinder pressure approximates the cylinder pressure signal and / or the cylinder pressure prevailing in at least one combustion chamber.

[0029] Preferably, it can be provided that - if the cylinder pressure signal is plausible according to the plausibility check - the cylinder pressure signal of the cylinder pressure sensor is used for the operation of the internal combustion engine.

[0030] It can be provided that the method is carried out in a time-resolved and / or crank angle-resolved manner - preferably in real time - during the operation of the internal combustion engine.

[0031] It is also conceivable that the procedure is carried out based on the engine cycle or at a specific point in time during the cycle (where, for example, the procedure is carried out when the data is available).

[0032] Preferably, it can be provided that the estimated cylinder pressure and / or the cylinder pressure signal of the cylinder pressure sensor is used for controlling or regulating the internal combustion engine - particularly preferably for approximating a desired drive power, energy requirement or emission of the internal combustion engine.

[0033] It can be provided that the plausibility of the cylinder pressure signal is determined with the aid of at least one further determined operating parameter of the internal combustion engine.

[0034] Such a further determined operating parameter can be at least one of the following operating parameters: an ignition timing, a drive power and / or a torque, an angular velocity and / or a grid frequency of a generator driven by the internal combustion engine or a grid connected thereto, a boost pressure, a charge air temperature, and / or a combustion temperature.

[0035] It can be provided that the further determined operating parameter is provided as a measured sensor signal by at least one sensor and / or by an engine control of the internal combustion engine.

[0036] Preferably, it can be provided that the cylinder pressure signal is plausible according to a plausibility check if the cylinder pressure signal satisfies a predefined relationship between a cylinder pressure signal and the further determined operating parameters, wherein particularly preferably the relationship defines a value range for the cylinder pressure signal.

[0037] The value range can correspond to a defined cylinder pressure signal for a specific operating parameter + / - a tolerance range.

[0038] This tolerance range can preferably tolerate a measurement inaccuracy, combustion indifference or other assumed and expected value deviations that concern an acceptable fluctuation.

[0039] It can also be provided that the plausibility of the cylinder pressure signal is determined without the aid of another operating parameter of the internal combustion engine.

[0040] For example, the plausibility of the cylinder pressure signal can be determined by comparing it with a predefined maximum, minimum and / or a range of values.

[0041] It can be provided that the comparison of the determined cylinder pressure signal with a predetermined drag curve, which is preferably calculated anyway during combustion, takes place, whereby the cylinder pressure signal no longer appears plausible if it deviates too far from the drag curve.

[0042] A general plausibility check is also conceivable, whereby, for example, negative values ​​or unexpected values ​​in certain areas of the combustion cycle are considered implausible.

[0043] It can be provided that, for the operation of the internal combustion engine, the cylinder pressure signal and / or the estimated cylinder pressure is used to control or regulate a manipulated variable of the internal combustion engine, preferably an ignition timing, a boost pressure, a supplied fuel quantity, a supplied charge air quantity and / or an exhaust gas recirculation rate.

[0044] Furthermore, protection is sought for an internal combustion engine, preferably a reciprocating piston engine, comprising: at least one combustion chamber, a cylinder pressure sensor arranged on at least one combustion chamber, which is designed to determine a cylinder pressure signal representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine, at least one knock sensor, which is designed to determine a representative knock signal of the internal combustion engine, preferably of the at least one combustion chamber, and at least one control or regulating device, which is designed to receive a cylinder pressure signal of the cylinder pressure sensor and the knock signal of the knock sensor, wherein the control or regulating device is further designed to carry out a method according to the invention.

[0045] Protection is also sought for a computer program product comprising instructions that cause an executing computer, in particular a control or regulating device of an internal combustion engine, to: to receive a knock signal from a knock sensor, to receive a cylinder pressure signal from a cylinder pressure sensor that is representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine, to determine an estimated cylinder pressure from a knock signal on the basis of a model, to subject the cylinder pressure signal to a plausibility check, and if the cylinder pressure signal is not plausible according to the plausibility check, to use or output the estimated cylinder pressure for the operation of the internal combustion engine.

[0046] Furthermore, protection is sought for a computer-readable storage medium on which a computer program product according to the invention is stored.

[0047] Further details and advantages of the present invention are explained in more detail below with reference to the figure.

[0048] This shows Fig. 1 a schematic flow diagram of a method according to the invention for operating an internal combustion engine.

[0049] In this exemplary embodiment, the internal combustion engine comprises a knock sensor 2, by which a knock signal 1 is detected, and a cylinder pressure sensor 4, by which a cylinder pressure signal 3 can be detected.

[0050] The cylinder pressure signal 3 of the cylinder pressure sensor 4 is representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine.

[0051] The knock sensor 1 can be arranged on the internal combustion engine corresponding to the same combustion chamber as the cylinder pressure sensor 4 (for example on a cylinder head of the respective combustion chamber) or globally collect a knock signal 1 for the entire internal combustion engine.

[0052] In a first step, the knock signal 1 of the knock sensor 2 is fed to a signal filter 10, which filters the knock signal 1 of the knock sensor 2 accordingly and prepares it for further processing, wherein disturbance variables are filtered and the sensor signal is cleaned accordingly, and the sensor signal is converted into a preferred signal variable if necessary.

[0053] The processed knock signal 1 is then passed on to the model 5, which model 5 reflects a relationship between the processed knock signal 1 and an estimated cylinder pressure 6, whereby the filtered knock signal 1 is converted into an estimated cylinder pressure 6.

[0054] The model 5 can also take into account further operating parameters 9 of the internal combustion engine, whereby, for example, the knock signal 1 is further processed into an estimated cylinder pressure 6 with crank angle resolution.

[0055] For example, further operating parameters 9 of the internal combustion engine can be a crank angle ω, a boost pressure P 2 ', a charge air temperature T 2 ' or an ignition timing ITP.

[0056] After the measurement by the cylinder pressure sensor 4, the cylinder pressure signal 3 is passed to a plausibility check 7, wherein the cylinder pressure signal 3 is subjected to a plausibility check 7 with the aid of further operating parameters 9.

[0057] The plausibility check 7 comprises a query in this exemplary embodiment, wherein a defined value range is represented with regard to the further operating parameters 9, wherein - if the cylinder pressure signal 3 corresponds to this defined value range - the cylinder pressure signal 3 is classified as plausible and the plausibility check 7 sets the switch in such a way that the cylinder pressure signal 3 is forwarded to the control or regulating device 8 of the internal combustion engine.

[0058] If the cylinder pressure signal 3 is not classified as plausible by the plausibility check 7, the switch is switched and the estimated cylinder pressure 6 is passed on to the control or regulating device 8 of the internal combustion engine instead of the cylinder pressure signal 3, wherein the further control or regulation of the internal combustion engine takes place on the basis of the estimated cylinder pressure 6 instead of the cylinder pressure signal 3.

[0059] By means of the plausibility check 7, for example, a defect in the cylinder pressure sensor 4 can be detected and corrected in a timely manner so that faulty cylinder pressure signals 3 are not used for control or regulation by the control or regulation device 8 of the internal combustion engine, which could possibly lead to faulty control or regulation of the internal combustion engine.

[0060] However, if the plausibility check 7 shows that the cylinder pressure signal 3 appears plausible, the model adaptation 11 is further activated by the plausibility check 7.

[0061] A difference between estimated cylinder pressure 6 and cylinder pressure signal 3 is supplied to this model adaptation 11 and, on the basis of this difference, the model 5 is adapted by the model adaptation 11 in such a way that the estimated cylinder pressure 6 is approximated to the cylinder pressure signal 3.

[0062] By means of a corresponding, continuous adaptation of model 5 - provided that cylinder pressure signal 3 appears plausible - a change in the operating conditions, wear and / or aging of the internal combustion engine can be incorporated into the model and it can be ensured that model 5 continues to provide a precise relationship between knock signal 1 and cylinder pressure.

[0063] After the plausibility check 7 forwards either the cylinder pressure signal 3 or the estimated cylinder pressure 6 to the control or regulating device 8 of the internal combustion engine, a further plausibility query 12 is carried out, which carries out an additional plausibility check taking into account further operating parameters 9 of the internal combustion engine in order to ensure that the cylinder pressure signal 3 or the estimated cylinder pressure 6 supplied to the control or regulating device 8 also corresponds to an actual value of the pressure in the combustion chamber.

[0064] The control or regulating device 8 of the internal combustion engine can then carry out a corresponding control or regulation of the internal combustion engine on the basis of the characteristic signal for the pressure in the combustion chamber by outputting the manipulated variables 13, wherein, for example, a fuel mass m G , an ignition timing ITP, an ignition misfire or other changes to manipulated variables of the internal combustion engine can be carried out.

[0065] The Fig. 1 The method shown is to be understood purely as an example, whereby it should be noted that these method steps can be integrated into the control or regulating device 8 of the internal combustion engine, for example by means of corresponding software modules.

[0066] This control or regulating device 8 of the internal combustion engine can, for example, be implemented as a central machine control of the internal combustion engine.

[0067] Furthermore, it should be noted that the Fig. 1The procedure described can be carried out individually for each combustion chamber of the internal combustion engine or globally across the entire internal combustion engine. List of reference symbols:

[0068] 1 Knock signal 2 Knock sensor 3 Cylinder pressure signal 4 Cylinder pressure sensor 5 Model 6 Estimated cylinder pressure 7 Plausibility check 8 Control or regulating device 9 Additional operating parameter 10 Signal filter 11 Model adaptation 12 Additional plausibility check 13 Actuated variable

Claims

1. Method for operating an internal combustion engine, wherein - a knock signal (1) of a knock sensor (2) is detected, - a cylinder pressure signal (3) of a cylinder pressure sensor (4) is detected, which cylinder pressure signal (3) is representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine, - an estimated cylinder pressure (6) is determined from a knock signal (1) on the basis of a model (5), - the cylinder pressure signal (3) is subjected to a plausibility check (7), and - if the cylinder pressure signal (3) is not plausible according to the plausibility check (7), the estimated cylinder pressure (6) is used for operating the internal combustion engine.

2. Method according to the preceding claim, wherein, preferably if the cylinder pressure signal (3) is plausible according to the plausibility check (7), the model (5) is adapted on the basis of the cylinder pressure signal (3) such that the estimated cylinder pressure (6) approximates the cylinder pressure signal (3) and / or the cylinder pressure prevailing in at least one combustion chamber.

3. Method according to one of the preceding claims, wherein if the cylinder pressure signal (3) is plausible according to the plausibility check (7), the cylinder pressure signal (3) of the cylinder pressure sensor (4) is used for the operation of the internal combustion engine.

4. Method according to at least one of the preceding claims, wherein the method is carried out in a time-resolved and / or crank angle-resolved manner, preferably in real time, during operation of the internal combustion engine.

5. Method according to at least one of the preceding claims, wherein the estimated cylinder pressure (6) and / or the cylinder pressure signal (3) of the cylinder pressure sensor (4) is used for controlling or regulating the internal combustion engine, preferably for approximating a desired drive power, energy requirement and / or emission of the internal combustion engine.

6. Method according to at least one of the preceding claims, wherein the plausibility of the cylinder pressure signal (3) is determined with the aid of at least one further determined operating parameter (9) of the internal combustion engine.

7. Method according to the preceding claim, wherein at least one of the following operating parameters is used as a further determined operating parameter (9): - an ignition point, - a drive power and / or a torque, - an angular velocity and / or a mains frequency, - a boost pressure, - a charge air temperature, and / or - a combustion temperature.

8. The method according to claim 6 or 7, wherein the further determined operating parameter (9) is provided as a measured sensor signal by at least one sensor and / or by a control or regulating device (8) of the internal combustion engine.

9. Method according to at least one of claims 6 to 8, wherein the cylinder pressure signal (3) is plausible according to the plausibility check (7) if the cylinder pressure signal (3) satisfies a predefined relationship between a cylinder pressure signal (3) and the further determined operating parameter (9), wherein the relationship preferably defines a value range for the cylinder pressure signal (3).

10. Method according to at least one of the preceding claims, wherein for the operation of the internal combustion engine the cylinder pressure signal (3) and / or the estimated cylinder pressure (6) is used to control or regulate a manipulated variable of the internal combustion engine, preferably an ignition timing, a boost pressure, a supplied fuel quantity, a supplied charge air quantity and / or an exhaust gas recirculation rate.

11. Method for operating an internal combustion engine, in particular according to one of the preceding claims, wherein - a knock signal (1) of a knock sensor (2) is recorded, - a cylinder pressure signal (3) of a cylinder pressure sensor (4) is recorded, which cylinder pressure signal (3) is representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine, - an estimated cylinder pressure (6) is determined from the knock signal (1) on the basis of a model (5), and - the model (5) is adapted on the basis of the cylinder pressure signal (3) such that the estimated cylinder pressure (6) approximates the cylinder pressure signal (3) and / or the cylinder pressure prevailing in at least one combustion chamber.

12. Internal combustion engine, preferably a reciprocating piston engine, comprising: - at least one combustion chamber, - a cylinder pressure sensor (4) arranged on at least one combustion chamber, which is designed to determine a cylinder pressure signal (3) representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine, - at least one knock sensor (2) designed to determine a representative knock signal (1) of the internal combustion engine, preferably of the at least one combustion chamber, and - at least one control or regulating device (8) designed to receive the cylinder pressure signal (3) of the cylinder pressure sensor (4) and the knock signal (1) of the knock sensor (2), characterized in that the control or regulating device (8) is further designed to carry out a method according to at least one of claims 1 to 11.

13. A computer program product comprising instructions which cause an executing computer, in particular a control or regulating device (8) according to claim 12, to - receive a knock signal (1) from a knock sensor (2), - receive a cylinder pressure signal (3) from a cylinder pressure sensor (4) which is representative of a cylinder pressure prevailing in at least one combustion chamber of the internal combustion engine, - determine an estimated cylinder pressure (6) from a knock signal (1) on the basis of a model (5), - subject the cylinder pressure signal (3) to a plausibility check (7), and - if the cylinder pressure signal (3) is not plausible according to the plausibility check (7), use or output the estimated cylinder pressure (6) for the operation of the internal combustion engine.

14. A computer-readable storage medium on which a computer program product according to claim 13 is stored.

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