Method and control unit for identifying a cylinder of an internal combustion engine subject to misfire

Abstract

A method for identifying cylinders of an internal combustion engine that have experienced a fire during operation includes: a step of determining whether the engine has experienced a misfire condition; a step of measuring vibrations generated when operating the engine; and a step of identifying at least one cylinder that has experienced a misfire based on the measured vibrations.

Description

Technical Field

[0001] The present invention relates to a method for identifying a cylinder of an internal combustion engine that has experienced a misfire during operation, and a control unit for an internal combustion engine for carrying out such a method. Background Art

[0002] To ensure high efficiency, internal combustion engines are designed to burn the air-fuel mixture in their cylinders in a timed-controlled manner, so as to form a peak pressure in their cylinders at an ideal time under ideal operating conditions, in order to regain the maximum amount of work from the expanding gases generated during combustion. For this purpose, the ignition of the air-fuel mixture and the propagation of the flame front in the combustion chamber need to be carried out according to a strictly defined pattern. However, any deviation from the ideal operating conditions may lead to less favorable combustion of the air-fuel mixture, and thus to a deterioration in the performance and efficiency of the engine.

[0003] During operation, the engine, i.e., its individual cylinders, may experience poor combustion or non-combustion, such that no significant energy conversion occurs, and thus no significant pressure and temperature rise is experienced in a single cylinder. These undesired and unexpected phenomena constitute a malfunction of the engine and are generally referred to as misfires or combustion misfires.

[0004] Combustion misfires can be caused by many different reasons. For example, a malfunction of the ignition system, i.e., the spark plugs, may lead to poor combustion or non-combustion in an individual cylinder of the engine. Alternatively, the intake system of the engine may experience a malfunction, such that the air-fuel mixture fed into the combustion chamber of the engine has an unfavorable composition, e.g., an air-fuel ratio outside the combustible range.

[0005] In addition to the deterioration of engine performance and efficiency, misfires may cause unburned fuel to enter the exhaust system of the engine. In this way, when the unburned fuel is discharged into the environment through the exhaust system, misfires may cause damage to the catalytic converter present in the exhaust system and environmental pollution. Furthermore, the analysis of misfire phenomena is a key contributing factor in many fault mode detection and emission-related control methods. Therefore, the detection and evaluation of misfire phenomena occurring during engine operation have been focused on in different engine types and applications.

[0006] From the prior art, it is known to identify a continuous misfire condition in an individual cylinder, i.e., a misfire that occurs continuously in subsequent operating cycles of the engine, for example by identifying defective spark plugs in the ignition system. However, the known methods are not suitable for detecting the occurrence of poor combustion or intermittent misfire phenomena, i.e., fault conditions that occur intermittently or only during a certain number of operating cycles. Summary of the Invention

[0007] Starting from the prior art, the aim is to propose an improved method for monitoring engine misfires, which method is in particular capable of more accurately evaluating the misfire phenomena occurring during operation and classifying them. Another aim is to provide a control unit for an internal combustion engine configured to carry out such a misfire monitoring method.

[0008] These aims are solved by means of the subject matter of the independent claims. Preferred embodiments are set forth in the description, the drawings and the dependent claims.

[0009] Accordingly, there is provided a method for identifying cylinders of an internal combustion engine that are experiencing misfires during operation, the method comprising the steps of: determining whether the engine is experiencing a misfire condition; measuring vibrations generated when operating the engine; and identifying at least one cylinder experiencing misfire based on the measured vibrations.

[0010] In addition, there is provided a control unit for an internal combustion engine for identifying cylinders of the engine that are experiencing misfires during engine operation. The proposed control unit is configured to carry out the method as described above. Accordingly, the technical features described in connection with the above method in the present disclosure may also refer to and apply to the proposed control unit and vice versa. Specifically, the control unit is configured to determine whether the engine is experiencing a misfire condition, to obtain at least one vibration signal indicative of vibrations generated by the engine during operation and measured by a vibration sensor, and to identify at least one cylinder experiencing misfire based on the vibration signal. Description of the Drawings

[0011] The present disclosure will be more readily understood by reference to the following detailed description considered in conjunction with the accompanying drawings, in which:

[0012] Figure 1 A power generation unit equipped with an internal combustion engine is schematically shown;

[0013] Figure 2 A flowchart is schematically shown, which shows an overview of a method for identifying cylinders experiencing misfires during operation of the internal combustion engine shown in Figure 1 ;

[0014] Figure 3 A program of steps of a method for determining the occurrence of misfire phenomena during engine operation is schematically shown;

[0015] Figure 4 A program of steps of a method for determining a set of suspected misfire cylinders is schematically shown;

[0016] Figure 5 A program of steps of a method for identifying cylinders experiencing misfires is schematically shown; and

[0017] Figure 6 A program schematically showing the steps of a method for determining the type of fire Detailed implementation mode

[0018] Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings. In the drawings, the same elements are denoted by the same reference numerals, and their repeated description may be omitted to avoid repetition.

[0019] Figure 1 A power generation unit 10 for generating electric power to be supplied to a power grid 12 is schematically shown. The power grid 12 can have any suitable size and, for example, can be a decentralized or national power grid connected to a plurality of power generation units, but is not limited to this configuration. On the contrary, in one configuration, the power grid 12 can be equipped with electric power generated by only one power generation unit. The power generation unit 10 can form or be part of a power plant and includes at least one generator 14 driven by an internal combustion engine 16 (hereinafter also referred to as an "engine") to convert mechanical energy into electric power fed to the power grid 12. Accordingly, the generator 14 is electrically connected to the power grid 12 and is coupled to the internal combustion engine 16 in a torque transmission manner. Specifically, the generator 14 is coupled to the output shaft 18 of the engine 16 such that the generator 14 is actuated by the output shaft 18 during operation of the engine 16.

[0020] The engine 16 is an internal combustion engine, particularly a reciprocating engine. Specifically, the engine 16 can be a stationary gas engine powered by a fuel-air mixture of gas fuel and air, such as a mixture of natural gas and air. The engine 16 includes a plurality of cylinders, such as eight or twelve or eighteen cylinders, which can be arranged according to an in-line engine configuration, a V-shaped configuration, or any other known cylinder configuration.

[0021] Each cylinder is provided with a combustion chamber defined by a piston received in the cylinder. The piston is configured to reciprocate and axially move within the cylinder and is coupled to the crankshaft of the engine such that the reciprocating movement of the piston is converted into rotational movement of the crankshaft.

[0022] During operation of the engine 16, an air-fuel mixture is supplied to each cylinder and ignited in each cylinder to produce high-temperature and high-pressure gases that exert a force on the associated piston and thus axially displace the associated piston, thereby rotating the crankshaft and thus rotating the output shaft 18, which is coupled to the crankshaft in a torque transmission manner. In this way, chemical energy is first converted into mechanical energy that drives the output shaft 18 of the generator 14 and then into electrical energy by means of the generator 14. In one configuration, fresh air can be mixed with the fuel medium to produce an air-fuel mixture before entering the combustion chamber. Alternatively, fresh air and the fuel medium can be supplied separately to the combustion chamber, for example by means of a fuel pump that injects the fuel medium into the combustion chamber, and thus mixed within the combustion chamber.

[0023] The engine 16 further includes a control unit 20, also referred to as the "engine control unit" or "engine control module", which is configured to control and monitor the operation of the engine 16. Specifically, the control unit 20 is of the electronic control unit type and is configured to read measurement data from a plurality of sensors that monitor various engine operating parameters. In addition, the control unit 20 is configured to process and interpret the measurement data thus obtained and, in response, control the actuation of a plurality of engine actuators, for example by controlling ignition characteristics such as the amount and composition of the air-fuel mixture to be fed into and ignited in the combustion chamber, ignition timing, valve actuation and timing, etc., in order to set and adjust the operating point of the engine.

[0024] The basic structure and function of such an internal combustion engine 16 and its components, in particular the control unit 20, are well known to those skilled in the art and are therefore not further described. Instead, a method for monitoring the operation of the engine and for identifying cylinders that are experiencing misfires, which is interconnected with the present invention, is discussed below. This method is intended and configured to detect and unambiguously identify misfire conditions that occur during operation of the engine 16 and is also referred to below as the "method".

[0025] In the context of the present disclosure, the terms "misfire condition", "misfire", or "combustion misfire" refer to any undesired and unexpected degradation of the combustion process occurring in at least one cylinder of an engine that affects the performance or efficiency of the engine during an operating cycle. For example, this may be the case when no combustion occurs or combustion is incomplete in at least one cylinder during operation. In the sense of the present disclosure, a misfire condition refers to at least one of a non-combustion condition and an incomplete or poor combustion condition. Specifically, in the context of the present disclosure, the term "non-combustion condition" refers to the operating cycle of a cylinder in which no combustion occurs. The term "incomplete combustion condition" or "poor combustion condition" refers to such an operating cycle of a cylinder during which the air-fuel mixture present in the associated combustion chamber is not completely combusted, i.e., only a part of it burns. In addition, the term "distorted combustion condition" refers to such an operating cycle of a cylinder in which the flame front generated in the air-fuel mixture present in the cylinder at ignition does not spread in a desired manner, e.g., due to engine knock, and / or combustion does not start at the desired time.

[0026] Generally, the term "operating cycle" refers to the combustion cycle of a cylinder, which includes the following steps: supplying an air-fuel mixture to the cylinder; combusting the air-fuel mixture; and subsequently discharging exhaust gas from the engine. Usually, the operating cycle is associated with one or more piston strokes within the cylinder.

[0027] The proposed method is suitable and configured to detect and classify different types of misfire conditions, i.e., to determine whether the detected misfire involves a non-combustion condition or an incomplete combustion condition. In the context of the present disclosure, the term "misfire condition type" refers to a misfire condition or a group of misfire conditions having a predetermined characteristic or characteristics within a predetermined range. In this way, the combustion characteristics of the misfire for a single operating cycle can be clarified.

[0028] In addition, the proposed method is suitable for detecting and clarifying different types of misfire events, such as continuous, intermittent, and single misfire events. Specifically, the term "continuous misfire event" refers to the failure condition of a cylinder in which misfires occur continuously, i.e., in subsequent operating cycles of the engine. The term "intermittent misfire event" is the failure condition of a cylinder in which misfires occur intermittently in subsequent operating cycles. In other words, in the cylinders affected by such a failure, proper operating conditions and misfire conditions can alternate. In addition, the term "single misfire event" is the failure condition of a cylinder in which misfires occur in only a single operating cycle within a set of subsequent operating cycles. By clarifying the type of misfire event, the combustion characteristics of the misfire for multiple subsequent operating cycles can be clarified.

[0029] In the illustrated configuration, the control unit 20 is configured to execute as described below with reference to Figures 2 to 6The method described by the flowchart shown in Figure 2 An overview of the general procedure of the method is described, and then reference is made to Figures 3 to 6 Individual method steps and their underlying procedures are described in more detail.

[0030] Figure 2 A general overview of a proposed method for monitoring misfire phenomena in engine 16 is shown. In the context of the present invention, it has been found that in order to provide an improved engine monitoring concept or method, for example, which is eligible as a key enabling factor for improved subsystem fault detection and assessment and emission control methods, more information is needed, which goes beyond simply detecting whether a misfire phenomenon has occurred. To this end, the proposed method is intended and configured to provide additional information about the detected misfire phenomenon by identifying the location where the misfire has occurred and by defining the combustion characteristics of the misfire.

[0031] To this end, when executed by control unit 20, the proposed method provides information about: whether a misfire condition has occurred or has occurred or when it has occurred or has occurred, see step S1; the location where the misfire has occurred, i.e., the cylinder that is or has been affected by the misfire, see steps S3 and S4; the type or combustion characteristics of the misfire, see step S5. In this way, the proposed method provides in-depth information about the misfire phenomenon that occurs during engine operation, thus allowing for improved assessment and analysis of the misfire condition.

[0032] The method starts when engine 16 is started. In a first step S1, control unit 20 determines or detects the occurrence of a misfire. In other words, in this step, control unit 20 determines whether engine 16 has experienced or has experienced a misfire condition during operation.

[0033] In parallel, step S2 is executed, in which the vibrations generated during engine operation are measured and provided to control unit 20. To this end, the method utilizes one or more vibration sensors attached to or provided in engine 16. Thus, control unit 20 obtains one or more vibration signals provided by at least one sensor unit, where each of the vibration signals indicates the vibrations generated by engine 16. In addition, each vibration signal can represent the vibrations generated during operation, which are measured at different parts of the engine, as will be described in more detail below.

[0034] If control unit 20 determines in step S1 that a misfire has occurred, the method proceeds to step S3 to determine a set of suspected misfire cylinders. The term "suspected misfire cylinder" refers to a cylinder that may or has experienced a misfire. In other words, in this step, a pre-selection or pre-determination is made to limit the number of cylinders whose operation is further calculated or determined. In this way, a multi-step method is provided that allows for effective and efficient monitoring and definition of the misfire condition.

[0035] Subsequently, the method proceeds to step S4, where the control unit 20 identifies those cylinders that have experienced misfires, i.e., the cylinders that have actually experienced or are experiencing misfires. To this end, the control unit 20 considers the vibration signals obtained in step S2. In other words, in this step, the control unit 20 identifies at least one cylinder experiencing misfire based on the measured vibration, i.e., the obtained vibration signal (as indicated by the dashed line in Figure 2 ). In this way, this step determines the misfire location, i.e., in which cylinder or cylinders the misfire has occurred or is occurring.

[0036] In the subsequent step S5, the control unit 20 further clarifies the detected misfire by determining the type of misfire based on combustion characteristics. This step is performed based on the measured vibration obtained in method step S2. Specifically, in this step, the type of misfire condition is determined, i.e., whether a non-combustion condition or an incomplete combustion has occurred. In addition, it is determined which misfire event the detected misfire event is associated with, i.e., whether the detected misfire constitutes or involves a continuous, intermittent, or single misfire event.

[0037] Then, the method proceeds to step S6, which provides misfire statistics and thus constitutes a misfire statistics development block. In this step, the occurrence and classification of misfires are monitored during the operation of the engine 16 and processed for further use of such information. For example, in this step, the occurrence of misfires can be accumulated over a certain period based on the classification, e.g., based on type and / or location, thus providing the function of a counter indicating the frequency of misfire occurrences during a certain period during the operation of the engine 16. In this way, misfire statistics can be provided.

[0038] The misfire statistics can be used to determine the proper functioning of the engine 16 and its components, such as the ignition system, or to evaluate whether the engine 16 should undergo maintenance work or further analysis. For example, the control unit 20 can accumulate the occurrence of misfire conditions, such as intermittent misfire conditions, during the operation of the engine 16 to determine the frequency of misfires occurring during operation. In addition, the control unit 20 can compare the frequency thus determined with a threshold value, and when the determined frequency reaches the threshold value, output a signal indicating that the engine will undergo maintenance work or further analysis.

[0039] All information related to the misfire statistics can be broadcast by the control unit 20, for example, via a CAN bus or Modbus or Ethernet communication link, to other components of the engine 16 or systems inside or outside the power generation unit 10.

[0040] The procedures shown in steps S1 to S6 constitute an analysis loop, which is repeatedly executed and initiated under a predetermined event. Specifically, the analysis loop can be executed during an associated time period or continuously for an associated time period during engine operation to determine whether misfire occurs and classify it during the considered time period. Specifically, the analysis loop can be initiated periodically, that is, at a predetermined timing and / or at regular intervals. The time period associated with the analysis loop can refer to one or more operating cycles of the engine. Specifically, the analysis loop can be initiated and executed for one or more operating cycles of each cylinder. In addition, the continuous analysis loop constituted by steps S1 to S6 can be executed in continuous cycles, that is, directly one after another, or with a delay time in between.

[0041] Hereinafter, with reference to Figure 3 Step S1 for determining the occurrence of misfire is further described below, which explains the underlying program of step S1, that is, its sub-steps and the interaction of the sub-steps. Generally speaking, step S1 is intended to and is executed to determine whether the engine 16 is affected by or undergoes misfire. This step is intended to detect whether misfire has occurred or has already occurred, but may not further classify the misfire. Instead, in order to further clarify and classify the misfire, steps S3 to S5 are executed after it has been determined in step S1 that misfire has occurred.

[0042] In the first sub-step S1.1, the control unit 20 determines whether the engine 16 is operating in a predetermined operating state, that is, a warm-up or mature operating state. In this way, it can be ensured that the engine 16 has reached a stable operating point at which the engine 16 can operate efficiently under stable conditions. The predetermined operating state can further serve as a reference state for the engine 16, which allows for an effective evaluation of the engine's operation. In this sub-step, the control unit 20 can monitor at least one engine operating parameter, such as engine speed, engine temperature, etc., and determine that the engine is in a mature state when at least one or each of the at least one operating parameter has reached a predetermined threshold or is within a predetermined range.

[0043] If it is determined that the engine 16 is not in its mature state, the method returns to the start of step S1, and the analysis loop, that is, step S1, is re-initiated after a predetermined delay time. However, when it is determined that the engine 16 is operating in a predetermined operating state, that is, a mature state, the method proceeds to the second step S1.2, in which the control unit 20 monitors the operation of the engine 16, that is, the performance of the engine 16. For this purpose, the control unit 20 receives or obtains at least one engine operating signal.

[0044] In the context of the present disclosure, the term "engine operating signal" refers to any parameter suitable for quantifying engine performance and operation over time (i.e., during the operation of engine 16), such as the operating point of the engine. Specifically, in sub-step 1.2, control unit 20 determines at least one engine operating signal that indicates engine speed or the power output by the engine over time. In a further development, control unit 20 may determine an engine operating signal that indicates at least one of engine load, the pressure prevailing in the engine, such as intake manifold pressure, and the differential pressure at the throttle of engine 16. To receive at least one engine operating signal, control unit 20 is connected to at least one measuring unit, which is configured to measure engine operating parameters, process the measured parameters, and transmit them to control unit 20 in the form of an engine operating signal. Alternatively, control unit 20 may be configured to receive the measured parameters and process them to generate an engine operating signal.

[0045] Thereafter, in sub-step S1.3, control unit 20 is configured to detect an unexpected performance change of the engine during its operation based on the obtained engine operating signals. In other words, in this step, control unit 20 determines whether engine 16 is subject to an unexpected performance change, in particular an unexpected performance degradation. This step refers to an associated time period. This means that control unit 20 determines whether engine 16 has experienced or has been subject to an unexpected performance change during the associated time period. To this end, control unit 20 analyzes the engine operating signals obtained in sub-step S1.2, which indicate the performance of the engine during the associated time period.

[0046] According to one configuration, during sub-step S1.3, control unit 20 may be configured to determine an engine power signal and / or an engine speed signal, where the engine power signal indicates the actual performance or the power output by engine 16, and the engine speed signal indicates the actual engine speed, i.e., the rotational frequency of the crankshaft and / or camshaft of the engine, in particular the number of rotations of the crankshaft and / or camshaft per unit of time. To obtain the engine power signal, control unit 20 may communicate with a first measuring unit, which is configured to perform current transformer measurement and voltage transformer measurement at generator 14. In other words, the first measuring unit is configured to measure the operation of generator 14 and generate an engine power signal based on the measurement. To obtain the engine speed signal, control unit 20 may communicate with a second measuring unit, which is provided in the form of at least one pick-up sensor coupled to the crankshaft and / or camshaft of engine 16. Thus, the second measuring unit is configured to measure the engine speed and generate an engine speed signal based thereon.

[0047] In addition, the control unit 20 may be configured to process the engine power signal and / or the engine speed signal thus obtained, for example, by performing a filtering step to eliminate spikes and high-frequency noise from the signal and / or by calculating derivatives. Then, the control unit 20 may analyze the engine power signal and / or the engine speed signal to determine whether an unexpected performance change has occurred during operation, i.e., within the associated time period. For this purpose, for example, the control unit 20 may compare the magnitude of the derivative of the engine power signal and / or the engine speed signal with an associated threshold or threshold range. Thus, in the case where the control unit 20 determines that the associated threshold or threshold range has not been reached, the control unit 20 does not detect an unexpected performance change and returns to the start of the analysis loop. However, if the control unit 20 determines that the associated threshold or threshold range has been reached, then the control unit 20 detects an unexpected performance change and proceeds to the sub-step S1.4 of verifying the measurement signal.

[0048] In sub-step S1.4, the engine operation signal obtained in sub-step S1.2 is analyzed to verify the function of the engine 16 in order to determine whether the unexpected performance change is caused by a misfire phenomenon. In other words, the control unit 20 checks and verifies whether the measured engine operation signal properly represents the operation and function of the engine 16. In this way, the condition and function of the engine 16 and the measurement unit used for the method are evaluated to exclude certain fault conditions that may cause or indicate an unexpected performance change of the engine but are not related to the misfire condition. Therefore, sub-step S1.4 may also be referred to as a recognition step.

[0049] When it is determined that the engine operation signal is not in an appropriate state, the method returns to the start of the analysis loop. However, if it is determined that the engine operation signal is in an appropriate state, the method proceeds to method step S3.

[0050] In addition, when a misfire condition is detected, the control unit 20 determines the misfire time point, i.e., the time point when the misfire occurs during engine operation. For this purpose, the control unit 20 determines when the unexpected performance change occurs. In other words, the control unit 20 performs the step of determining the misfire time point based on the engine operation signal. Alternatively or additionally, the control unit 20 may consider the vibration signal obtained in step S2 to determine the misfire time point.

[0051] As elaborated above and as can be learned from Figure 2 it is known that in parallel with step S1, step S2 is performed, in which the control unit 20 obtains a vibration signal indicating the measured vibration generated when the engine 16 operates. The vibration signal is generated and provided by at least one vibration sensor. In addition, the control unit 20 or the vibration sensor may be configured to process the vibration signal thus obtained, for example, by performing a filtering step to eliminate spikes and high-frequency noise from the signal.

[0052] In the configuration shown, a plurality of vibration sensors are used, and the plurality of vibration sensors are distributively arranged at or in the engine 16. Preferably, the vibration sensors are arranged such that they are associated with different cylinders of the engine 16. In this case, the vibration sensor associated with a cylinder indicates that it is arranged near that cylinder. Specifically, one vibration sensor may be provided for each cylinder or for every certain number of cylinders. According to one configuration, the number of vibration sensors may correspond to or be greater than the number of cylinders that operate, i.e., operate synchronously, during the same cycle or beat during the operation of the engine 16. In this way, at least one vibration sensor may be associated with or arranged near one of the plurality of cylinders that operate in the same cycle or beat.

[0053] The vibration sensors employed are configured to sense the vibrations generated when operating the engine 16 and to generate vibration signals respectively, which indicate the vibrations sensed by the vibration sensors over time. To this end, the vibration sensors may be configured to measure the movement of the engine 16, i.e., the oscillatory movement. To this end, the vibration sensors may be provided in the form of accelerometers. This accelerometer may be configured to sense the inertial forces acting on the test mass provided therein. In this way, the movement or vibration induced by the engine may be converted into an electrical signal, i.e., a vibration signal. According to one configuration, at least one vibration sensor may be provided in the form of a knock sensor, which is used in known engine configurations to detect engine knock. In other words, the vibration sensor may have the function of detecting and thus protecting the engine from abnormal combustion events such as combustion explosions or knock, especially the main function, where the proposed solution assigns an additional function to these sensors, i.e., identifying the cylinders that are experiencing misfires. In this way, the proposed method utilizes the hardware already present in known engine configurations to classify the misfire phenomenon without using any additional or extra sensors or measurement techniques, thus providing a cost-effective method. According to one configuration, when a misfire condition is detected, the control unit 20 may switch the function of the vibration sensor from monitoring the knock phenomenon to monitoring the misfire phenomenon. Alternatively or additionally, at least one vibration sensor may be provided in the form of a microphone device, which is configured to sense vibrations in the form of sound waves propagated through the engine 16 and / or the air around the engine 16.

[0054] As elaborated above, when it is determined in step S1 that the engine 16 is experiencing a misfire, the method proceeds to Figure 4Step S3 shown therein, where a set of suspected misfiring cylinders is determined. In this step, first, the control unit 20 obtains the misfire time points determined in step S1, referring to sub-step S3.1, and the ignition enabling pulses for each cylinder, referring to sub-step S3.2, which indicate the timing for providing an ignition pulse to ignite the fuel-air mixture in the corresponding cylinder. Thus, the term "ignition enabling pulse" refers to a pulse in response to which the ignition system, in particular, initiates combustion in the corresponding cylinder of the engine 16 by generating a spark with a spark plug in the associated combustion chamber. Then, in sub-step S3.3, the control unit 20 compares the misfire time points with the ignition enabling pulses for each cylinder. Specifically, for this purpose, the control unit 20 determines those ignition enabling pulses that are activated or generated within a predetermined time range around the misfire time point. Thereafter, those cylinders associated with the determined ignition enabling pulses that fall within this time range are identified. As a result, the cylinders so identified constitute the set of suspected misfiring cylinders. The set of suspected misfiring cylinders may include one or more identified cylinders.

[0055] Thereafter, the method proceeds to step S4, which identifies Figure 5 the cylinders that have experienced misfires shown therein. Performing this step enables at least one cylinder to be identified from the set of suspected misfiring cylinders determined in the previous method step S3.

[0056] In the first sub-step S4.1, a sensor status determination step is performed to evaluate whether the vibration sensor used to obtain the vibration signal is in a proper functional state. In other words, in this step, the function of the vibration sensor is verified, that is, it is determined whether the sensor is in a proper functional state. For this purpose, a likelihood check may be performed to evaluate the measured values provided by the vibration sensor. For example, the vibration signal provided by the sensor may be compared with a reference value or a threshold range. If the measured signal is within the threshold range, then the control unit 20 may determine that the corresponding vibration sensor is in a proper functional state.

[0057] If the control unit 20 determines that the vibration sensor is in a proper functional state, the method proceeds to sub-steps S4.2 to S4.4 to perform classification based on the vibration signal, that is, to determine the misfire location. However, when it is determined that the vibration sensor is not in a proper state, the method proceeds to step S4.5, during which classification based on a combustibility test is performed. In this way, a redundant method is provided to ensure that even when the vibration sensor is not working properly, the classification of misfires can be performed.

[0058] More specifically, in sub-step 4.5, the ignition system of the engine 16 is monitored and tested for misfire classification. During this step, a functional test of the engine 16 is performed, during which the engine 16 is operated in a test mode, in which the engine 16 is run at a reduced or decreased load. More specifically, the engine 16 is activated to a safe mode with reduced power of the engine. Then, for the suspected cylinders, the ignition angle is sequentially delayed in a predetermined manner, i.e., one by one for these cylinders. During each step of delaying the ignition angle, misfire statistics are carried out and monitored. Based on these statistics, the misfire location is determined, i.e., those cylinders affected by the misfire are identified.

[0059] As described above, when the control unit 20 determines that the vibration sensor is in an appropriate functional state, the method proceeds to sub-steps S4.2 to S4.4 for performing classification based on the vibration signal.

[0060] Specifically, in sub-step S4.2, the control unit 20 analyzes the vibration signals associated with the cylinders included in the set of suspected misfire cylinders by continuously monitoring the suspected cylinders, i.e., after a misfire occurrence has been detected, in particular by obtaining and analyzing the vibration signals associated therewith. Alternatively, the control unit 20 may analyze the vibration signals associated with the suspected cylinders within a time period associated with the misfire time point. In this way, the vibration signals can be retrospectively analyzed. For this purpose, the control unit 20 may be configured to store the vibration signals acquired within a predetermined time period in such a manner. The time period associated with the misfire time point may refer to a time period of a predetermined length around the misfire time point. In this way, the observation window can be improved to focus only on the relevant sensed vibrations.

[0061] In response thereto, in sub-step S4.3, the characteristics of the vibration signals within the considered time period are determined or obtained. Preferably, the considered time period may refer to a time period associated with one or more operating cycles after the misfire condition has been detected, i.e., after the misfire time point. Alternatively, the considered time period may refer to a time period associated with the misfire time point.

[0062] In particular, at least one of the frequency, magnitude, and process of the measured vibration, i.e., the form of the vibration signal, is determined and quantified in this sub-step. Thereafter, in sub-step S4.4, the characteristics so determined are compared with reference characteristics or values, i.e., reference frequencies, reference magnitudes, or reference forms, in order to identify those cylinders that have experienced misfires.

[0063] For example, in sub-step S4.3, the frequency of the vibration signal of each cylinder within the considered time period may be determined, and then compared with a threshold or threshold frequency in sub-step S4.4. In the case where the frequency of the vibration signal associated with a cylinder reaches the threshold or threshold frequency, the control unit 20 may determine that this cylinder has experienced a misfire.

[0064] Alternatively or additionally, in sub-step S4.3, the maximum value of the magnitude of the vibration signal of each cylinder can be determined over the considered time period, and this maximum value is then compared with a threshold or threshold magnitude in sub-step S4.4. In the case where the maximum magnitude of the vibration signal associated with a cylinder is equal to or exceeds the threshold or threshold magnitude, the control unit 20 can determine that the cylinder is experiencing misfire.

[0065] Alternatively or additionally, in sub-step S4.3, the form of the vibration signal of each cylinder can be compared with a reference form in order to quantify the similarity value therebetween. For example, for this purpose, the difference between the vibration signal and a reference signal constituting the reference form can be quantified, and this difference can represent the similarity value. Then, in step S4.4, the similarity value can be compared with a threshold. In the case where the similarity value drops below the threshold, the control unit 20 can determine that the cylinder under consideration (i.e., considering its associated vibration signal) is experiencing misfire.

[0066] The following refers to Figure 6 Method step S5 is further described below, which shows its underlying program, i.e., its sub-steps and their interactions. In step S5, the control unit 20 further clearly detects the misfire by determining the type of misfire based on its combustion characteristics. For this purpose, the type of misfire condition is clarified in the first sub-step S5.1. This step is performed based on the measured vibration obtained in method step S2. Specifically, in this step, the type of misfire condition is determined, i.e., whether a non-combustion condition or an incomplete combustion condition has occurred.

[0067] In order to determine the type of misfire condition, the control unit 20 analyzes the vibration signal associated with the identified cylinder over the considered time period. Specifically, the characteristics of the vibration signal considered in the time period of the considered misfire time point are determined or quantified, in particular at least one of the frequency, magnitude, and form of the vibration signal, and then compared with reference characteristics or values in order to determine the misfire condition. This procedure can be performed similarly to steps S4.2 to S4.4 described above, where the individual determined characteristics of the considered vibration signal are compared with different reference characteristics in order to distinguish different types of misfire conditions.

[0068] In the second sub-step S5.2, the control unit determines the type of misfire event to which the detected misfire will be associated. For this purpose, the control unit 20 compares the detected misfire with misfires that have been detected previously, i.e., in previous analysis cycles, in order to determine whether the misfire constitutes part of a continuous misfire event, an intermittent misfire event, or a single misfire event.

[0069] It will be apparent to those skilled in the art that these embodiments and items merely depict examples of various possibilities. Therefore, the embodiments shown herein should not be construed as forming limitations on these features and configurations. Any possible combination and configuration of the described features can be selected according to the scope of the present invention.

[0070] This is especially true for the following optional features, which can be combined in any technically feasible combination with some or all of the previously mentioned embodiments, items, and / or features.

[0071] Accordingly, a method for identifying a cylinder of an internal combustion engine that experiences a misfire during operation can be provided, which includes the steps of determining whether the engine experiences a misfire condition; measuring vibrations generated during operation of the engine; and identifying at least one cylinder that experiences a misfire based on the measured vibrations. Specifically, the term "misfire" can refer to at least one of an unburned condition and an incomplete combustion condition that occurs during at least one operating cycle of a cylinder.

[0072] The proposed method provides a way by which it is possible to first determine whether a misfire condition has occurred during engine operation. Thereafter, based on the measured vibrations generated during operation of the engine, the misfire is classified, that is, further clarified. In this way, a two-step method is provided such that a misfire condition can be detected in a short response time, that is, in real time or near real time, and when a misfire has been detected, the misfire is further clarified in another process. In this way, an effective and efficient method can be provided.

[0073] In addition, the proposed method can be used for misfire detection and classification in any suitable internal combustion engine, especially a reciprocating engine. For example, the method can be used for a stationary gas engine that is especially used for power generation, but is not limited to this application. Such a gas engine can be powered by a gaseous fuel and a fuel-air mixture of air, such as a mixture of natural gas and air.

[0074] In a further development, the step of determining whether the engine experiences a misfire condition can include a sub-step of determining an engine operation signal that indicates an engine speed or engine power of the engine output; and a sub-step of detecting an unexpected performance change of the engine based on the engine operation signal to determine whether the engine experiences a misfire.

[0075] In addition, the method can include the step of determining a misfire time point based on at least one of the measured vibrations and the determined engine operation signal.

[0076] In a further development, the step of measuring the vibration can be carried out by means of at least one vibration sensor, each of the at least one vibration sensor obtaining a vibration signal indicative of the vibration sensed by the vibration sensor over time, wherein the vibration sensor is at least one of an accelerometer, a knock sensor, and a microphone device. According to one configuration of the method, more than one, i.e., at least two, vibration sensors are used to measure the vibration, and the vibration sensors are mounted or arranged spaced apart from each other in or at the engine.

[0077] Alternatively or additionally, the method may further include the step of determining a set of suspected misfiring cylinders based on the misfire time point and the ignition enabling pulses, each ignition enabling pulse being associated with a cylinder. Specifically, the step of pre-determining a set of suspected misfiring cylinders includes a sub-step of determining the ignition enabling pulses that are activated within a predetermined time range around the misfire time point; and identifying those cylinders associated with the ignition enabling pulses that fall within this time range.

[0078] Furthermore, the step of identifying at least one cylinder can be performed such that at least one cylinder is identified from the set of suspected misfiring cylinders. In other words, only cylinders that form part of the set of suspected misfiring cylinders can be identified in this step.

[0079] In a further development, the step of identifying at least one cylinder can be carried out by analyzing the vibration measured during a time period associated with the misfire time point. Alternatively or additionally, in the step of identifying at least one cylinder, the characteristics of the measured vibration can be determined, in particular at least one of the frequency, magnitude, and course of the measured vibration, and compared with reference characteristics in order to identify at least one cylinder that has experienced misfire.

[0080] Moreover, the method may include the step of determining the type of misfire condition based on the measured vibration to distinguish between non-combustion conditions and incomplete combustion conditions. Specifically, in the step of determining the type of misfire condition, the characteristics of the measured vibration can be determined, in particular the magnitude, frequency, and course of the measured vibration, and compared with reference characteristics associated with different types of misfire conditions in order to identify the type of misfire condition.

[0081] In a further development, the method may include the step of verifying the function of at least one vibration sensor used to measure the vibration, wherein when it is determined that the vibration sensor is not in a proper functional state, a combustibility test of the engine is carried out, during which the engine is operated at a reduced load.

[0082] In addition, a control unit for an internal combustion engine can be provided, which is used to identify the cylinders of the engine that experience misfires during operation. The control unit can be configured to determine whether the engine experiences a misfire condition, to obtain at least one vibration signal that indicates vibrations generated by the engine during operation and measured by a vibration sensor, and to identify at least one cylinder experiencing a misfire based on the vibration signal.

[0083] Industrial applicability

[0084] With reference to the accompanying drawings and their descriptions, a method and a control unit for identifying cylinders of an internal combustion engine are proposed. The method and the control unit as described above are applicable to, for example, an internal combustion engine provided as a stationary gas engine. The proposed method can be implemented in or for a conventional internal combustion engine. In addition, the proposed control unit can replace a conventional control unit and can serve as a replacement or retrofit component.

Claims

1. A method for identifying cylinders of an internal combustion engine (16) that experience a fire during operation, comprising: - a step (S1) of determining whether the engine (16) is experiencing a misfire condition; - a step (S2) of measuring vibrations generated during operation of the engine (16) by means of a plurality of vibration sensors associated with different cylinders of the engine (16); - a step of determining a misfire time point based on the measured vibrations and an engine operating signal indicating engine speed or engine power output of the engine; - a step (S3) of determining a set of suspected misfire cylinders based on the misfire time point and ignition enabling pulses, each ignition enabling pulse being associated with a cylinder; and - a step (S4) of identifying at least one cylinder that experiences a misfire based on the measured vibrations.

2. The method according to claim 1, wherein the misfire refers to at least one of an unburned condition and an incomplete combustion condition that occurs during an operating cycle of a cylinder of the engine (16).

3. The method according to claim 1 or 2, wherein the step (S1) of determining whether the engine is experiencing a misfire condition includes a sub-step of determining the engine operating signal; and a sub-step of detecting an unexpected performance change of the engine based on the engine operating signal for determining whether the engine is experiencing a misfire.

4. The method according to claim 1 or 2, wherein each of the plurality of vibration sensors obtains a vibration signal indicating vibrations sensed by the vibration sensor over time, and wherein the vibration sensor is at least one of an accelerometer, a knock sensor, and a microphone device.

5. The method according to claim 4, wherein at least two vibration sensors spaced apart from each other are used to measure vibrations.

6. The method according to claim 1 or 2, wherein the step (S3) of determining a set of suspected misfire cylinders comprises: - a sub-step (S3.3) of determining ignition enabling pulses that are activated within a predetermined time range around the misfire time point; and - a sub-step (S3.4) of identifying at least one cylinder associated with ignition enabling pulses that fall within the time range.

7. The method according to claim 1 or 2, wherein the step (S4) of identifying the at least one cylinder is performed such that at least one cylinder is identified from the set of suspected misfire cylinders.

8. The method according to claim 1 or 2, wherein the step (S4) of identifying the at least one cylinder is performed by analyzing vibrations measured during a time period associated with the misfire time point.

9. The method according to claim 1 or 2, wherein in the step (S4) of identifying the at least one cylinder, characteristics of the measured vibrations are determined, including at least one of the frequency, magnitude, and process of the measured vibrations, and compared with reference characteristics in order to identify the at least one cylinder that experiences a misfire.

10. The method according to claim 1 or 2 further comprises a step (S5.1) of determining the type of misfire condition based on the measured vibration to distinguish between a non-combustion condition and an incomplete combustion condition, wherein, the characteristics of the measured vibration are determined, including the magnitude, frequency and process of the measured vibration, and compared with reference characteristics associated with different types of misfire conditions in order to identify the type of misfire condition.

11. The method according to claim 4 further comprises a step (S4.1) of verifying the function of the vibration sensor, wherein when it is determined that the vibration sensor is not in a proper functional state, a combustibility test is performed on the engine (16), and during the combustibility test, the engine (16) is operated at a reduced load.

12. A control unit (20) for an internal combustion engine (16), the control unit being configured to identify a cylinder of the engine (16) that experiences misfire during operation, wherein the control unit (20) is configured to: - determine whether the engine (16) experiences a misfire condition, - obtain at least one vibration signal indicative of vibrations generated by the engine (16) during operation and measured by a plurality of vibration sensors associated with different cylinders of the engine (16), - determine the misfire time point based on the measured vibration and an engine operating signal indicative of the engine speed and the engine power output of the engine, - determine a set of suspected misfire cylinders based on the misfire time point and ignition enable pulses, each ignition enable pulse being associated with a cylinder; and - identify at least one cylinder experiencing misfire based on the vibration signal.

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