Method and device for measuring combustion processes in an internal combustion engine

Abstract

A method and a device for measuring combustion processes in an internal combustion engine are proposed, comprising a sensor (2) that is attached to a surface of the internal combustion engine (1). The sensor measures deformations of the surface of the internal combustion engine that are generated by combustion processes in the internal combustion engine (1). The measured deformations are corrected using correction values, which are determined as a function of operating parameters of the internal combustion engine (1). The corrected deformations are used to evaluate the combustion processes.

Description

State of the art

[0001] The invention is based on a device and a method for measuring combustion processes in an internal combustion engine according to the preamble of the independent patent claims. Devices and methods for measuring combustion processes in an internal combustion engine are already known, in which an acceleration sensor is mounted on an internal combustion engine. Such acceleration sensors are typically suitable for measurements in a frequency range greater than 1 kHz. DE 100 18 265 B4 already discloses methods for measuring combustion chamber pressure, in which a strain gauge is positioned in the interior of the cylinder head. Such measuring arrangements are extremely sensitive with regard to the positioning of the strain gauges and exhibit significant distortion of the measurement signals due to changing temperatures. From the article "Amirante, R., Casavola, C., Distaso, E., and Tamburrano, P., "Towards the Development of the In-Cylinder Pressure Measurement Based on the Strain Gauge Technique for Internal Combustion Engines," SAE Technical Paper 2015-24-2419, 2015, doi:10.4271 / 2015-24-2419" already demonstrates the fundamental usability of a strain gauge for measuring combustion processes. For this purpose, such a strain gauge is placed in a cooling channel of an internal combustion engine. Therefore, the use of strain gauges requires direct on-site installation, which is problematic due to the temperature stress on the strain gauge measurement signal. Advantages of the invention

[0002] The device and method according to the invention with the features of the independent patent claims have the advantage that improved measurement and evaluation of combustion processes in an internal combustion engine is achieved. In particular, an adapted evaluation of the measured values ​​of the combustion processes can be performed. This can take into account special features of the operating parameters of the internal combustion engine and their influence on the measurement. Overall, an improved evaluation of combustion processes in an internal combustion engine is achieved, which can improve the operation of an internal combustion engine.

[0003] Further advantages and improvements arise from the measures of the dependent patent claims. In particular, individual correction values ​​can be taken into account for individual cylinders in order to account for different structural designs of the individual cylinders or the arrangement of the sensors relative to the cylinders. By selecting a suitable measuring window, the quality of the measurement is improved, as this allows the signals relevant to the measurement to be considered. A particularly simple comparison of the measured values ​​with a threshold value is carried out. This comparison can consist of an exceedance or undershoot or a relative deviation. Alternatively, the gradient of the corrected deformation or both the time and the magnitude of the maximum value of the deformation can be evaluated. Alternatively, an evaluation of an integral corrected deformation is also possible.The different evaluation methods allow optimal evaluation methods to be selected for each specific internal combustion engine or its operating procedure. Drawings

[0004] Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. It shows the Fig. 1 an internal combustion engine with a sensor for measuring combustion processes in the internal combustion engine and Fig. 2 a detailed view of the sensor and a cylinder of the internal combustion engine, Fig. 3 Process steps of the process according to the invention, Fig. 4 a first evaluation procedure, Fig. 5 a second method for evaluation and Fig. 6 a third method for evaluation. Description

[0005] In the Fig. 1 schematically shows an internal combustion engine 1 with a sensor 2 attached to its surface. The sensor 2 is designed to measure deformations of the surface of the internal combustion engine 1 and is connected to a control unit 4 via a connecting line 3. The control unit 4 determines information regarding the combustion processes taking place in the internal combustion engine 1 based on the signals from the sensor 2. Based on the information thus determined regarding the combustion processes in the internal combustion engine 1, the control unit 4 calculates control signals for actuators or control elements of the internal combustion engine 1 and sends corresponding control signals via line 5 to the control elements or actuators of the internal combustion engine 1.

[0006] To clarify the operation of the sensor 2 or the internal combustion engine 1, Fig. 2, a single cylinder 21 of the internal combustion engine 1 is shown schematically again. The internal combustion engine 1 has a cylinder 21 with a piston 22 arranged therein. The piston 22 and the cylinder 21 form a combustion chamber 20, into which fuel and air are introduced for the combustion processes of the internal combustion engine 1. The necessary actuators, such as air intake valves and air outlet valves and a corresponding fuel injection, are shown in the Fig. 2 not shown. Due to the combustion processes, the pressure in the combustion chamber 20 is periodically increased and converted into mechanical work by a movement of the piston 22 along the direction of movement 23 through a connecting rod on a crankshaft of the internal combustion engine. The up and down movement of the piston 22 is thus converted into a rotary movement of the crankshaft. In the case of multiple cylinders, the crankshaft is driven by several cylinders. The rotational axis of the crankshaft is always perpendicular to the direction of movement 22 of the pistons. This is a conventional Otto internal combustion engine. Depending on the pressure conditions in the combustion chamber 20, a superficial deformation of the cylinder 21 occurs, which is measurable by the sensor element 2 on an outer surface of the cylinder 21. In the Fig. 2, the sensor 2 is shown on an outer surface of the cylinder 21. Preferably, the sensor 2 is arranged in an area where the deformation of the cylinder 21 is particularly severe due to the pressure increase in the combustion chamber 20. Depending on the design details of the internal combustion engine 1, a suitable location on the surface of the internal combustion engine 1 must be determined empirically.

[0007] In the Fig. 2 shows a sensor 2 which consists of a two-part housing with a base plate 24 and a cover 25. A strain gauge element 26, which is preferably in the form of a piezo element 26, is arranged on the base plate 24. The base plate 24, in turn, is connected to the surface of the internal combustion engine 1, in particular to an outer surface of the cylinder 21. In typical Otto internal combustion engines with a plurality of cylinders 21, these multiple cylinders are typically designed as a cylinder block, i.e. as a one-piece metal block in which a plurality of cylinders are provided. This makes it possible to measure the signals of a plurality of cylinders using a single sensor. Even with individual cylinders, the cylinder 21 is also realized by a cylinder block, i.e. by a continuous metal workpiece.The sensor's location on the outer surface of the cylinder block ensures reliable detection of deformations. The cylinder block's design as a single, continuous metallic workpiece translates pressure increases in the internal combustion engine's combustion chamber into easily detectable deformations of the cylinder block's outer surface.

[0008] The housing of the sensor 2 is attached to the surface of the internal combustion engine using suitable joining techniques that ensure the transfer of surface deformations to the actual measuring element 26. Adhesive or screw fastening have proven particularly suitable.

[0009] In the Fig. 2, the direction of movement of the piston 22 in the cylinder 21 is represented by the arrow 23. It has been found that the deformations of the surface of the internal combustion engine 1 perpendicular to the direction of movement 23 of the piston 22, i.e. parallel to the rotational axis of the crankshaft, are relatively strong on the surface of the internal combustion engine. Furthermore, sensors for measuring deformations can have a preferred measuring direction. For this purpose, the measuring element 26 can, for example, be designed as an elongated strip, and the greatest sensitivity for deformations is accordingly along the longest extent of this strip. The sensor element as shown in the Fig. 2, is designed to be significantly longer parallel to the rotational axis of the crankshaft of the internal combustion engine 1 than in the two directions perpendicular to it. Fig. The sensor element shown in Figure 2 thus exhibits the greatest sensitivity parallel to the rotational axis of the crankshaft, and the deformation is particularly pronounced in this direction. This arrangement of the measuring element 26 or sensor 2, with its measuring direction parallel to the rotational axis of the crankshaft, ensures optimal measurement of the deformation of the internal combustion engine 1.

[0010] The deformation of the surface of the internal combustion engine 1 is suitable for providing a variety of information about the combustion processes in the internal combustion engine 1. This allows the pressure conditions in the combustion chamber 20 to be analyzed during the combustion process. Abnormal combustion processes, such as knocking, combustion misfires, and pre-ignition, can be detected. This allows the quality of combustion and the health of the internal combustion engine to be assessed. Furthermore, combustion can be continuously monitored and appropriate control or regulation interventions can be implemented. Overall, the quality of combustion in the internal combustion engine 1 is thus improved.

[0011] A particularly advantageous feature is that such a sensor for measuring the deformation of the surface of the internal combustion engine allows for a very favorable frequency range for measurement. This allows for the evaluation of deformations in a frequency range from greater than 0.5 Hz to several tens of kHz. The low frequency range, in particular, cannot be measured with the acceleration sensors commonly used for combustion analysis.

[0012] In the Fig. 3 shows a sequence of method steps for evaluating the measured deformation of the surface of the internal combustion engine. The method is started in a first step 31 when sufficient conditions for starting the method are met. This is usually the case when a sufficiently steady-state operating state of the internal combustion engine has been reached, for example a warm-up phase has been completed. The start in step 31 is followed by a first step 32 in which a measurement window is defined. This measurement window specifies the range in which the deformation signal for a specific cylinder is measured. This measurement window can be defined either as a time window or as an angular window. A time window specifies, for example relative to the time of combustion in the individual cylinder of the internal combustion engine, a time range in which the measurement for assessing the combustion of a specific cylinder is carried out.An angle window specifies an angular range, for example, relative to the ignition angle of the internal combustion engine, within which the measurement is taken to assess the combustion of a specific cylinder. The selection of the appropriate measurement window can depend on the operating parameters of the internal combustion engine or the operating parameters of the individual cylinders, such as the engine speed or load.

[0013] After the measurement window has been selected, step 33 occurs in which the actual measurement of the deformation signal for the respective cylinder takes place. Step 33 is followed by step 34 in which a correction value is read in. This correction value is made available from a step 39, for example from a memory in which correction values ​​are stored as a function of the operating parameters of the internal combustion engine or the individual cylinders. In the following step 35, a corrected deformation is calculated based on the measured deformation in step 33 and the correction value determined in step 34. This correction adapts the individual measured values ​​to the conditions of the individual cylinder. In this way, different conditions of the individual cylinders can be individually taken into account when measuring the signal.In the subsequent step 36, a comparison value is read in, which is provided by a step 37, for example, from a memory. The comparison values ​​can, for example, depend on operating parameters of the internal combustion engine or the cylinders. The comparison value from step 36 and the corrected deformation from step 35 are then fed to a step 38 for evaluation, in which the combustion is evaluated. The details of this evaluation step are explained in more detail in the following figures.

[0014] In the Fig. 4, the evaluation of the combustion with regard to combustion misfires is graphically represented. In the time course T, the intensity of the corrected deformations, which were determined in step 35, are shown for several combustions (7 in total) of an internal combustion engine with several cylinders, for example 4 cylinders. The individual measurement windows are represented on the time axis by the times T0, T1 ... to T7. Furthermore, the comparison value provided in step 37 is shown, which in the case of the evaluation whether a combustion misfire is present or not, simply consists of a threshold value 41 for the corrected deformation. As in the time course of the Fig. 4, the maximum value of the intensity I of the corrected deformation of the first (T0 - T1) and second (T1 - T2) combustion exceeds the threshold value 41. However, the maximum value of the intensity I of the corrected deformation of the third (T2 - T3) combustion is significantly lower than the threshold value 41. The intensity I of the maximum value of the corrected deformation of the fourth, fifth, sixth and also the seventh combustion each exceeds the threshold value 41. For an internal combustion engine with 4 cylinders, it is significant that the seventh (T6 - T7) combustion also exceeds the threshold value 41, although this combustion took place in the same cylinder as the third (T2 - T3) combustion. The representation of the Fig. Figure 4 thus shows only a single event for a combustion misfire in the third cylinder. The subsequent combustion in the same cylinder occurred normally again, i.e., no combustion misfire was detected. If this cylinder had been permanently impaired, the intensity I of the maximum deformation value would have remained below threshold 41 again during the seventh combustion. To determine whether a combustion misfire has occurred or not, the use of a simple threshold 41 as a comparison value for the evaluation is sufficient. The evaluation is then performed simply by determining whether the intensity I of the maximum value of a corrected deformation exceeds threshold 41 or not.

[0015] By using the corrected deformation, the actually measured deformations in an internal combustion engine with multiple cylinders are converted into corrected deformations, thus compensating for cylinder-specific differences. For example, the intensity of the deformation can vary for different cylinders due to the structural design of the internal combustion engine. This can also be due to the arrangement of the sensors relative to the cylinders. Furthermore, multiple cylinders can be evaluated by a single sensor. Depending on the distance of the sensor relative to the cylinder, this results in an offset in the measurement in step 33. Furthermore, the measured signals can also vary depending on different operating states of the internal combustion engine.In step 39, correction values ​​are therefore determined individually for each cylinder and for each operating state of the internal combustion engine, which are used to calculate the corrected deformation in step 35.

[0016] In the Fig. 4, markers (T0 .. T7) are shown on the time axis, each indicating the measurement window for a specific cylinder. In the representation of the Fig. 4, these measurement windows are designed to connect seamlessly to one another. However, it is also possible to use measurement windows separated by individual pauses or to use measurement windows that overlap one another. Furthermore, it is also possible to make these measurement windows dependent on the operating parameters of the internal combustion engine, for example, the engine's speed under load. The measurement windows can be defined as time windows or angle windows, for example, relative to an ignition point or an ignition angle.

[0017] In the Fig. 5, the evaluation of combustions with regard to the ratio of air to fuel, the so-called lambda, is shown by evaluating a corrected deformation. To evaluate a combustion with regard to the value of lambda, the intensity I of the corrected deformation is plotted against time T in the curves 52, 53, 54. The maximum value of the intensity I of the corrected deformation is compared with a reference value 51. In contrast to Fig. 4 However, it is not evaluated whether the intensity I of the deformation is greater or smaller than the comparison value 51, but rather the distance relative to the value 51 is evaluated. The comparison value 51 corresponds to a lambda of 1, as shown by curve 53. If the maximum value of the intensity I of the corrected deformation is greater than the comparison value 51, as shown in curve 54, then there is a fuel surplus, i.e. a lambda value of <1, whereby the height of the maximum value I is a measure of the undershoot of the lambda value. If the maximum value of the intensity I of the corrected deformation is smaller than the comparison value 51, as shown in curve 52, then there is a fuel shortage, i.e. a lambda value of >1, whereby the height of the maximum value I is a measure of the overshoot of the lambda value.The value for lambda is calculated according to the deviation of the intensity I of the maximum value of the corrected deformation.

[0018] In the Fig. 6 shows another form of evaluation of the corrected deformation with respect to the lambda value of a combustion. The corrected deformation of the Fig. 6 differs not only with regard to the intensity of the maximum value of the deformation, but also with regard to the time at which the maximum value occurs. With increasing leanness, i.e. an increase in the lambda value, the time at which the maximum value of the corrected combustion occurs is shifted to later times and at the same time the intensity I of the maximum value is reduced. A lambda value of 1 corresponds to curve 61, which has the comparison value 66 in terms of intensity and the comparison value 65 in terms of time. Curve 62, which corresponds to a lambda value of less than 1, i.e. an excess of fuel, has a higher intensity than the value 66 and an earlier time than the time 65 compared to curve 62 for the maximum value.Curve 63, which corresponds to a lambda value of more than 1, i.e. a lack of oxygen, has a lower intensity than the value 66 and a later time than time 65 compared to curve 62 for the maximum value. This evaluation with regard to the level of intensity and the time of occurrence of the maximum can be carried out, for example, by forming the quotient of intensity to time at time T0 and at the time of the maximum value of the intensity. The higher this quotient, the higher the intensity and the earlier the time was at which the maximum was reached. This quotient corresponds to the slope or gradient of a straight line which represents the curve of the corrected deformation in the . Fig. 6 at time T0 and at the time of occurrence of maximum intensity. The corresponding quotient of curve 62 is therefore higher than curve 61, and the quotient of curve 63 is lower than curve 61. The degree of deviation of this quotient then indicates the deviation of the lambda value from the value 1.

[0019] Alternatively to the Fig. 4 to 6 could also be an evaluation of an integral of the area under the Fig. 4 to 6 shown curves in the measurement window. The value of an integral formed in this way can then be compared with reference values ​​that allow a corresponding evaluation of the combustion. In the example after the Fig. 4 would simply check whether the integral is below a threshold. In the example after the Fig. 5, the total area could be evaluated in the time window T0 to T1. In the example after the Fig.6 a comparison value for the integral could be defined and it is checked at which point in time this comparison value is reached. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 100 18 265 B4

[0001] Cited non-patent literature

[0000] “Amirante, R., Casavola, C., Distaso, E., and Tamburrano, P., “Towards the Development of the In-Cylinder Pressure Measurement Based on the Strain Gauge Technique for Internal Combustion Engines,” SAE Technical Paper 2015-24-2419, 2015, doi:10.4271 / 2015-24-2419”

[0001]

Claims

[1] Method for measuring combustion processes in an internal combustion engine (1), with a sensor (2) which is attached to a surface of the internal combustion engine, wherein the sensor (2) measures deformations of the surface of the internal combustion engine (1) which are generated by combustion processes in the internal combustion engine, characterized by that the measured deformations are corrected by means of correction values, that the correction values ​​are determined as a function of operating parameters of the internal combustion engine (1) and that the corrected deformations are used to evaluate the combustion processes. [2] Method according to claim 1, characterized by that the correction values ​​are determined individually for each cylinder of the internal combustion engine (1) depending on the operating parameters of the respective cylinders. [3] Method according to one of the preceding claims, characterized bythat the measurement of the deformation takes place in a time window or angle window, and that the time window or angle window is determined individually for each cylinder of the internal combustion engine (1). [4] Method according to one of the preceding claims, characterized by that the evaluation of the combustion processes is carried out by comparing the corrected deformations with reference values, and that the reference values ​​are determined individually for each cylinder of the internal combustion engine (1). [5] Method according to claim 4, characterized by that to evaluate the combustion the maximum value of the corrected deformation is compared with a reference value. [6] Method according to claim 4, characterized by that, to evaluate the combustion, the gradient of the corrected deformation and the time of occurrence of the maximum gradient of the corrected deformation in the time window are compared with a reference value. [7] Method according to claim 4, characterized by that to evaluate the combustion an integral of the corrected deformation is compared with a reference value. [8] Device for measuring combustion processes in an internal combustion engine (1), comprising a sensor (2) which is attached to a surface of the internal combustion engine, wherein the sensor (2) measures deformations of the surface of the internal combustion engine (1) which are generated by combustion processes in the internal combustion engine, characterized by that means are provided which correct the measured deformations by means of correction values, wherein the correction values ​​are determined as a function of operating parameters of the internal combustion engine (1) and use the corrected deformations to evaluate the combustion processes.

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