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

Abstract

The invention relates to a method and a device for measuring combustion processes in an internal combustion engine, said device comprising a sensor (2), which is attached to a surface of the internal combustion engine (1), wherein the sensor measures deformations of the surface of the internal combustion engine which are caused by combustion processes in the internal combustion engine (1). The measured deformations are corrected by means of correction values, wherein the correction values 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

[0001] Description

[0002] title

[0003] Method and device for measuring combustion processes in an internal combustion engine

[0004] State of the art

[0005] 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.The fundamental usability of a strain gauge for measuring combustion processes is already known from the SAE Technical Paper 2015-24-2419, "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. For this purpose, such a strain gauge is arranged in a cooling channel of an internal combustion engine. The use of strain gauges therefore requires direct on-site installation, which is problematic for the strain gauge measurement signal due to the temperature stress.

[0006] Advantages of the Invention The device according to the invention and the method according to the invention with the features of the independent patent claims have the advantage that an 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.

[0007] 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.

[0008] Drawings

[0009] Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. It shows the

[0010] Figure 1 shows an internal combustion engine with a sensor for measuring combustion processes in the internal combustion engine and

[0011] Figure 2 shows a detailed view of the sensor and a cylinder of the internal combustion engine, Figure 3 shows process steps of the process according to the invention,

[0012] Figure 4 shows a first method for evaluation,

[0013] Figure 5 shows a second method for evaluation and

[0014] Figure 6 shows a third method for evaluation.

[0015] Description

[0016] Figure 1 schematically shows an internal combustion engine 1 with a sensor 2 attached to the 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.

[0017] To clarify the operation of the sensor 2 or the internal combustion engine 1, a single cylinder 21 of the internal combustion engine 1 is shown schematically again in Figure 2. 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 actuators required for this, such as air inlet valves and air outlet valves and a corresponding fuel injection system, are not shown in Figure 2. The combustion processes periodically increase the pressure in the combustion chamber 20 and convert it into mechanical work by a movement of the piston 22 along the direction of movement 23 via 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 rotational movement of the crankshaft.In the case of multiple cylinders, the crankshaft is driven by several cylinders. The axis of rotation 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 can be measured by the sensor element 2 on an outer surface of the cylinder 21. Figure 2 shows the sensor 2 on an outer surface of the cylinder 21. The arrangement of the sensor 2 is preferably in a region in which the deformation of the cylinder 21 is particularly severe due to the increase in pressure 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.

[0018] Figure 2 shows a sensor 2 which consists of a two-part housing with a base plate 24 and a cover 25. A strain measuring 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.

[0019] The housing of the sensor 2 is attached to the surface of the internal combustion engine using suitable joining techniques which ensure that the deformations of the surface are transferred to the actual measuring element 26. Adhesive bonding or fastening by screws has proven to be particularly suitable. In Figure 2, the arrow 23 represents the direction of movement of the piston 22 in the cylinder 21. 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 axis of rotation 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 to deformations is accordingly along the longest extent of this strip.The sensor element, as shown in Figure 2, is significantly longer parallel to the rotational axis of the crankshaft of the internal combustion engine 1 than in the two directions perpendicular to it. 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.

[0020] 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.

[0021] A particularly advantageous feature is that such a sensor for measuring the deformation of the surface of the internal combustion engine enables a very favorable frequency range for measurement. This allows deformations in a frequency range from greater than 0.5 Hz to several tens of kHz to be evaluated. The low frequency range, in particular, cannot be measured with the acceleration sensors commonly used for combustion analysis.

[0022] Figure 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 measuring window is defined. This measuring window specifies the range in which the deformation signal for a specific cylinder is measured. This measuring 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.

[0023] 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.

[0024] Figure 4 graphically illustrates the evaluation of combustion with regard to misfires. The intensity of the corrected deformations determined in step 35 for several combustions (7 in total) of an internal combustion engine with multiple cylinders, for example, four cylinders, is plotted over time T. 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 of whether a misfire is present or not, simply consists of a threshold value 41 for the corrected deformation. As can be seen in the time plot in Figure 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 occurred in the same cylinder as the third (T2 - T3) combustion. The illustration in Figure 4 therefore only shows a single event for a combustion misfire in the third cylinder. The next combustion in the same cylinder followed suit, i.e. no combustion misfire was detected.In the event of a permanent functional impairment of this cylinder, the intensity I of the maximum value of the deformation would have remained below the threshold value 41 again during the seventh combustion. To assess whether or not a combustion misfire has occurred, the use of a simple threshold value 41 as a comparison value for the evaluation is sufficient. The evaluation is then carried out simply by determining whether the intensity I of the maximum value of a corrected deformation exceeds the threshold value 41. 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 may vary for the various 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 during the measurement in step 33. Furthermore, the measured signals can also vary depending on different operating states of the internal combustion engine. Therefore, in step 39, correction values ​​are determined individually for each cylinder and for each operating state of the internal combustion engine. These correction values ​​are used to calculate the corrected deformation in step 35.

[0025] In Figure 4, markers (TO .. ​​T7) are shown on the time axis, each indicating the measuring window for a specific cylinder. In the illustration in Figure 4, these measuring windows are designed so that they follow one another seamlessly. However, it is also possible to use measuring windows with individual pauses between them or to use measuring windows that overlap one another. Furthermore, it is also possible to make these measuring windows dependent on operating parameters of the internal combustion engine, for example the speed of the internal combustion engine under load. The measuring windows can be defined as time windows or angular windows, for example relative to an ignition point or an ignition angle.

[0026] In Figure 5, the evaluation of combustion 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 curves 52, 53, 54. The maximum value of the intensity I of the corrected deformation is compared with a comparison value 51. In contrast to Figure 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, there is a fuel surplus, i.e.a lambda value of <1 is present, 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, there is a fuel shortage, i.e. a lambda value of >1 is present, whereby the height of the maximum value I is a measure of the overshoot of the lambda value. The value for lambda is thus calculated according to the deviation of the intensity I from the maximum value of the corrected deformation.

[0027] Figure 6 shows a further form of evaluation of the corrected deformation with regard to the lambda value of a combustion. The corrected deformation of Figure 6 differs not only with regard to the intensity of the maximum value of the deformation, but also with regard to the time of occurrence of the maximum value. With increasing leanness, i.e. an increase in the lambda value, the time of occurrence of the maximum value of the corrected combustion 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 with regard to intensity and the comparison value 65 with regard to time. Curve 62, which corresponds to a lambda value of less than 1, i.e.an excess of fuel, the curve 63, which corresponds to a lambda value of more than 1, i.e. a lack of oxygen, 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 the 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 the 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 at which the maximum was reached.This quotient corresponds to the slope or gradient of a straight line that intersects the corrected deformation curve in Figure 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.

[0028] As an alternative to the methods discussed in relation to Figures 4 to 6, an evaluation of an integral of the area under the curves shown in Figures 4 to 6 in the measurement window could also be used. The value of an integral formed in this way can then be compared with reference values ​​which allow a corresponding evaluation of the combustion. In the example in Figure 4, this would simply check whether the integral lies below a threshold value. In the example in Figure 5, the total area in the time window T0 to T1 could be evaluated. In the example in Figure 6, a reference value could be defined for the integral, and a check is carried out to determine at what point in time this reference value is reached.

Claims

Claims 1 . Method for measuring combustion processes in an internal combustion engine (1), with a sensor (2) which is fastened 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 in 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 in that the correction values ​​are determined individually for each cylinder of the internal combustion engine (1) as a function of operating parameters of the respective cylinders.

3. Method according to one of the preceding claims, characterized in that 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 in that the evaluation of the combustion processes is carried out by comparing the corrected deformations with comparison values, and that the comparison values ​​are determined individually for each cylinder of the internal combustion engine (1).

5. Method according to claim 4, characterized in that, in order to evaluate the combustion, the maximum value of the corrected deformation is compared with a reference value.

6. Method according to claim 4, characterized in that, in order 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 comparison value.

7. Method according to claim 4, characterized in that for the evaluation of 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), with a sensor (2) which is fastened 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 in 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.

Images