Device and method for measuring combustion processes in an internal combustion engine

Abstract

The invention relates to a device for measuring combustion processes in an internal combustion engine. The device comprises a sensor, which is attached to a surface of the internal combustion engine, the sensor being designed to measure deformations of the surface of the internal combustion engine which are caused by combustion processes in the internal combustion engine.

Description

[0001] Description

[0002] title

[0003] Device and method 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 and method according to the invention with the features of the independent patent claims have the advantage that the sensors are less sensitive to both assembly and temperature changes. It has surprisingly been found that commercially available sensors are suitable for measuring deformation of the surface of internal combustion engines due to combustion processes in the internal combustion engine. This enables a significantly simpler and more robust measurement of combustion processes in an internal combustion engine.

[0007] Further advantages and improvements arise from the measures of the dependent patent claims. It is particularly advantageous that sensors can be used in which a strain gauge is arranged in a housing. The actual measuring element is protected by the housing from both environmental influences and excessive temperatures. Surprisingly, strain gauges packaged in such a housing are also suitable for detecting combustion processes in an internal combustion engine. It has proven entirely sufficient to attach such sensors to the outside of a cylinder block of the internal combustion engine. Attachment can be achieved particularly easily by gluing or screwing. By aligning a preferred measuring direction of the sensor parallel to the rotational axis of the crankshaft of the internal combustion engine, an optimized measurement signal can be achieved.Combustion processes in internal combustion engines can be analyzed particularly effectively when signals with a frequency greater than 0.5 Hz are also evaluated. In particular, such signals, with a lower frequency than conventional acceleration sensors, can reliably detect combustion with pre-ignition. This improves the analysis of combustion processes in internal combustion engines. Particularly reliable and useful signals are provided by sensors that use a piezo element as a measuring element. The sensor signals are evaluated particularly effectively by evaluation electronics and used to control the internal combustion engine.

[0008] Drawings Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. It shows the

[0009] Figure 1 shows an internal combustion engine with a sensor for measuring combustion processes in the internal combustion engine and

[0010] Figure 2 shows a detailed view of the sensor and a cylinder of the internal combustion engine.

[0011] Description

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

Claims

Claims 1 . 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, characterized in that the sensor is designed to measure deformations of the surface of the internal combustion engine which are generated by combustion processes in the internal combustion engine.

2. Device according to claim 1, characterized in that the sensor is designed as a strain gauge in a housing.

3. Device according to one of the preceding claims, characterized in that the surface is an outer side of a cylinder block of the internal combustion engine.

4. Device according to claim 1 to 3, characterized in that the sensor is attached by gluing.

5. Device according to claim 1 to 3, characterized in that the sensor is fastened by screws.

6. Device according to one of the preceding claims, characterized in that the sensor has a measuring direction, and that the measuring direction is parallel to the axis of rotation of a crankshaft of the internal combustion engine.

7. Device according to one of the preceding claims, characterized in that the sensor has a measuring range for frequencies from 0.5 Hz to more than 10 Khz.

8. Device according to one of the preceding claims, characterized in that the sensor has a piezo element as a measuring element.

9. Device according to one of the preceding claims, characterized in that the sensor signals are evaluated by evaluation electronics and used to control the internal combustion engine.

10. Method for measuring combustion processes in an internal combustion engine, comprising a sensor that is attached to a surface of the internal combustion engine, characterized in that the sensor measures deformations of the surface of the internal combustion engine that are generated by combustion processes in the internal combustion engine.

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