Method for controlling an internal combustion engine

Abstract

A method for controlling an internal combustion engine (1) is proposed, in which a signal from a pressure sensor (9) in an exhaust system (6) of the internal combustion engine (1) is evaluated. The pressure signal is evaluated with regard to the standard deviation of the pressure signal in comparison to a moving average of the pressure signal over several combustion cycles.

Description

State of the art

[0001] The invention is based on a method according to the preamble of the independent patent claim. Various methods for controlling internal combustion engines that utilize sensor signals are already known. Furthermore, pressure sensors in the exhaust system of an internal combustion engine are known, which are typically used to assess the quality of exhaust gas components, in particular the exhaust back pressure of exhaust gas purification components. Advantages of the invention

[0002] The method according to the invention with the features of the independent patent claim has the advantage that the internal combustion engine can be controlled using a pressure sensor in the exhaust system of the internal combustion engine with particularly simple means. By evaluating the signal from a pressure transmitter in the exhaust system, the quality of combustion in the internal combustion engine can be assessed. Thus, a pressure sensor already provided in the exhaust system can be used to improve the quality of combustion in the internal combustion engine.

[0003] Further advantages and improvements arise from the features of the dependent patent claims. By determining an average before start, the relevant portion of the measured pressure signal can be better observed. Determining the average before start can be completed particularly easily when the pressure signal exceeds a predetermined threshold. By forming the moving average, a suitable signal is determined for comparison with the measured pressure signal. For reasons of simplicity, this is then simply compared with the standard deviation of the measured pressure signals. To enable a good assessment, the absolute value or amount is considered. A meaningful quality value for the combustion is then determined by setting the standard deviation in relation to the moving average.Various correction factors can be considered, resulting in an adjustment of the quality value to an easily interpretable range. Interpretation is also improved by limiting the quality value to a range between 0% and 100%. Drawings

[0004] Embodiments of the invention are illustrated in the drawings and explained in more detail in the description. They show: Fig. 1 is a schematic view of an internal combustion engine, and Fig. 2 a measured pressure signal and a moving average of the pressure signal. Description

[0005] In the Fig. 1 schematically shows an internal combustion engine 1 having a cylinder 2 and a piston 3 arranged in the cylinder 2. The cylinder 2 and the piston 3 define a combustion chamber 4, into which air is introduced through an air supply 5 and fuel by means not shown, for example an injection valve. After combustion in the combustion chamber 4, the combusted exhaust gases are guided away from the combustion chamber 4 through an exhaust line 6. The combustion chamber 4 is connected to the air supply 5 by means of an air inlet valve 7 and to the exhaust line 6 by an exhaust outlet valve 8. A pressure sensor 9 is arranged in the exhaust line 6, by which the pressure in the exhaust line 6 is measured. Furthermore, a computer 10 is provided, by which all combustion processes of the internal combustion engine 1 are controlled; in particular, the amount of air and fuel supplied is monitored by the controller 10.Furthermore, the computer 10 also evaluates the signals of all sensors, for example also the pressure sensor 9 in the exhaust system 6.

[0006] The internal combustion engine 1 after the Fig. 1 is thus a typical diesel or gasoline internal combustion engine. Furthermore, the internal combustion engine 1 typically has several cylinders, for example four cylinders. However, the method according to the invention can also be used for a single-cylinder engine. Other conventional means for controlling the internal combustion engine 1, such as a throttle valve for influencing the flow through the air supply 5 or means for cleaning the exhaust gas, are not shown for the sake of simplicity. Fig. 1 are not shown, as they are not important for understanding the invention.

[0007] By evaluating the signal from pressure sensor 9 in exhaust system 6, an evaluation of the combustion in combustion chamber 4 can be performed, which is then used to control the internal combustion engine. In particular, the quality of combustion in combustion chamber 4 can be assessed.

[0008] The evaluation of combustion in combustion chamber 4 is based on the Fig. 2. In the Fig. 2, the measured pressure from pressure sensor 9 in exhaust system 6 is plotted against time t. Shown are a moving average of the pressure signal across multiple combustions (continuous curve) and the measured pressure signal (curve with greater variations) of individual combustions. Fig.2 shows the start of combustion at time t0. Since no combustion processes occur in the combustion chamber 4 before the internal combustion engine is started, the pressure is essentially constant and approximately corresponds to the ambient pressure of the internal combustion engine. However, by rotating the engine using a starter and correspondingly opening and closing the air inlet valve 7 and the exhaust outlet valve 8, the engine acts as an air pump, so that there is a slight increase in pressure in the exhaust system 6 compared to the air pressure. This slight increase in pressure has not been shown here for the sake of simplicity. At time T0, the internal combustion engine 1 is started, i.e. from this point onwards, combustion occurs in the combustion chamber 4. This directly leads to pressure increases in the exhaust system 6, which are measured by the pressure sensor 9 as the pressure signal pExht (Exht stands for exhaust here).

[0009] From this pressure signal pExht, an average value for the pressure pExhtMeanZero before the start of the internal combustion engine is continuously determined before time t0, for example, by low-pass filtering. Such low-pass filtering can also be achieved, for example, by a corresponding summation: pExhtMeanZero=(∑npExht) / n.

[0010] As soon as the pressure signal pExht exceeds a minimum value pExhtMeanMin, the calculation of the mean value of the pressure before the start of pExhtMeanZero is stopped and the value of pExhtMeanZero is saved as a reference value for further calculations.

[0011] After time 0, a moving average pExhtDeltaMean is continuously calculated. Only the signal components that exceed the pre-start mean are considered. The moving average is calculated using the formula: pExhtDelta Mean=∑m(pExht−pExhtMeanZero) / m.

[0012] Typically, the moving average is calculated over the number of cylinders, ie for a four-cylinder engine the value of m would be 4.

[0013] Furthermore, a standard deviation Sigma (σ) of the pressure signal is calculated from the pressure signal pExht. For this purpose, the difference between the pressure signal pExht and the moving average pExhtDeltaMean is calculated, the absolute value or magnitude of these differences is calculated, and the sum of several measured values ​​relative to the number of measured values ​​is calculated. Squaring and subsequent root extraction are typically used to calculate the absolute value: σ=[∑m(pExht−pExhtDeltaMean)2]1 / 2 / m

[0014] The standard deviation Sigma is then set in relation to the moving average to derive a quality measure Q, taking into account adjustment parameters C1, C2, C3: Q=C1−C2*σ / (pExhtDeltaMean−C3)

[0015] The adjustment parameters C1, C2, C3 can be used to adjust the quality measure Q to a desired range.

[0016] The adjustment parameter C3 typically corresponds to the previously used minimum value for the pressure increase pExhtMeanMin, at which the calculation of the mean value was aborted before it started. Selecting this adjustment parameter T3 or pExhtMeanMin thus determines the point at which a relevant pressure difference is present for calculating the quality measure.

[0017] The adjustment parameter C2 provides a system-dependent gain factor in the range between 50 and 200. This allows the Q value to be adjusted within a reasonable range.

[0018] The adjustment parameter C1 is typically a percentage value between 100% and 120% and is also used to set the Q value within a reasonable range. This value must be selected to match the gain factor C2. Furthermore, to ensure interpretability, the Q value can be limited to values ​​between 0% and 100%: Q=min{max[C1−C2*σ / (pExthDeltaMean−C3);0];100%]}

[0019] By selecting the appropriate parameters C1, C2, C3, it can be achieved that after the combustion has started, high-quality combustion quickly reaches a value between 95% and 100%.

[0020] An assessment of the combustion quality Q can then be achieved simply by comparing it with a predefined threshold value for the quality Q, for example, at 80%. If the combustion quality Q is too poor, appropriate countermeasures are triggered, for example by influencing the ignition or air-fuel composition, to bring the combustion quality Q into an acceptable range.

Claims

[1] Method for controlling an internal combustion engine (1), in which a signal from a pressure sensor (9) in an exhaust system (6) of the internal combustion engine (1) is evaluated, characterized by that the pressure signal is evaluated with regard to the standard deviation of the pressure signal in comparison to a moving average of the pressure signal over several burns. [2] Method according to claim 1, characterized by that the pressure signal is measured before a start of the internal combustion engine (1), that an average value before the start is formed from the measured pressure signal before the start and that the average value before the start is used to evaluate the pressure signal after the start. [3] Method according to claim 2, characterized by that the averaging is terminated before the start if the pressure signal exceeds a specified threshold. [4] Method according to claim 2 or 3, characterized bythat to form the moving average, a difference between the measured pressure signals and the mean value before the start is formed, and that the difference is averaged over all cylinders (2) of the internal combustion engine (1). [5] Method according to claim 4, characterized by that a standard deviation of the pressure signal is calculated by forming a difference between the moving average and the pressure signal, that an absolute value is formed from this difference, and that a sum of these absolute values ​​is calculated. [6] Method according to claim 5, characterized by that a quality value for the combustion in the internal combustion engine is formed by setting the standard deviation in a ratio to the moving average. [7] Method according to claim 6, characterized bythat the formation of the quality value (Q) is supported by coefficients in that, for the determination of the quality value, a correction value C3 is subtracted from the moving average value, which corresponds to the threshold value for the determination of the average value before the start, that the ratio is multiplied by a gain factor C2 and that the difference is formed into a range factor. [8] Method according to claim 7, characterized by that the gain factor C2 is selected between 50 and 200 and the range factor is selected between 100% and 120%. [9] Method according to claims 6 to 8, characterized by that the quality value (Q) is limited to a range between 0% and 100%.

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