Method for controlling engine combustion noise

Abstract

A method for controlling engine combustion noise, comprising the steps of: calculating an engine combustion noise target value by a controller; measuring a cylinder pressure after fuel combustion depending on a main injection timing and a pilot injection fuel quantity based on the calculated engine combustion noise target value; calculating an engine combustion noise index (CNI) by converting the measured cylinder pressure into a cylinder pressure level; and controlling a feedback pilot injection in which the CNI is used in variable injection control while controlling the main injection timing and the pilot injection fuel quantity, characterized in that the cylinder pressure level is expressed as a noise (dB)-frequency (Hz) diagram by signal processing of the measured cylinder pressure using an FFT.the CNI is calculated using a noise (dB)-frequency (Hz) diagram of the cylinder pressure level, and a reference value of a mean effective pressure (BMEP) is used in the pilot injection control, the CNI is calculated as an uncorrected engine combustion noise prediction value without correcting the CNI at the reference value or less and then used in the variable injection control, and the CNI is calculated as a corrected engine combustion noise prediction value by correcting it at the reference value or more and then used in the variable injection control.

Description

TECHNICAL FIELDThe present disclosure relates to an engine noise control technique, and more particularly, to a method for reducing engine combustion noise, wherein injection variables are controlled.BACKGROUNDInternal combustion engines generate combustion noise occurring when burning fuel, which can be classified into direct combustion noise generated by combustion exciting force in a cylinder and indirect combustion noise generated when the combustion exciting force is applied to moving components with a clearance therebetween. In order to reduce the combustion noise, fuel injection control is executed by pilot injection into the engine, particularly a diesel engine having a high compression ratio.In the pre-injection, a total fuel injection amount is classified into a main injection amount and a pre-injection amount, and fuel injection timings are classified based on top dead center, thereby reducing a pressure increase gradient of a combustion pressure in a combustion chamber. Therefore, the pre-injection reduces the combustion noise by preventing the combustion pressure from rapidly increasing.The pilot injection amount as part of the total amount of fuel injection is set smaller than the main injection amount, thereby decreasing the pressure increase gradient of the combustion pressure.For this reason, the pilot injection method for controlling combustion noise makes a relatively low contribution in reducing the pressure increase gradient of the combustion pressure as compared with a combustion stability control method in which combustion control is stably performed against disturbances (environments, fuel differences, engine aging, etc.) to directly control a noise vibration exciting force using a pressure sensor.Therefore, there is a need for a technique in which the combustion stability control method of directly controlling the sound vibration exciting force can also control the combustion sound. Specifically, the combustion stability control method may be tuned to use a high-price combustion pressure sensor in consideration of a change in the environment in which the combustion pressure sensor is required in the cylinder of the combustion chamber due to specifications. In the prior art, engine noise control technology is described in particular in DE 10 2013 109 889 A1, DE 10 2012 208 784 B3, DE 10 2010 019 036 A1, DE 601 03 785 T2 and DE 10 2014 100 140 A1.SUMMARYThe method according to the invention is described in claim 1. Advantageous embodiments are evident from the dependent claims. An embodiment of the present invention is directed to an engine combustion noise control method that predicts an engine noise in such a manner that a combustion pressure waveform measured by a combustion pressure sensor installed in a cylinder of a combustion chamber is signal processed by a Fast Fourier Transform (FFT) to be digitized in a combustion noise index ("combustion noise index"="CNI"), and controls a combustion noise by injection variables (a main injection timing and a pilot injection fuel amount) to which a diesel combustion noise index is applied.Other objects and advantages of the present invention may be understood from the following description and will appear apparent with reference to the embodiments of the present invention. It will also be apparent to those skilled in the art to which the present invention pertains that the objects and advantages of the present invention can be realized by the means as claimed and combinations thereof.According to an embodiment of the present invention, a method for controlling engine combustion noise includes: calculating, by a controller, an engine combustion noise target value; measuring a cylinder pressure after engine combustion of fuel depending on a main injection timing and an amount of pilot injection fuel based on the calculated engine combustion noise target value; calculating a combustion noise index (CNI) by converting the measured cylinder pressure to a cylinder pressure level; and controlling feedback of the pilot injection in which the CNI is applied to variable injection control and injection parameter control, respectively, while controlling the main injection timing and the amount of pilot injection fuel.The target engine combustion noise value may be calculated in consideration of a fuel amount, an engine speed per minute (RPM), a gear shift stage, an intake air temperature, and a cooling water temperature. The cylinder pressure level is expressed as a noise (dB) frequency (Hz) map by signal processing the measured cylinder pressure by an FFT, and the CNI may be calculated from a frequency band of a 1 / 3 octave band filter stage in the cylinder pressure level map.The pilot injection control is performed to express the cylinder pressure as a noise (dB) frequency (Hz) map by signal processing the measured cylinder pressure by an FFT, calculate the CNI using the noise (dB) frequency (Hz) map of the cylinder pressure level, and employ a reference value of a brake mean effective pressure (BMEP) in the feedback pilot injection control, so that the CNI is calculated as an uncorrected engine combustion noise prediction value without correcting the CNI at the reference value or less, and then input to the variable injection control, and the CNI is calculated by correcting it as a corrected engine combustion noise prediction value at the reference value or more, and is then input to the variable injection control.In the (B), the CNI noise level (dB) may be calculated from a frequency band of a 1 / 3 octave band filter stage, and the CNI (dB) may be expressed as CNI (dB)=10LOG (10 (1000Hz Niveau / 10)+ 101250Hz Niveau / 10)+ 10(1600Hz Niveau / 10)+ 102000Hz Niveau / 10)+ 10(2500HzNiveau / 10)+ 10(3150Hz Niveau / 10)) ( Equation 1).The reference value of the BMEP may be in a range in which engine noise is increased by an increase in combustion pressure.The uncorrected combustion noise prediction value may be calculated from y=0.0479x 2- 15,982 x+1403.3, where y represents engine noise and x represents the combustion noise index.The corrected engine combustion noise prediction value may be calculated by converting y=0.0822x 2+ 2,6984 x+13.654 into a CNI correction value-BMEP map such that a combustion noise index correction value is calculated for each portion of the BMEP.BRIEF DESCRIPTION OF THE DRAWINGSFIGS. 1A and 1B are block flow charts showing a method for controlling engine combustion noise according to an embodiment of the present invention, in which the engine combustion noise control is divided into normal pilot injection control and pilot injection control in the method. FIGS. 2A and 2B are views for showing an example of calculation of a combustion noise index based on the pilot injection control according to the embodiment of the present invention. FIG. 3 is a view for showing an example of calculation of an uncorrected combustion noise prediction value to which correction of the combustion noise index is not applied when the pilot injection control according to the embodiment of the present invention is performed. FIGS. 4 and 5 are views for showing an example of calculation of a corrected engine combustion noise prediction value to which correction of the combustion noise index is applied when the pilot injection control according to the embodiment of the present invention is performed.DETAILED DESCRIPTIONExemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. However, the present invention may be embodied in various forms and should not be construed as limited to the embodiment described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Throughout the disclosure, like reference numerals refer to like parts throughout the various figures and embodiments of the present invention.FIGS. 1A and 1B are a block flow diagram illustrating a method for controlling engine combustion noise according to an embodiment of the present invention. Since the engine combustion noise feedback is controlled by an exclusive controller or an engine control unit or electronic control unit (ECU), an operation of the exclusive controller or the ECU is omitted.As shown in the figures, the engine combustion noise feedback is controlled as a normal pilot injection control in which a fuel is injected depending on an engine combustion noise target value after the engine combustion noise target value is calculated while an engine is running. The engine combustion noise feedback is then controlled as a pilot injection control in which an injection parameter is controlled by a combustion noise index (hereinafter referred to as a "CNI") using a cylinder pressure after combustion of the fuel using the normal pilot injection control.Referring to FIG. 1A, the normal pilot injection control is realized in steps S 10 to S 30. First, in step S 10, the engine combustion noise target value is calculated. An engine combustion noise may include a direct combustion noise generated by a combustion exciting force in a cylinder, an indirect combustion noise generated when the combustion exciting force is applied to moving components therebetween with a clearance therebetween, and may include an engine noise. In this regard, in step S 10, the fuel amount, an engine speed (RPM), a gear shift stage, an intake air temperature, a cooling water temperature, and the like are taken into account. Then, in step S 20, the injection parameter for fuel injection of an injector is controlled so as to follow the engine combustion noise target value. Main injection timing(s) and the pilot injection fuel amount are controlled by the engine combustion noise target value, which is fuel injection control by the pilot injection. Engine combustion is executed in step S30.The feedback pilot injection control is realized in steps S40 to S80. Specifically, since the CNI reflects only the direct combustion noise and the engine combustion noise includes the direct combustion noise, the indirect combustion noise, and the like in the pilot injection control, it is particularly assumed that the engine noise is also increased by a combustion pressure increase when an effective mean pressure (BMEP) is equal to or higher than 7 bar.Specifically, in step S40, the CNI is calculated by the engine combustion, and it is determined whether or not the CNI is corrected by considering the amount of fuel according to the BMEP in step S50. For example, a correlation between the CNI applied to a quadratic equation for predicting the engine combustion noise and the engine combustion noise changes depending on whether the BMEP is identical or less than 6 bar or is identical or greater than 6 bar. Therefore, in step S 60-1, with the fuel amount at the BMEP being 6 bar or less, where the correlation between the CNI and the engine combustion noise is high, the engine combustion noise is predicted by applying the CNI to the quadratic equation as shown in FIG. 3, and therefore an uncorrected engine combustion noise prediction value is obtained. On the other hand, in steps S 60-2a and S60-3b, in the fuel amount at the BMEP of 6 bar or more, where the correlation between the CNI and the engine combustion noise is low, the engine combustion noise is predicted by the quadratic equation using a CNI correction value to predict the correlation between the CNI and the engine combustion noise, as shown in FIGS. 4 and 5, and therefore a corrected engine combustion noise prediction value is obtained. Then, in step S 70, the uncorrected engine combustion noise prediction value or the corrected engine combustion noise prediction value is compared with the target engine combustion noise value, and an injection parameter control value is fed back in step S 80 using the comparison result. Although the injection parameter control value refers to the main injection timing and the pilot injection fuel amount, the injection parameter control value may include other injection parameter control values related to reduction in engine combustion noise as necessary.Consequently, the CNI which is continuously updated when the engine is running is reflected in the engine combustion noise control.FIGS. 2A to 5 show specific processes of CNI, BMEP, and CNI correction.Referring to FIGS. 2A and 2B, the CNI is calculated through steps S 41 and S 44. A cylinder pressure of the engine depending on engine combustion is measured in step S41 by a combustion pressure sensor mounted on the engine. In this case, the fuel amount, an engine speed (RPM), a gear shift stage, an intake air temperature, a cooling water temperature, an injection pressure, and the like are taken into account when measuring the cylinder pressure. A detection value of the cylinder pressure is signal-processed by a Fast Fourier Transform (FFT) in step S42, and a cylinder pressure level (CPL) is converted into a noise level (dB) frequency (Hz) map in step S43 using the FFT signal processing. Then, the CNI is calculated using the CPL expressed by the following equation 1 in step S44.Equation 1 is determined by filtering the CPL in a 1000-3150 Hz (1 / 3 octave) band and calculating the filtered CPL.Referring to FIG. 3, reference numeral S 60-1 refers to a method in which an engine combustion noise prediction value is calculated without correction of the CNI under a condition that the BMEP is 6 bar or less. The uncorrected engine combustion noise prediction value in step S 60-1 is expressed by the following equation 2. Here, y refers to engine noise and x refers to CNI.In Equation 2, y is obtained by applying the CNI to x, and the obtained y is used as an uncorrected engine combustion noise prediction value.Referring to FIG. 4, reference numeral S 60-2a refers to a method in which a CNI correction value is determined under a condition that the BMEP is 6 bar or more. As shown in the drawing, Equation 3 and a CNI correction value-BMEP chart are used together to calculate the CNI correction value in step S 60-2a. Here, y refers to engine noise, x refers to CNI, and BMEP refers to bar.Equation 3 is expressed by the CNI correction value-BMEP chart, and the CNI correction value is selected from the CNI correction value-BMEP chart depending on the amount of the BMEP. The CNI correction value at the BMEP of 7 bar is 1.5 dB, for example, the CNI correction value at the BMEP of 17 bar is 8.7 dB, etc. Specifically, the CNI correction value is obtained for each engine RPM, and the obtained value is established as a CNI correction value.Referring to FIG. 5, a corrected engine combustion noise prediction value is calculated in step S 60-2b by the CNI correction value under a condition that the BMEP is 6 bar or more. As shown in the figure, the corrected engine combustion noise prediction value in step S60-2b is expressed by the following equation 4. Here, y refers to engine noise and x refers to CNI.In Equation 4, y is obtained by applying the CNI correction value to x, and the obtained y is used as a corrected engine combustion noise prediction value.Therefore, the CNI which is continuously updated when the engine is running is reflected in the engine combustion noise control. Since the CNI is converted into the CNI correction value depending on the amount of the BMEP, the engine combustion noise control is executed using the uncorrected engine combustion noise prediction value or the corrected engine combustion noise prediction value.As described above, the method for controlling an engine combustion noise according to the embodiment of the present invention includes: calculating the target engine combustion noise value by the control and detecting the operation of the engine. The cylinder pressure is measured after the engine combustion depending on the main injection timing and the amount of pilot injection fuel based on the calculated target engine combustion noise value. The CNI is calculated by converting the measured cylinder pressure to the cylinder pressure level. The pilot injection is controlled, and the CNI is applied to the variable injection control during the control of the main injection timing and the amount of pilot injection fuel. Consequently, the engine combustion noise is predicted by the CNI that is continuously updated when the engine is running, and the engine noise is reduced by controlling the main injection timing and the amount of pilot injection fuel.According to the exemplary embodiment of the present invention, it may be possible to significantly improve combustion noise by controlling the combustion noise in such a manner that the noise vibration exciting force is directly controlled by a combustion pressure sensor, as in a combustion stability control method of directly controlling the noise vibration exciting force, compared to a pilot injection method.In addition, since a combustion noise index used for setting injection parameters (a main injection timing and an amount of pilot injection fuel) and used for controlling combustion noise is digitized based on a combustion pressure waveform measured by the combustion pressure sensor, the combustion pressure index can be easily established as a combustion noise map, and in particular, used as a standard combustion noise map by standardization of the combustion noise index.In addition, the present invention can be easily applied to all engines requiring combustion pressure sensors according to specifications by including a combustion map established by the combustion noise index in an ECU without design modification of the engines.While the present invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope and spirit of the invention as defined in the following claims.

Claims

A method for controlling an engine combustion noise, comprising the steps of: calculating, by a controller, an engine combustion noise target value; measuring a cylinder pressure after fuel combustion depending on a main injection timing and a pilot injection fuel amount based on the calculated engine combustion noise target value; calculating an engine combustion noise index (CNI) by converting the measured cylinder pressure into a cylinder pressure level; and controlling a feedback pilot injection in which the CNI is applied to a variable injection control while controlling the main injection timing and the pilot injection fuel amount, characterized in that the cylinder pressure level is expressed as a noise (dB) frequency (Hz) map by signal processing the measured cylinder pressure by an FFT, the CNI is calculated using the noise, a noise (dB) frequency (Hz) graph of the cylinder pressure level, and a reference value of an effective mean pressure (BMEP) is used in the pilot injection control, wherein the CNI is calculated as an uncorrected engine combustion noise prediction value without correcting the CNI at the reference value or less and is then used in the variable injection control, and the CNI is calculated as a corrected engine combustion noise prediction value by correcting it at the reference value or more and is then used in the variable injection control.The method of claim 1, wherein the target engine combustion noise value is calculated in consideration of a fuel amount, an engine speed per minute (RPM), a gear shift stage, an intake air temperature, and a cooling water temperature.The method according to claim 1 or 2, wherein the cylinder pressure level is expressed as a noise (dB) frequency (Hz) map by signal processing the measured cylinder pressure by a Fast Fourier Transform (FFT), and the CNI is calculated from a frequency band of a 1 / 3 octave band filter stage in a cylinder pressure level map.The method of claim 1, wherein the CNI noise level (dB) is calculated from a frequency band of a 1 / 3 octave band filter stage, and the CNI (dB) is expressed as CNI (dB) = 10LOG (10 (1000Hz Niveau / 10)+ 10(1250Hz Niveau / 10)+ 10(1600Hz Niveau / 10)+ 10(2000Hz Niveau / 10)+ 10(2500HzNiveau / 10)+ 10(3150Hz Niveau / 10)).The method according to claim 1, wherein the reference value of the BMEP is in a range in which an engine noise increases by an increase in a combustion pressure.Method according to claim 5, wherein the reference value is 6 bar.The method of any of claims 1 to 6, wherein the uncorrected engine combustion noise prediction value is calculated from y = 0.0479x 2- 15,982 x + 1403.3, where y is an engine noise and x is the CNI.The method of any of claims 1 to 7, wherein the corrected engine combustion noise prediction value is calculated by converting y = 0.0822x 2+ 2,6984 x + 13.654, where y is engine noise and x is the CNI, into a CNI correction value-BMEP plot such that a CNI correction value is calculated for each portion of the BMEP.The method of claim 8, wherein the CNI correction value is determined to correspond to an engine RPM.A method according to any preceding claim, wherein the controller is an engine control unit (ECU), and the cylinder pressure is measured by a combustion pressure sensor installed in an engine cylinder.

Images