JP2010174737A - Control device for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress variations in the actual ignition timing and the amount of EGR caused by the individual difference of an engine. <P>SOLUTION: The maximum combustion pressure Pmax_r and maximum combustion pressure change rate dPmax_r in a cycle are obtained from cylinder internal pressure Pθ with respect to each crank angle θ (S1-3), and errors between target values are obtained as ratios R_Pmax and R_dPmax (S4). When these ratios are deviated from 1 by a predetermined value ε (for example 5%) or more, the necessary correction amount ΔIT with respect to fuel injection timing IT and the necessary correction amount ΔEGR with respect to the opening EGR of an exhaust gas recirculation control valve 12 are obtained based on two ratios, and a map value is learned and corrected (S6-9). Thereby, the maximum combustion pressure and maximum combustion pressure change rate approach the target values. Since parameters are correlated with both the actual EGR amount and the actual ignition timing, in the same way as a binary simultaneous equation, the actual EGR amount and the actual ignition timing are matched with reference values with both the parameters simultaneously matched with the respective target values. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device for a diesel engine that appropriately controls an actual ignition timing and an actual EGR amount.

For example, a technique for detecting an actual combustion state of an internal combustion engine using an in-cylinder pressure sensor or the like and applying various corrections to basic control to cope with individual differences of the internal combustion engine has been conventionally known. Patent Document 1 relates to a gasoline engine that performs spark ignition on a premixed gas, detects the maximum combustion pressure for each combustion cycle, the indicated mean effective pressure, or the crank angle that generates the maximum combustion pressure, and changes in these parameters. It is disclosed that at least one of the fuel supply amount and the ignition timing is corrected so as to reduce the fuel consumption.
JP-A-2-19636

  In a diesel engine, as is well known, so-called external exhaust gas recirculation is performed in a wide operating range to reduce NOx, and a relatively large amount of exhaust gas is introduced into the cylinder. Smoke is in a trade-off relationship, and if the actual exhaust gas amount (EGR amount) varies due to individual differences, NOx in the exhaust gas increases or smoke deteriorates rapidly. It is difficult to directly detect this actual EGR amount. For example, a method of estimating from the amount of fresh air detected by the air flow meter or the opening degree of the exhaust gas recirculation control valve is adopted, but generally the accuracy is low and it is not always necessary. An appropriate amount of EGR cannot be obtained.

  Further, parameters such as the maximum combustion pressure and the crank angle at which this maximum combustion pressure is shown in Patent Document 1 are greatly influenced by the EGR amount in a diesel engine. Therefore, for example, even if an attempt is made to feedback control the fuel injection timing by the maximum combustion pressure or the like in order to obtain a desired ignition timing, as long as the EGR amount is uncertain due to individual differences or the like, the fuel injection timing or the like can be uniquely determined by this. It cannot be corrected.

  Therefore, the present invention uses at least two parameters correlated to both the actual ignition timing and the EGR amount in the cylinder, such as the maximum combustion pressure and the maximum change rate of the combustion pressure, so that the fuel injection timing and the EGR The amount is corrected at the same time, and both the ignition timing and the EGR amount are obtained in desired characteristics.

  That is, the control device for a diesel engine according to the present invention relates to a plurality of parameters that are correlated with both the actual ignition timing and the EGR amount in the cylinder and can be extracted from the change in the cylinder pressure in the diesel engine having the cylinder pressure sensor. Among them, at least two parameters are used, and both the fuel injection timing and the EGR amount are corrected so that these parameters become respective target values.

  For example, parameters such as the maximum combustion pressure, the ignition delay period, the maximum change rate of the combustion pressure, the crank angle at which the change rate of the combustion pressure becomes the maximum, the combustion period, etc. are detected by the in-cylinder pressure change. These parameters can be derived from the actual ignition timing and EGR amount in the cylinder (this is the total exhaust gas quantity in the cylinder including both external exhaust gas recirculation and internal exhaust gas recirculation). Corresponding to both, for example, the value of one parameter fluctuates due to variations in ignition timing, and the value of the same parameter also varies due to variations in EGR amount. Therefore, by using at least two parameters, necessary corrections for the fuel injection timing and the EGR amount are determined by the principle of a kind of simultaneous equations.

  According to the present invention, the ignition timing and the EGR amount correlated with each other in a diesel engine can be maintained at more appropriate characteristics by eliminating variations due to individual differences. For example, NOx and smoke that are in a trade-off relationship can be maintained. Can be reliably reduced.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows the configuration of the entire diesel engine according to the present invention. The diesel engine 1 includes a so-called common rail type fuel injection device as fuel injection means, and fuel pressurized to a predetermined pressure by a high pressure fuel pump (not shown) is supplied to a common rail (accumulation chamber) 6. It is introduced and supplied to the fuel injection nozzle 5 of each cylinder via the common rail 6. The fuel injection nozzle 5 is controlled to be opened and closed by a control signal from the control unit 8, and the fuel injection amount is controlled by the injection period. The fuel pressure of the common rail 6 is also variably controlled by a control signal from the control unit 8, and the fuel injection amount is determined by the fuel pressure and the injection period.

  The diesel engine 1 includes an external exhaust gas recirculation device. That is, an EGR passage 11 is provided between the exhaust passage 10 and the intake passage 9, and an exhaust recirculation control valve 12 is interposed therein. The exhaust gas recirculation control valve 12 uses, for example, a pulse motor as an actuator, and its opening degree is controlled by a drive signal output from the control unit 8. A NOx catalyst 16 for treating NOx in the exhaust is interposed downstream of the exhaust passage 10. The intake passage 9 is provided with an intake throttle valve 15 for limiting the flow rate of fresh air, and an air flow meter 3 for detecting the intake air amount is disposed upstream thereof.

  The diesel engine 1 includes, as well-known sensors, a water temperature sensor 2 that detects a cooling water temperature, a crank angle sensor 4 that detects a crank angle, an accelerator opening sensor 13 that detects an accelerator opening operated by a driver, a fuel A fuel temperature sensor 14 for detecting temperature is provided, and these detection signals are also input to the control unit 8. In order to detect the in-cylinder pressure, a known in-cylinder pressure sensor 17 is provided for each cylinder.

  Accordingly, from the change in the in-cylinder pressure detected by the in-cylinder pressure sensor 17, several parameters correlated to both the actual ignition timing and the EGR amount in the cylinder, such as the maximum combustion pressure, the ignition delay period, the combustion pressure It is possible to extract the crank angle at which the change rate of the maximum pressure, the change rate of the combustion pressure, the combustion period, etc. are extracted. In this embodiment, the maximum combustion pressure (Pmax), the combustion pressure, The fuel injection timing and the EGR amount (for example, the opening degree of the exhaust gas recirculation control valve 12) are corrected using the two parameters of the maximum change rate (dP / dθmax).

  FIG. 2 shows an example of the in-cylinder pressure change in a state where the combustion timing is relatively delayed for NOx reduction. As shown in the figure, the maximum combustion pressure (Pmax) is obtained as the peak of the in-cylinder pressure. The maximum rate of change in combustion pressure (dP / dθmax) is obtained by the rapid rise of the in-cylinder pressure after ignition. For example, as the EGR amount increases, the combustion becomes slow, so that the maximum combustion pressure ( Pmax) decreases, and the maximum rate of change in combustion pressure (dP / dθmax) also decreases. Although not shown, the maximum combustion pressure (Pmax) and the maximum rate of change in combustion pressure (dP / dθmax) also change depending on the actual ignition timing. For example, if the actual ignition timing is delayed, more than the premixed amount. Since the fuel burns at once, the maximum combustion pressure (Pmax) and the maximum change rate of the combustion pressure (dP / dθmax) increase. Note that the initial pressure increase in FIG. 2 is due to motoring.

  As described above, the maximum combustion pressure (Pmax) and the maximum rate of change (dP / dθmax) of the combustion pressure are correlated with both the actual EGR amount and the actual ignition timing. Even if one of the parameters (for example, the maximum combustion pressure (Pmax)) matches the reference value (target value), the actual EGR amount and the actual ignition timing are the reference values (target EGR amount and target ignition). It is not always in line with (time). However, as in the case of the two-variable simultaneous equations, in a state where the two parameters, that is, the maximum combustion pressure (Pmax) and the maximum change rate of the combustion pressure (dP / dθmax) simultaneously match the respective reference values (target values). It can be said that each of the actual EGR amount and the actual ignition timing matches the reference values (target EGR amount and target ignition timing).

  Therefore, in this embodiment, the processing shown in the flowchart of FIG. 3 is performed so that the maximum combustion pressure (Pmax) and the maximum change rate of the combustion pressure (dP / dθmax) simultaneously match the target values. Each of the quantity and the actual ignition timing is made to match the reference value (target EGR amount and target ignition timing) without variation due to individual differences.

  Hereinafter, in accordance with the flowchart of FIG. 3, first, in-cylinder pressure Pθ for each crank angle θ is read in step 1, maximum combustion pressure Pmax_r in the cycle is calculated in step 2, and maximum change in combustion pressure in the cycle is determined in step 3. The rate dPmax_r is calculated. The subscript “r” means an actual measurement value, and “t” means a target value.

  In step 4, the ratios R_Pmax and R_dPmax between the measured value and the target value are obtained for each of the maximum combustion pressure Pmax and the maximum change rate of combustion pressure dPmax. That is, “R_Pmax = Pmax_r / Pmax_t” and “R_dPmax = dPmax_r / dPmax_t”. Here, each target value Pmax_t and dPmax_t is set in advance corresponding to the engine operating condition, that is, the engine speed and the load (for example, the injection amount). For example, the target value Pmax_t of the maximum combustion pressure is shown in FIG. The target value dPmax_t of the combustion pressure maximum change rate is obtained from the characteristic control map as shown in FIG.

  In the present invention, it is possible to use a method for obtaining the difference between the measured value and the target value in order to indicate the difference between the measured value and the target value. However, as in the present embodiment, it is preferable to obtain the ratio between the two. , The influence of the operating point is reduced and the accuracy becomes higher.

  Next, in step 5, it is determined whether or not these ratios R_Pmax and R_dPmax are sufficiently close to “1”. Specifically, it is determined whether or not the absolute value of the value obtained by subtracting “1” from these ratios is smaller than a predetermined value ε (for example, 0.05 or 5%). Therefore, if the error between the actually measured value and the target value is less than 5%, for example, this is ignored and no correction is performed. Needless to say, the threshold value ε is not limited to 5% and can be set as appropriate.

  If either one has an error of 5% or more, the process proceeds to step 6 to obtain a necessary correction amount ΔIT for the fuel injection timing IT based on the two ratios R_Pmax and R_dPmax. Specifically, the correction amount ΔIT is obtained using a control map having characteristics as shown in FIG. The broken lines in the figure are lines whose ratios are “1”, and at the intersection (the two ratios are both 1), the correction amount ΔIT is 0 and the advance angle is on the upper left side of the figure. To the left and lower right, the correction is made to the retard side.

  Similarly, in step 7, a necessary correction amount ΔEGR for the opening degree EGR of the exhaust gas recirculation control valve 12 is obtained based on the two ratios R_Pmax and R_dPmax. Specifically, the correction amount ΔEGR is obtained using a control map having characteristics as shown in FIG. Note that the broken lines in the figure are lines whose ratios are “1”, and at the intersection (both ratios are both 1), the correction amount ΔEGR is 0 and negative to the lower left side of the figure. The correction amount is positive correction amount on the upper right side.

  These control maps in FIGS. 6 and 7 show the fuel injection timing IT, EGR amount (exhaust gas recirculation rate is used here), parameters (maximum combustion pressure (Pmax) and combustion pressure) as shown in FIG. It is derived based on the correlation with the maximum rate of change (dP / dθmax). In FIG. 8, the vertical axis represents the exhaust gas recirculation rate, the horizontal axis represents the injection timing (more specifically, the injection timing of the main injection) IT, the characteristic of the maximum combustion pressure (Pmax) with respect to these is a solid line, and the maximum change rate of the combustion pressure ( The characteristics of dP / dθmax are indicated by broken lines. As shown in FIG. 8, when the exhaust gas recirculation rate and the injection timing IT are changed, the maximum combustion pressure (Pmax) and the maximum change rate of the combustion pressure (dP / dθmax) change with monotonic characteristics. The control map of FIG. 7 is set so that the maximum combustion pressure Pmax_r and the maximum change rate of combustion pressure dPmax_r approach the target values by the respective corrections.

  In step 8, the correction amount ΔIT is added to the map value IT of the fuel injection timing IT set for the operating condition at that time to perform learning correction. Similarly, in step 9, the correction amount ΔEGR is added to the map value EGR of the target opening degree of the exhaust gas recirculation control valve 12 set for the operation condition at that time to perform learning correction. Thus, in the next cycle, the corrected fuel injection timing IT and the exhaust gas recirculation control valve opening EGR are used, and the maximum combustion pressure Pmax_r and the maximum combustion pressure change rate dPmax_r approach the target values. Therefore, as a result, the actual ignition timing and the actual in-cylinder EGR amount are respectively maintained at desired values. For example, the variation in characteristics due to individual differences among engines is reduced, and NOx and smoke are reduced. Reduction can be achieved.

  In the above embodiment, correction amounts ΔIT and ΔEGR are added at the time of correction. However, correction can be performed by obtaining a correction coefficient and multiplying it.

  In addition, a technique for variably controlling so-called internal exhaust gas recirculation by using a variable valve mechanism, for example, by variable control of valve overlap, is known in place of external exhaust gas recirculation or in addition to external exhaust gas recirculation. The present invention can also be applied to maintain a desired EGR amount by variable control of exhaust gas recirculation.

  In the above embodiment, the maximum combustion pressure (Pmax) and the maximum change rate of the combustion pressure (dP / dθmax) are used as the parameters as the basis of correction. As described above, the ignition delay period, the combustion pressure Other parameters such as the crank angle at which the rate of change becomes maximum, the combustion period, and the like can be used, and further, correction can be performed using three or more parameters. In this case, the required correction amount is obtained from the multidimensional correlation, but the simplest method is based on the error (ratio or difference) between the actual measurement value and the target value for any one parameter. A correction coefficient is set, and the value obtained from the control map may be corrected with this correction coefficient as shown in FIGS.

Explanatory drawing which shows the system configuration | structure of the diesel engine which concerns on this invention. The characteristic view which shows the example of the change of a cylinder pressure. The flowchart which shows the process in this Example. The characteristic view which shows the characteristic of the map of the target value of the maximum combustion pressure Pmax. The characteristic view which shows the characteristic of the map of the target value of combustion pressure maximum change rate dPmax. The characteristic view which shows the characteristic of the control map of correction amount (DELTA) IT. The characteristic view which shows the characteristic of the control map of correction amount (DELTA) EGR. The characteristic view which shows the correlation with fuel injection timing IT, an exhaust gas recirculation rate, the maximum combustion pressure, and the maximum change rate of combustion pressure.

DESCRIPTION OF SYMBOLS 1 ... Diesel engine 5 ... Fuel injection nozzle 8 ... Control unit 12 ... Exhaust gas recirculation control valve 17 ... In-cylinder pressure sensor

Claims (5)

  In a diesel engine equipped with an in-cylinder pressure sensor, at least two parameters are used among a plurality of parameters that correlate with both the actual ignition timing and the EGR amount in the cylinder and can be extracted from a change in the in-cylinder pressure. The diesel engine control apparatus corrects both the fuel injection timing and the EGR amount so that each becomes a target value.   2. The parameter is at least two of a maximum combustion pressure, an ignition delay period, a maximum change rate of the combustion pressure, a crank angle at which the change rate of the combustion pressure is maximum, and a combustion period. The control device of the diesel engine described in 1.   3. The diesel engine control device according to claim 1, wherein target values of the respective parameters are set in advance for each engine operating condition.   The diesel according to any one of claims 1 to 3, wherein a correction amount or a correction coefficient for each of the fuel injection timing and the EGR amount is set as a multidimensional map correlated with at least two parameters. Engine control device. An in-cylinder pressure sensor;
Means for calculating a first parameter and a second parameter correlated to both the actual ignition timing and the EGR amount in the cylinder based on the in-cylinder pressure change detected by the in-cylinder pressure sensor;
Means for determining a ratio between a predetermined first parameter target value corresponding to the operating condition and the actual first parameter;
Means for determining a ratio between a predetermined second parameter target value corresponding to the operating condition and the actual second parameter;
A three-dimensional first control map to which a fuel injection timing correction amount or correction coefficient is assigned corresponding to these two ratios;
Similarly, a three-dimensional second control map in which a correction amount or a correction coefficient of the EGR amount is assigned corresponding to these two ratios
Means for correcting the fuel injection timing using the correction amount or correction coefficient obtained from the first control map;
Means for correcting the EGR amount using the correction amount or correction coefficient obtained from the second control map;
A diesel engine control device comprising:

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