JP2006316709A - Detection device of egr gas flow rate and engine control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent deterioration of the detection accuracy of a flow sensor caused by dirt and breakage of the sensor due to overheat by a flow sensor provided upstream of a throttle and by providing a flow sensor between a junction of EGR gas and fresh air and an intake pipe collector. <P>SOLUTION: A detection device of an EGR gas flow rate has the flow sensors 9, 10 provided upstream and downstream of the junction of fresh air and EGR gas and obtains EGR gas volume from a flow rate difference between the two sensors. An EGR rate for every cylinder is estimated from the time-series values of EGR gas volume, and injection timing, an injection quantity, a pilot injection ratio and an EGR gas mixing means for every cylinder are controlled based on the estimated rate. The accuracy deterioration and breakage of the flow sensors caused by dirt and overheat can be thus prevented. Discharge of NOx and soot from the engine can be inhibited. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas recirculation gas flow rate detection apparatus and control method for an internal combustion engine that recirculates part of exhaust gas to intake air.

  In the combustion process of an internal combustion engine, increasing the amount of inert components in the air-fuel mixture decreases the combustion temperature due to an increase in the amount of gas per unit calorific value, and the amount of NOx contained in the exhaust gas decreases. Exhaust gas so-called EGR (Exhaust Gas Recirculation), in which a part of the discharged exhaust gas is recirculated to the intake side and NOx in the exhaust gas is reduced by lowering the combustion temperature of the air-fuel mixture, has been widely used.

  When this EGR is performed, a delay in the generation of flame nuclei, a delay in flame propagation, and the like occur. Therefore, appropriate control according to the operation state of the internal combustion engine is necessary, and in order to maintain a stable combustion state, the EGR control is concerned. Various proposals have been made.

  For example, in Japanese Patent Laid-Open No. 6-74100, a flow rate sensor is interposed in an exhaust gas recirculation passage extending from between the catalyst downstream side and the muffler upstream side of the exhaust pipe, and the exhaust gas recirculation passage is connected to the intake pipe. By providing a control valve at the junction, controlling the valve opening of the control valve based on the signal from the flow sensor, and performing feedback control so that the flow rate of the exhaust gas flowing through the exhaust gas recirculation passage becomes a target value, When performing exhaust gas recirculation, an EGR control technique is disclosed that enables accurate metering and mixing of the recirculated gas.

JP-A-6-74100

  Since the EGR gas contains fouling substances such as high-concentration soot and engine oil and is at a higher temperature, a flow sensor is provided in the exhaust gas recirculation passage as described in JP-A-6-74100. There is a possibility that the detection accuracy of the EGR gas flow rate may be lowered due to a change in sensor characteristics or clogging inside the sensor due to the pollutant in the EGR gas, or the sensor may be damaged due to overheating. In JP-A-6-74100, there is shown an example in which a filter is provided on the upper part of the flow sensor to prevent fouling, but for fouling substances such as carbon contained in EGR gas, fine particles of about several microns are shown. Since it is included, it is difficult to remove it with a filter.

  Further, since the exhaust gas recirculation passage is easily affected by exhaust gas pulsation, there is a problem that the flow rate error to be detected becomes large when a back flow occurs in the exhaust gas recirculation passage or the response of the flow sensor is low.

  Further, an ordinary engine is often composed of a plurality of cylinders. In this case, there is a possibility that a deviation occurs in the EGR gas flow rate for each cylinder due to a drift of the gas flow in the intake pipe. When the deviation of the EGR gas flow rate for each cylinder is large, a large amount of soot is discharged from the cylinder with a high EGR gas flow rate, or conversely, a large amount of NOx is discharged from a cylinder with a low EGR gas flow rate. For this reason, it is desirable to estimate the EGR gas flow rate for each cylinder and appropriately control the engine. However, the prior art has no means for solving such a problem.

  The object is to provide a first gas flow rate detection means upstream of the throttle, a second gas flow rate detection means between the confluence of EGR gas and fresh air and the intake pipe collector, and the second gas flow rate detection. An EGR gas flow rate detection device for obtaining an EGR gas flow rate flowing into a cylinder based on a difference between a gas flow rate value detected by the means and a gas flow rate value detected by the first gas flow rate detection means It is solved by.

  Further, the above-described problem is provided with an EGR gas flow rate detection device, and estimates the EGR gas flow rate for each cylinder by using time series values of EGR gas flow rates of at least several engine cylinders while the engine crankshaft rotates twice. In relation to the EGR gas flow rate for each cylinder estimated by the means, the fuel injection timing for each cylinder, the number of fuel injections for each cylinder, the fuel injection amount for each cylinder, or fresh air The problem can also be solved by an engine control method characterized in that the operation amount of the mixing control means with EGR gas is determined.

  Further, in the direct injection engine, the above-described problem is to advance the fuel injection timing of the cylinder that is estimated to have a high EGR gas flow rate for each cylinder more than the fuel injection timing of the cylinder that is estimated to have a low EGR gas flow rate. This is solved by an engine control method characterized by the above.

More preferably, in a direct injection engine that performs fuel injection a plurality of times in one stroke,
An engine characterized in that the number of fuel injections in one stroke of a cylinder estimated to have a high EGR gas flow rate is greater than the number of fuel injections in one stroke of a cylinder estimated to have a low EGR gas flow rate. This is solved by the control method.

More preferably, in a direct injection engine that performs fuel injection a plurality of times in one stroke,
The ratio of the front-stage injection amount of the cylinder estimated to have a high EGR gas flow rate is made larger than the ratio of the front-stage injection amount in one stroke of the cylinder estimated to have a low EGR gas flow rate. It is solved by the control method.

  More preferably, in the direct injection engine, the fuel injection ratio in one stroke of the cylinder estimated to have a high EGR gas flow rate is set to the fuel injection ratio in the one stroke of the cylinder estimated to have a low EGR gas flow rate. This is solved by an engine control method characterized in that the ratio is larger than the ratio.

  More preferably, the amount of operation of the mixing control means for adjusting the degree of mixing of the EGR gas and fresh air is determined so that the deviation of the EGR gas flow rate between the cylinders becomes smaller than a predetermined value. Solved by the method.

  As described above, according to the present invention, the flow rate sensor provided upstream of the throttle, the flow rate sensor provided between the EGR gas and fresh air merging portion, and the intake pipe collector are provided. The EGR gas flow rate can be detected without installing a flow sensor in the EGR gas pipe. Thereby, the fall of the detection accuracy by the contamination of a flow sensor and the damage of the sensor by overheating can be prevented.

Further, by estimating the EGR amount for each cylinder from the EGR gas flow rate detected in time series, and changing the fuel injection timing, fuel injection amount, and pilot injection ratio in relation to the EGR amount for each cylinder, soot and NOx Can be reduced simultaneously.

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

  FIG. 1 shows a configuration diagram of an EGR gas flow rate detection apparatus according to the present embodiment. The EGR gas flow rate detection device in this embodiment is applied to a vehicle equipped with a diesel internal combustion engine. The present invention is applicable not only to a diesel internal combustion engine but also to a gasoline internal combustion engine. The internal combustion engine 2 is a four-cycle four-cylinder engine and includes a turbocharger 3 to which an intake path 4 including an air cleaner 17, an intercooler 13, an intake manifold, a collector 16, and the like is connected. The internal combustion engine 2 is connected to an exhaust path 5 including an exhaust manifold, a catalyst 15, and the like.

  The internal combustion engine 2 is provided with an injector 6 for injecting fuel into the combustion chamber. The injector 6 is fuel injection means for supplying fuel to the combustion chamber, and is installed for each cylinder formed in the internal combustion engine 2. An EGR cooler 8 is provided in the middle of the circulation pipe 7 for circulating the EGR gas.

  The EGR cooler 8 is a cooling means for cooling the EGR gas flowing through the circulation pipe 7. As the EGR cooler 8, for example, a water-cooled type is used, and the EGR gas flowing through the circulation pipe 7 is cooled by circulation of cooling water. The EGR cooler 8 may be of any type such as a stacked type or a multi-tube type.

  An EGR control valve 10 is provided in the middle of the circulation pipe 7 and downstream of the EGR cooler 8. The EGR control valve 10 is a valve body that opens and closes the circulation pipe 7, and adjusts the flow rate of EGR gas by opening and closing the valve body. Although FIG. 1 shows a configuration example in which the EGR cooler 8 is arranged on the exhaust side, the arrangement relationship between the EGR cooler 8 and the EGR control valve 10 is not particularly limited.

The intake path 4 and the circulation pipe 7 are connected downstream of the throttle 14, and a flow rate sensor 9 is provided between the connecting portion and the collector 16. A flow rate sensor 12 is provided downstream of the air cleaner 17. The attachment position of the flow rate sensor 12 may be any location in the intake passage 4 as long as it is upstream from the connection portion between the intake passage 4 and the circulation pipe 7. The flow sensor 12 detects the mass flow rate of fresh air passing through the intake path, and the flow sensor 9 detects the mass flow rate of fresh air and EGR gas mixture passing through the intake path. By mixing fresh air with the EGR gas, the temperature of the air-fuel mixture and the concentration of fouling substances such as carbon dust and oil are significantly lower than that of the EGR gas. Therefore, the demand for heat resistance and antifouling property of the flow sensor 9 is significantly less than when the flow sensor is provided in the circulation pipe 7.

  It is desirable that the flow rate sensors 9 and 12 have a high response speed and a high antifouling property. As such a flow rate sensor, for example, a thermal flow rate using a hot wire or a hot film formed on a semiconductor substrate is used. There is a sensor. In a thermal type flow sensor, heating the sensor can evaporate oil mist and moisture adhering to the sensor surface, and prevent solid dust such as carbon from adhering to the sensor. Moreover, even when carbon adheres to the sensor, the carbon can be burned off by heating, so that the anti-fouling property against EGR gas is high.

  The ECU 11 controls the entire engine, and is mainly composed of a computer including a CPU, a ROM, and a RAM. Various control routines for the engine are stored in the ROM. Flow rate sensors 9 and 12 are connected to the ECU 11 and output signals from the flow rate sensors 9 and 12 are input. The ECU 11 is connected to the injector 6 of each cylinder and outputs an injection control signal to each injector 6 independently. The ECU 11 is connected to the EGR control valve 10 and outputs an EGR control signal to the EGR control valve 10.

  A crank angle signal of the engine 2 detected by the crank angle sensor 19 is input to the ECU 11.

A method for detecting the EGR gas flow rate in this embodiment will be described with reference to FIG. FIG. 2 shows the time change of the flow rate detected by the flow sensor 9 and the flow sensor 12. Detection values of the flow sensor 9 and the flow sensor 12 are taken into the ECU 11 at predetermined time intervals. The ECU 11 can obtain the EGR gas flow value 22 by subtracting the fresh air flow value 21 detected by the flow sensor 12 from the mixed gas flow value 20 of the fresh air and EGR gas detected by the flow sensor 9. .

In addition, when the position interval of the flow sensor 9 and the flow sensor 12 is large, or when the gas velocity is slow, the time difference becomes large until the fresh air detected by the flow sensor 12 comes to the position of the flow sensor 12, and at the same time. If the detected value is subtracted, the detection error of the EGR gas flow rate becomes large. Therefore, a time delay Δt until the fresh air detected by the flow sensor 12 arrives at the position of the flow sensor 12 is estimated, and the flow rate value 21 of the fresh air obtained by the flow sensor 12 as shown in FIG. If the delayed corrected detection value 21 ′ is obtained and the EGR gas flow rate 22 ′ is obtained from the difference between 20 and 21 ′, the detection accuracy of the EGR gas can be improved. Here, the time delay Δt can be estimated by Equation 1, for example. g1 is a fresh air flow value detected by the flow sensor 12, and is updated to the latest detected value every predetermined time. V is the volume of the intake path between the flow sensor 12 and the flow sensor 9, and ρ is the density of fresh air.

Next, a method for estimating the amount of EGR gas flowing into each cylinder of the engine will be described with reference to FIGS. In FIG. 4, (A) is the intake stroke discrimination value of each cylinder. The value is 1 when each cylinder is in the intake stroke, and 0 when the cylinder is not in the intake stroke. This intake stroke discrimination value is
It is created in the ECU 11 using the crank angle sensor signal of the engine taken into the ECU 11. In this embodiment, the intake stroke is switched every crank angle of 180 degrees in the order of the first cylinder, the second cylinder, the third cylinder, and the fourth cylinder. FIG. 4B shows the change over time of the flow rate detected by the flow rate sensor 9 and the flow rate sensor 12. 20 is an EGR gas obtained by subtracting 21 from 20 for the flow rates 21 and 22 of fresh air detected by the flow sensor 12. Flow rate value. FIG. 4C shows an estimation process of the EGR gas flow rate of each cylinder.

FIG. 5 shows a procedure for obtaining the EGR gas amount of each cylinder after the crankshaft has rotated twice. In step (51), the cylinder number is set to n, and in step (52), the array EGR (n) in which the EGR gas amount of the current cylinder is obtained is initialized to zero. In process (53), it is determined whether or not the current cylinder is in the intake stroke based on the intake stroke determination signal. If it is in the intake stroke, the flow rate value 21 of fresh air and the fresh air are determined from the flow rate sensor value in process (54). A gas mixture flow value 20 with EGR gas is read. Next, in the process (55), an EGR flow value 22 is obtained from the difference between the mixture flow value 20 of fresh air and EGR gas and the flow value 21 of fresh air. Subsequently, in the process (56), the product of the EGR flow rate value 22 and the flow rate detection interval δt is added to EGR (n), and time integration is performed. Processes (54) to (56) are repeated during the intake stroke of the current cylinder n, and EGR (n) flows into the current cylinder, ie, the time integral value of the EGR gas flow rate during the intake stroke. The amount of EGR gas is determined. When the intake stroke ends, the cylinder number n is updated to the next cylinder in the process (57), and the process returns to the process (52). When n> 4 in the process (58), the EGR gas amounts of all the cylinders are obtained in the array EGR (n).

  When the response times of the flow sensors 9, 12 are approximately the same as the intake stroke period, it is considered that the flow sensor does not capture fine flow rate fluctuations in the intake stroke, and detects an average flow rate during the intake stroke. In this case, the integral time interval δt of the flow rate may be substantially the same as the intake stroke period, and the flow rate may be detected only once during the intake stroke, and the EGR gas amount of the current cylinder may be obtained from the flow rate value. That is, the EGR amount for each cylinder can be obtained by performing the processes (54) to (56) at least once for each cylinder while the crankshaft rotates twice.

  By performing optimal control for each cylinder based on the EGR amount for each cylinder, engine emissions can be reduced. Next, a method for controlling the injection timing for each cylinder will be described with reference to FIG. FIG. 6 shows the correction characteristic of the fuel injection timing with respect to the EGR amount of each cylinder. In the present embodiment, the average EGR amount between the cylinders is obtained by, for example, the following arithmetic average.

EGR0 = {EGR (1) + EGR (2) + EGR (3) + EGR (4)} / 4
Based on the average EGR amount EGR0, the intake fresh air amount, the engine speed, and the like, a reference injection timing Ti0 is obtained based on an operation map stored in advance in a ROM in the ECU 11. Next, the fuel injection timing of each cylinder is determined based on the correction characteristics shown in FIG. In this correction characteristic, when the EGR amount for each cylinder is larger than EGR0, the injection timing is corrected to advance from the reference injection timing, and when the EGR amount for each cylinder is less than EGR0, the injection timing is corrected to be retarded from the reference injection timing. . This is due to the following reason. When a large amount of EGR gas is contained in the cylinder, the inert gas concentration is high, so that combustion after ignition becomes slow and soot tends to be generated. In this case, it is necessary to suppress the generation of soot by extending the combustion period by advancing the heat generation by advancing the fuel injection timing of the cylinder.

  On the other hand, when the amount of EGR gas in the cylinder is small, NOx emissions increase because the combustion speed increases. Therefore, it is effective in reducing NOx to delay ignition by delaying the injection timing of the cylinder and lower the maximum temperature reached in the cylinder.

  FIG. 7 is an example of correcting the fuel injection amount for each cylinder. In a cylinder having a large EGR amount, it is necessary to reduce the fuel injection amount in order to prevent generation of soot. Therefore, in the injection amount correction characteristic of FIG. 7, the injection amount is corrected to decrease in a cylinder having a large EGR amount. On the other hand, in a cylinder with a small EGR amount and a margin for soot, the engine torque is prevented from decreasing by correcting the injection amount to be increased.

  In a diesel engine, ignition delay after main injection can be reduced by pilot injection. Therefore, it is conceivable to control the ratio of pilot injection (the amount of pilot injection with respect to the total injection amount) according to the EGR amount for each cylinder. FIG. 8 shows the correction characteristic of the pilot injection ratio with respect to the EGR amount for each cylinder. In a cylinder where the EGR amount is larger than the average EGR amount, the ignition delay of main combustion is reduced by increasing the ratio of pilot injection, and soot generation is suppressed. On the other hand, in a cylinder having a small EGR amount, the ignition delay of main combustion can be increased to reduce NOx by reducing the ratio of pilot injection. The ratio of pilot injection can be changed by the injection pulse width of pilot injection or the number of pilot injections. Specifically, in order to increase the ratio of pilot injection, the number of pilot injections may be increased or the injection pulse width of pilot injection may be increased.

  In addition, a control method for operating the degree of mixing of EGR gas and fresh air based on the EGR amount deviation for each cylinder is also conceivable. An embodiment of a control method for operating the degree of mixing of EGR gas and fresh air based on the EGR amount deviation for each cylinder will be described with reference to FIGS.

FIG. 9 shows an example of means for adjusting the degree of mixing of EGR gas and fresh air. A butterfly valve 93 is provided on the downstream side of the junction between the circulation pipe 7 and the intake passage 4 so that the distribution amount of the air-fuel mixture to the bypass pipe 91 can be changed in opening degree based on a command value of an ECU (not shown). Adjust by. A porous plate 92 is provided in a cross section in the bypass pipe 91, and mixing of gas flowing in the bypass pipe is promoted by turbulent vortices generated by the porous plate 92. If the mixing adjusting means of FIG. 9 is used, when the butterfly valve 93 is closed, the gas distribution to the bypass pipe 91 increases.
The degree of mixing of EGR gas and fresh air increases. On the other hand, since the pressure loss in the bypass pipe 91 is large due to the perforated plate 92, the pressure loss of the fresh air and the EGR gas mixture increases as the butterfly valve 93 is closed. Therefore, the degree of mixing of EGR gas and fresh air and the pressure loss can be adjusted by the opening degree of the butterfly valve 93.

  FIG. 10 shows how to determine the opening degree of the butterfly valve 93 with respect to the EGR amount deviation (standard deviation) between the cylinders. When the EGR amount deviation between the cylinders is large, the opening degree of the butterfly valve 93 is reduced to further promote the mixing of fresh air and EGR gas, thereby reducing the EGR amount deviation between the cylinders. On the other hand, when the EGR amount deviation between the cylinders is small, the opening degree of the butterfly valve 93 is increased to reduce the pressure loss of the air-fuel mixture. In this way, by controlling the degree of mixing of fresh air and EGR gas based on the EGR amount deviation between the cylinders, it is possible to reduce the EGR gas inter-cylinder deviation and the pressure loss.

The basic block diagram of the engine provided with the detection apparatus of the EGR gas flow rate which concerns on this embodiment. The example of the detected value of the fresh air flow volume based on this embodiment, an EGR gas flow volume, a fresh air, and an EGR gas mixed gas flow volume. The example of the detected value of EGR gas mixture flow volume when the time delay correction | amendment of the fresh air which concerns on this embodiment is considered. The example of the detected value of the intake stroke signal for every cylinder which concerns on this embodiment, fresh air, EGR gas, and air-fuel | gaseous mixture flow volume. The procedure which calculates | requires EGR gas amount for every cylinder which concerns on this embodiment. The injection timing correction pattern with respect to EGR amount for every cylinder which concerns on this embodiment. The injection amount correction pattern with respect to the EGR amount for each cylinder according to the present embodiment. The pilot injection ratio correction pattern with respect to the EGR amount for each cylinder according to the present embodiment. The example of the mixing adjustment means of fresh air and EGR gas. The inter-cylinder EGR deviation and butterfly valve opening pattern according to the present embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Exhaust gas recirculation apparatus, 2 ... Engine, 3 ... Turbocharger, 4 ... Intake path, 5 ... Exhaust path, 6 ... Injector, 7 ... Recirculation piping, 8 ... EGR cooler, 9, 12 ... Flow sensor, 10 ...
EGR control valve, 11 ... ECU, 13 ... intercooler, 14 ... throttle, 15 ... catalyst, 16 ... collector, 17 ... air cleaner, 19 ... crank angle sensor, 20 ... fresh air and EGR gas mixture flow rate detection value, 21 ... Fresh air flow value, 22 ... EGR gas flow value, 91 ... Bypass pipe, 92 ... Perforated plate, 93 ... Butterfly valve.

Claims (8)

  A first gas flow rate detection means provided upstream of the throttle; a second gas flow rate detection means provided between a confluence of EGR gas and fresh air and the intake pipe collector; and the second gas flow rate detection An EGR gas flow rate detecting device for obtaining an EGR gas flow rate flowing into a cylinder based on a difference between a gas flow rate value detected by the means and a gas flow rate value detected by the first gas flow rate detecting means. .   2. The EGR gas detection device according to claim 1, wherein the gas flow rate detection means is a thermal flow rate sensor.   EGR gas flow rate detection device is provided, and means for estimating the EGR gas flow rate for each cylinder by using time series values of EGR gas flow rates of at least several engine cylinders while the engine crankshaft rotates twice In relation to the EGR gas flow rate for each cylinder estimated by the means, the fuel injection timing for each cylinder, the number of fuel injections for each cylinder, the fuel injection amount for each cylinder, or the mixture of fresh air and EGR gas An engine control method characterized by determining an operation amount of a control means.   The fuel injection timing of a cylinder estimated to have a large EGR gas flow rate per cylinder in a direct injection engine is advanced from the fuel injection timing of a cylinder estimated to have a low EGR gas flow rate. 3. The engine control method according to 3.   In a direct injection engine that performs fuel injection a plurality of times in one stroke, the number of fuel injections in one stroke of the cylinder that is estimated to have a high EGR gas flow rate is the same as the one stroke of the cylinder that is estimated to have a low EGR gas flow rate. 4. The method of controlling an engine according to claim 3, wherein the number of times of fuel injection in the engine is increased.   In a direct-injection engine that performs multiple fuel injections in one stroke, the ratio of the pre-stage injection amount of the cylinder that is estimated to have a high EGR gas flow rate is the same as that in one stroke of the cylinder that is estimated to have a low EGR gas flow rate. 4. The engine control method according to claim 3, wherein the ratio is larger than the ratio of the upstream injection amount.   In a direct injection engine, the fuel injection ratio in one stroke of a cylinder estimated to have a high EGR gas flow rate should be greater than the fuel injection ratio in one stroke of a cylinder estimated to have a low EGR gas flow rate. The engine control method according to claim 3. 4. The engine control method according to claim 3, wherein the operation amount of the mixing control means for adjusting the degree of mixing of EGR gas and fresh air is determined so that the deviation of the EGR gas flow rate between the cylinders becomes smaller than a predetermined value. .

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