JP2006214275A - Exhaust circulating device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust circulating device and a control method, always accurately adjusting the EGR gas quantity to a target value of EGR circulation quantity whether the circulation quantity of EGR gas is large or small even in a transient change by setting the fitting position of a flow rate sensor within a predetermined distance from an EGR control valve. <P>SOLUTION: In this exhaust circulating device, a pipeline connected between an exhaust passage and an intake passage to circulate some of exhaust emission and the control valve for adjusting the circulation quantity of exhaust emission are interposed in the pipeline. The flow rate sensor for detecting the circulation quantity of exhaust emission is disposed at a predetermined distance from the control valve, and a flow rate sensor signal is feedback-controlled to adjust the opening of the EGR control valve according to the operating condition. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas recirculation device 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 the combustion temperature of the air-fuel mixture is lowered to reduce NOx in the exhaust gas, 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 Patent Document 1, 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 control is performed at a junction portion of the exhaust gas recirculation passage to the intake pipe. By providing a valve, controlling the valve opening of the control valve based on a 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, An EGR control technique is disclosed that enables accurate reflux gas metering and mixing when implemented.

JP-A-6-74100

  In recent years, in an internal combustion engine for automobiles, there is an increasing demand for increasing the amount of EGR with the tightening of exhaust regulations. In the case of gasoline, the in-cylinder injection improves the fuel efficiency by realizing stratified combustion by utilizing the freedom of fuel injection, while increasing the NOx emission amount emitted from the internal combustion engine. There is a tendency to actively recirculate a large amount of EGR gas as a countermeasure in the combustion system for this problem. In particular, in diesel internal combustion engines, in order to simultaneously reduce NOx and PM, which is an exhaust issue, fuel spray atomization is promoted by increasing the fuel pressure by the common rail, and the EGR is made more uniform by making the mixture more uniform. Is realized. Although the operating conditions for performing EGR gas recirculation are limited by the combustion state, in the operating region where more EGR is recirculated, the recirculation of EGR gas equal to or higher than the fresh air sucked into the internal combustion engine is performed. Required. Moreover, since the driving state is always changing in an actual vehicle, high response and high institution of EGR control that can cope with transient changes are required.

  Incidentally, an EGR control valve that adjusts the flow rate of EGR is generally provided on the intake side due to thermal restrictions. In such an apparatus configuration, backflow or pulsation of EGR gas occurs in the EGR pipe due to the influence of exhaust pulsation. In the EGR control method disclosed in Japanese Patent Laid-Open No. 6-74100, there is a technique in which a hot wire type flow sensor is interposed on an EGR pipe and the valve opening degree of the control valve is controlled based on a signal from the flow sensor. Although it has been proposed, it is difficult in principle to detect a reverse flow with a hot wire type flow sensor. When a hot wire is applied, a means for suppressing the reverse flow is added or the influence of the reverse flow is small. If it is not interposed at the mounting position, the measurement accuracy will be significantly reduced.

  The present invention has been made in view of the above circumstances, and by arranging the mounting position of the flow sensor within a predetermined distance from the EGR control valve, regardless of the amount of recirculation of the EGR gas, and at the time of transient change, too. It is an object of the present invention to provide an exhaust gas recirculation device and a control method that can always adjust the EGR gas amount accurately with respect to the target value of the EGR recirculation amount.

  An exhaust gas recirculation apparatus and control method for an internal combustion engine according to the present invention includes a pipe for recirculating a part of exhaust gas connected between an exhaust path and an intake path, and a control valve for adjusting a recirculation amount of the exhaust gas. In the exhaust gas recirculation device interposed in the exhaust gas recirculation apparatus, a flow rate sensor for detecting the exhaust gas recirculation amount is disposed on the intake side of the control valve.

  Alternatively, in an exhaust gas recirculation device in which a pipe for recirculating a part of exhaust gas connected between the exhaust path and the intake path and a control valve for adjusting the exhaust gas recirculation amount are interposed in the pipe, A flow rate sensor for detecting a recirculation amount is arranged at a distance within 4 times the pipe diameter from the control valve, the flow rate sensor signal is feedback-controlled, and the opening degree of the EGR control valve is adjusted according to the operating state. And

  Alternatively, in a configuration in which a control valve for adjusting the exhaust gas recirculation amount is directly connected to the intake path, the flow sensor is located upstream (exhaust side) of the control valve and within a distance of three times the diameter of the pipe through which the exhaust gas is recirculated. The flow rate sensor signal is feedback-controlled, and the opening degree of the EGR control valve is adjusted according to the operating state.

  According to the present invention described above, a pipe for recirculating a part of the exhaust gas connected between the exhaust path and the intake path, and a control valve for adjusting the recirculation amount of the exhaust gas are interposed in the pipe. In the exhaust gas recirculation device, the flow rate sensor for detecting the recirculation amount of the exhaust gas is disposed at a predetermined distance from the control valve, so that the measurement error due to the backflow or pulsation of the EGR gas, which is a problem, can be suppressed. The feedback control of the signal makes it possible to control the opening degree of the control valve so that the exhaust gas recirculation amount becomes a target value in accordance with changes in the operating state of the engine. Since it is possible to recirculate, NOx discharged from the internal combustion engine can be greatly reduced.

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

  FIG. 1 shows a configuration diagram of an exhaust gas recirculation apparatus according to the present embodiment. As shown in the figure, the exhaust gas recirculation device 1 according to the present embodiment is a device for circulating the exhaust gas of the internal combustion engine to the intake side, and 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 includes a turbocharger 3 and is connected to an intake passage 4 including an intake manifold. The internal combustion engine 2 is connected to an exhaust path 5 made of an exhaust manifold or 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 pipe 7 for circulating the EGR.

  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.

  A flow rate sensor 9 is provided in the middle of the reflux pipe 7. In FIG. 1, the flow sensor 9 is arranged upstream of the arrangement of the EGR control valve 10. However, as shown in FIG. 2, the flow sensor 9 is arranged at a distance within four times the reflux pipe diameter D from the EGR control valve 10. If it is, there is no problem whether it is arranged upstream or downstream. The flow sensor 9 is a thermal flow sensor using, for example, a hot wire, and directly detects the mass flow rate of the EGR gas flowing through the reflux pipe 7.

  The exhaust gas recirculation device 1 is provided with an ECU 11. The ECU 11 controls the entire exhaust gas recirculation device, and is mainly composed of a computer including a CPU, a ROM, and a RAM. Various control routines including an exhaust gas recirculation routine are stored in the ROM. A flow sensor 9 is connected to the ECU 11 and an output signal of the flow sensor 9 is input. The ECU 11 is connected to each injector 6 and outputs an injection control signal to the injector 6. The ECU 11 is connected to the EGR cooler 8 and the EGR control valve 10 and outputs a cooling control signal to the EGR cooler 8 and an EGR control signal to the EGR control valve 10. By feedback control of the signal from the flow rate sensor 9, an optimal EGR recirculation amount can always be supplied to the intake side in accordance with changes in the operating state of the engine.

  In FIG. 1, reference numeral 12 is an intake flow meter, reference numeral 13 is an intercooler, reference numeral 14 is an intake throttle valve, and reference numeral 15 is a catalyst.

  The EGR control valve 10 is generally interposed on the intake side due to thermal restrictions. Next, as shown in FIG. 3, when the EGR control valve 10 is arranged on the intake side, the mass flow rate variation with respect to the crank angle at almost the midpoint of the return pipe 7, that is, the backflow and pulsation state in the return pipe 7 are shown in FIG. Will be described.

  FIG. 4 shows the backflow and pulsation effects of the opening degree of the EGR control valve 10 at the intermediate point of the reflux pipe 7. The conditions are the result of an engine speed of 1500 rpm, a net average effective pressure (BMEP) of 2.6 bar, and an intake throttle valve opening of 50 deg. When the opening degree of the EGR control valve is 20 deg, a reverse flow is generated, and when it is 40 deg or more, the reverse flow is hardly generated. It can be seen that the presence or absence of backflow in the reflux pipe depends on the opening of the EGR control valve 10. This is because when the opening degree of the EGR control valve 10 is small, the average flow rate in the recirculation pipe 7 is small, and the upstream of the EGR control valve 10 is greatly influenced by the exhaust pulsation amplitude, so the lower limit value of the amplitude is negative. This is because it becomes a value and flows backward. On the other hand, when the opening degree of the EGR control valve 10 is large, since the average flow rate in the recirculation pipe 7 is large, the lower limit value of the exhaust pulsation amplitude does not easily reach a negative value, so the backflow becomes small.

Next, the effects of backflow and pulsation due to differences in distance from the EGR control valve and operating conditions of the internal combustion engine will be described with reference to FIGS. From the EGR control valve 10 shown in FIG. 5 to the exhaust side, the intake throttle valve opening is 50 deg and the EGR control valve is opened at four locations corresponding to distances of 1, 2.5, 4, and 7 times the reflux pipe diameter. 1500rpm when the degree is kept constant at 20deg
The results of BMEP 2.6 bar, 2000 rpm · BMEP 2 bar, 3000 rpm · BMEP 2 bar are shown in FIG. In 1500 rpm, the backflow has generate | occur | produced in the reflux piping 7 in the position where the distance from the EGR control valve 10 separated 4 times or more. This is because when the opening of the EGR control valve 10 is small, the EGR control valve 10 becomes a fixed end, that is, a “node” of pulsation, and since the return pipe inlet is an open end, it becomes a “belly” of pulsation. This is because the pulsation amplitude increases as the distance increases. Further, when the engine speed increases, the average flow rate of the EGR gas flowing through the recirculation pipe 7 per unit time increases, so that the lower limit value of the exhaust pulsation amplitude does not easily reach a negative value and the backflow decreases. To summarize the above, although the magnitude differs depending on the operating state of the engine and the opening degree of the EGR control valve 10, it can be said that the closer to the EGR control valve 10 is, the smaller the backflow is in the upstream of the EGR control valve 10, that is, in the exhaust gas recirculation pipe 7. .

  Therefore, when the flow sensor is disposed on the exhaust side from the EGR control valve, it is preferable that the flow sensor be disposed close to a distance that is not more than four times the reflux pipe diameter from the EGR control valve.

  Next, the pulsation in the EGR control valve downstream, that is, in the intake side recirculation pipe 7 will be described. In order to confirm the pulsation in the recirculation pipe 7 on the intake side, an EGR control valve 10 is arranged at the midpoint of the recirculation pipe as shown in FIG. The distance from the EGR control valve 10 is the result of confirming four locations corresponding to distances of 1, 2, 2.5, 4 and 7 times the reflux pipe diameter on the intake side, contrary to the case on the exhaust side. is there. Other conditions are the same as in the case of FIG. It can be seen that the reverse flow occurs only at a position where the distance from the EGR control valve 10 is more than 7 times at 1500 rpm. This is because, as described above, the pulsation amplitude increases as the distance from the EGR valve increases. However, since the pulsation amplitude is smaller on the intake side than on the exhaust side, backflow does not occur at distances of 1D, 2.5D, and 4D. It is.

  For this reason, when the flow sensor is arranged on the intake side of the EGR control valve, the distance between the EGR control valve and the flow sensor is arranged farther from the viewpoint of backflow and pulsation than in the case of arrangement on the exhaust side. There is no problem. However, it is considered that the closer the EGR control valve is to the intake throttle valve, the better the response and the better the controllability at the time of transition. Therefore, it is ideal to arrange the EGR control valve closer to the intake throttle valve.

Therefore, when the flow rate sensor is arranged on the intake side of the EGR control valve, the recirculation pipe diameter of the EGR control valve is reduced from the EGR control valve in the same manner as in the case of the exhaust side arrangement due to the restriction of the distance between the EGR control valve and the intake throttle valve. It is preferable to arrange it at 4 times or less. Also, when placing on the intake side,
The EGR control valve is also advantageous for fouling such as fouling. Furthermore, arrange on the intake side,
If it is close to the EGR control valve, it may be affected by drift. Therefore, in the case of the close arrangement as in the configuration of FIG. 9, it is more stable if a means 16 for rectifying the flow of EGR gas such as a honeycomb or a filter is provided between the EGR control valve 10 and the flow rate sensor 9. Can be weighed.

  The optimum exhaust gas recirculation device configuration and backflow and pulsation in that case will be described with reference to FIGS. As shown in FIG. 10, the EGR control valve 10 is disposed at a distance of approximately 3D from the intake path 4. It can be seen from FIG. 11 that no reverse flow occurs on both the exhaust side and the intake side.

  The present invention is effective when a flow sensor capable of detecting a reverse flow is applied, but is more effective when applying a flow sensor using a heating element such as a hot wire that is difficult to detect a reverse flow. There is no particular restriction on the presence or absence of the backflow detection function.

The basic block diagram of the exhaust gas recirculation apparatus which concerns on this embodiment. Optimal mounting range for flow sensor. The 1st block diagram of the exhaust gas recirculation apparatus which concerns on this embodiment. The influence on the backflow and pulsation by the EGR control valve opening degree in the first configuration. The 1st block diagram of the exhaust gas recirculation apparatus which concerns on this embodiment. The reverse flow and pulsation waveform in the return pipe upstream of the EGR control valve. The 2nd block diagram of the exhaust gas recirculation apparatus which concerns on this embodiment. The reverse flow and pulsation waveforms in the return pipe downstream of the EGR control valve. Optimal exhaust gas recirculation system configuration for intake side arrangement. The optimal block diagram of the exhaust gas recirculation apparatus which concerns on this embodiment. Backflow and pulsation waveforms in the optimal configuration of the exhaust gas recirculation device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Exhaust gas recirculation apparatus, 2 ... Internal combustion engine, 3 ... Turbocharger, 4 ... Intake path, 5 ... Exhaust path, 6 ... Injector, 7 ... Recirculation piping, 8 ... EGR cooler, 9 ... Flow sensor, 10 ... EGR control valve 11 ... ECU, 12 ... intake flow meter, 13 ... intercooler, 14 ... intake throttle valve, 15 ... catalyst, 16 ... rectifying means.

Claims (3)

  A pipe for returning a part of the exhaust gas connected between the exhaust path and the intake path is provided, and a control valve for adjusting the exhaust gas recirculation amount is interposed in the pipe to detect the exhaust gas recirculation amount. An exhaust gas recirculation device for an internal combustion engine, wherein a flow sensor is disposed in the pipe on the intake side of the control valve.   A pipe for returning a part of the exhaust gas connected between the exhaust path and the intake path is provided, and a control valve for adjusting the exhaust gas recirculation amount is interposed in the pipe to detect the exhaust gas recirculation amount. An internal combustion engine characterized in that a flow sensor is arranged at a distance within 4 times the pipe diameter from the control valve, feedback control of the flow sensor signal is performed, and the opening of the EGR control valve is adjusted according to the operating state. Exhaust gas recirculation device. A control valve for adjusting the exhaust gas recirculation amount is directly connected to the intake passage, and a flow sensor is disposed on the exhaust side of the control valve and at a distance within three times the diameter of the pipe through which the exhaust gas is recirculated. An exhaust gas recirculation device for an internal combustion engine that performs feedback control and adjusts the opening degree of an EGR control valve according to an operating state.

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