JP4710666B2 - EGR system control method and EGR system - Google Patents

Description

  The present invention relates to an EGR system control method and an EGR system for a supercharged internal combustion engine such as a diesel engine.

  In an internal combustion engine such as a diesel engine, in order to reduce NOx, EGR is performed in which a part of exhaust gas is recirculated to the intake system to lower the combustion temperature in the cylinder and suppress NOx generation. An internal combustion engine that performs EGR has, for example, an EGR system 1 as shown in FIG. 1, and this EGR system 1 branches off from an exhaust manifold 11 or an exhaust pipe 12 of an engine (internal combustion engine) 10, An EGR pipe 15 connected to the manifold 13 or the intake pipe 14, an EGR cooler 16 and an EGR valve 17 provided in the EGR pipe 15, and an EGR control device 20 for controlling the valve opening (opening area) of the EGR valve 17. It consists of and.

  The EGR cooler 16 cools the EGR gas, and the EGR valve 17 adjusts the amount of EGR gas to adjust the EGR rate. The EGR control device 20 inputs the operating state of the engine 10 such as the engine speed Ne, the engine fuel injection amount (or load) Q, the intake air amount m, etc., and refers to preset map data, etc. The EGR rate is calculated, and the valve opening degree of the EGR valve 17 is controlled. Normally, the EGR control device 20 is configured to be incorporated in a control device called an engine control unit (ECU) that controls the entire engine. Further, a mass air flow sensor (MAF sensor) 18 is disposed in the intake pipe 14 in order to detect the intake air amount m. When the supercharger 19 is provided, the compressor 19a is disposed in the intake pipe 14, and the turbine 19b is disposed in the exhaust pipe 12.

  This EGR control includes a first method for performing EGR control with the valve opening degree of the EGR valve that is uniquely determined based on the data mapped with the engine speed and the fuel injection amount (or load) as parameters, and the engine speed. There is a second method for controlling the EGR valve so that the intake air amount is uniquely determined based on the data mapped by the speed and the fuel injection amount.

  In the first EGR control method, for example, the following control is performed according to a control flow as shown in FIG. An engine speed Ne and an engine fuel injection amount (or load) Q are detected, a predetermined target EGR rate ηe is calculated with reference to a predetermined map M1, and an EGR valve that achieves the target EGR rate ηe is obtained. The valve opening degree α (= b) of 17 is calculated with reference to a predetermined map M2. The EGR valve 17 is opened at this valve opening degree α (= b), and after waiting for a predetermined time (a time related to the intake air amount check interval), the process returns to the beginning. A predetermined target EGR rate is obtained by setting the valve opening degree α of the EGR valve 17 to the valve opening degree α (= b) obtained from the map M2.

  The second EGR control method is a control method called mass air flow (MAF) control, and is controlled as follows according to a control flow as shown in FIG. 4, for example. An engine speed Ne and an engine fuel injection amount (or load) Q are detected, a predetermined target EGR rate ηe is calculated with reference to a predetermined map M1, and an EGR valve that achieves the target EGR rate ηe is obtained. The valve opening degree α (= b) of 17 is calculated with reference to a predetermined map M2. Further, the target intake air amount m0 that becomes the target EGR rate ηe is calculated with reference to a predetermined map M3. This target intake air amount m0 is obtained by subtracting the EGR gas amount me from the intake air amount m1 without EGR (m0 = m1-me).

  Then, the EGR valve 17 is initially opened at this valve opening α (= b) and waits for a predetermined time (time related to the intake air amount check interval). Thereafter, the intake air amount m is detected, and the valve opening α of the EGR valve 17 is increased or decreased so that the detected intake air amount m becomes the set intake air amount m0. A target EGR rate ηe is obtained. When the detected intake air amount m reaches the set intake air amount m0, the process returns to the detection of the engine rotational speed Ne and the engine fuel injection amount (load) Q.

  However, in the case of a turbocharged engine equipped with a turbocharger, a turbo response delay occurs when the engine accelerates rapidly. Therefore, during rapid acceleration, the fuel injection amount injected into the cylinder increases instantaneously, but since the increase in the intake air amount is delayed, it is instantaneous (short time), but based on the engine speed and load. As a result, a phenomenon occurs in which the amount of intake air that is supercharged and sent to the engine is significantly smaller than that during steady operation.

  In the case of the first EGR control method, the valve opening degree of the EGR valve is set to a constant value α (= b) even when the intake air amount due to the supercharging delay is insufficient, so the EGR gas amount becomes excessive. The excess air ratio is greatly reduced, resulting in insufficient output and increased smoke emission during acceleration. Further, since the driver (driver) further depresses the accelerator to compensate for the output shortage at the time of acceleration, NOx increases despite the EGR.

  In the case of the second EGR control method, if the intake air amount does not reach the target intake air amount specified in the map due to a delay in supercharging, the EGR valve does not open, that is, does not perform EGR. During acceleration, NOx increases instantaneously but significantly. In particular, when driving in an urban area where the frequency of rapid acceleration is high, this instantaneous NOx emission amount shows a large proportion. Therefore, suppressing the instantaneous NOx emission amount becomes an important issue corresponding to the exhaust gas regulation.

  As one of the countermeasures for acceleration, the operation state of the internal combustion engine is shifted to the acceleration operation state for the purpose of suppressing the generation of smoke when the internal combustion engine is shifted to the acceleration operation state and maintaining good drivability. Accordingly, in the state where the EGR valve is controlled to be closed, the intake air amount at the time of opening when the EGR valve is opened is estimated, and the estimated opening amount is estimated. There has been proposed a control device for an internal combustion engine that opens an EGR valve when it is determined that the intake air amount during valve operation is larger than the required intake air amount required from the operating state of the internal combustion engine (for example, Patent Documents). 1).

  In this control device for an internal combustion engine, in EGR control in the acceleration state, the determination method based on the combination of the engine rotation speed and the accelerator opening change rate is not performed, and the intake air amount is used as a determination criterion, and the EGR valve is opened. Until the amount of intake air that is sucked in sometimes becomes larger than the required amount of intake air, that is, a sufficient amount of intake air can be obtained when the EGR valve is opened, and a large amount of smoke is eliminated Then, control is performed to close the EGR valve. Furthermore, when the EGR valve is opened, control is performed so that the EGR valve is opened from a valve opening smaller than the valve opening required from the operating state, and is opened to the required valve opening according to the rate of change of the intake air amount.

  In the case of this control device for an internal combustion engine, the effects of improving the drivability during acceleration and suppressing the occurrence of smoke can be enhanced, but the effect of reducing NOx is small. In other words, in an engine for complying with North American regulations with many acceleration modes, the intake air amount at the time of valve opening becomes the required intake air due to a response delay of the intake system including the turbo when the acceleration is suddenly higher than a predetermined acceleration. Although a region smaller than the amount is generated, in this region, since EGR is not performed, a large amount of NOx is generated although instantaneously.

  For example, according to the results of a vehicle test related to the FTP75 mode that simulates urban driving under North American gas regulations, the intake air amount of the engine during this moment due to the delay in the response of the turbocharger during sudden acceleration above a certain level. However, since the intake air amount in the case of performing EGR set based on the engine rotation speed and the fuel injection amount (load) is not reached, in this control device for the internal combustion engine, the valve opening degree of the EGR valve is set to 0 (zero). Since it is controlled and no EGR is performed, NOx increases during this moment.

  Vehicle tests have shown that the instantaneous NOx emissions generated by not performing EGR during this rapid acceleration account for a very high percentage of the total NOx emissions generated during all test modes. For example, in the urban driving mode in North America, this instantaneous NOx emissions account for the majority of the total NOx emissions, and the Bin5 and Bin8 regulation values in the North American FTP mode can be set only by the NOx emissions during this rapid acceleration. It will exceed. Rather, the first EGR control method of the prior art that uniquely determines the valve opening of the EGR valve only with the engine speed and load performs EGR during acceleration, so smoke is significantly increased, but NOx is reduced. To do.

Further, in the case of this internal combustion engine control device, the accuracy and responsiveness of the measurement system, the calculation speed of the computer when EGR control is performed using the rate of change of the intake air amount in response to instantaneous NOx generation during sudden acceleration. There is also a problem that it is difficult to correspond in the range of the total rotation speed and the total load because it is directly subject to the restrictions.
Japanese Patent Laid-Open No. 2005-83362

  The object of the present invention is to emphasize the generation of NOx rather than the generation of smoke, and forcibly perform EGR at the time of sudden acceleration of a vehicle in which a response delay of the turbocharger occurs, thereby instantaneously during sudden acceleration. An object of the present invention is to provide an EGR system control method and an EGR system that can suppress a large amount of NOx generation and reduce the total emission amount of NOx.

In order to achieve the above object, a control method for an EGR system according to the present invention calculates a target EGR rate, calculates a target intake air amount based on the calculated EGR rate, and detects an excess amount of an internal combustion engine with a supercharger. In an EGR system control method for opening an EGR valve by reducing the valve opening degree when the intake air amount from the feeder is smaller than the target intake air amount, the internal combustion engine performs an acceleration operation at a predetermined acceleration operation state or higher. In this state , the valve is opened to a predetermined valve opening larger than the fully closed state regardless of the amount of intake air .

The EGR system of the present invention for achieving the above object includes an EGR passage for recirculating a part of exhaust gas of an internal combustion engine with a supercharger to an intake passage of the internal combustion engine, and the exhaust gas to be recirculated. An EGR valve for adjusting the amount of the EGR, an EGR control device , a valve opening control means for opening the EGR valve in accordance with the valve opening of the EGR valve set by the EGR control device, and the operation of the internal combustion engine An operating state detecting means for detecting a state, and an intake air amount detecting means for detecting an intake air amount from the supercharger of the internal combustion engine, wherein the EGR control device detects a target EGR rate from the operating state of the internal combustion engine. is calculated, to calculate a target intake air quantity based on the target EGR rate issued the calculated, the when intake air amount is smaller than the target air amount, the EGR system be set to reduce the valve opening, the EGR system Control device, when the internal combustion engine is in an acceleration driving state of more than predetermined acceleration operating condition, the valve opening degree of despite the EGR valve on the intake air amount so as to set the fully closed greater than a predetermined valve opening Composed.

  As the operating state of the internal combustion engine, the engine speed and the fuel injection amount of the engine are used. Instead of the fuel injection amount of the engine, an engine load, an accelerator opening degree, and the like can be used. As the operating state detection means for detecting these, there are an engine speed sensor, an accelerator opening sensor, and the like. In some cases, the engine load is calculated from the accelerator opening, and the fuel injection amount is calculated from the accelerator opening and the engine load. Since it is calculated, a part of the operation part of the EGR control device for calculating these is also included in the operating state detection means. In addition, since the intake air amount is usually detected by a mass air flow sensor, this mass air flow sensor is also included in the operating state detection means. However, when calculating from the engine speed and the engine load, the calculation of the EGR control device A part of the calculation unit is included in the operation state detection means.

  With this configuration of the present invention, when constant rapid acceleration is performed, the EGR valve can be forcibly opened and EGR can be performed for a short time. Is suppressed, and the NOx emission amount as a whole is reduced.

  In the EGR system, the EGR control device determines whether the internal combustion engine is in an acceleration operation state equal to or higher than a predetermined acceleration operation state, whether the engine rotation speed is Ne (rpm), the engine horsepower point rotation speed (engine Judgment is made based on whether or not the temporal change dNe / dt (rpm / s) of the engine rotational speed is larger than 0.4 × Nmax (rpm / s) when the rotational speed of the maximum output point is Nmax (rpm). The ratio of the point of rapid acceleration of the horsepower point rotation speed with respect to Nmax is substantially the same for large engines and medium / small engines, so 0.4 (1 / s) is a generalized value. Since it can be applied to other engines, the acceleration state can be determined with a relatively simple determination.

  In particular, the accuracy and responsiveness of the measurement system can be improved at once by using the rate of change in engine rotation speed. In addition, even if the rate of change in engine speed is small due to changes in road slope, if the engine fuel injection amount (load) increases, the response delay of the intake system is less than that due to sudden acceleration or sudden acceleration due to overtaking. Since there are few, normal EGR control is possible, but in such a case, when determining the acceleration state, rapid acceleration is not performed, and appropriate EGR control is performed.

  In the EGR system described above, it is preferable that the EGR control device sets the predetermined valve opening to 2% or less of full opening and 0.5% or more. Since the optimum value of the predetermined valve opening differs depending on the characteristics of the engine, it should be determined by a test for each engine. However, according to the experimental results, the predetermined valve opening is less than 2% of the full opening. If it is increased, the effect of suppressing the generation of NOx is great, but EGR is excessively applied, and the output is reduced and the amount of smoke generated increases. On the other hand, if it is smaller than 0.5%, the effect of opening the EGR valve to a predetermined degree of valve opening is small, and the effect of suppressing the generation of NOx is small.

  The installation of DPF (Diesel Particulate Filter) equipment has become essential to comply with exhaust gas regulations, and in engines with this DPF equipment, the EGR rate during acceleration can be reduced to within a few percent. Experiments and the like have shown that PM (particulate matter: particulate matter) discharged from the tube into the atmosphere can be suppressed to a problem-free range. It has also been found that it is possible to minimize the shortening of the regeneration interval of the DPF device by suppressing the frequency of EGR during acceleration.

  According to the EGR system control method and the EGR system of the present invention, a large amount of instantaneous NOx at the time of sudden acceleration is obtained by forcibly performing EGR at the time of sudden acceleration of the vehicle in which a response delay of the turbocharger occurs. Generation | occurrence | production can be suppressed and the whole discharge | emission amount of NOx can be reduced.

  Hereinafter, an EGR system control method and an EGR system according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, this EGR system 1 is an exhaust manifold 11 or an exhaust pipe 12 which is an exhaust passage of a supercharged engine (internal combustion engine) 10 as an EGR system of a supercharged internal combustion engine such as a diesel engine. And an EGR pipe (EGR passage) 15 connected to the intake manifold 13 or the intake pipe 14 serving as an intake passage, and an EGR cooler 16 and an EGR valve 17 provided in the EGR pipe 15. A part of the exhaust gas of the engine 10 is recirculated to the intake manifold 13 or the intake pipe 14 through the EGR pipe 15.

  The EGR cooler 16 cools the EGR gas, and the EGR valve 17 adjusts the amount of EGR gas to be recirculated to adjust the EGR rate. Further, a mass air flow sensor (MAF sensor) 18 is disposed in the intake pipe 14 in order to detect the intake air amount m. Further, a compressor 19 a of a turbocharger (turbocharger) 19 is disposed in the intake pipe 14 and a turbine 19 b is disposed in the exhaust pipe 12.

  Further, the EGR control device 20 is configured to be incorporated in a control device called an engine control unit (ECU) that controls the entire engine. This EGR control device 20 includes an engine speed Ne that indicates the operating state of the internal combustion engine, an engine fuel injection amount Q, and an intake air amount m, and an engine speed detected by the operating state detecting unit. Ne, an EGR rate ηe is calculated from the engine fuel injection amount Q, and a target intake air amount calculation means for calculating a target intake air amount m0 so that the calculated EGR rate ηe is obtained, and a valve opening degree of the EGR valve is controlled. And a valve opening degree control means.

  The operating state detection means includes an engine speed sensor (not shown), an accelerator opening sensor (not shown), etc. In some cases, the engine fuel injection amount Q is calculated from the accelerator opening and the engine load. Therefore, a part of the calculation unit of the EGR control device 20 that calculates these is also included in the operating state detection means. In addition, since the intake air amount m is normally detected by the mass air flow sensor 18, the mass air flow sensor 18 is also included in the operating state detection means. However, when the intake air amount m is calculated from the engine speed Ne and the engine load. Therefore, a part of the calculation unit of the EGR control device 20 to be calculated is included in the operation state detection means. Note that the engine speed Ne and the fuel injection amount Q of the engine are used as the operating state of the engine 10, but an engine load, an accelerator opening, and the like can be used instead of the fuel injection amount Q of the engine.

  The target intake air amount calculation means is constituted by a part of the calculation unit of the EGR control device 20, and has map data M1 for calculating the target EGR rate based on the engine speed and the engine fuel injection amount (parameter). With reference to the detected engine speed Ne and the engine fuel injection amount Q, the target EGR rate ηe is calculated, and the target EGR rate is calculated based on the engine speed and the engine fuel injection amount (parameter). The target intake air amount m0 is calculated from the detected engine speed Ne and the engine fuel injection amount Q with reference to the map data M1 for calculation.

  The valve opening control means includes an actuator (not shown) that operates the EGR valve 17 and a part of the EGR control device 20 that instructs the actuator to open the valve, and the valve calculated by the EGR control device 20 is used. An instruction is given to the actuator so that the opening degree α is reached, and the valve opening degree of the EGR valve 17 is controlled.

  Next, a method for controlling the EGR system 1 by the EGR control device 20 will be described. This control method is performed according to a control flow as shown in FIG.

  First, when the engine key is turned on and the operation of the engine 10 is started, this control flow is called and started. When started, in step S11, initialization (initialization) of data used in this control flow is performed.

  In the next step S12, an engine speed Ne and an engine fuel injection amount Q indicating the operating state of the engine are detected. In the next step S13, the acceleration state of the engine 10 is detected. This acceleration state is detected when the engine speed Ne is set to Ne (rpm) and the engine horsepower point rotational speed is set to Nmax (rpm). The time change dNe / dt (rpm / s) of the engine speed Ne is 0.4 ×. Judgment is made based on whether it is greater than Nmax (rpm / s). For example, when the engine horsepower point rotation speed Nmax is 2000 rpm as in a large engine, 0.4 × Nmax = 800, and dNe / dt> 800 (rpm / s) is in a rapid acceleration state with this as a threshold value. .

  In this step S13, if dNe / dt> 0.4 × Nmax, it is determined that there is a rapid acceleration state, and in step S14, the valve opening α of the EGR valve 17 is set to a predetermined valve opening a, and in step S15, EGR The valve 17 is opened at this valve opening α (= a). This state is maintained for a predetermined time (time related to the acceleration state check interval), and then the process returns to step S12. In step S13, if dNe / dt ≦ 0.4 × Nmax, it is determined that there is no rapid acceleration state, and the process goes to step S21.

  Due to these steps S13 to S15, only during the rapid acceleration period, the opening degree α of the EGR valve 17 is not adjusted (steps S21 to S29) by the detected intake air amount m, and the opening of the constant EGR valve 17 is not performed. Through the part, EGR is performed only by the difference between the exhaust pressure of the engine 10 and the intake pressure. That is, when it is determined that the internal combustion engine is in an acceleration operation state equal to or higher than the predetermined acceleration operation state, the EGR valve 17 is opened until the engine is released from the acceleration operation state higher than the predetermined acceleration operation state. The valve is opened at a degree α (= a).

  Since the optimum value of the predetermined valve opening a varies depending on the characteristics of the engine 10, it should be determined by a test for each engine 10. However, according to the experimental results, the predetermined valve opening a is determined as EGR. It is preferable to set the valve opening of the valve 17 to 2% or less and 0.5% or more of full opening.

  In step S21, the EGR rate ηe is calculated with reference to the map M1 from the engine speed Ne and the engine fuel injection amount Q detected in step S12. Further, in the next step S22, the valve opening degree α (= b) at which the calculated EGR rate ηe is obtained is calculated from the detected engine speed Ne and engine fuel injection amount Q with reference to the map M2. To do. In the next step S23, the target intake air amount m0 is calculated from the detected engine speed Ne and engine fuel injection amount Q with reference to the map M3.

  In the next step S24, the EGR valve 17 is opened to the valve opening α. This state is maintained for a predetermined time (a time related to the check interval of the intake air amount m in steps S26 and S28). In the next step S25, the intake air amount m is detected, and the intake air amount m is checked in steps S26 and S28.

  If the intake air amount m is larger than the intake air amount m0 in the check in step S26, the valve opening degree α is increased by a predetermined amount Δα in step S27, and the process returns to step S24. If the intake air amount m is less than or equal to the intake air amount m0 in the check in step S26, the check in step S28 is performed. If the intake air amount m is smaller than the intake air amount m0 in the check in step S28, the valve opening α is decreased by a predetermined amount Δα in step S29, and the process returns to step S24. If it is determined in step S28 that the intake air amount m is equal to the intake air amount m0, the process returns to step S12.

  From step S24 to step S29, the valve opening degree α is started from the initial value b, and the valve solution degree α is set so that the intake air amount m becomes equal to the intake air amount m0. open.

  Further, by repeating step S12 to step S29, EGR is performed by controlling the valve opening degree α of the EGR valve 17, but when the operation of the engine 10 is stopped by turning off the engine key or the like, From each step, the process proceeds to the interruption in step S30, and the control flow is terminated by returning to the advanced flow.

  According to the EGR system control method and the EGR system 17 described above, the steps S13 to S15 are provided, and at the time of rapid acceleration, the intake air amount m and the intake air until dNe / dt ≦ 0.4 × Nmax. Regardless of the relationship of the amount m0, that is, including the case where the intake air amount m <the intake air amount m0, EGR is performed by opening the EGR valve 17 by a certain amount (valve opening a) for emergency evacuation. Therefore, EGR gas recirculates, and instantaneous generation of large amounts of NOx during sudden acceleration can be avoided.

  Note that when a transition is made from a sudden acceleration state where dN / dT> 0.4 × Nmax to a slow acceleration state where dN / dT ≦ 0.4 × Nmax or a steady state, the target intake air amount m0 <intake air amount m is reached. Therefore, the control enters the normal intake air amount m (steps S21 to S29).

Therefore, when the turbocharged engine 10 suddenly accelerates when the response of the turbocharger 19 is greatly delayed and the EGR is not performed, a large amount of NOx that is instantaneously generated in the prior art is generated by forcibly performing the EGR. Can be suppressed, and the total NOx emission amount can be reduced.

It is a block diagram of the EGR system of embodiment which concerns on this invention. It is a figure which shows the control flow of the EGR purification system of embodiment which concerns on this invention. It is a figure which shows an example of the control flow of the 1st EGR control method of a prior art. It is a figure which shows an example of the control flow of the 2nd EGR control method of a prior art.

Explanation of symbols

1 EGR system 10 Diesel engine (internal combustion engine)
11 Exhaust manifold (exhaust passage)
12 Exhaust pipe (exhaust passage)
13 Intake manifold (intake passage)
14 Intake pipe (intake passage)
15 EGR pipe (EGR passage)
17 EGR valve 18 Mass airflow sensor 19 Turbocharger
20 EGR control device a Predetermined valve opening degree Ne Engine speed m Intake air amount m0 Target intake air amount Q Fuel injection amount (load)
ηe target EGR rate

Claims (4)

A target EGR rate is calculated, a target intake air amount is calculated based on the calculated EGR rate, and when the intake air amount from the supercharger of the internal combustion engine with a supercharger is smaller than the target intake air amount, In the control method of the EGR system that opens the EGR valve by decreasing the opening degree,
A control method for an EGR system, wherein when the internal combustion engine is in an acceleration operation state equal to or higher than a predetermined acceleration operation state , the valve is opened to a predetermined valve opening larger than a fully closed state regardless of an intake air amount . An EGR passage for recirculating a part of exhaust gas of an internal combustion engine with a supercharger to an intake passage of the internal combustion engine, an EGR valve for adjusting an amount of the exhaust gas to be recirculated, an EGR control device, and the EGR control A valve opening degree control means for opening the EGR valve in accordance with a valve opening degree of the EGR valve set by the apparatus, an operating state detecting means for detecting an operating state of the internal combustion engine, and a supercharger for the internal combustion engine The EGR control device calculates a target EGR rate from the operating state of the internal combustion engine, and the target intake air based on the calculated target EGR rate. When the amount of intake air is less than the target amount of air, the EGR system is configured to decrease and set the valve opening .
The EGR control device, when the internal combustion engine is in an acceleration driving state of more than predetermined acceleration operating condition, sets the valve opening of despite the EGR valve is fully closed is greater than a predetermined valve opening degree to the intake air amount An EGR system characterized by that.   The EGR control device determines whether the internal combustion engine is in an acceleration operation state equal to or higher than a predetermined acceleration operation state, when the engine rotation speed is Ne (rpm) and the engine horsepower point rotation speed is Nmax (rpm). 3. The EGR system according to claim 2, wherein it is determined whether or not a time change dNe / dt (rpm / s) of the engine rotation speed is larger than 0.4 × Nmax (rpm / s).   The EGR system according to claim 2 or 3, wherein the EGR control device sets the predetermined valve opening to 2% or less and 0.5% or more of full opening.

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