JP6575480B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine. More specifically, the present invention relates to an exhaust gas recirculation device for an internal combustion engine that performs an exhaust gas recirculation (EGR) operation for recirculating a part of gas exhausted from the internal combustion engine to an intake system. About.

  Conventionally, for example, Patent Document 1 discloses an EGR device with an EGR cooler. This apparatus includes a flow rate adjustment valve that adjusts the mixing ratio of the EGR gas that passes through the EGR cooler and the EGR gas that does not pass through. In this apparatus, the temperature of the EGR gas after the EGR gas that has passed through the EGR cooler and the EGR gas that has not passed through is mixed is detected, and the flow rate ratio is adjusted by feedback control so that this temperature becomes the target EGR temperature. The valve opening degree of the valve is adjusted.

JP 2001-041110 A JP 2008-175101 A JP 2009-121358 A JP 2010-121554 A

  In the above conventional technique, the EGR gas temperature can be brought close to the target temperature. However, even if the EGR gas temperature is brought close to the target temperature, it is difficult to control the intake air temperature after the merging of fresh air and EGR gas to the target intake air temperature. This is because the degree of change in the intake air temperature is related not only to the temperature of the EGR gas but also to the recirculation amount of the EGR gas, that is, the EGR rate. Therefore, it is conceivable to control the mixture ratio by feedback control so that the intake air temperature approaches the target intake air temperature. However, such feedback control has a problem in setting the control gain. That is, the higher the EGR rate, the greater the influence of the EGR gas temperature on the intake air temperature. For this reason, if an optimal control gain is set when the EGR rate is high in the feedback control, the change in the intake air temperature when the EGR rate is low becomes slow. On the other hand, if an optimal control gain is set when the EGR rate is low in feedback control, the intake air temperature may change excessively when the EGR rate is high. As described above, when the control gain is set to a constant value in the feedback control, there is a possibility that the control followability varies depending on the level of the EGR rate, and the intake air temperature cannot be controlled with high accuracy.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an exhaust gas recirculation device for an internal combustion engine that can control the intake air temperature during recirculation of EGR gas with high accuracy.

  The present invention relates to an EGR passage that connects an exhaust passage and an intake passage of an internal combustion engine, an EGR cooler disposed in the EGR passage, a bypass passage that bypasses the EGR cooler from the EGR passage, an amount of gas that flows to the EGR cooler, and a bypass A flow rate adjustment valve that adjusts the flow rate ratio of the amount of gas flowing to the passage, and an EGR rate that is a ratio of the EGR gas that is recirculated into the cylinder of the internal combustion engine via the EGR passage to the entire intake air in the cylinder An exhaust gas recirculation device including an EGR rate adjusting valve and a control device that controls the EGR rate adjusting valve and the flow rate ratio adjusting valve is intended. The control device is configured to determine the operation amount of the EGR rate adjusting valve based on the operating state of the internal combustion engine. Further, the control device is configured to determine the flow rate ratio by feedback control so that the temperature of the intake air drawn into the cylinder approaches the target temperature. Further, the control device is configured such that the control gain of feedback control becomes a smaller value as the EGR rate is higher.

  The EGR path that passes through the EGR cooler has higher cooling efficiency than the EGR path that bypasses the EGR cooler. According to the present invention, the flow rate ratio is determined by feedback control so that the temperature of the intake air drawn into the cylinder approaches the target temperature. Further, the higher the EGR rate, the greater the influence of the reflux gas temperature on the mixed gas temperature. According to the present invention, the higher the EGR rate, the smaller the feedback control gain. Thereby, the followability of the actual intake air temperature to the target temperature can be made closer to a constant regardless of the EGR rate. By such control, it becomes possible to control the intake air temperature at the time of exhaust gas recirculation by EGR with high accuracy.

1 is a diagram showing a configuration of an engine system to which an exhaust gas recirculation apparatus according to an embodiment of the present invention is applied. It is the figure which compared the change of the intake temperature with respect to the flow rate ratio R for every EGR rate. It is an example of the figure which shows the weighting coefficient of the control gain with respect to an EGR rate. 3 is a flowchart of a routine that is executed when the system of the first embodiment performs intake air temperature control. It is a figure which shows the modification of a structure of the engine system with which the exhaust gas recirculation apparatus of embodiment of this invention is applied.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings.

[System Configuration of Embodiment 1]
FIG. 1 is a diagram showing a configuration of an engine system to which an exhaust gas recirculation apparatus according to an embodiment of the present invention is applied. As shown in FIG. 1, the system of the present embodiment includes an internal combustion engine 10. The internal combustion engine 10 is configured as an in-line three-cylinder diesel engine mounted on a moving body such as a vehicle. However, the type, the number of cylinders, and the cylinder arrangement of the internal combustion engine 10 are not limited to this. An intake passage 12 and an exhaust passage 14 communicate with each cylinder of the internal combustion engine 10.

  In the intake passage 12, a compressor 16a of the supercharger 16 is installed. The compressor 16a is driven by the rotation of the turbine 16b disposed in the exhaust passage 14. A water-cooled intercooler 18 is disposed in the intake passage 12 on the downstream side of the compressor 16a. The intake passage 12 downstream of the intercooler 18 is connected to an intake manifold (not shown) of the internal combustion engine 10.

  In addition, the system of the present embodiment includes an EGR passage 20 that connects an exhaust manifold (not shown) to which the exhaust passage 14 is connected and the intake passage 12 on the downstream side of the intercooler 18. An EGR valve 22 is provided in the EGR passage 20. The EGR valve 22 adjusts the EGR rate, which is the ratio of the EGR gas recirculated into the cylinder of the internal combustion engine 10 via the EGR passage 20 to the entire intake air in the cylinder. An EGR cooler 24 is provided on the exhaust side of the EGR valve 22 in the EGR passage 20. The EGR passage 20 is provided with a bypass passage 26 that bypasses the EGR cooler 24. In order to adjust the flow rate ratio between the exhaust gas flowing through the EGR cooler 24 (EGR gas) and the exhaust gas flowing through the bypass passage 26 (EGR gas) at the location where the bypass passage 26 branched from the EGR passage 20 joins the EGR passage 20 again. The flow ratio adjusting valve 28 is provided.

  The system according to the present embodiment includes an ECU (Electronic Control Unit) 30. The ECU 30 is a control device that comprehensively controls the entire engine system, and the control device according to the present invention is embodied as one function of the ECU 30. The ECU 30 includes at least an input / output interface, a memory, and a CPU. The input / output interface is provided to take in sensor signals from the internal combustion engine 10 and various sensors attached to the moving body and to output an operation signal to an actuator provided in the internal combustion engine 10. The sensor that the ECU 30 captures a signal is a temperature sensor 32 that detects the temperature of the intake air flowing downstream of the connection portion of the intake passage 12 with the EGR passage 20, that is, the temperature of the intake air taken into the cylinder of the internal combustion engine 10. Is included. The actuator from which the ECU 30 outputs an operation signal includes the EGR valve 22 and the flow rate adjustment valve 28 described above. The memory stores various control programs, maps, and the like for controlling the internal combustion engine 10. The CPU reads out and executes a control program or the like from the memory, and generates an operation signal based on the acquired sensor signal. There are many actuators and sensors connected to the ECU 30 other than those shown in the figure, but the description thereof will be omitted in this specification.

[Operation of Embodiment 1]
The engine control executed by the ECU 30 includes EGR control. In the EGR control of the present embodiment, feedback control or the like is performed so that the EGR rate or a state quantity such as an EGR gas amount correlated therewith becomes a target value determined from an operation state such as an engine speed and an injection quantity. The operation amount of the EGR valve 22 is determined.

  The engine control executed by the ECU 30 includes intake air temperature control. In the intake air temperature control of the present embodiment, when the EGR gas is recirculated into the cylinder, the temperature of the intake air drawn into the cylinder is adjusted by adjusting the temperature of the EGR gas introduced into the intake passage 12. Control is performed so as to approach the target intake air temperature determined from the operating state such as the engine speed and the injection amount.

  Note that the EGR path passing through the EGR cooler 24 has higher cooling efficiency than the EGR path passing through the bypass passage 26. Therefore, the flow rate adjustment valve 28 is used for adjusting the intake air temperature. In the following description, the total amount of EGR gas recirculated into the cylinder is expressed as Gegr, the flow rate of EGR gas passing through the EGR cooler 24 is expressed as GegrC, and the flow rate of EGR gas passing through the bypass passage 26 is expressed as GegrCbp. In the intake air temperature control of the present embodiment, the ratio of the flow rate GegrC of the EGR gas passing through the EGR cooler 24 to the total EGR gas amount Gegr is defined as a flow rate ratio R, which is required for the actual intake air temperature to approach the target intake air temperature. The flow rate ratio R to be calculated is calculated. Then, the intake air temperature is controlled to the target intake air temperature by determining the operation amount (opening degree) of the flow rate adjustment valve 28 so as to realize the calculated flow rate ratio R. Hereinafter, the intake air temperature control of the present embodiment will be described in more detail.

In the intake air temperature control of the present embodiment, first, the target intake air temperature is set using state quantities such as the engine speed, the fresh air amount Ga sucked into the cylinder, and the exhaust temperature of the gas exhausted into the exhaust passage 14. The EGR gas flow rates GegrC and GegrCbp required for the realization are calculated. Then, the base flow rate ratio R is calculated using the following equation (1) using the calculated EGR gas flow rates GegrC and GegrCbp.
Flow ratio R = GegrC / (GegrC + GegrCbp) = GegrC / Gegr (1)

Further, in the intake air temperature control of the present embodiment, the flow rate GegrC of EGR gas is corrected by feedback control so that the actual intake air temperature drawn into the cylinder approaches the target intake air temperature. Specifically, first, the correction amount Qfb of the EGR gas flow rate GegrC is calculated by the following equation. In the following equations, the base proportional gain, the base integral gain, and the base differential gain indicate the control gains of the feedback control proportional term, integral term, and differential term, respectively. Dtn is a deviation between the actual value of the intake air temperature detected by the temperature sensor 32 and the target intake air temperature. The calculated correction amount Qfb is added to the EGR gas flow rate GegrC. Thereby, the EGR gas flow rate GegrC is corrected.
Qfb = QfbPn + QfbIn + QfbDn (2)
Proportional term: QfbPn = Base proportional gain x dTn (3)
Integral term: QfbIn = QfbIn-1 + base integral gain x dTn (4)
Differential term: QfbDn = Base differential gain x (dTn-dTn-1) (5)

  Here, the feedback control performed in the intake air temperature control has the following problems. FIG. 2 is a diagram comparing changes in the intake air temperature with respect to the flow rate ratio R for each EGR rate. As shown in this figure, the degree of change in the intake air temperature with respect to the flow rate ratio R increases as the EGR rate increases. This is because the higher the EGR rate, the higher the proportion of the EGR gas amount in the intake air, and the higher the EGR rate, the higher the influence of the temperature change of the EGR gas on the intake air temperature. Therefore, in feedback control using the flow rate ratio R as the manipulated variable, if the difference between the target intake air temperature and the actual intake air temperature is reflected in the flow rate ratio R using a constant control gain, the actual EGR rate is Depending on the height, there is a difference in the convergence and followability of the intake air temperature to the target intake air temperature. Specifically, for example, if an optimal control gain is set when the EGR rate is low, the operation amount becomes excessive when the EGR rate is high, and excessive hunting may occur in the intake air temperature. Further, if an optimal control gain is set when the EGR rate is high, the operation amount becomes slow when the EGR rate is low, and the convergence of the intake air temperature may be deteriorated.

  Therefore, in the intake air temperature control of the present embodiment, the control gain in feedback control is weighted according to the EGR rate. FIG. 3 is an example of a diagram illustrating a weighting coefficient of the control gain with respect to the EGR rate. The weighting coefficient is a coefficient by which the control gain is multiplied, and as shown in this figure, the weighting coefficient is set to a smaller value as the EGR rate is higher. According to such control, since the control gain of feedback control is set to a smaller value as the EGR rate is higher, it is possible to reduce variations in convergence and followability of feedback control due to the difference in EGR rate. . Thereby, it is possible to ensure the convergence and followability of the feedback control in a wide range of EGR rates.

[Specific Processing in First Embodiment]
Next, specific processing of intake air temperature control executed in the first embodiment will be described with reference to a flowchart. FIG. 4 is a flowchart of a routine that is executed when the system of the first embodiment performs intake air temperature control. Note that the routine shown in FIG. 4 is repeatedly executed by the ECU 30 at a predetermined control cycle.

In the routine shown in FIG. 4, first, the total EGR gas amount Gegr is acquired (step S2). Here, specifically, state quantities such as the engine speed, the fresh air amount Ga, the supercharging pressure, and the gas temperature of the intake manifold are acquired. The total EGR gas amount Gegr is estimated by a known method using these state quantities. Next, the flow rate ratio R is calculated (step S4). Here, specifically, the EGR gas flow rate GegrC required for realizing the target intake air temperature is calculated using the map as the argument of the state quantity acquired in step S2. Then, by substituting the total EGR gas amount Gegr acquired in step S2 and the EGR gas flow rate GegrC calculated in this step into the above equation (1), the flow rate ratio R is calculated. In parallel with the process of step S4, the current EGR rate is estimated (step S6). Specifically, the current EGR rate is estimated by the following equation (6) using the current fresh air amount Ga and the total EGR gas amount Gegr.
EGR rate (%) = Gegr / (Ga + Gegr) × 100 (6)

  Next, the opening degree of the flow ratio adjusting valve 28 is calculated (step S8). Here, specifically, the opening degree of the flow rate adjusting valve 28 for realizing the flow rate ratio R calculated in step S4 is calculated from the map.

  Next, the actual value of the current intake air temperature is detected using the temperature sensor 32 (step S10). Next, a deviation dTn between the actual value of the intake air temperature detected in step S10 and the target intake air temperature is calculated (step S12). Next, a control gain used for feedback control of intake air temperature control is calculated (step S14). Specifically, the weighting coefficient corresponding to the EGR rate estimated in step S6 is calculated using the map shown in FIG. And the control gain used by each feedback term is calculated by multiplying each base control gain of a proportional term, an integral term, and a differential term by the calculated weighting coefficient.

  Next, the opening degree of the flow rate adjustment valve 28 is corrected by feedback control (step S16). Here, specifically, the EGR gas flow rate GegrC is corrected using the deviation dTn calculated in step S10. Next, the flow rate ratio R is calculated using the corrected EGR gas flow rate GegrC. Then, the opening degree of the flow ratio adjusting valve 28 for realizing the calculated flow ratio R is calculated from the map.

  Thus, according to the system of the first embodiment described above, the control gain in feedback control is weighted according to the EGR rate. This makes it possible to ensure stable feedback control convergence and followability over a wide range of EGR rates.

  By the way, in the system of Embodiment 1 mentioned above, although the system provided with the EGR valve 22 and the flow ratio adjustment valve 28 was demonstrated, the structure of these valves is not restricted to the thing of FIG. FIG. 5 is a diagram showing a modification of the configuration of the engine system to which the exhaust gas recirculation apparatus according to the embodiment of the present invention is applied. The system configuration shown in FIG. 5 has the same configuration as the system shown in FIG. 1 except that control valves 40 and 44 are provided instead of the EGR valve 22 and the flow rate ratio adjustment valve 28. In the EGR passage 20, the control valve 40 is disposed at a position on the intake side of the connection portion with the bypass passage 26 and on the exhaust side of the EGR cooler 24. The control valve 40 can adjust the EGR gas flow rate GegrC passing through the EGR cooler 24. Further, the control valve 42 is disposed in the middle of the bypass passage 26 and can adjust the EGR gas flow rate GegrCbp passing through the bypass passage 26. In the system shown in FIG. 5 configured as described above, the control valves 40 and 42 are operated so that the total EGR gas amount by EGR control and the corrected EGR gas flow rate GegrC by feedback control are realized. Control similar to the system shown in FIG.

  In the system of the first embodiment described above, the EGR gas flow rate GegrC passing through the EGR cooler 24 is corrected by feedback control. However, the correction target by the feedback control is not limited to this, and a configuration may be adopted in which the flow rate ratio R and the EGR gas flow rate GegrCbp passing through the bypass passage 26 are corrected. Further, the configuration of the feedback control is not limited to the configuration of the control described above, and any configuration using any of the proportional term, the integral term, and the derivative term may be used.

  Further, in the system of the first embodiment described above, the temperature sensor 32 is used to acquire the intake air temperature, but a configuration in which a known method is employed to estimate from the operating state may be used. Further, the method of estimating the EGR rate and acquiring the total EGR gas amount is not limited to the above-described method, and may be configured to detect directly using a sensor or the like, or may be configured to estimate using another sensor.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Intake passage 14 Exhaust passage 16 Supercharger 16a Compressor 16b Turbine 18 Intercooler 20 EGR passage 22 EGR valve 24 EGR cooler 26 Bypass passage 28 Flow rate adjustment valve 30 ECU (Electronic Control Unit)
32 Temperature sensor 40 Control valve 42 Control valve

Claims (1)

An EGR passage connecting an exhaust passage and an intake passage of the internal combustion engine;
An EGR cooler disposed in the EGR passage;
A bypass passage for bypassing the EGR cooler from the EGR passage;
A flow ratio adjusting valve that adjusts a flow ratio of the amount of gas flowing to the EGR cooler and the amount of gas flowing to the bypass passage;
An EGR rate adjusting valve that adjusts an EGR rate, which is a ratio of EGR gas recirculated into the cylinder of the internal combustion engine through the EGR passage to the entire intake air in the cylinder;
A controller for controlling the EGR rate adjusting valve and the flow rate adjusting valve;
The control device includes:
Based on the operating state of the internal combustion engine, an operation amount of the EGR rate adjusting valve is determined,
The flow rate ratio is determined by feedback control so that the temperature of the intake air sucked into the cylinder approaches the target temperature,
The exhaust gas recirculation device for an internal combustion engine, wherein the control device is configured such that the control gain of the feedback control becomes a smaller value as the EGR rate is higher.

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