JP4771977B2 - Fuel control device for internal combustion engine - Google Patents

Description

  The present invention relates to an apparatus for controlling fuel supplied to an internal combustion engine in accordance with the performance of a cooling device provided in an exhaust gas recirculation passage.

Conventionally, in order to reduce NOx contained in exhaust gas, it has been proposed to provide an exhaust gas recirculation passage between the exhaust side and the intake side of the internal combustion engine to recirculate part of the exhaust to the intake side to lower the combustion temperature. Has been. An EGR cooler (cooling device) that cools the exhaust gas flowing through the exhaust passage is attached to the exhaust gas recirculation passage. Patent Document 1 below discloses a technique for detecting deterioration of an EGR cooler and increasing the amount of exhaust gas that is recirculated as the deterioration is detected.
JP 2000-130266 A

  Due to the internal structure of the EGR cooler, soot and SOF (soluble organic components) and the like adhere to the EGR cooler and the cooling performance deteriorates. As the EGR cooler deteriorates, the temperature of the exhaust gas recirculated to the intake side rises, so the temperature of the intake air in the combustion chamber rises. The “ignition delay” period from when the fuel is injected to when the fuel is ignited is shortened, resulting in premature ignition. As a result, combustion may start abruptly and combustion noise may be deteriorated.

  This invention is made | formed in order to solve such a subject, and it aims at reducing the deterioration of the combustion sound accompanying EGR cooler deterioration.

  In order to achieve the above object, the invention according to claim 1 is directed to a fuel injection device (1, 8) for directly injecting fuel into a cylinder of the internal combustion engine (2), and a part of exhaust gas from the internal combustion engine to intake air. An EGR cooler for detecting the performance of the EGR cooler in a control device for an internal combustion engine having an exhaust gas recirculation passage (31) that recirculates and an EGR cooler (36) that is provided in the exhaust gas recirculation passage and cools the recirculated exhaust gas. Performance detection means (1, 61, steps S2, S13) and correction means (1, 62, 63) for correcting at least one of the fuel injection pressure and the fuel injection timing according to the detected performance of the EGR cooler Steps S3, S4, S14, and S17).

  According to the present invention, since at least one of the fuel injection pressure and the fuel injection timing is corrected according to the detected performance of the EGR cooler, the sudden rise of the fuel due to the ignition being too early is prevented. Therefore, the deterioration of combustion noise can be reduced. More specifically, by correcting the fuel injection pressure, the atomized fuel can be atomized and a predetermined ignition delay period can be secured. Thereby, the deterioration of combustion noise can be reduced. Moreover, since the predetermined ignition delay period is ensured by delaying the fuel injection timing, it is possible to reduce the deterioration of the combustion noise.

  According to a second aspect of the present invention, in the control device for an internal combustion engine according to the first aspect, the EGR cooler performance detecting means determines the performance of the EGR cooler based on an intake air temperature when the internal combustion engine is in an idle operation state. Detect (1, 62, 63, steps S1, S2, S11, S13).

  The EGR cooler is provided on a passage connecting the exhaust pipe and the intake pipe. Therefore, the cooling performance of the EGR cooler can be determined by examining the temperature of the intake pipe on the downstream side of the EGR cooler. Further, since the intake air temperature in the idle operation state is used, the performance of the EGR cooler can be determined more accurately.

The invention according to claim 3 is the control apparatus for an internal combustion engine according to claim 1,
The correction means increases the fuel injection pressure or retards the fuel injection timing as the performance of the EGR cooler detected by the EGR cooler performance detection means deteriorates (steps S3, S4, S14, S17). .

  According to the present invention, as the performance of the EGR cooler deteriorates, the fuel injection pressure is increased or the fuel injection timing is retarded. Therefore, even if the deterioration degree changes, an appropriate ignition delay period is ensured. The deterioration of combustion noise can be reduced.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter referred to as an engine) and its control device according to an embodiment of the present invention.

  An electronic control unit (hereinafter referred to as “ECU”) 1 is a computer including a central processing unit (CPU) and a memory. The memory can store a computer program for realizing various controls of the vehicle and data necessary for executing the program. The ECU 1 receives data sent from each part of the vehicle, performs calculation, and generates a control signal for controlling each part of the vehicle.

  In this embodiment, the engine 2 is a diesel engine. The engine 2 has, for example, four cylinders, and only one of them is shown in the figure.

  An intake pipe 3 and an exhaust pipe 4 are connected to the engine 2. A combustion chamber 5 is formed between the piston 6 and the cylinder head 7, and a fuel injection valve 8 is attached so as to face the combustion chamber 5. The fuel injection valve 8 is connected to a high-pressure pump 9 and a fuel tank (not shown) via a common rail (not shown). The high pressure pump 9 boosts the fuel in the fuel tank and then sends it to the fuel injection valve 8 through the common rail. The fuel injection valve 8 injects the received fuel into the combustion chamber 5. The fuel injection pressure (referred to as fuel pressure) can be changed by controlling the high-pressure pump 9 with a control signal from the ECU 1. The fuel pressure is detected by a fuel pressure sensor provided on the common rail, and the detection signal is sent to the ECU 1. Further, the injection time and injection timing of the fuel injection valve 8 are controlled in accordance with a control signal from the ECU 1.

  The engine 2 is provided with a crank angle sensor 10. The crank angle sensor 10 outputs a CRK signal and a TDC signal to the ECU 1 as the crankshaft 11 rotates. The CRK signal is a pulse signal output at every predetermined crank angle. The ECU 1 calculates the rotational speed NE of the engine 2 according to the CRK signal. The TDC signal is a pulse signal output at a crank angle related to the top dead center (TDC) position of the piston 6 at the start of the intake stroke. When there are four cylinders, the TDC signal is output every 180 degrees of crank angle.

  A supercharger 12 is provided. The supercharger 12 includes a rotatable compressor 13 provided in the intake pipe 3, a rotatable turbine 14 provided in the exhaust pipe 4, and a shaft 15 connecting them. It has. The turbine 14 is rotationally driven by the kinetic energy of the exhaust gas, and the compressor 13 is rotationally driven by the rotational drive of the turbine 14 to compress the intake air.

  The turbine 14 has a plurality of rotatable variable vanes (only two are shown) 16, and an actuator 17 is connected to each variable vane 16. The actuator 17 changes the opening degree of the variable vane 16 (referred to as a vane opening degree) in accordance with a control signal from the ECU 1. By changing the vane opening degree, the rotational speed of the turbine 14 can be changed. As the vane opening is closed, the rotational speed of the turbine increases and the supercharging pressure increases.

  The intake pipe 3 is provided with an airflow sensor 20 upstream of the compressor 13, and a water-cooled intercooler 21 and a supercharging pressure sensor 22 are provided downstream of the compressor 13. The air flow sensor 20 detects the amount of intake air introduced into the intake pipe 3, the supercharging pressure sensor 22 detects the supercharging pressure in the intake pipe 3, and these detection signals are sent to the ECU 1. The intercooler 21 cools the intake air when the temperature of the intake air rises due to the supercharging operation of the supercharger 12.

  A throttle valve 23 is provided downstream of the supercharging pressure sensor 22. An actuator 24 is connected to the throttle valve 23, and the actuator 24 controls the opening degree of the throttle valve 23 according to a control signal from the ECU 1.

  Downstream of the throttle valve 23, an intake manifold is branched corresponding to each cylinder, and each of the branched intake manifolds communicates with the combustion chamber of each cylinder via an intake port. The intake manifold is partitioned into two passages 25 and 26, and a swirl valve 27 is provided in one passage 25. An actuator 28 is connected to the swirl valve 27. The actuator 28 can change the opening degree of the swirl valve 27 in accordance with a control signal from the ECU 1. The strength of the swirl generated in the combustion chamber 5 can be controlled by the opening of the swirl valve 27.

  Further, the engine 2 has an EGR connected between the intake pipe 3 and the exhaust pipe 4, specifically, between the passage 26 in the collection section of the intake manifold and the upstream side of the turbine 14 of the exhaust pipe 4. A tube 31 is provided. A part of the exhaust gas of the engine 2 is recirculated to the intake pipe 3 as EGR gas via the EGR pipe 31. By this recirculation, the combustion temperature in the combustion chamber 5 is lowered, and NOx in the exhaust gas can be reduced.

  The EGR pipe 31 is provided with an EGR control valve 32. In one example, the EGR control valve 32 is constituted by a linear electromagnetic valve, and the valve lift amount of the EGR control valve 32 can be changed linearly according to a control signal from the EGU 1. The amount of EGR gas recirculated (referred to as EGR amount) can be controlled by the valve lift amount of the EGR control valve 32.

  The EGR pipe 31 is provided with a switching valve 35 and an EGR cooler 36. The passage 37 is a bypass passage for bypassing the EGR cooler 36. The switching valve 35 selectively switches a portion downstream of the switching valve 35 between the EGR pipe 31 and the bypass passage 37 in accordance with a control signal from the EGU 1. When switched to the bypass passage 37, the EGR gas is passed through the bypass passage 37 and returned to the intake pipe 3. When switched to the EGR pipe 31 side, the EGR gas is cooled by the EGR cooler 36 and then returned to the intake pipe 3.

  In the passage 26 to which the EGR pipe 31 is connected, a temperature sensor 38 is provided downstream of the EGR pipe 31. The temperature sensor 38 detects the temperature in the intake pipe 3 (referred to as intake air temperature), and the detected value is sent to the ECU 1. This intake air temperature indicates the temperature of EGR gas flowing through the passage 26 to the engine 2.

  Since the temperature sensor 38 is intended to detect the temperature of the EGR gas that has passed through the EGR cooler 36, it may be provided at another position as long as it is downstream of the EGR cooler 36. For example, the temperature sensor 38 may be provided between the EGR cooler 36 and the portion where the EGR pipe 31 is connected to the passage 26.

  A three-way catalyst 41 and a NOx catalyst 42 are provided downstream of the turbine 14 in the exhaust pipe 4. The three-way catalyst 41 purifies the exhaust gas by oxidizing HC and CO in the exhaust gas and reducing NOx when the air-fuel ratio is the stoichiometric air-fuel ratio (stoichiometric). When the air-fuel ratio is lean and the oxygen concentration in the exhaust gas is relatively high, the NOx catalyst 42 captures NOx in the exhaust gas and has a rich air-fuel ratio, and the reducing agent (HC, CO) in the exhaust gas. When the concentration of is relatively high, exhaust gas is purified by reducing the trapped NOx.

  Further, a LAF sensor 43 is provided upstream of the three-way catalyst 41. The LAF sensor 43 linearly detects the oxygen concentration in the exhaust gas in the air-fuel ratio region from the rich region to the lean region. The ECU 1 calculates an actual air-fuel ratio that represents the air-fuel ratio of the actual air-fuel mixture burned in the combustion chamber 5 based on the oxygen concentration detected by the LAF sensor 43.

  In one embodiment, an in-cylinder pressure sensor 45 may be provided. The in-cylinder pressure sensor 45 is a sensor made of a piezoelectric element, for example, and is attached so as to face the combustion chamber 5. The in-cylinder pressure sensor 45 detects a change in the pressure in the combustion chamber 5 (in-cylinder pressure), and the detected value is sent to the ECU 1.

  The ECU 1 is further connected to an access pedal opening sensor 46 that outputs a detection signal representing an operation amount (referred to as accelerator opening) of an accelerator pedal (not shown).

  In accordance with these input signals, the ECU 1 detects the operating state of the engine 2 according to the program and data (including a map) stored in the memory, and at the same time, the fuel injection amount, the fuel injection timing, the EGR amount, and the intake air amount Control supercharging pressure.

  Referring now to FIG. 2, an example of simulation results in a certain operating state of the engine is shown. The fuel is injected near the compression top dead center (TDC in the figure). (A) shows the temporal transition of the rate of heat release (ROHR) between when the EGR cooler is normal and when it is deteriorated. The former is indicated by reference numeral 51 and the latter is indicated by reference numeral 52. Here, the deterioration of the performance of the EGR cooler indicates the deterioration of the performance of cooling the refluxed EGR gas. The heat release rate ROHR indicates how active combustion of the fuel / air mixture in the combustion chamber is.

  When the EGR cooler deteriorates, the temperature of the recirculated EGR gas rises and the temperature in the cylinder rises. Therefore, the rise of the heat generation rate due to combustion when the EGR cooler is deteriorated (52) is steeper and has a larger peak value than the rise of the heat generation rate when the EGR cooler is normal (51). This indicates that when the EGR cooler is deteriorated, the combustion becomes rapidly active and the combustion noise may be deteriorated. Therefore, an object of the present invention is to reduce such deterioration of combustion noise.

  FIG. 2B shows the in-cylinder pressure increase rate dP / dθ when the EGR cooler is normal and deteriorated under the heat generation rate state as shown in FIG. Has been. The cylinder pressure increase rate dP / dθ is an index of combustion noise, as is well known. The former is indicated by reference numeral 53 and the latter is indicated by reference numeral 54. The rise of the in-cylinder pressure increase rate when the EGR cooler is deteriorated (54) is steeper and the peak value is larger than the rise of the in-cylinder pressure increase rate when the EGR cooler is normal (53). This indicates that the combustion noise may deteriorate if the EGR cooler deteriorates. Thus, the combustion noise can be evaluated using the peak value of the cylinder pressure increase rate dP / dθ.

  FIG. 3 is a functional block of the control device according to an embodiment of the present invention. These functional blocks are realized in the ECU 1.

The performance detection unit 61 detects the performance of the EGR cooler 36. More specifically, as shown in the following equation, the deviation (intake air temperature deviation) ΔT_EGR between the actual intake air temperature TA detected by the temperature sensor 38 when the engine 2 is in the idling operation state and the initial intake air temperature TA_INI. Is calculated.
ΔT_EGR = TA-TA_INI

  The initial intake air temperature is a predetermined reference value, and is set to represent the temperature detected by the temperature sensor 38 when the EGR cooler 36 is normal (for example, when the vehicle is shipped). As described above, since the temperature sensor 38 is provided on the downstream side of the EGR cooler 36, the temperature of the EGR gas that has passed through the EGR cooler 36 increases as the performance of the EGR cooler 36 deteriorates. The temperature detected by 38 increases. In other words, the intake air temperature deviation ΔT_EGR calculated here represents the degree of deterioration of the cooling performance of the EGR cooler, and the greater the intake air temperature deviation ΔT_EGR, the greater the degree of deterioration.

  The fuel pressure correction unit 62 corrects the fuel pressure according to the intake air temperature deviation ΔT_EGR, and calculates the final fuel pressure. More specifically, the fuel pressure is corrected to increase as the intake air temperature deviation ΔT_EGR increases. As a result, the fuel pressure increases as the degree of deterioration of the EGR cooler increases, so that a predetermined ignition delay period can be secured and deterioration of combustion noise can be reduced.

  The injection timing correction unit 63 corrects the injection timing according to the intake air temperature deviation ΔT_EGR, and calculates the final injection timing. More specifically, the injection timing is corrected in the retard direction as the intake air temperature deviation ΔT_EGR is larger. Thereby, since the injection timing is retarded as the degree of deterioration of the EGR cooler increases, a predetermined ignition delay period is ensured, and deterioration of combustion noise can be reduced.

  Thus, the fuel injection valve 8 performs fuel injection according to the final fuel pressure and the final injection timing.

  In this embodiment, both the fuel pressure and the injection timing are corrected. By correcting both, the deterioration of combustion noise can be more reliably reduced. However, only one of them may be corrected. In this case, only one of the fuel pressure correction unit 62 and the injection timing correction unit 63 is provided, and fuel is injected according to the obtained final fuel pressure or final injection timing.

  Alternatively, it may be determined whether the intake air temperature deviation ΔT_EGR is greater than or equal to a predetermined value. When the intake air temperature deviation ΔT_EGR is equal to or greater than a predetermined value, the fuel pressure and / or the injection timing are corrected. In this way, correction may be executed when the performance of the EGR cooler 36 deteriorates to some extent. Further, the number of times that the intake air temperature deviation ΔT_EGR becomes equal to or greater than a predetermined value may be counted, and the correction may be executed in response to the count value exceeding the predetermined value. Furthermore, any correction may be selected according to the operating state of the engine 2.

  With reference to FIG. 4, the process performed by the control apparatus shown in FIG. 3 will be described more specifically. The process is executed in synchronization with the input of the TDC signal.

  In step S1, it is determined whether the engine 2 is in an idle operation state. This is because the performance of the EGR cooler can be detected more accurately when the engine output is low because the variation in the intake air temperature used for detecting the performance of the EGR cooler is smaller. If it is not idle, the process is exited.

  If it is determined that the engine is in the idle operation state, the intake air temperature deviation ΔT_EGR is calculated by the performance detection unit 61 in step S2.

  Step S <b> 3 is executed by the fuel pressure correction unit 62. Based on the intake air temperature deviation ΔT_EGR, a map as shown in FIG. 5A is referred to, and a correction value ΔPrail for correcting the fuel pressure is obtained. The map is defined so that the fuel pressure increases as the intake air temperature deviation ΔT_EGR increases. The map can be stored in the memory of the ECU 1.

  Further, in step S3, the basic fuel pressure Prail is obtained by referring to a predetermined map (not shown) based on the operating state of the engine, more specifically, the engine speed NE and the accelerator pedal opening AP. The final fuel pressure FPrail is calculated by adding the obtained fuel pressure correction value ΔPrail to the basic fuel pressure Prail.

  Step S <b> 4 is executed by the injection timing correction unit 63. Based on the intake air temperature deviation ΔT_EGR, a map as shown in FIG. 5B is referred to, and a correction value ΔΦinj for correcting the injection timing is obtained. The map is defined such that the injection timing is corrected in the retard direction as the intake air temperature deviation ΔT_EGR is larger. The map can be stored in the memory of the ECU 1.

  Furthermore, in step S4, the basic injection timing Φinj is obtained by referring to a predetermined map based on the engine operating state, more specifically, the engine speed NE and the accelerator pedal opening AP. The final injection timing FΦinj is calculated by adding the obtained injection timing correction value ΔΦinj to the basic injection timing Φinj.

  Steps S3 and S4 may be executed in parallel or in reverse order. Thus, the fuel injection valve 8 is driven according to the final fuel pressure FPrail and the final injection timing FΦinj.

  FIG. 6 is a block diagram of a control device according to another embodiment of the present invention. These functional blocks are realized in the ECU 1. The same reference numerals are assigned to the same blocks as in FIG. The main difference from FIG. 3 is that a noise evaluation unit 71 is provided.

  In this embodiment, in the first combustion cycle, the fuel pressure correction unit 62 performs fuel pressure correction based on the intake air temperature deviation ΔT_EGR calculated by the performance detection unit 61, and performs fuel injection at the obtained final fuel pressure. Execute. Thereafter, the noise evaluation unit 71 determines whether or not the combustion noise has been improved by the fuel injection. Specifically, the deviation (in-cylinder pressure increase rate deviation) between the actual value and the initial value is calculated for the peak value of the in-cylinder pressure increase rate dP / dθ. The initial value is a predetermined reference value, and the peak value of the in-cylinder pressure increase rate calculated based on the detected value of the in-cylinder pressure sensor 45 when the EGR cooler 36 is normal (for example, when the vehicle is shipped). Set as shown.

  The actual value of the peak value of the in-cylinder pressure increase rate is calculated based on the detected value of the in-cylinder pressure sensor 45 during the first combustion cycle. For example, during the first combustion cycle, the actual value of the in-cylinder pressure increase rate is calculated from the detected value of the in-cylinder pressure sensor 45 at predetermined time intervals, and the peak value is detected from the calculated actual value. The deviation between the peak value and the initial value can be calculated as the in-cylinder pressure increase rate deviation.

  Since the in-cylinder pressure increase rate is an index representing combustion noise as described above, if the in-cylinder pressure increase rate deviation is not more than a predetermined value, it can be determined that the combustion noise has been improved by correcting the fuel pressure.

  If it is not determined that the combustion noise has been improved, in the second combustion cycle, the injection timing correction unit 63 performs the injection timing correction based on the intake air temperature deviation ΔT_EGR, and performs fuel injection at the obtained final injection timing. Execute.

  According to this embodiment, the correction of the injection timing can be suppressed if the combustion noise reaches a predetermined allowable level by first correcting the fuel pressure. Thereby, it is possible to avoid a reduction in fuel consumption that may occur due to correction of the injection timing.

  Alternatively, injection timing correction may be performed in the first combustion cycle, and as a result, if no improvement in combustion noise is observed, fuel pressure correction may be performed in the second combustion cycle. Further, the index representing the combustion noise used in the noise evaluation unit 71 may be an index different from the in-cylinder pressure increase rate dP / dθ.

  With reference to FIG. 7, the process executed by the control device shown in FIG. 6 will be described more specifically. The process is executed in synchronization with the input of the TDC signal.

  Step S11 is the same as step S1 shown in FIG. In step S12, it is determined whether or not the fuel pressure has already been corrected. When this step is executed for the first time, since this determination is No, the process proceeds to step S13, where the performance detecting unit 61 detects the performance of the EGR cooler, and in step S14, the fuel pressure correcting unit 62 corrects the fuel pressure. The final fuel pressure is calculated. These steps are the same as steps S2 and S3 in FIG. Fuel injection is performed according to the final fuel pressure, and this process is temporarily exited.

  Next, when this process is executed, since the previous fuel pressure is corrected in step S14, the determination in step S12 is Yes. In step S15, the noise evaluation unit 71 calculates an in-cylinder pressure increase rate deviation by subtracting an initial value from the actual value for the peak value of the in-cylinder pressure increase rate dP / dθ.

  In step S16, it is determined whether the in-cylinder pressure increase rate deviation is larger than a predetermined value. If this determination is No, it is determined that the combustion noise has been sufficiently improved by correcting the fuel pressure, and the process is exited. If this determination is Yes, it is determined that improvement of combustion noise is not sufficient only by correcting the fuel pressure. In step S17, the injection timing correction unit 63 corrects the injection timing based on the intake air temperature deviation ΔT_EGR calculated in step S13, and calculates the final injection timing. This step is the same as step S4 in FIG. In this way, fuel injection according to the final injection timing is performed.

  Alternatively, a step similar to step S13 may be provided between steps S16 and S17 to calculate the intake air temperature deviation ΔT_EGR again, and the injection timing correction may be performed using the calculated intake air temperature deviation.

  Although the said embodiment demonstrated the diesel engine as an example, this invention is applicable also to a gasoline engine etc. The present invention is applicable to general-purpose internal combustion engines (for example, outboard motors).

The figure which shows schematically the engine and its control apparatus according to one Example of this invention. The figure which shows the behavior of the heat release rate and the cylinder pressure increase rate when the EGR cooler is normal and when it is deteriorated. 1 is a block diagram of an apparatus for controlling fuel injection according to the performance of an EGR cooler according to one embodiment of the present invention. FIG. 5 is a process flow for controlling fuel injection according to the performance of an EGR cooler, in accordance with one embodiment of the present invention. FIG. The figure which shows the correction map of the fuel pressure and injection timing based on the deterioration degree of an EGR cooler according to one Example of this invention. FIG. 3 is a block diagram of an apparatus for controlling fuel injection according to the performance of an EGR cooler according to another embodiment of the present invention. FIG. 5 is a process flow for controlling fuel injection according to the performance of an EGR cooler, in accordance with another embodiment of the present invention. FIG.

Explanation of symbols

1 ECU
2 Engine 36 EGR cooler 38 Temperature sensor 45 In-cylinder pressure sensor

Claims (2)

A fuel injection device that directly injects fuel into a cylinder of an internal combustion engine, an exhaust gas recirculation passage that recirculates part of the exhaust gas of the internal combustion engine to intake air, and an EGR cooler that is provided in the exhaust gas recirculation passage and cools the recirculated exhaust gas In a control device for an internal combustion engine having
EGR cooler performance detecting means for detecting the cooling performance of the EGR cooler;
Correction means for performing at least one of the pressure increase of the fuel injection or the delay of the fuel injection timing as the cooling performance detected by the EGR cooler performance detecting means deteriorates ;
An internal combustion engine control device comprising: The EGR cooler performance detecting means detects the performance of the EGR cooler based on an intake air temperature when the internal combustion engine is in an idle operation state.
The control apparatus for an internal combustion engine according to claim 1.

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