JP4680638B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine.

In an air-fuel ratio control apparatus for an internal combustion engine that controls the air-fuel ratio of the internal combustion engine to a target air-fuel ratio by adjusting the fuel injection amount of the injector, conventionally, a technique has been proposed in which the pressure of fuel acting on the injector is variable. For example, in the technique described in Patent Document 1, the pressure of fuel is controlled by controlling the operation of an electric motor that drives a fuel pump based on the output of an air-fuel ratio sensor arranged in an exhaust system of an internal combustion engine. The fuel injection amount is adjusted by increasing / decreasing.
JP-A-11-125161 (paragraphs 0013 to 0016, FIG. 2, etc.)

  In addition, a technique has been proposed in which the energy loss is reduced by reducing the output of the fuel pressure adjusting means for adjusting the fuel pressure, such as a fuel pump, by reducing the fuel pressure at a low load with a small fuel injection amount. ing.

  By the way, when the pressure of the fuel is reduced, the fuel is vaporized by the boiling under reduced pressure at the time of fuel injection, and bubbles may be generated in the vicinity of the flow rate measuring portion of the injector. If bubbles are generated in the vicinity of the flow metering portion of the injector, the fuel injection amount is reduced, causing a problem that the air-fuel ratio becomes leaner than the target air-fuel ratio.

  The fuel vaporization can be suppressed by detecting the lean air-fuel ratio accompanying the vapor generation and increasing the fuel pressure. In order to detect the lean air-fuel ratio accompanying the generation of vapor, it is conceivable to use a feedback correction coefficient calculated by air-fuel ratio feedback control. Specifically, the feedback correction coefficient is a correction coefficient for the fuel injection amount, and its value is determined so that the output of the air-fuel ratio sensor matches the target air-fuel ratio, and as a learning value (reference value) at low load It is generally memorized. By comparing the calculated value of the feedback correction coefficient with the learned value, it is possible to detect leanness of the air-fuel ratio, that is, fuel vaporization.

  However, when the fuel vaporizes and the air-fuel ratio becomes lean, the feedback correction coefficient also increases greatly in conjunction with it. That is, if the feedback correction coefficient is learned in a state where the fuel pressure is reduced at low load (in other words, the fuel may vaporize), the learned value becomes inaccurate, and the vapor detection accuracy is reduced. It will decline. As a result, it is difficult to effectively suppress fuel vaporization, and there is a problem that the air-fuel ratio cannot be accurately controlled to the target air-fuel ratio.

  Accordingly, an object of the present invention is to solve the above-described problems, effectively suppress the fuel vaporization accompanying the pressure drop, and accurately control the air-fuel ratio to the target air-fuel ratio. Is to provide.

In order to solve the above-mentioned problem, according to claim 1, in the air-fuel ratio control apparatus for an internal combustion engine that controls the air-fuel ratio of the internal combustion engine to the target air-fuel ratio by adjusting the fuel injection amount of the injector, the internal combustion engine A fuel pressure adjusting means for adjusting the pressure of the fuel acting on the injector disposed in the fuel supply system, a fuel injection amount correcting means for correcting the fuel injection amount in accordance with the pressure of the fuel, and a load of the internal combustion engine A load state detecting means for detecting a state, and controlling the operation of the fuel pressure adjusting means so that the pressure of the fuel becomes the first pressure when the detected load state is in the first load state, When the detected load state is a second load state that is lower than the first load state, the fuel pressure becomes a second pressure lower than the first pressure. Operation of fuel pressure adjustment means First control means for controlling, an air-fuel ratio sensor disposed in an exhaust system of the internal combustion engine, and correcting the fuel injection amount so that the air-fuel ratio detected by the air-fuel ratio sensor matches the target air-fuel ratio Correction coefficient calculating means for calculating a feedback correction coefficient to be performed, correction coefficient learning means for storing the calculated feedback correction coefficient as a learning value, decompression based on the calculated feedback correction coefficient and the stored learning value The determination means for determining whether or not fuel vaporization due to boiling occurs, and the fuel pressure adjustment so that the fuel pressure becomes the first pressure when it is determined that the fuel vaporization occurs. It controls the operation of the unit, when the vapor of the fuel is determined not to occur, the pressure of the fuel so as to hold the second pressure Second correction means for controlling the operation of the pressure adjusting means, and the correction coefficient learning means is further configured such that when the detected load condition is in the second load condition, the fuel pressure is Third control means for controlling the operation of the fuel pressure adjusting means so that the pressure becomes 1, and the feedback correction coefficient calculated when the pressure of the fuel is rising to the first pressure It memorize | stored as a learning value. 3. The air / fuel ratio control apparatus for an internal combustion engine according to claim 2, wherein the fuel vaporization of the fuel occurs when the feedback correction coefficient exceeds the stored learning value for a predetermined time. It was configured to be judged. Further, in the air-fuel ratio control apparatus for an internal combustion engine according to claim 3, the third control means is characterized in that the detected load state is the second load state and the fuel injection time is a predetermined time or more. In this case, the operation of the fuel pressure adjusting means is controlled so that the pressure of the fuel becomes the first pressure. Further, in the air-fuel ratio control apparatus for an internal combustion engine according to claim 4, when the amount of hydrocarbons generated in the exhaust system of the internal combustion engine exceeds a predetermined value before the feedback correction coefficient is calculated or The fourth control means for controlling the operation of the fuel pressure adjusting means is provided so that the pressure of the fuel becomes the third pressure higher than the first pressure.

  In the air-fuel ratio control apparatus for an internal combustion engine according to claim 1, when the load state of the internal combustion engine is in the first load state, the operation of the fuel pressure adjusting means is performed so that the fuel pressure becomes the first pressure. On the other hand, when the load state is a second load state lower than the first load state, the fuel pressure adjusting means is configured so that the fuel pressure becomes a second pressure lower than the first pressure. Since the operation is controlled, the output of the fuel pressure adjusting means can be reduced according to the load of the internal combustion engine, and the energy loss can be reduced.

Further, when it is determined that fuel vaporization due to reduced-pressure boiling occurs based on the feedback correction coefficient of the fuel injection amount and the learning value thereof, the operation of the fuel pressure adjusting means so that the fuel pressure becomes the first pressure. When the fuel vaporization is determined not to occur, the fuel vaporization is suppressed by controlling the operation of the fuel pressure adjusting means so as to maintain the fuel pressure at the second pressure. It was configured as follows. Specifically, by detecting the fuel vaporization based on the comparison result of the feedback correction coefficient and the learning value, and when it is determined that the fuel vaporization has occurred, by increasing the fuel pressure, It was configured to suppress vaporization.

Further, when the load state is the second load state (that is, when the fuel pressure is the second pressure on the low pressure side), the fuel pressure is higher than the second pressure. The operation of the fuel pressure adjusting means is controlled so that the feedback correction coefficient calculated when the fuel pressure is rising to the first pressure is stored as a learned value. Thus, an accurate learning value can be obtained without being affected by the vaporization of the air (the lean air-fuel ratio), and the occurrence of vapor can be accurately detected. Accordingly, fuel vaporization can be effectively suppressed, and the air-fuel ratio can be accurately controlled to the target air-fuel ratio. Further, since the determination means is configured to determine that fuel vaporization occurs when the feedback correction coefficient exceeds the stored learning value continuously for a predetermined time, it is caused by instantaneous disturbance of the feedback correction coefficient. An increase in fuel pressure can be prevented. Further, the third control means is configured such that when the detected load state is the second load state and the fuel injection time is equal to or longer than a predetermined time, the fuel pressure becomes the first pressure. Therefore, in other words, since it is configured to avoid an increase in fuel pressure (and learning of the feedback correction coefficient), the injector can be stably operated, and the air-fuel ratio can be accurately controlled by the target air-fuel ratio. Can do. Further, before the feedback correction coefficient is calculated or when the amount of hydrocarbons generated in the exhaust system of the internal combustion engine exceeds a predetermined value, the fuel pressure becomes a third pressure higher than the first pressure. Since it is configured, atomization of the spray can be promoted and exhaust gas can be improved by maintaining the fuel pressure at a high pressure until the air-fuel ratio feedback control is started or when the amount of hydrocarbon is large.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing the entire air-fuel ratio control apparatus for an internal combustion engine according to the first embodiment of the present invention.

  In the figure, reference numeral 10 denotes an internal combustion engine (hereinafter referred to as “engine”) mounted on a vehicle (not shown). The engine 10 is, for example, an in-line 4-cylinder spark ignition engine.

  A throttle valve 14 is disposed on the upstream side of the intake pipe 12 of the engine 10. The throttle valve 14 is connected to an accelerator pedal provided on the driver's seat floor or an actuator (not shown) such as an electric motor, and is opened / closed according to the amount of depression of the accelerator pedal by the driver, and the intake of the engine 10 Weigh out.

  In the vicinity of the intake port downstream of the throttle valve 14, an injector (fuel injection valve) 16 is provided for each cylinder (not shown). The injector 16 is connected to the fuel supply system 20. The fuel supply system 20 includes a fuel tank 22, a fuel supply pipe 24, a fuel pump 26, a delivery pipe 28, and the like. The injector 16 is connected to the fuel tank 22 via a delivery pipe 28 and a fuel supply pipe 24, and a fuel pump 26 is provided at the most upstream position of the fuel supply pipe 24. For convenience of illustration, the delivery pipe 28 is shown at a position separated from the engine 10, but actually, it is attached near the cylinder head of the engine 10.

  The fuel pump 26 is driven by an electric motor (not shown) and sucks fuel (specifically gasoline fuel) stored in the fuel tank 22 and pumps the sucked fuel to the injector 16. The injector 16 opens at a predetermined fuel injection timing determined according to the operating state of the engine 10 and injects fuel supplied from the fuel supply system 20. The fuel pressure (hereinafter referred to as “fuel pressure”) acting on the injector 16 from the fuel supply system 20 is controlled by controlling the operation of the fuel pump 26 (specifically, the rotational speed of the electric motor that drives the pump). Adjustable. That is, the fuel pump 26 functions as fuel pressure adjusting means for adjusting the fuel pressure.

A throttle opening sensor 30 is provided in the vicinity of the throttle valve 14 described above. The throttle opening sensor 30 generates an output indicating the throttle opening θTH. Further, on the downstream side of the throttle valve 14 of the intake pipe 12 is attached an intake pipe pressure sensor 32 and an intake air temperature sensor 34 produces an output or signal respectively showing the intake pipe pressure (negative pressure) PB and the intake air temperature TA.

  A cooling water temperature sensor 36 is attached to a cylinder peripheral wall (not shown) filled with cooling water in the cylinder block of the ethidine 10. The cooling water temperature sensor 36 outputs a signal indicating the cooling water temperature TW. Further, a crank angle sensor 38 is attached near the crankshaft of the engine 10. The crank angle sensor 38 outputs a CRK signal at a predetermined crank angle (for example, 30 degrees).

  Further, a fuel pressure sensor 40 is disposed near the delivery pipe 28 in the fuel supply system 20. The fuel pressure sensor 40 generates an output indicating the fuel pressure PF acting on the injector 16. Further, an atmospheric pressure sensor 42 is provided at an appropriate position in the engine room (not shown), and an accelerator pedal operation amount sensor 44 is provided in the vicinity of the accelerator pedal. The atmospheric pressure sensor 42 and the accelerator pedal operation amount sensor 44 generate outputs indicating the atmospheric pressure PA and the operation amount AP of the accelerator pedal, respectively.

  The combustion gas of the engine 10 is discharged to the outside through an exhaust system 60 including an exhaust pipe 54 and a three-way catalyst 56 provided in the middle thereof. A wide area air-fuel ratio sensor (hereinafter referred to as “LAF sensor”) 62 and an HC sensor 64 are mounted in the middle of the exhaust pipe 54. The LAF sensor 62 generates an output indicating the air-fuel ratio of the engine 10 over a wide range from lean to rich. Further, the HC sensor 64 generates an output indicating the amount of HC (hydrocarbon) contained in the exhaust gas.

  The output of each sensor described above is input to an electronic control unit (hereinafter referred to as “ECU”) 70. The ECU 70 includes a microcomputer, and includes an input / output circuit, a CPU, and a storage medium (ROM or RAM) for storing various calculation programs, maps, calculation results, and the like executed by the CPU.

  The ECU 70 counts the CRK signal output from the crank angle sensor 38, and detects (calculates) the engine speed NE. Further, the ECU 70 executes various calculations based on the engine speed NE and other sensor outputs to determine the fuel injection amount of the injector 16, the ignition timing of the spark plug, the target fuel pressure DPF, and the like, and a control command corresponding thereto Send a value to each part to control its operation.

The air-fuel ratio of the engine 10 is controlled to the target air-fuel ratio by adjusting the fuel injection amount of the injector 16 by the ECU 70. Specifically, the fuel injection amount of the injector 16 is calculated according to the following formula as a fuel injection time (a valve opening time of the injector 16) Tout.
Tout = (Ti × KAF × KCMD × K1 + K2) × Kpf

  In the above equation, Ti is the basic injection time, and is set according to the engine speed NE and the intake pipe pressure PB. Kpf is a fuel pressure correction coefficient, and is set to a smaller value as the fuel pressure PF becomes higher. KAF is a feedback correction coefficient, and is calculated so that the air-fuel ratio detected by the LAF sensor 62 matches the target air-fuel ratio. That is, if the output of the LAF sensor 62 indicates lean, the value of KAF is increased, and if it indicates rich, it is decreased. KCMD is a target equivalent ratio, that is, a value corresponding to the target air-fuel ratio, and is set according to the operating state of the engine 10. K1 is a correction coefficient in the other multiplication format, and K2 is a correction variable in the addition format, which optimizes various characteristics such as fuel consumption characteristics and acceleration characteristics according to the operating state of the engine 10, as well as intake air temperature TA and cooling water temperature TW. It is set as appropriate so that the environmental correction according to the atmospheric pressure PA is performed.

  As described above, the fuel pressure PF can be adjusted by controlling the operation of the fuel pump 26. However, as described in the problem, when the fuel pressure PF is lowered, the fuel is vaporized by the boiling under reduced pressure, and the fuel injection amount is decreased, so that the air-fuel ratio may become leaner than the target air-fuel ratio. Therefore, in the air-fuel ratio control apparatus for an internal combustion engine according to the present invention, the fuel pressure PF is adjusted while suppressing the vaporization of the fuel.

  FIG. 2 is a first half of a flowchart representing a fuel pressure adjustment process executed by the ECU 70, and FIG. 3 is a second half thereof.

  The flowchart in FIG. 2 will be described. First, in S10, it is determined whether or not the warm-up of the engine 10 has been completed. This process is performed by determining whether a predetermined time t1 has elapsed since the engine 10 was started. The predetermined time t1 is set to a longer time as the coolant temperature TW at the time of starting the engine is lower.

  When the result in S10 is affirmative, the program proceeds to S12, in which it is determined whether the LAF sensor 62 is activated. This process detects the internal resistance R (electric resistance) of the LAF sensor 62 and determines whether the value is below a predetermined value Rref, in other words, whether the LAF sensor 62 has been heated to the activation temperature. Is done by. When the result in S12 is affirmative, the program proceeds to S14, in which it is determined whether the amount of HC generated exceeds the reference value HCref.

  When the determination at S12 is affirmative, that is, when the warm-up is completed after the elapse of a predetermined time t1 from the start of the engine 10 and the LAF sensor 62 is activated, the air-fuel ratio feedback control is performed in a program (not shown). Is started. By executing the air-fuel ratio feedback control, the calculation of the feedback correction coefficient KAF that is also used in the processing of the flowcharts of FIGS. 2 and 3 is started.

  When the result in S14 is negative, the program proceeds to S16, in which it is determined whether the load of the engine 10 is in a low load state below a predetermined value, specifically, whether the intake pipe pressure PB is above a predetermined value (for example, 450 mmhg). In this embodiment, a time when the load of the engine 10 exceeds a predetermined value is referred to as a “first load state”, and a time when the load is equal to or less than a predetermined value is referred to as a “second load state”.

  When the result in S16 is negative, that is, when it is determined that the load state of the engine 10 is in the first load state, the routine proceeds to S18, where the target fuel pressure DPF is set to the first pressure PFM and the fuel pressure (actual fuel pressure) is set. ) The operation of the fuel pump 26 is controlled so that the PF becomes the first pressure PFM. The first pressure PFM is set to a value that enables stable fuel injection from a low load to a high load (400 kPa in this embodiment). Next, in S20, the vaporization suppression flag bit (initial value 0) is reset to 0.

  On the other hand, when the result in S16 is affirmative, that is, when it is determined that the load state of the engine 10 is in the second load state having a lower load than the first load state, the routine proceeds to S22 and the vaporization suppression flag is set. It is determined whether or not the bit is set to 1. When the result in S22 is negative, the program proceeds to S24, in which the target fuel pressure DPF is set to the second pressure PFL, and the operation of the fuel pump 26 is controlled so that the fuel pressure PF becomes the second pressure PFL. Since the fuel injection amount decreases at low load, the second pressure PFL is set to a lower pressure than the first pressure PFM, specifically 250 kPa. Next, in S26, the bit of the vaporization suppression flag is set to 1. If the determination in S22 is affirmative, the processes in S24 and S26 are skipped.

Next, in S28, it is determined whether or not the feedback correction coefficient KAF is larger than the learning value KAFREF. The learning value KAFREF is a past value of KAF that is learned (stored) in steps to be described later. The feedback correction coefficient KAF is calculated so that the air-fuel ratio matches the target air-fuel ratio as described above. Therefore, if the current value of the feedback correction coefficient KAF exceeds the learning value KAFREF, it indicates that the air-fuel ratio is leaner than the target air-fuel ratio. As can be seen from the processes from S22 to S26, the process of S28 is executed when the fuel pressure PF is lowered to the second pressure PFL during the current or previous program execution. if it can be determined that vapor of the fuel due to flash boiling occurs. That is, in S28, the generation of vapor is detected by comparing KAF and KAFREF.

  When the determination in S28 is affirmative, that is, when fuel vaporization is detected, the process proceeds to S30, and it is determined whether or not vaporization is continuously detected over a predetermined time t2. When the result in S30 is affirmative, the program proceeds to S32, in which the target fuel pressure DPF is set to the first pressure PFM, and the operation of the fuel pump 26 is controlled. That is, fuel vaporization is suppressed by increasing the fuel pressure PF.

  On the other hand, when the result in S28 is NO, there is no need to increase the fuel pressure PF, so the routine proceeds to S34 and the current target fuel pressure DPF is held. When the result in S30 is negative, the program proceeds to S34 and the current target fuel pressure DPF is maintained. This is to prevent an increase in fuel pressure due to instantaneous disturbance of the feedback correction coefficient KAF.

  When the load of the engine 10 rises and shifts to the first load state, the target fuel pressure DPF is set to the first target fuel pressure PFM in S18 described above, and the vaporization suppression flag bit is set to 0 in S20. Reset. Therefore, when the second load state is entered again, the target fuel pressure DPF is set to the second pressure PFL in S24. When the load increases and the amount of fuel injection increases, relatively low temperature fuel reaches the injector 16 from the fuel tank 22, so that vapor is hardly generated. Therefore, when the first load state is shifted to the second load state, the target fuel pressure DPF is lowered again to the second pressure PFL, and it is reconfirmed whether vapor is generated.

  Next, the process proceeds to S36 in the flowchart of FIG. 3, and it is determined whether or not the bit (initial value 0) of the learning end flag is set to 1. When the result in S36 is negative, the program proceeds to S38, in which it is determined whether the operating state of the engine 10 and the fuel pressure PF are stable. Specifically, when the amount of change in the accelerator pedal operation amount AP is equal to or less than a predetermined value APref and the amount of change in the fuel pressure PF is equal to or less than a predetermined value PFref (for example, ± 20 Pa), it is determined to be stable.

  When the result in S38 is negative, the subsequent processing is skipped, while when the result in S38 is positive, the process proceeds to S40 to determine whether or not the fuel pressure PF is 400 kPa or more. As described above, since the target fuel pressure DPF is set to the first pressure PFM, that is, 400 kPa in the first load state, the determination here is to determine whether the first load state is present. Equivalent to.

  When the result in S40 is negative, that is, when it is determined that the vehicle is in the second load state, it is determined in S42 whether the fuel injection time Tout is equal to or longer than a predetermined time t3 (for example, 1.5 msec). When the result in S42 is affirmative, the current target fuel pressure DPF is stored as the store value DPFstr in S44, and then the target fuel pressure DPF is set to the first pressure PFM in S46 to control the operation of the fuel pump 26, and the fuel pressure PF is set. Raise to 400 kPa.

  Next, in S48, the value of the feedback correction coefficient KAF calculated after the fuel pressure PF has increased to the first pressure PFM is read. Thereafter, in S50, the target fuel pressure DPF is set to the store value DPFstr, and the fuel pressure PF is returned to the value before the increase. In S52, the KAF limit process read in S48 is performed, and the value is stored as a learned value KAFREF in S54.

  On the other hand, when the result in S40 is affirmative, that is, when it is determined that the load state of the engine 10 is in the first load state, the process proceeds to S56 and the value of the feedback correction coefficient KAF is read and the read KAF is read in S52. Then, the limit process is performed, and the learned value KAFREF is stored in S54.

  When the learning of the feedback correction coefficient KAF is completed in S54, the process proceeds to S58, and the bit of the learning end flag is set to 1. Accordingly, when the program is executed after the next time, an affirmative determination is made in S36, so that the processing from S38 to S58 is skipped.

  As described above, when the fuel pressure PF is lowered to the second pressure PFL, the fuel may vaporize due to the reduced-pressure boiling. When the fuel is vaporized, the air-fuel ratio becomes lean, and the feedback correction coefficient KAF greatly increases as shown in FIG. That is, if KAF learning is performed in a state where the fuel pressure PF is reduced (in other words, there is a possibility that the fuel is vaporized), the learning value KAFREF may be inaccurate.

  Therefore, in this embodiment, as described above, when the load state of the engine 10 is in the second load state (that is, when the fuel pressure PF is lowered to the second pressure PFL), temporarily. The operation of the fuel pump 26 is controlled so that the fuel pressure PF becomes the first pressure PFM to eliminate vaporization, and the feedback correction coefficient KAF calculated while the fuel pressure PF is rising to the first pressure PFM. Is stored as a learning value KAFREF. Thus, an accurate learning value KAFREF can be obtained without being affected by fuel vaporization (air-fuel ratio leaning) due to boiling under reduced pressure.

  Continuing the description of the flowchart of FIG. 3, when the result in S42 is negative, the processes after S46 are skipped. In general, the injector cannot be expected to operate stably when the fuel injection time is short. When the load is low, the fuel injection amount is originally small, and when the evaporation purge or the like is performed, the fuel injection amount further decreases. Therefore, if the fuel pressure is increased at a low load, the fuel injection time may become extremely short and the operation of the injector may become unstable. Therefore, in S42, it is determined whether the fuel injection time Tout is equal to or longer than the predetermined time t3. If the determination is negative, the processing after S46 is skipped to avoid an increase in the fuel pressure PF. It should be noted that the predetermined time t3 is set to an injection time that can guarantee a stable operation of the injector 16.

  Returning to the description of the flowchart of FIG. 2, when the result in S10 is negative, the program proceeds to S60, where the target fuel pressure DPF is set to the third pressure PFH, and the fuel pump 26 is set so that the fuel pressure PF becomes the third pressure PFH. Control the behavior. The third pressure PFH is set higher than the first pressure PFM, specifically 600 kPa. When the result in S12 is negative, the program proceeds to S60 where the target fuel pressure DPF is set to the third pressure PFH. Note that when the result in S10 or S12 is NO, the feedback control has not been started, that is, the calculation of the feedback correction coefficient KAF has not been started. Therefore, after performing the process of S60, the process returns to the process of S10 again. As described above, immediately after the engine 10 is started, and until the air-fuel ratio feedback control is started, the atomization of the spray is promoted by maintaining the fuel pressure PF at a high pressure, and the exhaust gas is improved. .

  Further, when the result in S14 is affirmative, that is, when the amount of HC generated exceeds the reference value, the process proceeds to S62, and the target fuel pressure DPF is set to the third pressure PFH as in S60 to operate the fuel pump 26. To control. Thereafter, the process proceeds to S64, the bit of the vaporization suppression flag is reset to 0, and the process proceeds to the process shown in the flowchart of FIG. Thus, even when the amount of HC generated is large, atomization of the spray is promoted by maintaining the fuel pressure PF at a high pressure, and the exhaust gas is improved.

  Thus, in the air-fuel ratio control apparatus for an internal combustion engine according to the first embodiment of the present invention, when the load state of the engine 10 is in the first load state (specifically, the load has a predetermined value). When the load state is in a second load state that is lower than the first load state, while controlling the operation of the fuel pump 26 to be the first pressure PFM of the fuel pressure PF, Since the operation of the fuel pump 26 is controlled so that the fuel pressure PF becomes the second pressure PFL lower than the first pressure PFM, the output (specifically, the output of the fuel pump 26 according to the load of the engine 10). The power consumption of the electric motor that drives the pump 26 can be reduced, and energy loss can be reduced.

  Further, fuel vaporization is suppressed by adjusting the fuel pressure PF by controlling the operation of the fuel pump 26 based on the feedback correction coefficient KAF of the fuel injection amount and the learned value KAFREF. Specifically, fuel vaporization is detected based on the comparison result between KAF and KAFREF, and when vaporization is detected, the fuel pressure PF is increased to suppress vaporization.

  Further, when the load state is the second load state (that is, when the fuel pressure PF is lowered to the second pressure PFL on the low pressure side), the fuel pressure PF is temporarily higher than the second pressure PFL. The operation of the fuel pump 26 is controlled so as to become the first pressure PFM, and the feedback correction coefficient KAF calculated while the fuel pressure PF is rising to the first pressure PFM is stored as the learning value KAFREF. Therefore, it is possible to obtain an accurate learning value without being affected by fuel vaporization (air-fuel ratio leaning) due to reduced-pressure boiling, and therefore it is possible to accurately detect the occurrence of vapor. Accordingly, fuel vaporization can be effectively suppressed, and the air-fuel ratio can be accurately controlled to the target air-fuel ratio.

  Further, when the fuel is in the second load state (that is, the low load state) and the fuel injection time Tout is less than the predetermined time t3, an increase in the fuel pressure PF (and learning of the feedback correction coefficient KAF) is avoided. As a result, the injector 16 can be stably operated, and the air-fuel ratio can be accurately controlled by the target air-fuel ratio.

  Further, immediately after the engine 10 is started or when the amount of HC generated is large, the atomization of the spray is promoted by maintaining the fuel pressure PF at a high pressure, so that the exhaust gas can be improved.

As described above, in the first embodiment of the present invention, the air-fuel ratio control of the internal combustion engine that controls the air-fuel ratio of the internal combustion engine (engine 10) to the target air-fuel ratio by adjusting the fuel injection amount of the injector (16). In the apparatus, a fuel pressure adjusting means for adjusting a pressure (fuel pressure PF) of the fuel acting on the injector disposed in the fuel supply system (20) of the internal combustion engine, and correcting the fuel injection amount according to the pressure of the fuel Fuel injection amount correction means (ECU 70) for performing load state detection means (intake pipe pressure sensor 32) for detecting the load state of the internal combustion engine, and when the detected load state is in the first load state (intake air) When the in-pipe pressure PB exceeds a predetermined value), the operation of the fuel pressure adjusting means is controlled so that the fuel pressure becomes the first pressure (PFM), while the detected load state is the first load. When the second load state is lower than the first state (when the intake pipe pressure PB is equal to or lower than a predetermined value), the fuel pressure is lower than the first pressure (PFL). First control means (ECU 70, S16, S18, S24 in the flowchart of FIG. 2) for controlling the operation of the fuel pressure adjusting means, and an air-fuel ratio sensor (LAF) disposed in the exhaust system (60) of the internal combustion engine Sensor 62), correction coefficient calculation means (ECU 70) for calculating a feedback correction coefficient (KAF) for correcting the fuel injection amount so that the air-fuel ratio detected by the air-fuel ratio sensor matches the target air-fuel ratio, Correction coefficient learning means (ECU 70, S54 in FIG. 3 flowchart) for storing the calculated feedback correction coefficient as a learning value (KAFREF), and the calculated A determination means (ECU 70, S28, S30 in the flowchart of FIG. 2) for determining whether or not fuel vaporization due to reduced-pressure boiling occurs based on the feedback correction coefficient and the stored learning value, and the fuel vaporization occurs. When it is determined that the fuel pressure is adjusted to control the operation of the fuel pressure adjusting means so that the fuel pressure becomes the first pressure, and when it is determined that the fuel is not vaporized, Second control means (ECU 70, S32, S34 in the flowchart of FIG. 2) for controlling the operation of the fuel pressure adjusting means so as to maintain the pressure at the second pressure (PFL), and the correction coefficient learning The means further operates the fuel pressure adjusting means so that the pressure of the fuel becomes the first pressure when the detected load state is the second load state. The third control means (ECU 70, S40, S44, S46, S50 in the flowchart of FIG. 3) for controlling the fuel, and the feedback correction coefficient calculated when the fuel pressure is increased to the first pressure Is stored as the learning value (S48 and S54 in the flowchart of FIG. 3). The determination means determines that the fuel is vaporized when the feedback correction coefficient (KAF) exceeds the stored learning value (KAFREF) for a predetermined time (ECU 70, FIG. 2). The configuration is as shown in the flowcharts S32 and S34. Further, the third control means is configured such that the fuel pressure becomes the first pressure when the detected load state is the second load state and the fuel injection time is a predetermined time or more. Thus, the operation of the fuel pressure adjusting means is controlled (ECU 70, S40, S42, S44, S46, S50 in the flowchart of FIG. 3). Further, before the feedback correction coefficient (KAF) is calculated or when the amount of hydrocarbon (HC) generated in the exhaust system (60) of the internal combustion engine exceeds a predetermined value (reference value), the pressure of the fuel is increased. 4th control means (ECU70, S60, S62 of the flowchart of FIG. 2) which controls operation | movement of the said fuel pressure adjustment means so that it may become 3rd pressure (PFH) higher than said 1st pressure is provided. Configured.

  In the above description, the fuel pressure PF is adjusted by controlling the operation of the fuel pump 26. However, the fuel pressure PF may be adjusted by a pressure regulator arranged in the fuel supply system. Further, although the intake pipe pressure PB is used as a parameter representing the load of the engine 10, other parameters may be used. Moreover, the above-mentioned numerical value is only an example and is not limited thereto.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an overall air-fuel ratio control apparatus for an internal combustion engine according to a first embodiment of the present invention. It is the first half part of the flowchart showing the adjustment process of the fuel pressure performed with the apparatus shown in FIG. It is the latter half part of the flowchart showing the adjustment process of the fuel pressure performed with the apparatus shown in FIG. It is a graph showing the change of a feedback correction coefficient when fuel vaporization arises with the apparatus shown in FIG.

Explanation of symbols

  10: engine (internal combustion engine), 16: injector, 20: fuel supply system, 26: fuel pump (fuel pressure adjusting means), 32: intake pipe pressure sensor (load state detecting means), 60: exhaust system, 62: LAF sensor (Air-fuel ratio sensor), 70: ECU (fuel injection amount correction means, first, second and third control means, correction coefficient calculation means, correction coefficient learning means)

Claims (4)

In an air-fuel ratio control apparatus for an internal combustion engine that adjusts the fuel injection amount of the injector to control the air-fuel ratio of the internal combustion engine to a target air-fuel ratio,
a. Fuel pressure adjusting means arranged in a fuel supply system of the internal combustion engine to adjust the pressure of fuel acting on the injector;
b. Fuel injection amount correction means for correcting the fuel injection amount in accordance with the pressure of the fuel;
c. Load state detecting means for detecting a load state of the internal combustion engine;
d. When the detected load state is the first load state, the operation of the fuel pressure adjusting means is controlled so that the pressure of the fuel becomes the first pressure, while the detected load state is the first load state. The fuel pressure adjusting means controls the operation of the fuel pressure adjusting means so that the fuel pressure becomes a second pressure lower than the first pressure when the second load state is lower than the first load state. Control means,
e. An air-fuel ratio sensor disposed in the exhaust system of the internal combustion engine;
f. Correction coefficient calculation means for calculating a feedback correction coefficient for correcting the fuel injection amount so that the air-fuel ratio detected by the air-fuel ratio sensor matches the target air-fuel ratio;
g. Correction coefficient learning means for storing the calculated feedback correction coefficient as a learning value;
h. Determining means for determining whether or not fuel vaporization due to reduced-pressure boiling occurs based on the calculated feedback correction coefficient and the stored learned value;
i. When it is determined that vaporization of the fuel has occurred, the operation of the fuel pressure adjusting means is controlled so that the pressure of the fuel becomes the first pressure, and vaporization of the fuel has not occurred. A second control means for controlling the operation of the fuel pressure adjusting means so as to maintain the pressure of the fuel at the second pressure when determined;
And the correction coefficient learning means further includes j. Third control means for controlling the operation of the fuel pressure adjusting means so that the pressure of the fuel becomes the first pressure when the detected load state is the second load state;
An air-fuel ratio control apparatus for an internal combustion engine, wherein the feedback correction coefficient calculated when the pressure of the fuel is rising to the first pressure is stored as the learning value.   2. The internal combustion engine according to claim 1, wherein the determination unit determines that the fuel is vaporized when the feedback correction coefficient continuously exceeds the stored learning value for a predetermined time. Air-fuel ratio control device.   The third control means is configured such that when the detected load state is the second load state and the fuel injection time is equal to or longer than a predetermined time, the fuel pressure becomes the first pressure. 3. An air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the operation of the fuel pressure adjusting means is controlled.   Before the feedback correction coefficient is calculated or when the amount of hydrocarbons generated in the exhaust system of the internal combustion engine exceeds a predetermined value, the fuel pressure becomes a third pressure that is higher than the first pressure. The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 3, further comprising fourth control means for controlling the operation of the fuel pressure adjusting means.

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