JP4489665B2 - Intake air amount calculation device considering secondary air - Google Patents

Description

  The present invention relates to an apparatus for calculating an intake air amount of an internal combustion engine (engine).

Patent Document 1 discloses a second intake air calculated based on a first intake air amount calculated based on a detection value of an air flow meter and a detection value of an absolute pressure sensor provided downstream of the intake pipe. It is described that a deviation from the quantity is calculated and it is determined that secondary air is supplied to the engine when the difference between the deviation and the average value of the deviation exceeds a predetermined value. According to this determination, the first intake air amount is corrected and used for air-fuel ratio control and other engine control.
JP2004-100533

  The above-described conventional technique is effective for detecting secondary air supplied from the master back (brake booster) to the intake pipe when the vehicle brake is depressed. On the other hand, for example, when the vehicle air conditioner is switched on and the engine load increases, the amount of intake air is increased by increasing the opening of the throttle located downstream of the air flow meter corresponding to this load. In the conventional method, it has been found that an increase in the intake air amount may be erroneously determined as the supply of secondary air due to such load fluctuation.

  If such an erroneous determination is made, an incorrect correction is made to the intake air amount which is the base of the air-fuel ratio control.

  In the apparatus of the present invention, secondary air is supplied to the internal combustion engine based on a deviation between the first intake air amount detected by the air flow meter and the second intake air amount detected based on the intake pipe pressure. It is an intake air amount calculation device provided with determination means for determining whether or not there is. The determination means calculates a deviation (DGAIR) between the first-order lag processing value of the first intake air amount detected by the air flow meter and the second intake air amount, and calculates the deviation (DGAIR) and an average value of the deviations. When the difference (DDGAIR) is greater than a predetermined value, it is determined that secondary air is being supplied.

  According to the present invention, the first intake air amount detected from the air flow meter is not used as it is, but its first-order lag processing value is used. As a result, the change in the first intake air amount due to the change in the throttle opening due to the transient load fluctuation is smoothed (smoothed). Therefore, the deviation (DGAIR) between the first-order lag processing value and the second intake air amount is not affected by the change in the throttle opening due to the load fluctuation. Thus, erroneous detection of secondary air as described above is prevented.

  In an embodiment of the present invention (claim 2), the update of the average value of the deviation (DGAIR) is stopped in response to the determination by the determination means that the secondary air is supplied. The first intake air amount is corrected based on the difference (DDGAIR) between the deviation (DGAIR) and the average value of the deviation, and thereby air-fuel ratio control and other controls are performed. As will be described in detail later, if the average value of the deviation (DGAIR) is updated for each process cycle, it is recognized that the difference (DDGAIR) becomes smaller and the correction for the first intake air amount becomes insufficient. It was. In order to avoid such a phenomenon, the update of the deviation (DGAIR) is stopped.

  Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of a car engine. A throttle valve 14 is disposed in the intake pipe 12 of the engine 10. The throttle valve 14 is opened and closed in accordance with the depression amount of the access pedal 18 provided on the driver's seat floor to adjust the intake air amount. An opening degree sensor 20 is provided in the vicinity of the throttle valve 14 and outputs a signal corresponding to the opening degree θTH of the throttle valve.

  An injector (fuel injection device) 24 is disposed near the intake port immediately after the intake manifold downstream of the throttle valve 14. The injector 24 is connected to the fuel tank 26 via a fuel supply pipe 28 and a fuel pump 30, and injects gasoline into the intake port.

  The fuel tank 26 is connected to the canister 34 via the charge passage 32. The canister 34 is connected to the downstream side of the throttle valve 14 of the intake pipe 12 via the purge passage 38 and purges the evaporated fuel to the intake pipe 12 via the purge control valve 40.

  The intake pipe 12 is provided with a bypass passage 44 that communicates the upstream side and the downstream side of the throttle valve 14. A control valve 46 is provided in the bypass passage 44.

  A brake pedal 50 provided on the driver's seat floor is connected to a master back (brake booster, booster) 52. The master back 52 includes an atmosphere introduction pipe 54 connected to the atmosphere and a negative pressure introduction pipe 56 connected downstream of the throttle valve of the intake pipe 12. When the brake pedal 50 is not depressed, negative pressure is introduced from one of the two chambers of the master back 52 through the negative pressure introduction pipe 56. When the brake pedal 50 is depressed, the atmosphere is introduced into the other chamber via the atmosphere introduction pipe. Due to the pressure difference between the two chambers, the force to depress the brake pedal is assisted. When the brake pedal 50 is depressed or released, the introduced atmosphere flows into the intake pipe 12 through the negative pressure introduction pipe.

  A purge passage 38, a bypass passage 44, a negative pressure introduction pipe 56, an EGR pipe 64, and a PCV (blow-by gas recirculation) pipe 70 are connected to the intake pipe 12 downstream of the throttle valve 14. The air flowing into the intake pipe 12 downstream of the throttle valve 14 through these passages is called secondary air.

  An air flow meter (for example, a hot wire type) 76 is provided upstream of the throttle valve 14 and outputs a signal indicating the intake air amount Gair. An absolute pressure sensor 78 for detecting the pressure (PBA) in the intake pipe and a temperature sensor 80 for detecting the temperature (TA) are provided on the downstream side of the throttle valve 14. In addition, a water temperature sensor 82, a cylinder discrimination sensor 84, a TDC sensor 86 that outputs a TDC signal, and a crank angle sensor 88 that outputs a CRK signal at every predetermined crank angle are provided. Further, the exhaust pipe 60 is provided with a wide area air-fuel ratio sensor (LAF sensor) 90 and a catalyst device 62.

  A vehicle speed sensor 92 is provided in the vicinity of the drive shaft of the vehicle. A sensor 94 for detecting the atmospheric pressure PA around the vehicle is attached to the vehicle.

  The electronic control unit (ECU) 98 is a microcomputer and includes a CPU 98a, a read-only memory (ROM) 98b for storing computer programs and various data, a random access memory (RAM) 98c for providing a work area to the CPU 98a, and various sensors. And an output circuit 98e for sending control signals to various parts of the engine.

  In this embodiment, the invention is implemented by a computer program, and the flowcharts of FIGS. 4 and 5 show the flow of processes executed by the computer program. FIG. 2 shows the behavior of various parameters when the intake air amount is calculated by the conventional method, and shows problems. FIG. 3 shows the behavior of various parameters when the intake air amount is calculated by the method of the present invention.

  First, a method for obtaining DGAIRAVE will be described with reference to FIGS. The process of FIG. 3 is repeatedly executed at every predetermined crank angle. A first-order lag process (smoothed) value GAIRTHAVE is obtained for the first intake air amount GAIRTH detected by the air flow meter 76 (S201). The first-order lag process is expressed by the following equation.

GAIRTHAVE (n) = C × GAIRTH (n) + (1-C) GAIRTHAVE (n-1) (1)
Here, n indicates that the sample value is the current value, and n-1 indicates that the sample value is the previous value. C is a constant smaller than 1. The smaller the C value, the more slowly GAIRTHAVE changes. Referring to FIG. 3, the first intake air amount GAIRTH is indicated by a dotted line in the waveform diagram of (E), and the smoothed value GAIRTHAVE by the first-order lag processing is indicated by a solid line.

  In step S203, the difference DGAIR between the second intake air amount GAIRPB calculated based on the absolute pressure PBA in the intake pipe and the first intake air amount smoothed value GAIRTHAVE obtained in S201 is obtained. GAIRPB is calculated according to the gas state equation using the average value of the output of the intake pipe pressure sensor and the intake air temperature TA.

  Referring to FIG. 2, the second intake air amount GAIRPB shown in (D) is determined by the secondary air introduced into the intake pipe from the master back when the pumping brake operation shown by the brake flag in (A) is performed. When the pumping brake operation is finished, the value returns to the original value. At this time, no change occurs in the first intake air amount GAIRAVE calculated from the output of the air flow meter and its smoothed value GAIRTHAVE.

  The waveform in FIG. 2B is a flag indicating that an accessory such as a car air conditioner has been activated. Now, when the air conditioner is switched on, the throttle opens transiently and greatly in response to an instruction from the ECU in order to cope with a sudden increase in engine load. Accordingly, the first intake air amount GAIRTH (dotted line) shown in (E) becomes transiently large and then settles to a value corresponding to the increase in load. At this time, the smoothed value GAIRTHAVE (solid line) of the first intake air amount changes gently and does not change suddenly as in the GAIRTH curve.

  Next, in step S205, it is determined whether the permission flag is set to 1. This permission flag is set to 1 in step S110 of FIG. 4 described later. If the permission flag is 1, it is determined whether a predetermined stabilization time has elapsed after the engine is started (S207). If Yes, whether the AFM mode in FIG. Judgment is made (S209). The AFM mode is a mode for correcting the first intake air amount according to the introduction of the secondary air, and 0 indicates that the mode is not entered.

  If the determination in step S209 is Yes, it is determined whether the change DPB of the internal pressure PB of the intake pipe is positive, that is, whether the internal pressure is increasing (S211). An increase in the internal pressure PB means that the engine load is increasing. If Yes, DGAIRAVE is obtained by smoothing the DGAIR (difference between the second intake air amount and the first intake air amount) obtained in step S203 (S215). The waveform of (F) in FIG. 2 indicates DGAIR, and the alternate long and short dash line indicates DGAIRAVE. The annealing process here may be based on the same arithmetic expression as the first-order lag process described above, or may be a moving average process.

  When the determination in step S211 is No, that is, when the change DPB in the intake pipe internal pressure PB is 0 or negative, the process proceeds to step S213, and DGAIR is smoothed to obtain DGAIRAVE. The smoothing coefficient C in step S213 is larger than the smoothing coefficient in step S215. As a result, DGAIRAVE changes immediately after the end of load fluctuation, and AFM mode determination preparation can be started quickly. When DPB changes to the minus side, DGAIRAVE is changed quickly, so AFM mode judgment preparation is quickly made. For example, this corresponds to a situation where the brake is stepped on immediately after the air conditioner is turned off. be able to.

  If the AFM mode is set to 1 in step S209, the DGAIRAVE smoothing process is not performed and the value of DGAIRAVE when the AFM mode is set to 1 is held. That is, in FIG. 2, DGAIRAVE shown in (F) is shown to rise gradually even after the AFM mode becomes 1, but in the embodiment of the present invention, after the AFM mode becomes 1. , Hold the value of AGAIRAVE without updating, so that the difference DDAIR between DGAIR and DGAIRAVE does not decrease.

  If the update of DGAIRAVE is continued as shown in (F) of FIG. 2, the difference DDAIR decreases while the supply of secondary air continues as shown in (G) of FIG. In this embodiment, the first intake air amount is corrected based on the difference DDAIR. If the difference DDAIR decreases while the inflow of secondary air continues, the first intake air amount used for air-fuel ratio control will not be sufficiently corrected, resulting in inconvenience in air-fuel ratio control. For this reason, after the AFM mode becomes 1, the value of AGAIRAVE is held without being updated.

  In step S219, a difference DDGAIRB between the difference DGAIR and the smoothed value DGAIRAVE is calculated. Next, in step S221, DDGAIRB is subjected to limit processing to obtain DDAIR. Thus, the parameter DDAIR for correcting the first intake air amount was obtained.

  Next, the procedure for setting the AFM mode shown in FIG. 2C will be described with reference to FIG. The process of FIG. 4 is repeatedly executed at every predetermined crank angle. In step S100, the engine speed NE is compared with a predetermined value (for example, 800 rpm). If NE is smaller, the process proceeds to step 102, and the intake pipe pressure PBA, which is a parameter indicating the engine load, is compared with the predetermined value. If PBA is smaller, the process proceeds to step S104, and it is determined whether or not the second intake air amount GAIRPB calculated based on the intake pipe pressure PBA is smaller than a predetermined value. When it is smaller, the routine proceeds to step S106, where it is determined whether or not the throttle opening degree θTH is an opening degree corresponding to full closing (below a predetermined low opening degree).

  If the determination in step S106 is Yes, it is determined whether the absolute value of the difference DPBA between the current value and the previous value of the intake pipe pressure PBA is equal to or less than a predetermined value (S108). That is, it is determined whether or not the engine load fluctuation is small. If all the determinations in S100 to S108 are Yes, it means that the engine is in an idle state. At this time, in step S100, a flag that permits calculation of the average value DGAIRAVE of the differential waveform DGAIR shown in FIG. This permission flag is referred to in step S205 in FIG. Thus, the average value DGAIRAVE is an average value of the deviation DGAIR between the first intake air amount and the second intake air amount in the idle state.

  When the determination in S108 is No, specifically, when the idle speed is not constant for some reason, or when the throttle valve 14 is decelerating (transient) immediately after being fully opened, Proceeding to S112, the permission flag is reset to zero.

  Next, in S114, it is determined whether or not the difference DDGAIR (calculated in step S221 in FIG. 3) is larger than the threshold for mode determination (straight line shown in (G) in FIG. 2). When Yes, the AFM mode is set to 1 (S116), and when No, the AFM mode is set to 0 (S118).

  If any of S100 to S106 is No and it is determined that the engine is not in a steady operation state, the process proceeds to S120, the permission flag is reset to 0, and the AFM mode is set to 0 in S118.

  Referring to FIG. 2 again, in the conventional method, DGAIR (dotted line) of (F) is calculated by the calculation formula of DGAIR = GAIRPB−GAIRTH. GARITH (first intake air amount) is indicated by a dotted waveform in (E). As described above, a surge is generated in the AA portion by turning on the air conditioner. This surge causes a change indicated by BB in the DGAIR waveform (dotted line) of (F). This change in BB appears as a change in CC in DDGAIR (dotted line) calculated by the conventional method in (G).

  Since the change in CC satisfies the condition of step S114 in FIG. 4, the process proceeds to step S116, and the AFM mode is set to 1. This is indicated by a dotted line in the DD portion in the waveform of FIG. The AA surge was caused by a transient phenomenon caused by turning on the air conditioner, and secondary air was not introduced into the intake pipe. Therefore, the AFM mode indicated by the dotted line in the DD part of (C) is incorrect.

  According to the present invention, as described above, DGAIR is calculated according to the equation DGAIR = GAIRPB−DGAIRTHAVE using the smoothed value (first-order lag processing value) GAIRTHAVE instead of the conventional GAIRTH. GAIRTHAVE does not generate a surge in the AA portion, as shown by the solid line waveform in (E). Therefore, the erroneous setting of the AFM mode as indicated by the dotted line in the DD part of (C) does not occur.

  As mentioned above, although this invention was demonstrated about the specific Example, this invention is not limited to such an Example.

1 is an overall configuration diagram of an example of an engine to which the present invention is applied. The wave form diagram which shows the behavior of each parameter. The figure which shows the processing flow of one Example of this invention. The figure which shows the flow of AFM mode setting in one Example of this invention.

Explanation of symbols

S201: calculating a first-order lag processing value of the first intake air amount
S203 Step to calculate deviation (DGAIR)
S221 Step of calculating the difference (DDGAIR) between the deviation (DGAIR) and the average value of this deviation
S114 Step of determining that secondary air is being supplied

Claims (1)

It is determined whether secondary air is being supplied to the internal combustion engine based on a deviation between the first intake air amount detected by the air flow meter and the second intake air amount detected based on the intake pipe pressure. In an intake air amount calculation device comprising a determination means,
The determination means calculates a deviation (DGAIR) between a first-order lag processing value of the first intake air amount detected by the air flow meter and the second intake air amount, and the deviation (DGAIR) and the deviation When the difference from the average value (DDGAIR) is greater than the predetermined value, it is determined that secondary air is being supplied ,
Intake air amount calculation characterized in that updating of the average value of the deviation (DGAIR) is stopped in response to a determination that secondary air is being supplied by the determination means. apparatus.

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