JP3761716B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine having a plurality of cylinders, and more particularly, to a fuel supply by so-called simultaneous injection that opens a plurality of fuel injection valves at the same time.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a control device for an internal combustion engine that performs simultaneous injection that opens a plurality of fuel injection valves provided in an intake pipe of an internal combustion engine having a plurality of cylinders at the same time has been known (Japanese Patent Laid-Open No. Sho). 60-1349). Further, a technique is widely used in which an oxygen concentration sensor is provided in an exhaust system of an internal combustion engine, and the fuel injection amount by the fuel injection valve is feedback controlled according to the output of the oxygen concentration sensor.
[0003]
[Problems to be solved by the invention]
However, in order to reduce the cost of an internal combustion engine having a plurality of cylinders, a configuration is adopted in which a so-called cylinder discrimination sensor that detects the position of a piston of a specific cylinder is not provided, and the stroke (intake, compression, explosion, exhaust) of each cylinder is adopted. When the simultaneous injection is executed without determining which is in the stroke) and the feedback control of the air-fuel ratio is performed according to the output of the oxygen concentration sensor arranged in the exhaust system of the internal combustion engine, the following is performed: There was a serious problem.
[0004]
That is, when simultaneous injection is performed on a plurality of cylinders, there are cylinders in which the injected fuel is sucked into the combustion chamber immediately after injection, and cylinders that are not sucked in only after several strokes after injection. Because of variations in the amount of fuel adhering to the intake pipe, or variations in the time delay from the execution of injection until it actually burns and reaches the exhaust system, correction by feedback control is inappropriate for some cylinders. The exhaust gas characteristics tended to deteriorate.
[0005]
Further, as a result of the feedback control correction not being properly executed, the influence of the characteristic variation such as the fuel injection valve is not sufficiently removed, which also contributes to the deterioration of the exhaust gas characteristic.
[0006]
The present invention has been made to solve this problem, and an object of the present invention is to provide an air-fuel ratio control apparatus that can obtain good exhaust gas characteristics when fuel is supplied by simultaneous injection.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is directed to an oxygen concentration sensor provided in an exhaust system of an internal combustion engine having a plurality of cylinders, and fuel provided in an intake passage of each of the cylinders. An air-fuel ratio control amount is calculated using a proportional term and an integral term in accordance with a comparison result between a plurality of fuel injection valves to be injected and an output of the oxygen concentration sensor and a reference value, and the fuel injection is calculated based on the air-fuel ratio control amount. comprising a feedback control means for calculating the opening time of the valve, and a simultaneous injection control means for over the valve opening time of the calculated opened on approximately the same time the plurality of fuel injection valves, the fuel supply at all times the air-fuel ratio control apparatus for an internal combustion engine performed by simultaneous injection, said feedback control means, predetermined from the time the oxygen concentration sensor output to large shifts from being smaller than the reference value, or changed to the reverse By the proportional term after extended time and updates the air-fuel ratio control amount.
[0008]
According to this configuration, the update timing of the air-fuel ratio control amount based on the proportional term is delayed relative to the change in the output of the oxygen concentration sensor, and the update cycle of the air-fuel ratio control amount becomes longer than before. For this reason, the oxygen storage capacity of the three-way catalyst provided in the exhaust system is effectively utilized, the influence of variations among cylinders is reduced, and a cylinder discrimination sensor for detecting the piston position of a specific cylinder is not provided. By adopting, it is possible to reduce the cost of the internal combustion engine, thereby reducing the cost of the internal combustion engine and improving the exhaust gas characteristics as a whole.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0010]
FIG. 1 is an overall configuration diagram of an internal combustion engine (hereinafter referred to as “engine”) and an air-fuel ratio control device thereof according to an embodiment of the present invention. For example, a throttle is placed in the middle of an intake passage 2 of a three-cylinder engine 1. Valve 3 is arranged. A throttle valve opening (θTH) sensor 4 is connected to the throttle valve 3, and an electric signal corresponding to the opening of the throttle valve 3 is output to output an engine control electronic control unit (hereinafter referred to as “ECU”) 5. To supply.
[0011]
The fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 3 and slightly upstream of the intake valve (not shown) in the intake passage 2, and each injection valve is connected to a fuel pump (not shown). At the same time, it is electrically connected to the ECU 5 and the valve opening time of the fuel injection valve 6 is controlled by a signal from the ECU 5.
[0012]
On the other hand, an intake pipe absolute pressure (PBA) sensor 7 is provided immediately downstream of the throttle valve 3, and the absolute pressure signal converted into an electric signal by the absolute pressure sensor 7 is supplied to the ECU 5. Further, an intake air temperature (TA) sensor 8 is attached downstream thereof, detects the intake air temperature TA, outputs a corresponding electric signal, and supplies it to the ECU 5.
[0013]
An engine water temperature (TW) sensor 9 mounted on the main body of the engine 1 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) TW, outputs a corresponding temperature signal, and supplies it to the ECU 5.
[0014]
An engine speed (NE) sensor 10 is attached around the camshaft or crankshaft (not shown) of the engine 1. The engine speed sensor 10 generates a TDC signal pulse at a crank angle position a predetermined crank angle before the top dead center (TDC) at the start of the intake stroke of each cylinder of the engine 1 (every crank angle 240 ° in a three-cylinder engine). This TDC signal pulse is supplied to the ECU 5.
[0015]
The exhaust pipe 12 is provided with a three-way catalyst 16 for purifying exhaust gas. The three-way catalyst 16 has an oxygen storage capacity, and most effectively reduces HC, CO, and NOx when the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is controlled near the stoichiometric air-fuel ratio. An oxygen concentration sensor (hereinafter referred to as “O2 sensor”) 14 is provided upstream of the three-way catalyst 16, and a detection signal thereof is supplied to the ECU 5.
[0016]
The ECU 5 shapes an input signal waveform from various sensors, corrects the voltage level to a predetermined level, converts an analog signal value into a digital signal value, and the like, and a central processing circuit (hereinafter referred to as “CPU”). 5b, storage means 5c for storing various calculation programs executed by the CPU 5b, calculation results, and the like, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like.
[0017]
The CPU 5b discriminates various engine operating states based on the various engine parameter signals described above, and the fuel synchronized with the TDC signal pulse based on the following equation (1) according to the determined engine operating states. The fuel injection time TOUT of the injection valve 6 is calculated.
[0018]
TOUT = TI × KO2 × K1 + K2 (1)
Here, TI is the basic fuel injection time of the fuel injection valve 6 and is determined according to the engine speed NE and the intake pipe absolute pressure PBA.
[0019]
KO2 is an air-fuel ratio correction coefficient calculated using a proportional term and an integral term as will be described later according to the output VO2 of the O2 sensor 14.
[0020]
K1 and K2 are other correction coefficients and correction variables that are calculated according to various engine parameter signals, respectively, and are predetermined values that can optimize various characteristics such as fuel efficiency characteristics and engine acceleration characteristics according to engine operating conditions. To be determined.
[0021]
The CPU 5b supplies a signal for driving the fuel injection valve 6 to the fuel injection valve 6 through the output circuit 5d based on the fuel injection time TOUT obtained as described above. In the present embodiment, since a configuration in which a cylinder discrimination sensor for detecting the piston position of a specific cylinder is not provided is employed, the CPU 5b cannot detect which stroke each of the three cylinders is in, so that it corresponds to each cylinder. Thus, simultaneous injection is performed to open the provided fuel injection valve 6 at substantially the same time. More specifically, one simultaneous injection is performed every time the TDC signal pulse is generated three times.
[0022]
FIG. 2 is a flowchart of the VO2 inversion determination process, and FIG. 3 is a flowchart of the KO2 calculation process for calculating the air-fuel ratio correction coefficient KO2 in accordance with the flag value set in the inversion determination process. These processes are executed in synchronization with the generation of the TDC signal pulse by the CPU 5b.
[0023]
The VO2 inversion determination process determines the magnitude relationship between the O2 sensor output VO2 and the reference value PVREF, sets a rich flag FPVREF indicating that the air-fuel ratio is richer than the stoichiometric air-fuel ratio, and sets its magnitude In order to update the air-fuel ratio correction coefficient KO2 with the proportional terms PR and PL after a predetermined delay time from the time of inversion of the relationship, the update timing of the air-fuel ratio correction coefficient KO2 with the proportional terms PR and PL is indicated by “1”. This is processing for setting the inversion flag FPO2REV.
[0024]
In step S11 of FIG. 2, it is determined whether or not the O2 sensor output VO2 is larger than a reference value PVREF substantially corresponding to the stoichiometric air-fuel ratio, and when VO2> PVREF and the air-fuel ratio is on the rich side from the stoichiometric air-fuel ratio. Sets the rich flag FPVREF to “1” (step S12), and when VO2 ≦ PVREF and the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the rich flag FPVREF is set to “0” (step S12). S13), the process proceeds to step S14.
[0025]
In step S14, it is determined whether or not the rich flag FPVREF is equal to the previous value, that is, whether or not the magnitude relationship between the O2 sensor output VO2 and the reference value PVREF is the same. If they are the same, the inversion flag FPO2REV is determined. Is set to “0” (step S15), the value of the delay counter CVREF for measuring the predetermined delay time is set to “0” (step S24), and this process is terminated.
[0026]
When the rich flag FPVREF is different from the previous value in step S14, that is, when the magnitude relationship is inverted, the inversion flag FPO2REF is set to “1” (step S16), and then the delay counter CVREF is incremented by “1”. (Step S19).
[0027]
In the following step S20, it is determined whether or not the rich flag FPVREF was “1” last time. If the previous FPVREF = 1, the predetermined count value NVREF is set to the rich side predetermined value NVREFR (step S21). When FPVREF = 0, the predetermined count value NVREF is set to the lean side predetermined value NVREFL (step S22), and the process proceeds to step S23.
[0028]
In step S23, it is determined whether or not the value of the delay counter CVREF is smaller than the predetermined count value NVREF. While CVREF <NVREF, the rich flag FPVREF is returned to the previous value (step S25), and the inversion flag FPO2REF is set to “ The value is returned to “0” (step S26), and this process is terminated.
[0029]
If CVREF = NVREF in step S23, the process proceeds to step S24. That is, in this case, since the rich flag FPVREF is held at the current value and the inversion flag FPO2REF is held at “1”, the air-fuel ratio correction coefficient KO2 is updated by the proportional terms PR and PL as described later. The
[0030]
The processing in FIG. 3 is executed after the processing in FIG. 2 is completed. First, in step S41, it is determined whether or not the inversion flag FPO2REV is “1”, and FPO2REV = 1 and the update timing by the proportional terms PR and PL. If it is, it is determined whether or not the rich flag FPVREF is “1” (step S42). As a result, when FPVREF = 0, the air-fuel ratio correction coefficient KO2 is updated by adding the proportional term PR (step S43). When FPVREF = 1, the air-fuel ratio correction coefficient KO2 is updated by the proportional term PL. It updates by subtracting (step S44), and this process is complete | finished.
[0031]
If FPO2REFV = 0 in step S41, it is determined in step S45 whether the rich flag FPVREF is “1”. If FPVREF = 0, the air-fuel ratio correction coefficient KO2 is set to the integral term IR. The value is updated by addition (step S46). When FPVREF = 1, the air-fuel ratio correction coefficient KO2 is updated by subtracting the integral term IL (step S47), and this process is terminated.
[0032]
FIG. 4 is a time chart for explaining the processing of FIGS. 2 and 3. When the O2 sensor output VO2 falls below the reference value PVREF at time t1, the delay counter CVREF starts incrementing, and the count value is a predetermined count. When the value NVREF is reached (time t2), the rich flag FPVREF is set to “0”, the inversion flag FPO2REF is set to “1”, and the air-fuel ratio correction coefficient KO2 is updated by adding the proportional term PR. The After time t2, updating with the integral term IR is performed, and the value of the air-fuel ratio correction coefficient KO2 gradually increases. Note that the count value of the delay counter CVREF and the inversion flag FPO2REV are immediately returned to “0”.
[0033]
At time t3, since the O2 sensor output VO2 exceeds the reference value PVREF, the delay counter CVREF starts incrementing. When the count value reaches the predetermined count value NVREF (time t4), the rich flag FPVREF is set to “1”. In addition, the inversion flag FPO2REV is set to “1”, and the air-fuel ratio correction coefficient KO2 is updated by subtracting the proportional term PL. After time t4, updating is performed with the integral term IL, and the value of the air-fuel ratio correction coefficient KO2 gradually decreases. Thereafter, the calculation of the air-fuel ratio correction coefficient KO2 is similarly performed. In the illustrated example, the operation when both the rich side predetermined value NVREFR and the lean side predetermined value NVREFL are set to values corresponding to 10 TDC (period in which the TDC signal pulse is generated 10 times) is shown.
[0034]
As described above, in this embodiment, the predetermined count value NVREF is set to a relatively large value in order to prevent deterioration of exhaust gas characteristics due to simultaneous injection. Thereby, the period in which the air-fuel ratio is continuously controlled to the rich side from the stoichiometric air-fuel ratio and the period in which the air-fuel ratio is continuously controlled to the lean side from the stoichiometric air-fuel ratio become longer, that is, the control cycle of the air-fuel ratio becomes longer. The oxygen storage capacity of the three-way catalyst 16 can be fully utilized, and the exhaust gas characteristics can be improved, more specifically, the NOx emission amount can be reduced.
[0035]
FIG. 5 is a diagram showing experimental results when the predetermined count value NVREF is changed. FIGS. 5A, 5B, and 5C show the CO, HC, and NOx emission amounts (downstream of the three-way catalyst 16, respectively). Side). In this experiment result, the rich side predetermined value NVREFR and the lean side predetermined value NVREFL are set to the same value.
[0036]
As is apparent from this figure, even if the predetermined count value NVREF is increased, the CO and HC emission amounts hardly change, but the NOx emission amount is greatly improved when the predetermined count value NVREF is increased. This is considered to be because the oxygen storage capacity of the three-way catalyst 16 is fully utilized, and the influence of variation among cylinders due to simultaneous injection is reduced. According to this experimental example, the predetermined count value NVREF is desirably set to 5 or more. However, if the predetermined count value NVREF is excessively increased, the engine output fluctuates due to the change in the air-fuel ratio and deteriorates the operability of the engine. Therefore, it is necessary to make the range within which the operability is not deteriorated (for example, about 15 TDC or less). is there.
[0037]
In the present embodiment, the feedback control means and the simultaneous injection control means are constituted by the CPU 5b of the ECU 5, more specifically, the processing of FIGS. 2 and 3 corresponds to the feedback control means, and the air-fuel ratio correction coefficient KO2 is the air-fuel ratio. It corresponds to the control amount, and the predetermined count value NVREF corresponds to the predetermined delay time.
[0038]
The present invention is not limited to the embodiment described above, and various modifications can be made. For example, the “predetermined delay time” described in the claims may be measured using a timer that measures the actual time, without using the counter CVREF.
[0039]
Further, in the above-described embodiment, the operation example (FIG. 4) in which the rich side predetermined value NVREFR corresponding to the “predetermined delay time” and the lean side predetermined value NVREFL are the same value is shown. A different value may be set in response to this, and the rich side predetermined value NVREFR applied when the O2 sensor output shifts from the rich side to the lean side of the reference value PVREF, or the O2 sensor output is lean of the reference value PVREF. One of the lean side predetermined values NVREFL applied when shifting from the rich side to the rich side is set to “0”, and the O2 sensor output shifts from the rich side to the lean side of the reference value PVREF, or the O2 sensor output is the reference Only when one of the values PVREF shifts from the lean side to the rich side, the air-fuel ratio correction coefficient KO2 is changed. It may be to delay.
[0040]
Further, the number of cylinders of the engine is not limited to three, and may be four or five.
[0041]
【The invention's effect】
As described above in detail, according to the present invention, the update timing of the air-fuel ratio control amount by the proportional term is relatively delayed with respect to the change in the oxygen concentration sensor output, and the update cycle of the air-fuel ratio control amount is longer than before. Become. For this reason, the oxygen storage capacity of the three-way catalyst provided in the exhaust system is effectively utilized, the influence of variations among cylinders is reduced, and a cylinder discrimination sensor for detecting the piston position of a specific cylinder is not provided. By adopting, it is possible to reduce the cost of the internal combustion engine, thereby reducing the cost of the internal combustion engine and improving the exhaust gas characteristics as a whole.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an internal combustion engine and an air-fuel ratio control device thereof according to an embodiment of the present invention.
FIG. 2 is a flowchart of a process for setting a flag used in the process of FIG. 3 in accordance with an oxygen concentration sensor output.
FIG. 3 is a flowchart of an air-fuel ratio correction coefficient (KO2) calculation process.
FIG. 4 is a time chart for explaining the processing of FIGS. 2 and 3;
FIG. 5 is a diagram for explaining the effect of the present invention.
[Explanation of symbols]
1 Internal combustion engine 2 Intake passage 5 Electronic control unit (feedback control means, simultaneous injection control means)
6 Fuel injection valve 12 Exhaust pipe 14 Oxygen concentration sensor 16 Three-way catalyst

Claims (1)

An oxygen concentration sensor provided in an exhaust system of an internal combustion engine having a plurality of cylinders; a plurality of fuel injection valves provided for each of the cylinders for injecting fuel into an intake passage of the engine; and an output of the oxygen concentration sensor; Feedback control means for calculating an air-fuel ratio control amount using a proportional term and an integral term according to a comparison result with a reference value, and calculating a valve opening time of the fuel injection valve based on the air-fuel ratio control amount; and the calculation An air-fuel ratio control device for an internal combustion engine, which comprises a simultaneous injection control means for opening the plurality of fuel injection valves at substantially the same time over the valve opening time, and performs fuel supply by simultaneous simultaneous injection ,
The feedback control means updates the air-fuel ratio control amount by the proportional term after a lapse of a predetermined delay time from the time when the oxygen concentration sensor output changes from a state smaller than the reference value to a larger state or vice versa. An air-fuel ratio control apparatus for an internal combustion engine characterized by the above.

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