JP7474207B2 - Air-fuel ratio control device - Google Patents

Description

The present invention relates to an air-fuel ratio control device that controls the air-fuel ratio in an internal combustion engine based on the oxygen concentration in the exhaust gas.

It is known that feedback control of the air-fuel ratio in the internal combustion process of an internal combustion engine is performed based on the air-fuel ratio obtained from the output information of an oxygen sensor provided in contact with the exhaust gas of the internal combustion engine (see, for example, Patent Document 1).

In the technology of Patent Document 1, a resistance-type oxygen sensor that detects oxygen based on the internal resistance of the detection section is used as the oxygen sensor. In this oxygen sensor, a first value indicating the oxygen content in the exhaust gas is determined based on the resistance of the detection section of the oxygen sensor. Also, a second value indicating the temperature of the oxygen sensor is determined based on the resistance of the heater portion of the oxygen sensor. Then, the air-fuel ratio as a function of the first value and the second value is determined as a third value.

According to this technology, the function for determining the third value includes a second value that affects the first value in real time, so the air-fuel ratio can be detected with high accuracy even if the output characteristics of the oxygen sensor change due to the temperature of the sensor.

U.S. Pat. No. 8,959,987

However, according to the technology of Patent Document 1, the air-fuel ratio is calculated based on the resistance value of the detection section of the oxygen sensor and the resistance value of the heater section. Therefore, if the resistance values vary due to manufacturing tolerances or changes over time, the air-fuel ratio obtained based on these may vary significantly. Accordingly, the accuracy of the air-fuel ratio feedback control may also be significantly reduced.

In view of the problems with the conventional technology, the object of the present invention is to provide an air-fuel ratio control device that can perform accurate air-fuel ratio feedback control regardless of variations in the resistance values of the oxygen sensors due to manufacturing tolerances and changes over time.

The air-fuel ratio control device of the present invention comprises:
a resistance-type oxygen sensor provided in contact with exhaust gas from an internal combustion engine having exhaust pulsation, the resistance-type oxygen sensor having a detection section whose resistance value changes in a substantially stepped manner at an oxygen concentration near the stoichiometric value of the exhaust gas, the detection value determined from the resistance value of the detection section exhibiting a pulse waveform having a peak value corresponding to the temperature of the detection section and the exhaust pulsation;
A temperature reading unit that estimates or detects the temperature of the detection unit;
an excess ratio calculation unit that calculates an excess air ratio by referring to a data map that indicates a correspondence relationship between a plurality of excess air ratio values and a plurality of first scale values for the temperature and a plurality of second scale values for the detection value,
An air-fuel ratio control device that performs air-fuel ratio feedback control based on a deviation between the air excess ratio and a target air excess ratio,
a storage unit that stores the data map and a lookup table that indicates a rich side threshold value and a lean side threshold value for determining whether the detected value corresponds to any one of a rich region, a stoichiometric region, and a lean region, in correspondence with the first scale value;
a characteristic checking unit that sets the target excess air ratio to a value close to the stoichiometric value, acquires a peak value of the detection value, and checks whether the peak value falls within any of the air-fuel ratio regions;
The present invention is characterized in that it includes a calibration unit that calibrates the data map and the look-up table in an affine transformation manner so that the crest value corresponds to the rich side threshold value and the lean side threshold value through the inspection.

In this configuration, the detection value of the detection section of the oxygen sensor is a pulse wave shape with a wave height value that responds to the exhaust pulsation of the internal combustion engine. In addition, the temperature of the detection section of the oxygen sensor affects the wave height. For example, at low temperatures (below 100 degC), the wave height is almost zero (oxygen sensor inactive).

In the present invention, the air-fuel ratio (excess air ratio) is calculated via a data map that shows a correspondence between multiple excess air ratio values and the resistance value (sensor voltage value) of the detection section of the oxygen sensor related to the detection value and the temperature value of the detection section obtained from the resistance value of the heater section. Therefore, if the resistance value of the detection section or the resistance value of the heater section varies, the excess air ratio obtained based on these resistance values will also be inaccurate, which may hinder proper air-fuel ratio feedback control.

Therefore, in the present invention, in order to ensure that the correspondence between the detection value and temperature in the data map exhibits an appropriate relationship for calculating an accurate air excess ratio, the target air excess ratio is set near stoichiometric and the peak of the detection value actually measured by the oxygen sensor is compared with the rich side and lean side thresholds which show standard (median) peak values, and based on the results of the inspection, the first and second scale values of the data map and the rich side and lean side thresholds of the lookup table which provide a correspondence such that the peak values of the actually measured detection value match the rich side and lean side thresholds (the peaks of the peaks overlap the thresholds) are determined by affine transformation, and thus the data map and lookup table are calibrated.

Therefore, according to the present invention, by calculating the excess air ratio using a data map and a lookup table calibrated to correspond to the variation in each resistance value, an accurate excess air ratio can be calculated and appropriate air-fuel ratio feedback control can be performed regardless of the variation in each resistance value of the oxygen sensor.

In the present invention, the characteristic inspection unit includes a temperature difference confirmation unit that acquires the deviation of the temperature of the detection unit from a reference value when a predetermined time has elapsed during which the temperature of the detection unit converges to the ambient temperature of the detection unit while the internal combustion engine is stopped, and a value obtained by correcting the temperature of the detection unit based on the deviation may be used as the detection unit temperature for control used in the inspection and the excess rate calculation unit.

With this, once a predetermined time has elapsed for the temperature of the detection section, which has been heated once, to converge to the ambient temperature of the oxygen concentration sensor, control is performed based on the detection section temperature for control, which has been corrected based on the deviation from the reference value, allowing for more accurate air-fuel ratio feedback control.

In this case, the characteristic inspection unit may include a voltage difference confirmation unit that acquires the deviation between the lean side threshold value and the average value of the detection value obtained from the resistance value of the detection unit within a predetermined time when the temperature of the detection unit for control is equal to or lower than a predetermined value, and may use a value obtained by correcting the detection value obtained from the resistance value based on the deviation as the detection value for control used in the inspection and the excess rate calculation unit.

With this, when the detection temperature is below a sufficiently low predetermined value, i.e. when the oxygen concentration sensor is inactive and the voltage indicating the detection value does not change, the deviation from the lean threshold is calculated, and control is performed based on the detection value for control that is corrected based on this deviation, allowing for more accurate air-fuel ratio feedback control.

In this case, a first calibration magnification value for calibrating the data map and the lookup table by enlarging or reducing the multiple first scale values is stored, and when a peak of a wave height close to the lean side threshold among the wave heights of the detection values for control that change over time is compared with the lean side threshold, if the peak is in the lean region, the first calibration magnification value may be increased, and if the peak is in the stoichiometric region, the first calibration magnification value may be decreased.

By doing this, the peak of the wave height close to the lean side threshold of the detected value approaches the lean side threshold, so the data map and lookup table can be calibrated so that the lean side wave height value corresponds to the lean side threshold.

In the present invention, the calibration unit has a second calibration multiplier value for calibrating the data map and the lookup table by multiplying the second scale values, the rich side threshold value, and the lean side threshold value, and may increase the second calibration multiplier value when the peak of the wave height of the detection value for control that changes over time and is close to the rich side threshold value is in the rich region, and decrease the second calibration multiplier value when the peak is in the stoichiometric region.

By doing this, the peak of the wave height close to the rich side threshold of the detected value approaches the rich side threshold, so the data map and lookup table can be calibrated so that the rich side wave height value corresponds to the rich side threshold.

1 is a schematic diagram showing a configuration of a main part of an internal combustion engine equipped with an air-fuel ratio control device according to an embodiment of the present invention; 2 is a block diagram showing a main configuration of an ECU of the internal combustion engine of FIG. 1 . 3 is a flowchart showing an excess ratio calculation process for calculating an air excess ratio by an excess ratio calculation unit in the ECU of FIG. 2 . 4 is a graph showing how an excess air ratio in a stoichiometric region is calculated in the process of FIG. 3 . 4 is a diagram showing a graph corresponding to a lookup table for determining a lean side threshold value LREF and a rich side threshold value RREF in the process of FIG. 3, and a data map for calculating an excess air ratio. FIG. 4 is a graph showing a schematic diagram of a change in an excess air ratio λ calculated by the process of FIG. 3 . 4 is a waveform diagram showing a voltage waveform indicating a change in a voltage value output by a voltage calculation unit over time obtained while driving a vehicle equipped with an internal combustion engine. FIG. 3A to 3D are diagrams illustrating an example of inspection by a characteristic inspection unit and calibration by a calibration unit in the configuration of FIG. 2.

The following describes an embodiment of the present invention with reference to the drawings. Figure 1 shows the configuration of the main parts of a four-stroke internal combustion engine equipped with an air-fuel ratio control device according to one embodiment of the present invention. This air-fuel ratio control device has a function of performing air-fuel ratio feedback control based on the deviation between an excess air ratio obtained based on the oxygen concentration in the exhaust gas of the internal combustion engine and a target excess air ratio.

As shown in the figure, the engine body 1 of this internal combustion engine is equipped with an intake pipe 2 provided at the intake port, and a throttle valve 3 provided within the intake pipe 2 to adjust the amount of intake air supplied to the intake port from an air cleaner 4 according to the opening degree.

The throttle valve 3 is provided with a throttle sensor 5 that detects the opening of the throttle valve 3. A fuel injection valve 6 that injects fuel is provided near the intake port of the intake pipe 2. Fuel is pumped from a fuel tank (not shown) to the fuel injection valve 6 by a fuel pump.

The intake pipe 2 is provided with an intake pressure sensor 7 that detects the intake pressure in the intake pipe 2 and an intake air temperature sensor 8 that detects the temperature of the intake air in the intake pipe 2. The exhaust pipe 10 connected to the exhaust port of the engine body 1 is provided with a catalyst 11 that reduces unburned components in the exhaust of the exhaust pipe 10 and an oxygen sensor 12 that detects the oxygen concentration in the exhaust.

An ignition plug 13 connected to an ignition device 14 is fixed to the engine body 1. When an ECU (electronic control unit) 15 issues an ignition timing command to the ignition device 14, a spark discharge occurs in the cylinder combustion chamber of the engine body 1.

The ECU 15 receives analog voltages indicating the detection values of the throttle sensor 5, intake pressure sensor 7, intake air temperature sensor 8, oxygen sensor 12, coolant temperature sensor 17, and atmospheric pressure sensor 20 that detects atmospheric pressure. The fuel injection valve 6 is also connected to the ECU 15.

The ECU 15 also receives a signal indicating the rotational angle position of the crankshaft 18 from a crank angle sensor 19. That is, the crank angle sensor 19 magnetically or optically detects multiple protrusions provided at predetermined angles (e.g., 15 degrees) on the outer periphery of a rotor 19a that rotates in conjunction with the crankshaft 18, using a pickup 19b located near the outer periphery of the rotor 19a, and generates a pulse (crank signal) from the pickup 19b every time the crankshaft 18 rotates by the predetermined angle.

Specifically, the crank angle sensor 19 outputs a signal indicating the reference angle to the ECU 15 each time the piston 9 reaches top dead center or each time the crankshaft 18 rotates 360 degrees.

Figure 2 shows the main components of the ECU 15. As shown in the figure, the oxygen sensor 12, which supplies the ECU 15 with a detection signal of the oxygen concentration in the exhaust, includes a sensor element 12a as a detector that is disposed in contact with the exhaust of an internal combustion engine having exhaust pulsation and detects the oxygen concentration in the exhaust, and a sensor heater 12b that is adjacent to the sensor element 12a and heats the sensor element 12a.

The sensor element 12a has a resistance value that changes in an approximately step-like manner when the exhaust gas from the internal combustion engine has an oxygen concentration close to stoichiometric, and the detection value obtained from the resistance value exhibits a pulse waveform having a peak value according to the temperature of the sensor element 12a and the exhaust pulsation. In this embodiment, the sensor element 12a is a titania-type sensor element, which is a resistive oxygen sensor whose resistance value changes according to the oxygen concentration.

The ECU 15 includes a heater controller 22 that controls the sensor heater 12b, a temperature calculation unit 23 that serves as a temperature reading unit that calculates a temperature value T that indicates the temperature of the sensor element 12a, and a voltage calculation unit 24 that converts the output signal of the sensor element 12a into a voltage value VHG that is a detection value that indicates the oxygen concentration in the exhaust gas.

The heater controller 22 controls the temperature of the sensor heater 12b by controlling the amount of current I supplied to the sensor heater 12b from a power source (storage battery) (not shown) by pulse width modulation (PWM) control by the ECU 15. The temperature calculation unit 23 calculates the temperature value T by, for example, reading the heater voltage and the amount of current I applied to the sensor heater 12b with the ECU 15 to obtain the resistance value of the sensor heater 12b, and converting the resistance value using table data or a formula that indicates the correspondence between the heater resistance value and the temperature value T, which is prepared in advance in the ECU 15. The calculation results in the temperature calculation unit 23 and the voltage calculation unit 24 are supplied to a substitute value calculation unit 26 of the excess rate calculation unit 25, which will be described later.

The ECU 15 also includes a rotation speed calculation unit 27 that calculates the rotation speed NE and angular speed NETC of the internal combustion engine based on the detection results of the crank angle sensor 19, and an excess ratio calculation unit 25 that calculates an air excess ratio λ based on the temperature value T from the temperature calculation unit 23, the voltage value VHG from the voltage calculation unit 24, and the angular speed NETC from the rotation speed calculation unit 27.

The ECU 15 further includes a target value calculation unit 28 that calculates the target excess air ratio λcmd based on an estimated value of the amount of oxygen stored in the catalyst 11, a basic injection amount calculation unit 29 that calculates a basic injection amount BJ based on the rotation speed NE from the rotation speed calculation unit 27 and the pressure PM in the intake pipe 2 from the intake pressure sensor 7, a feedback coefficient calculation unit 30 that determines a feedback coefficient k for correcting the basic fuel injection amount BJ calculated by the basic injection amount calculation unit 29 so that the excess air ratio λ calculated by the excess ratio calculation unit 25 matches the target excess air ratio λcmd, and an injection amount calculation unit 31 that calculates the injection amount Ti based on the feedback coefficient k and the basic injection amount BJ and operates the fuel injection valve 6.

In the feedback coefficient calculation unit 30, PID control is performed based on the deviation between the air excess ratio λ and the target air excess ratio λcmd, and the feedback coefficient k is calculated. Based on the injection amount Ti calculated by the injection amount calculation unit 31 based on the feedback coefficient k and the basic injection amount BJ, the fuel injection valve 6 is opened for a corresponding time. Thus, an amount of fuel according to the feedback coefficient k of the PID control based on the comparison between the air excess ratio λ and the target air excess ratio λcmd is injected into the cylinder combustion chamber of the engine body 1.

The excess ratio calculation unit 25 calculates the air excess ratio λ of the exhaust gas using data LD obtained by linearly converting the voltage value VHG with respect to the air excess ratio while compensating for its temperature characteristics, based on the voltage value VHG from the temperature calculation unit 23 and the temperature value T from the temperature calculation unit 23. However, as described below, this calculation is applied when the voltage value VHG is equal to or less than the lean side threshold value LREF, and when the voltage value VHG is greater than the lean side threshold value LREF, the air excess ratio λ is calculated by a different method.

The excess ratio calculation unit 25 includes a torque calculation unit 32 that calculates the torque value TQ of the internal combustion engine based on the crank angular velocity NETC of the internal combustion engine, a limit threshold setting unit 33 that sets the conversion limit threshold for the above-mentioned linearization conversion, a memory unit 34 that stores data required to calculate the alternative value R of the air excess ratio λ, as well as a data map and a lookup table described below, and an alternative value calculation unit 26 that calculates the alternative value R.

The limit threshold setting unit 33 sets the conversion limit thresholds, ie, the lean side threshold LREF, which is the lean side conversion limit range value, and the rich side threshold RREF, which is the rich side conversion limit threshold value, for the voltage value VHG from the voltage calculation unit 24. However, with the titania type sensor element 12a, when the temperature changes, the dynamic range of the output value (the minimum and maximum values of the linear region of the sensor output voltage) changes, so it is necessary to change the conversion limit thresholds according to the temperature value T from the temperature calculation unit 23.

Referring also to FIG. 5, FIG. 5 shows a data map having a first scale value G1 in the horizontal direction in FIG. 5 corresponding to the temperature value T calculated by the temperature calculation unit 23, and a second scale value G2 in the vertical direction in FIG. 5 corresponding to the voltage value VHG calculated by the voltage calculation unit 24, and in which the numerical values of a plurality of the data LD are set in correspondence with the voltage value VHG and the temperature value T as coordinates, and further shows examples of lookup tables corresponding to the graphs 35, 36 for determining the lean side threshold value LREF and the rich side threshold value RREF, each superimposed on the data map.

That is, the data map shows multiple excess air ratio values in correspondence with multiple first scale values G1 for the temperature value T and multiple second scale values G2 for the voltage value VHG (detected value). The lookup table shows the rich side threshold value RREF and the lean side threshold value LREF in correspondence with the first scale value G1 to determine whether the voltage value VHG falls into the rich region, the stoichiometric region, or the lean region.

By storing such a data map and a lookup table corresponding to the graphs 35 and 36 in advance in the memory unit 34 in the ECU 15, these can be used to easily obtain and set the data LD obtained by linearizing the voltage value VHG, the lean side threshold value LREF, and the rich side threshold value RREF.

Graph 35 is a graph in which, for example, the excess air ratio λ as the boundary between the lean region and the stoichiometric region is set to 1.02, a plurality of points are found on the data map with the voltage value VHG and temperature value T as coordinates for this value, and these plurality of points are connected by linear interpolation. Graph 36 is a graph in which, for example, the excess air ratio λ as the boundary between the lean region and the stoichiometric region is set to 0.98, a plurality of points are found on the data map with the voltage value VHG and temperature value T as coordinates for this value, and these plurality of points are connected by linear interpolation.

For example, from the lookup table corresponding to graph 35, when the temperature value T from the temperature calculation unit 23 is t0, the limit threshold setting unit 33 can set the voltage value v0 derived from the coordinate t0 as the lean side threshold LREF for the boundary between the lean region and the stoichiometric region. Similarly, from the lookup table corresponding to graph 36, when the temperature value T from the temperature calculation unit 23 is t0, the limit threshold setting unit 33 can set the voltage value v1 derived from the coordinate t0 as the rich side threshold RREF for the boundary between the stoichiometric region and the rich region.

In addition, when the voltage value VHG from the voltage calculation unit 24 is equal to or lower than the conversion limit threshold value LREF, the memory unit 34 stores the execution time Ti1 of the fuel injection by the fuel injection valve 6, the torque value TQ1, and the air excess ratio λb related to the conversion limit threshold value LREF as data necessary for calculating the replacement value R.

When the voltage value VHG exceeds the conversion limit threshold value LREF, the substitute value calculation unit 26 calculates a substitute value R by the following equation (1), using the execution time of the previous fuel injection as Ti2 and the previous torque value as TQ2.
R = ((Ti1 ÷ Ti2) ÷ (TQ1 ÷ TQ2)) × λb (1)

Then, when the voltage value VHG exceeds the conversion limit threshold LREF, the excess ratio calculation unit 25 regards the alternative value R as the exhaust excess air ratio λ instead of the air excess ratio λ as the linearized converted data LD described above.

Figure 3 shows the excess ratio (lambda) calculation process for calculating the air excess ratio λ in the excess ratio calculation unit 25. Note that the control by the ECU 15, including this excess ratio calculation process, is executed in synchronization with the stroke of the internal combustion engine based on a pulse signal indicating the rotational angle position of the crankshaft 18 from the crank angle sensor 19.

When the excess rate calculation process is started, in step S1, the torque calculation unit 32 calculates the torque TQ of the internal combustion engine based on the crank angular speed NETC from the rotation speed calculation unit 27.

When calculating torque TQ, two angular velocities of the crankshaft of the internal combustion engine, which correspond to two successive strokes of the internal combustion engine having intake, compression, combustion and expansion, and exhaust strokes, are calculated, and the torque generated by the internal combustion engine is calculated with high accuracy based on these (see Patent Publication No. 6254633).

Next, in step S2, the limit threshold setting unit 33 sets the lean side threshold LREF and the rich side threshold RREF based on the temperature value T from the temperature calculation unit 23 using lookup tables corresponding to the graphs 35 and 36 in FIG. 5.

Next, in step S3, the voltage value VHG is obtained from the voltage calculation unit 24, and the voltage value VHG is corrected by the deviation VD obtained by the voltage difference confirmation unit 43 described later to set the control voltage value (detection value) VHGcon.

Next, in step S4, the above-mentioned data map (Figure 5) is scanned based on the temperature value T obtained in step S2 and the voltage value VHGcon obtained in step S3, and thus data LD is obtained in which the voltage value VHGcon is linearly converted to the air excess factor λ while compensating for its temperature characteristics.

Next, in step S5, it is determined whether the voltage value VHGcon acquired in step S3 is smaller than the rich side threshold value RREF set in step S2. If it is determined that it is smaller, in the following step S6, the flag F_DETECT is set to zero, and the process proceeds to step S16, where the value of the data LD is set as the air ratio excess ratio λ value LAMBDA, and the excess ratio calculation process in FIG. 3 is terminated.

If it is determined in step S5 that the voltage value VHGcon is not less than the rich side threshold value RREF, it is determined in step S7 whether the voltage value VHGcon obtained in step S3 is greater than the lean side threshold value LREF set in step S2.

If it is determined in step S7 that the voltage value VHGcon is not large, in step S8, the air excess ratio λ is calculated as data LD obtained by linearizing the voltage value VHG from the voltage calculation unit 24 with respect to the air excess ratio while compensating for the temperature characteristics of the oxygen sensor 12, based on the voltage value lref of the lean side threshold LREF and the voltage value rref of the rich side threshold RREF obtained in step S2, the air excess ratio λ value (in this embodiment, λ = 1.02) as the boundary between the predetermined stoichiometric region and the lean region corresponding to the voltage value lref, the air excess ratio λ value (in this embodiment, λ = 0.98) as the boundary between the predetermined rich region and the stoichiometric region corresponding to the voltage value rref, and the voltage value VHG obtained in step S3, and proceeds to step S9.

4, if the air excess factor λ as the linearized converted data LD in step S8 is a variable #LLMD (e.g., 1.02) that can be set in advance as a numerical value of the air excess factor λ as the boundary between the predetermined stoichiometric region and the lean region, and a variable #RLMD (e.g., 0.98) that can be set in advance as a numerical value of the air excess factor λ as the boundary between the predetermined rich region and the stoichiometric region, then it can be expressed by a graph as shown in Fig. 4. In the graph, the horizontal axis in the left-right direction in Fig. 4 represents the voltage value VHG, and the vertical axis in the up-down direction in Fig. 4 represents the air excess factor λ. Therefore, for example, when the voltage value VHG is vhg1, the value λ1 of the corresponding air excess factor λ can be calculated by the following equation (2).
λ1=(((vhg1-rref)÷(lref-rref))×(#LLMD-#RLMD))＋＃RLMD (2)

In step S9, the execution time Ti of the most recent fuel injection by the fuel injection valve 6 and the torque TQ calculated in step S1 are set as Ti1 and TQ1, respectively, and the air excess ratio λ related to the lean side threshold LREF is stored as λb in the memory unit 34. Almost simultaneously, the countdown timer value TIMER indicating the effective time of the storage is reset to its predetermined initial value #TMINT. Next, the flag F_DETECT is set to 1 and the process proceeds to step S16, where the value of the data LD acquired in step S8 above is set as the air excess ratio λ value LAMBDA, and the excess ratio calculation process in FIG. 3 is terminated.

At this time, the value of the data LD acquired in step S8 is stored as λb. At this time, it is preferable to store the moving average of the values of the data LD as λb. For example, the exponential moving average λa of the air excess factor λ (data LD) calculated by the following formula (3) is stored as λb.
λa=LD×k1+λab×(1−k1) (3)

Here, k1 is the moving average coefficient, and λab is the moving average value in the previous control cycle stored in the memory unit 34. For example, 0.34 is used as the moving average coefficient k1.

At this time, it is preferable that the storage unit 34 stores moving average values as the fuel injection execution time Ti1 and the torque value TQ1, respectively. For example, an exponential moving average TiFLT of the fuel injection execution time Ti is calculated using the following equation (4) and stored as Ti1, and an exponential moving average TQFLT of the torque value TQ is calculated using the following equation (5) and stored as TQ1.
TiFLT = Ti × k2 + TiFLTb × (1-k2) (4)
TQFLT = TQ × k3 + TQFLTb × (1-k3) (5)

Here, k2 and k3 are moving average coefficients, and TiFLTb and TQFLTb are moving average values in the previous control cycle stored in the memory unit 34. In this embodiment, different values can be used as the moving average coefficients k1, k2, and k3.

Next, in step S7, if it is determined that the voltage value VHGcon acquired in step S3 is greater than the lean side threshold value LREF, then in step S10, it is determined whether the countdown timer value TIMER described above has reached zero. If TIMER has reached zero, then the flag F_DETECT is reset to 0 (step S11).

Next, the process proceeds to step S12, where it is determined whether the flag F_DETECT = 1. If F_DETECT = 1, this indicates that the air excess ratio λb related to the lean side threshold LREF, the fuel injection execution time Ti1, and the torque value TQ1 are stored in the memory unit 34, so the process proceeds to step S13, where the alternative value calculation unit 26 calculates the alternative value R using the above-mentioned formula (1), and sets the value of the data LD to the alternative value R.

Next, in step S14, it is determined whether the value of data LD set in step S13 is greater than a predetermined upper limit value #LLMT. If the value of data LD set in step S13 is greater than the upper limit value #LLMT, the value of data LD is set to the upper limit value #LLMT (step S15). In this case, the upper limit value #LLMT can be, for example, 1.25.

If F_DETECT = 0 in step S12, this indicates that no valid values for the air excess ratio λb related to the lean side threshold LREF, the fuel injection execution time Ti1, and the torque value TQ1 are stored in the memory unit 34, and therefore the alternative value R cannot be calculated. In this case, the value of data LD is also set to the upper limit value #LLMT (step S15).

Then, the value of data LD set in step S13 or step S15 is set as the air excess ratio λ value LAMBDA (step S16), thereby completing the excess ratio calculation process in FIG. 3.

When the excess ratio calculation process of FIG. 3 is completed, the ECU 15 controls the amount of fuel injected by the fuel injection valve 6 by PID control of the feedback coefficient calculation unit 30 so that the air excess ratio λ value LAMBDA calculated in the excess ratio calculation process of FIG. 3 coincides with the target air excess ratio λcmd from the target value calculation unit 28, as described above.

Figure 6 is a graph that shows a schematic diagram of the change in the air excess ratio λ value LAMBDA calculated by the excess ratio calculation process in Figure 3. The horizontal axis of the graph is a value indicating the passage of time, and the vertical axis is the air excess ratio λ.

Graph 37 in FIG. 6 shows the change in the numerical value of the air excess ratio λ when the actual exhaust air excess ratio λ is gradually increased at a constant rate of change in the range from the left end to near the center of the horizontal axis in the left-right direction in FIG. 6, and then gradually decreased at a constant rate of change in the range from near the center to the right end of the horizontal axis, and the air excess ratio λ is calculated using data obtained by directly linearizing the voltage value VHG read by the voltage calculation unit 24 of the ECU 15 while compensating for its temperature characteristics.

Graph 38 similarly shows the change in the air excess ratio λ value when the actual exhaust air excess ratio λ is gradually increased or decreased at a constant rate from the left end to the right end of the horizontal axis. When the voltage value VHG from the voltage calculation unit 24 is equal to or less than the voltage value lref of the lean side range value LREF, the air excess ratio λ value is calculated using the data obtained by directly linearizing the voltage value VHG using the above-mentioned data map (FIG. 5) or formula (2). However, when the voltage value VHG from the voltage calculation unit 24 exceeds the voltage value lref of the lean side range value LREF (corresponding to the air excess ratio λ value of 1.020), the data obtained by linearizing the voltage value VHG is replaced with the alternative value R obtained by the above-mentioned formula (1) and the air excess ratio λ value is shown.

Thus, when the actual exhaust air excess ratio λ is 1.020 or less, the voltage value VHG from the voltage calculation unit 24 responding thereto changes proportionally (linearly) to the actual exhaust air excess ratio λ, so that when the actual exhaust air excess ratio λ is 1.020 or less, both graphs 37 and 38 move linearly following the above-mentioned constant change in the actual exhaust air excess ratio λ, but when the exhaust air excess ratio λ exceeds 1.020, the voltage value VHG, which exhibits nonlinearity under that condition, changes sharply in the increasing direction, so that graph 37, which shows the air excess ratio λ value based on data obtained by directly linearizing the voltage value VHG, also changes sharply and nonlinearly in the increasing direction. On the other hand, in graph 38, even when the exhaust air excess ratio λ exceeds 1.020 (the above #LLMD), the air excess ratio λ value LAMBDA changes linearly with the exhaust air excess ratio λ (air-fuel ratio) and is linked to the actual exhaust air excess ratio λ.

Therefore, when the voltage value VHG is equal to or less than the lean threshold value LREF, the excess air ratio λ is calculated using the linearized data described above by the excess air ratio calculation process, and when the voltage value VHG exceeds the lean threshold value LREF, the excess air ratio λ is calculated using the above-mentioned formula (1) (graph 38). This means that the excess air ratio calculation unit 25 can supply the feedback coefficient calculation unit 30 with an air excess ratio λ value that changes in conjunction with and proportional to the actual exhaust air excess ratio λ over the entire range of the graph in FIG. 6. This prevents the feedback coefficient calculation unit 30 from interrupting PID control.

However, if the resistance values of the sensor element 12a (detection section) and the sensor heater 12b (heater section) vary due to manufacturing tolerances, etc., the excess air ratio obtained based on these resistance values will also be inaccurate, which may cause problems with air-fuel ratio feedback control.

Therefore, the excess rate calculation unit 25 includes a characteristic inspection unit 40 that inspects the characteristics of the voltage value VHG (detection value) that changes according to the variation in the resistance value, and a calibration unit 41 that calibrates the above-mentioned data map and lookup table based on the inspection results.

The characteristic inspection unit 40 has a temperature difference confirmation unit 42 that confirms the deviation TD of the temperature T from the reference value and sets the control temperature Tcon, and a voltage difference confirmation unit 43 that confirms the deviation VD between the average value VHGSTD of the voltage value VHG of the sensor element 12a within a predetermined time and the lean side threshold value LREF and sets the control voltage value (detection value) VHGcon, and is configured to check the output characteristics of the oxygen concentration sensor 12 connected to the ECU 15 according to the set control temperature Tcon and control voltage value (detection value) VHGcon.

The temperature difference confirmation unit 42 acquires the deviation TD of the temperature T from the reference value when a predetermined time has elapsed for the temperature T of the sensor element 12a to converge to the ambient temperature of the sensor element 12a while the internal combustion engine is stopped. The temperature difference confirmation unit 42 then sets a value Tcon (Tcon = T + TD in this embodiment) obtained by correcting the temperature T of the sensor element 12a based on the deviation TD as a control temperature used in checking the characteristics of the voltage value VHG and in the excess rate calculation unit 25.

The reference value Tref for setting the above temperature Tcon can be obtained, for example, by adding the engine temperature obtained by the cooling water temperature sensor 17 to the intake air temperature obtained by the intake air temperature sensor 8 and dividing the result by 2 {Tref = (engine temperature + intake air temperature) ÷ 2}. This reduces the effects of quantization errors in the readings of the cooling water temperature sensor 17 and the intake air temperature sensor 8, allowing the above control temperature Tcon to be set with high accuracy.

In this case, the control temperature Tcon is set to be the same as the engine temperature and intake air temperature at room temperature before starting. Thus, the temperature difference confirmation unit 42 essentially translates the lookup table corresponding to the above data map and graphs 35 and 36 in the left-right direction (the direction of the first scale value G1) in FIG. 5.

Next, when the control temperature Tcon of the sensor element 12a is equal to or lower than a predetermined value (e.g., equal to the reference value Tref), the voltage difference confirmation unit 43 obtains the deviation VD between the average value VHGSTD of the voltage value VHG calculated from the resistance value of the sensor element 12a within a predetermined time and the lean side threshold value LREF. Then, the voltage difference confirmation unit 43 sets the voltage value VHGcon (= VHG + VD) obtained by correcting the voltage value VHG calculated from the resistance value based on the deviation VD as the control voltage value (detection value) used in the above-mentioned characteristic inspection and excess rate calculation unit 25.

In this case, when the temperature Tcon of the sensor element 12a is low enough to deactivate the oxygen concentration sensor, the wave height of the voltage value VHG becomes almost zero (the voltage value VHG does not move), and the voltage value VHGref that can be read from the sensor element 12a having a standard resistance value becomes the same value as the graphs 35 and 36 (the voltage value VHGref and the graphs 35 and 36 overlap). In other words, when the control temperature Tcon is equal to or lower than a predetermined value, the standard voltage value VHGref becomes equal to the graph 35 (lean side threshold value LREF), so the reference value for setting the control voltage value (detection value) VHGcon can be obtained by scanning the lookup table corresponding to the graph 35 at the sufficiently low temperature Tcon. In addition, the average value VHGSTD can be calculated from the arithmetic mean value of the voltage values VHG read multiple times over a period of, for example, five seconds. This reduces the effect of quantization errors in reading the voltage values VHG, and allows the deviation VD to be obtained, while allowing the control voltage value VHGcon to be set with high accuracy.

Thus, the control voltage value (detection value) VHGcon is corrected to be the same as graph 35 (lean side threshold LREF) when the control temperature Tcon is equal to or lower than the predetermined value. As a result, the voltage difference confirmation unit 43 essentially translates the above data map in the vertical direction (towards the second scale value G2) in FIG. 5.

When actually inspecting the oxygen concentration sensor 12 connected to the ECU 15, the characteristic inspection unit 40 sets the target air excess ratio λcmd to near stoichiometric through the target value calculation unit 28, obtains the peak value of the voltage value VHGcon, and inspects whether this peak value falls within any of the air-fuel ratio regions.

In addition, when calibration is performed by the calibration unit 41, the lookup tables corresponding to the data maps and graphs 35 and 36 are calibrated based on the results of the inspection.

Figure 7 shows a voltage waveform 44 indicating the change over time of the voltage value (detected value) VHGref obtained while driving a vehicle equipped with an oxygen concentration sensor 12 having a standard resistance value in an internal combustion engine with the target excess air ratio λcmd set near stoichiometric by the characteristics inspection unit 40. Figure 7 also shows an air-fuel ratio waveform 45 indicating the waveform of the output signal of a wideband air-fuel ratio sensor temporarily installed for verification purposes.

In a four-stroke internal combustion engine, the exhaust gas in the exhaust pipe and the oxygen concentration contained therein pulsate, so that, as shown in FIG. 7, the voltage waveform 44 of the voltage value (detected value) VHGref read from the sensor element 12a of the oxygen concentration sensor 12 having a standard resistance value and the air-fuel ratio waveform 45 of the adjacent air-fuel ratio sensor are observed as waveforms with wave heights that transition in an oscillatory manner over time. In particular, during the illustrated period P in which the air-fuel ratio waveform 45 crosses the level at which the air excess ratio λ is 1.0, the resistance value of the sensor element 12a has the characteristic of changing abruptly in steps at oxygen concentrations near the stoichiometric value, so that the wave height M (peak value of the detected value) of the voltage waveform 44 is observed as a waveform that oscillates significantly more than the wave height of the air-fuel ratio waveform 45 during the same period P. The lookup tables corresponding to the above graph 36 (rich side threshold RREF) and graph 35 (lean side threshold LREF) are set to follow the transition of the wave height of the voltage waveform 44, which oscillates greatly in this way.

That is, during the illustrated period P, among the peaks of each wave height M in the voltage waveform 44 obtained from the oxygen concentration sensor 12 having a standard resistance value, many of the rich side peaks 46 that are close to the lower rich side threshold value RREF in FIG. 7 are located almost on the rich side threshold value RREF, while many of the lean side peaks 47 that are close to the upper lean side threshold value LREF in FIG. 7 are located almost on the lean side threshold value LREF.

In other words, the target excess air ratio λcmd is set close to stoichiometric and feedback control of the air-fuel ratio is performed to reproduce the state of the illustrated period P. The ECU 15 measures the wave height M expressed by the voltage value (detection value) VHGcon of the oxygen concentration sensor 12 actually connected to the ECU 15, and checks whether the peak of the wave height M matches the lean side threshold value LREF and the rich side threshold value RREF. This makes it possible to grasp and obtain the extent to which the characteristics of the voltage value VHGcon deviate from the characteristics of the voltage value VHGref at the above-mentioned standard resistance value.

Thus, the characteristic inspection unit 40 is configured to obtain the peak value of the wave height M for the voltage value (detection value) VHGcon of the oxygen concentration sensor 12 connected to the ECU 15 while performing air-fuel ratio feedback control by setting the target air excess ratio λcmd close to stoichiometric, and to inspect whether the peak value of the wave height M falls within the rich region, the stoichiometric region, or the lean region. Based on the inspection result, the calibration unit 41 can calibrate the data map and the lookup table by performing an affine transformation so that the peak value of the wave height M matches the rich side threshold value RREF and the lean side threshold value LREF.

Specifically, the calibration unit 41 has a first calibration magnification value C1 and a second calibration magnification value C2 for calibrating the data map and the lookup table by enlarging or reducing a plurality of first scale values G1 and a plurality of second scale values G2 in a manner similar to so-called affine transformation.

To explain in more detail with reference to Figures 8(a) to (d), when the calibration unit 41 compares the lean side peak value 47v of the control voltage value VHGcon, which changes over time, with the lookup table corresponding to graph 35 (lean side threshold value LREF), for example, if the lean side peak value 47v is in the lean region, the calibration unit 41 increases the first calibration multiplier value C1 to expand the data map and lookup table to the right in Figure 8 (see Figure 8(a)), and if the lean side peak value 47v is in the stoichiometric region, the calibration unit 41 decreases the first calibration multiplier value C1 to shrink the data map and lookup table to the left in Figure 8 (see Figure 8(b)).

That is, the calibration unit 41 performs calibration by multiplying the first scale value G1 of the data map and the lookup table by the increased or decreased first calibration magnification value C1, thereby substantially enlarging or reducing the data map and the lookup table in a manner of so-called affine transformation. Note that 0 Kelvin (minus 273.15 degC; absolute zero) can be used as the origin of the enlargement or reduction of the first scale value G1. In this case, if the pre-calibration values of the multiple first scale values G1 stored in the memory unit 34 are Tk (Celsius temperature), the post-calibration control first scale value Tkcal can be calculated by the following formula (6a).
Tkcal = (Tk + 273.15) × C1 - 273.15 (6a)

When the calibration unit 41 compares the rich side peak value 46v of the control voltage value VHGcon, which changes over time, with the lookup table corresponding to graph 36 (rich side threshold value RREF), for example, if the rich side peak value 46v is in the rich region, the calibration unit 41 increases the second calibration multiplier value C2 to expand the data map and lookup table downward in FIG. 8 (see FIG. 8(d)), and if the rich side peak value 46v is in the stoichiometric region, the calibration unit 41 decreases the second calibration multiplier value C2 to shrink the data map and lookup table upward in FIG. 8 (see FIG. 8(c)).

That is, the calibration unit 41 calibrates the data map and the lookup table by multiplying the second scale value G2 of the data map and the lookup table by the increased or decreased second calibration magnification value C2, thereby essentially enlarging or reducing the data map and the lookup table in a manner similar to a so-called affine transformation. Note that the value of the graph 35 (lean side threshold value LREF) when the above-mentioned control temperature Tcon is equal to or lower than a predetermined value can be used as the origin of the enlargement or reduction of the second scale value G2.

In this case, if the value of graph 35 when the control temperature Tcon is equal to or lower than a predetermined value is LREFanchor and the pre-calibration values of the multiple second scale values G2 stored in memory unit 34 are Vk, the post-calibration control second scale value Vkcal can be calculated using the following equation (7).
Vkcal = (Vk - LREFanchor) x C2 + LREFanchor
(7)

In this embodiment, when the first calibration magnification value C1 and the second calibration magnification value C2 are increased or decreased, the calibration unit 41 can be configured to include a transition process that gradually increases or decreases the first calibration magnification value C1 or the second calibration magnification value C2 using a predetermined increase rate and decrease rate to gradually transition to a calibration completion state.

As described above, according to this embodiment, the data map and lookup table are calibrated so that the peak value of the voltage value VHGcon when the target air excess ratio λcmd is set near the stoichiometric value corresponds to the rich side threshold value RREF and the lean side threshold value LREF. Therefore, regardless of the tolerance (variation) of the resistance values of the sensor element 12a and the sensor heater 12b, an accurate air excess ratio λ can be calculated to perform appropriate air-fuel ratio feedback control.

In addition, the temperature inspection unit 42 obtains the deviation TD of the temperature T of the sensor element 12a from the reference value, and corrects the temperature T based on the deviation TD, allowing for more accurate air-fuel ratio feedback control.

In addition, when the temperature of the sensor element 12a is below a sufficiently low predetermined value, for example when the wave height of the voltage value VHG is almost zero and the voltage VHG does not fluctuate, the voltage inspection unit 43 determines a correction value (deviation VD) for the voltage value VHG and corrects the voltage value VHG accordingly, thereby enabling more accurate air-fuel ratio feedback control.

In addition, the characteristic inspection unit 40 and the calibration unit 41 increase (gradually increase) the first calibration multiplier value C1 when the lean side peak value 47v is in the lean region, and decrease (gradually decrease) the first calibration multiplier value C1 when the lean side peak value 47v is in the stoichiometric region. This calibrates the data map and lookup table so that the observed lean side peak value 47v approaches the lean side threshold value LREF, thereby enabling more accurate air-fuel ratio feedback control.

In addition, the characteristic inspection unit 40 and the calibration unit 41 increase (gradually increase) the second calibration multiplier value C2 when the rich side peak value 46v is in the rich region, and decrease (gradually decrease) the second calibration multiplier value C2 when the rich side peak value 46v is in the stoichiometric region, thereby calibrating the data map and lookup table so that the observed rich side peak value 46v approaches the rich side threshold value RREF, thereby enabling more accurate air-fuel ratio feedback control.

In addition, when controlling the fuel injection amount Ti by PID control based on the excess air ratio λ, if the voltage value VHG indicating the oxygen concentration in the exhaust gas exceeds the lean side threshold value LREF, the replacement value R calculated by the above-mentioned formula (1) is regarded as the excess air ratio λ, so that interruptions of the PID control are suppressed, control accuracy is improved, and the efficiency of exhaust gas purification, etc. can be improved.

In addition, the moving average values of the fuel injection execution time Ti1, torque value TQ1, and air excess ratio λb are stored in the memory unit 34, so that the quantization noise (error) that occurs when these measurement values are converted to digital values can be reduced.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various design changes can be made without departing from the invention described in the claims.

For example, in the above embodiment, the data map and the lookup table are calibrated by multiplying each of the first calibration magnification value C1 by the first calibration magnification value C1, and thereby substantially enlarging or reducing the data map and the lookup table in a manner of so-called affine transformation (Equation (6a)), but the present invention is not limited to this. For example, even if the control temperature for scanning the data map and the lookup table is multiplied by the first calibration magnification value C1, it is possible to substantially enlarge or reduce the data map and the lookup table. In this case, if the pre-calibration value of the multiple first scale values G1 stored in the memory unit 34 is Tk (Celsius temperature) and the post-calibration control first scale value is Tkcal, the scan control temperature value Tcon (Celsius temperature) for scanning the data map and the lookup table can be obtained by the following equation (6b).
Tkcal = Tk
Tcon = (T + TD + 273.15) x (1/C1) - 273.15
(6b)

Whether the above-mentioned formula (6a) or formula (6b) is used, the peak value of the actually measured voltage value (detection value) VHGcon can be calibrated so that it matches the rich side and lean side thresholds (the peak of the peak overlaps the thresholds), allowing an accurate air excess ratio to be calculated and appropriate air-fuel ratio feedback control to be performed.

In addition, in the above-described embodiment, the reference value Tref for setting the temperature Tcon is set by adding the engine temperature obtained by the cooling water temperature sensor 17 to the intake air temperature obtained by the intake air temperature sensor 8 and dividing the result by 2 {Tref = (engine temperature + intake air temperature) ÷ 2}, but this is not limited thereto, and for example, the reference value Tref for setting the temperature Tcon may be calculated from only one of the engine temperature obtained by the cooling water temperature sensor 17 or the intake air temperature obtained by the intake air temperature sensor 8.

1...engine body, 2...intake pipe, 3...throttle valve, 4...air cleaner, 5...throttle sensor, 6...fuel injection valve, 7...intake pressure sensor, 8...intake temperature sensor, 9...piston, 10...exhaust pipe, 11...catalyst, 12...oxygen concentration sensor, 12a...sensor element (detection unit), 12b...sensor heater, 13...spark plug, 14...ignition device, 15...ECU (electronic control unit), 17...cooling water temperature sensor, 18...crankshaft, 19...crank angle sensor, 19a...rotor, 19b...pickup, 20...atmospheric pressure sensor, 22...heater controller, 23...temperature calculation unit, 2 4...Voltage calculation section, 25...Excess rate calculation section, 26...Alternative value calculation section, 27...Rotational speed calculation section, 28...Target value calculation section, 29...Basic injection amount calculation section, 30...Feedback coefficient calculation section, 31...Injection amount calculation section, 32...Torque calculation section, 33...Limit threshold setting section, 34...Memory section, 35-38, 35b, 36b, 35c, 36c, 35d, 36d, 35e, 36e...Graph, 40...Characteristics inspection section, 41...Calibration section, 42...Temperature inspection section, 43...Voltage inspection section, 44...Voltage waveform, 45...Air-fuel ratio waveform, 46...Rich side peak, 47...Lean side peak, 46v, 47v...Peak value.

Claims (5)

a resistance-type oxygen sensor provided in contact with exhaust gas from an internal combustion engine having exhaust pulsation, the resistance-type oxygen sensor having a detection section whose resistance value changes in a substantially stepped manner at an oxygen concentration near the stoichiometric value of the exhaust gas, the detection value obtained from the resistance value of the detection section exhibiting a pulse waveform having a peak value corresponding to the temperature of the detection section and the exhaust pulsation;
A temperature reading unit that estimates or detects the temperature of the detection unit;
an excess ratio calculation unit that calculates an excess air ratio by referring to a data map that indicates a correspondence relationship between a plurality of excess air ratio values and a plurality of first scale values for the temperature and a plurality of second scale values for the detection value,
An air-fuel ratio control device that performs air-fuel ratio feedback control based on a deviation between the air excess ratio and a target air excess ratio,
a storage unit that stores the data map and a lookup table that indicates a rich side threshold value and a lean side threshold value for determining whether the detected value corresponds to any one of a rich region, a stoichiometric region, and a lean region, in correspondence with the first scale value;
a characteristic checking unit that sets the target excess air ratio to a value close to the stoichiometric value, acquires a peak value of the detection value, and checks whether the peak value falls within any of the air-fuel ratio regions;
an air-fuel ratio control device comprising: a calibration unit that calibrates the data map and the look-up table in an affine transformation manner so that the peak value corresponds to the rich side threshold value and the lean side threshold value by the inspection. the characteristic inspection unit includes a temperature difference confirmation unit that acquires an amount of deviation of the temperature of the detection unit from a reference value when a predetermined time sufficient for the temperature of the detection unit to converge to an ambient temperature of the detection unit has elapsed while the internal combustion engine is stopped,
2. The air-fuel ratio control device according to claim 1, wherein a value obtained by correcting the temperature of said detection portion based on said deviation amount is used as the detection portion temperature for control used in said inspection and said excess rate calculation portion. the characteristic inspection unit includes a voltage difference confirmation unit that acquires a deviation between an average value of a detection value obtained from a resistance value of the detection unit within a predetermined time period and the lean side threshold value when the control detection unit temperature is equal to or lower than a predetermined value,
3. The air-fuel ratio control device according to claim 2, wherein a detection value obtained from said resistance value and corrected based on said deviation is used as a detection value for control used in said inspection and said excess rate calculation section. The calibration unit includes:
storing a first calibration scale factor value for calibrating the data map and the look-up table by scaling up or down the first plurality of scale values;
4. The air-fuel ratio control device according to claim 3, wherein, when a peak of a peak of a peak close to the lean side threshold among the peaks of the control detection values which change over time is compared with the lean side threshold, if the peak is in the lean region, the first calibration multiplier value is increased, and if the peak is in the stoichiometric region, the first calibration multiplier value is decreased. The calibration unit includes:
a second calibration factor value for multiplying the plurality of second scale values, the rich threshold value and the lean threshold value to calibrate the data map and the lookup table;
5. The air-fuel ratio control device according to claim 3, wherein the second calibration multiplier value is increased when a peak of a peak of the control detection value that changes over time and is close to the rich side threshold value is in the rich region, and the second calibration multiplier value is decreased when the peak is in the stoichiometric region.