JP2022070442A - Air excess rate calculation device - Google Patents

Abstract

To provide an air excess rate calculation device which can make control efficient by reducing the interruption of PID control when controlling an air excess rate.SOLUTION: An air excess rate calculation device comprises an excess rate calculation part 25 for calculating an air excess rate λ by using data which are obtained by linearization-converting a voltage value VHG indicating an oxygen concentration in the exhaust emission of an internal combustion engine to the air excess rate. When the voltage value VHG is equal to or lower than a lean-side threshold LREF, the excess rate calculation part 25 stores an execution time Ti1 of fuel injection, a torque value TQ1 of the internal combustion engine and an air excess rate λb, when the voltage value VHG exceeds the lean-side threshold LREF, calculates a substitution value R by the following formula with an execution time of this-time fuel injection as Ti2, and the torque value of the internal combustion engine as TQ2, and considers the calculated substitution value as the air excess rate λ. R=((Ti1/Ti2)/(TQ1/TQ2))×λb.SELECTED DRAWING: Figure 1

Description

The present invention relates to an air excess rate calculation device that calculates an air excess rate based on the oxygen concentration in the exhaust gas of an internal combustion engine.

Conventionally, a technique for detecting the air-fuel ratio or the excess air ratio has been known in order to purify the exhaust gas and reduce the fuel consumption rate by feeding back the air-fuel ratio or the excess air ratio to the fuel injection amount in the internal combustion engine. For example, see Patent Document 1).

In the technique of Patent Document 1, a sensor using an oxygen concentration cell type oxygen sensor using a zirconia tube is used as an exhaust gas sensor for detecting the air-fuel ratio or the excess air ratio. The electromotive force of the oxygen sensor is converted into linearized data having linear characteristics with respect to the air-fuel ratio, and the air-fuel ratio is detected based on the linearized data.

In the conversion formula for converting to the linearized data, the coefficient is changed according to the internal resistance Ri that correlates with the temperature of the oxygen sensor. According to this, even if the output characteristic of the oxygen sensor changes due to the temperature change, the air-fuel ratio can be detected with high accuracy.

On the other hand, as an exhaust gas sensor for detecting the air-fuel ratio or the excess air ratio, a resistance type oxygen sensor that detects oxygen based on the internal resistance of the oxygen sensor is also known (see, for example, Patent Document 2).

In the oxygen sensor of Patent Document 2, a first value indicating the oxygen content of the exhaust gas is determined based on the resistance of the oxygen sensing portion of the oxygen sensor. 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 the third value. According to this, even if the output characteristic of the resistance type oxygen sensor changes due to the temperature change, the air-fuel ratio can be detected with high accuracy.

Japanese Patent Application Laid-Open No. 2003-148235 US Pat. No. 8,959,987

However, according to the techniques of Patent Documents 1 and 2, in the lean side limit or rich side limit region of the voltage of the oxygen sensor, the output voltage of the oxygen sensor is linearized so as to have a linear characteristic with respect to the air-fuel ratio. It is difficult to do. That is, since the change of the output voltage with respect to the air-fuel ratio is steep in both limit regions, the resolution of the A / D converter that reads the output voltage becomes insufficient.

Therefore, when purifying the exhaust gas by PID control, which is preferably used for adjusting to these target values based on the detected value of the air-fuel ratio or the excess air ratio, the control is interrupted in the part where the change in the output voltage is steep. There is a problem that it has to be done.

An object of the present invention is to provide an air excess rate calculation device capable of reducing interruption of PID control when controlling an excess air rate and improving control efficiency in view of the problems of the prior art.

The air excess rate calculation device of the present invention is
It has a detection unit that is provided in contact with the exhaust of an internal combustion engine provided with a fuel injection valve and detects the oxygen concentration in the exhaust, and the temperature characteristic that the detection value from the detection unit changes according to the temperature of the detection unit. Based on the oxygen sensor having the In an air excess rate calculation device provided with an excess rate calculation unit for calculating the excess air rate λ of the exhaust using the obtained data.
The excess rate calculation unit
A torque calculation unit that calculates the torque value of the internal combustion engine based on the crank angular velocity of the internal combustion engine, and
A limit threshold setting unit for setting a conversion limit threshold for the linearize conversion, and a limit threshold setting unit.
When the detected value or the linearized data is equal to or less than the conversion limit threshold, the execution time of fuel injection by the fuel injection valve is stored as Ti1, the torque value is TQ1, and the air excess rate with respect to the conversion limit value is stored as λb. Memory unit and
An alternative value calculation unit that calculates an alternative value R by the following equation, where the execution time of the fuel injection when the detected value or the linearized data exceeds the conversion limit threshold is Ti2 and the torque value is TQ2. And with
R = ((Ti1 ÷ Ti2) ÷ (TQ1 ÷ TQ2)) × λb
When the detected value or the linearized converted data exceeds the conversion limit threshold value, the alternative value R is regarded as the exhaust air excess rate λ instead of the linearized converted data. And.

In general, PID (proportional integral differentiation) control is preferable when feedback control of a fuel injection valve or the like is performed based on an excess air ratio obtained based on an oxygen concentration detected by an oxygen sensor provided in an exhaust pipe of an internal combustion engine. Used.

The reason is that according to PID control, the controlled object can be accurately feedback-controlled with respect to the target value by quick control with less hunting than PI (proportional integral) control. By accurately controlling the excess air ratio (air-fuel ratio) toward the target value in this way, the exhaust gas of the internal combustion engine can be purified. Since the air-fuel ratio is equal to the value obtained by dividing the air-fuel ratio by the theoretical air-fuel ratio, the concept of the air-fuel ratio also includes the air-fuel ratio in the present invention.

By the way, PID control is usually intended for a linear system in which the output changes linearly with respect to the input. Therefore, when an oxygen sensor whose output voltage characteristics are partially non-linear is used on the input side, stable PID control cannot be performed in the non-linear region (measurement limit region), and air, which is the control target value, cannot be performed stably. There is a problem that the excess rate does not converge to the target value and diverges.

Therefore, for example, when a lean spike occurs in which the detection value of the oxygen sensor temporarily exceeds the measurement limit region on the dilute side of the oxygen sensor, it is necessary to temporarily stop the PID control.

In this regard, in the present invention, when the output of the oxygen sensor exceeds the conversion limit threshold and becomes non-linear, the ratio of the torque of the internal combustion engine is calculated by the alternative value calculation unit instead of the excess air ratio based on the detection value of the oxygen sensor. And the alternative value R calculated by using the ratio of the fuel injection amount is regarded as the excess air ratio. As a result, interruption of PID control can be suppressed, control accuracy can be improved, and efficiency of exhaust gas purification and the like can be improved.

Further, in the present invention, the storage unit may store the respective moving average values as the execution time Ti1 of the fuel injection and the torque value TQ1. According to this, it is possible to reduce the quantization noise (error) when converting the measured values of the execution time Ti1 and the torque value TQ1 into digital values.

Further, in the present invention, the excess rate calculation unit may store the moving average value of the linearized data as the air excess rate λb with respect to the conversion limit threshold value. According to this, it is possible to reduce the quantization noise (error) when converting the linearized data into a digital value.

Further, in the present invention, the excess rate calculation unit may use a predetermined value as the air excess rate λb with respect to the conversion limit threshold value. According to this, since the arithmetic processing for obtaining the air excess rate λb is omitted, the control in the high rotation speed range can be facilitated.

Further, in the present invention, the limit threshold value setting unit sets the conversion limit value according to the temperature of the detection unit based on a look-up table in which the temperature of the detection unit and the conversion limit threshold value are associated with each other. May be good.

When the temperature of the detection unit of the oxygen sensor decreases, the dynamic range of the output value (the ratio of the minimum value to the maximum value in the linear region of the sensor output voltage) changes. Therefore, it is necessary to change the conversion limit threshold value according to the temperature of the detection unit of the oxygen sensor. In this respect, since the limit threshold value setting unit includes the above-mentioned limit threshold value setting means, it is possible to set an appropriate conversion limit value according to the temperature of the detection unit.

The oxygen sensor is a resistance type oxygen sensor whose resistance value changes depending on the oxygen concentration, and the excess rate calculation unit determines the temperature and detection value of the detection unit of the resistance type oxygen sensor and the air excess rate λ of the exhaust. A data map associated with the data is provided, and the linearized data is acquired using the data map, and when the detected value or the linearized data is equal to or less than the conversion limit threshold, the linearized conversion is performed. The obtained data may be regarded as the excess air ratio λ of the exhaust.

According to this, when the value detected by the oxygen sensor or the linearized data is equal to or less than the conversion limit threshold value, the linearized data obtained by the data map is regarded as the air excess rate λ, so that it depends on the temperature. An appropriate excess air ratio λ can be obtained.

It is a schematic diagram schematically showing the structure of the main part of the internal combustion engine provided with the air excess rate calculation device which concerns on one Embodiment of this invention. It is a block diagram which shows the main structure in the ECU of the internal combustion engine of FIG. It is a flowchart which shows the excess rate calculation process which calculates the air excess rate by the excess rate calculation part in the ECU of FIG. FIG. 3 is a graph showing how the excess air ratio in the stoichiometric region is calculated in the process of FIG. 3 is a graph showing a graph corresponding to a look-up table for obtaining 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 air excess rate. It is a graph which shows the state of the change of the air excess rate λ calculated by the process of FIG. 3 schematically.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a main part of a four-cycle type internal combustion engine including an air excess rate calculation device according to an embodiment of the present invention. As shown in the figure, the engine body 1 of the internal combustion engine has an intake pipe 2 provided in the intake pipe and an opening degree of the amount of intake air supplied from the air cleaner 4 in the intake pipe 2 to the intake port. It is provided with a throttle valve 3 which is adjusted according to the above.

The throttle valve 3 is provided with a throttle sensor 5 that detects the opening degree of the throttle valve 3. A fuel injection valve 6 for injecting fuel is provided in the vicinity of the suction port of the intake pipe 2. Fuel is pumped to the fuel injection valve 6 from a fuel tank (not shown) 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.

In the exhaust pipe 10 connected to the exhaust port of the engine body 1, a catalyst 11 for reducing unburned components in the exhaust of the exhaust pipe 10 and an oxygen sensor 12 for detecting the oxygen concentration in the exhaust are provided.
Further, a spark plug 13 connected to the ignition device 14 is fixed to the engine body 1. When the ECU (electronic control unit) 15 issues an ignition timing command to the ignition device 14, spark discharge occurs in the cylinder combustion chamber of the engine body 1.

An analog voltage indicating the detection value of each of the throttle sensor 5, the intake pressure sensor 7, the intake temperature sensor 8, the oxygen sensor 12, the cooling water temperature sensor 17, and the atmospheric pressure sensor 20 for detecting the atmospheric pressure is input to the ECU 15. .. Further, the fuel injection valve 6 is connected to the ECU 15.

Further, a signal indicating the rotation angle position of the crank shaft 18 from the crank angle sensor 19 is input to the ECU 15. That is, in the crank angle sensor 19, a plurality of convex portions provided at predetermined angles (for example, 15 degrees) on the outer periphery of the rotor 19a that rotates in conjunction with the crank shaft 18 are arranged in the vicinity of the outer periphery of the rotor 19a. It is magnetically or optically detected by the pickup 19b, and a pulse (crank signal) is generated from the pickup 19b at each rotation of the crank shaft 18 at a predetermined angle.

Specifically, the crank angle sensor 19 outputs a signal indicating a reference angle to the ECU 15 every time the piston 9 reaches the top dead center or every time the crank shaft 18 rotates 360 degrees.
FIG. 2 shows the main configuration of the ECU 15. As shown in the figure, the oxygen sensor 12 that supplies the detection signal of the oxygen concentration in the exhaust to the ECU 15 is provided so as to be in contact with the exhaust of the internal combustion engine and is a sensor element as a detection unit that detects the oxygen concentration in the exhaust. A sensor heater 12b that heats the sensor element 12a adjacent to the sensor element 12a is provided.

The sensor element 12a has a temperature characteristic in which the detected value changes according to the temperature of the sensor element 12a. As the sensor element 12a, in the present embodiment, a titania type sensor element, which is a resistance type oxygen sensor whose resistance value changes according to the oxygen concentration, is used.

The ECU 15 uses a heater controller 22 for controlling the sensor heater 12b, a temperature calculation unit 23 for calculating a temperature value T indicating the temperature of the sensor element 12a, and a voltage indicating the oxygen concentration in the exhaust for the output signal of the sensor element 12a. A voltage calculation unit 24 for converting to a value VHG is provided.

The temperature of the sensor heater 12b is controlled by the heater controller 22 by pulse width modulation (PWM) control of the energization current amount I supplied to the sensor heater 12b from a power source (storage battery) (not shown) by the ECU 15. Further, the temperature value T is calculated by the temperature calculation unit 23, for example, by reading the resistance value of the sensor heater 12b with the ECU 15. The calculation results in the temperature calculation unit 23 and the voltage calculation unit 24 are supplied to the alternative value calculation unit 26 of the excess rate calculation unit 25, which will be described later.

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

Further, the ECU 15 has a target value calculation unit 28 that calculates a target air excess rate λcmd based on an estimated value of the stored oxygen amount in the catalyst 11, a rotation speed NE from the rotation speed calculation unit 27, and an intake pressure sensor. Match the air excess rate λ calculated by the basic injection amount calculation unit 29 that calculates the basic injection amount BJ based on the pressure PM in the intake pipe 2 from 7 and the excess rate calculation unit 25 with the target air excess rate λcmd. Therefore, the injection amount Ti is calculated based on the feedback coefficient calculation unit 30 for obtaining the feedback coefficient k for correcting the basic fuel injection amount BJ calculated by the basic injection amount calculation unit 29, and the feedback coefficient k and the basic injection amount BJ. In addition, an injection amount calculation unit 31 for operating the fuel injection valve 6 is provided.

In the feedback coefficient calculation unit 30, PID control is performed based on the comparison between the air excess rate λ and the target air excess rate 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 the corresponding time, and thus the engine body 1 An amount of fuel corresponding to the feedback coefficient k of the PID control based on the comparison between the excess air ratio λ and the target excess air ratio λcmd is injected into the cylinder combustion chamber.

The excess rate calculation unit 25 linearizes and converts the voltage value VHG to the air excess rate while compensating for the 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. The excess air rate λ of the exhaust gas is calculated using the obtained data LD. However, as will be described later, 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 larger than the lean side threshold value LREF, the air excess rate λ is obtained by another method.

The excess rate 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, and a limit threshold setting unit 33 that sets a conversion limit threshold for the linearization conversion described above. A storage unit 34 for storing data necessary for calculating an alternative value R of an air excess rate λ, and an alternative value calculation unit 26 for calculating an alternative value R are provided.

As the conversion limit threshold value, the limit threshold value setting unit 33 sets the lean side threshold value LREF, which is the conversion limit area value on the lean side, and the rich side threshold value RREF, which is the conversion limit value on the rich side, with respect to the voltage value VHG from the voltage calculation unit 24. Set. However, in the titania type sensor element 12a, when the temperature changes, the dynamic range of the output value (each value of the minimum value and the maximum value in the linear region of the sensor output voltage) changes, so that the temperature value from the temperature calculation unit 23 changes. It is necessary to change the conversion limit threshold according to T.

With reference to FIG. 5, FIG. 5 shows the horizontal axis scale value in the left-right direction and the voltage value VHG calculated by the voltage calculation unit 24 in FIG. 5 corresponding to the temperature value T calculated by the temperature calculation unit 23. In the corresponding FIG. 5, a data map having a vertical vertical scale value in the vertical direction and having a plurality of numerical values of the data LD associated with the voltage value VHG and the temperature value T as coordinates is posted. Moreover, each example of the lookup table corresponding to the graphs 35 and 36 for obtaining the lean side threshold LREF and the rich side threshold RREF is shown as a diagram superimposed on the data map.

By storing such a data map and the look-up table corresponding to the graphs 35 and 36 in advance in the ECU 15, the data LD obtained by linearizing and converting the voltage value VHG using these, and the lean side threshold LREF. And the rich side threshold value RREF can be easily acquired and set.

In the graph 35, for example, the excess air ratio λ as the boundary between the lean region and the stoichiometric region is set to 1.02, and the points on the data map having the voltage value VHG and the temperature value T as coordinates so as to have this value are shown. It is a graph obtained by finding multiple points and connecting these multiple points by line interpolation. Further, in the graph 36, for example, the excess air ratio λ as the boundary between the stoichiometric region and the rich region is set to 0.98, and the voltage value VHG and the temperature value T corresponding to this value are used as coordinates on the above data map. It is a graph in which a plurality of points are obtained and the points are connected to each other by line interpolation.

For example, from the look-up table corresponding to the graph 35, the limit threshold value setting unit 33 sets the voltage value v0 derived from the coordinates t0 as the lean region and the stochastic value when the temperature value T from the temperature calculation unit 23 is t0. It can be set as a lean threshold LREF for the boundary with the region. Similarly, from the look-up table corresponding to the graph 36, when the temperature value T from the temperature calculation unit 23 is t0, the voltage value v1 derived from the coordinates t0 is obtained with respect to the boundary between the stoichiometric region and the rich region. It can be set as the rich side threshold RREF.

When the voltage value VHG from the voltage calculation unit 24 is equal to or less than the conversion limit threshold LREF, the storage unit 34 stores the fuel injection execution time Ti1 by the fuel injection valve 6 and the torque value TQ1 as data necessary for calculating the alternative value R. The excess air ratio λb with respect to the conversion limit threshold LREF is stored.

When the voltage value VHG exceeds the conversion limit threshold value LREF, the alternative value calculation unit 26 calculates the alternative value R by the following equation (1), where the execution time of the immediately preceding fuel injection is Ti2 and the immediately preceding torque value is TQ2. do.
R = ((Ti1 ÷ Ti2) ÷ (TQ1 ÷ TQ2)) × λb (1)

Then, when the voltage value VHG exceeds the conversion limit threshold value LREF, the excess rate calculation unit 25 uses the alternative value R as the exhaust air instead of the air excess rate λ as the above-mentioned linearized converted data LD. It is regarded as an excess rate λ.

FIG. 3 shows an excess rate calculation process for calculating the air excess rate λ in the excess rate calculation unit 25. The control by the ECU 15 including the excess rate calculation process is executed in synchronization with the stroke of the internal combustion engine based on the pulse signal indicating the rotation angle position of the crank shaft 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 velocity NETC from the rotation speed calculation unit 27.

In calculating the torque TQ, the two angular speeds of the crank shaft of the internal combustion engine corresponding to each of the two consecutive strokes of the internal combustion engine having the intake, compression, combustion expansion, and exhaust strokes of the internal combustion engine are calculated. Based on this, the generated torque generated by the internal combustion engine is calculated accurately (see Japanese Patent No. 6254633).

Next, in step S2, based on the temperature value T from the temperature calculation unit 23, the limit region value setting unit 33 uses the look-up table corresponding to the graphs 35 and 36 of FIG. 5, and the lean side threshold LREF and rich. Set the side threshold RREF.

Next, in step S3, the voltage value VHG is acquired from the voltage calculation unit 24.

Next, in step S4, the above data map (FIG. 5) is scanned based on the temperature value T acquired in step S2 and the voltage value VHG acquired in step S3, and thus the value of the voltage value VHG is used for its temperature characteristics. The data LD linearized and converted to the air excess rate λ while compensating is acquired.

Next, in step S5, it is determined whether or not the voltage value VHG acquired in step S3 is smaller than the rich side threshold value RREF set in step S2. If it is determined to be small, the process proceeds to step S16 while setting the flag F_DEECT to zero in the following step S6, the value of the data LD is set as the air rate excess rate λ value LAMBDA, and the excess rate calculation process of FIG. 3 is performed. finish.

If it is determined in step S5 that the voltage value VHG is not smaller than the lean side threshold value RREF, the voltage value VHG acquired in step S3 in step S7 is larger than the lean side threshold value LREF set in step S2. Judge whether or not.

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

With reference to FIG. 4, for the air excess rate λ as the data LD linearized and converted in step S8, the air excess rate λ as the boundary between the predetermined stoichiometric region and the lean region is set numerically in advance. With the variable #LLMD (for example, 1.02) that can be set in advance, and the variable #RLMD (for example, 0.98) that can preset the excess air ratio λ as the boundary between the predetermined rich region and the stoichiometric region. If there is, it can be represented by a graph as shown in FIG. In FIG. 4, the horizontal axis in the left-right direction of the graph is the voltage value VHG, and the vertical axis in the vertical direction in FIG. 4 is the air excess rate λ. Therefore, for example, when the voltage value VHG is vhg1, the value λ1 of the air excess rate λ corresponding to this 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 fuel injection immediately before by the fuel injection valve 6 and the torque TQ calculated in step S1 are set to Ti1 and TQ1, respectively, and the air excess rate λ related to the lean side threshold LREF is stored in the storage unit 34 as λb. .. Almost at the same time, the countdown timer value TIMER indicating the effective time of the memory is reset by the predetermined initial value #TMINIT. Subsequently, the flag F_DESECT is set to 1 and the process proceeds to step S16, the value of the data LD acquired in step S8 is set as the air rate excess rate λ value AWS Lambda, and the excess rate calculation process of FIG. 3 is completed.

At this time, the value of the data LD acquired in step S8 is stored as λb. At that 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 rate λ (data LD) obtained by the following equation (3) is stored as λb.
λa = LD × k1 + λab × (1-k1) (3)

Here, k1 is a moving average coefficient, and λab is a moving average value in the previous control cycle stored in the storage unit 34. As the moving average coefficient k1, for example, 0.34 is used.

Further, at this time, it is preferable that the storage unit 34 stores the moving average value as the fuel injection execution time Ti1 and the torque value TQ1. For example, the exponential moving average TiFLT of the fuel injection execution time Ti is obtained by the following equation (4) and stored as Ti1, and the exponential moving average TQFLT of the torque value TQ is obtained by the following equation (5) and TQ1. Is remembered as.
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 storage unit 34. In this embodiment, different values can be used as the moving average coefficients k1, k2, and k3.

Next, in step S7, when it is determined that the voltage value VHG acquired in step S3 is larger than the lean side threshold value LREF, it is determined in step S10 whether or not the above-mentioned countdown timer value TIMER has reached zero. judge. Then, if the Timer has reached zero, the flag F_DEECT is reset to 0 (step S11).

Next, the process proceeds to step S12, and it is determined whether or not the flag F_DESECT = 1. If F_DESECT = 1, it means that the storage unit 34 stores the air excess rate λb with respect to the lean side threshold LREF, the fuel injection execution time Ti1, and the torque value TQ1, so the process proceeds to step S13 and substitutes. In the value calculation unit 26, the alternative value R is calculated by the above equation (1), and the value of the data LD is set to the alternative value R.

Next, in step S14, it is determined whether or not the value of the data LD set in step S13 is larger than the predetermined upper limit value #LLMT. When the value of the data LD set in step S13 is larger than the upper limit value #LLMT, the value of the data LD is set to the upper limit value #LLMT (step S15). In this case, for example, 1.25 can be used as the upper limit value #LLMT.

If F_DESECT = 0 in step S12, the storage unit 34 does not store valid values for the lean side threshold LREF, the air excess rate λb, the fuel injection execution time Ti1, and the torque value TQ1. Therefore, the alternative value R cannot be calculated. Also in this case, the value of the data LD is set to the above upper limit value #LLMT (step S15).

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

When the excess rate calculation process of FIG. 3 is completed, the ECU 15 sets the air excess rate λ value LAMBDA calculated by the excess rate calculation process of FIG. 3 as the target air excess from the target value calculation unit 28 as described above. The fuel injection amount by the fuel injection valve 6 is controlled by the PID control of the feedback coefficient calculation unit 30 in order to match the rate λcmd.

FIG. 6 is a graph schematically showing the state of change in the air excess rate λ value AWS Lambda calculated by the excess rate calculation process of FIG. The horizontal axis of the graph is a numerical value indicating the passage of time, and the vertical axis is the air excess rate λ.

FIG. 37 in FIG. 6 shows that the air excess rate λ of the actual exhaust is gradually increased at a constant rate of change in the range from the left end side to the vicinity of the center on the horizontal axis in the left-right direction in FIG. In the range from the vicinity of the center of the horizontal axis to the right end side, when the actual air excess rate λ of the exhaust is gradually reduced at a constant rate of change, the voltage value VHG read by the voltage calculation unit 24 of the ECU 15 is used. The numerical change of the air excess rate λ value when the air excess rate λ value is calculated using the data obtained by directly linearizing and converting the air excess rate λ while compensating for the temperature characteristic is shown.

Similarly, in the graph 38, when the air excess rate λ of the actual exhaust is gradually increased or decreased at a constant rate of change from the left end to the right end of the horizontal axis, the voltage value VHG from the voltage calculation unit 24 is lean. When the voltage value lref of the side region value LREF or less, the air excess rate λ value is calculated using the data obtained by directly linearizing and converting the voltage value VHG by the above data map (FIG. 5) or equation (2). However, when the voltage value VHG from the voltage calculation unit 24 exceeds the voltage value lref of the lean side region value LREF (corresponding to the value 1.020 of the air excess rate λ), the voltage value VHG is linearized. It shows the numerical change of the air excess rate λ value when the alternative value R obtained by the above formula (1) is used as the air excess rate λ value instead of the converted data.

Thus, when the actual excess air ratio λ of the exhaust is 1.020 or less, the voltage value VHG from the voltage calculation unit 24 in response to the excess air ratio λ of the actual exhaust is proportional to the excess air ratio λ of the actual exhaust. Since it changes linearly), when the air excess rate λ of the actual exhaust is 1.020 or less, both Graph 37 and Graph 38 follow the constant change of the air excess rate λ of the actual exhaust. Although it changes linearly, when the excess air ratio λ of the exhaust exceeds 1.020, the voltage value VHG showing non-linearity under that situation suddenly changes in the increasing direction, so the voltage value VHG The graph 37 showing the air excess rate λ value based on the data obtained by directly linearizing the above also changes steeply and non-linearly in the increasing direction. On the other hand, in Graph 38, even when the excess air ratio λ of the exhaust exceeds 1.020 (#LLMD above), the excess air ratio λ value LAMBDA changes linearly with respect to the excess air ratio λ (air-fuel ratio) of the exhaust. It is linked with the actual air-fuel ratio λ of the exhaust.

Therefore, when the voltage value VHG is equal to or less than the lean side threshold LREF by the excess rate calculation process, the air excess rate λ is calculated using the above linearized converted data, and the voltage value VHG exceeds the lean side threshold LREF. In this case, by calculating the excess air coefficient λ by the above formula (1) (graph 38), the excess rate calculation unit 25 is linked to the actual excess air coefficient λ of the exhaust over the entire range of the graph of FIG. It can be seen that the air excess rate λ value that changes proportionally can be supplied to the feedback coefficient calculation unit 30. As a result, interruption of PID control by the feedback coefficient calculation unit 30 is suppressed.

As described above, according to the present embodiment, when the fuel injection amount Ti is controlled by PID control based on the excess air ratio λ, the voltage value VHG indicating the oxygen concentration in the exhaust gas exceeds the lean side threshold LREF. Since the alternative value R calculated by the above equation (1) is regarded as the air excess rate λ, it is possible to suppress the interruption of PID control, improve the control accuracy, and improve the efficiency of exhaust gas purification and the like.

Further, since the moving average values are stored as the fuel injection execution time Ti1, the torque value TQ1, and the air excess rate λb stored in the storage unit 34, the quantization noise when converting these measured values into digital values. (Error) can be reduced.

Further, since the lean side threshold value LREF and the rich side threshold value RREF are set by using the look-up table corresponding to the graphs 35 and 36 as shown in FIG. 5, an appropriate lean side threshold value LREF corresponding to the temperature of the oxygen sensor 12 is set. And the rich side threshold RREF can be set.

Further, a resistance type oxygen sensor is used as the oxygen sensor 12, and air as data linearized using a data map as shown in FIG. 5 in which the temperature and the detected value thereof and the air excess rate λ of the exhaust are associated with each other. Since the excess rate λ is obtained, the excess air rate λ can be obtained quickly.

Further, since the excess rate calculation process in FIG. 3 calculates the air excess rate λ in synchronization with the stroke of the internal combustion engine, such calculation is often performed by a timer at a fixed cycle. The fuel injection amount and the torque value TQ can be acquired without any problem according to the control cycle even if the control cycle becomes short due to the increase in the fuel injection amount.

The present invention is not limited to the above-described embodiment. For example, the voltage value lref of the lean side threshold LREF and the voltage value rref of the rich side threshold RREF are set by using the lookup tables corresponding to the graphs 35 and 36 (step S2), respectively, and in step S8, the lean side Although it is configured to calculate the data LD linearized and converted by the equation (2) including the voltage value lref and the voltage value rref on the rich side, this step S8 is omitted and the data map (data map (step S4) described above is omitted. It may be set to the value of the data LD acquired by scanning FIG. 5).

In this case, further omitting the above step S2, the data LD acquired in step S3 is predetermined as a predetermined excess air ratio λ corresponding to the lean side threshold value LREF in steps S5 and S7 of FIG. 3, respectively. A value, for example 1.02 (air excess rate λ value of lean side threshold LREF #LLMD), a predetermined value as a predetermined air excess rate λ corresponding to the rich side threshold value RREF, for example 0.98 (rich side threshold value RREF). It can be configured to be compared with the air excess rate λ value # RLMD). According to this, the control of the ECU 15 at high rotation speed can be facilitated by the amount that the operation of scanning the look-up table (step S2) and the operation of the above equation (2) (step S8) are omitted.

Further, a predetermined value, for example, 1.02 may be used as the excess air ratio λb with respect to the conversion limit threshold value. According to this, it is possible to facilitate the control at high rotation speed by the amount that the above-mentioned calculation for obtaining the moving average for the excess air ratio λb is not required.

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 sensor, 12a ... sensor element, 12b ... sensor heater, 13 ... fire plug, 14 ... ignition device, 15 ... ECU (electronic control unit), 17 ... cooling water temperature sensor, 18 ... crank shaft, 19 ... crank angle sensor, 19a ... rotor, 19b ... pickup, 20 ... atmospheric pressure sensor, 22 ... heater controller, 23 ... temperature calculation unit, 24 ... voltage calculation unit, 25 ... excess rate calculation unit, 26 ... alternative value calculation Unit, 27 ... Rotation speed calculation unit, 28 ... Target value calculation unit, 29 ... Basic injection amount calculation unit, 30 ... Feedback coefficient calculation unit, 31 ... Injection amount calculation unit, 32 ... Torque calculation unit, 33 ... Limit threshold setting unit , 34 ... Memory unit, 35-38 ... Graph.

Claims (6)

It has a detection unit that is provided in contact with the exhaust of an internal combustion engine provided with a fuel injection valve and detects the oxygen concentration in the exhaust, and the temperature characteristic that the detection value from the detection unit changes according to the temperature of the detection unit. Based on the oxygen sensor having the In an air excess rate calculation device provided with an excess rate calculation unit for calculating the excess air rate λ of the exhaust using the obtained data.
The excess rate calculation unit
A torque calculation unit that calculates the torque value of the internal combustion engine based on the crank angular velocity of the internal combustion engine, and
A limit threshold setting unit for setting a conversion limit threshold for the linearize conversion, and a limit threshold setting unit.
When the detected value or the linearized data is equal to or less than the conversion limit threshold, the execution time of fuel injection by the fuel injection valve is Ti1, the torque value is TQ1, and the air excess rate for the conversion limit region value is λb. A storage unit to memorize and
An alternative value calculation unit that calculates an alternative value R by the following equation, where the execution time of the fuel injection when the detected value or the linearized data exceeds the conversion limit threshold is Ti2 and the torque value is TQ2. And with
R = ((Ti1 ÷ Ti2) ÷ (TQ1 ÷ TQ2)) × λb
When the detected value or the linearized converted data exceeds the conversion limit threshold value, the alternative value R is regarded as the exhaust air excess rate λ instead of the linearized converted data. An air excess rate calculation device characterized by. The air excess rate calculation device according to claim 1, wherein the storage unit stores the respective moving average values as the fuel injection execution time Ti1 and the torque value TQ1. The air excess rate calculation device according to claim 1 or 2, wherein the storage unit stores the moving average value of the linearized data as the air excess rate λb with respect to the conversion limit threshold value. The air excess rate calculation device according to claim 1 or 2, wherein the excess rate calculation unit uses a predetermined value as the air excess rate λb with respect to the conversion limit threshold value. The claim is characterized in that the limit threshold value setting unit sets the conversion limit area value according to the temperature of the detection unit based on a look-up table in which the temperature of the detection unit and the conversion limit threshold value are associated with each other. Item 6. The air excess rate calculation device according to any one of Items 1 to 4. The oxygen sensor is a resistance type oxygen sensor whose resistance value changes depending on the oxygen concentration.
The excess rate calculation unit includes a data map in which the temperature and detection value of the detection unit of the resistance type oxygen sensor are associated with the air excess rate λ of the exhaust gas.
The linearized data is acquired using the data map, and when the detected value or the linearized data is equal to or less than the conversion limit threshold value, the linearized data is used as the exhaust air. The air excess rate calculation device according to claim 5, wherein the excess rate is regarded as λ.

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