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WO2023181209A1 - Excess air ratio calculation device - Google Patents

Excess air ratio calculation device Download PDF

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Publication number
WO2023181209A1
WO2023181209A1 PCT/JP2022/013667 JP2022013667W WO2023181209A1 WO 2023181209 A1 WO2023181209 A1 WO 2023181209A1 JP 2022013667 W JP2022013667 W JP 2022013667W WO 2023181209 A1 WO2023181209 A1 WO 2023181209A1
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WO
WIPO (PCT)
Prior art keywords
value
excess air
air ratio
torque
excess
Prior art date
Application number
PCT/JP2022/013667
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French (fr)
Japanese (ja)
Inventor
勝明 和知
Original Assignee
日立Astemo株式会社
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Publication date
Application filed by 日立Astemo株式会社 filed Critical 日立Astemo株式会社
Priority to PCT/JP2022/013667 priority Critical patent/WO2023181209A1/en
Publication of WO2023181209A1 publication Critical patent/WO2023181209A1/en

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/30—Controlling fuel injection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D45/00—Electrical control not provided for in groups F02D41/00 - F02D43/00

Definitions

  • the present invention relates to an excess air ratio calculation device that calculates an excess air ratio based on the oxygen concentration in the exhaust gas of an internal combustion engine.
  • Patent Document 1 there is a known technology for detecting the air-fuel ratio or excess air ratio in order to feed back the air-fuel ratio or excess air ratio to the fuel injection amount in an internal combustion engine to purify exhaust gas or reduce the fuel consumption rate.
  • Patent Document 1 uses a zirconia-based oxygen sensor whose output signal suddenly changes near the stoichiometric air-fuel ratio when the air-fuel ratio of the fuel mixture supplied to the internal combustion engine changes from lean to rich or vice versa. The oxygen concentration in the exhaust gas of the internal combustion engine is detected. Then, the amount of fuel supplied to the internal combustion engine is controlled according to the detection result.
  • the output signal from the oxygen sensor is within a predetermined range (stoichiometric range) that includes the stoichiometric air-fuel ratio, it is converted into a signal with a predetermined value indicating that the air-fuel ratio is the stoichiometric air-fuel ratio.
  • a predetermined range that includes the stoichiometric air-fuel ratio
  • the signal value increases or decreases at a substantially constant slope from the predetermined value in response to the deviation of the air-fuel ratio from the stoichiometric air-fuel ratio. is converted to Then, the fuel supply amount is feedback-controlled so that the converted signal becomes the target value.
  • the first value indicating the oxygen content of exhaust gas is determined based on the resistance of the oxygen sensing portion of the oxygen sensor.
  • a second value indicative of the temperature of the oxygen sensor is determined based on the resistance of the heater portion of the oxygen sensor.
  • the air-fuel ratio as a function of the first value and the second value is then determined as a third value. According to this, even if the output characteristics of the resistance-type oxygen sensor change due to temperature changes, the air-fuel ratio can be detected with high accuracy.
  • the zirconia-based sensor used as an oxygen sensor is higher in cost and has lower responsiveness than a resistance-type oxygen sensor.
  • the technology of Patent Document 1 when converting the output signal of the oxygen sensor into an air-fuel ratio, the air-fuel ratio outside the stoichiometric range is converted as the detection signal and the air-fuel ratio change in a linear correspondence relationship. are doing. This linear correspondence is far from the original correspondence.
  • an object of the present invention is to provide an excess air ratio calculation device that can reduce interruptions in PID control when controlling the excess air ratio and improve control efficiency.
  • the excess air ratio calculation device of the present invention includes:
  • the temperature characteristic includes a detection part that is provided in contact with the exhaust gas of an internal combustion engine equipped with a fuel injection valve and detects the oxygen concentration in the exhaust gas, and the detected value from the detection part changes depending on the temperature of the detection part.
  • a temperature detection unit that estimates or detects the temperature of the detection unit; and a temperature detection unit that linearizes the detection value with respect to the excess air ratio while compensating the temperature characteristic based on the detection value and the temperature.
  • the excess rate calculation unit includes: a torque calculation unit that calculates a torque value of the internal combustion engine based on a crank angular velocity of the internal combustion engine; a limit threshold setting unit that sets a conversion limit threshold for the linearization conversion; Execution time of fuel injection by the fuel injector when the detected value or the linearized data is less than or equal to the conversion limit threshold; Ti1; storage torque value TQ1 for the torque value; and excess air ratio ⁇ with respect to the conversion limit threshold.
  • a storage unit that stores ⁇ b as a storage excess air ratio ⁇ b; a torque contribution rate setting unit that sets a torque contribution rate Tc;
  • PID proportional integral derivative
  • PID control allows accurate feedback control of a controlled object with respect to a target value through quick control with less hunting than PI (proportional-integral) control.
  • PI proportional-integral
  • the excess air ratio is equal to the value obtained by dividing the air-fuel ratio by the stoichiometric air-fuel ratio, so in the present invention, the concept of the excess air ratio includes the air-fuel ratio.
  • PID control is usually aimed at a linear system in which the output changes linearly with respect to the input. Therefore, when using an oxygen sensor whose output voltage characteristics partially exhibit nonlinear characteristics on the input side, stable PID control cannot be performed in the nonlinear region (measurement limit region), and the There is a problem that the excess rate does not converge to the target value but diverges.
  • an alternative value calculating section is used to calculate the torque ratio of the internal combustion engine instead of the excess air ratio based on the detected value of the oxygen sensor.
  • the alternative value R calculated using the ratio of the fuel injection amount and the fuel injection amount is regarded as the excess air ratio ⁇ .
  • the torque contribution rate setting unit sets the value of the torque contribution rate Tc according to the latest torque value TQ2 based on a lookup table in which the torque contribution rate Tc is associated with the torque value. It's okay. According to this, by using an appropriate lookup table, it is possible to easily set an appropriate value of the torque contribution rate Tc.
  • the storage unit may store moving average values of the fuel injection execution time Ti1 and the stored torque value TQ1. According to this, it is possible to reduce quantization noise (error) when converting the measured values of the execution time Ti1 and the stored torque value TQ1 into digital values.
  • the storage unit may store a moving average value of the linearized data as a stored excess air ratio ⁇ b regarding the conversion limit threshold. According to this, it is possible to reduce quantization noise (error) when converting linearized data into digital values.
  • the excess rate calculation unit may use a predetermined value as the stored excess air rate ⁇ b regarding the conversion limit threshold. According to this, the arithmetic processing for determining the stored excess air ratio ⁇ b is omitted, so that control in a high rotation range can be facilitated.
  • the limit threshold setting section sets the conversion limit threshold according to the temperature of the detecting section based on a lookup table that associates the temperature of the detecting section with the conversion limit threshold. Good too.
  • the limit threshold value setting section sets the conversion limit threshold value as described above, it is possible to set an appropriate conversion limit threshold value according to the temperature of the detection section.
  • the oxygen sensor is a resistance type oxygen sensor whose resistance value changes depending on the oxygen concentration
  • the excess rate calculation unit calculates the temperature and detected value of the detection unit of the resistance type oxygen sensor and the air excess rate ⁇ of the exhaust gas.
  • the data map is provided with an associated data map, and the linearized data is obtained using the data map, and when the detected value or the linearized data is less than or equal to the conversion limit threshold, the linearized data is performed.
  • the obtained data may be regarded as the excess air ratio ⁇ of the exhaust gas.
  • the linearized data obtained from the data map is regarded as the excess air ratio ⁇ , so the An appropriate excess air ratio ⁇ can be obtained.
  • FIG. 1 is a schematic diagram schematically showing the configuration of a main part of an internal combustion engine including an excess air ratio calculation device according to an embodiment of the present invention.
  • 2 is a block diagram showing the main configuration of an ECU of the internal combustion engine of FIG. 1.
  • FIG. 3 is a flowchart showing an excess rate calculation process in which an excess air rate ⁇ is calculated by an excess rate calculation unit in the ECU of FIG. 2; 4 is a graph showing how the excess air ratio ⁇ in the stoichiometric region is calculated in the process of FIG. 3.
  • FIG. 4 is a diagram showing a graph corresponding to a look-up table for calculating a lean side threshold value LREF and a rich side threshold value RREF, and a data map for calculating an excess air ratio ⁇ in the process of FIG. 3.
  • FIG. 4 is a graph schematically showing how the excess air ratio ⁇ calculated by the process of FIG. 3 changes;
  • 3 is a graph showing a lookup table in which the latest torque value TQ2 used for calculating the substitute value R in the ECU of FIG. 2 is associated with a torque contribution rate Tc.
  • 8 is a graph showing that the accuracy of the alternative value R is improved by using the torque contribution rate Tc of FIG. 7 for calculating the alternative value R.
  • FIG. 4 is a diagram showing a graph corresponding to a look-up table for calculating a lean side threshold value LREF and a rich side threshold value RREF, and a data map for calculating an excess air ratio ⁇ in the process of FIG. 3.
  • FIG. 4 is
  • FIG. 1 shows the configuration of the main parts of a four-cycle internal combustion engine equipped with an excess air ratio calculation device according to an embodiment of the present invention.
  • an engine body 1 of this internal combustion engine has an intake pipe 2 provided at an intake port, and an air cleaner 4 provided in the intake pipe 2 that controls the amount of intake air supplied to the intake port. and a throttle valve 3 that is adjusted according to the
  • 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 near the intake port of the intake pipe 2. Fuel is fed under pressure 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 temperature sensor 8 that detects the temperature of the intake air in the intake pipe 2.
  • a catalyst 11 that reduces unburned components in the exhaust gas from the exhaust pipe 10 and an oxygen sensor 12 that detects the oxygen concentration in the exhaust gas are provided.
  • a spark plug 13 connected to an ignition device 14 is fixed to the engine body 1.
  • the ECU (electronic control unit) 15 issues an ignition timing command to the ignition device 14, spark discharge occurs within the cylinder combustion chamber of the engine body 1.
  • Analog voltages indicating respective detection values of the throttle sensor 5, intake pressure sensor 7, intake temperature sensor 8, oxygen sensor 12, cooling water temperature sensor 17, and atmospheric pressure sensor 20 that detects atmospheric pressure are input to the ECU 15. .
  • the above-mentioned fuel injection valve 6 is connected to the ECU 15.
  • a signal indicating the rotational angular position of the crankshaft 18 from the crank angle sensor 19 is further input to the ECU 15. That is, the crank angle sensor 19 includes a plurality of convex portions provided at predetermined angle intervals (for example, 15 degrees) on the outer circumference of the rotor 19a that rotates in conjunction with the crankshaft 18, and arranged near the outer circumference of the rotor 19a.
  • the pickup 19b detects it magnetically or optically, and the pickup 19b generates a pulse (crank signal) every time the crankshaft 18 rotates by a predetermined angle.
  • crank angle sensor 19 outputs a signal indicating the reference angle to the ECU 15 every time the piston 9 reaches the top dead center or every time the crankshaft 18 rotates 360 degrees.
  • FIG. 2 shows the main configuration of the ECU 15.
  • the oxygen sensor 12 that supplies a detection signal of the oxygen concentration in the exhaust gas to the ECU 15 is a sensor element that is provided in contact with the exhaust gas of the internal combustion engine and serves as a detection unit that detects the oxygen concentration in the exhaust gas. 12a, 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 temperature characteristic in which a detected value changes depending on the temperature of the sensor element 12a.
  • a titania type sensor element which is a resistance type oxygen sensor whose resistance value changes depending on the oxygen concentration, is used.
  • the ECU 15 includes a heater controller 22 that controls the sensor heater 12b, a temperature calculation section (temperature detection section) 23 that calculates a temperature value T indicating the temperature of the sensor element 12a, and an output signal of the sensor element 12a. It includes a voltage calculation unit 24 that converts into a voltage value VHG indicating oxygen concentration.
  • the temperature of the sensor heater 12b is controlled by the heater controller 22 by performing pulse width modulation (PWM) control by the ECU 15 on the amount of current I supplied to the sensor heater 12b from an unillustrated power source (storage battery). 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 using the ECU 15. The calculation results from the temperature calculation section 23 and the voltage calculation section 24 are supplied to an alternative value calculation section 26 of the excess rate calculation section 25, which will be described later.
  • PWM pulse width modulation
  • the ECU 15 also includes a rotational speed calculation unit 27 that calculates the rotational speed NE and angular velocity NETC of the internal combustion engine based on the detection results of the crank angle sensor 19, and a rotational speed calculation unit 27 that calculates the rotational speed NE and angular velocity NETC of the internal combustion engine based on the detection results of the crank angle sensor 19, and a It includes an excess air ratio calculation section 25 that calculates an excess air ratio ⁇ based on the voltage value VHG and the angular velocity NETC from the rotational speed calculation section 27.
  • the ECU 15 includes a target value calculation unit 28 that calculates a target excess air ratio ⁇ cmd based on an estimated value of the amount of oxygen stored in the catalyst 11, etc., a rotation speed NE from a rotation speed calculation unit 27, and an intake pressure sensor.
  • the basic injection amount calculation unit 29 calculates the basic injection amount BJ based on the pressure PM in the intake pipe 2 from 7, and the excess air ratio ⁇ calculated by the excess ratio calculation unit 25 is made to match the target excess air ratio ⁇ cmd.
  • a feedback coefficient calculation section 30 calculates a feedback coefficient k for correcting the basic fuel injection amount BJ calculated by the basic injection amount calculation section 29, and calculates an injection amount Ti based on the feedback coefficient k and the basic injection amount BJ. It also includes an injection amount calculation section 31 that operates the fuel injection valve 6 .
  • PID control is performed based on a comparison between the excess air ratio ⁇ and the target excess air ratio ⁇ cmd, and the feedback coefficient k is calculated.
  • the fuel injection valve 6 is opened for a corresponding time, and the engine main body 1 Fuel is injected into the cylinder combustion chamber in an amount corresponding to the feedback coefficient k of the PID control based on a comparison between the excess air ratio ⁇ and the target excess air ratio ⁇ cmd.
  • the excess ratio calculation unit 25 linearizes the voltage value VHG with respect to the excess air ratio while compensating for its temperature characteristics.
  • the excess air ratio ⁇ of the exhaust gas is calculated using the data LD obtained. However, as will be described later, this calculation is applied when the voltage value VHG is less than or equal to the lean side threshold value LREF, and when the voltage value VHG is larger than the lean side threshold value LREF, the excess air ratio ⁇ is determined 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 speed NETC of the internal combustion engine, and a limit threshold setting unit 33 that sets a conversion limit threshold for the above-mentioned linearization conversion. , a storage unit 34 that stores data necessary to calculate an alternative value R for the excess air ratio ⁇ , an alternative value calculation unit 26 that calculates an alternative value R, and a torque contribution rate that sets a torque contribution rate Tc to be described later. and a setting section 44.
  • the limit threshold setting unit 33 sets a lean side threshold LREF, which is a conversion limit threshold on the lean side, and a rich side threshold RREF, which is a conversion limit threshold on the rich side, for the voltage value VHG from the voltage calculation unit 24, as conversion limit thresholds. do.
  • LREF lean side threshold
  • RREF rich side threshold
  • FIG. 5 shows the horizontal axis scale values in the horizontal direction in FIG. 5 corresponding to the temperature value T calculated by the temperature calculation unit 23, and the voltage value VHG calculated by the voltage calculation unit
  • a data map is posted, which has vertical axis scale values in the vertical direction, and in which the numerical values of the plurality of data LD are set, which are associated with the voltage value VHG and temperature value T as coordinates.
  • examples of look-up tables corresponding to graphs 35 and 36 for determining the lean-side threshold value LREF and the rich-side threshold value RREF are shown as diagrams superimposed on the data map, respectively.
  • Graph 35 shows, for example, when the excess air ratio ⁇ as the boundary between the lean region and the stoichiometric region is 1.02, and the points on the data map whose coordinates are the voltage value VHG and temperature value T that have this value are plotted. This is a graph obtained by finding multiple points and connecting these multiple points by line interpolation. Further, the graph 36 shows, for example, that the excess air ratio ⁇ as the boundary between the stoichiometric region and the rich region is set to 0.98, and the voltage value VHG and temperature value T corresponding to this value are set as coordinates on the above data map. This is a graph obtained by finding a plurality of points and connecting the plurality of points by line interpolation.
  • the limit threshold setting unit 33 determines that the voltage value v0 derived from the coordinate t0 is in the lean region and the stoichiometric range. It can be set as the lean-side threshold LREF for the boundary with the region.
  • the voltage value v1 derived from the coordinate t0 is It can be set as a rich-side threshold RREF.
  • the storage unit 34 stores, as data necessary for calculating the alternative value R, an execution time Ti1 of fuel injection by the fuel injection valve 6 and a stored torque value TQ1 when the voltage value VHG from the voltage calculation unit 24 is less than or equal to the lean side threshold value LREF. , the excess air ratio ⁇ b related to the lean side threshold value LREF is stored.
  • Tc is a torque contribution rate for improving the calculation accuracy of the alternative value R.
  • Tc 1
  • the torque contribution rate Tc is set in accordance with the torque value TQ2 by the torque contribution rate setting unit 44 using a lookup table as shown in FIG. 7 in which the torque contribution rate Tc is associated with the torque value TQ2.
  • FIG. 8 shows that the accuracy of the alternative value R is improved by using the torque contribution rate Tc for calculating the alternative value R.
  • Changes in the calculated value of the alternative value R when the value is 0.1 (10%) are illustrated for the lean region A, the stoichiometric region B, and the rich region C.
  • a graph 39 in FIG. 8 shows changes in the actual excess air ratio, and a graph 40 shows changes in the calculated value of the alternative value R.
  • a graph 41 shows the fuel injection amount Ti
  • a graph 42 shows the rotational speed NE of the internal combustion engine
  • a graph 43 shows the change in the opening degree of the throttle valve 3.
  • the calculation accuracy of the alternative value R is determined by the fact that the proportion of lean due to a decrease in the fuel injection amount Ti and the proportion of rich due to a decrease in torque due to lean are unmatched.
  • the actual excess air ratio and the alternative value R in the graph 40 deviate from each other, and the deviation width increases.
  • FIG. 8 shows a case where the torque TQ is small.
  • the substitute value R calculated in this way is determined by the excess air ratio ⁇ as the linearized data LD when the voltage value VHG exceeds the conversion limit threshold LREF in the excess ratio calculation unit 25. Instead, it is considered to be the excess air ratio ⁇ of the exhaust gas.
  • FIG. 3 shows an excess rate calculation process in which the excess air rate ⁇ is calculated by the excess rate calculation unit 25. Note that the control by the ECU 15 including this excess rate calculation process is executed in synchronization with the stroke of the internal combustion engine based on a pulse signal from the crank angle sensor 19 indicating the rotational angular position of the crankshaft 18.
  • 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 rotational speed calculation unit 27.
  • step S2 based on the temperature value T from the temperature calculation section 23, the limit threshold setting section 33 uses the lookup table corresponding to the graphs 35 and 36 in FIG. Set threshold RREF.
  • step S3 the voltage value VHG is obtained from the voltage calculation unit 24.
  • step S4 the above-mentioned data map (FIG. 5) is scanned based on the temperature value T obtained in step S2 and the voltage value VHG obtained in step S3.
  • Data LD is obtained which has been linearized into excess air ratio ⁇ while being compensated.
  • step S5 it is determined whether 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 that it is small, the flag F_DETECT is set to zero in the subsequent step S6, and the process proceeds to step S16, where the value of the data LD is set as the excess air ratio ⁇ value LAMBDA, and the excess ratio calculation process of FIG. 3 is performed. finish.
  • step S7 the voltage value VHG acquired in step S3 is larger than the lean side threshold LREF set in step S2. Determine whether or not.
  • step S7 when it is determined that the voltage value VHG is not large, in step S8, the voltage value lref of the lean side threshold LREF, the voltage value rref of the rich side threshold RREF, and the voltage value lref acquired in step S2 are determined.
  • the excess air ratio ⁇ is calculated as data LD obtained by linearizing the excess air ratio while compensating for the temperature characteristics of 12, and the process proceeds to step S9.
  • the excess air ratio ⁇ as the linearized data LD in step S8 is set in advance by numerically setting the excess air ratio ⁇ as the boundary between the predetermined stoichiometric region and the lean region.
  • a variable #LLMD (for example, 1.02) that can set If there is, it can be represented by a graph as shown in FIG. In this graph, the horizontal axis in the horizontal direction in FIG. 4 is the voltage value VHG, and the vertical axis in the vertical direction in FIG. 4 is the excess air ratio ⁇ . Therefore, for example, when the voltage value VHG is vhg1, the corresponding value ⁇ 1 of the excess air ratio ⁇ can be calculated using the following equation (2).
  • ⁇ 1 (((vhg1-rref) ⁇ (lref-rref)) ⁇ (#LLMD-#RLMD))+#RLMD (2)
  • step S9 the execution time Ti of the immediately preceding fuel injection by the fuel injection valve 6 and the torque TQ calculated in step S1 are respectively set as Ti1 and TQ1, and the excess air ratio ⁇ regarding the lean side threshold value LREF is stored as ⁇ b in the storage unit 34. .
  • the countdown timer value TIMER indicating the valid time of the memory is reset to its predetermined initial value #TMINIT.
  • 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 is set as the excess air ratio ⁇ value LAMBDA, and the excess ratio calculation process of FIG. 3 is ended.
  • the value of the data LD acquired in step S8 is stored as the stored excess air ratio ⁇ b.
  • k1 is a moving average coefficient
  • ⁇ ab is a moving average value in the previous control cycle stored in the storage unit 34.
  • 0.34 is used as the moving average coefficient k1.
  • the storage unit 34 stores moving average values as the fuel injection execution time Ti1 and the stored torque value TQ1, respectively.
  • the exponential moving average TiFLT of the fuel injection execution time Ti is calculated using the following equation (4) and stored as Ti1
  • the exponential moving average TQFLT of the torque value TQ is calculated using the following equation (5) and stored as Ti1. is stored as.
  • TiFLT Ti ⁇ k2+TiFLTb ⁇ (1-k2)
  • TQFLT TQ ⁇ k3+TQFLTb ⁇ (1-k3) (5)
  • k2 and k3 are moving average coefficients
  • TiFLTb and TQFLTb are moving average values in the previous control cycle stored in the storage unit 34.
  • different values can be used as the moving average coefficients k1, k2, and k3.
  • step S7 if it is determined that the voltage value VHG acquired in step S3 is larger than the lean side threshold value LREF, in step S10, it is determined whether the above-mentioned countdown timer value TIMER has reached zero. judge. If TIMER has reached zero, the flag F_DETECT is reset to 0 (step S11).
  • the alternative value calculation unit 26 calculates the alternative value R using the above-mentioned equation (1), and sets the value of the data LD to the alternative value R.
  • step S14 it is determined whether the value of the data LD set in step S13 is larger than a predetermined upper limit value #LLMT. If the value of data LD set in step S13 is larger than upper limit value #LLMT, the value of data LD is set to upper limit value #LLMT (step S15). In this case, for example, 1.25 can be used as the upper limit value #LLMT.
  • step S13 or step S15 The value of the data LD set in step S13 or step S15 is then set as the excess air ratio ⁇ value LAMBDA (step S16), thereby ending the excess ratio calculation process of FIG.
  • the ECU 15 converts the excess air rate ⁇ value LAMBDA calculated in the excess rate calculation process of FIG. In order to match the rate ⁇ cmd, the amount of fuel injected by the fuel injection valve 6 is controlled by PID control of the feedback coefficient calculation unit 30.
  • FIG. 6 is a graph schematically showing how the excess air ratio ⁇ value LAMBDA calculated by the excess air ratio calculation process of FIG. 3 changes.
  • the horizontal axis of the graph is a numerical value indicating the passage of time, and the vertical axis is the excess air ratio ⁇ .
  • Graph 37 in FIG. 6 shows that the actual exhaust air excess rate gradually increases at a constant rate of change in the range from the left end side to near the center of the horizontal axis in the left-right direction in FIG.
  • the voltage value VHG read by the voltage calculation unit 24 of the ECU 15 is The figure shows a numerical change in the excess air ratio ⁇ value when the excess air ratio ⁇ value is calculated using data directly linearized with respect to the excess air ratio while compensating for temperature characteristics.
  • the graph 38 shows that when the actual excess air ratio of the exhaust gas 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 on the lean side.
  • the excess air ratio ⁇ value is calculated using the data map described above ( Figure 5) or the data obtained by directly linearizing the voltage value VHG using equation (2).
  • 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 value of excess air ratio ⁇ of 1.020), the voltage value VHG is linearized.
  • the graph shows the numerical change in the excess air ratio ⁇ value when the substitute value R obtained by the above-mentioned formula (1) is used as the excess air ratio ⁇ value in place of the above data.
  • the excess ratio calculation unit 25 can interlock with the actual excess air ratio of exhaust gas over the entire range of the graph in FIG. It can be seen that the excess air ratio ⁇ value that changes proportionally can be supplied to the feedback coefficient calculation unit 30. This suppresses interruption of PID control by the feedback coefficient calculating section 30.
  • the lean side threshold value LREF and the rich side threshold value RREF are set using the lookup table corresponding to the graphs 35 and 36 as shown in FIG. and a rich-side threshold RREF.
  • a resistance type oxygen sensor is used as the oxygen sensor 12, and excess air is detected as data linearized using a data map as shown in FIG. Since the ratio ⁇ is obtained, the excess air ratio ⁇ can be obtained quickly.
  • the excess air rate ⁇ is calculated in synchronization with the stroke of the internal combustion engine. Even if the control period becomes short due to the increase in the fuel injection amount, the fuel injection amount and the torque value TQ can be obtained without any problem in accordance with the control period.
  • the torque contribution rate setting unit 44 sets the value of the torque contribution rate Tc according to the latest torque value TQ2 based on a lookup table in which the torque contribution rate Tc is associated with the torque value TQ2, so that an appropriate lookup is performed. By using the up-table, an appropriate value of the torque contribution rate Tc can be easily set.
  • the present invention is not limited to the above-described embodiments.
  • the voltage value lref of the lean side threshold LREF and the voltage value rref of the rich side threshold RREF are respectively set using lookup tables corresponding to graphs 35 and 36 (step S2), and in step S8
  • the configuration is such that linearized data LD is calculated using equation (2) including the voltage value lref and the rich side voltage value rref, this step S8 is omitted and the data map ( The value of the data LD obtained by scanning FIG. 5) may be set as the excess air ratio ⁇ value LAMBDA.
  • step S2 is omitted, and the data LD acquired in step S4 is determined in advance as a predetermined excess air ratio ⁇ corresponding to the lean side threshold LREF in steps S5 and S7 of FIG.
  • a value for example, 1.02 (excess air ratio ⁇ value #LLMD of lean side threshold value LREF), a value predetermined as a predetermined excess air ratio ⁇ corresponding to rich side threshold value RREF, for example 0.98 (excess air ratio ⁇ value #LLMD of lean side threshold value RREF). It can be configured to be compared with the excess air ratio ⁇ value #RLMD). According to this, the control of the ECU 15 at high rotation speeds can be facilitated by omitting the calculation of scanning the lookup table (step S2) and the calculation of the formula (2) (step S8).
  • a predetermined value for example 1.02, may be used as the stored excess air ratio ⁇ b regarding the conversion limit threshold. According to this, control at high rotation speeds can be facilitated by eliminating the need for calculation to obtain the above-mentioned moving average of the stored excess air ratio ⁇ b.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Abstract

Provided is an excess air ratio calculation device with which it is possible to reduce interruptions in a PID control when controlling the excess air ratio, thereby improving the control efficiency.　This excess air ratio calculation device comprises an excess ratio calculation unit (25) which calculates an excess air ratio λ, and a torque contribution setting unit (44) which sets a torque contribution Tc. The device stores a fuel injection duration Ti1, a stored torque value TQ1, and a stored excess air ratio λb when a voltage value VHG is at most a lean threshold LREF and, when the voltage value VHG exceeds the lean threshold LREF, uses the fuel injection duration as Ti2 and a torque value of an internal combustion engine as TQ2, and treats a substitution value R which is determined using the following equation as the excess air ratio λ.　R=((Ti1÷Ti2)÷(TQ1÷TQ2))×λb×Tc

Description

空気過剰率算出装置Excess air ratio calculation device
　本発明は、内燃機関の排気中の酸素濃度に基づいて空気過剰率を算出する空気過剰率算出装置に関する。 The present invention relates to an excess air ratio calculation device that calculates an excess air ratio based on the oxygen concentration in the exhaust gas of an internal combustion engine.
　従来、内燃機関における燃料噴射量に空燃比若しくは空気過剰率をフィードバックして排気ガスの浄化や燃料消費率の低減を図るために、空燃比若しくは空気過剰率を検出する技術が知られている（例えば、特許文献１参照）。 Conventionally, there is a known technology for detecting the air-fuel ratio or excess air ratio in order to feed back the air-fuel ratio or excess air ratio to the fuel injection amount in an internal combustion engine to purify exhaust gas or reduce the fuel consumption rate. For example, see Patent Document 1).
　特許文献１の技術においては、内燃機関に供給される燃料混合気の空燃比がリーンからリッチ又はその逆へと変化した際に出力信号が理論空燃比近傍で急変するジルコニア系の酸素センサを用いて、内燃機関の排気中の酸素濃度が検出される。そして、該検出結果に従い、内燃機関への燃料供給量が制御される。 The technology of Patent Document 1 uses a zirconia-based oxygen sensor whose output signal suddenly changes near the stoichiometric air-fuel ratio when the air-fuel ratio of the fuel mixture supplied to the internal combustion engine changes from lean to rich or vice versa. The oxygen concentration in the exhaust gas of the internal combustion engine is detected. Then, the amount of fuel supplied to the internal combustion engine is controlled according to the detection result.
　具体的には、酸素センサからの出力信号が、理論空燃比を含む所定領域（ストイキ領域）内の値であれば、空燃比が論理空燃比であることを表わす所定値の信号に変換される。一方、酸素センサからの出力信号が、所定領域内の値でなければ、空燃比の理論空燃比からのずれに対応して前記所定値から略一定の傾きで増加又は減少する信号値となるように変換される。そして、変換後の信号が目標値となるように、燃料供給量がフィードバック制御される。 Specifically, if the output signal from the oxygen sensor is within a predetermined range (stoichiometric range) that includes the stoichiometric air-fuel ratio, it is converted into a signal with a predetermined value indicating that the air-fuel ratio is the stoichiometric air-fuel ratio. . On the other hand, if the output signal from the oxygen sensor is not within the predetermined range, the signal value increases or decreases at a substantially constant slope from the predetermined value in response to the deviation of the air-fuel ratio from the stoichiometric air-fuel ratio. is converted to Then, the fuel supply amount is feedback-controlled so that the converted signal becomes the target value.
　他方、空燃比若しくは空気過剰率を検出する排気ガスセンサとして、酸素センサの内部抵抗に基づいて酸素を検出する抵抗型酸素センサを用いたものも知られている（例えば、特許文献２参照）。 On the other hand, as an exhaust gas sensor that detects the air-fuel ratio or excess air ratio, there is also known one that uses a resistance-type oxygen sensor that detects oxygen based on the internal resistance of the oxygen sensor (see, for example, Patent Document 2).
　特許文献２の酸素センサでは、排気ガスの酸素含有量を示す第１の値が、酸素センサの酸素感知部分の抵抗に基づいて決定される。酸素センサの温度を示す第２の値が、酸素センサのヒータ部分の抵抗に基づいて決定される。そして、第１の値及び第２の値の関数としての空燃比が、第３の値として決定される。これによれば、温度変化によって抵抗型酸素センサの出力特性が変化しても、空燃比が精度良く検出される。 In the oxygen sensor of Patent Document 2, the first value indicating the oxygen content of exhaust gas is determined based on the resistance of the oxygen sensing portion of the oxygen sensor. A second value indicative of the temperature of the oxygen sensor is determined based on the resistance of the heater portion of the oxygen sensor. The air-fuel ratio as a function of the first value and the second value is then determined as a third value. According to this, even if the output characteristics of the resistance-type oxygen sensor change due to temperature changes, the air-fuel ratio can be detected with high accuracy.
特許第２８０１５９６号公報Patent No. 2801596 米国特許第８９５９９８７号公報US Patent No. 8959987
　しかしながら、上記特許文献１の技術によれば、酸素センサとして使用されるジルコニア系のセンサは、抵抗型酸素センサに比べてコストが高く、応答性が低い。また、特許文献１の技術では、酸素センサの出力信号を空燃比に変換する際に、ストイキ領域外の空燃比については、検出信号と空燃比とが直線的な対応関係で変化するものとして変換している。この直線的な対応関係は、本来の対応関係からかけ離れている。 However, according to the technique disclosed in Patent Document 1, the zirconia-based sensor used as an oxygen sensor is higher in cost and has lower responsiveness than a resistance-type oxygen sensor. In addition, in the technology of Patent Document 1, when converting the output signal of the oxygen sensor into an air-fuel ratio, the air-fuel ratio outside the stoichiometric range is converted as the detection signal and the air-fuel ratio change in a linear correspondence relationship. are doing. This linear correspondence is far from the original correspondence.
　一方、上記特許文献２の技術によれば、抵抗型酸素センサの電圧のリーン側限界又はリッチ側限界域では、酸素センサの出力電圧を、空燃比に対して線形の特性を有するようにリニアライズすることが困難である。すなわち、両限界域での、空燃比に対する出力電圧の変化が急峻であるため、出力電圧を読み取るＡ／Ｄ変換器の分解能が不充分となる。 On the other hand, according to the technology disclosed in Patent Document 2, in the lean limit or rich limit range of the voltage of the resistance type oxygen sensor, the output voltage of the oxygen sensor is linearized so that it has a linear characteristic with respect to the air-fuel ratio. difficult to do. That is, since the output voltage changes sharply with respect to the air-fuel ratio in both limit regions, the resolution of the A/D converter that reads the output voltage becomes insufficient.
　したがって、空燃比若しくは空気過剰率の検出値に基づくこれらの目標値への調整に好ましく用いられるＰＩＤ制御により排気ガスの浄化等を行う際には、出力電圧の変化が急峻な部分において制御を中断せざるを得ないという問題がある。 Therefore, when purifying exhaust gas by PID control, which is preferably used to adjust the air-fuel ratio or excess air ratio to the target value based on the detected value, it is necessary to interrupt the control at a portion where the output voltage changes sharply. The problem is that we have no choice but to do so.
　本発明の目的は、かかる従来技術の問題点に鑑み、空気過剰率を制御する際のＰＩＤ制御の中断を減らして制御を効率化できる空気過剰率算出装置を提供することにある。 In view of the problems of the prior art, an object of the present invention is to provide an excess air ratio calculation device that can reduce interruptions in PID control when controlling the excess air ratio and improve control efficiency.
　本発明の空気過剰率算出装置は、
　燃料噴射弁を備える内燃機関の排気に接するように設けられて排気中の酸素濃度を検出する検出部を有し、その検出部からの検出値が前記検出部の温度に応じて変化する温度特性を有する酸素センサと、前記検出部の温度を推定又は検出する温度検出部と、前記検出値及び温度に基づき、前記検出値を、前記温度特性を補償しつつ空気過剰率に対してリニアライズ変換したデータを用いて前記排気の空気過剰率λを算出する過剰率算出部とを備える空気過剰率算出装置において、
　前記過剰率算出部は、
　前記内燃機関のクランク角速度に基づいて該内燃機関のトルク値を算出するトルク演算部と、
　前記リニアライズ変換についての変換限界閾値を設定する限界閾値設定部と、
　前記検出値又は前記リニアライズ変換したデータが前記変換限界閾値以下のときの前記燃料噴射弁による燃料噴射の実行時間をＴｉ１、前記トルク値を記憶トルク値ＴＱ１、前記変換限界閾値に関する空気過剰率λを記憶空気過剰率λｂとして記憶する記憶部と、
　トルク寄与率Ｔｃを設定するトルク寄与率設定部と、
　前記検出値又は前記リニアライズ変換したデータが前記変換限界閾値を超えているときの前記燃料噴射の実行時間をＴｉ２、最新（直近時）の前記トルク値をＴＱ２として、次式により代替値Ｒを算出する代替値演算部とを備え、
　Ｒ＝（（Ｔｉ１÷Ｔｉ２）÷（ＴＱ１÷ＴＱ２））×λｂ×Ｔｃ
　前記検出値又は前記リニアライズ変換したデータが前記変換限界閾値を超えている場合には、前記リニアライズ変換したデータに代えて、前記代替値Ｒを前記排気の空気過剰率λとみなすことを特徴とする。 The excess air ratio calculation device of the present invention includes:
The temperature characteristic includes a detection part that is provided in contact with the exhaust gas of an internal combustion engine equipped with a fuel injection valve and detects the oxygen concentration in the exhaust gas, and the detected value from the detection part changes depending on the temperature of the detection part. a temperature detection unit that estimates or detects the temperature of the detection unit; and a temperature detection unit that linearizes the detection value with respect to the excess air ratio while compensating the temperature characteristic based on the detection value and the temperature. an excess air ratio calculation unit that calculates the excess air ratio λ of the exhaust gas using the data obtained,
The excess rate calculation unit includes:
a torque calculation unit that calculates a torque value of the internal combustion engine based on a crank angular velocity of the internal combustion engine;
a limit threshold setting unit that sets a conversion limit threshold for the linearization conversion;
Execution time of fuel injection by the fuel injector when the detected value or the linearized data is less than or equal to the conversion limit threshold; Ti1; storage torque value TQ1 for the torque value; and excess air ratio λ with respect to the conversion limit threshold. a storage unit that stores λb as a storage excess air ratio λb;
a torque contribution rate setting unit that sets a torque contribution rate Tc;
The execution time of the fuel injection when the detected value or the linearized data exceeds the conversion limit threshold value is Ti2, the latest (most recent) torque value is TQ2, and the alternative value R is calculated by the following formula. and an alternative value calculation unit for calculating,
R=((Ti1÷Ti2)÷(TQ1÷TQ2))×λb×Tc
If the detected value or the linearized data exceeds the conversion limit threshold, the alternative value R is regarded as the excess air ratio λ of the exhaust gas in place of the linearized data. shall be.
　一般に、内燃機関の排気管に設けられる酸素センサにより検出される酸素濃度に基づいて得られる空気過剰率λに基づいて燃料噴射弁等をフィードバック制御する場合には、ＰＩＤ（比例積分微分）制御が好ましく用いられる。 Generally, when performing feedback control of fuel injection valves, etc. based on the excess air ratio λ obtained based on the oxygen concentration detected by an oxygen sensor installed in the exhaust pipe of an internal combustion engine, PID (proportional integral derivative) control is used. Preferably used.
　その理由は、ＰＩＤ制御によれば、ＰＩ（比例積分）制御に比べて、ハンチングの小さい素早い制御により、制御対象を目標値に対して正確にフィードバック制御することができるという点にある。このように空気過剰率λ（空燃比）を正確に目標値に向けて制御することにより、内燃機関の排気ガスを清浄化することができる。なお、空気過剰率は、空燃比を理論空燃比で除した値に等しいので、本発明では、空気過剰率の概念には空燃比も含まれる。 The reason is that PID control allows accurate feedback control of a controlled object with respect to a target value through quick control with less hunting than PI (proportional-integral) control. By accurately controlling the excess air ratio λ (air-fuel ratio) toward the target value in this manner, the exhaust gas of the internal combustion engine can be purified. Note that the excess air ratio is equal to the value obtained by dividing the air-fuel ratio by the stoichiometric air-fuel ratio, so in the present invention, the concept of the excess air ratio includes the air-fuel ratio.
　ところで、ＰＩＤ制御は、通常、出力が入力に対してリニアに変化する線形システムを対象としている。したがって、出力電圧特性の一部が非線形特性を呈する酸素センサを入力側に用いる場合、その非線形領域（計測限界領域）では、安定してＰＩＤ制御を行うことができず、制御対象値である空気過剰率が目標値に収束せずに発散するという問題がある。 By the way, PID control is usually aimed at a linear system in which the output changes linearly with respect to the input. Therefore, when using an oxygen sensor whose output voltage characteristics partially exhibit nonlinear characteristics on the input side, stable PID control cannot be performed in the nonlinear region (measurement limit region), and the There is a problem that the excess rate does not converge to the target value but diverges.
　このため、たとえば、酸素センサの検出値が一時的に酸素センサの希薄側の計測限界領域を超えるリーンスパイクが生じた場合には、ＰＩＤ制御を一時的に停止する必要がある。 Therefore, for example, if a lean spike occurs in which the detected value of the oxygen sensor temporarily exceeds the measurement limit region on the lean side of the oxygen sensor, it is necessary to temporarily stop the PID control.
　この点、本発明では、酸素センサの出力が変換限界閾値を超えて非線形となる場合には、酸素センサの検出値に基づく空気過剰率に代えて、代替値演算部により内燃機関のトルクの比及び燃料噴射量の比を用いて算出した代替値Ｒを空気過剰率λとみなしている。これにより、ＰＩＤ制御の中断を抑制して制御精度を高め、排気ガス浄化等の効率化を図ることができる。 In this regard, in the present invention, when the output of the oxygen sensor exceeds the conversion limit threshold and becomes non-linear, an alternative value calculating section is used to calculate the torque ratio of the internal combustion engine instead of the excess air ratio based on the detected value of the oxygen sensor. The alternative value R calculated using the ratio of the fuel injection amount and the fuel injection amount is regarded as the excess air ratio λ. Thereby, interruption of PID control can be suppressed, control accuracy can be improved, and efficiency of exhaust gas purification can be improved.
　また、代替値Ｒを算出する上述の式において、トルク寄与率Ｔｃの項がない（Ｔｃ＝１）場合には、燃料減少によりリーン化する割合と、リーン化でのトルク減少によるリッチ化する割合との不一致により実際の空気過剰率と代替値Ｒとの間に、トルク値の減少が大きいほど大きくなるずれが生じる。本発明では、トルク寄与率Ｔｃの項を採用しているので、トルク寄与率Ｔｃを適切に設定することにより、このずれ幅を小さくし、代替値Ｒの算出精度を向上させることができる。 In addition, in the above formula for calculating the alternative value R, if there is no torque contribution rate Tc term (Tc = 1), the ratio of lean due to fuel reduction and the rich ratio due to torque reduction due to lean conversion. Due to the discrepancy between the actual excess air ratio and the alternative value R, a deviation occurs which increases as the torque value decreases. In the present invention, since the term torque contribution rate Tc is adopted, by appropriately setting the torque contribution rate Tc, it is possible to reduce the width of this deviation and improve the calculation accuracy of the alternative value R.
　本発明において、前記トルク寄与率設定部は、前記トルク値に前記トルク寄与率Ｔｃを対応付けたルックアップテーブルに基づき、前記トルク寄与率Ｔｃの値を前記最新のトルク値ＴＱ２に応じて設定してもよい。これによれば、適切なルックアップテーブルを用いることにより、適切なトルク寄与率Ｔｃの値を容易に設定することができる。 In the present invention, the torque contribution rate setting unit sets the value of the torque contribution rate Tc according to the latest torque value TQ2 based on a lookup table in which the torque contribution rate Tc is associated with the torque value. It's okay. According to this, by using an appropriate lookup table, it is possible to easily set an appropriate value of the torque contribution rate Tc.
　また、本発明において、前記記憶部は、前記燃料噴射の実行時間Ｔｉ１及び前記記憶トルク値ＴＱ１として、それぞれの移動平均値を記憶してもよい。これによれば、実行時間Ｔｉ１、記憶トルク値ＴＱ１の計測値をデジタル値に変換する際の量子化ノイズ（誤差）を低減することができる。 Furthermore, in the present invention, the storage unit may store moving average values of the fuel injection execution time Ti1 and the stored torque value TQ1. According to this, it is possible to reduce quantization noise (error) when converting the measured values of the execution time Ti1 and the stored torque value TQ1 into digital values.
　また、本発明において、前記記憶部は、前記リニアライズ変換したデータの移動平均値を前記変換限界閾値に関する記憶空気過剰率λｂとして記憶してもよい。これによれば、リニアライズ変換したデータをデジタル値に変換する際の量子化ノイズ（誤差）を低減することができる。 Furthermore, in the present invention, the storage unit may store a moving average value of the linearized data as a stored excess air ratio λb regarding the conversion limit threshold. According to this, it is possible to reduce quantization noise (error) when converting linearized data into digital values.
　また、本発明において、前記過剰率算出部は、前記変換限界閾値に関する記憶空気過剰率λｂとして、あらかじめ定めた値を用いてもよい。これによれば、記憶空気過剰率λｂを求めるための演算処理が省略されるので、高回転域での制御を容易化することができる。 Furthermore, in the present invention, the excess rate calculation unit may use a predetermined value as the stored excess air rate λb regarding the conversion limit threshold. According to this, the arithmetic processing for determining the stored excess air ratio λb is omitted, so that control in a high rotation range can be facilitated.
　また、本発明において、前記限界閾値設定部は、前記検出部の温度と前記変換限界閾値とを対応付けたルックアップテーブルに基づき、前記変換限界閾値を前記検出部の温度に応じて設定してもよい。 Further, in the present invention, the limit threshold setting section sets the conversion limit threshold according to the temperature of the detecting section based on a lookup table that associates the temperature of the detecting section with the conversion limit threshold. Good too.
　酸素センサは、その検出部の温度が低下すると、出力値のダイナミックレンジ（センサ出力電圧の線形領域の最小値と最大値の比率）が変化する。このため、酸素センサの検出部の温度に応じて前記変換限界閾値を変化させる必要がある。この点、限界閾値設定部は、上記のように変換限界閾値を設定するので、検出部の温度に応じた適切な変換限界閾値を設定することができる。 When the temperature of the detection part of an 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 according to the temperature of the detection section of the oxygen sensor. In this regard, since the limit threshold value setting section sets the conversion limit threshold value as described above, it is possible to set an appropriate conversion limit threshold value according to the temperature of the detection section.
　前記酸素センサは、酸素濃度で抵抗値が変化する抵抗型酸素センサであり、前記過剰率算出部は、前記抵抗型酸素センサの検出部の温度及び検出値と前記排気の空気過剰率λとを対応付けたデータマップを備え、該データマップを用いて前記リニアライズ変換されたデータを取得するとともに、前記検出値又は前記リニアライズ変換されたデータが前記変換限界閾値以下のとき、前記リニアライズ変換されたデータを前記排気の空気過剰率λとみなすものであってもよい。 The oxygen sensor is a resistance type oxygen sensor whose resistance value changes depending on the oxygen concentration, and the excess rate calculation unit calculates the temperature and detected value of the detection unit of the resistance type oxygen sensor and the air excess rate λ of the exhaust gas. The data map is provided with an associated data map, and the linearized data is obtained using the data map, and when the detected value or the linearized data is less than or equal to the conversion limit threshold, the linearized data is performed. The obtained data may be regarded as the excess air ratio λ of the exhaust gas.
　これによれば、酸素センサによる検出値又はリニアライズ変換されたデータが変換限界閾値以下のとき、データマップにより得られるリニアライズ変換されたデータが空気過剰率λとみなされるので、温度に応じた適切な空気過剰率λを得ることができる。 According to this, when the detected value by the oxygen sensor or the linearized data is below the conversion limit threshold, the linearized data obtained from the data map is regarded as the excess air ratio λ, so the An appropriate excess air ratio λ can be obtained.
本発明の一実施形態に係る空気過剰率算出装置を備える内燃機関の主要部の構成を模式的に示す模式図である。1 is a schematic diagram schematically showing the configuration of a main part of an internal combustion engine including an excess air ratio calculation device according to an embodiment of the present invention. 図１の内燃機関のＥＣＵにおける主要な構成を示すブロック図である。2 is a block diagram showing the main configuration of an ECU of the internal combustion engine of FIG. 1. FIG. 図２のＥＣＵにおいて過剰率算出部により空気過剰率λを算出する過剰率算出処理を示すフローチャートである。3 is a flowchart showing an excess rate calculation process in which an excess air rate λ is calculated by an excess rate calculation unit in the ECU of FIG. 2; 図３の処理において、ストイキ領域における空気過剰率λを算出する様子を示すグラフである。4 is a graph showing how the excess air ratio λ in the stoichiometric region is calculated in the process of FIG. 3. 図３の処理において、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦを求めるためのルックアップテーブルに対応するグラフ、及び空気過剰率λを算出するためのデータマップを示す図である。4 is a diagram showing a graph corresponding to a look-up table for calculating a lean side threshold value LREF and a rich side threshold value RREF, and a data map for calculating an excess air ratio λ in the process of FIG. 3. FIG. 図３の処理によって算出される空気過剰率λの変化の様子を模式的に示すグラフである。4 is a graph schematically showing how the excess air ratio λ calculated by the process of FIG. 3 changes; 図２のＥＣＵにおける代替値Ｒの算出に使用する最新のトルク値ＴＱ２にトルク寄与率Ｔｃを対応付けたルックアップテーブルを示すグラフである。3 is a graph showing a lookup table in which the latest torque value TQ2 used for calculating the substitute value R in the ECU of FIG. 2 is associated with a torque contribution rate Tc. 図７のトルク寄与率Ｔｃを代替値Ｒの算出に使用することにより代替値Ｒの精度が向上することを示すグラフである。8 is a graph showing that the accuracy of the alternative value R is improved by using the torque contribution rate Tc of FIG. 7 for calculating the alternative value R. FIG.
　以下、図面を用いて本発明の実施形態を説明する。図１は、本発明の一実施形態に係る空気過剰率算出装置を備える４サイクル形式の内燃機関の主要部の構成を示す。同図に示すように、この内燃機関の機関本体１は、吸入ポートに設けられた吸気管２と、吸気管２内に設けられてエアクリーナ４から吸入ポートに供給される吸気の量を開度に応じて調整するスロットル弁３とを備える。 Hereinafter, embodiments of the present invention will be described using the drawings. FIG. 1 shows the configuration of the main parts of a four-cycle internal combustion engine equipped with an excess air ratio calculation device according to an embodiment of the present invention. As shown in the figure, an engine body 1 of this internal combustion engine has an intake pipe 2 provided at an intake port, and an air cleaner 4 provided in the intake pipe 2 that controls the amount of intake air supplied to the intake port. and a throttle valve 3 that is adjusted according to the
　スロットル弁３には、スロットル弁３の開度を検出するスロットルセンサ５が設けられる。吸気管２の吸入ポート近傍には、燃料を噴射する燃料噴射弁６が設けられる。燃料噴射弁６には、図示しない燃料タンクから燃料ポンプによって燃料が圧送される。 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 near the intake port of the intake pipe 2. Fuel is fed under pressure to the fuel injection valve 6 from a fuel tank (not shown) by a fuel pump.
　吸気管２には、吸気管２における吸気圧を検出する吸気圧センサ７及び吸気管２内の吸入空気の温度を検出する吸気温センサ８が設けられる。 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 temperature sensor 8 that detects the temperature of the intake air in the intake pipe 2.
　機関本体１の排気ポートに連結された排気管１０内には、排気管１０の排気中の未燃焼成分を低減させる触媒１１及び排気中の酸素濃度を検出する酸素センサ１２が設けられる。 In the exhaust pipe 10 connected to the exhaust port of the engine body 1, a catalyst 11 that reduces unburned components in the exhaust gas from the exhaust pipe 10 and an oxygen sensor 12 that detects the oxygen concentration in the exhaust gas are provided.
　また、エンジン本体１には、点火装置１４に接続された点火プラグ１３が固着される。ＥＣＵ（電子制御ユニット）１５が点火装置１４に対して点火タイミングの指令を発することにより、機関本体１のシリンダ燃焼室内で火花放電が生じる。 Further, a spark plug 13 connected to an 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 within the cylinder combustion chamber of the engine body 1.
　ＥＣＵ１５には、スロットルセンサ５、吸気圧センサ７、吸気温センサ８、酸素センサ１２、冷却水温センサ１７、及び大気圧を検出する大気圧センサ２０のそれぞれの検出値を示すアナログ電圧が入力される。また、ＥＣＵ１５には、上記の燃料噴射弁６が接続される。 Analog voltages indicating respective detection values of the throttle sensor 5, intake pressure sensor 7, intake temperature sensor 8, oxygen sensor 12, cooling water temperature sensor 17, and atmospheric pressure sensor 20 that detects atmospheric pressure are input to the ECU 15. . Moreover, the above-mentioned fuel injection valve 6 is connected to the ECU 15.
　ＥＣＵ１５には、さらに、クランク角度センサ１９からのクランク軸１８の回転角度位置を示す信号が入力される。すなわち、クランク角度センサ１９は、クランク軸１８に連動して回転するロータ１９ａの外周に所定角度（例えば、１５度）毎に設けられた複数の凸部を、ロータ１９ａの外周近傍に配置されたピックアップ１９ｂによって磁気的あるいは光学的に検出し、ピックアップ１９ｂからクランク軸１８の所定角度の回転毎にパルス（クランク信号）を発生する。 A signal indicating the rotational angular position of the crankshaft 18 from the crank angle sensor 19 is further input to the ECU 15. That is, the crank angle sensor 19 includes a plurality of convex portions provided at predetermined angle intervals (for example, 15 degrees) on the outer circumference of the rotor 19a that rotates in conjunction with the crankshaft 18, and arranged near the outer circumference of the rotor 19a. The pickup 19b detects it magnetically or optically, and the pickup 19b generates a pulse (crank signal) every time the crankshaft 18 rotates by a predetermined angle.
　具体的には、クランク角度センサ１９は、ピストン９が上死点に至る毎に、又はクランク軸１８が３６０度回転する毎に基準角度を示す信号をＥＣＵ１５に出力する。 Specifically, the crank angle sensor 19 outputs a signal indicating the reference angle to the ECU 15 every time the piston 9 reaches the top dead center or every time the crankshaft 18 rotates 360 degrees.
　図２は、ＥＣＵ１５における主要な構成を示す。同図に示すように、ＥＣＵ１５に排気中の酸素濃度の検出信号を供給する酸素センサ１２は、内燃機関の排気に接するように設けられて排気中の酸素濃度を検出する検出部としてのセンサ素子１２ａと、センサ素子１２ａに隣接して同センサ素子１２ａを加熱するセンサヒータ１２ｂとを備える。 FIG. 2 shows the main configuration of the ECU 15. As shown in the figure, the oxygen sensor 12 that supplies a detection signal of the oxygen concentration in the exhaust gas to the ECU 15 is a sensor element that is provided in contact with the exhaust gas of the internal combustion engine and serves as a detection unit that detects the oxygen concentration in the exhaust gas. 12a, and a sensor heater 12b that is adjacent to the sensor element 12a and heats the sensor element 12a.
　センサ素子１２ａは、検出値がセンサ素子１２ａの温度に応じて変化する温度特性を有する。センサ素子１２ａとしては、本実施形態では、酸素濃度に応じて抵抗値が変化する抵抗型酸素センサであるチタニア型のセンサ素子が用いられる。 The sensor element 12a has a temperature characteristic in which a detected value changes depending on the temperature of the sensor element 12a. As the sensor element 12a, in this embodiment, a titania type sensor element, which is a resistance type oxygen sensor whose resistance value changes depending on the oxygen concentration, is used.
　ＥＣＵ１５は、センサヒータ１２ｂを制御するヒータ制御器２２と、センサ素子１２ａの温度を示す温度値Ｔを算出する温度算出部（温度検出部）２３と、センサ素子１２ａの出力信号を、排気中の酸素濃度を示す電圧値ＶＨＧに変換する電圧算出部２４とを備える。 The ECU 15 includes a heater controller 22 that controls the sensor heater 12b, a temperature calculation section (temperature detection section) 23 that calculates a temperature value T indicating the temperature of the sensor element 12a, and an output signal of the sensor element 12a. It includes a voltage calculation unit 24 that converts into a voltage value VHG indicating oxygen concentration.
　ヒータ制御器２２によるセンサヒータ１２ｂの温度の制御は、不図示の電源（蓄電池）からセンサヒータ１２ｂに供給される通電電流量ＩをＥＣＵ１５でパルス幅変調（ＰＷＭ）制御することにより行われる。また、温度算出部２３による温度値Ｔの算出は、たとえば、センサヒータ１２ｂの抵抗値をＥＣＵ１５で読み取ることにより行われる。温度算出部２３及び電圧算出部２４における算出結果は、後述する過剰率算出部２５の代替値演算部２６に供給される。 The temperature of the sensor heater 12b is controlled by the heater controller 22 by performing pulse width modulation (PWM) control by the ECU 15 on the amount of current I supplied to the sensor heater 12b from an unillustrated power source (storage battery). 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 using the ECU 15. The calculation results from the temperature calculation section 23 and the voltage calculation section 24 are supplied to an alternative value calculation section 26 of the excess rate calculation section 25, which will be described later.
　また、ＥＣＵ１５は、クランク角度センサ１９の検出結果に基づいて内燃機関の回転速度ＮＥ及び角速度ＮＥＴＣを算出する回転速度演算部２７と、温度算出部２３からの温度値Ｔ、電圧算出部２４からの電圧値ＶＨＧ、及び回転速度演算部２７からの角速度ＮＥＴＣに基づいて空気過剰率λを算出する過剰率算出部２５とを備える。 The ECU 15 also includes a rotational speed calculation unit 27 that calculates the rotational speed NE and angular velocity NETC of the internal combustion engine based on the detection results of the crank angle sensor 19, and a rotational speed calculation unit 27 that calculates the rotational speed NE and angular velocity NETC of the internal combustion engine based on the detection results of the crank angle sensor 19, and a It includes an excess air ratio calculation section 25 that calculates an excess air ratio λ based on the voltage value VHG and the angular velocity NETC from the rotational speed calculation section 27.
　さらに、ＥＣＵ１５は、目標とする空気過剰率λcmdを触媒１１における貯蔵酸素量の推定値等に基づいて算出する目標値演算部２８と、回転速度演算部２７からの回転速度ＮＥ、及び吸気圧センサ７からの吸気管２内の圧力ＰＭに基づいて基本噴射量ＢＪを算出する基本噴射量演算部２９と、過剰率算出部２５により算出された空気過剰率λを目標空気過剰率λcmdに一致させるべく、基本噴射量演算部２９が算出した基本燃料噴射量ＢＪを補正するためのフィードバック係数ｋを求めるフィードバック係数演算部３０と、フィードバック係数ｋ及び基本噴射量ＢＪに基づいて噴射量Ｔｉを算出するとともに、燃料噴射弁６を作動させる噴射量演算部３１とを備える。 Furthermore, the ECU 15 includes a target value calculation unit 28 that calculates a target excess air ratio λcmd based on an estimated value of the amount of oxygen stored in the catalyst 11, etc., a rotation speed NE from a rotation speed calculation unit 27, and an intake pressure sensor. The basic injection amount calculation unit 29 calculates the basic injection amount BJ based on the pressure PM in the intake pipe 2 from 7, and the excess air ratio λ calculated by the excess ratio calculation unit 25 is made to match the target excess air ratio λcmd. In order to achieve this, a feedback coefficient calculation section 30 calculates a feedback coefficient k for correcting the basic fuel injection amount BJ calculated by the basic injection amount calculation section 29, and calculates an injection amount Ti based on the feedback coefficient k and the basic injection amount BJ. It also includes an injection amount calculation section 31 that operates the fuel injection valve 6 .
　フィードバック係数演算部３０においては、空気過剰率λと目標空気過剰率λcmdとの比較に基づいたＰＩＤ制御が行われてフィードバック係数ｋが演算される。噴射量演算部３１によりフィードバック係数ｋ及び基本噴射量ＢＪに基づいて算出される噴射量Ｔｉに基づき、これに対応する時間だけ、燃料噴射弁６が開弁され、而して、機関本体１のシリンダ燃焼室内には空気過剰率λと目標空気過剰率λcmdとの比較に基づいた上記ＰＩＤ制御のフィードバック係数ｋに応じた量の燃料が噴射される。 In the feedback coefficient calculating section 30, PID control is performed based on a comparison between the excess air ratio λ and the target excess air 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, and the engine main body 1 Fuel is injected into the cylinder combustion chamber in an amount corresponding to the feedback coefficient k of the PID control based on a comparison between the excess air ratio λ and the target excess air ratio λcmd.
　過剰率算出部２５は、電圧算出部２４からの電圧値ＶＨＧ及び温度算出部２３からの温度値Ｔに基づき、電圧値ＶＨＧを、その温度特性を補償しつつ空気過剰率に対してリニアライズ変換したデータＬＤを用いて排気の空気過剰率λを算出するものである。ただし、この算出は、後述するように、電圧値ＶＨＧがリーン側閾値ＬＲＥＦ以下の場合に適用され、電圧値ＶＨＧがリーン側閾値ＬＲＥＦより大きいときには、別の方法で空気過剰率λが求められる。 Based on the voltage value VHG from the voltage calculation unit 24 and the temperature value T from the temperature calculation unit 23, the excess ratio calculation unit 25 linearizes the voltage value VHG with respect to the excess air ratio while compensating for its temperature characteristics. The excess air ratio λ of the exhaust gas is calculated using the data LD obtained. However, as will be described later, this calculation is applied when the voltage value VHG is less than or equal to the lean side threshold value LREF, and when the voltage value VHG is larger than the lean side threshold value LREF, the excess air ratio λ is determined by another method.
　過剰率算出部２５は、内燃機関のクランク角速度ＮＥＴＣに基づいて内燃機関のトルク値ＴＱを算出するトルク演算部３２と、上述のリニアライズ変換についての変換限界閾値を設定する限界閾値設定部３３と、空気過剰率λの代替値Ｒを算出するのに必要なデータを記憶する記憶部３４と、代替値Ｒを算出する代替値演算部２６と、後述のトルク寄与率Ｔｃを設定するトルク寄与率設定部４４とを備える。 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 speed NETC of the internal combustion engine, and a limit threshold setting unit 33 that sets a conversion limit threshold for the above-mentioned linearization conversion. , a storage unit 34 that stores data necessary to calculate an alternative value R for the excess air ratio λ, an alternative value calculation unit 26 that calculates an alternative value R, and a torque contribution rate that sets a torque contribution rate Tc to be described later. and a setting section 44.
　限界閾値設定部３３は、変換限界閾値として、リーン側の変換限界閾値であるリーン側閾値ＬＲＥＦ及びリッチ側の変換限界閾値であるリッチ側閾値ＲＲＥＦを、電圧算出部２４からの電圧値ＶＨＧについて設定する。ただし、チタニア型のセンサ素子１２ａは、温度が変化すると、出力値のダイナミックレンジ（センサ出力電圧の線形領域の最小値と最大値の各値）が変化するため、温度算出部２３からの温度値Ｔに応じて変換限界閾値を変化させる必要がある。 The limit threshold setting unit 33 sets a lean side threshold LREF, which is a conversion limit threshold on the lean side, and a rich side threshold RREF, which is a conversion limit threshold on the rich side, for the voltage value VHG from the voltage calculation unit 24, as conversion limit thresholds. do. However, in the titania type sensor element 12a, when the temperature changes, the dynamic range of the output value (minimum and maximum values in the linear region of the sensor output voltage) changes. It is necessary to change the conversion limit threshold according to T.
　図５を併せて参照して、該図５は、温度算出部２３が算出する温度値Ｔに対応する図５において左右方向の横軸目盛値と、電圧算出部２４が算出する電圧値ＶＨＧに対応する図５において上下方向の縦軸目盛値とを有するとともに、電圧値ＶＨＧ及び温度値Ｔを座標として対応付けられた複数個の前記データＬＤの数値が設定されているデータマップを掲出したものであり、しかも、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦを求めるためのグラフ３５、３６に対応するルックアップテーブルの各一例をデータマップ上に夫々重ね合わせた図として示している。 Referring also to FIG. 5, FIG. 5 shows the horizontal axis scale values in the horizontal direction in FIG. 5 corresponding to the temperature value T calculated by the temperature calculation unit 23, and the voltage value VHG calculated by the voltage calculation unit In the corresponding FIG. 5, a data map is posted, which has vertical axis scale values in the vertical direction, and in which the numerical values of the plurality of data LD are set, which are associated with the voltage value VHG and temperature value T as coordinates. Moreover, examples of look-up tables corresponding to graphs 35 and 36 for determining the lean-side threshold value LREF and the rich-side threshold value RREF are shown as diagrams superimposed on the data map, respectively.
　このようなデータマップと、グラフ３５、３６に対応するルックアップテーブルとをＥＣＵ１５内に予め記憶しておくことにより、これらを用いて電圧値ＶＨＧをリニアライズ変換したデータＬＤと、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦとを容易に取得して設定することができる。 By storing such a data map and lookup tables corresponding to the graphs 35 and 36 in advance in the ECU 15, data LD obtained by linearizing the voltage value VHG and the lean side threshold value LREF are calculated using these data maps. and the rich side threshold RREF can be easily acquired and set.
　グラフ３５は、例えば、リーン領域とストイキ領域との境界としての空気過剰率λを１．０２とし、この値となるような電圧値ＶＨＧ及び温度値Ｔを座標とした上記データマップ上の点を複数点求め、これら複数の点の間をそれぞれ線補間で結んだグラフである。またグラフ３６は、例えば、ストイキ領域とリッチ領域との境界としての空気過剰率λを０．９８と設定し、この値に対応する電圧値ＶＨＧ及び温度値Ｔを座標とした上記データマップ上の複数の点を求め、これら複数の点の相互間をそれぞれ線補間で結んだグラフである。 Graph 35 shows, for example, when the excess air ratio λ as the boundary between the lean region and the stoichiometric region is 1.02, and the points on the data map whose coordinates are the voltage value VHG and temperature value T that have this value are plotted. This is a graph obtained by finding multiple points and connecting these multiple points by line interpolation. Further, the graph 36 shows, for example, that 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 temperature value T corresponding to this value are set as coordinates on the above data map. This is a graph obtained by finding a plurality of points and connecting the plurality of points by line interpolation.
　例えば、限界閾値設定部３３は、グラフ３５に対応するルックアップテーブルからは、温度算出部２３からの温度値Ｔがｔ０である場合、その座標ｔ０から導かれる電圧値ｖ０を、リーン領域とストイキ領域との境界についてのリーン側閾値ＬＲＥＦとして設定することができる。同様に、グラフ３６に対応するルックアップテーブルからは、温度算出部２３からの温度値Ｔがｔ０である場合、その座標ｔ０から導かれる電圧値ｖ１を、ストイキ領域とリッチ領域との境界についてのリッチ側閾値ＲＲＥＦとして設定することができる。 For example, from the lookup table corresponding to the graph 35, if the temperature value T from the temperature calculation unit 23 is t0, the limit threshold setting unit 33 determines that the voltage value v0 derived from the coordinate t0 is in the lean region and the stoichiometric range. It can be set as the lean-side threshold LREF for the boundary with the region. Similarly, from the lookup 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 coordinate t0 is It can be set as a rich-side threshold RREF.
　記憶部３４は、代替値Ｒの算出に必要なデータとして、電圧算出部２４からの電圧値ＶＨＧがリーン側閾値ＬＲＥＦ以下のとき、燃料噴射弁６による燃料噴射の実行時間Ｔｉ１、記憶トルク値ＴＱ１、リーン側閾値ＬＲＥＦに関する記憶空気過剰率λｂを記憶する。 The storage unit 34 stores, as data necessary for calculating the alternative value R, an execution time Ti1 of fuel injection by the fuel injection valve 6 and a stored torque value TQ1 when the voltage value VHG from the voltage calculation unit 24 is less than or equal to the lean side threshold value LREF. , the excess air ratio λb related to the lean side threshold value LREF is stored.
　代替値演算部２６は、電圧値ＶＨＧがリーン側閾値ＬＲＥＦを超えているとき、直前の燃料噴射の実行時間をＴｉ２、直前（最新）のトルク値をＴＱ２として、次式（１）により代替値Ｒを算出する。
　R=((Ti1÷Ti2)÷(TQ1÷TQ2))×λb×Tc　　　　　　　　　　　（１） When the voltage value VHG exceeds the lean side threshold value LREF, the alternative value calculation unit 26 calculates an alternative value using the following formula (1), setting the execution time of the immediately preceding fuel injection as Ti2 and the immediately preceding (latest) torque value as TQ2. Calculate R.
R=((Ti1÷Ti2)÷(TQ1÷TQ2))×λb×Tc (1)
　ここで、Ｔｃは、代替値Ｒの算出精度を高めるためのトルク寄与率である。すなわち、上記式（１）にトルク寄与率Ｔｃの項が存在しない（Ｔｃ＝１）とすれば、燃料噴射実行時間の減少により空気過剰率が増加する割合と、このリーン化でのトルク値の減少により空気過剰率が減少する割合とが一致しないため、実際の空気過剰率と算出される代替値Ｒとの間に、トルク値ＴＱ２が減少するほど大きなずれが発生する。 Here, Tc is a torque contribution rate for improving the calculation accuracy of the alternative value R. In other words, if there is no term for the torque contribution rate Tc in the above equation (1) (Tc = 1), the rate at which the excess air ratio increases due to a decrease in the fuel injection execution time and the torque value in this lean condition are Since the rate at which the excess air ratio decreases due to the decrease does not match, a larger deviation occurs between the actual excess air ratio and the calculated alternative value R as the torque value TQ2 decreases.
　このずれを極力小さくするために、上記式（１）にトルク寄与率Ｔｃの項を採用している。このトルク寄与率Ｔｃは、トルク寄与率設定部４４において、トルク値ＴＱ２にトルク寄与率Ｔｃを対応付けた図７で示すようなルックアップテーブルにより、トルク値ＴＱ２に応じて設定される。 In order to minimize this deviation, the term of torque contribution rate Tc is adopted in the above equation (1). The torque contribution rate Tc is set in accordance with the torque value TQ2 by the torque contribution rate setting unit 44 using a lookup table as shown in FIG. 7 in which the torque contribution rate Tc is associated with the torque value TQ2.
　図８は、トルク寄与率Ｔｃを代替値Ｒの算出に使用することにより代替値Ｒの精度が向上することを示す。図８において、左側のグラフは、上記式（１）においてトルク寄与率Ｔｃの項が存在しない場合（Ｔｃ＝１）、右側のグラフはトルク寄与率Ｔｃの項が存在し、トルク寄与率Ｔｃが０．１（１０％）である場合の代替値Ｒの算出値の変化を、リーン領域Ａ、ストイキ領域Ｂ及びリッチ領域Ｃについて例示している。 FIG. 8 shows that the accuracy of the alternative value R is improved by using the torque contribution rate Tc for calculating the alternative value R. In FIG. 8, the graph on the left shows the case where the term of torque contribution rate Tc does not exist in the above equation (1) (Tc=1), and the graph on the right shows that the term of torque contribution rate Tc exists, and the term of torque contribution rate Tc does not exist (Tc=1). Changes in the calculated value of the alternative value R when the value is 0.1 (10%) are illustrated for the lean region A, the stoichiometric region B, and the rich region C.
　図８中のグラフ３９は、実際の空気過剰率の変化を示しており、グラフ４０は代替値Ｒの算出値の変化を示している。グラフ４１は燃料噴射量Ｔｉ、グラフ４２は内燃機関の回転速度ＮＥ、グラフ４３はスロットル弁３の開度の変化をそれぞれ示している。 A graph 39 in FIG. 8 shows changes in the actual excess air ratio, and a graph 40 shows changes in the calculated value of the alternative value R. A graph 41 shows the fuel injection amount Ti, a graph 42 shows the rotational speed NE of the internal combustion engine, and a graph 43 shows the change in the opening degree of the throttle valve 3.
　代替値Ｒの算出精度は、燃料噴射量Ｔｉの減少によりリーン化する割合と、リーン化でのトルク減少によるリッチ化する割合がアンマッチ（不一致）であるため、トルクの減少が大きいほど、グラフ３９の実際の空気過剰率とグラフ４０の代替値Ｒとが乖離してずれ幅が大きくなる。図８では、トルクＴＱが小さい場合について示されている。 The calculation accuracy of the alternative value R is determined by the fact that the proportion of lean due to a decrease in the fuel injection amount Ti and the proportion of rich due to a decrease in torque due to lean are unmatched. The actual excess air ratio and the alternative value R in the graph 40 deviate from each other, and the deviation width increases. FIG. 8 shows a case where the torque TQ is small.
　この場合、トルク寄与率Ｔｃの項が存在しない（Ｔｃ＝１）図８の左側のグラフでは、グラフ３９の実際の空気過剰率に対して、グラフ４０の代替値Ｒは、リーン領域Ａにおいて、最大０．１２程度のずれ幅となっている。これに対し、トルク寄与率Ｔｃが０．１である右側のグラフでは、グラフ３９の実際の空気過剰率に対してグラフ４０の代替値Ｒは、リーン領域Ａにおいて、最大０．０５程度のずれ幅に収まっている。 In this case, there is no torque contribution factor Tc term (Tc=1). In the graph on the left side of FIG. The maximum deviation width is about 0.12. On the other hand, in the graph on the right where the torque contribution factor Tc is 0.1, the alternative value R in graph 40 for the actual excess air ratio in graph 39 has a maximum deviation of about 0.05 in lean region A. It fits within the width.
　このように、トルクの寄与率を調整可能にするトルク寄与率Ｔｃを追加し、トルクＴＱ２の値が小さい場合にはトルク寄与率Ｔｃを１よりも小さく設定することにより、実際の空気過剰率と代替値Ｒのずれ幅が減少し、より正確な代替値Ｒが得られることがわかる。 In this way, by adding the torque contribution rate Tc that makes it possible to adjust the torque contribution rate, and setting the torque contribution rate Tc smaller than 1 when the value of torque TQ2 is small, the actual excess air ratio can be adjusted. It can be seen that the deviation width of the alternative value R is reduced, and a more accurate alternative value R can be obtained.
　このようにして算出される代替値Ｒは、過剰率算出部２５において、電圧値ＶＨＧが変換限界閾値ＬＲＥＦを超えている場合には、上述のリニアライズ変換したデータＬＤとしての空気過剰率λに代えて、排気の空気過剰率λとみなされる。 The substitute value R calculated in this way is determined by the excess air ratio λ as the linearized data LD when the voltage value VHG exceeds the conversion limit threshold LREF in the excess ratio calculation unit 25. Instead, it is considered to be the excess air ratio λ of the exhaust gas.
　図３は、過剰率算出部２５における空気過剰率λを算出する過剰率算出処理を示す。なお、この過剰率算出処理を含むＥＣＵ１５による制御は、クランク角度センサ１９からのクランク軸１８の回転角度位置を示すパルス信号に基づき、内燃機関の行程に同期して実行される。 FIG. 3 shows an excess rate calculation process in which the excess air rate λ is calculated by the excess rate calculation unit 25. Note that the control by the ECU 15 including this excess rate calculation process is executed in synchronization with the stroke of the internal combustion engine based on a pulse signal from the crank angle sensor 19 indicating the rotational angular position of the crankshaft 18.
　過剰率算出処理が開始されると、ステップＳ１において、トルク演算部３２により、回転速度演算部２７からのクランク角速度ＮＥＴＣに基づいて内燃機関のトルクＴＱを算出する。 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 rotational speed calculation unit 27.
　なお、トルクＴＱの算出に際しては、内燃機関における吸気、圧縮、燃焼膨張、排気の各行程を有する内燃機関の連続する２つの行程の各々に対応した内燃機関のクランク軸の２つの角速度が算出され、これに基づき、内燃機関が発生する発生トルクが精度よく算出される（特許第６２５４６３３号公報参照）。 In addition, when calculating the torque TQ, two angular velocities of the crankshaft of the internal combustion engine corresponding to each of two consecutive strokes of the internal combustion engine, which has each stroke of intake, compression, combustion expansion, and exhaust, are calculated. , Based on this, the generated torque generated by the internal combustion engine is calculated with high accuracy (see Japanese Patent No. 6254633).
　次に、ステップＳ２において、温度算出部２３からの温度値Ｔに基づき、限界閾値設定部３３により、図５のグラフ３５、３６に対応するルックアップテーブルを用いて、リーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦを設定する。 Next, in step S2, based on the temperature value T from the temperature calculation section 23, the limit threshold setting section 33 uses the lookup table corresponding to the graphs 35 and 36 in FIG. Set threshold RREF.
　次に、ステップＳ３において、電圧算出部２４から電圧値ＶＨＧを取得する。 Next, in step S3, the voltage value VHG is obtained from the voltage calculation unit 24.
　次に、ステップＳ４において、ステップＳ２で取得した温度値Ｔ、ステップＳ３で取得した電圧値ＶＨＧに基づき上述のデータマップ（図５）が走査され、かくして、電圧値ＶＨＧの値をその温度特性を補償しつつ空気過剰率λへとリニアライズ変換したデータＬＤが取得される。 Next, in step S4, the above-mentioned data map (FIG. 5) is scanned based on the temperature value T obtained in step S2 and the voltage value VHG obtained in step S3. Data LD is obtained which has been linearized into excess air ratio λ while being compensated.
　次に、ステップＳ５において、ステップＳ３で取得した電圧値ＶＨＧが、ステップＳ２で設定したリッチ側閾値ＲＲＥＦよりも小さいか否かを判定する。小さいと判定した場合には、続くステップＳ６においてフラグＦ＿ＤＥＴＥＣＴをゼロに設定しつつステップＳ１６に進み、上記データＬＤの値を空気率過剰率λ値ＬＡＭＢＤＡとして設定し、図３の過剰率算出処理を終了する。 Next, in step S5, it is determined whether 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 that it is small, the flag F_DETECT is set to zero in the subsequent step S6, and the process proceeds to step S16, where the value of the data LD is set as the excess air ratio λ value LAMBDA, and the excess ratio calculation process of FIG. 3 is performed. finish.
　ステップＳ５において、電圧値ＶＨＧがリーン側閾値ＲＲＥＦよりも小さくはないと判定した場合には、ステップＳ７において、ステップＳ３で取得した電圧値ＶＨＧが、ステップＳ２で設定したリーン側閾値ＬＲＥＦよりも大きいか否かを判定する。 If it is determined in step S5 that the voltage value VHG is not smaller than the lean side threshold RREF, then in step S7 the voltage value VHG acquired in step S3 is larger than the lean side threshold LREF set in step S2. Determine whether or not.
　ステップＳ７において、上記電圧値ＶＨＧが大きくはないと判定した場合には、ステップＳ８において、ステップＳ２で取得したリーン側閾値ＬＲＥＦの電圧値ｌｒｅｆ及びリッチ側閾値ＲＲＥＦの電圧値ｒｒｅｆと、電圧値ｌｒｅｆに対応する所定のストイキ領域とリーン領域との境界としての空気過剰率λ値（この実施の形態においては、λ＝１．０２）と、電圧値ｒｒｅｆに対応する所定のリッチ領域とストイキ領域との境界としての空気過剰率λ値（この実施の形態においては、λ＝０．９８）と、ステップＳ３で取得した電圧値ＶＨＧとに基づき、電圧算出部２４からの電圧値ＶＨＧを、酸素センサ１２の温度特性を補償しつつ空気過剰率に対してリニアライズ変換したデータＬＤとしての空気過剰率λを算出し、ステップＳ９に進む。 In step S7, when it is determined that the voltage value VHG is not large, in step S8, the voltage value lref of the lean side threshold LREF, the voltage value rref of the rich side threshold RREF, and the voltage value lref acquired in step S2 are determined. The excess air ratio λ value (in this embodiment, λ=1.02) as a boundary between a predetermined stoichiometric region and a lean region corresponding to , and a predetermined rich region and stoichiometric region corresponding to a voltage value rref. Based on the excess air ratio λ value as a boundary (in this embodiment, λ=0.98) and the voltage value VHG acquired in step S3, the voltage value VHG from the voltage calculation unit 24 is The excess air ratio λ is calculated as data LD obtained by linearizing the excess air ratio while compensating for the temperature characteristics of 12, and the process proceeds to step S9.
　図４を併せて参照して、上記ステップＳ８におけるリニアライズ変換したデータＬＤとしての空気過剰率λは、前記所定のストイキ領域とリーン領域との境界としての空気過剰率λを予め数値設定することが可能な変数＃ＬＬＭＤ(たとえば１．０２）、及び、前記所定のリッチ領域とストイキ領域との境界としての空気過剰率λを予め設定することが可能な変数＃ＲＬＭＤ（たとえば０．９８）であるとすれば、図４に示すようなグラフで表すことができる。該グラフの、図４において左右方向の横軸は電圧値ＶＨＧであり、図４において上下方向の縦軸は空気過剰率λである。したがって、例えば電圧値ＶＨＧがｖｈｇ１である場合、これに対応する空気過剰率λの値λ１は、次式（２）により算出することができる。
　λ1=(((vhg1-rref)÷(lref-rref))×(#LLMD-#RLMD))＋＃RLMD　　（２） Referring also to FIG. 4, the excess air ratio λ as the linearized data LD in step S8 is set in advance by numerically setting the excess air ratio λ as the boundary between the predetermined stoichiometric region and the lean region. A variable #LLMD (for example, 1.02) that can set If there is, it can be represented by a graph as shown in FIG. In this graph, the horizontal axis in the horizontal direction in FIG. 4 is the voltage value VHG, and the vertical axis in the vertical direction in FIG. 4 is the excess air ratio λ. Therefore, for example, when the voltage value VHG is vhg1, the corresponding value λ1 of the excess air ratio λ can be calculated using the following equation (2).
λ1=(((vhg1-rref)÷(lref-rref))×(#LLMD-#RLMD))+#RLMD (2)
　ステップＳ９では、燃料噴射弁６による直前の燃料噴射の実行時間Ｔｉ、ステップＳ１で算出したトルクＴＱをそれぞれＴｉ１、ＴＱ１とし、リーン側閾値ＬＲＥＦに関する空気過剰率λをλｂとして記憶部３４により記憶する。ほぼ同時に、前記記憶の有効時間を示すカウントダウンタイマー値ＴＩＭＥＲをその所定の初期値である＃ＴＭＩＮＩＴでリセットする。続いて、フラグＦ＿ＤＥＴＥＣＴを１に設定するとともにステップＳ１６に進み、上記ステップＳ８で取得したデータＬＤの値を、空気率過剰率λ値ＬＡＭＢＤＡとして設定し、図３の過剰率算出処理を終了する。 In step S9, the execution time Ti of the immediately preceding fuel injection by the fuel injection valve 6 and the torque TQ calculated in step S1 are respectively set as Ti1 and TQ1, and the excess air ratio λ regarding the lean side threshold value LREF is stored as λb in the storage unit 34. . Almost simultaneously, the countdown timer value TIMER indicating the valid time of the memory is reset to its predetermined initial value #TMINIT. Subsequently, 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 is set as the excess air ratio λ value LAMBDA, and the excess ratio calculation process of FIG. 3 is ended.
　このとき、記憶空気過剰率λｂとしては、ステップＳ８で取得したデータＬＤの値が記憶される。その際に、データＬＤの値の移動平均を記憶空気過剰率λｂとして記憶するのが好ましい。例えば、次式（３）で求められる空気過剰率λ（データＬＤ）の指数移動平均λａがλｂとして記憶される。
　λａ＝ＬＤ×ｋ１＋λａｂ×（１－ｋ１）　　　　　　　　（３） At this time, the value of the data LD acquired in step S8 is stored as the stored excess air ratio λb. At that time, it is preferable to store the moving average of the values of the data LD as the stored excess air ratio λb. For example, the exponential moving average λa of the excess air ratio λ (data LD) obtained by the following equation (3) is stored as λb.
λa=LD×k1+λab×(1-k1) (3)
　ここで、ｋ１は移動平均係数であり、λａｂは記憶部３４が記憶している前回制御周期での移動平均値である。移動平均係数ｋ１としては、例えば０．３４が用いられる。 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. For example, 0.34 is used as the moving average coefficient k1.
　また、このとき、記憶部３４は、燃料噴射の実行時間Ｔｉ１及び前記記憶トルク値ＴＱ１として、それぞれ移動平均値を記憶するのが好ましい。例えば、燃料噴射の実行時間Ｔｉの指数移動平均ＴｉＦＬＴが次式（４）で求められてＴｉ１として記憶されるとともに、前記トルク値ＴＱの指数移動平均ＴＱＦＬＴが次式（５）で求められてＴＱ１として記憶される。
　ＴｉＦＬＴ＝Ｔｉ×ｋ２＋ＴｉＦＬＴｂ×（１－ｋ２）　　　　（４）
　ＴＱＦＬＴ＝ＴＱ×ｋ３＋ＴＱＦＬＴｂ×（１－ｋ３）　　　　（５） Moreover, at this time, it is preferable that the storage unit 34 stores moving average values as the fuel injection execution time Ti1 and the stored torque value TQ1, respectively. For example, the exponential moving average TiFLT of the fuel injection execution time Ti is calculated using the following equation (4) and stored as Ti1, and the exponential moving average TQFLT of the torque value TQ is calculated using the following equation (5) and stored as Ti1. is stored as.
TiFLT=Ti×k2+TiFLTb×(1-k2) (4)
TQFLT=TQ×k3+TQFLTb×(1-k3) (5)
　ここで、ｋ２、ｋ３は移動平均係数であり、ＴｉＦＬＴｂ、ＴＱＦＬＴｂは記憶部３４が記憶している前回制御周期での移動平均値である。この実施の形態においては、移動平均係数ｋ１、ｋ２、及びｋ３として、それぞれ異なる値を用いることができる。 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.
　次に、ステップＳ７において、ステップＳ３で取得した電圧値ＶＨＧがリーン側閾値ＬＲＥＦよりも大きいと判定した場合には、ステップＳ１０において、上述のカウントダウンタイマー値ＴＩＭＥＲがゼロに到達しているか否かを判定する。そして、ＴＩＭＥＲがゼロに到達しているならば、フラグＦ＿ＤＥＴＥＣＴを０にリセットする（ステップＳ１１）。 Next, in step S7, if it is determined that the voltage value VHG acquired in step S3 is larger than the lean side threshold value LREF, in step S10, it is determined whether the above-mentioned countdown timer value TIMER has reached zero. judge. If TIMER has reached zero, the flag F_DETECT is reset to 0 (step S11).
　次に、ステップＳ１２に進み、フラグＦ＿ＤＥＴＥＣＴ＝１であるか否かを判定する。Ｆ＿ＤＥＴＥＣＴ＝１であるならば、記憶部３４にリーン側閾値ＬＲＥＦに関する記憶空気過剰率λｂ、燃料噴射の実行時間Ｔｉ１、及び、記憶トルク値ＴＱ１が記憶されていることを示すので、ステップＳ１３に進み、代替値演算部２６において、上述の式（１）により代替値Ｒを算出するとともに、データＬＤの値を代替値Ｒに設定する。 Next, the process proceeds to step S12, and it is determined whether the flag F_DETECT=1. If F_DETECT=1, this indicates that the memory excess air ratio λb, the fuel injection execution time Ti1, and the memory torque value TQ1 regarding the lean side threshold value LREF are stored in the storage unit 34, so the process advances to step S13. , the alternative value calculation unit 26 calculates the alternative value R using the above-mentioned equation (1), and sets the value of the data LD to the alternative value R.
　次に、ステップＳ１４において、ステップＳ１３で設定したデータＬＤの値が所定の上限値＃ＬＬＭＴよりも大きいか否かを判定する。ステップＳ１３で設定したデータＬＤの値が上限値＃ＬＬＭＴよりも大きい場合には、データＬＤの値を上限値＃ＬＬＭＴに設定する（ステップＳ１５）。この場合、上限値＃ＬＬＭＴとして、例えば１．２５を用いることができる。 Next, in step S14, it is determined whether the value of the data LD set in step S13 is larger than a predetermined upper limit value #LLMT. If the value of data LD set in step S13 is larger than upper limit value #LLMT, the value of data LD is set to upper limit value #LLMT (step S15). In this case, for example, 1.25 can be used as the upper limit value #LLMT.
　なお、上記ステップＳ１２において、Ｆ＿ＤＥＴＥＣＴ＝０であるならば、記憶部３４にリーン側閾値ＬＲＥＦに関する記憶空気過剰率λｂ、燃料噴射の実行時間Ｔｉ１、及び、記憶トルク値ＴＱ１に関する有効な値が記憶されていないことを示すので、代替値Ｒを算出することができない。この場合も、データＬＤの値は上記上限値＃ＬＬＭＴに設定される（ステップＳ１５）。 In addition, in step S12, if F_DETECT=0, the storage unit 34 stores valid values regarding the stored excess air ratio λb, the fuel injection execution time Ti1, and the stored torque value TQ1 regarding the lean side threshold value LREF. Therefore, the alternative value R cannot be calculated. Also in this case, the value of data LD is set to the upper limit value #LLMT (step S15).
　而して、上記ステップＳ１３又はステップＳ１５で設定されたデータＬＤの値は空気率過剰率λ値ＬＡＭＢＤＡとして設定され(ステップＳ１６）、これにより、図３の過剰率算出処理を終了する。 The value of the data LD set in step S13 or step S15 is then set as the excess air ratio λ value LAMBDA (step S16), thereby ending the excess ratio calculation process of FIG.
　図３の過剰率算出処理が終了すると、ＥＣＵ１５は、図３の過剰率算出処理で算出された空気過剰率λ値ＬＡＭＢＤＡを、上述のように、目標値演算部２８からの目標とする空気過剰率λcmdに一致させるべく、フィードバック係数演算部３０のＰＩＤ制御により、燃料噴射弁６による燃料の噴射量を制御する。 When the excess rate calculation process of FIG. 3 is completed, the ECU 15 converts the excess air rate λ value LAMBDA calculated in the excess rate calculation process of FIG. In order to match the rate λcmd, the amount of fuel injected by the fuel injection valve 6 is controlled by PID control of the feedback coefficient calculation unit 30.
　図６は、図３の過剰率算出処理によって算出される空気過剰率λ値ＬＡＭＢＤＡの変化の様子を模式的に示すグラフである。グラフの横軸は時間経過を示す数値であり、縦軸は空気過剰率λである。 FIG. 6 is a graph schematically showing how the excess air ratio λ value LAMBDA calculated by the excess air ratio calculation process of FIG. 3 changes. The horizontal axis of the graph is a numerical value indicating the passage of time, and the vertical axis is the excess air ratio λ.
　図６におけるグラフ３７は、図６において左右方向の横軸の、左端側から中央付近までの範囲において、実際の排気の空気過剰率を一定の変化率で徐々に増加させ、且つ、続く上記横軸の中央付近から右端側までの範囲において、実際の排気の空気過剰率を一定の変化率で徐々に減少させた場合において、それをＥＣＵ１５の電圧算出部２４で読み取った電圧値ＶＨＧを、その温度特性を補償しつつ空気過剰率に対して直接的にリニアライズ変換したデータを用いて空気過剰率λ値を算出した場合の空気過剰率λ値の数値変化を示す。 Graph 37 in FIG. 6 shows that the actual exhaust air excess rate gradually increases at a constant rate of change in the range from the left end side to near the center of the horizontal axis in the left-right direction in FIG. In the range from near the center of the shaft to the right end side, when the actual excess air ratio of the exhaust gas is gradually decreased at a constant rate of change, the voltage value VHG read by the voltage calculation unit 24 of the ECU 15 is The figure shows a numerical change in the excess air ratio λ value when the excess air ratio λ value is calculated using data directly linearized with respect to the excess air ratio while compensating for temperature characteristics.
　グラフ３８は、同様に、上記横軸の左端から右端まで実際の排気の空気過剰率を一定の変化率で徐々に増加乃至減少させた場合において、電圧算出部２４からの電圧値ＶＨＧがリーン側域値ＬＲＥＦの電圧値ｌｒｅｆ以下であるときは、上述のデータマップ（図５）又は式（２）で電圧値ＶＨＧを直接的にリニアライズ変換したデータを用いて空気過剰率λ値を算出しているが、電圧算出部２４からの電圧値ＶＨＧがリーン側域値ＬＲＥＦの電圧値ｌｒｅｆ（空気過剰率λの値１．０２０に対応）を超える場合には、上記電圧値ＶＨＧをリニアライズ変換したデータに代えて上述の数式（１）により取得した代替値Ｒを空気過剰率λ値としたときのその空気過剰率λ値の数値変化を示している。 Similarly, the graph 38 shows that when the actual excess air ratio of the exhaust gas 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 on the lean side. When the voltage value lref is below the threshold value LREF, the excess air ratio λ value is calculated using the data map described above (Figure 5) or the data obtained by directly linearizing the voltage value VHG using equation (2). However, if 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 value of excess air ratio λ of 1.020), the voltage value VHG is linearized. The graph shows the numerical change in the excess air ratio λ value when the substitute value R obtained by the above-mentioned formula (1) is used as the excess air ratio λ value in place of the above data.
　斯くして、実際の排気の空気過剰率が１．０２０以下の場合には、それに応答する電圧算出部２４からの電圧値ＶＨＧは上記実際の排気の空気過剰率に対して比例的（線形）に変化するため、実際の排気の空気過剰率が１．０２０以下の場合には、グラフ３７およびグラフ３８は共に、上記実際の排気の空気過剰率の上記一定変化に追従して直線的に推移しているが、排気の空気過剰率が１．０２０を超える場合には、その状況下での非線形性を呈する電圧値ＶＨＧが急激に増加方向に変化するため、電圧値ＶＨＧを直接的にリニアライズ変換したデータに基づく空気過剰率λ値を示すグラフ３７も同じく増加方向へと急峻且つ非線形に変化する。一方、グラフ３８では、排気の空気過剰率が１．０２０（上記＃ＬＬＭＤ）を超える場合にも空気過剰率λ値ＬＡＭＢＤＡが排気の空気過剰率（空燃比）に対して直線状に変化しており、実際の排気の空気過剰率と連動している。 In this way, when the actual excess air ratio of the exhaust gas is 1.020 or less, the voltage value VHG from the voltage calculation unit 24 responsive thereto is proportional (linear) to the actual excess air ratio of the exhaust gas. Therefore, when the actual excess air ratio of the exhaust gas is 1.020 or less, both graphs 37 and 38 change linearly, following the constant change in the actual excess air ratio of the exhaust gas. However, when the excess air ratio of the exhaust exceeds 1.020, the voltage value VHG, which exhibits nonlinearity under that situation, rapidly changes in the increasing direction, so the voltage value VHG can be directly linearized. The graph 37 showing the excess air ratio λ value based on the rise-converted data similarly changes steeply and non-linearly in the increasing direction. On the other hand, in graph 38, even when the excess air ratio of the exhaust exceeds 1.020 (#LLMD above), the excess air ratio λ value LAMBDA changes linearly with the excess air ratio (air-fuel ratio) of the exhaust. This is linked to the actual exhaust air excess rate.
　したがって、過剰率算出処理により、電圧値ＶＨＧがリーン側閾値ＬＲＥＦ以下の場合には、上述のリニアライズ変換したデータを用いて空気過剰率λを算出し、電圧値ＶＨＧがリーン側閾値ＬＲＥＦを超える場合には、上述の数式（１）で空気過剰率λを算出する（グラフ３８）ことにより、過剰率算出部２５は、図６のグラフの全範囲にわたって実際の排気の空気過剰率と連動し比例的に変化する空気過剰率λ値をフィードバック係数演算部３０に供給できることがわかる。これにより、フィードバック係数演算部３０によるＰＩＤ制御の中断が抑制される。 Therefore, in the excess ratio calculation process, if the voltage value VHG is less than the lean side threshold LREF, the excess air ratio λ is calculated using the linearized data described above, and the voltage value VHG exceeds the lean side threshold LREF. In this case, by calculating the excess air ratio λ using the above-mentioned formula (1) (graph 38), the excess ratio calculation unit 25 can interlock with the actual excess air ratio of exhaust gas over the entire range of the graph in FIG. It can be seen that the excess air ratio λ value that changes proportionally can be supplied to the feedback coefficient calculation unit 30. This suppresses interruption of PID control by the feedback coefficient calculating section 30.
　以上のように、本実施形態によれば、空気過剰率λに基づいてＰＩＤ制御により燃料噴射量Ｔｉを制御するに際して、排気中の酸素濃度を示す電圧値ＶＨＧがリーン側閾値ＬＲＥＦを超える場合には、上述の数式（１）により計算した代替値Ｒが空気過剰率λとみなされるので、ＰＩＤ制御の中断を抑制して制御精度を高め、排気ガス浄化等の効率化を図ることができる。 As described above, according to the present embodiment, when controlling the fuel injection amount Ti by PID control based on the excess air ratio λ, when the voltage value VHG indicating the oxygen concentration in the exhaust exceeds the lean side threshold value LREF, Since the substitute value R calculated by the above-mentioned formula (1) is regarded as the excess air ratio λ, interruption of PID control can be suppressed, control accuracy can be increased, and efficiency of exhaust gas purification can be improved.
　また、記憶部３４に記憶する燃料噴射の実行時間Ｔｉ１、記憶トルク値ＴＱ１、記憶空気過剰率λｂとして、それぞれの移動平均値を記憶するので、これらの計測値をデジタル値に変換する際の量子化ノイズ（誤差）を低減することができる。 In addition, since the moving average values of the fuel injection execution time Ti1, the stored torque value TQ1, and the stored excess air ratio λb are stored in the storage unit 34, the quantum It is possible to reduce noise (error).
　また、図５に示すようなグラフ３５、３６に対応するルックアップテーブルを用いてリーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦが設定されるので、酸素センサ１２の温度に応じた適切なリーン側閾値ＬＲＥＦ及びリッチ側閾値ＲＲＥＦを設定することができる。 Furthermore, since the lean side threshold value LREF and the rich side threshold value RREF are set using the lookup table corresponding to the graphs 35 and 36 as shown in FIG. and a rich-side threshold RREF.
　また、酸素センサ１２として、抵抗型酸素センサを用い、その温度及び検出値と排気の空気過剰率とを対応付けた図５のようなデータマップを用いてリニアライズ変換されたデータとしての空気過剰率λが取得されるので、空気過剰率λを迅速に得ることができる。 In addition, a resistance type oxygen sensor is used as the oxygen sensor 12, and excess air is detected as data linearized using a data map as shown in FIG. Since the ratio λ is obtained, the excess air ratio λ can be obtained quickly.
　また、図３の過剰率算出処理は、内燃機関の行程に同期して空気過剰率λの算出を行うので、かかる算出はタイマで一定周期で行われる場合が多いところ、内燃機関の回転速度ＮＥが高くなって制御周期が短くなっても、制御周期に合わせて、燃料噴射量やトルク値ＴＱを支障なく取得することができる。 Furthermore, in the excess rate calculation process shown in FIG. 3, the excess air rate λ is calculated in synchronization with the stroke of the internal combustion engine. Even if the control period becomes short due to the increase in the fuel injection amount, the fuel injection amount and the torque value TQ can be obtained without any problem in accordance with the control period.
　また、代替値Ｒを算出する式（１）において、トルク寄与率Ｔｃの項がない（Ｔｃ＝１）場合には、燃料減少によりリーン化する割合と、リーン化でのトルク減少によるリッチ化する割合との不一致により実際の空気過剰率と算出による空気過剰率λとの間に、トルク値の減少が大きいほど大きくなるずれが生じるが、トルク寄与率Ｔｃを採用したので、このずれ幅を小さくし、代替値Ｒの算出精度を向上させることができる。 In addition, in equation (1) for calculating the alternative value R, if there is no term for torque contribution rate Tc (Tc = 1), the ratio of becoming leaner due to fuel reduction and the ratio becoming richer due to torque reduction due to leaner change. Due to the discrepancy with the ratio, a deviation occurs between the actual excess air ratio and the calculated excess air ratio λ, which increases as the torque value decreases. However, by adopting the torque contribution ratio Tc, the width of this deviation can be reduced. However, the calculation accuracy of the alternative value R can be improved.
　また、トルク寄与率設定部４４は、トルク値ＴＱ２にトルク寄与率Ｔｃを対応付けたルックアップテーブルに基づき、トルク寄与率Ｔｃの値を最新のトルク値ＴＱ２に応じて設定するので、適切なルックアップテーブルを用いることにより、適切なトルク寄与率Ｔｃの値を容易に設定することができる。 Further, the torque contribution rate setting unit 44 sets the value of the torque contribution rate Tc according to the latest torque value TQ2 based on a lookup table in which the torque contribution rate Tc is associated with the torque value TQ2, so that an appropriate lookup is performed. By using the up-table, an appropriate value of the torque contribution rate Tc can be easily set.
　なお、本発明は上述の実施形態に限定されない。例えば、リーン側閾値ＬＲＥＦの電圧値ｌｒｅｆ、及びリッチ側閾値ＲＲＥＦの電圧値ｒｒｅｆをグラフ３５、３６に対応するルックアップテーブルを用いてそれぞれ設定する（ステップＳ２）とともに、ステップＳ８において上記リーン側の電圧値ｌｒｅｆ及びリッチ側の電圧値ｒｒｅｆを含む式（２）によってリニアライズ変換したデータＬＤを算出するように構成しているが、このステップＳ８を省略して、上述のステップＳ４でデータマップ（図５）を走査して取得したデータＬＤの値を、空気率過剰率λ値ＬＡＭＢＤＡに設定してもよい。 Note that the present invention is not limited to the above-described embodiments. For example, the voltage value lref of the lean side threshold LREF and the voltage value rref of the rich side threshold RREF are respectively set using lookup tables corresponding to graphs 35 and 36 (step S2), and in step S8 Although the configuration is such that linearized data LD is calculated using equation (2) including the voltage value lref and the rich side voltage value rref, this step S8 is omitted and the data map ( The value of the data LD obtained by scanning FIG. 5) may be set as the excess air ratio λ value LAMBDA.
　この場合さらに、上記ステップＳ２を省略して、ステップＳ４で取得されたデータＬＤが、図３のステップＳ５、Ｓ７において、それぞれ、リーン側閾値ＬＲＥＦに対応する所定の空気過剰率λとしてあらかじめ定めた値、例えば１．０２（リーン側閾値ＬＲＥＦの空気過剰率λ値＃ＬＬＭＤ）、リッチ側閾値ＲＲＥＦに対応する所定の空気過剰率λとしてあらかじめ定めた値、例えば０．９８（リッチ側閾値ＲＲＥＦの空気過剰率λ値＃ＲＬＭＤ）と比較されるように構成することができる。これによれば、上記ルックアップテーブルを走査する演算（ステップＳ２）及び上記式（２）の演算（ステップＳ８）を省略した分だけ、ＥＣＵ１５の高回転での制御を容易化することができる。 In this case, furthermore, step S2 is omitted, and the data LD acquired in step S4 is determined in advance as a predetermined excess air ratio λ corresponding to the lean side threshold LREF in steps S5 and S7 of FIG. A value, for example, 1.02 (excess air ratio λ value #LLMD of lean side threshold value LREF), a value predetermined as a predetermined excess air ratio λ corresponding to rich side threshold value RREF, for example 0.98 (excess air ratio λ value #LLMD of lean side threshold value RREF). It can be configured to be compared with the excess air ratio λ value #RLMD). According to this, the control of the ECU 15 at high rotation speeds can be facilitated by omitting the calculation of scanning the lookup table (step S2) and the calculation of the formula (2) (step S8).
　また、変換限界閾値に関する記憶空気過剰率λｂとして、あらかじめ定めた値、例えば１．０２を用いてもよい。これによれば、記憶空気過剰率λｂについての上述の移動平均を求める演算を要しない分だけ、高回転での制御を容易化することができる。 Furthermore, a predetermined value, for example 1.02, may be used as the stored excess air ratio λb regarding the conversion limit threshold. According to this, control at high rotation speeds can be facilitated by eliminating the need for calculation to obtain the above-mentioned moving average of the stored excess air ratio λb.
　１…機関本体、２…吸気管、３…スロットル弁、４…エアクリーナ、５…スロットルセンサ、６…燃料噴射弁、７…吸気圧センサ、８…吸気温センサ、９…ピストン、１０…排気管、１１…触媒、１２…酸素センサ、１２ａ…センサ素子、１２ｂ…センサヒータ、１３…点火プラグ、１４…点火装置、１５…ＥＣＵ（電子制御ユニット）、１７…冷却水温センサ、１８…クランク軸、１９…クランク角度センサ、１９ａ…ロータ、１９ｂ…ピックアップ、２０…大気圧センサ、２２…ヒータ制御器、２３…温度算出部、２４…電圧算出部、２５…過剰率算出部、２６…代替値演算部、２７…回転速度演算部、２８…目標値演算部、２９…基本噴射量演算部、３０…フィードバック係数演算部、３１…噴射量演算部、３２…トルク演算部、３３…限界閾値設定部、３４…記憶部、３５～４３…グラフ、４４…トルク寄与率設定部。 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... Spark plug, 14... Ignition device, 15... ECU (electronic control unit), 17... Cooling water temperature sensor, 18... Crankshaft, 19... Crank angle sensor, 19a... Rotor, 19b... Pick-up, 20... Atmospheric pressure sensor, 22... Heater controller, 23... Temperature calculation section, 24... 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 value setting section , 34...Storage unit, 35-43...Graph, 44...Torque contribution rate setting unit.

Claims (7)

  1. 　燃料噴射弁を備える内燃機関の排気に接するように設けられて排気中の酸素濃度を検出する検出部を有し、その検出部からの検出値が前記検出部の温度に応じて変化する温度特性を有する酸素センサと、前記検出部の温度を推定又は検出する温度検出部と、前記検出値及び温度に基づき、前記検出値を、前記温度特性を補償しつつ空気過剰率に対してリニアライズ変換したデータを用いて前記排気の空気過剰率λを算出する過剰率算出部とを備える空気過剰率算出装置において、
    　前記過剰率算出部は、
    　前記内燃機関のクランク角速度に基づいて該内燃機関のトルク値を算出するトルク演算部と、
    　前記リニアライズ変換についての変換限界閾値を設定する限界閾値設定部と、
    　前記検出値又は前記リニアライズ変換したデータが前記変換限界閾値以下のときの前記燃料噴射弁による燃料噴射の実行時間をＴｉ１、前記トルク値を記憶トルク値ＴＱ１、前記変換限界閾値に関する空気過剰率λを記憶空気過剰率λｂとして記憶する記憶部と、
    　トルク寄与率Ｔｃを設定するトルク寄与率設定部と、
    　前記検出値又は前記リニアライズ変換したデータが前記変換限界閾値を超えているときの前記燃料噴射の実行時間をＴｉ２、最新の前記トルク値をＴＱ２として、次式により代替値Ｒを算出する代替値演算部とを備え、
    　Ｒ＝（（Ｔｉ１÷Ｔｉ２）÷（ＴＱ１÷ＴＱ２））×λｂ×Ｔｃ
    　前記検出値又は前記リニアライズ変換したデータが前記変換限界閾値を超えている場合には、前記リニアライズ変換したデータに代えて、前記代替値Ｒを前記排気の空気過剰率λとみなすことを特徴とする空気過剰率算出装置。     The temperature characteristic includes a detection part that is provided in contact with the exhaust gas of an internal combustion engine equipped with a fuel injection valve and detects the oxygen concentration in the exhaust gas, and the detected value from the detection part changes depending on the temperature of the detection part. a temperature detection unit that estimates or detects the temperature of the detection unit; and a temperature detection unit that linearizes the detection value with respect to the excess air ratio while compensating the temperature characteristic based on the detection value and the temperature. an excess air ratio calculation unit that calculates the excess air ratio λ of the exhaust gas using the data obtained,
    The excess rate calculation unit includes:
    a torque calculation unit that calculates a torque value of the internal combustion engine based on a crank angular velocity of the internal combustion engine;
    a limit threshold setting unit that sets a conversion limit threshold for the linearization conversion;
    Execution time of fuel injection by the fuel injector when the detected value or the linearized data is less than or equal to the conversion limit threshold; Ti1; storage torque value TQ1 for the torque value; and excess air ratio λ with respect to the conversion limit threshold. a storage unit that stores λb as a storage excess air ratio λb;
    a torque contribution rate setting unit that sets a torque contribution rate Tc;
    An alternative value for calculating an alternative value R using the following formula, where Ti2 is the execution time of the fuel injection when the detected value or the linearized data exceeds the conversion limit threshold, and the latest torque value is TQ2. Equipped with a calculation section,
    R=((Ti1÷Ti2)÷(TQ1÷TQ2))×λb×Tc
    If the detected value or the linearized data exceeds the conversion limit threshold, the alternative value R is regarded as the excess air ratio λ of the exhaust gas in place of the linearized data. Excess air ratio calculation device.
  2. 　前記トルク寄与率設定部は、前記トルク値に前記トルク寄与率Ｔｃを対応付けたルックアップテーブルに基づき、前記トルク寄与率Ｔｃの値を前記最新のトルク値ＴＱ２に応じて設定することを特徴とする請求項１に記載の空気過剰率算出装置。 The torque contribution rate setting unit sets the value of the torque contribution rate Tc according to the latest torque value TQ2 based on a lookup table in which the torque contribution rate Tc is associated with the torque value. The excess air ratio calculation device according to claim 1.
  3. 　前記記憶部は、前記燃料噴射の実行時間Ｔｉ１及び前記記憶トルク値ＴＱ１として、それぞれの移動平均値を記憶することを特徴とする請求項１に記載の空気過剰率算出装置。 The excess air ratio calculation device according to claim 1, wherein the storage unit stores moving average values of the fuel injection execution time Ti1 and the stored torque value TQ1.
  4. 　前記記憶部は、前記リニアライズ変換したデータの移動平均値を前記変換限界閾値に関する記憶空気過剰率λｂとして記憶することを特徴とする請求項１に記載の空気過剰率算出装置。 The excess air ratio calculation device according to claim 1, wherein the storage unit stores a moving average value of the linearized data as a stored excess air ratio λb regarding the conversion limit threshold.
  5. 　前記過剰率算出部は、前記変換限界閾値に関する記憶空気過剰率λｂとして、あらかじめ定めた値を用いることを特徴とする請求項１に記載の空気過剰率算出装置。。 The excess air ratio calculation device according to claim 1, wherein the excess air ratio calculation unit uses a predetermined value as the stored excess air ratio λb regarding the conversion limit threshold. .
  6. 　前記限界閾値設定部は、前記検出部の温度と前記変換限界閾値とを対応付けたルックアップテーブルに基づき、前記変換限界閾値を前記検出部の温度に応じて設定することを特徴とする請求項１に記載の空気過剰率算出装置。 2. The limit threshold setting unit sets the conversion limit threshold according to the temperature of the detection unit based on a lookup table that associates the temperature of the detection unit with the conversion limit threshold. 1. The excess air ratio calculation device according to 1.
  7. 　前記酸素センサは、酸素濃度で抵抗値が変化する抵抗型酸素センサであり、
    　前記過剰率算出部は、前記抵抗型酸素センサの検出部の温度及び検出値と前記排気の空気過剰率λとを対応付けたデータマップを備え、
    　該データマップを用いて前記リニアライズ変換されたデータを取得するとともに、前記検出値又は前記リニアライズ変換されたデータが前記変換限界閾値以下のとき、前記リニアライズ変換されたデータを前記排気の空気過剰率λとみなすものであることを特徴とする請求項１～６に記載の空気過剰率算出装置。
          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 that associates the temperature and detected value of the detection unit of the resistive oxygen sensor with the excess air rate λ of the exhaust gas,
    The data map is used to obtain the linearized data, and when the detected value or the linearized data is less than or equal to the conversion limit threshold, the linearized data is converted to the exhaust air. The excess air ratio calculation device according to any one of claims 1 to 6, characterized in that the excess air ratio calculation device is regarded as the excess ratio λ.
PCT/JP2022/013667 2022-03-23 2022-03-23 Excess air ratio calculation device WO2023181209A1 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5263358A (en) * 1992-02-28 1993-11-23 General Motors Corporation Closed-loop air-fuel ratio controller
US5826426A (en) * 1997-07-30 1998-10-27 Chrysler Corporation Oxygen sensor linearization system and method
US6481427B1 (en) * 2000-10-16 2002-11-19 General Motors Corporation Soft linear O2 sensor
JP2012013028A (en) * 2010-07-02 2012-01-19 Honda Motor Co Ltd Air-fuel ratio control apparatus for internal combustion engine
JP2022070442A (en) * 2020-10-27 2022-05-13 日立Astemo株式会社 Air excess rate calculation device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5263358A (en) * 1992-02-28 1993-11-23 General Motors Corporation Closed-loop air-fuel ratio controller
US5826426A (en) * 1997-07-30 1998-10-27 Chrysler Corporation Oxygen sensor linearization system and method
US6481427B1 (en) * 2000-10-16 2002-11-19 General Motors Corporation Soft linear O2 sensor
JP2012013028A (en) * 2010-07-02 2012-01-19 Honda Motor Co Ltd Air-fuel ratio control apparatus for internal combustion engine
JP2022070442A (en) * 2020-10-27 2022-05-13 日立Astemo株式会社 Air excess rate calculation device

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