JPH0681914B2 - Electronic control unit for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention calculates an atmospheric pressure-related value such as an atmospheric pressure value from other control parameters of an internal combustion engine, and uses this as an auxiliary parameter for control. The present invention relates to an electronic control unit of an engine.

[Conventional technology]

A conventional electronic control unit for an internal combustion engine will be described with reference to FIG. 1 according to an embodiment of the present invention. In FIG. 1, reference numeral 1 is mounted on, for example, an automobile and is composed of a plurality of cylinders.
The cylinders of the internal combustion engine 2 are shown, 2 is a cylinder of the internal combustion engine 1, 3 is an intake valve of the internal combustion engine 1 driven by a cam (not shown), and 4 is an intake manifold of the internal combustion engine 1. Reference numeral 5 is an injector provided for each cylinder of the intake manifold 4, 6 is a surge tank connected to the upstream side of the intake manifold 4, and 7 is an intake air amount of the internal combustion engine 1 provided in an intake passage upstream from the surge tank 6. Is a throttle valve that controls the throttle valve, and 8 is a throttle opening sensor that is connected to the throttle valve 7 and detects the opening of the throttle valve 7. Reference numeral 9 is a bypass passage that bypasses the upstream and downstream of the throttle valve 7, 10 is a bypass air amount regulator provided in the bypass passage 9, and 11 is provided further upstream of the throttle valve 7. For example, a temperature-dependent resistance is used for internal combustion. A hot-wire air flow sensor (hereinafter referred to as AFS) as an air flow rate sensor that detects the flow rate of air taken into the engine 1, 12 is an air temperature sensor that detects the temperature of the intake air before passing through the AFS 11, and 13 is the AFS 11 or An air cleaner provided at an intake port further upstream of the air temperature sensor 12. 14a is the internal combustion engine 1
Water temperature sensor, which is installed in the cooling passage of
14b is an O ₂ sensor as an air-fuel ratio sensor which is attached to the exhaust pipe and detects an air-fuel ratio, 15 is a crank angle sensor which detects a predetermined crank angle of the internal combustion engine 1, and 16 is that the internal combustion engine 1 has no load. It is a neutral detection switch for detecting. 17 is an electronic control unit (hereinafter referred to as ECU)
Then, the fuel injection amount is determined mainly based on the output signals from the AFS 11, the water temperature sensor 14a and the crank angle sensor 15, and the injector 5 is synchronized with the output signal of the crank angle sensor 15.
Is controlled to perform fuel injection. At this time, the output signals of the throttle opening sensor 8, the air temperature sensor 12, the O ₂ sensor 14b, and the neutral detection switch 16 are used by the ECU 17 as auxiliary parameters. The ECU 17 also controls the bypass air amount controller 10 to adjust the rotation speed of the internal combustion engine 1, but the details of the operation are omitted.

FIG. 3 is an enlarged view of the intake section of FIG. 1, where Ta is atmospheric temperature, Pa is atmospheric pressure, and Qa is ASF11.
Is the opening of the throttle valve 7, S (θ) is the throttle passage area when the throttle opening is θ, and Ps is the internal pressure of the surge tank 6.

FIG. 8 is a block diagram showing the internal configuration of the ECU 17 of the conventional apparatus, and FIG. 9 is a diagram in which the horizontal axis represents the pressure ratio Ps / Pa and the vertical axis represents the f value described later.

A conventional apparatus having such a structure is disclosed in, for example, Japanese Patent Laid-Open No. 59-162341.

Next, the operation will be described. The function generator 17a, to which the throttle opening signal θ detected by the throttle opening sensor 8 is input, outputs a signal of the ratio of the air flow rate value Q _{O to} the atmospheric pressure value P _{O in the} reference atmospheric condition, corresponding to the input signal. . This signal is input to the division circuit 17b together with the air flow rate value Qa, Is calculated. The output of the division circuit 17b corresponds to the value of Pa · f. Here, K is the specific heat ratio of air, Is established. Pa · f is guided to the division circuit 17d together with the intake pipe pressure signal Ps obtained from the input terminal 17c. Division circuit 17d
The signal obtained in Ps is input to the next comparison unit 17e, Ps
The pressure ratio of (Pa · f) is compared with a fixed value a of 0.52828, for example. As can be seen from FIG. 9, Ps / Pa =
Sound velocity choke occurs in a region of M (Mach number) = 1 less than a with a as a boundary, and f becomes a constant value. In a region of M <1 of a or more, f changes. Therefore, the switch 17f is opened / closed according to the result of comparison by the comparison unit 17e. Ps /
If (Pa · f) <a, the switch 17f is closed because the assumption of f = 1 is satisfied according to FIG. As a result, the atmospheric pressure value Pa is output from the division circuit 17b via the switch 17f. When Ps / (Pa · f) ≧ a, for example, the assumption of f = 1 does not hold, so the switch 17f is opened.

[Problems to be solved by the invention]

Since the conventional electronic control unit for an internal combustion engine is configured as described above, it utilizes the fact that f becomes a constant value in the region of M = 1 in order to obtain the atmospheric pressure. Therefore, Ps / P
It is limited to the area where a <0.52828, and it is in idling. However, in idling, the influence of temperature, the variation of throttle opening position, and the variation of bypass air flow rate when the throttle is fully closed are large There was a problem that the accuracy of the atmospheric pressure value was not good. For example, the volume capacity is 2 l
In the internal combustion engine of, the air flow rate at idle is 3 g / sec,
On the other hand, the leak flow rate of the throttle is about 0 to 0.5 g / sec. Further, the constant in the equation for obtaining the air flow rate from the throttle opening, the atmospheric pressure and the surge tank internal pressure is a function of the air temperature and is proportional to the square root value of the air temperature ratio, as described later. Further, the error in the throttle opening position cannot be ignored as an error because the air flow rate during idling is small.

The present invention has been made to solve the above problems, and provides an electronic control device for an internal combustion engine, which can obtain an accurate atmospheric pressure related value with an inexpensive configuration without using an expensive atmospheric pressure sensor. The purpose is to get.

[Means for solving problems]

The electronic control unit for an internal combustion engine according to the present invention detects that the air flow rate sensor is normal by the sensor state detecting means and detects a predetermined operating state of the internal combustion engine by the operating state detecting means, and the throttle in the standard atmospheric state. A value corresponding to the charging efficiency or the value corresponding to the intake air flow rate determined by the opening degree and the rotational speed is stored in the storage means as a two-dimensional map, and the detection signal of the intake air flow rate and the rotational speed of the internal combustion engine is used. The atmospheric pressure is calculated by the calculating means from a predetermined arithmetic expression that takes the ratio of the value corresponding to the charging efficiency or the value corresponding to the intake air flow rate obtained using the detection signal of the intake air flow rate and the stored value from the storage means. The related value is calculated only when the air flow sensor is normal and in a predetermined operating state of the internal combustion engine.

[Action]

The calculating means in the present invention is capable of controlling the reference atmospheric condition and a certain atmospheric condition at the same throttle opening and the same rotational speed. By taking the ratio of the values, the ratio becomes almost constant, and the atmospheric pressure related value is obtained only when the air flow sensor is normal and the internal combustion engine is operating in a predetermined condition. And positively utilize the region of M <1 in FIG.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
The drawings show the overall configuration of an electronic control unit for an internal combustion engine according to an embodiment of the present invention, particularly a hot-wire fuel injection control unit,
This configuration has already been described in the section of the conventional technique except for the ECU 17, and the description thereof will be omitted.

FIG. 2 shows the internal configuration of the ECU 17 shown in FIG. 1, in which 171 is a digital interface for digital signal input of the crank angle sensor 15, the neutral detection switch 16, etc., whose output is the port of the CPU 172 or Input to interrupt terminal. The CPU 172 is a ROM 1721 in which the control program and data of the flow shown in FIGS. 4 to 7 are written,
A well-known microprocessor including a RAM 1722 as a work memory and a timer 1723 generates, for example, a fuel injection pulse width calculated by a predetermined control program by a timer output. Reference numeral 173 is an analog interface for inputting analog signals from the throttle opening sensor 8, AFS 11, air temperature sensor 12, water temperature sensor 14a, O ₂ sensor 14, etc., whose output is sequentially selected by the multiplexer 174 and A / D converted. The analog-to-digital conversion is performed by the device 175, and the digital value is taken into the CPU 172. A first drive circuit 176 is a drive circuit for driving the injector 5 with the fuel injection pulse width calculated by the CPU 172. Reference numeral 177 is a second drive circuit, which is generated by a timer output calculated by the CPU 172 according to a predetermined control program.
It is a drive circuit that drives the bypass air amount adjuster 10 with an ISC drive pulse width.

The CPU 172 stores the filling efficiency η _CO in the ROM 1721 in the standard atmospheric condition of the atmospheric pressure P _O and the air temperature T _O as a two-dimensional map using the rotation speed and the throttle opening as parameters, and Setting data for judgment and calculation is stored in advance. Further, the CPU 172 stores, in the ROM ₁₇₂₁ , a map of the maximum air flow rate value Q _maxO in the reference atmospheric condition using, for example, the rotation speed as a parameter.

Next, the operation of the CPU 172 will be described.

First, Pa is used to control the operating characteristic amount of the internal combustion engine 1, for example, the atmospheric pressure value output by AFS, P _O is the atmospheric pressure set value in the standard atmospheric condition, and Ta is detected by the air temperature sensor 12. Output air temperature value, T _O is the reference air temperature set value in the standard atmospheric condition, η _C is the charging efficiency, η _CO
Is the filling efficiency in the standard atmospheric condition, the atmospheric pressure correction value is Is expressed by the above equation (1). The description of the rationale for this equation (1) is omitted. Next, the operation of obtaining the atmospheric pressure correction value using the equation (1) will be described with reference to FIG. In FIG. 4, the switch S0 is a process for determining whether or not the AFS11 is within the normal range. That is, AFS1
The output voltage of 1 is the voltage V ₁ or more set to the output voltage of the AFS11 when the air flow is stopped and the voltage V ₂ set to the output voltage of the AFS 11 corresponding to the maximum air flow rate (however, V ₂ If> V ₁ ) or less, the process proceeds to step S1. If not, it is determined that the AFS 11 has failed, and the process of FIG. Next, step S1 is a routine for identifying an operating zone in which atmospheric pressure is detected, and details thereof will be described with reference to the flowchart of FIG. When in the detection zone,
If not, the process of FIG. 4 is terminated. Step S2 is a routine for determining whether or not the operation is steady, the details of which will be described with reference to the flowchart of FIG. If it is in steady operation, the process proceeds to step S3, and if not, the process of FIG. 4 is terminated. Step S3 draws a two-dimensional map of the throttle opening and the number of revolutions by using the signals of the throttle opening θ detected by the throttle opening sensor 8 and the number of revolutions N detected by the crank angle sensor 15 to draw a reference atmospheric state. The filling efficiency η _{CO of} is calculated. Then step
At S4, the current charging efficiency η _{C is set} to the rotation speed signal N and the air flow rate value from the AFS11 (or the air flow rate value of FIG. 7 based on the detection of AFS11) Qa, the stroke volume V _H stored in advance and the reference. Using the value of the air density ρ _{O in} the atmospheric state, The calculation is performed according to the equation (1a) above. Next, in step S5, the air temperature set value T _O , the above-obtained filling efficiencies η _CO , η _C, and the air temperature value Ta detected by the air temperature sensor 12 are used to calculate according to the above equation (1) to calculate the atmospheric pressure. Correction value Ask for. Next, in step S6, the atmospheric pressure correction value C _P is filtered. C _P (i) = K _O · C _P (i-1) +
(1-K _O ) · C _P is a filter process by calculation, K _O is a value of 0 to 1, and C _P (i-1) is an atmospheric pressure correction value obtained by the previous process. Further, this atmospheric pressure correction value C _P or the current atmospheric pressure correction value C _P (i) after filtering is memorized even after the key switch is turned off, and when the key switch is turned on again, the atmospheric pressure is immediately measured. I am able to make corrections.

Next, the detection zone determination processing will be described with reference to the flowchart of FIG. In step S11, it is determined whether or not the throttle opening θ detected by the throttle opening sensor 8 is within a predetermined range. The lower limit value θ _L is selected to be larger than the idle opening degree, and the upper limit value θ _H is set within a range in which the influence of blowback of the internal combustion engine 1 does not occur. For example, if the idle opening is 10 °, it is desirable that θ _L = 15 ° and θ _H = 30 °. When the throttle opening θ is within a predetermined range of θ _L to θ _H , the process proceeds to step S12, and otherwise, it is determined to be outside the detection zone in step S1C. In step S12, it is determined whether the rotation speed N detected by the crank angle sensor 15 is within a predetermined range. Here, the upper and lower limit values N _H and N _L are not particularly limited, but it is desirable to set them to a normal rotation range of N _L = 1000 rpm, N _H = 4000 rpm. When the rotation speed N is within the predetermined range of N _{L to} N _H , the process proceeds to step S13, and otherwise, it is determined to be outside the detection zone at step S1C. In step S13, it is determined whether or not the water temperature T _W detected by the water temperature sensor 14a is within the predetermined range of T _{WL to} T _WH . This water temperature condition takes into consideration a case where air is supplied to the internal combustion engine 1 from a portion other than the throttle portion by the bypass air amount adjuster 10 at a low temperature. When the water temperature T _W is within the above predetermined range, step S14
Otherwise, at step S1C, it is determined to be outside the detection zone. Step S14 is the neutral detection switch 16
It is determined from the signal from the neutral or in-gear state. In this case, it is the case of M / T car and D in the case of A / T car
It can be replaced by the determination of the range or the N range.
This judgment is easy to change the driving state at neutral, so
This is to remove this. Therefore, it is outside the detection zone when idle. When the neutral detection switch 16 is off and the gear is not in the neutral state, step S1
Go to 6 and vice versa, if neutral, step S
It is judged to be outside the detection zone at 1C.

In step S16, it is determined whether or not the previously obtained filling efficiency η is within a predetermined range of η _L to η _H. Η within this condition
_As can be understood from the equation (1), the condition of _L ≤ η is a condition for preventing the filling efficiency error from greatly affecting the atmospheric pressure correction value C _P at the time of low filling efficiency. The condition of η ≦ η _{H is} a condition that the value in the blowback zone is not used when the air flow rate is very large. The packing efficiency η is η _L to η
When it is within the predetermined range of _H , the process proceeds to step S17, and otherwise it is determined to be outside the detection zone in step S1C. Step S17
In, is detected by AFS11 intake air flow rate Q is determined whether within a predetermined range of Q _L to Q _H. The determination in this step is equivalent to the content of the determination performed in step S16, so either step S16 or S17 may be executed. Step S17 at Q _L ≦ Q ≦ Q _H at the time of establishment step S18
If it is not established, it is determined to be outside the detection zone in step S1C. In step S18, it is determined whether the air temperature T _a detected by the air temperature sensor 12 is within a predetermined range of T _{aL to} T _aH (> T _aL ). This condition is a condition for using only the highly accurate portion of the air temperature sensor 12 when obtaining the atmospheric pressure correction value in the formula (1), and when obtaining the atmospheric pressure correction value in the formula (2) described later. Is a condition for the error in the atmospheric pressure correction value to be within the allowable range because there is no air temperature correction term. The detected atmospheric temperature _Ta is T
Within the predetermined range of _aL through T _aH proceeds to step S19, otherwise determines that the detection zone outside the step S1C. In step S19, it is determined whether or not the EGR (not shown) is off.
This determination is to prevent the influence of the EGR on the atmospheric pressure correction value. When the EGR is off, the process proceeds to step S1A, and otherwise the process is determined to be outside the detection zone in step S1C.

At step S1A, the air flow rate Q _B through the bypass air quantity regulator 10 determines whether it is within a predetermined range of Q _BL to Q _BH. This condition is for preventing the influence of the bypass air flow rate on the atmospheric pressure correction value. However, (3) described later
It is not necessary to perform this step when the filling efficiency is obtained from the formula.

If Q _BL ≦ Q _B ≦ Q _BH , the process proceeds to step S1B, and otherwise, it is determined to be outside the detection zone in step S1C.

In step S1B, it is determined whether the air-fuel ratio detected by the O ₂ sensor 14b is the stoichiometric air-fuel ratio. That is, the O ₂ sensor 14
The fuel injection amount is controlled by b, and the atmospheric pressure correction value is calculated only when the air-fuel ratio is stoichiometric. When it is determined to be the stoichiometric air-fuel ratio in step S1B, the process proceeds to step S1D, where it is determined to be within the detection zone, otherwise step S1
C is judged to be outside the detection zone. When the determination is made in step S1C or S1D, the series of determination processing shown in FIG. 5 is ended.

Next, the determination process of the steady operation will be described with reference to the flowchart of FIG. Step S21 is a step of determining whether or not the absolute value | Δθ | of the deviation value of the throttle opening for each predetermined time obtained by a routine (not shown) is not less than a predetermined value θ _T. Set the time in the timer. If it is less than the predetermined value θ _T, it is determined in step S23 whether the first timer is 0. If the first timer is 0, step S2
Go to 5. On the contrary, when the first timer is not 0, the first timer is decremented in step S24. Above, step S21 ~
The same processing as the processing in step S24 is performed for the rotation speed in steps S25 to S28. However, | ΔN | is the absolute value of the deviation value of the rotation speed, and N _T is a predetermined value.

Step S29 is a step of determining whether both the first timer and the second timer are 0, and when the condition is satisfied, step S2A
Then, it is determined to be a steady operation, and if the condition is not satisfied, step S2B
Is determined to be transient operation. That is, it is determined that both are in the transient state within the predetermined time after the throttle deviation or the rotation deviation is generated.

FIG. 7 is a flowchart of a routine for obtaining the air flow rate value Qa using the atmospheric pressure correction value. Step S71 is the maximum air flow rate value Q corresponding to each rotation speed in the standard atmospheric condition.
_{In the} step of _{obtaining maxO} , f (N) is a table of the maximum air flow rate value Q _maxO whose factor is the rotation speed, and the corresponding maximum air flow rate value is calculated from the rotation speed N issued based on the output signal from the crank angle sensor 15. _Issue Q _maxO .

The step S72 following the step S71 is a step of determining the blowback area of the internal combustion engine 1 by the rotation speed N. When the rotation speed N is in the range of N ₁ or more and N ₂ or less, go to step S73. If not, the process proceeds to step S74. Step S73 the maximum air flow rate value Q _MAXO reference atmospheric conditions mentioned above in to atmospheric pressure correction and the temperature correction determining the maximum air flow rate value Q _MAXO in the current atmospheric state calculated by (1b) the following equation.

Here, T _O is the air temperature set value in the standard atmospheric condition, and Ta is the current air temperature value detected by the air temperature sensor 12.
Further, the third term of the temperature correction on the right side can be omitted for the simplification of the system, or can be replaced with the correction by the water temperature using the water temperature sensor 14.

In step S74, the maximum air flow rate value Q _maxO in the standard atmospheric condition is set.
Substitute in Q _max . This is a processing step when using the AFS capable of accurately measuring the mass flow rate except for the blowback region, and otherwise, the processing of steps S72 and S74 is not performed. In addition, AFS that can accurately measure the mass flow rate
Even when is used, it is possible to omit the processing of steps S72 and S74. Step S73 or step S75 following S74 is a step of comparing the air flow rate value Qa measured by the AFS11 and the maximum air flow rate value Q _max , and when Qa ≧ Q _max , Qa is limited to Q _max in step S76. Also, Qa <Q _max
At that time, no processing is performed and the processing of FIG. 7 is terminated.

In the above embodiment, conditions such as throttle opening, rotation speed, water temperature, neutral detection switch state, intake air amount, filling efficiency, atmospheric temperature, air-fuel ratio, presence of EGR, and intake air flow rate of bypass passage are used as detection zone determination. Although all of the above are added to the determination, the detection zone may be determined only for a part of the above conditions for the sake of simplifying the system. The same can be said for the determination as to whether or not the operation is steady.

Further, although the filter processing is performed in the above embodiment, this step S6 is not always necessary.

Further, in the above embodiment, the amount of air passing through the bypass air amount adjuster 10 is greatly different from the amount of bypass air at the same rotation and the same throttle opening in the standard atmospheric condition depending on the water temperature, the air conditioner, the power steering, etc. May occur, and the atmospheric pressure correction value calculated at this time includes an error. Therefore, in order to compensate for this error, the formula for finding the filling efficiency η _C in step S4 is Can also be However, ΔQ _B is the variation amount of the bypass air amount due to the state of the water temperature, the air conditioner, the power steering, and the like. The filling efficiency may be obtained by using the above equation (2) instead of the above equation (1), and the atmospheric pressure correction value may be calculated using this filling efficiency.

Further, in the above embodiment, in step S5, The atmospheric pressure correction value may be obtained by using the equation. However, Q
_O is a reference air flow rate value in a reference atmospheric condition where Q _O = f (θ, N). Also, in each of the above equations, The temperature correction term of may be omitted for simplification of the system. For example, instead of the equation (1) in the above embodiment, Can also be used.

Although the atmospheric pressure correction value has been described as the atmospheric pressure-related value in the above-described embodiments, the present invention also applies, for example, to (1) to
(3) The atmospheric pressure value Pa is obtained by using any one of the equations and the value obtained by multiplying the value by P _O, and the operating characteristic amount of the internal combustion engine is obtained using the atmospheric pressure value Pa. May be.

Further, in the above embodiment, the case where the detected value of the intake air flow rate of the internal combustion engine is corrected to the atmospheric pressure has been described, but the present invention is not limited to this, and the fuel supply amount of the internal combustion engine, the ignition timing, the target rotation speed and the bypass air adjustment. It is needless to say that the present invention can be applied to the control of at least one of the operating characteristic amount of the internal combustion engine such as the amount.

〔The invention's effect〕

As described above, according to the present invention, the value corresponding to the charging efficiency in the standard atmospheric condition or the value corresponding to the intake air flow rate is stored and set in advance as two-dimensional map data of the throttle opening and the rotational speed, and the value is set to a certain large value. Atmospheric pressure-related values can be obtained only when the air flow rate sensor is normal and in a predetermined operating condition of the internal combustion engine from the value corresponding to the charging efficiency or the value corresponding to the intake air flow rate obtained in the atmospheric pressure state and the stored set value. Since it is configured as described above, there is an effect that an inexpensive, highly reliable and highly accurate one can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of the entire apparatus according to an embodiment of the present invention,
FIG. 2 is a block diagram showing the internal configuration of the ECU shown in FIG.
FIG. 3 is a schematic diagram of the intake section of FIG. 1, FIGS. 4 to 7 are flow charts showing the operation of the above-mentioned embodiment, respectively, and FIG. 8 is a block diagram showing the atmospheric pressure value of the conventional apparatus, and FIG. The figure is a characteristic diagram of the pressure ratio and the f value. In the figure, 1 ... Internal combustion engine, 5 ... Injector, 7 ... Throttle valve, 8 ... Throttle opening sensor, 9 ... Bypass passage, 10
... bypass air quantity regulator, 11 ... AFS, 12 ... air temperature sensor, 14a ... water temperature sensor, 14b ... O ₂ sensor, 15 ... crank angle sensor, 16 ... neutral detection switch, 17 ... ECU.

Claims (14)

[Claims] 1. An electronic control unit for an internal combustion engine, wherein an operating characteristic amount of an internal combustion engine is controlled by obtaining a parameter required for control via an auxiliary amount, and an electronic flow rate sensor for detecting an intake air flow rate of the internal combustion engine. A predetermined state of the internal combustion engine based on the detection signals from the sensor state detecting means for detecting that the air flow rate sensor is normal based on the output signal and the sensor means for detecting the state of the internal combustion engine other than the intake air flow rate. And a value corresponding to the charging efficiency or the intake air flow rate, which is determined by the throttle opening and the number of revolutions in the reference atmospheric condition, are stored in advance as a two-dimensional map and stored in advance. The throttle opening signal output by the throttle opening sensor that detects the opening of the throttle valve and the rotation speed output by the rotation speed sensor The storage means for outputting the stored set value according to the above, and a value corresponding to the charging efficiency obtained by using the detection signal of the intake air flow rate and the rotational speed of the internal combustion engine or the detection signal of the intake air flow rate. The calculating means is provided with a calculating means for calculating an atmospheric pressure-related value including at least an atmospheric pressure value according to a predetermined arithmetic expression that takes a ratio of a value corresponding to the intake air flow rate and a stored set value output from the storing means. An electronic control unit for an internal combustion engine, wherein the atmospheric pressure-related value is calculated only when the air flow rate sensor is normal and only when the internal combustion engine is in a predetermined operating state. 2. The sensor state detecting means is characterized in that the output voltage of the air flow sensor is equal to or higher than a first predetermined voltage which is lower than the output voltage of the air flow sensor when the air flow is stopped and corresponds to the maximum air flow rate. The electronic control unit for an internal combustion engine according to claim 1, wherein the air flow sensor is determined to be normal when the voltage is equal to or higher than an output voltage of the air flow sensor and equal to or lower than a second predetermined voltage. 3. The internal combustion engine according to claim 1, wherein the operating state detecting means detects that the opening of the throttle valve and the rotational speed of the internal combustion engine are within respective predetermined ranges. Electronic control unit. 4. The electronic control unit for an internal combustion engine according to claim 1, wherein the operating state detecting means detects that the temperature of the cooling water of the internal combustion engine is within a predetermined range. 5. The operating condition detecting means detects that the value corresponding to the charging efficiency of the internal combustion engine or the value corresponding to the intake air flow rate is within a predetermined range. Electronic control unit for internal combustion engine. 6. The electronic control unit for an internal combustion engine according to claim 1, wherein the operating state detecting means detects that the atmospheric temperature is within a predetermined range. 7. The electronic control device for an internal combustion engine according to claim 1, wherein the operating state detecting means detects that the air-fuel ratio of the internal combustion engine is within a predetermined range. 8. The electronic control unit for an internal combustion engine according to claim 1, wherein the operating state detecting means detects that the EGR is not operating. 9. The electronic control unit for an internal combustion engine according to claim 1, wherein the operating state detecting means detects that the amount of change in the number of revolutions within a predetermined time is less than or equal to a predetermined value. 10. The electronic control unit for an internal combustion engine according to claim 1, wherein the operating state detecting means detects that the amount of change in the throttle opening within a predetermined time is less than or equal to a predetermined value. . 11. The internal combustion engine according to claim 1, wherein the operating state detecting means detects that the air flow rate of the bypass passage that bypasses the upstream and downstream of the throttle valve is within a predetermined range. Electronic control unit. 12. The electronic control unit for an internal combustion engine according to claim 1, wherein the calculating means performs a filtering process on the calculated atmospheric pressure-related value. 13. A non-volatile storage means for storing the atmospheric pressure-related value or the filtered atmospheric pressure-related value even after the key switch is turned off. Item 12. An electronic control unit for an internal combustion engine according to item 12. 14. The internal combustion engine according to claim 1, wherein the calculating means corrects the atmospheric pressure-related value by a signal related to an air flow rate of a bypass passage bypassing the upstream and downstream of the throttle valve. Electronic control unit.