JPH0988711A - Intake air flow detector for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a back flow distinguished from a forward flow by deciding the maximum and minimum points of detection values of an intake air flow, comparing the maximum value with the set comparison value, and when the maximum value is smaller than the comparison value, judging the intake air flow detected between the minimum points before and after the maximum values as the back flow value. SOLUTION: An intake air flow detection signal from a hot-wire air flowmeter which detects the intake air flow regardless of a forward flow or a back flow is input in a variable acceleration operation means 1 and the variable acceleration is operated here. The positive/negative mark change in this variable acceleration is detected by a detection means 2 and after it is detected that the mark of the variable acceleration is inverted from the negative to the positive, whenever the same inversion is detected at the next time, the maximum value of the intake air flow is detected by a maximum value detection means 3. And the comparison value found in the operation means 5 based on an engine operation state and the maximum value are compared by the comparison means 6 and in the case of the maximum value < the comparison value, it is decided in the decision means 7 that the intake air flow detected between the minimum points before and after the maximum value is the back flow value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake air flow rate measuring device for an internal combustion engine, and more particularly to a device for detecting a backflow separately from a forward flow.

[0002]

2. Description of the Related Art In an electronically controlled fuel injection type internal combustion engine (gasoline engine), the intake air flow rate is used to determine the fuel injection amount, and in the diesel engine to determine the maximum fuel injection amount. Needs to be measured.
One of the means is a hot-wire type air flow meter, which has features such as low cost and wide dynamic range, and is widely adopted as an intake air flow rate detecting means of an internal combustion engine.

By the way, in the internal combustion engine, since the intake valve is opened before the completion of the exhaust stroke of the cylinder, the phenomenon that the exhaust gas flows back to the intake system occurs. This phenomenon is known as pulsation of intake or manifold negative pressure. When the flow rate of the intake air is low, the phenomenon of backflow of the intake air occurs due to this pulsation. In the hot wire type air flow meter, it is impossible to detect the flow direction, and even when the back flow is measured as a positive intake air flow rate,
At low flow rates, there is the problem that more than the true intake air flow rate is measured.

For this reason, it becomes impossible to perform accurate fuel injection according to the operating conditions, which causes problems such as deterioration of drivability.
Further, when an air flow meter is used for control of a diesel engine, especially for EGR control, a measurement error of the air flow meter causes deterioration of exhaust emission performance. That is,
From the intake air flow rate measured by the air flow meter,
In the case of a system that calculates exhaust pressure and intake pressure and controls the lift of the EGR valve so that an appropriate EGR rate is always maintained based on the differential pressure, the measured value of the air flow meter is the true intake air When measured more than the flow rate, the EGR rate becomes larger than the set value and the PM emission amount increases, while in the opposite case, the NOx emission amount increases and the exhaust emission performance deteriorates in both cases. .

Therefore, as a conventional technique for preventing erroneous detection due to the backflow, for example, Japanese Patent Laid-Open No. 57-56632
As described in Japanese Patent Publication No. JP-A-2003-264, when the load is higher than a predetermined throttle opening degree, the output is not based on the intake air flow rate detecting means such as the hot wire air flow meter, but based on the throttle valve opening degree and the engine rotation speed. There is a method in which the intake air flow rate is predicted using a value that is preset and stored.

[0006]

However, in the conventional method of predicting the intake air flow rate by using the preset value as described above, for example, the actual intake air flow rate is the same even when the throttle opening and the engine speed are the same. If the flow rate changes due to environmental changes or the like, an error will occur in the predicted value.

Therefore, the fuel injection amount control based on the intake air flow rate and the EGR amount control accuracy may be affected. The present invention has been made in view of such conventional problems, and provides an intake air flow rate detection device for an internal combustion engine capable of detecting a backflow separately from a forward flow without providing a special hardware mechanism. The purpose is to

[0008]

Therefore, the invention according to claim 1 is, as shown by the solid line in FIG. 1A, an intake air flow rate detecting means for detecting the intake air flow rate without distinction of the flow direction, and Pole detection means for detecting the maximum and minimum points of the detected value of the intake air flow rate, operating state detection means for detecting the operating state of the engine, and maximum value of the intake air flow rate at the maximum point detected by the pole detection means. Comparison value to be compared, comparison value setting means for setting based on the operating state of the engine, and the maximum value of the intake air flow rate and the set comparison value are compared, when the maximum value is smaller than the comparison value. A backflow determining unit that determines the intake air flow rate detected between the local minimum points before and after the local maximum value as a backflow value is included.

The operation of this one will be described. When no backflow occurs, the output of the intake air flow rate detection means has a waveform of the same cycle, but when backflow occurs, a combination of small peaks due to reversal during reverse flow and large peaks in the forward flow. . Therefore, if the comparison value is set to be smaller than the maximum value of the forward flow of the intake air flow rate and larger than the maximum value of the reverse flow, the reverse flow portion of the detected value can be determined.

Here, since the minimum value of the backflow changes depending on the operating condition of the engine, by setting the comparison value variably according to the operating condition, the backflow can be discriminated without being influenced by the operating condition. Specifically, the backflow is large when the flow rate of the intake air flow rate is small, because the counterbalance of the backflow is small. Therefore, as in the invention according to claim 2, by setting the operating state of the engine used to set the comparison value as the engine rotation speed, the comparison value with high accuracy can be set easily.

Further, as in the invention according to the third aspect, the comparison value can be set more accurately by setting the engine operating speed used for setting the comparison value to the engine rotation speed and the engine load. The invention according to claim 4 is shown in FIG.
As shown by the solid line in FIG. 3, the intake air flow rate detecting means for detecting the intake air flow rate without distinction of the flow direction, the intake air flow rate increasing time of the detected value of the intake air flow rate, and the decreasing time are distinguished. An increase / decrease time calculation means for calculating, and a flow direction determination means for comparing the continuously increasing time and the decreasing time of the intake air flow rate to determine whether the intake air flow rate is a forward flow or a reverse flow. It is characterized by including ,.

As described above, the output of the intake air flow rate detecting means is a combination of a small peak due to reversal at the time of reverse flow and a large peak corresponding to the forward flow when the reverse flow occurs, so that the continuous intake air flow rate is obtained. By comparing the increasing time and the decreasing time, the backflow portion can be determined. The invention according to claim 5 is the same as that shown in FIG.
As indicated by the alternate long and short dash line in (B), it includes advance processing means for performing advance processing for a response delay with respect to the detected value of the intake air flow rate detected by the intake air flow rate detection means. The determination means or the flow direction determination means is characterized by performing pole point detection and backflow determination on the detection value obtained by processing the advance of the intake air flow rate.

With this configuration, since the detected value of the intake air flow rate has a response delay, the intake air flow rate detected value in which the influence of the response delay is reduced by performing advance processing for the response delay. On the other hand, the backflow determination can be performed accurately.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a block diagram showing the configuration of the first embodiment. A detection signal of the intake air flow rate from an intake air flow rate detection means such as a hot-wire air flow meter that detects the intake air flow rate without distinction between forward flow and reverse flow. Enter
Means 1 for calculating the speed of change, means 2 for judging the change in the sign of the speed of change 2, means for judging the reversal of the sign of the speed of change from negative to positive, and inhalation every time the same inversion is judged next time A means 3 for detecting the maximum value of the air flow rate, a means 4 for storing a signal of the intake air flow rate while detecting the maximum value, and a comparison value (S) which is compared with the maximum value based on the operating state of the engine. / L), means 6 for calculating the maximum value and the comparison value, and forward flow and reverse flow for the stored intake air flow rate based on the comparison result of the maximum value and the comparison value. And a means 7 for determining whether the sign is positive or negative.

Next, the operation of this embodiment will be described with reference to the flowcharts of FIG. In FIG. 3 showing the main flow, in step (denoted as S in the drawing; the same applies hereinafter) 1, a detection value (voltage) output from a hot wire type air flow meter or the like which is an intake air flow rate detecting means is read. In step 2, the intake air flow rate Qas01 is converted using the voltage-flow rate conversion table as shown in FIG.

In step 3, the intake air flow rate Qas
01 is advanced to the response delay of the intake air flow rate detection means to obtain Qas02. This method will be described later. In step 4, backflow is detected and corrected from the intake air flow rate Qas02 to obtain Qas03. The backflow detection and correction method will be described later.

In step 5, the intake air flow rate Qas
The averaging process is performed on 03, Qas0 is set, and the process ends. FIG. 5 shows a flowchart of a method of performing advance processing for the response delay of the intake air flow rate detecting means 1.
Generally, the intake air flow rate detecting means has two time constants as shown in FIG.

In step 11, advance processing for the delay with respect to the one time constant T1 is performed according to the following equation. Qa11 = Qas01 _n-1 + (Qas01-Qas01
_n-1 ) * 0.004 / T1 In step 12, the advance processing for the delay with respect to the other time constant T2 is performed according to the following equation.

Qa02 = Qa11 _n-1 + (Qa11-Q
a11 _n-1 ) × 0.004 / T2 FIGS. 7 and 8 are flowcharts for determining and correcting backflow. In step 21, the comparison value Qa2sl is compared with the maximum value of the intake air flow rate described later from the engine operating state.
Is calculated. The method will be described later. Step 22
Then, Qas02 from the previous calculation (for example, 4 msec before)
Take the difference between (Qas02 _n-1 ) and this time Qas02
(Calculate the amount of change), and let ΔQa2.

In step 23, it is determined whether the ΔQa2 is negative. When it is determined to be negative in step 23, the process proceeds to step 24, and the previous value of ΔQa2 (ΔQa2 _n-1 )
Is 0 or more. And ΔQa2
_{If n-1} is greater than or equal to 0, proceed to step 25 and Q
Let as02 _n-1 be the maximum value Qa2m. In other words, in steps 3 to 5, when Qas02 changes from increasing to decreasing, the value before Qas02 is the maximum value, so that value is updated as Qa2m, and in other cases, the previous value is changed. Is going to hold.

In step 26, the code determination flag F1ag
The previous value of s (F1ags _n-1 ) is determined. And F
When 1ags _n-1 is 1, the process proceeds to step 30 and Sig
If n = 1 and F1ags _n-1 is 0, step 27
Then, it is determined whether or not the previous value ΔQa2 _n-1 is negative. If negative, the process proceeds to step 28, and it is determined whether the current value ΔQa2 is 0 or a positive value. If yes, the process proceeds to step 30. At Si
If gn = 1, otherwise go to step 29 and determine whether the maximum value Qa2m is greater than or equal to the comparison value Qa2sl.

If Qa2m ≧ Qa2sl,
Proceed to step 30, set Sign = 1, and set Qa2m <Qa.
If it is 2 sl, the flow advances to step 31 to set Sign = 0. In step 32, the previous value Qas02 _{n-1 is changed} to Sign.
And the backflow correction value Qas03 is calculated and output. At step 33, the current value Qas02 is set to Qas02 _n-1 , and the current value ΔQa2 is set to ΔQa2 _n-1 and stored in the memory.

At step 34, it is judged whether the maximum value Qa2m is equal to or more than the comparison value Qa2sl, and Qa2m ≧ Qa.
If it is 2 sl, go to step 36 and flag Flags
Is set to 0, and the process ends. Qa2m <Q in step 34
If it is determined to be a2sl, the process proceeds to step 35 and Sign
It is determined whether or not = -1, and if so, the process proceeds to step 37 to set the flag Flags as 1, and if not, the flag Flags is held at the previous value and the process ends.

FIG. 9 shows the comparison value Qa2s for backflow determination.
It is a flowchart which calculates l. In step 41,
The engine speed Ne is read as the operating state of the engine. In step 42, for example, a table as shown in FIG. 10 is searched, the comparison value Qa2sl is read, and the process is ended.

In the table setting example of FIG. 10, the backflow component decreases as the engine speed increases, so the comparison value Qa2sl is set to decrease accordingly. It should be noted that the backflow has been a problem in the low rotation range in the past, and the countermeasures in known examples are limited to the low rotation range. FIG. 11 shows the comparison value Qa2sl.
8 is a flowchart of another example of calculating The engine speed is read in step 51 as in the above embodiment,
At 52, the basic comparison value Qa2slb is searched.

Next, at step 53, the intake throttle valve opening is read, at step 54 the table as shown in FIG. 12 is searched, the correction coefficient Kqa2sl of the comparison value is read, and at step 55, the basic comparison value Qa2slb is set. Correction coefficient Kqa2s
The comparison value Qa2sl is set by multiplying by 1. The table in FIG. 12 is an example, but when the intake throttle valve opening is small, the intake air flow rate is reduced, and the backflow rate is also reduced by the increase in the flow rate, so the comparison value is reduced and As a problem, the backflow increases when the intake throttle valve opening is large, so the comparison value is also set to be large.

FIG. 13 is a flowchart of the averaging calculation of the intake air flow rate Qas03. In step 61, the values of the intake air flow rate Qas03 up to N-1 times before are averaged to obtain the intake air flow rate Qas0. Then, in step 62, the memory contents are shifted for each processing and the processing ends.

In this way, since the backflow is detected and the pulsation is averaged after the processing, the accurate intake air flow rate is calculated, and the air-fuel ratio control with high accuracy (including environmental change) is always possible. Becomes Further, particularly in the case of the EGR control of the diesel engine, the optimum EGR control can be performed, so that the PM (exhaust particulate) and NOx can be reduced,
Furthermore, since accurate fuel injection amount control is possible, it is possible to prevent smoke from increasing in any environment.

FIG. 14 shows an outline of the backflow correction method of this embodiment, and FIG. 15 shows an actual calculation example of this embodiment (when the EGR of a diesel engine is applied, the actual intake air flow rate Signal, intake air flow rate detected by air flow meter, calculation result of conventional intake air flow rate, result after advance process compensation, intake air flow rate after backflow correction), Fig. 16 shows the effect of this embodiment (from 10 seconds later) When the pulsation width is the same and the DC component is gradually decreased, that is, the backflow component is increased,
The change rate is shown. The thick broken line is the true intake air flow rate,
The solid line shows the present embodiment, and the thin broken line shows the conventional calculation result of the intake air flow rate).

Next, a second embodiment of the present invention will be described. FIG. 17 shows a system configuration when this embodiment is used for EGR control. A hot-wire type air flow meter 23, which is an intake air flow rate detecting means, is mounted on the upstream side of the intake passage 22 of the internal combustion engine 21, and connects the exhaust passage 24 and the intake passage 22 with each other.
An EGR valve 26 is provided in the GR passage 25.

The control unit 27 calculates the intake pressure and the exhaust pressure based on the signal from the air flow meter 23, sets the lift amount of the EGR valve 26 so that the EGR rate is appropriate, and outputs the lift amount signal to the EGR signal. It is output to the valve 26 to control the lift amount, thereby performing EGR control. Figure of control of this embodiment
18 The following flow chart will be described.

FIG. 18 shows the pole of the output value of the air flow meter 23.
It is a flow chart which distinguishes large time and minimum time. Step
The current value Q of the output value of the air flow meter 23_n
And the previous value Q_n-1Deviation from_n (= Q_n-Q_n-1) Is calculated
I do. In step 102, the current value of the deviation D_nIs positive
Value and the previous value D _n-1Whether is a negative value
To judge.

When the determination at step 102 is YES
Indicates that the change in the output value is changing from decreasing to increasing.
If it is judged that it is a small time, go to step 103 and
Flg Set min to 1. Format of step 102
If the determination is NO, the process proceeds to step 104, and the minimum flag F
lg After resetting min to 0, proceed to step 105.
No.

In step 105, the current value D of the deviation is_n
Is a negative value and the previous value D _n-1Is a positive value
Or not. If the determination in step 105 is YES
If the output value changes from increasing to decreasing
Then, it is judged that it is the maximum time, and the process proceeds to step 106, and
Large flag Flg Set max to 1, step 105
If the determination is NO, the process proceeds to step 107 and the maximum
Flg reset max to 0.

FIG. 19 is a flow chart for counting the output time when the intake air flow rate increases and when it decreases. In step 111, the count value C of the counter is reset to 0. In step 112, the count value C is incremented. In step 113, the minimum flag Flg m
It is determined whether or not in is set to 1. If it is set, it is determined that it is the minimum time, and the process proceeds to step 114, and the present count value C is set to the output time C in the decreasing direction of the intake air flow rate. Set as Dec.

If the determination in step 113 is NO, the step
Go to step 115 and set the maximum flag Flg. max set to 1
If it is set, it is maximum.
If it is time, go to step 116
The output value C in the direction of increasing the intake air flow rate Inc and
And set. If the determination in step 115 is NO,
The output in the same direction continues, not at the minimum or maximum.
Therefore, the process returns to step 112 and the output of the same direction output time is counted.
To continue.

Hereinafter, a method of making a backflow determination based on these values will be described. As shown in FIG. 20, when no backflow occurs, the output waveform of the airflow meter has a waveform of the same cycle, but when backflow occurs, a small peak due to reversal at the time of backflow and a large amount of forward flow. You can see that it is a combination of mountains. That is, the backflow time can be determined from the magnitude relationship between the increase time and the decrease time of the output waveform measured as described above.

In FIG. 21, the reverse flow determination is performed and the reversal flag Flg is set.
It is a flowchart which sets neg. Steps
In 121, the latest output reduction time C Dec and output increase time C Deviation DC from Inc (= C Dec-C I
nc) is calculated. In step 122, it is judged whether or not the deviation DC is a positive value, and if YES, the routine proceeds to step 123, where the inversion flag Flg. Neg is set to 1, and if NO, the process proceeds to step 124.

At step 124, the maximum flag Flg.
max and inversion flag Flg It is determined whether both neg are set to 1. If NO, the routine proceeds to step 125, where the inversion flag Flg is set. Reset neg to 0.
If the determination in step 124 is YES, the process proceeds to step 126, in which the previous value DC (n-1) of the deviation is negative and the minimum flag Flg. It is determined whether min is set to 1.

Then, the determination in step 126 is YES.
If it is, proceed to step 123 and reverse flag Flg n
If eg is set to 1, and if it is NO, the routine proceeds to step 127, where the inversion flag Flg Keep neg at the current value.
That is, when the deviation DC is a positive value and during the period from the minimum time when the DC value becomes 0 from the negative value to the next maximum time, and the DC
Is 0. Therefore, the case of the same condition is judged as the backflow, and the reversal flag Flg is set. Neg is set to 1.

From the above results, the inversion flag Flg ne
The signal obtained by inverting the signal when g is set to 1 is the Converted Signal shown in FIG. This Conver
An averaging process is performed on the basis of the ted signal to finally obtain an intake air flow rate signal used for fuel injection amount control and EGR control. In addition, in the present embodiment, as in the first embodiment,
As shown in 22, a backflow detection is performed on a signal obtained by advancing the output waveform of the hot-wire airflow meter and a backflow correction signal is obtained.

The result of confirming the effect of the present embodiment by simulation is as shown in FIG. 23, and it is shown that the EG changes with time during idling of the diesel engine.
The situation was set such that the R amount was increased and the actual intake air flow rate measured by the hot wire air flow meter was decreased. As the simulation setting conditions, the engine rotation speed was 850 rpm, the sampling period was 1 ms, and the intake pulsation was given as a sine wave. As shown in the figure, on the low flow rate side with respect to the true intake air flow rate
The values are almost the same even when the elapsed time is near 24 seconds, which shows that the intake air flow rate is measured correctly.

Further, in the present embodiment, as in the first embodiment, since the conventional hot-wire type air flow meter is used, there is no increase in cost, and there is no map or table to be newly added. No up occurs.

[0044]

As described above, according to the invention of claim 1, when the backflow of the intake air flow rate occurs, the detected values are small peaks due to the reversal at the time of backflow and the forward flow amount. Because of the combination of large peaks, the backflow portion of the detected value can be discriminated by using the comparison value set so as to be smaller than the maximum value of the forward flow of the intake air flow rate and larger than the maximum value of the backflow.

According to the second aspect of the present invention, the comparison value can be set easily and accurately based on the engine speed. According to the invention of claim 3, the comparison value can be set more accurately based on the engine speed and the engine load. Further, according to the invention according to claim 4, as described above, the output of the intake air flow rate detecting means is a combination of a small peak due to reversal at the time of reverse flow and a large peak for forward flow when the reverse flow occurs. Therefore, the backflow portion can be determined by comparing the time during which the continuous intake air flow rate is increasing and the time during which the continuous intake air flow rate is decreasing.

Further, according to the fifth aspect of the present invention, by performing the advance processing for the response delay of the detected value of the intake air flow rate, the backflow determination is performed with respect to the detected value of the intake air flow rate in which the influence of the response delay is reduced. Can be performed with high precision.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration and functions of the present invention.

FIG. 2 is a block diagram showing the configuration and functions of the first embodiment of the present invention.

FIG. 3 is a flowchart for reading an intake air flow rate according to the same embodiment.

FIG. 4 is a voltage / intake air flow rate conversion table.

FIG. 5 is a flowchart of the same advance processing.

FIG. 6 is a diagram showing a delay element of the air flow meter.

FIG. 7 is a flowchart of the preceding stage of the backflow determination.

FIG. 8 is a flowchart of the latter part of the same.

FIG. 9 is a flowchart of comparison value calculation.

FIG. 10 is a diagram similarly showing a comparison value with respect to the engine rotation speed Ne.

FIG. 11 is a flowchart showing another example of comparison value calculation.

FIG. 12 is a diagram showing a relationship between an intake throttle valve opening and a comparison value correction coefficient.

FIG. 13 is a flowchart similarly showing an averaging calculation.

FIG. 14 is a diagram showing an outline of backflow correction.

FIG. 15 is a diagram that similarly shows each operation of the present embodiment.

FIG. 16 is a diagram that similarly shows the effect of the present embodiment.

FIG. 17 is a system configuration diagram of the second embodiment of the present invention.

FIG. 18 is a flow chart of pole determination similarly.

FIG. 19 is a flowchart of counting the increase time and the decrease time.

FIG. 20 is a schematic diagram of the intake air flow rate and signals based on the same.

FIG. 21 is a flow chart of reverse determination similarly.

FIG. 22 is a diagram showing a raw output waveform of the air flow meter and a waveform after each process.

FIG. 23 is a diagram showing an effect of the present embodiment.

[Explanation of symbols]

 1 change speed calculation means 2 sign change determination means 3 maximum value detection means 4 storage means 5 comparison value calculation means 6 comparison means 7 sign setting means 21 internal combustion engine 22 intake passage 23 air flow meter 24 exhaust passage 25 EGR passage 26 EGR valve 27 control unit

Claims (5)

[Claims] 1. An intake air flow rate detecting means for detecting an intake air flow rate regardless of flow directions, a pole detecting means for detecting maximum and minimum points of a detected value of the intake air flow rate, and an operating state of an engine. Operating state detecting means, comparison value setting means for setting a comparison value to be compared with the maximum value of the intake air flow rate at the maximum point detected by the pole point detecting means based on the operating state of the engine, and the intake air flow rate And a comparison value that has been set, and when the maximum value is smaller than the comparison value, the backflow determination means that determines that the intake air flow rate detected between the minimum points before and after the maximum value is the backflow value. An intake air flow rate detecting device for an internal combustion engine, characterized in that: 2. The operating condition of the engine used for setting the comparison value is an engine rotation speed.
An intake air flow rate detection device for an internal combustion engine according to item 1. 3. The intake air flow rate detecting device for an internal combustion engine according to claim 1, wherein the operating states of the engine used for setting the comparison value are an engine speed and an engine load. 4. An intake air flow rate detection means for detecting an intake air flow rate without distinction of flow directions, and a time during which the detected value of the intake air flow rate is increasing and a time during which it is decreasing are calculated separately. An increase / decrease time calculation means, and a flow direction determination means for comparing the time during which the intake air flow rate is continuously calculated and the time during which it is decreasing to determine whether the intake air flow rate is a forward flow or a reverse flow. An intake air flow rate detection device for an internal combustion engine, characterized in that it is configured to include. 5. An advance processing means for performing advance processing for a response delay with respect to a detected value of the intake air flow rate detected by said intake air flow rate detection means, said pole point detection means, backflow determination means or said flow direction. The intake air of the internal combustion engine according to any one of claims 1 to 4, wherein the determining means performs a pole point detection and a backflow determination on the detection value obtained by processing the advance of the intake air flow rate. Flow rate detector.