JPH0472524A - Air flow meter - Google Patents

Abstract

PURPOSE:To determine the rate of air flow accurately and a low cost without use of plurality of heat emitting resistances by sensing a signal which bases itself upon the change in the resistance value of heat emitting resistance in the suction path, and judging correctly the signal of counterflow by a counterflow judging means. CONSTITUTION:A sensor circuit 22 senses the resistance value of a heat emitting resistance 11 installed on an air flow sensor 10, and then an electric signal is emitted in accordance with the rate air flow, and a CPU 25 converts the electric signal into rate of air flow. Three max. values of the rate of flow and two min. values between them are sensed, and when a counterflow judging means judges that it is a rippled flow including counterflow, a correction is made for the portion of counterflow, and the rate of air flow within a certain period of time is calculated. This eliminates necessity for provision of plurality of heat emitting resistances 11, and a signal resulting from counterflow in the suction passage can be judged accurately and at a low cost, which enables determining the rate of air flow with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an air flow meter for measurement. Regarding the air flow needle.

(Prior Art) A sensor (hereinafter referred to as an air flow sensor) that detects the flow rate of air passing through an intake passage using a heat generating resistor cannot detect the direction in which the air flows. Therefore, even when a reverse flow flows in the intake passage, it is measured as if it were flowing in the normal direction, making it impossible to measure the correct air flow rate.

In order to solve these problems, an air flow sensor using a heating resistor as shown in FIG. 9 has been considered (see Japanese Patent Laid-Open No. 116220/1983). In the figure, 54 is a cylindrical or hollow cylindrical bobbin. 5
1.52 is a film-like heating resistor.

The film-like heat generating resistor 51 is attached to the upstream side of the intake passage on the side surface of the bobbin 54, and detects the air flow (arrow A) flowing from the upstream to the downstream of the intake passage.

Furthermore, the resistance value of the film-like heating resistor 51 is the same as that of the signal line 61.
62.

The film-like heat generating resistor 52 is attached to the side surface of the bobbin 54 on the downstream side of the intake passage, and detects the air flow (arrow B) flowing from the downstream side to the upstream side of the intake passage.

Further, the resistance value of the film heating resistor 52 is the same as that of the signal line 63.
64.

53 is a linear heating resistor made of platinum wire, and the bobbin 5
The linear heat-generating resistor 53 is installed in a position where it is not affected by the air flow around the sensor 4, and detects the flow rate of air flowing in both directions. Moreover, the resistance value of the linear heating resistor 53 is the signal line 65
．． 66.

Film heating resistor 51, 52 and linear heating resistor 53
The amount of heat dissipated changes when air flows around it,
The resistance value also changes. And a film-like heating resistor 51.
52 and the resistance values of the linear heating resistor 53 are detected by a detection circuit (not shown). The detection circuit outputs a voltage signal V4. Outputs V2 and V3.

According to the above configuration, the linear heating resistor 53 always detects the air flow rate regardless of the direction of the air flow.

Further, when air flows from upstream to downstream of the intake passage (in the direction of arrow A in the figure), air flow also occurs on the surface of the film-like heating resistor 51. On the other hand, since the film-like heating resistor 52 is located downstream of the bobbin 54, almost no air flow occurs on the surface of the film-like heating resistor 52. As a result, the value of the voltage signal ■1 becomes larger than the value of the voltage signal ■2.

Conversely, when air flows from downstream to upstream in the intake passage (in the direction of arrow A in the figure), that is, when a backflow occurs, air flow occurs on the surface of the film-like heating resistor 52. on the other hand,
Since the film-like heat-generating resistor 51 is located downstream of the bobbin 54, almost no air flow occurs on the surface of the film-like heat-generating resistor 51. As a result, the value of the voltage signal 2 becomes larger than the value of the voltage signal v1.

Therefore, the voltage signal ■1. By comparing the values of V2 and determining which value is larger, it is possible to determine in which direction the air is flowing in the intake passage.

For example, if the value of the voltage signal 2 is larger than the value of the voltage signal V, it can be determined that a backflow is flowing in the intake passage. At this time, by inverting the sign of the value of the voltage signal v3, the voltage signal 3 can be corrected, and the air flow rate can be measured.

(Problem to be Solved by the Invention) In the above air flow sensor, in order to accurately determine the direction of air flow, the flow velocity in the direction of arrow A and the flow velocity in the direction of arrow B are
When the flow velocities in the directions are equal, the values of the voltage signals V and 2 must also be equal. However, if there are variations in the manufacturing process of the two film heating resistors 51 and 52, or if there is an error in the installation position or angle of the bobbin 54, the film heating resistance 51. There is a possibility that the resistance values of 52 will not be equal. Therefore, there was a possibility that signals caused by backflow could not be correctly determined and the air flow rate could not be measured correctly.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air flow rate of "1" that allows discrimination of signals caused by backflow without using a plurality of heat generating resistors.

(Means for Solving the Problems) The present invention provides a heating resistor installed in an intake passage, a signal output means for outputting an electrical signal based on the resistance value of the heating resistor, and an electric signal adjacent to the heating resistor. a detection means for detecting one local maximum value and one local minimum value sandwiched between the three local maximum values, and a ratio of the central maximum value to the local maximum values at both ends of the five local maximum values is all smaller than a predetermined value; or when the difference between the maximum value at both ends and the maximum value at the center is both greater than a predetermined value, the electrical signal between the two minimum values is determined to be a signal caused by reverse flow. It is characterized by comprising means.

(Function) According to the present invention, the amount of heat dissipated by the heat generating resistor changes depending on the air flow rate in the intake passage, and the resistance value of the heat generating resistor changes in accordance with the change in the amount of heat dissipated. Then, the signal output means outputs an electrical signal based on the resistance value of the heating resistor.

At this time, since the direction of the airflow is not detected by the heating resistor, the signal output means outputs a signal caused by the backward flow and a signal caused by the forward airflow without distinguishing between them.

Next, the detection means detects three adjacent maximum values and two minimum values sandwiched between the three maximum values of the electrical signal output from the signal output means.

When a pulsating flow including a backflow occurs in the intake passage, when the direction of the air flow changes, there is a moment when no air flow occurs in the intake passage, and the electrical signal output from the signal output means becomes a minimum value. Become. Furthermore, since the flow rate of the reverse flow is smaller than the m-view of the airflow in the forward flow direction, the signal caused by the reverse flow exhibits a smaller value than the signal caused by the pulsating flow.

Due to this property, when the ratio of the central maximum value to the maximum value at both ends among the three maximum values is higher than a predetermined value, or when the ratio of the maximum value at the WJ end among the three maximum values When the difference obtained by subtracting the central maximum value from the minimum value is both larger than a predetermined value, it is determined that the electrical signal between the two minimum values is a signal caused by backflow.

(Example) An example of the present invention will be described based on FIGS. 1 to 8. FIG. 1 shows the configuration of the present invention. In the figure, 4 is an air cleaner, 5 is an air flow sensor for engine control, 6 is a duct, 7 is a throttle valve, and 8 is an intake pipe, which constitute the intake system of the engine body 9. Reference numeral 10 denotes a measuring air flow sensor for measuring the flow rate of air passing through the intake passage and examining the characteristics of the intake system, and is connected to the detection circuit 20. The detection circuit 20 calculates the flow rate Q of air passing through the intake passage during a predetermined period.

The air flow tQ determined by the detection circuit 20 is displayed on the display section 2.
At the same time, it is displayed on the recorder 30 as an electrical signal.
The recorder 30 outputs the measurement results as a hard copy. The sinus results are used, for example, to calibrate the control layer airflow sensor 5.

Note that the air flow sensor 10 is not limited to being installed upstream of the air cleaner 4, and is not particularly limited as long as it is installed upstream of the throttle valve 7.

FIG. 2 shows the configuration of the air flow sensor 10. Reference numeral 11 denotes a heat generating resistor made of platinum wire, and its resistance value changes depending on the flow velocity of air. Both ends of the heating resistor 11 are connected to a connector section 14, and the connector section 14 is connected to the detection circuit 2.
0 input terminal (described later). , 12 is a rectifying adapter.

13a, 13b, and 13c are wire meshes for rectification.

Figure jN3 is a block diagram showing the configuration of the detection device 20. 21 is an input terminal of the detection device 2o, and is connected to the connector section 14 of the air flow sensor 10. A detection circuit 22 detects the resistance value of the heat generating resistor 11 installed in the air flow sensor 10, and outputs a voltage signal V corresponding to the flow velocity near the heat generating resistor 11 based on this resistance value.

23 is proofreading I! This is a setting device, and a calibration function for determining the instantaneous air flow rate q from the voltage signal V is input. The calibration function uses numerical values converted into table data in FIG. 4(b) based on the calibration curve shown in FIG. 4(a).

In FIG. 3, 24 is an input interface such as an A/D converter, and includes a detection circuit 22 and a calibration device (11 setting device 2).
Converts the analog voltage signal input from 3 into a digital signal.

Reference numeral 25 denotes a CPU, which discriminates between forward flow, pulsating flow including reverse flow, and pulsating flow not including reverse flow in the intake passage, and calculates intake flow tQ for a certain period of time.

Reference numeral 26 denotes a memory, into which data is written and read by the CPU 25.

27 is an output interface such as a D/A converter, which converts the digital voltage signal input from the CPU 25 into an analog signal.

28 is a display section that displays the air flow jlQ calculated by the CPU 25 for a certain period of time.

29 is an output terminal of the detection device 2o, and the recorder 30
is connected.

Next, the operation of the above device will be explained.

When the engine is running, there is a flow of air within the intake passage. Due to this air flow, the resistance value of the linear heating resistor 11 within the air flow sensor 10 changes. Then, the detection circuit 22 in the detection device 20 detects the resistance value of the linear heating resistor 11, and detects a voltage signal (2) corresponding to the air flow rate.

The voltage signal V is passed through the input interface 24 to the CP
It is input to U25. CPU25 is 1 [m5ec]
The voltage signal V is read every time. Then, the calibration value setter 2
After the calibration function inputted in step 3 is once written into the memory 26, a table lookup of the calibration function is performed, and the air flow rate q corresponding to the voltage signal V is read. In addition, if a voltage signal with a value that is not converted into table data is input,
Perform interpolation calculation to find air flow rate q. The air flow rate q converted from the voltage signal V is determined as one of a forward flow, a pulsating flow not including a backflow, and a pulsating flow including a backflow, according to a flowchart described below. Then, the sign of the backward flowing data is inverted, and the sign of the non-backward flowing data is left unchanged and written to the memory 26.

As shown in FIG. 5, the memory 26 has addresses from O to 99 for storing the air flow rate q, 1 [m5
ec] address O, address 1゜address 2.・
...and data is written sequentially.

After data is written to address 99, address O
New data is written to and old data is erased. In this way, the memory 26 always contains the latest 100
Data of [m5ec] will be written. C.P.
U25 is 100 [average of data from m5ec;
Output as air flow rate Q every l [m5ec].

The air flow iiQ for a certain period of time is averaged by the CPU 25.
The value of is displayed on the display unit 28 and is also displayed on the recorder 3
Recorded by 0.

Here, FIG. 6 shows the air flow rate q obtained by converting the voltage signal V output from the detection circuit 22 using a calibration function. Curves 41, 42° 43 in Fig. 6 are for forward flow,
This is the air flow rate q for pulsating flow not including backflow and pulsating flow including backflow. Further, in the curve 43, 5438 is a signal caused by the airflow in the forward direction, and 43b is a signal caused by the backward flow. As is clear from this figure, the maximum value of the signal 43b caused by the backward flow is smaller than the maximum value of the signal 43a caused by the forward air flow.

The reason why the backward flow is also detected as a forward flow, as shown by the curve 43, is that the linear heating resistor 11 cannot determine the direction of the air flow. Therefore, in order to accurately determine the total air flow rate, it is necessary to determine and correct the backflow.

According to the flowchart shown in FIG.
distinguishes forward flow, pulsating flow that does not include reverse flow, and pulsating flow that includes reverse flow.

In Fig. j17, step 100 indicates the start of the flowchart, and starts when the power of the aspect ratio device 2o is turned on and the CPU 25 is started up. In step 101, immediately after the flowchart starts, the first two maximum values q of the airflow ff1q are calculated. I+q engineering. 2 (see Figure 8A) Due to the nature of the signal caused by the pulsating flow including the reflux described above, it is considered that the maximum value that is larger than the other of these two maximum values is not due to reflux. So next step]
02, two local maximum values qTOII qTOI? Compare. The maximum value qTOI is the maximum value qTOI. When it is 2 or more (Yes in step 102), the maximum M q r. It is considered that the flow around 1 is not a reverse flow, and the process proceeds to step 103. Then, in step 103, the maximum value q is calculated. , and change the name to maximum 4mqr+. On the contrary, the maximum value q. 1
When is smaller than the maximum value qTO2 (No in step 102), it is considered that there is no reverse flow near the maximum (If q r. 2), and the process proceeds to step 104.
Now, change the name of local maximum value qTO2 to local maximum value QT+
shall be.

Through the above steps, the maximum M qTl is always set to the airflow in the forward direction.

Next, from step 111 onwards, two local maximum values that appear following the extremely thick M q T+ and the local maximum value qr+ are detected,
Detects whether the signal is due to backflow. First, in step 111, the maximum value q determined in steps 103, 104, and steps 117, 127, 137, which will be described later, is determined.
, and the time t□ corresponding to the local maximum value qT1. In step 112, the time te for the minimum value q81. and minimum value qBt appearing next to the maximum (+1 cir1) is calculated.
1 (see Figure 8C). In step 113,
The ratio ΔqTB of the minimum value qat to the maximum Mllq, is calculated.

In step 114, it is compared whether the ratio Δqts is greater than or equal to a predetermined value. When the ratio ΔqTB is greater than or equal to a predetermined value (step 11
4 Yes), that is, the minimum value 46 compared to the maximum value qTS
(If 181 is slightly smaller, the difference between the maximum value q and the minimum value qet is caused by variations in measurement and is not considered to be a pulsating flow (see Figure 8 C). Therefore, , the process proceeds to step 115, and the maximum 'a (I T□, and the maximum value cir
Read the time tT2 corresponding to 2.

Then, in step 116, from 1 hour tT1 to time tT,
The data of the air flow rate q up to that point is written in the memory 26, and in step 117, the maximum (1!!qT2 is renamed to maximum [q, 1), and then the process returns to step 112.

On the other hand, as a result of the comparison in step 114, the ratio ΔqT8
is smaller than a predetermined value (-) in step 114, that is, compared to the maximum value qr, the Il value qst
When is quite small, it is considered that a pulsating flow is flowing in the intake passage, and the process proceeds to step 122. Then, in step 122, the local maximum value q□2 that appears next to the local minimum value qBt and the time tT2 corresponding to the local maximum value qT2 are read (see the eighth diagram), and in step 123, the local maximum value q
Calculate the ratio Δ(ITS.) of the maximum value qfactor2 to rt.

In step 124, it is compared whether the ratio ΔqT12 is greater than or equal to a predetermined value. When the ratio ΔqTI2 is greater than or equal to a predetermined value (Yes at step 124), that is, when the local maximum value qT2 is slightly smaller than the local maximum value qr1, or when the local maximum value qT2 is larger than the local maximum value qT1, the pulsating flow including the backflow is Since it is considered that the flow is not flowing, the process proceeds to step 126. Then, in step 126, time L is changed from time trt.

The data of the air flow rate q up to this point is written in the memory 26. Then, in step 127, the local maximum value qT2 is renamed to local maximum value qvt, and then the process returns to step 112.

On the other hand, as a result of the comparison in step 124, the ratio △q
2 is smaller than the predetermined value (No in step 124)
, that is, when the local maximum value qTI is considerably smaller than the local maximum value qTI, it is considered that there is a possibility that a pulsating flow including a backflow is flowing in the intake passage around time tT2, and the process proceeds to step 131. Then, in step 131, the local minimum (11 (182) and the time tB2 corresponding to the local minimum value q82 appearing next to the maximum value q, 2 are read, and the time tB2 corresponding to the local minimum value q82 is read.
32, the smallest 4119El. The maximum M (T7
3 and the time tT3 corresponding to the local maximum value qr3. In step 133, the local maximum value '
IT? Calculate the ratio Δq□32.

In step 134, it is compared whether the ratio ΔqT32 is smaller than a predetermined value. When the ratio Δq 32 is smaller than the predetermined value (Yes at step 134; see FIG. 8C), that is, when the maximum W q T2 is considerably smaller than the maximum value 'TT3, a backflow occurs in the intake passage near time t TP. It is thought that a pulsating flow containing
Proceed to step 35. Then, in step 135, the time tet
The sign of the data of the air flow rate q from tB2 to time tB2 is inverted (see FIG. 8C).

At step 136, data on airflow jlq from time tTI to time tT2 is written to memory 26.

On the other hand, as a result of the comparison in step 134, the ratio Δ(I
When Ta2 is greater than or equal to the predetermined value (ho in step 134;
(see Figure 8C), that is, the local maximum value (local maximum value q, 2) is slightly smaller than the local maximum value qT3, or when the local maximum value (IT2 is larger than the local maximum value qT3, the local maximum value Mq,2 is larger than the local maximum value qTS). The reason for this decrease is due to a pulsating flow in which the air flow rate decreased rapidly.

It is thought that this is due to a pulsating flow including a backflow, so the process proceeds to step 136.
In the next step 137, data on the air flow rate q from time tT1 to time tT2 is written into the memory 26.
Maximum +11 (Change the name of I T3 to the maximum value qT1
After that, the process returns to step 112.

The data of the air flow rate q written in the memory 26 as described above is averaged by the CPU 25 and displayed on the display unit 28 or the recorder 30 as the air flow rate Q for a certain period of time.
is output to.

As described above, according to this embodiment, after the detection circuit 22 detects the resistance value of the linear heating resistor 11, the voltage signal V corresponding to the air flow rate is output, and the CPU 25 converts the voltage signal V into the air flow rate q. Converted.

Then, the maximum air flow rate q + 11q k, and the minimum value q8I
It is determined whether the flow is normal or pulsating from the ratio of the maximum value (
ITl and maximum * (Ratio of IT2 and maximum value qT3
It is determined from the ratio between the maximum value (I72) whether it is a pulsating flow that includes backflow or a pulsating flow that does not include backflow, and if it is determined that the flow is pulsating flow that includes backflow, the backflow is corrected and the The air flow rate Q is calculated. Therefore,
Backflow can be detected without using multiple heat generating resistors as in the past.

Compared to using a plurality of heat-generating resistors, it is possible to improve accuracy and reduce costs. Also,
In this embodiment, when it is determined in step 114 or step 124 that no backflow is included before detecting the local maximum value q-factor 3, the process returns to step 112 early, so that the calculation speed can be increased. .

Note that in this embodiment, steps 114, 124° 134
The maximum value q, the ratio of the minimum value (IBI), the maximum value (Ir
The ratio between + and the maximum 'Iiq, and the maximum (11! (I7
3 and maximum value 9 guns. What ratio is determined, and when the ratio is less than a predetermined value, a pulsating flow including a forward flow, a pulsating flow including a reverse flow, and a pulsating flow not including a forward flow is determined, but the present invention is not limited to this. That is, the respective differences may be calculated, and if the difference is greater than a predetermined value, it may be determined that the flow is a forward flow, a pulsating flow that does not include a reverse flow, or a pulsating flow that includes a reverse flow.

Further, the device of this embodiment requires one cycle of the engine rotation speed before determining a backflow, but this does not pose a problem since the device is used as a sub-meter.

(Effects of the Invention) According to the present invention, a heating resistor is installed in the intake passage, and the signal output means outputs an electric signal based on the resistance value of the heating resistor. Next, the detection means detects the three adjacent local maximum values and the three
Two local minimum values sandwiched between two local maximum values are detected, and when the ratio of the central maximum value to the local maximum values at both ends of the three local maximum values is smaller than a predetermined value, or from the local maximum values at both ends to the central maximum value, When the difference that eliminates the maximum value is larger than a predetermined value, the electric signal between the two minimum values is determined to be a signal caused by backflow.

Therefore, there is no need to provide a plurality of heat generating resistors, and the sensitivity does not change due to errors in the mounting of the heat generating resistors. Therefore, it is not necessary to match the sensitivities between the heat generating resistors, and it is possible to accurately discriminate signals caused by backflow in the intake passage at low cost. As a result, it is possible to obtain the air flow rate with high accuracy.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of this embodiment, Fig. 2 is a partial sectional view of the air flow sensor of this embodiment, Fig. 13 is a block diagram of the detection device of this embodiment, and Fig. 4 shows the calibration function. Fig. 5 is an explanatory diagram of memory addresses, Fig. 6 is an explanatory diagram of air flow rate, Fig. 7 is a flowchart showing the operation of the CPU, Fig. 8 is a characteristic diagram of air flow rate q in each state, and Fig. 9 is an explanatory diagram of air flow rate q. The figure is a perspective view showing the configuration of a conventional example. 10 Air flow sensor 20 Detection device Patent applicant Nissan Motor Co., Ltd. TO2 N. E qTOI = qTI qroz=≧qT blind qTI, tv, read qs+, ta+ tv's ID Aqrs=-inkstone- qtech1 Q82, tez QT3 r tT3 vk, m ++5 YES A q“°circle qT2. LT
2 i elbow 122 N. [,□+, tv:+]Write 9"'・1"', Eng 2
= QTI Otsuq, 12-OshiT1 124-. 3q, 1. Fire YES (tn, bz) 1m N. y2 T32=-T3 No4q'1']゛13 YES (ta+, tn2) and q=(-q) (tr+, tT3) 址qT2=qTl QT3=qTI Fig. Fig. t■1 jB+ T2 Fig. Fig. Tl tT2 T3

Claims (1)

[Scope of Claims] A heating resistor installed in an intake passage; signal output means for outputting an electrical signal based on the resistance value of the heating resistor; a detection means for detecting two local minimum values sandwiched between two local maximum values; A backflow determining means for determining that an electrical signal between the two minimum values is a signal caused by backflow when both of the differences obtained by subtracting the central maximum value are larger than a predetermined value. Air flow meter.