JPH0374548A - Air flow measuring device - Google Patents

Abstract

PURPOSE:To improve the air flow measuring precision by compensating a computed fuel supply quantity corresponding to the fuel pressure, temperature and jet mode, and computing a suction air flow for each cylinder corresponding to the compensated fuel supply quantity and air-fuel ratio for each cylinder. CONSTITUTION:An operation condition for an engine equipped with an injector for each cylinder is detected by a means (a). An air temperature in a combustion process is determined by a means (b), and an air-fuel ratio for each cylinder is detected by a means (c), while conditions of the pressure and temperature of supply fuel are detected by a means (d). In the meanwhile, a fuel supply quantity is computed by a means (e) based on the result of detection of the operation conditions, and a fuel jet mode is determined by a means (f) based on the result of cylinder determination and the result of computation of the fuel supply quantity. The result of computation of the fuel supply quantity is then compensated by a means (g) corresponding to the result of detection of the fuel conditions and the result of determination of the fuel jet mode. The suction air flow for each cylinder is then computed by a means (h) corresponding to the result of detection of the air-fuel ratio and the result of compensation of the fuel supply quantity for each cylinder.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an air flow rate measuring device, and more specifically, the present invention relates to an air flow rate measuring device that detects an air-fuel ratio signal and a fuel injection pulse for each cylinder, and calculates the air flow rate based on the detected air-fuel ratio signal and fuel injection pulse. Regarding measuring devices.

(Prior art) In recent years, electronic control of engine control has progressed, and the combustion state of the engine is determined by a microcomputer based on operating conditions, and parameters related to the combustion state (e.g., injection amount, ignition timing) are controlled. Electronic control devices are widespread. In addition, the requirements for internal combustion engines such as automobiles are becoming more sophisticated, and there is a tendency for mutually contradictory issues such as reduction of harmful exhaust gas, high output, and low fuel consumption to be achieved at a high level. The requirements can only be realized using microcomputers.

Therefore, when fuel is injected into each cylinder, it is necessary to accurately measure the air flow rate in each cylinder. The background to the necessity of measuring the air flow rate for each cylinder will be explained.

Sensors that directly measure the intake air flow rate of commercially available engines include flap types and hot wire types (for example, ■Automobile Engineering J 198, published by Railway Japan,
(See pages 35 to 38 of the December 2010 issue).

According to this example, intake air for all cylinders is measured by a hot wire air flow meter installed in the intake passage upstream of the throttle valve. This type, also known as a hot wire mass flow meter, uses a hot wire (
A hot wire (heated wire) is placed, the hot wire is cooled by intake air, and the amount of heat removed is electrically detected to measure the intake air flow rate and intake air temperature (that is, mass).

Note that fuel is intermittently injected from injectors installed at each branch of the intake manifold, mixes with intake air, and flows into each cylinder, but the fuel flow rate from these injectors is measured with an air flow meter. This is determined by a control unit consisting of a microcomputer so as to correspond to the air flow rate.

By the way, the pipe diameter, pipe length, shape, or degree of curvature of the intake manifold has a large effect on the efficiency of the engine. Therefore, when designing an intake manifold for a multi-cylinder engine, the most important issue is to evenly distribute the intake air flow (mixture in the case of a carburetor system) to each cylinder according to the load at that time. . Even if the same amount of fuel is injected, if different air flow rates are sucked between cylinders, misfires will occur in the cylinders that suck a lean mixture due to the large air flow rate. Additionally, if the air flow rate differs between the cylinders, even if the fuel amount is adjusted so that the mixture has the same richness, there will be a difference in the torque generated between the cylinders, resulting in unstable rotation in the low rotation range. This can also cause engine vibration.

The causes of differences in air flow to each cylinder are:
Resistance to air flow varies depending on the length of the intake manifold, bends, or branching conditions, and cylinders that are farther from the manifold collection point tend to have a lower intake amount. (The amount of intake tends to decrease), ■Due to the order of intake into the cylinders or the arrangement of the intake pipes, the pulsation of air flow in the pipes or changes in the direction of flow may cause differences in the intake inertia when each cylinder takes in, and this intake air It is said that inertial phenomena cause differences in the suction amount of each cylinder.

Therefore, in order to ensure equal air distribution to each cylinder, it is necessary to accurately measure the air flow rate flowing through each cylinder through experiments, and only by using the measurement results can it be ensured that the same air flow rate is inhaled. The dimensions, shape, etc. of the intake manifold can be determined.

However, since the air flow meter in the conventional device is installed upstream of the throttle valve, it only measures all cylinders at once, and therefore cannot accurately measure the air flow rate for each cylinder. , the optimum dimensions, shape, etc. of the intake manifold cannot be determined using the measured values.

In addition, laminar flow flow needles that use thin honeycomb-shaped laminar flow elements are widely used to measure air flow, but if each cylinder is equipped with a laminar flow needle, the entire measuring device must become larger. .

Therefore, the applicant of the present invention has previously proposed a device that solves the above-mentioned problems (see Japanese Patent Application No. 190191/1983).
. This device will be explained based on FIGS. 10 to 13. 10th
The figure shows the configuration of the device of the prior application, and is a system diagram assembled for bench testing. In the figure, injectors 21A to 21D having substantially the same flow rate characteristics are attached to the intake port of each cylinder, and these injectors are driven by drive pulses from the fuel control unit 22. The fuel control unit 22 is capable of controlling the valve opening timing and valve opening pulse width (T) of the injector according to the load state.

In addition, air-fuel ratio sensors 23A to 23 are installed on the exhaust boat of each cylinder.
D is attached, and the output from these air-fuel ratio sensors (V
) is input to the air-fuel ratio calculation device 26.

FIG. 11 shows the output characteristics of the air-fuel ratio sensor. If the same characteristics are made into a table and stored in the RAM in advance, the air-fuel ratio (m) at that time can be determined by table lookup. It is assumed that highly accurate air-fuel ratio sensors 23A to 23D are selected.

Now, considering measuring the air flow rate (mass flow rate) for each cylinder in a steady state, for example, the air flow rate of the No. 1 cylinder is QAl, and the same (actual fuel flow rate supplied from the injector of the No. 1 cylinder is Qy + , if the air-fuel ratio measured by the air-fuel ratio sensor of the No. 1 cylinder is ml, there is a relationship between them: m 1 = Qa + / QFI ・== (t), so Q□"" m I X Theoretically, the air flow rate (QA, ) in the No. 1 cylinder can be easily determined from Qy+.The flow rate characteristic of the injector is proportional to the valve opening pulse width (T), as shown by the solid line in Figure 12. The actual fuel flow rate shall be increased.

However, since there are variations in injectors during manufacture, the flow rate characteristics shown by the solid line in Figure 12 (regular characteristics)
For example, as shown by the dashed line, the fuel? ! t
It also occurs that it has the missing characteristics. According to the injector with dashed line characteristics, even if driven with the same pulse width,
Since the difference between the two straight lines occurs as an error, the larger the valve opening pulse width, the larger the error that appears in the actual fuel flow rate.

In other words, as the valve-opening pulse width increases, the measurement error occurring in QAI also increases, and the order of the error differs between small and large valve-opening pulse widths.

Now, in FIG. 12, assume a certain small constant pulse width (ΔT) and consider the fuel flow rate difference with respect to this ΔT. For example, on a solid line characteristic, different values of T, and T
z (T z > T r ) to ΔT (
>O) fuel flow rate difference ΔQ□ with respect to ΔT
and ΔQF2, according to the dashed line characteristics, ΔQ, , respectively.
' and ΔQvz', and in both cases, the error (ΔQ, -ΔQyi') and (ΔQF
z-ΔQ,,') occurs.

However, as long as ΔT is constant, ΔQ□=ΔQF
2%ΔQ,'=ΔQy2', so ΔQ, -ΔQ
Fl'=ΔQF! −ΔQF! ', that is, the error when considering the difference in fuel flow rate is related to the magnitude of the pulse width at that time (it is of a constant order. Therefore, in this case,
Even in a high load range where the fuel flow rate increases, the order of error does not increase accordingly.

Therefore, in this example, the fuel flow rate difference (ΔQ8, ΔQ, , (=ΔQ,)) is used instead of the fuel flow 1t(Q, ,) itself.
Calculate the air flow rate based on. In a steady state where equation (1) holds true, the air-fuel ratio for the No. 1 cylinder obtained when increasing the fuel flow rate (ΔQ, ) by a constant amount is m'''
1, m” 1 =QA+/(Qy++ΔQF)...
...(2), so from both equations (1) and (2), Q□
If we eliminate and organize QAI, we get QAI = (m I
"1))×ΔQ, (3) is obtained. Note that ΔQr may be decreased.

As mentioned above, the error that occurs in ΔQ is constant regardless of the magnitude of the pulse width at that time, so according to equation (3), although it cannot be said that there is no error, it is to the same extent over a wide operating range. QAI can be measured with an error of , that is, stable measurement of intake air flow rate is possible.

In FIG. 10, the air flow rate calculation device 27, which is a microcomputer, gives commands to the fuel control unit 22 and the air-fuel ratio calculation device 26, and also takes in measurement data from the air-fuel ratio calculation device 26, thereby controlling the air flow rate in the cylinders. Calculate another air flow rate.

FIG. t3 is a program for explaining the control operation of the air-fuel ratio calculating device 26, and this program is executed after the engine is operated to reach a steady state.

First, in step 31, i(
In the case of a four-cylinder engine, a command is issued to measure the air-fuel ratio of the cylinder (i is an integer from 1 to 4). In the following, the same operation is repeated for each cylinder to obtain the air flow rate of each cylinder, so cylinder No. 1 will be mainly explained.

The air-fuel ratio calculating device 26 selects the No. 1 cylinder according to the command and measures its air-fuel ratio, so in steps 32 and 33, this is read sequentially at predetermined intervals over a predetermined period of time (for example, 2 seconds), and in step 34. The averaged air-fuel ratio data is stored in a memory (RAM) as the air-fuel ratio data for the first cylinder.

Let the air-fuel ratio in this case be ml.

In step 35, a command is issued to the fuel control unit 22 to increase the valve opening pulse width (T) by a - constant width (ΔT). When the valve opening pulse width of the injector for the No. 1 cylinder increases in accordance with this command, additional fuel is supplied by the fuel flow rate (ΔQ,) corresponding to ΔT, so the air-fuel ratio of the No. 1 cylinder fluctuates for a while.

Note that, in order to ensure that a fuel flow rate larger than ΔQ is taken into the cylinder, the injection from the injector is performed in synchronization with the opening of the intake valve of the No. 1 cylinder.

In step 36, wait until the air-fuel ratio becomes stable, read the air-fuel ratio data again for a predetermined period of time (2 seconds), and store the averaged data in the memory separately from the air-fuel ratio data mentioned above (step 36). 37-39).

The air-fuel ratio in this case is assumed to be m''1.

In step 40, the two stored air-fuel ratio data (ml
and m”1) and the aforementioned ΔQ, Qa+= (m
I Xm” 1/ (m 1 m, “1))
×ΔQF (3A) Calculate the air flow rate (Q□) of the No. 1 cylinder.

The obtained results are displayed on, for example, a digital or analog display device (not shown). In addition, the weight flow rate (G
□), it can be calculated using GAl-TxQAI. However, T is specific weight.

This completes the process for cylinder 1, so step 3
Return to step 1 and select the next cylinder in the ignition order. Thereafter, the air flow rates of the remaining cylinders are sequentially determined in the same manner.

Next, to explain the operation of this example, the intake air amount QAi of the No. 1 cylinder is QAi = (m+, Xm", / (m, -m" =
)) × ΔQ, ... (3B) According to the open formula, the measurement accuracy of Qai is determined by the error of ΔQ, and ΔQ
As mentioned above with reference to FIG. 12, the degree of error that occurs in As long as it is limited to one cylinder, the air flow rate can be measured with the same accuracy no matter what load condition the engine is operating under.

However, if the injectors are different between cylinders, the flow characteristics will be different, so the degree of error occurring in ΔQ will also be different. However, in this example, all the injectors have the same flow rate characteristics, so even between cylinders ΔQr
This means that the errors that occur will be at the same level. Note that it is sufficient that the flow characteristics are the same, and T1+ΔT or T2+
It is not necessary to make ΔT the same for all cylinders.

As a result, it is possible to measure the air flow rate of all cylinders with the same accuracy in various operating ranges, and by using these measurement results, it is possible to determine the size and shape of the intake manifold that has excellent air distribution between the cylinders. etc. can be easily selected.

In addition, since it is sufficient to attach only the injector to the intake pipe, the entire device is compact, unlike the case where a laminar air flow meter is installed in each cylinder. It becomes possible.

(Problem B to be solved by the invention) By the way, although the device of the prior application described above can measure the air flow rate of all cylinders in various operating ranges, in reality, the pressure and temperature of the fuel ( Since the fuel pressure and fuel temperature (hereinafter referred to as "fuel pressure" and "fuel temperature" as appropriate) change, it has been found that there is room for improvement regarding the decrease in accuracy due to these influences.

Furthermore, some engine models use both group injection and sequential injection, and it is necessary to effectively handle this to ensure accuracy. For example, sequential mode is used in low rotation and low load areas. Therefore, measurement accuracy will deteriorate unless it also supports sequential mode.

(Object of the Invention) Therefore, the present invention provides an air flow rate measuring device which improves the device of the prior application and can accurately measure the air flow rate for each cylinder in all areas of the engine regardless of fuel pressure, fuel temperature, or injection mode. The purpose is to

(Means for Solving the Problems) In order to achieve the above object, the air flow rate measuring device according to the present invention has the following features:
As the basic conceptual diagram is shown in Fig. 1, there is an operating state detection means a for detecting the operating state of the engine, in which injectors with almost uniform flow characteristics are arranged in each cylinder, and a cylinder for determining which cylinder is in the combustion stroke. The cylinder signal generating means for outputting a discrimination signal includes an air-fuel ratio detecting means C for detecting the air-fuel ratio of each cylinder, a fuel condition detecting means d for detecting the pressure and temperature of the supplied fuel, and a cylinder signal generating means for outputting a discrimination signal based on the operating state of the engine. a supply amount calculation means e that calculates the fuel supply amount and outputs an injection pulse signal to the injector; a mode determination means f that determines the injection mode based on the cylinder determination signal and the injection pulse signal;
Fuel correction means g that corrects the injection pulse signal corresponding to the fuel supply amount calculated by the supply amount calculation means e according to the fuel pressure, temperature, and injection mode; and the detected air-fuel ratio of each cylinder and the fuel correction means g. and a flow rate operator stage that calculates the intake air flow rate for each cylinder based on the injection pulse signal corrected by.

(Function) In the present invention, the injection pulse signal corresponding to the fuel supply amount calculated by the supply amount calculation means is corrected according to the fuel pressure, temperature, and injection mode, and then the corrected fuel flow rate and each cylinder The intake air fLit is calculated for each cylinder based on the detected air-fuel ratio.

Therefore, the air flow rate can be accurately measured for each cylinder in all areas of the engine, regardless of fuel pressure, fuel temperature, or injection mode.

(Example) Hereinafter, the present invention will be explained based on the drawings.

2 to 5 are diagrams showing a first embodiment of the air flow rate measuring device according to the present invention. In Fig. 2, l is an in-line four-cylinder engine, intake air is supplied to each cylinder through an intake pipe 2, and fuel is injected by injectors 3A to 3D arranged for each cylinder based on an injection pulse signal. . The air-fuel mixture in the cylinder explodes and burns due to the discharge action of the spark plug, and is transferred from the exhaust adapter 4 of each cylinder to the exhaust manifold 5,
The exhaust front tube 6 is sequentially valved and discharged.

Intake air data for calculating the basic injection amount Tp of the engine 1 is detected by an air flow meter 7, and the flow rate of the intake air is controlled by a throttle valve 8 in the intake pipe 2.

The intake negative pressure (boost) in the intake pipe 2 is detected by the intake pressure sensor 9, and the crank angle of the engine 1 is detected by the crank angle sensor (cylinder signal generating means) 10 built into the distributor. For example, in addition to the crank angle unit signal, a cylinder discrimination signal is output simultaneously. Further, the oxygen concentration in the exhaust gas is detected by an oxygen sensor 11, and the oxygen sensor 11 is for feedback controlling the air-fuel ratio.

On the other hand, the air-fuel ratio of the exhaust adapter 4 discharged from each cylinder for calculating the air flow rate is determined by an air-fuel ratio sensor (air-fuel ratio detection means).
12A to 12D. Furthermore, fuel pipe 1
The temperature of the fuel flowing through the fuel tank 3 is detected by a temperature sensor 14, and the pressure of the fuel is detected by a pressure sensor 15. The temperature sensor 14 and the pressure sensor 15 are part of the fuel condition detection means 1
6.

The air flow meter 7, the intake pressure sensor 9, the crank angle sensor 10, and the oxygen sensor 11 as a whole set the operating state detecting means 17 to nil, and the operating state detecting means 1
The output of 7 is input to an engine control circuit 18. In this embodiment, the crank angle sensor 10 constitutes a part of the operating state detecting means 17 as described above, and also functions as a cylinder signal generating means.

The engine control circuit 18 has a function as a fuel supply amount calculation means, and is mainly controlled by a microcomputer, and calculates the fuel supply amount according to a program stored in an internal memory based on a signal from the operating state detection means 17. Calculate,
The injection pulse signal is output to the injectors 38 to 3D as well as to the intake air flow rate calculation circuit 19. The intake air flow rate calculation circuit 19 has the functions of a mode discrimination means, a fuel correction means, and a flow rate calculation means, and is also mainly controlled by a microcomputer and is connected to the engine control circuit 1.
Based on the cylinder discrimination signal from 8, the injection pulse signal, the fuel condition detection means 16, and the signals from the air-fuel ratio sensors 12A to 12D, the processing values necessary for calculating the intake air flow rate are calculated according to the program stored in the internal memory. Then, the final intake air flow rate is determined for each cylinder.

Next, the effect will be explained.

FIG. 3 is a flowchart showing a program for calculating the air flow rate executed in the engine control circuit 18 and the intake air flow rate calculation circuit 19, and this program is executed once every predetermined time. First, in step 51, necessary data, that is, signals from the operating state detecting means 17, the fuel state detecting means 16, and the air-fuel ratio sensors 2A to 12D, are read, and in step 52, the engine rotation speed N is calculated according to the following equation.

In the above equation, F is the frequency of the clock pulse of the microcomputer (1:Hz), and M is the cycle time of the cylinder discrimination signal (pulse signal output every 180 degrees, shown in Figure 4 (a)) in clock pulses. This is the count number when counting. Next, in step 53, the width of the fuel injection pulse Ti is counted. This is to obtain a calculated value of the fuel injection amount in order to obtain the fuel flow rate.

Simply, this is a process of determining the width Ti of the injection pulse signal Ti output from the engine control circuit 18 in the intake air flow rate calculation circuit 19. Note that the calculation of the fuel pulse Ti in the engine control circuit 18 is the same as that of the device of the prior application and is well known, so a description thereof will be omitted.

Next, in step 54, the cylinder discrimination signal (in this embodiment, the cylinder discrimination signal 180 shown in FIG. 4(a)
'signal) and determine the injection mode.

For example, as shown in FIG. 4(b), if the count number is the same as the number of cylinders in the count section (count number = 4)
It is determined that the mode is sequential injection mode, and if it is not (count number = 2) as shown in Fig. 4 (C), it is determined that it is group injection mode, and the fuel flow calculation 2 is changed according to each injection mode. . In the sequential mode, since injection is performed once per cycle, the fuel flow iW is determined in step 55.
F is calculated according to the following formula.

However, To: Inactive time of the injector N: In this rotation speed equation, G is the injection flow it for the pulse width Ti.
It represents the slope of W F, and as shown in Figure 5, G=
It is expressed as Note that FIG. 5 shows the injector characteristics when the predetermined reference rotational speed is N00, the fuel pressure difference is ΔP0, and the fuel temperature is to. On the other hand, in group mode, injection is performed twice in one cycle, so step 5
In step 6, the fuel flow iWF is calculated according to the following equation.

The reason why each mode is discriminated and the amount of fuel i is corrected is because there are engines that use both modes, and when the mode is different, the amount of injection pulse is different and consumed in one combustion. This is because the fuel flow rates used are different. Note that the differential pressure ΔP0 is the differential pressure between the fuel pressure and the intake pipe negative pressure, and is normally set to, for example, 2.55 kg/cnY by the regulator. Then,
In step 57, the fuel flow rate WF is corrected based on the fuel temperature and fuel pressure.

First, the fuel flow rate W obtained in the above step is corrected based on the current fuel temperature t according to the following equation.

WF' −Wr (1+Ct (t to )
) However, Ct: Coefficient to: Reference fuel temperature In the above equation, the reference fuel temperature to is set, and the optimum coefficient Ct is determined through experiments or the like. Similarly, the current fuel pressure (
In this embodiment, the fuel flow rate WF is calculated based on the differential pressure ΔP.
is corrected according to the following formula.

Wy' ”WF (1+CP (ΔP−ΔP0)
) However, Cp: Coefficient ΔPo: Reference differential pressure ΔP: Current differential pressure Note that Cp and ΔP0 are determined in the same manner as above. Next, in step 58, the intake air flow rate is calculated in the same manner as in the prior application based on the fuel flow rate WF' corrected by the injection mode, fuel temperature, and fuel pressure. However, in the example of the prior application, the actual fuel flow rate supplied from the injector of the No. 1 cylinder is set as QFl, but this Q is set as W, ′ in this embodiment.
The calculation will be performed in place of .

The effects of the above processing will be compared with x and the IJI example. First, cylinder discrimination is performed by reading the 180'' signal (Ref signal) from the crank angle sensor 10, and based on this, the injection pulse Ti is counted. Therefore, for the Ref signal of the #1 cylinder, the #1 The injection pulse width of the cylinder's injector 3A is read.

In the sequential injection mode, each cylinder injects, so there is a correspondence with the Ref signal, but in the group injection mode, there is no correspondence with the Ref signal. To put it a little more clearly, in sequential mode, 1 in 720°
In group injection, the injection is performed twice at 720'' (once in 360°), and when reading corresponding to the Ref signal, in the case of group injection, one of the two injections is read. In order to eliminate this error, in this example, in the case of group injection, the calculation formula is changed to assume that twice the read value is the amount of fuel?Jt consumed in one combustion. Therefore, in this embodiment, since the fuel flow rate is appropriately corrected in accordance with the injection mode, the accuracy of intake air flow rate calculation can be improved.

Next, correction of the fuel pressure difference ΔP and the fuel temperature t will be considered.

First of all, the differential pressure (Δp,) when measuring the basic characteristics of the injector is 2.55 kg, /c4 is the setting value of the regulator attached to the engine, but in reality it is the setting value of the regulator attached to the engine. It is not always maintained at 2.55 kg/cd, but often fluctuates. For example, when the injection port area of the injector is constant, it is natural that the injection flow rate increases as the differential pressure ΔP increases, and the amount of increase is proportional to the amount of increase in the differential pressure ΔP with respect to the reference differential pressure ΔP0.

Expressed as a formula, the increase amount cc(ΔP−ΔP,) is obtained. Therefore, by correcting the fuel flow rate based on the differential pressure due to the causal relationship that the differential pressure increases (indeed, the injection flow rate increases), the accuracy of the intake air flow rate calculation can be improved.

Regarding the fuel temperature t, like the differential pressure, the fuel temperature to when measuring the basic characteristics of the injector is set as a reference value, and varies in an actual engine. The fuel temperature affects the viscosity and specific gravity of the fuel, and as the fuel temperature increases, the viscosity decreases, making it easier to flow, and the flow rate increases. Conversely, the specific gravity becomes lighter as the fuel temperature increases, and the volumetric flow rate remains the same, but the mass flow rate decreases.Although these are contradictory phenomena, the effect of viscosity is ultimately greater, and as the fuel temperature increases, The fuel flow rate (mass flow rate) increases. Therefore, by correcting the fuel flow rate according to the fuel temperature as in this embodiment, it is possible to improve the accuracy of calculating the intake air ii amount. The relationship with the fuel flow rate depends on the viscosity and specific gravity characteristics of the fuel, and if the same fuel is used, it will not be affected even if the injector is different.

Next, FIGS. 6 to 9 are diagrams showing a second embodiment of the air flow rate measuring device according to the present invention. Since the hardware configuration of this embodiment is the same as that of the first embodiment, it will be omitted and the software portion will be described.

In the method of detecting the injection pulse signal and determining the fuel flow rate, the injector's ineffective time is given as a predetermined constant value, but in reality, variations occur, especially in the low load and low rotation region near the idling state. The pulse width is short,
The ratio of invalid time increases, and if the invalid time is not detected accurately, the error will increase.In this case, the invalid time is determined by the injector's needle lift amount, and the lift amount is determined by the solenoid's lift amount. Determined by current value.

Therefore, in this embodiment, in order to accurately detect the invalid time, the drive current of the injector is detected, and the injection time over a predetermined current value is measured to determine the actual injection time after subtracting the invalid time. There is. This makes it possible to determine the fuel flow rate with high precision even in low rotation and low load regions with short pulse widths, thereby improving the accuracy of air flow rate measurement.

FIG. 6 is a flowchart of the second embodiment. After passing through step 53 in FIG.
It is determined whether or not the engine is in a low rotation region.

This determination is to determine the area as shown in Figure 7.
For example, the engine load is determined based on the output of the throttle opening sensor and the intake pressure sensor 9, and the engine speed is determined based on the output of the crank angle sensor 10. this is,
This is because in the case of a low load and low rotation region, the width of the injection pulse Ti0 is small and the error in the actual injection amount due to the invalid time To becomes large, so the region is determined for correction in the subsequent steps. Note that the determination in step 60 may be made without depending on the sensor output, for example, by measuring the injection pulse width and proceeding to step 61 when the width is less than or equal to a predetermined pulse width. If the load is low and the rotation is low, the process proceeds to step 61; otherwise, the process proceeds to step 54. In step 61, a slice level is set for determining the actual injection time Tr for the injector drive current having a waveform as shown in FIG. 8, and in step 62, the time period during which the drive current of the injection pulse Ti exceeds the slice level is determined. Injection time Tr and fuel flow i
t w y is calculated according to the following formula, and then step 54
Proceed to.

However, Tr=Ti-T.

Here, in order to specifically describe the effect of considering the invalid time when detecting the fuel flow rate, first, the basic characteristics of the injector will be explained.

In the characteristic measurement experiment, the differential pressure ΔPo, fuel temperature to, injection frequency f
The measurement is carried out under the condition that is set constant to a predetermined value. Specifically, the fuel injection weight per unit time (gr/5ec) is determined while changing the pulse width at a differential pressure of 2.55 kg/aa, a fuel temperature of 20°C, and an injection frequency of 507. At this stage, the characteristics shown in FIG. 9(a) are obtained.

This is converted into an injection flow rate per injection and stored in the intake air flow rate calculation circuit 19. This is Figure 9(b)
It is a characteristic of In the case of Fig. 9(a), it is driven by 50 circles, so it is fully open at 20Ills (continuous ON state)
becomes. The meaning of 50Hz corresponds to the number of fuel injections at 6000 rpm. In addition, Fig. 9(b) shows the injection flow rate for one injection as a value obtained by multiplying 507 by 1150[,
At 3000 rpm, the characteristics are 1/2. As is clear from the basic characteristic diagrams shown in FIGS. 9(a) and 9(b), the injector has an invalid time To, and this influence cannot be ignored. In addition, the value varies depending on the individual injector, so in order to eliminate this influence, for example, measure the characteristics of all the injectors to be used in advance, and calculate them for each cylinder using the characteristic formula corresponding to each injector. Although this is possible, it increases the number of steps required for measurement, which is not preferable.

Therefore, the inventor investigated individual differences in injector ineffective time, and found that this is due to individual differences in the lift speed at which the needle is lifted by the solenoid, and furthermore, individual differences in the way the solenoid drive current rises. This was revealed through experiments. Furthermore, to conclude, what determines the ineffective time is not the individual difference between the needles, but the individual differences between the solenoids, and the fact that unless the drive current reaches a certain value, the needle will not operate and will not inject fuel. I figured it out.

Therefore, in this example, based on the above phenomenon results, a certain current level (slice level) is set for the injector drive current.
By detecting the above drive time, the actual injection time Tr
I'm looking for. Note that, as mentioned above, the basic characteristics of the injector are measured under certain conditions, and strictly speaking, there is no guarantee that the invalid time will be constant regardless of the engine condition.

In particular, in low load and low rotation regions where the injection pulse width is short, the influence of the ineffective time becomes large.

Therefore, in this embodiment, in addition to the effects of the previous embodiment, by determining the actual injection time Tr excluding the influence of the invalid time, the present embodiment achieves high accuracy even in low rotation and low load regions where the injection pulse width is short. The fuel flow rate is calculated, and the measurement accuracy of the intake air flow rate can be improved more than in the above embodiment.

Note that the drive current detection method of this embodiment may be extended not only to a part of the range but also to the entire operating range (that is, to include the high rotation range).

(Effects) According to the present invention, it is possible to accurately measure the intake air flow rate for each cylinder in all areas of the engine, regardless of fuel pressure, fuel temperature, and injection mode.

Furthermore, the second embodiment has the effect that the measurement accuracy can be further improved by eliminating the influence of the injector's ineffective time.

[Brief explanation of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, and FIGS. 2 to 5 are diagrams showing a first embodiment of the air flow rate measuring device according to the present invention.
Figure 3 is a flowchart showing the program for calculating the air flow rate, Figure 4 is a timing chart explaining the operation of determining the injection mode, Figure 5 is a characteristic diagram of the injector, and Figures 6- Fig. 9 is a diagram showing a second embodiment of the air flow measuring device according to the present invention, Fig. 6 is a flowchart showing the main part of the program for calculating the air flow rate, and Fig. 7 explains the determination of the operating region. Figure 8
The figure shows the waveform of the drive current of the injector.
Figures (a) and (b) are diagrams showing the basic characteristics of the injector, Figures 10 to 13 are diagrams showing the air flow rate measuring device according to the earlier application, Figure 10 is its overall configuration diagram, and Figure 11 is FIG. 12 is a diagram showing the characteristics of the air-fuel ratio sensor, FIG. 12 is a diagram showing the characteristics of the injector, and FIG. 13 is a flowchart showing the program for calculating the air flow rate. 1... Engine, 2... Intake pipe, 3A to 3D... Injector, 4...
Exhaust adapter, 5...Exhaust manifold, 6...Exhaust front tube, 7...
Air flow meter, 8... Throttle valve, 9... Intake pressure sensor, 10... Crank angle sensor (cylinder signal generation means), 11... Oxygen sensor , 12A to 12D... Air-fuel ratio sensor (air-fuel ratio detection means). 13... Fuel piping, 14... Temperature sensor, 15... Pressure sensor, 16... Fuel condition detection means, 17... Operation Condition detection means, 18...Engine control circuit (supply amount calculation means)
, 19... Intake air flow rate calculation circuit (mode discrimination means, fuel correction means, flow rate calculation means). Figure 3

Claims (1)

[Scope of Claims] a) Operating state detection means for detecting the operating state of an engine in which injectors with substantially uniform flow characteristics are arranged in each cylinder; and b) outputting a cylinder discrimination signal for discriminating a cylinder in a combustion stroke. c) air-fuel ratio detection means for detecting the air-fuel ratio of each cylinder; d) fuel condition detection means for detecting the pressure and temperature of supplied fuel; and e) fuel condition detection means for detecting the pressure and temperature of the supplied fuel. supply amount calculation means for calculating the supply amount and outputting an injection pulse signal to the injector; f) mode discrimination means for determining the injection mode based on the cylinder discrimination signal and the injection pulse signal; and g) supply amount calculation means. a) fuel correction means for correcting the injection pulse signal corresponding to the calculated fuel supply amount according to the fuel pressure, temperature, and injection mode; h) the detected air-fuel ratio of each cylinder and the injection pulse corrected by the fuel correction means; An air flow rate measuring device comprising: flow rate calculation means for calculating an intake air flow rate for each cylinder based on a signal.