JPH0333619A - Self-diagnostic apparatus in measuring apparatus of flow rate of suction air of internal combustion engine - Google Patents

Abstract

PURPOSE:To detect the detecting characteristic per every level of the flow rate of the suction air and to enable self-diagnosis of the abnormality of an apparatus by connecting a plurality of diagnosing resistances selectively to a bridge circuit. CONSTITUTION:A diagnostic resistance separately provided from a resistance to form a bridge circuit in a diagnostic resistance connecting means is selectively connected to the bridge circuit, so that the balance of the resistance in the bridge circuit when the general amount of the suction air is measured is forcibly changed thereby to produce the state where the amount of the suction air appears to be changed. A detecting value sampling means connects a plurality of the diagnosing resistances selectively to the bridge circuit by the diagnostic resistance connecting means when the engine is stopped, that is, when the flow rate is zero. Detecting signals of the flow rate of the suction air per every resistance value are sampled. A plurality of the sampled detecting signals are compared with an expecting value corresponding to the resistance value changed by the diagnostic resistance, whereby the abnormality of the measuring apparatus of the flow rate of the suction air can be detected by an abnormality detecting means.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a self-diagnosis device for an intake flow rate measuring device for an internal combustion engine, and more specifically, it utilizes the fact that the resistance value of a temperature-sensitive resistor changes depending on the fluid flow rate. The present invention relates to a device for self-diagnosing abnormalities in an intake flow rate measuring device that measures the intake air flow rate of an engine.

<Prior Art> As an internal combustion engine intake flow rate measuring device using a temperature-sensitive resistor, there is a conventional device as shown in FIG.

In FIG. 5, a temperature-sensitive resistor RH made of platinum (or an electrical resistor arranged in the form of a thin film on an insulating material) and a resistor RK are arranged in the intake passage of the engine.

RI + R21R3 forms a bridge circuit, and the current supplied from battery B to this bridge circuit via resistor R4 is the difference between the terminal voltage of resistor R2 and the terminal voltage of resistor R3, that is, the unbalanced voltage of the bridge circuit. Based on this, it is controlled via a differential amplifier OP and a transistor TR.

For example, when the intake air flow rate of the engine increases, the temperature-sensitive resistance R
, is further cooled, its resistance value decreases, but at this time, the terminal voltage of resistor R3 increases and the differential amplifier O
The output of P decreases, the base current of transistor TR increases, and the collector current increases, so that the supply current (2) to the bridge circuit increases. In other words, the intake air flow measuring device having the above configuration has a temperature-sensitive resistance R against changes in the intake air flow rate.
.

By changing the supply current so as to keep the terminal voltage constant, a terminal voltage Um of the resistor R3 proportional to this supply current is output as a detection signal of the intake air flow rate.

Then, the terminal voltage Um is manually input to the microcomputer 4 via the A/D converter 3 in the control unit 2, and the microcomputer 4 calculates and measures the intake air flow rate corresponding to the terminal voltage Um. ing.

Further, in this type of intake air flow measuring device, a temperature compensation resistor RK arranged in the intake passage together with a temperature sensitive resistor Ro compensates for fluctuations in the flow rate detection characteristics due to temperature changes in the intake air flow rate.

<Problems to be Solved by the Invention> By the way, in the method described above that measures the intake air flow rate based on the change in the resistance value of the temperature-sensitive resistor, dust may adhere to the temperature-sensitive resistor, the temperature-sensitive resistor may deteriorate, etc. When the change in resistance value becomes slower, as shown in FIG. 6, a characteristic change occurs in which the detection error increases as the intake air flow rate increases.

However, in the past, on/off abnormalities such as disconnections and short circuits could be easily diagnosed, but it was difficult to accurately capture changes in characteristics. In order to determine the true intake air flow rate for comparison with the value, it is necessary to separately install an expensive sensor to detect the operating conditions that affect the intake air flow rate, and to indirectly determine the intake air flow rate from this sensor. , there was a problem that an increase in cost was unavoidable in order to make diagnosis possible.

Furthermore, even if it is possible to detect an error in the detected value at a certain level of intake air flow rate, if a change in characteristics occurs as shown in Figure 6, diagnosis will only be possible in areas where the intake air flow rate is high. If the intake air flow rate level that is possible and diagnosable is low, there is a problem that a change in detection characteristics as shown in FIG. 6 cannot be diagnosed.

The present invention has been made in view of the above problems, and has a simple configuration that can detect the detection characteristics of an intake air flow measuring device for each intake air flow rate level, and can self-diagnose abnormalities in the measuring device based on the detection results. The purpose is to provide diagnostic equipment.

<Means for Solving the Problems> Therefore, in the present invention, as shown in FIG. A diagnostic resistor connecting means is selectively connected to the bridge circuit in order to change the resistance value of the resistor part to be removed to multiple types, and a plurality of diagnostic resistors are connected to the bridge circuit by the diagnostic resistor connecting means while the engine is stopped. a detection value sampling means that is selectively connected to and samples a detection signal of the intake air flow rate for each of the plurality of changed resistance values, and a plurality of detection signals sampled by the detection value sampling means and a diagnosis method. The self-diagnosis device is configured to include an abnormality determining means for determining an abnormality in the intake flow rate measuring device by comparing the resistance values changed by the resistors with the corresponding expected values.

Further, as shown by the dotted line in FIG. 1, it is preferable to provide sampling permission means for permitting the detection value sampling means to sample the detection signal after a predetermined period of time has elapsed since the engine has stopped.

Furthermore, as shown by the dotted line in Figure 1, the intake air flow rate is detected based on the deviation between the plurality of detection signals sampled by the detection value sampling means and each expected value corresponding to the resistance value changed by the diagnostic resistor. An intake air flow rate correction means for correcting the value may be provided.

<Operation> In such a configuration, the diagnostic resistance connecting means connects a plurality of diagnostic resistors provided separately from the resistors forming the bridge circuit to a plurality of resistance values of the resistance portions excluding the temperature-sensitive resistor forming the bridge circuit. It is selectively connected to the bridge circuit in order to change to Creates a state where the upper intake air flow rate changes.

The detected value sampling means selectively connects a plurality of diagnostic resistors to the bridge circuit by the diagnostic resistor connecting means when the engine is stopped, that is, when the flow rate is zero, and The intake air flow rate detection signal is sampled for each type of resistance value.

By changing the resistance value that makes up the bridge circuit in this way, the signal output as the detected intake air flow rate will be:
Since it is predicted according to this resistance value change, by comparing the multiple sampled detection signals and the expected value corresponding to the resistance value changed by the diagnostic resistor,
The abnormality determining means determines an abnormality in the intake flow rate measuring device.

In other words, by changing the resistance value of the bridge circuit to multiple types when the intake air flow rate is zero, multiple pseudo intake air flow rate level detection states are created, and the detection signal at that time is changed depending on the resistance value change. The detection characteristics are detected at a plurality of intake air flow rate levels depending on whether or not the expected value is met.

In addition, the sampling permission means does not permit detection value sampling for diagnosis until a predetermined period of time has elapsed after the engine has stopped, so there is a risk of erroneous diagnosis when the resistance of the temperature-sensitive resistor is not stable immediately after engine operation. Avoided.

Furthermore, the intake air flow rate correction means corrects the deviation between the expected value and the actual detection signal in a plurality of pseudo-created intake air flow rate level detection states by changing the resistance value of the bridge circuit to a plurality of types. Based on this, the detected value of the intake air flow rate is corrected.

<Example> The present invention will be described in detail below. Note that the same elements as in the conventional example shown in FIG. 5 are given the same reference numerals.

In FIG. 2 showing the configuration of an embodiment, a temperature-sensitive resistor R11 made of platinum is disposed in the intake passage of an engine (not shown).
(Or an electrical resistor arranged in a film-like manner on an insulating material)
and resistances RK, R,, R2, R.

A bridge circuit is formed by the above, and the terminal voltage of the resistor R3 and the terminal voltage of the resistor R2 are respectively inputted to the differential amplifier OP.

The output of the differential amplifier OP is applied to the base of the transistor TRI, and when the output of the differential amplifier OP decreases, the collector current of the transistor TRI increases.
The base voltage of the transistor TR2 drops, and as a result, the collector current of the transistor TR2 increases, and the temperature-sensitive resistor Rol and the resistors RK (temperature compensation resistor), R, , R2, R3
The current supplied to the bridge circuit formed by this increases.

Here, when the intake air flow rate increases and the temperature-sensitive resistor R□0 is further cooled and its resistance value decreases, the terminal voltage of the resistor R1 increases and the unbalanced voltage in this bridge circuit becomes In order to reduce the output of the bridge circuit, the current supplied to the bridge circuit is increased as described above, and the resistance balance of the bridge circuit is maintained by increasing the resistance value of the temperature sensitive resistor Ro.

Therefore, a resistor R3 proportional to the supply current to the bridge circuit
The terminal voltage Us is outputted to the control unit 2 side as a detection signal of the intake air flow rate, and is applied to the bridge circuit, differential amplifier OP, transistors TRI and TR.
2. Furthermore, the other resistors R3 to R8 constitute the intake flow rate measuring device 1 for an internal combustion engine.

Note that power is supplied to the intake flow rate measuring device 1 through a relay 5.
It is now distributed by IIJi.

The voltage Us outputted from the intake flow rate measuring device (1) is inputted to the microcomputer 4 as a digital signal via the A/D converter 3 in the control unit 2, and the microcomputer 4 outputs an intake signal corresponding to the voltage LJs. Air flow rate Q is calculated.

Although the above configuration is a general configuration of the intake flow rate measuring device 1, the following configuration according to the present invention is provided.

That is, the diagnostic resistor r1 is connected in parallel to the temperature compensation resistor RK.
~ r3 are provided independently, and these temperature compensation resistors RK2 diagnostic resistors -1 ~ r are connected in parallel.
3. Switches SWK and SWI to SW3 are interposed in series as diagnostic resistance connection means, and during normal intake air flow rate detection, only switch SWK is turned on and a bridge circuit is formed by temperature compensation resistor RK. However, by switching and controlling the switches SWK, SWI to SW3, the diagnostic r1 can be used instead of the temperature compensation resistor RK.
~r3 can be selectively connected to the bridge circuit to change the resistance value of the resistance section to which the temperature compensation resistor RK is connected to a plurality of types.

The switches SWK, SWI to SW3 have digital outputs I controlled by the microcomputer 4.
It is turned ON and OFF by C6, and the relay 5 is also turned ON and OFF by this digital output IC6.

Next, according to the flowcharts of FIGS. 3 and 4, the diagnostic resistors r1 to r3 and the switches SWK, SWI to S
A self-diagnosis of the intake flow rate measuring device 1 using W3 will be explained. In this embodiment, the detection value sampling means,
The functions as an abnormality determination means and a sampling permission means are as follows:
The software is provided as shown in the flowcharts of FIGS. 3 and 4.

The program shown in the flowchart of FIG. 3 is executed as a background job (BGJ), and first, in step 1 (indicated as SI in the figure; the same applies hereinafter), the ignition switch of the internal combustion engine (not shown) is turned on. Determine ON-OFF.

Here, when it is determined that the ignition switch is ON, it is necessary to detect the air flow rate Q in the suction chamber 3 of the engine, so proceed to step 2, and set flags F and F2, respectively, to be used during diagnosis, which will be described later. In addition to setting the initial value 1, in the next step 3, the relay 5 is turned on to connect the power to the intake air flow measuring device 1, and in step 4, only the switch SWK is turned on and the temperature compensation resistor RK is set. so that the bridge circuit is formed in the usual way. In addition, switch SWK
The ON control of the relay 5 is performed via the digital output IC 6 as described above.

On the other hand, if it is determined in step 1 that the ignition switch is OFF and the engine is stopped, the process proceeds to step 5 and flag F is determined.

The flag F is set to 1 in step 2 when the ignition switch is on (during engine operation), so if it is immediately after the ignition switch is turned off, it is determined to be 1 and the process proceeds to step 6. .

In step 6, flag F2 is determined. This flag F2 is also set to 1 when the ignition switch is ON, similar to the flag F.
If it is immediately after OFF, it will be determined that it is ■.

When flagged 2 is 1, the process proceeds to step 7, where the flag F2 is set to zero, so that the process proceeds to step 7 and step 8, which will be described later, only the first time the ignition switch is turned off.

In step 7, when the flag F2 is set to zero, in the next step 8, the timer Tmr is set to a predetermined value (for example, 50
0). The timer Tmr is set to decrease by 1 every 10 m5 until it reaches zero according to the program shown in the flowchart of FIG. The timer Tmr does not reach zero for 10 m5 (for example, 5 seconds).

Therefore, it can be determined by the timer Tmr whether a predetermined time or more has elapsed since the engine operation was stopped, and therefore, in the next step 5-9, it is determined whether or not the timer Tmr is zero. I do.

When the timer T゛mr is not zero, the predetermined time has not passed since the engine operation was stopped, and the temperature sensing resistor R1+
Since the resistance value (7R degrees) may not be stable depending on the heat capacity of

On the other hand, when it is determined in step 9 that the timer Tmr is zero, the engine is in a stable state where a predetermined period of time or more has passed since the engine stopped, so the process proceeds to step 10 and subsequent steps to diagnose the intake flow rate measuring device 1. .

In step 10, an initial value of zero is set to the count value cnt for controlling the switching of the diagnostic resistors r1 to r3;
In the next step 11, as will be described later, the temperature compensation resistor R
The standard intake air flow rate QREF is set to 10 kg/h, which is the expected detection value when a bridge circuit is formed using the diagnostic resistor rl instead of KO.

That is, in place of the temperature compensation resistor Rx, a diagnostic resistor r1 is installed in advance.
The detected intake air flow rate Q obtained when using any of the resistances r1 to r3 is calculated, and the intake air flow rate is determined depending on whether the expected detected value is obtained by actually using the diagnostic resistors r1 to r3. This is to diagnose the measuring device 1 (specifically, to diagnose deterioration of the temperature sensitive resistor RH, etc.), and since the reference intake air flow rate QREF corresponds to the expected value, a bridge circuit was formed with the diagnostic resistor rl. In this case, if a detection result equivalent to 10 kg/h is obtained, it is confirmed that there is no abnormality.

The intake flow rate measuring device 1 controls the resistance value of the temperature-sensitive resistor Ru by controlling the supply current so that the following equation holds true.

3R2 For this reason, if separate resistances r1 to r3 for diagnosis are connected instead of the temperature compensation resistor RKO, the resistance balance according to the above formula will be lost, and the supply current will be controlled to balance again, so the resistance for diagnosis r1 The output value when the diagnostic resistors r1 to r3 are connected in place of the temperature compensation resistor RKO is predicted based on the resistance values of the resistors r1 to r3.

7 In the next step 12, in order to form a bridge circuit with the diagnostic resistor rl instead of the temperature compensation resistor RK, switch S
While WK is turned OFF, step 7W1 is turned ON.

Then, in the next step 13, the actual resistance R3 terminal voltage Us when using the diagnostic resistor rl is sampled, and in the next step 14, the intake air flow rate Q is searched from the map based on this input terminal Us. and ask.

In step 15, it is detected whether a number cent error has occurred by determining the absolute value of 1.0-Q/QREF. If the error detected here is larger than the allowable range (for example, within 4%), it is determined that the detection error is larger than the allowable range at least at a level where the intake air flow rate Q is 10 kg/h. Proceeding to step 16, an abnormality (NG) of the intake flow rate measuring device 1 (AFM) is displayed.

The display in step 16 may be made, for example, by displaying numbers or letters on the dash board of a vehicle equipped with an internal combustion engine.

8 After displaying the abnormality, proceed to step 17 and set flag F.
set to zero. If flag F is set to zero here, the next time this program is executed, it will be determined that flag F is zero in step 5, and step 18 will be executed.
Then, the relay 5 is turned off and the diagnosis is completed.

If it is determined in step 15 that the error is within the allowable range, the process proceeds to step 19, where the count (i c n t) is incremented by 1, and in the next step 2, the count (i c n t) is determined. conduct.

If the diagnosis is made using the diagnostic resistor rl in step 15 this time, the result of the calculation in step 19 (i c n t is 1, so if the count value cnt is 1 in step 20) It is determined and the process proceeds to step 21.

In step 21, the standard intake air flow rate QREF is set to 50 kg/h, which is the expected detection value when using the diagnostic resistor r2.
In the next step 22, in order to form a bridge circuit with the diagnostic resistor r2 instead of the temperature compensation resistor RK, switch SWI, which was previously turned on, is turned off, while switch SW2 is turned on to form the diagnostic resistor r2. Resistor r2 is connected to the bridge circuit.

When the switch is changed in this way and the diagnostic resistor r2 is connected in place of the temperature compensation resistor RX, step 1 is resumed.
Return to step 3 and input the output voltage Us in this state,
In step 14, the detected value of the intake air flow rate Q is determined from the voltage Us, and in step 15, the detection error is determined. If the error exceeds the allowable range, the process proceeds to step 16 to display an abnormality and reset the flag F to zero. to finish the diagnosis.

Furthermore, when the error is small in the diagnosis using the diagnostic resistor r2, and the process proceeds from step 15 to step 19, the count value is set to 2, and the process proceeds from step 20 to step 23.

In step 23, the reference intake air flow rate Q RE F =100 kg/h is set corresponding to the diagnostic resistor r3, and in step 24, the switch SW2 is turned off in order to connect the diagnostic resistor r3 instead of the temperature compensation resistor RK. At the same time, switch SW3 is turned on.

0 Here, as described above, the actual detection result and the diagnostic resistance r
By comparing the detection value QREF expected from connection 3, it is determined whether the detection error at the 100 kg/h level is within the allowable level, and if there is an error exceeding the allowable level, it is displayed. , if the error is within the allowable range, the process returns to step 19 again.

In step 19, the count value cnt is counted up to 3, so in step 20, the count value cnt is increased to 3.
When it is determined that this is the case, the process proceeds to step 25, where the flag F is set to zero, and the diagnostic control is ended without being diagnosed as abnormal.

That is, instead of the temperature compensation resistor RK, the diagnostic resistors r1~
As a result of connecting r3 and comparing the expected value corresponding to the resistance value and the actual output value, if a large detection error is detected in any of the multiple types of resistance, an abnormality diagnosis is made. When no detection error is sampled, it is assumed that there is no abnormality in the intake air flow rate measuring device 1, and the diagnosis is terminated.

1 Here, since the detection expected value QREF and the actual detection result are compared for each of the plurality of intake air flow rate Q levels, the detection error for each intake air flow rate level is determined from this comparison result, and the detection error for each intake air flow rate level is determined. For example, the overall error characteristic as shown in FIG. 6 can be estimated based on the detection error of , so if the detection result by the intake flow rate measuring device 1 is corrected based on this estimation error, the initial detection characteristic can be obtained. can. This function corresponds to an intake air flow rate correction means.

In this embodiment, one of the diagnostic resistors r1 to r3 is connected to the bridge circuit instead of the temperature compensation resistor RKO, but a plurality of diagnostic resistors r1 to r3 may be combined and connected to the bridge circuit. You can do it like this.

Alternatively, the temperature compensation resistor RK may be left as it is, and the diagnostic resistors r1 to r3 may be connected in series to the temperature compensation resistor RK.

Furthermore, the resistance portion whose resistance value is changed by the diagnostic resistors r1 to r3 may be any of the resistors R1 to R3 other than the temperature compensation resistor RK, and the diagnostic resistors r1 to r3 are also limited to three types. It's not something you do.

<Effects of the Invention> As explained below, according to the present invention, by selectively connecting a plurality of diagnostic resistors to the bridge circuit, the resistance balance of the bridge circuit is forcibly disturbed and unbalanced voltage is reduced. Diagnose abnormalities in the intake flow rate measurement device at multiple intake air flow rate levels by comparing the expected detection value predicted based on the resistance value of the diagnostic resistor with the actual detection value. Therefore, even if the characteristics change such that a large error appears only at a specific intake air flow rate level, it is possible to detect an abnormality due to such a change in characteristics, and it is possible to select a diagnostic resistance. Since it is a configuration in which the devices are connected directly, a significant increase in cost can be avoided.

Furthermore, since the diagnosis is made after a predetermined period of time has elapsed since the engine has stopped, it is possible to prevent a misdiagnosis in a state where the resistance of the temperature-sensitive resistor is not stable immediately after the engine has stopped. Furthermore, the detection error can be determined from the comparison result between the expected value and the actual detected value, and the error in the intake air flow rate can be compensated for.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a circuit diagram showing an embodiment of the invention, and FIGS. 3 and 4 are flowcharts 1 and 4 showing diagnostic control in the above embodiment, respectively.
, FIG. 5 is a circuit diagram showing the configuration of a conventional intake flow rate measuring device, and FIG. 6 is a diagram showing an example of changes in detection characteristics in the intake flow rate measuring device.

Claims (3)

[Claims] (1) A bridge circuit formed by a temperature-sensitive resistor and a plurality of resistors placed in the intake passage of an internal combustion engine, and a bridge circuit that changes due to a change in the resistance value of the temperature-sensitive resistor according to the engine intake air flow rate. An intake air flow measuring device for an internal combustion engine, comprising: a control circuit that controls a current supplied to a bridge circuit based on a balanced voltage, and outputs a voltage corresponding to the supplied current as a detection signal of an intake air flow rate; A plurality of diagnostic resistors provided separately from the resistors forming the bridge circuit are selectively installed in the bridge circuit in order to change the resistance values of the resistance portion excluding the temperature-sensitive resistor forming the bridge circuit to multiple types. a diagnostic resistor connecting means to be connected; and a diagnostic resistor connecting means to selectively connect the plurality of diagnostic resistors to the bridge circuit while the engine is stopped, and for each of the plurality of changed resistance values. Detection value sampling means for sampling the detection signal of the intake air flow rate, respectively, and comparing the plurality of detection signals sampled by the detection value sampling means with an expected value corresponding to the resistance value changed by the diagnostic resistor, respectively. What is claimed is: 1. A self-diagnosis device for an intake flow rate measuring device for an internal combustion engine, comprising: abnormality determining means for determining an abnormality in the intake flow rate measuring device. (2) Measurement of intake flow rate of an internal combustion engine according to claim 1, further comprising sampling permission means for permitting sampling of the detection signal by the detection value sampling means after a predetermined time has elapsed since the engine has stopped. Self-diagnosis device in equipment. (3) Intake air flow rate for correcting the detected value of the intake air flow rate based on the deviation between the plurality of detection signals sampled by the detection value sampling means and each expected value corresponding to the resistance value changed by the diagnostic resistor. 3. A self-diagnosis device for an intake flow rate measuring device for an internal combustion engine according to claim 1, further comprising a correction means.