JP2535880B2 - Self-diagnosis device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an internal combustion engine that controls the air-fuel ratio by feedback control by detecting the oxygen concentration in exhaust gas, and in particular, determines the fuel supply state based on the oxygen concentration in exhaust gas. The present invention relates to a self-diagnosis device for making a diagnosis.

[Prior Art] Conventionally, a basic injection amount of a fuel injection valve is calculated according to an intake air amount and a rotation speed of an internal combustion engine, and an air-fuel ratio correction amount calculated based on a detection signal of an oxygen concentration in exhaust gas of the engine is used. There is known a multi-cylinder internal combustion engine equipped with an air-fuel ratio feedback-back type electronically controlled fuel injection device for appropriately maintaining the air-fuel ratio of the engine by correcting the basic injection amount accordingly. In such a fuel injection device, the injection amount is controlled by the valve opening time of the fuel injection valve, and the valve opening time is determined by the energization time to the fuel injection valve.

Here, in a so-called independent injection type fuel injection device in which one fuel injection valve is provided for each cylinder,
If the fuel injection valve is clogged, the signal line is broken, or dust is attached to the injection port, the engine may stop or the output may drop significantly even if the injection port is not closed properly or the signal line is shorted. There was no big change, and the discovery of anomalies was delayed.

Therefore, there has been proposed a device for self-diagnosing the air-fuel ratio control state of an internal combustion engine by using an oxygen concentration detection sensor mounted in the exhaust pipe for feed back control of the air-fuel ratio and counting the number of inversions of this oxygen concentration detection sensor. (For example, Japanese Patent Application No. 61-140384).

This is because, for example, when the air-fuel ratio is controlled from the rich side to the lean side, the oxygen concentration in the exhaust gas increases at a constant change rate at light load (during idling), so the oxygen concentration inversion frequency is predicted in advance. be able to. However, if the fuel is not injected from any one of the plurality of cylinders, the exhaust gas becomes uneven and only the exhaust gas at the time of combustion in that cylinder becomes lean exhaust gas, so the oxygen concentration sensor is reversed.
That is, the number of times of reversal is greater than the predetermined number of times, and by monitoring this every predetermined time, it is possible to detect the above-mentioned abnormality early.

[Problems to be Solved by the Invention] However, due to its characteristics, the oxygen concentration detection sensor is in an inactive state at a low temperature, and it is not possible to accurately obtain a minute change in the oxygen concentration of exhaust gas, resulting in a false diagnosis. There is. Therefore, the self-diagnosis at this low temperature has poor reliability.

In consideration of the above facts, the present invention estimates the temperature of the oxygen concentration detection sensor from the engine load without using new parts, and when the oxygen concentration detection sensor is low in activity, the diagnosis can be stopped to improve reliability. The purpose is to obtain a self-diagnosis device.

[Means for Solving Problems] In a self-diagnosis apparatus for an internal combustion engine according to the present invention, an oxygen concentration detection sensor detects an oxygen concentration in exhaust gas, and the output of the oxygen concentration detection sensor is reversed within a predetermined time. Which is a self-diagnosis device for diagnosing an abnormality of the fuel supply system of the internal combustion engine based on the calculation result, the load detection means detecting the load of the internal combustion engine, and the detection result of the load detection means. And a control unit for estimating the temperature of the oxygen concentration detection sensor and stopping the diagnosis when the estimated temperature is equal to or lower than a predetermined value.

[Operation] The oxygen concentration detection sensor has a characteristic that its output changes suddenly in the vicinity of the theoretical air-fuel ratio, and it is possible to judge whether the air-fuel ratio of the internal combustion engine is lean or rich based on this output value. it can.

By the way, when the internal combustion engine is idle, for example, since the intake air amount and the fuel supply amount are almost constant, the number of reversals of the air-fuel ratio from the lean side to the rich side or from the rich side to the lean side can be predicted. it can. Therefore, by comparing the number of times of reversal of the oxygen concentration detection sensor output within the predetermined time with the predicted number of times, it is possible to self-diagnose whether the fuel injection system is operating normally.

In the present invention, the temperature of the oxygen concentration detection sensor itself is estimated from the detection result of the load detection means, and the self-diagnosis is stopped in the inactive state, that is, when the oxygen concentration detection sensor is at a low temperature.

Explaining this in detail, the oxygen concentration sensor may not accurately perform reversal due to the air-fuel ratio in the inactive state due to its characteristics, and if the self-diagnosis is performed in such an inactive state, a false diagnosis is made. There is a risk. In the present invention, the temperature of the oxygen concentration detection sensor is estimated according to the detection result of the load detection means, and when the estimated temperature is equal to or lower than the predetermined value, it is determined that the oxygen concentration detection sensor is in the inactive state, and the self-diagnosis is stopped. .

In this way, since the diagnosis in the inactive temperature range of the oxygen concentration detection sensor is stopped, the reliability of the self-diagnosis function can be improved.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 (A) shows an outline of a spark ignition internal combustion engine (engine) provided with a fuel injection amount control device to which the present invention is applicable. An air flow meter 12 is arranged downstream of the air cleaner 10.

The air flow meter 12 detects an intake air amount Q from a compensation plate rotatably arranged in the dipping chamber, a media ring plate fixed to the media plate, and a change in the opening of the media plate. It consists of a potentiometer 12A. An intake air temperature sensor 12B that detects the intake air temperature is attached near the potentiometer 12A.

The air flow meter 12 includes an intake passage 14 and a surge tank 16
And the engine body 20 through the intake manifold 18.
It is connected to the intake port 22 of. A throttle valve 24 is arranged on the upstream side of the surge tank 16.

A fuel injection valve (injector) 26 is arranged in the intake manifold 18 so as to project for each cylinder. A bypass passage 24B is provided so as to bypass the throttle valve 24. In addition, a slot sensor (idle switch) 24A that detects the opening of the slot valve
Is attached, and it is turned on when the throttle valve is fully closed.

The intake port 22 is connected to the engine body 2 through the intake valve 20A.
It is communicated with a combustion chamber 28 formed in 0. The combustion chamber 28 is in communication with the exhaust passage 34 via the exhaust valve 20B, the exhaust port 30, and the exhaust manifold 32.
Further, the exhaust manifold 32 is provided with an oxygen concentration detection sensor (O ₂
A sensor) 40 is attached, and the exhaust passage 34 is connected to a catalyst device 46 filled with a three-way catalyst.

The engine body 20 has a cooling water temperature sensor 38 that penetrates the cylinder block and projects into the water jacket.
Is installed. Also, the combustion chamber 28 of the engine body 20
A spark plug 39 is attached to each cylinder so as to project inward, and the spark plug 39 is connected to a control circuit 45 including a microcomputer through a distributor 42 and an igniter.

A rotation angle sensor 48 composed of a signal rotor fixed to the distributor shaft and a pick-up fixed to the distributor housing is attached to the distributor 42. Rotation angle sensor 48 is 30 °
It is possible to output each rotation signal for each CA and calculate the engine rotation speed NE from the cycle of this rotation signal NS.

The potentiometer 12A, the intake air temperature sensor 12B, the throttle sensor 24A, the rotation angle sensor 48, the cooling water temperature sensor 36 and the O ₂ sensor 40 are connected to the control circuit 45 so as to input signals, and the igniter and the The fuel injection valve 26 is connected so as to be controlled by a control signal output from the control circuit 45.

As shown in FIG. 1 (B), the control circuit including the microcomputer includes a random access memory (RAM) 58, a read only memory (ROM) 60, a micro processing unit (MPU) 62, an output port 68, Analog digital (A / D) converter 74, rotation speed signal forming circuit 7
6 and a bus 72 such as a data bus or a control bus that connects them.

The slot sensor 24A, the potentiometer 12A, the intake air temperature sensor 12B, the water temperature sensor 38, and the O ₂ sensor 40 are connected to the A / D converter 74, and the A / D converter 74 is input from these. The signals are sequentially converted into digital signals. Further, the rotation angle sensor 48 is connected to the rotation speed signal forming circuit 76, and the engine rotation speed is calculated from the cycle of the signal output from the rotation angle sensor 48 every 30 ° CA. Output port 68
Is connected to the fuel injection valve 26 via a drive circuit 78.

The operation of this embodiment will be described below with reference to the flow charts of FIGS.

FIG. 2 shows a main routine for calculating the fuel injection amount. First, the engine speed NE and the intake air amount Q are taken in at step 100, and then step 10
In step 2, the basic fuel injection amount τ _B is calculated based on these values. Next, at step 104, the basic fuel injection amount τ _B is multiplied by the correction coefficient C to calculate the fuel injection amount τ. The engine burns and operates at an air-fuel ratio based on this fuel injection amount. One element for obtaining the correction coefficient C is an O ₂ sensor 40 attached to the exhaust manifold 32.
The oxygen concentration in the exhaust gas is detected by reversing the output of the O ₂ sensor 40, and the air-fuel ratio is controlled by feeding it back to the air-fuel ratio. The control is alternately performed to the rich side or the lean side. A signal is sent to the drive circuit 78 according to this fuel injection amount τ and fuel is injected from the fuel injection valve 26. However, when the idle switch is on and the engine speed NE is equal to or higher than the cut speed, the drive circuit 78 To the fuel cut state. This saves energy and prevents heating of the catalyst device 46. Further, the fuel cut state is released when the engine speed NE becomes lower than the return rotation speed (rotation speed lower than the cut rotation speed) when the idle switch is on or when the idle switch is turned off.

Next, the skip level Cskip routine of FIG. 3 will be described. This skip level Cskip indicates the number of reversals of the O ₂ sensor. First, at step 106, it is judged if the previous air-fuel ratio was lean. In the case of a positive determination, the routine proceeds to step 108, where it is determined whether or not the air-fuel ratio at this time is the latch. If an affirmative decision is made at step 108, then the routine proceeds to step 110, where the skip level Cskip is incremented, and this routine ends.

Next, in step 106, a negative determination is made, that is, if the previous air-fuel ratio was the latch, the routine proceeds to step 112, where it is determined whether the current air-fuel ratio is lean.
If an affirmative decision is made at step 112, the routine proceeds to step 110, where the skip level Cskip is incremented. Further, if the negative determination is made in step 108 or step 112, that is, if there is no change in the air-fuel ratio state from the previous time, the skip level Cskip is not incremented and this routine ends.

Next, the activity level CO ₂ S routine of FIG. 4 will be described.
This routine estimates the temperature of the O ₂ sensor 40, O ₂ sensor
It is a routine for judging the possibility of 40 inactivity.

First, at step 114, it is judged if the fuel is being cut. When a negative determination is made in step 114, the process proceeds to step 116, and the intake air amount Q and a predetermined value (for example, 40 m
³ / h). O ₂ when the intake air amount Q> 40m ³ h
The sensor 40 judges that the temperature is the active temperature, shifts to step 118, and if the active level CO ₂ S does not reach the predetermined level $ FF, the active level CO ₂ S is incremented at step 119 and this routine ends. To do. If the activation level CO ₂ S has reached $ FF at step 118, there is no need to increment it, so this routine ends at this point.

If Q ≦ 40 m ³ / h at step 116, the process proceeds to step 120 and this time the intake air amount Q is compared with 20 m ³ / h. This is a region where the exhaust gas temperature is low when the intake air amount is less than 20 m ³ / h, and the temperature of the O ₂ sensor 40 is likely to drop by this.
When it is 0 m ³ / h, or when it is determined in step 114 that the fuel is being cut, the process proceeds to step 122. Q ≧ 20m ³ / h
In the case of, the routine ends at step 122, and when it is judged that the activity level CO ₂ S has not reached 0, the routine proceeds to step 124 and decrements the activity level CO ₂ S by 1.
That is, the O ₂ sensor is inactive at a low temperature (O ₂ sensor 40
When the low temperature state) is continued for a predetermined time, activity levels CO ₂
The value of S becomes 0, and when it returns to the active state (normal temperature state of the O ₂ sensor 40), it increases or decreases in a positive integer from 1 to $ FF, and the O ₂ sensor is used for the self-diagnosis of the fuel injection state shown below. 40
It is possible to determine whether the product can be used or is not suitable for use.

That is, for example, even if there is a low load state for a short period after the high load state continues, the activation level CO ₂ S does not become 0 immediately and the O ₂ sensor 40 does not become the inactive state. On the contrary, the activation level CO ₂ S is not incremented even if the air amount Q continues to be less than 20 m ³ / h and the air amount slightly increases (Q = 30 m ³ / h) (step 116 and step 120). Negative judgment), it does not become active. In this way, the timing for stopping the self-diagnosis is made different depending on the previous load condition, so that a more accurate self-diagnosis can be performed.

FIG. 5 shows the injector fail routine.

At step 126, it is determined whether or not the idle rotation is currently being performed based on whether the idle switch is on or off. This is because the intake air amount is small and the fuel supply amount is small during the idling rotation, so that the number of times the O ₂ sensor 40 is inverted is small and the difference between the normal state and the abnormal state is likely to occur.

Activity levels CO ₂ S value obtained in said active level CO ₂ S routine next step 128 is compared with zero if it is determined that the idle rotation at step 126. As described above, when the activation level CO ₂ S value is 0, the O ₂ sensor 40 is in an inactive state, and even if the fuel injection state is diagnosed, there is a risk of erroneous diagnosis. Then, the self-diagnosis timing Cfail value and the skip level Cskip value are each set to 0, and then this routine ends. Here, the self-diagnosis timing Cfail value is a value provided with a timer function for performing a diagnosis by the skip level Cskip value at regular intervals, and at the step 128, the activity level CO ₂ S is a positive integer from 1 to $ FF. , That is, the O ₂ sensor 40
Is a value to be compared with a predetermined numerical value in step 132 to shift when is active. In the case of the present embodiment, the intake failure routine is a routine executed every 0.471 seconds, and when the reference value of the self-diagnosis timing Cfail value is 11 as in this embodiment, the diagnosis is executed about every 5 seconds ( 0.
471 x 11 = 5.181).

Therefore, in step 132, the self-diagnosis timing Cfail value is
If it has not reached 11, the process proceeds to step 134 and the self-diagnosis timing Cfail value is incremented. When the self-diagnosis timing Cfail is 11 or more, it is determined that the diagnostic timing is reached, and the process proceeds to step 135 to compare the skip level Cskip value with a predetermined value. At step 135, the skip level Cskip value, that is, the number of reversals of the O ₂ sensor 40 is 10
At least one of the fuel injection valves 26 is determined as above.
You can judge that one is out of order. This is because combustion in the combustion chambers 28 of the multi-cylinder is not performed uniformly, and the failure of the fuel injection valve 26 causes unevenness in the O ₂ content of the exhaust gas. For this reason, when detecting O ₂ with the O ₂ sensor 40, the oxygen concentration differs only in the exhaust gas from the cylinder corresponding to the failed fuel injection valve 26, and the O ₂ sensor 40 is inverted to a fine value. The number of reversals of the O ₂ sensor 40 can be predicted at idle rotation, and in this embodiment, the predicted value is set to 10, and the number of reversals of the O ₂ sensor 40 is compared with the predicted value 10 to determine the fuel injection valve.
26 is determined to be abnormal.

If it is determined to be abnormal in step 135, step 136
And move to the Ingeectail status. this is,
It is possible to warn the driver by displaying a lamp, etc. In addition to this, the pressure (negative pressure) in the delivery pipe (not shown) is measured for the fuel injection state and which cylinder does not drop the pressure at ignition. Can be calculated and stored in the control circuit 45. In this way, when the driver notices an abnormality and brings the vehicle to the maintenance shop, the defective fuel injection valve 26 can be easily identified by reading the calculation result stored in the control circuit 45.

Next, if a negative determination is made in step 135, step 1
Moving to 38, this time the skip level Cskip value is compared with the numerical value 3. If the skip level Cskip value is 3 or less, it can be determined that the fuel injection valve is operating normally, and the step
After a display (not displayed) indicating that the operation is normal is made at 140, the process proceeds to step 130. When the negative determination is made in step 138, the number of reversals of the O ₂ sensor 40 is larger than that in the normal idle rotation, but it is not so bad that it is difficult to make a determination.
Move to 0.

As described above, in this embodiment, the self-diagnosis of the fuel injection system is not always performed by the O ₂ sensor 40, but the self-diagnosis is stopped when the temperature of the O ₂ sensor 40 is low, that is, when the O ₂ sensor 40 is inactive which may cause a false diagnosis. Since this is done, the diagnosis result is reliable.

In this embodiment, the fuel cut means detects the deceleration state of the vehicle based on the engine speed NE and the intake air amount Q, and shuts off the signal from the control circuit 45 for operating the fuel injection valve 26. However, another fuel cut means may be used, such as attaching a solenoid valve to a part of the fuel supply system and operating this solenoid valve at the time of deceleration to stop fuel supply.

Although the intake air amount Q is used as the load, the intake pipe pressure may be used.

[Effects of the Invention] As described above, the self-diagnosis apparatus for an internal combustion engine according to the present invention estimates the temperature of the oxygen concentration detection sensor from the engine load without using new parts, and makes a diagnosis when the oxygen concentration detection sensor is in a low activity state. It has an excellent effect that it can be stopped and the reliability can be improved.

[Brief description of drawings]

FIG. 1 (A) is a schematic configuration diagram of an internal combustion engine according to the present embodiment,
FIG. 1 (B) is a block diagram of the control circuit, and FIGS.
The figure is a control flow chart. 20 …… Engine body, 26 …… Fuel injection valve, 32 …… Exhaust manifold, 40 …… O ₂ sensor, 45 …… Control circuit.

Claims (1)

(57) [Claims] 1. An oxygen concentration detection sensor detects the oxygen concentration in exhaust gas, the number of times of reversal of the output of this oxygen concentration detection sensor is calculated, and the fuel supply system of an internal combustion engine is calculated based on the calculation result. A self-diagnosis device for diagnosing an abnormality, wherein load detection means for detecting the load of an internal combustion engine, and the temperature of the oxygen concentration detection sensor is estimated according to the detection result of the load detection means, and this estimated temperature is below a predetermined value. In the case of, a self-diagnosis apparatus for an internal combustion engine, comprising: a control means for stopping the diagnosis.