JP2005042676A - Failure detecting device for oxygen concentration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately preform failure detection of an oxygen concentration sensor. <P>SOLUTION: This failure detecting device for the oxygen concentration sensor intentionally varies a combustion air-fuel ratio to a rich side, when a state where output of the oxygen concentration sensor is below a predetermined threshold is continued for a first predetermined period; monitors the output of the oxygen concentration sensor at the time of passing of a second predetermined period when the output would be fully changed if the oxygen concentration sensor operates normally; and determines that the oxygen concentration sensor fails to operate normally if the output change is not identified. Accordingly, since this detection is stopped in a range where an exhaust gas flow rate is small, detection accuracy can be enhanced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to failure detection of an oxygen sensor of an internal combustion engine.

Patent Document 1 is known as a technique for detecting a failure of an oxygen sensor installed downstream of an exhaust gas purification device of an internal combustion engine. According to this technology, when the secondary oxygen sensor downstream of the exhaust gas purification device outputs a lean air-fuel ratio for a predetermined period, the control to make the air-fuel ratio rich is started, and then the primary oxygen sensor installed upstream of the exhaust gas purification device When the secondary oxygen sensor outputs lean despite the rich air-fuel ratio, it is determined that the secondary oxygen sensor has failed.
Japanese Patent No. 3009668

  When the oxygen sensor has a failure such as a short circuit or disconnection, a situation may occur in which the output of the oxygen sensor does not show fluctuation for a predetermined period or the fluctuation range is small. However, such a situation is not a failure of the oxygen sensor, but is considered to be a state in which the air-fuel ratio is actually stable. In the latter case, the above-described method cannot accurately detect a failure of the oxygen sensor.

  Therefore, there is a need for a technique for more accurately detecting failure of the oxygen concentration sensor.

  One aspect of the present invention is an oxygen concentration sensor that is disposed in an exhaust system of an internal combustion engine and outputs an oxygen concentration in exhaust gas, a comparison unit that compares an output of the oxygen concentration sensor with a predetermined threshold value, An air-fuel ratio control means for making the air-fuel ratio of the internal combustion engine richer than the stoichiometric air-fuel ratio after the elapse of the first predetermined period after the comparison means determines that the oxygen concentration is lower than the threshold value; After a lapse of a second predetermined period from the start, when the output of the oxygen concentration sensor is lower than the threshold value, failure determination means for determining that the oxygen concentration sensor has failed, exhaust gas in the exhaust system, and A failure detection device for an oxygen concentration sensor, comprising: a canceling unit that cancels the determination of failure when the flow rate is small.

  According to this aspect, when the state in which the output of the oxygen concentration sensor is lower than the predetermined threshold value continues for the first predetermined period, the combustion air-fuel ratio is intentionally changed to the rich side so that the normal oxygen concentration sensor can be used. In the failure detection device that monitors the output of the oxygen concentration sensor when the second predetermined period when the output change sufficiently occurs and determines that there is no change in output, this detection is stopped in the region where the exhaust flow rate is low As a result, failure detection accuracy can be increased.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine (hereinafter referred to as “engine”) and an electronic control device (hereinafter referred to as “ECU”) including a failure detection device for an oxygen concentration sensor according to an embodiment of the present invention. The engine 1 is, for example, an in-line four cylinder engine. A throttle valve 3 is disposed in the middle of the intake pipe 2 that communicates with the engine 1. A throttle valve opening (THA) sensor 4 is connected to the throttle valve 3, and an electric signal corresponding to the opening of the throttle valve 3 is output and supplied to the ECU 5. The configuration of the ECU 5 will be described later.

  The fuel injection valve 6 is provided for each cylinder slightly upstream of the intake valve (not shown) of the engine 1. The fuel injection valve 6 is connected to a fuel tank (not shown) via a fuel pump. The fuel injection valve 6 is electrically connected to the ECU 5, and the fuel injection valve opening time is controlled by a signal from the ECU 5. The injected fuel is mixed with the air from the intake pipe 2 to become an air-fuel mixture and supplied to the engine 1.

  An intake pipe absolute pressure (PBA) sensor 8 and an intake air temperature (TA) sensor 9 are attached to the intake pipe 2, and the absolute pressure and the intake air temperature are detected and supplied to the ECU 5 as electrical signals.

  An engine water temperature (TW) sensor 10 mounted on the main body of the engine 1 includes a thermistor and the like, detects the engine water temperature (cooling water temperature) TW, and supplies it to the corresponding temperature signal ECU 5.

  An engine speed (NE) sensor 11 is attached around the camshaft or crankshaft (not shown) of the engine 1. The engine speed sensor 11 outputs a pulse (hereinafter referred to as “TDC signal pulse”) at each top dead center (TDC) at the start of the intake stroke of each cylinder of the engine 1. This TDC pulse is supplied to the ECU 5.

  The exhaust pipe 13 is provided with an exhaust purification device 14 including a three-way catalyst. The three-way catalyst accumulates O2 in the exhaust when the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set leaner than the stoichiometric air-fuel ratio and the O2 concentration in the exhaust is relatively high. In an exhaust rich state in which the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is set to a richer side than the stoichiometric air-fuel ratio and the O2 concentration in the exhaust gas is low and the HC and CO components are large, the accumulated O2 causes the HC and CO in the exhaust gas to accumulate. It has a function of oxidizing. A NOx purification device may be further provided on the downstream side of the exhaust purification device 14.

  A proportional oxygen concentration sensor 17 (hereinafter referred to as “LAF sensor”) is disposed upstream of the exhaust purification device 14. The LAF sensor 17 outputs an electric signal that is substantially proportional to the oxygen concentration (air-fuel ratio) in the exhaust gas and supplies it to the ECU 5.

  A binary oxygen concentration sensor (hereinafter referred to as “downstream oxygen sensor”) 18 is disposed downstream of the exhaust purification device 14, and detection signals from these sensors are supplied to the ECU 5. The downstream oxygen sensor 18 has a characteristic that the output changes abruptly before and after the stoichiometric air-fuel ratio. The output is high on the rich side of the stoichiometric air-fuel ratio, and the output is low on the lean side.

  The ECU 5 is configured by a computer, and temporarily stores an input interface 5a for processing input signals from various sensors, a CPU 5b for executing various control programs, a ROM for storing programs and data, and programs and data necessary for execution. A memory 5c including a RAM for providing a calculation work area, and an output interface 5d for sending a control signal to each unit are provided. Signals from the sensors are received by the input interface and processed according to a program stored in the ROM.

  The ECU 5 detects operating conditions such as the engine speed and the accelerator opening, and searches a predetermined map to calculate the required torque. Subsequently, a basic fuel injection amount corresponding to the required torque is calculated, and further a timing for injecting fuel is determined.

  Moreover, ECU5 discriminate | determines the driving | running state of the engine 1 based on the input of each sensor. Then, various calculations are executed according to a control program stored in the ROM, and a drive signal corresponding to the calculation result is output via the output interface 5d to control the intake throttle valve 3, the fuel injection valve 6, and the like.

  Next, the failure determination of the downstream oxygen sensor in the ECU 5 will be described.

  The failure mode of the downstream oxygen sensor can be considered that the output is stagnating around 5 V (disconnection) and around 0 V (short circuit) when a circuit inside or outside the sensor is disconnected or short-circuited. Therefore, the downstream sensor output is monitored, and if there is no or little fluctuation within a predetermined period, it can be considered that the sensor output is abnormal.

  However, even when the air-fuel ratio is controlled to be lean, the downstream sensor output is output in the vicinity of 0 V. Therefore, in order to distinguish this, the sensor output is in the vicinity of 0 V, or there is no fluctuation within a predetermined period, or the fluctuation is small. In this case, the combustion air-fuel ratio is deliberately changed to the rich side, and if it is a normal sensor, the output behavior of the downstream oxygen sensor is monitored when sufficient output change has elapsed. It is judged.

  A routine for detecting a short-circuit failure of the downstream oxygen sensor will be described with reference to FIG.

  First, it is determined whether or not the output SVO2 of the downstream oxygen sensor is smaller than a predetermined voltage Low failure determination value (S30). The voltage low failure determination value is set to a value (for example, 0.3 V) that is considered to be shown when the downstream oxygen sensor is short-circuited. If SVO2 is equal to or greater than the failure determination value, there is no possibility of a short circuit, so an initial value is set in the down timer (S35), and the integrated value of the exhaust gas flow SV (which will be described later) is cleared (S36). End the routine.

  When SVO2 is less than the failure determination value, it is determined whether or not an actual short circuit is made as follows. First, it is determined whether the detection execution condition is satisfied (S32). Here, with reference to FIG. 3, a routine for determining the conditions for detecting the failure of the downstream oxygen sensor will be described.

  First, it is determined whether or not a fuel cut is being executed (S50). Since an appropriate execution condition cannot be determined while the fuel cut is being executed, the process proceeds to S52, and it is determined whether or not the timer fct1 set in S55 has elapsed for a predetermined time (S52). This is to determine if the fuel cut continues for a predetermined period or longer, because the responsiveness of the oxygen sensor is lowered and accurate detection may not be possible. If the timer fct1 has not elapsed for a predetermined period, the failure detection execution condition is not satisfied (S68). If the timer fct1 has elapsed for a predetermined period, the timer fct2 is further set (S54). The timer fct2 is for stopping the failure detection for a predetermined period after returning from the fuel cut (see S58).

  When the fuel cut is not being executed, after setting the timer fct1 (S55), it is determined whether a predetermined condition is satisfied (S56). This condition is specifically as follows.

-The target air-fuel ratio is controlled to the stoichiometric air-fuel ratio (stoichiometric) (because the SO2 output is lean attached when the target air-fuel ratio is lean).
-LAF feedback is being executed (because the actual air-fuel ratio is indefinite while feedback is stopped)
-The feedback limit is not attached (because the stoichiometric air-fuel ratio may not be realized when the feedback limit is attached)
・ The temperature of the oxygen sensor is equal to or higher than the feedback start water temperature (because the oxygen sensor is not active at low temperatures).
It is.

  If even one is not satisfied, the failure detection condition is not satisfied (S68). If all are satisfied, it is subsequently determined whether the timer fct2 set in S54 has elapsed (S58). If it has not elapsed, the failure detection execution condition is not satisfied (S68), and if it has elapsed, the exhaust gas flow rate SV is calculated (S60). The exhaust gas flow rate is calculated using parameters correlated with the engine intake air amount, such as the air flow meter output, the engine speed, the engine load, and the fuel injection amount setting value. Then, an SV integrated value obtained by adding the exhaust gas flow rate SV calculated this time to the integrated value of the exhaust gas flow rate SV calculated up to the previous time is calculated (S62), and it is determined whether or not the SV integrated value is smaller than a predetermined value. (S64). When the predetermined value has not been reached, the failure detection condition is not satisfied (S68), and the failure detection condition is satisfied only when the predetermined value is reached (S66). If the exhaust gas flow rate is small, the time until the downstream oxygen sensor detects a change in the air-fuel ratio of the exhaust gas becomes longer. Then, the state in which the air-fuel ratio is changed becomes a long time and the exhaust gas purification performance may be deteriorated. To prevent this, failure detection is performed when the SV integrated value does not reach the predetermined value. To avoid it.

  Returning to FIG. 2, it is determined whether or not the failure detection execution condition described in FIG. 3 is satisfied (S34). If the condition is not satisfied, an initial value is set in the timer (S35), and the exhaust gas flow rate SV is further set. Is cleared (S36). When the failure detection execution condition is satisfied, it is determined whether or not the first predetermined period has elapsed (S38). When the predetermined period has not elapsed, this routine is terminated. When the first predetermined period has elapsed, it is determined whether or not the integrated value of the exhaust gas flow rate SV calculated in S60 is less than a predetermined value (S40). When the integrated value of the exhaust gas flow rate SV is less than the predetermined value, this routine is terminated without performing the subsequent processing. When the flow rate of exhaust gas is small, the time until the oxygen sensor detects the change of the air-fuel ratio becomes long, and the change of the air-fuel ratio may not be detected accurately within the first predetermined period. The detection accuracy can be increased by extending the detection time until the integrated value of the exhaust gas flow rate SV after the condition is satisfied exceeds a predetermined value.

  When the integrated value of the exhaust gas flow rate SV is greater than or equal to a predetermined value, there is no such possibility, so air-fuel ratio switching control is executed to detect whether or not the downstream oxygen sensor has failed (S42). . Then, it is determined whether or not the timer has passed the second predetermined period, that is, after the air-fuel ratio switching has been completed, a period of time that is normally expected to become rich has elapsed (S44). When the second predetermined period has not elapsed, this routine is terminated. In this case, the downstream oxygen sensor is normal, and the output SVO2 is stagnant at a low output. When the second predetermined period has elapsed, it is determined that the downstream oxygen sensor has failed (S46).

  As described above, when the downstream oxygen sensor output detects that there is no or little fluctuation within the first predetermined period, the air-fuel ratio switching control is performed, and the combustion air-fuel ratio is intentionally changed to normal. If the sensor is a simple sensor, the output behavior of the downstream oxygen sensor is monitored when the second predetermined period in which the output changes sufficiently, and if there is no fluctuation, it is determined that there is a failure, so the failure detection accuracy is improved. be able to.

  FIG. 4 is a timing chart of an example of specific failure detection.

  It is assumed that the detection condition described with reference to FIG. 3 is satisfied at time t1, and the detection condition flag indicates 1 as shown (72). When SVO2 (70), which is the output of the downstream oxygen sensor, falls below a predetermined value of 0.3 V at time t2, the down timer (74) is decremented by a predetermined value from the initial value. When the timer elapses for a first predetermined period at time t3 (see S38), the air-fuel ratio switching control is started on condition that the SV integrated value is equal to or greater than the predetermined value (see S40), and the air-fuel ratio is gradually decreased. A rich control signal is output (76). When the timer elapses for a second predetermined period at time t4, the value of the downstream oxygen sensor output SVO2 is checked. If the value exceeds the threshold value of 0.3 V at this time, the sensor is determined to be normal ( 80) If it is still less than 0.3 V, the sensor is judged to be faulty (82).

  Although one embodiment of the present invention has been described above, the present invention is not limited to this. For example, the present invention can also be applied to a marine vessel propulsion engine such as an outboard motor having a vertical crankshaft.

  According to the present invention, when the state in which the output of the oxygen concentration sensor is lower than the predetermined threshold value continues for the first predetermined period, the combustion air-fuel ratio is intentionally changed to the rich side so that the normal oxygen concentration sensor If there is a change in the output, the output of the oxygen concentration sensor is monitored when the second predetermined period of time in which the output changes sufficiently, and if there is no change in output, it is determined that there is a failure. Since it was canceled, the accuracy of failure detection can be increased.

It is the schematic of an internal combustion engine provided with the failure detection apparatus of this invention. It is a flowchart of a failure detection of an oxygen concentration sensor. It is a flowchart of failure detection execution condition judgment. It is a timing chart which shows an example of failure detection by the present invention.

Explanation of symbols

1 Internal combustion engine
2 Intake pipe 5 Electronic control unit (ECU)
6 Fuel injection valve 13 Exhaust pipe 14 Exhaust gas purification device 17 Proportional oxygen concentration sensor (LAF sensor)
18 Binary oxygen concentration sensor (downstream oxygen sensor)

Claims (1)

An oxygen concentration sensor arranged in an exhaust system of an internal combustion engine and outputting an oxygen concentration in the exhaust;
Comparison means for comparing the output of the oxygen concentration sensor with a predetermined threshold;
Air-fuel ratio control means for making the air-fuel ratio of the internal combustion engine richer than the stoichiometric air-fuel ratio after elapse of a first predetermined period after the comparison means determines that the oxygen concentration is lower than the threshold value;
Failure determination means for determining that the oxygen concentration sensor has failed when the output of the oxygen concentration sensor is lower than the threshold value after the elapse of the second predetermined period since the air-fuel ratio is made rich;
When the flow rate of the exhaust gas in the exhaust system is small, stop means for stopping the determination of failure,
An oxygen concentration sensor failure detection apparatus comprising:

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