JPH0315619A - Failure diagnosing device for secondary air induction system for internal combustion engine - Google Patents

Abstract

PURPOSE:To diagnose failure in a secondary air induction system with high accuracy by detecting temperature of a catalyzer whose reaction temperature is raised in proportion to induction of secondary air and by comparing temperature difference of the catalyzer between induction and non-induction of the secondary air with a reference value. CONSTITUTION:In an engine, a catalyzer 3 is provided in an exhaust passage 2, and a device 1 for selectively inducing secondary air is provided in a secondary air induction passage connected to the upstream side of the catalyzer 3. In the above constitution, temperature of the catalyzer 3 is detected by a means 4. And based on detected temperature at the time of induction and non- induction of the secondary air, failure of the secondary air inducing device 1 is discriminated by a means 5. That is, as reaction temperature is raised in proportion to induction of the secondary air in the catalyzer 3, temperature difference of the catalyzer 3 betwen induction and non-induction of the secondary air is compared with a reference value. And when the temperature difference is smaller than the reference value, it is judged as abnormality caused by blinding or the like takes place.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a failure diagnosis device for determining whether a secondary air introduction device for an internal combustion engine is functioning normally.

(Conventional technology) In an internal combustion engine equipped with a three-way catalyst that simultaneously converts Co and HCcr contained in the exhaust gas into Ii and reduces No, the air-fuel mixture is converted into a catalyst with the best exhaust purification efficiency. In order to maintain the stoichiometric air-fuel ratio, the amount of fuel supplied to the engine is feedback-controlled based on the output of an oxygen sensor installed upstream of the three-way catalyst.

However, depending on engine operating conditions, a mixture richer than the stoichiometric air-fuel ratio may be temporarily supplied in order to ensure high output performance, and in this case, naturally, the three-way catalyst Exhaust purification efficiency will be reduced.

Therefore, we installed a device that injects secondary air into the exhaust passage upstream of the oxygen sensor.
Some systems are designed to increase exhaust purification efficiency by introducing secondary air into the exhaust gas to promote the reaction in the three-way catalyst during operation where C and CH levels increase. Additionally, in this case, by feedback controlling the fuel supply amount based on the output of the oxygen sensor while introducing secondary air, the air-fuel mixture supplied to the engine can be controlled to a value richer than the stoichiometric air-fuel ratio. (See Japanese Patent Laid-Open No. 61-247811, etc.).

However, in a secondary air introduction device like this,
Since it does not have a self-diagnosis function to check whether the secondary air is being introduced correctly, even if a situation occurs where the exhaust purification efficiency deteriorates due to an abnormality in the secondary air introduction device, it can be determined. I can't row.

<Problem to be solved by the invention> Therefore, the applicant compared the output of the oxygen sensor when secondary air was introduced and when the introduction was shut off during a specific operation, etc., and determined that the difference was less than a predetermined value. A device has been proposed that determines that an abnormality has occurred when the value is small.

The output of a normal oxygen sensor changes depending on whether or not there is oxygen in the exhaust gas, and therefore the output rises rapidly when the stoichiometric air-fuel ratio of the air-fuel mixture is reached.

If secondary air is introduced into the exhaust, the oxygen concentration will increase, and if the introduction is stopped, the oxygen concentration will decrease. Therefore, by comparing the oxygen sensor output when the secondary air is introduced and when it is stopped, the oxygen concentration of the secondary air can be determined. This allows you to determine whether the installation has been carried out normally.

However, although this failure determination device can reliably determine an abnormality when the secondary air is not introduced at all or when it is significantly reduced, it is possible that the flow rate is lower than the normal flow rate due to clogging of the secondary air introduction passage. For example, it is very difficult to judge when the introduced flow rate has decreased by about 20%.

It depends on the air-fuel ratio of the exhaust before introducing secondary air, but even if the supply amount decreases by 20% at the time of introduction, the output of the oxygen sensor will change significantly if it becomes leaner than the buried air-fuel ratio, so it is normal. It is determined that it is 60-70 in extreme cases. Even if the air-fuel ratio decreases significantly, such as ≦, it will be determined to be normal as long as the air-fuel ratio becomes lean due to introduction.

The amount of fuel supplied is feedback-controlled based on the output of the oxygen sensor while introducing secondary air into the exhaust gas. When supplying a rich mixture, feedback control is performed by changing the amount of secondary air introduced. As the air-fuel ratio of the air-fuel mixture changes significantly, deterioration in engine output performance and fuel efficiency is unavoidable.

Furthermore, as a matter of course, if the amount of introduced secondary air changes even slightly from the appropriate range, there is a risk that the exhaust gas purification efficiency of the catalyst will decrease accordingly.

SUMMARY OF THE INVENTION An object of the present invention is to provide a failure diagnosis device capable of determining an abnormality even when the amount of secondary air introduced is slightly changed.

(Means for Solving the Problems) Therefore, the present invention provides a catalyst device 3 in the exhaust passage 2, as shown in FIG.
An internal combustion engine comprising a device 1 for selectively introducing secondary air into the engine, a means 4 for detecting the temperature of the catalyst device 3, and a means 4 for detecting the temperature of the catalyst device 3, based on the detected catalyst temperature when the secondary air is introduced and when the secondary air is not introduced. and a failure determination means 5 for determining an abnormality in the secondary air introduction device 1.

(Function) In the catalyst, the reaction temperature increases by introducing secondary air, and this temperature increase is proportional to the amount of secondary air introduced.

Therefore, when comparing the temperature when secondary air is not introduced and the temperature difference when it is introduced, the temperature difference becomes larger as the amount of air intake increases.

By setting a reference temperature range and comparing this with the temperature difference, if it is larger than the reference value, the amount of secondary air introduced is determined to be greater than the predetermined value and normal, and the On the other hand, if it is smaller than the reference value, it is determined that the amount of secondary air introduced is less than the allowable range and that an abnormality such as clogging of the primary air barrel entry passage has occurred.

(Actual Seed Example) Hereinafter, an example of the present Chomei will be explained based on the drawings. FIG. 2 is a configuration diagram showing an embodiment of the present invention, in which 10 is an engine, 11 is an intake passage, and 12 is an exhaust passage.

A throttle valve 1 is installed in the intake passage 11 during engine idling.
An air regulator 14 and the like are disposed to bypass the engine 3 and limit intake air, and a fuel injection valve 15 is disposed downstream of these for injecting and supplying fuel in synchronization with engine rotation.

An oxygen sensor 16 that detects the oxygen concentration in the exhaust gas is installed in the exhaust passage 12, and a three-way catalyst 17 that oxidizes CoHC in the exhaust gas and reduces NO is installed downstream thereof. As will be described later, the three-way catalyst 17 is provided with temperature sensors 4l and 42 for detecting the temperature of the inlet of the three-way catalyst 17 and the catalyst bed in order to extract information for determining failure of the secondary air introduction device. Note that 18 is a muffler.

A secondary air introduction passage 19 is opened upstream of the oxygen sensor 16 . The secondary air introduction passage 19 is connected to the air cleaner 20 of the intake passage 11 on the upstream side, and has a reed valve 2 in the middle that opens in response to exhaust pressure pulsations in the exhaust passage 12.
1 and a diaphragm-type control valve 22 that opens and closes the introduction passage 19. The control valve 22 has a negative pressure chamber 23 and a solenoid valve (three-way solenoid valve) 24.
connected to the intake passage ll downstream of the throttle valve 13 via
When engine suction negative pressure is introduced into the negative pressure chamber 23, the valve body 2
5 opens the introduction passage 19, while when the suction negative pressure is cut off and the negative pressure chamber 23 is released to the atmosphere, the valve body 25 closes the introduction passage 9.

Solenoid valve 2 that controls the supply of operating negative pressure to the control valve 22
4 is ON.4 from the control circuit 26. It is opened and closed by an OFF signal, and when opened, introduces suction negative pressure into the negative pressure chamber 23 of the control valve 22, and when closed, releases the negative pressure chamber 23 to the atmosphere.

27 is an air flow sensor that detects the intake air amount of the engine 0, 28 is a throttle valve opening sensor, 29 is a water temperature sensor that detects the cooling water temperature, 30 is a crank angle sensor that detects the rotation speed of the engine 10, and 31 is the vehicle speed. These detection signals from the sensor are sent to the control circuit 26 together with the detection signal from the oxygen sensor l6.2 The control circuit 26 sends an ON signal ( Open signal〉 is sent, the control valve 22 is opened, and the secondary air is controlled to flow from the secondary air barrel entry passage 19 to the exhaust passage 2, while
When the load is low or high, an OFF signal (close signal) is sent to the solenoid valve 24 to control the control valve 22 to close.

Further, the control circuit 26 controls the fuel injection amount of the fuel injection valve 15 based on each detection signal, and also adjusts the supplied air-fuel mixture to a predetermined air-fuel ratio corresponding to the operating conditions according to the detection signal of the oxygen sensor 16. Control the feedback bag as follows. On the other hand, a switch 32 is provided for diagnosing failures in the electromagnetic valve 24, control valve 22, etc.
When turned on, the control circuit 26 opens and closes the solenoid valve 24 for a predetermined period of time, and determines when the secondary air barrel enters and when the introduction is stopped based on the detection signals of the catalyst temperature sensors 41 and 42 at this time. It is determined whether there is an abnormality in the secondary air introduction device based on the change in catalyst temperature. By introducing secondary air, the catalytic reaction is promoted and the catalyst temperature increases, and this temperature increase is approximately proportional to the amount of secondary air introduced into the barrel. Therefore, by comparing the temperature change when secondary air is not introduced and when it is introduced, it is possible to determine whether the amount of secondary air in the barrel is greater or less than the required setting range. This allows you to determine whether it has been installed or not.

FIG. 3 shows an example of the control operation in the control circuit 26 for determining failure of the secondary air introduction device based on temperature changes in the catalyst bed.

In order to determine the failure, first, step 102) is selected under the operating conditions that the switch 32 is ON and the solenoid valve 24 is OFF, and it is detected that the switch 32 is in the ON state (Step 103). In this case, in this case, the air-fuel feedhack control based on the detection signal of the oxygen sensor is stopped (not shown). At this time, the solenoid valve 24
An ON signal is sent to the solenoid valve 24 for a predetermined time to introduce secondary air (step 104), and an OFF signal is then sent to the solenoid valve 24 for a predetermined time to stop the introduction during this time (step 106).
．． Then, the temperature of the catalyst bed when the ON signal is output and when the OFF signal is output is measured by the temperature sensor 42 respectively. Toff) is determined (step 108).

In step 109, this temperature difference (T on - T of
f) with a predetermined value, and if the temperature difference is smaller than the predetermined value, it is determined that an abnormality has occurred in the solenoid valve 24, control valve 22, secondary air introduction passage 19, etc., and the failure indicator lamp 33 in FIG. is turned on (step 110).

Note that if the temperature difference is greater than a predetermined value, it is determined that secondary air is being introduced normally. Note that this fault diagnosis is performed by manually turning on the switch 32, but in this case, it may be automatically performed at appropriate times during a predetermined operation using the control circuit 26 in addition to the switch 32. Next, a more detailed explanation including the overall effect will be given.

When the solenoid valve 24 and the control valve 22 are operating normally, a signal sent from the control circuit 26 to the solenoid valve 24 depending on the operating conditions causes the secondary air introduction passage 19 to be closed to the exhaust passage 1.
The introduction of secondary air into 2 is appropriately controlled. Therefore, during operation when a rich mixture is supplied or CO and HC increase, the reaction at the three-way catalyst 17 is promoted by the introduction of secondary air, and a good exhaust gas composition is ensured.

Whether the secondary air introduction devices such as the solenoid valve 24 and the control valve 22 are operating normally can be determined by turning on the switch 32.
An ON signal and an OFF signal are sent from the control circuit 26 to the solenoid valve 24 for a predetermined period of time, and the determination is made from the difference in the output of the temperature sensor 42 when secondary air is introduced and when it is not introduced. When the output difference of the temperature sensor 42 is larger than a predetermined value, it is determined that the solenoid valve 24, control valve 22, reed valve 21, etc. are operating normally, but when the output difference is smaller than a predetermined value, the control valve 24, control valve 22, reed valve 21, etc. Either the valve 22 does not operate and does not switch to the secondary air introduction side, or the secondary air introduction passage 19 is clogged, and the primary air is not fed into the barrel or it is determined that the amount is less than the set value. , the failure indicator lamp 33 is lit.

As mentioned before, the temperature change in the catalyst is approximately proportional to the amount of secondary air introduced, and even a small change in the amount of introduced air causes the catalyst temperature to rise or fall. Therefore, even if the amount of secondary air introduced is reduced by, for example, 2Q% from the normal state (100%), the temperature difference will be smaller by that amount compared to when no introduction is made, so the amount of secondary air This makes it possible to make appropriate judgments not only when no gas is introduced at all, but also when there is a slight decrease in the amount introduced due to passage clogging, etc. In this way, if even the slightest abnormality occurs in the secondary air introduction system, this can be known by the illumination of the failure indicator lamp 33, and the operation can therefore be continued with the exhaust composition deteriorated, or When the air-fuel ratio is feedback-controlled based on the output of the oxygen sensor 16 while introducing secondary air into the barrel, deviation of the actual fuel supply amount (air-fuel ratio) from the target value can be prevented.

The embodiment shown in FIG. 4 uses the inlet temperature in addition to the catalyst bed temperature of the three-way catalyst 17 as a determining factor, thereby reducing the influence of exhaust gas temperature and outside air temperature on failure determination accuracy at the time of determination.

In this example, in steps 105° and 107°, the catalyst inlet temperatures Tlon and Tlof are measured when the secondary air barrel is introduced and when it is not introduced.
f is detected, the difference between the catalyst temperatures TLlon and TBoff at that time is determined, and these temperature differences are compared with a predetermined value (Sten 7108', 1
0 9'), and when the temperature difference is smaller than a predetermined value, it is determined that there is a failure in the same manner as above.

Even if the same amount of secondary air flows into the three-way catalyst 17, the temperature after the reaction will differ depending on the exhaust temperature during operation, and the temperature of the introduced secondary air is similar to the outside temperature) Temperature differences can also be caused by Generally, if the exhaust temperature and secondary air temperature before the reaction are low, the temperature rise after the reaction will be low, but in this way, the inlet temperature is detected in advance when secondary air is introduced and when it is not introduced, and this is subtracted. By doing so, these effects can be removed and the amount of secondary air introduced can be determined with even greater precision.

(Effects of the Invention) As described above, according to the present invention, the amount of secondary air introduced is determined while detecting the temperature of the catalyst, which changes in temperature almost in proportion to the amount of introduced secondary air. Abnormalities can be accurately determined not only when the introduction device fails, but also when the amount introduced decreases due to clogging of the passage, etc., making it possible to prevent deterioration of exhaust purification efficiency in the catalyst device. .

[Brief explanation of drawings]

FIG. 1 is a diagram corresponding to claims of the present invention, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIGS. 3 and 4 are flowcharts showing control operations of the different embodiments. 12...Exhaust passage, 16...Oxygen sensor, 19...
Secondary air introduction passage, 22... Opening/closing valve, 24... Solenoid valve, 26... Control circuit, 32... Switch, 33...
・・Failure indicator lamp, 41.42 temperature sensor. Enshin

Claims (1)

[Claims] An internal combustion engine equipped with a catalyst device in an exhaust passage and a device for selectively introducing secondary air into the exhaust passage upstream of the catalyst device, comprising means for detecting the temperature of the catalyst device and introducing secondary air. 1. A failure diagnosis device for a secondary air introduction system of an internal combustion engine, comprising a failure determining means for determining an abnormality of the secondary air introduction device based on the detected catalyst temperature when the air is introduced and when the secondary air introduction device is not introduced.