JPH0543253Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Field of Application) This invention relates to an air-fuel ratio control device for an engine, particularly to one that determines response deterioration of a sensor that outputs an output according to the air-fuel ratio in exhaust gas.

(Prior art) Regarding an abnormality or deterioration of the oxygen sensor used in a three-way catalyst system, the output voltage of the oxygen sensor (hereinafter referred to as "sensor output") may drop for several seconds even if the air-fuel ratio feedback control conditions are met. The judgment is made based on the fact that it is not reversed. This is caused by disconnection or damage to the oxygen sensor.
It determines when the oxygen sensor becomes completely unusable, so it can be said to be a fail-safe. Therefore, it is not intended to determine a case where the responsiveness of the oxygen sensor has deteriorated.

However, in a three-way catalyst system, the air-fuel ratio is required to be maintained within a certain narrow range (called a window) around the stoichiometric air-fuel ratio.
As long as the response is outside this window, the three-way catalyst cannot work effectively due to deterioration in response.

Therefore, a device has been proposed that determines whether or not response deterioration has occurred in the oxygen sensor (see, for example, Japanese Patent Laid-Open No. 147034/1983).

This method involves installing one oxygen sensor on the upstream side and one downstream of the catalytic converter that houses the three-way catalyst, and using the downstream oxygen sensor to determine whether or not the upstream oxygen sensor has degraded in response. .

(Problem to be solved by the invention) By the way, with such a device, even if it is possible to determine the response deterioration of the oxygen sensor, two oxygen sensors are required, so the cost will increase compared to one. Become.

In addition, it is important to determine whether response deterioration has occurred in the upstream oxygen sensor because the exhaust temperature is higher upstream of the catalytic converter, which has a greater thermal effect on the oxygen sensor and is susceptible to poisoning. However, even if the downstream oxygen sensor has a low exhaust temperature and there is no risk of poisoning, it does not mean that it will not deteriorate at all, so if the downstream oxygen sensor deteriorates, In this case, the response deterioration of the upstream oxygen sensor will be incorrectly determined.

This idea was devised by focusing on these conventional problems, and while using only one oxygen sensor, it was designed to have a large proportional component so that the air-fuel ratio change in the exhaust becomes rapid near the stoichiometric air-fuel ratio. By performing fuel correction, it is possible to determine when the air-fuel ratio reverses from rich to lean or vice versa, and calculate the difference between the timing of the reversal and the point at which the sensor output crosses the slice level as the response delay of the oxygen sensor. The purpose of the present invention is to provide a device capable of measuring as follows.

(Means for solving the problem) As shown in FIG. 1, this invention consists of a sensor 1 that outputs an output according to the air-fuel ratio in the exhaust gas, and a slice level (S/
means 2 for determining whether or not the air-fuel ratio has been crossed; means 3 for calculating a proportional amount for changing the air-fuel ratio in steps when this is determined; and means 3 for calculating a proportional amount for changing the air-fuel ratio in steps, (α), and means 5 for determining the fuel injection amount (Ti) to be supplied to the cylinder by correcting the basic injection amount (Tp) according to the operating conditions using this correction amount (α). In the air-fuel ratio control device for an engine, the sensor output is brought to a slice level (S/ means 8 for measuring the elapsed time or elapsed crank angle until crossing L), and whether or not response deterioration has occurred in the sensor by comparing this measured value with a predetermined reference value (reference time or reference crank angle); means 9 for determining.

(Function) If the proportional component applied immediately after the exhaust air-fuel ratio is reversed is increased, the change at the time when the air-fuel ratio crosses the stoichiometric air-fuel ratio becomes rapid, so that the measurement at the time when the air-fuel ratio crosses the stoichiometric air-fuel ratio can be performed accurately.

On the other hand, since the air-fuel ratio change due to this large proportional fuel correction is transmitted through the combustion gas, the elapsed time (elapsed crank angle) from when the combustion gas is exhausted from the cylinder until the sensor output crosses the slice level is Once measured, this measurement value corresponds to the response delay of the sensor.

Therefore, if the response delay of a normal sensor is set as a reference value, when comparing this reference value with the measured value, if the measured value deviates from the reference value, it can be determined that the sensor has degraded in response. It is judged that.

Here, since only one sensor is provided for determining the response deterioration of the sensor, there is no increase in cost.

(Example) FIG. 2 is a system diagram of a four-cylinder engine in which a fuel injection valve 36 is provided in the intake port 26 of each cylinder. In the figure, the exhaust passage 22 on the downstream side
A catalytic converter 24 that houses a three-way catalyst is installed in the catalytic converter 24, and when the air-fuel ratio in the exhaust gas is maintained within the above-mentioned window, the three-way catalyst reduces the harmful three components (HC, CO, NOx) in the exhaust gas. ) are efficiently purified at the same time. An oxygen sensor 25 is attached to the upstream side of the converter 24, and generates different output voltages depending on whether the air-fuel ratio in the exhaust gas is lean or rich with respect to the stoichiometric air-fuel ratio.

A flap-type air flow meter 29 is provided in the intake passage 28 upstream of the throttle valve 27, and a water temperature sensor 33 is provided in the water jacket 32 at the intake manifold gathering portion.

The distributor 30 has a built-in crank angle sensor 31 therein. For example, the upper stage is a reference position signal (for a 4-cylinder engine,
A retractor and a pick-up coil for generating a 90° signal are set at the bottom, and external and internal teeth for generating a 1° signal, as well as a pick-up coil, are set at the bottom. When rotated synchronously, a reference position signal and a 1° signal are generated from a pair of pickup coils.

A control unit 35 consisting of a microcomputer inputs signals from various sensors, calculates an optimal injection amount according to a program stored in memory, and sends signals to the solenoid coil of an injection valve 36 in accordance with the injection amount. By determining the energization time, the optimum injection amount is injected into the intake port 26 of each cylinder.

In this case, the injection method is so-called sequential injection, and according to this method, fuel is injected once per two engine revolutions per cylinder, and the ignition order is (1→3→4→2). Then, it is injected into each cylinder. In other words, four injections are performed in one cycle.

The composition of the fuel injection amount per cylinder is "basic injection amount + various increase correction amounts." However, by keeping the fuel pressure acting on the injection valve constant, the injection amount corresponds to the valve opening pulse width (valve opening time) of the injection valve. Therefore, the injection pulse width (Ti) during normal operation is calculated using the following formula.

Ti=Tp×Co×K _FC ×α+Ts Here, the basic pulse width (Tp) is a value determined from the intake air amount measured by the air flow meter 29 and the engine speed detected by the crank angle sensor 31 ( (equivalent to the basic injection amount), this
According to Tp, an air-fuel mixture of approximately stoichiometric air-fuel ratio can be obtained.

Various correction coefficients (Co) are the sum of 1 and a water temperature increase correction coefficient (K _TW ), etc., and increase the Tp according to operating conditions input from sensors other than the air flow meter. For example, K _TW is water temperature sensor 33
It is introduced to enrich the air-fuel mixture as the cooling water temperature (T _W ) decreases as detected at 60°C or below. K _FC is the fuel cut coefficient.

α is an air-fuel ratio feedback correction coefficient, which is calculated based on the signal from the oxygen sensor 25. For example, if the actual air-fuel ratio measured by the oxygen sensor 25 is on the richer side than the stoichiometric air-fuel ratio, a value is calculated to reduce the Tp in order to return the air-fuel ratio to the lean side; If so, an increase correction value is calculated to return the air-fuel ratio to the rich side. In other words, α causes the exhaust air-fuel ratio to fall within the above-mentioned window, thereby allowing the three-way catalyst to function efficiently. However, when the clamp condition is satisfied (when the engine is cold, when the fuel is fully increased, when the sensor output does not fall within the specified value, etc.), the air-fuel ratio feedback control is stopped (α is set to 1).

Ts is a voltage correction amount introduced to compensate for the response delay of the injection valve 36.

Here, to further explain the well-known air-fuel ratio feedback control using FIG.
If the exhaust air-fuel ratio changes from rich to lean, S/L increases.
It has the characteristic of becoming smaller across the . In response to these sensor outputs, the control unit 35
According to the proportional-integral operation executed by the CPU, the above α is given in the form of a periodic waveform as shown in the upper part of FIG. That is, when the air-fuel ratio is reversed from lean to rich, it is changed stepwise to the lean side by a proportional amount (P _L ), and then gradually changed to the lean side by an integral amount (I _L ). Similarly, when the air-fuel ratio changes from rich to lean, it is changed to the rich side by a proportional amount (P _R ) in steps.
Thereafter, it is gradually changed to the rich side by the integral (I _R ). Note that the integrals (I _L , I _R ) are integrated at fixed time intervals or in synchronization with the crank angle.

Now, when the change in the exhaust air-fuel ratio at the mounting position of the oxygen sensor 25 is shown in the lower part of FIG. 3, the sensor output actually changes with a predetermined response delay with respect to this air-fuel ratio change. In other words, the T _DR shown in the figure (the elapsed time from the time when the exhaust air-fuel ratio reverses from lean to rich until the sensor output crosses the slice level) is the response delay time when the air-fuel ratio reverses from lean to rich, and the T DR shown in the diagram Conversely, _DL is the response delay time when the air-fuel ratio is reversed. This response delay is inherent to oxygen sensors even when they are normal.
In the case of a normal oxygen sensor, this response delay time falls within a predetermined range centered on a predetermined reference time ( _TR ).

However, if this response delay time becomes longer (or shorter) outside of a predetermined range due to changes over time, the efficiency of purifying exhaust components by the three-way catalyst decreases. For example, when T _DR exceeds the above reference time (T _R ), the average air-fuel ratio shifts to the rich side, causing HC and CO to increase, and vice versa.
When T _DR becomes shorter than T _R , the average air-fuel ratio shifts to the lean side, resulting in an increase in NOx. Similarly, when T _DL becomes shorter than the above reference time (T _R ), the average air-fuel ratio shifts to the rich side, and when it becomes longer than the reference time, it shifts to the lean side.

Therefore, the response delay time of the oxygen sensor is
Measure T _DR or T _DL and use this as the reference time (T _R ) above.
If you can determine whether the oxygen sensor has become longer or shorter by comparing _{it with}
To determine this, it is necessary to measure the point at which the exhaust air-fuel ratio reverses and the point at which the sensor output crosses S/L.

However, changes in the sensor output near S/L are inherently rapid due to sensor characteristics, so while it is possible to measure accurately when the sensor output crosses S/L, the exhaust air-fuel ratio changes from lean to lean. The point of reversal to richness or vice versa cannot be precisely determined. This is because the exhaust air-fuel ratio changes in any way depending on how the air-fuel ratio feedback correction coefficient (α) is applied, but the response of α is suppressed to some extent in order to balance the stability of the air-fuel ratio control. This is because the calculated value is adopted. In other words, as shown in the upper part of Figure 3, α changes only gradually (generally the period of change is 1 to 2 Hz, about 0.5 Hz during idling, etc.), so the change in exhaust air-fuel ratio also follows a gradual sine curve. When does the exhaust air-fuel ratio change to the stoichiometric air-fuel ratio (λ=1 in the figure)?
This makes it difficult to clearly distinguish whether the object has crossed the

Therefore, in the present invention, α is set so that the change in the exhaust air-fuel ratio is rapid near the point where the exhaust air-fuel ratio reverses from lean to rich or vice versa. This is the fourth
To explain this with a diagram, this figure corresponds to Figure 3. Immediately after the sensor output crosses S/L, the proportional components (P _L ^* , P _R
^* ) is applied only for a short time (T1).
This is because the proportional component that forms part of α is the value that determines the responsiveness of the control, so if fuel correction is performed using a large proportional component, the exhaust air-fuel ratio change that is under the control of α will change. This is because it becomes sharp near the point of reversal. Therefore, these proportional components (P _L ^* , P _R
^* ), the change in the exhaust air-fuel ratio becomes a substantially rectangular wave as shown in the lower part of FIG. 4, and it is possible to clearly see when the exhaust air-fuel ratio crosses the stoichiometric air-fuel ratio.

In addition, in normal air-fuel ratio control, the proportional component and the integral component are connected continuously as shown in the upper part of Figure 3, whereas in this example, after the proportional component (P _L ^* , P _R ^* ), Then the integrals to be applied (I _L ^* and I _R ^* shown)
are connected discontinuously to the proportional components (P _L ^* , P _R ^* ) to prevent the integral from becoming too large. This is the proportional component (P _L , P _R ) as shown in the upper part of Figure 3.
When the integrals (I _L and I _R ) are connected continuously, the exhaust air-fuel ratio can be changed rapidly simply by increasing the proportional components (P _R , P _L ). This is because if the proportional component and the integral component are connected continuously even in such a case, the fluctuation in the air-fuel ratio becomes too large and there is a risk that problems with drivability such as surge may occur. Note that the integrals (I _L ^* , I _R ^* ) in this embodiment that are applied after T1 have a smoother slope than during normal air-fuel ratio control shown in the upper part of FIG.

Further, although the change in the exhaust air-fuel ratio shown in the lower part of FIG. 4 must be at the mounting position of the oxygen sensor, it is not possible to directly measure the point in time when the exhaust air-fuel ratio reverses at this mounting position. However, the above proportional components (P _L ^* , P _R ^* )
The change in air-fuel ratio due to fuel correction is transmitted by the gas burned in the cylinder, so the time required for the combustion gas to flow from the exhaust port 21 to the oxygen sensor installation position is the exhaust transport delay time ( Tdt), the timing at which combustion gas is discharged from the cylinder (the start of the exhaust stroke) and the point at which the exhaust air-fuel ratio is reversed at the oxygen sensor installation position are different by this exhaust transport delay time (Tdt). It turns out.

Here, since the start time of the exhaust stroke is determined in advance, it can be determined based on the signal from the crank angle sensor 31, and the exhaust transport delay time (Tdt) can be estimated if the intake air amount and engine speed at that time are known. can do.

Figure 5 shows a program for determining the response deterioration of the oxygen sensor. This is a program for determining the response deterioration of the oxygen sensor. This program detects the amount of fuel corrected by the above proportion (P _L ^* , P _R ^* ) from the injector 36 immediately after the air-fuel ratio is reversed. Executed after being sprayed. Here, this program is given to the CPU in the control unit 35, and the control unit 35 performs the functions of means 8 and 9 in FIG. In the control unit 35, the functions of means 2 to 5 and 7 in FIG. 1 are also performed by separate programs not shown.

In P1, the elapsed time from the start of the exhaust stroke until the sensor output crosses the slice level (S/L) is measured by counting clock pulses, and the elapsed time measurement value (Td) is stored in the memory.
Store in RAM. Here, the elapsed time measurement value (Td) is the sum of the above-mentioned exhaust gas transport delay time (Tdt) and the response delay time (T _D ) of the sensor itself.

In addition, in a multi-cylinder engine, it is necessary to know which section of the periodic changes in the exhaust air-fuel ratio (or periodic changes in the sensor output) is due to the gas discharged from which cylinder, so the exhaust air-fuel ratio may be reversed. The detected cylinder is determined based on the signal from the crank angle sensor 31, and for the determined cylinder, fuel correction is performed according to the above proportional amount (P _L ^* , P _R ^* ), and then the elapsed time measurement value ( Td).

In P ₂ , the above exhaust transport delay time (Tdt) is calculated. If the engine speed and intake air amount are constant, Tdt is determined by the length and inner diameter of the exhaust pipe up to the oxygen sensor. Furthermore, if the length and inner diameter of the exhaust pipe are constant, Tdt becomes shorter as the engine speed increases or as the amount of intake air increases. Therefore, the value of Tdt when the engine speed and intake air amount are varied is determined through experiments, this is made into a table, stored in the memory ROM, and the engine speed and intake air amount at that time are calculated. If you perform a table pull-up according to the amount of intake air,
Tdt is required.

In _P3 , the response delay time T _D (=Td - Tdt) of the oxygen sensor is determined by subtracting this exhaust gas transport delay time (Tdt) from the elapsed time measurement value (Td) described above. Note that T _D takes different values when the air-fuel ratio is reversed from rich to lean and vice versa, so it is stored separately.
For example, as shown in FIG. 3, the case where the air-fuel ratio is reversed from lean to lean may be distinguished as T _DR , and the case where the air-fuel ratio is reversed is designated as T _DL . The difference between the two cases also applies to _TR , which will be described later.

In P ₄ , find the average value of the response delay time (T _D ) of the oxygen sensor. For example, methods for determining the average value include a simple average and a moving average, and statistical processing may also be used. The reason why we use the average value is because if it is a one-time value, it may happen to be a large value, and even in that case, if we were to make a judgment on response deterioration, which will be described later, we might make a mistake in judgment. It is.

In P ₅ , the average value of T _D is set at a predetermined reference time (T _R ).
If the absolute value of the difference (T _D −T _R ) is greater than a predetermined value (for example, β), it is determined that the oxygen sensor has degraded response. For example, if the air-fuel ratio is reversed from lean to rich, let T _D and T _R in that case be T _DR and T _RR , respectively.
If T _DR −T _RR |≧β, it is determined that response deterioration has occurred in the oxygen sensor. Although the determined results are not shown in the program, it may be possible to display them on a warning lamp installed in the driver's seat, or to provide the information to a self-diagnosis function.

Here, only one oxygen sensor is provided to determine whether or not response deterioration has occurred in the oxygen sensor, and therefore, it is not necessary to provide two oxygen sensors, so an increase in cost can be avoided.

The reference time (T _R ) varies depending on the engine operating conditions, so the T shown in FIG. _R
The contents of are stored in the ROM of the memory, and _TR is read out according to Ne and Tp at that time. This makes it possible to accurately determine response deterioration under any operating conditions.

FIG. 7 shows another embodiment, which is a program that adjusts the normal air-fuel ratio feedback control incorporated in the three-way catalyst system and the response deterioration determination of the oxygen sensor shown in FIG. _P6
Then, it is determined whether the operating conditions are convenient for determining the response deterioration of the oxygen sensor. As for this operating condition, it is better to be in a region where surges and the like are not a concern (relatively low rotation, not low load), and in a steady state. Further, when this operating condition is satisfied, it is not necessary to always perform the process, but it may be performed at a predetermined timing.

If it is determined in P ₆ that this operating condition is met, the process proceeds to P ₉ and the calculation of α (sudden change air-fuel ratio control) shown in the upper part of Fig. 4 is performed.
1 ₀ allows judgment of response deterioration. _P6
If the operating conditions are not met, the process proceeds to _P7 , where the calculation of α (normal air-fuel ratio feedback control) shown in the upper part of FIG. 3 is performed, and the determination of response deterioration is prohibited at _P8 .

In this way, by limiting the operating conditions under which the determination of response deterioration is made, a determination that would cause a sudden change in the air-fuel ratio is made only occasionally, so that the negative impact on drivability can be minimized.

In the example, the sensor output is S/ from the beginning of the exhaust stroke.
Although the description has been made using the measured value (Td) of the elapsed time until crossing L, it is also possible to measure the crank angle that elapses during that time. However, in this case,
The reference value to be compared with the elapsed crank angle measurement value is also in the unit of crank angle.

In addition, in the embodiment, the response deterioration of the oxygen sensor is determined by comparing the response delay time (T _D ) and the reference time (T _R ), and the feedback correction amount (proportional or integral) is determined according to the difference. It is possible to maintain the average air-fuel ratio at the stoichiometric air-fuel ratio by adjusting the following.

(Effects of the invention) This invention, while providing only one air-fuel ratio sensor, performs fuel correction by specially increasing the proportional component that acts immediately after the sensor output crosses the slice level. The elapsed time or elapsed crank angle from when the burned gas is exhausted from the cylinder until the sensor output crosses the slice level is measured by fuel correction based on minutes, and by comparing this measured value with a predetermined reference value, Since it is configured to determine whether or not response deterioration has occurred in the sensor, it is possible to accurately detect response deterioration of the air-fuel ratio sensor while suppressing increase in cost.

[Brief explanation of the drawing]

Fig. 1 is a complaint correspondence diagram of this invention, Fig. 2 is a system diagram of a control system of one embodiment when this invention is applied to a four-cylinder engine, and Fig. 3 is a diagram of the air-fuel ratio correction coefficient in a three-way catalyst system. FIG. 4 is a waveform diagram showing the change characteristics of the air-fuel ratio correction coefficient in the above embodiment. FIG. 5 is a flow chart for explaining the control operation of the control unit of this embodiment. is the reference time in this example
The characteristic diagram of T _R , FIG. 7, is a flowchart for explaining the control operation of another embodiment of this invention. 1...Air-fuel ratio sensor, 2...Cross-crossing determination means,
3... Proportional component calculation means, 4... Air-fuel ratio feedback correction amount calculation means, 5... Fuel injection amount determining means, 7... Proportional component increasing means, 8... Measuring means, 9
...Response deterioration determination means, 21...Exhaust port, 2
2...Exhaust passage, 24...Catalytic converter, 25
... Oxygen sensor (air-fuel ratio sensor), 26 ... Intake port, 27 ... Throttle valve, 29 ... Air flow meter, 31 ... Crank angle sensor, 3
5...Control unit, 36...Fuel injection valve.

Claims (1)

[Scope of utility model registration request] A sensor that outputs an output according to the air-fuel ratio in the exhaust,
A means for determining whether the sensor output crosses a slice level corresponding to the stoichiometric air-fuel ratio, a means for calculating a proportional amount for changing the air-fuel ratio in steps when this is determined, and a means for calculating the proportional amount for changing the air-fuel ratio in steps. An air-fuel ratio control system for an engine, comprising means for calculating a feedback correction amount of an air-fuel ratio using the correction amount, and means for correcting a basic injection amount according to operating conditions using this correction amount to determine a fuel injection amount to be supplied to a cylinder. In the device, there is provided a means for making the proportional portion particularly large, and a fuel correction based on the large proportional portion to calculate the elapsed time or elapsed crank angle from when the burned gas is exhausted from the cylinder until the sensor output crosses the slice level. An air-fuel ratio control device for an engine, comprising: means for measuring; and means for determining whether response deterioration has occurred in the sensor by comparing the measured value with a predetermined reference value.