JP2630371B2 - Air-fuel ratio feedback control method for an internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio feedback control method for an internal combustion engine, and more particularly, to an engine load and an engine load as a learning value of a feedback correction coefficient applied to the control. The present invention relates to a control method for appropriately calculating according to an engine temperature.

(Prior Art) Conventionally, as an air-fuel ratio feedback control method for an internal combustion engine, when the engine is operated in an air-fuel ratio feedback control operation region, the air-fuel ratio changes according to the output of an exhaust gas concentration detector arranged in an exhaust system of the engine. An average value of a coefficient (hereinafter referred to as a “feedback correction coefficient”) is calculated as a learning value for each of a plurality of operating regions in the air-fuel ratio feedback control operating region, and the calculated average value is used for the engine. There is known an apparatus in which an air-fuel ratio of a supplied air-fuel mixture is appropriately controlled.

Further, in such a control method, in order to prevent the average value from becoming abnormal at extremely low and high temperatures, the calculation of the average value is performed when the intake air temperature is within a predetermined range. Are also known (see, for example,
-60231).

(Problems to be Solved by the Invention) However, in order to prevent the vaporized fuel generated in the fuel tank from being released into the atmosphere, the internal combustion engine is supplied with the vaporized fuel during operation of the engine. When the conventional control method is applied to this type of internal combustion engine, the average value of the feedback correction coefficient cannot be calculated to be an appropriate value in each of the plurality of operating regions, and therefore, the appropriate air-fuel ratio However, there is a problem that it is not possible to perform an appropriate control.

That is, in general, when the engine temperature, for example, the intake air temperature is high, the temperature of the fuel supply system including the intake pipe is high, so that the fuel returned to the fuel tank via the pressure regulator (hereinafter referred to as "pressure regulating valve") is also high. When the temperature becomes high and the temperature in the fuel tank rises, multiple vaporized fuels are generated in the fuel tank. In this case, in the internal combustion engine of the type described above, the large amount of vaporized fuel is supplied to the engine together with the original supply fuel from a fuel supply device such as a fuel injection valve, so that the overall supply fuel charge increases, The supply air-fuel ratio is also enriched, and accordingly, the feedback correction coefficient and the average value calculated based on the coefficient fluctuate toward the lean side to correct the enrichment of the supply air-fuel ratio. The degree of the change of the average value to the lean side depends on the load state of the engine. For example, in the idling operation state where the intake air amount is small, the change amount of the supply air-fuel ratio is large, so that even if the engine temperature is relatively low, Whereas
In an operation state other than the idle operation state in which the intake air amount is large, the change amount of the supplied air-fuel ratio is small, so that even if the engine temperature is relatively high, it tends to be low.

However, in the conventional control method, the predetermined range of the intake air temperature for which the average value is to be calculated is uniformly set for the plurality of operation regions, and therefore, the average value according to the load state of the engine as described above. Since it is not possible to cope with the difference in the degree of the value fluctuation, it is not possible to calculate the appropriate average value in each of the plurality of operation regions, and thus it is not possible to perform appropriate control of the air-fuel ratio. In particular, when the average value calculated at the time of the feedback control is applied as an initial value of the feedback correction coefficient at the start of the next feedback control, the engine temperature at the time of the previous feedback control is high, and the next feedback control is performed. When the engine temperature at the time of control is low, the initial value of the feedback correction coefficient is set to a value on the lean side, so that the supplied air-fuel ratio becomes significantly lean, and when the degree of leaning is high, engine stall is caused. I will.

The present invention has been made in order to solve the above-described problems of the related art, and appropriately sets a calculation area of a learning value of a feedback correction coefficient in accordance with an engine load and an engine temperature, thereby reducing an air-fuel ratio supplied to an engine. It is an object of the present invention to provide an air-fuel ratio feedback control method for an internal combustion engine that can be appropriately controlled.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an internal combustion engine that operates according to an output of an exhaust gas concentration detector disposed in an exhaust system of the engine during operation in an air-fuel ratio feedback control operation region. In the air-fuel ratio feedback control method for an internal combustion engine, the average value of the coefficient that changes by the calculation is calculated as a learning value, and the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled using at least the average value. Calculating an average value of the coefficient for each of a plurality of operation regions in the air-fuel ratio feedback control operation region, and stopping calculation of the average value of the coefficient when the engine temperature is equal to or higher than a predetermined temperature corresponding to the operation region. It is something to do.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an overall configuration diagram of a fuel supply control device to which the control method of the present invention is applied. Reference numeral 1 denotes, for example, a four-cylinder internal combustion engine, and an intake pipe 2 is connected to the engine 1. An air cleaner 10 is provided on the upstream side, and a throttle valve 3 is provided on the way. A throttle valve opening sensor (hereinafter referred to as “θ _TH sensor”) 4 is connected to the throttle valve 3, converts the valve opening of the throttle valve 3 into an electric signal, and outputs the electric signal to an electronic control unit (hereinafter “ECU”) 5. Is to be sent.

A fuel injection valve 6 is provided in the intake pipe 2 between the engine 1 and the throttle valve 3. The fuel injection valve 6 is connected to the intake pipe 2
Are provided for each cylinder slightly upstream of an intake valve (not shown) .Each injection valve is connected to a fuel tank 23 via a pipeline 20, a fuel filter 21 and a fuel pump 22, and the ECU 5
The valve opening time of the fuel injection, that is, the supply amount of the liquid fuel is controlled by a signal from the ECU 5.

Reference numeral 24 denotes a pressure regulating valve, and the inside of the casing of the pressure regulating valve 24 is defined by a diaphragm 24b as a negative pressure chamber 24c and a fuel chamber 24d. The negative pressure chamber 24c is provided in the intake pipe 2 through a negative pressure passage 25. The fuel chamber 24d is connected to the pipe line 20 via a pipe line 26 and to the fuel tank 23 via a return pipe 27, while being connected to the downstream side of the throttle valve 3. A valve element 24a is fixed to the diaphragm 24b. The valve body 24a
Is formed at the open end of the return passage 27 by the balance between the urging force of a spring 24e interposed in the negative pressure chamber 24c and the fuel pressure in the fuel chamber 24d of the absolute pressure in the intake pipe 2. Open and close the valve seat 24f. That is, the pressure regulating valve 24 controls the fuel pressure supplied to the fuel injection valve 6 and the absolute pressure in the intake pipe 2 by opening and closing the valve body 24 a in accordance with the fuel pressure and adjusting the amount of recirculated fuel to the fuel tank 23. The difference from the pressure is kept at a predetermined constant value.

The upper space in the fuel tank 23 is connected to the vicinity of the throttle valve 3 of the intake pipe 2 via a vaporized fuel passage 28, and a two-way valve 29 is arranged in the middle of the vaporized fuel passage 28. When the pressure in the upper space in the fuel tank 23, that is, the vaporized fuel pressure reaches a set pressure due to a rise in the temperature in the fuel tank 23 or the like, the 2-way valve 29 opens its positive pressure valve 29a, and the vaporized fuel is released. While the fuel is supplied to the intake pipe 2 side, when the fuel tank 23 is cooled and the negative pressure in the upper space in the fuel tank 23 exceeds the set pressure, the negative pressure valve 29b is opened, and from the intake pipe 2 side, The vaporized fuel is returned to the fuel tank 23. Further, the vaporized fuel is supplied to the engine 1 through the intake pipe 2 by a negative pressure generated in the intake pipe 2 as the engine 1 operates.

On the other hand, the intake pipe absolute pressure sensor on the downstream side of the negative pressure passage 25 via a conduit 7 (hereinafter referred to as "P _BA sensor") 8 is provided in the intake pipe 2, an electrical signal by the P _BA sensor 8 The absolute pressure signal converted to is sent to the ECU 5.

Of P _BA intake air temperature sensor is downstream of the sensor 8 (hereinafter referred to as "T _A sensor") 9 is provided an intake pipe 2, an engine 1
The temperature of the intake air sucked into the ECU is detected, and the detected value signal is supplied to the ECU 5.

An engine cooling water temperature sensor (hereinafter, referred to as a “Tw sensor”) 15 is provided on the main body of the engine 1. The Tw sensor 15 is composed of a thermistor or the like, and is inserted into an engine cylinder peripheral wall filled with cooling water to detect the detected water temperature. Supply signal to ECU5.

Engine speed sensor (hereinafter referred to as “Ne sensor”) 16
Is mounted around the camshaft or the crankshaft (not shown) of the engine 1, and a TDC signal, that is, 1 at a predetermined crank angle position every 180 ° rotation of the crankshaft of the engine 1.
This pulse (hereinafter referred to as “TDC signal pulse”)
Is supplied to ECU5.

A three-way catalyst 18 is disposed in an exhaust pipe 17 of the engine 1 and performs a purifying action of HC, CO, and NOx components in exhaust gas. Exhaust pipe 1
An O ₂ sensor 19 is inserted as an exhaust gas concentration detector upstream of the three-way catalyst 18 of 7, and detects the oxygen concentration in the exhaust gas, and supplies a detection signal to the ECU 5.

The ECU 5 shapes input signal waveforms from various sensors, corrects a voltage level to a predetermined level, and converts an analog signal value to a digital signal value. The input circuit 5a has a function of a central processing unit (hereinafter referred to as a “CPU”). 5b), a storage means 5c for storing various calculation programs executed by the CPU 5b, calculation results, and the like, an output circuit 5d for supplying a drive signal to the fuel injection valve 6, and the like.

The CPU 5b determines various engine operating states such as a feedback control operating area and an open loop control operating area based on the above-mentioned various parameter parameters, and according to the engine operating state, based on the following equation (1). The fuel injection time _TOUT of the fuel injection valve 6 synchronized with the TDC signal pulse is calculated.

T _OUT = Ti × K _O2 × K ₁ + K ₂ (1) Here, Ti indicates the basic fuel injection time, and is stored in the above-mentioned storage means 5c according to, for example, the intake pipe absolute pressure _PBA and the engine speed Ne. It is calculated from the displayed Ti map (not shown). K _O2 is a feedback correction coefficient calculated by a K _O2 calculation subroutine (FIG. 2) described later. Also, K ₁ and
K ₂ is a correction coefficient and correction variable computed according to various engine parameter signals, set to the required value, such as fuel consumption characteristic according to engine operating conditions, the optimization of various properties such as the engine acceleration characteristics can be achieved Is done.

The CPU 5b outputs a drive signal for opening the fuel injection valve 6 based on the fuel injection time T _OUT obtained as described above in an output circuit.
The fuel is supplied to the fuel injection valve 6 via 5d.

FIG. 2 shows a flowchart of the sub-rating for calculating the feedback correction coefficient K _O2 . This program is executed in synchronization with each generation of a TDC signal pulse.

First, the absolute pressure P _{BA in the} intake pipe, the engine speed Ne, the engine coolant temperature Tw, and the throttle valve opening θ _TH are read (step 201). Next, it is determined whether or not the previous control was the feedback control (step 202). If the answer is negative (No), it is determined whether or not the last time was the holding mode of the correction coefficient _KO2 (step 203). . If the answer is affirmative (Yes), the routine proceeds to step 204, where the correction coefficient K _O2 is calculated by well-known integral control, and the program ends.

If the answer to the step 203 is negative (No), it is determined whether or not this time is in an idling operation region (hereinafter, referred to as an "idle region") (step 205). The determination as to whether or not the engine is in the idle range is performed by determining whether or not the engine speed Ne and the intake pipe absolute pressure _PBA are respectively smaller than predetermined values. If the answer is affirmative (Yes), the initial value of the correction coefficient K _O2 is set to the average value K _REF0 of the idle region K _O2 calculated as described later in the idle region (step 206), and then Proceeding to step 204, the integral control is executed, and this program ends.

If the answer to step 205 is negative (No), that is, if the current time is not in the idle range, the initial value of the correction coefficient _KO2 is set in a feedback control operation range other than the idle range (hereinafter referred to as “off-idle range”). set to the product K _REF1 × C _R between the calculated off average enrichment predetermined value larger consisting of K _REF1 and the value 1.0 of the idling region for the K _O2 C _R (e.g. 1.1) as (step 207), then After executing the step 204, the program ends.

When the answer to step 202 is affirmative (Yes), that is, when the previous control was the feedback control, it is determined whether or not the previous control was in the idle range (step 208). If this answer is affirmative (Yes), it is determined whether or not this time is in the idle range (step 209). If the answer is negative (No), that is, if the current loop is the first loop immediately after the transition from the idle region to the off-idle region, the process proceeds to step 207, where the initial value of the correction coefficient K _O2 is set, and then the step Execute 204 to end this program.

If the answer to step 209 is affirmative (Yes), it is determined whether or not the throttle valve 3 was fully closed in the previous loop (step 210). When the answer is affirmative (Yes), it is determined whether or not the throttle valve 3 is in the fully closed state in the current loop (step 211). If the answer is negative (No), that is, if the previous loop and the current loop are both in the idle range and the current loop is the first loop immediately after the throttle valve 3 has shifted from the fully closed state to the open state, for example, a down counter _Is set to a predetermined time t _FBT (for example, 4 seconds), which is started (step 212), and then the initial value of the correction coefficient K _O2 is calculated as described later. The average value of K _O2 is set to K _REF2 (Step 213), and Step 20 is performed.
Execute 4 to end this program.

If the answer in step 208 is negative (No), that is, if the previous time was in the off-idle range, or if the answer in step 210 was negative (No) or the answer in step 211 was affirmative (Ye
s), that is, if the current loop is not the first loop immediately after the throttle valve 3 has shifted from the fully closed state to the open state, is the count value t _FBT of the t _FBT timer started in step 212 equal to the value 0? It is determined whether or not it is (step 214). When this answer is affirmative (Yes), that is, when the predetermined time t _FBT has elapsed after the throttle valve 3 has shifted from the fully closed state to the open state, it is determined whether or not the flag F _THCH is equal to the value 1 (step). 215). The flag F _THCH is set to 1 only when the engine 1 is in the feedback control operation region and the throttle valve opening θ _TH is shifted from a state smaller than a predetermined value θ _THCH (for example, 2 degrees) to a larger state. In other cases, the value is cleared to zero.

If the answer to step 215 is affirmative (Yes), that is, F _THCH = 1
Is satisfied, the routine proceeds to the step 207, where the initial value of the correction coefficient K _O2 is set, and then the step 204 is executed to terminate the present program.

On the other hand, if the answer to step 215 is negative (No), that is, F _THCH
= When 0 is satisfied, the output level of the O ₂ sensor 19 is determined whether or not inverted (Step 216). When the answer is negative (No), the step 204 is executed,
When the result is affirmative (Yes), the correction coefficient K is obtained by the well-known proportional control.
_O2 is calculated (step 217), and this program ends.

As described above, the average value K _REF of K _O2 is calculated using the value of the correction coefficient K _O2 calculated by the subroutine of FIG. 2, and stored in the memory. The average value K _REF is calculated according to the following equation (2) based on the K _REF calculation _{salve routine} (FIG. 3) described later according to the feedback control operation region to which the loop corresponds, and K _REF0 , K _REF1 or K _{REF1 for} each region. K _REF2 is calculated.

K _REF n = K _O2 · (C _REF n / A) + K _REF n ′ · (A−C _REF n) / A (2) As described later, the average values K _REF0 and K _REF1 are proportional term operations. immediately after, the average value K _REF2 is generation of each TDC signal pulse, is calculated when the intake air temperature T _a is at a respective predetermined temperature range.

Here, A is a constant, C _REF n is a variable that is experimentally set for each region and is set to an appropriate value among 1 to A,
K _REF n ′ is the K _REF n value obtained up to the previous time in the operation region to which the current loop applies.

Since the ratio of the K _O2 value to the K _REF n ′ value changes depending on the value of the variable C _REF n, this C _REF n value is changed according to the specifications of the target air-fuel ratio feedback control device, engine, etc. By setting an appropriate value in the range of A, an optimum K _REF n (K _REF0 , K _REF1 or K _REF2 ) can be obtained for each region.

Figure 3 is a flow chart of Saburechin for calculating the average value K _REF, this subroutine is executed in synchronism with generation of each TDC signal pulse.

First, it is determined whether or not the count value t _FBT of the t _FBT timer, the operation of which is controlled in the subroutine of FIG. 2, is equal to 0 (step 301). This answer is negative (No)
, The variable C _REF is set to the third value C _REF2 for calculating the average value K _REF2 (step 302), and then the intake air temperature discrimination value T _AKARSP applied in step 315 described later is set to K _REF2.
After setting the third value T _AKARSP2 for calculation (for example, 50 ° C.) (step 303), the K _REF ′ value is set to the K _REF2 obtained up to the previous time.
A value is set (step 304), and the process proceeds to step 315 described later.

As described above, the average value K _REF2 is obtained when the count value t _FBT of the t _FBT timer is not equal to 0, that is, after the engine 1 is in the idle range and the throttle valve 3 shifts from the fully closed state to the open state. Is calculated until the predetermined time t _FBT elapses, and the third value T _AKARSP2 is applied as the intake air temperature determination value T _{AKARSP at} this time.

When the answer to step 301 is affirmative (Yes), that is, when t _FBT = 0 holds, the proportional term (P term) is used in the current loop.
Is determined, that is, whether the proportional control is executed (step 305). When the answer is negative (No), that is, when the proportional control is not executed in the current loop, the present program is terminated as it is, and the calculation of the average value K _REF is not performed.

On the other hand, when the answer to the step 305 is affirmative (Yes), that is, when the proportional control is being executed in the current loop, it is determined whether or not the engine 1 is in an idle range (step 306). When the answer to step 306 is affirmative (Yes), the first value C for the average value K _REF0 calculating the variable C _{REF REF0}
(Step 307), and then the intake air temperature determination value T
_{After setting AKARSP} to a first value T _AKARSP0 (for example, 40 ° C.) for calculating K _{REF0 that is smaller} than the third value T _AKARSP2 (step 308), the K _REF ′ value is obtained by the previously obtained K _REF ′ value. _REF0 value is set (step 309). Next, the correction coefficient K _O2 is
Whether it is larger than K _O2REFH (for example, 1.2) (step 31)
0), it is determined whether or not it is smaller than a lower limit value K _O2REFL (for example, 0.8) (step 311), and either one of the answers in step 310 or 311 is affirmative (Yes), that is, K _O2 > K
_{When either O2REFH} or K _O2 <K _O2REFL is established, the program is terminated as it is, and the calculation of the average value K _REF is stopped. On the other hand, the answer in steps 310 and 311 is both negative (No), that is, K _{When O2REFL} ≦ K _O2 ≦ K _O2REFH is satisfied, the process proceeds to step 315 or later described later.

That is, the average value K _REF0 is _calculated when the engine 1 is in the idling region and the proportional control is being performed, and when the correction coefficient K _O2 is within the predetermined range. the first value T _AKARSP0 is applied as _AKARSP.

If the answer to step 306 is negative (No), the variable C _REF is set to the second value C _REF1 for calculating the average value K _REF1 (step 312), and then the intake air temperature determination value T _AKARSP is _set to:
After setting the second value T _AKARSP1 (for example, 50 ° C.) for calculating K _{REF1 larger} than the first value T _AKARSP0 (step 31)
3) The K _REF 'value is set to the K _REF1 value obtained up to the previous time (step 314), and the process proceeds to step 315 described later.

That is, the average value K _REF1 is calculated when the engine 1 is in the off-idle range and the proportional control is being performed, and the second value T _AKARSP1 is applied as the intake air temperature determination value T _{AKARSP at} this time. You.

In step 315, the intake air temperature T _A is increased in steps 303 and 308.
Alternatively, it is determined whether the intake air temperature is greater than the intake air temperature determination value T _AKARSP set in 313. This answer is affirmative (Yes), that is, T _A > T
_{When AKARSP} is established, this program is terminated as it is, the calculation of the average value K _REF is stopped, while a negative (No),
That is, when T _A ≦ T _AKARSP is satisfied, the _routine proceeds to step 316, where the variable C set in step 302, 307 or 312 is set.
_REF and set in steps 304, 309 or 314
The average value K _REF is calculated by applying the value of K _REF ′ to the above equation (2), and the program ends.

As described above, when the intake air temperature T _A is higher than the intake air temperature determination value T _AKARSP , the calculation of the average value K _REF is stopped, and
The intake air temperature determination value T _AKARSP is set to a lower temperature when the engine 1 is in the idle range than in the off-idle range. As described above, in the idle range, the average value is obtained by the supply of vaporized fuel when the engine temperature is high.
Since the K _REF tends to fluctuate, by reducing the calculation area of the average K _REF to a lower temperature as described above, it is possible to prevent the fluctuation of the average K _{REF to} the lean side when the engine is at a high temperature. it can. On the other hand, in the variation is relatively small off the idling region of the average value K _REF, by enlarging the calculated area of the average value K _REF higher temperature side, a wider range of the K _REF value at the engine temperature range to an appropriate value Can be calculated. Therefore, the average value K _REF can be properly calculated in each operation region of the engine, and the air-fuel ratio supplied to the engine 1 can be appropriately controlled.

(Effects of the Invention) As described in detail above, the present invention has the following effects.

In the air-fuel ratio feedback control method for an internal combustion engine, an engine temperature is detected, and an average value of the coefficient is calculated as a learning value of a feedback correction coefficient of the air-fuel ratio for each of a plurality of operation regions in an air-fuel ratio feedback control operation region. Since the calculation of the average value of the coefficient is stopped during the operation at or above the predetermined temperature according to the operation region, the calculation region of the average value can be appropriately set with respect to the engine temperature in each operation region. Since the average value can be calculated to an appropriate value, the air-fuel ratio supplied to the engine can be appropriately controlled.

Also, by setting the predetermined temperature to be smaller as the engine is in the low load region, the calculation region of the average value of the low load region in which the average value of the coefficient is apt to fluctuate at a high load of the engine is shifted to a lower temperature side. Since it can be reduced, the air-fuel ratio supplied to the engine can be more appropriately controlled.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a fuel supply control device for implementing the control method of the present invention, and FIG. 2 is a feedback correction coefficient.
FIG. 3 is a flowchart showing a subroutine for calculating K _O2 , and FIG. 3 is a flowchart showing a subroutine for calculating an average value K _REF of K _O2 . 1 ...... internal combustion engine, 5 ...... electronic control unit (ECU), 9 ...... intake air temperature (T _A) sensor, 12 ...... exhaust pipe 1
9 ...... O ₂ sensor (exhaust gas concentration detector), the average value of K _O2 ...... feedback correction coefficient (coefficient), K _REF ...... K _O2.

Claims (2)

(57) [Claims] An average value of a coefficient that changes according to an output of an exhaust gas concentration detector disposed in an exhaust system of an internal combustion engine during an operation of an internal combustion engine in an air-fuel ratio feedback control operation region is calculated as a learning value. An air-fuel ratio feedback control method for an internal combustion engine that performs feedback control of an air-fuel ratio of an air-fuel mixture supplied to the engine using at least the average value, wherein an engine temperature is detected and a plurality of operation regions of the air-fuel ratio feedback control operation region are detected. An air-fuel ratio feedback control method for an internal combustion engine, wherein an average value of the coefficient is calculated and the calculation of the average value of the coefficient is stopped when the engine temperature is equal to or higher than a predetermined temperature corresponding to the operating region. 2. The method according to claim 1, wherein the predetermined temperature is set lower as the engine is in a low load range.