JPS62159749A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To satisfactorily hold the composition of exhaust gas over the entire operating range of an engine, by compensating the supply amount of fuel so that variations in air-fuel ration due to a fuel amount reserved in an intake-air system is compensated. CONSTITUTION:A fuel amount computing means 101 computes a fuel supply amount in accordance with the engine operating condition, and an equilibrium value computing means 102 computes an equilibrium value for a supply amount reserved in an engine air-intake system. Further, a subtracting means 103 computes the difference between the above-mentioned equilibrium value and a predicted value thereof, and an over- or under-amount computing means 104 computes an over- or under-fuel amount per cycle in accordance with the above-mentioned difference. Further, a predicted value computing means 105 computes a predicted value for the present equilibrium value in accordance with the over- or under-fuel amount and the predicted value for the previous equilibrium value. Then, a fuel amount compensating means 106 compensates the supply fuel amount in accordance with the over- or under-fuel amount, and a secondary air supply means 107 is allowed to feed secondary air when the compensated fuel amount becomes below a predetermined value.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more specifically, to improve air-fuel ratio control accuracy and exhaust emissions during transient operating conditions of a spark-ignition internal combustion engine. This invention relates to an improvement of an air-fuel ratio control device for the purpose of

(Prior art) In internal combustion engines for vehicles, it is important to appropriately control the amount of fuel supplied to the engine or the air-fuel ratio in order to improve the output performance and drivability that are originally required of the engine while meeting the demands for exhaust purification. The important issue is whether to do so. In particular, vehicle engines are used in a wide range of operating ranges, from low speeds and low loads to high speeds and high loads, so the suitability of air-fuel ratio control during transient operating conditions such as acceleration and deceleration has a significant impact on drivability and exhaust emissions. .

Therefore, based on an electronically controlled fuel injection system with excellent fuel metering accuracy, it is possible to obtain an appropriate air-fuel ratio in all driving conditions, including transient conditions, by increasing or decreasing the fuel injection amount during acceleration or deceleration. Control devices and control methods based on the above are being adopted in many vehicle engines. (For a known example of this type of control method, see, for example, Japanese Patent Laid-Open No. 144635/1983.) The reason why such transient correction is necessary is that the intake pipe and The phenomenon of adhering to the inner wall of the intake boat or the amount of fuel floating in the intake pipe without being inhaled (these adhering fuel and floating fuel in the intake system are collectively referred to as "intake system retained fuel") This is because it affects the air-fuel ratio or engine performance during transient periods. For example, if only an amount of fuel proportional to the intake air amount is supplied during acceleration, some of it will adhere to the intake system and cause a delay in the supply response, so the actual A problem arises in that the fuel ratio becomes too lean and acceleration performance deteriorates.

(Problem to be Solved by the Invention) By the way, the amount of fuel retained in the intake system changes depending on the operating condition of the engine, and is affected by the rotational speed, engine temperature, absolute pressure of the intake pipe, etc. However, in conventional air-fuel ratio control, the transient amount of fuel is approximately calculated using a correction method determined experimentally using the change in intake pipe pressure as a parameter, and then correction is made according to the engine cooling water temperature. The method is based on the method of optimizing the air-fuel ratio by applying However, it was inevitable that errors would occur except under specific operating conditions that correspond to the design point.

However, in order to solve this problem, it is necessary to detect and correct all the factors that affect the amount of fuel retained in the intake system in a transient state, but in this case, there are many criteria for determining whether correction is necessary or not. Therefore, many processes are required for matching work to satisfy the requirements for drivability and exhaust emissions.

In addition, especially in single-point injector type fuel injection devices and carburetors that supply fuel upstream of the intake pipe joint, the air-fuel mixture path from the fuel supply part to the engine cylinder is long, which increases the transient state. The influence of the retained fuel in the intake system on the air-fuel ratio becomes greater during deceleration, but when we focus on deceleration, the amount of retained fuel is so large that even if the fuel supply is cut off, a rich mixture may be generated. As a result, the problem tends to occur that a large amount of unburned components such as HC and CO are discharged.

The second invention was made by focusing on these problems.
By correcting the supplied fuel amount based on the equilibrium state amount of intake system retained fuel amount under steady conditions, the air-fuel ratio in transient conditions is appropriately controlled. The aim is to avoid deterioration of the exhaust gas composition by increasing the amount of air in the exhaust gas.

(Means for Solving the Problem) In order to achieve the above object, the present invention includes a fuel amount calculation means 101 that calculates the amount of fuel to be supplied according to the engine operating state, as shown in FIG. Equilibrium state that calculates the amount of retained fuel in the engine suction X system under steady operating conditions according to the operating state! A quantity calculating means 102 and this equilibrium state! ! ! A subtracting means 103 calculates the difference between the fuel amount and its predicted value, an excess/deficit amount calculating means 104 calculates the excess/deficit fuel amount per unit cycle based on the result of this subtraction, and Equilibrium! ! ! The current equilibrium state from the predicted value of the amount! ! !
A predicted value calculating means 105 calculates a predicted value of the fuel amount, a fuel amount correcting means 106 corrects the supplied fuel amount based on the excess/deficit fuel amount, A secondary air supply means 107 for supplying air to the intake system or exhaust system of the engine is provided.

Note that "operation" here means arithmetic processing in a broad sense, including not only mathematical operations but also logical operations and search processing in a processing system using a microcomputer, etc. For example, the above-mentioned calculation of the equilibrium state quantity This includes the process of finding the equilibrium state quantity by searching pre-tabled data as in the example described later, or the process of numerical calculation if the equilibrium state quantity can be converted into a function using predetermined operating state data as a variable. good.

(Function) As already mentioned, the amount of fuel retained in the intake system changes from moment to moment depending on the machine rotation status, so it is not easy to directly detect this and reflect it in air-fuel ratio control without delay in response. do not have. Further, since there are infinite ways in which the engine operating state can change, it is practically difficult to experimentally determine the transient amount of retained fuel in advance.

In contrast, the present invention is based on the amount of fuel retained in the intake system under steady-state operating conditions, which can be determined relatively easily experimentally as described above, and based on this and transient operating conditions determined by the above-described method. Since the amount of excess or deficiency of fuel or the basic air-fuel ratio correction amount is determined based on the difference between the predicted value and the predicted value, it is possible to calculate the amount of excess or deficiency of fuel or the basic air-fuel ratio correction amount. The air-fuel ratio can be controlled to an appropriate air-fuel ratio based on a information such as load, rotational speed, cooling water temperature, etc.

In addition, in this invention, when the corrected amount of supplied fuel becomes less than a predetermined value, secondary air is supplied to the intake system or exhaust system of the engine, so that unburned components due to over-enrichment of the air-fuel ratio during deceleration are removed. Emissions are definitely avoided. In addition, when supplying secondary air to the exhaust system, it is desirable to promote combustion of unburned components via a reactor, an oxidation catalyst device, or the like.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 2 shows the basic configuration of an embodiment of the present invention configured as an electronically controlled fuel injection device. In this case, processing related to air-fuel ratio control is performed by the CPU, RAMSROM, and
This is performed centrally by a control circuit 1 composed of a microcomputer consisting of 10 devices and the like. That is, the respective means 101 to 106 shown in FIG. 1 are integrated as the control circuit 1.

On the other hand, 2 is a spark, direct fire type internal combustion engine, 3 is its intake passage, 4 is an exhaust passage, 5 is a throttle body, 6 is an intake throttle valve, 7 is an electromagnetic fuel injection valve, 8 is an air cleaner, 9
is an oxidation catalyst (or three-way catalyst). The electromagnetic fuel injection valve 7 is supplied with fuel whose pressure is regulated to be constant through a fuel supply system (not shown), and whose pressure is proportional to the valve opening time ratio (duty ratio) of the drive signal from the control circuit 1. The amount of fuel is injected and supplied. That is, in this case, the control circuit 1
controls the air-fuel ratio by controlling the increase/decrease of the fuel injection amount via the electromagnetic fuel injection valve 7.

Further, 10 is a throttle sensor that detects the position and opening degree change of the throttle valve 6, and 11 is an air 70- that detects the intake flow rate.
12 is a rotation sensor that detects the rotational position and speed of the engine crankshaft, 13 is an oxygen sensor that detects the exhaust oxygen concentration, and 14 is a water temperature sensor that detects the engine cooling water temperature. The control circuit 1 determines the fuel injection amount or air-fuel ratio based on signals obtained from the engine neutral switch, clutch switch, etc.

The basic fuel injection amount control in the above configuration is well known. For example, a predetermined fuel injection amount is determined by table lookup based on the relationship between the intake air amount and rotational speed detected via the air 70-sensor 11 and rotation sensor 12. A basic fuel injection amount Tp (substantially the injection pulse width of the injection valve 7) for obtaining the fuel ratio is determined, and this is multiplied by a feedback correction coefficient α determined based on the output of the oxygen sensor 13 and a predetermined correction coefficient C0EF. , and a correction amount Ts, which is a supplementary signal of the dead time of the fuel injection valve 7 that is correlated with the battery voltage, is added to the electromagnetic fuel injection valve 7 as a drive signal TI (that is, TI=Tp-COEF-α+Ts).
. However, the C0EF is the sum of correction coefficients given according to engine conditions such as starting, warming up, and idling. Further, in the present invention, as will be described in detail later, in the process of the injection amount control, a transient correction is further performed based on the amount of fuel retained in the intake system, and furthermore, during deceleration, secondary air is supplied.

20 is a secondary air supply device corresponding to the secondary air supply means 107 in FIG. A secondary air passage 22 that is introduced into the port 21 and a negative pressure-driven (■ closed switching valve 23
Similarly, the secondary air control valve 24 and the switching valve 23
It consists of a solenoid valve 25 that is driven to open and close based on commands from the control circuit 1. The solenoid valve 25 selectively supplies the intake negative pressure obtained from the downstream part of the intake passage 3 and the atmospheric pressure to the on-off switching valve 23, and is normally in the atmospheric introduction position, but is not controlled. When the drive signal from circuit 1 is input, it switches to the negative pressure introduction position, and when the drive signal stops, it returns to the atmosphere introduction position again. The on-off switching valve 23 responds to pressure switching via the electromagnetic valve 25, and is elastically biased to close when atmospheric air is introduced, but when negative pressure is introduced, it opens only during that time and closes the secondary valve. Open air passage 22. On the other hand,
The secondary air control valve 24 has a reed valve configuration, and automatically opens when the pressure in the exhaust passage 4 becomes below atmospheric pressure due to the exhaust pulsation effect, and the atmosphere from the air cleaner 8 is transferred to the exhaust passage 4.
When the high-pressure component of the exhaust pulsating wave acts on the valve, the valve closes to prevent the exhaust from flowing back into the passage 22.

In addition, a secondary air supply system that utilizes the exhaust pulsation effect mentioned above! !
! 20 is suitable for 4-stroke engines with 4 cylinders or less, and for engines with 6 cylinders or more where noticeable exhaust pulsation does not occur, it is recommended to use an air pump etc. to actively supply secondary air. desirable.

Next, the details of control regarding air-fuel ratio correction and secondary air supply under the above configuration will be explained with reference to flowcharts. In addition,
tlS3 diagram and FIG. 4 correspond to the main routine of fuel injection control, and FIG. 5 and PIS6 diagram correspond to the subroutine for determining correction values, etc. used in the process.

In this control, as shown in FIG.
T p is determined (step 301) by the usual method of multiplying the ratio of these by a predetermined constant K using the intake air mqa and the rotational speed N as parameters, as described above.

Next, the equilibrium state amount MO of the intake system retained fuel amount under steady operating conditions, which is the basis for correction, is calculated (step 302).
. In this case, MO is a predetermined cooling water temperature range Two-Tw
4, the reserved fuel amounts MOO to MO4 are determined using the basic injection amount Tp and rotational speed N as parameters from a memory table formed in advance from actual measurements.

That is, a table is stored in the memory of the control circuit 1 that assigns MOn for each predetermined water temperature with the characteristics illustrated in FIG. 7, and as shown in FIG.
MO is determined by reading from the table using 1l, Tp, and N as parameters, and by interpolation calculation. The details include rwo-'w4 (however, Tu+O
> Tw4) For each reference temperature, five tables are prepared in which MOO to M04 are assigned using p and N as parameters, and the temperature range in which the actual water temperature TII+ detected via the water temperature sensor 14 is located. The MO number is finally determined by reading values individually from the table corresponding to the upper and lower reference temperatures that are the boundaries of T va and then performing complementary calculations using linear approximation from the difference between the actual temperature T va and the reference temperature.

Next, calculate the rate at which the predicted value M of the amount of fuel retained in the intake system at the present time approaches the MO obtained in this way per unit cycle (for example, every time the crank Tsumugi is busy). A coefficient DK representing the value is calculated (step 303). First, based on the fuel shortage amount DM per unit cycle and the water temperature T11 obtained in the previous process, DKTW is obtained by reading from the dimple formed in advance as shown in FIG. 8, and then N and Tp Based on
These are multiplied to give I)K (see Figure 6).

Furthermore, the calculation of multiplying the difference between MO and its predicted value M by this coefficient I) K - fuel surplus/deficiency per unit cycle fiD
Calculate M (step 304). The predicted value M at this time is the previous processing amount of M calculated in the process shown in FIG. Fuel equilibrium! ! ! Since the current surplus or shortage of fuel with respect to the amount is obtained, the surplus or shortage of fuel per unit cycle can be determined by multiplying this by the approach coefficient DK. In this case, the surplus/deficiency amount DM takes a positive value in the acceleration state to represent the fuel shortage amount, and takes a negative value to represent the fuel surplus amount in the deceleration state. This shows the process of calculating the final fuel injection amount TI by taking into account the predetermined excess or deficiency amount DM and controlling the secondary air supply. First, the previous basic injection amount Tp is added to the previous iDM and then New basic injection f
iTpf (step 401).

Next, the dead zone compensation numerator s of the injection valve 7 is added to the product obtained by multiplying this Tpf by the basic correction coefficient C0FF and the feedback correction coefficient a described above to obtain TI (step 402).
), inside the control circuit 1, the TI obtained in this way
The value of is written to the output register, and a drive signal according to TI is thereby supplied to the injection valve 7 via the I10 device, and fuel injection is performed (step 403).
. Finally, for the next process, a new M is set by adding the current shortage fiDM to the previous predicted value M (step 404). This is because DM is a quantity that represents the change in the amount of fuel retained in the intake system, whereas M gives the amount of retained fuel at the present moment, so M is successively corrected by the amount of DM. The prediction is made by setting M for the next correction as M+DM. Note that the processing of this m4 diagram is performed in synchronization with the fuel injection timing or crankshaft rotation, and, for example, TI is calculated every one revolution of the engine crank, and the predicted value M is updated each time.

On the other hand, after obtaining the corrected basic injection amount Tpf, it is compared with the reference value LEAi, and when Tpf<LEAi, the solenoid valve 25 of the secondary air supply device 20 is energized to supply secondary air ( Steps 405 and 406).

As a result, the unburned components in the exhaust gas discharged into the exhaust passage 4 are oxidized and further combusted in the catalyst 9, thereby sufficiently reducing the amount of harmful substances such as HC and CO that are finally discharged. be done. In other words, when deceleration is started under operating conditions with a large amount of fuel retained in the intake system, such as during high load, the value of DM in the negative direction becomes so large that Tpf decreases below zero, but this does not mean that the fuel supply is stopped. However, this means that a rich mixture is generated due to the retained fuel in the intake system, and as a result, even if the exhaust gas containing a large amount of unburned components is directly introduced into the catalyst 9, sufficient oxidation is not achieved. Since no reaction is obtained, secondary air is supplied to provide a sufficient oxidizing atmosphere.

In addition, in this case, by supplying secondary air even when the cooling water temperature Tw is at a low temperature below the predetermined reference value TwEAi, or when the injection system is in an operating state where the injection system is fully open and increasing, unburned components are likely to be generated. The exhaust gas purification process is performed under certain operating conditions, and the secondary air supply is stopped under other operating conditions (steps 407 to 4).
09). The above-mentioned full-open fuel increase state is determined based on the magnitude of TI, the signal from the throttle sensor 10, etc.

Figure 10 shows signal waveforms of changes in various amounts in the above control in response to changes in operating conditions, such as during acceleration, deceleration, and gear change during acceleration. The corrected fuel amount value DM obtained based on the equilibrium state amount MO of the system retained fuel amount under steady conditions and its predicted value M changes with characteristics that closely match the actual insufficient (or excess) fuel amount, This enables highly accurate air-fuel ratio control even during transient operation.

Incidentally, such air-fuel ratio correction can also be applied when performing recovery (injection restart) from fuel cut during deceleration or when starting the engine. Figure 11 shows an example of a correction process corresponding to air-fuel ratio correction during fuel cut recovery.
The difference from the diagram is that after calculating the basic injection amount Tp, it is determined whether or not there is a deceleration fuel cut condition, and if it is a fuel cut, zero or a predetermined value MFC that is much smaller than the normal MO is given as the MO value. It is in. Generally, when a fuel cut is performed, the retained fuel in the intake system is sucked into the engine, so during recovery, the actual amount of supplied fuel is insufficient due to the formation of new retained fuel by part of the re-injected fuel, and the engine runs out. The fuel ratio becomes diluted, but if we assign zero or a very small value to MO as described above,
As shown in Figure 12, the predicted value M changes to MO during fuel cut.
On the other hand, as MO increases rapidly due to recovery, the difference between MO and M increases, and eventually the amount of fuel must be increased. This avoids dilution of the air-fuel ratio. In addition, if the fuel cut time is short and recovery is started before M gets close enough to MO, as when acceleration is started in the middle of deceleration, the difference between MO and M at the time of recovery will not be that large. Therefore, the DM corresponding to the increased amount will also be smaller, but under these conditions, the peel coverage will be reduced.
Since the amount of reserved fuel consumed before entering the engine is small, it does not greatly affect the actual air-fuel ratio.

In addition, regarding the correction at the time of starting or after the start is completed, MO is set to zero by a separately prepared initialization routine when the ignition switch is turned on (not shown), and cranking is performed in the same way as during the recovery period described above. It is possible to automatically increase the amount according to the conditions during warm-up or warm-up.

However, at the time of a cold start, some of the supplied fuel may adhere to the cylinder wall, etc., resulting in a dilution of the actual air-fuel ratio, or may be exhausted without being combusted, so the fuel amount may be further increased to compensate for this. It is desirable to apply

In the above embodiment, the engine rotational speed N, basic injection amount Tp, cooling water temperature Tw, etc. were used as parameters to determine the equilibrium fi1Mo and coefficient DK of the intake system retained fuel amount under steady conditions. However, the same correction control can be performed even if, for example, the intake air amount, intake pipe pressure, and throttle valve opening are used instead of the basic injection ftTp, and the intake air temperature is used instead of the cooling water temperature. Is possible.

Further, the secondary air supply device 20 may be configured to supply secondary air to the intake passage 3 as shown by the imaginary line in FIG. Since the air-fuel mixture is diluted to optimize the air-fuel ratio, combustion itself is improved and the amount of unburned components is reduced.

(Effects of the Invention) As explained above, according to the present invention, the amount of retained fuel in the intake system that greatly affects the air-fuel ratio under transient operating conditions of the engine such as acceleration or deceleration is determined, and the air-fuel ratio is determined by this amount of retained fuel. Since the fuel supply amount is corrected to compensate for the variation, appropriate operating performance is ensured even under transient operating conditions. In addition, the amount of retained fuel in the intake system is not directly detected, but is predicted according to the engine operating state from the equilibrium state amount under steady operating conditions, which is determined experimentally in advance. The above-mentioned control can be performed without adding a detection means, and therefore there is no fear that the mechanical configuration of the fuel supply system will become unnecessarily complicated.

Furthermore, in this invention, secondary air is supplied to the engine's intake system or exhaust system in response to the overenrichment of the mixture during deceleration, which occurs under the influence of intake system retained fuel and is not corrected by fuel supply amount control. As a result, it is possible to reliably suppress the discharge of unburned components during deceleration in a single point fuel supply system in which a relatively large amount of fuel is retained in the intake system. In addition, the exhaust composition of the engine can be improved over the entire operating range.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the conceptual configuration of the present invention. FIG. 2 is a mechanical configuration diagram of an embodiment of the present invention. 3 to 6 are flowcharts showing the contents of the air-fuel ratio control corresponding to the embodiment described above. Figure 7 shows the equilibrium state of the amount of fuel retained in the intake system under steady conditions in the air-fuel ratio control. ! FIGS. 8 and 9 are characteristic diagrams showing an example of the contents of a table giving the i quantity MO, and FIGS. 8 and 9 are characteristic diagrams showing an example of the contents of a table giving the coefficient DK in the air-fuel ratio control. FIG. 10 is a waveform diagram showing, as a signal waveform, the relationship between changes in parameters or coefficients, etc. in the air-fuel ratio control and control characteristics of the fuel injection amount. Fig. 11 is a flowchart showing an example of the processing contents in which the air-fuel ratio control described above is applied from the deceleration fuel cut to the time of road recovery.
FIG. 2 is a waveform diagram corresponding to FIG. 101... Fuel amount calculation means, 102... Equilibrium state quantity calculation means, 103... Subtraction means, 104... Excess/deficiency amount calculation means, 105... Predicted value calculation means, 106...
・Fuel amount correction means, 107...Secondary air supply means, 1
... Control circuit, 2... Internal combustion engine, 3... Intake passage, 4... Exhaust passage, 5... Throttle body, 6...
...Intake throttle valve, 7...Electromagnetic fuel injection valve, 9...Oxidation catalyst, 10...Throntl sensor, 11...Air 70-sensor, 12...Rotation sensor, 13... Oxygen sensor, 14...Water temperature sensor, 20...Secondary air supply device, 22...Secondary air passage, 23...Open/close switching valve, 24...Secondary air control valve, 25... ·solenoid valve. Figure 4 Figure 5 Figure 10 Acceleration 5-rung key.

Claims (1)

[Claims] A fuel amount calculating means for calculating the amount of fuel to be supplied according to the engine operating state; an equilibrium state amount calculating means for calculating the equilibrium state amount of the engine intake system retained fuel amount under steady operating conditions according to the operating state; A subtraction means for calculating the difference between the state quantity and its predicted value, an excess/deficiency calculation means for calculating the excess/deficit fuel amount per unit cycle based on the subtraction result, and a previous equilibrium state between the excess/deficit fuel amount and the previous equilibrium state. a predicted value calculating means for calculating a predicted value of the current equilibrium state quantity from the predicted value of the quantity; a fuel quantity correcting means for correcting the supplied fuel quantity based on the excess/deficit fuel quantity; An air-fuel ratio control device for an internal combustion engine, comprising: secondary air supply means for supplying air to an intake system or an exhaust system of an engine when the air-fuel ratio becomes below a predetermined value.