JPS63195349A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To increase the control speed in the cooling time, and to improve the controllability regardless of the attachment of fuel to the wall surface of an intake pipe, by setting the control speed responding to the engine temperature related to the warm-up condition, in the air-fuel ratio feedback control. CONSTITUTION:A control circuit 44 computes a basic fuel injection quantity depending on the rotation frequencies from crank angle sensors 46 and 48, and the detected value from a suction pipe pressure sensor 49, and carries out the feedback control of air-fuel ratio depending on the detected value of an O2 sensor 58, when the feedback control condition other than the acceleration, the deceleration, and the warm-up conditions are accomplished. The control circuit 44 improves the responsiveness depending on the detected value from a water temperature sensor 54, making the proportional constant and the integral constant in the air-fuel ratio feedback control system in large values, for example, in the warm-up condition when the water temperature is 50 deg.C or less.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides an air-fuel ratio control device suitable for internal combustion engines that performs air-fuel ratio feedback even in rich air-fuel mixture ranges such as when the engine is at low temperature or during acceleration operation. Regarding.

[Conventional technology]

As is well known, in an air-fuel ratio control device for an electronically controlled fuel injection internal combustion engine, etc., an air-fuel ratio sensor is installed in the exhaust pipe, and a feedback signal is formed in response to an air-fuel ratio signal from the air-fuel ratio sensor. is driving. Conventionally, air-fuel ratio feedback control has typically been limited to low-load operation after engine warm-up. This is because the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio when the engine is cold or accelerates, but ordinary air-fuel ratio sensors such as O2 sensors and lean sensors cannot detect the rich side region of the air-fuel ratio. However, recently, improvements have been made in air-fuel ratio sensors that detect up to the rich range of the air-fuel ratio, and with this type of air-fuel ratio sensor, it is possible to perform air-fuel ratio feedback control up to the rich range.

When performing air-fuel ratio feedback control up to the rich region,
Compared to the lean region, the feedback control speed, that is, the proportional constant (skip constant) and integral constant, which are feedback speed factors in the feedback signal, are changed in accordance with the target air-fuel ratio. In other words, in the lean region, increasing the proportional constant and integral constant increases the air-fuel ratio control width (
The amplitude of the air-fuel ratio control signal becomes large, and the air-fuel ratio may become so lean that it exceeds the misfire limit during the control process, which is undesirable from an operational performance standpoint, so the proportional constant and integral constant must be set small. On the other hand, in the rich region, if the proportionality constant or the integral constant is small, the control width of the air-fuel ratio becomes too small, making it impossible to follow changes in the air-fuel ratio, resulting in poor controllability of the air-fuel ratio. Therefore, it is common to reduce the proportionality constant and integral constant when the engine is lean, and to increase the proportionality constant and integral constant when the engine is rich. For example, JP-A-61-961
No. 52 switches between operation at the stoichiometric air-fuel ratio and operation leaner than the stoichiometric air-fuel ratio, but when operating at the stoichiometric air-fuel ratio, the proportional constant and integral constant are increased, and operation in a lean air-fuel ratio region is used. A system with smaller proportional constants and integral constants has been proposed, and this concept can also be adopted in systems that switch between operation on the richer side and leaner side of the stoichiometric air-fuel ratio.

[Problem that the invention seeks to solve]

However, simply changing the feedback speed factor, that is, the proportionality constant or the integral constant depending on whether the air-fuel ratio is rich or lean, may result in poor controllability when the engine is at a low temperature.

That is, when the engine temperature is low, fuel tends to adhere to the wall of the intake pipe, and when the engine is on the lean side, the air-fuel ratio control becomes poor, so most operating ranges will be richly controlled by the correction coefficient according to the water temperature. However, depending on the load and rotation speed, the engine may be controlled to the lean side even at low temperatures without causing misfire. In this case, if the proportionality constant and the integral constant are set small, fuel adhesion to the wall surface may deteriorate air-fuel ratio controllability and driveability.

An object of the present invention is to improve the drivability of an engine when it is cold.

[Means for solving problems]

In FIG. 1, the control device for an internal combustion engine of the present invention is installed in an intake system LA of an internal combustion engine 1, and includes a fuel supply means 2 for supplying a desired amount of fuel to the internal combustion engine, and an exhaust system IB of the internal combustion engine. an air-fuel ratio detecting means 3 that generates a signal according to the air-fuel ratio; and a feedback signal forming means that forms a feedback signal to the fuel supply means 2 so that the air-fuel ratio becomes a set value according to the air-fuel ratio signal. means 4, engine temperature detection means 5 for generating a signal according to a temperature factor of the internal combustion engine related to the warm-up condition, and feedback signal forming means 4.
and a feedback speed setting means 6 for variably setting the feedback control speed factor in the feedback signal formed by the temperature factor according to the temperature factor.

〔Example〕

In FIG. 2, 10 is a cylinder block, 12 is a piston, 14 is a connecting rod, 16 is a cylinder head, 18 is a combustion chamber, 20 is a spark plug, 22 is an intake valve,
24 is an intake boat, 26 is an exhaust valve, 28 is an exhaust boat,
29 is a distributor. The intake boat 24 is
It is connected to an air cleaner 36 via an intake pipe 30, a surge tank 32, and a throttle valve 34. A fuel injector 38 is installed in the intake pipe 30 close to the intake boat 24. Exhaust boat 28 is connected to catalytic converter 42 via exhaust manifold 40 . 43 is an ignition device;
It consists of an igniter 43a and an ignition coil 43b.

The control circuit 44 is configured as a microcomputer system, and includes fuel injection control, ignition timing control, EGR control,
It controls other engine operations. The control circuit 54 is a micro processing unit 1-7 (MPU
) 44a, memory 44b, human-powered boat 44c, output boat 44d, and a bus 44e that connects these elements.
It consists of

The input boat 44c is connected to each sensor and receives engine operating condition signals. An intake pipe pressure sensor 49 is connected to the surge tank 32, detects the intake pipe pressure downstream of the throttle valve 34, and can obtain a signal corresponding to the engine load. A crank angle sensor 46.4B is installed on the distributor 29. The first crank angle sensor 46 is installed opposite the magnet piece 50 on the distributor shaft 29a, and generates a pulse signal every 720 rotations of the crankshaft, that is, every cycle of the engine, and serves as a reference signal. The second crank angle sensor 48 is installed opposite the magnet piece 52 on the distributor shaft 29a, and generates a signal every 30' of the crankshaft, which serves as a trigger signal for fuel injection control and ignition timing control. The water temperature sensor 54 detects the temperature of the cooling water in the cooling water jacket 10a of the cylinder block IO. The throttle sensor 56 is connected to the throttle valve 3
4, and the opening position of the throttle valve 34 can be known. An oxygen concentration sensor 58 is provided in the exhaust manifold 40 and generates a signal responsive to the oxygen concentration of the exhaust gas. The oxygen concentration signal from this oxygen concentration sensor 58 is for air-fuel ratio feedback control, and is of a type that can detect up to the rich region of the air-fuel ratio.

The MPU 44a executes arithmetic processing according to the program and data stored in the memory 44b, and obtains a fuel injection signal and other engine control signals, such as an ignition signal.

These signals are set to output port 44d. The output boat 44d is connected to the fuel injector 38 and the igniter 43a of the ignition device, and fuel injection control and ignition control are performed.

Next, the operation of the control circuit 44 will be explained with reference to a flow chart regarding fuel injection control. Since ignition control and other controls are not directly related to this invention, their explanation will be omitted. FIG. 3 shows a fuel injection routine, which is executed at a predetermined crank angle timing before the fuel injection start timing, during the crank angle interrupt routine started by the 30'' CA signal from the crank angle sensor 52. In step 70, the basic fuel injection time Tp is calculated from the intake pipe pressure PM and the engine speed NE.Here, the basic fuel injection amount refers to the air-fuel ratio at the intake pipe negative pressure and engine speed. This is the fuel injection time determined from experiments using the stoichiometric air-fuel ratio.

As is well known, the memory 44b has a data map of the basic fuel injection time Tp for each combination of intake pipe pressure and engine speed, and an interpolation calculation of 'rp is performed from the actually measured intake pipe pressure PM and engine speed. In step 72, the final fuel injection Tau is calculated as T a u = T p
Calculated by XFAF XKTAFX cx + β. As described later, FAF is a feedback correction coefficient, KTAF is an air-fuel ratio correction coefficient for correcting the fuel injection amount so that the air-fuel ratio becomes larger or smaller than the stoichiometric air-fuel ratio, and α and β are not directly related to this invention. A general term for correction coefficients and correction amounts whose explanations are omitted.

In step 74, the time TA calculated in step 72 is
Data is set in the output boat 44d so that fuel injection is performed only by XI. Since this method is well known, its explanation will be omitted.

FIG. 4 shows a correction coefficient calculation routine. This routine is executed at regular time intervals, such as 4 msec. From step 80 to step 86, the air-fuel ratio correction coefficient KTAF is calculated.

In step 80, intake pipe negative pressure PM and engine speed N
A correction coefficient KTAFO is calculated from E.

This correction coefficient is corrected so that more fuel is injected than the stoichiometric air-fuel ratio in the high load/high rotation range.
AFO>1.0), the air-fuel ratio is corrected so that less fuel is injected than the stoichiometric air-fuel ratio in the low load/low rotation range (KTAFO<1.0). The memory 44b stores TAFO data maps for combinations of intake pipe pressure and engine speed.
The MPU 44a performs an interpolation calculation of the KTAFOO value with respect to the measured intake pipe pressure PM and rotational speed NE.

Step 82 shows a routine for calculating the water temperature correction coefficient KTIIW. This correction coefficient is used to correct the air-fuel ratio so that more fuel is injected than the stoichiometric air-fuel ratio when the engine temperature is low. This compensates for an appropriate air-fuel ratio even if fuel adheres to the wall surface of the intake pipe due to poor atomization at low temperatures.

The relationship between KTHW and water temperature T)IW (7) is as shown in Figure 6, for example, and in this example, at 50@C, it has a value of 1.0 (no correction), and at temperatures below that, it changes depending on the temperature. Rich correction is now performed. Water temperature correction coefficient KTI
In relation to KTAFO, I- is set so that even if the final air-fuel ratio becomes lean during cold operation, it will not become leaner than the misfire limit. The data map of water temperature and KTH- created from FIG. 6 is stored in the memory 44b, and interpolation calculations are performed based on the actually measured water temperature THW. Steer 7”
84 "i' C Air-fuel ratio correction coefficient KTAF = KT
AFOx KTHW. That is, the target air-fuel ratio is corrected to be rich or lean with respect to the stoichiometric air-fuel ratio by the value of KTAF. In step 86, the air-fuel ratio correction coefficient KT
A target lean sensor output value IR is calculated from the AF. That is, the value of the air-fuel ratio correction coefficient KTAP corresponds to the value of the target air-fuel ratio after the stoichiometric air-fuel ratio is corrected to 7 inches or lean. There is a one-to-one correspondence between the lean sensor output value and the corrected target air-fuel ratio (see FIG. 7), and this is calculated from the map stored in the memory 44b.

In step 88 and subsequent steps, a feedback correction coefficient is calculated. In step 88, it is determined whether the internal combustion engine is under air/fuel ratio feedback control conditions. The system of the present invention provides feedback even in areas where normal systems do not provide feedback, such as at low temperatures or during accelerated driving (target air-fuel ratio is on the rich side), but when the fuel is cut or when the air-fuel ratio sensor 58 is inactive. Feedback control is not performed. If the non-feedbank condition is met, the process proceeds to step 90, where the feedback correction coefficient FAF is set to 1.

If the feedback condition is satisfied, step 92
In step 86, it is determined whether the actual output value LNSR of the air-fuel ratio sensor 58 is larger than the target value IR calculated in step 86. When LNSR>I R, it is recognized that the actual air-fuel ratio is leaner than the target air-fuel ratio, and step 9
The process proceeds to step 4, where it is determined whether flag XL=1. In the initial state when the actual air-fuel ratio is on the lean side compared to the target air-fuel ratio, XL=0, so the process goes to step 96, where XL=1, and then the process goes to step 98, where the feedback correction coefficient FAF is incremented by R3. be done. This R3
is a proportionality constant in the feedback signal, and is also called a skip constant. Next, enter this routine and if LNSR > I R continues, step 9
4, the process proceeds to step 100, where the feedback correction coefficient FAF is incremented by Ki (<R3). This Ki is an integral constant in the feedback signal.

In step 92, when LNSR<IR, it is recognized that the actual air-fuel ratio is on the richer side than the target air-fuel ratio,
Proceeding to step 102, it is determined whether flag XL=0. In the initial state where the actual air-fuel ratio is leaner than the target air-fuel ratio, XL=1, so the process goes to step 104, where XL=O, and then the process goes to step 106, where the feedback correction coefficient FAF is adjusted by the proportional control amount. It is decremented by R3. Next, if this routine is entered and the state of LNSR<I R continues, the process proceeds from step 102 to step 108, where the feedback correction coefficient FAF is decremented by Ki, which is the integral term.

Figure 5 shows the integral term Ki, which is the control speed factor of the control signal in air-fuel ratio feedback control, and the proportional term (skip amount).
The calculation process of R3 is shown. Although this routine is shown as a separate diagram for ease of understanding, it can be used together with the routine in FIG. In step 120, it is determined whether the engine is in an idle state. If it is determined that the time is idling, the process proceeds to step 122, and an integral term k for idling is added to Ki and RS.
, proportional term r are respectively inserted. FIG. 8 shows the fluctuation range of the air-fuel ratio and the change in responsiveness with respect to the magnitude of the integral constant and the skip constant. k and s are determined so as to obtain optimal results when idle.

If it is not idling, the process advances to step 124 and the water temperature T
It is determined whether HW is smaller than a predetermined value of 50"C. This value of 50"C is the water temperature correction coefficient K T II W〉l
, corresponds to the upper limit value of 0 (Fig. 6), step 1
At step 26, it is determined whether the air-fuel ratio correction coefficient KTAF<1.0. THW≧50″′C and air-fuel ratio correction coefficient KT
When AFk l, Q, proceed to step 128 and Ki
, R3 has a value K (
<k), R(<r) are entered. T HW<50'
C(7) or even when THW≧50°C, KTAF<
1. If Q, proceed to step 130 and Ki.

R+ΔR is put into R3 and +Δ.

FIG. 9(A) schematically shows the change in air-fuel ratio over time at low temperatures or during rich-side control after warm-up.

When switching between the rich and the
The execution interval of the routine in the figure) per Ki= is expressed by +ΔK. On the other hand, FIG. 9 (b) schematically shows the temporal change in the air-fuel ratio during lean side control after warm-up. When switching between rich and lean, R3=R changes proportionally, and the subsequent integral change is proportional to time (5th
The execution interval of the routine shown in the figure is expressed by Ki=K. That is, according to the present invention, the proportional constant and the integral constant, which are the feedback control speed factors in the feedback control signal, are set to be large not only when the engine is rich but also when the engine is lean. Therefore, the control signal amplitude increases (see Figure 8).
. At low temperatures, normal proportional and integral constants may result in poor air-fuel ratio control due to fuel adhesion to the intake pipe wall. However, by setting large proportional and integral constants, the air-fuel ratio can be Controllability can be improved.

〔Effect of the invention〕

According to the present invention, controllability is improved regardless of fuel adhesion to the intake pipe wall by selecting a large control speed factor, that is, a proportionality constant or an integral constant or both, in the air-fuel ratio feedback signal when the engine is cold. be able to. Therefore, drivability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of this invention. FIG. 2 is a schematic diagram showing the entire configuration of an embodiment of the present invention. 3, 4 and 5 are flowcharts illustrating the operation of the control circuit. FIG. 6 is a graph explaining the setting of the water temperature correction coefficient. FIG. 7 is a graph explaining the relationship between the air-fuel ratio correction coefficient and the sensor output. FIG. 8 is a graph illustrating the relationship between the integral constant and proportional constant, responsiveness, and air-fuel ratio swing. FIG. 9 is a diagram schematically showing an air-fuel ratio control waveform. 30...Intake pipe 34...Throttle valve 44...Control circuit 46.48...Crank angle sensor 49...Intake pipe pressure sensor 54...Water temperature sensor 58...Air-fuel ratio sensor 1A. ...@Kihaya 18...H) Kihaya 2...Fuel supply means water temperature (THW) Fig. 6 Fig. 7 Integral constant → Large scap constant Fig. 8

Claims (1)

[Scope of Claims] An air-fuel ratio control device for an internal combustion engine that includes the following elements; a fuel supply means installed in the intake system of the internal combustion engine for supplying a desired amount of fuel to the internal combustion engine; an air-fuel ratio detecting means installed in the exhaust system and generating a signal according to the air-fuel ratio; a feedback signal forming means forming a feedback signal to the fuel supply means so that the air-fuel ratio becomes a set value according to the air-fuel ratio signal; , engine temperature detection means for generating a signal according to a temperature factor of the internal combustion engine related to the warm-up state, and variably setting a feedback control speed factor in the feedback signal formed by the feedback signal formation means according to the temperature factor. feedback speed setting means.