JPS60243333A - Air-fuel ratio controlling method for fuel supply means used in internal-combustion engine - Google Patents

Abstract

PURPOSE:To improve the exhaust-gas purifying characteristics of an engine, by executing open-loop control of the fuel supply rate instead of feedback control of the same in case that the fuel supply rate is higher than a reference value, and varying the above reference value according to the temperature of cooling water. CONSTITUTION:In operation of an engine 4, judgement is made at first by a control circuit 16 whether activation of an O2-sensor 14 is completed. In case that the judgement is YES, judgement is made whether the temperature TW of cooling water detected by a water-temperature sensor 12 is higher than a feedback control starting temperature TW01. In case of TW>=TW01, a reference value Tr corresponding to the temperature TW is searched from a map. Here, the above reference value Tr is set at either of two prescribed values Tr1, Tr2 by using a prescribed water temperature TW02 (>TW01) as a threshold value. Then, judgement is made whether the calculated fuel injection period TOUT is greater than said reference value Tr. In case of TOUT>Tr, an injector 15 is controlled by way of open-loop control instead of feedback control.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control method for a fuel supply system for an internal combustion engine.

In order to provide appropriate fuel supply to the internal combustion engine, the basic supply amount is calculated based on basic engine parameters such as intake pipe pressure at a period synchronized with the engine speed, and the basic supply amount is calculated based on basic engine parameters such as intake pipe pressure, and incidental engine parameters such as engine cooling water temperature are calculated. Alternatively, the fuel supply amount is calculated by increasing or decreasing the basic supply amount based on transient changes in the engine, and fuel is supplied to the engine by a fuel supply device such as an injector for a time corresponding to the fuel supply amount. There is a device.

In such a fuel supply device, when a three-way catalyst is installed in the exhaust system for exhaust purification, the three-way catalyst is most effective when the air-fuel ratio of the supplied mixture is around the stoichiometric air-fuel ratio (for example, 14°7). Works effectively. Therefore, as one of the engine parameters, the oxygen concentration in the engine exhaust is detected by an oxygen concentration sensor installed in the exhaust system, and the basic supply amount is corrected according to the output signal of the oxygen concentration sensor to adjust the air-fuel ratio of the supplied mixture. Generally, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio.

This air-fuel ratio feedback control is not performed all the time; when the engine is in a specific operating state, such as when the cooling water temperature is low or the engine is under high load, the feedback control is stopped and the output signal of the oxygen concentration sensor is stopped in order to improve the operating state. The air-fuel ratio is enriched by performing open-loop control unrelated to the fuel consumption.

In a fuel supply system equipped with such an air-fuel ratio control operation function, when the amount of fuel supplied exceeds a predetermined amount, it is determined that the load is high, and air-fuel ratio feedback control is stopped to perform open-loop control. The control method is based on JP-A-59-54.
It is disclosed in Publication No. 8.

On the other hand, in recent years, in order to improve exhaust purification efficiency, there has been a trend to lower the feedback control start temperature of the cooling water temperature for determining the start of air-fuel ratio feedback control after engine startup, and to widen the feedback range. However, in the above control method, even when the cooling water temperature is lower than the feedback control start temperature, if the fuel supply amount is smaller than the predetermined amount, the mixture at the stoichiometric air-fuel ratio is supplied to the engine by feedback control, so the engine operating state is changed. may become unstable. Therefore, if the above predetermined amount is set to a small value so that the engine operating condition is stable at low cooling water temperatures, the feedback control range will be narrowed, and at high cooling water temperatures, the feedback control range will be open within the fuel supply amount range where a sufficiently stable operating condition can be obtained with feedback control. Since the exhaust gas is enriched by loop control, there arises the problem that exhaust gas purification deteriorates.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an air-fuel ratio control method that improves exhaust purification performance by setting a feedback control region according to cooling water temperature.

The air-fuel ratio control method of the present invention determines whether the amount of fuel supplied to the engine is greater than a reference amount, and determines whether the amount of fuel supplied to the engine is M.
Air-fuel ratio feedback control is performed to correct the air-fuel ratio of the mixture supplied to the engine according to the oxygen concentration in the engine exhaust when the fuel supply amount is smaller than the standard amount, and when the fuel supply amount is larger than the standard amount, the mixture is mixed regardless of the oxygen concentration. This method performs air-fuel ratio oven loop control to correct the air-fuel ratio of air, and is characterized by changing the reference amount according to the engine cooling water temperature.

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4.

In the electronically controlled fuel injection supply system to which the air-fuel ratio control method according to the present invention is applied, as shown in FIG. It has become. A throttle valve 5 is provided in the intake passage 3, and the intake air opening of the engine 4 is changed depending on the opening degree of the throttle valve 5. The exhaust passage 8 of the engine 4 has a harmful component (C) in the exhaust gas.
o.

A three-way catalyst9 to promote the reduction of HC and NOx)
is provided.

On the other hand, numeral 10 is a throttle opening sensor, which is composed of, for example, a potentiometer, and generates an output voltage at a level corresponding to the opening of the throttle valve 5;
12 is a cooling water temperature sensor that generates an output voltage at a level corresponding to the cooling water temperature of the engine 4; 13 is a crankshaft of the engine 4; This is a crank angle sensor that generates a pulse signal according to the rotation of the crankshaft (not shown), and generates a pulse every time the crankshaft rotates, for example, 120 degrees. 14 is an oxygen concentration sensor that generates an output voltage at a level corresponding to the oxygen concentration in the exhaust gas;
The three-way catalyst 9 is provided upstream from the location where the three-way catalyst 9 is located. 1
Reference numeral 5 denotes an injector provided in the intake passage 3 near the intake valve (not shown) of the engine 4. ° Throttle temperature sensor 101, absolute pressure sensor 11, cooling water temperature sensor 12,
The output terminals of the crank angle sensor 13 and the oxygen concentration sensor 14 and the input terminal of the injector 15 are connected to a control circuit 16.

As shown in FIG. 2, the control circuit 16 includes a level correction circuit 21 that corrects the output levels of the throttle angle sensor 10, absolute pressure sensor 11, water temperature sensor 12, and oxygen concentration sensor 14, and An input signal switching circuit 22 that selectively outputs one of the sensor outputs, an A/D converter 23 that converts the analog signal output from the input signal switching circuit 22 into a digital signal, and an output of the crank angle sensor 13. a counter 25 that measures the time between pulses of the TDC signal output from the waveform shaping circuit 24, a drive circuit 26 that drives the injector 15, and a digital calculation operation according to the program. A CPU (central processing circuit) 27, a ROM 28 in which various processing programs are stored, and a RAM 2
It consists of 9. Input signal switching circuit 22, A/D converter 23, counter 25, drive circuit 26, CPU 27
, ROM 28 and RAM 29 are connected by an input/output bus 30. Further, a TDC signal is supplied from the waveform shaping circuit 24 to the CPU 27.

In such a configuration, the A/D converter 23 selectively provides information on the throttle valve opening, intake absolute pressure, cooling water temperature, and exhaust oxygen concentration, and the counter 25 provides count value information representing the reciprocal of the engine speed. are respectively supplied to the CPU 27 via an input/output bus 30. ROM28 has a CPU
27 calculation programs and various data are stored in advance, and the CPU 27 reads each of the above information according to this calculation program, and based on the information, synchronizes with the TDC signal and sends it to the engine 4 from the calculation formula described later. The fuel injection time To L of the injector 15 corresponding to the fuel supply amount
Compute IT. And the fuel injection time TOUT
The drive circuit 26 drives the injector 15 to supply fuel to the engine 4.

For example, in the basic mode after the engine starting period, the fuel injection time TOLJT is calculated from the following equation.

TOUT=T1×(KTwaKAsTIIKAFcφK
woTa'Ko 2 ・KL s ) - (1) Here, T1 is the basic injection time corresponding to the basic supply amount determined from the engine speed and intake absolute pressure, KTW is the cooling water temperature increase coefficient, and KAS is the The increase coefficient after startup, KAFC is the increase coefficient after fuel cut, KwOT is the enrichment coefficient when the throttle valve 6 is fully open, KO2 is the air-fuel ratio feedback correction coefficient, and KLS is the lean coefficient. Each of the fuel injection times T o IJ T is calculated in a subroutine of the basic mode calculation routine.

Next, the procedure of the air-fuel ratio control method according to the present invention executed by the control circuit 16 will be explained according to the operational flow diagram of FIG.

In this procedure, the control circuit 16 determines whether activation of the oxygen m degree sensor 14 is completed in synchronization with the nTi-th (this time) TDC signal (step 51).

This activation determination is performed, for example, as the oxygen concentration sensor 14 is warmed up in a lean atmosphere, and the output voltage VO2 of the oxygen concentration sensor 14 once rises to a predetermined voltage Vx or higher before a predetermined time t02, and then returns to the predetermined voltage ■× Since the output voltage VO2 of the oxygen concentration sensor 14 becomes smaller than the predetermined voltage vx, the determination is made by determining whether or not the predetermined time tx has further elapsed.

If it is determined that the activation of the oxygen concentration sensor 14 has not been completed, the air-fuel ratio control system is made into an open loop by setting the feedback correction coefficient 02 to approximately 1 (step 52).

When it is determined that the activation of the oxygen concentration sensor 14 is completed, the cooling water temperature Tw becomes the feedback control start temperature Two.
It is determined whether the value is greater than or equal to + (step 53). Tw
If <Two+, the process moves to step 52 and open loop control is performed.

On the other hand, if Tw≧Two+, a reference value 'lr corresponding to the cooling water temperature Tw is searched from the data map previously stored in the ROM 28 (step 54). As shown in FIG. 4, the reference value Tr is set to one of the first and second predetermined values Tr I and Tr 2 using the predetermined water temperature TWO2 (>Two+) as a threshold value. That is, if Tw≧Two2, the first predetermined value Tr1 is extracted from the data map and set as the reference value 1-r, and if Tw<Tw O2, the second predetermined value Tr2 is extracted from the data map and set as the reference value Tr. .

When the reference value Tr is set in this way, the control circuit 16
It is determined whether the fuel injection time To UT calculated in synchronization with the first (previous) TDC signal is greater than the reference value 1-r (step 55). If To U T > Tr, then
As the engine is in a high load state, the process moves to step 52 to perform open loop control. T.

If UT≦Tr, step 5 determines whether other operating conditions requiring open loop control are satisfied.
6). If the operating state requires open loop control such as fuel cut or idling, the process moves to step 52. On the other hand, if other operating conditions requiring open-loop control are not established, a feedback coefficient KO2 is calculated for feedback control (step 57).
.

Therefore, in the air-fuel ratio control method according to the present invention, the cooling water temperature Tw is equal to the feedback control amount 913 temperature Tw.
greater than o+ and smaller than the predetermined water temperature Two2 (Two
+ ≦Tw<Two2), it is determined in step 55 that To u T >Tr 2, and T o U
In the case of T > Tr, 2, the air-fuel ratio feedback control is stopped and the air-fuel ratio is enriched by open loop control. Further, when the cooling water temperature Tw is lower than the predetermined water temperature TwO2 (Tw≧Tw02'), it is determined in step 55 that Tour>Tr+, and TouT>
Tr+(7) determination is performed, and if TouT>Tr+, the air-fuel ratio feedback control is stopped and the air-fuel ratio is enriched by open loop control.

In addition, feedback control of the air-fuel ratio determines the air-fuel ratio based on information on the oxygen concentration in the exhaust gas so that the air-fuel ratio is always the stoichiometric air-fuel ratio, and when the air-fuel ratio is rich, it is moved in the lean direction, and when it is lean, it is moved in the rich direction. This is done by determining the feedback coefficient KO2 so that

In the embodiments described above, the reference value, that is, the reference amount, was changed stepwise according to the cooling water temperature, but it is clear that the reference amount may be changed continuously according to the cooling water temperature.

As described above, according to the air-fuel ratio control method of the present invention, when the amount of fuel supplied to the engine is larger than the reference amount, feedback control is created to perform open loop control and the reference amount is set to the cooling water temperature. Since the reference amount is changed accordingly, when the cooling water temperature is low, which is slightly higher than the feedback control start temperature, the reference amount is set smaller than when the cooling water temperature is high.

Therefore, conventionally, in a load range where a sufficiently stable operating state can be obtained with feedback control at high cooling water temperatures, but an unstable operating state with feedback control at low cooling water temperatures, the air-fuel ratio is enriched by A-pun loop control at low cooling water temperatures. This stabilizes the operating state, and when the cooling water temperature is high, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio, resulting in good exhaust purification performance.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an electronically controlled fuel injection supply device to which the air-fuel ratio control method according to the present invention is applied, FIG. 2 is a block diagram specifically showing the control circuit in the device of FIG. 1, and FIG. The figure is an operation flow diagram of a control circuit showing an embodiment of the present invention, and FIG. 4 is a reference value setting characteristic diagram. Explanation of symbols of main parts 2... Air cleaner 3... Intake path 5... Throttle valve 8
...Exhaust path 9 three-way catalyst 10...
Throttle opening sensor 11...Absolute pressure sensor 12...Cooling water temperature sensor 13...Crank angle sensor 14...Oxygen concentration sensor 15...・Injector applicant Honda Motor Co., Ltd. agent Patent attorney Motohiko Fujimura Figure 2 Figure 3 Figure 4 Tr ↑ ■------ TwO2Tw

Claims (2)

[Claims] (1) Determine whether the amount of fuel supplied to the engine in the fuel supply device for an internal combustion engine is greater than a reference amount, and determine whether the amount of fuel supplied to the engine is smaller than the reference amount according to the oxygen concentration in the engine exhaust. An air-fuel ratio oven loop that performs air-fuel ratio feedback control to correct the air-fuel ratio of the air-fuel mixture supplied to the engine, and corrects the air-fuel ratio of the air-fuel mixture regardless of the oxygen concentration when the fuel supply amount is greater than the reference amount. 1. An air-fuel ratio control method comprising: changing the reference amount according to engine cooling water temperature. (2) the fuel supply device is a fuel injection supply device;
2. The air-fuel ratio control method according to claim 1, further comprising determining whether the fuel injection time corresponding to the fuel supply device is longer than a reference value corresponding to the reference amount.