JPS61142344A - Method of controlling air-fuel ratio of internal combustion engine - Google Patents

Abstract

PURPOSE:To maintain a satisfactory operating performance of an engine, by determining a reference rotational speed which decreases as the selected gear ratio of a speed change unit decreases, in accordance with the selected shift position, and by controlling the air-fuel ratio to be lean when an actual rotational speed exceeds the reference rotational speed and upon low load operation of the engine. CONSTITUTION:Upon operation of an engine, in a control circuit 22 which receives signals from sensors 20, 34, 36, 40, 42, 48 for detecting various operating conditions, a reference rotational speed NR is searched in accordance with the present gear shift position. This reference rotational speed NR is determined such that the smaller the gear ratio, the smaller the speed NR becomes. The determined reference rotational speed NR is compared with the present actual engine rotational speed Ne. Further, if Ne>NR, when a lean mixture condition is establied, that is, the engine is in a low load but high rotational speed range in which the temperature of cooling water is below a predetermined value (about 75 deg.C), and the opening degree of a throttle valve is less than, for example, 30 deg.. A lean mixture compensating coefficient is set in accordance with the pressure of an intake pipe. Further, a reference injection time which is obtained by calculating the rotational speed of the engine and the pressure of the intake-air pipe, is compensated.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an air-fuel ratio control method for an internal combustion engine - a method for controlling the air-fuel ratio of an internal combustion engine -
Regarding ttu<->, in particular, feedback control for controlling the air-fuel ratio so that the engine is operated at the stoichiometric air-fuel ratio;
The present invention relates to an air-fuel ratio control method for an internal combustion engine, which performs feedforward control of the air-fuel ratio so that the engine is operated at a leaner side than the stoichiometric air-fuel ratio;

[Background of the invention]

In general, in automobile engines equipped with exhaust gas purification measures using three-way catalysts, in order to improve exhaust emissions, it is necessary to control the air-fuel ratio, which indicates the combustion state of the engine, to near the stoichiometric air-fuel ratio. Feedback control has conventionally been performed to bring the air-fuel ratio to the stoichiometric air-fuel ratio in accordance with the output of an Ot sensor that detects the air-fuel ratio based on the residual oxygen concentration in exhaust gas.

When the engine is operating under light load, the amount of nitrogen oxides emitted from the exhaust gas is small, so even if the air-fuel ratio is shifted to a leaner side than the stoichiometric air-fuel ratio, the exhaust emissions will not deteriorate much and fuel efficiency will improve. can.

Based on these points, there is a feedback control that controls the air-fuel ratio so that the engine is operated at the stoichiometric air-fuel ratio, and a lean control that controls the air-fuel ratio so that the engine is operated on the lean side of the stoichiometric air-fuel ratio. An internal combustion engine for an automobile has been proposed in which control is switched according to driving conditions, thereby improving fuel efficiency.

In conventionally proposed air-fuel ratio control, one of the conditions for lean control is to determine whether the engine speed Ne is equal to or higher than a predetermined reference speed NR. Then, if the engine rotational speed N is equal to or higher than the reference rotational speed NR, and other lean conditions are satisfied, lean control is executed.

[Problem that the invention seeks to solve]

However, regardless of the shift position, in other words, regardless of the gear ratio of the selected transmission, the reference rotation speed N
R is constant υ, and under certain operating conditions, such as low gear ratio, low load, and low rotation, surges tend to occur and drive performance is impaired.

[Means and actions for solving problems]

In order to solve the above-mentioned problems, the present invention detects the engine load, engine speed, and shift position, and depending on the detected shift position, selects a gear ratio of the selected transmission such as #1, which is small. A preset reference rotation speed is determined so that the engine rotation speed is higher than the reference rotation speed, and the air-fuel ratio is controlled for lean control at least when the detected engine rotation speed is greater than the reference rotation speed and the engine load is low.

〔Example〕

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

FIG. 2 shows an example of a gasoline engine to which the method of the present invention is applied.

A throttle valve 18 is provided in the intake passage 12, and an intake pressure sensor 20 provided in a surge tank 24 downstream of the throttle valve 18 is connected to a control circuit 22 via a signal line 11. Generates voltage according to intake pressure. The intake air temperature sensor 21 is provided in the intake passage 12 upstream of the throttle valve 18, is connected to the control circuit 22 via the signal line 12, and generates a voltage according to the intake air temperature.

Throttle valve 18 linked to an accelerator pedal (not shown)
The intake air whose flow rate is controlled by the surge tank 24 is
The air is then introduced into the combustion chamber 14 of each cylinder via the intake valve 25.

The fuel injection valve 26 is provided for each cylinder, and the signal line 1
The opening/closing is controlled in response to an electric drive pulse signal 8B supplied from the control circuit 22 via 5, and pressurized fuel sent from a fuel supply system (not shown) is fed into the intake passage 12 near the intake valve 25, i.e. Injects intermittently into the intake port. The exhaust gas after being combusted in the combustion chamber 14 is discharged into the atmosphere via the exhaust valve 28, the exhaust passage 16, and the three-way catalytic converter 50.

Crank angle sensors 54 and 56 are attached to the distributor 32 of the engine.
4.56 is signal line 14,! 5 to the control circuit 22. These sensors 54 and 56 output /4 pulse signals each time the crankshaft rotates 50 degrees and 720 degrees, and these base pulse signals s5 and s6 are sent to the control circuit via signal lines 14 and 15, respectively. 22.

Distributor 52 is connected to igniter 3,
The igniter 58 is connected to the control circuit 22 via the signal line 16.

Reference numeral 40 is a throttle sensor that is linked to the throttle valve 1 and outputs a signal S7 according to the opening degree of the throttle valve 18, and is connected to the control circuit 22 via the signal line 17. is a sensor that outputs a signal responsive to the oxygen concentration in the exhaust gas, that is, generates an output voltage that changes depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio. A three-way catalyst converter 42 is provided, and its output signal is connected to the control circuit 22 via the signal line 18. It simultaneously purifies the three harmful components of HC, Co, and NOx.

Further, reference numeral 44 is a water temperature sensor that detects the engine cooling water temperature and generates a voltage according to the temperature, and is attached to the cylinder block 46 and connected to the control circuit 22 via the signal line 19. It is connected. The code 4 is a shift position sensor that detects the shift lever position, and a signal line 110
It is connected to the control circuit 22 via.

As shown in FIG. 3, the control circuit 22 includes a central processing unit (cpσ) 22 a1 that controls various devices. Random access memory (RAM) in which the program is written - only memory (ROM) 22b1 Numerical values and flags in the calculation process are written in a predetermined area
22 (!, A/D converter (ADC) that converts analog input signals into digital signals) 22 (1, Input/output interface (Ilo) where various digital signals are input and various digital signals are output) 22e% Assist when the engine is stopped It is composed of a backup memory (Bσ-RAM) 22f that is supplied with power from a power source and holds memory, and a path line 22g to which each of these devices is connected.A !program, which will be described later, is written in advance in the ROM 22b.

Then, an intake pressure sensor 20, an intake temperature sensor 21.0 .
Sensor 42, throttle sensor 40 and water temperature sensor 44
is connected to the A/D converter 22 (l), and the voltage signals s1, s2, s5, s4, s7 from each sensor are connected to CP[
In response to instructions from 722a, the signals are sequentially converted into binary signals.

a4 every 50 degrees of crank angle from crank angle sensor 54
The pulse signal S5 and the pulse signal 86 for every 720 degrees of crank angle from the crank angle sensor 564- are respectively l102.
The signal is taken into the control circuit 22 via 2e. - A binary signal representing the engine speed is formed based on the pulse signal S5, and the pulse signals S5 and S6 work together to generate a request signal for fuel injection and pulse width calculation, and an interrupt for starting fuel injection. A signal, a cylinder discrimination signal, etc. are formed. Furthermore, the opening status of the throttle valve 18 is determined based on the throttle signal S7. From the engine 1022f, a fuel injection signal S8 and an ignition signal S9 formed by various calculations are output to the fuel injection valves 26&~26d1 and the igniter 58, respectively. A signal E+10 from the shift position sensor 48 is also input to the switch 1022e.

In the engine described above, fuel is injected according to the flowchart shown in FIG. Referring to Figure 4,
In step P1, the engine speed Ne calculated based on the crank angle signal S5 is read, and the intake pipe pressure PM calculated based on the intake pressure signal S1 is read.

In step P2, the basic injection time TP is determined from a predetermined map based on the rotational speed Ne and the intake pipe pressure PM, and in step P5, a correction coefficient calculation process is executed according to the engine operating conditions. In P4, the corrected injection time τ is determined. In this example, the feedback correction coefficient FAF used for feedback control, the lean correction coefficient PLIfiAN used for IJ-on control, and other correction coefficients Fα are calculated, and τ=TPXFAF'XFLFiAN
The injection time τ is determined from the formula of XFα.

In step P5, the corrected injection time i is corrected according to the battery voltage to obtain the final injection time FT, and if the injection timing is determined in step P6, an injection signal S8 is sent to the fuel injection valves 2Sa to 26d at the timing of step P7. Then, fuel is injected from the injection valve for a time corresponding to the final injection time.

Note that the correction coefficient Fα is determined depending on the water temperature, intake air temperature, and the like.

-FAF calculation- Next, an example of the calculation process of the feedback correction coefficient FAF will be described.

An example of the calculation process of the feedback correction coefficient FAF is shown in the fifth example.
In step P11 shown in the figure, it is determined whether a feedback condition is satisfied.

For example, the conditions for feedback control are satisfied when the engine is not in a starting state, is not in the process of increasing the amount after starting, the engine water temperature THW is 40° C. or higher, and is not in the process of increasing the amount of arm water. If the feedback condition is not satisfied, the correction coefficient F'AIF is set to 1.0 in step P15. If established,
In step P12, if the air-fuel ratio is determined to be rich based on the air-fuel ratio signal S5 from the 0° sensor 42, the correction coefficient FAF is decreased to reduce the fuel injection amount;
Conversely, if it is determined that the engine is lean, the correction coefficient FAF is increased so that the air-fuel ratio is controlled close to the stoichiometric air-fuel ratio.

-FLKAN Calculation- Next, an example of the calculation process of the lean correction coefficient FLEAM will be described. Referring to Figure 1, the hand Itf
In the iP21, the current shift position Hp is determined from the shift signal 810.
, and proceed to step P22. The reference rotation speed NR for each shift position P is predetermined in the ROM 22'', and the reference rotation speed NR is searched from the read shift position P.Here, as shown in FIG. , in other words, N.-N, depending on the gear ratio of the selected transmission.
Reference rotation up to aN R camera retate, No > N1
>”!>N8 >N, )N, the smaller the gear ratio is, the smaller the setting is.For example, the shift points for each of these are 1st gear → 2nd gear 15 km/h, 2nd gear → 5th gear 25 km/h.
-/h 13th speed → 4th speed 40kn+/h, 4th speed → 5th speed 45K
If it is Il/h, it is preferable to set it in advance according to those vehicle speeds2. Furthermore, setting the largest value at the neutral position means that lean control is performed unconditionally at the neutral position. This is to prohibit it. In other words, combustion is inherently unstable when idling, and there is a need to avoid combustion with a lean mixture, so conditions are set to prohibit lean control when the throttle valve is fully closed and in the neutral position. However, since the determination logic becomes complicated, in this embodiment, the logic is such that lean control is unconditionally prohibited at the neutral position.

Next, in step P25, it is determined whether the current engine speed Ne and the reference speed NR are large or small, and if Ne is NR, the process proceeds to step P26, in order to prohibit the lean control, the lean correction coefficient FLB! AN f #1. □ Let it be z. On the other hand, if Ne)NR, it is determined in step P24 whether or not other link conditions are satisfied. The lean control conditions are, for example, the following conditions.

(1) The engine is not being started (2) The engine is not being increased after starting or the output is being increased (31 Water temperature is 75°C or higher (4) Intake pipe pressure PM is 650 Hg or less (the engine load is low) (5) Speed change ΔB PD72sec<5 r/h(
6) Throttle opening is 50 degrees or less and not fully closed. If an affirmative determination is made in step P24, the process proceeds to step P25, where a lean correction coefficient FLEiAN is calculated from a predetermined graph as a function of intake pipe pressure FM, for example. This lean correction coefficient FLI! :AN is a value smaller than 1.0.

It goes without saying that the calculation procedures for the feedback control and the lean control are not limited to the above embodiments, and the various calculation procedures for the fuel injection time are not limited to the above embodiments. Furthermore, the intake air amount/engine speed can also be used as the engine load.

Furthermore, the method of the present invention is not limited to internal combustion engines having fuel injection valves, but can also be applied to internal combustion engines having electronic carburetors, and the present invention fi is applicable to all types of internal combustion engines having fuel injection valves. [Effects of the Invention] As explained above, according to the present invention, various reference rotation speeds are set depending on the shift position, and the engine rotation speed is determined by comparing the engine rotation speed and the reference rotation speed. Since lean control is executed only when the engine speed is large and other lean control conditions are satisfied at the same time, driving performance is improved compared to when determining lean conditions by setting a uniform reference rotation speed. .

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing an example of the calculation procedure for the curve correction coefficient FLIAN, Fig. 2 is a block diagram showing an example of the internal combustion engine to which the method of the present invention is applied, and Fig. 5 is a block diagram showing details of the control circuit thereof. 4 is a flowchart showing an example of a procedure for fuel injection, FIG. 5 is a flowchart showing an example of a procedure for calculating the feedback correction coefficient FAF, and FIG. 6 is a flowchart showing an example of a procedure for calculating the feedback correction coefficient FAF. FIG. 6 shows the relationship between shift position P and reference rotation speed NR. It is a line diagram. 1st... Throttle valve, 20... Intake pressure sensor,
22... Control circuit, 26... Fuel injection valve, 5
4.56...Crank angle sensor, 40...Throttle sensor, 42...0. Sensor, 48...Shift sensor. Figure 1 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] (1) Feedback control that detects the air-fuel ratio according to the components in the exhaust gas and maintains the air-fuel ratio near the stoichiometric air-fuel ratio based on the detected air-fuel ratio, and at least when a low load high rotation speed region is detected. In performing alternative lean control, which controls the air-fuel ratio to be leaner than the stoichiometric air-fuel ratio, the engine load, engine speed, and shift position are detected, and the selected shift is performed according to the detected shift position. A preset reference rotation speed is determined so that the smaller the gear ratio of the engine is, the smaller the engine rotation speed is, and the detected engine rotation speed is compared with the determined reference rotation speed, and at least the detected engine rotation speed is determined to be smaller than the reference rotation speed. 1. An air-fuel ratio control method for an internal combustion engine, characterized in that the air-fuel ratio is controlled for lean control when the engine load is lower than the rotational speed and the engine load is low.