JPH0291438A - Air-fuel ratio control during low load time of internal combustion engine of vehicle - Google Patents

Abstract

PURPOSE:To attain both proper fuel consumption characteristics and exhaust gas characteristics at the time of deceleration by varying the degree of leaning for air fuel mixture supplied, according to the lapse of time after the operation is changed into the low load operation range. CONSTITUTION:An electronic control unit ECU 5 receives the signals of a throt tle valve opening (theta TH), a sensor 4, an engine speed (Ne) sensor 11, an O2 sensor 15, a car speed sensor 16, a gear position sensor 17 and an air conditioner switch 18 and makes lean the ratio of air fuel mixture fed for an internal com bustion engine with the engine within the specified low load operation range. In this method for controlling air-fuel ratio during low load, the degree of leaning air-fuel mixture supplied is set according to the lapse of time after the operation is changed to the low load operation range. Namely, it is set higher than that when the lapse of time is long. Thus the leaning of air fuel ratio at the time of deceleration may be executed suitably so that proper fuel consumption characteristics and exhaust gas characteristics may be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an air-fuel ratio control method for making the air-fuel ratio of a mixture supplied to a vehicle internal combustion engine lean during low-load operation of the engine.

(Prior Art) Conventionally, a vehicle is at a low speed and the engine rotational speed is equal to or higher than a predetermined rotational speed. By controlling the air-fuel ratio A/F of the air-fuel mixture supplied to the engine to be leaner than the stoichiometric mixture ratio (A/F = 14.7) during low-load operating conditions of the internal combustion engine, Efforts are being made to improve fuel efficiency.

In addition, in the case of a vehicle equipped with an automatic transmission, when the throttle valve is closed for deceleration, the engine speed rapidly decreases and immediately reaches the predetermined rotation speed F, which makes it difficult to achieve a lean air-fuel ratio. In order to prevent this problem, an air-fuel ratio control method has been proposed in which the predetermined rotational speed is reduced to expand the range in which the air-fuel ratio is made lean (for example, the present invention). (Japanese Patent Application Laid-Open No. 62-189337 by the applicant).

(Problem to be Solved by the Invention) For example, immediately after closing the throttle valve from a normal constant speed driving state and transitioning to the low-load operating region, fuel adhering to the inner wall of the intake pipe is sucked into the combustion chamber and the air is emptied. In order to prevent the fuel ratio from becoming over-rich and improve the combustion efficiency of the air-fuel mixture in the combustion chamber after transitioning to the low-load operation range, the actual air-fuel ratio in the combustion chamber is set to approximately A/F = 22.5. It is desirable to do so.

However, if a lean state where A/F = 22.5 is continued for a long time (e.g. about 80 seconds), the fuel will not burn sufficiently in the combustion chamber and will burn inside the exhaust gas purification device installed in the exhaust system. This causes a problem in that the temperature of the catalyst in the purification device rises to 900° C. or higher and the durability of the catalyst decreases.

On the other hand, if a mixture with a very high degree of lean (extremely lean state) such as Δ/F = 29.4 is supplied, immediately after the transition to the low-load operation region, the amount of gas that adheres to the inner wall of the intake pipe will increase. As a result of the fuel being sucked into the combustion chamber, the actual air-fuel ratio within the combustion chamber is within the above-mentioned appropriate value (A/F=22.
4) However, after a long period of time, the amount of fuel adhering to the inner wall of the intake pipe that is drawn into the combustion chamber decreases, resulting in a problem of lower combustion efficiency and lower output characteristics.

In particular, in the case of vehicles equipped with automatic transmissions, the air-fuel ratio lean region is expanded as described above, and the lean state often continues for a long time. In the extremely lean state, the above-mentioned problems are more likely to occur.

The present invention was made to solve these problems, and aims to appropriately lean the air-fuel ratio during deceleration to achieve good fuel efficiency and exhaust gas characteristics.
Temperature J- of the exhaust gas purification catalyst installed in the exhaust system? r
An object of the present invention is to provide a low-load air-fuel ratio control method for a dual-purpose internal combustion engine, which can prevent , and improve the durability of a catalyst.

(Means for Solving the Problems) In order to achieve the second object, the present invention provides a vehicle that leans the air-fuel ratio of the air-fuel mixture supplied to the engine when the internal combustion engine is in a predetermined low-load operating region. In the low-load air-fuel ratio control method for an internal combustion engine, the degree of lean air-fuel ratio of the supplied air-fuel mixture is changed depending on the elapsed time after the transition to the low-load operating region.

Further, when the elapsed time after the transition to the low-load operation region is short, it is desirable to make the air-fuel ratio of the supplied air-fuel mixture leaner to a greater degree than when it is long.

(Example) Hereinafter, one embodiment of the present invention will be described in detail based on the accompanying 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. A throttle body 3 is provided in the middle of an intake pipe 2 of an engine 1, and a throttle valve 3' is provided inside the throttle body 3. are arranged. A throttle valve opening (θT11) sensor 4 is connected to the throttle valve 3', and outputs an electric signal according to the opening of the throttle valve 3 to the 71IT-control unit (hereinafter referred to as 'T'rECL).
5).

The fuel injection valve 6 is located between the engine 1 and the throttle valve 3 and is connected to the intake air. ′? Each injector is provided for each cylinder a little upstream of the intake valve (not shown) in No. 2, and each injector is connected to a fuel pump (not shown) and electrically connected to the ECU 3 to receive a signal from the r=cus. The valve opening time of fuel injection is controlled.

On the other hand, an intake pipe absolute pressure (1)B^) sensor 8 is provided immediately downstream of the throttle valve r3 via a pipe 7.
The absolute pressure signal converted into an electrical signal by the absolute pressure sensor 8 is supplied to the ECtJ5.

Further, an intake air temperature ('I'^) sensor 9 is installed downstream thereof, which detects the intake air temperature 'I' A and outputs a corresponding electrical signal to be supplied to the ECU 3.

Engine water temperature installed in the main body of engine l (1'w)
The sensor 10 is composed of a thermistor or the like, detects the engine water temperature (cooling water temperature) 'I'w, outputs a corresponding temperature signal, and supplies it to the ECU 3. The engine rotation speed (Ne) sensor II and the cylinder discrimination (CY) sensor 12 are the engine 1
around the camshaft or crankshaft (not shown).
I'm being kicked. The engine rotation speed sensor 11 is the engine l
A pulse (hereinafter referred to as r=I'DC signal pulse J) is output at a predetermined crank angle position every 180 degree rotation of the crankshaft, and the cylinder discrimination sensor 12 outputs a signal pulse at a predetermined crank angle position of a specific cylinder. These signal pulses are supplied to the ECU 3.

The three-way catalyst 14 is disposed in the exhaust pipe 13 of the engine I, and purifies components such as IIc, Go, and NOx in the exhaust gas. The 02 sensor 15 as an exhaust gas concentration detector is installed on the upstream side of the three-way catalyst 14 in the exhaust pipe 13.
The oxygen concentration in the exhaust gas is detected and a signal corresponding to the detected value is output and supplied to the ECU 3.

The ECU 3 further includes a vehicle speed sensor 1 that detects the speed of the vehicle.
6. A gear position sensor 17 for detecting gear position and a near conditioner switch 18 are connected, and detection signals from these sensors and switch on/off signals are supplied.

The ECU 3 shapes the input signal waveforms from various sensors, corrects the voltage level to a predetermined level, and converts the analog signal (ilT
an input circuit 5a having functions such as converting into digital signal values, and a central processing circuit (hereinafter referred to as rcPUJ) 5b.
, C)) Storage means 5C1 for storing various calculation programs and calculation results executed by U5b, and the fuel injection block F6.
It is composed of an output circuit 5d and the like that supplies a drive signal to the output circuit 5d.

Based on the various engine parameter signals described above, the CPU 5b determines various engine operating states such as a feedback control operating region and an oven loop control operating region, and also determines, based on the following equation (1), according to the four-wheel rotation state of the engine.
1' I) Fuel injection valve 6 synchronized with C signal pulse
The fuel injection time 1'our is calculated.

′I”out=Ti
It is determined according to n^.

KLS is an air-fuel ratio lean coefficient set by the method shown in FIG. 2, for example, and is an engine! It is applied to lean the air-fuel mixture supplied to the engine l when the engine l is in a predetermined low-load operating region.

K1 and K2 are other correction coefficients and correction variables that are respectively calculated according to various engine parameter signals, and are used to optimize engine characteristics such as fuel consumption characteristics and engine acceleration characteristics according to engine operating conditions. It is determined to be a predetermined value.

C: PU5b is the fuel injection time T obtained as described above.
A drive signal for opening the fuel injection valve 6 based on OUT is supplied to the fuel injection valve 6 via the output circuit 5d.

FIG. 2 shows a flowchart of a subroutine for calculating the lean coefficient Kts. This program is 'I' D
This is executed in synchronization with each C signal pulse generation.

First, it is determined whether the throttle valve opening θTl+ is larger than a predetermined opening 0LS (for example, 3°) (step 21).
, the answer is affirmative (Yes), that is, when θT1>OLs is established, a predetermined time ^TLSDELAY (for example, 10 seconds) is set in the ^TtsDEL^Y timer and it is started (step 22). This ATLSD
The IELAY timer is used to determine in step 38, which will be described later, whether a predetermined time ATLSDELAY has elapsed since the throttle valve opening θT11 transitioned from a state larger than the predetermined opening Ots to a state below the predetermined opening Ots. used. Next, a lean determination absolute pressure PBALS for determining whether or not the engine operating state is in a low load region where the air-fuel ratio should be lean is calculated using the following equation (2) (step 23).

P BALS = P BAFC + ΔPBL8 − (
2) Here, PIIAFC is the fuel cut determination absolute pressure (for example, 180 mml1g), ΔP, for determining whether the engine operating state is in the fuel cut region or not.
BLS is set to, for example, about 20 mm and 11 g, and is a predetermined value that is set to 11α, which increases as the engine rotation speed Ne increases.

In step 24, it is determined whether the intake pipe absolute pressure Pq^ is higher than the lean determination absolute pressure PBALS calculated in step 23, and the answer is 11 (Yes), that is, P
B^) When P IIALS is established, it is not a low-load operation state, so the lean coefficients Kc and S are set to the value 1.0 (step 25), while the answer is negative (No).
, that is, in a low-load operating state where Ps^≦PBALS holds, the lean coefficient KLS is set to the first lean predetermined value XLS+ (for example, 0.95) (step 2).
6) Terminate this program.

The answer to step 2I is negative (NO), that is, θT11≦
When θLS is established, the vehicle equipped with the engine is equipped with an automatic transmission (hereinafter referred to as rAT vehicle).
It is determined whether or not (step 27). If this answer is negative (NO), that is, a vehicle that is not an AT vehicle (rM i”
Tw-NTIIL for MT cars
Select the S table and calculate the first lean determination rotation speed NTIILS according to the engine cooling water temperature 1'w (
Step 28). Here, the '1゛W-NTIILS table is a table set such that the higher the engine coolant temperature Tw is, the lower the first linearization discrimination rotation speed NTIILS is. When the temperature is 25℃, the lean determination rotation speed NTIILS is 2.0
It is set to 0Orpm. Next, it is determined whether or not the detected engine speed Ne is higher than the first lean determination engine speed NTIILS (Step 29), and when the answer is negative (No), that is, when Ne≦NTIILS holds true. While proceeding to step 23, if the answer is affirmative (Y
es), that is, when Ne)NTI+t,s holds true, the lean coefficient 1 (LS) is set to the predetermined vehicle lean value XLSO1IT (for example, 0.95) (step 30), and this program end.

When the answer to step 27 is affirmative (Yes), that is, Δ
In the case of a car, it is determined whether the engine cooling water temperature 'I'W is higher than a predetermined water temperature 'I'WATL8 (for example, 37°C) (step 31).
s), it is determined whether rIF and speed V are larger than a predetermined speed VI5K (for example, 15 km/h) (step 32). The answer to step 32 is affirmative (Yes)
In this case, it is determined whether the automatic transmission is in gear or not, that is, whether the automatic transmission's shift range setting is neutral or other than parking (step 33). If the answer is 1# constant (Yes), the near conditioner compressor is further changed. It is determined whether an electromagnetic clutch (not shown) that turns on/off the operation of is in the off state (step 34). If the answer to step 34 is affirmative (Yes), it is determined whether the engine speed Ne is higher than the second lean determination engine speed NATLS (step 35). Here, the second lean determination rotation speed NATLS is provided to expand the lean range in the case of Δ'l' jl[, and the higher the engine cooling water temperature "l' w, the smaller the value becomes. is set to

If the answers to steps 31 to 35 are all 11 (Yes), that is, 'l'w)'1'wAn, s, V>VI5
Ne) When all NATLS are established and the engine is in the in-gear state and the near conditioner compressor is not operating, it is determined that the engine l is in the air-fuel ratio lean region, and the A'l'LSDIELAY timer is set. Determine whether the count value of is equal to the value O (step 38)
.

If this answer is negative (No), that is, the throttle valve opening is 0.
From the state where T11 is (3ru)θLS, θTll≦OLs
After transitioning to the state (after the throttle valve is substantially fully closed), if the predetermined time A'rLsl)El, AV has not elapsed, the lean coefficient KLS is set to the second lean vehicle predetermined value XLSOAT2 ( For example, 0.5) (step 40).

On the other hand, when the answer to step 38 is affirmative (Yes), that is, from the time when the throttle valve is substantially fully closed, the predetermined time 1i11A
TLsl) After IELAY has elapsed, the lean coefficient Kts is changed to the lean predetermined value X LSO^T2 for the second A'r vehicle.
The larger the first Δ′l゛
Set tso^Tl (for example, 0.75) (step 39). After executing step 39 or 40, the program is ended.

Here, the predetermined time ATLsl)El, AM is set to, for example, about 10 seconds in consideration of the time required for the fuel attached to the inner wall of the intake pipe to be sucked into the combustion chamber, and the throttle valve is approximately fully closed. Predetermined time ATLsDEl,A from point in time
During V, the air-fuel ratio is maximized (see Section 2 (7) above).
When the predetermined phosphorization value for A'r cars XL80AT2=0.5, A/F=20.4) prevents the air-fuel ratio from becoming overrich due to fuel adhering to the inner wall of the intake pipe. , after the predetermined time A'r LSI)ELAY has passed, the air-fuel ratio is adjusted to the proper lean state (Jl(Xtso＾month=
When it is set to 0.75, A/F = 19.6) is used to prevent the temperature rise of the exhaust gas purifying catalyst and improve its durability.

The answer to any of steps 31 to 35 is negative (No).
When , the above M'r JlC'l"w -N
'FW for AT cars set in the same way as the TIILS table
- Select the NTIILS table and calculate the first lean determination rotation speed NTIILS (step 36). Next, it is determined whether or not the detected engine speed Ne is higher than this first lean determination engine speed NTIILS (step 37), and when the answer is negative (No), that is, Ne≦N.
When TIILS is established, the process proceeds to step 23. On the other hand, when the answer is affirmative (Yes), that is, N e
) When N TIILS is established, it is determined that the engine l is in the air-fuel ratio lean region, and the step 38 is performed.
Proceed to.

Here, the second lean determination rotation speed N^TLS is:
First lean determination rotation speed N calculated in step 36
It is set to a smaller value than TIILS (when compared at the same engine coolant temperature).

This means that the answers to steps 31 to 34 are all affirmative (Ye).
This is because only in the case of s), the air-fuel ratio lean region is intended to be expanded to the low engine speed range side. In other words, ■When the engine cooling water temperature '1°W is low (1'w≦'1°W), ■When the vehicle speed V is slow (V≦V1s), ■When the engine is not in gear, ■Near conditioner When the compressor is in operation, in any of the cases, the second lean determination rotation speed is set because expanding the air-fuel ratio lean region causes a drop in engine speed or an engine stall. The first lean determination rotation speed NTl1tJ, which is larger than N^dLS, is used to determine the air-fuel ratio equalization region, so as not to expand the air-fuel ratio lean region.

In addition, in the above-mentioned embodiment, in the case of an AT car, the degree of leanness of the air-fuel ratio is changed according to the elapsed time from the time when the throttle valve is opened almost fully, but this is not limited to this, and the degree of leanness of the air-fuel ratio is changed depending on the engine characteristics. Depending on the situation, it may be applied to MT vehicles.

(Effects of the Invention) As detailed above, the present invention provides a low-load vehicle internal combustion engine that leans the air-fuel ratio of the air-fuel mixture supplied to the engine when the internal combustion engine is in a predetermined 4° low-load operating region. In the temporal air-fuel ratio control method, the degree of lean air-fuel ratio of the supplied air-fuel mixture is changed depending on the elapsed time after the transition to the low-load operation region, so that the air-fuel ratio is appropriately leaned during deceleration. This has the effect that not only can good fuel efficiency and exhaust gas characteristics be obtained, but also that the temperature of the exhaust gas purifying catalyst provided in the exhaust system can be prevented from rising and the durability of the catalyst can be improved.

[Brief explanation of 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, and FIG. 2 is a flowchart showing a subroutine for calculating a lean coefficient KLS. Engine water temperature sensor, 1 engine speed sensor, 1
6...+1 is speed sensor, 17... gear position sensor,
18...Near conditioner switch.

Claims (1)

[Scope of Claims] 1. A low-load air-fuel ratio control method for a vehicle internal combustion engine, which leans the air-fuel ratio of an air-fuel mixture supplied to the engine when the internal combustion engine is in a predetermined low-load operating region, A low-load air-fuel ratio control method for a vehicle internal combustion engine, the method comprising changing the degree of lean air-fuel ratio of a supplied air-fuel mixture depending on the time elapsed after transition to an operating region. 2. The internal combustion engine for a vehicle according to claim 1, wherein the degree of leanness of the air-fuel ratio of the supplied air-fuel mixture is made greater when the elapsed time after the transition to the low-load operating region is short than when it is long. air-fuel ratio control method at low load.