JPS5853659A - Method of controlling air-fuel ratio in internal- combustion engine - Google Patents

Abstract

PURPOSE:To maintain a predetermined accelerating property while enabling an internal-combustion engine to be run with lean air-fuel ratio, by maintaining the air-fuel ratio in all cylinders at at least a first predetermined value when the engine load is smaller than a set value and maintaining same in some cylinders at a second predetermined value when the engine load is larger than the set value. CONSTITUTION:In an electronic control unit 40 receiving signals of respective sensors 28, 29, 30 of intake tempetature, throttle position, water temperature and an air flow meter 2, etc. to control a fuel injection valve 41, etc., a central processing unit 56, ROM 57, input/output interface 61, etc. are connected to each other through a bus 62. When an engine load is less than 3/4, air fuel ratio in all cylinders is maintained at 20-25, and when same exceeds 3/4, the air-fuel ratio in some cylinders maintained at 12-15, that in the other cylinders being varied according to the air-fuel ratio charcteristics stored in ROM 57. Thus, the mixture becomes sufficiently lean so that noxious components in exhaust gas are reduced to ensure sufficiently a desired accelerating property.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control method for an internal combustion engine that changes the air-fuel ratio according to engine load.

In order to increase fuel consumption efficiency and reduce the amount of harmful components in exhaust gas, it is necessary to set the air-fuel ratio to 20 to 25, which is considerably larger than the stoichiometric air-fuel ratio (about 15). In a vehicle with a large displacement compared to the vehicle weight, it is possible to obtain a specified acceleration, that is, torque, even if the engine is operated in this air-fuel ratio region, but in a vehicle with a small displacement compared to the vehicle weight, If the engine is operated at such an air-fuel ratio, the output torque of the engine will decrease and the acceleration performance will deteriorate significantly. Therefore, in the latter type of vehicle, the air-fuel ratio at which the engine is operated must be adjusted to the required torque. Depending on the increase, it is necessary to set the air-fuel ratio to 12 or more, which is richer than the above-mentioned air-fuel ratio.
The air-fuel ratio used in this process of changing the air-fuel ratio is from 20 to 15
In this case, it becomes difficult to sufficiently suppress the generation of nitrogen oxides. In order to suppress the generation of nitrogen oxides, switching the air-fuel ratio from 20 to 25 to 12 to 15, which is lower than the stoichiometric air-fuel ratio, for all cylinders at a given engine load at a given engine load causes a sudden change in engine output torque. As a result, the operating performance of the engine deteriorates, and fuel consumption efficiency also deteriorates.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air-fuel ratio control method for an internal combustion engine that is operated with a sufficiently lean air-fuel mixture that is advantageous in terms of exhaust gas regulations and fuel consumption efficiency, and that can ensure predetermined acceleration performance.

In the engine's low load region, the air-fuel ratio in the combustion chambers of all cylinders is maintained at a first predetermined value or higher, which is sufficiently larger than the stoichiometric air-fuel ratio (approximately 15). /4 to 1), the air-fuel ratio in the combustion chamber of some cylinders is decreased to increase the output torque of the engine as a whole.

The present invention will be described in detail with reference to the drawings.

FIG. 1 is an overall schematic diagram of an electronically controlled fuel injection engine to which the present invention is applied. Air taken in from the air cleaner is sent to the combustion chamber 8 of the engine body 7 through an intake passage 12 that includes an air flow meter 2, a throttle valve 3, a surge tank 4, an intake port 5, and an intake valve 6. The throttle valve 3 is linked to an accelerator pedal 13 in the driver's cab. The combustion chamber 8 is divided by a cylinder head 9, a cylinder block 10, and a piston +1, and the exhaust gas generated by combustion of the air-fuel mixture is passed through an exhaust valve 15, an exhaust port 16, an exhaust branch pipe 17, and an exhaust pipe 18. Released into the atmosphere. A bypass passage 21 connects the flow of the throttle valve 3 and the surge tank 4,
The bypass flow control valve 22 controls the flow cross-sectional area of the bypass passage 21 to maintain a constant engine rotational speed during idling. In order to suppress the generation of nitrogen oxides, exhaust gas is guided to the intake system (an exhaust gas recirculation (EGR) passage 23 connects the exhaust branch pipe 17 and the surge tank 4, and performs an on-off valve type exhaust gas recirculation). The (EGR) control valve 24 opens and closes the EGR passage 23 in response to electric pulses.The intake temperature sensor is installed in the air flow meter 2 to detect the intake temperature, and the throttle position sensor 29 detects the opening of the throttle valve 3. Detect degree.

The water temperature sensor 30 is attached to the cylinder block 10 to detect the cooling water temperature, that is, the engine temperature, and the air-fuel ratio sensor 31, which is a well-known oxygen concentration sensor, is attached to the collecting part of the exhaust branch pipe 17 to detect the oxygen concentration in the collecting part. The crank angle sensor 32 detects the crank angle of the crankshaft from the rotation of the shaft 34 of the power distributor 33 coupled to the crankshaft (not shown) of the engine body 7, and the vehicle speed sensor 35 detects the crank angle of the crankshaft from the rotation of the shaft 34 of the power distributor 33 coupled to the crankshaft (not shown) of the engine body 7. Detects the rotation speed of the output shaft. These elements 2, 28, 29, 30, 31, 32
, a and the voltage of the storage battery 37 are sent to the electronic control device 40. A fuel injection valve 41 is provided near each intake port 5 in correspondence with each cylinder, and a pump 42 supplies fuel from a fuel tank 43 to the fuel injection valve 41 via a fuel passage 44. The electronic control unit 40 calculates the fuel injection amount from the input signals from each sensor, and sends an electric pulse having a pulse width corresponding to the calculated fuel injection amount to the fuel injection valve 41. The electronic controller 40 also controls the bypass flow control valve 22, EG
It controls the R1 control valve 24, the solenoid 45 of the hydraulic control circuit of the automatic transmission 36, and the ignition device 46. The secondary side of the ignition coil of the ignition device 46 is connected to the power distributor 33 .

FIG. 2 is a block diagram of the inside of the electronic control device. C.P.
U (Central Processing Unit) 56, ROM (Read Only Memory) 57, RAM (Direct Access Memory) 58.59
, A/D with multiplexer (analog/digital)
The converter 60 and the input/output interface 61 are connected to each other via a bus 62 (R, A M 5
9 is connected to an auxiliary power source, and even when the ignition switch is opened and the engine is stopped, a predetermined power is supplied and the memory can be maintained. Analog signals from the air flow meter 2, intake temperature sensor 28, water temperature sensor 30, and air-fuel ratio sensor 31 are sent to the A/D converter 60. Throttle position sensor 29, crank angle sensor 32,
The output of the vehicle speed sensor 35 is input to the input/output interface 6.
1, bypass flow control valve 22, EGR.

The control valve 24, the fuel injection valve 41, the injection valve 45, and the ignition device 46 receive input signals from the input/output interface 6I.

FIG. 3 shows the basic changes in the air-fuel ratio in the combustion chamber.

The horizontal axis is the engine rotation speed, the vertical axis is the intake pipe pressure, and the parameter is A/F (air fuel ratio). The stoichiometric air-fuel ratio is approximately 15.
It is. As the intake pipe pressure and engine speed increase, the engine load increases.1. , the engine load decreases as the intake pipe pressure and engine speed decrease. The engine load can also be determined from the intake air flow rate and the engine rotational speed, and is proportional to the intake air flow rate per engine rotation. When the engine load is large, to ensure the desired engine output,
When the engine speed is low (°C), the air-fuel mixture is enriched to avoid deterioration of engine performance. The characteristics shown in Figure 3 are expressed as an air-fuel ratio map, that is, a map that determines the air-fuel ratio using engine speed and intake air flow rate as variables.
It is stored in OM57. In the characteristics shown in Figure 3, in the range of engine rotational speed from 800 to +20Or, p, m, the air-fuel ratio decreases by 1.25 every time the engine rotational speed decreases by 10Or, p, m, and the air-fuel ratio decreases by 1.25. Pressure is 640-760
In the range of mmH9, the intake pipe pressure is lO++tmHy
Each time the air-fuel ratio increases, the air-fuel ratio decreases by 0.5 to 1.0.

FIG. 4 shows the air-fuel ratio characteristics of the first embodiment. When the engine load (ratio of rotation to maximum torque) is less than 3/4, the air-fuel ratios in the combustion chambers of all cylinders are kept equal and at a value of 20 to 25. As a result, the air-fuel mixture becomes sufficiently lean, the amount of harmful components in the four-gas is reduced, and fuel consumption efficiency is improved. The throttle valve opening is wider than 3/4 (
- In some cases, the air-fuel ratio in the combustion chamber of some cylinders is maintained at 12 to 15 as shown by the solid line, and the air-fuel ratio in the combustion chamber of the remaining cylinders is maintained at 12 to 15 as shown by the broken line in the engine according to the characteristics in Figure 3. As the load increases, it gradually increases from 20 to 25 to 12.
to 15. In a four-cylinder internal combustion engine, some cylinders may have one, two, or three cylinders. As a result, the output torque of the engine as a whole increases and the desired acceleration performance is secured, and the air-fuel ratio in some combustion chambers is deviated from the air-fuel ratio of 15 to 19, which generates a large amount of nitrogen oxides. ,
Generation of nitrogen oxides is suppressed. Note that in the characteristics shown in Figure 4, the air-fuel ratios in the combustion chambers of other cylinders become the stoichiometric air-fuel ratio at a predetermined throttle valve opening, but the air-fuel ratios in the combustion chambers of all cylinders do not reach the air-fuel ratio of 15 to 19 at the same time. Since there are no nitrogen oxides, the amount of nitrogen oxides generated is sufficiently small.

FIG. 5 shows the air-fuel ratio characteristics of the second embodiment. When the throttle valve opening is smaller than 3/4, the air-fuel ratio in the combustion chambers of all cylinders should be maintained at 20 to 25. Throttle valve opening degree is 3/
If it is larger than 4, the air-fuel ratio of the combustion chamber is decreased from 20 to 25 to 12 to 15 in the order of cylinders A, B, and C as the throttle valve opening increases, that is, the engine load increases. The remaining cylinders are reduced according to the characteristics shown in FIG. 3, as in the case of the other cylinders in FIG. In this way, in the high load region of the engine, as the engine load increases, the number of cylinders in which the combustion chambers have an air-fuel ratio lower than the stoichiometric air-fuel ratio increases, and the torque of the engine as a whole is increased. acceleration is obtained.

FIG. 6 shows the air-fuel ratio characteristics of the third embodiment. When the throttle valve opening is smaller than 3/4, the air-fuel ratio in the combustion chambers of all cylinders is maintained at 20 to 25. Throttle valve opening degree is 3/
If it is larger than 4, the air-fuel ratio of the combustion chamber is gradually decreased from 20 to 25 to 12 to 15 in the order of cylinders A, B, and C. The air-fuel ratio in the combustion chamber of the cylinder is maintained at approximately 20 to 25 until just before the throttle valve opening reaches 1.0. In this embodiment as well, when the engine becomes highly loaded, the air-fuel mixture in the combustion chambers of some cylinders gradually shifts to the richer side, and the torque of the engine as a whole increases. Furthermore, since the combustion chambers of all cylinders do not reach the stoichiometric air-fuel ratio at the same time, the generation of nitrogen oxides is also suppressed.

As described above, according to the present invention, the air-fuel ratio is set to a value sufficiently larger than the stoichiometric air-fuel ratio in the low load region of the engine, the fuel consumption efficiency is improved, and the amount of harmful components in the exhaust gas is reduced.
Additionally, in high-load areas of the engine, the air-fuel ratio in the combustion chambers of some cylinders decreases, suppressing the generation of nitrogen oxides and increasing the torque of the engine as a whole, ensuring the desired acceleration. .

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an electronic control engine to which the present invention is applied, FIG. 2 is a block diagram of the inside of the electronic control device shown in FIG.
Figure 4 shows the basic changes in the air-fuel ratio in the combustion chamber.
FIG. 5 and FIG. 6 are diagrams showing air-fuel ratio characteristics in various embodiments of the present invention. 2... Air flow meter, 3... Throttle valve, 7...
Engine body, 8... Combustion chamber, 32... Crank angle sensor, 40... Electronic control device, 41... Fuel injection valve. Figure 3! mmlmml cors ) → Engine rotation speed Fig. 4 - Engine load (throttle valve opening) Fig. 5 - Engine load (throttle valve opening) Fig. 6 0 0.5 1.0 One engine load (throttle valve opening)

Claims (1)

[Claims] 1. When the engine load is smaller than a predetermined value, the air-fuel ratio in the combustion chambers of all cylinders is maintained at a first predetermined value or higher that is larger than the stoichiometric air-fuel ratio, and when the engine load is larger than the predetermined value, The air-fuel ratio of the combustion chambers of some cylinders is maintained at a second predetermined value smaller than the stoichiometric air-fuel ratio, and the air-fuel ratio of the combustion chambers of the remaining cylinders is gradually decreased as the engine load increases. and
Air-fuel ratio control method for internal combustion engines. 2 When the engine load is smaller than a predetermined value, the air-fuel ratio in the combustion chambers of all cylinders is maintained at a first predetermined value or higher that is larger than the stoichiometric air-fuel ratio, and when the engine load is larger than the predetermined value, the air-fuel ratio in the combustion chamber of all cylinders is maintained above the stoichiometric air-fuel ratio. An air-fuel ratio control method for an internal combustion engine, characterized in that the number of cylinders whose air-fuel ratio is maintained at an air-fuel ratio equal to or less than a second small predetermined value is increased as the engine load increases. 3. When the engine load is smaller than a predetermined value, the air-fuel ratio in the combustion chambers of all cylinders is maintained at a first predetermined value or higher, which is larger than the stoichiometric air-fuel ratio, and when the engine load is larger than the predetermined value, the air-fuel ratio is maintained as the engine load increases. The air-fuel ratio in the combustion chambers of some cylinders is gradually decreased from a first predetermined value or higher to a second predetermined value smaller than the stoichiometric air-fuel ratio, and the air-fuel ratio in the combustion chambers of the remaining cylinders is set to another predetermined value. An air-fuel ratio control method for an internal combustion engine, characterized in that the engine load is maintained at a first predetermined value or higher.