JPS629741B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to an air-fuel ratio control device for an internal combustion engine that employs a partial lean system.

An effective method to meet exhaust gas regulations and reduce fuel consumption is to use a three-way catalyst and an O ₂ sensor to simultaneously oxidize and reduce the three components of exhaust gas, CO, HC, and NOOC, to purify the exhaust gas. It is used. In order to simultaneously work on the three components in the exhaust gas at a high purification rate, the engine must always be operated near the stoichiometric air-fuel ratio. For this purpose, the output signal of the O ₂ sensor is applied to the fuel supply system as a feedback signal to keep the air-fuel ratio within a predetermined range.

By the way, when feedback control is performed over the entire operating range of the engine, there will be a range where fuel efficiency deteriorates. Therefore, in the light load region, a so-called partial lean system is adopted in which the air-fuel ratio is shifted to the lean side, feedback control in this region is stopped, and open loop control is performed. In this case, control may be performed, for example, by changing the intake pipe negative pressure (or equivalent output), specifically, as shown in _Fig . This makes the fuel ratio leaner.

By the way, in such a partial lean system, the air/fuel range (A/F) in the open loop region varies due to variations in parts, etc., which may lead to deterioration in emissions, fuel efficiency, drivability, etc. A method using learning control may be considered to solve this problem, but such learning control can currently only be performed from the feedback control area, and the open loop area is currently estimated using the learning results of the feedback area. However, it has the disadvantage of poor accuracy.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that reduces variations in air-fuel ratio in an open loop control region and eliminates the above-described conventional drawbacks.

In order to achieve the above object, the present invention aims to improve the accuracy of learning control and eliminate variations in air-fuel ratio in open loop control by providing feedback regions before and after a lean load region.

In other words, as shown in Figure 2, a feedback area (F/B) is provided above and below the lean area according to the intake pipe negative pressure, and this is used for learning control (note that VL is the full load area). ). The learning control referred to here uses the output signal of the O ₂ sensor,
This is to calculate the deviation from stoichiometry and correct the base. Since such learning control uses the output of the O ₂ sensor, it can only be performed when feedback control is being executed. In the case of partial lean, the problem is how to perform correction in the lean region, and generally learning is performed in the feedback region, and only estimation is performed in other regions. Therefore, in the past, learning was performed in the feedback region and estimation was performed in the lean region as shown in FIG. However, since the lean region is wide, the amount of estimation increases and the accuracy deteriorates. In contrast, the present invention can improve the accuracy associated with estimation by providing a feedback area of an appropriate width in the conventional lean area and performing learning as shown in FIG.

Next, the present invention will be specifically described with reference to Examples. FIG. 5 is a block diagram schematically showing an embodiment of the present invention.

In Fig. 5, 1 is an engine, 2 is an air cleaner, 3 is an intake pipe, 4 is a throttle valve, 5 is an injector, 6 is an exhaust manifold, 7 is an exhaust pipe, and 8 is a built-in air flow meter that detects the amount of intake air. potentiometer type intake air flow sensor, 9
10 is a water temperature sensor that detects the engine cooling water temperature; 11 is a rotational speed sensor that outputs a pulse signal with a frequency corresponding to the rotational speed of the crankshaft of the engine 1;
An O ₂ sensor, 13 a three-way catalyst device, and 20 a control device.

Air is taken into the intake pipe 3 via the air cleaner 2 by the negative pressure within the intake pipe 3. The amount of intake air is controlled by a throttle valve 4, and a predetermined amount is mixed with fuel injected from an injector 5 and sent to the combustion chamber of the engine 1. The combusted exhaust gas is purified by a three-way catalyst 13 provided in the exhaust pipe 7. The amount of fuel injected by the injector 5 is controlled by a control circuit 20 controlling a solenoid valve (not shown) provided in the injector. Information for performing this control is the output signal of each sensor: intake air amount sensor 8, intake temperature sensor 9, water temperature sensor 10, rotational speed sensor 11, and O ₂ sensor 12. Control circuit 20
Although it can be configured discretely, it is advantageous to use a microcomputer, considering the advantage of being able to perform other processes besides air-fuel ratio control.

FIG. 6 is a detailed block diagram when a microcomputer is used for the control circuit 20.

The control circuit 20 includes a central processing unit (CPU) 10
0 via the bus 150 to the revolution counter 101;
Interrupt control unit 102, digital input port 10
3. Analog input port 104, timer 10
5. The input relationships of RAM (Random Access Memory) 106 and ROM (Read Only Memory) 107 are connected to the memory section, and each of the counter 108 and power amplification section 109 is connected. A required voltage is supplied to each circuit from a power supply circuit 110. The rotational speed counter 101 counts the number of pulses from the rotational speed sensor 11 that outputs the engine rotational speed, and outputs an interrupt command signal to the interrupt control section 102 in synchronization with the engine rotation. When the interrupt control unit 102 receives the interrupt request signal, the interrupt control unit 102 sends the interrupt request signal to the CPU 100 via the bus 150.
Outputs an interrupt signal to That is, the engine speed is measured once per revolution of the engine, and when the measurement is finished, an interrupt command signal is supplied to the interrupt control unit 102. In response, the interrupt control unit 102 generates an interrupt signal and sends an interrupt command signal to the CPU 100. An interrupt processing routine for calculating the fuel injection amount is executed. Digital input port 103 is a starter (not shown)
Digital signals such as a starter signal from the starter switch 14 that turns on and off the operation of the CPU 10
The analog input port 104 is composed of an analog multiplexer and an A/D converter, and transmits each signal from the intake air amount sensor 8, intake air temperature sensor 9, cooling water temperature sensor 10, and O ₂ sensor 12. It has a function of A/D conversion and sequential reading into the CPU 100. The ROM 107 is a read-only memory that stores programs and various constants. The counter 108 is a fuel injection time control counter equipped with a register, and has a function as a down counter. It converts a digital signal representing the amount into a pulse signal with a pulse time giving the actual valve opening time of the injector 5. Power amplification section 109 has a function of driving an injector based on the output signal of counter 108. Note that the timer 105 measures the elapsed time and transmits it to the CPU 100, and power is supplied to the power supply circuit 110 from the battery 16 via the key switch 15.

Since the intake air amount Q is detected by the intake air amount sensor 8 and the engine rotation speed N is detected by the rotation speed sensor 11, the basic injection time T _p is calculated by the CPU 100 at any time. Therefore, as is clear from Figure 2, V∠-F/B-LEAN-F/B-LEAN
- You can determine which area of F/B you are currently in. Therefore, each time a preset feedback area is reached, the CPU 100 switches from another control mode to the feedback control mode.
Perform learning control.

In the above explanation, as shown in Fig. 2, an example was shown in which the LEAN area was divided into two blocks, but it can be further divided into multiple zones or only one zone, which can be selected as needed. can.
FIG. 8 shows a processing flowchart by the control circuit 20 when the LEAN area is one zone as shown in FIG.

In step 61, it is determined whether the throttle is fully open, that is, whether the basic injection time T _p is at T _po indicating the full load range. Here, if T _p ≧T _po , it is assumed that the load is in the full load range, and control in the VL region is executed, and if T _p ≧T _po does not hold, the process moves to step 63. In step 63, it is determined whether or not the fuel injection is in the F/B region based on whether or not there is a basic injection time T _p between the set values T _po and T _p . That is, (T _p
< _Tpo ) and ( _Tp ≧ _Tp〓 ) are both satisfied, it is determined that the current is in the F/B region, and feedback control based on the O ₂ sensor output is executed in step 64. Furthermore, when (T _p < T _p 〓), it is assumed that the area is neither the VL area nor the F/B area (that is, the LEAN area or the F/B area), and step 65
Move to. In step 65, the basic injection time T _p is
This is to determine whether it is on the LEAN area side or the F/B area side, and T _p 〓 is set at the boundary between the two areas. If ( _{T p} ≧ T _p 〓), as is clear _from FIG.
Since this is area B, feedback control is executed in step 64. Based on the calculation results in each mode, the correction amount is set in step 67, and all processing ends.

The above has been explained using the control mode shown in FIG. 7 as an example, but in the case of the process shown in FIG. 2, the setting for determining the third F/B area between T _p 〓 and T _p This can be done by adding points and corresponding steps to the flowchart.

As is clear from the above, according to the present invention, it is possible to reduce variations in air-fuel ratio control based on component variations in the open loop control region, and therefore it is possible to reduce variations in emissions, fuel efficiency, drivability, etc. . Furthermore, it is also possible to reduce the cost of parts that make up the electronic fuel injection device.

[Brief explanation of the drawing]

Fig. 1 is an intake pipe pressure characteristic diagram depending on engine speed and basic injection time, Fig. 2 is an explanatory diagram showing the control principle of the present invention, Fig. 3 is an explanatory diagram showing the conventional control principle, and Fig. 4 is an explanatory diagram showing the control principle of the present invention. An explanatory diagram showing learning control according to the invention, FIG. 5 is a configuration diagram showing an outline of an embodiment of the invention, FIG. 6 is a detailed block diagram of the control circuit 20 shown in FIG. 5, and FIG. 7 is a diagram showing the configuration of the embodiment of the invention. FIG. 8 is a flowchart showing an example of the process of the present invention. 1...Engine, 5...Injector, 11...
...Rotation speed sensor, 12...O ₂ sensor, 13...
... Three-way catalyst device, 20 ... Control circuit, 100 ...
Central processing unit (CPU), 101... Rotation counter, 102... Interrupt control unit, 106...
RAM, 107...ROM, 108...Counter,
109...power amplification section, 150...bus.

Claims (1)

[Claims] 1 A partial lean system is adopted in which the oxygen concentration in exhaust gas is detected and the air-fuel ratio is feedback controlled within the window of the three-way catalyst, and in a pre-considered load range, the feedback control is stopped and the air-fuel ratio is controlled in the lean range. An air-fuel ratio control device for an internal combustion engine characterized in that a feedback region of a predetermined width is provided in adjacent regions on both sides of the lean region.