JPH01224427A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce NOx and emission by supplying fuel with asynchronous injection in case feedback control is conducted while the target air-fuel ratio is changed from the lean side to the theoretical air-fuel ratio, and thereby improving follow-up characteristic of the air-fuel ratio after target air-fuel ratio. CONSTITUTION:A means M2 senses the operating condition including a load and the air-fuel ratio of an internal combustion engine M1. A means M3 sets the target air-fuel ratio to the lean side or the theoretical air-fuel ratio on the basis of sensed result by the means M2. A means M5 makes drive control of a fuel injection valve M14 on the basis of the target air-fuel ratio set by the means M3 and the sensed result from the means M2 and performs feedback control of the air-fuel ratio. In this device, a means M6 makes asynchronous injection of the fuel either in a constant amount or in a certain amount according to the operating condition in case the target air-fuel ratio is changed to the lean side or the theoretical air-fuel ratio. This enhances the follow-up characteristic of the air-fuel ratio after the target air-fuel ratio.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air-fuel ratio control device for an internal combustion engine.
The present invention relates to an air-fuel ratio control device that controls the air-fuel ratio by driving and controlling a fuel injection valve to adjust fuel injection timing and fuel injection amount.

[Prior Art] Conventionally, in internal combustion engines, especially vehicle engines, HC and Co are harmful components in exhaust gas.

Three-way catalysts are used to purify NOx. In order to maintain the purification efficiency of this three-way catalyst in a good condition, an air-fuel ratio sensor installed in the exhaust passage is used to
The air-fuel ratio of the fuel mixture is detected from the oxygen concentration in the exhaust gas, and the air-fuel ratio of the fuel mixture supplied to the engine (control air-fuel ratio) is controlled to the stoichiometric air-fuel ratio (stoichiometric) (stoichiometric feedback control). In addition to stoichiometric feedback control, the air-fuel ratio is also controlled to be leaner than the stoichiometric air-fuel ratio (lean feedback control) for the purpose of reducing fuel consumption. This lean feed pack control suppresses harmful components contained in exhaust gas by reducing the amount of fuel to be combusted.

In order to feedback-control the air-fuel ratio to the target air-fuel ratio of lean or stoichiometric, the fuel injection valve is electrically controlled according to the operating conditions such as the air-fuel ratio and load, and the fuel supply amount and timing are controlled. Air-fuel ratio control devices have been used that control the air-fuel ratio to a target air-fuel ratio by extremely precise adjustment.

In addition, as a technology for controlling the air-fuel ratio by controlling the fuel injection valve to supply fuel to the engine,
There are those that use the same injection system that supplies fuel in synchronization with the engine crank angle (see Japanese Patent Laid-Open No. 58-8238), and those that use asynchronous injection that is not synchronized with the crank angle (Japanese Patent Laid-Open No. 60-8238). 116834) was proposed.

[Problems to be Solved by the Invention] However, in a device that performs feedback control by switching the target air-fuel ratio according to the operating state, when switching the target air-fuel ratio from lean to stoichiometric, for example, when changing from a deceleration state to an acceleration state, In this case, even if the amount of fuel to be supplied is increased, the air-fuel ratio may not be able to fully follow the target air-fuel ratio.

This is because, as shown in Fig. 10, when switching the target air-fuel ratio, the fuel traveling in the six directions of the arrows adheres to the wall A2 of the intake passage A1, and the necessary amount of fuel is not supplied into the cylinder A3. This phenomenon occurred particularly when the intake passage A1 had a large bend. As a result, immediately after switching to stoichiometric feedback control, the air-fuel ratio shifts to the lean side, resulting in an increase in NOx.

An object of the present invention is to provide an air-fuel ratio control device that can effectively reduce emissions by preventing an increase in NOx when switching from lean feedback control to stoichiometric feedback control.

[Means for Solving the Problems] That is, the present invention provides an internal combustion engine M1 as illustrated in FIG.
an operating state detecting means M2 that detects the operating state including the air-fuel ratio and load; and an air-fuel ratio setting means M3 that sets the target air-fuel ratio to the lean side or the stoichiometric air-fuel ratio based on the detection result of the operating state detecting means M2. and, based on the detection result of the operating state detection means M2 and the target air-fuel ratio set by the air-fuel ratio setting means M3, drive control of the fuel injection valve M4, adjust the amount of injected fuel, and perform feedback control of the air-fuel ratio. In the air-fuel ratio control device for an internal combustion engine M1, the air-fuel ratio control device for an internal combustion engine M1 is equipped with feedback control means M5 for performing Internal combustion engine M characterized by comprising an asynchronous injection control means M6 that performs asynchronous injection of a predetermined amount of fuel depending on the state.
This article focuses on the air-fuel ratio control device of No. 1.

[Function] The air-fuel ratio control device for the internal combustion engine M1 of the present invention has the following functions:
The detection means M2 detects the operating state of the internal combustion engine M1, including the air-fuel ratio and load. Then, in response to changes in the operating state such as increases and decreases in load, the air-fuel ratio setting means M3 changes and sets the target air-fuel ratio to the lean side or to the stoichiometric air-fuel ratio. When this target air-fuel ratio is changed, the feedback control means M5 first sets the amount of fuel to be supplied so that the actual air-fuel ratio approaches the target air-fuel ratio, and then controls the driving of the fuel injection valve M4. The above amount of fuel is injected synchronously according to the crank angle. That is, lean feedback control or stoichiometric feedback control is performed by changing the amount of fuel to be supplied and performing synchronous injection according to the target air-fuel ratio and the operating state.

In addition to the above-mentioned operation, when the target air-fuel ratio is changed from the lean side to the stoichiometric air-fuel ratio, in order to quickly supplement the required fuel, the asynchronous injection control means M6 injects a fixed amount or Performs asynchronous injection of a predetermined amount of fuel depending on the situation. Thereby, the air-fuel ratio can be quickly brought close to the target air-fuel ratio, that is, the stoichiometric air-fuel ratio, and an increase in NOx due to a deviation in the air-fuel ratio can be prevented.

[Embodiment] The first embodiment will be described below with reference to the drawings. Figure 2 shows
1 is a schematic configuration diagram showing an air-fuel ratio control device 1 and its peripheral devices according to the present embodiment.

As shown in the figure, an intake pipe 4 of the engine 2 is provided with a throttle valve 8 that opens and closes in conjunction with an accelerator pedal 6. The throttle valve 8 is provided with a throttle opening sensor 14 that detects the opening of the throttle valve 8 (throttle opening). An intake air temperature sensor 12 is provided upstream of the throttle valve 8 to detect intake air temperature. Further, on the downstream side of the throttle valve 8, an intake pressure sensor 15 is provided for detecting the amount of intake air from the intake pressure. A fuel injection valve 18 injects fuel pumped from a fuel pump (not shown) into each cylinder 16 of the engine 2. An intake passage 20 that introduces the fuel mixture into the cylinder 16. An intake valve 24 that opens and closes an intake port 22 at the top of the cylinder 16 is provided.

As shown in FIG. 3, the intake passage 20 branches into two and leads to intake ports 22a and 22b of the cylinder 16, and at the branch point there is a passage for changing the intake amount of the fuel mixture. A switching valve 26 is provided.

Returning to FIG. 2, on the exhaust pipe 2 of the engine 2, there is an air-fuel ratio sensor 30 that detects the air-fuel ratio of the fuel mixture based on the oxygen content in the exhaust gas discharged from the engine 2, and an air-fuel ratio sensor 30 that detects harmful components in the exhaust gas. A purification device 32 containing a three-way catalyst for removal is provided. This air-fuel ratio sensor 30 is
This is a lean mixture sensor that outputs a signal according to the air-fuel ratio, not only near the stoichiometric air-fuel ratio but also on the lean side.

The engine 2 also includes an igniter 36 for outputting high voltage to the spark plug 34. Plug that power into the spark plug 34
A rotation speed sensor 42 that generates a pulse signal for detecting the rotation speed (engine rotation speed) of the engine 2 at every predetermined rotation angle (for example, 30° C.A.) of the distributor 3. A crank angle sensor 44 is provided that outputs a pulse signal for determining fuel injection timing and ignition timing twice per revolution of the distributor 2201 (ie, once per revolution of the engine 2). Furthermore, in order to detect the operating state in more detail, a water temperature sensor 45 that detects the cooling water temperature and a vehicle speed sensor 46 that detects the rotational speed of the output shaft of the transmission (not shown) are provided.

In addition, electronic control f and I devices (hereinafter simply E
4 days (referred to as CU) are provided.

This ECU 4B processes signal data from a human-powered boat 48a and a human-powered capo 48a that manually output signals from each sensor according to a control program, and outputs control signals for controlling the operation of each actuator. A central processing unit (hereinafter simply referred to as CPU) 48b, a read-only memory (hereinafter simply referred to as ROM) 48c, in which the control program and initial data are stored. *Random access memory (hereinafter referred to simply as RAM) in which data necessary for arithmetic control is read and written
) 48d, a timer 48e that measures time according to the necessity of calculation processing by the CPU 48b, an output capo 48f that outputs control signals to the actuator, and an ECU.
Pass line 48 that mediates the transmission of various signals within 48
It is composed of g.

Then, the intake temperature sensor 12. Throttle opening sensor 14. Intake pressure sensor 15. Air-fuel ratio sensor 30, water temperature sensor 459, rotation speed sensor 42. Crank angle sensor 44.
The vehicle speed sensor 46 and the like are connected to a human capo 48a,
The output signal is transmitted to the CPU 48b and the like. or,
The actuators such as the fuel injection valve and the igniter 36 are connected to the output capacitor 48f and are controlled in response to signals from the ECU 4B.

With such a configuration, the ECU 4B performs synchronous injection or asynchronous injection of fuel, and lean or stoichiometric air-fuel ratio foot-butter control adjusted by these injections.

Next, among the processes performed by the ECU 4B, normal lean or stoichiometric air-fuel ratio feedback control, that is, the process of controlling the fuel injection IiJ amount in accordance with the target air-fuel ratio to perform synchronous injection. This will be explained based on the flowchart shown in FIG. This air-fuel ratio feedback control is
It is switched depending on the operating state, and for example, lean feedback control is performed when the engine is decelerating or when the engine load is small, and stoichiometric feedback control is performed when the engine is idling or accelerating. Note that this routine is repeatedly executed for a sufficiently short time, for example, 50 m5ec, to ensure smooth control.

First, in step 100, based on the signals from the intake pressure sensor 15 and the rotation speed sensor 42, the engine rotation speed NE
The basic fuel for synchronous injection according to the load Q/NE of the engine 2 is determined based on a map or calculation formula using the engine speed NE and intake air amount Q as parameters. Calculate the injection amount τp. This basic fuel injection amount τp is an approximate injection amount calculated from the operating state of the engine 2.

In the subsequent step 110, it is determined based on the signal from the air-fuel ratio sensor 30 whether or not conditions for controlling the air-fuel ratio to the target air-fuel ratio, so-called air-fuel ratio feed pump control conditions, are satisfied. In other words, when the intake air temperature is low, the
When the torque opening is large and the engine 2 is rapidly accelerating or operating under high load, or when the coolant temperature detected by the water temperature sensor 45 is low, it is necessary to increase the torque of the engine 2. The basic fuel injection amount p is increased by correction, output increase correction, or warm air increase correction, but in such a case, feedback control is stopped.

If an affirmative determination is made in step 110 above, step 1
Proceed to step 20. In step 120, the difference Δd between the target air-fuel ratio set to lean or stoichiometric and the actual air-fuel ratio is determined depending on the operating state.

In the subsequent step 130, 1 is calculated for the air-fuel ratio sensor @ according to the difference Δd using an arithmetic formula or map, and in the subsequent step 140, fuel injection is determined based on the air-fuel ratio correction coefficient 1 or other correction coefficients. Find the quantity τ.

In the following step 150, the fuel injection time, TAU, corresponding to the fuel injection amount τ is determined.

Then, in the following step 210, the fuel injection time T
The opening start and end times of the fuel injection valve 18 are set from the AU, and based on the signal from the crank angle sensor 44, the fuel injection valve 1 is driven and controlled to perform synchronous injection of fuel, and then the main processing is performed. end.

That is, by adjusting the fuel injection amount τ and performing synchronous injection through the processes of steps 120 to 160 described above, lean feedback control or stoichiometric feedback control of the air-fuel ratio can be performed.

On the other hand, if a negative determination is made in step 110, that is, if feedback control of the air-fuel ratio is not performed, the process proceeds to step 170, based on the signals from the intake air temperature sensor 12, throttle opening sensor 14, water temperature sensor 45, etc. , 2 is calculated as the increase correction coefficient for the basic fuel injection amount τp, and the process proceeds to step 180.

In step 180, the basic fuel injection amount τp is corrected by the increase correction coefficient, such as 2, to calculate the fuel injection amount τ. Thereafter, in the same manner as described above, the fuel injection time TAU is obtained through step 150, and the process proceeds to step 160, where the synchronous injection of fuel is controlled and the present process is temporarily terminated.

Next, a description will be given of the asynchronous injection control process performed when the air-fuel ratio control is switched from lean feedback control to stoichiometric feedback control 1aIl.
First, flag X is set to detect this switching.
The LEAN setting process will be explained based on the flowchart of FIG.

First, step 200 to step 220 shown below
Now, the process for setting the flag XLEAN when the vehicle is in a stopped state will be described.

In step 200, it is determined based on the signal from the vehicle speed sensor 46 whether the vehicle speed is zero. If an affirmative determination is made here, the process proceeds to step 210.

In step 210, it is determined whether or not the idle switch LL is on, and if an affirmative determination is made here, step 2
The process proceeds to step 20, and if a negative determination is made, the process is temporarily terminated. Here, when the idle switch LL is on, it means that the throttle valve 8 is fully closed, and when it is off, it means that the throttle valve 8 is controlled to be in an open state.

In the following step 220, the flag XLEAN is set to 0, and the process ends once again. When this flag XLEAN is O, it indicates that stoichiometric feedback control is being performed.

That is, when it is determined in steps 200 and 210 that the vehicle is stopped and in an idling state, it is determined that the stoichiometric feedback control is being performed, and the flag XL is set.
This sets EAN to 0.

Next, steps 230 to 250 show a process for setting the flag XLEAN while the vehicle is in a running state.

First, in step 200, when it is determined that the vehicle is running and the process proceeds to step 230, the previously detected intake pipe negative pressure PMO is subtracted from the current intake pipe negative pressure PM by a signal from the intake pressure sensor 15. , it is determined whether the value is greater than a predetermined value A.

Note that the intake pipe negative pressures PM and PMO are calculated as negative values. If an affirmative determination is made here, the present process is temporarily terminated through step 220, whereas if a negative determination is made, the process proceeds to step 240. That is, by determining whether or not the intake pipe negative pressure PM is increasing, the acceleration state of the vehicle is detected, and if the vehicle is in the acceleration state, stoichiometric feedback control is performed, so the flag XLEAN is set to O, and the acceleration state is detected. If not, step 240 further adds the next determination.
Proceed to.

In step 240, the previously detected intake pipe negative pressure PMO is subtracted from the current intake pipe negative pressure PM, and it is determined whether the value is less than a predetermined value -8. If an affirmative determination is made here, the process proceeds to step 250, whereas if a negative determination is made, this process is temporarily terminated. That is, the deceleration state of the vehicle is detected by determining whether or not the intake pipe negative pressure PM is decreasing, and if the vehicle is decelerated, lean feedback control is performed, so the flag XLEAN is set to 1. .

That is, by the processing in step 200 to step 250, the idle switch LL and the intake pipe negative pressure PM are
A flag XLEAN indicating which control is being executed, lean feed puncture control or stoichiometric feedback control, is set in accordance with the change in .

The state of this air-fuel ratio control and the operating state are shown in the time chart of the vehicle speed V and intake pipe negative pressure PM during 10 mode driving in FIG. Time tO to t in FIG. 6(a)
2. t3-t5. t7-t8. The period from t9 to tlo is the period in which stoichiometric feedback control is performed, and the period from time t2 to t3. t5-t7. The period between t8 and t9 is the period in which lean feedback control is performed. And the flag XLEAN which is switching from lean side to stoichiometric
The switching from 1 to O occurs at time t3. in FIG. 6(b).
On the other hand, the switching from 0 to 1 of the flag XLEAN, which is switching from stoichiometric to lean side, occurs at time t2.t7 in FIG. 6(b). t5. Do it at t8.

Next, the process of calculating the injection amount of asynchronous injection performed in accordance with the flag XLEAN will be explained based on the flowchart of FIG. 7.

First, in step 300, the value of the flag XLEAN is read.

Subsequently, in step 310, the read flag XLEA
Determine whether N is 0 or not. Here the flag XLEAN is 0
In other words, if it is determined that stoichiometric feedback control is being performed, the process proceeds to step 320.

In step 320, it is determined whether the previous flag XLEANO is 1 or not. Here, if it is determined that the flag XLEANO indicating the previous control '+all' state is 1, that is, the previous control was in full-back feedback control, the process proceeds to step 330.

That is, by making an affirmative determination in steps 310 and 320, it is possible to detect that the lean feedback control has been switched to the stoichiometric feedback control.

In the following step 330, an asynchronous injection amount TAUASYS for performing asynchronous injection is calculated. This asynchronous injection amount TAUASYS is as shown in FIG. ``Determined from intake pipe negative pressure PM and engine speed NE. That is, the eighth
A negative pressure parameter meter ASYPM proportional to the intake pipe negative pressure PM is determined from the map shown in Figure 8(a) Cm, and a rotational speed parameter meter ASYNE proportional to the engine speed NE is determined from the map shown in Figure 8(b). , the product of these parameters is calculated as the asynchronous injection amount TAUASYS.

In the following step 340, the asynchronous injection amount TAUASYS
The fuel injection time TAU2 is set based on.

In the following step 350, control is performed to drive the fuel injection valve 19 to perform non-common fuel injection based on the fuel injection time TAU2, and the process proceeds to step 360.

Then, if a negative determination is made in step 310 or step 320, or in step 360 proceeding after step 350, it is determined whether the flag XLEAN is 1,
If it is determined that the flag XLEAN is 1, that is, lean feedback control fa is determined, the process proceeds to step 370, while if it is determined that stoichiometric feedback control is being applied, the process proceeds to step 380.

In step 370, a flag
Set ANO to 1, and then end this process. That is, since the current control is lean feedback control, the current value of the flag XLEAN is entered into the previous value of the flag XLEANO to update it to 1.

On the other hand, in step 380, flag XLEANO is set to 0.
, and then end this process. That is, since the current control is stoichiometric feedback control, the previous value of the flag XLEANO is similarly updated to 0.

That is, as soon as the control of the air-fuel ratio is switched from lean feedback control to stoichiometric feedback control by the processing of steps 300 to 380 described above, asynchronous injection can be performed.

Note that when the timings of asynchronous injection and synchronized injection match, the amount of fuel can be increased by increasing the fuel injection time TAU of synchronous injection by the fuel injection time TAU2 of asynchronous injection.

FIG. 9 shows the change in air-fuel ratio due to this asynchronous injection. In the figure, from top to bottom: target air-fuel ratio and synchronous injection.

It shows a time chart of asynchronous injection, a controlled air-fuel ratio, and an air-fuel ratio when asynchronous injection is not performed, which is indicated by a dotted line. As is clear from this time chart, when asynchronous injection is performed, the air-fuel ratio follows the target air-fuel ratio well, and the target air-fuel ratio is rapidly approached. Therefore, when feedback control is performed by switching the target air-fuel ratio from lean to stoichiometric, the air-fuel ratio can be quickly controlled to the stoichiometric air-fuel ratio, so NOx does not increase.

In the above embodiment, the asynchronous injection amount TAUSUS was calculated according to the operating conditions such as the intake pipe negative pressure PM and the engine speed NE, but a fixed amount may be asynchronously injected. Further, the number of times of asynchronous injection may be performed not once but a plurality of times, and furthermore, the amount of fuel to be supplied may be controlled by adjusting the number of times of the asynchronous injection.

[Effects of the Invention] The air-fuel ratio control device for an internal combustion engine of the present invention supplies fuel by asynchronous injection when changing the target air-fuel ratio from the lean side to the stoichiometric air-fuel ratio and performing feedback control.
The air-fuel ratio follows the target air-fuel ratio well. Therefore, even when the target air-fuel ratio is changed as described above, less NOx is generated, and there is an effect of reducing emissions.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the basic configuration of the present invention, FIG. 2 is a schematic configuration diagram of an embodiment, and FIG. 3 is an explanatory diagram showing an enlarged intake passage.
FIG. 4 is a flowchart showing the synchronous injection process executed by the ECU, FIG. 5 is a flowchart showing the flag XLEAN setting process, and FIG. 6 is a time chart showing the air-fuel ratio control that is switched depending on the operating state. FIG. 7 is a flowchart showing the process of asynchronous injection, FIG. 8 is a graph showing a map for determining the amount of asynchronous injection, and FIG. 9 is a graph showing the air-fuel ratio controlled by the same amount injection and the asynchronous injection. FIG. 10 is an explanatory diagram of the prior art. Ml...Internal combustion engine M2...Operating state detection means M3...Air-fuel ratio setting means M4...Fuel injection valve M5...Feedback control means M6...Asynchronous injection control 'a means 2... Engine 4... Intake pipe 8... Front valve 15... Intake pressure sensor 1 day... Fuel injection valve 20... Intake passage 30... Air fuel ratio sensor 42... Rotational speed sensor 44 ...Crank angle sensor 46...Vehicle speed sensor 48...ECU Agent Patent attorney Tsutomu Sadatsu (and 2 others) Fig. 1 M4...Fuel injection valve Fig. 3 Fig. 4 Fig. 5 Fig. 6 @藺(b) ro 1? r3
1M 1711111! M Fig. 7 Fig. 8 (a) (b) 1111 Fig. 9

Claims (1)

[Claims] Operating state detection means for detecting the operating state including the air-fuel ratio and load of the internal combustion engine; and setting the target air-fuel ratio to the lean side or the stoichiometric air-fuel ratio based on the detection result of the operating state detection means. and an air-fuel ratio setting means for controlling the fuel injection valve based on the detection result of the operating state detecting means and the target air-fuel ratio set by the air-fuel ratio setting means, and adjusting the amount of injected fuel to feed back the air-fuel ratio. In the air-fuel ratio control device for an internal combustion engine, the air-fuel ratio control device for an internal combustion engine is equipped with feedback control means for performing control, and when the target air-fuel ratio is changed from the lean side to the stoichiometric air-fuel ratio by the air-fuel ratio setting means, 1. An air-fuel ratio control device for an internal combustion engine, comprising an asynchronous injection control means for asynchronously injecting a predetermined amount of fuel according to the amount of fuel.