JPS62218632A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To permit a torque fluctuation caused when air-fuel ratio is switched to be absorbed, by providing a control means for opening and closing an intake air supply means when a setting of the air-fuel ratio is switched between rich and lean. CONSTITUTION:A control circuit 46 controls a fuel supply amount from a fuel injector 32 of which air-fuel ratio setting is switched between lean and rich depending upon a load on an engine. Further, there is disposed a bypass control valve 42 capable of controlling an intake air amount independent of a usual intake air throttle valve 38 in a bypass passage 40. The control circuit 46 controls opening and closing of the bypass control valve 42 according to an intake air pipe pressure sensed by an intake air pipe pressure sensor 54 when the air-fuel ratio setting is switched between lean and rich. That is, when a load is increased to a prescribed intake air pipe pressure, the air-fuel ratio becomes rich and the bypass control valve 42 is closed simultaneously and an amount of intake air is reduced by the amount. With this arrangement, a smooth switching can be carried out without causing an abrupt torque change.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an internal combustion engine equipped with a so-called lean combustion system that sets the air-fuel ratio to be ultra-lean in the low-medium load range of the engine.

[Conventional technology]

In an internal combustion engine equipped with a so-called lean combustion system, the air-fuel ratio is set to ultra-lean in the engine's low-to-medium load range, and the air-fuel ratio is switched to rich in the high-load operating range where the engine requires output. In order to prevent sudden changes in torque during this switching, there are methods that perform smoothing control so that the air-fuel ratio changes gradually (Japanese Patent Laid-Open No. 58-48746), or that temporarily retard the ignition timing. something is proposed.

[Problem that the invention seeks to solve]

When switching the air-fuel ratio between lean and rich, in the case of the conventional method of gradually changing the air-fuel ratio, the air-fuel ratio becomes rich even though the load is not high before switching, so the air-fuel ratio becomes rich when the load is not high. There is a problem of increased nitrogen oxide (Nox) emissions.

On the other hand, the countermeasure of retarding the ignition timing has problems that normally occur when retarding the ignition timing, such as an increase in the exhaust gas temperature and a deterioration of the fuel consumption rate.

[Means for solving problems]

In FIG. 1, the air-fuel ratio control device for an internal combustion engine according to the present invention includes an intake air supply means l that can control the amount of intake air to the internal combustion engine independently of a normal intake throttle valve, and means 2 for supplying fuel, means 3a for setting the amount of fuel supplied from the fuel supply means 2 so that the air-fuel ratio takes a value on the rich side, and means 3a for setting the amount of fuel supplied from the fuel supply means 2 so that the air-fuel ratio takes a value on the lean side. Means 3b for setting the amount of fuel supplied from the supply means, means 4 for detecting a load factor of the internal combustion engine, and means for switching the setting of the air-fuel ratio between lean and rich according to the load of the engine. 5, and a control means 6 for driving the intake air supply means to open and close when the air-fuel ratio setting is switched between lean and rich.

According to a preferred embodiment, said control means 6 include bistable means 6a for maintaining a signal to the intake air supply control means 1;
gate means 6b for outputting a signal for closing the intake air control means 1 when the load threshold set by the setting means 5 is exceeded; and means 6c for setting a second load threshold lower than the load threshold; , a second gate means 6d which outputs a signal to open the intake air control means 1 when the load falls below the second threshold.

〔Example〕

The present invention will be described in detail below. In FIG. 2, 1
0 is a cylinder block, 12 is a piston, 14 is a cylinder head, 16 is a combustion chamber, 1 (white) is a spark plug, 20 is an intake valve, and 22 is an intake boat. The intake boat 22 is the intake pipe 2
4. Connected to the air cleaner 30 via the surge tank 26 and throttle body 28. 32 is a fuel injector. The combustion chamber 16 is connected to an exhaust pipe 34 via an exhaust valve and an exhaust boat (not shown). 36 is a distributor.

An intake throttle valve (throttle valve) 38 is disposed within the throttle body 28. A bypass passage 40 is installed to bypass the throttle valve 38, and a bypass control valve 42 is installed in this bypass passage 40. By opening and closing the bypass control valve 42, the amount of intake air can be changed in steps.

The control circuit 46 is a control circuit for driving and controlling the fuel injector 32 and the bypass control valve 42, and is configured as a microcomputer system in the embodiment. The control circuit 46 is a microprocessing unit (MPU) 46a.
, a memory 46b, an output port 46C, an input port 46d, and a bus 46e connecting these elements.

Various engine operating condition sensors are connected to the input boat 46d, and engine operating condition signals are applied thereto. A crank angle sensor 50.52 is installed in the distributor 36. The first crank angle sensor 50 generates a pulse signal every 720° rotation of the crankshaft, which serves as a reference signal. On the other hand, the second crank angle sensor 52 generates a signal every 30 degrees of the crankshaft, which is used to determine the rotational speed and serves as a starting signal for the crank angle interrupt routine. An intake pipe pressure sensor 54 is installed in the surge tank 26, and can obtain an engine load state signal corresponding to the absolute pressure of the intake pipe. Engine water temperature sensor 5
6 is installed in the engine body 10, and can obtain a signal according to the temperature of the cooling water in the water jacket. An air-fuel ratio sensor 58 is installed in the exhaust pipe 34, and a signal corresponding to the air-fuel ratio can be obtained.

Output port 46C is connected to fuel injector 32 and bypass control valve 42. Actuation signals for the fuel injector 32 and the bypass control valve 42 are sent to the output port 46c according to a flowchart described later.

The operation of the present invention will be explained below using a flowchart. FIG. 3 shows a fuel injection routine, which is a crank angle interrupt routine that is started when the crank angle sensors 50 and 52 detect a predetermined crank angle corresponding to the fuel injection start time. In step 70, a basic fuel injection amount 'rp is calculated from the engine speed Ne and the intake pipe pressure PM as a representative load value. That is, the memory 46b has a map of the basic injection amount for the combination of engine speed and intake pipe pressure, and the MPU 46a stores the engine speed calculated by the crank angle sensor 52 and the intake pipe pressure actually measured by the intake pipe pressure sensor 54. A supplementary calculation of the basic fuel injection amount is executed.

In step 70, the final fuel injection ['l'AU is
It is calculated by =TPXKLEANXα+β. Here, KLEAN is a lean correction coefficient, which is set as described below. Further, α and β representatively represent correction coefficients and correction amounts whose explanations are omitted because they are not directly related to the present invention. It is well known that such corrections include feedback correction based on the air-fuel ratio signal detected by the air-fuel ratio sensor 58, water temperature correction based on the signal from the temperature sensor 56, and the like.

Step 74 shows the output of the fuel injection signal.

That is, a fuel injection signal is set to the output port, and TAU
When the fuel injection signal elapses based on , the fuel injection signal is stopped and fuel injection is terminated.

FIG. 4 shows a routine for setting the lean correction coefficient and driving the bypass control valve, and this routine is executed at predetermined short time intervals, for example, every 15 msec.

In step 80, intake pipe pressure PM≧predetermined value PM.

It is determined whether or not. PM in the low and medium load range of the engine
Since <PM, the answer is NO, and in step 82, the answer is K.
It is determined whether LEAN=1.0.

No. 1 because it is set to lean at low and medium loads.
If so, the process proceeds to step 84, where a signal to open the bypass control valve 42 is output from the output port. Next, in step 86, the lean correction coefficient KLEAN is set to, for example, 0.
It is set to 65. This value of KLEAN=0.65 is a value that sets the air-fuel ratio to a super-lean level of about 22.4, for example.

When the engine is under high load, PM≧PM, and the determination is YES, the process proceeds to step 88, and a signal will be applied from the output port to close the bypass control valve 42. Next, in step 90, the lean correction coefficient KLBAN is set to 1.0. In this case, the air-fuel ratio will be on the rich side, for example 1
It is set to 4.5.

After the air-fuel ratio is set rich in this way, the load decreases and PM<PM, so the determination is No at step 8°, the determination is Yes at step 82, and the process proceeds to step 92, where PM; :PM It is determined whether or not it is 2. If the pressure PM is still greater than PM2 (Yes)
, proceed to Ste Nob 88. When the pressure PM becomes smaller than PM (No), the process proceeds from step 88 to step 84, where a signal to open the bypass control valve 42 is output from the output port, and the air-fuel ratio is returned to the lean setting.

FIG. 5 is a diagram schematically showing torque changes in the present invention. When the air-fuel ratio is set to lean, the intake pipe pressure becomes PM.
The torque changes like l according to the characteristics when the air-fuel ratio is lean until it reaches the value . At this time, the bypass control valve 42 is in an open state. When the load increases to intake pipe pressure PM=PM (time point ■), the air-fuel ratio becomes rich and changes as shown in m according to the torque characteristic at the rich time. When entering the rich setting, the bypass control valve 42 is simultaneously closed.

Therefore, the amount of intake air decreases stepwise as shown by the straight line n, which reduces the torque generated by the engine (■
), this decrease is set to exactly offset the torque increase due to making the air-fuel ratio rich. In other words, the pressure is set so that the lean torque when the intake pipe pressure is PM is equal to the rich torque when the intake pipe pressure is PM2. In this way, sudden changes in torque at the time of air-fuel ratio switching are prevented, and smooth switching characteristics can be achieved.

FIG. 6 shows a second embodiment, in which the bypass control valve 42
Hysteresis is achieved by slightly differentiating the torque value when lean at intake pipe pressure PM+ when switching from open to closed and the torque when rich at intake pipe pressure PMff when switching from closed to open so that the latter becomes smaller. It is characterized by having the following.

In the first embodiment, the bypass control valve was explained as an 0N-OFF type, but in this second embodiment, the bypass control valve 42 is
is configured to have variable opening characteristics; for example, it is connected to a step motor so that it can have a desired opening degree. As will be understood from the explanation below, the bypass control valve 42 does not need to be able to open continuously and may be a simple opening/closing valve; It is necessary to configure the opening degree to be different from the opening degree when changing from the closed state to the open state.

FIG. 7 shows a flowchart illustrating the operation of the control circuit of the second embodiment. Since this is similar to FIG. 4, the explanation will focus on the differences, and the same numbers will be given to the same parts and detailed explanation will be omitted.

In the lean state, the determination in step 80.82 is Yes, so the process proceeds to step 84A, and in this step, the position of the step motor for driving the bypass control valve 42 is changed from ST to ST.
Set E P = a. Therefore, the bypass control valve 42 has an opening determined by this position of the step motor.

When the intake pipe pressure PM becomes larger than the predetermined value PM (7th
(■) in the figure, the process proceeds from step 80 to step 88A, where the step motor step number 5TEP is set to 0, so the bypass control valve 42 is closed, and at the same time it shifts to the rich state, and the intake pipe pressure at this time is equal to PM2. (■ in Figure 7). The opening degree of the bypass control valve 42 before it closes, that is, the number of steps a, is determined so that the torque does not change from opening to closing of the bypass control valve 42. That is, the step number a is determined so that the torque is the same when the intake pipe pressure PM,') opens the bypass with a lean setting at the switching point and when the bypass closes (intake pipe pressure PMz) with a rich setting. It will be done.

The load shifts to decrease and the intake pipe pressure PM reaches the predetermined value PM:
When l (< P MZ ) (■ in Fig. 7), the process proceeds from step 92A to step 84B, and the step number is 5.
TEP is set to b, and at the same time, the lean setting is returned and the intake pipe pressure PM becomes PM4 (■ in FIG. 7). The opening degree of the bypass control valve, that is, the number of steps, is determined so that the torque does not change when the bypass control valve 42 is closed to opened. That is,
The number of steps is determined so that the torque is the same when the bypass is closed (intake pipe pressure PMi) at the rich setting at the switching point and when the bypass is open (intake pipe pressure PM, ) at the lean setting. With such a setting, even though hysteresis is provided, smooth switching without shock can be performed both when the bypass control valve is changed from closed to open and when changed from open to idle.

〔Effect of the invention〕

FIG. 8 shows the torque characteristics when switching between lean and rich in the prior art. In this case, a shock occurs because the torque at the load at the time of switching between lean and rich changes suddenly as shown by p. In this invention, by controlling the opening and closing of the bypass control valve 42 at the time of switching, smooth switching without sudden changes in torque can be performed.

In the embodiment, a bypass passage is provided to bypass the throttle valve and the control valve on the bypass passage is driven, but instead of this, a double throttle valve is installed and this is driven by a rotary motor such as a step motor. You may.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of the present invention. FIG. 2 is a diagram showing the entire embodiment of the present invention. 3 and 4 are flowcharts illustrating the operation of the control circuit of FIG. 2. FIG. 5 is a graph explaining the torque characteristics in switching between rich and on in the first embodiment. FIG. 6 is a flowchart of a bypass control routine in the second embodiment. FIG. 7 is a graph illustrating torque characteristics at the time of air-fuel ratio switching in the second embodiment. FIG. 8 is a graph illustrating torque characteristics in conventional switching between rich and lean states. 10... Engine body 24... Intake pipe 26... Surge tank 32... Fuel injector 38... Throttle valve 40... Bypass passage 42... Bypass control valve 46... Control circuit 50 .52...Crank angle sensor 54...Intake pipe pressure sensor

Claims (1)

[Claims] 1. An air-fuel ratio control device for an internal combustion engine consisting of the following components, an intake air supply means capable of controlling the amount of intake air to the internal combustion engine independently of a normal intake throttle valve, and an internal combustion engine. means for supplying fuel to the engine; means for setting the amount of fuel supplied from the fuel supply means so that the air-fuel ratio takes a value on the rich side; and means for setting the fuel supply amount from the fuel supply means so that the air-fuel ratio takes a value on the lean side. means for setting the amount of fuel supplied from the engine; means for detecting load factors of the internal combustion engine; means for switching the air-fuel ratio setting between lean and rich depending on the engine load; control means for opening and closing the intake air supply means to absorb torque fluctuations at the time of switching between rich and rich; 2. The control means includes bistable means for holding a signal to the intake air supply control means, and a first control means set by the setting means.
gate means for outputting a signal to close the intake air control means when the load threshold of said first load is exceeded; means for setting a second load threshold lower than said first load threshold; a second gate means for outputting a signal for opening the intake air control means when the intake air control means is below a threshold value;
The air-fuel ratio control of an internal combustion engine according to claim 1, wherein the torque during lean operation at the first load threshold value and the torque during rich operation at the second load threshold value are set to be substantially equal. Device. 3. Claim 1, which provides hysteresis by changing the amount of air in the open state before switching the intake air supply means to the closed state and the amount of air in the open state after switching from the closed state. The air-fuel ratio control device for the internal combustion engine described above.