JPH06330794A - Idle speed control method for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent occurrence of an undesirable engine stall caused by change of characteristics of a sensor used for feedback control of an air-fuel ratio. CONSTITUTION:In a internal combustion engine, a feedback factor FAF indicated by a line (3) is obtained correspondingly to an air-fuel ratio indicated by a line (2), which is detected by an oxygen density sensor, and a fuel injection amount TAU indicated by a line (6) is corrected. When inactive condition of the sensor is detected based on lowering of a sensor temperature caused by long-time idling, feedback controlling is suspended. At this time, value DS is added to a Duty of a flow passage control valve of an idling bypass passage indicated by a line (7) for a predetermined time. It is thus possible of surely prevent occurrence of engine stall which be caused by abrupt change of the feedback factor FAF.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an idle speed of an internal combustion engine, and more particularly to a method for controlling an idle speed of an internal combustion engine in which a fuel injection amount is controlled by feeding back oxygen concentration in combustion exhaust gas. .

[0002]

2. Description of the Related Art Basically, a control system for an internal combustion engine determines an intake air amount from, for example, an intake pressure and a rotation speed of the internal combustion engine, and supplies an injection amount of fuel corresponding to the intake air amount from a fuel injection valve. It is configured to inject and atomize the intake air, and to control the ignition timing at an ignition timing corresponding to the intake air amount and the rotation speed. The fuel injection amount is the injection amount obtained from the intake pressure and the rotation speed as described above as a basic injection amount, and further corrected in accordance with the cooling water temperature and the property of the internal combustion engine obtained by learning. To be
Further, from the viewpoint of exhaust gas purification and low fuel consumption, an oxygen concentration sensor is provided in the exhaust gas so as to maintain the air-fuel ratio at the stoichiometric air-fuel ratio, and a correction coefficient corresponding to the output of the oxygen concentration sensor is set to the basic injection amount. The actual fuel injection amount is obtained by multiplying.

On the other hand, the oxygen concentration sensor is, for example, 3
If the internal combustion engine is left in an idle state and the exhaust gas temperature falls and becomes an inactive region, the active region where the operation can be guaranteed is from 00 to 400 ° C. or higher. The feedback control may malfunction. Therefore, in Japanese Patent Laid-Open No. 1-216046, which is a typical prior art proposed by the applicant of the present invention,
The erroneous control as described above is prevented as shown in FIG.

FIG. 19 is a timing chart for explaining the operation of a typical prior art. During normal operation of the internal combustion engine, when the output of the oxygen concentration sensor becomes leaner than the theoretical air-fuel ratio of 14.5 as shown in FIG. 19 (2), the correction coefficient is adjusted by the feedback control corresponding to this. It becomes larger than 1.0 as shown by 19 (3). When the output of the oxygen concentration sensor becomes rich due to such an increase in the correction coefficient, the correction coefficient becomes 1.
The output of the oxygen concentration sensor is maintained at a value near the stoichiometric air-fuel ratio.

When the accelerator pedal is released from the normal running as described above, and the rotation speed of the internal combustion engine decreases as shown in FIG. 19 (5), as shown in FIG. 19 (6). The fuel injection amount also decreases. When the throttle valve is fully closed at time t1 and the idle switch is turned on as shown in FIG. 19 (1), the flow control valve provided in the bypass passage for idle is as shown in FIG. 19 (7). And is driven at a predetermined control duty DT to maintain idle operation.

The flow rate control valve is constructed so as to change its opening amount by changing its control duty, for example.
Is a target rotational speed N that is determined according to the load state of the internal combustion engine, for example, whether the air conditioner is used, or whether the automatic transmission is in the D range, and the like.
The basic duty DI obtained based on the difference between T and the actual rotational speed NE is added to the duty DTH of the correction term associated with the cooling water temperature, the starting time, and the use of an electric load.
The actual control duty DUTY is obtained by adding W, DST, and DEL. By the duty control of the flow rate control valve with the control duty DUTY thus obtained, the idle rotation speed NE of the internal combustion engine is maintained at the target rotation speed NT.

Here, if the idle state as described above continues, the exhaust gas temperature lowers and the characteristic of the oxygen concentration sensor changes from the active region to the inactive region as described above. In such an inactive region, the oxygen concentration sensor is configured so that its output is held on the rich side or the lean side in order to prevent adverse effects due to sensor characteristic fluctuations. Therefore, for example, in the case where it is configured to be held on the lean side, when the exhaust temperature starts to drop at the time t1 as described above, the output of the oxygen concentration sensor gradually increases as shown in FIG. 19 (2). Deviate to the lean side. As a result, the correction coefficient based on the air-fuel ratio also increases as shown in FIG. 19 (3).

Therefore, according to this conventional technique, FIG.
As shown in, when the output of the oxygen concentration sensor becomes lean side at time t2, the duration time is counted, and when the count value reaches a predetermined time W1 such as 20 seconds or more, the oxygen is detected at time t3 when the time W1 has elapsed. It is determined that the concentration sensor is inactive, and the correction coefficient that has been changed to the maximum value of, for example, about 1.2 is shown in FIG.
9 (3), 1.0 at time t3
Will be returned to. Therefore, as shown in FIG. 19 (6), the fuel injection amount is also rapidly reduced. In this way, the erroneous correction due to the inactivation of the oxygen concentration sensor is prevented.

[0009]

However, in the above-mentioned prior art, when the oxygen concentration sensor is in the active state and the air-fuel ratio is actually lean, the fuel injection amount sharply decreases as shown in FIG. 19 (6). As a result, the rotational speed of the internal combustion engine decreases as shown in FIG. 19 (5), and engine stall occurs.

An object of the present invention is to provide an idle speed control method for an internal combustion engine capable of reliably preventing an undesired engine stall due to a change in characteristics of a feedback sensor.

[0011]

According to the present invention, an oxygen concentration sensor is provided in an exhaust passage of an internal combustion engine, and at least a fuel injection amount is controlled according to the oxygen concentration in exhaust gas detected by the oxygen concentration sensor. In an internal combustion engine idle speed control method, the output of the oxygen concentration sensor represents a lean state, and correspondingly corrects the fuel injection amount to be in a rich state, and the correction control is performed for a predetermined time or more. When continued for a long time, the correction control is stopped, and at the time of the stop or immediately before the stop, the flow control valve provided in the bypass passage for idling that connects the upstream side and the downstream side of the throttle valve is opened. The method is an idle speed control method for an internal combustion engine, wherein the degree is increased by a predetermined time.

According to the present invention, an oxygen concentration sensor is provided in the exhaust path of the internal combustion engine, and at least the idling speed of the internal combustion engine is controlled to control the fuel injection amount in accordance with the oxygen concentration in the exhaust gas detected by the oxygen concentration sensor. In the speed control method, the output of the oxygen concentration sensor represents a rich state,
Correspondingly, the fuel injection amount is corrected so as to be in a lean state, and when the correction control is continued for a predetermined time or more, the correction control is stopped and the stop time or immediately before the stop. In the idle speed control method for an internal combustion engine, the opening degree of a flow control valve provided in an idle bypass flow passage that connects the upstream side and the downstream side of the throttle valve is reduced by a predetermined time. is there.

Further, the amount of increase or decrease of the opening degree of the flow rate control valve of the present invention is characterized in that it is obtained corresponding to the cooling water temperature at the time when the predetermined time has elapsed.

The amount of increase or decrease of the opening of the flow control valve of the present invention corresponds to the difference between the actual idle speed of the internal combustion engine and the target idle speed at the time when the predetermined time has elapsed. Characterized by what is required.

Still further, according to the present invention, the control for increasing or decreasing the opening degree of the flow control valve is continued until the difference between the actual idle speed of the internal combustion engine and the target speed becomes within a predetermined value. Characterize.

Further, the present invention is characterized in that, after increasing or decreasing the opening degree of the flow control valve, the increasing amount or the decreasing amount is decreased corresponding to the cooling water temperature.

[0017]

According to the present invention, an oxygen concentration sensor is provided in the exhaust path of the internal combustion engine, for example, in front of the catalyst, and the fuel injection amount and the like are determined in accordance with the oxygen concentration in the exhaust gas detected by the oxygen concentration sensor. In the feedback control of the idle rotation speed of the internal combustion engine so as to control and always maintain the stoichiometric air-fuel ratio, when the output of the oxygen concentration sensor indicates either one of the lean and rich states, either the lean or the rich. Correction control is performed to increase or decrease the fuel injection amount so that the other state is achieved.

Despite the correction of the fuel injection amount, the lean or rich state continues,
When the correction control is continued for a predetermined time or longer, it is determined that the temperature of the oxygen concentration sensor is out of the allowable operating range and is inactive, or the oxygen concentration sensor is abnormal, The correction control is stopped. By stopping the correction control, the fuel injection amount is immediately set to a value in a state where the air-fuel ratio is at the stoichiometric air-fuel ratio.

Therefore, particularly when the oxygen concentration sensor is not abnormal and the lean state of the air-fuel ratio of the internal combustion engine is actually continuing, if the correction control is stopped, the air-fuel ratio becomes higher (lean). Therefore, the engine may be stalled.Therefore, in the present invention, when the correction control is stopped, the bypass for idle that connects the upstream side and the downstream side of the throttle valve for a predetermined time from the time of the stop or immediately before the stop. The opening degree of the flow control valve provided in the flow path is increased to prevent the engine stall. In this way, it is possible to reliably prevent undesired engine stalling due to changes in the characteristics of the feedback sensor.

Further, in the case where the correction control is stopped when the rich state continues for the predetermined time or more, the air-fuel ratio is further lowered (rich) by the stop of the correction control. There is a possibility that the rotation speed of the engine will increase, and in the present invention, with the stop of the correction control, the opening degree of the flow control valve is decreased for a predetermined time from the stop time or immediately before the stop, and the rotation speed May be prevented in advance. In this way, it is possible to reliably prevent an undesired increase in the rotation speed due to a change in the characteristics of the sensor.

[0021] Preferably, the amount of increase or decrease of the opening of the flow control valve is the cooling water temperature at the time when the predetermined time elapses, that is, when the feedback control is stopped corresponding to the detection result of the oxygen concentration sensor, or It may be obtained corresponding to the difference between the actual idle speed of the internal combustion engine and the target idle speed.

Further, preferably, such an increase or decrease control of the opening of the flow control valve is performed until the difference between the actual idle speed and the target speed becomes within a predetermined value, that is, the actual idle speed. It may be continued until the speed becomes close to the target rotation speed.

Still more preferably, the opening degree of the flow rate control valve increased or decreased as described above may be decreased or increased according to the cooling water temperature.

[0024]

1 is a block diagram showing an internal combustion engine control apparatus 1 according to an embodiment of the present invention and a configuration related thereto.
The combustion air introduced from the intake port 2 is supplied to the air cleaner 3
After being purified by, the amount of inflow is adjusted via the intake pipe 4 by the throttle valve 5 interposed in the intake pipe 4, and then flows into the surge tank 6. The combustion air flowing out from the surge tank 6 is mixed with the fuel injected from the fuel injection valve 8 interposed in the intake pipe 7, and passes through the intake valve 9 to the internal combustion engine 1
0 into the combustion chamber 11. A spark plug 12 is provided in the combustion chamber 11, and the exhaust gas from the combustion chamber 11 is discharged through an exhaust valve 13 and is discharged from the exhaust pipe 14 into the atmosphere through a three-way catalyst 15.

The intake pipe 4 is provided with an intake air temperature detector 21 for detecting the temperature of intake air, and the throttle valve 5
The throttle valve opening detector 22 and the idle detector 22a are provided in relation to the
An intake pressure detector 23 is provided to detect the pressure of. A cooling water temperature detector 24 is provided near the combustion chamber 11, an oxygen concentration sensor 25 is provided in the exhaust pipe 14 upstream of the three-way catalyst 15, and an exhaust temperature is provided inside the three-way catalyst 15. A detector 26 is provided. The rotation speed of the internal combustion engine 10, that is, the rotation speed per unit time is detected by the crank angle detector 27.

The control device 1 includes the detectors 21 to 27.
At the same time, the vehicle speed detector 28, the start detector 29 that detects whether or not the starter motor 33 that starts the internal combustion engine 10 is activated, the air conditioning detector 30 that detects the use of the air conditioner, and the internal combustion engine 10 When the vehicle equipped with is equipped with an automatic transmission, the detection result from the neutral detector 31 that detects whether or not the shift stage of the automatic transmission is in the neutral position is input.

Furthermore, the control device 1 includes a battery 3
4, the control device 1 controls the fuel injection amount and the ignition timing based on the detection results of the detectors 21 to 31 and the power supply voltage of the battery 34 detected by the voltage detector 20. And the like to control the fuel injection valve 8, the spark plug 12, and the like.

The intake pipe 4 is also formed with a side passage 35 that bypasses the upstream side and the downstream side of the throttle valve 5, and the side passage 35 is provided with a flow control valve 36. The flow rate control valve 36 is duty-controlled by the control device 1, and adjusts and controls the flow rate of the combustion air during idle when the throttle valve 5 is almost fully closed. The control device 1 also drives the fuel pump 32 when the internal combustion engine 10 is operating.

The flow rate control valve 36 has a valve shaft arranged in, for example, an electromagnetic solenoid, and by duty-controlling a coil of the electromagnetic solenoid, the valve shaft is displaced and fixed to one end of the valve shaft. This is a so-called linear solenoid type flow control valve in which the opening of the valve changes.

FIG. 2 is a block diagram showing a specific configuration of the control device 1. The detection results of the detectors 20 to 25 are
It is given from the input interface circuit 41 through the analog / digital converter 42 to the processing circuit 43 realized by a microcomputer or the like. Also, the detector 22,
The detection results of 27 to 31 are the input interface circuit 44.
To the processing circuit 43. Processing circuit 43
A memory 45 for storing various control maps and learning values is provided inside the processing circuit 4.
3, the electric power from the battery 34 is supplied to the constant voltage circuit 4
It is supplied via 6.

The control output from the processing circuit 43 is derived through the output interface circuit 47, is applied to the fuel injection valve 8 to control the fuel injection amount, and is also applied to the spark plug 12 via the igniter 48. The ignition timing is controlled, and the flow rate of the inflowing air through the side passage 35 at the time of idling is further controlled by being given to the flow rate control valve 36.
Further, the fuel pump 32 is driven.

The detection result of the exhaust gas temperature detector 26 is given to the exhaust gas temperature detection circuit 49 in the control unit 1. When the detection result is abnormally high, the warning lamp 51 is turned on via the drive circuit 50. To be done.

FIG. 3 is a timing chart for explaining the idle speed control operation by the control device 1 configured as described above. The controller 1 obtains the fuel injection amount TAU, that is, the valve opening time of the fuel injection valve 8 as follows.

TAU = TP * KG * FAF (1) However, TP is a basic injection amount, the pressure in the surge tank 6 detected by the intake pressure detector 23 and the internal combustion detected by the crank angle detector 27. Corresponding to the rotational speed of the engine 10 and the like, it is obtained by interpolation calculation from a map obtained in advance. KG is a coefficient obtained by learning as described later, and FAF is a feedback coefficient corresponding to the detection result of the oxygen concentration sensor 25 obtained as described below.

The output of the oxygen concentration sensor 25 corresponds to the oxygen concentration in the exhaust gas and, as shown in FIG. 3 (2), the reference voltage of 0. 45V as a reference, on the rich side, that is, 1
When it is less than 4.5, it exceeds 0.45 V, and when it is on the lean side, that is, when it exceeds 14.5, it is 0.
It will be less than 45V. In this way, the detection output of the oxygen concentration sensor 25 is 0.4 or less depending on whether the air-fuel ratio is rich or lean.
Invert around 5V.

Therefore, the feedback coefficient FAF changes as shown in FIG. 3C, that is, when the air-fuel ratio is in the lean state, the feedback coefficient FAF is larger than the reference value 1.0 so as to increase the fuel injection amount TAU. When the air-fuel ratio is in a rich state, the reference value is set to a value less than 1.0 in order to reduce the fuel injection amount TAU. When the detection result of the oxygen concentration sensor 25 is reversed, the feedback coefficient FAF is drastically changed as shown in FIG. 3C to improve the response. Thus, the feedback coefficient FAF changes with good responsiveness in response to the detection result of the oxygen concentration sensor 25 as shown before time t12 in FIG. 3C, whereby the air-fuel ratio and the feedback coefficient FAF are respectively shown in the figure. Three
As shown in (2) and FIG. 3 (3), for example, 1 Hz
It changes periodically with the degree.

On the other hand, the oxygen concentration sensor 25 is constructed so that the temperature of the detection portion is, for example, 300 to 400 ° C. or higher and becomes an active region where accurate rich or lean determination can be performed. Further, in the inactive region below the temperature, the output is fixed at either the rich side or the lean side in order to prevent undesired output fluctuation. Therefore, when the controller 1 detects such a fixed output of the oxygen concentration sensor 25, it sets the feedback coefficient FAF to the reference value of 1.0, stops the feedback control, and shifts to the open loop control.

Further, during the feedback control, when the air-fuel ratio becomes rich or lean, the feedback coefficient FAF is set to a value less than 1.0 or more than 1.0, respectively. Therefore, the average value of the feedback coefficient FAF is also the reference value 1 It should be 0. However, the average value of the feedback coefficient FAF may deviate from the reference value 1.0 due to a decrease in the discharge pressure of the fuel pump 32 due to aging, a decrease in the flow passage cross-sectional area of the fuel injection valve 8, and the like.

Therefore, the learning coefficient KG for long-term feedback is introduced together with the coefficient FAF for high-responsive short-term feedback control. Therefore, when the average value of the feedback coefficient FAF deviates from the above 1.0 due to the aging, etc.,
The learning coefficient KG is changed as follows, and the average value of the feedback coefficient FAF is maintained at the reference value 1.0. In this way, the stoichiometric air-fuel ratio is maintained by the learning coefficient KG even during the non-control of the feedback control described later in which the feedback coefficient is kept at the reference value 1.0.

The learning of the learning coefficient KG is indicated by reference numerals k1, k2, k3 in FIG. 3 (3) at the timing when the detection result of the oxygen concentration sensor 25 is inverted between the rich side and the lean side, for example. Feedback factor FA
The average value of the value of F for one cycle, that is, for example, (k1 +
k2) / 2, (k2 + k3) / 2, ... Are obtained. Next, when the average value is larger than 1.02, the learning coefficient KG
Is increased by 0.1%, the learning coefficient KG is not updated when the average value is 0.98 or more and 1.02 or less, and the learning coefficient KG is updated when the average value is less than 0.98.
Is reduced by 0.1%. In this way, as understood from the equation 1, the basic injection amount TP is corrected by the learning coefficient KG, and the feedback value FAF is further corrected by the feedback coefficient FAF in the range of ± 20%. It will be possible.

The controller 1 also controls the ignition plug 12 via the igniter 48 in accordance with the fuel injection amount TAU obtained as described above and the rotation timing of the internal combustion engine 10 detected by the crank angle detector 27. Drive control.

Next, the idle speed control operation by the controller 1 will be described with reference to FIG. When the accelerator pedal is returned and the rotation speed of the internal combustion engine 10 decreases as shown in FIG. 3 (5), the fuel injection amount TA as described above.
U also decreases as shown in FIG. Thus, at time t11, the throttle valve 5 is fully closed, and when the idle detector 22a conducts as shown in FIG. 3 (1), the idle rotation speed control is started.

When the engine is not in the idle state, the control duty DUTY of the flow rate control valve 36 is increased every predetermined time as will be described later, so that the normal running is continued as shown before time t11 in FIG. 3 (7). When it is set, the control duty DUTY is almost 100%. During normal running before time t11, the air-fuel ratio and the feedback coefficient F are set at about 1 Hz, for example, from the response speed of the oxygen concentration sensor 25 and the amount of change in the feedback coefficient FAF, as described above.
AF changes periodically.

The control duty DUTY is obtained from the following equation.

DUTY = DI + DFAF + DTHW + DAC + DNSW (2) However, DI is a basic duty, and as will be described later,
The actual rotational speed NE and the target rotational speed NT of the internal combustion engine 10
The increment .DELTA.DI corresponding to the difference between .alpha. The target rotation speed NT is the warm-up state of the internal combustion engine 10 detected by the cooling water temperature detector 24, the use of the air conditioner detected by the air conditioning detector 30, and the automatic shift detected by the neutral detector 31. It is a value determined corresponding to the load state of the internal combustion engine 10 such as turning on the drive position of the machine. DFAF is a correction term added at the time of switching from the feedback control to the open loop control.

DTHW is a correction term obtained corresponding to the cooling water temperature detected by the cooling water temperature detector 24. The DAC is a correction term that is added when the air conditioning detector 30 detects that cooling is being performed.
Similarly, DNSW is a correction term that is added when the neutral detector 31 detects that the gear position of the transmission has been shifted to a drive position or a reverse position other than the neutral position.

When the engine enters the idle state at the time t11, the exhaust gas flow rate decreases and the temperature of the oxygen concentration sensor 25 decreases. As a result, the air-fuel ratio detected by the oxygen concentration sensor 25 becomes a value fixed on the lean side, for example, as shown in FIG. 3 (2), and the oxygen concentration sensor 25 becomes an inactive region. Therefore, the feedback coefficient FAF increases as shown in FIG. 3C, and is maintained at the maximum value of 1.2, for example.

In order to stop the feedback control in such an inactive region, the control device 1 measures the time during which the air-fuel ratio is in the lean state as shown in FIG. 3 (4) and continues it. When the time reaches a predetermined time W11, for example, 20 seconds as shown between times t12 and t13, the output fixation of the oxygen concentration sensor 25 is determined at the time t13, and the feedback coefficient FAF is determined as shown in FIG. Is set to 1.0.

However, after this, the oxygen concentration sensor 25
Is actually in the output fixed state, as indicated by reference numeral α1 in FIG.
Although the air-fuel ratio corresponding to the detection result of will remain fixed, when the air-fuel ratio is actually lean,
As indicated by reference numeral α2, the air-fuel ratio becomes even higher and exceeds the combustible air-fuel ratio, which may cause engine stall.

Therefore, in this embodiment, the time t1 at which the feedback control is switched to the open loop control.
3, the control duty DUTY is added by a predetermined value DS, for example, 30%, as shown in FIG. 3 (7), and after this time t13 is kept for a predetermined time W12, for example, 2 seconds, the addition state is maintained. The value DS is gradually reduced from time t14 when the time W12 has elapsed, for example, it decreases by 5% every 100 msec. As a result, at time t13 in FIG.
As shown in (3), even if the feedback coefficient FAF is suddenly changed to the reference value of 1.0 and the fuel injection amount TAU shown in (3) of FIG. 3 decreases, the rotation speed of the internal combustion engine 10 still remains. As shown in FIG. 3 (5), it rises, or at least is maintained at present. It should be noted that the addition of the value DS may be started immediately before the time t13, for example, before 300 msec, in consideration of the time delay until the combustion air flowing from the flow rate control valve 36 reaches the combustion chamber 11. Good.

Thus, in this embodiment, the control duty DUTY is increased at the timing of switching from the feedback control to the open loop control at time t13, and so-called idle-up is performed. Therefore, the feedback coefficient FAF reaches the maximum value due to the switching. Even if the control value is switched from 1.0 to the reference value 1.0, the idle operation can be continued without engine stall.

The increment ΔDI is the actual rotation speed N
E is equal to or lower than the target rotation speed NT, that is, NT-NE
When ≧ 0, the value shown in FIG. 4 is set, while the actual rotation speed NE is less than the target rotation speed NT, that is, when the increment ΔDI where NT-NE <0 acts as a decrement, The value is as shown in FIG.
Therefore, as apparent from FIGS. 4 and 5,
Further, in the present embodiment, the increment ΔDI for increasing the control duty DUTY is made larger than the increment ΔDI at the time of decrease, so that the idle rotation speed NE can be rapidly increased when it should be increased, and sharply decreased when it is decreased. There is no risk of stalling due to descent.

6 to 8 are flow charts for explaining the duty control operation shown in FIG.
Step n1 every predetermined period, for example, every 4 msec
Then, it is judged whether or not it is a timing of 100 msec which is a predetermined calculation cycle for performing the subsequent duty calculation, and if not, step n4 described later.
The control operation of the flow control valve 36 after 1 is started, and if so, the process moves to step n2.

In step n2, it is carried out at the time of shipment,
It is determined whether or not the test mode in which the test terminal (not shown) of the processing circuit 43 is short-circuited is determined, and if so, the process proceeds to step n3, and the control duty DUTY is 50%.
Is set to a constant value and the process moves to step n41, and if not, the process moves to step n4.

At step n4, it is determined whether or not the starter motor 33 is being started and the start detector 2 is started.
It is judged from the detection result of No. 9, and if so, the routine proceeds to step n5, where the control duty DUTY is 100%.
Is set to move to step n41, and otherwise move to step n6.

In step n6, the idle detector 22a
It is judged from the detection result of whether it is in the idle state,
Otherwise, in step n7, the current control duty DUTY is 1.5% of the previous value DUTY (i-1).
The control duty DUTY is increased to 100% during normal running as described above, and if so, step n8.
Move on to.

At step n8, the neutral detector 3
It is determined by 1 whether or not the gear position of the transmission is the neutral position, and if not, that is, the reverse position or the drive position, in step n9, the correction term DNSW is set to 15%, and then step n10.
, And if so, go directly to step n10. At step n10, it is judged by the air conditioning detector 30 whether or not the cooling is being used, and if so, the correction term DAC is set to 40% at step n11, then the process proceeds to step n21, and if not, the direct step is carried out. Move to n21.

At step n21, it is judged if the feedback control is stopped and the flag F1 indicating that the open loop control is being performed is set to 1. FIG. 9 is a flowchart for explaining the setting operation of the flag F1. At a predetermined oxygen concentration reading timing of, for example, 8 mesc, the interrupt calculation process shown in FIG. 9 is started, and in step m0, the detection result of the oxygen concentration sensor 25 is read after being subjected to analog / digital conversion. In step m1, it is determined whether or not the read voltage value Vo is 0.45 V or more, which is the reference voltage Vref, and if so, it is determined that the state is rich and the count value C1 is 0 in step m2. And the flag F1 is also reset to 0, the process returns to the main process shown in FIGS.

When the air-fuel ratio is lean in step m1, the process proceeds to step m4, and the count value C1 is added and updated. Then step m5
Then, it is determined whether or not the count value C1 is equal to or more than the value corresponding to the time W11, and if so, the flag F1 is set to 1 in step m6, and then the process returns to the main process, otherwise. Sometimes it returns directly to the main process.

Step m3 or m6 as described above
The flag F1 set in step n21 is set as described above in step n21.
When the flag F1 is reset to 0, the process proceeds to step n22, where the flag F2 indicating the first calculation timing after the feedback control is stopped is reset to 0, and further at step n23, After the count value C2 for measuring the time W12 is reset to 0, the process proceeds to step n31.

When the flag F1 is set to 1 in step n21, step n2
5, it is determined whether or not the flag F2 is set to 1. If not, that is, at the first calculation timing when the feedback control is stopped, the process proceeds to step n26. At step n26, the control duty DU
The value DS is substituted into the correction term DFAF of TY, and the count value C2 is reset to 0 in step n27. Further, after the flag F2 is set to 1 in step n28, the process proceeds to step n31.

Furthermore, when the flag F2 is set to 1 in step n25, that is, at the second and subsequent calculation timings after the feedback control is stopped, the process proceeds to step n29 and the count value C2 is set.
Is added and updated. The process moves from step n29 to step n24, and the count value C2 is equal to the time W.
It is determined whether or not the value is equal to or greater than the value corresponding to 12, and if not, the process directly proceeds to step n31, and if so, that is, after the time t14, step n30.
Move on to. In step n30, the correction term DFAF is subtracted and updated by a predetermined ratio, for example, 5%, and then the process proceeds to step n31.

In step n31, the cooling water temperature detector 24
In step n32, the map showing the relationship between the cooling water temperature and the correction term DTHW of the control duty is read into the register, and in step n33 interpolation calculation is performed to obtain the correction term DTHW.

At step n34, the vehicle speed detected by the vehicle speed detector 28 is read, and at step n35, it is judged whether or not the feedback control condition is satisfied. The feedback control condition is, for example, that the vehicle speed is 0, that is, the vehicle is stopped and the cooling water temperature is 0.
° or more. When this feedback control condition is not satisfied, at step n36, the basic duty D
After I is set to 0%, the process proceeds to step n43, and when the feedback control condition is satisfied, step n43
Move to 37.

At step n37, the difference ΔN between the actual rotation speed NE and the target rotation speed NT is calculated, and step n3
At 8, it is determined whether the difference ΔN is negative, that is, whether the actual rotation speed NE is less than the target rotation speed NT. When the difference ΔN is not less than 0, step n
39, the increment ΔD for deceleration shown in FIG.
After the map of I is read, the process moves to step n41. When the difference ΔN is less than 0 in step n38, the process proceeds to step n40, and after the map of the increment ΔDI for acceleration shown in FIG. 4 is read, the process proceeds to step n41. At step n41, at step n3
From the map read at 9 or n40, the increment ΔDI corresponding to the difference ΔN is obtained by interpolation calculation.

At step n42, the basic duty DI this time is obtained by adding the increment ΔDI obtained at step n41 to the previous basic duty DI (i-1). In step n43, the correction terms DTHW, DAC, ...
From I and the correction term DFAF, the actual control duty DUTY is calculated according to the above equation 2.

FIG. 10 is a waveform diagram for explaining the control operation of the flow control valve 36 corresponding to the control duty DUTY. Similar to the counter for measuring the times W11 and W12, the processing circuit 43 is provided with a counter for controlling the opening time of the flow rate control valve 36. This counter is reset at every drive cycle W21 of the flow rate control valve 36, for example, every 100 msec as shown in FIG. The count value C
Until the ISC reaches the value WD corresponding to the control duty DUTY, the flow rate control valve 36 is opened as shown in FIG. 10 (2), and when it exceeds the value WD, it is closed. Thus, in the drive cycle W21, the flow rate control valve 36 is opened only during the period W22 corresponding to the control duty DUTY.

Steps n3, n5, n7 or n4
From step 3, the process proceeds to step n51, where the count value CIS
It is determined whether or not C has reached the time W21 of 100 msec, and if so, the count value CISC is reset to 0 in step n52 and then the process proceeds to step n53, otherwise, the process directly proceeds to step n53.
Move on to.

At step n53, the count value CI
It is determined whether SC is equal to or less than the value WD, and if so, the operation is ended after the flow rate control valve 36 is opened in step n54, and if it is not, after the valve is closed in step n55. The operation ends.

As described above, in this embodiment, when the feedback control of the fuel injection amount is stopped, the flow rate control valve 3
The control duty DUTY of 6 is added by the value DS over the time W12, and then gradually decreased. Also,
The increment ΔDI for the integral control of the flow control valve 36 is set to a larger change amount when the rotational speed of the internal combustion engine 10 is accelerated than when it is decelerated.

In this way, even if the oxygen concentration sensor 25 is determined to be inactive, the feedback coefficient FAF of the fuel injection amount TAU is suddenly changed from the maximum value of 1.2 to the reference value of 1.0. The idle rotation speed NE can be maintained at a speed at which engine stall does not occur. In this way, it is possible to reliably prevent undesired engine stall due to a change in the characteristics of the feedback sensor.

The rotation speed NE for obtaining the basic injection amount TP is 180 ° from the crank angle detector 27.
The intake pressure that is obtained by the interrupt process in response to the crank pulse for each CA and that fluctuates significantly is determined by the intake pressure detector 23.
The output from is read by being converted into analog / digital every predetermined 2 msec. Similarly, the counter for obtaining the count value CISC is, for example, 1
A counting operation is performed by interrupt processing every msec.

FIG. 11 is a flow chart for explaining a part of the duty control operation of another embodiment of the present invention, which is similar to FIG. 7 described above and the same reference numerals are given to corresponding parts. In this embodiment, when the flag F2 is not 1 in step n25, that is, at the first calculation timing after the feedback control is stopped, the process moves to step n61 and the detection result of the cooling water temperature detector 24 is read. At step n62, the cooling water temperature THW and the correction term DFAF stored in advance as shown in FIG.
Is read into the register, and the graph is interpolated in step n63 to obtain the correction term DFAF corresponding to the cooling water temperature THW.
Move on to.

Therefore, the value of the correction term DFAF of the control duty DUTY added when stopping the feedback control is replaced with the constant value DS of the above-mentioned embodiment, and the optimum value corresponding to the warm-up state of the internal combustion engine 10 is obtained. Can be set to.

FIG. 13 is a flow chart showing a part of the duty control operation of still another embodiment of the present invention, which is similar to the embodiment shown in FIGS. 7 and 11 and the corresponding parts are the same. Add a reference mark. In this embodiment, when the flag F2 is not set to 1 in step n25, the process proceeds to step n71 and the internal combustion engine 10
A difference ΔN between the actual rotation speed NE and the target rotation speed NT is calculated. At step n72, whether or not the difference ΔN is negative, that is, the actual rotation speed NE is the target rotation speed N
It is determined whether or not it is less than T. When the difference ΔN is not less than 0, that is, when the actual rotation speed NE is equal to or higher than the target rotation speed NT, the difference ΔN is determined in step n73.
Is regarded as 0 and the process proceeds to step n74, and if so, the process directly proceeds to step n74. In step n74, FIG. 14 showing the relationship between the difference ΔN and the correction term DFAF.
A graph as shown in (4) is read out to the register, and in step n75, the correction term DFAF corresponding to the difference ΔN is obtained from the graph by interpolation calculation.

As described above, the correction term DF corresponds to whether or not the actual rotation speed NE is equal to or higher than the target rotation speed NT, and when it is less than the target rotation speed NT.
By setting AF, the optimum control duty DUT corresponding to the state of the internal combustion engine 10 is also obtained.
Y can be added.

FIG. 15 is a flow chart showing a part of the duty control operation of another embodiment of the present invention. In this embodiment, the process moves from step n29 to step n81,
It is determined whether or not the actual rotation speed NE is lower than the target rotation speed NT, and if so, further step n8.
In step 2, the difference ΔN between the two is obtained. The difference ΔN thus obtained is a predetermined value, for example −5, at step n83.
It is determined whether or not it is less than 0 rpm, and when that is the case, that is, when the actual rotation speed NE is lower than the target rotation speed NT by more than 50 rpm, the process directly proceeds to step n31, otherwise, that is, the actual rotation speed. When NE is within 50 rpm from the target rotation speed NT, and when the actual rotation speed NE has already exceeded the target rotation speed NT in step n81,
After moving to step n30 and performing a decrease calculation of the correction term DFAF, the process proceeds to step n31.

As a result, after the actual rotation speed NE becomes close to the target rotation speed NT, the control duty DUTY that has been added can be started to decrease, and the idle rotation speed can be stabilized.

FIG. 16 is a flow chart showing a part of the duty control operation of still another embodiment of the present invention. In this embodiment, when the count value C2 becomes greater than or equal to the time W12 in step n24, the process moves to steps n91 to n93, and the correction term DFAF corresponding to the cooling water temperature is obtained as in steps n61 to n63 in FIG. This correction term D
FAF is further subtracted by a predetermined ratio, for example, 5% in step n94, and then the process proceeds to step n31.

The control duty DUT thus added
The attenuation rate of Y may be changed according to the cooling water temperature THW.

Each control operation according to the present invention as described above is
It can be particularly suitably used for the internal combustion engine 70 as shown in FIG. In this internal combustion engine 70, LP is used as fuel.
Since gas is used, most of the fuel used for combustion is sucked from the fuel tank 72 through the carburetor 73 into the intake pipe 4 in a gas state from the carburetor 71 or a regulator, and is corrected by feedback of the fuel amount. Since only the fuel injection valve 8 is performed, the intake amount of fuel from the carburetor 71 is also increased by the increase of the intake air amount, and the engine stall can be effectively prevented.

When the oxygen concentration sensor 25 is configured to be fixed to the rich side output when it becomes inactive, the oxygen concentration sensor 25 corresponds to the above-described FIGS. 3 (1) to 3 (7), respectively. As shown in FIGS. 18 (1) to 18 (7),
When the feedback control is switched to the open loop control at time t13 and the feedback coefficient FAF increases from the minimum value of 0.8 to 1.0, the fuel injection amount TAU is as indicated by reference numeral α11 in FIG. 18 (6). As a result, the rotation speed NE also rises, as indicated by reference numeral α12 in FIG. 18 (5), and so-called upstroke occurs.

Therefore, as another embodiment of the present invention, the control duty DUTY may be decreased by the value DS. As a result, the fuel injection amount TAU becomes as indicated by reference numeral α13, and as a result, it is possible to prevent the rotational speed from rising as indicated by reference numeral α14.

[0084]

As described above, according to the present invention, the oxygen concentration sensor is provided in the exhaust passage of the internal combustion engine, and at least the fuel injection amount is fed back in accordance with the oxygen concentration in the exhaust gas detected by the oxygen concentration sensor. When the oxygen concentration sensor becomes inactive, or when an abnormality occurs due to a short circuit or disconnection, the correction control by the feedback is stopped, and the opening degree of the flow control valve provided in the bypass passage for idle Is set to a so-called idle-up state, the oxygen concentration sensor becomes inactive and its output represents a lean state for a predetermined time, and the correction control for making the fuel injection amount rich is stopped. At this time, even if the air-fuel ratio is actually lean,
An engine stall can be prevented by the idle-up. In this way, it is possible to reliably prevent undesired engine stall due to a change in the characteristics of the feedback sensor.

When the oxygen concentration sensor becomes inactive and its output indicates a rich state, when the correction control for making the lean state is stopped,
The opening degree of the flow rate control valve may be reduced to prevent blow-up.

[Brief description of drawings]

FIG. 1 is a block diagram showing a control device 1 for an internal combustion engine of an embodiment of the present invention and a configuration related thereto.

FIG. 2 is a block diagram showing a specific configuration of the control device 1.

FIG. 3 is a feedback coefficient FA for fuel injection control.
6 is a timing chart for explaining a duty control operation of the idle flow control valve 36 with respect to a change in F.

FIG. 4 Increment ΔD for integral control of idle speed
6 is a graph showing a change with respect to a difference between a rotation speed NE and a target rotation speed NT during acceleration of I.

FIG. 5 is a rotational speed NE during deceleration of the increment ΔDI.
3 is a graph showing a change with respect to a difference between a target rotation speed NT and a target rotation speed NT.

FIG. 6 is a flow control valve 3 for idle according to an embodiment of the present invention.
6 is a flowchart for explaining a duty control operation of No. 6;

FIG. 7 is a flow control valve 3 for idle according to an embodiment of the present invention.
6 is a flowchart for explaining a duty control operation of No. 6;

FIG. 8 is a flow control valve for idle 3 according to an embodiment of the present invention.
6 is a flowchart for explaining a duty control operation of No. 6;

FIG. 9 is a flowchart for explaining a setting operation of a flag F1 indicating whether or not feedback control is being performed.

FIG. 10 is a waveform diagram for explaining a duty control operation of the flow rate control valve 36.

FIG. 11 is a flowchart for explaining a part of a duty control operation of another embodiment of the present invention.

FIG. 12 is a graph showing changes in the correction term DFAF of the control duty DUTY with respect to the cooling water temperature THW.

FIG. 13 is a flowchart for explaining a part of the duty control operation of still another embodiment of the present invention.

FIG. 14 is a graph showing a change in a correction term DFAF of the control duty DUTY with respect to a difference ΔN between an actual rotation speed NE and a target rotation speed NT.

FIG. 15 is a flowchart for explaining a part of the duty control operation of another embodiment of the present invention.

FIG. 16 is a flowchart for explaining a part of the duty control operation of still another embodiment of the present invention.

FIG. 17 is a simplified cross-sectional view showing the structure of an internal combustion engine 70 in which the present invention is preferably implemented.

FIG. 18 is a timing chart for explaining the duty control operation of the idle flow control valve 36 with respect to the change of the feedback coefficient FAF for fuel injection control according to another embodiment of the present invention.

FIG. 19 is a timing chart for explaining a duty control operation of a conventional idle flow control valve.

[Explanation of symbols]

 1 Control Device 5 Throttle Valve 8 Fuel Injection Valve 10,70 Internal Combustion Engine 14 Exhaust Pipe 20-24, 26-31 Detector 25 Oxygen Concentration Sensor 35 Bypass 36 Flow Control Valve 43 Processing Circuit 45 Memory 71 Carburettor

Claims (6)

[Claims] 1. An idle speed control method for an internal combustion engine, wherein an oxygen concentration sensor is provided in an exhaust path of the internal combustion engine, and at least a fuel injection amount is controlled in accordance with an oxygen concentration in exhaust gas detected by the oxygen concentration sensor. In the above, the output of the oxygen concentration sensor represents a lean state, and the fuel injection amount is corrected so as to be in a rich state corresponding to the lean state, and when the correction control is continued for a predetermined time or more, The correction control is stopped, and the opening degree of the flow rate control valve provided in the bypass passage for idle that connects the upstream side and the downstream side of the throttle valve is increased for a predetermined time while stopping the correction control or immediately before the stop. An idle speed control method for an internal combustion engine, comprising: 2. An idle speed control method for an internal combustion engine, wherein an oxygen concentration sensor is provided in an exhaust path of the internal combustion engine, and at least a fuel injection amount is controlled according to the oxygen concentration in the exhaust gas detected by the oxygen concentration sensor. In, the output of the oxygen concentration sensor represents a rich state, the fuel injection amount is corrected to be lean corresponding to this, when the correction control is continued for a predetermined time or more, The correction control is stopped, and the opening degree of the flow rate control valve provided in the bypass passage for idling that connects the upstream side and the downstream side of the throttle valve is decreased for a predetermined time while stopping the correction control or immediately before the stop. An idle speed control method for an internal combustion engine, comprising: 3. The internal combustion engine according to claim 1, wherein the increase amount or the decrease amount of the opening degree of the flow control valve is obtained corresponding to the cooling water temperature at the time when the predetermined time has elapsed. Engine idle speed control method. 4. The amount of increase or decrease of the opening degree of the flow control valve is obtained in correspondence with the difference between the actual idle speed of the internal combustion engine and the target idle speed at the time when the predetermined time has elapsed. The method for controlling idle speed of an internal combustion engine according to claim 1 or 2, characterized in that. 5. The control for increasing or decreasing the opening of the flow control valve is continued until the difference between the actual idle speed of the internal combustion engine and the target speed becomes within a predetermined value. An idle speed control method for an internal combustion engine according to any one of claims 1 to 4. 6. The method according to claim 1, wherein after increasing or decreasing the opening degree of the flow control valve, the increasing or decreasing amount is decreased corresponding to the cooling water temperature. An idle speed control method for an internal combustion engine according to claim 1.