JPH04362249A - Fail-safe system of variable valve timing device - Google Patents

Abstract

PURPOSE:To stabilize the combustion condition of engine by increasing a fuel injection amont when abnormality of a variable valve timing device is detected. CONSTITUTION:A variable valve timing device changes the period when each valve open period of a suction valve 26 and an exhaust valve 27 of internal combustion engine overlaps depending on operation condition. An abnormality detection means detects abnormality of the vatiable valve timing device. An air-fuel ratio control means performs feedback-control of a fuel injection amount with a fuel injection valve 16 so that air-fuel ratio of internal combustion engine becomes a target air-fuel ratio. A detection means detects that the air-fuel ratio control means is not operating and that open loop control of air-fuel ratio is performed. A fuel injection amount increase means increases the fuel injection amount by the fuel injection valve 16 when open loop control is detected by the detection means and abnormality is detected by the abnormality detection means.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a fail-safe system for a variable valve timing device, and in particular to prevent malfunctions in an internal combustion engine when a device that varies the valve timing of intake and exhaust valves according to operating conditions fails. Regarding fail-safe systems.

0002

[Prior Art] Conventionally, variable valves have been designed to obtain the optimum engine torque according to the operating conditions by varying the overlapping periods of the opening periods of the intake and exhaust valves depending on the operating conditions. In an internal combustion engine equipped with a timing device, a fail-safe system is known that increases the set idle speed when the variable valve timing device fails (Japanese Patent Laid-Open No. 1-110844).
Publication No.).

In other words, in this conventional fail-safe system, if the variable valve timing device fails and the valve timing is controlled at low to medium speeds and high loads, the opening periods of the intake and exhaust valves overlap when idling. If the amount is too large, the effective compression ratio may drop and engine stall may occur, so the idle speed control (ISC) system increases the target idle setting speed.

0004

[Problems to be Solved by the Invention] However, since this conventional fail-safe system does not take measures against failures other than when the engine is idling, it is particularly difficult to prevent the air-fuel ratio from occurring when the variable valve timing device fails in an operating range other than idling. There is a problem in that the feedback system cannot avoid engine malfunctions when the engine is not operating.

In other words, if the variable valve timing device fails and the valve timing remains the same at low, medium speeds and high loads, the valve overlap period will be too long during low load operation during air-fuel ratio feedback operation, resulting in unstable combustion. In that case, the oxygen concentration in the exhaust gas increases, so feedback control of the fuel injection amount is performed to make the air-fuel ratio rich, so there is no problem. Since the feedback control described above cannot be performed during loop control), there is a possibility that the engine stalls due to a failure of the variable valve timing device.

[0006] The present invention has been made in view of the above points.
It is an object of the present invention to provide a fail-safe system for a variable valve timing device that solves the above problems by increasing the fuel injection amount when an abnormality is detected in the variable valve timing device.

[0007]

[Means for Solving the Problems] Fig. 1 shows a diagram of the principle configuration of a fail-safe system for a variable valve timing device according to the present invention. In the figure, variable valve timing device 11
The period in which the opening periods of the intake valve and exhaust valve of the internal combustion engine 10 overlap is varied depending on the operating state. An abnormality detection means 12 detects an abnormality in this variable valve timing device 11.

The air-fuel ratio control means 13 performs feedback control on the amount of fuel injected by the fuel injection valve 16 so that the air-fuel ratio of the internal combustion engine 10 becomes the target air-fuel ratio. The detection means 14 detects that open loop control of the air-fuel ratio is being performed while the air-fuel ratio control means 13 is not operating. The fuel injection amount increasing means 15 increases the amount of fuel injected by the fuel injection valve 16 when the detection means 14 detects open loop control and when the abnormality detection means 12 detects an abnormality.

[0009]

[Operation] The abnormality detecting means 12 detects an abnormality in the variable valve timing device 11 when the valve timing of the variable valve timing device 11 remains the same as that of the high load operation even in the low load operation state and does not switch to the valve timing of the low load operation. Detected as. When this abnormality is detected and the air-fuel ratio is being controlled in an open-loop manner by the air-fuel ratio control means 13, the overlapping period between the opening periods of the intake valve and the exhaust valve is too long, so if it continues as it is, it will be rough. It becomes idle. However, in the present invention, in this case, since the fuel injection amount is increased by the fuel injection amount increasing means 15,
The combustion state of the engine can be stabilized.

0010

Embodiment FIG. 2 shows a system configuration diagram of an embodiment of the present invention. This embodiment is an example in which the internal combustion engine 10 is applied to a 4-cylinder 4-stroke spark ignition internal combustion engine (engine), and FIG.
2 shows a structural sectional view of an arbitrary cylinder, and each part of the system is controlled by a microcomputer 21, which will be described later.

In FIG. 2, a piston 23 that reciprocates vertically in the figure is housed in an engine block 22, and a combustion chamber 24 is communicated with an intake manifold 25 via an intake valve 26, while an exhaust valve 27 The exhaust manifold 28 is connected to the exhaust manifold 28 via the exhaust manifold 28. Also, the spark plug 2 is arranged so that the plug gap protrudes into the combustion chamber 24.
9 is provided.

The upstream side of the intake manifold 25 is commonly connected to an intake pipe 31 for all four cylinders via a surge tank 30. A throttle valve 33 is located inside this intake pipe 31.
, and an air flow meter 32 are provided, respectively. The opening degree of the throttle valve 33 is adjusted in conjunction with the accelerator pedal, and the opening degree is detected by a throttle position sensor 34. An intake temperature sensor 35 is provided downstream of the air flow meter 32 to measure intake air temperature. Moreover, the throttle valve 33 is bypassed, and the throttle valve 33
A bypass passage 36 is provided that communicates the upstream and downstream sides of the engine, and an idle speed control valve (ISCV) 37 whose opening degree is controlled by a solenoid is installed in the middle of the bypass passage 36.

Reference numeral 38 denotes a fuel injection valve, which is similar to the fuel injection valve 16.
The fuel is injected into the airflow passing through the intake manifold 25 according to instructions from the microcomputer 21, which will be described later. Further, an oxygen concentration detection sensor (O2 sensor) 39 is provided so as to partially protrude through the exhaust manifold 28, and detects the oxygen concentration in the exhaust gas before entering the catalyst device. A water temperature sensor 40 is provided so as to penetrate the engine block 22 and partially protrude into the water jacket, and detects the temperature of the engine cooling water. 41 is the igniter, and the ignition coil (
(not shown) opens and closes the primary current.

Further, 42 is a distributor, which includes a cylinder discrimination sensor 43 that generates a reference position detection signal of the engine crankshaft, and a cylinder discrimination sensor 43 that generates an engine rotation speed signal, for example.
It has a rotation angle sensor 44 that generates a rotation angle every ℃A.

Further, reference numeral 45 denotes a hydraulic control solenoid valve, which together with the valve operating mechanism 46 constitutes the variable valve timing device 11 described above. As will be described later, the valve operating mechanism 46 has a well-known structure that switches the opening/closing timing control of the intake valve 26 and the exhaust valve 27 in response to on/off of the hydraulic pressure from the hydraulic control solenoid valve 45.

The microcomputer 21 that controls the operation of each part of such a configuration has a hardware configuration as shown in FIG. In the figure, the same components as those in FIG. 2 are denoted by the same reference numerals, and the explanation thereof will be omitted. In FIG. 3, the microcomputer 21 is a central processing unit (CPU) 50.
, read-only memory that stores processing programs (
ROM) 51, random access memory (RAM) 52 used as a work area, backup RAM 53 that retains data even after the engine is stopped, input interface circuit 54, A/D converter with multiplexer 5
6 and an input/output interface circuit 55, which are connected to each other via a bus 57.

The A/D converter 56 receives an intake air amount detection signal from the air flow meter 32, an intake temperature detection signal from the intake temperature sensor 35, a detection signal from the throttle position sensor 34, a water temperature detection signal from the water temperature sensor 40, and a water temperature detection signal from the water temperature sensor 40.
2. The oxygen concentration detection signal from the sensor 39 is sequentially switched and taken in through the input interface circuit 54, converted from analog to digital, and sequentially sent to the bus 57.

The input/output interface circuit 55 receives a detection signal from the throttle position sensor 34 and a rotational speed signal corresponding to the engine rotational speed (NE) from the rotational angle sensor 44, and sends them to the CPU via a bus 57.
Enter 50.

Further, the CPU 50 executes various arithmetic processing based on each data input from the input/output interface circuit 55 and the A/D converter 56 through the bus 57, and transfers the obtained data to the bus 57 and the input. ISCV 37, fuel injection valve 38,
The igniter 41 and the hydraulic control solenoid valve 45 are selectively output as appropriate to control the opening degree of the ISCV 37 to control the idle rotation speed to the target rotation speed, and the fuel injection time by the fuel injection valve 38, that is, the fuel injection per unit time. The igniter 41 controls the ignition timing, and the valve operating mechanism 46 performs known valve timing control via the hydraulic control solenoid valve 45.

Next, this valve timing control will be explained. Figure 4 shows a characteristic diagram of the variable valve timing device, where the vertical axis is the throttle opening and the horizontal axis is the engine speed (
The unit is rpm). As shown in the figure, the hydraulic control solenoid valve 45 is turned off in the operating range I, which is a low-load operating state in which the throttle opening is below a predetermined value, and a high-speed operating state in which the engine speed is above a predetermined value N1.

As a result, the valve operating mechanism 46 delays the opening timing of the intake valve 26 with respect to the opening period T27 of the exhaust valve 27, as shown in FIG. 5(A). By overlapping the opening period T27 of the exhaust valve 27 with a small period θ1 after the intake valve 26 starts opening, gas blow-by in the combustion chamber is prevented and the engine torque is suppressed.

On the other hand, as shown by II in FIG. 4, when the throttle opening is above a predetermined value and the engine speed is
The hydraulic control solenoid valve 45 is turned on in a high-load operation range of less than 1. As a result, the valve operating mechanism 46 advances only the opening timing of the intake valve 26 as shown in FIG. By overlapping the opening period T27 of the exhaust valve 27 with a large period of θ2 (however, θ2 > θ1) after the intake valve 26 starts opening, a sufficient intake and exhaust period can be ensured to improve charging efficiency. and improve engine torque.

In an internal combustion engine equipped with a variable valve timing device that performs such an operation, this embodiment has the above-mentioned abnormality detection means 12, air-fuel ratio control means 13, and detection means 1.
4 and the fuel injection amount increasing means 15 are realized by a microcomputer 21, and then the abnormality detecting means 1
2 will be explained.

FIG. 6 shows a variable valve timing device (VVT).
3 shows a flowchart of an embodiment of an abnormality detection routine of the device. This routine is interrupted and started every 30°C. First, the CPU 50 calculates the current engine rotation speed NEi based on the detection signal from the rotation angle sensor 44 (step 101), and then calculates the current engine rotation speed NEi based on the following equation. A weighted average value NEAVi of the rotational speed is calculated (step 102).

[0025]

[Math 1]

However, in the above formula, NEAVi-1 represents the weighted average value calculated last time.

Next, the throttle position sensor 34
It is determined whether it is within 10 seconds after the signal indicating that the idle valve 33 is fully closed is input (from the idle contact turning on) (step 103), and if it is within 10 seconds, the rotation speed calculated in step 101 is determined. It is determined whether the absolute value of the difference between NEi and the weighted average value NEAVi of the rotational speed calculated in step 102 is greater than a predetermined value (for example, 100 rpm) (step 104). When an abnormality occurs in the hydraulic control solenoid valve 45 or the valve operating mechanism 46 that constitutes the variable valve timing device in an idle state, the valve timing relationship normally becomes as shown in FIG. If the valve timing becomes as shown in (B), the current engine speed NEi will fluctuate (varies) by at least 100 rpm with respect to the above weighted average value NEAVi.
. This is because the overlapping period between the intake valve 26 and the exhaust valve 27 is too long, causing gas to blow through, reducing charging efficiency and worsening combustion. Therefore, in step 104, it is detected whether or not this fluctuation has occurred, and if the engine speed fluctuation has occurred, the counter value C is incremented by "1" (step 105), and then this routine is ended (step 106). If there is no change in engine speed, the routine is ended with the counter value C unchanged (step 106).

[0028] While the idle state is within 10 seconds, the arithmetic processing of steps 101 to 105 is repeated every 30°C, and when 10 seconds have elapsed from the idle state, it is determined whether the counter value C is greater than "30" or not. No, it is determined (step 106). The counter value C indicates how many times the above-mentioned engine rotational speed fluctuation occurs during the 10 second idle state, and if this occurs 31 or more times, there is an abnormality in the hydraulic control solenoid valve 45 or the valve mechanism 46. It is determined that there is, and the abnormality determination flag f is set to "1" (step 107), and then the counter value C is cleared (step 108), and this routine is ended (step 109).
. When the counter value C is "30" or less, the counter value C is cleared without determining that it is abnormal (step 108).
, this routine ends (step 109). In addition,
The initial values of the counter value C and the abnormality determination flag f are set to "0" by the initial routine.

Next, the air-fuel ratio control means 13 and the detection means 14
I will explain about it. FIG. 7 shows a flowchart of an air-fuel ratio (A/F) feedback control routine that implements the air-fuel ratio control means 13 and the detection means 14. This A/F feedback control routine is a routine that is activated by an interrupt every 4ms, for example, and first the A/F feedback (F/F
B) Determine whether the condition is met (step 2)
01). When the F/B condition is not satisfied (for example, the cooling water temperature is below a predetermined value, the engine is starting, increasing after starting, increasing warm-up, increasing power, cutting fuel, etc.), A/F feedback control is determined. After setting the flag XAF to “0” (
Step 202), air-fuel ratio feedback correction coefficient FA
The value of F is set to "1.0" (step 203), and this routine ends (step 213). This allows A/
Open loop control of F is performed. Step 201
, 202 realize the detection means 14.

On the other hand, when the F/B condition is satisfied (other than when the above F/B condition is not satisfied), the process proceeds to step 204, and the A/F
After setting the feedback control determination flag XAF to "1", the detected voltage V1 of the O2 sensor 39 is converted and taken in (step 205). Next, in step 206, it is determined whether the detected voltage V1 is less than or equal to the comparison voltage VR1, thereby determining whether the air-fuel ratio is rich or lean. When it is rich (V1 > VR1), a determination is made as to whether it is in that state or a state reversed from the previous lean state to rich (step 207), and when the state is reversed to rich, the previous air-fuel ratio is The value obtained by subtracting the skip constant RSL from the value of the feedback correction coefficient FAF is set as a new air-fuel ratio feedback correction coefficient FAF (step 208
). On the other hand, if it was in a rich state last time and continues to be rich, the integral constant KI is subtracted from the previous FAF value to obtain a new FAF value (step 209), and this routine exits (step 213). .

On the other hand, when it is determined in step 206 that the fuel is lean (V1≦VR1), it is determined whether the state has reversed from the rich state to lean (step 210). When reversing to lean, the value obtained by adding the skip constant RSR from the previous FAF value is used as the new air-fuel ratio feedback correction coefficient FAF.
(Step 211). On the other hand, if it is determined that the state is still lean even though it was in a lean state last time, the integral constant KI is added to the FAF value to set a new FAF value (step 21).
2), this routine is ended (step 213). Here, the skip constants RSL and RSR are set to values that are sufficiently larger than the integral constant KI.

As a result, when the air-fuel ratio changes as schematically shown in FIG. 8(A), the air-fuel ratio feedback correction coefficient FAF changes from lean to rich as shown in FIG. 8(B). When the air-fuel ratio is reversed from rich to lean, the fuel injection time is greatly attenuated by the skip constant RSL in a skip-like manner, and when the air-fuel ratio is reversed from rich to lean, the fuel injection time is greatly increased by the skip constant RSR in a skip-like manner. Change TAU to a larger value. Furthermore, when the air-fuel ratio remains the same, FAF gradually changes from a larger value when lean to a smaller value when rich, according to the integral constant (time constant) KI, as shown in Figure 8 (B). do.

FIG. 9 shows a flowchart of an example of the fuel injection time TAU calculation routine. This TAU calculation routine is executed as a part of the main routine, and the CPU 50 takes in each value such as the engine speed NE, the intake air amount Q, and the air-fuel ratio feedback correction coefficient FAF from the backup RAM 53 (or RAM 52) (step 301
).

[0034] Next, the CPU 50 calculates the above intake air amount Q.
After calculating the basic fuel injection time TP in a well-known manner based on and the engine rotational speed NE, the final fuel injection time TAU is calculated based on the following equation (step 302).

[0035]TAU=TP×FAF×β
(2) However, in the above formula, β is a correction coefficient for the increase in power after starting, the increase in warm-up power, etc. In this way, the fuel injection time TAU (that is, the fuel injection amount per unit time) is controlled so that the air-fuel ratio of the internal combustion engine becomes, for example, the stoichiometric air-fuel ratio.

Next, the fuel injection amount increasing means 15, which constitutes the essential part of the present invention, will be explained. FIG. 10 is a flowchart showing a main routine of an embodiment of the essential part of the present invention, and FIG.
is a flowchart showing an example of fail processing in FIG. 10; 10 and 11 show fuel injection amount increasing means 1
5 is a flowchart for realizing step 5. When the main routine shown in FIG. 10 is started, first, it is determined whether the idle contact is on (throttle valve 33 is fully closed) based on the detection signal from the throttle position sensor 34 (step 401). .

When the idle contact is off, this routine is exited (step 405), and when the idle contact is on, it is determined whether the abnormality determination flag f is "1" or not (step 402). When the abnormality determination flag f is "0", this routine ends (step 405), but when the abnormality determination flag f is "1", fail processing is performed (
Step 403). After fail processing, abnormality determination flag f
After setting the value to "0" (step 404), this routine ends (step 405).

Fail processing 403 is executed by a subroutine shown in FIG. In FIG. 11, first, the value of the A/F feedback control flag XAF is "0".
In other words, it is determined whether the A/F feedback control is inactive and the air-fuel ratio is under open loop control (step 501).

When the value of the flag XAF is "0", the value obtained by multiplying the fuel injection time TAU calculated in the TAU calculation routine of FIG. 9 by 1.2 is used as the new fuel injection time (
As a TAU (step 502), this routine is exited (step 503). Also, in step 501, the flag
When the AF value is determined to be “1”, the fuel injection time TA
Exit this routine without changing U (step 503
).

As described above, according to this embodiment, when the air-fuel ratio is under open-loop control and the hydraulic control solenoid valve 45 or the valve operating mechanism 46 is abnormal, the intake valve 2
If the valve opening timing in No. 6 does not switch to the original late timing and remains at the early timing, the fuel injection time TAU will be multiplied by 1.2, so even if the above abnormality occurs, combustion will deteriorate at that time. This prevents engine stall from occurring and allows the vehicle to run.

By the way, in this embodiment, FIGS. 12 and 13
A known idle speed control (ISC) control is performed by the routine shown in FIG. When the ISC control routine shown in FIG. 12 is started at a predetermined timing, in step 601 it is determined whether the conditions are suitable for performing ISC F/B control, that is, based on the signal output from the throttle position sensor 34. It is determined whether conditions such as the throttle valve is fully closed and the vehicle speed is zero from a vehicle speed sensor (not shown) (hereinafter simply referred to as F/B conditions) are satisfied, and the F/B conditions are satisfied. If not, the process moves to the "guard processing" routine at step 614, and when it is determined that the F/B conditions are satisfied, the process moves to the process for F/B control shown at step 602.

In step 602, the backup RAM
The learning value DG already stored in the controller 53 is output to the ISCV 37 as a control value D, and the ISCV 37 is maintained at an opening degree corresponding to the control value D. As a result, the amount of air passing through the bypass passage 36 is controlled to an idle rotation speed corresponding to the amount of air. Also, the rotation speed NE at this time is the target value NF.
When it is different from the target value NF, processing is performed to increase or decrease the control value D of the ISCV 37 in order to bring the idle rotation speed closer to the target value NF.

Next, in step 603, it is determined whether the idle rotation speed NE is equal to or greater than "target value NF+α (α>0)", and if the determination result is "greater than", step 604 is performed.
, the magnitude of the control value D and the learning value DG is determined, and "
If D≦DG, the correction value G1 is subtracted from the learned value DG, the subtracted result is stored as a new learned value DG (step 605), and the process then proceeds to the "guard processing" routine (step 614). On the other hand, in step 604 “D
>DG", the process proceeds to the "guard processing" routine 614 without making any correction to the learned value DG.

On the other hand, if it is determined in step 603 that the idle rotation speed NE is smaller than "NF+α," the idle rotation speed NE and the target rotation speed NF are further compared in magnitude (step 606). This step 60
If it is determined in step 6 that "NE≧NF", the magnitude of the control value D and the learned value DG is determined (step 607).
, if "D≦DG", the correction value G2 is subtracted from the learned value DG (step 608), the subtraction result is stored as a new learned value DG, and the process moves to the "guard processing" routine 614. Further, if it is determined in step 607 that "D>DG", the process moves to the "guard processing" routine 614 without making any correction to the learned value DG.

Furthermore, in step 606, “NE<N
F", it is determined whether "NE≧NF-α" (step 609). This step 60
If it is determined in step 9 that “NE≧NF−α”, the control value D
The magnitude of the learning value DG is determined (step 610), and "
If it is determined that D<DG, the process moves to the "guard processing" routine 614, and if the determination result is "D≧DG", the correction value G2 is added to the learned value DG (step 611),
After storing the added result as a new learning value DG,
The process moves to the "guard processing" routine 614.

Furthermore, if it is determined in step 609 that the engine rotation speed NE is smaller than the "target rotation speed NF-α", it is determined whether "D<DG" (
Step 612), if the determination result is "D<DG", the process moves to the "guard processing" routine 614, and if "D≧DG", the correction value G1 is added to the learned value DG (step 613).
), and after storing the added result as a new learned value DG, the process moves to the "guard processing" routine 614.

Next, referring to FIG. 13, the above-mentioned "guard processing"
Routine 614 will now be described.

First, in step 701, it is determined whether the learned value DG is smaller than the upper limit value DGMAX, and when it is determined that the learned value DG is greater than or equal to the upper limit value DGMAX, the learned value DG is indicated as the upper limit value DGMAX. As the value (step 702), the processing of this routine is completed, and on the other hand, if it is determined that the learned value DG does not exceed the upper limit value DGMAX, it is determined whether the learned value DG is greater than the lower limit value DGMIN ( Step 703). The judgment result is “DG≦D”
GMIN", the learned value DG is set to the value indicated by the lower limit value DGMIN (step 704), and the processing of this routine is completed (step 705), and the determination result is "DG>DGMIN".
If so, the learning value DG is maintained at the same value and the processing of this routine ends (step 705).

That is, this routine sets the learning value DG to an upper limit.
This process is to provide a lower limit guard.

In this embodiment in which such ISC control is performed, the process shown in FIG. 14 is also performed as the fail process 403 shown in FIG. 10. In FIG. 14, the ISC upper limit value (DGMAX in FIG. 13) is increased as a fail process (step 801). As a result, when an abnormality occurs in which the valve opening timing of the intake valve 26 is too early during low-load operation, the valve overlap period becomes large and the engine malfunctions. is larger than normal, and the amount of air flowing through the bypass passage 36 is increased, so
Combustion is promoted and engine malfunctions can be prevented.

Note that in step 801, the ISC upper limit value D
I changed GMAX to a large value, but the ISC upper limit DGM
AX may be removed.

[0052]

As described above, according to the present invention, when the overlap period between the opening periods of the intake valve and the exhaust valve is too long due to an abnormality in the variable valve timing device during open loop control of the air-fuel ratio, The system increases the amount of fuel injected to stabilize the combustion state of the engine, allowing the vehicle to continue running without stalling the engine even in the event of an abnormality in the variable valve timing system. It has the following.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle configuration of the present invention.

FIG. 2 is a system configuration diagram of an embodiment of the present invention.

FIG. 3 is a hardware configuration diagram of the microcomputer in FIG. 2;

FIG. 4 is a characteristic explanatory diagram of the variable valve timing device.

FIG. 5 is a diagram illustrating the opening timing of the intake valve and exhaust valve by the variable valve timing device.

FIG. 6 is a flowchart showing a VVT abnormality detection routine according to an embodiment of the present invention.

FIG. 7 is a flowchart showing an air-fuel ratio feedback control routine.

8 is a diagram showing changes in the air-fuel ratio feedback coefficient calculated by the routine of FIG. 7. FIG.

FIG. 9 is a flowchart showing a fuel injection time calculation routine.

FIG. 10 is a flowchart showing a main routine of an embodiment of the essential part of the present invention.

FIG. 11 is a flowchart showing an example of the fail processing routine in FIG. 10;

FIG. 12 is a flowchart showing an example of an ISC control routine.

FIG. 13 is a flowchart showing the guard processing routine in FIG. 12;

FIG. 14 is a flowchart showing another embodiment of the fail processing routine in FIG. 10;

[Explanation of symbols]

10 Internal combustion engine 11 Variable valve timing device 12 Abnormality detection means 13 Air-fuel ratio control means 14 Detection means 15 Fuel injection amount increasing means 16, 38 Fuel injection valve 21 Microcomputer 45 Hydraulic control solenoid valve 46 Valve mechanism

Claims (1)

[Claims] 1. Abnormality detection means for detecting an abnormality in a variable valve timing device that changes the overlapping period of each valve opening period of an intake valve and an exhaust valve of an internal combustion engine according to the operating condition; an air-fuel ratio control means for feedback-controlling the fuel injection amount by the fuel injection valve so as to make the fuel ratio a target air-fuel ratio, and the air-fuel ratio control means is not in operation,
a detection means for detecting that open-loop control of an air-fuel ratio is being performed; and when the open-loop control is detected by the detection means and when an abnormality is detected by the abnormality detection means, the amount of fuel injected by the fuel injection valve is increased. What is claimed is: 1. A fail-safe system for a variable valve timing device, comprising fuel injection amount increasing means.