JPH04362245A - Fail-safe system of variable valve timing device - Google Patents

Abstract

PURPOSE:To prevent occurrence of engine stall when a vehicle stops after running by increasing the restoration number of revolutions for fuel cut when an abnormality of the variable valve timing device is detected. CONSTITUTION:A variable valve timing device 11 changes the period of time when each valve open period of a suction valve and an exhaust valve of an internal combustion engine 10 overlaps depending on the operation condition. An abnormality detection means 12 detects abnormality of the variable valve timing device 11. Also, a fuel injection control means 13 stops fuel injection by a fuel injection valve 16 when a throttle valve 15 is fully closed and the number of revolutions of the engine is abnormal, and resumes fuel injection when the number of revolutions of the engine is reduced below the restoration number of revolutions after stoppage. Further, when it is detected by a restoration number of revolutions control means 14 and abnormality detection means 12 that the variable valve timing device 11 is abnormal, the restoration number of revolutions of the fuel injection control means 13 is increased by the predetermined value.

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 depending on 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 in which the set idle speed is increased when the variable valve timing device fails (Japanese Patent Laid-Open No. 1-11084).
Publication No. 4).

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

0004

[Problem to be Solved by the Invention] In the conventional fail-safe system described above, even if the set idle speed is increased, if the fuel cut conditions are satisfied, the fuel cut is performed, and the engine speed becomes below the return speed. When this occurs, the fuel cut is canceled and fuel injection is restarted (recovered). However, if the variable valve timing device fails and the valve timing remains the same as when operating at low to medium speeds and high loads, the valve overlap period is too large and engine combustion is unstable, resulting in a state where fuel cut is performed. Even if the fuel cut is canceled when the engine speed drops below the reset speed, such as when the vehicle stops after driving, the engine speed may drop and an engine stall may occur.

[0005] 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-mentioned problems by increasing the number of rotations for returning from fuel cut when an abnormality is detected in the variable valve timing device.

[0006]

[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 the variable valve timing device 11. Furthermore, when the throttle valve 15 is fully closed, the fuel injection control means 13 stops the fuel injection by the fuel injection valve 16 when the engine speed is above a predetermined speed, and after the stop, the engine speed falls below the return speed. At this time, fuel injection is restarted.

Further, the return rotation speed control means 14 increases the return rotation speed of the fuel injection control means 13 by a predetermined value when the abnormality detection means 12 detects that the variable valve timing device 11 is abnormal.

[0008]

[Operation] While fuel injection is stopped by the fuel injection control means 13 (
(during fuel cut), when the abnormality detection means 12 detects an abnormality in which the variable valve timing device 11 does not switch to the valve timing for low-load operation while maintaining the valve timing for low-medium-speed high-load operation. If left as is, the overlapping period between the opening periods of the intake valve and the exhaust valve will be too long, resulting in a decrease in the effective compression ratio, and the combustion state of the engine will become unstable. Therefore, this variable valve timing device 1
Even if the engine rotational speed drops to the return rotational speed and the fuel injection control means 13 cancels the fuel cut while the abnormality occurrence state 1 remains, the original recovery rotational speed does not reach the engine stall. Since the engine speed is set at a fairly low speed, there is a high possibility that the engine will stall.

Therefore, in the present invention, in the above case, the return rotation speed control means 14 makes the return rotation speed higher by a predetermined value than when the variable valve timing device 11 is normal, and cancels the fuel cut earlier. By doing so, combustion in the engine combustion chamber can be stabilized when the engine speed subsequently drops to a low speed range where engine stall becomes a problem.

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.
shows a structural cross-sectional view of an arbitrary cylinder. Each part of this internal combustion engine is controlled by a microcomputer, 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.
(corresponding to the throttle valve 15) 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 determined by the throttle position sensor 3.
4 is configured to be detected. An intake temperature sensor 35 is provided downstream of the air flow meter 32 to measure intake air temperature.

Further, a bypass passage 36 is provided which bypasses the throttle valve 33 and communicates between the upstream side and the downstream side of the throttle valve 33.
An idle speed control valve (ISCV) 37 whose opening degree is controlled by a solenoid during
is installed.

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 rotational 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 this 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.

Thereby, as shown in FIG. 5A, 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, so that the opening period T26 of the intake valve 26 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 the low, medium speed, and high load operating 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.
(30° before top dead center to 40° after bottom dead center) Intake valve 2
By overlapping the opening period T27 of the exhaust valve 27 with a large period of θ2 (however, θ2 > θ1) after the exhaust valve 27 begins to open, a sufficient intake and exhaust period is ensured to increase charging efficiency and increase engine torque. Improve.

In this embodiment, in an internal combustion engine equipped with a variable valve timing device that performs such operations, the above-described abnormality detection means 12, fuel injection control means 13, and return rotation speed control means 14 are realized by a microcomputer 21. Next, the abnormality detection means 12 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).

[0026]

[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). In the idle state, an abnormality occurs in the hydraulic control solenoid valve 45 or the valve train 46 that constitutes the variable valve timing device, and the valve timing relationship normally occurs during low-load operation as shown in FIG. When the valve timing becomes as shown in FIG. 5(B) during high-load operation, the current engine speed NEi fluctuates (varies) by at least 100 rpm with respect to the 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 set to "
After incrementing the counter value C by 1" (step 105), this routine ends (step 106). Furthermore, if there is no change in the engine speed, this routine ends with the counter value C unchanged (step 106). ).

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 since the idle state, the counter value C is greater than "30". 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 fuel injection control means 13 will be explained. The fuel injection control means 13 controls the air-fuel ratio (A/F
) Feedback control routine, fuel cut control routine shown in FIG. 9, and fuel injection time (TAU) shown in FIG.
This is realized by the microcomputer 21 executing the calculation routine.

The A/F feedback control routine shown in FIG. 7 is a well-known routine, and is activated by interruption every 4 ms, for example. First, 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. On the other hand, when the F/B condition is met (other than when the above F/B condition is not met), the process proceeds to step 204, and after setting the A/F feedback control determination flag XAF to "1", the detection voltage V1 of the O2 sensor 39 is set. Convert and import (step 205)
. Next, in step 206, the detection voltage V1 is changed to the comparison voltage VR1.
By determining whether or not the air-fuel ratio is below, it is determined whether the air-fuel ratio is rich or lean. When it is rich (V1 > VR1), it is determined whether it is in that state or a state reversed from a lean state to a rich state (step 207).
), when reversing to rich, the value obtained by subtracting the skip constant RSL from the previous value of the air-fuel ratio feedback correction coefficient FAF is used as the 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 21).
3).

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.

Next, the fuel cut control routine will be explained. FIG. 9 is a flowchart showing an example of a fuel cut control routine.
An interrupt is activated every ms. First, it is determined whether the throttle valve 33 is fully closed or not based on the output detection signal of the throttle position sensor 34 (step 3).
01), when the throttle valve 33 is fully closed, proceed to step 302, and when not fully closed, proceed to step 30, which will be described later.
Proceed to step 6.

[0035] In step 302, the CPU 50 loads the ROM 51.
The predetermined cut rotation speed NEcut read from the rotation angle sensor 44 is compared with the current engine rotation speed NE obtained based on the rotation speed signal from the rotation angle sensor 44.
When the fuel cut flag (F
After setting the value of (denoted as cut) to "1" in the next step 303, this routine ends.

When the value of Fcut becomes "1", that is, when it is determined that the throttle valve 33 is fully closed and the engine speed NE is higher than the predetermined cut speed NEcut, As will be described later, the microcomputer 21 sets the fuel injection time TAU to zero and substantially stops fuel injection by the fuel injection valve 38 (performs a fuel cut). This allows hydrocarbons (
HC) and improve fuel efficiency.

On the other hand, when it is determined in step 302 that the engine rotation speed NE is equal to or less than the cut rotation speed NEcut, in the next step 304, the amount of change in the engine rotation speed NE per unit time ΔNE (=dNE/ dt), and it is determined whether the calculated amount of change ΔNE is less than or equal to ΔNE0 (which is negative).

When the amount of change △NE is less than the predetermined value △NE0, the process proceeds to step 306, which will be described later.
>ΔNE0, in the next step 305, the engine speed NE and the return speed NERTN are compared in magnitude. When the determination result of NE>NERTN is obtained in this step 305, this main routine is ended,
The value of Fcut described above is held as is.

On the other hand, in step 304, the drop in engine speed △NE is more severe than the predetermined value △NE0, and △NE
When it is determined that ≦NE0, or when the engine rotational speed NE falls below the return rotational speed NERTN in step 305 and it is determined that NE≦NERTN, if the fuel is being cut at that time, an engine stall will occur. Therefore, in the next step 306, it is determined whether or not the fuel cut is in progress based on whether the flag Fcut is "1", and when it is determined that the fuel cut is in progress (Fcut = 1), the flag Fcut is set. Set the value to “0” (step 3
07), cancel the fuel cut.

On the other hand, if △NE≦△NE0 or N
Even if a determination result of E≦NERTN is obtained, an engine stall will not occur unless fuel cut is in progress, so a determination result of "Fcut = 0" (determination result that fuel cut is not in progress) is obtained in step 306. If this happens, this routine is terminated without doing anything, and the normal fuel injection control state is continued.

Next, the TAU calculation routine will be explained with reference to FIG. The TAU calculation routine shown in FIG. 10 is executed as part of the main routine, and the CPU 50 first determines whether the value of the fuel cut determination flag Fcut is "1" (step 401), and if it is not "1", the Engine speed NE, intake air amount Q
, the air-fuel ratio feedback correction coefficient FAF, etc. are taken in (step 402).

[0042] 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 403).

[0043]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.

On the other hand, when the value of the fuel cut flag FCUT is determined to be "1" in step 401,
The fuel injection time TAU is set to zero (step 40).
4) As a result, fuel injection by the fuel injection valve 38 is stopped.

Next, the return rotation speed control means 14, which constitutes the main part of the present invention, will be explained. FIG. 11 is a flowchart showing an embodiment of the main part of the present invention, and FIG. 12 is a flowchart showing an embodiment of the fail processing in FIG. Figure 11
12 is a flowchart for realizing the return rotation speed control means 14. When the main routine shown in FIG. 11 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 501). .

When the idle contact is off, this routine is exited (step 505), and when the idle contact is on, it is determined whether the abnormality determination flag f is "1" or not (step 502). When the abnormality determination flag f is "0", this routine ends (step 505), but when the abnormality determination flag f is "1", fail processing is performed (
Step 503). After fail processing, abnormality determination flag f
After setting the value to "0" (step 504), this routine ends (step 505).

Fail processing 503 is executed by a subroutine shown in FIG. In the subroutine of Figure 12,
The return rotation speed NERTN is increased by 500 (rpm) (step 601). This return rotation speed NERTN is normally determined by referring to a map (stored in the ROM 51) with the engine cooling water temperature THW shown as III in FIG. However, in this embodiment, due to the fail processing, the relationship between the recovery rotation speed NERTN and the engine cooling water temperature THW is determined by the characteristic II, as shown by IV in FIG.
The characteristic is changed to such that the return rotational speed NERTN is increased by 500 rpm compared to I.

As a result, according to this embodiment, during deceleration with the throttle valve fully closed, the hydraulic control solenoid valve 45 or the valve operating mechanism 46 is abnormal, and the intake valve 26
When the valve opening timing does not switch to the original late timing but remains at the early timing and fuel is being cut, the return rotation speed NERTN is changed to a value 500 rpm higher than normal, so the above abnormality occurs. In some cases, the fuel cut is canceled early and fuel injection is restarted, so that engine stall can be prevented even when the vehicle subsequently stops running.

[0049]

As described above, according to the present invention, when the variable valve timing device is abnormal, the fuel cut is canceled earlier by raising the fuel cut return rotation speed by a predetermined value than in normal conditions. When the engine speed drops to the low speed range where engine stalling becomes a problem, it is possible to stabilize combustion in the engine's combustion chamber, so it is possible to prevent engine stalling when the vehicle is stopped, etc. It has certain characteristics.

[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 shows changes in the air-fuel ratio feedback coefficient calculated by the routine of FIG. 7. FIG.

FIG. 9 is a flowchart showing a fuel cut control routine.

FIG. 10 is a flowchart showing a fuel injection time calculation routine.

FIG. 11 is a flowchart showing a main routine of an embodiment of the essential part of the present invention.

FIG. 12 is a flowchart showing one embodiment of the fail processing routine in FIG. 11;

FIG. 13 is a diagram illustrating a map of the return rotation speed before and after fail processing.

[Explanation of symbols]

10 Internal combustion engine 11 Variable valve timing device 12 Abnormality detection means 13 Fuel injection control means 14 Return rotation speed control means 15, 33 Throttle valves 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 operating conditions; a fuel injection control means for stopping fuel injection by the fuel injection valve when the engine speed is equal to or higher than a predetermined rotation speed, and restarting the fuel injection when the engine speed decreases to a return speed or less after the stop; and the above-mentioned abnormality. 1. A fail-safe system for a variable valve timing device, comprising a return rotation speed control means for increasing the return rotation speed of the fuel injection control means by a predetermined value when an abnormality is detected by the detection means.