JP2639144B2 - Exhaust gas recirculation valve control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas recirculation valve control device, and more particularly to an opening degree of an exhaust gas recirculation valve for recirculating exhaust gas of an internal combustion engine into an intake air-fuel mixture. The present invention relates to an exhaust gas recirculation valve control device that controls the exhaust gas.

[Conventional technology]

Conventionally, carbon monoxide (CO) in the exhaust gas of internal combustion engines,
BACKGROUND ART An exhaust gas recirculation device (EGR: exhaust gas recirculation) that reduces NOx among harmful components such as hydrocarbons (HC) and nitrogen oxides (NOx) is known. According to this EGR device, a part of the exhaust gas is sucked into the engine through an exhaust gas recirculation valve (EGR valve) provided in the exhaust gas recirculation passage connecting the exhaust passage and the intake passage of the internal combustion engine. NOx is reduced by recirculating in the air-fuel mixture and causing heat from combustion in the engine cylinder to be deprived of the inert gas in the exhaust gas to lower the maximum combustion temperature.

However, when exhaust gas recirculation is performed, a decrease in output and instability of combustion are caused, so that drivability is deteriorated and HC is increased. For this reason, in order to reduce these problems, it is necessary to appropriately control the exhaust gas recirculation amount according to the operation state, and for that purpose, the opening degree (opening area) of the EGR valve is controlled. This EGR valve can be controlled by open-loop digital control, has a superior position accuracy, and has a small accumulated error.Because of this, a step motor is generally used, and the valve body is raised or lowered by rotating the step motor rotor. A structure for adjusting the opening is known (for example, Japanese Utility Model Application Laid-Open No. 62-136680, Japanese Patent Application Laid-Open No. 61-76748).
No.).

In the conventional exhaust gas recirculation valve control device that controls the opening degree of the EGR valve having such a structure, if at least one phase of the excitation coil or wiring of the step motor is disconnected or short-circuited, the same drive as in normal operation is performed. The EGR valve is fully closed by driving the step motor by the method, and the EGR is stopped.

[Problems to be solved by the invention]

However, conventionally, even when a step motor failure occurs, since the step motor is driven at the same drive cycle as in normal operation, the failure of the step motor causes the rotor of the step motor to step out due to step-out as shown in FIG. If the rotor is driven at a timing when the amount of vibration (the amount of overshoot and the amount of undershoot) is large, and the rotor is vibrating in the direction opposite to the direction in which the rotor should be driven, the rotor deviates from the normal rotation position. .

Therefore, in the related art, step-out occurs due to occurrence of a failure such as disconnection of at least one phase of the excitation coil and wiring of the step motor, short-circuit, and the like. In some cases, the rotor may rotate in the valve opening direction, and the rotation of the rotor is extremely unstable. For this reason, in the conventional device, the value indicating the target opening (target step position) is set to zero (ie, fully closed), and the value indicating the current opening (current step position or position) to be changed corresponding to the rotation control of the step motor. Even if computer control of the step motor of the exhaust gas recirculation valve is performed so that the actual step position becomes equal to the target step position, the value of the current step position and the opening degree of the exhaust gas recirculation valve do not correspond correctly, and the exhaust gas Before the recirculation valve is fully closed, the current step position becomes zero. As a result, the conventional device determines that the current step position has become equal to the target step position and ends the control.

For this reason, conventionally, if the above-mentioned failure occurs when the EGR valve is opened, the EGR valve will not be fully closed even if it is to be fully closed, causing problems such as a decrease in engine output, deterioration of drivability, idle instability, and engine stall. May occur.

The present invention has been made in view of the above points, and when the above-described failure of the step motor of the EGR valve occurs, by driving the step motor at a longer cycle than at the normal time, the exhaust gas which can control the EGR valve to be fully closed is provided. It is an object to provide a recirculation valve control device.

[Means for solving the problem]

FIG. 1 shows a principle configuration diagram of the present invention. In the figure, reference numeral 11 denotes an internal combustion engine, and a fuel mixture is sucked through an intake passage 12,
The exhaust gas is exhausted through the exhaust passage 13. An exhaust gas recirculation valve 15 having a step motor 15a and a valve body 15b is provided in the middle of an exhaust gas recirculation passage 14 that connects the exhaust passage 13 and the intake passage 12. This exhaust gas recirculation valve 15
Is controlled by driving the stepping motor 15a to vary the lift amount of the valve body 15b.

In the exhaust gas recirculation valve control device having such a configuration, the present invention provides a failure detection unit 16, a drive signal generation unit 17, a counter 1
8. A configuration including target lift amount setting means 19 and count value changing means 20 is provided. Here, the failure detection means 16
Detects a failure in the exciting coil or wiring of at least one of the phases of the step motor 15a. The counter 18 counts operation steps of the step motor. The target lift amount setting means 19 sets the target lift amount of the valve body according to the operation state of the internal combustion engine, and sets the target lift amount to 0 when a failure detection signal is input. The drive signal generation means 17 supplies a drive signal to the stepping motor so that the count value of the counter becomes a value corresponding to the target lift amount of the valve body, and compares the cycle of the drive signal when a failure detection signal is input with that when the failure detection signal is normal. And make it longer. Further, the count value changing means 20 changes the count value of the counter to a value larger than the actually counted value when the failure detection signal is input.

[Action]

In the present invention, the step motor 15
When a failure of the excitation coil or wiring of a is detected, a drive signal from the drive signal
Is driven in a longer cycle than in the normal state where there is no failure. For this reason, in the present invention, the energization period and energization cycle of the step motor 15a are longer than normal, and even if the rotor of the step motor 15a starts to attenuate and vibrate due to the above-described failure, the vibration is sufficiently attenuated before the step motor 15a , The influence of the step-out can be greatly reduced.

Further, in the present invention, when the failure detecting means 16 detects a failure in the excitation coil or the wiring of the step motor 15a, the target lift amount of the valve body 15b is set to zero. When the target lift amount of the valve body 15b is set to 0, the target step number of the step motor 15b is changed to a value corresponding to the lift amount “0” (hereinafter, this step number is referred to as a fully closed step number). . Thereafter, the drive signal generation means 17 outputs a drive signal having a longer cycle than that in the normal state to the step motor 15a until the count value of the counter 18 matches the fully closed step number.

The count value of the counter 15a is changed to a value larger than the actual count value when the failure detection means 16 detects a failure in the excitation coil or the wiring of the step motor 15a. For this reason, the drive signal generation means 17 outputs a drive signal exceeding the minimum number of times required to set the number of steps of the step motor 15a to the number of fully closed steps. Therefore, even if the step motor 15a loses synchronism in the process in which the number of steps reaches the number of fully closed steps, the valve body 15b is reliably brought into the fully closed state.

〔Example〕

FIG. 2 is a configuration diagram of an exhaust gas recirculation device for an internal combustion engine having one embodiment of the exhaust gas recirculation valve control device according to the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals. The present embodiment is an example in which the present invention is applied to a four-cylinder four-cycle spark ignition type internal combustion engine (engine) as the internal combustion engine 11, and is controlled by a microcomputer 21 described later.

In FIG. 2, a surge tank 24 is provided downstream of the air cleaner 22 via a throttle valve 23. An intake air temperature sensor 25 for detecting the intake air temperature is attached near the air cleaner 22.
An idle switch 26 that is turned on when the throttle valve 23 is fully closed is attached. Further, a diaphragm type pressure sensor 27 is attached to the surge tank 24.

Also, a bypass passage bypassing the throttle valve 23 and communicating between the upstream side and the downstream side of the throttle valve 23.
An idle speed control valve (ISCV) 29 whose degree of opening is controlled by a solenoid is provided in the middle of the bypass passage. this
The idling rotational speed is controlled to the target rotational speed by controlling the valve opening degree by controlling the duty ratio of the current flowing through the ISCV 29 and thereby adjusting the amount of air flowing through the bypass passage 28.

A surge tank 24 is connected to an engine 32 through an intake manifold 30 and an intake port 31 corresponding to the intake passage 12.
(Corresponding to the internal combustion engine 11). A fuel injection valve 10 is provided for each cylinder so that a part thereof projects into the intake manifold 30, and fuel is injected into the air flow passing through the intake manifold 30 by the fuel injection valve 10.

The combustion chamber 33 is connected to a catalyst device 36 via an exhaust port 34 and an exhaust manifold 35 corresponding to the exhaust passage 13. 37 is an ignition flag, a part of which is in the combustion chamber 33.
It is provided so as to protrude. Reference numeral 38 denotes a piston which reciprocates vertically in the figure.

The igniter 39 generates a high voltage, and the high voltage is distributed and supplied to the ignition plug 37 of each cylinder by the distributor 40. The rotation angle sensor 41 detects the rotation of the shaft of the distributor 40 and outputs an engine rotation signal to the microcomputer 21 every 30 ° CA, for example.

A water temperature sensor 42 is provided so as to penetrate through the engine block 43 and partially project into the water jacket, and detects the temperature of the engine cooling water to output a water temperature sensor signal. Further, 44 is an oxygen concentration detection sensor (O ₂
Sensor), a part of which is disposed so as to protrude through the exhaust manifold 35, and detects the oxygen concentration in the exhaust gas before entering the catalyst device 36.

Further, the upstream side exhaust manifold of the O ₂ sensor 44
A recirculation passage corresponding to the exhaust gas recirculation passage 14 is provided between the exhaust gas recirculation passage 14 and the intake manifold 30 downstream of the throttle valve 23.
The EGR cooler 46 and the exhaust gas recirculation valve (hereinafter referred to as EGRV) 15 are provided in the middle of the recirculation passage 45.

The EGR cooler 46 is for lowering the temperature of the exhaust gas flowing through the recirculation passage 45. The EGRV 15 has a known structure in which the opening degree of the valve changes according to a drive signal input from the microcomputer 21 to be described later through the motor drive circuit 47 and the disconnection detection circuit 48.

That is, as shown in FIG. 9, the EGRV 15 includes a step motor 15a, a valve body 15b, etc., the step motor 15a includes a stator 111 and a rotor 112, and the valve body 15b has a valve 113 and a valve 113 at the tip. It comprises a rod 114 which is fixed and is movable in the vertical direction in the figure. Reference numeral 115 denotes an inlet port through which exhaust gas flows, and reference numeral 116 denotes an outlet port from which exhaust gas is discharged.

The drive signal input to the step motor 15a
Is rotated, the rotational motion is converted to linear motion by the screw 117 and transmitted to the motor shaft 118. At this time, when the rotation direction of the step motor 15a is the forward rotation direction, the motor shaft 118 pulls the rod 114 upward in the drawing against the spring force of the spring 119,
When the valve 113 is moved away from the seat member 120 (opening direction), while the rotation direction is the reverse direction, the motor shaft 118 moves the rod 114 downward in the drawing together with the spring force of the spring 119, The sheet 113 is moved in a direction to approach the sheet member 120 (close direction).

As a result, the exhaust gas flowing into the inlet port 115 is
It is led out of the outlet port 116 by a flow rate corresponding to the distance (opening degree) between the valve 113 and the seat member 120. As shown in the figure, in the fully closed state where the valve 113 and the seat member 120 are in close contact, no exhaust gas is led out. Therefore, this EGRV47
By controlling the opening degree of the exhaust gas, the flow rate of the exhaust gas input through the EGR cooler 46 is controlled, whereby the amount of exhaust gas recirculated to the intake manifold 30 is controlled.

The motor drive circuit 47 is a circuit that generates a multi-phase drive signal for sequentially energizing the multi-phase excitation coils of the step motor 15a, and the output drive signal is supplied to the excitation coil of the step motor 15a via the disconnection detection circuit 48. Is done. The disconnection detecting circuit 48 detects a disconnection of the exciting coil of the stepping motor 15a, and supplies a detection signal to the microcomputer 21. Reference numeral 49 denotes an ignition switch.

The microcomputer 21 for controlling the operation of each unit having such a configuration has a hardware configuration as shown in FIG. 2, the same components as those of FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 3, the microcomputer 21 has a central processing unit (CPU) 60, a read-only memory (RO) storing a processing program and a map described later.
M) 61, random access used as work area
A memory (RAM) 62, a backup RAM 63 for holding data even after the engine is stopped, and a clock generator 64 for supplying the master clock to the CPU 60 are connected to each other via a bidirectional bus line 65, and are connected to each other. Output port 6
6. The input port 67 is connected to the output ports 68 to 71, respectively.

Further, the microcomputer 21 converts the pressure detection signal from the pressure sensor 27 extracted through the filter 73 and the buffer 74 in series, the intake temperature detection signal from the intake air temperature sensor 25 extracted through the buffer 75, and the buffer 76. A multiplexer 78 selectively outputs a water temperature sensor signal (THW) from the water temperature sensor 42 taken out via the multiplexer 78.
The above-described filter 73 is a filter for removing a pulsating component of the intake pipe pressure included in the output detection signal of the pressure sensor 27.

Thereby, the output signals of the respective sensors input to the multiplexer 78 are sequentially controlled under the control of the CPU 60.
After being selectively output, the digital signal is converted into a digital signal by the A / D converter 79 and then stored in the RAM 62.

Also, the microcomputer 21 inputs the oxygen concentration detection signal from the O ₂ sensor 44 to the comparator 81 via the buffer 80, shapes the waveform here and supplies it to the input port 67, and the waveform shaping circuit 82 controls the rotation angle sensor. A signal obtained by shaping each detection signal from the disconnection detection circuit 41 and the disconnection detection circuit 48 and an output signal of the idle switch 26 through a buffer (not shown) are supplied to an input port 67, respectively.

Further, the microcomputer 21 has drive circuits 83 to 86, supplies a signal from the output port 68 to the igniter 39 via the drive circuit 83, and outputs a signal from the output port 69 to a drive circuit having a down counter. 84 through fuel injector 10
, The signal from the output port 70 is supplied to the ISCV 29 via the drive circuit 85, and the output signal from the output port 71 is supplied to the motor drive circuit 47 via the drive circuit 86.

The microcomputer 21 having such a hardware configuration
Together with the motor drive circuit 47 constitute the drive signal generation means 17 described above.

Next, the configuration and operation of the disconnection detection circuit 48 that constitutes the failure detection means 16 will be described with reference to FIGS. FIG. 4 is a circuit diagram of one embodiment of the disconnection detecting circuit 48. As shown in the figure, the disconnection detection circuit 48 NPN transistors Tr1 to Tr4, an emitter resistor R ₁ to R _4, comparators C ₁ ~
C ₄ , delay circuits 51 _{1 to} 51 ₄ , D-type flip-flops 52 _{1 to} 52
₄ , composed of an AND circuit 53.

NPN transistors Tr1, Tr2, Tr3 and Tr4 are connected to each one end of the exciting coil S _1, S _2, S ₃ and S ₄ of the collector step motor 15a, emitter resistors R _1, R _2, R ₃ and R ₄ , And the base is connected to the output terminal of the motor drive circuit 47. The emitter of the transistor Tr1, Tr2, Tr3 and Tr4 are connected to the non-inverting input terminal of the comparator C _1, C _2, C ₃ and C _4. Each output terminal of the comparator C ₁ -C ₄ is connected to the data input terminal of the D-type flip-flop 52 _{1-52 4} Rui. Delay circuits 51 ₁ to 51 ₄ are delayed a predetermined time τ the input drive signal is applied to the trigger input terminal T of the D-type flip-flop 52 _{1-52 4.} AND circuit 53 takes a logical product of the Q output signal of the D-type flip-flop 52 _{1-52 4,} and supplies its output signal to the microcomputer 21.

In such a configuration, the phase is now shifted from the motor drive circuit 47 to each base of the transistors Tr1 to Tr4 as shown in FIG.
When four-phase drive signals (symmetric square waves) different by 90 ° are supplied, the transistors Tr1 to Tr4 are turned on while the base input drive signal is at a high level and turned off during a low level. The collector of the on-period of the transistor Tr1 resistor R ₇ → the exciting coil S ₁ → transistors Tr1, the emitter → the resistor R
A current flows _first order with, the exciting coil S ₁ is being energized, the comparator C ₁ by the voltage drop due to the resistance R ₁
Becomes high level. The inverting input terminal of the comparator C ₁ voltage obtained by dividing the power supply voltage Vc by the resistors R ₅ and R ₆ is applied, but a voltage generated across the resistor R ₁ by a current flowing through the resistor R ₁ ( since the input voltage) of the non-inverting input terminal of the comparator C ₁ is set to be higher than the divided voltage, the output voltage of the comparator C ₁ this time is high.

On the other hand, the off period of the transistor Tr1 from the above current does not flow to the exciting coil S ₁ and resistor R _1, the comparator C ₁
The input voltage at the non-inverting input terminal becomes lower than the divided voltage, the output voltage of the comparator C ₁ becomes low.

By the same operation principle as the for the other transistors Tr2～Tr4, the ON period of the transistor Tr2～Tr4, exciting coils S ₂ to S ₄ is energized, and the output voltage of the comparator C ₂ -C ₄ becomes high level , On the other hand, transistor Tr2
Off period of ~Tr4 exciting coil S ₂ to S ₄ is not energized, the output voltage of the comparator C ₂ -C ₄ becomes low. As a result, the step motor 15a is driven to rotate by the two-phase excitation method.

Further, the output voltage of the comparator C ₁ -C ₄ is C ₁ ~ in Figure 5
Becomes as indicated by C ₄ (as will be provided that will be described later, only the output voltage of the comparator C ₃ show things burnout in FIG. 5).

The output voltage of the comparator C ₁ -C ₄ is applied to the data input terminal of the D-type flip-flop 52 _{1-52 2,} wherein the delay circuit 51 ₁ to 51 ₄ by a predetermined time τ delayed the trigger terminal T ₁ through T in FIG. 5 to be input to the ₄ are latched on the rising edge input point of the drive signal shown in T ₁ through T _4.

When the rising edge position of the input drive signal of the trigger terminals T _{1 to} T ₄ is equal to the predetermined time τ, the D-type flip-flops 52 _{1 to} 52 ₄
Of normal for that is set to a high level period of the input voltage to the data input terminal (the output voltage of the comparator C ₁ -C ₄₎ are each Q output terminal of the D-type flip-flop 52 _{1-52 4} All output signals are at high level. Therefore,
A high-level signal is normally extracted from the AND circuit 53.

Here, if assuming that disconnection exciting coil S ₃ occurs, even if the driving signal of high level to the base of the transistor Tr3 is supplied, flows to the collector of the transistor Tr3 via a resistor R ₇ and the excitation coil S ₃ Current does not flow and the transistor Tr3 remains off.
_As indicated by C3 in FIG. 5, the output voltage of No. _{3 is} at a low level during a period which should be at a high level as indicated by a broken line.

Therefore, among the output signals of the D-type flip-flop 52 _{1-52 4,} since only the output signal of the D-type flip-flop 52 ₃ becomes the low level at its T ₃ input drive signal rise time t _1, the low The output signal of the level AND circuit 53 is input to the microcomputer 21 as a disconnection detection signal. When this disconnection detection signal is input, the microcomputer 21 sets the value of the failure flag FEGRFAIL to “1” and sets the CPU 60
Set to the register inside.

Next, the software operation of the microcomputer 21 for realizing the drive signal generation means 17 will be described in the sixth.
This will be described with reference to FIGS. FIG. 6 is a flowchart for explaining the operation of one embodiment of the main part of the present invention, and shows a main routine for controlling the opening of the EGRV15. In the figure, the CPU 60
First, in step 91, the intake pipe pressure PM based on the detection signal of the pressure sensor 27, the number of times NE obtained from the output rotation signal of the rotation angle sensor 41, and the like are read from the RAM 62, and the failure flag FEGRFAIL is read from a register.

Subsequently, the failure flag FEGR just read in step 92
It is determined whether or not the value of FAIL is “1”. If the value is not “1” (ie, “0” is normal when normal), the process proceeds to step 93, and the value of the EGR on condition determination flag FEGRON is not “1”. Is determined. The EGR ON condition determination flag FEGRON is
For example, based on the opening degree (throttle opening degree) TA of the throttle valve 23 and the engine cooling water temperature THW based on the output of the water temperature sensor 42, the EGR on condition that the THW is equal to or more than a predetermined value at off-idling is satisfied. When "1"
If not satisfied, it is set to “0” and set in the register of the CPU 60.

Accordingly, when it is determined in step 93 that the value of the flag FEGRON is "1", the process proceeds to step 94 to perform the EGR operation, and the target step position STEP of the EGRV15 is calculated by a table search. This table is a two-dimensional table of the engine line speed NE and the intake pipe pressure PM as shown in FIG. In FIG. 7, values between cells are calculated by interpolation calculation.
The target step position STEP corresponds to an instruction value of the opening of the EGRV15.

On the other hand, when it is determined in step 93 that the value of the flag FEGRON is “0”, the flow proceeds to step 95 to stop the EGR operation because the EGR condition is not satisfied, and the value of the target step position STEP is changed. Set to “0” and instruct the opening degree of EGRV15 to be zero (fully closed).

When the processing of step 94 or 95 described above is completed, it is determined in step 96 whether or not the value of the ON flag FIGON of the ignition switch 49 is “1”. When the value is “1” (when it is ON)
Returns to step 91 again, and when it is "0", this main routine ends.

By the way, the above is a normal processing operation and the same EGRV
In this embodiment, the opening degree control processing is 15, but when it is determined in step 92 that the value of the failure flag FEGRFAIL is "1" (that is, when it is determined that a failure such as a disconnection has occurred in the step motor 15a). ) Is different from the related art in that the process of step 97 is performed.

That is, in the above step 97, the CPU 60 reads the current step position (opening degree) ESTEP of the EGRV 15 read from the RAM 62.
Is changed as a current step position (hereinafter, also referred to as an actual step position) ESTEP and stored in the RAM 62 again, and the value of the target step position STEP is set to “0”. Then, after the processing of step 97, the routine proceeds to step 96, where it is determined whether or not the value of the ignition switch on flag FIGON is "1".

Target step position calculated by the above main routine
Based on the STEP, the opening of the EGRV 15 is controlled by the routine shown in FIG. FIG. 8 shows an EGRV opening control routine, which is interrupted every 4 ms during the operation of the main routine. When this routine is started by interruption, it is first determined whether or not the value of the failure flag FEGRFAIL is "1". When the value is "1", it is determined in step 102 whether or not the counter value CECNT is "16". Is done. Since this counter value CECNT is initially set to zero, the CECNT is not “16” when this routine is started for the first time.
Proceeding to step 103, the value is updated to the value obtained by adding one and the process exits this routine.

In this way, when this routine is started 16 times while the failure flag FEGRFAIL is “1”, the step 10
Since it is determined in Step 2 that the value of the counter value CECNT is “16”, the process proceeds to Step 104 for the first time. When the failure flag FEGRFAIL is “0”, the process immediately proceeds to step 104 without passing through step 102.

In step 104, the target step position STEP calculated in the main routine described above is compared in magnitude with the current step position ESTEP. When STEP> ESTEP, the step motor 15a is rotated in the opening direction by one step (step 10).
5) Increment the value of ESTEP by “1” (step
106) On the other hand, when STEP> ESTEP, the step motor 15a is rotated by one step in the closing direction (step 10).
7), decrement the value of ESTEP by “1” (step 10)
8) After that, the counter value CECNT is reset to "0" (step 109), and this interrupt routine is ended and the process returns to the main routine. It should be noted that, in Step 104, STEP
When = ESTEP, the interrupt routine is terminated via step 109 without driving the step motor 15a.

Thus, according to the EGRV control routine shown in FIG. 8, the current step position ESTEP indicating the actual opening of the EGRV 15
When is smaller than the target step position STEP, the opening of the EGRV15 is driven by one step in the opening direction, when it is larger, the opening is driven by one step in the closing direction, and when both are equal, the opening at that time is left as it is. EGRV will be held
The control operation is performed every time this control routine is started 16 times when a failure is detected. Therefore, according to the present embodiment, the cycle of the drive signal output from the microcomputer 21 to the motor drive circuit 47 is 16 times the cycle in the normal state.

As a result, the output signal of the drive circuit 47 is the same as that in the normal state in that the output signal is a four-phase symmetrical square wave whose phase is sequentially different by 90 °, but the pulse width and the period are 16 times those in the normal state.

As a result, the disconnected excitation coil (for example, S ₃ ) of the excitation coils S _{1 to} S ₄ of the step motor 15 a shown in FIG.
Excitation coils S ₁ , S ₂ and S ₄ except for
The power is continuously supplied at twice the period and 16 times the normal period. As a result, even if the rotor of the step motor 15a is attenuated due to the disconnection, the drive signal is supplied to the step motor 15a after the reverse vibration is sufficiently attenuated, so that the step motor can be prevented from stepping out as much as possible. Also, for example, when the viscosity of the lubricating oil of the step motor is large, the motor is hard to rotate, but the spring (119 in FIG. 9) provided in the EGRV 15 always urges the valve body 15b in the closing direction. Therefore, when closing the valve element, the occurrence of step-out can be reduced.

Then, due to the above-mentioned step-out, one step is performed in the closing direction.
When the drive signal for rotating the step motor 15a is output, even if the value of the actual step position ESTEP is reduced by one, the step motor 15a may not always rotate, so that the value of ESTEP is accurately set to the opening of the EGRV15. Although not correspond to, because in the present embodiment is changed to twice the value of the value of the actual step position ESTEP at fault time t _0, as shown by III in FIG. 10 (B) of (Figure 6 step 97), in the process of changing to the zero indicated by the target step position STEP indicated by the solid line IV in FIG. 10B, the EGRV 15 always closes as indicated by II in FIG. 10A.

Thus, according to the present embodiment, the EGRV15
Can be fully closed, so that there is no need to provide a fail-safe mechanism for the occurrence of a failure in the EGRV 15, and the size of the EGRV 15 can be made smaller and the cost can be reduced as compared with an EGRV provided with a fail-safe mechanism.

In addition, since the EGRV 15 valve closing control can be performed in the event of a failure by electrical control, the closing time of the EGRV 15 can be substantially predicted, so that the accuracy of ignition timing and air-fuel ratio control is improved, and damage to the engine due to knocking or the like is avoided. be able to.

The present invention is not limited to the above examples, the disconnection detecting circuit 48 can detect even if the one end of the exciting coil S ₁ to S ₄ is short-circuited to ground, also the step motor 15a other May be used. Furthermore, the value of the actual step position ESTEP is doubled when the excitation coil of the stepping motor 15a or the wiring is faulty.
The value of the actual step position ESTEP may be changed and set to a large value so that is completely closed, and is not limited to twice.

〔The invention's effect〕

As described above, according to the present invention, when the exciting coil and the wiring of the step motor fail, the energizing period and energizing cycle to the exciting coil are changed to values larger than the normal state, and the count value of the counter is set to the actual value. Since the value is changed to a value larger than the value, the influence of the step-out of the step motor can be significantly reduced, and a sufficient number of drive signals can be supplied to the step motor. Therefore, the exhaust gas recirculation valve can be fully closed at the time of the above failure.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the principle of the present invention, FIG. 2 is a block diagram of an exhaust gas recirculation system for an internal combustion engine having an embodiment of the present invention, and FIG. 3 is a hardware diagram of the microcomputer in FIG. FIG. 4 is a circuit diagram of an embodiment of a disconnection detecting circuit, FIG. 5 is a signal waveform diagram for explaining operation of FIG. 4, and FIG. 6 is an operation of an embodiment of a main part of the present invention. FIG. 7 is an explanatory view of a table searched at a predetermined step in FIG. 6, FIG. 8 is a flowchart of another embodiment of the main part of the present invention, and FIG. 9 is an exhaust gas recirculation valve. FIG. 10 is a view for explaining a change in valve lift and the like of the apparatus of the present invention and the conventional apparatus, and FIG. 11 is an explanatory view of displacement of a step rotor at the time of step-out. 11 ... internal combustion engine, 12 ... intake passage, 13 ... exhaust passage, 14
…… Exhaust gas recirculation passage, 15 …… Exhaust gas recirculation valve (EGR
V), 15a: Step motor, 15b: Valve element, 16: Failure detection means, 17: Drive signal generation means, 21: Microcomputer, 48: Disconnection detection circuit.

Claims (1)

(57) [Claims] An opening degree of an exhaust gas recirculation valve having a step motor and a valve body provided in the middle of an exhaust gas recirculation passage communicating an exhaust gas passage of an internal combustion engine with an intake passage is adjusted in accordance with an operation state. An exhaust gas recirculation valve control device which controls a stepping motor by driving a valve lift to vary a lift amount of the valve body, wherein a failure detection for detecting a failure of an exciting coil or a wiring of at least one phase among a plurality of phases of the stepping motor. Means, a counter for counting operation steps of the step motor, and a target lift amount of the valve body is set according to an operation state of the internal combustion engine, and when a failure detection signal is input from the failure detection means, Target lift amount setting means for setting the target lift amount to 0; and driving the step motor so that the count value of the counter becomes a value corresponding to the target lift amount. A drive signal generating unit that supplies a dynamic signal and, when a failure detection signal is input from the failure detection unit, lengthens a cycle of the drive signal as compared with a normal state, and a failure detection signal from the failure detection unit. Exhaust gas recirculation characterized by comprising: count value changing means for changing, when input, the count value of the counter to a value larger than the value actually counted by the counter. Valve control device.